JP5399886B2 - Method for producing hollow inorganic particles, and hollow inorganic particles - Google Patents

Description

  The present invention relates to a method for producing hollow inorganic particles in which inorganic particles are present in the hollow part, and hollow inorganic particles.

  Inorganic particles are widely used as fillers for various resin materials. In recent years, a method for synthesizing hollow inorganic particles used as a light diffusion filler among inorganic particles has been proposed (see Patent Document 1). Patent Document 1 discloses a hollow inorganic particle having an outer shell part and an inner shell part that is in contact with the outer shell part and forms a convex part toward the center. The hollow inorganic particles are obtained by firing silica composite polymer particles. Silica composite polymer particles are produced by forming a polymer portion derived from a polymerizable vinyl monomer using aqueous colloidal silica as a starting material, and then forming a polyalkoxysiloxane portion by polymerization of a polyalkoxysiloxane oligomer. Yes.

International Publication No. 2007-037202 Pamphlet

  This invention is made | formed by discovering that the hollow inorganic particle in which an inorganic particle exists in a hollow part can be manufactured from organoalkoxysilane as a starting material. The objective of this invention is providing the manufacturing method and hollow inorganic particle of a hollow inorganic particle in which an inorganic particle exists in a hollow part.

  In order to achieve the above object, according to the first aspect of the present invention, the first monomer containing the first polymer in the droplet state is formed by polymerizing the first monomer containing the organoalkoxysilane. A second monomer containing a vinyl monomer other than vinylalkoxysilane is brought into contact with the first particle in the emulsified state with respect to the first particle and the second particle. A second particle forming step of forming second particles having absorbed the body, a polymerization step of forming polymer particles by polymerizing the second monomer absorbed by the second particles, and a polyorgano The gist is to include a coating step of obtaining coated polymer particles by forming a siloxane film on the polymer particles, and a firing step of firing the coated polymer particles.

  According to this method, the organic component contained in the coated polymer particles is removed by the firing step. At this time, an outer shell of an inorganic component is formed from the polyorganosiloxane film. Here, the polymer produced from the second monomer includes a vinyl polymer produced from a vinyl monomer other than vinylalkoxysilane. A hollow portion is formed by removing organic components mainly contained in the vinyl polymer. At this time, inorganic particles derived from the first monomer are formed inside the hollow inorganic particles.

  According to a second aspect of the present invention, in the method for producing hollow inorganic particles according to the first aspect, the coating step includes a dispersion of the polymer particles and an organoalkoxysilane as a raw material for the polyorganosiloxane coating. In the mixed solution, the organoalkoxysilane is hydrolyzed and condensed in the presence of a basic catalyst, and the dispersion of the polymer particles is a dispersion obtained by performing a polymerization reaction in the polymerization step. It is a summary.

  According to this method, the polymer particles are subjected to the coating step as a dispersion obtained in the polymerization step, so that the dispersibility of the polymer particles can be easily maintained, so that aggregation of the resulting coated polymer particles is suppressed. Become so.

  According to a third aspect of the present invention, in the method for producing hollow inorganic particles according to the first or second aspect, the coating step comprises using an organoalkoxysilane as a raw material for the polyorganosiloxane coating in the presence of a basic catalyst. Hydrolyzing and condensing under the first stage to form droplets of the organoalkoxysilane condensate and to attach the droplets of the organoalkoxysilane condensate to the outer surface of the polymer particles, and the condensation proceeds And the second stage of solidifying the droplets of the organoalkoxysilane condensate.

  According to this method, in the first stage, the formation of solid polyorganosiloxane particles is suppressed by attaching the polyorganosiloxane droplets to the polymer particles. By carrying out the second stage in this state, it becomes possible to form a polyorganosiloxane film while suppressing the formation of solid fine particles of polyorganosiloxane.

  Invention of Claim 4 is a manufacturing method of the hollow inorganic particle of Claim 3, WHEREIN: In the said coating process, the addition amount of the said basic catalyst in the said 1st step is a raw material of the said polyorganosiloxane film. The content is 0.015 mol or less per 1 mol of the organoalkoxysilane.

According to this method, it is possible to significantly suppress the formation of polyorganosiloxane solid fine particles.
Invention of Claim 5 is a hollow inorganic particle obtained by the manufacturing method as described in any one of Claim 1 to 4, Comprising: It originates in a hollow part from the said 1st monomer. The gist is that inorganic particles exist.

The gist of the invention according to claim 6 is that, in the hollow inorganic particles according to claim 5, the hollow portion is closed by the outer shell.
The gist of the invention according to claim 7 is that, in the hollow inorganic particles according to claim 5, the outer surface of the outer shell has an opening communicating with the hollow portion.

  According to said method, the hollow inorganic particle of Claims 5-7 can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and hollow inorganic particle of a hollow inorganic particle in which an inorganic particle exists in a hollow part can be provided.

The optical micrograph which shows the hollow inorganic particle obstruct | occluded by the outer shell. (A) And (b) is an electron micrograph which shows the hollow inorganic particle obstruct | occluded by the outer shell. (A) And (b) is an electron micrograph which shows the cross-sectional structure of the hollow inorganic particle obstruct | occluded by the outer shell. (A) And (b) is an electron micrograph which shows the cross-sectional structure of the hollow inorganic particle obstruct | occluded by the outer shell. (A) And (b) is an electron micrograph which shows the hollow inorganic particle which has opening in an outer shell. (A) And (b) is a hollow inorganic particle obstruct | occluded by the outer shell, Comprising: The electron micrograph which shows an example which changed the conditions of the coating | coated process (1st step).

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail.
The method for producing hollow inorganic particles of the present embodiment includes a coating step of obtaining coated polymer particles by forming a polyorganosiloxane film on the polymer particles, and a firing step of firing the coated polymer particles.

  The polymer particles include a first particle forming step for forming first particles including the first polymer in a droplet state, and second particles for forming second particles in which the second monomer is absorbed by the first particles. It is manufactured through a forming step and a polymerization step in which the second monomer absorbed in the second particles is polymerized.

  In the first particle forming step, the first monomer containing organoalkoxysilane is polymerized. Examples of the organoalkoxysilane include at least one selected from the following general formula (1) and general formula (2).

R ¹ _n —Si— (OR ² ) _4-n (1)
In the general formula (1), R ¹ is a non-hydrolyzable group, an alkyl group having 1 to 20 carbon atoms, (meth) acrylic alkyl group having 1 to 20 carbon atoms having acryloyloxy group or epoxy group, the carbon number An alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms, R ² represents an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 or 2 When there are a plurality of R ^{1 s} , each R ¹ may be the same as or different from each other, and each OR ² may be the same as or different from each other.

Si- (OR ³ ) ₄ (2)
In General Formula (2), R ³ represents an alkyl group having 1 to 6 carbon atoms, and each OR ³ may be the same as or different from each other.

  In the first particle forming step, after dissolving the first monomer containing the organoalkoxysilane in an aqueous solvent, a basic catalyst is added to hydrolyze and condense the organoalkoxysilane in the aqueous solvent.

  Examples of the aqueous solvent include a mixed solvent of water and a water-miscible organic solvent, or water. Examples of the water-miscible organic solvent include lower alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone, dimethyl ketone and methyl ethyl ketone, and ethers such as diethyl ether and dipropyl ether. These water-miscible organic solvents may be mixed with water alone or in combination of two or more.

  The basic catalyst for hydrolysis and condensation includes at least one of ammonia and amine. Examples of the amine include monomethylamine, dimethylamine, monoethylamine, diethylamine, and ethylenediamine. These basic catalysts may be used alone or in combination of two or more. Among the catalysts, ammonia is preferable from the viewpoint of low toxicity, easy removal from the particles, and low cost.

  Examples of the reaction form of hydrolysis and condensation using a basic catalyst include a mixed homogeneous reaction or a two-layer reaction. The mixed homogeneous reaction is a reaction in which after the first monomer containing the organoalkoxysilane and the basic catalyst are dissolved in an aqueous solvent, the solution is stirred and hydrolyzed and condensed. In this mixed homogeneous reaction, the pH at the start of the reaction is preferably 9.7 to 11.7, more preferably 9.7 to 11.2. And reaction is advanced until it falls in the range of 0.7-1.5 rather than pH at the time of reaction start. The pH at the end of the reaction is, for example, in the range of 9.0 to 11.0. The reaction temperature in the mixed homogeneous reaction is appropriately set according to, for example, the type of organoalkoxysilane, but is preferably in the range of 0 to 50 ° C, for example.

  In the two-layer reaction, an organoalkoxysilane having a specific gravity (23 ° C.) of 1 or less is used as a raw material. In the two-layer reaction, the organoalkoxysilane is hydrolyzed at the interface between the organoalkoxysilane and the aqueous solution while maintaining the two-layer state formed from the organoalkoxysilane and the aqueous solution in which the basic catalyst is dissolved. Allow to condense. At this time, you may stir in the range which maintains the state of two layers. The addition amount of the basic catalyst is not particularly limited, but it is preferable to set the addition amount so that the pH of the lower layer is in the range of, for example, 9.0 to 12.0. By such a two-layer reaction, the upper organoalkoxysilane is hydrolyzed and transferred to the lower layer, and polyorganosiloxane fine particles are generated in the lower layer. Although the reaction temperature in a two-layer system reaction is suitably set according to the kind of organoalkoxysilane, for example, the range of 0-50 degreeC is suitable, for example.

  As described above, a dispersion of the first particles can be obtained by hydrolyzing and condensing the first monomer containing the organoalkoxysilane. The first particles contain polyorganosiloxane in a droplet state.

  The first monomer may contain a monomer other than the organoalkoxysilane. As a monomer other than the organoalkoxysilane, for example, a vinyl monomer (however, excluding the above vinylalkoxysilane) may be mentioned.

  The content of the organoalkoxysilane in the first monomer is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably relative to the total molar amount of the first monomer. Is 70 mol% or more. The average particle diameter of the first particles is preferably in the range of 0.1 to 100 μm, for example.

  In the second particle forming step, a second monomer containing a vinyl monomer is brought into contact with the first particle in an emulsified state. Such a second monomer is capable of forming oil droplets of an oil-in-water emulsion.

  A vinyl monomer other than vinylalkoxysilane is polymerized in the polymerization step, and then, most of the vinyl monomer is removed by the firing step, thereby forming hollow portions of the hollow inorganic particles. The vinyl monomer other than vinylalkoxysilane is not particularly limited as long as it can form a polymer that becomes a base material of the coating when forming the coated polymer particles, that is, a solid polymer. Examples of vinyl monomers other than vinylalkoxysilane include aromatic vinyl monomers, (meth) acrylic acid ester monomers, and vinyl ester monomers. In addition, the (meth) acrylic acid ester monomer indicates an acrylic acid ester monomer and a methacrylic acid ester monomer.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-ethylstyrene.

  Examples of (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, β-hydroxyethyl acrylate, β-aminoethyl acrylate, N , N-dimethylaminoethyl acrylate, γ-hydroxypropyl acrylate, and methacrylate monomers corresponding to these acrylate monomers.

  The vinyl monomer is preferably a monofunctional vinyl monomer from the viewpoint of easy removal of an organic component derived from the vinyl monomer in the firing step of firing the polymer particles. That is, when a polyfunctional vinyl monomer is used, a polymer having a high degree of polymerization is likely to be formed, and thus it may be difficult to remove the organic component.

  Examples of the polyfunctional vinyl monomer include (meth) acrylates of polyhydric alcohols and divinyl monomers. Examples of polyhydric alcohol (meth) acrylates include ethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, ethylene glycol dimethacrylate, glycerol dimethacrylate, glycerol trimethacrylate, trimethylolpropane trimethacrylate, and polyethylene glycol dimethacrylate. Is mentioned. Examples of the divinyl monomer include divinylbenzene, divinylxylene, and divinylnaphthalene.

  These vinyl monomers may be used alone or in combination of two or more. The second monomer may contain a monomer other than the vinyl monomer. Examples of the monomer other than the vinyl monomer include the above organoalkoxysilane. The content of the vinyl monomer in the second monomer is preferably 50 mol% or more, more preferably 60 mol% or more, and further preferably 70 mol% or more.

  The amount of the second monomer added is not particularly limited. As addition amount of vinyl-type monomers other than vinyl alkoxysilane, Preferably it is 0.1-5000 mass parts with respect to 100 mass parts of organoalkoxysilane added as a 1st monomer, More preferably, it is 1-3000. It is a range that becomes a mass part.

  A 2nd monomer is made into an emulsified state by disperse | distributing to an aqueous dispersion medium with an emulsifier. Examples of the aqueous dispersion medium include a mixed solvent of water and a water-miscible organic solvent, or water. Examples of the water-miscible organic solvent include lower alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone, dimethyl ketone and methyl ethyl ketone, and ethers such as diethyl ether and dipropyl ether. These water-miscible organic solvents may be mixed with water alone or in combination of two or more.

  As the emulsifier, an emulsifier having the second monomer as the oil phase of the oil-in-water emulsion can be appropriately selected and used, for example, using the HLB value (hydrophilic / lipophilic balance value) as an index. As the emulsifier, for example, an alkyl sulfate having an alkyl group having 6 to 30 carbon atoms is preferably used. Examples of the alkyl sulfate salt include potassium salt, sodium salt, ammonium salt and the like. The amount of the emulsifier is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, with respect to 100 parts by mass of the first monomer. When the compounding quantity of an emulsifier exceeds 100 mass parts with respect to 100 mass parts of monomers, there exists a possibility that a 1st monomer may become difficult to be absorbed by 1st particle | grains.

  In the present embodiment, the emulsion is brought into an emulsified state together with a radical polymerization initiator that initiates radical polymerization of the vinyl monomer contained in the second monomer. The type of radical polymerization initiator is not particularly limited, and examples thereof include azo polymerization initiators such as 2,2′-azobisisobutyronitrile and peroxides such as benzoyl peroxide. The addition amount of this radical polymerization initiator is preferably in the range of 0.001 to 20 mol, more preferably 0.01 to 10 mol with respect to 1 mol of the monomer.

  In order to make the second monomer into an emulsified state, for example, it is obtained by mixing the second monomer, the aqueous dispersion medium, the emulsifier, and the radical polymerization initiator using a stirrer such as a homogenizer. The oil-in-water emulsion thus obtained and the first particles are mixed to bring the emulsified second monomer into contact with the first particles.

  In this way, the second particles are formed by absorbing the second monomer into the first particles. That is, the first particles become seed particles and the second particles grow. In the obtained dispersion liquid of the second particles, second particles having a particle diameter larger than that of the first particles are confirmed in the particle diameter measurement.

  The time for absorbing the second monomer in the second particle forming step is preferably less than 24 hours. When the absorption time exceeds 24 hours, the productivity is lowered, and the stability of the second particles is lowered. As a result, the particles may be aggregated or the particle size distribution may be polydispersed.

  Subsequently, in the polymerization step, the radical polymerization reaction of the vinyl monomer is started by heating the dispersion of the second particles to a predetermined temperature according to the type of the radical polymerization initiator. By such radical polymerization reaction, a dispersion of polymer particles is obtained.

  The average particle diameter of the polymer particles is, for example, in the range of 0.1 to 200 μm, and the CV value of the polymer particles is preferably in the range of 15% or less. The CV value (variation coefficient of the particle size distribution) is obtained by the following equation.

CV value (%) = {[standard deviation of particle diameter (μm)] / [average particle diameter (μm)]} × 100
In the coating step, a polyorganosiloxane film is formed on the polymer particles. The polyorganosiloxane film can be formed by hydrolysis and condensation of organoalkoxysilane as a raw material in the presence of a basic catalyst. Examples of the organoalkoxysilane include at least one selected from the above general formula (1) and general formula (2). The basic catalyst includes at least one of ammonia and amine. Examples of the amine include monomethylamine, dimethylamine, monoethylamine, diethylamine, and ethylenediamine. These basic catalysts may be used alone or in combination of two or more. Among the catalysts, ammonia is preferable from the viewpoint of low toxicity, easy removal from the particles, and low cost.

  In the coating step, polymer particles, organoalkoxysilane, and basic catalyst are mixed in an aqueous dispersion medium. The coating step is preferably performed while stirring using a stirrer. The reaction conditions in the coating step are appropriately set according to the reaction conditions of the organoalkoxysilane. The polymer particles may be subjected to a coating process as a powder, or may be subjected to a coating process as a dispersion of polymer particles. Here, by providing the polymer particles as a dispersion obtained in the above polymerization step, the dispersibility of the polymer particles is easily maintained, and thus aggregation of the resulting coated polymer particles is suppressed. .

  In such a coating process, a part of the polyorganosiloxane may not adhere to the polymer particles, and solid organopolysiloxane fine particles may be generated. If the amount of such solid fine particles generated increases, the yield of the coated polymer particles may be reduced, and the classification operation of the coated polymer particles may be complicated. In this regard, the coating step preferably includes a first stage in which the polyorganosiloxane droplets adhere to the outer surface of the polymer particles and a second stage in which the polyorganosiloxane droplets are solidified. In the first step, the organoalkoxysilane is hydrolyzed and condensed in the presence of a basic catalyst to form droplets of the organoalkoxysilane condensate. By attaching such droplets to the polymer particles, the formation of solid fine particles of polyorganosiloxane is suppressed in the first stage. In the second stage, the condensation of the organoalkoxysilane condensate proceeds. Thereby, the organoalkoxysilane condensate is solidified on the outer surface of the polymer particles to form a polyorganosiloxane film.

  In the first stage, droplets of the organoalkoxysilane condensate are formed by relaxing the conditions for the condensation reaction of the organoalkoxysilane. Such droplets are easily formed by setting the addition amount of the basic catalyst to a predetermined amount or less. The addition amount of the basic catalyst in the first stage is 0.015 mol or less with respect to 1 mol of the organoalkoxysilane as a raw material of the polyorganosiloxane film from the viewpoint of suppressing the formation of polyorganosiloxane solid fine particles. It is preferred that That is, when the addition amount of the basic catalyst in the first stage exceeds 0.015 mol with respect to 1 mol of the organoalkoxysilane, the condensation of the organoalkoxysilane easily proceeds in a short time. The amount of polyorganosiloxane that produces solid particulates without increasing on the outer surface of the particles will increase. In addition, it is preferable that the minimum of the addition amount of the basic catalyst in a 1st step shall be 0.0001 mol or more with respect to 1 mol of organoalkoxysilane.

  The addition amount of the basic catalyst in the second stage is not particularly limited, but is preferably 0.1 to 10.0 mol with respect to 1 mol of the organoalkoxysilane as a raw material for the polyorganosiloxane coating. When the addition amount of the basic catalyst in the second stage is less than 0.1 mol with respect to 1 mol of the organoalkoxysilane, the time during which the coating is formed tends to be long, so that the coating process time can be shortened. May be difficult. On the other hand, when the addition amount of the basic catalyst in the second stage exceeds 10.0 mol with respect to 1 mol of the organoalkoxysilane, there is no problem in production, but excessive addition causes waste. become.

  The resulting coated polymer particles are washed as necessary. In the washing step, after the coated polymer particles and the dispersion medium are separated, the coated polymer particles are washed with an aqueous dispersion medium or the like. The washed coated polymer particles are dried to form a powder.

  The average particle diameter of the coated polymer particles is, for example, in the range of 0.1 to 200 μm, and the CV value of the coated polymer particles is preferably in the range of 15% or less. The CV value (variation coefficient of the particle size distribution) is obtained by the above-described formula.

  Next, the coated polymer particles are subjected to a firing step. In the baking step, the coated polymer particles are baked in a baking furnace to remove organic components contained in the coated polymer particles. Thereby, hollow inorganic particles are obtained. The outer shell of the hollow inorganic particles is formed from a polyorganosiloxane film formed in the coating process. The hollow part of the hollow inorganic particles is formed by mainly removing the polymer based on the vinyl monomer contained in the second monomer. Furthermore, inorganic particles derived from the first monomer are formed inside the hollow particles. That is, silica particles are formed from the organoalkoxysilane contained in the first monomer.

  In the firing step, the atmosphere in the firing furnace may be in the air or an atmosphere in which the oxygen concentration is adjusted with an inert gas such as nitrogen or argon. The firing temperature is set, for example, in the range of 200 ° C. to 1000 ° C. according to the decomposition temperature of the organic component. The firing time is set in the range of 3 to 100 hours, for example.

  Here, the state of the outer shell of the hollow inorganic particles can be changed by changing the conditions in the coating step. For example, by adjusting the thickness of the polyorganosiloxane coating, the hollow portion can be closed by the outer shell, or an opening communicating with the hollow portion can be formed on the outer surface of the outer shell. In the case of hollow inorganic particles having an opening in the outer shell, the opening is smaller than the particle size of the inorganic particles derived from the first monomer, so that the inorganic particles exist in a movable state in the hollow part. The inorganic particles are held in the hollow part. Further, for example, in the hollow inorganic particles having an opening in the outer shell, when the opening is larger than the particle size of the inorganic particles derived from the first monomer, the inorganic particles are connected to the outer shell, The particles are held in the hollow part. Moreover, the hollow inorganic particle in which the hollow part was biased can also be obtained by adjusting a stirring state etc. in a coating | coated process.

  The average particle diameter of the obtained hollow inorganic particles is, for example, in the range of 0.1 to 200 μm, and the CV value of the hollow inorganic particles is preferably in the range of 15% or less. The CV value (variation coefficient of the particle size distribution) is obtained by the above-described formula.

  The use of the hollow inorganic particles thus obtained is not particularly limited. The hollow inorganic particles are suitably used, for example, as spacers, fillers, ceramic raw materials, etc. for liquid crystal display devices. Since the hollow inorganic particles can be imparted with light diffusibility to the resin material by being blended with the resin material, the hollow inorganic particles can be suitably used as a filler for light diffusion. The hollow inorganic particles can be used as a functional filler that exhibits functions such as improvement of heat insulation, weight reduction, porosity, and low dielectric constant based on the hollow structure.

According to the embodiment described in detail above, the following effects are exhibited.
(1) By forming a polyorganosiloxane film on polymer particles, a coating step for obtaining coated polymer particles and a firing step for firing the coated polymer particles include inorganic particles in the hollow portion. Hollow inorganic particles can be produced.

  (2) By subjecting the polymer particles to the coating step as a dispersion obtained in the polymerization step, the dispersibility of the polymer particles is easily maintained, so that aggregation of the resulting coated polymer particles is suppressed. Become. Thereby, it becomes easy to improve the yield of the hollow inorganic particles.

  (3) In the coating step, a part of the polyorganosiloxane may not adhere to the polymer particles, and may produce polyorganosiloxane solid fine particles. In this regard, in the first step, the formation of polyorganosiloxane solid fine particles is suppressed by attaching droplets of the organoalkoxysilane condensate to the polymer particles. By carrying out the second stage in this state, it becomes possible to form a polyorganosiloxane film while suppressing the formation of the solid fine particles.

  (4) When the droplets of the organoalkoxysilane condensate adhere to the polyorganosiloxane that is being solidified on the outer surface of the polymer particles, the droplets are solidified in a protruding shape, so that the polyorganosiloxane film It is considered that the smoothness of the outer surface is lowered. In this regard, in the coating step including the first and second stages, droplets of the organoalkoxysilane condensate are attached to the polymer particles in the first stage, and the droplets are solidified in the second stage. For this reason, it is presumed that the solidification of the droplets proceeds more uniformly on the outer surface of the polymer particles, and as a result, the smoothness of the outer surface of the polyorganosiloxane film can be improved.

  (5) The addition amount of the basic catalyst in the first stage is 0.015 mol or less with respect to 1 mol of the organoalkoxysilane as the raw material of the polyorganosiloxane film, so that the solid fine particles of the polyorganosiloxane are reduced. Generation | occurrence | production can be suppressed notably.

  (6) According to the above-described method for producing hollow inorganic particles, hollow inorganic particles in which the hollow portion is closed by the outer shell, and hollow inorganic particles having an opening communicating with the hollow portion on the outer surface of the outer shell can be obtained. .

The embodiment may be modified as follows.
-You may make the 1st monomer or the 2nd monomer contain additives, such as a dispersing agent and a coloring agent. That is, additives such as a dispersant and a colorant may be contained in the first polymer or the second polymer.

-A polyorganosiloxane film having a multilayer structure may be formed by repeating the coating step a plurality of times.
-The polyorganosiloxane film may contain additives such as colorants. In the coating step, the polyorganosiloxane film may be formed by forming a polyorganosiloxane film together with an additive such as a colorant.

In the coating step, a predetermined amount of organoalkoxysilane may be gradually added to the reaction system by dropping, for example, organoalkoxysilane into the dispersion of polymer particles.
In the firing step, by adjusting conditions such as temperature and time, for example, to obtain hollow inorganic particles in which a part of the organic component remains without completely removing the organic component derived from the second monomer You can also.

The technical idea that can be grasped from the above embodiment will be described below.
(A) Hollow inorganic particles in which a hollow portion is closed by an outer shell and inorganic particles are present in the hollow portion.

(B) The hollow inorganic particle according to (a), wherein the inorganic particle is connected to the outer shell.
(C) The hollow inorganic particles according to (a), wherein the inorganic particles exist in a movable state in the hollow part.

  The hollow inorganic particles can be used, for example, as a functional filler that exhibits functions such as imparting light diffusibility, improving heat insulation, reducing weight, making it porous, and reducing the dielectric constant.

Next, the embodiment will be described more specifically with reference to examples.
(Example 1: Production of hollow inorganic particles closed by outer shell)
<First particle forming step>
After putting 500 g of ion-exchanged water into a 1-liter glass separable flask, the separable flask was placed in a thermostat adjusted to 40 ° C. Next, 25 g of vinyltrimethoxysilane as organoalkoxysilane (first monomer) was added while stirring the ion-exchanged water with a stirring blade, followed by stirring for 1 hour. Subsequently, after adding 5.0 ml of 1N aqueous ammonia as a basic catalyst, the mixture was further stirred for 15 minutes to obtain a first particle dispersion. The first particle dispersion is prepared by a mixed homogeneous reaction.

<Second particle forming step>
An emulsion (O / W emulsion) in which the second monomer was emulsified was prepared. This emulsified liquid was charged with 750 g of ion-exchanged water in a 2 liter glass separable flask, and then added to 250 g of methyl methacrylate as an acrylic monomer (second monomer) as a radical polymerization initiator. A solution in which 2.5 g of 2,2'-azobis (isobutyronitrile) was dissolved and 7.3 g of a 20% by mass aqueous ammonium dodecyl sulfate solution as an emulsifier were added, and the mixture was stirred for 3 minutes with a homogenizer. Next, after the separable flask containing the emulsion is placed in a thermostatic chamber adjusted to 30 ° C., the total amount of the first particle dispersion is added to the emulsion while stirring the emulsion with a stirring blade. added. Thereby, the formation of the second particles is started together with the swelling of the first particles because the first particles absorb methyl methacrylate. And the 2nd particle dispersion liquid was obtained by stirring for 1 hour in the state which maintained the thermostat at 30 degreeC.

<Polymerization process>
With the second particle dispersion kept stirring, the thermostatic bath was heated to 70 ° C. to initiate radical polymerization reaction of methyl methacrylate contained in the second particles. By maintaining the thermostat at 70 ° C. and continuing stirring for 5 hours, a polymer particle dispersion was obtained. Next, the radical polymerization reaction was stopped by stopping the stirring and stopping the heating in the thermostatic bath. The average particle size of the polymer particles obtained was 1.09 μm as measured with a Coulter counter manufactured by Beckman Coulter, Inc., trade name “Multisizer III”. Further, the CV value of the obtained polymer particles was 10.1%.

<Coating process (first stage)>
After putting 800 g of ion-exchanged water into a 2 liter glass separable flask, the separable flask was placed in a thermostatic chamber adjusted to 30 ° C. Next, 100 g of methyltrimethoxysilane was added and stirred for 3 hours while ion-exchanged water was stirred with a stirring blade. Subsequently, 200 g of the polymer particle dispersion liquid was added, and the mixture was stirred for 5 minutes to uniformly disperse the polymer particles in the system. Subsequently, 1.0 ml of 1N ammonia water was added as a basic catalyst and stirred for 90 minutes, whereby droplets of the organoalkoxysilane condensate were adhered to the outer surface of the polymer particles.

<Coating process (second stage)>
Next, a mixed solution of 100 g of 25% by mass of ammonia water and 400 g of ion-exchanged water was added and stirred for 12 hours, thereby proceeding with the condensation of the organoalkoxysilane condensate. Thereby, a dispersion of coated polymer particles was obtained by solidifying the droplets of the organoalkoxysilane condensate.

<Washing process>
In the washing step, the obtained polyorganosiloxane-coated polymer particles and the dispersion medium were separated by a centrifugal separator, the supernatant was discarded, and methanol was added to re-disperse the coated polymer particles. By repeating this operation three times, the coated polymer particles were washed, and finally methanol was removed. Next, the coated polymer particles were dried in an oven at 120 ° C. for 1 hour to obtain coated polymer particles as a powder. The average particle diameter of the coated polymer particles was 1.92 μm, and the CV value was 6.9%.

<Baking process>
The obtained coated polymer particles were placed in a box-type electric furnace, heated to 500 ° C., and held for 32 hours. By this firing step, organic components in the coated polymer particles were removed. Thereafter, the temperature in the electric furnace was lowered to room temperature to obtain hollow inorganic particles. The average particle diameter of the hollow inorganic particles was 1.59 μm, and the CV value was 6.7%.

<Microscopic observation of hollow inorganic particles>
The hollow inorganic particles were observed with an optical microscope and an electron microscope (electrolytic emission scanning electron microscope). FIG. 1 shows an optical micrograph, and FIGS. 2 and 3 show electron micrographs. From the optical micrograph of FIG. 1, it was confirmed that there are portions having different refractive indexes in the hollow inorganic particles. Moreover, it was confirmed from the electron micrographs of FIGS. 2A and 2B that the hollow portions of the hollow inorganic particles are completely closed by the outer shell.

<Section observation of hollow inorganic particles>
After the hollow inorganic particles were dispersed in the uncured epoxy resin, a curing agent was added and cured. This was cut out with a microtome, and the cross section of the hollow inorganic particles was observed with an electron microscope (electrolytic emission scanning electron microscope). 3 (a), 3 (b), 4 (a) and 4 (b) show electron micrographs of the cross section of the hollow inorganic particles. From FIG. 3A, FIG. 3B, and FIG. 4A, it was confirmed that inorganic particles were present in the hollow portion. Moreover, presence of the hollow inorganic particle in which the hollow part was deviated and formed was confirmed from FIG.4 (b).

(Example 2: Production of hollow inorganic particles having different average particle diameters)
In Example 2, the first particle formation step described as Example 1 was hollow as in Example 1 except that 1N ammonia water added as a basic catalyst was changed from 5.0 ml to 3.0 ml. Inorganic particles were obtained. The average particle diameter of the polymer particles obtained in the polymerization step was 1.52 μm, and the CV value was 8.1%. Moreover, the average particle diameter of the coated polymer particles obtained in the coating step was 2.67 μm, and the CV value was 3.9%. The average particle diameter of the hollow inorganic particles obtained in the firing step was 2.14 μm, and the CV value was 3.7%.

(Example 3: Production of hollow inorganic particles having openings)
<First particle forming step>
After 100 g of ion-exchanged water was put into a 1-liter glass separable flask, the separable flask was placed in a thermostat adjusted to 30 ° C. Next, 20 g of vinyltrimethoxysilane as organoalkoxysilane (first monomer) was added while stirring the ion-exchanged water with a stirring blade, followed by stirring for 1 hour. Subsequently, after adding 0.3 ml of 1N ammonia water as a catalyst, the mixture was further stirred for 15 minutes to obtain a first particle dispersion. The first particle dispersion is prepared by a mixed homogeneous reaction.

<Second particle forming step>
An emulsion (O / W emulsion) in which the second monomer was emulsified was prepared. This emulsified liquid was charged with 600 g of ion-exchanged water in a 2 liter glass separable flask, and then added to 180 g of methyl methacrylate as an acrylic monomer (second monomer) as a radical polymerization initiator. A solution in which 2.0 g of 2,2'-azobis (isobutyronitrile) was dissolved and 10.0 g of a 20% by mass aqueous ammonium dodecyl sulfate solution as an emulsifier were added, and the mixture was stirred for 3 minutes with a homogenizer. Next, after placing the separable flask containing the emulsion in a thermostat adjusted to 30 ° C., 115 g of the first particle dispersion is added to the emulsion while stirring the emulsion with a stirring blade. It was. Thereby, the formation of the second particles is started together with the swelling of the first particles because the first particles absorb methyl methacrylate. And the 2nd particle dispersion liquid was obtained by stirring for 1 hour in the state which maintained the thermostat at 30 degreeC.

<Polymerization process>
A polymer particle dispersion was obtained in the same manner as in the polymerization step of Example 1. The average particle diameter of the obtained polymer particles was 4.59 μm, and the CV value was 3.3%.

<Coating process (first stage)>
After putting 4000 g of ion-exchanged water into a 7-liter glass separable flask, the separable flask was placed in a thermostat adjusted to 30 ° C. Next, 500 g of methyltrimethoxysilane was added and the mixture was stirred for 3 hours while ion-exchanged water was being stirred with a stirring blade. Subsequently, 1000 g of the above polymer particle dispersion was added, and the mixture was stirred for 5 minutes to uniformly disperse the polymer particles in the system. Subsequently, 5.0 ml of 1N ammonia water was added as a basic catalyst and stirred for 120 minutes, whereby droplets of the organoalkoxysilane condensate were adhered to the outer surface of the polymer particles.

<Coating process (second stage)>
Next, a mixed solution of 200 g of 25% by mass of ammonia water and 800 g of ion-exchanged water was added and stirred for 12 hours to proceed the condensation of the organoalkoxysilane condensate. Thereby, a dispersion of coated polymer particles was obtained by solidifying the droplets of the organoalkoxysilane condensate.

<Washing process>
The coated polymer particles were obtained as a powder by the same operation as in the washing step of Example 1. The average particle diameter of the coated polymer particles was 6.04 μm, and the CV value was 3.5%.

<Baking process>
Hollow inorganic particles were obtained by the same operation as in the firing step of Example 1. The average particle diameter of the hollow inorganic particles was 4.82 μm, and the CV value was 2.6%.

<Microscopic observation of hollow inorganic particles>
The hollow inorganic particles were observed with an electron microscope (electrolytic emission scanning electron microscope). Fig.5 (a) and FIG.5 (b) have shown the electron micrograph of the hollow inorganic particle. From the electron micrographs of FIGS. 5 (a) and 5 (b), the presence of hollow inorganic particles having openings in the outer shell was confirmed.

(Examples 1a to 1d)
In Examples 1a to 1d, hollow inorganic particles were produced in the same manner as in Example 1 except that the addition amount of the basic catalyst was changed as shown in Table 1 in the coating step (first stage).

The solid fine particles contained in the hollow inorganic particle group produced as Example 1a and Example 1b were observed with an electron microscope (electrolytic emission scanning electron microscope), and the solid fine particles contained in the hollow inorganic particle group produced as Example 1 were observed. The amount was compared visually. As a result, it was confirmed that Example 1a and Example 1b had the same amount as Example 1. Here, Fig.6 (a) and FIG.6 (b) have shown the electron microscope (electrolytic emission scanning electron microscope) photograph of the hollow inorganic particle group manufactured as Example 1c. From these electron micrographs, it was confirmed that the amount of solid fine particles was increased in Example 1c than in Example 1. Also in Example 1d, solid fine particles contained in the hollow inorganic particle group were observed with an electron microscope (electrolytic emission scanning electron microscope). As a result, a large amount of solid fine particles was confirmed as in Example 1c.

Claims (7)

A first particle forming step of forming first particles containing a first polymer in a droplet state by polymerizing a first monomer containing an organoalkoxysilane;
A second monomer containing a vinyl monomer other than vinylalkoxysilane is brought into contact with the first particle in an emulsified state, thereby allowing the first particle to absorb the second monomer. A second particle forming step of forming two particles;
A polymerization step for forming polymer particles by polymerizing the second monomer absorbed in the second particles;
A coating step of obtaining coated polymer particles by forming a polyorganosiloxane film on the polymer particles;
A method of producing hollow inorganic particles, comprising a firing step of firing the coated polymer particles. The covering step is
A step of hydrolyzing and condensing the organoalkoxysilane in the presence of a basic catalyst in a mixed solution of the dispersion of polymer particles and the organoalkoxysilane as a raw material for the polyorganosiloxane coating;
The method for producing hollow inorganic particles according to claim 1, wherein the dispersion of polymer particles is a dispersion obtained by performing a polymerization reaction in the polymerization step. The covering step is
By hydrolyzing and condensing organoalkoxysilane as a raw material for the polyorganosiloxane coating in the presence of a basic catalyst, droplets of the organoalkoxysilane condensate are generated and the organoalkoxysilane is formed on the outer surface of the polymer particles. 2. The method according to claim 1, further comprising: a first step of attaching droplets of the silane condensate; and a second step of solidifying the droplets of the organoalkoxysilane condensate by advancing the condensation. 2. The method for producing hollow inorganic particles according to 2. In the coating step, the addition amount of the basic catalyst in the first stage is 0.015 mol or less with respect to 1 mol of organoalkoxysilane as a raw material of the polyorganosiloxane coating. The method for producing hollow inorganic particles according to claim 3. It is a hollow inorganic particle obtained by the manufacturing method as described in any one of Claims 1-4, Comprising: The inorganic particle derived from the said 1st monomer exists in a hollow part, It is characterized by the above-mentioned. Hollow inorganic particles. The hollow inorganic particle according to claim 5, wherein the hollow portion is closed by an outer shell. The hollow inorganic particle according to claim 5, wherein an outer surface of the outer shell has an opening communicating with the hollow portion.