JP3173744B2 - Fine grinding method of polyvinyl alcohol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for finely pulverizing polyvinyl alcohol.

[0002]

2. Description of the Related Art Polyvinyl alcohol is widely used in dispersants, adhesives, sizing agents, and the like, utilizing its unique property of water solubility. Polyvinyl alcohol and its characteristics are various even if it is just a word, its performance varies widely depending on the average degree of polymerization, average degree of saponification, average particle size, etc. It is being used.

[0003]

Heretofore, polyvinyl alcohols having a very low molecular weight of about 50 in average polymerization degree to high molecular weight of 6000 or more in terms of average degree of polymerization have been known. It is well known that a completely saponified product having a degree of saponification of 100 mol% to a partially saponified product having several tens mol%. Furthermore, from the aspect of average particle size, ordinary industrial products are about 200 to 1000 μm. Therefore, when producing finely divided polyvinyl alcohol for use in special applications, mechanical pulverization or the like is required. It is.

[0004] However, according to the conventional mechanical pulverization method, although it slightly varies 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 very difficult to pulverize the particles to a satisfactory particle diameter. Difficult. In order to obtain polyvinyl alcohol fine particles having a smaller particle size than this, a chemical pulverization method can be considered.
However, in such a method, it is very difficult to control the particle size, so that it is difficult to obtain polyvinyl alcohol having a desired particle size, and it cannot be said that this method is not suitable for implementation on an industrial scale.

[0005] Accordingly, if polyvinyl alcohol fine particles having a smaller particle size can be obtained by a mechanical pulverization method capable of easily controlling the particle size, the performance of polyvinyl alcohol can be improved by a combination of the average polymerization degree, the average saponification degree, and the average particle size. Needless to say, it is further useful to expand the range of industrial use, which is extremely useful in industry.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to obtain polyvinyl alcohol having a smaller particle size by using a mechanical pulverizing method. As a result, aqueous polyvinyl alcohol gel having a polyvinyl alcohol concentration of 25% by weight or less is obtained. After pulverizing the gel, the pulverized gel was brought into contact with an organic solvent which does not dissolve polyvinyl alcohol, and subsequently, the gel was dried. As a result, it was found that extremely finely divided 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 pulverizing the aqueous gel.
Hereinafter, the present invention will be described in detail.

[0007] The polyvinyl alcohol used in the present invention is usually produced by a known method. Such polyvinyl alcohol includes not only partially saponified or completely saponified polyvinyl acetate, but also a vinyl ester and a monomer copolymerizable therewith, such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and 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, etc., acrylonitrile, nitriles such as methacrylonitrile, acrylamide, Amides such as methacrylamide, olefin sulfonic acids or salts thereof such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid, alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltriene 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,
Particularly suitable is 500 to 3000, and a preferable average saponification degree is 60 to 100 mol%, particularly preferably 80 to 100 mol%. Thus, polyvinyl alcohol is 200 ~
Since it is obtained as coarse particles of about 300 μm, it is then pulverized by a pulverizing step. In this pulverization step, first, polyvinyl alcohol is prepared so as to form a polyvinyl alcohol aqueous gel having 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 low temperature, add a solvent such as methanol or acetone, add a gelling agent such as boric acid, borax, sodium sulfate, or freeze or irradiate with radiation. Means are used.

The gel is subsequently pulverized by mechanical pulverization so that the average particle size is 25 μm or less, preferably 15 to 20 μm or less. Such a particle size is 25 μm
When the ratio exceeds the above, the excellent effects as in the present invention cannot be exhibited.

The pulverizing method is not particularly limited, and any method can be employed. 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 mills, centrifugal classifier mills, etc., ball mills (rolling mills, vibrating ball mills, planetary mills), stirring mills (tower mills, stirring tank mills, flow tube mills, annular mills) , A lab mill, a jet mill, a shearing mill, a compression mill, a colloid mill, and the like.

Next, the ground gel is brought into contact with an organic solvent in which polyvinyl alcohol is not dissolved. As a contact method, usually pulverized gel is poured into an organic solvent with stirring,
A method of adding an organic solvent to the polyvinyl alcohol gel, or a method of bringing the polyvinyl alcohol gel and the organic solvent into countercurrent contact is also used. The organic solvent in the present invention includes acetone, methanol, ethanol, DMSO and the like. Next, the gel that has been brought into contact with the organic solvent is separated from the solvent by a known method such as filtration, and is subjected to drying.
The drying method in the present invention is not particularly limited, and any method can be used. The resulting powder has an average particle size of 5 to 15 μm
It is very fine and has a sharp particle size distribution. The polyvinyl alcohol fine powder thus obtained can be suitably used for various applications including an emulsifying dispersant, a thermoplastic resin modifier, an adhesive, a fiber processing agent, a sizing agent, a paper processing agent, and a paint.

[0012]

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

[0013]

The present invention will be described below in more detail with reference to examples. In Examples, “parts” and “%” are based on weight unless otherwise specified. Example 1 Polyvinyl alcohol having an average degree of polymerization of 500 and an average degree of saponification of 99.0 mol% ("Gosenoh" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
Le NL-05 ”) was prepared, and the aqueous solution was left in a freezer at -10 ° C for 48 hours to obtain an aqueous polyvinyl alcohol gel. Next, the aqueous gel is pulverized to 20 mesh or less using a sample mill (AP-S type, manufactured by Hosokawa Micron Corp.), and subsequently, a micromill grinder (Bel-Art Products Co., Ltd.)
For about 1 hour. When the average particle diameter of polyvinyl alcohol of this gel was measured, it was 21 μm. Next, 10 parts of the pulverized gel was supplied into 200 parts of an acetone solvent, and the mixture was stirred for 3 hours, and then filtered to remove polyvinyl alcohol. The polyvinyl alcohol was dried using a Nauter mixer (manufactured by Hosokawa Micron Corporation) at a powder temperature of 70 ° C. under reduced pressure (40 Torr) for about 12 hours to obtain polyvinyl alcohol fine particles having an average particle diameter of 11 μm. Examples 2 to 5 and Comparative Examples 1 and 2 An experiment was performed in the same manner as in Example 1 except that the conditions shown in Tables 1 and 2 were used. Examples 2 to 5 and Comparative Examples 1 to 2
The polyvinyl alcohol used in
You. Example 2: Vinyl acetate was used in the presence of azobis
Methanol / acetic acid using isobutyronitrile as an initiator
Polymerized with vinyl (charge ratio by weight) = 3.1, polymerization rate 96%
And, carried out what was saponified Example 3: The Nippon Synthetic Chemical Industry Co., Ltd. "Gohsenol NL
-05 ”and vinyl acetate in the presence of methanol
Methanol / vinegar with isobutyronitrile as initiator
Polymerization with vinyl acetate (weight ratio) = 1.7, polymerization rate 95%
And, carried out what was saponified Example 4: The Nippon Synthetic Chemical Industry Co., Ltd. "Gohsenol NL
-05 " Example 5:" GOHSENOL NM "manufactured by Nippon Synthetic Chemical Industry Co., Ltd.
-14 " Example 6: Azobis in the presence of methanol in the presence of methanol
Methanol / acetic acid using isobutyronitrile as an initiator
Polymerized with vinyl (prepared weight ratio) = 0.05, polymerization rate 50%
And, example comparison that was saponified 1, 2: The Nippon Synthetic Chemical Industry Co., Ltd. "Gohsenol
NL-05],

[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 prepared using a sample mill (Hosokawa Micron).
Using a micromill grinder (Bel-Art Product).
(manufactured by s Corporation) for about 1 hour. The average particle diameter of the obtained polyvinyl alcohol was 25 μm. Comparative Example 4 Grinding was carried out 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 Grinding was carried out 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 of a plastic molded article when the polyvinyl alcohol obtained in Example 2 was used as a plastic modifier was evaluated. . In addition, the experiment was similarly performed about the polyvinyl alcohol obtained by the comparative example 2 and the comparative example 4 as a comparison. The results are shown in Table 3.

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

Peeling test The same plate as above was allowed to stand at 40 ° C. and 95% RH for 48 hours, and then left at 40 ° C. and 15% RH for 48 hours. The operation was repeated 20 times. Was observed.

[0020]

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

[0021]

According to the present invention, a finer polyvinyl alcohol can be produced by a mechanical pulverization method in which the particle diameter can be easily controlled.

Claims (2)

(57) [Claims] 1. Polyvinyl alcohol concentration of 25% by weight
After pulverizing the following polyvinyl alcohol aqueous gel, a method of pulverizing polyvinyl alcohol, comprising contacting the pulverized gel with an organic solvent that does not dissolve polyvinyl alcohol, followed by drying the gel 2. An aqueous polyvinyl alcohol gel having a particle size of 25 μm.
2. The fine pulverization method according to claim 1, wherein the pulverization is carried out until the particle size becomes less than m.