Polyvinyl alcohol resin, method for producing polyvinyl alcohol resin, dispersant, and dispersant for suspension polymerization

Abstract

The present invention provides a PVA-based resin having a saponification degree of 68 to 85 mol% (i.e., an average saponification degree) obtained in the middle stage of the reaction, a narrow saponification degree distribution, and excellent dispersion stability. The present invention also relates to a polyvinyl alcohol-based resin having an average saponification degree of 68 to 85 mol% and a quarter-value width of 7.0 minutes or less of the saponification degree distribution as determined by high-performance liquid chromatography under specific conditions.

Description

Technical Field

[0001] The present invention relates to a polyvinyl alcohol-based resin and a method for producing the same, and more particularly to a polyvinyl alcohol-based resin having a narrow saponification degree distribution and excellent dispersion stability and a method for producing the same. Background Art

[0002] Polyvinyl alcohol-based resins (hereinafter sometimes referred to as "PVA-based resins") have been conventionally used as various dispersants, including dispersants for monomer polymerization (eg, dispersants for emulsion polymerization, dispersants for suspension polymerization, etc.).

[0003] In addition, as a method for industrially producing vinyl chloride resin, a method of suspension polymerization of a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer is known. In addition, a dispersant (hereinafter also referred to as a "dispersion stabilizer") such as a PVA-based resin, methylcellulose, vinyl acetate-maleic anhydride copolymer, and gelatin is used during the polymerization. Among them, various PVA-based dispersion stabilizers have been studied in order to improve the physical properties of the obtained vinyl chloride polymer (resin) particles, such as bulk density, particle size distribution, porosity, plasticizer absorption, and residual monomers. Among these PVA-based dispersion stabilizers, from the viewpoint of improving the surface activity of the PVA-based dispersion stabilizer, a dispersion stabilizer for a PVA-based resin has been proposed that focuses on the carbonyl group in the PVA molecule and the vinylidene group adjacent thereto.

[0004] PVA resins undergo dehydration or deacetylase reactions upon heat treatment, generating vinylidene groups in the main chain. PVA resins having this structure are used as suspension stabilizers and water-retaining materials in the production of polyvinyl chloride. It is also known that heat treatment of PVA resins in film or fiber form can improve their strength.

[0005] Various studies have been conducted on PVA-based resins intended for use as dispersants. For example, Patent Document 1 discloses a dispersing aid for suspension polymerization, comprising a polyvinyl alcohol-based polymer (A) containing an acetal group (a) having an olefinic unsaturated double bond, a saponification degree of 45 to 60 mol%, an average degree of polymerization of 120 to 400, and a block character of 0.5 or greater. Furthermore, Patent Document 2 discloses a polyvinyl alcohol having a saponification degree of 80 to 99.5 mol%, a viscosity-average degree of polymerization of 200 to 5000, and a symmetry coefficient according to JIS K 0124 (2011) as measured by reverse-phase partition gradient high-performance liquid chromatography using a water-acetone eluent.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-105997

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-20436 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] When using a PVA resin as a dispersant, it is important to narrow the saponification degree distribution of the PVA resin to achieve good dispersion stability. Saponification proceeds gradually in the early stages of the reaction, rapidly in the middle stages, and slowly in the late stages. Therefore, when producing a PVA resin with a saponification degree obtained in the early or late stages of the reaction, as in the PVA resins of Patent Documents 1 or 2, a PVA resin with a narrow saponification degree distribution can be relatively easily obtained.

[0012] On the other hand, when attempting to produce a PVA-based resin having a saponification degree obtained in the middle stage of the reaction, it is difficult to obtain a PVA-based resin having a narrow saponification degree distribution because the saponification rate in the middle stage of the reaction is high.

[0013] Therefore, an object of the present invention is to provide a PVA-based resin having a saponification degree obtained in the middle stage of the reaction, that is, a PVA-based resin having an average saponification degree of 68 to 85 mol %, a narrow saponification degree distribution, and excellent dispersion stability.

[0014] Solutions for solving problems

[0015] The present inventors have conducted intensive studies in view of the above circumstances and have found that a PVA-based resin having a narrow saponification degree distribution can be obtained by controlling the saponification rate in the saponification step, thereby completing the present invention.

[0016] That is, the gist of the present invention is as follows.

[0017] [1] A polyvinyl alcohol resin having an average saponification degree of 68 to 85 mol%.

[0018] The 1 / 4 width of the saponification degree distribution determined by high performance liquid chromatography under the following conditions is 7.0 minutes or less.

[0019] (Conditions) Apparatus: Liquid chromatograph (LC-10AD, manufactured by Shimadzu Corporation), Detector: Corona charged particle detector (Corona plus, manufactured by ESA Corporation), Column: 5 μm particle size, 4.6 mm (inner diameter) × 250 mm (length) (Nucleosil 100-5C18 B column, manufactured by GLSciences Inc.), Mobile phase flow rate: 0.5 mL / min, Injection volume: 50 μL, Eluent: (Solvent A) ultrapure water, (Solvent B) tetrahydrofuran, High-pressure gradient: Gradient elution method set to Solvent A / Solvent B (volume ratio) = 90 / 10 (0 minute), 90 / 10 (5 minutes), 14 / 86 (43 minutes), 14 / 86 (58 minutes), Measurement temperature: 50°C, Sample: 10 vol% tetrahydrofuran aqueous solution (concentration: 2 mg / mL), Data acquisition interval: 1 second.

[0020] [2] A method for producing a polyvinyl alcohol-based resin, which is a method for producing the polyvinyl alcohol-based resin described in [1] above, wherein the width of the 1 / 4 value of the saponification degree distribution of the obtained polyvinyl alcohol-based resin is adjusted by a saponification step in which the saponification rate is controlled.

[0021] [3] The method for producing a polyvinyl alcohol-based resin according to [2], wherein the saponification step includes at least one step selected from the group consisting of a step of controlling the water content of the solvent of the vinyl ester polymer solution, a step of controlling the water content of the catalyst, a step of controlling the saponification time, a step of controlling the saponification temperature, and a step of controlling the catalyst concentration.

[0022] [4] A dispersant comprising the polyvinyl alcohol-based resin described in [1].

[0023] [5] A dispersant for suspension polymerization, comprising the polyvinyl alcohol-based resin described in [1].

[0024] Effects of the Invention

[0025] According to the present invention, a PVA-based resin can be obtained, which is a PVA-based resin with a saponification degree obtained in the middle stage of the saponification reaction, which is a range that has conventionally been considered to have a fast saponification rate, that is, a PVA-based resin with an average saponification degree of 68 to 85 mol%, and has a narrow saponification degree distribution, thereby excellent in dispersion stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the high performance liquid chromatography of the PVA-based resin of Example 1.

[0027] Figure 2 This is the high performance liquid chromatography of the PVA-based resin of Comparative Example 1.

[0028] Figure 3 Graphs showing the results of a dispersion stability test of the PVA-based resins of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below, but these are merely examples of preferred embodiments, and the present invention is not limited to these contents.

[0030] [Polyvinyl alcohol resin]

[0031] The average saponification degree of the PVA-based resin according to the embodiment of the present invention is 68 to 85 mol %, and the 1 / 4 width of the saponification degree distribution determined by high performance liquid chromatography under the following conditions is 7.0 minutes or less.

[0032] (Conditions) Apparatus: Liquid chromatograph (LC-10AD, manufactured by Shimadzu Corporation), Detector: Corona charged particle detector (Corona plus, manufactured by ESA Corporation), Column: 5 μm particle size, 4.6 mm (inner diameter) × 250 mm (length) (Nucleosil 100-5C18 B column, manufactured by GLSciences Inc.), Mobile phase flow rate: 0.5 mL / min, Injection volume: 50 μL, Eluent: (Solvent A) ultrapure water, (Solvent B) tetrahydrofuran, High-pressure gradient: Gradient elution method set to Solvent A / Solvent B (volume ratio) = 90 / 10 (0 minute), 90 / 10 (5 minutes), 14 / 86 (43 minutes), 14 / 86 (58 minutes), Measurement temperature: 50°C, Sample: 10 vol% tetrahydrofuran aqueous solution (concentration: 2 mg / mL), Data acquisition interval: 1 second.

[0033] Generally, a PVA-based resin is a resin obtained by saponifying a vinyl ester homopolymer or a copolymer of a vinyl ester and other monomers using an alkali catalyst or the like.

[0034] The average saponification degree of the PVA resin according to an embodiment of the present invention is 68 to 85 mol%, preferably 70 mol% or higher and 83 mol% or lower. By achieving an average saponification degree within this range, the PVA resin molecules contain acetic acid groups (hydrophobic groups) in addition to hydroxyl groups (hydrophilic groups), thereby imparting surface activity to the PVA resin and facilitating uniform dispersion in a dispersion medium.

[0035] In addition, the average saponification degree refers to the value measured according to JIS K 6726:1994.

[0036] The average degree of polymerization of the PVA resin is preferably 300 to 3000, more preferably 400 or higher, and even more preferably 2800 or lower. If the average degree of polymerization is too low, the surface activity tends to decrease, and when used as a dispersant for suspension polymerization of vinyl chloride, aggregation is likely to occur during suspension polymerization. On the other hand, if the average degree of polymerization is too high, the viscosity of the PVA resin aqueous solution increases, reducing workability.

[0037] In addition, the average degree of polymerization refers to a value measured in accordance with JIS K 6726:1994.

[0038] The 1 / 4 width of the saponification degree distribution of the PVA-based resin determined by high performance liquid chromatography under the above-mentioned conditions is 7.0 minutes or less, preferably 6.8 minutes or less, and more preferably 6.5 minutes or less.

[0039] The method for determining the 1 / 4 value width is to use the HPLC obtained under the above conditions. Figure 1 The line with intensity (Intensity) 0 is set as the base line, and the intensity height of the peak is set as h peak , the intensity height is set to 1 / 4h peak . And the intensity is high 1 / 4h peak The peak width is taken as the 1 / 4 value width (W 1 / 4hpeak , minutes) to find out.

[0040] As the saponification degree distribution, the 1 / 4 value width is used instead of h peak The peak width (half-peak width, 1 / 2 value width) of 1 / 2 intensity height is increased, thereby increasing the correlation between the peak width and the effect of dispersion stability.

[0041] [Method for producing polyvinyl alcohol-based resin]

[0042] The method for producing a PVA-based resin according to an embodiment of the present invention is characterized in that the 1 / 4 value width of the saponification degree distribution of the obtained polyvinyl alcohol-based resin is adjusted by a saponification step of controlling the saponification rate.

[0043] For the other steps, conventionally known methods can be used. For example, the above-mentioned production method may include a step of polymerizing a monomer composition containing a vinyl ester monomer to form a vinyl ester polymer, and then further saponifying the polymer in a saponification step, wherein the saponification rate is controlled. These steps are described below in order.

[0044] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, and other linear or branched saturated fatty acid vinyl esters. From a practical standpoint, vinyl acetate is preferably used as the vinyl ester monomer, and more preferably, vinyl acetate is used alone or in combination with a fatty acid vinyl ester compound other than vinyl acetate.

[0045] When polymerizing vinyl ester monomers, particularly monomer compositions containing vinyl acetate, any known polymerization method can be used without particular limitation. For example, solution polymerization using an alcohol such as methanol, ethanol, or isopropanol as a solvent can be performed. Bulk polymerization, emulsion polymerization, and suspension polymerization are also possible. In the solution polymerization described above, the vinyl ester monomers can be added either separately or together.

[0046] The polymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, azobisdimethylvaleronitrile, or azobismethoxyvaleronitrile. The reaction temperature is selected from the range of 40°C to the boiling point.

[0047] Furthermore, chain transfer agents that can be used in the polymerization of the monomer composition include, for example, aldehydes and ketones. Examples of aldehydes include acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde. Examples of ketones include acetone, methyl ethyl ketone, hexanone, and cyclohexanone. Among these, aldehydes are preferred as chain transfer agents, and acetaldehyde is particularly preferred from the perspective of productivity, such as solvent recovery.

[0048] The amount of chain transfer agent added varies depending on the chain transfer constant of the added chain transfer agent, the target average degree of polymerization of the PVA resin, and other factors. However, for example, 0.1 to 5% by weight relative to the vinyl ester monomer is sufficient, preferably 0.5% by weight or greater, and preferably 3% by weight or less. The chain transfer agent can be added either initially or during the polymerization reaction. By adding the chain transfer agent by either method, the molecular weight distribution of the PVA resin can be controlled.

[0049] The vinyl ester monomer can be used alone, but can also be copolymerized with a monomer polymerizable with the vinyl ester monomer as needed. That is, the monomer composition can contain a monomer polymerizable with the vinyl ester monomer.

[0050] Examples of the monomer include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or salts thereof, mono- or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylenesulfonic acid, allylsulfonic acid, and methallylsulfonic acid, or salts thereof; alkyl vinyl ethers; N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinyl pyrrolidone; vinyl chloride, vinylidene chloride; polyoxyalkylenes such as polyoxyethylene (meth)allyl ether and polyoxypropylene (meth)allyl ether. (Meth)allyl ether, polyoxyethylene (meth)acrylate, polyoxypropylene (meth)acrylate and other polyoxyalkylene (meth)acrylates, polyoxyethylene (meth)acrylamides, polyoxypropylene (meth)acrylamides and other polyoxyethylene (meth)acrylamides, polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl), polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, hydroxyl group-containing α-olefins such as 3-butene-1-ol, 4-pentene-1-ol, and 5-hexene-1-ol, and their acylated derivatives, etc. When the monomer composition contains these monomers, the content of the monomer component in the vinyl ester polymer after copolymerization is preferably about 0.1 to 10 mol%.

[0051] Examples of monomers polymerizable with vinyl ester monomers include 3,4-dihydroxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-hydroxy-1-butene, 4-acyloxy-3-hydroxy-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4,5-dihydroxy-1-pentene, 4,5-diacyloxy-1-pentene, 4,5-dihydroxy-3-methyl-1-pentene, 4,5-diacyloxy-3-methyl- Compounds containing a diol group, such as 1-pentene, 5,6-dihydroxy-1-hexene, 5,6-diacyloxy-1-hexene, glycerol monoallyl ether, 2,3-diacetoxy-1-allyloxypropane, 2-acetoxy-1-allyloxy-3-hydroxypropane, 3-acetoxy-1-allyloxy-2-hydroxypropane, glycerol monovinyl ether, glycerol monoisopropenyl ether, vinyl ethylene carbonate, and 2,2-dimethyl-4-vinyl-1,3-dioxolane. When the monomer composition contains these monomers, the content of the monomer component in the vinyl ester polymer after copolymerization is preferably about 0.1 to 10 mol%.

[0052] In the production method according to the embodiment of the present invention, the saponification rate is controlled in the saponification step of the vinyl ester polymer obtained above. The vinyl ester polymer is dissolved in a solvent and saponified in the presence of a catalyst.

[0053] The method for controlling the saponification rate is not particularly limited as long as the 1 / 4 value width of the saponification degree distribution of the obtained PVA-based resin can be adjusted. For example, it preferably includes a method selected from the group consisting of

[0054] (1) a step of controlling the water content of the solvent of the vinyl ester polymer solution,

[0055] (2) Process for controlling the moisture content of the catalyst,

[0056] (3) Process for controlling catalyst concentration,

[0057] (4) Controlling the saponification time process, and

[0058] (5) At least one step selected from the group consisting of steps of controlling the saponification temperature.

[0059] Each step will be described in detail below.

[0060] (1) Step of controlling the water content of the solvent of the vinyl ester polymer solution

[0061] As a solvent for dissolving the vinyl ester polymer, an organic solvent or a mixed solvent of an organic solvent and water is generally used. Meanwhile, in this step, a mixed solvent of an organic solvent and water is used as the solvent, and the water content of the mixed solvent is controlled. This can slow the saponification rate and narrow the width of the 1 / 4 value of the saponification degree distribution.

[0062] Examples of the organic solvent include alcohols such as methanol, ethanol, and butanol, and ketones such as acetone. From the viewpoint of handling properties, alcohols, particularly lower alcohols such as methanol, ethanol, and butanol, are preferably used.

[0063] When a mixed solvent of an organic solvent and water is used, the ratio of the organic solvent to water (organic solvent:water) is preferably 99.99:0.01 to 90:10 (weight ratio), and more preferably 99.9:0.1 to 95:5.

[0064] In particular, a mixed solvent of alcohol and water is preferably used. In this case, the ratio of alcohol to water (alcohol:water) is preferably 99.9:0.1 to 90:10 (weight ratio), more preferably 99.9:0.1 to 95:5.

[0065] The concentration of the vinyl ester polymer in the solvent is preferably 20 to 65% by weight.

[0066] (2) Step of controlling the moisture content of the catalyst

[0067] As a catalyst for saponification, an alkali catalyst or an acid catalyst can be used. As an alkali catalyst, for example, alkali metal hydroxides and alkoxides such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, and potassium methoxide can be used. As an acid catalyst, for example, aqueous solutions of inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as p-toluenesulfonic acid can be used. In addition, two or more catalysts can be used to control the saponification rate.

[0068] By using these catalysts and controlling the water content of the catalyst, the saponification rate can be adjusted. By increasing the water content of the catalyst, the saponification rate can be slowed down and the width of the 1 / 4 value of the saponification degree distribution can be narrowed.

[0069] The moisture content of the catalyst is adjusted by adding water to the catalyst solution.

[0070] The catalyst's water content is preferably 5% or more by weight, more preferably 10% or more, and even more preferably 13% or more. On the other hand, from the perspective of increasing the amount of catalyst used, the catalyst's water content is preferably 30% or less, more preferably 20% or less. The catalyst's water content is determined by the Karl Fischer method.

[0071] (3) Process for controlling catalyst concentration

[0072] Furthermore, the saponification rate can be adjusted by controlling the catalyst concentration. The amount of catalyst used is generally about 1 to 30 millimoles equivalent to the vinyl ester polymer. On the other hand, when controlling the saponification rate by catalyst concentration, the saponification rate can be slowed by adjusting the catalyst concentration to an optimal amount relative to the vinyl ester polymer.

[0073] (4) Step of controlling saponification time, and (5) Step of controlling saponification temperature

[0074] The saponification rate can also be adjusted by controlling the saponification time and / or saponification temperature. Generally, the saponification time and saponification temperature are not particularly limited, but are generally about 5 minutes to 1 hour and about 20 to 60°C.

[0075] On the other hand, when controlling the saponification rate using saponification time and temperature, the saponification rate can be slowed by extending the saponification time and / or lowering the saponification temperature. However, considering productivity, it is preferable to control the saponification degree distribution by shortening the saponification time and increasing the temperature. Specifically, the appropriate saponification time and saponification temperature vary depending on the vinyl ester polymer, the type of catalyst, the moisture content of the catalyst, and other factors, and cannot be generally specified. However, they are preferably approximately 10 to 30 minutes and / or 30 to 55°C.

[0076] The PVA resin obtained by saponification is then dried to form a powdered PVA resin. Examples of drying methods include reduced pressure drying, normal pressure drying, and hot air drying. The drying time is, for example, 10 minutes to 20 hours, preferably 1 hour to 15 hours. The drying temperature is, for example, 40 to 120°C, preferably 40 to 100°C, and more preferably 50°C or higher and less than 80°C.

[0077] [Dispersant]

[0078] When the PVA resin of the embodiment of the present invention is used as a dispersant, examples of the dispersed body include polymerizable monomers and powders. The PVA resin of the embodiment of the present invention is preferably used as a dispersant for suspension polymerization by dispersing a polymerizable monomer.

[0079] Examples of polymerizable monomers that can be subjected to suspension polymerization include vinyl chloride, vinylidene halides, vinyl ethers, vinyl acetate, vinyl benzoate, acrylic acid, methacrylic acid, maleic acid or its anhydride, ethylene, propylene, and styrene. The dispersant for the PVA-based resin according to an embodiment of the present invention is preferably used for homopolymerization of vinyl chloride or copolymerization with a monomer copolymerizable with vinyl chloride.

[0080] [Dispersants for suspension polymerization]

[0081] Specific examples of using the PVA-based resin according to the embodiment of the present invention as a dispersant for suspension polymerization are shown below, but the present invention is not limited thereto.

[0082] The amount of PVA resin used can be appropriately adjusted depending on the monomer being suspended. For example, when used in suspension polymerization of vinyl chloride monomer, it is preferably used in an amount of 5 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.2 parts by weight or less per 100 parts by weight of vinyl chloride monomer. The amount of PVA resin used within this range is preferred because it does not reduce the amount of PVA resin that functions as a dispersant. Furthermore, the amount of PVA resin used is preferably 0.01 parts by weight or more, and more preferably 0.02 parts by weight or more.

[0083] In the case of suspension polymerization, for example, a PVA-based resin is added as a dispersant to water or a heated aqueous medium to disperse the vinyl chloride-based monomer, and the polymerization is carried out in the presence of an oil-soluble catalyst.

[0084] The PVA resin may be added as a powder directly or in a dispersed or dissolved form in water, an organic solvent, or a mixture of water and an organic solvent. Examples of the organic solvent include alcohols, ketones, and esters.

[0085] The dispersant may be added together at the initial stage of polymerization or added together or separately during the polymerization.

[0086] Furthermore, as additives during polymerization, other stabilizers, polymerization aids, polymerization catalysts, and the like may be used.

[0087] As other stabilizers, known stabilizers can be used in combination, for example, polymers can be used in combination. As polymers, PVA resins other than the PVA resin of the present embodiment can be listed, for example, unmodified PVA resins, modified PVA resins, etc. can be used.

[0088] Examples of the polymerization aid include various surfactants and inorganic dispersants. The PVA-based resin of the present embodiment can also be used as a polymerization aid.

[0089] The polymerization catalyst may be any oil-soluble catalyst, for example, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, α,α'-azobisisobutyronitrile, α,α'-azobis-2,4-dimethylvaleronitrile, acetylcyclohexylsulfonyl peroxide, or a mixture thereof.

[0090] Example

[0091] The present invention will be described in more detail below with reference to Examples. However, the present invention is not limited to the following Examples unless the scope of the present invention is exceeded. In the examples, "parts" and "%" are based on weight.

[0092] (Example 1)

[0093] 100 parts of vinyl acetate, 20 parts of methanol, and 0.005% azobisisobutyronitrile relative to the vinyl acetate were placed in a polymerization tank and the atmosphere was purged with nitrogen. Polymerization was initiated at the boiling point by heating and terminated after approximately 5 hours of reaction, when the polymerization rate reached 60%. Unpolymerized vinyl acetate was then removed.

[0094] The resulting vinyl ester polymer was adjusted to a resin content (concentration of the vinyl ester polymer in the solvent) of 42% and saponified at 45°C for 15 minutes. A methanol solution of sodium hydroxide with a water content of 15% was used as a catalyst, with the catalyst amount being 8 millimoles equivalent to the vinyl ester polymer. After saponification, the mixture was dried at 95°C for 6 hours to obtain a PVA resin.

[0095] (Comparative Example 1)

[0096] The resulting vinyl ester polymer was adjusted to a resin content of 42% in the same manner as in Example 1 and saponified at 45°C for 15 minutes. A methanol solution of sodium hydroxide with a water content of 9% was used as a catalyst for the saponification, and the amount of catalyst used was 8 millimoles equivalent to the vinyl ester polymer. After saponification, the product was dried at 95°C for 6 hours to obtain a PVA resin.

[0097] (Evaluation method)

[0098] When producing the PVA-based resin, the water content of the catalyst during saponification was measured by the Karl Fischer method. The results are shown in Table 1.

[0099] The average polymerization degree and saponification degree of the PVA resin were measured in accordance with JIS K 6726: 1994. The results are shown in Table 1.

[0100] The 1 / 4 width of the saponification degree distribution of the PVA resin is determined by high performance liquid chromatography under the following conditions: the line with an intensity of 0 is defined as the baseline, and the peak height is defined as h peak , becoming 1 / 4 of its intensity height (1 / 4h peak ) as the 1 / 4 value width (W 1 / 4hpeak , minutes) to find out.

[0101] (Conditions) Apparatus: Liquid chromatograph (LC-10AD, manufactured by Shimadzu Corporation), Detector: Corona charged particle detector (Corona plus, manufactured by ESA Corporation), Column: 5 μm particle size, 4.6 mm (inner diameter) × 250 mm (length) (Nucleosil 100-5C18 B column, manufactured by GLSciences Inc.), Mobile phase flow rate: 0.5 mL / min, Injection volume: 50 μL, Eluent: (Solvent A) ultrapure water, (Solvent B) tetrahydrofuran, High-pressure gradient: Gradient elution method set to Solvent A / Solvent B (volume ratio) = 90 / 10 (0 minute), 90 / 10 (5 minutes), 14 / 86 (43 minutes), 14 / 86 (58 minutes), Measurement temperature: 50°C, Sample: 10 vol% tetrahydrofuran aqueous solution (concentration: 2 mg / mL), Data acquisition interval: 1 second.

[0102] The results are shown in Table 1, and the HPLC of Example 1 is as shown in Table 1. Figure 1 As shown, the high performance liquid chromatography of Comparative Example 1 is as follows Figure 2 shown.

[0103] As a dispersion stability test, 10 g of a 4% aqueous solution of a PVA resin and 2.5 g of vinyl acetate were placed in a sample bottle and stirred at 25°C to disperse the vinyl acetate. The sample bottle was then placed in a thermostat at 40°C for 24 hours. The dispersion after 24 hours was visually observed and evaluated according to the following criteria. The results are as follows: Figure 3 As shown in Table 1.

[0104] A (pass): maintain uniform dispersion and stability

[0105] B (fail): Unable to maintain dispersion and separated into two layers

[0106] [Table 1]

[0107]

[0108] In the dispersion stability test using the PVA resin of Example 1, in which the width of the 1 / 4 value of the saponification degree distribution is 7.0 minutes or less, the dispersion state was maintained even after standing for 24 hours, indicating that good dispersion stability was exhibited. On the other hand, in the dispersion stability test using the PVA resin of Comparative Example 1, as shown in FIG. Figure 3 As shown by the arrows in the figure, the dispersion separated into two layers after standing for 24 hours. This indicates that although the average polymerization degree and average saponification degree of the PVA resin in Comparative Example 1 are the same as those of the PVA resin in Example 1, its dispersion stability is low due to the wide 1 / 4 width of the saponification degree distribution of 7.6 minutes.

[0109] The present invention has been described with reference to detailed or specific embodiments, but it is obvious to those skilled in the art that various changes and modifications may be added without departing from the spirit and scope of the present invention. This application is based on Japanese patent application (Japanese Patent Application No. 2019-068411) filed on March 29, 2019, the contents of which are incorporated herein by reference.

[0110] Industrial applicability

[0111] Since the PVA-based resin of the present invention can provide very excellent dispersion stability as a dispersant, it is very useful as a dispersant, particularly a dispersant for suspension polymerization.

Claims

1. A method for producing a polyvinyl alcohol-based resin having an average saponification degree of 68 to 85 mol%. The polyvinyl alcohol-based resin has a 1 / 4 width of a saponification degree distribution determined by high performance liquid chromatography under the following conditions of 7.0 minutes or less, and the polyvinyl alcohol-based resin has an average degree of polymerization of 2200 to 3000. The method for producing a polyvinyl alcohol-based resin includes a saponification step of saponifying a vinyl ester-based polymer. In the saponification step, the saponification rate is controlled by at least one of a step of controlling the water content of the solvent of the vinyl ester polymer solution and a step of controlling the water content of the catalyst, thereby adjusting the 1 / 4 value width of the saponification degree distribution of the obtained polyvinyl alcohol resin. The water content of the catalyst used in the production of the polyvinyl alcohol-based resin is 10% to 30% by weight. The conditions are: Apparatus: Liquid chromatograph LC-10AD manufactured by Shimadzu Corporation, Detector: ESA's Corona plus, Chromatographic column: Nucleosil 100-5C18 B column manufactured by GL Sciences Inc., particle size 5 μm, inner diameter 4.6 mm × length 250 mm, Mobile phase flow rate: 0.5 mL / min, Injection volume: 50μL, Eluent: Solvent A is ultrapure water, Solvent B is tetrahydrofuran, High pressure gradient: gradient elution was performed to form a solvent A / solvent B volume ratio of 90 / 10 at 0 minutes, 90 / 10 at 5 minutes, 14 / 86 at 43 minutes, and 14 / 86 at 58 minutes. Measuring temperature: 50℃, Sample: 10% by volume aqueous solution of tetrahydrofuran, with a concentration of 2 mg / mL, Data acquisition interval: set to every 1 second. 2 . A dispersant comprising a polyvinyl alcohol-based resin produced by the production method according to claim 1 . 3 . A dispersant for suspension polymerization, comprising a polyvinyl alcohol-based resin produced by the production method according to claim 1 .

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