JP6948925B2 - Crosslinked product obtained by using a novel modified vinyl alcohol polymer - Google Patents

Description

The present invention relates to a novel modified vinyl alcohol polymer, a method for producing the same, and a crosslinked product obtained by using the same.

A vinyl alcohol-based polymer having a reactive functional group (hereinafter, may be abbreviated as "PVA") has conventionally been a suspension of an adhesive, a paper coating agent, a polarizing film, and a vinyl compound (for example, vinyl chloride). It is used in various products such as dispersion stabilizers for turbid polymerization. In particular, the cross-linked polymer synthesized by the cross-linking reaction between the reaction active site and the cross-linking agent is usually stronger, heat-resistant, and resistant than the same type of linear polymer because the movement of the molecular chain is restricted in the three-dimensional direction. Its usefulness is high because it has excellent solvent properties, and in particular, its water resistance is enhanced.

As a modified PVA having a reactive functional group having particularly high cross-linking performance, a modified PVA having a methylene hydrogen structure sandwiched between two carbonyl groups typified by an acetoacetyl group can be mentioned (Patent Document 1). However, diketene, which is highly toxic to living organisms and has a risk of explosion when air and steam are mixed, is used for its production, and the development of a safer method for synthesizing modified PVA having a reactive functional group is required. Was being done.

Japanese Unexamined Patent Publication No. 2014-205826

The present invention has been made to solve the above problems, and an object of the present invention is to provide a modified PVA having high cross-linking performance and excellent water resistance when a cross-linked body is formed more safely.

［式（１）中、Ｒ^１は水素原子又は炭素数１〜４のアルキル基であり、Ｒ^２は水素原子又はアルカリ金属である。］ As a result of diligent studies, the present inventor includes a vinyl alcohol unit and a structural unit represented by the following formula (1), has a saponification degree of 68 mol% or more and less than 99.9 mol%, and 1,2-glycol. It has been found that the above problems can be solved by providing the modified vinyl alcohol-based polymer (A) having a binding amount of less than 1.9 mol%, and the present invention has been completed.

[In the formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ² is a hydrogen atom or an alkali metal. ]

That is, the above-mentioned problem is a modified vinyl alcohol-based polymer (A) containing a vinyl alcohol unit and a structural unit represented by the formula (1), and the degree of saponification is 68 mol% or more and less than 99.9 mol%. It is solved by providing the modified vinyl alcohol-based polymer (A) having a 1,2-glycol bond amount of less than 1.9 mol%.

At this time, the content of the structural unit represented by the formula (1) with respect to all the monomer units of the modified vinyl alcohol polymer (A) is preferably 0.1 to 10 mol%.

The modified vinyl alcohol polymer (A) is a crosslinked product (C) crosslinked with a crosslinking agent (B), and a film having a thickness of 100 μm made of the crosslinked product (C) is immersed in hot water at 80 ° C. for 1 hour. A crosslinked product (C) having an elution rate of less than 10% is also a preferred embodiment of the present invention.

［式（２）中、Ｒ^１は式（１）と同義である。］ The method for producing the above-mentioned modified vinyl alcohol-based polymer (A) in which the raw material vinyl alcohol-based polymer (D) and the compound represented by the following formula (2) are subjected to an esterification reaction is also a preferred embodiment of the present invention. ..

[In equation (2), R ¹ is synonymous with equation (1). ]

Since the modified vinyl alcohol polymer (A) of the present invention has a structure of methylene hydrogen sandwiched between two carbonyl groups, it can form a crosslinked product with various crosslinking agents. The formed crosslinked body is excellent in water resistance. Furthermore, according to the production method of the present invention, the modified vinyl alcohol-based polymer (A) having the above structure can be produced more safely.

(Modified vinyl alcohol polymer (A))
The modified vinyl alcohol-based polymer (A) of the present invention (hereinafter, may be abbreviated as "modified PVA (A)") is a modified PVA containing a vinyl alcohol unit and a structural unit represented by the following formula (1). (A), the saponification degree is 68 mol% or more and less than 99.9 mol%, and the 1,2-glycol bond amount is less than 1.9 mol%. The method for producing the modified PVA (A) of the present invention is not particularly limited, but a method for producing the modified PVA (A) by subjecting the raw material vinyl alcohol polymer (D) and the compound represented by the following formula (2) to an esterification reaction is simple. preferable. Here, the raw material vinyl alcohol-based polymer (D) is a PVA that does not have a structural unit represented by the following formula (1) (hereinafter, referred to as “raw material PVA (D)” or “raw material PVA”). May be described).

［式（１）中、Ｒ^１は水素原子又は炭素数１〜４のアルキル基であり、Ｒ^２は水素原子又はアルカリ金属である。］

[In the formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ² is a hydrogen atom or an alkali metal. ]

［式（２）中、Ｒ^１は式（１）と同義である。］

[In equation (2), R ¹ is synonymous with equation (1). ]

^{R 1} in the formula (1) is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and specific examples thereof include a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group and the like. However, a hydrogen atom or a methyl group is preferable from the viewpoint of cross-linking performance. R ² is a hydrogen atom or an alkali metal, and specific examples thereof include a hydrogen atom, a sodium atom, a potassium atom, a rubidium atom, and a cesium atom, but a hydrogen atom or a sodium atom is preferable from the viewpoint of cross-linking performance and economic efficiency.

The content of the structural unit represented by the above formula (1) with respect to all the monomer units of the modified PVA (A) is not particularly limited, but from the viewpoint of the balance between the cross-linking performance and the formation of insoluble matter, 0. It is preferably 1 mol% or more and 10 mol% or less, and more preferably 0.15 mol% or more and 7 mol% or less. The content is the number of moles of the structural unit represented by the formula (1) with respect to 100 moles of all the monomer units of the modified PVA (A).

The content of the structural unit represented by the above formula (1) in the modified PVA (A) can be measured by a known method. Specifically, the ^{measurement by 1} H-NMR is simple, and the method of obtaining the measurement is not particularly limited. For example, if the modified PVA (A) in response esterified with methyl malonate, modified PVA (A) was dissolved in _{D 2} O, measured by ¹ H-NMR of 400 MHz. The peak derived from methine of vinyl alcohol unit is assigned to 3.2 to 4.0 ppm (integral value a), and the peak derived from methyl of methylmalonic acid unit is assigned to around 0.8 to 1.3 ppm (integral value b). The content of the structural unit (1) is calculated by the formula.
Content of structural unit (1) (mol%) = (b / 3) / a × 100

The viscosity average degree of polymerization of the modified PVA (A) (hereinafter, may be simply abbreviated as "degree of polymerization") is not particularly limited, but is preferably 200 or more and less than 4000, and 500 or more and less than 3500. More preferably. The viscosity average degree of polymerization is a value obtained by measuring according to JIS-K6726 (1994). Specifically, when the degree of saponification is less than 99.5 mol%, the PVA saponified to a degree of saponification of 99.5 mol% or more is subjected to the ultimate viscosity [η] (liter / liter /) measured at 30 ° C. in water. Using g), the viscosity average degree of polymerization (P) was determined by the following formula.
P = ([η] × 10 ⁴ / 8.29) ^{(1 / 0.62)}

In the present invention, it is important that the saponification degree of the modified PVA (A) is 68 mol% or more and less than 99.9 mol%. The saponification degree is a value obtained by measuring according to JIS-K6726 (1994). If the saponification degree is less than 68 mol%, the water solubility is lowered and a film cannot be formed, and the handleability is lowered. Those with a saponification degree of more than 99.9 mol% are difficult to produce. The degree of saponification is preferably 75 mol% or more and 99.7 mol% or less.

In the present invention, it is important that the amount of 1,2 glycol bound to the modified PVA (A) is less than 1.9 mol%. When the amount of 1,2-glycol bond is 1.9 mol% or more, the water resistance of the modified PVA (A) becomes insufficient. The amount of 1,2-glycol bond is preferably less than 1.7 mol%. The lower limit of the 1,2-glycol bond amount is not particularly limited, but is preferably 1.0 mol% or more. If the amount of 1,2-glycol bond is less than 1.0 mol%, it is necessary to polymerize at a low temperature, for example, and the productivity tends to decrease.

The amount of 1,2-glycol bond is determined from the peak of ^{1 1 H-NMR.} Specifically, PVA (A) was saponified to a saponification degree of 99.9 mol% or more, thoroughly washed with methanol, and then PVA dried under reduced pressure at 90 ° C. for 2 days was dissolved in _{DMSO-d 6 and trifluoro.} A sample to which a few drops of acetic acid was added was measured at 80 ° C. using ^{1 H-NMR at 500 MHz.} The peak derived from methine of vinyl alcohol unit is 3.2 to 4.0 ppm (integral value A), and the peak derived from one methine of 1,2-glycol bond is around 3.15 to 3.35 ppm (integral value B). The amount of 1,2-glycol bond is calculated by the following formula.
1,2-Glycol bond amount (mol%) = B / A x 100

(Manufacturing method of modified PVA (A))
The raw material PVA (D) is obtained by saponifying the polyvinyl ester. Here, the polyvinyl ester can polymerize the vinyl ester monomer by adopting a conventionally known method such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or a dispersion polymerization method. From an industrial point of view, preferred polymerization methods are a solution polymerization method, an emulsion polymerization method and a dispersion polymerization method. In the polymerization operation, any of a batch method, a semi-batch method and a continuous method can be adopted.

Examples of the vinyl ester monomer that can be used for polymerization include vinyl acetate, vinyl formate, vinyl propionate, vinyl caprylate, vinyl versatic acid, and the like. Among these, vinyl acetate is from an industrial point of view. preferable.

When polymerizing the vinyl ester monomer, other monomers may be copolymerized as long as the gist of the present invention is not impaired. Other monomers that can be used include, for example, α-olefins such as ethylene, propylene, n-butyl, isobutylene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid. Acrylic acid esters such as i-propyl, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; methacrylic acid Methyl, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Methacrylic acid esters; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts or quaternary salts thereof, Acrylamide derivatives such as N-methylol acrylamide and derivatives thereof; methacrylamide, N-methylmethacrylate, N-ethylmethacrylate, methacrylamide propanesulfonic acid and its salts, methacrylicamidepropyldimethylamine and its salts or quaternary salts thereof, Methylamide derivatives such as N-methylolmethacrylate and derivatives thereof; methylvinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether. Vinyl ethers such as; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride Examples include unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid and salts thereof or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. The copolymerization amount of such other monomers is usually 10 mol% or less.

Further, in the polymerization of the vinyl ester monomer, a chain transfer agent may coexist for the purpose of adjusting the degree of polymerization of the obtained polyvinyl ester. Chain transfer agents include aldehydes such as acetaldehyde, propionaldehyde, butylaldehyde and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone and cyclohexanone; mercaptans such as 2-hydroxyethanethiol and dodecyl mercaptan; trichloroethylene and perchloroethylene. Halogenated hydrocarbons such as, among them, aldehydes and ketones are preferably used. The amount of the chain transfer agent added is determined according to the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target polyvinyl ester, but is generally 0.1 to 10% by mass based on the vinyl ester monomer. Is desirable.

The saponification reaction of the polyvinyl ester thus obtained is hydrolyzed by alcohol using a conventionally known basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxyde, or an acidic catalyst such as p-toluenesulfonic acid. Hydrolysis reaction can be applied. Examples of the solvent used in the saponification reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene. Can be used alone or in combination of two or more. Above all, it is convenient and preferable to carry out the saponification reaction in the presence of sodium hydroxide, which is a basic catalyst, using methanol or a mixed solution of methanol and methyl acetate as a solvent. As a result, the raw material PVA (D) is obtained.

The method for producing the modified PVA (A) is not particularly limited, but a suitable production method is a method in which the raw material PVA (D) and the compound represented by the formula (2) are subjected to an esterification reaction. Examples of the esterification reaction method include a method using a known acid catalyst, a method involving dehydration by heat, and the like. As the acid catalyst, any of inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as paratoluenesulfonic acid can be preferably used. At this time, in order to accelerate the reaction, it is preferable to heat the reaction when the reaction is carried out. The heating temperature is preferably 80 to 180 ° C, more preferably 90 to 140 ° C. The heating time is appropriately set in relation to the heating temperature, but is preferably 10 minutes to 24 hours, more preferably 30 minutes to 20 hours.

［式（２）中、Ｒ^１は式（１）と同義である。］

[In equation (2), R ¹ is synonymous with equation (1). ]

As a method for esterifying the raw material PVA (D) and the compound represented by the formula (2), a solution obtained by dissolving the compound represented by the formula (2) in a solvent is obtained, and then the raw material is added to the solution. A method is preferable in which a powder of PVA (D) is added and swollen, and then the solvent is removed to obtain a mixed powder, and the obtained mixed powder is heated. By reacting by such a method, it is possible to suppress the progress of an undesired cross-linking reaction, and it is possible to obtain modified PVA (A) made of a powder having good water solubility. As the solvent for dissolving the compound represented by the formula (2), alcohol such as methanol, ethanol and propanol, water and the like are used. The solvent can be removed by heating or reducing the pressure, preferably by reducing the pressure. After reacting the raw material PVA (D) with the compound represented by the formula (2), the carboxylic acid moiety derived from the compound represented by the formula (2) in the modified PVA (A) is neutralized with a base. You may.

Examples of the compound represented by the formula (2) used in the esterification reaction include malonic acid, methylmalonic acid, ethylmalonic acid, propylmalonic acid, isopropylmalonic acid, butylmalonic acid, and isobutylmalonic acid, which are available. From the viewpoint of, malonic acid or methylmalonic acid is preferable. ^{That is, it is preferable that R 1} in the formula (2) is a hydrogen atom or a methyl group.

In the above reaction method, the content of the compound represented by the formula (2) in the mixed powder before heating is preferably 0.01 part by mass or more with respect to 100 parts by mass of the raw material PVA (D). , 0.1 part by mass or more is more preferable, and 0.5 part by mass or more is particularly preferable. On the other hand, the content of the compound represented by the formula (2) in the mixed powder before heating is preferably 35 parts by mass or less, preferably 30 parts by mass or less, with respect to 100 parts by mass of the raw material PVA (D). It is more preferably 25 parts by mass or less, and particularly preferably 20 parts by mass or less.

(Crosslinking agent (B))
The cross-linking agent (B) to be used is not particularly limited, but dialdehydes such as glyoxal, malondialdehyde and glutaaldehyde, glyoxylates such as sodium glyoxylate and calcium glyoxylate, ethanediamine, propanediamine, 1,3 -Diamines such as bisaminomethylcyclohexane, dihydrazides such as adipic acid dihydrazide, and acids such as phosphoric acid, hydrochloric acid and sulfuric acid can be mentioned. Among them, at least one selected from the group consisting of glyoxyphosphates, dialdehydes and acids is preferably used as the cross-linking agent (B).

The method of using the cross-linking agent (B) is not particularly limited. It may be used as it is or dissolved in a solvent. Further, when mixing with the modified PVA (A), the modified PVA (A) aqueous solution may be mixed with the cross-linking agent (B) after preparation, or the cross-linking agent (B) may be simultaneously prepared when the modified PVA (A) aqueous solution is prepared. ) May be mixed and dissolved, but a method of preparing a modified PVA (A) aqueous solution and then mixing it with the cross-linking agent (B) is preferable from the viewpoint of suppressing side reactions.

The amount of the cross-linking agent (B) used is not particularly limited, but it is preferable that the amount of the cross-linking agent (B) is 0.01 parts by mass or more and 5 parts by mass or less with respect to 10 parts by mass of the modified PVA (A). If the amount of the cross-linking agent (B) used is less than 0.01 parts by mass, the cross-linked product may not be formed well, and more preferably 0.05 parts by mass or more. On the other hand, when the amount of the cross-linking agent (B) used exceeds 5 parts by mass, the relative concentration of the modified PVA (A) decreases, so that the cross-linked product may not be formed well, and the amount is more preferably 3 parts by mass or less. ..

(Crosslinked body (C))
The modified PVA (A) is a crosslinked product (C) crosslinked with a crosslinking agent (B), and elution when a film having a thickness of 100 μm made of the crosslinked product (C) is immersed in hot water at 80 ° C. for 1 hour. A crosslinked product (C) having a rate of less than 10% is a preferred embodiment of the present invention, and a crosslinked product (C) having an elution rate of less than 8% is a more preferred embodiment of the present invention.

[Use]
The PVA (A) of the present invention is used for various purposes. Examples are given below, but the present invention is not limited to this.
(1) Vinyl chloride dispersant Applications: Dispersion stabilizers and dispersion aids for suspension polymerization of vinyl chloride and vinylidene chloride (2) Coating agents Applications: Sizing agents, fiber processing agents, leather finishes, paints, antifogging agents, Metal corrosion inhibitor, brightener for zinc plating, antistatic agent (3) Adhesive / binder Applications: Adhesives, adhesives, re-wet adhesives, various binders, additives for cement and mortar (4) Dispersion stabilizer applications : Dispersion stabilizers for organic and inorganic pigments such as paints and adhesives, dispersion stabilizers for emulsification and polymerization of various vinyl compounds, post-embroidery materials such as bitumen (5) Paper processing applications: Paper strength enhancers, oil and solvent resistance imparting agents , Smoothness improver, surface gloss improver, sealant, barrier agent, light resistance imparting agent, water resistance agent, dye / color developer dispersant, adhesive strength improver, binder (6) Agricultural use: For pesticides Binders, spreading agents for pesticides, coating agents for agriculture, soil conditioners, anti-erosion agents, dispersants for pesticides (7) Medical / cosmetic applications: granulation binders, coating agents, emulsifiers, patches, binders, film preparations Base material, film forming agent (8) Viscosizing agent Application: Thickener, Leology adjuster (9) Aggregating agent Application: Aggregating agent for suspensions and dissolved substances in water, Metal coagulant (10) Film Application: Water-soluble Films, polarizing films, barrier films, textile packaging films, seed curing sheets, vegetation sheets, seed tapes, hygroscopic films (11) Mold applications: Fibers, films, sheets, pipes, tubes, leak-proof films, chemical laces Water-soluble fiber for use, sponge (12) Resin raw material Applications: Polyvinyl butyral raw materials, photosensitive resin raw materials, graft polymer raw materials, various gel raw materials (13) Post-reaction applications: Low molecular weight organic compounds, high molecular weight organic compounds, inorganic compounds Post-reaction application

Among them, the modified PVA (A) of the present invention has higher viscosity, higher water resistance, and higher water resistance than the same type of linear polymer because the movement of the molecular chain is restricted in the three-dimensional direction by using the cross-linking agent (B). Since the crosslinked body (C) having excellent strength, heat resistance, and solvent resistance can be synthesized, the above (2) coating agent application, (3) adhesive / binder application, (10) film application, (12) resin raw material application, etc. Suitable for use.

Hereinafter, the present invention will be described in more detail with reference to Examples. In the following examples and comparative examples, “parts” and “%” indicate parts by mass and% by mass, respectively, unless otherwise specified.

[Viscosity average degree of polymerization of PVA]
The viscosity average degree of polymerization of PVA was measured according to JIS-K6726 (1994). Specifically, when the degree of saponification is less than 99.5 mol%, the PVA saponified to a degree of saponification of 99.5 mol% or more is subjected to the ultimate viscosity [η] (liter / liter /) measured at 30 ° C. in water. Using g), the viscosity average degree of polymerization (P) was determined by the following formula.
P = ([η] × 10 ⁴ / 8.29) ^{(1 / 0.62)}

[Saponification degree of PVA]
The degree of saponification of PVA was measured according to JIS-K6726 (1994).

[Amount of 1,2-glycol binding of PVA]
The amount of 1,2-glycol bound to PVA was determined from the following formula by the ^{above-mentioned analysis by 1 H-NMR.}
1,2-Glycol bond amount (mol%) = B / A x 100
(In the formula, A represents the integral value of the methine-derived peak (3.2-4.0 ppm) of the vinyl alcohol unit, and B is the methine-derived peak (3.15 to 3) of the 1,2-glycol bond. Represents the integral value of .35ppm).)

[Content of the structural unit represented by the formula (1) in the modified PVA (A)]
A 10% aqueous solution of modified PVA (A) was prepared. 5 g of this aqueous solution was added dropwise to a solution of 500 g of methyl acetate / water = 95/5 to precipitate modified PVA (A), which was recovered and dried. For the isolated modified PVA (A), the content of the structural unit represented by the formula (1) introduced into the modified PVA (A) was measured using ^{1 1 H-NMR.} The content is the number of moles of the structural unit represented by the formula (1) with respect to 100 moles of all the monomer units of the modified PVA (A).

Production Example 1 (Production of modified PVA (A1))
100 parts of PVA having a degree of polymerization of 1000, a degree of saponification of 99 mol%, and a 1,2-glycol bond amount of 1.6 mol% as a raw material PVA (D), and 18.8 parts of malonic acid as a compound represented by the formula (2). Was added to a solution dissolved in 100 parts of methanol, allowed to stand for 10 minutes, and then the methanol was removed by a vacuum dryer. After that, esterification is performed by heat treatment at 120 ° C. for 6 hours using a dryer, and the content of the structural unit represented by the formula (1) (malonic acid modification amount) is 4.0 mol% of the modified PVA (modified PVA). A1) was obtained.

Production Examples 2 to 7 (Production of modified PVA (A2 to A7))
Modification in the same manner as in the production of modified PVA (A1) except that the type of raw material PVA (D) used, the type and amount of the compound represented by the formula (2), and the heat treatment reaction conditions were changed as shown in Table 1. PVA (A2 to A7) was produced. The production results are shown in Table 1.

Example 1
10 parts of the modified PVA (A1) was dissolved in distilled water to make 100 parts of a 10% aqueous solution, 0.5 part of sodium glyoxylate was added as a cross-linking agent (B), and the mixture was mixed and stirred to obtain an aqueous solution. Such an aqueous solution was cast on a polyethylene terephthalate (PET) film, left at 23 ° C. and 50% RH for 48 hours, and then heat-treated at 70 ° C. for 5 minutes to obtain a thickness of the crosslinked product (C). A 100 μm film was obtained. When the water resistance of the obtained film was evaluated by the following indexes, the elution rate was 2.8%. The results are shown in Table 2.

(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 elution rate (%), the dry weight X1 (g) of the film before immersion in hot water and the dry weight X2 (g) of the film after immersion in hot water were obtained, and the elution rate (%) was calculated by the following formula. ) Was calculated.
Elution rate (%) = [(X1-X2) / X1] x 100

Examples 2-5
A film having a thickness of 100 μm made of a crosslinked body (C) in the same manner as in Example 1 except that the type of modified PVA (A) used, the type of crosslinking agent (B) and the amount thereof were changed as shown in Table 2. Got The water resistance of the obtained film was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1
An attempt was made to prepare a 100 μm-thick film made of the crosslinked product (C) in the same manner as in Example 1 except that the modified PVA (A5) was used as the modified PVA (A), but the modified PVA (A5) was saponified. The film could not be produced because the degree was too low.

Comparative Example 2
A film having a thickness of 100 μm made of the crosslinked product (C) was produced in the same manner as in Example 1 except that the modified PVA (A6) was used as the modified PVA (A). The water resistance of the obtained film was evaluated in the same manner as in Example 1, but the modified PVA (A6) did not have the structural unit represented by the formula (1), so that the water resistance was hardly exhibited. rice field.

Comparative Example 3
A film having a thickness of 100 μm made of the crosslinked product (C) was prepared in the same manner as in Example 1 except that the modified PVA (A7) was used as the modified PVA (A). The water resistance of the obtained film was evaluated in the same manner as in Example 1, but the modified PVA (A7) had insufficient water resistance because the amount of 1,2-glycol bond was too large.

Comparative Example 4
The same as in Example 1 except that Z-100 (acetoacetyl group-containing modified vinyl alcohol-based polymer) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. was used as the modified PVA (A) and phosphoric acid was used as the cross-linking agent (B). A 100 μm-thick film made of the crosslinked product (C) was prepared. An attempt was made to evaluate the water resistance of the obtained film in the same manner as in Example 1, but the water resistance was hardly exhibited because it did not have the structural unit represented by the formula (1).

As shown in the examples, the modified PVA (A) having the structure represented by the formula (1) was formed into a crosslinked body (C) by using an appropriate crosslinking agent to form a good crosslinked structure. It has excellent water resistance and can be expected to be used as an adhesive layer between a polarizing film and a protective film in an adhesive or a polarizing plate, and as a protective layer for a heat-sensitive recording medium. Therefore, the industrial usefulness of the present invention is extremely high.

Claims (2)

The modified vinyl alcohol polymer (A) is a crosslinked product (C) crosslinked by a crosslinking agent (B).
The modified vinyl alcohol-based polymer (A) is a modified vinyl alcohol-based polymer (A) containing a vinyl alcohol unit and a structural unit represented by the following formula (1), and has a saponification degree of 68 mol% or more 99. less than .9 mole%, and 1,2-glycol bond content Ri der less than 1.9 mol%,
The crosslinked product (C) having an elution rate of less than 10% when a film having a thickness of 100 μm made of the crosslinked product (C) is immersed in hot water at 80 ° C. for 1 hour.

[In the formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ² is a hydrogen atom or an alkali metal. ] The crosslinked product (C ) according to claim 1, wherein the content of the structural unit represented by the formula (1) is 0.1 to 10 mol% with respect to all the monomer units of the modified vinyl alcohol polymer (A). ).