JPH08188620A - Production of fine polyvinyl alcohol polymer particle - Google Patents

Abstract

PURPOSE: To produce fine polyvinyl alcohol polymer particles having good dispersion stability by polymerizing a vinyl ester monomer in a specified solvent and saponifying the obtained polymer. CONSTITUTION: A vinyl ester monomer is pqlymerized under agitation in a solvent in which at most 1wt.% polyvinyl ester is soluble at the polymerization temperature and in which at most 30wt.% vinyl ester monomer is soluble at the polymerization temperature, and the obtained polymer is saponified. An example of this solvent is an at least dihydric alcohol. The charge ratio of the solvent to the vinyl ester monomer in the polymerization is desirably such that 30-200 pts.wt. vinyl ester monomer is used per 100 pts.wt. solvent. It is desirable that a dispersant is used in the polymerization, and that its amount of use is 1-40 pts.wt. per 100 pts.wt. vinyl ester monomer. It is desirable the initiator used is the one soluble in the dispersion medium and insoluble in the vinyl ester monomer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine particles of a polyvinyl alcohol polymer by polymerizing a polyvinyl ester by a specific method and saponifying it.

[0002]

2. Description of the Related Art Conventional polyvinyl alcohol (hereinafter abbreviated as PVA) has an average particle size of 200.
Industrial production of ~ 1000 μm PVA. PVA
Is an excellent film-forming property and strength, so it is a paper modifier (clear coating agent, pigment coating agent) and a paper modifier such as an internal additive for paper; an adhesive agent for paper, wood and inorganic substances. Widely used for various purposes such as warp sizing agents. Usually, PVA is used in the form of an aqueous solution, but in coating at a high shear rate, problems such as increased viscosity (dilatancy), streaking of the coating film, and scattering of the coating liquid occur. Studies have been conducted on making an aqueous slurry using PVA having a small particle size. As a method for producing PVA having a particle size smaller than that of general PVA, a method of mechanically pulverizing industrially produced PVA using a jet mill or the like (Japanese Patent Laid-Open No. 2-225506: hereinafter referred to as Prior Art A is abbreviated). ); An industrially produced dimethyl sulfoxide solution of PVA is passed through a sprayer to give an average particle size of 1 m.
After forming a droplet of less than m to several mm, the droplet is subjected to PVA.
Method for precipitating PVA by adding it to the non-solvent of JP
No. 98023: hereinafter referred to as Prior Art B); an oily dispersion obtained by dispersing an industrially produced dimethyl sulfoxide solution of PVA in a dispersion medium such as silicone oil is referred to as PV.
A method of precipitating PVA by adding it to the non-solvent of A and stirring the mixture (JP-A-5-98024: Prior art C
Abbreviated); a method of saponifying a polyvinyl ester in a non-aqueous dispersion of polyvinyl ester having an average particle diameter of 0.05 to 50 μm obtained by dispersion polymerization using a surfactant (UK Patent 1,199,651). No .: hereinafter referred to as Prior Art D) is known.

However, according to the method of the prior art A, only PVA having an average particle size of 3 to 30 μm was obtained, and the obtained P was obtained.
When an aqueous slurry prepared using VA is heated,
There is a problem that the dissolution rate of PVA is low. According to the method of the prior art B, the range of particle size distribution of the obtained PVA is 1
Since it is as large as less than μm to 1 mm or more, the obtained P
When an aqueous slurry prepared using VA is heated,
There is a problem that the dissolution rate of PVA is low. In the method of Prior Art C, since the range of the particle size distribution of the obtained PVA is as large as 0.1 μm to 100 μm, the dissolution rate of PVA when the aqueous slurry prepared using the obtained PVA is heated. Has the problem that
There is a problem that it is difficult to remove the dispersion medium such as silicone oil adhered to the PVA when adjusting the PVA. According to the method of the prior art D, the particle size distribution range of the obtained PVA was 0.
Since it is as large as 01 μm to 100 μm, the obtained P
When an aqueous slurry prepared using VA is heated,
There is a problem that the dissolution rate of PVA is low.
There is a problem that the binder force of PVA is lowered because a surfactant is used during dispersion polymerization.

[0004]

An object of the present invention is to provide PVA fine particles having good dispersion stability.

[0005]

Means for Solving the Problems As a result of earnest studies to solve the above problems, as a result of stirring in a solvent having a solubility of polyvinyl ester at a polymerization temperature of 1% by weight or less and a vinyl ester monomer solubility of 30% by weight or less. The present invention has been completed by finding a method for producing fine particles of polyvinyl alcohol-based polymer characterized by polymerizing a vinyl ester monomer and subsequently performing saponification.

Next, the present invention will be described in detail.

The solvent used in the present invention has a solubility of the polyvinyl ester at the polymerization temperature of the vinyl ester monomer of 1% by weight or less and a solubility of the vinyl ester monomer of 30% by weight or less. Two such solvents are
Examples thereof include polyhydric alcohols having a valence of at least 3, such as ethylene glycol, propylene glycol and glycerin.

Examples of the vinyl ester monomer used in the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, vinyl pivalate and the like.

The charging ratio of the vinyl ester monomer to the solvent at the time of polymerization is preferably 30 to 200 parts by weight of the vinyl ester monomer with respect to 100 parts by weight of the solvent.
0 to 180 parts by weight is more preferable, and 80 to 150 parts by weight is particularly preferable. If the vinyl ester monomer is too much, the stability of the polymer fine particles will be impaired, and if it is too small, it will be difficult to obtain a polyvinyl ester having a high degree of polymerization.

Further, by using a dispersant during the polymerization, the particles are stabilized during the polymerization and during the subsequent saponification,
Polyvinyl ester fine particles with excellent dispersibility and PV
A dispersion liquid of A fine particles can be prepared. Specific examples of such a dispersant include sorbitan alkyl ester,
Surfactants such as polyoxyethylene alkyl ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sorbitan alkyl ester, polyoxyalkylene compounds such as polyethylene glycol and polypropylene glycol, polyvinyl methyl ether, polyvinyl ethyl ether Examples thereof include polyvinyl ethers, polyvinylpyrrolidone, polymeric dispersants such as partially saponified polyvinyl acetate, and the like, and polyvinylpyrrolidone is particularly preferable.

From the viewpoint of polymerization stability, the amount of the dispersant used is preferably 0.1 to 40 parts by weight, more preferably 0.3 to 30 parts by weight, based on 100 parts by weight of the vinyl ester monomer. , 0.5 to 20 parts by weight is particularly preferable.

Although a conventionally known initiator can be used,
Those which are soluble in the dispersion medium are preferable, and those which are soluble in the dispersion medium and insoluble in the vinyl ester monomer are particularly preferable in order to increase the polymerization degree of polyvinyl ester. Such initiators include 2,2'-azobis (2-methylpropionamidine) dihydrochloride, 2,2 '
-Hydrophilic azo initiators such as azobis [N- (2-hydroxyethyl) -2-methylpropionamidine] hydrochloride, hydrophilic peroxides such as potassium persulfate and ammonium persulfate, hydrogen peroxide-ferrous iron Examples include hydrophilic redox initiators such as salts and persulfates-sodium acid sulfite.

The polymerization temperature is not particularly limited, but -60 to 2
00 ° C is preferable, -30 to 150 ° C is more preferable, and 5 to 90 ° C is particularly preferable. The polymerization of the present invention is carried out with stirring, and it is particularly important to uniformly stir the entire system.

The degree of polymerization of the polyvinyl ester thus obtained is not particularly limited, but is preferably 300 to 30,000, more preferably 500 to 20,000, and 700 to 700 in order to sufficiently exhibit the physical properties of PVA. 1
0000 is particularly preferable. The average particle size of the polyvinyl ester is preferably 0.05 to 10 μm.

The polyvinyl ester of the present invention may be copolymerized with another unsaturated monomer copolymerizable with the vinyl ester within a range (preferably 20 mol% or less) that does not impair the effects of the present invention. As the unsaturated monomer, olefins such as ethylene, propylene, α-hexene and α-octene; unsaturated acids such as (meth) acrylic acid, crotonic acid, maleic acid, itaconic acid, maleic anhydride, or Salts thereof, or mono- or dialkyl esters; acrylamide, N-alkylacrylamide, N, N-
Acrylamides such as dialkylacrylamide, 2-acrylamidopropanesulfonic acid or its salt, acrylamidopropyldimethylamine or its acid salt or its quaternary salt; methacrylamide, N-alkylmethacrylamide, N, N-dialkylmethacrylamide, 2- Methacrylamides such as methacrylamidopropanesulfonic acid or its salts, methacrylamidopropyldimethylamine or its acid salts or its quaternary salts; styrenes; vinyl ethers such as methyl vinyl ether and t-butyl vinyl ether; N-vinyl pyrrolidone, N -N-vinylamides such as vinylformamide and N-vinylacetamide; allyl acetate, allyl chloride, allyl alcohol, allyl sulfonic acid or salts thereof, 8-hydroxy-1
-Allyl compounds such as octene; Vinyl cyanides such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; Silicon-containing monomers such as vinyltrimethoxysilane And so on.

By polymerizing the vinyl ester monomer by the above-mentioned method, a dispersion liquid of polyvinyl ester fine particles is obtained, which is subsequently subjected to a saponification reaction. Examples of the saponification catalyst include alkali catalysts and acid catalysts, and conventionally known ones can be used. Examples of the alkali catalyst include sodium hydroxide, potassium hydroxide, ammonia, sodium methylate and the like. Examples of the acid catalyst include sulfuric acid, hydrochloric acid, P-toluenesulfonic acid and the like. The molar ratio of alkali to polyvinyl ester at the time of saponification is 0.0 from the viewpoint of saponification rate.
05-0.5 are preferable, 0.01-0.2 are more preferable, 0.02-0.1 are especially preferable. From the viewpoint of saponification rate, the saponification temperature is preferably 5 ° C or higher, more preferably 20 ° C or higher. Also, it is preferably 150 ° C or lower, and 10
It is more preferably 0 ° C or lower.

The degree of saponification of the PVA polymer fine particles is not particularly limited, but is preferably 50 mol% or more, and 70 mol%
The above is more preferable.

Further, when saponification proceeds to about 30 to 70 mol% or during the saponification reaction, a liquid which is a poor solvent for PVA and which can be uniformly mixed with the dispersion medium can be added. Is. Examples of the liquid to be added include methanol, ethanol, propanol, isopropanol, acetone, tetrahydrofuran and the like. As an addition method, it may be added all at once, but it is more preferable to gradually add it from the viewpoint of suppressing aggregation of particles. If the amount added is too small, the effect of suppressing aggregation is small, and if it is too large, handling after saponification becomes difficult. Therefore, it is preferably 5 to 300 parts by weight, and 10 to 250 parts by weight with respect to 100 parts by weight of the dispersion medium. Is more preferable and 15 to 200 parts by weight is particularly preferable.

The average particle size of the PVA-based fine particles is 3 in order to improve the dissolution rate of the fine particles after coating and improve the physical properties after coating when the PVA-based fine particles are made into an aqueous slurry.
0 μm or less is preferable, 10 μm or less is more preferable,
It is more preferably 5 μm or less, particularly preferably 1 μm or less. The lower limit of the particle size of the PVA-based fine particles is not particularly limited, but 0.01 μm or more is preferable.

After the saponification reaction, the PVA type fine particles can be separated and purified from the liquid phase reaction medium by methods such as decantation, liquid separation operation and centrifugation. The PVA-based fine particles obtained as a powder can be rendered substantially insoluble in cold water by performing heat treatment after ordinary drying or by redispersing PVA such as methanol in a poor solvent and performing heat treatment. The lower limit of the temperature of the heat treatment is preferably 70 ° C., more preferably 80 ° C., particularly preferably 100 ° C. from the viewpoint of increasing the crystallinity and making it substantially insoluble in cold water. The upper limit of the heat treatment temperature is preferably 200 ° C., from the viewpoint of suppressing aggregation during heat treatment and improving the rate of dissolution in hot water, 180 ° C.
C. is more preferable, and 160.degree. C. is particularly preferable. In the present invention, “substantially insoluble in cold water” means that the solubility in water at 20 ° C. is 50% by weight or less, preferably 20% by weight or less,
It means that it is more preferably 10% by weight or less, and particularly preferably 5% by weight or less. Further, by post-treating the aqueous slurry of PVA-based fine particles with a homogenizer or an ultrasonic homogenizer,
It is possible to reduce the particle size and further improve the dispersibility.

[0021]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following examples, "%" and "parts" mean "% by weight" and "parts by weight", respectively, unless otherwise specified. The physical property values in the examples were measured by the following methods.

(Average particle size of PVA particles) PVA particles were dispersed in acetone, measured using an electrophoretic light scattering photometer (Model ELS-800 manufactured by Otsuka Electronics Co., Ltd.), and calculated by the cumulant method. .

(Polymerization degree of PVA) PVA was completely saponified and measured according to JIS-K-6726.

Example 1 Polyvinyl alcohol as a dispersant in 200 parts of ethylene glycol (ethylene glycol exhibits a solubility of 1% by weight or less of polyvinyl ester at a polymerization temperature of 60 ° C. and a solubility of 30% by weight or less of vinyl ester monomer). 5 parts of pyrrolidone (Mw = 40,000) was dissolved, 70 parts of vinyl acetate was added, and the temperature was raised to 60 ° C. while bubbling nitrogen while propeller stirring at 300 rpm. Polymerization was carried out by adding 0.05 part of 2,2'-azobis (2-methylpropionamidine) dihydrochloride as an initiator (polymerization time 4 hours, polymerization rate 97%). After the temperature was subsequently lowered to 40 ° C., the residual vinyl acetate was distilled off under reduced pressure with an aspirator, and then 15.8 parts of an ethylene glycol solution of sodium hydroxide (concentration: 10
%, A molar ratio of 0.05 to polyvinyl acetate) was added and stirred for 4 hours to obtain PVA fine particles. The sodium hydroxide in the system was neutralized by adding 3 parts of acetic acid. The ethylene glycol dispersion liquid of PVA fine particles is separated by sedimenting the PVA fine particles by centrifugation,
Washing was performed three times by adding methanol and washing. The obtained PVA fine particles were dried at 120 ° C. for 2 hours. The polymerization conditions are shown in Tables 1 and 2.
Table 3 shows the saponification conditions and the physical properties of the PVA fine particles.

Example 2 The conditions shown in Table 1, Table 2 and Table 3 (propylene glycol / methanol = 9/1, the solubility of polyvinyl ester at a polymerization temperature of 40 ° C. is 1% by weight or less and the solubility of vinyl ester monomer is 30% by weight. PVA fine particles were obtained in the same manner as in Example 1 except that the solubility was changed to the following). The polymerization conditions are shown in Tables 1 and 2, and the saponification conditions and the physical properties of the PVA particles are shown in Table 3.

Example 3 200 parts of glycerin (glycerin exhibits a solubility of 1% by weight or less of polyvinyl ester and a solubility of 30% by weight or less of vinyl ester monomer at a polymerization temperature of 60 ° C.) in 200 parts of polyvinylpyrrolidone (as a dispersant) Mw = 40000) 5 parts were dissolved, and vinyl acetate 120
Parts were added, and the temperature was raised to 60 ° C. while bubbling nitrogen while stirring with a peller at 300 rpm. Polymerization was carried out by adding 0.07 part of 2,2'-azobis (2-methylpropionamidine) dihydrochloride as an initiator (polymerization time: 4 hours, polymerization rate: 95.5%). After the temperature was subsequently lowered to 40 ° C., the residual vinyl acetate was distilled off under reduced pressure with an aspirator, and then 26.7 parts of sodium hydroxide ethylene glycol solution (concentration 10%, molar ratio to polyvinyl acetate 0.05) was added. did. 10 minutes after the addition of the alkali catalyst, the dropping of methanol was started, and 100 ml was put into the system in 30 minutes. After the addition of the alkali catalyst, PVA fine particles were obtained by stirring for 4 hours. The sodium hydroxide in the system was neutralized by adding 3 parts of acetic acid. The glycerin / methanol mixed dispersion liquid of PVA fine particles was separated by settling the PVA fine particles by centrifugation, and washed by adding methanol for washing three times. Obtained PVA
The fine particles were dried at 120 ° C. for 2 hours. The polymerization conditions are shown in Tables 1 and 2, and the saponification conditions and the physical properties of the PVA particles are shown in Table 3.

Comparative Examples 1 to 2 The conditions shown in Table 1, Table 2 and Table 3 (propylene glycol / methanol = 6/4 and glycerin / ethanol = 5/5 are 1% by weight of the solubility of polyvinyl ester at a polymerization temperature of 40 ° C.). PVA fine particles were obtained in the same manner as in Example 11 except that the solubility was higher and the solubility of the vinyl ester monomer was higher than 30% by weight. Polymerization conditions are shown in Tables 1 and 2, saponification conditions and PVA.
Table 3 shows the physical property values of the fine particles.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

EFFECTS OF THE INVENTION According to the present invention, a non-aqueous dispersion of PVA fine particles having extremely excellent dispersion stability can be prepared, and PVA fine particles can be obtained in the form of powder by separating from the solvent. In addition, the PVA fine particles may be formed into an aqueous slurry having excellent viscosity characteristics, which is substantially insoluble in cold water through a heat treatment process if necessary, and dissolves in a drying process after coating to form a film. It is possible.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Sato, 1621 Sakata, Kurashiki, Okayama Prefecture, Kuraray Co., Ltd. (72) Inventor, Hitoshi Maruyama, 1621 Sakata, Kurashiki, Okayama

Claims (1)

[Claims] 1. A method in which a vinyl ester monomer is polymerized with stirring in a solvent having a solubility of polyvinyl ester at a polymerization temperature of 1% by weight or less and a solubility of a vinyl ester monomer of 30% by weight or less, followed by saponification. A method for producing fine particles of polyvinyl alcohol polymer.