JP5350847B2 - Method for producing plate-like silica particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a plate-like silica particle having low relative permittivity and/or low dielectric loss tangent and having high anisotropy, and the plate-like silica particle. <P>SOLUTION: (1) The method for producing the plate-like silica particle having the relative permittivity of &le;3.5 and/or the dielectric loss tangent of &le;0.01 includes a step of pulverizing a hollow silica particle in which nanopores are substantially not present and (2) the plate-like silica particle having the relative permittivity of &le;3.5 and/or the dielectric loss tangent of &le;0.01 is obtained by using the production method. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for producing plate-like silica particles having a low relative dielectric constant and / or dielectric loss tangent and high anisotropy, and the plate-like silica particles.

In recent years, in order to realize miniaturization of semiconductor devices and the like, high-speed operation, and low power consumption operation, a multilayer wiring structure having a low dielectric constant insulating film has become necessary. Conventionally, as a dielectric film having a multilayer wiring structure, silica having a relative dielectric constant of 3.8, SiOC in which silica is doped with carbon by a chemical vapor deposition method, a silica film in which an organic polymer-based low dielectric constant material is applied, etc. are known. ing.
For example, Patent Document 1 discloses hollow silica fine particles obtained by drying a substantially hollow silica sol having an amorphous silicon oxide as a main component and having nanopores, as a low dielectric constant component. It is considered useful. However, hollow silica fine particles having nanopores are materials in which the pores contain a large amount of air to reduce the dielectric constant, and the dielectric constant of the silica skeleton itself is not particularly low.
Patent Document 2 discloses an insulating composition containing a fluoropolymer and an inorganic filler selected from spherical amorphous silica, hollow silica fine particles and the like. Patent Document 3 discloses a method for forming a low dielectric constant insulating film in which a solution containing fine particles, resin, and solvent obtained by mechanically pulverizing mesoporous silica is applied onto a substrate and heated. . However, these are not fully satisfactory as low dielectric constant materials, and further improvements are desired.

On the other hand, fused silica has a relative dielectric constant of about 3 compared to general silica, and is known as a low dielectric constant material. However, since fused silica is prepared by completely melting silica at a high temperature of about 2000 ° C., it has a lump shape or a spherical shape, and it is difficult to obtain a highly anisotropic form such as a plate shape or a rod shape. . Lumped or spherical fused silica has the disadvantage that the effect of improving strength is insufficient even when kneaded with a resin to form a composite.
In addition, silica-based materials such as talc and clay minerals, which are excellent in strength improving effect, have a drawback that the dielectric constant and dielectric loss tangent are high because the material contains many polar substances and polar groups such as ions and silanols. .

JP 2006-342023 A JP 2007-266606 A JP 2005-167266 A

  An object of the present invention is to provide a method for producing plate-like silica particles having a low relative dielectric constant and / or dielectric loss tangent and high anisotropy, and the plate-like silica particles.

The inventors have made the dielectric constant and / or the dielectric loss tangent by crushing the hollow silica particles that have substantially lost the nano-sized pores and reduced the relative dielectric constant and / or the dielectric loss tangent by high-temperature firing. It has been found that plate-like silica particles having a low and high anisotropy can be obtained efficiently.
That is, the present invention provides the following (1) and (2).
(1) A method for producing plate-like silica particles having a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent of 0.01 or less, comprising a step of pulverizing hollow silica particles substantially free of nanopores .
(2) Plate-like silica particles having a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent of 0.01 or less obtained by the production method of (1) above.

According to the present invention, an efficient method for producing plate-like silica particles having a low relative dielectric constant and / or dielectric loss tangent and high anisotropy can be provided.
The obtained plate-like silica particles have dielectric properties such as low relative dielectric constant and / or low dielectric loss tangent and high anisotropy. Therefore, they have excellent strength improvement effect when composited with resin, and have low dielectric constant. It is useful as a rate material.

3 is a SEM image of the hollow silica particles after firing obtained in Example 1. FIG. 2 is an SEM image of plate-like particles obtained by pulverizing the hollow silica particles obtained in Example 1.

The method for producing plate-like silica particles having a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent of 0.01 or less according to the present invention includes a step of pulverizing hollow silica particles substantially free of nanopores. It is characterized by including.
Here, the relative dielectric constant refers to a ratio [ε / ε ₀ ] between the dielectric constant ε of a substance and the dielectric constant ε ₀ of a vacuum, and is a parameter indicating the degree of polarization in the dielectric.
Dielectric loss tangent is the tangent of the residual angle δ (dielectric loss angle) of the phase difference angle between the current flowing in the dielectric and the current component having the same frequency as the current flowing through the dielectric when a sinusoidal voltage is applied to the dielectric ( tan δ), a parameter indicating the amount of electrical energy loss in the dielectric.
The plate-like silica particles of the present invention are excellent as an insulator because the relative dielectric constant is 3.5 or less or the dielectric loss tangent is 0.01 or less, and the consumed energy is reduced. Can be used continuously.
The dielectric constant and dielectric loss tangent can be measured by the methods described in the examples.
Hereinafter, the hollow silica particles as a raw material, and the pulverization process thereof will be described.

[Hollow silica particles]
In the present invention, the hollow silica particles used as a raw material are substantially free of nanopores. The phrase “nanopores are substantially absent” means that the pore size distribution of the hollow silica particles does not substantially exhibit a pore distribution of 1 nm or more.
Further, the hollow silica particles do not substantially show a peak at a diffraction angle (2θ) corresponding to a range where the crystal lattice spacing (d) is less than 1 nm in powder X-ray diffraction (XRD) measurement. It is preferable.
The hollow silica particles preferably have a silica skeleton that is not substantially porous and has a BET specific surface area of less than 100 m ² / g. Since the BET specific surface area is not substantially porous, it is more preferably 90 m ² / g or less, more preferably 80 m ² / g or less, more preferably 70 m ² / g or less, and further preferably 60 m ² / g. It is as follows.

The average thickness of the outer shell is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less, from the viewpoint of facilitating pulverization and making the silica particles plate-like.
The number average particle diameter of the hollow silica particles is preferably 0.1 to 1 μm, more preferably 0.15 to 0.9 μm, and still more preferably 0.2 to 0.8 μm.
The ratio of [average thickness of outer shell / average particle diameter] of the hollow silica particles is usually 0.01 to 0.5, preferably 0.01 to 0.3, more preferably 0.01 to 0. .2.
As will be described later, the average particle diameter of the hollow silica particles and the average thickness of the outer portion are the production conditions of the hollow silica particles (A) or the core-shell type silica particles (B) used as the raw material, and the particle diameter of the hollow part forming material. It can be appropriately prepared depending on the firing conditions and the like.
The average particle diameter of hollow silica particles and hollow silica particles (A), the average thickness of the outer shell, the BET specific surface area, the average pore diameter, and the powder X-ray diffraction (XRD) pattern are measured by the methods described in the examples. It can be carried out.

[Production of hollow silica particles]
In the present invention, the method for producing hollow silica particles used as a raw material is not particularly limited, but according to the method including the following steps (I) and (II), it can be produced efficiently.
Step (I): a hollow silica particle (A) containing air inside the particle (hereinafter also simply referred to as “hollow silica particle (A)”), or a core shell containing a material that disappears by firing to form a hollow part Step of preparing silica particles (B) (hereinafter also simply referred to as “core-shell silica particles (B)”).
Step (II): A step of heat-treating the hollow silica particles (A) or the core-shell type silica particles (B) obtained in the step (I) at 900 ° C. or higher.
The details of the steps (I) and (II) and the components used therein will be described below.

Process (I)
Step (I) is a step of preparing hollow silica particles (A) or core-shell type silica particles (B). The method is not particularly limited as long as it is a method capable of producing the hollow silica particles (A) or the core-shell type silica particles (B), but a method including the following steps A to D is more preferable.
Step A: 0.1 to 50 g / L of the polymer particles (a-1) or 0.1 to 100 mmol / L of the hydrophobic organic compound (a-2), and the following general formulas (1) and (2) And 0.1 to 100 mmol / L of one or more (b) selected from quaternary ammonium salts represented by the formula (1)) and 0.1 to 100 mmol of silica source (c) that produces a silanol compound by hydrolysis. Step of preparing an aqueous solution containing / L.
[R ¹ (R ³ ) ₃ N] ⁺ X ⁻ (1)
[R ¹ R ² (R ³ ) ₂ N] ⁺ X ⁻ (2)
(In the formula, R ¹ and R ² each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, R ³ represents an alkyl group having 1 to ³ carbon atoms, and X represents a monovalent negative group. Indicates ions.)
Step B: The aqueous solution obtained in Step A is stirred at a temperature of 10 to 100 ° C., has an outer shell composed of silica, and has polymer particles (a-1) or a hydrophobic organic compound (a -2) Step of preparing an aqueous dispersion of core-shell type silica particles Step C: Step of separating the core-shell type silica particles (B) from the aqueous dispersion obtained in Step B Step D: obtained in Step C A step of firing the core-shell type silica particles (B) to obtain hollow silica particles (A)

Hereinafter, steps A to D will be described.
[Step A]
[Polymer particles (a-1)]
As the polymer particles (a-1) used in the step A, particles of one or more polymers selected from a cationic polymer, a nonionic polymer and an amphoteric polymer are preferable, and a substantially water-insoluble polymer is preferable.
The average particle size of the polymer particles used in Steps A to D is preferably a fine particle size and a uniform particle size distribution characteristic of the hollow silica particles of the present invention. It is desirable that the thickness is 0.02 μm to 1 μm, more preferably 0.05 μm to 0.9 μm, still more preferably 0.1 μm to 0.8 μm, and particularly preferably 0.12 μm to 0.7 μm. Further, the polymer particles preferably have a particle size of 80% or more, more preferably 85% or more, further preferably 90% or more, particularly preferably 95% or more of the whole particles within an average particle size of ± 30%. It is desirable that the particles are composed of a group of particles having a very uniform particle diameter.

[Cationic polymer]
The cationic polymer is preferably a polymer that can be dispersed as a polymer emulsion in a medium containing a continuous phase in an aqueous system in the presence of a cationic surfactant, and is cationic in the presence of a cationic surfactant. Those obtained by emulsion polymerization of a monomer mixture, particularly a monomer mixture containing an ethylenically unsaturated monomer having a cationic group, by a known method are preferred.
Examples of the cationic monomer include an acid neutralized product of a monomer having an amino group, or a quaternary ammonium salt obtained by quaternizing the monomer with a quaternizing agent.
As a specific example of the cationic monomer, a (meth) acrylate having a dialkylamino group or a trialkylammonium group is more preferable, and a (meth) acrylate having a dialkylamino group or a trialkylammonium group is most preferable.
In the present specification, (meth) acrylate means acrylate, methacrylate, or both.

  The cationic polymer contains a structural unit derived from the cationic monomer, but in addition to the cationic monomer structural unit, it is derived from a hydrophobic monomer such as an alkyl (meth) acrylate or an aromatic ring-containing monomer. It is more preferable to contain a structural unit. Preferable examples thereof include styrenic monomers such as alkyl (meth) acrylate, styrene or 2-methylstyrene having an alkyl group having 1 to 30 carbon atoms, preferably 3 to 22 carbon atoms, more preferably 3 to 18 carbon atoms. , Aryl esters of (meth) acrylic acid such as benzyl (meth) acrylate, aromatic group-containing vinyl monomers having 6 to 22 carbon atoms, or vinyl acetate. Of these, alkyl (meth) acrylate and styrene are most preferred.

The hydrophobic monomer means a polymerizable organic compound that has low solubility in water and forms a phase separation with water. Examples of the hydrophobic monomer include compounds having a LogP value of 0 or more, preferably 0.5 or more, and 25 or less. Here, LogP means a logarithmic value of a 1-octanol / water partition coefficient of a chemical substance, and is a numerical value calculated by a fragment approach by SRC's LOGKOW / KOWWIN Program. Specifically, it is obtained by decomposing the chemical structure of a chemical substance into its components and integrating the hydrophobic fragment constants of each fragment (Meylan, WM and PH Howard. 1995. Atom / fragment contribution method for octanol-water partition coefficients. See J. Pharm. Sci. 84: 83-92).
The cationic monomer constituting unit constituting the cationic polymer may be a small amount, and most constituting the cationic polymer may be constituted by a constituent unit derived from the hydrophobic monomer. The total amount of the cationic monomer constituent unit and the constituent unit derived from the hydrophobic monomer in the cationic polymer is 70 to 100% by mass, more preferably 80 to 100% by mass, and particularly preferably 95 to 100% by mass. In particular, the weight ratio of [(constituent unit derived from cationic monomer) / (constituent unit derived from hydrophobic monomer)] is preferably 0.001 to 0.5, more preferably 0.002 from the viewpoint of particle formation. It is -0.3, Most preferably, it is 0.003-0.1.

[Nonionic polymer]
Nonionic polymer means a polymer that has no charge in aqueous solution. The nonionic polymer is a polymer derived from a monomer having no charge, that is, a nonionic monomer, and can be obtained by polymerizing a nonionic monomer by a known emulsion polymerization method, non-emulsifier polymerization method or the like.
Nonionic monomers include the hydrophobic monomers (paragraph [0017]) mentioned in the description of the cationic polymer. Preferred examples thereof are preferably selected from alkyl (meth) acrylates, vinyl acetate, and styrene having an alkyl group having 1 to 30 carbon atoms, more preferably 3 to 22 carbon atoms, and still more preferably 3 to 18 carbon atoms. One or more.
Specific examples of nonionic polymers include polystyrene, ethyl acrylate / ethyl methacrylate copolymer, ethyl acrylate / methyl methacrylate copolymer, octyl acrylate / styrene copolymer, butyl acrylate / vinyl acetate copolymer, methyl methacrylate / butyl. Examples thereof include acrylate / octyl acrylate copolymers, vinyl acetate / styrene copolymers, vinyl pyrrolidone / styrene copolymers, butyl acrylate, and polystyrene acrylate resins.

Among the cationic polymer, the nonionic polymer and the amphoteric polymer, the cationic polymer and the nonionic polymer are preferable, and the cationic polymer is more preferable from the viewpoint of easy formation of the hollow silica particles (A).
For the production of the hollow silica particles (A), a polymer that does not substantially dissolve in water is used. For this purpose, a method for increasing the polymerization ratio of a hydrophobic monomer, a method for crosslinking, and the like can be employed.
Preferred examples of such a polymer include a copolymer of a hydrophobic monomer selected from alkyl (meth) acrylate and styrene and a (meth) acrylate having a cationic group, and one or more hydrophobic properties selected from alkyl (meth) acrylate and styrene. Mention may be made of nonionic polymers composed of monomers.
Said polymer can be used individually or in mixture of 2 or more types.
The shape of the polymer particles is not particularly limited, and the particle size of the hollow silica particles (A) and the size of the hollow part can be changed by changing the size and the particle size distribution of the polymer particles by forming them into a true sphere or egg shape. It can be prepared appropriately.

[Hydrophobic organic compound (a-2)]
In the present invention, the hydrophobic organic compound (a-2) means a compound that has low solubility in water and forms a phase separation with water. Preferably, the compound is dispersible in the presence of the quaternary ammonium salt. Examples of such hydrophobic organic compounds include compounds having a LogP value of 1 or more, preferably 2 to 25.
(C) Examples of the hydrophobic organic compound include oils such as hydrocarbon compounds, ester compounds, fatty acids having 6 to 22 carbon atoms, alcohols having 6 to 22 carbon atoms, and silicone oils, and various kinds such as fragrances, agricultural chemicals, and pharmaceuticals. A base material etc. can be mentioned.
When a hydrophobic organic compound is used, the particle size of the hollow silica particles (A) and the size of the hollow part are affected by the size of the droplets of the hydrophobic organic compound, so the melting point and reaction temperature of the hydrophobic organic compound , And can be appropriately adjusted depending on the stirring speed, the surfactant used, and the like.

[Quaternary ammonium salt (b)]
The quaternary ammonium salt (b) is represented by the following general formulas (1) and (2), and is the formation of mesopores and the dispersion of the polymer particles (a-1) or the hydrophobic organic compound (a-2). Used for.
[R ¹ (R ³ ) ₃ N] ⁺ X ⁻ (1)
[R ¹ R ² (R ³ ) ₂ N] ⁺ X ⁻ (2)
R ¹ and R ² in the general formulas (1) and (2) are linear or branched alkyl groups having 4 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and more preferably 8 to 16 carbon atoms. is there. Examples of the alkyl group having 4 to 22 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, and various hexadecyl groups. , Various octadecyl groups, various eicosyl groups, and the like. R ³ is an alkyl group having 1 to 3 carbon atoms, preferably a methyl group.
X in the general formulas (1) and (2) includes at least one selected from monovalent anions such as halogen ions, hydroxide ions, nitrate ions, and sulfate ions, preferably halogen ions. More preferably a chlorine ion or a bromine ion, and still more preferably a bromine ion.

Examples of the alkyltrimethylammonium salt represented by the general formula (1) include butyltrimethylammonium chloride, hexyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethyl Ammonium chloride, stearyltrimethylammonium chloride, butyltrimethylammonium bromide, hexyltrimethylammonium bromide, octyltrimethylammonium bromide, decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide Bromide, stearyl trimethyl ammonium bromide, and the like.
Examples of the dialkyldimethylammonium salt represented by the general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, didodecyldimethylammonium bromide, ditetradecyl. Examples thereof include dimethylammonium bromide.
Among these quaternary ammonium salts (b), from the viewpoint of forming regular mesopores, alkyltrimethylammonium salts represented by the general formula (1) are particularly preferred, and alkyltrimethylammonium bromide or alkyltrimethyl Ammonium chloride is more preferred, and dodecyltrimethylammonium bromide or dodecyltrimethylammonium chloride is particularly preferred.

[Silica source (c)]
A silica source (c) produces | generates a silanol compound by hydrolysis of alkoxysilane etc., and can mention the compound shown by following General formula (3)-(7).
SiY ₄ (3)
R ⁴ SiY ₃ (4)
R ⁴ ₂ SiY ₂ (5)
R ⁴ ₃ SiY (6)
Y ₃ Si—R ⁵ —SiY ₃ (7)
(In the formula, each R ⁴ independently represents an organic group in which a carbon atom is directly bonded to a silicon atom, R ⁵ represents a hydrocarbon group or a phenylene group having 1 to 4 carbon atoms, and Y represents A monovalent hydrolyzable group that becomes a hydroxy group by hydrolysis.)
More preferably, in the general formulas (3) to (7), each R ⁴ is independently a hydrocarbon group having 1 to 22 carbon atoms in which a part of hydrogen atoms may be substituted with fluorine atoms, Specifically, it is an alkyl group having 1 to 22 carbon atoms, preferably 4 to 18 carbon atoms, more preferably 6 to 18 carbon atoms, and particularly preferably 8 to 16 carbon atoms, a phenyl group, or a benzyl group, and R ⁵ Is an alkanediyl group having 1 to 4 carbon atoms (methylene group, ethylene group, trimethylene group, propane-1,2-diyl group, tetramethylene group, etc.) or phenylene group, and Y is more preferably 1 to 22 carbon atoms. Is a C1-C8, particularly preferably C1-C4 alkoxy group or a halogen group excluding fluorine.

Preferable examples of the silica source (c) include the following compounds.
-The silane compound in which Y is a C1-C3 alkoxy group or a halogen group except a fluorine in General formula (3).
In general formulas (4) to (6), R ⁴ is a phenyl group, a benzyl group, or a hydrogen atom part of which is substituted with a fluorine atom, having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms. A trialkoxysilane, dialkoxysilane or monoalkoxysilane which is preferably a hydrocarbon group having 1 to 5 carbon atoms.
A compound in which Y is a methoxy group and R ⁵ is a methylene group, an ethylene group or a phenylene group in the general formula (7).
Among these, tetramethoxysilane, tetraethoxysilane, phenyltriethoxysilane, and 1,1,1-trifluoropropyltriethoxysilane are particularly preferable.
A silica source (c) can be used individually or in mixture of 2 or more types.

Polymer particles (a-1) or hydrophobic organic compound (a-2) in the aqueous solution in step A (hereinafter, both are also collectively referred to as “component (a)”), quaternary ammonium salt (b), And the content of the silica source (c) is as follows.
The content of the component (a-1) is preferably 0.1 to 50 g / L, more preferably 0.3 to 40 g / L, and particularly preferably 0.5 to 30 g / L.
The content of the component (a-2) is 0.1 to 100 mmol / L, more preferably 1 to 100 mmol / L, and particularly preferably 5 to 80 mmol / L.
The content of component (b) is preferably 0.1 to 100 mmol / L, more preferably 1 to 100 mmol / L, particularly preferably 5 to 80 mmol / L, and the content of component (c) is And preferably 0.1 to 100 mmol / L, more preferably 1 to 100 mmol / L, and particularly preferably 5 to 80 mmol / L.
There is no restriction | limiting in particular in the order which contains (a)-(c) component. For example, a method of adding the suspension of the component (a), the component (b), and the component (c) in this order while stirring the aqueous solution can be mentioned.
As long as the aqueous solution containing the components (a) to (c) does not inhibit the formation of the core-shell particles, other components such as an organic compound such as methanol and an inorganic compound may be added. As mentioned above, when it is desired to carry other elements other than silica and organic groups, metal raw materials such as alkoxy salts and halogenated salts containing these metals can be added during or after production.

[Step B]
Step B is a step of preparing an aqueous dispersion of core-shell type silica particles. The aqueous solution obtained in Step A is stirred for a predetermined time at a temperature of 10 to 100 ° C., preferably 10 to 80 ° C., and then allowed to stand to leave the polymer particles (a-1) or the hydrophobic organic compound (a-2). Core-shell type in which mesopores are formed on the surface of quaternary ammonium salt (b) and silica source (c), and polymer particles (a-1) or hydrophobic organic compound (a-2) are included inside Silica particles can be precipitated. Although the stirring treatment time varies depending on the temperature, the core-shell type silica particles are usually formed at 10 to 80 ° C. for 0.1 to 24 hours. The mesopores of the core-shell type silica particles obtained at this time are clogged with the surfactant used in the production.
The obtained core-shell type silica particles are obtained in a state suspended in water.
When the core-shell type silica particles obtained in Step B contain a cationic surfactant or the like, the cationic surfactant or the like can be removed by contacting the acidic solution once or a plurality of times. Examples of the acidic solution to be used include inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid; organic acids such as acetic acid and citric acid; liquids obtained by adding a cation exchange resin or the like to water or ethanol. Hydrochloric acid is particularly preferable. The pH is usually adjusted to 1.5 to 5.0.
The particles from which the surfactant has been removed from the pores by the above method have a mesopore structure on the surface, and have a high BET specific surface area. Polymer particles (a-1) or hydrophobic organic compounds (a-2) Are core-shell type silica particles.

[Steps C and D]
Step C is a step of separating the core-shell type silica particles (B) from the aqueous dispersion obtained in Step B. Step D is a step of firing the core-shell type silica particles (B) obtained in Step C. This is a step of obtaining hollow silica particles (A).
In step C, the core-shell type silica particles (B) can be separated from the aqueous dispersion, and contacted with an acidic aqueous solution, washed with water, and dried as necessary. Moreover, after processing at high temperature, in process D, it is preferably fired in an electric furnace or the like at 350 to 800 ° C., more preferably at 450 to 700 ° C. for 1 to 10 hours, and the inner polymer (a-1) or hydrophobic The organic compound (a-2) is removed. Although the basic structure of the outer shell part of the obtained hollow silica particles (A) is not changed, the inner polymer (a-1) or the hydrophobic organic compound (a-2) is removed by calcination.
In the present invention, since the core-shell type silica particles containing the polymer (a-1) or the hydrophobic organic compound (a-2) are fired, the shape and form of the polymer particles (a-1) to be included are particularly desired. By controlling in advance to the state, hollow silica particles (A) having a desired shape and form can be easily produced. For example, by firing core-shell type silica particles having a true spherical polymer inside, hollow silica particles (A) having an internal hollow shape and a true spherical shape can be produced.

Of the hollow silica particles (A) and the core-shell type silica particles (B) obtained as described above, in the powder X-ray diffraction measurement, the diffraction angle (2θ corresponding to the range of the surface spacing (d) of 1 nm to 12 nm. ) Is preferred.
The average pore diameter of the mesopore structure of the hollow silica particles (A) obtained in the step (I) is preferably 1 to 8 nm, more preferably 1 to 5 nm, and the mesopore diameter is determined by the hollow silica particles (A 70 mass% or more, preferably 75 mass% or more, more preferably 80 mass% or more of the average pore diameter is within ± 30 mass%.
The BET specific surface area of the hollow silica particles (A) is preferably 100 to 1500 m ² / g, more preferably 200 to 1500 m ² / g, and still more preferably 300 to 1500 m ² / g.
The average particle diameter of the hollow silica particles (A) is preferably 0.05 to 2 μm, more preferably 0.05 to 1.5 μm, still more preferably 0.1 to 1.2 μm.
The average thickness of the outer shell part (mesoporous silica part) is preferably 200 nm or less, more preferably 100 nm or less, and still more preferably 50 nm or less from the viewpoint of facilitating pulverization and making it into a plate shape.

Process (II)
Step (II) is a step of heat-treating the hollow silica particles (A) or core-shell type silica particles (B) obtained in step (I) at 900 ° C. or higher.
The heat treatment temperature is preferably 900 to 1500 ° C., more preferably 950 to 1300 ° C. from the viewpoint that the silica skeleton is not substantially porous and the BET specific surface area is less than 50 m ² / g. Preferably it is 980-1200 degreeC.
The heat treatment can be performed using an electric furnace or the like, and the heat treatment time varies depending on the heat treatment temperature and the like, but is usually 0.5 to 100 hours, preferably 1 to 80 hours.
In the present invention, hollow silica particles (A) are produced once in step (I) and heat-treated at 900 ° C. or higher in step (II), whereby hollow silica particles (A) obtained in step (I) are obtained. ), The silica skeleton is not substantially porous, and hollow silica particles with a reduced BET specific surface area can be obtained. Furthermore, since the particles are spherical, they are easy to maintain their shape even after high-temperature treatment, are less likely to aggregate, and can be easily crushed even if aggregated. In addition, the core-shell type silica particles (B) obtained in the step (I) may be directly heat-treated at 900 ° C. or more to obtain hollow silica particles. Thus, a method of obtaining hollow silica particles having a small BET specific surface area is more preferable.

[Production of hollow silica particles]
The plate-like silica particles having a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent of 0.01 or less according to the present invention are hollow silica particles substantially free from nanopores obtained by the above method. Is produced by a method including a step of pulverizing.
The method for pulverizing the hollow silica particles is not particularly limited as long as a strong compressive shearing force can be applied, and a method for wet pulverizing a slurry containing hollow plate-like silica particles, hollow silica particle powder A method of dry pulverizing the body is mentioned.

The pulverization apparatus that can be used for wet and / or dry pulverization is not particularly limited.
For example, the pulverizer described in pages 826 to 838 of Chemical Engineering Handbook (5th revised edition) (edited by Chemical Society of Japan, published by Maruzen Co., Ltd.), specifically, (1) Crushing by pressure or impact force Apparatus: For example, jaw crusher, gyratory crusher, roll crusher, roll mill, etc. (2) A striking plate is fixed around the rotor that rotates at high speed, and the processing object is pulverized by shearing force between the rotor and the striking plate: Hammer mill, impact crusher, pin mill, etc. (3) A device that rotates while a roll or ball is pressed on a ring and grinds and grinds the processed material between them: for example, a ring roller mill, ring ball mill, centrifugal roller mill, ball bearing (4) A cylindrical crushing chamber is provided, and a ball or the like is used as a crushing medium in the crushing chamber. A crushing device for crushing a processed product by inserting or rotating or vibrating a pad: for example, a ball mill, a vibration mill, a planetary ball mill, or the like. An apparatus for putting a medium and pulverizing the processed material by a shearing or frictional action using a disk-type or annular-type stirring mechanism inserted into the medium: for example, a tower mill, an attritor, a sand mill, and the like.
Among these, a powder device capable of imparting a compressive shear force between powders using the rollers and balls of (3) to (5) as a medium is preferable, and the ball medium mill of (4) and (5) is particularly preferable. Is preferred.

  Examples of the ball medium mill include a medium stirring ball mill, a planetary ball mill, a vibration ball mill (circular vibration mill, rotational vibration mill, centrifugal mill, etc.), and a rolling ball mill (pot mill, tube mill, conical mill, etc.). From the viewpoint of productivity, a medium stirring ball mill and a planetary ball mill (consisting of a mill pot that rotates in the same direction as the revolving mill body and in the opposite direction) are preferable.

The material of the ball used as the medium is not particularly limited, and examples thereof include high-hardness metals such as iron and stainless steel, and high-hardness ceramics such as alumina, zirconia, zircon, and titania. Among these, high-hardness ceramics such as alumina, zirconia, and titania having a relatively large specific gravity and high wear resistance are more preferable.
The outer diameter of the ball is not particularly limited, but is preferably 0.1 to 100 mm, more preferably 0.5 to 50 mm, and still more preferably 1 to 30 mm from the viewpoint of operability. Further, as the shape of the medium, a rod shape or a tube shape can be used in addition to the ball.
The filling rate of a medium such as a ball is usually 10 to 97%, preferably 20 to 90%, more preferably 25 to 80% from the viewpoint of grinding efficiency, although it depends on the model. Here, the filling rate refers to the apparent volume of the ball relative to the volume of the stirring unit of the ball medium mill.
The pulverization time varies depending on the type of pulverizer, medium, etc., the processing amount of the hollow silica particles, etc., but is preferably 2 minutes to 24 hours, more preferably 5 minutes to 5 hours. Further, the temperature of the pulverization treatment is preferably 250 ° C. or less, more preferably 5 to 200 ° C. from the viewpoint of suppressing denaturation due to heat generation. Moreover, it can grind | pulverize in inert gas atmosphere, such as nitrogen, as needed.

[Plate-like silica particles]
According to the method of the present invention, plate-like silica particles having a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent of 0.01 or less can be efficiently produced. The relative dielectric constant of the plate-like silica particles of the present invention is 3.5 or less, preferably 3.3 or less, more preferably 3.0 or less, and the dielectric loss tangent is 0.01 or less, preferably 0.8. 009 or less, more preferably 0.008 or less. The closer to 1 which is the lower limit of the relative dielectric constant or 0 which is the lower limit of the dielectric loss tangent, the better. The plate-like silica particles have a silica skeleton that is not substantially porous and a specific surface area of preferably 100 m ² / g or less, more preferably 80 m ² / g or less, and even more preferably 70 m ² / g or less. Is desirable.
Further, since the plate-like silica particles of the present invention are obtained by pulverizing hollow silica particles substantially free of nanopores, the anisotropy is high, and the strength improvement effect when composited with a resin Is excellent.
Here, “high anisotropy” means that the minor axis of the particle is smaller than the other two axes, in other words, the plate-like ratio (maximum diameter / thickness) of the particle exceeds 2, Means 4 to 100, more preferably 6 to 80, still more preferably 8 to 50. Further, the “plate shape” is not limited to a flat plate shape (curvature 0), and may have a curved surface.
The thickness of the plate-like silica particles of the present invention is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less, but the thickness may be uniform or not uniform.

Various measurements of the hollow silica particles obtained in Production Examples and Examples were performed by the following methods.
(1) Measurement of powder X-ray diffraction (XRD) Using a powder X-ray diffraction apparatus (manufactured by Rigaku Denki Kogyo Co., Ltd., trade name: RINT2500VPC), X-ray source: Cu-kα, tube voltage: 40 mA, tube current: Powder X-ray diffraction measurement was performed under the conditions of 40 kV, sampling width: 0.02 °, divergence slit: 1/2 °, divergence slit length: 1.2 mm, scattering slit: 1/2 °, and light receiving slit: 0.15 mm. went. A continuous scanning method was used in which the scanning range was a diffraction angle (2θ) of 1 to 70 ° and the scanning speed was 4.0 ° / min. The measurement was performed by packing the pulverized sample in an aluminum plate.
(2) Observation of particle shape The particle shape was observed using an electrolytic emission type high resolution scanning electron microscope (manufactured by Hitachi, Ltd., trade name: FE-SEM S-4000).
(3) Measurement of average primary particle diameter, average hollow part diameter, and average outer shell part thickness Particles at an acceleration voltage of 160 kV using a transmission electron microscope (TEM) (trade name: JEM-2100, manufactured by JEOL Ltd.) Was observed. The diameter, hollow diameter, and outer shell thickness of all particles in five fields of view containing 20-30 particles were measured on a photograph, and the average primary particle diameter, average hollow diameter, and average outer shell thickness were measured. Asked. In addition, observation was performed using what attached to Cu mesh (200-A mesh by Oken Shoji Co., Ltd.) with the carbon support film for high resolution, and removed the excess sample by the blow.
(4) Measurement of BET specific surface area and average pore diameter Using a specific surface area / pore distribution measuring device (manufactured by Shimadzu Corporation, trade name: ASAP2020), the BET specific surface area is determined by a multipoint method using liquid nitrogen. Measurements were made and values were derived in the range where parameter C was positive. The BJH method was adopted to derive the average pore diameter, and the pore diameter at the peak value was defined as the average pore diameter. The sample was pretreated at 250 ° C. for 5 hours.

(5) Measurement of relative permittivity and dielectric loss tangent E8361A 10MHz-67GHz made by Agilent PNA Series Network Analyzer Using a device connected to a dielectric constant measuring device (resonator, 5.8GHz) made by Kanto Electronics Application Development The dielectric constant and dielectric loss tangent were measured at 5.8 GHz using the cavity resonator perturbation method.
Since it is difficult to measure a powder sample as it is, a heat-shrinkable tube (PFA-1.5) manufactured by Freon Chemical is cut into a length of 10 cm, and a cell with 3 to 5 mm of sealing tape packed on one side is prepared. A sample was filled in this and used for measurement. From the true density, weight and volume of the sample, the filling rate of the sample was calculated and measured.
The cavity resonator perturbation method is based on the deviation of the resonance frequency when the inside of the resonator that resonates at a specific frequency is empty and when a sample (dielectric material) is inserted, and the change in the Q value that represents the sharpness of the peak. In order to calculate the dielectric constant, an empty cell was used as a blank at the time of measurement, and only a sample was measured.

Production Example 1 (Production of hollow silica particles (A1))
In a 20 L reactor, 16 kg of water, 66 g of 25% tetramethylammonium hydroxide, 68 g of dodecyltrimethylammonium bromide, and 192 g of polymer particles “Fine Sphere FS-501” (cationic acrylic resin, average particle diameter 500 nm) made by Nippon Paint The aqueous solution was slowly added with 68 g of tetramethoxysilane, stirred at room temperature (25 ° C.) for 5 hours, and then aged for 12 hours.
Next, the obtained white precipitate is filtered through a membrane filter having a pore size of 0.2 μm, washed with 10 L of water, and dried at a temperature of 100 ° C. for 5 hours to obtain silica particles that are core-shell type silica particles. It was.
The obtained dry powder was heated to 600 ° C. at a rate of 1 ° C./min with an air flow (3 L / min) using a baking furnace (manufactured by Motoyama Co., Ltd., trade name: SK-2535E). The organic component was removed by baking at 2 ° C. for 2 hours to obtain hollow silica particles (A1).
As a result of powder X-ray diffraction (XRD) measurement of the powder of the hollow silica particles (A1), the hollow silica particles (A1) had a very strong peak with a crystal lattice spacing (d) = 2.9 nm, d = 1 It was confirmed by the weak peaks of 0.7 nm and d = 1.5 nm that the mesopores of the hollow silica particles (A1) had a hexagonal arrangement. No XRD peak was observed in the region of d = 1.0 nm or less. Further, it was confirmed by SEM observation that the hollow silica particles (A1) had a spherical particle shape.
Furthermore, from TEM observation, the hollow silica particles (A1) have a hollow structure, the average primary particle diameter is 560 nm, the average hollow part diameter is 530 nm, the average outer shell part thickness is 20 nm, and the outer shell part is a hexagonal array. It was confirmed that the mesopores showed a radial direction from the center of the particle toward the outside of the outer shell. All primary particles had a primary particle size within an average primary particle size of ± 30%.
The hollow silica particles (A1) powder had a BET specific surface area of 1300 m ² / g and an average pore diameter of 1.7 nm. As a result of measuring the electrical characteristics of the hollow silica particles (A1), the dielectric constant was 2.86 and the dielectric loss tangent was 0.0017.

Example 1
50 g of the hollow silica particles (A1) obtained in Production Example 1 were transferred to an alumina crucible and calcined at 1000 ° C. for 72 hours in air using a high-temperature heating electric furnace manufactured by Motoyama Co., Ltd., trade name: SK-2535E. As a result, hollow silica particles were obtained.
In the measurement of the average pore diameter of the hollow silica particles after firing, it was confirmed that there was no peak at 1 nm or more. Further, in the powder X-ray diffraction measurement, it was confirmed that there was no peak in the diffraction angle (2θ) corresponding to the range where the crystal lattice spacing (d) was less than 1 nm. From TEM observation, it was confirmed that the hollow silica particles had a hollow structure, the average primary particle diameter was 420 nm, the average hollow part diameter was 390 nm, and the average outer shell part thickness was 15 nm.
Subsequently, the hollow silica particles obtained by the above method were pulverized. 20 g of hollow silica particles were placed in a polypropylene plastic bottle (500 ml), and zirconia beads (manufactured by ASONE, 10 mm) were further added so that the filling rate was about 80% of the bottle. The bottle was sealed, placed in a mix rotor VMR-5 (manufactured by Inoue Seieido), and pulverized at a speed of 80 rpm for 12 hours.
When the shape of the obtained sample was observed with an SEM, the hollow silica particles were sufficiently pulverized to produce plate-like particles. The average thickness of the plate-like particles was 15 nm, and the specific surface area was 47 m ² / g. As a result of measuring the electrical properties of the plate-like particle powder, the dielectric constant was 2.89 and the dielectric loss tangent was 0.0065.
FIG. 1 shows an SEM image of the hollow silica particles after firing, and FIG. 2 shows an SEM image of plate-like particles obtained by pulverizing the hollow silica particles.

The production method of the present invention is useful as an efficient method for producing plate-like silica particles having a low relative dielectric constant or dielectric loss tangent and high anisotropy.
Since the obtained plate-like silica particles have high anisotropy, the effect of improving the strength when composited with a resin is excellent, and can be used for a wide range of applications as a low dielectric constant material.

Claims (9)

Including a step of pulverizing hollow silica particles substantially free of nanopores and having a BET specific surface area of 70 m ² / g or less, and having a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent of 0.01 A method for producing plate-like silica particles, wherein the plate-like ratio (maximum diameter / thickness) of the particles is 4 to 100 . The method for producing plate-like silica particles according to claim 1, wherein the hollow silica particles are hollow silica particles obtained by heat treatment at 900 to 1200 ° C.   The method for producing plate-like silica particles according to claim 1 or 2, wherein the average thickness of the outer shell of the hollow silica particles is 200 nm or less. The manufacturing method of the plate-like silica particle in any one of Claims 1-3 whose thickness of a plate-like silica particle is 100 nm or less. The method for producing plate-like silica particles according to any one of claims 1 to 4, wherein the hollow silica particles are produced by a method comprising the following steps (I) and (II).
  Step (I): A step of preparing hollow silica particles (A) containing air inside the particles, or core-shell type silica particles (B) containing a material that disappears by firing to form a hollow part.
  Step (II): a step of heat-treating the hollow silica particles (A) or the core-shell type silica particles (B) obtained in the step (I) at 900 to 1200 ° C. The plate-like silica particles according to claim 5, wherein the hollow silica particles (A) or the core-shell type silica particles (B) are produced by a method comprising the following steps A to D.
  Step A: 0.1 to 50 g / L of the polymer particles (a-1) or 0.1 to 100 mmol / L of the hydrophobic organic compound (a-2), and the following general formulas (1) and (2) And 0.1 to 100 mmol / L of one or more (b) selected from quaternary ammonium salts represented by the formula (1)) and 0.1 to 100 mmol of silica source (c) that produces a silanol compound by hydrolysis. Step of preparing an aqueous solution containing / L.
    [R ¹ (R ^Three ) _Three N] ⁺ X ^-              (1)
    [R ¹ R ² (R ^Three ) ₂ N] ⁺ X ^-           (2)
(Wherein R ¹ And R ² Each independently represents a linear or branched alkyl group having 4 to 22 carbon atoms; ^Three Represents an alkyl group having 1 to 3 carbon atoms, and X represents a monovalent anion. )
  Step B: The aqueous solution obtained in Step A is stirred at a temperature of 10 to 100 ° C., has an outer shell composed of silica, and has polymer particles (a-1) or a hydrophobic organic compound (a -2) to prepare an aqueous dispersion of core-shell type silica particles
  Step C: Step of separating the core-shell type silica particles (B) from the aqueous dispersion obtained in Step B
  Step D: A step of firing the core-shell type silica particles (B) obtained in Step C to obtain hollow silica particles (A). Claim 1 obtained by the production method according to any one of 6, a relative dielectric constant of 3.5 or less and / or a dielectric loss tangent is 0.01 or less plate-shaped silica particles. The plate-like silica particles according to claim 7 , wherein the silica skeleton is not substantially porous. The plate-like silica particles according to claim 7 or 8 , wherein the specific surface area is 70 m ² / g or less.