Surface-modified inorganic oxide powder and method for producing the same

Abstract

To provide a powder that exhibits both high hydrophobicity and fluidity without relying on hexamethyldisilazane. [Solution] A surface-modified inorganic oxide powder comprising particles including inorganic oxide particles and a reactive silicone oil-containing layer formed on the surface of the particles, characterized in that (1) the value obtained by dividing the carbon content (weight %) in the powder by the specific surface area of ​​the inorganic oxide particles is 1.0 to 2.8%, (2) the hydrophobicity is 75% or more, (3) the charge is -72 to -160 μC / g, and (4) the free oil content is 0.3% by weight or less.

Description

[Technical Field]

[0001] The present invention relates to surface-modified inorganic oxide powder and a method for producing the same. [Background technology]

[0002] By treating the surface of fine inorganic oxide powders such as silica, titania, and alumina with organic matter, the electrostatic properties and hydrophobicity of the powder surface can be modified. Surface-modified inorganic oxide powders obtained in this way are widely used as fluidity improvers and electrostatic modifiers in toners used in electrophotography, including in copiers, laser printers, and plain paper facsimile machines. Such surface-modified inorganic oxide powders used in toner applications are known as external additives.

[0003] For use in such applications, organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil are used as surface treatment agents for inorganic oxide powders. Surface treatment with these organosilicon compounds allows for hydrophobic treatment, for example, by substituting silanol groups on the surface of silica fine particles with organic groups. Among these organosilicon compounds, hexamethyldisilazane is known as a hydrophobic treatment agent that can impart high fluidity and hydrophobicity to toners and the like because it exhibits sufficient hydrophobicity and has a low surface energy (Patent Documents 1, 2, etc.). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International release WO2013 / 18704 [Patent Document 2] Japanese Patent Publication No. 2009-15260 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in recent years, concerns have arisen regarding the safety of hexamethyldisilazane, and there is a growing demand to replace it with alternative materials. In this regard, silicone oil is a representative example of a surface treatment agent that can impart high hydrophobicity. However, when silicone oil is used as a surface treatment agent, its fluidity can be extremely reduced, and there is room for further improvement in this respect.

[0006] Therefore, the main objective of the present invention is to provide a powder that can exhibit both high hydrophobicity and fluidity without relying on hexamethyldisilazane. [Means for solving the problem]

[0007] In light of the problems of the prior art, the inventors conducted extensive research and, as a result, discovered that the objective of the present invention can be achieved by applying a specific silicone oil at a specific immobilization rate, thus leading to the present invention.

[0008] In other words, the present invention relates to the following surface-modified inorganic oxide powder and a method for producing the same. 1. A powder comprising particles containing inorganic oxide particles and a reactive silicone oil-containing layer formed on the surface of the particles, (1) The carbon content (by weight) in the powder is the specific surface area (m²) of the inorganic oxide particles. 2 The value obtained by dividing by ( / g) is 1.0-2.8%, (2) The hydrophobicity is 75% or more, (3) The charge is -72 to -160 μC / g, (4) The free oil content is 0.3% by weight or less. A surface-modified inorganic oxide powder characterized by the following features. 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 obtained by dividing the energy value of the fluidity measured by the dry fluidity evaluation method when added to toner by the energy value before addition is 0.47 or less. 4. A 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 its kinematic viscosity is 30 to 100 cs. 5. An external additive for toner or powder coating containing the surface-modifying inorganic oxide powder described in any of items 1 to 4 above. 6. An electrophotographic toner composition or powder coating composition comprising the external additive described in item 5 above and binding resin particles. 7. A method for producing surface-modified inorganic oxide powder, (a) A step of preparing a mixture containing inorganic oxide powder and reactive silicone oil, (b) A step of heat-treating the mixture at a temperature of 80 to 380°C. A method for producing surface-modified inorganic oxide powder, characterized by containing the following: [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a powder that exhibits both high hydrophobicity and fluidity without relying on hexamethyldisilazane. In particular, because the structure has inorganic oxide particles covered with a reactive silicone oil (especially hydroxyl group-containing silicone oil) layer and is controlled within a specific range of physical properties, it exhibits high hydrophobicity and, especially when added to toner, can impart high fluidity.

[0010] Therefore, an electrophotographic toner composition containing the powder of the present invention exhibits excellent fluidity and antistatic properties, and can effectively suppress or prevent fogging and various problems (such as poor cleaning, adhesion of toner to the photoreceptor, and image defects).

[0011] Such powders of the present invention are extremely useful industrially as surface-modifying inorganic oxide powders added to powder material systems such as electrophotographic toners, powder coatings, and cosmetics for purposes such as improving fluidity, preventing caking, and adjusting static charge. [Modes for carrying out the invention]

[0012] 1. Surface-modified inorganic oxide powder The surface-modified inorganic oxide powder (the powder of the present invention) of the present invention is a powder composed of particles including inorganic oxide particles and a reactive silicone oil-containing layer formed on the particle surface, (1) The value obtained by dividing the carbon content rate (wt%) in the powder by the specific surface area (m 2 / g) of the inorganic oxide particles is 1.0 to 2.8%, (2) The hydrophobicity rate is 75% or more, (3) The triboelectric charge amount is -72 to -160 μC / g, (4) The free oil content is 0.3 wt% or less, which is characterized by the above.

[0013] <Configuration (Composition) of the Powder of the Present Invention> The particles constituting the powder of the present invention include inorganic oxide particles and a reactive silicone oil-containing layer formed on the particle surface. That is, with the inorganic oxide particles as core particles (original bodies), a structure (coated particles) in which part or all of the surface thereof is coated with a reactive silicone oil-containing layer is the basic configuration.

[0014] The types of the inorganic oxide particles serving as core particles are not limited, and examples include silicon oxide, titanium oxide, aluminum oxide, etc., but are not limited thereto. Among these, in the present invention, silicon oxide (silica) (especially fumed silica) can be preferably used. These may be used alone or in combination of two or more. These particles themselves can be known or commercially available ones.

[0015] The particle size of the inorganic oxide particles is not limited, but usually, the primary particle size is in the range of about 5 to 150 nm, and can be appropriately selected according to the range of the average particle size of the target surface-modified inorganic oxide powder, etc. Further, the inorganic oxide particles have a specific surface area by the nitrogen adsorption method (BET) of about 10 to 104 m 2 / g, particularly 20 to 100 m 2It is desirable that the BET specific surface area be around / g. If the BET specific surface area is too small, its effect as a fluidizing agent will be reduced when added to electrophotographic toner. Conversely, if the BET specific surface area is too large, when added to electrophotographic toner, it will be embedded in the toner quickly, leading to a greater deterioration in performance over time.

[0016] Furthermore, it is preferable to use powder produced by the fumed method for manufacturing inorganic oxide particles. The fumed method is a known manufacturing method, and silica can be synthesized by a method that includes a step of introducing a silicon compound (such as silicon tetrachloride) or metallic silicon into an oxygen-hydrogen flame and causing a hydrolysis reaction. Since such powders have a particle shape that is less spherical than silica produced by, for example, the sol-gel method, advantages such as being able to effectively suppress liberation from the toner surface are obtained. In addition, since no solvent is used, there is also the advantage that aggregated particles are less likely to be generated during drying.

[0017] Commercially available inorganic oxide particles produced by such a fumed process can also be used. For example, the commercially available products shown in the examples below can be suitably used.

[0018] In this invention, a reactive silicone oil-containing layer is formed on the surface of inorganic oxide particles. That is, a reactive silicone oil is used as the organosilicon compound that coats the surface of the inorganic oxide particles.

[0019] The reactive silicone oil contained in the reactive silicone oil-containing layer is a silicone oil having a functional group at both ends, one end, and at least one side chain of the main chain, which consists of siloxane bonds. In the present invention, by using a reactive silicone oil, the reactivity of the silicone oil with respect to inorganic oxide particles can be increased, thereby increasing the fixation rate. The proportion of reactive silicone oil in the above layer can be, for example, about 90 to 100% by weight, but is not limited thereto.

[0020] The main chain (main skeleton) consisting of the siloxane bonds described above is not limited, but poly(dimethylsiloxane) and the like can be particularly preferred. Furthermore, the functional group is not particularly limited, and at least one of the following can be cited: a hydroxyl group, an amino group, a carbinol group, an epoxy group, a carboxyl group, and so on.

[0021] Therefore, in the present invention, a reactive silicone oil represented by the following formula can be suitably used, for example.

[0022] [ka] (However, R 1 (where m and n represent integers greater than or equal to 1.)

[0023] As shown in the formula above, a reactive silicone oil can be suitably used, which has a siloxane bond-(Si-O)- as a repeating unit and hydroxyl groups at both ends of the main chain, which consists of at least one siloxane bond. In other words, a structure in which at least one hydroxyl group is bonded to the silicon atoms at both ends can be suitably adopted.

[0024] These reactive silicone oils themselves can be known or commercially available. Furthermore, the reactive silicone oils can be used individually or in combination of two or more types.

[0025] The kinematic viscosity (measured at 25°C) of the reactive silicone oil (hereinafter referred to as "viscosity") is not particularly limited, but is usually preferably 30 to 100 cs. If the viscosity is less than 30 cs, low molecular weight reactive silicone oil may volatilize during heat treatment, making it difficult to perform sufficient surface treatment, and it may also be undesirable from an environmental perspective. On the other hand, if the viscosity exceeds 100 cs, the reactive silicone oil may promote the aggregation of inorganic oxide particles, which may severely impair fluidity.

[0026] Furthermore, the molecular weight range of the reactive silicone oil is not limited to that range, as long as it satisfies the viscosity range mentioned above. For example, it can be applied in the range of approximately 3000 to 7500, but it is not limited to this range.

[0027] The content of reactive silicone oil is not particularly limited as long as it is within the above carbon content range, but is generally preferably about 1 to 20 parts by weight per 100 parts by weight of inorganic oxide powder, more preferably 2 to 15 parts by weight, and most preferably 3 to 12 parts by weight. If the reactive silicone oil content is too low, it will not be possible to obtain surface-modified inorganic oxide powder with high hydrophobicity. On the other hand, if the reactive silicone oil content is too high, particle aggregation is likely to occur, which may impair fluidity.

[0028] In the present invention, a non-reactive silicone oil can be used as long as it does not hinder the effects of the present invention. In this case, the content of the non-reactive silicone oil may be, for example, within the range of 1 part by weight or less per 100 parts by weight of inorganic oxide powder.

[0029] Furthermore, organosilicon compounds other than silicone oil may be included, as long as they do not hinder the effects of the present invention. In particular, the content of hexamethyldisilazane (alkylsilazanes, and even silazanes) is preferably 0.1 parts by weight or less per 100 parts by weight of inorganic oxide powder, and more preferably substantially 0 parts by weight.

[0030] <Characteristics of the powder of this invention> The properties of the powder of the present invention are as follows: (1) The carbon content (by weight) in the powder is the specific surface area (m²) of the inorganic oxide particles. 2 The value obtained by dividing by ( / g) (carbon value) is 1.0-2.8%, (2) The hydrophobicity is 75% or more, (3) The charge is -72 to -160 μC / g, (4) The free oil content is 0.3% by weight or less. It is characterized by the following:

[0031] The carbon content in the powder of the present invention is typically 1.0 to 2.8%, as described above. If the carbon content is less than 1.0%, there is not enough organic matter on the surface to coat the inorganic powder surface, and it will not be able to exhibit sufficient hydrophobicity and fluidity. On the other hand, if the carbon content exceeds 2.8%, the amount of organic matter coating the surface becomes excessive, negatively affecting fluidity. As for the method of calculating the carbon content, for example, if the carbon content (carbon amount) is 4.6% by weight and the specific surface area of ​​the inorganic oxide particles is 200 m²... 2 If it's in grams, it can be calculated as [4.6 / 200] × 100 = 2.3%.

[0032] In relation to the carbon content, the carbon content of the powder of the present invention is not limited, but is usually about 0.3 to 3% by weight, and is particularly preferably 0.5 to 2.5% by weight.

[0033] The hydrophobicity is usually 75% or higher, and preferably 78-99%. If the hydrophobicity is less than 75%, problems arise, particularly under high temperature and high humidity conditions, where sufficient charge cannot be obtained.

[0034] The charge is typically around -72 to -160 μC / g, and particularly preferably -75 to -155 μC / g. If the charge approaches zero, below -72 μC / g, it becomes difficult to achieve stable charging characteristics in the toner when the powder is added, making it difficult to control the toner within a predetermined charge range. On the other hand, if the charge becomes even more negative than -160 μC / g, it also becomes difficult to control stable charging characteristics in the toner to which it is added.

[0035] The amount of free oil in the powder of the present invention is usually 0.3% by weight or less. If the amount of free oil exceeds 0.3% by weight, sufficient fluidity may not be obtained.

[0036] Furthermore, in the powder of the present invention, a ratio based on the energy value measured by a powder rheometer serves as an indicator of its ability to impart fluidity to toner and the like. Specifically, it is desirable that the value obtained by dividing the energy value of the fluidity measured by the dry fluidity evaluation method when the powder of the present invention is added to toner by the energy value before the addition is 0.47 or less. By setting this value to 0.47 or less, the toner product to which the powder of the present invention is added can be given even higher fluidity.

[0037] Furthermore, the average particle size of the powder of the present invention is not particularly limited, but is usually in the range of greater than 18 nm and less than or equal to 150 nm. Therefore, for example, it can be set to 19 to 130 nm. In this invention, the average particle size refers to the arithmetic mean of the particle diameters of 1000 particles arbitrarily selected by observation using a transmission electron microscope (TEM).

[0038] 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 a powder having the above-described composition and characteristics can be obtained, but it can be suitably produced by a method including, for example, (a) a step of preparing a mixture containing inorganic oxide powder and reactive silicone oil (mixture preparation step), and (b) a step of heat-treating the mixture at a temperature of 80 to 380°C (heat treatment step).

[0039] Mixture preparation process The mixture preparation step is not limited to any method that can coat the surface of each particle constituting the inorganic oxide powder with reactive silicone oil. For example, a method of mixing the inorganic oxide powder with vaporized reactive silicone oil under stirring, or a method of spraying reactive silicone oil onto the inorganic oxide powder under stirring can be suitably employed.

[0040] In this case, the reactive silicone oil can be used diluted to approximately 5-70% by weight using, for example, hexane, toluene, alcohol (aliphatic alcohols with 1-8 carbon atoms such as methanol, ethanol, and propanol), acetone, or, in some cases, water.

[0041] 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 thereto. 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.

[0042] The type and amount of organosilicon compounds used can be the same as those described in "1. Surface-Modified Inorganic Oxide Powder" above.

[0043] Heat treatment process The heat treatment temperature in the heat treatment process is not limited, but is generally preferably 80 to 380°C (particularly 150 to 380°C, and even more preferably 280 to 380°C). If the heat treatment temperature exceeds 380°C, partial decomposition of the reactive silicone oil occurs, which is undesirable from a thermal energy and environmental perspective. If the heat treatment temperature is below 80°C, the immobilization of the reactive silicone oil onto the inorganic oxide powder is insufficient, increasing the amount of free oil and potentially reducing hydrophobicity or fluidity.

[0044] The heat treatment atmosphere, as in the previous step, 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 previous step can be carried out in a sealed reactor, and the heat treatment step can be suitably carried out while maintaining the same atmosphere.

[0045] The heat treatment time should be sufficient to allow the reactive silicone oil to fix (adhere) to the surface of each particle constituting the inorganic oxide powder, and can be, for example, 5 to 180 minutes, but is not limited to this.

[0046] 3. Use of the powder of the present invention The powder of the present invention can be used, for example, as a fluidity improver, electrostatic modifier, etc., in toners used in electrophotography, including photocopiers, laser printers, and plain paper facsimile machines, as well as in powder coatings, cosmetics, etc. In particular, the powder of the present invention can be suitably used as an external additive for toners. Therefore, the present invention also encompasses electrophotographic toner compositions or powder coating compositions (hereinafter, both are collectively referred to as "the composition of the present invention") that contain the powder of the present invention and binding resin particles.

[0047] The composition of the present invention contains the surface-modified inorganic oxide powder of the present invention described above, and there are no particular restrictions on its composition, manufacturing method, etc., and known compositions and methods can also be used.

[0048] 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 is contained in an amount of about 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 improvement effect of fluidity or the stabilization effect of electrostatic properties due to the addition of the surface-modified inorganic oxide powder may not be sufficiently obtained. Furthermore, if the content of the surface-modified inorganic oxide powder exceeds 5.0% by weight, the amount of surface-modified inorganic oxide powder acting independently increases, which may cause problems such as image quality and cleaning properties.

[0049] In addition to binder resin particles, the composition of the present invention may also contain, for example, pigments, charge control agents (static control agents), waxes, etc. These components may be the same as those in known or commercially available toner compositions. Furthermore, a negatively charged toner is preferred as the toner type. There are no particular limitations on other aspects. Therefore, for example, either a magnetic or non-magnetic one-component toner or a two-component toner may be used. Moreover, it may be either monochrome or color.

[0050] The powder of the present invention can be suitably used as an external additive (external additive for toner) for binding resin particles, which may include at least one of the following: a styrene-acrylic copolymer resin, a polyester resin, or an epoxy resin.

[0051] In the 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 powders according to the purpose of use and the like. 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.

Examples

[0052] Examples and comparative examples are shown below to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples.

[0053] The specifications of the fumed silica, reactive silicone oil, and non-reactive silicone oil used in each example and comparative example are as follows.

[0054] <Fumed silica> · Fumed silica 90: manufactured by Nippon Aerosil Co., Ltd., trade name "AEROSIL (registered trademark) 90G" (BET specific surface area 90 m 2 / g) · Fumed silica 50: manufactured by Evonik, trade name "AEROSIL (registered trademark) OX 50" (BET specific surface area 50 m 2 / g) · 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)

[0055] <Reactive silicone oil> · DMO-SiOH (30 cs): a reactive silicone oil having hydroxyl groups at both ends of poly(dimethylsiloxane) (viscosity 30 cs) · DMO-SiOH (40 cs): a reactive silicone oil having hydroxyl groups at both ends of poly(dimethylsiloxane) (viscosity 40 cs) • DMO-SiOH (60 cs): A reactive silicone oil (viscosity 60 cs) with hydroxyl groups at both ends of poly(dimethylsiloxane).

[0056] <Non-reactive silicone oil> • PDMS (50 cs): Poly(dimethylsiloxane) (viscosity 50 cs)

[0057] [Examples 1-4] 100 parts by weight of fumed silica shown in Table 1 were placed in a reactor and, under a nitrogen gas atmosphere and stirring, the reactive silicone oil shown in Table 1 was diluted with hexane and added in the amount of reactive silicone oil shown in Table 1. Surface treatment was carried out while stirring was continued. To break the loose aggregation of the surface-treated silica, it was crushed using a sample mill (manufactured by Nara Machine Works Co., Ltd.) at the end. In this way, surface-treated fumed silica was obtained.

[0058] [Comparative Examples 1-5] Surface-treated fumed silica was obtained by performing surface treatment in the same manner as in Example 1, except that the composition was as shown in Table 1.

[0059] [Test Example 1] The free oil content, carbon content, hydrophobicity, charge, and fluidity of the surface-treated fumed silica obtained in each example and comparative example were measured. The results are shown in Table 1. The average particle size of each surface-treated fumed silica powder was in the range of greater than 18 nm and less than or equal to 150 nm.

[0060] The following are the methods for measuring the free oil content, carbon content, hydrophobicity, charge content, and fluidity of surface-treated fumed silica powder.

[0061] (1) Free oil content and carbon content Using a Soxhlet extraction apparatus manufactured by BUCHI, 0.5 g of surface-treated fumed silica was placed in a cylindrical filter paper with a diameter of 28 mm. Hexane was used as the extraction solvent, and free oil was extracted from the surface-treated fumed silica under the conditions of extraction time of 60 minutes and rinsing time of 30 minutes. The carbon content of the surface-treated fumed silica after oil extraction and removal was measured, and the difference between the carbon content of the surface-treated fumed silica before extraction and the carbon content after extraction was defined as the amount of free oil. The carbon content of surface-treated fumed silica was measured using a metal carbon decomposition system (EMIA-110) manufactured by Horiba, Ltd.

[0062] (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 stoppered, and the mixture was shaken in a turbler mixer for 10 minutes. After shaking, it was allowed to stand for 10 minutes. After standing, 20-30 mL of the lower layer was withdrawn from the funnel, and the lower layer mixture was divided into a 10 mm quartz cell. Using pure water as a blank, the mixture was subjected to a colorimeter test, and the transmittance of light at a wavelength of 500 mm was defined as the hydrophobicity. A higher light transmittance indicates higher hydrophobicity. This is because surface-treated fumed silica powder, which has high hydrophobicity, tends to float on the water surface without dispersing in the water, thus reducing turbidity and increasing light transmittance.

[0063] (3) Liquidity Using a Henschel mixer, 1 g of surface-treated fumed silica powder obtained in each example and comparative example was added to 99 g of toner (negatively charged styrene-acrylic toner base (binding resin), average particle size 6 μm). The resulting mixed powder was then subjected to a permeability test of the toner sample using a powder rheometer. A total of 13 total energy values ​​were measured for each sample. The first measurement was taken without permeability, and subsequent measurements were taken while permeating at a linear velocity of 0.04 mm / s. The total energy value E1 (mJ) from the 13th measurement was then recorded. Except for not adding surface-treated fumed silica powder, the total energy value E0 of the toner alone was measured in the same manner as described above. Next, [E1 / E0] was calculated based on the values ​​E1 and E0 obtained above. A smaller value of [E1 / E0] indicates a higher liquidity-enhancing capability.

[0064] (4) Charge A sample containing 0.2 parts by weight of surface-treated fumed silica per 100 parts by weight of carrier (reduced iron powder) was mixed in a turbler mixer for a certain period of time to induce triboelectric charging. The amount of charge (triboelectric charge) was then measured using a blow-off powder charge measuring device under conditions of 20°C and 45% RH.

[0065] [Table 1]

[0066] As is clear from the results in Table 1, the powders of each example satisfy all the properties defined in the present invention and possess both high hydrophobicity and fluidity.

Claims

1. Specific surface area of ​​10 to 104 m² ２ A powder comprising particles containing fumed silica, which is an inorganic oxide particle weighing / g, and a reactive silicone oil-containing layer formed on the surface of the particles, the layer having OH groups at both ends of a main chain made of siloxane bonds, (1) The carbon content (by weight) in the powder is the specific surface area (m²) of the inorganic oxide particles. ２ The value obtained by dividing by ( / g) is between 1.0% and 2.8%. (2) The hydrophobicity is 75% or more, (3) The charge is -72 to -160 μC / g, (4) The free oil content is 0.3% by weight or less, (5) The reactive silicone oil is 1 to 4 parts by weight per 100 parts by weight of the inorganic oxide particles. A surface-modified inorganic oxide powder characterized by the following features.

2. The surface-treated inorganic oxide powder according to claim 1, wherein the free oil content is 0% by weight.

3. An external additive for toner or powder coating, comprising the surface-modifying inorganic oxide powder described in claim 1 or 2.

4. An electrophotographic toner composition or powder coating composition comprising the external additive described in claim 3 and binding resin particles.

Images