JP2007230059A - Polymer latex for ink jet recording medium and coating composition for ink jet recording medium - Google Patents

Abstract

Disclosed is a coating composition for an ink jet recording medium, which is excellent in surface strength and water resistance, further has excellent ink acceptability during ink jet printing, and forms a clear ink receiving layer in the obtained printed matter, and the coating composition A polymer latex suitable as a binder for forming an ink jet recording medium, and an ink jet recording medium obtained by coating the coating composition on a support.
A latex obtained by polymerizing a monomer in the presence of a neutralized product of an alkali-soluble copolymer, the alkali-soluble copolymer comprising a cationic group, an anionic group, and A polymer latex for an ink jet recording medium, which is a water-soluble polymer compound having an alcoholic hydroxyl group. A coating composition comprising the polymer latex. An ink jet recording medium obtained by coating the coating composition on a support.
[Selection figure] None

Description

  The present invention relates to a polymer latex for an ink jet recording medium, a coating composition for an ink jet recording medium containing the polymer latex, and an ink jet recording medium formed by coating the same.

In recent years, it has been strongly demanded that an ink jet recording medium in which improvement in print quality and higher resolution of a printed image are required have further offset printing suitability. For example, for personal printed matter such as direct mail, it is economically advantageous to print general information with an offset printer capable of high-speed printing, and to print personal variable information with an inkjet printer. Such an ink jet recording medium needs to have both ink jet printability and offset printability.
Specifically, there is a demand for an ink jet recording medium that has excellent ink acceptability during ink jet printing, has good water resistance of printed matter, and has ink jet printing suitability and has surface strength capable of offset printing.

  Conventionally, Patent Document 1 discloses that an adhesive prepared by mixing polyvinyl alcohol and ethylene / vinyl acetate copolymer in a specific ratio, synthetic silica, acrylic amide based cationic polymer, dimethyldiallylammonium chloride / sulfur dioxide copolymer, and A postcard recording paper having an ink-receiving layer for inkjet printing capable of offset printing, to which a coating liquid containing a specific amount of polyamide polyurea resin is applied, is disclosed. However, this recording paper is relatively excellent in ink acceptability during ink jet printing, but has insufficient water resistance and surface strength.

  Patent Document 2 discloses a heavy-duty material for an ink jet recording medium comprising a polymer obtained by polymerizing a monomer in the presence of a water-soluble polymer, and the content of tetrahydrofuran insoluble in the polymer is 80% by weight or less. A combined latex is disclosed. The ink jet recording medium obtained using this latex has excellent ink absorbability and good water resistance of the printed matter, but there is no description about having a surface strength capable of offset printing.

JP-A-10-337980 JP 2003-312126 A

  In view of the above circumstances, an object of the present invention is an ink jet recording for forming an ink receiving layer having excellent ink acceptability during ink jet printing, good water resistance of printed matter, and having surface strength capable of offset printing. An object of the present invention is to provide a medium coating composition, a polymer latex suitable as a binder constituting the coating composition, and an ink jet recording medium obtained by coating the coating composition on a support.

  As a result of intensive studies to achieve the above object, the present inventors have found that the alkali-soluble copolymer in the latex obtained by polymerizing the monomer in the presence of a neutralized product of the alkali-soluble copolymer. A polymer latex characterized in that the polymer is a water-soluble polymer compound having a cationic group, an anionic group, and an alcoholic hydroxyl group can achieve the above object, and the present invention is completed. I came to let you.

Thus, according to the present invention, the following inventions 1 to 6 are provided.
1. A latex obtained by polymerizing a monomer in the presence of a neutralized product of an alkali-soluble copolymer,
A polymer latex for an ink jet recording medium, wherein the alkali-soluble copolymer is a water-soluble polymer compound having a cationic group, an anionic group, and an alcoholic hydroxyl group.
2. 2. The polymer latex for inkjet recording media according to 1, wherein the ratio of the neutralized product of the alkali-soluble copolymer to 10 parts by weight of the monomer is 10 to 40 parts by weight.
3. 3. The polymer latex for inkjet recording media according to 1 or 2 above, wherein the cationic group of the alkali-soluble copolymer is a tertiary amine.
4). 4. The polymer latex for ink jet recording medium according to any one of 1 to 3, wherein the alkali-soluble copolymer comprises a cation-modified vinyl alcohol polymer as a copolymerization component.
5). A coating composition for an ink jet recording medium, comprising the polymer latex for an ink jet recording medium according to any one of 1 to 4 above.
6). 6. An ink jet recording medium obtained by coating the support composition with the coating composition for ink jet recording medium according to 5 above.

  According to the present invention, the coating composition for an ink jet recording medium for forming an ink receiving layer having excellent surface strength and water resistance, high ink acceptability during ink jet printing, and a clear printed matter is obtained. A polymer latex suitable as a binder constituting the coating composition and an ink jet recording medium obtained by coating the coating composition on a support can be provided.

  The latex of the present invention is produced by polymerizing the monomer (B) in the presence of a neutralized product of the alkali-soluble copolymer (A).

Neutralized product of alkali-soluble copolymer (A) The neutralized product of the alkali-soluble copolymer (A) used in the present invention is an alkali-soluble material having a cationic group, an anionic group, and an alcoholic hydroxyl group. It is obtained by neutralizing a copolymer with a basic substance.
The alkali-soluble copolymer (A) according to the present invention is preferably an anionic group-containing ethylenically unsaturated monomer and a cationic group in the presence of an alcoholic hydroxyl group-containing water-soluble polymer compound (a1). It is obtained by polymerizing a monomer mixture (a2) for an alkali-soluble copolymer comprising an ethylenically unsaturated monomer containing and another monomer copolymerizable therewith.

  The alcoholic hydroxyl group-containing water-soluble polymer compound (a1) means a water-soluble polymer compound containing 5 to 25 alcoholic hydroxyl groups per 1,000 molecular weight. Examples of the alcoholic hydroxyl group-containing water-soluble polymer compound (a1) include vinyl alcohol polymers such as polyvinyl alcohol and various modified products thereof; co-polymerization of vinyl acetate and acrylic acid, methacrylic acid or maleic anhydride Saponified products of coalescence; cellulose derivatives such as alkyl cellulose, hydroxyalkyl cellulose, alkyl hydroxyalkyl cellulose; starch derivatives such as alkyl starch, carboxymethyl starch and oxidized starch; gum arabic, tragacanth gum; polyalkylene glycol;

Among these, a vinyl alcohol polymer is preferable because it is easy to obtain industrially stable quality.
The vinyl alcohol polymer used in the present invention preferably has a cationic group from the viewpoint of excellent ink acceptability, and among them, a cation-modified vinyl alcohol polymer having a quaternary ammonium salt in the side chain. Is preferred. Examples of the cation-modified vinyl alcohol polymer having a quaternary ammonium salt in the side chain include, for example, product names C-506 and CM-318, which are cation-modified polyvinyl alcohols manufactured by Kuraray Co., Ltd., and products manufactured by Nippon Synthetic Chemical Co., Ltd. Name K210 etc. can be mentioned.

  The weight average molecular weight of the alcoholic hydroxyl group-containing water-soluble polymer compound (a1) is not particularly limited, but is 10,000 to 500,000, preferably 20,000 to 150,000. If the weight average molecular weight is too small, the dispersion stabilizing effect may be lowered. On the other hand, when the weight average molecular weight is too large, the viscosity at the time of polymerization becomes high and the polymerization may be difficult.

  The ratio of the alcoholic hydroxyl group-containing water-soluble polymer (a1) to the monomer mixture (a2) for the alkali-soluble copolymer is not particularly limited, but is preferably based on 100 parts by weight of the monomer mixture. Is 0.2 to 15 parts by weight, more preferably 0.8 to 8 parts by weight.

The anionic group-containing ethylenically unsaturated monomer is not particularly limited, and examples thereof include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid; itaconic acid, maleic acid, fumaric acid, and butenetricarboxylic acid. Ethylenically unsaturated polyvalent carboxylic acid monomer such as acid; partial ester monomer of ethylenically unsaturated polyvalent carboxylic acid such as monobutyl fumarate, monobutyl maleate, mono 2-hydroxypropyl maleate; maleic anhydride Ethylenically unsaturated carboxylic acid monomers such as styrene sulfonic acid, allyloxybenzene sulfonic acid, methallyloxybenzene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid , Sulfone such as methallyl sulfonic acid, 4-sulfonic acid butyl methacrylate And monomers having acid groups. These monomers can be used alone or in combination of two or more.
Among these anionic group-containing ethylenically unsaturated monomers, an ethylenically unsaturated carboxylic acid monomer and a monomer having a sulfonic acid group are preferable. It is preferable to use a monomer having an acid group in combination.
As the ethylenically unsaturated carboxylic acid monomer, (meth) acrylic acid [meaning methacrylic acid and / or acrylic acid. An ethylenically unsaturated monocarboxylic acid such as The monomer having a sulfonic acid group is preferably styrene sulfonic acid. When a monomer having a sulfonic acid group is used, the resulting polymer latex is excellent in blending stability.

  The amount of the anionic group-containing ethylenically unsaturated monomer is preferably 5 to 80% by weight, more preferably 10 to 50% by weight, based on 100% by weight of the whole monomer mixture (a2). When there are too few ethylenically unsaturated carboxylic acid monomers, the obtained copolymer may not become soluble in an alkali. On the other hand, if the amount is too large, the dispersion stabilizing effect may be reduced.

Examples of the cationic group-containing ethylenically unsaturated monomer include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, diisopropylaminoethyl (meth) acrylate, dibutylaminoethyl ( (Meth) acrylate, diisobutylaminoethyl (meth) acrylate, di-t-butylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide, dipropylaminopropyl (meth) acrylamide, diisopropylaminopropyl (Meth) acrylamide, dibutylaminopropyl (meth) acrylamide, diisobutylaminopropyl (meth) acrylamide, di-t-butylaminopropyl (Meth) acrylic acid ester or (meth) acrylamide having a dialkylamino group such as pill (meth) acrylamide, styrene having a dialkylamino group such as dimethylaminostyrene or dimethylaminomethylstyrene, 4-vinylpyridine, 2- Acid neutralized products of monomers having amino groups such as vinylpyridines such as vinylpyridine, N-vinyl heterocyclic compounds such as N-vinylimidazole, vinyl ethers such as aminoethyl vinyl ether and dimethylaminoethyl vinyl ether, or 4 Secondary ammonium salts; diallyl-type quaternary ammonium salts such as dimethyldiallylammonium chloride and diethyldiallylammonium chloride.
Among these, the cationic group is preferably a tertiary amine from the viewpoint of ion binding, and an ethylenically unsaturated monomer having a dialkylamino group such as dimethylaminoethyl (meth) acrylate is preferable.

  The amount of the cationic group-containing ethylenically unsaturated monomer used is preferably 5 to 50% by weight, more preferably 8 to 30% by weight, based on 100% by weight of the whole monomer mixture (a2). When there are too few cationic group containing ethylenically unsaturated monomers, water resistance may be inferior. On the other hand, if the amount is too large, the dispersion stabilizing effect may be reduced.

  Examples of other monomers copolymerizable with an anionic group-containing ethylenically unsaturated monomer and a cationic group-containing ethylenically unsaturated monomer include, but are not limited to, for example, styrene, α-methylstyrene, Aromatic vinyl monomers such as vinyltoluene and chlorostyrene; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, ( N-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, 2-hydroxy (meth) acrylate Ethylenically unsaturated carboxylic acids such as ethyl, hydroxypropyl (meth) acrylate and glycidyl (meth) acrylate Ter monomers; sulfonic acid group-containing ethylenically unsaturated monomers such as vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid and sodium styrene sulfonate; cyano group-containing ethylenic unsaturated such as (meth) acrylonitrile Monomer; Ethylenically unsaturated glycidyl ether monomer such as allyl glycidyl ether; Ethylenically unsaturated amide monomer such as (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide Conjugated diene monomers such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene; carboxylic acid vinyl esters such as vinyl acetate; These monomers can be used alone or in combination of two or more.

The amount of other copolymerizable monomer used is preferably 14 to 85% by weight, more preferably 40 to 80% by weight, based on 100% by weight of the whole monomer mixture (a2).

  Of the monomer mixture (a2) used for the production of the alkali-soluble copolymer, a monomer having a relatively low solubility in water, that is, a monomer having a solubility in 100 g of water at 20 ° C. of less than 0.2 g. The amount of the monomer used is preferably 30% by weight or less. If the amount is too large, the resulting copolymer may not be soluble in alkali.

  The alkali-soluble copolymer (A) comprises an anionic group-containing ethylenically unsaturated monomer and a cationic group-containing ethylenically unsaturated monomer in the presence of the alcoholic hydroxyl group-containing water-soluble polymer (a1). It can be obtained by polymerizing a monomer mixture (a2) composed of a monomer and another monomer copolymerizable therewith in an aqueous medium. At this time, a method in which the alcoholic hydroxyl group-containing water-soluble polymer and the monomer mixture are collectively added to the reactor before the start of polymerization and then polymerized may be employed, or before the start of polymerization. Alternatively, a method may be employed in which only a part is added and divided addition or continuous addition is performed after the start of polymerization. In addition, in the case of divided addition or continuous addition, the addition amount and the addition time may be adjusted as appropriate. For example, the addition amount is made uniform, the addition time is made constant, or the addition amount and the addition time are polymerized. It can be changed according to the progress stage.

  The alcoholic hydroxyl group-containing water-soluble polymer compound (a1) and the monomer mixture (a2) may be separately added to the reactor, or these may be dispersed in water in advance to obtain a dispersion. It may be added to the reactor. Among these addition methods, a method of dispersing in water in advance and dividing or continuously adding to the reactor as a dispersion is preferable. By adopting such a method, it is possible to make the chain distribution of anionic groups and cationic groups in the polymer chain uniform in the obtained alkali-soluble copolymer.

  Alternatively, when the alcoholic hydroxyl group-containing water-soluble polymer compound (a1) and the monomer mixture (a2) are added separately, it is desirable to start both additions almost simultaneously. If only a large amount of the monomer mixture is added first, aggregates are likely to be generated. On the other hand, when only a large amount of the alcoholic hydroxyl group-containing water-soluble polymer compound is added in advance, the polymerization system thickens or aggregates are easily generated. The addition of both does not necessarily have to be at the same time, but it is desirable that the addition be almost the same.

  The polymerization initiator for polymerizing the monomer mixture (a2) for the alkali-soluble copolymer is not particularly limited, and examples thereof include sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and peroxidation. Inorganic peroxides such as hydrogen; diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide, iso And organic peroxides such as butyryl peroxide and benzoyl peroxide; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and methyl azobisisobutyrate; These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used varies depending on the type, but is 0.2 to 15 parts by weight, preferably 0.8 to 5 parts by weight, based on 100 parts by weight of the whole monomer mixture for the alkali-soluble copolymer. It is.

  These polymerization initiators can also be used as a redox polymerization initiator in combination with a reducing agent. The reducing agent used in this case is not particularly limited. For example, a compound having a metal ion in a reduced state such as ferrous sulfate and cuprous naphthenate; a sulfonic acid compound such as sodium methanesulfonate; dimethylaniline And the like, and the like. These reducing agents can be used alone or in combination of two or more. Although the usage-amount of a reducing agent changes with the kinds, Preferably it is 0.03-10 weight part with respect to 1 weight part of polymerization initiators.

  In the production of the alkali-soluble copolymer, a chain transfer agent can be used as necessary. Although it does not specifically limit as a chain transfer agent, From the viewpoint of the efficiency of chain transfer, the compound which has a mercapto group is preferable. Among them, particularly preferred are alkyl mercaptans such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, octyl thioglycolate, 3-mercaptopropionic acid and the like, which are compounds having 20 or less carbon atoms.

  When using a chain transfer agent, the addition amount is preferably 1 to 15 parts by weight, more preferably 5 to 12 parts by weight, based on 100 parts by weight of the whole monomer mixture (a2) for the alkali-soluble copolymer. Part. When the addition amount of the chain transfer agent is too small, the viscosity after neutralization tends to be high and handling tends to be difficult. On the other hand, when the amount is too large, the molecular weight of the resulting polymer is remarkably lowered, and it does not function as a dispersion stabilizer. The method of adding the chain transfer agent to the polymerization system is not particularly limited, and a method of batch addition may be adopted, or a method of adding intermittently or continuously may be adopted.

  The polymerization temperature when producing the alkali-soluble copolymer is preferably 0 to 100 ° C, more preferably 30 to 90 ° C.

And the neutralized product of an alkali-soluble copolymer (A) can be obtained by neutralizing the alkali-soluble copolymer (A) manufactured as mentioned above with a basic substance.
The basic substance used for neutralizing the alkali-soluble copolymer (A) is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; calcium hydroxide and hydroxide. Examples include alkaline earth metal hydroxides such as magnesium; ammonia; amines such as triethylamine and triethanolamine; and the like, and mixtures thereof. Of these, ammonia is preferred.

  In addition, the neutralization degree of the neutralized product of the alkali-soluble copolymer (A) used in the present invention is not particularly limited, and usually the neutralization degree (base to the molar equivalent of the ethylenically unsaturated acid monomer). The molar equivalent of the active substance) is 70% or more, preferably 95% or more.

Polymerization of the monomer (B) in the presence of the neutralized product of the alkali-soluble copolymer (A) Next, in the presence of the neutralized product of the alkali-soluble copolymer (A) obtained above, The latex of the present invention is obtained by polymerizing the monomer (B).
Although it does not specifically limit as a monomer (B) for superposing | polymerizing in presence of the neutralized material of an alkali-soluble copolymer, For example, aromatic vinyl, such as styrene, (alpha) -methylstyrene, vinyl toluene, chlorostyrene, etc. Monomer; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl (meth) acrylate, (meta ) Isoamyl acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, Ethylenically unsaturated carboxylic acid ester monomers such as (meth) acrylic acid glycidyl; (meth) acrylonitrile Cyano group-containing ethylenically unsaturated monomers; ethylenically unsaturated glycidyl ether monomers such as allyl glycidyl ether; ethylenically unsaturated amide monomers such as (meth) acrylamide and N-methylol (meth) acrylamide; Conjugated diene monomers such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene; carboxylic acid vinyl esters such as vinyl acetate; acrylic acid, methacrylic acid, fumaric acid And ethylenically unsaturated carboxylic acid monomers such as maleic acid and monoethyl maleate; and crosslinkable monomers such as divinylbenzene, ethylene glycol di (meth) acrylate and tetraethylene glycol di (meth) acrylate. These monomers can be used alone or in combination of two or more.

  The ratio between the neutralized product of the alkali-soluble copolymer (A) and the monomer (B) polymerized in the presence of the neutralized product is preferably set in the following range. That is, the ratio of the neutralized product of the alkali-soluble copolymer (A) to 100 parts by weight of the monomer is preferably 10 to 40 parts by weight, more preferably 20 to 35 parts by weight. When the neutralized product of the alkali-soluble copolymer is too little, the effect of dispersing and dispersing the polymer is lowered, aggregates are generated, and latex may not be stably obtained. On the other hand, if the amount is too large, the viscosity of the resulting latex becomes high, making it difficult to handle, and the water resistance of the resulting inkjet recording medium may deteriorate.

  The latex of the present invention can be obtained by polymerizing the monomer (B) in an aqueous medium in the presence of a neutralized product of the alkali-soluble copolymer (A). At this time, a method may be employed in which the neutralized product of the alkali-soluble copolymer (A) and the monomer (B) are collectively added to the reactor before the polymerization is started and then polymerized. Alternatively, a method may be adopted in which only a part of the neutralized product and the monomer is added before the start of polymerization, and then added in portions or continuously after the start of the polymerization. In addition, in the case of divided addition or continuous addition, the addition amount and the addition timing may be appropriately adjusted. For example, the addition amount is made uniform, the addition timing is made constant, or these are added to the progress stage of polymerization. It can be changed accordingly.

  The neutralized product of the alkali-soluble copolymer (A) and the monomer (B) may be added separately to the reactor, or they may be dispersed in water in advance to form a dispersion. It may be added to the vessel. When the neutralized product of the alkali-soluble copolymer and the monomer are added separately, it is desirable to start both additions almost simultaneously. If only a monomer is added in a large amount first, aggregates are likely to be generated. On the other hand, when only a neutralized product of the alkali-soluble copolymer is added in a large amount in advance, the polymerization system is thickened or aggregates are easily generated. The addition of both does not necessarily have to be at the same time, but it is desirable that the addition be almost the same.

  The temperature at which the monomer (B) is polymerized is preferably 0 to 100 ° C, more preferably 30 to 90 ° C. The polymerization time is usually 30 minutes to 50 hours. The polymerization reaction can be stopped by adding a known polymerization terminator to the reaction system or by cooling the reaction system. The polymerization conversion rate when stopping the polymerization reaction can be appropriately adjusted as desired. After the completion of the polymerization, a polymer latex can be obtained by performing a post-treatment such as removing unreacted monomers as necessary.

  (Coating composition for ink jet recording medium) The coating composition for ink jet recording medium of the present invention comprises the copolymer latex. The copolymer latex functions as a medium for dispersing necessary components or optional components that are usually blended in this type of coating composition, and fixes them to a suitably selected support to form an ink receiving layer. It has a binder function for forming.

  In addition to the polymer latex described above, the components blended in the present coating composition include, for example, inorganic void forming materials, pigments, pigment dispersants, dyes, thickeners, fluidity improvers, antifoaming agents, suppressors. Foaming agent, mold release agent, foaming agent, penetrating agent, fluorescent whitening agent, ultraviolet absorber, antioxidant, preservative, antibacterial agent, water resistant agent, wet paper strength enhancer, dry paper strength enhancer, dye Examples thereof include a fixing agent. The amount of these components used, the method of blending them into the coating composition, and the like are appropriately selected within a range not impairing the object of the present invention.

  The inorganic void forming material is used to fix the ink adhering to the surface of the recording medium to the vicinity of the surface of the recording medium within a short time before the area of the ink is increased. In order to have the function of absorbing and fixing, it is preferably blended into the coating composition. Examples of such inorganic void forming materials include silica and alumina, and these also function as pigments. The compounding amount of the inorganic void forming material is usually in the range of 100 to 1000 parts by weight, preferably 200 to 500 parts by weight with respect to 100 parts by weight of the solid content of the polymer latex. When there are too many compounding quantities of an inorganic space | gap formation material, the film formability of the coating composition obtained and the adhesiveness on a support body may be inferior. On the other hand, if the amount is too small, the effect of blending the inorganic void forming material can hardly be obtained.

  Examples of the pigment include silica, alumina, calcium carbonate, magnesium carbonate, kaolin, talc, titanium oxide, zinc oxide, aluminum oxide, barium sulfate, calcium sulfate, magnesium silicate, aluminum silicate, diatomaceous earth, zeolite, aluminum hydroxide, And inorganic pigments such as magnesium hydroxide; organic pigments such as hollow particles, styrene plastic pigments, and acrylic plastic pigments. Among these, inorganic pigments are preferable, and silica is particularly preferable. A compounding quantity is 100-1000 weight part normally with respect to 100 weight part of solid content of polymer latex, Preferably it is the range of 200-500 weight part.

  The method for preparing the coating composition is not particularly limited, and is generally prepared by using a disperser and adding and dispersing the polymer latex, other compounding components, and water as required. The total solid 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-mentioned coating composition on a support, and the coating composition is applied to at least one surface of the support and dried. It can be obtained by forming a coating film as an ink receiving layer.

  The support constituting the 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. Base paper, coated paper, and synthetic paper are preferable.

The method of applying on the support using the coating composition is not particularly limited. For example, it can apply | 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, 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 . The thickness of the coating film is usually 20 to 60 μm. After applying the coating composition to the support, the ink receiving layer can be formed by heating at an appropriate temperature in the range of 50 to 150 ° C., if necessary.

  The recording medium of the present invention can impart smoothness and gloss to the ink receiving layer by calendering the obtained coating film as necessary. 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.

  The ink jet recording medium of the present invention is particularly useful as an ink jet recording method for recording by ejecting small droplets of ink, and further as a recording medium (sheet) by an offset printing method because of excellent surface strength, such as flexographic printing. It can also be used as a water-based ink printing sheet.

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) Weight average particle diameter (nm)
The weight average particle diameter of the polymer latex was measured with Coulter LS230 (Culter particle diameter measuring machine).
(2) Glass transition temperature Polymer latex was cast on a framed glass plate, left in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 65% for 48 hours, and dried to obtain a polymer latex film. .
The glass transition temperature of the film was measured 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 5 ° C./min.

(3) Surface strength Using a RI tester (manufactured by Akashi Seisakusho) with a printing ink (tack value: TV-20) 0.4 cm ³ attached to a rubber roll, the coating composition for an inkjet recording medium of the present application was applied. The resulting ink jet recording medium was overprinted 4 times. The state of peeling (picking) of the paper surface was observed and evaluated by a 5-point method. The higher the score, the higher the dry pick strength.
(4) Ink acceptability 5 μL of distilled water was dropped onto the surface of the obtained inkjet recording medium, and the time until all of the dropped distilled water was absorbed by the inkjet recording medium was measured. It was visually confirmed that distilled water was absorbed.
The faster the distilled water is absorbed, the better the ink acceptability.

(5) Vividness Printing was performed on an inkjet recording medium using an inkjet printer (PM-870C: manufactured by Seiko Epson Corporation) in an atmosphere of 23 ° C. and relative humidity of 65%. The ink bleeding of this printing was visually evaluated according to the following criteria.
○: No blurring △: Slightly blurring ×: Clearly blurring

(6) Water resistance 100% red, 100% green, 100% blue mixed color solid print (PM photo paper mode, high-definition) is printed on the ink jet recording sheet by Seiko Epson's ink jet printer PM-970C. One drop of water was dropped on the part using a dropper and left for 1 minute, then covered with plain paper, rubbed by hand, and the degree of ink transferred to the plain paper was visually evaluated.
○: Ink does not transfer.
Δ: Ink is slightly transferred.
X: The ink is clearly transferred.

(Examples 1-3, Comparative Examples 1-3)
Example 1
Preparation of neutralized product of alkali-soluble copolymer (A) Methyl methacrylate: 17.5 parts, methacrylic acid: 6.5 parts, sodium styrenesulfonate: 1 part, N, N dimethylaminoethyl (meth) acrylate: 5 parts, octyl thioglycolate: 2.35 parts, polyvinyl alcohol (polymerization degree 500, saponification degree 88 mol%, manufactured by Kuraray Co., Ltd.): 2 parts and ion-exchanged water: 30 parts were stirred and mixed to prepare a dispersion. did. On the other hand, 85 parts of ion-exchanged water was charged into a reactor equipped with a stirrer with nitrogen inside, and then heated to 80 ° C., and 40 parts of 5% aqueous potassium persulfate solution was added to the reactor. The monomer was polymerized by continuously adding the dispersion prepared above to the reactor maintained at 80 ° C. over 2 hours. After completing the addition of the dispersion, the mixture was further maintained at 80 ° C. for 30 minutes to obtain an aqueous dispersion of an alkali-soluble copolymer. Subsequently, 28% ammonia water was added to the obtained aqueous dispersion of the alkali-soluble copolymer so as to have an equimolar amount with methacrylic acid constituting the copolymer, and then the solid content concentration was adjusted to 25. % Neutralized aqueous solution of alkali-soluble copolymer was obtained.

Production of Latex Subsequently, the neutralized aqueous solution of the alkali-soluble copolymer obtained above was charged into a 30-part reactor in terms of solid content, then heated to 80 ° C., and 5% aqueous potassium persulfate solution: 12 .6 parts were added to the reactor. By continuously adding a mixture of monomers (B) obtained by mixing 42 parts of methyl methacrylate and 58 parts of butyl acrylate into a reactor maintained at 80 ° C. over 2 hours, The monomer was polymerized. After the addition of the monomer (B) mixture was completed, the mixture was further polymerized for 3 hours, and finally cooled to 30 ° C. to obtain a latex having a solid content concentration of 35% and a pH of 7.2.
About the obtained latex, the weight average particle diameter and the glass transition temperature were measured. The results are shown in Table 1.

(Coating composition)
In a disperser, 100 parts of silica (Fine Seal X-45: manufactured by Tokuyama) and 0.5 parts of sodium polyphosphate are dispersed in water, and then adjusted to 10% polyvinyl alcohol (PVA117: manufactured by Kuraray) with a solid content. And 15 parts of each of the above polymer latexes in solid content were added and mixed for 30 minutes to obtain a coating composition having a solid content concentration of 20%.
When the coating compositions obtained using the latexes of Examples 1 to 3 were filtered using a 200-mesh stainless wire mesh, there were no aggregates remaining on the stainless wire mesh, and the blending stability was good.
This coating composition was coated on a high-quality base paper having a basis weight of 130 g / m ² using a wire bar so that the dry weight was 15 g / m ^{2 on} one side, and dried for 60 seconds with a 120 ° C. hot air dryer. did. The obtained coated paper was allowed to stand for 5 hours in a constant temperature and humidity chamber having a temperature of 23 ° C. and a relative humidity of 65% to obtain an ink jet recording medium. Various evaluation was implemented about the inkjet recording medium produced using polymer latex 1A-3A and 1B-2B. The evaluation results are shown in Table 1.

Table 1 shows the following.
An ink jet recording medium obtained using a water-soluble polymer compound containing no alcoholic hydroxyl group or a water-soluble polymer compound containing no cationic group is inferior in surface strength and ink acceptability during printing, and It can be seen that the sharpness and water resistance are also poor. (Comparative Examples 1 and 2).

Compared to these comparative examples, a recording medium prepared using a polymer latex within the scope of the present invention is excellent in surface strength and water resistance, has high ink acceptability, and has a clear printed matter. It can be seen that a recording medium can be obtained (Examples 1 to 3).

Claims (6)

A latex obtained by polymerizing a monomer in the presence of a neutralized product of an alkali-soluble copolymer,
A polymer latex for an ink jet recording medium, wherein the alkali-soluble copolymer is a water-soluble polymer compound having a cationic group, an anionic group, and an alcoholic hydroxyl group.   The polymer latex for inkjet recording media according to claim 1, wherein the ratio of the neutralized product of the alkali-soluble copolymer to 10 parts by weight of the monomer is 10 to 40 parts by weight.   The polymer latex for inkjet recording media according to claim 1 or 2, wherein the cationic group of the alkali-soluble copolymer is a tertiary amine.   The polymer latex for an ink jet recording medium according to any one of claims 1 to 3, wherein the alkali-soluble copolymer comprises a cation-modified vinyl alcohol polymer as a copolymerization component.   The coating composition for inkjet recording media containing the polymer latex for inkjet recording media in any one of Claims 1-4. An ink jet recording medium obtained by coating the coating composition for ink jet recording medium according to claim 5 on a support.