JP7748205B2 - Surface-modified inorganic oxide powder and its manufacturing method - Google Patents

Description

The present invention relates to a 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 chargeability, hydrophobicity, and other properties of the powder surface. The surface-modified inorganic oxide powders obtained in this manner are widely used as flow improvers and chargeability adjusters for toners used in electrophotography, including copiers, laser printers, and plain paper facsimiles. Surface-modified inorganic oxide powders used in such toner applications are known as external additives.

Organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil have traditionally been used as surface treatment agents for inorganic oxide powders. Surface treatment with these organosilicon compounds, for example, substitutes silanol groups on the surface of silica fine particles with organic groups, thereby rendering the particles hydrophobic.

Of these organosilicon compounds, silicone oil is used to treat the surface of inorganic oxide powder. Products with silicone oil exhibit sufficient hydrophobicity, and when used as an external toner additive, they exhibit good cleaning properties, making silicone oil known as an effective surface treatment agent. For this reason, external additives using non-reactive silicone oil as a surface treatment agent have also been proposed (see, for example, Patent Document 1).

Patent Publication No. 2014-162681

However, when silicone oil-treated products are used, the fluidity of the toner powder to which it is added is significantly impaired compared to toner powder that uses external additives that have been surface-treated with other surface treatment agents (such as hexamethyldisilane).

Furthermore, when silicone oil is used as a surface treatment agent, its charging properties tend to be highly negative, making it difficult to control the charging characteristics.

Therefore, the main object of the present invention is to provide a surface-modified inorganic oxide powder that is highly hydrophobic, has high fluidity, and has a charge amount controlled within a predetermined range.

As a result of extensive research into the problems of the prior art, the inventors discovered that the above objectives could be achieved by applying a specific silicone oil to inorganic oxide powder at a specific fixation rate, leading to the completion of 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 comprising particles including inorganic oxide particles and a layer containing reactive silicone oil and non-reactive silicone oil formed on the surface of the particles,
(1) The carbon content (wt%) in the powder is 0.5 to 6.0 wt%;
(2) the value obtained by dividing the carbon content by the specific surface area (m ² /g) of the inorganic oxide particles is 1.9 to 5.0%;
(3) The hydrophobicity is 95% or more;
(3) The charge amount is −65 to −170 μC/g,
(4) The free oil content is 3% by weight or less.
A surface-modified inorganic oxide powder characterized by:
2. The surface-modified inorganic oxide powder according to Item 1, wherein the inorganic oxide powder is fumed silica.
3. The surface-treated inorganic oxide powder according to item 1 or 2, wherein the value of the fluidity energy value when added to a toner, as measured by a dry fluidity evaluation method, divided by the energy value before addition, is 0.55 or less.
4. The surface-modified inorganic oxide powder according to any one of items 1 to 3, wherein the reactive silicone oil has OH groups at both ends of a main chain consisting of siloxane bonds, and has a kinematic viscosity of 10 to 200 cs.
5. The surface-modified inorganic oxide powder according to any one of items 1 to 4, wherein the non-reactive silicone oil has a kinematic viscosity of 10 to 200 cs.
6. The surface-modified inorganic oxide powder according to any one of items 1 to 5, wherein the weight ratio of the non-reactive silicone oil to the reactive silicone oil is 1:0.2 to 1:4.0.
7. An external additive for toner or powder coating, comprising the surface-modified inorganic oxide powder according to any one of items 1 to 6.
8. A toner composition or a powder coating composition for electrophotography, comprising the external additive according to item 7 and binder resin particles.
9. A method for producing a surface-modified inorganic oxide powder, comprising:
(a) preparing a mixture containing an inorganic oxide powder, a reactive silicone oil, and a non-reactive silicone oil;
(b) heat-treating the mixture at a temperature of 80 to 380°C.
10. A method for producing a surface-modified inorganic oxide powder, comprising:
(a) preparing a first mixture comprising an inorganic oxide powder and a reactive silicone oil;
(b) heat-treating the first mixture at a temperature of 80 to 380°C;
(c) preparing a second mixture comprising the heat-treated first mixture and a non-reactive silicone oil;
(d) heat treating the second mixture at a temperature of 80 to 380°C;
A method for producing a surface-modified inorganic oxide powder, comprising:
11. A method for producing a surface-modified inorganic oxide powder, comprising:
(a) preparing a first mixture comprising an inorganic oxide powder and a non-reactive silicone oil;
(b) heat-treating the first mixture at a temperature of 80 to 380°C;
(c) preparing a second mixture comprising the heat-treated first mixture and a reactive silicone oil;
(d) heat treating the second mixture at a temperature of 80 to 380°C;
A method for producing a surface-modified inorganic oxide powder, comprising:

The present invention makes it possible to provide a surface-modified inorganic oxide powder that is highly hydrophobic, has high fluidity, and has a charge amount controlled within a predetermined range.

In particular, the surface-modified inorganic oxide powder of the present invention combines specific physical properties because it is surface-treated with both reactive and non-reactive silicone oils. Therefore, it can be said to be industrially more advantageous as a surface-modified inorganic oxide powder added to powder material systems such as powder coatings, electrophotographic toners, and cosmetics for purposes such as improving fluidity, preventing caking, and adjusting charge, compared to conventional products treated only with non-reactive silicone oil.

1. Surface-modified inorganic oxide powder The surface-modified inorganic oxide powder of the present invention (powder of the present invention) is a powder comprising particles including inorganic oxide particles and a layer containing reactive silicone oil and non-reactive silicone oil formed on the surface of the particles,
(1) The carbon content (wt%) in the powder is 0.5 to 6.0 wt%;
(2) the value obtained by dividing the carbon content by the specific surface area (m ² /g) of the inorganic oxide particles is 1.9 to 5.0%;
(3) The hydrophobicity is 95% or more;
(3) The charge amount is −65 to −170 μC/g,
(4) The free oil content is 3% by weight or less.
It is characterized by:

<Configuration (Composition) of the Powder of the Present Invention>
The particles constituting the powder of the present invention include inorganic oxide particles and a layer containing reactive silicone oil and non-reactive silicone oil formed on the surface of the particles (hereinafter also referred to as a "silicone oil layer"). That is, the basic structure is a structure (coated particle) in which an inorganic oxide particle is used as a core particle (base particle) and part or all of its surface is coated with a silicone oil-containing layer.

The inorganic oxide particles that serve as core particles are not limited to any particular type, and examples include, but are not limited to, silicon oxide, titanium oxide, and aluminum oxide. Among these, silicon oxide (silica) (particularly fumed silica) is preferred for use in the present invention. These particles may be used alone or in combination of two or more types. These particles themselves may be publicly known or commercially available.

The particle size of the inorganic oxide particles is not limited, but can usually be selected appropriately from a range of primary particle sizes of approximately 5 to 150 nm depending on the average particle size range of the desired surface-modified inorganic oxide powder.

Furthermore, the inorganic oxide particles preferably have a specific surface area of about 10 to 104 m ² /g, particularly about 20 to 100 ^{m 2} /g, as measured by nitrogen adsorption (BET). If the BET specific surface area is too small, the effect as a fluidizing agent will be reduced when added to electrophotographic toner. If the BET specific surface area is too large, the particles will quickly sink into the toner when added to electrophotographic toner, resulting in significant deterioration of performance over time.

Furthermore, the preferred method for producing inorganic oxide particles is powder produced by the fumed method. The fumed method is a well-known manufacturing method that can synthesize silica, for example, by introducing a silicon compound (such as silicon tetrachloride) or metallic silicon into an oxygen-hydrogen flame to cause a hydrolysis reaction. This type of powder has a particle shape that is less spherical than silica produced by the sol-gel method, for example, and therefore has the advantage of being able to effectively prevent separation from the toner surface. Another advantage is that, because no solvent is used, agglomerated particles are less likely to form during drying.

Commercially available inorganic oxide particles can also be used for such fumed inorganic oxide particles. For example, the commercially available products shown in the examples below can also be suitably used.

The silicone oil layer that coats the surface of the inorganic oxide particles contains reactive silicone oil and non-reactive silicone oil. In the present invention, the silicone oil layer may have any of the following layer configurations: a) inorganic oxide particles/(a mixed layer containing reactive silicone oil and non-reactive silicone oil), b) inorganic oxide particles/a layer containing reactive silicone oil/a layer containing non-reactive silicone oil, c) inorganic oxide particles/a layer containing non-reactive silicone oil/a layer containing reactive silicone oil, etc.

Reactive silicone oil is a silicone oil that has functional groups at both ends of the main chain consisting of siloxane bonds, at one end, and at least one side chain. In the present invention, the use of reactive silicone oil increases the reactivity of the silicone oil with inorganic oxide particles and increases the fixation rate. The proportion of reactive silicone oil in the layer can be, for example, approximately 90 to 100% by weight, but is not limited to this.

The main chain (main skeleton) consisting of the above-mentioned siloxane bond is not limited to, but poly(dimethylsiloxane) is particularly suitable. The functional group is not particularly limited to, but may be at least one of, for example, a hydrogen atom, a hydroxyl group, an amino group, a carbinol group, an epoxy group, or a carboxyl group.

Therefore, modified silicone oils such as amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, carbinol-modified silicone oil, methacrylic-modified silicone oil, mercapto-modified silicone oil, phenol-modified silicone oil, silanol dimethyl oil at both ends, reactive-modified silicone oil at one end, heterofunctional group-modified silicone oil, polyether-modified silicone oil, higher fatty acid ester-modified silicone oil, special hydrophilic modified silicone oil, higher alkoxy-modified silicone oil, higher fatty acid-containing modified silicone oil, and fluorine-modified silicone oil can be suitably used.

Among these, reactive silicone oils containing at least one type of hydroxyl group as a functional group are preferred, as they can react with OH groups on the surface of inorganic oxide particles to form Si-O-Si bonds. By using reactive silicone oils containing hydroxyl groups, Si-OH groups on the particle surfaces of inorganic oxide particles can react with Si-OH groups in the reactive silicone oil to form Si-O-Si bonds.

In particular, in the present invention, at least one of dimethyl oil having silanol groups at both ends and dimethyl hydrogen polysilicone can be preferably used. Therefore, as the dimethyl oil having silanol groups at both ends, for example, a reactive silicone oil represented by the following formula (1) can be preferably used.

(wherein R ¹ represents an organic group other than a methyl group, m represents an integer of 1 or more, and n represents 0 or an integer of 1 or more, satisfying m+n≧1. The repeating units —(Si(CH ₃ ) ₂ —O)— and —(SiR ¹ (CH ₃ )—O)— may be bonded in any form of alternating copolymer, random copolymer, or block copolymer.)

As shown in the formula above, a reactive silicone oil can be used that has a siloxane bond -(Si-O)- as a repeating unit and has hydroxyl groups at both ends of the main chain consisting of at least siloxane bonds. Therefore, for example, in the general formula above, a reactive silicone oil that has hydroxyl groups at both ends of a polydimethylsiloxane structure where m is 1 or greater and n is 0 can be preferably used. In other words, a structure in which at least one hydroxyl group is bonded to the silicon atoms at both ends can be preferably used.

As a dimethylhydrogen polysilicone, for example, a reactive silicone oil having hydrogen atoms in the side chains of the polysiloxane structure, as shown in the following formula (2), can be suitably used.

(wherein m represents an integer of 0 or 1 or more, and n represents an integer of 1 or more, satisfying m+n≧1. The repeating units —(Si(CH ₃ ) ₂ —O)— and —(SiH(CH ₃ )—O)— may be bonded in any form of an alternating copolymer, a random copolymer, or a block copolymer.)

These reactive silicone oils can be publicly known or commercially available. One or more types of reactive silicone oils can be used.

The kinematic viscosity (measured at 25°C) (hereinafter referred to as "viscosity") of the reactive silicone oil is not particularly limited, but is generally preferably 30 to 100 cs. If the viscosity is less than 30 cs, the low-molecular-weight reactive silicone oil will volatilize during heat treatment, making it difficult to perform adequate surface treatment, and is also undesirable from an environmental standpoint. On the other hand, if the viscosity exceeds 100 cs, the reactive silicone oil may promote aggregation of the inorganic oxide particles, severely impairing fluidity.

Furthermore, the molecular weight range of the reactive silicone oil may be any range that satisfies the above viscosity range, and may be, for example, in the range of approximately 3000 to 7500, but is not limited to this.

The amount of reactive silicone oil is not particularly limited as long as it falls within the above carbon content range, but it is generally preferred to use approximately 1 to 15 parts by weight per 100 parts by weight of inorganic oxide powder, with 2 to 12 parts by weight being more preferred, and 3 to 10 parts by weight being most preferred. If the amount of reactive silicone oil is too low, it will be impossible to obtain a surface-modified inorganic oxide powder with a high hydrophobicity. On the other hand, if the amount of reactive silicone oil is too high, particle aggregation may occur, impairing fluidity.

The non-reactive silicone oil may be any oil that does not have a reactive functional group, and examples thereof include dimethyl silicone oil, as well as silicone oils in which R ¹ in the formula (1) is an alkyl group other than a methyl group, an aralkyl group, a polyether group, a fluoroalkyl group, an ester group, a phenyl group, etc. These non-reactive silicone oils themselves can be publicly known or commercially available. In addition, one or more types of non-reactive silicone oils can be used.

The viscosity of the non-reactive silicone oil (measured at 25°C) is not particularly limited, but is generally preferably 5 to 300 cs. If the viscosity is less than 5 cs, the low-molecular-weight silicone oil will volatilize during heat treatment, making it difficult to perform adequate surface treatment, and is also undesirable from an environmental standpoint. On the other hand, if the viscosity exceeds 300 cs, the silicone oil may promote aggregation of the inorganic oxide particles, severely impairing fluidity.

Furthermore, the molecular weight range of the non-reactive silicone oil may be any range that satisfies the above viscosity range, and is applicable in the range of approximately 850 to 16,000, for example, but is not limited to this.

The amount of non-reactive silicone oil is not particularly limited as long as it falls within the carbon content range described above, but it is generally preferred to use approximately 1 to 15 parts by weight per 100 parts by weight of inorganic oxide powder, with 2 to 12 parts by weight being more preferred, and 3 to 10 parts by weight being most preferred. If the amount of non-reactive silicone oil is too low, it will be impossible to obtain a surface-modified inorganic oxide powder with a high hydrophobicity. On the other hand, if the amount of non-reactive silicone oil is too high, particle aggregation may occur, reducing fluidity.

The ratio of non-reactive silicone oil to reactive silicone oil is not limited, but it is particularly desirable for the weight ratio of non-reactive silicone oil to reactive silicone oil to be between 1:0.2 and 1:4.0. By setting this ratio, not only can higher fluidity be achieved, but the chargeability can also be more reliably controlled within a specified range.

<Characteristics of the powder of the present invention>
The characteristics of the powder of the present invention are as follows:
(1) The carbon content (wt%) in the powder is 0.5 to 6.0 wt%;
(2) the value (carbon value) obtained by dividing the carbon content by the specific surface area (m ² /g) of the inorganic oxide particles is 1.9 to 5.0%;
(3) The hydrophobicity is 95% or more;
(3) The charge amount is −65 to −170 μC/g,
(4) The free oil content is 3% by weight or less.
It is characterized by:

As mentioned above, the carbon content is typically 0.5 to 6.0% by weight, with 0.6 to 5.5% by weight being particularly preferred. In the present invention, the carbon content is an indicator of the amount of surface treatment agent fixed, and achieving a carbon content within the above range indicates that the desired surface treatment has been achieved.

As described above, the carbon value of the powder of the present invention is usually 1.9 to 5.0%. If the carbon value is less than 1.9%, the amount of organic matter present on the surface is insufficient to coat the inorganic powder surface, and sufficient hydrophobicity and fluidity cannot be achieved. On the other hand, if the carbon value exceeds 5.0%, the amount of organic matter coating the surface becomes too excessive, adversely affecting fluidity. Regarding the method for calculating the carbon value, for example, if the carbon content (carbon amount) is 4.6 wt% and the specific surface area of the inorganic oxide particles is 200 ^{m 2} /g, the carbon value can be calculated as [4.6/200] × 100 = 2.3%.

The hydrophobicity is usually 95% or higher, and preferably 98-99%. If the hydrophobicity is less than 95%, sufficient charging properties may not be achieved under high temperature and high humidity conditions.

The charge amount is typically around -65 to -170 μC/g, and preferably -70 to -150 μC/g. If the charge amount approaches zero below -65 μC/g, it becomes difficult to achieve stable charge characteristics in the toner when the powder is added to the toner, making it difficult to control the toner within the specified charge amount range. On the other hand, if the triboelectric charge amount becomes more negative than -170 μC/g, it also becomes difficult to achieve stable charge characteristics in the toner to which it is added.

The amount of free oil in the powder of the present invention is typically 3% by weight or less. If the amount of free oil exceeds 3% by weight, sufficient fluidity may not be achieved.

In addition, an index of the ability of the powder of the present invention to impart fluidity to toners and the like is a ratio based on the energy value measured by a powder rheometer. That is, the fluidity energy value measured by a dry fluidity evaluation method when the powder of the present invention is added to toner divided by the energy value before addition is desirably 0.55 or less. By keeping this value 0.55 or less, even higher fluidity can be imparted to toner products to which the powder of the present invention is externally added.

The average particle size of the powder of the present invention is not particularly limited, but should generally be in the range of more than 18 nm and not more than 150 nm. Therefore, it can be set to, for example, 19 to 130 nm. Note that the average particle size in this invention refers to the arithmetic mean value of the particle sizes of 1,000 particles randomly selected by observation with a transmission electron microscope (TEM).

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-described structure and properties, but it is preferable to carry out the method by any of the following methods 1 to 3.

(1) First Method The first method is a method for producing a surface-modified inorganic oxide powder,
(a) preparing a mixture containing an inorganic oxide powder, a reactive silicone oil, and a non-reactive silicone oil (mixture preparation step);
(b) a step of heat-treating the mixture at a temperature of 80 to 380°C (heat-treatment step);
The method is characterized by comprising:

Mixture Preparation Step In the mixture preparation step, there are no particular limitations on the method as long as it can coat the surface of each particle constituting the inorganic oxide powder with reactive silicone oil. For example, a method of mixing inorganic oxide powder with vaporized reactive silicone oil and non-reactive silicone oil under stirring, or a method of spraying reactive silicone oil and non-reactive silicone oil onto inorganic oxide powder under stirring, etc. can be suitably employed.

In this case, the reactive silicone oil or non-reactive silicone oil can be diluted with water or an organic solvent before blending. The organic solvent can be selected appropriately depending on the type of reactive or non-reactive silicone oil used, and examples include hexane, toluene, alcohol (aliphatic alcohols having 1 to 8 carbon atoms, such as methanol, ethanol, and propanol), and acetone. The concentration when diluted is not limited, and can be, for example, approximately 5 to 70% by weight.

The temperature conditions in the mixture preparation process are not particularly limited, and may be, for example, within the range of 10 to 40°C, but are not limited to this. Furthermore, it is generally 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 reactive or non-reactive silicone oil used can be the same as those described above in "1. Surface-modified inorganic oxide powder."

Heat Treatment Step The heat treatment temperature in the heat treatment step is not limited, but is usually preferably 80 to 380°C (particularly 280 to 380°C). If the heat treatment temperature exceeds 380°C, partial decomposition of the reactive silicone oil or non-reactive silicone oil occurs, which is undesirable in terms of thermal energy and the environment. Also, if the heat treatment temperature is less than 150°C, the reactive silicone oil or non-reactive silicone oil is not sufficiently fixed to the inorganic oxide powder, the amount of free oil increases, and there is a risk of reduced hydrophobicity or fluidity.

As with the above process, the heat treatment is preferably carried out 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 carried out in a sealed reactor, and the heat treatment process can be carried out while maintaining the same atmosphere.

The heat treatment time should be long enough to allow the reactive silicone oil and non-reactive silicone oil to be fixed (adhered) to the surface of each particle that makes up the inorganic oxide powder, and can be, for example, approximately 5 to 80 minutes, but is not limited to this.

(2) Second Method The second method is a method for producing a surface-modified inorganic oxide powder,
(a) preparing a first mixture comprising an inorganic oxide powder and a reactive silicone oil;
(b) heat-treating the first mixture at a temperature of 80 to 380°C;
(c) preparing a second mixture comprising the heat-treated first mixture and a non-reactive silicone oil;
(d) heat treating the second mixture at a temperature of 80 to 380°C;
The method is characterized by comprising:

The second method involves first surface-treating the inorganic oxide powder with reactive silicone oil, and then surface-treating it with non-reactive silicone oil. Otherwise, the same conditions as in the first method can be used.

(3) Third Method The third method is a method for producing a surface-modified inorganic oxide powder,
(a) preparing a first mixture comprising an inorganic oxide powder and a non-reactive silicone oil;
(b) heat-treating the first mixture at a temperature of 80 to 380°C;
(c) preparing a second mixture comprising the heat-treated first mixture and a reactive silicone oil;
(d) heat treating the second mixture at a temperature of 80 to 380°C;
The method is characterized by comprising:

The third method involves first surface-treating the inorganic oxide powder with a non-reactive silicone oil, and then surface-treating it with a reactive silicone oil. Otherwise, the same conditions as in the first method can be used.

3. Use of the Powder of the Present Invention The powder of the present invention can be used as, for example, a flowability improver or a chargeability adjuster in toners used in electrophotography, including copiers, laser printers, and plain paper facsimiles, as well as in powder coatings and cosmetics. In particular, the powder of the present invention can be suitably used as an external additive for toners. Therefore, the present invention also encompasses an electrophotographic toner composition or a powder coating composition containing the powder of the present invention and binder resin particles (hereinafter, both will be 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. There are no particular restrictions on its composition or manufacturing method, and known compositions and methods can 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 it be contained in an amount of approximately 0.01 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 0.01% by weight, the effect of improving fluidity or stabilizing chargeability achieved by adding the surface-modified inorganic oxide powder may not be fully achieved. Furthermore, if the content of the surface-modified inorganic oxide powder exceeds 5.0% by weight, the surface-modified inorganic oxide powder may act independently more, which may cause problems, for example, with images, cleaning properties, etc.

In addition to the binder resin particles, the composition of the present invention may also contain, for example, pigments, charge control agents (charge control agents), waxes, etc. These components may be the same as those in known or commercially available toner compositions. Furthermore, the toner type is preferably a negatively charged toner. Other than that, there are no particular limitations. Therefore, for example, it may be either a magnetic or non-magnetic one-component toner or a two-component toner. Furthermore, it may be either monochrome or color.

The powder of the present invention can be suitably used as an external additive (external toner additive) for binder resin particles containing at least one of, for example, styrene-acrylic copolymer resin, polyester resin, epoxy resin, etc.

In addition, in the composition 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 intended use, etc. For example, the surface-modified inorganic oxide powder of the present invention can 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 needed.

The following examples and comparative examples will explain the features of the present invention in more detail. However, the scope of the present invention is not limited to these examples.

The specifications of the fumed silica, reactive silicone oil, and non-reactive silicone oil used in each example and comparative example are as follows:

<Fumed silica>
Fumed silica 90: Nippon Aerosil Co., Ltd., trade name "AEROSIL (registered trademark) 90G" (BET specific surface area 90 m ² /g)
Fumed silica 50: AEROSIL (registered trademark) OX50 (BET specific surface area 50 m ² /g), manufactured by Evonik
Fumed silica 40: a sample prepared by a known fumed method (BET specific surface area 40 m ² /g)
Fumed silica 30: a sample prepared by a known fumed method (BET specific surface area 30 m ² /g)

<Reactive silicone oil>
DMO-SiOH (A): reactive silicone oil (viscosity 30 cs) having hydroxyl groups at both ends of poly(dimethylsiloxane)
DMO-SiOH (B): reactive silicone oil (viscosity 40 cs) having hydroxyl groups at both ends of poly(dimethylsiloxane)
DMO-SiOH (C): reactive silicone oil (viscosity 60 cs) having hydroxyl groups at both ends of poly(dimethylsiloxane)

<Non-reactive silicone oil>
PDMS (100cs): Polydimethylsiloxane (viscosity 100cs)
PDMS (50cs): Polydimethylsiloxane (viscosity 50cs)
PDMS (20 cs): Polydimethylsiloxane (viscosity 20 cs)

[Examples 1 to 4]
100 parts by weight of the fumed silica shown in Table 1 was placed in a reactor, and under stirring in a nitrogen gas atmosphere, reactive silicone oil or non-reactive silicone oil shown in Table 1 diluted with hexane was added in the manner and amount shown in Table 1, and surface treatment was carried out while continuing stirring. Finally, in order to break up loose agglomerates of the surface-treated silica, it was crushed using a sample mill (manufactured by Nara Machinery Works, Ltd.). In this way, surface-treated fumed silica was obtained.
In Table 1, the "treatment method" symbol A indicates the first method, symbol B indicates the second method, and symbol C indicates the third method. In Table 1, "surface treatment condition 1" indicates the first treatment condition in the two-stage surface treatment, and "surface treatment condition 2" indicates the second treatment condition in the two-stage surface treatment.

[Comparative Examples 1 to 4]
Surface-treated fumed silica was prepared in the same manner as in Example 1, except that the conditions shown in Table 1 were used.

[Test Example 1]
The surface-treated fumed silica obtained in each Example and Comparative Example was measured for free oil content, hydrophobicity, charge amount, and flowability. The results are shown in Table 1. The average particle size of each surface-treated fumed silica powder was in the range of more than 18 nm and not more than 150 nm.

The free oil content, hydrophobicity, charge amount, and fluidity of surface-treated fumed silica powder were measured as follows:

(1) Amount of free oil and carbon Using a Buchi Soxhlet extraction apparatus, 0.5 g of surface-treated fumed silica was placed in a cylindrical filter paper with a diameter of 28 mm, and the free oil on the surface-treated fumed silica was extracted using hexane as the extraction solvent under the conditions of an extraction time of 60 minutes and a rinse time of 30 minutes. The amount of carbon in the surface-treated fumed silica after the oil was extracted and removed was measured, and the difference between the amount of carbon in the surface-treated fumed silica before extraction and the amount of carbon after extraction was taken as the amount of free oil.
The carbon content of the surface-treated fumed silica was measured using a carbon-in-metal decomposition device (EMIA-110) manufactured by Horiba Ltd.

(2) Hydrophobicity 1 g of surface-treated fumed silica was weighed into a 200 mL separatory funnel, 100 mL of pure water was added, the funnel was plugged, and the funnel was shaken for 10 minutes using a Turbula mixer. After shaking, the funnel was left to stand for 10 minutes. After standing, 20 to 30 mL of the lower layer was removed from the funnel, and the lower layer mixture was dispensed into a 10 mm quartz cell. The colorimeter was then run using pure water as a blank, and the transmittance of light at a wavelength of 500 mm was determined as the hydrophobicity. A higher light transmittance indicates higher hydrophobicity. This is because highly hydrophobic surface-modified inorganic oxide powders tend to float on the surface of water without dispersing in the water, which makes the water less likely to become cloudy and increases the light transmittance.

(3) Fluidity Using a Henschel mixer, 1 g of surface-treated fumed silica powder from each of the Examples and Comparative Examples was externally added to 99 g of toner (negatively charged styrene acrylic toner base (binding resin) powder, average particle size 6 μm), and then the toner samples were subjected to an air permeability test using a powder rheometer. The total energy value was measured 13 times for each sample, the first time without air permeation and the second and subsequent times with air permeation at a linear velocity of 0.04 mm/s. The total energy value of the 13th measurement was then evaluated as fluidity. A smaller energy value indicates higher fluidity.

(4) Charge Amount A sample containing 100 parts by weight of carrier (reduced iron powder) and 0.2 parts by weight of surface-treated fumed silica was mixed for a certain period of time in a Turbula mixer to be frictionally charged, and then the charge amount was measured using a blow-off powder charge amount measuring device under conditions of a temperature of 20°C and a humidity of 45% RH.

As is clear from the results in Table 1, the powders of each example satisfy all of the properties specified in this invention, and possess both high hydrophobicity and fluidity.

Claims (9)

A powder comprising particles including inorganic oxide particles and a layer containing reactive silicone oil and non-reactive silicone oil formed on the surface of the inorganic oxide particles,
(1) The carbon content (wt%) in the powder is 0.5 to 6.0 wt%;
(2) the value obtained by dividing the carbon content by the specific surface area (m ² /g) of the inorganic oxide particles is 1.9 to 5.0%;
(3) The hydrophobicity is 95% or more;
(4) The charge amount is −65 to −150 μC/g,
(5) The free oil content is 3% by weight or less,
(6) The reactive silicone oil has OH groups at both ends of a main chain formed of a siloxane bond.
A surface-modified inorganic oxide powder characterized by: The surface-modified inorganic oxide powder according to claim 1, wherein the inorganic oxide particles are fumed silica. 3. The surface-modified inorganic oxide powder according to claim 1 , wherein the inorganic oxide particles have a specific surface area of 10 to 104 ^{m 2} /g as determined by a nitrogen adsorption method (BET). An external additive for toner or powder coating, comprising the surface-modified inorganic oxide powder according to any one of claims 1 to 3 . 5. A toner composition or powder coating composition for electrophotography, comprising the external additive according to claim 4 and binder resin particles. 2. A method for producing the surface-modified inorganic oxide powder of claim 1, comprising:
(a) preparing a mixture containing an inorganic oxide powder, a reactive silicone oil having OH groups at both ends of a main chain formed by a siloxane bond and having a kinematic viscosity of 30 to 100 cs, and a non-reactive silicone oil having a kinematic viscosity of 5 to 300 cs;
(b) heat-treating the mixture at a temperature of 80 to 380°C. 2. A method for producing the surface-modified inorganic oxide powder of claim 1, comprising:
(a) preparing a first mixture containing an inorganic oxide powder and a reactive silicone oil having OH groups at both ends of a main chain formed by a siloxane bond and having a kinematic viscosity of 30 to 100 cs;
(b) heat-treating the first mixture at a temperature of 80 to 380°C;
(c) preparing a second mixture comprising the heat-treated first mixture and a non-reactive silicone oil having a kinematic viscosity of 5 to 300 cs;
(d) heat treating the second mixture at a temperature of 80 to 380°C;
A method for producing a surface-modified inorganic oxide powder, comprising: 2. A method for producing the surface-modified inorganic oxide powder of claim 1, comprising:
(a) preparing a first mixture containing an inorganic oxide powder and a non-reactive silicone oil having a kinematic viscosity of 5 to 300 cs;
(b) heat-treating the first mixture at a temperature of 80 to 380°C;
(c) preparing a second mixture containing the heat-treated first mixture and a reactive silicone oil having OH groups at both ends of a main chain formed by a siloxane bond and having a kinematic viscosity of 30 to 100 cs;
(d) heat treating the second mixture at a temperature of 80 to 380°C;
A method for producing a surface-modified inorganic oxide powder, comprising: The method according to any one of claims 6 to 8 , wherein the weight ratio of the non-reactive silicone oil to the reactive silicone oil is 1:0.2 to 1:4.0.