Surface-treated sol-gel silica particles, method for producing surface-treated sol-gel silica particles, and external toner additive for electrostatic image development

Abstract

Provided are surface-treated sol-gel silica particles or the like which have little change in charge when the environment changes, and which can impart good printing characteristics to a toner when used as an external additive for the toner. Surface-treated sol-gel silica particles having R2SiO3 / 2 units and R43SiO1 / 2 units (R2 and R4 are monovalent hydrocarbon groups) on the surface, satisfying (1) to (7) (1) a median diameter as determined by a dynamic light scattering method of 50 nm to 300 nm, (2) an average circularity of 0.80 to 1.0, (3) a refractive index of 1.380 to 1.420, (4) a true density of 1.7000 g / cm < 3 > or more and less than 1.9000 g / cm < 3 >, (5) a volume resistivity of 1011 Omega cm or more, and (6) a ratio represented by water vapor adsorption specific surface area / nitrogen adsorption specific surface area of 2.00 to 10.0. And (7) the moisture absorption rate when exposed at 30 DEG C / 90% RH for 2 hours is 6.0-11 mass% with respect to the dry mass when dried at 150 DEG C for 1 day.

Description

Technical Field

[0001] This invention relates to surface-treated sol-gel silica particles, their manufacturing method, and toner additives for electrostatic image development, used for developing electrostatic images in electrophotography, electrostatic recording, and the like. Background Technology

[0002] Dry developers used in electrophotographic processes can be broadly categorized into one-component developers, which disperse the toner in a binder resin, and two-component developers, in which a carrier is mixed into the toner. Furthermore, when using these developers for copying operations, excellent properties such as flowability, anti-caking, fixing, electrostatic properties, and cleaning properties are required for process suitability. In particular, inorganic microparticles are often used as toner additives to improve flowability, anti-caking, fixing, and cleaning properties.

[0003] However, the dispersibility of inorganic microparticles has a significant impact on toner properties. In cases of uneven dispersibility, the desired properties in terms of flowability, anti-caking, and fixing cannot be achieved, or the cleanliness becomes insufficient, leading to toner fixation on the photoreceptor and sometimes causing black dot-like image defects. To improve these aspects, various schemes have been proposed that involve hydrophobicating the surface of inorganic microparticles.

[0004] Furthermore, recent demands for high-speed, low-energy-consumption copiers necessitate higher degradation resistance compared to existing toners. If the toner's degradation resistance is low, its transfer efficiency cannot be maintained at a high level from the start to the end of use. As a countermeasure, a toner degradation suppression technology utilizing the spacer effect of large-particle-size toner additives has been proposed (Patent Documents 1 and 2).

[0005] Furthermore, as toner additives, small-particle-size toner additives and large-particle-size toner additives are often used in combination. Due to the presence of large-particle-size toner additives adhering to the surface of toner particles, the frequency of small-particle-size toner additives adhering to the surface of nearby toner particles being directly subjected to external forces such as shear force and impact force is reduced. This can prevent the small-particle-size toner additives from being buried into the surface of toner particles due to such external forces (spacer effect), thus suppressing the deterioration of the toner.

[0006] In addition, by adding large-particle-size toner additives, the toner can easily detach from the photoreceptor, and the toner loaded on the photoreceptor can be quickly transferred to the paper, thus maintaining a high transfer efficiency. Therefore, it is believed that large-particle-size toner additives also function as transfer aids.

[0007] In the use of large-particle-size toner additives that are expected to have a spacer effect, fumed silica particles manufactured using existing combustion methods have been used. However, in recent years, large-particle-size spherical silica particles with uniform particle size distribution have become available using the sol-gel method. Therefore, a technique has been proposed to use spherical silica particles with an average particle size of about 50 nm to 150 nm as additives (Patent Document 3).

[0008] Furthermore, in order to suppress the burial of additives and maintain high developability and transferability over time from the initial stage, it has been disclosed that using monodisperse spherical large-particle-size silica with a true specific gravity of 1.9 or less is effective (Patent Document 4). It is known that this low-specific-gravity monodisperse spherical silica, due to its rolling action, easily settles between the doctor blade and the image carrier, effectively reducing friction and improving cleanliness (Patent Documents 4 and 5).

[0009] However, increasing the particle size of spherical silica particles reduces the surface area per unit mass, thus decreasing the electrical charge. This weakens the Coulomb force, which dominates the adhesion between the silica particles and toner particles, resulting in reduced adhesion and easier detachment. It is also known that if silica particles detach from toner particles, a photoreceptor will form due to the detached silica and toner particles. Electric roller Contamination of the developing roller and gaps in the cleaning blade can cause image defects due to contamination of this component (Patent Document 3).

[0010] Generally, the charge of toner and silica particles varies depending on the environment. Under high temperature and high humidity, the charge decreases, reducing the adhesion of silica particles to toner particles, making it easier for silica particles to detach from toner particles. On the other hand, under low temperature and low humidity, the charge increases excessively, causing the charge on the toner to transfer to other objects, which can easily lead to image degradation.

[0011] Silica particles used as colorant additives have the problem of difficulty in controlling their charge when the environment changes, so silica particles with good charge control are needed.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent Application Publication No. 06-027718

[0015] Patent Document 2: Japanese Patent Application Publication No. 11-143118

[0016] Patent Document 3: Japanese Patent Application Publication No. 2007-264142

[0017] Patent Document 4: Japanese Patent Application Publication No. 2001-066820

[0018] Patent Document 5: Japanese Patent Application Publication No. 2005-004051 Summary of the Invention

[0019] The problem that the invention aims to solve

[0020] Therefore, the object of the present invention is to provide surface-treated sol-gel silica particles with small changes in charge under environmental changes, that is, surface-treated sol-gel silica particles that can impart good printing properties to toners when used as toner additives, a method for manufacturing the same, and toner additives containing the surface-treated sol-gel silica particles.

[0021] Methods for solving problems

[0022] To achieve the above objectives, the inventors conducted in-depth research and discovered that when surface-treated sol-gel silica particles with specific siloxane units on the surface, specific particle size, average sphericity, refractive index, true density, water vapor adsorption specific surface area / nitrogen adsorption specific surface area ratio, and moisture absorption rate are used as toner additives, the charge change during environmental changes is small, thus providing the toner with good printing properties, and the present invention was completed.

[0023] That is, the present invention provides the following surface-treated sol-gel silica particles, a method for manufacturing surface-treated sol-gel silica particles, and an additive for electrostatic imaging toner.

[0024] [1] Surface-treated sol-gel silica particles are formed on a surface with R 2 SiO 3 / 2 Unit (where R) 2 (substituted or unsubstituted monovalent hydrocarbon groups with 1 to 20 carbon atoms) and R 4 3SiO 1 / 2 Unit (where R) 4 Surface-treated sol-gel silica particles (containing monovalent hydrocarbon groups with 1-6 carbon atoms, either substituted or unsubstituted, with the same or different substituted or unsubstituted groups).

[0025] (1) The median diameter in the dynamic light scattering method is 50 nm to 300 nm.

[0026] (2) The average roundness is 0.80 to 1.0.

[0027] (3) The refractive index is 1.380–1.420.

[0028] (4) The true density is 1.7000 g / cm³. 3 Above but less than 1.9000 g / cm 3,

[0029] (5) The volume resistivity is 10 11 Ω cm or more

[0030] (6) The ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area is 2.00 to 10.0.

[0031] (7) The moisture absorption rate after exposure at 30°C / 90%RH for 2 hours is 6.0 to 11 times the mass of the product after drying at 150°C for 1 day.

[0032] [2] According to the surface-treated sol-gel silica particles described in [1], wherein the R 2 and R 4 It is a methyl group.

[0033] [3] The method for manufacturing surface-treated sol-gel silica particles according to [1] includes the following steps (A1) to (A6):

[0034] Step (A1): A step of obtaining a mixed solvent dispersion of hydrophilic sol-gel silica particles by hydrolyzing and condensing a 4-functional silane compound represented by formula (I), its partially hydrolyzed condensate, or a mixture thereof, in a mixture containing a hydrophilic organic solvent and water in the presence of an alkaline substance.

[0035] Si(OR) 1 4 (I)

[0036] In the formula R 1 Independently representing monovalent hydrocarbon groups with 1 to 6 carbon atoms.

[0037] Step (A2): A step in which the hydrophilic organic solvent in the dispersion medium of the mixed solvent dispersion of hydrophilic sol-gel silica particles obtained in step (A1) is replaced with water to obtain an aqueous dispersion of hydrophilic sol-gel silica particles.

[0038] Step (A3): The aqueous dispersion of hydrophilic sol-gel silica particles obtained in step (A2) is refluxed at the reflux temperature of water for more than 5 hours.

[0039] Step (A4): To the aqueous dispersion of hydrophilic sol-gel silica particles following step (A3), add 0.01 to 0.5 moles of a trifunctional silane compound, its partially hydrolyzed condensate, or a mixture thereof, represented by formula (II), relative to 1 mole of Si atoms of the hydrophilic sol-gel silica particles, thereby introducing R onto the surface of the hydrophilic sol-gel silica particles. 2 SiO 3 / 2The unit is a process for obtaining an aqueous dispersion of pre-surface-treated sol-gel silica particles.

[0040] R 2 Si(OR) 3 3 (II)

[0041] In the formula, R 2 R represents a monovalent hydrocarbon group with 1 to 20 carbon atoms that can be replaced by halogen atoms. 3 Independently representing monovalent hydrocarbon groups with 1 to 6 carbon atoms.

[0042] Step (A5): The process of replacing the dispersion medium of the aqueous dispersion of pre-surface-treated sol-gel silica particles obtained in step (A4) with a ketone solvent to obtain a ketone solvent dispersion of pre-surface-treated sol-gel silica particles.

[0043] Step (A6): In the ketone solvent dispersion of the pre-surface-treated sol-gel silica particles obtained in step (A5), 0.1 to 0.5 moles of a silazane compound represented by formula (III), a monofunctional silane compound represented by formula (IV), or a mixture thereof are added relative to 1 mole of Si atoms of the pre-surface-treated sol-gel silica particles to introduce R onto the surface of the pre-surface-treated sol-gel silica particles. 4 3SiO 1 / 2 The unit is the process of obtaining surface-treated sol-gel silica particles.

[0044] R 4 3SiNHSiR 4 3 (III)

[0045] R 4 3SiX (IV)

[0046] In the formula, R 4 Independently represents a monovalent hydrocarbon group with 1 to 6 carbon atoms that can be substituted by a halogen atom, where X represents a hydroxyl group, an alkoxy group with 1 to 6 carbon atoms, or a chlorine atom.

[0047] [4] According to the method for manufacturing surface-treated sol-gel silica particles described in [3], wherein R 2 and R 4 It is a methyl group.

[0048] [5] A toner additive for electrostatic imaging development, comprising surface-treated sol-gel silica particles as described in [1] or [2].

[0049] The effects of the invention

[0050] When the surface-treated sol-gel silica particles of the present invention are used as toner additives, their charge changes little with environmental changes, thus imparting good printing properties to the toner. Therefore, they are extremely useful as toner additives. Detailed Implementation

[0051] The present invention will now be described in detail.

[0052] [Surface-treated sol-gel silica particles]

[0053] The surface-treated sol-gel silica particles of the present invention are those with R on their surface. 2 SiO 3 / 2 Unit (where R) 2 (substituted or unsubstituted monovalent hydrocarbon groups with 1 to 6 carbon atoms) and R 4 3SiO 1 / 2 Unit (where R) 4 Surface-treated sol-gel silica particles (with the same or different substituted or unsubstituted monovalent hydrocarbon groups with 1 to 6 carbon atoms) satisfy all of the following (1) to (7).

[0054] (1) The median diameter in the dynamic light scattering method is 50 nm to 300 nm.

[0055] (2) The average roundness is 0.8 to 1.0.

[0056] (3) The refractive index is 1.38–1.42.

[0057] (4) The true density is 1.7 g / cm³. 3 Above and less than 1.9 g / cm 3 ,

[0058] (5) The volume resistivity is 10 11 Ω cm or more

[0059] (6) The ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area is 2 to 10.

[0060] (7) The moisture absorption rate after exposure at 30°C / 90%RH for 2 hours is 6 to 11 times the mass of the product after drying at 150°C for 1 day.

[0061] R 2 It is a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably having 1 to 8 carbon atoms, and more preferably having 1 to 3 carbon atoms. As a monovalent hydrocarbon group composed of R... 2The monovalent hydrocarbon group can be represented by, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, and decyl, cycloalkyl groups such as cyclohexyl, vinyl, allyl, n-butenyl, n-hexenyl, and n-octenyl, aryl groups such as phenyl, etc., with methyl being particularly preferred. Furthermore, some or all of the hydrogen atoms in these monovalent hydrocarbon groups may be replaced by halogen atoms such as fluorine, chlorine, and bromine, preferably fluorine.

[0062] R 4 It is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, and particularly preferably an alkyl group having 1 to 2 carbon atoms. As a group composed of R... 3 The monovalent hydrocarbon group can be represented by, for example, methyl, ethyl, propyl, butyl, vinyl, phenyl, etc., preferably methyl, ethyl, propyl and butyl, and particularly preferably methyl and ethyl. In addition, some or all of the hydrogen atoms of these monovalent hydrocarbon groups can be replaced by halogen atoms such as fluorine, chlorine, and bromine atoms, preferably fluorine atoms.

[0063] The surface-treated sol-gel silica particles of the present invention possess the above-mentioned physical properties (1) to (7) simultaneously, thereby exhibiting small changes in charge under environmental changes when used as an additive for toners, thus providing good printing characteristics for toners.

[0064] (1) Median diameter in dynamic light scattering method

[0065] In the dynamic light scattering method of surface-treated sol-gel silica particles of the present invention, the median diameter is 50 nm to 300 nm, preferably 50 nm to 200 nm. If the median diameter is less than 50 nm, it is not preferred in terms of not being able to exert a sufficient spacer effect when used as a toner additive. In addition, if the median diameter exceeds 300 nm, the reduction in surface area easily leads to a decrease in charge and a decrease in adhesion to the toner particles, which is also not preferred.

[0066] The median diameter is a value derived from the particle size distribution of surface-treated sol-gel silica particles, measured using the dynamic light scattering method. The dynamic light scattering method utilizes a dynamic light scattering particle size distribution measuring device (e.g., the MicrotracBEL Nanotrac Wave II-Ex150) to determine the particle size distribution based on the phenomenon that the intensity of scattered light obtained by irradiating a dispersion of silica particles with a laser varies with the particle size of the silica particles.

[0067] (2) Average roundness

[0068] The sphericity of the surface-treated sol-gel silica particles of the present invention is defined as (circumference of a circle with an area equal to that of the particle / particle circumference) when the particles are projected two-dimensionally. The average sphericity is the average of the sphericity of 10 random silica particles observed using a scanning electron microscope. The average sphericity of the surface-treated sol-gel silica particles of the present invention is 0.80 to 1.0, preferably 0.92 to 1.0. If the average sphericity is lower than 0.80, the proportion of irregularly shaped particles increases, which can easily cause contamination of the toner, and is therefore not preferred.

[0069] (3) Refractive index

[0070] The refractive index indicates the porosity within the surface-treated sol-gel silica particles, and ranges from 1.380 to 1.420. If the refractive index is less than 1.380, it indicates a large number of porosity particles, resulting in a brittle cross-linked structure of the sol-gel silica particles, which is therefore undesirable. Conversely, if the refractive index exceeds 1.420, there are fewer porosity particles, leading to a higher specific gravity. This can sometimes result in a lower charge or reduced adhesion to the toner particles, which is also undesirable.

[0071] In this invention, the refractive index of the surface-treated sol-gel silica particles is set as the refractive index of the mixed solvent at the point where the visible light transmittance of the dispersion is highest at 25°C (the point where the refractive index of the mixed solvent is consistent with that of the surface-treated silica particles) by adding and dispersing the surface-treated sol-gel silica particles in a mixed solvent of toluene (refractive index 1.4962) and methyl isobutyl ketone (refractive index 1.3958), adjusting the refractive index using the ratio of the above solvents.

[0072] (4) True density

[0073] The true density is 1.7000 g / cm³. 3 Above but less than 1.9000 g / cm 3 The preferred value is 1.7500 g / cm³. 3 ~1.8500g / cm 3 If the true density is less than 1.7000 g / cm³ 3 Sometimes, the strength of surface-treated sol-gel silica particles decreases, making it less desirable. Additionally, the true density is 1.9000 / cm³. 3 In the above cases, since the mass of each silica particle increases, the impact on the toner particles increases when it is used as an additive in toners, which is not preferred in this respect.

[0074] (5) Volume resistivity

[0075] Volume resistivity is an indicator of the insulating and conductive properties of particles; a volume resistivity of 10⁻⁶ is... 11 Ω cm or more. If less than 10 cm 11 Ω cm, sometimes exhibiting conductivity, which adversely affects the charged properties of the toner and is therefore not preferred. Furthermore, regarding the upper limit, from the perspective of obtaining suitable charged properties as a toner additive, 5.0 × 10⁻⁶ is preferred. 14 Ω Below approximately 1 cm.

[0076] (6) Ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area

[0077] The ratio of water vapor adsorption surface area to nitrogen adsorption surface area is a measure of hygroscopicity, and the adsorption surface area of ​​each gas can be obtained using the BET method. Since water molecules (approximately 2 Å) are smaller than nitrogen molecules (approximately 3 Å), a small ratio of water vapor adsorption surface area to nitrogen adsorption surface area indicates the presence of pores that are difficult for water molecules to pass through but allow nitrogen to pass through.

[0078] The ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area is 2.00 to 10.0, preferably 5.00 to 10.0. If this ratio is less than 2.00, the hygroscopicity is poor, and the charged environment of the toner cannot be adjusted well, so it is not preferred. If it is greater than 10.0, the hygroscopicity is too high, and the charge of the toner is significantly affected by humidity, so it is also not preferred.

[0079] (7) Moisture absorption rate

[0080] In this invention, the moisture absorption rate is a value obtained by measuring the mass (a) of silica particles exposed at 30°C and 90% RH for 2 hours and the mass (b) of silica particles dried at 150°C for 1 day, respectively, and calculating the percentage of moisture absorption relative to the mass at drying [(a)-(b)] / (b)×100 (mass%). The moisture absorption rate of the surface-treated sol-gel silica particles of this invention is 6.0 to 11% by mass, preferably 9.0 to 11% by mass. If the moisture absorption rate is less than 6.0% by mass, it cannot suppress changes in charge due to environmental changes and is therefore not preferred. On the other hand, if the moisture absorption rate exceeds 11% by mass, the charge tends to decrease, and therefore is not preferred.

[0081] [Method for manufacturing surface-treated sol-gel silica particles]

[0082] The surface-treated sol-gel silica particles of the present invention can be obtained by a manufacturing method having the following steps (A1) to (A6).

[0083] Step (A1): Step to obtain a mixed solvent dispersion of hydrophilic sol-gel silica particles.

[0084] Process (A2): Displacement process into water-dispersing medium

[0085] Process (A3): The process of heating the aqueous dispersion of hydrophilic sol-gel silica particles.

[0086] Process (A4): Surface treatment process using trifunctional silane compounds

[0087] Step (A5): Displacement process into the dispersion medium of ketone solvents

[0088] Process (A6): Surface treatment process using a functional silane compound.

[0089] Step (A1): Step to obtain a mixed solvent dispersion of hydrophilic sol-gel silica particles.

[0090] This process involves hydrolyzing and condensing a 4-functional silane compound represented by formula (I), its partial hydrolysis condensate, or a mixture thereof in the presence of an alkaline substance in a mixture containing a hydrophilic organic solvent and water, thereby obtaining a mixed solvent dispersion of hydrophilic sol-gel silica particles.

[0091] Si(OR) 1 4 (I)

[0092] (where R) 1 (Independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)

[0093] In equation (I) above, R 1 It is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms, and particularly preferably a monovalent hydrocarbon group having 1 to 2 carbon atoms. As a group composed of R... 1 The monovalent hydrocarbon group represented can be, for example, methyl, ethyl, propyl, butyl, phenyl, etc., preferably methyl, ethyl, propyl and butyl, and particularly preferably methyl and ethyl.

[0094] Examples of tetrafunctional silane compounds represented by formula (I) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, and tetraalkoxysilanes and tetraphenoxysilanes, with tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane being preferred, and tetramethoxysilane and tetraethoxysilane being particularly preferred. Furthermore, examples of hydrolysis condensates of tetrafunctional silane compounds represented by formula (I) include methyl silicate and ethyl silicate.

[0095] Examples of alkaline substances include ammonia, dimethylamine, and diethylamine, with ammonia and diethylamine being preferred, and ammonia being particularly preferred. These alkaline substances can be used as products that are dissolved in water in the required amount.

[0096] As a hydrophilic organic solvent, there are no particular limitations as long as the compound represented by formula (I) above and / or its partial hydrolysis condensate and water can be dissolved. Examples include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and tert-butanol; ethers such as tetrahydrofuran and dioxane; and diols such as diethylene glycol and dipropylene glycol, with alcohols being preferred. If the number of carbon atoms in the alcohol increases, the particle size of the generated silica particles increases, thus allowing the type of alcohol to be selected based on the particle size of the target silica particles.

[0097] The amount of water used in this process is preferably 0.5 to 5 moles, more preferably 0.6 to 2 moles, and particularly preferably 0.7 to 1 mole, relative to the total hydroxyl groups of the 4-functional silane compound and / or its partially hydrolyzed condensate represented by formula (I) above, which is 1 mole. It should be noted that when the above-mentioned alkaline substance is used after being dissolved in water, the water in which the alkaline substance is dissolved is also included in the "water" in this process.

[0098] The ratio of the hydrophilic organic solvent to water, taken into account the affinity between the silica particles and the mixed solvent and the ease of manufacture, is preferably 0.2 to 10 by mass, and more preferably 0.3 to 5.

[0099] The amount of alkaline substance, in terms of the size of the obtained silica particles, is preferably 0.01 to 2 moles, more preferably 0.03 to 0.5 moles, relative to 1 mole of the total hydroxyl groups of the 4-functional silane compound and / or its partial hydrolysis condensation products represented by formula (I) above.

[0100] The hydrolysis and condensation of 4-functional silane compounds can be carried out by a known method, namely, by adding a 4-functional silane compound and a basic substance to a mixture of a hydrophilic organic solvent and water.

[0101] The preferred temperature for hydrolysis and condensation is 20–50°C. The higher the temperature, the smaller the silica particles obtained.

[0102] The concentration of the mixed solvent dispersion of hydrophilic sol-gel silica particles obtained in this process (A1) is generally 3 to 15% by mass, preferably 5 to 10% by mass.

[0103] Process (A2): Displacement process into water-dispersing medium

[0104] This step involves replacing the hydrophilic organic solvent in the mixed solvent dispersion of hydrophilic sol-gel silica particles obtained in step (A1) with water. The hydrophilic organic solvent replaced in step (A2) includes the hydrophilic organic solvent used in step (A1) and volatile byproducts such as alcohols generated due to condensation.

[0105] As a replacement method, a heating concentration method is used, in which the surface-treated colloidal silica obtained in step (A1) is heated and concentrated while adding water of an equal amount or more to the distillate produced by heating, or an ultrafiltration method using a filter is used. These methods can easily and economically obtain an aqueous dispersion.

[0106] From the viewpoint of the stability of water-dispersed colloidal silica in surface treatment, the amount of water added is preferably 0.5 to 2 times the total amount of hydrophilic organic solvent used and alcohol generated, expressed as a mass ratio. More preferably, it is 0.9 to 1.3 times the total amount of water added.

[0107] Process (A3): The process of heating the aqueous dispersion of hydrophilic sol-gel silica particles.

[0108] This step involves reacting the aqueous dispersion of the hydrophilic sol-gel silica particles obtained in step (A2) at a reflux temperature of water for at least 5 hours, preferably 7 to 12 hours. It is believed that this step promotes the hydrolysis (silanolization) of residual alkoxy groups within the sol-gel silica particles, thereby increasing their affinity for water molecules and thus improving the hygroscopicity of the sol-gel silica particles. The reflux temperature of water can be set to 99 to 100°C, for example, when step (A3) is performed at 1 atmosphere; however, it is not limited to this temperature range depending on the pressure.

[0109] Using this process (A3), surface-treated sol-gel silica particles that meet the required ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area and the required moisture absorption rate (7) are obtained.

[0110] Process (A4): Surface treatment process using trifunctional silane compounds

[0111] This step involves adding a trifunctional silane compound represented by formula (II), its partially hydrolyzed condensate, or a mixture thereof, to the aqueous dispersion of hydrophilic sol-gel silica particles after step (A3), thereby introducing R onto the surface of the sol-gel silica particles. 2 SiO 3 / 2 The unit is a process for obtaining an aqueous dispersion of pre-surface-treated sol-gel silica particles.

[0112] R 2 Si(OR) 3 3 (II)

[0113] (where R) 2 R represents a monovalent hydrocarbon group with 1 to 20 carbon atoms that can be replaced by halogen atoms. 3 (Independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)

[0114] In equation (II) above, R 2 It is a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably having 1 to 10 carbon atoms, and particularly preferably having 1 to 3 carbon atoms. As a monovalent hydrocarbon group composed of R... 2 The monovalent hydrocarbon group can be represented by, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, and decyl, with methyl, ethyl, and propyl being particularly preferred. Furthermore, some or all of the hydrogen atoms in these monovalent hydrocarbon groups may be replaced by halogen atoms such as fluorine, chlorine, or bromine, with fluorine being preferred.

[0115] In equation (II) above, R 3 It is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms, and particularly preferably a monovalent hydrocarbon group having 1 to 2 carbon atoms. As a group composed of R... 3 The monovalent hydrocarbon group represented can be, for example, methyl, ethyl, propyl, butyl, phenyl, etc., preferably methyl, ethyl, propyl and butyl, and particularly preferably methyl and ethyl.

[0116] Specific examples of trifunctional silane compounds represented by formula (II) above include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, (heptadecyl-1,1,2,2-tetrahydrodecyl)trimethoxysilane, etc.

[0117] The amount of the trifunctional silane compound represented by formula (II) above is 0.01 to 0.5 moles relative to 1 mole of Si atoms in the hydrophilic sol-gel silica particles, preferably 0.01 to 0.1 moles.

[0118] There are no restrictions on the reaction conditions in this step (A4), but the preferred reaction temperature is 20-60°C and the reaction time is 1-24 hours.

[0119] Step (A5): Displacement process into the dispersion medium of ketone solvents

[0120] This process involves replacing the dispersion medium, consisting of water, hydrophilic organic solvent, and volatile byproducts such as alcohols generated during condensation, in the aqueous dispersion of pre-surface-treated sol-gel silica particles obtained in process (A4) with a ketone solvent.

[0121] Specific examples of ketone solvents include methyl ethyl ketone, methyl isobutyl ketone, and acetylacetone, with methyl isobutyl ketone being the preferred choice.

[0122] From the viewpoint of inhibiting the aggregation of silica particles and the concentration of the reaction system in the surface treatment process using a functional silane compound in the next step, the amount of ketone solvent added is preferably 0.5 to 5 times the mass ratio of the pre-surface treated sol-gel silica particles obtained in step (A4), more preferably 1 to 2 times the mass ratio.

[0123] As a method for replacing the hydrophilic organic solvent, water, and volatile byproducts such as alcohols generated during condensation in a dispersion of hydrophobic spherical silica particles with a ketone solvent, methods such as concentration (atmospheric pressure or reduced pressure) and ultrafiltration using a filter can be included. Preferably, a ketone solvent with a higher boiling point than the water and hydrophilic organic solvent contained in the aqueous dispersion of pre-surface-treated sol-gel silica particles obtained in step (A4) is added to the aqueous dispersion of pre-surface-treated sol-gel silica particles obtained in step (A4) for concentration.

[0124] Process (A6): Surface treatment process using a functional silane compound.

[0125] This step involves adding 0.1 to 0.5 moles of a silazane compound represented by formula (III), a monofunctional silane compound represented by formula (IV), or a mixture thereof, relative to 1 mole of Si atoms in the ketone solvent dispersion of the pre-surface-treated sol-gel silica particles obtained in step (A5), thereby introducing R onto the surface of the pre-surface-treated sol-gel silica particles. 4 3SiO 1 / 2 The unit is a process for obtaining surface-treated sol-gel silica particles.

[0126] R 4 3SiNHSiR 4 3 (III)

[0127] R 4 3SiX (IV)

[0128] (where R) 4 Independently represents a monovalent hydrocarbon group with 1 to 6 carbon atoms that can be substituted by a halogen atom, where X represents a hydroxyl group, an alkoxy group with 1 to 6 carbon atoms, or a chlorine atom.

[0129] In equations (III) and (IV) above, R 4 Preferably, it is a monovalent hydrocarbon group having 1 to 4 carbon atoms, and particularly preferably 1 to 2 carbon atoms. As a group composed of R... 4The monovalent hydrocarbon group can be represented by, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, and butyl, with methyl, ethyl, and propyl being preferred, and methyl and ethyl being particularly preferred. Furthermore, some or all of the hydrogen atoms in these monovalent hydrocarbon groups may be replaced by halogen atoms such as fluorine, chlorine, or bromine, with fluorine atoms being more preferred.

[0130] As the alkoxy group represented by X, alkoxy groups with 1 to 4 carbon atoms are preferred, and methoxy and ethoxy groups are particularly preferred.

[0131] Examples of silazane compounds represented by formula (III) above include hexamethyldisilazane and hexaethyldisilazane, with hexamethyldisilazane being preferred. Examples of monosilane compounds represented by formula (IV) above include monosilanol compounds such as trimethylsilanol and triethylsilanol; monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane; and monoalkoxysilanes such as trimethylmethoxysilane and trimethylethoxysilane, with trimethylsilanol and trimethylmethoxysilane being preferred.

[0132] The amount of the compound represented by formulas (III) and (IV) above used is preferably 0.1 to 0.5 moles, more preferably 0.2 to 0.4 moles, and particularly preferably 0.25 to 0.35 moles, relative to 1 mole of Si atoms in the pre-treated sol-gel silica particles. Within this range, good positive charge, environmental charge characteristics, and flowability can be obtained.

[0133] The preferred reaction conditions for surface treatment in this step (A6) are a reaction temperature of 40–130°C and a reaction time of 1–10 hours, and more preferably a reaction temperature of 60–120°C and a reaction time of 2–8 hours.

[0134] After the reaction, volatile byproducts such as ketone solvents, water, and alcohols are appropriately removed from the ketone solvent dispersion of the surface-treated sol-gel silica particles, thereby obtaining surface-treated sol-gel silica particles.

[0135] [Toner Additives for Electrostatic Imaging Development]

[0136] The surface-treated sol-gel silica particles of the present invention are preferably used as toner additives, particularly toner additives for electrostatic imaging development. The amount of the toner additive using the surface-treated sol-gel silica particles of the present invention relative to the toner is preferably 0.01 to 20 parts by weight, more preferably 0.1 to 5 parts by weight, relative to 100 parts by weight of the toner. If this amount is 0.01 parts by weight or more, sufficient adhesion of the toner is achieved, and sufficient toner flowability is obtained. Therefore, it is preferable if it is 20 parts by weight or less, as this has a positive effect on the chargeability of the toner and is also economically preferable.

[0137] As a toner for electrostatic imaging development, which incorporates the surface-treated sol-gel silica particles of the present invention as an additive, known toners composed primarily of binder resin and colorant can be used. Additionally, a charge control agent can be added as needed. The toner can be used as a one-component developer, or it can be mixed with a carrier to be used as a two-component developer. When used as a two-component developer, the electrostatic imaging toner additive of the present invention can be added to the toner during mixing with the carrier, without prior addition, thus coating the surface of the toner. Known carriers such as iron powder or carriers with resin coating on their surfaces are used as carriers.

[0138] Example

[0139] The present invention will be specifically described below using examples and comparative examples. It should be noted that the following examples are not intended to limit the present invention in any way. Various evaluations, such as particle size distribution measurement and particle shape observation of the silica particles obtained in the examples and comparative examples, were performed under the following conditions, and the results are shown in Table 1.

[0140] [(1) Median diameter in dynamic light scattering method]

[0141] The silica particle dispersion was diluted with methanol with silica particles as 0.5% by mass. The particle size distribution after 10 minutes of ultrasonic irradiation was measured using a particle size distribution measuring device (MicrotracBEL, Nanotrac Wave II-EX150) using dynamic light scattering. The median diameter was calculated based on the obtained volume-based particle size distribution.

[0142] [(2) Average roundness]

[0143] The shape of the silica particles was confirmed by observation using a field emission scanning electron microscope (S-4700 model manufactured by Hitachi High Technologies Co., Ltd.). The roundness of the particles when projected in two dimensions was calculated as (circumference of a circle with the same area as the particle) / (particle circumference). The average roundness of 10 silica particles was set as the average roundness.

[0144] [(3) Refractive index]

[0145] 1 g of surface-treated silica particles were added to 20 g of a mixed solvent of toluene (refractive index 1.4962) and methyl isobutyl ketone (refractive index 1.3958) and dispersed. Using the above solvent ratio, the refractive index was adjusted, and the refractive index of the mixed solvent that resulted in the highest visible light transmittance of the dispersion was set as the refractive index of the silica particles. It should be noted that the refractive index of the mixed solvent was measured at 25°C using a digital refractometer (ATAG RX-9000α), and the visible light transmittance of the dispersion was the average of the transmittance at 25°C (wavelengths 380–780 nm) measured using a spectrophotometer (Hitachi High Tech Science Co., Ltd. U-3900H).

[0146] [(4)True density]

[0147] The true density of silica particles was determined using an automated true density measuring device (MAT-7000 manufactured by Seishin Enterprise Co., Ltd.) that utilizes the liquid-phase displacement method.

[0148] [(5) Volume resistivity]

[0149] The volume resistivity of silica particles under a 4.0 kN load was measured using a powder resistivity system (MCP-PD51 manufactured by Mitsubishi Chemical Co., Ltd., Analitek).

[0150] [(6) Ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area]

[0151] Using a high-precision gas adsorption capacity measuring device (MicrotracBEL BELSORP MAX II), the specific surface area of ​​silica particles relative to water vapor and nitrogen media was measured using the BET1 point method, and the ratio of water vapor adsorption specific surface area to nitrogen adsorption specific surface area was calculated.

[0152] [(7) Moisture absorption rate]

[0153] The mass of silica particles exposed at 30℃ and 90% RH for 2 hours (a) and the mass of silica particles dried at 150℃ for 1 day (b) were measured respectively. The moisture absorption rate relative to the mass of silica particles dried was calculated as [(a)-(b)] / (b)×100 (mass%).

[0154] [Example 1-1]

[0155] Step (A1): Step to obtain a mixed solvent dispersion of hydrophilic sol-gel silica particles.

[0156] In a 3-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer, 623.7 g of methanol, 41.4 g of water, and 49.8 g of 28% ammonia solution were added and mixed. The solution was adjusted to 35°C, and while stirring, 1163.7 g (7.66 mol) of tetramethoxysilane and 418.1 g of 5.4% ammonia solution were simultaneously added dropwise over 6 hours for the former and 4 hours for the latter. After the addition was complete, stirring was continued for another 0.5 hours to carry out hydrolysis, resulting in 2295 g of a mixed solvent dispersion of hydrophilic sol-gel silica particles.

[0157] Process (A2): Displacement process into water-dispersing medium

[0158] An ester adapter and a condenser were installed in the reaction vessel after the above step (A1), and the mixture was heated to 60-70°C to remove 1132g of methanol. At this time, 1200g of water was added, and the mixture was then heated to 70-90°C to remove 273g of methanol, thus obtaining an aqueous dispersion of hydrophilic sol-gel silica particles.

[0159] Process (A3): The process of heating the aqueous dispersion of hydrophilic sol-gel silica particles.

[0160] After the above process (A2), the internal temperature of the aqueous dispersion of hydrophilic sol-gel silica particles was maintained at 99-100°C, and it was stirred for 10 hours while being refluxed.

[0161] Process (A4): Surface treatment process using trifunctional silane compounds

[0162] After 0.5 hours in the reaction vessel following the above step (A3), 11.6 g of methyltrimethoxysilane (equivalent to 0.1 molar equivalent relative to 1 mole of Si atoms in silicon dioxide) was added dropwise at 25°C, and then stirred at 25°C for 12 hours to obtain an aqueous dispersion of pre-surface treated sol-gel silicon dioxide particles.

[0163] Step (A5): Displacement process into the dispersion medium of ketone solvents

[0164] 1440 g of methyl isobutyl ketone was added to the reaction vessel after the above step (A4) at 25 °C. The mixture of methanol and water was distilled off after heating to 80–110 °C for 10 hours to obtain a ketone solvent dispersion of pre-surface treated sol-gel silica particles.

[0165] Process (A6): Surface treatment process using a functional silane compound.

[0166] In the reaction vessel following the above step (A5), 357.6 g of hexamethyldisilazane (0.29 molar equivalents relative to 1 mole of Si atoms in silicon dioxide) was added at 25°C, and the reaction was carried out at a reaction temperature of 120°C for 8 hours to perform trimethylsilylation of the silicon dioxide particle surface. The dispersion medium was then distilled off under reduced pressure to obtain 470 g of white surface-treated sol-gel silicon dioxide particles (i).

[0167] [Examples 1-2]

[0168] In step (A1) of Example 1-1, the reaction temperature was set to 42°C, and in step (A3), the mixture was stirred while being refluxed for 12 hours. In the same manner as in Example 1-1, 463g of surface-treated sol-gel silica particles (ii) were obtained.

[0169] [Examples 1-3]

[0170] In step (A1) of Example 1-1, the reaction temperature was set to 45°C, and in step (A3), the mixture was stirred while being refluxed for 11 hours. In the same manner as in Example 1-1, 471g of surface-treated sol-gel silica particles (iii) were obtained.

[0171] [Examples 1-4]

[0172] In step (A1) of Example 1-1, the reaction temperature was set to 25°C, and in step (A3), the mixture was stirred while being refluxed for 9 hours. In the same manner as in Example 1-1, 468 g of surface-treated sol-gel silica particles (iv) were obtained.

[0173] [Comparative Example 1-1]

[0174] In Example 1-1, except for step (A3), 474 g of surface-treated sol-gel silica particles (v) were obtained in the same manner as in Example 1-1.

[0175] [Comparative Examples 1-2]

[0176] In step (A3) of Example 1-1, except that the time for reflux and stirring was 4 hours, 472g of surface-treated sol-gel silica particles (vi) were obtained in the same manner as in Example 1.

[0177] Table 1

[0178] As shown in Table 1, the surface-treated sol-gel silica particles of Examples 1-1 to 1-4 exhibit high hygroscopicity. On the other hand, in Comparative Examples 1-1 and 1-2, the ratio of water vapor adsorption surface area to nitrogen adsorption surface area was small, resulting in poor hygroscopicity.

[0179] [Examples 2-1 to 2-4, Comparative Examples 2-1 and 2-2]

[0180] (Manufacturing of additives and colorants)

[0181] 96 parts by mass of polyester resin with a Tg of 60°C and a softening point of 110°C were melt-blended with 4 parts by mass of Corn 6BC (manufactured by Sumik Kaka Co., Ltd.) as a colorant. After melting, pulverizing, and classifying, a colorant with a median volume diameter of 7 μm was obtained. 10 g of this colorant was mixed with 0.2 g of each surface-treated sol-gel silica particles obtained in Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2 using a sample grinder to obtain an additive-mixed colorant.

[0182] (Preparation of two-component developer)

[0183] A two-component developer was prepared by mixing 3 parts by mass of the above-mentioned additive toner with 97 parts by mass of ferrite (Puddingtech Co., Ltd., EL-35) as a carrier. The results of the measurements of the two-component developer obtained by the above process are shown in Table 2, which were performed according to the methods (8) to (12) described below.

[0184] (8) The charge of the toner

[0185] After exposing the two-component developer to high temperature and high humidity (30°C, 90%RH) and low temperature and low humidity (10°C, 15%RH) conditions for one day, the charge of each sample when rubbed was measured under the same conditions using a powder charge measuring device (Toshiba Chemical Co., Ltd., TB-200).

[0186] (9) Applying toner to the photoreceptor

[0187] The two-component developer was placed in a developer equipped with an organic photosensitive material, and a printing test of 30,000 sheets was conducted at 25°C and 50% RH. At this time, the adhesion of the toner to the photosensitive material could be used as a measure of white gaps in the fully coated image. Specifically, regarding the degree of white gaps, each 1cm... 2 A number of exposed white areas (10 or more) is rated as "many", 1 to 9 as "few", and 0 as "none".

[0188] (10) Photoreceptor wear

[0189] In the printing test described above (9), the following criteria are used to evaluate photoreceptor wear as a measure of image disorder.

[0190] A: Disorder without image

[0191] B: No major image distortion

[0192] C: Image disorder

[0193] (11) Evaluation of image missing (white spots)

[0194] The two-component developer was exposed to 30°C and 90%RH for one day. Then, 5000 consecutive prints of 20cm square full-coverage printing (100% image density) were performed. The developer was then allowed to stand again at 30°C and 90%RH. This process was repeated 60 times, resulting in a total of 300,000 prints. The 10th print of the first day is designated as Print 1, and the final print of the last day is designated as Print 2.

[0195] The presence or absence of image defects (white spots) in the above-mentioned printed matter 2 obtained by image observation was evaluated using the following criteria.

[0196] A: Visual inspection revealed no image defects (no white spots).

[0197] B: Visual inspection is used; there are more than one and fewer than four white spots (images showing white particles).

[0198] C: Visual inspection is used; there are 5 to 9 white spots.

[0199] D: Visual inspection is used; there are more than 10 white spots.

[0200] (12) Evaluation of concentration change (ΔE)

[0201] For the density change of printed material 2 relative to printed material 1, the color difference (ΔE) in the CIE1976 (L*a*b*) color space was measured using an X-rite 938 reflectance density meter (manufactured by X-rite Corporation) according to JIS Z 8781-5, and evaluated according to the following standards.

[0202] A: ΔE is less than 1

[0203] B: The difference in ΔE is greater than 1 but less than 2.5.

[0204] C: The difference in ΔE is greater than 2.5 but less than 3.0.

[0205] D: ΔE difference is 3.0 or higher.

[0206] Table 2

[0207] As shown in Table 2, the toner charge of the two-component developer using the surface-treated sol-gel silica particles obtained in Examples 1-1 to 1-4 as toner additives exhibits minimal environmental-induced variation and no printing image defects. It is believed that the surface-treated sol-gel silica particles of the present invention, due to their moderate hygroscopicity, absorb moisture from the environment near the toner particle surface in high-humidity environments, thereby suppressing the decrease in charge charge. Furthermore, in low-humidity environments, they release the moisture retained within the silica particles, thus minimizing environmental changes near the toner particle surface.

[0208] On the other hand, the toner charge of the two-component developer that uses surface-treated sol-gel silica particles obtained in Comparative Examples 1-1 and 1-2 as toner additives varies greatly due to environmental factors, resulting in poor printing characteristics.

Claims

1. Surface-treated sol-gel silica particles having on the surface R 2 SiO 3 / 2 units (in the formula, R 2 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which can be substituted with a halogen atom) and R 4 3SiO 1 / 2 units (in the formula, R 4 is independently a monovalent hydrocarbon group having 1 to 6 carbon atoms which can be substituted with a halogen atom).

2. The surface-treated sol-gel silica particles according to claim 1, wherein the monovalent hydrocarbon group having 1 to 6 carbon atoms which can be substituted with a halogen atom is a monovalent hydrocarbon group having 1 to 6 carbon atoms which can be substituted with a fluorine atom.

3. The surface-treated sol-gel silica particles according to claim 1 or 2, wherein the monovalent hydrocarbon group having 1 to 6 carbon atoms which can be substituted with a halogen atom is a monovalent hydrocarbon group having 1 to 6 carbon atoms which can be substituted with a chlorine atom.

4. The surface-treated sol-gel silica particles according to any one of claims 1 to 3, wherein the monovalent hydrocarbon group having 1 (1) the median diameter in dynamic light scattering method is 50 nm to 300 nm, (2) the average circularity is 0.80 to 1.0, (3) the refractive index is 1.380 to 1.420, (4) true density is 1.7000 g / cm 3 above and less than 1.9000 g / cm 3 , (5) Volume resistivity is 10 11 Ω cm or more, (6) the ratio expressed by the water vapor adsorption specific surface area / nitrogen adsorption specific surface area is 2.00 to 10.0, (7) the moisture absorption rate when exposed for 2 hours at 30°C / 90% RH relative to the dry mass when dried for 1 day at 150°C is 6.0 to 11 mass%.

2. The surface treated sol-gel silica particles according to claim 1, wherein, R 2 and R 4 is methyl.

3. The production method of the surface-treated sol-gel silica particles according to claim 1, having the following steps (Al) to (A6): Step (Al): a step of obtaining a mixed solvent dispersion liquid of hydrophilic sol-gel silica particles by hydrolysis-condensation of a 4-functional silane compound represented by the following formula (I), a partial hydrolysis-condensate thereof, or a mixture thereof in a mixed liquid containing a hydrophilic organic solvent and water in the presence of an alkaline substance, Si(OR 1 )4 (I) wherein R 1 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, Step (A2): a step of replacing the hydrophilic organic solvent in the dispersion medium of the mixed solvent dispersion liquid of the hydrophilic sol-gel silica particles obtained in step (Al) with water to obtain an aqueous dispersion liquid of the hydrophilic sol-gel silica particles, Step (A3): a step of refluxing the aqueous dispersion liquid of the hydrophilic sol-gel silica particles obtained in step (A2) at the reflux temperature of water for 5 hours or more, Step (A4): To the aqueous dispersion of hydrophilic sol-gel silica particles following step (A3), add 0.01 to 0.5 moles of a trifunctional silane compound, its partially hydrolyzed condensate, or a mixture thereof, represented by formula (II), relative to 1 mole of Si atoms of the hydrophilic sol-gel silica particles, thereby introducing R onto the surface of the hydrophilic sol-gel silica particles. 2 SiO 3 / 2 The unit is a process for obtaining an aqueous dispersion of pre-surface-treated sol-gel silica particles. R 2 Si(OR 3 )3 (II) wherein R 2 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms which can be substituted with a halogen atom, R 3 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, Step (A5): a step of replacing the dispersion medium of the aqueous dispersion liquid of the pre-surface-treated sol-gel silica particles obtained in step (A4) with a ketone-based solvent to obtain a ketone-based solvent dispersion liquid of the pre-surface-treated sol-gel silica particles, Step (A6): 0.1 to 0.5 moles of a silazane compound represented by the following formula (III), a 1-functional silane compound represented by the following formula (IV), or a mixture thereof is added with respect to 1 mole of Si atoms of the pre-surface-treated sol-gel silica particles in the ketone-based solvent dispersion of the pre-surface-treated sol-gel silica particles obtained in step (A5), and R 4 3SiO 1 / 2 unit, a step of obtaining surface-treated sol-gel silica particles, R 4 3SiNHSiR 4 3 (III) R 4 3SiX (IV) wherein R 4 independently represent a monovalent hydrocarbon group having 1 to 6 carbon atoms which can be substituted with a halogen atom, and X represents a hydroxyl group, an alkoxy group having 1 to 6 carbon atoms, or a chlorine atom.

4. The method for producing surface-treated sol-gel silica particles according to claim 3, wherein R 2 and R 4 is methyl.

5. An external agent for toner for electrostatic charge image development, comprising the surface-treated sol-gel silica particles according to claim 1 or 2.

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