JP2006346908A - Manufacturing method of cast-coated paper, coating liquid for underlayer and inkjet cast-coated paper using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of an inkjet cast-coated paper, which is excellent in ink absorbency, surface gloss and image quality and in which no microcrack develops. <P>SOLUTION: In this manufacturing method of the cast-coated paper, an upperlayer is coated on an underlayer formed by a coating liquid including at least a pigment, a binder and polyhydric alcohols on a support and, while being under a moist state, brought into a pressingly contact with a heated solid mirror-finished surface so as to give gloss to the surface of the coated layer. Further, the coating liquid for an underlayer used for the manufacturing method and the obtained inkjet cast-coated paper are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet cast paper excellent in ink absorbability and free of microcracks, a lower layer coating liquid useful for efficiently producing the cast paper, and a method for producing the cast paper.

  Inkjet recording methods are used in a wide range of fields because they have low noise during recording, are easy to color, and can be recorded at high speeds. Since the ink absorbability and dryness are inferior and the image quality such as resolution is also inferior, special papers that have improved these have been proposed. In order to improve the color development and reproducibility of the ink, various kinds of paper such as amorphous silica have been proposed. Recording media coated with inorganic pigments are disclosed (Patent Documents 1 and 2). In recent years, technological development of ink jet recording media for obtaining high image quality comparable to silver halide photography has been progressing, but the cast coating method is widely known as a method for imparting such glossiness to the surface of the recording media. It has been.

  In the cast coating method, a coating liquid composition mainly composed of a pigment or an adhesive is coated on a base paper, and then pressed onto the surface of a heated drum that is mirror-finished while the coating layer is in a wet state. Wet cast method (direct method) to dry, exfoliate, and wet coating layer once dried or semi-dried to solidify, then wet plasticized with rewetting liquid, and crimped to mirror-finished heated drum 3 types of rewetting cast method to dry and peel, and gelled cast method (coagulation method) to make wet coating layer into a gel state by coagulation treatment, press dry onto mirror-finished heating drum, dry and peel Methods are generally known, and in any of these cast coating methods, the coating layer in a wet plasticized state is pressure-bonded to a mirror-finished heating drum and dried, and then the mirror surface is peeled off from the heating drum. It is common that you take.

These casting methods are said to be excellent in terms of productivity, and the surface of the recording medium obtained by the cast coating method is highly glossy and smooth, but the surface of the coating layer has a size of several microns or less. There are many small cracks in the form of cracks (hereinafter referred to as microcracks), and there is a problem that it is difficult to obtain a high-resolution image.
A method for producing an inkjet recording medium that does not generate the microcracks is disclosed in Patent Document 3, and a solution is achieved by including a (meth) acrylamide copolymer or a resin having a lactam group. Since an emulsion is not formed, the viscosity when added to the coating liquid tends to be high, and in order to perform a uniform and smooth coating, it is necessary to keep the content of the resin in the coating liquid low. Yes, the effect was limited.
More recently, sufficient ink absorptivity has been required for both pigment inks and dye inks. In that case, if a pigment having a relatively small particle size is used in the lower layer, printability may be improved. Known (Patent Document 4, Patent Document 5). However, these are not obtained by the cast coating method.
Patent Documents 6 and 7 disclose a technique relating to a cast coating method in which silica having a relatively small particle diameter is used as a lower layer. However, the absorbability of pigment ink and dye ink and the microscopic properties of the coating layer surface are disclosed. Crack prevention is not satisfactory.

JP-A-55-51583 JP-A-56-148585 JP 2000-218927 A JP 2000-37944 A International Publication No. 02/034541 Pamphlet Japanese Patent Laid-Open No. 7-89216 JP-A-7-89220

  The present invention relates to a lower layer coating solution that is excellent in ink absorbability, surface gloss, and image quality and does not generate microcracks, a method for producing cast paper using the coating solution as a lower layer, and a cast produced by the method. The purpose is to provide paper.

  As a result of various studies to solve the above problems, the present inventors applied an upper layer on a lower layer formed of a coating liquid containing at least a pigment, a binder, and a polyhydric alcohol on a support. A method for producing a cast paper, characterized in that the coated layer surface is glossed by press-bonding to a mirror-finished solid surface heated while being wet and the coating liquid solves the above-mentioned problem The present invention has been found to be effective.

That is, the present invention is as follows.
(1) A mirror-finished solid that is coated on a lower layer formed of a coating solution containing at least a pigment, a binder, and a polyhydric alcohol on a support and heated while it is wet. A method for producing cast paper, characterized in that the surface of the coated layer is pressure-bonded to give gloss to the surface of the coating layer.
(2) The method for producing cast paper as described in (1) above, wherein the binder is polyvinyl alcohol.

(3) The method for producing cast paper as described in (1) or (2) above, wherein the polyhydric alcohol is a plasticizer of polyvinyl alcohol.
(4) A coating solution for a lower layer used in the method for producing cast paper according to any one of (1) to (3) above.
(5) An inkjet cast paper produced by the cast paper production method according to any one of (1) to (3) above.

  According to the present invention, an undercoat coating liquid that is excellent in ink absorbability, surface gloss, and image quality and does not generate microcracks, a method for producing cast paper using the coating liquid as a lower layer, and an ink jet produced by the production method Cast paper was provided.

The present invention will be specifically described below.
Examples of the pigment used in the present invention include kaolin, deramikaolin, clay, aluminum hydroxide, satin white, heavy calcium carbonate, light calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, calcined kaolin, talc, colloidal silica, and dry type. Silica, wet silica, wet pulverized product of silica aggregates, porous inorganic fine particles described in WO 03/066799 pamphlet, WO 02/000550 pamphlet, zinc oxide, zinc carbonate, zinc sulfide, alumina, fine particles Mineral pigments such as alumina, diatomaceous earth, calcined diatomaceous earth, aluminum silicate, calcium silicate, magnesium silicate, magnesium oxide, magnesium carbonate, aluminosilicate, activated clay, bentonite, zeolite, sericite, lithopone, porous pigment and poly Styrene resins, urea resins, acrylic resins, melamine resins, benzoguanamine resins, other organic pigments.

When the pigment is an organic compound, for example, radical polymerization in an aqueous medium, anionic polymerization,
Conventionally known poly (meth) acrylate type, polyvinyl acetate type, vinyl acetate-acrylic type, ethylene vinyl acetate type, silicone type, polybutadiene type, styrene butadiene type, NBR type, polyvinyl chloride type, chlorine obtained by cationic polymerization, etc. Polypropylene-based, polyethylene-based, polystyrene-based, vinylidene chloride-based, polystyrene- (meth) acrylate-based, styrene-maleic anhydride-based copolymers, three-dimensional cross-linked resins, etc., silicone-modified acrylic, fluorine- Modified copolymers such as acrylic, acrylic silicone, and epoxy-acrylic are also included, and one or more of these can be contained. Here, the (meth) acrylate system is a simple description of a methacrylate system (or methacrylate system) or an acrylate system. In particular, an ink in which an organic polymer compound classified into a poly (meth) acrylate (acrylic polymer) and / or a polystyrene- (meth) acrylate (styrene-acrylic polymer) is finally obtained. It is preferably used from the viewpoints of transparency of the absorbing layer, light yellowing resistance, storage stability of the obtained cast paper, and the like.

  In the case of an organic polymer compound, the pigment is preferably obtained as a polymer emulsion, and is obtained by using a widely known polymer emulsion production technique. In addition to the method of dissolving the activator, emulsifying by adding the monomer components described later, adding a radical polymerization initiator and carrying out emulsion polymerization by a batch charging reaction, the above-mentioned co-polymerization is added to the reaction system by methods such as continuous dripping and divided addition. The method of supplying a polymerization component and a radical polymerization initiator to a reaction system is mentioned.

  As a monomer for obtaining a pigment in the case of an organic polymer compound, one or a combination of two or more ethylenically unsaturated monomers can be used. Specifically, (meth) acrylic acid ester , (Meth) acrylamide monomers, vinyl cyanides and the like. Examples of (meth) acrylic acid esters include (meth) acrylic acid alkyl esters having 1 to 18 carbon atoms in the alkyl part, carbons in the alkyl part. 1 to 18 (meth) acrylic acid hydroxyalkyl ester, 1 to 100 (poly) oxyethylene (meth) acrylate having 1 to 100 ethylene oxide groups, 1 to 100 (poly) propylene oxide groups (poly) Oxypropylene (meth) acrylate, (poly) oxyethylene diethylene glycol having 1 to 100 ethylene oxide groups Meth) acrylate.

  Specific examples of (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl part include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic. Examples include 2-ethylhexyl acid, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, dodecyl (meth) acrylate, and the like. Specific examples of the hydroxyalkyl ester of (meth) acrylic acid having 1 to 18 carbon atoms in the alkyl portion include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, (meth) acrylic acid 2 -Hydroxycyclohexyl, dodecyl (meth) acrylate, and the like.

  Specific examples of the (poly) oxyethylene (meth) acrylate having 1 to 100 ethylene oxide groups include (meth) acrylic acid ethylene glycol, methoxy (meth) acrylic acid ethylene glycol, (meth) acrylic acid diethylene glycol, Examples include methoxy (meth) acrylic acid diethylene glycol, (meth) acrylic acid tetraethylene glycol, and methoxy (meth) acrylic acid tetraethylene glycol. Specific examples of the (poly) oxypropylene (meth) acrylate having 1 to 100 propylene oxide groups include propylene glycol (meth) acrylate, propylene glycol methoxy (meth) acrylate, and dipropylene (meth) acrylate. Examples thereof include glycol, methoxy (meth) acrylic acid dipropylene glycol, (meth) acrylic acid tetrapropylene glycol, and methoxy (meth) acrylic acid tetrapropylene glycol.

  Specific examples of (poly) oxyethylene di (meth) acrylate having 1 to 100 ethylene oxide groups include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and methoxy (meth) acrylic acid. Examples include diethylene glycol and tetraethylene glycol di (meth) acrylate. Examples of (meth) acrylamide monomers include (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, and diacetone acrylamide. Examples of vinyl cyanides include: (Meth) acrylonitrile and the like. Specific examples other than the above include, for example, olefins such as ethylene, propylene and isobutylene, dienes such as butadiene, haloolefins such as vinyl chloride and vinylidene chloride, vinyl acetate, vinyl propionate, vinyl n-butyrate, Carboxylic acid vinyl esters such as vinyl benzoate, p-t-butyl vinyl benzoate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl versatate, vinyl laurate, etc. Carboxyl such as isopropenyl acetate and isopropenyl propionate Acid isopropenyl esters, ethyl vinyl ether, isobutyl vinyl ether, vinyl ethers such as cyclohexyl vinyl ether, styrene derivatives such as styrene and methyl styrene, aromatic vinyl compounds such as vinyl toluene, allyl acetate, allyl benzoate Allyl esters, allyl ethyl ether, allyl glycidyl ether, allyl phenyl ether and other allyl ethers, γ- (meth) acryloxypropyltrimethoxysilane, vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, vinyldimethylethoxysilane , Vinyldimethylmethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine, 4- (meth) acryloyloxy-1,2,2, 6,6-pentamethylpiperidine, perfluoromethyl (meth) acrylate, perfluoropropyl (meth) acrylate, perfluoropropylmethyl (meth) acrylate, vinyl pyrrolidone, trimethylolpropane tri (me Acrylate), glycidyl (meth) acrylate, 2,3-cyclohexene oxide (meth) acrylate, allyl (meth) acrylate, acid phosphooxyethyl methacrylate, 3-chloro-2-acid phosphooxypropyl methacrylate, Examples include methyl propane sulfonic acid acrylamide and divinyl benzene. Here, (meth) acryl is a simple description of methacryl (or methacryl) or acryl.

In the case of an organic polymer compound, the glass transition point of the pigment is preferably 50 to 150 ° C., more preferably 90 to 150 ° C. from the viewpoint of ink absorbability of the cast paper to be obtained.
As the lower layer pigment, colloidal silica, dry silica, wet silica, a wet pulverized product of silica aggregates, and porous inorganic fine particles are preferably used. Furthermore, in order to sufficiently absorb both the pigment ink and the dye ink, those having an average particle diameter of 3 μm or less are preferable, and further, the average particle diameter is preferably 300 nm or less.

  As the upper layer pigment, it is preferable to use colloidal silica, dry silica, the aforementioned porous inorganic fine particles, alumina sol, pseudoboehmite-based alumina, and γ-alumina, improving the image quality when printed on the resulting cast paper, and gloss Can be granted. As the colloidal silica, anionic colloidal silica, cationic colloidal silica obtained by a method of reacting a polyvalent metal compound such as aluminum ion, or a material whose surface is modified with a silane coupling agent is preferably used. As dry silica, vapor phase silica synthesized by burning silicon tetrachloride with hydrogen and oxygen is preferably used. The dry silica may be used as it is, but from the viewpoints of easy adjustment of the coating solution and stability of the coating solution viscosity over time, a product whose surface is modified with a silane coupling agent is preferably used. Those modified with a silane coupling agent having a group are more preferably used.

In addition, by using alumina sol, pseudoboehmite-based alumina, and γ-alumina fine particles, recording paper with higher gloss can be easily obtained, image quality when printed on cast paper is improved, and image water resistance is imparted. can do.
Moreover, when using polyvinyl alcohol as a binder, it is especially preferable to use dry silica. Polyvinyl alcohol has a hydroxyl group in its structural unit, but this hydroxyl group and the silanol group on the surface of the silica fine particle form a hydrogen bond, and it is easy to form a three-dimensional network structure in which the secondary particle of the silica fine particle is a chain unit. To do. By forming the three-dimensional network structure, a porous structure having a high porosity can be formed, and a coating layer having good ink absorbability can be obtained. Furthermore, the thickening due to cooling immediately after coating is also improved by the formation of hydrogen bonds between the hydroxyl groups of polyvinyl alcohol and the silanol groups on the surface of the silica fine particles.

The upper layer pigment used in the present invention may be used as primary particles or in a state in which secondary particles are formed. In addition, any particle diameter can be used for the pigment for the upper layer, but in order to obtain a cast paper having a smooth surface, those having a number average particle diameter of 10 μm or less are usually used, preferably those having a particle diameter of 1 μm or less. Is used. Furthermore, when producing cast paper for inkjet, the average particle diameter of primary particles is 200 nm or less for the purpose of increasing the optical density (color density) of the printed part after printing and obtaining a gloss similar to silver salt photography. Are preferably used, more preferably those having an average particle diameter of 100 nm or less, and still more preferably 50 nm or less.
The lower limit of the particle diameter of the pigment for the upper layer is not particularly limited, but an average particle diameter of about 3 nm or more is desirable from the viewpoint of pigment production efficiency.

  As the binder for the lower layer used in the present invention, for example, gelatin or gelatin derivatives, polyvinylpyrrolidone, pullulan, polyvinyl alcohol or derivatives thereof, chitins, chitosans, starch, polyethylene oxide which is an ether bond, polypropylene oxide, Polyethylene glycol, polyvinyl ether, water-soluble resins such as polyacrylamide, polyvinyl pyrrolidone, polyacrylate, maleic acid resin, alginate, and gelatin, which are resins having an amide group or amide bond, polyethylene glycol, carboxymethyl cellulose, hydroxyethyl cellulose Dextran, dextrin, polyacrylic acid and salts thereof, agar, κ-carrageenan, λ-carrageenan, ι-carrageenan, xanthine Ngam, locust bean gum, alginic acid, gum arabic, pullulan, casein, soy protein, synthetic starch and other starches, various starches such as starch and oxidized starch, JP-A-7-195826 and JP-A-7-9757 A polyalkylene oxide copolymer, a water-soluble polyvinyl butyral, or a vinyl monomer having a carboxyl group or a sulfonic acid group described in JP-A-62-245260, or by repeating these vinyl monomers. Polymers such as copolymers can be mentioned, but polyvinyl alcohol or polyvinyl alcohol derivatives are most preferably used.

  Polyvinyl alcohol and / or polyvinyl alcohol derivatives are not particularly limited, but as polyvinyl alcohol, polyvinyl alcohol having a saponification degree of 96% to 100% generally called fully saponified polyvinyl alcohol, and saponification generally called partially saponified polyvinyl alcohol Examples of the polyvinyl alcohol derivative include silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, mercapto group-containing polyvinyl alcohol, and keto group-containing polyvinyl alcohol.

The polyvinyl alcohol preferably used in the present invention preferably has an average degree of polymerization of 300 to 4000, and those having an average degree of polymerization of 1000 or more have good viscosity increase during coating, and the obtained coating It is preferable because the film strength of the layer is good. The saponification degree of polyvinyl alcohol is preferably 70 to 100%, particularly preferably 80 to 100%.

  A preferable addition amount of the binder is 5 to 100% by mass, more preferably 20 to 50% by mass with respect to 100% by mass of the pigment for the lower layer. If the added amount of the binder is less than 5% by mass, the strength of the lower layer cannot be said to be sufficient, and if it exceeds 100% by mass, the ink absorbability tends to decrease. Moreover, it is 5-50 mass% with respect to 100 mass parts of pigments for upper layers, More preferably, it is 10-30 mass%. If the added amount of the binder is less than 5% by mass, the strength of the upper layer cannot be said to be sufficient, and if it exceeds 50% by mass, the ink absorbability tends to decrease.

In the cast paper for inkjet of the present invention, the binder may be hardened with a hardener in order to obtain high strength of the coating layer.
The hardener is generally a compound having a group capable of reacting with the binder or a compound that promotes the reaction between different groups of the binder, and is appropriately selected depending on the kind of the binder.

Specific examples of the hardener include, for example, epoxy hardeners (diglycidyl ethyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-diglycidyl cyclohexane, N, N- Diglycidyl 4-glycidyloxyaniline, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, etc.), aldehyde hardeners (formaldehyde, glioxal, etc.), active halogen hardeners (2,4-dichloro-4-hydroxy-1, 3,5-s-triazine, etc.), active vinyl compounds (1,3,5-trisacryloyl-hexahydro-s-triazine, bisvinylsulfonylmethyl ether, etc.), borax, boric acid, borates (for example, orthoborate, InBO _3, ScBO _{3 YBO 3, LaBO 3, Mg 3} (BO 3) 2, Co 3 (BO 3) 2, diborate salts _{(e.g., Mg 2 B 2 O 5,} Co 2 B 2 O 5), metaborate (e.g., LiBO ₂ , Ca (BO ₂ ) ₂ , NaBO ₂ , KBO ₂ ), tetraborate (eg Na ₂ B ₄ O ₇ .10H ₂ O), pentaborate (eg KB ₅ O ₈ .4H ₂₎ O, Ca ₂ B ₆ O ₁₁ · 7H ₂ O, CsB ₅ O ₅ ), glyoxal, melamine / formaldehyde (for example, methylolmelamine, alkylated methylolmelamine), methylolurea, resol resin, polyisocyanate, aluminum alum, etc. It is done.

  When gelatin is used as the binder, the following compounds known as gelatin hardeners can be used as hardeners. For example, aldehyde compounds such as formaldehyde, glyoxal and glutaraldehyde, ketone compounds such as diacetyl and cyclopentanedione, bis (2-chloroethylurea) -2-hydroxy-4,6-dichloro-1,3,5- Active halogen compounds such as triazine, 2,4-dichloro-6-S-triazine sodium salt, divinylsulfonic acid, 1,3-vinylsulfonyl-2-propanol, N, N′-ethylenebis (vinylsulfonylacetamide) ), Active vinyl compounds such as 1,3,5-triacryloyl-hexahydro-S-triazine, N-methylol compounds such as dimethylolurea and methyloldimethylhydantoin, isocyanate compounds such as 1,6-hexamethylene diisocyanate, US Patent No. 3017280 , Aziridine compounds described in U.S. Pat. No. 2,983,611, carboximide compounds described in U.S. Pat. No. 3,100,704, epoxy compounds such as glycerol triglycidyl ether, 1,6-hexamethylene-N, N Ethyleneimino compounds such as' -bisethyleneurea, halogenated carboxaldehyde compounds such as mucochloric acid and mucophenoxycyclolic acid, dioxane compounds such as 2,3-dihydroxydioxane, chromium alum, potash alum, zirconium sulfate And chromium acetate. In addition, the said hardening agent may be single 1 type, or may combine 2 or more types.

When polyvinyl alcohol is used as a particularly preferred binder, at least one hardener selected from boric acid and its salts and / or epoxy hardeners is used from the viewpoint of the coating strength of the coating layer. Of these, boric acid and / or borax are most preferable in view of the thickening (gelation) of the coating solution immediately after coating.
The amount of boric acid or its salt used is selected from a wide range depending on the concentration, pH, etc. of other components in the coating liquid, such as inorganic fine particles, polyvinyl alcohol or polyvinyl alcohol derivatives, but is approximately 1 with respect to polyvinyl alcohol. It is preferable that it is -60 mass%, and 5-40 mass% is still more preferable.

  The above hardener is preferably used by dissolving the hardener in water and / or an organic solvent from the viewpoint of ease of adjustment of the coating liquid, stability, and the like. The concentration of the hardener in the hardener solution is preferably 0.05 to 20% by mass, particularly preferably 1 to 10% by mass. As a solvent constituting the hardener solution, water is generally used, and an aqueous mixed solvent containing an organic solvent miscible with water may be used. The organic solvent can be arbitrarily used as long as it can dissolve the hardener, for example, alcohols such as methanol, ethanol, isopropyl alcohol and glycerin; ketones such as acetone and methyl ethyl ketone; methyl acetate and ethyl acetate. An ester such as toluene; an aromatic solvent such as toluene; an ether such as tetrahydrofuran; and a halogenated carbon-based solvent such as dichloromethane;

  In the present invention, polyhydric alcohols are aliphatic or alicyclic compounds containing two or more hydroxyl groups and derivatives thereof. Specifically, ethylene glycol derivatives such as ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol isopropyl ether, ethylene glycol monobutyl ether, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, etc. Diethylene glycol derivatives, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, and other triethylene glycol derivatives, polyethylene glycol, propylene glycol, propylene glycol monomethyl ether, propylene Propylene glycol derivatives such as ethylene glycol monoethyl ether, propylene glycol monobutyl ether, polypropylene glycol, trimethylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,5 pentanediol, Examples include hexylene glycol, octylene glycol, glycerol, glycerol monoacetate, glycerol diacetate, glycerol triacetate, glycerol derivatives such as glycerol monobutyrate, 1,2,6-hexanetriol, and the like.

  The polyhydric alcohols play a role of forming a uniform lower layer by suppressing the aggregation of the pigment and the binder. From such a viewpoint, the polyhydric alcohols preferably have excellent compatibility with the binder. Particularly preferred are polyhydric alcohols which can function as plasticizers for polyvinyl alcohol. Examples of polyhydric alcohols that function as plasticizers for polyvinyl alcohol include ethylene glycol, trimethylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, propylene glycol, glycerin, and diethylene glycol. Triethylene glycol and the like are preferably used. These polyhydric alcohols can be used alone or in combination of two or more.

It is preferable to add 0.5 mass%-200 mass% of polyhydric alcohol with respect to the pigment for lower layers. More preferably, it is 3 mass%-20 mass%. If it is less than 0.5% by mass, the pigment aggregation suppressing effect cannot be said to be sufficient, and if it exceeds 200% by mass, the drying process may be prolonged. It is speculated that suppressing the aggregation of the pigment in the lower layer in this way promotes uniform void formation in the lower layer, suppresses non-uniform drying when forming the upper layer, and consequently suppresses microcracks. . In addition, the addition of polyhydric alcohols improves the wettability of the lower layer, and even in inks with relatively poor absorbability, such as pigment ink, the ink solvent quickly penetrates from the upper layer to the lower layer, absorbing the pigment ink. It is thought that it does not inhibit sex.

  In the present invention, when producing cast paper for inkjet, it is preferable that at least one of the coating layers contains a cationic polymer. By containing the cationic polymer, the water resistance of the printed portion is improved. As the cationic polymer, any cationic polymer can be used, and at least one of primary amine, secondary amine, tertiary amine substituents and salts thereof, and quaternary ammonium salt substituents can be used. The inclusion is preferably used. Examples include dimethyldiallylammonium chloride polymer, dimethyldiallylammonium chloride-acrylamide copolymer, alkylamine polymer, polyamine dicyan polymer, polyallylamine hydrochloride, and the like. The cationic polymer preferably has a weight average molecular weight of 1,000 to 200,000. The amount of the cationic polymer used is preferably 0.1 to 200 parts by weight, more preferably 1 to 100 parts by weight, and still more preferably 5 to 100 parts by weight with respect to 100 parts by weight of the polymer emulsion. 20 parts by mass. Furthermore, it is preferable to use a cationic polymer having only a quaternary ammonium substituent from the viewpoint of the degree of fading that occurs when the printed material is exposed to sunlight or fluorescent light.

  In the present invention, when producing cast paper for inkjet, at least one of the coating layers contains one or more of an ultraviolet absorber, a hindered amine light stabilizer, a singlet oxygen quencher, an antioxidant and the like. It is preferable. By containing this substance, the light resistance of the printed part is improved. Although it does not specifically limit as a ultraviolet absorber, A benzotriazole type, a benzophenone type, a titanium oxide, a cerium oxide, a zinc oxide, etc. are used preferably. Although it does not specifically limit as a hindered amine light stabilizer, N atom of a piperidine ring is N-R (R is a hydrogen atom, an alkyl group, a benzyl group, an allyl group, an acetyl group, an alkoxyl group, a cyclohexyl group, a benzyloxy group, etc. ) Is preferably used. As the singlet oxygen quencher, an aniline derivative, an organic nickel system, a spirochroman system, or a spiroindane system is preferably used. As the antioxidant, phenol, hydroquinone, organic sulfur, phosphorus, and amine are preferably used. The amount of the substance used is preferably 0.0001 to 5 parts by mass with respect to 100 parts by mass of the ink absorbing layer in the coating layer containing the substance.

  In the present invention, when producing a cast paper for inkjet, it is preferable that at least one of the coating layers contains an alkaline earth metal compound. Light resistance improves by containing an alkaline-earth metal compound. As alkaline earth metal compounds, oxides, halides and hydroxides of magnesium, calcium and barium are preferably used. As a method of incorporating an alkaline earth metal compound into the ink absorption layer, it may be added to the coating liquid, or after forming the ink absorption layer, the ink absorption layer is impregnated with an aqueous solution of an alkaline earth metal compound. May be. The content of the alkaline earth metal compound is preferably 0.5 to 5 parts by mass in terms of oxide with respect to 100 parts by mass of the solid content in the ink absorption layer in the ink absorption layer containing the alkaline earth metal compound. .

In the present invention, it is preferable that the coating layer contains a thiocyanic acid compound because ozone resistance and light resistance can be improved. Examples of the thiocyanate compound include ammonium thiocyanate, zinc thiocyanate, calcium thiocyanate, potassium thiocyanate, sodium thiocyanate, magnesium thiocyanate, aluminum thiocyanate, lithium thiocyanate, silver thiocyanate, chloromethyl thiocyanate, and thiocyanate. Cobalt, copper thiocyanate, lead thiocyanate, barium thiocyanate, benzyl thiocyanate, and the like, and ammonium thiocyanate, zinc thiocyanate, and calcium thiocyanate are preferable in terms of further improving ozone resistance and light resistance. Particularly preferred are ammonium acid and zinc thiocyanate.

  As content of said thiocyanic acid compound, 0.3-10 mass% is preferable with respect to the total solid of a coating layer, and 0.5-8 mass% is further more preferable. When the content is in the range of 0.3 to 10% by mass, it is preferable in terms of ozone resistance, water resistance, and aging blur (a phenomenon in which bleeding occurs due to the printing portion being passed for a long time). Moreover, the said thiocyanic acid compound may be used individually by 1 type, and may use 2 or more types together.

In the recording medium coating liquid of the present invention, a pigment dispersant, a thickener, a flow regulator, an antifoaming agent, a defoaming agent, a release agent, a foaming agent, a colorant, and the like are blended as necessary. can do.
Lower coating liquid of the present invention, the solid content concentration was adjusted to about 5 to 65 wt%, 1 to 30 g / m ² dry weight on the support of the above, preferably 2 to 20 g / m ² It is obtained by coating and drying with various publicly known coating apparatuses such as a blade coater, an air knife coater, a roll coater, a brush coater, a chamber coater, a bar coater, and a gravure coater. Furthermore, if necessary, after the recording layer is dried, a smoothing process such as super calendering or brushing can be performed.

  Moreover, it is preferable to contain the above-mentioned cationic polymer in a lower layer coating liquid. By containing the cationic polymer, the water resistance of the printed portion is improved. The content of the cationic polymer is preferably 1 to 30 parts by mass, more preferably 100 parts by mass with respect to 100 parts by mass of the pigment in the undercoat layer, from the viewpoint of the above-described addition effect and the water resistance and ink absorbability of the undercoat layer itself. Is 3 to 20 parts by mass.

The upper layer coating liquid of the present invention is adjusted to a solid content concentration of about 5 to 65% by mass, and ^{2 to} 30 g / m ² , preferably 5 in terms of dry weight, from the viewpoint of surface gloss and occurrence of powder falling off of the ink absorbing layer. It is preferable to perform coating by a coating method described later so as to be ˜20 g / m ² .
As means for coating on the lower layer, various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters, curtain flow coaters, gate roll coaters, short dwell coaters, extrusion die coaters, size presses, sprays, etc. Various devices can be used on-machine or off-machine.

  In forming a plurality of coating layers on a support, simultaneous multilayer coating can be performed. The simultaneous multilayer coating can be performed, for example, by a coating method using an extrusion die coater or a curtain flow coater. An extrusion die coater is more preferable for the purpose of avoiding mixing or coalescence of a plurality of coating layers. When using an extrusion die coater, a plurality of coating solutions discharged at the same time are layered near the extrusion die coater discharge port, i.e., just before moving onto the support, and in that state, a multilayer coating is applied on the support. Is done. When performing the simultaneous multi-layer coating, in order to avoid mixing of a plurality of coating liquids, a barrier layer liquid (intermediate layer liquid) may be interposed between the coating layers and the coating layers simultaneously. it can. The barrier layer solution can be selected without particular limitation as long as it is difficult to mix with the upper and lower coating layers, but a liquid having thixotropic properties is preferably used. Examples of the liquid preferably used include aqueous solutions of polymers such as hydroxypropylmethylcellulose, methylcellulose, hydroxyethylmethylcellulose, polyvinylpyrrolidone and gelatin.

The support used in the present invention may be transparent or opaque as long as it has air permeability. In the present invention, for example, high-quality paper, photographic paper base paper, drawing paper, image paper, art paper, coated paper, cast paper, kraft paper, and the like, non-woven fabrics, and the like can be used as appropriate. From the viewpoint of recording paper productivity, the air permeability of the support measured in accordance with JIS-P-8117 is preferably 1,000 seconds / 100 ml or less, more preferably 500 seconds / 100 ml or less. Further, if the air permeability is too low, it can be easily damaged in actual use of the obtained recording medium.

Various back coat layers can be coated on the support in the present invention for antistatic properties, transport properties, anticurling properties, and the like. The backcoat layer can contain an appropriate combination of inorganic antistatic agent, organic antistatic agent, latex, curing agent, pigment, surfactant and the like.
Further, regarding the thickness of the support, a paper having good surface smoothness, such as applying pressure on a paper during or after paper making and compressing it, is preferable, and its basis weight is 30 to 450 g / m ^2. preferable.

  The method of performing the cast finish in the present invention is a method in which, when the coating layer is in a wet state, the coating layer is pressed onto a heated mirror-finished solid surface and dried, and then peeled off from the solid surface to copy the mirror surface. This is generally called the cast method. The casting method is roughly classified into a wet casting method (direct method), a gelled casting method (solidification method), and a rewet casting method (rewetting method). The direct method is a method in which a coating solution is applied and then pressed onto a mirror-finished solid surface heated in an undried state (wet state) and dried. The solidification method is a method in which the coating layer composition is acidified. This is a method of coagulating with a solution, an alkaline solution or the like, and pressing it onto a heated mirror-finished solid surface. The solidification method includes a thermal solidification method in which the composition is irradiated with infrared rays to solidify the surface. The rewet method is a method in which a coating liquid is applied and dried, and then the coating layer composition is rewet with a liquid mainly composed of water, and is pressed onto a heated mirror-finished solid surface and dried. is there. In the present invention, any casting method may be used as necessary, but a direct method or a re-wetting method is preferable from the viewpoints of homogeneity inside the obtained coating layer and in-plane homogeneity of ink absorption, The direct method is most preferable from the viewpoint of productivity.

In the present invention, the mirror-finished solid material used for the cast finish includes, for example, metals such as stainless steel, glass, polyacryl, polyethylene terephthalate, silicone resin, fluororesin, etc., but metals such as stainless steel Is the most excellent and presently preferred from the viewpoint of surface smoothness, and preferred shapes are cylindrical, flat, etc., but cylindrical is most preferred.
As means for drying the coating layer, known drying means such as a hot air dryer, a steam heating dryer, a far-infrared dryer and the like can be used. A hot air dryer is preferably used, and examples thereof include a drum dryer, an air cap dryer, an air foil dryer, an air conditioner dryer, and combinations thereof. The drying temperature varies depending on the type of dryer, but the temperature inside the dryer is 50 to 200 ° C, preferably 100 to 150 ° C.

The ink-jet cast paper of the present invention is useful for recording using an ink composition containing a water-soluble dye, an oil-soluble dye, an aqueous pigment, an oily pigment and the like. Examples of the recording method include an ink jet recording method in which printing is performed by ejecting fine droplets of the ink composition to attach the ink composition to the surface of the recording medium, and printing is performed by coloring the ink composition by heating. Examples include thermal recording, gravure printing, offset printing, and other various printing methods, recording with a writing instrument such as a pen, and the like. In particular, the cast paper of the present invention is preferably used for printing by an inkjet recording method.
That is, the present invention is excellent in ink absorptivity, surface gloss, and image quality, and does not generate microcracks, and further, a cast paper manufacturing method using the coating solution as a lower layer, and the manufacturing method. Concerning cast paper.

Hereinafter, the present invention will be described more specifically based on examples and the like, but the present invention is not limited to these examples and the like.
In the following Examples and Comparative Examples, “parts” and “%” mean “parts by mass” and “% by mass”.

The average particle diameter by the dynamic light scattering method was measured using “Microtrac UPA-9230” manufactured by Nikkiso Co., Ltd.
The ink absorption during printing is sensory using a commercially available inkjet printer using dye ink (Seiko Epson; PM-G800) and a commercially available inkjet printer using pigment ink (Seiko Epson; PX-V600). Evaluated. The evaluation result was evaluated by a 10-level evaluation. The extremely good result was 10, the good result was 8, the slightly good result was 6, the slightly inferior result was 2, the inferior result was 2, and the extremely inferior result was 1.

Micro-cracks on the cast paper surface were observed with a digital microscope (manufactured by Scalar; DG-2), magnified 200 times and evaluated on a 10-point scale. Ten very good results with almost no micro-cracks were obtained. 8. A slightly good result was 6, a slightly inferior result was 4, an inferior result was 2, and a very inferior result was 1.
The gloss of cast paper was evaluated sensuously by looking at the reflection of fluorescent light. The evaluation results were evaluated on a 10-point scale, with 10 being a very good result, 8 being a good result, 6 being a slightly good result, 4 being a slightly inferior result, 2 being a poor result, and 1 being a very poor result.

(Preparation Example 1)
Water is added to dry silica (trade name: Aerosil A50, manufactured by Nippon Aerosil Co., Ltd., hereinafter referred to as “A50”) so as to have a solid content of 15%, and dispersed using an ultrasonic disperser. 1 was obtained.

(Preparation Example 2)
Distilled water is mixed with a sodium silicate solution having a SiO ₂ concentration of 30% by mass and a SiO ₂ / Na ₂ O molar ratio of 3.1 (manufactured by Tokuyama Corp., No. 3 sodium silicate), and a SiO ₂ concentration of 4.0% by mass. A dilute aqueous sodium silicate solution was prepared. This aqueous solution was passed through a column filled with a hydrogen-type cation exchange resin (Diaion SK-1B, manufactured by Mitsubishi Chemical Corporation) to prepare an active silicic acid aqueous solution. The obtained active silicic acid aqueous solution had a SiO ₂ concentration of 4.0% by mass and a pH of 2.9.
In a glass reaction vessel, 500 g of distilled water was heated to 100 ° C. While maintaining the hot water at 100 ° C., a total of 660 g of the above active silicic acid aqueous solution was added at a rate of 2 g / min.
The reaction solution was a semi-gelled suspension that was viscous and translucent as a whole.

An amount of 6.28 g of trimethoxymethylsilane corresponding to 23.8% by mass of SiO ₂ contained in this dispersion was added all at once, and the mixture was kept at 100 ° C. for 30 minutes with stirring to prepare a seed solution. The seed particles had a specific surface area of 810 m ² / g and a pore volume of 0.5 ml / g. To the seed solution, 0.030 mol of potassium hydroxide was added and stabilized, and the mixture was heated to 100 ° C. A total of 2480 g of the above active silicic acid aqueous solution was added to the seed solution at a rate of 2 g / min. After the addition of activated silicic acid was completed, the solution was kept as it was at 100 ° C. and heated to reflux for 6 hours to obtain a silica fine particle aggregate suspension.
The pH of the silica fine particle aggregate suspension was 9.7, and white silica aggregates settled when left standing. The above-mentioned silica fine particle aggregate suspension is treated twice at a treatment pressure of 1500 kg / m ² using an ultra-high pressure homogenizer [manufactured by Mizuho Kogyo Co., Ltd., Microfluidizer M110-E / H type] to disperse colloidal silica. Liquid 2 was prepared to 20%.
The average particle size of the silica dispersion 2 was about 200 nm.

(Preparation Example 3)
Water was added to wet silica (trade name: Fine Seal X37B, manufactured by Tokuyama Soda Co., Ltd., average agglomerated particle size 3.7 μm, hereinafter referred to as “X37B”) to a solid content of 15%, and an ultrasonic disperser To obtain silica dispersion 3.

(Preparation Example 4)
Commercially available dry silica (trade name: Aerosil A200, manufactured by Nippon Aerosil Co., Ltd., hereinafter referred to as “A200”) was dispersed using an ultrasonic disperser to prepare a 15% dispersion. 10 parts of diallyldimethylammonium chloride-acrylamide copolymer (trade name: PAS-J-81, manufactured by Nitto Boseki Co., Ltd.) was added as a cationic compound to the dispersion, and again using an ultrasonic disperser. Dispersion was made with water so that a 10% dispersion was obtained, and silica dispersion 4 was obtained.

(Preparation Example 5)
Ion exchange water 1200 g and isopropyl alcohol 900 g were charged into a 3 l reactor and heated to 75 ° C. 408 g of aluminum isopropoxide was added, and hydrolysis was performed at 75 ° C. for 24 hours and then at 95 ° C. for 10 hours. After hydrolysis, 24 g of nitric acid was added and stirred at 95 ° C. for 48 hours. Next, it was concentrated so that the solid content concentration was 15% by mass to obtain a dispersion of white fine particle alumina hydrate. When this sol was dried at room temperature and measured for X-ray diffraction, it showed a pseudo-boehmite structure. Further, when the average particle diameter was measured with a transmission electron microscope, it was 30 nm and was a plate-like fine particle alumina hydrate having an aspect ratio of 6.0. Water was added to the alumina hydrate, and a 10% alumina dispersion 5 was obtained using an ultrasonic disperser.

[Example 1]
5% aqueous solution of partially suspended polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA235: trade name), 3% boric acid aqueous solution, glycerin A50 / PVA235 / boric acid / glycerin in silica dispersion 1 obtained in Preparation Example 1 = 100/30/4/5 (dry mass ratio), and then coated with a bar coater on one side of 190 g / m ² base paper (Zita Snow Kona Snow 190: trade name) It dried and the lower layer was obtained. The coating amount at this time was 10 g / m ² in terms of dry mass.

Next, to the silica dispersion 4 obtained in Preparation Example 4, A200 / PVA235 / boric acid = 100/20/4 (dry mass ratio) was added and mixed at 60 ° C. to prepare a coating liquid 1 did.
On the lower layer, after applying the 60 ° C. coating solution with a bar coater heated to 60 ° C., the coating layer is wet and the surface temperature is 100 ° C. The film was pressure-bonded at a pressure of 100 kg / cm, dried and then released to obtain cast paper. The coating amount of the coating liquid 1 at this time was 10 g / m ² in terms of dry mass. The evaluation results of this ink-jet cast paper are shown in Table 1.

[Example 2]
A cast paper was obtained in the same manner as in Example 1 except that propylene glycol was used instead of glycerin in Example 1. The evaluation results of this ink-jet cast paper are shown in Table 1.
[Example 3]
Cast paper was obtained in the same manner as in Example 1 except that the silica dispersion 2 obtained in Preparation Example 2 was used instead of the dispersion 1 in Example 1. The evaluation results of this ink-jet cast paper are shown in Table 1.

[Example 4]
A cast paper was obtained in the same manner as in Example 1 except that the alumina dispersion 5 obtained in Preparation Example 5 was used instead of the dispersion 4 in Example 1. The evaluation results of this ink-jet cast paper are shown in Table 1.
[Example 5]
A cast paper was obtained in the same manner as in Example 1 except that the silica dispersion 3 obtained in Preparation Example 3 was used instead of the dispersion 1 in Example 1. The evaluation results of this ink-jet cast paper are shown in Table 1.

[Comparative Example 1]
A cast paper was obtained in the same manner as in Example 1 except that glycerin in Example 1 was not added. The evaluation results of this ink-jet cast paper are shown in Table 1.
[Comparative Example 2]
Cast paper was obtained in the same manner as in Comparative Example 1 except that the silica dispersion 3 obtained in Preparation Example 3 was used instead of the dispersion 1 in Comparative Example 1. The evaluation results of this ink-jet cast paper are shown in Table 1.

  According to the present invention, it is possible to efficiently produce an ink-jet cast paper that does not generate microcracks excellent in ink absorbability, surface gloss, and image quality, and its industrial utility value is extremely large.

Claims (5)

  The upper layer is coated on the lower layer formed of a coating solution containing at least pigments, binders, and polyhydric alcohols on the support, and pressed onto a mirror-finished solid surface heated while wet. And providing a gloss to the surface of the coating layer.   The method for producing cast paper according to claim 1, wherein the binder is polyvinyl alcohol.   The method for producing cast paper according to claim 1 or 2, wherein the polyhydric alcohol is a plasticizer of polyvinyl alcohol.   It is used for the manufacturing method of the cast paper as described in any one of Claims 1-3, The coating liquid for lower layers characterized by the above-mentioned.   An ink-jet cast paper produced by the method for producing a cast paper according to any one of claims 1 to 3.