JPH08188619A - Production of fine polyvinyl alcohol polymer particle - Google Patents

Abstract

PURPOSE: To produce fine polyvinyl alcohol polymer particles which are substantially insoluble in cold water, can therefore take a state of a good aqueous slurry having good viscosity properties and can dissolve and form a coating film when it is applied in the form of an aqueous slurry and dried. CONSTITUTION: A polyvinyl ester dispersed in a dispersion medium substantially insoluble in any of a polyvinyl ester, a polyvinyl alcohol and a lower alcohol with the aid of 1-50wt.%, based on the polyvinyl ester, a dispersant is saponified to obtain fine polyvinyl alcohol polymer particles.

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 polyvinyl alcohol polymer by saponifying polyvinyl ester by a specific method.

[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]

DISCLOSURE OF THE INVENTION The object of the present invention is to obtain a liquid dispersion which is substantially insoluble in cold water and maintains a good state of the aqueous dispersion, and in the drying process after coating the aqueous dispersion,
It is to provide PVA fine particles having a property of being dissolved to form a film.

[0005]

[Means for Solving the Problems] As a result of earnest studies for solving the above problems, 1 to 1
Polyvinyl alcohol-based polymer fine particles characterized by saponifying polyvinyl ester dispersed in a dispersion medium in which none of polyvinyl ester, polyvinyl alcohol and lower alcohol is substantially dissolved using 50% by weight of a dispersant. The present invention has been completed by discovering a manufacturing method of.

Next, the present invention will be described in detail.

The polyvinyl ester used in the present invention is obtained by homopolymerizing or copolymerizing vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate and vinyl pivalate. Among these, a homopolymer of polyvinyl acetate is industrially most desirable.

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) which 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.

The degree of polymerization of the polyvinyl ester is preferably 300 or more, more preferably 500 or more, as the degree of polymerization of PVA obtained by completely saponifying the polyvinyl ester, from the viewpoint of physical properties after coating the aqueous dispersion. , 700 or more is particularly preferable. The upper limit of the degree of polymerization of PVA is preferably 30,000 or less in view of easiness of industrial synthesis, and 20,000.
The following is more preferable, and 10,000 or less is particularly preferable.

The polyvinyl ester in the present invention is used in the form of a solution. As the solvent used for preparing the polyvinyl ester solution, from the viewpoint of the saponification reaction rate after dispersion, at least one of lower alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and ethylene glycol is used. It is preferable to use, and it is particularly preferable to contain methanol from the viewpoint of saponification reaction rate and industrial viewpoint. As other solvent, it is possible to dissolve polyvinyl ester,
Aromatic solvents such as benzene, toluene and chlorobenzene, ether solvents such as tetrahydrofuran and dioxane, ketone solvents such as acetone and methyl ethyl ketone, and aprotic substances such as dimethylformamide and dimethylsulfoxide, as long as the dispersibility in the dispersion medium is not impaired. You may add a solvent, an ester solvent, etc.

The concentration of the polyvinyl ester solution is not particularly limited, but when the concentration is low, the dispersibility is impaired and coarse particles are likely to occur, and when the concentration is high, the scale increases and the PVA becomes strand-like. It is easy to become 0.5, so
70 wt% is preferable, 2 to 50 wt% is more preferable, and 3 to 40 wt% is particularly preferable.

The dispersion medium in which none of polyvinyl ester, PVA and lower alcohol is substantially dissolved is, for example, one selected from aliphatic hydrocarbons, aromatic hydrocarbons and alicyclic hydrocarbons, or Examples of the mixture include octane, isooctane, nonane,
Methylcyclohexane, kerosene, liquid paraffin and the like can be mentioned. In the present invention, the phrase "the dispersion medium does not substantially dissolve the above three components" means that the solubility at 20 ° C is preferably 5% by weight or less, and more preferably 1% by weight or less.

From the viewpoint of dispersibility, the mixing ratio of the polyvinyl ester solution to the dispersion medium in which none of polyvinyl ester, PVA and polyvinyl ester is substantially dissolved is 1 to 100 parts by weight with respect to 100 parts by weight of the dispersion medium. Preferably 3 to 50 parts by weight, more preferably 5 to 30
Part by weight is especially preferred.

In the present invention, it is essential to use a dispersant, and specific examples of such a dispersant include sorbitan alkyl ester, polyoxyethylene alkyl ester, polyoxyethylene alkyl ether and polyoxyethylene alkylphenyl ether. , Nonionic surfactants such as polyoxyethylene sorbitan alkyl ester, polyoxyalkylene compounds such as polyethylene glycol and polypropylene glycol, polyvinyl ethers such as polyvinyl methyl ether and polyvinyl ethyl ether, alcohols such as polyvinyl pyrrolidone and polymethacrylamide. Solvent-soluble polymer dispersants, poly 2-ethylhexyl (meth) acrylate, polylauryl (meth) acrylate, polystearyl (meth) acrylate Long-chain alkyl (meth) acrylates, polyvinyl versatate, higher fatty acid vinyl esters such as polyvinyl 2-ethylhexanoate, and other dispersant-soluble polymer dispersants. Soluble polymeric dispersants are most preferred.
The method of adding the dispersant is not particularly limited except that it is present in the system before starting the saponification reaction, but it is mixed in advance with the polyvinyl ester solution or the dispersion medium and then mixed with the other and stirred at high speed. As a result, the method of finely dispersing is efficient and leads to miniaturization of the particle size. As a method of dispersing the polyvinyl ester, it is important to uniformly stir the entire system, and the dispersion diameter of the polyvinyl ester is not particularly limited, but 0.3 to 2
0 μm is preferable. At that time, it is possible to further improve the dispersibility by using a homogenizer or an ultrasonic homogenizer.

If the amount of the dispersant used is too small, the dispersibility will be poor, and if it is too large, it will be difficult to wash the dispersant from the PVA-based polymer obtained, so 100 parts by weight of the polyvinyl ester is used. 1 to 50 parts by weight is preferable, and 3 to
40 parts by weight is more preferable, and 5 to 30 parts by weight is particularly preferable.

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 preferably 0.005 to 0.5 from the viewpoint of the saponification reaction rate, and 0.01
˜0.2 is more preferable, and 0.02 to 0.1 is particularly preferable.

From the viewpoint of the saponification reaction rate, the lower limit of the saponification reaction temperature is preferably 20 ° C., more preferably 25 ° C., and 3
0 ° C. is particularly preferred. From the viewpoint of dispersion stability, the upper limit of the saponification reaction temperature is preferably 200 ° C, more preferably 150 ° C, and particularly preferably 100 ° C. Further, the saponification reaction temperature may be changed within a range that does not impair the stability of the dispersoid, the dispersion medium and the dispersant after the addition of the saponification catalyst. The degree of saponification of the PVA-based polymer is preferably 90 mol% or more, more preferably 95 mol% or more, in order to suppress elution when the PVA-based fine particles are made into an aqueous slurry.
98 mol% or more is particularly preferable.

The particle size of the PVA-based fine particles is 30 μ 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.
m or less, preferably 10 μm or less, more preferably 5 μm
m or less is more preferable, and 1 μm or less is particularly preferable.
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.

[0020]

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.

(Solubility of PVA fine particles in warm water) The dissolution time at 90 ° C. was measured for a 5% aqueous slurry of PVA fine particles obtained by adding PVA fine particles to water and stirring.

(Cold water solubility of PVA fine particles) A 5% aqueous slurry of PVA fine particles obtained by adding PVA fine particles to water and stirring was stirred at 20 ° C. for 30 minutes, and then the PVA fine particles were separated by centrifugation. PV in the supernatant
A concentration was measured and calculated.

Example 1 20 parts of a methanol solution of polyvinyl acetate having a degree of polymerization of 700 (concentration 40%) in 100 parts of liquid paraffin, molecular weight 1
Add 0.5 parts of 00000 polyvinylpyrrolidone,
Polyvinyl acetate was finely dispersed by stirring at 0 ° C. at 300 rpm for 5 minutes with a peller. Next, the molar ratio to polyvinyl acetate (hereinafter, abbreviated as PVAc) is 0.
05 sodium hydroxide solution in methanol (concentration 10
%) 1.6 parts and saponified at 40 ° C. for 1 hour to obtain PVA fine particles. Next, the washing operation of neutralizing sodium hydroxide in the dispersion medium with 0.2 part of acetic acid and then adding hexane to the PVA fine particles obtained by centrifugation and performing centrifugation was repeated 3 times. 1 PVA fine particle after washing
It was dried at 20 ° C. for 2 hours. Table 2 shows the physical property values of the obtained PVA fine particles.

Examples 2 to 7 PVA fine particles were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were changed. Table 2 shows the physical property values of the PVA fine particles.

Comparative Example 1 20 parts of a methanol solution of polyvinyl acetate having a degree of polymerization of 2000 (concentration 40%) was added to 100 parts of liquid paraffin, and a Peller stirring was carried out at 300 rpm for 5 minutes at 40 ° C. without adding a dispersant. As a result, polyvinyl acetate was finely dispersed. Next, a methanol solution of sodium hydroxide with a molar ratio of 0.05 to polyvinyl acetate (concentration 10%) 1.
Add 6 parts and saponify at 40 ° C for 1 hour to produce PV
A fine particles were used. Next, sodium hydroxide in the dispersion medium was neutralized with 0.2 part of acetic acid and then centrifuged to obtain P
The washing operation of adding hexane to the VA particles and centrifuging was repeated 3 times. The washed PVA fine particles were dried at 120 ° C. for 2 hours. Table 2 shows the physical property values of the obtained PVA fine particles.
Shown in

Comparative Example 2 PVA having a degree of polymerization of 1700 and a degree of saponification of 99 mol% obtained by saponification by a conventional method was pulverized with a jet mill (an ultrasonic jet pulverizer manufactured by Nippon Pneumatic Mfg. Co., Ltd.) and then at 100 ° C. It was re-dried for 2 hours to obtain PVA fine particles. Table 2 shows the physical property values of the PVA fine particles.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

According to the present invention, the aqueous slurry is substantially insoluble in cold water, the good state of the aqueous slurry is maintained, the aqueous slurry has good viscosity characteristics, and in the drying process after coating the aqueous slurry. Provides PVA fine particles having the property of dissolving to form a film. The PVA fine particles of the present invention, particularly an aqueous slurry containing PVA fine particles as a dispersoid,
It can be applied to various fields such as paper coating agents, fiber sizing agents, and adhesives.

Claims (1)

[Claims] 1. Saponification of polyvinyl ester dispersed in a dispersion medium in which none of polyvinyl ester, polyvinyl alcohol and lower alcohol is substantially dissolved, using a dispersant of 1 to 50% by weight based on polyvinyl ester. A method for producing fine particles of a polyvinyl alcohol-based polymer, comprising: