JP3440197B2 - Method for producing flat irregular shaped fine particles and emulsion containing the fine particles - 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 producing flat irregular-shaped fine particles useful as an additive for a coating agent used for paints, papers, information recording papers, light-diffusing films and the like, an additive for cosmetics and the like.

[0002]

2. Description of the Related Art In recent years,
It is known that polymer fine particles whose particle shape is controlled can be produced by emulsion polymerization, and such fine particles are used as an additive for a coating agent.
For example, USP 4,427,836 shows that hollow particles of 0.3 to 0.6 μm can be produced by swelling alkali-swellable core particles with thermoplastic shell particles at high temperature. . The hollow fine particles produced by this method are used as a high hiding organic pigment in place of titanium oxide in water-based paints, and are also used in the field of paper coating for improving whiteness and gloss.

In addition, Japanese Patent Application Laid-Open No. 2-14222 and Abstracts of the 19th Surface Modification Workshop, pages 16 to 21 (19)
(1994), a method for producing flat fine particles having depressions on a flat surface similar to red blood cells is shown. That is, a production method is disclosed in which water, a polymerization initiator, a monomer, and a mixed emulsion containing an organic solvent are continuously added to an emulsion containing seed particles made of a vinyl polymer to carry out polymerization. It has been shown that when such flat fine particles are used in paints, cosmetics, paper coating agents, information recording papers, etc., they have excellent properties such as gloss, hiding power and whiteness.

However, in this production method, since an organic solvent such as isooctane is present in the seed particles, it is necessary to remove the water-insoluble organic solvent by steam distillation after the polymerization, which complicates the production process. There was a problem of becoming. Further, when steam distillation is not carried out, a non-water-soluble organic solvent is evaporated together with water into the atmosphere when the emulsion is dried in the coating step, which is an environmental problem.

[0005]

Means for Solving the Problems As a result of intensive investigations by the inventors of the present invention, a method for producing convex-shaped vinyl polymer irregular-shaped fine particles having depressions therein without using a water-insoluble organic solvent was obtained. Weight average molecular weight 5,000 to 15
50,000 vinyl-based polymer particles as seed particles, a (meth) acrylic acid ester-based monomer as a main component, and a monomer mixture containing a crosslinkable vinyl-based monomer are absorbed in the seed particles, Using a water-soluble polymerization initiator, a water-insoluble organic solvent
By emulsion polymerization in the absence of, it found that irregular particles of interest is obtained, and have completed the present invention.

The "flat irregularly shaped fine particles" in the present invention have a substantially circular plane shape, a convex surface, and a back surface (bottom portion).
Are irregularly shaped fine particles in which the diameter of the bottom is (D)
Is 0.3 to 5 μm, and the ratio (D / H) of this diameter (D) to the thickness (H) from the bottom to the tip of the convex surface is 1.5 to
4 means a fine particle having a concave inner surface with an inner diameter of 0.1 μm or more corresponding to the convex surface at the bottom.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The seed particles composed of vinyl-based polymer particles used in the present invention include styrene, aromatic vinyl monomers such as α-methylstyrene, methyl (meth) acrylate,
(Meth) acrylic acid ester monomers such as ethyl (meth) acrylate and butyl (meth) acrylate, vinyl acetate,
Alternatively, examples thereof include homopolymers of other copolymerizable monomers, or block, ramdam, and graft copolymers of these. Here, (meth) acrylic acid means both acrylic acid and methacrylic acid.

Incidentally, if the monomers constituting the seed particles are the same as or similar to the monomers contained in the below-mentioned monomer mixture, transparent irregular fine particles can be obtained. It is preferable because it is easy. The method for producing seed particles is not particularly limited, but methods such as emulsion polymerization, soap-free emulsion polymerization, suspension polymerization and the like can be used. Considering the uniformity of the particle size of the seed particles and the simplicity of the production method, the emulsion polymerization and soap-free emulsion polymerization methods are preferable.

The weight average molecular weight of the seed particles used in the present invention is in the range of 5,000 to 150,000 as measured by gel permeation chromatography.
It is preferably 10,000 to 80,000, more preferably 15,000 to 50,000. By adjusting the amount of polymerization initiator used or adding a molecular weight modifier,
The weight average molecular weight of the seed particles can be adjusted within this range. As the molecular weight modifier, mercaptans such as n-octyl mercaptan and t-dodecyl mercaptan, and halogenated hydrocarbons such as carbon tetrachloride can be used. The weight average molecular weight of the seed particles can also be adjusted by adjusting the addition amount of these molecular weight adjusting agents.

The weight average molecular weight of the seed particles is 150,000.
If it is larger, the degree of flatness of the obtained irregularly shaped fine particles is reduced, and spherical fine particles are mixed. That is, when the weight average molecular weight of the seed particles is larger than 150,000, the monomer absorption capacity of the seed particles becomes small, and the monomers of the monomer mixture polymerize independently without being absorbed by the seed particles. It is considered that spherical fine particles different from the above shape are generated.

On the other hand, the seed particles have a weight average molecular weight of 5,000.
If it is less than 0, it is difficult to obtain the desired seed particles even if a large amount of the molecular weight modifier is used, and the strength of the finally obtained flat irregularly shaped fine particles is lowered. The size and shape of the seed particles are not particularly limited, but spherical particles of 0.1 to 2 μm are usually used.

Examples of the (meth) acrylic acid ester-based monomer used in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate. The glass transition temperature of the polymer obtained as the flat irregular-shaped fine particles is preferably 50 ° C. or higher, more preferably 70 ° C. or higher in order to avoid adverse effects such as binding and coalescence when handled as a powder. for that purpose,
Methyl (meth) acrylate is preferred, and (meth)
50 to 97% by weight of methyl acrylate in the monomer mixture
It is preferably contained to some extent.

As the other monomer, a crosslinkable vinyl-based monomer, for example, a polymerizable vinyl group such as divinylbenzene, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, etc. is contained in 2 molecules per molecule.
A polyfunctional monomer having three or more is used. The amount of the crosslinkable vinyl monomer used in the present invention is adjusted to 3 to 15% by weight based on the total amount of the monomer mixture.

When the proportion of the crosslinkable vinyl monomer is less than 3% by weight, the degree of flattening is small and particles having a nearly spherical shape are obtained. On the contrary, the ratio of the crosslinkable vinyl monomer is 1
Similar results are obtained with greater than 5% by weight. If desired, a copolymerizable monomer other than the above may be used in combination.

Examples of such a monomer include styrene and α
-Aromatic vinyl compounds such as methylstyrene, vinyl acetate, acrylonitrile, (meth) acrylic acid, (meth)
Acrylamide, 2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate and the like can be mentioned. The amount of the monomer mixture used in the present invention is preferably 3 to 30 parts by weight, more preferably 5 to 25 parts by weight, and particularly preferably 7 to 19 parts by weight, relative to 1 part by weight of the seed particles. Is.

When the amount of the monomer mixture used is less than 3 parts by weight with respect to 1 part by weight of the seed particles, the degree of flattening of the resulting flat irregular shaped fine particles tends to be small. On the other hand, if the amount used exceeds 30 parts by weight, the monomer absorption capacity of the seed particles becomes insufficient, and the number of monomers that are not absorbed by the seed particles increases, so that fine particles other than the desired shape are obtained. Is easy to generate.

The method of adding the monomer mixture to the seed particles is not particularly limited, and the monomer can be absorbed into the seed particles by adding them all at once, or in portions or continuously. . In this invention, a water-soluble radical initiator is used as the water-soluble polymerization initiator. Examples of the water-soluble radical initiator include persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate, organic peroxides such as benzoylhydroperoxide, and 4,4′-azobis (4-cyanopentanoic acid). Azo compounds such as
Examples thereof include redox initiators such as potassium persulfate-sodium thiosulfate and hydrogen peroxide-ascorbic acid.

If an oil-soluble polymerization initiator such as benzoyl peroxide or azoisobisbutyronitrile is used in the method of the present invention, the desired flat irregular shaped fine particles cannot be obtained. The polymerization temperature is preferably 65 ° C to 90 ° C, more preferably 70 ° C to 80 ° C. If the polymerization temperature is less than 65 ° C, the degree of flattening tends to be small,
On the contrary, when the temperature exceeds 90 ° C., the polymerization initiator is easily decomposed and the polymerization initiator is deactivated, so that the polymerization is difficult to complete.

A surfactant may be used in the polymerization. Preferred surfactants are sodium alkylbenzenesulfonate, sodium alkylsulfonate,
Examples include anionic surfactants such as sodium dialkylsulfosuccinate, and nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene alkylphenyl ether. These surfactants may be used alone or in combination of two or more. Can be used in combination. When these surfactants are used, the amount used is preferably below the critical micelle concentration and as small as possible. If the amount of the surfactant used is large, particles outside the intended particle size range are likely to be generated, which is not preferable.

A dispersion stabilizer may be used in the method of the present invention. Preferred dispersion stabilizers include water-soluble polymers such as polyvinyl alcohol, hydroxyethyl cellulose and carboxymethyl cellulose. The flat irregular-shaped fine particles thus obtained have a bottom diameter (D) of 0.3 to 5 μm, and the ratio of this diameter (D) to the thickness (H) from the bottom to the apex of the convex surface. (D / H)
Is in the range of 1.5 to 4 and has a concave inner surface having an inner diameter of 0.1 μm or more corresponding to the convex surface at the center of the bottom of the particle.

Although the mechanism by which the flat irregular shaped fine particles are obtained by the method of the present invention is not clear, it is presumed as follows. First, the seed particles are in a state of absorbing the monomer and swelling. Then, since the polymerization is performed with the water-soluble polymerization initiator, the radicals generated in the aqueous phase penetrate into the monomer oil droplets from the aqueous phase. The reaction is initiated on the surface of the monomer oil droplets, but since the crosslinking monomer is contained, the outer shape of the particles is determined at a relatively low polymerization rate stage. Then, as the polymerization proceeds, the polymer of seed particles dissolved in the monomer is deposited. Further, the polymerization proceeds and the strain of polymerization shrinkage in the particles increases. Since the polymer of the precipitated seed particles has a high compatibility with the generated crosslinked polymer and the amount of the crosslinkable monomer is relatively small, voids are not formed and a depression is formed in the central portion due to polymerization shrinkage.

The present invention also provides an aqueous emulsion containing the thus obtained flat irregular-shaped fine particles. This emulsion may be the reaction mixture obtained by the above polymerization reaction as it is, or may be one in which the concentration of the solid component in the emulsion is appropriately adjusted by a known means according to the purpose of use.

Further, the emulsion may be one in which flat irregular shaped fine particles, which have been once isolated from the reaction mixture through dehydration and drying steps, are dispersed in water. In this case, a known emulsifier may be added if necessary. The flat irregular-shaped fine particles and the aqueous emulsion containing the same obtained by the present invention do not contain an organic solvent,
It is used as an additive for paints, cosmetics, etc., or as an additive for coating agents such as paper, information recording paper, light diffusing films, etc., and improves the working environment and atmospheric environment, and exhibits an excellent light diffusing effect.

[0024]

EXAMPLES The specific production method of the present invention will be described below with reference to examples, but the method of the present invention is not limited to these examples. In addition, the numerical values of the particle size, diameter, thickness, major axis, minor axis, etc. in the examples are all average values.

The method of measuring the weight average molecular weight in the examples is as follows. Measuring instrument: Gel permeation chromatography Model name: Shimadzu Corporation Chromatopack CR
4A Solvent: THF Measurement temperature: 40 ° C. Seed particles were prepared according to Synthesis Examples 1 to 8 shown below.

(Synthesis Example 1) In a separable flask equipped with a stirrer, a thermometer and a reflux condenser, 600 g of water and 10 parts of methyl methacrylate were placed.
0 g and 0.5 g of n-octyl mercaptan (n-OM) as a molecular weight modifier are charged, and the temperature is raised to 70 ° C. while substituting with nitrogen while stirring. After keeping the internal temperature at 70 ° C and adding 0.5 g of potassium persulfate as a polymerization initiator,
Polymerize for a period of time. The obtained emulsion contained 14% of solid content, and the solid component was a true spherical particle having a particle size of 0.4 μm and a weight average molecular weight of 45,000.

(Synthesis Examples 2 to 4) Table 1 shows the amount of n-OM added.
Polymerization was carried out in the same manner as in Synthesis Example 1 except that it was changed as shown in.

(Synthesis Example 5) Polymerization was carried out in the same manner as in Synthesis Example 1 except that the polymerization temperature was 80 ° C.

(Synthesis Example 6) Polymerization was carried out in the same manner as in Synthesis Example 5 except that the amount of n-OM added was 2 g.

(Synthesis Example 7) Polymerization was carried out in the same manner as in Synthesis Example 5 except that the amount of n-OM added was 5 g.

(Synthesis Example 8) In a separable flask equipped with a stirrer, a thermometer and a reflux condenser, 900 g of water, 100 g of styrene and
As a molecular weight modifier t- dodecylmercaptan (t-D
1 g of M) was charged, and the temperature was raised to 70 ° C. while substituting with nitrogen while stirring. The internal temperature is kept at 70 ° C., 1 g of potassium persulfate is added as a polymerization initiator, and then a polymerization reaction is carried out for 24 hours. The obtained emulsion contains 10% of solid content, and the solid component has a particle size of 0.5 μm and a weight average molecular weight of 75.0.
It was a true spherical particle of No. 00.

The particle size and weight average molecular weight of the polymer particles (seed particles) obtained in Synthesis Examples 1 to 8 are shown in Table 1.

[0033]

[Table 1]

Example 1 71.5 g of the emulsion produced in Synthesis Example 1 (10 g in terms of solid content as seed particles),
Sodium lauryl sulfate 0.15g, ion-exchanged water 50
0 g, 95 g of methyl methacrylate and 5 g of ethylene glycol dimethacrylate were mixed and stirred at 30 ° C. for 2 hours to allow the seed particles to absorb the monomer. Next, this mixture was heated to 70 ° C. under a nitrogen stream, 50 g of ion-exchanged water in which 0.5 g of potassium persulfate was dissolved was added as a polymerization initiator, and polymerization was carried out for 5 hours. Then, it was cooled to room temperature, suction-filtered and washed using a filter paper having a pore size of 0.8 μm, and then vacuum-dried at 60 ° C. When the obtained polymer fine particles were observed by a scanning electron microscope, the diameter of the bottom was 1.1 μm, the thickness (H) from the bottom to the apex of the convex surface was 0.6 μm, and the center of the bottom of the particle was Diameter 0.5
The particles were flat irregular-shaped fine particles having concave portions of μm. A scanning electron micrograph of the fine particles obtained in this example is shown in FIG.

Example 2 Polymerization was carried out under the same conditions as in Example 1 except that the polymerization temperature was 85 ° C. When the obtained polymer fine particles were observed with a scanning electron microscope,
The flat irregular-shaped fine particles were the same as in Example 1.

Example 3 Polymerization was carried out under the same conditions as in Example 1 except that the seed particles produced in Synthesis Example 2 were used.
When the obtained polymer fine particles were observed by a scanning electron microscope, the diameter of the bottom was 1 μm, the thickness from the bottom to the apex of the convex surface was 0.5 μm, and the diameter was 0.2 μm at the center of the bottom of the particles. It was a flat-shaped irregular-shaped fine particle having concave portions.

Example 4 The amount of methyl methacrylate was adjusted to 9
0g, the amount of ethylene glycol dimethacrylate 10
Polymerization was performed under the same conditions as in Example 1 except that g was used. Observation of the obtained polymer fine particles with a scanning electron microscope revealed that the diameter of the bottom was 1 μm, the thickness from the bottom to the apex of the convex surface was 0.5 μm, and the diameter of the center of the particle was 0.2 μm. It was a flat-shaped irregular-shaped fine particle having concave portions.

(Example 5) The amount of methyl methacrylate was adjusted to 8
5g, the amount of ethylene glycol dimethacrylate 15
Polymerization was performed under the same conditions as in Example 1 except that g was used. Observation of the obtained polymer fine particles with a scanning electron microscope revealed that the diameter of the bottom was 1 μm, the thickness from the bottom to the apex of the convex surface was 0.6 μm, and the diameter was 0.1 μm at the center of the bottom of the particles. It was a flat-shaped irregular-shaped fine particle having concave portions.

(Example 6) Polymerization was carried out under the same conditions as in Example 1 except that 3.3 g of the seed particles produced in Synthesis Example 5 were used in terms of solid content. The obtained polymer fine particles have a bottom diameter of 1.2 when observed with a scanning electron microscope.
μm, thickness from bottom to apex of convex surface is 0.6 μm
Then, it was a flat irregular shaped fine particle having a concave portion with a diameter of 0.5 μm in the center of the bottom of the particle.

Example 7 Polymerization was carried out under the same conditions as in Example 1 except that 20 g of the seed particles produced in Synthesis Example 1 was used in terms of solid content. The obtained polymer fine particles have a bottom diameter of 1.0 μm when observed with a scanning electron microscope.
m, the thickness from the bottom to the apex of the convex surface is 0.6 μm
Then, it was a flat irregular shaped fine particle having a concave portion with a diameter of 0.2 μm at the center of the bottom of the particle.

Example 8 Polymerization was carried out under the same conditions as in Example 1 except that the polystyrene particles produced in Synthesis Example 8 were used as seed particles. The obtained polymer fine particles have a bottom diameter of 1. when observed with a scanning electron microscope.
2μm, the thickness from the bottom to the apex of the convex surface is 0.5μ
m, the particles were flat irregular-shaped fine particles having a recess having a diameter of 0.5 μm in the center of the bottom of the particle.

Example 9 Polymerization was carried out under the same conditions as in Example 1 except that 75 g of methyl methacrylate, 20 g of normal butyl methacrylate and 5 g of ethylene glycol dimethacrylate were used as monomers. Observation of the obtained polymer fine particles with a scanning electron microscope revealed that the diameter of the bottom was 1.1 μm, the thickness from the bottom to the apex of the convex surface was 0.6 μm, and the diameter was 0.
The particles were flat irregular-shaped fine particles having recesses of 5 μm.

Example 10 Polymerization was carried out under the same conditions as in Example 1 except that the seed particles produced in Synthesis Example 6 were used. Observation of the obtained polymer fine particles with a scanning electron microscope revealed that the diameter of the bottom was 1.1 μm, the thickness from the bottom to the apex of the convex surface was 0.5 μm, and the diameter was 0.5 μm at the center of the particle. It was a flat-shaped irregular-shaped fine particle having concave portions.

(Example 11) Polymerization was carried out under the same conditions as in Example 1 except that the seed particles produced in Synthesis Example 7 were used. Observation of the obtained polymer fine particles with a scanning electron microscope revealed that the diameter of the bottom was 1.1 μm, the thickness from the bottom to the apex of the protrusions was 0.5 μm, and the diameter was 0.
The particles were flat irregular-shaped fine particles having recesses of 5 μm.

(Example 12) 10 g of the flat irregular-shaped fine particles obtained in Example 1 was mixed with 500 ml of sodium lauryl sulfate.
An emulsion was obtained by dispersing in 100 ml of water containing ppm.

Comparative Example 1 Polymerization was carried out under the same conditions as in Example 1 except that the seed particles produced in Synthesis Example 3 were used.
When the obtained polymer fine particles were observed with a scanning electron microscope, they were substantially spherical fine particles having a particle size of 0.9 μm, and no recesses were seen.

(Comparative Example 2) In place of potassium persulfate as the polymerization initiator in Example 1, azoisobisbutyronitrile (oil-soluble polymerization initiator) dissolved in methyl methacrylate was used. Polymerization was carried out under the same conditions as in Example 1. When the obtained polymer fine particles were observed with an electron microscope, they were found to be true spheres having a particle size of 0.7 μm.

Comparative Example 3 The amount of methyl methacrylate was adjusted to 8
Polymerization was carried out under the same conditions as in Example 1 except that the amount of ethylene glycol dimethacrylate was changed to 0 g and the amount of ethylene glycol dimethacrylate was changed to 20 g. When the obtained polymer fine particles were observed by a scanning electron microscope, the major axis was 0.9 μm and the minor axis was 0.1 μm.
It had an irregular shape of 7 μm, but the diameter was 0.1 μm.
The above concave portions were not recognized.

(Comparative Example 4) The amount of methyl methacrylate was changed to 9
Polymerization was carried out under the same conditions as in Example 1 except that the amount of ethylene glycol dimethacrylate was changed to 9 g and the amount of ethylene glycol dimethacrylate was changed to 1 g. The obtained polymer microparticles were observed by a scanning electron microscope to find that the major axis was 0.9 μm and the minor axis was 0.7.
It had a distorted shape of μm, but no recess was observed.

Comparative Example 5 10 g of seed particles produced in Synthesis Example 1 in terms of solid content, sodium lauryl sulfate 0.15
g, ion-exchanged water 500 g, styrene 95 g and divinylbenzene 5 g are mixed and stirred at 30 ° C. for 2 hours,
The seed particles were allowed to absorb the monomer. The temperature of this mixture was raised to 70 ° C. under a nitrogen stream, and 50 g of ion-exchanged water in which 0.5 g of potassium persulfate was dissolved was added as a polymerization initiator.
Polymerization was performed for 0 hours. When the obtained polymer fine particles were observed with a scanning electron microscope, they were true spherical fine particles having a particle size of 1.1 μm.

[0051]

According to the method of the present invention, flat irregular shaped fine particles can be easily produced without using a water-insoluble organic solvent. The flat irregular-shaped fine particles and the emulsion containing the fine particles obtained by the method of the present invention are used as additives for paints, cosmetics, etc. or paper, information recording paper,
It can be used as an additive of a coating agent such as a light diffusing film, and has an excellent light diffusing effect derived from a unique shape.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of flat irregular-shaped fine particles obtained by the method of Example 1.

Claims (2)

(57) [Claims] 1. A weight average molecular weight of 5,000 to 150,0.
00 in the presence of seed particles consisting of vinyl polymer particles,
(Meth) mainly composed of acrylic acid ester monomer, and a monomer mixture containing 3-15% by weight crosslinkable vinyl monomer, using a water-soluble polymerization initiator, in an aqueous medium, the non water
A method for producing flat irregular shaped fine particles, which comprises performing emulsion polymerization in the absence of a soluble organic solvent . 2. An aqueous emulsion in which the fine particles produced by the method according to claim 1 are dispersed in an aqueous medium.