JP2007099582A - Highly hydrophobic spherical sol-gel silica fine particle, method for producing the same, toner external additive for electrostatic charge image development composed of the fine particle, and developer using the toner external additive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide highly hydrophobic spherical sol-gel silica fine particles; a method for producing the same; a toner external additive for electrostatic charge image development, which is excellent in flowability of a toner, caking resistance, fixability, cleaning property, environmental stability of the electrified charge amount, or the like and useful for an electrophotographic method, and to provide a developer containing the toner additive. <P>SOLUTION: The method for producing the highly hydrophobic spherical sol-gel silica fine particles having a hydrophobicity of ≥50 and comprising primary particles having an average particle diameter of 0.01-5 μm includes: a process for obtaining heat treated spherical sol-gel silica fine particles having a hydrophobicity of <50 by heat treating hydrophobic spherical sol-gel silica fine particles having a hydrophobicity of ≥50 and comprising primary particles having an average particle diameter of 0.01-5 μm, which are obtained by making hydrophilic spherical sol-gel silica fine particles, obtained by the hydrolysis condensation of hydrocarbyloxysilane, hydrophobic; and a process for making the heat treated spherical sol-gel silica fine particles hydrophobic. The silica fine particles obtained by the method is also provided. The toner external additive comprises the silica fine particles, and the developer contains the toner external additive. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a highly hydrophobic spherical sol-gel silica fine particle and a method for producing the same. Further, the present invention is a toner external additive for developing an electrostatic charge image, which is composed of the highly hydrophobic spherical sol-gel silica fine particles and used for developing an electrostatic charge image in electrophotography, electrostatic recording method, etc. The present invention relates to an external additive for a small particle diameter toner used for improving image quality, and a developer using the same.

  Dry developers used in electrophotography and the like can be roughly classified into a one-component developer using a toner itself in which a colorant is dispersed in a binder resin and a two-component developer in which a carrier is mixed with the toner. When performing a copying operation using these developers, in order to have process compatibility, the developer needs to be excellent in fluidity, caking resistance, fixing properties, charging properties, cleaning properties, and the like. . In order to improve fluidity, caking resistance, fixing properties, cleaning properties, etc., inorganic fine particles are often added to the toner. However, the inorganic fine particles have a great influence on the chargeability. For example, in the case of generally used silica-based fine powder, the negative polarity is strong, and particularly the chargeability of the negatively chargeable toner is excessively increased under low temperature and low humidity, while moisture is increased under high temperature and high humidity. Since the chargeability is reduced by taking in, there is a problem that a large difference is caused in the chargeability between the two. As a result, density reproduction failure and background fogging may occur. In addition, the dispersibility of the inorganic fine particles has a great influence on the toner characteristics. If the dispersibility is not uniform, the desired characteristics cannot be obtained in the fluidity, caking resistance, and fixability, or the cleaning properties are insufficient. As a result, toner sticking or the like may occur on the photoreceptor, which may cause black spot image defects. In order to improve these points, various types in which the surface of inorganic fine particles has been subjected to a hydrophobic treatment have been proposed (Patent Documents 1 to 3). Further, it has been proposed to treat a powder such as silica with silicone oil (Patent Documents 4 to 5). However, sufficient effects may not always be obtained simply by using these inorganic fine particles.

  In addition, when using an organophotoreceptor for higher image quality or using a toner with a smaller particle size, sufficient performance cannot be obtained by using the above-mentioned inorganic fine particles. There is. Organic photoreceptors tend to have a shorter life because their surfaces are softer and more reactive than inorganic photoreceptors. Therefore, when such an organic photoreceptor is used, the photoreceptor is easily altered or scraped by the inorganic fine particles added to the toner. Further, when the toner has a small particle size, the powder fluidity is poor as compared with a toner having a particle size that is usually used, so that a larger amount of inorganic fine particles must be added and used. The fine particles sometimes cause toner adhesion to the photoreceptor.

  In order to improve these points, hydrophobic spherical sol-gel silica particles obtained by hydrophobizing spherical sol-gel silica particles obtained by hydrolyzing tetraalkoxysilane have been proposed (Patent Documents 6 to 7). These hydrophobic spherical sol-gel silica fine particles are not only excellent in toner fluidity, caking resistance, fixing property, cleaning property, etc., but also when added to the toner, compared to silica of other production methods. The charge amount does not increase, and as a result, the difference in charge amount between low temperature and low humidity and high temperature and high humidity is reduced, and the environmental stability is excellent.

  However, since the charge amount of the toner is not high, it is complicated and difficult to control various processes of electrophotography.

JP-A-46-5782 JP-A-48-47345 JP-A-48-47346 JP-A-49-42354 JP 55-26518 A JP 2000-330328 A JP 2001-194824 A

  The present invention is not only excellent in the fluidity, caking resistance, fixing property, and cleaning property of the toner when added to the toner, but also has a sufficient charge amount when added to the toner. Therefore, it is possible to provide a toner external additive for developing an electrostatic charge image, which has less restrictions on the conditions in each process of electrophotography, and is excellent in environmental stability of charge amount, and a developer containing the toner external additive. With the goal.

  As a result of intensive investigations to achieve the above object, the present inventors have achieved this object by the following highly hydrophobic spherical sol-gel silica fine particles, a production method thereof, a toner external additive for developing electrostatic images and a developer. I came to find out what to do. The action is considered as follows.

  That is, the conventional hydrophobic spherical sol-gel silica fine particles are caused by the production method thereof, and the amount of silanol groups in the vicinity of the particle surface and inside the particles is much larger than that of silica of other production methods, so that the toner charge amount is lowered. Yes. By heat-treating the hydrophobic spherical sol-gel silica fine particles, the amount of silanol groups near and inside the particles can be reduced by heat condensation. At this time, the hydrophobic group on the particle surface is thermally decomposed to produce a surface silanol group. However, the amount of the surface silanol group can be reduced by hydrophobizing the heat-treated spherical sol-gel silica fine particles. The highly hydrophobic spherical sol-gel silica particles thus highly hydrophobicized have a low amount of silanol groups on the particle surface, in the vicinity of the particle surface and inside the particle, and since the surface has been hydrophobized, the toner charge amount is high and the charge is charged. The amount of environmental stability is considered to be excellent.

  In the present invention, firstly, a hydrophilic spherical sol-gel silica fine particle obtained by hydrolyzing and condensing hydrocarbyloxysilane or a partial hydrolysis-condensation product thereof or a combination thereof is subjected to a hydrophobic treatment. A step of heat-treating hydrophobic spherical sol-gel silica fine particles having a degree of conversion of 50 or more and an average primary particle diameter of 0.01 to 5 μm to obtain heat-treated spherical sol-gel silica fine particles having a degree of hydrophobicity of less than 50; Including a step of hydrophobizing the heat-treated spherical sol-gel silica fine particles, and a method for producing highly hydrophobic spherical sol-gel silica fine particles having a hydrophobicity of 50 or more and an average primary particle size of 0.01 to 5 μm To do.

  Secondly, the present invention provides highly hydrophobic spherical sol-gel silica fine particles obtained by the above production method.

  Thirdly, the present invention provides a toner external additive for developing an electrostatic charge image obtained from the above highly hydrophobic spherical sol-gel silica fine particles.

  Fourthly, the present invention provides a developer containing the toner external additive and toner particles.

  By applying the production method of the present invention, highly hydrophobic spherical sol-gel silica fine particles that are highly hydrophobized can be easily produced. The toner external additive for electrostatic image development composed of silica fine particles, when added to the toner, fluidity, caking resistance, fixing property, and cleaning property of the toner (this property remarkably suppresses photoreceptor wear). In addition, the charge amount is sufficiently high, so that there are few restrictions on the conditions in each process of electrophotography, and the environmental stability of the charge amount is excellent. Therefore, a developer containing this toner external additive is also useful because it has these characteristics.

  Hereinafter, the present invention will be described in more detail.

  In the present specification, the “hydrophobicity” is determined by a methanol titration test. The value expressed by the percentage of methanol in the mixture of methanol and water when the silica fine particles added to the water are wet. The higher this value, the higher the hydrophobicity, and the lower the value, the higher the hydrophilicity. Indicates.

  “Average particle diameter” means volume average particle diameter. The volume average particle diameter can be determined, for example, by measuring the particle size distribution with a laser diffraction / scattering particle size distribution measuring apparatus (trade name: LA910, manufactured by Horiba, Ltd.).

  The term “spherical” includes not only a true sphere but also a slightly distorted sphere having a sphericity in the range of 0.6 to 1, preferably 0.8 to 1. Here, the sphericity means (surface area of a sphere having the same volume as an actual particle) / (surface area of an actual particle).

  Synthetic silica fine particles are produced by combustion method silica obtained by burning a silane compound (that is, fumed silica), deflagration silica obtained by explosively burning metal silicon powder, sodium silicate and mineral acid. Wet silica obtained by the neutralization reaction of the above (the one synthesized under alkaline conditions is precipitated silica, the one synthesized under acidic conditions is gel silica), the sol-gel silica obtained by hydrolysis of hydrocarbyloxysilane (so-called Stoeber method). Of these, the present invention relates to sol-gel silica.

<Hydrophobic spherical sol-gel silica fine particles>
Hydrophobic spherical sol-gel silica fine particles subjected to heat treatment in the present invention are hydrophilic spherical sol-gel silica fine particles obtained by hydrolyzing and condensing hydrocarbyloxysilane or a partial hydrolysis-condensation product thereof or a combination thereof. Hydrophobic spherical sol-gel silica particles having a degree of hydrophobicity of 50 or more and an average primary particle diameter of 0.01 to 5 μm, obtained by hydrophobization treatment.

  The degree of hydrophobicity of the hydrophobic spherical sol-gel silica fine particles needs to be 50 or more so that no aggregates are formed during the heat treatment described later. If it is less than 50, there are many silanol groups present on the surface of the particles, and a condensation reaction of silanol occurs between the particles during the heat treatment described later, and agglomeration occurs due to fusion between the primary particles. is there. Since the toner external additive exhibits various excellent functions by adhering to the toner surface in the form of primary particles, it is a great disadvantage that an aggregate is formed.

  The average particle size of the primary particles of the hydrophobic spherical sol-gel silica fine particles is 0.01 to 5 μm from the viewpoint of improving the flowability, caking resistance and fixability of the developer and reducing adverse effects on the photoreceptor. Necessary, preferably 0.05 to 0.5 μm. When the primary particle size is smaller than 0.01 μm, the developer fluidity, caking resistance, and fixability may not be obtained due to aggregation. When the primary particle diameter exceeds 5 μm, the photoconductor may be modified or scraped. The adhesion to the toner may be reduced.

-Method for producing hydrophobic spherical sol-gel silica fine particles-
Hydrophobic spherical sol-gel silica fine particles subjected to heat treatment are as described above, but hydrolyze and condense hydrocarbyloxysilane, preferably tetrahydrocarbyloxysilane, or a partial hydrolysis-condensation product thereof, or a combination thereof. (Hereinafter referred to as “Step A”), the surface of the hydrophilic spherical sol-gel silica fine particles consisting essentially of SiO ₂ units, R ³ ₃ SiO _1/2 units [wherein R ³ is the same or different. And a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and specifically, as described in the general formula (3) described later. ] Is preferably prepared by a hydrophobizing treatment (hereinafter referred to as “step B”) including a step of introducing a thiol.

Incidentally, the hydrophilic silica particles "consisting essentially of SiO ₂ units" refers to more than 90% by weight of the silica fine particles, preferably means that at least 99 wt% of SiO ₂ units.

-Step A (Preparation of hydrophilic spherical sol-gel silica fine particles)-
Step A is, for example, the following general formula (1):
Si (OR ¹ ) ₄ (1)
[Wherein R ¹ is the same or different and is a monovalent hydrocarbon group having 1 to 6 carbon atoms]
Hydrophilic spheres obtained by hydrolyzing and condensing a tetrafunctional silane compound represented by the formula (1) or a partial hydrolysis-condensation product thereof or a combination thereof in a mixture of a hydrophilic organic solvent containing a basic substance and water. A step of generating sol-gel silica fine particles is preferable.

  The hydrophilic spherical sol-gel silica fine particles are usually obtained as a mixed solvent dispersion of a water-hydrophilic organic solvent. As will be described later, if necessary, a hydrophilic spherical sol-gel silica fine particle aqueous dispersion can be prepared by converting the dispersion medium of the hydrophilic spherical sol-gel silica fine particle mixed solvent dispersion into water.

In the general formula (1), R ¹ is preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms, particularly preferably 1 to 2 carbon atoms. Examples of the monovalent hydrocarbon group represented by R ¹ include a methyl group, an ethyl group, a propyl group, a butyl group, and a phenyl group, preferably a methyl group, an ethyl group, a propyl group, and a butyl group, and particularly preferably , Methyl group, and ethyl group.

  Examples of the tetrafunctional silane compound represented by the general formula (1) include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, tetraphenoxysilane, and the like. Methoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, particularly preferably tetramethoxysilane and tetraethoxysilane. Examples of the partial hydrolysis-condensation product of the tetrafunctional silane compound represented by the general formula (1) include methyl silicate and ethyl silicate.

The hydrophilic organic solvent is not particularly limited as long as it dissolves the tetrafunctional silane compound represented by the general formula (1), a partial hydrolysis-condensation product thereof, and water. , Alcohols, methyl cellosolve, ethyl cellosolve, butyl cellosolve, cellosolves such as acetic acid cellosolve, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane and tetrahydrofuran, preferably alcohols, cellosolves, particularly preferably alcohols Can be mentioned. As alcohols, the following general formula (2):
R ² OH (2)
[Wherein R ² is a monovalent hydrocarbon group having 1 to 6 carbon atoms]
The alcohol represented by these is mentioned.

In the general formula (2), R ² is preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms, particularly preferably 1 to 2 carbon atoms. Examples of the monovalent hydrocarbon group represented by R ² include an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group, preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, More preferably, a methyl group and an ethyl group are mentioned. Examples of the alcohol represented by the general formula (2) include methanol, ethanol, propanol, isopropanol, butanol and the like, preferably methanol and ethanol. As the number of carbon atoms in the alcohol increases, the particle size of the generated hydrophilic spherical sol-gel silica particles increases. Therefore, it is desirable to select the type of alcohol according to the particle size of the desired hydrophilic spherical sol-gel silica fine particles.

  Examples of the basic substance include ammonia, dimethylamine, diethylamine and the like, preferably ammonia, diethylamine, and particularly preferably ammonia. These basic substances may be dissolved in water in a required amount, and the obtained aqueous solution (basic) may be mixed with the hydrophilic organic solvent.

  The amount of water used at this time is 0.5-5 mol with respect to a total of 1 mol of the hydrocarbyloxy group of the tetrafunctional silane compound represented by the above general formula (1) and / or its partial hydrolysis-condensation product. It is preferable that it is 0.6-2 mol, and it is especially preferable that it is 0.7-1 mol. The ratio of the hydrophilic organic solvent to water is preferably 0.5 to 10 in terms of mass ratio, more preferably 1 to 5, and particularly preferably 1.5 to 2. The amount of the basic substance is 0.01 to 2 mol with respect to a total of 1 mol of the hydrocarbyloxy group of the tetrafunctional silane compound represented by the general formula (1) and / or the partial hydrolysis-condensation product thereof. Is more preferable, 0.5 to 1.5 mol is more preferable, and 1.0 to 1.2 mol is particularly preferable.

  Hydrolysis and condensation of the tetrafunctional silane compound represented by the general formula (1) and / or a partial hydrolysis-condensation product thereof are carried out by a well-known method, that is, a hydrophilic organic solvent containing a basic substance, water and Is added by adding the tetrafunctional silane compound represented by the above general formula (1) and / or a partial hydrolysis-condensation product thereof.

  The hydrophilic spherical sol-gel silica fine particles may be in the state of a mixed solvent dispersion containing the fine particles obtained above. However, water is added to the hydrophilic spherical sol-gel silica fine particle mixed solvent dispersion to retain the hydrophilic organic solvent. It may be left and converted into an aqueous dispersion. When converted to an aqueous dispersion in this manner, the remaining hydrocarbyloxy groups are hydrolyzed and the amount thereof is reduced. Accordingly, an aqueous dispersion containing hydrophilic spherical sol-gel silica fine particles is preferable.

  The step of converting the dispersion medium of the hydrophilic spherical sol-gel silica fine particle mixed solution dispersion into water, which is performed as necessary, is, for example, an operation of adding water to the dispersion and distilling off the hydrophilic organic solvent (if necessary) Repeat this operation). The amount of water added at this time is preferably 0.5 to 2 times, more preferably 0.7 to 1.2 times, on a mass basis with respect to the total amount of the hydrophilic organic solvent used and the amount of alcohol produced. The amount is particularly preferably about 1 time.

Step B (hydrophobization treatment of hydrophilic spherical sol-gel silica fine particles)
Step B is a step of subjecting the surface of the hydrophilic spherical sol-gel silica fine particles to a hydrophobic treatment.

The production of the hydrophobic spherical sol-gel silica fine particles is performed by a hydrophobic treatment including a step of introducing R ³ ₃ SiO _1/2 units on the surface of the hydrophilic spherical sol-gel silica fine particles consisting essentially of the SiO ₂ units. This is a step of obtaining silica fine particles. Here, a method using the hydrophilic spherical sol-gel silica fine particles prepared by the above method will be described as an example. However, when another hydrophilic spherical sol-gel silica fine particle is used, first, water-hydrophilicity such as an alcohol mixed solvent is used. It is preferable to carry out the following steps after preparing a mixed solvent dispersion of a basic organic solvent or a dispersion of a hydrocarbon solvent, an aromatic solvent, a ketone solvent or the like. Moreover, when performing the below-mentioned T unit process process in advance, it is preferable to perform the following processes after converting the dispersion medium of the spherical sol-gel silica fine particle dispersion after the process into a ketone solvent.

  The conversion to a ketone solvent performed as necessary is performed by adding a ketone solvent to the dispersion after the treatment and distilling off water and / or the hydrophilic organic solvent in the dispersion (necessary). This operation can be repeated accordingly.

  The amount of the ketone solvent added at this time is 0.5 to 5 times, preferably 2 to 5 times, particularly preferably 3 to 4 times the mass ratio of the hydrophilic spherical sol-gel silica fine particles. Examples of the ketone solvent include methyl ethyl ketone, methyl isobutyl ketone, acetyl acetone, and preferably methyl isobutyl ketone.

Step B is, for example, the above-mentioned hydrophilic spherical sol-gel silica fine particles (or surface-treated spherical sol-gel silica fine particles subjected to the T unit treatment step described later, and hereinafter, simply referred to as “hydrophilic spherical sol-gel silica fine particles” in this section) In an organic dispersion such as an aqueous dispersion, a hydrocarbon solvent, an aromatic solvent, a ketone solvent dispersion, or a mixed solvent dispersion of a water-hydrophilic organic solvent, the following general formula (3):
R ³ ₃ SiNHSiR ³ ₃ (3)
[Wherein R ³ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms]
Or a silazane compound represented by the following general formula (4):
R ³ ₃ SiX (4)
[Wherein R ³ is the same as above, and X is an OH group or a hydrolyzable group]
A step of adding a monofunctional silane compound represented by the above or a combination thereof and triorganosilylating the reactive group remaining on the surface of the hydrophilic spherical sol-gel silica fine particles is preferable.

In the above general formulas (3) and (4), R ³ is preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms, particularly preferably 1 to 2 carbon atoms. The monovalent hydrocarbon group represented by R ³ is, for example, an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, or a butyl group, preferably a methyl group, an ethyl group, or a propyl group. Includes a methyl group and an ethyl group. Further, some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine atom, chlorine atom, bromine atom, preferably fluorine atom.

  Examples of the hydrolyzable group represented by X include a chlorine atom, an alkoxy group, an amino group, and an acyloxy group, preferably an alkoxy group and an amino group, and particularly preferably an alkoxy group.

  Examples of the silazane compound represented by the general formula (3) include hexamethyldisilazane and hexaethyldisilazane, preferably hexamethyldisilazane. Examples of the monofunctional silane compound represented by the general formula (4) include monosilanol compounds such as trimethylsilanol and triethylsilanol, monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane, trimethylmethoxysilane, and trimethylethoxysilane. Monoalkoxysilane, trimethylsilyldimethylamine, monoaminosilane such as trimethylsilyldiethylamine, monoacyloxysilane such as trimethylacetoxysilane, preferably trimethylsilanol, trimethylmethoxysilane, trimethylsilyldiethylamine, particularly preferably trimethylsilanol, trimethylmethoxysilane .

The amount of these used is 0.05-0.5 mol with respect to 1 mol of SiO ₂ units of the hydrophilic spherical sol-gel silica fine particles used.

  The hydrophobic spherical sol-gel silica fine particles thus obtained may be obtained as a powder by a conventional method, or may be obtained as a dispersion by adding an organic compound after reaction with a silazane compound, a silane compound or a combination thereof.

-Another embodiment-
In another embodiment of the present invention, before introducing R ³ ₃ SiO _1/2 units into the surface of hydrophilic spherical sol-gel silica fine particles, R ⁴ SiO _3/2 units (wherein R ⁴ is substituted) Or an unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, specifically as described in the general formula (5) described later) to obtain surface-treated spherical sol-gel silica fine particles. Then, hydrophobic spherical sol-gel silica fine particles can be obtained by introducing R ³ ₃ SiO _1/2 units into the surface of the surface-treated sol-gel silica fine particles. Here, the method using the hydrophilic spherical sol-gel silica fine particles prepared by the above method will be described as an example. However, when another hydrophilic spherical sol-gel silica fine particle is used, first, the hydrophilic mixture such as the alcohol mixed solvent described above is used. The following steps after preparing a mixed organic solvent-water solvent dispersion, a hydrophilic silica fine particle aqueous dispersion, or a dispersion of a hydrocarbon solvent, an aromatic solvent, a ketone solvent, etc. It is preferable to carry out.

Specifically, for example, in the mixed solvent dispersion or the aqueous dispersion containing the hydrophilic spherical sol-gel silica fine particles, the following general formula (5):
R ⁴ Si (OR ⁵ ) ₃ (5)
[Wherein, R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and R ⁵ is the same or different and is a monovalent hydrocarbon group having 1 to 6 carbon atoms]
A surface-treated spherical sol-gel silica fine particle aqueous dispersion is obtained by adding a trifunctional silane compound represented by the above or a partial hydrolysis-condensation product thereof or a combination thereof and treating the surface of the hydrophilic spherical sol-gel silica fine particles. A process having These trifunctional silane compounds and their partial hydrolysis-condensation products may be used alone or in combination of two or more.

In the general formula (5), R ⁴ is preferably a monovalent hydrocarbon group having 1 to 3 carbon atoms, particularly preferably 1 to 2 carbon atoms. Examples of the monovalent hydrocarbon group represented by R ⁴ include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a butyl group, and a hexyl group, preferably a methyl group, an ethyl group, An n-propyl group and an isopropyl group, particularly preferably a methyl group and an ethyl group are exemplified. Further, some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine atom, chlorine atom, bromine atom, preferably fluorine atom.

In the general formula (5), R ⁵ is preferably a monovalent hydrocarbon group having 1 to 3 carbon atoms, particularly preferably 1 to 2 carbon atoms. Examples of the monovalent hydrocarbon group represented by R ⁵ include an alkyl group such as a methyl group, an ethyl group, a propyl group, and a butyl group, preferably a methyl group, an ethyl group, and a propyl group, and particularly preferably a methyl group. Group and ethyl group.

  Examples of the trifunctional silane compound represented by the general formula (5) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, and n-propyl. Trialkoxysilanes such as triethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, trifluoropropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, etc. Preferably, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, more preferably methyltrimethoxysilane, methyltriethoxysilane. , Or their partial hydrolysis condensation product thereof.

The addition amount of the trifunctional silane compound represented by the general formula (5) is 0.001 to 1 mol, preferably 0.01 to 0.1 mol, particularly preferably, per 1 mol of SiO ₂ unit of the hydrophilic spherical sol-gel silica fine particles used. Is 0.01-0.05 mol.

  Thus, the surface-treated spherical sol-gel silica fine particles are obtained as a mixed solvent dispersion or aqueous dispersion of a hydrophilic organic solvent-water such as an alcohol mixed solvent.

<Highly hydrophobic, highly hydrophobic spherical sol-gel silica particles>
The toner external additive for developing an electrostatic image of the present invention is composed of highly hydrophobic spherical sol-gel silica fine particles having an average primary particle diameter of 0.01 to 5 μm and a hydrophobicity of 50 or more. . The highly hydrophobic spherical sol-gel silica fine particles are obtained by heat-treating the above-mentioned hydrophobic spherical sol-gel silica fine particles to obtain heat-treated spherical sol-gel silica fine particles having a hydrophobization degree of less than 50 (hereinafter referred to as “Step C”), And a step of hydrophobizing the heat-treated spherical sol-gel silica fine particles (hereinafter referred to as “step D”).

  The average particle diameter of the primary particles of the highly hydrophobic spherical sol-gel silica fine particles is 0.01 to 5 μm from the viewpoint of improving the flowability, caking resistance and fixing property of the toner and reducing the adverse effect on the photoreceptor. Necessary, preferably 0.05 to 0.5 μm. If the primary particle size is smaller than 0.01 μm, the fluidity, caking resistance and fixing property of the toner may not be obtained due to agglomeration. Decrease in adhesion to the surface may occur.

  The degree of hydrophobicity of the highly hydrophobic spherical sol-gel silica fine particles needs to be 50 or more in order to reduce the amount of silanol and increase the charge amount of the toner, and prevent toner aggregation and increase the fluidity. When the degree of hydrophobicity is less than 50, not only the toner charge amount cannot be increased but also toner aggregation may occur.

Step C (heat treatment of hydrophobic spherical sol-gel silica fine particles)
The step of heat-treating the hydrophobic spherical sol-gel silica fine particles as a starting material may be performed under conditions such that the degree of hydrophobicity of the heat-treated spherical sol-gel silica fine particles obtained after the treatment is less than 50. Specifically, if the heating conditions are such that the hydrophobized groups on the particle surface are thermally decomposed to generate surface silanol groups, the silanol groups are reduced by thermally condensing the silanol groups near and within the target particle surface. It is considered possible. From this viewpoint, the degree of hydrophobicity of the heat-treated spherical sol-gel silica fine particles needs to be less than 50. When the degree of hydrophobicity is 50 or more, thermal condensation of silanol groups in the vicinity of the particle surface and inside the particle may be insufficient.

  The heat treatment may be performed for a time sufficient to make the degree of hydrophobicity less than 50, and the hydrophobic spherical sol-gel silica fine particles are usually exposed to a temperature of 320 to 600 ° C.

-Step D (hydrophobization treatment after heat treatment of hydrophobic spherical sol-gel silica fine particles)-
The step of hydrophobizing the heat-treated spherical sol-gel silica fine particles is such that the degree of hydrophobicity of the highly hydrophobic spherical sol-gel silica fine particles obtained after the treatment is 50 or more and the average particle diameter of the primary particles is 0.01 to 5 μm. It can be done under conditions. Specifically, the heat-treated spherical sol-gel silica fine particles are preferably subjected to a hydrophobizing treatment with a hydrophobizing agent composed of silicone oil, silazane compound, silane compound, or a combination thereof.

  Examples of the silicone oil include the following general formula (6):

(式中、Ｒは同一または異なり、炭素原子数１〜３のアルキル基であり、Ｒ'は同一または異なり、非置換または置換のアルキル基またはフェニル基を表し、Ｒ''は炭素原子数１〜３のアルキル基またはアルコキシ基を表し、ｎおよびｍは独立に０〜10000の整数であり、但し、同時に０ではない。)
で表わされるシリコーンオイル等が挙げられる。

Wherein R is the same or different and is an alkyl group having 1 to 3 carbon atoms, R ′ is the same or different and represents an unsubstituted or substituted alkyl group or phenyl group, and R ″ is 1 carbon atom. Represents an alkyl group or an alkoxy group of -3, and n and m are each independently an integer of 0-10000, provided that they are not 0 at the same time.
The silicone oil etc. which are represented by these are mentioned.

  In the general formula (6), examples of the alkyl group represented by R include a methyl group, an ethyl group, an n-propyl group, and an isopropyl group.

  In the general formula (6), the alkyl group represented by R ′ is the same type as that described as the alkyl group represented by R. Examples of the substituted alkyl group include halogenated alkyl groups such as 3,3,3-trifluoropropyl group substituted with a halogen atom. Examples of the substituted phenyl group include a chlorophenyl group substituted with a halogen atom.

  In the general formula (6), the alkyl group represented by R ″ is the same type as that described as the alkyl group represented by R. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, and an isopropoxy group.

  n is preferably an integer of 0 to 5000, m is preferably an integer of 0 to 5000, and it is particularly preferable that n and m satisfy these preferred ranges simultaneously.

  Specific examples of the silicone oil represented by the general formula (6) include dimethyl silicone oil, methylphenyl silicone oil, alkyls in which part of these methyl groups and phenyl groups are substituted with ethyl groups, propyl groups, and the like. Examples thereof include modified silicone oil, and among them, dimethyl silicone oil is preferable.

  As said silazane compound, what is represented by the said General formula (3) is mentioned, for example. Moreover, as said silane compound, what is represented by the said General formula (4) is mentioned, for example. These silazane compounds and silane compounds are the same as those described in the hydrophobization treatment of the hydrophilic spherical sol-gel silica fine particles described above.

  In order to surface-treat the heat-treated spherical sol-gel silica fine particles with the hydrophobizing agent, a known method may be applied. For example, the silica fine particles and the hydrophobizing agent may be directly mixed using a mixer such as a Henschel mixer. Alternatively, the hydrophobizing agent may be sprayed onto the silica fine particles, or the hydrophobizing agent may be dissolved or dispersed in an appropriate solvent, mixed with the silica fine particles, and then the solvent removed. Good.

The amount of the hydrophobizing agent used for the surface treatment varies depending on the type. When the hydrophobizing agent is silicone oil, the amount used is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the heat-treated spherical sol-gel silica fine particles. If the amount of the hydrophobizing agent used is too large, the fluidity and cleaning properties of the toner may deteriorate. When the hydrophobizing agent is a silazane compound or a silane compound, the amount used is preferably 0.001 to 0.5 mol, more preferably 0.005 to 0.1 mol, per 1 mol of SiO ₂ units in the heat-treated spherical sol-gel silica fine particles. It is. When the amount of the hydrophobizing agent used satisfies such a preferable range, the hydrophobizing agent is not wasted and highly hydrophobic spherical sol-gel silica fine particles having a desired degree of hydrophobization of 50 or more can be obtained.
These hydrophobizing agents may be used alone or in combination of two or more.

<Toner external additive, developer>
The thus produced highly hydrophobic spherical sol-gel silica fine particles are used as a toner external additive, particularly as a toner external additive for developing an electrostatic image. These toner external additives may be used alone or in combination of two or more.

  The blending amount of the toner external additive is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the toner particles. When this blending amount satisfies this range, adhesion to the toner particles occurs sufficiently, and not only good fluidity can be obtained, but also the chargeability of the toner particles is excellent.

  The adhesion (state) of the highly hydrophobic spherical sol-gel silica fine particles to the toner particle surface may be merely mechanical adhesion or may be loosely fixed to the surface. The entire surface of the toner particles may be coated or a part thereof may be coated. The hydrophobic spherical sol-gel silica fine particles may be coated with toner particles in a partially agglomerated state, but is preferably coated in a single-layer particle state.

  As the toner particles to which the toner external additive is added, known particles containing a binder resin and a colorant can be used. A charge control agent may be added to the toner particles as necessary.

  The electrostatic image developing toner to which the toner external additive of the present invention is added can be used as a one-component developer, but it can also be mixed with a carrier and used as a two-component developer. When used as a two-component developer, the toner external additive may not be added to the toner particles in advance, but may be added when the toner particles and the carrier are mixed to coat the surface of the toner particles. As the carrier, iron powder or the like, or a known carrier whose surface is resin-coated can be used.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the Examples, hexamethyldisilazane is abbreviated as “HMDS”, and 1,3-dioctyl-1,1,3,3-tetramethyldisilazane is abbreviated as “OctDS”. Further, the average particle size and the degree of hydrophobicity of the silica fine particles obtained in the examples were measured according to the following measuring methods.

<Measurement method>
[Measurement of average particle size of primary particles of silica fine particles]
After adding silica fine particles to methanol at a mass ratio of 1: 0.005, the silica fine particles were dispersed in methanol with an ultrasonic irradiator. The particle size distribution of the silica fine particles treated in this way was measured with a laser diffraction / scattering particle size distribution analyzer (trade name: LA910, manufactured by Horiba, Ltd.), and the average particle size was determined (the average particle size thus determined is So-called volume average particle diameter). In addition, the average particle diameter of the silica fine particles was measured using an electron microscope, and compared with the average particle diameter obtained from the measurement result by the apparatus, it was confirmed that those values coincided, and further the silica By confirming that the aggregation of fine particles did not occur, it was determined that the average particle size was that of primary particles.

[Hydrophobicity]
The degree of hydrophobicity was measured by a methanol titration test. Specifically, methanol is added dropwise from a burette while titrating the silica fine particle mixture until the total amount of 0.2 g of silica fine particles added in 50 ml of water is wetted, and methanol and water at the end point are The value represented by the percentage of methanol in the mixture was taken as the degree of hydrophobicity.

<Synthesis Example 1> (Synthesis of hydrophobic spherical sol-gel silica fine particles (1))
-Synthesis of hydrophilic spherical sol-gel silica particles-
In a 3 liter glass reactor equipped with a stirrer, a dropping funnel, and a thermometer, 623.7 g of methanol, 41.4 g of water, and 49.8 g of 28% by mass ammonia water were mixed. The resulting solution was adjusted to 35 ° C., and 1163.7 g (7.65 mol) of tetramethoxysilane and 418.1 g of 5.4 mass% ammonia water were simultaneously added while stirring. Tetramethoxysilane was added to ammonia over 6 hours. Water was added dropwise over 5 hours. Even after the dropping was finished, the mixture was further stirred for 0.5 hours for hydrolysis to obtain a methanol-water dispersion of hydrophilic spherical sol-gel silica fine particles. Next, an ester adapter and a condenser tube were attached to a glass reactor, and the dispersion was heated to 60 to 70 ° C. to distill off 1200 g of methanol, and then 1200 g of water was added. Subsequently, the obtained dispersion was heated to 70 to 90 ° C. to distill off 484 g of methanol, thereby obtaining an aqueous dispersion of hydrophilic spherical sol-gel silica fine particles.

-Hydrophobic treatment of hydrophilic spherical sol-gel silica particles-
To this aqueous dispersion, 11.6 g (0.085 mol) of methyltrimethoxysilane was added dropwise at room temperature over 0.5 hours, and stirring was continued for 12 hours after the addition, thereby hydrophobizing the surface of the hydrophilic spherical sol-gel silica particles. An aqueous dispersion of T unit-treated spherical sol-gel silica fine particles was obtained.

  After adding 1440 g of methyl isobutyl ketone to the obtained aqueous dispersion of T unit-treated spherical sol-gel silica fine particles, 1340 g of a mixture of methanol and water was distilled off over 10 hours by heating to 80 to 110 ° C. After adding 150 g (0.93 mol) of hexamethyldisilazane to the obtained dispersion at room temperature, the silica fine particles in the dispersion were trimethylsilylated by heating to 110 ° C. and reacting for 3 hours. Next, the solvent in the dispersion was distilled off at 80 ° C. under reduced pressure (6650 Pa) to thereby form hydrophobic spherical sol-gel silica fine particles (1) having an average primary particle size of 0.11 μm and a hydrophobization degree of 66. 463 g was obtained.

<Synthesis Example 2> (Synthesis of hydrophobic spherical sol-gel silica fine particles (2))
-Synthesis of hydrophilic spherical sol-gel silica particles-
In a 3 liter glass reactor equipped with a stirrer, a dropping funnel, and a thermometer, 693.0 g of methanol, 46.0 g of water, and 55.3 g of 28 mass% aqueous ammonia were added and mixed. The resulting solution was adjusted to 35 ° C., and 1293.0 g (8.5 mol) of tetramethoxysilane and 464.5 g of 5.4% by mass ammonia water were simultaneously added while stirring. The former was added dropwise over 6 hours and the latter over 4 hours. did. Stirring was continued for 0.5 hour after the dropping, and hydrolysis was carried out to obtain a methanol-water dispersion of hydrophilic spherical sol-gel silica fine particles.

-Hydrophobic treatment of hydrophilic spherical sol-gel silica particles-
To this methanol-water dispersion, 547.4 g (3.39 mol) of hexamethyldisilazane was added at room temperature, heated to 60 ° C., and reacted for 3 hours to trimethylsilylate the hydrophilic spherical sol-gel silica fine particles. Thereafter, the solvent in the dispersion was distilled off under reduced pressure to obtain 553.0 g of hydrophobic spherical sol-gel silica fine particles (2) having an average primary particle size of 0.12 μm and a hydrophobization degree of 58.

<Example 1> (Synthesis of highly hydrophobic spherical sol-gel silica fine particles)
-Heat treatment of hydrophobic spherical sol-gel silica particles-
100 g of hydrophobic spherical sol-gel silica fine particles (1) were placed in an electric furnace at 350 ° C. and heat-treated for 1 hour. 99.2 g of heat-treated spherical sol-gel silica fine particles having a hydrophobization degree of 41 were obtained.

-Hydrophobization of heat-treated spherical sol-gel silica particles-
70 g of the obtained heat-treated spherical sol-gel silica fine particles were placed in a 250 ml plastic bottle, 0.7 g of water was added thereto, sealed and left at 50 ° C. for 21 hours. Next, after allowing to cool, 3.5 g (0.018 mol) of hexamethyldisilazane was added and mixed as a hydrophobizing agent at room temperature, then sealed and left at 50 ° C. for 3 days. Thereafter, the film was dried at 100 ° C. for 16 hours under open conditions to obtain 65.9 g of highly hydrophobic spherical sol-gel silica fine particles having an average primary particle diameter of 0.11 μm and a hydrophobicity of 52. Using this highly hydrophobic spherical sol-gel silica fine particle, a test was conducted according to the following criteria. The results obtained are shown in Table 1.

[Preparation of external additive mixed toner (one-component developer)]
96 parts by mass of a polyester resin having a glass transition point (Tg) of 60 ° C. and a softening point of 110 ° C. and 4 parts by mass of a colorant (trade name: Carmine 6BC, manufactured by Sumika Color Co., Ltd.) are kneaded while melting and pulverized. After classification, a toner having an average particle diameter of 7 μm was obtained. 10 g of this toner was mixed with 0.3 g of highly hydrophobic spherical sol-gel silica fine particles by a sample mill to obtain an external additive mixed toner. The degree of aggregation of the external additive mixed toner was calculated by the following method.

[Cohesion]
The degree of aggregation is a value representing the fluidity of the powder. For the degree of aggregation, powder tester (manufactured by Hosokawa Micron Co., Ltd.) and 200 mesh (ie, 75 μm openings), 100 mesh (ie, 150 μm openings) and 60 mesh (ie, 250 μm openings) are screened in this order. Measured using a three-stage sieve piled up. The measuring means put 5g of toner powder on the upper 60 mesh sieve of the three-stage sieve, applies a voltage of 2.5V to the powder tester and vibrates the three-stage sieve for 15 seconds, then 60 From the powder mass a (g) remaining on the mesh sieve, the powder mass b (g) remaining on the 100 mesh sieve, and the powder mass c (g) remaining on the 200 mesh sieve, the following formula This is a method for calculating the degree of aggregation (%).

Aggregation degree (%) = (a + b × 0.6 + c × 0.2) × 100/5
It can be evaluated that the smaller the degree of aggregation, the better the fluidity, and the higher the degree of aggregation, the poorer the fluidity.

[Preparation of two-component developer]
A two-component developer was prepared by mixing 3 parts by mass of the external additive mixed toner and 97 parts by mass of ferrite (trade name: FL100, manufactured by Powdertech) as a carrier. Using this, the toner charge amount was measured by the following method, and the toner adhesion to the photoreceptor was evaluated.

[Toner charge amount]
The two-component developer is allowed to stand for 1 day under high temperature and high humidity (30 ° C, 90% RH) and low temperature and low humidity (10 ° C, 15% RH) conditions. Went. The charge amount of each sample was measured under the same conditions using a blow-off powder charge amount measuring device (Toshiba Chemical Co., Ltd., TB-200 type).

[Toner adherence to photoconductor and photoconductor wear]
The developer was put into a two-component modified developing machine equipped with an organic photoconductor, and a print test of 30,000 sheets was performed. At this time, the adhesion of the toner to the photoconductor can be detected as white spots in all solid images. Here, the degree of white spots, the white number of missing points are "many" more than 10 / cm ^2, 1-9 / cm ² or "small", and the 0 / cm ² was evaluated as "none" .

  Further, the photoconductor wear is detected as image disturbance in the print test. Here, an image having no image disturbance is evaluated as good and indicated as “A”, and an image having no large image disturbance (no problem in practical use) is evaluated as slightly good and indicated as “B”. An image having a disturbance in the image is evaluated as defective and indicated as “C”.

<Examples 2 to 5>
In the same manner as in Example 1, except that the hydrophobic spherical sol-gel silica fine particles, the heat treatment conditions and the hydrophobizing agent used in the hydrophobizing treatment were changed as shown in Table 1, the highly hydrophobic spherical sol-gel silica fine particles were used. Were prepared and tested. The results obtained are shown in Table 1.

<Comparative Synthesis Example 1> (Synthesis of hydrophobic spherical sol-gel silica fine particles (3))
-Synthesis of hydrophilic spherical sol-gel silica particles-
In a 3 liter glass reactor equipped with a stirrer, a dropping funnel, and a thermometer, 693.0 g of methanol, 46.0 g of water, and 55.3 g of 28 mass% ammonia water were added and mixed. The obtained solution was adjusted to 35 ° C., and 1293.0 g (8.5 mol) of tetramethoxysilane and 464.5 g of 5.4 mass% ammonia water were simultaneously added while stirring. The former was added dropwise over 6 hours and the latter over 4 hours. did. Stirring was continued for 0.5 hour after the dropping, and hydrolysis was carried out to obtain a methanol-water dispersion of hydrophilic spherical sol-gel silica fine particles.

-Hydrophobic treatment of hydrophilic spherical sol-gel silica particles-
To the obtained methanol-water dispersion, 48.4 g (0.3 mol) of hexamethyldisilazane was added at room temperature, heated to 60 ° C., and reacted for 3 hours to trimethylsilylate the hydrophilic spherical sol-gel silica fine particles. Thereafter, the solvent in the dispersion was distilled off under reduced pressure to obtain 548.3 g of hydrophobic spherical sol-gel silica fine particles (3) having an average primary particle size of 0.12 μm and a degree of hydrophobicity of 43.

<Comparative Synthesis Example 2> (Synthesis of hydrophobic spherical silica fine particles (5))
A 0.3 liter glass reactor equipped with a stirrer and a thermometer was charged with 100 g of deflagration silica (trade name: SO-C1, manufactured by Admatechs), 1 g of pure water was added with stirring, and after sealing, another 60 Stir at 0 ° C. for 10 hours. Subsequently, after cooling to room temperature, 2 g of HMDS was added with stirring, and after sealing, the mixture was further stirred for 24 hours. The temperature was raised to 120 ° C., and the remaining raw material and generated ammonia were removed while ventilating nitrogen gas. Hydrophobic spherical silica fine particles (5) of 100 g having a degree of hydrophobicity of 58 and an average primary particle size of 0.3 μm were added. Obtained.

<Comparative Examples 1-11>
In Example 1, high-hydrophobic silica fine particles were prepared in the same manner as in Example 1 except that the silica fine particles, the heat treatment conditions thereof, and the hydrophobizing agent used for the hydrophobizing treatment were changed as shown in Table 2 or 3. The test was conducted. The results obtained are shown in Table 1.

* Silica fine particles (4): Hydrophobic silica obtained by hydrophobizing fumed silica (trade name: Aerosil R972, manufactured by Nippon Aerosil Co., Ltd., degree of hydrophobicity 52, aggregate of primary particles)
* Silica fine particles (6): Hydrophobic silica with hydrophobized silica surface (trade name: Nipsil SS50F, manufactured by Nippon Silica Co., Ltd., degree of hydrophobicity 64, aggregate of primary particles)

Claims (12)

  Hydrophobyl oxysilane or its partially hydrolyzed condensation product or a combination thereof hydrolyzed and condensed hydrophilic spherical sol-gel silica fine particles obtained by hydrolyzing and having a hydrophobization degree of 50 or more A step of heat-treating hydrophobic spherical sol-gel silica fine particles having an average primary particle diameter of 0.01 to 5 μm to obtain heat-treated spherical sol-gel silica fine particles having a degree of hydrophobicity of less than 50; A method for producing highly hydrophobic spherical sol-gel silica fine particles having a hydrophobization degree of 50 or more and an average primary particle diameter of 0.01 to 5 μm. Hydrophobic spherical sol-gel silica fine particles subjected to the heat treatment have R ³ ₃ SiO _1/2 units (wherein R ³ is the same or different on the surface of hydrophilic spherical sol-gel silica fine particles consisting essentially of SiO ₂ units. , A substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms). Before the hydrophobic treatment of the hydrophilic spherical sol-gel silica fine particles introduces R ³ ₃ SiO _1/2 units on the surface of the hydrophilic spherical sol-gel silica fine particles, R ⁴ SiO _3/2 units (in the formula, , R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms).   The manufacturing method according to any one of claims 1 to 3, wherein the heat treatment is performed at a temperature of 320 to 600 ° C.   The manufacturing method according to any one of claims 1 to 4, wherein the hydrophobizing treatment of the heat-treated spherical sol-gel silica fine particles is performed by a hydrophobizing agent comprising a silicone oil, a silazane compound, a silane compound, or a combination thereof.   The manufacturing method according to claim 5, wherein the silicone oil is dimethyl silicone oil. The silazane compound is represented by the following general formula (3):
R ³ ₃ SiNHSiR ³ ₃ (3)
(Wherein R ³ is the same as above)
The production method according to claim 5 or 6, which is a silazane compound represented by the formula: The silane compound is represented by the following general formula (4):
R ³ ₃ SiX (4)
(Wherein R ³ is the same as above, and X is an OH group or a hydrolyzable group)
The production method according to claim 5, wherein the monofunctional silane compound is represented by the formula:   Highly hydrophobic spherical sol-gel silica fine particles obtained by the production method according to any one of claims 1 to 8.   A toner external additive for developing electrostatic images obtained from the highly hydrophobic spherical sol-gel silica fine particles according to claim 9.   A developer comprising the toner external additive according to claim 10 and toner particles. The developer according to claim 11, further comprising a carrier.