Silica particles and method for producing silica particles

Abstract

The present invention relates to: a method for producing silica particles without using citric acid; and silica particles having excellent true density and dispersibility. The silica particles have (1) a true density of 0.8-1.4 g / cm3, (2) a frequency distribution value of particles greater than twice the average particle diameter in the particle size distribution of 15% or less, and (3) a water absorption of 1.0 mass% or less.

Description

Technical Field

[0001] The present invention relates to silicon dioxide particles and a method for producing silicon dioxide particles. Background Art

[0002] Patent document 1 is a technology disclosed by the applicant of the present application, which discloses a hollow nano-silica particle, wherein (1) the average particle size is 50 to 150 nm, (2) the average shell thickness is 5 to 25 nm, and (3) the average particle size is 100 to 200 nm under solid NMR ( 29 In the measurement of Si / MAS, the integrated intensity (I Q2 ) and the integrated intensity (I Q4 ) ratio (I Q2 / I Q4 ) is less than 0.20, (4) the ratio of the peak intensity Psa of aggregated particles in the particle size distribution within the particle size range of 50 to 500 nm measured by a disc centrifugal particle size distribution measuring device to the peak intensity Psm of the main particles as non-aggregated hollow nano-silica particles is Psa / Psm is less than 0.4. This technology is a technology that improves dispersibility by sintering at a temperature of 700°C in the presence of an organic acid such as citric acid. Since this hollow nano-silica particle suppresses the generation of aggregated particles and suppresses the reflection of light, it can be used in various items that require anti-light reflection performance.

[0003] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2020-176037 Summary of the invention

[0004] Problems to be solved by the invention The present invention provides a method for producing silicon dioxide particles without using citric acid, and provides silicon dioxide particles having excellent true density and dispersibility.

[0005] Technical solutions to solve problems The inventors of the present invention conducted intensive research and developed a new type of silica particles (preferably hollow silica particles) having low true density and excellent dispersibility by carbonizing core-shell particles before firing when manufacturing silica particles.

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

[0007] Item 1: A silicon dioxide particle, wherein: (1) True density is 0.8g / cm 3 ~1.4g / cm3 , (2) The frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, (3) The water absorption is less than 1.0 mass %.

[0008] Item 2 The silica particles according to item 1 above, wherein the silica particles have been subjected to (4) carbonization and firing.

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

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

[0011] Item 5 A method for producing silicon dioxide particles, comprising the steps of first carbonizing the core-shell particles and then sintering them. Silica particles (1) True density is 0.8g / cm 3 ~1.4g / cm 3 , (2) The frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, (3) The water absorption is less than 1.0 mass %.

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

[0013] Effects of the Invention The present invention provides a method for producing silicon dioxide particles without using citric acid, and provides silicon dioxide particles excellent in true density and dispersibility. DETAILED DESCRIPTION

[0014] The present invention is described in detail below.

[0015] The specific embodiments of the present invention are provided to better understand the purpose of the present invention and do not constitute a limitation on the content of the invention unless otherwise stated.

[0016] In the present specification, “include” and “contain” are concepts that include “comprise”, “consist essentially of”, and “consist of”.

[0017] In the present specification, when a numerical range is expressed as "A to B", it means "A or more and B or less".

[0018] In this specification, expressions such as "part" and "%" are generally used.

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

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

[0021] The silica particles of the present invention have a true density of (1) 0.8 g / cm 3 ~1.4g / cm 3 , (2) the frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, and (3) the water absorption is less than 1.0 mass %.

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

[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 low true density and excellent dispersibility.

[0026] The silica particles of the present invention can be effectively used for multilayer printed circuit boards, wire covering materials, semiconductor packaging materials, and the like.

[0027] Silica compounds and metal oxides The silica-based compound forming the silica particles is not particularly limited as long as it contains silica, and may consist only of 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, the metal oxide is an oxide of aluminum, titanium, zirconium, or the like.

[0030] As the metal oxide, these metal oxides may be used alone or in combination of two or more.

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

[0032] When oxides of titanium and zirconium are used as the metal oxide, the refractive index of the outer shell of the silica particles can be adjusted.

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

[0034] Since the silica particles of the present invention have a low-density air layer, their true density is lower than that of conventional silica (2.2 g / cm 3 ).

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

[0036] The true density of the silica particles to be measured is preferably obtained by drying the powder thereof at 120° C. under reduced pressure for 2 hours and then measuring the true density of the dried silica particles.

[0037] The true density of silica particles is 0.8 g / cm 3 ~1.4g / cm 3 , preferably 0.8 g / cm 3 ~1.3g / cm 3 , more preferably 0.9 g / cm 3 ~1.2g / cm 3 , more preferably 0.9 g / cm 3 ~1.1g / cm 3 By adjusting the true density within the above range, it is possible to produce silica particles well, and silica particles having a low true density and excellent dispersibility without damage to the outer shell can be obtained.

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

[0039] The object of "particles larger than twice the average particle size" is not particles having a particle size twice the average particle size, but particles having a particle size larger than twice the average particle size.

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

[0041] The frequency distribution value of particles greater than twice the average particle size in the particle size distribution of silica particles is preferably as low as possible. The frequency distribution value of particles greater 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 further preferably 6% or less. The lower limit of the frequency distribution value of particles greater than twice the average particle size in the particle size distribution of silica particles is 0%. By adjusting the frequency distribution value of particles with a particle size of 1 μm or more in the particle size distribution to the above range, silica particles can be well manufactured to form silica particles with low true density and excellent dispersibility.

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

[0043] Water absorption test of silica particles The water absorption of the silica particles is a value obtained by storing the silica particles (1 g of powder) at a temperature of 50° C. and a humidity of 75% for 7 days, taking a 0.1 g powder sample, and measuring the water content of the silica particles using a Karl Fischer moisture analyzer (MKA-610, manufactured by Kyoto Electronics Co., Ltd.).

[0044] The water absorption value of the silica particles is preferably as low as possible. 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 further 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 to the above range, the silica particles can be well manufactured to form silica particles with low true density and excellent dispersibility.

[0045] (4) Carbonization and sintering of silica particles The silica particles of the present invention are preferably carbonized and fired. Carbonizing and firing the silica particles can produce silica particles with 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 is obtained by taking a picture of the particles using a SEM (scanning electron microscope: JSM-7900F, manufactured by JEOL Ltd.) at an accelerating voltage of 8 kV, measuring the minor axis diameters 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, further preferably 0.4 μm to 0.8 μm, and particularly preferably 0.4 μm to 0.7 μm. By adjusting the average particle size to the above range, silica particles can be well produced, and silica particles with low true density and excellent dispersibility can be formed.

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

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

[0052] Since the silica particles are hollow silica particles, silica particles having a low true density and excellent dispersibility can be preferably produced.

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

[0054] The MEK filterability of silica particles is firstly to mix silica particles (2g powder) and butanone (MEK) (8g) with stirring at 500rpm for 2 hours, and then to filter the mixture of silica particles and MEK using a syringe filter with a pore size of 5μm (filter paper that can filter materials with a size of 5μm or less).

[0055] The MEK filterability (mass %) of the silica particles is a value calculated by weighing the amount of the mixed liquid passing through and using the following formula.

[0056] MEK filterability (mass%, wt%) = [liquid throughput (g)] ÷ [amount of MEK dispersion of silica particles (10 g)] × 100.

[0057] The MEK filterability of the silica particles is preferably as high as possible. The MEK filterability of the silica particles is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. The upper limit of the MEK filterability of the silica particles is 100%. By adjusting the MEK filterability of the silica particles within the above range, the silica particles can be well manufactured to form silica particles with low true density and excellent dispersibility.

[0058] Average thickness of the outer shell (film) of silica particles The average thickness of the outer 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.

[0059] The average thickness of the shell forming the silica particles is obtained by taking a picture of the particles using a TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.) at an accelerating voltage of 200 kV, measuring the shell thickness of 100 particles at random, and calculating the average value.

[0060] By adjusting the average thickness of the outer shell to be within the above range, it is possible to produce silica particles well, and the outer shell is not damaged and the true density is low and the dispersibility is excellent.

[0061] The silica particles of the present invention are silica particles having low true density and excellent dispersibility. The silica particles of the present invention are silica particles having low true density and high dispersibility by optimizing the firing conditions (carbonization pretreatment).

[0062] [2] Core-shell particles The present invention comprises core-shell particles.

[0063] The core-shell particles of the present invention are core-shell particles having an organic polymer particle as a core and a silicon dioxide coating the organic polymer particle as an outer shell. The silicon dioxide particles of the present invention can be preferably produced by thermally decomposing the organic polymer particle of the core-shell particle.

[0064] Organic polymer particles The organic polymer particles are not particularly limited. The organic polymer particles are preferably organic polymer particles that are easily burned out by thermal decomposition after forming the shell. Specifically, the organic polymer particles are polystyrene particles, polymethyl methacrylate (PMMA) (resin) particles, and the like.

[0065] When polystyrene particles are used as the organic polymer particles, a positive zeta potential can be imparted to the polystyrene particles, thereby suppressing the generation of aggregated particles.

[0066] Dispersants The organic polymer particles preferably contain a dispersant. When the organic polymer particles contain a dispersant, the dispersant can be present on the surface of the organic polymer particles, thereby further suppressing aggregation of the organic polymer particles.

[0067] The dispersant is not particularly limited as long as it can produce organic polymer particles. Specifically, the dispersant is polyvinyl pyrrolidone (PVP), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene glycol (PPG), polypropylene oxide (PPO), collagen, polysaccharide (gum arabic), etc.

[0068] When polyvinyl pyrrolidone, hydroxypropyl cellulose or the like is used as the dispersant, aggregation of the organic polymer particles can be suppressed, thereby suppressing aggregation of the core-shell particles.

[0069] As the dispersant, one of these dispersants may be used alone, or two or more of them may be mixed (blended) and used.

[0070] 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% to 100% by mass, and more preferably 0.05% to 100% by mass relative to 100% by mass of the organic polymer particles. By adjusting the content of the dispersant to the above range, agglomeration of the organic polymer particles can be suppressed.

[0071] Silicon dioxide coated with organic polymer particles The silica compound forming the shell covering the organic polymer particles is the same as the silica compound forming the above-mentioned 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) forming the above-mentioned silica particles.

[0072] The 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 further preferably 0.4 μm to 0.8 μm.

[0073] The average particle size of the core-shell particles is the same as the average particle size of the silica particles described above. The particles are photographed using a SEM (scanning electron microscope: JSM-7900F, manufactured by JEOL Ltd.) at an accelerating voltage of 8 kV, and the sizes of the minor axis diameters of 100 particles are measured and the average value is calculated.

[0074] Image analysis was performed using the image analysis and measurement software WinROOF.

[0075] By using core-shell particles, silica particles can be produced well, and silica particles having a low true density and excellent dispersibility can be obtained.

[0076] [3] Method for producing silicon dioxide particles The method for producing the silicon dioxide particles of the present invention preferably comprises: (1) a step 1 of preparing organic polymer particles by polymerizing an organic monomer in a solution containing an organic monomer, a dispersant and a solvent; (2) a step 2 of adding the organic polymer particles obtained in step 1, alkoxysilane or alkoxysilane and metal alkoxide, and a basic catalyst to a solvent and stirring the mixture to prepare a solution, and forming core-shell particles having an organic polymer particle as a core and an outer shell covering the organic polymer particle in the solution; (3) a step 3 of first subjecting the core-shell particles obtained in step 2 to carbonization (thermal decomposition) and then subjecting them to calcination to remove the organic polymer particles serving as the inner core of the core-shell particles; and (4) After step 3, step 4 is to perform a hydrophobic treatment (hydrophobic surface treatment) on the hollow silica particles obtained in step 3.

[0077] In the method for producing silicon dioxide particles of the present invention, the above step 3 includes the steps of first carbonizing the core-shell particles and then calcining them, and the silicon dioxide particles that can be produced are: (1) True density is 0.8g / cm 3 ~1.4g / cm 3 , (2) The frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, (3) The water absorption is less than 1.0 mass %.

[0078] In the method for producing silica particles of the present invention, in the process of producing silica particles, by carbonizing the core-shell particles before firing, novel silica particles having a low true density and excellent dispersibility can be produced.

[0079] In the method for producing silica particles of the present invention, it is preferred that the carbonization treatment is performed at a temperature of 400° C. to 1,200° C., and the calcination treatment is performed for 3 hours or more.

[0080] The silica particles of the present invention are preferably produced favorably through the following steps.

[0081] (1) Step 1 (Production of organic polymer particles) Step 1 is a step of preparing organic polymer particles by polymerizing an organic monomer in a solution containing an organic monomer, a dispersant and a solvent.

[0082] Organic monomer The organic monomer is not particularly limited as long as it can produce organic polymer particles.

[0083] The organic monomer is preferably an organic monomer that can be formed into organic polymer particles that can be easily burned out by thermal decomposition after forming an outer shell. Specifically, the organic monomer is styrene used to produce polystyrene, methyl methacrylate used to produce polymethyl methacrylate (PMMA) (resin), and the like.

[0084] When styrene is used as the organic monomer, a positive zeta potential can be imparted to the polystyrene particles, thereby suppressing the generation of aggregated particles.

[0085] The polystyrene is not particularly limited. The polystyrene is preferably a polystyrene containing a structural unit derived from a hydrophobic monomer such as an alkyl (meth)acrylate and a structural unit of another copolymerizable monomer. The polystyrene is preferably an alkyl (meth)acrylate styrene having an alkyl group with 3 to 22 carbon atoms, 2-methylstyrene, or the like.

[0086] 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% to 20% by mass, more preferably 0.2% to 10% by mass, relative to 100% by mass of the solution. By adjusting the concentration of the organic monomer to the above range, the average particle size of the final product silica particles can be well controlled.

[0087] Dispersants The dispersant is not particularly limited as long as it can produce organic polymer particles. Specifically, the dispersant is polyvinyl pyrrolidone (PVP), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene glycol (PPG), polypropylene oxide (PPO), collagen, polysaccharide (gum arabic), etc.

[0088] When polyvinyl pyrrolidone, hydroxypropyl cellulose or the like is used as the dispersant, aggregation of the polystyrene particles can be suppressed, and aggregation of the core-shell particles formed in the subsequent step 2 can be suppressed.

[0089] As the dispersant, one of these dispersants may be used alone, or two or more of them may be mixed (blended) and used.

[0090] 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% to 10% by mass, more preferably 0.05% to 5% by mass, relative to 100% by mass of the solution. By adjusting the concentration of the dispersant to the above range, the aggregation of the organic polymer particles can be suppressed, and the aggregation of the core-shell particles formed in the subsequent step 2 can be suppressed.

[0091] Solvents As the solvent used in step 1, water is preferably used.

[0092] The solvent is preferably a hydrophilic solvent.

[0093] As the hydrophilic solvent, alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, and 1,4-butanediol are preferably used. Ketones such as acetone and butanone are preferably used. Esters such as ethyl acetate are preferably used as the hydrophilic solvent.

[0094] As the hydrophilic solvent, alcohols are preferably used, and methanol, ethanol, isopropanol, etc. are more preferably used.

[0095] As the solvent, one of these solvents may be used alone, or two or more of them may be mixed (blended) and used.

[0096] The solvent used in step 1 is preferably a mixed solvent of water and methanol. When a mixed solvent of water and methanol is used, aggregation of organic polymer particles can be suppressed, and aggregation of core-shell particles formed in the subsequent step 2 can be suppressed.

[0097] 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 further preferably 10:90 to 30:70. By adjusting the mass ratio of water to methanol to the above range, agglomeration of the organic polymer particles can be suppressed, and agglomeration of the core-shell particles formed in the subsequent step 2 can be suppressed.

[0098] 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 organic polymer particles can be obtained. The cationic polymerization initiator is preferably an inorganic peroxide, an organic initiator, a redox agent, etc. The cationic polymerization initiator is more preferably a free radical polymerization initiator such as an organic oxide or an azo compound.

[0099] Organic oxides are represented by the general formula RO-OR.

[0100] Azo compounds are represented by the general formula A-CN=CN-A.

[0101] Specifically, benzoyl peroxide, 2,2'-azobis(isobutyramidine) dihydrochloride (AIBA), 4,4'-azobis-4-cyanovaleric acid, azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylpropionamide) dihydrochloride (AAPH), etc. are used as the cationic polymerization initiator.

[0102] The cationic polymerization initiator is preferably 2,2'-azobis(isobutyramidine) dihydrochloride (AIBA) or 2,2'-azobis(2-methylpropionamide) dihydrochloride (AAPH), more preferably 2,2'-azobis(isobutyramidine) dihydrochloride (AIBA) or 4,4'-azobis-4-cyanovaleric acid, and still more preferably 2,2'-azobis(isobutyramidine) dihydrochloride (AIBA).

[0103] As the cationic polymerization initiator, these cationic polymerization initiators may be used alone or in combination of two or more.

[0104] In step 1, the concentration of the cationic polymerization initiator in the solution is not particularly limited. When the solution is 100% by mass, the concentration of the cationic polymerization initiator is preferably 0.01% to 1% by mass. By adjusting the concentration of the cationic polymerization initiator to the above range, the average particle size of the final product silica particles can be well controlled.

[0105] Polymerization In step 1, a polymerization reaction of an organic monomer is carried out in a solution containing an organic monomer, a dispersant and a solvent. The polymerization reaction is preferably carried out by mixing and stirring the solution.

[0106] The temperature during the polymerization reaction of the solution in step 1 is not particularly limited. The reaction temperature of the polymerization reaction is preferably 40° C. or higher and below the boiling point of the solvent used, and more preferably 50° C. to 90° C. By adjusting the reaction temperature of the polymerization reaction to the above range, the polymerization reaction can be carried out well without evaporating the solvent.

[0107] 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, more preferably 10 minutes to 10 hours. By adjusting the reaction time of the polymerization reaction to the above range, the polymerization reaction can be carried out well.

[0108] The organic polymer particles are prepared by performing 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 further preferably 0.3 μm to 0.7 μm. By adjusting the average particle size of the organic polymer particles to the above range, the average particle size of the core-shell particles formed in the subsequent step 2 and the average particle size of the hollow silica particles produced in step 3 can be formed in an appropriate range.

[0109] According to step 1, organic polymer particles can be produced well.

[0110] Yield of organic polymer particles (polystyrene particles, etc.) 2 g of the reaction solution of organic polymer particles was weighed in a petri dish and dried on a hot plate at 120° C. for 1 hour. The yield of the organic polymer particles was calculated according to the following formula.

[0111] Yield of organic polymer particles (%) ={[(weight of sample after drying (g)) - (amount of dispersant (PVP, etc.) fed into the sample before drying (g))] ÷[amount of organic monomer (styrene, etc.) fed into the sample before drying]} × 100.

[0112] (2) Step 2 (Manufacturing of core-shell particles) Step 2 is a step of adding the organic polymer particles prepared in step 1, alkoxysilane or alkoxysilane and metal alkoxide, and an alkaline catalyst to a solvent, stirring to form a solution, and forming core-shell particles having an organic polymer particle as a core and an outer shell covering the organic polymer particle in the solution.

[0113] Solvents Water is preferably used as the solvent used in step 2. When water is used, core-shell particles can be formed at low cost and safely.

[0114] The solvent is preferably a hydrophilic solvent.

[0115] As the hydrophilic solvent, alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, and 1,4-butanediol are preferably used. Ketones such as acetone and butanone are preferably used. Esters such as ethyl acetate are preferably used as the hydrophilic solvent.

[0116] As the hydrophilic solvent, alcohols are preferably used, and methanol, ethanol, isopropanol, etc. are more preferably used.

[0117] The solvent is preferably an alcohol of the same type as the alcohol generated by hydrolysis of the silicon compound. When the same type of alcohol is used as the alcohol generated by hydrolysis of the silicon compound, the solvent can be easily recovered and reused.

[0118] As the solvent, one of these solvents may be used alone, or two or more of them may be mixed (blended) for use.

[0119] The solvent is preferably a mixed solvent of water and a hydrophilic solvent. In the mixed solvent, the mass ratio of the hydrophilic solvent (methanol, etc.) to water is not particularly limited. In the mixed solvent, the hydrophilic solvent: water (mass ratio) is preferably 50:50 to 90:10, more preferably 60:40 to 80:20. By adjusting the mass ratio of the hydrophilic solvent to water in the mixed solvent to the above range, the average particle size of the silica particles can be set within an appropriate range.

[0120] 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 a temperature of 100° C. The hydrophobic solvent is preferably a straight-chain, branched or cyclic alkane having a carbon number of 6 to 10. Specifically, the hydrophobic solvent is hexane, cyclohexane, heptane, octane, isooctane, etc. Octane is more preferably used as the hydrophobic solvent.

[0121] Organic polymer particles The organic polymer particles used in step 2 are the organic polymer particles prepared in step 1 above.

[0122] The concentration of the organic polymer particles in the solution is preferably 0.01% by mass to 50% by mass, more preferably 0.01% by mass to 20% by mass.

[0123] Alkoxysilane The alkoxysilane used in step 2 is not particularly limited.

[0124] As the alkoxysilane, it is preferable to use a tetraalkoxysilane represented by the general formula (1) or a derivative thereof.

[0125] General formula (1) Si(OR 1 ) 4 (1) In the general formula (1), R 1 The same or different groups 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 further preferably lower alkyl groups having 1 to 3 carbon atoms.

[0126] In the general formula (1), R 1 Specifically, they include methyl, ethyl, propyl, isobutyl, butyl, pentyl and hexyl.

[0127] In general formula (1), when R is used 1 Methyl tetramethoxysilane (TMOS) and R 2 When tetraethoxysilane (TEOS) is ethyl, silicon dioxide can be well generated to obtain a dense shell. The alkoxysilane used in step 2 is more preferably tetramethoxysilane (TMOS). A dense shell refers to a shell formed by (or substantially formed by) siloxane bonds and having few residual silanol groups.

[0128] As the alkoxysilane, it is preferable to use a trialkoxysilane represented by the general formula (2) or a derivative thereof.

[0129] General formula (2) Si(OR 1 ) 3 R 2 (2) In general formula (2), R 1 R in the above general formula (1) 1 In general formula (2), R 2 is hydrogen or 1 The alkyl group (R 1 ) have the same alkyl group.

[0130] The derivative of alkoxysilane is preferably an oligocondensate obtained by partial hydrolysis of alkoxysilane.

[0131] As the alkoxysilane, these alkoxysilanes may be used alone or in combination of two or more.

[0132] When trialkoxysilane or tetraalkoxysilane is used as the alkoxysilane, aggregation of core-shell particles can be prevented and surface modification by a silane coupling agent or the like can be easily performed.

[0133] 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, further preferably 5% by mass to 50% by mass, particularly preferably 10% by mass to 40% by mass.

[0134] Metal alkoxide In step 2, alkoxysilane and metal alkoxide may be used in a mixed manner.

[0135] The metal alkoxide is not particularly limited, but aluminum alkoxide, titanium alkoxide, zirconium alkoxide, etc. are preferably used as the metal alkoxide.

[0136] When aluminum alkoxide is used, the surface charge (zeta potential etc.) of the outer shell can be adjusted.

[0137] When titanium alkoxide and zirconium alkoxide are used, the refractive index of the outer shell can be adjusted.

[0138] As the metal alkoxide, these metal alkoxides may be used alone or in combination of two or more.

[0139] The concentration of the metal alkoxide in the solution is preferably 0.01% by mass to 50% by mass, more preferably 0.01% by mass to 20% by mass.

[0140] In step 2, the alkoxysilane and the metal alkoxide may be added separately to prepare a solution.

[0141] In step 2, alkoxysilane and metal alkoxide may be mixed and hydrolyzed before being added to the solution. By mixing alkoxysilane and metal alkoxide and hydrolyzing them before being added to the solution, a shell having a bond represented by the following formula (1) and in which the metal represented by M in the formula (1) is uniformly distributed can be formed.

[0142] Si-OM (1) In the formula (1), M represents a metal, which is a metal derived from a metal alkoxide, and preferably represents aluminum, titanium or zirconium.

[0143] The method of mixing the alkoxysilane and the metal alkoxide, hydrolyzing them, and then adding them to the solution adopts the method described in Japanese Patent Application Laid-Open No. 2005-41722, for example.

[0144] Basic catalyst The basic catalyst used in step 2 is not particularly limited.

[0145] When an organic base catalyst containing no metal component or an inorganic catalyst containing no metal component is used as the alkaline catalyst, it is possible to avoid the mixing of metal impurities during the manufacturing process.

[0146] The organic base catalyst is preferably a nitrogen-containing organic base catalyst such as ethylenediamine, diethylenetriamine, triethylenetetramine, urea, ethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, or basic amino acid.

[0147] In step 2, when an organic base catalyst with low volatility is used, it will not volatilize within the temperature range of step 2, and the reaction can proceed well; and when a volatile base is used, the base can be continuously added to maintain the pH value of the solution.

[0148] The inorganic base catalyst is preferably ammonia water. In the case of using ammonia water, it is cheap, economically efficient, and can react well.

[0149] As the basic catalyst, one of these basic catalysts may be used alone, or two or more of them may be mixed (blended) and used.

[0150] The concentration of the basic catalyst in the solution is preferably 0.1% by mass to 5% by mass, more preferably 0.5% by mass to 3% by mass.

[0151] In step 2, the organic polymer particles (polystyrene particles, etc.) prepared in step 1, alkoxysilane or alkoxysilane and metal alkoxide, and an alkaline catalyst are added to a solvent and stirred to form a solution, thereby forming core-shell particles having an organic polymer particle as a core and an outer shell covering the organic polymer particle in the solution.

[0152] Fabrication of core-shell particles The solution temperature in step 2 is not particularly limited. The solution temperature in step 2 is preferably 5° C. to 200° C., more preferably 5° C. to 150° C. By adjusting the solution temperature in step 2 to the above range, the reaction can be carried out well without evaporating the solvent.

[0153] The stirring time in step 2 is not particularly limited. The stirring time in step 2 is preferably 1 minute to 1,200 minutes, more preferably 1 minute to 600 minutes. By adjusting the stirring time in step 2 to the above range, the reaction can be preferably performed.

[0154] According to step 2, core-shell particles having the organic polymer particles (polystyrene particles, etc.) prepared in step 1 as the inner core and the silica-based outer shell covering the polystyrene particles can be smoothly formed.

[0155] (3) Step 3 (Production of silica particles) The method for producing silica particles of the present invention comprises firstly subjecting the core-shell particles (core-shell particles obtained in step 2) to carbonization treatment (thermal decomposition) and then subjecting the core-shell particles to calcination treatment (step 3), thereby removing the organic polymer particles serving as the inner core of the core-shell particles.

[0156] The carbonization treatment is preferably performed at a temperature ranging from 400°C to 1,200°C.

[0157] The firing treatment is preferably performed for a treatment time of 3 hours or more.

[0158] Step 3 is a step of removing the organic polymer particles serving as the inner core of the core-shell particles by carbonizing (thermally decomposing) the core-shell particles obtained in step 2. The core-shell particles are filled with organic polymer particles as the inner core, and by carbonizing (thermally decomposing) the organic polymer particles, the organic polymer particles serving as the inner core of the core-shell particles can be removed, and the outer shell is made hollow, thereby producing silica particles that can be used as a high-performance material.

[0159] In the method for producing silica particles of the present invention, in the process of producing silica particles, by carbonizing the core-shell particles before firing, novel silica particles having low true density and excellent dispersibility can be produced.

[0160] In step 3, the organic polymer particles are removed by thermal decomposition. The thermal decomposition is performed by first performing a carbonization treatment and then performing a calcination treatment. By adjusting the temperatures of the carbonization treatment and the calcination treatment, the organic polymer particles and other organic components that may remain in the silica particles (hollow silica particles) can be removed without destroying the outer shell of the silica particles (hollow silica particles).

[0161] Carbonization treatment In step 3, the core-shell particles are treated by first carbonizing them and then calcining them.

[0162] When the core-shell particles are heat-treated in air, the organic polymer in the core of the silica particles is cracked and gasified (cracking gas). Once the cracking gas is generated, it is possible that the cracking gas burns in the electric furnace or passes through the outer shell of the silica particles and sprays out, thereby forming through holes in the outer shell and reducing the true density of the hollow silica.

[0163] Based on this point, the carbonization treatment is preferably performed as a heat treatment under a low oxygen state.

[0164] The carbonization treatment is preferably a heat treatment under low oxygen conditions, for example, by filling a heating furnace with an inert gas (Ar gas, CO 2 etc.), N 2 Gas or water vapor (H 2 O), to prevent the generation of cracking gas. Carbonization can also be used in an inert gas, N 2 Carbonization device used in an environment of gas or water vapor.

[0165] When carbonization is carried out in an inert gas or N 2 When the process is carried out under a gas environment, it is preferred to use, for example, a batch furnace (where N 2 , CO 2 A gas environment device in which inert gases such as Ar are introduced into the furnace to perform heat treatment at a low oxygen concentration, and the heat treatment temperature is about 550°C, such as the hot air circulation inert gas environment device and the medium temperature heat treatment device RBA type from Thearmaru Inc.).

[0166] When carbonization is carried out in an inert gas or N 2 When the carbonization is carried out in a gas environment, it is preferable to use, for example, a continuous furnace (a gas heating device that performs carbonization treatment continuously in a single pipe body at a heat treatment temperature of about 450° C. to 800° C., such as a gas-heated rotary kiln manufactured by Takasago Industry Co., Ltd.).

[0167] When the carbonization treatment is performed under a superheated steam atmosphere, it is preferable to use, for example, a batch furnace (for example, a batch carbonization device manufactured by CYC Corporation, CYT series CYT-200, etc.).

[0168] The carbonization treatment (thermal decomposition) is carried out using a carbonization device, preferably a batch carbonization device.

[0169] When using an intermittent carbonization device, (1) direct heating has a good thermal effect, (2) the convection effect can make the temperature in the carbonization treatment chamber (thermal decomposition chamber, distillation container) uniform, (3) the convection effect can expand the contact area with the carbonization treatment object, and (4) it is a (double-layer structure) closed equipment that can isolate oxygen (under anaerobic conditions) to heat the thermal decomposition chamber, so carbonization can be carried out well.

[0170] Carbonization of core-shell particles (dry powder) using a carbonization device will enable efficient carbonization. In the carbonization device, when the carbonization chamber is heated to about 400°C using superheated steam, the water content of the organic polymer particles being carbonized is evaporated.

[0171] The carbonization treatment is to place the core-shell particles (dry powder) in a carbonization treatment chamber (dry distillation container), supply superheated steam to the carbonization treatment chamber (dry distillation container), and heat the carbonization treatment chamber (dry distillation container) from the outside with fuel gas. In the carbonization treatment, the core-shell particles (dry powder) are carbonized by supplying superheated steam to the carbonization treatment chamber (dry distillation container).

[0172] The carbonization treatment is preferably performed by carbonizing the core-shell particles (dried powder) using superheated water vapor in a temperature range of 400° C. to 1,200° C. In the carbonization step, the core-shell particles (dried powder) are more preferably carbonized using superheated water vapor in a temperature range of 450° C. to 800° C., and further preferably in a temperature range of 500° C. to 700° C. (low temperature region).

[0173] The time of the carbonization treatment is not particularly limited. The carbonization treatment time can be adjusted appropriately, but is preferably 1 to 12 hours, more preferably 2 to 10 hours, and even more preferably 4 to 8 hours.

[0174] The carbonization process can be carried out by using superheated steam to reduce the temperature difference in the carbonization process chamber (dry distillation container) by utilizing the convection effect.

[0175] The carbonization treatment is preferably performed using a commercially available carbonization apparatus at a temperature range of about 450° C. to 550° C. using superheated steam for 4 to 8 hours. For example, a batch carbonization apparatus manufactured by CYC Corporation (CYT series CYT-200, etc.) can be used.

[0176] In the method for producing silica particles of the present invention, when producing silica particles, the core-shell particles can be carbonized before sintering, thereby producing novel silica particles having a low true density and excellent dispersibility.

[0177] Firing treatment Step 3 is implemented by first performing a carbonization treatment and then performing a firing treatment.

[0178] The firing treatment is preferably performed using an electric furnace.

[0179] The calcination treatment is performed by calcining the carbonized core-shell particles (dried powder) in an electric furnace at a temperature preferably in the range of 350°C to 1,500°C, more preferably in the range of 400°C to 1,200°C, and even more preferably in the range of 600°C to 1,100°C (high temperature range).

[0180] The calcination treatment time is preferably 3 hours or more. The calcination treatment time is more preferably 4 hours or more, further preferably 5 hours or more, and particularly preferably 6 hours or more. The upper limit of the calcination treatment time is about 10 hours.

[0181] Since the organic polymer particles are removed, damage to the outer shell can be suppressed by performing a calcination treatment after the carbonization treatment, and the organic polymer particles can be removed smoothly from the core-shell particles.

[0182] The firing treatment can preferably be performed using a commercially available electric furnace within a temperature range of about 1,000° C. to 1,100° C. for a treatment time of 3 hours or more.

[0183] 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 by a dispersing device and then subjected to a hydrophobic treatment.

[0184] As the dispersing device, an ultrasonic homogenizer, a bead mill or the like is preferably used.

[0185] According to step 3, the organic polymer particles serving as the inner core of the core-shell particles can be removed by thermally decomposing the organic polymer particles.

[0186] According to process 3, after the subsequent process, it can be well manufactured (1) True density is 0.8g / cm3 ~1.4g / cm 3 , (2) The frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, (3) Silica particles (hollow silica particles) having a water absorption amount of 1.0 mass % or less.

[0187] (4) Shell coating process The method for producing silica particles of the present invention may further include, after step 3, a step of further coating the surface of the silica particles (hollow silica particles) with a shell.

[0188] By further coating the surface of the silica particles with a shell, the average thickness of the shell of the silica particles can be adjusted.

[0189] The method of coating the surface of the silica particles with a shell is not particularly limited. The method of coating the surface of the silica particles with a shell can preferably be carried out by following the method for producing core-shell particles in step 2, converting the organic polymer particles in step 2 into hollow silica particles obtained in step 3, and further coating the surface of the hollow silica particles with a shell.

[0190] (5) Step 4 (Hydrophobic treatment of hollow silica particles) The method for producing silica particles of the present invention preferably comprises, after step 3 or after the step of coating with an outer shell, step 4 of subjecting the hollow silica particles obtained in step 3 to a hydrophobic treatment (hydrophobic surface treatment). According to step 4, the surface of the hollow silica particles can be made to have excellent hydrophobicity.

[0191] The method of hydrophobization is not particularly limited. The hydrophobization method is preferably a method of adding trialkoxysilane or organosilazane to the hollow silica particles obtained in step 3 or the step of coating with a shell in a solvent and heating the resultant hollow silica particles.

[0192] Trialkoxysilane and organosilazane may be used in combination.

[0193] Solvents As the solvent used in step 4, water is preferably used.

[0194] The solvent is preferably a hydrophilic solvent.

[0195] As the hydrophilic solvent, alcohols such as methanol, ethanol, n-propanol, isopropanol (IPA), ethylene glycol, propylene glycol, and 1,4-butanediol are preferably used. Ketones such as acetone and butanone are preferably used. Esters such as ethyl acetate are preferably used as the hydrophilic solvent.

[0196] As the hydrophilic solvent, alcohols are preferably used, and methanol, ethanol, isopropanol, etc. are more preferably used.

[0197] When alcohols such as isopropyl alcohol are used as the solvent, the hollow silica particles can be smoothly subjected to hydrophobic treatment.

[0198] As the solvent, one of these solvents may be used alone, or two or more of them may be mixed (blended) for use.

[0199] The solvent is preferably a mixed solvent of water and a hydrophilic solvent. The mass ratio of the hydrophilic solvent (methanol, etc.) to water in the mixed solvent is not particularly limited. In the mixed solvent, the hydrophilic solvent: water (mass ratio) is preferably 90:10 to 10:90, more preferably 30:70 to 10:90. By adjusting the mass ratio of the hydrophilic solvent to water in the mixed solvent to the above range, the hollow silica particles can be smoothly hydrophobized.

[0200] Trialkoxysilane Trialkoxysilane is not particularly limited. Trialkoxysilane preferably uses 3-acryloxypropyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-glycidyloxypropyl trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, vinyl trimethoxysilane, phenyl trimethoxysilane, N-phenyl-3-aminopropyl trimethoxysilane, trifluoropropyl trimethoxysilane, etc. Trialkoxysilane more preferably uses 3-methacryloxypropyl trimethoxysilane, N-phenyl-3-aminopropyl trimethoxysilane, trifluoropropyl trimethoxysilane, etc.

[0201] These trialkoxysilanes may be used alone or in combination of two or more.

[0202] The concentration of the trialkoxysilane in the solution is preferably 0.01% by mass to 30% by mass, more preferably 0.05% by mass to 25% by mass.

[0203] The amount of trialkoxysilane used is not particularly limited. Relative to 100 mass % of silica, the amount of trialkoxysilane used is preferably 0.01 mass % to 10 mass %, more preferably 0.05 mass % to 5 mass %, and further preferably 0.1 mass % to 3 mass %. By adjusting the amount of trialkoxysilane used to the above range, the hollow silica particles can be smoothly hydrophobized.

[0204] The hydrophobization treatment using trialkoxysilane is performed by heating, preferably at a temperature of 30° C. or higher, more preferably 40° C. or higher, and further preferably 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 of the hydrophobization treatment using trialkoxysilane to the above range, the reaction between the silica particles and the trialkoxysilane can be well performed without agglomeration in the solvent.

[0205] The heating time of 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.

[0206] Organosilazane The organosilazane is not particularly limited, but tetramethyldisilazane, hexamethyldisilazane, pentamethyldisilazane, etc. are preferably used as the organosilazane.

[0207] As the organosilazane, these organosilazanes may be used alone or in combination of two or more.

[0208] The amount of organosilazane used is not particularly limited. Relative to 100 mass % of silica, the amount of organosilazane used is preferably 10 mass % to 100 mass %, more preferably 20 mass % to 90 mass %, and further preferably 40 mass % to 80 mass %. By adjusting the amount of trialkoxysilane used to the above range, the hollow silica particles can be smoothly hydrophobized.

[0209] The hydrophobization treatment using the organosilazane is performed by heating, preferably at a temperature of 30° C. or higher, more preferably 40° C. or higher, and further preferably 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 of the hydrophobization treatment using the organosilazane to the above range, the reaction between the silica particles and the organosilazane can be well performed without agglomeration in the solvent.

[0210] The heating time for the hydrophobization 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.

[0211] Trialkoxysilane and organosilazane may be used in combination.

[0212] In the solution containing the hollow silica particles subjected to the hydrophobic treatment, the solvent may be replaced with another solvent (water, etc.). Alternatively, the solution containing the hollow silica particles subjected to the hydrophobic treatment may be filtered, dried (vacuum drying, etc.) to remove the solvent, thereby preparing a solution powder containing the hollow silica particles subjected to the hydrophobic treatment.

[0213] [4] Method for producing core-shell particles The method for producing the core-shell particles of the present invention preferably comprises: (1) a step 1 of preparing organic polymer particles by polymerizing an organic monomer in a solution containing an organic monomer, a dispersant and a solvent; and (2) Step 2 of adding the organic polymer particles obtained in step 1, alkoxysilane or alkoxysilane and metal alkoxide, and a basic catalyst to a solvent and stirring to prepare a solution, thereby forming core-shell particles having an organic polymer particle as a core and an outer shell covering the organic polymer particle in the solution.

[0214] Step 1 and Step 2 are the same as Step 1 and Step 2 described in the above-mentioned method for producing silica particles.

[0215] The core-shell particles produced by the method for producing core-shell particles of the present invention are preferably used as the core-shell particles used in step 3 of the method for producing silica particles of the present invention, by removing the organic polymer particles serving as the inner core of the core-shell particles through carbonization (thermal decomposition).

[0216] Example The present invention is specifically described below with reference to examples.

[0217] However, the present invention is not limited to these Examples.

[0218] Polystyrene particles and core-shell particles were prepared according to the formulation and manufacturing conditions in Table 1 to produce hollow silica particles. The details are as follows.

[0219] (1) Examples and Comparative Examples Example 1 Process 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-necked flask, and the internal temperature was heated to 55° C. to 70° C. under a nitrogen atmosphere while stirring at 250 rpm.

[0220] Then, a 5 wt % AIBA (2,2'-azobis(isobutylamidine) dihydrochloride) aqueous solution (7 g AIBA, 140 g ultrapure water) dissolved in ultrapure water as a polymerization initiator was added, and a polymerization reaction was carried out at a temperature of 55° C. to 75° C. for 3 hours.

[0221] Then, a 5% methanol aqueous solution of PVP (polyvinyl pyrrolidone) (37 g of PVP, 560 g of methanol, and 140 g of water) was added as a dispersant, and the temperature was further increased and heated under reflux for 3 hours to obtain a polystyrene particle reaction liquid.

[0222] As PVP, "PVP K-90 manufactured by Ashaland" and "PITZCOL K-60L manufactured by Daiichi Kogyo Co., Ltd." are available. In the examples, "PVP K-90 manufactured by Ashaland" was used as PVP.

[0223] The polystyrene particle reaction solution was poured into another four-necked flask, and heated with an electric mantle heater to replace methanol. When the internal temperature reached 70°C, the treatment was terminated.

[0224] Polystyrene particles were prepared as organic polymer particles in methanol.

[0225] <Production Rate of Polystyrene Particles> 2 g of the polystyrene particle reaction solution was weighed into a petri dish and dried on a hot plate at 120° C. for 1 hour. The yield of the polystyrene particles was calculated according to the following formula.

[0226] Yield of polystyrene particles (%) ={[(weight of sample after drying (g) - (amount of PVP added in the sample before drying (g))] ÷[amount of styrene added in the sample before drying (g)]}×100.

[0227] Process 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.

[0228] Liquid A was prepared by mixing 376 g of TMOS (tetramethoxysilane) (alkoxysilane) with 744 g of methanol.

[0229] Furthermore, 1,427 g of the polystyrene particle dispersion (polystyrene concentration 7.6 wt %) prepared in step 1 was added to a flask, 829 g of water and 823 g of methanol were added as solvents, and 268 g of a 28% ammonia aqueous solution (alkaline catalyst) was added to prepare liquid B.

[0230] Solution B was kept at 30° C. and stirred at 250 rpm, and solution A was added over 190 minutes.

[0231] In the solution, core-shell particles having polystyrene particles as the core and a silica shell covering the polystyrene particles are formed to prepare a core-shell particle dispersion. Water is then added dropwise, and water and ammonia in the concentrate are replaced with water by heated atmospheric distillation while ensuring a constant volume or more, to prepare a core-shell particle aqueous dispersion.

[0232] Step 3: Production of hollow silica particles (carbonization treatment) The core-shell particle aqueous dispersion obtained in the above step 2 was dried on a hot plate at 130° C. to obtain a powder of core-shell particles.

[0233] First, the obtained core-shell particle powder was carbonized at 500° C. for 4 hours using superheated steam using a batch carbonization device (CYT-200 manufactured by CYC Corporation).

[0234] Thereafter, the resultant was calcined (heat treated) at 1,050° C. for 3 hours in an electric furnace to remove the polystyrene particles, thereby obtaining a powder of hollow silica particles.

[0235] Pure water was added to the obtained powder of hollow silica particles (silicon dioxide concentration: 20 wt %), and a dispersion treatment was performed for 135 minutes using an ultrasonic homogenizer (UP-400S, manufactured by Hielscher).

[0236] The obtained dispersion was centrifuged at 3,200 rpm for 10 minutes using a micro high-speed centrifuge (himac CF-16N, manufactured by Hitachi Koki Co., Ltd.), and the supernatant was collected and filtered with 7 μm quantitative filter paper to obtain a hollow silica particle dispersion (silicon dioxide concentration: 16 wt %).

[0237] The silica concentration was calculated from the residual amount of the hollow silica particle dispersion after drying and solidifying the dispersion and then burning it at 800°C.

[0238] Step 4: Production of surface-treated hollow silica particles First, a reaction apparatus equipped with a four-necked flask, a stirring blade, and a water bath was prepared. 400 g of the hollow silica aqueous dispersion obtained in the above step 3, 274 g of ultrapure water, 404 g of IPA (isopropyl alcohol), and 1.4 g of N-phenyl-3-aminopropyltrimethoxysilane (KBM-573 manufactured by Shin-Etsu Chemical Co., Ltd.) (trialkoxysilane) were mixed and stirred in a flask, and heated at 75°C for 1 hour.

[0239] Then, 39 g of hexamethyldisilazane (SZ-31 manufactured by Shin-Etsu Chemical Co., Ltd.) (organosilazane) was added dropwise, and the mixture was heated for further 2 hours.

[0240] Thereafter, the reaction solution was cooled to 50° C., 559 g of ultrapure water and 31 g of 3M sulfuric acid were added in sequence, and the solid component was recovered by vacuum filtration.

[0241] The recovered solid components were washed with ultrapure water and vacuum dried at 120° C. to prepare hollow silica particles.

[0242] Example 2 In step 4 of Example 1, N-phenyl-3-aminopropyltrimethoxysilane was not mixed, and only 394 g of hexamethyldisilazane was added dropwise.

[0243] The above conditions were the same as those in Example 1.

[0244] Example 3 In step 4 of Example 1, 400 g of the hollow silica 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.

[0245] The above conditions were the same as those in Example 1.

[0246] Comparative Example 1 In step 3 of Example 1, the core-shell particle powder was not subjected to carbonization treatment, but was fired (heat treated) in an electric furnace at 1,050° C. for 3 hours.

[0247] The above conditions were the same as those in Example 1.

[0248] Comparative Example 2 In step 3 of the above-mentioned Example 1, the core-shell particle powder was first carbonized at 500°C for 4 hours using superheated steam in a batch carbonization device (CYC Corporation, CYT-200), and then fired (heat treated) at 1,075°C for 2 hours in an electric furnace.

[0249] The above conditions were the same as those in Example 1.

[0250] Comparative Example 3 In step 3 of the above-mentioned Example 1, the core-shell particle powder is first carbonized at 500°C for 4 hours using superheated steam in a batch carbonization device (CYC Corporation, CYT-200), and then fired (heat treated) at 1,000°C for 1 hour in an electric furnace.

[0251] The other conditions were the same as those in Example 1.

[0252] Comparative Example 4 In step 3 of Example 1, 7.7 g of citric acid (citric acid (anhydrous) manufactured by Fuso Chemical Industry Co., Ltd.) was added to the core-shell particle aqueous dispersion and dried on a hot plate at 130° C. to obtain a core-shell particle powder.

[0253] The obtained core-shell particle powder was heat-treated in an electric furnace at 1,050° C. for 3 hours without being carbonized.

[0254] The above conditions were the same as those in Example 1.

[0255] The properties of the particles obtained in Examples and Comparative Examples were measured by the following methods.

[0256] (2) Evaluation test Particle size The hollow silica particles obtained in step 4 were photographed using a SEM (scanning electron microscope: JSM-7900F, manufactured by JEOL Ltd.) at an accelerating voltage of 8 kV. The minor axis diameters of 100 particles were randomly selected and measured to obtain an average value.

[0257] The image analysis and measurement software WinROOF was used for image analysis.

[0258] True density 0.3 g of the powder of the hollow silica particles obtained in step 4 was measured using a nitrogen pycnometer (Ultrapyc 5000 Micro, manufactured by Anton Paar Japan Co., Ltd.) to measure the true density of the powder of the hollow silica particles.

[0259] Water absorption test 1 g of the powder of the hollow silica particles obtained in step 4 was stored at 50° C. and 75% humidity for 7 days, and 0.1 g of the powder sample was taken therefrom and the moisture content (mass %) was measured using a Karl Fischer moisture analyzer (MKA-610, manufactured by Kyoto Electronics Co., Ltd.).

[0260] MEK Filterability 2 g of the powder of the hollow silica particles obtained in step 4 and 8 g of methyl ethyl ketone (MEK) were stirred and mixed for 2 hours, filtered using a syringe filter with a pore size of 5 μm (filter paper that can filter materials with a size of 5 μm or less), and the amount of liquid passing through was measured.

[0261] MEK filterability (mass %, wt %) = [liquid throughput (g)] ÷ [amount of MEK dispersion of silica particles (10 g)] × 100.

[0262] Number of particles larger than 1 μm (particle size distribution) The particle size distribution of the powder of the hollow silica particles obtained in step 4 was measured using a laser diffraction / scattering particle size distribution measuring device (LA-950, manufactured by Horiba, Ltd.), and the frequency distribution value (%) of the particles with a particle size of 1 μm or more in the powder of the hollow silica particles was calculated. The results are shown in Table 1.

[0263] Table 1 (3) Evaluation results Comparative Example 1 is hollow silica particles produced by firing the core-shell particle powder without carbonization. The frequency distribution value of particles larger than twice the average particle size in the particle size distribution of the hollow silica particles of Comparative Example 1 exceeds 15%.

[0264] Comparative Example 2 is hollow silica particles prepared by carbonizing the core-shell particle powder and then calcining for 2 hours. The frequency distribution value of the particles larger than twice the average particle size in the particle size distribution of the hollow silica particles of Comparative Example 2 exceeds 15%.

[0265] Comparative Example 3 is a hollow silica particle prepared by carbonizing the core-shell particle powder and performing a sintering treatment for 1 hour. The frequency distribution value of the particles larger than twice the average particle size in the particle size distribution of the hollow silica particles of Comparative Example 3 exceeds 15%, and the water absorption exceeds 1.0 mass%.

[0266] Comparative Example 4 is a hollow silica particle prepared by adding citric acid to the core-shell particle aqueous dispersion and then only subjecting the core-shell particle powder to a calcination treatment without carbonization. The frequency distribution value of the particles larger than twice the average particle size in the particle size distribution of the hollow silica particles of Comparative Example 3 exceeds 15%.

[0267] Examples 1 to 3 are embodiments of the present invention, and are hollow silica particles prepared by carbonizing the core-shell particle powder at a temperature range of 400°C to 1,200°C and calcining the core-shell particle powder for a treatment time of more than 3 hours. The hollow silica particles of Examples 1 to 3 satisfy (1) a true density of 0.8 g / cm 3 ~1.4g / cm 3 , (2) the frequency distribution value of particles larger than twice the average particle size in the particle size distribution is 15% or less, and (3) the water absorption amount is 1.0 mass % or less.

[0268] (4) Industrial applicability The hollow silica particles of the present invention are novel hollow silica particles having low true density and excellent dispersibility.

[0269] According to the method for producing hollow silica particles of the present invention, novel hollow silica particles with low true density and excellent dispersibility can be produced by carbonizing the core-shell particles before firing during the production of the hollow silica particles.

[0270] The hollow silica particles of the present invention can be effectively used for multilayer printed circuit boards, wire covering materials, semiconductor packaging materials, and the like.

Claims

1. A silicon dioxide particle, It is characterized in that (1) True density is 0.8g / cm 3 ~1.4g / cm 3 , (2) The frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, (3) The water absorption is less than 1.0 mass %.

2. The silicon dioxide particles according to claim 1, It is characterized in that The silica particles are (4) carbonized and fired.

3. The silicon dioxide particles according to claim 1 or 2, It is characterized in that (5) The average particle size of the silica particles is 0.2 μm to 1.0 μm.

4. The silicon dioxide particles according to claim 1 or 2, It is characterized in that The silicon dioxide particles are hollow silicon dioxide particles.

5. A method for producing silicon dioxide particles, It is characterized in that The process includes firstly carbonizing the core-shell particles and then sintering them. Silica particles (1) True density is 0.8g / cm 3 ~1.4g / cm 3 , (2) The frequency distribution value of particles larger than twice the average particle size in the particle size distribution is less than 15%, (3) The water absorption is less than 1.0 mass %.

Images