Surface-modified silica powder using precipitated silica and method for producing the same

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 having an amino group 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 wt.%, (5) the drying loss is 0.1-3.0%, and (6) the frictional electrification amount is +10-+450 μC / g.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a novel surface-modified silica powder using precipitated silica and a method for producing the same.

Background Art

[0002] By treating the surfaces of inorganic oxide powders such as fine silica, titania, and alumina with organic substances, the chargeability, hydrophobicity, etc. of the powder surfaces can be modified. The surface-modified inorganic oxide powders thus obtained are widely used, for example, as fluidity improvers, chargeability adjusters, etc. for toners used in electrophotography including copiers, laser printers, plain paper facsimiles, etc. The surface-modified inorganic oxide powders used for such toner applications are known as so-called external additives.

[0003] Examples of surface treatment agents for inorganic oxide powders used for toner applications include organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil. By surface treatment with these organosilicon compounds, for example, the silanol groups on the surface of silica fine particles can be substituted with organic groups to perform a hydrophobization treatment. As these surface-treated inorganic oxide powders, fumed oxides are widely used as materials that impart high fluidity to toner materials.

[0004] Toner is stirred in a device such as a copier and becomes charged (i.e., acquires an electric charge) by friction with a carrier or the like. Then, the highly controlled chargeability enables the development function to be exhibited. However, if the toner continues to be stirred in the device for a long time, the strong frictional force becomes stress, and the deterioration of the toner progresses. For example, when the external additive is buried in the toner surface, the function as a contact point between the toner surface and the external environment is lost. Moreover, the mechanical load on the toner has increased in recent years, and as a result of the softening design of the binder resin (toner matrix resin) constituting the toner, the hardness of the toner matrix has decreased, making it easier for the external additive to be buried. Therefore, the importance of countermeasures against the burial of the above-mentioned external additives is increasing more and more.

[0005] In particular, in recent years, due to the improvement of electrophotographic image quality, the toner particle size has been decreasing. In addition, due to high speed and colorization, the mechanical load on the toner has been increasing. Therefore, the durability of toner performance over time (control of deterioration behavior) has become more important. On the other hand, for the purpose of shortening the printing waiting time and energy saving, low-temperature fixability is required for the binder resin used in the toner. Under such circumstances, it is becoming the mainstream to adopt components that are softened and have a lower melting point as the toner matrix resin.

[0006] With the lowering of the melting point of such toner resins, etc., the surface-treated fumed oxide is embedded in the toner resin during long-term operation, resulting in a phenomenon of reduced fluidity. Therefore, for the purpose of enhancing the durability of the toner, submicron-sized silica powder is added to the toner surface together with the fumed oxide, and a measure is taken to prevent the embedding of the fumed oxide into the toner by the spacer effect of the submicron-sized silica powder. And as this submicron-sized silica, silica powder mainly produced by the sol-gel method is used (see Patent Document 1, etc.).

[0007] However, the silica powder produced by the sol-gel method has a problem that its charging characteristics are weak. This is considered to be partly due to the high amount of adsorbed moisture in the particles constituting the silica powder produced by the sol-gel method.

[0008] Moreover, since the silica powder produced by the sol-gel method has a particle shape close to spherical, there is also a problem that it is likely to be released from the toner surface during long-term use.

[0009] Furthermore, since the silica powder produced by the sol-gel method itself easily retains or adsorbs a lot of moisture, strong triboelectric charging characteristics cannot be obtained. For this reason, the low charging property of the silica powder must be improved for materials that adjust the charge, such as toner.

[0010] On the one hand, it is also called the dry method or the vapor phase method (hereinafter, both are collectively referred to as the "fumed method").) The silica powder produced by the fumed method has a particle shape that deviates from a spherical shape compared to the silica produced by the sol-gel method. Therefore, an effect of suppressing release from the toner surface, which is a problem of the sol-gel silica, can be expected. However, generally, silica powder and the like by the fumed method have a small primary particle size and disperse as particles with a size of submicron or less on the toner surface. Therefore, the spacer effect cannot be fully exerted, and generally, the charging characteristics are too high, and the addition amount and dispersibility must be precisely controlled to control the chargeability of the toner within an appropriate range.

[0011] Regarding silica as described above, precipitated silica produced by the wet method is known (for example, Patent Document 2). Precipitated silica 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 silica has problems such as strong aggregation between particles, difficulty in uniformly applying (externally adding) to the toner surface, and inability to exhibit sufficient charges. If precipitated silica can be used for toner (especially for toner external additives), there is a possibility of imparting new functions by utilizing its pore characteristics. However, toner materials using precipitated silica have not yet been developed.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] Accordingly, the main object of the present invention is to provide a powder suitable for toners and the like by utilizing the original characteristics of precipitated silica while making use of the characteristics of precipitated silica itself. In particular, the present invention aims to provide a surface-modified precipitated silica powder having good dispersibility, appropriate charging characteristics, and a high spacer effect.

Means for Solving the Problems

[0014] As a result of intensive studies in view of the problems of the prior art as described above, the present inventors have found that specific physical properties can be obtained when a specific surface treatment is applied to precipitated silica powder, and have completed the present invention.

[0015] That is, the present invention relates to the following surface-modified precipitated silica powder and a method for producing the same. 1. a) In the particle size distribution based on volume, d 50 : 150 to 1000 nm and d 90 : 500 to 7000 nm, and b) a powder comprising particles having a coating layer containing an organosilicon compound having an amino group formed on the surface of precipitated silica particles having a silanol group density of 2.5 to 8 OH / nm 2 , wherein (1) Bulk density: 40 to 150 g / L, (2) Moisture adsorption amount at a relative water vapor 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) Loss on drying: 0.1 to 3.0% and (6) Triboelectric charge amount: +10 to +450 μC / g The surface-modified precipitated silica powder is characterized by the above. 2. The surface-treated precipitated silica powder according to item 1 above, wherein the value obtained by dividing the energy value of fluidity by the dry fluidity evaluation method when added to toner by the energy value before addition is 0.35 or less. 3. The surface-modified precipitated silica powder according to item 1 above, wherein the organosilicon compound having an amino group is at least one of aminosilane and amino group-modified silicone oil. 4. An external additive for toner or powder paint containing the surface-modified precipitated silica powder according to any one of Items 1 to 3 above. 5. An electrophotographic toner composition or powder paint composition containing the external additive according to Item 4 above and binder resin particles. 6. A method for producing a surface-modified precipitated silica powder, (a) A step of preparing a mixture containing precipitated silica powder and an organosilicon compound having an amino group, (b) A step of heat-treating the mixture at a temperature of 120 to 360 °C A method for producing a surface-modified precipitated silica powder, characterized by including the above. 7. The production method according to Item 6 above, wherein the steps (a) and (b) are carried out under stirring.

Advantages of the Invention

[0016] According to the present invention, by using precipitated silica, while taking advantage of the original properties of precipitated silica, a powder suitable for toner or the like can be provided. In particular, the present invention can provide a surface-modified precipitated silica powder having good dispersibility, appropriate charging characteristics, and a high spacer effect.

[0017] The surface-modified precipitated silica powder of the present invention surface-modifies precipitated silica powder having a median diameter or the like controlled within a specific range with an organosilicon compound, resulting in specific properties such as bulk density and moisture adsorption amount. As a result, it is possible to provide a submicron-sized aggregated powder having good fluidity with low bulk density, good dispersibility, and appropriate charging characteristics.

[0018] More specifically, the surface-modified precipitated silica powder of the present invention surface-modifies precipitated silica powder with a predetermined organosilicon compound, resulting in controlling each property such as bulk density, hydrophobicity, moisture adsorption amount, surface area, and carbon content within a certain range. As a result, it exhibits higher charging characteristics compared to particles obtained by the sol-gel method, enables uniform application to the surface of toner (binder resin particles), and can secure a particle size sufficient to exhibit a spacer effect that cannot be obtained with silica oxide powder produced by the conventional fumed method.

[0019] As described above, the present invention focuses on precipitated silica and, as part of the development of its new uses, selectively uses specific precipitated silica powder and modifies its surface. By doing so, while leveraging the original properties of precipitated silica (such as mass productivity and pore properties), in addition to good dispersibility, it has achieved high charging properties and low bulk density, which are difficult to obtain with sol-gel silica, and a high spacer effect, which is difficult to obtain with fumed silica.

[0020] The powder of the present invention having such characteristics can be suitably used particularly as an external additive for toner or powder coating. Therefore, the electrophotographic toner composition or powder coating composition of the present invention contains surface-modified precipitated silica powder having such high fixing rate, high hydrophobicity, etc., and thus is also excellent in dispersibility, fluidity, antistatic property, etc., and fogging or poor cleaning is suppressed. Furthermore, it is possible to obtain the effect that adhesion of toner or the like to the photoreceptor hardly occurs and image defects hardly occur. Also, according to these compositions of the present invention, effects such as long-term storage stability and control of developer deterioration behavior can be obtained.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] 1. Surface-Modified Precipitated Silica Powder The surface-modified precipitated silica powder (the powder of the present invention) of the present invention has, in the particle size distribution based on volume, (a) d 50 : 150 to 1000 nm and d 90 : 500 to 7000 nm, and (b) a coating layer containing an organosilicon compound having an amino group is formed on the surface of precipitated silica particles having a silanol group density of 2.5 to 8 OH / nm 2 , and it is a powder composed of particles, (1) Bulk density: 40 to 150 g / L, (2) Moisture adsorption amount at a relative water vapor 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% by weight, (5) Loss on drying: 0.1 to 3.0% and (6) Amount of triboelectric charge: +10 to +450 μC / g characterized by being as described above.

[0023] <Constitution (composition) of the powder of the present invention> The particles constituting the powder of the present invention include precipitated silica particles and a coating layer formed on the particle surface. That is, the powder has a basic structure in which the precipitated silica particles are used as core particles (base bodies), and a coating layer containing an organosilicon compound having an amino group is formed on the surface thereof.

[0024] As the precipitated silica particles serving as the core particles, those having a specific particle size (particle size distribution) and silanol group density are used.

[0025] Regarding the particle size distribution, in the particle size distribution based on volume, d 50 (median diameter): 150 to 1000 nm and d 90 : 500 to 7000 nm, characterized by being as described above.

[0026] When the above d 50 is less than 150 nm, the aggregated particle diameter of the powder after surface treatment with the organosilicon compound is too fine, and when it is dispersed in the toner, a sufficient spacer effect cannot be exhibited. On the other hand, when the above d 50 exceeds 1000 nm, the aggregated particle diameter is too large, making it difficult to uniformly disperse on the toner surface.

[0027] Also, when the above d 90 is less than 500 nm, the development of its chargeability and spacer effect becomes insufficient. On the other hand, when the above d 90 exceeds 7000 nm, the number of coarse particles increases, making it difficult to uniformly disperse on the toner surface.

[0028] Note that in the present invention, d 50 and d90 refers to the value (volume basis) calculated by a particle size distribution measuring device (laser diffraction / scattering type particle size distribution measuring device, manufactured by Horiba, Ltd.).

[0029] Regarding the silanol group density, it is usually 2.5 - 8 OH / nm 2 and particularly preferably 3.1 - 5.0 OH / nm 2 If the silanol group density is too small, the charge amount of the powder after surface treatment with the organosilicon compound is too high and it is difficult to control within a certain range. On the other hand, if the silanol group density is too large, there is a problem that the moisture adsorption amount increases and the charge amount becomes too low.

[0030] Also, the BET specific surface area of the precipitated silica particles is not particularly limited, but it is preferably in the range of 100 - 350 m 2 / g. By this, the distribution of surface pores becomes an appropriate range, and it becomes possible to control the moisture adsorption amount within an appropriate range. As a result, appropriate chargeability can be exhibited after modifying with an organosilicon compound having an amino group.

[0031] As for the precipitated silica particles themselves, known or commercially available ones can be used. For example, the precipitated silica powder described in Patent Document 2 can be preferably used. Therefore, in the present invention, the precipitated silica obtained according to the production method described in Patent Document 2 can also be used.

[0032] More specifically, "the following characteristics: 10 - 30 ml / (5 g) of shares - number, 100 - 350 m 2A method for producing precipitated silica, which has a BET surface area of / g, a loss on drying of 2 to 8% by mass, a loss on ignition of 2 to 9% by mass, a pH value of 4 to 9, and a DBP value of 230 to 400 g / 100 g, is pulverized and simultaneously classified to obtain pulverized silica. In the method for producing precipitated silica, the pulverization and simultaneous classification are carried out using one pulverizer. In the method for producing precipitated silica, the mill of the pulverizer is operated in one pulverization phase using a working medium selected from the group consisting of gas, steam, water vapor, gas containing water vapor, and mixtures thereof; and the pulverization chamber is heated in a heating stage, i.e., before the specific operation using the working medium, so that the temperature in the pulverization chamber and / or at the mill outlet is higher than the dew point of the working medium; and the pulverized silica is classified to a d 50 -value of 150 to 2000 nm and a d 90 -value of 500 to 7000 nm. Precipitated silica can be preferably prepared by the method for producing precipitated silica characterized by the above.

[0033] The coating layer coats the surface of the particles constituting the powder of the present invention, thereby imparting predetermined hydrophobicity, chargeability, etc. to the particles constituting the powder of the present invention. The coating layer contains an organosilicon compound having an amino group. In the coating layer, the content of the organosilicon compound having an amino group is not particularly limited, but can usually be appropriately set to about 5 to 100% by weight. Therefore, for example, it can also be 20 to 60% by weight.

[0034] The organosilicon compound having an amino group is not particularly limited as long as it can modify the precipitated silica particles to be positively charged, and those known as positive charge imparting agents can also be used. In the present invention, in particular, at least one of aminosilane and amino group-modified silicone oil can be preferably used. The amino group in these compounds can be any of primary to tertiary.

[0035] As the aminosilane, for example, amino group-containing alkoxysilanes such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane can be preferably used. These can also be those that are known or commercially available.

[0036] As the amino group-modified silicone oil, for example, silicone oils in which an amino group or an organic group containing the same (such as an aminoalkyl group) is introduced into the side chain and / or the terminal of the silicone chain can be preferably used. These can also be those that are known or commercially available.

[0037] In addition, the viscosity range (measurement temperature: 25 °C) of the amino group-modified silicone oil is not particularly limited, but is usually preferably 20 to 300 cs. When the viscosity is less than 20 cs, volatilization of low molecular weight polysiloxane or the like occurs during surface treatment, which is not preferable from the viewpoints of energy efficiency and the environment. On the other hand, when the viscosity exceeds 300 cs, higher aggregation occurs, and there is a risk that the dispersibility of the obtained powder may be impaired.

[0038] The content of the organosilicon compound having an amino group in the powder of the present invention is not particularly limited as long as it is within the range of the above carbon content, but is usually about 0.5 to 30 parts by weight, particularly preferably 1 to 20 parts by weight, based on 100 parts by weight of the precipitated silica powder.

[0039] In the coating layer, components other than the organosilicon compound having an amino group may be contained within a range that does not interfere with the effects of the present invention. For example, an organosilicon compound having no amino group can be mentioned. The organosilicon compound having no amino group is not particularly limited, and for example, those that are known or commercially available and known as a hydrophobizing agent can also be used.

[0040] More specifically, alkylsilazane compounds such as hexamethyldisilazane, alkyalkoxysilane compounds such as dimethyldimethoxysilane, diethyldiethoxysilane, trimethylmethoxysilane, methyltrimethoxysilane, butyltrimethoxysilane, chlorosilane compounds such as dimethyldichlorosilane, trimethylchlorosilane, silicone oils such as polydimethylsiloxane (PDMS), silicone varnishes, etc. can be used. These may be used alone or in combination of two or more.

[0041] Among these, it is preferable to use at least one of an alkylsilazane compound, an alkoxysilane compound, and a silicone oil in terms of more surely obtaining the effects of the present invention.

[0042] In particular, the alkoxysilane is not particularly limited as long as it is an alkoxysilane substituted with an alkyl group. Generally, trimethoxyalkoxysilane, triethoxyalkoxysilane, etc. are used. The number of carbon atoms of the alkyl group is not particularly limited, but is preferably C2 - C18. If it is less than C2, there is a risk of volatilization of the alkoxysilane during the surface treatment. On the other hand, if it exceeds C16, strong aggregation may occur due to the influence of its high viscosity, and the dispersibility of the obtained powder may be impaired.

[0043] In particular, as the silicone oil, in addition to polydimethylsiloxane, modified silicone oils introduced with, for example, an alkyl group, -OH group, etc. can also be used.

[0044] The viscosity range (measurement temperature 25°C) of these organosilicon compounds is not particularly limited, but is usually preferably 20 - 300 cs. When the viscosity is less than 20 cs, volatilization of low molecular weight polysiloxane, etc. occurs during the surface treatment, which is not preferable from the viewpoints of energy efficiency and environmental aspects. On the other hand, when the viscosity exceeds 300 cs, higher aggregation may occur, and the dispersibility of the obtained powder may be impaired.

[0045] The content of the organosilicon compound having no amino group in the powder of the present invention is not particularly limited as long as it is within the range of the above carbon content, but generally it is about 5 to 20 parts by weight, particularly preferably 10 to 15 parts by weight, based on 100 parts by weight of the inorganic oxide powder.

[0046] In the following, unless otherwise specified, when simply referring to an "organosilicon compound", it refers to two meanings: (a) the meaning of "an organosilicon compound having an amino group alone", and (b) the meaning of "both an organosilicon compound having an amino group and an organosilicon compound having no amino group".

[0047] <Properties of the powder of the present invention> The powder of the present invention has the following properties: (1) Tapped density: 40 to 150 g / L, (2) Moisture adsorption amount at a relative water vapor 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) Loss on drying: 0.1 to 3.0% and (6) Amount of triboelectric charge: +10 to +450 μC / g All satisfy.

[0048] Tapped density The tapped density of the precipitated silica surface-modified with an organosilicon compound is 40 to 150 g / L. When the tapped density is less than 40 g / L, when the powder is dispersed on the toner surface, it cannot be dispersed with an appropriate aggregate particle size and cannot exhibit a sufficient spacer effect. Also, when the tapped density exceeds 150 g / L, a large amount of equipment volume is required during mixing with the toner, and there are problems in industrial use.

[0049] 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. The moisture adsorption amount greatly affects the charging characteristics, and appropriate charging properties can be imparted by setting it within the above range. If the moisture adsorption amount is less than 3% by weight, the positive charging property becomes too strong. On the other hand, if the moisture adsorption amount exceeds 6% by weight, sufficient charging characteristics cannot be exhibited.

[0050] BET specific surface area The BET specific surface area of the precipitated silica surface-modified with an organosilicon compound is usually 50 to 200 m 2 / g. When the BET specific surface area is less than 50 m 2 / g, the aggregate particle size is too large, resulting in insufficient dispersibility when dispersed in the toner. When the BET specific surface area exceeds 200 m 2 / g, when dispersed in the toner, the appropriate aggregate diameter cannot be maintained, and a sufficient spacer effect cannot be exhibited.

[0051] Carbon content The carbon content of the precipitated silica surface-modified with an organosilicon compound is usually 1.0 to 8.0% by weight. In particular, when the surface treatment agent (hydrophobizing agent) is HMDS, it is preferably about 1.0 to 3.0% by weight, when it is PDMS or OH-PDMS, it is preferably about 1.0 to 8.0% by weight, and when it is an alkylalkoxysilane, it is preferably about 1.0 to 8.0% by weight. The carbon content is an index indicating the degree (fixed amount) of immobilization of the organosilicon compound as the surface treatment agent on the precipitated silica powder. If the carbon content is too low, sufficient surface modification is not performed, and the charging characteristics, dispersibility, etc. become insufficient. On the other hand, if the carbon content is too high, the content of organic substances is too high, particle aggregation occurs, sufficient fluidity and dispersibility cannot be obtained, and a sufficient spacer effect cannot be exhibited even when this powder is applied to the toner.

[0052] Loss on drying The loss on drying is usually 0.1 to 3.0%. Since the loss on drying greatly affects the charging characteristics, appropriate charging properties can be imparted by setting it within the above range. When the loss on drying exceeds 3% by weight, the amount of moisture held and adsorbed is close to that of silica by the sol-gel method, so sufficient charging characteristics cannot be exhibited.

[0053] Chargeability The triboelectric charge amount of the precipitated silica surface-modified with an organosilicon compound is usually +10 to +450 μC / g. When the triboelectric charge amount approaches the zero side from +10 μC / g, it becomes difficult to exhibit strong charging characteristics in the toner when the powder is added to the toner, similar to negative charging, and it becomes difficult to control the toner within a predetermined charge amount range. On the other hand, when the triboelectric charge amount becomes more positive than +450 μC / g, it becomes difficult to control the charging characteristics of the toner to which it is added due to its strong triboelectric charge amount.

[0054] Particle size The average particle size of the powder of the present invention is not particularly limited, but in terms of effectively exerting the function as a spacer, the particle size distribution measured by a particle size distribution measuring device is about 0.1 to 1 μm, preferably 0.2 to 0.8 μm. The average particle size in the present invention refers to the value (arithmetic mean diameter (volume standard)) calculated by a particle size distribution measuring device (laser diffraction / scattering type particle size distribution measuring device manufactured by Horiba, Ltd.).

[0055] Flowability In the powder of the present invention, there is a ratio based on the energy value by a powder rheometer as an index of the performance capable of imparting flowability to a toner or the like. That is, it is the value obtained by dividing the energy value of the flowability by the dry flowability evaluation method when the powder of the present invention is added to the toner by the energy value before addition, and it is desirable that this value is 0.35 or less in the present invention. By setting the above value to 0.35 or less, the toner product to which the powder of the present invention is externally added can give even higher flowability.

[0056] 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 configuration and characteristics can be obtained. For example, it can be preferably produced by a method including (a) a step of preparing a mixture containing precipitated silica powder and an organosilicon compound having an amino group (mixture preparation step), and (b) a step of heat-treating the mixture at a temperature of 120 to 360°C (heat treatment step).

[0057] Mixture preparation step In the mixture preparation step, there is no limitation as long as the surface of each particle constituting the precipitated silica powder can be coated with a coating layer containing an organosilicon compound. For example, a method of mixing the precipitated silica powder and the vaporized organosilicon compound under stirring, a method of spraying the organosilicon compound onto the precipitated silica powder under stirring, etc. can be preferably adopted.

[0058] In this case, the organosilicon compound can also be used in a state of 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, etc.

[0059] Further, in the present invention, water, a catalyst (such as an amine), etc. can be appropriately blended into the mixture as necessary.

[0060] The temperature conditions in the mixture preparation step are not particularly limited. For example, it may be within the range of 10 to 40°C, but it is not limited thereto. Also, the atmosphere is usually preferably carried out in an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be preferably used.

[0061] Regarding the type, usage amount, etc. of the organosilicon compound, etc., those similar to those described in the above "1. Surface-modified precipitated silica powder" can be adopted.

[0062] Heat treatment step Although the heat treatment temperature in the heat treatment step is not limited, it is usually preferably 120 to 360 °C (particularly 150 to 300 °C). When the heat treatment temperature exceeds 360 °C, partial decomposition of the organosilicon compound may occur. Also, when it is less than 120 °C, sufficient surface modification of the organosilicon compound is not performed, and the desired chargeability cannot be obtained.

[0063] The heat treatment atmosphere is preferably usually carried out in an inert gas atmosphere, similar to the above step. For example, nitrogen gas, helium gas, argon gas, etc. can be suitably used. In particular, the above step can be carried out in a sealed reactor, and the heat treatment step can be suitably carried out while maintaining the atmosphere as it is continuously.

[0064] The heat treatment time may be a time sufficient for the organosilicon compound to be immobilized (fixed) on the surface of each particle constituting the precipitated silica powder. For example, it can be about 10 to 200 minutes, but is not limited thereto.

[0065] 3. Use of the powder of the present invention Since the powder of the present invention has all of the characteristics (1) to (6) shown in the above "1. Surface-modified precipitated silica powder", in addition to the excellent characteristics of the precipitated silica powder, it can exhibit both a good spacer effect and appropriate charge characteristics. Therefore, the powder of the present invention can be suitably used, for example, as an additive (particularly an external additive for toner) for toner, powder paint, etc. Therefore, the present invention also includes an electrophotographic toner composition or a powder coating composition (hereinafter, both are also collectively referred to as "the composition of the present invention") containing the powder of the present invention and binder resin particles.

[0066] The composition of the present invention contains the above-described surface-modified precipitated silica powder of the present invention, and there are no particular restrictions on its composition, production method, etc., and known compositions and methods can also be adopted.

[0067] 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 can be obtained, but it is usually preferably contained in an amount of about 0.1 to 5.0% by weight. If the content of the surface-modified precipitated silica powder of the present invention in the composition of the present invention is less than 0.1% by weight, the effect of improving fluidity or the effect of stabilizing chargeability by adding the surface-modified precipitated silica powder may not be sufficiently obtained. On the other hand, if the content of the surface-modified precipitated silica powder exceeds 5.0% by weight, the number of substances that act independently of the surface-modified precipitated silica powder increases, and problems may occur, for example, in images, cleaning properties, etc.

[0068] In the composition of the present invention, in addition to the binder resin particles, if necessary, for example, pigments, charge control agents (electrostatic charge control agents), waxes, etc. may be included. These components can be the same as those in known or commercially available toner compositions. Also, the type of toner is preferably a positively chargeable toner, but is not particularly limited in other respects. Therefore, for example, either a magnetic or non-magnetic one-component toner or a two-component toner may be used. Furthermore, it can be either monochrome or color.

[0069] In particular, since the powder of the present invention has an excellent spacer effect, it can be more preferably used as an external additive for binder resin particles containing a resin component that is easily softened (for example, at least one of a styrene-acrylic copolymer resin, a polyester resin, an epoxy resin, etc.).

[0070] Note that 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 it may be used in combination with other metal oxide fine powders according to the purpose. For example, the surface-modified precipitated silica 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 necessary.

[0071] Furthermore, the precipitated silica powder surface-modified with the organosilicon compound in the present invention exists on the toner surface as submicron-sized aggregates, and due to the numerous irregularities on its surface, it has the effectiveness of being less likely to detach from the toner surface compared to sol-gel silica.

Examples

[0072] 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.

[0073] Note that the components used in each example and comparative example are as follows. (A) Silica raw material (A1) Precipitated silica Samples A to E: Precipitated silica prepared according to the production method described in Patent Document 2 (A2) Sol-gel silica Sample manufactured by a known sol-gel method (A3) Fumed silica Commercially available product a: Product name "AEROSIL OX50" (registered trademark, manufactured by Nippon Aerosil Co., Ltd.) Commercially available 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) OH-PDMS: Silicone oil having hydroxyl groups at both ends of polydimethylsiloxane (product name "PMX-0930", manufactured by Toray Dow Corning Co., Ltd.) (B4) Aminosilane (product name "KBE-903" (registered trademark), manufactured by Shin-Etsu Chemical Co., Ltd.) (the component described as "positive charge imparting agent" in Table 1) (B5) Amino-modified silicone oil (product name "X22-161A" (registered trademark), manufactured by Shin-Etsu Chemical Co., Ltd.) (the component described as "positive charge imparting agent" in Table 1)

[0074] [Example 1] Sample A as precipitated silica powder (median diameter d 50 = 155 nm, d 90 = 540 nm, silanol group density: 3.5 OH / nm 2 )(100 parts by weight) was placed in a reactor, and a mixed solution of OH-PDMS (10 parts by weight) and KBE903 (3 parts by weight) as a surface treatment agent was added under stirring in a nitrogen atmosphere, and heat treatment was carried out at 300 °C for 20 minutes while continuing stirring. In this way, surface-modified silica powder was obtained.

[0075] [Examples 2 to 6] Surface-modified silica powder was obtained in the same manner as in Example 1, except that the conditions shown in Table 1 were changed.

[0076] [Comparative Examples 1 to 6] Surface-modified silica powder was obtained in the same manner as in Example 1, except that the conditions shown in Table 1 were changed.

[0077] [Test Example 1] For the surface-modified silica powder obtained in each example and comparative example, the following physical properties were measured. The results are also shown in Table 1.

[0078] (1) Bulk density Place a graduated cylinder on an upper-pan balance, tare it, put the sample in the graduated cylinder, weigh the mass (mass A), and read the volume (volume B) after standing for 2 minutes. Calculate the bulk density using the following formula. Bulk density (g / L) = (mass A / volume B) × 1000

[0079] (2) Measurement of water adsorption amount The surface-modified silica powder is heated at 150 °C under vacuum for 2 hours or more to be sufficiently dried, and then measured with a high-precision gas adsorption measurement device (product name "BELSORP-max", manufactured by MicrotracBEL Corp.) under the conditions of an evacuation time of 15 minutes and a pressure increase allowable amount of 5.000E-1 Pa / min. Analyze the adsorption isotherm, and the value in the range of a water vapor relative pressure of 0.8 to 0.95 is taken as the water adsorption amount.

[0080] (3) BET specific surface area BET {specific surface area (m 2 / g)} was determined by using a fully automatic specific surface area measuring device (product name: "Macsorb", manufactured by Mountech). After pretreating the sample at 100 °C for 10 minutes, the surface area of the sample was determined from the amount of nitrogen adsorbed and desorbed by the BET one-point method, and then divided by its weight to obtain the specific surface area.

[0081] (4) Carbon content The carbon content was measured using a carbon analyzer (product name: "SUMIGRAPH NC-22", manufactured by Sumika Chemical Analysis Service, Ltd.).

[0082] (5) Loss on drying After sampling about 1 g of the surface-modified silica powder into a weighing bottle, it was dried at 105 °C for 2 hours and the weight was measured. The percentage (%) of the weight reduction amount before and after drying was calculated and taken as the adsorbed moisture content.

[0083] (6) Amount of triboelectric charge A sample containing 0.2 parts by weight of the surface-modified silica powder with respect to 100 parts by weight of the carrier (reduced iron powder) was mixed in a Turbula mixer for a certain period of time to cause triboelectric charging, and then the amount of charge was measured with a blow-off powder electrification measuring device under the conditions of a temperature of 20 °C and a humidity of 45% RH.

[0084] (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 (binder resin), average particle size 6 μm). Then, a ventilation test of the toner sample was performed on the obtained mixed powder with a powder rheometer. The total energy value was measured 13 times for each sample. For the first time, there was no ventilation, and for the second time and later, the measurement was performed while ventilating at a linear velocity of 0.04 mm / s. Then, the total energy value E1 (mJ) at the 13th time was measured. The total energy value E0 of the toner alone was measured in the same manner as above except that the surface-modified silica powder was not externally added. Next, based on the values E1 and E0 obtained above, [E1 / E0] was determined. The smaller the value of [E1 / E0], the higher the performance of imparting high fluidity is indicated.

[0085] [Test Example 2] The surface-modified silica powder obtained in each example and comparative example and the polyester toner mother body (binding resin) powder produced by the polymerization method were mixed at a weight ratio of [binding resin powder: surface-modified silica powder = 99:1], and after preliminary mixing with a Henschel mixer at 600 rpm for 1 minute, they were 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 with a particle size of 0.1 μm or more adhering per 1 μm 2 on the surface of the toner sample particles was measured. The results are also shown in Table 1. For the measurement, one toner mother body (toner particle) was arbitrarily selected within the field of view of the SEM, and as shown in Fig. 1, after setting so that the inside of the field of view S was filled with the surface of 10 toner particles and as many surface-modified silica particles 11 as possible were included, the total number of surface-modified silica particles 11 within the field of view S was measured, and then the number was divided by the field of view area to calculate the number of surface-modified silica particles per unit area (per 1 μm 2 per). In this case, surface-modified silica particles that protrude even slightly from the field of view S shall not be counted. The larger the number of surface-modified silica particles per unit area, the more uniformly the surface-modified silica powder is dispersed.

[0086]

Table 1

[0087] As is clear from the results in Table 1, it can be seen that the surface-modified silica powder of the examples satisfies all the characteristics defined in the present invention.

Claims

1. a) In the particle size distribution based on volume, d50: 150 to 1000 nm and d90: 500 to 7000 nm, and b) the silanol group density is 2.5 to 8 OH / nm ２ A powder comprising particles having a coating layer containing an organosilicon compound having an amino group formed on the surface of precipitated silica particles which are as described above (1) Bulk density: 40 to 150 g / L, (2) Moisture adsorption amount at a relative water vapor pressure of 0.8 to 0.95: 3 to 6% (3) BET specific surface area: 50 to 200 m ２ / g, (4) Carbon content: 2.4 to 8.0% by weight, (5) Loss on drying: 0.1 to 3.0% and (6) Triboelectric charge amount: +10 to +450 μC / g A surface-modified precipitated silica powder, characterized by the above.

2. The surface-treated precipitated silica powder according to Claim 1, wherein the value obtained by dividing the energy value of fluidity by the dry fluidity evaluation method when added to toner by the energy value before addition is 0.35 or less.

3. The surface-modified precipitated silica powder according to Claim 1, wherein the organosilicon compound having an amino group is at least one of aminosilane and amino group-modified silicone oil.

4. An external additive for toner or powder coating containing the surface-modified precipitated silica powder according to any one of Claims 1 to 3.

5. An electrophotographic toner composition or powder coating composition containing the external additive according to Claim 4 and binder resin particles.

6. A method for producing the surface-modified precipitated silica powder according to any one of Claims 1 to 3, (a) a) In the particle size distribution based on volume, d50: 150 to 1000 nm and d90: 500 to 7000 nm, and b) A step of preparing a mixture containing a precipitated silica powder having a silanol group density of 2.5 to 8 OH / nm2 and an organosilicon compound having an amino group, (b) A step of heat-treating the mixture at a temperature of 120 to 360°C A method for producing a surface-modified precipitated silica powder, characterized by including the above.

7. The production method according to Claim 6, wherein the steps (a) and (b) are carried out under stirring.

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