JP2009280754A - Resin composition, coat layer and inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition containing a cross-linked structure of a polyvinyl alcohol resin, which the structure is hardly discolored with time. <P>SOLUTION: The resin composition contains the cross-linked structure (C), which is obtained by cross-linking the polyvinyl alcohol resin (A) having an acetoacetate group by using a hydrazine compound (B), and a reductant (D). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a resin composition containing a cross-linked structure formed by cross-linking a polyvinyl alcohol resin, and more specifically, a cross-link formed by cross-linking an acetoacetate group-containing polyvinyl alcohol resin with a hydrazine compound. The present invention relates to a resin composition containing a structure. The present invention also relates to a coating layer containing such a resin composition and an inkjet recording medium having at least one layer containing such a resin composition on a supporting substrate.

  Polyvinyl alcohol-based resins (hereinafter abbreviated as PVA-based resins) are made of dispersants, emulsifiers, emulsifiers, etc. using excellent water solubility, interface properties, film properties (film forming properties, strength, oil resistance, etc.), etc. Widely used in suspending agents, fiber processing agents, paper processing agents, binders, adhesives, films and the like. However, since PVA-based resins are water-soluble, they have poor water resistance, and studies aimed at improving them, particularly water resistance studies by crosslinking, have been widely conducted.

  However, in the case of a general PVA-based resin, the functional group that can be used for the crosslinking reaction is only the secondary hydroxyl group, and the crosslinking methods and crosslinking agents that can be used are limited. Therefore, various modified PVA-based resins into which functional groups rich in reactivity have been introduced have been proposed in order to increase the options for the crosslinking reaction and improve the crosslinking efficiency. Among them, it is known that a crosslinked structure obtained by crosslinking a modified PVA resin having an acetoacetate group that can be applied with various crosslinking agents and has excellent reactivity is excellent in water resistance. A resin composition containing a structure is widely used for a protective layer of thermal paper.

Examples of the compound suitably used as a crosslinking agent for the acetoacetate group-containing PVA resin (hereinafter abbreviated as AA-PVA resin) include aldehyde compounds, amine compounds, hydrazine compounds, methylol compounds, and metal compounds. It is known and used in various applications depending on its properties.
Among these, hydrazine compounds are suitable for applications requiring a relatively fast crosslinking rate. For example, an aqueous coating solution containing an AA-PVA-based resin, a hydrazine compound, and inorganic fine particles is coated on a supporting substrate. Ink jet recording media have been proposed in which a glossy layer is formed by heating, crosslinking and gelation, and drying under mild conditions. (For example, refer to Patent Document 1.)

JP 2005-145043 A

However, the cross-linked structure obtained by cross-linking AA-PVA-based resin with a hydrazine compound has a tendency to color over time depending on the storage environment and use conditions, etc. In applications where coloring is disliked, the improvement is a major issue.
That is, the present invention aims to suppress coloration with time in a crosslinked structure obtained from an AA-PVA-based resin and a hydrazine compound.

  As a result of intensive studies in view of the above circumstances, the present inventor contains a crosslinked structure (C) obtained by crosslinking the AA-PVA-based resin (A) with a hydrazine compound (B) and a reducing agent (D). The present invention has been completed by finding that the above-mentioned problems can be solved by a resin composition characterized by:

  The resin composition of the present invention is extremely suitable as a coating layer for various substrates or a glossy layer of an ink jet recording medium because of less coloring over time.

しかしながら、かかる架橋構造の一部では、その後、ヒドラジン化合物に由来するＮＨ基窒素がアセト酢酸エステル基に由来するカルボニル基炭素を求核攻撃し、続いてエステル基が切断し、下記式に示すように、ＰＶＡ系樹脂側がビニルアルコール構造となるとともに、ピラゾロン環を有する化合物が生成する。

The AA-PVA-based resin and the hydrazine compound are considered to have a crosslinked structure formed by a reaction between an acetoacetate group represented by the following formula and a hydrazino group.

However, in some of these cross-linked structures, NH group nitrogen derived from the hydrazine compound subsequently nucleophilically attacks the carbonyl group carbon derived from the acetoacetate group, followed by cleavage of the ester group, as shown in the following formula: In addition, the PVA resin side has a vinyl alcohol structure and a compound having a pyrazolone ring is formed.

  In the present invention, in the cross-linked structure of the AA-PVA-based resin and the hydrazine compound, the oxide of the pyrazolone ring-containing compound is a causative agent for coloring, and the use of a reducing agent in combination suppresses the generation of the oxide. It is speculated that coloring was reduced.

The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

[AA-modified PVA resin (A)]
First, the AA-PVA-based resin (A) used in the present invention will be described.
The AA-PVA-based resin (A) used in the present invention is a PVA-based resin having an acetoacetyl group in the side chain.
The method for producing the AA-PVA-based resin (A) is not particularly limited. For example, the PVA-based resin is reacted with diketene, and the PVA-based resin is reacted with acetoacetate for transesterification. Method, a method of saponifying a copolymer of vinyl acetate and vinyl acetoacetate, etc., but since the production process is simple and a good quality AA-PVA-based resin is obtained, the PVA-based resin and diketene It is preferable to manufacture by the method of reacting. Hereinafter, this method will be described.

  As the PVA resin used as a raw material, a saponified product of a vinyl ester monomer polymer or a derivative thereof is generally used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, and valeric acid. Examples include vinyl, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, and vinyl acetate is preferably used from the viewpoint of economy.

  Further, a saponified product of a copolymer of a vinyl ester monomer and a monomer copolymerizable with the vinyl ester monomer can be used. Examples of the copolymer monomer include ethylene, propylene, isobutylene, α- Olefins such as octene, α-dodecene, α-octadecene, hydroxy such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 3,4-dihydroxy-1-butene Derivatives such as group-containing α-olefins and acylates thereof, unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, undecylenic acid, salts, monoesters, or dialkyl esters thereof , Nitriles such as acrylonitrile and methacrylonitrile, diacetone acrylate Amides such as amide, acrylamide and methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid or salts thereof, alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl Vinyl compounds such as ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerol monoallyl ether, substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate, vinylidene chloride, 1, Examples include 4-diacetoxy-2-butene, 1,4-dihydroxy-2-butene, vinylene carbonate, and the like.

  The introduction amount of the copolymerization monomer varies depending on the type of the monomer and cannot be generally specified. However, it is usually 10 mol% or less, particularly 5 mol% or less. Since it may become a reaction inhibition factor, it is not preferable.

  In the case of ordinary PVA-based resins, the main chain bonding mode is mainly 1,3-diol bonds, and the content of 1,2-diol bonds is about 1.5 to 1.7 mol%. It is also possible to use those having a content of 1.7 to 3.5 mol% by increasing the polymerization temperature when polymerizing the vinyl ester monomer.

  The introduction of acetoacetyl groups by the reaction between the PVA resin obtained by saponifying the polymer and copolymer of the vinyl ester monomer and the diketene is obtained by directly reacting the PVA resin with a gaseous or liquid diketene. Alternatively, an organic acid such as acetic acid is adsorbed and occluded in advance in a PVA resin, and then a gaseous or liquid diketene is sprayed and reacted in an inert gas atmosphere, or the organic acid and liquid are liquidized in the PVA resin. Methods such as spraying and reacting a mixture of diketene are used.

  As a reaction apparatus for carrying out the above reaction, any apparatus that can be heated and has a stirrer is sufficient. For example, a kneader, a Henschel mixer, a ribbon blender, and other various blenders can be used.

  The average polymerization degree of the AA-PVA-based resin (A) thus obtained (based on JIS K6726) may be appropriately selected depending on the application, but is usually 300 to 4000, particularly 400 to 3500, and more particularly 500 to 3000. Are preferably used. If the average degree of polymerization is too small, sufficient water resistance may not be obtained or a sufficient crosslinking rate may not be obtained. On the other hand, if it is too large, the viscosity becomes too high when used as an aqueous solution. Application to various processes tends to be difficult, for example, coating on a substrate becomes difficult.

  The saponification degree of the AA-PVA-based resin (A) used in the present invention is usually 80 mol% or more, more preferably 85 mol% or more, and particularly preferably 90 mol% or more. When the degree of saponification is low, it tends to be difficult to make an aqueous solution, the stability of the aqueous solution is lowered, and the water resistance of the obtained crosslinked polymer tends to be insufficient.

  Further, the content of acetoacetyl group in the AA-PVA-based resin (A) (hereinafter abbreviated as AA degree) is usually 0.1 to 20 mol%, and further 0.2 to 15 mol%. In particular, those of 0.3 to 10 mol% are generally widely used. If the content is too small, sufficient water resistance tends to be insufficient, or a sufficient crosslinking rate tends not to be obtained. On the other hand, if the content is too large, water solubility decreases or the stability of the aqueous solution decreases. Tend to.

In the present invention, it is preferable that all of the PVA-based resins are AA-based PVA-based resins, but PVA-based resins other than the AA-based PVA-based resins may be used in combination, and the content thereof is usually 60% by weight. In particular, it is preferably 50% by weight or less, more preferably 30% by weight or less.
Examples of PVA resins other than the AA-modified PVA resin include unmodified PVA resins and various modified PVA resins obtained by copolymerizing various monomers having copolymerizability with the above-mentioned vinyl ester monomers. Can be mentioned.

  In addition, the AA-PVA-based resin (A) of the present invention includes an alkali metal acetate such as sodium acetate used or produced as a by-product in the production process (mainly alkali metal hydroxide and polyacetic acid used as a saponification catalyst). Derived from a reaction product with acetic acid produced by saponification of vinyl), organic acid such as acetic acid (organic acid occluded in PVA at the time of reaction with diketene when introducing acetoacetate group into PVA resin, etc. ), Organic solvents such as methanol and methyl acetate (derived from a reaction solvent for PVA resin, a cleaning solvent for producing AA-PVA, etc.) may partially remain.

[Hydrazine Compound (B)]
Next, the hydrazine compound (B) used in the present invention will be described.
The hydrazine compound (B) is a compound having a hydrazino group (H ₂ N—NH—) in the molecule. Specifically, hydrazine, hydrazine hydrochloride, sulfuric acid, nitric acid, sulfurous acid, phosphoric acid, thiocyanic acid, carbonic acid Inorganic acid salts such as formic acid, acetic acid, oxalic acid and the like, monosubstituted hydrazines such as methyl, ethyl, propyl, butyl, allyl, etc., symmetrical 1,2-dimethyl, 1,1-diethyl, etc. Substituted hydrazine derivatives, carbohydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, glutaric acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide dihydrazide dihydride dihydride , Diglycolic acid dihydrazide, tartaric acid dihydrazide , Malic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, citric acid trihydrazide, 1,3-bis (hydrazinocarbonoethyl) -5-isopropylhydantoin (such as “Amicure VDH” manufactured by Ajinomoto Fine Techno Co., Ltd.), Dihydrazide compounds such as 11-octadecadien-1,18-dicarbohydrazide (“Amicure UDH” manufactured by Ajinomoto Fine Techno Co.), polyacrylic acid hydrazide, N-aminopolyacrylamide, N-aminoacrylamide / acrylamide copolymer Multivalent hydrazide compounds such as and the like can be mentioned, and those that are water-soluble are particularly preferred, and among them, adipic acid dihydrazide is preferably used because it can remarkably achieve the object of the present invention.

  The amount of the hydrazine compound (B) used can be appropriately selected depending on the water resistance, crosslinking rate, etc. required for the resulting crosslinked structure, but is usually 100% by weight of AA-PVA-based resin (A). A range of 1 to 20 parts by weight, particularly 2 to 10 parts by weight, and further 3 to 7 parts by weight is preferably used. If the blending amount of the hydrazine compound (B) is too small, the water resistance of the crosslinked structure tends to decrease or a desired crosslinking rate tends not to be obtained. If the blending amount is too large, the crosslinking rate is low. In some cases, the pot life of the aqueous solution in which the AA-PVA-based resin (A) and the hydrazine compound (B) are mixed becomes extremely short, or the viscosity increases and gels during coating.

  In addition, in this invention, it is also possible to use together with the well-known crosslinking agent used for AA-ized PVA-type resin other than the said hydrazine compound (B), As this crosslinking agent, aldehyde compounds, such as a glyoxal, and methylolation are used. Examples include methylol compounds such as melamine and metal compounds such as basic zirconyl chloride.

[Reducing agent (D)]
Next, the reducing agent (D) used in the present invention will be described.
In the present invention, a known reducing agent can be used as the reducing agent (D). However, both the AA-PVA-based resin (A) and the hydrazine compound (B) are water-soluble, and these aqueous solutions Since there are many cases where they are used in combination, a water-soluble reducing agent can be particularly preferably used. Typical examples of the water-soluble reducing agent (D) include sulfites such as ammonium sulfite, potassium sulfite, sodium sulfite, calcium sulfite, and zinc sulfite, sodium hydrogen sulfite, potassium hydrogen sulfite, calcium hydrogen sulfite, and sulfurous acid. Bisulfite such as ammonium hydrogen, sodium pyrosulfite, calcium pyrosulfite, pyrosulfite such as ammonium pyrosulfite, sodium dithionite, ammonium dithionite, potassium dithionite, formaldehyde sodium sulfoxylate dihydrate Dithionites such as salts (Longalite), trithionates such as sodium trithionate and potassium trithionate, tetrathionates such as sodium tetrathionate and potassium tetrathionate, sodium thiosulfate, thiosulfate Potassium etc. Thiosulfate, ammonium phosphite, sodium phosphite, potassium phosphite, calcium phosphite, ferrous phosphite, ferric phosphite, copper phosphite, barium phosphite, hydrazinium phosphite Such as phosphite, ammonium hydrogen phosphite, sodium hydrogen phosphite, potassium hydrogen phosphite, potassium hydrogen phosphite, calcium hydrogen phosphite, ferrous hydrogen phosphite, hydrogen phosphite second Hydrogen phosphite such as ferric iron, magnesium hydrogen phosphite, hydrazinium hydrogen phosphite, ammonium nitrite, sodium nitrite, potassium nitrite, calcium nitrite, zinc nitrite, silver nitrite, nickel nitrite, magnesium nitrite , Nitrites such as lithium nitrite, diethylamine, triethylamine, hydroxylamine, hydroxylamine hydrochloride, Amine compounds such as hydrazine, formic acid, oxalic acid, citric acid, L- organic acids and salts thereof such as ascorbic acid, may be mentioned.
Among them, a water-soluble inorganic reducing agent selected from sulfites and dithionite is preferably used as the effect of the present invention can be remarkably obtained.

  The amount of the reducing agent (D) used is usually 0.1 to 20 parts by weight, particularly 0.5 to 10 parts by weight, and further 1 to 5 parts per 100 parts by weight of the AA-PVA-based resin (A). A range of parts by weight is preferably used. If the blending amount of the reducing agent (D) is too small, the effect of suppressing coloration with time, which is the effect of the present invention, may not be sufficiently obtained. Conversely, if it is too much, it is excessive from the obtained resin composition. The reducing agent may be deposited, hindering the appearance and contaminating the surroundings.

[Crosslinked structure (C) and resin composition]
The resin composition of the present invention contains a crosslinked structure (C) obtained by crosslinking the AA-PVA-based resin (A) with a hydrazine compound (B) and a reducing agent (D). Since it is difficult to uniformly mix the reducing agent (D) with the structure (C), the AA-PVA-based resin (A) or hydrazine compound (B) before crosslinking is usually used. At least one of the reducing agent (D) is blended, and then the AA-PVA-based resin (A) and the hydrazine compound (B) are mixed and subjected to a crosslinking reaction, whereby the crosslinked structure (C) and the reducing agent (D) A method of obtaining a resin composition containing s is adopted. The resin composition of the present invention obtained by such a method exists in a state where the reducing agent (D) is uniformly dispersed at the molecular level in the crosslinked structure (C).

The AA-PVA-based resin (A) is a water-soluble resin, and a method of mixing them in an aqueous medium by using a water-soluble hydrazine compound (B) is preferably used.
As such a mixing method, (i) a method in which both the AA-PVA-based resin (A) and the hydrazine compound (B) are poured into water and dissolved; (Iii) AA-PVA-based resin (A) and a hydrazine crosslinking agent separately dissolved, and the like. However, since the cross-linking reaction between the AA-PVA resin (A) and the hydrazine compound (B) proceeds rapidly at a low temperature, the method (i) can be used before the AA-PVA resin is completely dissolved. In the case of the method (ii), the hydrazine compound (B) may not be sufficiently dissolved or dispersed in the solution, and therefore the method (iii) is preferable. After mixing both aqueous solutions, it is desirable to use them immediately.
In this case, the reducing agent (D) may be previously mixed with either or both of the aqueous solution of AA-PVA-based resin (A) and the aqueous solution of hydrazine compound (B).

The concentration of the AA-PVA-based resin (A) aqueous solution used here is usually 0.05 to 40% by weight, more preferably 1 to 30% by weight, and particularly preferably 1 to 20% by weight. If the concentration is too large, the viscosity becomes too high, and application to a substrate or application to various processes may be difficult. On the other hand, if the concentration is too small, the amount of resin is insufficient, and it takes a long time for drying.
Further, the concentration of the aqueous hydrazine compound (B) varies depending on the solubility of the hydrazine compound to be used, so it cannot be generally stated, but usually a range of 1 to 50% by weight, particularly 5 to 30% by weight is preferably used. . If the concentration is too small, the amount of water in the resulting mixed aqueous solution increases and tends to require a long time for drying. Conversely, if the concentration is too large, the reaction with the AA-PVA-based resin (A) occurs quickly, May not be able to mix well.

The mixed aqueous solution containing the AA-PVA-based resin (A), the hydrazine compound (B), and the reducing agent (D) thus obtained is applied to various uses by known methods such as coating, casting, and dipping. Thereafter, the crosslinking reaction of the AA-PVA-based resin (A) and the hydrazine compound (B) proceeds to obtain a crosslinked structure (C). At the same time or thereafter, moisture is removed by drying. .
The resin composition containing the crosslinked structure of the present invention using an AA-PVA-based resin and a hydrazine compound is useful for various applications requiring water resistance, and particularly various adhesive applications, binder applications, and coating agents. Suitable for applications and the like. In particular, the resin composition of the present invention is preferably used for a surface layer because it has excellent water resistance and less coloration with time, and forms a coating layer and a surface layer for various substrates. It is preferable to use it as a binder.

[Coat layer]
Next, the coat layer of the present invention will be described.
The coat layer of this invention contains the resin composition containing the above-mentioned AA-ized PVA-type resin (A), the crosslinked structure (C) by a hydrazine compound (B), and a reducing agent (D).
The production method involves applying an aqueous solution containing the AA-PVA-based resin (A), the hydrazine compound (B), and the reducing agent (D) obtained in the above-described resin composition production method to various substrates. The method obtained by drying this is usually used.
The resin composition in the coat layer is present in a state where the reducing agent (D) is uniformly dispersed at the molecular level in the crosslinked structure (C).

  Any material such as paper, wood material, plastic material, or metal material can be used as the base material. However, as a material that makes use of the features of the present invention, a transparent material such as glass or transparent plastic, or a white or light color is used. These materials are preferably used.

  The thickness of the coat layer varies depending on the purpose of use, and a desired thickness can be selected, but it is usually 1 to 1000 μm, particularly 5 to 500 μm, and more preferably 10 to 300 μm.

  In addition, as drying conditions after coating the above-mentioned aqueous solution, although it selects suitably by a usage form, Usually, it is 5-150 degreeC, Furthermore, 30-150 degreeC, Especially the temperature of 50-150 degreeC Depending on the conditions, a drying time of 0.1 to 60 minutes, further 0.1 to 30 minutes, particularly 0.2 to 20 minutes is preferably used.

[Inkjet recording medium]
Next, the ink jet recording medium of the present invention will be described.
The ink jet recording medium of the present invention is a resin composition of the present invention, that is, a resin composition containing a cross-linked structure (C) and a reducing agent (D) by an AA-PVA-based resin (A) and a hydrazine compound (B). It is preferable to use at least one layer containing a product on a supporting substrate, and particularly to use as a layer for forming a resurface layer of a recording medium. In addition, when the resin composition of the present invention is applied to such a use, inorganic fine particles (E) are further added to the resin composition for the purpose of forming voids for ink reception, improving glossiness, and improving surface hardness. ) Is contained.

The supporting substrate is not particularly limited, but paper (manila ball, white ball, liner paper, general high quality paper, medium quality paper, gravure paper, printing paper, upper / middle / lower grade paper, newsprint paper, release paper, etc. Carbon paper, non-carbon paper, glassine paper, etc.), resin-coated paper, synthetic paper, non-woven fabric, cloth, metal foil, polyolefin resin (for example, polyethylene, PET, polypropylene, polyvinyl chloride, ethylene-propylene copolymer, ethylene- A film or sheet made of a thermoplastic resin such as a vinyl acetate copolymer) can be used. In particular, as the photo-like paper, a support substrate having high smoothness such as RC (resin coated) paper or a plastic film is preferably used.
Furthermore, you may interpose a primer layer between a support base material and the layer containing the resin composition of this invention as needed.

  Examples of the inorganic fine particles (E) include amorphous synthetic silica such as gas phase method silica, wet method silica and colloidal silica, alumina, alumina sol, alumina hydrate, aluminum compounds such as aluminum hydroxide, zeolite, magnesium hydroxide, Calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide, zinc carbonate, hydrotalcite, aluminum silicate, magnesium silicate, calcium silicate, etc. These are used alone or in combination. Among these, amorphous synthetic silica and alumina are preferably used from the viewpoint of ink absorbability, productivity, and economy.

  As the inorganic fine particles (E), those having an average secondary particle diameter of 3 to 500 nm are usually used from the viewpoint of glossiness, and those having an average secondary particle diameter of 3 to 200 nm, more preferably 10 to 50 nm are preferably used. If the average particle size is too small, the amount of voids due to the inorganic fine particles may be reduced, or the size of the voids may be too small, which may inhibit ink absorbability and cause feathering or image spots. On the contrary, if it is too large, the glossiness tends to be impaired.

  The content of the inorganic fine particles (E) is usually 200 to 2000 parts by weight with respect to 100 parts by weight of the AA-PVA-based resin (A), and a range of 300 to 1000 parts by weight is particularly preferably used. If the content of the inorganic fine particles (E) is too large, the gloss may be lowered, or the binder strength by the resin may be insufficient, and the powder of the inorganic fine particles may be liberated during storage and use. If the amount is too large, the amount of voids in the layer tends to be small, and ink tends not to be sufficiently absorbed.

  In the ink jet recording medium of the present invention, the AA-PVA-based resin (A), the hydrazine compound (B), the inorganic fine particles (E), and an additive to be added as desired are added to water on the above-mentioned supporting substrate. It is formed by applying an aqueous coating liquid obtained by dispersing and drying the liquid.

  The total solid content in such an aqueous composition is usually in the range of 5 to 60% by weight, preferably 10 to 50% by weight, and more preferably 10 to 30% by weight of the total composition. If the total solid content is too small, the drying load increases, and the uniformity of the thickness of the recording layer formed by coating may decrease. Conversely, if the total solid content is too large, coating at high speed becomes difficult, Since workability may deteriorate, it is not preferable.

The thickness of the layer containing the resin composition of the present invention can be appropriately selected from the viewpoints of ink absorbency, strength of the glossy layer, etc., but usually 5 to 50 g as the solid content of inorganic fine particles. / M ² , particularly 10 to 40 g / m ² , and further 20 to 30 g / m ² is preferably used.

As a method for coating the aqueous coating solution on the support, known coating methods such as a bar coater method, an air knife coater method, a blade coater method, and a curtain coater method are used.
Also. The coating amount of the aqueous composition can be appropriately selected from the ink absorbency of the obtained glossy layer, the strength of the layer, etc., but the thickness after drying is usually 3 to 100 μm, and further 5 A range of ˜80 μm, particularly 10˜50 μm is preferably used.

  After coating, the coating solution may be dried, but in order to obtain a particularly excellent gloss layer, the coating solution is gelled by heating in a wet state after coating, and there is no fluidity. A method of removing moisture by drying after making it into a state is preferably used. As heating conditions for such gelation, a temperature range of 30 to 100 ° C., particularly 40 to 90 ° C., and a range of 1 second to 5 minutes, particularly 5 seconds to 5 minutes is preferably used. Moreover, what is necessary is just to make it dry about 1 to 30 minutes normally at 50-120 degreeC as subsequent drying conditions. In addition, a method of imparting high surface gloss and smoothness by pressing the cast drum in a wet state before drying and further drying in that state is also preferably used.

In addition, the resin composition aqueous coating liquid for producing the ink jet recording medium of the present invention includes, as necessary, (1) a resin having a cationic group as a fixing agent for anionic ink, 2) You may contain water-soluble resin and water-dispersible resin other than PVA-type resin, (3) Other components, etc.
(1) Cationic group-containing resin Polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, secondary polymers, acrylic polymers having tertiary amino groups and quaternary ammonium salts, polyvinylamine Polymers, polyvinylamidine copolymers, dicyandiamide / formalin copolymers, dimethylamine / epichlorohydrin copolymers, acrylamide / diallylamine copolymers, diallyldimethylammonium chloride copolymers, and the like.

(2) Water-soluble resins, water-dispersible resins Starch derivatives such as starch, oxidized starch and cationic modified starch; natural proteins such as gelatin and casein, cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose and CMC, sodium alginate , Natural polymer polysaccharides such as pectic acid, water-soluble resins such as polyvinylpyrrolidone and poly (meth) acrylate, SBR latex, NBR latex, vinyl acetate resin emulsion, ethylene-vinyl acetate copolymer emulsion, (meta ) Acrylic ester resin emulsion, vinyl chloride resin emulsion, urethane resin emulsion, etc.

(3) Others Pigment dispersants, thickeners, fluidity improvers, surfactants, antifoaming agents, mold release agents, penetrants, dyes, pigments, fluorescent brighteners, UV absorbers, antioxidants, antiseptics Agent, antifungal agent, paper strength enhancer, etc.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
[Production of AA-PVA Resin (A)]
A reaction vessel equipped with a reflux condenser, a dropping funnel, and a stirrer was charged with 1000 parts of vinyl acetate, 300 parts of methanol, and 0.05 mol% of azobisisobutyronitrile (vs. vinyl acetate) and stirred under a nitrogen stream. While raising the temperature, polymerization was carried out at the boiling point for 5 hours. When the degree of polymerization of vinyl acetate reaches 70%, m-dinitrobenzene is added to complete the polymerization, and then unreacted vinyl acetate monomer is removed out of the system by blowing methanol vapor. A combined methanol solution (41% resin content) was obtained. Subsequently, the solution was diluted with methyl acetate (dielectric constant 7.03), adjusted to a concentration of 29.5% (dielectric constant of saponification solvent 23.7), charged into a kneader, and the solution temperature was raised to 35 ° C. While maintaining, sodium hydroxide was added for neutralization. Further, 11 mmol of sodium hydroxide is added to 1 mol of vinyl acetate unit in the polymer to saponify, the precipitate is filtered, washed well with methanol, dried in a hot air dryer, and further at 80 ° C. A PVA resin was obtained by heat treatment for 60 minutes.
The saponification degree of the obtained PVA-based resin was 92.5 mol% when analyzed by the alkali consumption required for hydrolysis of residual vinyl acetate, and the average degree of polymerization was analyzed according to JIS K 6726. Was 1700, and the sodium acetate content was 0.5%.
3600 parts of the PVA resin is charged in a kneader, 540 parts of acetic acid is added to the kneader, and the mixture is swollen. After stirring at 20 rpm, the temperature is raised to 60 ° C., and 420 parts of diketene is added dropwise over 3 hours. The reaction was carried out for 1 hour. After completion of the reaction, the mixture was washed with methanol and dried at 70 ° C. for 6 hours to obtain an AA-PVA-based resin (A1). The AA-modified PVA resin (A1) has a degree of AA conversion of 4.4 mol%, and the degree of saponification and the average degree of polymerization are the same as those of the PVA-based resin used.

[Production of resin composition and its evaluation]
To 1000 parts of a 10% aqueous solution of the resulting AA-modified PVA resin (A1), 5 parts of adipic acid dihydrazide as a hydrazine compound (B) and 10 parts of sodium hydrogen sulfite as a reducing agent (D) were added and stirred. The crosslinking reaction proceeds within a few minutes, and an aqueous gel containing a resin composition containing a crosslinked structure (C) and a reducing agent (D) by AA-PVA-based resin (A) and hydrazine compound (B) is generated. did.
The aqueous gel was allowed to stand at room temperature for 2 weeks and then heat-treated at 80 ° C. for 4 hours, and the colored state was visually observed. The results are shown in Table 1.

Example 2
In Example 1, an aqueous gel was prepared in the same manner as in Example 1 except that sodium dithionite was used in place of sodium hydrogen sulfite as the reducing agent (D), and was similarly evaluated. The results are shown in Table 1.

Comparative Example 1
In Example 1, an aqueous gel was prepared and evaluated in the same manner as in Example 1 except that sodium bisulfite was not blended. The results are shown in Table 1.

[Table 1]
──────────────────────────────────────
Reducing agent Colored state ──────────────────────────────────────
Example 1 Sodium bisulfite White 〃 2 Sodium dithionite White ──────────────────────────────────── ───
Comparative Example 1 None Yellow ──────────────────────────────────────

As is clear from these results, the AA-PVA-based resin of Comparative Example 1 containing no reducing agent and the crosslinked structure of the hydrazine compound are colored over time and by heat treatment that promotes it. It can be seen that the blended resin composition is not colored at all, is stable for a long period of time, and can maintain excellent quality.
In this example, the evaluation of the colored state is performed only on the crosslinked structure resin composition, but these results are obtained when the coating layer containing the resin composition and an inkjet recording medium are evaluated. A similar result can be obtained.

  The resin composition of the present invention is extremely suitable as a coating layer for various substrates, particularly as a gloss layer in an ink jet recording medium, because it is less colored over time.

Claims (5)

A resin composition comprising a crosslinked structure (C) obtained by crosslinking an acetoacetate group-containing polyvinyl alcohol resin (A) with a hydrazine compound (B) and a reducing agent (D). The resin composition according to claim 1, wherein the reducing agent (D) is a water-soluble inorganic reducing agent. The resin composition according to claim 1 or 2, wherein the content of the reducing agent (D) is 0.1 to 20 parts by weight with respect to 100 parts by weight of the crosslinked structure (C). A coating layer comprising the resin composition according to claim 1. An ink jet recording medium comprising at least one layer containing the resin composition according to claim 1.