Aqueous emulsion and adhesive

Abstract

To provide an aqueous emulsion having superior water resistance and heat resistance.SOLUTION: An aqueous emulsion comprises a modified polyvinyl alcohol (A) and a polymer (B) containing an ethylenically unsaturated monomer unit. The modified polyvinyl alcohol (A) contains an ethylene unit and a specific monomer unit.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous emulsion containing a specific modified polyvinyl alcohol and a method for producing the same. The present invention also relates to an adhesive containing the aqueous emulsion.

Background Art

[0002] Vinyl alcohol polymers typified by polyvinyl alcohol (hereinafter sometimes abbreviated as "PVOH") are known as water-soluble synthetic polymers, and in addition to uses as raw materials for fibers and films, they are also used as paper processing agents, fiber processing agents, binders for inorganic substances, adhesives, stabilizers for emulsion polymerization and suspension polymerization, etc. In particular, PVOH is known as a protective colloid for emulsion polymerization of vinyl ester monomers typified by vinyl acetate. An aqueous vinyl ester emulsion obtained by emulsion polymerization using PVOH as a stabilizer for emulsion polymerization is widely used in various fields such as various adhesives including those for woodworking, paint bases, coating agents, various binders for impregnated paper and non-woven products, admixtures, caulking materials, paper processing, and fiber processing.

[0003] An aqueous emulsion obtained by emulsion polymerization using PVOH as a stabilizer for emulsion polymerization is known to have low water resistance. In order to solve such problems, Patent Document 1 proposes an emulsion obtained by copolymerizing a vinyl acetate monomer and N-methylolacrylamide, and high water resistance is achieved by a cross-linking reaction of a structure derived from the N-methylolacrylamide monomer. However, in this method, the viscosity of the emulsion increases over time due to the cross-linking reaction, so the storage stability is insufficient, and there is also an environmental problem that formaldehyde, which is one of the causative substances of sick house syndrome, is generated.

[0004] As another method for improving water resistance, a method of modifying PVOH, which is a stabilizer for emulsion polymerization, has been proposed. In Patent Document 2, an aqueous emulsion has been proposed in which the dispersant is PVOH containing an α-olefin unit having 4 or less carbon atoms at a specific ratio, and the dispersed substance is a polymer of an ethylenically unsaturated monomer. While this aqueous emulsion can achieve high water resistance, there is room for improvement in heat resistance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made based on the circumstances as described above, and an object thereof is to provide an aqueous emulsion excellent in water resistance and heat resistance. Another object is to provide a method for producing the aqueous emulsion and an adhesive containing the aqueous emulsion.

Means for Solving the Problems

[0007] The above problems are solved by [1] An aqueous emulsion containing a modified polyvinyl alcohol (A) and a polymer (B) containing an ethylenically unsaturated monomer unit, wherein the modified polyvinyl alcohol (A) contains an ethylene unit and a monomer unit represented by the following formula (I);

[0008]

Chemical Formula

[0009] (In formula (I), W and Z are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a group represented by -COOR 2 wherein R1 and R 2 is each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an alkylene group having 1 to 5 carbon atoms. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. * represents a bonding site.) The aqueous emulsion of [1], wherein the saponification degree of the modified polyvinyl alcohol (A) is 80 mol% or more and 99.9 mol% or less; The aqueous emulsion of [1] or [2], wherein the viscosity-average degree of polymerization of the modified polyvinyl alcohol (A) is 500 to 5000; The aqueous emulsion according to any one of [1] to [3], wherein the monomer unit represented by the formula (I) is a monomer unit derived from at least one selected from the group consisting of a monomer having a carboxy group and its derivatives; The aqueous emulsion of [4], wherein the monomer having a carboxy group and its derivatives are at least one selected from the group consisting of ethylenically unsaturated dicarboxylic acids, and their mono-esters, di-esters, anhydrides and metal salts; The aqueous emulsion according to [4] or [5], wherein the monomer having a carboxy group and its derivatives are at least one selected from the group consisting of maleic acid, maleic acid monoalkyl ester, maleic acid dialkyl ester, maleic anhydride, metal salts of maleic acid, metal salts of maleic acid monoalkyl ester, fumaric acid, fumaric acid monoalkyl ester, fumaric acid dialkyl ester, metal salts of fumaric acid and metal salts of fumaric acid monoalkyl ester; The aqueous emulsion according to any one of [1] to [6], wherein the modified polyvinyl alcohol (A) contains a carbon-carbon double bond; The aqueous emulsion according to any one of [1] to [7], wherein the modified polyvinyl alcohol (A) contains a monomer unit represented by the following formula (II);

[0010] [Chemical formula]

[0011] (In formula (II), Z is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or -COOR 2 and is a group represented by R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an alkylene group having 1 to 5 carbon atoms. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. * represents a bonding site.) [9] An aqueous emulsion according to any one of [1] to [8], wherein the molar ratio of the ethylene unit to the monomer unit represented by formula (I) (ethylene unit / monomer unit represented by formula (I)) is 50 / 50 to 99.9 / 0.1;

[10] An aqueous emulsion according to any one of [1] to [9], wherein the modified polyvinyl alcohol (A) contains a modified polyvinyl alcohol (A-1) and a modified polyvinyl alcohol (A-2), the modified polyvinyl alcohol (A-1) contains an ethylene unit, and the modified polyvinyl alcohol (A-2) contains a monomer unit represented by formula (I);

[11] The aqueous emulsion according to

[10] , wherein the content of the ethylene unit in the modified polyvinyl alcohol (A-1) is 1 mol% or more and 20 mol% or less based on all the monomer units of the modified polyvinyl alcohol (A-1);

[12] The aqueous emulsion according to

[10] or

[11] , wherein the saponification degree of the modified polyvinyl alcohol (A-1) is 90 mol% or more and 99.9 mol% or less;

[13] The aqueous emulsion according to any one of

[10] to

[12] , wherein the content of the monomer unit represented by formula (I) in the modified polyvinyl alcohol (A-2) is 0.05 mol% or more and 10 mol or less based on all the monomer units of the modified polyvinyl alcohol (A-2);

[14] The aqueous emulsion according to any one of

[10] to

[13] , wherein the saponification degree of the modified polyvinyl alcohol (A-2) is 80 mol% or more and 98 mol% or less;

[15] The aqueous emulsion according to any one of [1] to

[14] , wherein the ethylenically unsaturated monomer unit is at least one selected from the group consisting of a vinyl ester monomer unit, a (meth)acrylate monomer unit, a styrene monomer unit, and a diene monomer unit;

[16] An aqueous emulsion according to any one of [1] to

[15] , wherein at least a part of the modified polyvinyl alcohol (A) and at least a part of the polymer (B) have a chemical bond;

[17] An aqueous emulsion according to any one of [1] to

[16] , wherein the mass ratio (A / B) of the modified polyvinyl alcohol (A) to the polymer (B) is from 2 / 98 to 40 / 60;

[18] A method for producing an aqueous emulsion according to any one of [1] to

[17] , the method comprising a step of emulsion-polymerizing the ethylenically unsaturated monomer in the presence of the modified polyvinyl alcohol (A);

[19] An adhesive containing an aqueous emulsion according to any one of [1] to

[17] ; is solved by providing any of the above.

Effects of the Invention

[0012] The aqueous emulsion of the present invention is excellent in water resistance and heat resistance.

Modes for Carrying Out the Invention

[0013] (Aqueous Emulsion) The aqueous emulsion of the present disclosure contains a modified polyvinyl alcohol (A) and a polymer (B) containing an ethylenically unsaturated monomer unit, and the modified polyvinyl alcohol (A) contains an ethylene unit and a monomer unit represented by the following formula (I).

[0014]

Chemical formula

[0015] (Modified Polyvinyl Alcohol (A)) The aqueous emulsion of the present disclosure preferably contains modified PVOH (A) as a dispersant.

[0016] In formula (I), W and Z are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or -COOR 2 which is a group represented by, preferably a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or -COOR 2 which is a group represented by, more preferably a hydrogen atom, a methyl group or -COOR 2 which is a group represented by. R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom or a methyl group. X is a single bond or an alkylene group having 1 to 5 carbon atoms, preferably a single bond or an alkylene group having 1 to 3 carbon atoms, and more preferably a single bond or a methylene group. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom or a methyl group.

[0017] The saponification degree of the modified PVOH (A) is preferably 80 to 99.9 mol%. When the saponification degree is 80 mol% or more, the water resistance of the aqueous emulsion tends to be more excellent. The saponification degree is more preferably 85 mol% or more, and further preferably 90 mol% or more. On the other hand, when the saponification degree is 99.9 mol% or less, the production of the modified PVOH (A) is likely to be easy, and the viscosity stability of the aqueous emulsion tends to be excellent. The saponification degree is more preferably 99.8 mol% or less, and further preferably 99.5 mol% or less. The saponification degree is a value obtained by measuring according to JIS K6726 (1994). When the modified PVOH (A) contains modified PVOH (A-1) and modified PVOH (A-2) as described later, the saponification degree of the modified PVOH (A) is a value obtained by measuring according to JIS K6726 (1994) in a state where the modified PVOH (A-1) and the modified PVOH (A-2) are mixed.

[0018] The viscosity average degree of polymerization of the modified PVOH (A) is preferably from 500 to 5000. When the viscosity average degree of polymerization is 500 or more, the storage stability of the aqueous emulsion tends to be excellent. The viscosity average degree of polymerization is more preferably 600 or more, still more preferably 700 or more, and particularly preferably 800 or more. On the other hand, when the viscosity average degree of polymerization is 5000 or less, the viscosity of the aqueous emulsion tends to be moderately low, and handling becomes easier. The viscosity average degree of polymerization is more preferably 4500 or less, still more preferably 4000 or less, and particularly preferably 3500 or less. The viscosity average degree of polymerization is a value obtained by measuring in accordance with JIS K6726 (1994), and specifically, it can be measured by the method described in the examples. When the modified PVOH (A) contains the modified PVOH (A-1) and the modified PVOH (A-2) as described later, the viscosity average degree of polymerization of the modified PVOH (A) is a value obtained by measuring in accordance with JIS K6726 (1994) in a state where the modified PVOH (A-1) and the modified PVOH (A-2) are mixed.

[0019] The monomer unit represented by the formula (I) is preferably a monomer unit derived from at least one selected from the group consisting of monomers having a carboxy group and derivatives thereof. Examples of the monomer having a carboxy group and derivatives thereof include ethylenically unsaturated monocarboxylic acids and their monoesters or metal salts, and ethylenically unsaturated dicarboxylic acids, their monoesters, diesters, anhydrides or metal salts. Among them, from the viewpoints of reactivity with vinyl ester monomers, and water resistance and heat resistance of the aqueous emulsion, it is preferably at least one selected from the group consisting of ethylenically unsaturated dicarboxylic acids, and their monoesters, diesters, anhydrides and metal salts. Examples of the metal salt include sodium salts, potassium salts, calcium salts and the like.

[0020] Examples of the monomer having a carboxy group and its derivatives include maleic acid, maleic acid monoalkyl ester, maleic acid dialkyl ester, maleic anhydride, metal salts of maleic acid, metal salts of maleic acid monoalkyl ester, fumaric acid, fumaric acid monoalkyl ester, fumaric acid dialkyl ester, metal salts of fumaric acid, metal salts of fumaric acid monoalkyl ester, itaconic acid, itaconic acid monoalkyl ester, itaconic acid dialkyl ester, itaconic anhydride, metal salts of itaconic acid, metal salts of itaconic acid monoalkyl ester, acrylic acid, acrylic acid alkyl ester, metal salts of acrylic acid, methacrylic acid, methacrylic acid alkyl ester, and metal salts of methacrylic acid. Among them, from the viewpoints of reactivity with vinyl ester monomers and water resistance and heat resistance of aqueous emulsions, it is preferably at least one selected from the group consisting of maleic acid, maleic acid monoalkyl ester, maleic acid dialkyl ester, maleic anhydride, metal salts of maleic acid, metal salts of maleic acid monoalkyl ester, fumaric acid, fumaric acid monoalkyl ester, fumaric acid dialkyl ester, metal salts of fumaric acid, and metal salts of fumaric acid monoalkyl ester, and more preferably at least one selected from the group consisting of maleic acid, maleic acid monoalkyl ester, maleic acid dialkyl ester, maleic anhydride, metal salts of maleic acid, and metal salts of maleic acid monoalkyl ester.

[0021] The modified PVOH (A) preferably contains a carbon-carbon double bond. The modified PVOH (A) also preferably contains a monomer unit represented by the following formula (II). In these cases, the water resistance and heat resistance of the aqueous emulsion tend to be more excellent. The reason is presumed as follows. When an ethylenically unsaturated monomer is emulsion-polymerized using the modified PVOH (A) containing a carbon-carbon double bond or a monomer unit represented by the formula (II), the carbon-carbon double bond promotes the reaction between a part of the modified polyvinyl alcohol (A) and the polymer (B). As a result, an aqueous emulsion with a high content of a component in which the modified PVOH (A) and the polymer (B) are chemically bonded is obtained. Such an aqueous emulsion is more excellent in water resistance due to the component in which the modified PVOH (A) and the polymer (B) are chemically bonded. Further, compared with the polymer (B) to which the modified PVOH (A) is not bonded, the polymer (B) to which the modified PVOH (A) is bonded has a higher glass transition point, so the heat resistance of the aqueous emulsion is more excellent.

[0022] [Chemical formula] (In formula (II), Z is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a group represented by -COOR 2 . R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an alkylene group having 1 to 5 carbon atoms. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. * represents a bonding site.)

[0023] The preferred embodiments of X, Y, Z, R 1 and R 2 in formula (II) are the same as those described above as the preferred embodiments of X, Y, Z, R 1 and R 2 in formula (I).

[0024] In the modified PVOH (A), the molar ratio of the ethylene unit to the monomer unit represented by the formula (I) (ethylene unit / monomer unit represented by the formula (I)) is preferably from 50 / 50 to 99.9 / 0.1. When the molar ratio is 99.9 / 0.1 or less, the heat resistance of the aqueous emulsion tends to be more excellent. When the molar ratio is 50 / 50 or more, the reaction control becomes easier when emulsion-polymerizing the ethylenically unsaturated monomer. The molar ratio is more preferably from 75 / 25 to 99.5 / 0.5, and may preferably be 80 / 20 to 99 / 1 or 85 / 15 to 98.5 / 1.5.

[0025] The modified PVOH (A) may be a terpolymer containing an ethylene unit, a monomer unit represented by the formula (I), and a vinyl alcohol unit (that is, a copolymer containing an ethylene unit, a monomer unit represented by the formula (I), and a vinyl alcohol unit in one polymer chain), or may be a mixture of a modified PVOH (A-1) containing an ethylene unit and a modified PVOH (A-2) containing a monomer unit represented by the formula (I).

[0026] The terpolymer may contain vinyl ester units. Further, it may contain ethylene units, monomer units represented by formula (I), vinyl alcohol units, and other monomer units other than vinyl ester units. Examples of the other monomer units include those described later as the other monomer units that modified PVOH (A-1) and modified PVOH (A-2) may contain. The content of the other monomer units is preferably 10 mol% or less, more preferably less than 5 mol%, still more preferably less than 1 mol%, particularly preferably less than 0.5 mol%, based on all the monomer units of the terpolymer, and it may not substantially contain them. When modified PVOH (A) contains the terpolymer, the content of the terpolymer in modified PVOH (A) is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 95% by mass or more, and modified PVOH (A) may consist only of the terpolymer. Modified PVOH (A) may contain a dispersant other than the terpolymer. Examples of the dispersant other than the terpolymer include modified PVOH (A-1), modified PVOH (A-2), unmodified PVOH, etc.

[0027] From the viewpoint of ease of production, it is preferable that modified PVOH (A) contains modified PVOH (A-1) and modified PVOH (A-2), modified PVOH (A-1) contains ethylene units, and modified PVOH (A-2) contains monomer units represented by formula (I). When modified PVOH (A) contains modified PVOH (A-1) and modified PVOH (A-2), the total content of modified PVOH (A-1) and modified PVOH (A-2) in modified PVOH (A) is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 95% by mass or more, and modified PVOH (A) may consist only of modified PVOH (A-1) and modified PVOH (A-2). Modified PVOH (A) may contain a dispersant other than modified PVOH (A-1) and modified PVOH (A-2). Examples of the dispersant other than modified PVOH (A-1) and modified PVOH (A-2) include, for example, the terpolymer, unmodified PVOH, etc.

[0028] The content ratio of ethylene units in the modified PVOH (A-1) is preferably 1 mol% or more and 20 mol% or less based on all monomer units of the modified PVOH (A-1). When the content ratio of ethylene units is 1 mol% or more, the water resistance of the aqueous emulsion tends to be more excellent. The content ratio of ethylene units is preferably 1.5 mol% or more, and more preferably 2 mol% or more. On the other hand, when the content ratio of ethylene units is 20 mol% or less, the modified PVOH (A-1) is easily soluble in water, and it becomes easier to produce an aqueous emulsion. The content ratio of ethylene units is preferably 15 mol% or less, more preferably 10 mol% or less, and even more preferably 8.5 mol% or less.

[0029] The saponification degree of the modified PVOH (A-1) is preferably 90 mol% or more and 99.9 mol% or less. The saponification degree is more preferably 92 mol% or more, and may be preferably 95 mol% or more. When the saponification degree is at least the lower limit value, the water resistance of the aqueous emulsion tends to be more excellent. The saponification degree is more preferably 99.8 mol% or less, and even more preferably 99.5 mol% or less. When the saponification degree is at most the upper limit value, the production of the modified PVOH (A-1) is easy, and the viscosity stability of the aqueous emulsion tends to be excellent. The saponification degree is a value obtained by measuring according to JIS K6726 (1994).

[0030] The content rate of the monomer unit represented by the formula (I) in the modified PVOH (A-2) is preferably 0.05 mol% or more and 10 mol% or less with respect to all the monomer units of the modified PVOH (A-2). When the monomer unit represented by the formula (I) is 0.05 mol% or more, the content of the component in which the modified PVOH (A) and the polymer (B) in the aqueous emulsion are chemically bonded increases, and the water resistance and heat resistance of the aqueous emulsion tend to be more excellent. The content rate of the monomer unit represented by the formula (I) is more preferably 0.1 mol% or more, and even more preferably 0.3 mol% or more. On the other hand, when the monomer unit represented by the formula (I) is 10 mol% or less, the performance of the modified PVOH (A-2) as a dispersant is excellent, or the component in which the modified PVOH (A) and the polymer (B) in the aqueous emulsion are chemically bonded does not increase too much, and the aggregation of the aqueous emulsion tends to be suppressed. The content rate of the monomer unit represented by the formula (I) is more preferably 6 mol% or less, even more preferably 3 mol% or less, and particularly preferably 1 mol% or less.

[0031] The saponification degree of the modified PVOH (A-2) is preferably 80 mol% or more and 98 mol% or less. The saponification degree is more preferably 82 mol% or more, and even more preferably 85 mol% or more. When the saponification degree is at least the lower limit value, the water resistance of the aqueous emulsion tends to be more excellent. The saponification degree is more preferably 96 mol% or less, even more preferably 94 mol% or less, and may be preferably 90 mol% or less in some cases. When the saponification degree is at most the upper limit value, the production of the modified PVOH (A-2) is easy, and the viscosity stability of the aqueous emulsion tends to be excellent. The saponification degree is a value obtained by measuring according to JIS K6726 (1994).

[0032] The modified PVOH (A-1) and modified PVOH (A-2) may contain vinyl ester units. Further, within a range not impairing the gist of the present invention, they may contain ethylene units, monomer units represented by formula (I), vinyl alcohol units, and other monomer units other than vinyl ester units. Examples of the other monomers include α-olefins such as propylene, n-butene, and isobutylene; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts or its quaternary salts, N-methylolacrylamide and its derivatives; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or its quaternary salts, N-methylolmethacrylamide and its derivatives; vinyl ethers such as methyl vinyl 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, and stearyl vinyl ether; 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; vinyl silyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate. The content of such other monomers is preferably 10 mol% or less, more preferably less than 5 mol%, still more preferably less than 1 mol%, particularly preferably less than 0.5 mol%, and may not substantially contain, based on all the monomer units of the modified PVOH (A-1) and / or modified PVOH (A-2).

[0033] The method for producing the modified PVOH (A) is not particularly limited, but a preferred production method is a method of copolymerizing a vinyl ester monomer with ethylene and / or an ethylenically unsaturated monomer having a specific structure, and saponifying the obtained modified polyvinyl ester. For example, a terpolymer containing an ethylene unit, a monomer unit represented by the formula (I), and a vinyl alcohol unit can be produced by copolymerizing a vinyl ester monomer, ethylene, and an ethylenically unsaturated monomer having a specific structure, and saponifying the obtained modified polyvinyl ester. The modified PVOH (A-1) can be produced by copolymerizing a vinyl ester monomer and ethylene, and saponifying the obtained modified polyvinyl ester. The modified PVOH (A-2) can be produced by copolymerizing a vinyl ester monomer and an ethylenically unsaturated monomer having a specific structure, and saponifying the obtained modified polyvinyl ester. Here, the ethylenically unsaturated monomer having the specific structure means one that gives a monomer unit represented by the formula (I) by copolymerization.

[0034] Examples of the vinyl ester monomer include vinyl acetate, vinyl formate, vinyl propionate, vinyl caprylate, vinyl versatate, etc. Among these, vinyl acetate is preferable from an industrial viewpoint.

[0035] There is no particular limitation on the copolymerization method, and conventionally known methods such as bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method, and dispersion polymerization method can be used. Preferred polymerization methods from an industrial viewpoint are the solution polymerization method, emulsion polymerization method, and dispersion polymerization method. In the polymerization operation, any of the batch method, semi-batch method, and continuous method can be adopted.

[0036] Examples of the ethylenically unsaturated monomer having the specific structure include those described above as monomers having a carboxy group and their derivatives.

[0037] Upon copolymerization, a chain transfer agent may coexist for the purpose of adjusting the degree of polymerization of the resulting modified polyvinyl ester. Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol and dodecyl mercaptan; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene. Among them, aldehydes and ketones are preferably used. The addition amount of the chain transfer agent is determined according to the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target modified polyvinyl ester, but generally 0.1 to 10% by mass based on the modified polyvinyl ester is desirable.

[0038] Examples of the initiator used in copolymerization include known initiators such as azo initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-valeronitrile), benzoyl peroxide, and n-propyl peroxydicarbonate, or peroxide initiators.

[0039] For the saponification reaction of the thus obtained modified polyvinyl ester, an alcoholysis or hydrolysis reaction using a conventional basic catalyst such as sodium hydroxide, potassium hydroxide, sodium methoxide, or an acidic catalyst such as p-toluenesulfonic acid 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; and aromatic hydrocarbons such as benzene and toluene. These can be used alone or in combination of two or more. Among them, it is simple and preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide as a basic catalyst.

[0040] (Polymer (B)) The aqueous emulsion of the present disclosure contains a polymer (B) containing ethylenically unsaturated monomer units. The aqueous emulsion of the present disclosure preferably contains the polymer (B) as a disperse phase. Examples of the ethylenically unsaturated monomer include olefinic monomers such as ethylene, propylene, and isobutylene; halogenated olefinic monomers such as vinyl chloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride; vinyl ester monomers such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate; (meth)acrylic acid ester monomers such as (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; (meth)acrylamide monomers such as dimethylaminoethyl (meth)acrylate and its quaternized products, (meth)acrylamide, N-methylol (meth)acrylamide, N,N-dimethyl (meth)acrylamide, (meth)acrylamide-2-methylpropanesulfonic acid and its sodium salt; styrene monomers such as styrene, α-methylstyrene, p-styrenesulfonic acid and its sodium salt and potassium salt; diene monomers such as butadiene, isoprene, and chloroprene; and N-vinylpyrrolidone. These can be used alone or in combination of two or more. Among them, the ethylenically unsaturated monomer unit is preferably at least one selected from the group consisting of vinyl ester monomer units, (meth)acrylic acid ester monomer units, styrene monomer units, and diene monomer units, and more preferably a vinyl ester monomer unit. In the present specification, “(meth)acrylic” means acrylic and methacrylic.

[0041] The content rate of the ethylenically unsaturated monomer unit in the polymer (B) is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, based on all the monomer units of the polymer (B). The polymer (B) may be composed only of the ethylenically unsaturated monomer unit. Among them, the content rate of the vinyl ester monomer unit in the polymer (B) is preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, based on all the monomer units of the polymer (N).

[0042] The mass ratio (A / B) of the modified PVOH (A) to the polymer (B) is preferably from 2 / 98 to 40 / 60. When the mass ratio is 2 / 98 or more, the heat resistance and storage stability of the aqueous emulsion tend to be more excellent. When the mass ratio is 40 / 60 or less, the water resistance of the aqueous emulsion tends to be more excellent. The mass ratio (A / B) of the modified PVOH (A) to the polymer (B) is more preferably from 3 / 97 to 30 / 70, and still more preferably from 5 / 95 to 20 / 80.

[0043] In the aqueous emulsion of the present disclosure, it is preferable that at least a part of the modified PVOH (A) and at least a part of the polymer (B) have a chemical bond. When the modified PVOH (A) contains the modified PVOH (A-1) and the modified PVOH (A-2), it is preferable that at least a part of the modified PVOH (A-2) and at least a part of the polymer (B) have a chemical bond. In such a case, the water resistance and heat resistance of the aqueous emulsion tend to be more excellent.

[0044] The aqueous emulsion of the present disclosure preferably contains a gel component (C) that is insoluble in either acetone at 56°C or water at 100°C in an amount of 20% by mass or more and 60% by mass or less based on the total solid content. In some cases, the content of the gel component (C) is preferably 22% by mass or more, or 25% by mass or more. When the gel component (C) is equal to or greater than the lower limit, the water resistance and heat resistance of the aqueous emulsion tend to be more excellent. The content of the gel component (C) is more preferably 50% by mass or less, further preferably 45% by mass or less, and may be preferably 40% by mass or less. The gel component (C) can be measured by the method described in the examples.

[0045] There is no particular limitation on the solid content in the aqueous emulsion of the present disclosure, but preferably it is 30% by mass or more and 60% by mass or less, and more preferably 35% by mass or more and 56% by mass or less. In this specification, "solid content" means the total amount of dry solids contained in the aqueous emulsion, that is, the total amount of solids remaining when the medium such as water is removed from the aqueous emulsion.

[0046] The dispersion medium in the aqueous emulsion of the present disclosure is preferably an aqueous medium mainly composed of water. The aqueous medium mainly composed of water may contain a water-soluble organic solvent (such as alcohols, ketones, etc.) that is soluble in water in an arbitrary ratio. In this specification, "aqueous medium mainly composed of water" means a dispersion medium containing 50% by mass or more of water. From the viewpoints of cost and environmental load, the dispersion medium is preferably an aqueous medium containing 90% by mass or more of water, and more preferably water.

[0047] (Additive) The aqueous emulsion of the present disclosure may contain additives. Examples of the additives include organic solvents (aromatic compounds such as toluene and xylene, alcohols, ketones, esters, halogen-containing solvents, etc.), film-forming aids, crosslinking agents, surfactants, plasticizers, anti-precipitation agents, thickeners, fluidity improvers, preservatives, defoamers, fillers, wetting agents, colorants, binders, water retention agents, etc. These may be used alone or in combination of two or more. The additives may be added during emulsion polymerization or may be post-added to the aqueous emulsion obtained by emulsion polymerization.

[0048] Examples of the film-forming aids include propylene glycol-mono-2-ethylhexanoate (Widinol (registered trademark) EHP01), diethylene glycol monobutyl ether (DEMB), dipropylene glycol monobutyl ether (DPMB), dipropylene glycol monomethyl ether (DPM), tripropylene glycol monomethyl ether (TPM), ethylene glycol monobutyl ether (EMB), ethylene glycol mono-t-butyl ether (ETB), ethylene glycol monophenyl ether, propylene glycol monomethyl ether (PM), 2,2,4-trimethylpentane-1,3-diol monoisobutyrate (Texanol (registered trademark)), ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol and other monoalkyl ethers, polyethylene glycol monophenyl ether and other polyalkylene glycol adducts.

[0049] There is no particular limitation on the content of the additives in the aqueous emulsion. Preferably, it is 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and still more preferably 1.0 to 7.5 parts by mass with respect to 100 parts by mass of the solid content. For example, when the additive is a film-forming aid, when the content of the additive is 0.1 part by mass or more, the film-forming property at low temperature is good and the film tends to be uniform. On the other hand, when the content of the additive is 10 parts by mass or less, the additive is less likely to segregate on the film surface and the adhesion to the adherend tends to be excellent.

[0050] (Method for producing an aqueous emulsion) The method for producing the aqueous emulsion of the present disclosure preferably includes a step of emulsion-polymerizing the ethylenically unsaturated monomer in the presence of the modified PVOH (A), and more preferably includes a step of emulsion-polymerizing the ethylenically unsaturated monomer using a polymerization initiator in the presence of the modified PVOH (A). The aqueous emulsion thus obtained has less formation of aggregates and is excellent in water resistance.

[0051] In the above method, there is no particular limitation on the method of adding the modified PVOH (A) into the polymerization system, and examples include a method of adding it all at once initially into the polymerization system and a method of continuously adding it during the emulsion polymerization. Among them, from the viewpoint of increasing the chemical bonding amount between the modified PVOH (A) and the polymer (B), a method of adding the modified PVOH (A) all at once initially into the polymerization system is preferred. At this time, a method of adding the modified PVOH (A) to cold water or pre-warmed warm water, heating it to 80 to 90 °C and stirring to uniformly disperse the modified PVOH (A) is preferred. When the modified PVOH (A) contains the modified PVOH (A-1) and the modified PVOH (A-2), the modified PVOH (A-1) and the modified PVOH (A-2) may be added simultaneously or separately.

[0052] In the above emulsion polymerization, as the polymerization initiator, a water-soluble single initiator or a water-soluble redox initiator commonly used in emulsion polymerization can be used. These initiators may be used alone or in combination of two or more. Among them, a redox initiator is preferred.

[0053] Examples of the water-soluble single initiator include azo initiators, hydrogen peroxide, peroxides such as persulfates (potassium, sodium or ammonium salts), etc. Examples of the azo initiator include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc.

[0054] As the redox initiator, a combination of an oxidizing agent and a reducing agent can be used. As the oxidizing agent, peroxides are preferred. Examples of the reducing agent include metal ions and reducing compounds. Examples of the combination of the oxidizing agent and the reducing agent include a combination of a peroxide and a metal ion, a combination of a peroxide and a reducing compound, and a combination of a peroxide with a metal ion and a reducing compound. Examples of the peroxide include hydroxy peroxides such as hydrogen peroxide, cumene hydroxy peroxide, and t-butyl hydroxy peroxide, persulfates (potassium, sodium, or ammonium salts), t-butyl peracetate, and peresters (t-butyl perbenzoate). Examples of the metal ions include metal ions capable of undergoing one-electron transfer such as Fe 2+ 、Cr 2+ 、V 2+ 、Co 2+ 、Ti 3+ 、Cu + and the like. Examples of the reducing compound include sodium bisulfite, sodium hydrogen carbonate, tartaric acid, fructose, dextrose, sorbose, inositol, Rongalit, and ascorbic acid. Among these, a combination of one or more oxidizing agents selected from the group consisting of hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate and one or more reducing agents selected from the group consisting of sodium bisulfite, sodium hydrogen carbonate, tartaric acid, Rongalit, and ascorbic acid is preferred, and a combination of hydrogen peroxide and one or more reducing agents selected from the group consisting of sodium bisulfite, sodium hydrogen carbonate, tartaric acid, Rongalit, and ascorbic acid is more preferred.

[0055] In addition, in emulsion polymerization, an alkali metal compound, a surfactant, a buffer, a polymerization degree regulator, etc. may be appropriately used as long as the effects of the present invention are not impaired.

[0056] The alkali metal compound is not particularly limited as long as it contains an alkali metal (sodium, potassium, rubidium, cesium), and may be the alkali metal ion itself or a compound containing an alkali metal.

[0057] The content of the alkali metal compound (in terms of alkali metal) can be appropriately selected according to the type of the alkali metal compound used. Preferably, it is 100 to 15000 ppm, more preferably 120 to 12000 ppm, and even more preferably 150 to 8000 ppm based on the total solid content of the aqueous emulsion. When the content of the alkali metal compound is 100 ppm or more, the emulsion polymerization stability tends to be excellent. On the other hand, when it is 15000 ppm or less, the coloring of the resulting film tends to be suppressed. The content of the alkali metal compound can be measured by an ICP emission spectrometer. In this specification, "ppm" means "mass ppm".

[0058] Specific examples of the compound containing an alkali metal include weakly basic alkali metal salts (for example, alkali metal carbonates, alkali metal acetates, alkali metal bicarbonates, alkali metal phosphates, alkali metal sulfates, alkali metal halide salts, alkali metal nitrates), strongly basic alkali metal compounds (for example, hydroxides of alkali metals, alkoxides of alkali metals), and the like. These alkali metal compounds can be used alone or in combination of two or more.

[0059] Examples of the weakly basic alkali metal salts include alkali metal carbonates (for example, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate), alkali metal bicarbonates (for example, sodium hydrogen carbonate, potassium hydrogen carbonate, etc.), alkali metal phosphates (sodium phosphate, potassium phosphate, etc.), alkali metal carboxylates (sodium acetate, potassium acetate, cesium acetate, etc.), alkali metal sulfates (sodium sulfate, potassium sulfate, cesium sulfate, etc.), alkali metal halide salts (cesium chloride, cesium iodide, potassium chloride, sodium chloride, etc.), alkali metal nitrates (sodium nitrate, potassium nitrate, cesium nitrate, etc.). Among these, from the viewpoint of the inside of the emulsion being basic, alkali metal carboxylates, alkali metal carbonates, and alkali metal bicarbonates that act as salts of weak acids and strong bases during dissociation are preferably used, and alkali metal carboxylates are more preferred.

[0060] By using these weakly basic alkali metal salts, in emulsion polymerization, the weakly basic alkali metal salts act as pH buffers, enabling the emulsion polymerization to proceed stably.

[0061] As the surfactant, any of a nonionic surfactant, an anionic surfactant, and a cationic surfactant may be used. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, polyoxyalkylene alkyl ether, polyoxyethylene derivative, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, and the like. Examples of the anionic surfactant include alkyl sulfate, alkyl aryl sulfate, alkyl sulfonate, sulfate of hydroxyalkanol, sulfosuccinic acid ester, sulfate and phosphate of alkyl or alkyl aryl polyethoxyalcohol, and the like. Examples of the cationic surfactant include alkylamine salt, quaternary ammonium salt, polyoxyethylene alkylamine, and the like. The amount of the surfactant used is preferably 2% by mass or less based on the total amount of the ethylenically unsaturated monomer (for example, vinyl acetate) from the viewpoints of water resistance, hot water resistance, and boiling resistance.

[0062] Examples of the buffer include acids such as acetic acid, hydrochloric acid, and sulfuric acid; bases such as ammonia, amine, caustic soda, potassium hydroxide, and calcium hydroxide; or alkali carbonates, phosphates, acetates, and the like. Examples of the polymerization degree regulator include mercaptans, alcohols, and the like.

[0063] The temperature of the emulsion polymerization is not particularly limited, but is preferably about 20 to 90 °C, more preferably about 50 to 85 °C.

[0064] [Adhesive] The aqueous emulsion of the present disclosure can be used in applications such as adhesives for woodworking and paper processing, as well as in paints, fiber processing, etc. Among them, adhesive applications are particularly suitable. Therefore, the adhesive containing the aqueous emulsion of the present disclosure is also one of the present disclosures. The adhesive may consist only of the aqueous emulsion of the present disclosure, but various conventionally known emulsions and commonly used additives may be used in combination as long as the effects of the present invention are not impaired. Examples of the additives include those exemplified as additives that the aqueous emulsion of the present disclosure may contain.

[0065] As the adherend of the adhesive of the present disclosure, paper, wood, plastic, etc. can be applied. The adhesive is particularly suitable for wood among these materials and can be applied to applications such as glued laminated timber, plywood, decorative plywood, and fiberboard.

[0066] In addition to adhesives, the aqueous emulsion of the present disclosure can be used in a wide range of applications, such as inorganic binders, cement admixtures, and mortar primers. Furthermore, it can be effectively used as a so-called powder emulsion obtained by powderizing the aqueous emulsion of the present disclosure by spray drying or the like.

Examples

[0067] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples in any way.

[0068] [Viscosity-average degree of polymerization of modified PVOH (A)] The viscosity-average degree of polymerization of modified PVOH (A) was measured according to JIS K6726 (1994). Specifically, when the saponification degree was less than 99.5 mol%, for the modified PVOH (A) saponified until the saponification degree reached 99.5 mol% or more, the viscosity-average degree of polymerization (P) was determined by the following formula using the limiting viscosity [η] (liter / g) measured in water at 30°C. P = ([η] × 10000 / 8.29) (1 / 0.62)

[0069] [Saponification degree of modified PVOH (A)] The saponification degree of the modified PVOH (A) was determined by the method described in JIS K6726 (1994).

[0070] [Amount of ethylene units and monomer units represented by formula (I) introduced into modified PVOH (A)] The amount of ethylene units and monomer units represented by formula (I) introduced into modified PVOH (A) was determined by 1H-NMR of the modified PVOH (A) precursor (modified polyvinyl ester before saponification) or the modified polyvinyl ester that was re-acetylated. That is, after subjecting the obtained modified polyvinyl ester to reprecipitation purification three or more times using a mixed solution of n-hexane and acetone, drying under reduced pressure at 80 °C was carried out for 3 days to prepare a modified polyvinyl ester for analysis. The modified polyvinyl ester copolymer for analysis was dissolved in DMSO-d6 and 1H-NMR (500 MHz) was measured at 80 °C. 1 H-NMR (500 MHz) was measured. 1

[0071] [Water resistance and heat resistance] In accordance with EN204 / 205 and WATT’91, the water-resistant adhesiveness (water resistance) and heat-resistant adhesiveness (heat resistance) of the aqueous emulsion were evaluated. (Adhesion conditions) Adherend: beech Coating amount: 200 g / m 2 (Coated on both sides) Compression conditions: 20 °C, 2 hours, pressure 0.7 N / mm 2 (Measurement conditions for water-resistant adhesiveness) The test piece cured for 7 days in an environment of 20 °C and 65% RH was immersed in water at 20 °C for 4 days, and then measured in a wet state, and the adhesive strength (unit: N / mm 2 ) was measured. (Measurement conditions for heat-resistant adhesiveness) The test piece cured for 7 days in an environment of 20 °C and 65% RH was left standing in a dryer at 80 °C for 1 hour, then the test piece was taken out and immediately the adhesive strength (unit: N / mm 2 ) was measured.

[0072] [Storage stability] 50 g of the aqueous emulsion was sealed in a closed container and left standing in a dryer at 50°C for 4 hours. After that, the viscosity of the aqueous emulsion taken out from the dryer was measured and used as the reference viscosity value. Then, the aqueous emulsion was left standing in the dryer at 50°C for 4 weeks again. The viscosity of the aqueous emulsion taken out from the dryer was measured, and the storage stability was evaluated according to the following evaluation criteria. A: The viscosity after 4 weeks was less than twice the reference viscosity. B: The viscosity after 4 weeks was 2 times or more and less than 4 times the reference viscosity. C: The viscosity after 4 weeks was 4 times or more the reference viscosity. D: It was difficult to measure the viscosity due to separation by sedimentation of the dispersed substance or gelation.

[0073] [Gel content (C)] The aqueous emulsion was diluted to a concentration of 10% by mass, cast into a 20 cm × 20 cm PET mold, and dried in an environment of 20°C and 65% RH for 1 week to obtain a film with a thickness of 0.4 mm. After cutting off the edges of the film and cutting it to 18 cm × 18 cm, 5 film pieces of about 3 cm × 3 cm were cut out. Three film pieces were left standing in a dryer at 105°C for 8 hours, and the water content of the film was calculated from the average value of the weight change before and after drying. The weight of another film piece was measured, and the solid content weight was calculated using the water content. Further, another film piece was subjected to Soxhlet extraction using an acetone solvent for 8 hours or more, and the film piece after Soxhlet extraction was boiled in a sufficient amount of water. The boiling operation was repeated twice, and the remaining undissolved film piece was left standing in a dryer at 105°C for 8 hours. The gel content (C) was calculated from the weight after drying.

[0074] [Example 1] (Synthesis of modified PVOH (A-1)) A continuous polymerization tank (hereinafter referred to as "polymerization tank") equipped with a reflux condenser, a raw material supply line, a reaction solution extraction line, a thermometer, a nitrogen inlet, an ethylene inlet, and a stirring blade was used. 671 L / hr of vinyl acetate, 147 L / hr of methanol, and 2.6 L / hr of a 1% methanol solution of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) were continuously supplied to the polymerization tank using a metering pump. The ethylene pressure in the tank was adjusted to 0.23 MPa. The polymerization solution was continuously withdrawn from the polymerization tank so that the liquid level in the polymerization tank became constant. The polymerization rate at the outlet of the polymerization tank was adjusted to 30%. The residence time of the polymerization tank was 5 hours. The temperature at the outlet of the polymerization tank was 60 °C. The polymerization solution was taken out from the polymerization tank, and methanol vapor was introduced into the polymerization solution to remove unreacted vinyl acetate monomer, and a methanol solution (concentration 32% by mass) of an ethylene-vinyl ester copolymer was obtained.

[0075] A methanol solution (concentration 4% by mass) of sodium hydroxide, which is a saponification catalyst, was added to the methanol solution (concentration 32% by mass) of the ethylene-vinyl ester copolymer obtained in the polymerization step so that the molar ratio of sodium hydroxide to the vinyl acetate unit in the ethylene-vinyl ester copolymer was 0.015. The ethylene-vinyl ester copolymer solution and the saponification catalyst solution were mixed with a static mixer to obtain a mixture. The paste of the obtained mixture was placed on a belt and held at 40 °C for 18 minutes to allow the saponification reaction to proceed. The gel obtained by the saponification reaction was pulverized, impregnated in a washing liquid having a methanol / methyl acetate ratio of 35 / 65 (volume ratio), and then dewatered using a centrifugal dewaterer to obtain a polymer. 600 kg / hr (resin content) of the polymer was continuously supplied to a dryer whose temperature was controlled so that the resin temperature became 105 °C. The average residence time of the polymer in the dryer was 6 hours. Thereafter, it was pulverized until it passed through a filter with an aperture of 1.00 mm to obtain modified PVOH (A-1).

[0076] (Synthesis of modified PVOH (A-2)) Into the polymerization tank, 963 L / hr of vinyl acetate, 47 L / hr of methanol, 11 L / hr of a 20% methanol solution of monomethyl maleate, and 6 L / hr of a 2% methanol solution of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) were continuously supplied using a metering pump. The polymerization solution was continuously withdrawn from the polymerization tank so that the liquid level in the polymerization tank remained constant. The polymerization rate of vinyl acetate in the polymerization solution withdrawn from the polymerization tank was adjusted to 32%. The residence time in the polymerization tank was 4 hours. The temperature of the polymerization solution withdrawn from the polymerization tank was 63°C. The polymerization solution was withdrawn from the polymerization tank, and methanol vapor was introduced into the polymerization solution to remove unreacted vinyl acetate, obtaining a methanol solution (concentration 36%) of a vinyl ester-monomethyl maleate copolymer.

[0077] To the methanol solution (concentration 36% by mass) of the vinyl ester-monomethyl maleate copolymer obtained in the polymerization step, a methanol solution (concentration 4% by mass) of sodium hydroxide, which is a saponification catalyst, was added so that the molar ratio of sodium hydroxide to vinyl acetate units in the vinyl ester-monomethyl maleate copolymer was 0.01. The vinyl ester-monomethyl maleate copolymer solution and the saponification catalyst solution were mixed with a static mixer to obtain a mixture. The paste of the obtained mixture was placed on a belt and held at 40°C for 18 minutes to allow the saponification reaction to proceed. The gel obtained by the saponification reaction was pulverized, impregnated in a washing liquid having a methanol / methyl acetate ratio of 35 / 65 (volume ratio), and then dehydrated using a centrifugal dehydrator to obtain a polymer. 600 kg / hr (resin content) of the polymer was continuously supplied to a dryer whose temperature in the dryer was controlled so that the resin temperature was 105°C. The average residence time of the polymer in the dryer was 6 hours. Thereafter, it was pulverized until it passed through a filter with a mesh size of 1.00 mm to obtain modified PVOH (A-2).

[0078] (Preparation of Aqueous Emulsion) Into a 1-liter glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen inlet, 275 g of ion-exchanged water was charged and heated to 85°C. 20.9 g of modified PVOH (A), which was a mixture of modified PVOH (A-1) and modified PVOH (A-2) obtained by the aforementioned method in a mass ratio of 90 / 1, was added and stirred for 45 minutes to dissolve. Further, 0.3 g of sodium acetate was added and mixed to dissolve. The obtained aqueous solution was cooled, purged with nitrogen, and then heated to 60°C while stirring at 200 rpm. Next, 2.4 g of a 20% by mass aqueous solution of tartaric acid and 3.2 g of a 5% by mass hydrogen peroxide solution were added in one shot, and then 27 g of vinyl acetate was added to initiate polymerization. It was confirmed that the initial polymerization was completed 30 minutes after the start of polymerization (the remaining amount of vinyl acetate became less than 1%). After adding 1 g of a 10% by mass aqueous solution of tartaric acid and 3.2 g of a 5% by mass hydrogen peroxide solution in one shot, 251 g of vinyl acetate was continuously added over 2 hours, and the polymerization temperature was maintained at 80°C to complete the polymerization, obtaining a polyvinyl acetate-based emulsion with a solid content concentration of 49.8% by mass.

[0079] An appropriate amount of 28% aqueous ammonia was added to the obtained aqueous emulsion and stirred well to adjust the pH of the aqueous emulsion to the range of 5.0 - 5.5. Subsequently, 4 parts by mass of ethylene glycol monophenyl ether (manufactured by Toho Chemical Industry Co., Ltd., Hisolve (registered trademark)) was added to 100 parts by mass (solid content) of the aqueous emulsion and mixed to obtain an aqueous emulsion (Em-1). The results of evaluating the water resistance, heat resistance, storage stability, and gel content (C) of the obtained aqueous emulsion according to the above-mentioned method are summarized in Table 2.

[0080] [Examples 2 - 5, Comparative Examples 1 - 4] Except for changing the type of PVOH used as modified PVOH (A-1) and modified PVOH (A-2), the molar ratio of ethylene units to monomer units represented by formula (I), and the mass ratio of modified PVOH (A) to polymer (B) as described in Table 1, an aqueous emulsion was prepared in the same manner as in Example 1. The results of evaluating the water resistance, heat resistance, storage stability, and gel content (C) of the obtained aqueous emulsion according to the above-mentioned method are summarized in Table 2. The PVOH used as modified PVOH (A-1) and modified PVOH (A-2) can be produced by adjusting the ethylene pressure in the polymerization tank, the feeding rate of the raw material solution, the polymerization rate of the vinyl ester copolymer, and the molar ratio of sodium hydroxide, which is a saponification catalyst, to the vinyl acetate unit, according to the production method described in Example 1.

[0081]

Table 1

[0082]

Table 2

[0083] As shown in Examples 1 to 5, the aqueous emulsion containing modified PVOH (A) and polymer (B) was excellent in heat resistance and water resistance. On the other hand, when modified PVOH (A) did not contain the structural unit represented by formula (I), the water resistance and / or heat resistance were inferior (Comparative Examples 1 and 4). When modified PVOH (A) did not contain ethylene units, a stable aqueous emulsion could not be obtained (Comparative Example 2), or the water resistance was inferior (Comparative Example 3).

Industrial Applicability

[0084] As described above, the aqueous emulsion of the present disclosure is excellent in water resistance and heat resistance. Therefore, the aqueous emulsion of the present disclosure is suitably used for various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers, and the like.

Claims

1. An aqueous emulsion containing a modified polyvinyl alcohol (A) and a polymer (B) containing an ethylenically unsaturated monomer unit, wherein the modified polyvinyl alcohol (A) contains an ethylene unit and a monomer unit represented by the following formula (I). (In formula (I), W and Z are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a group represented by -COOR 2 The group represented by R 1 And R 2 Are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an alkylene group having 1 to 5 carbon atoms. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. * Represents a bonding site.)

2. The aqueous emulsion according to claim 1, wherein the saponification degree of the modified polyvinyl alcohol (A) is 80 mol% or more and 99.9 mol% or less.

3. The aqueous emulsion according to claim 1, wherein the viscosity average degree of polymerization of the modified polyvinyl alcohol (A) is 500 to 5000.

4. The aqueous emulsion according to claim 1, wherein the monomer unit represented by the formula (I) is a monomer unit derived from at least one selected from the group consisting of a monomer having a carboxy group and its derivatives.

5. The aqueous emulsion according to claim 4, wherein the monomer having a carboxy group and its derivatives are at least one selected from the group consisting of an ethylenically unsaturated dicarboxylic acid, and its monoester, diester, anhydride and metal salt.

6. The aqueous emulsion according to claim 4, wherein the monomer having a carboxy group and its derivatives are at least one selected from the group consisting of maleic acid, maleic acid monoalkyl ester, maleic acid dialkyl ester, maleic anhydride, metal salt of maleic acid, metal salt of maleic acid monoalkyl ester, fumaric acid, fumaric acid monoalkyl ester, fumaric acid dialkyl ester, metal salt of fumaric acid and metal salt of fumaric acid monoalkyl ester.

7. The aqueous emulsion according to claim 1, wherein the modified polyvinyl alcohol (A) contains a carbon-carbon double bond.

8. The aqueous emulsion according to claim 1, wherein the modified polyvinyl alcohol (A) contains a monomer unit represented by the following formula (II). (In formula (II), Z is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or -COOR 2 which is a group represented by. R 1 and R 2 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. X is a single bond or an alkylene group having 1 to 5 carbon atoms. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. * represents a bonding site.)

9. The aqueous emulsion according to claim 1, wherein the molar ratio of the ethylene unit to the monomer unit represented by the formula (I) (ethylene unit / monomer unit represented by the formula (I)) is 50 / 50 to 99.9 / 0.

1.

10. The aqueous emulsion according to claim 1, wherein the modified polyvinyl alcohol (A) contains a modified polyvinyl alcohol (A-1) and a modified polyvinyl alcohol (A-2), the modified polyvinyl alcohol (A-1) contains an ethylene unit, and the modified polyvinyl alcohol (A-2) contains a monomer unit represented by the formula (I).

11. The aqueous emulsion according to claim 10, wherein the content of ethylene units in the modified polyvinyl alcohol (A-1) is 1 mol% or more and 20 mol% or less based on all monomer units of the modified polyvinyl alcohol (A-1).

12. The aqueous emulsion according to claim 10, wherein the saponification degree of the modified polyvinyl alcohol (A-1) is 90 mol% or more and 99.9 mol% or less.

13. The aqueous emulsion according to claim 10, wherein the content of the monomer unit represented by the formula (I) in the modified polyvinyl alcohol (A-2) is 0.05 mol% or more and 10 mol or less based on all monomer units of the modified polyvinyl alcohol (A-2).

14. The aqueous emulsion according to claim 10, wherein the saponification degree of the modified polyvinyl alcohol (A-2) is 80 mol% or more and 98 mol% or less.

15. The aqueous emulsion according to claim 1, wherein the ethylenically unsaturated monomer unit is at least one selected from the group consisting of vinyl ester monomer units, (meth)acrylate monomer units, styrene monomer units, and diene monomer units.

16. The aqueous emulsion according to claim 1, wherein at least a part of the modified polyvinyl alcohol (A) and at least a part of the polymer (B) have a chemical bond.

17. The aqueous emulsion according to claim 1, wherein the mass ratio (A / B) of the modified polyvinyl alcohol (A) to the polymer (B) is 2 / 98 to 40 / 60.

18. A method for producing an aqueous emulsion, which is the method for producing an aqueous emulsion according to any one of claims 1 to 17 and includes a step of emulsion-polymerizing the ethylenically unsaturated monomer in the presence of the modified polyvinyl alcohol (A).

19. An adhesive containing the aqueous emulsion according to any one of claims 1 to 17.

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