Vinyl alcohol polymers, powders containing the same, methods for manufacturing the same, paper processing agents, and dispersants for emulsifying polymerization.

Abstract

A vinyl alcohol polymer comprising a structural unit derived from at least one of the group consisting of monomers having a carboxyl group and their derivatives, having an absolute molecular weight in the range of 200,000 to 800,000, a minimum branching degree of 0.93 or less, a viscosity-average degree of polymerization of 750 or less, and a degree of saponification of 65 moles or more.

Description

Technical Field

[0001] This invention relates to a vinyl alcohol-based polymer, a powder comprising the polymer, a method for manufacturing the polymer, a paper processing agent, and a dispersant for emulsifying polymerization. Prior Technology

[0002] Vinyl alcohol polymers (hereinafter sometimes referred to as "PVA") are known as water-soluble synthetic polymers and are widely used in paper processing, fiber processing, adhesives, stabilizers for emulsion polymerization and suspension polymerization, adhesives for inorganic materials, films and other applications.

[0003] As a type of modified PVA, PVA containing structural units derived from carboxylic acids or their derivatives is known (see Patent Document 1). The aforementioned PVA utilizes the reactivity of carboxylic acids and is used in sizing agents for acidic paper containing aluminum sulfate, water-resistant coatings combined with crosslinking agents, adhesives, etc. Furthermore, it has good water solubility, making it useful and widely used as a packaging film for water-soluble pesticides, laundry detergents, and industrial pharmaceuticals. [Previous Technical Documents] [Patent Literature]

[0004] Patent Document 1: International Publication No. 2018 / 061272 Summary of the Invention

[0005] [The problem the invention aims to solve]

[0006] In the industrial manufacture of PVA films, considering environmental and economic factors, PVA aqueous solutions using water as a solvent are generally used as film-forming solutions. Furthermore, when PVA is used as a coating agent or adhesive, water is often also used as the solvent. From the perspective of shortening drying time and reducing the energy required for drying, it is preferable to use PVA aqueous solutions at a high concentration when using them as film-forming solutions, coating agents, adhesives, or paper processing agents. Additionally, PVA is sometimes used at a high concentration when used as a dispersant in emulsion polymerization. However, conventional PVA aqueous solutions, when at high concentrations, exhibit a significant increase in viscosity and a decrease in coatability.

[0007] The present invention is made to solve the above-mentioned problems, and aims to provide a PVA that suppresses the increase of viscosity when it is a high-concentration aqueous solution, a powder containing the aforementioned PVA, a method for manufacturing the above, and a paper processing agent and a dispersant for emulsification polymerization containing the aforementioned PVA. [Methods used to solve problems]

[0008] The above objective is achieved by providing any of the following. [1] A PVA comprising a structural unit derived from at least one of the group consisting of monomers having a carboxyl group and their derivatives, having an absolute molecular weight of 200,000 to 800,000, a minimum branching degree of 0.93 or less, a viscosity-average degree of polymerization of 750 or less, and a degree of saponification of 65 moles or more; [2] PVA as in [1], wherein at least one of the groups comprising monomers having a carboxyl group and their derivatives is selected from at least one of the groups comprising vinyl unsaturated dicarboxylic acids, and their monoesters, diesters and anhydrides; [3] PVA as in [1], wherein at least one of the group consisting of monomers having a carboxyl group and their derivatives is selected from at least one of the group consisting of maleic acid, monoalkyl maleate, dialkyl maleate, maleic anhydride, fumaric acid, monoalkyl fumarate and dialkyl fumarate; [4] The PVA of any one of [1] to [3] satisfies the following equation (I); S×P>250 ···(I) In formula (I), S is the percentage (in moles) of the structural unit derived from at least one of the group consisting of monomers having a carboxyl group and their derivatives, relative to all structural units. P is the viscosity-average degree of polymerization. [5] The PVA of any one of [1] to [4] satisfies the following equation (II); 1.0 <g A / g B<9.0 ···(II) In formula (II), gA represents the branching degree in an absolute molecular weight of 200,000, and gB represents the branching degree in an absolute molecular weight of 800,000. [6] For any of the PVAs in [1] to [5], when 4 parts by weight of the above PVA are added to 96 parts by weight of water and stirred at 60°C for 1 hour, the undissolved portion is more than 0.1 ppm and less than 2000 ppm; [7] A powder containing PVA as described in any one of [1] to [6]; [8] The powder of [7], wherein the content of powder passing through a sieve with an aperture of 180 μm is less than 12% by mass; [9] The powder as in [7] or [8], wherein the content of powder passing through a sieve with an aperture of 1.00 mm is 97% by mass or more, and the content of powder passing through a sieve with an aperture of 500 μm is 40% by mass or more;

[10] A method for manufacturing PVA according to any one of [1] to [6], comprising: a step (1) of obtaining a copolymer of at least one selected from the group consisting of monomers having carboxyl groups and their derivatives with ethylene ester, a step (2) of obtaining a saponified product of the copolymer, and a step (3) of heat treating the saponified product, wherein the heat treatment temperature in step (3) is 110°C or higher, and the heat treatment time is 1 hour or higher;

[11] A method for manufacturing a powder, which is a method for manufacturing a powder according to any one of [7] to [9], comprising: a step (1) of obtaining a copolymer of at least one selected from the group consisting of monomers having carboxyl groups and their derivatives with ethylene ester, a step (2) of obtaining a saponified product of the copolymer, and a step (3) of heat treating the saponified product, wherein at the end of step (3), the content of powder passing through a sieve with a pore size of 180 μm in the saponified product is 12% by mass or less;

[12] A paper processing agent containing PVA as described in any one of [1] to [6];

[13] A dispersant for emulsification polymerization, comprising PVA as described in any one of [1] to [6]. [Effects of the Invention]

[0009] According to the present invention, a PVA that suppresses the increase in viscosity when used as a high-concentration aqueous solution, a powder containing PVA as described above, a method for manufacturing the above, and a paper processing agent and a dispersant for emulsification polymerization containing PVA as described above can be provided. Simple Explanation of the Diagram

[0010] Figure 1 is a graph showing the relationship between the absolute molecular weight of PVA-1 and PVA-1' in the embodiments and their intrinsic viscosity ([η] branch and [η] straight line). Figure 2 is a graph showing the relationship between the absolute molecular weight and branching degree (gm) of PVA-1 in the examples. Implementation

[0011] [The form in which the invention is carried out]

[0012] The following describes an embodiment of the invention. Furthermore, in this specification, the upper and lower limits of the numerical ranges (content of each component, numerical values ​​calculated from each component, and physical properties, etc.) can be appropriately combined.

[0013] <pva> The PVA (vinyl alcohol polymer) of the present invention comprises a PVA derived from at least one structural unit selected from the group consisting of monomers having a carboxyl group and their derivatives, having an absolute molecular weight in the range of 200,000 to 800,000, a minimum branching degree of 0.93 or less, a viscosity-average degree of polymerization of 750 or less, and a degree of saponification of 65 moles or more. Hereinafter, "at least one of the group consisting of monomers having a carboxyl group and their derivatives" is sometimes referred to as "monomer (a)".

[0014] The PVA of the present invention comprises structural units derived from vinyl alcohol units and monomer (a). This PVA is typically obtained by saponifying an vinyl ester polymer (a copolymer of monomer (a) and vinyl ester) containing structural units derived from monomer (a). Examples of derivatives of the monomer having a carboxyl group include monomer esters and anhydrides. The carboxyl group (-COOH) may also exist in the form of a salt (-COONa, etc.). The structural units derived from monomer (a) may also form cross-linked structures and combine with other structural units. Examples of monomer (a) include vinyl unsaturated monocarboxylic acids, vinyl unsaturated dicarboxylic acids, and their derivatives.

[0015] Examples of vinyl unsaturated monocarboxylic acids and their derivatives include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate.

[0016] Examples of vinyl unsaturated dicarboxylic acids and their derivatives include vinyl unsaturated dicarboxylic acids, their monoesters, diesters, and anhydrides. Examples of vinyl unsaturated dicarboxylic acids include maleic acid, fumaric acid, citraconic acid, mesoconic acid, and itaconic acid. Examples of monoesters of vinyl unsaturated dicarboxylic acids include monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl itaconic acid, and monoethyl itaconic acid, among other monoalkyl ester unsaturated dicarboxylic acid esters. Examples of diesters of vinyl unsaturated dicarboxylic acids include dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl citrate, diethyl citrate, dimethyl citrate, diethyl citrate, dimethyl citrate, diethyl citrate, dimethyl itaconic acid, and diethyl itaconic acid. Examples of vinyl unsaturated dicarboxylic acid anhydrides include maleic anhydride and citrate anhydride.

[0017] From an industrial perspective and from the viewpoint of reactivity with vinyl esters, monomer (a) is preferably an vinyl unsaturated dicarboxylic acid, and its monoesters, diesters, and anhydrides; more preferably, maleic acid, monoalkyl maleate, dialkyl maleate, maleic anhydride, fumaric acid, monoalkyl fumarate, and dialkyl fumarate; particularly preferably, monomethyl maleate, dimethyl maleate, maleic anhydride, monomethyl fumarate, and dimethyl fumarate. Monomer (a) may be one or more types.

[0018] The lower limit of the content (S) of the structural units derived from monomer (a) of all structural units of the PVA of the present invention is preferably 0.1 mol%, more preferably 0.5 mol%, further preferably 1.0 mol%, and especially preferably 1.5 mol%. On the other hand, the upper limit of the above-mentioned content (S) is sometimes preferably 15 mol%, more preferably 10 mol%, more preferably 5 mol%, and even more preferably 3 mol%. By setting the above-mentioned content (S) within the above range, the effect of carboxylic acid modification can be fully utilized, that is, the effect of introducing structural units derived from monomer (a), and the increase in viscosity when used as a high-concentration aqueous solution can be sufficiently suppressed. Furthermore, by setting the above-mentioned content (S) below the above-mentioned upper limit, excessive cross-linking is suppressed. The portion that produces excessive cross-linking has reduced solubility in water and becomes an insoluble portion. As mentioned above, the insoluble portion causes uneven coating when used as an aqueous solution, and it becomes difficult to prepare a high-concentration aqueous solution. Therefore, by setting the water content (S) below the aforementioned upper limit, there is a tendency for the undissolved portion to decrease, and the coatability is improved when used as an aqueous solution. The aforementioned water content (S) can be determined by 1H-NMR analysis of the ethylene ester polymer of the PVA of the present invention before saponification.

[0019] In the PVA of this invention, the minimum branching degree within the absolute molecular weight range of 200,000 to 800,000 is 0.93 or less. Branching degree is an indicator of the degree of branching structure of a polymer, and it is defined as 1 for linear polymers, i.e., those without branching structures, with the branching degree closer to 0 indicating more branching. For the PVA being measured, the branching degree of each absolute molecular weight within the range of 200,000 to 800,000 is determined. Then, the minimum branching degree within the above range is defined as the minimum branching degree. Furthermore, when the absolute molecular weight of the PVA does not cover the entire range of 200,000 to 800,000, for example, when only PVA with an absolute molecular weight of 600,000 or less is included, the minimum branching degree within the range of 200,000 to 600,000 is also defined as the minimum branching degree. That is, the PVA of this invention, which contains multiple molecules, includes molecules within the range of 200,000 to 800,000, but the absolute molecular weight may not cover the entire range of 200,000 to 800,000.

[0020] The branching degree gm of each absolute molecular weight of the PVA of the present invention is obtained by the following formulas (1) and (2). g m'=[η] branch / [η] line···(1) gm=g m' (1 / ε )···(2) In formula (1), [η] branch represents the intrinsic viscosity of the PVA (branched PVA) of the present invention with a branched structure, in terms of absolute molecular weight x (x is between 200,000 and 800,000), and is a value calculated by a differential refractive index detector, a light scattering detector, and a viscosity detector. [η] straight line represents the intrinsic viscosity of the linear PVA in terms of the aforementioned absolute molecular weight x, and is also a value calculated by a differential refractive index detector, a light scattering detector, and a viscosity detector. Furthermore, as a linear PVA, an unmodified PVA (saponified form of a homopolymer of vinyl acetate) with a viscosity within ±20% of the PVA of the present invention being measured and a saponification degree within ±3 moles of a 4% by mass aqueous solution was used. Specifically, the intrinsic viscosity of the PVA of the present invention and the linear PVA in terms of each absolute molecular weight can be determined by the method described in the examples. The ratio g_m' of the intrinsic viscosity shown in formula (1) above and the branching degree g_m are related to formula (2) above. In equation (2), ε is the structural factor and is set to ε = 0.7.

[0021] In the PVA of the present invention, the minimum branching degree is 0.93 or less, and sufficient branching structure (crosslinking) is formed. Therefore, the PVA according to the present invention suppresses the increase in viscosity when used as a high-concentration aqueous solution. To further improve the aforementioned effect, the upper limit of the minimum branching degree is sometimes preferably 0.8, more preferably 0.6, and even more preferably 0.4, 0.25 or 0.18.

[0022] On the other hand, the lower limit of the minimum branching degree can be, for example, 0.01 or 0.05, sometimes preferably 0.11, and sometimes even more preferably 0.20. By setting the minimum branching degree to above the above lower limit, the insoluble parts caused by excessive cross-linking can be reduced, and the coatability when used as an aqueous solution can be improved.

[0023] The branching in this PVA is presumably formed through heat treatment and ester bonding between the carboxyl and hydroxyl groups of PVA. Therefore, the minimum degree of branching can be adjusted by heat treatment conditions such as heat treatment temperature and time, the content of structural units derived from monomer (a), and the degree of saponification.

[0024] The PVA of the present invention includes PVA with an absolute molecular weight of 200,000 to 800,000. Furthermore, the PVA of the present invention preferably includes PVA with an absolute molecular weight of 200,000 and PVA with an absolute molecular weight of 800,000, and more preferably, the absolute molecular weight distribution covers at least the entire range of 200,000 to 800,000.

[0025] The upper limit of the viscosity-average degree of polymerization (P) of the PVA of the present invention is 750, preferably 700, more preferably 600, and even more preferably 500. When the viscosity-average degree of polymerization (P) is higher than 750, it does not have the effect of suppressing the increase in viscosity when used as a high-concentration aqueous solution; on the contrary, it tends to have a higher viscosity compared to unmodified PVA. The lower limit of the above-mentioned viscosity-average degree of polymerization (P) can be, for example, 100, or 150 or 200. The viscosity-average degree of polymerization (P) is a value measured according to JIS K6726:1994. Specifically, it can be determined by the method described in the examples.

[0026] The lower limit of the content of the vinyl alcohol unit relative to all structural units in the PVA of the present invention is sometimes preferably 65 mol%, more preferably 70 mol%, and even more preferably 80 mol% or 85 mol%. On the other hand, the upper limit of the content of the vinyl alcohol unit is preferably 99.9 mol%, and more preferably 99 mol.

[0027] The lower limit of the degree of saponification of PVA in this invention is 65 mol%, preferably 80 mol%, and more preferably 85 mol%. By setting the degree of saponification above the above lower limit, water solubility is increased and the undissolved portion is reduced, making it easier to prepare a high-concentration, homogeneous PVA aqueous solution. On the other hand, the upper limit of the above saponification degree can be 100 mol%, but sometimes it is more preferably 99.9 mol%, more preferably 99 mol%, and even more preferably 92 mol%. By setting the degree of saponification below the above upper limit, there is a tendency to form sufficient branched structures through heat treatment. The degree of saponification is a value determined by the method described in JIS K 6726:1994.

[0028] The PVA of the present invention preferably satisfies the following formula (I). S×P>250 ···(I) In equation (I), S is the content (moles%) of structural units derived from monomer (a) for all structural units. P is the viscosity-average degree of polymerization.

[0029] When formula (I) is satisfied, a balance is achieved between the degree of effect caused by carboxylic acid modification (such as the formation of branched structures) and the degree of effect caused by the degree of polymerization, further improving coatability, etc. Specifically, for example, when formula (I) is satisfied, there is a tendency to further suppress coating unevenness during coating and increase the strength of the obtained film. The lower limit of S×P is preferably 300, and sometimes more preferably 400, 500, 600 or 700. On the other hand, the upper limit of S×P is preferably 4,000, more preferably 3,000, and more preferably 2,000.

[0030] Regarding the branching degree mentioned above, the PVA of the present invention preferably satisfies the following formula (II). 1.0 <g A / g B<9.0 ···(II) In formula (II), gA represents the branching degree of a PVA with an absolute molecular weight of 200,000 (the branching degree of the PVA with an absolute molecular weight of 200,000 in this invention). gB represents the branching degree of a PVA with an absolute molecular weight of 800,000 (the branching degree of the PVA with an absolute molecular weight of 800,000 in this invention).

[0031] As mentioned above, crosslinking with sufficient heat treatment yields PVA with a low degree of branching. However, if the degree of crosslinking is uneven depending on the molecular weight, the excessively crosslinked PVA (usually the component with a large molecular weight) tends to become insoluble in water, affecting the water solubility of PVA and the coatability of PVA aqueous solutions. Furthermore, if the unevenness of crosslinking is large depending on the molecular weight, the ratio gA / gB in formula (II) becomes larger. From the aforementioned point of view, the above-mentioned ratio gA / gB is sometimes preferably less than 7.0, further preferably less than 6.0, and particularly preferably less than 5.0, less than 4.0, less than 3.5, or less than 3.0.

[0032] The insoluble portion, which is the result of adding 4 parts by weight of the PVA of the present invention to 96 parts by weight of water and stirring at 60°C for 1 hour, is preferably 0.1 ppm or more and less than 2000 ppm. The aforementioned insoluble portion is sometimes more preferably less than 1500 ppm, and sometimes even more preferably less than 1000 ppm. As mentioned above, because the insoluble portion is small, the coatability of the PVA aqueous solution can be improved. On the other hand, the aforementioned insoluble portion can be 1 ppm or more, or 10 ppm or more, or 100 ppm or more. Furthermore, "ppm" is a mass standard, and the aforementioned insoluble portion (ppm) indicates the proportion of insoluble portion contained in the PVA. Specifically, the insoluble portion can be determined by the method described in the examples.

[0033] The aforementioned g A / g B ratio and the content of the aforementioned insoluble fraction tend to increase due to excessive heating and an increase in the proportion of excessively cross-linked PVA. Therefore, as described later, when heat-treating the saponified product of the vinyl ester polymer (polymer), the aforementioned g A / g B ratio and the aforementioned content of the insoluble fraction can be reduced by pre-removing the microparticles that are prone to overheating, performing heat treatment while removing the microparticles, and removing the microparticles after heat treatment.

[0034] The PVA of the present invention may also include vinyl alcohol units, vinyl ester units, and other structural units other than those derived from monomer (a). Examples of monomers to which these other structural units are derived include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, and 2-acrylamide-2-methylpropanesulfonic acid; methacrylamide derivatives such as N-methylmethacrylamide and N-ethylmethacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; hydroxyl-containing vinyl ethers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol vinyl ether; allyl acetate; and 3,4-diethoxylated vinyl ethers. -1-Butene; allyl ethers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers containing oxyalkyl groups; α-olefins containing hydroxyl groups such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, and 3-methyl-3-buten-1-ol; monomers containing silyl groups such as ethylene trimethoxysilane, ethylene methyl dimethoxysilane, ethylene dimethyl methoxysilane, ethylene triethoxysilane, ethylene methyl diethoxysilane, ethylene dimethyl ethoxysilane, 3-(meth)acrylamide propyltrimethoxysilane, and 3-(meth)acrylamide propyltriethoxysilane.

[0035] The content of the other structural units mentioned above relative to all structural units of the PVA of the present invention is sometimes preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 3 mol% or less, 1 mol% or less, or 0.1 mol% or less. On the other hand, the content of the other structural units mentioned above may be, for example, 0.1 mol% or more, or 1 mol% or more.

[0036] The PVA of the present invention may be either aliphatic hydrocarbon group without 12 carbon atoms at the end, or aliphatic hydrocarbon group with 6 to 18 carbon atoms at the end. The aforementioned terminal aliphatic hydrocarbon group can be introduced, for example, by a chain transfer agent having an aliphatic hydrocarbon group with 6 to 18 carbon atoms. Examples of such chain transfer agents include alkyl thiols with 6 to 18 carbon atoms, such as n-dodecylthiol.

[0037] <Powder> The powder of this invention is a powder containing the PVA of this invention. Because this powder contains the PVA of this invention, even when the PVA is dissolved in water at a high concentration, the increase in the viscosity of the aqueous solution can be suppressed.

[0038] In the powder of the present invention, the PVA of the present invention is generally the main component. The main component refers to the component with the highest content based on mass. The lower limit of the content of the PVA of the present invention in the non-volatile matter of the powder of the present invention is sometimes preferably 50% by mass, more preferably 70% by mass, even more preferably 90% by mass, and even more preferably 99% by mass. The upper limit of the content of the PVA of the present invention in the non-volatile matter of the powder of the present invention can also be 100% by mass. Examples of non-volatile matter other than the PVA of the present invention that may be included in the powder of the present invention include PVA other than the PVA of the present invention, resins other than PVA, surfactants, plasticizers, and other additives, as well as various compounds used in the manufacturing process. Furthermore, the volatile matter content in the powder of the present invention is generally 20% by mass or less, preferably 15% by mass or less, and even more preferably 10% by mass or less. Examples of volatile matter that may be included in the powder of the present invention include alcohols and water. The powder of the present invention can also be a powder of the PVA of the present invention.

[0039] In the powder of the present invention, the upper limit of the content of powder (micron powder) passing through a sieve with a pore size of 180 μm is sometimes preferably 12% by mass, more preferably 10% by mass, 8% by mass, or 5% by mass. As mentioned above, micron powder is prone to overheating during heat treatment and is prone to becoming an insoluble part due to excessive cross-linking. Therefore, by setting the content of powder passing through a sieve with a pore size of 180 μm below the above-mentioned upper limit, the insoluble part is reduced, and the coating properties are improved when used as an aqueous solution. Furthermore, the lower limit of the content of powder passing through a sieve with a pore size of 180 μm can be 0.1% by mass or 1% by mass. The pore size of the sieve is based on the nominal pore size W of JIS Z 8801-1-2006 (hereinafter the same).

[0040] In the powder of the present invention, it is preferable that the powder content passing through a sieve with an aperture of 1.00 mm is 97% by mass or more, and the powder content passing through a sieve with an aperture of 500 μm is 40% by mass or more. The lower limit of the powder content passing through a sieve with an aperture of 1.00 mm is more preferably 98% by mass, and even more preferably 99% by mass. On the other hand, the upper limit of the powder content passing through a sieve with an aperture of 1.00 mm can be 100% by mass or 99.9% by mass. The upper limit of the powder content passing through a sieve with an aperture of 500 μm can be 70% by mass or 60% by mass. When the powder of the present invention has the size described above, because there are fewer coarse powder particles and the particle size uniformity is high, the water solubility and coating properties when used as an aqueous solution are improved.

[0041] The particle size distribution in the powder of the present invention can be adjusted by means of the manufacturing process or by screening after manufacturing.

[0042] Add 4 parts by mass of the powder of the present invention to 96 parts by mass of water, and stir at 60°C for 1 hour. The undissolved portion is preferably 0.1 ppm or more and less than 2000 ppm. The above-mentioned undissolved portion is sometimes more preferably less than 1,500 ppm, and sometimes even more preferably less than 1,000 ppm. As described above, since the above-mentioned undissolved portion is small, the coating property and the like of the aqueous solution obtained from the powder of the present invention can be improved. On the other hand, the above-mentioned undissolved portion can be 1 ppm or more, or can be 10 ppm or more or 100 ppm or more. The measurement of the undissolved portion of the powder can be carried out in the same manner as the measurement of the undissolved portion of PVA.

[0043] <Uses of PVA and powder> The PVA and powder of the present invention can be used for various uses similar to those of conventional PVA and its powder. Examples are given below, but are not limited thereto. (1) Use as a vinyl chloride dispersant: a dispersion stabilizer and a dispersion aid for suspension polymerization of vinyl chloride and vinylidene chloride (2) Use as a coating agent: a sizing agent, a fiber processing agent, a leather finishing agent, a paint, an anti-fogging agent, an anti-metal corrosion agent, a brightening agent for electrogalvanizing, an antistatic agent (3) Use as an adhesive: an adhesive, a binder, a rewetting adhesive, various adhesives, an additive for cement or mortar (4) Agricultural uses: an adhesive for pesticides, a spreading agent for pesticides, a coating agent for agriculture, a soil conditioner anti-erosion agent, a dispersant for pesticides (5) Medical and cosmetic uses: a granulation binder, a coating agent, an emulsifier, an adherent, a binder, a base material for film preparations, a film-forming agent (6) Use as a viscosity modifier: a thickening agent (7) Use as a flocculant: a flocculant for suspended solids and dissolved substances in water, a metal flocculant (8) Film uses: a water-soluble film, a polarizing film, a barrier film, a film for packaging fiber products, a seed care sheet, a vegetation sheet, a seed tape, a hygroscopic film (9) Molded product uses: fibers, pipes (pipe), tubes (tube), leak-proof membranes, water-soluble fibers for chemical lace, sponges (10) Use as a resin raw material: a raw material for polyvinyl butyral, a photosensitive resin raw material, a graft polymer raw material, various gel raw materials (11) Post-reaction uses: post-reaction uses with low molecular weight organic compounds, high molecular weight organic compounds, and inorganic compounds (12) Dispersants for emulsification polymerization: dispersants for emulsification polymerization of vinyl acetate emulsions, dispersants for emulsification polymerization of ethylene-vinyl acetate. (13) Paper processing agents: sizing agents for general Western paper, fillers for release paper, protective film agents for thermal paper, and silica binders for inkjet paper.

[0044] The PVA and powder of the present invention suppress the increase in viscosity when used as a high-concentration aqueous solution. Therefore, it is particularly suitable for applications where it is used in aqueous solution form. Examples of applications as described above include adhesives, films (film-forming solutions), paper processing agents, and dispersants for emulsification polymerization. That is, suitable forms of the present invention include aqueous solutions containing the PVA of the present invention, adhesives containing the PVA of the present invention, films containing the PVA of the present invention, paper processing agents containing the PVA of the present invention, and dispersants for emulsification polymerization containing the PVA of the present invention. The content of the PVA of the present invention in the above-mentioned aqueous solutions, adhesives, film-forming solutions, etc., is, for example, 1% by mass or more and 30% by mass or less, 5% by mass or more and 20% by mass or less, or 10% by mass or more. The above-mentioned aqueous solutions, adhesives, film-forming solutions, etc., may further contain other components besides the PVA of the present invention and water. Examples of other components as described above include those contained in conventionally known adhesives and film-forming solutions.

[0045] Paper processing agents The paper processing agent of the present invention contains the PVA of the present invention. The paper processing agent of the present invention can be in powder form or in liquid form such as an aqueous solution. The paper coating agent of the present invention can also be a coating agent for paper. This paper processing agent, except for using the PVA of the present invention, can be defined as being the same as conventionally known paper processing agents. This paper processing agent may further contain other components besides the PVA of the present invention. Examples of other components include, for example, pigments, dispersants, plasticizers, pH adjusters, defoamers, surfactants, and resins other than the PVA of the present invention.

[0046] <Dispersants for Emulsification Polymerization> The dispersant for emulsion polymerization of the present invention contains the PVA of the present invention. The dispersant for emulsion polymerization of the present invention can be in the form of powder or in the form of a liquid such as an aqueous solution. In addition to using the PVA of the present invention, the dispersant for emulsion polymerization can be defined as the same as the well-known dispersants for emulsion polymerization in the past. The dispersant for emulsion polymerization can further contain other components other than the PVA of the present invention. Examples of other components include, for example, surfactants, buffers, polymerization degree regulators, PVAs other than the PVA of the present invention, and the like. The dispersant for emulsion polymerization is particularly suitable for use as a dispersant for emulsion polymerization of ethylenically unsaturated monomers.

[0047] <Method for manufacturing PVA and powder> The method for manufacturing the PVA or powder of the present invention is not particularly limited, but the following method is preferred. That is, the method for manufacturing the PVA or powder of the present invention includes: Step (1) of obtaining a copolymer of monomer (a) and vinyl ester, Step (2) of obtaining a saponified product of the copolymer, and Step (3) of heat-treating the above saponified product.

[0048] (Step (1)) In step (1), a copolymer of monomer (a) and vinyl ester is obtained. Specific examples and suitable examples of monomer (a) are as described above. Examples of vinyl esters include, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caproate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl trimethylacetate, vinyl neodecanoate, and the like. Among them, vinyl acetate is preferred.

[0049] Examples of polymerization methods include well-known methods such as bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method, and the like. Among these methods, the bulk polymerization method carried out without a solvent and the solution polymerization method using a solvent such as an alcohol are preferred, and the solution polymerization method carried out in the presence of a lower alcohol is more preferred. As the above lower alcohol, an alcohol having 3 or less carbon atoms is preferred, methanol, ethanol, n-propanol, and isopropanol are more preferred, and methanol is further more preferred. When carrying out the polymerization reaction by the bulk polymerization method or the solution polymerization method, the reaction mode can also adopt either a batch mode or a continuous mode.

[0050] Examples of initiators used in polymerization reactions include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanonitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile); and well-known initiators such as benzoyl peroxide and n-propyl peroxide carbonate. There are no particular restrictions on the polymerization temperature, but a range of 5°C to 200°C is appropriate.

[0051] During the copolymerization of monomer (a) with ethylene ester, copolymerizable monomers may be further copolymerized without prejudice to the intent of the invention. Specific examples of other monomers as described above, such as monomers imparting other structural units, are also possible.

[0052] During copolymerization, chain transfer agents can be coexisted to adjust the degree of polymerization of the resulting PVA. Examples of chain transfer agents include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; thiols such as 2-hydroxyethanethiol and 3-mercaptopropionic acid; thiocarboxylic acids such as thioacetic acid; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene. Aldehydes and ketones can be used appropriately. The amount of chain transfer agent added depends on the chain transfer constant of the added chain transfer agent and the degree of polymerization of the desired PVA, but it is generally preferred to be 0.1 to 10% by mass relative to the vinyl ester used.

[0053] (Step (2)) Step (2): The copolymer (ethylene ester polymer) obtained in step (1) is saponified in solution using an alkaline catalyst or an acid catalyst to obtain a saponified product. The saponification reaction can be carried out using alkaline catalysts such as sodium hydroxide, potassium hydroxide, and sodium methoxide, or acidic catalysts such as p-toluenesulfonic acid, via alcoholysis or hydrolysis. Examples of solvents used for the saponification reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These can be used alone or in combination of two or more. Among these, using methanol or a mixture of methanol and methyl acetate as the solvent, and conducting the saponification reaction in the presence of sodium hydroxide as an alkaline catalyst, is simpler and therefore preferred.

[0054] Saponification can be carried out using a belt reactor, kneader reactor, or tower reactor. There is no particular limitation on the saponification temperature, but it is preferably between 20°C and 60°C. When a gel-like product precipitates during saponification, the product can be pulverized and further saponified. Afterwards, the resulting solution is neutralized to complete saponification, and then washed to obtain the saponified product. The saponification method is not limited to the methods described above; well-known methods can be used.

[0055] (Step (3)) Step (3) involves heat-treating the saponified product obtained in step (2). The heat treatment is preferably carried out in an air or nitrogen environment. The heat treatment is preferably performed on a solid saponified product, more preferably on a powdered (particle) product. Alternatively, the saponified product can be pre-dried, and heat treatment can be performed on saponified products to which volatile matter has been removed to a certain extent. The heat treatment can also be carried out while the saponified product is being stirred. For example, a cylindrical stirred dryer can be used for the heat treatment.

[0056] In one embodiment of the method for manufacturing PVA or powder according to the present invention, the heat treatment temperature is set to 110°C or higher, and the heat treatment time is set to 1 hour or higher. By performing heat treatment under the aforementioned conditions, sufficient cross-linking reaction is generated, and PVA with a minimum branching degree of 0.93 or lower is efficiently obtained. The lower limit of the heat treatment temperature can be 115°C or 120°C. The upper limit of the heat treatment temperature can be 150°C, 140°C, 130°C, or 125°C. The lower limit of the heat treatment time is preferably 2 hours, more preferably 3 hours, even more preferably 4 hours, and even more preferably 5 hours. The upper limit of the heat treatment time can be 24 hours, 12 hours, or 8 hours. By setting the heat treatment temperature and heat treatment time to the above-mentioned upper limits or lower, excessive cross-linking formation can be suppressed, and the undissolved portion of the obtained PVA or powder can be reduced.

[0057] In one embodiment of the powder manufacturing method of the present invention, the content of powder passing through a sieve with a pore size of 180 μm in the saponified product at the end of step (3) is set to 12% by mass or less. The upper limit of the content of powder passing through the sieve with a pore size of 180 μm is sometimes preferably 10% by mass, 8% by mass or 5% by mass. As mentioned above, by reducing the amount of micronized powder that is prone to overheating, a powder of PVA with less insoluble portion that suppresses the formation of excessive cross-linking can be obtained efficiently.

[0058] As a method to ensure that the content of powder passing through a sieve with an aperture of 180 μm in the saponified product at the end of step (3) is 12% by mass or less, examples include a method of heat-treating the saponified product after sieving, and a method of heat-treating while removing the generated fine powder. For example, the heat treatment can also be performed in multiple stages, with sieving performed between each heat treatment to remove the fine powder. Alternatively, the fine powder can be removed after heat treatment.

[0059] Between step (2) and step (3), a step of crushing the saponified material into particles and a step of screening the particles of saponified material may also be set. [Example]

[0060] The present invention will be described in more detail with reference to the following embodiments, but the invention is not limited to these embodiments. Furthermore, in the following embodiments and comparative examples, "parts" and "%" refer to mass unless otherwise specified. The various measurement methods used in the following embodiments and comparative examples are shown below.

[0061] [Viscosity-average degree of polymerization] The viscosity-average degree of polymerization (P) of PVA was determined according to JIS K6726:1994. Specifically, for PVA that has been saponified to a degree of saponification of 99.5 moles or more and has been purified to contain structural units derived from monomer (a), the limiting viscosity [η] (unit: liters / g) was determined in a sodium chloride aqueous solution (0.5 moles / L) at 30°C. For PVA that does not contain structural units derived from monomer (a), the limiting viscosity [η] (unit: liters / g) was determined in an aqueous solution at 30°C. The viscosity-average degree of polymerization (P) of PVA was then calculated from the limiting viscosity [η] using the following formula. P=([η]×10 4 / 8.29) (1 / 0.62)

[0062] [Degree of saponification] The degree of saponification of PVA was determined by the method described in JIS K 6726:1994.

[0063] [Quality Improvement Rate] The modification rate of PVA (derived from the content of structural units of monomer (a) in PVA) was determined by using 1H-NMR with ethylene ester polymers as precursors of PVA. For example, when using monomethyl maleate as monomer (a), the aforementioned modification rate is determined by the following steps: Using hexane / acetone as the solvent, the vinyl ester polymer, a precursor of PVA, is thoroughly purified by reprecipitation at least three times. The resulting purified product is then dried at 70°C for one day to prepare an analytical sample. This sample is dissolved in CDCl₃ and analyzed using 1H-NMR at room temperature. The modification rate (the content S of the structural units derived from monomer (a)) can be calculated using the following formula: the peak value α (4.7–5.2 ppm) of the methylene structure of the vinyl ester unit in the vinyl ester polymer and the peak value β (3.6–3.8 ppm) of the methyl ester moiety of the structural unit derived from monomer (a). S(Mohr%) = {(Number of protons in β / 3) / (Number of protons in α + (Number of protons in β / 3))} × 100

[0064] Branching degree First, hexafluoroisopropanol was used as the mobile phase, and gel permeation chromatography (GPC) was performed using a differential refractive index detector, a light scattering detector, and a viscosity detector to determine the intrinsic viscosity of each absolute molecular weight of the PVA (branched PVA) being tested and the corresponding linear PVA serving as a reference, ranging from 200,000 to 800,000. Second, for linear PVA, unmodified PVA with a viscosity within ±20% of the viscosity of the PVA being tested and a saponification degree within ±3 moles was used. The specific measurement conditions for GPC are shown below. Solvent: Hexafluoroisopropanol (containing sodium trifluoroacetate at a concentration of 20 mmol / L) Tubing: Two Shodex HFIP-806M tubing units and one Shodex HFIP-LG tubing unit. Column temperature: 40℃ Flow rate: 1.0 mL / min Sample concentration: 0.1 mass / vol% Injection volume: 100μL Sample: Relative molecular weight using polymethyl methacrylate Absolute molecular weight using polymethyl methacrylate Using the intrinsic viscosity [η] of PVA for each absolute molecular weight, and the intrinsic viscosity [η] of linear PVA, the branching degree gm for each absolute molecular weight is calculated using equations (1) and (2) above. The smallest branching degree gm in the range of absolute molecular weights between 200,000 and 800,000 is defined as the minimum branching degree. Furthermore, the ratio gA / gB of the branching degree gA in an absolute molecular weight of 200,000 to the branching degree gB in an absolute molecular weight of 800,000 is calculated. As an example of the test results, the results of PVA-1 are shown in Figures 1 and 2. Figure 1 is a graph (Mark-Houwink graph) plotting the absolute molecular weight of the tested PVA-1 and the corresponding linear PVA PVA-1' against the intrinsic viscosity ([η] branching or [η] linear). PVA-1' is an unmodified PVA with a viscosity of 9.2 mPa·s in a 4% aqueous solution and a saponification degree of 88 moles. Figure 2 is a graph plotting the branching degree gm of each absolute molecular weight of PVA-1 obtained by formulas (1) and (2) above, based on the results shown in Figure 1.

[0065] [Particle size distribution] The particle size distribution of PVA powder was determined using the dry sieving method described in JIS Z8815:1994. Using sieves with apertures of 1.00 mm, 500 μm, and 180 μm, the proportions of powder passing through the 1.00 mm sieve (content: mass%), the 500 μm sieve, and the 180 μm sieve (content: mass%) of the PVA powder before sieving were calculated respectively. Furthermore, the apertures mentioned above refer to the nominal aperture W as defined in JIS Z8801-1-2006.

[0066] [Undissolved portion] In a 500mL flask equipped with a stirrer, set to 60°C, 288g of distilled water was added to the flask, and stirring was started at 300rpm. 12g of PVA powder was weighed and slowly added to the flask. The total amount of PVA powder (12g) was added, and stirring continued for 60 minutes to obtain a PVA solution. Then, using the obtained PVA solution, undissolved particles (insoluble particles) were filtered through a 63μm pore size metal filter. Next, the filter was thoroughly washed with 30°C warm water to remove the solution adhering to it, leaving only insoluble particles. The filter was then dried in a 120°C heat dryer for 1 hour. The mass of the dried filter was compared with the mass of the filter before filtration to calculate the mass of the insoluble particles. The mass of insoluble particles relative to the amount of PVA powder (12g) used was defined as the insoluble fraction content (ppm).

[0067] [Aqueous solution viscosity] A PVA aqueous solution was prepared, and its viscosity (mPa·s) was measured using a Type B viscometer (rotor speed 12 rpm, temperature 20°C). The method for preparing the PVA aqueous solution is as follows: 10 parts by mass of PVA were added to 90 parts by mass of water, and the mixture was heated to 90°C while stirring, and then cooled after 1 hour. Furthermore, the same unmodified PVA used in the GPC determination at the time of branching was selected as the reference unmodified PVA. Viscosity measurements were also performed on the unmodified PVA in the same manner. The viscosity ratio (viscosity of the reference unmodified PVA / PVA of the example or comparative example) was calculated. A viscosity ratio greater than 1.0 was considered to suppress the increase in viscosity, and a viscosity ratio greater than 1.2 was considered to sufficiently suppress the increase in viscosity.

[0068] [Example 1] (Manufacturing of PVA-1) In a reactor equipped with a stirrer, reflux cooling pipe, nitrogen inlet pipe, comonomer dropper, and polymerization initiator inlet, 700 parts by mass of vinyl acetate and 1050 parts by mass of methanol were added. Nitrogen substitution was performed in the system for 30 minutes while nitrogen bubbles were generated. Alternatively, monomethyl maleate was used as monomer (a), and a 10% methanol solution of monomethyl maleate was nitrogen substituted using nitrogen bubble generation. The reactor was heated to 60°C, and then 0.84 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The methanol solution of monomethyl maleate was added dropwise to the reactor to maintain a constant monomer composition ratio in the polymerization solution. Polymerization was carried out at 60°C for 5 hours, followed by cooling to stop the polymerization. The total amount of monomer (a) added until polymerization stopped was 12.1 parts by mass, the solids concentration at polymerization stop was 23.6%, and the polymerization rate was 60%. Next, under reduced pressure at 30°C, methanol was added intermittently while unreacted monomers were removed to obtain a methanol solution of vinyl ester polymers (concentration 36.7%). Then, 569.2 parts by mass of a methanol solution of vinyl ester polymers (containing 150.0 parts by mass of the polymer) was prepared by further adding methanol to this methanol solution. Water was added to make the water content in the system 1% by adding 26.0 parts by mass of a 10% methanol solution of sodium hydroxide, and saponification was carried out at 40°C (polymer concentration in the saponification solution 25%, molar ratio of sodium hydroxide to vinyl acetate units in the polymer 0.009, water content 1%). Since a gel-like substance was formed approximately 10 minutes after adding the methanol solution of sodium hydroxide, it was pulverized and further placed at 40°C for 1 hour for saponification. Then, 600 parts by mass of methyl acetate was added to neutralize the residual alkali. Phenolphthalein indicator was used to confirm the neutralization was complete, and the solution was filtered to obtain a white solid. 600 parts by weight of methanol were added to the white solid, and the mixture was washed at 40°C for 30 minutes. This washing operation was repeated twice, followed by centrifugation to remove the liquid, and the resulting white solid was dried overnight. Then, while removing the micronized powder, the solid was heat-treated at 120°C for 6 hours to obtain PVA (PVA-1) powder. The physical properties and evaluation results of PVA-1 are shown in Table 2.

[0069] [Examples 2-7 and Comparative Examples 1-5] (Manufacturing of PVA-2-PVA-12) The polymerization conditions, such as the amount of vinyl acetate and methanol used, the type or amount of monomer (a), the concentration of the vinyl ester polymer in saponification, the molar ratio of sodium hydroxide to vinyl acetate units, and the heat treatment conditions were all modified as shown in Table 1. Otherwise, the powders of each PVA (PVA-2 to PVA-12) in Examples 2 to 7 and Comparative Examples 1 to 5 were obtained by the same method as in Example 1. The physical properties and evaluation results of these PVAs are shown in Table 2.

[0070] [Comparative Example 6] (Manufacturing of PVA-13) In a reactor equipped with a stirrer, reflux cooling pipe, nitrogen inlet pipe, and initiator addition port, 700 parts by mass of vinyl acetate and 1050 parts by mass of methanol were added. Nitrogen bubbles were generated while the system underwent nitrogen substitution for 30 minutes. The reactor temperature was then raised to 60°C, and 0.84 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. After polymerization at 60°C for 3 hours, cooling was performed to stop the polymerization. The solids concentration at polymerization termination was 24.0%, and the polymerization rate was 60%. Subsequently, under reduced pressure at 30°C, methanol was added intermittently to remove unreacted monomers, yielding a methanol solution of the vinyl acetate polymer (concentration 36.7%). Next, 569.2 parts by mass of a methanol solution of an ethylene ester polymer (containing 150.0 parts by mass of the polymer) was prepared by further adding methanol to the methanol solution. Water was added to make the water content in the system 1% by adding 26.0 parts by mass of a 10% methanol solution of sodium hydroxide. Saponification was carried out at 40°C (polymer concentration in the saponification solution: 25%; molar ratio of sodium hydroxide to vinyl acetate units in the polymer: 0.009; water content: 1%). Since a gel-like substance was formed approximately 10 minutes after adding the sodium hydroxide to the methanol solution, it was pulverized and further placed at 40°C for 1 hour for saponification. Then, 600 parts by mass of methyl acetate was added to neutralize the residual alkali. After confirming the neutralization was complete using phenolphthalein indicator, the mixture was filtered to obtain a white solid. 600 parts by mass of methanol was added to this white solid, and the mixture was washed at 40°C for 30 minutes. This washing operation was repeated twice, followed by centrifugation to remove the liquid, and the resulting white solid was dried overnight. Subsequently, while removing the micronized powder, the powder was heat-treated at 120°C for 6 hours using a dryer to obtain PVA (PVA-13) powder. The physical properties and evaluation results of PVA-13 are shown in Table 2.

[0071] Furthermore, unmodified PVA (linear PVA) corresponding to each manufactured PVA (PVA-1 to 13) was manufactured according to the manufacturing method of Comparative Example 6 above, serving as a benchmark for the determination of branching degree and the evaluation of aqueous solution viscosity. However, in the unmodified PVA, the heat treatment after pre-drying was not performed.

[0072] [Table 1] Usage Polymerization rate (%) Saponification conditions Heat treatment conditions Vinyl acetate (parts by weight) methanol (parts by weight) Monomer (a) AIBN (parts by weight) Ethylene ester system polymer concentration (%) NaOH Mörby Moisture content (%) temperature (°C) time (hr) type Usage (parts by weight) Example 1 PVA-1 700 1050 Monomethyl maleate 12.1 0.84 60 25 0.009 1 120 6 Example 2 PVA-2 300 1400 Monomethyl maleate 12.6 0.50 50 30 0.010 1 120 4.5 Example 3 PVA-3 700 1050 Monomethyl maleate 12.1 0.84 60 25 0.006 1 120 6 Example 4 PVA-4 700 1050 Monomethyl maleate 12.1 0.84 60 25 0.020 1 120 6 Example 5 PVA-5 700 1050 Monomethyl maleate 20.7 1.20 60 25 0.009 1 120 6 Example 6 PVA-6 700 1050 Dimethyl maleate 12.1 0.84 60 25 0.009 1 120 6 Example 7 PVA-7 700 1050 Monomethyl fumarate 12.1 0.84 60 25 0.009 1 120 6 Comparative Example 1 PVA-8 920 80 Monomethyl maleate 0.6 0.25 25 20 0.010 1 120 4.5 Comparative Example 2 PVA-9 900 300 Monomethyl maleate 6.8 0.05 25 20 0.010 1 120 6 Comparative Example 3 PVA-10 880 720 Monomethyl maleate 11.1 0.90 65 25 0.008 1 120 6 Comparative Example 4 PVA-11 700 1050 Monomethyl maleate 12.1 0.84 60 25 0.006 1 120 6 Comparative Example 5 PVA-12 700 1050 Monomethyl maleate 12.1 0.84 60 25 0.009 1 105 6 Comparative Example 6 PVA-13 700 1050 - 0.0 0.84 60 25 0.009 1 120 6

[0073] [Table 2] average viscosity Degree of aggregation: P Improvement rate: S (mol%) S×P degree of saponification (mol%) Minimum Branching Particle size distribution Undissolved portion (ppm) 10% aqueous solution viscosity ratio g A / g B 180μm pore size Sieve aperture (mass %) Aperture 1.00mm Sieve aperture (mass %) 500μm pore size Sieve aperture (mass %) Example 1 PVA-1 420 1.9 798 88 0.22 2.59 3.4 99.6 45.0 700 1.3 Example 2 PVA-2 200 5.0 1000 88 0.10 4.20 3.5 99.4 43.1 1800 3.9 Example 3 PVA-3 420 2.0 840 80 0.11 3.31 6.9 99.7 50.1 950 2.9 Example 4 PVA-4 420 2.0 840 95 0.75 1.15 5.7 99.2 52.5 1000 1.1 Example 5 PVA-5 420 4.0 1680 88 0.10 5.10 10.3 99.3 47.3 1750 3.3 Example 6 PVA-6 420 1.9 798 88 0.15 3.60 3.4 99.6 44.9 1200 2.5 Example 7 PVA-7 420 1.9 798 88 0.36 2.71 3.4 99.1 45.5 530 1.3 Comparative Example 1 PVA-8 3500 0.2 700 88 0.65 1.12 11.6 99.2 40.3 1100 0.6 Comparative Example 2 PVA-9 2000 0.5 1000 88 0.72 1.33 7.8 99.2 56.2 870 0.8 Comparative Example 3 PVA-10 800 1.0 800 83 0.60 1.23 6.6 99.7 40.7 1600 0.9 Comparative Example 4 PVA-11 420 2.0 840 60 - ※1 - ※1 10.9 99.4 44.1 10200 - ※1 Comparative Example 5 PVA-12 420 2.0 840 88 0.98 1.01 10.2 99.1 47.8 300 1.0 Comparative Example 6 PVA-13 420 0 0 88 - ※2 - ※2 4.4 99.7 45.5 120 1.0 ※1: In Comparative Example 4, PVA-11, a homogeneous aqueous solution could not be obtained, therefore the degree of branching and the viscosity of the aqueous solution were not measured. ※2: In the unmodified PVA-13 of Comparative Example 6, the branching structure was not substantially formed, so the degree of branching was not measured.

[0074] As shown in Table 2, the PVAs in Examples 1-7 inhibited the increase in viscosity when used as high-concentration aqueous solutions. In particular, the PVAs in Examples 1 and 7, in addition to their sufficient viscosity-inhibiting effect, were also excellent in terms of having minimal undissolved portions. The aforementioned minimum branching degree was within an appropriate range, and the branching degree ratio gA / gB was small.

[0075] On the other hand, the PVAs of Comparative Examples 1-3 showed high degrees of polymerization, and the viscosity further increased due to the introduction of branched structures. The PVA of Comparative Example 4 had a low degree of saponification and was easily cross-linked by heat, resulting in more thermally cross-linked sites and making it impossible to obtain a homogeneous aqueous solution. The PVA of Comparative Example 4 could not produce a high-concentration aqueous solution of 10% by mass, therefore it was determined that the problem of suppressing the increase in viscosity when used as a high-concentration aqueous solution could not be solved. The PVA of Comparative Example 5 had few branches, therefore no viscosity-inhibiting effect was observed. The PVA of Comparative Example 6 did not contain structural units derived from monomer (a), and even after heat treatment, no branches were formed, therefore no viscosity-inhibiting effect was observed. [Potential for industrial application]

[0076] The PVA of this invention can be used in various applications such as coating agents, adhesives, film raw materials, paper processing agents, and dispersants for emulsification polymerization.

[0077] none< / pva>

Claims

1. A vinyl alcohol polymer comprising a vinyl alcohol polymer obtained by saponifying a vinyl ester polymer by saponifying a structural unit derived from at least one of the group consisting of monomers having a carboxyl group and their derivatives, wherein the absolute molecular weight is in the range of 200,000 to 800,000, the minimum branching degree is 0.93 or less, the viscosity-average degree of polymerization is 750 or less, and the degree of saponification is 65 moles or more.

2. The vinyl alcohol polymer of claim 1, wherein at least one of the groups comprising monomers having a carboxyl group and their derivatives is selected from at least one of the groups comprising vinyl unsaturated dicarboxylic acids, and their monoesters, diesters and anhydrides.

3. The vinyl alcohol polymer of claim 1, wherein at least one of the groups comprising monomers having a carboxyl group and their derivatives is selected from at least one of the groups comprising maleic acid, monoalkyl maleate, dialkyl maleate, maleic anhydride, fumaric acid, monoalkyl fumarate and dialkyl fumarate.

4. The vinyl alcohol polymer of claim 1 or 2, which satisfies the following formula (I); S×P>250 ・・・(I) In formula (I), S is the content (moles%) of the structural unit derived from at least one of the group consisting of monomers having carboxyl groups and their derivatives, relative to all structural units; P is the viscosity-average degree of polymerization.

5. The vinyl alcohol polymers of claim 1 or 2 satisfy the following formula (II): 1.0 < gA / gB < 9.0 ・・・(II) In formula (II), gA is the degree of branching in an absolute molecular weight of 200,000; gB is the degree of branching in an absolute molecular weight of 800,000.

6. For the vinyl alcohol polymer of claim 1 or 2, when 4 parts by weight of the vinyl alcohol polymer are added to 96 parts by weight of water and stirred at 60°C for 1 hour, the undissolved portion is more than 0.1 ppm and less than 2000 ppm.

7. A powder comprising an ethylene alcohol polymer as claimed in any one of claims 1 to 6.

8. The powder of claim 7, wherein the content of powder passing through a sieve with an aperture of 180 μm is less than 12% by mass.

9. The powder as requested in item 7 or 8, wherein the powder content passing through a sieve with an aperture of 1.00 mm is 97% by mass or more, and the powder content passing through a sieve with an aperture of 500 μm is 40% by mass or more.

10. A method for manufacturing a vinyl alcohol-based polymer as claimed in any one of claims 1 to 6, comprising: a step (1) of obtaining a copolymer of at least one selected from the group consisting of a monomer having a carboxyl group and its derivatives with an ethylene ester, a step (2) of obtaining a saponified product of the copolymer, and a step (3) of heat treating the saponified product, wherein the heat treatment temperature in step (3) is 110°C or higher, and the heat treatment time is 1 hour or higher.

11. A method for manufacturing a powder, comprising the method for manufacturing a powder according to any one of claims 7 to 9, comprising: a step (1) obtaining a copolymer of at least one selected from the group consisting of monomers having carboxyl groups and their derivatives with ethylene esters; a step (2) obtaining a saponified product of the copolymer; and a step (3) heat-treating the saponified product, wherein at the end of step (3), the content of powder passing through a sieve with a pore size of 180 μm in the saponified product is 12% by mass or less.

12. A paper processing agent comprising an ethylene alcohol polymer as claimed in any one of claims 1 to 6.

13. A dispersant for emulsifying polymerization, comprising an ethylene alcohol-based polymer as claimed in any one of claims 1 to 6.

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