Hollow particles and method for producing the same

Abstract

To provide hollow particles having pores inside the particles and capable of homogenizing the properties of a material to which the hollow particles are applied, and to provide a method for producing the hollow particles.SOLUTION: The present invention is a hollow particle containing a structure derived from a cyclic siloxane compound, wherein the cyclic siloxane compound has a cyclic skeleton composed of a siloxane bond, a polymerizable unsaturated group is bonded to at least one of silicon atoms constituting the cyclic skeleton, and the coefficient of variation of the particle diameter is 25% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Hollow silicone particles and hollow silica particles obtained by baking them have attracted attention as additives for various resins and various base materials, taking advantage of their hollow structure. For example, they are expected to be used in lightweight materials, heat insulating materials, low-reflectivity materials, low-refractive-index materials, low-dielectric materials, microcapsules, etc.

[0003] Patent Document 1 discloses a method for producing silicone particles, which includes the steps of: hydrolyzing and condensing a silane monomer having a polymerizable unsaturated group in a solvent A containing water to obtain a dispersion of a polysiloxane compound having a polymerizable unsaturated group; mixing the dispersion with a solvent X that is incompatible with solvent A and also incompatible with the polysiloxane compound; and radically polymerizing the polysiloxane compound; the polysiloxane compound is preferably a chain polysiloxane compound, and the method describes that silicone particles having defects on the surface or inside the particles can be obtained by this production method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-176314 Summary of the Invention [Problem to be solved by the invention]

[0005] According to SEM observation images of silicone particles obtained in Patent Document 1, silicone particles having open defects on the particle surface are disclosed. However, in order to fully utilize properties such as a low bulk density and a low dielectric constant due to the voids inside the particles, hollow particles having a structure with voids inside the particles, i.e., a structure in which the voids are not open on the particle surface, are desired. In addition, it is also desirable that the properties of the hollow particles themselves or the material such as resin in which the hollow particles are filled are uniform regardless of the part of the material.

[0006] Therefore, an object of the present invention is to provide hollow particles having voids inside the particles, which can homogenize the properties of materials to which the hollow particles are applied, and a method for producing the same. [Means for solving the problem]

[0007] The present invention, which has achieved the above object, is as follows. [1] Hollow particles containing a structure derived from a cyclic siloxane compound, The cyclic siloxane compound has a cyclic skeleton formed of siloxane bonds, a polymerizable unsaturated group is bonded to at least one of the silicon atoms constituting the cyclic skeleton, Hollow particles with a particle size variation coefficient of 25% or less. [2] The hollow particles according to [1], which have a hollow ratio of 20 to 70%. [3] The hollow particles according to [1] or [2], which have an average particle diameter of 0.1 to 100 μm. [4] The hollow particles according to any one of [1] to [3], wherein the silicon ratio is 10 to 40 mass %. [5] A step of hydrolyzing and condensing a silane-based monomer having a polymerizable functional group, either alone or together with other silane-based monomers, in a solvent containing water to prepare an aqueous dispersion containing a cyclic siloxane compound having a polymerizable functional group; adding an organic solvent that is incompatible with water and can dissolve the cyclic siloxane compound to the aqueous dispersion; and a step of radically polymerizing the cyclic siloxane compound. [6] The method according to [5], wherein the silane monomer having a polymerizable functional group is represented by the following formula (1): [ka] In formula (1), Y 1 is a polymerizable functional group represented by the following formula (2), an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and Y 1 At least one of X is a polymerizable functional group represented by the following formula (2): 1 is a hydrolyzable group. [ka] In formula (2), R 11 represents hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms; R 12 represents an alkylene group having 1 to 10 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, m is 0 or 1, n is 0 or 1, and * is a bond to silicon in formula (1). [7] The method according to [5] or [6], wherein the organic solvent is 15 to 100 parts by mass per 100 parts by mass of the total of the silane-based monomer having a polymerizable functional group and the other silane-based monomer. [8] Hollow particles are produced by the production method according to any one of [5] to [7], A method for producing hollow silica particles, comprising calcining the hollow particles. [Effects of the Invention]

[0008] According to the present invention, hollow particles with a reduced coefficient of variation of particle diameter can be realized, which makes it possible to realize properties attributable to the pores inside the particles (e.g., small bulk density, low dielectric constant, etc.) and to homogenize the properties of materials to which the hollow particles are applied. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a photograph, substituted for a drawing, showing a transmission SEM image of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1. Cyclic siloxane compounds The cyclic skeleton of the cyclic siloxane compound, which is composed of siloxane bonds, is preferably a structure in which two or more consecutive -Si-O- units are bonded in a ring, and is preferably a cyclic skeleton composed only of siloxane bonds. The number of -Si-O- units in one molecule of the cyclic siloxane compound is 2 or more, and the upper limit may be, for example, 8, preferably 3 to 6, and more preferably 3 to 4.

[0011] At least one of the silicon atoms forming the cyclic skeleton formed by siloxane bonds is bonded to a polymerizable unsaturated group.Preferably, each of the silicon atoms forming the cyclic skeleton formed by siloxane bonds is bonded to two O atoms and two groups selected from polymerizable unsaturated groups and organic groups X other than polymerizable unsaturated groups, and at least one of the silicon atoms forming the cyclic skeleton is bonded to a polymerizable unsaturated group.The two groups bonded to each silicon atom may be the same or different, and the combination of the two groups bonded to each silicon atom may be the same or different for each silicon atom.

[0012] The polymerizable unsaturated group may be a group having a vinyl group or a (meth)acryloyl group at its terminal, and is preferably a group represented by the following formula (2).

[0013] [ka] In formula (2), R 11 represents hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms; R 12 represents an alkylene group having 1 to 10 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, m is 0 or 1, n is 0 or 1, and * is a bond to silicon.

[0014] R 11Examples of the alkyl group having 1 to 10 carbon atoms in the formula (I) include linear alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups; and branched alkyl groups such as isopropyl, isobutyl, isopentyl, neopentyl, and 2-ethylhexyl groups. Of these, linear alkyl groups are preferred, and the linear alkyl group preferably has 1 to 7 carbon atoms, more preferably 1 to 4, still more preferably 1 or 2, and even more preferably 1.

[0015] R 11 Examples of the aryl group having 6 to 10 carbon atoms in the formula (I) include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 2-ethylphenyl group, a 3-ethylphenyl group, a 4-ethylphenyl group, a 2,3-dimethylphenyl group, a 2,4-dimethylphenyl group, an o-isopropylphenyl group, an m-isopropylphenyl group, a p-isopropylphenyl group, and a 4-butylphenyl group.

[0016] Of these, R 11 is preferably hydrogen or an alkyl group having 1 to 10 carbon atoms, more preferably hydrogen or a linear alkyl group having 1 to 7 carbon atoms, even more preferably hydrogen or an alkyl group having 1 to 2 carbon atoms (methyl group or ethyl group), and particularly preferably hydrogen or a methyl group.

[0017] R 12 Examples of the alkylene group having 1 to 10 carbon atoms in the formula (I) include linear alkylene groups such as methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, and decylene; and branched alkylene groups such as methylmethylene, dimethylmethylene, methylethylene, dimethylethylene, methylpropylene, and dimethylpropylene. Of these, linear alkylene groups are preferred. The alkylene group preferably has 1 to 7 carbon atoms, more preferably 1 to 5, even more preferably 2 to 4, and even more preferably 3, with a propylene group being particularly preferred.

[0018] R12 The divalent aromatic hydrocarbon group having 6 to 10 carbon atoms in the formula (I) is preferably a divalent aromatic hydrocarbon group having 6 to 8 carbon atoms, and specific examples thereof include a phenylene group, a methylphenylene group, a dimethylphenylene group, and an ethylphenylene group, with a phenylene group being particularly preferred.

[0019] In formula (2), it is preferred that m is 1 and n is 1, or that m is 0 and n is 0.

[0020] Specific examples of the group represented by the formula (2) include vinyl groups; (meth)acryloyloxy groups; (meth)acrylic acid alkyl groups such as methyl (meth)acrylate groups, ethyl (meth)acrylate groups, propyl (meth)acrylate groups, n-butyl (meth)acrylate groups, isobutyl (meth)acrylate groups, t-butyl (meth)acrylate groups, n-pentyl (meth)acrylate groups, isopentyl (meth)acrylate groups, t-pentyl (meth)acrylate groups, n-hexyl (meth)acrylate groups, and n-heptyl (meth)acrylate groups; and styryl groups. 1-7 It is more preferably an alkyl group, and more preferably a vinyl group or a (meth)acrylic acid C 1-5 Alkyl groups are more preferred, vinyl groups or (meth)acrylic acid C 2-4 An alkyl group is more preferred, and a vinyl group or a (meth)acrylate propyl group is particularly preferred.

[0021] Examples of the organic group X other than the polymerizable unsaturated group include an alkyl group having 1 to 10 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0022] Among the organic groups X other than the polymerizable unsaturated groups which may be bonded to the silicon atoms constituting the cyclic skeleton, examples of alkyl groups having 1 to 10 carbon atoms include linear alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl; and branched alkyl groups such as isopropyl, isobutyl, isopentyl, neopentyl, and 2-ethylhexyl. Of these, linear alkyl groups are preferred, and the linear alkyl group preferably has 1 to 7 carbon atoms, more preferably 1 to 4, even more preferably 1 or 2, and even more preferably 1.

[0023] Among the organic groups X other than the polymerizable unsaturated groups which may be bonded to the silicon atoms constituting the cyclic skeleton, examples of the aryl group having 6 to 10 carbon atoms include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 2-ethylphenyl group, a 3-ethylphenyl group, a 4-ethylphenyl group, a 2,3-dimethylphenyl group, a 2,4-dimethylphenyl group, an o-isopropylphenyl group, an m-isopropylphenyl group, a p-isopropylphenyl group, and a 4-butylphenyl group.

[0024] The organic group X is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 5 carbon atoms, and even more preferably an alkyl group having 1 to 2 carbon atoms.

[0025] It is preferable that at least one silicon atom constituting the cyclic skeleton has a polymerizable unsaturated group and an alkyl group having 1 to 10 carbon atoms bonded thereto, and that 3 / 10 or more of the silicon atoms constituting the cyclic skeleton have a polymerizable unsaturated group (vinyl group or (meth)acrylic acid C 1-5 Alkyl groups are preferred, vinyl groups or (meth)acrylic acid C 2-4 It is more preferable that a polymerizable unsaturated group (a vinyl group or a (meth)acrylic acid C group is more preferable) and an alkyl group having 1 to 10 carbon atoms are bonded to all silicon atoms constituting the cyclic skeleton. 1-5 Alkyl groups are preferred, vinyl groups or (meth)acrylic acid C 2-4It is more preferable that the alkyl group having 1 to 2 carbon atoms is bonded to the aryl group (an alkyl group is more preferable).

[0026] 2.Hollow particles The hollow particles of the present invention are hollow particles containing a structure derived from a cyclic siloxane compound, the cyclic siloxane compound having a cyclic skeleton formed of siloxane bonds, at least one of the silicon atoms constituting the cyclic skeleton having a polymerizable unsaturated group bonded thereto, and having a particle size coefficient of variation of 25% or less. Hereinafter, the hollow particles of the present invention may be referred to as hollow silicone particles.

[0027] The hollow structure of the hollow particles of the present invention is such that pores are present inside the particles without opening on the particle surface, unlike the defects that are open on the particle surface as disclosed in Patent Document 1. The hollow particles of the present invention are preferably composed only of particles having such a shape, but it is sufficient if pores are present inside the particles without opening on the particle surface in 95% or more of the particles by number.

[0028] The hollow particles having a structure derived from a cyclic siloxane compound means that the hollow particles are formed by radical polymerization of polymerizable unsaturated groups contained in the cyclic siloxane compound. In other words, the hollow particles have a cyclic skeleton formed from siloxane bonds contained in the cyclic siloxane compound. When an organic group X other than the above-mentioned polymerizable unsaturated group is bonded to a silicon atom forming the cyclic skeleton, the hollow particles have a cyclic skeleton formed from siloxane bonds to which the organic group X is bonded.

[0029] The coefficient of variation (CV value) of the particle diameter (outer diameter) of the hollow particles is 25% or less, which allows the quality of materials such as resins filled with hollow particles to be homogenized. The coefficient of variation is preferably 25 to 2%, more preferably 20 to 3%. The coefficient of variation is the ratio (percentage) of the standard deviation of the particle diameter (outer diameter) to the average particle diameter (outer diameter).

[0030] The average particle size is preferably 0.1 to 100 μm, more preferably 0.3 to 20 μm, and even more preferably 0.5 to 5 μm. The average particle size can be calculated by measuring the outer diameters of, for example, approximately 500 to 1,500 particles using a transmission electron microscope and determining the arithmetic mean value. The average sphericity (major axis / minor axis) of the hollow particles of the present invention is, for example, 1 to 1.5, preferably 1 to 1.3, more preferably 1 to 1.2, and even more preferably 1 to 1.1.

[0031] The hollow silicone particles preferably have a void ratio of 20 to 70%, more preferably 25 to 60%, and even more preferably 30 to 55%.

[0032] The silicon ratio of the hollow particles is preferably 10 to 40% by mass, more preferably 15 to 25% by mass. As mentioned above, cyclic siloxane compounds contain both silicon and organic groups, and the hollow particles obtained by polymerizing them are composite particles of an organic component and an inorganic component (silicon). Because they contain a silicon component along with an organic component, they can have good heat resistance. The silicon ratio in the hollow particles can be calculated from the composition and amount ratio of the silane monomers used.

[0033] 3. Manufacturing method of hollow particles The method for producing hollow particles includes the steps of: (1) hydrolyzing and condensing a silane-based monomer having a polymerizable functional group, either alone or together with other silane-based monomers (these two may be collectively referred to simply as "silane-based monomers") in a solvent containing water to prepare an aqueous dispersion containing a cyclic siloxane compound having a polymerizable functional group; (2) adding an organic solvent that is incompatible with water and can dissolve the cyclic siloxane compound to the aqueous dispersion; and (3) radically polymerizing the cyclic siloxane compound.

[0034] 3-1. Process (P1) In step (P1), a silane-based monomer having a polymerizable functional group is hydrolyzed and condensed, either alone or together with other silane-based monomers, in a solvent containing water. A cyclic skeleton consisting of siloxane bonds is formed by hydrolysis and condensation of the hydrolyzable groups of the silane-based monomer having a polymerizable functional group, and a cyclic siloxane compound is obtained in which a polymerizable functional group is bonded to at least one silicon atom of the cyclic skeleton.

[0035] In other words, the polymerizable functional group in the silane monomer having a polymerizable functional group means the same as the polymerizable unsaturated group possessed by the cyclic siloxane compound. Therefore, for the polymerizable functional group in the silane monomer having a polymerizable functional group, the description of the polymerizable unsaturated group possessed by the cyclic siloxane compound, including the preferred range, can be referenced in its entirety. One type of silane monomer having a polymerizable functional group may be used, or two or more types may be combined. The silane monomer having a polymerizable functional group is preferably a compound in which at least one polymerizable functional group and two hydrolyzable groups are bonded to a silicon atom, and the remaining bond of the silicon atom may be bonded to another polymerizable functional group or to an organic group X other than the polymerizable functional group. The two hydrolyzable groups bonded to the silicon atom of the silane monomer may be the same or different, and may be -OR a1 (R a1 represents an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an acyl group having 2 to 10 carbon atoms), a halogen atom, a cyano group, an isocyanate group, etc., and -OR a1 More preferred is a group represented by R a1 is an alkyl group having 1 to 4 carbon atoms -OR a1 It is more preferable that:

[0036] The silane monomer having a polymerizable functional group is preferably represented by the following formula (1).

[0037] [ka] In formula (1), Y 1is a polymerizable functional group represented by the above formula (2), an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and Y 1 At least one of X is a polymerizable functional group represented by the above formula (2), 1 is a hydrolyzable group. In the polymerizable functional group represented by the above formula (2), * in the above formula (2) bonds to the silicon atom in the formula (1).

[0038] In equation (1), Y 1 When both are polymerizable functional groups represented by the above formula (2), the two polymerizable functional groups may be the same or different.

[0039] For the hydrolyzable group in formula (1), reference can be made to all of the hydrolyzable groups exemplified above, including the preferred ranges thereof.

[0040] The silane monomer represented by the above formula (1) is a compound having two Y 1 One of the Y 1 is a polymerizable functional group represented by the above formula (2), and the other Y 1 is preferably an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms, and in this case, X 1 -OR a1 (R a1 represents an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an acyl group having 2 to 10 carbon atoms).

[0041] Examples of silane-based monomers represented by the formula (1) include dialkoxysilanes having (meth)acryloxyalkyl groups, such as γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropylethyldiethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-acryloxypropylethyldimethoxysilane, γ-acryloxypropylmethyldiethoxysilane, and γ-acryloxypropylethyldiethoxysilane; dialkoxysilanes having vinyl groups, such as vinylmethyldimethoxysilane and vinylmethyldiethoxysilane; and dialkoxysilanes having allyl groups, such as allylmethyldimethoxysilane. Of these, dialkoxysilanes having (meth)acryloxyalkyl groups or dialkoxysilanes having vinyl groups are more preferred. These may be used alone or in combination of two or more, but are preferably used alone.

[0042] Another silane monomer that can be used together with the silane monomer having a polymerizable functional group is preferably a compound in which two hydrolyzable groups and two organic groups Y, which are other than hydrolyzable groups and other than polymerizable functional groups, are bonded to a silicon atom. The two organic groups Y may be the same or different, but are preferably the same. As with the organic group X, examples of the organic group Y include alkyl groups having 1 to 10 carbon atoms and aryl groups having 6 to 10 carbon atoms. All references to the alkyl groups having 1 to 10 carbon atoms and aryl groups having 6 to 10 carbon atoms in the organic group X, including preferred ranges, can be made. The organic group Y is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 5 carbon atoms, and even more preferably an alkyl group having 1 to 2 carbon atoms.

[0043] The amount of the silane monomer having a polymerizable functional group relative to the total amount of the silane monomer having a polymerizable functional group and the other silane monomers is preferably 3 / 10 to 1 in molar ratio.

[0044] In the cyclic siloxane compound obtained by hydrolysis and condensation of the silane monomer, the number of oxygen atoms (excluding oxygen atoms in the siloxane bond) is preferably 20 or less per 100 carbon atoms, preferably 20 to 0, more preferably 18 to 2, even more preferably 16 to 4, and even more preferably 14 to 6. This allows for more uniform mixing of the organic solvent and the cyclic siloxane compound in the subsequent step (P2). The ratio of oxygen atoms to carbon atoms in the cyclic siloxane compound can be controlled by adjusting the ratio of carbon atoms to oxygen atoms in groups other than hydrolyzable groups bonded to silicon atoms in the silane monomer. When the cyclic siloxane compound is composed of multiple silane monomers, the ratio can be calculated from the molar ratio of each silane monomer in the cyclic siloxane compound and the ratio of carbon atoms to oxygen atoms in each silane monomer (groups other than hydrolyzable groups bonded to silicon atoms). The molar ratio of each silane monomer in the cyclic siloxane compound can be the ratio of the amounts of each silane monomer used. For example, it is preferable to use a compound represented by the above formula (1) as the silane monomer having a polymerizable functional group, which has a polymerizable functional group in formula (2) where m is 0, and / or to use a compound in which two hydrolyzable groups and two organic groups Y, each of which is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms, are bonded to a silicon atom as another silane monomer.

[0045] The water-containing solvent may contain other solvents such as alcohol-based solvents in addition to water, and the proportion of water in 100% by mass of the solvent is preferably 20 to 100% by mass, more preferably 40 to 100% by mass. The total amount of silane monomers charged is, for example, 2 to 25 parts by mass per 100 parts by mass of water charged. The hydrolysis and condensation reaction of the silane-based monomer is carried out in a solvent containing water, preferably in the presence of a catalyst, which may be an acid catalyst or a basic catalyst. The hydrolysis and condensation reaction of the silane-based monomer may be carried out in a single step in a solvent containing water in the presence of an acid catalyst or a base catalyst, or may be carried out in two steps, consisting of a hydrolysis step and a condensation step of the hydrolyzate, as described below.

[0046] In the step (P1) of preparing an aqueous dispersion containing a cyclic siloxane compound having a polymerizable functional group, it is preferable to prepare the aqueous dispersion containing a cyclic siloxane compound having a polymerizable functional group by the following steps: (P1a) mixing a silane monomer having a polymerizable functional group alone, or a silane monomer having a polymerizable functional group and another silane monomer, with a solvent containing water and an acid catalyst; and (P1b) mixing the mixture obtained in the step (P1a) with a base catalyst. In the step (P1a), the silane monomer is hydrolyzed, and in the subsequent step (P1b), the hydrolyzate of the silane monomer obtained in the step (P1a) can be condensed.

[0047] The acid catalyst used in step (P1a) may be, for example, acetic acid, citric acid, or formic acid, and is more preferably acetic acid. The amount of the acid catalyst charged is preferably, for example, 0.05 to 3 parts by mass per 100 parts by mass of the total amount of the silane-based monomers charged.

[0048] In the step (P1a), a surfactant may be mixed with the silane monomer, the water-containing solvent, and the acid catalyst, and the use of the surfactant can reduce the particle size of the resulting cyclic siloxane compound. The surfactant may be any of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and a polymer surfactant. The amount of surfactant charged is, for example, 0.01 to 5 parts by mass with respect to 100 parts by mass of the total amount of the silane-based monomers charged.

[0049] In the step (P1a), it is preferable to prepare a liquid mixture of water, an acid catalyst, and a surfactant used as needed, and then add the silane-based monomer to the mixture and stir it, the stirring temperature being, for example, 20 to 50°C, and the stirring time being, for example, 10 minutes to 24 hours.

[0050] Examples of the base catalyst used in step (P1b) include metal hydroxides such as NaOH and KOH, and nitrogen-based compounds such as ammonia, amines, and compounds having a guanidine structure. The amount of the base catalyst charged is, for example, 0.5 to 5 parts by mass relative to the total amount of the silane-based monomers charged in step (P1a).

[0051] It is preferable to add a base catalyst in step (P1b) and then stir the mixture. It is also preferable to add a surfactant during the stirring in step (P1b). The surfactant to be added in step (P1b) can be any of those exemplified as the surfactant to be used in step (P1a), and a polymer surfactant is particularly preferable. Examples of polymer surfactants include polyvinyl alcohol, polyethylene glycol, sodium poly(meth)acrylate, potassium poly(meth)acrylate, ammonium poly(meth)acrylate, polyhydroxyethyl (meth)acrylate, and polyhydroxypropyl (meth)acrylate.

[0052] 3-2.Process (P2) In step (P2), a water-immiscible organic solvent capable of dissolving the cyclic siloxane compound is added to the aqueous dispersion containing the cyclic siloxane compound having a polymerizable functional group obtained in step (P1). Step (P2) is preferably performed at a temperature of 20 to 50°C, and it is particularly preferable to stir the mixture at 20 to 50°C after adding the organic solvent. By adding the organic solvent to the aqueous dispersion containing the cyclic siloxane compound, the cyclic siloxane compound and the organic solvent are uniformly mixed in the aqueous dispersion. In the next step (P3), radical polymerization of the cyclic siloxane compound is allowed to proceed. Due to the difference in polarity, the silicone component obtained by polymerization of the cyclic siloxane compound and the organic solvent undergo phase separation in one step of step (P3). At the same time, the silicone component collects on the more polar solvent side (outside) containing water, forming a shell, and silicone particles encapsulating the organic solvent, i.e., hollow silicone particles, can be formed. Furthermore, according to the method of step (P1), the CV value of the particle size of the obtained cyclic siloxane compound (oily particles) can be kept low. By adding the organic solvent to such an aqueous dispersion of the cyclic siloxane compound, the organic solvent can be encapsulated in the cyclic siloxane compound while maintaining a low CV value of the particle size, and the CV value of the particle size of the hollow silicone particles obtained in the subsequent step (P3) can also be reduced.

[0053] The organic solvent that is incompatible with water and capable of dissolving the cyclic siloxane compound is, for example, an organic solvent that has a solubility in water of 0.1 g / 100 mL or less at a temperature of 20°C and is capable of dissolving 50% or more (usually 600% or less) of the cyclic siloxane compound by mass at a temperature of 20°C to 50°C.

[0054] Examples of the organic solvent include hydrocarbon solvents. The hydrocarbon solvent may be an aliphatic hydrocarbon solvent, an alicyclic hydrocarbon solvent, or an aromatic hydrocarbon solvent, and may be used alone or in combination of two or more. In particular, an embodiment in which one or more aliphatic hydrocarbon solvents are used in combination with one or more aromatic hydrocarbon solvents, or an embodiment in which one or more aliphatic hydrocarbon solvents are used alone (without an aromatic hydrocarbon solvent) is preferred. The aliphatic hydrocarbon solvent is preferably a linear saturated hydrocarbon solvent, more preferably a linear saturated hydrocarbon solvent having 5 to 20 carbon atoms, even more preferably octane or hexadecane, and even more preferably octane. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, trimethylbenzene, etc., and toluene is preferred.

[0055] The amount of the organic solvent is preferably 15 to 100 parts by mass, and more preferably 20 to 80 parts by mass, relative to 100 parts by mass of the total amount of silane-based monomers charged in step (P1). By adjusting the amount of the organic solvent, the hollow ratio of the hollow particles (hollow silicone particles) and hollow silica particles can be controlled.

[0056] It is preferable that the organic solvent is mixed with water and a polymerization initiator, and the resulting mixture is added to the aqueous dispersion containing the cyclic siloxane compound obtained in step (P1). It is more preferable that the organic solvent is mixed with water, a surfactant, and a polymerization initiator to prepare an emulsion, and this emulsion is added to the aqueous dispersion containing the cyclic siloxane compound having a polymerizable functional group obtained in step (P1), followed by further stirring.

[0057] The surfactant may be any of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and a polymer surfactant, and it is preferable to use an anionic surfactant (anionic emulsifier). As the anionic surfactant, alkyl sulfates such as ammonium dodecyl sulfate and sodium dodecyl sulfate are preferably used.

[0058] Examples of the polymerization initiator include peroxide-based polymerization initiators and azo compound-based polymerization initiators. Examples of the peroxide-based polymerization initiator include benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate, cumene hydroperoxide, cyclohexanone peroxide, t-butyl hydroperoxide, and diisopropylbenzene hydroperoxide. Examples of azo compound polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,3-dimethylbutyronitrile), 2,2'-azobis-(2-methylbutyronitrile), 2,2'-azobis(2,3,3-trimethylbutyronitrile), 2,2'-azobis(2-isopropylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-4-methoxy-2,4-dimethylvaleronitrile, 2-(carbamoylazo)isobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and dimethyl-2,2'-azobisisobutyrate. These may be used alone or in combination of two or more. Among these, azo compound polymerization initiators are preferred. The amount of the polymerization initiator charged is preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the total amount of the silane-based monomers charged in the step (P1).

[0059] 3-3.Process (P3) In step (P3), the temperature for radically polymerizing the cyclic siloxane compound can be appropriately selected depending on the radical polymerization initiator used, but is preferably 30 to 100°C, more preferably 50 to 80°C, from the standpoint of ease of reaction control. The reaction time for radical polymerization is preferably 0.5 to 40 hours, more preferably 1 to 30 hours. The radical polymerization is also preferably carried out in an inert gas atmosphere such as nitrogen. Step (P3) is also preferably carried out in the presence of a surfactant, and it is particularly preferred to use a polymeric surfactant.

[0060] The hollow particles obtained in step (P3) may be isolated from the emulsion using a conventional method such as filtration, centrifugation, or vacuum concentration. The hollow particles are then washed and dried as needed. Washing may be performed using ion-exchanged water or an alcohol such as methanol.

[0061] 4. Manufacturing method of hollow silica particles The hollow particles can be calcined to obtain hollow silica particles. The calcination conditions can be adjusted appropriately based on the temperature and time at which the resin is generally incinerated.

[0062] 5.Applications The hollow silicone particles and hollow silica particles of the present invention can be used for lightweight materials, heat insulating materials, low reflectivity materials, low refractive index materials, low dielectric materials, microcapsules, and the like. [Example]

[0063] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can of course be practiced with appropriate modifications within the scope of the above and below-described aims, all of which are included in the technical scope of the present invention.

[0064] The measurement and evaluation methods in each example are as follows.

[0065] <Measurement of outer diameter OD, inner diameter ID, and outer shell thickness> A particle dispersion liquid dispersed in water or a solvent was collected and observed using a transmission electron microscope at a measurement magnification such that the number of particles in one field of view was 100 to 300. In the transmission electron microscope images obtained from five or more fields of view, the outer diameter OD (primary particle diameter) of all particles in the electron microscope images was measured and the number average value was calculated. The inner diameter ID of the particle's outer shell was measured on the particle center side (inside), and was observed and measured using a transmission electron microscope in the same manner as the outer diameter OD, and the number average value was calculated. The thickness of the outer shell was calculated based on the following formula. Shell thickness (nm) = (number average value of outer diameter OD - number average value of inner diameter ID) / 2

[0066] <Measurement of the coefficient of variation (CV value) of outer diameter OD> The coefficient of variation of the outer diameter OD was calculated based on the following formula using the number average value of the outer diameter OD and the standard deviation of the outer diameter OD. Coefficient of variation of outer diameter (OD) (%) = (standard deviation of outer diameter (OD) / number average value of outer diameter (OD)) x 100

[0067] <Measurement of hollowness> Using the outer diameter OD and the inner diameter ID, the hollow ratio of each particle was calculated based on the following formula, and the number average value was determined. Hollowness ratio (%) = (inner diameter OD) 3 / (Outer diameter OD) 3 ×100

[0068] <Silicon ratio of hollow particles> The silicon ratio was determined based on the composition of the silane monomer and the mass ratio of the silane monomer used.

[0069] Example 1 A reaction vessel equipped with a stirrer, dropping device, and thermometer was charged with 700 parts of ion-exchanged water and 0.35 parts of aqueous acetic acid solution, and the liquid temperature was adjusted to 25±0.5°C while stirring. To this was added 13.3 parts of 3-methacryloxypropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., "KBM502", hereinafter referred to as MPDS) and 16.0 parts of dimethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., "KBM22", hereinafter referred to as DMDS) as silane monomers (silane coupling agents), and stirring was continued to carry out the hydrolysis reaction of the silane monomers.

[0070] After 60 minutes, 1.55 parts of a 48% aqueous solution of sodium hydroxide was added to condense the hydrolyzed silane monomer. After 30 minutes, 2.90 parts of a 10% aqueous solution of polyvinyl alcohol was added to obtain an emulsion of cyclic siloxane compound particles. The structure of the cyclic siloxane compound can be confirmed by gel permeation chromatography (GPC) (see, for example, Patent Application No. 2023-089754).

[0071] Next, a solution of 0.1 parts of sodium dodecyl sulfate (emulsifier) ​​dissolved in 14.7 parts of ion-exchanged water was added to a solution of 14.7 parts of n-octane and 0.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (Wako Pure Chemical Industries, Ltd., "V-65") as a polymerization initiator. The mixture was emulsified and dispersed at 10,000 rpm for 5 minutes using a TK Homomixer (Tokushu Kika Kogyo Co., Ltd.) to prepare an emulsion. This emulsion was then added to the emulsion of polysiloxane particles (i.e., cyclic siloxane compounds) and further stirred. One hour after the addition of the emulsion, a sample of the reaction solution was taken and observed under a microscope. It was confirmed that the polysiloxane particles had absorbed the octane and slightly enlarged. The solubility of octane in water (20° C.) is approximately 0.066 mg / 100 mL, and octane can dissolve 50% or more of the cyclic siloxane compound obtained in this example.

[0072] Next, 2.90 parts of a 10% aqueous solution of polyvinyl alcohol was added, and the polysiloxane particle emulsion was heated to 65°C under a nitrogen atmosphere and maintained at 65°C for 2 hours to carry out radical polymerization. After cooling the reaction solution, the resulting emulsion was subjected to solid-liquid separation, and the resulting cake was washed with ion-exchanged water and then with methanol to obtain Silicone Particle Powder 1. The physical properties of the resulting particles are shown in Table 1.

[0073] Example 2 Silicone particle powder 2 was obtained in the same manner as in Example 1, except that the silane coupling agent used was changed to 13.3 parts of 3-methacryloyloxypropylmethyldimethoxysilane and 16.0 parts of dimethyldimethoxysilane, and a cyclic siloxane compound was obtained using 13.3 parts of 3-methacryloyloxypropylmethyldimethoxysilane and 16.0 parts of dimethoxymethylvinylsilane (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter referred to as DMVS). From the ratio of the amounts of the silane monomers used, the number of oxygen atoms in the cyclic siloxane compound obtained in this example can be calculated to be 13.8 per 100 carbon atoms. Moreover, octane can dissolve 50% or more of the cyclic siloxane compound obtained in this example.

[0074] Example 3 Silicone particle powder 3 was obtained in the same manner as in Example 2, except that the amounts of n-octane and ion-exchanged water used to prepare the emulsion were each changed to 10.3 parts. A transmission SEM image of the obtained silicone particle powder 3 is shown in Figure 1. The transmission SEM image confirmed that the silicone particle powder 3 had a hollow structure.

[0075] Comparative Example 1 A reaction vessel equipped with a stirrer, dropping device, and thermometer was charged with 600 parts of ion-exchanged water and 6.0 parts of a 25% aqueous ammonia solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the liquid temperature was adjusted to 25±0.5°C while stirring. 15 parts of 3-methacryloxypropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., "KBM502," hereafter referred to as MPDS) and 30.0 parts of dimethyldimethoxysilane (hereafter referred to as DMDS) were added as silane monomers (silane coupling agents), and stirring was continued for 60 minutes to carry out a hydrolysis and condensation reaction of the silane monomers, yielding an emulsion of polysiloxane (cyclic siloxane compound) particles.

[0076] The resulting emulsion of polysiloxane particles was centrifuged to separate an aqueous layer and an oil layer, and then the aqueous layer was removed to obtain polysiloxane compound X.

[0077] A reaction vessel equipped with a stirrer, a dropping device and a thermometer was charged with 180 parts of ion-exchanged water and 20 parts of a 10% aqueous solution of polyvinyl alcohol, and the liquid temperature was adjusted to 25±0.5°C with stirring.

[0078] Next, 20 parts of the polysiloxane compound X obtained by the above method, 10 parts of n-octane, and 0.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (Wako Pure Chemical Industries, Ltd., "V-65") as a polymerization initiator were added to a solution of 1.0 parts of a 10% aqueous solution of polyvinyl alcohol as an emulsifier dissolved in 20 parts of ion-exchanged water, and the mixture was emulsified and dispersed at 8000 rpm for 2 minutes using a TK Homomixer (Tokushu Kika Kogyo Co., Ltd.) to prepare an emulsion. This emulsion was added to a reaction vessel and further stirred. The mixture was then heated to 65°C under a nitrogen atmosphere and maintained at 65°C for 2 hours to carry out radical polymerization. After cooling the reaction solution, the resulting emulsion was subjected to solid-liquid separation, and the resulting cake was washed with ion-exchanged water and then with methanol to obtain silicone particle powder 4.

[0079] [Table 1]

[0080] Example 4 The obtained silicone (hollow) particle powder 1 was placed in a crucible, heated from room temperature to 1000°C over 5 hours using an electric furnace, held at that temperature for 1 hour, and then cooled to obtain hollow-structured calcined silica particles.

Claims

1. Hollow particles containing a structure derived from a cyclic siloxane compound, The cyclic siloxane compound has a cyclic skeleton formed of siloxane bonds, a polymerizable unsaturated group is bonded to at least one of the silicon atoms constituting the cyclic skeleton, Hollow particles having a particle size variation coefficient of 25% or less.

2. 2. The hollow particles according to claim 1, wherein the hollow ratio is 20 to 70%.

3. 2. The hollow particles according to claim 1, having an average particle size of 0.1 to 100 μm.

4. 2. The hollow particles according to claim 1, wherein the silicon content is 10 to 40% by mass.

5. a step of hydrolyzing and condensing a silane-based monomer having a polymerizable functional group, either alone or together with other silane-based monomers, in a solvent containing water to prepare an aqueous dispersion containing a cyclic siloxane compound having a polymerizable functional group; adding an organic solvent that is incompatible with water and can dissolve the cyclic siloxane compound to the aqueous dispersion; and a step of radically polymerizing the cyclic siloxane compound.

6. The method according to claim 5 , wherein the silane-based monomer having a polymerizable functional group is represented by the following formula (1): 【Chemistry 1】 In formula (1), Y １ is a polymerizable functional group represented by the following formula (2), an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and Y １ At least one of X is a polymerizable functional group represented by the following formula (2): １ is a hydrolyzable group. 【Chemistry 2】 In formula (2), R １１ represents hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms; R １２ represents an alkylene group having 1 to 10 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, m is 0 or 1, n is 0 or 1, and * is a bond to silicon in formula (1).

7. 6. The method according to claim 5, wherein the organic solvent is used in an amount of 15 to 100 parts by mass per 100 parts by mass of the total of the silane-based monomer having a polymerizable functional group and the other silane-based monomer.

8. hollow particles are produced by the production method according to claim 5, A method for producing hollow silica particles, comprising calcining the hollow particles.

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