Silica particles and method for producing the same

Abstract

To provide a silica particle having a narrow charge distribution when taking an electrical charge.SOLUTION: A silica particle includes: a silica mother particle; and a structure which is composed of a reaction product of a three-functional silane coupling agent, and coats at least a part of the surface of the silica mother particle, where a nitrogen element containing-compound is contained, the content of the nitrogen element containing-compound to the silica particle is 0.005 mass% or more and 0.50 mass% or less in terms of N element, the hydrophobicity is 10% or more and 60% or less, and the volume resistivity is 1×108 Ω cm or higher and 1×1012.5 Ω cm or lower.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] 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 suppressing packing.

[0003] 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 is 0.1 mass% or more, and (3) the X and the extractable amount Y of the compound in water satisfy the following formula (I): Y / X<0.15."

[0004] Furthermore, Patent Document 2 discloses "silica powder containing a plurality of silica particles in which a quaternary ammonium salt is introduced into a silica structure having an "Si-O" bond as a repeating unit."

[0005] Furthermore, Patent Document 3 discloses "external charge control particles comprising carrier particles made of hydrophobic spherical silica microparticles with an average particle size of 20 to 500 nm obtained by subjecting the surface of hydrophilic spherical silica microparticles obtained by a sol-gel method to a hydrophobic treatment, and a charge control agent adhered to the surface of the carrier particles."

[0006] Furthermore, Patent Document 4 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."

[0007] Furthermore, Patent Document 5 discloses "particles in which silica microparticles having a hydrophobicity of 80% or more are treated with an amphoteric surfactant, and particles in which silica microparticles having a hydrophobicity of 80% or more are treated with a quaternary ammonium salt or a polymer having a quaternary ammonium group." [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-073418 [Patent Document 2] Japanese Patent Application Publication No. 2017-039618 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-185998 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-194825 [Patent Document 5] Japanese Patent Application Publication No. 09-166884 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a method for producing a silica matrix particle having a structure composed of a reaction product of a trifunctional silane coupling agent, in which a nitrogen-containing compound is adsorbed on the silica matrix particle, in which the content of the nitrogen-containing compound is less than 0.005 mass% in terms of N atoms, in which the hydrophobicity is less than 10% or more than 60%, or in which the volume resistivity is less than 1×10 12.5 The object of the present invention is to provide silica particles that, when charged, have a narrow charge distribution compared to when the charge is greater than Ω. [Means for solving the problem]

[0010] Specific means for solving the above problems include the following aspects. <1> Silica base particles; a structure comprising a reaction product of a trifunctional silane coupling agent, the structure covering at least a portion of the surface of the silica base particle; and The silica particle contains a nitrogen-containing compound, and the content of the nitrogen-containing compound relative to the silica particle is 0.005% by mass or more and 0.50% by mass or less in terms of N atoms; The degree of hydrophobicity is 10% or more and 60% or less, Volume resistivity is 1×10 8 Ω cm or more 1×10 12.5 Silica particles with a density of Ω·cm or less. <2> In the pore size distribution curve obtained by nitrogen gas adsorption, the first peak is in the pore size range of 0.01 nm to 2 nm, and the second peak is in the pore size range of 1.5 nm to 50 nm. <1> The silica particles according to claim 1. <3> The nitrogen-containing compound is adsorbed in at least a portion of the pores of the reaction product of the trifunctional silane coupling agent. <1> or <2> The silica particles according to claim 1. <4> The hydrophobicity is 10% or more and 50% or less. <1> ~ <3> The silica particles according to any one of the preceding claims. <5> The volume average particle size is 10 nm or more and 200 nm or less <1> ~ <4> The silica particles according to any one of the preceding claims. <6> The volume average particle size is 10 nm or more and 80 nm or less <5> The silica particles according to claim 1. <7> The average circularity is 0.60 or more and 0.96 or less <1> ~ <6> The silica particles according to any one of the preceding claims. <8> The average circularity is 0.70 or more and 0.92 or less <7> The silica particles according to claim 1. <9> 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. <1> ~ <8> The silica particles according to any one of the preceding claims.

[0011] <1> , or <3> According to the invention, when a nitrogen-containing compound is adsorbed on silica base particles that do not have a structure composed of a reaction product of a trifunctional silane coupling agent, when the content of the nitrogen-containing compound is less than 0.005 mass% in terms of N atoms, when the hydrophobicity is less than 10% or more than 60%, or when the volume resistivity is less than 1×10 12.5 This provides silica particles with a narrow charge distribution when charged compared to when the charge density exceeds Ω·cm.

[0012] <2> According to the invention relating to (1), silica particles are provided which, when charged, have a narrower charge distribution than silica particles which do not have a second peak in the pore size distribution curve measured by nitrogen gas adsorption.

[0013] <4> According to the invention relating to (1), silica particles are provided which, when charged, have a narrower charge distribution than silica particles having a hydrophobicity of less than 10% or more than 60%.

[0014] <5> , or <6> According to the invention, when a nitrogen-containing compound is adsorbed on silica base particles that do not have a structure composed of a reaction product of a trifunctional silane coupling agent, when the content of the nitrogen-containing compound is less than 0.005 mass% in terms of N atoms, when the hydrophobicity is less than 10% or more than 60%, or when the volume resistivity is less than 1×10 12.5 Compared with a volume average particle diameter exceeding Ω·cm, silica particles having a narrow charge distribution when charged can be provided even if the volume average particle diameter is 10 nm or more and 200 nm or less, or 10 nm or more and 80 nm or less.

[0015] <7> , or <8> According to the invention, when a nitrogen-containing compound is adsorbed on silica base particles that do not have a structure composed of a reaction product of a trifunctional silane coupling agent, when the content of the nitrogen-containing compound is less than 0.005 mass% in terms of N atoms, when the hydrophobicity is less than 10% or more than 60%, or when the volume resistivity is less than 1×10 12.5 Compared with a case where the average circularity is more than Ω·cm, silica particles having a narrow charge distribution when charged can be provided even if the average circularity is 0.60 or more and 0.96 or less, or 0.70 or more and 0.92 or less.

[0016] <9> According to the invention, when a nitrogen-containing compound is adsorbed on silica base particles that do not have a structure composed of a reaction product of a trifunctional silane coupling agent, when the content of the nitrogen-containing compound is less than 0.005 mass% in terms of N atoms, when the hydrophobicity is more than 60%, or when the volume resistivity is less than 1×10 12.5 Compared with silica particles having a resistivity of more than Ω·cm, silica particles containing at least one nitrogen-containing compound 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 are provided, which have a narrow charge distribution when charged. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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.

[0018] In the present specification, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range. In addition, in the numerical ranges described in this disclosure, the upper or lower limit of the numerical range may be replaced by the values ​​shown in the examples.

[0019] 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.

[0020] <Silica particles> The silica particles according to this embodiment include a silica base particle and a structure that covers at least a portion of the surface of the silica base particle and is composed of a reaction product of a trifunctional silane coupling agent. The silica particles according to this embodiment have the following properties (1) to (3). (1) The silica particle contains a nitrogen-containing compound, and the content of the nitrogen-containing compound relative to the silica particle is 0.005% by mass or more and 0.50% by mass or less in terms of N atoms. (2) The degree of hydrophobicity is 10% or more and 60% or less. (3) Volume resistivity is 1×10 8 Ω cm or more 1×10 12.5 Ω·cm or less.

[0021] The silica particles according to this embodiment have the above-described structure, and when charged, the charge distribution is narrow. The reason for this is presumed to be as follows.

[0022] Silica particles have a high negative chargeability and can become excessively charged, resulting in a wide charge distribution. 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.

[0023] On the other hand, when a nitrogen-containing compound is contained in silica particles, excessive negative charging can be suppressed when the silica particles are charged. The nitrogen-containing compound has positive charging properties, and the silica particles containing the nitrogen-containing compound cancel out the excessive negative charging and suppress the excessive negative charging. Therefore, when the silica particles are charged, the charge distribution becomes narrow.

[0024] However, nitrogen-containing compounds have positive charging properties, and when they are contained on the outermost surface of silica particles, the charge distribution spreads to include negative and positive charges.

[0025] Therefore, in the silica particles according to the present embodiment, a structure (e.g., SiO ) composed of a reaction product of a trifunctional silane coupling agent is added to the silica base particle. 2 / 3A nitrogen-containing compound is contained in an amount of 0.005% by mass or more and 0.50% by mass or less in terms of the content of N atoms. The hydrophobicity is set to 10% or more and 60% or less, and the volume resistivity is set to 1×10 8 Ω cm or more 1×10 12.5 By reducing the resistivity to Ω·cm or less, excessive charging of silica particles is suppressed. Therefore, the charge distribution can be narrowed more effectively by the nitrogen-containing compound.

[0026] From the above, it is presumed that the silica particles according to this embodiment have a narrow charge distribution when charged.

[0027] For example, when the silica particles according to this embodiment are used as an external additive in powder paint, the charge of the powder paint is less likely to vary, and the amount of powder paint adhering to the object to be coated can be made uniform.

[0028] Hereinafter, the silica particles according to this embodiment will be described in detail.

[0029] (Composition of Silica Particles) The silica particles according to this embodiment include silica base particles and structures that cover the surfaces of the silica base particles and are composed of a reaction product of a trifunctional silane coupling agent. It is preferred that the nitrogen element-containing compound be adsorbed in at least some of the pores of the reaction product of the functional silane coupling agent. Furthermore, the silica particles according to this embodiment may have a hydrophobic treated structure on the surface of the structure made of the reaction product of the trifunctional silane coupling agent.

[0030] -Silica mother particles- The silica base particles are silica particles on which a structure composed of a reaction product of a functional silane coupling agent is formed. 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 the neutralization reaction of sodium silicate and mineral acid (precipitation silica synthesized and agglomerated under alkaline conditions, and gel-process 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 organic silane compounds (e.g., alkoxysilanes). Among these, sol-gel silica particles are preferred as the silica base particles from the viewpoint of narrowing the charge distribution.

[0031] -Reaction products of trifunctional silane coupling agents- The adsorption structure composed of the reaction product of a trifunctional silane coupling agent is low-density and has a high affinity for nitrogen-containing compounds, making it easy for the nitrogen-containing compounds to adsorb deep into the pores, resulting in a high 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 effectively counteracts excess negative charge. Furthermore, because the nitrogen-containing compounds are adsorbed within the low-density structure rather than on the outermost surface of the silica particles, they prevent the charge distribution from becoming too strong and widening, and only counteract excess negative charge, further narrowing the charge distribution.

[0032] The reaction product of a trifunctional silane coupling agent is, for example, a compound represented by the following general formula (TA): OR 2 The reaction product, OR, is substituted with an OH group. 2 The reaction product of polycondensation between the OH-substituted OR 2 The reaction products of the trifunctional silane coupling agent are those in which the OH group is substituted with the OH group and those in which the OH group is polycondensed with the SiOH group of the silica particle. 2 This includes fully or partially substituted reaction products and fully or partially polycondensed reaction products.

[0033] 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

[0034] In the general formula (TA), R 1 represents a saturated or unsaturated aliphatic hydrocarbon group having 1 to 20 carbon atoms or an aromatic hydrocarbon group having 6 to 20 carbon atoms, and R 2 represents a halogen atom or an alkoxy group. 2 may be the same group or different groups.

[0035] R 1 The aliphatic hydrocarbon group represented by the formula (I) 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.

[0036] 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).

[0037] 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.).

[0038] R 1 The aromatic hydrocarbon group represented by the formula (I) 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 1 to 10 carbon atoms.

[0039] Examples of the aromatic hydrocarbon group include a phenylene group, a biphenylene group, a terphenylene group, a naphthalene group, and an anthracene group.

[0040] R 2 Examples of the halogen atom represented by the formula (I) 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.

[0041] R 2 Examples of the alkoxy group represented by the formula (I) 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 the substituent 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.

[0042] The trifunctional silane coupling agent represented by the general formula (TA) is R 1 is a saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms, and R 2 A trifunctional silane coupling agent in which is a halogen atom or an alkoxy group is preferred.

[0043] 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, R 1 is an unsubstituted aliphatic hydrocarbon group or an unsubstituted aromatic hydrocarbon group); 3-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-glycidyloxypropylmethyldimethoxysilane (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.

[0044] Among these, from the viewpoint of narrowing the charge distribution, the trifunctional silane coupling agent is preferably an alkyl trifunctional silane coupling agent, and in the general formula (TA), R 1 represents an alkyl group having 1 to 20 carbon atoms (preferably 1 to 15 carbon atoms), and R 2 More preferred is an alkyl trifunctional silane coupling agent in which represents an alkyl group having 1 to 2 carbon atoms.

[0045] 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 0.005% by mass or more and 0.5% by mass or less, and more preferably 0.005% by mass or more and 0.2% by mass or less, relative to the toner base particles.

[0046] -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.

[0047] 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. Here, 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.

[0048] 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.

[0049] 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 of two or more.

[0050] [ka]

[0051] In the general formula (AM), R 1 , R 2 , R 3 and R 4 each independently represents a hydrogen atom, or an alkyl group, an aralkyl group, or an aryl group which may have a substituent; X - represents an anion, where R 1 , R 2 , R 3 and R 4 At least one of R represents an alkyl group, an aralkyl group, or an aryl group which may have a substituent. 1 , R 2 , R 3 and R 4 Two or more of these may be linked to form an aliphatic ring, an aromatic ring, or a heterocycle.

[0052] R 1 ~R 4Examples of the alkyl group represented by the formula 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, R 1 ~R 4 The alkyl group represented by the formula (I) is preferably an alkyl group having 1 to 15 carbon atoms, such as a methyl group, an ethyl group, a butyl group, or a tetradecyl group.

[0053] R 1 ~R 4 Examples of the aralkyl group represented by the formula (I) include aralkyl groups having 7 to 30 carbon atoms. Examples of aralkyl groups having 7 to 30 carbon atoms include benzyl, phenylethyl, phenylpropyl, 4-phenylbutyl, phenylpentyl, phenylhexyl, phenylheptyl, phenyloctyl, phenylnonyl, naphthylmethyl, naphthylethyl, anthrathymethyl, and phenylcyclopentylmethyl. Among the above, R 1 ~R 4The aralkyl group represented by the formula (I) is preferably an aralkyl group having 7 to 15 carbon atoms, such as a benzyl group, a phenylethyl group, a phenylpropyl group, or a 4-phenylbutyl group.

[0054] R 1 ~R 4 Examples of the aryl group represented by the formula include 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, R 1 ~R 4 The aryl group represented by the formula (I) is preferably an aryl group having 6 to 10 carbon atoms, such as a phenyl group.

[0055] X - Examples of the anion represented by the formula (I) include 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). Inorganic anions include molybdate ions (MoO4 2- , Mo2O7 2- , Mo3O 10 2- , Mo4O 13 2- , Mo7O 24 2- , Mo8O 26 4- etc.), OH - , F - , Fe(CN)6 3- , Cl - , Br - , NO2 - , NO3 - , CO3 2- , PO4 3- , SO4 2- etc.

[0056] In the general formula (AM), R 1 , R2 , R 3 and R 4 Two or more of R may be linked to each other to form a ring. 1 , R 2 , R 3 and R 4 Examples of the ring formed by linking two or more of the above include an alicyclic ring having 2 to 20 carbon atoms, and a heterocyclic amine having 2 to 20 carbon atoms.

[0057] 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. R 1 , R 2 , R 3 and R 4 each independently preferably represents 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.

[0058] Among these, from the viewpoint of narrowing the charge distribution, the compound represented by general formula (AM) preferably has a total of 18 to 35 carbon atoms, more preferably 20 to 32 carbon atoms.

[0059] X in the compound represented by general formula (AM) - Examples of structures other than those are shown below, but the present embodiment is not limited to these.

[0060] [ka]

[0061] 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 quaternary ammonium salts containing molybdenum (particularly, quaternary ammonium salts containing molybdenum), and mixtures of quaternary ammonium salts and metal oxides 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.

[0062] Quaternary ammonium salts containing molybdenum include [N + (CH)3(C 14 C 29 )2]4Mo8O 28 4- , [N + (C4H9)2(C6H6)2]2Mo2O7 2- , [N + (CH3)2(CH2C6H6)(CH2) 17 CH3]2MoO4 2- , [N + (CH3)2(CH2C6H6)(CH2) 15 CH3]2MoO4 2- etc. Metal oxides containing molybdenum include molybdenum oxides (molybdenum trioxide, molybdenum dioxide, Mo9O 26 ), alkali metal molybdates (lithium molybdate, sodium molybdate, potassium molybdate, etc.), alkaline earth metal molybdates (magnesium molybdate, calcium molybdate, etc.), other composite oxides (Bi2O3·2MoO3, γ-Ce2Mo3O 13 etc.)

[0063] The content of the nitrogen-containing compound is 0.005% by mass or more and 0.50% by mass or less in terms of N atoms relative to the silica particles, and from the viewpoint of narrowing the charge distribution, it is preferably 0.015% by mass or more and 0.20% by mass or less, and more preferably 0.018% by mass or more and 0.10% by mass or less.

[0064] The content of nitrogen element-containing compounds in terms of N atoms is measured as follows. Using an oxygen / nitrogen analyzer (e.g., HORIBA EMGA-920) for 45 seconds, the amount of nitrogen present is measured 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 at least 24 hours.

[0065] 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 fluorescent X-ray 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.

[0066] From the viewpoint 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.

[0067] The net intensity of molybdenum element and silicon element is measured as follows.

[0068] Approximately 0.5 g of silica particles is compressed under a load of 6 t for 60 seconds using a compression molding machine to produce a disk with a diameter of 50 mm and a thickness of 2 mm. This disk is used as a sample and qualitative and quantitative elemental analysis is performed 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 and silicon elements. Tube voltage: 40kV ·Tube current: 90mA ·Measurement area (analysis diameter): Diameter 10mmφ Measurement time: 30 minutes Anticathode: Rhodium

[0069] -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 preferably satisfy the formula: Y / X<0.3.

[0070] That is, the nitrogen-containing compound has a property of being difficult to dissolve in water, that is, it is 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 even when there is a large amount of moisture in the air (even under high humidity conditions), and the nitrogen-containing compound is less likely to detach, making it easier to maintain a narrow charge distribution.

[0071] The extracted amount X of the nitrogen-containing compound is preferably 50% by mass, 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 amount of nitrogen-containing compound extracted X to the amount of nitrogen-containing compound extracted Y is preferably less than 0.3. 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.

[0072] 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 (for example, a gas chromatograph mass spectrometer manufactured by Netsch Japan Co., Ltd.), and the integrated mass fraction of compounds in which hydrocarbons with at least one carbon atom are covalently bonded to nitrogen atoms relative to the silica particles is measured and designated as W1.

[0073] Separately, 1 part by mass of the silica particles to be measured was added to 30 parts by mass of an ammonia / methanol solution (Sigma-Aldrich, ammonia / methanol mass ratio = 1 / 5.2) at 25°C, and after 30 minutes of ultrasonic treatment, the silica powder and the extract were separated. The separated silica particles were dried in a vacuum dryer at 100°C for 24 hours, and the mass fraction of compounds in which hydrocarbons with at least one carbon atom are covalently bonded to nitrogen atoms was measured with a thermogravimetric-mass spectrometer at a constant temperature of 400°C, and this was designated W2. Then, the extracted amount X of the nitrogen element-containing compound is calculated using the following formula. ·Formula:X=W1-W2

[0074] In addition, 1 part by mass of silica particles to be measured is added to 30 parts by mass of water at 25°C, and after 30 minutes of ultrasonic treatment, the silica particles are separated from the extract. 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 with at least one carbon atom are covalently bonded to nitrogen atoms is measured relative to the silica particles using a thermogravimetric / mass spectrometer at a constant temperature of 400°C, and this 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

[0075] (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:

[0076] (Characteristics of silica particles) - Hydrophobicity - The hydrophobicity of the silica particles according to this embodiment is 10% or more and 60% or less, and from the viewpoint of narrowing the charge distribution, it is 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 spread. On the other hand, when the hydrophobicity of silica particles exceeds 60%, the density of the structure increases due to the reaction of the trifunctional silane coupling agent, the pores decrease, and the content of nitrogen-containing compounds decreases, which makes the charge distribution more likely to spread.

[0077] 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.

[0078] -OH group amount- In the silica particles according to this embodiment, the amount of OH groups measured by the Sears method is 0.05 / nm 2 More than 5 pieces / nm 2 From the viewpoint of narrowing the charge distribution, it is preferable that the number of particles is 0.1 particles / nm or less. 2 More than 4 pieces / nm 2 Less than 0.2 particles / nm is more preferable. 2 More than 3 pieces / nm 2 The following is even more preferred: The amount of OH groups measured by the Sears method can be adjusted to fall within the above range by forming a sufficient amount of a structure composed of a reaction product of a trifunctional silane coupling agent on the silica base particles.

[0079] 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 particle structure. This allows for hydrophobic interactions with the nitrogen-containing compounds, strengthening their adhesion to the silica particles. This increases the amount of nitrogen-containing compounds adsorbed. Additionally, the nitrogen-containing compounds are less likely to detach. This improves the narrowing of the charge distribution by the nitrogen-containing compounds, and also improves the maintenance of the narrow charge distribution.

[0080] Furthermore, by reducing the amount of OH groups to the above range, the environmental dependency of the charging characteristics is reduced, and it becomes easier to achieve narrowing of the charge distribution by the nitrogen-element-containing compound in any environment.

[0081] The amount of OH groups is measured by the Sears method, specifically as follows. 1.5g of silica particles are added to a mixture of 50g of pure water and 50g of ethanol and stirred for 2 minutes with an ultrasonic homogenizer to create a dispersion. While stirring at 25°C, 1.0g of 0.1mol / L hydrochloric acid solution is added dropwise to obtain the test solution. The resulting test solution is placed in an automatic titrator and subjected to potentiometric titration with 0.01mol / L sodium hydroxide solution, and a derivative curve of the titration curve is created. Among the inflection points where the derivative value of the titration curve is 1.8 or greater, the titer E is the one where the titer of 0.01mol / L sodium hydroxide solution is the largest. Using the following formula, the surface silanol group density ρ (particles / nm 2 ) is calculated. Formula: ρ=((0.01×E-0.1)×NA / 1000) / (M×S BET x10 18 ) E: Among the inflection points where the derivative of the titration curve is 1.8 or more, the titer of 0.01 mol / L sodium hydroxide solution is the largest. NA: Avogadro's number M: Silica particle amount (1.5g) 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.

[0082] -Volume resistivity- In the silica particles according to this embodiment, the volume resistivity is 1×10 8 Ω cm or more 1×10 12.5 Ω·cm or less, but from the viewpoint of narrowing the charge distribution, it is 1.0×10 8 Ω cm or more 1.0×10 11.5 Ω·cm or less is preferable, and 1.0×10 9 Ω cm or more 1.0×1011.0 Ω·cm or less is more preferable. By reducing the volume resistivity to the above range, excessive charging of the silica particles is suppressed, and therefore, the charge distribution is further narrowed. The volume resistivity can be adjusted by the content of the nitrogen-containing compound.

[0083] The volume resistivity is measured as follows: The measurement environment is a temperature of 20°C and a humidity of 50% RH. 20cm 2 The silica particles to be measured are placed on the surface of a circular jig on which the electrode plate is arranged, to a thickness of about 1 mm to 3 mm, forming a silica particle layer. 2 The silica particle layer is sandwiched between two electrode plates. 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 (Solartron Analytical). -3 Hz over 10 6 Hz or less are measured to obtain a Nyquist plot. This is fitted to an equivalent circuit, assuming the existence of three resistance components: bulk resistance, particle interface resistance, and electrode contact resistance, to determine the bulk resistance R. The formula for calculating the volume resistivity (Ω·cm) of silica particles is shown below. ·Formula:ρ=R / L In the formula, ρ represents the volume resistivity of the silica particles (Ω·cm), R represents the bulk resistance (Ω), and L represents the thickness of the silica particle layer (cm).

[0084] -Pore volume- In the silica particles according to this embodiment, it is preferable that the first peak be in the pore diameter range of 0.01 nm or more and 2 nm or less, and that the second peak be in the pore diameter range of 1.5 nm or more and 50 nm or less, it is more preferable that the second peak be in the pore diameter range of 2 nm or more and 50 nm or less, it is even more preferable that the second peak be in the pore diameter range of 2 nm or more and 40 nm or less, and it is even more preferable that the second peak be in the pore diameter range of 2 nm or more and 30 nm or less. In the pore size distribution curve obtained by the nitrogen gas adsorption method, the first and second peaks are located within the above-mentioned pore size range, which allows the nitrogen-containing compound to penetrate deep into the pores of the structure and be easily adsorbed, thereby further improving the narrowing of the charge distribution.

[0085] The pore size distribution curve for the nitrogen gas adsorption method is derived from an adsorption isotherm obtained by measuring the amount of adsorbed nitrogen gas using various calculation formulas. First, the silica particles to be measured are cooled to liquid nitrogen temperature (-196°C), nitrogen gas is introduced, and the amount of adsorption is determined by constant volume or gravimetric methods. 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, with the vertical axis representing frequency and the horizontal axis representing pore diameter, is calculated using the BJH method formula. Then, from the obtained pore distribution curve, an integrated pore volume distribution, where the vertical axis is volume and the horizontal axis is pore diameter, is calculated, and the position of the pore diameter peak is confirmed.

[0086] -Method for detecting that a reaction product of a trifunctional silane coupling agent has a structure in which a nitrogen-containing compound is adsorbed in at least some of the pores- If a nitrogen-containing compound is adsorbed in at least some of the pores of the reaction product of a trifunctional silane coupling agent, the nitrogen-containing compound will be detected when heated at a temperature between 300°C and 600°C, and the volume of pores with diameters between 1nm and 50nm, as determined from the pore distribution curve of the nitrogen gas adsorption method, will increase before and after baking at 350°C. This allows detection. Specifically, this is as follows.

[0087] Nitrogen-containing compounds can be detected using, for example, 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 peaks. Examples of components generated by thermal decomposition from silica particles containing a nitrogen-containing compound include primary to tertiary amines or aromatic nitrogen compounds represented by the following general formula (N). In the following general formula (N), R N1 ~R N3 each independently represents a hydrogen atom, or an alkyl group, an aralkyl group, or an aryl group which may have a substituent; R N1 ~R N3 is R in general formula (AM) 1 , R 2 , and R 3 is synonymous with. For example, if 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. [ka]

[0088] The increase in the volume of pores with a diameter of 1 nm or more and 50 nm or less, determined from the pore distribution curve obtained by nitrogen gas adsorption method, before and after firing at 350° C., is specified as follows. First, the increase rate of the pore volume, for example, 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 set to 1.2 or more and 5 or less.

[0089] 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 rate of 10°C / min and held at 350°C for 3 hours. After that, they are cooled to room temperature (25°C) at a rate of 10°C / min.

[0090] The volume of pores with a diameter of 1 nm or more and 50 nm or less is determined by the following method. First, the silica particles to be measured are cooled to liquid nitrogen temperature (-196°C), nitrogen gas is introduced, and the amount of adsorption is determined by constant volume or gravimetric methods. 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, with the vertical axis representing frequency and the horizontal axis representing pore diameter, is calculated using the BJH method formula. Then, from the obtained pore size distribution curve, the cumulative pore volume distribution, where the vertical axis is volume and the horizontal axis is pore diameter, is calculated. From the obtained cumulative 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."

[0091] -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.

[0092] 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.

[0093] 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 circular 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, and the particle size at 50% of the cumulative diameter from the smallest diameter side, the number-average particle size, is determined. 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 is.

[0094] -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 0.94 or less, and even more preferably 0.70 or more and 0.92 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.

[0095] 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.). The circularity of at least 200 particles is determined, and the arithmetic mean is calculated to determine the average circularity. 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.

[0096] <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 the surface of silica base particles; a first step of adsorbing a nitrogen-containing compound onto at least a portion of the structure; 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.

[0097] The steps of the method for producing silica particles according to this embodiment will be described in detail below.

[0098] [Preparation process] First, the step of preparing silica base particles will be described.

[0099] 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. (ii) A step of granulating silica base particles by a sol-gel method to obtain a silica base particle suspension etc. Examples of the silica base particles used in (i) include sol-gel silica particles (silica particles obtained by the 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) above may be a solvent containing alcohol alone, or may be a mixed solvent containing 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, more preferably 90% by mass or more.

[0100] 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 a solvent containing alcohol; 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:

[0101] The alkaline catalyst solution preparation step is preferably a step of preparing a solvent containing alcohol and mixing the solvent with an alkaline catalyst to obtain an alkaline catalyst solution.

[0102] The alcohol-containing solvent may be a solvent containing only alcohol, or a mixed solvent containing 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, more preferably 90% by mass or more.

[0103] The alkaline catalyst is a catalyst for promoting the reaction (hydrolysis reaction and condensation reaction) of tetraalkoxysilane, and examples thereof include basic catalysts such as ammonia, urea, and monoamine, with ammonia being particularly preferred.

[0104] The concentration of the alkali catalyst in the alkali 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.

[0105] The silica base particle production step is a step in which tetraalkoxysilane and an alkali catalyst are supplied to an alkali catalyst solution, and the tetraalkoxysilane is reacted (hydrolysis reaction and condensation reaction) in the alkali catalyst solution to produce silica base particles.

[0106] In the silica base particle generation process, core particles are generated by the reaction of tetraalkoxysilane at the initial stage of supplying tetraalkoxysilane (core particle generation stage), and then these core particles grow (core particle growth stage) to generate silica base particles.

[0107] Examples of tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, etc. From the viewpoint of controllability of the reaction rate and uniformity of the shape of the produced silica base particles, tetramethoxysilane or tetraethoxysilane is preferred.

[0108] Examples of the alkali catalyst supplied to the alkali catalyst solution include basic catalysts such as ammonia, urea, monoamines, and quaternary ammonium salts, with ammonia being particularly preferred. The alkali catalyst supplied together with the tetraalkoxysilane may be of the same type as the alkali catalyst already contained in the alkali catalyst solution, or may be of a different type, but is preferably of the same type.

[0109] The method for supplying the tetraalkoxysilane and the alkali catalyst into the alkali catalyst solution may be a continuous supply method or an intermittent supply method.

[0110] In the silica base particle production step, the temperature of the alkaline catalyst solution (temperature at the time of supply) is preferably 5°C or higher and 50°C or lower, more preferably 15°C or higher and 45°C or lower.

[0111] [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.

[0112] 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.

[0113] [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.

[0114] 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.

[0115] In the alcohol liquid containing the 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.

[0116] [Third step] In the third step, after or during the second step, a hydrophobic treatment is performed on silica base particles that 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 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 its functional groups and with the OH groups of the silica base particles.

[0117] 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.

[0118] [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.

[0119] 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 below 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 below 40°C, the solids are not sufficiently dried and adhere to the inside of the device. A more preferable inlet temperature is in the range of 100°C to 300°C. The silica particle concentration in 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.

[0120] In supercritical drying, the solvent is removed using a supercritical fluid, which makes 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, making it easier to obtain silica particles with a highly uniform particle size.

[0121] Examples of substances that can be used as supercritical fluids include carbon dioxide, water, methanol, ethanol, acetone, etc. From the viewpoints of treatment efficiency and suppressing the generation of coarse particles, the solvent removal step is preferably a step that uses supercritical carbon dioxide.

[0122] 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., the critical point of carbon dioxide is 31.1°C / 7.38 MPa, and the temperature and pressure are, for example, 40°C to 200°C and 10 MPa to 30 MPa.

[0123] The flow rate of the supercritical fluid in the supercritical drying is preferably 80 mL / sec or more and 240 mL / sec or less.

[0124] The obtained silica particles are preferably crushed or sieved as necessary to remove coarse particles and aggregates. Crushing is performed using, for example, a dry grinding device such as a jet mill, a vibration mill, a ball mill, or a pin mill. Sieving is performed using, for example, a vibration sieve or an air sieving machine. [Example]

[0125] Hereinafter, embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, all "%" is by mass.

[0126] <Production of Silica Particles> [Examples 1, 3 to 25, 27 to 32, Comparative Examples 1 to 4] A suspension containing silica particles in each example was prepared as follows.

[0127] -Preparation of alkaline catalyst solution- Methanol, ion-exchanged water, and 10% aqueous ammonia (NH4OH) in the amounts 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.

[0128] - Granulation of silica base particles using 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 ammonia water (NH4OH) with a catalyst (NH3) concentration of 7.9% were simultaneously added dropwise to obtain a silica base particle suspension.

[0129] - 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.

[0130] - Addition of nitrogen-containing compounds - The nitrogen-containing compounds shown in Table 1 were diluted with butanol to prepare alcohol solutions. Next, an alcohol solution prepared by diluting a 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.

[0131] -Drying- Next, 300 parts by mass of the suspension was placed in a reaction vessel, and CO2 was added while stirring, and the temperature and pressure inside the reaction vessel were raised to the temperature and pressure shown in Table 1. While stirring 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.

[0132] [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.

[0133] [Example 26] After adding the nitrogen-containing compound, hexamethyldisilazane (HMDS) was added in an amount of 50 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 surface of the silica base particles. Silica particles were obtained in the same manner as in Example 1, except that the amount of the nitrogen-containing compound was 50 parts.

[0134] [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) Hydrophobicity - Amount of OH groups measured by the Sears method (referred to as "Amount of OH groups" in the table) Volume resistivity Peak positions on the pore size distribution curve of the nitrogen gas adsorption method (in the table, indicated as "pore size distribution curve first peak position" and "pore size distribution curve second peak position")

[0135] (Low humidity charge amount and high humidity charge amount) The high humidity charge amount and the high humidity charge amount of the silica particles of each example were measured as follows. 5 g of the prepared silica particles added to the surface of MBX-12 manufactured by Sekisui Chemical Co., Ltd. at 2% by mass was weighed out and mixed with 50 g of SPL-100 manufactured by Unitika Ltd. The mixed sample was stirred for 2 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 taken as FC, and the result was stirred for 2 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 (charge amount at high humidity / charge amount at low humidity ratio), was used for evaluation. G1(◎): FA / FC (charge amount at high humidity / charge amount at low humidity ratio) is 0.8 or more and less than 1.1 G2 (Good): FA / FC (charge amount at high humidity / charge amount at low humidity ratio) is 0.65 or more and less than 0.8 G3 (△): FA / FC (ratio of charge amount at high humidity to charge amount at low humidity) is 0.5 or more and less than 0.65 G4(×): FA / FC (high humidity charge amount / low humidity charge amount ratio) is less than 0.5

[0136] (Charge distribution in a high temperature and humidity environment) The charge distribution of the silica particles in each example was evaluated as follows. Five grams of the prepared silica particles were added to the surface of Sekisui Chemical's MBX-12 at 2% by mass, and 50 grams of Unitika's SPL-100 were weighed and mixed. The mixed sample was stirred for two minutes using a Turbula shaker in a chamber at 30°C and 90% RH, and evaluated using CSG (charge spectrograph) image analysis. The charge distribution is defined as the difference between the 20% charge Q(20) and the 80% charge Q(80) of the cumulative charge distribution divided by the 50% charge Q(50), i.e., [Q(80) - Q(20)] / Q(50). The evaluation criteria are as follows: G1(◎): [Q(80)-Q(20)] / Q(50) value is less than 0.7 G2(○): [Q(80)-Q(20)] / Q(50) value is less than 0.8 and 0.7 or more G3(△): [Q(80)-Q(20)] / Q(50) value is less than 1.0 and 0.8 or more G4(×): [Q(80)-Q(20)] / Q(50) value is 1.0 or more

[0137] The evaluation results are shown in Table 1. Details of the abbreviations in Table 1 are as follows: MTMS: Methyltrimethoxysilane DTMS: n-dodecyltrimethoxysilane

[0138] ·TP415:[N + (CH)3(C 14 C 29 )2]4Mo8O 28 4- (Hodogaya Chemical Co., Ltd., N,N-Dimethyl-N-tetradecyl-1-tetradecanaminium, hexa-μ-oxotetra-μ3-oxodi-μ5-oxotetradecaoxooctamolybdate(4-) (4:1)) (amount extracted with ammonia / methanol mixed solution X = 61 to 89 mass%, ratio of extract amount X to extract amount Y with water X / Y = 0.03 to 0.26) P51: "Bontron P51" manufactured by Orient Chemical Co., Ltd., benzyltributylammonium 4-hydroxynaphthalene-1-sulfonate represented by the following formula (amount extracted with ammonia / methanol mixed solution X = 0.78 mass%, ratio of extractable amount X to extractable amount Y with water X / Y = 0.19) [ka] Tridecylamine (amount extracted with ammonia / methanol mixed solution X = 66 mass%, ratio of extractable amount X to extractable amount Y with water X / Y = 0.19) Dimethyloctadecyl[3-(trimethoxysilyl)propyl] (ammonium chloride Aminopropyltrimethoxysilane (amount extracted with ammonia / methanol mixed solution X = 78 mass%, ratio of extractable amount X to extractable amount Y with water X / Y = 0.16) Quaternium-80 (amount extracted with ammonia / methanol mixed solution X = 80 mass%, ratio of extracted amount X to extracted amount Y with water X / Y = 0.09) Ditetrakis(dibutyldibenzylammonium)molybdic acid (amount extracted with ammonia / methanol mixed solution X = 65% by mass, ratio of extracted amount X to extracted amount Y with water X / Y = 0.15) Phenethylamine (amount extracted with ammonia / methanol mixed solution X = 55% by mass, ratio of extractable amount X to extractable amount Y with water X / Y = 0.28) 4-(2-octylamino)diphenylamine (amount extracted with ammonia / methanol mixed solution X = 78% by mass, ratio of extractable amount X to extractable amount Y with water X / Y = 0.14) N-benzyl-N-methylethanolamine (amount extracted with ammonia / methanol mixed solution X = 58 mass%, ratio of extract amount X to extract amount Y with water X / Y = 0.27) 2,3-bis(2,6-diisopropylphenylimino)butane (amount extracted with ammonia / methanol mixed solution X = 81 mass%, ratio of extracted amount X to extracted amount Y with water X / Y = 0.11) 3-indoleacetonitrile (amount extracted with ammonia / methanol mixed solution X = 80 mass%, ratio of extracted amount X to extracted amount Y with water X / Y = 0.12)

[0139] [Table 1-1]

[0140] [Table 1-2]

[0141] 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

1. Silica base particles; a structure comprising a reaction product of a trifunctional silane coupling agent, the structure covering at least a portion of the surface of the silica base particle; and a nitrogen-containing compound is contained, and the content of the nitrogen-containing compound relative to the silica particles is 0.005% by mass or more and 0.50% by mass or less in terms of N atoms; The hydrophobicity is 10% or more and 60% or less, Volume resistivity is 1×10 ８ Ω・cm or more 1×10 １２．５ Ω cm or less, the nitrogen-containing compound is adsorbed in at least a portion of the pores of the reaction product of the trifunctional silane coupling agent; The silica particles, 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.

2. 2. The silica particles according to claim 1, wherein a pore size distribution curve measured by a nitrogen gas adsorption method has a first peak in a pore diameter range of 0.01 nm or more and 2 nm or less and a second peak in a pore diameter range of 1.5 nm or more and 50 nm or less.

3. 3. The silica particles according to claim 1, wherein the hydrophobicity is 10% or more and 50% or less.

4. The silica particles according to any one of claims 1 to 3, having a volume average particle size of 10 nm or more and 200 nm or less.

5. 5. The silica particles according to claim 4, having a volume average particle size of 10 nm or more and 80 nm or less.

6. 6. The silica particles according to claim 1, wherein the average circularity is 0.60 or more and 0.96 or less.

7. 7. The silica particles according to claim 6, having an average circularity of 0.70 or more and 0.92 or less.

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