JP2007171713A - Modified silica powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modified silica powder of which variation in a charging level by stress is small, which is excellent in capability of giving flow property, and is especially useful as an additive material of a toner for electrophotography used on a copier, a laser printer, and the like. <P>SOLUTION: The modified silica power is obtained by surface-treating a silica powder with a silane coupling agent expressed by C<SB>n</SB>H<SB>2n+1</SB>Si(OR)<SB>3</SB>(n indicates an integer of 8 or more, and R an alkyl group), and hexamethyldisilazane. The amount of the silane coupling agent is 1.0-3.0/nm<SP>2</SP>of the raw material silica powder surface, and the amount of the surface treatment with the hexamethyldisilazane is 0.2-1.5/nm<SP>2</SP>of the raw material silica powder surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel modified silica powder. More specifically, the present invention relates to a modified silica powder that, when used as an external additive for an electrophotographic toner, effectively suppresses a change in charge amount due to stress on the toner and has excellent fluidity imparting power.

  The electrophotographic method typically forms a latent image on the surface of a photoreceptor by charging and exposure, develops the latent image with charged toner, transfers the toner on the surface of the photoreceptor to paper, an intermediate transfer body, etc. The toner transferred onto paper or the like is fixed by applying heat. An external additive such as silica adheres to the surface of the toner and exhibits effects such as imparting fluidity to the toner, improving charging efficiency, and improving transferability.

  In recent years, reduction of environmental load has been regarded as important, and in a developing machine using electrophotography such as a copying machine or a printer, reduction of power consumption is required.

  In order to reduce power consumption, it is effective to reduce the amount of heat applied when fixing toner. For this reason, the softening point of the toner resin tends to decrease. When the softening point of the toner resin is lowered, the external additive is easily embedded in the toner due to stress received in the developing machine, for example, pressure received from the carrier or the charging blade when the toner is charged.

  When such external additives are buried, there arises a problem that the charge amount of the toner changes. In order to solve this problem, adding an external additive having a large average particle diameter of about 50 to 200 nm to the toner has an effect of preventing the external additive from being buried, thereby reducing the charge amount due to the stress of the toner. It is known to suppress changes (see Patent Documents 1, 2, and 3).

  However, even when the above-described large particle size external additive is used, the change in the charge amount due to stress cannot be sufficiently suppressed, and further improvement has been demanded.

JP-A-60-3260 JP-A 64-68765 JP 2002-154820 A

  Accordingly, an object of the present invention is to provide a modified silica powder that can effectively suppress a change in charge amount due to stress on the toner and can be suitably used as an external additive for toner.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the present inventors have found that the modified silica powder treated with a specific silane coupling agent containing an alkyl group having 8 or more carbon atoms is highly effective in suppressing the change in charge amount due to stress on the toner. It became clear by experiment. This is presumed that the lubricity of the long-chain alkyl group acts so as to release stress on the toner well.

  However, the silica powder treated with the above silane coupling agent sacrifices the fluidity imparting power to the toner, which is the performance originally required as an external additive for the toner, to some extent.

  Therefore, the present inventors have further studied to improve the fluidity imparting power of the silica powder treated with the specific silane coupling agent. As a result, the treatment with hexamethyldisilazane is used in combination with the treatment with the silane coupling agent containing an alkyl group having 8 or more carbon atoms, and the amount of treatment with each treatment agent is appropriately adjusted. Thus, it has been found that the fluidity imparting power to the toner can be improved without impairing the excellent suppression effect on the change in the charge amount by the specific silane coupling agent, and thus the object can be achieved. The present invention has been made successful.

That is, according to the present invention, the silica powder is mixed with a silane coupling agent represented by C _n H _{2n + 1} Si (OR) ₃ (wherein n represents an integer of 8 or more and R represents an alkyl group), and hexa It is a modified silica powder surface-treated with methyldisilazane, and 1.0 to 3.0 of the silane coupling agent per 1 nm ^{2 of the} silica powder surface, and the trimethylsilyl group introduced by the surface treatment of hexamethyldisilazane There is provided a modified silica powder characterized in that it is present in a proportion of 0.2 to 1.5.

In the present invention, the surface treatment amount of the silane coupling agent and trimethylsilyl group present on the surface of the modified silica powder can be quantified by ²⁹ Si-solid NMR method. The details will be described in the examples described later. As an outline, a sample having a known surface treatment amount of the silane coupling agent (silica powder) and the amount of trimethylsilyl group introduced by the surface treatment of hexamethyldisilazane as a standard sample. And a sample (silica powder) having a known chemical shift by ²⁹ Si-solid NMR method, a chemical shift peak derived from ²⁹ Si atoms of the silane coupling agent, a peak of −67 to −49 ppm, and a ²⁹ Si atom of the trimethylsilyl group. The ratio between the peak area of the chemical shift derived from 8 ppm and the peak plane line of the chemical shift of -108 ppm derived from the ²⁹ Si atom of the raw silica powder is obtained. Further, the ratio of peak areas is obtained by the same method for the modified silica powder to be measured, and is obtained by comparing with the peak area ratio of the standard sample.

Then, a specific surface area of the silica powder, the modified silica powder at 600 ° C. in a nitrogen atmosphere, after removing the surface treatment agent by heating 1 hour, determined by measuring the BET method, above ^{29 Si-} solid NMR The surface treatment amount per silica surface area can be calculated by dividing the surface treatment amount obtained by the method by the specific surface area of the silica powder.

The silane coupling agent present on the surface of the modified silica powder of the present invention may exist in the structure of the following formula (1), but usually a part of three alkoxy groups. Alternatively, all of them are present on the surface of the silica powder or in a state where the structure is changed by reacting with the silane coupling agent. However, in any of these cases, a peak at a chemical shift of −67 to −49 ppm derived from ²⁹ Si atoms of the silane coupling agent present on the surface of the silica powder is detected, and the amount is regarded as the abundance of the silane coupling agent. It can be quantified.

In addition, since the peak derived from the ²⁹ Si atom of the silane coupling agent and the trimethylsilyl group does not overlap, the presence of the silane coupling agent and hexamethyldisilazane present on the surface of the modified silica powder The amount can be determined reliably.

  Since the silica powder of the present invention can extremely effectively suppress a change in charge amount due to stress on the toner, and has such performance, it also has excellent fluidity imparting power. It can be suitably used as an external additive for toner.

  In the present invention, silica powder (hereinafter, also referred to as “raw silica powder”) that is a base of the modified silica powder is silica obtained by a known method without particular limitation. Typical examples include wet silica and sol-gel silica. Further, these silicas may be silica partially or wholly melted.

  The fumed silica refers to silica particles produced by burning a silicon compound, particularly a halide of silicon, generally a chloride of silicon, usually purified silicon tetrachloride, in an oxyhydrogen flame. The fumed silica is sometimes referred to as “dry silica” or “vapor phase silica” in order to distinguish it from silica produced by a wet method such as precipitated silica.

  Moreover, the wet silica is typically precipitated silica in which silica is precipitated in a solution by neutralizing sodium silicate with a mineral acid. Generally, it is also called “white carbon”.

  Similarly, gel silica prepared by neutralizing sodium silicate with an acid is also a kind of wet silica, and a pulverized one can be used as the raw silica powder of the present invention.

Various types of wet silica are also obtained by changing the production conditions, and those having a specific surface area in the range of about 50 to 1000 m ² / g are obtained. Wet silica is considered to be agglomerated particles obtained by aggregating fine particles having a primary particle diameter of about 3 to 50 nm in the course of synthesis due to the production method. These wet silicas are usually obtained as a powder by filtering or washing after the neutralization reaction, drying and then pulverizing as necessary. Generally, the average particle diameter of the available wet silica particles is 1 to several 100 μm.

  Further, the sol-gel silica is produced by hydrolyzing a silicon alkoxide such as tetramethoxysilane or tetraethoxysilane in an acidic or alkaline water-containing organic solvent. Although silicon alkoxides are expensive, they are characterized in that extremely high purity silica can be obtained because the raw material can be highly purified by distillation. When hydrolysis is carried out in an acidic or alkaline concentrated solution, bulk silica is obtained, and by pulverizing it, amorphous silica particles of 1 to several hundred μm are obtained.

  In the present invention, the active silica powder may be selected from the above-mentioned types, and suitable silica and particle size (specific surface area) may be selected depending on the application. Among them, fumed silica having excellent fluidity-imparting effect and excellent dispersibility on the toner surface is preferably used.

In the present invention, the raw silica powder having known physical properties is used without any limitation, but the specific surface area is preferably 10 to 400 m ² / g, particularly 10 to 380 m ² / g. That is, when used as an external additive for toner, the higher the specific surface area, the better the fluidity imparting force, and the lower the specific surface area, the better the transferability improving effect. For the purpose of imparting the effect of improving transferability, the specific surface area is particularly preferably 10 to 50 m ² / g.

  Furthermore, the raw silica powder is not limited to a single component of silica, and silica-based composite oxides such as silica and titania, or silica and alumina, or powder having a silica surface coated with titania, alumina, or the like may be used. Can do.

  The silane coupling agent used for the modified silica powder of the present invention is represented by the following formula (1).

C _n H _{2n + 1} Si (OR) ₃ (1)
(In the formula, n represents an integer of 8 or more, and R represents an alkyl group.)
In the above formula (1), n indicating the length of the alkyl chain needs to be 8 or more. That is, when n having a value smaller than 8 is used, it is difficult to suppress the change in the charge amount due to stress, and the object of the present invention cannot be achieved. Those having n of 12 or less can be suitably used since they have good heat stability.

  Examples of silane coupling agents used in the present invention include octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, tetradecyltrimethoxysilane, tetradecyl. Examples include triethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane.

It is necessary to adjust the surface treatment amount of the silane coupling agent in the modified silica powder of the present invention so that the surface treatment amount per 1 nm ² of the raw silica powder is 1.0 to 3.0. When the amount is less than this range, it is difficult to effectively suppress the change in the charge amount due to stress. When the amount is more than this range, the fluidity improvement effect due to the treatment effect by hexamethyldisilazane is sufficiently exhibited. When the resulting modified silica powder is used as an external toner additive, the ability to impart fluidity is inferior.

  In the present invention, the amount of trimethylsilyl groups introduced by the surface treatment of hexamethyldisilazane present on the surface of the modified silica powder needs to be adjusted to be about 0.2 to 1.5. That is, when the amount of the trimethylsilyl group is smaller than this range, the effect of imparting fluidity when used as an external additive of the toner is reduced. The effect of the agent is reduced, and the stress resistance when used as an external additive for the toner is reduced.

  The modified silica powder of the present invention can achieve the object by satisfying the above-described configuration, but it is further preferable to reduce the physical adsorption in the surface treatment amount of the silane coupling agent. When the silica powder of the present invention is used as an external additive for toner, the physical adsorption of the silane coupling agent may cause filming by adhering to the photoreceptor.

The amount of physical adsorption of the silane coupling agent is determined by the difference (ΔC (%)) between the carbon amount C ₁ (%) of the silica powder and the carbon amount C ₂ (%) after the silica powder is extracted with chloroform. Can do. ΔC (%) is preferably 0.2% or less.

  The ΔC (%) varies depending on the surface treatment method of the silane coupling agent. Specifically, ΔC (%) tends to increase when the wet processing method is used. Moreover, when it processes by the said dry processing method, (DELTA) C (%) tends to become large, so that process temperature is low. For the purpose of reducing ΔC (%), it is preferable to perform the treatment at a temperature of 200 ° C. or higher.

  The surface treatment of the silica powder of the present invention is not necessarily performed only with a silane coupling agent and hexamethyldisilazane, and may be used in combination with a surface treatment agent such as silicone oil or dimethyldichlorosilane depending on the purpose. it can.

  The surface treatment method of the raw silica powder with silane coupling agent and hexamethyldisilazane for obtaining the modified silica powder of the present invention is not particularly limited. For example, it can be processed by contacting the raw silica powder with an appropriate amount of a silane coupling agent and hexamethyldisilazane.

  In this case, the treatment with the silane coupling agent and hexamethyldisilazane may be performed simultaneously or sequentially. A method of treating with hexamethyldisilazane after moderately treating with a silane coupling agent is preferable because each surface treatment amount can be easily controlled.

  The treatment with the silane coupling agent is not particularly limited, but is preferably performed by the following two methods.

  1. A method of removing a solvent after dissolving a certain amount of a silane coupling agent in a solvent in which a raw silica powder is dispersed and reacting with the surface of the silica powder. This method can be suitably carried out in the presence of a catalyst such as amines, ammonia, acetic acid, hydrochloric acid and the like.

  2. A method of spraying the processing agent while stirring and mixing the raw silica powder in a mixer, holding it for a certain period of time, and removing the unreacted processing agent by nitrogen purge or the like. (Hereinafter, it may be referred to as a “dry method.”) A treatment agent diluted with a solvent can be preferably sprayed. This method can be carried out in the presence of a catalyst such as amines, ammonia, acetic acid and hydrochloric acid.

  Of the above two surface treatment methods, the treatment with the silane coupling agent of the present invention is performed by a dry method in terms of surface uniformity and the absence of agglomeration of silica powder that is likely to occur due to the step of drying the solvent. Is preferred.

  In a preferred embodiment when the treatment with the silane coupling agent is performed by a dry method, the raw silica powder is placed in a reaction vessel, the inside of the vessel is replaced with an inert gas such as nitrogen, and the temperature is about 200 ° C. to 260 ° C. In this processing temperature, there can be mentioned a method in which the processing agent is sprayed using a nozzle or the like while the container is sealed, and the state is maintained as it is for a certain period of time, preferably about 30 minutes to 2 hours. In the above treatment, it is preferable that water vapor of about 30 to 100 kPa exists in advance in the mixer so as to promote the reactivity of the silane coupling agent.

  On the other hand, for the surface treatment of the raw silica powder in the present invention with hexamethyldisilazane, a known method is adopted without limitation. Preferably, it can be performed by the dry method described in the surface treatment method using a silane coupling agent.

  As a preferred embodiment of the treatment with hexamethyldisilazane, at a treatment temperature of about 200 ° C. to 300 ° C., the reaction vessel is sealed in a state where silica powder is present inside, and hexamethyldisilazane is added using a nozzle or the like. A method of spraying and maintaining the state as it is for a certain period of time, preferably about 30 minutes to 2 hours can be mentioned. In the above treatment, it is preferable that water vapor having a partial pressure of about 30 to 100 kPa is previously present in the reaction vessel in order to promote the reactivity of hexamethyldisilazane.

  In the above-described treatment method, the surface treatment amount of the silane coupling agent in the resulting modified silica powder can be adjusted by adjusting the reaction rate and addition amount of the silane coupling agent. For example, the surface treatment amount can be adjusted to the above range by adding a silane coupling agent having a reaction rate of about 50% to 80% and a theoretical amount of about 1.2 to 2 times.

  Moreover, in the above-mentioned processing method, the adjustment of the surface treatment amount with hexamethyldisilazane in the obtained modified silica powder is performed when the surface treatment of hexamethyldisilazane is performed before the surface treatment of the silane coupling agent. This can be done by adjusting the amount of disilazane added. Since hexamethyldisilazane is highly reactive, a reaction rate close to 100% is usually obtained. It can be adjusted by adding as the theoretical amount.

  In a preferred embodiment, when hexamethyldisilazane is treated after treatment with a silane coupling agent, it is preferable to treat with supersaturated hexamethyldisilazane. Since hexamethyldisilazane reacts with the silanol groups on the surface of the raw silica powder remaining after the treatment with the silane coupling agent, the amount of the silane coupling agent treated is moderate, that is, within the scope of the present invention. The amount of hexamethyldisilazane can also be adjusted by adjusting to.

  The present invention also provides an external additive for an electrophotographic toner comprising the above-described modified silica powder.

  As a toner to which the external additive for toner of the present invention can be applied, any of black toner and color toner can be used, and any electrophotographic system such as magnetic one component, non-magnetic one component, two component, etc. Can also be used. The binder resin for the toner can also be applied without particular limitation, such as commonly used styrene / acrylic copolymer resins, polyester resins, epoxy resins and the like. The toner production method can be applied not only to mainstream pulverization / kneading methods but also to toners obtained by polymerization methods such as suspension polymerization and emulsion polymerization.

  The toner external additive of the present invention can also be applied to toners that are arbitrarily blended with other toner constituent materials. Black colorants, color colorants such as cyan, magenta, and yellow, positive and negative charge control agents, and release agents such as wax can be used without any limitation in materials normally used in this field.

  The amount of the external additive of the present invention added to the toner is not particularly limited as long as the obtained toner has desired characteristics, but is usually 0.05 to 5% by weight, preferably 0.1 to 0.1%. The amount is preferably 4% by weight and can be added to the toner by a known method.

  Furthermore, when the toner is produced, the external additive of the present invention may be used alone, or if necessary, combined with hydrophobic silica particles other than the external additive of the present invention, titania, alumina, etc. Other additives such as oxide fine particles other than silica, lubricants such as Teflon (registered trademark), zinc stearate, polyvinylidene fluoride, and fixing aids such as polyethylene and polypropylene can be used in combination.

  EXAMPLES Hereinafter, examples and comparative examples will be shown to specifically describe the present invention, but the present invention is not limited only to these examples.

The measuring method of various physical properties regarding the silica powder of the present invention is as follows.
(Measurement of specific surface area of active silica powder)
-Sample pretreatment The modified silica powder was placed in an electric furnace and the surface treatment agent was removed by heating at 600 ° C for 1 hour in a nitrogen atmosphere. The carbon amount of the sample subjected to this treatment was measured, and it was confirmed that the surface treatment agent was removed. When the removal of the surface treatment agent was insufficient, heating was further performed at 600 ° C. for 1 hour in a nitrogen atmosphere, and the treatment was repeated until the surface treatment agent was sufficiently removed.
-Measurement of specific surface area It measured by BET method (one-point method) using Shibata Kagaku company make and SA-1000.
(Measurement of surface treatment amount with silane coupling agent of modified silica powder and hexamethyldisilazane)
Standard sample As the standard sample 1, a sample having a known amount of the silane coupling agent is manufactured by Tokuyama Co., Ltd., Leorosil, QS-102 (specific surface area 200 m ² / g, untreated product) 10 g and decyltrimethoxysilane 2 .6 g was made by mixing in a coffee mill for 1 minute. The amount of silane coupling agent present in this sample is 3.0 per 1 nm ^{2 of} the silica powder surface. As a standard sample 2, the known sample introduction amount of trimethylsilyl groups, manufactured by Tokuyama Corp., REOLOSIL, HM-20S (bulk specific surface area 200 meters ² / g, the silica powder surface 1 nm ² per trimethylsilyl group introduced amount 2.2 Were used.
·Measuring method
^It was performed by ²⁹ Si-solid state NMR method (single pulse method). As the NMR apparatus, GSX-270 manufactured by JEOL Ltd. was used. The measurement conditions were a magnetic field of 53.54 MHz and a cumulative number of 30000 times. In this measurement conditions, measuring the standard sample of the peak area of the chemical shift 8ppm derived peak of the chemical shift -67~-49ppm derived from ²⁹ Si atom of the silane coupling agent, and ²⁹ Si atoms trimethylsilyl group And the ratio of the chemical shift derived from ²⁹ Si atoms of the raw silica to -108 ppm and the peak plane line. Thereafter, the ratio of peak areas was determined for the modified silica powder to be measured by the same method. The surface treatment amount was determined by the following formula.

Abundance of silane coupling agent = 3.0 × (P ₁₂ / P ₁₁ ) × (200 / S) (Formula 1)
Abundance of trimethylsilyl group = 2.2 × (P ₂₂ / P ₂₁ ) × (200 / S) (Formula 2)
P ₁₁ = A1 / A2 (Formula 3)
P ₁₂ = A3 / A4 (Formula 4)
P ₂₁ = A5 / A6 (Formula 5)
P ₂₂ = A7 / A8 (Formula 6)
A1: Peak area of −67 to −49 ppm in standard sample 1 A2: Peak area of −108 ppm in standard sample 1 A3: Peak area of −67 to −49 ppm in modified silica powder A4: − in modified silica powder 108 ppm peak area A5: 8 ppm peak area in standard sample 2 A6: -108 ppm peak area in standard sample 2 A7: 8 ppm peak area in modified silica powder A8: -108 ppm peak area in modified silica powder S: Specific surface area of raw silica powder (silica powder extracted with chloroform)
After suspending 1.0 g of silica powder in 40 ml of chloroform and dispersing it with an ultrasonic disperser for about 30 minutes, the silica powder was separated with a centrifuge. After separation, chloroform was further added, ultrasonic dispersion was performed, and the operation of separating the silica powder with a centrifuge was repeated three times. Thereafter, chloroform contained in the silica powder was completely removed by a vacuum dryer.

(Measurement of carbon content)
The carbon amount C ₁ of the silica powder and the carbon amount C ₂ after chloroform extraction were measured using a carbon amount analyzer (trade name: EMIA-110 type) manufactured by Horiba.

(Generation of pseudo toner under normal conditions and stress conditions)
Styrene-acrylic resin (glass transition point 61 ° C.) was pulverized with a jet mill to obtain resin powder having an average particle size of 8 μm. 34.3 g of this resin powder and 0.7 g of silica powder are put into a 250 ml polyethylene container, 200 g of 5 mm glass beads are added as a mixing aid, and a pseudo toner is prepared by shaking and mixing with a shaker for a certain period of time. did. The shaking time was 30 minutes as a normal condition and 120 minutes as a stress condition.

(Measurement of charge amount)
1 g of the pseudo toner prepared under the above normal conditions and stress conditions was put in a sample bottle together with 99 g of a ferrite carrier coated with a silicone resin and conditioned for 12 hours or more in an environment of 35 ° C. and 85% RH. After humidity conditioning, under the same environment, friction was charged by mixing pseudo toner and ferrite carrier for 60 minutes with a desktop roller mill, and manufactured by Toshiba Chemical, blow-off method charge measurement device (trade name: Model TB-200) The amount of charge was measured at. The charge amount of the pseudo toner shaken under the normal condition was compared with the charge amount of the pseudo toner measured under the stress condition, and the effect of improving the durability of the toner was measured.

(Measurement of fluidity)
The loose bulk density of the pseudo toner prepared under the above normal conditions was measured with a powder tester PT-R type manufactured by Hosokawa Micron Corporation and used as an index of fluidity. The larger the loose apparent specific gravity, the better the fluidity.

Example 1
100 parts by weight of raw silica powder (fumed silica, specific surface area 30 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 1.3 parts by weight of decyltrimethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. This was maintained for 1 hour, and the inside of the mixer was purged with nitrogen. Again, water vapor was introduced to a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Example 2
The treatment was performed in the same manner as in Example 1 except that the amount of decyltrimethoxysilane added was 2.6 parts by weight. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Example 3
The treatment was performed in the same manner as in Example 1 except that the amount of decyltrimethoxysilane added was 5.2 parts by weight. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Example 4
100 parts by weight of raw silica powder (fumed silica, specific surface area 30 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 120 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 2.6 parts by weight of decyltrimethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. This was maintained for 1 hour, and the inside of the mixer was purged with nitrogen. Again, water vapor was introduced to a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Comparative Example 1
The treatment was performed in the same manner as in Example 1 except that the addition amount of decyltrimethoxysilane was 0.6 parts by weight. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Comparative Example 2
The treatment was performed in the same manner as in Example 1 except that the amount of decyltrimethoxysilane added was 13.3 parts by weight. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Comparative Example 3
100 parts by weight of raw silica powder (fumed silica, specific surface area 30 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer at a partial pressure of 60 kPa, and 5.2 parts by weight of decyltrimethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Comparative Example 4
100 parts by weight of raw silica powder (fumed silica, specific surface area 30 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added in a state where the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 1 and 2.

Example 5
100 parts by weight of raw silica powder (fumed silica, specific surface area 60 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 10.4 parts by weight of decyltrimethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. This was maintained for 1 hour, and the inside of the mixer was purged with nitrogen. Again, water vapor was introduced to a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 3 and 4.

Example 6
100 parts by weight of raw silica powder (fumed silica, specific surface area 60 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 5.4 parts by weight of octyltriethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. This was maintained for 1 hour, and the inside of the mixer was purged with nitrogen. Again, water vapor was introduced to a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 3 and 4.

Comparative Example 5
100 parts by weight of raw silica powder (fumed silica, specific surface area 60 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer at a partial pressure of 60 kPa, and 4.0 parts by weight of hexyltrimethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. This was maintained for 1 hour, and the inside of the mixer was purged with nitrogen. Again, water vapor was introduced to a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 3 and 4.

Comparative Example 6
100 parts by weight of raw silica powder (fumed silica, specific surface area 60 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 10.4 parts by weight of decyltrimethoxysilane was sprayed and added through a one-fluid nozzle while the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 3 and 4.

Comparative Example 7
100 parts by weight of raw silica powder (fumed silica, specific surface area 60 m ² / g) was placed in a mixer, and the temperature in the mixer was adjusted to 250 ° C. while stirring and nitrogen substitution. Thereafter, water vapor was introduced into the mixer so as to have a partial pressure of 60 kPa, and 30 parts by weight of hexamethyldisilazane was added in a state where the container was sealed. It was kept for 1 hour as it was, and cooled to room temperature while performing nitrogen substitution. Thereafter, the treated silica powder was extracted. The physical properties of the obtained silica powder are shown in Tables 3 and 4.

  The silica powder produced according to the above examples has the physical properties described in the claims of the present invention, and when added to the toner, the change in the amount of charge due to stress is small and imparts good fluidity. Has the effect of

  Since the silica powder described in Comparative Examples 4 and 7 has not been treated with a silane coupling agent, the change in charge amount due to stress is large.

  Since the silica powder described in Comparative Example 1 is insufficiently treated with the silane coupling agent, the change in the charge amount due to stress is large.

  Since the silica powders described in Comparative Examples 2, 3, and 6 are not treated with hexamethyldisilazane or are insufficient, the silica powders of the examples obtained by subjecting the same raw silica powder to surface treatment Compared to the ability to impart fluidity.

In the silica powder described in Comparative Example 5, the silane coupling agent used in the treatment is out of the scope of the present invention, and the change in charge amount due to stress is large.

Claims (3)

The silica powder was surface-treated with a silane coupling agent represented by C _n H _{2n + 1} Si (OR) ₃ (wherein n represents an integer of 8 or more and R represents an alkyl group) and hexamethyldisilazane. 1.0 to 3.0 silane coupling agents and 0.2 to 1.5 trimethylsilyl groups introduced by the surface treatment of hexamethyldisilazane per 1 nm ^{2 of the} silica powder surface. Modified silica powder, characterized in that it is present in a proportion of The modified silica powder according to claim 1, wherein a difference (ΔC (%)) between a carbon amount C ₁ (%) before chloroform extraction and a carbon amount C ₂ (%) after extraction is 0.2% or less. An external toner additive for electrophotography, comprising the silica powder according to claim 1.