JP7624286B2 - Surface-modified inorganic oxide powder and its manufacturing method - Google Patents

Description

The present invention relates to a novel surface-modified inorganic oxide powder and a method for producing the same.

By treating the surface of fine inorganic oxide powders such as silica, titania, and alumina with an organic substance, it is possible to modify the electrostatic chargeability, hydrophobicity, and other properties of the powder surface. The surface-modified inorganic oxide powders thus obtained are widely used as flowability improvers and electrostatic charge adjusters for toners used in electrophotography, including copying machines, laser printers, and plain paper facsimiles. Such surface-modified inorganic oxide powders used for toner applications are known as so-called external additives.

Surface treatment agents for inorganic oxide powders used in toner applications include organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil. Surface treatment with these organosilicon compounds can, for example, replace the silanol groups on the surface of silica fine particles with organic groups to provide a hydrophobic treatment. As part of these surface-treated inorganic oxide powders, fumed oxides are widely used as materials that impart high fluidity to toner materials.

The toner is stirred in a copying machine or other device, and is charged (i.e., electrified) by friction with the carrier, etc. Then, the toner can exhibit its developing function due to its highly controlled electrification. However, if the toner is continuously stirred in the device for a long time, the strong frictional force becomes stressful, and the toner deteriorates. For example, if an external additive is embedded in the toner surface, it loses its function as a contact point between the toner surface and the external environment. Moreover, the mechanical burden on the toner has increased in recent years, and the hardness of the toner matrix has decreased due to the softening design of the binding resin (toner matrix resin) that constitutes the toner, making it easier for the external additive to be embedded. For this reason, the importance of measures to prevent the embedding of external additives as described above is increasing.

In particular, in recent years, the improvement in image quality of electrophotography has led to the reduction in the particle size of toner particles, and in addition, the increase in speed and color printing has placed a greater mechanical load on the toner. As a result, the durability of toner performance over time (control of deterioration behavior) is becoming increasingly important, but at the same time, the binding resin used in toner is required to have low-temperature fixability in order to reduce printing standby time and save energy. For these reasons, it is becoming mainstream to use softened and low-melting point components as the toner base resin.

As the melting point of toner resins becomes lower, the surface-treated fumed oxides become embedded in the toner resin during long-term operation, reducing its fluidity. To improve the durability of the toner, submicron-sized silica powder is added to the toner surface together with the fumed oxides, and the submicron-sized silica powder exerts a spacer effect to prevent the fumed oxides from becoming embedded in the toner. As the submicron-sized silica, silica powder produced by the sol-gel method is mainly used (see Patent Document 1, etc.).

However, silica powder produced by the sol-gel method has the problem of weak electrostatic charging properties. One of the reasons for this is thought to be the high amount of moisture adsorbed by the particles that make up the silica powder produced by the sol-gel method.

Furthermore, the silica powder produced by the sol-gel method has a nearly spherical particle shape, which means that it tends to separate from the toner surface over long periods of use.

Furthermore, silica powder produced by the sol-gel method tends to retain or adsorb a large amount of moisture, making it impossible to obtain strong triboelectric charging properties. For this reason, in order to produce materials that adjust the charge, such as toner, the low charging properties must be improved.

In contrast, silica powder produced by the dry method or gas phase method (hereinafter, both are collectively referred to as the "fumed method") has a particle shape that is less spherical than silica produced by the sol-gel method, so it is expected to suppress the problem of sol-gel silica being released from the toner surface. However, silica powder produced by the fumed method generally has a small primary particle size and is dispersed on the toner surface as particles of submicron size or less, so it cannot fully exert the spacer effect, and in addition, its charging characteristics are generally too high, so the amount added and dispersibility must be precisely controlled to control the charging characteristics of the toner within an appropriate range.

JP 2013-249215 A

For the reasons mentioned above, there is a strong demand for the development of toner additives (particles) that have suitable charging properties while still being submicron sized enough to fully obtain the spacer effect, but such materials have yet to be developed.

The main objective of the present invention is therefore to provide a powder that takes advantage of the excellent properties of inorganic oxide powder produced by the fumed method while also having a good spacer effect and suitable charging properties.

As a result of extensive research into the problems of the prior art, the inventors discovered that the above objectives could be achieved by using particles with specific structures and characteristics as external additives, and thus completed the present invention.

That is, the present invention relates to the following surface-modified inorganic oxide powder and a method for producing the same.
1. A powder consisting of particles containing inorganic oxide particles and an organosilicon compound that coats the surfaces of the particles, the powder having the following physical properties:
(1) Average particle size: 0.1 to 1 μm,
(2) Bulk density: 20 to 100 g / L,
(3) Hydrophobicity: 60% or more,
(4) Water adsorption amount at a water vapor relative pressure of 0.8 to 0.95: 2 to 5%;
(5) BET specific surface area: 25 to 150 m ² /g,
(6) Carbon content: 0.5 to 8% by weight, and (7) Triboelectric charge: -100 to -500 μC/g
A surface-modified inorganic oxide powder exhibiting negative charging properties, characterized in that it has
2. The surface-modified inorganic oxide powder according to item 1, wherein the organosilicon compound is at least one of hexamethyldisilazane, polydimethylsiloxane, and alkylsilane.
3. The surface-modified inorganic oxide powder according to item 1, wherein the inorganic oxide particles are fumed silica particles having a BET specific surface area of 100 to 250 m ² /g.
4. An external additive for toner or powder coating, comprising the surface-modified inorganic oxide powder according to any one of items 1 to 3.
5. A toner composition or a powder coating composition for electrophotography, comprising the external additive according to Item 4 and binder resin particles.
6. A method for producing a surface-modified inorganic oxide powder, comprising the steps of:
(a) preparing a mixture containing an inorganic oxide powder and an organosilicon compound;
(b) heat-treating the mixture at a temperature of 120 to 360° C.
7. The method according to item 6, wherein the steps (a) and (b) are carried out under stirring.

According to the present invention, it is possible to provide a powder that has both a good spacer effect and appropriate charging properties while taking advantage of the excellent properties of inorganic oxide powder produced by the fumed method. In particular, inorganic oxide particles produced by a dry method (fumed method or gas phase method) have unique internal pores, and by subjecting the surfaces of such particles to the surface modification specified by the present invention, the bulk density, water adsorption amount, etc. become unique properties, and it is possible to provide a submicron-sized powder that has a low bulk density but appropriate charging properties (negative charging).

More specifically, the surface-modified inorganic oxide powder of the present invention is an inorganic oxide powder having internal pores that has been surface-modified with a specific organosilicon compound, and as a result, the bulk density, hydrophobicity, water adsorption amount, surface area, carbon content, and other properties are controlled within a certain range. As a result, the powder exhibits higher charging properties than particles produced by the sol-gel method, and is capable of achieving sufficient cohesiveness to exhibit a spacer effect that cannot be obtained with silicon oxide powder produced by the conventional fumed method.

As described above, in order to solve the problems associated with surface-treated sol-gel silica produced by a wet method, the present invention has succeeded in providing a surface-modified inorganic oxide powder that has been surface-treated to improve problems associated with toners that reduce environmental impact, such as reduced toner fluidity, by producing an inorganic oxide powder with internal pores produced by a dry method, and that combines high charging properties with low bulk density, which was previously difficult to achieve with sol-gel silica.

The powder of the present invention having such characteristics can be suitably used as an external additive, particularly for toners or powder coatings. Therefore, the toner composition for electrophotography or the powder coating composition containing the surface-modified inorganic oxide powder of the present invention contains the surface-modified inorganic oxide powder having such a high fixation rate and high hydrophobicity, and therefore has excellent fluidity, antistatic properties, etc., and suppresses fogging or cleaning failure. Furthermore, it is difficult for the toner to adhere to the photoreceptor, and image defects are unlikely to occur. In addition, the composition of the present invention can also provide effects such as long-term storage stability and control of developer deterioration behavior.

FIG. 2 is a particle size distribution diagram of the powder obtained in the examples. FIG. 2 is a particle size distribution diagram of the powder obtained in the comparative example. FIG. 11 is a schematic diagram of a method for observing toner particles with an SEM in Test Example 2.

1. Surface-modified inorganic oxide powder The surface-modified inorganic oxide powder exhibiting negative charging property (the powder of the present invention) of the present invention is a powder consisting of particles containing inorganic oxide particles and an organosilicon compound that coats the surfaces of the particles, and has the following physical properties:
(1) Average particle size: 0.1 to 1 μm,
(2) Bulk density: 20 to 100 g / L,
(3) Hydrophobicity: 60% or more,
(4) Water adsorption amount at a water vapor relative pressure of 0.8 to 0.95: 2 to 5%;
(5) BET specific surface area: 25 to 150 m ² /g,
(6) Carbon content: 0.5 to 8% by weight, and (7) Triboelectric charge: -100 to -500 μC/g
The present invention is characterized by having the following.

<Constitution (composition) of the powder of the present invention>
The particles constituting the powder of the present invention include inorganic oxide particles and an organosilicon compound that coats the surfaces of the particles. That is, the powder has a basic structure in which an inorganic oxide particle is used as a core particle (base particle), and the surface of the core particle is partially or entirely coated with an organosilicon compound.

The inorganic oxide particles that become the core particles are not limited in type, and examples include, but are not limited to, silicon oxide, titanium oxide, aluminum oxide, etc. Among these, silicon oxide (silica) is preferably used in the present invention. These particles themselves can be publicly known or commercially available.

The particle size of the inorganic oxide particles is not limited, but may usually be a primary particle size of about 5 to 150 nm, and the BET specific surface area of the inorganic oxide may usually be, but is not limited to, about 30 to 400 m ² /g.

The method for producing inorganic oxide particles preferably uses powder produced by the fumed method. The fumed method is a known method, and can synthesize silica by a method including a step of introducing a silicon compound (such as silicon tetrachloride) or metallic silicon into an oxygen-hydrogen flame to cause a hydrolysis reaction. As described above, such powder has a particle shape that is less spherical than silica produced by the sol-gel method, and therefore has the advantage of being able to effectively suppress separation from the toner surface. In addition, since no solvent is used, there is also the advantage that no aggregated particles are generated during drying.

The inorganic oxide particles produced by the fumed method can be publicly known or commercially available. For example, the commercially available products shown in the examples below can be suitably used.

The organosilicon compound that coats the surface of the inorganic oxide particles is not particularly limited, and for example, publicly known or commercially available compounds known as hydrophobic treatment agents can be used.

More specifically, alkylsilazane compounds such as hexamethyldisilazane, alkylalkoxysilane compounds such as dimethyldimethoxysilane, diethyldiethoxysilane, trimethylmethoxysilane, methyltrimethoxysilane, and butyltrimethoxysilane, chlorosilane compounds such as dimethyldichlorosilane and trimethylchlorosilane, silicone oils such as polydimethylsiloxane (PDMS), silicone varnishes, etc. can be used. These may be used alone or in combination of two or more.

Among these, it is preferable to use at least one of an alkylsilazane compound, an alkylalkoxysilane compound, and a silicone oil, in order to more reliably obtain the effects of the present invention. In particular, at least one of hexamethyldisilazane, polydimethylsiloxane, and an alkylalkoxysilane is more preferable.

In particular, the alkylalkoxysilane compound is not particularly limited as long as it is an alkoxysilane having an alkyl group, and examples include trimethoxyalkoxysilane and triethoxyalkoxysilane. The number of carbon atoms (C) of the alkyl group is not particularly limited, but it is preferably C2 to C18. If it is less than C2, there is a risk of the alkoxysilane volatilizing during the surface treatment. Furthermore, if it exceeds C16, strong aggregation may occur due to the effect of the high viscosity, and the dispersibility of the obtained powder may be impaired.

In particular, in addition to polydimethylsiloxane, modified silicone oils into which alkyl groups, -OH groups, etc. have been introduced can also be used as silicone oils.

The viscosity range of the organosilicon compound (measurement temperature 25°C) is not particularly limited, but is usually preferably 20 to 300 cs. If the viscosity is less than 20 cs, low molecular weight polysiloxanes and the like will volatilize during surface treatment, which is undesirable from the standpoint of energy efficiency and the environment. On the other hand, if the viscosity exceeds 300 cs, higher aggregation will occur, and the dispersibility of the resulting powder may be impaired.

The content of the organosilicon compound in the powder of the present invention is not particularly limited as long as it is within the range of the carbon content described above, but it is generally about 5 to 20 parts by weight, and preferably 10 to 15 parts by weight, per 100 parts by weight of the inorganic oxide powder.

<Characteristics of the powder of the present invention>
The powder of the present invention has the following properties:
(1) Average particle size: 0.1 to 1 μm,
(2) Bulk density: 20 to 100 g / L,
(3) Hydrophobicity: 60% or more,
(4) Water adsorption amount at a water vapor relative pressure of 0.8 to 0.95: 2 to 5%;
(5) BET specific surface area: 25 to 150 m ² /g,
(6) Carbon content: 0.5 to 8% by weight, and (7) Triboelectric charge: -100 to -500 μC/g
Satisfy all of the following.

Average particle size The average particle size is usually about 0.1 to 1 μm, and preferably 0.2 to 0.8 μm. By having a particle size within the above range, the function as a spacer can also be effectively fulfilled. The average particle size in the present invention refers to a value (arithmetic mean diameter (volume standard)) calculated using a particle size distribution measuring device (laser diffraction scattering type particle size distribution measuring device (manufactured by Horiba, Ltd.)).

Bulk density The bulk density is usually about 20 to 100 g/L, and preferably 30 to 80 g/L. If the bulk density is less than 20 g/L, the powder cannot be dispersed with an appropriate aggregate particle size when dispersed on the toner surface, and a sufficient spacer effect cannot be exhibited. If the bulk density exceeds 100 g/L, a large device volume is required when mixing with the toner, which is problematic for industrial use.

Hydrophobicity The hydrophobicity is usually about 60% or more, preferably 97% or more, and more preferably 99% or more. The hydrophobicity in the present invention is an index showing the degree of hydrophobicity of the surface-modified inorganic oxide powder. If the hydrophobicity is less than 60%, the inorganic oxide powder may not be able to retain strong electrostatic properties due to the residual silanol groups, and a submicron-sized powder with excellent electrostatic properties may not be obtained. The upper limit of the hydrophobicity is not particularly limited, but is usually 100%.

Moisture adsorption amount The moisture adsorption amount at a water vapor relative pressure of 0.8 to 0.95 is usually about 2 to 5% by weight, and preferably 2.5 to 4.0% by weight. The moisture adsorption amount has a large effect on the charging characteristics, and by setting it within the above range, it is possible to impart an appropriate charging property. If the moisture adsorption amount is less than 2% by weight, for example, silica powder will exhibit the charging characteristics specific to fumed silica, and will become too strongly negatively charged. If the moisture adsorption amount exceeds 5% by weight, the amount of moisture retained and adsorbed will be close to that of silica produced by the sol-gel method, and sufficient charging characteristics will not be exhibited.

BET specific surface area The BET specific surface area is usually about 25 to 150 m ² /g, and preferably 30 to 130 m ² /g. If the BET specific surface area is less than 25 m ² /g, the aggregate particle size is too large, resulting in insufficient dispersibility when dispersed in toner. If the BET specific surface area is more than 150 m ² /g, the appropriate aggregate size is not maintained when dispersed in toner, and a sufficient spacer effect cannot be achieved.

Carbon Content The carbon content is usually about 0.5 to 8% by weight, preferably 0.8 to 6.0% by weight. In particular, when the surface treatment agent (hydrophobic treatment agent) is HMDS, it is preferably about 0.5 to 2.0% by weight, when it is PDMS, it is preferably about 0.5 to 8.0% by weight, and when it is alkylalkoxysilane, it is preferably about 0.5 to 8.0% by weight. The carbon content is an index showing the degree of fixation (fixed amount) to the inorganic oxide powder by the organic silicon compound which is the surface treatment agent. If the carbon content is too low, the surface is not sufficiently modified, the hydrophobicity cannot be sufficiently given, and the charging characteristics, dispersibility, etc. become insufficient. On the other hand, if the carbon content is too high, the organic matter content is too high, so that the particles aggregate, and sufficient fluidity and dispersibility cannot be obtained, and even if this powder is applied to a toner, a sufficient spacer effect cannot be expressed.

Triboelectric charge amount The triboelectric charge amount is usually about -100 to -500 μC/g, and preferably -150 to -350 μC/g. If the triboelectric charge amount approaches zero from -100 μC/g, it becomes difficult to develop strong charging characteristics in the toner when the powder is added to the toner, and it becomes difficult to control the toner within a predetermined charge amount range. On the other hand, if the triboelectric charge amount becomes more negative than -500 μC/g, it becomes difficult to control the charging characteristics of the toner to which it is added due to the strong triboelectric charge amount.

2. Method for Producing the Powder of the Present Invention The method for producing the powder of the present invention is not particularly limited as long as it can produce a powder having the above-mentioned composition and characteristics. For example, the powder of the present invention can be suitably produced by a method including: (a) a step of preparing a mixture containing an inorganic oxide powder and an organosilicon compound (mixture preparation step); and (b) a step of heat-treating the mixture at a temperature of 120 to 360° C. (heat treatment step).

Mixture Preparation Step The mixture preparation step can be performed by any method that can coat the surface of each particle constituting the inorganic oxide powder with an organosilicon compound. For example, a method of mixing an inorganic oxide powder with a vaporized organosilicon compound under stirring, or a method of spraying an organosilicon compound onto an inorganic oxide powder under stirring can be suitably used.

In this case, the organosilicon compound can be used in a state of being dissolved or dispersed in a solvent (e.g., an organic solvent such as hexane or toluene) as necessary. In this case, the concentration of the organosilicon compound can be appropriately set depending on the type of organosilicon compound used, etc.

In addition, in the present invention, water and a catalyst (such as an amine) can be appropriately added to the mixture as needed.

The temperature conditions in the mixture preparation process are not particularly limited, and may be within the range of, for example, 10 to 40°C, but are not limited thereto. In addition, it is usually preferable to carry out the process in an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be suitably used.

The type and amount of the organosilicon compound used may be the same as those described in "1. Surface-modified inorganic oxide powder" above.

Heat Treatment Step The heat treatment temperature in the heat treatment step is not limited, but is usually preferably 120 to 360°C (particularly 150 to 300°C). If the heat treatment temperature exceeds 360°C, the organosilicon compound may partially decompose. If the heat treatment temperature is less than 120°C, the surface of the organosilicon compound may not be sufficiently modified, and the desired hydrophobicity may not be obtained.

As in the above process, the heat treatment is preferably performed in an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be suitably used. In particular, the above process can be performed in a sealed reactor, and the heat treatment process can be suitably performed while maintaining the atmosphere.

The heat treatment time should be long enough to allow the organosilane compound to be fixed (adhered) to the surface of each particle constituting the inorganic oxide powder, and can be, for example, about 10 to 200 minutes, but is not limited to this.

3. Use of the Powder of the Present Invention The powder of the present invention has all of the properties (1) to (7) shown in "1. Surface-modified inorganic oxide powder" above, and therefore exhibits both a good spacer effect and moderate charging properties in addition to the excellent properties of inorganic oxide powder produced by the fumed method. Therefore, the powder of the present invention can be suitably used as an additive (particularly an external additive for toner) for toners, powder coatings, etc. Therefore, the present invention also includes an electrophotographic toner composition or powder coating composition containing the powder of the present invention and binder resin particles (hereinafter, both are also collectively referred to as "the composition of the present invention").

The composition of the present invention contains the surface-modified inorganic oxide powder of the present invention described above, and there are no particular limitations on its composition or manufacturing method, and any known composition and method may be used.

The content of the powder of the present invention in the composition of the present invention is not particularly limited as long as the desired property improvement effect is obtained, but it is usually preferable that the content is about 0.1 to 5.0% by weight. If the content of the surface-modified inorganic oxide powder of the present invention in the composition of the present invention is less than 0.1% by weight, the effect of improving the flowability or stabilizing the chargeability due to the addition of the surface-modified inorganic oxide powder may not be sufficiently obtained. In addition, if the content of the surface-modified inorganic oxide powder exceeds 5.0% by weight, the surface-modified inorganic oxide powder acts independently more, and there is a risk of problems occurring, for example, in images, cleaning properties, etc.

In addition to the binder resin particles, the composition of the present invention may contain, as necessary, for example, a pigment, a charge control agent (charge control agent), wax, etc. These components may be the same as those in known or commercially available toner compositions. In addition, the type of toner is preferably a negatively charged toner, but is not otherwise particularly limited. Therefore, for example, either a magnetic or non-magnetic one-component toner or a two-component toner may be used. Furthermore, either monochrome or color may be used.

The powder of the present invention has a particularly excellent spacer effect, and can therefore be used more suitably as an external additive for adhesive resin particles that contain a resin component that is easily softened (e.g., at least one of styrene-acrylic copolymer resin, polyester resin, epoxy resin, etc.).

In the toner composition for electrophotography of the present invention, the powder of the present invention as an external additive is not limited to being used alone, but may be used in combination with other metal oxide fine powders depending on the purpose. For example, the surface-modified inorganic oxide powder of the present invention may be used in combination with other surface-modified dry silica fine powders, surface-modified dry titanium oxide fine powders, surface-modified wet titanium oxide fine powders, etc., as necessary.

The following examples and comparative examples are presented to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples.

The components used in each of the examples and comparative examples are as follows.
(A) Silica Powder (A1) Sol-gel Silica Sample produced by a known sol-gel method (BET specific surface area 30 m ² /g)
(A2) Sample A
A sample having internal porosity produced by a known fumed method (BET specific surface area 110 m ² /g)
(A3) Sample B
A sample having internal porosity produced by a known fumed method (BET specific surface area 120 m ² /g)
(A4) Commercially available product a
Product name: "AEROSIL TT600" (registered trademark) manufactured by Nippon Aerosil Co., Ltd. (fumed silica, BET specific surface area: 135 m ² /g)
(A5) Sample C
A sample with internal porosity produced by a known fumed process (BET specific surface area 165 m ² /g)
(A6) Sample D
A sample having internal porosity produced by a known fumed method (BET specific surface area 210 m ² /g)
(A7) Commercially available product b
Product name: "AEROSIL OX50" (registered trademark) manufactured by Nippon Aerosil Co., Ltd. (fumed silica, BET specific surface area 50 m ² /g)
(A8) Commercially available product c
Product name: "AEROSIL 90G" (registered trademark) manufactured by Nippon Aerosil Co., Ltd. (fumed silica, BET specific surface area 90 m ² /g)
(B) Surface treatment agent (B1) HMDS
Hexamethyldisilazane (product name: "Dynasilane HMDS" (registered trademark), manufactured by Evonik Corporation)
(B2) PDMS (A)
Polydimethylsiloxane (product name "KF96-20cs" manufactured by Shin-Etsu Chemical Co., Ltd.)
(B3) PDMS (B)
Polydimethylsiloxane (product name "KF96-300cs" manufactured by Shin-Etsu Chemical Co., Ltd.)
(B4) Alkylsilane A
Alkylsilane-based surface treatment agent (product name: DOWSIL Z-6329 (registered trademark), manufactured by Dow and Toyay Co.)
(B5) Alkylsilane B
Alkylsilane-based surface treatment agent (product name "Dynasilan 9116" (registered trademark) manufactured by Evonik)

[Example 1]
Sample A (100 parts by weight) was placed in a reactor as silica powder, and alkylsilane B (10 parts by weight) was added as a surface treatment agent under stirring in a nitrogen atmosphere. With stirring continued, the mixture was heat-treated at 150°C for 60 minutes to obtain a surface-modified silica powder having internal pores.

[Example 2]
A surface-modified silica powder was obtained in the same manner as in Example 1, except that the silica powder was changed to Sample B (100 parts by weight) and the surface treatment agent was changed to PDMS (B) (15 parts by weight).

[Example 3]
A surface-modified silica powder having internal pores was obtained in the same manner as in Example 1, except that the silica powder was changed to commercially available product A4 and the surface treatment agent was changed to HMDS.

[Example 4]
A surface-modified silica powder having internal voids was obtained in the same manner as in Example 1, except that the doped silica powder was changed to commercially available product A4 and the surface treatment agent was changed to PDMS (A).

[Example 5]
The surface treatment of the dry silica having internal voids was carried out in the same manner as in Example 4, except that the amount of PDMS (A) added was changed to 15 parts by weight.

[Example 6]
A surface-modified silica powder having internal voids was obtained in the same manner as in Example 1, except that sample C (100 parts by weight) was used as the silica powder and PDMS (A) (15 parts by weight) was used as the surface treatment agent.

[Example 7]
A surface-modified silica powder having internal pores was obtained in the same manner as in Example 1, except that sample C (100 parts by weight) was used as the silica powder and alkylsilane (A) was used as the surface treatment agent.

[Example 8]
A surface-modified silica powder having internal pores was obtained in the same manner as in Example 1, except that sample D (100 parts by weight) was used as the silica powder and alkylsilane (A) (15 parts by weight) was used.

[Example 9]
A surface-modified silica powder having internal pores was obtained in the same manner as in Example 1, except that sample D (100 parts by weight) was used as the silica powder and the surface treatment agent was changed to 5 parts by weight of HDMS and 5 parts by weight of PDMS (A) (total 10 parts by weight).

[Example 10]
A surface-modified silica powder having internal pores was obtained in the same manner as in Example 1, except that sample A (100 parts by weight) was used as the silica powder and the surface treatment agent was changed to 5 parts by weight of alkylsilane B and 5 parts by weight of PDMS (B) (total 10 parts by weight).

[Comparative Examples 1 to 3]
Sol-gel silica (100 parts by weight) was placed in a reactor as silica powder, and while stirring in a nitrogen atmosphere, the surface treatment agent shown in Table 2 was added in a predetermined amount, and the mixture was heat-treated while continuing to stir, thereby obtaining a surface-modified silica powder.

[Comparative Examples 4 to 6]
Commercially available product b (100 parts by weight) was placed in a reactor as silica powder, and while stirring in a nitrogen atmosphere, a surface treatment agent shown in Table 2 was added in a predetermined amount, and the mixture was heat-treated while continuing to stir, thereby obtaining a surface-modified silica powder.

[Comparative Examples 7 to 9]
Commercially available silica powder c (100 parts by weight) was placed in a reactor, and while stirring in a nitrogen atmosphere, a surface treatment agent shown in Table 2 was added in a predetermined amount, and the mixture was heat-treated while continuing to stir, thereby obtaining a surface-modified silica powder.

[Test Example 1]
The surface-modified silica powders obtained in the Examples and Comparative Examples were measured for the following physical properties. The results are shown in Tables 1 and 2.

(1) Bulk density Place a measuring cylinder on a balance, remove the tare, add a sample to the measuring cylinder and measure the mass (mass A), and read the volume (volume B) after leaving it to stand for 2 minutes. Calculate the bulk density using the following formula.
Bulk density (g/L) = (mass A/volume B) x 1000

(2) Hydrophobicity 1 g of surface-modified silica powder was weighed into a 200 mL separatory funnel, 100 mL of pure water was added to it, and the funnel was plugged and shaken with a Turbula mixer at 90 rpm for 10 minutes. After shaking, the funnel was left to stand for another 10 minutes, and then 20 to 30 mL of the lower layer was removed from the funnel. The lower layer mixture was then separated into a 10 mm quartz cell, and pure water was used as a blank, and the light transmittance (%) at a wavelength of 500 nm was taken as the hydrophobicity. The higher the light transmittance, the higher the hydrophobicity. This is because highly hydrophobic surface-modified inorganic oxide powders tend to float on the water surface without dispersing in the water, which makes the water less likely to become cloudy and increases the light transmittance.

(3) Moisture adsorption measurement The surface-modified silica powder was heated under vacuum at 150°C for 2 hours or more and thoroughly dried, and then measured using a high-precision gas adsorption measurement device (product name "BELSORP-max" manufactured by Microtrack-Bell Co., Ltd.) under conditions of an evacuation time of 15 minutes and a pressure rise allowance of 5.000E-1 Pa/min. The adsorption isotherm was analyzed, and the value within the range of water vapor relative pressure of 0.8 to 0.95 was taken as the moisture adsorption amount.

(4) BET Specific Surface Area The BET {surface area ( ^m2 /g)} was determined by using a fully automatic specific surface area measuring device (product name "Macsorb", Mountech Co., Ltd.) to pretreat a sample at 100°C for 10 minutes, and then calculating the surface area of the sample from the amount of nitrogen adsorbed and desorbed by the BET single-point method, and dividing the surface area by the weight to obtain the specific surface area.

(5) Carbon Content The carbon content was measured using a carbon analyzer (product name "SUMIGRAPH NC-22" manufactured by Sumika Chemical Analysis Center).
(6) Amount of triboelectric charge

2 g of surface-modified silica powder and 48 g of iron powder carrier were placed in a glass container (volume 75 mL) and shaken for 10 minutes with a Turbula mixer. 0.05 g of the mixture was then sampled and the amount of triboelectric charge was measured using a suction blow-off type Q/M meter (product name "MODEL 230TO" Trek Japan Co., Ltd.).

(7) Particle size distribution measurement Measurement was performed using a laser diffraction particle size distribution measurement device (product name "LA-920" manufactured by Horiba, Ltd.). Ethanol was used as a dispersion medium, and after adding a sample, measurement was performed under dispersion conditions of circulation intensity: 10, ultrasonic intensity: 7, and ultrasonic irradiation time: 3 minutes, and the range of particle size distribution in the arithmetic mean diameter was determined as the aggregate particle diameter.

[Test Example 2]
The surface-modified silica powder obtained in each of the Examples and Comparative Examples was mixed with a commercially available negatively charged polyester toner base (binding resin) powder produced by a polymerization method in a weight ratio of 99:1, and the mixture was premixed in a Henschel mixer at 600 rpm for 1 minute, and then mixed at 3,000 rpm for 30 minutes to prepare a toner sample for dispersibility evaluation.
Next, the obtained toner sample was observed with a scanning electron microscope (SEM), and the number of surface-modified silica particles with a particle size of 0.1 μm or ^more attached per 1 μm2 of the toner sample particle surface was counted. The results are also shown in Table 1. In the measurement, one toner base (toner particle) was arbitrarily selected within the field of view of the SEM, and the field of view S was set as shown in FIG. 3 so that the field of view S was filled with the surface of the toner particle 10 and contained as many surface-modified silica particles 11 as possible. After that, the number of all the surface-modified silica particles 11 within the field of view S was counted, and the number was divided by the field of view area to calculate the number of surface-modified silica particles per unit area (per ¹ μm2). In this case, surface-modified silica particles protruding even slightly from the field of view S were not counted.

[Test Example 3]
The particle size distribution of each of the powders obtained in Examples 3, 6, and 8, and Comparative Examples 3 and 8 was examined. The particle size distribution was measured in the same manner as described in "(7) Particle Size Distribution Measurement" above. The results are shown in Figures 1 and 2.

As is clear from the results in Tables 1 and 2 and Figures 1 and 2, the powders of the examples satisfy all of the characteristics stipulated in the present invention. In particular, they are submicron-sized powders with a low bulk density of 35 to 82 g/L and appropriate charging characteristics (negative charging of -150 to -482 μC/g).

Claims (5)

A powder comprising particles containing silicon oxide particles as inorganic oxide particles and an organosilicon compound coating the surfaces of the particles, the powder having the following physical properties:
(1) Average particle size: 0.1 to 1 μm,
(2) Bulk density: 20 to 82 g / L,
(3) Hydrophobicity: 60% or more,
(4) Water adsorption amount at a water vapor relative pressure of 0.8 to 0.95: 2 to 5%;
(5) BET specific surface area: 25 to 150 m ² /g,
(6) Carbon content: 0.5 to 8% by weight, and (7) Triboelectric charge: -100 to -500 μC/g
A surface-modified inorganic oxide powder exhibiting negative charging properties, characterized in that it has The surface-modified inorganic oxide powder according to claim 1, wherein the organosilicon compound is at least one of hexamethyldisilazane, polydimethylsiloxane, and alkylalkoxysilane. 2. The surface-modified inorganic oxide powder according to claim 1, wherein the inorganic oxide particles are fumed silica particles having a BET specific surface area of 100 to 250 m ² /g. An external additive for toner or powder coating containing the surface-modified inorganic oxide powder according to any one of claims 1 to 3. An electrophotographic toner composition or powder coating composition comprising the external additive according to claim 4 and binder resin particles.