Silica particles and method for producing silica particles

Abstract

To provide a method for producing silica particles without using citric acid, and silica particles having excellent true density and dispersibility.SOLUTION: Silica particles (1) have a true density of 0.8 g / cm3 to 1.4 g / cm3, (2) the frequency of particles larger than 2 times the average particle diameter in the particle size distribution thereof is 15% or less, and (3) the amount of water absorption thereof is 1.0 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to silica particles and a method for producing silica particles. [Background technology]

[0002] Patent Document 1 is a technology disclosed by the present applicant, and (1) the average particle size is 50 to 150 nm, (2) the average shell thickness is 5 to 25 nm, and (3) solid-state NMR ( 29 In the Si / MAS measurement, the integrated intensity (I Q2 ) and the integrated intensity (I Q4 ) and the ratio (I Q2 / I Q4 (4) The ratio Psa / Psm of the peak intensity Psa of the associated particles to the peak intensity Psm of the main particles, which are unassociated hollow nanosilica particles, in the particle size distribution in the particle diameter range of 50 to 500 nm measured using a disc centrifugal particle size distribution analyzer is 0.4 or less. This technology involves calcining at 700°C in the presence of an organic acid such as citric acid to improve dispersibility. These hollow nanosilica particles suppress the formation of associated particles and light reflection, making them suitable for use in a variety of products requiring anti-reflection properties. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-176037 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a method for producing silica particles without using citric acid, and also provides silica particles having excellent true density and dispersibility. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have developed new silica particles (preferably hollow silica particles) that have a low true density and excellent dispersibility by subjecting core-shell particles to a carbonization treatment before firing when producing silica particles.

[0006] The present invention encompasses the following silica particles and a method for producing silica particles.

[0007] Section 1. (1) True density is 0.8 g / cm 3 ~1.4g / cm 3 and (2) In the particle size distribution, the frequency of particles larger than twice the average particle size is 15% or less; (3) The water absorption is 1.0% by mass or less. Silica particles.

[0008] Section 2. (4) The silica particles according to item 1, wherein the silica particles are carbonized and calcined.

[0009] Section 3. (5) The silica particles according to item 1 or 2, wherein the silica particles have an average particle size of 0.2 μm to 1.0 μm.

[0010] Section 4. Item 3. The silica particles according to item 1 or 2, wherein the silica particles are hollow silica particles.

[0011] Section 5. A method for producing silica particles, comprising: The method includes a step of first carbonizing the core-shell particles and then calcining them, Silica particles are (1) True density is 0.8 g / cm 3 ~1.4g / cm 3 and (2) In the particle size distribution, the frequency of particles larger than twice the average particle size is 15% or less; (3) The water absorption is 1.0% by mass or less. Method for producing silica particles.

[0012] The silica particles of the present invention are novel silica particles (preferably hollow silica particles) that have a low true density and excellent dispersibility. [Effects of the Invention]

[0013] The present invention provides a method for producing silica particles without using citric acid, and also provides silica particles having excellent true density and dispersibility. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] The embodiments of the present invention are intended to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the content of the invention.

[0016] In this specification, the terms "comprise" and "contain" are concepts that encompass all of "comprise," "consist essentially of," and "consist only of."

[0017] In this specification, when a numerical range is expressed as "A to B," it means "not less than A and not more than B."

[0018] In this specification, the expressions parts, % and the like are generally used.

[0019] In this specification, unless otherwise specified, all parts by mass or % by mass (wt%) are used.

[0020] [1] Silica particles The present invention encompasses silica particles.

[0021] The silica particles of the present invention are (1) True density is 0.8 g / cm3 ~1.4g / cm 3 and (2) In the particle size distribution, the frequency of particles larger than twice the average particle size is 15% or less; (3) The water absorption is 1.0% by mass or less.

[0022] The silica particles are preferably (4) carbonized and calcined.

[0023] The silica particles preferably have (5) an average particle size of 0.2 μm to 1.0 μm.

[0024] The silica particles are preferably hollow silica particles.

[0025] The silica particles of the present invention are novel silica particles having a low true density and excellent dispersibility.

[0026] The silica particles of the present invention are useful for multilayer printed circuit boards, wire coating materials, semiconductor encapsulants, etc.

[0027] Silica-based compounds and metal oxides The silica-based compound that forms the silica particles is not particularly limited as long as it contains silica, and the silica particles may be formed solely from silica.

[0028] When the silica-based compound contains a compound other than silica, the silica particles preferably contain silica and a metal oxide.

[0029] The metal oxide is preferably an oxide of a metal capable of forming a metal alkoxide, specifically an oxide of aluminum, titanium, zirconium, etc.

[0030] The metal oxide may be used alone or in the form of a mixture (blend) of two or more kinds.

[0031] When aluminum oxide is used as the metal oxide, the surface charge (zeta potential, etc.) of the shell of the silica particles can be adjusted.

[0032] When titanium or zirconium oxide is used as the metal oxide, the refractive index of the shell of the silica particle can be adjusted.

[0033] (1) True density of silica particles The silica particles of the present invention have a true density of 0.8 g / cm 3 ~1.4g / cm 3 is.

[0034] The silica particles of the present invention have a low-density air layer, and therefore have a true density that is lower than that of general silica (2.2 g / cm 3 ) is lower than

[0035] The true density of the silica particles is a value obtained by measuring the true density of silica particles (0.2 g of powder) using a nitrogen gas pycnometer (Ultrapyc 5000 Micro, manufactured by Anton Paar Japan Co., Ltd.).

[0036] The silica particles for which the true density is to be measured are preferably dried under reduced pressure at a temperature of 120° C. for 2 hours, and then the true density of the dried silica particles is measured.

[0037] The true density of silica particles is 0.8 g / cm 3 ~1.4g / cm 3 and preferably 0.8 g / cm 3 ~1.3g / cm 3 and more preferably 0.9 g / cm 3 ~1.2g / cm 3 and more preferably 0.9 g / cm 3 ~1.1g / cm 3 By adjusting the true density to fall within the above range, the silica particles can be produced satisfactorily, and the shells are not broken, the true density is low, and the dispersibility is excellent.

[0038] (2) Particle size distribution of silica particles In the silica particles of the present invention, the frequency of particles having a particle size larger than twice the average particle size in the particle size distribution is 15% or less.

[0039] "Particles larger than twice the average particle size" refers to particles that are larger than twice the average particle size, but do not include particles that are twice the average particle size.

[0040] The frequency of particles larger than twice the average particle size in the particle size distribution of silica particles is a value obtained by measuring the particle size distribution of silica particle powder using a laser diffraction / scattering particle size distribution analyzer (LA-950, manufactured by Horiba, Ltd.) and calculating the frequency (%) of particles larger than twice the average particle size within the silica particle powder.

[0041] The lower the frequency of particles larger than twice the average particle size in the particle size distribution of silica particles, the better. The frequency of particles larger than twice the average particle size in the particle size distribution of silica particles is 15% or less, preferably 12% or less, more preferably 9% or less, and even more preferably 6% or less. The lower limit of the frequency of particles larger than twice the average particle size in the particle size distribution of silica particles is about 0%. By adjusting the frequency of particles with a particle size of 1 μm or more in the particle size distribution to fall within the above range, silica particles can be produced well, resulting in silica particles with low true density and excellent dispersibility.

[0042] (3) Water absorption of silica particles The silica particles of the present invention have a water absorption of 1.0% by mass or less.

[0043] Water absorption test for silica particles The water absorption of silica particles was determined by storing silica particles (1 g of powder) for 7 days in an environment with a temperature of 50°C and a humidity of 75%, sampling 0.1 g of the powder, and measuring the water content of the silica particles using a Karl Fischer moisture meter (MKA-610, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0044] The lower the water absorption of the silica particles, the more preferable. The water absorption of the silica particles is 1.0% by mass or less, preferably 0.9% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.7% by mass or less. The lower limit of the water absorption of the silica particles is about 0.1% by mass. By adjusting the water absorption within the above range, the silica particles can be produced well, and the silica particles have a low true density and excellent dispersibility.

[0045] (4) Carbonization and calcination of silica particles The silica particles of the present invention are preferably carbonized and calcined. By being carbonized and calcined, the silica particles can be produced well, and the silica particles have a low true density and excellent dispersibility.

[0046] (5) Average particle size of silica particles The silica particles of the present invention preferably have an average particle size of 0.2 μm to 1.0 μm.

[0047] The average particle size of the silica particles was determined by taking photographs of the particles using an SEM (scanning electron microscope: JSM-7900F, manufactured by JEOL Ltd.) at an acceleration voltage of 8 kV, measuring the minor axes of 100 randomly selected particles, and calculating the average value.

[0048] Image analysis was performed using the image analysis and measurement software WinROOF.

[0049] The average particle size of the silica particles is preferably 0.2 μm to 1.0 μm, more preferably 0.3 μm to 0.9 μm, even more preferably 0.4 μm to 0.8 μm, and particularly preferably 0.4 μm to 0.7 μm. By adjusting the average particle size within the above range, the silica particles can be produced more efficiently, and the silica particles have a low true density and excellent dispersibility.

[0050] (6) Hollow silica particles The silica particles of the present invention may have a particle structure of a dense type, a porous type, a hollow type, or the like.

[0051] The silica particles are preferably hollow silica particles, which preferably have a hollow portion (cavity) formed therein.

[0052] The silica particles can be produced more easily because they are hollow silica particles, and the silica particles have a low true density and excellent dispersibility.

[0053] (7) MEK filterability of silica particles The silica particles of the present invention preferably have a methyl ethyl ketone (MEK) filterability of 80 mass % or more.

[0054] The MEK filterability of silica particles was measured by first mixing 2 g of silica particles (powder) with 8 g of methyl ethyl ketone (MEK) at 500 rpm for 2 hours, and then filtering the mixture of silica particles and MEK using a syringe filter with a pore size of 5 μm (filter paper that allows particles with a size of 5 μm or less to pass through).

[0055] The MEK filterability (mass %) of the silica particles is a value calculated by weighing the amount of the mixed liquid that passed through and using the following formula. (MEK filtration (mass%, wt%)) = [Amount of liquid passed (g)] ÷ [Amount of MEK dispersion of silica particles (10 g)] × 100

[0056] The higher the MEK filterability of the silica particles, the more preferable. The MEK filterability of the silica particles is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. The upper limit of the MEK filterability of the silica particles is about 100%. By adjusting the MEK filterability within the above range, the silica particles can be produced well, and the silica particles have a low true density and excellent dispersibility.

[0057] Average shell (film) thickness of silica particles The average thickness of the shell (film) forming the silica particles of the present invention is preferably 25 nm to 170 nm, more preferably 30 nm to 150 nm, and even more preferably 35 nm to 100 nm.

[0058] The average thickness of the shells forming the silica particles was determined by taking photographs of the particles using a TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.) at an acceleration voltage of 200 kV, measuring the shell thicknesses of 100 randomly selected particles, and calculating the average value.

[0059] By adjusting the average shell thickness within the above range, silica particles can be produced satisfactorily, and the shell is not broken, and the silica particles have a low true density and excellent dispersibility.

[0060] The silica particles of the present invention are silica particles having a low true density and excellent dispersibility. The silica particles of the present invention are silica particles that exhibit a low true density and high dispersibility by optimizing the firing conditions (pre-carbonization treatment).

[0061] [2] Core-shell particles The present invention encompasses core-shell particles.

[0062] The core-shell particles of the present invention are core-shell particles having organic polymer particles as a core and silica coating the organic polymer particles as a shell. The silica particles of the present invention can be produced satisfactorily by pyrolyzing the organic polymer particles of the core-shell particles.

[0063] organic polymer particles The organic polymer particles are not particularly limited. The organic polymer particles are preferably organic polymer particles that are easily burned away by thermal decomposition after forming a shell. Specific examples of the organic polymer particles include polystyrene particles and polymethyl methacrylate (PMMA) (resin) particles.

[0064] When polystyrene particles are used as the organic polymer particles, a positive zeta potential is imparted to the polystyrene particles, making it possible to suppress the formation of associated particles.

[0065] Dispersants The organic polymer particles preferably contain a dispersant. When the organic polymer particles contain a dispersant, the dispersant is present on the surface of the organic polymer particles, and aggregation of the organic polymer particles can be further suppressed.

[0066] The dispersant is not particularly limited as long as it can produce organic polymer particles, and specific examples of the dispersant include polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene glycol (PPG), polypropylene oxide (PPO), collagen, and polysaccharides (gum arabic).

[0067] When polyvinylpyrrolidone, hydroxypropyl cellulose, or the like is used as a dispersant, aggregation of the organic polymer particles can be suppressed, and aggregation of the core-shell particles can also be suppressed.

[0068] The dispersant may be used alone or in combination of two or more kinds (blended).

[0069] The content of the dispersant in the organic polymer particles is not particularly limited. The content of the dispersant in the organic polymer particles is preferably 0.01% by mass to 100% by mass, more preferably 0.05% by mass to 100% by mass, relative to 100% by mass of the organic polymer particles. By adjusting the content of the dispersant within the above range, it is possible to suppress aggregation of the organic polymer particles.

[0070] Silica coating organic polymer particles The silica-based compound that forms the shell that covers the organic polymer particles is the same as the silica-based compound that forms the silica particles. The average thickness of the shell (film) of the core-shell particles is the same as the film thickness (average thickness) of the shell (film) that forms the silica particles.

[0071] Average particle size of core-shell particles The average particle size of the core-shell particles is preferably 0.2 μm to 1 μm, more preferably 0.3 μm to 0.9 μm, and even more preferably 0.4 μm to 0.8 μm.

[0072] The average particle diameter of the core-shell particles is a value obtained by taking photographs of the particles using an SEM (scanning electron microscope: JSM-7900F, manufactured by JEOL Ltd.) at an acceleration voltage of 8 kV, measuring the minor axes of 100 randomly selected particles, and calculating the average value, similar to the average particle diameter of the silica particles.

[0073] Image analysis was performed using the image analysis and measurement software WinROOF.

[0074] By using core-shell particles, silica particles can be produced satisfactorily, and the silica particles have a low true density and excellent dispersibility.

[0075] [3] Manufacturing method of silica particles The method for producing silica particles of the present invention preferably includes the steps of: (1) Step 1: Preparing organic polymer particles by polymerizing an organic monomer in a solution containing an organic monomer, a dispersant, and a solvent; (2) adding the organic polymer particles obtained in step 1, an alkoxysilane or an alkoxysilane and a metal alkoxide, and a basic catalyst to a solvent and stirring to prepare a solution, and forming core-shell particles in the solution, each having the organic polymer particle as a core and a shell covering the organic polymer particle; (3) Step 3, in which the core-shell particles obtained in step 2 are first carbonized (thermally decomposed) and then calcined to remove the organic polymer particles that are the cores of the core-shell particles; and (4) After step 3, the hollow silica particles obtained in step 3 are subjected to a hydrophobic treatment (hydrophobic surface treatment). Includes:

[0076] In the method for producing silica particles of the present invention, the step 3 is The method includes a step of first carbonizing the core-shell particles and then calcining them, Silica particles are (1) True density is 0.8 g / cm 3 ~1.4g / cm 3 and (2) In the particle size distribution, the frequency of particles larger than twice the average particle size is 15% or less; (3) Silica particles with a water absorption of 1.0% by mass or less can be produced.

[0077] In the method for producing silica particles of the present invention, when producing silica particles, core-shell particles are subjected to a carbonization treatment before being fired, thereby making it possible to produce new silica particles having a low true density and excellent dispersibility.

[0078] In the method for producing silica particles of the present invention, preferably, The carbonization treatment is carried out at 400°C to 1,200°C, The baking treatment is carried out for 3 hours or more.

[0079] The silica particles of the present invention can be preferably produced satisfactorily through the following steps.

[0080] (1) Step 1 (Production of organic polymer particles) Step 1 is a step of preparing organic polymer particles by carrying out a polymerization reaction of an organic monomer in a solution containing an organic monomer, a dispersant, and a solvent.

[0081] organic monomers The organic monomer is not particularly limited as long as it can produce organic polymer particles.

[0082] The organic monomer is preferably an organic monomer capable of forming organic polymer particles that are easily burned away by pyrolysis after forming the shell, specifically, styrene for producing polystyrene, methyl methacrylate for producing polymethyl methacrylate (PMMA) (resin), etc.

[0083] When styrene is used as the organic monomer, a positive zeta potential is imparted to the polystyrene particles, making it possible to suppress the formation of aggregated particles.

[0084] The polystyrene is not particularly limited. The polystyrene is preferably a polystyrene containing a structural unit derived from a hydrophobic monomer such as alkyl(meth)acrylate, and other copolymerizable monomer structural units. The polystyrene is preferably an alkyl(meth)acrylate styrene having an alkyl group having 3 to 22 carbon atoms, 2-methylstyrene, or the like.

[0085] In step 1, the concentration of the organic monomer in the solution is not particularly limited. The concentration of the organic monomer in the solution is preferably 0.1% by mass to 20% by mass, and more preferably 0.2% by mass to 10% by mass, relative to 100% by mass of the solution. By adjusting the concentration of the organic monomer within the above range, the average particle size of the silica particles in the final product can be well controlled.

[0086] Dispersants The dispersant is not particularly limited as long as it can produce organic polymer particles, and specific examples of the dispersant include polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene glycol (PPG), polypropylene oxide (PPO), collagen, and polysaccharides (gum arabic).

[0087] When polyvinylpyrrolidone or hydroxypropyl cellulose is used as a dispersant, aggregation of the polystyrene particles can be suppressed, and aggregation of the core-shell particles formed in the next step 2 can also be suppressed.

[0088] The dispersant may be used alone or in combination of two or more kinds (blended).

[0089] In step 1, the concentration of the dispersant in the solution is not particularly limited. The concentration of the dispersant in the solution is preferably 0.01% by mass to 10% by mass, and more preferably 0.05% by mass to 5% by mass, relative to 100% by mass of the solution. By adjusting the concentration of the dispersant within the above range, aggregation of the organic polymer particles can be suppressed, and aggregation of the core-shell particles formed in the next step 2 can also be suppressed.

[0090] solvent The solvent used in step 1 is preferably water.

[0091] The solvent is preferably a hydrophilic solvent.

[0092] The hydrophilic solvent is preferably an alcohol such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1,4-butanediol, etc. The hydrophilic solvent is preferably a ketone such as acetone or methyl ethyl ketone, etc. The hydrophilic solvent is preferably an ester such as ethyl acetate, etc.

[0093] The hydrophilic solvent is preferably an alcohol, more preferably methanol, ethanol, isopropanol, or the like.

[0094] The solvent may be one of these solvents or a mixture (blend) of two or more of them.

[0095] The solvent used in step 1 is preferably a mixed solvent of water and methanol. Use of a mixed solvent of water and methanol can suppress aggregation of the organic polymer particles, and can also suppress aggregation of the core-shell particles formed in the next step 2.

[0096] The mass ratio of water to methanol (water:methanol) in the mixed solvent is preferably 5:95 to 50:50, more preferably 8:92 to 40:60, and even more preferably 10:90 to 30:70. By adjusting the mass ratio of water to methanol within the above range, aggregation of the organic polymer particles can be suppressed, and aggregation of the core-shell particles formed in the next step 2 can also be suppressed.

[0097] cationic polymerization initiator In step 1, the solution preferably contains a cationic polymerization initiator. The cationic polymerization initiator is not particularly limited as long as it can produce organic polymer particles. The cationic polymerization initiator is preferably an inorganic peroxide, an organic initiator, a redox agent, or the like. A radical polymerization initiator such as an organic oxide or an azo compound is more preferably used as the cationic polymerization initiator.

[0098] The organic oxide is represented by the general formula RO-OR.

[0099] Azo compounds are represented by the general formula A-CN=CN-A.

[0100] Specific examples of the cationic polymerization initiator include benzoyl peroxide, 2,2'-azobis(isobutylamidine) dihydrochloride (AIBA), 4,4'-azobis-4-cyanovaleric acid, azobisisobutyronitrile (AIBN), and 2,2'-azobis(2-methylpropioamide) dihydrochloride (AAPH).

[0101] The cationic polymerization initiator is preferably 2,2'-azobis(isobutylamidine) dihydrochloride (AIBA) or 2,2'-azobis(2-methylpropioamide) dihydrochloride (AAPH), more preferably 2,2'-azobis(isobutylamidine) dihydrochloride (AIBA) or 4,4'-azobis-4-cyanovaleric acid, and even more preferably 2,2'-azobis(isobutylamidine) dihydrochloride (AIBA).

[0102] The cationic polymerization initiator may be used alone or in the form of a mixture (blend) of two or more of these.

[0103] In step 1, the concentration of the cationic polymerization initiator in the solution is not particularly limited. The concentration of the cationic polymerization initiator is preferably 0.01% by mass to 1% by mass, with the solution being 100% by mass. By adjusting the concentration of the cationic polymerization initiator within the above range, the average particle size of the silica particles in the final product can be well controlled.

[0104] polymerization reaction In step 1, a polymerization reaction of the organic monomer is carried out in a solution containing the organic monomer, a dispersant, and a solvent. The polymerization reaction is preferably carried out by mixing and stirring the solution.

[0105] There are no particular limitations on the temperature during the polymerization reaction of the solution in step 1. The reaction temperature of the polymerization reaction is preferably 40°C or higher and not higher than the boiling point of the solvent used, more preferably 50°C to 90°C. By adjusting the reaction temperature of the polymerization reaction within the above range, the solvent does not evaporate and the polymerization reaction can proceed smoothly.

[0106] The reaction time of the polymerization reaction is not particularly limited. The reaction time of the polymerization reaction is preferably 1 minute to 12 hours, and more preferably 10 minutes to 10 hours. By adjusting the reaction time of the polymerization reaction within the above range, the polymerization reaction can proceed smoothly.

[0107] Organic polymer particles are prepared by carrying out a polymerization reaction. The average particle size of the organic polymer particles is preferably 0.1 μm to 0.9 μm, more preferably 0.2 μm to 0.8 μm, and even more preferably 0.3 μm to 0.7 μm. By adjusting the average particle size of the organic polymer particles within the above range, the average particle size of the core-shell particles formed in the next step 2 and the average particle size of the hollow silica particles produced in step 3 can be adjusted to appropriate ranges.

[0108] According to step 1, organic polymer particles can be successfully produced.

[0109] Yield of organic polymer particles (polystyrene particles, etc.) 2 g of the organic polymer particle reaction liquid is weighed out in a petri dish and dried on a hot plate at 120° C. for 1 hour, and the yield of the organic polymer particles is calculated according to the following formula.

[0110] (Yield of organic polymer particles (%)) = {[(sample weight after drying (g)) - (weight (g) of dispersant (PVP, etc.) in sample before drying) ÷[Weight (g) of organic monomer (styrene, etc.) in sample before drying] × 100

[0111] (2) Step 2 (production of core-shell particles) Step 2 is a step in which the organic polymer particles prepared in Step 1, an alkoxysilane or an alkoxysilane and a metal alkoxide, and a basic catalyst are added to a solvent, and the mixture is stirred to prepare a solution, and core-shell particles having the organic polymer particles as a core and a shell covering the organic polymer particles are formed in the solution.

[0112] solvent Water is preferably used as the solvent used in step 2. When water is used, core-shell particles can be formed inexpensively and safely.

[0113] The solvent is preferably a hydrophilic solvent.

[0114] The hydrophilic solvent is preferably an alcohol such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1,4-butanediol, etc. The hydrophilic solvent is preferably a ketone such as acetone or methyl ethyl ketone, etc. The hydrophilic solvent is preferably an ester such as ethyl acetate, etc.

[0115] The hydrophilic solvent is preferably an alcohol, more preferably methanol, ethanol, isopropanol, or the like.

[0116] The solvent is preferably the same alcohol as that produced by hydrolysis of the silicon compound, since the solvent can be easily recovered and reused.

[0117] The solvent may be one of these solvents or a mixture (blend) of two or more of them.

[0118] The solvent is preferably a mixed solvent of water and a hydrophilic solvent. In the mixed solvent, the mass ratio of the hydrophilic solvent (e.g., methanol) to water is not particularly limited. In the mixed solvent, the hydrophilic solvent:water (mass ratio) is preferably 50:50 to 90:10, and more preferably 60:40 to 80:20. By adjusting the mass ratio of the hydrophilic solvent to water in the mixed solvent within the above range, the average particle size of the silica particles can be adjusted to an appropriate range.

[0119] The solvent is preferably a hydrophobic solvent. The hydrophobic solvent is preferably an organic hydrocarbon solvent having a water solubility of less than about 1 g per 100 g at 100°C. The hydrophobic solvent is preferably a linear, branched, or cyclic alkane having 6 to 10 carbon atoms. Specific examples of the hydrophobic solvent include hexane, cyclohexane, heptane, octane, and isooctane. Octane is more preferably used as the hydrophobic solvent.

[0120] organic polymer particles The organic polymer particles used in step 2 are the organic polymer particles prepared in step 1.

[0121] The concentration of the organic polymer particles in the solution is preferably 0.01% by mass to 50% by mass, and more preferably 0.01% by mass to 20% by mass.

[0122] Alkoxysilane The alkoxysilane used in step 2 is not particularly limited.

[0123] The alkoxysilane preferably has the general formula (1): Si(OR 1 )4(1) The compound is a tetraalkoxysilane represented by the formula: or a derivative thereof.

[0124] In general formula (1), R 1 are the same or different and are alkyl groups, preferably lower alkyl groups having 1 to 8 carbon atoms, more preferably lower alkyl groups having 1 to 4 carbon atoms, and even more preferably lower alkyl groups having 1 to 3 carbon atoms.

[0125] In general formula (1), R 1 Specifically, is a methyl group, an ethyl group, a propyl group, an isobutyl group, a butyl group, a pentyl group, or a hexyl group.

[0126] In general formula (1), R 1 Tetramethoxysilane (TMOS), where R is a methyl group 2 When tetraethoxysilane (TEOS), in which the alkoxysilane group is an ethyl group, is used, silica is effectively generated and a dense shell can be obtained. The alkoxysilane used in step 2 is preferably tetramethoxysilane (TMOS). A dense shell is a shell in which siloxane bonds are more (or almost completely) formed and there are fewer remaining silanol groups.

[0127] The alkoxysilane preferably has the general formula (2): Si(OR 1 )3R 2 (2) or a derivative thereof.

[0128] In general formula (2), R 1 is R in the general formula (1). 1 In general formula (2), R 2is hydrogen, or 1 (R in general formula (1) 1 ) is the same alkyl group as

[0129] The alkoxysilane derivative is preferably a low condensate obtained by partially hydrolyzing the alkoxysilane.

[0130] The alkoxysilane may be used alone or in the form of a mixture (blend) of two or more kinds.

[0131] When trialkoxysilane or tetraalkoxysilane is used as the alkoxysilane, aggregation can be prevented at the core-shell particle stage, and surface modification with a silane coupling agent or the like can be easily performed.

[0132] The concentration of the alkoxysilane in the solution is preferably 0.1% by mass to 70% by mass, more preferably 1% by mass to 60% by mass, even more preferably 5% by mass to 50% by mass, and particularly preferably 10% by mass to 40% by mass.

[0133] Metal alkoxide In step 2, the alkoxysilane and the metal alkoxide may be mixed and used.

[0134] The metal alkoxide is not particularly limited, and aluminum alkoxide, titanium alkoxide, zirconium alkoxide, or the like is preferably used as the metal alkoxide.

[0135] The use of aluminum alkoxide makes it possible to adjust the surface charge (zeta potential, etc.) of the shell.

[0136] The refractive index of the shell can be adjusted by using titanium alkoxide or zirconium alkoxide.

[0137] The metal alkoxide may be used alone or in the form of a mixture (blend) of two or more kinds.

[0138] The concentration of the metal alkoxide in the solution is preferably 0.01% by mass to 50% by mass, and more preferably 0.01% by mass to 20% by mass.

[0139] In step 2, the alkoxysilane and the metal alkoxide may be added separately to prepare the solution.

[0140] In step 2, an alkoxysilane and a metal alkoxide may be mixed, hydrolyzed, and then added to the solution. By mixing an alkoxysilane and a metal alkoxide, hydrolyzing, and then adding to the solution, the following reaction formula (1): Si-OM (1) and can form a shell in which the metal represented by M in formula (1) is uniformly contained.

[0141] In formula (1), M represents a metal, and is a metal derived from a metal alkoxide, and preferably represents aluminum, titanium, or zirconium.

[0142] The method of mixing the alkoxysilane and metal alkoxide, hydrolyzing the mixture, and then adding the mixture to the solution is, for example, the method described in JP-A-2005-41722.

[0143] Basic catalyst The basic catalyst used in step 2 is not particularly limited.

[0144] When an organic base catalyst containing no metal components or an inorganic catalyst containing no metal components is used as the basic catalyst, it is possible to avoid contamination with metal impurities during the production process.

[0145] The organic base catalyst is preferably a nitrogen-containing organic base catalyst such as ethylenediamine, diethylenetriamine, triethylenetetraamine, urea, ethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, or a basic amino acid.

[0146] In step 2, if a low-volatility organic base catalyst is used, the reaction can proceed smoothly without volatilization within the temperature range used in step 2. When a volatilizable base is used, the pH of the solution can be maintained by continuously adding the base.

[0147] The inorganic base catalyst is preferably aqueous ammonia, which is inexpensive, economically advantageous, and allows the reaction to proceed smoothly.

[0148] The basic catalyst may be used alone or in the form of a mixture (blend) of two or more kinds.

[0149] The concentration of the basic catalyst in the solution is preferably 0.1% by mass to 5% by mass, and more preferably 0.5% by mass to 3% by mass.

[0150] In step 2, the organic polymer particles (such as polystyrene particles) prepared in step 1, an alkoxysilane or an alkoxysilane and a metal alkoxide, and a basic catalyst are added to a solvent and stirred to prepare a solution, and core-shell particles having the organic polymer particles as a core and a shell covering the organic polymer particles can be formed in the solution.

[0151] Production of core-shell particles There are no particular limitations on the temperature of the solution in step 2. The temperature of the solution in step 2 is preferably 5°C to 200°C, and more preferably 5°C to 150°C. By adjusting the temperature of the solution in step 2 within the above range, the solvent does not evaporate and the reaction can proceed smoothly.

[0152] The stirring time in step 2 is not particularly limited. The stirring time in step 2 is preferably 1 minute to 1,200 minutes, and more preferably 1 minute to 600 minutes. By adjusting the stirring time in step 2 within the above range, the polymerization reaction can proceed smoothly.

[0153] Step 2 makes it possible to successfully form core-shell particles having the organic polymer particles (such as polystyrene particles) prepared in step 1 as cores and a silica-based shell covering the polystyrene particles.

[0154] (3) Step 3 (Production of Silica Particles) The method for producing silica particles of the present invention includes a step (step 3) of first carbonizing (thermally decomposing) the core-shell particles (the core-shell particles obtained in step 2) and then calcining them, thereby removing the organic polymer particles that are the cores of the core-shell particles.

[0155] The carbonization treatment is preferably carried out in the temperature range of 400°C to 1,200°C.

[0156] The calcination treatment is preferably carried out for a treatment time of 3 hours or more.

[0157] Step 3 is a step of removing the organic polymer particles that form the core of the core-shell particles by carbonizing (thermal decomposition) the core-shell particles obtained in step 2. The interior of the core-shell particles is filled with organic polymer particles as the core, and by carbonizing (thermal decomposing) these organic polymer particles, the organic polymer particles that form the core of the core-shell particles are removed, making the shell hollow, and it is possible to produce silica particles that can be used favorably as a highly functional material.

[0158] In the method for producing silica particles of the present invention, when producing silica particles, core-shell particles are subjected to a carbonization treatment before being fired, thereby making it possible to produce new silica particles having a low true density and excellent dispersibility.

[0159] In step 3, the organic polymer particles are removed by thermal decomposition. The thermal decomposition is carried out by first carbonizing the silica particles and then calcining them. The temperatures of the carbonizing and calcining processes are adjusted so that the shells of the silica particles (hollow silica particles) are not destroyed, and the organic polymer particles and any other organic components that may remain inside the silica particles are removed.

[0160] Carbonization Step 3 is carried out by first carbonizing the core-shell particles and then calcining them.

[0161] When core-shell particles are heat-treated in air, the organic polymer in the core of the silica particles decomposes and gasifies (cracked gas). The generated cracked gas may ignite in an electric furnace, or may pass through the shell of the silica particles and be ejected, creating holes in the shell, which may reduce the true density of the hollow silica.

[0162] From this point of view, the carbonization treatment is preferably a heat treatment performed in a low-oxygen state.

[0163] The carbonization treatment is preferably a heat treatment under a low-oxygen condition, for example, by filling a heating furnace with an inert gas (Ar gas, CO, etc.), N gas, or water vapor (H O) to prevent the generation of decomposition gases. The carbonization treatment can be performed using a carbonization device that can be used appropriately under an atmosphere of an inert gas, N gas, or water vapor (H O).

[0164] When the carbonization treatment is carried out in an inert gas or N2 gas atmosphere, for example, a batch furnace (a gas atmosphere device in which an inert gas such as N2, CO2, or Ar is introduced into the furnace and heat treatment is carried out in a low oxygen concentration, heat treatment temperature: about 550°C, for example, a hot air circulation type inert gas atmosphere device, medium temperature heat treatment machine RBA type, manufactured by Thermal Co., Ltd.) is preferably used.

[0165] When the carbonization treatment is carried out in an inert gas or N2 gas atmosphere, for example, a continuous furnace (heat treatment temperature: approximately 450°C to 800°C, a gas heating device that continuously carries out the carbonization treatment within a single tube, for example, Takasago Kogyo Co., Ltd., gas heated rotary kiln) is preferably used.

[0166] When the carbonization treatment is carried out in a superheated steam atmosphere, for example, a batch furnace (for example, a batch type carbonization apparatus, CYT series, CYT-200, etc., manufactured by CYC Corporation) is preferably used.

[0167] The carbonization treatment (pyrolysis) is carried out using a carbonization apparatus, preferably a batch-type carbonization apparatus.

[0168] When a batch-type carbonization device is used, 1. the thermal effect due to direct heating is excellent, 2. the temperature inside the carbonization chamber (pyrolysis chamber, dry distillation box) can be made uniform due to the convection effect, 3. the contact area with the material being carbonized can be increased due to the convection effect, and 4. it is a sealed (double-structured) device that blocks oxygen (under oxygen-free conditions) and heats the pyrolysis chamber, allowing for smooth carbonization.

[0169] Carbonization of core-shell particles (dry powder) can be carried out efficiently using a carbonization device. In the carbonization device, the carbonization chamber is heated and superheated steam is used to evaporate the water content of the organic polymer particles when the temperature reaches around 400°C.

[0170] In the carbonization process, the core-shell particles (dry powder) are placed in a carbonization chamber (carbonization box), and while superheated steam is supplied into the carbonization chamber (carbonization box), the particles are heated by combustion gas from outside the carbonization chamber (carbonization box). In the carbonization process, the core-shell particles (dry powder) are carbonized by supplying superheated steam into the carbonization chamber (carbonization box).

[0171] In the carbonization treatment, the core-shell particles (dry powder) are carbonized using superheated steam, preferably in a temperature range of 400° C. to 1,200° C. In the carbonization step, the core-shell particles (dry powder) are carbonized using superheated steam, more preferably in a temperature range of 450° C. to 800° C., and even more preferably in a temperature range of 500° C. to 700° C. (low temperature region).

[0172] The time for the carbonization treatment is not particularly limited and may be adjusted as appropriate, preferably from 1 hour to 12 hours, more preferably from 2 hours to 10 hours, and even more preferably from 4 hours to 8 hours.

[0173] The carbonization process uses superheated steam, which reduces the temperature difference within the carbonization chamber (distillation box) due to the convection effect, allowing the carbonization process to proceed smoothly.

[0174] The carbonization treatment can be preferably carried out using a commercially available carbonization apparatus using superheated steam at a temperature range of about 450° C. to 550° C. for 4 to 8 hours. The carbonization apparatus can be, for example, a batch-type carbonization apparatus (CYT series, CYT-200, etc.) manufactured by CYC Corporation.

[0175] In the method for producing silica particles of the present invention, when producing silica particles, core-shell particles are subjected to a carbonization treatment before being fired, thereby making it possible to produce new silica particles having a low true density and excellent dispersibility.

[0176] firing treatment Step 3 is carried out by first carbonizing the material and then calcining it.

[0177] The firing treatment is preferably carried out using an electric furnace.

[0178] The calcination treatment is carried out by calcining the core-shell particles (dry powder) after carbonization in an electric furnace, preferably in a temperature range of 350°C to 1,500°C, more preferably in a temperature range of 400°C to 1,200°C, and even more preferably in a temperature range of 600°C to 1,100°C (high temperature range).

[0179] The calcination treatment is preferably carried out for a treatment time of 3 hours or more, more preferably 4 hours or more, even more preferably 5 hours or more, and particularly preferably 6 hours or more, with the upper limit of the calcination treatment time being approximately 10 hours.

[0180] In order to remove the organic polymer particles, a baking treatment is carried out after the carbonization treatment, whereby destruction of the shell is suppressed and the organic polymer particles can be removed well from the core-shell particles.

[0181] The firing treatment can be preferably carried out using a commercially available electric furnace at a temperature range of about 1,000°C to 1,100°C for a treatment time of 3 hours or more.

[0182] The powder of hollow silica particles obtained by removing the organic polymer particles from the organic core-shell particles is referred to as "hollow silica particles." The obtained powder of hollow silica particles can be dispersed in a solvent using a disperser, and subsequently subjected to a hydrophobic treatment.

[0183] A dispersing machine, preferably an ultrasonic homogenizer, a bead mill or the like, is used.

[0184] In step 3, the organic polymer particles, which are the cores of the core-shell particles, are thermally decomposed, and the organic polymer particles can be removed.

[0185] Through step 3 and the subsequent steps, (1) True density is 0.8 g / cm 3 ~1.4g / cm 3 and (2) In the particle size distribution, the frequency of particles larger than twice the average particle size is 15% or less; (3) Silica particles (hollow silica particles) with a water absorption of 1.0% by mass or less can be produced.

[0186] (4) Shell coating process The method for producing silica particles of the present invention may further include, after step 3, a step of coating the surfaces of the silica particles (hollow silica particles) with a shell.

[0187] The average thickness of the shell of the silica particles can be adjusted by further coating the surface of the silica particles with a shell.

[0188] The method for coating the surface of the silica particles with a shell is not particularly limited. The method for coating the surface of the silica particles with a shell is preferably similar to the method for producing core-shell particles in step 2, in which the organic polymer particles in step 2 are replaced with hollow silica particles obtained in step 3, and the surfaces of the hollow silica particles can be further coated with a shell.

[0189] (5) Step 4 (Hydrophobic treatment of hollow silica particles) The method for producing silica particles of the present invention preferably includes, after step 3 or the shell-coating step, step 4 of subjecting the hollow silica particles obtained in step 3 to a hydrophobic treatment (hydrophobic surface treatment). Step 4 can effectively impart hydrophobicity to the surfaces of the hollow silica particles.

[0190] The hydrophobic treatment method is not particularly limited, and is preferably a method in which, after step 3 or the shell coating step, trialkoxysilane and organosilazane are added to the hollow silica particles obtained in step 3 or the shell coating step in a solvent, and the mixture is heated.

[0191] Trialkoxysilane and organosilazane may be used in combination.

[0192] solvent The solvent used in step 4 is preferably water.

[0193] The solvent is preferably a hydrophilic solvent.

[0194] The hydrophilic solvent is preferably an alcohol such as methanol, ethanol, n-propanol, isopropanol (IPA), ethylene glycol, propylene glycol, 1,4-butanediol, etc. The hydrophilic solvent is preferably a ketone such as acetone, methyl ethyl ketone, etc. The hydrophilic solvent is preferably an ester such as ethyl acetate, etc.

[0195] The hydrophilic solvent is preferably an alcohol, more preferably methanol, ethanol, isopropanol, or the like.

[0196] When an alcohol such as isopropanol is used as the solvent, the hollow silica particles can be effectively subjected to the hydrophobic treatment.

[0197] The solvent may be one of these solvents or a mixture (blend) of two or more of them.

[0198] The solvent is preferably a mixed solvent of water and a hydrophilic solvent. The mass ratio of the hydrophilic solvent (e.g., methanol) to water in the mixed solvent is not particularly limited. The mass ratio of the hydrophilic solvent to water in the mixed solvent is preferably 90:10 to 10:90, and more preferably 30:70 to 10:90. By adjusting the mass ratio of the hydrophilic solvent to water in the mixed solvent to fall within the above range, the hollow silica particles can be satisfactorily hydrophobized.

[0199] trialkoxysilane The trialkoxysilane is not particularly limited. The trialkoxysilane preferably includes 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, trifluoropropyltrimethoxysilane, etc. The trialkoxysilane more preferably includes 3-methacryloxypropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, trifluoropropyltrimethoxysilane, etc.

[0200] The trialkoxysilane may be used alone or in the form of a mixture (blend) of two or more trialkoxysilanes.

[0201] The concentration of trialkoxysilane in the solution is preferably 0.01% by mass to 30% by mass, and more preferably 0.05% by mass to 25% by mass.

[0202] The amount of trialkoxysilane used is not particularly limited. The amount of trialkoxysilane used is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, and even more preferably 0.1% by mass to 3% by mass, relative to 100% by mass of silica. By adjusting the amount of trialkoxysilane used within the above range, the hollow silica particles can be effectively hydrophobized.

[0203] The hydrophobic treatment using trialkoxysilane is carried out by heating, preferably at 30° C. or higher, more preferably at 40° C. or higher, and even more preferably at 50° C. or higher. The upper limit of the heating temperature is preferably 90° C. or lower, more preferably 80° C. or lower. By adjusting the heating temperature for the hydrophobic treatment using trialkoxysilane within the above range, the reaction between the silica particles and the trialkoxysilane can be favorably carried out in the solvent without aggregation.

[0204] The heating time for the hydrophobization treatment using trialkoxysilane is not particularly limited, and is preferably 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, and even more preferably 1 hour to 20 hours.

[0205] Organosilazanes The organosilazane is not particularly limited, but preferably, tetramethyldisilazane, hexamethyldisilazane, pentamethyldisilazane, or the like is used.

[0206] The organosilazanes may be used singly or in the form of a mixture (blend) of two or more.

[0207] The amount of organosilazane used is not particularly limited. The amount of organosilazane used is preferably 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and even more preferably 40% by mass to 80% by mass, relative to 100% by mass of silica. By adjusting the amount of trialkoxysilane used within the above range, the hollow silica particles can be effectively hydrophobized.

[0208] The hydrophobic treatment using organosilazane is carried out by heating, preferably at 30° C. or higher, more preferably at 40° C. or higher, and even more preferably at 50° C. or higher. The upper limit of the heating temperature is preferably 90° C. or lower, more preferably 80° C. or lower. By adjusting the heating temperature for the hydrophobic treatment using organosilazane within the above range, the reaction between the silica particles and the organosilazane can be favorably carried out in the solvent without aggregation.

[0209] The heating time for the hydrophobic treatment using organosilazane is not particularly limited and is preferably 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, and even more preferably 1 hour to 20 hours.

[0210] Trialkoxysilane and organosilazane may be used in combination.

[0211] The solvent of the solution containing the hydrophobized hollow silica particles may be replaced with another solvent (such as water), and the solution containing the hydrophobized hollow silica particles may be filtered or dried (such as vacuum dried) to remove the solvent, thereby preparing a solution powder containing the hydrophobized hollow silica particles.

[0212] [4] Manufacturing method for core-shell particles The method for producing core-shell particles of the present invention preferably includes the steps of: (1) Step 1 of preparing organic polymer particles by carrying out a polymerization reaction of an organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent; and (2) The method includes a step 2 of adding the organic polymer particles obtained in the step 1, an alkoxysilane or an alkoxysilane and a metal alkoxide, and a basic catalyst to a solvent, and stirring the mixture to prepare a solution, thereby forming core-shell particles in the solution, each having an organic polymer particle as a core and a shell covering the organic polymer particle.

[0213] Steps 1 and 2 are the same as steps 1 and 2 described in the method for producing silica particles.

[0214] The core-shell particles produced by the core-shell particle production method of the present invention are suitable as core-shell particles to be used in step 3 of the silica particle production method of the present invention, after the organic polymer particles that form the core of the core-shell particles have been removed by carbonization treatment (thermal decomposition). [Example]

[0215] The present invention will be specifically explained by showing examples.

[0216] However, the present invention is not limited to the examples.

[0217] Polystyrene particles and core-shell particles were prepared and hollow silica particles were produced according to the formulation and production conditions in Table 1. Specifically, the procedures are as follows.

[0218] (1) Examples and Comparative Examples Example 1 Step 1: Production of polystyrene particles First, 737 g of ultrapure water, 2949 g of methanol, and 369 g of styrene monomer (organic monomer) were poured into a four-neck flask, and the mixture was heated to an internal temperature of 55°C to 70°C while stirring at 250 rpm in a nitrogen atmosphere.

[0219] Next, a 5 wt % aqueous solution of AIBA (2,2'-azobis(isobutylamidine) dihydrochloride) (AIBA 7 g, ultrapure water 140 g) previously dissolved in ultrapure water was added as a polymerization initiator, and a polymerization reaction was carried out at 55°C to 75°C for 3 hours.

[0220] Thereafter, a 5% aqueous solution of polyvinylpyrrolidone (PVP) in methanol (37 g of PVP, 560 g of methanol, 140 g of water) was added as a dispersant, and the mixture was further heated under reflux for 3 hours to prepare a polystyrene particle reaction solution.

[0221] As PVP, "PVP K-90 manufactured by Ashaland" and "Pitscol K-60L manufactured by Daiichi Kogyo Co., Ltd." are available. In the examples, "PVP K-90 manufactured by Ashaland" was used as PVP.

[0222] The polystyrene particle reaction solution was poured into another four-necked flask and heated with a mantle heater to replace the contents with methanol, and the reaction was completed when the internal temperature reached 70°C.

[0223] Polystyrene particles, which are organic polymer particles, were prepared in methanol.

[0224] <Polystyrene particle yield> 2 g of the polystyrene particle reaction solution was weighed out into a petri dish and dried on a hot plate at 120° C. for 1 hour, and the yield of polystyrene particles was calculated according to the following formula.

[0225] (Polystyrene particle yield (%)) = {[(Sample weight after drying (g)) - (PVP charge weight in sample before drying (g))] ÷ [Styrene charge weight in sample before drying (g)]} × 100

[0226] Step 2: Production of core-shell particles First, a reaction apparatus equipped with a four-necked flask, a stirring blade, and a water bath was prepared.

[0227] Liquid A was prepared by mixing 376 g of TMOS (tetramethoxysilane) (alkoxysilane) and 744 g of methanol.

[0228] Furthermore, 1,427 g of the polystyrene particle dispersion liquid (polystyrene concentration 7.6 wt%) produced in step 1 was placed in a flask, and 829 g of water and 823 g of methanol were added as solvents, followed by 268 g of 28% aqueous ammonia solution (basic catalyst) to prepare liquid B.

[0229] While maintaining the temperature of solution B at 30°C and stirring at 250 rpm, solution A was added over 190 minutes.

[0230] The core-shell particle dispersion was prepared by adding water dropwise to the solution, and the water and ammonia in the concentrated solution were replaced with water by heating and atmospheric distillation while maintaining the same volume or more.

[0231] Step 3: Production of hollow silica particles (carbonization treatment) The aqueous dispersion of core-shell particles obtained in step 2 was dried on a hot plate at a temperature of 130° C. to obtain a powder of core-shell particles.

[0232] First, the obtained core-shell particle powder was carbonized using superheated steam at a temperature of 500° C. for 4 hours in a batch carbonizer (CYT-200, manufactured by CYC Corporation).

[0233] Next, the mixture was calcined (heat treated) in an electric furnace at 1,050°C for 3 hours to remove the polystyrene particles and produce a powder of hollow silica particles.

[0234] Pure water was added to the obtained powder of hollow silica particles (silica concentration 20 wt%), and the mixture was dispersed for 135 minutes using an ultrasonic homogenizer (UP-400S, manufactured by Hielscher).

[0235] The resulting dispersion was centrifuged at 3,200 rpm for 10 minutes using a high-speed microcentrifuge (Hitachi Koki Co., Ltd., himac CF-16N), and the supernatant was collected and filtered using a 7 μm quantitative filter paper to obtain a hollow silica particle dispersion (silica concentration 16 wt%).

[0236] The silica concentration was calculated from the remaining amount after drying the hollow silica particle dispersion and then heating it at 800°C.

[0237] Step 4: Preparation of surface-treated hollow silica particles First, a reaction apparatus equipped with a four-neck flask, a stirring blade, and a water bath was prepared. 400 g of the hollow silica aqueous dispersion obtained in step 3, 274 g of ultrapure water, 404 g of IPA (isopropanol), and 1.4 g of N-phenyl-3-aminopropyltrimethoxysilane (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.) (trialkoxysilane) were mixed in the flask, stirred, and heated at 75°C for 1 hour.

[0238] Next, 39 g of hexamethyldisilazane (SZ-31 manufactured by Shin-Etsu Chemical Co., Ltd.) (organosilazane) was added dropwise, and the mixture was heated for a further 2 hours.

[0239] The reaction solution was then cooled to 50°C, and 559 g of ultrapure water and 31 g of 3M sulfuric acid were added in that order, after which the solid content was collected by filtration under reduced pressure.

[0240] The recovered solid was washed with ultrapure water and dried in vacuum at 120°C to prepare hollow silica particles.

[0241] Example 2 In step 4 of Example 1, N-phenyl-3-aminopropyltrimethoxysilane was not mixed, and only 394 g of hexamethyldisilazane was added dropwise.

[0242] Other than that, the same conditions as in Example 1 were used.

[0243] Example 3 In step 4 of Example 1, 400 g of the hollow silica particle aqueous dispersion, 274 g of ultrapure water, 404 g of IPA, and 1.1 g of N-phenyl-3-aminopropyltrimethoxysilane were mixed and stirred, and heated at 75° C. for 1 hour.

[0244] Other than that, the same conditions as in Example 1 were used.

[0245] Comparative Example 1 In step 3 of Example 1, the core-shell particles were not carbonized but instead calcined (heat treated) in an electric furnace at 1,050° C. for 3 hours.

[0246] Other than that, the same conditions as in Example 1 were used.

[0247] Comparative Example 2 In step 3 of Example 1, the core-shell particle powder was first carbonized using superheated steam in a batch carbonizer (CYT-200, manufactured by CYC Corporation) at a temperature of 500°C for 4 hours, and then calcined (heat-treated) in an electric furnace at a temperature of 1,075°C for 2 hours.

[0248] Other than that, the same conditions as in Example 1 were used.

[0249] Comparative Example 3 In step 3 of Example 1, the core-shell particle powder was first carbonized using superheated steam in a batch carbonizer (CYT-200, manufactured by CYC Corporation) at a temperature of 500°C for 4 hours, and then calcined (heat-treated) in an electric furnace at a temperature of 1,000°C for 1 hour.

[0250] Other than that, the same conditions as in Example 1 were used.

[0251] Comparative Example 4 In step 3 of Example 1, 7.7 g of citric acid (anhydrous citric acid, manufactured by Fuso Chemical Co., Ltd.) was added to the aqueous dispersion of core-shell particles, and the mixture was dried on a hot plate at a temperature of 130°C to obtain a powder of core-shell particles.

[0252] The obtained core-shell particle powder was heat treated in an electric furnace at 1,050° C. for 3 hours without being carbonized.

[0253] Other than that, the same conditions as in Example 1 were used.

[0254] The properties of the particles obtained in the examples and comparative examples were measured by the following methods.

[0255] (2) Evaluation test Particle size The powder of hollow silica particles obtained in step 4 was photographed using an SEM (scanning electron microscope: JSM-7900F, manufactured by JEOL Ltd.) at an acceleration voltage of 8 kV, and the minor diameters of 100 randomly selected particles were measured and their average value was calculated.

[0256] Image analysis was performed using the image analysis and measurement software WinROOF.

[0257] true density The true density of 0.3 g of the hollow silica particle powder obtained in step 4 was measured using a nitrogen gas pycnometer (Ultrapyc 5000 Micro, manufactured by Anton Paar Japan Co., Ltd.).

[0258] Water absorption test 1 g of the hollow silica particle powder obtained in step 4 was stored for 7 days in an environment with a temperature of 50°C and a humidity of 75%, and 0.1 g of the powder was sampled and the moisture content (mass%) was measured using a Karl Fischer moisture meter (MKA-610, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0259] MEK filterability 2 g of the hollow silica particle powder obtained in step 4 and 8 g of methyl ethyl ketone (MEK) were mixed and stirred for 2 hours, then filtered using a 5 μm pore size syringe filter (filter paper that allows substances with a size of 5 μm or less to pass through), and the amount of liquid passing through was weighed.

[0260] (MEK filtration performance (mass%, wt%)) = [Amount of liquid passed (g)] ÷ [Amount of MEK dispersion of hollow silica particles (10 g)] × 100

[0261] Number of particles over 1μm (particle size distribution) The particle size distribution of the hollow silica particle powder obtained in step 4 was measured using a laser diffraction / scattering particle size distribution analyzer (LA-950, manufactured by Horiba, Ltd.), and the frequency (%) of particles with a particle diameter of 1 μm or more in the hollow silica particle powder was calculated.

[0262] The results are shown in Table 1.

[0263] [Table 1]

[0264] (3) Evaluation results The hollow silica particles in Comparative Example 1 were prepared by subjecting the core-shell particle powder to only a calcination treatment without carbonization treatment. The hollow silica particles in Comparative Example 1 had a particle size distribution in which the frequency of particles larger than twice the average particle size exceeded 15%.

[0265] The hollow silica particles of Comparative Example 2 were prepared by carbonizing the core-shell particle powder and then calcining it for 2 hours. The hollow silica particles of Comparative Example 2 had a particle size distribution in which the frequency of particles larger than twice the average particle size exceeded 15%.

[0266] The hollow silica particles of Comparative Example 3 were prepared by carbonizing the core-shell particle powder and then calcining it for 1 hour. The hollow silica particles of Comparative Example 3 had a particle size distribution in which the frequency of particles larger than twice the average particle size exceeded 15%, and a water absorption of more than 1.0% by mass.

[0267] The hollow silica particles of Comparative Example 4 were prepared by adding citric acid to an aqueous dispersion of core-shell particles, and then calcining the resulting core-shell particle powder without carbonizing it. The hollow silica particles of Comparative Example 3 had a particle size distribution in which the frequency of particles larger than twice the average particle size exceeded 15%.

[0268] Examples 1 to 3 are embodiments of the present invention, and are hollow silica particles prepared by carbonizing a core-shell particle powder at a temperature range of 400°C to 1,200°C and then calcining the powder for 3 hours or more. The hollow silica particles of Examples 1 to 3 have the following characteristics: (1) a true density of 0.8 g / cm 3 ~1.4g / cm 3 (2) In the particle size distribution, the frequency of particles larger than twice the average particle size was 15% or less, and (3) the amount of water absorption was 1.0% by mass or less.

[0269] (4) Industrial applicability The hollow silica particles of the present invention are novel hollow silica particles having a low true density and excellent dispersibility.

[0270] According to the method for producing hollow silica particles of the present invention, when producing hollow silica particles, core-shell particles are subjected to a carbonization treatment before being fired, thereby making it possible to produce new hollow silica particles having a low true density and excellent dispersibility.

[0271] The hollow silica particles of the present invention are useful for multilayer printed circuit boards, wire coating materials, semiconductor encapsulants, etc.

Claims

1. (1) True density is 0.8 g / cm 3 ~1.4g / cm 3 and (2) When mixed with methyl ethyl ketone and filtered through a syringe filter with a pore size of 5 μm, the filterability is 80% by mass or more; (3) The water absorption is 1.0% by mass or less. Silica particles.

2. The silica particles according to claim 1, wherein the silica particles are hollow silica particles.

3. A method for producing silica particles, comprising: The method includes a step of first carbonizing the core-shell particles and then calcining them, The carbonization treatment is carried out for a treatment time of 1 hour to 12 hours at a temperature range of 400°C to 1,200°C, The firing treatment is carried out for a treatment time of 3 to 10 hours at a temperature range of 350°C to 1,500°C, Silica particles are (1) True density is 0.8 g / cm 3 ~1.4g / cm 3 and (2) When mixed with methyl ethyl ketone and filtered through a syringe filter with a pore size of 5 μm, the filterability is 80% by mass or more; (3) The water absorption is 1.0% by mass or less. Method for producing silica particles.

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