JP2007268923A - Manufacturing process of inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining an inkjet recording medium which raises no peeling of powder omission at the time of cutting and a coating layer when bending especially by a cutter and has a good printability and a high gloss in relation with a high gloss inkjet recording medium. <P>SOLUTION: An upper layer and an underlayer are prepared at least on a support of gas permeability. In the inkjet recording medium which carries out cast processing, an underlayer containing an absorptivity inorganic pigment and a latex (A) is prepared on the support. After the coating liquid containing a colloidal silica and a latex (B) is applied and making an underlayer absorb, an upper layer containing a submicron pigment and a polyvinylalcohol is provided and carries out the cast processing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a high-gloss ink-jet recording medium, and in particular, a high-gloss ink-jet recording medium having good printability and no peeling of a coating layer when the ink-jet recording medium is cut by a cutter or bent. About.

  In recent years, the technology of inkjet printers has advanced rapidly, and the fields of use have expanded such as substitution of silver salt photographic printing paper, printing proofing, label printing, and on-demand printing. Along with this, it is also required that inkjet recording media be handled in the same way as silver salt photographic printing paper and offset printed matter, and the coating layer does not peel off or fall off when cut or bent with a cutter. It is demanded.

  As a means for solving such a problem, as exemplified in Patent Document 1, it has been proposed to apply an overcoat containing a urethane resin after applying an ink receiving layer. Although this method can prevent powder falling off when the surface of the ink jet recording medium is rubbed, the inventors of the present invention have verified that powder falling off or coating when the ink jet recording medium is cut or bent with a cutter. The peeling of the layer could not be prevented. In addition, there is a problem that the ink absorbability decreases when the coating amount of the overcoat increases.

In Patent Document 2, an ink jet recording medium in which one or more under layers containing a pigment and a binder are provided, and one or more ink receiving layers containing the pigment and the binder are provided on the surface of the under layer. It has been proposed to prevent powder falling by selecting the particle size. However, as a result of verification by the proposer of the present invention, it was not possible to sufficiently prevent peeling of the coating layer when the inkjet recording medium was cut or bent with a cutter. Further, when the amount of the binder is increased in order to obtain a sufficient coating layer strength, there is a problem that the ink absorbability is lowered.
JP 9-156206 A JP 2005-288700 A

  An object of the present invention is to provide a high-gloss inkjet recording medium that prevents powder falling off when cut with a cutter, which has been difficult to realize in the past, and peeling off of a coating layer when folded, and also has good ink absorbability. It is to provide.

  In an ink jet recording medium in which at least an upper layer and a lower layer are provided on a gas-permeable support and cast, a lower layer containing a water-absorbing inorganic pigment and latex (A) is provided on the support, and colloidal silica and latex (B). After coating with a coating liquid containing lysine and absorbing it in the lower layer, with an ink jet recording medium provided with an upper layer containing a submicron pigment and polyvinyl alcohol, when powdered or bent when cut with a cutter, etc. Thus, it is possible to produce a high-gloss ink-jet recording medium having no ink peeling and good ink absorbability.

  Furthermore, by using latex resin as the latex (B), peeling of the coating layer due to powder falling and bending of the coating layer was further improved.

  Furthermore, by containing boric acid or a salt thereof in the coating liquid containing colloidal silica and latex (B), a higher gloss surface quality could be obtained.

  Furthermore, by including a penetrating agent in the coating liquid containing colloidal silica and latex (B), powder falling and peeling of the coating layer could be further improved.

  The present invention provides a high-gloss inkjet recording medium that prevents powder falling off when cut with a cutter, which has been difficult to realize in the past, and prevents the coating layer from peeling off when folded, and also has good ink absorptivity. I was able to do it.

  In the present invention, paper is mainly used as the air-permeable support, but non-woven fabrics, plastic films, and the like can also be used.

  In the present invention, the cast process is a process of transferring the mirror surface shape to the surface of the coating layer by pressing the wet coating layer onto the heated mirror surface, and drying and removing moisture to give the recording medium a gloss. Say. The apparatus used for the casting process (casting apparatus) is usually an apparatus that continuously presses the coated paper onto the surface of the cylinder whose surface is chrome-plated using an elastic roll. You may use the apparatus of the other structure which has. As a method of casting treatment used in producing the ink jet recording medium of the present invention, a so-called rewetting method in which each coating liquid is applied, dried and then rehydrated, and then pressure-bonded to the mirror surface of the casting apparatus, or The so-called direct method can be used in which the coating liquid of each layer is applied to the mirror surface of the casting apparatus without being dried after coating, but is not limited thereto.

  The water-absorbing inorganic pigment used in the ink jet recording medium of the present invention and the water-absorbing inorganic pigment used in the lower layer containing latex are water absorption instead of linseed oil, and a method for testing the oil absorption determined in JIS K 5101 Means an inorganic pigment in which 100 mL or more of water is used per 100 g by the end point, for example, heavy calcium carbonate, light calcium carbonate, wet synthetic silica, diatomaceous earth, silica Calcium acid, talc, magnesium hydroxide, halloysite, activated clay, acid clay, hydrotalcite, alumina hydrate, aluminum hydroxide, bentonite clay, zeolite, kaolin, calcined kaolin, gypsum, titanium oxide, barium sulfate, etc. be able to. These pigments may be used alone or in combination of two or more.

  Among such water-absorbing inorganic pigments, wet synthetic silica is particularly preferably used because an inkjet recording medium having good ink absorbability can be obtained even with a small coating amount. In the present invention, wet synthetic silica refers to porous silicon dioxide obtained by mixing a silicate such as sodium silicate and an acid such as sulfuric acid, followed by steps such as washing, aging and grinding. As the production method, a precipitation method and a gel method are known, and any of them can be preferably used for the lower layer coating liquid of the present invention.

  The oil absorption amount of the wet synthetic silica used in the lower layer of the present invention is preferably higher from the viewpoint of ink absorbability, but if the oil absorption amount is too high, the strength of the coating layer may be lowered. Specifically, the oil absorption amount of the wet synthetic silica used for the lower layer of the present invention is preferably 1 to 5 mL / g, and more preferably 2 to 4 mL / g. In addition, if the particle size of the wet synthetic silica used in the lower layer of the present invention is too small, the viscosity of the coating liquid may increase and the coating operation may become difficult. It may be difficult to do. Specifically, the particle size of wet synthetic silica used for the lower layer of the present invention, measured by the Marvin method, is preferably 2 to 20 μm, and more preferably 3 to 15 μm.

It is preferable to add boric acid or a salt thereof to the lower layer of the present invention because the effect of increasing the strength and gloss of the layer containing the submicron pigment and polyvinyl alcohol can be obtained. The amount added depends on the amount of boric acid or its salt added to the other layers and the pH of the coating solution, but if the total amount added to each layer is too small, cracks will occur in the upper layer after drying. The gloss may decrease, and if it is too much, the strength of the coating layer may decrease. Therefore, the water-absorbing inorganic pigment is converted to H ₃ BO ₃ on the basis of the boron atom and is 0.2 to 10 It is preferable to set it as the mass%, and it is more preferable to set it as 0.4-5 mass%.

In the present invention, it is preferable that colloidal silica is contained in the lower layer because an ink jet recording medium having excellent ink absorbability can be obtained. In the present invention, colloidal silica is a method in which an acid such as sulfuric acid is allowed to act on an aqueous silicate solution such as sodium silicate, or a metal ion is removed by a cation exchange resin and then a process such as aging is performed. It is an aqueous dispersion of a silicic acid polymerized body to be produced, and is usually composed of spherical silicic acid particles having a specific surface area of 15 to 700 m ² / g by BET method.

When colloidal silica has a specific surface area that is too small, gloss after casting may be difficult to develop, and when a specific surface area that is too large is used, the effect of improving ink absorbability is not sufficient. Therefore, those having a specific surface area of 50 to 500 m ² / g by the BET method are preferably used, and those having a specific surface area of 100 to 350 m ² / g are more preferably used. Further, if the addition amount is too small, the effect of improving the ink absorbability may not be sufficient, and if it is too large, the gloss after the cast treatment may be difficult to express. It is preferable to set it as the mass%, and it is more preferable to set it as 15-60 mass%.

  The latex (A) contained in the lower layer of the present invention refers to a liquid material in which a substantially water-insoluble thermoplastic polymer compound is dispersed in water, and is water-soluble in that it does not substantially dissolve in hot water after drying. It is distinguished from an aqueous solution of a functional polymer compound. Examples thereof include vinyl acetate polymer, ethylene-vinyl acetate copolymer, (meth) acrylic acid ester polymer, styrene- (meth) acrylic acid ester copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene. Copolymers, isoprene copolymers, chloroprene copolymers, urethane polymers, copolymers in which two or more of the monomers constituting these polymers are combined in a random, graft or block manner, etc. And an aqueous dispersion of the synthetic polymer compound, natural rubber latex, and the like. These latexes may be used alone or in combination of two or more.

  In the present invention, if the content of the latex (A) in the lower layer is too small, the resulting recording medium may not have sufficient mechanical strength. Since the subsequent gloss may not be sufficiently obtained, the mass ratio of latex / (water-absorbing inorganic pigment + colloidal silica) is preferably 10/100 to 80/100, and 20/100 to 60/100. More preferably.

  A water-soluble polymer compound such as a vinylpyrrolidone polymer, a (meth) acrylic acid polymer, or a (meth) acrylamide polymer can be added to the lower layer of the present invention to such an extent that the effects of the present invention are not impaired. However, it is preferable that the water-soluble polymer compound having high crystallinity such as polyvinyl alcohol is not substantially contained since the gloss of the ink jet recording medium obtained after the cast treatment is remarkably lowered.

  The latex used in the coating liquid containing colloidal silica and latex (B) of the present invention (hereinafter referred to as latex (B) -containing coating liquid) is the same as that contained in the lower layer, and the latex is used alone. Or two or more types may be used in combination. As the addition amount of latex (B) contained in the latex (B) -containing coating solution, if it is too small, the effect of preventing powder falling off when cutting with a cutter or film peeling when folded may not be expressed, If the amount is too large, ink absorbability may be insufficient, or gloss after casting may not be sufficiently obtained. For this reason, the addition amount of the latex (B) contained in the latex (B) -containing coating liquid is such that the mass ratio of latex / colloidal silica to the non-volatile content of the colloidal silica contained in the latex (B) -containing coating liquid is 10 / It is preferable that it is 100-70 / 100, and 15 / 100-50 / 100 is more preferable.

  Water-soluble polymer compounds such as vinylpyrrolidone polymer, (meth) acrylic acid polymer and (meth) acrylamide polymer are added to the latex (B) -containing coating liquid of the present invention to such an extent that the effects of the present invention are not impaired. You can also do it.

The colloidal silica contained in the latex (B) -containing coating liquid of the present invention is necessary to ensure ink absorbability, and the colloidal silica contained in the latex (B) -containing coating liquid should be used in the above-described lower layer. It is produced in the same manner as colloidal silica, and usually consists of spherical silicic acid particles having a specific surface area of 15 to 700 m ² / g by the BET method.

The colloidal silica of the latex (B) -containing coating solution has a specific surface area that is too small, and the effect of preventing powder falling off when cutting with a cutter or film peeling when folded is not expressed or cast The gloss afterwards may be difficult to develop, and when the specific surface area is too large, the effect of improving the ink absorbability may be insufficient. Therefore, the specific surface area by the BET method is 50 to 500 m ² / g. Are preferably used, and those of 100 to 350 m ² / g are more preferably used.

  If the concentration of the colloidal silica in the latex (B) -containing coating solution is too high, the latex (B) -containing coating solution is difficult to be absorbed by the layer containing the water-absorbing inorganic pigment, and powdered or folded when cut with a cutter. The effect of preventing film peeling at the time cannot be obtained, and if it is too low, the ink absorbability is lowered. Therefore, the non-volatile content of colloidal silica is preferably 1 to 50% by mass, more preferably 3 to 30% by mass with respect to the coating liquid preferable.

  In the present invention, it is preferable that the latex (B) contained in the latex (B) -containing coating liquid is polyurethane because the coating layer can be further prevented from falling off or being bent. The polyurethane resin is a polymer obtained by reacting a compound having two or more isocyanate groups with a compound having two or more active hydrogen groups, and was obtained by reacting an isocyanate with a polyvalent active hydrogen compound. A case where the bond is other than a urethane bond such as a urea bond is also included.

  As the polyurethane resin used in the present invention, a urethane polymer is mixed with water in the presence of a surfactant and dispersed in water by applying a strong shearing force, or an acetone solution of a polyurethane resin is mixed and emulsified with water. A dispersion in which a polyurethane resin is dispersed in the form of fine particles in an aqueous medium can be used by a so-called acetone method in which acetone is volatilized and removed under reduced pressure.

  The compound having two or more isocyanate groups is not particularly limited, and examples thereof include chain aliphatic isocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate, etc. Aliphatic isocyanate having a cyclic structure of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene dii Cyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3 ' -Dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate Aromatic isocyanates such as One of these may be used alone, or two or more thereof may be used in combination. Among these isocyanates, aliphatic isocyanates are particularly preferable in terms of cutting strength because a flexible coating film can be formed.

  Examples of the compound having two or more active hydrogen groups include polyhydric alcohols and polyamines. Examples of the polyhydric alcohol include polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyester amide polyols, polythioether polyols, polybutadiene-based polyolefin polyols, and the like.

  As the polyester polyol, polyester obtained by dehydration condensation reaction of polyvalent carboxylic acid and polyhydric alcohol, polyester obtained by ring-opening polymerization reaction of cyclic ester, polyester obtained by condensation polymerization of hydroxycarboxylic acid, or , And these copolyesters.

  Examples of the polyvalent carboxylic acid include succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, and 1,4-cyclohexanedicarboxylic acid. Aliphatic dicarboxylic acids such as polymellitic acids, polyfunctional carboxylic acids such as trimellitic acid, pyromellitic acid and cyclohexanetricarboxylic acid and their anhydrides or ester-forming derivatives, terephthalic acid, isophthalic acid, phthalic acid, 1 Fragrance such as 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2-bis (phenoxy) ethane-p, p'-dicarboxylic acid Group dicarboxylic acids and their anhydrides or ester-forming derivatives It can be. These polyvalent carboxylic acids may be used alone or in combination of two or more. Examples of cyclic esters that can be used include ε-caprolactone and γ-valerolactone. Moreover, as hydroxycarboxylic acid, p-hydroxybenzoic acid, lactic acid, etc. can be used.

  On the other hand, as the polyhydric alcohol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, Neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl 1,3-propanediol, With aliphatic diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, bisphenol A, hydroquinone, bishydroxyethoxybenzene and their alkylene oxides Body polyols, also glycerol as a multifunctional component, trimethylolpropane, polyols such as pentaerythritol, and the like. These may be used alone or in combination of two or more.

  The polyether polyol may be used alone or in combination with a cyclic ether compound such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, or epichlorohydrin, using a compound having an active hydrogen atom as a catalyst. A polymer obtained by, for example, mixing ring-opening polymerization by mixing more than one species. Specific examples include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These may be used alone or in combination of two or more.

  Examples of the polycarbonate polyol include diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol, and phosgene. And a reaction product with a dialkyl carbonate such as dimethyl carbonate or a cyclic carbonate such as ethylene carbonate. These may be used alone or in combination of two or more.

  Examples of the polyvalent amines described above as the constituent components of the polyurethane resin include 1,2-diaminoethane, 1,2- or 1,3-diaminopropane, 1,2- or 1,3- or 1,4- Diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, piperazine, N, N′-bis- (2-aminoethyl) piperazine, 1-amino-3-aminomethyl-3,5,5-trimethyl Cyclohexane (isophoronediamine), bis- (4-aminocyclohexyl) methane, bis- (4-amino-3-butylcyclohexyl) methane, 1,2-, 1,3- or 1,4-diaminocyclohexane or 1, Diamines such as 3-diaminopropane, polyamines such as diethylenetriamine and triethylenetetramine, hydrazine, or azide Hydrazine derivatives such as phosphate dihydrazide, N-(2-sulfoethyl) ethylenediamine metal salt and 2-(beta-amino alkyl - amino propionamide) - can be used diaminosulphonate such as alkane sulfonic acid salts. These may be used alone or in combination of two or more.

  In addition, when the polyurethane resin has a tensile strength specified in JIS K7311 of 30 to 70 MPa and an elongation specified in JIS K7311 of 300 to 800%, the coating layer is high when powdered or bent. It is preferable because an effect of preventing peeling of the film can be obtained.

  The test piece used for the test was a 150 μm-thick film obtained by drying the resin for 1 day under the conditions of 23 ° C. and 65% RH and then drying at 150 ° C. for 5 minutes. The tensile strength and elongation are measured using an autograph AG-IS manufactured by Shimadzu Corporation according to the method defined in JIS K7311 under the condition of a tensile speed of 300 mm / min.

The latex (B) -containing coating liquid of the present invention contains boric acid or a salt thereof. This is because high gloss can be obtained by containing boric acid or a salt thereof in the latex (B) -containing coating liquid. The amount added depends on the amount of boric acid or its salt added to the other layers and the pH of the coating solution, but if the total amount added to each layer is too small, cracks will occur in the upper layer after drying. If the amount is too large, the effect of preventing powder falling off when cutting with a cutter or film peeling when folded may be lost. In terms of colloidal silica, it is preferably 0.2 to 10% by mass, more preferably 0.4 to 5% by mass in terms of H ₃ BO _{3 based} on boron atoms.

  The latex (B) -containing coating liquid of the present invention preferably contains a surfactant as a penetrating agent because it can prevent the coating layer from falling off or peeling off when folded.

  The above surfactants are classified into water-soluble surfactants and oil-soluble surfactants, and water-soluble surfactants are used in the latex (B) -containing coating liquid of the present invention. A water-soluble surfactant is a substance that exhibits high surface activity on the surface of a solution and forms a micelle colloid in a solution at a critical micelle concentration or higher, and adsorbs well on a two-phase interface due to a balance between hydrophilicity and lipophilicity. It has the effect of significantly reducing the free energy of. These hydrophilic and lipophilic adsorption capacities include at least one polar group that affects the dipole moment of the molecule and one nonpolar group that hardly affects the structure, and the former functions as a hydrophilic group. The latter acts as a lipophilic group along with the long chain alkyl group.

  Lipophilic groups are mainly composed of hydrocarbons, and are classified into aliphatic hydrocarbons, aromatic hydrocarbons, and aromatic hydrocarbon groups with aliphatic hydrocarbons as side chains. There is a shape and a branch-like thing. Examples of linear products include natural fats and oils (fatty acids, higher alcohols, etc.), mineral oils (paraffins, olefins, kerosene, etc.), Ziegler synthetic alcohols, etc., branched ones are polymerized olefins, orexo synthetic alcohols, synthetic fatty acids. Many of the raw materials have 12 to 20 carbon atoms. Lipophilic groups include one or more linking groups such as esters, ethers, amides, thioethers, thioamides, sulfoamides, urea bonds, urethane bonds, acyl groups, alkoxyl groups, heterocyclic rings, etc. There are also some special hydrophobic groups, such as those in which hydrocarbon hydrogen is partially or entirely substituted with fluorine, and organometallic systems in which metals are introduced.

  Examples of hydrophilic groups include organic acid salts (carboxylates, sulfate esters, polyether sulfates, phosphites, phosphates, phosphonates, polyether phosphates, etc.), amine salts, quaternary ammonium salts, There are hydroxyl groups that do not dissociate, ether bonds, semipolar bonds O, and the like.

  These surfactants are classified into cationic surfactants, anionic surfactants, and amphoteric surfactants depending on the type of ions generated in the aqueous solution, and those that do not generate ions are classified as nonionic surfactants. The If the amount of these activators added to the latex (B) -containing coating solution is too large or too small, the effect of preventing powder falling off at the time of cutting with a cutter or film peeling when bent may not be sufficiently obtained. is there. The specific addition amount is preferably 0.01 to 5%, more preferably 0.03 to 2%, based on the colloidal silica contained in the latex (B) -containing coating solution. In the present invention, these surfactants may be used alone or in combination of two or more.

The coating amount of the latex (B) -containing coating liquid of the present invention needs to be adjusted by the coating amount of the layer containing the water-absorbing inorganic pigment and latex and the support, but is usually 0 as the coating amount after drying. .1 to ²⁰ m ² / g is preferable, and 2 to 8 m ² / g is more preferable.

  In addition, the latex (B) -containing coating liquid is absorbed by the lower layer, thereby obtaining the effect of preventing powder falling off at the time of cutting or film peeling when bent by the cutter of the present invention. As a method for confirming whether or not the latex (B) -containing coating liquid is absorbed in the lower layer, the latex (B) -containing coating liquid is coated on the lower layer and dried, and then a cross section of the coating layer is photographed with an electron microscope. (B) It is possible by confirming that the layer of the latex (B) -containing coating liquid is not formed on the lower layer as compared with that before the coating liquid containing the coating liquid.

  The submicron pigment used in the upper layer containing the submicron pigment of the present invention and polyvinyl alcohol is a particle in the observation field when the dispersion is dispersed on a suitable substrate such as glass and observed with a scanning electron microscope. Inorganic pigments occupy 80% or more of the area occupied by particles having a long side of 1 μm or less. The type is not particularly limited, and examples thereof include gel method silica, precipitation method silica, colloidal silica, gas phase method silica, gas phase method alumina, and pseudoboehmite. In particular, it is preferable to use an inorganic pigment in which particles having a long side of 400 nm or less occupy 80% or more of the area occupied by the particles in the observation field because particularly high surface gloss can be obtained. In addition, when an inorganic pigment occupying 80% or more of the area occupied by particles in the observation field and having particles having a long side of 100 nm or more is used, defects such as cracks in the coating layer may occur even when the upper layer coating liquid is dried at high speed. Is preferred because

Further, as the submicron pigment used for the upper layer of the present invention, it is preferable to use a pigment having a specific surface area of a certain level or more because a high printing density can be obtained. On the other hand, if the specific surface area is too large, the ink absorbability may be lowered, which is not preferable. Specifically, the specific surface area by the BET method of the submicron pigment is preferably from 60~600m ² / g, more preferably 150 to 400 m ² / g. In addition, the pigment having such a specific surface area is usually a pigment in which primary particles having a diameter of several tens of nm or less are bonded and a higher order structure having voids therein is formed. These water-absorbing inorganic pigments may be used alone or in combination of two or more.

  In the present invention, when the rewetting method is used as the casting method, pseudoboehmite is preferably used as the upper submicron pigment because an ink jet recording medium having a particularly high gloss can be obtained.

In the present invention, a submicron pigment and a cationic polymer can be used in combination. Addition of a cationic polymer is preferable because water resistance, light resistance and ink absorbability are improved. Examples of the cationic polymer include polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, acrylic resins having secondary amine groups, tertiary amine groups, and quaternary ammonium groups, dicyandiamide-formalin polycondensates, dicyanamide-diethylenetriamines. dicyan cationic polymer of polycondensates such as polyalkylene polyamines and dicyandiamide copolymers dicyandiamide based resins, polymers of allylamine salts, acrylamide - diallylamine salt copolymers, diallylamine salt -SO ₂ copolymer, dimethyl diallyl ammonium chloride -SO ₂ copolymer, dimethyl diallyl ammonium chloride polymer, dialkyl aminomethyl (meth) acrylate quaternary salt polymers, polyvinyl amine, polyvinyl Amidine polymer, epichlorohydrin - cationic polymers, such as dimethylamine addition polymers are preferable.

  As the polyvinyl alcohol used in the upper layer of the present invention, polyvinyl alcohol having various saponification degrees from 70 mol% to 100 mol% can be used. It is also possible to use modified polyvinyl alcohol in which various functional groups such as silyl group, carboxyl group, amino group, and acetoacetyl group are introduced, or other repeating units such as ethylene are introduced randomly, grafted or in blocks. it can. If the amount of polyvinyl alcohol added in the present invention is too small, cracks may occur during drying, or the surface strength of the formed inkjet recording medium may be insufficient. On the other hand, if the added amount of polyvinyl alcohol is too large, the ink absorbability may decrease. Specifically, the addition amount of polyvinyl alcohol is preferably 2 to 60% by mass of the submicron pigment, and more preferably 5 to 25% by mass.

  The polyvinyl alcohol used in the upper layer of the present invention has a higher viscosity of the aqueous solution, so that cracking is less likely to occur when the applied coating liquid is dried, so that the amount added can be reduced, resulting in ink absorptivity. Can be improved, which is preferable. However, if the viscosity of the aqueous solution is too high, the viscosity of the coating liquid obtained by the present invention becomes too high, which may make the coating operation difficult, which is not preferable. Specifically, the viscosity of an aqueous solution having a solid content concentration of 4% by mass measured at 25 ° C. using an Ubbelohde viscometer based on JIS Z8803 is preferably 25 to 400 mPa · sec, and 50 to 200 mPa · sec. More preferably. One of these polyvinyl alcohols may be used alone, or two or more thereof having different saponification degree, viscosity, modification and the like may be used in combination.

  Various additives such as a surfactant, an antifoaming agent, a thickening agent, a color adjusting agent, an antioxidant, an ultraviolet absorber, and a pH adjusting agent are added to the coating layer of the present invention as necessary. You can also

In the present invention, there is no particular limitation on the method of coating the coating liquid of each layer, and various coating methods such as an air knife coater, reverse roll coater, comma coater, etc. can be used, such as a lip coater, a die coater, a curtain coater, etc. The pre-weighing coater of the present invention has a high uniformity of the coating layer obtained, and in addition, when coating the upper layer, it does not easily penetrate into the layer containing the water-absorbing pigment in the upper layer and gives a very good surface quality. It is preferably used for coating of a working layer, particularly an upper layer coating solution. Although there is no restriction | limiting in particular in the quantity which coats the coating liquid of this invention on a base material, in order to make ink absorptivity and economical efficiency compatible normally, each layer is 10-20 g / m < ² >, respectively, and 10 in total It is preferable to apply ˜30 g / m ² . However, when it is particularly required to absorb a large amount of ink, it may be preferable to apply a maximum of about 50 g / m ^{2 in} total for both layers.

  Moreover, after each coating liquid is applied and dried, or both of them, cast treatment can be performed after increasing the smoothness by a calendar device such as a soft calendar or a super calendar.

  In addition, a release agent such as an oily substance or an aqueous dispersion of an oily substance may be added to the coating liquid of the present invention for the purpose of improving the peelability from the mirror surface of the casting apparatus, or may be applied prior to the casting process. When the rewetting method is used as the casting method, it is preferable to add to the water used for the rewetting because stable production can be achieved over a long period of time. Examples of substances that can be used as a releasing agent in the present invention include higher alkylamines such as dimethyloctylamine and dimethyloctadecylamine or salts thereof, higher alkyl quaternary ammoniums such as trimethyloctylammonium chloride and trimethyloctadecylammonium chloride. Examples thereof include salts, higher carboxylic acids such as oleic acid, stearic acid and caprylic acid or salts thereof, higher alcohols such as octyl alcohol and octadecyl alcohol, liquid paraffin, polyethylene wax and silicone oil.

  Examples of the present invention will be described below. In the examples, unless otherwise specified, parts are parts by mass, and% is mass%.

[Preparation of lower layer coating solution]
In 350 parts of water, 10 parts of sodium tetraborate decahydrate (1.62 parts in terms of H ₃ BO ₃ ) was dissolved, and 100 parts of wet synthetic silica (Fine Seal X-37B manufactured by Tokuyama Corporation) was added thereto. It was fully dispersed using a disperser having a post-saw blade. Thereafter, 83.3 parts of styrene-butadiene (SBR) latex having a solid content of 48% (0623N manufactured by JSR Corporation) (40 parts as a nonvolatile content) was added and mixed to obtain a lower coating solution 1. In addition, about the wet synthetic silica used here, water was used instead of linseed oil, and when a test according to the oil absorption test defined in JIS K5101 was performed, 300 mL of water per 100 g was used by the end point. It was done.

[Preparation of coating solution containing latex (B)]
100 parts of colloidal silica (GR-40 manufactured by GRACE Davison) having a solid content of 49.5% is dispersed in 400 parts of water, and styrene-butadiene (SBR) having a solids content of 48% with respect to 100 parts of the non-volatile content of colloidal silica. ) 62.5 parts of latex (0623N manufactured by JSR) (30 parts as a nonvolatile content) was added to prepare a latex (B) -containing coating solution. In addition, the specific surface area by BET method of said colloidal silica was 228 m < ² > / g.

[Preparation of upper layer coating solution]
Amorphous silica gel slurry of the submicron pigment used GRACE Davison's silo jet 703A (average particle size 330 nm, anion) was diluted 100 times and dispersed on a glass plate, and observed with a scanning electron microscope. The particles having a long side of 1 μm or less occupied 90% or more of the area occupied by the particles in the observation field. 100 parts of this amorphous silica gel slurry (solid content 20.9 parts) 30 parts of 10% aqueous solution of polyvinyl alcohol (PVA235 manufactured by Kuraray Co., Ltd.) having a saponification degree of 88 mol% and a 4% aqueous solution with a viscosity of 95 mPa · s at 25 ° C. (3 parts of solid content) was added to prepare an upper layer coating liquid.

[Preparation of inkjet recording medium]
^On the base paper (Diafoam manufactured by Mitsubishi Paper Industries Co., Ltd.) with a basis weight of 157 g / m ² , the lower layer coating solution is applied with an air knife coater so that the coating amount after drying is 10 g / m ² , and a hot air dryer is used. And dried. The resulting coated paper was then processed using a soft calendar. Thereafter, the latex (B) -containing coating solution was applied with an air knife coater so that the coating amount after drying was 1 g / m ² , and dried using a hot air dryer. Thereafter, the upper layer coating solution was applied with an air knife coater so that the coating amount after drying was 10 g / m ² and dried using a hot air dryer. Subsequently, the obtained coating layer was processed using the soft calender. Then, the coated surface is wetted with water, and the wet coated surface is pressure-bonded to a mirror chrome plating cylinder of a casting apparatus heated to 95 ° C. at a linear pressure of 20 kN / m and a speed of 5 m / min. The ink jet recording medium of Example 1 was produced.

An inkjet recording medium of Example 2 was produced in the same manner as Example 1 except that the coating amount after drying of the latex (B) -containing coating liquid was 2 g / m ² .

An inkjet recording medium of Example 3 was produced in the same manner as in Example 1 except that the coating amount after drying of the latex (B) -containing coating liquid was changed to 5 g / m ² .

An inkjet recording medium of Example 4 was produced in the same manner as in Example 1 except that the coating amount after drying of the latex (B) -containing coating liquid was 9 g / m ² .

  An inkjet recording medium of Example 5 was produced in the same manner as Example 3 except that the latex contained in the latex (B) -containing coating liquid was changed to the same amount of urethane resin as the solid content. The urethane resin had a tensile strength and elongation of 46 MPa and an elongation of 610%. The test piece used for the test was a 150 μm thick film obtained by drying the resin for 1 day under the conditions of 23 ° C. and 65% RH and then drying at 150 ° C. for 5 minutes. The tensile strength and elongation were measured using an autograph AG-IS manufactured by Shimadzu Corporation according to the method defined in JIS K7311 under the condition of a tensile speed of 300 mm / min.

  A surfactant (manufactured by Nissin Chemical Industry Co., Ltd., Olphine E1010, nonionic surfactant) is added to the latex (B) -containing coating solution in an amount of 0. 0 to the solid content of colloidal silica contained in the latex (B) -containing coating solution. Example 6 was produced in the same manner as Example 5 except that 2 parts were included.

  Example 7 in the same manner as in Example 6 except that 1 part of sodium tetraborate decahydrate contained in the lower layer was 1 part and 20 parts of sodium tetraborate decahydrate was contained in the latex (B) -containing coating solution. An ink jet recording medium was prepared.

  The ink jet recording media of Examples 1 to 7 were coated and dried with a latex (B) -containing coating solution, and the cross-section was photographed with an electron microscope, and there was no coating solution layer containing latex (B) on the lower layer. confirmed.

[Comparative Example 1]
An inkjet recording medium of Comparative Example 1 was produced in the same manner as in Example 1 except that the latex (B) -containing coating solution was not applied.

[Comparative Example 2]
Comparative Example 2 was prepared in the same manner as in Example 3 except that 100 parts of water in the latex-containing coating liquid (B) was used. After coating and drying the latex-containing coating liquid (B), the cross section of the coating layer was observed with an electron microscope, and it was confirmed that the coating layer of the latex-containing coating liquid (B) was present on the lower layer.

[Evaluation]
The recording medium obtained in each of Examples and Comparative Examples was evaluated with respect to powder falling at the time of cutting, film peeling at the time of bending, ink absorbency, and gloss. The evaluation method for each item will be described.

[Powder falling when cutting cutter]
The coated surface of the inkjet recording medium was linearly cut twice with a length of 10 cm using a scale and a cutter, and dropping of the coated film on the cut surface was visually evaluated in four stages. A (no dropout), B (slight dropout), C (allowable), D (not acceptable).

[Film peeling during bending]
The ink jet recording medium was cut into a width of 10 cm, and the film surface side was turned upside down, and the film peeling of the bent portion was visually evaluated in four stages. A (No film peeling), B (Slightly peeling part), C (Acceptable), D (Unacceptable).

[Ink absorbency]
A predetermined evaluation image was printed by an ink jet printer that performs printing using dye ink (PM-G800 type manufactured by Seiko Epson Corporation), and then left for 1 hour to evaluate bleeding of the image. A (no bleeding), B (slight bleeding), C (acceptable), D (unacceptable).

[Gloss evaluation]
The gloss was evaluated by measuring the image clarity having a good correlation with the visual gloss. In addition, the measurement was performed using a Suga Test Instruments Co., Ltd. image clarity measuring instrument at a measurement angle of 45 ° and an optical comb width of 2.0 mm. In the measurement by this method, in general, a recording medium giving image clarity of 60 or more has high gloss, and a recording medium giving image clarity of 65 or more has very high gloss. A (having a mapping property of 65 or more), B (having a mapping property of 60 or more and less than 65), C (having a mapping property of less than 60).

  Table 1 shows the evaluation results of the powder falling at the time of cutter cutting of the ink jet recording media obtained by the respective examples and comparative examples, film peeling at the time of bending, ink absorbency, and gloss.

  By comparing Comparative Example 1 with Examples 1 to 7, after the ink jet recording medium provided a lower layer containing a water-absorbing inorganic pigment and latex (A) on the support, colloidal silica and latex (B) were added. After coating the coating liquid containing and absorbing it in the lower layer, after providing the upper layer containing the submicron pigment and polyvinyl alcohol, by casting, powder falling off at the time of cutter cutting and film peeling at the time of bending It can be seen that an improved effect is obtained.

  The coating liquid containing colloidal silica and latex (B) is absorbed in the lower layer by comparing Comparative Example 2 having a three-layer structure that does not absorb the coating liquid containing colloidal silica and latex (B) with Examples 1 to 7. By this, it turns out that the effect which the powder fall at the time of a cutter cutting | disconnection and the film peeling at the time of bending is improved is acquired.

  By comparing Comparative Example 1 and Example 3 with Example 5 to make the latex contained in the latex (B) -containing coating liquid into a urethane resin, powder falling at the time of cutting the cutter and peeling of the film at the time of bending are further observed. It can be seen that an improved ink jet recording medium is obtained.

  By comparing Comparative Example 1 and Example 5 with Examples 6 and 7, the latex (B) -containing coating liquid contained a penetrant, which further improved powder falling off during cutter cutting and film peeling during folding. It can be seen that an ink jet recording medium is obtained.

  By comparing Comparative Example 1 and Example 6 with Example 7, it can be seen that an ink jet recording medium having improved gloss can be obtained by containing boric acid or a salt thereof in the latex (B) -containing coating liquid.

Claims (4)

  In an ink jet recording medium in which at least an upper layer and a lower layer are provided on a gas-permeable support and cast, a lower layer containing a water-absorbing inorganic pigment and latex (A) is provided on the support, and colloidal silica and latex (B). An ink jet recording medium comprising: a coating liquid containing a coating liquid and absorbing the lower layer; then, an upper layer containing a submicron pigment and polyvinyl alcohol is provided and cast.   The ink jet recording medium according to claim 1, wherein the latex (B) is a urethane resin.   3. The ink jet recording medium according to claim 1, wherein the coating liquid containing colloidal silica and latex (B) contains boric acid or a salt thereof.   The ink jet recording medium according to any one of claims 1 to 3, wherein the coating liquid containing colloidal silica and latex (B) further contains a penetrating agent.