JP4145225B2 - Cast coated paper for inkjet recording - Google Patents

Description

  The present invention relates to a cast coated paper for ink jet recording suitable for an ink jet recording system.

  Due to the remarkable progress of ink jet printers in recent years and the remarkable spread of digital cameras, the quality required for ink jet recording media has been increasing year by year. In particular, this tendency is remarkable in an ink jet recording medium having a gloss against conventional silver salt photography. This glossy ink jet recording medium can be produced by various methods, but the cast coating method using a cast coater has the greatest cost merit.

  The cast coating method is a method in which a coating liquid is applied onto a base paper, and this coating layer is gloss-finished with a cast drum. Specifically, (1) while the coating layer is in a wet state, a mirror surface is used. Wet cast method (direct method), which is pressure-bonded to the finished heated drum and dried, (2) The wet coating layer is once dried or semi-dried, and then swollen and plasticized with a rewetting liquid, resulting in a mirror-finished heated drum There are three types of methods: a rewetting method in which pressure is applied and dried, and (3) a gelled cast method (coagulation method) in which a wet coating layer is gelled by a solidification treatment and then pressed onto a mirror-finished heating drum and dried. Are known. The principle of each manufacturing method is the same in that the wet coating layer is pressed against the mirror-finished surface to give gloss to the coating layer surface.

  By the way, in general, an ink jet recording medium is formed by coating an ink receiving layer containing a porous pigment such as silica or alumina and a binder on a base paper, and the discharged ink is absorbed by the ink receiving layer. It is supposed to be fixed. As the binder, polyynyl alcohol, casein, starch, SBR, acrylic resin, styrene-acrylic copolymer resin, vinyl acetate resin, urethane resin, or the like is used depending on the purpose.

  Various techniques for improving the components in the ink receiving layer have been reported in order to improve the glossiness, ink absorbability, color developability, etc. of the ink jet recording medium (cast coated paper for ink jet recording) by the cast coating method. . For example, a technique for imparting high glossiness by incorporating colloidal particles having an average particle size of 300 nm or less and a cationic resin in an ink receiving layer is disclosed (for example, see Patent Document 1). In addition, a technique is disclosed in which an aqueous urethane resin is contained in the coating layer to improve ink acceptability and color developability (see, for example, Patent Documents 2 and 3). Furthermore, a technique is disclosed in which two types of polyvinyl alcohol having different average saponification degrees are contained in the ink receiving layer to impart glossiness and printability (see, for example, Patent Document 4).

  Apart from these, a technique for imparting glossiness and printability by incorporating an ethylene monomer having a glass transition point of 40 ° C. or higher and an aqueous polyurethane resin into the ink receiving layer is also disclosed (for example, patents). References 5 and 6).

Japanese Patent Laid-Open No. 9-263039 JP-A-8-246392 JP 9-156210 A JP 2002-293004 A JP 7-89220 A Japanese Patent Laid-Open No. 11-180036

However, each of the above-described techniques can improve the glossiness and printability of the recording medium, but has a problem of poor print unevenness, particularly cyan print unevenness. The printing unevenness here refers to unevenness in density that occurs when a solid portion is output by an inkjet recording method.
Accordingly, an object of the present invention is to provide a cast coated paper for ink jet recording which is excellent in gloss and has no printing unevenness, particularly cyan printing unevenness.

As a result of the investigation, the inventors have found that cracks occur on the surface of the coating layer provided by the cast coating method, and that ink is selectively absorbed in the cracks, and there are cracked portions and uncracked portions. As a result, it was found that a density difference occurred and printing unevenness occurred as a result.
Therefore, as a result of various studies, as a binder for the ink receiving layer, a mixture of two kinds of resins having the following glass transition temperatures at a predetermined ratio was used, and the following colloidal silica was used as a pigment. The present inventors have found that the above problems can be solved and have reached the present invention.
That is, the ink-jet recording cast-coated paper of the present invention is an ink-jet recording cast-coated paper in which an ink receiving layer containing a pigment and a binder is provided on at least one surface of a base paper by a cast coating method, The binder comprises a resin A having a glass transition temperature of −60 ° C. or more and less than 20 ° C. and a resin B having a glass transition temperature of 20 ° C. or more and less than 100 ° C. (mixed weight of resin A) / (of resin B The resin A and the resin B are urethane resins, and the pigment is dispersed in the coating liquid that forms the ink receiving layer. In this state, a plurality of spherical colloidal silicas having a primary particle diameter of 10 to 100 nm are aggregated in a tuft shape and contain colloidal silica that does not form a ring.

The pigment is preferably further contains a pigment component having a BET specific surface area 200~600m ² / g. The cast coating method is preferably a gelled cast coating method.

  According to the present invention, it is possible to obtain a cast-coated paper for ink jet recording which is excellent in glossiness, print density and ink absorbency, and has no print unevenness (particularly cyan color).

  Hereinafter, embodiments of the present invention will be described. The cast coated paper for ink-jet recording of the present invention is obtained by providing an ink receiving layer containing a pigment and a binder on at least one surface of a base paper by a cast coating method.

(Base paper)
As the base paper used in the present invention, paper such as coated paper and uncoated paper is used. The raw material pulp of the paper includes chemical pulp (conifer bleached or unbleached kraft pulp, hardwood bleached or unbleached kraft pulp, etc.), mechanical pulp (ground pulp, thermomechanical pulp, chemisermomechanical pulp, etc.), deinking Pulp or the like can be used alone or mixed at an arbitrary ratio. The pH of the paper may be acidic, neutral or alkaline. Further, in order to improve the opacity of the base paper, it is preferable to contain a filler in the paper. This filler is composed of hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide, synthetic resin. It can be used by appropriately selecting from known fillers such as fine particles. From the viewpoint of operability, the air permeability of the base paper is preferably 1000 seconds or less, and from the viewpoint of coating properties, the Steecht size of the base paper is preferably 5 seconds or more.

(Pigment of ink receiving layer)
As the pigment contained in the ink receiving layer, a pigment containing colloidal silica that aggregates a plurality of spherical colloidal silica particles having a primary particle diameter of 10 to 100 nm in a state of being dispersed in a coating liquid and does not form a ring is used. When the primary particle diameter of the spherical colloidal silica is less than 10 nm, the ink absorbability is lowered, and when it exceeds 100 nm, the ink absorbability is improved, but the ink coloring property is lowered.

  Here, “the colloidal silica is agglomerated in a plurality of tufts” means that when the colloidal silica is dispersed (before coating and drying), the short direction of the aggregated colloidal silica (the longest direction of the aggregate) When viewed from a direction perpendicular to the surface), there is a portion where at least two spherical colloidal silicas are bonded. Hereinafter, colloidal silica aggregated in a plurality of tufts is appropriately referred to as “tufted colloidal silica”.

  What illustrated typically the state which colloidal silica aggregated in the shape of a tuft is shown in Drawings 1-3. FIG. 1 shows a case where two spherical colloidal silicas are bonded in the short direction at the silica portions a and b. For example, when there is no silica of the symbols a and b in the figure, there is only one colloidal silica in the short direction, and the silica is aggregated in a chain shape and is not included in the present invention. FIG. 2 shows a case where 3 to 4 spherical colloidal silicas are bonded in the short direction, and the number of bonded silicas in the short direction decreases from the top to the bottom of the figure. It is the aggregation state like this. In FIG. 3, the lengths of the agglomerated silica in the short side direction and the long side direction are substantially equal, and the number of silica bonds in the short side direction from the top to the bottom is almost the same (3 to 4). In addition, “substantially” means that when the colloidal silica in a dispersed state is observed, the chain silica is hardly observed, and that a single colloidal silica that does not aggregate may be present. Show.

  The reason why printing unevenness (particularly cyan unevenness) can be improved by using the tufted colloidal silica is not clear, but is considered as follows. That is, when the ink receiving layer is formed by the cast coating method, cracks are generated on the surface. However, if tufted aggregated silica is present in the coating liquid, the size of individual cracks in the ink receiving layer (the length of cracks and the like) (Width, depth) becomes smaller, while the number of cracks in the surface unit area increases. As a result, the cracks are uniformly dispersed on the surface of the ink receiving layer, and the difference in ink density between the cracked portion and the portion where the crack does not become conspicuous, and unevenness is suppressed.

  Moreover, it is preferable that the secondary particle diameter of the above-mentioned tufted colloidal silica in a state dispersed in the coating liquid is 50 to 800 nm. This secondary particle size is also an index reflecting the aggregation state of the spherical colloidal silica. If the secondary particle size is less than 50, the ink absorbability of the ink receiving layer is lowered, and if it exceeds 800 nm, the gloss of the ink receiving layer is decreased. It tends to decrease. The primary particle diameter can be measured by the BET method, and the secondary particle diameter can be measured by a dynamic light scattering method or the like.

  Further, as the tufted colloidal silica, spherical colloidal silica having a primary particle diameter of 10 to 100 nm (BET method particle diameter) is coated and joined with colloidal aluminum phosphate, and this is aggregated to obtain a secondary particle diameter (dynamic light scattering method). It is preferable to use a particle diameter of 50 to 800 nm. Specific examples of such agglomerated silica include Snowtex HS series manufactured by Nissan Chemical Industries, Ltd.

  Furthermore, to the extent that the effects of the present invention are not impaired, in addition to the above-mentioned tufted colloidal silica, conventionally known pigment components, specifically alumina such as aluminum hydroxide, alumina sol, colloidal alumina, pseudoboehmite and alumina hydrate, Synthetic silica, kaolin, talc, calcium carbonate, titanium dioxide, clay, zinc oxide and the like can be used as the pigment.

In the present invention, from the viewpoint of improving the ink absorption of the ink receiving layer further addition of the tufted colloidal silica, BET specific surface area of 200~600m ² / g, more preferably a pigment component 250~450m ² / g Is preferably used. Increasing the BET specific surface area improves the ink absorbency. However, if the BET specific surface area exceeds 600 m ² / g, a large crack is generated in the ink receiving layer, and printing unevenness increases. Among the pigment components having such a BET specific surface area, it is more preferable to use a synthetic amorphous silica produced by a wet method because color development is improved in addition to ink absorptivity. This synthetic amorphous silica may be used in combination with a pigment component other than the synthetic amorphous silica.

  In order to improve printing unevenness, when the tufted colloidal silica and other pigment components are used in combination, the tufted colloidal silica is preferably contained in an amount of not less than 5% by weight, more preferably not less than 10% by weight. In order to improve ink absorbability, when the tufted colloidal silica is used in combination with other pigment components, the tufted colloidal silica is preferably contained in the total pigment in an amount of 50% by weight or less, more preferably 30% by weight or less. .

(Binder for ink receiving layer)
As the binder contained in the ink receiving layer, resin A having a glass transition temperature of −60 ° C. or higher and lower than 20 ° C. and resin B having a glass transition temperature of 20 ° C. or higher and lower than 100 ° C. (mixing of resin A) Weight) / (weight of resin B) is 20/80 to 80/20.
The above-mentioned resin A has a function of reducing the size and depth of microcracks that occur when forming an ink receiving layer by the cast coating method and suppressing printing unevenness (particularly cyan printing unevenness). Thus, the resin B is considered to have a function of suppressing the strength reduction of the ink receiving layer that occurs when only the resin A is used.
Here, the glass transition temperature (Tg) is measured by a dynamic viscoelastic method.

As the resin A, a urethane resin having film forming properties and having a glass transition temperature of −60 ° C. or higher and lower than 20 ° C. is used . By setting the glass transition temperature within the above range, the effect of reducing the size and depth of the microcracks described above can be obtained. Preferably, the glass transition temperature of the resin A is set to −60 ° C. or higher and lower than 0 ° C.

As the resin B, a urethane resin having film forming properties and having a glass transition temperature of 20 ° C. or higher and lower than 100 ° C. is used . Preferably, the glass transition temperature of the resin B is 20 ° C. or higher and lower than 60 ° C.

  Here, when only the resin A is used as described above, the layer strength of the ink receiving layer is lowered, and stickiness and scratches are generated, so that the gloss of the ink receiving layer is lowered. Therefore, by using the resin B together, it is possible to increase the layer strength of the ink receiving layer.

  In the present invention, (the blending weight of resin A) / (the blending weight of resin B) needs to be 20/80 to 80/20, and preferably 30/70 to 70/30. Here, as long as the weight ratio of the resins A and B is within the above range, the total binder may contain components other than the water-soluble resins A and B as described later. Here, when the ratio is less than 20/80, the size and depth of cracks in the ink receiving layer increase and printing unevenness increases, and when it exceeds 80/20, the strength of the ink receiving layer decreases and the scratching property is increased. Deteriorates.

  In each of the present inventions, it is preferable that the resins A and B are both aqueous. “Aqueous” means that the resin is dissolved or dispersed and stabilized in water or a medium composed of water and a small amount of an organic solvent. In the case of using an organic solvent, it is necessary that it is less than 50% by weight, preferably less than 10% by weight, and that there is no flash point of the resin liquid. In the coating liquid, each of the water-soluble resins A and B is dissolved or dispersed as particles, but in the ink receiving layer after coating and drying, each of the water-soluble resins A and B is a binder of pigment. Become an agent.

In addition to the resins A and B, other binder components can be used in combination with the binder within a range not impairing the effects of the present invention. Other binder components include film-forming resins such as starches such as oxidized starch and esterified starch, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, polyvinylpyrrolidone, casein, gelatin, soy protein, styrene- Examples thereof include acrylic resins and derivatives thereof, styrene-butadiene latex, acrylic emulsion, vinyl acetate emulsion, vinyl chloride emulsion, urethane emulsion, urea emulsion, alkyd emulsion, and derivatives thereof.
In particular, when a gelled cast coating method is used for forming the ink receiving layer, in order to improve the coating property of the coating liquid, in addition to the resins A and B, a casein is added as a binder. This is preferable because the coating property of the ink receiving layer coating solution is improved.

  It is preferable that the blending amount of each of the above resins A and B or each of the above resins A and B and other binder components is 5 to 50 parts by weight with respect to 100 parts by weight of the pigment. However, it is not particularly limited as long as the required coating layer strength can be obtained. Moreover, when using each said resin A and B and another binder component together, it is preferable that each resin A and B is 70 weight% or more in all the binders, and it is 80 weight% or more especially. Is preferred.

  In the present invention, it is preferable that each of the resins A and B is a urethane resin from the viewpoint of improving ink absorbability. The urethane resin used as each of the resins A and B is obtained, for example, by a reaction between a suitable polyisocyanate compound and an active hydrogen compound. As the polyisocyanate compound, an aliphatic or alicyclic compound can be suitably used, and the kind thereof is not particularly limited. Examples of polyisocyanate compounds that can be easily obtained industrially include hexamethylene diisocyanate, isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, norbornene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and m-tetramethylxylylene. Examples thereof include so-called non-yellowing type or hard yellowing type polyisocyanate compounds such as range isocyanate. Moreover, the alkyl substituted body of the said non-yellowing type or a hardly yellowing type polyisocyanate compound, an alkoxy substituted body, and a nitro substituted body are mentioned. Further, as a modified product or modified product of a polyisocyanate compound of the above non-yellowing type or hard yellowing type and a polyhydric alcohol, a prepolymer type modified product, a carbodiimide modified product, a burette modified product, a dimerization reaction modified product, and a trimerization Reaction modified products and the like can be mentioned.

  Examples of the active hydrogen compound that can react with the polyisocyanate compound include a polyether polyol compound. The polyether polyol compound is obtained by ring-opening polymerization or copolymerization of a cyclic ether compound, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and polytetramethylene ether glycol, and their ethylene oxide-modified products and propylene oxide-modified products. Products and the like. These may be used alone or in combination of two or more. Moreover, the said polyether polyol compound can also be obtained by well-known ring-opening polymerization or copolymerization.

  Initiators that can be used when the polyether polyol compound is produced by ring-opening polymerization or copolymerization include ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,3-butanediol, propylene glycol, Dipropylene glycol, butylene glycol, neopentyl glycol, glycerin, trimethylolethane, trimethylolpropane, butanetriol, pentaerythritol, dipentaerythritol, tripentaerythritol, hexanetriol, tris (2-hydroxyethyl) isocyanurate, cyclopentane Diol, cyclohexanediol, cyclohexanedimethanol, dicyclohexanediol and other aliphatic polyols, dihydroxybenzene, Aromatic polyols such as phenol A, bisphenol F, xylylene glycol, bisphenol A-bis- (2-hydroxyethyl ether), bisphenol S; ethylenediamine, diethylenetriamine, triethylenetetramine, propylenediamine, butylenediamine, hexamethylenediamine, cyclohexane Examples include active hydrogen compounds such as silylenediamine, phenylenediamine, tolylenediamine, xylenediamine, m-xylenediamine, isophoronediamine, norbornenediamine.

  Examples of cyclic ether compounds that can be used when the polyether polyol compound is produced by ring-opening polymerization or copolymerization include ethylene oxide, propylene oxide, trimethylene oxide, butylene oxide, α-methyltrimethylene oxide, 3,3′- Examples thereof include dimethyltrimethylene oxide, tetrahydrofuran, and dioxane.

  Moreover, when making it react with the said polyisocyanate compound, the said polyether polyol compound and another active hydrogen compound can be used together. Examples of such active hydrogen compounds include ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,3-butanediol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, glycerin, and trimethylol. Fats such as ethane, trimethylolpropane, butanetriol, pentaerythritol, dipentaerythritol, tripentaerythritol, hexanetriol, tris (2-hydroxyethyl) isocyanurate, cyclopentanediol, cyclohexanediol, cyclohexanedimethanol, dicyclohexanediol Group polyol, dihydroxybenzene, bisphenol A, bisphenol F, xylylene glycol, bisphenol Polyol compounds such as aromatic polyols such as A-bis- (2-hydroxyethyl ether) and bisphenol S; polyester polyol, polycarbonate polyol, polycaprolactone polyol, silicon polyol; oxalic acid, glutamic acid, adipic acid, acetic acid, phthalic acid , Isophthalic acid, salicylic acid, pyromellitic acid and other organic acids and the above-mentioned polyols condensation reaction products; ethylenediamine, diethylenetriamine, triethylenetetramine, propylenediamine, butylenediamine, hexamethylenediamine, cyclohexylenediamine, phenylenediamine, tolylenediamine Polyamines such as amine, xylenediamine, m-xylenediamine, isophoronediamine and norbornenediamine can be used. These may be used alone or in combination of two or more.

  The ink receiving layer (coating liquid) in the cast coated paper for inkjet recording of the present invention contains the above-described pigment and binder, but does not exclude the inclusion of other components. For example, the ink receiving layer may be a thickener, an antifoaming agent, an antifoaming agent, a pigment dispersant, a release agent, a foaming agent, a pH adjusting agent, a surface sizing agent, a coloring dye, a coloring pigment, a fluorescent dye, or an ultraviolet absorber. Antioxidants, light stabilizers, preservatives, water resistance agents, dye fixing agents, surfactants, wet paper strength enhancers, and the like can be contained within a range that does not impair the effects of the present invention. These are preferably contained in the ink receiving layer in a range not exceeding 15% by weight.

  As a means for applying a coating liquid for forming an ink receiving layer on a base paper, various blade coaters, roll coaters, air knife coaters, bar coaters, curtain coaters, gravure coaters, gate roll coaters, short dwell coaters, etc. The known coating apparatus can be used on-machine or off-machine.

The coating amount of the coating liquid used as the ink receiving layer can be arbitrarily adjusted as long as it covers the surface of the base paper and the ink receiving layer provides sufficient ink absorbability. From the viewpoint of achieving compatibility, it is preferably 5 to 30 g / m ² in terms of solid content per side, and particularly preferably 10 to 25 g / m ² in consideration of productivity. If it exceeds 30 g / m ² , the peelability from the cast drum mirror-finished surface is lowered, and problems such as adhesion of the ink receiving layer to the mirror-finished surface occur.
In the present invention, when a large coating amount of the ink receiving layer is required, the ink receiving layer can be multi-layered. Further, an undercoat layer having various functions such as ink absorptivity and adhesiveness may be provided between the support and the ink receiving layer. Further, a back coat layer having various functions such as ink absorbability, writing property, printer printability and the like may be further provided on the side opposite to the surface on which the ink receiving layer is provided.

  In the present invention, gloss is imparted by forming at least the outermost ink receiving layer by a cast coating method. The cast coating method is a method in which a coated surface in a wet state after coating is pressed onto a heated finished surface and dried. In particular, the outermost ink-receiving layer is preferably formed by a gelled cast coating method (coagulation method) from the viewpoint that a surface feeling and gloss comparable to a silver salt photograph can be provided.

  In the case of forming an ink receiving layer using the gelled cast coating method, after applying the ink receiving layer coating liquid with the known coating device, the undried ink receiving layer is gelled with a coagulation liquid. And press-bonded to the heated finished surface and dried. As the coagulant used in the coagulation liquid, various salts such as calcium, zinc, magnesium and the like such as formic acid, acetic acid, citric acid, tartaric acid, lactic acid, hydrochloric acid and sulfuric acid are used. The method for applying the coagulating liquid is not particularly limited as long as it can be applied to the recording layer, and can be appropriately selected from known methods (for example, roll method, spray method, curtain method, etc.).

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. “Part” and “%” represent “part by weight” and “% by weight”, respectively, unless otherwise specified.

(Preparation of base paper)
4 parts of calcium carbonate, 1 part of cationized starch, 0.3 part of polyacrylamide, 0.5 part of alkyl ketene dimer emulsion to 100 parts hardwood kraft pulp (L-BKP) beaten to a freeness of 350 ml csf Is added, and papermaking is carried out by a conventional method using a long paper machine, followed by pre-drying, and then a liquid containing 5% phosphoric esterified starch and 0.5% polyvinyl alcohol is dried with a size press. After applying to ² g / m ² , post-drying and machine calendering were performed to obtain a base paper having a basis weight of 100 g / m ² .

(Production of water-based urethane resin (UD-1))
In a 3000 ml four-necked flask equipped with a thermometer, a nitrogen inlet tube, and a condenser tube, 205.0 g of polypropylene glycol having a number average molecular weight of 2000, 91.8 g of neopentyl glycol, 9.2 g of trimethylolpropane, 2,2- 53.8 g of dimethylolpropionic acid, 429.4 g of methyl ethyl ketone, 85.9 g of N-methyl-2-pyrrolidone, and 390.2 g of isophorone diisocyanate were charged and reacted at 80 ° C. for 10 hours. When the weight percentage of NCO in the system reached 1.7%, the system was cooled to 60 ° C., 32.5 g of triethylamine was added, and the mixture was further stirred for 30 minutes. The obtained neutralized prepolymer solution and 1631.7 g of ion-exchanged water were mixed, and the remaining methyl ethyl ketone was distilled off under reduced pressure at 50 ° C., whereby a non-volatile content of 30%, a viscosity of 200 mPa · s, a pH of 7.9, An aqueous urethane resin (hereinafter referred to as UD-1) having a weight average particle diameter of 170 nm, a minimum film-forming temperature of 10 ° C., and a resin solid content acid value of 30 KOH mg / g was obtained. Here, the weight average particle size was determined by measurement using a dynamic light scattering particle size measuring device (manufactured by Otsuka Electronics Co., Ltd .; trade name LPA-3000) (hereinafter the same). The obtained resin (UD-1) had a glass transition temperature of 36 ° C. In the following description, the resin is water-soluble, but once it is dried, it becomes unnecessary for water, so it is referred to as “aqueous” instead of “water-soluble”.

  In the following Examples and Comparative Examples, the glass transition temperature of the resin is a dynamic viscoelasticity method, and a DVE-V4 FT Rheospectr manufactured by Rheology is used as a measuring device, 5 mm wide, 20 mm long, and thick. The temperature at which the loss elastic modulus (E ″) peaked when measured at a frequency of 10 Hz and a heating rate of 3 ° C./min using a test piece having a thickness of about 600 μm was defined as the glass transition temperature (Tg).

Synthetic amorphous silica (trade name: Fine Seal X-37B, manufactured by Tokuyama Corporation, BET specific surface area of 260 to 320 m ² / g) as pigments and tufted colloidal silica (trade name: Snowtex HS-M-20, 20 parts by NISSAN CHEMICAL INDUSTRIES, primary particle size 20-30 nm, secondary particle size 150-300 nm, aqueous urethane resin A (trade name: TAP-218, manufactured by Arakawa Chemical Industries, Ltd., glass transition temperature as binder) −50 ° C.) and aqueous urethane resin B (UD-1, glass transition temperature is 36 ° C.), 30 parts of a mixture having a weight ratio of 20/80 and 10 parts of casein (ALACID liquid casein (New Zealand), release) An ink receiving layer coating solution having a solid content concentration of 30% containing 5 parts of an agent (trade name: Nopcoat SYC, manufactured by San Nopco) was prepared.
Next, using a comma coater, the above coating liquid was applied to the base paper at a target coating amount of 18 g / m ² , and then coagulated with the following coagulating liquid, while the coating layer was in a wet state. Then, it was pressure-bonded to a mirror-finished metal surface heated to 100 ° C. and dried to produce a cast paper for ink jet recording.
(Preparation of coagulation liquid)
A coagulation liquid containing 5% calcium formate (manufactured by Asahi Chemical Industry Co., Ltd.) and 1% of a dye fixing agent (trade name: DAIFIX YK-50, manufactured by Daiwa Chemical Co., Ltd.) was prepared as a coagulation liquid.

  For inkjet recording, exactly the same as in Example 1, except that the blending weight ratio of the aqueous urethane resins A and B in Example 1 was (aqueous urethane resin A) / (aqueous urethane resin B) = 50/50. Cast coated paper was produced.

  For inkjet recording, exactly the same as in Example 1, except that the weight ratio of the aqueous urethane resins A and B in Example 1 was (aqueous urethane resin A) / (aqueous urethane resin B) = 80/20 Cast coated paper was produced.

  As water-based urethane resin A, instead of the one in Example 2, Superflex 361 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., glass transition temperature: −47 ° C.) was used. Thus, a cast coated paper for ink jet recording was produced.

  As water-based urethane resin B, instead of the one in Example 2, HUX-540 (trade name, manufactured by Asahi Denka Kogyo Co., Ltd., glass transition temperature: 40 ° C.) was used in exactly the same manner as in Example 2. A cast coated paper for inkjet recording was produced.

  As tufted colloidal silica, instead of the one in Example 2, tufted colloidal silica (trade name: Snowtex HS-L, manufactured by Nissan Chemical Industries, Ltd., primary particle size 20-30 nm, secondary particle size 200-400 nm) A cast coated paper for ink jet recording was produced in the same manner as in Example 2 except that was used.

(Comparative Example 1)
Except for using 30 parts of water-based urethane resin A (trade name: TAP-218, manufactured by Arakawa Chemical Industries, glass transition temperature of −50 ° C.) and 10 parts of casein (ALACID liquid casein (New Zealand)) as the binder. In the same manner as in Example 1, a cast coated paper for inkjet recording was produced.

(Comparative Example 2)
Except for using 30 parts of aqueous urethane resin B (trade name: UD-1, manufactured by Mitsui Chemicals, glass transition temperature: 36 ° C.) and 10 parts of casein (ALACID lactic casein (made in New Zealand) as a binder, A cast coated paper for inkjet recording was produced in exactly the same manner as in Example 1.

(Comparative Example 3)
As a binder, vinyl acetate resin (trade name: Yodosol VQ-553, manufactured by NSC Japan, glass transition temperature is 30 ° C.) and casein (ALACID lactic casein (made in New Zealand) 10 parts are used as a binder. Except for the above, cast coated paper for ink jet recording was produced in the same manner as in Example 1.

(Comparative Example 4)
Instead of the tufted colloidal silica of Example 1, spherical colloidal silica (trade name: Snowtex N30G, manufactured by Nissan Chemical Industries, Ltd., primary particle diameter of 10 to 20 nm, in which individual colloidal silica is dispersed without being aggregated) is used. Except for the above, cast coated paper for ink jet recording was produced in the same manner as in Example 1.

  In each Example and Comparative Example, the compounding ratio of the synthetic amorphous silica and the colloidal silica in the pigment was 80/20, and the compounding ratio of all the pigments and the resin in the binder was 100/30.

The cast coated paper for inkjet recording of each Example and Comparative Example was evaluated according to the following items.
(Evaluation)
(1) Inkjet recording quality evaluation A predetermined solid pattern was recorded using an inkjet printer (trade name: PM-970C, manufactured by Seiko Epson Corporation), and the following evaluation was performed on the obtained printed matter.
(2-1) Printing unevenness The printing unevenness (darkness unevenness) of the cyan solid printing portion was visually evaluated according to the following criteria.
◎: Good level with no print unevenness ○: There is some print unevenness but satisfactory level for practical use △: Some level of print unevenness and slightly unsatisfactory for practical use ×: Level of print unevenness is extremely low and cannot be used at all (2-3) Scratch resistance Two 50 sheets of the above-mentioned cast-coated paper for ink-jet recording, which is a sample, are stacked with the glossy surface (ink-receiving layer) facing upward, and 50 sheets of PPC paper are stacked. This laminate (52 sheets in total) was set in the printer paper feed section with the cast coated paper facing up. When this paper was printed, scratches on the glossy surface caused by rubbing the glossy surface (ink receiving layer surface) and the non-glossy surface (the surface opposite to the ink receiving layer) of each sample were visually evaluated according to the following criteria. .
◎: Good level with no scratches found ○: Slightly scratched but practically satisfactory level △: Slightly scratched, slightly unsatisfactory practical level ×: Level of scratches markedly unusable

(2) Glossiness of white paper According to the method of JIS K7105, the 20-degree specular glossiness of the white paper portion of the sample was measured using a gloss meter (trade name: GM-26PRO, manufactured by Murakami Color Research Laboratory Co., Ltd.).

  The obtained results are shown in Table 1. In addition, when the evaluation symbols in the table are ○ and ○, they can be used practically without any problem, but Δ and × have practical problems.

As is clear from Table 1, in each of the examples, the evaluation of printing unevenness, scratch resistance, and glossiness were all good .

  On the other hand, in Comparative Example 1 in which a resin having a glass transition temperature of 20 ° C. or higher and lower than 100 ° C. was not contained in the ink receiving layer, although the gloss value was high, the scratch resistance was lowered and the surface of the ink receiving layer was reduced. Scratches occurred, and the glossiness of the appearance was inferior. In Comparative Examples 2 and 3 in which a resin having a glass transition temperature of −60 ° C. or more and less than 20 ° C. was not contained in the ink receiving layer, the evaluation of printing unevenness was inferior. In particular, in Comparative Example 3 in which a resin that is not a urethane resin was contained in the ink receiving layer, the scratch resistance was reduced in addition to the printing unevenness.

  Further, in the case of Comparative Example 4 in which the tuft-like colloidal silica was not blended as a pigment, printing unevenness occurred and gloss was lowered, which was not suitable for practical use.

It is a schematic diagram which shows the state which colloidal silica aggregated in the shape of a tuft. It is another schematic diagram which shows the state which colloidal silica aggregated in the shape of a tuft. It is another schematic diagram which shows the state which colloidal silica aggregated in the shape of a tuft.

Explanation of symbols

a, b Spherical colloidal silica

Claims (3)

A cast coated paper for ink-jet recording in which an ink receiving layer containing a pigment and a binder is provided on at least one surface of a base paper by a cast coating method, and the binder has a glass transition temperature of −60 ° C. or higher. The resin A having a temperature of less than 20 ° C. and the resin B having a glass transition temperature of 20 ° C. or more and less than 100 ° C. have a ratio of (weight of resin A) / (weight of resin B) of 20/80 to 80/20. The resin A and the resin B are urethane resins, and the pigment is a spherical colloidal silica having a primary particle size of 10 to 100 nm in a state of being dispersed in a coating liquid that forms the ink receiving layer. A cast-coated paper for ink-jet recording, comprising a colloidal silica that agglomerates in a tuft and does not form a ring. ^{2. The} cast-coated paper for ink-jet recording according to claim 1, wherein the pigment further contains a pigment component having a BET specific surface area of 200 to 600 m ² / g. The cast coat paper for ink jet recording according to claim 1 or 2, wherein the cast coat method is a gelled cast coat method.