JP2010085837A - Hydrophobic silica fine particle and electrophotographic toner composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silica fine particles which have small primary particle diameters and are useful as an external additive for a toner, wherein: the silica fine particles do not contain coarse agglomerate particles, which are causative of lowering in the dispersibility in a toner and/or in the fluidity of a toner, and rarely cause the separation from a toner; and the silica fine particles are therefore excellent in the uniform dispersibility in a toner and in the effect of imparting fluidity to a toner, and can inhibit the occurrence of white spots on a printed image. <P>SOLUTION: Hydrophobic silica fine particles obtained by subjecting hydrophilic silica fine particles which are prepared by a gas-phase process and have a mean primary particle diameter of 20 to 100 nm to hydrophobization with either hexamethyldisilazane or a polysiloxane, wherein the hydrophobic silica fine particles are characterized in that the content of agglomerate particles having volume-based particle diameters of 1.5 μm or above is less than a prescribed value 8% as determined when the volume-based diameter of the particles is measured by the laser diffraction method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to hydrophobic silica fine particles which are added for the purpose of improving fluidity, preventing caking, adjusting the charge, etc. in powder materials such as powder paints, electrophotographic toners and cosmetics, and the hydrophobic silica fine particles The present invention relates to a toner composition for electrophotography using

  The so-called silica fine particles, which have improved the chargeability and hydrophobicity by treating the surface of inorganic oxide powders such as fine silica, titania, and alumina with organic substances, are used in electrophotography including copying machines, laser printers, plain paper facsimiles, etc. Widely used as a toner fluidity improver or a charge control agent.

  Conventionally, among inorganic oxide powders used in such applications, gas phase method silica (silica produced by a dry method) has a small primary particle size, and it is possible to control chargeability by surface treatment and hydrophobization treatment. Therefore, it is expected to exhibit an excellent function as a toner external additive, and is most commonly used (for example, Patent Documents 1 to 3).

  However, although vapor phase silica has a small primary particle size, it is easy to aggregate because of its small primary particle size, and many agglomerated particles are formed, and the aggregated particle size is usually 10 μm to 200 μm or more.

  Such agglomerated particles are dispersed between the toners while being loosened by receiving a strong frictional force in the dispersion process to the toner. Unfortunately, when such agglomerated particles are mixed in the toner, the fluidity is lowered, and the toner easily drops off from the toner and causes a problem of an abnormal image appearing as a white spot on the paper surface.

Patent Document 4 states that “silica fine particles obtained by combustion of a silicon compound having an average particle diameter in the range of 0.05 μm or more and less than 0.1 μm, and a particle size represented by a rosin-Rammler diagram. Silica fine particles characterized by having a distribution gradient n of 2 or more and not containing molten particles of 1 μm or more as measured by a laser diffraction / scattering method. ” Although the embedding in the particles can be suppressed, aggregated particles are formed in the process of surface treatment such as hydrophobization by mixing the surface treatment agent and silica fine particles, so that the toner has sufficient dispersibility and fluidity. Can't get. In addition, silica fine particles having a primary particle diameter exceeding 100 nm cannot impart sufficient fluidity to the toner.
JP 2004-145325 A JP 2006-99006 A JP 2007-34224 A JP 2006-206414 A

  The present invention does not include coarse agglomerated particles that cause a decrease in toner dispersibility and toner fluidity, and can prevent detachment from the toner. An object of the present invention is to provide fine silica particles having a fine primary particle size suitable as an external toner additive, which is excellent in fluidity imparting effect and can suppress generation of white spots on a printed image.

  Another object of the present invention is to provide an electrophotographic toner composition using such highly dispersible hydrophobic silica fine particles.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that the average primary particle diameter of the vapor-phase method silica fine particles and the hydrophobic silica obtained by subjecting the vapor-phase method silica fine particles to a specific hydrophobic treatment By controlling the ratio of aggregated particles of fine particles, there is no problem of desorption from the toner, it is excellent in the effect of imparting uniform dispersibility and fluidity to the toner, and the generation of white spots on the printed image can be suppressed. It has been found that hydrophobic silica fine particles suitable as an external additive can be obtained, and the present invention has been completed.

  That is, the gist of the present invention is as follows.

[1] Hydrophobic silica fine particles obtained by hydrophobizing hydrophilic silica fine particles having an average primary particle diameter of 20 to 100 nm obtained by a gas phase method with hexamethyldisilazane, and the volume of the particles by laser diffraction method Hydrophobic silica fine particles characterized in that the ratio of aggregated particles having a particle size of 1.5 μm or more is less than 8% as measured by reference particle size.

[2] Hydrophobic silica fine particles according to [1], wherein the hydrophilic silica fine particles have an average primary particle size of less than 50 nm.

[3] Hydrophobic silica fine particles according to [2] or [2], wherein the hydrophobic rate is 95% or more.

[4] The hydrophobic silica fine particles according to any one of [1] to [3], which are silica fine particles for external toner addition.

[5] A toner composition for electrophotography, wherein the hydrophobic silica fine particles according to any one of [1] to [4] are externally added.

Hydrophobic silica fine particles of the present invention are obtained by hydrophobizing hydrophilic silica fine particles, which are obtained by a gas phase method, consisting of very fine primary particles having an average primary particle diameter of 20 to 100 nm with hexamethyldisilazane. In addition, since the ratio of aggregated particles having a particle size of 1.5 μm or more is less than 8% in the volume-based particle size measurement by laser diffraction, almost no coarse aggregated particles are contained. In addition, the fluidity improvement effect inherent in silica fine particles can be effectively exhibited, and there is no problem of falling off from the toner, so that the generation of white spots on the printed image can be suppressed.
Such hydrophobic silica fine particles of the present invention are silica fine particles that are added for the purpose of improving fluidity, preventing caking, and adjusting the charge in powder material systems such as powder paints, electrophotographic toners, and cosmetics. As industrially very useful.

  The average primary particle diameter of the hydrophilic silica fine particles according to the present invention is preferably 50 nm or less (claim 2).

  Further, the hydrophobic rate of the hydrophobic silica fine particles of the present invention is preferably 95% or more (claim 3).

  Further, the hydrophobic silica fine particles of the present invention are effective as silica fine particles for external addition of toner (claim 4).

  The toner composition for electrophotography of the present invention is an external addition of the hydrophobic silica fine particles of the present invention, and has excellent fluidity and is unlikely to cause image defects such as white spot images. Toner composition.

  Hereinafter, embodiments of the hydrophobic silica fine particles and the electrophotographic toner composition of the present invention will be described in detail.

[Hydrophobic silica fine particles]
The hydrophobic silica fine particles of the present invention are hydrophobic silica fine particles obtained by hydrophobizing a hydrophilic silica fine particle having an average primary particle diameter of 20 to 100 nm obtained by a gas phase method with hexamethyldisilazane, which is a laser. The ratio of aggregated particles having a particle size of 1.5 μm or more is less than 8% as measured by volume-based particle size of particles by a diffraction method.

<Hydrophilic silica fine particles by vapor phase method>
The hydrophilic silica fine particles by the vapor phase method according to the present invention are also called dry silica, and the production method thereof is manufactured by flame hydrolysis of a silicon compound, oxidation by a flame combustion method, or a combination of these reactions. There is no particular limitation as long as it is a thing. Among these, gas phase method silica produced by a flame hydrolysis method is preferably used. Examples of the commercially available products include “Aerosil” manufactured by Nippon Aerosil Co., Ltd. or Evonik Degussa, “Cabosil” manufactured by Cabot, “HDK” manufactured by Wacker, “Reolosil” manufactured by Tokuyama, and the like.

  The method for producing vapor phase silica by the flame hydrolysis method is, for example, introducing a raw material silicon compound gas such as silicon tetrachloride together with an inert gas into a mixing chamber of a combustion burner and mixing it with hydrogen and air at a predetermined ratio. In this method, the mixed gas is produced by burning the mixed gas in a reaction chamber at a temperature of 1000 to 3000 ° C., and after cooling, the produced silica is collected by a filter. As a more detailed production method for the flame hydrolysis method, methods described in German Patent Nos. 974,793, 974,974, and 909,339 can be referred to.

  The combustion method in flame is a method in which alkylsilane, alkoxysilane and / or a partial hydrolysis condensate thereof are burned and decomposed in a flame. That is, the alkylsilane, alkoxysilane and / or the partial hydrolysis condensate thereof is evaporated by heating and entrained in an inert gas such as nitrogen gas or sprayed and introduced into a flame such as an oxyhydrogen flame, It is burned and decomposed in this flame.

  Examples of the silicon compound used as a raw material for the vapor phase method silica include various inorganic silicon compounds and organic silicon compounds. For example, inorganic silicon compounds such as silicon tetrachloride, silicon trichloride, silicon dichloride, siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, octamethyltrisiloxane, Alkoxysilanes such as methyltrimethoxysilane, tetramethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, methyltributoxysilane, diethyldipropoxysilane, trimethylbutoxysilane, tetramethylsilane, diethylsilane, hexamethyldisilazane Or organic silicon compounds such as oligomers and polymers thereof.

  Hydrolysis and combustion decomposition of such a silicon compound in a flame is carried out by purifying the silicon compound by distillation or the like, if necessary, and then evaporating it by heating to wake it with an inert gas such as nitrogen gas. In the entrainment method or the method of atomizing the silicon compound and supplying it into the flame, it may be introduced into a flame such as an oxyhydrogen flame and reacted in this flame. Further, a flammable gas such as methane gas may be used as the auxiliary combustion gas. Any auxiliary combustion gas can be used as long as no residue remains, and there is no particular limitation.

  Silica produced by hydrolysis or combustion decomposition of a silicon compound is collected by a known method such as a bag filter or a cyclone.

  Such gas phase method silica may be used alone or in combination of two or more.

<Average primary particle size>
In the present invention, hydrophilic silica fine particles obtained by a gas phase method and subjected to a hydrophobization treatment have an average primary particle diameter of 20 to 100 nm. When the average primary particle diameter of the hydrophilic silica fine particles is larger than 100 nm, the dispersibility of the resulting hydrophobic silica fine particles in the toner is poor and the effect of improving the fluidity is inferior. Vapor phase silica fine particles having an average primary particle size of less than 20 nm are not preferred because they tend to aggregate and the proportion of aggregated particles increases.

In particular, from the viewpoint of fluidity imparting effect, the average primary particle diameter of the hydrophilic silica fine particles is preferably 50 nm or less, for example, 45 nm or less.
In particular, the average primary particle diameter of the hydrophilic silica fine particles is preferably 30 nm or more from the aspect of the aggregate particle ratio.

  In addition, the average primary particle diameter of the hydrophilic silica fine particles according to the present invention is determined by observation with a transmission electron microscope, as shown in the Examples section described later.

<BET specific surface area>
The BET specific surface area of the hydrophilic silica fine particles obtained by the gas phase method mainly depends on the average primary particle diameter, but the BET specific surface area of the hydrophilic silica fine particles subjected to the hydrophobization treatment in the practice of the present invention is 10 to 120 m. ² / g is preferable, and 15 to 90 m ² / g is more preferable. When the BET specific surface area of the hydrophilic silica fine particles is too small, the dispersibility of the obtained hydrophobic silica fine particles in the toner is poor and the effect of improving the fluidity is inferior. Vapor-phase silica fine particles having an excessively large BET specific surface area are not preferred because they tend to aggregate after pulverization and have a strong cohesive force.

In particular, from the viewpoint of fluidity imparting effect, the BET specific surface area of the hydrophilic silica fine particles is preferably 25 to 90 m ² / g.

  The BET specific surface area of the hydrophilic silica fine particles according to the present invention is determined by the BET method as shown in the Examples section described later.

<Hydrophobic treatment>
The hydrophobic silica fine particles of the present invention are obtained by hydrophobizing hydrophilic silica fine particles by the gas phase method having the above average primary particle diameter with hexamethyldisilazane.

  As a method for hydrophobizing silica fine particles, for example, a method using a silane coupling agent and silicone oil as described in Japanese Patent No. 3229174, or an organo as described in Japanese Patent Publication No. 61-50882. Examples thereof include a method using a halogen silane, a method using an organopolysiloxane as described in JP-B-57-2641, and a method using a siloxane oligomer as described in JP-A-62-171913.

  Among these, in particular, the present invention employs a method using hexamethyldisilazane, which is a surface treatment method having high hydrophobicity and high fluidity-imparting effect.

  Specifically, the hydrophobization treatment with hexamethyldisilazane is performed as follows.

  100 parts by weight of gas phase method silica powder having an average primary particle size of 20 to 100 nm is put in a reaction vessel, and sprayed with 0.1 to 20 parts by weight of water and 0.5 to 30 parts by weight of hexamethyldisilazane in a nitrogen atmosphere. . The reaction mixture is stirred at 50 to 250 ° C. for 0.5 to 3 hours, and further stirred at 140 to 250 ° C. for about 0.5 to 3 hours under a nitrogen stream and dried. By cooling this, hydrophobized silica fine particles are obtained.

In such a hydrophobic treatment, the amount of water and hexamethyldisilazane used for the hydrophobic treatment of 100 parts by weight of the hydrophilic silica fine particles is as follows with respect to the BET specific surface area of the hydrophilic silica fine particles subjected to the hydrophobic treatment. It is preferable that it is the quantity calculated by such a formula.
Hexamethyldisilazane (parts by weight)
= BET specific surface area of hydrophilic silica fine particles (m ² / g) / H
In the above formula, H is preferably 3 to 30, particularly 5.
Water (parts by weight) = BET specific surface area of hydrophilic silica fine particles (m ² / g) / W
In the above formula, W is preferably 5 to 200, particularly 18.
When the amount of hexamethyldisilazane is larger than the above range, a large amount of aggregates are generated in the product after the hydrophobization treatment, and when it is small, sufficient hydrophobicity as a toner external additive is not imparted. In addition, when the amount of water used is large, the aggregates increase, and further sufficient hydrophobicity cannot be obtained. If the amount of water used is small, the reaction between hexamethyldisilazane and the silica surface does not proceed sufficiently, and sufficient hydrophobicity cannot be obtained.

  Hexamethyldisilazane and water may be sprayed separately on the hydrophilic silica fine particles, but each may be sprayed after being diluted with a solvent such as alcohol. Both disilazane and water may be dissolved and sprayed simultaneously.

  In the present invention, it is preferable to obtain silica fine particles having a hydrophobicity of 95% or more, particularly 97% or more, measured by the method described in the Examples section below, by such a hydrophobization treatment.

<Ratio of aggregated particles>
The hydrophobic silica fine particles of the present invention have a proportion of agglomerated particles having a particle diameter of 1.5 μm or more as measured by a volume diffracted particle size by a laser diffraction method (hereinafter, this proportion may be referred to as a “laser diffraction method agglomerated particle proportion”). Is less than 8%. That is, for example, in the diffraction chart for measuring the volume-based particle diameter of particles by the laser diffraction method shown in FIG. 1, the distribution ratio of aggregated particles of 1.5 μm or more is less than 8%.
When the ratio of the aggregated particles by laser diffraction method is 8% or more, since there are many large aggregated particles, the uniform dispersibility in the toner is inferior, and good fluidity and good print image quality with few white spots cannot be obtained.

  The smaller the ratio of agglomerated particles by laser diffraction method, the better. Particularly, it is preferably 6% or less, particularly 3% or less.

  The ratio of the aggregated particles by laser diffraction method is measured with respect to an ethanol dispersion of silica fine particles using a laser diffraction particle size distribution analyzer “LA920” manufactured by Horiba, Ltd. as shown in the Examples section below. Is required.

The above-mentioned hydrophobic silica fine particles of the present invention having the ratio of the aggregated particles by the laser diffraction method are obtained by using a raw material obtained by hydrophobizing the hydrophilic silica fine particles produced by the gas phase method using hexamethyldisilazane. After pulverization with a pulverizer such as a jet mill, classification is performed by an airflow classification method or the like to collect only fine powder, and this pulverization and classification can be repeated as necessary.
At this time, it is preferable in terms of the efficiency of the process that the coarse particles separated by classification are circulated to the pulverization process.
In addition, when using a pulverizer equipped with a mechanism for performing classification and pulverization at the same time, or using a pulverizer in which the classification process is incorporated into the pulverizer, if it is determined that the classification is insufficient, a separate classifier is used. It is preferable to install and perform a more advanced classification process.

  Since the silica particles are aggregated by the hydrophobization treatment, the hydrophobization treatment is performed prior to the pulverization / classification treatment, and the pulverization / classification treatment is performed after the hydrophobization treatment.

[Toner composition for electrophotography]
The toner composition for electrophotography of the present invention is obtained by externally adding the above-described hydrophobic silica fine particles of the present invention. There is no particular limitation on the composition and the production method thereof, and a known composition and method should be adopted. Can do.

  In the production of the electrophotographic toner composition of the present invention, the amount of the hydrophobic silica fine particles of the present invention added is not particularly limited as long as the desired effect of improving the properties can be obtained. The toner composition preferably contains 0.1 to 6.0% by weight of the hydrophobic silica fine particles of the present invention. When the content of the hydrophobic silica fine particles of the present invention in the electrophotographic toner composition is less than 0.1% by weight, the effect of improving fluidity and the effect of stabilizing the charging property are sufficiently obtained by adding the silica fine particles. I can't. On the other hand, when the content of the silica fine particles exceeds 6.0% by weight, many particles are detached from the surface of the toner and act by the silica fine particles alone, resulting in problems in image and cleaning properties.

  The content S (% by weight) of the hydrophobic silica fine particles of the present invention in the toner composition for electrophotography is also based on the average primary particle diameter R (nm) of the hydrophilic silica fine particles used in the production of the hydrophobic silica fine particles. Thus, R / 40 ≦ S ≦ R / 7 is preferable, and S = R / 20 is particularly preferable.

  In general, the toner contains a small amount of a pigment, a charge control agent, and other external additives in addition to the thermoplastic resin. In the present invention, as long as the silica fine particles are blended, the other components may be the same as those in the past, and may be either a magnetic or nonmagnetic one-component toner or two-component toner. Further, either negatively chargeable toner or positively chargeable toner may be used, and either monochrome or color may be used.

  In the production of the electrophotographic toner composition of the present invention, the hydrophobic silica fine particles of the present invention as an external additive are not limited to being used alone, but may be other metal oxide fine particles depending on the purpose. You may use together. For example, the silica fine particles can be used in combination with other surface-modified dry silica fine particles, surface-modified dry titanium oxide fine particles, surface-modified wet titanium oxide fine particles, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

  In addition, the evaluation method of the silica fine particles and the toner composition in the following examples and comparative examples is as follows.

[Evaluation of silica fine particles]
<Average primary particle size>
On a transmission electron microscope image, the particle diameter of 2500 or more random particles was measured from the silica fine particle sample, and the average primary particle diameter was determined by number average.

<BET specific surface area>
It was measured by the BET method.

<Laser diffraction method aggregated particle ratio>
A laser diffraction particle size distribution analyzer “LA920” manufactured by HORIBA, Ltd. was used for the measurement of the aggregated particle ratio. Ethanol was used as a measurement solvent. Using about 0.2 g of a hydrophobic silica fine particle sample, the measurement was performed according to a method prescribed by the apparatus. As a measurement pretreatment, the sample was dispersed by irradiating with ultrasonic waves of intensity 30 W for 5 minutes. From the measurement result of the volume average particle diameter as shown in FIG. 1, the ratio of aggregated particles having a particle diameter of 1.5 μm or more was determined.

<Hydrophobic rate>
A 1 g sample of hydrophobic silica fine particles was weighed into a 200 mL separatory funnel, 100 mL of pure water was added thereto, the stopper was plugged, and the mixture was shaken with a tumbler mixer for 10 minutes. After shaking, it was allowed to stand for 10 minutes. After standing, after removing 20-30 mL of the lower layer from the funnel, the lower layer mixed solution is dispensed into a 10 mm quartz cell, subjected to a colorimeter using pure water as a blank, and the transmittance of light having a wavelength of 500 nm is determined as the hydrophobicity. It was.

[Evaluation of Toner Composition]
<Repose angle>
The angle of repose of the toner composition was measured using a powder tester PT-S (manufactured by Hosokawa Micron). About 20 g of the toner sample was placed on a sieve having an opening of 355 μm, and the toner sample dropped by vibration was deposited through a funnel on a circular table having a diameter of 8 cm installed about 6.5 cm below the tip of the funnel. The angle of repose of the side surface of the deposited toner sample formed in a conical shape with respect to the horizontal plane was defined as the repose angle.
The smaller the angle of repose of the measured toner composition, the smaller the aggregated particles in the silica fine particles and the better the fluidity.
In the present invention, the angle of repose was set to 39 ° or less.

<Evaluation method of white spot image>
Fill the commercially available copier with the toner composition, print a solid image of 3 cm × 3 cm with 1000 continuous sheets of paper, count the number of white spots with a diameter of 0.1 mm or more seen on the image, The average number per sheet was calculated.
In the present invention, the average number of the white spot images is 4 or less, which is acceptable.

[Example 1]
The product name “AEROSIL (registered trademark) 90” (BET specific surface area 90 m ² / g, average primary particle size 20 nm) manufactured by Nippon Aerosil Co., Ltd. was used as the gas phase method silica fine particles. After hydrophobizing under the conditions, pulverization and classification were performed under the following conditions to obtain silica fine particles having the average primary particle diameter and the ratio of laser diffraction aggregated particles shown in Table 1.

<Hydrophobic treatment>
100 parts by weight of vapor phase method silica fine particles were put in a reaction vessel, and sprayed with 5 parts by weight of water and 18 parts by weight of hexamethyldisilazane in a nitrogen atmosphere. The reaction mixture was stirred at 150 ° C. for 2 hours and further stirred at 220 ° C. for 2 hours under a nitrogen stream and dried. This was cooled to obtain hydrophobic silica.

<Crushing and classification processing>
Using a counter jet mill (manufactured by Hosokawa Micron Corporation) as a pulverizer and a turboplex 1000ATP (manufactured by Hosokawa Micron Corporation) as a classifier, pulverization / classification treatment was performed. The separated coarse powder was continuously circulated and introduced into a jet mill through a pipe and again subjected to pulverization and classification.

  The obtained hydrophobized / low-aggregated silica fine particles were evaluated for the ratio of aggregated particles and the hydrophobicity, and the results are shown in Table 1.

  Further, a toner composition was prepared by using the silica fine particles with the following composition, evaluated, and the results are shown in Table 1.

<Preparation of toner composition>
A negatively charged styrene-acrylic resin two-component toner (manufactured by Mikasa Sangyo Co., Ltd.) having an average particle diameter of 8 μm produced by a pulverization method is used, and the amount of silica fine particles blended with respect to a total of 100 parts by weight of the toner and silica fine particles. Were mixed so as to have the following ratio.
Silica fine particle content (parts by weight)
= Average primary particle diameter of hydrophilic silica fine particles (nm) / 20
The mixture was placed in a Henschel-type mixer, stirred at 600 rpm for 1 minute, and further stirred at 3000 rpm for 3 minutes to disperse the silica fine particles on the toner surface to prepare a toner composition.

[Examples 2 to 4, Comparative Examples 1 to 4]
In Example 1, as the vapor-phase process silica fine particles, those shown in Table 1 were used to produce hydrophobized / classified silica fine particles by changing the hydrophobization, pulverization / classification conditions, and the same toner composition using the silica fine particles. A product was prepared.

The amount of hexamethyldisilazane and water used per 100 parts by weight of the silica fine particles in the hydrophobization treatment was an amount calculated by the following formula according to the BET specific surface area of the silica fine particles subjected to the hydrophobization treatment. .
Hexamethyldisilazane (parts by weight)
= BET specific surface area of hydrophilic silica fine particles (m ² / g) / 5
Water (parts by weight) = BET specific surface area of hydrophilic silica fine particles (m ² / g) / 18
The evaluation results of the obtained silica fine particles and the toner composition are shown in Table 1.

  The particle size distribution of the hydrophobized / classified silica fine particles obtained in Comparative Example 4 in the volume-based particle size measurement by laser diffraction method is shown in FIG.

  From Table 1, according to the present invention, a toner composition having good fluidity and high image quality can be realized by using silica fine particles having a uniform particle diameter with small and few aggregated particles and excellent uniform dispersibility in the toner. You can see that

It is a figure which shows the particle size distribution of the silica fine particle of the comparative example 4 in the volume reference | standard particle diameter measurement of the particle | grains by the laser diffraction method.

Claims (5)

  Hydrophobic silica fine particles obtained by hydrophobizing hydrophilic silica fine particles having an average primary particle diameter of 20 to 100 nm obtained by a gas phase method with hexamethyldisilazane, and the volume-based particle size of the particles by laser diffraction method Hydrophobic silica fine particles characterized in that the proportion of aggregated particles having a particle diameter of 1.5 μm or more is less than 8% by measurement.   The hydrophobic silica fine particles according to claim 1, wherein the hydrophilic silica fine particles have an average primary particle diameter of 50 nm or less.   3. Hydrophobic silica fine particles according to claim 1, wherein the hydrophobic rate is 95% or more.   4. Hydrophobic silica fine particles according to claim 1, which are silica fine particles for external toner addition.   An electrophotographic toner composition, wherein the hydrophobic silica fine particles according to any one of claims 1 to 4 are externally added.

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