JP2009154507A - Inkjet recording paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide plain paper type inkjet recording paper excellent in the clearness and ink coloring density of printing recorded on the rear surface of the inkjet recording paper by reducing the stain of ink when the ink is printed on the rear surface of the inkjet recording paper by improving the difference of the back and front surface of the inkjet recording paper due to the missing of minute fiber and the two sidedness of filler distribution in the paper layer when the inkjet recording paper is manufactured by using a Fourdrinier paper making machine. <P>SOLUTION: In the inkjet recording paper, clear coating layers are respectively provided on the back and front surfaces of a base material which contains pulp as the main component of a raw material, and is made by the Fourdrinier paper making machine. The clear coating layers are provided by different coating means in the front and rear surfaces, and those clear coating layers both contain a water soluble binder and a cationic polymer fixing agent as the main components. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ink jet recording paper which improves the difference between the front and back sides of paper when paper is made with a long paper machine and is excellent in printability on both the front and back sides. In particular, the present invention relates to a plain paper type ink jet recording paper that improves ink bleeding when printed on the back side and is excellent in the clearness of printed recording on the back side and the ink color density.

  Inkjet recording is a method for recording images, characters, etc. by attaching micro droplets of ink to a recording material according to various operating principles, and has the advantages of high speed, low noise, and easy multi-coloring. With recent technological advances, it is possible to record with high print quality.

  In recent years, from the viewpoint of environmental protection and recycling, there is an increasing demand for paper that can be printed not only on one side but also on both sides. However, most of the plain paper type ink jet recording papers that are currently widely used can only print on one side, or even when double-sided printing is possible, ink is smeared on one side or the printing is sharp. In addition, there are drawbacks such as lack of ink color density.

  As described above, the difference in the ink bleeding method, the clearness of printing, and the ink color density due to the front and back sides of the paper is due to insufficient adjustment of dewatering on the wire when paper is made. This is because the dehydration of the front and back sides in the press section is not controlled, and the paper filling rate on the front and back sides is different. .

  By the way, in the paper making method, the paper machine is well known in the paper making industry, such as a long paper machine, a twin wire paper machine, a combination paper machine, a round paper machine, and a Yankee paper machine. Differences in ink bleeding, image sharpness, and ink color density due to differences are phenomena that are more prominent when using a long net paper machine.

  The long net paper machine, which has long been known as a paper machine, is a system in which pulp slurry discharged from a stock inlet is naturally dehydrated from below through a dewatering zone provided at the bottom of the long net, but only from below. For this reason, the fine fibers are lost, the two-sidedness is generated in the filler distribution in the paper layer, and the inkjet suitability on the back surface is lower than that on the front surface.

  In this regard, as an example of improving the recording density on both the front and back sides of an ink jet recording sheet, a recording sheet (for example, see Patent Document 1) in which the filler ratio in the front and back layers of the base paper is adjusted, and a twin wire region are used. There has been proposed a dewatering device or the like that improves the formation dispersibility at the time of paper making by a dewatering device provided in (see, for example, Patent Document 2).

However, in Patent Document 1, when using a long paper machine, the quality of the paper surface on the front and back sides is adjusted even if the use of a yield improver, the adjustment of dehydration on the wire, and the dehydration of the front and back sides in the press section are adjusted. It is difficult to improve the difference. Moreover, since patent document 2 provides a twin wire area | region connected to the initial stage dewatering zone of a long net paper machine, there exists a problem which installation cost increases.
JP-A-8-260382 JP-A-8-92991

  The main problem to be solved by the present invention is to improve the difference between the front and back due to the two-sidedness of fine fibers and filler distribution in the paper layer when an inkjet recording paper is manufactured using a long net paper machine, especially on the back side. An object of the present invention is to provide a plain paper type ink jet recording paper that reduces ink bleeding when printed, and is excellent in the clearness of printed recording on the back surface and the ink color density.

The present invention that has solved this problem is as follows.
[Invention of Claim 1]
Inkjet recording paper comprising a pulp as a main component and a clear coat layer on each of the front and back surfaces of a base material made by a long paper machine,
The clear coat layer on the front surface and the clear coat layer on the back surface are provided by different coating means,
These clear coat layers are ink jet recording papers characterized in that a water-soluble binder and a cationic polymer fixing agent are the main components.

[Invention of Claim 2]
The time until the ultrasonic transmission intensity of the initial water absorption property in the dynamic water absorption test reaches 100% is set to 0.10 seconds to 0.50 seconds on both the front surface side and the back surface side,
The inkjet recording paper according to claim 1, wherein the Steecht sizing degree according to JIS P 8122 is 11 seconds to 45 seconds on both the front surface side and the back surface side.

[Invention of Claim 3]
The coating amount of the clear coat layer of the surface, 0.5 to 1.5 g / m ^2, the coating amount of the back surface of the clearcoat layer is a 1.5~2.5g / m ^2, wherein Item 3. The ink jet recording paper according to item 1 or 2.

[Invention of Claim 4]
The clear coating layer on the front surface is coated by a roll coating method, and the clear coating layer on the back surface is coated by a blade coating method, and “the coating amount of the clear coating layer on the back surface” — “clear surface coating” coating amount "are as ^{0.4g / m 2 ~2.0g / m 2} , the ink jet recording sheet according to claim 1 of the coating layer.

  According to the present invention, when ink jet recording paper is manufactured using a long paper machine, the front and back difference due to the two-sidedness of fine fibers and filler distribution in the paper layer is improved, and particularly when ink is printed on the back side. This is a plain paper type ink jet recording paper with reduced bleeding and excellent print clarity and ink color density on the back side.

Next, the ink jet recording paper according to the embodiment of the present invention will be described. It should be noted that the present invention is not necessarily limited to the following embodiment, and it goes without saying that the configuration can be appropriately changed without departing from the scope of the claims.
The ink jet recording paper of this embodiment is one in which a clear coat layer is provided on each of the front and back surfaces of a substrate.

〔Base material〕
In this embodiment, the type of raw material pulp of the base material is not particularly limited. For example, softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), semi-chemical pulp (SCP), ground wood pulp (GP), ChemiGrand Pulp (CGP), refiner ground pulp (RGP), diinking pulp (DIP), waist pulp (WP) and the like can be used. Among them, it is preferable to use hardwood kraft pulp from the viewpoint of inkjet suitability. In the raw material pulp, it is preferable that hardwood kraft pulp is contained in an amount of 30 to 50% by weight.
Further, in this embodiment, in order to meet the trend of environmental protection and effective use of resources, it is preferable to make high-grade waste paper pulp in all raw pulp components and make paper in a neutral pH region.

  As the types of waste paper used as raw materials for waste paper pulp, various known waste papers such as magazine waste paper, leaflet waste paper, colored waste paper, newspaper waste paper, Kent waste paper, Kami white waste paper, coat waste paper, and copy waste paper can be used. These waste papers can be used after being disaggregated and deinked or bleached. The waste paper pulp is preferably contained in an amount of 20% by mass or more, more preferably 40 to 60% by mass, based on the total raw material pulp. When the content of the used paper pulp is 20% by mass or more, the ash content in the used paper pulp can be effectively used, and the opacity of the resulting ink jet recording paper can be effectively increased.

  In addition, various additives such as internal sizing agents, fillers, yield improvers, paper strength enhancers, etc., may be added as appropriate to pulp slurries made from these raw pulps, and papermaking should be performed with a long net paper machine. Can do.

(Internal sizing agent)
In this embodiment, the substrate may contain an internal sizing agent. Examples of the internal sizing agent include rosin sizing agents for acidic papermaking, modified rosin sizing agents for neutral papermaking, and alkenyl succinic acid-based sizes. Agent, alkyl ketene dimer sizing agent, alkenyl succinic anhydride sizing agent, wax sizing agent, styrene resin sizing agent, olefin resin sizing agent, styrene-acrylic resin sizing agent, higher fatty acid sizing agent, cationic polymer Mold sizing agents and the like.

  In this embodiment, the internally added sizing agent is a component that imparts a size effect to the substrate. Although there is no limitation in particular as an internal sizing agent used for this form, The alkyl ketene dimer sizing agent which expresses the stable size effect also in a neutral area | region is preferable. Alkyl ketene dimers (AKD) are believed to improve in size over time. That is, as the alkyl ketene dimer is gradually hydrolyzed and decarboxylated into a ketone, the size component (AKD / ketone mixture) becomes more hydrophobic and has a characteristic of improving the sizing degree. In this embodiment for improving ink bleeding on both sides, it is preferably used. In addition, when an alkyl ketene dimer sizing agent is used, the compatibility with a clear coat layer described later is good, and a good layered structure can be maintained between the substrate and the clear coat layer.

  The alkyl ketene dimer is preferably contained in the raw material pulp so as to be 0.20 to 0.40% by mass, preferably 0.25 to 0.30% by mass in terms of solid content. If the amount is less than 0.20% by mass, a sufficient size effect cannot be obtained, the ink penetrates into the base material, and there is a problem of ink penetration, and if it exceeds 0.40% by mass, there is a problem of poor drying of the ink. is there.

[Filler]
In this embodiment, the base material can contain a filler, such as calcium carbonate, clay, calcined clay, aluminum hydroxide, titanium dioxide, magnesium silicate, magnesium sulfate, aluminosilicate, silica. , Mineral fillers such as pyroferrite, sericite, bentonite, polystyrene resin fine particles, urea formalin resin fine particles and thermally expandable fine hollow particles and other organic fillers are used as appropriate, and may be used alone or in combination. May be used. However, in this embodiment, calcium carbonate is preferable because it is excellent in printing quality such as ink setting property. The calcium carbonate content is preferably 5 to 20% by mass with respect to the raw material pulp. The reason for this is that when the calcium carbonate content is less than 5% by mass, the ink drying property deteriorates, the ink adhesion of the printing press roll increases, the frequency of cleaning increases, the opacity of the paper decreases, On the other hand, when the content of calcium carbonate exceeds 20% by mass, there is a problem of reduction in surface strength.

  Further, the entire paper (base material and clear coat layer) preferably contains a filler so that the ash content according to JIS P 8251 is 5 to 20% by mass, preferably 8 to 13% by mass. If the ash content is less than 5% by mass, the smoothness of the front and back surfaces of the base material (particularly the back surface) is lowered and the ink coloring property is deteriorated. This is not preferable because the amount of paper dust increases.

  Other additives include, for example, polyacrylamide, polyvinyl alcohol polymer compounds, urea resins, melamine resins, paper strength enhancers such as starch, chemical fixing agents such as sulfuric acid bands, polyacrylamide, acrylamide-aminomethyl acrylamide. Copolymer salt, cationized starch, polyethyleneimine, polyethylene oxide, acrylamide-sodium acrylate copolymer drainage or yield improver, antifoaming agent, dye, antibacterial agent, ultraviolet absorber, crosslinking agent Etc.

[Paper making method]
The base material of this embodiment can be manufactured by making paper using the above raw materials. The papermaking can be performed using a paper machine such as a long web paper machine, a twin wire paper machine, an on-top paper machine, a hybrid paper machine, a round paper machine, etc. The purpose of this paper is to improve the print clarity on the back side, ink back-through, ink color development, and ink drying by the removal of fine fibers, which is a problem when making paper using a machine. Is used.

[Clear coat layer]
In the ink jet recording paper of this embodiment, a clear coat layer mainly comprising a water-soluble binder and a cationic polymer fixing agent (50% by mass or more) is provided on the front surface and the back surface of the substrate.

  The water-soluble binder is not particularly limited. For example, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, oxidized starch, acetylated starch, esterified starch, etherified starch, cationized starch, hydroxylethyl etherified starch (HES), Self-modified starch (APS starch), enzyme-modified starch, urea phosphated starch, positive starch, urethane esterified starch, starches such as dextrin, cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, casein, synthetic protein, soybean Binders such as proteins such as proteins can be used as appropriate, and may be used alone or in combination. In this embodiment, it is preferable to use oxidized starch since the stability of the mucus is good and the cost can be reduced. The water-soluble binder content is preferably 0.5 to 12% by mass in terms of solid content, more preferably 2.0 to 10% by mass, and more preferably 5.0 to 9.0% by mass. It is preferable in terms of the print clarity and surface strength on both the front and back sides. If the amount is less than 0.5% by mass, the print definition, ink penetration, and ink coloring are inferior. If the amount exceeds 12% by mass, the ink drying property is inferior.

In addition, the cationic polymer fixing agent can fix the ink to the base material and improve the water resistance of the printing portion. Examples of the cationic polymer fixing agent include a dicyan ink fixing agent typified by dicyandiamide / formalin polycondensate, a polyamine ink fixing agent typified by dicyandiamide / diethylenetriamine polycondensate, an epichlorohydrin / dimethylamine addition polymer, dimethyldiallylammonium chloride · SO ₂ copolymer, diallylamine salt · SO ₂ copolymer, dimethyl diallyl ammonium chloride polymer, polymer of allylamine salt, dialkylaminoethyl (meth) acrylate polycationic such quaternary salt polymer Examples thereof include an ink fixing agent. In this embodiment, it is preferable to use a modified polyamine ink fixing agent. The content of the cationic polymer fixing agent is preferably 0.5 to 2.0% by mass in terms of solid content, from the viewpoint of print clarity on both the front and back surfaces and ink coloring property. When the sharpness is inferior and exceeds 2.0% by mass, the ink coloring property is inferior.

  Furthermore, in this embodiment, it is preferable that a surface sizing agent is contained in the clear coat layer. Examples of the surface sizing agent include paraffin wax emulsion, alkyl ketene dimer, alkenyl succinic anhydride, rosin, silicone resin emulsion, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, vinyl acetate-maleic acid Copolymer, styrene-acrylic acid-acrylic acid ester copolymer, styrene-maleic acid-maleic acid ester copolymer, olefin-maleic acid copolymer, etc. It is preferable to use a styrene-acrylic acid copolymer. The styrene-based sizing agent has a characteristic of expressing a size effect by reacting with a sulfuric acid band (metal ion) in a substrate to hydrophobize a hydrophilic group. That is, the anion group of the pulp fiber and the styrene-based sizing agent is bonded via the cationic group (aluminum ion) of the sulfate band, and the sizing agent is fixed to the pulp fiber. At that time, a hydrophobic effect (a structure that repels water) covers the surface of the fiber, so that a size effect appears. Further, by using a styrene-based fixing agent, it is possible to improve the fixing property of the toner. This is because the binder for adhering the colored particles contained in the toner to the paper is a styrene resin and has good compatibility. On the other hand, when an olefin-based surface sizing agent is used, the contact angle between the base material surface and the ink in accordance with TAPPI T458 om-89 is increased, so that the ink absorption rate is slow and the ink drying property is poor. There is a problem. The styrene-based surface sizing agent has a characteristic that it is difficult to see through the ink when it is printed, while having a certain level of ink absorption speed.

  In the present embodiment, the content of the styrene-acrylic acid copolymer is preferably 0.05 to 0.2% by mass in terms of solid content from the viewpoint of print clarity on both the front and back surfaces, and less than 0.05% by mass. When the print definition is inferior and exceeds 0.2% by mass, the reproducibility of halftone dots may be deteriorated, and the readability may be inferior when a barcode is printed. Further, the ink drying property is inferior.

  The mass ratio of the water-soluble binder, the cationic polymer fixing agent, and the styrene-based sizing agent contained in the clear coat layer is not particularly limited as long as the effects of each component are expressed in a balanced manner, but the water-soluble binder: cationic high The molecular fixing agent: styrene-based sizing agent is preferably 40: 5: 0 to 40: 25: 3, and more preferably 40: 10: 0.5 to 40: 20: 2.

  To simply provide a clear coat layer containing a water-soluble binder, a cationic polymer fixing agent and a styrenic surface sizing agent on both sides of the substrate, for example, a water-soluble binder, a cationic polymer fixing agent and a styrenic surface size. According to a method of coating a clear coat liquid appropriately blended with a mass ratio in the above range using, for example, a calendar coater, a size press coater, a bill blade coater, a metal ring bar coater, an air knife coater, a gravure coater, etc. However, in this embodiment, it is preferable to employ a method using a bill blade coater that coats both surfaces of the substrate.

  The bill blade coater is a facility that performs coating on both sides simultaneously with a single-sided blade and a single-sided roll. The substrate moves down through the paint reservoir. At this time, the paint is applied to both sides of the substrate, and then the substrate passes through a nip (contact portion) formed by a flexible blade and a backing roll attached to a holder. As it passes through this nip, it is weighed and smoothed on both sides of the substrate and applied.

  In this embodiment, the clear coat layer on the substrate surface is preferably applied by a film transfer coating method using a roll. This is because the film transfer coating method is excellent in terms of stability because the substrate does not catch on the coating machine. Further, it is preferable to use a blade coating method in which the clear coat layer on the back surface is scraped with a blade. In the base material of ink jet recording paper produced by a long net paper machine, the two-sidedness of fine fibers and filler distribution in the paper layer is a phenomenon that is noticeable on the back side. Therefore, in this embodiment, the back surface of the base material is applied by a blade method, so that the clear coating liquid is applied so as to correct the fiber omission and the distribution of the filler distribution regardless of the fine unevenness of the base material surface. And very high smoothness can be obtained. On the other hand, when the back surface is coated by the roll coating method, the coating is applied according to the shape of the unevenness due to the variation in the filler, so the smoothness on the paper surface is not improved. However, since the surface has few omissions and variations of fine fibers and fillers at the time of paper making and is excellent in surface properties, it can be applied by a roll coating method while obtaining a coating property with a small amount of clear coating solution.

In this embodiment, in order to improve the difference between the front and back of the filler distribution in the paper layer by the long paper making, the coating amount of the clear coat liquid is 0.5 to 1.5 g of the “coating amount of the surface clear coat layer”. / M ² , “the coating amount of the clear coat layer on the back surface” is preferably 1.5 to 2.5 g / m ² . If the coating amount of the clear coat liquid applied to the front and back surfaces is less than the lower limit, the effect of providing the clear coat layer is not sufficiently exhibited, and the bleeding of the printed portion and the color density can be improved. I can't. On the other hand, when the value exceeds the upper limit, the cost is increased, and coating layers are formed on both sides of the base paper, the ink absorption drying property is lowered, and there is a possibility that the ink will be rubbed.

Furthermore, "The coating amount of the back surface of the clear coat layer" - "coverage of the clearcoat layer of the surface", it is more preferable that is ^{0.4g / m 2 ~2.0g / m 2} . "The coating amount of the back surface of the clear coat layer" - for the coated amount difference of "coverage of the clearcoat layer of the surface" and 0.4g / m ² ~2.0g / m ^2, the paper layer This is because the two-sidedness of the fine fibers and filler distribution is a phenomenon that is remarkably seen on the back surface, and it is necessary to increase the coating amount on the back surface so that the front surface and the back surface have the same quality.

  Furthermore, the surface of the clear coat layer is preferably subjected to a flattening treatment. In the ink jet recording paper of this embodiment, for example, variable information can be printed and printed on the clear coat layer on the front or back surface by ink jet recording.

  For example, a soft calender having a heat roll can be used to perform the flattening treatment of the clear coat layer on the front surface or the back surface. The gentle flattening process on the paper fiber by the soft calender having the heat roll improves the bonding between the fibers by the relatively high temperature heat roll, improves the strength of the paper, and improves the runnability in the printing press. In addition, since the elastic roll is highly deformable, micro smoothness is improved by a soft nip and a thin portion of paper. Furthermore, when the soft nip is heated, the thermal compression of the surface becomes very uniform, eliminating the small compression difference inside the paper layer, making the micro profile uniform and improving the ink paste, and the printing screen is harmonized. It will be a thing. In this embodiment, by performing a flattening treatment on the clear coat layer on the front surface and the clear coat layer on the back surface, the unevenness caused by the immersion of the water-soluble binder and the cationic polymer fixing agent on the clear coat layer surface is flattened. In addition, it is possible to improve the precision of printing and printing information during ink jet recording.

  The above flattening treatment may be performed by a so-called on-machine calendar that forms a series with the bill blade coating machine, or by a completely separate off-machine calendar instead of a series of coating machines. Also good.

[Inkjet recording paper]
In the ink jet recording paper of this embodiment, from the viewpoint of ensuring the absorption drying property of the ink jet ink on both the front and back surfaces and the clearness of the print information, the ultrasonic transmission strength of the initial water absorption characteristic in the dynamic water absorption test is 100%. The time is preferably 0.10 seconds to 0.50 seconds on both the front surface side and the back surface side, and more preferably 0.20 seconds to 0.40 seconds. If the water absorption time is less than 0.10 seconds, the water resistance of the ink jet recording paper may be insufficient. Conversely, if it exceeds 0.50 seconds, the developer layer of the ink-jet ink may be used. The fixing property of the ink is low, and there is a risk that the printed surface will be smudged or blurred. By adjusting the water absorption time to 0.10 to 0.50 seconds, for example, even when printing is performed at 100 m / min on a high-speed inkjet printer (product number: S6240J, manufactured by Hiroyuki Uchida), Clear printing is possible, and the printed surface is not smudged or blurred.

  The method for adjusting the water absorption time can be adjusted by the addition amount of the internal sizing agent, the coating amount of the clear coat liquid, the blending amount of the surface sizing agent contained in the clear coat liquid, etc. In particular, it is preferable to adjust the water absorption time by coating a predetermined amount of a predetermined clear coat liquid on the front surface by a roll coating method and applying a predetermined amount of a predetermined clear coat liquid on the back surface by a blade coating method.

  Moreover, in performing this water absorption test, it is preferable to use an EST size meter (trade name: EST, manufactured by Emtec). Modern inkjet printers are extremely fast and require quality control under conditions that are close to actual printing conditions. Momentary water absorption management of paper (in a dynamic state where printing is actually performed) Is required. In view of the need for higher quality printing paper under such circumstances, in this embodiment, an instantaneous water absorption test value is obtained using an EST size meter. taking measurement.

  On the other hand, the ink jet recording paper of this embodiment preferably has a steecht degree according to JIS P 8122 of 11 seconds to 45 seconds on both the front side and the back side, and is set to 20 seconds to 39 seconds. More preferably, it is most preferably set to 28 seconds to 32 seconds. If the Steecht sizing degree is less than 11 seconds, there is a problem that print sharpness, ink penetration, and color development of ink deteriorate, and if it exceeds 45 seconds, the ink absorbability is low and the ink accumulates on the recording surface. There are problems that rubbing and set-off tend to occur, and that ink drying properties deteriorate. By using the ink jet recording paper of a predetermined steecht size degree according to this embodiment, the ink is absorbed into the paper very quickly, the ink is easy to dry, the dot diameter is not increased more than necessary, and the inks overlap. No longer bleed.

  The method for adjusting the degree of sizing can be adjusted by the addition amount of the internal sizing agent and the coating amount of the clear coating solution, depending on the blending amount of the surface sizing agent contained in the clear coating solution. In particular, it is preferable to adjust the water absorption time after applying a predetermined amount of a predetermined clear coat liquid on the surface by a roll coating method and applying a predetermined amount of a clear coating liquid on the back surface by a blade coating method.

  Next, examples of the present invention will be described, and technical advantages of the present invention will be shown.

[Example 1]
A pulp slurry having a ratio of 50% by mass of waste paper pulp (DIP) was adjusted to 50% by mass of hardwood kraft pulp (LBKP). The pulp slurry thus obtained was blended with 0.24% by mass of an alkyl ketene dimer (AKD, manufactured by Seiko PMC Co., Ltd .: AS-267) as an internal sizing agent, and calcium carbonate (Toyo Denka) as a filler. Kogyo Co., Ltd .: TNC-C30) was blended so that the ash content would be 10% by mass, and papermaking was performed using a long net paper machine. Thereafter, oxidized starch (manufactured by Nippon Food Processing Co., Ltd .: MS-3800) as a water-soluble binder in a bill blade coater is 3.0% by mass in terms of solid content, and a modified polyamine-based ink fixing agent (Starlight) as a cationic polymer fixing agent. PMC product: T-DK168) is 0.75 mass% in terms of solid content, and the surface sizing agent is styrene-acrylic acid copolymer (Seiko PMC Co., Ltd .: SS-2700) 0.075 mass in terms of solid content. A clear coating solution containing 2% is applied to the surface of the base material at 1.0 g / m ² and on the back surface of the base material at 2.0 g / m ^{2. Two} test papers were obtained.

  And it printed with the inkjet printer (PM950C: Seiko Epson company make) on the conditions of temperature 20 degreeC and humidity 20% with respect to both the surface of this test paper and the back surface. This printing was performed so that the size of the three primary colors (cyan, magenta, and yellow) composed of overlapping colors of red, green, and purple alternately became 3.0 cm × 3.0 cm.

[Other Examples and Comparative Examples]
About Example 1, various conditions were changed as shown in Table 1, and it was set as Examples 2-33 and a comparative example. Further, for all of the examples and comparative examples, dynamic water absorption, sizing degree, print definition, ink penetration, ink color development, and ink drying property were evaluated and are shown in Table 2.

  Details of various conditions and evaluation items are as follows.

(Dynamic water absorption)
The water absorption time when the ultrasonic transmission intensity reached 100% was measured using an EST sizing meter (trade name: EST, manufactured by Emtec). In this measurement, first, a test paper (75 mm × 50 mm) is fixed to a folder with a double-sided tape, and is submerged in a test container filled with a solvent (350 ml of water). At this time, the folder is sunk between the ultrasonic wave transmitting element and the receiving element provided in the test container. The measurement is started 0.025 seconds after contact between the test paper and the solvent. Since the ultrasonic transmission intensity changes as the solvent penetrates into the test paper, a graph of the ultrasonic transmission intensity (%) and the elapsed time (s) is displayed on the monitor of the EST size meter. The water absorption time can be obtained by reading this graph. The ultrasonic frequency for measurement is 2 MHz.

(Size)
The Steecht sizing degree was measured according to JIS P8122.

(Print sharpness)
Using an inkjet printer (model number: BJ series) manufactured by Canon Inc., with the printing mode set to plain paper: document, and blotting when alphabets and numbers are printed with ink (model number: 1069) manufactured by Cytex The presence or absence of a phenomenon (flowing along the fiber) was visually observed and evaluated.
A: No ink bleeding.
○: Slight ink bleeding is observed, but there is no problem in character discrimination.
Δ: Slight ink bleeding is observed, and character discrimination is somewhat difficult.
X: Ink bleeding is large and character discrimination is difficult.

(Ink breakthrough)
Use Canon Inc. inkjet printer (model number: BJ series), print mode as document: pattern, and make solid print with Cytex ink (model number: 1069). The presence or absence was visually observed and evaluated.
A: The print is not seen through.
◯: The print appears slightly transparent, but there is no problem in distinguishing characters printed on the surface.
Δ: The print appears slightly transparent, and the character printed on the surface is somewhat difficult to distinguish.
X: The printing is seen through as a whole, and it is difficult to distinguish characters printed on the surface.

(Ink coloring)
Use a Canon Inc. inkjet printer (model number: BJ series), set the print mode to document: pattern, print solid with Cytex ink (model number: 1069), and then adjust the density of the solid print area. Measurement was made with an ink densitometer (manufactured by Macbeth) and evaluated.
A: Ink density 1.20 or more.
○: Ink density 1.16 to 1.19.
(Triangle | delta): Ink density 1.00-1.15.
X: Ink density is less than 1.00.

(Ink drying)
Use a Canon Inc. inkjet printer (model number: BJ series), print the document as a pattern, print a solid with Cytex ink (model number: 1069), and print the solid part 5 seconds later. Rubbing with a finger The degree of ink adhesion to the finger was visually determined.
A: No dirt on fingers.
○: There is almost no dirt on the fingers, and there is no hindrance to discrimination by rubbing characters.
Δ: There is some dirt on the finger and it is somewhat difficult to discriminate by rubbing characters.
X: The finger is dirty and it is difficult to discriminate due to the rubbing of characters.

  In particular, the present invention improves the difference between the front and the back of the paper when paper is made on a long mesh, improves the bleeding of ink when printed on the back, and is a plain paper excellent in the clearness of printed recording on the back and the ink color density It can be applied as a type of inkjet recording paper.

Claims (4)

Inkjet recording paper comprising a pulp as a main component and a clear coat layer on each of the front and back surfaces of a base material made by a long paper machine,
The clear coat layer on the front surface and the clear coat layer on the back surface are provided by different coating means,
These clear coat layers are ink jet recording papers characterized in that a water-soluble binder and a cationic polymer fixing agent are the main components. The time until the ultrasonic transmission intensity of the initial water absorption property in the dynamic water absorption test reaches 100% is set to 0.10 seconds to 0.50 seconds on both the front surface side and the back surface side,
The inkjet recording paper according to claim 1, wherein the Steecht sizing degree according to JIS P 8122 is 11 seconds to 45 seconds on both the front surface side and the back surface side. The coating amount of the clear coat layer of the surface, 0.5 to 1.5 g / m ^2, the coating amount of the back surface of the clearcoat layer is a 1.5~2.5g / m ^2, wherein Item 3. The ink jet recording paper according to item 1 or 2. The clear coating layer on the front surface is coated by a roll coating method, and the clear coating layer on the back surface is coated by a blade coating method, and “the coating amount of the clear coating layer on the back surface” — “clear surface coating” coating amount "are as ^{0.4g / m 2 ~2.0g / m 2} , the ink jet recording sheet according to claim 1 of the coating layer.