JP2004306616A5 - - Google Patents

Description

Inkjet recording paper

  The present invention relates to an ink jet recording paper, and more particularly to an ink jet recording paper excellent in gloss and excellent in ink jet recording suitability.

  Recording by an ink jet printer is used in various fields because of low noise, high-speed recording, and easy multi-color printing. As the ink jet recording paper, high quality paper devised so as to be rich in ink absorbency, coated paper having a surface coated with a porous pigment, and the like are applied. By the way, since all of these papers are mainly ink jet recording papers having a low surface gloss, so-called matte tone, there is a demand for an ink jet recording paper having a high surface gloss and an excellent appearance.

  In general, as a paper having a high surface gloss, a coated paper having a high gloss obtained by coating a plate-like pigment on the surface and further performing a calender treatment as necessary, or a heating drum having a wet coating layer having a mirror surface A so-called cast-coated paper obtained by copying a mirror surface by pressing and drying the surface is known. This cast coated paper has higher surface gloss and better surface smoothness compared to ordinary super calendered coated paper, and provides excellent printing effect. However, when it is used for ink jet recording paper, it has various difficulties.

  That is, a conventional cast coated paper is generally disclosed in, for example, US Pat. No. 5,275,846. A film-forming substance such as an adhesive in the pigment composition constituting the coating layer transfers the mirror surface drum surface of the cast coater to obtain a high gloss. On the other hand, the presence of this film-forming substance causes a problem that the porosity of the coating layer is lost and the absorption of ink during ink jet recording is extremely reduced. In order to improve the ink absorbency, it is important that the cast coating layer is made porous so that the ink can be easily absorbed. For this purpose, it is necessary to reduce the film forming property. Reducing the amount of film-forming material results in a reduction in blank gloss.

  As described above, it was extremely difficult to simultaneously satisfy both the surface gloss of the cast coated paper and the suitability for inkjet recording. As a method for solving the above-mentioned problem, a polymer having a glass transition point of 40 ° C. or higher obtained by polymerizing a monomer having an ethylenically unsaturated bond on a base paper provided with a recording layer containing a pigment and an adhesive as main components. A coating liquid containing the coalesced composition as a main component is applied to form a coating layer for casting, and the coating layer for casting is pressed against a heated mirror drum while the coating layer is in a wet state, and is finished by drying. The present inventors have found that a cast paper for ink jet recording having both excellent gloss and ink absorbability can be obtained, and proposed as Japanese Patent Application Laid-Open No. 7-89220.

  By the way, in recent years, with the expansion of applications such as high-speed inkjet recording, high definition of recorded images, and full colorization, there is a demand for higher gloss, higher image quality, and higher recording density. Although gloss and recording quality comparable to photographic paper are required, it is currently difficult to meet such demands by using the previously proposed technology.

US Pat. No. 5,275,846 JP-A-7-89220

  The present invention provides an ink jet recording paper having excellent glossiness and excellent ink jet recording suitability such as print density and recording image quality.

The present invention includes the following embodiments.
[1] At least one undercoat layer containing a pigment and an adhesive is provided on a base material, and further, in an inkjet recording sheet provided with a cast coating layer on the undercoat layer, the cast coating layer is made of amorphous silica. Ink jet recording characterized by containing silica fine particles having an average primary particle diameter of 3 nm or more and 40 nm or less and an average secondary particle diameter of 10 nm or more and 400 nm or less, obtained by treatment with mechanical means. Paper.

[2] The ink jet recording paper according to [1], wherein the cast coating layer contains a cationic compound.
[3] The ink jet recording paper according to [2], wherein the undercoat layer does not contain a cationic compound, and the cast coating layer contains a cationic compound.
[4] The cast coating layer was heated by applying the coating liquid for the cast coating layer on the undercoat layer, and while the coating layer was in a wet state or after re-wetting after drying. The ink jet recording paper according to [1], [2] or [3], which is pressed against a mirror surface drum, dried and finished.
[5] The ink jet recording paper according to [1], [2], [3] or [4], wherein the pigment of the undercoat layer contains at least one of amorphous silica, alumina and zeolite.
[6] The pigment of the undercoat layer contains amorphous silica particles having an average secondary particle diameter of 2 μm to 8 μm [1], [2], [3], [4] or [5]. The ink jet recording paper according to the above.

  The present invention is a method for producing an ink jet recording paper which is excellent in ink drying property, appearance and glossiness, and excellent in ink jet recording suitability such as print density, recording image quality and solid uniformity.

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 is appropriately used. In addition, air-permeable resin sheets can also be used. The paper base is composed mainly of wood pulp and, if necessary, pigment.
As the wood pulp, various chemical pulp, mechanical pulp, recycled pulp and the like can be used, and the degree of beating of these pulp can be adjusted by a beating machine in order to adjust paper strength, suitability for papermaking, and the like. The beating degree (freeness) of the pulp is not particularly limited, but is about 250 to 550 ml (CSF: JISP-8121).
The pigment is compounded for the purpose of imparting opacity or the like or adjusting the ink absorbency, and calcium carbonate, calcined kaolin, silica, titanium oxide and the like can be used. In this case, the compounding amount is preferably about 1 to 20%. If it is too large, the paper strength may be reduced. As auxiliaries, a sizing agent, a fixing agent, a paper strength enhancer, a cationizing agent, a retention enhancer, a dye, a fluorescent whitening agent and the like can be added.

Further, in the size press step of the paper machine, starch, polyvinyl alcohol, a cationic resin or the like can be applied and impregnated to adjust the surface strength, sizing degree, and the like. The size is preferably about 1 to 200 seconds. When the degree of size is low, there may be a problem in operation such as wrinkles at the time of coating, and when the degree of size is high, the ink absorbency may decrease, and curling or cockling after printing may become remarkable. The basis weight of the substrate is not particularly limited, but is about ²⁰ to 400 g / m ² .

  As a gas-permeable resin sheet, a transparent or opaque resin film or sheet having a through-porosity imparted by mechanical treatment, a resin or the like mixed with a pigment or the like, molded into a film or sheet shape, and then stretched to form a porous film. A resin or a resin or other substance that elutes with a solvent such as a pigment, compounded into a film or sheet, and then treated with a solvent to form a porous material in which the pigment or compound is eluted. Etc. can be used.

  An undercoat layer is provided on the substrate for the purpose of increasing the ink absorption capacity and absorption speed. The undercoat layer provided on the base material is mainly composed of a pigment and an adhesive. The pigment in the undercoat layer is kaolin, clay, calcined clay, amorphous silica (also called amorphous silica), synthetic amorphous silica, zinc oxide, aluminum oxide, aluminum hydroxide, calcium carbonate, satin white, aluminum silicate , Alumina, colloidal silica, 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. One or more of various publicly known pigments in the general coated paper manufacturing field can be used in combination. Among these, it is preferable to use amorphous silica, alumina, and zeolite having high ink absorbability as main components.

  In a preferred embodiment, the pigment in the recording layer contains silica particles having an average secondary particle diameter of 2 μm or more and 8 μm or less. If it is less than 2 μm, the ink absorption speed is reduced, and if the amount of ink is large, bleeding of the ink may occur. If the thickness is more than 8 μm, the smoothness of the surface after the undercoat layer is provided becomes insufficient, so that the gloss may be insufficient or the appearance may be poor. Further, as described later, when the gloss layer is provided by the casting method, the adhesion to the cast drum becomes insufficient, and the surface may become rough or uneven gloss, resulting in poor appearance. The amorphous silica secondary particles are preferably 50% or more of the total pigment in order to obtain the desired appearance and print quality of the present invention. The average primary particle size is not particularly limited, but is, for example, 3 nm to 50 nm.

  Examples of the adhesive in the undercoat layer include proteins such as casein, soy protein, and synthetic protein; various starches such as starch and oxidized starch; and various modified polyvinyl alcohols such as polyvinyl alcohol, cationic polyvinyl alcohol, and silyl-modified polyvinyl alcohol. Polyvinyl alcohols, cellulose derivatives such as carboxymethyl cellulose and methyl cellulose, styrene-butadiene copolymer, conjugated diene-based polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer latex, ethylene-vinyl acetate copolymer, etc. Conventionally known adhesives generally used for coated paper, such as a vinyl polymer latex, can be used alone or in combination.

  The mixing ratio of the pigment and the adhesive depends on the type thereof, but is generally adjusted in the range of 1 to 100 parts by weight, preferably 2 to 50 parts by weight of the adhesive with respect to 100 parts by weight of the pigment. In addition, various auxiliaries such as a dispersant, a thickener, an antifoaming agent, an antistatic agent and a preservative used in the production of general coated paper are appropriately added. A fluorescent dye and a coloring agent can be added to the undercoat layer.

  In order to fix the dye component in the ink for inkjet recording, a cationic compound may be blended in the undercoat layer. However, as described later, it is preferable to fix the ink dye to the cast coating layer provided on the undercoat layer as much as possible, since the printing (recording) density becomes higher. It is preferable to incorporate a large amount of a cationic compound in the coating layer. More preferably, the cationic compound is blended only in the cast coating layer, and the cationic compound is substantially not present in the undercoat layer. The term "substantially absent" excludes, for example, adding a small amount of a cationic surfactant or the like as an auxiliary agent. When a cationic compound is blended only in the cast coating layer, and the cationic compound is not substantially present in the undercoat layer, the gloss when the cast coating layer is provided is most easily developed.

  When a composite of colloidal silica and a polymer resin obtained by polymerizing a monomer having an ethylenically unsaturated bond is blended in the undercoat layer, the gloss when the cast coating layer is provided is more exhibited. The reason for this is not necessarily clear, but it is presumed that the presence of the composite suppresses penetration into the undercoat layer of the coating composition for the cast coating layer while maintaining the ink absorbency of the undercoat layer. . Further, although the reason is unknown, there is a tendency that the releasability from the cast drum is improved when the cast coating layer is provided by the cast method.

  Examples of the polymer resin obtained by polymerizing a monomer having an ethylenically unsaturated bond include, for example, alkyl group carbon atoms 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- Methylstyrene, vinyltoluene, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl propionate, acrylamide, N-methylol acrylamide , Ethylene monomer polymerization to obtain a polymer of butadiene, and the like. The polymer may be a copolymer using two or more types of ethylenic monomers as needed, or may be a polymer or a substituted derivative of the copolymer. Incidentally, examples of the substituted derivative include, for example, those which are carboxylated, or those which are alkali-reactive.

  The complexation with colloidal silica is carried out by polymerizing the above-mentioned ethylenic monomer with a silane coupling agent or the like in the presence of colloidal silica to form a complex through a Si-OR bond (R: polymer component), or In which a polymer resin modified with a silanol group or the like is reacted with colloidal silica to form a composite by a Si-OR bond (R: polymer component). The Tg (glass transition point) of the polymer component of the composite is preferably 40 ° C. or higher, more preferably 50 to 100 ° C. If the Tg is low, the film formation may proceed too much during drying, or the absorption of the ink may be slow and bleeding may occur. Further, although the reason is unknown, when Tg is 40 ° C. or higher, the releasability from a cast drum when a cast coating layer is provided by a casting method tends to be further improved.

The coating liquid for an undercoat layer composed of the above-mentioned materials is generally adjusted to a solid content concentration of about 5 to 50% by weight, and dried on a paper substrate in a dry weight of ^{2 to} 100 g / m ² , preferably 5 to 50 g / m ² . m ² approximately, more preferably coated so that the order of 10 to 20 g / ^{m 2.} If the coating amount is small, the ink absorbency may be poor, or the gloss may not be sufficiently obtained when the cast layer is provided.If the coating amount is large, the print density may decrease or the strength of the coating layer may decrease. In some cases, powder may be easily dropped or scratched.

  The coating liquid for the undercoat layer is applied by various 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. Worked and dried. Further, if necessary, the recording layer (undercoat layer) may be subjected to a smoothing process such as super calendering or brushing after drying.

  In the present invention, a cast coating layer is further provided on the undercoat layer (recording layer) containing the pigment and the adhesive provided on the base material. The cast coating layer contains specific silica fine particles and an adhesive as main components. First, the silica fine particles will be described. The silica fine particles used in the present invention are those obtained by processing by mechanical means. For example, a commercially available synthetic amorphous silica (for example, having an average secondary particle size of about several microns) is obtained by applying a strong force by mechanical means to reduce the average secondary particle size. Can be done. 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, and a sand grinder. The silica fine particles thus treated are generally obtained as an aqueous dispersion (slurry or colloidal particles) having a solid content of about 5 to 20%.

  The average particle diameter referred to in the present invention is a particle diameter observed with an electron microscope (SEM and TEM) (take an electron microscope photograph of 10,000 to 400,000 times, measure a Martin diameter of particles in 5 cm square, The average value is described in “Particle Handbook” (Asakura Shoten), p. 52, 1991, etc.).

  The average particle diameter of the silica fine particles (substantially mainly of secondary particles) used in the present invention is 10 nm or more and 400 nm or less, preferably 10 nm or more and 300 nm or less, more preferably 15 nm or more and 150 nm or less, and most preferably. It is adjusted to 20 nm or more and 100 nm or less. When the average particle diameter of the secondary silica fine particles exceeds 400 nm, the transparency of the cast coating layer is reduced, the coloring property of the dye fixed in the cast coating layer is reduced, and the desired print density is reduced. Can not be obtained. Further, when silica fine particles having an extremely small average particle diameter of the secondary particles are used, the ink absorbency decreases, and a desired image quality cannot be obtained.

  The average particle size of the primary silica fine particles must be adjusted to 3 nm or more and 40 nm or less, preferably 5 nm to 30 nm, more preferably 7 nm to 20 nm. When the average of the primary particle diameters is less than 3 nm, the voids between the primary particles become extremely small, the ability to absorb the solvent in the ink and the ink is reduced, and the desired image quality cannot be obtained. When the average primary particle diameter exceeds 40 nm, the aggregated secondary particles become large, the transparency of the cast coating layer is reduced, and the coloring property of the dye fixed in the cast coating layer is reduced. The desired print density cannot be obtained. Pigments other than the above specific silica fine particles (for example, those exemplified for the undercoat layer) can be used in combination within a range not to impair the effects of the present invention, but the particle size is preferably 500 nm or less, more preferably silica fine particles. This is the range of the average secondary particle diameter described above.

  The proportion of the silica fine particles in all the pigments in the cast coating layer is preferably 50% or more in order to maintain the transparency of the recording layer. If the ratio of the silica fine particles in all the pigments is less than 50%, the transparency is significantly reduced, and the image quality such as the print density may be reduced. Examples of the adhesive include water-soluble resins (eg, polyvinyl alcohols such as polyvinyl alcohol, cation-modified polyvinyl alcohol, and modified polyvinyl alcohol such as silyl-modified polyvinyl alcohol, polyvinylpyrrolidone, casein, soybean proteins, synthetic proteins, starch, carboxymethylcellulose, and the like). Water dispersibility such as conjugated diene-based polymer latex such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, and vinyl-based copolymer latex such as styrene-vinyl acetate copolymer. Resins, water-based acrylic resins, water-based polyurethane resins, water-based polyester resins, and the like, and other generally known and used adhesives in the coated paper field are used alone or in combination.

  The amount of the adhesive is adjusted in the range of 1 to 200 parts by weight, more preferably 10 to 100 parts by weight, based on 100 parts by weight of the pigment. Here, if the amount of the adhesive is small, the strength of the coating layer may be weakened, the surface may be easily damaged, or powder may fall off. Conversely, if the amount of the adhesive is large, the ink absorbency may decrease, and the desired inkjet recording suitability may not be obtained.

  The cast coating layer preferably contains a cationic compound for the purpose of fixing the dye component in the ink. The compounding method may be such that the fine particles are mixed with the fine silica particles. However, the fine silica particles are generally anionic, and when the fine particles are mixed, agglomeration may occur to increase the particle size. In this case, when a commercially available amorphous silica (having an average secondary particle diameter of several microns) is subjected to a fine particle treatment by applying a strong force by mechanical means, the amorphous silica before the treatment is used. And then disperse and pulverize by mechanical means, or mix with the finely divided silica secondary particle dispersion, once thicken and aggregate, and then mechanically disperse and pulverize again The specific average secondary particle diameter can be obtained by adopting a method or the like. Incidentally, the average primary particle diameter does not change even after the pulverization treatment.

  Examples of the cationic compound include a cationic resin and a low molecular weight cationic compound (for example, a cationic surfactant). A cationic resin is preferred from the viewpoint of improving the print density, and can be used as a water-soluble resin or an emulsion. Further, it can be used as a cationic organic pigment in which a cationic resin is insolubilized by means of crosslinking or the like to form a particulate form. Such a cationic organic pigment, when polymerizing a cationic resin, copolymerizes a polyfunctional monomer to form a crosslinked resin, or has a reactive functional group (hydroxyl group, carboxyl group, amino group, acetoacetyl group, etc.). A cross-linking agent is added to the cationic resin having the above as required, and the cross-linked resin is formed by means such as heat and radiation. Cationic compounds, especially cationic resins, may also serve as adhesives.

The following can be illustrated as the cationic resin. Specifically, 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 , Polyvinylamidines, 4) dicyan cation resin represented by dicyandiamide-formalin polycondensate, 5) polyamine cation resin represented by dicyandiamide-diethylenetriamine polycondensate, 6) epichlorohydrin-dimethylamine addition polymer, 7 ) dimethyldiallylammonium chloride -SO ₂ copolymer, 8) diallylamine salt -SO ₂ copolymer, 9) dimethyldiallylammonium chloride polymer, 10) polymers of allylamine salts, 11) dialkylaminoethyl (meth) Acrylate quaternary salt polymer, 12) acrylamide - diallylamine salt copolymers and cationic compounds of.

  The cationic compound also has the effect of improving the printed image water resistance. The cationic compound to be added to the cast coating layer can be used in an amount of 1 to 100 parts by weight, more preferably 5 to 50 parts by weight, based on 100 parts by weight of the pigment. If the compounding amount is small, it is difficult to obtain the effect of improving the print density, and if it is too large, the print density may be reduced or the image may be blurred.

  The casting method means that the coating layer is dried on a smooth cast drum (drum of mirror-finished metal, plastic, glass, etc.), mirror-finished metal plate, plastic sheet or film, glass plate, etc. This is a method of obtaining a smooth and glossy coating layer surface by copying the surface onto the coating layer. A smooth surface such as a mirror surface preferably has a surface roughness (JIS B-0601) of Ra of 0.5 μm or less, more preferably 0.05 μm or less. As a method for providing a cast coating layer, it is preferable to obtain a smooth coating layer by contacting a smooth surface under heating. For example, a method of applying the above coating liquid for a cast coating layer on an undercoat layer, pressing the coated liquid onto a mirror-surface drum heated while the coating layer is in a wet state, and drying and finishing the film (wet casting method) ), Or a method of once drying, re-wetting, pressing against a heated mirror drum, drying and finishing (rewet casting method), and the like. Generally, the wet cast method tends to be excellent in gloss and ink absorbency, and the rewet cast method tends to be excellent in productivity.

  Alternatively, a coating solution for a cast coating layer is applied directly to a heated mirror drum, and then pressed and dried on the substrate surface or the undercoat layer surface of the substrate provided with an undercoat layer (precast method). Can be adopted. The heating temperature is, for example, 40 to 200 ° C., preferably 70 to 150 ° C., and the time for contact with the mirror drum or the like is not limited, but is, for example, about 1 to 60 seconds.

  Furthermore, the coating liquid for the cast coating layer is applied on the undercoat layer provided on the base material, and the cast coating layer is dried to a certain extent. Pressing and finishing the drum by pressing is particularly preferable because a uniform coating layer is easily formed, and a cast coating layer having high print density and excellent gloss is easily obtained. Here, "semi-dried" means a state in which the fluidity of the coating layer is almost lost but contains a large amount of water, and is 20 to 400% of the absolute dry weight of the coating layer. (Including moisture of 20 to 400 parts by weight with respect to 100 parts by weight of absolute dry weight), and is preferably adjusted in the range of 50 to 200%. If the water content is low, the transfer of the mirror surface when pressed against the mirror drum becomes insufficient, and it is difficult to sufficiently exhibit gloss. If the amount is too large, the coating layer is crushed when pressed against the mirror drum, and a uniform coating layer with a sufficient coating amount cannot be obtained, and the print density and gloss tend to be insufficient. Further, the coating layer is transferred to and adheres to the mirror-surface drum, causing a decrease in gloss, and the mirror-surface drum becomes dirty, which may cause a problem in operation.

When applying the coating liquid for the cast coating layer on the undercoat layer provided on the base material, pressing the mirror coating drum heated while the cast coating layer is in a wet state, and drying to finish, uniform In order to obtain a coating layer having a sufficient coating amount, a method of promoting immobilization of the coating liquid for the cast coating layer can be adopted. As this method, for example, (1) a gelling agent which promotes immobilization of a coating liquid for a cast coating layer is blended in an undercoat layer, and (2) a casting agent is cast on a substrate or an undercoat layer. Coating and impregnating a gelling agent that promotes immobilization of the coating liquid for the coating layer. (3) After coating the coating liquid for the cast coating layer, the coating liquid for the cast coating layer (4) A gel that promotes immobilization in the process of drying the coating liquid in the coating liquid for the cast coating layer, by coating and impregnating the surface with a gelling agent that promotes the immobilization of the coating liquid. An agent may be added. Examples of such a gelling agent include boric acid and formic acid which are crosslinking agents for an adhesive in a coating liquid for a cast coating layer, and salts thereof, aldehyde compounds, epoxy compounds and the like.
After coating the same composition as the coating composition for cast coating layer on the undercoat layer and drying or semi-drying, further applying the coating composition for cast coating layer on the coating layer It can also be dried on a cast drum.

In the coating composition for the cast coating layer, in order to adjust the whiteness, viscosity, fluidity, etc., pigments used in general printing coated paper and inkjet paper, defoamers, coloring agents, Various assistants such as a fluorescent whitening agent, an antistatic agent, a preservative and a dispersant, and a thickener are appropriately added. In addition, a release agent can be added for the purpose of imparting releasability from a cast drum or the like. 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 known coating apparatuses such as a coater can be used. The coating amount of the cast-coated layer is dried solids at 1 to 30 g / ^{m 2,} preferably from 1.5 to 20 / ^{m 2,} more preferably 3 to 15 g / ^{m 2.} If the amount is less than 1 g / m ² , the print density and gloss may not be sufficiently obtained, and if the amount exceeds 30 g / m ² , the effect is saturated, the drying is burdensome, and the operability may be reduced. After providing the cast coating layer by the cast finish, a smoothing treatment can be further performed by a super calender or the like.

The reason why an inkjet paper having particularly excellent gloss and inkjet recording suitability can be obtained by the present invention is considered as follows. First, the reason for improving the print quality will be described. When the secondary particle size of the silica fine particles used 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 glossy layer increases. It is thought that the image quality (print density) is improved as a result.
Further, in a mode in which the 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 above-described effects are more exhibited, which is preferable. Further, the presence of the undercoat layer acts to quickly absorb the ink, but in an embodiment in which the cast coating layer contains a cationic compound, and the undercoat layer contains substantially no cationic compound, The coating layer selectively fixes the dye component in the ink, and the undercoat layer is excellent in print density and absorptivity, probably because it absorbs the solvent component in the ink quickly.
Next, the reason why the glossiness is improved will be described. Since the cast coating layer is provided by the cast method, the smoothness of the cast drum is transferred and the gloss is excellent, and the secondary particle diameter of the silica fine particles used in the cast coating layer is sufficiently small. Therefore, the irregular reflection of light is small, and the gloss of the surface of the cast coating layer is further increased. Incidentally, the 75 degree glossiness is preferably 30% or more, more preferably 35% or more, and most preferably 50% or more.

  Hereinafter, the present invention will be described more specifically with reference to examples, but is not limited thereto. Parts and% in Examples are parts by weight and% by weight, respectively, unless otherwise specified.

"Preparation of paper substrate"
100 parts of wood pulp (LBKP; freeness 500 ml CSF), 10 parts of calcined kaolin (trade name: Ansilex, manufactured by Engelhard Mineral Co., Ltd.), 0.05 parts of commercially available sizing agent, 1.5 parts of sulfuric acid band, wet paper strength agent A paper base material having a basis weight of 120 g / m ² was produced by a fourdrinier paper machine using a papermaking material comprising 0.5 part and 0.75 part of starch. The Stockigt sizing degree of this paper substrate was 10 seconds. This paper substrate was used in all examples and comparative examples of the present invention.

"Preparation of silica fine particles"
[Silica fine particles A]
Using an aqueous dispersion of synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Corporation, average secondary particle diameter 4.5 μm, average primary particle diameter 15 nm), a pressure homogenizer (manufactured by SMT, The operation of pulverization was repeated using a trade name: ultrahigh-pressure homogenizer GM-1) (pressurization: 500 kg / cm ² ). The silica in the dispersion after the treatment had an average secondary particle diameter of 50 nm and a solid content of 12% (the average primary particle diameter remained at 15 nm).

[Silica fine particles B]
Using an aqueous dispersion of synthetic amorphous silica (trade name: Nipsil HD-2, manufactured by Nippon Silica Co., Ltd., average secondary particle diameter: 3 μm, average primary particle diameter: 11 nm), a pressure-type homogenizer (manufactured by SMT) The operation of pulverization was repeated using an ultra high pressure homogenizer (GM-1) (pressurization: 500 kg / cm ² ). The average secondary particle size of the silica in the dispersion after the treatment was 200 nm, and the solid content concentration was 12% (the average primary particle size remained at 11 nm).

[Silica fine particles C]
A pressure-type homogenizer (manufactured by SMT, trade name: Nippil LP, manufactured by Nippon Silica Co., Ltd., trade name: Nipsil LP, average secondary particle diameter 9 μm, average primary particle diameter 16 nm) is used. The pulverization operation was repeated using an ultrahigh-pressure homogenizer (GM-1) (pressurization: 500 kg / cm ² ). The average secondary particle diameter of the silica in the dispersion after the treatment was 500 nm, and the solid content concentration was 12% (the average primary particle diameter remained at 16 nm).

"Mixing of silica fine particles and cationic compounds"
In the following Examples and Comparative Examples, when mixing the above-mentioned silica fine particles A, B or C and the cationic compound, after mixing and dispersing both, a pressure homogenizer (trade name: ultra high pressure type manufactured by SMT) The dispersion was pulverized using a homogenizer (GM-1) (pressurization: 500 kg / cm ² ) and treated until the average secondary particle diameter of silica in the dispersion became the average secondary particle diameter of the original silica fine particles. (The average primary particle size is the same as before the treatment).

Example 1
The following undercoat layer coating liquid was applied on a paper base material using an air knife coater and dried so as to have a dry weight of 12 g / m ² . Next, the following coating liquid for a cast coating layer is coated 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 (moisture content based on the absolute dry amount of the coating layer). 150%) and pressed against a mirror-surface drum having a surface temperature of 90 ° C., dried, and released to obtain a glossy inkjet recording paper. The coating amount of the cast coating layer at this time was 5 g / m ² in terms of solid content weight. The mirror drum is a steel roll whose surface is mirror-finished by plating nickel on the surface of a steel roll, and then plating and polishing chrome thereon. The surface roughness Ra was 0.03 μm.

[Coating liquid for undercoat layer] (solids concentration 17%, parts are parts by weight of solids)
80 parts of synthetic amorphous silica (Fine Seal X-60; manufactured by Tokuyama, average secondary particle diameter 6.0 μm, average primary particle diameter 15 nm), zeolite (Toyo Builder; manufactured by Tosoh, average particle diameter 1.5 μm) 20 Parts, a silyl-modified polyvinyl alcohol (R1130; manufactured by Kuraray Co., Ltd.), 20 parts, a composite emulsion of a styrene-2-methylhexyl acrylate copolymer having a glass transition point of 75 ° C. and colloidal silica having a particle diameter of 30 nm (the copolymer and colloidal silica are 40 parts by weight, 40 parts by weight, emulsion particle size: 80 nm) 40 parts, 2 parts of fluorescent dye (WhitexBPSH; manufactured by Sumitomo Chemical).

[Coating liquid for cast coating layer] (solid content: 12%, parts are by weight solids)
100 parts of silica fine particles A, 10 parts of diallyldimethylammonium chloride-acrylamide copolymer (cationic compound: manufactured by Nitto Boseki Co., trade name; PAS-J-81), 10 parts of cationic acrylic resin (XC-2010; manufactured by Hoshiko Chemical Co., Ltd.) 20 parts of a quaternary amine-modified acrylic aqueous resin, Tg 85 ° C.), 10 parts of silyl-modified polyvinyl alcohol (R1130; manufactured by Kuraray), and 2 parts of a release agent (lecithin).

Example 2
An undercoat layer coating liquid similar to that of Example 1 was applied on a paper base material using an air knife coater so as to have a dry weight of 12 g / m ² and dried. Next, the same coating liquid for a cast coating layer as in Example 1 was applied on the undercoat layer by an air knife coater, immediately pressed against a mirror drum having a surface temperature of 90 ° C., dried, and then separated. Then, a gloss type ink jet recording paper was obtained. The coating amount of the cast coating layer at this time was ² g / m ² in terms of solid content weight.

Example 3
A gloss type inkjet recording paper was obtained in the same manner as in Example 1 except that the following coating liquid for undercoat layer was used.
[Coating liquid for undercoat layer] (solids concentration 18%, parts indicate parts by weight of solids)
80 parts of synthetic silica (Fine Seal X-60; manufactured by Tokuyama), 20 parts of zeolite (Toyo Builder; manufactured by Tosoh), 20 parts of silyl-modified polyvinyl alcohol (R1130; manufactured by Kuraray), styrene-2-methylhexyl having a glass transition point of 75 ° C 40 parts of a composite emulsion of an acrylate copolymer and colloidal silica having a particle diameter of 30 nm (the weight ratio of the copolymer and the colloidal silica is 40:60, the particle diameter of the emulsion is 80 nm), 40 parts, a fluorescent dye (WhitexBPSH; manufactured by Sumitomo Chemical) 2 parts, 10 parts of diallyldimethylammonium chloride-acrylamide copolymer (cationic compound: Nitto Boseki Co., trade name; PAS-J-81).

Example 4
A glossy inkjet recording paper was obtained in the same manner as in Example 1, except that the silica fine particles were changed from A to B in the coating liquid for the cast coating layer used in Example 1.

Example 5
A gloss type inkjet recording paper was obtained in the same manner as in Example 1 except that the following were used as the coating liquid for the undercoat layer and the coating liquid for the cast coating layer.
[Coating liquid for undercoat layer] (solids concentration 17%, parts are parts by weight of solids)
80 parts of synthetic silica (Fine Seal X-60; manufactured by Tokuyama, average secondary particle diameter 6.0 μm, average primary particle diameter 15 nm), 20 parts of zeolite (Toyo Builder; manufactured by Tosoh), 20 parts of silyl-modified polyvinyl alcohol (R1130; Kuraray) 20 parts, a composite emulsion of a styrene-2-methylhexyl acrylate copolymer having a glass transition point of 75 ° C. and colloidal silica having a particle diameter of 30 nm (the copolymer and the colloidal silica are in a weight ratio of 40:60, particles of the emulsion) 40 parts of a fluorescent dye (WhitexBPSH; manufactured by Sumitomo Chemical), 10 parts of diallyldimethylammonium chloride-acrylamide copolymer (cationic compound: manufactured by Nitto Boseki Co., trade name; PAS-J-81).

[Coating liquid for cast coating layer] (solids concentration: 12%, parts are parts by weight of solids)
100 parts of silica fine particles A, 20 parts of silyl-modified polyvinyl alcohol (R1130; manufactured by Kuraray), 2 parts of a release agent (lecithin).

Example 6
A glossy inkjet recording paper was obtained in the same manner as in Example 1 except that the following coating liquid for the undercoat layer was used.
[Coating liquid for undercoat layer] (solids concentration 17%, parts are parts by weight of solids)
80 parts of synthetic silica (Fine Seal X-60; manufactured by Tokuyama, average secondary particle diameter 6.0 μm, average primary particle diameter 15 nm), 20 parts of zeolite (Toyo Builder; manufactured by Tosoh), 20 parts of silyl-modified polyvinyl alcohol (R1130; Kuraray) 20 parts) and 2 parts of a fluorescent dye (WhitexBPSH; manufactured by Sumitomo Chemical).

Example 7
The same coating liquid for a cast coating layer as in Example 1 was applied directly on a paper base material (without providing an undercoat layer) with an air knife coater, dried with cold air for 20 seconds, and then placed in a semi-dry state. (Water content of 150% based on the absolute drying amount of the coating layer), and pressed against a mirror-surface drum having a surface temperature of 100 ° C., dried and released, to obtain a gloss type ink jet recording paper. At this time, the coating amount of the cast layer was 10 g / m ² .
Comparative Example 1
A gloss type inkjet recording paper was obtained in the same manner as in Example 1 except that the silica fine particles in the coating liquid for the cast layer used in Example 1 were changed from A to C.

Comparative Example 2
The following coating liquid for a cast coating layer was coated on the undercoat layer of Example 1 using a roll coater, immediately pressed against a mirror-surface drum having a surface temperature of 85 ° C., dried, and released from the mold. A type of ink jet recording paper was obtained. The coating amount of the cast coating layer at this time was 6 g / m ² in terms of solid content weight.
[Coating liquid for cast coating layer] (solids concentration 25%, parts are parts by weight of solids)
Complex emulsion of styrene-2-methylhexyl acrylate copolymer having a glass transition point of 75 ° C. and colloidal silica having a particle diameter of 30 nm (dispersion of primary particles and not agglomerated) (copolymer and colloidal silica are weight In a ratio of 40:60, the particle size of the emulsion is 80 nm), 100 parts, a thickener / dispersant (alkyl vinyl ether / maleic acid derivative copolymer) 5 parts, and a release agent (lecithin) 3 parts.

Comparative Example 3
In Example 1, a layer provided with an undercoat layer was used (no cast coating layer).
Comparative Example 4
In Example 3, one provided with an undercoat layer was used (without a cast coating layer).
Comparative Example 5
The paper substrate was used as it was.

Table 1 summarizes the suitability for ink jet recording and the glossiness of white paper of the ink jet recording paper thus obtained. In addition, about the said evaluation, evaluation was performed by the following methods.
[Inkjet recording suitability]
Printing was performed using an inkjet printer BJC600J (manufactured by Canon Inc.).
(Uniformity of solid printing area)
The printing unevenness (shading unevenness) of a solid printing portion of a mixture of two colors of a cyan ink and a magenta ink was visually evaluated.
：: Excellent level without any printing unevenness.
−-: Good level with almost no printing unevenness.
Δ: Printing unevenness, which is a level that is somewhat problematic in practical use.
X: A level at which printing unevenness is remarkable and becomes a serious problem in practical use.
(Dryness of ink)
The dryness of the ink was evaluated for the solid printing portion where two colors of the cyan ink and the magenta ink were mixed.
：: 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 inkjet recording)
The print density of the black solid print portion was measured by Macbeth RD-914.

(Glossiness)
According to JIS-P8142, 75 ° gloss of a blank portion was measured.
(Visual appearance)
The glossiness and smoothness were visually evaluated. ：: extremely excellent.
：: Excellent.
Δ: Slightly inferior.
×: Poor.

〔Comprehensive evaluation〕
Comprehensive evaluation of print quality and gloss 5: Excellent.
4: Excellent.
3: Normal.
2: Slightly inferior.
1: Poor.

"Mixing of silica fine particles and cationic compounds"
When the silica fine particles A and the cationic compound are mixed, the two are mixed and dispersed, and then pulverized using a pressure-type homogenizer (trade name: Ultra High Pressure Type Homogenizer GM-1 manufactured by SMT) (pressurization). 500 kg / ^cm 2), an average secondary particle size of the silica in the dispersion, is processed (primary particle size to an average secondary particle size of the original fine silica particles remains 15 nm).

Reference Experimental Example 1
The following coating solution for undercoat layer was coated on a paper base material with an air knife coater and dried so as to be 10 g / m ² in dry weight. Next, the following coating liquid for a cast coating layer is coated 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 (moisture content based on the absolute dry amount of the coating layer). 150%) and pressed against a mirror-surface drum having a surface temperature of 90 ° C., dried, and released to obtain a glossy inkjet recording paper. The coating amount of the cast coating layer at this time was 4 g / m ² in terms of solid content weight.

[Coating liquid for undercoat layer] (solids concentration 17%, parts are parts by weight of solids)
80 parts of synthetic amorphous silica (Fine Seal X-45; manufactured by Tokuyama, average secondary particle diameter 4.5 μm, average primary particle diameter 15 nm), zeolite (Toyo Builder; manufactured by Tosoh, average particle diameter 1.5 μm) 20 Parts, a silyl-modified polyvinyl alcohol (R1130; manufactured by Kuraray Co., Ltd.), 20 parts, a composite emulsion of a styrene-2-methylhexyl acrylate copolymer having a glass transition point of 75 ° C. and colloidal silica having a particle diameter of 30 nm (the copolymer and colloidal silica are 40 parts by weight, 40 parts by weight, emulsion particle size: 80 nm) 40 parts, 2 parts of fluorescent dye (WhitexBPSH; manufactured by Sumitomo Chemical).

[Coating liquid for cast coating layer] (solid content: 12%, parts are by weight solids)
100 parts of silica fine particles A, 10 parts of diallyldimethylammonium chloride-acrylamide copolymer (cationic compound: manufactured by Nitto Boseki Co., trade name; PAS-J-81), cationic aqueous urethane resin (F-8564D; Daiichi Kogyo) Pharmaceutical, Tg = 73 ° C) 25 parts, stearamide 5 parts

Reference Experimental Example 2
Reference experiment example except that FineSeal X-37 (manufactured by Tokuyama, average secondary particle size 2.5 μm, average primary particle size 15 nm) was used instead of FineSeal X-45 as synthetic amorphous silica. In the same manner as in Example 1, a gloss type ink jet recording paper was obtained.

Reference experiment example 3
Reference experiment example except that Fine Seal X-12 (manufactured by Tokuyama, average secondary particle diameter 12.5 μm, average primary particle diameter 15 nm) was used as synthetic amorphous silica instead of Fine Seal X-45. In the same manner as in Example 1, a gloss type ink jet recording paper was obtained.

Reference experiment example 4
Reference experiment example except that FineSeal F-80 (manufactured by Tokuyama, average secondary particle size 1.5 μm, average primary particle size 15 nm) was used instead of FineSeal X-45 as synthetic amorphous silica. In the same manner as in Example 1, a gloss type ink jet recording paper was obtained.

  Table 2 summarizes the ink jet recording aptitude and blank gloss of the thus obtained ink jet recording paper. In addition, about the said evaluation, evaluation was performed by the following methods.

[Inkjet recording suitability]
Printing was performed using an inkjet printer BJC600J (manufactured by Canon Inc.).
(Uniformity of solid printing area)
The printing unevenness (shading unevenness) of a solid printing portion of a mixture of two colors of a cyan ink and a magenta ink was visually evaluated.
：: good level without printing unevenness
Δ: Printing unevenness is a little, and is a level that is somewhat problematic in practical use.
X: A level at which printing unevenness is remarkable and becomes a serious problem in practical use.

(Bleeding)
The degree of bleeding when the solid printing portions of the cyan ink and the magenta ink were printed with the boundary in contact with each other was visually evaluated.
◎: Good level without bleeding
：: Bleeding is slightly observed, but there is no practical problem.
Δ: Bleeding is noticeable, which is a practically problematic level.
X: A level at which bleeding is remarkable and becomes a serious problem in practical use.

(Dryness of ink)
The dryness of the ink was evaluated for the solid printing portion where two colors of the cyan ink and the magenta ink were mixed.
：: No stain at all even if touched with a finger immediately after printing.
Δ: Slightly stained when touched with a finger immediately after printing, but no practical problem.
X: Smear is noticeable when touched with a finger immediately after printing.
(Print density after inkjet recording)
The print density of the black solid print portion was measured by Macbeth RD-914.

(Glossiness)
According to JIS-P8142, 75 ° gloss of a blank portion was measured.
〔appearance〕
Roughness of the surface such as gloss unevenness and roughness is visually evaluated. Excellent: extremely excellent.
：: Excellent.
Δ: Slightly inferior, but no practical problem.
×: Extremely poor.