JPH11180036A - Inkjet recording sheet - Google Patents

Abstract

(57) [Summary] [Problem] To provide an ink jet recording sheet excellent in gloss, print density, and recorded image quality. SOLUTION: An undercoat layer containing a pigment and an adhesive and a cast coating layer are sequentially provided on a base material, and an average primary particle diameter of 3 nm to 40 nm, 10 nm
Fine silica particles having an average secondary particle diameter of about 300 nm are used, and an aqueous polyurethane resin is used as an adhesive for a cast coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording sheet, and more particularly to an ink jet recording sheet having excellent gloss and excellent ink jet recording suitability.

[0002]

2. Description of the Related Art A recording method using an ink-jet printer has been used in various fields because of low noise, high-speed recording, and easy multi-color printing. As the ink jet recording sheet, high quality paper designed so as to be rich in ink absorbency, coated paper in which a porous pigment is coated on a base paper surface, or the like is applied. By the way, these ink jet recording sheets mainly have low surface gloss,
Since so-called matte recording paper is used, there is a demand for providing an inkjet recording sheet having a high surface gloss and an excellent appearance.

[0003] Generally, as a paper having a high surface gloss, a plate-like pigment is coated on the surface of a base paper and, if necessary, a calender-treated high-gloss coated paper or a wet-coated paper on the base paper is used. There is known a so-called cast coated paper obtained by pressing a working layer onto a heating drum surface having a mirror surface, drying the mirror surface and copying the mirror surface. This cast coated paper has higher surface gloss and better surface smoothness than super calendered normal coated paper, and provides excellent printing effect. It is used for applications such as printed matter, but when it is used as ink jet recording paper, various problems occur.

In general, a conventional cast coated paper is made of a cast coater, as disclosed in US Pat. No. 5,275,846, in which a film-forming substance such as an adhesive in a pigment composition constituting the coated layer is used. High gloss is obtained by copying the mirror surface drum surface. However, the porosity of the coating layer is lost due to the presence of the film-forming substance, which causes problems such as extremely lowering ink absorption during inkjet recording. In order to improve the ink absorbency, it is important to make the structure of the cast coating layer porous so that the ink can be easily absorbed. For that purpose, it is necessary to reduce the film formability of the cast coating layer. Required. However, reducing the amount of the film-forming substance causes a problem that gloss of white paper is reduced as a result. That is, it is extremely difficult to simultaneously satisfy both the surface gloss of cast coated paper and the suitability for ink jet recording.

As a method for solving the above-mentioned problems, the present inventors have disclosed in Japanese Patent Application Laid-Open No. 7-89220 a method in which an undercoat layer containing a pigment and an adhesive as main components is provided on cardboard.
Further, a coating liquid obtained by polymerizing a monomer having an ethylenically unsaturated bond and containing a copolymer composition having a glass transition point of 40 ° C. or higher as a main component is applied and cast. The cast coating layer is formed, and while the cast coating layer is in a wet state, it is pressed against a heated mirror-surface drum and dried to form a cast coating layer. We proposed a cast paper for inkjet recording that has both gloss and ink absorbency.

[0006] In recent years, with the increase in the speed of ink-jet recording, the increase in definition of recorded images, and the expansion of applications due to full colorization,
High gloss, high image quality, high recording density, and other qualities have been desired for ink jet recording sheets.For example, gloss and recording quality comparable to silver halide photographic printing paper are required. In order to satisfy such requirements, it is necessary to further improve the quality.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording sheet which is excellent in glossiness and excellent in ink jet recording suitability such as print density and recording image quality.

[0008]

The ink jet recording sheet according to the present invention comprises a sheet on a substrate, at least one undercoat layer formed on the substrate sheet and containing a pigment and an adhesive, A cast coating layer formed on the undercoat layer and containing a pigment and an adhesive, wherein the pigment in the cast coating layer has a primary particle average particle size of 3 nm to 40 nm and a secondary particle of 10 nm to 300 nm. The present invention is characterized in that it contains silica fine particles having an average particle size and the adhesive in the cast coating layer contains an aqueous polyurethane resin. In the inkjet recording sheet of the present invention, the aqueous polyurethane resin contained in the cast coating layer preferably contains a cationic aqueous polyurethane resin. In the inkjet recording sheet of the present invention, it is preferable that the aqueous polyurethane resin contained in the cast coating layer has a glass transition temperature of 40 ° C or higher. In the inkjet recording sheet of the present invention, the cast coating layer may further contain a cationic compound. In the ink jet recording sheet of the present invention, it is preferable that the undercoat layer contains a composite of colloidal silica and a polymer resin of a monomer having an ethylenically unsaturated bond.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substrate used in the present invention is not particularly limited, and a paper substrate such as acidic paper or neutral paper used for general coated paper can be used as appropriate. . Air-permeable resin sheets can also be used in the present invention. The paper base material used for the ink jet recording sheet of the present invention is mainly composed of wood pulp and, if necessary, a pigment. As wood pulp, various chemical pulp, mechanical pulp, regenerated pulp, etc. can be used, and the degree of beating of these pulp is appropriately adjusted by a beating machine, whereby the paper strength of the obtained paper base material, Papermaking suitability can be adjusted. The degree of freeness (freeness) of the pulp is not particularly limited, but 250 to 550 ml (C
SF: JISP-8121). The pigment contained in the paper base is effective for imparting opacity to the paper base and adjusting the ink absorbency thereof,
Calcium carbonate, calcined kaolin, silica, titanium oxide and the like can be used. The blending amount of the pigment in the paper substrate is preferably about 1 to 20%. If the amount of the pigment is too large, the paper strength of the obtained paper base material may be reduced. A sizing agent, a fixing agent, a paper strength enhancer, a cationizing agent, a retention improver, a dye, a fluorescent whitening agent, and the like can be added to the paper base as auxiliaries. Furthermore, in the size press step of the paper machine, starch, polyvinyl alcohol, a cationic resin, or the like can be applied and impregnated on the paper base material, thereby adjusting the surface strength, sizing degree, and the like of the paper base material. Generally, the size of the paper substrate is preferably about 1 to 200 seconds. When the sizing degree is less than 1 second, there may be a problem in operation such as generation of wrinkles at the time of coating, and when the sizing degree is higher than 200 seconds, the ink absorbency of the obtained paper base material is reduced or printing is performed. Later, curling and cockling may become significant. The basis weight of the paper base material is not particularly limited,
It is preferably about 00 g / m ² .

The undercoat layer provided on the paper substrate contains a pigment and an adhesive as main components. Pigments in the undercoat layer include, for example, kaolin, clay, calcined clay, amorphous silica (amorphous silica), zinc oxide, aluminum oxide,
Aluminum hydroxide, calcium carbonate, satin white, aluminum silicate, alumina, colloidal silica,
General coated paper manufacturing fields such as zeolite, synthetic zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene plastic pigment, hydrotalcite, urea resin plastic pigment, benzoguanamine plastic pigment, etc. Can be selected from various pigments used together, and these can be used alone or in combination of two or more. Among these, it is preferable to use amorphous silica, alumina, and / or zeolite having high ink absorbency as a main component.

Examples of the adhesive for the undercoat layer include proteins such as casein, soybean protein and synthetic protein, various starches such as starch and oxidized starch, polyvinyl alcohol, cellulose derivatives such as carboxymethylcellulose and methylcellulose, and styrene-butadiene copolymer. Coalescence, methyl methacrylate-
Conjugated diene polymer latex of butadiene copolymer,
Acrylic polymer latex, vinyl polymer latex such as ethylene-vinyl acetate copolymer, and the like can be appropriately selected from adhesives generally used for coated paper, and these can be used alone or in combination of two or more. These are used in combination.

The mixing ratio of the pigment for the undercoat layer and the adhesive is as follows:
Although it depends on the type, the adhesive is generally preferably 1 to 100 parts by weight, more preferably 2 to 50 parts by weight, based on 100 parts by weight of the pigment. If necessary, various auxiliaries such as a dispersant, a thickener, an antifoaming agent, an antistatic agent, and a preservative may be appropriately added to the undercoat layer. Also, a fluorescent dye and / or a colorant can be added to the undercoat layer.

The undercoat layer may contain a cationic compound for the purpose of fixing the dye component in the ink for ink jet recording. However, as described later, it is preferable that the ink dye is fixed in the cast coating layer provided on the undercoat layer as much as possible, because the printing (recording) density becomes high. Is preferably incorporated in the cast coating layer more than in the undercoat layer. More preferably, a cationic compound is blended only in the cast coating layer so that the cationic compound is not substantially present in the undercoat layer. The fact that the cationic compound is not substantially present in the undercoat layer means that, for example, a small amount of a cationic surfactant may be added as an auxiliary. When the cationic compound is blended only in the cast coating layer, and the cationic compound is not substantially present in the undercoat layer, the gloss of the cast coating layer is the highest.

When a composite of colloidal silica and a polymer resin of a monomer having an ethylenically unsaturated bond is blended in the undercoat layer, the gloss of the cast coating layer formed thereon can be further improved. . Although the reason for this is not specifically known, the presence of the above-mentioned complex is intended to suppress the penetration of the undercoat layer into the undercoat layer of the coating composition for the cast coating layer while maintaining the ink absorbency of the undercoat layer. Presumed. Further, the use of the above composite tends to improve the releasability of the cast coating layer from the cast drum. However, the reason is unknown.

Examples of the polymer resin of a monomer having an ethylenically unsaturated bond include those having an alkyl group carbon number such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, and glycidyl acrylate. 1 to 18 acrylates, methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate and the like having 1 to 18 alkyl group carbon atoms, methacrylate, styrene, α-methyl Styrene, vinyltoluene, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl acetate,
Polymers obtained by polymerizing ethylenic monomers such as vinyl propionate, acrylamide, N-methylolacrylamide, ethylene, and butadiene are exemplified.
In addition, this polymer may be a copolymer using two or more types of ethylenic monomers as needed, or may be a substituted derivative of these polymers or copolymers. Examples of the substituted derivative include a carboxyl group-derivative and an alkali-reactive one thereof.

The composite of colloidal silica and the polymer resin is obtained by polymerizing the above-mentioned ethylenic monomer in the presence of a silane coupling agent or the like and colloidal silica to form a Si—OR (R: polymer component) bond. A polymer resin modified with a silanol group or the like and colloidal silica, if necessary, to form a composite by Si-OR (R: polymer component) bond. It can be obtained by a method.

The composition for the undercoat layer composed of the above components is generally adjusted to a solid content concentration of about 5 to 50% by weight, and is dried on a paper substrate in a dry weight of ^{2 to} 100 g / m ² , preferably 5 to 100 g / m ² . About 50 g / m ² , more preferably 10 to 20
g / m ² . Coating amount 2g /
If it is less than m ² , the ink absorbency may be poor or the gloss may not be sufficiently obtained when a cast coating layer is provided. If the coating amount is more than 100 g / m ² ,
In some cases, the print density is reduced, and the strength of the undercoat layer is reduced, so that powder dropping and scratching are likely to occur. The composition for the undercoat layer,
Coating and drying on the substrate by various known and publicly-known coating devices such as a blade coater, an air knife coater, a roll coater, a brush coater, a chaplex coater, a bar coater, a lip coater, a die coater, a gravure coater, and a curtain coater. An undercoat layer is formed. Further, if necessary, a smoothing treatment such as super calendering or brushing can be performed after the undercoat layer is dried.

In the present invention, a cast coating layer is further provided on the undercoat layer containing the pigment and the adhesive. This cast coating layer contains specific silica fine particles and an aqueous polyurethane resin as main components. First,
The silica fine particles will be described. The method for preparing the silica fine particles used in the present invention is not particularly limited. For example, a commercially available synthetic amorphous silica (for example, having a secondary particle diameter of about several μm) may be prepared by mechanical means. By giving a stronger shearing force to reduce the secondary particle diameter. Examples of the mechanical means include an ultrasonic homogenizer, a pressure homogenizer, a high-speed rotation mill, a roller mill, a container driving medium mill, a medium stirring mill,
A jet mill, a sand grinder, and the like. The silica fine particles thus treated are generally obtained as an aqueous dispersion (slurry or colloid particles) having a solid content of about 5 to 20%.

In the present invention, the average particle diameter of the silica fine particles is a particle diameter observed and measured by an electron microscope (SEM and TEM) (take an electron microscope photograph of 10,000 to 400,000 times, and Measured and averaged the Martin diameter of the particles.P in "Particle Handbook" (Asakura Shoten)
52, 1991 and the like. The average particle size of the secondary particles of the silica fine particles (substantially mainly of secondary particles) used in the present invention is 10 nm to 300 nm, preferably 15 nm to 150 nm, and more preferably 20 nm.
Adjusted to 100 nm. When the average particle diameter of the secondary silica fine particles exceeds 300 nm, the transparency of the resulting cast coating layer is reduced, and the color density of the image due to the dye fixed in the cast coating layer is reduced. Is not obtained. The average particle diameter of the secondary particles is 10
When silica fine particles having a particle size of less than nm are used, the ink absorptivity of the obtained coating layer is reduced, and a desired high quality cannot be obtained.

The average primary particle diameter of the silica fine particles must be adjusted to 3 nm to 40 nm, preferably 5 nm to 30 nm, more preferably 7 nm to 20 nm.
m. When the primary particle diameter is less than 3 nm, the gap between the primary particles becomes extremely small, and therefore, the ability of the secondary particles to absorb the solvent and the ink in the ink is reduced, and a desired high-quality image can be obtained. Can not. Further, when the average particle size of the primary particles exceeds 40 nm, the secondary particles formed by aggregation of the primary particles become excessive, the transparency of the cast coating layer decreases, and the cast coating layer is fixed in the cast coating layer. As a result, the color density of the image due to the dye decreases, and the desired print density cannot be obtained. The content ratio of the silica fine particles to all the pigments in the cast coating layer is desirably 50% or more in order to maintain the transparency of the cast coating layer. When the content ratio of the silica fine particles to all the pigments is less than 50%, the transparency of the cast coating layer obtained is reduced, and the image quality such as print density may be reduced.

The adhesive for the cast coating layer contains an aqueous polyurethane resin. The cast coating layer has excellent releasability from the cast drum by containing the aqueous polyurethane resin. Further, the obtained recording sheet has excellent ink absorbency, print density, water resistance, surface strength, and gloss. Aqueous polyurethane resin is
It is also commonly called urethane emulsion, urethane latex, polyurethane latex, or the like. A polyurethane resin is obtained from a reaction between a polyisocyanate compound and an active hydrogen-containing compound, and is defined as a polymer compound containing a relatively large number of urethane bonds and urea bonds.

The polyisocyanate compound for producing an aqueous polyurethane resin is not particularly limited. For example, aromatic polyisocyanates such as tolylene diisocyanate and 4,4'-diphenylmethane diisocyanate;
In addition, aliphatic and alicyclic polyisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate are used.

As the active hydrogen-containing compound for producing an aqueous polyurethane resin, a compound having a hydroxyl group or an amino group is generally used. As the compound having a polymer, polyester diol, polyether diol, and polycarbonate diol are exemplified. Examples of those having a molecular weight include glycols such as ethylene glycol, 1,4-butanediol, and 1,6-hexanediol, and diamines such as isopropyldiamine and hexamethylenediamine.

The aqueous polyurethane resin is dispersed or emulsified in the form of fine particles in an aqueous medium, and the dispersed particles have a particle size of about 0.001 to 20 μm. And a milky white emulsion. In the present invention, these are collectively referred to as an aqueous polyurethane resin. Aqueous polyurethane resin is a forced emulsification type in which forced mechanical emulsification is performed with high mechanical shear force in the presence of an emulsifier, and a hydrophilic group such as an ionic group is introduced into the molecular chain to impart hydrophilicity without the aid of the emulsifier. And a self-emulsifying type which can be stably dispersed in water, and a dissolving type which is further dissolved in water. Among them, the self-emulsifying aqueous polyurethane resin is excellent in gloss, water resistance and the like, and is preferably used in the present invention. Depending on the type of hydrophilic group introduced into the self-emulsifying type aqueous polyurethane resin, a cationic type (introducing an amino group or the like), an anionic type (introducing a carboxyl group, a sulfone group, or the like), or a nonionic type (polyethylene glycol) may be used. Groups are introduced). Among them, a cationic aqueous polyurethane resin (cationic aqueous polyurethane resin) in which a cationic group such as a tertiary amino group is introduced and neutralized or quaternized with an acid.
Is preferred. In the case where the aqueous polyurethane resin is cationic, a cast coating layer having particularly excellent ink absorbency and print density is obtained. As described later, a cationic compound as an aqueous ink fixing agent is incorporated in the cast coating layer. If it is, it is excellent in miscibility with it. When the glass transition temperature of the aqueous polyurethane resin is 40 ° C. or higher, the obtained cast coating layer has excellent releasability from the cast drum. The glass transition temperature of the aqueous polyurethane resin is more preferably 60 ° C. or higher. Although there is no particular upper limit for the glass transition temperature, it is generally preferable that the glass transition temperature is 150 ° C. or lower. The amount of the aqueous polyurethane resin in the cast coating layer is preferably 1 to 200 parts by weight, more preferably 10 to 100 parts by weight, based on 100 parts by weight of the pigment. If the amount of the aqueous urethane resin is less than 1 part by weight, the desired effect cannot be sufficiently obtained, the strength of the cast coating layer becomes weak, the surface is easily damaged, and powder fall occurs. There is. If the amount is more than 200 parts by weight, the resulting cast coating layer may have reduced ink absorbency, and may not be able to achieve desired inkjet recording suitability.

In the present invention, in addition to the above-mentioned aqueous polyurethane resin, the cast coating layer may contain a water-soluble resin, for example, a modified polyvinyl alcohol such as polyvinyl alcohol, cation-modified polyvinyl alcohol, silyl-modified polyvinyl alcohol, polyvinylpyrrolidone, casein, or the like. Soy protein, synthetic proteins, starch, cellulose derivatives such as carboxymethylcellulose and methylcellulose, water-dispersible resins such as latexes of conjugated diene polymers such as styrene-butadiene copolymer and methylmethacrylate-butadiene copolymer, acrylics Polymer latex, styrene-vinyl acetate latex of vinyl copolymer such as vinyl acetate copolymer, and other various adhesives generally used in the coated paper field, as long as the effects of the present invention are not impaired. Also There. However, the mixing ratio of the aqueous urethane resin to the total adhesive in the cast coating layer is desirably 50% or more in order to maintain a desired effect. If the mixing ratio of the aqueous urethane resin to all the adhesives is less than 50%, the resulting cast coating layer may have reduced gloss, strength, and water resistance, and may also have reduced image quality such as print density. is there.

It is preferable to incorporate a cationic compound into the cast coating layer for the purpose of fixing the dye component in the ink. The method of blending the cationic compound may be such that the silica fine particles are mixed with the silica fine particles. However, the silica fine particles generally show an anionic property, and thus aggregation may occur due to the mixing of the cationic compound. In this case, when a commercially available amorphous silica (having a secondary particle diameter of several μm) is subjected to a strong shearing force by mechanical means to obtain fine particles, the amorphous silica before the treatment is treated with a cation. After mixing and dispersing the hydrophilic compound (the whole or a part of the cationic resin to be mixed into the cast coating layer), the mixture is subjected to dispersion / pulverization by mechanical means, or a finely divided silica secondary particle dispersion liquid And a method in which the mixture is once thickened and aggregated, and then subjected to mechanical dispersion and pulverization again.

As the cationic compound, a cationic resin or a low molecular weight cationic compound (for example, a cationic surfactant) can be used. From the viewpoint of the effect of improving the print density, it is preferable to use a cationic resin, which can be used as a water-soluble resin or an emulsion.
Further, a cationic organic pigment in which the cationic resin is insolubilized by means such as cross-linking and made into a particulate form may be used. When polymerizing a cationic resin, such a cationic pigment is prepared by copolymerizing a polyfunctional monomer to form a crosslinked resin, or a reactive functional group (hydroxyl group, carboxyl group, amino group, acetoacetyl group, etc.). Can be produced by adding a cross-linking agent to the cationic resin having the above as required, and forming the cross-linked resin by means of heat, radiation or the like. Cationic compounds, especially cationic resins,
In some cases, it may serve as an adhesive.

The following are examples of the cationic resin used in the present invention. 1) Polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, 2) Acrylic resin having a secondary amine group, tertiary amine group, or quaternary ammonium group, 3) Polyvinylamine and polyvinylamidine 4) dicyanic cation resin represented by dicyandiamide-formalin polycondensate; 5) polyamine based cation resin represented by dicyandiamide-diethylenetriamine polycondensate; 6) epichlorohydrin-dimethylamine addition polymer; 7) dimethyldiallylammonium chloride -S0 ₂
Copolymer, 8) diallylamine salt -S0 ₂ copolymer, 9) dimethyldiallylammonium chloride polymer, 10) polymers of allylamine salts, 11) dialkylaminoethyl (meth) acrylate 4
Grade salt polymers, 12) Cationic compounds such as acrylamide-diallylamine salt copolymers.

The cationic compound contained in the cast coating layer has an effect of further improving the water resistance of a printed image. The amount of the cationic compound incorporated in the cast coating layer is not particularly limited, but is usually preferably used in an amount of 1 to 100 parts by weight, more preferably 5 to 100 parts by weight, based on 100 parts by weight of the pigment. It is used in a blending amount in the range of ５０50 parts by weight. If the amount is too small, the effect of improving the print density may not be obtained, and if it is too large,
Conversely, the print density may be reduced, or image blurring may occur.

As a method of forming the cast coating layer,
A method in which the above coating liquid for the cast coating layer is coated on the undercoat layer, and while this coating layer is in a wet state, it is pressed against a cast surface such as a heated mirror-surface drum and dried to finish. (Wet cast method), and a method of once drying the coating layer, rewetting it, pressing it against a cast surface such as a heated mirror drum, drying and finishing (rewet cast method). Generally, the wet cast method is superior in gloss and ink absorbency of the cast coating layer obtained, but the rewet cast method is superior in productivity. Another method used to form the cast coating layer is to apply a coating liquid for the cast coating layer directly onto a heated mirror-surface drum, press it against the undercoat layer surface of the substrate, and finish by drying. (Precast method) can also be used. Further, the above-mentioned coating liquid for a cast coating layer is applied on the undercoat layer, and the cast coating layer is dried to a certain extent, and while it is in a semi-dry state, it is heated to a heated mirror-surface drum. When pressed and dried to finish, a uniform cast coating layer is formed, and a cast coating layer having high print density and excellent gloss can be obtained. Here, semi-dry means that the fluidity of the coating layer is almost lost, but contains a large amount of water,
The water content in this state is preferably about 20 to 400% with respect to the absolute dry weight of the coating layer (that is, containing 20 to 400 parts by weight of water based on 100 parts by weight of the absolute dry weight of the coating layer). Preferably, it is adjusted within the range of 50 to 200%. If the water content is too low, the transfer of the mirror surface when pressed against the mirror drum becomes insufficient, and it may be difficult to obtain a surface having sufficiently high gloss, and if the water content becomes excessive, When pressed against the mirror drum, the cast coating layer is crushed and a uniform and sufficient coating amount of the cast coating layer cannot be obtained, and the print density and gloss of the obtained cast coating layer may be insufficient.

When the coating liquid for the cast coating layer is coated on the undercoat layer, and the coating liquid layer is pressed against a heated mirror drum and dried while the coating liquid layer is in a wet state, the coating is uniform and sufficient. For the purpose of obtaining a cast coating layer having a coating amount, a means for promoting immobilization of the coating liquid for the cast coating layer may be provided. As this means, for example, (1) a gelling agent having a property of promoting the immobilization of the coating liquid for the cast coating layer is blended in the undercoat layer, and (2) the cast coating is applied on the undercoat layer. Coating and impregnating a gelling agent having a property of promoting the immobilization of the coating liquid for the coating layer; (3) applying the coating liquid for the cast coating layer, and then applying the cast coating layer on the surface thereof (4) coating and impregnating a gelling agent having a function of promoting the immobilization of the coating liquid for casting, and (4) removing the immobilization during the drying of the coating liquid in the coating liquid for the cast coating layer. Mixing a gelling agent having an accelerating property. Examples of the above-mentioned gelling agent include boric acid and formic acid, which are effective as a crosslinking agent for the adhesive in the coating liquid for the cast coating layer, and salts, aldehyde compounds, and epoxy compounds thereof.

In the coating composition for the cast coating layer, pigments used for general printing coated paper and ink jet paper for controlling whiteness, viscosity, fluidity, etc.
Various auxiliaries such as an antifoaming agent, a coloring agent, a fluorescent whitening agent, an antistatic agent, a preservative and a dispersant, and a thickener may be appropriately added. In addition, a release agent may be added to the coating composition for the purpose of imparting releasability from the cast drum. When applying the coating liquid for the cast coating layer described above on the undercoat layer, a blade coater, an air knife coater, a roll coater, a brush coater, a chaplex coater, a bar coater, a gravure coater, a lip coater, a die coater, a curtain Various coating devices such as a coater can be used. The coating amount of the cast coating layer is 1 to 30 as a dry solid content.
g / m ² , more preferably 1.
5 to 20 g / m ^2, more preferably 3 to 15 g / m ²
It is. If the coating amount is less than 1 g / m ² , the printing density and gloss of the resulting cast coating layer may be insufficient, and if it exceeds 30 g / m ² , the effect is saturated and the Load and the operability may be reduced. After the cast coating layer is formed by casting, the layer may be further subjected to a smoothing treatment using a super calender or the like.

The reason why an ink jet paper having particularly excellent gloss and ink jet recording suitability can be obtained by the present invention is considered as follows. First, the reason for improving the printing quality will be described. When the secondary particle size of the silica fine particles contained in the cast coating layer is reduced, the transparency of the cast coating layer increases, and the color development of the ink held in the cast coating layer is hindered by the cast coating layer. It is considered that the image quality (print density) is improved as a result. In addition, since the cast coating layer contains an aqueous polyurethane resin as an adhesive, the silica fine particles adhere firmly, and therefore the amount of the adhesive can be reduced, and as a result, excess adhesive can be used. Without losing the porosity of the coating layer, the resulting cast coating layer is excellent in ink absorbency and strength. Further, when a cationic compound is contained in the cast coating layer, the dye component in the ink is selectively fixed to the cast coating layer, so that the effect of improving image quality (print density) is more preferably exhibited. Also, the presence of the undercoat layer
It acts to quickly absorb the ink, but when the cast coating layer contains a cationic compound and the undercoat layer contains substantially no cationic compound, the cast coating layer Fix the dye component selectively,
It is considered that the undercoat layer functions to quickly absorb the solvent component in the ink. Next, the reason why the glossiness is improved will be described. Since the cast coating layer is formed by the cast method, the high smoothness of the mirror surface of the cast drum is transferred, and in addition to the cast coating layer surface having excellent gloss, the silica contained in the cast coating layer Since the secondary particles of the fine particles are sufficiently small, irregular reflection of light is reduced, and the gloss of the surface of the cast coating layer is further increased. Although the specific reason is not clear, the effect of enhancing the gloss of the cast coating layer is recognized in the aqueous polyurethane resin used as an adhesive in the cast coating layer.

[0034]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted thereto.
Parts and% in the examples are parts by weight and% by weight, respectively, unless otherwise specified. Preparation of paper substrate Wood pulp (LBKP; CSF500ml) 100 parts,
Paper making material consisting of 10 parts of calcined kaolin (trade name: Ansilex, manufactured by Engelhard Minerals Co., Ltd.), 0.05 parts of commercially available sizing agent, 1.5 parts of sulfuric acid band, 0.5 part of wet paper strength agent, and 0.75 part of starch Was used to produce a paper substrate having a basis weight of 120 g / m ² by a fourdrinier paper machine. The Stockigt sizing degree of this paper substrate was 10 seconds. This paper substrate was used in all of the following Examples and Comparative Examples.

Preparation of Silica Fine Particles [Silica Fine Particles A] Synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Co., Ltd .;
The aqueous dispersion having a particle size of 5 μm and a primary particle diameter of 15 nm was subjected to a pulverizing step using a pressure-type homogenizer (trade name: ultrahigh-pressure homogenizer GM-1 manufactured by SMT), and this operation was repeated (pressurization: 500 kg / cm). ² ). The average secondary particle diameter of the particles in the dispersion after the treatment was 50 nm, and the solid content concentration was 12%. [Silica fine particles B] A pressure-type homogenizer (manufactured by SMT) using an aqueous dispersion of synthetic amorphous silica (manufactured by Nippon Silica Co., Ltd., trade name: Nipsil HD-2, secondary particle diameter: 3 μm, primary particle diameter: 11 nm) The product was subjected to a pulverizing step using an ultrahigh-pressure homogenizer GM-1), and this operation was repeated (pressurization: 500 kg / cm ² ). The average secondary particle diameter of the particles in the dispersion after the treatment is 200 nm,
Its solids concentration was 12%. [Silica fine particles C] Synthetic amorphous silica (manufactured by Nippon Silica Industry Co., Ltd., trade name: Nipsil LP, secondary particle diameter 9μ)
m, an aqueous dispersion having a primary particle diameter of 16 nm) and subjected to a pulverizing step using a pressure-type homogenizer (trade name: ultrahigh-pressure type homogenizer GM-1 manufactured by SMT), and this operation was repeated (pressurization: 500 kg / cm). ² ). The average secondary particle diameter of the particles in the dispersion after the treatment was 500 nm, and the solid content concentration was 12%. The silica fine particles A and B
The average particle size of the primary particles after the pulverization process of the samples C and C was the same as before the pulverization.

Example 1 An undercoat layer was formed by applying an undercoat layer coating solution having the following composition on the paper base material using an air knife coater so as to have a dry weight of 12 g / m ^2. did. Next, a coating liquid for a cast coating layer having the following composition is applied on the above-mentioned undercoat layer with an air knife coater, and dried for 20 seconds with cold air to be in a semi-dry state (the absolute dry amount of the coating layer). Moisture content of 150
%), Which was pressed against a mirror surface drum having a surface temperature of 100 ° C., dried, and then released to form a cast coating layer, thereby obtaining a gloss type inkjet recording paper. The coating amount of the cast coating layer at this time was 6 g / m ² in terms of solid content weight.

Undercoat layer coating liquid (solid content: 17%) , synthetic silica (Fine Seal X-60, manufactured by Tokuyama, average secondary particle diameter 6.0 μm, primary particle diameter 15 nm) 80 parts zeolite (Toyobuilder) 20 parts; Silyl-modified polyvinyl alcohol (R1130; manufactured by Kuraray) 20 parts; Styrene-2-methylhexyl acrylate copolymer having a glass transition point of 75 ° C. and colloidal silica having a particle diameter of 30 nm; 40 parts of a composite emulsion (weight ratio of copolymer and colloidal silica of 40:60, particle size of emulsion is 80 nm) 40 parts of fluorescent dye (WhitexBPSH; manufactured by Sumitomo Chemical)

Coating solution for cast coating layer (solid content: 12%) , 100 parts of silica fine particles A, diallyldimethylammonium chloride-acrylamide copolymer (trade name; PAS-J-81, manufactured by Nitto Boseki Co., Ltd.) 10 parts-Cationic aqueous polyurethane resin (F-8554D; manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Tg = 73 ° C) 25 parts-Release agent (lecithin) 1 part

Example 2 A gloss type ink jet recording sheet was produced in the same manner as in Example 1. However, in the preparation of the coating liquid for the coating layer, silica fine particles B were used instead of silica fine particles A.

Example 3 A gloss type ink jet recording paper was manufactured in the same manner as in Example 1. However, in the preparation of the coating liquid for the coating layer, Pateracol SH3202 (manufactured by Dainippon Ink Industries, Tg = 60) was used as the cationic aqueous polyurethane resin.
° C).

Example 4 A gloss type ink jet recording sheet was produced in the same manner as in Example 1. However, the following composition was used as the coating liquid for the cast coating layer. Coating liquid for cast coating layer (solid content: 12%)・ 100 parts of silica fine particles A ・ 25 parts of anionic aqueous polyurethane resin (Superflex 126; manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Tg = 72 ° C.) 25 parts ・ Release agent (Lecithin) 1 copy

Example 5 A gloss type ink jet recording sheet was produced in the same manner as in Example 1. However, the following composition was used as the coating liquid for the cast coating layer. Coating liquid for cast coating layer (solid content: 12%)・ 100 parts of silica fine particles A ・ 25 parts of anionic aqueous polyurethane resin (Superflex 150D; manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Tg = 22 ° C.) 25 parts ・ Release agent (Lecithin) 1 copy

Comparative Example 1 A gloss type ink jet recording sheet was produced in the same manner as in Example 1. However, in the preparation of the coating liquid for the gloss layer,
Silica fine particles C were used in place of silica fine particles A.

Comparative Example 2 A gloss type ink jet recording sheet was produced in the same manner as in Example 1. However, the following composition was used as the coating liquid for the cast coating layer. 100 parts of coating liquid for cast coating layer (solid content: 12%) , 100 parts of silica fine particles A, 25 parts of anionic aqueous polyester resin (Vylonal MD1400; manufactured by Toyobo, Tg = 23 ° C.) 25 parts, release agent (lecithin) 1 Department

Comparative Example 3 A gloss type ink jet recording sheet was produced in the same manner as in Example 1. However, the following composition was used as the coating liquid for the cast coating layer. Coating liquid for cast coating layer (solid content: 12%)・ 100 parts of silica fine particles A ・ 25 parts of anionic aqueous acrylic resin (John Krill 7001; manufactured by Johnson Polymer, Tg = 12 ° C.) 25 parts ・ Release agent (lecithin) 1 copy

COMPARATIVE EXAMPLE 4 An ink jet recording sheet was prepared in the same manner as in Example 1 except that the undercoat layer was provided and the cast coating layer was not formed.

Comparative Example 5 A paper substrate was used as it was as ink jet recording paper.

The ink jet recording papers of Examples 1 to 5 and Comparative Examples 1 to 5 were tested for ink jet recording suitability and white paper gloss, and the results are shown in Table 1. The above test method is as follows.

[Appropriateness of Inkjet Recording] Printing was performed using an inkjet printer BJC420J (manufactured by Canon Inc.), and the obtained prints were subjected to the following tests and evaluations. (Uniformity of solid printing portion) Printing unevenness (shading unevenness) of a solid printing portion in which two colors of cyan ink and magenta ink were mixed was visually evaluated according to the following criteria. ：: good level without printing unevenness −-: There is some printing unevenness, but the level is practically satisfactory. Δ: There is some printing unevenness, and the level is somewhat unsatisfactory in practical use. X: A level at which printing unevenness is remarkable and cannot be used. (Dryability of ink) 2 of cyan ink and magenta ink
The dryness of the ink was evaluated visually for the solid printed portion of the color mixture according to the following criteria. ：: No stain at all even if touched with a finger immediately after printing. ×: Stained when touched with a finger immediately after printing. (Print density after ink jet recording) The print density of the black solid print portion was measured by Macbeth RD-914.

[Glossiness] A 75 ° glossiness of a blank portion was measured according to JIS-P8142. [Visual Appearance] The glossiness and smoothness were visually evaluated according to the following criteria. ：: extremely excellent ：: Excellent. −-: slightly inferior Δ: Poor. X: There is no gloss.

[Overall Evaluation] The print quality and gloss were comprehensively evaluated according to the following criteria. 5: Excellent. 4: Excellent. 3: Normal. 2: Slightly inferior. 1: Poor.

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[Table 1]

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The ink jet recording sheet according to the present invention has a high gloss, is excellent in ink jet recording suitability such as print density and recorded image quality, and is extremely useful in practical use.

Claims (5)

[Claims] 1. A base sheet, at least one undercoat layer formed on the base sheet and containing a pigment and an adhesive, and formed on the undercoat layer and containing a pigment and an adhesive Having a cast coating layer, wherein the pigment in the cast coating layer contains silica fine particles having a primary particle average particle size of 3 nm to 40 nm and a secondary particle average particle size of 10 nm to 300 nm, and An ink jet recording sheet, wherein the adhesive in the cast coating layer contains an aqueous polyurethane resin. 2. The ink jet recording sheet according to claim 1, wherein the aqueous polyurethane resin contained in the cast coating layer contains a cationic aqueous polyurethane resin. 3. The ink jet recording sheet according to claim 1, wherein the aqueous polyurethane resin contained in the cast coating layer has a glass transition temperature of 40 ° C. or higher. 4. The ink jet recording sheet according to claim 1, wherein the cast coating layer further contains a cationic compound. 5. The method according to claim 1, wherein the undercoat layer comprises colloidal silica;
2. The ink jet recording sheet according to claim 1, comprising a complex of a monomer having an ethylenically unsaturated bond with a polymer resin.