Process for producing surface-treated fumed silica particles, surface-treated fumed silica particles, and external additive for electrostatic image developing toner

Abstract

The present invention is a production method of surface-treated fumed silica particles, characterized by comprising the following steps: (A1): a step of adding 1,3-divinyl-1,1,3,3-tetramethyldisilazane to raw fumed silica particles, thereby introducing a vinyl dimethyl silyl group to the surface of the raw fumed silica particles, to obtain pretreated silica particles, and (A2): a step of adding hexamethyldisilazane to the pretreated silica particles, thereby introducing a trimethyl silyl group to the surface of the pretreated silica particles, to obtain surface-treated fumed silica particles. Thus, it is possible to provide surface-treated fumed silica particles having few coarse aggregated particles and capable of imparting good fluidity when added to toner, a production method thereof, and a toner external additive composed of the surface-treated fumed silica particles.

Description

TECHNICAL FIELD

[0001] The present application relates to surface-treated fumed silica particles, a method for producing the same, and an external additive for toner for developing an electrostatic image used in electrophotography, electrostatic recording, and the like. BACKGROUND

[0002] Dry developers used in electrophotography and the like can be roughly classified into single-component developers using toner itself in which a colorant is dispersed in a binder resin and two-component developers in which a carrier is mixed in the toner, and in order to make process adaptability when copying is performed using these developers, the developers need to have excellent flowability, anti-caking property, fixing property, charging property, cleaning property, and the like. Also, in particular, in order to improve the flowability, anti-caking property, fixing property, and cleaning property, inorganic fine particles are often used as a toner external additive.

[0003] However, the dispersibility of inorganic fine particles has a large influence on toner characteristics, and when the dispersibility is not uniform, the flowability, anti-caking property, fixing property cannot have desired characteristics or the cleaning property is insufficient, and toner adhesion occurs on a photoreceptor, thereby becoming a cause of image defects such as black point-like defects. For the purpose of improving these defects, various proposals have been made for hydrophobically treating the surface of inorganic fine particles.

[0004] It is known that in inorganic fine particles for use as described above, fumed silica has a small primary particle diameter, and by controlling the charging property thereof formed by surface treatment, it has an excellent function as a toner external additive (Patent Documents 1, 2, and 3).

[0005] However, although fumed silica has a small primary particle diameter, it is easily aggregated, and the aggregated particle diameter thereof is usually 10 μm or more. Such aggregated particles are dissociated and dispersed in toner by strong friction in the process of being dispersed in toner, but if larger aggregates are formed, the dispersibility in toner is poor, and due to the presence of such aggregated particles in toner, the flowability is sometimes decreased, toner is caused to be peeled off, or problems such as the occurrence of white points in a printed image are caused.

[0006] From the above-described viewpoint, a method of classifying and pulverizing aggregated particles produced after hydrophobic treatment and using only fine powder thereof has been proposed (Patent Document 4). However, as described above, the manufacturing efficiency of classified pulverization is poor, and costs are consumed, and thus it is not a preferable method.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT DOCUMENTS

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-145325

[0010] Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 2006-99006

[0011] Patent Literature 3: Japanese Patent Application Laid-Open (JP-A) No. 2007-34224

[0012] Patent Literature 4: Japanese Patent Application Laid-Open (JP-A) No. 2010-085837 SUMMARY

[0013] Technical Problem to be Solved by the Invention

[0014] The present invention has been achieved in view of the above-described circumstances, and aims to provide surface-treated fumed silica particles having few coarse aggregated particles and capable of imparting good fluidity when added to toner, a method for producing the same, and a toner external additive composed of the surface-treated fumed silica particles.

[0015] Technical Means for Solving the Technical Problem

[0016] To solve the above-described technical problem, the present invention provides a method for producing surface-treated fumed silica particles, the method having the following steps:

[0017] (A1) a step of adding 1,3-divinyl-1,1,3,3-tetramethyldisilazane to raw fumed silica particles, thereby introducing a vinyl dimethylsilyl group to the surface of the raw fumed silica particles, to obtain pretreated silica particles, and

[0018] (A2) a step of adding hexamethyldisilazane to the pretreated silica particles, thereby introducing a trimethylsilyl group to the surface of the pretreated silica particles, to obtain surface-treated fumed silica particles.

[0019] If the above-described method for producing surface-treated fumed silica particles is used, surface-treated fumed silica particles having few coarse aggregated particles and capable of imparting good fluidity when added to toner can be produced.

[0020] Further, it is preferable that the BET specific surface area of the raw fumed silica particles be 40 to 400 m 2 / g.

[0021] If the above-described raw fumed silica particles are used, dispersibility is excellent and aggregation is unlikely to occur when surface treatment is performed with a silazane compound.

[0022] Further, in the process (Al), the amount (g) of the 1,3-divinyl-1, 1,3,3- tetramethyldisilazane added is preferably an amount represented by {the amount (g) of the raw fumed silica particles used in the process (Al) x the BET specific surface area (m2 / g) of the raw fumed silica particles} / B, 2

[0023] where B is a number of 5,000 to 100,000.

[0024] If the amount of the 1,3-divinyl-1, 1,3,3-tetramethyldisilazane added is within such a range, it is preferable in terms of cost, and the efficiency of the hydrophobating treatment by the hexamethyldisilazane in the process (A2) can be improved.

[0025] Further, in the process (A2), the amount (g) of the hexamethyldisilazane added is preferably an amount represented by {the amount (g) of the pretreated silica particles used in the process (A2) x the BET specific surface area (m2 / g) of the raw fumed silica particles} / C, 2

[0026] where C is a number of 150 to 3,000.

[0027] By making the amount of the hexamethyldisilazane added within such a range, the generation of agglomerates at the time of reaction can be suppressed, and the hydrophobicity of the silica particles can be further improved.

[0028] Further, the present application provides a surface-treated fumed silica particle which is obtained by treating the surface of a fumed silica particle with 1,3-divinyl-1, 1,3,3-tetramethyldisilazane and hexamethyldisilazane,

[0029] The BET specific surface area of the surface-treated fumed silica particle is 30 m 2 / g or more and less than 400 m 2 / g,

[0030] The proportion of particles of 1.5 μm or more of the surface-treated fumed silica particle, which is calculated from the volume-based standard particle size distribution obtained using a laser diffraction method, is less than 10%,

[0031] The methanol hydrophobicity of the surface-treated fumed silica particle is 68% or more and 78% or less, and

[0032] When 1 part by mass of the surface-treated fumed silica particle is mixed with 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm to form a mixture, the agglomeration degree of the mixture is 20% or less.​​

[0033] In the present application, surface-treated fumed silica particles having the above-described characteristics can be produced.

[0034] Further, in the present application, an external additive for toner for electrostatic image development containing the above-described surface-treated fumed silica particles is provided.

[0035] The surface-treated fumed silica particles of the present application, when used as an external additive for toner, can impart good flowability and printing characteristics to the toner.

[0036] Effects of the Invention

[0037] According to the present application as described above, surface-treated fumed silica particles capable of improving the printing image defects or low toner flowability when a small particle size fumed silica of the related art is used as an external additive, and an electrostatic charge developing toner and an electrostatic charge developing toner external additive using the surface-treated fumed silica particles can be provided. DETAILED DESCRIPTION

[0038] As described above, development of an external additive for toner composed of surface-treated fumed silica particles having little agglomerated particles and capable of imparting good flowability when added to toner is sought.

[0039] To achieve the above object, the present inventors have conducted earnest research, and as a result, have found that by surface-treating fumed silica particles with vinyltetramethyldisilazane and hexamethyldisilazane, surface-treated fumed silica particles having little agglomeration, further excellent dispersibility when added to toner, and no printing image defects can be obtained, and thus have completed the present application.

[0040] That is, the present application is a method for producing surface-treated fumed silica particles, the method having the following steps:

[0041] (A1) a step of adding 1,3-divinyl-1,1,3,3-tetramethyldisilazane to raw fumed silica particles, thereby introducing a vinyl dimethylsilyl group to the surface of the raw fumed silica particles, to obtain pretreated silica particles, and

[0042] (A2) a step of adding hexamethyldisilazane to the pretreated silica particles, thereby introducing a trimethylsilyl group to the surface of the pretreated silica particles, to obtain surface-treated fumed silica particles.

[0043] Hereinafter, the present application will be described in detail, but the present application is not limited thereto.

[0044] (Starting material fumed silica particles)

[0045] The fumed silica particles (fumed silica fine particles) used as the starting material in the present application are also referred to as dry-process silica, and the method of production thereof is not particularly limited as long as it is produced by a method of flame hydrolysis of a silicon compound, oxidation by a flame combustion method, or a method of simultaneously using these reactions. Among them, fumed silica particles produced by a flame hydrolysis method are suitably used. As commercially available products, "AEROSIL" manufactured by NIPPON AEROSIL CO., LTD. or Evonik Degussa Co., Ltd., "CAB-O-SIL" manufactured by Cabot Corporation, "HDK" manufactured by Wacker Chemie AG, "REOLOSIL" manufactured by Tokuyama Corporation, and the like are available.

[0046] The method of production of fumed silica particles by a flame hydrolysis method is, for example, a method in which a gas of a starting material silicon compound such as silicon tetrachloride is introduced into a mixing chamber of a burner together with an inert gas, mixed with hydrogen and air to form a mixed gas at a prescribed ratio, and the mixed gas is combusted at a temperature of 1,000 to 3,000°C in a reaction chamber to produce, and after cooling, the produced silica is captured by a filter.

[0047] As the silicon compound used as the starting material of the fumed silica particles, various inorganic silicon compounds and organic silicon compounds can be listed. For example, inorganic silicon compounds such as silicon tetrachloride, silicon trichloride, and silicon dichloride; siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, and octamethyltrisiloxane; alkoxysilanes such as methyltrimethoxysilane, tetramethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, methyltributoxysilane, diethyldipropoxysilane, and trimethylbutoxysilane; and organic silicon compounds such as tetramethylsilane, diethylsilane, hexamethyldisilazane, and oligomers and polymers of these components can be listed.

[0048] For the hydrolysis and combustion decomposition of such a silicon compound in a flame, after the silicon compound is purified as needed by distillation or the like, it is introduced into a flame such as an oxyhydrogen flame by a method of heating and evaporating it to flow it with an inert gas such as nitrogen or a method of atomizing and supplying it to a flame, and it is reacted in the flame, but at this time, a combustible gas such as hydrogen gas or methane gas can be used as a combustion-supporting gas. As the combustion-supporting gas, as long as it is a gas that does not leave a residue, any gas can be used, and there is no particular limitation. The silica produced in the hydrolysis or combustion decomposition of these silicon compounds can be captured by a known method such as a bag filter or a cyclone separator.

[0049] The BET specific surface area of the raw fumed silica particles in the present application is preferably 40 to 400 m2 / g 2 If it is within this range, the dispersibility is excellent and agglomeration is unlikely to occur during the surface treatment with a silazane compound described later.

[0050] The raw fumed silica particles can be used singly or in combination of two or more kinds.

[0051] (Method for producing surface-treated fumed silica particles)

[0052] The method for producing the surface-treated fumed silica particles of the present application has the following step (Al) and step (A2).

[0053] Step (Al): Step of introducing a vinyl dimethylsilyl unit to the surface of silica

[0054] Step (A2): Step of introducing a trimethylsilyl unit to the surface of silica

[0055] Process (A1): Process for introducing a vinyl dimethylsilyl unit to the surface of silica

[0056] Step (Al) is a step of adding 1,3-divinyl-1,1,3,3-tetramethyldisilazane (hereinafter, referred to as divinyltetramethyldisilazane) to the raw fumed silica particles, thereby introducing a vinyl dimethylsilyl group to the surface of the raw fumed silica particles to obtain a pretreated silica particle. By this step, the surface treatment in the following step (A2) is performed more uniformly and highly.

[0057] As the raw fumed silica particles, the above-described fumed silica particles can be used.

[0058] As the method for surface treatment of the raw fumed silica particles in step (Al) with divinyltetramethyldisilazane, a dry method and a wet method for surface treatment of general powders can be used. From the viewpoint of productivity, it is preferable to use a dry method, and as the method for adding divinyltetramethyldisilazane in the dry method, it can be added by dropping, spraying with a sprayer, or the like while stirring the raw fumed silica particles in a reactor. In addition, divinyltetramethyldisilazane can be used as it is or can be used after being diluted with a solvent such as toluene, xylene, hexane, or the like.

[0059] When the raw fumed silica particles are surface-treated, the surface treatment efficiency is made high by previously causing the silica surface to contain water, and therefore, it is preferable that, at this time, the stirring is performed for about 0.5 to 2.0 hours after the addition of water.

[0060] As the method of adding water, in addition to the method of adding or spraying water while stirring the raw fumed silica particles in the reactor, water can be added in the form of steam.

[0061] The amount of water to be added with respect to the raw fumed silica particles is preferably an amount calculated by the following formula.

[0062] Amount of water to be added (g) = {amount of raw fumed silica particles used in Step (Al) (g) x BET specific surface area of raw fumed silica particles (m 2 / g)} / A

[0063] In the above formula, A is preferably a number of 300 to 200,000, and more preferably a number of 500 to 2,500. If A is 300 or more, the aggregation of the raw fumed silica particles due to water can be suppressed, and thus is preferred. If A is 200,000 or less, the reactivity of the silazane compound can be further improved, and thus is preferred.

[0064] The amount of divinyltetramethyldisilazane to be added with respect to the raw fumed silica particles is preferably an amount calculated by the following formula.

[0065] Amount of divinyltetramethyldisilazane to be added (g) = {amount of raw fumed silica particles used in Step (Al) (g) x BET specific surface area of raw fumed silica particles (m 2 / g)} / B

[0066] In the above formula, B is preferably a number of 5,000 to 100,000, and more preferably a number of 10,000 to 80,000. If B is 5,000 or more, the cost is taken into consideration, and thus is preferred. If B is 100,000 or less, the efficiency of the hydrophobizing treatment by hexamethyldisilazane in Step (A2) can be improved, and thus is preferred.

[0067] The reaction of the raw fumed silica particles with divinyltetramethyldisilazane in Step (Al) can be performed under the conditions generally used for the surface treatment of silica with a silazane compound, and although the reaction can be performed at room temperature, it is preferred that the mixture be stirred at 50 to 70°C for 0.5 to 3 hours after the addition of divinyltetramethyldisilazane.

[0068] Process (A2): Process for introducing a trimethylsilyl unit to the surface of silica

[0069] The step (A2) is a step of adding hexamethyldisilazane to the pretreated silica particles obtained in the step (Al) to introduce trimethylsilyl groups to the surface of the pretreated silica particles, thereby obtaining surface-treated fumed silica particles subjected to hydrophobization.

[0070] As the method for surface treatment of the pretreated silica particles in the step (A2) with hexamethyldisilazane, a dry method and a wet method which can be used for surface treatment of general powders can be used. From the viewpoint of productivity, it is preferable to use a dry method, and as the method for adding hexamethyldisilazane in the dry method, it can be performed by dropping, spraying with a sprayer, or the like while stirring the pretreated silica particles in a reactor. In addition, hexamethyldisilazane can be used as it is, or can be used after being diluted with a solvent such as toluene, xylene, hexane, or the like.

[0071] Further, as in the step (Al), in the step (A2) as well, it is preferable that the silica surface contains water, because this further improves the efficiency of surface treatment. As described above, it is sufficient that water is added in the step (Al), but water can also be added separately in the step (A2).

[0072] The amount of hexamethyldisilazane added with respect to the pretreated silica particles is preferably an amount calculated by the following formula.

[0073] Amount of hexamethyldisilazane added (g) = {amount of pretreated silica particles used in the step (A2) (g) x BET specific surface area of raw fumed silica particles (m 2 / g)} / C

[0074] In the above calculation formula, C is preferably a number from 150 to 3,000, and more preferably a number from 200 to 1,000. If C is 150 or more, the generation of agglomerates at the time of reaction can be suppressed, and if C is 3,000 or less, the degree of hydrophobicity of the silica particles can be further improved.

[0075] The reaction of the pretreated silica particles in the step (A2) with hexamethyldisilazane can be performed under conditions used for surface treatment of silica with general silazane compounds, and although the reaction can be performed at room temperature, it is preferable to stir the mixture at 50 to 100°C for 0.5 hours to 3 hours after the addition of hexamethyldisilazane.

[0076] Process (A3): Process for drying the surface-treated fumed silica particles

[0077] The production method of the surface-treated fumed silica particles of the present application can directly air-dry, naturally cool, or the like, the surface-treated fumed silica particles after the step (A2), but preferably further has a step (A3) of drying the surface-treated fumed silica particles. The drying conditions are not particularly limited, and preferably drying at 140°C to 250°C under a nitrogen stream for about 0.5 hours to 3 hours.

[0078] (Surface-treated fumed silica particles)

[0079] The surface-treated fumed silica particles obtained by the production method of the surface-treated fumed silica particles of the present application are surface-treated fumed silica particles in which the surface of fumed silica particles has been treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane and hexamethyldisilazane,

[0080] (1) The BET specific surface area of the surface-treated fumed silica particles is 30 m 2 / g or more and less than 400 m 2 / g,

[0081] (2) The proportion of particles of 1.5 μm or more, calculated from the volume standard particle size distribution obtained by a laser diffraction method, of the surface-treated fumed silica particles is less than 10%,

[0082] (3) The methanol hydrophobicity of the surface-treated fumed silica particles is 68% or more and 78% or less, and

[0083] (4) When 1 part by mass of the surface-treated fumed silica particles is mixed with 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm to form a mixture, the coagulation degree of the mixture is 20% or less.

[0084] By simultaneously having the above properties (1) to (4), when used as an external additive for toner, the surface-treated fumed silica particles impart good flowability and printing characteristics to the toner.

[0085] (1) BET specific surface area

[0086] The BET specific surface area depends on the primary particle diameter, and is particularly preferably 40 to 200 m 2 / g. If the BET specific surface area is less than 30 m 2 / g, the dispersibility in toner is poor when added to toner as an external additive for electrostatic image developing toner, the flowability-improving effect is poor, and if it is 400 m 2 / g or more, coagulation is easy.

[0087] (2) Aggregated particle ratio

[0088] The volume standard particle size distribution obtained by the laser diffraction method can be the volume standard particle size distribution obtained by the laser diffraction method for a 0.5 mass% methanol dispersion liquid of the surface-treated fumed silica particles (dispersed by irradiation of ultrasonic waves at an output of 30 W / L for 10 minutes). If the proportion of particles of 1.5 μm or more is 10% or more, the dispersibility in the toner is poor when added to the toner as an external additive for electrostatic image developing toner, and the flowability and print quality of the toner are deteriorated because of the presence of many large agglomerated particles. The proportion is more preferably 8% or less, and particularly preferably 5% or less.

[0089] (3) Methanol hydrophobicity

[0090] If the methanol hydrophobicity of the surface-treated fumed silica particles is less than 68%, the dispersibility in the toner is poor when added to the toner as an external additive for electrostatic image developing toner, and the flowability and print quality of the toner are deteriorated because of the agglomeration of the silica particles with each other due to the residual silanol groups on the surface of the silica. If the methanol hydrophobicity is more than 78%, the charge amount of the toner becomes too high when added to the toner. In addition, the methanol hydrophobicity of the present application refers to the value measured under the following conditions.

[0091] <Measurement method of methanol hydrophobicity>

[0092] To 60 ml of a methanol aqueous solution having a volume concentration of 50% (temperature: 25°C), 0.2 g of the surface-treated fumed silica particles were added, and stirring was performed using a stirrer. Then, while adding methanol to the liquid on which the silica particles were floating on the surface, the transmittance was measured by irradiating light having a wavelength of 780 nm to the methanol aqueous solution, and the volume concentration (%) of methanol in the methanol aqueous solution at which the transmittance was 80% was defined as the methanol hydrophobicity.

[0093] (4) Toner aggregation degree

[0094] The agglomeration degree of the mixture of the polyester resin particles and the surface-treated fumed silica particles indicates the agglomeration of the toner when the silica particles are dispersed in the toner, and the smaller the value of the agglomeration degree, the less the amount of the agglomeration of the toner, and the better the toner can be evaluated.

[0095] If the agglomeration degree of a mixture of 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm and 1 part by mass of surface-treated fumed silica particles is higher than 20%, when the surface-treated fumed silica particles are added to toner as an external additive for electrostatic image developing toner, the generation of agglomerates increases due to the adhesion of toner to each other, or the flowability of toner becomes poor. The agglomeration degree is preferably 10% or less. In addition, the agglomeration degree in the present application means a value measured under the following conditions.

[0096] <Measurement method of agglomeration degree>

[0097] A mixture of 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm obtained by a laser diffraction / scattering method and 1 part by mass of surface-treated fumed silica particles was formed using a mixer, and 2 g of the mixture was vibrated for 60 seconds using a sieve having a mesh size of 150 μm, 75 μm, and 45 μm from the top and an amplitude of 1 mm and a frequency of 1 Hz. After the vibration, the amounts remaining on the sieves were measured, and the calculation was performed by the following formula.

[0098] Agglomeration degree (%) = (W1 + 0.6 x W2 + 0.2 x W3) / 2 x 100

[0099] W1: amount remaining on a 150 μm mesh sieve (g)

[0100] W2: amount remaining on a 75 μm mesh sieve (g)

[0101] W3: amount remaining on a 45 μm mesh sieve (g)

[0102] (Electrostatic image developing toner external additive)

[0103] In addition, in the present application, an electrostatic image developing toner external additive containing the above-described surface-treated fumed silica particles is provided. The surface-treated fumed silica particles of the present application, when used as a toner external additive, can impart good flowability and printing properties to toner.

[0104] Examples

[0105] Hereinafter, the present application will be specifically described using examples and comparative examples, but the present application is not limited by these examples.

[0106] (Production of surface-treated fumed silica particles)

[0107] [Example 1-1]

[0108] Into a 5 liter reaction device equipped with a stirrer, a spray device, and a thermometer, 240 g of surface-treated fumed silica particles having a BET specific surface area of 50 m 2 / g of fumed silica particles. After purging the air in the reaction apparatus with dry nitrogen, 18g of water was sprayed onto the surface while stirring. After stirring at 25°C for 1 hour, 0.6g of divinyltetramethyldisilazane was sprayed onto the surface and stirred at 60°C for 1 hour. After temporarily cooling to 25°C, 60g of hexamethyldisilazane was sprayed onto the surface and stirred at 60°C for 1 hour. The surface was then further dried at 150°C under a nitrogen flow while stirring for 3 hours. After cooling, 243g of white powder of surface-treated fumed silica particles (I) was obtained.

[0109] [Examples 1-2]

[0110] Except that the amount of divinyltetramethyldisilazane added in Example 1-1 was 1.2 g, the same steps as in Example 1-1 were performed to obtain 244 g of white powder of surface-treated fumed silica particles (II).

[0111] [Examples 1-3]

[0112] In addition to using a BET specific surface area of ​​90m² in Example 1-1 2 / g of fumed silica particles replaced BET, with a specific surface area of ​​50m². 2 Apart from the fumed silica particles of / g, the same steps as in Example 1-1 were performed to obtain 242g of white powder of surface-treated fumed silica particles (III).

[0113] [Examples 1-4]

[0114] 148g of BET with a specific surface area of ​​130m² was added to a 5-liter reaction vessel equipped with a mixer, spray device, and thermometer. 2 / g of fumed silica particles. After purging the air in the reaction apparatus with dry nitrogen, 13g of water was sprayed onto the surface with stirring using a sprayer. After stirring at 25°C for 1 hour, 0.4g of divinyltetramethyldisilazane was sprayed onto the surface and stirred at 60°C for 1 hour. After temporarily cooling to 25°C, 60g of hexamethyldisilazane was sprayed onto the surface and stirred at 60°C for 1 hour. The surface was then further dried at 150°C under a nitrogen stream with stirring for 3 hours. After cooling, 51g of white powder of surface-treated fumed silica particles (IV) was obtained.

[0115] [Examples 1-5]

[0116] In addition to using a BET specific surface area of ​​200m² in Examples 1-4 2 / g of fumed silica microparticles replaces BET, resulting in a specific surface area of ​​130m². 2Apart from the fumed silica particles, the same steps as in Examples 1-4 were performed to obtain 153g of white powder of surface-treated fumed silica particles (V).

[0117] [Comparative Example 1-1]

[0118] 240g of BET with a specific surface area of ​​50m² was added to a 5-liter reaction vessel equipped with a mixer, spray device, and thermometer. 2 / g of fumed silica particles. After purging the air in the reaction apparatus with dry nitrogen, 18g of water was sprayed onto the surface with stirring using a spraying device. After stirring at 25°C for 1 hour, 60g of hexamethyldisilazane was sprayed onto the surface with stirring at 60°C for 1 hour, and then further dried at 150°C under a nitrogen flow with stirring for 3 hours. After cooling, 243g of white powder of surface-treated fumed silica particles (VI) was obtained.

[0119] [Comparative Examples 1-2]

[0120] 148g of BET with a specific surface area of ​​130m² was added to a 5-liter reaction vessel equipped with a mixer, spray device, and thermometer. 2 / g of fumed silica particles. After purging the air in the reaction apparatus with dry nitrogen, 13g of water was sprayed onto the surface with stirring using a spraying device. After stirring at 25°C for 1 hour, 60g of hexamethyldisilazane was sprayed onto the surface with stirring at 60°C for 1 hour, and then further dried at 150°C under a nitrogen flow with stirring for 3 hours. After cooling, 51g of white powder of surface-treated fumed silica particles (VII) was obtained.

[0121] [Comparative Examples 1-3]

[0122] 240g of BET with a specific surface area of ​​50m² was added to a 5-liter reaction vessel equipped with a mixer, spray device, and thermometer. 2 / g of fumed silica particles. After purging the air in the reaction apparatus with dry nitrogen, 18g of water was sprayed onto the surface with stirring using a spraying device. After stirring at 25°C for 1 hour, 60g of divinyltetramethyldisilazane was sprayed onto the surface with stirring at 60°C for 1 hour, and then further dried at 150°C under a nitrogen flow with stirring for 3 hours. After cooling, 247g of white powder of surface-treated fumed silica particles (VIII) was obtained.

[0123] The surface-treated fumed silica particles (I) to (VIII) obtained through the above process were measured according to the following measurement methods (1) to (4), and the results are shown in Table 1.

[0124] [Determination Method]

[0125] (1) BET specific surface area

[0126] The BET specific surface area was measured by the BET single point method using nitrogen gas with a full-automatic BET specific surface area measuring device (Macsorb HM model-1201 manufactured by Mountech Co., Ltd.).

[0127] (2) Agglomerated particle ratio

[0128] A glass bottle was charged with 0.1 g of the surface-treated fumed silica particles and 19.9 g of methanol, and placed in an ultrasonic cleaner, and ultrasonic waves with an output power of 30 W / L were irradiated for 10 minutes to disperse the silica particles in the methanol. The dispersion was measured using a laser diffraction / scattering type particle size distribution measuring device (LA-950V2 manufactured by HORIBA, Ltd.), and the agglomerated particle ratio of 1.5 μm or more in particle size was calculated from the volume-standard particle size distribution obtained by the measurement.

[0129] (3) Methanol hydrophobicity

[0130] A powder wettability tester (WET101P manufactured by RHESCA CO., LTD.) was used to add 0.2 g of the surface-treated fumed silica particles to 60 ml of a methanol aqueous solution having a volume concentration of 50% (temperature: 25°C), and stirring was performed using a stirrer. Subsequently, while methanol was added dropwise to the liquid on which the silica particles were floating on the surface, the methanol aqueous solution was irradiated with light having a wavelength of 780 nm, and the transmittance was measured. The transmittance was measured while the spherical silica particles were suspended and settled, and the volume concentration (%) of methanol in the methanol aqueous solution at which the transmittance was 80% was taken as the methanol hydrophobicity.

[0131] (4) Toner agglomeration degree

[0132] A mixer was used to mix 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm obtained by the laser diffraction / scattering method with 1 part by mass of the surface-treated fumed silica particles. A powder property evaluation device (Powder Tester Model PT-X manufactured by Hosokawa Micron Corporation) was used to vibrate 2 g of the mixture for 60 seconds with a sieve having mesh openings of 150 μm, 75 μm, and 45 μm from the top, and an amplitude of 1 mm and a frequency of 1 Hz, and then the amount remaining on the sieve was measured, and the agglomeration degree was calculated by the following formula.

[0133] Agglomeration degree (%) = (W1 + 0.6 x W2 + 0.2 x W3) / 2 x 100

[0134] W1: amount remaining on the 150 μm mesh sieve (g)

[0135] W2: Residual amount (g) on 75 μm mesh sieve

[0136] W3: Residual amount (g) on 45 μm mesh sieve

[0137] [Table 1]

[0138]

[0139] As shown in Table 1, the surface-treated fumed silica particles obtained in Examples 1-1 to 1-5 had a small proportion of agglomerated silica particles, a sufficient methanol hydrophobicity, and further, a small degree of agglomeration of toner. On the other hand, in Comparative Examples 1-1 and 1-2 in which surface treatment was not performed using divinyltetramethyldisilazane, and in Comparative Example 1-3 in which surface treatment was not performed using hexamethyldisilazane, the surface-treated fumed silica particles were observed to have a large amount of agglomeration of silica particles with each other, a low methanol hydrophobicity, and a high degree of agglomeration when added to toner.

[0140] (Manufacture of external additive mixed toner and two-component developer)

[0141] [Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-3]

[0142] After 96 parts by weight of a polyester resin having a Tg of 60°C and a softening point of 110°C was melt-kneaded with 4 parts by weight of CARMINE 6BC (manufactured by SUMIKA COLOR CO., LTD.) as a colorant, the mixture was pulverized and classified to obtain a toner having a volume median particle diameter of 7 μm. Using a sample mill, 10 g of the toner was mixed with 0.2 g of the surface-treated fumed silica particles obtained in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-3 to obtain an external additive mixed toner.

[0143] A two-component developer was prepared by mixing 3 parts by mass of the above external additive mixed toner with 97 parts by mass of a standard ferrite L (The Imaging Society of Japan) as a carrier. The two-component developer obtained by the above procedure was measured according to the following methods (5) to (9), and the results of the measurement are shown in Table 2.

[0144] (5) Toner charge amount

[0145] After exposing the above-mentioned two-component developer to each condition of high temperature and high humidity (30°C, 90% RH), medium temperature and medium humidity (25°C, 55% RH), and low temperature and low humidity (10°C, 15% RH) for 1 day, the amount of triboelectric charging of each sample was measured under the same condition using a blow off powder triboelectric charging amount measuring device (manufactured by KYOCERA Chemical Corporation, TB-200).

[0146] (6) Adhesion of toner to photoreceptor

[0147] The above-mentioned two-component developer was put into a developing machine equipped with an organic photoreceptor, and a print test of 30,000 sheets was performed in an environment of 25°C, 50% RH. At this time, the adhesion of toner to photoreceptor was observed in the reverse white in a full solid image (full-bet image). Among them, with respect to the degree of reverse white, the number of reverse white sites per 1 cm 2 was 10 or more, the number was 1 to 9, and the number was 0, respectively.

[0148] (7) Photoreceptor wear

[0149] In the print test of the above-mentioned (6), the photoreceptor wear where image disorder was detected was evaluated according to the following criteria.

[0150] A: No image disorder

[0151] B: No large-area image disorder

[0152] C: Presence of image disorder

[0153] (8) Evaluation of image loss (white spot)

[0154] The above-mentioned two-component developer was exposed to an environment of 30°C, 90% RH for 1 day, and then, after performing solid printing (image density: 100%) of 20 cm square for 5,000 sheets continuously, the above-mentioned two-component developer was again left to stand in an environment of 30°C, 90% RH. This operation was repeated 60 times, and printing of a total of 300,000 sheets was performed. The 10th printed matter on the first day was taken as printed matter 1, and the last printed matter on the last day was taken as printed matter 2.

[0155] The image of the above-mentioned obtained printed matter 2 was observed, and the presence or absence of image loss (white spot) was evaluated according to the following criteria.

[0156] A: No image loss (no white spot) observed with the naked eye

[0157] B: One or more white spots (images in which reverse white is in a granular form) observed with the naked eye

[0158] C: More than 5 and less than 9 white spots observed with the naked eye

[0159] D: More than 10 white spots observed with the naked eye

[0160] (9) Evaluation of concentration change (ΔΕ)

[0161] The color difference (ΔΕ) in the CIE 1976 (L*a*b*) color space was measured using a reflection densitometer X-rite 938 (manufactured by X-rite Inc.) with JIS Z 8781-5 as the standard, and the concentration change of the printed matter 2 relative to the above-mentioned printed matter 1 was evaluated according to the following standards.

[0162] A: ΔΕ difference less than 1

[0163] B: ΔΕ difference of 1 or more and less than 2.5

[0164] C: ΔΕ difference of 2.5 or more and less than 3.0

[0165] D: ΔΕ difference of 3.0 or more

[0166] [Table 2]

[0167]

[0168] As shown in Table 2, the surface-treated fumed silica particles obtained in Examples 1-1 to 1-5 were used as a toner external additive for a two-component developer, and no printed image defects were observed. In contrast, the toner charge amount of the developer using the surface-treated fumed silica particles obtained in Comparative Examples 1-1 to 1-3 varied greatly depending on the environment, and the print characteristics were poor.

[0169] In addition, the present application is not limited to the above-described embodiments. The above-described embodiments are examples, and technical solutions having substantially the same composition and exerting the same effects as the technical concept described in the claims of the present application are included within the technical scope of the present application.

Claims

1. A method for producing surface-treated fumed silica particles, characterized by, The production method has the following steps: (A1): a step of adding 1,3-divinyl-1,1,3,3-tetramethyldisilazane to raw fumed silica particles to introduce a vinyl dimethyl silyl group to the surface of the raw fumed silica particles, thereby obtaining pretreated silica particles, and (A2): a step of adding hexamethyldisilazane to the pretreated silica particles to introduce a trimethyl silyl group to the surface of the pretreated silica particles, thereby obtaining surface-treated fumed silica particles, wherein the surface-treated fumed silica particles have a BET specific surface area of 30 m 2 / g or more and less than 400 m 2 / g, the proportion of particles of 1.5 μm or more of the surface-treated fumed silica particles calculated from a volume standard particle size distribution obtained using a laser diffraction method is less than 10%, the methanol hydrophobicity of the surface-treated fumed silica particles is 68% or more and 78% or less, and when 1 part by mass of the surface-treated fumed silica particles is mixed with 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm to form a mixture, the coaggregation degree of the mixture is 20% or less.

2. The method for manufacturing surface-treated fumed silica particles according to claim 1, characterized by, The raw fumed silica particles have a BET specific surface area of 40 to 400 m 2 / g.

3. The production method of surface-treated fumed silica particles according to claim 1, characterized in that In the process (A1), the amount (g) of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane to be added is an amount represented by {the amount (g) of the raw material fumed silica particles used in the process (A1) x the BET specific surface area (m2 / g) of the raw material fumed silica particles} / B, wherein B is a number of 5,000 to 100,000. 2 / g)} / B, wherein B is a number of 5,000 to 100,000.

4. The production method of surface-treated fumed silica particles according to claim 2, characterized in that In the process (A1), the amount (g) of the 1,3-divinyl-1,1,3,3-tetramethyldisilazane to be added is an amount represented by {the amount (g) of the raw material fumed silica particles used in the process (A1) x the BET specific surface area (m2 / g) of the raw material fumed silica particles} / B, wherein B is a number of 5,000 to 100,000. 2 / g)} / B, wherein B is a number of 5,000 to 100,000.

5. The production method of surface-treated fumed silica particles according to any one of claims 1 to 4, characterized in that In the process (A2), the amount (g) of the hexamethyldisilazane added is represented by {the amount (g) of the pretreated silica particles used in the process (A2) x the BET specific surface area (m2 / g) of the raw gas-phase process silica particles} / C, wherein C is a number from 150 to 3,000. 2 / g)} / C, wherein C is a number from 150 to 3,000.

6. Surface-treated fumed silica particles produced by the production method of surface-treated fumed silica particles according to any one of claims 1 to 5, characterized in that The BET specific surface area of the surface-treated fumed silica particles is 30 m 2 / g or more and less than 400 m 2 / g, the proportion of particles of 1.5 μm or more of the surface-treated fumed silica particles calculated from a volume standard particle size distribution obtained using a laser diffraction method is less than 10%, the methanol hydrophobicity of the surface-treated fumed silica particles is 68% or more and 78% or less, and when 1 part by mass of the surface-treated fumed silica particles is mixed with 100 parts by mass of polyester resin particles having a volume median particle diameter of 5 to 8 μm to form a mixture, the coaggregation degree of the mixture is 20% or less.

7. An external additive for toner used in electrostatic image development, characterized in that, The external additive contains the surface-treated fumed silica particles according to claim 6.

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