Polyvinyl alcohol polymers and their manufacturing methods

Abstract

This invention provides a polyvinyl alcohol-based polymer, etc. The polyvinyl alcohol polymer of the present invention has an ionic backbone and satisfies at least one of the following necessary conditions 1, 2 and 3. Necessary condition 1: The water insoluble fraction is less than 30% by mass. Necessary condition 2: The transmittance (430nm) of the 4% by mass aqueous solution is ≥1%. Necessary condition 3: The YI value of the 4% by mass dimethyl sulfoxide solution is below 30.

Description

[Technical Field]

[0001] This invention relates to a polyvinyl alcohol polymer having ionic groups and a method for manufacturing the same. [Previous Technology]

[0002] Polyvinyl alcohol polymers with ionic groups (hereinafter, polyvinyl alcohol polymers or vinyl alcohol polymers are sometimes simply referred to as "PVA" or "PVA-based polymers") can significantly improve hydrophilicity compared to PVA without ionic groups due to the presence of their ionic groups, and there are many differences in physical properties between them and PVA without ionic groups. Such PVAs are suitable for applications such as water-soluble films that require a high rate of dissolution in water. In addition, water dispersibility or water solubility can be imparted to PVAs that are not originally water-soluble but have a low degree of saponification (e.g., a saponification degree of 70 mol% or less). By thus enabling PVAs with a low degree of saponification to have water solubility or water dispersibility, various applications such as water-soluble hot melt adhesives can be developed.

[0003] For example, Patent Document 1 discloses a modified vinyl alcohol polymer having sulfonic acid groups or their salts in the side chains, wherein the modification amount of the sulfonic acid or its salt is 0.01 mol% to 10 mol%, and the block character of the residual vinyl ester units is 0.55 to 1, and a method for manufacturing the same. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1]WO2019 / 159757 [Summary of the Invention]

[0005] [Problem to be Solved by the Invention] The object of the present invention is to provide a polyvinyl alcohol (PVA) based polymer, etc. [Technical Means for Solving the Problem]

[0006] As described above, PVA with ionic groups (modified PVA) is known as described in Patent Document 1, etc. According to the research of the inventors of the present invention, PVA with ionic groups sometimes has the following problems: it is easy to color, it is easy to generate (byproduct) water-insoluble components, and depending on the situation, it is sometimes not only not soluble in water, but even insoluble.

[0007] However, it is extremely difficult to explore PVA with ionic groups and less coloring or PVA with less water-insoluble components (excellent water dispersibility or solubility).

[0008] For example, in Patent Document 1, ionic radicals are introduced by mixing and reacting PVA with an aldehyde having a sulfonic acid group or its salt under heating. However, according to the research of the inventors of the present invention, depending on the reaction conditions [and the characteristics of the PVA used (degree of polymerization, degree of saponification, particle size)], the mixing sometimes becomes uneven or insufficient, and the reaction spots (uneven reaction) become larger. Perhaps due to the above situation, the amount of water-insoluble components increases. Or, on the other hand, if heating is carried out under conditions that allow the PVA to completely melt in order to achieve uniform mixing, there is a situation where it is easy to color or easy to become insoluble.

[0009] Under such circumstances, the inventors discovered that by selecting the conditions for introducing an ionic framework (ionic group, framework having ionic group) (and further, selecting the method for introducing the ionic framework), even PVA having an ionic framework can efficiently achieve the reduction of coloring or water-insoluble components, the inhibition or prevention of insolubility, etc. In particular, even if it is not a high degree of saponification such as a fully saponified type, it can maintain a high degree of water solubility or water dispersibility, and efficiently achieve the reduction of coloring or water-insoluble components, the inhibition or prevention of insolubility, etc. Through repeated research, the present invention was completed.

[0010] That is, the present invention relates to the following inventions, etc. [1] A polyvinyl alcohol polymer (A) having an ionic backbone (a backbone having ionic groups) and sufficiently satisfying the following necessary condition 1; Necessary condition 1: The water insoluble fraction is 30% by mass or less. [2] A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary condition 2; Necessary condition 2: The transparency of a 4% by mass aqueous solution [430 nm (e.g., transparency at 20°C)] is 1% or more. [3] A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary condition 3; Necessary condition 3: The YI value of a 4% by mass dimethyl sulfoxide solution [e.g., the YI value at 20°C (e.g., the YI value calculated and measured in the wavelength range of 360 to 830 nm)] is 30 or less. [4] A polyvinyl alcohol polymer (A) having an ionic backbone and fully satisfying the following necessary conditions 1 and 2: Necessary condition 1: The water insoluble fraction is less than 30% by mass. Necessary condition 2: The transparency (430 nm) of a 4% by mass aqueous solution is more than 1%. [5] A polyvinyl alcohol polymer (A) having an ionic backbone and fully satisfying the following necessary conditions 1 and / or necessary conditions 2 and 3: Necessary condition 1: The water insoluble fraction is less than 30% by mass. Necessary condition 2: The transparency (430 nm) of a 4% by mass aqueous solution is more than 1%. Necessary condition 3: The YI value of a 4% by mass dimethyl sulfoxide solution is less than 30. [6] A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary conditions 1, 2 and 3: Necessary condition 1: The water insoluble fraction is less than 30% by mass; Necessary condition 2: The transparency (430 nm) of a 4% by mass aqueous solution is more than 1%; Necessary condition 3: The YI value of a 4% by mass dimethyl sulfoxide solution is less than 30. [7] The polyvinyl alcohol polymer (A) of any one of [1], [4] to [6], wherein in necessary condition 1, the water insoluble fraction is less than 10% by mass. [8] The polyvinyl alcohol polymer (A) of any one of [2], [4] to [6], wherein in necessary condition 2, the transparency (430 nm) of a 4% by mass aqueous solution is more than 2%. [9] The polyvinyl alcohol polymer (A) of any one of [3] to [6], wherein in necessary condition 3, the YI value of a 4% by mass dimethyl sulfoxide solution is less than 10.

[10] A polyvinyl alcohol polymer (A) of any one of [1] to [9], wherein in necessary condition 1, the water insoluble fraction is less than 5% by mass, in necessary condition 2, the transparency (430 nm) of a 4% by mass aqueous solution is more than 10%, and in necessary condition 3, the YI value of a 4% by mass dimethyl sulfoxide solution is less than 5.

[11] A polyvinyl alcohol polymer (A) of any one of [1] to

[10] , wherein the ionic backbone has at least one ionic group selected from carboxyl groups and their salts (carboxylate groups, carboxyl salt-forming groups).

[12] A polyvinyl alcohol polymer (A) of any one of [1] to

[11] , wherein the ionic backbone contains a backbone derived from a polycarboxylic acid component (a backbone derived from a polycarboxylic acid component having at least one ionic group selected from carboxyl groups and their salts).

[13] A polyvinyl alcohol polymer (A) of any one of [1] to

[12] , wherein the ionic backbone contains a backbone derived from at least one polycarboxylic acid component selected from dicarboxylic acid components and tricarboxylic acid components.

[14] A polyvinyl alcohol polymer (A) of any one of [1] to

[13] , wherein the ionic backbone contains a backbone introduced via a hydroxyl group of a vinyl alcohol unit (a vinyl alcohol unit present in the polyvinyl alcohol polymer).

[15] Polyvinyl alcohol polymer (A) of any one of [1] to

[14] , wherein the ionic backbone contains an ester bond backbone of hydroxyl groups derived from the vinyl alcohol unit and carboxyl groups (e.g., 1 carboxyl group) of the polycarboxylic acid component [a backbone formed by ester bonding with carboxyl ester (formed by ester bonding, having at least one ionic group selected from carboxyl groups and their salts)].

[16] A polyvinyl alcohol polymer (A) of any one of [1] to

[15] , wherein the ionic backbone comprises an ester bond backbone of a hydroxyl group derived from a vinyl alcohol unit and a carboxyl group of a polycarboxylic acid component, the polycarboxylic acid component comprising at least one selected from aliphatic dicarboxylic acids (e.g., succinic acid, maleic acid, methyl maleic acid, itconic acid, fumaric acid, etc.), aromatic dicarboxylic acids (e.g., phthalic acid), aliphatic tricarboxylic acids (e.g., citric acid), aromatic tricarboxylic acids, anhydrides of such acids (e.g., succinic anhydride, maleic anhydride, methyl maleic anhydride, itconic anhydride, phthalic anhydride), esters of such acids (especially some esters, e.g., monomethyl succinate, monomethyl maleic acid, methyl maleic acid, monomethyl itconic acid, monomethyl phthalate, monomethyl citrate), and salts of such acids (e.g., alkali metal salts such as sodium).

[17] The polyvinyl alcohol polymer (A) of any one of [1] to

[16] , wherein the content of the ionic backbone in each monomer unit is 0.01 to 10 mol%.

[18] The polyvinyl alcohol polymer (A) of any one of [1] to

[17] , wherein the block character is 0.35 to 0.7.

[19] The polyvinyl alcohol polymer (A) of any one of [1] to

[18] , wherein the degree of saponification is 20 to 90 mol%.

[20] The polyvinyl alcohol polymer (A) of any one of [1] to

[19] , wherein the degree of saponification is less than 70 mol%.

[21] The polyvinyl alcohol polymer (A) of any one of [1] to

[20] , wherein the degree of polymerization is 120 to 3000.

[22] The polyvinyl alcohol polymer (A) of any one of [1] to

[21] , wherein the pH value of a 4% by mass aqueous solution of the polyvinyl alcohol polymer (A) is 5 to 9.

[23] The polyvinyl alcohol polymer (A) of any one of [1] to

[22] , wherein the pH value of a 4% by mass aqueous solution of the polyvinyl alcohol polymer (A) is 5.5 to 8.5 (e.g., 5.8 to 8, 5.5 to 7.5, 6 to 7.5, 6 to 7, etc.).

[24] A method for manufacturing a polyvinyl alcohol polymer (A), which is a method for manufacturing a polyvinyl alcohol polymer (A) having an ionic backbone, and comprising a heating step of heating a composition containing a polyvinyl alcohol polymer (B) and a component of the corresponding ionic backbone.

[25] The manufacturing method of

[24] , wherein the component of the corresponding ionic backbone contains a polycarboxylic acid component (e.g., at least one selected from polycarboxylic acids, polycarboxylic anhydrides, partial esters of polycarboxylic acids, and salts thereof).

[26] The manufacturing method of

[24] or

[25] , wherein the component of the corresponding ionic skeleton contains at least one selected from dicarboxylic acids, tricarboxylic acids, anhydrides of the like, partial esters of the like, and salts of the like.

[27] The manufacturing method of any one of

[24] to

[26] , wherein the composition contains a pH adjuster (heated in the presence of the pH adjuster).

[28] The manufacturing method of any one of

[24] to

[27] , wherein the composition contains sodium acetate (sodium acetate as a pH adjuster).

[29] The manufacturing method of any one of

[24] to

[28] , wherein the composition contains a pH adjuster at a ratio of 0.5 to 1.9 mol relative to 1 mol of the component of the corresponding ionic skeleton.

[30] The manufacturing method of any one of

[24] to

[29] , wherein in the heating step, the heating temperature is 80 to 240°C.

[31] The manufacturing method of any one of

[24] to

[30] , wherein the heating time in the heating step is 5 minutes to 5 hours.

[32] The manufacturing method of any one of

[24] to

[31] includes a solvent removal step of removing the solvent from a composition containing a polyvinyl alcohol polymer (B), a component with a corresponding ionic backbone, and a solvent, wherein the heating step is performed after the solvent removal step or in parallel or continuously with the solvent removal step.

[33] The manufacturing method of

[32] , wherein the solvent contains at least one selected from water, alcohol, and ester.

[34] The manufacturing method of

[32] or

[33] , wherein the solvent contains methanol.

[35] The manufacturing method of any one of

[24] to

[34] , wherein the polyvinyl alcohol polymer (A) satisfies at least one of the following necessary conditions selected from necessary condition 1, necessary condition 2 and necessary condition 3: Necessary condition 1: The water insoluble fraction is less than 30% by mass; Necessary condition 2: The transparency (430 nm) of the 4% by mass aqueous solution is more than 1%; Necessary condition 3: The YI value of the 4% by mass dimethyl sulfoxide solution is less than 30.

[36] A hot melt adhesive containing a polyvinyl alcohol polymer (A) as described in any one of [1] to

[23] .

[37] A dispersant for suspension polymerization containing a polyvinyl alcohol polymer (A) as described in any one of [1] to

[23] . [Effects of the invention].

[0011] According to the present invention, a PVA (novel or specific PVA) or its use [hot melt adhesive (e.g., water-soluble hot melt adhesive), dispersant, etc.] can be provided.

[0012] The PVA of the present invention, in a single-state sample, has ionic groups and a low amount of water-insoluble components and / or high transparency of the aqueous solution. It is believed that these physical properties can serve as an indicator of the uniformity of PVA (especially the uniform introduction of ionic groups) (fewer reaction spots), and can efficiently exert the functions of PVA (e.g., water solubility or dispersibility).

[0013] The PVA of the present invention has ionic radicals and a specific hue (coloring characteristics) in a single state sample.

[0014] In one state of the PVA of the present invention, it is possible to simultaneously achieve having ionic groups and a small amount of water-insoluble components and / or high transparency of the aqueous solution, as well as a specific hue (coloring characteristics).

[0015] Therefore, the PVA according to the present invention has characteristics arising from ionic groups (especially water solubility (dispersion)) and can achieve high efficiency in suppressing such characteristics or coloring.

[0016] In particular, even in one state of the PVA of the present invention, even if it is not a high degree of saponification like that of a fully saponified type [for example, even if the degree of saponification is 90 mol% or less, and even if the degree of saponification is not originally showing or difficult to show water solubility (dispersibility) (for example, saponification of 70 mol% or less, 60 mol% or less, 50 mol% or less)], the above-mentioned characteristics or the high efficiency of color suppression can still be achieved.

[0017] Furthermore, in one embodiment of the present invention, a method for manufacturing PVA can be provided. According to this manufacturing method, even if it has ionic groups, PVA as described above (e.g., PVA with suppressed coloring, PVA with high water solubility or dispersibility) can still be easily and efficiently obtained.

Implementation Method

[0018] Hereinafter, a detailed description will be given of the methods for implementing the present invention. However, the present invention is not limited to the embodiments described below.

[0019] In this invention, a specific polyvinyl alcohol-based polymer may be provided, namely, polyvinyl alcohol-based polymer (A) (hereinafter sometimes referred to as PVA-based polymer (A), PVA (A) etc.). Hereinafter, the invention will be described in detail.

[0020] [Polyvinyl alcohol polymer (A)] PVA polymer (A) typically has ethylene alcohol units [in the form of monomer units], and in particular, at least has ethylene alcohol units and ethylene ester units (units derived from ethylene esters, such as vinyl acetate units).

[0021] Furthermore, the PVA-based polymer (A) of the present invention generally has an ionic backbone (a backbone having ionic groups) (and thus has).

[0022] As ionic groups, examples include: anionic groups {e.g., acid groups [e.g., carboxyl groups, sulfonic acid groups (-SO3H), phosphate groups, etc.]}, cationic groups [e.g., amino groups, ammonium (ammonium cations)], and other salts (such as those that form salt groups).

[0023] As a salt, its properties depend on whether it is anionic or cationic. Examples include: metal salts [such as alkali or alkaline earth metals (such as lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, etc.)], halides (such as chlorides, bromides, iodides, etc.). When the ionic group is a polybasic acid, the salt can be a single (same) salt or a combination of two or more salts.

[0024] An ionic framework may have one or more ionic groups. When there are two or more ionic groups, the ionic groups may be the same or different.

[0025] The plasma group is preferably an acid group (especially a carboxyl group or a sulfonic acid group) and its salt {a salt of an acid group, such as a carboxyl salt [e.g., -COOM (M is an alkali metal such as sodium (or its cation))], a sulfonate [e.g., -SO3M (M is an alkali metal such as sodium (or its cation))], and more preferably a carboxyl group and its salt group (a carboxyl salt group or a carboxyl group forming a salt group).

[0026] Therefore, the ionic group (ionic skeleton) may contain at least one ionic group selected from acid groups (especially carboxyl groups) and their salt groups (especially carboxylate groups).

[0027] The PVA-based polymer (A) may have one ionic backbone or a combination of two or more ionic backbones.

[0028] As long as the ionic skeleton has ionic groups, its state is not limited. It can be selected according to the type or number of ionic groups. A representative example is that it has ionic groups via vinyl alcohol units (hydroxyl groups of vinyl alcohol units) (it can have ionic groups via vinyl alcohol units in the side chain).

[0029] Such an ionic framework may be, for example, a base (framework) represented by the following formula (X).

[0030] -CH2-CH(OX)- (X) (where X represents a group having at least one ionic group)

[0031] In the above formula (X), the ionic groups that are exemplified above (carboxyl group, carboxylate group, etc.) can be used as ionic groups.

[0032] X may have two or more ionic groups (e.g., 2 to 6, 2 to 4, etc.). When there are two or more, they may be the same ionic group or different ionic groups.

[0033] X can be an ionic group, depending on the type of ionic group, but it can usually be a group that has an ionic group (substituting a group that has an ionic group).

[0034] Examples of this type of X include: -X1-Y (where X1 represents a linking group and Y represents a group containing an ionic group), etc.

[0035] As a linking group X1, examples include: direct bond, -CO- (carbonyl), -CS- (thiocarbonyl), -CO-NH-, etc. In particular, -CO- (carbonyl) etc.

[0036] As a group Y containing an ionic group, examples include: ionic groups (carboxyl groups, their salt groups, etc.), groups having ionic groups (hydrocarbon groups, etc.), etc.

[0037] Furthermore, the group having an ionic group (hydrocarbon group, etc.) may have substituents other than the ionic group (e.g., hydroxyl, side oxygen, acetyl, etc.).

[0038] As such a group having an ionic group (substituting a group having an ionic group, or a skeleton having an ionic group), examples include: aliphatic hydrocarbons [e.g., saturated aliphatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, octane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, northoalkyl, adamantane, etc., saturated aliphatic hydrocarbons with approximately 1 to 20 carbons), unsaturated aliphatic hydrocarbons (e.g., ethylene, propylene, butene, pentene, hexene, octene, hexadiene, cyclohexene, northoalkyl, 7-oxabicyclo[2.2.1]hept-5-ene, etc., unsaturated aliphatic hydrocarbons with approximately 2 to 10 carbons)], aromatic hydrocarbons (e.g., benzene, toluene, xylene, naphthalene, etc., aromatic hydrocarbons with approximately 6 to 20 carbons), etc. (substituting a group having an ionic group on the hydrocarbon). Furthermore, in this type of ionic group, the substitution position of the ionic group is not particularly limited.

[0039] In formula (X), X, as a representative example, as described below, can be a base corresponding to a polycarboxylic acid (e.g., dicarboxylic acid, tricarboxylic acid) component.

[0040] By using the vinyl alcohol unit, and in conjunction with the selection of the following introduction conditions, it is easy to efficiently and fully satisfy the following characteristics (amount of water-insoluble components, transparency of aqueous solution, YI value, etc.). Furthermore, by using the vinyl alcohol unit, in addition to the easy and efficient introduction of ionic groups, it is also easy to introduce ionic groups more uniformly, which is also a major reason for the efficient and full satisfaction of the following characteristics (amount of water-insoluble components, transparency of aqueous solution, YI value, etc.).

[0041] Furthermore, as mentioned above, the ionic skeleton is preferably a skeleton having at least one selected from carboxyl groups and their salts, and such ionic skeleton may be derived from polycarboxylic acid components.

[0042] As a polycarboxylic acid component, it is generally acceptable to be a component that can introduce carboxyl groups or their salts into PVA-based polymers (A). Examples include: polycarboxylic acids (e.g., dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids, etc.), derivatives of polycarboxylic acids [e.g., polycarboxylic anhydrides (e.g., dicarboxylic anhydrides), polycarboxylic acid esters (especially mono- or diesters of dicarboxylic acids, etc., partial esters of polycarboxylic acids), and their salts (e.g., sodium salts, etc.)].

[0043] Furthermore, among polycarboxylic acid esters, examples of esters include: alkyl esters [e.g., alkyl esters such as methyl esters and ethyl esters (e.g., lower alkyl esters with about 1 to 4 carbon atoms)] etc.

[0044] Among the polycarboxylic acid components, examples of polycarboxylic acids include: dicarboxylic acids, tricarboxylic acids, and polycarboxylic acids having four or more carboxyl groups (e.g., tetracarboxylic acids, etc., which have two or six carboxyl groups), among which dicarboxylic acids and tricarboxylic acids are preferred.

[0045] As polycarboxylic acids, examples include aliphatic carboxylic acids, aromatic carboxylic acids, etc.

[0046] Polycarboxylic acids may have unsaturated bonds (polymeric unsaturated bonds) or cyclic structures.

[0047] Specific examples of polycarboxylic acids (dicarboxylic acids or tricarboxylic acids) include: dicarboxylic acids {e.g., aliphatic dicarboxylic acids [e.g., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid, oxaloacetic acid, maleic acid, fumaric acid, methyl maleic acid, methyl fumaric acid, itaconic acid, cis-1,2-cyclohexanedicarboxylic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, 5-norphene-2,3-dicarboxylic acid, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic acid, 1,3-adamantanedicarboxylic acid, etc., saturated or unsaturated aliphatic dicarboxylic acids (e.g., dicarboxylic acids with approximately 2 to 30 carbon atoms (e.g., 2 to 20 carbon atoms)], aromatic dicarboxylic acids [e.g., phthalic acid, etc.], saturated or unsaturated aliphatic dicarboxylic acids [e.g., phthalic acid, etc. ... Aromatic dicarboxylic acids such as dicarboxylic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid (e.g., dicarboxylic acids with approximately 8 to 30 carbon atoms, e.g., 8 to 20), etc.; tricarboxylic acids {e.g., aliphatic tricarboxylic acids [e.g., saturated or unsaturated aliphatic tricarboxylic acids such as citric acid and aconitic acid, e.g., tricarboxylic acids with approximately 6 to 30 carbon atoms, e.g., 2 to 20]; aromatic tricarboxylic acids [e.g., aromatic tricarboxylic acids such as trimellitic acid, e.g., tricarboxylic acids with approximately 9 to 30 carbon atoms, e.g., 2 to 20]; polycarboxylic acids having four or more carboxyl groups (e.g., tetracarboxylic acids such as butanetetracarboxylic acid, phenyltetracarboxylic acid, naphthalenedicarboxylic acid, biphenyltetracarboxylic acid, benzophenonetetracarboxylic acid, etc.; pentacarboxylic acids such as phenylpentacarboxylic acid; hexacarboxylic acids such as phenylhexacarboxylic acid, etc.); etc. Furthermore, when isomers (e.g., cis-trans isomers) exist in polycarboxylic acids, any isomer (e.g., both the cis and trans isomers, etc.) is included.

[0048] Polycarboxylic acid components can be used alone or in combination of two or more.

[0049] Furthermore, the polycarboxylic acid component is preferably introduced into the PVA polymer (A) via a vinyl alcohol unit (hydroxyl group of the vinyl alcohol unit) with a carboxyl group or its salt group.

[0050] Therefore, the ionic framework may contain at least this kind of ionic framework.

[0051] A representative ionic skeleton contains an ester bond between a hydroxyl group derived from a vinyl alcohol unit and a carboxyl group (especially one carboxyl group) of a polycarboxylic acid component [a skeleton formed by ester bonding with a carboxyl group (formed by ester bonding, having at least one ionic group selected from carboxyl groups and their salts)]. In other words, the ionic skeleton may contain a skeleton obtained by esterification of a hydroxyl group (the hydroxyl group of a vinyl alcohol unit) with a polycarboxylic acid component.

[0052] Furthermore, as mentioned above, the polycarboxylic acid component is usually a component that can introduce carboxyl groups or their salts, and in the PVA-based polymer (A), it becomes a source of carboxyl groups or their salts.

[0053] For example, a polycarboxylic acid introduces a carboxyl group (residual carboxyl group) into a PVA-based polymer (A) by esterifying a portion of the carboxyl group with the hydroxyl group of the vinyl alcohol unit. As a more specific example, for instance, when using a di(tri)carboxylic acid, a PVA-based polymer (A) having an ionic group derived from the di(tri)carboxylic acid can be obtained by esterifying the hydroxyl group in the PVA-based polymer with the carboxyl group (COOH group) of the di(tri)carboxylic acid.

[0054] Furthermore, regarding polycarboxylic acid esters, it also depends on whether they are partial esters of polycarboxylic acids (e.g., alkyl esters, etc.). For example, if they are partial esters, the carboxyl groups constituting the partial ester can be introduced (into residual form) into the PVA-based polymer by transesterification of the ester portion with the hydroxyl group of the vinyl alcohol unit. As a more specific example, for instance, when using a dicarboxylic acid monoalkyl ester, a PVA-based polymer (A) with ionic groups derived from dicarboxylic acid can be obtained by transesterification of the hydroxyl group in the PVA-based polymer with the dicarboxylic acid monoalkyl ester.

[0055] Furthermore, regarding polycarboxylic anhydrides, they can be converted into polycarboxylic acids or their partial esters by reacting with vinyl alcohol units (hereinafter, PVA-based polymer (B)) or by dissolving them in a suitable solvent (e.g., methanol), thereby introducing carboxyl groups in the same manner as described above. As a more specific example, for instance, when using dicarboxylic anhydrides, a PVA-based polymer (A) having ionic groups derived from dicarboxylic acids can be obtained by esterifying the hydroxyl groups in the PVA-based polymer with carboxyl groups or ester moieties derived from dicarboxylic anhydrides.

[0056] Regarding carboxyl groups, besides using salts of polycarboxylic acids as polycarboxylic acid components, salts can be formed in the reaction process described above using components of the corresponding salt (e.g., sodium hydroxide, sodium acetate, etc. if sodium is used), or after the reaction (carboxyl group introduction), salts can be formed using components of the corresponding salt (e.g., sodium hydroxide, sodium acetate, etc. if sodium is used). Furthermore, components of the corresponding salt, such as sodium acetate, can be contained in (derived from) the PVA-based polymer (B) used as a raw material.

[0057] This ionic skeleton [the ester bond skeleton of the hydroxyl group of the vinyl alcohol unit and the carboxyl group (especially one carboxyl group) of the polycarboxylic acid component] can be the one corresponding to the above formula (X), for example, in the above formula (X), X is -CO-Y1 (where Y1 represents a group containing at least one ionic group selected from carboxyl groups and their salts), etc.

[0058] As a specific ionic skeleton [for example, an ionic skeleton derived from polycarboxylic acid components such as dicarboxylic acid and tricarboxylic acid (a skeleton with ionic groups)], it contains the skeleton (structural unit) represented by the following formula (1).

[0059] [Chemical 1] [In the formula, R represents a direct bond or linking group, and M represents a hydrogen atom or the chemical species of the corresponding salt (e.g., alkali metals such as sodium)]

[0060] As a linking group, examples include: hydrocarbon group (hydrocarbon, group corresponding to hydrocarbon). Examples of hydrocarbon groups include: those shown above (e.g., aliphatic saturated hydrocarbon group, aliphatic unsaturated hydrocarbon group, aromatic hydrocarbon group, etc.).

[0061] This linker (hydrocarbon group) may have one or more carboxyl groups or their bases. In this way, it becomes a skeleton having two or more carboxyl groups or their bases.

[0062] As an aliphatic saturated hydrocarbon group, for example, the group (skeleton) represented by the following formula (2) can be cited.

[0063] [Chemical 2] [In the formula, R1 to R4 are hydrogen atoms or substituents (hydrocarbon groups, carboxyl groups, their bases, etc.); R1 or R2 and R3 or R4 can be linked via other linking groups (hydrocarbon groups, etc.) (for example, they can form cycloalkane structures)]

[0064] As an aliphatic unsaturated hydrocarbon group, examples include the group (skeleton) represented by the following formula (3).

[0065] [Chemical 3] [In the formula, R1 and R2 are hydrogen atoms or substituents (hydrocarbon group, carboxyl group, their salt group, etc.); R1 and R2 can be linked by other linking groups (hydrocarbon group, etc.) (for example, they can form a cycloalkane structure)]

[0066] As an aromatic hydrocarbon group, examples include the group (skeleton) represented by the following formula (4).

[0067] [Chemical 4] [In the formula, R1 to R4 are hydrogen atoms or substituents (hydrocarbon groups, carboxyl groups, their bases, etc.); two or more of R1 to R4 can be linked by other linking groups (hydrocarbon groups, etc.) (for example, they can form polycyclic aromatic hydrocarbon structures)]

[0068] PVA-based polymers (A) may be one or more of two having ionic backbones.

[0069] In the PVA-based polymer (A), the content (ratio, percentage) of the ionic backbone (or ionic group, such as the backbone represented by formula (X) or (1)) in each monomer unit (relative to the total of other monomer units such as vinyl alcohol units and vinyl ester units) can be selected from a range of about 0.001 mol% or more (e.g., 0.005 mol% or more), for example, it can be 0.01 mol% or more, preferably 0.05 mol% or more, and even more preferably 0.1 mol% or more, and can be 30 mol% or less (e.g., 20 mol% or less, 15 mol% or less), for example, it can be 10 mol% or less, preferably 5 mol% or less, and even more preferably 2 mol% or less.

[0070] Furthermore, the range (upper limit and lower limit) can be appropriately combined to select a range (e.g. 0.05 to 2 mol%, 0.1 to 5 mol%, etc., the same applies to the ranges described below).

[0071] Specifically, the content of the ionic framework in each monomer unit may be 0.01 to 10 mol%, preferably 0.05 to 5 mol%, and more preferably about 0.1 to 2 mol%.

[0072] Furthermore, the content of 1 mole% in each monomer unit refers to the following situation: in every 100 monomer units (e.g., the total of monomer units such as vinyl alcohol units, vinyl ester units, etc.), there is 1 ionic group derived from di(tri)carboxylic acid (e.g., the skeleton represented by formula (X) or (1)).

[0073] In the PVA-based polymer (A), the content (ratio, in the case of introducing an ionic backbone through a vinyl alcohol unit, the ratio of ionic backbone introduced into the vinyl alcohol unit when the ionic backbone is introduced through a vinyl alcohol unit) of the total amount of vinyl alcohol units (e.g., vinyl alcohol units that remain after being introduced) and the total amount of the ionic backbone (total) can be selected from, for example, a range of about 0.005 mol% or more (e.g., 0.01 mol% or more), for example, 0.02 mol% or more. Preferably, the content is 0.05 mol% or more (e.g., 0.1 mol% or more), more preferably 0.2 mol% or more (e.g., 0.3 mol% or more, 0.5 mol% or more, 1 mol% or more, 1.5 mol% or more, 2 mol% or more, 2.5 mol% or more, 3 mol% or more), and can be 80 mol% or less (e.g., 50 mol% or less), for example, 30 mol% or less, preferably 20 mol% or less, and more preferably 10 mol% or less (e.g., 8 mol% or less, 5 mol% or less). Specifically, the content of the ionic skeleton relative to the total amount (total) of the vinyl alcohol units and the ionic skeleton can be, for example, 0.01 to 50 mol%, preferably 0.1 to 30 mol%, and more preferably about 0.3 to 10 mol%.

[0074] If the content is as described above, the hydrophilicity of the PVA-based polymer (A) can be improved efficiently. In particular, even PVA with a saponification degree that does not originally exhibit water solubility (dispersibility) (e.g., saponification degree of 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, etc.) can be easily and efficiently imparted with water solubility (dispersibility).

[0075] Furthermore, by not making the upper limit too high, it is easy to suppress the formation or coloring of water-insoluble components.

[0076] Furthermore, there is no particular limitation on the method for determining the content of ionic groups (e.g., the skeleton represented by formula (X) or (1)). For example, it can be determined by NMR, titration, UV absorbance, etc. As a specific example, the content of the skeleton represented by formula (X) or (1) can be determined by dissolving the PVA-based polymer (A) in a suitable solvent (d6-DMSO, etc.) and measuring it by 1H-NMR to resolve the signal originating from a specific substituent (e.g., hydrogen). In addition, if necessary, the sample after Soxhlet extraction (e.g., removal of sodium acetate) can be dissolved in water and titrated with dilute hydrochloric acid to determine the amount of carboxyl groups from the amount of hydrochloric acid titrated. Also, when the ionic group has UV (ultraviolet) absorption, the content of the ionic group can be determined by measuring the UV absorbance of an aqueous solution containing the PVA-based polymer (A).

[0077] There are no particular limitations on the method of introducing ionic groups into the PVA-based polymer (A), and conventional methods can be used.

[0078] Among the representative methods, as described below, examples include: a method of reacting a PVA-based polymer (B) with a component of a corresponding ionic backbone (ionic group) [e.g., a polycarboxylic acid component such as di(tri)carboxylic acid or its derivatives (e.g., carboxylic anhydride, di(tri)carboxylic acid salt, monoalkyl di(tri)carboxylic acid ester or its salt, dialkyl di(tri)carboxylic acid ester, etc.)] (e.g., esterification).

[0079] The PVA-based polymer (A) has at least vinyl alcohol units, but may also have units that do not hydrolyze (saponify) with vinyl alcohol units [e.g., vinyl ester units (or units derived from vinyl ester monomers, such as vinyl acetate units, etc.)]. Furthermore, it may have units derived from other monomers exemplified in the items of the PVA-based polymer (B) below. Moreover, when other units are present, the content of these other units may be appropriately selected based on the monomers used, for example, relative to the PVA-based polymer (A) (or the total amount of its polymeric components), for example, it may be 20% by mass or less (e.g., 0.1 to 20% by mass, 15% by mass or less, 10% by mass or less), etc.

[0080] The block characterization (block characterization of residual vinyl ester units) of the PVA-based polymer (A) is not particularly limited and can be selected from the range of 0 to 2. It also depends on its application. From the viewpoint of maximizing the efficiency of the PVA-based polymer (A)'s function, it can be, for example, 0.2 or higher (e.g., 0.25 or higher), preferably 0.3 or higher (e.g., 0.32 or higher), and even more preferably 0.35 or higher (e.g., 0.38 or higher, 0.4 or higher), and can be 1.5 or lower (e.g., 1.2 or lower), preferably 1 or lower (e.g., 0.9 or lower), and even more preferably 0.8 or lower (e.g., 0.75 or lower, 0.7 or lower). Specific block characterization ranges include, for example, 0.3 to 1, 0.35 to 0.85, 0.38 to 0.8, 0.4 to 0.75, and approximately 0.35 to 0.7.

[0081] Here, the so-called block characteristic (block characteristic of residual vinyl ester units) (η) refers to an index representing the distribution of residual vinyl ester units (-CH2-CH(OCOR)-) in PVA, which is obtained by resolving three peaks appearing in the methylene region of the 13C-NMR spectrum. The above three peaks correspond to three biunit chain structures corresponding to (OH,OH), (OH,OCOR), and (OCOR,OCOR), and their absorption intensity is proportional to the three structures. The block characteristic (η) is represented by the following formula (1).

[0082] η=(OH,OCOR) / [2(OH)(OCOR)] Equation (1) [Where (OH,OCOR) represents the ratio of the biunit chain structure adjacent to the OH group and the OCOR group, (OH) represents the ratio of the vinyl alcohol unit, and (OCOR) represents the ratio of the remaining vinyl ester unit, expressed in molar fraction]

[0083] The value of this block characteristic is between 0 and 2. The closer it is to 0, the higher the blockiness of the vinyl ester group distribution; the closer it is to 1, the higher the randomness; and the closer it is to 2, the higher the alternation. Furthermore, the determination method for this block characteristic is described in detail in Macromolecules, 10, 532 (1977).

[0084] The block characteristics of the PVA-based polymer (A) can be adjusted, for example, by the block characteristics of the PVA-based polymer (B) used as its raw material or by the manufacturing conditions of the PVA-based polymer (A). Furthermore, it is believed that the change (increase) in the block characteristics depends on the transesterification reaction between the hydroxyl and ester groups in the PVA-based polymer, and this transesterification reaction can be affected by manufacturing conditions that can influence hue, transparency, or water insolubility, as described below. Therefore, the change (increase) in the block characteristics reflects more of the following: hue (coloring), transparency, or water insolubility (for example, when the change in block characteristics is suppressed, it is easier to fully satisfy the following: hue, higher transparency, or lower water insolubility (and thus lower YI)).

[0085] The lower limit of the degree of saponification of the PVA-based polymer (A) may be, for example, 10 mol% or more (e.g., 15 mol% or more), preferably 20 mol% or more (e.g., 22 mol% or more), more preferably 25 mol% or more (e.g., 27 mol% or more), and may be 30 mol% or more (e.g., 32 mol% or more).

[0086] The upper limit of the degree of saponification of the PVA-based polymer (A) may be, for example, 100 mol% or less (e.g., 99.9 mol% or less, 99 mol% or less, 98 mol% or less, 97 mol% or less, 95 mol% or less), but may be a saponification degree that is not too high [e.g., 90 mol% or less (e.g., 85 mol% or less), preferably 80 mol% or less (e.g., 75 mol% or less), and further 70 mol% or less (e.g., less than 70 mol%, 65 mol% or less, 60 mol% or less, 60 mol% or less, 55 mol% or less, 50 mol% or less, less than 50 mol%, 45 mol% or less, 40 mol% or less, less than 40 mol% or less, 38 mol% or less).

[0087] Specifically, the degree of saponification of the PVA-based polymer (A) may be, for example, 20 to 90 mol%, preferably 25 to 80 mol%, and even more preferably around 30 to 70 mol%, especially below 70 mol% (e.g., below 70 mol%, below 65 mol%, below 60 mol%, below 60 mol%, below 55 mol%, below 50 mol%, below 50 mol%, below 45 mol%, below 40 mol%, below 40 mol%, below 38 mol%).

[0088] In particular, in the present invention, even with a lower degree of saponification (a degree of saponification that does not originally show or is difficult to show water solubility), a PVA-based polymer (A) that fully satisfies the following requirements of higher transparency, lower water insoluble fraction or lower YI water solubility or dispersibility can be provided.

[0089] Furthermore, when introducing an ionic framework via a vinyl alcohol unit, the introduction (reaction) efficiency can be improved by ensuring that the degree of saponification is not too low, which is therefore better. As long as the degree of saponification is not too high, the industrial productivity of the PVA-based polymer (A) is excellent, which is also better.

[0090] Furthermore, the degree of saponification is obtained, for example, by means of the method for determining the degree of saponification of PVA as specified in JIS K 6726.

[0091] The degree of saponification of PVA-based polymer (A) can be adjusted, for example, by the degree of saponification of PVA-based polymer (B) used as its raw material. Furthermore, when PVA-based polymer (B) is transformed into PVA-based polymer (A), there may be a change in the degree of saponification. In such cases, the change can be anticipated and the degree of saponification of PVA-based polymer (B) can be adjusted.

[0092] The viscosity (20°C) of a 4% by mass aqueous solution of the PVA-based polymer (A) is not particularly limited. For example, it can be selected from a range of about 1 mPa·s or more (e.g., 1.1 mPa·s or more), preferably 1.2 mPa·s or more (e.g., 1.3 mPa·s or more), more preferably 1.4 mPa·s or more (e.g., 1.5 mPa·s or more), and even more preferably 1.6 mPa·s or more (e.g., 1.7 mPa·s or more, 1.8 mPa·s or more, 1.9 mPa·s or more).

[0093] There is no particular limitation on the upper limit of the viscosity (20°C) of a 4% by mass aqueous solution of PVA-based polymer (A). For example, it can be selected from a range of about 2000 mPa·s or less (e.g., 1500 mPa·s or less, 1000 mPa·s or less, 500 mPa·s or less), and typically from a range of about 300 mPa·s or less (e.g., 250 mPa·s or less, 200 mPa·s or less, 150 mPa·s or less, 120 mPa·s or less, 100 mPa·s or less, 80 mPa·s or less, 50 mPa·s or less). It can be 30 mPa·s or less (e.g., 20 mPa·s or less), preferably 15 mPa·s or less (e.g., 10 mPa·s or less), and even more preferably 9 mPa·s or less (e.g., 8 mPa·s or less).

[0094] Specifically, the viscosity (20°C) of a 4% by mass aqueous solution of the PVA-based polymer (A) can be, for example, about 1 to 500 mPa·s (e.g., 1.2 to 300 mPa·s, 1.3 to 100 mPa·s, 1.4 to 100 mPa·s, 1.5 to 30 mPa·s), or about 20 mPa·s or less (e.g., 1.6 to 15 mPa·s, 1.7 to 10 mPa·s, 1.8 to 9 mPa·s, 1.9 to 8 mPa·s).

[0095] The (average) degree of polymerization of the PVA-based polymer (A) is not particularly limited, for example, it can be 100 or more (e.g., 120 or more), preferably 140 or more (e.g., 160 or more), and even more preferably 180 or more (e.g., 200 or more, 220 or more, 250 or more), etc.

[0096] There is no particular limit to the upper limit of the (average) degree of polymerization of the PVA-based polymer (A). For example, it can be selected from a range of about 10,000 or less (e.g., 8,000 or less, 5,000 or less), or less than 3,000 or less (e.g., 2,500 or less), preferably less than 2,000 or less (e.g., 1,500 or less), and even more preferably less than 1,000 or less (e.g., 800 or less).

[0097] Specifically, the (average) degree of polymerization of the PVA-based polymer (A) may be, for example, 120 to 3000 (e.g., 140 to 2000), preferably 160 to 1500, and even more preferably around 180 to 1000.

[0098] As long as the viscosity or degree of polymerization of the 4% by mass aqueous solution of PVA-based polymer (A) is not too low, the PVA-based polymer (B) used as its raw material has excellent productivity, and is therefore preferred. Furthermore, as long as the viscosity or degree of polymerization of the 4% by mass aqueous solution is not too high, the industrial productivity of PVA-based polymer (A) is excellent, and it is also easier to achieve a lower water-insoluble fraction of PVA-based polymer (A), which is therefore preferred.

[0099] Furthermore, the viscosity of the 4% by mass aqueous solution (20°C) is obtained, for example, by the method specified in JIS K 6726. Also, the degree of polymerization can be obtained, for example, by the method specified in JIS K 6726, or it can be a calculated (converted) value based on other analytical methods [for example, a calculated (converted) value based on the viscosity of the 4% by mass aqueous solution].

[0100] Furthermore, the viscosity or (average) degree of polymerization of a 4% aqueous solution of PVA-based polymer (A) can be adjusted, for example, by the viscosity or degree of polymerization of a 4% aqueous solution of PVA-based polymer (B) used as its raw material, and can usually reflect the viscosity or degree of polymerization of a 4% aqueous solution of PVA-based polymer (B).

[0101] The pH value of a 4% by mass aqueous solution of PVA-based polymer (A) (e.g., pH value at 20°C) also depends on the type of ionic skeleton or its introduction ratio, and can usually exceed 3 [e.g., 3.2 or above, 3.5 or above, 4 or above, 4.5 or above, preferably 5 or above (e.g., 5.5 or above, 6 or above)] and can be less than 10 [e.g., 9.5 or below, 9 or below, 8.5 or below, 8 or below, 7.5 or below, 7.2 or below), preferably 7 or below (e.g., less than 7, 6.9 or below, 6.8 or below, 6.7 or below, 6.6 or below, 6.5 or below)]. Specific pH values ​​(e.g., pH value at 20°C) for a 4% by mass aqueous solution of PVA-based polymer (A) can be exemplified by: 3.5 to 8.5, 5 to 7, 5.5 to 6.5, etc. In particular, from the viewpoint of the desired function or stability of PVA-based polymers (A) (and thus a better balance of these), a pH range that is neither too low nor too high is preferred (e.g., 5–9, 5.5–8.5, 5.5–8, 6–9, etc.).

[0102] PVA-based polymers (A) may or may not contain sodium acetate. Depending on its content, sodium acetate may affect hue (coloring properties) or the efficient introduction of the ionic framework. Therefore, even when present, it is preferable to contain only a small amount. Thus, PVA-based polymers (A) may not contain sodium acetate (virtually not) or, if present, may contain it at a low percentage. For example, when the PVA-based polymer (A) contains sodium acetate, the ratio of sodium acetate in each monomer unit of the PVA-based polymer (A) (relative to the sum of other monomer units such as vinyl alcohol units and vinyl ester units) can be selected from a range of about 2 mol% or less (e.g., 1.5 mol% or less), preferably 1.2 mol% or less (e.g., 1 mol% or less), more preferably 0.8 mol% or less (e.g., 0.7 mol% or less), and even more preferably about 0.5 mol% or less (e.g., 0.4 mol% or less), or 0.3 mol% or less (e.g., 0.2 mol% or less, 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less), etc. Similarly, when the PVA-based polymer (A) contains sodium acetate, the proportion of sodium acetate may be 3% or less by mass (e.g., 2.5% or less by mass), preferably 2% or less by mass (e.g., 1.5% or less by mass), and even more preferably 1.2% or less by mass (e.g., 1% or less by mass, 0.8% or less by mass, 0.5% or less by mass, 0.3% or less by mass, 0.2% or less by mass, 0.1% or less by mass, 0.05% or less by mass), etc.

[0103] Furthermore, when the PVA polymer (A) contains sodium acetate, examples of lower limits for the content ratio can be given as follows: in each monomer unit of the PVA polymer (A) (relative to the total of other monomer units such as vinyl alcohol units and vinyl ester units), for example, 0.0001 mol% or more (e.g., 0.001 mol% or more, 0.01 mol% or more, 0.03 mol% or more, 0.05 mol% or more, 0.1 mol% or more), and in the PVA polymer (A) (PVA polymer (A) containing sodium acetate), 0.0001 mass% or more (e.g., 0.001 mass% or more, 0.05 mass% or more, 0.1 mass% or more).

[0104] When the PVA polymer (A) contains sodium acetate, the specific ratio of sodium acetate is 0.01 to 1 mol% in each monomer unit of the PVA polymer (A) (relative to the total of other monomer units such as vinyl alcohol units and vinyl ester units), preferably 0.03 to 0.7 mol%, and more preferably about 0.05 to 0.5 mol%.

[0105] Furthermore, the ratio of sodium acetate can be determined or determined, for example, by NMR [e.g., by 1H-NMR determination of PVA-based polymers (A), and by quantifying and calculating the signal from sodium acetate].

[0106] The YI (yellowness, yellow index) of a 4% by mass dimethyl sulfoxide (DMSO) solution of PVA-based polymer (A) can be selected from a range of about 30 or less (e.g., less than 25, less than 20, less than 18), for example, less than 15 (e.g., less than 12), preferably less than 10 (e.g., less than 9), further preferably less than 8 (e.g., less than 6), and even more preferably less than 5 (e.g., less than 4, less than 3.5, less than 3, less than 2.5, less than 2, less than 1.5, less than 1.2, less than 1, less than 1, less than 0.8, less than 0.5, less than 0.3, less than 0.1), etc.

[0107] Furthermore, the YI of a 4% by mass DMSO solution of PVA-based polymer (A) can be measured at 20°C using a UV-Vis spectrophotometer (e.g., a quartz cell with an optical path length of 10 mm) (wavelength range of 360–830 nm), and calculations can be performed from the obtained data.

[0108] This type of YI reflects coloring, and if it is this type of YI, the hue is excellent (coloring is suppressed). Furthermore, as described below, YI can be easily and efficiently produced within the range described above by selecting the manufacturing conditions of the PVA-based polymer (A).

[0109] The PVA-based polymer (A) is preferably dissolved or dispersed in water.

[0110] The transparency (430 nm) of a 4% by mass aqueous solution of PVA-based polymer (A) can be selected from a range of about 0.5% or more, for example, it can be 1% or more, preferably 2% or more (for example, 3% or more, 4% or more), and even more preferably 5% or more (for example, 7% or more), or it can be 10% or more (for example, more than 10%, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more). In particular, the transparency (at 20°C) of a 4% by mass aqueous solution of PVA-based polymer (A) can be 40% or more, 50% or more, 60% or more, 68% or more (e.g., 70% or more, 72% or more, 75% or more, 77% or more, 80% or more, 82% or more, 85% or more, etc.).

[0111] Furthermore, the transparency (430 nm) of a 4% by mass aqueous solution can be obtained, for example, by measuring the transmittance at 430 nm (e.g., a quartz trough with an optical path length of 20 mm) using a UV-Vis spectrophotometer at 20°C with water as a control.

[0112] The water insoluble fraction of the PVA-based polymer (A) can be selected from a range of less than 50% by mass (e.g., less than 45% by mass), for example, less than 40% by mass (e.g., less than 35% by mass, less than 30% by mass, less than 25% by mass, less than 20% by mass, less than 18% by mass), and preferably less than 15% by mass (e.g., less than 12% by mass, less than 10% by mass, less than 8% by mass). In particular, the water-insoluble fraction of the PVA-based polymer (A) can be 20% by mass or less (e.g., 15% by mass or less), preferably 10% by mass or less (e.g., 8% by mass or less), and even more preferably 5% by mass or less (e.g., less than 5% by mass, less than 4% by mass, less than 3% by mass, less than 2% by mass, less than 1.5% by mass, less than 1% by mass, less than 0.8% by mass, less than 0.6% by mass, less than 0.5% by mass, less than 0.4% by mass, less than 0.3% by mass, less than 0.2% by mass, less than 0.1% by mass, less than 0.1% by mass, less than 0.08% by mass, less than 0.06% by mass, less than 0.04% by mass, less than 0.02% by mass, less than 0.01% by mass, etc.).

[0113] Furthermore, the water-insoluble fraction can be obtained, for example, by dissolving in water at 50°C (e.g., dissolving in 50 times its mass of water), cooling to room temperature (e.g., 15–30°C), passing the resulting solution (mixture) through a filter (metal mesh) with a specified mesh size (e.g., 100 mesh), measuring the amount remaining that does not pass through the filter (metal mesh) (water-insoluble fraction), and calculating the water-insoluble fraction / total amount of PVA-based polymer (A) × 100 (%). Specifically, it can be obtained by the method described in the following examples.

[0114] The transparency or water insoluble fraction of a 4% (w / w) aqueous solution can serve as an indicator of water solubility or dispersibility. Higher transparency and / or lower water insoluble fraction indicate better water solubility or dispersibility. Furthermore, it is believed that decreased transparency, or the presence of PVA-based polymers that are not adequately incorporated into the ionic framework, or certain other factors (such as the presence of highly polymerized PVA-based polymers, reaction temperature, the composition of the corresponding ionic framework (ionic group), the amount of pH adjuster, and the conditions for incorporating the ionic framework) can lead to the formation (byproduct) of crosslinking compounds.

[0115] Furthermore, it is believed that transparency or water insoluble content is also related to the degree of reaction spots [e.g., the uniformity of the reaction (esterification reaction) that introduces a backbone with ionic groups derived from polycarboxylic acid components]. Therefore, in the manufacture of PVA-based polymers (A), by suppressing such reaction spots (improving the uniformity of the reaction), it is easy to efficiently and sufficiently satisfy the aforementioned transparency or water insoluble content. The uniformity of reactivity, as described below, can be improved by selecting the manufacturing conditions of PVA-based polymers (A).

[0116] The PVA-based polymer (A) can fully satisfy at least one of the following necessary conditions selected from the above-mentioned water insoluble fraction (necessary condition 1), transparency of 4% by mass aqueous solution (20°C, 430 nm) (necessary condition 2), and YI of 4% by mass dimethyl monoxide (DMSO) solution (necessary condition 3), preferably fully satisfying two or more of the necessary conditions (e.g., necessary conditions 1 and 2, necessary conditions 1 and / or necessary conditions 2 and necessary conditions 3, etc.), and even more preferably fully satisfying all necessary conditions 1 to 3.

[0117] [Manufacturing Method] There is no particular limitation on the method for manufacturing the PVA-based polymer (A). Conventional methods can be used. In this invention, a representative example is that the PVA-based polymer (A) can be manufactured by reacting a polyvinyl alcohol-based polymer (B) with a component of the corresponding ionic backbone (ionic group) (e.g., a polycarboxylic acid component). Hereinafter, representative or specific examples (PVA-based polymer (B), esterification, etc.) will be given regarding this reaction and manufacturing method.

[0118] [Polyvinyl alcohol polymer (B)] There is no particular limitation on the polyvinyl alcohol polymer (sometimes called PVA polymer (B), PVA (B) etc.). For example, PVA polymers obtained by saponifying (reacting) ethylene ester polymers can be used [saponification of ethylene ester polymers (polymers with ethylene ester monomers as polymer components)].

[0119] Ethylene ester polymers can be obtained by polymerizing at least one ethylene ester monomer (polymerizing it as a polymerizing component). There is no particular limitation on the polymerization method; previously known methods can be used, such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. However, considering the control of the degree of polymerization or the saponification reaction after polymerization, solution polymerization using methanol as a solvent or suspension polymerization using water or water / methanol as a dispersion medium is preferred, but it is not limited to these methods.

[0120] There are no particular limitations on the vinyl ester monomers that can be used in the above polymerization. Examples include vinyl acetate, vinyl formate, vinyl propionate, vinyl octanoate, vinyl terephthalate, and other fatty acid vinyl esters. One or more of these vinyl ester monomers can be used. From an industrial point of view, vinyl acetate is preferred.

[0121] When polymerizing ethylene ester monomers, as long as the effects of the present invention are achieved, ethylene ester monomers can be copolymerized with other monomers. In other words, the polymer composition of ethylene ester polymers can contain ethylene ester monomers and other monomers. Other monomers that can be used are not particularly limited, and examples include: α-olefins (e.g., ethylene, propylene, n-butene, isobutene, etc.), (meth)acrylates [e.g., (meth)acrylate alkyl esters (e.g., (meth)acrylate methyl acrylate, (meth)acrylate ethyl acrylate, (meth)acrylate n-propyl acrylate, (meth)acrylate isopropyl acrylate, (meth)acrylate n-butyl acrylate, (meth)acrylate isobutyl acrylate, (meth)acrylate tributyl acrylate, (meth)acrylate 2-ethylhexyl acrylate, (meth)acrylate dodecyl acrylate, (meth)acrylate octadecyl acrylate, etc. (meth)acrylate C1-20 alkyl esters, etc.)], (meth)acrylamide, (meth)acrylamide derivatives (e.g., N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide). Amines, diacetone (meth)acrylamide, (meth)acrylamide propanesulfonic acid and its salts, (meth)acrylamide propyl dimethylamine and its salts or quaternary salts, N-hydroxymethyl (meth)acrylamide, etc.), vinyl ethers (e.g., methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tributyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc., C1-20 alkyl vinyl ethers, etc.), nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), halogenated vinylides (e.g., vinyl chloride, vinyl fluoride, etc.), vinylidene dihaloethyleneides (e.g., vinylidene chloride, vinylidene fluoride, etc.), allyl compounds (e.g., allyl acetate, allyl chloride, etc.), vinyl silyl compounds (e.g., vinyltrimethoxysilane, etc.), fatty acid olefins (e.g., isopropyl acetate, etc.). One or more of these other monomers may be used.

[0122] When other monomers are used, the content of the other monomers relative to the total amount of monomers is, for example, 0.1 to 20% by mass.

[0123] Furthermore, during the polymerization of vinyl ester monomers, chain transfer agents can be coexisted to adjust the degree of polymerization of the obtained vinyl ester polymer. There are no particular limitations on the chain transfer agent; examples include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; thiols such as 2-hydroxyethanethiol, dodecyl mercaptopropionic acid, mercaptosuccinic acid, and sodium 3-mercapto-1-propanesulfonate; and organohalides such as carbon tetrachloride, trichloroethylene, and perchloroethylene. Aldehydes and ketones are preferred. The amount of chain transfer agent added is determined based on the chain transfer constant of the added chain transfer agent and the degree of polymerization of the target vinyl ester polymer; ideally, it is 0.1 to 10% by mass relative to the total amount of monomers.

[0124] PVA-based polymers (B) can be manufactured by saponifying the vinyl ester polymer obtained as described above. The method for saponifying the vinyl ester polymer is not particularly limited and can be based on previously known methods. For example, alcoholysis or hydrolysis reactions using alkaline catalysts (alkali catalysts, such as sodium hydroxide, potassium hydroxide, etc.) or acidic catalysts [acid catalysts, such as inorganic acids (e.g., hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc.), organic acids (e.g., carboxylic acids (e.g., formic acid, acetic acid, oxalic acid, etc.), sulfonic acids (e.g., p-toluenesulfonic acid)] can be used. The catalyst can be used alone or in combination of two or more.

[0125] In addition to water, the solvents used in the saponification reaction can include: alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene, etc., which can be used alone or in combination of two or more.

[0126] After the saponification reaction, a neutralizing agent may be used (added) depending on the type of residual catalyst. When using an alkaline catalyst, an acidic substance [e.g., organic acids (e.g., carboxylic acids such as formic acid, acetic acid, propionic acid, etc.), inorganic acids (e.g., phosphoric acid, hydrogen phosphate, sulfuric acid, hydrochloric acid, nitric acid, etc.)] is used as a neutralizing agent; when using an acidic catalyst, an alkaline substance (or basic material, such as alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, etc.) is used. The neutralizing agent may be used alone or in combination of two or more.

[0127] In this invention, from the viewpoint of high-efficiency saponification (saponification speed, etc.), it is preferable to use an alkaline catalyst in the saponification reaction as a neutralizing agent, preferably at least one selected from carboxylic acids (fatty acids such as acetic acid), phosphoric acid and hydrogen phosphate.

[0128] There are no particular restrictions on the block characteristics or saponification degree of PVA-based polymer (B). Since the block characteristics or saponification degree of PVA-based polymer (A) may change from the PVA-based polymer (B) used as raw material during subsequent esterification reactions, it is preferable to adjust the block characteristics or saponification degree of PVA-based polymer (B) in order to anticipate such changes in such cases.

[0129] Furthermore, there are no particular limitations on the viscosity or degree of polymerization of a 4% by mass aqueous solution of PVA-based polymer (B). Generally, the viscosity or degree of polymerization of a 4% by mass aqueous solution of PVA-based polymer (A) can reflect the PVA-based polymer (B) used as a raw material during subsequent esterification reactions, etc. Therefore, it is preferable to adjust it to the target 4% by mass aqueous solution viscosity or degree of polymerization of PVA-based polymer (A). Moreover, depending on the degree of saponification of PVA-based polymer (B) (in the case of a low degree of saponification), there may be cases where it is insoluble in water. Therefore, in such cases, the degree of polymerization can be used as the standard.

[0130] The PVA-based polymer (B) may or may not contain sodium acetate. When sodium acetate is present, the proportion of sodium acetate in the PVA-based polymer (B) may be, for example, 0.001 mol% or more (e.g., 0.005 mol% or more) in each monomer unit (relative to the total of other monomer units such as vinyl alcohol units and vinyl ester units), preferably 0.03 mol% or more (e.g., 0.05 mol% or more), and more preferably 0.07 mol% or more (e.g., 0.08 mol% or more), or approximately 0.1 mol% or more (e.g., 0.12 mol% or more, 0.15 mol% or more, 0.18 mol% or more, 0.2 mol% or more, 0.22 mol% or more, 0.25 mol% or more).

[0131] The upper limit of the sodium acetate ratio in the PVA-based polymer (B) in each monomer unit (relative to the total of other monomer units such as vinyl alcohol units and vinyl ester units) may be, for example, 10 mol% or less, 8 mol% or less, 6 mol% or less, 5 mol% or less, 4 mol% or less, 3 mol% or less, 2.5 mol% or less, 2.2 mol% or less, 2 mol% or less, 1.8 mol% or less, 1.5 mol% or less, 1.2 mol% or less, 1 mol% or less, 0.9 mol% or less, 0.8 mol% or less, 0.7 mol% or less, 0.6 mol% or less, 0.5 mol% or less, 0.4 mol% or less, 0.3 mol% or less, etc.

[0132] When sodium acetate is present, the proportion of sodium acetate in the PVA-based polymer (B) may be, for example, 0.001% by mass or more (e.g., 0.005% by mass or more), preferably 0.03% by mass or more (e.g., 0.05% by mass or more), and more preferably 0.07% by mass or more (e.g., 0.08% by mass or more), or may be 0.1% by mass or more (e.g., 0.12% by mass or more, 0.15% by mass or more, 0.18% by mass or more, 0.2% by mass or more, 0.22% by mass or more, or 0.25% by mass or more).

[0133] The upper limit of the proportion of sodium acetate in PVA-based polymers (B) may be, for example, 10% by mass or less, 8% by mass or less, 6% by mass or less, 5% by mass or less, 4% by mass or less, 3% by mass or less, 2.5% by mass or less, 2.2% by mass or less, 2% by mass or less, 1.8% by mass or less, 1.5% by mass or less, 1.2% by mass or less, 1% by mass or less, 0.9% by mass or less, 0.8% by mass or less, 0.7% by mass or less, 0.6% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, etc.

[0134] This sodium acetate can be added or blended into the PVA-based polymer (B) beforehand, or it can be generated or remain as a byproduct during the manufacturing process of the PVA-based polymer (B) (e.g., saponification step), and can be combined with other components to be contained in the PVA-based polymer (B). Furthermore, as described below, sodium acetate can also function as a pH adjuster [an alkaline pH adjuster (alkaline component) in the reaction (esterification)]. When using sodium acetate for this purpose, it is sufficient that sodium acetate is present in the reaction; it does not need to be contained in the PVA-based polymer (B). The amount of sodium acetate in the reaction can be adjusted by adding or blending sodium acetate according to the amount of sodium acetate contained in the PVA-based polymer (B).

[0135] [Reaction (esterification, etc.)] As described above, PVA-based polymer (A) can be manufactured by reacting PVA-based polymer (B) with components of the corresponding ionic backbone (ionic group).

[0136] In this method, an ionic skeleton can usually be introduced via a vinyl alcohol unit (vinyl alcohol unit of PVA-based polymer (B)). In particular, when a polycarboxylic acid component is used as the component corresponding to the ionic skeleton (ionic group), a PVA-based polymer (A) having an ionic skeleton (an ionic skeleton derived from a polycarboxylic acid component, such as a carboxyl group or its salt group) can be produced by reacting the vinyl alcohol unit with the polycarboxylic acid component (esterification reaction).

[0137] This reaction (the method of introducing ionic groups into PVA-based polymers (B), esterification reaction, esterification method) is not particularly limited, and the following methods can be used for example.

[0138] Specific esterification methods (esterification steps) may include: heating steps involving heating a composition containing a PVA-based polymer (B) and a corresponding ionic backbone component [e.g., di(tri)carboxylic acid and / or its derivatives, or other polycarboxylic acid components] (in a solid or molten state) {heating steps involving heating a polyvinyl alcohol-based polymer (B) in the presence of a corresponding ionic backbone component [e.g., di(tri)carboxylic acid and / or its derivatives, or other polycarboxylic acid components] (heating steps involving heating a polyvinyl alcohol-based polymer (B) with a corresponding ionic backbone component)}, etc.

[0139] Representative examples may be cited as follows: (i) A method of obtaining a solution (homogeneous solution, solution composition, solvent composition) containing a PVA-based polymer (B), a component with a corresponding ionic backbone [e.g., polycarboxylic acid components such as di(tri)carboxylic acid and / or its derivatives], and a pH adjuster as needed, removing (evaporating) the solvent from the solution, and heating the composition after removing the solvent to cause a reaction {esterification [esterification in a solid state (or solid composition) or a molten state (or molten composition)] to obtain a PVA-based polymer (A)}; (ii) A method of not making the PVA-based polymer (B), the component with a corresponding ionic backbone [e.g., polycarboxylic acid components such as di(tri)carboxylic acid and / or its derivatives], and the pH adjuster as needed into a solution, but heating it in a solid state (at least the PVA-based polymer (B) is in a solid state) to cause a reaction {esterification [esterification in a solid state (or solid composition) or a molten state (or molten composition), especially in a molten state]}, etc.

[0140] Among these, from the viewpoint of efficiently and sufficiently satisfying the hue, transparency, or water insolubility as described above, method (a) is preferred (furthermore, selecting and adjusting the following conditions such as heating temperature, heating time, type of solvent, use of pH adjuster, or type thereof). This method (a) may be, for example, the following method: a solvent removal step that removes the solvent from a composition (solvent composition, solution composition, solution) containing a PVA-based polymer (B), a component with a corresponding ionic backbone [e.g., a polycarboxylic acid component such as di(tri)carboxylic acid and / or its derivatives] and a solvent; a heating step performed after the solvent removal step (e.g., after recovering the composition obtained in the solvent removal step, the composition is subjected to a separate heating step) or in parallel or continuously with the solvent removal step (e.g., the composition obtained in the solvent removal step is directly (in parallel or continuously) heated in the system in which the solvent removal step is performed)).

[0141] In method (a), as a method for obtaining a solution of PVA-based polymer (B), (i) it can be obtained by dissolving PVA-based polymer (B) in a solvent, and (ii) it can be obtained by saponifying ethylene ester polymer in a solvent such as methanol with an alkaline catalyst such as sodium hydroxide.

[0142] As a representative method (method of esterification), examples include: (i) a method of removing (e.g., evaporating) the solvent from a solution (homogeneous composition, solvent composition) to obtain a solid composition, and then heating the solid composition under specified conditions; (ii) a method of simultaneously or continuously evaporating the solvent and heating the composition while heating the solution (homogeneous composition, solvent composition).

[0143] Here, depending on the heating conditions, the composition (the composition from which the solvent has been removed) becomes solid or molten during heating [for example, when the heating temperature is below the melting point of the PVA-based polymer (B) (and thus the PVA-based polymer (A)), it becomes solid, and when the heating temperature is above the melting point of the PVA-based polymer (B), it becomes molten].

[0144] As a solvent, there are no particular limitations as long as it can dissolve PVA-based polymers (B). However, since the solvent needs to be evaporated during the reaction (esterification reaction, etc.), from the viewpoint of evaporating it efficiently (e.g., evaporating easily without excessive heating), the boiling point of the solvent is preferably 150°C or less under normal pressure, more preferably 130°C or less, and even more preferably 110°C or less.

[0145] In addition to water, specific solvents may include: methanol, alcohols such as ethanol, esters such as methyl acetate and ethyl acetate, ethers such as diethyl ether and tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, aromatic compounds such as benzene and toluene (aromatic hydrocarbons, etc.). It is preferable to use one or more solvents or mixed solvents selected from water, alcohols (methanol, etc.), and esters (methyl acetate, etc.). In particular, it is preferable to use solvents containing methanol (at least methanol).

[0146] Furthermore, since the PVA-based polymer (B) can be completely dissolved, it is appropriate to change the type of solvent or the ratio of mixed solvents.

[0147] In solution, the concentration of PVA-based polymer (B) is not particularly limited and can be selected according to the type or properties (degree of saponification, etc.) of the PVA-based polymer (B). For example, the concentration of PVA-based polymer (B) is usually around 5 to 70% by mass, and in cases where the degree of polymerization is below 500, the concentration can be made higher (e.g., around 40 to 70% by mass). A higher concentration of PVA-based polymer (B) can reduce the amount of solvent evaporated in the reaction (esterification, etc.) steps, which is advantageous.

[0148] By reacting (esterification, etc.) with such a solution (solvent composition) (by performing a heating step), reaction spots can be suppressed, and the reaction (esterification, etc.) can be carried out with high efficiency. It is also easy to efficiently and fully satisfy the above-mentioned YI value, transparency, water insoluble fraction, etc.

[0149] Furthermore, there are no particular limitations on the components corresponding to the ionic framework, as long as they have the corresponding ionic group and can be introduced into the ionic group. Examples of such components corresponding to the ionic framework, as mentioned above, include: polycarboxylic acid components (di(tri)carboxylic acid, derivatives of di(tri)carboxylic acid, etc.). Examples of di(tri)carboxylic acids include the components listed above, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, trans-butenedioic acid, methyl maleic acid, methyl trans-butenedioic acid, itconic acid, malic acid, oxaloacetic acid, cis-1,2-cyclohexanedicarboxylic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, 5-norphene-2,3-dicarboxylic acid, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic acid, etc. (aliphatic dicarboxylic acids), citric acid, aconitic acid, etc. (aliphatic tricarboxylic acids), phthalic acid, isophthalic acid, terephthalic acid, etc. (aromatic dicarboxylic acids), trimellitic acid, etc. (aromatic tricarboxylic acids), among which succinic acid, maleic acid, methyl maleic acid, itconic acid, phthalic acid, citric acid, etc. are preferred. As derivatives of di(tri)carboxylic acids, examples of the components described above can be cited, such as monoalkyl esters of di(tri)carboxylic acids or their salts, and more preferably monomethyl esters of di(tri)carboxylic acids or their salts. Specifically, monomethyl succinate, monomethyl maleate, methyl maleate, monomethyl isconate, monomethyl phthalate, monomethyl citrate, or their salts (alkali metal salts) are preferred. Furthermore, as derivatives, as described above, carboxylic anhydrides can also be used, such as succinic anhydride, maleic anhydride, methyl maleic anhydride, isconate anhydride, phthalic anhydride, cis-4-cyclohexene-1,2-dicarboxylic anhydride, cis-1,2-cyclohexanedicarboxylic anhydride, 5-norphene-2,3-dicarboxylic anhydride, trimellitic anhydride, etc.

[0150] Components corresponding to the ionic framework [e.g., di(tri)carboxylic acids and / or their derivatives, etc., polycarboxylic acid components] can be added directly to the solution of the PVA-based polymer (B) in their original state or as a solution dissolved in a suitable solvent (water, methanol, etc.). Generally, if a carboxylic anhydride is dissolved in water, it is partially or completely transformed into the corresponding polycarboxylic acid (dicarboxylic acid, etc.). Also, if a carboxylic anhydride is dissolved in methanol, it is partially or completely transformed into the corresponding polycarboxylic acid monomethyl ester (dicarboxylic acid monomethyl ester, etc.). In this invention, polycarboxylic acids (dicarboxylic acids, etc.) generated by the reaction of carboxylic anhydride with water, or polycarboxylic acid esters (e.g., dicarboxylic acid monomethyl ester, etc.) generated by the reaction of carboxylic anhydride with alcohol (methanol, etc.) can also be used.

[0151] The amount of the component corresponding to the ionic backbone [e.g., polycarboxylic acid components such as di(tri)carboxylic acid and / or its derivatives] added also depends on the amount of the component corresponding to the ionic backbone [e.g., ionic groups derived from polycarboxylic acid components such as di(tri)carboxylic acid and / or its derivatives] introduced. For example, relative to 100 parts by weight of PVA-based polymer (B), it is preferably 0.1 parts by weight or more, preferably 0.3 parts by weight or more, and more preferably 0.5 parts by weight or more. Furthermore, it is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and more preferably 10 parts by weight or less.

[0152] A pH adjuster (e.g., selected from at least one of acidic and alkaline components) is not necessary, but by being present in the reaction system as needed, it is easy to achieve (1) improved reaction efficiency, (2) inhibition of coloring of PVA-based polymer (A), (3) improved water solubility (water dispersibility) of PVA-based polymer (A), and (4) inhibition of insolubility of PVA-based polymer (A), and can easily and efficiently meet the above-mentioned YI value, transparency, water insolubility, etc.

[0153] For example, when the acidity of the reaction system is high [and consequently the pH value of the obtained 4% by mass aqueous solution of PVA-based polymer (A) is low (e.g., below 4.5)], the water insoluble fraction tends to increase, so it is preferable to add an alkaline pH adjuster. Furthermore, when the acidity of the reaction system is low (e.g., alkalinity) [and consequently the pH value of the obtained 4% by mass aqueous solution of PVA-based polymer (A) is high (e.g., above 6.5, above 7, or above 7)], the reaction efficiency decreases or the color (YI) tends to deteriorate, so it is preferable to add an acidic pH adjuster. Moreover, the pH adjuster can be selected according to the component with the corresponding ionic skeleton; for example, for polycarboxylic acid components, an alkaline pH adjuster (alkaline component) is preferable.

[0154] Examples of acidic pH adjusters (acidic components) include: organic acids (e.g., carboxylic acids such as formic acid, acetic acid, and propionic acid), and inorganic acids (e.g., phosphoric acid, hydrogen phosphate, sulfuric acid, hydrochloric acid, and nitric acid). These pH adjusters can be used alone or in combination of two or more. Examples of alkaline pH adjusters (alkali components) include: alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, or carbonates such as sodium carbonate and potassium carbonate, bicarbonates such as sodium bicarbonate and potassium bicarbonate, and organic acid salts such as sodium acetate. These pH adjusters can be used alone or in combination of two or more.

[0155] The amount of pH adjuster present in the reaction system can be selected, for example, based on the type and amount of the component corresponding to the ionic skeleton [e.g., polycarboxylic acid components such as di(tri)carboxylic acid and / or its derivatives], and is particularly preferably selected based on the amount of the component corresponding to the ionic skeleton [e.g., polycarboxylic acid components such as di(tri)carboxylic acid and / or its derivatives] [e.g., the amount of the component (or ionic group) corresponding to the ionic skeleton (or ionic group) is less than or equal to 1 mol. For example, the pH adjuster [e.g., an alkaline pH adjuster (alkaline component)] can be 0.3 to 3 mol (equivalent) relative to 1 mol of the component corresponding to the ionic skeleton (e.g., polycarboxylic acid component), preferably 0.5 to 1.9 mol (e.g., 0.55 to 1.8 mol, 0.8 to 1.5 mol), and more preferably 0.9 to 1.3 mol (e.g., 0.95 to 1.2 mol), etc., and can be present in the reaction system in such a way.

[0156] Furthermore, as described above, when the PVA-based polymer (B) contains sodium acetate, the amount of sodium acetate can be added according to its quantity or the desired pH value, and the type or quantity of the added pH adjuster can be readjusted.

[0157] As described above, method (a) includes a step (solvent removal step) of removing (evaporating) the solvent from a composition (solvent composition, solution, homogeneous composition) containing a PVA-based polymer (B), a component with a corresponding ionic backbone [e.g., di(tri)carboxylic acid and / or its derivatives, or other polycarboxylic acid components], and a pH adjuster as needed. In this solvent removal step, the method for removing the solvent is not particularly limited, but the method for evaporating the solvent is relatively simple. Examples of methods for evaporating the solvent (drying method) include: natural drying, heat drying, reduced pressure, and methods combining the above. In the case of heat drying, the drying temperature can be selected according to the type of solvent, etc. Furthermore, the composition after the solvent removal step, as described above, is supplied to the heating step after the solvent removal step, or in parallel with or continuously with the solvent removal step.

[0158] The heating temperature (the heating temperature of the heating step) is preferably 80°C or higher, more preferably 100°C or higher, 120°C or higher, and may also be 130°C or higher. It is also preferably 240°C or lower, more preferably 220°C or lower, 200°C or lower, and may also be 190°C or lower.

[0159] When the heating temperature is too low, there is a possibility that the reaction (such as esterification) is not fully carried out. On the other hand, when the heating temperature is too high, it is also difficult to efficiently and fully satisfy the above-mentioned hue, transparency or water insolubility (and thus, the PVA-based polymer (A) becomes insoluble or the color becomes heavier).

[0160] In method (a), the PVA-based polymer (B) and the corresponding ionic backbone component [e.g., di(tri)carboxylic acid and / or its derivatives and other polycarboxylic acid components] are mixed uniformly in solution (in solution state) beforehand. Therefore, it is not necessary to raise the heating temperature to a temperature above the melting point of the PVA-based polymer (B). Even at a temperature below the melting point, the reaction (esterification, etc.) can be carried out more uniformly, and it is even easier to efficiently and fully meet the above-mentioned YI value, transparency, water insoluble fraction, etc.

[0161] There is no particular limitation on the heating time, but it is preferably about 5 minutes or more, more preferably 7 minutes or more, and may also be 10 minutes or more. Furthermore, it is preferably 5 hours or less, more preferably 3 hours or less, 2 hours or less, and may also be 1 hour or less. Moreover, in the case where the solvent evaporation and composition heating are carried out in parallel or continuously, the temperature inside the container differs from the heating temperature during the solvent evaporation from the composition, therefore this period (the drying time of the aforementioned solvent removal step) is not included in the heating time.

[0162] When the heating time is too short, there is a situation where the reaction (esterification, etc.) is not fully carried out. On the other hand, when the heating time is too long, it is also difficult to efficiently and fully satisfy the above-mentioned hue, transparency or water insolubility (and thus, the PVA-based polymer (A) becomes insoluble or the color becomes heavier).

[0163] As a heating device, in the case of batch processing, a blower dryer or a vacuum dryer with temperature adjustment function can be used. In the case of continuous processing, a thin-film evaporation and concentration device or the like can be used.

[0164] [Applications, etc.] PVA-based polymers (A) can be used for a variety of applications, as described above, and are particularly preferred as hot melt adhesives (e.g., water-soluble hot melt adhesives), dispersants [or dispersing aids, such as dispersants (dispersing aids) for polymerization (e.g., suspension polymerization).

[0165] Furthermore, in these various applications, the PVA-based polymer (A) can be used alone or in combination of two or more. For example, a PVA-based polymer (A) with a higher 4% by mass aqueous solution viscosity (degree of polymerization) or saponification degree can be combined with a PVA-based polymer (A) with a lower 4% by mass aqueous solution viscosity (degree of polymerization) or saponification degree.

[0166] As one example of this application, the following describes the use of a dispersant (or a PVA-based polymer (A), hereinafter the same) or the manufacturing method of an ethylene-based polymer by polymerization (especially suspension polymerization) of an ethylene-based monomer using the dispersant.

[0167] Suspension polymerization refers to a polymerization process in which an insoluble vinyl monomer and an oil-soluble polymerization initiator are added to an aqueous medium and stirred to form tiny droplets containing the vinyl monomer, in which polymerization takes place. The aqueous medium used herein is not particularly limited, and examples include: water, aqueous solutions containing various additives, and mixtures of water and organic solvents that are miscible with water.

[0168] The PVA-based polymer (A) can be used as a dispersant in the suspension polymerization of ethylene monomers. There are no particular limitations on the ethylene monomer used; for example, vinyl chloride, vinylidene chloride, styrene, acrylates, methacrylates, vinyl acetate, acrylonitrile, and other ethylene monomers commonly used in suspension polymerization are preferred, with vinyl chloride monomers being particularly preferred.

[0169] Examples of vinyl chloride monomers include, for example, vinyl chloride monomer (vinyl chloride), and also, for example, mixtures of vinyl chloride monomer with other monomers that can copolymerize with it. Examples of other monomers that can copolymerize with vinyl chloride monomer include, for example, vinylidene chloride, vinyl acetate, ethylene, propylene, acrylic acid, acrylate, methacrylic acid, methacrylate, styrene, vinylalkoxysilane, maleic acid, hydroxyalkyl acrylate, allyl sulfonic acid, vinyl sulfonic acid, etc.

[0170] Therefore, the dispersant (PVA-based polymer (A)) is suitable for suspension polymerization of vinyl monomers containing vinyl chloride monomers (especially vinyl chloride), and is particularly well used for homopolymerization of vinyl chloride by suspension polymerization. It can also be used for binary or multi-component copolymerization of vinyl chloride with one or more known monomers selected from those that can copolymerize with vinyl chloride by suspension polymerization. It is particularly well used as a dispersing aid in the copolymerization of vinyl chloride and vinyl acetate by suspension polymerization.

[0171] A vinyl chloride resin can be obtained by suspension polymerization of vinyl chloride-containing ethylene monomers. In the manufacture of the vinyl chloride resin, it is preferable that the total amount of ethylene monomers used is 50 to 100 moles (or 50 to 100% by mass) of vinyl chloride.

[0172] The polymerization initiators used in the suspension polymerization of ethylene monomers can also be known, such as: diisopropyl peroxide, di-2-ethylhexyl peroxide, diethoxyethyl peroxide, etc., percarbonate compounds, benzoyl peroxide, tert-butyl peroxydecanoate, α-isopropylphenyl peroxydecanoate, tert-butyl peroxydecanoate, etc., perester compounds, acetylated cyclohexyl sulfonylurea peroxide, 2-peroxyphenoxyacetic acid 2,4,4-trimethylpentyl ester, etc., 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylpentanitrile, azobis(4-methoxy-2,4-dimethylpentanitrile), benzoyl peroxide, lauryl peroxide, etc., and potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. can also be used in combination with these.

[0173] There is no particular limitation on the amount of PVA-based polymer (A) (or dispersant) used. For example, it may be less than 1 part by mass (e.g., 0.002 to 0.5 parts by mass, 0.005 to 0.2 parts by mass) relative to 100 parts by mass of ethylene monomer.

[0174] Polymerization (suspension polymerization) can be carried out in the presence of a dispersant (other dispersants, dispersion stabilizers). In other words, the PVA-based polymer (A) can be used in combination with a dispersant (other dispersants, dispersion stabilizers) [which may be a dispersant used in the application (dispersant for suspension polymerization, etc.)].

[0175] Other dispersants may include, for example, water-soluble polymers [e.g., cellulose derivatives (e.g., water-soluble cellulose ethers such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, etc.), gelatin, polyvinyl alcohol polymers, polyvinylpyrrolidone, etc.], emulsifiers or surfactants [e.g., sorbitan monolaurate, sorbitan trioleate, glyceryl tristearate, ethylene oxide-propylene oxide block polymers, polyoxyethylene glyceryl oleate, sodium laurylate, etc.]. One or more of these other dispersants may be used simultaneously.

[0176] Among these, PVA-based polymers (PVA-based polymers that do not fall under the category of PVA-based polymers (A)) are preferred.

[0177] PVA-based polymers (such as polyvinyl alcohol) are any PVA-based polymers that do not belong to the category of PVA-based polymers (A). They can usually be different from PVA-based polymers (A) in terms of degree of saponification or viscosity (degree of polymerization) of 4% by mass aqueous solution (for example, the larger one).

[0178] For example, the degree of saponification of PVA-based polymers can be 60 mol% or more, 70 mol% or more, 75 mol% or more, 65 to 90 mol% or more, etc. Furthermore, the degree of polymerization of PVA-based polymers can be 300 or more (e.g., 500 or more, 1000 or more, 2000 or more, etc.) and can be 10000 or less (e.g., 8000 or less, 5000 or less, 3000 or less, etc.).

[0179] Furthermore, other dispersants may sometimes perform specific functions depending on the type of PVA-based polymer (A) or the type of monomers used in the polymerization. For example, other dispersants (such as water-soluble polymers) may function as dispersants (primary dispersants, other dispersing aids) to stabilize the dispersibility of vinyl chloride monomers and to adjust the particle size of the manufactured vinyl chloride-based resin. PVA-based polymer (A) may function as dispersants (secondary dispersants, dispersing aids) to increase the porosity of vinyl chloride-based resins.

[0180] In the suspension polymerization of ethylene monomers, there are no particular restrictions on the amount of other dispersants used. For example, it can be less than 5 parts by mass relative to 100 parts by mass of ethylene monomers (e.g., 0.005 to 1 part by mass, 0.01 to 0.2 parts by mass).

[0181] In addition to polymerization initiators and other dispersants, chain transfer agents, polymerization inhibitors, pH adjusters, anti-fouling agents, crosslinking agents and other additives known in the suspension polymerization of ethylene compounds may be used together.

[0182] The polymerization temperature of suspension polymerization is not limited and can be arbitrarily selected according to the type of ethylene monomer used, the degree of polymerization of the target polymer, and the polymerization yield, etc., but is usually preferred to be 40-70°C. The polymerization time is also not particularly limited and can be set appropriately according to the target polymerization yield, etc. [Example]

[0183] The following examples illustrate the present invention in further detail, but the present invention is not limited by these examples. Furthermore, in the following examples and comparative examples, "%" and "parts" unless otherwise specified, represent "mass%" (or "weight%") and "parts by mass" (or "parts by weight").

[0184] First, the methods for determining the degree of polymerization, degree of saponification, YI, block characteristics of residual ethylene ester units of PVA(A), transparency of 4% aqueous solution, and water insoluble fraction of this embodiment are shown below.

[0185] (Method for determining degree of polymerization) The degree of polymerization shall be determined according to the method specified in JIS K 6726.

[0186] (Method for determining saponification degree) The determination shall be performed according to the method specified in JIS K 6726.

[0187] (Method for determining YI) A 4% DMSO (dimethyl sulfoxide) solution of PVA(A) was placed in a quartz cell with an optical path length of 10 mm. The UV-Vis spectrum (wavelength range of 360–830 nm, blank sample was DMSO) was measured at 20°C using a UV-Vis spectrophotometer (manufactured by Japan Spectrophotometer Co., Ltd.; V-730). The YI of the 4% DMSO solution was calculated from the obtained data. During the calculation, the colorimetric system "Lab", light source "D65", color matching function "JIS Z8701:1999", field of view angle "2 degrees", wavelength range "360–830 nm", and data interval "5 nm" were selected.

[0188] (Method for determining block characteristics) First, using a 400 MHz nuclear magnetic resonance (NMR) instrument manufactured by Bruker Corporation, a 13C-NMR analysis was performed on a mixed solution of PVA / D₂O / MeOH (methanol) (the components of which were appropriately varied according to the degree of polymerization and saponification of PVA) (analysis temperature = 50°C), and the integral values ​​A to C of the following signals were obtained. • Signal with integral value A = 37.2 to 40.4 ppm: attributed to (OCOR, OCOR) • Signal with integral value B = 40.4 to 41.8 ppm: attributed to (OH, OCOR) • Signal with integral value C = 41.8 to 44.9 ppm: attributed to (OH, OH) Then, using the integral values ​​obtained above, the block characteristic (η) was calculated using the following formula. • Block feature (η) = (OH, OCOR) / [2(OH)(OCOR)] Here, (OH, OCOR), (OH), and (OCOR) are calculated as follows: • (OH, OCOR) = B • (OH) = (OH, OH) + (OH, OCOR) / 2 • (OCOR) = (OCOR, OCOR) + (OH, OCOR) / 2 Furthermore, (OH, OH) and (OCOR, OCOR) are as follows: • (OH, OH) = C • (OCOR, OCOR) = A

[0189] (Method for determining the 4% transparency of PVA aqueous solution) A 4% aqueous solution of PVA(A) was placed in a quartz cell with an optical path length of 20 mm, and its transmittance at 430 nm was measured at 20°C using a UV-Vis spectrophotometer (manufactured by Japan Spectrophotometer Co., Ltd.; V-730). Pure water was used as a blank sample.

[0190] (Method for determining the water-insoluble fraction of PVA) Dissolve 10 g of PVA(A) in 500 g of water at 50°C while stirring for 1 hour to prepare an aqueous solution of PVA(A). Pass the entire volume of the PVA(A) aqueous solution through a pre-weighed 100-mesh metal wire mesh to capture the water-insoluble components. Dry the metal wire mesh containing the water-insoluble components at 110°C and measure the weight of the dried metal wire mesh. Calculate the percentage of water-insoluble components [%] using the formula (B - A) / 10 × 100. Here, A is the weight of the metal wire mesh before filtration [g], and B is the weight of the metal wire mesh after filtration [g].

[0191] (Sodium acetate content) Dissolved in d6-DMSO, ¹H-NMR was performed using a 400 MHz NMR spectrometer manufactured by Bruker. The sodium acetate content was calculated using the signal from the sodium acetate.

[0192] (pH value) The pH value was determined (20°C) according to the method specified in JIS K 6726.

[0193] [Example 1] (Synthesis of PVA-based polymer (B)) 2.3 parts of a 3% methanol solution of sodium hydroxide (0.3 mol relative to 100 mol of polyvinyl acetate monomer units) and 1 part of water were added to 100 parts of a 50% methanol solution of polyvinyl acetate with a degree of polymerization of 250. The mixture was thoroughly mixed and saponified at 40°C for 20 minutes. After saponification, 0.7 parts of a 5% aqueous acetic acid solution (0.1 mol relative to 100 mol of polyvinyl acetate monomer units) were added to stop the saponification reaction. The resulting reaction solution was homogeneous. The obtained solution was dried at 60°C for 1 hour under reduced pressure of 100 Pa to obtain PVA(B). The analysis results showed a saponification degree of 35 mol%, an average degree of polymerization of 250, and a block characterization of 0.44. PVA(B) is completely insoluble in water. Furthermore, PVA(B) contains sodium acetate at a concentration of 0.3 mol (0.43 mol by mass) relative to 100 mol of the monomer unit of polyvinyl acetate (PVB(B)).

[0194] (Synthesis of PVA-based polymer (A)) 100 parts of PVA (B) obtained above were dissolved in 100 parts of methanol to prepare a homogeneous solution. 7.6 parts of a 20% methanol solution of monomethyl phthalate (0.60 mol relative to 100 mol of monomer units of PVA-based polymer (B)) and 3.5 parts of a 10% methanol solution of sodium acetate as a pH adjuster (0.30 mol relative to 100 mol of monomer units of PVA-based polymer (B)) were added to this solution and mixed thoroughly. The homogeneous solution was dried at 60°C for 1 hour under reduced pressure of 100 Pa (to evaporate the solvent) to obtain a solid. Furthermore, the amount of sodium acetate (total amount, added amount) relative to 1 mol of monomethyl phthalate used (added amount) was 1 mol.

[0195] The solid was heated at 150°C for 30 minutes under reduced pressure of 100 Pa to obtain PVA(A). The analytical results of PVA(A) were as follows: degree of saponification 35 mol%, average degree of polymerization 250, block character 0.46, and 1H-NMR determination of phthalic acid unit content: 0.5 mol% per monomer unit of PVA(A) (equivalent to 1.4 mol% of vinyl alcohol unit). PVA(A) showed water solubility with a 4% transparency of 83%. Furthermore, the proportion of water-insoluble components was less than 0.1%, and the YI of a 4% DMSO solution was less than 1. Moreover, the pH (20°C) of PVA(A) in a 4% DMSO aqueous solution was 6.1, indicating that it did not contain sodium acetate.

[0196] [Examples 2-23, Reference Example 1] Except for suitable changes to the degree of polymerization and saponification of PVA(B), the content of sodium acetate, the concentration and solvent composition of the PVA(B) solution, the type and amount of di(tri)carboxylic acid or its derivatives, the amount of sodium acetate added, and the heating conditions during the synthesis of PVA(A), the PVA-based polymer (A) shown in Table 1 was synthesized in the same manner as in Example 1. Furthermore, it is clear that the aqueous solution of PVA(A) obtained in Reference Example 1 has very low transparency, and the DMSO solution is also significantly colored. The transparency of the 4% by mass aqueous solution is quite small, and the YI of the 4% by mass DMSO solution is quite large. Therefore, these values ​​were not measured.

[0197] [Examples 24, 25] In Example 22, PVA(B) was used (in its solid state) without being made into a solution to obtain PVA(A). Specifically, the powder mixture of PVA(B) shown in Table 1 with phthalic acid and sodium acetate (sodium acetate was not added in Comparative Example 3) was fed into a polymer extrusion molding apparatus (Mini Lab III manufactured by Thermo SCIENTIFIC) and heated and mixed under the following conditions to obtain PVA(A): • Screw speed: 100 rpm • Heating (mixing) temperature: 150°C • Heating (mixing) time: 30 minutes

[0198] The results are summarized in Table 1.

[0199] [Table 1] Table 1 PVA(B) Manufacturing of PVA-based polymers (A) PVA-based polymers (A) Degree of aggregation degree of saponification Sodium acetate PVA(B) concentration solvent Polycarboxylic acid components Sodium acetate Polycarboxylic acid components / pH adjusters (Morby) temperature time Degree of aggregation degree of saponification Degree of modification Segment features 4% pH value 4% transparency water insoluble ingredients YI Moer% mol% % [type] [type] mol% mol% ℃ min Moer% Moer% % % Example 1 250 35 0.3 50 methanol Monomethyl phthalate 0.60 0.3 1 150 30 250 35 0.5 0.48 6.1 83 Less than 0.1 Less than 1 Example 2 250 35 0.3 50 methanol Monomethyl succinate 0.60 0.3 1 170 30 250 35 0.3 0.55 6.1 53 Less than 0.1 Less than 1 Example 3 250 35 0.3 50 methanol Maleic acid monomethyl ester 0.60 0.3 1 150 30 250 35 0.5 0.48 6.1 80 Less than 0.1 Less than 1 Example 4 250 35 0.3 50 methanol Iconate monomethyl ester 0.60 0.3 1 150 30 250 35 0.4 0.49 6.1 62 Less than 0.1 Less than 1 Example 5 250 35 0.3 50 methanol Methylmaleic acid monomethyl ester 0.60 0.3 1 150 30 250 35 0.5 0.47 6.2 82 Less than 0.1 Less than 1 Example 6 250 35 0.3 50 methanol Phthalic acid 0.60 0.3 1 150 30 250 35 0.4 0.46 5.8 67 Less than 0.1 Less than 1 Example 7 250 35 0.3 50 methanol maleic acid 0.60 0.3 1 150 30 250 35 0.4 0.47 5.8 63 Less than 0.1 Less than 1 Example 8 250 35 0.3 50 methanol Iconic acid 0.60 0.3 1 150 30 250 35 0.4 0.47 5.8 60 Less than 0.1 Less than 1 Example 9 250 35 0.3 50 methanol Methylmaleic acid 0.60 0.3 1 150 30 250 35 0.5 0.46 5.8 75 Less than 0.1 Less than 1 Example 10 250 35 0.3 50 methanol Citric acid 0.60 0.3 1 150 30 250 35 0.3 0.48 5.8 50 Less than 0.1 Less than 1 Example 11 250 65 0.6 50 Methanol / water = 1 / 1 Monomethyl phthalate 0.60 - 1 150 30 250 65 0.5 0.48 6.2 94 Less than 0.1 Less than 1 Example 12 250 80 0.6 40 Methanol / water = 1 / 1 Monomethyl phthalate 0.60 - 1 150 30 250 80 0.5 0.50 6.3 97 Less than 0.1 Less than 1 Example 13 500 35 0.3 40 methanol Monomethyl phthalate 0.60 0.3 1 150 30 500 35 0.5 0.48 6.1 80 Less than 0.1 Less than 1 Example 14 500 65 0.6 40 Methanol / water = 1 / 1 Monomethyl phthalate 0.60 - 1 150 30 500 65 0.5 0.48 6.2 93 Less than 0.1 Less than 1 Example 15 500 80 0.6 30 Methanol / water = 1 / 1 Monomethyl phthalate 0.60 - 1 150 30 500 80 0.5 0.50 6.3 95 Less than 0.1 Less than 1 Example 16 1500 25 0.3 30 methanol Monomethyl phthalate 0.60 0.3 1 150 30 1500 25 0.4 0.49 6.0 40 1 Less than 1 Example 17 250 35 0.3 50 methanol Monomethyl phthalate 0.20 - 0.67 150 30 250 35 0.15 0.51 6.3 10 Less than 0.1 Less than 1 Example 18 250 35 0.3 50 methanol Monomethyl phthalate 2.00 1.7 1 150 30 250 35 1.5 0.53 6.8 87 I 3 Example 19 250 35 0.3 50 Methanol / methyl acetate / water = 1 / 1 / 1 Monomethyl phthalate 0.60 0.3 1 150 30 250 35 0.50 0.47 6.1 85 Less than 0.1 Less than 1 Example 20 250 35 0.3 50 methanol Monomethyl phthalate 0.60 0.3 1 120 30 250 35 0.2 0.45 6.1 33 Less than 0.1 Less than 1 Example 21 250 35 0.3 50 methanol Monomethyl phthalate 0.60 1.0 1 170 30 250 35 0.5 0.63 6.8 60 Less than 0.1 5 Example 22 250 35 0.3 50 methanol Monomethyl phthalate 0.60 1.0 0.46 200 30 250 35 0.3 0.70 6.8 2 3 15 Example 23 250 35 0.3 50 methanol Monomethyl phthalate 0.60 1.0 0.46 200 300 250 38 0.1 0.80 6.4 Less than 0.1 20 45 Reference Example 1 250 35 0.3 50 methanol Citric acid 0.60 - 2 170 30 250 35 - - 4.5 - 50 - Example 24 250 35 0.3 None (powder mixture) Phthalic acid 0.60 0.3 1 150 30 250 35 0.5 0.48 5.0 34 5 Less than 1 Example 25 250 65 0.6 None (powder mixture) Phthalic acid 0.60 - 1 150 30 250 65 0.5 0.48 5.1 68 15 2

[0200] [Polymerization Example 1] (Suspension Polymerization of Vinyl Chloride) Using the PVA-based polymer (A) obtained in Example 1 above as a dispersant, suspension polymerization of vinyl chloride was carried out under the conditions shown below. In a 100-liter polymerizer (pressure-resistant autoclave), 0.05 parts by weight of saponified polyvinyl alcohol (80 mol% saponification, 2500% polymerization) and 0.02 parts by weight of saponified polyvinyl alcohol (72 mol% saponification, 800% polymerization) were dissolved in 100 parts by weight of deionized water and added. Then, 0.75 parts by weight of the aqueous solution obtained in Example 1 above (PVA-based polymer (A) content of 4 wt%) (0.03 parts by weight of PVA-based polymer (A)) were added, followed by 0.05 parts by weight of tributyl peroxyneodecanoate. Next, after degassing the polymerizer to 40 mmHg, 100 parts by weight of vinyl chloride monomer were added, and polymerization began. The polymerization temperature was 57°C, and this temperature was maintained until the polymerization was complete. The reaction was terminated when the polymerization conversion reached 80%. After recovering the unreacted monomers from the polymerizer, the polymer slurry was removed from the system and dehydrated and dried to obtain vinyl chloride resin. The evaluation method for vinyl chloride resin is shown below.

[0201] (Evaluation of vinyl chloride resin) The average particle size, plasticizer absorption and sheet colorability of the obtained vinyl chloride resin were evaluated as follows.

[0202] <Average Particle Size> The average particle size is determined by measuring the particle size distribution using a Rotap vibrating screen (using a JIS screen).

[0203] <Plasticizer Absorption> The obtained resin was added to a cylindrical container with a glass fiber lining at the bottom, and excess dioctyl phthalate (hereinafter referred to as DOP) was added. After standing for 30 minutes to allow DOP to permeate into the resin, the resin was centrifuged at 3000 rpm to remove excess DOP. The weight of the resin was then measured, and the DOP absorption per 100 parts of polymer was calculated. The higher the DOP absorption, the better the plasticizer absorption and the better the molding processability.

[0204] <Evaluation of the Colorimetric Properties of Vinyl Chloride Polymer Sheets> A mixture of 100 parts by weight of a vinyl chloride polymer, 50 parts by weight of di-2-ethylhexyl phthalate, 0.8 parts by weight of a dioctyltin mercaptan stabilizer, 0.1 parts by weight of a polyethylene lubricant, and 0.8 parts by weight of a calcium-zinc onepack stabilizer was kneaded at 160°C for 5 minutes using a test roller to form a sheet with a thickness of 0.45 mm. Several sheets of the above material were overlapped and pressed at 160°C for 5 minutes to produce a 40 mm × 40 mm × 15 mm (thickness) test piece. The YI of the test piece was measured using a colorimeter.

[0205] [Polymerization Examples 2-7] Except that the PVA(A) obtained in Examples 2-5, 22, and 23 was used instead of the PVA(A) obtained in Example 1, the suspension polymerization of vinyl chloride was carried out in the same manner as in Polymerization Example 1. The evaluation results of the obtained vinyl chloride resins are shown in Table 2.

[0206] [Table 2] Table 2 Using PVA PVA-based polymers (A) Evaluation of vinyl chloride resin Degree of aggregation degree of saponification aldehyde Degree of modification YI Average particle size Plasticizer absorption Sheet colorability Moer% [type] Moer% 4% DMSO μm % YI Example 1 of Aggregation Example 1 250 35 Monomethyl phthalate 0.5 Less than 1 140 twenty four 18 Example 2 of Aggregation Example 2 250 35 Monomethyl succinate 0.3 Less than 1 142 25 18 Example 3 of Aggregation Example 3 250 35 Maleic acid monomethyl ester 0.5 Less than 1 139 twenty four 18 Example 4 of Aggregation Example 4 250 35 Iconate monomethyl ester 0.4 Less than 1 138 twenty four 18 Example 5 of Aggregation Example 5 250 35 Methylmaleic acid monomethyl ester 0.5 Less than 1 142 twenty four 18 Example 6 of Aggregation Example 22 250 35 Monomethyl phthalate 0.30 15 145 twenty three twenty two Example 7 of Aggregation Example 23 250 38 Monomethyl phthalate 0.10 45 160 twenty two twenty three

[0207] [Application of Hot Melt Adhesive] PVA(A) obtained in Example 1 was used as a hot melt adhesive in the following manner to evaluate its adhesion strength and water solubility. PVA(A) was coated onto kraft paper with a basis weight of 100 g / m² at a coating amount of 20 g / m² at a coating temperature of 150°C. Other kraft paper was then placed on top, and a load of 2 kg / cm² was applied at 135°C for 5 seconds to perform hot pressing. After being placed at 20°C and 65%RH for 24 hours, the adhesion was evaluated by peeling at 180 degrees. The results showed no interface damage or agglomeration failure, indicating that the bonded portion had sufficient strength. Furthermore, the bonded paper sheet was immersed in water at 30°C and slowly stirred to confirm the peeling of the bonded portion. The adhesive can be easily removed during waste paper recycling, thus improving recycling efficiency. [Industrial Applicability]

[0208] Specific polyvinyl alcohol-based polymers can be provided in this invention. Such polymers are preferably used as hot melt adhesives, dispersants (dispersion aids), etc.

Claims

1. A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary condition 1; Necessary condition 1: The water insoluble fraction is less than 30% by mass.

2. A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary condition 2; Necessary condition 2: The transmittance (430 nm) of a 4% by mass aqueous solution is 1% or more.

3. A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary condition 3; Necessary condition 3: The YI value of a 4% by mass dimethyl sulfoxide solution is 30 or less.

4. A polyvinyl alcohol polymer (A) having an ionic backbone and fully satisfying the following necessary conditions 1 and 2: Necessary condition 1: The water insoluble fraction is less than 30% by mass; Necessary condition 2: The transmittance (430 nm) of a 4% by mass aqueous solution is more than 1%.

5. A polyvinyl alcohol polymer (A) having an ionic backbone and sufficiently satisfying the following necessary conditions 1 and / or necessary conditions 2 and 3: Necessary condition 1: The water insoluble fraction is less than 30% by mass; Necessary condition 2: The transmittance (430 nm) of a 4% by mass aqueous solution is more than 1%; Necessary condition 3: The YI value of a 4% by mass dimethyl sulfoxide solution is less than 30.

6. A polyvinyl alcohol polymer (A) having an ionic backbone and fully satisfying the following necessary conditions 1, 2 and 3: Necessary condition 1: The water insoluble fraction is less than 30% by mass; Necessary condition 2: The transmittance (430 nm) of a 4% by mass aqueous solution is more than 1%; Necessary condition 3: The YI value of a 4% by mass dimethyl sulfoxide solution is less than 30.

7. The polyvinyl alcohol polymer (A) of any one of claims 1, 4 to 6, wherein, in necessary condition 1, the water insoluble fraction is less than 10% by mass.

8. The polyvinyl alcohol polymer (A) of any one of claims 2, 4 to 6, wherein, in necessary condition 2, the transmittance (430 nm) of a 4% by mass aqueous solution is 2% or more.

9. Polyvinyl alcohol polymer (A) of any one of claims 3, 5, and 6, wherein, in necessary condition 3, the YI value of the 4% by mass dimethyl sulfoxide solution is less than 10.

10. The polyvinyl alcohol polymer (A) of claim 5 or 6, wherein, in necessary condition 1, the water insoluble fraction is less than 5% by mass, in necessary condition 2, the transmittance (430 nm) of the 4% by mass aqueous solution is more than 10%, and in necessary condition 3, the YI value of the 4% by mass dimethyl sulfoxide solution is less than 5.

11. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the ionic backbone has at least one ionic group selected from carboxyl groups and their salts.

12. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the ionic backbone contains a backbone derived from a polycarboxylic acid component.

13. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the ionic backbone contains a backbone derived from at least one polycarboxylic acid component selected from dicarboxylic acid components and tricarboxylic acid components.

14. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the ionic backbone contains a backbone introduced via hydroxyl groups of vinyl alcohol units.

15. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the ionic backbone comprises an ester bond backbone of hydroxyl groups derived from vinyl alcohol units and carboxyl groups of polycarboxylic acid components.

16. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the ionic backbone comprises an ester bond backbone of a hydroxyl group derived from a vinyl alcohol unit and a carboxyl group of a polycarboxylic acid component, the polycarboxylic acid component comprising at least one selected from aliphatic dicarboxylic acids, aromatic dicarboxylic acids, aliphatic tricarboxylic acids, aromatic tricarboxylic acids, anhydrides of the like, esters of the like, and salts of the like.

17. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the content of the ionic backbone is 0.01 to 10 mol per monomer unit.

18. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein the block composition is 0.35 to 0.

70.

19. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6 has a saponification degree of 20 to 90 moles.

20. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6 has a saponification degree of 70 moles or less.

21. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6 has a degree of polymerization of 120 to 3000.

22. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein a 4% by mass aqueous solution of the polyvinyl alcohol polymer (A) has a pH value of 5 to 9.

23. The polyvinyl alcohol polymer (A) of any one of claims 1 to 6, wherein a 4% by mass aqueous solution of the polyvinyl alcohol polymer (A) has a pH value of 5.5 to 8.

5.

24. A method for manufacturing a polyvinyl alcohol polymer (A), comprising a method for manufacturing a polyvinyl alcohol polymer (A) having an ionic backbone, and comprising a heating step of heating a composition containing a polyvinyl alcohol polymer (B) and a component having a corresponding ionic backbone.

25. The manufacturing method of claim 24, wherein the component corresponding to the ionic framework contains a polycarboxylic acid component.

26. The manufacturing method of claim 24, wherein the component corresponding to the ionic skeleton contains at least one selected from dicarboxylic acids, tricarboxylic acids, anhydrides of the like, partial esters of the like, and salts of the like.

27. The manufacturing method of claim 24, wherein the composition contains a pH adjuster.

28. The manufacturing method of claim 24, wherein the composition contains sodium acetate.

29. The manufacturing method of claim 24, wherein the composition contains a pH adjuster at a ratio of 0.5 to 1.9 moles relative to 1 mole of the corresponding ionic skeleton component.

30. The manufacturing method of claim 24, wherein in the heating step, the heating temperature is 80 to 240°C.

31. The manufacturing method of claim 24, wherein the heating time in the heating step is 5 minutes to 5 hours.

32. The manufacturing method of claim 24, comprising a solvent removal step of removing solvent from a composition containing a polyvinyl alcohol polymer (B), a component with a corresponding ionic backbone and a solvent, wherein a heating step is performed after the solvent removal step or in parallel or continuously with the solvent removal step.

33. The manufacturing method of claim 32, wherein the solvent contains at least one selected from water, alcohol and ester.

34. The manufacturing method of claim 32, wherein the solvent contains methanol.

35. The manufacturing method of claim 24, wherein the polyvinyl alcohol polymer (A) satisfies at least one of the following necessary conditions selected from necessary condition 1, necessary condition 2, and necessary condition 3: Necessary condition 1: The water insoluble fraction is less than 30% by mass; Necessary condition 2: The transmittance (430 nm) of the 4% by mass aqueous solution is more than 1%; Necessary condition 3: The YI value of the 4% by mass dimethyl sulfoxide solution is less than 30.

36. A hot melt adhesive comprising a polyvinyl alcohol polymer (A) as claimed in any one of claims 1 to 6.

37. A dispersant for suspension polymerization, comprising a polyvinyl alcohol polymer (A) as claimed in any one of claims 1 to 6.