JP7708604B2 - Surface-modified silica powder using precipitated silicic acid and its manufacturing method - Google Patents

Description

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

By treating the surface of fine inorganic oxide powders such as silica, titania, and alumina with an organic substance, it is possible to modify the electrostatic chargeability, hydrophobicity, and other properties of the powder surface. The surface-modified inorganic oxide powders thus obtained are widely used as flowability improvers and electrostatic charge adjusters for toners used in electrophotography, including copying machines, laser printers, and plain paper facsimiles. Such surface-modified inorganic oxide powders used for toner applications are known as so-called external additives.

Surface treatment agents for inorganic oxide powders used in toner applications include organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil. Surface treatment with these organosilicon compounds can, for example, replace the silanol groups on the surface of silica fine particles with organic groups to provide a hydrophobic treatment. As part of these surface-treated inorganic oxide powders, fumed oxides are widely used as materials that impart high fluidity to toner materials.

The toner is stirred in a copying machine or other device, and is charged (i.e., electrified) by friction with the carrier, etc. Then, the toner can exhibit its developing function due to its highly controlled electrification. However, if the toner is continuously stirred in the device for a long time, the strong frictional force becomes stressful, and the toner deteriorates. For example, if an external additive is embedded in the toner surface, it loses its function as a contact point between the toner surface and the external environment. Moreover, the mechanical burden on the toner has increased in recent years, and the hardness of the toner matrix has decreased due to the softening design of the binding resin (toner matrix resin) that constitutes the toner, making it easier for the external additive to be embedded. For this reason, the importance of measures to prevent the embedding of external additives as described above is increasing.

In particular, in recent years, the improvement in image quality of electrophotography has led to the reduction in the particle size of toner particles, and in addition, the increase in speed and color printing has placed a greater mechanical load on the toner. As a result, the durability of toner performance over time (control of deterioration behavior) is becoming increasingly important, but at the same time, the binding resin used in toner is required to have low-temperature fixability in order to reduce printing standby time and save energy. For these reasons, it is becoming mainstream to use softened and low-melting point components as the toner base resin.

As the melting point of toner resins becomes lower, the surface-treated fumed oxides become embedded in the toner resin during long-term operation, reducing its fluidity. To improve the durability of the toner, submicron-sized silica powder is added to the toner surface together with the fumed oxides, and the submicron-sized silica powder exerts a spacer effect to prevent the fumed oxides from becoming embedded in the toner. As the submicron-sized silica, silica powder produced by the sol-gel method is mainly used (see Patent Document 1, etc.).

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

Furthermore, the silica powder produced by the sol-gel method has a nearly spherical particle shape, which means that it tends to separate from the toner surface over long periods of use.

Furthermore, silica powder produced by the sol-gel method tends to retain or adsorb a large amount of moisture, making it impossible to obtain strong triboelectric charging properties. For this reason, in order to produce materials that adjust the charge, such as toner, the low charging properties must be improved.

On the other hand, silica powder produced by the dry method or gas phase method (hereinafter, both are collectively referred to as the "fumed method") has a particle shape that is less spherical than silica produced by the sol-gel method, so it is expected to suppress the problem of sol-gel silica being released from the toner surface. However, silica powder produced by the fumed method generally has a small primary particle size and is dispersed on the toner surface as particles of submicron size or less, so it cannot fully exert the spacer effect, and in addition, its charging characteristics are generally too high, so the amount added and dispersibility must be precisely controlled to control the charging characteristics of the toner within an appropriate range.

In contrast to the above-mentioned silica, precipitated silica produced by a wet method is known (for example, Patent Document 2). Precipitated silica is suitable for mass production and has many pores in its particle structure, so it is widely used as an adsorbent. However, precipitated silica has problems such as strong interparticle aggregation, making it difficult to apply uniformly to the toner surface (external addition), and not being able to express a sufficient charge. If precipitated silica could be used for toner (especially as a toner external additive), it may be possible to impart new functions by utilizing its pore characteristics, but toner materials using precipitated silica have not yet been developed.

JP 2013-249215 A Patent No. 5295261

Therefore, the main object of the present invention is to provide a powder suitable for use in toners, etc., by using precipitated silica, while taking advantage of the inherent properties of precipitated silica. In particular, the present invention is to provide a surface-modified precipitated silica powder that has good dispersibility, appropriate charging properties, and a high spacer effect.

The inventors conducted extensive research in light of the problems with the prior art described above, and discovered that unique physical properties can be obtained when precipitated silica powder is subjected to a specific surface treatment, leading to the completion of the present invention.

That is, the present invention relates to the following surface-modified precipitated silicic acid powder and a method for producing the same.
1. A powder comprising precipitated silica particles having a volumetric particle size distribution of _d50 : 150-1000 nm and _d90 : 500-7000 nm, and a silanol group density of 2.5-8 OH/ ^nm2 , the surface of which is coated with a coating layer containing an organosilicon compound having an amino group,
(1) Bulk density: 40 to 150 g / L,
(2) Water 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) Drying loss: 0.1 to 3.0%; and (6) Triboelectric charge: +10 to +450 μC/g.
A surface-modified precipitated silica powder characterized in that:
2. The surface-treated precipitated silica powder according to claim 1, wherein the value of the fluidity energy value when added to a toner, as determined by a dry fluidity evaluation method, divided by the energy value before addition is 0.35 or less.
3. The surface-modified precipitated silica powder according to the above 1, wherein the organosilicon compound having an amino group is at least one of aminosilane and amino-modified silicone oil.
4. An external additive for toner or powder coating, comprising the surface-modified precipitated silica powder according to any one of items 1 to 3.
5. A toner composition or a powder coating composition for electrophotography, comprising the external additive according to Item 4 and binder resin particles.
6. A method for producing a surface-modified precipitated silica powder, comprising the steps of:
(a) preparing a mixture containing a precipitated silicic acid powder and an organosilicon compound having an amino group;
(b) heat-treating the mixture at a temperature of 120-360° C.
7. The method according to item 6, wherein the steps (a) and (b) are carried out under stirring.

According to the present invention, by using precipitated silica, it is possible to provide a powder suitable for use in toners, etc., while taking advantage of the inherent properties of precipitated silica. In particular, the present invention can provide a surface-modified precipitated silica powder that has good dispersibility, appropriate charging properties, and a high spacer effect.

The surface-modified precipitated silica powder of the present invention is a precipitated silica powder whose median diameter, etc., is controlled within a specific range, and the surface is modified with an organosilicon compound to give it specific properties such as bulk density and water adsorption. As a result, it is possible to provide a submicron-sized aggregate powder that has low bulk density, good dispersibility, and good fluidity with appropriate charging properties.

More specifically, the surface-modified precipitated silica powder of the present invention is a precipitated silica powder that has been surface-modified with a specific organosilicon compound, and as a result, the bulk density, hydrophobicity, water adsorption, surface area, carbon content, and other properties are controlled within a certain range. As a result, the powder exhibits higher charging properties than particles produced by the sol-gel method, can be uniformly applied to the surface of toner (binding resin particles), and a particle size sufficient to produce a spacer effect that cannot be obtained with silicon oxide powder produced by the conventional fumed method can be secured.

As described above, the present invention focuses on precipitated silica, and as part of the development of new applications for it, selectively uses a specific precipitated silica powder and modifies its surface, thereby making use of the inherent properties of precipitated silica (mass productivity, pore characteristics, etc.), while successfully achieving not only good dispersibility, but also high charging properties and low bulk density that were difficult to achieve with sol-gel silica, and a high spacer effect that was difficult to achieve with fumed silica.

The powder of the present invention having such characteristics can be suitably used as an external additive, particularly for toners or powder coatings. Therefore, the toner composition or powder coating composition for electrophotography of the present invention contains a surface-modified precipitated silica powder having such a high fixation rate and high hydrophobicity, and therefore has excellent dispersibility, flowability, antistatic properties, etc., and suppresses fogging or cleaning failure. Furthermore, it is possible to obtain the effect that the toner, etc. is less likely to adhere to the photoreceptor, and image defects are less likely to occur. Furthermore, these compositions of the present invention can obtain the effects of long-term storage stability, control of developer deterioration behavior, etc.

FIG. 11 is a schematic diagram of a method for observing toner particles with an SEM in Test Example 2.

1. Surface-modified precipitated silica powder The surface-modified precipitated silica powder of the present invention (powder of the present invention) is a powder consisting of particles having a coating layer containing an organosilicon compound having an amino group formed on the surface of precipitated silica particles having a particle size distribution based on volume of a) _d50 : 150-1000 nm and _d90 : 500-7000 nm and b) a silanol group density of 2.5-8 OH/ ^nm2 ,
(1) Bulk density: 40 to 150 g / L,
(2) Water 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% by weight;
(5) Drying loss: 0.1 to 3.0%; and (6) Triboelectric charge: +10 to +450 μC/g.
It is characterized in that:

<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 surface of the particles. That is, the basic structure is a precipitated silica particle as a core particle (base material), on the surface of which a coating layer containing an organosilicon compound having an amino group is formed.

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

As regards the particle size distribution, the particle size distribution on a volume basis is characterized by d ₅₀ (median diameter): 150-1000 nm and d ₉₀ : 500-7000 nm.

If the _d50 is less than 150 nm, the aggregate particle size of the powder after surface treatment with an organosilicon compound is too small to exhibit a sufficient spacer effect when dispersed in a toner, whereas if the _d50 is more than 1000 nm, the aggregate particle size is too large to be uniformly dispersed on the toner surface.

If the _d90 is less than 500 nm, the chargeability and spacer effect are insufficient, whereas if the _d90 is more than 7000 nm, the number of coarse particles increases, making it difficult to uniformly disperse the particles on the toner surface.

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

The silanol group density is usually 2.5 to 8 OH/ ^nm2 , and preferably 3.1 to 5.0 OH/ ^nm2 . If the silanol group density is too low, the charge of the powder after surface treatment with an organosilicon compound will be too high and difficult to control within a certain range. On the other hand, if the silanol group density is too high, the amount of water adsorption will increase, resulting in a problem of the charge being too low.

The BET specific surface area of the precipitated silica particles is not particularly limited, but is preferably in the range of 100 to 350 ^m2 /g. This allows the distribution of surface pores to be in an appropriate range, making it possible to control the amount of water adsorption in an appropriate range. As a result, appropriate charging properties can be achieved after modification with an organosilicon compound having an amino group.

The precipitated silica particles themselves may be publicly known or commercially available. For example, the precipitated silica powder described in Patent Document 2 may be suitably used. Therefore, in the present invention, precipitated silica obtained according to the manufacturing method described in Patent Document 2 may also be used.

More specifically, the present invention relates to a process for producing precipitated silica by grinding and simultaneously classifying a precipitated silica having the following properties: a Shears number of 10-30 ml/(5 g), a BET surface area of 100-350 ^{m 2} /g, a loss on drying of 2-8% by weight, a loss on ignition of 2-9% by weight, a pH value of 4-9 and a DBP value of 230-400 g/100 g, in which ground silica is obtained, in which the grinding and simultaneous classification are carried out using a grinding apparatus, the mill of the grinding apparatus being operated in a grinding phase with a working medium from the group consisting of gas, steam, water vapor, gases containing water vapor and mixtures thereof; and the grinding chamber is heated in a heating stage, i.e. before the specific operation with a working medium, in such a way that the temperature in the grinding chamber and/or at the mill outlet is higher than the dew point of the working medium; and the ground silica is treated with a d ₅₀ of 150-2000 nm. The precipitated silicic acid can be preferably prepared by the method of the present invention, characterized in that the precipitated silicic acid is classified to a d ₉₀ value of 500 to 7000 nm and a d 90 value of 500 to 7000 nm.

The coating layer coats the surface of the particles that make up the powder of the present invention, thereby imparting a certain level of hydrophobicity, electrostatic charge, etc. to the particles that make up the powder of the present invention. The coating layer contains an organosilicon compound having an amino group. The content of the organosilicon compound having an amino group in the coating layer is not particularly limited, but can usually be appropriately set to about 5 to 100% by weight. Therefore, it can be, for example, 20 to 60% by weight.

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, at least one of aminosilane and amino group-modified silicone oil can be particularly preferably used. The amino groups in these compounds may be any of primary, secondary, and tertiary.

As the aminosilane, for example, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, and other amino group-containing alkoxysilanes can be suitably used. These can also be publicly known or commercially available products.

As the amino group-modified silicone oil, for example, a silicone oil in which an amino group or an organic group containing an amino group (such as an aminoalkyl group) is introduced into the side chain and/or end of the silicone chain can be suitably used. These can be publicly known or commercially available products.

The viscosity range of the amino-modified silicone oil (measurement temperature 25°C) is not particularly limited, but is usually preferably 20 to 300 cs. If the viscosity is less than 20 cs, low molecular weight polysiloxanes and the like will volatilize during surface treatment, which is undesirable from the standpoint of energy efficiency and the environment. On the other hand, if the viscosity exceeds 300 cs, higher aggregation will occur, and the dispersibility of the resulting powder may be impaired.

The content of the amino group-containing organosilicon compound in the powder of the present invention is not particularly limited as long as it is within the range of the carbon content described above, but it is usually about 0.5 to 30 parts by weight, and preferably 1 to 20 parts by weight, per 100 parts by weight of the precipitated silica powder.

The coating layer may contain components other than the organosilicon compound having an amino group, as long as the effects of the present invention are not hindered. For example, an organosilicon compound not having an amino group can be included. There are no particular limitations on the organosilicon compound not having an amino group, and for example, publicly known or commercially available compounds known as hydrophobic treatment agents can be used.

More specifically, alkylsilazane compounds such as hexamethyldisilazane, alkylalkoxysilane compounds such as dimethyldimethoxysilane, diethyldiethoxysilane, trimethylmethoxysilane, methyltrimethoxysilane, and butyltrimethoxysilane, chlorosilane compounds such as dimethyldichlorosilane and 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.

Among these, it is preferable to use at least one of alkylsilazane compounds, alkoxysilane compounds, and silicone oils, in order to more reliably obtain the effects of the present invention.

In particular, the alkoxysilane is not particularly limited as long as it is an alkoxysilane substituted with an alkyl group, but typically trimethoxyalkoxysilane, triethoxyalkoxysilane, etc. are used. The number of carbon atoms in the alkyl group is not particularly limited, but is preferably C2 to C18. If it is less than C2, there is a risk of the alkoxysilane volatilizing during the surface treatment. Furthermore, if it exceeds C16, strong aggregation may occur due to the effect of the high viscosity, and the dispersibility of the obtained powder may be impaired.

In particular, in addition to polydimethylsiloxane, modified silicone oils into which alkyl groups, -OH groups, etc. have been introduced can also be used as silicone oils.

The viscosity range of these organosilicon compounds (measurement temperature 25°C) is not particularly limited, but is usually preferably 20 to 300 cs. If the viscosity is less than 20 cs, low molecular weight polysiloxanes and the like will volatilize during surface treatment, which is undesirable from the standpoint of energy efficiency and the environment. On the other hand, if the viscosity exceeds 300 cs, higher aggregation will occur, and the dispersibility of the resulting powder may be impaired.

The content of the organosilicon compound not 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 carbon content described above, but it is generally about 5 to 20 parts by weight, and preferably 10 to 15 parts by weight, per 100 parts by weight of the inorganic oxide powder.

In the following, unless otherwise specified, the term "organosilicon compound" refers to two meanings: (a) "an organosilicon compound having an amino group alone" and (b) "an organosilicon compound having an amino group and an organosilicon compound not having an amino group."

<Characteristics of the powder of the present invention>
The powder of the present invention has the following characteristics:
(1) Bulk density: 40 to 150 g / L,
(2) Water 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) Drying loss: 0.1 to 3.0%; and (6) Triboelectric charge: +10 to +450 μC/g.
Satisfy all of the following.

Bulk density The bulk density of precipitated silicic acid surface-modified with an organosilicon compound is 40 to 150 g/L. If the bulk density is less than 40 g/L, the powder cannot be dispersed with an appropriate aggregate particle size when dispersed on the toner surface, and a sufficient spacer effect cannot be exhibited. If the bulk density exceeds 150 g/L, a large device volume is required when mixing with the toner, which is problematic for industrial use.

Moisture adsorption amount The moisture adsorption amount at a water vapor relative pressure of 0.8 to 0.95 is usually 3 to 6% by weight. The moisture adsorption amount has a large effect on the charging characteristics, and by setting it within the above range, it is possible to impart appropriate charging characteristics. If the moisture adsorption amount is less than 3% by weight, the positive charging characteristics will be too strong. If the moisture adsorption amount exceeds 6% by weight, sufficient charging characteristics will not be exhibited.

BET specific surface area The BET specific surface area of precipitated silicic acid surface-modified with an organosilicon compound is usually 50 to 200 ^m2 /g. If the BET specific surface area is less than 50 ^m2 /g, the aggregate particle size is too large, resulting in insufficient dispersibility when dispersed in a toner. If the BET specific surface area is more than 200 ^m2 /g, the appropriate aggregate size is not maintained when dispersed in a toner, and a sufficient spacer effect cannot be achieved.

Carbon content The carbon content of precipitated silicic acid surface-modified with an organosilicon compound is usually 1.0 to 8.0% by weight. In particular, when the surface treatment agent (hydrophobic treatment 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 alkylalkoxysilane, it is preferably about 1.0 to 8.0% by weight. The carbon content is an index showing the degree of fixation (fixed amount) of the organosilicon compound, which is the surface treatment agent, to the precipitated silicic acid powder. If the carbon content is too low, the surface is not sufficiently modified, and the charging characteristics, dispersibility, etc. are insufficient. On the other hand, if the carbon content is too high, the organic matter content is too high, causing particle aggregation, and sufficient fluidity and dispersibility cannot be obtained, and even if this powder is applied to a toner, it is not possible to exhibit a sufficient spacer effect.

Loss on drying The loss on drying is usually 0.1 to 3.0%. The loss on drying has a large effect on the charging characteristics, and by setting it within the above range, it is possible to impart an appropriate charging characteristic. If the loss on drying exceeds 3% by weight, the amount of water retained and adsorbed becomes close to that of silica produced by the sol-gel method, and sufficient charging characteristics cannot be expressed.

Charging property The triboelectric charge of precipitated silicic acid surface-modified with an organosilicon compound is usually +10 to +450 μC/g. When the triboelectric charge approaches zero from +10 μC/g, it becomes difficult to develop strong charging properties in the toner when the powder is added to the toner, as with negative charging, and it becomes difficult to control the toner to a predetermined charge range. On the other hand, when the triboelectric charge becomes more positive than +450 μC/g, it becomes difficult to control the charging properties of the toner to which it is added due to the strong triboelectric charge.

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, it is desirable that the particle size distribution measured by a particle size distribution measuring device is about 0.1 to 1 μm, and preferably 0.2 to 0.8 μm. The average particle size in the present invention refers to a 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.)).

Fluidity In the powder of the present invention, a ratio based on the energy value measured by a powder rheometer is used as an index of the ability to impart fluidity to toners, etc. That is, it is a value obtained by dividing the fluidity energy value measured by a dry fluidity evaluation method when the powder of the present invention is added to a toner by the energy value before the addition, and in the present invention, this value is desirably 0.35 or less. By making this value 0.35 or less, it is possible to impart even higher fluidity to toner products to which the powder of the present invention is externally added.

2. Method for Producing the Powder of the Present Invention The method for producing the powder of the present invention is not particularly limited as long as it can produce a powder having the above-mentioned composition and characteristics. For example, the powder of the present invention can be suitably produced by a method including: (a) a step of preparing a mixture containing a precipitated silicic acid 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).

Mixture Preparation Step The mixture preparation step can be performed by any method that can coat the surface of each particle constituting the precipitated silica powder with a coating layer containing an organosilicon compound. For example, a method of mixing the precipitated silica powder with a vaporized organosilicon compound under stirring, or a method of spraying the organosilicon compound onto the precipitated silica powder under stirring can be suitably used.

In this case, the organosilicon compound can be used in a state of being dissolved or dispersed in a solvent (e.g., an organic solvent such as hexane or toluene) as necessary. In this case, the concentration of the organosilicon compound can be appropriately set depending on the type of organosilicon compound used, etc.

In addition, in the present invention, water and a catalyst (such as an amine) can be appropriately added to the mixture as needed.

The temperature conditions in the mixture preparation process are not particularly limited, and may be within the range of, for example, 10 to 40°C, but are not limited to this. In addition, it is usually preferable to carry out the process in an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be suitably used.

The type and amount of organic silicon compound used may be the same as those described in "1. Surface-modified precipitated silica powder" above.

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

As in the above process, the heat treatment is preferably performed in an inert gas atmosphere. For example, nitrogen gas, helium gas, argon gas, etc. can be suitably used. In particular, the above process can be performed in a sealed reactor, and the heat treatment process can be suitably performed while maintaining the atmosphere.

The heat treatment time should be long enough to allow the organosilicon compound to be fixed (adhered) to the surface of each particle constituting the precipitated silica powder, and can be, for example, about 10 to 200 minutes, but is not limited to this.

3. Use of the Powder of the Present Invention The powder of the present invention has all of the properties (1) to (6) shown in "1. Surface-modified precipitated silica powder" above, and therefore exhibits both a good spacer effect and moderate charging properties in addition to the excellent properties of precipitated silica powder. Therefore, the powder of the present invention can be suitably used as an additive (particularly an external additive for toner) for toners, powder coatings, etc. Therefore, the present invention also includes an electrophotographic toner composition or powder coating composition containing the powder of the present invention and binding resin particles (hereinafter, both are also collectively referred to as "the composition of the present invention").

The composition of the present invention contains the above-mentioned surface-modified precipitated silica powder of the present invention, and there are no particular limitations on its composition or manufacturing method, and known compositions and methods can be used.

The content of the powder of the present invention in the composition of the present invention is not particularly limited as long as the desired property improvement effect is obtained, but it is usually preferable that the content is 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 stabilizing electrostatic chargeability due to the addition of the surface-modified precipitated silica powder may not be sufficiently obtained. Furthermore, if the content of the surface-modified precipitated silica powder exceeds 5.0% by weight, the surface-modified precipitated silica powder will act independently more, and problems may occur, for example, in images, cleaning properties, etc.

In addition to the binder resin particles, the composition of the present invention may contain, as necessary, for example, a pigment, a charge control agent (charge control agent), wax, etc. These components may be the same as those in known or commercially available toner compositions. In addition, the type of toner is preferably a positively charged toner, but is not otherwise particularly limited. Therefore, for example, either a magnetic or non-magnetic one-component toner or a two-component toner may be used. Furthermore, either monochrome or color may be used.

The powder of the present invention has a particularly excellent spacer effect, and can therefore be used more suitably as an external additive for adhesive resin particles that contain a resin component that is easily softened (e.g., at least one of styrene-acrylic copolymer resin, polyester resin, epoxy resin, etc.).

In the toner composition for electrophotography of the present invention, the powder of the present invention as an external additive is not limited to being used alone, but may be used in combination with other metal oxide fine powders depending on the purpose. For example, the surface-modified precipitated silicic acid powder of the present invention may 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.

In addition, the precipitated silica powder surface-modified with an organosilicon compound in this invention exists on the toner surface as submicron-sized aggregates, and because the surface has numerous irregularities, it is less likely to detach from the toner surface than sol-gel silica.

The following examples and comparative examples are presented to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples.

The components used in each of the examples and comparative examples are as follows.
(A) Silica raw material (A1) Precipitated silica Samples A to E: Precipitated silica prepared according to the method described in Patent Document 2 (A2) Sol-gel silica Sample produced by a known sol-gel method (A3) Fumed silica Commercial product a: Product name "AEROSIL OX50" (registered trademark) manufactured by Nippon Aerosil Co., Ltd.
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 Dow Corning Toray Co., Ltd.)
(B4) Aminosilane (product name "KBE-903" (registered trademark), manufactured by Shin-Etsu Chemical Co., Ltd.) (component shown 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.) (component shown as "positive charge imparting agent" in Table 1)

[Example 1]
Sample A (100 parts by weight) as precipitated silica powder (median diameter _d50 = 155 nm, _d90 = 540 nm, silanol group density: ^3.5 OH/nm2) was placed in a reactor, and a mixture 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 performed at 300°C for 20 minutes while continuing to stir. In this way, a surface-modified silica powder was obtained.

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

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

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

(1) Bulk density Place a measuring cylinder on a balance, remove the tare, add a sample to the measuring cylinder and measure the mass (mass A), and read the volume (volume B) after leaving it to stand for 2 minutes. Calculate the bulk density using the following formula.
Bulk density (g/L) = (mass A/volume B) x 1000

(2) Moisture adsorption measurement The surface-modified silica powder was heated under vacuum at 150°C for 2 hours or more and thoroughly dried, and then measured using a high-precision gas adsorption measurement device (product name "BELSORP-max" manufactured by Microtrack-Bell Co., Ltd.) under conditions of an exhaust time of 15 minutes and a pressure rise allowance of 5.000E-1 Pa/min. The adsorption isotherm was analyzed, and the value within the range of water vapor relative pressure of 0.8 to 0.95 was taken as the moisture adsorption amount.

(3) BET Specific Surface Area The BET {surface area ( ^m2 /g)} was determined by using a fully automatic specific surface area measuring device (product name "Macsorb", Mountech Co., Ltd.) to pretreat a sample at 100°C for 10 minutes, and then calculating the surface area of the sample from the amount of nitrogen adsorbed and desorbed by the BET single-point method, and dividing the surface area by the weight to obtain the specific surface area.

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

(5) Loss on Drying Approximately 1 g of the surface-modified silica powder was sampled in a weighing bottle, dried at 105° C. for 2 hours, and the weight was measured. The percentage of the weight loss before and after drying was calculated to obtain the amount of adsorbed water.

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

(7) Fluidity Using a Henschel mixer, 1 g of the surface-modified silica powder obtained in each Example and Comparative Example was externally added to 99 g of toner (polyester toner base (binding resin), average particle size 6 μm), and then the resulting mixed powder was subjected to an air permeability test for the toner sample using a powder rheometer. The total energy value was measured 13 times for each sample, the first time without air passage, and the second time and thereafter while air passage was performed at a linear velocity of 0.04 mm/s. The total energy value E1 (mJ) of the 13th measurement was then 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 added externally.
Next, [E1/E0] was calculated based on the values E1 and E0 obtained above. A smaller value of [E1/E0] indicates a higher ability to impart fluidity.

[Test Example 2]
The surface-modified silica powder obtained in each of the Examples and Comparative Examples was mixed with a polyester toner base (binding resin) powder produced by a polymerization method in a weight ratio of [binding resin powder: surface-modified silica powder = 99:1], and the mixture was premixed in a Henschel mixer at 600 rpm for 1 minute, and then mixed at 3000 rpm for 30 minutes to prepare a toner sample for dispersibility evaluation.
The obtained toner sample was then observed under a scanning electron microscope (SEM) to count the number of surface-modified silica particles with a particle size of 0.1 μm or more attached per 1 ^μm2 of the toner sample particle surface. The results are also shown in Table 1.
The measurement was carried out by arbitrarily selecting one toner base (toner particle) within the field of view of the SEM, setting the field of view S as shown in Fig. 1 so that the field of view S was filled with the surfaces of the toner particles 10 and contained as many surface-modified silica particles 11 as possible, and then measuring the number of all the surface-modified silica particles 11 within the field of view S, and dividing the number by the field of view area to calculate the number of surface-modified silica particles per unit area (per 1 ^µm2 ). In this case, surface-modified silica particles protruding even slightly from the field of view S were not counted. The greater the number of surface-modified silica particles per unit area, the more uniformly the surface-modified silica powder is dispersed.

As is clear from the results in Table 1, the surface-modified silica powders of the Examples satisfy all of the characteristics specified in the present invention.

Claims (7)

a) in the particle size distribution based on volume, d50: 150-1000 nm and d90: 500-7000 nm; and b) a silanol group density of 2.5-8 OH/ ^nm2. The powder is composed of precipitated silica particles having a coating layer formed on the surface thereof, the coating layer containing an organosilicon compound having an amino group,
(1) Bulk density: 40 to 150 g / L,
(2) Water 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: 2.4 to 8.0% by weight,
(5) Drying loss: 0.1 to 3.0%; and (6) Triboelectric charge: +10 to +450 μC/g.
A surface-modified precipitated silica powder characterized in that: 2. The surface-treated precipitated silica powder according to claim 1, wherein a value of the fluidity energy value when added to a toner, as determined by a dry fluidity evaluation method, divided by the energy value before addition is 0.35 or less. 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-modified silicone oil. An external additive for toner or powder coating containing the surface-modified precipitated silica powder according to any one of claims 1 to 3. An electrophotographic toner composition or powder coating composition comprising the external additive according to claim 4 and binder resin particles. A method for producing a surface-modified precipitated silica powder according to any one of claims 1 to 3 , comprising the steps of:
(a) preparing a mixture comprising a precipitated silicic acid powder having a particle size distribution based on volume of d50: 150-1000 nm and d90: 500-7000 nm and b) a silanol group density of 2.5-8 OH/nm2 ^, and an organosilicon compound having an amino group;
(b) heat-treating the mixture at a temperature of 120-360° C. The method according to claim 6, wherein steps (a) and (b) are carried out under stirring.