JPH11199604A - Production of spherical fine particle of vinyl-based polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing fine particles having a fixed average particle diameter free from coarse particles and agglomerated particles. SOLUTION: A polyfunctional monomer containing two or more vinyl groups and a vinyl-based monomer are subjected to suspension polymerization in an aqueous medium containing a slightly water-soluble inorganic salt and an anionic surfactant. At the stage of 10-40% polymerization ratio of the vinyl-based monomer, the anionic surfactant is added to the polymerization reaction system to produce spherical fine particles of a vinyl-based polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suspension polymerization method for obtaining spherical fine particles of a vinyl-based crosslinked polymer free from coarse particles and aggregated particles.

[0002]

2. Description of the Related Art In recent years, spherical fine particles of a crosslinked polymer, particularly spherical fine particles having an average particle diameter of 1 to 50 .mu.m,
It is widely used in the fields of toners, matting agents for paints, light diffusing agents for resins, and the like. Such spherical fine particles are usually produced by seed emulsion polymerization, dispersion polymerization, suspension polymerization, or the like.

[0003] However, in the seed emulsion polymerization, it is necessary to repeat the seed emulsion polymerization a plurality of times in order to obtain particles having a particle size of about 1 to 5 µm.
Obtaining particles of m or more is substantially difficult. In addition, it is difficult to obtain particles having an average particle size of 10 μm or more even in dispersion polymerization, and when particles having a mean particle size of 10 μm or less are used, a solvent such as alcohol is used, so that the production cost is high and it is not industrial.

Further, in the suspension polymerization, particles can be produced at a low cost. However, in order to obtain particles having an average particle diameter of 100 μm or less, droplets are produced while repeating dispersion and collision under high shear. Agglomerates and coarse particles are still likely to form. On the other hand, in the case of producing fine particles of a crosslinked polymer by polymerizing a polyfunctional monomer having two or more vinyl groups (crosslinking agent) and a vinyl monomer, in the case of seed emulsion polymerization, the monomer is coated on the particle surface. Since the layer becomes rich and the viscosity increases, and the surface of the particles is not smooth in dispersion polymerization, the generated particles tend to aggregate. Further, even if particles having a desired particle size are formed, the amount of cross-linking is limited, so that the cross-linked fine particles cannot be used in fields requiring solvent resistance and the like. Moreover, it is difficult to expect reproducibility. In particular, when performing a suspension polymerization by adding a crosslinking agent,
Droplets become unstable by the addition of the crosslinking agent, and aggregated particles and coarse particles are more likely to be generated than when no crosslinking agent is added.

[0005] When aggregated or coarse particles, particularly amorphous aggregates, are used as a slipperiness imparting agent for cosmetics or the like, the slipperiness is reduced because the aggregates are not spherical,
In addition, when used as a matting agent for paints, agglomerates cause roughness and variations in design. Therefore, it is necessary to remove agglomerated particles and coarse particles from the fine particles obtained by the polymerization reaction, and various tasks are required for classification and the like.

Various methods have been proposed to solve such a problem. For example, in JP-A-52-47881, JP-A-52-47882 and JP-A-52-51483, a vinyl monomer is subjected to suspension polymerization in an aqueous medium in the presence of a sparingly soluble phosphate. At this time, a nonionic surfactant is used as a suspending aid, and an anionic surfactant, a sparingly soluble phosphate, and a water-soluble polymer protective colloid are added during the polymerization, so that the particle size of the polymer particles is reduced. A method for narrowing the diameter distribution is disclosed.

In Japanese Patent Application Laid-Open No. 3-64308, when a styrene monomer is subjected to suspension polymerization in an aqueous medium containing a hardly water-soluble inorganic salt and a neutral water-soluble inorganic salt, an anion There is disclosed a method of narrowing the particle size distribution of polymer particles by adding a surfactant and a poorly water-soluble inorganic salt. However, even in these methods, since a nonionic surfactant or a water-soluble inorganic salt is used as a suspending aid,
There is a disadvantage that it is difficult to produce fine particles of 100 μm or less.

[0008]

Conventionally, fine particles of a crosslinked polymer consisting of a polyfunctional monomer having two or more vinyl groups (crosslinking agent) and a vinyl monomer have been produced by suspension polymerization. Was difficult. An object of the present invention is to provide a method for producing crosslinked spherical fine particles in which no aggregated particles and coarse particles are formed by suspension polymerization.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventor has found that a vinyl crosslinking agent and a vinyl monomer are prepared in an aqueous medium containing a poorly water-soluble inorganic salt and an anionic surfactant. Add a polymerization initiator to the mixture with, and polymerize under high shear,
The inventors have found that by adding an anionic surfactant during the polymerization reaction, it is possible to obtain crosslinked fine particles free of coarse particles and aggregated particles, and thus completed the present invention.

That is, the present invention relates to a polyfunctional monomer having two or more vinyl groups (crosslinking agent) in an aqueous medium containing a poorly water-soluble inorganic salt and an anionic surfactant as a suspending aid. In suspension polymerization of the vinyl monomer and the vinyl monomer, by adding an anionic surfactant to the reaction mixture at a stage where the polymerization rate of the vinyl monomer is 10 to 40%,
An object of the present invention is to provide a method for producing vinyl polymer fine particles, characterized by obtaining spherical fine particles free from coarse particles and aggregated particles.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. As the vinyl monomer used in the present invention,
Although not particularly limited, acrylates such as methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methacrylates such as methyl methacrylate, butyl methacrylate, hexyl methacrylate, styrene, p-methylstyrene, α -Aromatic vinyl monomers such as methylstyrene, vinyl acetate, acrylonitrile and the like. Further, as a vinyl monomer, another monomer which is mainly composed of (meth) acrylic acid ester and can be copolymerized therewith can be used. The effect of the present invention is particularly remarkable in the suspension polymerization of a monomer having a (meth) acrylic acid ester as a main component and a polyfunctional monomer having two or more vinyl groups.

The polyfunctional monomer having two or more vinyl groups used as a crosslinking agent in the present invention is not particularly limited, but ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Divinylbenzene and the like. The amount of the polyfunctional monomer used is preferably about 0.3 to 15% by weight based on the vinyl monomer.

When the amount of the polyfunctional monomer used is less than 0.3% by weight, the resulting vinyl polymer fine particles have insufficient solvent resistance and thermal stability, and such fine particles are not matted for coating. It is difficult to expect a desired effect when used for an agent or a light diffusing agent. If the amount used exceeds 15% by weight, it is difficult to obtain a sufficient aggregation-preventing effect even if an anionic surfactant is added during the polymerization.

The poorly water-soluble inorganic salt used in the present invention is not particularly limited, and examples thereof include poorly water-soluble tertiary calcium phosphate, calcium carbonate, magnesium carbonate, pyrophosphate and the like. Calcium and pyrophosphate are particularly preferred. The amount of the poorly water-soluble inorganic salt to be used is usually about 0.2 to 20% by weight, preferably about 0.5 to 10% by weight, based on the vinyl monomer.

If the amount of the hardly water-soluble inorganic salt is less than 0.2% by weight, the dispersion stability of the obtained fine particles is poor, and large amounts of coarse particles may be formed or poor dispersion may occur. . On the other hand, if the amount exceeds 20% by weight, the viscosity of the whole polymerization reaction system becomes too high to exhibit thixotropic properties, and it is difficult to obtain the effect of stirring.

The anionic surfactant used in the present invention is not particularly limited, but includes sodium alkyl sulfate, sodium α-olefin sulfonate, sodium alkyl benzene sulfonate, sodium alkyl naphthalene sulfonate, sodium dodecyl benzene sulfonate, And sodium lauryl sulfate. The initial amount of the anionic surfactant is usually 0.00
About 2 to 0.5% by weight, preferably 0.005 to
It is about 0.3% by weight.

The amount of the anionic surfactant used is 0.
If the content is less than 002% by weight, the average particle size of the obtained particles is less likely to be 100 μm or less even if the suspension is stirred with high shear. The system monomer may be dissolved in water and emulsified. The polymerization initiator used in the present invention is not particularly limited, and examples thereof include peroxide catalysts such as benzoyl peroxide and lauroyl peroxide, and azo catalysts such as azobisisobutyronitrile.

The anionic surfactant added during the polymerization of the present invention includes the same ones as the anionic surfactant added to the aqueous medium before the polymerization reaction. May also be of different types.
The timing of adding the anionic surfactant during the polymerization is preferably when the polymerization rate of the vinyl monomer is in the range of about 10 to 40%. If an anionic surfactant is added when the polymerization rate of the vinyl monomer is less than 10%, the effect of preventing aggregation is inferior, and an emulsion is likely to be produced. In addition, the polymerization rate is 40
%, The effect of preventing aggregation is hardly obtained even if an anionic surfactant is added.

The polymerization rate of the vinyl monomer is about 10 to 40%
The amount of anionic surfactant used at the stage of
Usually about 0.001 to 0.5% by weight based on the aqueous medium is preferable. When the amount of the anionic surfactant is 0.0
When the amount is less than 01% by weight, the effect of preventing the aggregation of particles is not sufficient, and when the amount exceeds 0.5% by weight, an emulsion is undesirably formed in the polymerization reaction system.

In the suspension polymerization, the peripheral velocity at the tip of the stirring blade is preferably 0.6 m / s or more. If the peripheral velocity is lower than this, spherical fine particles having a target average particle diameter of 100 μm or less are obtained. It is hard to be. The shape of the stirring blade may be any of a fan turbine, a Fadler type, etc., and the stirring blade may have one stage or a plurality of stages.

The average particle size of the spherical fine particles obtained by the present invention is in the range of about 1 to 100 μm.

[0022]

EXAMPLES The method of the present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. The average particle diameter and the size of the coarse particles in the following Examples and Comparative Examples are values measured by a Coulter counter (manufactured by Coulter Co., Ltd.), and the presence or absence of agglomeration of particles is based on the result of observation with a microscope. The presence or absence of the coarse particles was determined by the presence or absence of particles having a particle size three times or more the average particle size.

The measurement conditions using the Coulter counter are as follows. Equipment used: Coulter Coulter Multisizer

Example 1 In a jacketed 5-liter autoclave equipped with a stirrer, 30 g of magnesium pyrophosphate as a poorly water-soluble inorganic salt and 1.5 g of sodium lauryl sulfate as an anionic surfactant were added to water 3.
An aqueous medium dissolved in kg was added. Aside from this,
990 g of methyl methacrylate, 10 g of ethylene glycol dimethacrylate and 5 g of azobisisobutyronitrile
Was added to prepare a monomer solution, and this monomer solution was placed in the above autoclave. While maintaining the temperature in the autoclave at 70 ° C., the peripheral velocity at the tip of the stirring blade is 5.0 m / s.
When the rate of polymerization reached 20%, 1.5 g of sodium dodecylbenzenesulfonate was added as an anionic surfactant, and suspension polymerization was further performed for 6 hours. The reaction mixture was cooled, filtered, the residue was washed and dried to obtain fine particles. The obtained fine particles had an average particle size of 6.7 μm, no coarse particles having a particle size of 20 μm or more, and no aggregated particles were observed. FIG. 1 shows a micrograph of the obtained fine particles.

Table 1 shows the measurement results of the particle size distribution.
The graph is shown in FIG.

[0026]

[Table 1]

Example 2 Fine particles were produced in the same manner as in Example 1, except that 10 g of trimethylolpropane trimethacrylate was used instead of ethylene glycol dimethacrylate. The obtained fine particles had an average particle size of 8.2 μm, had no coarse particles of 20 μm or more, and did not show any aggregated particles.

Example 3 The peripheral velocity at the tip of the stirring blade was 2.5
Fine particles were produced by performing the same operation as in Example 1 except that m / s was set. The obtained fine particles have an average particle diameter of 27.
4 μm, no coarse particles of 80 μm or more, and no aggregated particles were observed.

Comparative Example 1 Fine particles were produced in the same manner as in Example 1, except that sodium dodecylbenzenesulfonate added during the polymerization was added when the polymerization rate reached 5%. A large amount of emulsion was formed in the obtained fine particles, and aggregated particles were also observed.

Comparative Example 2 Fine particles were produced in the same manner as in Example 1, except that sodium dodecylbenzenesulfonate added during the polymerization was added when the polymerization rate reached 50%. Most of the obtained fine particles were aggregated. FIG. 3 shows a micrograph of the obtained fine particles.

Comparative Example 3 The peripheral velocity at the tip of the stirring blade was 0.3
Fine particles were produced by performing the same operation as in Example 1 except that m / s was changed. The obtained fine particles have an average particle size of 25.
0 μm, and the target fine particles of 100 μm or less were not obtained.

[0032]

According to the method of the present invention, fine particles free of aggregated particles and coarse particles can be obtained by suspension polymerization, so that it is not necessary to classify and remove the coarse particles and aggregated particles, and the desired average particle diameter can be obtained. In addition, fine particles having a narrow particle size distribution can be easily produced. Further, in the method of the present invention, since an organic dispersant such as polyvinyl alcohol is not used as the dispersant, it is possible to avoid adverse effects on the final product due to the dispersant remaining on the surface of the formed particles.

[Brief description of the drawings]

FIG. 1 is a micrograph of the fine particles obtained in Example 1.

FIG. 2 is a graph showing the particle size distribution of the fine particles obtained in Example 1.

FIG. 3 is a micrograph of the particles obtained in Comparative Example 2.

Claims (8)

[Claims] Claims: 1. A polyfunctional monomer having two or more vinyl groups and a vinyl monomer are subjected to suspension polymerization in an aqueous medium containing a poorly water-soluble inorganic salt and an anionic surfactant. A method for producing spherical fine particles of a vinyl polymer, comprising adding an anionic surfactant to a polymerization reaction system at a stage where the polymerization rate of the system monomer is 10 to 40%. 2. The spherical fine particles have an average particle diameter of 1 to 100 μm.
2. The method of claim 1, wherein m. 3. The method according to claim 1, wherein the spherical fine particles do not contain particles having a particle diameter three times or more the average particle diameter. 4. The method according to claim 1, wherein the amount of the polyfunctional monomer having two or more vinyl groups is 0.3 to 15% by weight based on the vinyl monomer. . 5. The method according to claim 1, wherein the suspension polymerization is carried out while stirring at a peripheral speed of the stirring blade tip of 0.6 m / s or more. 6. The method according to claim 1, wherein the vinyl monomer is mainly composed of an acrylate or a methacrylate. 7. The method according to claim 1, wherein the vinyl monomer is an acrylate or a methacrylate. 8. The method according to claim 1, wherein the poorly water-soluble inorganic salt is poorly water-soluble tribasic calcium phosphate or pyrophosphate.