JP2005262619A - Coating composition for inkjet recording medium, and inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording medium of which the glossiness on a non-printed surface and a printed surface is high, of which the printing density is high, and which is excellent in surface strength, and to provide a coating composition for inkjet recording medium which is suitable for the recording medium. <P>SOLUTION: This coating composition for the inkjet recording medium contains a pigment and a binder. In this case, the pigment contains an organic pigment comprising a polymer which is obtained by polymerizing a monomer under the existence of a water-soluble polymer containing an alcoholic hydroxy group in an aqueous medium, and of which the glass transition temperature is 60°C or higher. Also, this inkjet recording medium is constituted by coating the coating composition on a supporting body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coating composition for an inkjet recording medium and an inkjet recording medium, and more specifically, an inkjet recording medium having high gloss, non-printing surface and high printing density, and excellent surface strength. It is related with the coating composition for inkjet recording media suitable for.

The ink jet recording system is a method in which fine droplets of water-based ink are ejected from nozzles by various operating principles, and are adhered to a recording medium to record characters and images. This recording method is characterized in that it can be easily increased in speed and multicolored, and does not require processing such as development and fixing, and is rapidly spreading in recording apparatuses such as printers and plotters.
As a recording medium used for such a recording method, an ink jet recording medium coating composition capable of forming a porous ink-receiving layer on a support for the purpose of easily absorbing ink is used. It is widely used.
However, the ink jet recording medium provided with the ink receiving layer as described above tends to be inferior in adhesive strength between the support and the ink receiving layer, and the ink receiving layer is easily peeled off during use (inferior in surface strength). ), It is required to improve the surface strength while suppressing a decrease in printing density.
Conventional ink jet recording media have a low surface gloss, but in recent years, an ink jet recording medium having a high surface gloss has been required as the resolution of the ink jet recording system increases. Therefore, studies are being made on an ink jet recording medium having a high surface gloss and excellent ink jet recording suitability.

  For example, Patent Document 1 discloses a polymer having a glass transition temperature of 40 ° C. or higher in the presence of colloidal silica on an ink receiving layer formed from a coating composition for an inkjet recording medium containing a specific inorganic pigment. An inkjet recording medium having a gloss layer formed of a composite obtained by polymerizing monomers that can be formed is disclosed. However, the ink jet recording medium as described above is relatively excellent in gloss, but has insufficient surface strength and print density.

  Patent Document 2 discloses colloidal silica and a binder having a specific average particle diameter on an ink receiving layer formed from a coating composition for an inkjet recording medium containing an organic pigment having a void, an inorganic pigment, and a binder. An ink jet recording medium having a gloss layer formed thereon is disclosed. However, the ink jet recording medium as described above is excellent in gloss, but has insufficient surface strength and print density.

  Further, Patent Document 3 discloses an ink jet recording medium having an ink receiving layer formed from a coating composition for an ink jet recording medium having a cationic group and a hollow polymer particle having a specific average particle diameter. Has been. However, such an ink jet recording medium is excellent in print density but insufficient in gloss and surface strength.

Japanese Patent Laid-Open No. 10-264507 JP 2000-289327 A JP 2001-191737 A

  In view of the above circumstances, an object of the present invention is to provide an inkjet recording medium having high gloss on the non-printing surface and the printing surface, high printing density, and excellent surface strength, and a coating composition for an inkjet recording medium suitable for the recording medium. Is to provide.

  As a result of diligent efforts to solve the above problems, the present inventors have obtained a glass transition obtained by polymerizing monomers in the presence of a water-soluble polymer containing an alcoholic hydroxyl group in an aqueous medium. When a coating composition for an ink jet recording medium comprising a pigment containing an organic pigment composed of a polymer having a temperature equal to or higher than a specific temperature and a binder is used, the gloss of the non-printing surface and the printing surface is high, and the printing density is high. In addition, the present inventors have found that an ink jet recording medium excellent in surface strength can be obtained, and have completed the present invention based on this finding.

Thus, according to the present invention, an organic material comprising a polymer having a glass transition temperature of 60 ° C. or higher obtained by polymerizing a monomer in the presence of a water-soluble polymer containing an alcoholic hydroxyl group in an aqueous medium. There is provided a coating composition for an ink jet recording medium comprising a pigment containing a pigment and a binder.
Moreover, according to this invention, the inkjet recording medium formed by apply | coating said coating composition for inkjet recording media to a support body is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the glossiness of a non-printing surface and a printing surface is high, the printing density is high, and the coating composition for inkjet recording media suitable for this recording medium which is excellent in surface strength is provided.

(Organic pigment)
The organic pigment used in the present invention is obtained by polymerizing a monomer in an aqueous medium in the presence of a water-soluble polymer containing an alcoholic hydroxyl group, and has a glass transition temperature of 60 ° C. or higher, preferably 70 ° C. or higher. It consists of a polymer of When an organic pigment having a low glass transition temperature is used, the gloss of the obtained ink jet recording medium is inferior.
The upper limit of the glass transition temperature of the polymer is not particularly limited, but is 120 ° C, preferably 110 ° C. While it tends to be difficult to produce a polymer having a glass transition temperature significantly exceeding 120 ° C., the use of a coating composition for an inkjet recording medium containing an organic pigment made of such a polymer results in a decrease in surface strength. Tend.

  Examples of the monomer used in the present invention include conjugated diene monomers, aromatic vinyl monomers, ethylenically unsaturated nitrile monomers, ethylenically unsaturated carboxylic acid monomers, and ethylenically unsaturated carboxylic acids. Examples include acid alkyl ester monomers and ethylenically unsaturated carboxylic acid amide monomers.

  Examples of the conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2- Examples include chloro-1,3-butadiene and 1,3-pentadiene. Of these, 1,3-butadiene can be preferably used.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, monochlorostyrene, dichlorostyrene, trichlorostyrene, methylstyrene, dimethylstyrene, trimethylstyrene, and hydroxymethylstyrene. Of these, styrene can be preferably used.

  Examples of the ethylenically unsaturated nitrile monomer include acrylonitrile, methacrylonitrile, 2-chloropropenenitrile, 2-butenenitrile and the like. Of these, acrylonitrile can be preferably used.

  Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid, methacrylic acid, and crotonic acid; fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride Ethylenically unsaturated polyvalent carboxylic acid monomers such as acids and anhydrides thereof; partially esterified products of ethylenically unsaturated polyvalent carboxylic acid monomers such as monoethyl fumarate, monomethyl maleate and monomethyl itaconate; Can be mentioned.

  Examples of the ethylenically unsaturated carboxylic acid alkyl ester monomer include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dimethyl fumarate, Examples include diethyl maleate and diisopropyl itaconate.

  Examples of the ethylenically unsaturated carboxylic acid amide monomer include (meth) acrylamide, N, N-dimethylacrylamide, N-methylolacrylamide and the like.

In addition to the above monomers, for example, carboxylic acid vinyl ester monomers such as vinyl acetate, vinyl propionate and vinyl versatate; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride Monomers such as ethylene, propylene, 1-butene and isobutene; vinyl ether monomers such as methyl vinyl ether, n-propyl vinyl ether, isobutyl vinyl ether and dodecyl vinyl ether; vinyl trimethoxysilane, vinyl pyridine, N- Vinyl pyrrolidone or the like can be used.
The above monomers can be used alone or in combination of two or more.

  Among the above monomers, conjugated diene monomer, aromatic vinyl monomer, ethylenically unsaturated carboxylic acid alkyl ester monomer, ethylenically unsaturated nitrile monomer, ethylenically unsaturated carboxylic acid amide monomer A monomer and an ethylenically unsaturated carboxylic acid monomer can be preferably used.

It is preferable to use an aromatic vinyl monomer as an essential component in terms of obtaining an ink jet recording medium having an excellent balance between gloss and print density, and the preferred amount used is based on the total amount of monomers used for polymerization. 70% by weight or more.
In addition, it is preferable to use an ethylenically unsaturated carboxylic acid monomer as an essential component in terms of excellent mechanical stability and blending stability of latex containing an organic pigment, and the amount used is used for polymerization. Preferably it is 0.5 to 20 weight% with respect to the monomer whole quantity.

  In order to bring the glass transition temperature of the polymer obtained by the polymerization into the above range, the composition of the monomer used in the polymerization may be appropriately selected based on a conventional method.

  There are no particular restrictions on the method of adding the monomer. For example, the method of adding the entire amount to the reaction vessel before the start of polymerization or the monomer is added to the reaction vessel continuously or intermittently in parallel with the polymerization reaction. A method of adding a part to the reaction vessel before the start of polymerization and starting the polymerization, and then adding the remainder at a specific time, a part of the reaction vessel being charged before starting the polymerization and starting the polymerization Then, the method of adding the remainder to the polymerization system continuously or intermittently can be employed. Especially, the method of adding a monomer to a reaction container continuously can be employ | adopted in parallel with a polymerization reaction at the point which is excellent in polymerization stability.

  The monomer addition rate when the monomer is continuously added to the reaction vessel is not particularly limited, but the polymerization conversion rate in the polymerization system is 10% by weight or more, more preferably 20% by weight or more. It is preferable to control to maintain 30% by weight or more. If this addition rate is too fast, the polymerization stability tends to be reduced and coarse agglomerates tend to be generated. On the other hand, if it is too slow, the viscosity of the polymerization system increases and it becomes difficult to remove the heat of polymerization reaction. Tend.

  Examples of the water-soluble polymer containing an alcoholic hydroxyl group used in the present invention (hereinafter sometimes abbreviated as “alcoholic hydroxyl group-containing water-soluble polymer compound”) include polyvinyl alcohol and various modified products thereof. Vinyl alcohol polymers; cellulose derivatives such as alkyl cellulose, hydroxyalkyl cellulose, alkyl hydroxyalkyl cellulose, and carboxymethyl cellulose; starch derivatives such as alkyl starch, carboxymethyl starch, and oxidized starch; gum arabic, tragacanth rubber, polyalkylene glycol, etc. be able to. Among these, a vinyl alcohol polymer can be preferably used because it is easy to obtain an industrially stable product.

  The vinyl alcohol polymer is not particularly limited as long as it is a substantially water-soluble and stable latex can be obtained, and an ethylenic polymer mainly composed of a carboxylic acid vinyl ester monomer. Carboxylic acid vinyl ester polymer obtained by polymerizing a saturated monomer by a conventionally known method (that is, a homopolymer of a carboxylic acid vinyl ester monomer and a copolymer of two or more carboxylic acid vinyl ester monomers) And saponified by a conventional method), and a copolymer of a carboxylic acid vinyl ester monomer and another ethylenically unsaturated monomer copolymerizable therewith. Moreover, what introduce | transduced modifying groups, such as a mercapto group, into the principal chain, side chain, or terminal of a molecule | numerator can also be used.

  As the carboxylic acid vinyl ester monomer, any monomer capable of radical polymerization can be used, and specific examples thereof include vinyl formate, vinyl acetate, vinyl propionate, isopropenyl acetate, vinyl valerate, capric acid. Examples thereof include vinyl, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, and vinyl pivalate. Of these, industrially produced and inexpensive vinyl acetate is common.

  It is also possible to co-polymerize one or more ethylenically unsaturated monomers copolymerizable with a carboxylic acid vinyl ester monomer. Examples of these copolymerizable ethylenically unsaturated monomers include, for example, monoolefin monomers such as ethylene, propylene, 1-butene and isobutene; acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid and fumaric acid. Ethylenically unsaturated carboxylic acid monomers such as monoethyl acid, maleic anhydride, phthalic anhydride, trimetic anhydride, itaconic anhydride; methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid n -Ethylenically unsaturated carboxylic acid alkyl ester monomers such as butyl, 2-ethylhexyl (meth) acrylate, dimethyl fumarate, diethyl maleate, diisopropyl itaconate; methyl vinyl ether, n-propyl vinyl ether, isobutyl vinyl ether, dodecyl vinyl ether Vinyl ethere Monomers; Ethylenically unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile; Vinyl halide monomers such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; Allyl such as allyl acetate and allyl chloride Compound; sulfonic acid group-containing monomer such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid; and 3-acrylamidopropyltrimethylammonium chloride, 3-methacrylamidopropyltrimethyl Examples include quaternary ammonium group-containing monomers such as ammonium chloride; vinyltrimethoxysilane.

  The saponification degree of the carboxylic acid vinyl ester polymer varies depending on the presence or absence of the modifying group and the type thereof, but is 40 to 99.99 mol% from the viewpoint of the water solubility of the resulting vinyl alcohol polymer. It is preferably 50 to 99.9 mol%, more preferably 60 to 99.5 mol%. When the degree of saponification is less than 40 mol%, the dispersion stability of the polymer particles decreases. The viscosity average polymerization degree of the carboxylic acid vinyl ester polymer is usually 50 to 8,000, preferably 100 to 6,000, more preferably 100 to 5,000.

  The amount of the alcoholic hydroxyl group-containing water-soluble polymer compound used is preferably 0.5 to 100 parts by weight, more preferably 0.5 to 50 parts by weight, particularly 100 parts by weight of the monomer used for the polymerization. Preferably it is 1-20 weight part. If the amount used is too small, the stability at the time of polymerization is poor, and a large amount of agglomerates are generated, and the mechanical stability and chemical stability of the latex containing the organic pigment tend to be reduced. If the amount is too large, it tends to be difficult to remove the reaction heat due to an increase in the viscosity of the polymerization system, or the viscosity of the latex containing the organic pigment becomes too high, making it difficult to handle.

  There is no particular limitation on the method of adding the alcoholic hydroxyl group-containing water-soluble polymer compound. For example, the method of introducing the entire amount into the reaction vessel before the start of polymerization or the alcoholic hydroxyl group-containing water-soluble polymer in parallel with the polymerization reaction. A method of adding a compound continuously or intermittently to a reaction vessel, a method of adding a part to a reaction vessel before the start of polymerization and starting the polymerization, and then adding the remainder at a specific time, before the start of polymerization A method may be employed in which a part of the reaction vessel is charged and polymerization is started, and then the remainder is continuously or intermittently added to the polymerization system. Among them, a method of continuously adding an alcoholic hydroxyl group-containing water-soluble polymer compound to the reaction vessel in parallel with the polymerization reaction can be preferably employed from the viewpoint of excellent polymerization stability.

  As a method for adding the monomer and the alcoholic hydroxyl group-containing water-soluble polymer compound, both may be added separately to the reaction vessel, or both may be mixed and added to the reaction vessel. Among them, a method of mixing both of them and adding them to a reaction vessel is preferable because of excellent polymerization stability, and a monomer, a monomer obtained by mixing an alcoholic hydroxyl group-containing water-soluble polymer compound and an aqueous medium. A method of adding the emulsion to the reaction vessel is more preferably employed.

In the polymerization of the present invention, it is particularly preferable not to use various surfactants such as nonionic, anionic, cationic or amphoteric surfactants which are usually used in emulsion polymerization. As long as it is within a range that is not impaired, it may be used in combination.
Examples of anionic surfactants include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, polyoxyethylene alkylaryl sulfonates, polyphosphates, and other nonionic surfactants. Examples of cationic surfactants such as polyethylene glycol alkyl ester type, alkyl phenyl ether type or alkyl ether type include aliphatic amine salts and quaternary ammonium salts, aromatic quaternary ammonium salts, heterocyclic rings Examples of amphoteric surfactants such as quaternary ammonium salts include carboxybetaine, sulfobetaine, aminocarboxylate, and imidazoline derivatives. These surfactants may be used alone or in combination of two or more. When these surfactants are used, the amount used is usually 2 parts by weight or less, preferably 0.5 parts by weight or less, based on 100 parts by weight of the monomer used for the polymerization.

As the aqueous medium used in the present invention, water can be usually used, and an aqueous solution containing an alcohol such as methanol and ethanol; and an aqueous organic solvent such as acetone and tetrahydrofuran can also be used.
The amount of the aqueous medium used is preferably 90 to 900 parts by weight, more preferably 100 to 500 parts by weight with respect to 100 parts by weight of the monomer used for the polymerization.

The polymerization in the present invention is preferably performed in the presence of an alcohol. By polymerizing in the presence of alcohol, the polymerization reaction can be performed stably while suppressing the generation of coarse aggregates.
The alcohol that can be used here is not particularly limited and may be monovalent or polyvalent, but is preferably water-soluble. Specific examples of such alcohols include methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, glycerol and the like. The amount of alcohol used is preferably 1 to 50 parts by weight, more preferably 2 to 20 parts by weight, based on 100 parts by weight of the monomer used for the polymerization.

  There are no particular restrictions on the method of adding the alcohol. For example, a method in which the entire amount is charged into the reaction vessel before the start of polymerization, or a part of the reaction vessel before the start of polymerization is charged to start the polymerization, and then the remaining part is specified. For example, a method of additionally adding at the time, a method of adding a part to the reaction vessel before starting the polymerization and starting the polymerization, and then adding the remainder continuously or intermittently to the polymerization system may be employed. Of these, a method in which the entire amount is charged into the reaction vessel before the start of polymerization can be preferably employed.

In the present invention, it is preferable to use a polymerization initiator that generates a peroxide radical. Specific examples of polymerization initiators that generate peroxide radicals include water-soluble peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide; t-butyl hydroperoxide, benzoyl peroxide, and di-t-butyl. Examples include oil-soluble peroxides such as peroxides; redox initiators based on combinations of peroxides and various reducing agents such as sodium bisulfite, among which water-soluble peroxides are preferred. Persulfate is particularly preferred.
The usage-amount of a polymerization initiator is 0.05-5 weight part normally with respect to 100 weight part of monomers, Preferably it is 0.1-4 weight part.
There is no particular limitation on the method of adding the polymerization initiator, for example, a method in which the entire amount is charged into the reaction vessel before the start of polymerization, or after a portion of the reaction vessel is charged into the reaction vessel before the start of polymerization to start polymerization, A method of additionally adding at a specific time, a method of adding a part to the reaction vessel before starting the polymerization and starting the polymerization, and then adding the remainder to the polymerization system continuously or intermittently can be employed.

  In the polymerization, a chain transfer agent can be used as necessary. The chain transfer agent is not particularly limited as long as chain transfer occurs. For example, n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan , Compounds having a mercapto group such as thioglycolic acid, thiomalic acid, 2-ethylhexylthioglycolate; xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide; α-methylstyrene dimer, 2,4-diphenyl-4- Α-methylstyrene dimers such as methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, 1,1,3-trimethyl-3-phenylindane; tetramethylthiuram disulfide, Thiuram compounds such as traethylthiuram disulfide and tetramethylthiuram monosulfide; phenol compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; allyl such as allyl alcohol, acrolein and methacrolein Compound: Halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrachloride, carbon tetrabromide; α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, terpinolene, triphenylethane, pentaphenylethane And so on. These chain transfer agents may be used alone or in combination of two or more.

  When a chain transfer agent is used, the amount used is usually 5 parts by weight or less with respect to 100 parts by weight of the monomer. The method for adding the chain transfer agent is not particularly limited, and it may be added all at once or intermittently or continuously to the polymerization system.

  In the polymerization, in addition to those described above, polymerization auxiliary materials such as a particle size adjusting agent, a chelating agent, an oxygen scavenger, a dispersing agent, a pH adjusting agent, and an inorganic salt that are usually used in emulsion polymerization can be appropriately used. .

  Although there is no restriction | limiting in particular in superposition | polymerization temperature, Usually, 0-100 degreeC, Preferably it is 50-95 degreeC.

  The polymerization reaction is performed as described above, and when the predetermined polymerization conversion rate is reached, a polymerization terminator is added or the polymerization system is cooled to stop the polymerization reaction. The polymerization conversion rate when stopping the polymerization reaction is preferably 92% by weight or more, more preferably 95% by weight or more. After stopping the polymerization reaction, if desired, a latex containing an organic pigment can be obtained by removing unreacted monomers and adjusting pH and solid content concentration.

The polymer constituting the organic pigment used in the present invention is a polymer in which the polymer derived from the monomer used for the polymerization and a part of the alcoholic hydroxyl group-containing water-soluble polymer compound used for the polymerization are combined. It is preferable.
The ratio of the alcoholic hydroxyl group-containing water-soluble polymer compound bonded to the polymer derived from the monomer used for the polymerization (hereinafter sometimes referred to as “grafting ratio”) is derived from the monomer used for the polymerization. Preferably it is 0.5-50 weight% with respect to the polymer to perform, More preferably, it is 0.5-20 weight%, Most preferably, it is 1-15 weight%. If this amount is too small, the surface strength of the ink jet recording medium tends to be inferior. On the other hand, if the amount is too large, the latex viscosity increases and it becomes difficult to handle, and the gloss and print density of the ink jet recording medium tend to decrease. There is.

  The volume average particle diameter of the polymer particles constituting the organic pigment used in the present invention is preferably 60 to 800 nm, more preferably 70 to 600 nm. If the volume average particle diameter is too small, the latex viscosity will increase and it will be difficult to handle, and the surface strength of the ink jet recording medium will tend to decrease. Conversely, if it is too large, the gloss of the ink jet recording medium will tend to decrease. is there.

  The latex containing the organic pigment used in the present invention may optionally contain additives such as a dispersant, a plasticizer, an antifoaming agent, a pH adjuster, an anti-aging agent, an antiseptic, an antibacterial agent, and a fluidity improver. Can be added as appropriate.

(Coating composition for inkjet recording medium)
The coating composition for inkjet recording media of the present invention comprises a pigment containing the organic pigment and a binder.

  The content of the organic pigment is preferably 0.1 to 40% by weight, and more preferably 5 to 30% by weight in the total pigment. If the content is too small, the gloss of the ink jet recording medium tends to decrease, and conversely if it is too large, the print density of the ink jet recording medium tends to decrease.

As the pigment component other than the organic pigment, an organic pigment and an inorganic pigment other than the organic pigment can be used. Among these, inorganic pigments can be preferably used.
Examples of organic pigments other than the organic pigment include solid polymer particles made of polystyrene resin, acrylic resin, styrene-acrylic resin, urea-formalin resin, etc .; polystyrene resin, acrylic resin, styrene-acrylic resin, etc. Hollow polymer particles or bowl-shaped polymer particles; and the like.
Examples of the inorganic pigment include, for example, amorphous silica, crystalline silica, alumina, calcium carbonate, magnesium carbonate, kaolin, calcined kaolin, talc, titanium oxide, zinc oxide, aluminum oxide, barium sulfate, calcium sulfate, magnesium silicate, Examples thereof include aluminum silicate, amorphous calcium silicate, diatomaceous earth, zeolite, aluminum hydroxide, and magnesium hydroxide. Among these, a white inorganic pigment is preferable, and silica is particularly preferable in that the printing density can be further increased.

  The binder is not particularly limited as long as it is used in the field of paper coating. For example, water-soluble binders such as starch, oxidized starch, carboxymethylcellulose, casein, soy protein, and polyvinyl alcohol; styrene-butadiene copolymer And a polymer latex binder made of a water-insoluble polymer such as latex, styrene-methyl methacrylate-butadiene copolymer latex, and acrylate polymer latex.

  The amount of the binder used is preferably 5 to 50 parts by weight, more preferably 10 to 40 parts by weight with respect to 100 parts by weight of the total pigment. If the amount used is too small, the surface strength of the ink jet recording medium tends to decrease, and conversely if too large, the print density and gloss of the ink jet recording medium tend to decrease.

  The coating composition for an inkjet recording medium of the present invention may further include a pigment dispersant, a dye, a thickener, a fluidity improver, an antifoaming agent, a defoaming agent, a release agent, a foaming agent, if necessary. Add auxiliary materials such as penetrants, fluorescent brighteners, UV absorbers, antioxidants, preservatives, antibacterial agents, water resistance agents, wet paper strength enhancers, dry paper strength enhancers, dye fixing agents, etc. Can do. The amount of these components used, the method of blending them into the coating composition, and the like are appropriately selected within a range that does not impair the object of the present invention.

  The method for preparing the coating composition for an ink jet recording medium is not particularly limited. Generally, using a disperser, the pigment containing the organic pigment, the binder, and other compounding ingredients are added with water as necessary. And dispersed. In addition, the total solid content concentration of the coating composition is usually 5 to 50% by weight, preferably 10 to 40% by weight.

(Inkjet recording medium)
The inkjet recording medium of the present invention is obtained by coating the above-described coating composition for an inkjet recording medium on a support. The coating composition is applied to at least one surface of the support and dried. It can be obtained by forming a coating layer.

  The support constituting the ink jet recording medium is not particularly limited, and may be appropriately selected according to the purpose of use of the recording medium and the recording apparatus. For example, base paper such as newspaper base paper, high-quality base paper, medium base paper, etc .; coated paper coated with polyvinyl alcohol, starch, etc. on the base paper; coated paper with a coating layer mainly composed of pigment, art paper Coated paper such as cast paper; synthetic paper (polypropylene resin-based multilayer film, paper with both sides covered with polyethylene); polyester film, resin film such as PVC film; metal, glass, ceramic, etc. And the like. Of these, base paper, coated paper and synthetic paper can be preferably used.

The method for coating the inkjet recording medium coating composition on the support is not particularly limited. For example, it can coat using common coaters, such as a roll coater, an air knife coater, a blade coater, a rod blade coater, a curtain coater, a bar coater, a die coater, and a gravure coater.
The coating amount on the support is not particularly limited, but is usually 1 to 50 g / m ² , preferably 3 to 30 g / m ² .
After applying the coating composition to the support, it is possible to form a coating layer that functions as an ink receiving layer by heating at an appropriate temperature in the range of 50 to 150 ° C. and drying as necessary. it can.

  In the ink jet recording medium of the present invention, the obtained coating layer can be calendered as necessary to give smoothness and gloss to the ink receiving layer. Further, it may be applied directly on the support to form a single ink-receiving layer, or a multilayer structure including an ink-receiving layer may be used as necessary. For example, an anchor layer may be provided below the ink receiving layer, and a gloss layer may be further provided on the ink receiving layer.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples. Further, “parts” and “%” in these examples are based on weight unless otherwise specified.

The evaluation method will be described below.
(1) Volume average particle diameter (nm)
The volume average particle diameter of the organic pigment was measured with Coulter LS230 (manufactured by Coulter).
(2) Glass transition temperature (° C)
A latex containing an organic pigment is cast on a framed glass plate and left in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 65% for 48 hours to obtain a dry product having a thickness of about 0.3 mm. A sample was used.
The glass transition temperature of the sample was measured according to JIS K 7121 using a differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd .: SSC5200) under the conditions of a starting temperature of −100 ° C. and a heating rate of 20 ° C./min. Measured.

(3) Graft ratio in organic pigment The solid content concentration of the latex containing the organic pigment is adjusted to 10%, and 60 g thereof is used as a sample. The sample is centrifuged at 13,000 rpm for 60 minutes at 5 ° C., and 40 g of the supernatant is recovered. After adding 40 g of distilled water to the sedimented layer (20 g) to make it uniform, the solution is centrifuged again under the same conditions to recover 40 g of the supernatant and the same operation is repeated again for the sedimented layer. A total of 120 g of the solid content of the supernatant obtained by three times of centrifugation is measured, and the amount of solid content in the supernatant is calculated. This is the amount (A) of polyvinyl alcohol that did not bind to the polymer produced by polymerization. By subtracting (A) from the weight (B) of the total polyvinyl alcohol calculated from the charge in the sample, the amount (C) of polyvinyl alcohol bound to the polymer produced by the polymerization is obtained. From these values, the graft ratio (the ratio (%) of the alcoholic hydroxyl group-containing water-soluble polymer compound bonded to the polymer to the polymer derived from the monomer used for the polymerization) is calculated by the following formula. To do.
Graft rate = [C / (6-B)] × 100 (%)

(4) Gloss of non-printing part of inkjet recording medium (%)
Measurement was performed according to JIS P 8142.
(5) Print density of ink jet recording medium and gloss of printed part Using an ink jet printer (PM-870C: manufactured by Seiko Epson Corporation) in an atmosphere of 23 ° C. and relative humidity of 65%, the Japanese Standard Association The issued standard image data (image name: N5A) was printed. The print density of the black solid portion of the printed material was measured using a Macbeth ink densitometer. The higher the value, the higher the print density.
The gloss of the black solid part was measured according to JIS P 8142.

(6) Surface strength of inkjet recording medium A commercially available cellophane tape was applied to the surface of the coating layer, and then the cellophane tape was peeled off. The adhesive surface of the peeled cellophane tape was observed and judged according to the following criteria.
○: There is almost no exfoliation from the coating layer.
(Triangle | delta): The peeling thing from a coating layer is observed slightly.
X: The peeled material of the coating layer is observed on almost the entire surface.

(Example 1)
(Manufacture of organic pigments)
In a pressure vessel equipped with a stirrer, 130 parts of deionized water, 89 parts of styrene, 1 part of methacrylic acid, 10 parts of 1,3-butadiene and polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd., average polymerization degree 500, saponification degree 88 mol) %) 12 parts were added and stirred to obtain a monomer emulsion.
In a pressure-resistant reaction vessel equipped with a stirrer, 62 parts of deionized water and 8 parts of ethanol are added, the temperature is raised to 80 ° C., and 1 part of potassium persulfate is dissolved in 20 parts of deionized water while maintaining 80 ° C. The polymerization initiator aqueous solution was added to the reaction vessel. Thereafter, the monomer emulsion was continuously added to the reaction vessel over 4 hours 30 minutes. After the continuous addition of the monomer emulsion was completed, the reaction was performed after another 3 hours. Thereafter, the polymerization reaction was terminated by cooling. The polymerization conversion rate at this time was 96%.
After removing the unreacted monomer, the solid content concentration and pH were adjusted to obtain a latex containing organic pigment A having a solid content concentration of 30% and a pH of 8. The volume average particle diameter, glass transition temperature, and graft ratio of the organic pigment A were measured, and the results are shown in Table 1.

(Preparation of inkjet recording medium)
In a disperser, 85 parts of silica (Mizukasil P-78 manufactured by Mizusawa Chemical Industry Co., Ltd.), 15 parts of the organic pigment A (in terms of solid content) and 0.8 part of sodium polyacrylate were dispersed in water, and then a binder. An aqueous solution in which 25 parts of polyvinyl alcohol (PVA-117: manufactured by Kuraray Co., Ltd.) was dissolved was added and dispersed for another 30 minutes to obtain a coating composition for an ink jet recording medium having a solid content concentration of 20%.
The coating composition, the quality base paper having a basis weight of 60 g / m ^2, at a coat weight after drying was coated with a wire bar so as to 15g / m ^2, 100 ℃ hot air dryer 20 Dry for 2 seconds. The obtained coated paper was allowed to stand for 5 hours in a constant temperature and humidity chamber adjusted to a temperature of 23 ° C. and a humidity of 65%. Furthermore, the ink-jet recording medium was obtained by performing surface treatment twice with an experimental minicalender adjusted to a temperature of 40 ° C. and a linear pressure of 50 kg / cm.
The resulting inkjet recording medium was evaluated for gloss, print density and surface strength, and the results are shown in Table 1.

(Examples 2 to 4)
Except having changed into the monomer composition and the usage-amount of polyvinyl alcohol which are shown in Table 1, it superposed | polymerized similarly to Example 1 and obtained organic pigment BD. These physical properties were measured, and the results are shown in Table 1.
A coating composition for an inkjet recording medium was prepared and applied in the same manner as in Example 1 except that organic pigments B to D were used in place of the organic pigment A to obtain inkjet recording media. The gloss, print density, and surface strength of the obtained inkjet recording medium were evaluated, and the results are shown in Table 1.

(Comparative Example 1)
A pressure vessel was charged with 50 parts of deionized water, 0.2 part of sodium lauryl sulfate, 99 parts of styrene and 1 part of methacrylic acid and stirred to obtain a monomer emulsion.
A pressure-resistant reactor was charged with 60 parts of deionized water and 0.6 part of sodium lauryl sulfate, and then heated to 80 ° C. While maintaining 80 ° C., an aqueous solution in which 0.5 part of potassium persulfate was dissolved in 10 parts of deionized water was added, and the monomer emulsion was continuously added to the reactor for 4 hours and 30 minutes. Added. The addition of an aqueous solution in which 0.5 part of potassium persulfate was dissolved in 15 parts of deionized water was started simultaneously with the start of the addition of the monomer emulsion, and continued to the reactor for 4 hours and 30 minutes. Was added.
After the addition of the monomer emulsion was completed, the reaction was continued for another 3 hours and cooled to stop the polymerization reaction. The polymerization conversion rate at this time was 97%.
After removing unreacted monomers from the obtained reaction product, the solid content concentration was adjusted to 40% and the pH was adjusted to 8 to obtain a latex containing the organic pigment E. The glass transition temperature and volume average particle diameter of the organic pigment E were measured, and the results are shown in Table 1.
A coating composition for an inkjet recording medium was prepared and applied in the same manner as in Example 1 except that the organic pigment E was used in place of the organic pigment A, thereby obtaining an inkjet recording medium. The gloss, print density, and surface strength of the obtained inkjet recording medium were evaluated, and the results are shown in Table 1.

(Comparative Example 2)
An organic pigment F was obtained by polymerization in the same manner as in Example 1 except that the monomer composition and the amount of polyvinyl alcohol used were changed as shown in Table 1. The physical properties were measured and the results are shown in Table 1.
A coating composition for an inkjet recording medium was prepared and applied in the same manner as in Example 1 except that the organic pigment F was used in place of the organic pigment A, thereby obtaining an inkjet recording medium. The gloss, print density, and surface strength of the obtained inkjet recording medium were evaluated, and the results are shown in Table 1.

(Comparative Example 3)
Example 1 except that instead of the organic pigment A, hollow polymer particles (Rohpaque HP-1055 (Rohm and Haas Co., Ltd.): average particle size 1,000 nm, porosity 55%) were used in a solid content of 15 parts. In the same manner as described above, a coating composition for an inkjet recording medium was prepared and coated to obtain an inkjet recording medium, respectively. The gloss, print density, and surface strength of the obtained inkjet recording medium were evaluated, and the results are shown in Table 1.

Table 1 shows the following.
When organic pigment E obtained by polymerizing monomers using sodium lauryl sulfate that is usually used in emulsion polymerization is used, the gloss of the ink jet recording medium is lowered, and the print density and surface strength are also inferior (comparison). Example 1).
When an organic pigment F obtained by polymerizing a monomer in the presence of polyvinyl alcohol and having a glass transition temperature lower than the range defined in the present invention is used, the gloss of the ink jet recording medium is lowered (Comparative Example 2).
When the coating composition for inkjet recording media containing hollow polymer particles is used, the printing density and surface strength of the inkjet recording medium are inferior (Comparative Example 3).
Compared with these comparative examples, when the coating composition for inkjet recording media containing the organic pigments A to D of the present invention is used, the gloss of the non-printing surface and the printing surface is high, the printing density is high, and the surface strength is excellent. Inkjet recording media have been obtained (Examples 1 to 4).

Claims (4)

Contains a pigment and a binder containing an organic pigment made of a polymer having a glass transition temperature of 60 ° C. or higher, obtained by polymerizing a monomer in the presence of a water-soluble polymer containing an alcoholic hydroxyl group in an aqueous medium. An ink jet recording medium coating composition. 2. The coating composition for an ink jet recording medium according to claim 1, wherein the content of the organic pigment is 0.1 to 40% by weight in the total pigment. The coating composition for an ink jet recording medium according to claim 1 or 2, wherein the binder is used in an amount of 5 to 50 parts by weight with respect to 100 parts by weight of the total pigment. The inkjet recording medium formed by coating the support body with the coating composition for inkjet recording media as described in any one of Claims 1-3.