JP2011032114A - Hydrophobic spherical silica fine particle, method for producing the same and toner external additive for electrostatic charge image development using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrophobic spherical silica fine particle useful as a toner external additive and capable of improving the environmental stability of electrostatic charge of a toner. <P>SOLUTION: The hydrophobic spherical silica fine particle is obtained by a hydrophobic treatment comprising: introducing an R<SP>4</SP>SiO<SB>3/2</SB>unit (wherein R<SP>4</SP>is a 1-20C monovalent hydrocarbon group) into a surface of a hydrophilic spherical silica fine particle comprising an SiO<SB>2</SB>unit obtained by hydrolyzing and condensing at least one compound selected from the group consisting of tetrahydrocarbyloxysilane compounds represented by the general formula (1): Si(OR<SP>1</SP>)<SB>4</SB>(1) (wherein R<SP>1</SP>s are the same or different and each is a 1-6C monovalent hydrocarbon group) and partial hydrolysis/condensation products thereof; and further introducing an R<SP>6</SP><SB>3</SB>SiO<SB>1/2</SB>unit (wherein R<SP>6</SP>s are the same or different and each is a 1-20C monovalent hydrocarbon group). The hydrophobic spherical silica fine particle has a carbon content of 2-5 mass%, a hydrocarbyloxy group content of 0.3-5 mass% and a particle diameter of 0.01-5 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to hydrophobic spherical silica fine particles, and particularly to hydrophobic spherical silica fine particles having a high carbon content and high hydrocarbyloxy group content. Further, the present invention relates to a small particle size toner external additive for developing an electrostatic image used for improving image quality.

  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 particular, inorganic fine particles are often added to the toner in order to improve fluidity, caking resistance, fixing properties, and cleaning properties. However, the dispersibility of the inorganic fine particles has a great influence on the toner characteristics, and when the dispersibility is not uniform, 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 photoconductor, which may cause black spot image defects. For the purpose of improving these problems, various inorganic fine particles whose surface has been subjected to a hydrophobic treatment have been proposed, and many silica fine particles whose surface has been subjected to a hydrophobic treatment have been proposed.

  Synthetic silica fine particles that are the base material are combusted silica (that is, fumed silica) obtained by burning a silane compound, explosive silica obtained by explosively burning metal silicon powder, sodium silicate. From wet silica obtained by neutralization reaction of mineral acid with mineral acid (among those synthesized and agglomerated under alkaline conditions are precipitated silica, and those synthesized and agglomerated under acidic conditions are called gel silica), sodium silicate Colloidal silica (silica sol) obtained by alkalizing and polymerizing acidic silicic acid obtained by sodium removal with an ion exchange resin, and sol-gel silica (so-called Stöber method) obtained by hydrolysis of hydrocarbyloxysilane. The

  As the hydrophobizing method, hydrophobizing treatment is performed by bringing silica fine particle powder into contact with a hydrophobizing agent such as a surfactant, silicone oil, or a silylating agent such as alkylhalogenosilane, alkylalkoxysilane, or alkyldisilazane. And a hydrophobization treatment by contacting with a silylating agent in a mixed solvent of water and a hydrophilic organic solvent.

  For example, inorganic fine particles treated with silicone oil (JP-A-8-292598: Patent Document 1), silica fine particles treated with silicone oil (JP-A 2000-172003, JP-A 2003-195556, JP-A 2006). -206413 gazette: Patent Documents 2 to 4) and silica treated with silane (Japanese Patent Laid-Open Nos. 2005-3726 and 2005-121835: Patent Documents 5 and 6).

  Further, the surface of the hydrophilic spherical silica fine particles produced by hydrolysis of alkoxysilane is subjected to a first-stage hydrophobization treatment, and the surface of the resulting hydrophobic silica fine particles is triorganosilylated, that is, a second-stage hydrophobized. Hydrophobization has been proposed by a hydrophobizing process (Japanese Patent Laid-Open No. 2000-330328: Patent Document 7).

  Although the silica fine particles whose surface has been subjected to a hydrophobic treatment improve the fluidity of the toner, the charging characteristics of the toner, particularly the environmental stability of charging, are deteriorated.

JP-A-8-292598 JP 2000-172003 A JP 2003-195556 A JP 2006-206413 A Japanese Patent Laid-Open No. 2005-3726 JP 2005-121835 A JP 2000-330328 A

The present invention has been made in view of the above circumstances, and an object thereof is to provide a hydrophobic spherical silica fine particle capable of improving the environmental stability of charging of a toner and a method for producing the same.
Another object of the present invention is to provide an external toner additive for developing electrostatic images using the hydrophobic spherical silica fine particles.

As a result of intensive studies to achieve the above object, the present inventors have converted a tetrafunctional silane compound and / or a partially hydrolyzed condensation product thereof into a hydrophilic organic solvent and water in the presence of a basic substance. When the hydrophilic spherical silica fine particles are produced by hydrolysis and condensation in a mixed medium, a hydrophilic spherical silica fine particle mixed medium dispersion having a water content of 20% by mass or less is obtained, and the water content is 20% by mass. By introducing R ⁴ SiO _3/2 units and then R ⁶ ₃ SiO _1/2 units into the silica fine particles in the following dispersion, the carbon content is 2 to 5% by mass and the hydrocarbyloxy group content is 0.3. It has been found that high hydrophobic spherical silica fine particles of ˜5% by mass can be obtained, and the silica fine particles can be used as an external toner additive to improve the environmental stability of toner charging.

That is, the inventors first
(A) (a-1) General formula (1):
Si (OR ¹ ) ₄ (1)
(In the formula, R ¹ are identical or different, is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Hydrolysis of at least one compound selected from the group consisting of a tetrafunctional silane compound and a partial hydrolysis-condensation product thereof in a mixed medium of a hydrophilic organic solvent and water in the presence of a basic substance Condensing to produce hydrophilic spherical silica fine particles;
(A-2) An aqueous dispersion of hydrophilic spherical silica fine particles having a water content of 90% by mass or more by removing the hydrophilic organic solvent from the mixed medium used as a solvent and replacing the medium with water. Obtaining
(B) R ⁴ SiO _3/2 units on the surface of the hydrophilic spherical silica fine particles in the hydrophilic spherical silica fine particle aqueous dispersion (wherein R ⁴ is a substituted or unsubstituted 1 to 1 carbon atom having 1 to 20 carbon atoms). A first-order hydrophobic spherical silica fine particle,
(C) R ⁶ ₃ SiO _1/2 unit (wherein R ⁶ is the same or different and is substituted or unsubstituted, 1 to 6 carbon atoms) on the surface of the obtained primary hydrophobic spherical silica fine particles. A secondary hydrocarbon silica fine particle by introducing a secondary hydrocarbon silica fine particle),
Proposed to obtain hydrophobic cyclic silica fine particles having a hydrocarbyloxy group content of 1,000 ppm or less (Japanese Patent Laid-Open No. 2008-174430).
On the other hand, as described above, when the carbon content and the amount of hydrocarbyloxy group are increased, it has been surprisingly found that the environmental stability of toner charging can be improved, and the present invention has been made. .

As a means for solving the above problems, the present invention firstly
The following general formula (1):
Si (OR ¹ ) ₄ (1)
(In the formula, R ¹ are identical or different, is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Surface of hydrophilic spherical silica fine particles comprising SiO ₂ units obtained by hydrolyzing and condensing at least one compound selected from the group consisting of tetrahydrocarbyloxysilane compounds and partial hydrolysis-condensation products thereof R ⁴ SiO _3/2 unit (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) is further introduced into R ⁶ ₃ SiO _1/2 unit ( In which R ⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms.) Hydrophobic spherical silica fine particles having a carbon content of 2 to 5% by mass, a hydrocarbyloxy group content of 0.3 to 5% by mass, and a particle size of 0.01 to 5 μm are provided.

The present invention secondly, as a method for producing the above-mentioned hydrophobic spherical silica fine particles,
(A) The following general formula (1):
Si (OR ¹ ) ₄ (1)
(In the formula, R ¹ are identical or different, is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Hydrolysis of at least one compound selected from the group consisting of a tetrafunctional silane compound and a partial hydrolysis-condensation product thereof in a mixed medium of a hydrophilic organic solvent and water in the presence of a basic substance And condensing to produce hydrophilic spherical silica fine particles to obtain a hydrophilic spherical silica fine particle mixed medium dispersion having a water content of 20% by mass or less;
(B) R ⁴ SiO _3/2 units on the surface of the hydrophilic spherical silica fine particles in the hydrophilic spherical silica fine particle mixed medium dispersion (wherein R ⁴ is a substituted or unsubstituted 1 to 20 carbon atom number 1). A first-order hydrophobic spherical silica fine particle,
(C) R ⁶ ₃ SiO _1/2 unit (wherein R ⁶ is the same or different and is a substituted or unsubstituted monovalent valence of 1 to 6 carbon atoms) on the surface of the obtained primary hydrophobic spherical silica fine particles. A hydrocarbon group) to obtain secondary hydrophobic silica fine particles,
A production method is provided.
Furthermore, the present invention provides an external toner additive for developing electrostatic images comprising the hydrophobic spherical silica fine particles.

  The hydrophobic spherical silica fine particles of the present invention are useful as an external toner additive, and can improve the environmental stability of toner charging. Further, since the toner external additive does not react or interact with the organic photoreceptor, the photoreceptor is unlikely to be altered or scraped. Further, since it has excellent dispersibility and good fluidity, toner adhesion to the photoreceptor does not occur, and the charging property does not depend on environmental conditions. By using this toner external additive, high image quality can be achieved by applying it to the development of electrostatic images in electrophotography, electrostatic recording, and the like.

Hereinafter, the present invention will be described in detail.
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 (Stober method). Of these, the present invention relates to sol-gel silica.

<Characteristics of hydrophobic spherical silica fine particles>
First, the characteristics of the hydrophobic spherical silica fine particles of the present invention will be described in detail. The silica fine particles of the present invention have R ⁴ SiO _{3 on} the surface of hydrophilic spherical silica fine particles composed of SiO ₂ units obtained by hydrolysis and condensation of a tetrafunctional silane compound and / or a partial hydrolysis condensation product thereof. _{/ 2} unit (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms), and further R ⁶ ₃ SiO _1/2 unit (wherein R ⁶ is The same or different, substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms), which is obtained by hydrophobizing spherical silica fine particles having a carbon content of 2 to 5 mass %, Preferably 2 to 4% by mass.
When the carbon content is less than 2% by mass, the environmental stability of toner charging is deteriorated, and when it exceeds 5% by mass, the charge amount of the toner is lowered.

  The hydrocarbyloxy group content of the silica fine particles is 0.3 to 5% by mass, preferably 2 to 5% by mass, and particularly preferably 3 to 5% by mass. When the hydrocarbyloxy group content is less than 0.3% by mass, the environmental stability of charging of the toner is deteriorated. When the hydrocarbyloxy group content exceeds 5% by mass, the fluidity of the toner becomes insufficient due to the influence of this polar group, or the charge amount Is lowered.

  With respect to the hydrophobic spherical silica fine particles of the present invention, “spherical” includes not only true spheres but also slightly distorted spheres. Specifically, “spherical” means that the circularity when particles are projected two-dimensionally is in the range of 0.8-1. Here, the circularity means (peripheral length of a perfect circle equal to the area of the figure when an actual particle is projected two-dimensionally) / (perimeter of the area of the figure when an actual particle is projected two-dimensionally) To do.

  The particle diameter of the fine particles is 0.01 to 5 μm, preferably 0.05 to 0.5 μm, and particularly preferably 0.1 to 0.2 μm. When the particle diameter is smaller than 0.01 μm, the fine particles aggregate to cause insufficient developer fluidity, caking resistance, fixing properties, and the like. This causes inconveniences such as deterioration or shaving of the toner and a decrease in adhesion of the fine particles to the toner. Here, “particle diameter” means a volume-based median diameter.

<Synthesis of hydrophobic spherical silica fine particles>
Next, the method for producing the hydrophobic spherical silica fine particles of the present invention will be described in detail. The hydrophobic spherical silica fine particles are, for example, a step of producing hydrophilic spherical silica fine particles having many hydrocarbyloxy groups by a sol-gel method (step (A)), and the surface of the hydrophilic spherical silica fine particles is hydrophobized in the first stage. A step of treating (step (B)), a step of triorganosilylation of the surface of the obtained primary hydrophobic spherical silica fine particles, ie, a second step of hydrophobizing treatment (step (C)), and It is obtained by a method having Hereinafter, each process will be described.

-Synthesis of hydrophilic spherical silica fine particles (step (A))-
(A) A process is the following general formula (1):
Si (OR ¹ ) ₄ (1)
(In the formula, R ¹ are identical or different, is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
In a mixed medium of a hydrophilic organic solvent and water in the presence of a basic substance, at least one compound selected from the group consisting of a tetrafunctional silane compound and / or a partially hydrolyzed condensation product thereof In this step, hydrophilic spherical silica fine particles are produced by hydrolysis and condensation to obtain a hydrophilic spherical silica fine particle mixed medium dispersion having a water content of 20% by mass or less.

  In the above process, when the water content exceeds 20% by mass, the hydrocarbyloxy group is sufficiently hydrolyzed because the amount of water in the dispersion is large, and the residual hydrocarbyloxy group content in the silica fine particles is reduced. End up.

The hydrolyzable group OR ¹ is a hydrocarbyloxy group, and examples thereof include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a hexyloxy group, and a phenoxy group, preferably a methoxy group and an ethoxy group. It is done.

In the general formula (1), R ¹ is preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms, more preferably 1 to 4, and still more preferably 1 to 2. 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. Silane, 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), the partial hydrolysis-condensation product, and water. For example, alcohols Cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve acetate, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane and tetrahydrofuran, preferably alcohols and cellosolves, particularly preferably alcohols . As alcohols, the following general formula (2):
R ³ OH (2)
(In the formula, R ³ is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
The alcohol shown by is mentioned.

In the general formula (2), R ³ 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 ³ include alkyl groups 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 spherical silica fine particles to be generated increases. Therefore, it is desirable to select the type of alcohol according to the particle diameter of the target spherical silica fine particles.

  Examples of the basic substance include ammonia and di-lower alkylamines such as dimethylamine and diethylamine, preferably ammonia and 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 total amount of water used in this hydrolysis reaction is 0. 0 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 its partial hydrolysis condensation product. It is preferably 5 to 5 mol, more preferably 0.6 to 2 mol, and particularly preferably 0.7 to 1 mol. The ratio of the hydrophilic organic solvent to water is preferably 0.5 to 10 by 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 1 mol in total of the hydrocarbyloxy groups 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 or the like represented by the general formula (1) can be carried out by a well-known method, that is, in a mixture of a hydrophilic organic solvent containing a basic substance and water by the general formula (1). It is performed by adding a tetrafunctional silane compound or the like shown. In this case, the hydrolysis and condensation temperatures are usually 10 to 60 ° C., particularly 20 to 50 ° C., and the time is not particularly limited, but is usually 1 to 10 hours.

  The hydrophilic spherical silica fine particles obtained in this manner are subjected to a first-stage hydrophobization treatment in the step (B).

-Surface hydrophobization treatment of hydrophilic spherical silica fine particles (step (B))-
In the step (B), R ⁴ SiO _3/2 units are formed on the surface of the hydrophilic spherical silica fine particles (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms). Is a step of obtaining primary hydrophobic spherical silica fine particles, that is, a step of performing a first-stage hydrophobic treatment. For example, in the mixed medium dispersion containing the hydrophilic spherical silica fine particles and having a water content of 20% by mass or less, the following general formula (3):
R ⁴ Si (OR ⁵ ) ₃ (3)
(In the formula, R ⁴ is the same as above, and R ⁵ is the same or different and is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
The surface of the hydrophilic spherical silica fine particles is treated by adding a trifunctional silane compound represented by the formula (1) or a partially hydrolyzed condensation product thereof, or a mixture thereof to obtain a mixed medium dispersion of primary hydrophobic spherical silica fine particles. .

In the general formula (3), 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 (3), 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 (3) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, and n-propyltriethoxy. Trialkoxysilanes such as silane, isopropyltrimethoxysilane, isopropyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, trifluoropropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, etc., preferably , Methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, more preferably methyltrimethoxysilane, methyltriethoxysilane, These partial hydrolysis-condensation product thereof.

The addition amount of the trifunctional silane compound represented by the general formula (3) is 0.001 to 1 mol, preferably 0.01 to 0.1 mol, per mol of SiO ₂ unit of the hydrophilic spherical silica fine particles used. Especially preferably, it is 0.01-0.05 mol. In this step, the treatment temperature can be 10 to 70 ° C., particularly 20 to 60 ° C., and the treatment time is not particularly limited, but is usually 1 to 5 hours.

-Surface triorganosilylation treatment of hydrophobic spherical silica fine particles (step (C))-
In the step (C), R ⁶ ₃ SiO _1/2 units (wherein R ⁶ is the same or different and substituted or unsubstituted are present on the surface of the primary hydrophobic spherical silica fine particles obtained in the step (B). A monovalent hydrocarbon group having 1 to 6 carbon atoms), that is, a step of performing a second-stage hydrophobization treatment. For example, the dispersion medium of the hydrophobic spherical silica fine particle mixed medium dispersion is converted into a ketone solvent to obtain a ketone solvent dispersion of the hydrophobic spherical silica fine particles, and the ketone solvent dispersion of the hydrophobic spherical silica fine particles. The following general formula (4):
R ⁶ ₃ SiNHSiR ⁶ ₃ (4)
(Wherein R ⁶ is the same as above)
Or a silazane compound represented by the following general formula (5):
R ⁶ ₃ SiX (5)
(In the formula, R ⁶ is the same as above, and X is an OH group or a hydrolyzable group.)
The monofunctional silane compound shown by these, or a mixture thereof, is added, and the reactive group which remains on the surface of the hydrophobic spherical silica fine particles is triorganosilylated.

In the general formulas (4) and (5), R ⁶ 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 ⁶ 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 an alkoxy group such as a chlorine atom, a methoxy group and an ethoxy group, an acyloxy group such as an amino group, an acetoxy group and a propionyloxy group, preferably an alkoxy group and an amino group. Particularly preferred is an alkoxy group.

  In order to convert the dispersion medium of the spherical silica fine particle mixed medium dispersion into a ketone solvent, an operation of adding a ketone solvent to the dispersion liquid and distilling off the mixed solvent from the mixture (repeating this operation as necessary) ).

  The amount of the ketone solvent added at this time is 0.5 to 5 times, preferably 2 to 5 times, particularly, 2 to 5 times by mass with respect to the hydrophilic spherical silica fine particles in the spherical silica fine particle mixed medium dispersion. The amount is preferably 3 to 4 times. Examples of the ketone solvent include methyl ethyl ketone, methyl isobutyl ketone, and acetylacetone, and methyl isobutyl ketone is preferable.

  Examples of the silazane compound represented by the general formula (4) include hexamethyldisilazane and hexaethyldisilazane, and hexamethyldisilazane is preferable. Examples of the monofunctional silane compound represented by the general formula (5) include monosilanol compounds such as trimethylsilanol and triethylsilanol, monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane, and monoalkoxy such as trimethylmethoxysilane and trimethylethoxysilane. Examples include monoaminosilanes such as silane, trimethylsilyldimethylamine, and trimethylsilyldiethylamine, and monoacyloxysilanes such as trimethylacetoxysilane, preferably trimethylsilanol, trimethylmethoxysilane, and trimethylsilyldiethylamine, and particularly preferably trimethylsilanol and trimethylmethoxysilane. .

These are used in an amount of 0.05 to 0.5 mol, preferably 0.1 to 0.3 mol, particularly preferably 0.15 to 0 mol, based on 1 mol of SiO ₂ units of the hydrophilic spherical silica fine particles used. .25 moles. In this step, the processing temperature is usually 40 to 140 ° C, particularly 60 to 120 ° C. The treatment time is not particularly limited, but is usually 1 to 10 hours.

  The hydrophobic spherical silica fine particles 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 silazane.

<Toner external additive comprising hydrophobic spherical silica fine particles>
The hydrophobic spherical silica fine particles of the present invention are useful as an external toner additive. The blending amount of the toner external additive composed of fine particles (hereinafter also simply referred to as “fine particles”) with respect to the toner is usually 0.01 to 20 parts by mass, preferably 0.1 to 100 parts by mass with respect to 100 parts by mass of the toner. 5 parts by mass, particularly preferably 1 to 2 parts by mass. If the blending amount is too small, the adhesion amount to the toner is small and sufficient fluidity cannot be obtained, and if it is too large, the chargeability of the toner is adversely affected.

  The adhesion state of the fine particles to the toner particle surface may be merely mechanically adhered or may be loosely fixed. The adhered fine particles may cover the entire surface of the toner particles or only a part thereof. Further, the fine particles may partially form aggregates and cover the surface of the toner particles, but are preferably covered in the form of single layer particles.

  Examples of the toner particles to which the fine particles of the present invention can be applied include known toner particles containing a binder resin and a colorant as main components, and a charge control agent or the like is further added as necessary. Also good.

  The toner to which the toner external additive comprising fine particles of the present invention is added is used, for example, for developing an electrostatic image used for developing an electrostatic image by electrophotography, electrostatic recording method or the like. The The toner can be used as a one-component developer, but it can also be used as a two-component developer by mixing it with a carrier. When used as a two-component developer, the toner external coating may not be added to the toner particles in advance, but may be added when the toner and the carrier are mixed to cover the surface of the toner. As the carrier, known ones, for example, ferrite, iron powder and the like, or those coated on the surface thereof can be used.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The following examples do not limit the present invention.

[Example 1]
[Synthesis of hydrophobic spherical silica-based fine particles]
-Synthesis of hydrophilic spherical silica fine particles (step (A))-
In a 3 liter glass reactor equipped with a stirrer, a dropping funnel, and a thermometer, 690 g of methanol, 26 g of water, and 58 g of 25 mass% aqueous ammonia were mixed. The solution was adjusted to 30 ° C., and 1,200 g (7.88 mol) of tetramethoxysilane and 432 g of 5.4 mass% ammonia water were simultaneously added while stirring, and each was added dropwise over 5 hours. . Even after the completion of the dropwise addition, the mixture was further stirred for 0.5 hour for hydrolysis and condensation to obtain a mixed medium dispersion of hydrophilic spherical silica fine particles. At this time, according to gas chromatographic analysis, the water content in the mixed medium dispersion was 16.1% by mass.

-Surface hydrophobization treatment of hydrophilic spherical silica fine particles (first step hydrophobization step) ((B) step)-
To this mixed medium dispersion liquid, 12 g (0.088 mol) of methyltrimethoxysilane was added dropwise at room temperature over 0.5 hours, and then heated to 50 ° C. for 1 hour to hydrophobize the surface of silica fine particles. Thus, a hydrophobic spherical silica fine particle mixed medium dispersion was obtained.

-Surface triorganosilylation treatment of hydrophobic spherical silica particles (second stage hydrophobization process)
(Step (C))-
Next, an ester adapter and a condenser tube are attached to a glass reactor, and the suspension is heated to 60 to 70 ° C. to distill off 345 g of a mixture of methanol and water, and then methyl isobutyl ketone is added. A mixture of methanol, water and methyl isobutyl ketone was distilled off simultaneously until the dispersion reached 115 ° C. At this time, the amount of methyl isobutyl ketone added was 1,954 g, and the amount of distillate was 1,954 g. After adding 150 g (0.93 mol) of hexamethyldisilazane to the obtained methyl isobutyl ketone dispersion at room temperature, this dispersion is heated to 110 ° C. and allowed to react for 3 hours. Silica fine particles were trimethylsilylated. Next, the solvent in this dispersion was distilled off at 80 ° C. under reduced pressure (6,650 Pa) to obtain 466 g of hydrophobic spherical silica-based fine particles.

  The final hydrophobic spherical silica fine particles obtained by the above steps were measured for carbon content, alkoxy group content, particle size, and shape according to the following measurement methods 1 to 4. The obtained results are shown in Table 1.

Measurement method 1: Carbon content of hydrophobic spherical silica fine particles The measurement was performed using EMIA-110 manufactured by Horiba, Ltd. by a combustion method. A sample of 0.1 g was carefully evaluated as a magnetic board, burned at about 1,200 ° C., and the amount of carbon was calculated from the amount of CO ₂ .

Measurement method 2: Alkoxy group content of hydrophobic spherical silica fine particles 10 g of 1N potassium hydroxide-isopropyl alcohol solution is added to 5 g of silica fine particles, heated at 70 ° C. for 1 hour to decompose the silica, and then the liquid content is reduced. Taken by distillation. The fraction of the alkoxy groups contained in the silica fine particles was quantified by gas chromatographic analysis of this fraction and quantifying the amount of methanol contained.

Measurement method 3: Measurement of particle diameter of hydrophobic spherical silica fine particles Silica fine particles were added to methanol so as to be 0.5% by mass and subjected to ultrasonic waves for 10 minutes to disperse the fine particles. The particle size distribution of the 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 volume-based median diameter was defined as the particle size. The median diameter is a particle diameter corresponding to 50% cumulative when the particle size distribution is expressed as a cumulative distribution.

Measurement method 4: Shape measurement of hydrophobic spherical silica fine particles The shape was confirmed by observation with an electron microscope (manufactured by Hitachi, trade name: S-4700 type, magnification: 100,000 times). “Spherical” means that the degree of circularity when the particles are projected two-dimensionally is in the range of 0.8 to 1, as described above.

[Preparation of external additive mixed toner]
96 parts by mass of a polyester resin having a glass transition temperature T _{g of} 60 ° C. and a softening point of 110 ° C. and 4 parts by mass of a colorant (manufactured by Sumitomo Color Co., Ltd., trade name: Carmine 6BC) are melt-kneaded, pulverized and classified. As a result, a toner having an average particle diameter of 7 μm was obtained. 40 g of this toner was mixed with 1 g of the above surface-treated spherical hydrophobic silica fine particles by a sample mill to obtain an external additive mixed toner.

[Developer preparation]
5 parts by weight of the external additive mixed toner prepared above and 95 parts by weight of a carrier coated with a polymer obtained by polyblending a perfluoroalkyl acrylate resin and an acrylic resin on a ferrite core having an average particle diameter of 85 μm are mixed together to prepare a developer. Was prepared. Using this developer, the toner charge amount, toner adhesion to the photoreceptor, and toner fluidity were measured according to the following measurement methods 5 to 7. The obtained results are shown in Table 1.

Measurement method 5: Measurement of toner charge amount The developer is left for one day under conditions of high temperature and high humidity (30 ° C., 90% RH) or low temperature and low humidity (10 ° C., 15% RH), and then shaken. The mixture was mixed for 30 seconds to perform tribocharging. The charge amount of each sample was measured using a blow-off powder charge amount measuring device (trade name: TB-200, manufactured by Toshiba Chemical Corporation) under the same conditions. By determining the difference in toner charge amount under the above two conditions, the environmental dependency of the toner was evaluated.

Measurement method 6: Measurement of toner adhesion to the photoconductor The above developer was placed in a two-component modified developer equipped with an organic photoconductor, and a 30,000 print test was performed. The poor adhesion of toner to the photoreceptor can be detected as white spots in all solid images. The degree of white spots was evaluated according to the following criteria.
White spots more than 10 / cm ^2: many white spots 1 to 9 / cm ^2: little white spots 0 / cm ^2: None

Measurement method 7: Measurement of toner fluidity The toner fluidity was measured using a powder fluidity analyzer FT-4 (manufactured by Sysmex Corporation). The measurement principle of this apparatus will be described. A cylindrical container placed vertically is filled with powder, and while rotating two rotating blades (blades) provided at the tip of a vertical shaft rod in the powder, a certain distance (from height H1) Down to H2. The force received from the powder at this time is measured separately for the torque component and the load component, so that each work (energy) associated with the blade descending from H1 to H2 is obtained, and then the total energy amount of both Asked. The smaller the total energy measured in this way, the better the fluidity of the powder, so it was used as an index of powder fluidity.
··conditions:
Container: In the test, a glass cylindrical container having a volume of 120 ml, an inner diameter of 80 mm, and a length of 60 mm was used.
Blade: Two blades were attached horizontally facing the tip of a stainless steel shaft rod inserted vertically into the center of the cylindrical container. A blade having a diameter of 48 mm was used in the case of a container having a volume of 120 ml.
Length from H1 to H2: 50 mm for a container with a volume of 120 ml.
..Stability test:
As described above, the powder flow characteristics were observed when the powder filled in the measurement container was allowed to flow from a stationary state. The total energy amount was continuously measured 7 times under the condition that the rotational speed of the blade tip was 100 mm / sec. Table 7 shows the total amount of energy for the seventh time (referred to as basic fluidity energy because it is the most stable state).

[Example 2]
Hydrophobic hydrophobicity was obtained in the same manner as in Example 1 except that the hydrophilic spherical silica fine particle synthesis step (step (A)) was changed to a hydrolysis temperature of 35 ° C. to obtain a mixed medium dispersion of hydrophilic spherical silica fine particles. 461 g of spherical silica fine particles were obtained as a dry powder. Measurement was performed in the same manner as in Example 1 using the hydrophobic spherical silica fine particles. The results are shown in Table 1.

[Comparative Example 1]
The mixed medium dispersion of the hydrophilic spherical silica fine particles obtained in the step of synthesizing the hydrophilic spherical silica fine particles in Example 1 (step (A)) is heated to 60 to 70 ° C. to distill off 1,132 g of methanol. Thereafter, 1,200 g of water was added, and then the mixture was further heated to 70 to 90 ° C. to distill away 273 g of methanol to obtain an aqueous suspension of hydrophilic spherical silica fine particles (water content: 87.2% by mass). It was.
This aqueous suspension was subjected to the first step hydrophobization step ((B) step) and the second step hydrophobization step ((C) step) in the same manner as in Example 1, and 472 g of the hydrophobic spherical silica fine particles were dried into powder. Got as. Evaluation was performed in the same manner as in Example 1 using the hydrophobic spherical silica fine particles. The results are shown in Table 1.

[Comparative Example 2]
240 g of hexamethyldisilazane was added at room temperature to the mixed medium dispersion of the hydrophilic spherical silica fine particles obtained in the step of synthesizing the hydrophilic spherical silica fine particles (step (A)) in Example 1, and heated to 120 ° C. The silica fine particles were trimethylsilylated by reacting for 3 hours. Subsequently, water was distilled off at 120 ° C. under reduced pressure (6,650 Pa) to obtain 448 g of hydrophobic spherical silica fine particles as a dry powder. Evaluation was performed in the same manner as in Example 1 using the hydrophobic spherical silica fine particles. The results are shown in Table 1.

[Comparative Example 3]
240 g of hexamethyldisilazane is added at room temperature to the aqueous suspension of hydrophilic spherical silica fine particles obtained in Comparative Example 1 (water content: 87.3% by mass), heated to 120 ° C., and reacted for 3 hours. As a result, the silica fine particles were trimethylsilylated. Subsequently, the mixture of methanol and water was distilled off at 80 ° C. under reduced pressure (6,650 Pa) to obtain 463 g of hydrophobic spherical silica fine particles as a dry powder. Evaluation was performed in the same manner as in Example 1 using the hydrophobic spherical silica fine particles. The results are shown in Table 1.

[Comparative Example 4]
In Example 1, the surface hydrophobization treatment (step (B)) of silica fine particles using methyltrimethoxysilane which is the first step hydrophobization step is omitted, and the step of synthesizing hydrophilic spherical silica fine particles (step (A)) ) To the second-stage hydrophobizing step (step (C)) and adding 1,440 g of methyl isobutyl ketone. Then, the mixture was heated to 80 to 110 ° C. and 800 g of a mixture of methanol and water was distilled off over 6 hours. As a result, the dispersion of hydrophilic spherical silica fine particles coagulated.

[Comparative Example 5]
In Example 1, the surface hydrophobization treatment (step (B)) of silica fine particles using methyltrimethoxysilane, which is the first step hydrophobization step, was omitted, and the hydrophilic spherical silica fine particles obtained in Comparative Example 1 were omitted. The aqueous suspension (water content 87.0% by mass) was directly subjected to the second-stage hydrophobization step (step (C)), 1,440 g of methyl isobutyl ketone was added, and then heated to 80 to 110 ° C., When 820 g of a mixture of methanol and water was distilled off over 6 hours, a dispersion of hydrophilic spherical silica fine particles coagulated.

[Comparative Example 6]
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 under stirring, and after sealing, Furthermore, it stirred at 60 degreeC for 10 hours. Next, after cooling to room temperature, 2 g of hexamethyldisilazane 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 to obtain 100 g of hydrophobic spherical silica fine particles. Evaluation was performed in the same manner as in Example 1 using the hydrophobic spherical silica fine particles. The results are shown in Table 2.

[Comparative Example 7]
Hydrophobic silica obtained by hydrophobizing fumed silica (trade name: Aerosil R972, manufactured by Nippon Aerosil Co., Ltd., primary particle aggregate, dimethyldichlorosilane treatment instead of the hydrophobic spherical silica fine particles prepared in Example 1 Product) was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[Comparative Example 8]
Instead of the hydrophobic spherical silica fine particles prepared in Example 1, hydrophobic silica (trade name: Nipsil SS50F, manufactured by Nippon Silica Co., Ltd., primary particle aggregate) whose surface was subjected to a hydrophobization treatment was used. Evaluation was conducted in the same manner as in Example 1. The results are shown in Table 2.

<Evaluation>
In Examples 1 and 2, hydrophobic spherical silica fine particles satisfying the conditions of the present invention were obtained, and thus a toner external additive having desired characteristics was obtained.
In Comparative Example 1, since the water content in the aqueous suspension of hydrophilic spherical silica fine particles is high in the step (A), the obtained hydrophobic spherical silica fine particles satisfy the conditions of the present invention in terms of carbon content. As a result, the toner external additive composed of the fine particles could not impart good fluidity and chargeability independent of environmental conditions to the toner.
In Comparative Example 2, the hydrophilic spherical silica fine particles obtained in the step (A) were not subjected to the first-stage hydrophobization treatment essential in the method of the present invention, and trimethylsilyl in an aqueous suspension having a low water content. It has become. The toner external additive composed of the fine particles cannot impart good fluidity and chargeability independent of environmental conditions to the toner, and further causes toner adhesion to the photoreceptor.
In Comparative Example 3, trimethylsilyl which does not correspond to the first-stage hydrophobization treatment, which is essential in the method of the present invention, in the water suspension containing the hydrophilic spherical silica fine particles obtained in the step (A). It has been processed. The obtained hydrophobic spherical silica fine particles did not satisfy the conditions of the present invention in terms of carbon content. As a result, the toner external additive composed of the fine particles cannot impart good fluidity to the toner, and further causes toner adhesion to the photoreceptor.
Comparative Example 4 is an example in which the first-stage hydrophobic treatment, which is essential in the method of the present invention, is not performed, and the second-stage hydrophobic treatment is directly performed. A dispersion of hydrophilic spherical silica fine particles coagulated during the hydrophobic treatment.
In Comparative Example 5, the surface hydrophobization treatment step of silica fine particles using methyltrimethoxysilane as the step (B) is omitted, and an aqueous suspension (high water content) of hydrophilic spherical silica fine particles obtained in Comparative Example 1 is used. ) Directly subjected to step (C), but the dispersion of hydrophilic spherical silica fine particles coagulated during step (C).
In Comparative Example 6, deflagration method silica was trimethylsilylated, but the obtained hydrophobic spherical silica fine particles were not sol-gel method silica and were not hydrophobized with R ⁴ SiO _3/2 units. The toner external additive composed of the fine particles does not satisfy the conditions of the invention, and as a result, it cannot impart good fluidity and chargeability independent of environmental conditions to the toner, and furthermore, the toner adheres to the photoreceptor. Etc. occurred.
In Comparative Examples 7 and 8, respectively, fumed silica and precipitated silica were hydrophobized, but these hydrophobic silica fine particles were agglomerated due to aggregation, were not sol-gel silica, and R ^{4 The} toner external additive comprising fine particles does not satisfy the conditions of the present invention in that it is not hydrophobized with SiO _3/2 units. As a result, the toner external additive comprising the fine particles has good fluidity and chargeability independent of environmental conditions. In addition, toner adheres to the photosensitive member.

Claims (8)

The following general formula (1):
Si (OR ¹ ) ₄ (1)
(In the formula, R ¹ are identical or different, is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Surface of hydrophilic spherical silica fine particles comprising SiO ₂ units obtained by hydrolyzing and condensing at least one compound selected from the group consisting of tetrahydrocarbyloxysilane compounds and partial hydrolysis-condensation products thereof R ⁴ SiO _3/2 unit (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) is further introduced into R ⁶ ₃ SiO _1/2 unit ( In which R ⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms.) Hydrophobic spherical silica fine particles having a carbon content of 2 to 5% by mass, a hydrocarbyloxy group content of 0.3 to 5% by mass, and a particle size of 0.01 to 5 μm. (A) The following general formula (1):
Si (OR ¹ ) ₄ (1)
(In the formula, R ¹ are identical or different, is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Hydrolysis of at least one compound selected from the group consisting of a tetrafunctional silane compound and a partial hydrolysis-condensation product thereof in a mixed medium of a hydrophilic organic solvent and water in the presence of a basic substance And condensing to produce hydrophilic spherical silica fine particles to obtain a hydrophilic spherical silica fine particle mixed medium dispersion having a water content of 20% by mass or less;
(B) R ⁴ SiO _3/2 units on the surface of the hydrophilic spherical silica fine particles in the hydrophilic spherical silica fine particle mixed medium dispersion (wherein R ⁴ is a substituted or unsubstituted 1 to 20 carbon atom number 1). A first-order hydrophobic spherical silica fine particle,
(C) R ⁶ ₃ SiO _1/2 unit (wherein R ⁶ is the same or different and is substituted or unsubstituted monovalent monovalent having 1 to 6 carbon atoms) on the surface of the obtained primary hydrophobic spherical silica fine particles. A hydrocarbon group) to obtain secondary hydrophobic silica fine particles,
The method for producing hydrophobic spherical silica fine particles according to claim 1, comprising: The hydrophilic organic solvent is represented by the following general formula (2):
R ³ OH (2)
(In the formula, R ³ is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
The production method according to claim 2, which is an alcohol solvent represented by the formula:   The method according to claim 2 or 3, wherein the basic substance is ammonia. In the step (B), the hydrophilic spherical silica fine particle mixed medium dispersion is subjected to the following general formula (3):
R ⁴ Si (OR ⁵ ) ₃ (3)
(In the formula, R ⁴ is the same as above, and R ⁵ is the same or different and is a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
A mixed medium dispersion of primary hydrophobic spherical silica fine particles by treating the surface of the hydrophilic spherical silica fine particles by adding a trifunctional silane compound represented by the formula (1) or a partial hydrolysis condensation product thereof or a mixture thereof. The manufacturing method of any one of Claims 2 thru | or 4 including obtaining. The step (C) converts the dispersion medium of the mixed medium dispersion of the primary hydrophobic spherical silica fine particles into a ketone solvent to obtain a ketone solvent dispersion of the primary hydrophobic spherical silica fine particles. In the ketone solvent dispersion of the primary hydrophobic spherical silica fine particles, the following general formula (4):
R ⁶ ₃ SiNHSiR ⁶ ₃ (4)
(In the formula, R ⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Or a silazane compound represented by the following general formula (5):
R ⁶ ₃ SiX (5)
(In the formula, R ⁶ is the same as above, and X is an OH group or a hydrolyzable group.)
And adding a monofunctional silane compound represented by the formula (1) or a mixture thereof to triorganosilylate reactive groups remaining on the surface of the primary hydrophobic spherical silica fine particles. The manufacturing method of any one of these.   The production method according to claim 6, wherein the ketone solvent is methyl isobutyl ketone.   A toner external additive for developing electrostatic images comprising the hydrophobic spherical silica fine particles according to claim 1.