Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-03-13
2001-11-13
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
Reexamination Certificate
active
06316155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an external additive for an electrostatically charged latent image developing toner which is used to develop an electrostatically charged latent image in electrophotography, electrostatic recording, and the like, and particularly it relates to an external additive for a toner with a small particle size used for obtaining images of high quality.
2. Description of the Prior Arts
Dry developers used in electrophotography and so forth are generally classified into a one-component developer which consist of a toner prepared by dispersing a coloring agent in a binding resin and a two-component developer consisting of the toner and a carrier. In using these developers in copying operation, the developers are required to have good flowability, anti-caking property, fixing property, electrification property, and cleaning properties so as to be adapted to the process. In order to improve especially the flowability, anti-caking property, fixing property, and cleaning properties, inorganic fine particles are frequently added to the toner.
However, the dispersibility of the inorganic fine particles affect toner properties. Non-uniform dispersion of a toner may not give desired flowability, anti-caking property or fixing property, or may result in insufficient cleaning property, causing adhesion of the toner on a photoreceptor and image defect in black spots. For the purpose of improvement at to these problems, the use of inorganic fine particles having been surface-treated to make the surfaces thereof hydrophobic in Japanese Laying-open Publication Nos. 46-5782, 48-47345 and 48-47346.
However, when an organic photoreceptor or a toner with a smaller particle size is used to improve image quality, the use of the inorganic fine particles does not give sufficient performance. The organic photoreceptor has a softer surfaces and a higher reactivity than inorganic photoreceptor; therefore, the life of the organic photoreceptor is liable to become shorter. Such an organic photoreceptor is liable to change in quality or to be scraped at its surface. When a toner with a smaller particle size is used, the toner is low in flowability as compared to toners with a conventional particle size. Therefore, the amount of inorganic particles has to be increased, and thereby the inorganic fine particles may have caused the toner to adhere to the photoreceptor.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to provide an external additive comprising silica fine particles which do not react with or have any interaction with an organic photoreceptor and thereby do not cause the photoreceptor to change in quality or to be scraped and which has good flowability and therefore do not cause the toner to adhere to the photoreceptor.
The inventors of the present invention studied earnestly to solve the problems stated above and have discovered that the problems can be solved by an external additive for electrostatically charged latent image developing toner, comprising spherical hydrophobic fine silica particles having primary particles having a particle diameter of from 0.01 to 5 &mgr;m, which fine silica particles fulfill the following conditions (i) and (ii): (i) When an organic compound which is liquid at room temperature and has a dielectric constant of from 1 to 40 F/m and fine silica particles are mixed in a weight ratio of 5:1 and shaken, the fine silica particles disperse uniformly in the organic compound. (ii) The quantity of primary particles remaining as primary particles when methanol is evaporated under heating by means of an evaporator from a dispersion prepared by dispersing the fine silica particles in methanol and thereafter the particles are held at a temperature of 100° C. for 2 hours, represents at least 20% of the quantity of primary particles originally present.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hydrophobic fine silica particles used in the present invention are spherical hydrophobic fine silica particles of which primary particles have an average of 0.01 to 5 &mgr;m and which meet the conditions (i) and (ii) stated above.
The hydrophobic silica fine particles have been obtained by the step of introducing an R
2
SiO
3/2
unit (wherein R
2
represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) onto the surfaces of hydrophilic fine silica particles comprising an SiO
2
unit to obtain hydrophobic fine silica particles to produce first hydrophobic silica particles; and introducing an R
3
1
SiO
1/2
unit (wherein R
1
′ s may be the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms) onto the surfaces of the first hydrophobic fine silica particles.
An example of a more specific method of producing the hydrophobic fine silica particles is as described below.
The hydrophobic silica fine particles according to the present invention can be produced by a process comprising:
the step of subjecting one or more compounds selected from the group consisting of a tetrafunctional silane compound represented by the general formula (I):
Si(OR
3
)
4
(I)
(wherein R
3
's may be the same or different and each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms) or a partial hydrolysis-condensation product thereof, to hydrolysis and condensation in a mixed solvent of a hydrophilic organic solvent such as methanol, ethanol and the like, water and a basic compound such as ammonia and an organic amine, to obtain a hydrophilic fine silica particle dispersion;
the step of adding water to the hydrophilic fine silica particle dispersion thus obtained, distilling of the hydrophilic solvent to convert the dispersion into an aqueous dispersion to completely hydrolyzing alkoxyl groups remaining on the surfaces of the fine particles;
the step of adding to the hydrophilic silica fine particles thus treated, one or more compounds selected from the group consisting of a trifunctional silane compound represented by the general formula (II):
R
2
Si(OR
4
)
3
(II)
(wherein R
2
represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and R
4
's may be the same or different and each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms) and a partial hydrolysis -condensation product thereof, to treat the surfaces of the hydrophilic fine silica particles with it to obtain a first hydrophobic fine silica particle in aqueous dispersion;
the step of adding a ketone solvent to said hydrophobic silica fine particle aqueous dispersion followed by distilling off water to thereby convert the aqueous hydrophobic fine silica particle dispersion into a hydrophobic silica fine particle ketone solvent dispersion, and
the step of adding to the hydrophobic fine silica particle ketone solvent dispersion at least one compound selected from the group consisting of a silazane compound represented by the general formula (III):
R
1
3
SiNHSiR
1
3
(III)
(wherein R
1
's may be the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms), and a monofunctional silane compound represented by the general formula (IV):
R
1
3
SiX (IV)
(wherein R
1
's are as defined in the general formula (III), and X represents a hydroxyl group or a hydrolyzable group) to permit the compound to react with silanol groups remaining on the silica fine particles, thereby the silanol groups being triorganosilylated, to enhance the hydrophobic nature of the silica fine particles.
Specific examples of the tetrafunctional silane compound represented by the general formula (I) include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and tetrabutoxysilane. Specific examples of the partial hydrolysis-condensation product of the tetrafunctional silane compound represented by the general formula (I) includ
Asai Mitsuo
Ichinohe Shoji
Kudo Muneo
Sakatsume Yoshiteru
Tanaka Masaki
Goodrow John
Pillsbury & Winthrop LLP
Shin-Etsu Chemical Co. , Ltd.
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