JP5153125B2 - Resin composition and use thereof - Google Patents

Description

  The present invention relates to a polyvinyl alcohol-based resin composition, more specifically, relates to a resin composition containing an acetoacetate group-containing polyvinyl alcohol-based resin and its crosslinking agent, and is excellent in storage stability when used as an aqueous solution. It aims at obtaining the resin composition from which the crosslinking reaction material excellent in water resistance and discoloration resistance is obtained.

  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 the PVA-based resin is a water-soluble resin, it has poor water resistance, and studies aimed at improving it, particularly water resistance studies using a crosslinking agent, have been widely conducted.

  However, the functional group which general PVA-type resin has is only a secondary hydroxyl group, and the crosslinking agent which can be utilized was also limited. Therefore, various modified PVA resins have been proposed in which functional groups rich in reactivity are introduced into the side chains of the PVA resin in order to increase the options for the crosslinking reaction and to efficiently cause the crosslinking reaction. Among them, acetoacetate group-containing PVA resin (hereinafter abbreviated as AA-modified PVA resin) is known as a modified PVA resin having a wide variety of cross-linking agents and having an acetoacetyl group in the side chain, which is excellent in cross-linking reactivity. A resin composition obtained by combining this with various crosslinking agents is widely used for water-resistant adhesives, thermal paper overcoat applications, and the like.

  Alkyl compounds, amine compounds, hydrazide compounds, methylol compounds, metal compounds, and the like are known as cross-linking agents that are suitably used for such AA-PVA-based resins. Glyoxal, which is an aldehyde compound, is most widely used because it is distributed in an aqueous solution and can be easily applied to PVA resins generally used in aqueous systems.

However, such glyoxal has mutagenicity, contains a small amount of formalin, may cause chemical hypersensitivity, and has a fast cross-linking reaction with the acetoacetate group-containing PVA resin. When an aqueous resin composition is used, there is a problem that the viscosity tends to increase with time and the pot life is short, and there has been a strong demand for a cross-linking agent to replace this.
Therefore, the present applicant also uses a cyclic acetal compound in which an aldehyde group in a dialdehyde compound such as glyoxal is acetalized by a specific polyhydric alcohol compound as a cross-linking agent suitable for an AA-PVA resin instead of glyoxal. And a thermal recording medium using a resin composition containing AA-PVA-based resin (see, for example, Patent Document 1).
JP 2004-291519 A

However, the cross-linked reaction product by the resin composition containing the AA-PVA-based resin and the cyclic acetal compound described in Patent Document 1 exhibits water resistance equivalent to that when glyoxal is used, and the discoloration resistance is considerably improved. However, there is room for improvement in the discoloration resistance when stored for a long time under harsh conditions such as high temperature and high humidity.
In addition, the aqueous liquid containing the resin composition described in Patent Document 1 can be used stably without thickening during work under normal use conditions, that is, near room temperature, but at a higher temperature. In the case of use or storage for a long period of time, the cyclic acetal part is converted into an aldehyde group by hydrolysis to form a dialdehyde compound, which is an acetoacetate group (hereinafter referred to as AA group) in the AA-PVA-based resin. It has a problem that it is easy to increase the viscosity of the aqueous liquid by reacting with.

  That is, when an aqueous solution is used, an AA-PVA-based resin composition capable of obtaining a cross-linked product having excellent storage stability under severer conditions and excellent color fastness and a cross-linking agent used therefor are desired. It is where

  As a result of intensive studies in view of the above circumstances, the inventor of the present invention uses an acetoacetate group-containing polyvinyl alcohol resin composition comprising an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule. The present invention was completed by finding that the object was achieved.

  Since the dialkyl acetal group in the acetal compound used in the present invention stably maintains the acetal structure at 5 to 40 ° C. which is the environmental temperature at the time of storage and use of the AA-PVA-based resin composition aqueous liquid, It does not react with the AA group in the PVA-based resin, and the aqueous liquid is used for various purposes. At the time of drying or subsequent heat treatment, for example, at 40 to 200 ° C., the dialkylacetal group is converted into an aldehyde group by hydrolysis. As a result, it becomes a compound having a plurality of aldehyde groups, and these aldehyde groups react with acetoacetate groups to crosslink the PVA resin, thereby imparting excellent hot water resistance to the AA-PVA resin cross-linked product. .

  The resin composition of the present invention is excellent in handleability because it is excellent in stability when made into an aqueous solution, and further, a crosslinking reaction product having excellent discoloration resistance and water resistance can be obtained from the resin composition of the present invention. Therefore, it is suitable for applications such as adhesives and paper processing agents that require high water resistance and aesthetics, and is industrially useful.

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.

  The present invention relates to an acetoacetate group-containing polyvinyl alcohol resin composition comprising a compound having a dialkyl acetal group and one aldehyde group in the molecule.

First, the acetal compound used as a crosslinking agent for AA-PVA-based resin in the present invention will be described.
The acetal compound used in the present invention is a compound having a dialkyl acetal group represented by the following general formula (1) in the molecule and one aldehyde group. In other words, it corresponds to a compound obtained by dialkyl acetalization leaving only one aldehyde group of a compound having a plurality of aldehyde groups in the molecule.

R ¹ and R ² in the dialkyl acetal group represented by the general formula (1) are alkyl groups, which may be either linear or branched, and the number of carbon atoms is usually 1-6. In particular, an alkyl group having 1 to 4 carbon atoms is preferable. If the carbon number is too large, the boiling point of the alcohol represented by R ¹ OH or R ² OH generated by hydrolysis of the dialkyl acetal group at the time of drying or heat treatment after application to various applications becomes high, and the dried film Is not preferable because it may not volatilize sufficiently. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, and the like. Among them, a methyl group is preferably used.
The alkyl groups represented by R ¹ and R ² may be the same or different, but usually the same one is used. In addition, a part of the hydrogen atoms in the alkyl group may be substituted with a halogen, a hydroxyl group, an alkoxy group, an ester group, a carboxylic acid group, a sulfonic acid group, or the like, as long as the effect of the present invention is not significantly impaired.
Moreover, when it has two or more dialkyl acetal groups in a molecule | numerator, those dialkyl acetal groups may be the same or different.

  The number of dialkyl acetal groups in the acetal compound is not particularly limited. However, since it is a hydrophobic group, if it is too much, the water solubility may decrease, and usually 1 to 5, preferably 1 to 3. What is a piece is used.

  In addition, the number of aldehyde groups in the acetal compound is one, and when the number is two or more, the stability when the resin composition is made into an aqueous liquid is not preferable. This is because the aldehyde group easily reacts with the AA group in the AA-PVA-based resin at room temperature, but if there is only one in the molecule, the PVA-based resin is less likely to be cross-linked. This is because a crosslinked structure is easily formed, and as a result, the aqueous solution is thickened.

  In the acetal compound used in the present invention, the chemical structure of the portion other than the dialkyl acetal group and the aldehyde group is not particularly limited. Those in which both functional groups are bonded are usually used. The molecular weight of the acetal compound is usually from 104 to 300, more preferably from 104 to 200, and particularly preferably from 104 to 150. The smaller the molecular weight, the greater the effect on the added amount, which is preferable. If the molecular weight is too large, the water solubility becomes poor, the amount added to obtain the desired water resistance increases, or sufficient water resistance cannot be obtained.

Specific examples of the acetal compound include dimethoxyethanal (dimethoxyacetaldehyde), diethoxyethanal (diethoxyacetaldehyde), dialkoxyethanal such as di-n-propoxyethanal, dimethoxypropanal (dimethoxypropionaldehyde), Dialkoxypropanal such as diethoxypropanal (diethoxypropionaldehyde), dialkoxybutanal such as dimethoxybutanal, diethoxybutanal, etc. can be mentioned, among them dialkoxyethanal in terms of low molecular weight, In particular, dimethoxyethanal is preferably used.
In addition, “High Link DM” manufactured by Clariant is listed as a commercial product containing such dimethoxyethanal.

  In addition, the manufacturing method of this acetal compound is not specifically limited, What was obtained by the well-known method can be used, For example, dialkoxyethanal which is the most preferable compound for the objective of this application is used. Examples of the production method include a method in which an α, β-unsaturated dialkyl acetal is subjected to ozone oxidation and then the ozonized product is catalytically hydrogenated as disclosed in JP-A-5-246926.

  The resin composition of the present invention contains the acetal compound as described above, and the content thereof is not particularly limited, but is usually 100 parts by weight of AA-PVA-based resin in the resin composition. The range of 0.1 to 100 parts by weight, more preferably 0.5 to 50 parts by weight, and particularly 1 to 20 parts by weight is preferably used. The molar ratio (Y / X) of the total amount (Y) of dialkylacetal groups and aldehyde groups to the total amount of AA groups (X) in the AA-PVA-based resin is usually 0.01 to 100, preferably 0.1 to 0.1. 50, especially in the range of 0.3-30. If the content of the acetal compound is too small, the resulting cross-linked reaction product may have insufficient water resistance. Conversely, if the content is too large, the aqueous solution will tend to thicken depending on the usage environment, etc. Since time may become short, it is not preferable.

Next, the AA-PVA-based resin targeted in the present invention is a known resin that is commercially available, and the structure and production method thereof are described, for example, in JP-A-55-094904 and JP-A-55- No. 137107, Japanese Patent Laid-Open No. 57-040508, etc., the outline of which will be described in detail.
The AA-PVA resin used in the present invention is one in which an AA group is introduced into the side chain of the PVA resin, and the content of the AA group in the AA-PVA resin is usually 0.1 to 20 mol%. The remaining portion is composed of a vinyl alcohol structural unit corresponding to the degree of saponification and a slight amount of vinyl acetate structural unit, as in the case of a normal PVA resin.

  In order to obtain such an AA-PVA-based resin, a method of reacting a PVA-based resin with diketene, a method of reacting a PVA-based resin with acetoacetate, a transesterification, and a saponification of a copolymer of vinyl acetate and vinyl acetoacetate Although it is easy to manufacture and a good quality AA-PVA-based resin can be obtained, it is preferable to manufacture by reacting the PVA-based resin with diketene, which will be described below. It is not limited to.

  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, vinylene carbonates, unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, undecylenic acid, salts thereof or mono Or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid, or salts thereof, alkyl vinyl ether , N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyldiallylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth) allyl ether, polyoxypropylene (meta ) Polyoxyalkylene (meth) allyl ether such as allyl ether, polyoxyalkylene (meth) acrylate such as polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, polyoxyethylene (meth) acrylamide, polyoxypropylene Polyoxyalkylene (meth) acrylamide such as (meth) acrylamide, diacetone acrylamide, polyoxyethylene (1- (me ) Acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, nyl, vinylethylene carbonate, 2,2-dialkyl-4-vinyl-1, 3-Dioxolane, glycerol monoallyl ether, 3,4-diacetoxy-1-butene, 1,4-diacetoxy-2-butene and the like can be mentioned.
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. The compatibility with the agent may be lowered, which is not preferable.

  In addition, by using a high boiling point polymerization solvent or by performing polymerization under pressure to make the polymerization temperature 100 ° C. or higher, 1,2-diol bonds are added to 1.6 to 3.5 in the PVA main chain. It is possible to use those introduced at about mol%.

  The saponification of the obtained polyvinyl acetate resin can be carried out by a known method, but usually it is carried out in the presence of an alkali catalyst or an acid catalyst after dissolving the polyvinyl acetate resin in an alcohol solvent. . As the alcohol solvent, for example, methanol, ethanol, butanol, isopropanol, a mixed solvent of various alcohols such as methanol and methyl acetate, and a mixed solvent of methyl acetate can be used. The concentration of the polyvinyl acetate resin in the alcohol solvent is selected from the range of 10 to 60% by weight.

As the alkali catalyst, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate and potassium methylate, and alkali catalysts such as alcoholate can be used. As the acid catalyst, an inorganic acid aqueous solution such as hydrochloric acid or sulfuric acid, or an organic acid such as p-toluenesulfonic acid can be used. The amount of the alkali catalyst used is usually 1 to 100 mmol, preferably 1 to 40 mmol, particularly 1 to 20 mmol, based on 1 mol of the vinyl acetate structural unit in the polyvinyl acetate resin. If the amount of the alkali catalyst used is too small, it tends to be difficult to increase the saponification degree to the target degree of saponification, and if it is too much, it tends to be too high than the target saponification degree and difficult to control. This is not preferable.
Moreover, especially the temperature when performing saponification is although it does not restrict | limit, Usually, it is 10-70 degreeC, and 20-50 degreeC is more preferable.

Next, the PVA resin obtained by saponification of the polyvinyl acetate resin and the diketene are reacted. In this case, the PVA resin and the gaseous or liquid diketene may be directly reacted. An organic 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 a mixture of an organic acid and a liquid diketene is sprayed and reacted in a PVA resin. Etc. are used.
As the 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, other various blenders, and a stirring and drying apparatus can be used.

  The acetoacetate group content (degree of acetoacetate esterification, hereinafter abbreviated as AA degree) in the AA-PVA-based resin thus obtained is usually 0.1 to 20 mol%, preferably 0.2 to 15 mol%, especially 0.3 to 10 mol%. If the content is too small, sufficient water resistance may not be obtained, or a sufficient crosslinking rate may not be obtained. Since water solubility may fall or stability of aqueous solution may fall, it is not preferable.

  Moreover, the average degree of polymerization (based on JIS K6726) of the AA-PVA-based resin is usually 300 to 4000, preferably 400 to 3500, particularly 500 to 3000. If the average degree of polymerization is too small, sufficient water resistance is achieved. May not be obtained or sufficient crosslinking rate may not be obtained. Conversely, if it is too large, the viscosity of the aqueous solution will be too high, making it difficult to apply to the substrate, etc. Is not preferable because it may be difficult.

  Further, the saponification degree of the AA-PVA-based resin of the present invention is usually 80 mol% or more, preferably 85 mol% or more, particularly 90 mol% or more. Is not preferred because it may decrease.

  The AA-PVA-based resin of the present invention includes alkali metal acetates such as sodium acetate used or produced as a by-product in the production process (mainly the alkali metal hydroxide used as the saponification catalyst and the polyvinyl acetate kenne). Derived from a reaction product with acetic acid produced by the chemical conversion), an organic acid such as acetic acid (derived from an organic acid occluded in PVA during reaction with diketene when introducing an acetoacetate group into a PVA resin) , Methanol, methyl acetate and other organic solvents (derived from the reaction solvent for PVA resin, the cleaning solvent for the production of AA-PVA, etc.) may partially remain.

  In the present invention, a mixture of two or more AA-PVA-based resins having different polymerization degrees, saponification degrees, and AA group contents may be used. In addition, a PVA resin different from the PVA resin used in the present invention, for example, unmodified PVA or the above-mentioned, within a range not impairing the basic physical properties of the resin composition of the present invention, usually 50% by weight or less, particularly 30% by weight or less. You may mix and use the modification | denaturation PVA-type resin which copolymerized various unsaturated monomers.

The resin composition of the present invention contains the above-described AA-PVA-based resin and an acetal compound as a crosslinking agent, but a crosslinking agent other than the acetal compound may be used in combination.
As such other crosslinking agents, those known as crosslinking agents for AA-PVA-based resins can be used, and examples thereof include aldehyde compounds, methylol compounds, amine compounds, hydrazine compounds, and polyvalent metal compounds. However, from the viewpoint of stability when the aqueous solution is the object of the present invention, the cross-linking agent used together does not react rapidly with the AA group at a room temperature where the cross-linkable functional group is 40 ° C. or lower, and the temperature is raised to a higher temperature. The thing which a crosslinking reaction advances by this is preferable. Examples of the cross-linking agent having such properties include polyvalent metal compounds, compounds in which functional groups are protected, for example, compounds in which all aldehyde groups are acetalized, and compounds in which methylol groups are etherified.

  Specific examples of the polyvalent metal compound include zirconium compounds such as zirconyl chloride, basic zirconyl chloride, zirconyl sulfate, zirconyl nitrate, zirconyl carbonate, ammonium zirconium carbonate, potassium zirconium carbonate and zirconyl acetate.

  Specific examples of the compounds in which all aldehyde groups are acetalized include 1,1,2,2-tetramethoxyethane, 1,1,2,2-tetraethoxyethane, 1,1,3,3- Hydrocarbon compounds having a plurality of acetal groups such as tetramethoxypropane, 1,1,3,3-tetraethoxypropane, 1,1,6,6-tetramethoxyhexane, and bis-1,3- (2,2 -Dimethoxy-1-hydroxyethyl) urea (trade name “Hilink DU”, manufactured by Clariant), bis-1,3- (2,2-dimethoxy-1-hydroxyethyl) -2-imidazolidinone (trade name) “Hilink DMU” (manufactured by Clariant), 1,1 ′, 1 ″-(1,3,5-triazine-2,4,6-triyltriimino) tris [2,2-dimethoxyethanol ] And the like (trade name "High Link DMM" manufactured by Clariant), compound dimethoxyethanal was obtained by adding to the urea or melamine, such as.

Further, in the resin composition of the present invention, other resins such as polysaccharides such as starch and cellulose, polyethylene glycol, polyvinyl pyrrolidone, poly (polyethylene glycol), in a range not impairing the basic physical properties, usually 30% by weight or less, particularly 20% by weight or less. Water-soluble resins such as oxazoline, water-soluble polyamide, water-soluble polyester, polyacrylamide, and polyethyleneimine can be used in combination.
Similarly, as various additives, colorants, dyes, pigments, fluorescent brighteners, pigments, ultraviolet absorbers, antioxidants, fillers, plasticizers, antistatic agents, heat stabilizers, surfactants, A desiccant, a deodorant, an antibacterial agent, an antiseptic, an antifoaming agent and the like can be included.

Next, the manufacturing method of the resin composition of this invention is demonstrated. The resin composition of the present invention is not particularly limited as long as the AA-PVA-based resin and the acetal compound are mixed, but such a resin composition is applied as an aqueous solution to various applications. In many cases, a method for producing an aqueous resin composition will be described below.
Such an aqueous solution is (i) a method in which a mixture of an AA-PVA-based resin and an acetal compound is added to water and dissolved, (ii) a method in which an AA-PVA-based resin and an acetal compound are separately dissolved in advance, and (Iii) Although it can be prepared by a method in which an acetal compound is added to an aqueous solution of an AA-PVA-based resin and dissolved, etc., since the acetal compound is often distributed in the market in the form of an aqueous solution, usually (ii) It is desirable to use it for various uses as an aqueous solution of a resin composition by mixing both using a method.

  The above aqueous solution may be blended with additives such as antifoaming agents, antifungal agents, preservatives, leveling agents and the like within a range not impairing the characteristics of the present invention, and these are AA-PVA-based resins. You may mix | blend after aqueous solution, the aqueous solution of an acetal compound, or its mixture.

The aqueous solution of the resin composition of the present invention thus adjusted is applied to various uses by a known method such as coating, casting, dipping, etc., and then heat-dried or low to normal temperature as necessary. By drying, the purpose of water resistance of the PVA resin can be achieved.
Such drying conditions are not particularly limited and are appropriately selected depending on the form of use, but are usually 5 to 150 ° C, more preferably 30 to 150 ° C, and particularly 50 to 150 ° C. 0.1 to 60 minutes, more preferably 0.1 to 30 minutes, and particularly preferably 0.2 to 20 minutes.
In addition, as other usage methods, after applying AA-PVA-based resin to a coating film, a film, and various uses in advance or forming into various shapes, an aqueous solution of an acetal compound is sprayed, applied, dipped, and then dried. Is mentioned.

The thus obtained resin composition of the present invention uses a PVA-based resin, and is particularly suitable for applications requiring water resistance. Specific examples thereof include the following.
(1) Paper processing agent Recording layer binder of thermal recording paper, thermal recording paper protective layer binder, thermal recording paper undercoat layer binder, pigment binder of sublimation type thermal recording medium, inorganic fine particle binder of void type inkjet recording medium, and Undercoat layer, ink-receiving layer and undercoat layer for swelling ink jet recording media, paper clear coating agent, pigment binder for coated paper, pigment binder for electrophotographic recording medium, surface coating agent for release paper, release agent (2) Adhesives Two-component adhesives, honeymoon adhesives, pressure-sensitive adhesives, humectants, binders for nonwoven fabrics, binders for building materials (gypsum board, fiberboard, etc.), various powders Binder for granulation, pressure sensitive adhesive, anionic paint fixing agent, adhesive for polarizing film and polarizing film protective film (3) Covering agents Textile finishing agents, leather finishes, paints, anti-fogging agents, metal corrosion inhibitors, galvanizing brighteners, antistatic agents, conductive agents, provisional paints, provisional protective films, water-resistant coatings for fibers (4 ) Film, membrane Electrolyte membrane, packaging film

In particular, the paper processing agent is one of the uses that fully utilize the characteristics of the PVA resin such as affinity with paper fibers, adhesiveness, and compatibility with water-based ink, and in particular, when applied to a thermal recording medium, In addition to these properties, solvent resistance is required to prevent color development of thermal dyes due to contact with organic solvents and oils, and water resistance is required so that the properties can be obtained even when wet. This is one of the applications that are most demanded.
Hereinafter, a thermal recording medium having a layer containing the AA-PVA-based resin of the present invention will be described.

The heat-sensitive recording medium of the present invention comprises a heat-sensitive color-developing layer and / or protective layer on a supporting substrate containing a crosslinking reaction product of the resin composition of the present invention.
When used in such applications, the saponification degree of the AA-PVA-based resin is usually 65 to 99.9 mol%, preferably 75 to 99.8 mol%, particularly 80 to 99.5 mol%, and average The degree of polymerization is usually 150 to 4000, preferably 200 to 3000, particularly 250 to 2500, and the AA degree is usually 0.3 to 25 mol%, preferably 0.5 to 20 mol%, particularly 1 to 15 Mol%.

  Although the compounding quantity of the acetal compound with respect to AA-ized PVA-type resin in this use is not specifically limited, 0.1-50 weight part normally with respect to 100 weight part of AA-ized PVA-type resin in conversion of solid content, Preferably 0.5- 20 parts by weight, in particular 1 to 10 parts by weight.

  In addition, there is no restriction | limiting in particular as a support base material used for the heat-sensitive recording medium of this invention, Paper (Board paper, such as a manila ball, a white ball, a liner, printing papers, such as general fine paper, medium quality paper, gravure paper, Upper / middle / lower grade paper, newsprint, release paper, carbon paper, non-carbon paper, glassine paper, synthetic paper, etc., non-woven fabric, plastic film (polyester film, nylon film, polyolefin film, polyvinyl chloride film, and these) These composite sheets can be used, such as laminates or synthetic resin-laminated paper.

Hereinafter, each of these layers will be described in detail.
The thermosensitive coloring layer can be formed by coating an aqueous coating solution containing a leuco dye, a developer and a binder resin on a supporting substrate. In the present invention, the binder resin is used as the binder resin. These resin compositions are used. The blending amount of the resin composition at this time is suitably 10 to 200% by weight based on the total amount of the leuco dye and the developer as the AA-PVA-based resin.

  Examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide [crystal violet lactone], 3 , 3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, etc., triarylmethane compounds, 4,4 Diphenylmethane compounds such as' -bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleucooramine, rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-di Xanthene compounds such as benzylaminofluorane, benzoylleuco Chirenburu, p- nitrobenzoyl leuco methylene blue, thiazine compounds such as 3-methyl-spiro naphthopyran, 3-ethyl-spiro Gina shift pyran, spiro compounds such as and the like. Moreover, these leuco dyes can be used alone or in admixture of two or more as required.

  Further, the developer is one that reacts with the leuco dye when heated and develops color. For example, phenol, p-methylphenol, p-tertiary butylphenol, p-phenylphenol, α-naphthol, β-naphthol, 4 , 4′-isopropylidene diphenol [bisphenol A], 4,4′-secondary butylidene diphenol, 4,4′-cyclohexylidene diphenol, 4,4′-isopropylidene bis (2-tertiary butylphenol), 4 , 4 ′-(1-methyl-n-hexylidene) diphenol, 4,4′-isopropylidene dicatechol, 4,4′-pentylidene diphenol, 4,4-isopropylidenebis (2-chlorophenol), Phenyl-4-hydroxybenzoate, salicylic acid, 3-phenylsa Examples include licylic acid, 5-methylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 1-oxy-2-naphthoic acid, m-oxybenzoic acid, 4-oxyphthalic acid, gallic acid, and the like. The developer is not limited to these.

  As the binder resin used in the thermosensitive coloring layer, in addition to using the resin composition of the present invention, for example, unmodified fully saponified PVA, unmodified partially saponified PVA, carboxyl group-modified, silicon-modified, sulfonic acid group-modified Various modified PVA resins such as cation group modification, ethylene modification, acetoacetyl group modification, diacetone acrylamide modification, water soluble resins such as starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl acetate, polyurethane And emulsions such as polyacrylates and ethylene-vinyl acetate copolymers, and various latexes such as styrene / butadiene resin, acrylic resin, and urethane resin.

  Further, in the thermosensitive coloring layer, if necessary, inorganic pigments such as calcium carbonate, silica, kaolin, aluminum hydroxide, aluminum oxide, zinc oxide, titanium dioxide, clay, talc, barium sulfate, urea-formalin resin, Nylon resin, acrylic resin, organic resin powder such as styrene / methacrylic acid copolymer, higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin, polyethylene wax and other lubricants, benzophenone and benzotriazole It is also possible to add ultraviolet absorbers, anionic and nonionic surfactants, fluorescent dyes and the like.

  The coating solution for the thermosensitive coloring layer is a fine dispersion obtained by pulverizing the above leuco dye and developer separately using a known disperser such as a ball mill, attritor or sand grinder until the particle size becomes 1 to 3 μm. And AA-PVA-based resin, a crosslinking agent, and, if necessary, the above-mentioned additives and antifoaming agents as a binder resin. The solid content concentration of the coating solution is selected from a range of 10 to 40% by weight in consideration of workability.

In coating the coating liquid on the supporting substrate, any known method such as a roll coater method, an airy tractor method, a blade coater method, a bar coater method, a size press method, a gate roll method, or the like is employed. The coating amount of the aqueous solution is preferably about 0.1 to ²⁰ g / m ² , more preferably 0.5 to 15 g / m ² , particularly about 1 to 10 g / m ² in terms of dry weight.

Next, the protective layer will be described.
The protective layer is prepared by applying the protective layer coating liquid prepared by mixing and stirring the resin composition of the present invention and, if necessary, an inorganic pigment, a lubricant, etc., onto the above-mentioned thermosensitive coloring layer. It is formed by processing and drying, and is effective in improving water resistance, chemical resistance, recording running property, and the like.

  Examples of the inorganic pigment include inorganic pigments such as calcium carbonate, silica, zinc oxide, aluminum oxide, aluminum hydroxide, titanium dioxide, talc, kaolin, and clay, nylon resin filler, urea / formalin resin filler, and starch particles. In particular, organic pigments are used. In particular, in the case where gloss is imparted to the protective layer, inorganic ultrafine particles such as colloidal silica, vapor phase silica, and alumina sol are preferably used. The preferable average particle diameter of such inorganic fine particles is 3 to 200 nm, further 3 to 100 nm, and particularly 10 to 50 nm. If the average particle diameter is excessively small, writing property and sealability may be deteriorated. On the other hand, when the amount is too large, the smoothness of the surface of the gloss layer is impaired, and the gloss may be lowered.

  In addition, in such protective layers, higher fatty acid metal salts such as zinc stearate and calcium stearate, lubricants such as paraffin and polyethylene wax, UV absorbers such as benzophenone and benzotriazole, anionic and nonionic surfactants It is also possible to add a fluorescent dye or the like.

The coating of the protective layer coating liquid can be carried out by any means such as a roll coater method, an airy coater method, a blade coater method, a bar coater method, a size press method, a gate roll method, and the coating amount is The dry weight is preferably about 0.5 to 10 g / m ^2. After coating, the target coating layer is formed by air drying or mild heat treatment.
In addition, after applying the thermosensitive coloring layer or after applying the protective layer, it is possible to improve the smoothness and gloss by performing a super calender treatment.

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
10% aqueous solution of AA-modified PVA resin having an average degree of polymerization of 1200, a saponification degree of 99.0 mol%, and an AA degree of 5.0 mol%, and dimethoxyethanal (trade name “Hilink DM”, manufactured by Clariant , 60% aqueous solution) was mixed with 100 parts by weight of AA-PVA-based resin so that dimethoxyethanal was 5 parts by weight in solid content, and mixed and stirred to obtain a resin composition aqueous solution. At this time, the molar ratio (Y / X) of the sum (X) of the amount of dimethylacetal groups and the amount of aldehyde groups in dimethoxyethanal to the amount of AA groups (Y) in the AA-PVA-based resin was 1.
This aqueous solution was cast on a PET film, allowed to stand for 48 hours under conditions of 23 ° C. and 50% RH, and then heat-treated at 70 ° C. for 5 minutes to obtain a resin composition film having a thickness of 100 μm.
The water resistance and discoloration resistance of the obtained film were evaluated as follows.

(water resistant)
The obtained film was immersed in hot water at 80 ° C. for 1 hour, and the elution rate (%) of the film was measured. In calculating the dissolution rate (%), the dry weight of the film before immersion in hot water (X ₁ ) and the dry weight of the film after immersion in hot water (X ₂ ) (both in g) were obtained and The elution rate (%) was calculated. The results are shown in Table 1.
Elution rate (%) = [(X ₁ −X ₂ ) / X ₁ ] × 100

(Discoloration resistance)
The obtained film was stored for 1 week under the conditions of 40 ° C. and 90% RH, and the degree of coloring (yellowing) of the film was visually observed and evaluated as follows. The results are shown in Table 1.
○ ・ ・ ・ No coloring is observed △ ・ ・ ・ Slight yellowing is observed × ・ ・ ・ Yellow yellowing is recognized

(Stability of aqueous solution)
After measuring the viscosity (a) at 23 ° C. of a 7% aqueous solution of the obtained resin composition with a Brookfield viscometer (Brookfield, rotor No. 2, rotation speed 100 rpm), the aqueous solution was measured at 23 ° C. The solution was placed in an atmosphere, the aqueous solution viscosity (b) after 6 days was measured, and the thickening ratio before and after was shown as (b) / (a).

Example 2
In Example 1, the resin composition was the same as in Example 1 except that the amount of dimethoxyethanal was 1 part by weight (Y / X = 5 ) with respect to 100 parts by weight of the AA-PVA-based resin. Films were prepared and evaluated similarly. The results are shown in Table 1.

Example 3
Resin in the same manner as in Example 1 except that the blending amount of dimethoxyethanal was 50 parts by weight (Y / X = 0.1 ) with respect to 100 parts by weight of AA-PVA resin in Example 1. A composition film was prepared and evaluated in the same manner. The results are shown in Table 1.

Example 4
In Example 1, a resin composition was used in the same manner as in Example 1 except that an AA-PVA resin having an average polymerization degree of 1700, a saponification degree of 92 mol%, and an AA degree of conversion of 2 mol% was used as the AA-PVA resin. A product film was prepared and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 1
In Example 1, a resin composition was used in the same manner as in Example 1 except that instead of dimethoxyethanal, a cyclic acetal compound (trade name “Secaretz 755”, manufactured by Omninova), which is a reaction product of glucose and glyoxal, was used. A product film was prepared and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 2
In Example 1, a resin composition film was prepared in the same manner as in Example 1 except that glyoxal was used in place of dimethoxyethanal, and was evaluated in the same manner. The results are shown in Table 1.

  The resin composition of the present invention is excellent in stability when made into an aqueous solution, and since a cross-linked reaction product excellent in discoloration resistance and water resistance is obtained, an adhesive that requires high aesthetics and water resistance, Suitable for applications such as paper processing agents.

Claims (5)

An acetoacetate group-containing polyvinyl alcohol resin composition comprising an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule. The resin composition according to claim 1, wherein the acetal compound is dialkoxyethanal. The resin composition according to claim 1 or 2, wherein the amount of the acetal compound is 0.1 to 100 parts by weight with respect to 100 parts by weight of the acetoacetate group-containing polyvinyl alcohol resin. A paper processing agent comprising the resin composition according to claim 1. A heat-sensitive recording medium comprising a layer containing a cross-linked reaction product of an acetoacetate group-containing polyvinyl alcohol resin and an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule.