Vinyl alcohol polymers, powders containing the same, methods for producing the powders, coating agents, coated products, methods for producing coated products, stabilizers for emulsion polymerization, aqueous emulsions, and adhesives.

Abstract

Provided is a vinyl alcohol-based polymer (PVA) that contains structural units derived from at least one type selected from the group consisting of carboxyl group-containing monomers and derivatives thereof. The minimum degree of branching is 0.93 or less within an absolute molecular weight range of 200,000-800,000. When 4 parts by mass of the PVA is added to 96 parts by mass of water and stirred for 1 hour at 60ºC, the amount of insoluble components is not less than 0.1 ppm and less than 2000 ppm.

Description

Technical Field

[0001] The present invention relates to a vinyl alcohol polymer, a powder containing the same, a method for producing the powder, a coating agent, a coated article, a method for producing the coated article, a stabilizer for emulsion polymerization, an aqueous emulsion, and an adhesive.

Background Art

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

[0003] As a kind of modified PVA, PVA containing a structural unit derived from a carboxylic acid or its derivative is known (see Patent Document 1). Such PVA is used as a sizing agent for acid paper containing sulfate bands, a water-resistant coating film combined with a crosslinking agent, an adhesive, etc. by utilizing the reactivity of carboxylic acids. In addition, because of its good water solubility, it is also useful as a water-soluble packaging film for agricultural chemicals, laundry detergents, industrial chemicals, etc., and is widely used. Regarding adhesives using PVA, Patent Document 2 describes an adhesive composition containing an alkyl-modified PVA having a specific viscosity range and a (meth)acrylic emulsion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In applications involving the application of PVA-containing solutions such as coating agents and adhesives, good coating properties are required, including minimal splashing of the coating solution during application, minimal unevenness in the coating, and the formation of a highly uniform coating film. Furthermore, even with conventional PVA-containing adhesives, improvements are needed in areas such as the occurrence of coating streaks and splashing (adhesive splatter) during roll coating.

[0006] The present invention was made to solve the above problems and aims to provide PVA with good coating properties, a powder containing such PVA, a method for producing this powder, and a coating agent, a coated product, and a method for producing a coated product using the above PVA. The present invention also aims to provide an adhesive that reduces the occurrence of coating streaks and liquid splashing during roll coating, and an emulsion polymerization stabilizer and aqueous emulsion that can obtain such an adhesive. [Means for solving the problem]

[0007] The above purpose is, [1] PVA comprising a structural unit selected from the group consisting of monomers having a carboxyl group and derivatives thereof, wherein the minimum degree of branching in the range of absolute molecular weight from 200,000 to 800,000 is 0.93 or less, and the insoluble matter when 4 parts by mass of the above PVA is added to 96 parts by mass of water and stirred at 60°C for 1 hour is 0.1 ppm or more and less than 2000 ppm; [2] PVA of [1] having a viscosity-average degree of polymerization of 300 or more and 5000 or less; [3] PVA of [1] or [2], wherein at least one selected from the group consisting of monomers having a carboxyl group and derivatives thereof is at least one selected from the group consisting of ethylenically unsaturated dicarboxylic acids and their monoesters, diesters and anhydrides; [4] PVA of [1] or [2], wherein at least one selected from the group consisting of monomers having a carboxyl group and derivatives thereof is at least one selected from the group consisting of maleic acid, monoalkyl maleic acid, dialkyl maleic acid, maleic anhydride, fumaric acid, monoalkyl fumaric acid, and dialkyl fumaric acid; [5] Any PVA from [1] to [4] that satisfies the following equation (I); S×P>250 ···(I) In formula (I), S is the content (mol%) of structural units derived from at least one selected from the group consisting of monomers having a carboxyl group and their derivatives, relative to the total structural units. P is the viscosity-average degree of polymerization. [6] Any PVA from [1] to [5] that satisfies the following equation (II); 1.0 <g A / g B <3.0 ···(II) In formula (II), g A This is the degree of branching at an absolute molecular weight of 200,000. B This represents the degree of branching at an absolute molecular weight of 800,000. [7] Any PVA from [1] to [6] with a degree of saponification of 65 mol% or more and 99 mol% or less; A powder containing any of the following PVA: [8][1]~[7]; [9] The powder of [8], wherein the content of the powder that passes through a sieve with a mesh size of 180 μm is 12% by mass or less;

[10] Powder of [8] or [9] having a powder content of 97% by mass or more that passes through a sieve with a mesh size of 1.00 mm and a powder content of 40% by mass or more that passes through a sieve with a mesh size of 500 μm;

[11] A method for producing a powder containing PVA, comprising the steps of (1) obtaining a copolymer of at least one selected from the group consisting of monomers having a carboxyl group and derivatives thereof with a vinyl ester, (2) obtaining a saponified product of the copolymer, and (3) heat-treating the saponified product, wherein the content of powder that passes through a sieve with a mesh size of 180 μm in the saponified product at the end of step (3) is 12% by mass or less;

[12] A method for producing the powder of

[11] , wherein the heat treatment temperature in step (3) above is 110°C or higher and the heat treatment time is 1 hour or longer; A coating agent containing any of the PVAs listed in

[13] [1] to [7]; A coated product obtained by applying the coating agent

[14]

[13] onto a substrate;

[15] A coating of

[14] which is a thermal recording material;

[16] The release paper base, which is the coating of

[14] ;

[17] Oil-resistant paper, coating of

[14] ;

[18] Inkjet recording material, coating of

[14] ;

[19] A coating of

[14] which is gas barrier paper or flavor barrier paper;

[20] White cardboard, coated with

[14] ; A method for manufacturing a coated product, comprising the step of applying the coating agent

[21]

[13] onto a substrate using a curtain coater; A stabilizer for emulsion polymerization containing any of the PVAs listed in

[22] [1] to [7]; Aqueous emulsion containing the emulsion polymerization stabilizer

[23]

[22] and a polymer containing ethylenically unsaturated monomer units; Adhesives containing aqueous emulsions of

[24]

[23] ; This is achieved by providing one of the following: [Effects of the Invention]

[0008] According to the present invention, it is possible to provide PVA with good coating properties, a powder containing such PVA, a method for producing this powder, and a coating agent, a coated product, and a method for producing a coated product using the above PVA. Furthermore, according to the present invention, it is possible to provide an adhesive that reduces the occurrence of coating streaks and the scattering of coating liquid during roll coating, and an emulsion polymerization stabilizer and aqueous emulsion that can obtain such an adhesive. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a graph showing the relationship between the absolute molecular weight and intrinsic viscosity ([η]branch and [η]linear) of PVA-3 and PVA-17 in the examples. [Figure 2] Figure 2 is a graph showing the relationship between the absolute molecular weight and the degree of branching (gm) of PVA-3 in the examples. [Figure 3] Figure 3 illustrates the method for evaluating splashing (liquid splatter) in the example. [Modes for carrying out the invention]

[0010] Embodiments for carrying out the present invention will be described below. In this specification, the upper and lower limits of numerical ranges (such as the content of each component, the values ​​calculated from each component, and physical properties) can be combined as appropriate.

[0011] <pva> The PVA (vinyl alcohol polymer) of the present invention is a PVA containing structural units selected from the group consisting of monomers having a carboxyl group and derivatives thereof, wherein the minimum degree of branching in the range of absolute molecular weight from 200,000 to 800,000 is 0.93 or less, and when 4 parts by mass of the above PVA is added to 96 parts by mass of water and stirred at 60°C for 1 hour, the insoluble matter is 0.1 ppm or more and less than 2000 ppm.

[0012] This PVA exhibits good coatability when applied as an aqueous solution. Furthermore, coating agents containing this PVA suppress the occurrence of defects even when applied at high speeds, resulting in superior coatability. The reason for these effects is not entirely clear, but the following reasons are speculated. The degree of branching of a polymer, as will be explained in detail later, is an index that represents the degree of branching of a polymer's structure on a scale from 0 to 1, with smaller values ​​indicating a greater branching structure. This PVA has a minimum branching degree of 0.93 or less in the range of absolute molecular weight between 200,000 and 800,000, indicating the formation of a sufficient branching structure, which results in a small difference in first normal stress when applied as an aqueous solution. Normal stress is the stress generated in a direction perpendicular to the direction of shear when rotational deformation is applied to a viscoelastic fluid object being measured. Aqueous solutions with a small difference in first normal stress tend to reduce splatter and uneven coating during application. In addition, this PVA has a low amount of insoluble matter, which is one of the other factors that cause splatter and uneven coating during application. Thus, because this PVA has a sufficiently branched structure and contains little insoluble matter, it is presumed to have good coating properties when used as an aqueous solution.

[0013] The PVA of the present invention comprises a vinyl alcohol unit and a structural unit selected from the group consisting of monomers having a carboxyl group and their derivatives. Hereinafter, "at least one selected from the group consisting of monomers having a carboxyl group and their derivatives" may be referred to as "monomer (a)". The PVA is usually obtained by saponifying a vinyl ester polymer (a copolymer of monomer (a) and a vinyl ester) containing a structural unit derived from monomer (a). Examples of monomer derivatives having a carboxyl group include esters and anhydrides of monomers having a carboxyl group. The carboxyl group (-COOH) may exist in the form of a salt (-COONa, etc.). The structural unit derived from monomer (a) may be bonded to other structural units by forming a crosslinked structure. Examples of monomer (a) include ethylenically unsaturated monocarboxylic acids, ethylenically unsaturated dicarboxylic acids, and their derivatives.

[0014] Examples of ethylenically unsaturated monocarboxylic acids and their derivatives include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate.

[0015] Examples of ethylenically unsaturated dicarboxylic acids and their derivatives include ethylenically unsaturated dicarboxylic acids, their monoesters, their diesters, and their anhydrides. Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. Examples of monoesters of ethylenically unsaturated dicarboxylic acids include monoalkyl unsaturated dicarboxylic acid esters such as monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl mesaconic acid, monoethyl mesaconic acid, monomethyl itaconic acid, and monoethyl itaconic acid. Examples of diesters of ethylenically unsaturated dicarboxylic acids include dialkyl unsaturated dicarboxylic acid esters such as dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl citraconic acid, diethyl citraconic acid, dimethyl mesaconic acid, diethyl mesaconic acid, dimethyl itaconic acid, and diethyl itaconic acid. Examples of ethylenically unsaturated dicarboxylic acid anhydrides include maleic anhydride and citraconic anhydride.

[0016] From the viewpoint of industrial availability and reactivity with vinyl esters, ethylenically unsaturated dicarboxylic acids, as well as their monoesters, diesters, and anhydrides, are preferred as monomer (a). Maleic acid, monoalkyl maleic acid, dialkyl maleic acid, maleic anhydride, fumaric acid, monoalkyl fumarate, and dialkyl fumarate are more preferred, and monomethyl maleic acid, dimethyl maleic acid, maleic anhydride, monomethyl fumarate, and dimethyl fumarate are particularly preferred. Monomer (a) can be used in the form of one or more types.

[0017] The lower limit of the content (S) of structural units derived from monomer (a) relative to the total structural units of the PVA of the present invention is preferably 0.1 mol%, more preferably 0.5 mol%, even more preferably 1.0 mol%, and particularly preferably 1.5 mol%. On the other hand, the upper limit of the above content (S) is preferably 15 mol%, more preferably 10 mol%, even more preferably 5 mol%, and even more preferably 3 mol%. By setting the above content (S) within the above range, the effect of carboxylic acid modification, that is, the effect of introducing structural units derived from monomer (a), can be fully exhibited, and the coating properties can be further improved. Furthermore, by setting the above content (S) below the above upper limit, the formation of excessive crosslinking is suppressed. The portion where excessive crosslinking occurs has reduced solubility in water and becomes an insoluble portion. Therefore, by setting the above water content (S) below the above upper limit, the insoluble portion tends to decrease. The above content (S) is the vinyl ester polymer before saponification of the PVA of the present invention. 1 This can be determined by 1H-NMR analysis.

[0018] In the PVA of the present invention, the minimum branching degree in the absolute molecular weight range of 200,000 to 800,000 is 0.93 or less. The branching degree is an index that represents the degree of branching structure of a polymer. A linear polymer, i.e., a polymer without a branched structure, has a branching degree of 1, and a value closer to 0 indicates a greater branching structure. For the PVA to be measured, the branching degree for each absolute molecular weight in the absolute molecular weight range of 200,000 to 800,000 is determined. The smallest branching degree in the above range is then defined as the minimum branching degree. Note that if the absolute molecular weight of the PVA is not distributed across the entire range of 200,000 to 800,000, for example, if it only contains PVA with an absolute molecular weight of 600,000 or less, the smallest branching degree in the absolute molecular weight range of 200,000 to 600,000 will be the minimum branching degree. In other words, the PVA of the present invention, which consists of multiple molecules, contains molecules with an absolute molecular weight in the range of 200,000 to 800,000, but the absolute molecular weight does not need to be distributed across the entire range of 200,000 to 800,000.

[0019] The degree of branching g at each absolute molecular weight of the PVA of the present invention m It is obtained from the following formulas (1) and (2). g m ’ = [η] branch / [η] linear ···(1) g m = g m ’ (1 / ε) ···(2) In formula (1), [η] branch is the intrinsic viscosity at the absolute molecular weight x (x is 200,000 or more and 800,000 or less) of the PVA (branched PVA) of the present invention having a branched structure, and is a value calculated from a differential refractive index detector, a light scattering detector, and a viscosity detector. [η] linear is the intrinsic viscosity at the above absolute molecular weight x of linear PVA, and similarly, it is a value calculated from a differential refractive index detector, a light scattering detector, and a viscosity detector. Note that as the linear PVA, a non-modified PVA (saponified product of a vinyl acetate homopolymer) having a 4% by mass aqueous solution viscosity within ±20% of the PVA of the present invention to be measured and a saponification degree within ±3 mol% is used. The intrinsic viscosity at each absolute molecular weight of the PVA of the present invention and the linear PVA can be specifically measured by the method described in the examples. The ratio g m ’ of the intrinsic viscosity represented by the above formula (1) and the branching degree g m have the relationship of the above formula (2). In formula (2), ε is a structure factor, and ε = 0.7 is assumed.

[0020] In the PVA of the present invention, the minimum branching degree is 0.93 or less, and a sufficient branched structure (crosslinking) is formed. Therefore, according to the PVA of the present invention, the first normal stress difference in the case of an aqueous solution becomes small, and the splashing and uneven coating of the coating liquid during coating are reduced. In order to further enhance such an effect, the upper limit of the above minimum branching degree is preferably 0.85, more preferably 0.6, and may be even more preferably 0.4, 0.25, or 0.18.

[0021] On the other hand, the lower limit of the above minimum branching degree may be, for example, 0.01 or 0.05, may be preferably 0.15, and may be more preferably 0.20. By setting the minimum branching degree to be above the above lower limit, the insoluble components caused by excessive crosslinking formation can be reduced, and the coating properties and the like can be improved.

[0022] The branching in the PVA is presumed to be formed by ester bonding between the carboxyl and hydroxyl groups of the PVA during heat treatment. 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.

[0023] The PVA of the present invention includes PVA having an absolute molecular weight in the range of 200,000 to 800,000. Preferably, the PVA of the present invention 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 is distributed across the entire range of at least 200,000 to 800,000.

[0024] The upper limit of the viscosity-average degree of polymerization (P) of the PVA of the present invention may be, for example, 8,000, but is preferably 5,000 and more preferably 4,000. On the other hand, the lower limit of the viscosity-average degree of polymerization (P) may be, for example, 100 or 200, but is preferably 300, more preferably 400, and even more preferably 500 or 1,000. When the viscosity-average degree of polymerization (P) is within the above range, the coating properties tend to be higher. The viscosity-average degree of polymerization (P) is a value measured in accordance with JIS K6726:1994. Specifically, it can be determined by the method described in the examples.

[0025] The lower limit of the vinyl alcohol unit content relative to the total structural units in the PVA of the present invention is preferably 35 mol%, more preferably 50 mol%, even more preferably 70 mol%, and in some cases, 80 mol% or 85 mol% may be even more preferred. On the other hand, the upper limit of the vinyl alcohol unit content is preferably 99.9 mol%, and more preferably 99 mol%.

[0026] The lower limit of the degree of saponification of the PVA in the present invention is preferably 65 mol%, more preferably 80 mol%, and even more preferably 85 mol%. By setting the degree of saponification to above the lower limit, water solubility is increased and insoluble matter is reduced, resulting in improved coating properties. On the other hand, the upper limit of the degree of saponification may be 100 mol%, but is preferably 99 mol%, more preferably 95 mol%, and even more preferably 92 mol%. Setting the degree of saponification to below the upper limit tends to facilitate the formation of a sufficient branched structure by heat treatment. The degree of saponification is a value measured by the method described in JIS K6726:1994.

[0027] The PVA of the present invention preferably satisfies the following formula (I). S×P>250 ···(I) In formula (I), S is the percentage (mol%) of structural units derived from monomer (a) relative to the total structural units. P is the viscosity-average degree of polymerization.

[0028] When formula (I) is satisfied, a balance is struck between the degree of effect due to carboxylic acid modification (such as the formation of branched structures) and the degree of effect due to the degree of polymerization, resulting in improved coatability. Specifically, for example, when formula (I) is satisfied, uneven coating during application is suppressed, and the strength of the resulting film tends to increase. The lower limit of S×P is more preferably 300, and may be even 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, even more preferably 2,000, and even more preferably 1,500.

[0029] With regard to the degree of branching described above, the PVA of the present invention preferably satisfies formula (ii), and more preferably satisfies formula (II). 1.0 <g A / g B <5.0 ···(ii) 1.0 <g A / g B <3.0 ···(II) In equations (ii) and (II), g A This is the degree of branching at an absolute molecular weight of 200,000 (the degree of branching of the PVA in the present invention that has an absolute molecular weight of 200,000). B This is the degree of branching at an absolute molecular weight of 800,000 (the degree of branching of the PVA in the present invention whose absolute molecular weight is 800,000).

[0030] As described above, sufficient heat treatment promotes crosslinking, resulting in PVA with a small minimum branching degree. However, if there are inconsistencies in the degree of crosslinking due to differences in molecular weight, the excessively crosslinked PVA (usually the component with a large molecular weight) tends to become insoluble in water, affecting the coating properties of the aqueous solution. Furthermore, if there are large inconsistencies in crosslinking due to differences in molecular weight, the specific g A / g B The ratio g becomes larger. From this perspective, the above ratio g A / g B A value less than 2.7 is preferable.

[0031] When 4 parts by mass of the PVA of the present invention are added to 96 parts by mass of water and stirred at 60°C for 1 hour, the insoluble content is 0.1 ppm or more and less than 2000 ppm. The above insoluble content is preferably less than 1,750 ppm, and more preferably less than 1,600 ppm. By having such a low amount of insoluble content, coating properties can be improved. On the other hand, the above insoluble content may be 1 ppm or more, 10 ppm or more, or 100 ppm or more. Note that "ppm" is based on mass, and the above insoluble content (ppm) indicates the percentage of insoluble content in the PVA. Specifically, the insoluble content can be determined by the method described in the examples.

[0032] The above ratio g A / g B The value and the content of the above-mentioned insoluble matter tend to increase as the proportion of PVA that is excessively heated and undergoes excessive crosslinking increases. Therefore, as described later, when heat-treating saponified vinyl ester polymers (copolymers), the above ratio g can be improved by removing fine powders that are easily overheated beforehand, performing heat treatment while removing fine powders, or removing fine powders after heat treatment. A / g B Furthermore, the proportion of the above-mentioned insoluble matter can be reduced.

[0033] The PVA of the present invention may contain structural units other than vinyl alcohol units, vinyl ester units, and structural units derived from monomer (a). Monomers that give the above other structural units 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 group-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-diacetate. Examples include C-1-butene; allyl ethers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers having an oxyalkylene group; hydroxyl group-containing α-olefins 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; and monomers having a silyl group such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamidepropyltrimethoxysilane, and 3-(meth)acrylamidepropyltriethoxysilane.

[0034] The upper limit of the content of the other structural units relative to the total structural units of the PVA of the present invention is preferably 20 mol%, more preferably 10 mol%, and even more preferably 3 mol%, 1 mol%, or 0.1 mol%. For example, if the content of structural units derived from α-olefins as the other structural units is high, foaming may easily occur when it is dissolved in an aqueous solution. For this reason, coating properties may be further improved by setting the content of the other structural units relative to the total structural units of the PVA to the upper limit mentioned above. On the other hand, the lower limit of the content of the other structural units may be, for example, 0.1 mol%, or 1 mol%.

[0035] Furthermore, the PVA of the present invention is expected to be relatively unaffected by pH and to exhibit good coating properties even under acidic or alkaline conditions.

[0036] <Powder> The powder of the present invention is a powder containing the PVA of the present invention. Because the powder contains the PVA of the present invention, it has good coating properties when dissolved in water and applied as a coating.

[0037] In the powder of the present invention, the PVA of the present invention is usually the main component. The main component refers to the component with the highest mass content. The lower limit of the content of the PVA of the present invention relative to the nonvolatile content of the powder of the present invention is preferably 50% by mass, more preferably 70% by mass, even more preferably 90% by mass, and in some cases, even more preferably 99% by mass. The upper limit of the content of the PVA of the present invention relative to the nonvolatile content of the powder of the present invention may be 100% by mass. Nonvolatile components other than the PVA of the present invention that may be contained in the powder of the present invention include PVA other than the PVA of the present invention, resins other than PVA, additives such as surfactants and plasticizers, and various compounds used during manufacturing. Furthermore, the volatile content in the powder of the present invention is usually 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. Volatile components that may be contained in the powder of the present invention include alcohol and water. The powder of the present invention may be a powder of the PVA of the present invention.

[0038] In the powder of the present invention, the upper limit of the content of powder (fine powder) that passes through a sieve with a mesh size of 180 μm is preferably 12% by mass, and may be more preferably 10% by mass, 8% by mass, or 5% by mass. As described above, fine powder is easily overheated by heat treatment, and crosslinking progresses too much, making it prone to becoming insoluble. Therefore, by keeping the content of powder that passes through a sieve with a mesh size of 180 μm below the above upper limit, the amount of insoluble material is reduced, improving the coating properties when used as an aqueous solution. The lower limit of the content of powder that passes through a sieve with a mesh size of 180 μm may be 0.1% by mass or 1% by mass. The mesh size of the sieve conforms to the nominal mesh size W of JIS Z 8801-1-2006 (the same applies hereinafter).

[0039] In the powder of the present invention, it is preferable that the content of powder that passes through a sieve with a mesh size of 1.00 mm is 97% by mass or more, and the content of powder that passes through a sieve with a mesh size of 500 μm is 40% by mass or more. The lower limit of the content of powder that passes through a sieve with a mesh size 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 content of powder that passes through a sieve with a mesh size of 1.00 mm may be 100% by mass or 99.9% by mass. The upper limit of the content of powder that passes through a sieve with a mesh size of 500 μm may be 70% by mass or 60% by mass. When the powder of the present invention has such a size, there is less coarse powder and the particle size uniformity is high, which improves the coating properties when it is dissolved in an aqueous solution.

[0040] The particle size distribution in the powder of the present invention can be adjusted by sieving during the manufacturing process or after manufacturing.

[0041] When 4 parts by mass of the powder of the present invention is added to 96 parts by mass of water and stirred at 60°C for 1 hour, the insoluble matter is preferably 0.1 ppm or more and less than 2000 ppm. More preferably, the insoluble matter is less than 1,750 ppm, and even more preferably less than 1,600 ppm. By having less insoluble matter in this way, the coating property and the like of the aqueous solution obtained from the powder of the present invention can be enhanced. On the other hand, the insoluble matter may be 1 ppm or more, and may be 10 ppm or more or 100 ppm or more. The measurement of the insoluble matter of the powder can be carried out in the same manner as the measurement of the insoluble matter of PVA.

[0042] <Uses of PVA and powder> The PVA and powder of the present invention can be used in various applications similar to conventional PVA and its powder. Examples are given below, but it is not limited thereto. (1) Vinyl chloride dispersant use: Dispersing stabilizer and dispersing aid for suspension polymerization of vinyl chloride and vinylidene chloride (2) Coating agent use: Sizing agent, fiber treating agent, leather finishing agent, paint, anti-fogging agent, metal corrosion inhibitor, brightening agent for zinc plating, antistatic agent (3) Adhesive and binder use: Adhesive, tackifier, rewet adhesive, various binders, additives for cement and mortar (4) Agricultural use: Binder for agricultural chemicals, spreading agent for agricultural chemicals, coating agent for agriculture, soil conditioner, erosion inhibitor, dispersing agent for agricultural chemicals (5) Medical and cosmetic use: Granulation binder, coating agent, emulsifier, patch, binder, film preparation base material, film forming agent (6) Coagulant use: Coagulant for suspended substances and dissolved substances in water, metal coagulant (7) Film use: Water-soluble film, polarizing film, barrier film, film for packaging fiber products, seed dressing sheet, vegetation sheet, seed tape, hygroscopic film (8) Molded product use: Fiber, pipe, tube, leak-proof film, water-soluble fiber for chemical lace, sponge (9) Resin raw material use: Raw material for polyvinyl butyral, photosensitive resin raw material, graft polymer raw material, various gel raw materials (10) Post-reaction use: Post-reaction use with low molecular organic compounds, high molecular organic compounds, and inorganic compounds (12) Dispersing agents for emulsion polymerization: Dispersing agents for emulsion polymerization of vinyl acetate emulsions, dispersing agents for emulsion polymerization of ethylene-vinyl acetate (13) Paper processing agents: Surface sizing agents for general printing paper, blocking agents for release paper, overcoat agents for thermal paper, silica binders for inkjet paper

[0043] The PVA and powder of the present invention have good coating properties when made into an aqueous solution. Therefore, it is particularly suitable for applications where it is dissolved in water and coated. Such applications include adhesives, films (film-forming solutions), etc. That is, an aqueous solution containing the PVA of the present invention, an adhesive containing the PVA of the present invention, a film containing the PVA of the present invention, etc. are also preferred embodiments of the present invention. The content of the PVA of the present invention in the above aqueous solution, adhesive, film-forming solution, etc. is, for example, 1% by mass or more and 30% by mass or less, and may be 5% by mass or more and 20% by mass or less, or may be 10% by mass or more. In the above aqueous solution, adhesive, film-forming solution, etc., other components other than the PVA and water of the present invention may be further contained. Such other components include the components contained in conventionally known adhesives, film-forming solutions, etc.

[0044] <Manufacturing method of PVA and powder> The manufacturing method of the PVA or powder of the present invention is not particularly limited, but the following method is preferred. That is, the manufacturing method of the PVA or powder of the present invention is Step (1) of obtaining a copolymer of monomer (a) and vinyl ester, Step (2) of obtaining a saponified product of the above copolymer, and Step (3) of heat-treating the above saponified product is provided.

[0045] (Step (1)) In step (1), a copolymer of monomer (a) and a vinyl ester is obtained. Specific examples and preferred examples of monomer (a) are as described above. Examples of vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred.

[0046] Examples of polymerization methods include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Of these methods, bulk polymerization carried out without a solvent and solution polymerization carried out using a solvent such as an alcohol are preferred, and solution polymerization carried out in the presence of a lower alcohol is more preferred. As the lower alcohol, alcohols with 3 or fewer carbon atoms are preferred, methanol, ethanol, n-propanol, and isopropanol are more preferred, and methanol is even more preferred. When carrying out polymerization reactions using bulk polymerization or solution polymerization, either batch or continuous reaction methods can be employed.

[0047] Examples of initiators used in polymerization reactions include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and known initiators such as organic peroxide initiators such as benzoyl peroxide and n-propyl peroxycarbonate. There are no particular restrictions on the polymerization temperature during the polymerization reaction, but a range of 5°C to 200°C is appropriate.

[0048] When copolymerizing monomer (a) with a vinyl ester, copolymerizable monomers can be further copolymerized without impairing the spirit of the present invention. Specific examples of such other monomers are those described above as monomers that provide other structural units.

[0049] During copolymerization, a chain transfer agent may be added 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; mercaptans such as 2-hydroxyethanethiol and 3-mercaptopropionic acid; thiocarboxylic acids such as thioacetic acid; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene. Among these, aldehydes and ketones are preferred. The amount of chain transfer agent added is determined according to the chain transfer constant of the added chain transfer agent and the desired degree of polymerization of the PVA, but generally, 0.1 to 10% by mass relative to the vinyl ester used is preferred.

[0050] (Process (2)) In step (2), the copolymer (vinyl ester polymer) obtained in step (1) is saponified in solution using an alkaline catalyst or an acid catalyst to obtain a saponified product. For the saponification reaction, conventionally known basic catalysts such as sodium hydroxide, potassium hydroxide, or sodium methoxide, or acidic catalysts such as p-toluenesulfonic acid, can be used for alcohol decomposition or hydrolysis reactions. Solvents used in the saponification reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These can be used individually or in combination of two or more. Among these, it is convenient and preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide, which is a basic catalyst.

[0051] The saponification reaction can be carried out using a belt reactor, kneader reactor, column reactor, etc. While there are no particular limitations on the saponification temperature, 20°C to 60°C is preferred. If a gel-like product precipitates as saponification progresses, the product should be crushed and the saponification process should be continued. Afterward, the resulting solution can be neutralized to terminate the saponification, and the saponified product can be obtained by washing. The saponification method is not limited to the method described above; other known methods can be used.

[0052] (Step (3)) In step (3), the saponified product obtained in step (2) is heat-treated. The heat treatment is preferably carried out in an air atmosphere or a nitrogen atmosphere. The heat treatment is preferably carried out on a solid, more preferably powdered (particulate) saponified product. The saponified product may be pre-dried to remove some of the volatile components before heat treatment. The heat treatment may be carried out while stirring the saponified product. The heat treatment can be carried out using, for example, a cylindrical stirring dryer.

[0053] In the powder production method of the present invention, the content of powder that passes through a sieve with a mesh 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 that passes through this 180 μm sieve may preferably be 10% by mass, 8% by mass, or 5% by mass. By reducing the amount of fine powder that is easily overheated in this way, it is possible to efficiently obtain PVA powder with low insoluble content and suppressed excessive crosslinking formation.

[0054] Methods to ensure that the content of powder passing through a sieve with a mesh size of 180 μm in the saponified product at the end of step (3) is 12% by mass or less include sieving the saponified product before heat treatment, and removing the generated fine powder while performing heat treatment. For example, the heat treatment may be performed in multiple stages, and sieving may be performed between each heat treatment to remove the fine powder. Alternatively, the fine powder may be removed after the heat treatment.

[0055] In one embodiment of the method for producing PVA or powder according to the present invention, it is preferable to perform heat treatment at a heat treatment temperature of 110°C or higher and for a heat treatment time of 1 hour or more. By performing heat treatment under these conditions, a sufficient crosslinking reaction occurs, and PVA with a minimum branching degree of 0.93 or less can be efficiently obtained. The lower limit of the heat treatment temperature may be 115°C or 120°C. The upper limit of the heat treatment temperature may 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 may be 24 hours, 12 hours, or 8 hours. By setting the heat treatment temperature and heat treatment time below the above upper limits, the formation of excessive crosslinks can be suppressed, and the insoluble content of the obtained PVA or powder can be reduced.

[0056] Between step (2) and step (3), steps such as crushing the saponified material into particles and sieving the saponified material into particles may be provided.

[0057] <Coating agent> The coating agent of the present invention contains the PVA of the present invention. The coating agent has good coatability, and particularly good coatability even when coating is performed at high speeds. The coating agent can exhibit good coatability even when coating is performed using a curtain coater at a coating speed of more than 800 m / min or 1,000 m / min or more. The coating agent usually contains water as a solvent or dispersion medium. The coating agent may contain an organic solvent instead of water, or together with water, as a solvent or dispersion medium. The upper limit of the organic solvent content is preferably 50 parts by mass, more preferably 30 parts by mass, and even more preferably 10 parts by mass, 5 parts by mass, or 1 part by mass per 100 parts by mass of water. On the other hand, the lower limit of the above content is preferably 0 parts by mass, more preferably 10 parts by mass, per 100 parts by mass of water. The coating agent may not contain an organic solvent.

[0058] Examples of organic solvents include alcohol-based solvents such as methanol and ethanol; ester-based solvents such as methyl acetate and ethyl acetate; ether-based solvents such as diethyl ether and 1,4-dioxane; ketone-based solvents such as acetone and diethyl ketone; glycol-based solvents such as ethylene glycol and propylene glycol; glycol ether-based solvents such as diethylene glycol monomethyl ether and propylene glycol monomethyl ether; and glycol ester-based solvents such as ethylene glycol monomethyl ether acetate and propylene glycol monomethyl ether acetate.

[0059] The coating agent may further contain other components. Examples of other components include fillers, dispersants, water-soluble polymers, synthetic resin emulsions, plasticizers, pH adjusters, defoamers, release agents, and surfactants.

[0060] Examples of fillers include kaolin, clay, calcined clay, calcium carbonate, titanium dioxide, diatomaceous earth, aluminum oxide, aluminum hydroxide, synthetic aluminum silicate, synthetic magnesium silicate, polystyrene microparticles, polyvinyl acetate microparticles, urea-formaldehyde resin microparticles, settling silica, gel-like silica, silica synthesized by the gas phase method (hereinafter referred to as gas phase silica), colloidal silica, colloidal alumina, pseudoboehmite, talc, zeolite, alumina, zinc oxide, satin white, and organic pigments.

[0061] Examples of dispersants include sodium pyrophosphate, sodium hexametaphosphate, and sodium polyacrylate.

[0062] Examples of water-soluble polymers include other PVAs besides those mentioned above, vinyl alcohol-vinyl ester copolymers, polyacrylamide, polyacrylic acid, carboxymethylcellulose, hydroxyethylcellulose, hydroxymethylpropylcellulose, casein, and starches such as oxidized starch.

[0063] Examples of synthetic resin emulsions include styrene-butadiene copolymers, polyacrylic acid esters, polymethacrylic acid esters, vinyl acetate-ethylene copolymers, and vinyl acetate-acrylic acid ester copolymers. In other words, the coating agent may contain these synthetic resins in emulsion form.

[0064] Examples of plasticizers include glycols and glycerin. Examples of pH adjusters include ammonia, caustic soda, sodium carbonate, and phosphoric acid.

[0065] The solid content concentration in the coating agent is not particularly limited and can be adjusted as appropriate depending on the application, but considering the applicability, it is preferably 1% by mass or more and 65% by mass or less. The upper limit of the solid content concentration may be 60% by mass, 50% by mass, 40% by mass, 30% by mass, 20% by mass, or 15% by mass. The lower limit of the solid content concentration may be 3% by mass, 5% by mass, 10% by mass, 20% by mass, or 30% by mass.

[0066] The PVA content in the solids of the coating agent may be, for example, 0.1% by mass or more and 100% by mass or less. The upper limit of the above content may be 80% by mass, 50% by mass, 30% by mass, or 10% by mass. The lower limit of the above content may be 1% by mass, 10% by mass, 30% by mass, or 50% by mass.

[0067] <Coated materials> The coated product of the present invention is obtained by coating a substrate with the coating agent of the present invention. In other words, the coated product typically has a substrate and a layer containing PVA laminated on the substrate. Part or all of the PVA may be impregnated into the substrate. The coated product has minimal coating unevenness. The coated product can be suitably used for, for example, thermal recording materials, release paper base paper, oil-resistant paper, inkjet recording materials, gas barrier paper, flavor barrier paper, white cardboard, etc. In the coated product, the coating agent may be coated on only one side of the substrate, or on both sides.

[0068] The substrate for the coated product can be appropriately selected depending on the application, but examples include paper, cloth, wooden boards, and resin boards. The coated product may also be coated paper with paper as the substrate. Examples of paper include cardboard such as Manila cardboard, white cardboard, and linerboard; and printing paper such as general fine paper, medium-fine paper, and gravure paper. Examples of cloth include nonwoven fabric, woven fabric, and knitted fabric. Examples of wooden boards include single-piece boards, plywood, and laminated wood. Examples of resin boards include polyvinyl chloride boards and acrylic boards.

[0069] There are no particular restrictions on the amount of the coating agent applied to the substrate, but typically it is 0.1 g / m² in terms of solid content per side of the substrate. 2 More than 100g / m 2 It is approximately 1 g / m 2 More than 40g / m 2 The following is also acceptable.

[0070] [Thermal recording material] The thermal recording material is a coated product obtained by coating a substrate with the coating agent of the present invention. Examples of substrates for the thermal recording material include paper, as illustrated in the examples provided, with printing paper being preferred among them. Furthermore, while the basis weight of the substrate for the thermal recording material is not particularly limited, considering ease of handling, 10 g / m² is preferred. 2 More than 100g / m 2 The following is preferable: 35 g / m 2 More than 80g / m 2 The following are preferable. Note that basis weight refers to the mass per unit area.

[0071] The coating agent applied to the thermal recording material preferably contains a filler. Furthermore, the solid content concentration of the coating agent applied to the thermal recording material can be appropriately adjusted, for example, within a range of 10% by mass or more and 65% by mass or less.

[0072] [Release paper base] The release paper base is a coated product in which the coating material of the present invention is applied to a paper base. In the release paper base, the coating agent forms a sealing layer. By forming a release layer using a silicone release agent on this sealing layer, release paper can be manufactured. Because the release paper base uses the coating agent, a highly uniform sealing layer is formed.

[0073] Examples of the base material for the release paper include the paper exemplified as the base material for the coating, with fine paper, medium-quality paper, alkaline paper, glassine paper, and semi-glassine paper being preferred, and semi-glassine paper being more preferred. Furthermore, known adhesives can be used as the adhesive constituting the adhesive layer.

[0074] While there are no particular limitations on the basis weight of the base material for the release paper, considering the sealing properties and handling characteristics of the release paper base, 10 g / m² is recommended. 2 More than 120g / m 2 The following is preferable: 40 g / m 2 More than 100g / m 2 The following are preferable.

[0075] The solid content concentration of the coating agent applied to the release paper base is preferably 1% by mass or more and 15% by mass or less, and more preferably 2% by mass or more and 10% by mass or less.

[0076] [Oil-resistant paper] Oil-resistant paper is a coated product in which the base material is paper and the coating material of the present invention is applied to the base material. This oil-resistant paper can be suitably used as a packaging material for food and the like.

[0077] Examples of suitable substrates for oil-resistant paper include the papers exemplified as substrates for the coated product, such as fine paper, medium-quality paper, unbleached kraft paper, bleached kraft paper, alkaline paper, glassine paper, semi-glassine paper, corrugated cardboard base paper, white cardboard base paper, chipboard base paper, etc.

[0078] While there are no particular limitations on the basis weight of the base material for oil-resistant paper, considering oil resistance and other factors, 20 g / m² is recommended when using oil-resistant paper as packaging paper. 2 More than 150g / m 2 The following is preferable; when used as a box-shaped molded container, 150 g / m² 2 More than 500g / m 2 The following are preferable.

[0079] [Inkjet recording materials] The inkjet recording material is a coated product obtained by coating a substrate with the coating agent of the present invention. In the inkjet recording material, it is preferable to use the coating agent as a filler binder for the ink receiving layer. In this case, it is preferable that the coating agent contains a filler. The filler content is preferably 50 parts by mass or more and 300 parts by mass or less, and more preferably 80 parts by mass or more and 250 parts by mass or less, per 100 parts by mass of PVA. As a substrate for the inkjet recording material, paper as exemplified as a substrate for the coated product can be used.

[0080] [Gas barrier paper or flavor barrier paper] Gas barrier paper or flavor barrier paper is a coated product obtained by coating a paper substrate with the coating material of the present invention. That is, the coating agent can also be used as a barrier agent. In this case, it is preferable that the coating agent contains a filler. The filler content is preferably 3% to 95% by mass, more preferably 5% to 90% by mass, and even more preferably 10% to 85% by mass, based on the total solid content. In this case, it is also preferable that the coating agent further contains a binder component other than PVA, such as a synthetic resin emulsion. Note that PVA also functions as a binder component. Examples of substrates for gas barrier paper or flavor barrier paper include the paper exemplified as a substrate for coated products.

[0081] The lower limit of the air permeability resistance of the coated material, which is gas barrier paper or flavor barrier paper, is preferably 500 seconds, and more preferably 1,000 seconds. When the air permeability resistance is high, the barrier against gases and flavors is high, making it suitable as gas barrier paper or flavor barrier paper. On the other hand, the upper limit of this air permeability resistance may be, for example, 20,000 seconds, 10,000 seconds, 5,000 seconds, or 3,000 seconds. This air permeability resistance shall be the value measured by the Wang Gan testing machine method described in JIS P 8117:2009. It is preferable to use this gas barrier paper or flavor barrier paper after further applying a coating formulation containing barrier material, etc., to adjust the air permeability resistance to 100,000 seconds or more.

[0082] [White paperboard] White cardboard is a coated product in which the base material is cardboard and the coating material of the present invention is applied to the base material. Typically, in this case, the coating agent contains a white filler (white pigment). The content of the white filler (white pigment) is preferably 30% by mass or more and 95% by mass or less, and more preferably 50% by mass or 90% by mass or less, based on the total solid content.

[0083] <Method of manufacturing coated products> A known method can be used as the method for manufacturing the coated product of the present invention. The method for applying the coating agent to the substrate is not particularly limited, and a known coater such as a curtain coater, size press coater, air knife coater, blade coater, or roll coater may be used. Among these, the method using a curtain coater is preferred. That is, the method for manufacturing the coated product of the present invention comprises a step of applying the coating agent to the substrate using a curtain coater. The coating speed in this manufacturing method may be, for example, 500 m / min or more and 2,000 m / min or less, 800 m / min or more and 1,600 m / min or less, 900 m / min or more and 1,500 m / min or less, or 1,000 m / min or more and 1,300 m / min or less.

[0084] The manufacturing method may include a step of drying the coating agent after application. It may also include other steps, such as a calendering process when the substrate is paper.

[0085] <Stabilizer for emulsion polymerization> The emulsion polymerization stabilizer of the present invention contains the PVA of the present invention. By using this emulsion polymerization stabilizer, an adhesive can be obtained that reduces the occurrence of coating streaks and liquid splashing during roll coating. The emulsion polymerization stabilizer may contain other components, such as surfactants, to the extent that they do not interfere with the effects of the present invention.

[0086] Examples of surfactants include anionic surfactants such as alkylnaphthalene sulfonates and dialkyl sulfosuccinates; cationic surfactants such as alkylamine salts and lauryltrimethylammonium chloride; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and sorbitan fatty acid esters; amphoteric surfactants such as alkyl betaines and amine oxides; and polymeric surfactants such as vinyl alcohol polymers other than PVA in the present invention and hydroxyethylcellulose.

[0087] Other components besides surfactants include buffers and polymerization modifiers. Examples of buffers include acids such as acetic acid, hydrochloric acid, and sulfuric acid; bases such as ammonia, amine-charged sodium, charged potassium, and calcium hydroxide; or alkali carbonates, phosphates, and acetates. Examples of polymerization modifiers include mercaptans and alcohols.

[0088] The lower limit of the PVA content in the emulsion polymerization stabilizer of the present invention may be 10% by mass, or 50% by mass, 70% by mass, 80% by mass, 90% by mass, 95% by mass, 99% by mass, or 99.5% by mass. The upper limit of this content may be 100% by mass, or 99.99% by mass.

[0089] <Water-based emulsion> The aqueous emulsion of the present invention contains the above-mentioned emulsion polymerization stabilizer and a polymer containing ethylenically unsaturated monomer units. By using this aqueous emulsion, an adhesive can be obtained that reduces the occurrence of coating streaks and liquid splashing during roll coating. In this aqueous emulsion, the polymer containing ethylenically unsaturated monomer units is usually contained as a dispersed phase. In addition, this aqueous emulsion usually contains water as a dispersion medium.

[0090] The ethylenically unsaturated monomer units contained in the polymer are: Vinyl ester monomers such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate; (Meth)acrylic acid monomers such as acrylic acid and methacrylic acid; (Meth)acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and quaternaries thereof; Styrene monomers such as styrene, α-methylstyrene, p-styrenesulfonic acid, and their sodium and potassium salts; Diene monomers such as butadiene, isoprene, and chloroprene; Olefin monomers such as ethylene, propylene, and isobutylene; Acrylamide monomers such as acrylamide, methacrylamide, N-methylolacrylamide, N,N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid, and their sodium salts; Examples of units derived from polyvinyl chloride, polyvinyl fluoride, vinylidene chloride, vinylidene fluoride, and other halogenated olefins; N-vinylpyrrolidone; etc.

[0091] The polymer is preferably a polymer containing monomer units derived from at least one selected from the group consisting of vinyl ester monomers, (meth)acrylic acid monomers, styrene monomers, and diene monomers. Furthermore, the total content of vinyl ester monomers, (meth)acrylic acid monomers, styrene monomers, and diene monomers relative to the total monomer units of the polymer is preferably 70% by mass or more, and more preferably 75% by mass or more. In particular, it is especially preferable that the polymer contains vinyl ester monomer units at a concentration of 75% by mass or more relative to the total monomer units.

[0092] A preferred method for producing the aqueous emulsion of the present invention is to emulsion polymerize an ethylenically unsaturated monomer using a polymerization initiator in the presence of the emulsion polymerization stabilizer.

[0093] In the above method, there are no particular restrictions on the method of preparing or adding the emulsion polymerization stabilizer to the polymerization tank. Examples include adding the emulsion polymerization stabilizer to the polymerization tank all at once at the beginning, or adding it continuously during polymerization. Among these, from the viewpoint of increasing the grafting rate of the emulsion polymerization stabilizer to the ethylenically unsaturated monomer, the method of adding the emulsion polymerization stabilizer all at once at the beginning is preferred. In this case, it is preferable to add the emulsion polymerization stabilizer to cold water or preheated warm water, and then heat and stir it to 80°C to 90°C or lower in order to uniformly disperse the emulsion polymerization stabilizer.

[0094] The amount of emulsion polymerization stabilizer added during emulsion polymerization is preferably 0.2 parts by mass or more and 80 parts by mass or less per 100 parts by mass of ethylenically unsaturated monomer. When the amount of emulsion polymerization stabilizer added is 0.2 parts by mass or more, aggregation of dispersed particles in the aqueous emulsion is less likely to occur, and the polymerization stability when preparing the aqueous emulsion tends to be excellent. The amount of emulsion polymerization stabilizer added is more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, particularly preferably 2 parts by mass or more, and most preferably 4 parts by mass or more. On the other hand, when the amount of emulsion polymerization stabilizer added is 80 parts by mass or less, the viscosity of the polymerization solution does not become too high, polymerization tends to proceed more uniformly, and the heat of polymerization tends to be efficiently removed. The amount of emulsion polymerization stabilizer added is more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 40 parts by mass or less.

[0095] For polymerization initiators in emulsion polymerization, water-soluble single initiators or water-soluble redox initiators commonly used in emulsion polymerization can be used. These initiators may be used individually or in combination of two or more. Among these, redox initiators are preferred.

[0096] Examples of water-soluble solitary initiators include azo initiators, hydrogen peroxide, and peroxides such as persulfates (potassium, sodium, or ammonium salts). Examples of azo initiators include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).

[0097] As a redox initiator, a combination of an oxidizing agent and a reducing agent can be used. Peroxides are preferred as the oxidizing agent. Examples of reducing agents include metal ions and reducing compounds. Combinations of oxidizing and reducing agents include peroxides and metal ions, peroxides and reducing compounds, and peroxides, metal ions, and reducing compounds. Examples of peroxides include hydrogen peroxide, hydroxyperoxides such as cumene hydroxyperoxide and t-butyl hydroxyperoxide, persulfates (potassium, sodium, or ammonium salts), t-butyl peracetate, and peracid esters (t-butyl perbenzoate). Examples of metal ions include Fe. 2+ , Cr 2+ , V 2+ Co 2+ Ti 3+ Cu + Examples of metal ions capable of undergoing electron transfer include sodium bisulfite, sodium bicarbonate, tartaric acid, fructose, dextrose, sorbose, inositol, rongalit, and ascorbic acid. Among these, a combination of one or more oxidizing agents selected from the group consisting of hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate, and one or more reducing agents selected from the group consisting of sodium bisulfite, sodium bicarbonate, tartaric acid, rongalit, and ascorbic acid is preferred, and a combination of hydrogen peroxide and one or more reducing agents selected from the group consisting of sodium bisulfite, sodium bicarbonate, tartaric acid, rongalit, and ascorbic acid is more preferred.

[0098] During emulsion polymerization, alkali metal compounds, surfactants, buffers, polymerization degree regulators, etc., may be used as appropriate, as long as they do not impair the effects of the present invention.

[0099] Alkali metal compounds are not particularly limited, but examples include compounds containing sodium, potassium, rubidium, cesium, etc. The alkali metal compound may be the alkali metal ion itself, or it may be a compound containing an alkali metal.

[0100] Examples of buffering agents include acids such as acetic acid, hydrochloric acid, and sulfuric acid; bases such as ammonia, amine-charged sodium, charged potassium, and calcium hydroxide; or alkali carbonates, phosphates, and acetates. Examples of polymerization degree regulators include mercaptans and alcohols.

[0101] The emulsion polymerization temperature is not particularly limited, but is preferably between 20°C and 85°C, and more preferably between 40°C and 85°C.

[0102] The aqueous emulsion of the present invention may contain conventionally known additives such as fillers such as titanium dioxide, organic solvents such as toluene, plasticizers such as dibutyl phthalate, and film-forming aids such as glycol ethers. Furthermore, the aqueous emulsion can be powdered by spray drying or other methods to obtain a so-called powder emulsion. By mixing the powder emulsion with water, an aqueous emulsion can be obtained. Such aqueous emulsions are suitably used in a wide range of applications, including various adhesives, paints, textile processing agents, paper processing agents, inorganic binders, cement admixtures, and mortar primers.

[0103] <Adhesive> The adhesive of the present invention comprises the aqueous emulsion of the present invention. This adhesive has the effect of reducing the occurrence of coating streaks and liquid splashing during roll coating. This adhesive may be an aqueous adhesive. Furthermore, the adhesive of the present invention can be made less prone to foaming and less affected by pH by, for example, using PVA with a low content of the other structural units mentioned above.

[0104] The lower limit of the PVA content in the adhesive of the present invention is preferably 0.1% by mass. When the PVA content is 0.1% by mass or more, the high-speed coating properties, film strength, initial adhesion, dynamic water resistance, and acid resistance tend to improve. The lower limit of the PVA content is more preferably 1% by mass, even more preferably 3% by mass, particularly preferably 5% by mass, and most preferably 6% by mass. On the other hand, the upper limit of the PVA content is preferably 50% by mass. When the PVA content is 50% by mass or less, the viscosity of the adhesive becomes appropriate and easier to handle. The upper limit of the PVA content is more preferably 35% by mass, even more preferably 25% by mass, particularly preferably 18% by mass, and most preferably 13% by mass.

[0105] In the adhesive and aqueous emulsion of the present invention, the mass ratio (A) / (B) of PVA (A) to polymer (B) containing ethylenically unsaturated monomer units is preferably 2 / 98 to 80 / 20. When the mass ratio (A) / (B) is 2 / 98 or higher, the adhesive strength is improved. From this point of view, the lower limit of the above mass ratio (A) / (B) is more preferably 5 / 95, and even more preferably 8 / 92. On the other hand, when the above mass ratio (A) / (B) is 80 / 20 or lower, water-resistant adhesion is good. From this point of view, the upper limit of the above mass ratio (A) / (B) is more preferably 70 / 30, even more preferably 60 / 40, and even more preferably 50 / 50.

[0106] The lower limit of the solid content in the adhesive of the present invention is preferably 10% by mass, more preferably 20% by mass, even more preferably 25% by mass, and even more preferably 30% by mass. On the other hand, the upper limit of the solid content is preferably 60% by mass, more preferably 55% by mass, and even more preferably 50% by mass. When the solid content is 10% by mass or more, the viscosity stability of the adhesive tends to be excellent. On the other hand, when the solid content is 60% by mass or less, the open time tends to be long and the handling properties tend to be excellent.

[0107] The adhesive may contain various additives, as long as they do not impair the effects of the present invention. Examples of such additives include inorganic particles such as calcium carbonate, clay, kaolin, talc, and titanium dioxide; organic solvents (aromatic compounds such as toluene and xylene, alcohols, ketones, esters, halogenated solvents, etc.); crosslinking agents; plasticizers; anti-precipitation agents; thickeners; flow improvers; preservatives; defoaming agents; organic fillers; wetting agents; colorants; binders; water-retaining agents; polyethylene oxide; antifungal agents; deodorants; and fragrances.

[0108] Other additives include metal salts of phosphate compounds such as sodium polyphosphate and sodium hexametaphosphate, inorganic dispersants such as water glass, polyacrylic acid and its salts, sodium alginate, anionic polymer compounds such as α-olefin-maleic anhydride copolymers and their metal salts, and surfactants such as nonionic surfactants such as ethylene oxide adducts of higher alcohols and copolymers of ethylene oxide and propylene oxide. Adding these improves the fluidity of the adhesive. To improve dynamic water resistance, one or more crosslinking agents selected from water-soluble metal compounds, colloidal inorganic substances, polyamidoamine epichlorohydrin adducts, and glyoxal resins may also be included. Examples of water-soluble metal compounds include aluminum chloride, aluminum nitrate, zirconium ammonium carbonate, and titanium lactate. Examples of colloidal inorganic substances include colloidal silica and alumina sol. Examples of polyamidoamine epichlorohydrin adducts include those obtained by adding epichlorohydrin to various polyamidoamines. Examples of glyoxal resins include urea-glyoxal resins. Furthermore, methylol group-containing compounds (resins), epoxy compounds (resins), aziridine group-containing compounds (resins), oxazoline group-containing compounds (resins), carbodiimide compounds, aldehyde compounds (resins), etc., can also be used in combination with the above crosslinking agent, provided that performance is not impaired. To improve adhesive strength, water-soluble boron compounds such as boric acid esters of polyhydric alcohols like glycerin and ethylene glycol, and sodium naphthalene sulfonate formalin condensates can also be added. Additionally, other additives such as natural adhesives like starch, casein, gelatin, guar gum, gum arabic, and sodium alginate; and processed natural adhesives like carboxymethylcellulose, oxidized starch, and methylcellulose can also be added. These may be used individually or in combination of two or more. [Examples]

[0109] The present invention will be specifically described by the following examples, but the present invention is not limited in any way by these examples. In the following examples and comparative examples, "parts" and "%" refer to mass unless otherwise specified. The measurement methods and evaluation methods used in the following examples and comparative examples are shown below.

[0110] [Viscosity average degree of polymerization] The viscosity-average degree of polymerization of PVA was measured in accordance with JIS K6726:1994. Specifically, PVA was saponified to a degree of saponification of 99.5 mol% or higher, purified, and then the intrinsic viscosity [η] (unit: liters / g) was measured in a 30°C sodium chloride aqueous solution (0.5 mol / L) for PVA containing structural units derived from monomer (a). For PVA not containing structural units derived from monomer (a), the intrinsic viscosity [η] (unit: liters / g) was measured in a 30°C aqueous solution. The viscosity-average degree of polymerization (P) of PVA was calculated from this intrinsic viscosity [η] using the following formula. P = ([η] × 10 4 (8.29) (1 / 0.62)

[0111] [Degree of saponification] The degree of saponification of PVA was determined by the method described in JIS K6726:1994.

[0112] [Degeneration rate] The denaturation rate of PVA (the content of structural units derived from monomer (a) in PVA) is determined using vinyl ester polymers, which are precursors of PVA. 1 This was determined using a method employing H-NMR. For example, when monomethyl maleate is used as monomer (a), the above denaturation rate can be determined by the following procedure. That is, the vinyl ester polymer, which is a precursor of PVA, is thoroughly reprecipitated and purified at least three times using n-hexane / acetone as the solvent, and the resulting purified product is dried at 70°C for one day to prepare a sample for analysis. This sample is dissolved in CDCl3, 1 The measurement is performed at room temperature using 1H-NMR. From the peak α (4.7-5.2 ppm) originating from the methine structure of the vinyl ester unit in the vinyl ester polymer and the peak β (3.6-3.8 ppm) originating from the methyl group of the methyl ester portion of the structural unit derived from monomer (a), the denaturation rate (content S of the structural unit derived from monomer (a)) can be calculated using the following formula. S (mol%) = {(number of protons in β / 3) / (number of protons in α + (number of protons in β / 3))} × 100

[0113] [Branching degree] First, using hexafluoroisopropanol as the mobile phase, gel permeation chromatography (GPC) measurements were performed using a differential refractive index detector, a light scattering detector, and a viscometer to determine the intrinsic viscosity for each absolute molecular weight between 200,000 and 800,000 for the target PVA (branched PVA) and the corresponding reference linear PVA. For the linear PVA, unmodified PVA was used, where the viscosity of a 4% by mass aqueous solution was within ±20% of the target PVA, and the degree of saponification was within ±3 mol%. The specific measurement conditions for GPC are shown below. Solvent: Hexafluoroisopropanol (containing sodium trifluoroacetate at a concentration of 20 mmol / L) Columns: Two Shodex HFIP-806M and one HFIP-LG Column temperature: 40℃ Flow rate: 1.0mL / min Sample concentration: 0.1 mass / vol% Injection volume: 100μL Standard: Polymethyl methacrylate for relative molecular weight Absolute molecular weight polymethyl methacrylate Intrinsic viscosity [η] of the PVA being measured for each measured absolute molecular weight. branch and the intrinsic viscosity [η] of linear PVA linear Using the above formulas (1) and (2), the degree of branching g for each absolute molecular weight is obtained. m We determined the smallest degree of branching g within the range of absolute molecular weight between 200,000 and 800,000. m This was defined as the minimum degree of branching. Furthermore, the degree of branching g at an absolute molecular weight of 200,000 was also defined. A And the degree of branching g at an absolute molecular weight of 800,000 B The ratio of g A / g B They sought it. As an example of the measurement results, the results for PVA-3 are shown in Figures 1 and 2. Figure 1 shows the absolute molecular weight and intrinsic viscosity ([η]) of PVA-3 and its corresponding linear PVA, PVA-17. branch or [η] linear Figure 2 is a graph (Mark-Houwink plot) showing the branching degree (g) for each absolute molecular weight of PVA-3, calculated using equations (1) and (2) above based on the results shown in Figure 1. m This is a graph plotting ).

[0114] [Particle size distribution] The particle size distribution of PVA powder was measured using the dry sieving method described in JIS Z8815:1994. Using sieves with mesh sizes of 1.00 mm, 500 μm, and 180 μm, the percentage of the mass of powder passing through the 1.00 mm sieve (content: mass%), the percentage of the mass of powder passing through the 500 μm sieve (content: mass%), and the percentage of the mass of powder passing through the 180 μm sieve (content: mass%) relative to the mass of PVA powder before sieving was determined. The above mesh sizes conformed to the nominal mesh size W of JIS Z8801-1-2006.

[0115] [Insoluble matter] A 500 mL flask equipped with a stirrer was prepared in a water bath set to 60°C. 288 g of distilled water was added to the flask, and stirring was started at 300 rpm. 12 g of PVA powder was weighed and gradually added to the flask. After adding the entire amount of PVA powder (12 g), stirring was continued for 60 minutes to obtain a PVA solution. The obtained PVA solution was then filtered to remove undissolved particles (insoluble particles) through a metal filter with a mesh size of 63 μm. Next, the filter was thoroughly washed with 30°C warm water to remove any remaining solution, leaving only the insoluble particles on the filter. The filter was then dried in a 120°C heating dryer for 1 hour. The mass of the dried filter was compared to the mass of the filter before filtration to calculate the mass of the insoluble particles. The mass of the insoluble particles relative to the PVA powder used (12 g) was defined as the content percentage (ppm) of the insoluble matter.

[0116] [Difference in stress from the first normal] A PVA aqueous solution was prepared, and the first normal stress difference of the PVA aqueous solution was measured when shear stress was applied. The method for preparing the PVA aqueous solution was as follows: 90 parts by mass of water were added to 10 parts by mass of PVA, and the temperature was raised to 90°C while stirring, and then cooled after 1 hour. Flow curve measurement was performed using a rheometer to measure the first normal stress difference. In addition, the same unmodified PVA used in the GPC measurement was selected as the reference unmodified PVA. The first normal stress difference was similarly determined for the unmodified PVA. The specific measurement conditions for measuring the stress difference of the first normal are shown below. Measuring device: MCR Rheometer 102 (manufactured by Antonpaar) Jig: Parallel plate (25mm diameter) Plate gap: 0.05 mm Shear rate range: 10 -2 ~10 5 s -1 Measurement temperature: 20℃ Shear rate is 10 5 s -1 The ratio of the first normal stress difference of the standard unmodified PVA aqueous solution to the first normal stress difference of the PVA aqueous solution being measured (first normal stress difference of standard unmodified PVA / PVA of the example or comparative example) was calculated and evaluated according to the following criteria. A: Greater than 4.0 B: Greater than 2.0 and less than or equal to 4.0 C: Greater than 1.5 and less than or equal to 2.0 D: Greater than 1.2 and less than or equal to 1.5 E: 1.2 or less

[0117] [splattering] Five parts by mass of PVA were added to 95 parts by mass of water, and a 5% by mass PVA aqueous solution was prepared using the same procedure as above, and this was used as the coating solution. The following evaluation was performed using the three rolls 1 to 3 shown in Figure 3. The surface temperature of each roll 1 to 3 was adjusted to 30°C. The prepared coating solution 4 was added between roll 2 and roll 3, and roll 1 was rotated at a surface speed of 300 m / min. The following criteria were used to visually evaluate whether droplets of the coating solution 4 (aqueous solution) were ejected from between roll 1 and roll 2. A: No droplets came out at all. B: A few droplets were released. C: Numerous droplets were ejected.

[0118] [Uneven coating] A 5% by mass aqueous solution of PVA was prepared using the same procedure as described above, and this was used as the coating solution. A basis weight of 70 g / m² was measured using a test shim sizer (manufactured by Kumagai Riki Kogyo). 2 The coating solution was applied to the paper at a speed of 300 m / min. The coated paper was dried in a hot air dryer at 100°C for 5 minutes. The resulting coated paper was conditioned at 20°C and 65% RH for 72 hours. The conditioned coated paper was cut into pieces measuring 1 cm x 2 cm, one drop of 1 / 200 N iodine solution was added, and the surface of the coated paper was observed. On the surface of the coated paper, the areas where the coating solution was applied were stained bluish-purple, and the areas where the coating solution was not applied were stained reddish-purple. Based on this difference, the unevenness of the coating was evaluated according to the following criteria. A: Uniform B: Partially uneven C: Overall unevenness

[0119] [Coating defects] Using a pilot curtain coater, the coating agent is applied to the base paper at a coating speed of 600 m / min at a rate of 10 g / m². 2 Coated paper was produced by coating. Furthermore, coated paper was produced under different coating speed conditions (800 m / min, 1000 m / min, 1200 m / min, 1400 m / min, 1600 m / min), while all other conditions remained the same. Each coated paper, prepared at coating speeds ranging from 600 m / min to 1600 m / min, was immersed in a 2% ammonium chloride aqueous solution and heated at 200°C for 3 minutes to color the paper fibers. The coated papers were then observed under a 50x optical microscope to assess the state of coating defects. Papers without coating defects were rated "A," and those with coating defects were rated "B."

[0120] [Air permeability resistance of coated paper] In evaluating the coating defects described above, the air permeability resistance of coated paper prepared at a speed of 1000 m / min was measured using the Oguri-type testing machine described in JIS P 8117:2009.

[0121] [Viscosity of water-based adhesives] For the water-based adhesive, the viscosity was measured using a BH-type viscometer (Toki Sangyo's "BII-type viscometer") under conditions of 30°C and 2 rpm, and under conditions of 30°C and 20 rpm.

[0122] [Roll coating properties] The following evaluation of the water-based adhesive was performed using the three rolls 1-3 shown in Figure 3. The surface temperature of each roll was adjusted to 30°C. The prepared water-based adhesive was added between roll 2 and roll 3, and roll 1 was rotated at a surface speed of 100 m / min. (liquid splashing) The following criteria were used to visually determine whether droplets of water-based adhesive were ejected (jumping phenomenon) from between roll 1 and roll 2. A: No droplets came out at all. B: A few droplets were released. C: Numerous droplets were ejected. (Liquid film streaks on the roll) The state of streaking in the liquid film on roll 1 was observed visually and judged according to the following criteria. The liquid film streaks that occur on roll 1 are reflected in the coating streaks on the coated object. A: No liquid film streaks were observed on the roll. B: The formation of liquid film streaks was observed on a portion of the roll. C: The formation of liquid film streaks was observed across the entire surface of the roll.

[0123] [Example 1] (Production of PVA-1) In a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer dropper port, and polymerization initiator port, 700 parts by mass of vinyl acetate and 1050 parts by mass of methanol were charged, and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. Monomethyl maleate was used as monomer (a), and a methanol solution of monomethyl maleate (10% concentration) was added and nitrogen was purged by bubbling nitrogen gas. The reactor was heated, and when the internal temperature reached 60°C, 0.84 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. The methanol solution of monomethyl maleate was added dropwise to the reactor to maintain a constant monomer composition ratio in the polymerization solution, and polymerization was carried out at 60°C for 5 hours, after which it was cooled to stop the polymerization. The total amount of monomer (a) added until polymerization was stopped was 12.1 parts by mass, the solid content concentration at the time of polymerization stoppage was 23.6%, and the polymerization rate was 60%. Next, unreacted monomers were removed by adding methanol occasionally under reduced pressure at 30°C to obtain a methanol solution of the vinyl ester polymer (concentration 36.7%). Then, 569.2 parts by mass of the methanol solution of the vinyl ester polymer (150.0 parts by mass of the polymer in the solution), prepared by adding more methanol to this methanol solution, were mixed with 6.28 parts by mass of a 10% methanol solution of sodium hydroxide and water to bring the water content of the system to 1%, and saponification was carried out at 40°C (polymer concentration in the saponified solution: 25%, molar ratio of sodium hydroxide to vinyl acetate units in the polymer: 0.009, water content: 1%). A gel-like substance was formed about 10 minutes after the addition of the methanol solution of sodium hydroxide, so this was pulverized with a pulverizer, and saponification was allowed to proceed further by leaving it at 40°C for 1 hour. After that, 600 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming that neutralization was complete using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. 600 parts by mass of methanol were added to this white solid and it was washed by standing at 40°C for 30 minutes. After repeating this washing operation twice, the white solid obtained by centrifugation was pre-dried overnight. Then, while removing fine powder, it was heat-treated in a dryer at 120°C for 6 hours to obtain PVA (PVA-1) powder. The physical properties and evaluation results of PVA-1 are shown in Tables 2 to 4.

[0124] [Examples 2-10 and Comparative Examples 2, 4] (Production of PVA-2-PVA-10, PVA-12, and PVA-14) Except for the following changes, which were made to the polymerization conditions such as the amounts of vinyl acetate and methanol used, the type and amount of monomer (a) used, the saponification conditions such as the concentration of the vinyl ester polymer in saponification and the molar ratio of sodium hydroxide to vinyl acetate units, and the heat treatment conditions as shown in Table 1, powders of PVA (PVA-2 to PVA-10, PVA-12, PVA-14) for Examples 2 to 10 and Comparative Examples 2 and 4 were obtained by the same method as in Example 1. The physical properties and evaluation results of these PVAs are shown in Tables 2 to 4.

[0125] [Comparative Example 1] (Manufacturing of PVA-11) The PVA (PVA-11) powder of Comparative Example 1 was obtained using the same method as in Example 3, except that fine particles were not removed during the heat treatment. The physical properties and evaluation results of this PVA are shown in Tables 2 to 4.

[0126] [Comparative Example 3] (Manufacturing of PVA-13) In a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer dropper port, and polymerization initiator port, 920 parts by mass of vinyl acetate and 80 parts by mass of methanol were charged, and the system was purged with nitrogen for 30 minutes while bubbling with nitrogen. The reactor was heated, and when the internal temperature reached 60°C, 0.25 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. Polymerization was carried out at 60°C for 3 hours, and then cooled to stop the polymerization. At the time of polymerization cessation, the solid content concentration was 9.0%, and the polymerization rate was 25%. Subsequently, unreacted monomers were removed by occasionally adding methanol at 30°C under reduced pressure to obtain a methanol solution (concentration 25.3%) of the vinyl ester polymer. Next, 724.07 parts by mass of a methanol solution of a vinyl ester polymer (150 parts by mass of the polymer in the solution) was prepared by adding more methanol to the methanol solution. To this, 6.97 parts by mass of a 10% methanol solution of sodium hydroxide and water were added to bring the water content of the system to 1%, and saponification was carried out at 40°C (polymer concentration in the saponified solution: 20%, molar ratio of sodium hydroxide to vinyl acetate units in the polymer: 0.01, water content: 1%). After about 10 minutes after adding the methanol solution of sodium hydroxide, a gel-like substance was formed. This was pulverized using a pulverizer, and after letting it stand at 40°C for 1 hour to allow saponification to proceed, 750 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming that neutralization was complete using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. 750 parts by mass of methanol was added to this white solid and it was washed by letting it stand at 40°C for 3 hours. After repeating this washing operation three times, the liquid was removed by centrifugation, and the resulting white solid was vacuum dried overnight at 40°C. Subsequently, the powder was heat-treated in a dryer at 120°C for 4.5 hours while removing fine particles to obtain PVA (PVA-13) powder. The physical properties and evaluation results of PVA-13 are shown in Tables 2 to 4.

[0127] [Synthesis Examples 1-8] (Production of PVA-15 to PVA-22) Except for the following changes, which were made to the polymerization conditions such as the amounts of vinyl acetate and methanol used; the saponification conditions such as the concentration of the vinyl ester polymer and the molar ratio of sodium hydroxide to vinyl acetate units during saponification, as well as the heat treatment conditions as shown in Table 1, unmodified PVA powders (PVA-15 to PVA-22) that serve as a standard for measuring the degree of branching and evaluating the difference in first normal stress were obtained using the same method as in Comparative Example 3. Note that PVA-15 corresponds to PVA-1, PVA-16 corresponds to PVA-2, PVA-17 corresponds to PVA-3, 8, 10, and 11, PVA-18 corresponds to PVA-4, PVA-19 corresponds to PVA-5 and 9, PVA-20 corresponds to PVA-6, PVA-21 corresponds to PVA-7, and PVA-22 corresponds to PVA-12 and 14.

[0128] [Table 1]

[0129] [Table 2]

[0130] [Table 3]

[0131] [Table 4]

[0132] As shown in Table 4, each PVA in Examples 1 to 10, which has a minimum branching degree of 0.93 or less and an insoluble content of less than 2000 ppm, exhibits good coating properties, with suppressed splatter and uneven coating. Furthermore, regarding the first normal stress difference, it was rated A to C when the minimum branching degree was 0.93 or less, and rated A when the minimum branching degree was 0.50 or less, indicating that as the minimum branching degree decreases, the first normal stress difference becomes sufficiently smaller compared to the standard unmodified PVA. In addition, regarding uneven coating, PVA-2, 3, 8 to 10, which have a degree of polymerization of 500 or more, a minimum branching degree of 0.85 or less, an insoluble content of less than 1,750 ppm, and a degree of saponification of 85 mol% or more, were rated A, indicating that uneven coating is particularly reduced.

[0133] On the other hand, PVA-11 in Comparative Example 1 had a high amount of fine powder, resulting in an increase in undissolved material, scattering, and uneven coating. PVA-12 to 14 in Comparative Examples 2 to 4 did not have a sufficiently formed branched structure, or did not contain structural units derived from monomer (a), and therefore did not form branches even after heat treatment, making it impossible to suppress scattering and uneven coating.

[0134] [Example 11] (Preparation of coating agent) 350 parts by mass of calcium carbonate slurry (Imeris "Carbital 97": 75% solids by mass) were mixed with 200 parts by mass of water. To this slurry, 100 parts by mass of styrene-butadiene copolymer latex (BASF "Styronal BN4606": 50% solids by mass) was added and stirred for 20 minutes to prepare a mixed slurry. In addition, 90 parts by mass of water were added to 10 parts by mass of PVA-1, and the mixture was heated to 90°C while stirring, then cooled after 1 hour to prepare an aqueous PVA solution. 20 parts by mass of the prepared aqueous PVA solution were added to the mixed slurry prepared above, and then 40 parts by mass of water were added and stirred for 20 minutes to prepare the coating agent of Example 11 with a viscosity of approximately 1000 cps at 20°C and 60 rpm. Using the above method, the coating defects of the coating agent were evaluated and the air permeability resistance of the obtained coated paper was measured. The results are shown in Table 5.

[0135] [Examples 12-20 and Comparative Examples 5-8] (Preparation of coating agents) Coating agents for Examples 12-20 and Comparative Examples 5-8 were prepared using each of the PVAs listed in Table 5 instead of PVA-1. The coating defects of each obtained coating agent were evaluated, and the air permeability resistance of the obtained coated paper was measured. The results are shown in Table 5. In preparing the coating agents, the concentration of the PVA aqueous solution and the mixing ratio of the mixed slurry to the PVA aqueous solution were appropriately adjusted for each PVA so that the viscosity at 20°C and 60 rpm was approximately 1000 cps.

[0136] [Table 5]

[0137] As shown in Table 5, each coating agent in Examples 11 to 20 exhibited good coating properties, with no coating defects occurring even at a coating speed of 1,000 m / min. Furthermore, the coated paper (coated material) obtained using each coating agent in Examples 11 to 20 had a gas permeability resistance exceeding 1,000 seconds, indicating high gas barrier properties.

[0138] [Example 21] (Manufacturing of water-based emulsion Em-1) 232 g of deionized water was placed in a 1-liter glass polymerization vessel equipped with a reflux condenser, dropping funnel, thermometer, and nitrogen inlet, and heated to 95°C. 27.2 g of PVA-1 was added and stirred for 45 minutes to dissolve. 0.27 g of sodium acetate was then added and mixed to dissolve. Next, the aqueous solution containing the dissolved PVA-1 was cooled, purged with nitrogen, and heated to 85°C while stirring at 200 rpm. 29.8 g of 1% by mass ammonium persulfate aqueous solution and 8.29 g of 1% by mass sodium bicarbonate aqueous solution were then added. 272 ​​g of vinyl acetate and 29.8 g of 1% by mass ammonium persulfate aqueous solution were added continuously over 3 hours. The polymerization was then completed by maintaining the polymerization temperature at 90°C to obtain the polyvinyl acetate aqueous emulsion (Em-1) of Example 21. In Example 21, the amount of PVA-1 added during emulsion polymerization was 10 parts by mass per 100 parts by mass of vinyl acetate.

[0139] (Preparation of water-based adhesive) To the aqueous emulsion Em-1 (100 parts by mass) obtained in Example 21, 2.5 parts by mass of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (trade name "CS-12", manufactured by Chisso Corporation) and an appropriate amount of water were added at room temperature to obtain the aqueous adhesive of Example 21 with a solid content concentration of 50% by mass. The viscosity and roll coating properties (liquid splashing and liquid film streaks) of the obtained aqueous adhesive were evaluated according to the method described above. The results are shown in Table 6.

[0140] [Examples 22-29 and Comparative Examples 9-12] (Manufacturing of aqueous emulsions Em-2 to Em-14) Except for using a predetermined amount of each PVA listed in Table 6 instead of PVA-1, and using the amount of plasticizer listed in Table 6, aqueous emulsions Em-2 to Em14 of Examples 22 to 29 and Comparative Examples 9 to 12 were obtained in the same manner as in Example 21.

[0141] (Preparation of water-based adhesive) Except for using each of the aqueous emulsions listed in Table 6 instead of aqueous emulsion Em-1, aqueous adhesives for Examples 22-29 and Comparative Examples 9-12 were obtained in the same manner as in Example 21, having the solid content concentrations listed in Table 6. The viscosity and roll coating properties (liquid splashing and liquid film streaks) of the obtained aqueous adhesives were evaluated according to the method described above. The results are shown in Table 6.

[0142] [Table 6]

[0143] As shown in Table 6, each of the aqueous adhesives in Examples 21-29 exhibited minimal liquid splashing and fewer liquid film streaks during roll coating. [Industrial applicability]

[0144] The PVA of the present invention can be used in various applications such as coating agents, adhesives, and film raw materials. [Explanation of Symbols]

[0145] 1, 2, 3 rolls 4. Coating liquid or water-based adhesive< / pva>

Claims

1. A vinyl alcohol polymer comprising a structural unit selected from the group consisting of monomers having a carboxyl group and derivatives thereof, wherein the minimum branching degree in the absolute molecular weight range of 200,000 to 800,000 is 0.93 or less, and the insoluble content when 4 parts by mass of the vinyl alcohol polymer is added to 96 parts by mass of water and stirred at 60°C for 1 hour is 0.1 ppm or more and less than 2000 ppm.

2. The vinyl alcohol-based polymer according to claim 1, wherein the viscosity-average degree of polymerization is 300 or more and 5000 or less.

3. The vinyl alcohol polymer according to claim 1, wherein at least one selected from the group consisting of monomers having a carboxyl group and derivatives thereof is at least one selected from the group consisting of ethylenically unsaturated dicarboxylic acids, and their monoesters, diesters, and anhydrides.

4. The vinyl alcohol-based polymer according to claim 1, wherein at least one selected from the group consisting of monomers having a carboxyl group and derivatives thereof is at least one selected from the group consisting of maleic acid, monoalkyl maleic acid, dialkyl maleic acid, maleic anhydride, fumaric acid, monoalkyl fumaric acid, and dialkyl fumaric acid.

5. A vinyl alcohol-based polymer according to claim 1, satisfying the following formula (I). S×P>250...(I) In formula (I), S is the content (mol%) of structural units derived from at least one selected from the group consisting of monomers having a carboxyl group and their derivatives, relative to the total structural units. P is the viscosity-average degree of polymerization.

6. A vinyl alcohol-based polymer according to claim 1, satisfying the following formula (II). ..|. Ａ / Ｂ <>.. ・・・(##) In formula (II), g Ａ This represents the degree of branching at an absolute molecular weight of 200,000. Ｂ This represents the degree of branching at an absolute molecular weight of 800,000.

7. The vinyl alcohol-based polymer according to claim 1, wherein the degree of saponification is 65 mol% or more and 99 mol% or less.

8. A powder containing the vinyl alcohol-based polymer described in any one of claims 1 to 7.

9. The powder according to claim 8, wherein the content of powder that passes through a sieve with a mesh size of 180 μm is 12% by mass or less.

10. The powder according to claim 8, wherein the content of powder that passes through a sieve with a mesh size of 1.00 mm is 97% by mass or more, and the content of powder that passes through a sieve with a mesh size of 500 μm is 40% by mass or more.

11. A method for producing a powder containing the vinyl alcohol polymer described in Claim 8, comprising the steps of: (1) obtaining a copolymer of a vinyl ester with at least one selected from the group consisting of monomers having a carboxyl group and derivatives thereof; (2) obtaining a saponified product of the copolymer; and (3) heat-treating the saponified product, wherein the content of powder that passes through a sieve with a mesh size of 180 μm in the saponified product at the end of step (3) is 12% by mass or less.

12. The method for producing powder according to claim 11, wherein the heat treatment temperature in step (3) above is 110°C or higher and the heat treatment time is 1 hour or longer.

13. A coating agent comprising a vinyl alcohol-based polymer according to any one of claims 1 to 7.

14. A coated article obtained by applying the coating agent described in claim 13 onto a substrate.

15. A coated article according to claim 14, which is a thermal recording material.

16. The coated product according to claim 14, wherein the base paper is a release liner.

17. The coated article according to claim 14, wherein the paper is oil-resistant.

18. The coated article according to claim 14, which is an inkjet recording material.

19. The coated article according to claim 14, wherein the paper is a gas barrier paper or a flavor barrier paper.

20. The coated material according to claim 14, wherein the material is white cardboard.

21. A method for manufacturing a coated product, comprising the step of applying the coating agent described in claim 13 onto a substrate using a curtain coater.

22. A stabilizer for emulsion polymerization containing the vinyl alcohol polymer described in any one of claims 1 to 7.

23. An aqueous emulsion containing the emulsion polymerization stabilizer described in claim 22, and a polymer containing ethylenically unsaturated monomer units.

24. An adhesive comprising the aqueous emulsion described in claim 23.

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