Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-06-26
2004-08-17
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137100
Reexamination Certificate
active
06777152
ABSTRACT:
This invention relates to a developer for developing electrostatic images in electrophotography and electrostatic recording process.
BACKGROUND OF THE INVENTION
Dry developers used in electrophotography and similar processes are generally divided into a one-component developer using a toner having a colorant dispersed in a binder resin alone and a two-component developer using the toner in admixture with a carrier. When these developers are used in copying operation, the developers must satisfy many factors such as fluidity, anti-caking, fixation, charging ability and cleanability in order that they adapt to the process.
For the purpose of improving the fluidity, anti-caking, fixation and cleanability, and adjusting and stabilizing the charging ability, inorganic fine particles of silica, titania, alumina, etc. having a smaller particle size than the toner particles are often added as the external additive.
As the copying speed is accelerated in the recent years, the developer is required to have more fluidity, cleanability, and stable and uniform charging ability. To produce images of better quality, the toner has shifted to a small particle size one. As compared with conventional toners commonly used in the art, the small particle size toner is poor in powder flow and its charging ability is readily altered by additives such as external additive. Then, depending on the type and particle size of inorganic fine particles such as silica fine particles added to the toner, the small particle size toner does not necessarily promise satisfactory results with respect to fluidity, charging ability and cleanability. A choice of the inorganic fine, particles added thereto is important. Commonly used silica fine particles, whose mean particle size of primary particles is as small as 10 to 20 nm, are highly cohesive to each other and poorly dispersible, failing to meet the requirements of fluidity and cleanability. Using spherical silica fine particles is effective in improving fluidity and increasing the charge quantity, but due to an excessive charge quantity, the electrostatic adhesive force of fine particles to the toner support becomes stronger, resulting in a lowering of development, a lower image density and density variations. The silica fine particles used sometimes contain impurities, which affect the charging ability of the developer.
On the other hand, titania fine particles having a low charging ability are further added for the purpose of controlling the charge quantity. However, crystalline titania fine particles used in the art are poor in fluidity and dispersibility due to their non-spherical shape. If a certain amount of crystalline titania fine particles are added for adjusting the charge quantity, they aggravate fluidity and dispersion, which are likely to incur liberation of the developer from the toner support, resulting in images being fogged (background staining). A compromise approach is to provide for fluidity by taking advantage of spherical silica fine particles and to adjust the charge quantity by blending silica fine particles with titania fine particles. In order that these functions be exerted in a satisfactory and consistent manner, the silica and titania fine particles must be intimately and completely mixed in a predetermined mixing proportion. However, complete mixing of fine particles is difficult, and such mixing is frequently accompanied with segregation and local variation of charging ability.
SUMMARY OF THE INVENTION
An object of the invention is to provide an electrostatic image developer having improved fluidity and cleanability as well as a stable charging ability.
We have found that when spherical complex oxide fine particles of amorphous silica-titania obtained by atomizing a siloxane and an organic titanium compound in a flame for combustion, having a particle size of 10 to 300 nm, a specific surface area of 10 to 100 m
2
/g, and a titania content of 1 to 99% by weight are added as inorganic fine particles to toner particles, there is obtained an electrostatic image developer which exhibits smooth flow, effective cleaning and uniform and stable charging performance. As used herein, silica is silicon oxide and titania is titanium oxide.
Accordingly, the invention provides an electrostatic image developer comprising spherical complex oxide fine particles of amorphous silica-titania obtained by atomizing a siloxane and an organic titanium compound in a flame for combustion, having a particle size of 10 to 300 nm, a specific surface area of 10 to 100 m
2
/g, and a titania content of 1 to 99% by weight.
Preferably, the complex oxide fine particles are substantially free of chlorine. The organic titanium compound is typically selected from among a tetraalkoxytitanium compound, titanium acylate compound, alkyltitanium compound and titanium chelate compound.
In one preferred embodiment, the complex oxide fine particles have been prepared by simultaneously atomizing the siloxane and the organic titanium compound into a flame for oxidative combustion, in which method, based on the siloxane, the organic titanium compound, a combustion-assisting gas and a combustion-supporting gas fed to a burner, the siloxane, the organic titanium compound and the combustion-assisting gas when burned have an adiabatic flame temperature within a range of 1,650° C. to 4,000° C.
The complex oxide fine particles are preferably hydrophobized fine particles having introduced at their surface units represented by the following formula (1):
R
1
x
R
2
y
R
3
z
SiO
(4−x−y−z)/2
(1)
wherein R
1
, R
2
and R
3
each are independently a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, x, y and z each are an integer of 0 to 3, x+y+z is from 1 to 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The electrostatic image developer of the invention is arrived at by adding spherical complex oxide fine particles of silica-titania to toner particles.
The toner used herein may be any of well-known toners primarily comprising a binder resin and a colorant. If necessary, a charge controlling agent may be added to the toner. Examples of the binder resin used in the toner include homopolymers and copolymers of styrenes such as styrene, chlorostyrene and vinylstyrene, monoolefins such as ethylene, propylene, butylene and isobutylene, vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl lactate, acrylates and methacrylates 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, and ketones such as vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone and vinyl ketone, though the resin is not limited thereto. Typical binder resins are polystyrene, styrene-alkyl acrylate copolymers, styrene-acrylonitrile copolymers, styrene-butadiene copolymers, styrene-maleic anhydride copolymers, polyethylene and polypropylene. Besides, polyesters, polyurethanes, epoxy resins, silicone resins, polyamides, modified rosin, paraffin and wax are also useful.
The colorant used in the toner is not critical. Typical colorants 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. Another useful toner powder is a magnetic toner powder having a magnetic material incorporated therein.
The spherical complex oxide fine particles of silica-titania are obtained by simultaneously atomizing a siloxane and an organic titanium compound in a flame for oxidative combustion.
The siloxane used herein is typically a halogen-free organopolysiloxane which is selected, for example, from among linear organosiloxanes having the following general formula (2):
(R
4
)
3
SiO[SiR
5
R
6
O]
m
Si(R
4
)
3
(2)
wherein each of R
4
Konya Yoshiharu
Ueno Susumu
Watanabe Koichiro
Birch & Stewart Kolasch & Birch, LLP
Goodrow John
Shin-Etsu Chemical Co. , Ltd.
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