JP2002053616A - Polyvinyl alcoholic polymer and powder comprising the polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcoholic polymer having a high crystallinity, and further to provide a polyvinyl alcoholic powder comprising the polymer. SOLUTION: This polyvinyl alcoholic polymer is obtained by introducing an azo-based compound catalyst having <=64 deg.C half life temperature by 10 hr to a polymerization system while keeping the temperature at the temperature >=10 deg.C lower than the half life temperature to polymerize (1) vinyl acetate or (2) the vinyl acetate and other unsaturated monomers to provide a polyvinyl acetate-based polymer, and saponifying the resultant polyvinyl acetate-based polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a highly crystalline polyvinyl alcohol based on saponification of vinyl acetate or a polyvinyl acetate polymer obtained by polymerizing vinyl acetate and other unsaturated monomers. The present invention also relates to a polymer, and more particularly to a polyvinyl alcohol-based polymer powder comprising a polyvinyl alcohol-based polymer and having good solubility in warm water or hot water and having a high degree of saponification.

[0002]

2. Description of the Related Art Hitherto, a polyvinyl alcohol polymer has been produced by polymerizing vinyl acetate and then saponifying it. Known polymerization methods include a solution polymerization method, a bulk polymerization method, a suspension polymerization method and an emulsion polymerization method. ing. At that time, as the polymerization initiator (catalyst), a persulfate such as potassium persulfate, an azo compound catalyst such as azobisisobutyronitrile, and an organic peroxide such as benzoyl peroxide are generally used. I have. A polyvinyl acetate polymer obtained by polymerizing vinyl acetate is converted into an industrially useful polyvinyl alcohol polymer by saponification.

[0003] By selecting a polymerization initiator, the physical properties of the polyvinyl alcohol-based polymer also exhibit unique performance. Therefore, those skilled in the art have studied various polymerization initiators. JP-A-9-3161
No. 10 discloses a method for producing a vinyl acetate polymer by homopolymerization of a vinyl acetate monomer or copolymerization with a vinyl acetate monomer and another monomer copolymerizable with the vinyl acetate monomer. A method for producing a vinyl acetate polymer using an organic peroxide having a half-life at 60 ° C. of 10 to 110 minutes as a polymerization initiator and allowing a specific carboxylic acid or a salt thereof to be present in a polymerization solution, Patent No. 2555137
Japanese Patent Application Laid-Open Publication No. HEI 7-64, discloses one of the components of the photosensitive resin composition as 6
A polyvinyl alcohol-based resin having an average degree of polymerization of 1000 or less obtained by saponifying a polyvinyl ester-based resin polymerized using a polymerization catalyst having a half-life at 0 ° C. of 200 minutes or less is used. On the other hand, JP-A-58-20660
No. 6 describes a method for producing a saponified product of an ethylene-vinyl acetate copolymer and specifies a relational expression such as a half-life of a polymerization initiator as a polymerization condition of the ethylene-vinyl acetate copolymer. It is described that a molded product of the obtained saponified ethylene-vinyl acetate copolymer has little fisheye in the film.

[0004]

However, as a result of a detailed study of the above disclosed technology, the present inventor has disclosed that in Japanese Patent Application Laid-Open No. 9-316110, an organic peroxide is used as a catalyst, Chain transfer to the molecular chain was apt to occur, and the number of branches increased, resulting in a decrease in the crystallinity of the obtained polyvinyl alcohol-based polymer and a problem in the solubility of the polymer in water. Further, in Japanese Patent No. 2555137 and Japanese Patent Application Laid-Open No. 58-206606, it is likely that the effective concentration of the catalyst is liable to fluctuate due to insufficient temperature control of the solution in which the catalyst is dissolved. There is a drawback that it is difficult to control the degree of polymerization and the quality of the product varies.

[0005]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have obtained an azo compound catalyst having a half-life temperature of 10 hours or less of 64 ° C. or less.
Introduced into the polymerization system while maintaining the temperature at least 10 ° C. lower than the half-life temperature, to saponify vinyl acetate or a polyvinyl acetate-based polymer obtained by polymerizing vinyl acetate and other unsaturated monomers. The present inventors have found that a polyvinyl alcohol-based polymer having high crystallinity and a powder made of the polymer have a high effect of improving the solubility in hot water or hot water, thereby completing the present invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The polyvinyl alcohol-based polymer of the present invention is produced by polymerizing vinyl acetate or vinyl acetate and other unsaturated monomers to obtain a polyvinyl acetate-based polymer, which is further saponified. Other unsaturated monomers include, for example, ethylene, propylene, isobutylene, α-octene, α
Olefins such as dodecene and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid or salts thereof, and mono- or dialkyl esters; acrylonitrile, methacrylonitrile, etc. Nitriles, acrylamide, methacrylamide, amides such as diacetone acrylamide, ethylene sulfonic acid, allyl sulfonic acid,
Olefinsulfonic acids such as methallylsulfonic acid or salts thereof, alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallylvinylketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene ( Polyoxyalkylene (meth) allyl ethers such as (meth) allyl ether and polyoxypropylene (meth) allyl ether; polyoxyalkylene (meth) acrylates such as polyoxyethylene (meth) acrylate and polyoxypropylene (meth) acrylate; Polyoxyalkylene (meth) acrylamides such as oxyethylene (meth) acrylamide and polyoxypropylene (meth) acrylamide; Len (1- (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, etc. Is mentioned.

As an azo compound catalyst having a half-life temperature of 10 ° C. or less of 64 ° C. or less (hereinafter abbreviated as “azo compound catalyst”) used as a polymerization initiator, 2,2′-azobis (2-methylbutanamide) is used. Oxime) dihydrochloride tetrahydrate [10 hour half-life temperature 57
° C, for example, “OTAZO-3” manufactured by Otsuka Chemical Co., Ltd.
0 ”], 1,1′-azobis (1-acetoxy-1-phenylethane) [10 hour half-life temperature 61 ° C., for example,“ OTAZO-15 ”manufactured by Otsuka Chemical Co., Ltd.], 2,2′-
Azobis- (2,4-dimethyl-4-methoxyvaleronitrile) [10-hour half-life temperature 30 ° C.], 2,2′-azobis- (2,4-dimethyl-valeronitrile) [10
Time half-life temperature of 52 ° C.], and the like. Particularly, 2,2′-azobis (2-methylbutanamide oxime) dihydrochloride tetrahydrate, from the viewpoint that the odor of the obtained polyvinyl alcohol-based polymer can be reduced.
1,1′-azobis (1-acetoxy-1-phenylethane) is preferred.

The azo compound catalyst has a half-life temperature of 0.05 to 0.1 mol / l using a solvent inert to the polymerization initiator, for example, benzene. Is prepared, poured into a glass tube, replaced with nitrogen, sealed, and then placed in a thermostat set at each temperature. And 10
After a lapse of time, the concentration of the azo compound catalyst is measured by a known method, and defined as a temperature at which the concentration of the azo compound catalyst is half of the initial concentration from the relationship between the temperature and the polymerization initiator concentration.

As the solvent (polymerization solvent) used in the polymerization, a solvent mainly containing an alcohol having 4 or less carbon atoms is preferably used. Examples of the alcohol include methanol, ethanol, and propanol. Among them, methanol is preferred. The amount of the solvent used may be selected in the range of 0.01 to 4 times the weight of the above or in accordance with the degree of polymerization of the desired polymer.

In the polymerization of vinyl acetate or vinyl acetate and other unsaturated monomers in the present invention, the above or the above polymerization solvent and an azo compound catalyst are charged in a polymerization vessel. The greatest feature of the present invention resides in maintaining the temperature at a temperature lower by at least 10 ° C. than the half-life temperature at the time of charging the system compound catalyst.
The temperature is 15 ° C. lower. When the temperature is lower than the half-life temperature by less than 10 ° C. or higher than the half-life temperature, the decomposition of the polymerization catalyst partially starts in the charging line, the activity of the polymerization catalyst decreases, and the target polymerization rate at the time of polymerization decreases. Not achieved,
It is not preferable because the control of the polymerization rate becomes difficult.

As a method for keeping the azo compound catalyst at a low temperature, (a) the catalyst charging line is cooled with a cooling medium. That is, the entire line for charging the polymerization catalyst dissolution tank and the polymerization can is formed as a double tube, and cooling is performed by flowing a refrigerant outside the double tube. (B) A method of cooling the solvent in which the catalyst is dissolved and charging the solution while dissolving the catalyst little by little, and the like, may be mentioned, but the method (a) is preferred. In the method (a), the charging line is formed of an aqueous solution in which salts such as magnesium chloride, sodium chloride, and calcium chloride are dissolved, or a refrigerant composed of ammonium chloride / potassium nitrate, ammonium chloride / sodium nitrate, sodium nitrate / ammonium nitrate, ammonium nitrate / ammonium thiocyanate, and the like. Cool with.

In the present invention, if this charging method is satisfied,
Other polymerization conditions may be selected from known methods, for example, either of a continuous type or a batch type, and the polymerization conditions may be appropriately set according to each polymerization type. The azo compound catalyst is used for polymerization in the form of a polymerization solvent or the above or dissolved in the above. The concentration of the catalyst at the time of polymerization is 7.5 × 10 ^{−3 to} 6.5 with respect to the above or 1 mol.
× 10 ^-8 mol, furthermore 1.0 × 10 ^{-4 to} 6.5 × 10 ^-7
Mol is preferable, and if it is less than 6.5 × 10 ⁻⁸ mol, the polymerization rate is not stable, which is not preferable. Conversely, if it exceeds 7.5 × 10 ^-3 mol, alcohol insolubles will increase in the polymer before saponification, which will cause contamination of the final product with foreign substances, which is not preferable in terms of quality.

In the case of continuous polymerization, the polymerization is carried out while continuously charging or in a polymerization vessel and withdrawing the produced polyvinyl acetate polymer from the vessel. The preparation of the azo compound catalyst and the polymerization solvent is not particularly limited, and they may be mixed singly or singly or mixed. Also, in the batch polymerization, a polymerization solvent or an azo polymerization catalyst may be charged into a polymerization vessel by any means. Typically, a polymerization solvent is charged into a reaction vessel, and the polymerization catalyst or the polymerization catalyst is added thereto. Are polymerized by dropping all at once, or by dividing or continuously dropping.

Thus, polymerization is started in a polymerization vessel or by charging a polymerization catalyst and a polymerization solvent. The polymerization temperature is not particularly limited, but is usually 40 to 80 ° C., and more preferably 55 to 80 ° C. It is. Such temperature is 40 ° C
When the temperature is less than the above, a long time is required for polymerization, and when the polymerization time is to be shortened, a large amount of the catalyst is required.

The polymerization time is 4 in the case of batch polymerization.
It is preferably 10 to 10 hours (more preferably 6 to 9 hours). If the polymerization time is less than 4 hours, the polymerization temperature must be raised or the amount of catalyst must be set large. There is a problem in the aspect, and it is not preferable. In the case of continuous polymerization,
The average residence time in the polymerization vessel is 2 to 8 hours (further 2 to 6 hours).
Time) is preferred, and if the residence time is less than 2 hours, the polymerization temperature must be increased or the amount of catalyst must be set large,
If the time exceeds 8 hours, there is a problem in productivity, which is not preferable.

The polymerization rate of vinyl acetate is set as high as possible within the range in which polymerization can be controlled from the viewpoint of productivity, and is 20 to 80% in the case of continuous polymerization. If the polymerization rate is less than 20%, there are problems such as productivity and a large amount of unreacted vinyl acetate is present. On the other hand, if it exceeds 80%, polymerization control becomes difficult, which is not preferable. In the case of batch polymerization, the polymerization rate is preferably 20 to 98%. If the polymerization rate is less than 20%, there are problems such as productivity and a large amount of unreacted vinyl acetate. If it exceeds, polymerization control becomes difficult or chain transfer to the polymer occurs, which is not preferable.

The amount of the polymerization solvent is determined by the weight ratio (S / M) of the amount S of the polymerization solvent to the amount M of the polymerization solvent depending on the desired degree of polymerization. When using methanol as polymerization solvent S
/ M is generally 0.1 to 0.4. Conventionally 1500
In order to obtain a polymer having a relatively high degree of polymerization as described above, S / M
It is necessary to drive down the polymerization rate (polyvinyl acetate-based polymer concentration is about 50% or more) in order to lower the
As a result, there was a problem that chain transfer to the polymer occurred and branching was easily caused. However, in the present invention, even if the concentration of the polyvinyl acetate-based polymer was as high as 50% or more, a good quality polymer with few branches was obtained. Since a vinyl acetate polymer is obtained, the yield can be improved even with a polyvinyl acetate polymer having a degree of polymerization of 1500 or more.

The polyvinyl acetate polymer obtained by carrying out such polymerization is saponified to give a polyvinyl alcohol polymer. Such a saponification reaction is carried out in the presence of a saponification catalyst. . In the saponification, the polyvinyl acetate polymer is dissolved in alcohol, benzene, methyl acetate, or the like. Examples of the alcohol include methanol, ethanol, isopropanol, butanol and the like. As the saponification catalyst, sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate,
An alkali catalyst such as an alkali metal hydroxide or an alcoholate such as potassium methylate is used, and an acid catalyst such as sulfuric acid or hydrochloric acid can also be used. The amount of the alkali catalyst used is 1 to 100 millimolar equivalents, preferably 1 to 50 millimolar equivalents, and more preferably 1 to 30 millimolar equivalents, per mole of vinyl acetate units. The saponification reaction is carried out by setting the concentration of the polymer in the alcohol to 20 to 50% by weight.
It is carried out at a temperature between 0 ° C and 60 ° C. By such saponification, the degree of saponification is 98.5 to 100 mol% (further 99 to 100 mol%).
(100 mol%).

The polyvinyl alcohol-based polymer is usually handled as a powder in the form of the final product. Then, in practical use in various application fields, since the powder is used as an aqueous solution dissolved in water, its solubility is a serious problem in practical use. That is, under the present situation where powders that dissolve quickly in water without forming a flour under hot or hot water are generally considered useful, the present invention further limits the saponification conditions to 50 ° C. The polyvinyl alcohol-based polymer powder which can be dispersed without generating a joint powder even when poured into the above-mentioned warm water or hot water and becomes an aqueous solution completely dissolved at 90 ° C to 95 ° C is obtained. Hereinafter, the production of the polyvinyl alcohol-based polymer powder will be described in detail.

To produce such a polyvinyl alcohol polymer powder: (a) A mixture of a methanol solution of a polyvinyl acetate polymer having a concentration of 20 to 50% by weight and a methanol solution of sodium hydroxide is continuously fed onto a belt conveyor. A method of pulverizing and drying a gel-like substance obtained by a methanolysis reaction using a wet pulverizer or the like. (USP 2,642,
419) (b) A mixture of a methanol solution of a polyvinyl acetate polymer having a concentration of 20 to 50% by weight and a methanol solution of sodium hydroxide is supplied to a twin-screw kneader-type reactor or an extruder-type reactor for methanolysis. A method in which a gel obtained by the reaction is pulverized and dried using a wet pulverizer or the like. (C) A method of saponifying a mixture of a partially saponified polyvinyl alcohol polymer solution having a degree of saponification of 20 to 60 mol% and a polyvinyl ester solution, and pulverizing and drying a gel-like material (Japanese Patent Laid-Open No. 9-316272), etc. Method. In each of the above methods, drying after pulverization is usually performed at a powder temperature of 50 to 130 ° C, preferably 100 to 120 ° C, for 1 to 5 hours, preferably 1 to 3 hours.

With respect to the particle size of the polyvinyl alcohol-based polymer powder, the ratio of 200 mesh passes is preferably 1% or less. The upper limit of the particle size is preferably 10 mesh passes, more preferably 16 mesh passes. The range of 60 mesh on to 10 mesh pass, and more preferably 32 mesh on to 16 mesh pass, is preferable from the viewpoint of improving the dissolution rate of the polyvinyl alcohol polymer having a high saponification degree.

Thus, the polyvinyl alcohol-based polymer of the present invention can be obtained. However, a post-reaction such as formalization, acetalization, butyralization, urethanization, acetoacetate esterification, sulfonation, and carboxylation can be performed. All of them have high crystallinity as compared with the polyvinyl alcohol-based polymer obtained by the prior art, and thus exhibit water resistance when used in various applications such as films.

The polyvinyl alcohol-based polymer powder obtained by the above method may be appropriately mixed with additives such as a bulking agent, an antifoaming agent, a release agent and an ultraviolet curing agent. If necessary, ordinary resins such as polyvinyl alcohol, starch, and carboxymethyl cellulose may be mixed as long as the properties are not lost. The polyvinyl alcohol-based polymer powder of the present invention can be widely used for the following applications.

(1) Molded products Fibers, films, sheets, pipes, tubes, leakproof membranes,
Temporary film, for chemical lace, water-soluble fiber (2) Adhesives Adhesives for wood, paper, aluminum foil, plastic, etc., adhesives, nonwovens, binders for fabrics, binders for various building materials such as gypsum board and fiberboard , Binders for various powder granulations, additives for cement and mortar, hot melt type adhesives, pressure sensitive adhesives, fixing agents for anionic paints

(3) Coating agent Clear coating agent for paper, pigment coating agent for paper, internal sizing agent for paper, sizing agent for textile products, warp sizing agent, fiber processing agent, leather finishing agent, paint, antifogging Agent, metal corrosion inhibitor, brightener for galvanizing, antistatic agent, conductive agent,
Temporary paints (4) Blend-related additives Antistatic agent for hydrophobic resin and hydrophilicity-imparting agent, composite fiber, film and other additives for moldings (5) Suspension dispersion stabilizer-related paints, ink, water-based color, adhesives, etc. A pigment dispersion stabilizer,
Dispersion stabilizer for suspension polymerization of various vinyl compounds such as vinyl chloride, vinylidene chloride, styrene, (meth) acrylate and vinyl acetate

(6) Emulsification dispersion stabilizers Emulsifiers for emulsion polymerization of ethylenically unsaturated compounds, butadiene compounds, hydrophobic resins such as polyolefins and polyester resins, post-emulsifiers such as epoxy resins, paraffin, bitumen, etc. (7) Thickening Agents Thickeners for various aqueous solutions and emulsions (8) Coagulants Coagulants for suspensions and dissolved materials in water, drainage improvers for pulp and slurry (9) Soil improvers (10) Photosensitizers, electrosensitive Relation, photosensitive resist resin relation (11) Other, ion exchange resin, ion exchange membrane relation,
Chelate exchange resin

[0027]

The present invention will be specifically described below with reference to examples. Note that “parts” and “%” are based on weight unless otherwise specified. Example 1 As a polymerization catalyst, a 20-L capacity polymerization canister having a cooling coil inside and a 4-blade paddle-type stirrer was used.
Using 2,2′-azobis- (2,4-dimethyl-4-methoxyvaleronitrile), vinyl acetate was continuously polymerized under the following conditions. Supply amount of vinyl acetate 2000 g / hr Supply amount of 0.08% methanol solution of 2,2'-azobis- (2,4-dimethyl-4-methoxyvaleronitrile) 80 g / hr [Half-life temperature of the above catalyst: 30] ° C] Temperature in polymerization catalyst charging line 10 ° C Supply amount of polymerization solvent (methanol) 400 g / hr Polymerization temperature 60 ° C Average residence time 5 hr The polymerization solution was supplied to the middle stage of the vinyl acetate monomer discharge tower,
In addition, methanol vapor was supplied from the bottom of the column, and unreacted vinyl acetate was expelled from the top of the column to obtain a methanol solution of polyvinyl acetate. Sodium hydroxide was added to the polyvinyl acetate solution, saponified using a kneader at an internal temperature of 40 ° C., dried at 120 ° C. for 3 hours, and dried at 120 ° C. for 3 hours to obtain a polyvinyl alcohol powder having a polymerization degree of 1600 and a saponification degree of 99.2 mol%. I got The polyvinyl alcohol was evaluated as follows.

(A) Iodine Color Degree Iodine 2 × 10 ^-3 mol / l, Potassium Iodine 8 × 10 ^-3
An equal amount of an aqueous solution containing 2.5 mol / l of the above-mentioned polyvinyl alcohol dissolved in 2.5 g / l is mixed at 20 ° C.
For 24 hours, and the absorbance at 610 mμ was measured. The higher the absorbance, the higher the crystallinity of polyvinyl alcohol.

(B) Infrared absorption spectrum An aqueous polyvinyl alcohol solution was cast on a vinyl chloride plate, air-dried for 10 days, and then dried under reduced pressure at room temperature for 3 days to obtain a film having a thickness of 0.01 mm. The infrared spectrum of the film was measured, and the ratio of the absorption at 8.7 μ and 9.1 μ was determined. The higher the ratio, the higher the crystallinity of the polyvinyl alcohol.

(C) Solubility of Polyvinyl Alcohol Powder at Elevated Temperature
It was sorted to 32 mesh on and evaluated by the following method. 250 g of distilled water was put into a 500 ml separal flask equipped with a stirrer, a reflux condenser and a thermometer, and put in a hot water bath.
The temperature was raised while stirring at 250 rpm, and when the internal temperature reached 50 ° C, 15 g of polyvinyl alcohol powder was added. The temperature was raised to 95 ° C over time, and the solubility of polyvinyl alcohol at the time when the temperature reached 95 ° C was measured. I asked. The solubility is determined by weighing the polyvinyl alcohol contained in the solution obtained by filtering the contents of the separal flask by a gravimetric method (evaporating the solution to dryness and measuring the amount of solids contained in the solution) to determine the solubility. I asked.

Example 2 Using a 20 L capacity polymerization canister having a cooling coil inside and a 4-blade paddle type stirrer,
Using 2,2′-azobis (2-methylbutanamide oxime) dihydrochloride tetrahydrate,
Vinyl acetate was subjected to batch polymerization under the following conditions. Vinyl acetate 10 kg 2,2′-azobis (2-methylbutanamide oxime) dihydrochloride tetrahydride 0.012 mol% late (vs. vinyl acetate) [Half-life temperature of the above catalyst: 57 ° C.] Temperature 42 ° C Methanol 2.9 kg Polymerization temperature 60 ° C Polymerization time 7 hours The polymerization solution was fed to the middle stage of the vinyl acetate monomer purging tower,
In addition, methanol vapor was supplied from the bottom of the column, and unreacted vinyl acetate was expelled from the top of the column to obtain a methanol solution of polyvinyl acetate. Sodium hydroxide was added to the polyvinyl acetate solution, saponified at 40 ° C. using a kneader, dried at 120 ° C. for 3 hours, and dried at 120 ° C. for 3 hours to obtain a polyvinyl alcohol powder having a polymerization degree of 1500 and a saponification degree of 99.3 mol%. I got

Example 3 The same procedure as in Example 2 was repeated except that the polymerization catalyst was changed to a 10-hour half-life temperature of 61.
A polyvinyl alcohol was produced according to Example 2, except that the temperature was changed to 1,1'-azobis (1-acetoxy-1-phenylethane) at a temperature of ° C. The obtained polyvinyl alcohol powder had a degree of polymerization of 1540 and a degree of saponification of 99.5 mol%.

Comparative Example 1 An experiment was performed in the same manner as in Example 1 except that the polymerization catalyst was charged at a charging temperature of 25 ° C. (5 ° C. lower than the half-life temperature). The polymerization degree of the obtained polyvinyl alcohol powder is higher than the target polymerization degree of 1600, and the polymerization degree is 18
40, the degree of saponification was 99.2 mol%.

Comparative Example 2 In Example 1, the polymerization catalyst was changed to a 10-hour half-life temperature of 65
Azobisisobutyronitrile at ℃
Production of polyvinyl alcohol was carried out according to Example 1. Polyvinyl alcohol powder obtained, degree of polymerization 164
0 and the degree of saponification was 99.2 mol%. Comparative Example 3 An experiment was performed in the same manner as in Example 2, except that the polymerization catalyst was replaced with lauryl peroxide.
The resulting polyvinyl alcohol powder has a degree of polymerization of 152.
0 and the degree of saponification was 99.5 mol%. Table 1 shows the evaluation results of the examples and the comparative examples.

[Table 1] (A) (B) (C) Example 1 0.33 0.75 100% Example 2 0.43 0.77 100% Example 3 0.42 0.76 100% Comparison example 2 0.29 0.71 98% (when dispersed at 50 ° C. warm water, there lump slight part) during dispersion in Comparative example 3 0.27 0.68 97% (50 ℃ hot water, slightly splicing part With powder)

[0036]

The polyvinyl alcohol polymer of the present invention introduces an azo compound catalyst having a half-life temperature of 64 ° C. or less in 10 hours into a polymerization system while maintaining the half-life temperature at a temperature lower by 10 ° C. or more. Then, since the polyvinyl acetate or the polyvinyl acetate-based polymer obtained by polymerizing vinyl acetate and other unsaturated monomers is saponified, the crystallinity is high.
Even if it is poured into hot water or hot water at a temperature of at least 0 ° C, it can be dispersed without generating a joint powder, and an aqueous solution completely dissolved at 90 to 95 ° C is obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4J015 AA01 AA03 AA04 AA05 AA06 AA07 4J100 AA02Q AA03Q AA06Q AA15Q AA19Q AA21Q AC03Q AC04Q AD02P AE02Q AE09Q AF10Q AG04P AJ02Q AJ08QAJQ AQ08 AQ08 AQ08 AQ08 DA01 DA38 EA05 FA08 HA09

Claims (6)

[Claims] An azo compound catalyst having a half-life temperature of not more than 64 ° C. for 10 hours is introduced into a polymerization system while keeping the temperature at least 10 ° C. lower than the half-life temperature, and vinyl acetate or
A polyvinyl alcohol-based polymer obtained by saponifying a polyvinyl acetate-based polymer obtained by polymerizing vinyl acetate and another unsaturated monomer. 2. The polyvinyl alcohol-based polymer according to claim 1, wherein the polymerization is a continuous polymerization. 3. The polyvinyl alcohol-based polymer according to claim 1, wherein the polymerization is a batch polymerization. 4. The method according to claim 2, wherein the concentration of the polyvinyl acetate polymer at the end of the polymerization is 50% by weight or more, and the degree of polymerization of the vinyl acetate polymer is 1500 or more.
Or the polyvinyl alcohol polymer according to 3. 5. The polyvinyl alcohol polymer according to claim 1, wherein the saponification is performed until the degree of saponification becomes 98.5 mol% or more. 6. The polyvinyl alcohol-based polymer according to any one of claims 1 to 5, which can be dispersed without hot-rolling even when poured into hot water or hot water at 50 ° C. or more, and A polyvinyl alcohol-based polymer powder characterized in that a completely dissolved aqueous solution is obtained at a temperature of from 95C to 95C.