JPH0471081B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for obtaining fine powders of polymers or copolymers containing methyl methacrylate, styrene or acrylonitrile in a substantially impurity-free state.

As a method for producing fine powder polymers, an emulsion polymerization method using an anionic emulsifier, a cationic emulsifier, or a nonionic emulsifier is generally used. According to this method, the dispersed particle size of the polymer emulsion is reduced to 0.1.
It can be controlled within the range of ~1 μm.
However, since an emulsifier coexists in this type of emulsion, it is technically extremely difficult to recover polymer particles from the emulsion without containing an emulsifier. Therefore, the fine powder polymer produced by the emulsion polymerization method described above usually contains an emulsifier, and contamination of the fine powder polymer with the emulsifier can be avoided by using the polymer. This has an undesirable impact on the final product.

By the way, a so-called soap-free emulsion polymerization method is known as a method for obtaining a hard polymer by performing heterogeneous polymerization in an aqueous medium without using an emulsifier. According to this method, it is possible to obtain a polymer that does not contain impurities such as emulsifiers, but since this method does not use emulsifiers or emulsion stabilizers, the polymer particles in the reaction system are
When it grows to 0.3 μm or more, the emulsion becomes unstable and aggregates occur. Therefore, in practice, polymerization must be carried out under limited conditions, such as emulsion polymerization in a diluted state so as not to hinder production. The powder obtained is also 0.1 to 0.3 μm.
Only a limited amount of fine powder can be obtained. Of course,
These disadvantages can be overcome by using an appropriate amount of water-soluble polymer as an emulsion stabilizer during polymerization, and thereby the polymer particle size in the emulsion can be controlled within the range of 0.1 to 1 μm. In addition, a considerable degree of freedom is obtained in the practical polymerization conditions.

However, the use of water-soluble polymers has the same problems as the use of emulsifiers, and it is not possible to prevent water-soluble polymers from contaminating the polymer particles recovered from the emulsion after the polymerization reaction. Incidentally, the polymer particles can be separated from the aqueous medium by passing through the emulsion after the polymerization reaction, and a fine powder polymer can be obtained by drying the polymer particles. However, the fine powder thus obtained is contaminated with impurities other than the intended polymer, and these impurities cannot be removed even if the polymer particles are repeatedly washed with water.
From this, impurities contaminating polymer particles are
It is presumed that the water-soluble polymer, monomer, and initiator decomposition product used in emulsion polymerization are water-insoluble by-products that are involved in a complex manner. Contamination of the combined particles or the finely powdered polymer is undesirable because it adversely affects the final product using the finely divided polymer.

As a result of repeated research into methods for producing finely powdered polymers that do not contain impurities, the present inventors have discovered that monomers that provide hard polymers can be used in emulsion polymerization methods that only use water-soluble polymers as emulsion stabilizers. By polymerizing or copolymerizing to produce an emulsion of polymer particles, drying the polymer particles produced from this emulsion, and then crushing and classifying this in a jet mill, a fine powder polymer containing no impurities can be obtained. We obtained the knowledge that this can be obtained.

That is, the method for producing a finely powdered polymer according to the present invention involves the use of one or more monomers selected from methyl methacrylate, styrene, and acrylonitrile in the presence or absence of other monomers capable of emulsion copolymerization therewith. Below, an emulsion of polymer particles is prepared by emulsion polymerization in an aqueous medium in which a water-soluble polymer is dissolved as a protective colloid, and the polymer particles are collected from this emulsion and dried.
Thereafter, it is crushed in a jet mill and then classified.

In the method of the present invention, since the polymer particles obtained by emulsion polymerization are separated from impurities by mechanical means, it is preferable that the polymer constituting the particles is hard. Typically, one or more selected from methyl methacrylate, styrene and acrylonitrile are used. However, other monomers that can be emulsion copolymerized with the above monomers can also be used, provided that the glass transition temperature (Tg) of the resin obtained by copolymerization is 40°C or higher. Examples include acrylic esters having an alkyl group having 8 or less carbon atoms, methacrylic esters, vinyl acetate, acrylic acid, methacrylic acid, itaconic acid, maleic acid, acrylamide,
Examples include N-methylol acrylamide, diacetone acrylamide, dimethylaminoethyl methacrylate, divinylbenzene, and ethylene glycol dimethacrylate.

The emulsion polymerization of the present invention is carried out in an aqueous medium in which about 0.01 to 5 wt% of a water-soluble polymer is dissolved, and the aqueous medium does not contain a synthetic surfactant-based emulsifier. The water-soluble polymer of the present invention contributes to the emulsion stability of monomer and polymer particles and functions as a protective colloid, and includes polyvinyl alcohol, polyacrylamide, polyacrylic acid and its salts, polymethacrylic acid and its salts, In addition to polyethylene oxide, polyvinyl pyrrolidone, polyvinyl methyl ether, etc., carboxymethyl cellulose,
Gelatin, casein, etc. can be used.

For other emulsion polymerization conditions, the conditions normally employed in conventionally known emulsion polymerization methods can also be employed in the present invention. For example, as a polymerization initiator, a persulfate such as potassium persulfate, ammonium persulfate, or A redox system that combines these with a reducing agent such as sodium thiosulfate can be employed. Further, the reaction temperature can be about 40°C to 90°C. A desired monomer and a polymerization initiator are added to an aqueous medium in which a water-soluble polymer is dissolved, and the mixture is heated while stirring to initiate a polymerization reaction, and the reaction system is maintained at the desired reaction temperature for about 2 to 6 hours. The emulsion polymerization of the present invention is completed by maintaining the temperature at .

The emulsion of polymer particles obtained by emulsion polymerization is then dried. In this case, the emulsion may be subjected to a filtration or centrifugal separation operation to separate the polymer particles from the dispersion medium and then dried, but the emulsion may also be dried with hot air or spray dried to obtain dry particles. . As mentioned above, the polymer particles obtained in this way are contaminated with water-insoluble impurities,
This impurity cannot be removed by normal means.

Therefore, in the present invention, the dried polymer particles are crushed in a jet mill to separate impurities that have contaminated the polymer particles from the polymer particles. That is, when the dried polymer particles are crushed with an ultrafine pulverizer such as a jet mill, since the polymer of the present invention is hard, the particle size (primary particle size) is reduced to the size that was dispersed in the emulsion. The impurities are then separated from the polymer particles according to the invention. Moreover, since there are differences in shape and physical properties between polymer particles and impurities, it is possible to distinguish between the fine powder polymer of the present invention and impurities. Either a jetomizer or a micronizer can be used as a jet mill, but no matter which jet mill is used, the operating conditions must be selected to crush the polymer particles into primary particles. Of course. By classifying the crushed product in the jet mill, the fine powder polymer, which is the object of the present invention, can be obtained as a fine powder component with good purity.

The fine powder polymer obtained by the method of the present invention can be used in paste resins for plastisols, powder anti-blocking agents, powder fluidity improvers, body lubricants, rubber compounding agents, cosmetics, abrasives, and thickeners. agents, plastic pigments, retention agents for fragrances and pesticides, materials and super-aids, gelling agents, flocculants, additives for paints, gloss modifiers, molding materials and modifiers, oil absorbers, mold release agents, for chromatography The finely powdered polymer of the present invention can be used in a wide range of applications such as fillers and microencapsulation aids, and when dissolved in organic solvents, it can be used as a coating agent for preventing migration of PVC plasticizers, a heat-resistant coating agent, and a weather-resistant coating agent. It can also be used as a coating agent.

In the Examples and Comparative Examples shown below, "parts" means "parts by weight."

Example 1 Distilled water was added to a 1-volume separable flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser.
Add 200 parts, 0.2 parts of polyvinyl alcohol, and 100 parts of methyl methacrylate (MMA), and under a nitrogen stream,
Under constant stirring, add 0.3 parts of a polymerization initiator, potassium persulfate (KPS), and adjust the temperature of the reaction system.
Polymerization was initiated by raising the temperature to 65°C. Thereafter, the temperature of the reaction system was maintained at 82°C, and the polymerization was completed in about 3 hours. The dispersed particle size of the obtained emulsion is the average
It was 1 μm. This emulsion was dried by leaving it in a hot air dryer kept at 70°C overnight to obtain a white powder.

Next, this white powder is crushed with a jet mill (using compressed air, nozzle pressure 3 to 10 Kg/cm ² ), and then classified with a cyclone separator to convert more than 80% of the white powder into fine powder components with a particle size of 2 μm or less. The remainder was separated as a coarse powder component with a particle size of 2 to 50 μm. The average particle size of the fine powder component was 1 μm. A polymer solution prepared by dissolving 10 parts of this fine powder component in 90 parts of toluene was completely transparent and no undissolved matter was observed.

On the other hand, a polymer solution prepared by dissolving 10 parts of the coarse powder component in 90 parts of toluene was translucent, and precipitation of undissolved substances was observed. When this precipitate was taken out and analyzed, it was confirmed that it was a modified product of polyvinyl alcohol.

Comparative Example 1 The white powder obtained in Example 1 was ground with a ball mill and then classified with a vibrating sieve to obtain a powder that passed through 400 meshes. A polymer solution prepared by dissolving 10 parts of this powder in 90 parts of toluene was translucent, and the presence of precipitates was observed. When this precipitate was collected and analyzed, it was found to be a denatured product of polyvinyl alcohol.

Example 2 300 parts of distilled water, 0.2 parts of polyvinyl alcohol, 100 parts of MMA, and 0.5 parts of lauryl mercaptan were placed in the same apparatus as in Example 1, and 0.3 parts of the polymerization initiator KPS was added under constant stirring under a nitrogen stream. Add
The temperature of the reaction system was raised to 65°C to initiate polymerization. Thereafter, the temperature of the reaction system was maintained at 75°C, and the polymerization was completed in about 5 hours. The average dispersed particle size of the obtained emulsion was 0.3 μm. This emulsion was left overnight in a hot air dryer kept at 70°C to obtain a white powder.

Next, the white powder was crushed under the same conditions as in Example 1 and then classified, with 85% or more of the white powder being fine powder components with a particle size of 1 μm or less (average particle size 0.3 μm), and the remainder having a particle size of 1 to 50 μm. It was obtained as a coarse powder component. The sheet obtained by press-molding this fine powder component was transparent.

On the other hand, the sheet obtained by press-molding the coarse powder component was milky white.

Comparative Example 2 The white powder obtained in Example 2 was ground with a ball mill and then classified with a vibrating sieve to obtain a fine powder that passed through 400 meshes. A sheet obtained by press-molding this fine powder was milky white.

Example 3 200 parts of distilled water, 0.2 parts of polymethacrylic acid, 50 parts of MMA, and 50 parts of styrene were placed in the same apparatus as in Example 1, and under constant stirring under a nitrogen stream, 0.3 parts of polymerization initiator KPS was added. The temperature of the reaction system was maintained at 80°C, and the polymerization was completed in about 6 hours.
The average dispersed particle size of the obtained emulsion was 0.5 μm.
It was hot.

The emulsion was passed through a cloth to obtain an agglomerate-free emulsion, which was then introduced in cocurrent with air into a spray dryer equipped with two nozzles, yielding a fine white powder at an exit temperature of 65°C.

This white powder was crushed using a jet mill, and the crushed particles were classified using a classifier. The fine powder classified by the classifier has an average particle size of 0.5 μm and 95% of the particles are 2 μm or less.
It included the above. A polymer solution prepared by dissolving 10 parts of this fine powder in 90 parts of toluene was completely transparent and no undissolved substances were observed.

On the other hand, the coarse powder removed by the classifier had a particle size of 2 to 100 μm, and a polymer solution prepared by dissolving 10 parts of this coarse powder in 90 parts of toluene was translucent, and insoluble matter was precipitated. When this precipitate was taken out and analyzed, it was confirmed that it was a modified product of polymethacrylic acid.

Comparative Example 3 The white powder obtained by spray drying in Example 3 was redispersed in water, filtering was repeated, and the powder was washed with water.
The water-washed powder was left to dry overnight in a hot air dryer at 70°C to obtain a white powder. A polymer solution prepared by dissolving 10 parts of this white powder in 90 parts of toluene was translucent, and insoluble matter was precipitated. Analysis of this precipitate confirmed that it was a modified polymethacrylic acid.

Example 4 500 parts of distilled water, 0.2 parts of polyvinyl alcohol, and 100 parts of MMA were placed in the same apparatus as in Example 1, and a polymerization initiator was added under constant stirring under a nitrogen stream.
0.3 part of KPS was added and polymerization was carried out at 82°C for 2 hours.
After 2 hours, 3 parts of MAA was added without lowering the reaction temperature, and the polymerization was continued for an additional 1 hour to complete the polymerization. The dispersed particle size of the obtained emulsion is the average
It was 0.15 μm. This emulsion was introduced in parallel with air into a spray dryer equipped with two nozzles to obtain a fine white powder at an exit temperature of 65°C.

This white powder was crushed using a jet mill, and the crushed particles were classified using a classifier. The fine powder classified by the classifier contains more than 90% of fine particles with a particle size of 0.3 μ or less, and the polymer composition is MMA/MMA = 100/3
It was hot. Add 10 parts of this fine powder to 45 parts of MEK and 45 parts of toluene.
The polymer solution dissolved in the above mixed solvent was completely transparent and no undissolved matter was observed.

On the other hand, the coarse powder removed by the classifier has a particle size of 1 μm to 30 μm, and a polymer solution made by dissolving 10 parts of this coarse powder in a mixed solvent of 45 parts of MEK and 45 parts of toluene is translucent and contains no insoluble matter. It was precipitated. When this precipitate was analyzed, it was confirmed that it was a modified product of polyvinyl alcohol.

Claims (1)

[Claims] 1. An aqueous polymer containing one or more monomers selected from methyl methacrylate, styrene, and acrylonitrile in the presence or absence of other monomers that can be emulsion copolymerized with the monomer, and a water-soluble polymer dissolved as a protective colloid. A method for producing a finely powdered polymer, which comprises preparing an emulsion of polymer particles by emulsion polymerization in a medium, drying the polymer particles produced from this emulsion, and then crushing this with a jet mill and classifying it. .