Surface-modified silica powder using precipitated silicic acid 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 on the surface of a precipitated silicic acid particle having (a) a d50 of 150-1000 nm and a d90 of 500-7000 nm in a volumetric basis particle distribution, and (b) a silanol group density of 2.5-8 OH / nm2, where (1) the bulk density is 40-150 g / L, (2) the moisture absorption amount is 3-6% at a water vapor relative pressure of 0.8-0.95, (3) the BET specific surface area is 50-200 m2 / g, (4) the carbon content is 1.0-8.0 wt.%, (5) the drying loss is 0.1-3.0%, and (6) the frictional electrification amount is -50 to -200 μC / g.SELECTED DRAWING: None

Description

Technical Field

[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 surface of inorganic oxide powders such as fine silica, titania, alumina, etc. with an organic substance, the chargeability, hydrophobicity, etc. of the powder surface can be modified. The surface-modified inorganic oxide powder thus obtained is widely used, for example, as a fluidity improver, chargeability adjuster, etc. for toner used in electrophotography including copiers, laser printers, plain paper facsimiles, etc. The surface-modified inorganic oxide powder used for such toner applications is known as a so-called external additive.

[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 is charged (i.e., electrified) by friction with a carrier or the like. And its highly controlled chargeability can exhibit a developing function. However, when the toner is continuously 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 external additive as described above is increasing more and more.

[0005] In particular, in recent years, due to the improvement of image quality in electrophotography, the toner particle size has been reduced, and in addition, due to high speed and colorization, the mechanical load on the toner has become greater. 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 mainstream to adopt components that have been softened and have a lower melting point as the toner matrix resin.

[0006] With the reduction of the melting point of such toner resins, etc., the phenomenon that the surface-treated fumed oxide is embedded in the toner resin during long-term operation and its fluidity decreases has occurred. 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 fumed oxide from being embedded inside 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 of 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 holds 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 other hand, it is also called the dry method or the vapor phase method (hereinafter, both are collectively referred to as the "fumed method"). Since the silica powder produced by the dry method or the vapor phase method has a particle shape that deviates from a spherical shape more than the silica produced by the sol-gel method, an effect of suppressing the 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 diameter and are dispersed as particles with a size of submicron or less on the toner surface. Therefore, the spacer effect cannot be sufficiently exhibited, and generally, the charging characteristics are too high, and the addition amount and dispersibility thereof must be precisely controlled in order 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 charge. If precipitated silica can also 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 making use of the original characteristics of precipitated silica while taking advantage 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 thus 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 coating layer containing an organosilicon compound is formed on the surface of precipitated silica particles having a silanol group density of 2.5 to 8 OH / nm 2 . The powder is 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 8.0% by weight, (5) Loss on drying: 0.1 to 3.0% and (6) Triboelectric charge amount: -50 to -200 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 0.31 or less. 3. The surface-modified precipitated silica powder according to item 1 above, wherein the organosilicon compound is at least one of hexamethyldisilazane, polydimethylsiloxane, and alkylsilane. 4. An external additive for toner or powder coating containing the surface-modified precipitated silica powder according to any one of the above items 1 to 3. 5. An electrophotographic toner composition or powder coating composition containing the external additive according to item 4 and binder resin particles. 6. A method for producing surface-modified precipitated silica powder, (a) A step of preparing a mixture containing precipitated silica powder and an organosilicon compound, (b) A step of heat-treating the mixture at a temperature of 120 to 360°C A method for producing surface-modified precipitated silica powder, characterized by including the above steps. 7. The production method according to item 6, 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, it is possible to provide a powder suitable for toner, etc., while making use of the original properties of precipitated silica. In particular, the present invention can provide a surface-modified precipitated silica powder having good dispersibility, appropriate charging properties, and a high spacer effect.

[0017] The surface-modified precipitated silica powder of the present invention is obtained by surface-modifying precipitated silica powder having a median diameter and 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 properties.

[0018] More specifically, the surface-modified precipitated silica powder of the present invention is obtained by surface-modifying precipitated silica powder with a predetermined organosilicon compound, resulting in the control of various properties such as bulk density, hydrophobicity, moisture adsorption amount, surface area, and carbon content within a certain range. As a result, it exhibits higher charging properties 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 silicon 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, by selectively using specific precipitated silica powder and modifying its surface, while taking advantage of 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 achieve with sol-gel silica, and a high spacer effect, which is difficult to achieve 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 such surface-modified precipitated silica powder having high fixing rate, high hydrophobicity, etc., so it is also excellent in dispersibility, fluidity, antistatic property, etc., fogging or cleaning defects are suppressed, and furthermore, it is difficult for toner etc. to adhere to the photoreceptor, and it is possible to obtain the effect that image defects are less likely to occur. Also, according to these compositions of the present invention, effects such as long-term storage stability and control of developer deterioration behavior can also 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 is formed on the surface of precipitated silica particles having a silanol group density of 2.5 to 8 OH / nm 2 , and the powder is 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 8.0 wt%, and (5) Loss on drying: 0.1 to 3.0% (6) Triboelectric charge amount: -50 to -200 μC / g It is characterized by being as follows.

[0023] <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 surface of the particles. That is, the basic structure is composed of precipitated silica particles as core particles (matrix) and a coating layer containing an organosilicon compound 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, which is characterized by being as follows.

[0026] When the above d 50 is less than 150 nm, the aggregated particle diameter of the powder after surface treatment with an 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 d 90It 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. Thereby, since the distribution of the surface pores is in an appropriate range, it becomes possible to control the moisture adsorption amount within an appropriate range. As a result, appropriate chargeability can be exhibited after modifying with the organosilicon compound.

[0031] As 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 having 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, which comprises pulverizing and simultaneously classifying the precipitated silica to obtain the pulverized silica. In the method for producing precipitated silica in which the pulverization and the simultaneous classification are carried out using one pulverizing device, the mill of the pulverizing device is operated in one pulverizing phase using a working medium selected from the group consisting of gas, steam, water vapor, gas containing water vapor, and mixtures thereof; and the pulverizing chamber is heated in a heating stage, i.e., before the specific operation using the working medium, so that the temperature in the pulverizing 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.

[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. In the coating layer, the content of the organosilicon compound is not particularly limited, but can usually be appropriately set to about 5 to 100% by weight. Therefore, for example, it can be 80 to 99% by weight, or for example, 90 to 100% by weight.

[0034] The organosilicon compound is not particularly limited, and for example, known or commercially available ones known as hydrophobizing agents can also be used.

[0035] 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.

[0036] Among these, in terms of more surely obtaining the effects of the present invention, it is preferable to use at least one of alkylsilazane compounds, alkoxysilane compounds, and silicone oils.

[0037] In particular, the alkoxysilane is not particularly limited as long as it is an alkoxysilane substituted with an alkyl group, but 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. Also, 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.

[0038] In particular, as the silicone oil, in addition to polydimethylsiloxane, modified silicone oils into which, for example, an alkyl group, -OH group, etc. are introduced can also be used.

[0039] 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.

[0040] The content of the organosilicon compound in the powder of the present invention is not particularly limited as long as it is within the range of the above carbon content. Generally, it is about 5 to 30 parts by weight, particularly preferably 10 to 20 parts by weight, based on 100 parts by weight of the precipitated silica particles.

[0041] <Properties of the powder of the present invention> The powder of the present invention has the following properties: (1) Bulk density: 40 - 150 g / L, (2) Moisture adsorption amount at a relative water vapor pressure of 0.8 - 0.95: 3 - 6%, (3) BET specific surface area: 50 - 200 m 2 / g, (4) Carbon content: 1.0 - 8.0 wt%, (5) Loss on drying: 0.1 - 3.0% and (6) Triboelectric charge amount: -50 - -200 μC / g satisfies all of them.

[0042] Bulk density The bulk density of the precipitated silica surface - modified with an organosilicon compound is usually 40 - 150 g / L. When the bulk 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 bulk density exceeds 150 g / L, a large amount of equipment volume is required during mixing with the toner, which causes problems in industrial use.

[0043] Moisture adsorption amount The moisture adsorption amount at a relative water vapor pressure of 0.8 - 0.95 is usually 3 - 6 wt%. The moisture adsorption amount greatly affects the charging characteristics. By setting it within the above range, appropriate charging properties can be imparted. When the moisture adsorption amount is less than 3 wt%, the strong negative charging becomes too strong. Also, when the moisture adsorption amount exceeds 6 wt%, sufficient charging characteristics cannot be exhibited.

[0044] BET specific surface area The BET specific surface area of the precipitated silica surface - modified with an organosilicon compound is usually 50 - 200 m 2 / g. When the BET specific surface area is less than 50 m2 If it is less than / g, since the aggregated particle diameter is too large, the dispersibility when dispersed in the toner becomes insufficient. When the BET specific surface area exceeds 200 m 2 If it exceeds / g, when dispersed in the toner, the appropriate aggregation diameter cannot be maintained and a sufficient spacer effect cannot be exhibited.

[0045] 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, 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 serves as 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 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 even when this powder is applied to the toner, a sufficient spacer effect cannot be exhibited.

[0046] Loss on drying The loss on drying is usually 0.1 to 3.0%. The loss on drying greatly affects the charging characteristics, and by setting it within the above range, an appropriate chargeability can be imparted. If the loss on drying exceeds 3% by weight, the amount of water held and adsorbed is close to that of silica by the sol-gel method, and sufficient charging characteristics cannot be exhibited.

[0047] Chargeability The triboelectric charge amount of the precipitated silica surface-modified with an organosilicon compound is usually -50 to -200 μC / g. When the triboelectric charge amount approaches the zero side from -50 μC / g, it becomes difficult to exhibit strong charging characteristics in the toner when adding the powder to the toner in the same way as 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 negative than -200 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.

[0048] Particle size The average particle size of the powder of the present invention is not particularly limited. However, from the viewpoint 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 particle size distribution measuring device manufactured by Horiba, Ltd.).

[0049] Flowability In the powder of the present invention, as an index of the performance capable of imparting flowability to toner or the like, there is a ratio based on the energy value measured by a powder rheometer. That is, it is the value obtained by dividing the energy value of flowability by the dry flowability evaluation method when the powder of the present invention is added to toner by the energy value before addition, and it is desirable that this value be 0.31 or less in the present invention. By setting the above value to 0.31 or less, the toner product externally added with the powder of the present invention can give even higher flowability.

[0050] 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 (mixture preparation step) and (b) a step of heat-treating the mixture at a temperature of 120 to 360°C (heat treatment step).

[0051] Mixture preparation step In the mixture preparation step, it is not limited as long as the surface of each particle constituting the precipitated silica powder can be coated with 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 employed.

[0052] 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 and the like.

[0053] In the present invention, water, a catalyst (such as an amine), etc. can also be appropriately blended into the mixture as necessary.

[0054] The temperature conditions in the mixture preparation step are not particularly limited, and for example, it may be within the range of 10 to 40 °C, but it is not limited to this. Also, the atmosphere is preferably usually carried out in an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be preferably used.

[0055] Regarding the type, usage amount, etc. of the organosilicon compound, those similar to those described in the above "1. Surface-modified precipitated silica powder" can be adopted.

[0056] Heat treatment step The heat treatment temperature in the heat treatment step is not limited, but usually it is 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.

[0057] The heat treatment atmosphere is preferably usually carried out in an inert gas atmosphere as in the above step. For example, nitrogen gas, helium gas, argon gas, etc. can be preferably used. In particular, the above step can be carried out in a sealed reactor, and the heat treatment step can be preferably carried out while continuously maintaining that atmosphere as it is.

[0058] The heat treatment time may be a time sufficient for the organosilane compound to be immobilized (fixed) on the surface of each particle constituting the precipitated silica powder, and for example, it can be about 10 to 200 minutes, but it is not limited to this.

[0059] 3. Use of the powder of the present invention Since the powder of the present invention has all 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 charging characteristics. Therefore, the powder of the present invention can be suitably used as an additive (especially an external additive for toner), such as toner, powder paint, etc. Accordingly, 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.

[0060] The composition of the present invention contains the surface-modified precipitated silica powder of the present invention as described above, and there are no particular restrictions on its composition, manufacturing method, etc., and known compositions and methods can also be adopted.

[0061] 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 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.

[0062] 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 negatively charged toner, and there are no particular limitations on other points. 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.

[0063] Since the powder of the present invention is particularly excellent in the spacer effect, it can be more preferably used as an external additive for binder resin particles containing a resin component that is easy to soften (for example, at least one of styrene-acrylic copolymer resin, polyester resin, epoxy resin, etc.).

[0064] In addition, in the electrophotographic toner composition of the present invention, the powder of the present invention as an external additive is not limited to being used alone, and may be used in combination with other metal oxide fine 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 needed.

[0065] Furthermore, the precipitated silica powder surface-modified with an 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

[0066] 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.

[0067] The components used in each example and comparative example are as follows. (A) Regarding precipitated silica powder (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 produced 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) Commercial product C4: Alkylsilane-based surface treatment agent (product name "IBTMO" (registered trademark), manufactured by Evonik) (B4) Commercial product C10: Alkylsilane-based surface treatment agent (product name "KBM-3103C" (registered trademark), manufactured by Shin-Etsu Chemical Co., Ltd.)

[0068] [Example 1] Sample A (median diameter d 50 = 155 nm, d 90 = 540 nm) (100 parts by weight) of precipitated silica powder was placed in a reactor, and under stirring in a nitrogen atmosphere, HMDS (20 parts by weight) was added as a surface treatment agent, and heat treatment was carried out at 200 °C for 60 minutes while continuing stirring. In this way, surface-modified silica powder was obtained.

[0069] [Examples 2 to 10] Surface-modified silica powder was obtained in the same manner as in Example 1, except that the conditions shown in Table 1 were changed.

[0070] [Comparative Examples 1 to 8] Surface-modified silica powder was obtained in the same manner as in Example 1, except that the conditions shown in Table 2 were changed.

[0071] [Test Example 1] For the surface-modified silica powders obtained in each Example and Comparative Example, the following physical properties were measured. The results are shown together in Tables 1 to 2.

[0072] (1) Bulk density Place a graduated cylinder on an upper pan balance, zero the tare weight, put the sample in the graduated cylinder, measure 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

[0073] (2) Measurement of water adsorption capacity The surface-modified silica powder is heated at 150 °C under vacuum for 2 hours or more and dried sufficiently. Then, it is measured using a high-precision gas adsorption capacity 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 capacity of 5.000E-1 Pa / min. The adsorption isotherm is analyzed, and the value within the range of a water vapor relative pressure of 0.8 to 0.95 is taken as the water adsorption capacity.

[0074] (3) BET specific surface area BET {specific surface area (m 2 / g)} is determined by using a fully automatic specific surface area measurement device (product name: "Macsorb", manufactured by Mountech). After pretreating the sample at 100 °C for 10 minutes, the surface area of the sample is obtained 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.

[0075] (4) Carbon content The carbon content is measured using a carbon analyzer (product name: "SUMIGRAPH NC-22", manufactured by Sumika Chemical Analysis Service, Ltd.).

[0076] (5) Loss on drying After sampling about 1 g of the surface-modified silica powder into a weighing bottle, it is dried at 105 °C for 2 hours and the weight is measured. The ratio (%) of the weight loss before and after drying is calculated and taken as the adsorbed moisture content.

[0077] (6) Amount of triboelectrification 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) is mixed in a Turbula mixer for a certain period of time to cause triboelectrification, and then the amount of electrification is measured using a blow-off powder electrification measurement device under the conditions of a temperature of 20 °C and a humidity of 45%RH.

[0078] (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, an air permeability test of the toner sample was performed on the obtained mixed powder using a powder rheometer. The total energy value was measured 13 times for each sample. The first measurement was taken without air permeability, and the subsequent measurements were taken while allowing air to permeate at a linear velocity of 0.04 mm / s. Then, the total energy value E1 (mJ) of the 13th measurement 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. A smaller value of [E1 / E0] indicates a performance capable of imparting higher fluidity.

[0079] [Test Example 2] The surface-modified silica powder obtained in each example and comparative example and the polyester toner base (binder resin) powder produced by the polymerization method were mixed at a weight ratio of [binder resin powder: surface-modified silica powder = 99:1]. After preliminary mixing at 600 rpm for 1 minute using a Henschel-type mixer, the mixture was further 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 to the surface of the toner sample particles per 1 μm 2 was measured. The results are also shown in Tables 1 to 2. The measurement was carried out by arbitrarily selecting one toner base (toner particle) within the field of view of the SEM. As shown in Figure 1, after setting the inside of the field of view S to be filled with the surface of 10 toner particles and containing as many surface-modified silica particles 11 as possible, the total number of surface-modified silica particles 11 within the field of view S was measured. Then, the number was divided by the field of view area to obtain the number per unit area (1 μm 2The number of surface-modified silica particles per hit) was calculated. In this case, surface-modified silica particles that protrude even slightly from the visual field 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.

[0080] [Table 1]

[0081] [Table 2]

[0082] As is clear from the results in Tables 1 to 2, 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 is from 150 to 1000 nm and d90 is from 500 to 7000 nm, and (b) the surface density of silanol groups is 2.5 to 8 OH / nm ２ A powder comprising particles having a coating layer containing an organosilicon compound formed on the surface of precipitated silica particles, (1) Bulk density: 40 to 150 g / L, (2) Moisture adsorption amount at a water vapor relative pressure of 0.8 to 0.95: 3 to 6% (3) BET specific surface area: 50 to 200 m ２ / g, (4) Carbon content: 1.0 to 8.0% by weight, (5) Loss on drying: 0.1 to 3.0% and (6) Triboelectric charge amount: -50 to -200 μC / g A surface-modified precipitated silica powder used as an external additive for toner, 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 the toner by the energy value before addition is 0.31 or less.

3. The surface-modified precipitated silica powder according to Claim 1, wherein the organosilicon compound is at least one of hexamethyldisilazane, polydimethylsiloxane, and alkylsilane.

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

5. An electrophotographic toner 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 / nm 2 and an organosilicon compound, (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 of (a) and (b) above are carried out under stirring.

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