JP6105267B2 - Method for producing black powder - Google Patents

Description

The present invention relates to a method for manufacturing a Kokushokuko body.

  For example, black particles are used as spacers for liquid crystal display devices (see Patent Documents 1 and 2). Patent Document 1 discloses black-based particles obtained by heat-treating particles obtained by particle growth using a metal alkoxide decomposition product. Patent Document 2 discloses black silica particles obtained by heating after contacting a fluorinating agent and an organic solvent with silica particles.

Japanese Patent Publication No. 07-82172 Japanese Patent Laid-Open No. 03-279209

  By the way, when a display device such as a liquid crystal display device is narrowed, light emitted from the backlight easily leaks to the front side through a seal portion in the frame. Since narrowing of the frame of the display device is expected to further progress, it is required that the particles used as spacers in the seal portion have excellent blackness in order to suppress light leakage. . On the other hand, for example, from the viewpoint of protecting the wiring formed in the seal portion while exhibiting the function as a spacer used in the seal portion in the frame, it can be said that the black particles preferably have appropriate flexibility.

The objective of this invention is providing the manufacturing method of black powder which is easy to exhibit blackness and moderate softness | flexibility.

Method for producing a black powder to solve the above problems is a method for producing a black powder obtained and organopolysiloxane and a vinyl polymer from the powder of the composite composite particles, wherein the organopolysiloxane is represented by the following General formula (1):
R ¹ Si (OR ² ) ₃ (1)
(In the general formula (1), R ¹ is a non-hydrolyzable group and has an alkyl group having 1 to 20 carbon atoms, a (meth) acryloyloxy group, or an epoxy group having 1 to 20 carbon atoms, carbon An alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms; R ² represents an alkyl group having 1 to 6 carbon atoms; and each OR ² is identical to each other. The vinyl polymer contains a vinyl polymer having a nitrile group and constitutes the black powder. The black particles include carbon generated by carbonizing the organic component in the composite particles as a coloring material, and the Y value in the XYZ color system is 6% or less, and the 10% K value is 2000 to 25000. / Mm are ^two der, the manufacturing method, the composite by polymerizing the monomer after imbibed a vinyl monomer having a particle nitrile group containing condensate obtained from the trialkoxysilane A composite step of forming particles, and a carbonization step of carbonizing organic components in the composite particles .

In the above black powder production method , the vinyl polymer having a nitrile group includes a vinyl polymer containing acrylonitrile as a structural unit, and the black particles have a mass ratio of acrylonitrile to the trialkoxysilane of 0.00. It is preferably obtained from composite particles in the range of 1-2. Here, the said mass ratio is a value calculated | required from each mass part of trialkoxysilane and acrylonitrile used as a raw material of black powder.

  According to the present invention, it is easy to exhibit blackness and appropriate flexibility.

Hereinafter, embodiments of the black powder and the manufacturing method thereof will be described.
<Black powder>
The black powder is obtained from a powder of composite particles in which an organopolysiloxane and a vinyl polymer are combined. The organopolysiloxane contains a condensate obtained from trialkoxysilane represented by the following general formula (1).

R ¹ Si (OR ² ) ₃ (1)
In the general formula (1), R ¹ is a non-hydrolyzable group, an alkyl group having 1 to 20 carbon atoms, (meth) acrylic alkyl group having 1 to 20 carbon atoms having acryloyloxy group or epoxy group, the carbon number R ² represents an alkyl group having 1 to 6 carbon atoms, R ² represents an alkyl group having 1 to 6 carbon atoms, and each OR ² is the same as each other. It may or may not be.

  Examples of trialkoxysilanes represented by the general formula (1) include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, and propyltriethoxysilane. , Butyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-acryloyloxypropyltrimethoxysilane, and γ-methacryloyloxy And propyltrimethoxysilane.

The trialkoxysilane represented by the general formula (1) can be used alone or in combination of two or more.
The organopolysiloxane may contain a condensate obtained from at least one organoalkoxysilane selected from dialkoxysilane and monoalkoxysilane.

  The vinyl polymer includes a vinyl polymer having a nitrile group. Examples of the vinyl polymer having a nitrile group include those containing at least one of acrylonitrile and methacrylonitrile as a structural unit. The structural unit of the vinyl polymer having a nitrile group may include, for example, methyl acrylate, vinyl acetate, methyl methacrylate, and the like.

  The vinyl polymer having a nitrile group preferably contains a vinyl polymer containing acrylonitrile as a constituent unit, and more preferably contains 50 mol% or more of acrylonitrile.

  The black particles constituting the black powder are preferably obtained from composite particles in which the mass ratio of acrylonitrile to trialkoxysilane is in the range of 0.1 to 2. When the mass ratio of acrylonitrile to trialkoxysilane is 0.1 or more, the blackness is easily increased, and the hardness of the black particles can be easily controlled. When the mass ratio of acrylonitrile to trialkoxysilane is 2 or less, the aggregation of black particles is easily suppressed, and the insulation properties of the black particles are easily increased.

The black particles contain carbon generated by carbonizing the organic component in the composite particles as a colored substance. The organic component comprises the general formula R ¹ (1), and a vinyl polymer described above. Carbonization of the organic component is performed by heating the powder of the composite particles.

The Y value in the XYZ color system of the black powder is 6% or less, and the 10% K value is 2000 to 25000 N / mm ² . The Y value in the XYZ color system is a value measured in accordance with JIS Z8701: 1999. The Y value is preferably 3% or less from the viewpoint of more exhibiting blackness.

  The blackness of the black powder can also be evaluated by, for example, the luminance of the black powder magnified with a transmission microscope. In this evaluation, an image of a black powder enlarged by a transmission microscope is taken into a storage device using an image sensor such as a CCD image sensor, and then a contrast ratio between black particles and the background is calculated using image analysis software. . The blackness can be evaluated by comparing the contrast ratios of the black particles having different configurations. The contrast ratio is represented by L1 / L2, where the luminance of the black particles is L1 and the luminance of the background is L2.

The contrast ratio of the black particles is preferably 0.5 or less from the viewpoint of more exhibiting light shielding properties.
The 10% K value is obtained by measuring the displacement [mm] when compressed under the conditions of a compression speed of 0.029 g / second and a maximum load of 10 g using a micro compression tester, and is obtained by the following relational expression.

10% K value [N / mm ² ] = (3/2 ^1/2 ) × F × S ^−3/2 × R ^−1/2
F in the above relational expression is a load [N] in 10% compression deformation of the black powder, S is a displacement [mm] in 10% compression deformation of the black powder, and R is a radius [mm] of the black particles. ].

The average particle diameter of the black powder is preferably 1 to 100 μm, more preferably 1 to 20 μm. The particle size distribution of the black powder is indicated by the following CV value (coefficient of variation).
CV value (%) = {standard deviation of particle diameter [μm] / average particle diameter [μm]} × 100
The CV value of the black powder is preferably 5% or less.

  The black powder is suitable as a spacer such as a liquid crystal display device spacer, an EL display device spacer, a touch panel spacer, or a spacer for maintaining a uniform distance between various substrates. The black powder is, for example, a core material for conductive particles, an additive for a coating film, an additive for a light diffusion film, an unevenness imparting agent, an additive for cosmetics, an additive for paint or ink, and an adhesive. It can also be used as an additive and various fillers.

<Method for producing black powder>
Next, the manufacturing method of black powder is demonstrated. The manufacturing method of black powder includes a composite process and a carbonization process. In the composite step, the vinyl monomer having a nitrile group is absorbed into particles containing a trialkoxysilane condensate. Further, in the composite process, composite particles are formed by polymerizing a vinyl monomer having a nitrile group.

Particles containing a trialkoxysilane condensate are obtained through a seed particle formation step and a growth particle formation step.
(Seed particle formation process)
In the seed particle forming step, the organoalkoxysilane is hydrolyzed and condensed by adding a catalyst to a solution in which an organoalkoxysilane containing at least trialkoxysilane is dissolved in an aqueous solvent. Thereby, seed particles containing a condensate of trialkoxysilane are formed. In the seed particle forming step, an aqueous seed particle dispersion medium in which the seed particles are dispersed in the aqueous dispersion medium as droplets is obtained.

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

  The aqueous solvent can contain a stabilizer from the viewpoint of enhancing the solubility of the organoalkoxysilane and stabilizing the generated seed particles. Examples of the stabilizer include a surfactant and a polymer dispersant. When it is desired to reduce the ionic substance remaining in the black particles, it is preferable to use a nonionic stabilizer.

  Examples of the catalyst include at least one of ammonia and amine. Examples of the amine include monomethylamine, dimethylamine, monoethylamine, diethylamine and ethylenediamine. A catalyst can be used 1 type or in combination of 2 or more types. Among the catalysts, ammonia is preferable from the viewpoint of low toxicity, easy removal from the particles, and low cost.

  The hydrolysis and condensation reaction is carried out while stirring the organoalkoxysilane and the catalyst in an aqueous solvent. The catalyst amount at the start of the reaction can be set according to a conventional method. The amount of catalyst at the start of the reaction can be set according to, for example, the type and concentration of the organoalkoxysilane and the particle size of the resulting particles. Although reaction temperature is suitably set according to the kind of organoalkoxysilane, the range of 0-50 degreeC is suitable, for example.

  The average particle diameter of the seed particles in the aqueous seed particle dispersion is preferably 0.3 to 15 μm. The CV value of the seed particles in the aqueous seed particle dispersion is not particularly limited, but is preferably 5% or less.

(Growth particle formation process)
In the growth particle forming step, an organoalkoxysilane aqueous solution is used as the particle growth solution. The organoalkoxysilane aqueous solution and the seed particle aqueous dispersion are mixed, and the organoalkoxysilane is absorbed by the seed particles. As a result, grown particles are formed by growing seed particles. Growing particles are particles containing a condensate of trialkoxysilane. In this growth particle forming step, a growth particle aqueous dispersion is obtained.

  The organoalkoxysilane in the solution for particle growth is preferably a trialkoxysilane represented by the above general formula (1) from the viewpoint of excellent hydrolysis and condensation reactivity, preferably methyltrimethoxysilane or vinyltrimethoxysilane. Is more preferable.

Examples of the aqueous solvent used for the particle growth solution include those exemplified as the aqueous solvent used in the seed particle forming step.
From the viewpoint of enhancing the solubility of the organoalkoxysilane and increasing the stability of the grown particles, the particle growing solution may contain a stabilizer as in the seed particle forming step.

(Composite process)
In the composite step, first, an emulsion containing a vinyl monomer having a nitrile group is prepared. A vinyl monomer having a nitrile group is dispersed in an aqueous dispersion medium together with an emulsifier according to a conventional method, whereby an emulsion in which the monomer is dispersed as oil droplets is obtained. As the aqueous dispersion medium, those exemplified as the aqueous solvent used in the seed particle forming step can be used.

The content of the vinyl monomer having a nitrile group in the emulsion is, for example, 10 to 70% by mass.
The emulsifier can be appropriately selected and used, for example, using the HLB value (hydrophilic / lipophilic balance value) as an index. As the emulsifier, for example, an alkyl sulfate having an alkyl group having 6 to 30 carbon atoms is preferably used. Examples of the alkyl sulfate salt include potassium salt, sodium salt, ammonium salt and the like.

  The emulsion further contains a radical polymerization initiator. The type of radical polymerization initiator is not particularly limited, and examples thereof include azo polymerization initiators such as azobisisobutyronitrile and peroxides such as benzoyl peroxide. The content of the radical polymerization initiator in the emulsion is preferably in the range of 0.001 to 20 mol, more preferably 0.01 to 10 mol, with respect to 1 mol of the monomer.

The emulsion may contain a vinyl monomer other than the monomer having a nitrile group.
The prepared emulsion is mixed with the aqueous growth particle dispersion. In the obtained mixed solution, the vinyl monomer is absorbed by the growing particles. Then, the vinyl monomer is radically polymerized by heating the mixed solution. Thereby, solid composite particles are formed. In the composite process, composite particles are obtained by washing and separating the composite particles.

(Carbonization process)
In the carbonization step, the organic component in the composite particles is carbonized by heating the powder of the composite particles. The carbonization step is preferably performed in a gas having a lower oxygen concentration than air. Examples of the gas having a lower oxygen concentration than air include an inert gas and a reducing gas. Examples of the inert gas include nitrogen gas, helium gas, neon gas, and argon gas. As reducing gas, ammonia gas is mentioned, for example. In the carbonization step, a mixed gas mixed with at least one selected from an inert gas and a reducing gas and air may be used, or only at least one selected from an inert gas and a reducing gas may be used.

  The heating temperature in the carbonization step is, for example, 350 to 800 ° C. The heating time in the carbonization step is, for example, 2 to 48 hours. In the carbonization step, the blackness and flexibility of the black powder can be controlled by changing the heating conditions. For example, increasing the heating temperature tends to increase the blackness of the black powder and decrease the flexibility. In addition, the softness | flexibility of black powder can also be reduced by adding and heating a small amount of bifunctional alkoxysilane (dialkoxysilane), for example.

<Operation of black powder and manufacturing method thereof>
The organopolysiloxane in the composite particles contains a condensate obtained from trialkoxysilane represented by the general formula (1). For this reason, it is estimated that a defect occurs in the siloxane bond that is the main skeleton of the black particles by carbonizing the non-hydrolyzable group of the trialkoxysilane. This makes it easier to obtain a flexible black powder. Further, the vinyl polymer in the composite particle includes a vinyl polymer having a nitrile group. When carbon derived from a vinyl polymer having a nitrile group is contained in the black particles as a coloring substance, a black powder with high blackness is easily obtained.

According to the embodiment described in detail above, the following effects are exhibited.
(1) The composite particles include a condensate obtained from trialkoxysilane represented by the general formula (1) and a vinyl polymer having a nitrile group. The black particles constituting the black powder contain carbon generated by carbonizing the organic component in the composite particles as a coloring substance. The Y value in the XYZ color system of the black powder is 6% or less, and the 10% K value is 2000 to 25000 N / mm ² . According to the black powder comprised in this way, it becomes easy to exhibit blackness and moderate softness | flexibility.

  (2) The black particles constituting the black powder are preferably obtained from composite particles in which the mass ratio of acrylonitrile to trialkoxysilane is in the range of 0.1-2. In this case, it becomes easy to further increase the blackness and flexibility of the black powder.

  (3) The manufacturing method of black powder has a composite process and a carbonization process. In the compounding step, a vinyl monomer having a nitrile group is absorbed in particles containing a trialkoxysilane condensate, and then the vinyl monomer is polymerized to form composite particles. In the carbonization step, the organic component in the composite particles is carbonized. According to this manufacturing method, it becomes easy to exhibit blackness and appropriate flexibility.

The embodiment may be modified as follows.
-Seed particles grown larger can be obtained by repeating the seed particle formation step a plurality of times.

-The growth particle forming step may be omitted.
-A growth particle formation process and a composite process can also be performed simultaneously. In this case, for example, a first modification example and a second modification example are given.

  In the first modification, an emulsion further containing an organoalkoxysilane is used in the emulsion of the above embodiment. By contacting the emulsion with the seed particles, the seed particles absorb the organoalkoxysilane and the vinyl monomer having a nitrile group. Thereafter, hydrolysis and condensation of the organoalkoxysilane and radical polymerization of a vinyl monomer having a nitrile group are performed.

  In the second modified example, the organoalkoxysilane is further absorbed after the vinyl monomer having a nitrile group is absorbed in the seed particles using the emulsion of the above embodiment. Thereafter, hydrolysis and condensation of the organoalkoxysilane and radical polymerization of a vinyl monomer having a nitrile group are performed.

  -Surface treatment may be given to black particles. For example, the insulating properties of the black particles can be improved by coating the surface of the black particles with an insulating material. For example, when black particles are mixed with a resin material, the dispersibility of the black particles in the resin can be improved by subjecting the black particles to a surface treatment using a material having a high affinity with the resin material.

The technical idea that can be grasped from the above embodiment will be described below.
(A) A black powder having an average particle diameter of 1 to 100 μm and a CV value of 5% or less in the black powder.

  (B) In the method for producing the black powder, the absorption in the combining step is an aqueous dispersion of an emulsion containing a vinyl monomer having a nitrile group and a condensate obtained from the trialkoxysilane. The manufacturing method of the black powder performed by mixing a liquid.

Next, examples and comparative examples will be described.
Example 1
<Preparation of seed particles>
After 120 g of methyltrimethoxysilane (MTMS) and 1200 g of water were stirred at 20 ° C. for 1 hour, 12 g of 1N ammonia aqueous solution was added and further stirred for 20 minutes to obtain a dispersion of MTMS seed particles.

<Growth of seed particles (preparation of organopolysiloxane dispersion)>
13 g of 1% ammonium dodecyl sulfate aqueous solution was mixed with a solution obtained by stirring 96 g of methyltrimethoxysilane and 467 g of water at 25 ° C. for 1 hour. 180 g of the seed particle dispersion was added to the resulting mixture and stirred for 20 minutes to prepare an organopolysiloxane dispersion.

<Preparation of monomer emulsion>
A mixed solution was prepared by dissolving 5 g of azobisisobutyronitrile (AIBN) as a polymerization initiator in 50 g of acrylonitrile. By stirring this mixed solution and a solution prepared by dissolving 3 g of a sulfate ester salt (trade name: New Coal 707SF, Nippon Emulsifier Co., Ltd.) with 100 g of ion-exchanged water as an emulsifier at 20000 rpm for 1 minute using a homogenizer, A body emulsion was prepared.

<Composite of vinyl polymer>
After adding the monomer emulsion to the organopolysiloxane dispersion and stirring for 1 hour, in order to perform radical polymerization of the monomer, a dispersion of composite particles was prepared by holding at 70 ° C. for 6 hours.

  After cooling this dispersion, decantation using isopropyl alcohol as the cleaning liquid was repeated three times to wash the composite particles. After removing isopropyl alcohol from the supernatant, the composite particles were dried in an oven at 80 ° C. for 1 hour to obtain composite powder. The obtained powder was white.

<Carbonization of organic components>
The composite particle powder was heated at 600 ° C. for 160 minutes in a nitrogen atmosphere. A black powder was obtained by carbonizing the organic component contained in the composite particles by this heating.

(Example 2)
In Example 2, a black powder was prepared in the same manner as in Example 1 except that the preparation conditions for seed particles and the heating conditions for carbonization of the organic component were changed. In Example 2, 125 g of vinyltrimethoxysilane (VTMS) and 1000 g of water were stirred at 25 ° C. for 1 hour, 0.4 g of 1N aqueous ammonia solution was added, and the mixture was further stirred for 40 minutes, whereby VTMS seed particles were mixed. A dispersion was obtained. In the carbonization of the organic component, the heating temperature was changed to 650 ° C.

(Example 3)
In Example 3, a black powder was prepared in the same manner as in Example 1 except that the heating temperature was changed to 400 ° C. in the carbonization of the organic component.

Example 4
In Example 4, a black powder was prepared in the same manner as in Example 2 except that the amount of acrylonitrile was changed to 15 g in the preparation of the monomer emulsion.

(Example 5)
In Example 5, a black powder was prepared in the same manner as in Example 1 except that the conditions for preparing seed particles and the conditions for growing seed particles were changed. The seed particles were prepared by stirring 240 g of methyltrimethoxysilane (MTMS) and 32 g of water at 30 ° C. for 1 hour, adding it to a mixed solution of 1200 g of water and 12 g of 1N aqueous ammonia solution, and stirring for 40 minutes. Thus, a dispersion of MTMS seed particles was obtained. Seed particle growth was prepared in the same manner as in Example 1 except that the seed particle addition amount was changed to 250 g.

(Example 6)
In Example 6, a black powder was prepared in the same manner as in Example 2 except that the amount of acrylonitrile was changed to 170 g in the preparation of the monomer emulsion.

(Comparative Example 1)
In Comparative Example 1, the vinyl polymer composite was omitted, and the organopolysiloxane dispersion was washed and dried in the same manner as the composite particle dispersion in Example 1 to obtain organopolysiloxane particle powder. It was. The obtained powder of organopolysiloxane particles was heated at 650 ° C. for 160 minutes in a nitrogen atmosphere. By this heating, the organic component contained in the organopolysiloxane particles was carbonized to obtain a powder.

(Comparative Example 2)
In Comparative Example 2, a powder was obtained in the same manner as in Comparative Example 1 except that the heating temperature in carbonization of the organic component was changed to 1000 ° C.

(Measurement of Y value)
The Y value in the XYZ color system of the black powder of each example was measured according to JIS Z8701: 1999. First, a quartz powder holder was set in a spectrophotometer (V-670, manufactured by JASCO Corporation), and zero point correction was performed. Next, black powder was put in the powder holder, and the Y value was measured. The Y value was similarly measured for the powders of the comparative examples. The results are shown in Table 1.

(Contrast ratio measurement)
The black powder of each example was dispersed in water or an aqueous solution containing a surfactant. The dispersion was set on a transmission optical microscope so that the black particles did not overlap each other, and then photographed on an 8-bit gray scale. The luminance was measured using the image. At the time of shooting, the exposure time was adjusted so that the average value of the brightness was 130 to 160 for an area of 500 pixels or more in the background of the image. For the measurement of luminance, image analysis software (trade name: Image J) was used. The luminance of the black particles was an average value of values measured arbitrarily at 10 points for black particles existing in an area of 30 pixels or more. In this luminance measurement, the central part of the black particles was measured without including the end part of the black particles. Next, the contrast ratio was calculated from the luminance of the black particles and the luminance of the background. Contrast ratios were similarly calculated for the powders of each comparative example. The results are shown in Table 1.

(Measurement of 10% K value)
Using a micro compression tester (MCTE-200, manufactured by Shimadzu Corporation), 10% K values of 10 black particles in the black powder of each Example were measured, and the average value of these 10% K values. Asked. The average value of 10% K value was similarly obtained for the powders of each comparative example. The results are shown in Table 1.

(Average particle size and CV value)
In each example, each of the seed particle dispersion, the composite particle powder, and the black powder was sampled, and the average particle size and CV value were obtained using a Coulter counter. The average particle diameter and CV value were similarly determined for each comparative example. The results are shown in Table 1.

As shown in Table 1, in the black powder of each example, the Y value is 6% or less and the 10% K value is 2000 to 25000 N / mm ² . In the powder of Comparative Example 1, since the black powder was obtained without combining the vinyl polymer, the Y value exceeded 10%. In Comparative Example 2, the Y value of the powder was decreased by increasing the heating temperature in the carbonization step as compared with Comparative Example 1, but the 10% K value of the powder exceeded 25000 N / mm ² .

Claims (2)

A method for producing a black powder obtained from a powder of composite particles obtained by combining an organopolysiloxane and a vinyl polymer,
The organopolysiloxane has the following general formula (1):
R ¹ Si (OR ² ) ₃ (1)
(In the general formula (1), R ¹ is a non-hydrolyzable group and has an alkyl group having 1 to 20 carbon atoms, a (meth) acryloyloxy group, or an epoxy group having 1 to 20 carbon atoms, carbon An alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms; R ² represents an alkyl group having 1 to 6 carbon atoms; and each OR ² is identical to each other. Or different.)
A condensate obtained from a trialkoxysilane represented by
The vinyl polymer includes a vinyl polymer having a nitrile group,
The black particles constituting the black powder include carbon generated by carbonizing an organic component in the composite particles as a coloring substance.
The Y value in the XYZ color system is 6% or less,
10% K value Ri 2000~25000N / mm ² der,
The manufacturing method includes a composite step of forming the composite particles by polymerizing the monomer after the vinyl monomer having a nitrile group is absorbed into the particles containing the condensate obtained from the trialkoxysilane. ,
Method for producing a black powder and having a carbonization step of carbonizing the organic component in the composite particles. The vinyl polymer having a nitrile group includes a vinyl polymer containing acrylonitrile as a constituent unit,
The method for producing a black powder according to claim 1, wherein the black particles are obtained from composite particles in which a mass ratio of acrylonitrile to the trialkoxysilane is in a range of 0.1 to 2.