Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-03-03
2001-06-19
Rodee, Christopher (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
06248495
ABSTRACT:
This invention relates to an electrostatic image developer for use in the development of electrostatic images in electrophotography and electrostatic recording process.
BACKGROUND OF THE INVENTION
Dry developers used in electrophotography are generally classified into one-component developers using just a toner having a colorant dispersed in a binder resin and two-component developers comprising a toner and a carrier. In effecting duplication using such developers, the developer must be improved in such characteristics as fluidity, anti-caking, fixation, charge acceptance and cleanability in order to be compliant to the process. One common practice for enhancing these characteristics is to add to the toner inorganic microparticulates having a smaller particle size than the toner particles, for example, silica and titania microparticulates.
As the copying speed increases, the recent electrophotographic art places a greater demand for further improvements in fluidity, charging stability and uniformity, and cleanability. Also for better image quality, smaller particle size toners are utilized. However, the smaller particle size toners are poor in powder fluidity than the conventional toners of ordinary particle size and their charging characteristics are readily affected by additives such as external additives. Then a choice of inorganic microparticulates such as silica microparticulates to be added to the toner becomes more important.
Since commonly used silica microparticulates are very fine as demonstrated by a primary particle mean particle size of 10 to 20 nm, they have a strong tendency to agglomerate together and are poorly dispersible, failing to help the toner fully exert fluidity, anti-caking and cleaning characteristics. Silica microparticulates contain impurities which affect the charging characteristics of the toner. If the impurity content of inorganic microparticulates varies between different manufacturing lots, the toner varies in charge quantity, which can cause a significant variation in the density of images developed therewith.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a novel and improved electrostatic image developer having improved fluidity, anti-caking and cleaning characteristics as well as stable and uniform charging characteristics.
The inventor has found that when amorphous spherical silica microparticulates having a specific surface area of 5 to 50 m
2
/g and a particle size distribution of 5 to 1,000 nm are added to toner particles as the inorganic microparticulates, there is obtained an electrostatic image developer which is improved in fluidity, anti-caking and cleaning characteristics and has stable and uniform charging characteristics.
Thus the invention provides an electrostatic image developer comprising amorphous spherical silica microparticulates having a specific surface area of 5 to 50 m
2
/g and a particle size distribution of 5 to 1,000 nm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention, the electrostatic image developer is generally defined as comprising toner particles and spherical silica microparticulates added thereto. The toner used herein may be any conventional toner comprising a colorant, a binder resin and optionally, a charge control agent. The binder resin used in the toner may be any of well-known binder resins, for example, homopolymers and copolymers of styrenes such as styrene, chlorostyrene and vinylstyrene; monoolefins such as ethylene, propylene, butylene and isobutyrene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate; acrylic or methacrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and dodecyl methacrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl butyl ether; vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone. Typical binder resins are polystyrene, styrene-alkyl acrylate copolymers, styrene-acrylonitrile copolymers, styrene-butadiene copolymers, styrene-maleic anhydride copolymers, polyethylene, and polypropylene. Also useful are polyesters, polyurethanes, epoxy resins, silicone resins, polyamides, modified rosin, paraffin and wax.
The colorant used in the toner is not critical. Typical examples include carbon black, Nigrosine dyes, Aniline Blue, Chalcoyl Blue, Chrome Yellow, ultramarine blue, Dupont oil red, quinoline yellow, Methylene Blue chloride, phthalocyanine blue, Malachite Green oxalate, lamp black, and Rose Bengale. The toner powder may also be a magnetic toner powder having magnetic material included therein.
The spherical silica microparticulates used herein are preferably the one described in JP-A 2-188421. Specifically, spherical silica microparticulates are prepared by combustionpyrolysis in flame of an alkoxysilane and/or a partial hydrolytic condensate thereof. The alkoxysilane used herein is represented by the general formula: R
2
a
Si(OR
3
)
4-a
wherein R
2
and R
3
are monovalent hydrocarbon groups of 1 to 4 carbon atoms and a is an integer of 0 to 4. Exemplary alkoxysilanes are tetrametoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, dipropyldimethoxysilane, dipropyldiethoxysilane, dibutyldimethoxysilane, dibutyldiethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylpropoxysilane, trimethylbutoxysilane, triethylmethoxysilane, triethylethoxysilane, triethylpropoxysilane, triethylbutoxysilane, tripropylmethoxysilane, tripropylethoxysilane, tributylmethoxysilane, and tributylethoxysilane, with tetramethoxysilane and methyltrimethoxysilane being especially preferred.
The spherical silica microparticulates used herein should be substantially free of chlorine and have a content of metal impurities other than silicon of up to 5 ppm. If the spherical silica microparticulates contain chlorine or if the content of metal impurities other than silicon exceeds 5 ppm, they can adversely affect the stabilization and consistency of the charging characteristics of the toner. The preferred content of metal impurities other than silicon is up to 1 ppm. Such spherical silica microparticulates of high purity are available using an alkoxysilane which has been purified as by distillation.
Spherical silica microparticulates having a specific surface area of more than 50 m
2
/g or a particle size of less than 5 nm are likely to agglomerate, adversely affecting the fluidity, anti-caking and fixation characteristics of the associated developer. Silica microparticulates having a specific surface area of less than 5 m
2
/g or a particle size in excess of 1,000 nm can cause alteration and abrasion of the photoconductor, which in turn, exacerbates the adhesion of the toner. For this reason, the spherical silica microparticulates should have a specific surface area of 5 to 50 m
2
/g and preferably 10 to 30 m
2
/g. The particle size distribution should range from 5 nm to 1,000 nm, and preferably from 20 nm to 300 nm.
A method for the preparation of spherical silica microparticulates may follow JP-A 2-188421 as previously mentioned. More particularly, an alkoxysilane and/or a partial hydrolytic condensate is heat evaporated and carried by an inert gas such as nitrogen gas, or sprayed whereupon the vapor or spray is introduced into a flame such as oxyhydrogen flame in which the reactant is subject to combustion pyrolysis. At this point of time, the heat quantity required per unit silica particulate calculated from the total calorific value is set in the range
Inokuchi Yoshinori
Shimizu Takaaki
Tanaka Masaki
Birch & Stewart Kolasch & Birch, LLP
Rodee Christopher
Shin-Etsu Chemical Co. , Ltd.
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