JP2008265110A - Ink-absorptive recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain at first an improvement in ink absorbency and also enlargement of a dot diameter of an ink droplet, to attain secondly both of the improvement in the ink absorbency and prevention of bronzing of cyan ink, and to attain thirdly the excellent ink absorbency and also the enlargement of the dot diameter of the ink droplet even in the case where a minute ink droplet is given. <P>SOLUTION: The upper layer contains an alumina hydrate and a binder and the mass ratio of (binder)/(alumina hydrate)×100 between the alumina hydrate and the binder in the upper layer is 4-6%. The lower layer contains the alumina hydrate and the binder and the mass ratio of (binder)/(alumina hydrate)×100 between the alumina hydrate and the binder in the lower layer is 7-12%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ink-absorbing recording medium having a highly ink-absorbing ink-receiving layer that has high ink-absorbing properties. In particular, the present invention relates to a technique applicable to all ink-absorbing recording media capable of performing printing and image formation with a plurality of inks each having a plurality of different color materials.

  In recent years, an improvement in image quality in an ink jet printer has been desired, and studies have been made from both aspects of an ink jet recording medium and improvements in ink and color material itself. In particular, in the printers after the fall of 2004, color materials that emphasize the light resistance of the color materials themselves are used, and a great technological innovation has been seen.

  In recent years, the technical content of this color material technology development has been almost concentrated. For example, black ink is mainly composed of carbon black, and yellow ink is D.I. Y. Those mainly composed of 132, 92, etc. are useful and are generally used. Further, as magenta ink, an anthrapyridone color material having three or more sulfone groups as water-solubilizing groups and having an additional structure such as a triazine ring has been used from a quinacridone dye. In particular, phthalocyanine dyes having an additional structure such as a triazine ring with improved light resistance have been used for cyan inks of phthalocyanine color materials.

  In addition, pigment ink has been gathered into superposition ink on glossy media, and many color materials remain on the surface area of the media. For this reason, a method of further applying a transparent liquid is employed to protect the surface color material.

  On the other hand, an ink jet recording medium generally has an ink-absorbing and porous ink-receiving layer in which silica particles or alumina hydrate particles, which are pigment particles, are held with a binder. Since the general color material imparted to the ink jet recording medium is anionic, a cationic additive is generally added to the ink receiving layer of the ink jet recording medium. In the ink receiving layer, polyvinyl alcohol having a binder function (hereinafter referred to as “PVA”) is often used to form a porous structure.

  Heretofore, an ink jet recording medium in which the ink receiving layer has a multilayer structure and each layer has a different function has been studied. For example, Patent Document 1 is characterized in that the ink receiving layer has a two-layer structure, and the upper hydrophilic binder / inorganic pigment particles (B / P) are larger than the lower hydrophilic binder / inorganic pigment particles (B / P). The invention is disclosed. However, the technical content of Patent Document 1 is to gradually add a hydrophilic binder (cationic polymer) to the anion of the inorganic pigment and neutralize with the cation of the hydrophilic binder. Further, it is described that an inorganic pigment is polymer-dispersed by cationization with an excess cation. In the specific example of Patent Document 1, the upper layer (B / P) is 23.8 / 100, and the lower layer (B / P) is 16.4 / 100. It has a configuration. Further, this Patent Document 1 suggests that a cationic polymer is added to at least one of the upper layer and the lower layer, and that a cationic polymer is added to both the upper layer and the lower layer. There is also a disclosure of a configuration in which the ink jet recording medium has a pH of 3.5 or more in order to prevent bronzing.

On the other hand, in the examples and comparative examples of Patent Document 2, the upper binder / inorganic pigment particles (B / P) are 20/100 and the lower binder / inorganic pigment particles (B / P) are 22/100. 100 is disclosed. However, the prevention of bronzing which is the object of the invention of Patent Document 2 is solved by adding zirconium or an aluminum compound.
Further, Patent Document 3 discloses an ink jet recording medium having a pH of 8.5 or more in order to prevent bronzing.
JP 2003-72229 A JP 2006-110771 A JP 2004-314635 A

However, the ink jet recording media described in Patent Documents 1 to 3 are still insufficient in ink absorbability. In some cases, bronze prevention is still insufficient. Further, it has not been sufficiently studied about the compatibility between the ink absorptivity and the enlargement of the dot diameter of ink droplets or the prevention of bronzing. Further, it has not been sufficiently studied about ink absorbency, optimization of the dot diameter of ink droplets, and realization of a higher image density at the same time.
Therefore, the present inventor has studied the fixing state of the ink and the color material in the ink jet recording medium. As a result, the following findings were obtained.

  It has been found that there is a difference in the fixing area in the depth direction of the ink jet recording medium depending on the color material type of the ink. As a specific example, yellow ink, cyan ink, and magenta ink were imprinted on an inkjet recording medium. As a result, the yellow ink main fixing area was within the range of 5 μm in the depth direction from the surface of the ink jet recording medium, and the cyan ink main fixing area was in the upper surface area and in the vicinity of the surface area. In addition, there was a main fixing area of magenta ink in a relatively deep portion exceeding 10 μm in the depth direction from the surface of the ink jet recording medium. That is, it has been found that the color material causes variations in the fixing region in the depth direction in the ink jet recording medium.

  The tendency that the fixing area varies due to the above-mentioned ink is particularly remarkable when the ink droplets are 5.5 picoliters or less (preferably 1 picoliter or more), and particularly small droplets of about 2 picoliters. It was getting bigger. At the same time, there was a difference in the size of the dot diameter formed for the ink droplets.

  The present invention is an invention made for these new findings, and provides an ink-absorbing recording medium that has excellent ink absorptivity for at least one kind of ink and can form an appropriate image. This is the main issue.

  In other words, (1) the first problem is to improve the ink absorbency and to form a high-quality recorded image by expanding the dot diameter of the ink droplet after the ink droplet is applied and before the fixing. And providing an ink-absorbing recording medium.

  (2) A second problem is to provide an ink-absorbing recording medium having excellent image quality by achieving both improvement of ink absorbability and prevention of bronze of cyan ink.

  (3) The third problem is that even when a minute ink droplet is applied, the ink absorbability is excellent, and after the ink droplet is applied, the dot diameter of the ink droplet is expanded before fixing. Another object is to provide a high-quality ink-absorbing recording medium.

  (4) A fourth problem is to provide an ink-absorbing recording medium excellent in image quality by preventing bronzing of cyan ink.

  (5) The fifth problem is to improve the ink absorbability, increase the dot diameter of the ink droplet before the ink is fixed, and further increase the image density. Thus, an ink-absorbing recording medium capable of forming a high-quality recorded image is provided.

The first invention solves the first problem.
In other words, the first invention is an ink having a support and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder. An absorbent recording medium,
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer, and the mass ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less. The present invention relates to an ink absorptive recording medium. The total thickness of the upper layer and the lower layer is preferably 30 μm or more. The upper layer preferably has a thickness of 2.0 μm or more and 10 μm or less.

The second invention solves the second problem.
That is, the second invention is an ink having a support, and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder. An absorbent recording medium,
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less, and the thickness of the upper layer is 3 μm or more,
The lower layer constitutes a layer immediately below the upper layer, and the mass ratio of the alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less,
The mass ratio of the alumina hydrate and methanesulfonic acid (methanesulfonic acid) / (alumina hydrate) × 100 in the upper layer and the lower layer is 1.3% to 2.1%, The present invention relates to an ink-absorbing recording medium.

The third invention solves the third problem.
That is, the third invention provides an ink absorptive recording for image formation with an ink droplet of 5.5 pl or less having a support and an ink receiving layer provided on the support and having at least an upper layer and a lower layer. A medium,
The upper layer is a layer in which a porous structure is formed of alumina hydrate and a binder as a surface layer of the ink receiving layer, and the mass ratio of the alumina hydrate and the binder in the upper layer (binder) / (Alumina hydrate) x 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer and has a lower ink permeability than the upper layer, and an ink droplet on the upper layer of the ink receiving layer due to a difference in ink permeability between the upper layer and the lower layer. The present invention relates to an ink-absorbing recording medium characterized in that the dot diameter at the time of fixing an ink droplet to a lower layer can be made larger than that at the time of applying the ink.

The fourth invention solves the fourth problem.
That is, an ink-absorbing recording medium comprising a support and an ink receiving layer provided on the support and having at least an upper layer as a surface layer and a lower layer located immediately below the upper layer,
The upper layer is a layer in which a porous structure is formed by an alumina hydrate and a binder, contains the alumina hydrate and the binder, and the mass ratio of the alumina hydrate and the binder in the upper layer (the binder). ) / (Alumina hydrate) × 100 is 4% or more and 6% or less. The total thickness of the upper layer and the lower layer is preferably 30 μm or more. The upper layer preferably has a thickness of 2.0 μm or more and 10 μm or less.

The fifth invention solves the fifth problem.
That is, an ink-absorbing recording medium comprising: a support; and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder. And
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer, and the ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less,
The present invention relates to an ink-absorbing recording medium, wherein the ink receiving layer has an average pore diameter of 7 nm or more and 10 nm or less. The total thickness of the upper layer and the lower layer is preferably 30 μm or more. The upper layer preferably has a thickness of 2.0 μm or more and 10 μm or less.

The sixth invention solves the first problem.
That is, an ink-absorbing recording medium comprising: a support; and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder. And
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer, and the mass ratio of the alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less,
Mass ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100, Mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) The present invention relates to an ink-absorbing recording medium characterized in that a difference from x100 is 1.5% or more. The average pore diameter of the ink receiving layer is preferably 7 nm or more and 10 nm or less. The total thickness of the upper layer and the lower layer is preferably 30 μm or more. The upper layer preferably has a thickness of 2.0 μm or more and 10 μm or less.

  In the third invention, the upper layer is “ink-permeable” means that at least a part of the ink component applied on the surface of the upper layer is a surface opposite to the surface from the upper layer surface (boundary with the lower layer). Surface).

  (1) In the first invention, the upper layer has excellent ink absorptivity, and ink droplets applied on the upper layer can be transmitted through the upper layer at a high speed to prevent bleeding. The ink absorbency in the lower layer is lower than the ink absorbability in the upper layer. For this reason, it is possible to obtain an excellent recorded image in which the dot diameter of the ink droplet is increased and the interval between the dots is small in the boundary portion or the lower layer between the upper layer and the lower layer while preventing bleeding.

  (2) In the second invention, the upper layer has excellent ink absorptivity, and ink droplets imparted on the upper layer can be transmitted through the upper layer at a high speed to prevent bleeding. Further, it is possible to prevent the occurrence of bronzing by preventing aggregation of ink, particularly cyan ink, in the ink receiving layer.

  (3) In the third invention, the upper layer has excellent ink absorptivity, and ink droplets applied on the upper layer can pass through the upper layer at a high speed to prevent bleeding. Even when ink droplets of 5.5 picoliters or less, in which the interval between the dots tends to be large with respect to the dot diameter of the ink droplets, are applied, the ink droplets are appropriately spread in the lower layer to form dots. The interval between them can be reduced. As a result, a high-quality and high-definition recorded image can be obtained.

  (4) In the fourth invention, it is possible to prevent the occurrence of bronzing by preventing aggregation of ink, particularly cyan ink, in the ink receiving layer.

  (5) In the fifth invention, the upper layer has excellent ink absorptivity, and ink droplets applied on the upper layer can be transmitted through the upper layer at a high speed to prevent bleeding. The ink absorbency in the lower layer is lower than the ink absorbability in the upper layer. For this reason, it is possible to obtain an excellent recorded image in which the dot diameter of the ink droplet is increased and the interval between the dots is small in the boundary portion or the lower layer between the upper layer and the lower layer while preventing bleeding. Furthermore, a recording image with a high image density can be obtained by using a highly transparent ink-receiving layer.

  (5) In the sixth invention, the upper layer has excellent ink absorptivity, and ink droplets applied on the upper layer can be transmitted through the upper layer at a high speed to prevent bleeding. The ink absorbency in the lower layer is lower than the ink absorbability in the upper layer. For this reason, it is possible to obtain an excellent recorded image in which the dot diameter of the ink droplet is increased and the interval between the dots is reduced in the boundary portion between the upper layer and the lower layer or in the lower layer while preventing bleeding.

The best mode of the present invention will be described below including the configuration of each invention.
A) Best production conditions (1) Coating liquid for upper layer Alumina hydrate Disperal HP14 (manufactured by Sasol) was added to pure water so as to be 30% by mass as inorganic pigment particles. Next, methanesulfonic acid is added to the alumina hydrate so that the mass ratio (methanesulfonic acid) / (alumina hydrate) × 100 is 1.7%, and the mixture is stirred to obtain a colloidal sol. Obtained. The obtained colloidal sol was appropriately diluted so that the alumina hydrate was 27% by mass to obtain colloidal sol A.

  On the other hand, polyvinyl alcohol PVA235 (manufactured by Kuraray Co., Ltd.) was dissolved in ion-exchanged water to obtain a PVA aqueous solution having a solid content of 8% by mass. The PVA solution prepared in the colloidal sol A prepared above is 5% in terms of PVA solid content converted mass ratio (binder) / (alumina hydrate) × 100) with respect to the solid content of alumina hydrate. It mixed so that it might become. Next, 3 mass% boric acid aqueous solution is mixed so that it may become 1.0 mass% in boric acid solid content conversion with respect to the solid content of an alumina hydrate, and the upper layer coating liquid (1) is obtained. It was.

(2) Lower layer coating solution Into pure water, alumina hydrate Disperal HP14 (manufactured by Sasol Corporation) was added as inorganic pigment particles so as to be 30% by mass. Next, methanesulfonic acid was added to the alumina hydrate so that the mass ratio (methanesulfonic acid) / (alumina hydrate) × 100 was 1.7%. Thereafter, the diallylamine hydrochloride / sulfur dioxide copolymer (PAS-92, molecular weight 5000, manufactured by Nittobo Co., Ltd.) is used in a mass ratio (diallylamine hydrochloride / sulfur dioxide copolymer) / (alumina water). (Japanese product) × 100 was added to 0.5%. Thereafter, the mixed solution was stirred to obtain a colloidal sol. The obtained colloidal sol was appropriately diluted so that the alumina hydrate was 27% by mass to obtain colloidal sol A.

  On the other hand, polyvinyl alcohol PVA235 (manufactured by Kuraray Co., Ltd.) was dissolved in ion-exchanged water to obtain a PVA aqueous solution having a solid content of 8% by mass. Then, the prepared PVA solution is mixed with the colloidal sol A prepared above so that the mass ratio (binder) / (alumina hydrate) × 100) is 8% with respect to the solid content of the alumina hydrate. did. Next, 3 mass% boric acid aqueous solution is mixed so that it may become 1.7 mass% in conversion of boric acid solid content with respect to the solid content of an alumina hydrate, and the coating liquid (2) for lower layers is obtained. It was.

(3) Coating The lower layer coating liquid (2) and the upper layer coating liquid (1) were simultaneously coated on a support and dried to obtain an ink-absorbing recording medium. . At this time, by containing the alumina hydrate and the cationic polymer in the lower layer coating liquid, coagulation of the alumina hydrate and the cationic polymer occurs during mixing and dispersion of the lower layer coating liquid. Further, in the drying process at the time of coating, a rapid coagulation of the alumina hydrate and the cationic polymer is caused by the colloidal interaction accompanying the evaporation of moisture. For this reason, the cationic polymer can be fixed in the lower layer by the dispersion in the production process and coagulation during evaporation and drying, and the cationic polymer in the lower layer does not diffuse into the upper layer. In the best mode of the present invention, alumina hydrate is used as the upper and lower inorganic pigments.

B) Ink-absorbing recording medium The obtained ink-absorbing recording medium takes advantage of the characteristics of the coating liquid. That is, the upper layer has a mass ratio (methanesulfonic acid) / (alumina hydrate) × 100 of 1.7%, a mass ratio (binder) / (alumina hydrate) × 100 of 5%, and a layer thickness of 5 μm. Met. In the lower layer, the mass ratio (methanesulfonic acid) / (alumina hydrate) × 100 is 1.7%, and the mass ratio (diallylamine hydrochloride / sulfur dioxide copolymer) / (alumina hydrate) × 100 is 0.00. It was 5%. The mass ratio (binder) / (alumina hydrate) × 100 was 8%, and the layer thickness was 30 μm.

  In particular, in this case, since the alumina hydrate and binder used are the same, the boundary region between the upper layer and the lower layer is in close contact with each other. Since the upper layer and lower layer are produced by contact with each other in the liquid, the lower layer of diallylamine hydrochloride / sulfur dioxide copolymer slightly diffuses into the upper layer of the boundary area in the upper and lower boundary areas as seen from the thickness. It was. However, an upper region where the diallylamine hydrochloride / sulfur dioxide copolymer did not exist was confirmed on the surface side of the upper layer.

C) Printing characteristics and evaluation for ink-absorbing recording medium B) The following results were obtained when printing was performed on the ink-absorbing recording medium B) using a color material having a special structure described later. It was.
First, the anthrapyridone dye did not penetrate deep into the ink-absorbing recording medium, and a fixing area could be secured above the lower layer (a desired area inside the ink-absorbing recording medium). That is, it was possible to secure a prescribed region for the presence of the cationic polymer in the lower layer, and to secure a desired concentration. As a result, the occurrence of migration of magenta ink could be prevented.

  In the ink-absorbing recording medium B), the mass ratio of the upper layer (binder) / (alumina hydrate) × 100 has a specific value, and the ink absorptivity is improved. For this reason, most of the phthalocyanine dye can be absorbed, no bronze is present, and a high image density can be sufficiently secured. At the same time, since the upper layer has a region on the surface side where the cationic polymer present in the lower layer is not diffused, generation of bronze due to the cationic polymer was prevented.

  That is, in the above-mentioned best mode, it was possible to obtain an innovative ink-absorbing recording medium that solved the two causes of the occurrence of bronzing by using both of these configurations. Further, when other inks were also evaluated, an image density superior to that of the conventional ink could be obtained. Moreover, when viewed imagewise, the intercolor bleed has been greatly improved mainly by the upper layer having improved ink absorbability.

D) Technical Contents Included in the Best Mode Generally, a more appropriate mode for the magenta ink is to have a cationic polymer on the recording medium side. On the other hand, however, the bronze effect of cyan ink due to the cationic polymer is the worst. Accordingly, the ink-absorbing recording medium of the present invention has the above-described excellent effects because the region where the cationic polymer is present is determined as a specific region of the ink-receiving layer as in the above-described configuration. it can.

  When the ink absorbency is improved as in the above upper layer structure, the magenta ink is more likely to penetrate into the inside. In the present invention, a stable image forming region is included in the specific fixing region in the upper layer. have. At the same time, this upper layer prevents the occurrence of bleeding due to the effect of improving the ink absorbency, and for cyan ink, the surface remains less due to the ink absorption inside. As a result, bronzing can be prevented.

  Since the image density of the fixed ink is largely due to the thickness of the upper layer, the thickness of the upper layer is preferably 2 μm or more and 10 μm or less, more preferably 8 μm or less. In addition, the upper limit of the upper layer thickness is more preferably 3 μm or more from the viewpoint of the stability of the upper layer. Furthermore, the thickness of the upper layer is more preferably 5 μm. As the cationic polymer, a diallylamine hydrochloride / sulfur dioxide copolymer obtained by combining yellowing prevention effects is preferable.

  Considering full solid printing, the total thickness of the upper layer and the lower layer is preferably 30 μm or more. This is because when the support is made of so-called resin-coated paper, the series of water, solvent, etc. in the ink may not be sufficient. The best mode is more preferably 35 μm.

  The upper layer and the lower layer further contain an alkyl sulfonic acid, and the mass ratio of the alumina hydrate to the alkyl sulfonic acid in the upper layer and the lower layer (alkyl sulfonic acid) / (alumina hydrate) × 100 is 1.3. % Or more and 2.1% or less is preferable.

  It is known that when the pH of the ink receiving layer is too low, aggregation of dyes such as cyan ink is promoted to cause bronze. For this reason, the pH of the entire ink receiving layer is preferably adjusted to a range of 4.5 to 5.5, more preferably adjusted to a range of 4.8 to 5.3, more preferably to 5.1. More preferably.

  As the acid having such a paper pH, monovalent acids having a low acid dissociation constant are effective. Specifically, alkylsulfonic acid, nitric acid, and hydrochloric acid are conceivable. However, nitrate has a problem in terms of chemical safety, and hydrochloric acid has a problem of corroding a metal part of a production line such as SUS. For this reason, it is preferable to use alkylsulfonic acid as the acid for adjusting the paper surface pH. Therefore, in the above best mode, the mass ratio of alkylsulfonic acid to alumina hydrate (alkylsulfonic acid) / (alumina hydrate) × 100 in the upper layer and the lower layer is 1.3% or more and 2.1% or less. It is said. As a result, the entire ink receiving layer can be adjusted within the above pH range.

  In addition, even when the ink receiving layer is composed of two layers of the upper layer and the lower layer or when the ink receiving layer is composed of three or more layers, the total of the upper layer and the lower layer is (alkyl sulfonic acid) / (alumina hydrate) × 100 may be 1.3% or more and 2.1% or less. This alkyl sulfonic acid is easier to adjust the pH of the ink receiving layer than a weak acid having a buffer function such as formic acid, acetic acid and glycolic acid.

  Examples of the alkyl sulfonic acid include methane sulfonic acid, ethane sulfonic acid, butane sulfonic acid, and iso-propane sulfonic acid. Among these alkyl sulfonic acids, it is preferable to use methane sulfonic acid because of easy pH adjustment. In the present invention, a strong acid such as hydrochloric acid or nitric acid may be used in addition to the alkylsulfonic acid.

  The mass ratio of alkyl sulfonic acid (alkyl sulfonic acid) / (alumina hydrate) × 100 is preferably 1.5% or more and 1.9% or less, and more preferably 1.7% by mass. . Thereby, when this alkylsulfonic acid is added to the ink receiving layer, it is possible to further improve the migration resistance of the magenta dye and to improve the color stability during black ink printing.

  The ink absorptive recording media of the first to sixth inventions have a support and an ink receiving layer composed of two or more layers on the support. The ink receiving layer has at least an upper layer and a lower layer, and the number of layers is not particularly limited as long as it is composed of two or more layers. This upper layer constitutes the surface layer (outermost layer) of the ink receiving layer, and is composed of a porous and excellent ink permeability composition. Ink droplets applied on the upper layer permeate the inside at a high speed. A possible ink permeable layer. The ink absorptive recording media of the first to sixth inventions can have high ink absorptivity by having such an upper layer.

Further, the lower layer constitutes a layer immediately below the upper layer, and the upper layer and the lower layer are in contact with each other through the boundary surface. This lower layer has a specific composition, structure, and the like, and therefore has a lower ink permeability than the upper layer.
Hereinafter, each material used in the first to sixth inventions will be described in detail.

(Support)
Examples of the support used in the first to sixth inventions include papers such as cast-coated paper, baryta paper, and resin-coated paper (resin-coated paper coated on both sides with a resin such as polyolefin) and films. A thing etc. are used preferably. As this film, for example, the following transparent thermoplastic resin film can be used.
-Polyethylene, polypropylene, polyester, polylactic acid, polystyrene, polyacetate, polyvinyl chloride, cellulose acetate, polyethylene terephthalate, polymethyl methacrylate, polycarbonate.

In addition to this, non-size paper or coated paper, which is appropriately sized paper, or a sheet-like substance (synthetic paper or the like) made of a film made opaque by filling with inorganic substances or fine foaming can be used. Further, a sheet made of glass or metal may be used. Furthermore, in order to improve the adhesive strength between the support and the ink receiving layer, the surface of the support can be subjected to corona discharge treatment or various undercoat treatments.
Among the above-mentioned supports, it is preferable to use resin-coated paper from the viewpoint of quality such as glossiness of the recording medium after forming the ink receiving layer.

(Alumina hydrate)
In the first to sixth inventions, alumina hydrate is used in the upper layer and the lower layer to form a porous structure and satisfy the dye fixing property, transparency, printing density, color developability, and glossiness. As this alumina hydrate, what is represented by the following general formula (X) can be used suitably, for example.
Al ₂ O _3-n (OH) _2n · mH ₂ O ... (X)
(In the above formula, n represents any of 0, 1, 2, or 3, and m represents a value in the range of 0 to 10, preferably 0 to 5. However, m and n are not 0 at the same time. MH ₂ O often represents a detachable aqueous phase that does not participate in the formation of the crystal lattice, so m can be an integer or non-integer value. When heated, m can reach a value of 0).

  As the crystal structure of the alumina hydrate, amorphous, kibsite type, and boehmite type are known according to the heat treatment temperature, and any of these crystal structures can be used.

  Among these, a preferred alumina hydrate is an alumina hydrate that exhibits a boehmite structure or an amorphous state by analysis by an X-ray diffraction method. Specific examples include alumina hydrates described in JP-A-7-232473, JP-A-8-132731, JP-A-9-66664, JP-A-9-76628, and the like. .

  In the fifth invention, it is necessary to use an ink receiving layer having an average pore diameter of 7 nm to 10 nm, and in the sixth invention, an ink receiving layer having an average pore diameter of 7 nm to 10 nm is used. Is preferred. More preferably, an ink receiving layer having an average pore diameter of 8.0 nm or more and 10 nm or less is used. When the average pore diameter of the ink receiving layer is within these ranges, excellent ink absorbability and color developability can be exhibited. Further, if the average pore diameter of the ink receiving layer is smaller than these ranges, the ink absorbing property of the ink receiving layer is insufficient, and even if the amount of the binder with respect to the alumina hydrate is adjusted, sufficient ink absorption is achieved. You may not get it. Further, when the average pore diameter of the ink receiving layer is larger than this range, the haze of the ink receiving layer increases, and good color developability may not be obtained.

  The pore volume of the entire ink receiving layer is preferably 0.50 ml / g or more in terms of the total pore volume. If the total pore volume is less than this value, the ink absorption of the entire ink receiving layer is insufficient, and even if the amount of the binder relative to the alumina hydrate is adjusted, sufficient ink absorption may not be obtained. is there.

  Furthermore, it is preferable that pores having a pore radius of 25 nm or more do not exist in the ink receiving layer. When pores of 25 nm or more are present, the haze of the ink receiving layer is increased, and good color developability may not be obtained.

  The average pore diameter, the total pore volume, and the pore radius are the BJH (Barrett-Joyner-Halenda) method based on the adsorption / desorption isotherm of nitrogen gas measured on the recording medium by the nitrogen adsorption / desorption method. This is a value obtained using. In particular, the average pore diameter is a value obtained by calculation from the total pore volume and specific surface area measured during nitrogen gas desorption.

  Note that when the ink-absorbing recording medium is measured by the nitrogen adsorption / desorption method, the measurement is also performed on portions other than the ink receiving layer. However, the components other than the ink receiving layer (for example, the pulp layer of the substrate, the resin coating layer, etc.) do not have pores in the range of 1 to 100 nm, which is a range generally measurable by the nitrogen adsorption / desorption method. For this reason, when the entire ink-absorbing recording medium is measured by the nitrogen adsorption / desorption method, it is considered that the average pore diameter of the ink receiving layer is measured. This is also inferred from the fact that the resin-coated paper has no pores between 1 and 100 nm when the pore distribution is measured by the nitrogen adsorption / desorption method.

Moreover, in order to obtain the average pore diameter when forming the ink receiving layer as described above, it is preferable to use an alumina hydrate having a BET specific surface area of 100 m ² / g or more and 200 m ² / g or less. More preferably, the average pore diameter of the ink receiving layer is 125 m ² / g or more and 175 m ² / g or less.

  The BET method is a method for measuring the surface area of a powder by a vapor phase adsorption method, and is a method for obtaining the total surface area, that is, the specific surface area of a 1 g sample from an adsorption isotherm. In this BET method, nitrogen gas is usually used as an adsorbed gas, and the most frequently used method is to measure the amount of adsorption from the change in pressure or volume of the gas to be adsorbed. At this time, the most prominent expression representing the isotherm of multimolecular adsorption is the Brunauer, Emmett, and Teller equation, which is called the BET equation and is widely used for determining the specific surface area. In the BET method, the specific surface area is obtained by calculating the amount of adsorption based on the BET formula and multiplying the area occupied by one adsorbed molecule on the surface. In the BET method, in the nitrogen adsorption / desorption method, the relationship between the adsorption amounts at a certain relative pressure is measured at several points, and the specific surface area is derived by obtaining the slope and intercept of the plot by the least square method. For this reason, in order to increase the accuracy of measurement, it is preferable to measure at least 5 points, and more preferably 10 points or more, between the relative pressure and the amount of adsorption.

  Further, the preferred shape of the alumina hydrate is preferably a flat plate having an average aspect ratio of 3.0 to 10 and an aspect ratio of the flat plate surface of 0.60 to 1.0. The aspect ratio can be determined by the method described in Japanese Patent Publication No. 5-16015. That is, the aspect ratio is expressed by the ratio of (diameter) to (thickness) of particles. Here, the “diameter” indicates a diameter (equivalent circle diameter) of a circle having an area equal to the projected area of the particles when the alumina hydrate is observed with a microscope or an electron microscope. Similarly to the aspect ratio, the aspect ratio of the flat plate surface indicates the ratio of the diameter indicating the minimum value of the flat plate surface and the diameter indicating the maximum value when the particles are observed with a microscope.

  When alumina hydrate having an aspect ratio outside the above range is used, the pore distribution range of the formed ink receiving layer may be narrowed. For this reason, it may be difficult to produce the alumina hydrate with the same particle size. Similarly, when a material having an aspect ratio outside the above range is used, the pore diameter distribution of the ink receiving layer becomes narrow.

  Rocek J. et al. , Et al. As described in Applied Catalysis, Vol. 74, p29-36, 1991, it is known that some alumina hydrates are ciliated and non-ciliated. According to the knowledge of the present inventor, even with the same alumina hydrate, the plate-like alumina hydrate has better dispersibility than the ciliated alumina hydrate. In addition, cilia-like alumina hydrate may have small pores formed by being oriented parallel to the surface of the support during coating, and the ink absorbability of the ink receiving layer may be reduced. On the other hand, the plate-like alumina hydrate has a small tendency to be oriented by coating, and does not adversely affect the pore size and ink absorbability of the ink receiving layer formed. For this reason, it is preferable to use a plate-like alumina hydrate.

(binder)
The ink receiving layers of the first to sixth inventions contain a binder. As the binder, particularly if it is a material capable of binding the above-mentioned alumina hydrate and forming a film, and that does not impair the effects of the first to sixth inventions. Can be used without restriction. Examples of the binder include the following.
-Starch derivatives such as oxidized starch, etherified starch and phosphate esterified starch.
-Cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose.
Casein, gelatin, soy protein, polyvinyl alcohol or derivatives thereof.
Conjugated polymer latex such as polyvinylpyrrolidone, maleic anhydride resin, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer.
-Acrylic polymer latex such as acrylic acid ester and methacrylic acid ester polymers.
-Vinyl polymer latex such as ethylene-vinyl acetate copolymer.
-Functional group-modified polymer latex with functional group-containing monomers such as carboxyl groups of the above-mentioned various polymers.

-Those obtained by cationizing the above-mentioned various polymers using a cationic group, or those obtained by cationizing the surface of the above-mentioned various polymers using a cationic surfactant.
A polymer obtained by polymerizing the above various polymers under cationic polyvinyl alcohol and distributing the polyvinyl alcohol on the surface of the polymer.
A polymer obtained by polymerizing the above-mentioned various polymers in a suspension dispersion of cationic colloidal particles and distributing the cationic colloidal particles on the surface of the polymer.
-Aqueous binders such as thermosetting synthetic resins such as melamine resin and urea resin.
A polymer or copolymer resin of acrylic acid ester or methacrylic acid ester such as polymethyl methacrylate.
Synthetic resin binders such as polyurethane resin, unsaturated polyester resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, alkyd resin.

  The said binder can be used individually or in mixture of multiple types. Among them, the most preferably used binder is polyvinyl alcohol. As this polyvinyl alcohol, the normal polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate can be mentioned. As this polyvinyl alcohol, those having an average degree of polymerization of 1500 or more are preferably used, and those having an average degree of polymerization of 2000 or more and 5000 or less are more preferred. The degree of saponification is preferably from 80 to 100, more preferably from 85 to 100.

  In addition to these, modified polyvinyl alcohols such as polyvinyl alcohols whose ends are cationically modified and anionic modified polyvinyl alcohols having an anionic group can be used.

  By the way, when using polyvinyl alcohol, the terminal group of polyvinyl alcohol has a hydroxyl group or an acetate group, and is composed of a monomer component having a hydroxyl group and a monomer component having an acetate group. When modified polyvinyl alcohol is used, the terminal hydroxyl group or acetic acid group is substituted with a substituent such as a cationic group or an anionic group. For this reason, it is comprised by the monomer component which has an acetic acid group, the monomer component which has a hydroxyl group, and the monomer component which has a substitution machine, and a polymerization degree is equivalent and a saponification degree differs. Or when polyvinyl alcohol is modified | denatured, mass is the same and the quantity as polyvinyl alcohol which has an effect as a binder component may differ.

  In the present invention, since the porous structure formed by making alumina hydrate and the binder into a special ratio is important, the presence of polyvinyl alcohol effective as a binder component is important. Therefore, in the present invention, when polyvinyl alcohol is used, the amount thereof is kept constant, and therefore, when mixed with alumina hydrate, it is converted into polyvinyl alcohol having a saponification degree of 88% for mass calculation. It was decided.

(Other materials)
In the 1st-6th invention, the following material can be contained in an ink receiving layer (upper layer and lower layer) as needed.
Boric acid and borate In the ink receiving layer, at least one of boric acid and borate may be added. By adding boric acid and borate, the occurrence of cracks in the ink receiving layer can be prevented. In this case, examples of boric acid that can be used include not only orthoboric acid (H ₃ BO ₃ ) but also metaboric acid and hypoboric acid. The borate is preferably a water-soluble salt of boric acid. Specific examples include the following alkaline earth metal salts of boric acid.
・ Boric acid sodium salt (Na ₂ B ₄ O ₇ .10H ₂ O, NaBO ₂ .4H ₂ O, etc.), boric acid potassium salt (K ₂ B ₄ O ₇ .5H ₂ O, KBO ₂ etc.), etc. Alkali metal salt.
Ammonium salts of boric acid _{(NH 4 B 4 O 9 ·} 3H 2 O, NH 4 BO 2 , etc.).
-Magnesium and calcium salts of boric acid.

  Among these boric acids and the like, it is preferable to use orthoboric acid from the viewpoint of the temporal stability of the coating solution and the effect of suppressing the occurrence of cracks. Moreover, as usage-amounts, such as a boric acid, it is preferable to use in boric acid solid content 10 mass% or more and 50.0 mass% or less with respect to the binder in an upper layer and a lower layer. When the above range is exceeded, the temporal stability of the coating solution may be lowered. That is, when producing an ink-absorbing recording medium, the coating liquid is used for a long time, and when the content of boric acid is large, the viscosity of the coating liquid increases and the generation of a gelled product occurs. May happen. For this reason, it is necessary to frequently change the coating liquid, clean the coater head, and the like, and the productivity may be significantly reduced. Further, when the above range is exceeded, dot-like surface defects tend to occur in the ink receiving layer, and a uniform and good glossy surface may not be obtained. Even if the amount of boric acid used is within the above range, cracks may occur in the ink-receiving layer depending on the production conditions, etc., so it is necessary to select an appropriate amount range.

(Cationic polymer)
In the present specification, the “cationic polymer” is a general term for polyallylamine hydrochloride, methyldiallylamine hydrochloride polymer, and diallylamine hydrochloride / sulfur dioxide copolymer. That is, the cationic polymer represents at least one selected from the group consisting of polyallylamine hydrochloride, methyldiallylamine hydrochloride polymer, and diallylamine hydrochloride / sulfur dioxide copolymer.

  A magenta dye, which is a coloring material of magenta ink, has a characteristic that insolubilization and aggregation due to acid precipitation hardly occur in an acidic region, unlike azo dyes and phthalocyanine dyes. For this reason, a sufficient migration preventing effect cannot be obtained only by lowering the pH of the paper surface. Therefore, by containing a cationic polymer in the lower layer, it is possible to effectively agglomerate and fix the magenta dye, which is the color material of the magenta ink, and to suppress migration. This cationic polymer exhibits an excellent effect in fixing the quinacridone dye, and exhibits the most excellent effect in fixing the anthrapyridone dye.

Cationic polymers that can be used in the present invention are shown below.
Polyallylamine hydrochloride is a compound represented by the following formula (1).

  The methyl diallylamine hydrochloride polymer is a compound represented by the following formula (2).

  The diallylamine hydrochloride / sulfur dioxide copolymer is a compound represented by the following formula (3).

  Further, since alumina hydrate is used as the pigment particles, the dispersibility of alumina can be improved by the interaction with the cationic polymer. Further, among these cationic polymers, it is preferable to use a diallylamine hydrochloride / sulfur dioxide copolymer from the viewpoint of suppression of yellowing with time and OD. Further, since the diallylamine hydrochloride / sulfur dioxide copolymer has a bulky portion, it can prevent diffusion of the copolymer to the surface of the ink-receiving layer when the lower coating liquid is applied. it can.

  The cationic polymer is more preferably 0.5 parts by mass and 0.75 parts by mass with respect to 100 parts by mass of the alumina hydrate in the upper layer and the lower layer. Furthermore, the mass ratio of (total amount of cationic polymer and methanesulfonic acid) / (alumina hydrate) in the upper layer and the lower layer is preferably 1.5% by mass or more and 2.7% by mass or less.

The mass ratio of (total amount of cationic polymer and methanesulfonic acid) / (alumina hydrate) in the lower layer is preferably 1.5% or more and 2.7% or less.
When the total amount of the cationic polymer and methanesulfonic acid is within these ranges, magenta ink migration, black ink color stability, and bronzing can be simultaneously achieved.

  If the cationic polymer is present on the upper layer surface of the ink receiving layer, it is effective in suppressing the migration of the magenta dye, but bronzing may occur when cyan ink is printed. In particular, this bronze is more noticeably generated in a cyan ink using a cyan dye whose cohesiveness is improved in order to improve fastness. For this reason, both the migration of the magenta dye and the occurrence of bronzing of the cyan ink can be effectively prevented by allowing a large amount of the cationic polymer to be present in the lower layer rather than the upper surface of the ink receiving layer.

  In a typical example, when magenta ink is driven onto the surface of the ink receiving layer, the magenta dye penetrates to a depth of 10 μm from the surface of the ink receiving layer. For this reason, even if the cationic polymer is present in a portion deeper than the dyeing position of the magenta dye, a sufficient magenta ink migration suppressing effect cannot be obtained. For this reason, the cationic polymer is preferably not present on the upper layer surface of the ink receiving layer but at a position deeper than 10 μm from the upper layer surface of the ink receiving layer.

  In order to optimize the existence position of the cationic polymer in the ink receiving layer as described above, it is preferable not to contain the cationic polymer in the upper layer but to contain the cationic polymer only in the lower layer.

  Further, if the weight average molecular weight of the cationic polymer added to the coating solution is small, the cationic polymer may diffuse into the upper layer during coating of the upper layer and the lower layer, thereby causing bronze deterioration. Also, when the ink receiving layer contains a high content of moisture, such as when stored under high humidity, the cationic polymer diffuses to the upper layer surface of the ink receiving layer and causes migration. For this reason, it is preferable that the weight average molecular weight of a cationic polymer is 3000 or more at the point of preventing the spreading | diffusion of the cationic polymer to the surface side of an upper layer. On the other hand, if the weight average molecular weight of the cationic polymer is too large, the cationic polymer causes an agglomeration reaction with the alumina hydrate when the alumina hydrate such as alumina hydrate is dispersed, thereby improving the transparency of the ink receiving layer. In some cases, the image quality may be lowered to lower the image density. For this reason, the weight average molecular weight of the cationic polymer is preferably 15000 or less. The weight average molecular weight of the cationic polymer is more preferably 5000.

  In addition, since the diffusion of the cationic polymer to the upper layer surface of the ink receiving layer occurs through moisture, it is preferable to use a cationic polymer that does not have many solubilizing groups or a cationic polymer that has a bulky portion. . For this reason, it is more preferable to use a bulky diallylamine hydrochloride / sulfur dioxide copolymer in the polymer main chain.

-PH adjuster In the coating liquid for forming an ink receiving layer (upper layer, lower layer), for example, the following acids or salts can be appropriately added as a pH adjuster.
-Formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, malonic acid, succinic acid, adipic acid, maleic acid, malic acid, tartaric acid, citric acid, benzoic acid, phthalic acid.
-Isophthalic acid, terephthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, pimelic acid, suberic acid, methanesulfonic acid.
-Inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid.
-Salts of the above acids.

  It is preferable to use a monobasic acid to disperse the alumina hydrate in water. For this reason, it is preferable to use organic acids, such as formic acid, acetic acid, glycolic acid, and methanesulfonic acid, hydrochloric acid, nitric acid, etc. among the said pH adjusters.

・ Additives Other additives for coating liquids include pigment dispersants, thickeners, fluidity improvers, antifoaming agents, antifoaming agents, surfactants, mold release agents, penetrating agents, and coloring pigments Colored dyes can be used. In addition, a fluorescent brightener, an ultraviolet absorber, an antioxidant, an antiseptic, an antifungal agent, a water resistant agent, a dye fixing agent, a curing agent, a weather resistant material, and the like can be appropriately added as necessary.

・ Coating liquid coating method The upper layer coating liquid for forming the ink receiving layer and the lower layer coating liquid are coated with two or more layers and an appropriate coating amount. As obtained, for example, the following coating method can be used, and coating is performed on-machine and off-machine.
・ Various curtain coaters and coaters using the extrusion method.
・ Coater using slide hopper method.
In addition, at the time of coating, for the purpose of adjusting the viscosity of the coating solution, the coating solution may be heated, or the coater head can be heated.

  For drying the coating liquid after coating, for example, a hot air dryer such as a straight tunnel dryer, an arch dryer, an air loop dryer, a sine curve air float dryer, or the like can be used. In addition, a dryer using infrared rays, a heated dryer, a microwave, or the like can be appropriately selected and used.

  In the first to sixth inventions, content components move between the upper layer and the lower layer by selecting a coating liquid having an appropriate viscosity and physical properties as described above and a suitable coating method. There can be little or no happening. For this reason, the state of the binder component in the boundary region between the upper layer and the lower layer is separated so that a desired amount is obtained in the upper layer and the lower layer, and the concentration of the binder component exists in the interface region at different concentrations in the upper layer and the lower layer. There may be. Alternatively, when the binder component in the lower layer slightly moves to the upper layer in the interface region, there may be a portion where the concentration is different in three stages from the upper layer, the interface region, and the lower layer. However, by selecting a coating solution having an appropriate viscosity and physical properties as described above, and a suitable coating method, there is almost no movement of content components between the upper layer and the lower layer, which affects the effect of the present invention. The content component does not move as much as given.

Examples of the method for confirming the concentration distribution of the binder component in the coating layer include the following methods.
That is, the ink-absorbing recording medium is cut out in the cross-sectional direction with microtorr or the like, and the binder component is dyed with osmic acid. Thereafter, by using EPMA element color mapping and preparing a calibration curve with a sample having a known binder amount, the amount of the binder component in the upper layer and the lower layer can be quantified.
Next, each color dye used in the ink used for printing will be described.

(Dye used for cyan ink)
At the time of 2003, a phthalocyanine dye of the following formula (4) having a structure containing a plurality of solubilizing groups such as sodium sulfonate at an arbitrary position was common.

On the other hand, phthalocyanine dyes that have been used since autumn 2004 are those in which a solubilizing group-substituted triazine ring is introduced as a solubilizing group in order to improve light resistance and gas resistance. The use of a phthalocyanine dye into which a solubilizing group-substituted triazine ring has been introduced in recent years is the best embodiment of the present invention.
As the phthalocyanine dye into which the solubilizing group-substituted triazine ring is introduced, a compound of the following formula (5) can be used.

Here, l, m, and n are l = 0-2, m = 1-3, and n = 1-3 (however, l + m + n = 3-4).

(Dye used for magenta ink)
As an anthrapyridone dye, C.I. I. Acid Red 80, C.I. I. Acid Red 81, C.I. I. Acid Red 82, C.I. I. Acid Red 83, C.I. I. Acid Violet 39 is mentioned. Moreover, the dye of following formula (6) can be mentioned.

  Until 2003, the anthrapyridone dyes exemplified above were mainly used. On the other hand, since the fall of 2004, in order to improve anthrapyridone dyes, those in which a substituted triazine ring is introduced as a solubilizing group as a solubilizing group as in the following formula (7) have been used.

A recent embodiment using an anthrapyridone dye into which a solubilizing group-substituted triazine ring is introduced is the best embodiment of the present invention.

(Dye used for yellow ink)
Yellow ink is C.I. I. A general dimer of an azo compound represented by Direct Yellow 132 (the following formula (8)) can be used.

(Dye used for black ink)
As the black ink, a polyazo compound represented by the following formulas (9) and (10) can be used.

Hereinafter, the first to sixth inventions will be described in detail.

(1) 1st invention 1st invention is related with the ink absorptive recording medium which has a support body and the ink receiving layer provided on the support body, as shown in FIG. This ink receiving layer has at least an upper layer a and a lower layer b in which a porous structure is formed by alumina hydrate and a binder. Further, the mass ratio of the alumina hydrate and the binder in the upper layer (binder) / (alumina hydrate) × 100 is 4.0% or more and 6.0% or less.

  The lower layer constitutes a layer immediately below (directly below) the upper layer, and contains alumina hydrate and a binder. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the alumina hydrate and binder in the lower layer is 7% or more and 12% or less.

  In the present invention, the upper layer contains alumina hydrate and binder in a special ratio of (binder) / (alumina hydrate) × 100 of 4.0% to 6.0%. For this reason, the upper layer maintains the mechanical strength required for the ink receiving layer and retainability of the layer, and reduces the portion of the porous structure c in the upper layer that is blocked by the binder as much as possible, thereby reducing the porous structure. The pore volume can be increased. As a result, high ink permeability (ink absorbability) can be obtained, and ink bleeding on the upper layer surface can be effectively prevented.

Here, when (binder) / (alumina hydrate) × 100 is less than 4.0%, the amount of alumina hydrate necessary to form a layer and the binder are not bonded. As a result, cracks are likely to occur in the ink receiving layer, and the mechanical strength of the ink receiving layer tends to be insufficient and powder falling tends to occur. On the other hand, when (binder) / (alumina hydrate) × 100 exceeds 6.0% by mass, a large number of porous structures of the ink receiving layer are blocked by the binder. As a result, the pore volume of the porous structure of the ink receiving layer is reduced, and the permeation of ink droplets into the upper layer is inhibited. For example, when a solid print of a different color is printed in an adjacent state, another ink may ooze out from each other at the boundary portion.
In addition, it is preferable that (binder) / (alumina hydrate) × 100 in the upper layer is 4.5% or more and 5.5% or less.

  In the present invention, the lower layer contains alumina hydrate and binder at a special ratio of (binder) / (alumina hydrate) × 100 of 7.0% to 12%. For this reason, the lower layer can be bonded to the upper layer with high adhesive strength while maintaining the mechanical strength required for the ink receiving layer and the characteristics required for the upper support layer.

  Further, the ink permeability in the lower layer can be lowered in the lower layer than in the upper layer by increasing the binder amount with respect to the alumina hydrate. That is, as shown in FIG. 2, the porous structure in the lower layer is closed with a binder at an appropriate mass ratio, and the pore volume of the porous structure can be set to an amount suitable for slowing ink permeability. . Further, since the ink droplet that has passed through the upper layer reaches the lower layer, the ink transmission speed is relatively lowered when the lower layer reaches due to the transmission resistance in the upper layer. For this reason, in the lower layer, the ink permeability can be made slower than the upper layer.

  Thus, by making the ink permeability in the lower layer lower than the ink permeability in the upper layer, the ink transmission speed can be changed abruptly in the vicinity of the interface with the upper layer of the lower layer. As a result, as shown in FIG. 3, ink droplets stay in the vicinity of the interface with the upper layer of the lower layer, and the ink droplets can exist in a specific region for a long time. At this time, ink droplets spread in a direction perpendicular to the thickness direction of the lower layer (horizontal direction of the lower layer; surface direction of the lower layer), and the dot diameter of the printed dots increases. However, at this time, the dot diameter does not spread so large as to be recognized as bleeding due to the composition and structure of the lower layer.

  For this reason, when the dot diameter is appropriately increased in this manner, the recording surface is easily covered with the print dots, and the image characteristics can be improved. Further, for example, it is possible to avoid unevenness on white stripes in the print scanning direction when high-speed printing is performed with a small amount of ink shot, and white haze-like unevenness during solid printing.

  Here, when (binder) / (alumina hydrate) × 100 in the lower layer exceeds 12%, the porous structure in the lower layer is excessively blocked by the binder, and the pore volume of the porous structure Will decrease. For this reason, the ink permeability in the lower layer becomes very slow, and the fixability of the ink droplets becomes very poor. More specifically, the ink permeability in the upper layer is high while the ink permeability is very low in the lower layer, so that ink droplets are formed in a specific region in the lower layer (for example, near the interface with the upper layer). It will exist for quite some time. As a result, bleeding is likely to occur. Further, for example, when different color solid prints are printed adjacent to each other, other ink may ooze out from each other at the boundary portion.

  Further, when (binder) / (alumina hydrate) × 100 is less than 7.0%, the difference in permeability between the upper and lower ink droplets is reduced. For this reason, it becomes difficult for ink droplets that have passed through the upper layer to stay in a specific region in the lower layer for a long time, and the dot diameter cannot be increased in the specific region.

    The (binder) / (alumina hydrate) × 100 in the lower layer is preferably 7.0% or more and 10% or less, more preferably 8.0% or more and 10% or less, and 8.0. % To 9.0% is more preferable.

  In 1st invention, it is preferable that the sum total of the thickness of an upper layer and a lower layer is 30 micrometers or more. If the total thickness of the upper layer and the lower layer is less than 30 μm, the ink absorption amount of the entire ink receiving layer may be insufficient, and ink bleeding may occur. Further, the total thickness of the upper layer and the lower layer is more preferably 33 μm or more, and further preferably 35 μm.

  In consideration of increasing the dot diameter, the distance until the ink droplet passes through the upper layer and reaches the interface between the upper layer and the lower layer, that is, the thickness of the upper layer is also an important factor. Here, the thickness of the upper layer is preferably 2.0 μm or more and 10 μm or less, and more preferably 2.0 μm or more and 7.0 μm or less.

  By setting the thickness of the upper layer in the above range, for example, a sufficient amount of ink droplets can reach the interface between the upper layer and the lower layer even when solid printing is performed with a reduced ink ejection amount. be able to. As a result, a sufficient dot diameter spreads in the lower layer, and image unevenness can be avoided more effectively.

  On the other hand, when the thickness of the upper layer is greater than 10 μm, the amount of ink absorbed in the upper layer increases, so the amount of ink droplets that reach the lower layer may decrease relatively. That is, an amount of ink sufficient to increase the dot diameter does not reach the interface between the upper layer and the lower layer, the dot diameter is not sufficiently expanded, and unevenness is likely to occur in the image.

  Further, when the thickness of the upper layer is less than 2.0 μm, the effect of high ink absorbability of the upper layer cannot be exhibited, and ink bleeding may occur. In addition, since the distance that the ink droplet has passed through the upper layer before reaching the lower layer is shortened, the effect of increasing the dot diameter due to the difference in the ink permeability between the upper layer and the lower layer may be difficult to achieve.

(2) Second invention The second invention relates to an ink-absorbing recording medium comprising a support and an ink receiving layer provided on the support and having at least an upper layer and a lower layer. This upper layer is an ink-permeable layer constituting the surface layer of the ink receiving layer, and contains alumina hydrate and a binder. The ink receiving layer has a porous structure formed of alumina hydrate and a binder.

The mass ratio of the alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4.0% or more and 6.0% or less, and the thickness of the upper layer is 3.0 μm or more. It has become.
The lower layer constitutes a layer immediately below (directly below) the upper layer, and contains alumina hydrate and a binder. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the alumina hydrate and binder in the lower layer is 7% or more and 12% or less.
Furthermore, the mass ratio of methanesulfonic acid to hydrated alumina (methanesulfonic acid) / (alumina hydrate) × 100 in the upper and lower layers is 1.3% or more and 2.1% or less.

  In the present invention, the upper layer contains alumina hydrate and binder in a special ratio of (binder) / (alumina hydrate) × 100 of 4.0% to 6.0%. For this reason, the upper layer is porous so that the portion blocked by the binder is reduced as much as possible in the porous structure in the upper layer while maintaining the mechanical strength and retention of the layer required for the ink receiving layer. The pore volume of the structure can be increased. As a result, high ink permeability can be obtained, and ink bleeding on the upper layer surface can be effectively prevented.

Here, when (binder) / (alumina hydrate) × 100 is less than 4.0%, the ink receiving layer has insufficient mechanical strength for the same reason as described in the first invention. Become. Further, when (binder) / (alumina hydrate) × 100 exceeds 6.0%, the penetration of ink droplets into the upper layer is hindered for the same reason as described in the first invention. Ink may ooze out.

  On the other hand, even if the upper layer has a mass ratio of the binder and alumina hydrate as described above, if the thickness of the upper layer is thin, the pore volume of the entire upper layer is reduced. When the ink passes through the ink, the dye in the ink tends to be densely present in the pores of the layer having a porous structure. As a result, depending on the ink, the dyes in the ink may aggregate in the upper layer and bronze may be generated.

  In particular, cyan ink can be cited as an ink that easily causes this bronze phenomenon. The reason for this is considered that the cyan dye in the cyan ink has a characteristic of easily aggregating. As described in (Problem to be Solved by the Invention) of the present specification, the present inventor printed cyan ink on the ink receiving layer and observed the penetration distance of the cyan ink in the cross-sectional direction of the ink receiving layer. As a result, the cyan dye was often present at the shallowest position from the surface of the ink receiving layer as compared with other inks. From this fact, it can be seen that cyan dyes easily aggregate and easily bronze. Further, in recent years, phthalocyanine dyes having a solubilizing group-substituted triazine ring introduced as a solubilizing group have been used as means for improving the fastness of cyan dyes. This dye is more susceptible to bronzing than conventional dyes. For this reason, it has become necessary for the ink receiving layer to have a configuration in which ink aggregation is unlikely to occur (a bronzing phenomenon is unlikely to occur).

  Therefore, in the present invention, by setting the thickness of the upper layer to 3.0 μm or more, the pore volume of the entire upper layer is increased, and the dye in the ink is densely present in the pores of the layer having a porous structure. By preventing this, aggregation of the inks can be prevented, and the occurrence of bronzing can be prevented.

  In addition, it is preferable that (binder) / (alumina hydrate) × 100 in the upper layer is 4.5% or more and 5.5% or less. Further, the thickness of the upper layer is preferably 3.0 μm or more and 8.0 μm or less, and more preferably 5 μm.

  In the present invention, the lower layer contains alumina hydrate and binder at a special mass ratio of (binder) / (alumina hydrate) × 100 of 7.0% to 12%. For this reason, the lower layer can be bonded to the upper layer with high adhesive strength while maintaining the mechanical strength required for the ink receiving layer and the characteristics required for the upper support layer. At the same time, the ink residence time in the boundary region between the upper layer and the lower layer can be set to an appropriate range. For this reason, it is possible to effectively suppress the occurrence of bronzing due to the dense presence of dyes in the ink in the upper layer.

  There is also a relationship between the pH of the ink receiving layer and the cohesiveness (generation of bronzes) of dyes, particularly cyan ink. That is, when the pH of the ink receiving layer is too low, aggregation of dyes such as cyan ink may be promoted to cause bronze. On the other hand, if the pH of the ink receiving layer is too high, the dye is difficult to fix on the ink receiving layer. For this reason, the pH of the entire ink receiving layer is preferably adjusted to a range of 4.5 to 5.5, more preferably adjusted to a range of 4.8 to 5.3, more preferably to 5.1. More preferably.

  In the present invention, the mass ratio of methanesulfonic acid to hydrated alumina (methanesulfonic acid) / (alumina hydrate) × 100 in the upper layer and the lower layer is 1.3% or more and 2.1% or less. ing. As a result, the entire ink receiving layer can be adjusted within the above pH range. Note that (methanesulfonic acid) / (alumina hydrate) × 100 with respect to the entire two layers of the upper layer and the lower layer, regardless of whether the ink receiving layer has two layers of the upper layer and the lower layer, or three layers or more. Needs to be 1.3% or more and 2.1% or less.

This methanesulfonic acid is easier to adjust the pH of the ink receiving layer than a weak acid having a buffer function such as formic acid, acetic acid and glycolic acid. In the present invention, in addition to methanesulfonic acid, a strong acid such as hydrochloric acid or nitric acid may be used.
The mass ratio of methanesulfonic acid (methanesulfonic acid) / (alumina hydrate) × 100 is preferably 1.5% or more and 1.9% or less, and 1.6% or more and 1.8% or less. More preferably, it is 1.7%.

  Furthermore, in the present invention, yellowing of the ink receiving layer can be prevented by adjusting the pH of the entire ink receiving layer to a range of 4.5 or more and 5.5 or less using the methanesulfonic acid. There are various causes for this yellowing. Generally, after an antioxidant such as BHT (2,6-t-dibutylhydroxyltoluene) adheres to the ink receiving layer, BHT itself is oxidized. It is thought that this is because it changes to yellow.

  Here, this yellowing is affected by the pH of the ink receiving layer, and if the pH of the ink receiving layer is small and a large amount of hydrogen ions are present, the oxidation of BHT itself can be suppressed, so that the yellowing of the ink receiving layer is suppressed. be able to.

  In the present invention, considering the above-described balance between the occurrence of bronzing and yellowing, the pH of the entire ink receiving layer is preferably adjusted to a range of 4, 5 to 5, 5 and more preferably the pH. The range is from 4, 8 to 5, 3.

(3) Third invention The third invention is for image formation with an ink droplet of 5.5 pl or less having a support and an ink receiving layer provided on the support and having at least an upper layer and a lower layer. The present invention relates to an ink-absorbing recording medium.
This upper layer is an ink-permeable layer constituting the surface layer of the ink receiving layer, and a porous structure is formed by alumina hydrate and a binder. The lower layer is a layer immediately below the upper layer and has a lower ink permeability than the upper layer. The upper layer and the lower layer are configured so that the dot diameter at the time of fixing can be made larger than when the ink droplet is applied on the upper layer of the ink receiving layer by utilizing the difference in ink permeability.

  In the present invention, the ink permeability is lower in the lower layer than in the upper layer. That is, the pore volume of the porous structure per unit volume of the lower layer is smaller than the pore volume of the porous structure per unit volume of the upper layer. For this reason, ink droplets are less likely to pass through the lower layer than the upper layer.

  Here, in order to form a high-definition image, when an image is formed by applying a small ink droplet of 5.5 pl or less to a conventional inkjet recording medium, the ink droplet does not necessarily spread after being applied. The target high-definition image could not be obtained. In contrast, in the present invention, since the ink permeability in the lower layer is lower than the ink permeability in the upper layer, the ink transmission speed can be changed abruptly in the vicinity of the interface with the upper layer of the lower layer. it can. As a result, ink droplets stay in the vicinity of the interface with the upper layer of the lower layer, and the ink droplets can exist in a specific region for a long time.

  At this time, the ink droplets spread in the direction perpendicular to the thickness direction of the lower layer (the lateral direction of the lower layer; the surface direction of the lower layer), and even if the ink droplets are 5.5 pl or less, the printed ink Can be fixed by increasing the dot diameter. That is, the dot diameter of the ink droplet can be made larger during fixing than when the ink droplet is applied. As described above, when the dot diameter is increased, the recording surface is easily covered with the print dots, so that the image characteristics can be improved. In the present invention, it is preferably used as an ink-absorbing recording medium for image formation with ink droplets of 1 pl or more and 5.5 pl or less.

The ink permeability can be evaluated by the following method using, for example, a dynamic absorption tester (DAT) manufactured by Fibro.
First, 4.0 μl (microliter) of distilled water (23 ° C.) is dropped by a microsyringe onto an ink-absorbing recording medium adjusted to an environment of 23 ° C. and 50% RH. After that, the outline of the dropped droplet is photographed with a video camera, the volume of the droplet is obtained by analyzing the photographed image, and it can be evaluated by obtaining the absorption amount and the absorption time from the change with time of the volume. .

  The ink permeability of the upper layer and the lower layer can be controlled by selecting a specific composition and manufacturing method for each layer. For example, an alumina hydrate and a binder are contained in the lower layer, and a mass ratio of the alumina hydrate and the binder in the lower layer (binder) / (alumina hydrate) × 100 is 7.0% or more and 12% or less. Just do it.

(4) 4th invention 4th invention is an ink absorptivity which has a support body and the ink receiving layer which is provided on a support body and contains at least the upper layer as a surface layer, and the lower layer located just under an upper layer. It is a recording medium. The upper layer has a porous structure formed of alumina hydrate and binder, and contains alumina hydrate and binder. Further, the mass ratio of the alumina hydrate and the binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less.

  For this reason, the upper layer is porous so that the portion blocked by the binder is reduced as much as possible in the porous structure in the upper layer while maintaining the mechanical strength and retention of the layer required for the ink receiving layer. The pore volume of the structure can be increased. Here, in the conventional ink jet recording medium, when the pore volume of the entire upper layer is reduced, the dye in the ink tends to be densely present in the pores of the layer having a porous structure when the ink passes through the upper layer. It was. As a result, the dyes in the ink may aggregate in the upper layer and bronze may occur.

  Therefore, in the fourth invention, the upper layer contains alumina hydrate and binder in a special ratio of (binder) / (alumina hydrate) × 100 of 4.0% to 6.0%. ing. This increases the pore volume of the entire upper layer, prevents the dye in the ink from being densely present in the pores of the layer having a porous structure, prevents ink from agglomerating, and prevents bronzing can do.

  In 4th invention, it is preferable that the sum total of the thickness of an upper layer and a lower layer is 30 micrometers or more. If the total thickness of the upper layer and the lower layer is less than 30 μm, the ink absorption amount of the entire ink receiving layer may be insufficient, and ink bleeding may occur. Further, the total thickness of the upper layer and the lower layer is more preferably 33 μm or more, and further preferably 35 μm.

  The thickness of the upper layer is also an important factor. Here, the thickness of the upper layer is preferably 2.0 μm or more and 10 μm or less, and more preferably 2.0 μm or more and 7.0 μm or less. By setting the thickness of the upper layer in the above range, for example, a sufficient amount of ink droplets can reach the interface between the upper layer and the lower layer even when solid printing is performed with a reduced ink ejection amount. be able to. As a result, a sufficient dot diameter spreads in the lower layer, and image unevenness can be avoided more effectively.

  On the other hand, when the thickness of the upper layer is greater than 10 μm, the amount of ink absorbed in the upper layer increases, so the amount of ink droplets that reach the lower layer may decrease relatively. That is, an amount of ink sufficient to increase the dot diameter does not reach the interface between the upper layer and the lower layer, the dot diameter is not sufficiently expanded, and unevenness is likely to occur in the image.

  Further, when the thickness of the upper layer is less than 2.0 μm, the effect of high ink absorbability of the upper layer cannot be exhibited, and ink bleeding may occur.

(5) Fifth Invention The fifth invention relates to an ink-absorbing recording medium having a support and an ink receiving layer provided on the support and having at least an upper layer and a lower layer. The upper layer and the lower layer are layers in which a porous structure is formed of alumina hydrate and a binder as a surface layer of the ink receiving layer, and contain the alumina hydrate and the binder. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of alumina hydrate and binder in the upper layer is 4.0% or more and 6.0% or less.

  The lower layer constitutes a layer immediately below (directly below) the upper layer, and contains alumina hydrate and a binder. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the alumina hydrate and binder in the lower layer is 7.0% to 12%. Furthermore, the average pore diameter of the alumina hydrate is 7.0 nm or more and 10 nm.

  In the present invention, the upper layer contains alumina hydrate and binder in a special ratio of (binder) / (alumina hydrate) × 100 of 4.0% to 6.0%. For this reason, the upper layer is porous so as to minimize the portion blocked by the binder in the porous structure in the upper layer while maintaining the mechanical strength and layer retention required for the ink receiving layer. The pore volume of the structure can be increased. As a result, high ink permeability can be obtained, and ink bleeding on the upper layer surface can be effectively prevented.

Here, when (binder) / (alumina hydrate) × 100 is less than 4.0%, the ink receiving layer has insufficient mechanical strength for the same reason as described in the first invention. Become. Further, when (binder) / (alumina hydrate) × 100 exceeds 6.0%, the penetration of ink droplets into the upper layer is hindered for the same reason as described in the first invention. Ink may ooze out.

In the present invention, the lower layer contains alumina hydrate and binder at a special ratio of (binder) / (alumina hydrate) × 100 of 7.0% to 12%. For this reason, the lower layer can adhere to the upper layer with high adhesive strength while maintaining the mechanical strength required for the ink receiving layer and the properties required for the upper support layer. Even when (binder) / (alumina hydrate) × 100 is used, when the average pore diameter of the entire ink receiving layer is increased, the haze of the ink receiving layer is increased and the transparency is impaired. Therefore, the image density when the image is printed may be lowered.

  Therefore, in the present invention, by setting the average pore diameter of the entire ink receiving layer to 7.0 nm or more and 10 nm, the haze of the entire ink receiving layer is reduced and the transparency is ensured, so that a high image density can be obtained during image printing. Obtainable.

  In 5th invention, it is preferable that the sum total of the thickness of an upper layer and a lower layer is 30 micrometers or more. If the total thickness of the upper layer and the lower layer is less than 30 μm, the ink absorption amount of the entire ink receiving layer may be insufficient, and ink bleeding may occur. The total thickness of the upper layer and the lower layer is more preferably 33 μm or more, and further preferably 35 μm.

  The thickness of the upper layer is also an important factor. Here, the thickness of the upper layer is preferably 2.0 μm or more and 10 μm or less, and more preferably 2.0 μm or more and 7.0 μm or less. By setting the thickness of the upper layer in the above range, for example, a sufficient amount of ink droplets can reach the interface between the upper layer and the lower layer even when solid printing is performed with a reduced ink ejection amount. be able to. As a result, a sufficient dot diameter spreads in the lower layer, and image unevenness can be avoided more effectively.

  On the other hand, when the thickness of the upper layer is greater than 10 μm, the amount of ink absorbed in the upper layer increases, so the amount of ink droplets that reach the lower layer may decrease relatively. That is, an amount of ink sufficient to increase the dot diameter does not reach the interface between the upper layer and the lower layer, the dot diameter is not sufficiently expanded, and unevenness is likely to occur in the image.

  Further, when the thickness of the upper layer is less than 2.0 μm, the effect of high ink absorbability of the upper layer cannot be exhibited, and ink bleeding may occur.

(6) Sixth Invention The sixth invention relates to an ink-absorbing recording medium comprising a support and an ink receiving layer provided on the support and having at least an upper layer and a lower layer. The upper layer and the lower layer have a porous structure formed of alumina hydrate and a binder. The upper layer is an ink-permeable layer constituting the outermost layer of the ink receiving layer, and contains alumina hydrate and a binder. Further, the mass ratio of the alumina hydrate and the binder in the upper layer (binder) / (alumina hydrate) × 100 is 4.0% or more and 6.0% or less.

The lower layer constitutes a layer immediately below (directly below) the upper layer, and contains alumina hydrate and a binder. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the alumina hydrate and binder in the lower layer is 7.0% to 12%.
Further, mass ratio of alumina hydrate and binder in lower layer (binder) / (alumina hydrate) × 100, mass ratio of alumina hydrate and binder in upper layer (binder) / (alumina hydrate) The difference from x100 is 1.5% or more. That is, (binder) / (alumina hydrate) × 100 (lower layer) − (binder) / (alumina hydrate) × 100 (upper layer) is 1.5% or more.

  In the present invention, the upper layer contains alumina hydrate and binder in a special ratio of (binder) / (alumina hydrate) × 100 of 4.0% to 6.0%. For this reason, the upper layer is porous so that the portion blocked by the binder is reduced as much as possible in the porous structure in the upper layer while maintaining the mechanical strength and retention of the layer required for the ink receiving layer. The pore volume of the structure can be increased. As a result, high ink permeability can be obtained, and ink bleeding on the upper layer surface can be effectively prevented.

Here, when (binder) / (alumina hydrate) × 100 is less than 4.0%, the ink receiving layer has insufficient mechanical strength for the same reason as described in the first invention. Become. Further, when (binder) / (alumina hydrate) × 100 exceeds 6.0%, the penetration of ink droplets into the upper layer is hindered for the same reason as described in the first invention. Ink may ooze out.

In the present invention, the lower layer contains alumina hydrate and binder at a special ratio of (binder) / (alumina hydrate) × 100 of 7.0% to 12%. For this reason, the lower layer can adhere to the upper layer with high adhesive strength while maintaining the mechanical strength required for the ink receiving layer and the characteristics required for the upper support layer. The difference between the mass ratio of the product and the binder (binder) / (alumina hydrate) × 100 and the ratio of the alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 1.5. % Or more. Thus, the amount of the binder with respect to the alumina hydrate is increased in the lower layer than in the upper layer due to a special difference. As a result, the ink permeability in the lower layer can be effectively lowered with respect to the ink permeability in the upper layer. That is, the inside of the lower porous structure can be blocked with a binder at an appropriate ratio, and the pore volume of the porous structure can be set to an amount suitable for slowing ink permeability. Further, since the ink droplet that has passed through the upper layer reaches the lower layer, the ink transmission speed is relatively lowered when the lower layer reaches due to the transmission resistance in the upper layer. For this reason, in the lower layer, the ink permeability can be made slower than the upper layer.

  Thus, by making the ink permeability in the lower layer lower than the ink permeability in the upper layer, the ink transmission speed can be changed abruptly in the vicinity of the interface with the upper layer of the lower layer. As a result, ink droplets stay in the vicinity of the interface with the upper layer of the lower layer, and the ink droplets can exist in a specific region for a long time. At this time, ink droplets spread in a direction perpendicular to the thickness direction of the lower layer (horizontal direction of the lower layer; surface direction of the lower layer), and the dot diameter of the printed dots increases. However, at this time, the dot diameter does not spread so large as to be recognized as bleeding due to the composition and structure of the lower layer.

  For this reason, when the dot diameter is increased in this way, the recording surface is easily covered with the print dots, and the image characteristics can be improved. Further, for example, it is possible to avoid unevenness on white stripes in the printing scanning direction when high-speed printing is performed with a small amount of ink applied, and white haze-like unevenness during solid printing.

  The difference between (binder) / (alumina hydrate) × 100 in the lower layer and (binder) / (alumina hydrate) × 100 in the upper layer is preferably 2.0% or more. More preferably, it is 5% or more.

  In the sixth invention, the total thickness of the upper layer and the lower layer is preferably 30 μm or more. If the total thickness of the upper layer and the lower layer is less than 30 μm, the ink absorption amount of the entire ink receiving layer may be insufficient, and ink bleeding may occur. Further, the total thickness of the upper layer and the lower layer is more preferably 33 μm or more, and further preferably 35 μm.

  The thickness of the upper layer is also an important factor. Here, the thickness of the upper layer is preferably 2.0 μm or more and 10 μm or less, and more preferably 2.0 μm or more and 7.0 μm or less. By setting the thickness of the upper layer in the above range, for example, a sufficient amount of ink droplets can reach the interface between the upper layer and the lower layer even when solid printing is performed with a reduced ink ejection amount. be able to. As a result, a sufficient dot diameter spreads in the lower layer, and image unevenness can be avoided more effectively.

  On the other hand, when the thickness of the upper layer is greater than 10 μm, the amount of ink absorbed in the upper layer increases, so the amount of ink droplets that reach the lower layer may decrease relatively. That is, an amount of ink sufficient to increase the dot diameter does not reach the interface between the upper layer and the lower layer, the dot diameter is not sufficiently expanded, and unevenness is likely to occur in the image.

  Further, when the thickness of the upper layer is less than 2.0 μm, the effect of high ink absorbability of the upper layer cannot be exhibited, and ink bleeding may occur.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these examples.
First, measurement methods of various physical property values measured for the ink-absorbing recording media prepared in Examples and Comparative Examples will be described below.

<Average pore diameter of ink receiving layer>
The following apparatus was used for the measurement.
Measurement of average pore diameter: Automatic specific surface area / pore distribution measuring device TriStar 3000 manufactured by Shimadzu Corporation
Sample pretreatment: Vacuprep 061, manufactured by Shimadzu Corporation.

  Moreover, the measurement was performed as follows. The ink absorptive recording media prepared in Examples and Comparative Examples were cut to a size of 5.0 × 10 cm, and then cut into sizes that could fit in a 3/8 inch cell for measuring average pore diameter. Thereafter, this was put into a cell, and deaerated and dried using Baculo Prep 061, according to the manual, until it became 20 millitorr or less while being heated to 80 ° C.

  The average pore diameter of the sample that had been degassed and dried was measured using a TriStar 3000 according to the manual by the nitrogen adsorption / desorption method. After the measurement, the average pore diameter value was finally obtained using the obtained data on the nitrogen desorption side.

<Surface pH of ink receiving layer>
JAPAN TAPPI Paper Pulp Test Method No. According to 49-1, it was set as the value of the measured surface pH after 3 minutes.

Example 1
(Production Example 1 of Support)
A support was prepared as follows.
First, a paper stock having the following composition was prepared.
-Pulp slurry 100 parts by weight Freeness 450 ml CSF (Canadian Standard Freeness) 80 parts by weight of hardwood bleached kraft pulp (LBKP).

Freeness 480ml CSF, softwood bleached kraft pulp (NBKP)
20 parts by weight.
-Cationized starch 0.60 mass part.
-Heavy calcium carbonate 10 mass parts.
-Light calcium carbonate 15 mass parts.
-Alkyl ketene dimer 0.10 mass part.
-Cationic polyacrylamide 0.030 mass part.

Next, this stock was made with a long paper machine, subjected to a three-stage wet press, and then dried with a multi-cylinder dryer. Thereafter, the starch starch aqueous solution was impregnated with a size press device so that the solid content was 1.0 g / m ² and dried. Thereafter, machine calendar finishing was performed to obtain a base paper A having a basis weight of 170 g / m ² , a Steecht size of 100 seconds, an air permeability of 50 seconds, a Beck smoothness of 30 seconds, and a Gurley stiffness of 11.0 mN.

On the base paper A, 25 g / m ^{2 of a} resin composition comprising low density polyethylene (70 parts by mass), high density polyethylene (20 parts by mass), and titanium oxide (10 parts by mass) was applied. Furthermore, a resin-coated support 1 was obtained by applying 25 g / m ² of a resin composition comprising high-density polyethylene (50 parts by mass) and low-density polyethylene (50 parts by mass) on the back surface.

(Ink Absorbent Recording Medium Production Example 1)
On the support 1, an upper layer forming coating solution and a lower layer forming coating solution were applied and dried to form an ink receiving layer. The composition of each coating liquid, the coating method, etc. at this time are as follows.

(Preparation of coating liquid A for lower layer formation)
First, alumina hydrate Disperal HP14 (manufactured by Sasol Co., Ltd.) was added as an inorganic alumina hydrate to pure water so as to be 30% by mass. Next, methanesulfonic acid was added to the alumina hydrate so that (methanesulfonic acid) / (alumina hydrate) × 100 was 1.7%, and stirred to obtain a colloidal sol. . The obtained colloidal sol was appropriately diluted so that the alumina hydrate was 27% by mass to obtain colloidal sol A.

  On the other hand, polyvinyl alcohol PVA235 (manufactured by Kuraray Co., Ltd., polymerization degree: 3500, saponification degree: 88%) was dissolved in ion-exchanged water to obtain a PVA aqueous solution having a solid content of 8.0% by mass. And, the PVA solution prepared in the colloidal sol A prepared above is 7% in terms of PVA solid content ((binder) / (alumina hydrate) × 100) with respect to the solid content of alumina hydrate. It mixed so that it might become. Next, a 3.0 mass% boric acid aqueous solution is mixed with the solid content of the alumina hydrate so as to be 1.7 mass% in terms of solid content of boric acid, to form a coating solution A for forming the lower layer. Got.

(Creation of coating liquid A for upper layer formation)
First, alumina hydrate Disperal HP14 (manufactured by Sasol Co., Ltd.) was added as an inorganic alumina hydrate to pure water so as to be 30% by mass. Next, methanesulfonic acid is added to the alumina hydrate so that the mass ratio (methanesulfonic acid) / (alumina hydrate) × 100 is 1.7%, and the mixture is stirred to obtain a colloidal sol. Obtained. Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) was added as a surfactant to the obtained colloidal sol so as to be 0.10% by mass with respect to the colloidal sol. Furthermore, the colloidal sol B was obtained by appropriately diluting the alumina hydrate to 21 mass%.

  On the other hand, polyvinyl alcohol PVA235 (manufactured by Kuraray Co., Ltd., polymerization degree: 3500, saponification degree: 88%) was dissolved in ion-exchanged water to obtain a PVA aqueous solution having a solid content of 8.0% by mass. The PVA solution prepared above in the colloidal sol B prepared above is 4.0 in terms of PVA solid content ((binder) / (alumina hydrate) × 100) with respect to the solid content of alumina hydrate. It mixed so that it might become%. Next, a 3.0% by mass boric acid aqueous solution is mixed with the solid content of the alumina hydrate so as to be 1.0% by mass in terms of the solid content of boric acid. Obtained.

(Coating method of ink receiving layer)
At the same time, the thickness after drying the coating liquid A for forming the lower layer is 30 μm and the thickness after drying the coating liquid A for forming the upper layer is 5 μm on the support 1 in order from the side closer to the support. Multi-layer coating was applied. In addition, the coating of the two-layer coating liquid was performed at 40 ° C. using a slide die. Next, this was dried at 40 ° C. to prepare an ink-absorbing recording medium 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 1 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 2)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was set to 5.0%. Except for this, an ink-absorbing recording medium 2 was prepared in the same manner as in Example 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 2 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 3)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 6.0%. Except for this, an ink-absorbing recording medium 3 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 3 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

Example 4
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 12%. Except for this, an ink-absorbing recording medium 4 was prepared in the same manner as in Example 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 4 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 5)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was set to 5.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 12%. Except for this, an ink-absorbing recording medium 5 was prepared in the same manner as in Example 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 5 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 6)
An ink-absorbing recording medium 6 was prepared in the same manner as in Example 5 except that the support was changed to the support 2 shown below in Example 5. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 6 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Production Example 2 of Support)
On the base paper A, an undercoat layer was formed as follows.
First, as a coating liquid for forming an undercoat layer, 100 parts by mass of a filling ratio of kaolin (Ultra White 90, manufactured by Engelhard) / zinc oxide / aluminum hydroxide having a mass ratio of 65/10/25 was prepared. With respect to 100 parts by mass of the filling amount, 7.0 parts by mass of a commercially available styrene-butadiene latex is added to a slurry having a solid content concentration of 70% by mass with addition of 0.10 parts by mass of a commercially available polyacrylic acid dispersant. And it was set as the composition of 60 mass% of solid content. Next, it was coated on both sides of the base paper A by a blade coater so that the dry coating amount of this composition was 15 g / m ² and dried. After this, machine calendar finishing (linear pressure 150 kgf / cm), basis weight 185 g / m ² , steecht sizing degree 300 seconds, air permeability 3,000 seconds, Beck smoothness 200 seconds, Gurley stiffness 11.5 mN A support 2 with an undercoat layer was obtained.

(Example 7)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 6.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 12%. Except for this, an ink-absorbing recording medium 7 was prepared in the same manner as in Example 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 7 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 8)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was set to 5.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 8.0%. Except for this, an ink-absorbing recording medium 8 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 8 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

Example 9
In Example 8, an ink-absorbing recording medium 9 was prepared in the same manner as in Example 8, except that the lower layer forming coating solution A was changed to the lower layer forming coating solution B shown below.

(Preparation of coating liquid B for lower layer formation)
First, alumina hydrate Disperal HP14 (manufactured by Sasol Co., Ltd.) was added as an inorganic alumina hydrate to pure water so as to be 30% by mass. Next, methanesulfonic acid was added to the alumina hydrate so that (methanesulfonic acid) / (alumina hydrate) × 100 was 1.7%. Next, further, PAS-92 (manufactured by Nitto Boseki Co., Ltd.) was added to the alumina hydrate so as to be 1.0% by mass in terms of solid content and stirred to obtain a colloidal sol. The obtained colloidal sol was appropriately diluted so that the alumina hydrate was 27% by mass to obtain colloidal sol A.

  On the other hand, polyvinyl alcohol PVA235 (manufactured by Kuraray Co., Ltd., polymerization degree: 3500, saponification degree: 88%) was dissolved in ion-exchanged water to obtain a PVA aqueous solution having a solid content of 8.0% by mass. Then, the PVA solution prepared in the colloidal sol A prepared above is 7% in terms of PVA solid content ((binder) / (alumina hydrate) × 100) with respect to the solid content of alumina hydrate. It mixed so that it might become. Next, a 3.0% by mass boric acid aqueous solution is mixed with the solid content of the alumina hydrate so as to be 1.7% by mass in terms of the solid content of boric acid, and the lower layer forming coating solution B Got.

(Example 10)
In Example 8, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was 9.0%. Other than this, an ink-absorbing recording medium 10 was prepared in the same manner as in Example 8. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 10 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 11)
In Example 8, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 10%. Except for this, an ink-absorbing recording medium 11 was prepared in the same manner as in Example 8. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 11 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 12)
In Example 8, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was 11%. Except for this, an ink-absorbing recording medium 12 was prepared in the same manner as in Example 8. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 12 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Comparative Example 1)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was set to 3.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 12%. Except for this, an ink-absorbing recording medium 13 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 13 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Comparative Example 2)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was set to 1.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 12%. Except for this, an ink-absorbing recording medium 14 was prepared in the same manner as in Example 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 14 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Comparative Example 3)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 7.0%. Except for this, an ink-absorbing recording medium 15 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 15 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Comparative Example 4)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 9.0%. Except for this, an ink-absorbing recording medium 16 was prepared in the same manner as in Example 1. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 16 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Comparative Example 5)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 13%. Except for this, an ink-absorbing recording medium 17 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 17 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Comparative Example 6)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 17%. Except for this, an ink-absorbing recording medium 18 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 18 thus prepared were measured, the average pore diameter was 7.9 nm and the surface pH was 5.1.

(Comparative Example 7)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 6.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was 6.0%. Except for this, an ink-absorbing recording medium 19 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 19 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Comparative Example 8)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 6.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA to the solid content of the alumina hydrate of the coating liquid A for lower layer formation was 4.0%. Except for this, an ink-absorbing recording medium 20 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 20 thus prepared were measured, the average pore diameter was 8.2 nm and the surface pH was 5.1.

(Comparative Example 9)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was set to 3.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was set to 13%. Except for this, an ink-absorbing recording medium 21 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 21 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Comparative Example 10)
In Example 1, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the upper layer was 7.0%. Moreover, the mass ratio (binder) / (alumina hydrate) × 100 of the solid content of PVA with respect to the solid content of the alumina hydrate of the coating liquid A for forming the lower layer was 6.0%. Except for this, an ink-absorbing recording medium 22 was prepared in the same manner as in Example 1. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 22 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 13)
An ink-absorbing recording medium 23 was prepared in the same manner as in Example 1 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 23 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 14)
An ink-absorbing recording medium 24 was prepared in the same manner as in Example 2 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 24 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 15)
An ink-absorbing recording medium 25 was prepared in the same manner as in Example 3, except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 25 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 16)
An ink-absorbing recording medium 26 was prepared in the same manner as in Example 4 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 26 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 17)
In Example 5, an ink-absorbing recording medium 27 was prepared in the same manner as in Example 5 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 27 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 18)
An ink-absorbing recording medium 28 was prepared in the same manner as in Example 7, except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 28 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 19)
In Example 8, an ink-absorbing recording medium 29 was produced in the same manner as in Example 8, except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 29 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 20)
In Example 10, an ink-absorbing recording medium 30 was prepared in the same manner as in Example 10 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 30 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 21)
In Example 11, an ink-absorbing recording medium 31 was prepared in the same manner as in Example 11 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 31 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 22)
In Example 12, an ink-absorbing recording medium 32 was produced in the same manner as in Example 12 except that the thickness after drying of the upper layer was 10 μm and the thickness after drying of the lower layer was 20 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 32 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 23)
Ink-absorbing recording medium 33 was prepared in the same manner as in Example 1, except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 33 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 24)
In Example 2, an ink-absorbing recording medium 34 was prepared in the same manner as in Example 2, except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 34 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 25)
An ink-absorbing recording medium 35 was prepared in the same manner as in Example 3 except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 35 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 26)
An ink-absorbing recording medium 36 was prepared in the same manner as in Example 4 except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 36 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 27)
An ink-absorbing recording medium 37 was prepared in the same manner as in Example 5, except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 37 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 28)
An ink-absorbing recording medium 38 was prepared in the same manner as in Example 7, except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 38 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 29)
In Example 8, an ink-absorbing recording medium 39 was prepared in the same manner as in Example 8, except that the thickness after drying the upper layer was 2.0 μm and the thickness after drying the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 39 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 30)
An ink-absorbing recording medium 40 was prepared in the same manner as in Example 10 except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 40 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 31)
An ink-absorbing recording medium 41 was prepared in the same manner as in Example 11 except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 41 thus prepared were measured, the average pore diameter was 8.1 nm and the surface pH was 5.1.

(Example 32)
An ink-absorbing recording medium 42 was prepared in the same manner as in Example 12 except that the thickness after drying of the upper layer was 2.0 μm and the thickness after drying of the lower layer was 28 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 42 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 33)
In Example 4, an ink-absorbing recording medium 43 was prepared in the same manner as in Example 4 except that the thickness after drying of the upper layer was 11 μm and the thickness after drying of the lower layer was 19 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 43 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 34)
In Example 4, an ink-absorbing recording medium 44 was prepared in the same manner as in Example 4 except that the thickness after drying of the upper layer was 13 μm and the thickness after drying of the lower layer was 17 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 44 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 35)
An ink-absorbing recording medium 45 was prepared in the same manner as in Example 4 except that the thickness after drying of the upper layer was 7.0 μm and the thickness after drying of the lower layer was 23 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 45 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 36)
An ink-absorbing recording medium 46 was prepared in the same manner as in Example 1, except that the thickness after drying of the upper layer was 1.0 μm and the thickness after drying of the lower layer was 29 μm. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 46 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 37)
In Example 7, an ink-absorbing recording medium 47 was prepared in the same manner as in Example 7, except that the thickness after drying the upper layer was 3.0 μm and the thickness after drying the lower layer was 27 μm. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 47 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.1.

(Example 38)
In Example 7, the amount of methanesulfonic acid (methanesulfonic acid) / (alumina hydrate) × 100 with respect to the solid content of colloidal sol B alumina hydrate was set to 1.3%. Then, (methanesulfonic acid) / (alumina hydrate) × 100 in the upper layer and the lower layer was set in the range of 1.3% to 2.1%. Except for this, an ink-absorbing recording medium 48 was prepared in the same manner as in Example 7. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 48 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.3.

(Example 39)
In Example 7, the amount of methanesulfonic acid (methanesulfonic acid) / (alumina hydrate) × 100 with respect to the solid content of colloidal sol B alumina hydrate was 2.1%. Then, (methanesulfonic acid) / (alumina hydrate) × 100 in the upper layer and the lower layer was set in the range of 1.3% to 2.1%. Except for this, an ink-absorbing recording medium 49 was prepared in the same manner as in Example 7. When the average pore diameter and the surface pH of the ink receiving layer in the ink-absorbing recording medium 49 thus prepared were measured, the average pore diameter was 8.0 nm and the surface pH was 5.3.

(Example 40)
In Example 2, the inorganic alumina hydrate of colloidal sol B was alumina hydrate Dispersal HP14 (manufactured by Sasol): alumina hydrate Dispersal HP18 (manufactured by Sasol) = 80: 20 (mass basis). Moreover, the inorganic alumina hydrate of colloidal sol A was made into alumina hydrate Dispersal HP14 (made by Sasol): alumina hydrate Dispersal HP18 (made by Sasol) = 80: 20 (mass basis). Other than this, an ink-absorbing recording medium 50 was prepared in the same manner as in Example 2. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 50 thus prepared were measured, the average pore diameter was 8.4 nm and the surface pH was 5.0.

(Example 41)
In Example 2, the inorganic alumina hydrate of colloidal sol B was alumina hydrate Dispersal HP14 (manufactured by Sasol): alumina hydrate Dispersal HP18 (manufactured by Sasol) = 60: 40 (mass basis). Moreover, the inorganic alumina hydrate of colloidal sol A was made into the alumina hydrate Dispersal HP14 (made by Sasol): Alumina hydrate Dispersal HP18 (made by Sasol) = 60: 40 (mass basis). Except for this, an ink-absorbing recording medium 51 was prepared in the same manner as in Example 2. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 51 thus prepared were measured, the average pore diameter was 8.9 nm and the surface pH was 4.9.

(Example 42)
In Example 2, the inorganic alumina hydrate of colloidal sol B was alumina hydrate Dispersal HP14 (manufactured by Sasol): alumina hydrate Dispersal HP18 (manufactured by Sasol) = 40: 60 (mass basis). In addition, the inorganic fine particles of colloidal sol A were alumina hydrate Dispersal HP14 (manufactured by Sasol): alumina hydrate Dispersal HP18 (manufactured by Sasol) = 40: 60 (mass basis). Except for this, an ink-absorbing recording medium 52 was prepared in the same manner as in Example 2. When the average pore diameter and surface pH of the ink receiving layer in the ink-absorbing recording medium 52 thus prepared were measured, the average pore diameter was 9.5 nm and the surface pH was 4.8.
The following evaluations were performed on the ink-absorbing recording media obtained in the examples and comparative examples as described above. The results are shown in Tables 1-3.

<Evaluation method>
1) Ink bleeding The following image was printed on an ink-absorbing recording medium by using a super photo paper mode (default setting) of an inkjet printer PIXUS iP8600 manufactured by Canon Inc.
An ink bleeding image in which black and yellow solid images are adjacent to each other. An ink bleeding image in which black and red solid images are adjacent to each other.

Then, in accordance with the following evaluation criteria, the bleeding of black in the yellow or red print area was evaluated.
Evaluation criteria A: Bleeding is not observed, and it is good.
B: Black is slightly blurred in the red printing area, but it is an acceptable level.
C: Black is slightly blurred in the yellow and red print areas, but this is an acceptable level.
D: Black is blurred in the red printing area so that it can be easily visually recognized.
E: Black is blurred in the yellow and red print areas so that they can be easily recognized.

2) Cracks in ink-receiving layer After the ink-receiving layer was formed, the length of cracks on the upper layer surface of the ink-absorbing recording medium was visually confirmed. And it evaluated in accordance with the following evaluation criteria.
Evaluation criteria A: There is no occurrence of cracks.
B: Although the crack has generate | occur | produced, all are cracks of length less than 1.0 mm.
C: There is a crack of 1.0 mm or more.

3) Powder falling off of ink receiving layer Evaluation was performed as follows using a Gakushin type friction tester type II (manufactured by Tester Sangyo Co., Ltd.) defined in JIS-L0849.
A black rusha paper was attached to a friction piece of a testing machine on which a 300 g weight was placed, and a sample piece was set on a vibrating table so that the upper layer of the ink receiving layer was on top and rubbed 20 times. Thereafter, the black reflection density of the portion where the Rash paper was rubbed and the other portion were measured with 310TR manufactured by X-Rite, and from this density difference, the black density residual rate was determined according to the following equation: Evaluation was performed based on the following evaluation criteria.
Evaluation Criteria A: Residual rate is 95% or more B: Residual rate is 90% or more and less than 95% C: Residual rate is less than 90% Residual rate (%) = [1− (Concentration other than test part−Concentration of test part)] / (Concentration other than test part)] × 100.

4) Printing unevenness Solid images of black, cyan, magenta, and yellow were printed on the ink-absorbing recording medium by the super photo paper mode (fast setting) of an ink jet printer PIXUS iP8600 manufactured by Canon Inc. Thereafter, the unevenness of the print area of each color was evaluated according to the following evaluation criteria.
Evaluation criteria A: In any color, no unevenness is observed in the image.
B: In any of the colors, white unevenness is slightly observed in the image, but it is an acceptable level.
C: In any of the colors, some white stripe-like unevenness is observed in the image, but it is an acceptable level.
D: In any of the colors, unevenness on the white haze is seen in the image.
E: In any of the colors, white stripe-like unevenness that can be easily visually recognized is seen in the image.

5) Bronze Using an inkjet printer PIXUS iP8600 manufactured by Canon Inc., a cyan solid image was printed on the ink-absorbing recording medium while changing the print duty in 13 steps as follows.
-5, 12, 21, 29, 35, 43, 51, 58, 66, 74, 85, 90, 100%.

For this printed matter, the duty at which the bronzing phenomenon started to occur was visually evaluated, and the duty was defined as the bronzing duty. It can be said that the higher the bronzing duty is, the harder the ink-absorbing recording medium is to bronz. The bronze generation duty thus obtained was evaluated based on the following evaluation criteria.
Evaluation criteria A: Bronze generation duty of 88% or more (a level at which it is not known whether bronzing occurs in the actual image or whether bronzing occurs in the actual image by visual judgment).
B: Bronze generation duty of 63% or more and less than 88% (this is a level at which occurrence of bronze may be found by visual judgment in an actual image).
C: Bronze generation duty of 43% or more and less than 63% (a level at which bronze generation can be detected by visual judgment in a real image having a high image density).
D: Bronze generation duty less than 43% (a level at which bronze generation can be determined by visual judgment in a real image with low image density)
6) Image density A black solid image was printed on an ink-absorbing recording medium by using a super photo paper mode (default setting) of an inkjet printer PIXUS iP8600 manufactured by Canon Inc. Thereafter, the reflection density of the black print portion was measured with 310TR manufactured by X-Rite.

  From Tables 1 and 3, the mass ratio of the alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 was adjusted to a low region that has not existed before. Thereby, it turns out that the porous structure formed in a layer by an alumina hydrate can fully be utilized. Further, the ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 was made larger than the upper layer. Thereby, it can be seen that the ink absorbability that is not found in the past can be expressed without causing defects such as cracks in the ink receiving layer. It can be seen that the present invention can provide an ink-absorbing recording medium having excellent image characteristics in which ink bleeding does not occur.

  In addition, it can be seen that by setting the thickness of the upper layer within a range in which the difference between the absorption speed of the upper layer and the absorption speed of the lower layer can be effectively used, the dot diameter can be increased in the lower layer after printing, and printing unevenness can be suppressed. It can also be seen that an ink-absorbing recording medium excellent for bronze can be provided by setting the thickness of the upper layer to a certain thickness or more.

Explanatory drawing of an example of the schematic diagram of the cross-sectional direction of an ink receiving layer Explanatory drawing of an example showing a state where ink is printed on the ink receiving layer Illustration of an example showing the process of ink permeation into the ink receiving layer

Explanation of symbols

a Upper layer ink receiving layer b Lower layer ink receiving layer c Porous portion in ink receiving layer d Alumina hydrate + Binder e Ink droplet f Ink penetrating into upper layer g Ink existing in upper layer lower layer boundary area Permeating into lower layer Ink

Claims (9)

An ink-absorbing recording medium comprising: a support; and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder,
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer, and the mass ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less. An ink-absorbing recording medium. An ink-absorbing recording medium comprising: a support; and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder,
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less, and the thickness of the upper layer is 3 μm or more,
The lower layer constitutes a layer immediately below the upper layer, and the mass ratio of the alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less,
The mass ratio of the alumina hydrate and methanesulfonic acid (methanesulfonic acid) / (alumina hydrate) × 100 in the upper layer and the lower layer is 1.3% to 2.1%, Ink-absorbing recording medium. An ink-absorbing recording medium for image formation with ink droplets of 5.5 pl or less, comprising a support and an ink receiving layer provided on the support and having at least an upper layer and a lower layer,
The upper layer is a layer in which a porous structure is formed of alumina hydrate and a binder as a surface layer of the ink receiving layer, and the mass ratio of the alumina hydrate and the binder in the upper layer (binder) / (Alumina hydrate) x 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer and has a lower ink permeability than the upper layer, and an ink droplet on the upper layer of the ink receiving layer due to a difference in ink permeability between the upper layer and the lower layer. An ink-absorbing recording medium characterized in that the dot diameter at the time of fixing ink droplets to the lower layer can be made larger than at the time of application of the ink. An ink-absorbing recording medium comprising: a support; and an ink receiving layer provided on the support and having at least an upper layer as a surface layer and a lower layer located immediately below the upper layer,
The upper layer is a layer in which a porous structure is formed by an alumina hydrate and a binder, contains the alumina hydrate and the binder, and the mass ratio of the alumina hydrate and the binder in the upper layer (the binder). ) / (Alumina hydrate) × 100 is 4% or more and 6% or less. An ink-absorbing recording medium comprising: a support; and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder,
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer, and the ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less,
An ink-absorbing recording medium, wherein the ink receiving layer has an average pore diameter of 7 nm or more and 10 nm or less. An ink-absorbing recording medium comprising: a support; and an ink receiving layer having at least an upper layer and a lower layer provided on the support and having a porous structure formed of alumina hydrate and a binder,
The mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) × 100 is 4% or more and 6% or less,
The lower layer constitutes a layer immediately below the upper layer, and the mass ratio of the alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100 is 7% or more and 12% or less,
Mass ratio of alumina hydrate and binder in the lower layer (binder) / (alumina hydrate) × 100, Mass ratio of alumina hydrate and binder in the upper layer (binder) / (alumina hydrate) An ink-absorbing recording medium having a difference from x100 of 1.5% or more.   The ink-absorbing recording medium according to claim 6, wherein an average pore diameter of the ink receiving layer is 7 nm or more and 10 nm or less.   8. The ink-absorbing recording medium according to claim 1, wherein the total thickness of the upper layer and the lower layer is 30 μm or more.   9. The ink-absorbing recording medium according to claim 1, wherein the upper layer has a thickness of 2 μm or more and 10 μm or less.

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