JP2023019806A - Surface-modified silica powder using precipitated silicic acid, and production method of the same - Google Patents

Abstract

To provide a powder particularly suitable for a tonner and the like while taking advantage of characteristics original to precipitated silicic acid, by using the precipitated silicic acid.SOLUTION: The surface-modified precipitated silicic acid powder is a powder comprising a particle provided with a coated layer including an organosilicon compound on the surface of a precipitated silicic acid particle having (a) a d50 of 150-1000 nm and a d90 of 500-7000 nm in a volumetric basis particle distribution, and (b) a silanol group density of 2.5-8 OH/nm2, where (1) the bulk density is 40-150 g/L, (2) the moisture absorption amount is 3-6% at a water vapor relative pressure of 0.8-0.95, (3) the BET specific surface area is 50-200 m2/g, (4) the carbon content is 1.0-8.0 wt.%, (5) the drying loss is 0.1-3.0%, and (6) the frictional electrification amount is -50 to -200 μC/g.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a novel surface-modified silica powder using precipitated silicic acid and a method for producing the same.

By treating the surface of fine inorganic oxide powder such as silica, titania, and alumina with an organic substance, the chargeability, hydrophobicity, etc. of the powder surface can be modified. The surface-modified inorganic oxide powder obtained in this manner is widely used as a fluidity improving agent, a charge control agent, etc. for toners used in electrophotography, including copiers, laser printers, plain paper facsimiles, and the like. ing. Surface-modified inorganic oxide powders used for such toner applications are known as so-called external additives.

Examples of surface treatment agents for inorganic oxide powders used in toner applications include organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil. By surface treatment with these organosilicon compounds, for example, silanol groups on the surface of silica fine particles can be substituted with organic groups for hydrophobization. Among these surface-treated inorganic oxide powders, fumed oxides are widely used as materials that impart high fluidity to toner materials.

Toner is agitated in an apparatus such as a copier and is charged (that is, electrified) by friction with a carrier or the like. Further, the developing function can be expressed by the highly controlled chargeability. However, if the toner continues to be stirred in the apparatus for a long time, the strong frictional force becomes stress, and the deterioration of the toner progresses. For example, if the external additive is buried in the toner surface, it loses its function as a contact point between the toner surface and the external environment. In addition, the mechanical burden on the toner has increased in recent years, and the hardness of the toner base has been lowered due to the softening design of the binder resin (toner base resin) that constitutes the toner. easier to bury. Therefore, the importance of countermeasures against the burial of external additives as described above is increasing.

In particular, in recent years, due to the improvement in image quality of electrophotography, the particle size of toner particles has been reduced, and in addition, the mechanical load on the toner has been increased due to the increase in speed and colorization. Therefore, the durability of toner performance over time (control of deterioration behavior) is becoming more and more important. Low-temperature fixability is required. Under these circumstances, it is becoming mainstream to use a softened/low-melting component as the toner base resin.

As the melting point of the toner resin becomes lower, the surface-treated fumed oxide becomes embedded in the toner resin during long-term operation, resulting in a decrease in the fluidity of the toner resin. Submicron-sized silica powder is added to the surface of the toner together with the fumed oxide for the purpose of improving the properties of the toner. is taken. Silica powder produced by a sol-gel method is mainly used as the submicron-sized silica (see Patent Document 1, etc.).

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

Moreover, since the silica powder produced by the sol-gel method has a nearly spherical particle shape, there is also the problem that the silica powder tends to separate from the toner surface after long-term use.

Furthermore, the silica powder produced by the sol-gel method itself tends to retain or adsorb a large amount of water, so that strong triboelectrification properties cannot be obtained. Therefore, charge regulating materials such as toners must improve their low charging properties.

On the other hand, the dry method or the vapor phase method (both are collectively referred to as the “fumed method” hereinafter). ) has a particle shape that is more non-spherical than the silica produced by the sol-gel method, so it can be expected to have the effect of suppressing the separation from the toner surface, which is the problem of the sol-gel silica. However, in general, the silica powder produced by the fumed method has a small primary particle size and disperses on the toner surface as particles of submicron size or less. is too high, and in order to control the chargeability of the toner within an appropriate range, its addition amount and dispersibility must be precisely controlled.

Precipitated silicic acid produced by a wet method is known for the silica as described above (for example, Patent Document 2). Precipitated silicic acid is suitable for mass production and has a large number of pores in its particle structure, so it is widely used as an adsorbent. However, precipitated silicic acid has problems such as strong agglomeration between particles, difficulty in uniform application (external addition) to the toner surface, and inability to develop sufficient charge. If precipitated silicic acid can be used for toners (especially for toner external additives), it may be possible to add new functions by utilizing its pore characteristics. etc. have not yet been developed.

JP 2013-249215 A Patent No. 5295261

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide a powder suitable for toner and the like by using precipitated silicic acid while making use of the inherent properties of precipitated silicic acid. In particular, the present invention is to provide a surface-modified precipitated silicic acid powder that has both good dispersibility and suitable charging properties, as well as a high spacer effect.

The inventors of the present invention conducted intensive research in view of the problems of the prior art as described above, and as a result, found that specific physical properties can be obtained when the precipitated silicic acid powder is subjected to a specific surface treatment. Completed.

That is, the present invention relates to the following surface-modified precipitated silicic acid powder and its production method.
1. (a) in the volume ^- based particle size distribution, d ₅₀ : 150 to 1000 nm and d ₉₀ : 500 to 7000 nm; A powder composed of particles having a coating layer containing an organosilicon compound formed thereon,
(1) Bulk density: 40 to 150 g/L,
(2) Moisture adsorption amount at water vapor relative pressure of 0.8 to 0.95: 3 to 6%
(3) BET specific surface area: 50 to 200 m ² /g,
(4) carbon content: 1.0 to 8.0% by weight;
(5) Weight loss on drying: 0.1 to 3.0% and (6) Triboelectrification amount: -50 to -200 μC/g
A surface-modified precipitated silicic acid powder characterized by:
2. 2. The surface-treated precipitated silicic acid powder according to item 1, wherein the value obtained by dividing the fluidity energy value when added to the toner by the dry fluidity evaluation method and the energy value before addition is 0.31 or less.
3. 2. The surface-modified precipitated silicic acid powder according to item 1, wherein the organosilicon compound is at least one of hexamethyldisilazane, polydimethylsiloxane and alkylsilane.
4. An external additive for toners or powder coatings containing the surface-modified precipitated silicic acid powder according to any one of the above items 1 to 3.
5. 5. An electrophotographic toner composition or a powder coating composition comprising the external additive according to item 4 and binder resin particles.
6. A method for producing a surface-modified precipitated silicic acid powder, comprising:
(a) preparing a mixture comprising precipitated silicic acid powder and an organosilicon compound;
(b) A method for producing a surface-modified precipitated silicic acid powder, comprising the step of heat-treating the mixture at a temperature of 120-360°C.
7. 7. The production method according to Item 6, wherein the steps (a) and (b) are carried out under stirring.

According to the present invention, by using precipitated silicic acid, it is possible to provide a powder suitable for toners and the like while taking advantage of the inherent properties of precipitated silicic acid. In particular, the present invention can provide a surface-modified precipitated silicic acid powder that has both good dispersibility and moderate charging properties as well as a high spacer effect.

The surface-modified precipitated silicic acid powder of the present invention has specific properties such as bulk density and water adsorption amount by modifying the surface of the precipitated silicic acid powder whose median diameter etc. is controlled within a specific range with an organosilicon compound. As a result, it is possible to provide a submicron-sized agglomerated powder having a low bulk density, good dispersibility, suitable charging properties, and good fluidity.

More specifically, the surface-modified precipitated silicic acid powder of the present invention can be improved in bulk density, hydrophobicity, water adsorption amount, surface area, carbon content, etc. by surface-modifying the precipitated silicic acid powder with a predetermined organosilicon compound. As a result of controlling the properties of the It is possible to secure a particle size sufficient to exhibit a spacer effect that cannot be obtained with the silicon oxide powder produced by the fumed method.

As described above, the present invention focuses on precipitated silicic acid, and as part of the development of new uses for it, selectively uses a specific precipitated silicic acid powder and modifies its surface to achieve the properties inherent to precipitated silicic acid ( (mass productivity, pore characteristics, etc.), in addition to good dispersibility, high chargeability and low bulk density, which were considered difficult with sol-gel silica, and high spacer effect, which was considered difficult with fumed silica. was successful in obtaining

The powder of the present invention having such characteristics can be suitably used as an external additive for toners or powder coatings. Therefore, the electrophotographic toner composition or powder coating composition of the present invention contains the surface-modified precipitated silicic acid powder having such high fixation rate, high hydrophobicity, etc. It is also excellent in preventive properties, suppresses fogging or cleaning failure, and furthermore, it is possible to obtain the effect that the adhesion of toner or the like to the photoreceptor is less likely to occur, and image defects are less likely to occur. Further, according to these compositions of the present invention, effects such as long-term storage stability and control of developer deterioration behavior can be obtained.

6 is a schematic diagram of a method for observing toner particles with an SEM in Test Example 2. FIG.

1. Surface-Modified Precipitated Silicic Acid Powder The surface-modified precipitated silicic acid powder of the present invention (powder of the present invention) has (a) a volume-based particle size distribution of d ₅₀ of 150 to 1000 nm and d ₉₀ of 500 to 7000 nm, and (b ) A powder composed of precipitated silicic acid particles having a silanol group density of 2.5 to 8 OH/nm ² and a coating layer containing an organosilicon compound formed on the surface thereof,
(1) Bulk density: 40 to 150 g/L,
(2) Moisture adsorption amount at water vapor relative pressure of 0.8 to 0.95: 3 to 6%
(3) BET specific surface area: 50 to 200 m ² /g,
(4) Carbon content: 1.0 to 8.0% by weight, and (5) Loss on drying: 0.1 to 3.0%
(6) Amount of triboelectric charge: -50 to -200 μC/g
It is characterized by

<Configuration (composition) of the powder of the present invention>
The particles constituting the powder of the present invention include precipitated silicic acid particles and coating layers formed on the particle surfaces. That is, it has a basic structure in which a precipitated silicic acid particle is used as a core particle (original material) and a coating layer containing an organosilicon compound is formed on the surface of the core particle.

The precipitated silicic acid particles used as core particles have a specific particle size (particle size distribution) and silanol group density.

Regarding the particle size distribution, the volume-based particle size distribution is characterized by d ₅₀ (median diameter) of 150 to 1000 nm and d ₉₀ of 500 to 7000 nm.

When the above _d50 is less than 150 nm, the aggregated particle diameter of the powder after surface treatment with the organosilicon compound is too small, and a sufficient spacer effect cannot be exhibited when dispersed in the toner. On the other hand, when the above _d50 exceeds 1000 nm, the diameter of the aggregated particles is too large, making uniform dispersion on the toner surface difficult.

If the _d90 is less than 500 nm, the chargeability and the spacer effect will be insufficient. On the other hand, if the _d90 exceeds 7000 nm, the number of coarse particles increases, making it difficult to uniformly disperse them on the toner surface.

In addition, _d50 and _d90 in the present invention refer to values (volume basis) calculated by a particle size distribution analyzer (laser diffraction scattering type particle size distribution analyzer (manufactured by HORIBA, Ltd.)).

The silanol group density is usually 2.5-8 OH/nm ² , preferably 3.1-5.0 OH/nm ² . If the silanol group density is too low, the amount of charge on the powder after surface treatment with the organosilicon compound is too high, making it difficult to control the charge within a certain range. On the other hand, if the silanol group density is too high, there is a problem that the water adsorption amount increases and the charge amount becomes too low.

Although the BET specific surface area of the precipitated silicic acid particles is not particularly limited, it is preferable to use a range of 100 to 350 m ² /g. As a result, the distribution of the surface pores is within an appropriate range, so that the moisture adsorption amount can be controlled within an appropriate range. As a result, proper chargeability can be exhibited after modifying the organosilicon compound.

As the precipitated silicic acid particles themselves, known or commercially available ones can be used. For example, powder of precipitated silicic acid described in Patent Document 2 can be preferably used. Therefore, in the present invention, precipitated silicic acid obtained according to the production method described in Patent Document 2 can also be used.

More specifically "the following properties: Shears number of 10-30 ml/(5 g), BET-surface area of 100-350 m ² /g, loss on drying of 2-8% by weight, ignition of 2-9% by weight Precipitated silica having a weight loss, a pH value of 4 to 9 and a DBP value of 230 to 400 g/100 g is prepared by a method of comminution and simultaneous classification to obtain comminuted silica. A process for the production of precipitated silica in which grinding and simultaneous classification are carried out using one grinding apparatus, wherein the mill of the grinding apparatus is in one grinding phase gas, steam, steam, steam-containing gas and working with a working medium from the group consisting of these mixtures; and the grinding chamber, in a heating phase, i.e. before specific operation with the working medium, the temperature in this grinding chamber and/or at the mill outlet is heating to a temperature above the dew point of the working medium; and classifying the ground silica to ad ₅₀ -values between 150 and 2000 nm and ad ₉₀ -values between 500 and 7000 nm, Precipitated silicic acid can be suitably prepared by the method for producing precipitated silicic acid.

The coating layer coats the surface of the particles constituting the powder of the present invention, and imparts predetermined hydrophobicity, chargeability, etc. to the particles constituting the powder of the present invention. And the coating layer contains an organosilicon compound. The content of the organosilicon compound in the coating layer is not particularly limited, but usually can be appropriately set at about 5 to 100% by weight. Therefore, it may be, for example, 80 to 99% by weight, and may be, for example, 90 to 100% by weight.

The organosilicon compound is not particularly limited, and for example, known or commercially available agents known as hydrophobizing agents can also be used.

More specifically, alkylsilazane compounds such as hexamethyldisilazane, alkylalkoxysilane compounds such as dimethyldimethoxysilane, diethyldiethoxysilane, trimethylmethoxysilane, methyltrimethoxysilane and butyltrimethoxysilane, and dimethyldichlorosilane. , chlorosilane compounds such as trimethylchlorosilane, silicone oils such as polydimethylsiloxane (PDMS), silicone varnishes, and the like can be used. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

Among these, at least one of alkylsilazane-based compounds, alkoxysilane-based compounds, and silicone oil is preferably used in order to more reliably obtain the effects of the present invention.

In particular, the alkoxysilane is not particularly limited as long as it is an alkoxysilane substituted with an alkyl group, but trimethoxyalkoxysilane, triethoxyalkoxysilane and the like are generally used. Although the number of carbon atoms in the alkyl group is not particularly limited, it is preferably C2 to C18. If it is less than C2, volatilization of alkoxysilane may occur during surface treatment. On the other hand, if it exceeds C16, strong aggregation may occur due to the influence of the high viscosity, and the dispersibility of the obtained powder may be impaired.

In particular, as the silicone oil, in addition to polydimethylsiloxane, modified silicone oil into which an alkyl group, --OH group, or the like is introduced can also be used.

The viscosity range of these organosilicon compounds (measuring temperature: 25° C.) is not particularly limited, but it is usually preferably from 20 to 300 cs. If the viscosity is less than 20 cs, volatilization of low-molecular-weight polysiloxane occurs during surface treatment, which is undesirable from the viewpoint of energy efficiency, environment, and the like. On the other hand, if the viscosity exceeds 300 cs, higher aggregation may 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 falls within the range of the carbon content described above. It is desirable to use 10 to 20 parts by weight.

<Characteristics of the powder of the present invention>
The powder of the invention has the following properties:
(1) Bulk density: 40 to 150 g/L,
(2) Moisture adsorption amount at water vapor relative pressure of 0.8 to 0.95: 3 to 6%
(3) BET specific surface area: 50 to 200 m ² /g,
(4) carbon content: 1.0 to 8.0% by weight;
(5) Weight loss on drying: 0.1 to 3.0% and (6) Amount of triboelectrification: -50 to -200 μC/g
meet all

Bulk Density The bulk density of precipitated silicic acid surface-modified with an organosilicon compound is usually between 40 and 150 g/l. If the bulk density is less than 40 g/L, when the powder is dispersed on the surface of the toner, it cannot be dispersed with an appropriate aggregated particle size, and a sufficient spacer effect cannot be exhibited. On the other hand, if the bulk density exceeds 150 g/L, a large volume of equipment is required for mixing with the toner, which poses a problem for industrial use.

Moisture adsorption amount The moisture adsorption amount at a water vapor relative pressure of 0.8 to 0.95 is usually 3 to 6% by weight. Since the amount of water adsorption has a great influence on charging characteristics, setting the amount within the above range can impart appropriate charging characteristics. If the water adsorption amount is less than 3% by weight, the strong negative charge becomes too strong. On the other hand, if the water adsorption amount exceeds 6% by weight, it becomes impossible to develop sufficient charging characteristics.

BET Specific Surface Area The BET specific surface area of the precipitated silicic acid surface-modified with an organosilicon compound is usually from 50 to 200 m ² /g. If the BET specific surface area is less than 50 m ² /g, the aggregated particle diameter is too large, resulting in insufficient dispersibility when dispersed in a toner. If the BET specific surface area exceeds 200 m ² /g, when dispersed in the toner, a proper aggregate size cannot be maintained, and a sufficient spacer effect cannot be exhibited.

Carbon Content The carbon content of the organosilicon compound surface-modified precipitated silicic acid is usually between 1.0 and 8.0% by weight. In particular, when the surface treatment agent (hydrophobizing treatment agent) is HMDS, it is about 1.0 to 3.0% by weight, when it is PDMS, it is about 1.0 to 8.0% by weight, and when it is alkylalkoxysilane, it is 1.0% by weight. It is preferable to make it about 0 to 8.0% by weight. The carbon content is an index indicating the degree (fixed amount) of fixation to the precipitated silicic acid powder by the organosilicon compound, which is a surface treatment agent. If the carbon content is too low, sufficient surface modification is not achieved, resulting in insufficient charging properties, dispersibility, and the like. On the other hand, if the carbon content is too high, the organic matter content is too high, causing particle agglomeration and sufficient fluidity and dispersibility. cannot be expressed.

Loss on Drying Loss on drying is usually 0.1 to 3.0%. The weight loss on drying has a great influence on charging properties, and by setting it within the above range, appropriate charging properties can be imparted. If the loss on drying exceeds 3% by weight, the amount of retained/adsorbed water becomes close to that of silica obtained by the sol-gel method, and sufficient charging characteristics cannot be exhibited.

Electrification The triboelectrification amount of precipitated silicic acid surface-modified with an organosilicon compound is usually -50 to -200 μC/g. When the amount of triboelectric charge approaches the zero side from −50 μC/g, when the powder is added to the toner, it becomes difficult to express strong charging characteristics in the toner, and the toner is charged to a predetermined level. It becomes difficult to control the volume range. On the other hand, when the amount of triboelectric charge becomes more negative than -200 μC/g, it becomes difficult to control the charge characteristics of the toner to which it is added due to the strong amount of triboelectric charge.

Particle size The average particle size of the powder of the present invention is not particularly limited. It is preferably 0.2 to 0.8 μm. The average particle diameter in the present invention refers to a value (arithmetic mean diameter (volume standard)) calculated with a particle size distribution analyzer (laser diffraction scattering particle size distribution analyzer (manufactured by HORIBA, Ltd.)).

Fluidity In the powder of the present invention, a ratio based on an energy value measured by a powder rheometer is used as an index of the ability to impart fluidity to a toner or the like. That is, it is a value obtained by dividing the fluidity energy value obtained by the dry fluidity evaluation method when the powder of the present invention is added to the toner by the energy value before addition, and the value is 0.31 or less in the present invention. desirable. By setting the value to 0.31 or less, it is possible to impart even higher fluidity to the toner product to which the powder of the present invention is externally added.

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 the powder having the above constitution and properties can be obtained. (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 is not limited as long as the surface of each particle constituting the precipitated silicic acid powder can be coated with the organosilicon compound. For example, the precipitated silicic acid powder and the vaporized organosilicon compound are mixed under stirring. method, a method of spraying an organosilicon compound onto the precipitated silicic acid powder under stirring, and the like can be suitably employed.

In this case, the organosilicon compound can be used after being dissolved or dispersed in a solvent (for example, an organic solvent such as hexane or toluene) as necessary. The concentration of the organosilicon compound in that case can be appropriately set according to the type of the organosilicon compound used.

In addition, in the present invention, water and a catalyst (amine, etc.) can be appropriately blended in the mixture, if necessary.

The temperature conditions in the mixture preparation step are not particularly limited, and may be, for example, within the range of 10 to 40° C., but are not limited thereto. Moreover, the atmosphere is preferably an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be preferably used.

As for the type and amount of the organosilicon compound, the same ones as described in the above "1. Surface-modified precipitated silicic acid powder" can be employed.

Heat Treatment Process The heat treatment temperature in the heat treatment process is not limited, but it is usually preferably 120 to 360° C. (especially 150 to 300° C.). If the heat treatment temperature exceeds 360°C, the organosilicon compound may be partially decomposed. If the temperature is less than 120° C., the surface of the organosilicon compound is not sufficiently modified, and the desired chargeability cannot be obtained.

As for the heat treatment atmosphere, it is usually preferable to carry out the heat treatment in an inert gas atmosphere, as in the above process. For example, nitrogen gas, helium gas, argon gas, etc. can be preferably used. In particular, it is possible to carry out the above process in a closed reactor, and continue the heat treatment process while maintaining the atmosphere.

The heat treatment time may be a time sufficient for the organic silane compound to be fixed (adhered) to the surface of each particle constituting the precipitated silicic acid powder. Not limited.

3. Use of the Powder of the Present Invention The powder of the present invention has all of the properties (1) to (6) shown in "1. Surface-modified precipitated silicic acid powder" above. It is possible to exhibit both a good spacer effect and an appropriate charging property. Therefore, the powder of the present invention can be suitably used as an additive (especially an external additive for toner) for toners, powder coatings, and the like. Therefore, the present invention also includes an electrophotographic toner composition or a powder coating composition containing the powder of the present invention and the binder resin particles (hereinafter both are collectively referred to as the "composition of the present invention"). .

The composition of the present invention contains the surface-modified precipitated silicic acid powder of the present invention described above, and its composition, production method, etc. are not particularly limited, and known compositions and methods can be employed.

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 effect of improving properties can be obtained, but it is usually preferably contained in an amount of about 0.1 to 5.0% by weight. When the content of the surface-modified precipitated silicic acid powder of the present invention in the composition of the present invention is less than 0.1% by weight, the addition of the surface-modified precipitated silicic acid powder has the effect of improving fluidity or stabilizing charging properties. Sometimes you don't get enough. On the other hand, when the content of the surface-modified precipitated silicic acid powder exceeds 5.0% by weight, the surface-modified precipitated silicic acid powder alone increases the tendency to cause problems such as images and cleanability.

The composition of the present invention may contain pigments, charge control agents (charge control agents), waxes, etc., if necessary, in addition to the binding resin particles. These ingredients can also be similar to known or commercially available toner compositions. Further, the type of toner is preferably a negatively charged toner, and is not particularly limited in other respects. Therefore, for example, either magnetic or non-magnetic one-component toner or two-component toner may be used. Furthermore, either monochrome or color may be used.

Since the powder of the present invention is particularly excellent in the spacer effect, the binder resin particles containing easily softening resin components (for example, at least one of styrene-acrylic copolymer resin, polyester resin, epoxy resin, etc.) It can be used more preferably as an additive.

In the electrophotographic toner composition of the present invention, the powder of the present invention as an external additive is not limited to being used alone, and may be used in combination with other metal oxide fine powder depending on the purpose. . For example, the surface-modified precipitated silicic acid powder of the present invention and other surface-modified dry-type silica fine powders, surface-modified dry-type titanium oxide fine powders, surface-modified wet-type titanium oxide fine powders, etc. are required. They can be used in combination depending on the situation.

Furthermore, the precipitated silicic acid powder surface-modified with an organosilicon compound in the present invention exists on the surface of the toner as submicron-sized aggregates, and the surface has many irregularities. It is effective in that it is difficult to detach from.

EXAMPLES Examples and comparative examples are shown below to describe the features of the present invention more specifically. However, the scope of the present invention is not limited to the examples.

The components used in each example and comparative example are as follows.
(A) Precipitated silicic acid powder (A) Silica raw material (A1) Precipitated silicic acid Samples A to E: Precipitated silicic acid prepared according to the production method described in Patent Document 2 (A2) Sol-gel silica Samples produced by a known sol-gel method (A3) Fumed silica Commercial product a: Product name “AEROSIL OX50” (registered trademark) manufactured by Nippon Aerosil Co., Ltd.)
Commercial product b: Product name “AEROSIL 200” (registered trademark) manufactured by Nippon Aerosil Co., Ltd.)
(B) Surface treatment agent (B1) HMDS: hexamethyldisilazane (product name “Dynasilane HMDS” (registered trademark) manufactured by Evonik)
(B2) PDMS: polydimethylsiloxane (product name “KF96-100cs” manufactured by Shin-Etsu Chemical Co., Ltd.)
(B3) Commercial product C4: Alkylsilane-based surface treatment agent (product name “IBTMO” (registered trademark) manufactured by Evonik)
(B4) Commercial product C10: Alkylsilane-based surface treatment agent (product name “KBM-3103C” (registered trademark) manufactured by Shin-Etsu Chemical Co., Ltd.)

[Example 1]
Sample A (median diameter d ₅₀ =155 nm, d ₉₀ =540 nm) (100 parts by weight) as precipitated silicic acid powder was placed in a reactor, and HMDS (20 parts by weight) was added as a surface treatment agent while stirring in a nitrogen atmosphere. Then, heat treatment was performed at 200° C. for 60 minutes while stirring was continued. Thus, a surface-modified silica powder was obtained.

[Examples 2 to 10]
A surface-modified silica powder was obtained in the same manner as in Example 1, except that the conditions shown in Table 1 were used.

[Comparative Examples 1 to 8]
A surface-modified silica powder was obtained in the same manner as in Example 1, except that the conditions shown in Table 2 were used.

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

(1) Bulk Density A graduated cylinder is placed on a precision balance, the tare is removed, a sample is placed in the graduated cylinder, the mass is weighed (mass A), and the volume (volume B) after standing for 2 minutes is read. Calculate the bulk density using the following formula:
Bulk density (g/L) = (mass A/volume B) x 1000

(2) Water adsorption measurement After heating the surface-modified silica powder at 150 ° C. under vacuum for 2 hours or more and drying it sufficiently, use a high-precision gas adsorption measuring device (product name “BELSORP-max” Microtrack Bell Co., Ltd.) (manufactured by the company) under the conditions of an exhaust time of 15 minutes and an allowable pressure rise of 5.000E-1 Pa/min. The adsorption isotherm was analyzed, and the value within the range of the water vapor relative pressure of 0.8 to 0.95 was taken as the water adsorption amount.

(3) BET specific surface area BET {surface area (m ² /g)} is a fully automatic specific surface area measuring device (product name “Macsorb” manufactured by Mountec), and after pretreatment of the sample at 100 ° C. for 10 minutes, BET 1 point The surface area of the sample was obtained from the amount of adsorbed and desorbed nitrogen by the method, and the specific surface area was obtained by dividing it by the weight.

(4) Carbon content The carbon content was measured using a carbon analyzer (product name “SUMIGRAPH NC-22” manufactured by Sumika Chemical Analysis Service).

(5) After about 1 g of the surface-modified silica powder was sampled in a weighing bottle, dried at 105 ° C. for 2 hours, the weight was measured, and the weight loss ratio (%) before and after drying was calculated. Quantity.

(6) Amount of triboelectrification A sample containing 0.2 parts by weight of surface-modified silica powder with 100 parts by weight of carrier (reduced iron powder) was mixed in a Turbula mixer for a certain period of time and triboelectrified. C. and humidity of 45% RH, the charge amount was measured with a blow-off powder charge amount measuring device.

(7) Fluidity Using a Henschel mixer, 1 g of the surface-modified silica powder obtained in each example and comparative example was externally added to 99 g of toner (polyester toner base (binding resin), average particle size 6 μm). After that, the mixed powder obtained was subjected to an air permeability test of a toner sample using a powder rheometer. The total energy value was measured 13 times in total for each sample. The first measurement was performed without aeration, and the second and subsequent measurements were performed while aeration was performed at a linear velocity of 0.04 mm/s. Then, the 13th total energy value E1 (mJ) was measured.
The total energy value E0 of the toner alone was measured in the same manner as described above, except that the surface-modified silica powder was not externally added.
Next, [E1/E0] was obtained based on the values E1 and E0 obtained above. A smaller value of [E1/E0] indicates the ability to impart higher fluidity.

[Test Example 2]
The weight ratio of the surface-modified silica powder obtained in each example and comparative example to the polyester toner base (binding resin) powder produced by the polymerization method [binding resin powder: surface-modified silica powder = 99:1], pre-mixed with a Henschel mixer at 600 rpm for 1 minute, and then mixed at 3000 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 having a particle size of 0.1 μm or more attached per 1 μm ² of the toner sample particle surface was counted. . The results are also shown in Tables 1 and 2.
In the measurement, one toner base (toner particle) is arbitrarily selected within the field of view of the SEM, and as shown in FIG. After setting so that the silica particles 11 are included, after counting all the number of surface-modified silica particles 11 in the field of view S, the number is divided by the field of view area per unit area (per 1 μm ² ) The number of surface-modified silica particles was calculated. In this case, the surface-modified silica particles protruding from the field of view S are not counted. The larger the number of surface-modified silica particles per unit area, the more uniformly the surface-modified silica powder is dispersed.

As is clear from the results in Tables 1 and 2, the surface-modified silica powders of Examples satisfy all the properties defined in the present invention.

Claims (7)

(a) in the volume ^- based particle size distribution, d ₅₀ : 150 to 1000 nm and d ₉₀ : 500 to 7000 nm; A powder composed of particles having a coating layer containing an organosilicon compound formed thereon,
(1) Bulk density: 40 to 150 g/L,
(2) Moisture adsorption amount at water vapor relative pressure of 0.8 to 0.95: 3 to 6%
(3) BET specific surface area: 50 to 200 m ² /g,
(4) carbon content: 1.0 to 8.0% by weight;
(5) Weight loss on drying: 0.1 to 3.0% and (6) Amount of triboelectrification: -50 to -200 μC/g
A surface-modified precipitated silicic acid powder characterized by: 2. The surface-treated precipitated silicic acid powder according to claim 1, wherein the value obtained by dividing the fluidity energy value when added to the toner by the dry fluidity evaluation method and the energy value before addition is 0.31 or less. 2. The surface-modified precipitated silica powder of claim 1, wherein the organosilicon compound is at least one of hexamethyldisilazane, polydimethylsiloxane and alkylsilane. An external additive for toners or powder coatings containing the surface-modified precipitated silicic acid 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. A method for producing a surface-modified precipitated silicic acid powder, comprising:
(a) preparing a mixture comprising precipitated silicic acid powder and an organosilicon compound;
(b) A method for producing a surface-modified precipitated silicic acid powder, comprising the step of heat-treating the mixture at a temperature of 120-360°C. 7. The production method according to claim 6, wherein the steps (a) and (b) are carried out under stirring.

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