JPH05339380A - Method for finely grinding polyvinyl alcohol - Google Patents

Abstract

PURPOSE:To obtain a finely divided PVA with the particle diameter easy to control, by grinding an aqueous PVA gel of a specified concentration, bringing the ground gel into contact with an organic solvent that will not dissolve PVA, and then drying the gel. CONSTITUTION:An aqueous PVA gel having a PVA concentration of at most 25wt.% is ground, and the ground gel is brought into contact with an organic solvent that will not dissolve PVA and then dried. Examples of the PVA are a partially or completely saponified polyvinyl acetate and a saponified copolymer of a vinyl ester and a monomer copolymerizable therewith, wherein the average degree of polymerization and the average degree of saponification are preferably 300 to 5000 and 60 to 100mol%, respectively. Such gels can form fine particles having a mean particle diameter of 25mum or smaller, preferably 15-20mum, by subsequent mechanical grinding. If the particle diameter is above 25mum, no excellent effect can be revealed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an excellent method for finely pulverizing polyvinyl alcohol.

[0002]

2. Description of the Related Art Polyvinyl alcohol is widely used as a dispersant, an adhesive, a sizing agent, etc. by utilizing its unique property of being water-soluble. Polyvinyl alcohol has a variety of properties, and its performance varies depending on the average degree of polymerization, the average degree of saponification, the average particle size, etc., and each characteristic is applied to each of the above applications. It is being used.

[0003]

From the point of view of average degree of polymerization, polyvinyl alcohols having an ultra low molecular weight of about 50 to a high molecular weight of 6000 or more have been known, and the degree of saponification is also known. It is well known that a completely saponified product having a saponification degree of 100 mol% to a partially saponified product having a saponification degree of several tens mol%. Further, from the aspect of average particle size, a normal industrial product has a particle size of about 200 to 1000 μm. Therefore, when finely particulate polyvinyl alcohol is produced for use in a special purpose, mechanical pulverization or the like is required. Is.

However, according to the conventional mechanical pulverization method, although it may be slightly different depending on the average degree of polymerization,
When the average degree of polymerization is about 300 to 4000, the particle diameter of the obtained polyvinyl alcohol is limited to about 20 to 30 μm. Particularly, when finely pulverizing polyvinyl alcohol having a high degree of polymerization, it is extremely difficult to grind to a satisfactory particle diameter. Difficult to do. A chemical pulverization method can be considered for obtaining polyvinyl alcohol fine particles having a particle size smaller than this.
However, since it is very difficult to control the particle size in such a method, it is difficult to obtain a polyvinyl alcohol having a target particle size, and it must be said that it is unsuitable for implementation on an industrial scale.

Therefore, if polyvinyl alcohol fine particles having a smaller particle size can be obtained by a mechanical pulverization method in which the particle size can be easily controlled, the performance of polyvinyl alcohol can be improved by combining the average degree of polymerization, the average degree of saponification, and the average particle size. Needless to say, it will be further expanded, and the industrial application range will be expanded, which is extremely useful in industry.

[0006]

However, as a result of intensive studies by the present inventors to obtain polyvinyl alcohol having a smaller particle size by using a mechanical pulverization method, a polyvinyl alcohol aqueous gel having a polyvinyl alcohol concentration of 25% by weight or less is obtained. After crushing, the crushed gel was brought into contact with an organic solvent that does not dissolve polyvinyl alcohol, and then the gel was dried, whereby it was found that extremely fine-grained polyvinyl alcohol was obtained, and the present invention was completed.
In such a method, the particle size of the obtained polyvinyl alcohol can be freely selected by controlling the particle size at the stage of crushing the aqueous gel.
Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol used in the present invention is usually produced by a known method. Such polyvinyl alcohol is not only a partially saponified product or a completely saponified product of polyvinyl acetate, but also a vinyl ester and a monomer copolymerizable therewith, such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene. Olefins such as, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, unsaturated acids such as itaconic acid or salts or mono- or dialkyl esters thereof, acrylonitrile, nitriles such as methacrylonitrile, acrylamide, Amides such as methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid or salts thereof, alkyl vinyl ethers, N-acrylamidomethyl trimethyl ammonium chloride, allyl tricarboxylic acid Chill ammonium chloride, dimethyl diallyl vinyl ketone, N- vinylpyrrolidone, vinyl chloride, a copolymer saponified vinylidene chloride and the like, not necessarily limited thereto.

The preferred average degree of polymerization is 300 to 5000,
In particular, 500 to 3000 is suitable, and the preferable average saponification degree is 60 to 100 mol%, particularly 80 to 100 mol%. Thus, polyvinyl alcohol is 200 ~
Since it is obtained as coarse particles of about 300μ, it is then atomized by a crushing process. In such a pulverizing step, first, polyvinyl alcohol is prepared so that the polyvinyl alcohol aqueous gel has a concentration of 25% by weight or less, preferably 20% by weight or less, and more preferably 3 to 15% by weight. For gelation, leave the polyvinyl alcohol aqueous solution at a low temperature, add a solvent such as methanol or acetone, add a gelling agent such as boric acid, borax, sodium sulfate, etc., or freeze or irradiate it. Means are used.

The gel is then pulverized by mechanical pulverization so as to have an average particle size of 25 μm or less, preferably 15 to 20 μm. Such particle size is 25 μm
If it exceeds, the excellent effects of the present invention cannot be exhibited.

The pulverization method is not particularly limited and any method can be adopted. For example, a roll mill, a stamp mill, an edge runner, a cutting / shearing mill, a rod mill, an autogenous pulverizer, a roller mill, a high speed rotary pulverizer (hammer mill, cage mill). , Pin mills, disintegrators, screen mills, turbo type mills, centrifugal classification mills, etc.), ball mills (rolling mills, vibrating ball mills, planetary mills), stirring mills (tower mills, stirring tank type mills, flow tube type mills, annular mills) , A lab mill, a jet mill, a shear mill, a compression grinding type pulverizer, a colloid mill and the like are used.

Then, the crushed gel is contacted with an organic solvent in which polyvinyl alcohol is insoluble. As the contact method, usually, crushed gel is put into an organic solvent with stirring, or
A method in which an organic solvent is added to the polyvinyl alcohol gel, or a method in which the polyvinyl alcohol gel and the organic solvent are brought into countercurrent contact is also used. Examples of the organic solvent in the present invention include acetone, methanol, ethanol, DMSO and the like. Next, the gel brought into contact with the organic solvent is separated from the solvent by a known method such as filtration and dried.
The drying method in the present invention is not particularly limited and any method can be used. The obtained powder has an average particle size of 5 to 15 μm.
It is extremely fine powder and the particle size distribution is sharp. The polyvinyl alcohol fine powder thus obtained can be suitably used for various purposes such as an emulsifying dispersant, a thermoplastic resin modifier, an adhesive, a fiber processing agent, a sizing agent, a paper processing agent, and a paint.

[0012]

The present invention is industrially extremely advantageous because it is possible to produce a finer polyvinyl alcohol than before by a mechanical pulverization method in which the particle size can be easily controlled.

[0013]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the examples, "part" and "%" are based on weight unless otherwise specified. Example 1 A 25% aqueous solution of polyvinyl alcohol having an average degree of polymerization of 500 and an average degree of saponification of 99.0 mol% was prepared, and the aqueous solution was allowed to stand in a freezer at -10 ° C for 48 hours to obtain a polyvinyl alcohol aqueous gel. Next, the aqueous gel was pulverized to 20 mesh or less by using a sample mill (AP-S type, manufactured by Hosokawa Micron Co., Ltd.), and subsequently about 1 by a micromill grinder (manufactured by Bel-Art Products Co., Ltd.). Milled for hours. The polyvinyl alcohol average particle diameter of the gel was 21 μm. Then, 10 parts of the crushed gel was supplied into 200 parts of an acetone solvent, stirred for 3 hours, and then filtered to remove polyvinyl alcohol by filtration. This polyvinyl alcohol was dried for about 12 hours at a powder temperature of 70 ° C. under reduced pressure (40 Torr) using a Nauta mixer (manufactured by Hosokawa Micron Co., Ltd.) to obtain polyvinyl alcohol fine particles having an average particle diameter of 11 μm. Examples 2 to 5 and Comparative Examples 1 to 2 An experiment was conducted in the same manner as in Example 1 except that the conditions shown in Table 1 and Table 2 were used.

[0014]

[Table 1]

[0015]

[Table 2]

Comparative Example 3 A polyvinyl alcohol having an average degree of polymerization of 500 and an average degree of saponification of 99.0 mol% was sample milled (Hosokawa Micron).
(Manufactured by K.K.) for 20 minutes, followed by micromill grinder (Bel-Art Product).
s Co., Ltd.) for about 1 hour. The obtained polyvinyl alcohol average particle diameter was 25 μm. Comparative Example 4 Pulverization was performed in the same manner as in Comparative Example 1 using polyvinyl alcohol having an average degree of polymerization of 1500 and an average degree of saponification of 99.0 mol%. The average particle size of the obtained polyvinyl alcohol is 2
It was 7 μm. Comparative Example 5 Pulverization was performed in the same manner as in Comparative Example 1 using polyvinyl alcohol having an average degree of polymerization of 3000 and an average degree of saponification of 99.0 mol%. The average particle size of the obtained polyvinyl alcohol is 3
It was 8 μm.

Performance Evaluation of Polyvinyl Alcohol In order to evaluate the performance of the finely divided polyvinyl alcohol of the present invention, the quality evaluation of the plastic molded article was carried out when the polyvinyl alcohol obtained in Example 2 was used as a plastic modifier. .. As a comparison, the same experiment was conducted for the polyvinyl alcohols obtained in Comparative Example 2 and Comparative Example 4. The results are shown in Table 3.

Test under high humidity condition Mixed pellets of polyester resin (PE) and polyvinyl alcohol resin (PVA) in a mixing ratio shown in Table 3 were formed into plates by injection molding. After the plate was left (1) at 20 ° C. and 90% RH for 48 hours and (2) left at 40 ° C. and 95% RH for 48 hours on the plate, the surface of the molded body was observed with a microscope of 200 magnifications.
The evaluation criteria are as follows. ◎ No dewdrops were observed ○ Some small dewdrops × Dewdrops × × The entire surface was wet

Peeling test The same plate as above was left at 40 ° C. and 95% RH for 48 hours, and then left at 40 ° C. and 15% RH for 48 hours. After repeating 20 times, the presence or absence of surface peeling was observed by an electron microscope. Was observed.

[0020]

[Table 3] * ¹ () shows the average particle size (μm) of PVA

[0021]

INDUSTRIAL APPLICABILITY According to the present invention, a finer polyvinyl alcohol than before can be produced by a mechanical pulverization method in which the particle size can be easily controlled.

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[Procedure amendment]

[Submission date] February 3, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

The polyvinyl alcohol used in the present invention is usually produced by a known method. Such polyvinyl alcohol is not only a partially saponified product or a completely saponified product of polyvinyl acetate, but also a vinyl ester and a monomer copolymerizable therewith, such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene. Olefins such as, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, unsaturated acids such as itaconic acid or salts or mono- or dialkyl esters thereof, acrylonitrile, nitriles such as methacrylonitrile, acrylamide, Amides such as methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid or salts thereof, alkyl vinyl ethers, N-acrylamidomethyl trimethyl ammonium chloride, allyl tricarboxylic acid Chill ammonium chloride, dimethyl diallyl vinyl ketone, N- vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth) Ariruete
, Polyoxypropylene (meth) allyl ether, etc.
Polyoxyalkylene (meth) allyl ether, poly
Oxyethylene (meth) acrylate, polyoxypro
Pyrene (meth) acrylate, polyoxyethylene (meth
A) acrylamide, polyoxypropylene (meth) a
Crylamide, polyoxyethylene (1- (meth) ac
Rylamide-1,1-dimethylpropyl) ester, po
Lioxyethylene vinyl ether, polyoxypropylene
Vinyl ether, polyoxyethylene allylamine,
Polyoxypropylene such as polyoxypropylene allylamine
Xylene allylamine, polyoxyethylene vinylami
Polyoxy, such as polyoxyethylene, polyoxypropylene vinylamine
Examples thereof include saponified products of copolymers with alkylene vinyl amine and the like, but not limited thereto.

Claims (2)

[Claims] 1. The polyvinyl alcohol concentration is 25% by weight.
A method for finely pulverizing polyvinyl alcohol, which comprises pulverizing the following polyvinyl alcohol aqueous gel, contacting the pulverized gel with an organic solvent that does not dissolve polyvinyl alcohol, and subsequently drying the gel: 2. A polyvinyl alcohol aqueous gel containing 25 μm
The finely pulverizing method according to claim 1, wherein the finely pulverizing method is performed until the particle size becomes m or less.