JP7803063B2 - Silica particles and method for producing the same - Google Patents

Description

The present invention relates to silica particles and a method for producing the same.

Silica particles are used as an additive or main component in powder coatings, cosmetics, rubber, abrasives, etc., and play roles such as improving the strength of resins, improving the fluidity of powders, and preventing packing.

For example, Patent Document 1 discloses "a hydrophobic silica powder, (1) having a hydrophobicity of 50% or more, (2) an extractable amount X of at least one compound selected from the group consisting of quaternary ammonium ions, monoazo complexes, and mineral acid ions in a mixed solvent of methanol and an aqueous methanesulfonic acid solution of 0.1% by mass or more, and (3) wherein X and the extractable amount Y of the compound in water satisfy the following formula (I): Y/X<0.15."

Patent Document 2 also discloses "a silica powder containing a plurality of silica particles in which a quaternary ammonium salt has been introduced into a silica structure having an "Si-O" bond as a repeating unit."

Patent Document 3 also discloses "external charge control particles composed of carrier particles made of hydrophobic spherical silica microparticles with an average particle size of 20 to 500 nm obtained by hydrophobizing the surface of hydrophilic spherical silica microparticles obtained by the sol-gel method, and a charge control agent coated on the surface of the carrier particles."

Patent Document 4 also discloses "silica microparticles obtained by treating spherical hydrophobic silica microparticles having an average primary particle size of 0.01 to 5 μm with a compound selected from the group consisting of quaternary ammonium salt compounds, fluoroalkyl group-containing betaine compounds, and silicone oils."

Furthermore, Patent Document 5 discloses "particles in which silica microparticles with a hydrophobicity of 80% or more are treated with an amphoteric surfactant, and particles in which silica microparticles with a hydrophobicity of 80% or more are treated with a quaternary ammonium salt or a polymer having a quaternary ammonium group."

Japanese Patent Application Laid-Open No. 2019-073418 JP 2017-039618 A JP 2011-185998 A Japanese Patent Application Laid-Open No. 2001-194825 Japanese Patent Application Publication No. 09-166884

An object of the present invention is to provide silica particles containing a nitrogen-containing compound, wherein the ratio C/D, where C is the integral value of signals observed in a chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum measured by cross polarization/magic angle spinning (CP/MAS) and D is the integral value of signals observed in a chemical shift range of −90 ppm to −120 ppm , is less than 0.10 or exceeds 0.75, and the amount X of the nitrogen-containing compound extracted with an ammonia/methanol mixed solution is less than 0.1 mass %, or the ratio Y of the amount X of the nitrogen-containing compound extracted with water to the amount Y of the nitrogen-containing compound extracted with water does not satisfy the formula: Y/X<0.3.

Specific means for solving the above problems include the following aspects.
<1>
Contains a nitrogen-containing compound,
a ratio C/D of an integral value C of a signal observed in a chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum by cross polarization/magic angle spinning (CP/MAS) to an integral value D of a signal observed in a chemical shift range of −90 ppm to −120 ppm is 0.10 or more and 0.75 or less;
Silica particles, wherein an extractable amount X of the nitrogen-containing compound with an ammonia/methanol mixed solution is 0.1 mass % or more, and the extractable amount X of the nitrogen-containing compound and an extractable amount Y of the nitrogen-containing compound with water satisfy the formula: Y/X<0.3.
<2>
<1> The silica particles according to <1>, having a number average particle diameter of 10 nm or more and 200 nm or less.
<3>
<2> The silica particles according to <2>, having a number average particle diameter of 10 nm or more and 80 nm or less.
＜4＞
<4> The silica particles according to any one of <1> to <3>, wherein the average circularity is 0.60 or more and 0.96 or less.
<5>
<4> The silica particles according to <4>, wherein the average circularity is 0.70 or more and 0.92 or less.
<6>
<5> The silica particles according to any one of <1> to <5>, which have a volume resistivity of 1.0×10 ⁷ Ωcm or more and 1.0×10 ^11.5 Ωcm or less.
＜７＞
<6> The silica particles according to any one of <1> to <6>, wherein Ra/Rb is 0.01 or more and 0.8 or less, where Ra and Rb are volume resistivities before and after baking at 350°C, respectively.
＜8＞
<7> The silica particles according to any one of <1> to <7>, wherein A and B are the pore volumes of pores having a diameter of 1 nm or more and 50 nm or less obtained from a pore distribution curve obtained by a nitrogen gas adsorption method before and after calcination at 350°C, respectively, and B/A is 1.2 or more and 5 or less, and B is 0.2 cm ³ /g or more and 3 cm ³ /g or less.
＜９＞
<8> The silica particles according to any one of <1> to <8>, wherein the nitrogen-containing compound is at least one selected from the group consisting of a quaternary ammonium salt, a primary amine compound, a secondary amine compound, a tertiary amine compound, an amide compound, an imine compound, and a nitrile compound.
<10>
Silica base particles;
a structure that covers at least a portion of the surface of the silica base particle, is composed of a reaction product of a trifunctional silane coupling agent, and has a nitrogen-element-containing compound adsorbed in at least a portion of the pores of the reaction product of the trifunctional silane coupling agent;
<9> The silica particles according to any one of <1> to <9>,
<11>
a first step of forming a structure composed of a reaction product of a trifunctional silane coupling agent on at least a portion of the surface of a silica base particle;
a second step of adsorbing a nitrogen-containing compound into at least a portion of the pores of the reaction product of the trifunctional silane coupling agent;
<10> The method for producing silica particles according to any one of <1> to <10>,

According to the invention related to <1>, there is provided silica particles containing a nitrogen-containing compound, wherein the ratio C/D of the integral value C of signals observed in a chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum measured by cross polarization/magic angle spinning (CP/MAS) to the integral value D of signals observed in a chemical shift range of −90 ppm to −120 ppm is less than 0.10 or exceeds 0.75, and the amount X of the nitrogen-containing compound extracted with an ammonia/methanol mixed solution is less than 0.1 mass %, or the ratio of the amount X of the nitrogen-containing compound extracted with water to the amount Y of the nitrogen-containing compound extracted with water does not satisfy the formula: Y/X<0.3.

According to the invention of <2> or <3>, there is provided silica particles containing a nitrogen-containing compound, wherein the ratio C/D of the integral value C of signals observed in a chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum measured by a cross polarization/magic angle spinning (CP/MAS) method to the integral value D of signals observed in a chemical shift range of −90 ppm to −120 ppm is less than 0.10 or exceeds 0.75, the amount X of the nitrogen-containing compound extracted with an ammonia/methanol mixed solution is less than 0.1 mass%, or the ratio of the amount X of the nitrogen-containing compound extracted with water to the amount Y of the nitrogen-containing compound extracted with water does not satisfy the formula: Y/X<0.3, even if the number average particle diameter is 10 nm or more and 200 nm or less and the particle size distribution is 1.1 to 2.0 or 10 nm or more and 80 nm or less.

According to the invention of <4> or <5>, there is provided silica particles containing a nitrogen-containing compound, which have a narrow charge distribution when charged, even when the average circularity is ^0.60 to 0.96 or 0.70 to 0.92, compared to silica particles containing a nitrogen-containing compound, in which the ratio C/D of the integral value C of signals observed in a chemical shift range of −50 ppm to −75 ppm in a 29Si solid-state nuclear magnetic resonance (NMR) spectrum measured by a cross polarization/magic angle spinning (CP/MAS) method and the integral value D of signals observed in a chemical shift range of −90 ppm to −120 ppm is less than 0.10 or exceeds 0.75, the amount X of the nitrogen-containing compound extracted with an ammonia/methanol mixed solution is less than 0.1 mass%, or the ratio of the amount X of the nitrogen-containing compound extracted with water to the amount Y of the nitrogen-containing compound extracted with water does not satisfy the formula: Y/X<0.3.

According to the sixth aspect of the present invention, silica particles are provided that have a narrow charge distribution when charged, compared with silica particles having a volume resistivity of more than 1.0×10 ^11.5 Ωcm.
According to the invention related to <7>, when the volume resistivities before and after firing at 350°C are Ra and Rb, respectively, silica particles are provided which, when charged, have a narrower charge distribution than when Ra/Rb is less than 0.01.

According to the invention of <8>, when the pore volumes of pores with diameters of 1 nm or more and 50 nm or less obtained from the pore distribution curve of the nitrogen gas adsorption method before and after calcination at 350°C are A and B, respectively, silica particles are provided which have a narrower charge distribution when charged than when B/A is less than 1.2 or B is less than 0.2 cm ³ /g.

According to the invention related to <9>, there is provided silica particles containing a nitrogen-element-containing compound, wherein the ratio C/D of the integral value C of the signal observed in the chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum measured by a cross polarization/magic angle spinning (CP/MAS) method to the integral value D of the signal observed in the chemical shift range of −90 ppm to −120 ppm is less than 0.10 or exceeds 0.75, the amount X of the nitrogen-element-containing compound extracted with an ammonia/methanol mixed solution is less than 0.1 mass%, or the ratio of the amount X of the nitrogen-element-containing compound extracted with water to the amount Y of the nitrogen-element-containing compound does not satisfy the formula: Y/X<0.3, and wherein the silica particles contain at least one element-containing compound selected from the group consisting of a quaternary ammonium salt, a primary amine compound, a secondary amine compound, a tertiary amine compound, an amide compound, an imine compound, and a nitrile compound, and have a narrow charge distribution when charged, compared to silica particles containing a nitrogen-element-containing compound in a cross polarization/magic angle spinning (CP/MAS) solid-state nuclear magnetic resonance (NMR) spectrum measured by a cross polarization/magic angle spinning (CP/MAS) method.

According to the invention related to <10>, there is provided silica particles containing a nitrogen-containing compound, wherein the ratio C/D of the integral value C of the signal observed in the chemical shift range of −50 ppm to −75 ppm in a 29Si solid-state nuclear magnetic resonance (NMR) spectrum by cross polarization/magic angle spinning (CP/MAS) to the integral value D of the signal observed in the chemical shift range of ⁻⁹⁰ ppm to −120 ppm is less than 0.10 or exceeds 0.75, the amount X of the nitrogen-containing compound extracted with an ammonia/methanol mixed solution is less than 0.1 mass%, or the ratio of the amount X of the nitrogen-containing compound extracted with water to the amount Y of the nitrogen-containing compound extracted with water does not satisfy the formula: Y/X<0.3. The silica particles have a narrow charge distribution when charged, the silica particles comprising silica base particles and a structure that coats at least a portion of the surface of the silica base particles and is composed of a reaction product of a trifunctional silane coupling agent, and in which the nitrogen-containing compound is adsorbed into at least a portion of the pores of the reaction product of the trifunctional silane coupling agent.

The invention according to item <11> provides a method for producing silica particles that have a narrow charge distribution when charged, compared to a method for producing silica particles in which a nitrogen-containing compound is adsorbed onto silica base particles that do not have structures composed of a reaction product of a trifunctional silane coupling agent on at least a portion of their surfaces.

The following describes embodiments of the present invention. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

In the numerical ranges described in stages in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with the value shown in the examples.

In this specification, each component may contain multiple types of corresponding substances.
In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

<Silica particles>
The silica particles according to this embodiment contain a nitrogen-containing compound and satisfy the following characteristics (1) and (2).
Feature (1): In a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum (hereinafter also referred to as "Si-CP/MAS NMR spectrum") by cross polarization/magic angle spinning (CP/MAS), the ratio C/D of the integral value C of a signal observed in a chemical shift range of -50 ppm to -75 ppm to the integral value D of a signal observed in a chemical shift range of -90 ppm to -120 ppm is 0.10 or more and 0.75 or less. Feature (2): The amount X of the nitrogen-containing compound extracted by the ammonia/methanol mixed solution is 0.1 mass % or more, and the amount X of the nitrogen-containing compound extracted by the ammonia/methanol mixed solution and the amount Y of the nitrogen-containing compound extracted by water satisfy the formula: Y/X<0.3.

Due to the above-described structure, the silica particles according to this embodiment have a narrow charge distribution when charged. The reason for this is presumed to be as follows.

Silica particles have a high negative chargeability and can become excessively charged, resulting in a wide charge distribution. In particular, in a low-temperature, low-humidity environment, excessive charging is likely to occur, increasing the tendency for the charge distribution to become wide.
For example, in powder coating, powder paint is charged by a method such as contact charging or corona discharge, sprayed onto the object to be coated, and electrostatically adheres to it, and then heated to form a coating film.
However, when silica particles, which have a wide charge distribution, are used as an external additive to powder paint, the charge of the powder paint varies, making it difficult to achieve a uniform amount of powder paint adhered to the object to be coated.

On the other hand, when nitrogen-containing compounds are adsorbed onto silica particles, excessive negative charging can be suppressed when the silica particles are charged. Nitrogen-containing compounds have positive charging properties, and silica particles with nitrogen-containing compounds adsorbed thereon cancel out excess negative charging and suppress excessive negative charging.

However, nitrogen-containing compounds have positive charging properties, and if they are adsorbed onto the outermost surface of silica particles, the charge distribution will spread to negative and positive charges. Therefore, it is preferable that the nitrogen-containing compound be present in the pores of the silica particles rather than coating the surface.

Therefore, in the silica particles according to this embodiment, the ratio C/D of the integral value C of the signal observed in the chemical shift range of −50 ppm to −75 ppm in the Si-CP/MAS NMR spectrum to the integral value D of the signal observed in the chemical shift range of −90 ppm to −120 ppm is set to the above range.

The signal integral value satisfying the above range indicates that a low-density structure (e.g., SiO2/ _3CH3 layer) composed of the reaction product of the trifunctional silane coupling agent, which has sufficient adsorption capacity for the nitrogen-containing compound, is formed on at least _a portion of the silica particle surface. The structure composed of the reaction product of the trifunctional silane coupling agent has a low density and a pore shape that allows the nitrogen-containing compound to be easily adsorbed.
Furthermore, by reducing the amount of OH groups that inhibit the adsorption of nitrogen-containing compounds, it becomes easier for a sufficient amount of nitrogen-containing compounds to be adsorbed onto the structure composed of the reaction product of the trifunctional silane coupling agent, and the amount of adsorption increases.

Additionally, in the silica particles according to the present embodiment, the amount X of the nitrogen-containing compound extracted by the ammonia/methanol mixed solution is 0.1 mass % or more, and the amount X of the nitrogen-containing compound extracted by the water and the amount Y of the nitrogen-containing compound extracted by water satisfy the formula: Y/X<0.3.
That is, the nitrogen-containing compound used is one that is difficult to dissolve in water, that is, that has the property of being difficult to adsorb moisture in the air.
In silica particles containing a nitrogen-element-containing compound, when the nitrogen-element-containing compound adsorbs moisture, the charge distribution becomes broader and the nitrogen-element-containing compound becomes more likely to separate from the silica particles.
However, silica particles containing a nitrogen-containing compound that does not easily adsorb moisture in the air are less likely to have a widening charge distribution, and the nitrogen-containing compound is less likely to detach, even when there is a large amount of moisture in the air (even in a high-temperature, high-humidity environment), making it easier to maintain a narrow charge distribution.

As a result, the charge distribution is improved by using nitrogen-containing compounds.

From the above, it is speculated that the silica particles according to this embodiment have a narrow charge distribution when charged.

For example, when the silica particles according to this embodiment are used as an external additive in powder paint, variations in the charge of the powder paint are less likely to occur, even in low-temperature, low-humidity environments, and the amount of powder paint adhered to the object to be coated is made more uniform.

Furthermore, in the silica particles according to this embodiment, when A and B are the pore volumes of pores with diameters of 1 nm to 50 nm determined from a pore distribution curve obtained by a nitrogen gas adsorption method before and after firing at 350°C, it is preferable that B/A is 1.2 to 5 and B is 0.2 cm ³ /g to 3 cm ³ /g.
Hereinafter, "pore volume A of pores with diameters of 1 nm or more and 50 nm or less obtained from the pore distribution curve of the nitrogen gas adsorption method before firing at 350°C" will also be referred to as "pore volume A before firing at 350°C."
On the other hand, "pore volume B of pores with diameters of 1 nm or more and 50 nm or less obtained from a pore distribution curve by nitrogen gas adsorption method after firing at 350°C" is also referred to as "pore volume B after firing at 350°C".

The pore volume B after firing at 350°C is the pore volume after firing and evaporation of the nitrogen-containing compound that had been adsorbed into the pores of the silica particles and blocked some of the pores. Therefore, when B/A is 1.2 or more and 5 or less and B is 0.2 ^cm3 /g or more and 3 ^cm3 /g or less, it indicates that a sufficient amount of the nitrogen-containing compound is adsorbed into at least some of the pores of the silica particles. Therefore, the narrowing of the charge distribution by the nitrogen-containing compound is improved.

The silica particles according to this embodiment are described in detail below.

(CP/MAS NMR spectrum)
The ratio C/D of the integral value C of the signal observed in the chemical shift range of −50 ppm to −75 ppm in the Si-CP/MAS NMR spectrum to the integral value D of the signal observed in the chemical shift range of −90 ppm to −120 ppm is 0.10 or more and 0.75 or less, and from the viewpoint of narrowing the charge distribution, is preferably 0.12 or more and 0.45 or less, and more preferably 0.15 or more and 0.40 or less.
From the viewpoint of narrowing the charge distribution, when the integral value of all signals in the Si-CP/MAS NMR spectrum is taken as 100%, the ratio (signal ratio) of the integral value C of signals observed in the chemical shift range of −50 ppm to −75 ppm is preferably 5% or more,
The upper limit of the ratio of the signal integral value C is, for example, 60% or less.

The Si-CP/MAS NMR spectrum can be obtained by carrying out measurement by nuclear magnetic resonance spectroscopy under the following conditions.
Spectrometer: AVENCE 300 (manufactured by Brunker)
・Resonance frequency: 59.6MHz
・Measurement nucleus: ²⁹ Si
Measurement method: CPMAS method (using Bruker's standard Palk Sequence cp.av)
Waiting time: 4 seconds Contact time: 8 milliseconds Accumulation count: 2048 Measurement temperature: Room temperature (actual measurement value 25°C)
・Observation center frequency: -3975.72Hz
・MAS rotation speed: 7.0 mm - 6 kHz
・Reference substance: hexymethylcyclotrisiloxane

(Extraction amount of nitrogen-containing compounds)
The amount X of the nitrogen-containing compound extracted by the ammonia/methanol mixed solution is 0.1 mass % or more, and the amount X of the nitrogen-containing compound extracted by the water and the amount Y of the nitrogen-containing compound extracted by the water satisfy the formula: Y/X<0.3.

The extracted amount X of the nitrogen-containing compound is preferably 50% by mass or more, but the upper limit of the extracted amount X of the nitrogen-containing compound is, for example, 95% by mass or less, because the solution is difficult to penetrate into the pores due to surface tension, and a portion of the nitrogen-containing compound remains undissolved.
The ratio "Y/X" of the extracted amount X of the nitrogen-containing compound to the extracted amount Y of the nitrogen-containing compound is preferably less than 0.3, and preferably 0.15 or less. However, the lower limit of the ratio "Y/X" is ideally 0, but since the measurement error range of X and Y is about ±1%, the lower limit is, for example, 0.01 or more.

Here, the extracted amounts X and Y of the nitrogen-containing compound are measured as follows.
First, the silica particles to be measured are analyzed at a constant temperature of 400°C using a thermogravimetric/mass spectrometer (e.g., a gas chromatograph mass spectrometer manufactured by Netsch Japan Co., Ltd.), and the integrated mass fraction of compounds in which hydrocarbons having at least one carbon atom are covalently bonded to nitrogen atoms relative to the silica particles is measured and designated as W1.

Separately, 1 part by mass of silica particles to be measured is added to 30 parts by mass of an ammonia/methanol solution (Sigma-Aldrich, ammonia/methanol mass ratio = 1/5.2) at a liquid temperature of 25°C, and after 30 minutes of ultrasonic treatment, the silica powder and the extract are separated. The separated silica particles are dried in a vacuum dryer at 100°C for 24 hours, and the mass fraction of compounds in which hydrocarbons having at least one carbon atom are covalently bonded to a nitrogen atom relative to the silica particles is measured using a thermogravimetric/mass spectrometer at a constant temperature of 400°C, and this mass fraction is designated as W2.
Then, the extracted amount X of the nitrogen element-containing compound is calculated using the following formula.
・Formula: X=W1-W2

Furthermore, 1 part by mass of silica particles to be measured is added to 30 parts by mass of water at a liquid temperature of 25°C, and after 30 minutes of ultrasonic treatment, the silica particles and the extract are separated. The separated silica particles are dried in a vacuum dryer at 100°C for 24 hours, and the mass fraction of compounds in which hydrocarbons having at least one carbon atom are covalently bonded to a nitrogen atom relative to the silica particles is measured at a constant temperature of 400°C using a thermogravimetric/mass spectrometer, and this mass fraction is designated as W3.
Then, the extracted amount Y of the nitrogen element-containing compound is calculated using the following formula.
・Formula: Y=W1-W3

(Pore volume)
In the silica particles according to this embodiment, the ratio B/A of the pore volume B after firing at 350°C to the pore volume A before firing at 350°C is 1.2 or more and 5 or less, but from the viewpoint of narrowing the charge distribution, it is preferably 1.4 or more and 3 or less, and more preferably 1.4 or more and 2.5 or less.

The pore volume B after firing at 350° C. is 0.2 cm ³ /g or more and 3 cm ³ /g or less, but from the viewpoint of narrowing the charge distribution, 0.3 cm ³ /g or more and 1.8 cm ³ /g or less is preferable, and 0.6 cm ³ /g or more and 1.5 cm ³ /g or less is more preferable.

Specifically, the 350° C. firing is carried out as follows.
In a nitrogen environment, the silica particles to be measured are heated to 350° C. at a heating rate of 10° C./min and held at 350° C. for 3 hours, and then cooled to room temperature (25° C.) at a heating rate of 10° C./min.

Pore volume is measured as follows.
First, the silica particles to be measured are cooled to the temperature of liquid nitrogen (-196°C), nitrogen gas is introduced, and the amount of adsorption is determined by a constant volume method or a gravimetric method. The pressure of the introduced nitrogen gas is gradually increased, and an adsorption isotherm is created by plotting the amount of nitrogen gas adsorbed for each equilibrium pressure. From this adsorption isotherm, a pore size distribution curve, expressed as frequency on the vertical axis and pore diameter on the horizontal axis, is calculated using the BJH method formula.
From the obtained pore size distribution curve, an integrated pore volume distribution is calculated, where the vertical axis represents volume and the horizontal axis represents pore diameter. From the obtained integrated pore volume distribution, the pore volume in the pore diameter range of 1 nm to 50 nm is integrated, and this is defined as the "pore volume of pore diameters of 1 nm to 50 nm."

(Configuration of Silica Particles)
The silica particles according to this embodiment contain a nitrogen-containing compound.
Specifically, the silica particles according to this embodiment have a structure in which at least a portion of the surface of the silica base particle is coated with a reaction product of a trifunctional silane coupling agent, and a nitrogen-containing compound is adsorbed to at least a portion of the reaction product. By forming this structure, the pore volume characteristics and Si-CP/MASNMR spectrum characteristics can be controlled. Furthermore, the degree of hydrophobicity and the amount of OH groups, which will be described later, can also be controlled.
Furthermore, in the silica particles according to this embodiment, the surface of the structure may have a hydrophobic treated structure.

-Silica mother particles-
The silica base particles are silica particles on which at least a portion of the surface is composed of a reaction product of a trifunctional silane coupling agent, and on which a structure is formed in which a nitrogen-element-containing compound is adsorbed into at least a portion of the pores of the reaction product of the trifunctional silane coupling agent.
Examples of the silica base particles include dry silica particles and wet silica particles.
Examples of dry silica particles include combustion silica (fumed silica) obtained by burning a silane compound and deflagration silica obtained by explosively burning metallic silicon powder.
Examples of wet silica particles include wet silica particles obtained by a neutralization reaction between sodium silicate and a mineral acid (precipitation silica synthesized and agglomerated under alkaline conditions, and gel silica particles synthesized and agglomerated under acidic conditions), colloidal silica particles (silica sol particles) obtained by polymerizing acidic silicic acid in an alkaline state, and sol-gel silica particles obtained by hydrolysis of an organic silane compound (e.g., alkoxysilane).
Among these, sol-gel silica particles are preferred as the silica base particles from the viewpoint of narrowing the charge distribution.

-Reaction product of trifunctional silane coupling agent-
The adsorption structure formed by the reaction product of the trifunctional silane coupling agent has a low density and a high affinity for nitrogen-containing compounds, which allows the nitrogen-containing compounds to be easily adsorbed deep into the pores, resulting in a large adsorption amount (i.e., content) of the nitrogen-containing compounds. The adhesion of the positively charged nitrogen-containing compounds to the negatively charged silica surface has the effect of counteracting excessive negative charges. Furthermore, since the nitrogen-containing compounds are adsorbed not on the outermost surface of the silica particles but within the low-density structure, they prevent the charge distribution from becoming too strong and widening, and only counteract the excessive negative charges, further improving the narrowing of the charge distribution.

Examples of the reaction product of a trifunctional silane coupling agent include a reaction product in which ^OR2 is substituted with an OH group in the following general formula (TA), a reaction product in which ^OR2 is substituted with an OH group and another reaction product in which ^OR2 is substituted with an OH group and an SiOH group of silica particles are polycondensed. Furthermore, the reaction product of a trifunctional silane coupling agent includes a reaction product in which all or part of ^OR2 is substituted, and a reaction product in which all or part of OR2 is polycondensed.

The trifunctional silane coupling agent is a non-nitrogen element-containing compound that does not contain N (nitrogen).
Specifically, the trifunctional silane coupling agent may be a trifunctional silane coupling agent represented by the following general formula (TA).
General formula (TA): R ¹ -Si(OR ² ) ₃

In general formula (TA), ^R1 represents a saturated or unsaturated aliphatic hydrocarbon group having from 1 to 20 carbon atoms or an aromatic hydrocarbon group having from 6 to 20 carbon atoms, and ^R2 represents a halogen atom or an alkoxy group. Multiple ^R2s may be the same group or different groups.

The aliphatic hydrocarbon group represented by ^R1 may be linear, branched, or cyclic, but is preferably linear or branched. The number of carbon atoms in the aliphatic hydrocarbon group is preferably 1 to 20, more preferably 1 to 18, even more preferably 1 to 12, and still more preferably 1 to 10. The aliphatic hydrocarbon group may be saturated or unsaturated, but is preferably a saturated aliphatic hydrocarbon group, and more preferably an alkyl group.

Examples of saturated aliphatic hydrocarbon groups include linear alkyl groups (methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, hexadecyl, and icosyl groups), branched alkyl groups (isopropyl, isobutyl, isopentyl, neopentyl, 2-ethylhexyl, tertiary butyl, tertiary pentyl, and isopentadecyl groups), and cyclic alkyl groups (cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, tricyclodecyl, norbornyl, and adamantyl groups).

Examples of unsaturated aliphatic hydrocarbon groups include alkenyl groups (vinyl groups (ethenyl groups), 1-propenyl groups, 2-propenyl groups, 2-butenyl groups, 1-butenyl groups, 1-hexenyl groups, 2-dodecenyl groups, pentenyl groups, etc.), and alkynyl groups (ethynyl groups, 1-propynyl groups, 2-propynyl groups, 1-butynyl groups, 3-hexynyl groups, 2-dodecenyl groups, etc.).

The aromatic hydrocarbon group represented by ^R1 preferably has 6 to 20 carbon atoms, more preferably 6 to 18 carbon atoms, even more preferably 6 to 12 carbon atoms, and still more preferably 6 to 10 carbon atoms.

Examples of aromatic hydrocarbon groups include phenylene groups, biphenylene groups, terphenylene groups, naphthalene groups, and anthracene groups.

Examples of the halogen atom represented by ^R2 include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. The halogen atom is preferably a chlorine atom, a bromine atom, or an iodine atom.

Examples of the alkoxy group represented by ^R2 include alkoxy groups having 1 to 10 carbon atoms (preferably 1 to 8, more preferably 1 to 4). Examples of the alkoxy group include a methoxy group, an ethoxy group, an isopropoxy group, a t-butoxy group, an n-butoxy group, an n-hexyloxy group, a 2-ethylhexyloxy group, and a 3,5,5-trimethylhexyloxy group. The alkoxy group also includes a substituted alkoxy group. Examples of substituents that can be substituted on the alkoxy group include a halogen atom, a hydroxyl group, an amino group, an alkoxy group, an amide group, and a carbonyl group.

The trifunctional silane coupling agent represented by general formula (TA) is preferably a trifunctional silane coupling agent in which R ¹ is a saturated aliphatic hydrocarbon group having from 1 to 20 carbon atoms and R ² is a halogen atom or an alkoxy group.

Examples of trifunctional silane coupling agents include:
vinyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane, decyltrichlorosilane, phenyltrichlorosilane (all of the above compounds in which R ¹ is an unsubstituted aliphatic hydrocarbon group or an unsubstituted aromatic hydrocarbon group);
3-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-glycidyloxypropylmethyldimethoxysilane (all of these compounds in which R ¹ is a substituted aliphatic hydrocarbon group or a substituted aromatic hydrocarbon group);
Examples include:
The trifunctional silane coupling agents may be used alone or in combination of two or more.

Among these, from the viewpoint of narrowing the charge distribution, alkyltrialkoxysilanes are preferred as trifunctional silane coupling agents, and alkyltrialkoxysilanes in which, in general formula (TA), R ¹ represents an alkyl group having 1 to 20 carbon atoms (preferably 1 to 15 carbon atoms) and R ² represents an alkyl group having 1 to 2 carbon atoms are more preferred.

From the viewpoint of narrowing the charge distribution, the amount of the structure composed of the reaction product of the trifunctional silane coupling agent attached is preferably 5.5% by mass or more and 30% by mass or less, and more preferably 7% by mass or more and 22% by mass or less, relative to the silica particles.

- Nitrogen-containing compounds -
The nitrogen-containing compound is a nitrogen-containing compound excluding ammonia and compounds that are in a gaseous state at temperatures between -200°C and 25°C.
The nitrogen-containing compound is preferably adsorbed to at least a portion of the pores of the reaction product of the trifunctional silane coupling agent.

Examples of the nitrogen-containing compound include at least one selected from the group consisting of quaternary ammonium salts, primary amine compounds, secondary amine compounds, tertiary amine compounds, amide compounds, imine compounds, and nitrile compounds.
Examples of the primary amine compound include phenethylamine, toluidine, catecholamine, and 2,4,6-trimethylaniline.
The secondary amine compounds include dibenzylamine, 2-nitrodiphenylamine, and 4-(2-octylamino)diphenylamine.
Examples of the tertiary amine compound include 1,8-bis(dimethylamino)naphthalene, N,N-dibenzyl-2-aminoethanol, and N-benzyl-N-methylethanolamine.
Examples of the amide compound include N-cyclohexyl-p-toluenesulfonamide, 4-acetamido-1-benzylpiperidine, and N-hydroxy-3-[1-(phenylthio)methyl-1H-1,2,3-triazol-4-yl]benzamide.
Examples of the imine compound include diphenylmethanimine, 2,3-bis(2,6-diisopropylphenylimino)butane, and N,N'-(ethane-1,2-diylidene)bis(2,4,6-trimethylaniline).
Examples of the nitrile compound include 3-indoleacetonitrile, 4-[(4-chloro-2-pyrimidinyl)amino]benzonitrile, and 4-bromo-2,2-diphenylbutyronitrile.

Among these, from the viewpoint of narrowing the charge distribution, quaternary ammonium salts are preferred as the nitrogen element-containing compound.
The quaternary ammonium salts may be used alone or in combination of two or more.
The quaternary ammonium salt is not particularly limited, and any known quaternary ammonium salt can be used.

From the viewpoint of narrowing the charge distribution, the quaternary ammonium salt preferably contains a compound represented by general formula (AM). The compound represented by general formula (AM) may be used alone or in combination with two or more types.

In general formula (AM), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, or an alkyl group, aralkyl group or aryl group which may have a substituent, and X ^- represents an anion. However, at least one of R ¹ , R ² , R ³ and R ⁴ represents an alkyl group, aralkyl group or aryl group which may have a substituent. Furthermore, two or more of R ¹ , R ² , R ³ and R ⁴ may be linked to form an aliphatic ring, aromatic ring or heterocycle.

Examples of the alkyl group represented by R ¹ to R ⁴ include a linear alkyl group having 1 to 20 carbon atoms and a branched alkyl group having 3 to 20 carbon atoms.
Examples of the linear alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, and an n-hexadecyl group.
Examples of branched alkyl groups having 3 to 20 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an isodecyl group, a sec-decyl group, and a tert-decyl group.
Among the above, the alkyl groups represented by R ¹ to R ⁴ are preferably alkyl groups having 1 to 15 carbon atoms, such as a methyl group, an ethyl group, a butyl group, or a tetradecyl group.

The aralkyl group represented by R ¹ to R ⁴ includes an aralkyl group having 7 to 30 carbon atoms.
Examples of the aralkyl group having from 7 to 30 carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, a 4-phenylbutyl group, a phenylpentyl group, a phenylhexyl group, a phenylheptyl group, a phenyloctyl group, a phenylnonyl group, a naphthylmethyl group, a naphthylethyl group, an anthrathymethyl group, and a phenyl-cyclopentylmethyl group.
Among the above, the aralkyl groups represented by R ¹ to R ⁴ are preferably aralkyl groups having 7 to 15 carbon atoms, such as benzyl, phenylethyl, phenylpropyl, and 4-phenylbutyl.

The aryl group represented by R ¹ to R ⁴ includes an aryl group having 6 to 20 carbon atoms.
Examples of the aryl group having 6 to 20 carbon atoms include a phenyl group, a pyridyl group, and a naphthyl group.
Among the above, the aryl group represented by R ¹ to R ⁴ is preferably an aryl group having 6 to 10 carbon atoms, such as a phenyl group.

The anion represented by X ⁻ includes organic anions and inorganic anions.
Examples of organic anions include polyfluoroalkylsulfonate ions, polyfluoroalkylcarboxylate ions, tetraphenylborate ions, aromatic carboxylate ions, and aromatic sulfonate ions (such as 1-naphthol-4-sulfonate ions).
Examples of inorganic anions include molybdate ions (MoO ₄ ²⁻ , Mo ₂ O ₇ ²⁻ , Mo ₃ O ₁₀ ²⁻ , Mo ₄ O ₁₃ ²⁻ , Mo ₇ O ₂₄ ²⁻ , Mo ₈ O ₂₆ ^{4− ,} etc.), OH ⁻ , F ⁻ , Fe(CN) ₆ ³⁻ , Cl ⁻ , Br ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , PO ₄ ³⁻ , and SO ₄ ²⁻ .

In general formula (AM), two or more of R ¹ , R ² , R ³ and R ⁴ may be bonded to each other to form a ring. Examples of the ring formed by bonding two or more of R ¹ , R ² , R ³ and R ⁴ to each other include an alicyclic ring having from 2 to 20 carbon atoms and a heterocyclic amine having from 2 to 20 carbon atoms.

In the compound represented by general formula (AM), R ¹ , R ² , R ³ and R ⁴ may each independently have a substituent, such as a nitrile group, a carbonyl group, an ether group, an amide group, a siloxane group, a silyl group, or a silane alkoxy group.
Preferably, R ¹ , R ² , R ³ and R ⁴ each independently represent an alkyl group having 1 to 16 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

Among these, from the viewpoint of narrowing the charge distribution, the compound represented by general formula (AM) preferably has a total carbon number of 18 to 35, and more preferably 20 to 32.

Examples of structures other than X 1 ^- in the compound represented by general formula (AM) are shown below, but the present embodiment is not limited thereto.

From the viewpoint of narrowing the charge distribution and maintaining the charge distribution, the nitrogen-containing compound is preferably a nitrogen-containing compound containing molybdenum, and is preferably at least one selected from the group consisting of a quaternary ammonium salt containing molybdenum (particularly, a quaternary ammonium salt containing molybdenum), and a mixture of a quaternary ammonium salt and a metal oxide containing molybdenum.
When the nitrogen compound contains molybdenum, the activity of the nitrogen element is enhanced, and even if the nitrogen-containing compound is present inside the pores of the silica particles rather than on the outermost surface, the positive chargeability of the nitrogen element can be adequately exhibited, resulting in a narrow charge distribution when charged, and the charge distribution is likely to be well maintained.
In particular, in the case of a quaternary ammonium salt containing molybdenum, the anion containing molybdenum, which is an anion, is strongly bonded to the quaternary ammonium cation, which is a cation, and therefore the charge distribution is highly maintainable.

Examples of quaternary ammonium salts containing molybdenum include [N ⁺ (CH) ₃ (C ₁₄ C ₂₉ ) ₂ ] ₄ Mo ₈ O ₂₈ ⁴⁻ , [N ⁺ (C ₄ H ₉ ) ₂ (C ₆ H ₆ ) ₂ ] ₂ Mo ₂ O ₇ ²⁻ , [N ⁺ (CH ₃ ) ₂ (CH ₂ C ₆ H ₆ ) (CH ₂ ) ₁₇ CH ₃ ] ₂ MoO ₄ ²⁻ , and [N ⁺ (CH ₃ ) ₂ (CH ₂ C ₆ H ₆ ) (CH ₂ ) ₁₅ CH ₃ ] ₂ MoO ₄ ²⁻ .
Examples of metal oxides containing molybdenum include molybdenum oxides (molybdenum trioxide, molybdenum dioxide, _Mo9O26 ), alkali metal molybdates (lithium molybdate, sodium molybdate, potassium molybdate _, etc.), alkaline earth metal molybdates (magnesium molybdate, calcium molybdate, etc.), and other composite oxides _{( Bi2O3.2MoO3} , _γ - _{Ce2Mo3O13 , etc.} ).

- Detection and content of nitrogen-containing compounds -
When the silica particles according to this embodiment are heated in a temperature range of 300° C. to 600° C., a nitrogen-containing compound is detected. Specific examples of the detection are as follows.
Nitrogen-containing compounds can be detected, for example, using a heating furnace-type drop-type pyrolysis gas chromatograph mass spectrometer using He as a carrier gas. Nitrogen-containing compounds can be detected under pyrolysis temperature conditions of 300°C to 600°C under inert gas. Specifically, 0.1 mg to 10 mg of silica particles are introduced into the pyrolysis gas chromatograph mass spectrometer, and the presence or absence of nitrogen-containing compounds can be confirmed from the MS spectrum of the detected peak. Examples of components generated by pyrolysis from silica particles containing nitrogen-containing compounds include primary to tertiary amines or aromatic nitrogen compounds represented by the following general formula (N):
In the following general formula (N), R ^N1 to R ^N3 each independently represent a hydrogen atom, or an alkyl group, an aralkyl group, or an aryl group which may have a substituent, and R ^N1 to R ^N3 have the same meanings as R ¹ , R ² , and R ³ in general formula (AM).
For example, when the nitrogen-containing compound is a quaternary ammonium salt, part of the side chain is eliminated by thermal decomposition at 600° C., and detected as a tertiary amine.

From the viewpoint of narrowing the charge distribution, the content of the nitrogen-containing compound, calculated as N atoms, relative to the silica particles is preferably 0.008% by mass or more and 0.45% by mass or less, more preferably 0.015% by mass or more and 0.20% by mass or less, and even more preferably 0.018% by mass or more and 0.10% by mass or less.

The content of the nitrogen element-containing compound in terms of N atoms is measured as follows.
Using an oxygen/nitrogen analyzer (for example, EMGA-920 manufactured by Horiba, Ltd.), measurements are taken over an accumulation time of 45 seconds to obtain the amount of nitrogen present as the ratio of N (N/Si). As a sample pretreatment, impurities such as ammonia are removed from the silica particles by drying them in a vacuum dryer at 100°C for 24 hours or more.

Here, when a nitrogen-containing compound containing molybdenum is used as the nitrogen-containing compound, from the viewpoint of narrowing the charge distribution, the ratio of the net intensity of molybdenum to the net intensity of silicon (Mo/Si), measured by X-ray fluorescence analysis, is preferably 0.035 or more and 0.35 or less, more preferably 0.07 or more and 0.32 or less, and more preferably 0.10 or more and 0.30 or less.

From the perspective of narrowing the charge distribution, the net strength of the molybdenum element is preferably 5 kcps or more and 75 kcps or less, 7 kcps or more and 50 kcps or less, 8 kcps or more and 55 kcps or less, or 10 kcps or more and 40 kcps or less.

The net strength of molybdenum and silicon elements is measured as follows:

Approximately 0.5 g of silica particles are compressed using a compression molding machine under a load of 6 t for 60 seconds to produce a disk with a diameter of 50 mm and a thickness of 2 mm. This disk is used as a sample for qualitative and quantitative elemental analysis using a scanning X-ray fluorescence analyzer (XRF-1500, manufactured by Shimadzu Corporation) under the following conditions to determine the net intensities (unit: kilocounts per second, kcps) of the molybdenum element and the silicon element.
Tube voltage: 40 kV
・Tube current: 90mA
・Measurement area (analysis diameter): diameter 10mmφ
Measurement time: 30 minutes Anticathode: Rhodium

(Hydrophobic Treated Structure)
The hydrophobic treated structure is a structure that has been reacted with a hydrophobic treatment agent.
As the hydrophobic treatment agent, for example, an organosilicon compound is applied.
Examples of organosilicon compounds include:
Alkoxysilane compounds or halosilane compounds having a lower alkyl group, such as methyltrimethoxysilane, dimethyldimethoxysilane, trimethylchlorosilane, and trimethylmethoxysilane;
Alkoxysilane compounds having a vinyl group, such as vinyltrimethoxysilane and vinyltriethoxysilane;
alkoxysilane compounds having an epoxy group, such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane;
alkoxysilane compounds having a styryl group, such as p-styryltrimethoxysilane and p-styryltriethoxysilane;
Alkoxysilane compounds having an aminoalkyl group, such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane;
Alkoxysilane compounds having an isocyanate alkyl group, such as 3-isocyanatepropyltrimethoxysilane and 3-isocyanatepropyltriethoxysilane;
silazane compounds such as hexamethyldisilazane and tetramethyldisilazane;
Examples include:

(Characteristics of Silica Particles)
- Hydrophobicity -
From the viewpoint of narrowing the charge distribution, the hydrophobicity of the silica particles according to this embodiment is preferably 10% or more and 60% or less, more preferably 20% or more and 55% or less, and even more preferably 28% or more and 53% or less.
If the hydrophobicity of the silica particles is 10% or less, the amount of coating on the structure due to the reaction product of the trifunctional silane coupling agent is low, and the content of the nitrogen element-containing compound is reduced, which makes it easier for the charge distribution to widen.
On the other hand, when the hydrophobicity of the silica particles exceeds 60%, the density of the structure increases due to the reaction product of the trifunctional silane coupling agent, the number of pores decreases, and the content of the nitrogen-containing compound decreases, which makes the charge distribution more likely to spread.

The hydrophobicity of silica particles is measured as follows.
0.2% by mass of sample silica particles is placed in 50 ml of ion-exchanged water, and methanol is added dropwise from a burette while stirring with a magnetic stirrer. The mass fraction of methanol in the methanol-water mixed solution at the end point when the entire sample has sunk is determined as the degree of hydrophobicity.

- Number average particle size and number particle size distribution index -
The number average particle size of the silica particles according to this embodiment is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 80 nm or less, and even more preferably 10 nm or more and 60 nm or less.
When the number-average particle diameter of the silica particles is within the above range, the specific surface area is large and excessive charging is likely to occur. However, the silica particles according to the present embodiment achieve a narrow charge distribution even when the number-average particle diameter is within the above range.

The number particle size distribution index of the silica particles according to this embodiment is preferably 1.1 or more and 2.0 or less, and more preferably 1.15 or more and 1.6 or less.
When the number particle size distribution index of the silica particles according to this embodiment is within the above range, there is little coarse powder, which tends to have a large charge amount, and little fine powder, which tends to have a small charge amount, and therefore it is easy to achieve a narrow charge distribution.

Here, the number average particle size and number particle size distribution index of the silica particles are measured as follows.
Silica particles are observed at 40,000x magnification using a scanning electron microscope (SEM), and the images of the observed silica particles are analyzed using image processing and analysis software WinRoof (manufactured by Mitani Shoji Co., Ltd.) to determine the circle-equivalent diameters of at least 200 particles. A cumulative distribution of the number of individual particles is then drawn, starting from the smallest diameter side, to determine the particle size at 50% of the cumulative diameter from the smallest diameter side, that is, the number-average particle size.
The square root of the particle diameter D84 at 84% cumulative size from the smallest diameter side divided by the particle diameter D16 at 16% cumulative size is defined as the "number particle size distribution index" (GSD). That is, the number particle size distribution index (GSD) = (D84/D16) ^0.5 .

- Circularity -
The average circularity of the silica particles according to this embodiment is preferably 0.60 or more and 0.96 or less, more preferably 0.70 or more and 0.92 or less, and even more preferably 0.75 or more and 0.90 or less.
When the average circularity of silica particles is within the above range, the specific surface area is large and excessive charging is likely to occur. However, the silica particles according to this embodiment achieve a narrow charge distribution even when the average circularity is within the above range.

Here, the circularity of the silica particles is measured as follows.
Silica particles are observed at 40,000x magnification using a scanning electron microscope (SEM), and the images of the observed silica particles are analyzed using image processing analysis software WinRoof (manufactured by Mitani Shoji Co., Ltd.) to determine the circularity of at least 200 particles, and the average circularity is calculated by arithmetic averaging.
The circularity is calculated by the following formula.
Circularity = equivalent circle diameter/perimeter = [2 × (Aπ) ^1/2 ]/PM
In the above formula, A represents the projected area, and PM represents the perimeter.

-Volume resistivity-
The volume resistivity of the silica particles according to this embodiment (i.e., the volume resistivity before firing at 350° C.) is preferably 1.0×10 ⁷ Ωcm or more and 1.0×10 ^11.5 Ωcm or less, and more preferably 1.0×10 ⁸ Ωcm or more and 1.0×10 ¹¹ Ωcm or less.
When the volume resistivity of the silica particles according to this embodiment is within the above range, the content of the nitrogen element-containing compound is large, excessive charging is unlikely to occur, and narrowing of the charge distribution is easily achieved.

In the silica particles according to this embodiment, when the volume resistivities of the silica particles before and after firing at 350°C are Ra and Rb, respectively, Ra/Rb is preferably 0.01 or more and 0.8 or less, and more preferably 0.015 or more and 0.6 or less.
When Ra/Rb is within the above range, the content of the nitrogen element-containing compound is large, excessive charging is unlikely to occur, and a narrow charge distribution can be easily achieved.

The 350° C. baking is carried out as described above.
On the other hand, the volume resistivity is measured as follows: The measurement environment is a temperature of 20° C. and a humidity of 50% RH.
The silica particles to be measured are placed on the surface of a circular jig equipped with a 20 ^cm2 electrode plate, with a thickness of approximately 1 mm to 3 mm, to form a silica particle layer. A 20 ^cm2 electrode plate similar to the one described above is placed on top of this, sandwiching the silica particle layer. To eliminate gaps between the silica particles, a pressure of 0.4 MPa is applied to the electrode plate placed on the silica particle layer, and the thickness (cm) of the silica particle layer is then measured. Both the top and bottom electrodes of the silica particle layer are connected to an impedance analyzer (manufactured by Solartron Analytical Inc.), and measurements are made over a frequency range of ^10-3 Hz to ¹⁰⁶ Hz, to obtain a Nyquist plot. This is fitted to an equivalent circuit, assuming the presence of three resistance components: bulk resistance, particle interface resistance, and electrode contact resistance, to determine the bulk resistance R.
The volume resistivity (Ω·cm) of silica particles is calculated using the following formula:
・Formula: ρ=R/L
In the formula, ρ represents the volume resistivity (Ω·cm) of the silica particles, R represents the bulk resistance (Ω), and L represents the thickness (cm) of the silica particle layer.

(OH group amount)
In the silica particles according to this embodiment, the amount of OH groups measured by the Sears method is preferably 0.2 to ^5.5 / ^nm² , and from the viewpoint of narrowing the charge distribution, more preferably 0.2 to ⁴ / ^nm² , and even more preferably 0.2 to ³ / ^nm² .
The amount of OH groups measured by the Sears method can be adjusted to fall within the above range by sufficiently forming a structure composed of a reaction product of a trifunctional silane coupling agent on the silica base particles.

By reducing the amount of OH groups that inhibit the adsorption of nitrogen-containing compounds to the above range, the nitrogen-containing compounds can easily penetrate deep into the pores of the silica particles (for example, the pores of the adsorption layer described below). Then, hydrophobic interactions with the nitrogen-containing compounds occur, strengthening their adhesion to the silica particles. This increases the amount of nitrogen-containing compounds adsorbed. In addition, the nitrogen-containing compounds become less likely to detach. This improves the narrowing of the charge distribution by the nitrogen-containing compounds, and also improves the maintenance of that narrow charge distribution.

In addition, by reducing the amount of OH groups to the above range, the environmental dependency of the charging characteristics becomes less, making it easier to narrow the charge distribution using nitrogen-containing compounds in any environment (particularly in low-temperature, low-humidity environments where excessive negative charging is likely to occur).

The amount of OH groups is measured by the Sears method, specifically as follows.
1.5 g of silica particles were added to a mixture of 50 g of pure water and 50 g of ethanol and stirred for 2 minutes using an ultrasonic homogenizer to create a dispersion. While stirring at 25°C, 1.0 g of 0.1 mol/L aqueous hydrochloric acid was added dropwise to obtain a test solution. The resulting test solution was placed in an automatic titrator and subjected to potentiometric titration using 0.01 mol/L aqueous sodium hydroxide solution, and a derivative curve of the titration curve was created. Among the inflection points where the derivative of the titration curve was 1.8 or greater, the titration amount at which the 0.01 mol/L aqueous sodium hydroxide solution was the largest was designated as E.
The surface silanol group density ρ (number/nm ² ) of the silica particles is calculated using the following formula.
Formula: ρ=((0.01×E-0.1)×NA/1000)/(M×S _BET ×10 ¹⁸ )
In the formula, the details of the symbols are as follows:
E: the titration amount of the 0.01 mol/L sodium hydroxide aqueous solution at the inflection point where the differential value of the titration curve is 1.8 or more, where the titration amount is the largest. NA: Avogadro's number. M: amount of silica particles (1.5 g).
S _BET : Specific surface area of silica particles (m ² /g) The specific surface area of silica particles is measured by the BET nitrogen adsorption three-point method, with the equilibrium relative pressure set to 0.3.

<Method for producing silica particles>
An example of a method for producing silica particles according to this embodiment is
a first step of forming a structure composed of a reaction product of a trifunctional silane coupling agent on at least a portion of the surface of a silica base particle;
a second step of adsorbing a nitrogen-containing compound into at least a portion of the pores of the reaction product of the trifunctional silane coupling agent;
It has.
The method for producing silica particles according to this embodiment may further include a third step of hydrophobizing the silica base particles, which have at least a portion of the surface coated thereon after or during the second step, and which are composed of a reaction product of a trifunctional silane coupling agent and have a structure in which a nitrogen-containing compound is adsorbed in at least a portion of the pores of the reaction product of the trifunctional silane coupling agent.

The steps of the method for producing silica particles according to this embodiment are described in detail below.

[Preparation process]
First, the step of preparing silica base particles will be described.

The preparation process includes, for example,
(i) a step of preparing a silica base particle suspension by mixing an alcohol-containing solvent with silica base particles; and (ii) a step of granulating the silica base particles by a sol-gel method to obtain a silica base particle suspension.
Examples of the silica base particles used in (i) include sol-gel silica particles (silica particles obtained by a sol-gel method), aqueous colloidal silica particles, alcoholic silica particles, fumed silica particles obtained by a gas phase method, and fused silica particles.
The alcohol-containing solvent used in (i) may be a solvent containing alcohol alone, or may be a mixed solvent of alcohol and other solvents. Examples of alcohol include lower alcohols such as methanol, ethanol, n-propanol, isopropanol, and butanol. Examples of other solvents include water; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve acetate; and ethers such as dioxane and tetrahydrofuran. In the case of a mixed solvent, the proportion of alcohol is preferably 80% by mass or more, and more preferably 85% by mass or more.

The step (1-a) is preferably a step of granulating silica base particles by a sol-gel method to obtain a silica base particle suspension.
More specifically, step (1-a) may be carried out, for example, by
an alkaline catalyst solution preparation step of preparing an alkaline catalyst solution containing an alkaline catalyst in an alcohol-containing solvent;
a silica base particle producing step of producing silica base particles by supplying tetraalkoxysilane and an alkali catalyst into an alkali catalyst solution;
Preferably, the method is a sol-gel method comprising:

The alkaline catalyst solution preparation step preferably involves preparing a solvent containing alcohol and mixing this solvent with an alkaline catalyst to obtain an alkaline catalyst solution.

The alcohol-containing solvent may be a solvent containing alcohol alone, or a mixed solvent containing alcohol and another solvent. Examples of alcohol include lower alcohols such as methanol, ethanol, n-propanol, isopropanol, and butanol. Other solvents include water; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve acetate; and ethers such as dioxane and tetrahydrofuran. In the case of a mixed solvent, the alcohol content is preferably 80% by mass or more, and more preferably 85% by mass or more.

Alkaline catalysts are catalysts that promote the reactions (hydrolysis and condensation reactions) of tetraalkoxysilanes. Examples include basic catalysts such as ammonia, urea, and monoamines, with ammonia being particularly preferred.

The concentration of the alkaline catalyst in the alkaline catalyst solution is preferably 0.5 mol/L or more and 1.5 mol/L or less, more preferably 0.6 mol/L or more and 1.2 mol/L or less, and even more preferably 0.65 mol/L or more and 1.1 mol/L or less.

The silica base particle production process involves supplying tetraalkoxysilane and an alkaline catalyst to an alkaline catalyst solution, and then reacting the tetraalkoxysilane (through hydrolysis and condensation reactions) in the alkaline catalyst solution to produce silica base particles.

In the silica base particle production process, nucleus particles are produced by the reaction of tetraalkoxysilane at the initial stage of supply (nucleus particle production stage), and then these nucleus particles grow (nucleus particle growth stage) to produce silica base particles.

Examples of tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. From the standpoint of reaction rate control and uniformity of the shape of the resulting silica base particles, tetramethoxysilane or tetraethoxysilane is preferred.

Examples of alkaline catalysts supplied to the alkaline catalyst solution include basic catalysts such as ammonia, urea, monoamines, and quaternary ammonium salts, with ammonia being particularly preferred. The alkaline catalyst supplied together with the tetraalkoxysilane may be the same type as the alkaline catalyst already contained in the alkaline catalyst solution, or a different type, but it is preferable that it be the same type.

The method for supplying the tetraalkoxysilane and the alkaline catalyst into the alkaline catalyst solution may be a continuous supply method or an intermittent supply method.

In the silica base particle production process, the temperature of the alkaline catalyst solution (temperature at the time of supply) is preferably 5°C or higher and 50°C or lower, and more preferably 15°C or higher and 45°C or lower.

[First step]
In the first step, a structure composed of a reaction product of a trifunctional silane coupling agent is formed.
Specifically, in the first step, for example, a trifunctional silane coupling agent is added to a silica base particle suspension, and the trifunctional silane coupling agent is reacted with the surfaces of the silica base particles to form a structure composed of a reaction product of the trifunctional silane coupling agent. The trifunctional silane coupling agent reacts with its functional groups and with OH groups on the surfaces of the silica particles to form a structure composed of the reaction product of the trifunctional silane coupling agent.

The reaction of the trifunctional silane coupling agent is carried out by adding the trifunctional silane coupling agent to a suspension of silica base particles, and then heating the suspension while stirring.
Specifically, for example, the suspension is heated to 40° C. to 70° C., a trifunctional silane coupling agent is added, and then the suspension is stirred. The stirring time is preferably 10 minutes to 24 hours, more preferably 60 minutes to 420 minutes, and even more preferably 80 minutes to 300 minutes.

[Second process]
In the second step, a nitrogen-containing compound is adsorbed into at least some of the pores of the reaction product of the trifunctional silane coupling agent.
Specifically, in the second step, first, for example, a nitrogen-containing compound is added to a silica base particle suspension, and the mixture is stirred at a temperature ranging from 20° C. to 50° C. As a result, the nitrogen-containing compound is adsorbed into at least some of the pores of the reaction product of the trifunctional silane coupling agent.

In the second step, for example, an alcohol liquid containing a nitrogen-containing compound may be added to the silica particle suspension.
The alcohol may be the same type as the alcohol contained in the silica base particle suspension or may be a different type, but it is more preferable that the alcohol be the same type.

In an alcohol solution containing a nitrogen-containing compound, the concentration of the nitrogen-containing compound is preferably 0.05% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 6% by mass or less.

[Third step]
In the third step, after or during the second step, a hydrophobic treatment is performed on silica base particles having a structure in which a nitrogen-containing compound is adsorbed in at least some of the pores of the reaction product of the trifunctional silane coupling agent.
Specifically, in the third step, for example, a nitrogen-containing compound is added to the silica base particle suspension in which the structures have been formed, and then a hydrophobic treatment agent is added.
The hydrophobic treatment agent forms a hydrophobic treatment layer by reacting with the functional groups of the hydrophobic treatment agent and with the OH groups of the silica base particles.

The reaction of the hydrophobic treatment agent is carried out by adding a trifunctional silane coupling agent to a suspension of silica base particles, and then heating the suspension while stirring.
Specifically, for example, the suspension is heated to 40° C. to 70° C., the hydrophobic treatment agent is added, and then the suspension is stirred. The stirring time is preferably 10 minutes to 24 hours, more preferably 20 minutes to 120 minutes, and even more preferably 20 minutes to 90 minutes.

[Drying process]
In the method for producing silica particles according to the present embodiment, a drying step for removing the solvent from the suspension may be carried out after the second step or the third step. The drying step may be carried out during the second step or the third step.

The drying method may be, for example, heat drying, spray drying, or supercritical drying.
Spray drying can be performed by a conventional method using a commercially available spray dryer (including disk rotation type and nozzle type). For example, spraying the spray liquid into a hot air stream at a rate of 0.2 L/h to 1 L/h is performed. In this case, the hot air temperature is preferably in the range of 70°C to 400°C at the inlet and 40°C to 120°C at the outlet. If the inlet temperature is less than 70°C, the solids contained in the dispersion are not sufficiently dried. If the temperature exceeds 400°C, the particle shape is distorted during spray drying. If the outlet temperature is less than 40°C, the solids are not dried sufficiently and adhere to the inside of the device. A more preferred inlet temperature is in the range of 100°C to 300°C.
The silica particle concentration of the silica particle suspension during spray drying is preferably in the range of 10% by mass or more and 30% by mass or less in terms of solid content.

Supercritical drying uses a supercritical fluid to remove the solvent, making it difficult for surface tension to act between particles, and the primary particles contained in the suspension are dried in a state where aggregation is suppressed. This makes it easier to obtain silica particles with a highly uniform particle size.

Substances that can be used as supercritical fluids include carbon dioxide, water, methanol, ethanol, and acetone. From the standpoints of processing efficiency and suppressing the generation of coarse particles, it is preferable that the solvent removal process be a process that uses supercritical carbon dioxide.

Specifically, supercritical drying is carried out, for example, by the following procedure.
The suspension is placed in a sealed reactor, and then liquefied carbon dioxide is introduced into the reactor. The sealed reactor is then heated and the pressure inside the sealed reactor is increased by a high-pressure pump, thereby bringing the carbon dioxide inside the sealed reactor into a supercritical state. The liquefied carbon dioxide is then flowed into the sealed reactor and the supercritical carbon dioxide is flowed out of the sealed reactor, thereby causing the supercritical carbon dioxide to flow through the suspension inside the sealed reactor. While the supercritical carbon dioxide flows through the suspension, the solvent dissolves in the supercritical carbon dioxide, and the solvent is removed along with the supercritical carbon dioxide flowing out of the sealed reactor.
The temperature and pressure in the sealed reactor are set to those that put carbon dioxide into a supercritical state, i.e., a temperature of 40°C to 200°C and a pressure of 10 MPa to 30 MPa, for example, since the critical point of carbon dioxide is 31.1°C/7.38 MPa.

The flow rate of the supercritical fluid during supercritical drying is preferably 80 mL/sec or more and 240 mL/sec or less.

The obtained silica particles are preferably crushed or sieved as needed to remove coarse particles and agglomerates. Crushing is performed using, for example, a dry grinding device such as a jet mill, vibration mill, ball mill, or pin mill. Sieving is performed using, for example, a vibrating sieve or an air-powered sieving machine.

The following examples will explain the embodiments of the invention in detail, but the embodiments of the invention are in no way limited to these examples. In the following description, all percentages are by mass unless otherwise specified.

<Production of Silica Particles>
[Examples 1, 3 to 36, 39 to 44]
A suspension containing silica particles in each example was prepared as follows.

- Preparation of alkaline catalyst solution -
Methanol, ion-exchanged water, and aqueous ammonia (NH ₄ OH) in the amounts and concentrations shown in Table 1 were placed in a glass reaction vessel equipped with a metal stirring rod, a dropping nozzle, and a thermometer, and the mixture was stirred to obtain an alkaline catalyst solution.

- Granulation of silica base particles by the sol-gel method -
The temperature of the alkaline catalyst solution was adjusted to 40° C., and the alkaline catalyst solution was purged with nitrogen. Next, while stirring the alkaline catalyst solution, tetramethoxysilane (TMOS) in the amounts shown in Table 1 and 124 parts by mass of aqueous ammonia (NH ₄ OH) with a catalyst (NH ₃ ) concentration of 7.9% were simultaneously added dropwise to obtain a silica base particle suspension.

- Addition of trifunctional silane coupling agent -
The silica base particle suspension was heated to 40°C and stirred, while which trifunctional silane coupling agents of the types and amounts shown in Table 1 were added to the suspension. Stirring was then continued for 120 minutes to allow the trifunctional silane coupling agents to react, thereby forming an adsorption structure.

- Addition of nitrogen-containing compounds -
Nitrogen-containing compounds of the types shown in Table 1 were diluted with butanol to prepare alcohol solutions.
Next, an alcohol solution prepared by diluting the nitrogen-containing compound with butanol was added to the suspension. The alcohol solution was added so that the number of parts of the nitrogen-containing compound per 100 parts by mass of the solid content of the silica base particle suspension was the amount shown in Table 1. The mixture was then stirred at 30° C. for 100 minutes to obtain a suspension containing the nitrogen-containing compound.

- Drying -
Next, 300 parts by mass of the suspension was placed in a reaction vessel, and _CO2 was introduced while stirring, and the temperature and pressure inside the reaction vessel were raised to the temperature and pressure shown in Table 1. While stirring was continued while maintaining the temperature and pressure, _CO2 was introduced and discharged at a flow rate of 5 L/min. Thereafter, the solvent was removed over 120 minutes to obtain silica particles of each example.

[Example 2]
Silica particles were obtained in the same manner as in Example 1, except that spray drying was performed using a Mini Spray Dryer B-290 (manufactured by Nippon Buchi Co., Ltd.) under conditions where the temperature and pressure inside the cylinder were set as shown in Table 1 and the silica particle suspension was fed at a feed rate of 0.2 L/hour.

[Example 37]
After the addition of the nitrogen-containing compound, hexamethyldisilazane (HMDS) was added in an amount of 100 mass% based on the solid content of the silica base particles, and the mixture was stirred at 65°C for 3 hours to hydrophobize the surfaces of the silica base particles. Except for this, silica particles were obtained in the same manner as in Example 1.

[Example 38]
Silica particles were obtained in the same manner as in Example 1, except that 30 g of dry-process silica AEROSIL 130 (manufactured by Nippon Aerosil) was dispersed in 300 g of methanol to obtain a silica base particle suspension.

[Comparative Examples 1, 2, and 3]
Silica particles were obtained in the same manner as in Example 1, except that the amounts of the trifunctional silane coupling agent and the nitrogen-containing compound added were set as shown in Table 1.

[evaluation]
(Various characteristics)
The following properties of the obtained silica particles were measured according to the methods described above.
- Number average particle size (referred to as "particle size" in the table)
・Average circularity (referred to as "circularity" in the table)
Pore volume A having a pore diameter of 1 nm or more and 50 nm or less obtained from the pore distribution curve of the nitrogen gas adsorption method before firing at 350 ° C. (referred to as "Pore volume A before firing at 350 ° C." in the table).
Pore volume B of pores with a diameter of 1 nm to 50 nm obtained from the pore distribution curve of the nitrogen gas adsorption method after firing at 350 ° C. (referred to as "Pore volume B after firing at 350 ° C." in the table)
Volume resistivity Ra before firing at 350 ° C. (referred to as "volume resistivity Ra before firing" in the table)
Volume resistivity Rb after firing at 350 ° C. (referred to as "volume resistivity Rb after firing" in the table)
- Amount of OH groups measured by the Sears method (referred to as "Amount of OH groups" in the table)
The ratio of the integral value C of signals observed in the chemical shift range of -50 ppm to -75 ppm when the integral value of all signals in the Si-CP/MAS NMR spectrum is taken as 100% (referred to as "(Si-CP/MAS area ratio C)" in the table).
The ratio C/D of the integral value C of the signal observed in the chemical shift range of -50 ppm to -75 ppm in the Si-CP/MAS NMR spectrum to the integral value D of the signal observed in the chemical shift range of -90 ppm to -120 ppm (represented as "(Si-CP/MAS ratio C/D)" in the table).

(Charge Dependence of Charge Amount at Low Humidity and Charge Amount at High Humidity/Capacitance)
The low humidity and high humidity charge amounts of the silica particles in each example were measured and the environmental dependency of the capacitance was evaluated as follows. Among the criteria, A to B are acceptable.
The evaluation method is as follows.
5 g of MA1010 manufactured by Nippon Shokubai, with 2% by mass of the prepared silica particles added to the surface, was mixed with 50 g of KNI106GSM manufactured by JFE Chemical Co., Ltd. The mixed sample was stirred for 5 minutes using a turbula shaker in a chamber at 10°C and 10% RH, and the charge was measured using a TB200 manufactured by Toshiba Corporation. The result was designated as FC, and the result was also measured for 5 minutes using a turbula shaker in a chamber at 30°C and 90% RH, and the charge was measured using the TB200 manufactured by Toshiba Corporation. The ratio of these values, FA/FC, was used for evaluation.
A (◎): FA/FC is 0.8 or more and less than 1.1 B (◯): FA/FC is 0.65 or more and less than 0.8 C (△): FA/FC is 0.5 or more and less than 0.65 D (×): FA/FC is less than 0.5

(Charge distribution in a low-temperature, low-humidity environment)
The silica particles of each example were evaluated for charge distribution in a low-temperature, low-humidity environment (10° C., 10% RH) as follows.
5 g of the prepared silica particles were added to the surface of MA1010 manufactured by Nippon Shokubai at 2% by mass, and mixed with 50 g of KNI106GSM manufactured by JFE Chemical Corporation. The mixed sample was stirred for 5 minutes using a Turbula shaker in a 10°C, 10% RH chamber and evaluated by CSG (charge spectrograph) image analysis. The charge distribution is defined as the difference between the 20% charge amount Q(20) and the 80% charge amount Q(80) of the cumulative integrated charge distribution divided by the 50% charge amount Q(50), i.e., [Q(80) - Q(20)]/Q(50). The evaluation criteria are as follows:
A (◎): [Q(80) - Q(20)] / Q(50) value is less than 0.7 B (○): [Q(80) - Q(20)] / Q(50) value is less than 0.8, 0.7 or more C (△): [Q(80) - Q(20)] / Q(50) value is less than 1.0, 0.8 or more D (×): [Q(80) - Q(20)] / Q(50) value is 1.0 or more

(Ability to maintain narrow charge distribution under normal temperature and humidity conditions)
The silica particles of each example were evaluated for their ability to maintain a narrow charge distribution in a normal temperature and humidity environment (20° C., 50% RH environment) as follows.
5 g of the prepared silica particles were added to the surface of MA1010 manufactured by Nippon Shokubai at 2% by mass, and mixed with 50 g of KNI106GSM manufactured by JFE Chemical Corporation. The mixed sample was stirred for 100 minutes using a Turbula shaker in a chamber at 20°C and 50% RH, and evaluated by CSG (charge spectrograph) image analysis. The charge distribution is defined as the difference between the 20% charge amount Q(20) and the 80% charge amount Q(80) of the cumulative integrated charge distribution divided by the 50% charge amount Q(50), i.e., [Q(80) - Q(20)]/Q(50). The evaluation criteria are as follows:
A (◎): [Q(80) - Q(20)] / Q(50) value is less than 0.75 B (○): [Q(80) - Q(20)] / Q(50) value is less than 0.85 and 0.75 or more C (△): [Q(80) - Q(20)] / Q(50) value is less than 1.0 and 0.85 or more D (×): [Q(80) - Q(20)] / Q(50) value is 1.0 or more

The evaluation results are shown in Table 1.
Details of the abbreviations in Table 1 are as follows:
MTMS: methyltrimethoxysilane DTMS: n-dodecyltrimethoxysilane

・TP-415: [N ⁺ (CH) ₃ (C ₁₄ C ₂₉ ) ₂ ] ₄ Mo ₈ O ₂₈ ^4- (manufactured by Hodogaya Chemical Co., Ltd., N,N-Dimethyl-N-tetradecyl-1-tetradecanaminium, hexa-μ-oxotetra-μ3-oxodi-μ5-oxotetradecaoxooctamolybdate (4-) (4:1)

From the above results, it can be seen that the silica particles of the Examples have a narrower charge distribution when charged than the silica particles of the Comparative Examples.

Claims (10)

Contains a nitrogen-containing compound,
a ratio C/D of an integral value C of a signal observed in a chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum by cross polarization/magic angle spinning (CP/MAS) to an integral value D of a signal observed in a chemical shift range of −90 ppm to −120 ppm is 0.10 or more and 0.75 or less;
an extractable amount X of the nitrogen-containing compound with the ammonia/methanol mixed solution is 0.1 mass% or more, and the extractable amount X of the nitrogen-containing compound and the extractable amount Y of the nitrogen-containing compound with water satisfy the formula: Y/X<0.3;
Silica particles in which, when A and B are the pore volumes of pores with diameters of 1 nm or more and 50 nm or less obtained from a pore distribution curve obtained by a nitrogen gas adsorption method before and after calcination at 350°C, respectively, B/A is 1.2 or more and 5 or less, and B is 0.2 cm ³ /g or more and 3 cm ³ /g or less . Contains a nitrogen-containing compound,
a ratio C/D of an integral value C of a signal observed in a chemical shift range of −50 ppm to −75 ppm in a ^29Si solid-state nuclear magnetic resonance (NMR) spectrum by cross polarization/magic angle spinning (CP/MAS) to an integral value D of a signal observed in a chemical shift range of −90 ppm to −120 ppm is 0.10 or more and 0.75 or less;
an extractable amount X of the nitrogen-containing compound with the ammonia/methanol mixed solution is 0.1 mass% or more, and the extractable amount X of the nitrogen-containing compound and the extractable amount Y of the nitrogen-containing compound with water satisfy the formula: Y/X<0.3;
Silica base particles;
a structure that covers at least a portion of the surface of the silica base particle, is composed of a reaction product of a trifunctional silane coupling agent, and has the nitrogen-element-containing compound adsorbed in at least a portion of the pores of the reaction product of the trifunctional silane coupling agent;
Silica particles having 3. The silica particles according to claim 1, wherein the number average particle diameter is 10 nm or more and 200 nm or less. 4. The silica particles according to claim 3 , having a number average particle size of 10 nm or more and 80 nm or less. 5. The silica particles according to claim 1 , wherein the average circularity is 0.60 or more and 0.96 or less. 6. The silica particles according to claim 5 , having an average circularity of 0.70 or more and 0.92 or less. 7. The silica particles according to claim 1 , wherein the volume resistivity is 1.0×10 ⁷ Ωcm or more and 1.0×10 ^11.5 Ωcm or less. 8. The silica particles according to claim 1 , wherein Ra/Rb is 0.01 or more and 0.8 or less, where Ra and Rb are volume resistivities before and after firing at 350° C., respectively. Silica particles according to any one of claims 1 to 8, wherein the nitrogen-containing compound is at least one selected from the group consisting of quaternary ammonium salts, primary amine compounds, secondary amine compounds, tertiary amine compounds, amide compounds, imine compounds, and nitrile compounds. Contains a nitrogen-containing compound,
a ratio C/D of an integral value C of a signal observed in a chemical shift range of −50 ppm to −75 ppm in a 29Si solid-state nuclear magnetic resonance (NMR) spectrum by cross polarization/magic angle spinning (CP/MAS) to an integral value D of a signal observed in a chemical shift range of −90 ppm to −120 ppm ^is 0.10 or more and 0.75 or less;
a method for producing silica particles, wherein an extractable amount X of the nitrogen-containing compound with an ammonia/methanol mixed solution is 0.1 mass % or more, and the extractable amount X of the nitrogen-containing compound and an extractable amount Y of the nitrogen-containing compound with water satisfy the formula: Y/X<0.3,
a first step of forming a structure composed of a reaction product of a trifunctional silane coupling agent on at least a portion of the surface of a silica base particle;
a second step of adsorbing the nitrogen-element-containing compound into at least a portion of the pores of the reaction product of the trifunctional silane coupling agent;
A method for producing silica particles having the formula: