Vinyl alcohol polymer, vinyl-alcohol-polymer-containing aqueous solution, coating material, and cement admixture

Abstract

Provided is a vinyl alcohol polymer, wherein expression (1) is satisfied by: an aqueous solution viscosity X [cp], at 20°C and a shear rate of 1 [1 / s], of an aqueous solution in which the content of the vinyl alcohol polymer is 1.5 mass% and which exhibits a pH of 4 at 20°C; and an aqueous solution viscosity Y [cp], at 20°C and a shear rate of 1 [1 / s], of an aqueous solution in which the content of the vinyl alcohol polymer is 1.5 mass% and which exhibits a pH of 10 at 20°C.　(1): 1.5<Y / X<1,500

Description

Vinyl alcohol polymer, aqueous solution containing vinyl alcohol polymer, paint and cement admixture

[0001] The present invention relates to a vinyl alcohol polymer, and a vinyl alcohol polymer-containing aqueous solution, a paint, and a cement admixture, each of which contains the vinyl alcohol polymer.

[0002] Vinyl alcohol polymers have excellent film properties (mechanical strength, oil resistance, film-forming ability, oxygen gas barrier property, etc.) due to their hydrophilicity or high crystallinity. Taking advantage of these properties, vinyl alcohol polymers are therefore widely used as raw materials for viscosity modifiers (thickeners), adhesives, paper coating agents, fiber processing agents, binders, emulsion stabilizers, films, fibers, etc. Furthermore, in order to improve the performance of vinyl alcohol polymers according to their applications, modified vinyl alcohol polymers have been developed by introducing functional groups, controlling crystallinity, etc.

[0003] For example, when used as a viscosity modifier (thickener), even ordinary vinyl alcohol polymers have an excellent thickening effect due to the interaction between the hydroxyl groups of the vinyl alcohol polymer. However, when a higher aqueous solution viscosity is required, modified vinyl alcohol polymers into which a small amount of hydrophobic groups such as saturated hydrocarbon groups have been introduced have been proposed (Patent Documents 1 and 2). These modified vinyl alcohol polymers exhibit an even higher thickening effect due to the interaction between the hydrophobic groups in aqueous solution in addition to the interaction between the hydroxyl groups.

[0004] JP 2008-291120 A International Publication No. 2019 / 189402

[0005] The modified vinyl alcohol polymers described in Patent Documents 1 and 2 exhibit excellent thickening properties at low concentrations. However, in the process of mixing these modified vinyl alcohol polymers with an object to be thickened (e.g., an emulsion), when delivering the modified vinyl alcohol polymer to the object, it is necessary to prepare a high-concentration modified vinyl alcohol polymer solution at the time of delivery, taking into consideration that the concentration of the modified vinyl alcohol polymer decreases after mixing. As a result of investigations by the present inventors, it was found that the above-mentioned modified vinyl alcohol polymers have problems in terms of handleability, such as being unable to deliver the solution at high concentrations due to their high viscosity or being unable to dissolve at all.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a vinyl alcohol-based polymer from which an aqueous vinyl alcohol-based polymer solution can be obtained whose viscosity can be easily and greatly changed, an aqueous vinyl alcohol-based polymer solution whose viscosity can be easily and greatly changed, and a paint and a cement admixture containing the vinyl alcohol-based polymer.

[0007] The present invention encompasses the following inventions: [1] A vinyl alcohol-based polymer, wherein, in an aqueous solution state where the content of the vinyl alcohol-based polymer is 1.5% by mass and the pH at 20°C is 4, the aqueous solution viscosity X [cp] at a shear rate of 1 [1 / s] at 20°C and the aqueous solution viscosity Y [cp] at a shear rate of 1 [1 / s] at 20°C and the aqueous solution content of the vinyl alcohol-based polymer is 1.5% by mass and the pH at 20°C is 10 satisfy the following formula (1): 1.5<Y / X<1,500 (1) [2] The vinyl alcohol-based polymer according to the above [1], wherein the aqueous solution viscosity Y is 20 cp or more. [3] The vinyl alcohol-based polymer according to the above [1] or [2], wherein the aqueous solution viscosity Y [cp] and the aqueous solution viscosity Z [cp] of the aqueous solution at a shear rate of 100 [1 / s] at 20°C in an aqueous solution state having a vinyl alcohol-based polymer content of 1.5% by mass and a pH of 10 at 20°C satisfy the following formula (2): 1.5<Y / Z<100 (2). [4] The vinyl alcohol-based polymer according to any of the above [1] to [3], which contains a structural unit (A) having a lactone ring. [5] The vinyl alcohol-based polymer according to any of the above [1] to [4], which contains a structural unit (B) having an ionic group. [6] The vinyl alcohol-based polymer according to any of the above [1] to [5], which contains a structural unit (C) having a hydrophobic group composed of a hydrocarbon having 3 or more carbon atoms. [7] The vinyl alcohol-based polymer according to any one of the above [1] to [3], which comprises a structural unit (A) having a lactone ring, a structural unit (B) having an ionic group, and a structural unit (C) having a hydrophobic group made of a hydrocarbon having 3 or more carbon atoms, and satisfies the following formula (3), where the content of the structural unit (A) relative to all structural units of the vinyl alcohol-based polymer is (a), the content of the structural unit (B) is (b), the content of the structural unit (C) is (c), the number of carbon atoms in the hydrophobic group in the structural unit (C) is (d), and the number of ionic groups in the structural unit (B) is (e). 5<(c×(d−3) ２) / (a+b×e)<95 (3) [8] A vinyl alcohol-based polymer-containing aqueous solution containing the vinyl alcohol-based polymer according to any one of [1] to [7] above and water. [9] The vinyl alcohol-based polymer-containing aqueous solution according to [8] above, having a vinyl alcohol-based polymer content of 1 to 3% by mass, a pH of 7 or more at 20°C, and an aqueous solution viscosity of 20 to 1,000,000 cp at a shear rate of 1 [1 / s] at 20°C.

[10] The vinyl alcohol-based polymer-containing aqueous solution according to [8] above, having a vinyl alcohol-based polymer content of 1 to 3% by mass, a pH of less than 7 at 20°C, and an aqueous solution viscosity of 20 to 100,000 cp at a shear rate of 1 [1 / s] at 20°C.

[11] A paint containing the vinyl alcohol-based polymer according to any one of [1] to [7] above.

[12] A cement admixture containing the vinyl alcohol-based polymer according to any one of [1] to [7] above.

[0008] According to the present invention, it is possible to provide a vinyl alcohol-based polymer from which an aqueous vinyl alcohol-based polymer solution whose viscosity can be easily and greatly changed can be obtained, an aqueous vinyl alcohol-based polymer solution whose viscosity can be easily and greatly changed, and a paint and a cement admixture containing the vinyl alcohol-based polymer.

[0009] An example of an embodiment to which the present invention is applied will be described below. Note that other embodiments are also included in the present invention as long as they are consistent with the spirit of the present invention. In this specification, the property of being able to easily and significantly change the viscosity is referred to as "viscosity changeability." In this specification, the term "aqueous solution state" refers to a state in which components other than the solvent (water) are dissolved or dispersed in water.

[0010] [Vinyl Alcohol Polymer] The vinyl alcohol polymer according to the present invention is a vinyl alcohol polymer, in which, in an aqueous solution state in which the content of the vinyl alcohol polymer is 1.5% by mass and the pH at 20°C is 4, the aqueous solution viscosity X [cp] of the aqueous solution at a shear rate of 1 [1 / s] at 20°C, and the aqueous solution viscosity Y [cp] of the aqueous solution at a shear rate of 1 [1 / s] at 20°C, in which the content of the vinyl alcohol polymer is 1.5% by mass and the pH at 20°C is 10, satisfy the following formula (1): 1.5<Y / X<1,500 (1)

[0011] The vinyl alcohol polymer according to the present invention has a large viscosity ratio (Y / X) of more than 1.5. Therefore, the vinyl alcohol polymer according to the present invention can easily and significantly change the viscosity of an aqueous solution of the vinyl alcohol polymer by changing the pH of the aqueous solution. Therefore, when an aqueous solution of the vinyl alcohol polymer is transported through a pipe or the like, the pH can be lowered by adding an acid or the like to easily reduce the viscosity of the aqueous solution, thereby enabling smooth transport. Furthermore, when the vinyl alcohol polymer is used as a thickener or the like, the pH can be increased by adding an alkali or the like to easily increase the viscosity of the aqueous solution.

[0012] <Viscosity Ratio (Y / X)> The viscosity ratio (Y / X) is greater than 1.5 and less than 1,500. If the viscosity ratio is 1.5 or less, the viscosity of the aqueous solution of the vinyl alcohol polymer cannot be easily changed, making it impossible to achieve both thickening and liquid transportability by adjusting the pH. If the viscosity ratio is 1,500 or more, the viscosity changes significantly with a slight change in pH, making viscosity adjustment difficult and reducing convenience. From this perspective, the viscosity ratio (Y / X) is preferably greater than 1.5 and less than 1,000, more preferably greater than 1.5 and less than 800, even more preferably greater than 1.5 and less than 500, still more preferably 3.0 to 500, even more preferably 5.0 to 500, still more preferably 5.0 to 300, still more preferably 10 to 300, even more preferably 15 to 300, and even more preferably 25 to 300.

[0013] The viscosity ratio (Y / X) tends to increase when a structural unit having a hydrophobic group with a large number of carbon atoms is introduced, the content of structural units having a hydrophobic group is increased, the degree of polymerization is increased, the content of structural units having an ionic group is increased, or the vinyl ester monomer unit is decreased. Conversely, the viscosity ratio (Y / X) tends to decrease when a structural unit having a hydrophobic group with a small number of carbon atoms is introduced, the content of structural units having a hydrophobic group is decreased, the degree of polymerization is lowered, the content of structural units having an ionic group is decreased, or the vinyl ester monomer unit is increased.

[0014] <Viscosity X> The viscosity X [cp] is preferably 6,000 cp or less from the viewpoint of improving the liquid transportability of the aqueous solution of the vinyl alcohol polymer. Furthermore, the viscosity X [cp] is preferably 1 cp or more from the viewpoint of thickening of the aqueous solution of the vinyl alcohol polymer after changing its viscosity. From this viewpoint, the viscosity X [cp] is preferably 1 to 6,000, more preferably 10 to 5,500, even more preferably 20 to 5,500, still more preferably 25 to 5,500, even more preferably 100 to 5,500, still more preferably 100 to 3,000, still more preferably 100 to 2,500, and still more preferably 130 to 2,500.

[0015] When a highly acidic ionic group is modified, when the degree of polymerization is increased, or when the vinyl ester monomer unit is reduced, the viscosity X [cp] tends to increase, and when the degree of polymerization is reduced or when the vinyl ester monomer unit is increased, the viscosity X [cp] tends to decrease.

[0016] <Viscosity Y> The viscosity Y [cp] is preferably 20 cp or more from the viewpoint of viscosity changeability and thickening of the aqueous solution of the vinyl alcohol polymer. Furthermore, from the viewpoint of handleability, the viscosity Y [cp] is preferably 500,000 cp or less. From this viewpoint, the viscosity X [cp] is preferably 20 to 500,000, more preferably 100 to 300,000, even more preferably 100 to 200,000, still more preferably 200 to 200,000, even more preferably 500 to 200,000, still more preferably 2,000 to 200,000, even more preferably 5,000 to 200,000, still more preferably 6,000 to 200,000, and even more preferably 10,000 to 150,000.

[0017] The viscosity Y [cp] tends to increase when a structural unit having a hydrophobic group with a large number of carbon atoms is introduced, the content of structural units having a hydrophobic group is increased, the degree of polymerization is increased, the content of structural units having an ionic group is increased, or the amount of vinyl ester monomer units is decreased. On the other hand, the viscosity Y [cp] tends to decrease when a structural unit having a hydrophobic group with a small number of carbon atoms is introduced, the content of structural units having a hydrophobic group is decreased, the degree of polymerization is decreased, the content of structural units having an ionic group is decreased, or the amount of vinyl ester monomer units is increased.

[0018] <Viscosity Ratio (Y / Z)> The aqueous solution viscosity Y [cp] and the aqueous solution viscosity Z [cp] of the aqueous solution at a shear rate of 100 [1 / s] at 20°C, in an aqueous solution state in which the content of the vinyl alcohol polymer is 1.5% by mass and the pH at 20°C is 10, preferably satisfy the following formula (2): 1.5<Y / Z<100 (2) When the viscosity ratio (Y / Z) is greater than 1.5, the thixotropy is excellent. When the viscosity ratio (Y / Z) is less than 100, the handleability is excellent. From this viewpoint, the viscosity ratio (Y / Z) is more preferably 2.0 to 80, even more preferably 5 to 80, still more preferably 10 to 80, even more preferably 20 to 80, still more preferably 20 to 60, and even more preferably 20 to 50.

[0019] When a structural unit having a hydrophobic group with a large number of carbon atoms is introduced, when the content of structural units having a hydrophobic group is increased, when the content of structural units having an ionic group is increased, or when the vinyl ester monomer unit is decreased, the viscosity ratio (Y / Z) tends to increase. On the other hand, when a structural unit having a hydrophobic group with a small number of carbon atoms is introduced, when the content of structural units having a hydrophobic group is decreased, when the content of structural units having an ionic group is decreased, or when the vinyl ester monomer unit is increased, the viscosity ratio (Y / Z) tends to decrease.

[0020] <Viscosity Z> The viscosity Z [cp] is preferably 10,000 cp or less from the viewpoint of improving the liquid transportability of an aqueous solution of a vinyl alcohol polymer. Furthermore, from the viewpoint of thickening, the viscosity Z [cp] is preferably 10 cp or more. From this viewpoint, the viscosity Z [cp] is preferably 10 to 10,000, more preferably 50 to 10,000, even more preferably 100 to 10,000, still more preferably 100 to 6,000, still more preferably 100 to 4,000, still more preferably 500 to 4,000, and still more preferably 1,000 to 3,000.

[0021] When a structural unit having a hydrophobic group with a large number of carbon atoms is introduced, when the content of the structural unit having a hydrophobic group is increased, or when the content of the structural unit having an ionic group is increased, the viscosity Z [cp] tends to increase; and when a structural unit having a hydrophobic group with a small number of carbon atoms is introduced, when the content of the structural unit having a hydrophobic group is reduced, or when the content of the structural unit having an ionic group is reduced, the viscosity Z [cp] tends to decrease.

[0022] The aqueous solution viscosity X [cp], aqueous solution viscosity Y [cp], aqueous solution viscosity Z [cp], and aqueous solution viscosity W [cp] can be measured using a rheometer, and more specifically, can be measured by the method described in the examples.

[0023] <pH Adjuster> There are no particular limitations on the method for adjusting the pH of the aqueous solution of the vinyl alcohol polymer, but it is preferable to add an acidic compound or a basic compound to the aqueous solution.

[0024] Examples of acidic compounds include inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and hydrofluoric acid; and organic acids such as formic acid, acetic acid, trichloroacetic acid, propionic acid, butanoic acid, chloroacetic acid, methanesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, and citric acid. Among these, p-toluenesulfonic acid, citric acid, hydrochloric acid, nitric acid, sulfuric acid, and acetic acid are preferred, and citric acid is more preferred. One type of acidic compound may be used alone, or two or more types may be used in combination.

[0025] Examples of basic compounds include alkali metal hydrides such as sodium hydride and potassium hydride; alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium hydrogencarbonate and potassium hydrogencarbonate; tertiary amines such as triethylamine, tributylamine, and diazabicyclo[2.2.2]octane; and nitrogen-containing heterocyclic aromatic compounds such as pyridine and 2,6-lutidine. Among these, alkali metal hydroxides are preferred, and sodium hydroxide is more preferred. The basic compounds may be used alone or in combination of two or more.

[0026] <Structural Units of Vinyl Alcohol-Based Polymer> (Structural Unit (A) Having a Lactone Ring) The vinyl alcohol-based polymer according to the present invention preferably contains a structural unit (A) having a lactone ring. When the vinyl alcohol-based polymer according to the present invention has a lactone ring, the surface of the vinyl alcohol-based polymer is prevented from dissolving and adhering to form a mass, and as a result, the vinyl alcohol-based polymer is prevented from becoming difficult to dissolve when it is made into an aqueous solution. The lactone ring can be obtained, for example, by copolymerizing a vinyl ester and a (meth)acrylic acid ester, followed by saponification. Specific examples of the vinyl ester are the same as the specific examples of the (vinyl ester monomer unit) described below. Specific examples of the (meth)acrylic acid ester are the same as the specific examples of the acrylic acid ester and methacrylic acid ester in the (structural unit (B) having an ionic group) described below. The structural unit (A) having a lactone ring is preferably at least one selected from the group consisting of units represented by the following structural formula (1), units represented by the following structural formula (2), and units represented by the following structural formula (3), more preferably at least one selected from the group consisting of units represented by the following structural formula (1) and units represented by the following structural formula (2), and even more preferably a unit represented by the following structural formula (1). In structural formulas (1), (2), and (3), * represents a bond bonding to an adjacent structural unit. In structural formulas (2) and (3), R represents a methyl group, a carboxy group, or a salt of a carboxy group.

[0027]

[0028] (Structural Unit (B) Having an Ionic Group) The vinyl alcohol-based polymer according to the present invention preferably contains a structural unit (B) having an ionic group. Since the vinyl alcohol-based polymer according to the present invention contains the structural unit (B) having an ionic group, the solubility in water when it is made into an aqueous solution is improved, and when the pH of the aqueous solution is lowered, the structural unit (B) reacts with the hydroxyl groups in the vinyl alcohol-based polymer to form a lactone ring structure, or the ionic groups are protonated, thereby reducing the viscosity, and therefore the aqueous solution can be smoothly transferred.

[0029] The ionic group is not particularly limited, and examples thereof include a carboxy group, a salt of a carboxy group, a sulfo group, a salt of a sulfo group, an amino group, a salt of an amino group, and a salt of a quaternary ammonium group. As the salt, an alkali metal salt is preferred from the viewpoint of industrial availability and cost, and a sodium salt is more preferred. These ionic groups may be used alone or in combination of two or more. Among these, a carboxy group and a salt of a carboxy group are preferred from the viewpoint of viscosity modification and acidity.

[0030] Examples of the monomer constituting the structural unit (B) having an ionic group include a monomer having a carboxy group or a salt thereof, an ester of a monomer having a carboxy group, a monomer having a sulfo group or a salt thereof, a monomer having an amino group or a salt thereof, and a monomer having a salt of a quaternary ammonium group. These monomers may be used alone or in combination of two or more. Among these, from the viewpoint of viscosity modification and acidity, a monomer having a carboxy group or a salt thereof and an ester of a monomer having a carboxy group are preferred. Furthermore, the structural unit (B) having an ionic group may be a structural unit represented by the structural formula (6) described below.

[0031] <<Monomer Having a Carboxy Group or a Salt Thereof, and Ester of a Monomer Having a Carboxy Group>> The monomer having a carboxy group or a salt thereof, and the ester of a monomer having a carboxy group may be any monomer that is copolymerizable with a vinyl ester monomer and in which a carboxy group or a salt thereof is present in the vinyl alcohol polymer after saponification, and examples thereof include acrylic acid or a salt thereof; acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, and isopropyl acrylate; methacrylic acid or a salt thereof; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and isopropyl methacrylate; maleic acid or a salt thereof; monomethyl maleate, maleic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and isopropyl methacrylate; Examples of suitable carboxylic acids include maleic acid esters such as dimethyl maleate, monoethyl maleate, and diethyl maleate; itaconic acid or a salt thereof; itaconic acid esters such as monomethyl itaconate, dimethyl itaconate, monoethyl itaconate, and diethyl itaconate; fumaric acid or a salt thereof; fumaric acid esters such as monomethyl fumarate, dimethyl fumarate, monoethyl fumarate, and diethyl fumarate; maleic anhydride, itaconic anhydride, or a derivative thereof; formylcarboxylic acids such as phthalaldehyde acid, isophthalaldehyde acid, terephthalaldehyde acid, glyoxylic acid, formylacetic acid, and formylpropanoic acid, or salts thereof. These may be used alone or in combination of two or more. Among these, from the viewpoints of reactivity and industrial availability, methyl acrylate, acrylic acid, maleic acid, monomethyl maleate, dimethyl maleate, itaconic acid, monomethyl itaconate, phthalaldehyde acid, isophthalaldehyde acid, terephthalaldehyde acid, glyoxylic acid, or a salt thereof is preferred, and methyl acrylate, acrylic acid, or a salt thereof is more preferred.

[0032] <<Monomer Having a Sulfo Group or a Salt Thereof>> The monomer having a sulfo group or a salt thereof is not particularly limited, and examples thereof include unsaturated sulfonic acids or salts of these unsaturated sulfonic acids, such as vinyl sulfonic acid, allyl sulfonic acid, (meth)acrylic sulfonic acid, styrene sulfonic acid, benzaldehyde sulfonic acid (orthobenzaldehyde sulfonic acid, metabenzaldehyde sulfonic acid, parabenzaldehyde sulfonic acid), 2-acrylamido-2-phenylpropanesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS); and unsaturated disulfonic acids or salts of these unsaturated disulfonic acids, such as benzaldehyde-2,4-disulfonic acid. These monomers having a sulfo group or a salt thereof may be used alone, or two or more types may be used. Among these, from the viewpoints of reactivity and industrial availability, orthobenzaldehyde sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), benzaldehyde-2,4-disulfonic acid, or a salt thereof is preferred, and benzaldehyde sulfonic acid or a salt thereof is more preferred.

[0033] <<Monomer Having an Amino Group or a Salt Thereof>> The monomer having an amino group or a salt thereof is a monomer having an amino group (—NH ２ ) or a salt thereof, a methylamino group (—NHCH ３ ) or a salt thereof, a dimethylamino group (—N(CH ３ ) ２ ) or a salt thereof, a diethylamino group (-N(CH ２ CH ３ ) ２ ) or its salt, diphenylamino group (-NPh ２ ) or a salt thereof, for example, unsaturated amines or salts thereof such as vinyldimethylamine, vinyldiethylamine, vinyldiphenylamine, allyldimethylamine, methacryldiethylamine, etc. These monomers having an amino group or a salt thereof may be used alone or in combination of two or more. Among these, vinyldimethylamine is preferred from the viewpoint of industrial availability.

[0034] <<Monomer Having a Salt of a Quaternary Ammonium Group>> In this specification, the term "quaternary ammonium group" refers to a cation formed by four carbon atoms bonded to one nitrogen atom. However, the four carbon atoms do not necessarily have to be different carbon atoms, and may be the same carbon atom. Examples of monomers having a salt of a quaternary ammonium group include quaternary ammonium chloride (-N+(CH ３ ) ３ There are no particular limitations on the monomer as long as it has a salt of a quaternary ammonium group such as 3-(methacrylamido)propyltrimethylammonium chloride (MAPTAC), and examples thereof include 3-(methacrylamido)propyltrimethylammonium chloride (MAPTAC). These monomers having a salt of a quaternary ammonium group may be used alone, or in combination of two or more. Among these, 3-(methacrylamido)propyltrimethylammonium chloride (MAPTAC) is preferred from the viewpoint of industrial availability. <<Structural Unit Represented by Structural Formula (6)>> The structural unit (B) having an ionic group may be a structural unit represented by the following structural formula (6): In the structural formula (6), * represents a bond connecting to an adjacent structural unit. ５ is an ionic group. The ionic group is preferably the above-mentioned ionic group, and more preferably a carboxy group or a salt thereof.

[0035] (Structural unit (C) having a hydrophobic group made of hydrocarbon having 3 or more carbon atoms) The vinyl alcohol polymer according to the present invention preferably contains a structural unit (C) having a hydrophobic group made of hydrocarbon having 3 or more carbon atoms. Since the vinyl alcohol polymer according to the present invention contains a structural unit (C) having a hydrophobic group made of hydrocarbon having 3 or more carbon atoms, physical crosslinks are formed by interaction between the hydrophobic groups when left to stand, thereby improving the viscosity. Furthermore, when shear stress is applied by stirring or the like, the physical crosslinks are temporarily broken and the viscosity decreases. As a result, the vinyl alcohol polymer according to the present invention exhibits thixotropy. Examples of the structural unit (C) include a structural unit represented by the following structural formula (4) and a structural unit represented by the following structural formula (5).

[0036]

[0037] In the structural formula (4), * represents a bond connecting to an adjacent structural unit. １ is a single bond, an amide bond (—C(═O)—NH—), or an ether bond (—O—). ２ R is a hydrophobic group made of a hydrocarbon having 3 or more carbon atoms, and is preferably an alkyl or alkenyl group having 3 or more carbon atoms. ３ is hydrogen or a methyl group. The number of carbon atoms in the alkyl or alkenyl group is preferably 3 to 25. When the number of carbon atoms is 3 or more, thixotropy is well exhibited. When the number of carbon atoms is 25 or less, the vinyl alcohol polymer is well soluble in water. From these viewpoints, the number of carbon atoms in the alkyl or alkenyl group is more preferably 4 to 25, even more preferably 6 to 20, still more preferably 6 to 12, and even more preferably 10 to 12. The number of carbon atoms in the alkyl or alkenyl group may be linear or branched, but from the above viewpoint, it is preferably linear. The alkyl group is preferably a hexyl group, octyl group, decyl group, dodecyl group, or the like.

[0038]

[0039] In the structural formula (5), * represents a bond connecting to an adjacent structural unit. ２ is R in structural formula (4) ２The structural formula (5) can be produced by binding an aldehyde or a derivative thereof to two hydroxyl groups bonded to two carbon atoms bonded to both ends of a methylene group in a vinyl alcohol polymer. The number of carbon atoms in the aldehyde or derivative thereof is preferably 4 to 20. When the number of carbon atoms is 4 or more, thixotropy is well exhibited. When the number of carbon atoms is 20 or less, the vinyl alcohol polymer is well soluble in water. From this viewpoint, the number is more preferably 4 to 16, even more preferably 6 to 14, and even more preferably 10 to 12. The aldehyde is preferably 1-butanal, isobutyraldehyde, tert-butyraldehyde, pentanal, 3-methyl-butanal, 1-hexanal, 1-heptanal, 1-octanal, 2-ethylhexanal, 1-nonanal, 1-decanal, 3,7-dimethyl-1-octanal, 1-undecanal, 1-dodecanal, 3-methyl-3-butenal, citral, citronellal, or 7-octenal, and more preferably at least one selected from dodecanal, decanal, and hexanal.

[0040] (Vinyl Alcohol Monomer Unit) The vinyl alcohol polymer according to the present invention preferably contains a vinyl alcohol monomer unit.

[0041] (Vinyl ester monomer unit) The vinyl alcohol polymer according to the present invention preferably contains a vinyl ester monomer unit. Examples of the vinyl ester monomer unit include vinyl acetate, vinyl formate, vinyl propionate, vinyl caprylate, and vinyl versatate. Among these, vinyl acetate is preferred from an industrial viewpoint. These may be used alone or in combination of two or more.

[0042] The vinyl alcohol polymer of the present invention may further contain structural units other than the structural units (A), (B), (C), vinyl alcohol monomer units, and vinyl ester monomer units, as long as the effects of the present invention are obtained. Examples of such structural units include structural units derived from ethylenically unsaturated monomers copolymerizable with vinyl esters, and structural units that have been post-modified by acetalization or the like. Examples of the ethylenically unsaturated monomer include α-olefins such as ethylene, propylene, n-butene, and isobutylene; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl cyanides 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; and vinylsilyl compounds such as vinyltrimethoxysilane.

[0043] (Content of Structural Unit) The content (a) of the structural unit (A) in the vinyl alcohol polymer according to the present invention is preferably 0.1 to 10 mol%. When it is 0.1 mol% or more, excellent solubility in water is achieved. When it is 10 mol% or less, excellent effects are achieved due to structural units other than the structural unit (A). From this viewpoint, the content (a) of the structural unit (A) is more preferably 0.1 to 8.0 mol%, even more preferably 0.1 to 6.0 mol%, still more preferably 1.0 to 6.0 mol%, even more preferably 2.0 to 6.0 mol%, still more preferably 3.0 to 5.5 mol%, and even more preferably 3.0 to 5.0 mol%.

[0044] The content (b) of the structural unit (B) in the vinyl alcohol polymer according to the present invention is preferably 0.1 to 10 mol%. When the content (b) is 0.1 mol% or more, the solubility in water of the aqueous solution is improved. Furthermore, when the pH of the aqueous solution is lowered, the structural unit (B) reacts with the hydroxyl groups in the vinyl alcohol polymer to form a lactone ring structure or is protonated, thereby reducing the viscosity, thereby enabling smooth transfer of the aqueous solution. When the content (b) is 10 mol% or less, the effects attributable to structural units other than the structural unit (B) are excellent. From this viewpoint, the content (b) of the structural unit (B) is more preferably 0.1 to 8.0 mol%, even more preferably 0.1 to 6.0 mol%, even more preferably 1.0 to 6.0 mol%, even more preferably 2.0 to 6.0 mol%, even more preferably 2.0 to 5.5 mol%, and even more preferably 2.0 to 5.0 mol%.

[0045] The content (c) of the structural unit (C) in the vinyl alcohol polymer according to the present invention is preferably 0.1 to 10 mol%. When it is 0.1 mol% or more, the viscosity of the resulting aqueous solution is improved. When it is 10 mol% or less, the effects attributable to structural units other than the structural unit (C) are excellent. From this viewpoint, the content (c) of the structural unit (C) is more preferably 0.1 to 8.0 mol%, even more preferably 0.5 to 8.0 mol%, still more preferably 1.2 to 8.0 mol%, even more preferably 1.2 to 5.5 mol%, and even more preferably 1.2 to 3.0 mol%.

[0046] The content of vinyl alcohol monomer units in the vinyl alcohol-based polymer according to the present invention is preferably 60 to 99 mol%. When it is 60 mol% or more, the effects resulting from water solubility are excellent. When it is 99 mol% or less, the effects resulting from structural units other than vinyl alcohol monomer units are excellent. From this viewpoint, the content of vinyl alcohol monomer units is more preferably 65 to 98 mol%, even more preferably 70 to 97 mol%, still more preferably 75 to 97 mol%, and even more preferably 77 to 96 mol%.

[0047] The content of vinyl ester monomer units in the vinyl alcohol polymer according to the present invention is preferably 0.01 to 20 mol%. When it is 0.01 mol% or more, the storage stability of the aqueous solution is excellent. When it is 20 mol% or less, the effects attributable to structural units other than the vinyl ester monomer units are excellent. From this viewpoint, the content of vinyl ester monomer units is more preferably 0.01 to 12.0 mol%, even more preferably 0.05 to 5.0 mol%, still more preferably 0.05 to 1.0 mol%, and even more preferably 0.05 to 0.5 mol%.

[0048] The vinyl alcohol polymer according to the present invention preferably contains a structural unit (A) having a lactone ring, a structural unit (B) having an ionic group, and a structural unit (C) having a hydrophobic group made of a hydrocarbon having 3 or more carbon atoms, and satisfies the following formula (3), where (a) is the content of the structural unit (A), (b) is the content of the structural unit (B), (c) is the content of the structural unit (C), (d) is the number of carbon atoms in the hydrophobic group in the structural unit (C), and (e) is the number of ionic groups in the structural unit (B), relative to all structural units of the vinyl alcohol polymer. 5<(c×(d−3) ２ ) / (a+b×e)<95 (3)

[0049] The number of carbon atoms (d) of the hydrophobic group in the structural unit (C) is R １ , and R ２ The sum of the carbon atoms contained in the structural formula (5) is d. ２ The sum of the number of carbon atoms in the alkyl group and the number of carbon atoms in the acetal moiety was defined as d.

[0050] The middle part of the formula (3) is "(c×(d−3) ２ ) / (a+b×e)) where the numerator is "(c×(d-3) ２ The denominator "(a+b×e)" is an index showing the strength of the interaction between the hydrophobic groups of the resin, and the denominator "(c×(d−3) ２ ) / (a+b×e)) is an index showing the balance between hydrophobicity and hydrophilicity. ２When the middle side "(c×(d−3) / (a+b×e)" is greater than 5, an excellent effect of thickening is obtained. When the middle side "(c×(d−3)" is less than 95, an excellent effect of exhibiting high viscosity changeability while maintaining solubility in water is obtained. From this viewpoint, the middle side "(c×(d−3) ２ ) / (a+b×e)" is more preferably 6 to 70, even more preferably 10 to 60, still more preferably 10 to 55, even more preferably 13 to 55, even more preferably 15 to 55, even more preferably 15 to 50, even more preferably 15 to 45, and even more preferably 15 to 40.

[0051] (Physical Properties of Vinyl Alcohol Polymer) <<Modification Amount>> The modification amount of the vinyl alcohol polymer according to the present invention is not particularly limited, but is preferably 0 to 30.0 mol%. When it is 30.0 mol% or less, the effects attributable to the vinyl alcohol polymer are excellent. From this viewpoint, the modification amount is more preferably 0 to 20.0 mol%, even more preferably 0 to 15.0 mol%, still more preferably 0 to 10.0 mol%, even more preferably 0 to 8.0 mol%, or may be 0 to 6.0 mol%, or may be 0.1 to 8.0 mol%, even more preferably 0.1 to 6.0 mol%, and even more preferably 1.0 to 6.0 mol%. <<Polymerization Degree>> The polymerization degree of the vinyl alcohol polymer according to the present invention is not particularly limited, but is preferably 100 to 5,000. When it is 100 or more, the aqueous solution viscosity is excellent. When the polymerization degree is 5,000 or less, industrial production is easy. More preferably, it is 200 to 4,500, even more preferably 300 to 4,000, even more preferably 400 to 2,500, even more preferably 500 to 2,500, even more preferably 600 to 2,500, even more preferably 700 to 2,500, still more preferably 700 to 2,000, still more preferably 800 to 1,800, and still more preferably 900 to 1,800.

[0052] [Method for Producing Vinyl Alcohol Polymer] The method for producing the vinyl alcohol polymer according to the present invention is not particularly limited, and the polymer can be produced, for example, by the following production method.

[0053] (1) A vinyl alcohol polymer is produced by polymerizing a vinyl ester monomer and a monomer having an ionic group or an ester thereof, followed by saponification. The hydroxyl groups in the vinyl alcohol polymer are then acetalized with an aldehyde to obtain the vinyl alcohol polymer of the present invention. (2) The hydroxyl groups in the vinyl alcohol polymer are acetalized with an aldehyde, and the vinyl alcohol polymer is then acetalized with an aldehyde having an ionic group, thereby imparting ionic groups to the side chains of the vinyl alcohol polymer, thereby obtaining the vinyl alcohol polymer of the present invention. (3) A vinyl ester monomer, a monomer having an ionic group or the ester, and a monomer having a hydrophobic group are polymerized, followed by saponification to obtain the vinyl alcohol polymer of the present invention. (4) A vinyl ester monomer and a monomer having a hydrophobic group are polymerized, followed by saponification to obtain the vinyl alcohol polymer of the present invention.

[0054] (Polymerization) Examples of methods for producing vinyl alcohol polymers (polymerization methods) include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these, bulk polymerization, which involves polymerization without a solvent, or solution polymerization, which involves polymerization in various organic solvents, is preferred from the viewpoint of obtaining a polymer with a narrow molecular weight distribution. Bulk polymerization is preferred from the viewpoint of not using solvents or dispersion media that may cause side reactions such as chain transfer, while solution polymerization is preferred from the viewpoint of adjusting the viscosity of the reaction solution and controlling the polymerization rate. Examples of organic solvents used in solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as toluene; and lower alcohols such as methanol and ethanol. Among these, lower alcohols are preferred from the viewpoint of cost, and methanol is more preferred. The amount of organic solvent added may be selected taking into consideration chain transfer of the solvent depending on the degree of polymerization of the desired vinyl alcohol polymer. For example, the mass ratio of the organic solvent to the vinyl ester monomer (organic solvent / vinyl ester monomer) is preferably in the range of 0.01 to 10. The mass ratio (organic solvent / vinyl ester monomer) is preferably 0.1 or more and preferably 5 or less.

[0055] (Radical Polymerization Initiator) The radical polymerization initiator (initiator) may be appropriately selected from conventionally known azo initiators, peroxide initiators, redox initiators, etc. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-70"). Examples of peroxide initiators include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and t-butyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide; diisobutyryl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. These may also be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like to form a peroxide initiator. Examples of redox initiators include combinations of the above peroxides with reducing agents such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and Rongalit. Among these, azo initiators are preferred, and 2,2'-azobisisobutyronitrile is more preferred from the viewpoints of polymerization at relatively low temperatures and suppression of side reactions. The amount of the initiator to be added varies depending on the polymerization catalyst and cannot be generally determined, but is selected as appropriate depending on the polymerization rate. The amount of the initiator to be added is preferably 0.001 to 1.0 part by mass, more preferably 0.005 to 0.1 part by mass, and even more preferably 0.008 to 0.05 part by mass, relative to 100 parts by mass of the raw material monomers for the vinyl alcohol polymer.

[0056] The polymerization temperature is preferably 0°C to 80°C. When the polymerization temperature is 0°C or higher, the polymerization rate is sufficient and productivity is improved. On the other hand, when the polymerization temperature is 80°C or lower, a vinyl alcohol polymer with a narrow molecular weight distribution can be obtained. From this viewpoint, the polymerization temperature is preferably 10 to 80°C, more preferably 20 to 80°C, even more preferably 40 to 70°C, and still more preferably 50 to 70°C.

[0057] When the target polymerization rate is reached, the polymerization reaction is terminated by rapidly cooling the reaction system, adding a polymerization terminator, or both at the same time. When rapidly cooling the reaction system, cooling water can be run through the reactor jacket, but a method of adding a pre-cooled liquid medium to the reactor is preferred.

[0058] (Saponification) Saponification is preferably carried out in a state where the vinyl alcohol polymer before saponification is dissolved in alcohol or aqueous alcohol.

[0059] Examples of alcohols used in the saponification reaction include lower alcohols such as methanol and ethanol, with methanol being preferred. The alcohol used in the saponification reaction may contain other solvents such as acetone, esters such as methyl acetate and ethyl acetate, and toluene, but the content of other solvents contained in the alcohol is preferably 10% by mass or less, more preferably 5% by mass or less. The concentration of the alcohol solution after addition is preferably 1.0 to 50% by mass, more preferably 5 to 45% by mass, and even more preferably 8 to 40% by mass. Examples of catalysts used in the saponification reaction include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali catalysts such as sodium methylate, and acid catalysts such as mineral acids. Among these, sodium hydroxide is preferred from the viewpoint of ease of handling.

[0060] The temperature of the saponification reaction is preferably, for example, 20 to 70° C. At 20° C. or higher, the saponification reaction can proceed rapidly. If a gel-like product precipitates as the saponification reaction proceeds, the product is separated at that point, pulverized, washed, and dried to obtain the vinyl alcohol polymer of the present invention.

[0061] (Acetalization) The reaction between a vinyl alcohol polymer and an aldehyde (acetalization reaction) can be carried out by a known method. Examples include an aqueous medium method in which an aqueous solution of a vinyl alcohol polymer and an aldehyde are subjected to an acetalization reaction in the presence of an acid catalyst to precipitate particles of an acetalized vinyl alcohol polymer; a solvent method in which a vinyl alcohol polymer is dispersed in an organic solvent, subjected to an acetalization reaction with an aldehyde in the presence of an acid catalyst, and the resulting reaction mixture is mixed with water, a poor solvent for the vinyl alcohol polymer, to precipitate an acetalized vinyl alcohol polymer; and a method in which a vinyl alcohol polymer is dispersed in an organic solvent, subjected to an acetalization reaction with an aldehyde in the presence of an acid catalyst to obtain an acetalized vinyl alcohol polymer. The acid catalyst is not particularly limited, and examples include organic acids such as acetic acid and p-toluenesulfonic acid; inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid; gases that exhibit acidity when dissolved in aqueous solution, such as carbon dioxide; and solid acid catalysts such as cation exchange resins and metal oxides.

[0062] [Aqueous Solution of Vinyl Alcohol-Based Polymer] The aqueous solution of the vinyl alcohol-based polymer according to the present invention contains the above-mentioned vinyl alcohol-based polymer and water. Since the aqueous solution of the vinyl alcohol-based polymer according to the present invention contains the above-mentioned vinyl alcohol-based polymer, it is possible to easily change the viscosity greatly.

[0063] The content of the vinyl alcohol polymer in the aqueous solution of the vinyl alcohol polymer according to the present invention is preferably 0.1 to 10% by mass, more preferably 0.5 to 5.0% by mass, even more preferably 1.0 to 4.0% by mass, and even more preferably 1.3 to 3.0% by mass. The content of water in the aqueous solution is preferably 80% by mass or more, more preferably 90% by mass or more. The aqueous solution may contain a pH adjuster. Suitable pH adjusters include those described above. The suitable pH range of the aqueous solution varies depending on the application, but is preferably 1 to 14, more preferably 3 to 12, and even more preferably 4 to 10. The aqueous solution may further contain additives such as surfactants, various plasticizers, antifoaming agents, ultraviolet absorbers, fillers, and water-resistant agents, as long as they do not impair the spirit of the present invention.

[0064] An aqueous solution of a vinyl alcohol polymer according to one embodiment of the present invention has a vinyl alcohol polymer content of 1 to 3 mass%, a pH of 7 or more at 20° C., and an aqueous solution viscosity of 20 to 1,000,000 cp at a shear rate of 1 [1 / s] at 20° C. Furthermore, an aqueous solution of a vinyl alcohol polymer according to another embodiment of the present invention has a vinyl alcohol polymer content of 1 to 3 mass%, a pH of less than 7 at 20° C., and an aqueous solution viscosity of 20 to 100,000 cp at a shear rate of 1 [1 / s] at 20° C.

[0065] [Paint and Cement Admixture] The paint according to the present invention contains the vinyl alcohol polymer and water, and the cement admixture according to the present invention contains the vinyl alcohol polymer and water.

[0066] The coating material according to the present invention may further contain other components as necessary in addition to the vinyl alcohol polymer and water. The other components are not particularly limited, and examples thereof include aqueous emulsion resins, pigments, curing catalysts, crosslinking agents, fillers, antifoaming agents, matting agents, crosslinking reaction catalysts, antiskinning agents, dispersants, wetting agents, surfactants, light stabilizers, antifungal agents, antialgae agents, anti-yellowing agents, reducing agents, UV absorbers, freeze stabilizers, antioxidants, film-forming aids, organic solvents, rust inhibitors, plasticizers, antistatic agents, lubricants, deodorizers, antiseptics, and charge control agents. These may be used alone or in combination of two or more.

[0067] The content of the vinyl alcohol polymer can be set arbitrarily depending on the physical properties required for the coating material. It is not particularly limited, but is preferably 0.001 to 10% by mass. The content of the pigment is not particularly limited, but the mass ratio of the pigment to the resin solid content of the coating material (PWC) is preferably 1 to 70% by mass.

[0068] The coating material according to the present invention can be applied by a suitable method depending on the intended use, the material to be coated, and the like. Application methods include, but are not limited to, flow coating, spraying, brush coating, flexographic printing, dip coating, spin coating, roll coating, casting, screen printing, and gravure printing. After application to a desired coating target, the coating is dried to remove volatile components, thereby obtaining a coating film. At this time, ultraviolet irradiation treatment or heat treatment at a temperature of about 40 to 120°C may be performed, if necessary.

[0069] The substrate to be coated is not particularly limited as long as a coating film can be formed on its surface, and may be either an inorganic substrate or an organic substrate. The substrate material is not limited to the following, and examples thereof include organic substrates such as natural resins and synthetic resins; and inorganic substrates such as ceramics, metals, glass, stone, concrete, and cement. These may be used alone or in combination of two or more.

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "%" and "parts" represent "% by mass" and "parts by mass", respectively, unless otherwise specified.

[0071] Synthesis Example 1 (Polymerization Step) A reactor equipped with a reflux condenser, a stirrer, a thermometer, a nitrogen inlet tube, a post-addition liquid feed section, and a pump was charged with 640 parts by mass of vinyl acetate, 254 parts by mass of methanol, and 1.05 parts by mass of methyl acrylate to prepare a mixed solution. The system was purged with nitrogen while stirring the mixed solution. Separately, a methanol solution of methyl acrylate (concentration: 20% by mass) was prepared as a comonomer sequential addition solution, and nitrogen bubbling was performed for 30 minutes. The reactor temperature was raised, and when it reached 60°C, 0.06 parts by mass of 2,2'-azobis(isobutyronitrile) (AIBN) was added to initiate polymerization. During the polymerization reaction, the prepared methanol solution of methyl acrylate was added dropwise to the system to maintain a constant monomer composition (molar ratio of vinyl acetate to methyl acrylate) in the polymerization solution. The polymerization was terminated when the conversion of vinyl acetate to vinyl acetate reached 30 mol%.

[0072] (Saponification step) Next, unreacted vinyl acetate monomer was removed under reduced pressure to prepare a methanol solution of polyvinyl acetate (PVAc). Methanol was added to the obtained PVAc solution to adjust the concentration to 10% by mass. Next, while maintaining the temperature at 60°C, a methanol solution of sodium hydroxide at a concentration of 10% by mass was added in a ratio of 10 mmol of sodium hydroxide per 1 mole of vinyl acetate monomer unit in the copolymer, and the saponification reaction was carried out for 2 hours.

[0073] (Post-treatment step) After that, the mixture was cooled to room temperature (20 ° C.), and 900 parts by mass of methanol and 100 parts by mass of water were added to the white solid product obtained by filtration. A sodium hydroxide solution was added in a ratio of 3 moles per mole of methyl acrylate units in the copolymer, and the temperature was maintained at 60 ° C. and stirred for 2 hours. 1000 parts by mass of methanol was added to the white solid obtained by filtration and left to stand at room temperature for 1 hour for washing. 1000 parts by mass of methanol and 15 parts by mass of acetic acid were added to the white solid obtained by filtration and left to stand at room temperature for 3 hours for washing. 1000 parts by mass of methanol was added to the white solid product obtained by filtration and left to stand at room temperature for 3 hours for washing. After repeating the above washing operation twice, the product obtained by centrifugation was dried in a dryer at 40 ° C. and 1.3 Pa for 20 hours to obtain "PVOH-A" as vinyl alcohol polymer (a).

[0074] Synthesis Example 2 (Polymerization Step) A reactor equipped with a reflux condenser, a stirrer, a thermometer, a nitrogen inlet tube, a post-addition liquid feed section, and a pump was charged with 640 parts by mass of vinyl acetate, 243 parts by mass of methanol, and 0.34 parts by mass of itaconic acid to form a mixed solution. The mixed polymerization solution was stirred and purged with nitrogen, and then heated. When the temperature reached 60°C, 0.1 parts by mass of 2,2'-azobis(isobutyronitrile) (AIBN) was added to initiate polymerization. From the start of polymerization, a 5% by mass methanol solution of itaconic acid was added dropwise to proceed with polymerization, while analyzing the concentration of the vinyl alcohol polymer in the polymerization system. Within 215 minutes from the start of polymerization, 68 parts by mass of a 5% by mass methanol solution of itaconic acid was added dropwise almost uniformly, and then the mixture was cooled to room temperature (20°C) to terminate the polymerization.

[0075] (Saponification Step) Next, unreacted vinyl acetate monomer was removed under reduced pressure to prepare a methanol solution of polyvinyl acetate (PVAc). Methanol was added to the obtained PVAc solution to adjust the concentration to 35% by mass. 286 parts by mass of the PVAc methanol solution was added with 15.7 parts by mass of an alkaline solution (a 12% by mass methanol solution of NaOH) and 31.9 parts by mass of methanol, and saponification was carried out at 40°C. That is, after the addition of the alkaline solution, the gel was pulverized in a pulverizer and left to stand at 40°C for 1 hour to carry out the saponification reaction.

[0076] (Post-treatment step) The mixture was then cooled to room temperature (20°C), and 200 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, 1,000 parts by mass of methanol was added to the white solid product obtained by filtration, and the product was left to stand at room temperature for 3 hours for washing. The above washing operation was repeated three times, and the product obtained by centrifugal dewatering was dried in a dryer at 40°C and 1.3 Pa for 20 hours, thereby obtaining "PVOH-B" as a vinyl alcohol polymer (a).

[0077] Synthesis Example 3: 30.0 parts by mass of methanol and 0.5 parts by mass of dodecanal were added to a three-necked flask equipped with a reflux condenser and a thermometer at room temperature (20°C). While stirring with a mechanical stirrer, 10 parts by mass of PVOH-A obtained in Synthesis Example 1 was added over 1 minute. 0.4 parts by mass of p-toluenesulfonic acid was added to the reaction solution, and the temperature was raised to 65°C and the reaction was carried out for 5 hours. 0.3 parts by mass of an 8 mol / L aqueous sodium hydroxide solution was added, and the reaction was carried out at 65°C for 2 hours. 100 parts by mass of methanol was added to the white solid product obtained by filtration and washed with stirring. The above washing operation was repeated three times, and the product obtained by filtration was dried in a dryer at 40°C and 1.3 Pa for 20 hours to obtain "PVOH-C", which would become the vinyl alcohol polymer (a).

[0078] Synthesis Example 4 40.0 parts by mass of methanol and 2.9 parts by mass of sodium benzaldehyde sulfonate were added to a three-necked flask equipped with a reflux condenser and a thermometer at room temperature (20°C). While stirring with a mechanical stirrer, 10 parts by mass of a commercially available vinyl alcohol polymer (manufactured by Kuraray Co., Ltd., brand 28-98) was added over 1 minute. 1.4 parts by mass of p-toluenesulfonic acid was added to the reaction solution, and the temperature was raised to 65°C, followed by a reaction for 5 hours. 0.9 parts by mass of an 8 mol / L aqueous sodium hydroxide solution was added, followed by a reaction for 2 hours at 65°C. 100 parts by mass of methanol was added to the white solid product obtained by filtration, followed by stirring and washing. The above washing procedure was repeated three times, and the product obtained by filtration was then dried in a dryer at 40°C and 1.3 Pa for 20 hours, yielding "PVOH-D", which would become the vinyl alcohol polymer (a).

[0079] <Evaluation> The following measurements were carried out on the vinyl alcohol polymers PVOH-A and PVOH-B obtained in Synthesis Examples 1 and 2. The results are shown in Table 1.

[0080] <Modification Amount> The modification amount of the comonomer in the vinyl alcohol polymers obtained in Synthesis Examples 1 and 2 can be, for example, １ For example, the vinyl ester polymer, which is a precursor of the vinyl alcohol polymer, can be obtained by H-NMR. １ In Synthesis Example 1, a vinyl ester polymer (0.05 g), which is a precursor of PVOH-A, was dissolved in chloroform-d (0.95 g) and subjected to 1H-NMR at 500 MHz. １ H-NMR measurement was carried out. The degree of modification was calculated from the integrated values ​​of the peak (4.7-5.1 ppm) derived from the main chain methine proton of the vinyl ester monomer unit and the peak (3.6-3.7 ppm) derived from the side chain methyl group of methyl acrylate. In Synthesis Example 2, a vinyl ester polymer (0.05 g), which is a precursor of PVOH-B, was dissolved in dimethyl sulfoxide-d6 (0.95 g) and subjected to 1H-NMR measurement at 500 MHz. １ H-NMR measurement was carried out. The degree of modification was calculated from the integral values ​​of the peak (4.5-5.0 ppm) derived from the main chain methine proton of the vinyl ester monomer unit and the peak (3.0-3.2 ppm) derived from the side chain methylene group of itaconic acid. Here, the degree of modification corresponds to the content of the structural unit consisting of the comonomer relative to all structural units constituting the vinyl alcohol polymer (a). Note that NMR analysis may be combined with measurements under various temperature conditions, using various nuclides, or using additives in order to clarify the structure of the target product.

[0081] <Vinyl Ester Monomer Unit Content> The vinyl ester monomer unit contents of the vinyl alcohol polymers obtained in Synthesis Examples 1 and 2 are, for example, １ The vinyl alcohol polymer (0.05 g) obtained in Synthesis Examples 1 and 2 was dissolved in dimethyl sulfoxide-d6 (0.95 g), and the resulting polymer was subjected to 1H-NMR at 500 MHz. １ H-NMR measurement was carried out. １From the H-NMR spectrum, the content of vinyl ester monomer units relative to all structural units constituting the vinyl alcohol polymer (a) was determined using a peak (1.9-2.0 ppm) derived from methyl protons in the side chains of the vinyl ester monomer units. Note that, in order to clarify the structure of the target product, NMR analysis may be performed in combination with measurements under various temperature conditions and using various nuclides, or measurements using additives.

[0082] <Degree of Polymerization> The viscosity-average degree of polymerization is measured in accordance with JIS K 6726-1994. The obtained vinyl alcohol polymer is resaponified and purified, and then the intrinsic viscosity [η] (unit: deciliter / g) is measured in water at 30°C.

[0083]

[0084] Example 1 56.7 parts by mass of methanol and 0.6 parts by mass of dodecanal were added to a three-necked flask equipped with a reflux condenser and a thermometer at room temperature (20°C). While stirring with a mechanical stirrer, 10 parts by mass of PVOH-A obtained in Synthesis Example 1 was added over 1 minute. 1.3 parts by mass of p-toluenesulfonic acid was added to the reaction solution, and the temperature was raised to 65°C and the reaction was carried out for 5 hours. 1.7 parts by mass of an 8 mol / L aqueous sodium hydroxide solution was added, and the reaction was carried out at 65°C for 2 hours. 100 parts by mass of methanol was added to the white solid product obtained by filtration and washed with stirring. The above washing procedure was repeated three times, and the product obtained by filtration was dried in a dryer at 40°C and 1.3 Pa for 20 hours to obtain "PVOH-1," which would become the vinyl alcohol polymer (X). The conditions are shown in Table 2.

[0085] (Example 2) "PVOH-2" to be used as the vinyl alcohol polymer (X) was obtained in the same manner as in Example 1, except that the amounts of methanol, dodecanal, p-toluenesulfonic acid, and 8 mol / L aqueous sodium hydroxide solution were changed. The respective conditions are shown in Table 2.

[0086] (Example 3) "PVOH-3" which becomes vinyl alcohol polymer (X) was obtained in the same manner as in Example 1, except that the amount of methanol added, the addition of 0.8 parts by mass of decanal instead of dodecanal, and the addition amount of 8 mol / L aqueous sodium hydroxide solution were changed. The respective conditions are shown in Table 2.

[0087] (Example 4) "PVOH-4" which becomes vinyl alcohol polymer (X) was obtained in the same manner as in Example 3, except that the amount of decanal added was changed. The respective conditions are shown in Table 2.

[0088] (Example 5) "PVOH-5" to be the vinyl alcohol polymer (X) was obtained in the same manner as in Example 2, except that the amount of methanol added was changed and 1.6 parts by mass of hexanal was added instead of dodecanal. The conditions are shown in Table 2.

[0089] (Example 6) "PVOH-6" which becomes vinyl alcohol polymer (X) was obtained in the same manner as in Example 1, except that the amount of dodecanal added, the addition of PVOH-B obtained in Synthesis Example 2 instead of PVOH-A, the amount of p-toluenesulfonic acid added, and the amount of 8 mol / L aqueous sodium hydroxide solution added were changed. The respective conditions are shown in Table 2.

[0090] (Example 7) "PVOH-7" to be used as the vinyl alcohol polymer (X) was obtained in the same manner as in Example 1, except that the amount of methanol added, the addition of 0.9 parts by mass of sodium benzaldehyde sulfonate instead of dodecanal, the addition of PVOH-C obtained in Synthesis Example 3 instead of PVOH-A, the addition of p-toluenesulfonic acid, and the addition of an 8 mol / L aqueous sodium hydroxide solution were changed. The conditions are shown in Table 2.

[0091] (Example 8) "PVOH-8" to be the vinyl alcohol polymer (X) was obtained in the same manner as in Example 5, except that the amount of hexanal added was changed. The conditions are shown in Table 2.

[0092] (Comparative Example 1) 578.0 parts by mass of water was added to a three-necked flask equipped with a reflux condenser and a thermometer at room temperature (20 ° C.), and 10 parts by mass of a commercially available vinyl alcohol polymer (manufactured by Kuraray Co., Ltd., brand 28-98) was added over 1 minute while stirring with a mechanical stirrer. The temperature was raised to 90 ° C. and the mixture was stirred for 1 hour to dissolve. After cooling this solution to 40 ° C., 0.6 parts by mass of decanal and 1.2 parts by mass of 20% hydrochloric acid were added, and the reaction was carried out at 40 ° C. for 3 hours. 0.3 parts by mass of an 8 mol / L aqueous sodium hydroxide solution was added, and the reaction was carried out at 65 ° C. for 2 hours to obtain an aqueous solution of "PVOH-9" which would become the vinyl alcohol polymer (X).

[0093] Comparative Example 2 The "PVOH-A" obtained in Synthesis Example 1 was designated as "PVOH-10" which was to become the vinyl alcohol polymer (X).

[0094] Comparative Example 3 "PVOH-11" which becomes vinyl alcohol polymer (X) was obtained in the same manner as in Example 1, except that the amount of dodecanal added and the amount of 8 mol / L sodium hydroxide aqueous solution added were changed. The respective conditions are shown in Table 2.

[0095] Comparative Example 4 "PVOH-12" which would become the vinyl alcohol polymer (X) was obtained in the same manner as in Example 1, except that the amount of dodecanal added, the addition of PVOH-D obtained in Synthesis Example 4 instead of PVOH-A, the amount of p-toluenesulfonic acid added, and the amount of 8 mol / L aqueous sodium hydroxide solution added were changed. The respective conditions are shown in Table 2.

[0096]

[0097] <Evaluation> The vinyl alcohol polymers (X) obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 3 and 4.

[0098] <Content of each structural unit> The vinyl alcohol polymer (0.05 g) obtained in each of the examples and comparative examples was dissolved in dimethyl sulfoxide-d6 (0.95 g), and １ H-NMR measurement was carried out. １From the H-NMR spectrum, the contents of the structural unit (A) having a lactone ring, the structural unit (B) having an ionic group, the structural unit (C) having a hydrophobic group, the vinyl alcohol monomer unit, and the vinyl ester monomer unit were calculated. In the present invention, "structural unit" refers to a repeating unit having a functional group, and a structural unit having a lactone ring, an ionic group introduced by acetalization, and a hydrophobic group were also considered to be "one unit." When a dicarboxylic acid monomer was used in which one carboxy group formed a lactone ring and the other formed an ionic group, the structural unit (A) having a lactone ring and the structural unit (B) having an ionic group were calculated in duplicate. In the lactone ring, for example, one unit of a monomer unit having a carboxy group reacts with one unit of a vinyl alcohol monomer unit adjacent to it to produce one lactone ring unit. Furthermore, an acetalized structure is also produced by reacting one acetal unit with two vinyl alcohol monomer units to produce one acetalized structure unit. Taking this into consideration, the lactone ring and acetalized structure were counted as "2 units" in the vinyl alcohol polymer unit in the denominator.

[0099] <Degree of Polymerization> The measured value of the vinyl alcohol polymer (a) was used.

[0100] <Method of Preparing Aqueous Solution> Ion-exchanged water was added to a vinyl alcohol polymer (X) or an aqueous solution of the vinyl alcohol polymer (X), and an 8 mol / L aqueous sodium hydroxide solution was added in an amount of 2 / 3 molar of the structural unit (A) having a lactone ring contained in the vinyl alcohol polymer. The mixture was stirred at 95°C to dissolve, thereby preparing an aqueous solution having a vinyl alcohol polymer (X) content of 1.6% by mass. The 1.6% by mass aqueous vinyl alcohol polymer solution was allowed to cool to 20°C, and while stirring the aqueous solution using a magnetic stirrer, ion-exchanged water and a 20% by mass aqueous citric acid solution or a 2 mol / L aqueous sodium hydroxide solution were added to prepare a 1.5% by mass aqueous solution having a pH of 4 or 10 at 20°C. The mixture was further stirred at 20°C for 5 minutes. The pH was measured using a commercially available pH meter (LAQUA Twin compact pH meter manufactured by HORIBA, Ltd.). When an 8 mol / L aqueous solution of sodium hydroxide was added in an amount of 2 / 3 molar of the structural unit (A) having a lactone ring and stirred at 95°C, if the solution did not dissolve uniformly, it was deemed insoluble and no pH adjustment was performed. The content of the vinyl alcohol polymer (X) was calculated using the following formula: Content [mass %] = Amount of vinyl alcohol polymer (X) added [g] / Total weight of aqueous solution [g] × 100

[0101] <Viscosity X, Y> After adjusting the pH to 4 according to the method described above, the viscosity X of a 1.5% by mass aqueous solution (for viscosity X) after 5 minutes was determined using a rotational rheometer (a rheometer Discovery HR-2 manufactured by TA Instruments-Waters LLC) under the following measurement conditions: a shear rate of 1.0 [1 / s], and a measurement time of 182 seconds. Furthermore, after adjusting the pH to 10 according to the method described above, the viscosity Y of a 1.5% by mass aqueous solution (for viscosity Y) after 5 minutes was determined using a rotational rheometer (a rheometer Discovery HR-2 manufactured by TA Instruments-Waters LLC) under the following measurement conditions: a shear rate of 1.0 [1 / s], and a measurement time of 182 seconds. <Measurement conditions> Jig used: Stainless steel Peltier cone geometry with solvent trap (HRx0, stainless steel, 40 mm, 1° cone) Measurement temperature: 20°C Measurement time: 300 seconds Shear rate: 1.0 [1 / s] Viscosity Y was scored according to the following criteria. Note that the higher the viscosity Y, the higher the viscosity even at low concentrations, and therefore the better the thickening properties. 5 points: 10,000 cp or more 4 points: 5,000 cp or more and less than 10,000 cp 3 points: 1,000 cp or more and less than 5,000 cp 2 points: 400 cp or more and less than 1,000 cp 1 point: Less than 400 cp

[0102] <Viscosity ratio Y / X> The viscosity ratio Y / X of viscosities X and Y measured by the above method was evaluated by the following criteria. The larger the viscosity ratio Y / X, the easier it is to change the viscosity, and the better the viscosity changeability. 5 points: 50.0 or more 4 points: 10.0 or more and less than 50.0 3 points: 5.0 or more and less than 10.0 2 points: 1.5 or more and less than 5.0 1 point: less than 1.5

[0103] <Viscosity Z> The viscosity of an aqueous solution prepared to pH 10 according to the above-described method was measured using a rotational rheometer (Discovery HR-2 rheometer manufactured by TA Instruments-Waters LLC) under the following measurement conditions. The shear rate was maintained at 0.01 [1 / s] for 30 seconds, followed by intermittent changes to a shear rate of 0.1 [1 / s] for 30 seconds. This operation was carried out in the following six shear rate stages, starting with the lowest (6 stages x 30 seconds = 180 seconds), and the viscosity at each shear rate was measured. Table 4 shows the viscosity Z measured 28 seconds after switching to a shear rate of 100 [1 / s]. <Measurement conditions> Jig used: Stainless steel Peltier cone geometry with solvent trap (HRx0, stainless steel, 40 mm, 1° cone) Measurement temperature: 20°C Measurement time: 180 seconds Shear rate: 0.01, 0.1, 1, 10, 100, 1000 [1 / s]

[0104] <Viscosity ratio Y / Z> The viscosity ratio Y / Z of the viscosities Y and Z measured by the method described above was evaluated by the following criteria. The larger the viscosity ratio Y / Z, the more easily the viscosity can be lowered depending on the shear rate during liquid transfer, and the better the liquid transferability. 5 points: 10.0 or more 4 points: 5.0 or more but less than 10.0 3 points: 2.0 or more but less than 5.0 2 points: 1.5 or more but less than 2.0 1 point: less than 1.5

[0105] <Overall Evaluation of Thickener> The sum of the scores for the above three evaluation items (viscosity Y, viscosity ratios Y / X, and Y / Z) was used to evaluate the overall performance of the vinyl alcohol polymer. The results are shown in Table 4. <Viscosity Changeability> While stirring the aqueous solution in which viscosity X was measured at 20°C, a 2 mol / L aqueous sodium hydroxide solution was added to adjust the pH to 10, and the solution was then stirred at 20°C for 5 minutes. The viscosity W at 1.0 [1 / s] was then determined under the same measurement conditions as for viscosity X. If the viscosity at this time was 4.0 times or more than viscosity X, it was rated as A; if it was 2.5 times or more but less than 4.0 times, it was rated as B; if it was 1.5 times or more but less than 2.5 times, it was rated as C; and if it was less than 1.5 times, it was rated as D. The results are shown in Table 4.

[0106]

[0107]

Claims

1. A vinyl alcohol polymer, the content of the vinyl alcohol polymer is 1.5% by mass, and the pH at 20° C. is 4, the aqueous solution viscosity X [cp] of the aqueous solution at a shear rate of 1 [1 / s] at 20° C.; The vinyl alcohol-based polymer has a content of 1.5% by mass and a pH of 10 at 20° C. in an aqueous solution state, and the aqueous solution viscosity Y [cp] of the aqueous solution at a shear rate of 1 [1 / s] at 20° C. satisfies the following formula (1): 1.5<Y / X<1,500 (1)

2. The vinyl alcohol polymer according to claim 1 , wherein the aqueous solution viscosity Y is 20 cp or more.

3. 2. The vinyl alcohol-based polymer according to claim 1, wherein the aqueous solution viscosity Y [cp] and the aqueous solution viscosity Z [cp] of the aqueous solution at a shear rate of 100 [1 / s] at 20° C. in an aqueous solution state having a vinyl alcohol-based polymer content of 1.5% by mass and a pH of 10 at 20° C. satisfy the following formula (2): 1.5<Y / Z<100 (2)

4. The vinyl alcohol polymer according to claim 1 , which comprises a structural unit (A) having a lactone ring.

5. The vinyl alcohol polymer according to claim 1 , which comprises a structural unit (B) having an ionic group.

6. 2. The vinyl alcohol polymer according to claim 1, which comprises a structural unit (C) having a hydrophobic group made of a hydrocarbon having 3 or more carbon atoms.

7. The copolymer comprises a structural unit (A) having a lactone ring, a structural unit (B) having an ionic group, and a structural unit (C) having a hydrophobic group composed of a hydrocarbon having 3 or more carbon atoms, 2. The vinyl alcohol-based polymer according to claim 1, which satisfies the following formula (3), where a content of the structural unit (A) is (a), a content of the structural unit (B) is (b), a content of the structural unit (C) is (c), the number of carbon atoms of the hydrophobic group in the structural unit (C) is (d), and the number of ionic groups in the structural unit (B) is (e) relative to all structural units of the vinyl alcohol-based polymer: 5<(c×(d-3) ２ ) / (a+b×e)<95 (3)

8. A vinyl alcohol polymer-containing aqueous solution comprising the vinyl alcohol polymer according to any one of claims 1 to 7 and water.

9. The content of the vinyl alcohol polymer is 1 to 3% by mass, the pH at 20°C is 7 or more, and the aqueous solution viscosity at a shear rate of 1 [1 / s] at 20°C is 20 to 1,000,000 cp. The aqueous solution containing the vinyl alcohol polymer according to claim 8.

10. The content of the vinyl alcohol polymer is 1 to 3% by mass, the pH at 20°C is less than 7, and the aqueous solution viscosity at a shear rate of 1 [1 / s] at 20°C is 20 to 100,000 cp. The aqueous solution containing the vinyl alcohol polymer according to claim 8.

11. A paint comprising the vinyl alcohol polymer according to any one of claims 1 to 7.

12. A cement admixture comprising the vinyl alcohol polymer according to any one of claims 1 to 7.