JP2002256170A - Hydrophobic silica powder and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrophobic silica powder which can stably maintain excellent hydrophobicity and fluidity and is useful as the fluidizing agent for various organic and inorganic powders, and the thickening agent and the reinforcing filler for resins and the like. SOLUTION: The hydrophobic silica powder is a silica powder having been surface treated with a polysiloxane and a trimethylsilylating agent, and 0.3-1.5 trimethylsilyl groups per 1 nm<2> surface area of the original silica powder of the silica powder are allowed to be present and, at the same time, the polysiloxane is attached at a ratio of A/20 pts.wt. to A/5 pts.wt. [provided that A is a specific surface area (m<2> /g) of the original silica powder] based on 100 pts.wt. original silica powder of the silica powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel hydrophobic silica powder. Specifically, hydrophobic silica that can stably maintain excellent hydrophobicity and fluidity, is useful as a fluidizing agent for various organic and inorganic powders, a thickener for resins, and a reinforcing filler The present invention relates to a powder and a method for producing the powder.

[0002]

2. Description of the Related Art Silica powder is used as a thickener for resins, reinforcing fillers and fluidizing agents for various inorganic and organic powders. Hydrophobic silica powder is preferably used.

That is, when hydrophobic silica powder is used as a thickening agent such as a resin and a reinforcing filler, the wettability with a matrix such as a resin is changed, thereby increasing the viscosity and increasing the filling amount. The effect appears. In these applications, a high degree of stability is required in which these effects are not reduced even by contact with a matrix such as a resin.

When hydrophobic silica powder is used as a fluidizing agent for the powder, silanol groups (-SiO 2) on the silica surface are compared with the case where hydrophilic silica powder is used.
Since the adhesive force of hydrogen bonding by H) is reduced, the fluidity is improved. In particular, when used as a fluidizing agent for a toner resin in electrophotographic technology represented by a copying machine and a laser printer, the chargeability changes due to moisture absorption, so that high hydrophobicity is required together with fluidity.

Conventionally, as a method for producing a hydrophobic silica powder, a raw silica powder is treated by contacting a gas of a reaction treating agent, for example, a silylating agent such as dimethyldichlorosilane or hexamethyldisilazane, with the raw silica powder. That is being done.

[0006] The hydrophobic silica powder obtained by the above-mentioned treatment method is uniformly treated, and a silica powder having high fluidity can be obtained. However, since the surface modifying group derived from the treating agent has a certain three-dimensional size, it is not possible to treat all of the silanol groups on the silica surface, which is the reaction point, and unreacted silanol groups always remain. It is desired to further reduce the remaining silanol groups and improve the hydrophobicity.

In order to improve the hydrophobicity of the powder, it is effective to spray a compound having an appropriately large molecular weight, such as polysiloxane, in the form of fine droplets to coat the silica powder. However, in this method, although the hydrophobicity increases, it is difficult to perform a uniform treatment, and there is a problem in that the fluidity is deteriorated due to excessive polysiloxane.

In view of the above, in order to produce a hydrophobic silica powder having both uniformity, fluidity and hydrophobicity, a method of coating with a polysiloxane after treating with a treating agent gas such as hexamethyldisilazane has been proposed. It has been proposed (Japanese Patent Publication No. 7-113783). However, the polysiloxane adhering to the surface of the hydrophobic silica powder obtained by this method is easily detached, and there is still room for improvement in stability.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hydrophobic silica powder having excellent hydrophobicity and fluidity and having these properties highly stabilized. .

[0010] Another object of the present invention is to provide a suitable method for producing the above-mentioned hydrophobic silica powder by a simple method.

[0011]

Means for Solving the Problems The present inventors have intensively studied to solve the above problems. As a result, the silica powder treated with a polysiloxane after being treated with a trimethylsilylating agent such as the above hexamethyldisilazane is treated with the polysiloxane after the silica surface has been covered by the trimethylsilyl group. Has been found that most polysiloxanes are extracted by an extraction test using, for example, a chloroform solvent.

As a result of further studies based on the above findings, it was found that the amount of trimethylsilyl groups present on the surface of the silica powder was within a specific range by performing the double treatment of the trimethylsilylating agent and the polysiloxane by a specific method. Succeeded in obtaining a novel hydrophobic silica powder controlled to, such hydrophobic silica powder has excellent hydrophobicity and fluidity, the extraction amount of polysiloxane in an extraction test with a chloroform solvent is extremely small, The inventors have found that they have extremely stable properties chemically, and have completed the present invention.

That is, the present invention is a silica powder surface-treated with a polysiloxane and a trimethylsilylating agent, wherein the trimethylsilyl group has a surface area of 1 n of the original silica powder.
0.3 to 1.5 parts per m ² , and the polysiloxane is based on 100 parts by weight of the raw silica powder.
A hydrophobic silica powder characterized by being adhered at a ratio of A / 20 to A / 5 parts by weight (where A is the specific surface area (m ² / g) of the original silica powder).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, silica powder obtained by a known method is used without any particular limitation as a raw silica powder which is a silica powder before a treatment, and dry silica, wet silica, sol -Gel silica is typical. In addition, these silicas may be partially or entirely fused silica powder.

The above-mentioned fumed silica is generally obtained by burning a silicon compound such as silicon tetrachloride in an oxyhydrogen flame. Generally, it is also called fumed silica. Dry silica has a specific surface area of about 5 by changing the manufacturing conditions.
Silica ranging 0~500m ² / g is obtained. The primary particle diameter of silica calculated from the specific surface area is about 5 to 2
It is in the range of 00 nm, but usually exists as an aggregate of 1 μm or more.

A typical example of wet silica is precipitated silica in which sodium silicate is neutralized with a mineral acid to precipitate silica in a solution. Generally, it is also called white carbon.

Gel silica produced by neutralizing sodium silicate with an acid is also a kind of wet silica.
The pulverized product can be used as the raw silica powder of the present invention.

Various silicas have been obtained by changing the production conditions of the wet silica, and the specific surface area is about 50 to 50.
Those having a range of 1000 m ² / g are obtained. The wet silica has a primary particle diameter of about 3 to 5 depending on the production method.
It is considered that 0 nm fine particles are aggregated particles that are aggregated during synthesis. These wet silicas are usually filtered or washed after the neutralization reaction, dried, and, if necessary, pulverized to obtain powders. Generally, the average particle size of available wet silica particles is from 1 to several hundreds μm.

Further, the sol-gel method silica is produced by hydrolyzing a silicon alkoxide such as tetramethoxysilane or tetraethoxysilane in an acidic or alkaline aqueous organic solvent. Silicon alkoxides are expensive, but have the characteristic that extremely high-purity silica can be obtained because the raw materials can be highly purified by distillation. When the hydrolysis is carried out in an acidic or alkaline concentrated solution, bulk silica is obtained, and by crushing the silica, amorphous silica particles of 1 to several hundred μm are obtained.

As the sol-gel silica, so-called silica-based composite oxides such as silica-titania, silica-alumina and silica-zirconia can be used as the raw silica powder of the hydrophobic silica powder of the present invention. These are silicon alkoxides and titanium, aluminum,
It is obtained by co-hydrolyzing a metal alkoxide such as zirconium. These silica-based composite oxides can exhibit useful properties not found in ordinary silica, depending on the chemical and physical properties of the metal oxide other than silicon used. For example, the refractive index of the silica-based composite oxide can be adjusted by changing the content of the metal oxide.

In the present invention, as the raw silica powder, silica having a suitable particle size and specific particle size (specific surface area) may be selected from the above-mentioned types and used. Preferably, fumed silica can be used.

It is an object of the present invention that the amount of the introduced trimethylsilyl group in the hydrophobic silica powder of the present invention is adjusted to 0.3 to 1.5 per 1 nm ² of the surface area of the raw silica powder. It is extremely important to achieve.

When the introduction amount of the above trimethylsilyl group is larger than the range of 1.5 per 1 nm ² of the surface area of the raw silica powder, the polysiloxane as another hydrophobizing agent is easily released, and the hydrophobic silica The effect of the powder is not maintained stably. The ease of desorption of polysiloxane can be confirmed by an extraction test with chloroform. When the number of trimethylsilyl groups exceeds 1.5, the residual amount of polysiloxane in the extraction test is extremely reduced.

Incidentally, when the silica surface is treated with a trimethylsilylating agent such as hexamethyldisilazane by a general method, the surface area of the raw silica powder is 1n.
Approximately 2.2 trimethylsilyl groups per m ² are introduced and reach saturation, and the effect of the present invention cannot be achieved. Of the attached amount of polysiloxane on the hydrophobic silica described in detail in A / 2
5 or more (where A is the specific surface area of the original silica powder (m ² /
g). ) Remains, and extremely high stability can be obtained.

In addition, the hydrophobic silica powder of the present invention has a hydrophobicity even if the content of polysiloxane is the same as that of the above-mentioned hydrophobic silica powder in which the ratio of trimethylsilyl groups exceeds the upper limit of the range of the present invention. Has a surprising effect of greatly improving

On the other hand, when the amount of trimethylsilyl group introduced is less than the range of 0.3 per 1 nm ² of surface area of the raw silica powder, the effect of improving the fluidity and hydrophobicity exhibited in cooperation with the polysiloxane is obtained. Do not appear sufficiently, and the object of the present invention cannot be achieved.

In the hydrophobic silica powder of the present invention, the amount of polysiloxane adhered to the silica powder is A / 20 to A / 5, preferably A / 14 to A / 6 (100 parts by weight of the original silica powder). Here, A is the specific surface area (m ² / g) of the raw silica powder.)

That is, when the amount of the polysiloxane is more than A / 5 based on 100 parts by weight of the raw silica powder, the silica is agglomerated and the fluidity is remarkably reduced. When the amount of the polysiloxane is less than A / 20, the effect of improving the hydrophobicity by the polysiloxane is not sufficiently exhibited.

In the hydrophobic silica powder of the present invention, the attached polysiloxane includes those that are chemically bonded to the surface of the raw silica powder and those that are not chemically bonded. .

In the present invention, the polysiloxane is not particularly limited, and a known one can be used without any particular limitation. For example, those represented by the following general formula are typical.

[0031]

Embedded image

(Where R is an alkyl group, R ′ is hydrogen,
The same or different groups selected from an alkyl group, a halogen-modified alkyl group and a phenyl group, R ″ represents an alkyl group or an alkoxy group, and R ′ ″ represents an alkyl group or an alkoxy group, respectively. Specific examples include dimethylpolysiloxane, methylphenyl silicone oil, methyl hydrogen silicone oil, alkyl-modified silicone oil, fluorine-modified silicone oil, and terminal-reactive silicone oil. Among them, dimethylpolysiloxane (R, R ′, R ″, R ′ ″ in the formula, which is inexpensive and easy to handle)
Are all methyl groups).

With respect to the hydrophobic silica powder of the present invention, the amount of trimethylsilyl groups present in the surface area of 1 nm ² of the raw silica powder, the amount of polysiloxane attached to the silica powder,
The amount of the polysiloxane remaining after the extraction can be measured by the following method.

(1) Put the hydrophobic silica powder in an electric furnace,
Hold at 500 ° C. for 1 hour or more in a nitrogen atmosphere.
The absence of the treatment agent adhering to the surface is confirmed by floating on water and mixing the silica powder with water. The specific surface area of the silica powder heat treated by this method is determined by BE
By measuring by the T method, the specific surface area of the raw silica powder can be confirmed.

The specific surface area of this bulk silica powder is S (m ²
/ G). The mass before heat treatment is W ₁ and the mass after heat treatment is W _2, and the ratio (G) of the original silica powder to the weight of the hydrophobic silica powder is calculated.

G = W ₂ / W ₁

(2) Next, the amount of trimethylsilyl groups present in the silica powder was determined by first using a hydrophobic silica powder having a known amount of trimethylsilyl groups in an inert gas.
Pyrolyze at a temperature of 0 ° C., measure the peak of hexamethyldisiloxane by gas chromatography, and draw a calibration curve. It can be confirmed by measuring the target hydrophobic silica powder by the same method. At this time,
It is necessary to correct the mass of the hydrophobic silica powder to be introduced at the time of measurement to the mass of the raw silica powder by the G obtained in the above (1). The amount of trimethylsilyl groups present per 100 parts by weight of the raw silica powder is defined as T (parts by weight).

The number (N; number) of trimethylsilyl groups per 1 nm ^{2 of the} bulk silica powder is determined by the following equation.

N = T × 82.2 / S

(3) The carbon content of the hydrophobic silica powder is measured by a trace carbon analyzer (EMIA manufactured by Horiba). The measured carbon content is defined as C ₁ (%).

(4) The amount of the polysiloxane adhering to the surface is determined by first extracting the polysiloxane adhering to the surface with chloroform, evaporating the chloroform of the extract to make only polysiloxane, and reducing the carbon content of the polysiloxane. CHN coder (YANACO MT-5)
Measured by The obtained carbon content is defined as C ₂ (%). According to the following formula, the original silica powder of polysiloxane 100
The amount of adhesion to the parts by weight (P ₁ ; parts by weight) is calculated.

P ₁ = (49.2T-100C ₁ -C
_{1 T) / (C 1 -C} 2)

(5) The amount of polysiloxane remaining after the extraction is determined by soxhlet extraction using hydrophobic silica powder with chloroform as a solvent for 8 hours. The carbon content of the hydrophobic silica powder after extraction was determined using a trace carbon analyzer (Hori
It is measured by EMIA manufactured by Ba. The measured carbon content is defined as C ₃ (%). The adhesion amount (P ₂ ; parts by weight) of the polysiloxane remaining after the extraction to 100 parts by weight of the raw silica powder is calculated by the following equation.

P ₂ = (49.2T-100C ₃ -C ₃ T)
/ (C ₃ -C ₂₎

The amount of trimethylsilyl group in the surface area of 1 nm ² of the raw silica powder, the amount of the polysiloxane adhered to the silica powder, and the amount of the polysiloxane remaining after the extraction, calculated by the above method, are shown in Examples described later. As described above, the values almost coincide with the values calculated from the manufacturing method, and it is understood that these amounts can be accurately obtained.

The method for producing the hydrophobic silica powder of the present invention comprises:
Although not particularly limited, the following method is preferred.

That is, according to the present invention, there is provided a method for producing a hydrophobic silica powder, which comprises treating a silica powder with a polysiloxane and then a trimethylsilylating agent.

In the method for producing hydrophobic silica powder of the present invention, the treatment with polysiloxane can be performed by a known method. For example, the method can be carried out by putting silica powder into a mixer, spraying the polysiloxane with stirring under a nitrogen atmosphere, and keeping the mixture at a predetermined temperature for a certain time.

The polysiloxane to be sprayed may be dissolved in a solvent in advance.

The temperature at the time of the above treatment depends on the kind of the polysiloxane, but it is necessary that the temperature be lower than the decomposition temperature of the polysiloxane. On the other hand, if the treatment temperature is too low, the bonding force between the polysiloxane and the raw silica powder is low, and the effect of the treatment cannot be obtained. Therefore, it is necessary to perform the treatment at an appropriate temperature according to the treatment agent. For example, in the case of using dimethylpolysiloxane, it is performed in the range of 200 to 300 ° C.

Further, the holding time depends on the type of the treating agent and the treating temperature.
When the reaction is performed for 10 to 120 minutes, preferably,
30 to 60 minutes.

The amount of the polysiloxane adhered to the raw silica powder can be appropriately adjusted by the amount added in the above treatment.

The polysiloxane that can be used in the above method is not particularly limited, and known polysiloxanes can be used without any particular limitation. Of which 10 to 100 at 25 ° C
Those having a viscosity of 0 cSt are preferred. Further, dimethylpolysiloxane is most preferred.

On the other hand, the treatment with the trimethylsilylating agent is performed after the treatment with the polysiloxane. The treatment with the trimethylsilylation agent can be obtained, for example, by putting silica powder treated with the polysiloxane into a mixer, introducing a certain amount of the trimethylsilylation agent into the mixer, and maintaining the mixture at a predetermined temperature for a predetermined time.

The amount of the trimethylsilylating agent to be introduced must be greater than the desired reaction amount. When the treatment is performed at a temperature equal to or higher than the boiling point of the trimethylsilylating agent, it is preferable to keep the partial pressure of the trimethylsilylating agent in the mixer at a certain level or more in order to shorten the treatment time. For example, using hexamethyldisilazane as a trimethylsilylating agent,
When the treatment temperature is 250 ° C., it is preferable to maintain the partial pressure in the mixer at 5 kPa or more.

Prior to the introduction of the trimethylsilylating agent, it is also possible to introduce steam. The treatment temperature may be lower than the decomposition temperature of the treatment agent, but is preferably at a temperature higher than the boiling point of the trimethylsilylating agent. The processing time depends on the type of the processing agent, the processing temperature, and the amount of the processing agent to be added, but hexamethyldisilazane is reacted at 250 ° C., and the partial pressure of hexamethyldisilazane in the mixer is reduced to 20%.
When the pressure is set to kPa, the treatment is performed for 5 minutes or more, preferably 15 minutes or more.

The trimethylsilylating agent that can be used in the present invention is not particularly limited, but for example, those represented by the following general formula are preferably used.

(Me ₃ Si) _n Z wherein Me is a methyl group, n is an integer of 1 or 2, Z is —OH, —OR, —NR ′ _2- nx, —ONR ′ ₂ , R ′ Is an alkyl group having 1 to 4 carbon atoms, X is the same as H or R ′] or Me ₃ SiY (where Me is a methyl group, Y is a halogen atom)

Specific examples of the trimethylsilylating agent suitably used in the present invention include trimethylsilanol,
Trimethylmethoxysilane, trimethylchlorosilane,
Aminomethyltrimethylsilane, hexamethyldisilazane, dimethylaminotrimethylsilane, and diethylaminotrimethylsilane. Preferably, hexamethyldisilazane is used.

[0060]

As will be understood from the above description, the hydrophobic silica powder of the present invention restricts the amount of trimethylsilyl groups to a specific range, thereby simultaneously reducing the bonding force of polysiloxane which is simultaneously attached to the surface. This makes it possible to improve the composition, exhibit extremely high stability, and exhibit excellent performance in fluidity and hydrophobicity.

Accordingly, it is possible to exhibit good performance in use as a thickener such as a resin, a thickener such as a resin, and a filler, in addition to a fluidizing agent for toner and the like, and it can be said that its industrial value is extremely high. .

[0062]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

The properties of the samples (silica powders according to Examples and Comparative Examples) were evaluated by measuring the following values.

1. Measurement of the amount of the trimethylsilyl group, the amount of the attached polysiloxane, and the amount of the polysiloxane remaining after the extraction on the obtained hydrophobic silica powder (sample) were carried out according to the above-described measurement methods.

2. The amount of the trimethylsilyl group, the amount of the attached polysiloxane, and the amount of the polysiloxane remaining after the extraction were confirmed by the following method from the production method, and the confirmation values were shown in parentheses to the right of the measured values.

(1) The carbon content of the hydrophobic silica powder was determined by measuring with a trace carbon analyzer (EMIA manufactured by Horiba). The value of the obtained carbon content is defined as C ₁ %.

(2) The adhesion amount of the polysiloxane silica powder is the same as the amount of the added polysiloxane. The amount of polysiloxane adhered to 100 parts by weight of the raw silica powder in the hydrophobic silica powder is defined as P ₁ (parts by weight).

(3) The amount of trimethylsilyl group per 100 parts by weight of the raw silica powder (T; parts by weight) and the number of the raw silica powder per 1 nm ² of surface area (N; pieces) were calculated by the following equations. At this time, the carbon content of the polysiloxane, which can be calculated from the molecular formula of the attached polysiloxane, is C _2, and the specific surface area of the raw silica powder is S (m ² / g).

T = (C ₂ P ₁ -100 C ₁ -C ₁ P ₁ ) / (C ₁ -49.
2) N = T × 82.2 / S

(4) The amount of polysiloxane remaining after the extraction was determined by soxhlet extraction using hydrophobic silica as a solvent with chloroform for 8 hours. The hydrophobic silica after extraction was measured and determined by a trace carbon analyzer (EMIA manufactured by Horiba). The obtained carbon content was defined as C ₃ (%), and the ratio (P ₂ ; parts by weight) of the polysiloxane remaining after extraction to 100 parts by weight of the raw silica was calculated by the following equation. The amount of polysiloxane remaining after the extraction and P _2.

P ₂ = (49.2T-100C ₃ -C ₃ T)
/ (C ₃ -C ₂₎

3. Hydrophobicity test The degree of hydrophobicity was measured by the following method and used as an index of hydrophobicity. 0.2 g of hydrophobic silica powder was added to 50 ml of water in a 250 ml beaker. Methanol was added from the burette until all of the silica was suspended. At this time, the solution was introduced into the solution with a tube so that methanol did not directly touch the sample. The solution in the beaker was constantly stirred with a magnetic stirrer. The time when the entire amount of the hydrophobic silica powder was suspended in the solution was defined as the end point, and the percentage of the methanol volume in methanol water at the end point was defined as the degree of hydrophobicity.

4. Fluidity test The fluidity of the sample was examined by the following method. Particle size is 10μ
1% hydrophobic silica powder to spherical acrylic resin
Add, mix well with a mixer, 35 ° C, 85% humidity
For 2 days. The fluidity of the mixed powder was evaluated by measuring the degree of compression with a powder tester (manufactured by Hosokawa Micron Corporation, PT-R type). The compression degree is represented by the following equation. The loose apparent specific gravity in the formula is an apparent specific gravity measured in a state in which the mixed powder is put in a 100 ml cup without tapping, and the solidified apparent specific gravity is an apparent specific gravity after tapping 180 times.

Compressibility = (solid apparent specific gravity−loose apparent specific gravity) / solid apparent specific gravity × 100 When 1% compressibility is changed by this method, it can be said that fluidity is greatly different.

Example 1 Dry silica having a specific surface area of 200 m ² / g was put in a mixer and dimethylpolysiloxane (kinematic viscosity: 50 c
St) was added at 20 parts by weight and kept at 250 ° C. for 30 minutes. Subsequently, after adding 10 parts by weight of hexamethyldisilazane, the mixer was closed and kept at 250 ° C. for 30 minutes. At this time, the partial pressure of hexamethyldisilazane in the mixer was 3
It was 0 kPa. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows physical properties.
Shown in

Example 2 A treatment was performed under the same conditions as in Example 1 except that the amount of dimethylpolysiloxane was changed to 30 parts by weight. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows the physical properties.

Example 3 Processing was performed under the same conditions as in Example 1 except that the processing temperature was 220 ° C. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows the physical properties.

Example 4 A treatment was performed under the same conditions as in Example 2 except that the specific surface area of the raw silica powder was changed to 300 m ² / g. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows the physical properties.

Comparative Example 1 Hydrophilic dry silica having a specific surface area of 200 m ² / g was put in a mixer, 10 parts by weight of hexamethyldisilazane was added under a nitrogen atmosphere, and then the mixer was closed and kept at 250 ° C. for 30 minutes. At this time, the partial pressure of hexamethyldisilazane in the mixer was 30 kPa. Subsequently, 20 parts by weight of dimethylpolysiloxane (kinematic viscosity: 50 cSt) was added,
It was kept at 250 ° C. for 30 minutes. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows physical properties.

Comparative Example 2 Hydrophilic dry silica having a specific surface area of 200 m ² / g was put in a mixer and dimethylpolysiloxane (kinematic viscosity) was placed under a nitrogen atmosphere.
50 cSt) was added, and the mixture was kept at 250 ° C. for 60 minutes. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows the physical properties.

Comparative Example 3 A hydrophilic dry silica having a specific surface area of 200 m ² / g was put in a mixer and dimethylpolysiloxane (kinematic viscosity
50 cSt) was added, and the mixture was kept at 250 ° C. for 60 minutes. Table 1 shows the amounts of trimethylsilyl groups and polysiloxane in the obtained hydrophobic silica powder, and Table 2 shows the physical properties.

[0082]

[Table 1]

[0083]

[Table 2]

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G072 AA41 GG01 GG02 GG03 HH14 HH28 HH29 4J002 AA001 DJ016 FB146 FB266 GS00 4J037 AA18 CB23 CB26 CC28 EE02 EE03 EE04 EE25 EE43 EE44 EE50 FF17

Claims (6)

[Claims] 1. A silica powder obtained by subjecting an original silica powder to a surface treatment with a polysiloxane and a trimethylsilylating agent, wherein the ratio of trimethylsilyl groups is 0.3 to 1.5 per 1 nm ² of surface area of the original silica powder. A / 20 to A / 5 parts by weight (where A is a specific surface area (m ² / g) of the original silica powder) with respect to 100 parts by weight of the original silica powder. A) a hydrophobic silica powder which is attached at a ratio of 2. The hydrophobic silica powder according to claim 1, wherein the polysiloxane is dimethylpolysiloxane. 3. The method according to claim 1, wherein the silica powder is fumed silica.
Or the hydrophobic silica powder according to 2. 4. The residual amount of polysiloxane after the extraction treatment with chloroform is based on 100 parts by weight of the raw silica powder.
A / 25 parts by weight (where, A is the specific surface area of the drug substance silica powder (m ² / g).) Or a hydrophobic silica powder according to any of claims 1 to 3. 5. A method for producing a hydrophobic silica powder, comprising treating a silica powder with a polysiloxane and then a trimethylsilylating agent. 6. The method according to claim 5, wherein the polysiloxane is dimethylpolysiloxane and the trimethylsilylating agent is hexamethyldisilazane.