JP6894572B1 - Polyvinyl acetal resin composition and adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl acetal resin composition having excellent storage stability and capable of imparting high adhesiveness. Further, a polyvinyl acetal resin composition capable of preventing corrosion of an adherend when used for adhering a metal is provided. In addition, an adhesive containing the polyvinyl acetal resin composition is provided. SOLUTION: The polyvinyl acetal resin and a lower carboxylic acid are contained, and the content of the lower carboxylic acid is 3 to 30 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin, and the content of the polyvinyl acetal resin is 3 to 30 parts by weight. A polyvinyl acetal resin composition having a hydroxyl group content of 50 to 95 mol% and a pH of 3 to 6 at 20 ° C. [Selection diagram] None

Description

The present invention relates to a polyvinyl acetal resin composition which is excellent in storage stability and can impart high adhesiveness. Further, the present invention relates to a polyvinyl acetal resin composition capable of preventing corrosion of an adherend when used for adhering metals. The present invention also relates to an adhesive containing the polyvinyl acetal resin composition.

Polyvinyl acetal resin is a resin synthesized from polyvinyl alcohol as a raw material, and by having an acetyl group, a hydroxyl group, and an acetal group in the side chain, it exhibits excellent toughness, adhesiveness, crosslinkability, and hygroscopicity. Can be done. Further, the physical characteristics of the resin can be changed by changing the ratio of the side chain groups. Utilizing these characteristics, it is used in a wide range of applications such as laminated glass interlayer films for automobiles and ceramic green sheets.

For example, Patent Document 1 describes, as a polyvinyl acetal resin suitable as a ceramic binder, a water-soluble polyvinyl acetal resin obtained by acetalizing polyvinyl alcohol having a predetermined degree of polymerization and saponification in the range of 10 to 50 mol%. Has been done.

Japanese Unexamined Patent Publication No. 4-178404

However, when a polyvinyl acetal resin is used as an adhesive component, it can impart toughness as compared with polyvinyl alcohol or the like, but has a problem of low adhesiveness. In particular, a polyvinyl acetal resin having a high hydroxyl group amount is used in an aqueous adhesive, but the polyvinyl acetal resin having a high hydroxyl group amount has a particularly low adhesiveness, and a composition change or a pH change occurs due to desorption of an acetyl group. There is a problem that it easily deteriorates with time and the durability and storage stability of the adhesive are inferior.

An object of the present invention is to provide a polyvinyl acetal resin composition which is excellent in storage stability and can impart high adhesiveness. Another object of the present invention is to provide a polyvinyl acetal resin composition capable of preventing corrosion of an adherend when used for adhering a metal. Another object of the present invention is to provide an adhesive containing the polyvinyl acetal resin composition.

The present invention contains a polyvinyl acetal resin and a lower carboxylic acid, and the content of the lower carboxylic acid is 3 to 30 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin, and the content of the polyvinyl acetal resin is 3 to 30 parts by weight. A polyvinyl acetal resin composition having a hydroxyl group content of 50 to 95 mol% and a pH of 3 to 6 at 20 ° C.
The present invention will be described in detail below.

As a result of diligent studies, the present inventors have added a predetermined amount of lower carboxylic acid to a polyvinyl acetal resin having a predetermined amount of hydroxyl groups, and set the pH of the composition within a predetermined range to increase the amount of hydroxyl groups. It has been found that a composition having excellent adhesiveness and storage stability can be obtained even when the polyvinyl acetal resin of No. 1 is used, and the present invention has been completed.

The polyvinyl acetal resin composition of the present invention contains a polyvinyl acetal resin.
The polyvinyl acetal resin has a structural unit having a hydroxyl group represented by the following formula (1).

The polyvinyl acetal resin has a content of a structural unit having a hydroxyl group represented by the above formula (1) (hereinafter, “hydroxyl group amount”) of 50 to 95 mol%.
When the amount of the hydroxyl group is in the above range, high solubility in an aqueous medium can be exhibited.
The amount of the hydroxyl group is preferably 60 mol% or more, and preferably 90 mol% or less.
The amount of hydroxyl groups can be measured by, for example, NMR.

The polyvinyl acetal resin preferably has a structural unit having an acetyl group represented by the following formula (2).

In the polyvinyl acetal resin, the preferable lower limit of the content of the structural unit having an acetyl group represented by the above formula (2) (hereinafter, “acetyl group amount”) is 0.1 mol%, and the preferable upper limit is 20 mol%. ..
When the amount of the acetyl group is in the above range, the adhesive strength of the polyvinyl acetal resin composition can be enhanced.
The more preferable lower limit of the amount of acetyl groups is 10 mol%, and the more preferable upper limit is 19.5 mol%.
The amount of the acetyl group can be measured by, for example, NMR.

The polyvinyl acetal resin preferably has a structural unit having an acetal group represented by the following formula (3).

In the above formula (3), R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

Examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group and a dodecyl group. Examples thereof include a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecil group and an eicosyl group. Of these, a methyl group, an ethyl group and a propyl group are preferable.

The polyvinyl acetal resin has a preferable lower limit of 1 mol%, a more preferable lower limit of 3 mol%, a preferable upper limit of 30 mol%, and a more preferable upper limit of the content of the structural unit having an acetal group represented by the above formula (3). Is 25 mol%.
The content of the structural unit having an acetal group represented by the above formula (3) can be measured by, for example, NMR.

In the polyvinyl acetal resin, the preferable lower limit of the content of the structural unit having an acetal group (hereinafter, “total acetal group amount”) is 1 mol%, and the preferable upper limit is 30 mol%.
When the total amount of acetal groups is in the above range, there is an advantage that the resin has appropriate flexibility and water solubility.
The more preferable lower limit of the total acetal group amount is 3 mol%, and the more preferable upper limit is 25 mol%.
The total amount of acetal groups can be measured by, for example, NMR.
As for the calculation method of the amount of acetal groups, since the acetal group of the polyvinyl acetal resin is obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, a method of counting the two acetalized hydroxyl groups is adopted. can do.

The polyvinyl acetal resin may further have a structural unit having a functional group such as a carboxyl group, a sulfonic acid group, an alkylene oxide group, and an amide group.

Examples of the structural unit having a carboxyl group include a structural unit represented by the following formula (4-1), a structural unit represented by the following formula (4-2), and a constitution represented by the following formula (4-3). Units and the like can be mentioned.

In the above formula (4-1), R ² and R ³ are independent and represent an alkylene group having 0 to 10 carbon atoms, and X ¹ and X ² are independent of each other and are a hydrogen atom, a metal atom or a methyl group. Represents.

In the above formula (4-1), ^{the preferable lower limit of the number of carbon atoms of the alkylene group represented by R 2} and R ³ is 0, the preferable upper limit is 5, the more preferable lower limit is 1, and the more preferable upper limit is 3.
The above R ² and R ³ may be the same or different, but different ones are preferable. Further, it is preferable that at least one of them is a single bond.

Examples of the alkylene group having 0 to 10 carbon atoms include a linear alkylene group such as a single bond, a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, and a decamethylene group. Group, branched alkylene group such as methylmethylene group, methylethylene group, 1-methylpentylene group, 1,4-dimethylbutylene group, cyclic alkylene group such as cyclopropylene group, cyclobutylene group, cyclohexylene group and the like. Be done. Among them, a linear alkylene group such as a single bond, a methylene group, an ethylene group, an n-propylene group and an n-butylene group is preferable, and a single bond, a methylene group and an ethylene group are more preferable.

In the above (4-1), when ^{at least one} of X 1 and X ² is a metal atom, examples of the metal atom include a sodium atom, a lithium atom, a potassium atom and the like. Of these, a sodium atom is preferable.

The structural unit represented by the above formula (4-1) is preferably derived from an α-dicarboxymonomer. Examples of the α-dicarboxy monomer include dicarboxylic acids having a radically polymerizable unsaturated double bond such as methylene malonic acid, itaconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, and 2-methylene sebacic acid, and the like. Examples thereof include metal salts or methyl esters thereof. Of these, itaconic acid, a metal salt thereof, or a methyl ester thereof is preferably used.
In the present specification, the α-dicarboxymonomer represents a monomer having two carboxyl groups at the α-carbon.

In the above formula (4-2), R ⁴ , R ⁵ and R ⁶ independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ⁷ is an alkylene group having 0 to 10 carbon atoms. the stands, X ³ represents a hydrogen atom, a metal atom or a methyl group.

In the above formula (4-2), ^{the preferable lower limit of the number of carbon atoms of the alkyl group represented by R 4} , R ⁵ and R ⁶ is 1, the preferable upper limit is 5, and the more preferable upper limit is 3.

R ⁴ , R ⁵ , and R ⁶ may be the same or different, but the same one is more preferable. Further, R ⁴ , R ⁵ and R ⁶ are preferably hydrogen atoms.

Examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a propyl group, an n-butyl group, an n-pentyl group, an n-heptyl group, an n-octyl group, an n-nonyl group and an n-. Linear alkyl group such as decyl group, isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, 2,2-dimethylpropyl group, 1,1,3,3-tetramethylbutyl group, Examples thereof include branched alkyl groups such as 2-ethylhexyl groups, cyclopropyl groups, cyclopropylmethyl groups, cyclobutyl groups, cyclopentyl groups, cycloalkyl groups such as cyclohexyl groups and the like. Of these, linear alkyl groups such as methyl group, ethyl group, propyl group and n-butyl group are preferable, and methyl group and ethyl group are more preferable.

^{Examples of R 7} in the above formula (4-2) ^{include those similar to those exemplified in R 2} and R ³ in the above formula (4-1), among which single bonds, methylene groups, and ethylenes are used. A linear alkylene group such as a group, a trimethylene group, or a tetramethylene group is preferable, a single bond, a methylene group, or an ethylene group is more preferable, and a single bond is further preferable.

In the above formula (4-2), when X ³ is a metal atom, examples of the metal atom include a sodium atom, a lithium atom, a potassium atom and the like. Of these, a sodium atom is preferable.

The structural unit represented by the above formula (4-2) is preferably derived from a monocarboxymonomer. Examples of the monocarboxymonomer include monocarboxylic acids having a radically polymerizable unsaturated double bond such as acrylic acid, crotonic acid, methacrylic acid, and oleic acid, metal salts thereof, and methyl esters thereof. Of these, crotonic acid, a metal salt thereof, or a methyl ester thereof is preferably used.

In the above formula (4-3), R ⁸ and R ¹⁰ independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ⁹ and R ¹¹ are alkylene groups having 0 to 10 carbon atoms. the stands, ^{X 4} and ^{X 5} represents a hydrogen atom, a metal atom or a methyl group.

In the above formula (4-3), ^{the preferable lower limit of the number of carbon atoms of the alkyl group represented by R 8} and R ¹⁰ is 1, the preferable upper limit is 5, and the more preferable upper limit is 3.

The R ⁸ and R ¹⁰ may be the same or different, but the same one is more preferable.

^{Examples of R 8} and R ¹⁰ in the above formula (4-3) ^{include those similar to those exemplified in R 4} , R ⁵ and R ⁶ in the above formula (4-2), and among them, hydrogen. Atoms are preferred.

^{Examples of R 11} in the above formula (4-3) ^{include those similar to those exemplified in R 2} and R ³ in the above formula (4-1), among which single bonds, methylene groups, and ethylenes are used. A linear alkylene group such as a group, a trimethylene group, or a tetramethylene group is preferable, a single bond, a methylene group, or an ethylene group is more preferable, and a single bond is further preferable.

In the above formula (4-3), when X ⁴ and X ⁵ are metal atoms, examples of the metal atoms include sodium atom, lithium atom, potassium atom and the like. Of these, a sodium atom is preferable.

Examples of the structural unit having the sulfonic acid group include a structural unit represented by the following formula (5).

In the formula (5), R ¹² represents an alkylene group having 0 to 10 carbon ^{atoms, and X 5} represents a hydrogen atom, a metal atom or a methyl group.

^{Examples of R 12} in the above formula (5) ^{include those similar to those exemplified in R 2} and R ³ in the above formula (4-1), among which single bond, methylene group, ethylene group, and the like. Linear alkylene groups such as trimethylene group and tetramethylene group are preferable, single bond, methylene group and ethylene group are more preferable, and single bond and methylene group are further preferable.

In the above formula (5), when X ⁵ is a metal atom, examples of the metal atom include a sodium atom, a lithium atom, a potassium atom and the like. Of these, a sodium atom is preferable.

Examples of the structural unit having the alkylene oxide group include a structural unit represented by the following formula (6).

In formula (6), R ¹³ represents a group having an alkylene oxide group having 2 to 6 carbon atoms.

Examples of the alkylene oxide group having 2 to 6 carbon atoms include an ethylene oxide group, a propylene oxide group, a butylene oxide group, a pentylene oxide group, and a hexylene oxide group. Of these, an ethylene oxide group is preferable.
Examples of the structural unit having an alkylene oxide group represented by the above formula (6) include those having a plurality of ethylene oxide groups such as polyethylene glycol, those having an ethylene oxide group alone, and those having a different alkylene oxide group. And so on.

The structural unit having an alkylene oxide group is preferably a structural unit having an ethylene oxide group represented by the following formula (7).

In the above formula (7), R ¹⁴ and R ¹⁵ represent a linking group or a single bond having at least one selected from the group consisting of C and O, and n represents an integer.

R ¹⁴ is a linking group or a single bond having at least one selected from the group consisting of C and O. The R ¹⁴ is preferably an alkylene group or a carbonyl group having 1 to 10 carbon atoms.
Examples of the R ¹⁴ include a methylene group, an ethylene group, a carbonyl group, an ether group and the like. Further, the R ¹⁴ may be a single bond.
The R ¹⁵ is a linking group or a single bond with at least one selected from the group consisting of C and O. The R ¹⁵ is preferably an alkylene group or a carbonyl group having 1 to 10 carbon atoms. As the R ^15, for example, methylene group, ethylene group, propylene group, a carbonyl group, and ether groups. Further, the R ¹⁵ may be a single bond.
Further, the integer n, which is the number of repetitions of the alkylene oxide, is not particularly limited, but is preferably 2 to 50, more preferably 5 to 20.

Examples of the structural unit having the amide group include a structural unit represented by the following formula (8).

In the above formula (8), R ¹⁶ represents an alkyl group having 1 to 10 carbon atoms.

^{Examples of R 16} in the above formula (8) ^{include those similar to those exemplified in R 4} , R ⁵ and R ⁶ in the above formula (4-2), and among them, a hydrogen atom. Linear alkyl groups such as methyl group, ethyl group, propyl group and n-butyl group are preferable, and hydrogen atom, methyl group and ethyl group are more preferable.

Regarding the content of the structural unit having the functional group in the polyvinyl acetal resin, the preferable lower limit is 0.1 mol%, the more preferable lower limit is 0.5 mol%, the preferable upper limit is 5 mol%, and the more preferable upper limit is 3 mol%. Is.

The average degree of polymerization of the polyvinyl acetal resin is preferably 1800.
When the average degree of polymerization is in the above range, the adhesive strength can be increased and the resin composition has a viscosity suitable for coating.
The more preferable lower limit of the average degree of polymerization is 300, and the more preferable upper limit is 1500.
The average degree of polymerization can be measured in accordance with JIS K 6726.

In the polyvinyl acetal resin composition of the present invention, the content of the polyvinyl acetal resin is such that the preferable lower limit is 15% by weight, the more preferable lower limit is 20% by weight, the preferable upper limit is 35% by weight, and the more preferable upper limit is 30% by weight. ..

The acetalization can be carried out by a known method, and is preferably carried out in an aqueous solvent, in a mixed solvent of water and an organic solvent compatible with water, or in an organic solvent.
As the organic solvent compatible with water, for example, an alcohol-based organic solvent can be used.
Examples of the organic solvent include alcohol-based organic solvents, aromatic organic solvents, aliphatic ester-based solvents, ketone-based solvents, lower paraffin-based solvents, ether-based solvents, amide-based solvents, amine-based solvents and the like.
Examples of the alcohol-based organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol and the like.
Examples of the aromatic organic solvent include xylene, toluene, ethylbenzene, methyl benzoate and the like.
Examples of the aliphatic ester solvent include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetoacetate, ethyl acetoacetate and the like.
Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, benzophenone, acetophenone and the like.
Examples of the lower paraffin solvent include hexane, pentane, octane, cyclohexane, decane and the like.
Examples of the ether solvent include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol diethyl ether and the like.
Examples of the amide-based solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, acetanilide and the like.
Examples of the amine-based solvent include ammonia, trimethylamine, triethylamine, n-butylamine, din-butylamine, trin-butylamine, aniline, N-methylaniline, N, N-dimethylaniline, and pyridine.
These can be used alone or in combination of two or more kinds of solvents. Among these, ethanol, n-propanol, isopropanol, and tetrahydrofuran are particularly preferable from the viewpoint of solubility in the resin and simplicity during purification.

The acetalization is preferably carried out in the presence of an acid catalyst.
The acid catalyst is not particularly limited, and mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, carboxylic acids such as formic acid, acetic acid, and propionic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and paratoluenesulfone are used. Examples include sulfonic acids such as acids. These acid catalysts may be used alone or in combination of two or more compounds. Of these, hydrochloric acid, nitric acid, and sulfuric acid are preferable, and nitric acid is particularly preferable.

Examples of the aldehyde used for the acetalization include aldehydes having a chain aliphatic group having 1 to 10 carbon atoms, a cyclic aliphatic group or an aromatic group. Conventionally known aldehydes can be used as these aldehydes. The aldehyde used in the acetalization reaction is not particularly limited, and examples thereof include aliphatic aldehydes and aromatic aldehydes.
Examples of the aliphatic aldehyde include formaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde, isobutylaldehyde, n-barrelaldehyde, n-hexylaldehyde, 2-ethylbutylaldehyde, 2-ethylhexylaldehyde, n-heptylaldehyde, and n-. Examples thereof include octylaldehyde, n-nonylaldehyde, n-decylaldehyde, and amylaldehyde.
Examples of the aromatic aldehyde include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde and the like.
These aldehydes may be used alone or in combination of two or more. Among the aldehydes, formaldehyde, acetaldehyde, butyraldehyde, 2-ethylhexyl aldehyde, which have excellent acetalization reactivity, can bring about a sufficient internal plasticizing effect on the produced resin, and as a result can impart good flexibility. n-nonylaldehyde is preferred. Further, formaldehyde, acetaldehyde, and butyraldehyde are more preferable because an adhesive composition having particularly excellent impact resistance and adhesiveness to a metal can be obtained.

The amount of the aldehyde added can be appropriately set according to the amount of acetal groups of the target polyvinyl acetal resin.

The polyvinyl acetal resin composition of the present invention contains a lower carboxylic acid.
The content of the lower carboxylic acid is 3 parts by weight at the lower limit and 30 parts by weight at the upper limit with respect to 100 parts by weight of the polyvinyl acetal resin.
When the content of the lower carboxylic acid is in the above range, it is possible to prevent the acetyl group from being removed from the polyvinyl acetal resin over time, and to prevent deterioration due to a change in the composition of the resin. The content of the lower carboxylic acid capable of imparting flexibility and enhancing adhesive strength has a preferable lower limit of 5 parts by weight and a preferable upper limit of 20 parts by weight.

Examples of the lower carboxylic acid include carboxylic acids having 1 to 4 carbon atoms.
Examples of the lower carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid and the like. Of these, acetic acid, propionic acid and butyric acid are preferable, and acetic acid is more preferable.
In the present specification, the lower carboxylic acid may contain a salt of the lower carboxylic acid. However, from the viewpoint of imparting flexibility to the polyvinyl acetal resin and enhancing the adhesive strength, a lower carboxylic acid is more preferable, and acetic acid is further preferable.
Examples of the salt of the lower carboxylic acid include sodium salt, potassium salt, lithium salt and the like.
Even when a salt of a lower carboxylic acid is contained, the above content is a value converted to the weight of the lower carboxylic acid. For example, when the salt of the lower carboxylic acid contained is sodium acetate, the content in terms of lower carboxylic acid is calculated by the following formula based on the content of sodium acetate and the molecular weight ratio of acetic acid and sodium acetate. To.
Content of lower carboxylic acid = Sodium acetate content x (Molecular weight of acetic acid / Molecular weight of sodium acetate)

The total content of the structural unit having an acetyl group represented by the above formula (2) and the above lower carboxylic acid in the polyvinyl acetal resin composition of the present invention has a preferable lower limit with respect to 100 parts by weight of the polyvinyl acetal resin. 10 parts by weight, a more preferable lower limit is 20 parts by weight, a preferable upper limit is 55 parts by weight, and a more preferable upper limit is 50 parts by weight.
The total content of the structural unit having an acetyl group represented by the formula (2) and the lower carboxylic acid is the content of the lower carboxylic acid in the polyvinyl acetal resin composition of the present invention and the polyvinyl acetal resin. Can be determined based on the content of the above and the amount of the acetyl group of the polyvinyl acetal resin.

In particular, when the lower carboxylic acid is acetic acid, the total content of the structural unit having an acetyl group represented by the formula (2) and the acetic acid in the polyvinyl acetal resin composition of the present invention is the polyvinyl acetal resin 100. With respect to parts by weight, the preferred lower limit is 15 parts by weight, the more preferable lower limit is 25 parts by weight, the preferred upper limit is 55 parts by weight, and the more preferable upper limit is 45 parts by weight.
The total content (parts by weight) of the acetic acid and the structural unit having an acetyl group represented by the above formula (2) is the content (parts by weight) of the acetic acid in the polyvinyl acetal resin composition of the present invention. It can be determined based on the content (parts by weight) of the polyvinyl acetal resin and the acetyl group content (% by weight) of the polyvinyl acetal resin. The acetyl group content (% by weight) of the polyvinyl acetal resin is calculated based on the degree of polymerization of the polyvinyl acetal resin and the content (mol%) of each structural unit, and has an acetyl group in the molecule. It can be obtained by calculating the ratio (% by weight) of the constituent units.

In the polyvinyl acetal resin composition of the present invention, the structural unit having an acetyl group represented by the above formula (2), the total content of the above lower carboxylic acid, and the structural unit having a hydroxyl group represented by the above formula (1). The weight ratio of the content (total weight of the structural unit having an acetyl group and the lower carboxylic acid / the weight of the structural unit having a hydroxyl group) is preferably 0.3 or more, and more preferably 0.4 or more. It is preferably 0.85 or less, and more preferably 0.75 or less.
The content (parts by weight) of the structural unit having a hydroxyl group is the content (parts by weight) of the polyvinyl acetal resin in the polyvinyl acetal resin composition of the present invention, and the hydroxyl group content (% by weight) of the polyvinyl acetal resin. Can be obtained based on. Further, the amount of hydroxyl groups (% by weight) of the polyvinyl acetal resin is calculated by calculating the calculated molecular weight based on the degree of polymerization of the polyvinyl acetal resin and the content (mol%) of each structural unit, and the structural unit having a hydroxyl group in the molecule. It can be obtained by calculating the ratio (% by weight) of.

In particular, when the lower carboxylic acid is acetic acid, the total content of the acetic acid and the structural unit having an acetyl group represented by the above formula (2) in the polyvinyl acetal resin composition of the present invention and the above formula (1) The weight ratio of the content of the represented structural unit having a hydroxyl group (total weight of the structural unit having an acetyl group and acetic acid / the weight of the structural unit having a hydroxyl group) is preferably 0.3 or more, and 0. It is more preferably 4 or more, preferably 0.85 or less, and more preferably 0.75 or less.

The modified polyvinyl acetal resin of the present invention may be a copolymer of an ethylenically unsaturated monomer as long as the effects of the present invention are not impaired. The ethylenically unsaturated monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, (phthalic anhydride) phthalic acid, (maleic anhydride) maleic acid, and (anhydrous) itaconic acid. Examples thereof include acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl- (3-acrylamide-3-dimethylpropyl) -ammonium chloride, acrylamide-2-methylpropanesulfonic acid and sodium salts thereof. Further, ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinylsulfonate, sodium allylsulfonate and the like can be mentioned. In addition, a terminal-modified polyvinyl alcohol obtained by copolymerizing ethylene with a vinyl ester-based monomer such as vinyl acetate in the presence of a thiol compound such as thiol acetic acid or mercaptopropionic acid and saponifying it should also be used. Can be done.

The polyvinyl acetal resin composition of the present invention preferably has a chloride ion concentration of 50 μg / g or less.
When the chloride ion concentration is in the above range, the metal adherend is less likely to corrode.
The chloride ion concentration is more preferably 30 μg / g or less, and further preferably 10 μg / g or less. The lower limit of the chloride ion concentration is not particularly limited, but is preferably 0 μg / g.
When chloride ions are contained in an amount of 10 μg / g or less, residual chloride ions contained in the pure water (ion-exchanged water) used can be mentioned.

The polyvinyl acetal resin composition of the present invention has a pH of 3 to 6 at 20 ° C.
When the pH is in the above range, it is possible to prevent desorption of the acetyl group from the polyvinyl acetal resin over time and prevent deterioration due to a change in the composition of the resin.
The pH is preferably 3.5 or higher, and preferably 5.5 or lower.

As a method for producing the polyvinyl acetal resin composition of the present invention, for example, a lower carboxylic acid and other, if necessary, are added to a polyvinyl acetal resin aqueous solution obtained by acetalizing polyvinyl alcohol with an aldehyde. Examples thereof include a method of adding an additive and mixing.

The polyvinyl acetal resin composition of the present invention can be suitably used for applications in which ordinary polyvinyl acetal resins are used, for example, ceramic molded products, metal pastes, heat-developable photosensitive materials, paints, inks, reflective sheets. Etc. can be obtained as a coating solution for producing the above. Further, it can be used for an adhesive composition for a film for a display, an interlayer adhesive for a ceramic laminate, a liquid adhesive, a solid adhesive, and the like.
In particular, the polyvinyl acetal resin composition of the present invention can be suitably used for an adhesive composition such as an aqueous adhesive because water can be used as a solvent instead of the organic solvent. Furthermore, since the chloride ion content is very low, it can be used as an adhesive that does not easily corrode even if the adherend is a metal.

The adhesive composition containing the polyvinyl acetal resin composition of the present invention further comprises a curable resin such as an organic solvent, water, and an epoxy resin, or a phenol resin, a nitrile butadiene rubber, a polyamide resin, and a polyimide. It may contain a polymer compound such as a based resin, a polyurethane resin, a polyolefin resin, a polyester resin, or a bismaleimide triazine resin. In addition, if necessary, hardeners, flame retardants, effect promoters, antioxidants, coupling agents, thickeners, leveling agents, defoamers, inorganic fillers such as silica, calcium carbonate, and hydrotalcite, etc. May contain the additive of.

As the organic solvent, for example, ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol and butanol, and arbitrary solvents such as aromatic hydrocarbons such as toluene and xylene can be used, and one of them can be used. It can be used as a single solvent or as a mixed solvent of two or more kinds.

The content of the organic solvent in the entire adhesive composition is preferably 70% by weight or less. By setting the content of the organic solvent with respect to the entire adhesive composition in such a range, the adhesiveness of the adhesive composition can be improved.

The content of water with respect to the entire adhesive composition is preferably 70% by weight or less. By setting the content of the water in the entire adhesive composition in such a range, the adhesiveness of the adhesive composition can be improved.

The adhesive composition can be dried to obtain a dried product. The residual amount of the organic solvent with respect to the entire dried body is preferably 10% by weight or less, and the residual amount of water with respect to the entire dried body is preferably 10% by weight or less. By setting the residual amount of the organic solvent and water in such a range, the adhesiveness of the dried product obtained by drying the adhesive composition can be improved.

According to the present invention, it is possible to provide a polyvinyl acetal resin composition having excellent storage stability and capable of imparting high adhesiveness. Further, it is possible to provide a polyvinyl acetal resin composition capable of preventing corrosion of an adherend when used for adhering a metal. In addition, an adhesive containing the polyvinyl acetal resin composition can be provided.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
(Preparation of polyvinyl acetal resin)
500 g of polyvinyl alcohol having a degree of polymerization of 600 and a degree of saponification of 88 mol% was added to 1500 g of pure water, and the mixture was dissolved by stirring at a temperature of 90 ° C. for about 2 hours. This solution was cooled to 40 ° C., 10 g of nitric acid having a concentration of 67.5% by weight and 35 g of n-butylaldehyde were added thereto, and the liquid temperature was maintained at 40 ° C. for 3 hours to complete the acetalization reaction. Neutralization was performed by adding 25 g of a weight% diluted sodium hydroxide aqueous solution to obtain a polyvinyl acetal resin aqueous solution (resin content: 25% by weight). After volatilizing the water content of the obtained polyvinyl acetal resin aqueous solution, it was dissolved in ^{DMSO-D 6 (dimethyl sulfoxide) and analyzed using 1} H-NMR (nuclear magnetic resonance spectrum). As a result, the total amount of acetal groups was measured. The amounts of acetyl groups and hydroxyl groups are as shown in Table 1.

(Preparation of polyvinyl acetal resin composition)
5 g of acetic acid was added to 100 g of the obtained aqueous solution of polyvinyl acetal resin (resin content: 25 g) to obtain a polyvinyl acetal resin composition.
The pH of the obtained polyvinyl acetal resin composition at 20 ° C. was 3.6.
The chloride ion concentration of the obtained polyvinyl acetal resin composition was measured by ion chromatography and found to be 10 μg / g or less.

(Example 2)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of acetic acid added was 1 g.
When measured in the same manner as in Example 1, the pH was 4.2 and the chloride ion concentration was 10 μg / g or less.

(Example 3)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of acetic acid added was 7 g.
When measured in the same manner as in Example 1, the pH was 3.2 and the chloride ion concentration was 10 μg / g or less.

(Example 4)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of n-butyraldehyde added was 15 g and the amount of acetic acid added was 2 g.
When measured in the same manner as in Example 1, the pH was 3.9 and the chloride ion concentration was 10 μg / g or less.

(Example 5)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of n-butyraldehyde added was 7 g.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 6)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that 70 g of acetaldehyde was added instead of n-butyraldehyde.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 7)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that 32 g of acetaldehyde was added instead of n-butyraldehyde.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 8)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of n-butyraldehyde added was 19 g and 31 g of acetaldehyde was further added.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 9)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 600 and a degree of saponification of 98 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 10)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 600 and a degree of saponification of 80 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 11)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that a polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 88 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 12)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that a polyvinyl alcohol having a degree of polymerization of 300 and a saponification degree of 88 mol% was used and 47 g of acetaldehyde was added instead of n-butyraldehyde.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 13)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 88 mol% was used and the amount of n-butyraldehyde added was 15 g.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 14)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that a polyvinyl alcohol having a degree of polymerization of 1200 and a degree of saponification of 88 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 15)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 1200 and a degree of saponification of 88 mol% was used and the amount of n-butyraldehyde added was 15 g.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 16)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 1700 and a degree of saponification of 88 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 17)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that a carboxylic acid-modified polyvinyl alcohol having a degree of polymerization of 600 and a saponification degree of 88 mol% was used.
As the carboxylic acid-modified polyvinyl alcohol, in the structural unit represented by the above formula (4-1) (in the formula (4-1), R ² is a single bond, R ³ is a methylene group, X ¹ and X ^2). The content of (hydrogen atom) is 1.2 mol%.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 18)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that a sulfonic acid-modified polyvinyl alcohol having a degree of polymerization of 600 and a saponification degree of 88 mol% was used.
The sulfonic acid-modified polyvinyl alcohol contains 1.0 mol% of the structural unit represented by the above formula (5) (in the formula (5), R ⁸ is a methylene group and X ^{4 is a sodium atom).} Was used.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 19)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that an ethylene oxide-modified polyvinyl alcohol having a degree of polymerization of 600 and a degree of saponification of 88 mol% was used.
The ethylene oxide-modified polyvinyl alcohol is a structural unit represented by the above formula (7) (in the formula (7), R ¹⁰ is an ethylene group, R ¹¹ is a single bond, and the average value of n is 7.5). The content of ethylene was 0.8 mol%.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 20)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that an amide-modified polyvinyl alcohol having a degree of polymerization of 600 and a degree of saponification of 88 mol% was used.
As the amide-modified polyvinyl alcohol, one having a content of the structural unit represented by the above formula (8) (R ¹² is a methyl group in the formula (8)) was 1.3 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 21)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 2000 and a degree of saponification of 88 mol% was used.
When measured in the same manner as in Example 1, the pH was 3.5 and the chloride ion concentration was 10 μg / g or less.

(Example 22)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of nitric acid added having a concentration of 67.5% by weight was 9.5 g and 0.5 g of hydrochloric acid having a concentration of 35% by weight was further added.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 86 μg / g.

(Example 23)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of the 20 wt% sodium hydroxide diluted aqueous solution added was 21 g.
When measured in the same manner as in Example 1, the pH was 3.1 and the chloride ion concentration was 10 μg / g or less.

(Example 24)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of the 20 wt% sodium hydroxide diluted aqueous solution added was 48.5 g.
When measured in the same manner as in Example 1, the pH was 5.7 and the chloride ion concentration was 10 μg / g or less.

(Example 25)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of acetic acid added was 4 g and 1 g of sodium acetate was added.
When measured in the same manner as in Example 1, the pH was 3.8 and the chloride ion concentration was 10 μg / g or less.

(Example 26)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 600 and a degree of saponification of 98 mol% was used and the amount of n-butyraldehyde added was 15 g.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Example 27)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that 90 g of acetaldehyde was added instead of n-butyraldehyde using polyvinyl alcohol having a degree of polymerization of 300 and a degree of saponification of 88 mol%.
When measured in the same manner as in Example 1, the pH was 3.7 and the chloride ion concentration was 10 μg / g or less.

(Example 28)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that 5 g of propionic acid was added instead of acetic acid.
When measured in the same manner as in Example 1, the pH was 3.8 and the chloride ion concentration was 10 μg / g or less.

(Example 29)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that 5 g of butyric acid was added instead of acetic acid.
When measured in the same manner as in Example 1, the pH was 3.8 and the chloride ion concentration was 10 μg / g or less.

(Comparative Example 1)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that acetic acid was not added.
When measured in the same manner as in Example 1, the pH was 5.1 and the chloride ion concentration was 10 μg / g or less.

(Comparative Example 2)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of acetic acid added was 0.5 g.
When measured in the same manner as in Example 1, the pH was 4.9 and the chloride ion concentration was 10 μg / g or less.

(Comparative Example 3)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of acetic acid added was 10 g.
When measured in the same manner as in Example 1, the pH was 3.0 and the chloride ion concentration was 10 μg / g or less.

(Comparative Example 4)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that polyvinyl alcohol having a degree of polymerization of 600 and a saponification degree of 99.5 mol% was used and the amount of n-butyraldehyde added was 3 g.
When measured in the same manner as in Example 1, the pH was 3.6 and the chloride ion concentration was 10 μg / g or less.

(Comparative Example 5)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of the 20 wt% sodium hydroxide diluted aqueous solution added was 15 g and the neutralization after the acetalization reaction was partially performed.
When measured in the same manner as in Example 1, the pH was 2.5 and the chloride ion concentration was 10 μg / g or less.

(Comparative Example 6)
A polyvinyl acetal resin composition was obtained in the same manner as in Example 1 except that the amount of the 20 wt% sodium hydroxide diluted aqueous solution added was 38 g and the neutralization after the acetalization reaction was excessive to make the resin aqueous solution basic. ..
When measured in the same manner as in Example 1, the pH was 8.2 and the chloride ion concentration was 10 μg / g or less.

<Evaluation>
The polyvinyl acetal resin compositions obtained in Examples and Comparative Examples were evaluated as follows. The results are shown in Table 1.

(1) Peeling Adhesive Strength A polyvinyl acetal resin composition was applied to a stainless steel (SUS304) substrate having a length of 80 mm, a width of 30 mm, and a thickness of 1 mm to a thickness of 0.5 mm, and dried by heating at 100 ° C. for 3 hours. After drying, it is allowed to stand in a constant temperature and humidity chamber (temperature 25 ° C., humidity 50%) for 24 hours, and then a 180 ° peel test is performed using a tensile tester based on JIS K 6854-2, and the peeling adhesive strength (N). ) Was asked.

(2) Change in pH over time Using a pH meter (portable pH meter D-74 manufactured by Horiba Seisakusho), the pH immediately after the polyvinyl acetal resin composition was prepared and the pH one year after the preparation were measured, and each of them was measured. The difference in pH (pH immediately after preparation-pH one year after preparation) was used as the value of pH change over time.

(3) Changes in composition over time
^{1 1} H NMR was used to measure the amount of acetyl groups immediately after the preparation of the polyvinyl acetal resin composition and the amount of acetyl groups one year after the preparation. When the ratio of the amount of acetyl group after 1 year to the amount of acetyl group immediately after preparation ([acetyl group after 1 year / amount of acetyl group immediately after preparation] x 100) is 98% or more, from ⊚, 95% The case of less than 98% was evaluated as ◯, the case of 90% to less than 95% was evaluated as Δ, and the case of less than 90% was evaluated as ×.

(4) Metal corrosiveness Similar to "(1) Peeling adhesive strength", a polyvinyl acetal resin composition is applied to an SPCC steel sheet having a length of 80 mm, a width of 30 mm, and a thickness of 1 mm, and then left as it is for one week before being used as a base. The surface condition of the material was confirmed, and the case where rust could not be confirmed was evaluated as 0, the case where rust was confirmed at 1 to 2 places was evaluated as Δ, and the case where rust was confirmed at 3 or more places was evaluated as ×.

(5) Tension Elastic Modulus By applying the polyvinyl acetal resin composition on a PET film that has been demolded to a thickness of 20 μm after drying using a coater, and then heating and drying at 100 ° C. for 3 hours. , A resin sheet was prepared. In accordance with JIS K 7113, the tensile elastic modulus (MPa) of the resin sheet prepared under the condition of a tensile speed of 20 mm / min was measured using a tensile tester (AUTOGRAPH AGS-J manufactured by Shimadzu Corporation).

(6) Flexibility After producing a resin sheet in the same manner as in "(5) Tension elastic modulus", the central part of the resin sheet is pressed with a glass core rod having a diameter of 2 mm, and a 180 ° bending test centered on this is performed. The flexibility was evaluated according to the following criteria.
〇: No cracks could be confirmed.
Δ: Cracks were confirmed in a small part of the resin sheet.
X: Breakage was confirmed in the resin sheet.

According to the present invention, it is possible to provide a polyvinyl acetal resin composition having excellent storage stability and capable of imparting high adhesiveness. Further, it is possible to provide a polyvinyl acetal resin composition capable of preventing corrosion of an adherend when used for adhering a metal. In addition, an adhesive containing the polyvinyl acetal resin composition can be provided.

Claims (8)

It contains a polyvinyl acetal resin and a lower carboxylic acid having 1 to 4 carbon atoms.
The content of the lower carboxylic acid is 3 to 30 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin.
The amount of hydroxyl groups of the polyvinyl acetal resin is 50 to 95 mol%, and the amount of hydroxyl groups is 50 to 95 mol%.
A polyvinyl acetal resin composition having a pH of 3 to 6 at 20 ° C. The polyvinyl acetal resin composition according to claim 1, wherein the lower carboxylic acid is acetic acid. The polyvinyl acetal resin composition according to claim 1 or 2, wherein the total amount of acetal groups in the polyvinyl acetal resin is 1 to 30 mol%. The polyvinyl acetal resin composition according to any one of claims 1 to 3, wherein the polyvinyl acetal resin has an average degree of polymerization of 1800 or less. The polyvinyl acetal resin composition according to any one of claims 1 to 4, wherein the polyvinyl acetal resin has an acetyl group content of 0.1 to 20 mol%. Weight ratio of the total content of the structural unit having an acetyl group and the lower carboxylic acid to the content of the structural unit having a hydroxyl group (total weight of the structural unit having an acetyl group and the lower carboxylic acid / the weight of the structural unit having a hydroxyl group) The polyvinyl acetal resin composition according to any one of claims 1 to 5, wherein) is 0.3 to 0.85. The polyvinyl acetal resin composition according to any one of claims 1 to 6, wherein the chloride ion concentration is 50 μg / g or less. An adhesive containing the polyvinyl acetal resin composition according to any one of claims 1 to 7.