JPH0640951B2 - Method for producing uniformly coated composite particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a composite particle in which the surface of a core particle composed of inorganic particles or polymer particles is uniformly coated with shell-forming particles composed of inorganic particles or polymer particles. And a method for producing composite particles, in which the composite particles are used as core particles and further uniformly coated with shell-forming particles one or more times.

[Prior art and its drawbacks] Conventionally, an inorganic material and a resin have been blended to improve workability, improve physical properties, impart heat resistance, impart flame retardancy, improve chemical resistance and electrical properties. Has been. However, since it is difficult to disperse the inorganic fine particles in the resin by simply mixing the resin and the inorganic fine particles, there is a drawback that a non-uniform composite is obtained and thus various characteristics are uneven. Further, as an improved method, (a) mechanochemical modification in which a monomer is grafted or a polymer is grafted while being cut depending on the activity of a new surface while pulverizing an inorganic substance, and (b) using a high-energy electron beam For example, there is a method of modifying by binding a vinyl polymer to the surface of the inorganic particles, or (c) a method of adsorbing a polymerization initiator, a monomer, a polymer, etc. on the inorganic material, and then modifying by suspension or emulsion polymerization. However, these modification methods have the drawback that the coating cannot be performed uniformly and the process becomes complicated. In particular, (C) has a drawback that the yield is low because the resin is not sufficiently complexed with the inorganic substance, and only a large amount of the polymer is produced.

[Means for Solving the Problems] In view of the necessity and the problem of such a modifying method, the present inventors not only uniformly coat the surface of the inorganic particles with the polymer particles, but also As a result of earnest research to obtain a composite particle in which the particles are uniformly coated, or the inorganic particles are uniformly coated with the inorganic particles, or the polymer particles are uniformly coated with the polymer particles, the oppositely charged particles are identified. The present invention has been completed by discovering that composite particles can be obtained which are extremely strongly and uniformly coated by mixing under the conditions.

That is, the present invention, (A) a core particle composed of charged inorganic particles or polymer particles, and (B) a particle diameter smaller than the core particles, and for forming a shell composed of oppositely charged inorganic particles or polymer particles. The ratio of the particle diameter of the shell-forming particles to the particle diameter of the core particles (particle diameter of the core particles / particle diameter of the forming particles) (P) is 1.7 <P <120 and the shell-forming The particle number ratio (R) obtained by dividing the number of particles for use by the number of core particles is A composite in which core particles are uniformly coated with shell-forming particles, which are mixed in a dispersion state under the condition that [a = average radius of core particles, b = average radius of particles for shell-forming] It is a method for producing particles, and a method for producing composite particles in which multi-layer coating is performed by repeating the method a plurality of times.

[Description of Configuration] In the present invention, the inorganic particles or polymer particles, the requirements to make a composite particle uniformly coated with other inorganic particles or polymer particles, (1) particles to be coated (hereinafter, shell The forming particles are smaller than the particle diameter of the particles to be coated (hereinafter referred to as core particles), and the ratio of the particle diameter of the shell forming particles to the particle diameter of the core particles (particle diameter of core particles / shell forming particles). Value (P) is 1.7 <P ≦ 12
Must be 0.

Therefore, the narrower the particle size distribution, the more uniform the coating.

(2) Shell-forming particles and core particles must be mixed in a dispersion state.

(3) The shell-forming particles and the core particles must be oppositely charged. To that end, the pH of the dispersion may be an important point.

(4) The forming particles and the core particles may be either inorganic particles or polymer particles. However, in practice, composite particles obtained by coating inorganic particles with polymer particles or composite particles obtained by coating polymer particles with inorganic particles are preferable.

(5) The most important requirement for uniform coating is the ratio of the particle numbers of shell-forming particles and core particles, that is, the particle number ratio (R) obtained by dividing the number of shell-forming particles by the number of core particles. It is to satisfy the following formula.

N × 2 ≧ R ≧ N × 0.5 N: Number of shell-forming particles required to cover the surface of one core particle in the closest packing P: Surface area of one core particle when the shell-forming particle is covered = radius (a + b) Sphere = 4π (a + b) ² ……
(FIG. 1) Q: Occupy per shell-forming particle when the shell-forming particle covers the surface of the core particle at the closest density. In the present invention, the uniform coating does not need to be the densest coating, and it is important that the coating is uniform without unevenness. For that purpose, (R) must be 50% or more, preferably 70% or more of N. This is shown in FIG. 3 as a model diagram.

When (R) is less than 50% of N, the exposed portion becomes large, and thus large aggregates are formed. This is shown in FIG. 4 as a model diagram. That is, other core particles adhere to each other through the positive particles that are sparsely covered by the negative ionicity of the exposed core particles, and agglomerate into large aggregates. The upper limit of (R) is 200%, and since the extra shell-forming particles are only floating inadvertently, practically,
150% or less is suitable.

The inorganic particles used in the present invention include gold, silver, copper, iron,
Suitable are metal powders such as aluminum, metal oxides such as silica, alumina, iron oxide, titanium oxide and zinc oxide, salts such as calcium carbonate, calcium oxalate and barium sulfate. Therefore, it is suitable that these inorganic particles have an average particle size of 0.005 to 100 μm.

The polymer particles used in the present invention include polyvinyl acetate,
Polyacrylic acid ester, polyethylene, polypropylene, polystyrene, vinyl acetate-ethylene copolymer,
Vinyl acetate- (meth) acrylic acid ester copolymer,
Thermoplastic polymer particles such as styrene- (meth) acrylic acid ester copolymer and vinyl acetate-Veoba (vinyl ester manufactured by Shell Chemical Co., Ltd.) copolymer, polyester, epoxy resin, urea resin, melamine resin, silicone resin, fluororesin Such as thermosetting polymer particles. It is suitable that these polymer particles have an average particle size of 0.01 to 50 μm.

An aqueous dispersion is most preferable as a dispersion of these particles, but a non-aqueous dispersion may be used as long as it contains water that can dissociate into ions. The non-aqueous solvent that can be used is preferably a non-polar organic solvent such as cyclohexane, heptane or hexane.

In order to make a dispersion liquid of inorganic particles, the above-mentioned inorganic substance is crushed and dispersed in water or a non-aqueous solvent containing water by a known method such as three rolls, pebble mill, ultrasonic dispersion, or by a colloid sol synthesis method. Just synthesize them.

In this way, a dispersion liquid of inorganic particles having a particle diameter of 0.005 to 100 μm is obtained.

The obtained dispersion liquid is positively or negatively charged depending on the type of the inorganic substance, but in some cases, the ζ potential is changed by changing the pH, and thus it is changed to negative or positive. Such charges are
It is provided by hydrogen ions, hydroxide ions, potential determining ions, or counterions with high valence. Its strength can be measured as the ζ potential. The same applies to polymer particles described later.

The dispersion liquid of polymer particles can be prepared by an emulsion polymerization method or a suspension polymerization method. It can also be made by post-emulsifying the polymer. In this way the average particle size
A dispersion liquid of polymer particles in the range of 0.01 to 50 μm is obtained.
“The obtained dispersion liquid can be positively or negatively charged depending on the composition and the production method. As a method for charging, a cationic or anionic monomer, and a polymerization initiator which gives a positive or negative polymer terminal, and A method is used in which either a cationic or anionic polymerizable emulsifying agent is selectively used alone or in combination, and radical polymerization is optionally carried out together with a nonionic monomer or other emulsifying agent.

Examples of the cationic monomer include diethylaminoethyl methacrylate and dimethylaminoethyl methacrylate, and examples of the anionic monomer include acrylic acid and methacrylic acid. Each of these ionic monomers may be polymerized alone,
It may also be used in combination with other ionic monomers.

In order to charge with only the ionic monomer, it is preferable to use 0.01 part by weight or more, especially 0.2 part by weight or more of the ionic monomer with respect to 100 parts by weight of the nonionic monomer. If the amount is less than 0.01 parts by weight, the amount of charge of the obtained particles is insufficient and the particles cannot be used for the purpose of the present invention.

Examples of the polymerization initiator that gives a positive polymer terminal include 2,2'-azobis (2-amidinopropane) hydrochloride. Examples of the polymerization initiator that gives a negative polymer terminal include sodium persulfate, potassium persulfate, and ammonium persulfate. These polymerization initiators are 0.01 to 2 with respect to 100 parts by weight of the radical polymerizable monomer.
Preference is given to using 0 parts by weight, especially 0.2 to 10 parts by weight.

Further, a polymerization initiator which does not give a positive or negative polymer terminal,
For example, benzoyl peroxide, lauryl peroxide and the like may be used in combination.

As the cationic polymerizable emulsifier, there is a synthetic compound of alkyldimethylammonium chloride and an allyl ether compound, and as the anionic polymerizable emulsifier,
Examples thereof include alkali salts of alkylallyl sulfosuccinate and alkali salts of vinyl sulfonic acid. Of course, you may use together with another emulsifier.

However, an emulsion polymer obtained by a so-called soap-free polymerization method, which is polymerized using a polymerizable emulsifier or no emulsifier at all, is particularly suitable for producing uniformly coated composite particles. Is.

In order to produce the composite particles of the present invention, the case of producing composite particles in which inorganic particles are uniformly coated with polymer particles will be described as an example. For example, the composite particles are dispersed in water and have an average particle diameter of 1.5.
Inorganic particles such as silica particles of μm are selected as core particles, an acid or a base is added to the surface of the core particles to charge them positively or negatively, and the mixture is stirred and mixed to adjust the pH, and the desired charge, for example, negatively charged. Next, polystyrene particles having an average particle diameter of 0.3 μm dispersed in water, which are positively charged at the same pH, are selected as the shell-forming particles. In this case, N is 130. 130 ×
If both dispersions are adjusted and mixed so that 0.5 = 65 or more, and gently stirred for 10 minutes to 2 hours, the shell-forming particles adhere to the core particles extremely uniformly and firmly, and the inorganic particles are removed. A dispersion liquid of composite particles uniformly coated with polymer particles is obtained.

When mixing both dispersions, adding an inorganic electrolyte such as potassium sulfate, magnesium chloride, aluminum chloride is considered to bring about an increase in coverage because the inorganic electrolyte reduces the shadow effect of the shell-forming particles. .

Further, by using the polymer particle dispersion liquid produced by the soap-free method, it is possible to coat more uniformly and strongly.
It is considered that this is because the polymer dispersion does not contain polymer substances such as polyvinyl alcohol and methyl cellulose, and other so-called emulsifiers, so that the coating does not hinder these.

Further, according to the present invention, it is possible to produce particles in which the composite is further multilayered. As a method for producing the same, the particle surface obtained by the above is positively or negatively charged, and the dispersion liquid of the uniformly coated composite particles has a particle diameter smaller than that of the composite particles, and is oppositely charged. The dispersion liquid of the inorganic particles or polymer particles may be added and gently mixed with stirring.

By repeating this operation, composite particles coated in more layers can be obtained.

[Effect] The formation mechanism by which the composite particles uniformly coated according to the present invention are obtained is considered to be due to electrostatic interaction between the surface charge of the core particles and the opposite charge of the shell-forming particles. When dispersions having opposite charges are mixed with each other, aggregation and precipitation occur. However, according to the present invention, a dispersion liquid in which the composite particles coated extremely uniformly are stably dispersed individually without aggregation is obtained. Even if the particles may settle due to the specific gravity of the particles, they can be easily redispersed by simply shaking them. Further, the coating is extremely strong and shows an excellent effect that the shell-forming particles are hardly detached even by washing with water several times. This is because the value (P) and the particle number ratio (R) of the particle diameters of the core particles and the shell-forming particles to be added are limited.

After the completion of the composite particles, if the charges of the particles attached to the core particles and the particles attached to the particles are maintained with different signs, there is almost no desorption,
It becomes a stable dispersion system of the composite particles stabilized by the charge of the adhered particles.

Next, the present invention will be described with reference to production examples, examples and comparative examples.

Production Example 1 Volume 2 equipped with stirrer, reflux condenser, dropping funnel, thermometer
In a four-necked flask, 36.1 g of water, 28% ammonia water 280.
After adding 4 g and 793 g of ethanol and stirring, 58.3 g of ethyl altosilicate was added and stirred for 30 minutes. Then 466.6 g
Ethyl orthosilicate was added and stirred, and then dialyzed to obtain a solid content of 1
An aqueous silica colloidal dispersion having 9.2% and an average particle diameter of 1.59 μm was obtained.

Production Example 2 Water in a four-necked flask similar to that used in Production Example 1 was used.
50 g and 17.5 g of diethylaminoethyl methacrylate are added, and hydrochloric acid is added so that the pH of this mixed solution becomes 1.2.
Then, 158.6 g of styrene and 3.5 g of potassium persulfate were added, the atmosphere was replaced with nitrogen, the temperature was raised to 70 ° C., and a polymerization reaction was carried out for 6 hours. After cooling, aggregates were removed and dialyzed to obtain a latex having a solid content of 9.8% and an average particle size of 0.25 μm.

Production Example 3 Water in a four-necked flask similar to that used in Production Example 1 was used.
12 g, acrylamide 14 g, dimethylformamide 168 g,
Sodium chloride (4 g) and potassium persulfate (6 g) were added, the atmosphere was replaced with nitrogen, and the temperature was raised to 70 ° C. to carry out a polymerization reaction for 1 hour. Next, 280 g of styrene was added and the polymerization reaction was carried out at 70 ° C for 4 hours, then 14 g of diethylaminoethyl methacrylate was added.
In addition, the polymerization reaction was further performed for 1 hour. After cooling, aggregates were removed and dialyzed to obtain a latex having an average particle size of 1.8 μm.

Production Example 4 Water in a four-necked flask similar to that used in Production Example 1 was used.
40g, styrene 310g, potassium persulfate 0.12g, 70 ℃
The temperature was raised to and the polymerization reaction was carried out for 8 hours. After cooling, aggregates were removed and dialyzed to obtain a latex having an average particle size of 0.44 μm.

Production Example 5 Water in a four-necked flask similar to that used in Production Example 1 was used.
Add 00g, 93g of diethylaminoethyl methacrylate, 52g of styrene, 18.5g of Latemur K-180 (Cationic polymerizable emulsifier manufactured by Kao Soap Co., Ltd.), heat to 80 ° C, and add V-50.
(Wako Pure Chemical Industries, Ltd., product name of 2,2'-azobis (2-amidinopropane) hydrochloride) 5% aqueous solution 30g,
The polymerization reaction was carried out for 5 hours. After cooling, remove agglomerates,
A latex having an average particle size of 0.06 μm was obtained.

Production Example 6 Water in a four-necked flask similar to that used in Production Example 1 was used.
00g, styrene 70g, methylmethacrylate 70g, ketamine 86P conc (cationic emulsifier manufactured by Kao Soap Co., Ltd.) 1
2 g was added, the temperature was raised to 70 ° C., 28% of a 5% aqueous solution of V-50 was added, and a polymerization reaction was carried out for 6 hours. After cooling, the agglomerates were removed to obtain a latex having a particle size of 0.1 μm.

The relationship between pH and charge of the particles of Production Examples 1 to 6 is as shown in Table 1.

Example 1 The silica colloidal dispersion obtained in Production Example 1 was diluted to 5% with water, 2.0 g of the diluted solution was adjusted to pH 6 with hydrochloric acid, and gently stirred. This diluted colloidal dispersion was negatively charged. Separately, the latex obtained in Production Example 2 was diluted to 2% with water,
The pH was adjusted to 6 with hydrochloric acid. This diluted latex was positively charged.

1.74g of this diluted latex. It was gradually added to the diluted colloidal dispersion and gently stirred to obtain a dispersion of composite particles in which inorganic particles were uniformly coated with polymer particles. This dispersion was positively charged. At this time, the particle number ratio (R) is about 100% of N.

When observed under a microscope, the surface of the silica colloid particles was sufficiently uniformly covered with the latex particles, and even if it settled by standing, it was easily redispersed by shaking gently.

Example 2 The latex obtained in Production Example 3 was diluted to 10% with water and p-diluted with hydrochloric acid.
Adjusted H to 5. This diluted latex was positively charged.

Separately, a 10% dispersion of Snowtex 0 (silica sol manufactured by Nissan Chemical Industries, Ltd.) having an average particle diameter of 0.015 μm was adjusted to pH 5. This Snowtex dispersion was negatively charged. 0.42 g of this dispersion was added to 10 g of the diluted latex and gently stirred to obtain a dispersion of composite particles in which polymer particles were uniformly coated with inorganic particles. At this time, the particle number ratio (R) is about 60% of N. When observed with a scanning electron microscope, the surface of the latex particles was sufficiently uniformly covered with silica particles, and even if it settled by standing, it was easily redispersed by only shaking gently.

Example 3 A 10% dispersion of Snowtex 0 having an average particle diameter of 0.015 μm was adjusted to pH 4. This Snowtex dispersion was negatively charged. 0.19 g of this snowtex dispersion was gradually added to 10 g of the dispersion of positively charged silica colloid / latex composite particles obtained in Example 1 and gently stirred to uniformly coat with polymer particles. The inorganic particles were further uniformly coated with the inorganic particles to obtain a dispersion liquid of the multilayer composite particles.

When the charge of this dispersion liquid was measured by an electrophoretic device, it showed the same negative charge as the added silica colloid, demonstrating that multilayer composite particles were formed. Even if it settled by standing, it was easily redispersed by only shaking gently.

Example 4 The latex obtained in Preparation Example 3 was diluted to 10% with water and the pH was adjusted to 6.5.
Adjusted to. This diluted latex was positively charged.

Separately, titanium oxide JR (manufactured by Teikoku Kako Co., Ltd. average particle size 0.3
μm rutile type titanium oxide) was dispersed in water with a ball mill to prepare a 5% aqueous dispersion, and the pH was adjusted to 6.5. This dispersion was negatively charged.

47 g of this dispersion was added to 10 g of the diluted latex and gently stirred to obtain a dispersion of composite particles in which polymer particles were uniformly coated with inorganic particles.

When observed under a microscope, the surface of the latex particles was sufficiently uniformly coated with titanium oxide particles, and even if it settled by standing, it was easily redispersed by shaking gently.

Example 5 In Example 1, with the diluted latex, 0.1 mol /
Example 1 except that 1 g of an aqueous potassium sulfate solution was added.
In the same manner as above, a dispersion liquid of the composite particles in which the inorganic particles were uniformly coated with the polymer particles was obtained.

Even if it settled by standing, it was easily redispersed by shaking gently. When observed under a microscope, the surface of the silica colloidal particles was very densely covered with the latex particles. When these composite particles were collected by sedimentation and the ratio of silica and latex resin was examined by a differential thermal analysis method, about 10% more latex resin than that obtained in Example 1 was detected.
This is considered to be due to the action of potassium sulfate.

Example 6 The latex obtained in Production Example 4 was diluted to 5% with water and adjusted to pH with hydrochloric acid.
Was adjusted to 5. This latex was negatively charged.

Separately, the latex obtained in Production Example 2 was diluted to 5% with water, and the pH was adjusted to 5 with hydrochloric acid. This latex was positively charged.

This positively charged latex (76 g) and the negatively charged latex (10 g) are mixed and gently stirred to obtain a dispersion liquid of composite particles in which polymer particles are uniformly coated with polymer particles. I got it.

When the obtained composite particles were measured by an electrophoresis apparatus, they had a positive potential, and it was observed under a microscope that the small latex particles covered the large latex particles uniformly.

Example 7 The silica colloidal dispersion obtained in Production Example 1 was diluted to 5% with water, and 100 g of the diluted solution was taken and the pH was adjusted to 7 with hydrochloric acid. This diluted colloidal dispersion was negatively charged.

Separately, the latex obtained in Production Example 5 was diluted to 2% with water, and the pH was adjusted to 7 with sodium hydroxide. This diluted latex was positively charged. 32.8 g of this diluted latex was gradually added to the above-mentioned diluted colloidal dispersion and gently stirred to obtain a dispersion of composite particles in which inorganic particles were uniformly coated with polymer particles. The particle number ratio (R) at this time is about 2 of N.
Hits 00%.

Observing the obtained composite particles with a scanning electron microscope,
The surface of the silica particles was sufficiently uniformly covered with the latex particles, and the composite particles settled by standing were easily redispersed by shaking gently.

Comparative Example 1 Example 1 was repeated except that the pH of the system was adjusted to 9. At this time, the silica colloid was negatively charged, and the latex was also negatively charged.

In the mixed solution, silica colloid and latex were individually dispersed, and no silica particles were coated with latex.

Comparative Example 2 In Example 1, the amount of diluted latex added was 1.74 g to 0.3
Example 1 was repeated except that the amount was changed to 5 g. The particle number ratio (R) at this time was about 20% of N.

When observed under a microscope, silica colloid and latex were aggregated to form many large aggregates, and almost no silica particles were uniformly coated with latex particles.

Comparative Example 3 In place of 32.8 g of the diluted latex used in Example 7, the latex obtained in Production Example 6 was diluted to 2% with water and the pH was adjusted to 7 with sodium hydroxide.
The same procedure as in Example 7 was repeated except that g was changed. At this time, the silica colloid was negatively charged and the latex was positively charged. When observing the mixed particles with a scanning electron microscope,
Some silica particles were covered with 10 to 20 latex particles, but most of the silica particles were covered with only a few latex particles.

Comparative Example 4 Instead of the Snowtex 0 used in Example 2, the silica colloidal dispersion obtained in Production Example 1 was diluted with water to 10%.
The same procedure as in Example 2 was repeated, except that 250 g of the diluted dispersion liquid whose pH was adjusted to 5 was used. At this time, the particle number ratio
(R) was about 100% of N, and the particle diameter ratio value (P) was 1.13.

When observed under a microscope, latex and silica colloid aggregated to form a large number of large aggregates, and almost no latex particles were uniformly coated with silica particles.

Comparative Example 5 Comparative Example 4 except that the silica colloidal dispersion obtained in Production Example 1 was diluted to 10% with water and the pH of the diluted dispersion was adjusted to 5 to 125 g. It carried out similarly to. At this time, the particle number ratio (R) was about 50% of N.

When observed under a microscope, latex and silica colloid aggregated to form a large number of large aggregates, and almost no latex particles were uniformly coated with silica particles.

Table 2 is a summary of the production specifications and results for the examples and comparative examples.

[Brief description of drawings]

FIG. 1 and FIG. 2 are drawings for explaining calculation of the number N of shell-forming particles required to cover the surface of one core particle most closely, but the area where the dotted line in FIG. 1 makes one rotation 2 is P, and FIG. 2 shows the area Q occupied by one shell-forming particle.
Indicates. FIG. 3 is a model diagram of the uniformly coated composite particles, and FIG. 4 shows the aggregated state of the sparsely coated composite particles. In addition, in the reference numerals used in the drawings, 1
Is a core particle, and 2 is a shell-forming particle. or,
Indicates a positive charge and indicates a negative charge.

Claims (3)

[Claims] 1. A shell for forming (A) core particles composed of charged inorganic particles or polymer particles, and (B) a smaller particle size than the core particles and composed of oppositely charged inorganic particles or polymer particles. The ratio of the particle diameter of the shell-forming particles to the particle diameter of the core particles (particle diameter of the core particles / particle diameter of the shell-forming particles) (P) is 1.7 <P ≦ 120, and the shell The particle number ratio (R) obtained by dividing the number of forming particles by the number of core particles is The method for producing composite particles, wherein the core particles are uniformly coated with the shell-forming particles, characterized in that they are mixed in a dispersion state under the condition. 2. A shell formation comprising I (A) core particles composed of charged inorganic particles or polymer particles, and (B) a core particle composed of smaller particle diameters than the core particles and oppositely charged inorganic particles or polymer particles. For particles, the ratio (P) of the particle diameter of the shell-forming particles to the particle diameter of the core particles (particle diameter of the core particles / particle diameter of the shell-forming particles) is 1.7 <P ≦ 120, and The particle number ratio (R) obtained by dividing the number of shell-forming particles by the number of core particles is Under the condition that the above condition is satisfied, particles in which the core particles are uniformly coated with the shell-forming particles by mixing in a dispersion state are used as secondary core particles, and the secondary core particles and the II particle diameter are larger than those of the secondary core particles. Particle ratio (R ') obtained by dividing the number of secondary shell-forming particles by the number of secondary core-forming particles with secondary shell-forming particles composed of inorganic particles or polymer particles that are small and oppositely charged.
But The method for producing composite particles, wherein secondary core particles are uniformly coated with secondary shell-forming particles, characterized in that mixing in a dispersion state is repeated one or more times under the condition. 3. The method for producing composite particles according to claim 1 or 2, wherein the polymer particles are obtained by a soap-free manufacturing method.