JP2014205826A - Crosslinking agent, crosslinked polymer, and their applications - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel crosslinking agent used for forming a crosslinked polymer, above all to provide a crosslinking agent suitable as a crosslinking agent for crosslinking and polymerizing an acetoacetyl group-containing polyvinyl alcohol resin and yielding a crosslinked polymer having an extremely superior water resistance.SOLUTION: The provided crosslinking agent includes an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid.

Description

  The present invention relates to a crosslinking agent capable of forming a crosslinked polymer having excellent water resistance, a crosslinked polymer formed by crosslinking with such a crosslinking agent, and uses thereof.

Cross-linked polymers are usually superior in strength, heat resistance, solvent resistance, and the like to the same type of linear polymers because the movement of molecular chains is restricted in a three-dimensional direction.
Such cross-linked polymers are broadly classified into (i) those obtained by polymerizing monomers together with a cross-linking agent to polymerize into a network, and (ii) those obtained by intermolecular cross-linking of linear polymers with a cross-linking agent. The

  The cross-linked polymer according to (i) is obtained by reacting a monomer and a cross-linking agent in advance to form a cross-linkable monomer, which is heated and polymerized using a catalyst as necessary. Many examples include thermosetting resins such as urea resins, melamine resins, and phenol resins. These are all monomers, ureas, melamines, phenols added with an aldehyde compound such as formaldehyde as a cross-linking agent to form a methylol group, and a cross-linked structure is formed by a condensation reaction between the methylol groups. .

Regarding (ii), various linear polymers have been studied for cross-linking methods and put into practical use. Among them, a polyvinyl alcohol resin (hereinafter, polyvinyl alcohol is abbreviated as PVA) which is a water-soluble resin can impart water resistance by crosslinking, and is one of the resins in which formation of a crosslinked structure is extremely important in practice. One.
In the case of such PVA-based resins, examples using a hydroxyl group bonded to the main chain as a crosslinking group are also widely known. However, in order to increase the crosslinking efficiency and form a strong crosslinked structure, a modified PVA having reactivity. For example, a PVA resin having an acetoacetyl group is used for applications that require high water resistance.

  Various compounds are known as crosslinking agents for such acetoacetyl group-containing PVA resins (hereinafter, acetoacetyl group-containing PVA resins are abbreviated as AA-PVA resins). Among them, aldehyde compounds are acetoacetyl groups. It is widely used in various applications because it has a high reactivity with the above and the crosslinking reaction proceeds at a relatively low temperature.

  For example, Patent Document 1 proposes a crosslinking agent containing glyoxylate as a crosslinking agent having an aldehyde group as an effective functional group, and is characterized by no odor and superior safety compared to formaldehyde. In addition, when used as a cross-linking agent for linear polymers, particularly AA-PVA-based resins, the cross-linking reaction is excellent, and the stability of the liquid mixture with AA-PVA-based resins is excellent, and the water resistance is improved. In addition, it is described that a crosslinked polymer having the characteristics of excellent coloration with little coloration with time can be obtained. Further, among glyoxylates, particularly when an alkali metal salt of glyoxylic acid or an alkaline earth metal salt of glyoxylic acid is used as a crosslinking agent, the water resistance of a crosslinked polymer formed by crosslinking an AA-PVA resin is improved. It is described that it is excellent.

JP 2010-77385 A

  However, although the obtained crosslinked polymer has sufficient water resistance, it is used for adhesion of a polarizing plate (adhesive layer between a polarizing film and a protective film in a polarizing plate) and for a thermal recording medium (protective layer for a thermal recording medium). In the field of application where higher water resistance is required, such as a polymer having a higher water resistance than ever before, further improvement is required as the required performance increases in recent years. There is a need for a cross-linking agent to form it.

  Therefore, in the present invention, an object is to provide a cross-linking agent that is an aldehyde-based cross-linking agent that is used for forming a cross-linked polymer and that can provide a cross-linked polymer that is extremely excellent in water resistance. To do.

  However, as a result of intensive studies in view of the above circumstances, the present inventor has obtained both an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid, which can obtain a crosslinked polymer having some excellent water resistance. It has been found that a cross-linked polymer having higher water resistance than ever can be obtained synergistically by the combined use, and the present invention has been completed.

  That is, the gist of the present invention relates to a crosslinking agent comprising an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid.

The alkali metal salt of glyoxylic acid and the alkaline earth metal salt of glyoxylic acid have an aldehyde group in the molecule, and the aldehyde group is a monomer such as ureas, melamines, phenols, or a linear high salt. It functions as a cross-linking agent by reacting with a molecular functional group, particularly an acetoacetyl group.
The cross-linking agent of the present invention includes an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid as active ingredients. The active ingredient means that it substantially functions as a cross-linking agent. It is.

Furthermore, the present invention relates to a crosslinked polymer obtained by crosslinking a compound capable of reacting with the crosslinking agent to form a crosslinked structure by the crosslinking agent.
The present invention also provides a polarizing plate having an adhesive layer containing the crosslinked polymer, a thermal recording medium having at least one layer containing the crosslinked polymer, and an aqueous emulsion composition containing the crosslinking agent. Is.

The present invention is characterized in that both an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid are used in combination. It is usually difficult to think of blending an alkaline earth metal salt of glyoxylic acid with an alkaline earth metal salt of glyoxylic acid that is less water resistant than a crosslinking agent of the alkaline earth metal salt of glyoxylic acid, Surprisingly, as a result of studying the combined use of both as a crosslinking agent, the water resistance of the resulting crosslinked polymer was determined by crosslinking using only a crosslinking agent containing an alkaline earth metal salt of glyoxylic acid. The synergistic effect of improving the water resistance of the polymer has been found.
This is presumably due to the following reasons.

The cross-linking reaction using glyoxylate is considered to proceed in two stages. For example, taking a linear polymer as described below as an example, it is presumed as follows. That is, the aldehyde group of glyoxylate reacts with the functional group of the polymer chain of the linear polymer in the first stage, and then reacts again with the unreacted functional group of the polymer chain and the carboxyl group of glyoxylate in the second stage. By doing so, a crosslinked structure is formed and water resistance is imparted.
Here, the alkaline earth metal salt is a divalent salt, and the first stage reaction proceeds rapidly between the polymer chains, and the two-dimensional crosslinking reaction proceeds, but the second stage reacts. Unreacted functional groups in the polymer chain are reduced, and the second-stage reaction does not proceed smoothly.
Therefore, when an alkaline earth metal salt and an alkali metal salt are used in combination, an alkaline earth metal salt of glyoxylic acid that exhibits a one-dimensional crosslinkability is added to an alkaline earth metal salt of glyoxylic acid that undergoes a crosslinking reaction in a two-dimensional structure. As a result, free functional groups with high reactivity remain in the polymer chain, and a smooth and efficient second-stage cross-linking reaction proceeds with glyoxylate. It is presumed that a crosslinked structure is formed and higher water resistance is imparted.

  The crosslinking agent of the present invention is useful as a compound capable of reacting with the crosslinking agent to form a crosslinked structure, particularly a linear polymer crosslinking agent. Among them, it is effective in crosslinking water-soluble polymers such as PVA resins to make them water resistant, and is particularly useful as a cross-linking agent for AA-PVA resins, and has excellent cross-linking reactivity and is extremely excellent. In addition, a crosslinked polymer having high water resistance can be formed. The resulting crosslinked polymer is effective for various uses such as a polarizing plate, a thermal recording medium, and an aqueous emulsion composition.

  Hereinafter, the present invention will be described in detail.

[Crosslinking agent]
The crosslinking agent in the present invention is a crosslinking agent comprising an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid as active ingredients.
Examples of the alkali metal salt of glyoxylic acid include salts of alkali metal such as lithium, sodium and potassium with glyoxylic acid. Examples of the alkaline earth metal salt of glyoxylic acid include salts of alkaline earth metals such as magnesium and calcium and glyoxylic acid.

  In the present invention, it is assumed that the hydrophilicity of the carboxylate group derived from the glyoxylate introduced into the crosslinked structure is small compared to the carboxylic acid group, which contributes to the improvement of the water resistance of the crosslinked polymer. Therefore, it is preferable that the alkali metal salt of glyoxylic acid and the alkaline earth metal salt of glyoxylic acid have low water solubility. Specifically, the water solubility at 23 ° C. is 0.01-100. %, Particularly 0.1 to 50%, more preferably 0.5 to 20% are preferably used. For example, the solubility of sodium glyoxylate is about 17% and the solubility of calcium glyoxylate is about 0.7%.

  Therefore, in the present invention, from the standpoint of solubility in water and ease of synthesis, sodium glyoxylate and potassium glyoxylate are used as the alkali metal salt of glyoxylic acid, and calcium glyoxylate and the alkaline earth metal salt of glyoxylic acid are used. Magnesium glyoxylate is preferably used. Specifically, a combination of sodium glyoxylate and calcium glyoxylate is most preferable in terms of solubility in water.

  A known method can be used as a method for producing an alkali metal salt of glyoxylic acid or an alkaline earth metal salt of glyoxylic acid. For example, (1) a method based on a neutralization reaction of glyoxylic acid, (2) glyoxylic acid and Examples thereof include a method by a salt exchange reaction with an acid salt having an acid dissociation constant larger than glyoxylic acid, and (3) a method by alkaline hydrolysis of glyoxylic acid ester (see, for example, JP-A-2003-300996). . In particular, when the alkaline compound used in the neutralization reaction with glyoxylic acid is highly water-soluble, the method (1) is low, and the resulting alkali metal salt of glyoxylic acid or alkaline earth metal salt of glyoxylic acid has low water solubility. When the acid dissociation constant of the acid salt larger than glyoxylic acid is high in water solubility, the method (2) is preferably used.

The method (1) is usually carried out using water as a medium. Glyoxylic acid and an alkaline compound, for example, various metal hydroxides are reacted in water, and the precipitated alkali metal salt of glyoxylic acid or alkali of glyoxylic acid is used. The earth metal salt can be produced by filtration and drying.
The method (2) is also generally carried out in water, and an alkali metal salt of glyoxylic acid or an alkaline earth metal salt of glyoxylic acid can be obtained in the same manner as the method (1). Examples of the acid salt having a larger dissociation constant than glyoxylic acid used in the method (2) include, for example, alkali metal or alkaline earth metal salts of aliphatic carboxylic acids such as sodium acetate, calcium acetate, and calcium propionate. Can be mentioned.

  It is also possible to carry out the reaction (1) or (2) in the system and use the glyoxylic acid alkali metal salt or glyoxylic acid alkaline earth metal salt as it is without isolation.

According to the above, an alkali metal salt of glyoxylic acid or an alkaline earth metal salt of glyoxylic acid can be produced. The method for producing the crosslinking agent of the present invention includes (i) an alkali metal glyoxylic acid and an alkali of glyoxylic acid. A method in which earth metal salts are separately manufactured and mixed, or (b) a method in which one of the other raw materials is charged and both are present in the manufacturing system, C) Arbitrary methods, such as a method in which both raw materials are charged and both exist in the production system, can be mentioned. Especially, the method of manufacturing separately (a) each and mixing both is preferable at the point which can change a content ratio easily.
In the above method (b), for example, (i) an alkali metal hydroxide is reacted with glyoxylic acid in water to synthesize an alkali metal salt of glyoxylic acid, and then an alkaline earth metal acetate is added. A method of synthesizing a mixture of an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid; or (ii) an alkaline earth metal salt of glyoxylic acid by reacting glyoxylic acid with an alkaline earth metal acetate in water. Can be prepared by adding an alkali metal hydroxide and synthesizing a mixture of an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid.

The alkali metal salt and alkaline earth metal salt of glyoxylic acid synthesized above are powders, and the crosslinking agent of the present invention containing them is also usually a powder.
The average particle diameter of the alkali metal salt of glyoxylic acid is usually 5 to 1000 μm, preferably 10 to 500 μm, particularly preferably 30 to 300 μm. If the average particle diameter is too small, it tends to be scattered and difficult to handle. Yes, if it is too large, it tends to be difficult to dissolve.
The average particle size of the alkaline earth metal salt of glyoxylic acid is usually 5 to 1000 μm, preferably 10 to 500 μm, particularly preferably 30 to 300 μm. When it is too large, it tends to be difficult to dissolve.
Furthermore, the average particle diameter of the crosslinking agent containing the glyoxylic acid alkali metal salt and the glyoxylic acid alkaline earth metal salt is usually 5 to 1000 μm, preferably 10 to 500 μm, more preferably 30 to 300 μm. is there. If the average particle size is too large, the solubility in water tends to decrease, and the crosslinking reaction may be insufficient.

As a method for adjusting the average particle system, it can be obtained, for example, by pulverizing, sizing, pulverizing or sieving with various mills.
When adjusting the average particle size of the cross-linking agent of the present invention, glyoxylic acid alkali metal salt and glyoxylic acid alkaline earth metal salt prepared by the above methods can be blended. In addition, it is possible to adjust a mixture of both in advance by the above method.

  The average particle diameter can be measured by a conventional method, for example, a laser diffraction particle size distribution analyzer “MASTERSIZER2000” (manufactured by Sysmex Corporation).

  The alkali metal salt of glyoxylic acid or the alkaline earth metal salt of glyoxylic acid contained in the crosslinking agent in the present invention has an aldehyde group such as alcohol having 3 or less carbon atoms such as methanol and ethanol, ethylene glycol, propylene glycol, etc. Including a compound acetalized and hemiacetalized with a diol having 3 or less carbon atoms. Such an acetal group and a hemiacetal group easily desorb alcohol in water or at a high temperature and take an equilibrium state with the aldehyde group. It functions as.

In the crosslinking agent of the present invention, the content ratio (by weight) of the alkali metal salt of glyoxylic acid with respect to the alkaline earth metal salt of glyoxylic acid is preferably 0.01 to 1, particularly from the viewpoint of water resistance. Preferably it is 0.015-0.5, More preferably, it is 0.02-0.3, Most preferably, it is 0.1-0.2.
If the content ratio of the alkali metal salt of glyoxylic acid to the alkaline earth metal salt of glyoxylic acid is too small or too large than the above range, the water resistance tends not to improve or decrease, and glyoxylic acid If the content of the alkaline earth metal salt is too large, it tends to be difficult to dissolve in water.

  The cross-linking agent of the present invention may contain impurities used in the production of alkali metal salts of glyoxylic acid and alkaline earth metal salts of glyoxylic acid, impurities contained in the raw materials, and by-products during production. For example, glyoxylic acid, metal hydroxide, aliphatic carboxylate, glyoxal, oxalic acid, oxalate, glycolic acid or glycolate may be contained.

  In particular, when glyoxylic acid is used as a raw material, glyoxal, which is a by-product at the time of production thereof, may be contained in the crosslinking agent, and the content of such glyoxal is most desirably 0% by weight. Is preferably 5% by weight or less, particularly 2% by weight or less, and more preferably 1% by weight or less. If the content of glyoxal is large, for example, the stability of the aqueous solution mixed with the AA-PVA-based resin is lowered, the pot life is shortened, or the resulting cross-linked polymer of the AA-PVA-based resin depends on the storage conditions. It may be colored over time.

[Crosslinked polymer]
In the present invention, although it varies depending on the type of the compound, it is preferable to add a crosslinking agent to the compound in an amount of usually 0.1% by weight or more, more preferably 1 to 20% by weight, particularly preferably 2 to 10% by weight. In particular, it is preferable to blend 3 to 7% by weight. If the blending amount is too small, the water resistance tends to be difficult to improve, and if it is too large, the crosslinking agent tends to be difficult to dissolve in water.
As a method of blending the crosslinking agent of the present invention into a compound capable of reacting with a crosslinking agent to form a crosslinked structure, an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid were separately produced and isolated. Each may be blended using a product, or a mixture of both may be blended. Moreover, when mix | blending, you may mix | blend collectively and may divide | segment and mix | blend continuously. In addition, when blending, the powder may be used as it is, or it may be blended as an aqueous solution or a dispersion.

  The compound capable of reacting with the cross-linking agent of the present invention to form a cross-linked structure is polymerized together with the cross-linking agent of the present invention to form a polymer cross-linked product that is network-like (i) a monomer compound And (ii) linear polymers which are cross-linked by the cross-linking agent of the present invention to become a cross-linked polymer.

 (I) As a monomer compound, if it is used for the thermosetting resin which uses conventional aldehyde compounds, such as formaldehyde, as a crosslinking agent, it can use similarly. Specific examples include phenols, amine compounds such as urea and melamine, and ketone compounds such as acetone, with phenols being particularly preferred.

  Specific examples of such phenols include, for example, phenol, o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, 2,3-xylenol, 2,5- Xylenol, 3,5-xylenol, 3,4-xylenol, 2-propiophenol, 2-isopropylphenol, 3-propylphenol, 3-isopropylphenol, 4-propylphenol, 4-isopropylphenol, 2-sec-butylphenol 2-tert-butylphenol, 3-sec-butylphenol, 3-tert-butylphenol, 4-sec-butylphenol, 4-tert-butylphenol, 3-cyclohexylphenol, 4-cyclohexylphenol, 2-do Silphenol, 3-dodecylphenol, 4-dodecylphenol, 2-octadecylphenol, 3-octadecylphenol, 4-octadecylphenol, 2-isopropyl-5-methylphenol, 2-methyl-4-tert-butylphenol, 3-methyl -6-tert-butylphenol, 2,3,5-trimethylphenol, 2,3,5-triethylphenol, o-isopropenylphenol, m-isopropenylphenol, p-isopropenylphenol, 2-methyl-4-iso Alkylphenols such as propenylphenol and 2-ethyl-4-isopropenylphenol, halogenated phenols such as fluorophenol, chlorophenol, bromophenol and iodophenol, 2-phenylphenol Phenylphenols such as 3-phenylphenol and 4-phenylphenol, naphthylphenols such as 2-naphthylphenol, 3-naphthylphenol and 4-naphthylphenol, o-methoxyphenol, m-methoxyphenol, p-ethoxyphenol , Alkoxyphenols such as o-ethoxyphenol, m-ethoxyphenol, p-ethoxyphenol, o-propoxyphenol, m-propoxyphenol, p-propoxyphenol, bisphenol A, bisphenol F, bis (2-methylphenol) A , Bis (2-methylphenol) F, bisphenol S, bisphenol E, bisphenol Z, 4,4′-dihydroxybiphenyl, resorcinol, hydroquinone, pyrogallol and other polyhydrides Examples include but are not limited to loxyphenols, α-naphthol, β-naphthol, dihydroxynaphthalene, and the like, and each may be used alone or in combination of two or more. May be.

  (Ii) The linear polymer is not particularly limited as long as it has a functional group capable of reacting with an aldehyde group. Examples of the functional group include an acetoacetyl group, a carboxyl group, a silicon group, and a sulfonic acid group. , A cation group, an ethylene group, an acrylamide group, an amide group, and the like. Among them, an acetoacetyl group is the most preferable functional group because it has excellent reactivity with the crosslinking agent of the present invention.

  The polymer having a functional group such as an acetoacetyl group in the side chain is not particularly limited as long as it is a linear polymer. For example, polyolefin resins such as polyethylene and polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene Polyester resins such as naphthalate, polyamide resins such as nylon 6, nylon 11, nylon 12 and nylon 66, polyvinyl resins such as polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyacrylic acid and polymethyl methacrylate, Polydiolefin resins such as polybutadiene and polyisoprene, polyether resins such as polyacetal and polyethylene oxide, polyurethane resins, polycarbonate resins, polyimide resins, formaldehyde resins , And the like polyol resin. In addition, these linear polymers may be linear or branched.

Such an acetoacetyl group can be introduced into the aforementioned polymer by either copolymerization or post-reaction methods.
The monomer used in the production of a linear polymer having an acetoacetyl group by copolymerization has an acetoacetyl group, and the structure of the other part is determined from the polymerization method and the main monomer. What is necessary is just to select suitably according to copolymerization property etc., Especially the vinyl acetoacetate and acetoacetoxyalkyl (meth) acrylate etc. which are ethylenically unsaturated monomers can be mentioned.
As a method for introducing an acetoacetyl group by post-reaction, transesterification reaction between a hydroxyl group in a linear polymer and acetoacetate ester, similarly, an amide exchange reaction between amino group and acetoacetamide, or hydroxyl group or amino acid Examples thereof include a method of reacting a diketene with a group.

  Next, (i) a crosslinked polymer obtained by polymerizing a monomer compound in a network form with the crosslinking agent of the present invention, that is, a so-called thermosetting resin type crosslinked polymer will be described.

  The cross-linked polymer in which the monomer is polymerized by the cross-linking agent is prepared by reacting the monomer and the cross-linking agent in advance to form a cross-linkable monomer. There are many that can be obtained by polymerizing them, and hereinafter, a crosslinkable monomer using the crosslinking agent of the present invention and a crosslinked polymer obtained by further polymerizing will be described.

The addition reaction of the crosslinking agent of the present invention to the monomer is usually a solution reaction or a solvent-free reaction using an alkaline catalyst. Examples of the alkaline catalyst include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. And alkaline earth metal hydroxides such as calcium hydroxide, and amine compounds such as ammonia, methylamine and dimethylamine are preferred.
The amount of the alkaline catalyst used is usually such that the pH of the reaction system is in the range of 8 to 12, more preferably 9 to 11. When the amount of alkaline catalyst used is small and the pH is low, the reaction takes a long time, which is not economical. Increasing the amount of use and increasing the pH increases the reaction rate proportionally, but the pH is 12 If it exceeds, the reaction rate becomes constant or tends to decrease.

  Examples of the solvent used in the addition reaction include alcohol solvents such as methanol, ethanol, and propanol, ketone solvents such as acetone, methyl ethyl ketone, methyl isopropyl ketone, and methyl isobutyl ketone, and water. In particular, when the obtained addition compound, that is, the crosslinkable monomer is used in a solid state, a method of reacting in an aqueous solution and taking out the precipitated reaction product is preferably used. Moreover, when apply | coating and impregnating various base materials as a crosslinkable monomer as a solvent solution, it is preferable to use an alcohol solvent or a ketone solvent.

The amount of the crosslinking agent of the present invention used for each monomer varies depending on the type of monomer, but in order to obtain a crosslinked polymer, it is essential that the molar ratio exceeds 2 times. This is the maximum amount of aldehyde compound added to the monomer, and is usually near the upper limit. For example, in the case of using phenols, the molar ratio is 2-3 times, in the case of ureas, 2-4 times, in the case of melamines, 2-6 times.
In addition, the reaction temperature of this addition reaction is not specifically limited, What is necessary is just to carry out within the range of the boiling point of the solvent to be used from room temperature. However, if it is carried out at too high a temperature, it is not preferable because it does not stop at the addition reaction and may cause a crosslinking reaction. Similarly, in the case of solution reaction, it is not preferable to carry out at a too high concentration.

A crosslinkable monomer in which a plurality of the crosslinking agents of the present invention are added to the monomer used as a raw material is obtained by the above addition reaction, but usually a mixture of different addition amounts. The structure varies depending on the monomer used as a raw material, but when phenol is used, an addition reaction occurs at the ortho-position and para-position of the hydroxyl group, for example, a compound represented by the following formula (A) is obtained.
In addition, X in the formula represents a metal element, and typically illustrates the case of an alkali metal salt of glyoxylic acid which is a monovalent metal, but in the case of a polyvalent metal such as an alkaline earth metal, In some cases, the metal shares a cross-linked structure or free glyoxylic acid.

Formula (A)

  The crosslinkable monomer thus obtained is first heated to dehydrate and condense with each other to form an ether bond, and when one molecule of OHC-COOX is desorbed to form a methylene bond to form a strong crosslinked structure. A crosslinked polymer is formed. The following formula (B) shows a part of a structure example of a crosslinked polymer when phenol is used as a monomer.

Formula (B)

  The crosslinked polymer thus obtained has excellent strength and heat resistance, and is widely used as various molded articles and binders. In particular, crosslinkable monomers that use phenols as a raw material are generally called resol-type phenol resins, and are made by laminating various adhesives and binders for plywood, etc., and paper and cloth impregnated and dried. The laminate obtained by thermal crosslinking can be used for a printed wiring board or the like. Crosslinked polymers obtained from ureas are, for example, various molded articles such as daily necessities, crosslinkable monomers obtained from melamines are components of paints and adhesives, and are obtained by further crosslinking them. The polymer can be used as molded articles such as tableware and decorative plates.

The cross-linking monomer and cross-linking polymer having a cross-linking functional group obtained by adding the cross-linking agent of the present invention to a monomer such as phenols, ureas, and melamines under alkaline conditions are described above. However, when an aldehyde compound is reacted with phenols under acidic conditions, a condensation reaction occurs simultaneously with the formation of a methylol group by addition of an aldehyde to the phenol nucleus, resulting in a polynuclear compound having no crosslinkable functional group (usually 6 Or less), which is usually referred to as a novolac-type phenolic resin.
The crosslinking agent of the present invention can be used as an aldehyde compound for obtaining such a novolak-type phenol resin, and the novolak-type phenol resin obtained thereby has, for example, the structure shown below.
In the formula, X represents a metal element.

As phenols used as a raw material for such novolak type phenol resins, various phenols can be used as in the case of the above-mentioned resol type phenol resins.
As a method for producing the novolak type phenol resin, a known method can be used. Generally, phenols and an aldehyde compound which is a crosslinking agent of the present invention are mixed with inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, Phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, ethylenediaminetetrakismethylenephosphonic acid, aminotrismethylenephosphonic acid, 1-hydroxyethylidene-1,1′-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid In the presence of an acidic catalyst such as organic phosphonic acids such as p-toluenesulfonic acid, xylenesulfonic acid, and oxalic acid, the reaction is usually performed at 50 ° C. to reflux temperature for 1 to 50 hours. is there.

  When the novolac type phenol resin is produced, the amount of the crosslinking agent of the present invention to be used for phenols is usually about 0.3 to 1 mol with respect to 1 mol of phenols, and it is sufficient that the amount used is too small. However, if the amount is too large, the crosslinking reaction proceeds too much, the molecular weight becomes too large, and the subsequent handling tends to be difficult.

The novolac type phenol resin using the crosslinking agent of the present invention thus obtained is further added to an aldehyde compound together with an alkaline catalyst such as ammonia, alkali metal hydroxide, alkaline earth metal hydroxide and the like, preferably the crosslinking of the present invention. By adding the agent and heating, the crosslinking reaction further proceeds, and a crosslinked polymer having the same structure as that represented by the formula (B) is obtained.
As its application, if it is an application in which a normal novolac type phenol resin is used, it can be used similarly, for example, mixed with filler such as wood powder, glass fiber, calcium carbonate, injection molding, extrusion molding, After filling into a predetermined mold by press molding or the like, it is cured by heat to obtain a molded product excellent in heat resistance, solvent resistance, strength, etc., and can be used as a housing for electronic parts and various devices.

Furthermore, the novolak-type phenol resin using the crosslinking agent of the present invention thus obtained can be used as an epoxy resin by introducing a glycidyl group by reacting its phenolic hydroxyl group with epihalohydrin.
A typical structure of an epoxy resin composed of a novolac type phenol resin obtained by using the crosslinking agent of the present invention is shown below.
In the formula, X represents a metal element.

  Such an epoxy resin is prepared by adding 2 to 20 mol of epihalohydrin such as epichlorohydrin, epibromohydrin, β-methylepichlorohydrin or the like to 1 mol of phenolic hydroxyl group in the novolak type phenol resin, and further, using the phenolic as a catalyst. It can be obtained by reacting at a temperature of 10 to 200 ° C. for 0.5 to 10 hours while adding 0.9 to 2 mol% of the basic catalyst to 1 mol of hydroxyl group at once or gradually adding.

Specific examples of the basic catalyst used in the reaction include alkaline earth metal hydroxides, alkali metal hydroxides, alkali metal carbonates, and preferably sodium hydroxide or potassium hydroxide. Is used.
The reaction can be carried out without a solvent, but preferably ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, ethanol, isopropyl alcohol, n-propyl alcohol and n-butanol, methyl cellosolve, Solution reaction using cellosolves such as ethyl cellosolve, ethers such as tetrahydrofuran, 1,4-dioxane, 1,3-dioxane and diethoxyethane, aprotic organic solvents such as acetonitrile, dimethyl sulfoxide and dimethylformamide as solvents It is preferable to carry out with. Such solvents may be used alone or in combination of two or more kinds of solvents in order to adjust the polarity.

  The epoxy resin based on the novolak-type phenol resin using the crosslinking agent of the present invention thus obtained can be mixed with a curing agent such as an amine compound and heated as necessary to obtain a crosslinked polymer. It is possible to apply to applications where resin is used.

  Next, (ii) a crosslinked polymer obtained by intermolecular crosslinking of a linear polymer with the crosslinking agent of the present invention will be described.

As described above, the linear polymer used for the crosslinked polymer is preferably a linear polymer having an acetoacetyl group from the viewpoint of excellent reactivity with the crosslinking agent of the present invention.
The reaction between the acetoacetyl group in the linear polymer and the crosslinking agent of the present invention is based on the fact that the active methylene sandwiched between the two carbonyl groups of the acetoacetyl group is an alkali metal salt of glyoxylic acid or an alkaline earth metal of glyoxylic acid. It occurs by nucleophilic attack on the aldehyde carbon in the salt, and the cross-linked structure portion is assumed to be represented by the following structural formula.
In addition, X in the formula represents a metal element, and typically illustrates the case of an alkali metal salt of glyoxylic acid which is a monovalent metal, but in the case of a polyvalent metal such as an alkaline earth metal, In some cases, the metal shares a cross-linked structure or free glyoxylic acid.

Here, it is possible to improve heat resistance and solvent resistance by cross-linking the linear polymer, but in the case of PVA resin in particular, the water-soluble one should be a cross-linked polymer. Since the water resistance can be improved by this, the effect of crosslinking can be exhibited extremely remarkably. Furthermore, since the alkali metal salt of glyoxylic acid and the alkaline earth metal salt of glyoxylic acid, which are the main components of the crosslinking agent of the present invention, have an ionic group (carboxylate) in the molecule, a PVA resin and an acetoacetyl group As a result, a highly uniform crosslinked structure with little variation in crosslinking density can be obtained.
Therefore, it is considered that the crosslinking agent of the present invention can exert its ability most strongly when combined with the AA-PVA-based resin.
Hereinafter, the AA-PVA-based resin and the crosslinked polymer thereof will be described in detail.

[AA-modified PVA resin and its crosslinked polymer]
The AA-PVA resin used in the present invention is a PVA resin having an acetoacetyl group in the side chain.
The method for producing the AA-PVA-based resin is not particularly limited. For example, a method of reacting a PVA-based resin with diketene, a method of reacting a PVA-based resin with acetoacetate, and transesterification, acetic acid A method of saponifying a copolymer of vinyl and vinyl acetoacetate can be mentioned, but since the production process is simple and a high-quality AA-PVA-based resin is obtained, the PVA-based resin and diketene are reacted. It is preferable to manufacture by a method.
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, 4-diacetoxy-2-butene, 1,4-dihydroxy-2-butene, vinylene carbonate and the like can be mentioned.

Furthermore, polyoxyethylene (meth) allyl ether, polyoxyethylene (meth) acrylamide, polyoxypropylene (meth) acrylamide, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, polyoxyethylene (1- ( Poly) alkylene groups such as (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine Containing monomer, N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylic Amidopropyltrimethylammonium chloride, 2-acryloxyethyltrimethylammonium chloride, 2-methacryloxyethyltrimethylammonium chloride, 2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, 3- Examples also include cation group-containing monomers such as butenetrimethylammonium chloride, dimethyldiallylammonium chloride, and diethyldiallylammonium chloride.
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 of the total structural unit, and if it is too much, the water solubility is impaired. Or the compatibility with the cross-linking agent may be reduced.

  In addition, by increasing the polymerization temperature when polymerizing and copolymerizing vinyl ester monomers and other monomers, the amount of heterogeneous bonds produced mainly with respect to 1,3-bonds produced is increased, and 1 in the PVA main chain is increased. , 2-diol bond having a content of about 1.6 to 3.5 mol% can be used.

  The introduction of acetoacetyl groups by the reaction of PVA resin obtained by saponifying the polymer and copolymer of the above vinyl ester monomer and diketene involves direct reaction of PVA resin with gaseous or liquid diketene. Alternatively, after adsorbing and occluding an organic acid in a PVA resin in advance, 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 applied to the PVA resin. Methods such as spraying and reacting are used.

  As a reaction apparatus for carrying out the above reaction, an 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 average polymerization degree of the AA-PVA-based resin thus obtained may be appropriately selected depending on the use, but is usually 300 to 4000, and particularly 400 to 3500, and more preferably 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 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 obtain an aqueous solution, the stability of the aqueous solution is lowered, or the water resistance of the resulting crosslinked polymer tends to be insufficient. The average degree of polymerization and the degree of saponification are measured according to JIS K6726.

  Further, the content of acetoacetyl groups in the AA-PVA-based resin (hereinafter abbreviated as AA degree) is usually 0.1 to 20 mol%, further 0.2 to 15 mol%, especially What is 0.3-10 mol% is generally used widely. If the content is too small, the water resistance tends to be insufficient or a sufficient crosslinking rate may not be obtained. Conversely, if the content is too large, the water solubility tends to decrease or the stability of the aqueous solution tends to decrease. There is.

  In the present invention, the AA-PVA-based resin generally has a hydroxyl group average chain length of 10 or more, and more preferably 15 or more. If the hydroxyl chain length is too short, the water resistance of the resulting crosslinked reaction product tends to decrease.

“Hydroxyl group average chain length” [l (OH)] refers to 3- (trimethylsilyl) -2,2,3,3-d ₄ -propionic acid sodium salt (3- (trimethylsilyl) propionic- Absorption based on the methylene carbon moiety found in the range of 38-46 ppm in ¹³ C-NMR measurements (solvent: D ₂ O) using 2,2,3,3-d ₄ -acid sodium salt) ((OH, OH ) Absorption of dyad = absorption having a peak top between 43 and 46 ppm, Absorption of (OH, OR) dyad = absorption having a peak top between 41 and 43 ppm, Absorption of (OR, OR) dyad = 38 to 41 ppm It is a value calculated from the following formula.
l (OH) = [2 (OH, OH) + (OH, OR)] / (OH, OR)
(However, the absorption intensity ratios of (OH, OR) and (OH, OH) are all calculated as mole fractions.)
With regard to the hydroxyl group average chain length and the measuring method thereof, “Poval” (Publisher: Kobunshi Shuppankai, page 248, 1981) and Macromolecules, Vol. 10, p532 (1977).

  The method for controlling the hydroxyl group average chain length of the AA-PVA-based resin is not particularly limited, but the dielectric constant at 20 ° C. is 32 or less in the saponification step of polyvinyl acetate or the like when producing the PVA-based resin used as a raw material. It is preferable to perform alkali saponification in the presence of such a solvent. Usually, the dielectric constant is preferably 6 to 28, and more preferably 12 to 25. When the dielectric constant is too high, the block property of the remaining acetate group arrangement in the PVA resin is lowered, and the hydroxyl chain length of the resulting AA-PVA resin tends to be shortened.

  As a solvent having a dielectric constant of 32 or less at 20 ° C., methanol (31.2), methyl acetate / methanol = 1/3 (27.1), methyl acetate / methanol = 1/1 (21.0), methyl acetate / Methanol = 3/1 (13.9), methyl acetate (7.03), isopropyl acetate (6.3), trichlorethylene (3.42), xylene (2.37), toluene (2.38), benzene (2.28), acetone (21.4) and the like. Of these, a mixed solvent of methyl acetate / methanol is preferably used.

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 20% by weight or less. In particular, it is preferably 10% by weight or less.
Examples of various PVA-based resins other than the AA-PVA-based resin include unmodified PVA and various modified PVA-based resins, such as a vinyl ester monomer and a monomer copolymerizable with the vinyl ester monomer. Copolymer saponified products can be used. Examples of such monomers include ethylene, propylene, isobutylene, α-octene, α-dodecene, olefins such as α-octadecene, 3-buten-1-ol, 4 -Derivatives such as hydroxy group-containing α-olefins such as penten-1-ol, 5-hexen-1-ol, 3,4-dihydroxy-1-butene and acylated products thereof, acrylic acid, methacrylic acid, crotonic acid, Unsaturated acids such as maleic acid, maleic anhydride, itaconic acid, undecylenic acid, their salts, monoesters, Or nitriles such as dialkyl esters, acrylonitrile and methacrylonitrile, amides such as diacetone acrylamide, acrylamide and methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid or salts thereof, alkyl vinyl ether , Dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, vinyl compounds such as glycerol monoallyl ether, isopropenyl acetate, 1- Examples thereof include substituted vinyl acetates such as methoxyvinyl acetate, vinylidene chloride, 1,4-diacetoxy-2-butene, 1,4-dihydroxy-2-butene, vinylene carbonate and the like.

  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.

  The crosslinked polymer obtained by crosslinking the AA-PVA resin thus obtained with the crosslinking agent of the present invention comprises the AA-PVA resin as described above, an alkali metal salt of glyoxylic acid, and an alkaline earth metal of glyoxylic acid. A cross-linking agent obtained by reacting a cross-linking agent containing a salt. In such a cross-linking reaction, an AA-PVA-based resin, an alkali metal salt of glyoxylic acid, and an alkaline earth metal salt of glyoxylic acid are used as active ingredients. The blending ratio is preferably in the range of 0.1 to 200 parts by weight, more preferably 0.5 to 100 parts by weight, especially 1 to 50 parts by weight of the crosslinking agent with respect to 100 parts by weight of the AA-PVA resin. Used. The molar ratio (X / Y) of the amount of aldehyde groups (X) in the crosslinking agent to the total amount of AA groups (Y) in the AA-PVA-based resin is usually 0.01 to 50, preferably 0.05 to 20 In particular, it is in the range of 0.1-10. If the amount of the aldehyde group is too small, the water resistance of the resulting crosslinked polymer may be insufficient. Conversely, if the amount is too large, the mixed aqueous solution tends to thicken depending on the use environment and the pot life is shortened. There is a case.

  The crosslinked polymer obtained by crosslinking the AA-PVA resin with the crosslinking agent of the present invention is usually a resin composition aqueous solution containing the AA-PVA resin and the crosslinking agent of the present invention, and then a coating agent. It is applied to various uses such as uses and paints. Such an aqueous resin composition solution is (i) a method in which a mixture of an AA-PVA resin and a cross-linking agent is poured into water and dissolved, and (ii) a solution in which an AA-PVA resin and a cross-linking agent are separately dissolved in advance. Or (iii) a method in which a crosslinking agent is added to an aqueous solution of an AA-PVA-based resin and mixed. In addition, when glyoxylate is produced in the system as described above and used without isolation, it is possible to perform such a reaction in the presence of an AA-PVA-based resin. For example, glyoxylic acid is alkaline. In the case of obtaining an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid by neutralization with a compound, a method of adding an alkaline compound to a mixed aqueous solution of AA-PVA-based resin and glyoxylic acid can also be used. .

  The concentration of the AA-PVA-based resin aqueous solution in the method for preparing the resin composition aqueous solution is preferably 0.05 to 40% by weight, more preferably 1 to 30% by weight, and particularly preferably 1 to 20% by weight. If the concentration of the AA-PVA-based resin aqueous solution is too large, the viscosity becomes too high, which may make it difficult to apply to a substrate or to various processes. On the other hand, if the concentration is too small, the amount of resin tends to be insufficient or a long time is required for drying.

 The pH of the aqueous resin composition solution is usually 2 to 10, preferably 3 to 10, and more preferably 4 to 9. If the pH is too low, it may lead to corrosion of the device used for application of the resin composition aqueous solution, so that countermeasures are necessary, and conversely if too high, the resin composition aqueous solution tends to thicken, The pot life tends to be shorter.

  In addition, the above-mentioned aqueous solution may be blended with other known crosslinking agents within a range that does not impair the properties of the present invention. Examples of such crosslinking agents include water-soluble titanium compounds, water-soluble zirconium, Polyvalent metal compounds such as water-soluble aluminum compounds, boron compounds such as boric acid and borax, amine compounds (diamine compounds, polyamine compounds, polyallylamine, etc.), hydrazine compounds (eg, adipoyl dihydrazide), polymers Hydrazide (polyaminoacrylamide manufactured by Otsuka Chemical Co., Ltd.), silane compounds, methylol group-containing compounds (such as methylolated melamine), aldehyde group-containing compounds (glyoxal, dimethoxyethanal, glutaraldehyde, glyoxylic acid, and their hemiacetals and acetals Derivatives), epoxy Compound, thiol compound, isocyanate compound, polyisocyanate compound (such as “Hydran Assist C1” manufactured by Dainippon Ink & Chemicals, Inc.), block isocyanate compound (such as ketoxime block or phenol block), water-soluble or water-dispersed Epoxy resin or compound (polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, diglycerin diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether Ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, resorcin diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, sorbitan polyglycidyl ether, polyglycerol polyglycidyl ether Etc.), water-soluble or water-dispersible oxetane resins or compounds, polyamidoamine-epichlorohydrin resins, polyethyleneimine, and the like. These may be used alone or in combination of two or more.

 In the above aqueous solution, additives such as antifoaming agents, antifungal agents, preservatives, leveling agents, various emulsions, polyester ionomer-type urethane resins (for example, Dainippon) are used within the range not impairing the characteristics of the present invention. "Hydran AP-20" and "Hydran APX-101H" "manufactured by Ink Chemical Industry Co., Ltd.), various polymer dispersions typified by polyurethane dispersion and polyester dispersion, polyhydroxyethyl methacrylate, polyhydroxyethyl acrylate Further, a water-soluble resin such as polyacrylic acid, a compound having a glycidyloxy group, a metal colloid such as aluminum (for example, “Alumina sol-10A” manufactured by Kawaken Fine Chemical Co., Ltd.), and the like may be blended.

The aqueous solution of the resin composition thus prepared is applied to various uses by a known method such as coating, casting, and dipping, and then is heat-dried or dried at low temperature to room temperature as necessary. 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.

  The crosslinked polymer obtained by crosslinking the AA-PVA-based resin using the crosslinking agent of the present invention is useful for various applications that require water resistance, particularly various adhesive applications, binder applications, and coating applications. It is suitable for etc.

  Hereinafter, a polarizing plate, a heat-sensitive recording medium, and an aqueous emulsion using a cross-linked polymer of AA-PVA-based resin by the cross-linking agent of the present invention will be described.

〔Polarizer〕
First, the polarizing plate which has the crosslinked polymer of AA-PVA-type resin by the crosslinking agent of this invention in the adhesive bond layer between a polarizing film and a protective film is demonstrated.
There is no restriction | limiting in particular as a polarizing film used for the polarizing plate of this invention, A well-known thing can be used. For example, (i) A dichroic material such as iodine or a dichroic dye is adsorbed on a vinyl alcohol resin film such as a PVA film, a partially formalized PVA film, or an ethylene-vinyl alcohol resin film. A stretched one (see, for example, JP-A-2001-296427 and JP-A-7-333426), (ii) a birefringent material having liquid crystallinity together with a dichroic material, and a vinyl alcohol resin film (Iii) a uniaxially stretched thermoplastic norbornene resin film containing a dichroic material (for example, see JP-A-2001-356213) .), (Iv) PVA-based resin and ethylene-vinyl alcohol resin are dehydrated or deaceticated and continuously. Introduced polyene structure, a polyene-based film obtained by stretching them (e.g., see JP Patent 2007-17845.), And the like.

Among them, a polarizing film containing a PVA film and a dichroic material such as iodine is preferable. Hereinafter, a PVA film and a polarizing film containing iodine will be described.
The PVA-based resin used for the PVA-based film is usually produced by saponifying a polyvinyl ester obtained by polymerizing a fatty acid vinyl ester typified by vinyl acetate. Copolymers may be used, for example, unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers. A saponified copolymer of a component copolymerizable with vinyl acetate such as an unsaturated sulfonate may be used. The degree of saponification of the PVA-based resin is usually 85 to 100 mol%, particularly 90 to 100 mol%, more preferably 95 to 100 mol%. When the degree of saponification is too low, the water resistance tends to be insufficient when forming a polarizing film.

  The average degree of polymerization of the PVA resin may be any, but is usually 1200 to 7000, particularly 1500 to 5000, and more preferably 1600 to 4000. If the average degree of polymerization is too low, it tends to be difficult to stretch the film at the time of forming the polarizing film, and if it is too high, the surface smoothness and transmittance of the film tend to be lowered. In addition, the saponification degree and average polymerization degree of PVA-type resin are measured according to JISK6726.

A method for producing such a polarizing film is not particularly limited, and a known method may be adopted. A typical example will be described below.
First, a raw film is formed from an aqueous solution of PVA resin. As such a method, a known film forming method can be used, and a solution casting method is usually employed, but a dry / wet film forming method or a gel film forming method can also be carried out. When such a solution casting method is used, the concentration of the PVA-based resin aqueous solution is usually 1 to 50% by weight, and the raw film can be obtained by casting the aqueous solution on a metal roll or the like and drying by heating.

  It is also possible to add various additives to the PVA-based resin aqueous solution as long as the quality of the polarizing plate is not hindered. For example, various solvents can be used alone for the purpose of adjusting affinity and volatility to the substrate, Or it is also a preferable embodiment to mix and mix. Examples of such solvents include monohydric alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and butyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, glycerin, trimethylolpropane, and the like. And polyhydric alcohols, phenols such as phenol and cresol, amines such as ethylenediamine and trimethylenediamine, dimethyl sulfoxide, dimethylacetamide, N-methylpyrrolidone and the like.

  The film thickness of the raw film is usually 10 to 100 μm, preferably 20 to 90 μm, and more preferably 30 to 70 μm. If the film thickness is too thin, stretching tends to be impossible, and if it is too thick, film thickness accuracy tends to decrease.

  Such a raw film then becomes a polarizer through a process of uniaxial stretching, adsorption of a dichroic material such as iodine or dichroic dye, and crosslinking with a boron compound. Each of these processes is performed separately. However, the order of each step is not particularly limited. In particular, it is preferable in terms of productivity to perform uniaxial stretching in at least one of the dichroic material adsorption step and the boron compound treatment step.

  Moreover, in the manufacturing process of this polarizer, you may perform the ozone treatment process immersed in the process liquid containing ozone with respect to the PVA original fabric film for the purpose of an optical characteristic improvement. The ozone treatment process can be provided as an independent process separate from the iodine adsorption process, the crosslinking process, and the stretching process, and the treatment liquid used in at least one of the iodine adsorption process, the crosslinking process, and the stretching process Ozone may be contained therein.

  The draw ratio during uniaxial stretching is usually 3.5 to 10 times, and a range of 4.5 to 7 times is particularly preferably selected. At this time, the film may be slightly stretched in the direction perpendicular to the above (stretching to prevent shrinkage in the width direction or more). The temperature conditions during stretching are usually selected from the range of 40 to 130 ° C. The stretching operation is not limited to one stage, and can be performed in multiple stages. Furthermore, the stretching operation can be performed individually at any stage of the manufacturing process. May be finally set within the above range.

  The adsorption of iodine to the PVA stretched film is performed by bringing the film into contact with a liquid containing iodine. As the iodine solution, an iodine-potassium iodide aqueous solution is usually used. In this case, the iodine concentration is 0.1 to 2 g / L, the potassium iodide concentration is 10 to 50 g / L, and potassium iodide / The weight ratio of iodine is preferably 20-100. Moreover, about 3 to 500 second is practical as the time which makes a PVA-type stretched film contact a dichroic material solution, and the temperature of a bath has preferable 30-80 degreeC. In addition, as a contact means, arbitrary means, such as immersion, application | coating, and spraying, are applicable.

  The PVA-based stretched film on which iodine is adsorbed is then subjected to a crosslinking treatment with a boron compound. As the boron compound, boric acid and borax are typically used. Such crosslinking treatment is performed by bringing the film obtained above into contact with an aqueous solution of a boron compound or a water-organic solvent mixed solution. As such a contact method, a dipping method is typically used, but a coating method or a spray method is also used. It can be implemented. In the case of the immersion method, the concentration is usually selected within the range of 0.5 to 2 mol / L, the bath temperature is usually about 50 to 70 ° C., and the treatment time is usually preferably about 5 to 20 minutes.

  The PVA-based film thus obtained and a polarizing film containing iodine are then laminated with a protective film via an adhesive layer. The thickness of the protective film is usually 10 to 100 μm, preferably 20 to 80 μm, and the material thereof is not particularly limited, and it is preferable if it is transparent and excellent in durability. Suitable examples include cellulose ester resin films, cyclic olefin resin films, (meth) acrylic resin films, α-olefin resin films, and the like.

  Examples of cellulose ester resins used in such cellulose ester resin films include triacetyl cellulose and diacetyl cellulose, but other lower fatty acid esters of cellulose, cellulose acetate propionate and cellulose acetate. Mixed fatty acid esters such as butyrate can be used. The cellulose ester resin film is subjected to a saponification treatment with an aqueous alkaline solution or the like in order to increase the affinity with the polarizing film or the PVA resin used as an adhesive thereof, but is not limited thereto. Absent. Moreover, the thing which apply | coated the antistatic agent on the surface or contained in the film is used preferably.

Typical examples of the cyclic olefin-based resin used in the above-mentioned cyclic olefin-based resin film include a norbornene-based resin. Examples of the norbornene-based resin include ring-opening (co) polymerization of a norbornene-based monomer. Examples thereof include resins obtained by addition polymerization of norbornene monomers, and resins obtained by addition copolymerization with norbornene monomers and olefin monomers such as ethylene and α-olefin. Specific examples of norbornene-based monomers include dimers such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene and dihydroxypentadiene; heptacyclics such as tetracyclopentadiene; these methyl, ethyl, propyl and butyl Substituents such as alkyl, alkenyl such as vinyl, alkylidene such as ethylidene, aryl such as phenyl, tolyl, and naphthyl; and ester groups, ether groups, cyano groups, halogens, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carvone Examples include substituents having groups containing elements other than carbon and hydrogen, such as acid groups, amino groups, hydroxyl-free groups, silyl groups, epoxy groups, acryloyl groups, and methacryloyl groups.
Commercially available products of cyclic olefin-based resin films include “ARTON” manufactured by JSR, “ZEONOR”, “ZEONEX” manufactured by Nippon Zeon, “OPTOREZ” manufactured by Hitachi Chemical, “APEL” manufactured by Mitsui Chemicals, and Sekisui Chemical “Essina” and “SCA40” manufactured by the company can be mentioned.

Moreover, as a (meth) acrylic-type resin used for the above-mentioned (meth) acrylic-type resin film, poly (meth) acrylic acid ester, such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymer, Methyl methacrylate- (meth) acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymer, (meth) acrylic acid methyl-styrene copolymer, alicyclic hydrocarbon group Polymer (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.), high Tg (meth) obtained by intramolecular crosslinking or intramolecular cyclization reaction Acrylic resins, rubber-acrylic graft type core-shell polymers, and the like can be mentioned.
Examples of such commercially available (meth) acrylic resin films include “Acrypet VRL20A”, “Acrypet IRD-70” manufactured by Mitsubishi Rayon Co., Ltd., “MUX-60” manufactured by UMGABS, and the like.

  The α-olefin resin used in the α-olefin resin film described above is, for example, an α-olefin resin mainly composed of 4-methylpentene-1 unit, In addition to a homopolymer, a copolymer with other monomer having 4-methylpentene-1 as a main structural unit and copolymerizable therewith is also included. Other monomers that can be copolymerized with 4-methylpentene-1 include ethylene and other α-olefins, cyclic olefins, and the like. Examples of the α-olefins include 1-alkenes having 2 to 20 carbon atoms (for example, octene, decene, dodecene, octadecene, etc.), α-olefins having 8 to 18 carbon atoms, and the like. Examples of the cyclic olefins include bicyclo [2.2.1] hept-2-ene (commonly called norbornene) and derivatives thereof.

  In addition to these protective films, polyester resin films such as polyethylene terephthalate and polyethylene naphthalate, polystyrene resin films such as polystyrene and acrylonitrile / styrene copolymers, polyolefin resins such as polypropylene, and polyarylate resin films Water-soluble polyether sulfone resin film, polycarbonate resin film, vinyl chloride resin film, amide resin film such as nylon and aromatic polyamide, (fluorine-containing) polyimide resin film, polyether ether ketone resin film , Polyphenylene sulfide resin films, vinyl alcohol resin films, vinylidene chloride resin films, polyvinyl acetal resin films such as polyvinyl butyral, Riarireto resin film, a polyoxymethylene-based resin films, and the like epoxy resin film. As protective films, for example, acrylic, urethane, acrylic urethane, epoxy, fluororesin films such as tetrafluoroethylene / hexafluoropropylene copolymer, silicone-based thermosetting, ultraviolet curable, etc. And a polymer film described in JP-A-2001-343529 (specifically, a resin film containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer) ) Etc. can also be used.

  On these protective films, a liquid crystal polymer, a polymer such as polyimide, or an organically modified clay composite is coated and cured to provide an optical functional layer, or a predetermined birefringence is obtained by an operation such as uniaxial or biaxial stretching. Those having characteristics (so-called A plate, C plate, X plate, n-TAC, B-TAC, F-TAC, etc.) and those provided with various easy-adhesion layers are also included. In the case of stretching uniaxially or biaxially, the stretching ratio is usually about 1.1 to 5 times, preferably 1.1 to 3 times.

Furthermore, a cured coating film layer is formed on the surface of these protective films, and the moisture permeability is lowered to a level of 400 g / m ² · 24 hr or less as a value measured at a temperature of 40 ° C. Measures may be taken to protect the polarizing film from condensed water and to suppress the occurrence of minute streak defects that are likely to occur at the end of the polarizing plate due to environmental changes.

  The cured coating film layer is a layer obtained by forming a coating liquid with a curable resin material and curing it by irradiation with heat or active energy rays. The material of the cured coating film layer is not particularly limited, and a curable resin material such as silicone, acrylic or urethane acrylate, or a mixture of the resin with a filler can be employed. Especially, what formed the coating film layer using the acrylic curable resin is preferable.

  Such acrylic curable resins include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, (meth ) N-butyl acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, acetoacetoxy Various (meth) acrylic acid or its ester monomers such as ethyl (meth) acrylate, acetoacetoxybutyl (meth) acrylate, glycerin triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, di Pentaerythrito Tetraacrylate, it is an dipentaerythritol pentaacrylate, dipentaerythritol such acrylate monomers hexaacrylate, methacrylate monomers corresponding to them or curable component an oligomer containing a unit derived from them. A photopolymerization initiator is mixed with these curing components to prepare a coating liquid, and the coating film obtained by applying the coating liquid is cured by irradiation with light, generally ultraviolet rays, to obtain a cured coating film layer. . You may mix a solvent with a coating liquid as needed.

  Various photopolymerization initiators are commercially available. For example, from “Irgacure” series manufactured by Ciba Specialty Chemicals, “Kayacure” series manufactured by Nippon Kayaku Co., Ltd. In addition, it may be selected as appropriate.

Urethane acrylate-based curable resins are also often cured by light irradiation, particularly ultraviolet irradiation. On the other hand, silicone-based curable resins are often cured by heat.
Therefore, the cured coating layer in the present invention is applied to the surface of the cellulose acetate film by a known method such as a spin coating method or a micro gravure coating method using the coating liquid containing the curable resin as described above. It can be provided by curing or thermosetting. The thickness of the cured coating film layer is about 1 to 30 μm, preferably 2 to 20 μm.

  Among these protective films, cellulose ester-based resin films and cyclic olefin-based resin films are preferably used from the viewpoints of transparency, heat resistance, mechanical strength, durability, etc. Among them, triacetyl cellulose or norbornene-based resins are preferable. Used.

Such a protective film can be subjected to various surface treatments in order to increase the affinity with the polarizing film and the PVA resin used as an adhesive thereof. In addition to the saponification treatment in a resin film, an easy-adhesion layer containing (meth) acrylate latex, styrene latex, polyethyleneimine, polyurethane / polyester copolymer, various metal colloids, etc. on the surface of the protective film A method of imparting hydrophilicity to the surface by providing an anchor coat layer, corona discharge treatment, reduced pressure plasma treatment or atmospheric pressure plasma treatment, reduced pressure UV treatment, and ion assist method (for example, IRA method of Micro Technology Laboratory), Couplings such as silane coupling agents and titanium coupling agents In and the like surface treatment method. In addition, it is also possible to use together the above-mentioned various surface treatment methods.
In addition, such a protective film can be provided with a hard coat layer on a surface not laminated with the polarizing film, or can be subjected to various treatments such as anti-sticking, anti-reflection, and anti-glare. Furthermore, various optical functional films such as a phase difference plate and a viewing angle widening film can be laminated.

  Examples of such an optical functional film include an optical compensation film, a reflective polarization separation film, a film with an antiglare function, a film with a surface antireflection treatment, a reflective film having a reflective function, and a transflective film having both a reflective function and a transmissive function. Etc. Commercially available products corresponding to the optical compensation film include “WV film” manufactured by Fuji Photo Film Co., Ltd., “NH film” and “NR film” manufactured by Nippon Oil Corporation (both are trade names). Commercially available products corresponding to the reflective polarizing separation film include “DBEF” manufactured by Minnesota Mining and Manufacture (3M) (Sumitomo 3M in Japan).

The polarizing plate of the present invention is such that a transparent protective film is bonded to at least one surface, preferably both surfaces, of such a polarizing film via an adhesive layer, and the adhesive layer crosslinks the AA-PVA-based resin of the present invention. Containing a crosslinked polymer obtained by crosslinking with an agent.
The content of the crosslinked polymer in the adhesive layer is usually 50 to 100 parts by weight, particularly preferably 70 to 100 parts by weight, and more preferably 80 to 100 parts by weight. If the content is too small, the adhesive strength tends to decrease or the water resistance of the adhesive tends to decrease.
Such an adhesive layer is usually obtained by uniformly applying a water-based adhesive containing the AA-PVA-based resin and the cross-linking agent of the present invention to a polarizing film or a protective film, or both, and then bonding them together, It is formed by heating and drying.
When coating such a water-based adhesive on a polarizing film or a protective film, a roll coater method, for an air doctor, a blade coater method, a spray method, a dipping method, or just before bonding a polarizing film and a protective film, A known method such as supplying an appropriate amount of an agent (water) solution between the films and pouring the solution and then bonding them together and drying can be used. The coating amount of the aqueous adhesive is usually selected from the range of 1 to 1000 nm, particularly 1 to 500 nm, and more preferably 1 to 300 nm as the thickness of the adhesive layer after drying, and the thickness becomes too thick. Uniform coating tends to be difficult and thickness unevenness tends to occur. Moreover, as heat drying conditions after apply | coating and bonding water-based adhesive, it is 5 to 150 degreeC normally, 30 to 120 degreeC, Furthermore, in 50 to 90 degreeC, 10 second-60 minutes, Furthermore, 30 second-30 minutes In particular, it is performed under conditions of 1 minute to 20 minutes.

  The viscosity of the aqueous adhesive is usually 5 to 10000 mPa · s, further 5 to 5000 mPa · s, particularly 10 to 1000 mPa · s at 23 ° C. If the viscosity is too high, the water-based adhesive may not be defoamed smoothly or may cause uneven thickness of the adhesive layer. The viscosity of the aqueous adhesive can be measured with, for example, a Brookfield viscometer.

Moreover, the solid content concentration of the aqueous adhesive is usually 0.1 to 20%, further 0.5 to 15%, and particularly 1 to 10%. If the concentration is too low, the adhesive strength is insufficient, and if it is too high, the viscosity becomes too high, and the defoaming of the aqueous adhesive may not be performed smoothly, or the thickness of the adhesive layer may be uneven.

As described above, after the transparent protective film is bonded to at least one side, preferably both sides, of the polarizing film via an adhesive layer, sufficient curing strength is usually obtained by curing for several hours to several days. It is done. The preferred temperature for such curing is 30-50 ° C. The relative humidity is in the range of about 0 to 70% RH.

[Thermal recording medium]
Next, a thermal recording medium having at least one layer containing a crosslinked polymer obtained by crosslinking the AA-PVA-based resin with the crosslinking agent of the present invention will be described.
The heat-sensitive recording medium of the present invention is preferably used in the heat-sensitive color forming layer and / or protective layer on the support substrate, or in the intermediate layer between the heat-sensitive color developing layers of multilayer multicolor heat sensitive paper (for example, ZINK paper). It contains a polymer.

  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 layer of the thermal recording medium 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 support substrate. In the present invention, as the binder resin, AA is used. A cross-linked polymer obtained by cross-linking a PVA resin with the cross-linking agent of the present invention is used. The content of the cross-linked polymer at this time is usually 10 to 200 parts by weight with respect to 100 parts by weight of the total amount of the leuco dye and the developer, particularly 30 to 150 parts by weight, and more preferably 50 to 100 parts by weight. Is appropriate.

  As the leuco dye, known ones can be used, and examples thereof include 3,3-bis (p-dimethylaminophenyl) -phthalide and 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, Triarylmethane compounds such as 4,4′-bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleucooramine, and other diphenylmethane compounds, rhodamine B anilinolactam, rhodamine Bp-chloro Anilinolactam, 3-diethylamino-7-dibenzylaminofluorane, Xanthene-based compounds, benzoyl leuco methylene blue, 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.

  In the thermosensitive coloring layer, inorganic pigments such as calcium carbonate, silica, kaolin, aluminum hydroxide, aluminum oxide, zinc oxide, titanium dioxide, clay, talc, and barium sulfate, urea-formalin resin, nylon resin are used as necessary. , Acrylic resin, organic resin powders such as styrene / methacrylic acid copolymer, higher fatty acid metal salts such as zinc stearate and calcium stearate, lubricants such as paraffin and polyethylene wax, UV absorption such as benzophenone and benzotriazole It is also possible to add agents, anionic and nonionic surfactants, fluorescent dyes and the like.

  The coating solution for the thermosensitive coloring layer is finely pulverized by separately dispersing the above leuco dye and developer using a known disperser such as a ball mill, attritor or sand grinder until the particle size becomes 0.5 to 3 μm. As a dispersion, these are obtained by mixing the crosslinking agent of the present invention and the AA-PVA-based resin as the binder resin, and further, if necessary, the above additives and antifoaming agents. 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 provided on the above-mentioned thermosensitive coloring layer for the purpose of improving water resistance, chemical resistance, recording running property, etc., using water as a medium, a binder resin, an inorganic pigment, and, if necessary, a lubricant, etc. The coating solution for protective layer prepared by mixing and stirring is applied on the thermosensitive coloring layer and dried. In the present invention, a crosslinked polymer obtained by crosslinking an AA-PVA-based resin with the crosslinking agent of the present invention is used as the binder resin. The content of the crosslinked polymer at this time is suitably 10 to 200 parts by weight with respect to 100 parts by weight of the inorganic pigment.

  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 preferred average particle size of such inorganic fine particles is 3 to 200 nm, more preferably 3 to 100 nm, and particularly 10 to 50 nm. If the average particle size is excessively small, writing property and sealability may be deteriorated. If it is too large, the smoothness of the surface of the gloss layer is impaired, and the gloss may be lowered.

The coating of the protective layer coating liquid can be performed by any means such as a roll coater method, an air doctor 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. Moreover, it is also possible to prepare separately the aqueous solution containing each of the crosslinking agent and AA-PVA-based resin used in the present invention, and laminate these to form a protective layer. Various auxiliaries are preferably blended in an aqueous solution of AA-PVA-based resin. As a result, the resin composition of the present invention is contained in the protective layer, and the content ratio, coating amount, and the like conform to the above. Adjust it.

Next, the intermediate layer between the thermosensitive coloring layers in the multilayer multicolor thermal paper will be described.
Such an intermediate layer is provided to protect the thermosensitive coloring layer from organic solvents, moisture, various gases, etc., or to prevent the components of each layer from being mixed when the thermosensitive coloring layer is formed. Similarly to the protective layer, an aqueous coating solution containing an AA-PVA-based resin and the crosslinking agent of the present invention is applied on each heat-sensitive color forming layer and dried.
In addition, the compounding ratio of the crosslinking agent to the AA-PVA-based resin in the coating solution, other blends, the coating method, the coating amount, and the like are in accordance with the above-described protective layer.

In forming such a thermal recording medium, the AA-PVA-based resin and the crosslinking agent of the present invention can be contained in separate layers, and both can be reacted after coating to form a crosslinked structure.
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.

[Aqueous emulsion composition]
Next, an aqueous emulsion containing an AA-PVA-based resin as a dispersant and containing the crosslinking agent of the present invention in a dispersion medium will be described.
The dispersoid of such an aqueous emulsion is usually a polymerization containing repeating structural units derived from an ethylenically unsaturated monomer.
Such ethylenically unsaturated monomers mainly include monomers frequently used in emulsion polymerization, and typical examples include vinyl ester monomers, acrylic acid or its ester monomers, and diene monomers. Examples thereof include olefin monomers, acrylamide monomers, acrylonitrile monomers, styrene monomers, vinyl ether monomers, allyl monomers, and the like.

  Such vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate. , Vinyl versatate, 1-methoxyvinyl acetate, isopropenyl acetate, (meth) acrylic acid or its ester monomers include (meth) acrylic acid, methyl (meth) acrylate, (meth) acrylic acid Ethyl, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, (meth) 2-ethylhexyl acrylate, dodecyl (meth) acrylate, octade (meth) acrylate , Acetoacetoxyethyl (meth) acrylate, acetoacetoxybutyl (methacrylate), etc., as diene monomers, butadiene-1,3,2-methylbutadiene, 1,3 or 2,3-dimethylbutadiene- 1,3,2-chlorobutadiene-1,3 etc. can be mentioned, respectively.

  Furthermore, as olefin monomers, olefin monomers such as ethylene, propylene, 1-butene, isobutene, and halogenated olefins such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, acrylamide As the monomer, (meth) acrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid, diacetone acrylamide, etc., and as the acrylonitrile monomer, (meth) Acrylonitrile, etc., as styrene monomer, 3-isopropenyl-α, α′-dimethylbenzylacetoacetamide, styrene, α-methylstyrene, etc., as vinyl ether, methyl vinyl ether, n-propyl vinyl ether I-propyl vinyl ester Ether, n- butyl vinyl ether, i- butyl vinyl ether, t- butyl ether, dodecyl vinyl ether, stearyl vinyl ether, the allyl-based monomers, mention may be made of allyl acetate, allyl chloride, respectively.

  In addition to the above, carboxyl group-containing compounds such as fumaric acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, trimetic anhydride, and esters thereof, ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamide Examples include sulfonic acid group-containing compounds such as 2-methylpropanesulfonic acid, vinylsilane compounds such as vinyltrimethoxysilane, isopropenyl acetate, and 3- (meth) acrylamidopropyltrimethylammonium chloride.

The polymer containing a repeating structural unit derived from the above-mentioned monomer may be selected according to the intended use and purpose of the aqueous emulsion composition, and is not particularly limited. When used as an adhesive, it is preferable to use a vinyl acetate resin as the dispersoid. Similarly, an acrylic resin is used for pressure-sensitive adhesives, and an acrylic resin or acrylic-styrene resin is used for paints and coatings. An acrylic resin is preferably used for a fiber treatment agent, an acrylic resin is used for papermaking, and an ethylene-vinyl acetate resin or an acrylic resin is preferably used for civil engineering.
In addition, the above-described polymer is a copolymer including a repeating structural unit derived from two or more types of monomers even if the polymer includes a repeating structural unit derived from a single monomer. May be.

Next, a method for producing such an aqueous emulsion composition will be described.
Such an aqueous emulsion composition is obtained by blending the above crosslinking agent in an aqueous emulsion in which the AA-PVA-based resin is a dispersant and the polymer containing a repeating structural unit derived from an ethylenically unsaturated monomer is a dispersoid. Is. In preparing such an aqueous emulsion, (I) a method of emulsion polymerization of an ethylenically unsaturated monomer using an AA-PVA resin as an emulsifier or protective colloid, and (II) a repetition derived from the ethylenically unsaturated monomer A method of post-emulsifying a polymer solution or melt containing a structural unit in the presence of an AA-PVA-based resin, (III) including a repeating structural unit derived from an ethylenically unsaturated monomer obtained by any method Examples thereof include a method of producing a more stable emulsion by adding an AA-PVA resin to an aqueous emulsion of a polymer, and these will be described in detail, but are not limited to these methods.

[(I) Method by emulsion polymerization]
Add ethylenically unsaturated monomer and / or diene monomer temporarily or continuously in the presence of polymerization catalyst such as water, AA-PVA resin and polymerization initiator, and heat and stir. In the presence of water, an AA-PVA resin and a polymerization catalyst, an ethylenically unsaturated monomer and / or a diene monomer were mixed and dispersed in an AA-PVA resin aqueous solution. An emulsion polymerization method in which a dispersion (pre-emulsion) is added temporarily or continuously, followed by heating and stirring can be carried out.

  The amount of AA-PVA-based resin used varies slightly depending on the resin content of the emulsion and the like, but is usually 0.5 to 40% by weight, more preferably 1 to 35% by weight, in particular, based on the total amount of monomers in the emulsion polymerization reaction system It is preferably 3 to 30% by weight. If the amount of the AA-PVA-based resin used is too small, it will be difficult to maintain the polymer particles in a stable emulsified state, and conversely if too large, the viscosity of the emulsion will increase too much. Therefore, workability tends to decrease and the water resistance of the emulsion film tends to decrease.

  As the polymerization initiator, usually potassium persulfate, ammonium persulfate, potassium bromate, etc. are used alone or in combination with sodium sulfite, and further hydrogen peroxide-tartaric acid, hydrogen peroxide-iron salt, hydrogen peroxide Redox polymerization initiators such as ascorbic acid-iron salt, hydrogen peroxide-longalit, hydrogen peroxide-longalit-iron salt aqueous solution are used, and oil-soluble such as azobisisobutyronitrile, benzoyl peroxide, etc. A polymerization initiator can also be used.

The addition method of the polymerization initiator is not particularly limited, and a method of adding all at once in the initial stage, a method of adding continuously as the polymerization progresses, or the like can be employed.
In the above emulsion polymerization, a water-soluble polymer, a nonionic surfactant, or an anionic surfactant can be used in combination as an emulsion dispersion stabilizer.

  As water-soluble polymers, non-modified PVA, carboxyl group-containing PVA, PVA formalized product, acetalized product, butyralized product, urethanized product, sulfonic acid, carboxylic acid, etc. other than AA-modified PVA resin And saponified copolymer of vinyl ester and a monomer copolymerizable therewith. Monomers copolymerizable with vinyl esters include olefins such as ethylene, butylene, isobutylene, α-octene, α-dodecene, α-octadecene, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, Unsaturated acids such as itaconic acid or salts thereof, mono- or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide, diacetone acrylamide and methacrylamide, ethylene sulfonic acid, allyl sulfonic acid, methallyl Examples thereof include olefin sulfonic acids such as sulfonic acid or salts thereof, alkyl vinyl ethers, vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, and vinylidene chloride.

  Further, as water-soluble polymers other than the above PVA, cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxybutyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, aminomethyl hydroxypropyl cellulose, aminoethyl hydroxypropyl cellulose, etc. , Starch, tragacanth, pectin, glue, alginic acid or its salt, gelatin, polyvinylpyrrolidone, polyacrylic acid or its salt polymethacrylic acid or its salt, polyacrylamide, polymethacrylamide, vinyl acetate and maleic acid, maleic anhydride, acrylic Copolymer with unsaturated acid such as acid, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, Copolymers of emissions and the unsaturated acid, salts or esters of the copolymer and the copolymer of vinyl ether and the unsaturated acid.

  Examples of the nonionic surfactant include polyoxyethylene-alkyl ether type, polyoxyethylene-alkylphenol type, polyoxyethylene-polyhydric alcohol ester type, ester of polyhydric alcohol and fatty acid, oxyethylene / oxypropylene block Examples thereof include polymers.

Examples of anionic surfactants include higher alcohol sulfates, higher fatty acid alkali salts, polyoxyethylene alkylphenol ether sulfates, alkylbenzene sulfonates, naphthalene sulfonate formalin condensates, alkyl diphenyl ether sulfonates, and dialkyl sulfosuccinates. Higher alcohol phosphate ester salts and the like.
Furthermore, plasticizers such as phthalic acid esters such as dibutyl phthalate and phosphoric acid esters, pH adjusters such as sodium carbonate, sodium acetate and sodium phosphate may be used in combination.

[(II) Method by post-emulsification]
In producing an emulsion by the post-emulsification method, an AA-PVA-based resin is dissolved in water, and a repeating structural unit derived from a solution-like ethylenically unsaturated monomer and / or diene-based monomer is added thereto. The polymer containing may be dropped and stirred, or the aqueous PVA solution may be dropped and stirred in the polymer in a solution state. There is no particular need for heating or the like for emulsification, but it may be heated to about 45 to 85 ° C. if necessary. The above-mentioned polymer is preferable as the substance to be emulsified, but besides the above-mentioned polymer, epoxy resin, urethane resin, urea-formalin initial condensate, phenol-formaldehyde initial condensate, alkyd resin, ketene dimer, rosin, silicon resin , Wax, polypropylene, polyethylene, asphalt and the like.

  The amount of AA-PVA-based resin used varies slightly depending on the required resin content of the emulsion, but is usually in the range of about 0.5 to 40% by weight, preferably about 1 to 35% by weight with respect to the object to be emulsified. Selected from. If necessary, a nonionic activator such as polyoxyethylene-alkyl ether type, polyoxyethylene-alkylphenol type, polyhydric alcohol ester type or the like, or a cationic activator such as a higher alkylamine salt is appropriately used together with the resin. You can also Further, these active agents can be mixed in the object to be emulsified.

  Emulsification as described above, including nonionic active agents such as polyoxyethylene-alkyl ether type, polyoxyethylene-alkylphenol type, polyhydric alcohol ester type, or cationic active agents such as higher alkylamine salts, if necessary. Any of various surfactants used in the polymerization can be used in combination. Further, these active agents can be mixed in the object to be emulsified. Furthermore, pH adjusters such as phthalate esters, sodium acetate, and sodium phosphate can be used in combination.

[(III) Method by post-addition]
In this method, an AA-PVA-based resin is added to an emulsion of a synthetic resin obtained by an arbitrary method. Examples of the target emulsion include styrene / butadiene emulsion, cis-1,4 polyisoprene emulsion, and chloroprene emulsion. , Acrylonitrile / butadiene emulsion, vinyl pyridine emulsion, methyl methacrylate / butadiene emulsion, polyurethane emulsion, acrylic ester emulsion, vinyl acetate emulsion, ethylene / vinyl acetate emulsion, vinyl chloride emulsion, polystyrene emulsion, polyethylene emulsion, silicone emulsion , Polybutene emulsion, thiocol emulsion, etc., among them ethylenically unsaturated monomer or diene based monomer Polymer emulsions containing repeating structural units derived from the body are preferred.

  When the AA-PVA-based resin is added to the emulsion, when the AA-PVA-based resin is added as an aqueous solution, the aqueous solution may be added to the emulsion while stirring the emulsion at room temperature. When adding the powder of the system resin, it is preferable to add the powder while stirring the emulsion and to heat to 50 to 85 ° C. because uniform mixing is completed in a short time.

The amount of the AA-PVA-based resin used is usually 0.5 to 40% by weight, more preferably about 1 to 35% by weight, based on the solid content of the emulsion. If the amount used is too small or too large, the stability of the emulsion tends to decrease.
The aqueous emulsion may be one in which the AA-PVA-based resin is used as a dispersant.

The aqueous emulsion obtained above contains an AA-PVA-based resin as described above, and the final content ratio of the AA-PVA-based resin in the aqueous emulsion is not particularly limited. .1 to 40% by weight, preferably 0.5 to 35% by weight, particularly 1 to 30% by weight. If the content is too small, the adhesive strength and water resistance when applied to the adhesive are lowered, and vice versa. If the amount is too large, the adhesive layer tends to swell with water when used in an adhesive, and the adhesive strength tends to decrease.
It is possible to obtain an aqueous emulsion by using any of the above methods (I) to (III), and in particular, control of adhesive strength, water resistance, and permeability to a substrate when used for an adhesive. Considering the degree of freedom and the like, the method (I) is particularly preferable.

  In addition, the aqueous emulsion using the AA-PVA-based resin as a dispersant can also be made into a powder emulsion by spray drying, in which case, in order to improve powdering and redispersibility It is preferable to post-add PVA-based resin, particularly ethylene-modified PVA, partially saponified PVA, and the like.

By blending the cross-linking agent of the present invention into an aqueous emulsion having the AA-PVA-based resin thus obtained as a dispersant and a polymer containing a repeating structural unit derived from an ethylenically unsaturated monomer as a dispersoid. The aqueous emulsion composition of the present invention is obtained. The method of blending the crosslinking agent into the aqueous emulsion is not particularly limited, but usually, a method of adding and mixing a solution of the crosslinking agent to the aqueous emulsion is preferably used.
Also, for such a powder emulsion of the aqueous emulsion, a method of dry blending the crosslinking agent of the present invention, a method of spraying and mixing an aqueous solution of the crosslinking agent, and an aqueous emulsion by redispersing the powder emulsion in water Any of the blending methods is possible.

The mixing ratio of the crosslinking agent to the aqueous emulsion is usually 1 to 100 parts by weight, more preferably 5 to 50 parts by weight, particularly 10 to 30 parts by weight with respect to 100 parts by weight of the AA-PVA-based resin in the aqueous emulsion. A range of parts is preferably used. The molar ratio (X / Y) of the amount of aldehyde groups (X) in the crosslinking agent to the total amount of AA groups (Y) in the AA-PVA-based resin is usually 0.1 to 10, particularly 0.5 to 5. Range. If the amount of the aldehyde group is too small, the water resistance of the dry film of the aqueous emulsion may be insufficient. Conversely, if the amount is too large, the aqueous emulsion tends to thicken depending on the use environment.

  The solid content concentration of the aqueous emulsion composition of the present invention may be appropriately selected according to its use and purpose, but is preferably 10 to 85% by weight, more preferably 20 to 75% by weight, and particularly 30 to 65%. Used in the range of% by weight. If the solid content concentration is too small, it is not economical, and the adhesiveness is also insufficient. On the other hand, if it is too large, the viscosity of the emulsion becomes too high and the workability may be lowered. Is not preferable.

  In addition, the aqueous emulsion composition of the present invention may contain a thermosetting resin such as urea / formalin resin, melamine / formalin resin, phenol / formalin resin, acetoyl such as trimethylolpropane triacetoacetate, glycidyl acetoacetate, if necessary. Hydrophilic compound clay having acetyl group, filler such as kaolin and calcium carbonate, cross-linking agent such as boric acid, titanium compound, zirconium compound, hydrazide compound, other pigments, antifoaming agent, thickener, freezing Various additives such as an inhibitor, an antiseptic, and a rust inhibitor can be added.

  The aqueous emulsion composition of the present invention thus obtained is used by being applied to the substrate surface, impregnated on the substrate, or mixed with other materials depending on the intended use. In order to efficiently express the target water resistance or hot water resistance, heat treatment is preferably performed. The method of such heat treatment is not particularly limited, but after applying the aqueous emulsion composition of the present invention as an aqueous liquid, it is performed simultaneously with drying the moisture contained therein, or is further subjected to heat treatment after drying. Examples of the apparatus include a hot air dryer and infrared heating, and depending on the applied application, heating by a metal roll or a hot press can be used. Whatever method is adopted, the heat treatment is usually performed at a temperature of 40 to 200 ° C., preferably 50 to 180 ° C., particularly 60 to 160 ° C. If the temperature is too low, sufficient water resistance is achieved. In some cases, it takes a long time to obtain the properties, and conversely, if the temperature of the heat treatment is too high, coloring due to decomposition of PVA may occur.

In addition to the above, the composition containing the crosslinking agent of the present invention and the AA-PVA-based resin, and the crosslinked product thereof can be applied to applications requiring water resistance, and specific examples thereof. Examples include the following.
(1) Paper processing agent Undercoat layer and backcoat layer of various processed papers, coloring layer and intermediate layer of sublimation type thermal recording medium, inorganic fine particle binder of void type inkjet recording medium, ink of swelling type inkjet recording medium Receiving layer, clear coating agent for paper, pigment binder for coated paper, pigment binder for electrophotographic recording medium, surface coating agent and pigment binder for release paper, heat-resistant protective layer for thermal transfer recording medium, etc.
(2) Adhesives Two-component adhesives, honeymoon adhesives, pressure-sensitive adhesives, rehumidifiers, nonwoven fabric binders, building material binders (gypsum board, fiberboard, etc.), various powder granulation binders, pressure sensitive adhesives Agent, anionic paint fixing agent, etc.
(3) Aqueous gel Wastewater treatment carrier, water retention agent, cold insulation agent, bioreactor, fragrance, ground strengthening agent, organ model, artificial joint, artificial muscle, artificial food, etc.
(4) Coating agent Textile finishing agent, leather finishing agent, paint, antifogging agent, metal corrosion inhibitor, galvanizing brightener, antistatic agent, conductive agent, provisional paint, provisional protective film, etc.
(5) Film, membrane, fiber Electrolyte membrane, film for packaging, nonwoven fabric for separator, nonwoven fabric for organic solvent filter, nonwoven fabric for sound absorbing material, nonwoven fabric for packaging, nanofiber nonwoven fabric, 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.

Production Example 1: Cross-linking agent (sodium glyoxylate)
To 456 g (3.10 mol) of 50% aqueous glyoxylic acid was added 645 g (3.22 mol) of 20% aqueous sodium hydroxide solution, and the resulting white crystals were filtered, washed with water, dried at 50 ° C. for 1 hour, 210 g (1.84 mol, yield 59.5%, powder) of sodium glyoxylate was obtained.
The solubility of the obtained sodium glyoxylate in water at 23 ° C. was 17.1%.

Production Example 2: Cross-linking agent (calcium glyoxylate)
After adding 101 g of water to 101 g (0.68 mol) of 50% aqueous glyoxylic acid solution to make a 25% aqueous solution, 268 g (0.34 mol) of 20% aqueous calcium acetate solution was added dropwise over 2 hours, and the resulting white color was produced. The crystals were filtered, washed with water, and then dried at 50 ° C. for 1 hour to obtain 70.3 g of calcium glyoxylate (0.32 mol, yield 93.6%, powder).
The solubility of the obtained calcium glyoxylate in water at 23 ° C. was 0.7%.

<Example 1>
To 100 parts of a 10% aqueous solution of AA-modified PVA resin having an average polymerization degree of 1200, a saponification degree of 99 mol%, an AA degree of conversion of 5.0 mol% and a hydroxyl group average chain length of 22, a crosslinking agent (sodium glyoxylate to calcium glyoxylate) Content ratio = 0.25) (0.5% with respect to AA-PVA resin) was added and mixed and stirred to obtain an aqueous resin composition solution.
This aqueous solution was cast on a polyethylene terephthalate (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 film having a thickness of 100 μm.
The water resistance of the obtained film was 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

<Examples 2 and 3 and Comparative Examples 1 to 3>
In Example 1, a resin composition aqueous solution was obtained in the same manner except that the blending amount of the crosslinking agent with respect to the AA-PVA resin and the content ratio of sodium glyoxylate with respect to calcium glyoxylate were as shown in Table 1. Were prepared and evaluated in the same manner. The results are shown in Table 1.

As shown in Table 1 above, the AA-PVA resin film cross-linked using the cross-linking agent containing sodium glyoxylate and calcium glyoxylate obtained in the examples is glyoxylic acid obtained in the comparative example. Compared to AA-PVA resin film crosslinked using only sodium or calcium glyoxylate as a crosslinking agent, the elution rate was low and the water resistance was excellent.
Therefore, it can be seen that the AA-PVA resin film crosslinked using a crosslinking agent containing an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid is excellent in water resistance.

The cross-linking agent of the present invention is suitable as a cross-linking agent used for forming a cross-linked polymer. For example, there is no odor and safety with respect to formaldehyde frequently used in thermosetting resins such as urea resin, melamine resin, and phenol resin. It has the characteristic that it is excellent in property. Furthermore, the crosslinking agent of the present invention can impart antistatic properties to a crosslinked product using the same.
The cross-linking agent of the present invention is useful as a cross-linking agent for linear polymers, particularly acetoacetyl group-containing PVA resins, and is excellent in storage stability of a mixed aqueous solution, and has a long pot life during use. The cross-linked polymer obtained by cross-linking this has a good cross-linked structure, so it is very excellent in water resistance, and further, there is no coloration over time It is useful as an adhesive layer between a polarizing film and a protective film in a polarizing plate, a protective layer of a thermal recording medium, and the like.

Claims (11)

A crosslinking agent comprising an alkali metal salt of glyoxylic acid and an alkaline earth metal salt of glyoxylic acid. 2. The crosslinking agent according to claim 1, wherein the alkali metal salt of glyoxylic acid is sodium glyoxylate. The crosslinking agent according to claim 1 or 2, wherein the alkaline earth metal salt of glyoxylic acid is calcium glyoxylate. The crosslinking agent according to any one of claims 1 to 3, wherein the content ratio (by weight) of the alkali metal salt of glyoxylic acid to the alkaline earth metal salt of glyoxylic acid is 0.01 to 1. A crosslinked polymer obtained by crosslinking a compound capable of reacting with the crosslinking agent to form a crosslinked structure by the crosslinking agent according to claim 1. 6. The crosslinked polymer according to claim 5, wherein the crosslinking polymer is blended in an amount of 0.1% by weight or more based on a compound capable of reacting with the crosslinking agent to form a crosslinked structure. The crosslinked polymer according to claim 5 or 6, wherein the compound capable of reacting with a crosslinking agent to form a crosslinked structure is an acetoacetyl group-containing polyvinyl alcohol resin. A polarizing plate comprising an adhesive layer containing the crosslinked polymer according to claim 7 between the polarizing film and the protective film. A heat-sensitive recording medium comprising at least one layer containing the crosslinked polymer according to claim 7. An aqueous emulsion composition, wherein the dispersant is an acetoacetyl group-containing polyvinyl alcohol-based resin, and the crosslinking agent according to any one of claims 1 to 4 is contained in the dispersion medium. An aqueous emulsion composition, wherein the dispersoid is an acetoacetyl group-containing resin, and the crosslinking agent according to any one of claims 1 to 4 is contained in the dispersion medium.