JP4111530B2 - Inkjet recording medium - Google Patents

Description

  The present invention relates to an ink jet recording medium, and more particularly to an ink jet recording medium excellent in ink absorbability.

  The inkjet recording method has been developed rapidly in recent years, and has features such as full color, easy speeding up, low printing noise, etc. Also, since the device is compact and inexpensive, it can be used in homes and offices. It is becoming popular as a color printing machine. The ink jet recording method is a non-impact printing method in which ink droplets are ejected from a nozzle toward a recording medium such as paper to form an image, and the recording medium and the printer are not in direct contact.

  Ink for ink jet recording contains a large amount of solvent in the ink in order to form stable droplets. Therefore, in order to obtain good image quality, it is necessary for the recording medium to absorb ink droplets promptly. In particular, in recent years, higher ink absorptivity has been demanded for ink jet recording media due to higher speed printers and the use of multicolor inks. Therefore, a recording medium having an ink receiving layer provided on a support is on the market. The ink receiving layer is generally composed of a pigment that absorbs ink and develops color, a binder that binds the pigment onto the support, an ink fixing agent for fixing the ink to the ink receiving layer, and various auxiliaries. Synthetic amorphous silica excellent in ink absorbability and color developability is generally used as the pigment for the ink receiving layer, but various properties (particle size, oil absorption, etc.) are used to improve print quality and workability. (For example, see Non-Patent Document 1).

  However, with the development of color reproducibility in recent printers, an ink jet recording medium that can absorb more ink is desired. For these reasons, it has been proposed to provide an under layer between the support and the ink receiving layer. For example, a technique of providing an under layer containing silica as a pigment under the ink receiving layer and a technique of using a mixture of synthetic amorphous silica and heavy calcium carbonate fine particles as an under layer pigment have been proposed (Patent Document 2, 3)

"Development technology of ink, media, and printer for inkjet recording", first printing, publisher Kazuhiro Takashiro, Technical Information Association, Inc., August 28, 2000, p123, p146 JP 2003-260862 A JP 2003-285543 A

However, in the case of the technology described in Patent Document 2, although the silica ink that is a pigment has high ink absorbability, silica adsorbs the binder in the underlayer coating liquid (the binder has a large amount of requirement). There is a problem that the amount of the effective binder is insufficient and the strength of the under layer is lowered. Further, if the amount of the binder is increased in order to ensure the layer strength, the ink absorbability is lowered. On the other hand, when silica having a low oil absorption amount is used, the required amount of binder is low, but the ink absorbability is poor.
In the case of the technique described in Patent Document 3, the strength of the under layer is increased, but the ink absorption is inferior because the absorption characteristics of calcium carbonate are low.
In addition, when the under layer strength is low, when the roll-shaped recording medium (paper) is wound up in the manufacturing process, the under layer or the ink receiving layer on the upper layer may be lost and caught between the paper and the paper. y occurs. In this case, irregularities such as dents are formed on the paper surface, which may impair the aesthetic appearance, and is particularly noticeable in highly smooth cast paper.
Accordingly, an object of the present invention is to provide an ink jet recording medium having excellent ink absorbability and high under layer strength.

As a result of investigations to solve the above problems, the inventors have found that any of the above problems can be solved by using a specific pigment in the under layer. This is considered to be because the pigment has a good balance of the absorption characteristics of the pigment, and the ink absorbency is improved without much adsorption of the binder.
Therefore, the object of the present invention is an ink jet recording medium in which an under layer containing a pigment and a binder is provided on at least one surface of a support, and an ink receiving layer is provided on the surface of the under layer. The underlayer pigment contains light calcium carbonate-silica composite particles in which the surface of the light calcium carbonate particles is coated with silica in which silicic acid is deposited on the surface of the light calcium carbonate particles. Achieved by the recording medium.

In the light calcium carbonate-silica composite particles, the light calcium carbonate / silica solid content mass ratio (CaCO ₃ / SiO ₂ ) is preferably 25/75 to 75/25. In the light calcium carbonate-silica composite particles, the light calcium carbonate particles are preferably Rosetta-type calcite light calcium carbonate in which spindle-shaped primary particles aggregate to form secondary particles.
The outermost surface of the ink receiving layer is provided after the coating layer is pressed against a heated mirror surface while the surface of the coating layer formed by applying the coating material for the ink receiving layer is in a wet state, and then dried. It is preferred that

  According to the present invention, an ink jet recording medium having excellent ink absorbability and high under layer strength can be obtained.

  Embodiments of the present invention will be described below. The ink jet recording medium of the present invention is configured by providing an under layer and an ink receiving layer in this order on a support.

<Support>
As the support, known materials can be appropriately selected and used, but it is particularly preferable to use paper (coated paper, uncoated paper, etc.). Paper pulp includes chemical pulp (coniferous bleached or unbleached kraft pulp, hardwood bleached or unbleached kraft pulp, etc.), mechanical pulp (ground pulp, thermomechanical pulp, chemithermomechanical pulp, etc.), deinked pulp Etc. may be used singly or in an arbitrary ratio. The pH of the paper may be any of acidic, neutral and alkaline. Moreover, it is preferable to improve the opacity of paper by containing a filler in the paper. The filler can be appropriately selected from known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide, and synthetic resin filler.

<Under layer>
The under layer contains a pigment and a binder, and the pigment contains light calcium carbonate-silica composite particles.
[Pigment]
As the pigment, light calcium carbonate-silica composite particles in which the surface of light calcium carbonate particles is coated with silica are used. The composite particles are used as all or part of the pigment. The light calcium carbonate-silica composite particles are obtained by bonding silica (SiO ₂ ) particles having a primary particle diameter of about 20 to 60 nm to the surface of light calcium carbonate having a particle diameter of about 0.9 to 9.0 μm, for example. Light calcium carbonate can be synthesized, for example, by calcining limestone and chemical reaction, but is not limited thereto.

The crystal form (homogeneous image) of light calcium carbonate (CaCO ₃ ) may be either calcite or aragonite. The light calcium carbonate may have any of a needle shape, a column shape, a spindle shape, a spherical shape, a cubic shape, and a rosette type. The rosetta type refers to a shape in which spindle-shaped light calcium carbonate primary particles are aggregated in a chestnut shape, and has a higher specific surface area and oil absorption than those in other forms.
In particular, it is preferable to use rosetta-type calcite light calcium carbonate because the resulting composite particles have good absorption characteristics and ink absorbability of the ink jet recording medium is improved. In the case of Rosetta-type light calcium carbonate, since the light calcium carbonate particles are brown chestnut-shaped, it is considered that the voids in the particles increase and the ink absorbability is improved. Light calcium carbonate may be used after being pulverized.

  FIG. 1 is an SEM (electron microscope) image showing an example of the form of light calcium carbonate (Rosetta calcite system) dispersed in a liquid, and FIG. 2 shows the light calcium carbonate dispersed in the liquid. -It is a SEM image which shows an example of the form of a silica composite particle. FIG. 2 shows that substantially spherical silica primary particles are bonded (precipitated) to the surface of light calcium carbonate. In the example of FIG. 2, there are three composite particles.

The reason why ink absorbency and under layer strength are improved by using the above light calcium carbonate-silica composite particles as a pigment is not clear, but is considered as follows. In other words, the light calcium carbonate-silica composite particles have a large amount of oil absorption compared to calcium carbonate of the same particle size and absorb a large amount of ink in the pigment because the primary particles of silica adhere to the surface of the light calcium carbonate. can do. In particular, when light calcium carbonate as a core forms secondary particles, a space is formed between the primary particles of calcium carbonate, resulting in a further increase in oil absorption.
In the case of the composite particles, since silica is arranged around the light calcium carbonate, the specific surface area is smaller than that of single silica having the same particle diameter, and the ratio of the pigment adsorbing the binder is reduced. Therefore (because the required amount of binder decreases), it is considered that an effective amount of binder is secured and the strength of the under layer is increased. Moreover, if the specific surface area of a pigment becomes small, the stability of the coating material containing this will also become high.

Light calcium carbonate-silica composite particles are considered to have both the characteristics of silica and light calcium carbonate. By adjusting the blending ratio, ink absorbency, print density, vividness, etc. There is an advantage that it can be adjusted. Here, the vividness is an index for neatly printing an image, and is a comprehensive evaluation of print density, image reproducibility, and presence / absence of image unevenness. Therefore, the light calcium carbonate / silica solid content mass ratio (CaCO ₃ / SiO ₂ ) in the light calcium carbonate-silica composite particles is preferably 25/75 to 75/25. When the ratio is less than 25/75, the characteristics of the silica are manifested throughout, and the under layer strength tends to decrease due to the adsorption characteristics being too high to adsorb the binder. On the other hand, when the ratio exceeds 75/25, the characteristics of light calcium carbonate are greatly exhibited, the adsorption characteristics are deteriorated, and the ink absorbability and the print density are easily lowered. The solid content mass ratio can be obtained by, for example, analyzing light calcium carbonate-silica composite particles by fluorescent X-ray analysis and quantifying Ca and Si.

The oil absorption of the light calcium carbonate-silica composite particles is preferably 100 to 250 ml / 100 g. When the oil absorption amount of the composite particles is less than 100 ml / 100 g, the ink absorbability is lowered, and when it exceeds 250 ml / 100 g, the under layer strength may be lowered. A more preferred oil absorption is 120 to 200 ml / 100 g, and a further preferred range is 140 to 180 ml / 100 g.
The oil absorption can be measured according to JIS K5101.

The light calcium carbonate-silica composite particles preferably have a BET specific surface area of 5 to 150 m ² / g. If the BET specific surface area of the composite particles is less than 5 m ² / g, the ink absorbability is lowered, and if it exceeds 150 m ² / g, the under layer strength is lowered and the viscosity of the coating liquid is increased to lower the operability. There is a case. A more preferable BET specific surface area is 10 to 100 m ² / g, and a further preferable range is 20 to 50 m ² / g.
The BET specific surface area can be measured by a nitrogen adsorption method.

Moreover, it is preferable that the average particle diameter of a light calcium carbonate-silica composite particle is 1-10 micrometers. When the average particle size of the composite particles is less than 1 μm, voids in the composite particles are reduced and ink absorbability is lowered. On the other hand, when the average particle diameter exceeds 10 μm, the smoothness of the under layer is impaired, and it may be difficult to uniformly provide the ink receiving layer. A more preferable average particle diameter is 2 to 9 μm, and a further preferable range is 3 to 8 μm.
The average particle diameter can be measured using a laser particle size measuring instrument (for example, trade name: Mastersizer S type manufactured by Malvern).

[Other effects of light calcium carbonate-silica composite particles]
Further, when the light calcium carbonate-silica composite particles are used for the pigment of the under layer, there is an effect that the air permeability of the recording medium is increased. In particular, the present invention is effective when an inkjet recording medium is manufactured by a cast coating method. In other words, in any of the cast coating methods, it is necessary to press the coating layer against the cast drum to obtain a glossy surface, and therefore the drying of the coating layer proceeds only from the surface that does not contact the cast roll of the support. Therefore, the cast coating method has a low drying rate and low productivity, but the productivity can be improved by increasing the air permeability of the under layer.
This reason is considered to be because the light calcium carbonate-silica composite particles include voids as described above. In order to increase the air permeability of the under layer, the average particle diameter of the composite particles is preferably 1 μm or more. In addition, the above-mentioned rosette-type light calcium carbonate has a lot of voids due to its chestnut shape, and has a great effect of improving the air permeability of the under layer.
The air permeability of the support provided with the under layer is preferably 300 seconds or less, more preferably less than 100 seconds.

[Method for producing light calcium carbonate-silica composite particles]
The light calcium carbonate-silica composite particles can be obtained, for example, by adding mineral acid at a temperature equal to or lower than the boiling temperature to a liquid obtained by mixing light calcium carbonate and an alkaline metal silicate aqueous solution, and adjusting the pH of the liquid to 7-9. . In addition, according to such a manufacturing method, it is thought that it becomes the composite particle by which the surface of the light calcium carbonate was coat | covered with the silica.
Specifically, in the production method, first, the light calcium carbonate is dispersed in water, and an alkali solution of silicic acid (alkali is, for example, sodium or potassium) is added thereto. Although the molar ratio of silicic acid and alkali is not limited, No. 3 silicic acid (SiO ₂ / Na ₂ O = (3.1 to 3.4) / 1) is generally easily available and can be suitably used. The solid content mass ratio (CaCO ₃ / SiO ₂ ) of the intended light calcium carbonate-silica composite particles can be adjusted by adjusting the charge mass ratio between the light calcium carbonate and the alkali solution of silicic acid.

  Next, after stirring and dispersing these mixtures, light calcium carbonate-silica composite particles can be produced by neutralizing with a mineral acid. The mineral acid may be anything, and the mineral acid may contain an acidic metal salt such as sulfate band or magnesium sulfate. Addition of mineral acid (or acid containing the above acidic metal salt aqueous solution in mineral acid) is performed at a temperature not higher than the boiling point of the above mixture, and silicic acid is deposited on the surface of the light calcium carbonate particles to form amorphous silicic acid. It is formed and coated to obtain light calcium carbonate-silica composite particles. It is important to complete this neutralization reaction at pH = 7-9. If the pH is less than 7, decomposition of light calcium carbonate occurs. If the pH exceeds 9, precipitation of silicic acid is not performed sufficiently, and unreacted silicic acid remains. This is not preferable because it causes loss.

  Adjustment of the average particle size of the light calcium carbonate-silica composite particles is carried out by vigorous stirring and pulverization during aging during the neutralization reaction, or after completion of the neutralization reaction, or by solid-liquid separation after completion of the reaction. It can be performed by pulverization using a pulverizer. These methods may be combined. The aging means that the addition of the acid to be added at the time of neutralization is temporarily interrupted and left only after stirring.

[Other fillers]
In addition to the light calcium carbonate-silica composite particles, inorganic pigments and organic pigments can be used together as the under layer pigment, as long as the effects of the present invention are not impaired. These can be used without any limitation as long as they are usually pigments used in coated paper. For example, synthetic silica, alumina and alumina hydrate (alumina sol, colloidal alumina, pseudoboehmite, etc.), aluminum silicate, magnesium silicate, magnesium carbonate, light calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, titanium dioxide, One or more kinds selected from inorganic pigments such as zinc oxide, zinc carbonate, calcium silicate, and aluminum hydroxide; organic pigments such as urea-formalin resin, polystyrene resin, and phenol resin can be used in combination. When the light calcium carbonate-silica composite particles are used in combination with another pigment, it is preferable that the light calcium carbonate-silica composite particles are contained in an amount of 60% by mass or more in the total pigment.

[Binder]
Any binder can be used as long as it is a polymer compound capable of forming a film. Specifically, fully saponified or partially saponified polyvinyl alcohol; carboxylic acid-modified polyvinyl alcohol; silyl-modified polyvinyl alcohol; acetoacetyl group-modified polyvinyl alcohol; polyvinyl acetal resin; starches such as oxidized starch and esterified starch; carboxymethylcellulose, hydroxy Cellulose derivatives such as ethyl cellulose; polyvinylpyrrolidone; casein; gelatin; soy protein; styrene-acrylic resin and derivatives thereof; styrene-butadiene latex, acrylic emulsion, vinyl acetate emulsion, vinyl chloride emulsion, urethane emulsion, urea emulsion, alkyd emulsion and the like These derivatives may be used alone or in combination. In particular, it is preferable to use polyvinyl alcohol (including a modified product) because the transparency of the under layer is improved and the color developability of the ink remaining in this layer is improved.
The blending amount of the binder in the under layer is not particularly limited as long as the required layer strength is obtained, but it is preferably 3 to 70 parts by weight, and 10 to 50 parts by weight with respect to 100 parts by weight of the pigment. It is more preferable. If the blending amount of the binder is small, the strength of the under layer tends to decrease, and if the blending amount is large, the ink absorbency tends to decrease.

[Other auxiliaries]
In order to improve the fixing property of the dye ink and to make the fixed dye ink water resistant, a cationic polymer compound can be contained in the under layer.
Examples of the cationic polymer compound include primary amines, secondary amines, tertiary amines, quaternary ammonium salts and cyclic amines, or polymer compounds containing these salts as monomers. Specific examples include vinylimine, alkylamine, alkyleneamine, vinylamine, allylamine, alicyclic amine, epihalohydrin, dialkylaminoethyl methacrylate, dialkylaminoalkyl acrylate, dialkylaminoalkylacrylamide, diallyldimethylammonium salt, acrylamide, amidoamine, amidine, etc. Is a so-called polyethyleneimine resin, polyamine resin, polyamide resin, polyamide epichlorohydrin resin, polyamine epichlorohydrin resin, polyamide polyamine epichlorohydrin resin, polydiallylamine resin, Examples thereof include dicyandiamide condensates. Two or more of these cationic polymer compounds can be used in combination.

In particular, using either dye ink or pigment ink, excellent print quality, especially high print density and water resistance, dialkyl (alkylene) amine epihalohydrin and diallyldimethylammonium salt condensate (homopolymer), co-polymer Combined and derivatives thereof are preferred. A polymer (homopolymer), copolymer, and derivative of dialkyl (alkylene) amine epihalohydrin are most preferable because they hardly inhibit the ink absorbability of the ink receiving layer even at a low molecular weight.
In addition, for the under layer, pigment dispersant, fluidity improver, water retention agent, thickener, antifoaming agent, foam suppressor, mold release agent, surface modifier, foaming agent, penetrating agent, coloring as necessary Various auxiliary agents such as dyes, coloring pigments, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, antibacterial agents, pH adjusters, and softeners can also be added.

<Coating method>
Next, a method for providing an under layer on the support will be described.
The under layer can be formed as one or more layers on one or both sides of the support. When a plurality of under layers are provided, the components of the coating liquid may be different within the range specified in the present invention. In addition, for example, the coating can be layered a plurality of times with a slide die coater or the like, applied onto the support and then dried. Normally, when coating is applied multiple times, there is a boundary surface between the coating layers. For example, the boundary surface is observed with an electron microscope or an optical microscope, and the cross-section of the ink-receiving layer is thinned by a gas adsorption method or a mercury porosimeter. It can be identified by measuring the pore size distribution. Preferably the coating amount of the under layer is 3 to 30 g / ^{m 2,} more preferably from 5 to 20 g / ^{m 2.} When it is less than 3 g / m ² , the support cannot be sufficiently covered, and coating unevenness occurs. When it exceeds 30 g / m ² , the coating layer strength is lowered, which may cause the under layer to peel off.

Actually, when a predetermined paint is applied, the physical properties of the paper after coating may differ between when it is applied once and when it is applied twice. In this case, as described above, the coating layer interface when applied twice by microscopic observation or the like can be easily observed.
When the coating is performed once and twice, the physical properties of the coated paper may be different due to binder migration or the like. Therefore, the number of coatings may be determined according to the required characteristics.
Further, in order to apply a predetermined coating amount at a time, the drying load of the coater becomes large and is affected by the equipment. Therefore, in the case of a small coater, it may be inevitably applied twice.

Equipment for coating the under layer includes various blade coaters, roll coaters, air knife coaters, bar coaters, gate roll coaters, curtain coaters, die coaters, short dwell coaters, gravure coaters, flexographic gravure coaters, spray coaters, size presses, etc. Various devices can be used on-machine or off-machine.
It is also possible to perform surface treatment with a calendar device such as a machine calendar, a super calendar, or a soft calendar before or after coating the under layer.

<Ink receiving layer>
The ink receiving layer contains a pigment and / or a binder and retains a coloring component in the ink.
[Pigment]
As the pigment, the same pigment as that used for the under layer can be used. For example, synthetic amorphous silica, colloidal silica, light calcium carbonate-silica composite particles, kaolin, clay, calcium carbonate, talc, alumina, hydrated alumina (alumina sol, colloidal alumina, pseudoboehmite, etc.), aluminum hydroxide, magnesium carbonate, Satin white, titanium dioxide, montmorillonite, plastic pigment, etc. can be used alone or in combination of two or more.
It is also possible to form an ink-receiving layer without using a binder by using a pigment having a so-called self-binding function (for example, colloidal silica) that can form a film without using a binder. .

[Binder]
As a binder, the thing similar to what is used for an under layer can be used. For example, polyvinyl alcohol and derivatives thereof; starches such as oxidized starch and esterified starch; cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; polyvinylpyrrolidone; casein; gelatin; soy protein; styrene-acrylic resin and derivatives thereof; Latex, acrylic emulsion, vinyl acetate emulsion, vinyl chloride emulsion, urethane emulsion, urea emulsion, alkyd emulsion and derivatives thereof can be used alone or in combination.

[Other ingredients]
In addition, for the ink receiving layer, a pigment dispersant, a fluidity improver, a water retention agent, a thickener, an antifoaming agent, a defoaming agent, a release agent, a surface property modifier, a foaming agent, and a penetrating agent are necessary. Various auxiliary agents such as coloring dyes, coloring pigments, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, antibacterial agents, pH adjusters, softeners, and ink fixing agents can also be added.

[Coating amount of ink receiving layer]
The coating amount of the ink receiving layer can be arbitrarily adjusted within the range that covers the surface of the under layer and sufficient ink absorbency can be obtained, but from the viewpoint of achieving both recording density and ink absorbency, The solid content is preferably ³ to 30 g / m ² . A more preferable range is 5 to 20 g / m ² . If the coating amount is less than 3 g / m ² , the under layer may not be sufficiently coated and uneven coating may occur. If it exceeds 30 g / m ² , The peelability from the mirror drum may be reduced, and the coating layer may adhere to the mirror drum.

[Method of forming ink receiving layer]
The ink receiving layer can be formed by applying an ink receiving layer coating solution. As a coating method, from among coating methods using a known coating machine such as a blade coater, air knife coater, roll coater, brush coater, kiss coater, squeeze coater, curtain coater, die coater, bar coater, gravure coater, etc. It can be selected appropriately. The following cast coating method (coating with a cast coater) is preferable from the viewpoint of obtaining an inkjet recording medium having particularly high gloss.

[Method of forming ink receiving layer (cast coating method)]
In view of obtaining an ink jet recording medium having gloss as high as that of a silver salt photograph, it is preferable to form an ink receiving layer by a so-called cast coating method. This cast coating method is performed by pressing the coating layer against a heated mirror surface and then drying it while the surface of the coating layer to which the ink receiving layer coating is applied is in a wet state. Here, in the present invention, since the under layer contains light calcium carbonate-silica composite particles, an appropriate gap is formed in the layer, and when the ink receiving layer coating liquid is pressed against the cast drum and dried, Since the vapor evaporated from the coating liquid is easily removed, it is easy to dry, and troubles such as fogging of the cast drum and adhesion of the coating layer to the cast drum are reduced.

The cast coating method includes (1) a wet casting method (direct method) in which a coating layer is pressed (pressure-welded) to a mirror-finished heating drum while the coating layer is in a wet state (as is), and (2) wet. Re-wet casting method (re-wetting method) in which the coating layer in a state is once (semi-) dried and then swollen and plasticized (wet) with a re-wetting liquid, and then pressed onto a mirror-finished heating drum and dried (3) The coating layer can be generally divided into three types: a gelation cast method (coagulation method) in which a coating layer is made into a gel state by a coagulation treatment such as a coagulation liquid, and is pressed onto a mirror-finished heating drum and dried.
Both methods are similar in that a mirror surface (for example, a metal mirror surface such as a heated mirror drum or a flat mirror surface) is pressed against a coating layer in a wet state (including a gel state in a wet state).
In the present invention, any of the methods described above can be used, but the coagulation method is preferable from the viewpoint of obtaining high gloss, and the rewet method is preferable from the viewpoint of improving productivity.

  In the case of the rewet cast coating method, a treatment liquid that has the effect of drying the coating layer coated with the ink-receiving layer coating liquid and plasticizing the binder of the coating layer (plasticization treatment liquid) Is applied to the coating layer, and then the coating layer is pressure-bonded to a heated mirror surface to give gloss. In this method, since the ink receiving layer is in a dry state when applying the treatment liquid, it is difficult to copy the surface of the mirror drum, there are many fine irregularities on the surface, and the glossiness tends to be slightly lowered. Since the coating speed can be increased as compared with the above method, productivity is improved.

  In the case of the coagulation method cast coating method, while the coating layer to which the ink receiving layer coating solution is applied is in a wet state, a treatment solution that solidifies (or crosslinks) the binder is applied thereto. Then, the coated layer is pressure-bonded to the heated mirror surface to give gloss. For example, when polyvinyl alcohol is used as the binder for the coating layer, any aqueous solution containing a compound capable of coagulating polyvinyl alcohol can be used. And a treatment solution containing borate. By mixing and using boric acid and borate, it is easy to obtain a solidified state with an appropriate hardness, and an ink jet recording medium having a good gloss feeling can be obtained. When casein is used as the binder, an aqueous solution containing a compound having a function of coagulating casein can be used as the treatment liquid.

  In addition, the above treatment liquids (coagulation liquid and plasticizing liquid) include pigment dispersants, water retention agents, thickeners, antifoaming agents, antiseptics, colorants, water resistance agents, wetting agents, fluorescent agents as necessary. A dye, an ultraviolet absorber, a cationic polymer electrolyte, and the like can be appropriately added. Examples of the method for applying the treatment liquid include, but are not limited to, a roll, a spray, and a curtain method.

<Other layers>
In the present invention, an overcoat layer composed of a coating layer containing organic fine particles, inorganic fine particles, or a polymer compound may be provided on the ink receiving layer for the purpose of adjusting glossiness and friction coefficient. . In addition, if necessary, a back layer for providing writing property, antistatic property, antifouling property, slipperiness, etc. can be provided on the support opposite to the surface on which the ink receiving layer is provided. It is.

<Example>
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. Further, the following “parts” and “%” represent “parts by mass” and “mass%” unless otherwise specified.

(Production of light calcium carbonate-silica composite particles)
1) Light calcium carbonate-silica composite particles A
In a reaction vessel (12 L), 262 g of commercially available Rosetta-type light calcium carbonate (trade name: Albuquer 5970, manufactured by Specialty Minerals Inc., average particle size: 3.0 μm) was dispersed in water, and this was mixed with a sodium silicate solution (SiO 2 ₍₂ concentration 18.0 wt / wt%, Na ₂ O concentration 6.1 wt / wt%) 3,400 g was added, then water was added to make the total volume 12L. This mixed slurry was heated to 85 ° C. with sufficient stirring with a laboratory agitator. A 10% sulfuric acid solution was added to the slurry by a rotary pump, and at this time, the sulfuric acid-added portion was added immediately below the stirring blade of the laboratory agitator. Under the above conditions in which the added sulfuric acid was sufficiently dispersed, sulfuric acid was added at a constant temperature and at a constant rate so that the final pH of the slurry after completion of sulfuric acid addition was 8.0 and the total sulfuric acid addition time was 240 minutes. After the obtained slurry was passed through a 100 mesh sieve to separate coarse particles, No. Using a filter paper No. 2, suction filtration was performed to obtain light calcium carbonate-silica composite particles A having a light calcium carbonate / silica mass ratio of 30/70. The oil absorption of the composite particles was 180 ml / 100 g, the BET specific surface area was 30 m ² / g, and the average particle size was 7.3 μm.

<Production of light calcium carbonate-silica composite particles B>
Except that the amount of dispersion of the Rosetta-type light calcium carbonate was 612 g, the light calcium carbonate / silica mass ratio was 50/50 and the oil absorption was exactly the same as the production of the light calcium carbonate-silica composite particles A. Light calcium carbonate-silica composite particles B having 160 ml / 100 g, a BET specific surface area of 28 m ² / g, and an average particle size of 4.4 μm were obtained.

<Production of light calcium carbonate-silica composite particles C>
Except that the amount of dispersion of the Rosetta-type light calcium carbonate was 1436 g, the light calcium carbonate / silica mass ratio was 70/30 and the oil absorption was exactly the same as the production of the light calcium carbonate-silica composite particles A. Light calcium carbonate-silica composite particles C having 140 ml / 100 g, a BET specific surface area of 26 m ² / g, and an average particle size of 3.6 μm were obtained.

(Manufacture of support)
A pulp consisting of 100 parts of hardwood bleached kraft pulp (L-BKP) having a freeness of 350 ml c · s · f, 4 parts of titanium oxide, and 0.4 parts of cationic starch (Kate 304L: product name of Nippon SC Co., Ltd.) Then, 1.0 part of aluminum sulfate, 0.1 part of a synthetic sizing agent, and 0.02 part of a yield improver were added to obtain a pulp slurry. Paper was made from this slurry by using a paper machine, and starch was impregnated on both sides with a size press so that the dry coating amount per side was 1.5 g / m ² to obtain a support.

(Formation of under layer)
On one side of this support, coating liquid A was applied using a blade coater so that the coating amount was 10 g / m ^2, and an under layer was provided to obtain a coated paper having a basis weight of 180 g / m ² . .
Coating liquid A: 100 parts of light calcium carbonate-silica composite particles A as a pigment, 30 parts of polyvinyl alcohol (PVA117: manufactured by Kuraray Co., Ltd.) and 5 parts of an ethylene vinyl acetate emulsion (BE7000: manufactured by Chuo Rika Kogyo Co., Ltd.), a cation Coating liquid (solid content: consisting of 5 parts of functional resin (polyamine ammonia epichlorohydrin, molecular weight 100,000), 2 parts of cationic sizing agent (Polymaron 360: manufactured by Arakawa Chemical Industries), and 0.5 part of antifoaming agent 23%) was prepared.

(Formation of ink receiving layer)
Next, 20 g / m ^{2 of} coating liquid B is applied onto the coating surface of coating liquid A using a roll coater, and solidified using coagulating liquid C while the coating layer is in a wet state, and then pressed. The coating layer was pressure-bonded to a mirror-finished surface having a surface temperature of 100 ° C. through a roll, and the mirror surface was copied and dried to obtain an inkjet recording medium having a basis weight of 200 g / m ² .
Coating liquid B: 100 parts of synthetic silica (Fine Seal X-37: manufactured by Tokuyama Co.) as a pigment, 5 parts of latex (LX438C: manufactured by Sumitomo Chemical Co., Ltd.) and polyvinyl alcohol (PVA117: manufactured by Kuraray Co., Ltd.) An aqueous coating solution B having a concentration of 20% was prepared by blending 24 parts and 5 parts of a sizing agent (Polymaron 360: manufactured by Arakawa Chemical Industries).
Coagulating liquid C: 2% borax, 2% boric acid (mass ratio of borax / boric acid = 1/1, calculated in terms of Na ₂ B ₄ O ₇ and H ₃ BO ₃ ), release agent (FL-48C: Toho Coagulation liquid was prepared by blending 0.2% (made by Chemical Industry Co., Ltd.).

  An ink jet recording medium was obtained in the same manner as in Example 1 except that 100 parts of light calcium carbonate-silica composite particles B were blended in place of the light calcium carbonate-silica composite particles A as the pigment of the coating liquid A. .

  Ink jet recording medium exactly the same as Example 1 except that 100 parts of light calcium carbonate-silica composite particles C were blended in place of the light calcium carbonate-silica composite particles A as the pigment of the coating liquid A for the under layer. Got.

As the ink receiving layer coating liquid, the following coating liquid B1 was used instead of the coating liquid B, and the coagulating liquid C1 was used instead of the coagulating liquid C. Thus, an ink jet recording medium was obtained.
Coating liquid B1: 100 parts of synthetic silica (Fine Seal X-37: manufactured by Tokuyama Co., Ltd.) as a pigment, 30 parts of aqueous urethane resin (HUX-980: manufactured by Asahi Denka Kogyo Co., Ltd.) as a binder and casein (ALACID liquid casein) An aqueous coating solution B1 having a concentration of 30% was prepared by blending 10 parts and 5 parts of a release agent (Nopcoat SYC: manufactured by San Nopco).
Coagulating liquid C1: A coagulating liquid was prepared by blending 5% calcium formate (manufactured by Asahi Chemical Industry Co., Ltd.) and 1% dye fixing agent (Daifix YK-50: manufactured by Yamato Chemical Co., Ltd.).

[Comparative Example 1]
Instead of the light calcium carbonate-silica composite particles A as the pigment of the under layer coating liquid A, silica (AY-603: manufactured by Tosoh Silica Co., Ltd., oil absorption amount of 290 ml / 100 g, BET specific surface area of 300 m ² / g, average An ink jet recording medium was obtained in the same manner as in Example 1 except that 100 parts of a particle size of 6.5 μm) were blended.

[Comparative Example 2]
As a pigment for the under layer coating liquid A, instead of the light calcium carbonate-silica composite particles A, rosetta type light calcium carbonate (trade name: Albuquer 5970, manufactured by Specialty Minerals Inc., oil absorption 120 ml / 100 g, BET ratio An ink jet recording medium was obtained in exactly the same manner as in Example 1 except that 100 parts of a surface area of 12 m ² / g and an average particle size of 3.0 μm were blended.

[Comparative Example 3]
As a pigment of the under layer coating liquid A, instead of the light calcium carbonate-silica composite particles A, 50 parts of silica (AY-603: the above-mentioned product manufactured by Tosoh Silica Co., Ltd.), Rosetta type light calcium carbonate (trade name) : Albuquer 5970, as described above by Specialty Minerals Inc.) An ink jet recording medium was obtained in the same manner as in Example 1 except that 50 parts were blended.

The physical properties of the pigment in the under layer, and the ink jet recording media of the examples and comparative examples were evaluated by the following methods.
1) Physical property value of pigment in under layer (1-1) Light calcium carbonate / silica solid content mass ratio (CaCO ₃ / SiO ₂ ): Light calcium carbonate-silica composite particles were analyzed by fluorescent X-ray, and Ca and Si Was quantified.
(1-2) Average particle size: A slurry of each pigment was added dropwise to pure water to which a dispersant (sodium hexametaphosphate 0.2% by mass) was added to form a uniform dispersion. (Part number: Mastersizer S type) was used to measure the particle size, and the average particle size was determined.
(1-3) Oil absorption: According to the method of JIS K5101.
(1-4) BET specific surface area: The BET specific surface area was determined by the nitrogen adsorption amount using an automatic specific surface area measuring device (Gemini 2360 manufactured by Micromeritics) by the volume method. When the sample was a slurry, this was dispersed in ethanol so as to have a solid content of 10%, dried at 105 ° C., and then the BET specific surface area was measured.

2) Evaluation of each inkjet recording medium The following items can be used practically without any problem if the evaluation is good or bad.
(2-1) Under layer strength For a sample in which only the under layer is provided on the base paper without providing the ink receiving layer, cello tape (registered trademark) having a width of 18 mm is pasted on the surface of the under layer, and one end of the tape is attached to the digital force gauge. The maximum value read with a digital force gauge when the tape was peeled off from the surface of the under layer was taken as the following measured value. The strength of the coating layer of the under layer can be measured by removing the tape. In addition, the following “paper peeling” indicates a case of peeling from the base paper instead of the under layer, and a case where the portion having the lowest peel strength is the base paper. In this case, it can be visually confirmed that the base paper fibers adhere to the tape. The case where paper peeling occurs indicates a case where the strength of the interface between the under layer and the base paper is low, and indicates that peeling of the coating layer or cast coating property is deteriorated.
A: The measured value is 1000 gf or more, and there is no paper peeling.
○: The measured value is 700 gf or more, and there is no paper peeling.
(Triangle | delta): A measured value is 500 gf or more and less than 700 gf. Or more than that, there is paper peeling.
X: The measured value is less than 500 gf.

(2-2) Ink absorbability (bleeding)
Using an ink jet printer using dye ink (PM-950C: Epson Corporation product name), a spreadsheet image “Excel” was used to record a solid image of red and green on a recording medium, and mixed red and green. The bleeding was visually evaluated at the boundary of the part.
A: The color boundary portion is clearly separated. ○: The color boundary portion has a slight blur and the blur is small. Δ: The color boundary portion has a slight blur and the degree of the blur is small. Relatively large x: A color boundary portion with very large blurring (2-3) Vividness Predetermined using an ink jet printer (PM-950C: trade name of Epson Corporation) using dye ink The pattern was printed on a recording medium, and the vividness of the image area was visually evaluated. Vividness is an index that prints an image neatly, and is an overall evaluation of print density, image reproducibility, and the presence or absence of unevenness in the image. Here, the print image is visually judged and the following evaluation is performed. It was.
◎: Very vivid ○: Vivid △: Slightly inferior x: Invisible

(2-4) Air Permeability Regarding the recording medium before forming the ink receiving layer (only the under layer is formed on one side of the support), the Japan Paper Pulp Technology Association (J.TAPPI) NO. The air permeability was measured according to 5.
A: The measured value is less than 100 s.
○: The measured value is 100 s or more and less than 300 s.
(Triangle | delta): A measured value is 300 to 600 s.
X: The measured value is 600 s or more.

(2-5) Cast layer appearance The surface of the ink receiving layer (cast layer) after the ink receiving layer was formed by a casting method was visually observed.
○: Unevenness caused by the missing under layer is not seen.
X: There is unevenness caused by the missing under layer.
(2-6) Casting operability When the ink-receiving layer was cast, the mirror-finished surface (cast drum surface) was visually evaluated. ○: No surface contamination Δ: Surface slightly clouded ×: A part of the coating layer (ink receiving layer) is adhered to the surface. The obtained results are shown in Tables 1 and 2.

  As is clear from Tables 1 and 2, in each case, both the under layer strength and the ink absorbency were excellent. In each of the examples, the gas permeability was high, and the castability (the appearance and operability of the cast layer) was excellent. Further, in each of the examples, the vividness of the recorded image was excellent.

On the other hand, in the case of Comparative Example 1 using only silica as a pigment for the under layer, the strength of the under layer was deteriorated, the air permeability was lowered, and the castability (appearance and operability of the cast layer) was also lowered. The reason for this is considered to be that the amount of oil absorption of silica is too much to adsorb the binder, and the amount of the effective binder is reduced.
Further, in Comparative Example 2 in which only light calcium carbonate was used as the pigment for the under layer, the ink absorbability deteriorated and the vividness of the recorded image also decreased. The reason for this is considered to be that the amount of oil absorption is small with calcium carbonate alone.
In the case of Comparative Example 3 in which a mixture of silica and light calcium carbonate was used as the pigment for the under layer, the ink absorbability was deteriorated. From this, it has been found that the ink absorbability cannot be improved simply by mixing silica and light calcium carbonate.

  As described above, by using the light calcium carbonate-silica composite particles as a pigment, an ink jet recording medium having excellent under layer strength and ink absorbability can be obtained.

It is a figure which shows an example of the form of the light calcium carbonate (Rosetta-type calcite type) of the state disperse | distributed in the liquid. It is a figure which shows an example of the form of the light calcium carbonate-silica composite particle of the state disperse | distributed in the liquid.

Claims (4)

On at least one surface of a support, an under layer containing a pigment and a binder provided an ink jet recording medium provided with an ink receiving layer on the surface of the under layer, the pigment of the under layer, light carbonate An ink jet recording medium comprising light calcium carbonate-silica composite particles in which the surface of the light calcium carbonate particles is coated with silica in which silicic acid is deposited on the surface of the calcium particles . _2. The inkjet recording according to claim 1, wherein the light calcium carbonate / silica composite particles have a light calcium carbonate / silica solid content mass ratio (CaCO ₃ / SiO ₂ ) of 25/75 to 75/25. Medium.   2. The light calcium carbonate-silica composite particles, wherein the light calcium carbonate particles are Rosetta-type calcite light calcium carbonate in which spindle-shaped primary particles are aggregated to form secondary particles. Item 3. The ink jet recording medium according to Item 1 or 2. The outermost surface of the ink receiving layer is provided after the coating layer is pressed against a heated mirror surface while the surface of the coating layer formed by applying the coating material for the ink receiving layer is in a wet state, and then dried. The ink jet recording medium according to claim 1, wherein the ink jet recording medium is used.