JP2008174430A - Hydrophobic spherical silica fine particles, production method thereof, and toner external additive for developing electrostatic image using the same - Google Patents

Abstract

The present invention provides a hydrophobic spherical silica fine particle capable of improving the fluidity of a toner and a method for producing the same.
A 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]
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 A step of introducing R ⁴ SiO _3/2 units (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms), and then R ⁶ ₃ SiO _1/2 units (Wherein R ⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) and a hydrophobic sphere obtained by hydrophobization treatment Hydrophobic spherical silica fine particles having a hydrocarbyloxy group content of 1000 ppm or less and a particle size of 0.01 to 5 μm, which are silica fine particles.
[Selection figure] None

Description

  The present invention relates to hydrophobic spherical silica fine particles, and in particular, to hydrophobic spherical silica fine particles having high dispersibility and low aggregation.

  Further, the present invention relates to an external additive for a small particle size toner 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. In order to improve these problems, various inorganic fine particles having a hydrophobic surface have been proposed. For example, colloidal silica particles surface-treated with an organosilicon compound (Patent Document 1), colloidal silica surface-treated with at least one organosilicon compound having a hydrocarbon group bonded to a silicon atom and a hydrolyzable group (Patent Literature 2, Patent Literature 3).

  However, when using an organic photoreceptor or a toner having a smaller particle diameter in order to achieve higher image quality, sufficient performance cannot be obtained by using the inorganic fine particles described above. In addition, organic photoreceptors have a softer surface and higher reactivity than inorganic photoreceptors, so their lifetime is likely to be shortened. Therefore, when such an organic photoreceptor is used, the photoreceptor is easily altered or scraped by the inorganic fine particles added to the toner. Furthermore, 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 a larger amount of inorganic fine particles must be added. May cause toner adhesion to the photoreceptor.

  Therefore, the step of hydrophobizing the surface of the hydrophilic spherical silica fine particles produced by hydrolysis of alkoxysilane, and the step of triorganosilylation of the surface of the resulting hydrophobic silica fine particles, that is, the second step. Hydrophobization has been proposed by the process of hydrophobizing (Patent Document 4).

  However, the hydrophobic spherical silica fine particles obtained by hydrophobizing the hydrophilic spherical silica fine particles produced by hydrolysis of the alkoxysilane described above have insufficient fluidity and are used as an external toner additive. In some cases, however, the required fluidity cannot be imparted to the toner.

JP-A-46-5782 JP-A-48-47345 JP-A-48-47346 JP 2000-330328 A

  An object of the present invention is to provide hydrophobic spherical silica fine particles capable of improving the fluidity of a toner and a method for producing the same.

  Another object of the present invention is to provide an external toner additive using the hydrophobic spherical silica fine particles.

As a means for solving the above problems, the present invention firstly
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]
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 A step of introducing R ⁴ SiO _3/2 units (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms), and then R ⁶ ₃ SiO _1/2 units (Wherein R ⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) and a hydrophobic sphere obtained by hydrophobization treatment Hydrophobic spherical silica fine particles having a hydrocarbyloxy group content of 1000 ppm or less and a particle diameter 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) (a-1) 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]
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 the solvent and replacing the medium with water. Obtaining
(B) R ⁴ SiO _3/2 unit 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. Is a monovalent hydrocarbon group] to obtain primary hydrophobic spherical silica fine particles,
(C) R ⁶ ₃ SiO _1/2 unit on the surface of the obtained primary hydrophobic spherical silica fine particles [wherein R ⁶ is the same or different and is substituted or unsubstituted, 1 to 6 carbon atoms. Is a valent hydrocarbon group] to obtain secondary hydrophobic silica fine particles,
A production method is provided.

  Furthermore, the present invention provides a toner external additive for developing an electrostatic image 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 fluidity of the toner. Furthermore, the toner external additive can give the toner the necessary charge, and further, since there is no reaction or interaction with the organic photoreceptor, the photoreceptor is unlikely to be altered or scraped. Since it has excellent dispersibility and fluidity, toner adhesion to the photoreceptor does not occur, and it has a charging property that does not depend on environmental conditions. By using this toner external additive, high image quality can be expected 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 Stoeber 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 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 partially hydrolyzed condensation product thereof. A step of introducing ₂ units (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms), then R ⁶ ₃ SiO _1/2 units (wherein R ⁶ is Hydrophobic spherical silica fine particles obtained by two-stage hydrophobizing treatment including a step of introducing the same or different, substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) The hydrocarbyloxy group content is 1000 ppm or less, preferably 500 ppm or less, particularly preferably 10 ppm or less. When the hydrocarbyloxy group content exceeds 1000 ppm, the fluidity of the toner becomes insufficient due to the influence of this polar group.

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, particularly preferably 0.1 to 0.2 μm. When the particle diameter is smaller than 0.01 μm, the fine particles aggregate to result in insufficient developer fluidity, caking resistance, fixability, and the like. Inconveniences such as alteration or shaving and a decrease in adhesion of the fine particles to the toner occur. 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 may be produced, for example, by a step of producing hydrophilic spherical silica fine particles having reduced hydrocarbyloxy groups by a sol-gel method (step (A)), and the surface of the hydrophilic spherical silica fine particles is a first step hydrophobic particle. Step ((B)), and a step of triorganosilylation of the surface of the obtained primary hydrophobic spherical silica fine particles, that is, a second step hydrophobization (step (C)) It is obtained by the method which has these. Hereinafter, each process will be described.

-Synthesis of hydrophilic spherical silica fine particles (step (A))-
In this step, (a-1) 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 spherical silica fine particles are produced by hydrolyzing and condensing the tetrafunctional silane compound and / or its partial hydrolytic condensation product represented by the formula (a-2), and then the hydrocarbyloxy group content of the silica fine particles is reduced. And having a process. As a result, the hydrocarbyloxy group content of the hydrophobic spherical silica fine particles finally obtained by this method can be reduced to 1000 ppm or less, and adverse effects due to this polar group can be eliminated, so that the toner fluidity is improved.

  Examples of the hydrolyzable group include a hydrocarbyloxy group, an amino group, and an acyloxy group, preferably a hydrocarbyloxy group and an amino group, and particularly preferably a hydrocarbyloxy group. Examples of the hydrocarbyloxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a hexyloxy group, and a phenoxy group, and a methoxy group and an ethoxy group are preferable.

The step (A) is more specifically,
(A-1) 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]
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 the solvent and replacing the medium with water. And obtaining a step.
In the step (a-2), if the water content in the aqueous dispersion is less than 90% by mass, the hydrocarbyloxy group is sufficiently hydrolyzed because the amount of the hydrophilic organic solvent in the dispersion is large. Otherwise, the residual hydrocarbyloxy group content in the silica fine particles is increased.

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, general formula (2):
R ³ OH (2)
[Wherein 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 0.5 to a total of 1 mol of hydrocarbyloxy groups of the tetrafunctional silane compound represented by the general formula (1) and / or the partial hydrolysis condensation product thereof. 5 mol is preferable, 0.6 to 2 mol is more preferable, and 0.7 to 1 mol is particularly preferable. 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 hydrocarbyloxy groups of the tetrafunctional silane compound represented by the general formula (1) and / or a partial hydrolysis condensation product thereof. Preferably, it is 0.5 to 1.5 mol, more preferably 1.0 to 1.2 mol.

  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.

The step of converting the dispersion medium of the hydrophilic spherical silica fine particle mixed solution into water is performed by, for example, an operation of adding water to the dispersion and distilling off the hydrophilic organic solvent (repeat this operation as necessary). It can be carried out. The total amount of water added at this time is preferably more than twice the amount of the total amount of the hydrophilic organic solvent used and the amount of alcohol produced, more preferably 2.5 to The amount is 3.5 times, particularly preferably 3 times, so that the water content of the dispersion is finally 90% by mass or more, preferably 98% by mass or more. When the water content in the dispersion liquid is converted to an aqueous dispersion liquid of 90% by mass or more in this way, the remaining hydrocarbyloxy group (OR ¹ ) derived from the tetrafunctional silane compound represented by the general formula ( ¹ ) Is hydrolyzed to form hydrophilic spherical silica fine particles in which the amount of hydrocarbyloxy groups is reduced.

  The hydrophilic spherical silica fine particles obtained in this way are subjected to a first 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 [wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms] on the surface of the hydrophilic spherical silica fine particles. Is a step for obtaining primary hydrophobic spherical silica fine particles, that is, a step for performing a first-stage hydrophobic treatment. For example, an aqueous dispersion containing the hydrophilic spherical silica fine particles and having a water content of 90% by mass or more in the dispersion is represented by the general formula (3):

R ⁴ Si (OR ⁵ ) ₃ (3)
[Wherein, R ⁴ is the same as defined above, and R ⁵ is the same or different and is a monovalent hydrocarbon group having 1 to 6 carbon atoms]
A trifunctional silane compound represented by the above, a partial hydrolysis-condensation product thereof, or a mixture thereof is added, and the surface of the hydrophilic spherical silica fine particles is treated to obtain an aqueous 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, particularly preferably 0.01 to 0.1 mol per mol of SiO ₂ unit of the used hydrophilic spherical silica fine particles. 0.05 mole.

-Surface triorganosilylation treatment of hydrophobic spherical silica fine particles (step (C))-
In the step (C), R ⁶ ₃ SiO _1/2 unit [wherein R ⁶ is the same or different and substituted or unsubstituted on the surface of the primary hydrophobic spherical silica fine particles obtained in the step (B) , Which is 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 aqueous dispersion is converted from water to a ketone solvent to obtain a hydrophobic spherical silica fine particle ketone solvent dispersion, and the hydrophobic spherical silica fine particle ketone solvent dispersion In general formula (4):

R ⁶ ₃ SiNHSiR ⁶ ₃ (4)
[Wherein R ⁶ is the same or different and is the same as above]
Or a silazane compound represented by the general formula (5):
R ⁶ ₃ SiX (5)
[Wherein R ⁶ is the same or different and is the same as above, and X is an OH group or a hydrolyzable group]
A monofunctional silane compound represented by the formula (1) or a mixture thereof is added, and the reactive group remaining 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 aqueous dispersion or the mixed solvent dispersion from water or a mixed solvent to a ketone solvent, a ketone solvent is added to the dispersion and water or the mixed solvent is distilled from the mixture. It can be performed by the operation to leave (repeat 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 preferably 3 by mass ratio with respect to the hydrophilic spherical silica fine particles in the spherical silica fine particle aqueous dispersion. ~ 4 times the amount. Examples of the ketone solvent include methyl ethyl ketone, methyl isobutyl ketone, acetyl acetone, and preferably methyl isobutyl ketone.

  Examples of the silazane compound represented by the general formula (4) include hexamethyldisilazane and hexaethyldisilazane, preferably hexamethyldisilazane. 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 thereof include monoaminosilanes such as silane, trimethylsilyldimethylamine and trimethylsilyldiethylamine, and monoacyloxysilanes such as trimethylacetoxysilane, preferably trimethylsilanol, trimethylmethoxysilane and trimethylsilyldiethylamine, 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 0.25 mol, based on 1 mol of SiO ₂ units of the hydrophilic spherical silica fine particles used.

  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 amount of the toner external additive composed of the fine particles (hereinafter also simply referred to as “fine particles”) to the toner is usually 0.01 to 20 parts by mass, preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the toner. Especially preferably, it is 1-2 mass parts. 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 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, etc., or those coated on the surface with resin can be used.

  Furthermore, the present inventors have found that the toner external additive comprising the hydrophobic spherical silica fine particles according to the present invention imparts charging properties independent of the environment to the toner in addition to the desired characteristics. I found it.

  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 fine particles]
-(I) 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, 623.7 g of methanol, 41.4 g of water, and 49.8 g of 28% by mass ammonia water were mixed. The 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 begun to be added at the same time while stirring. Each was added dropwise over 5 hours. Even after the completion of the dropwise addition, the suspension was further stirred for 0.5 hour to carry out hydrolysis to obtain a suspension of hydrophilic spherical silica fine particles. Next, an ester adapter and a condenser tube were attached to a glass reactor, and the suspension was heated to 60 to 70 ° C. to distill off 1200 g of methanol, and then 1200 g of water was added. Then, 300 g of methanol water was distilled off and the addition of 300 g of water was repeated three times until the suspension reached 100 ° C., and 300 g of methanol water was further distilled off to obtain an aqueous suspension of hydrophilic spherical silica fine particles. At this time, according to gas chromatographic analysis, the water content in the water suspension was 99.9% by mass.

-(II) Hydrophobic spherical silica fine particle surface first-stage hydrophobization treatment (step (B))-
11.6 g (0.085 mol) of methyltrimethoxysilane was added dropwise to the aqueous suspension obtained in the above step (A) at room temperature over 0.5 hours, and stirring was continued for 12 hours after the addition. Thus, the first hydrophobic spherical silica fine particle aqueous dispersion was obtained by subjecting the surface of the silica fine particle to the first-stage hydrophobic treatment.

-(III) Second-stage hydrophobization treatment (triorganosilylation treatment) on the surface of primary hydrophobic spherical silica fine particles (step (C))-
After adding 1440 g of methyl isobutyl ketone to the dispersion obtained in the step (B), 1794 g of water was distilled off over 10 hours by heating the dispersion to 80 to 110 ° C. After adding 150 g (0.93 mol) of hexamethyldisilazane to the resulting dispersion at room temperature, this dispersion is heated to 110 ° C. and reacted for 3 hours to trimethylsilylate the silica fine particles in the dispersion. did. Subsequently, the solvent in this dispersion was distilled off at 80 ° C. under reduced pressure (6650 Pa) to obtain 475 g of hydrophobic spherical silica fine particles as a powder.

  With respect to the final hydrophobic spherical silica fine particles obtained by the above steps (A) to (C), the alkoxy group content, particle diameter, and shape were measured according to the following measurement methods 1 to 3. The obtained results are shown in Table 1.

Measurement method 1: 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 and heated at 70 ° C. for 1 hour to decompose the silica, and then the liquid is distilled. Take it. The fraction of the alkoxy group contained in the silica fine particles is quantified by gas chromatographic analysis of this fraction and quantifying the amount of methanol contained.

Measurement method 2: Measurement of particle diameter of hydrophobic spherical silica fine particles Silica fine particles were added to methanol so as to be 0.5 mass%, and the fine particles were dispersed by applying ultrasonic waves for 10 minutes. The particle size distribution of the fine particles treated in this way was measured by 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 3: 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.

[Production 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. Using this, toner fluidity was measured according to the following measurement method 4. The obtained results are shown in Table 1.

Measurement method 4: Measurement of toner fluidity The fluidity of the toner 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. By measuring the force received from the powder separately for the torque component and the load component, the respective work (energy) associated with the blade descending from H1 to H2 is obtained, and then the total energy of both Find the amount. The smaller the total energy measured in this way, the better the fluidity of the powder, so it is used as an index of powder fluidity.

A stability test, a flow rate test, an aeration test, and a compression test were performed.
··conditions:
Container: In the stability, flow rate, and ventilation tests, a glass cylindrical container having a volume of 120 ml, an inner diameter of 80 mm, and a length of 60 mm was used. In the compression test, a glass cylindrical container having a volume of 25 ml, an inner diameter of 25 mm, and a length of 52.5 mm was used. It is comprised so that air can be introduce | transduced from the lower part of a container.
Blades: Two blades are mounted horizontally facing the tip of a stainless steel shaft rod inserted vertically into the center of the cylindrical container. A blade with a diameter of 48 mm is used for a container with a volume of 120 ml, and a blade with a diameter of 23.5 ml is used for a container with a volume of 25 ml.
Length from H1 to H2: 50 mm for a container with a volume of 120 ml and 47.5 mm for a container with a volume of 25 ml.

  .. Stability test: As described above, the powder flow characteristics when the powder filled in the measurement container is allowed to flow from a static state are observed. Measure the total energy amount 7 times continuously with the blade tip rotation speed as 100mm / sec. Table 7 shows the total energy amount for the seventh time (referred to as basic fluidity energy because it is the most stable state). The smaller the value, the higher the stability.

  ・ ・ Velocity test: The powder flow characteristics with respect to the change of the flow velocity are observed. Table 1 shows the total energy when the rotational speed of the blade tip was measured at 10 mm / sec. The smaller the value, the higher the fluidity.

  ・ ・ Aeration test: Check the powder flow characteristics according to the aeration rate. The rotation speed of the blade tip is set to 100 mm / sec, the air flow rate introduced from the bottom of the container is increased from 0 mm / sec in increments of 0.1 mm / sec, and measured separately in six steps from 0.5 mm / sec to the smallest Table 1 shows the total energy amount at the air flow rate (0 mm / sec) and the maximum air flow rate (0.5 mm / sec). The smaller the value, the higher the powder fluidity when air is involved.

  ・ ・ The compression test examines the powder flow characteristics with respect to compression. After applying a weight to the powder through a piston and pressurizing and compressing with 10 N, the rotational speed of the blade tip was measured at 100 mm / sec to determine the total energy amount. The results are shown in Table 1. The smaller the powder, the higher the powder fluidity when the powder is compressed.

[Preparation of developer]
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 and toner adhesion to the photoreceptor were measured according to the following measurement methods 5 and 6. The obtained results are shown in Table 1.

・ Measurement method 5: Measurement of toner charge amount The developer is left in a high temperature and high humidity (30 ° C, 90% RH) or low temperature and low humidity (10 ° C, 15% RH) condition for 1 day, and then shaken. Mixing for 30 seconds, triboelectric charging was performed. 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 5: Measurement of toner adhesion to the photoconductor The above developer was put into a two-component modified developer equipped with an organic photoconductor, and a print test of 30,000 sheets was performed. The 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

<Example 2>
In Example 1, in step (A), the suspension of hydrophilic spherical silica fine particles was heated to 60 to 90 ° C., 420 g of methanol water was distilled off, and 250 g of water was added four times, and further heated to 90 to 98 ° C. In the same manner as above except that 351 g of methanol was distilled off to obtain an aqueous suspension of hydrophilic spherical silica fine particles (water content was 98.8% by mass), 479 g of hydrophobic 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>
In Example 1, in step (A), the suspension of hydrophilic spherical silica fine particles was heated to 60 to 70 ° C. to distill off 1132 g of methanol, then 1200 g of water was added, and then 70 to 90 ° C. In the same manner except that 273 g of methanol was distilled off to obtain an aqueous suspension of hydrophilic spherical silica fine particles (water content was 87.2% by mass), 479 g of hydrophobic spherical silica fine particles were used as a dry powder. Obtained. 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>
In Example 1, 240 g of hexamethyldisilazane was added to the aqueous suspension of the hydrophilic spherical silica fine particles obtained in the step (A) at room temperature, heated to 120 ° C., and reacted for 3 hours. The fine particles were trimethylsilylated. Subsequently, water was distilled off at 120 ° C. under reduced pressure (6650 Pa) to obtain 465 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>
By adding 240 g of hexamethyldisilazane at room temperature to the aqueous suspension of the hydrophilic spherical silica fine particles obtained in the step (A) in Comparative Example 1, the silica fine particles are heated at 120 ° C. and reacted for 3 hours. Was trimethylsilylated. Next, the mixture of methanol and water was distilled off at 80 ° C. under reduced pressure (6650 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 hydrophobic treatment step of silica fine particles using methyltrimethoxysilane as the step (B) is omitted, and the aqueous suspension of hydrophilic spherical silica fine particles obtained in the step (A) is directly processed. In (C), after adding 1440 g of methyl isobutyl ketone, heating to 80-110 ° C. and distilling off 820 g of a mixture of methanol and water over 6 hours, a dispersion of hydrophilic spherical silica fine particles was obtained. It solidified.

<Comparative Example 5>
In Example 1, the surface hydrophobic treatment step of silica fine particles using methyltrimethoxysilane as the step (B) was omitted, and the aqueous suspension of hydrophilic spherical silica fine particles obtained in the step (A) in Comparative Example 1 was omitted. The solution was directly subjected to step (C), 1440 g of methyl isobutyl ketone was added, heated to 80 to 110 ° C., and 820 g of a mixture of methanol and water was distilled off over 6 hours. Hydrophilic spherical silica fine particles The dispersion was solidified.

<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 with stirring, and after sealing, another 60 Stir at 0 ° C. for 10 hours. Subsequently, 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 instead of the hydrophobic spherical silica particles prepared in Example 1 (trade name: Aerosil R972, manufactured by Nippon Aerosil Co., Ltd., primary particle aggregate, dimethyldichlorosilane Evaluation was performed in the same manner as in Example 1 using the processed product. 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. Then, evaluation was made in the same manner as in Example 1. The results are shown in Table 2.

(note)
(1) In aqueous suspension of hydrophilic spherical silica fine particles (step (A))
(2) 7th time
(3) Blade speed 10mm / s
(4) Ventilation rate 0mm / s
(5) Ventilation rate 0.5mm / s
(6) Pressure 10N

(note)
(1) In aqueous suspension of hydrophilic spherical silica fine particles (step (A))
(2) 7th time
(3) Blade speed 10mm / s
(4) Ventilation rate 0mm / s
(5) Ventilation rate 0.5mm / s
(6) Pressure 10N
<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 in the step (A) is less than 90% by mass, the obtained hydrophobic spherical silica fine particles have an alkoxy group content. Thus, the toner external additive composed of the fine particles could not give good fluidity 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 high water content. It has become. The resulting treated silica fine particles became amorphous due to incomplete hydrophobization treatment and aggregation. 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, the hydrophilic spherical silica fine particles obtained in the step (A) were subjected to a first-stage hydrophobization treatment essential in the method of the present invention in an aqueous suspension having a water content of less than 90% by mass. A trimethylsilylation treatment not applicable. The obtained hydrophobic spherical silica fine particles did not satisfy the conditions of the present invention in terms of alkoxy group 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 the aqueous suspension of hydrophilic spherical silica fine particles obtained in the step (A) in Comparative Example 1 is omitted. The suspension (low water content) was 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 the environmental state 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)

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]
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 A step of introducing R ⁴ SiO _3/2 units (wherein R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms), and then R ⁶ ₃ SiO _1/2 units (Wherein R ⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) and a hydrophobic sphere obtained by hydrophobization treatment Hydrophobic spherical silica fine particles having a hydrocarbyloxy group content of 1000 ppm or less and a particle size of 0.01 to 5 μm, which are silica fine particles. (A) (a-1) 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]
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 the solvent and replacing the medium with water. Obtaining
(B) R ⁴ SiO _3/2 unit 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. Is a monovalent hydrocarbon group] to obtain primary hydrophobic spherical silica fine particles,
(C) R ⁶ ₃ SiO _1/2 unit on the surface of the obtained primary hydrophobic spherical silica fine particles [wherein R ⁶ is the same or different and is substituted or unsubstituted, 1 to 6 carbon atoms. Is a valent hydrocarbon group] to obtain secondary hydrophobic silica fine particles,
The manufacturing method of the hydrophobic spherical silica fine particle of Claim 1 which has these. The hydrophilic organic solvent has the general formula (2):
R ³ OH (2)
[Wherein 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), an aqueous dispersion of the hydrophilic spherical silica fine particles is added to the general formula (3):
R ⁴ Si (OR ⁵ ) ₃ (3)
[Wherein, 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, and an aqueous dispersion of primary hydrophobic spherical silica fine particles is obtained. The manufacturing method which concerns on any one of Claims 2-4 including obtaining. The step (C) converts the dispersion medium of the aqueous 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 general formula (4):
R ⁶ ₃ SiNHSiR ⁶ ₃ (4)
[Wherein 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 general formula (5):
R ⁶ ₃ SiX (5)
[Wherein R ⁶ is the same as above, and X is an OH group or a hydrolyzable group]
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 according to any one of 5.   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.