Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-01-24
2001-09-25
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...
C430S120400
Reexamination Certificate
active
06294303
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electrostatography, particularly toners for electrostatographic image development methods.
DESCRIPTION RELATIVE TO THE PRIOR ART
In electrostatography, an image comprising a pattern of electrostatic potential (also referred to as an electrostatic latent image), is formed on a surface of an electrophotographic element and is then developed into a toner image by contacting the latent image with an electrophotographic developer. If desired, the latent image can be transferred to another surface following development. The toner image may be transferred to a receiver, to which it is fused, typically by heat and pressure.
Electrostatographic developers can be monocomponent or two component developers. Two component developers comprise a mixture of carrier and toner particles. Monocomponent developers comprise nonmagnetic or magnetic toner particles but do not have separate carrier particles. Monocomponent developers can have additional components such as flow agents, and cleaning aids.
Cleaning aids in monocomponent developers are present to prevent an accumulation of toner or toner components on photoconductive elements. Silica, titania, alumina, zirconium oxide and cerium dioxide among others are disclosed as cleaning aids.
U.S. Pat. No. 4,824,752 discloses use of cerium oxide particles with the function of disintegrating silicon dioxide particulates thereby enhancing the attachment thereof to the toner particles. The hydrophobic silicon dioxide particulates provide flowability to the toner particles and assist in the negative chargeability. The hydrophobic silicon dioxide particulates also serve as an abrasive in a cleaning step.
U.S. Pat. No. 5,348,829 discloses a problem in non-contact monocomponent development in which development performance is degraded due to an increased force of attachment of magnetic toner particles in the vicinity of the developing roll sleeve surface. When a monocomponent-type developer comprising an external mixture of a magnetic toner and inorganic fine powder is used, the inorganic fine powder is selectively applied in the vicinity of the developer roll sleeve to form a very thin layer of the inorganic fine powder. As a result, the magnetic toner does not directly contact the developer roll sleeve surface, so that the magnetic toner is prevented from sticking onto the sleeve surface due to an image force, thus not being liable to cause a coating irregularity of the developer. This patent discloses that a fine powder of strontium titanate shows excellent results.
These and other prior art monocomponent developers fail to provide outstanding image quality, good fusing to receivers, acceptable release from the fusing member, and adequate suppression of contamination of photoconductor and developer roll sleeve surfaces. Many image quality artifacts are associated with and caused by contamination of the surface of the developer roll sleeve, or by the accumulation of magnetic toner or other inorganic fine particles in the vicinity of the developer roll sleeve. These image quality artifacts are not completely suppressed by the use of strontium titanate or other cleaning aids or abrasive surface additives disclosed in the prior art.
SUMMARY OF THE INVENTION
The present invention is an improved monocomponent electrostatographic developer. The developer includes negatively charging toner particles. The particles include a polymeric binder and magnetic material wherein the toner particle surface contains particles of positively chargeable inorganic fine powder particles. The invention is characterized in that:
the inorganic fine powder particles have a mean volume average particle size of about 0.5 to 7 &mgr;m, and a cleaning ratio between 0.1 and 5.0;
the cleaning ratio being the volume fraction of particles between 0 and 1.0 &mgr;m, divided by the volume fraction of particles greater than 1.0 &mgr;m; and
the particles having on the surface thereof a flowability improving agent having a BET surface area of at least 30 m
2
/g.
This developer provides outstanding image quality, superior fusing to receivers, acceptable release from the fusing member, excellent suppression of photoconductor contamination, and excellent suppression of developer roll sleeve contamination.
DETAILED DESCRIPTION OF THE INVENTION
The toners of the monocomponent developer composition of the invention contain a polymeric binder and magnetic material. Optionally the toner may include a charge control agent, a release agent such as a wax, colorants and other additives.
As noted above, it is conventional to include a cleaning aid in a monocomponent developer composition. We have found that certain specific characteristics of the cleaning aid and other features provide for improved results. In preparing the monocomponent composition of the invention the toner is first treated with a flowability improvement agent, such as silicon dioxide. Thereafter the toner is treated with a positively chargeable inorganic fine powder (IFP). In the first step the toner surface is treated with 0.2 to 1.0 weight percent silicon dioxide based on the weight of the toner, the silicon dioxide having a BET surface area of at least 30 m
2
/g. In the second step the toner is treated with from 1.0 to 6.0 weight percent IFP based on the total weight of the mixture of toner and silicon dioxide.
The flowability improvement agent can be treated silica dioxide. A useful treated silicon dioxide is hexamethyldisalizane treated silicon dioxide that is commercially available from Degussa Corporation as Aerosil™ R8 12. The IFP added to the developer can be pure cerium dioxide, pure strontium titanate or cerium oxide-rich or strontium titanate rich polishing aids. Useful positively chargeable inorganic fine powders have a mean volume average particle size of about 0.5 to 7 &mgr;m. Cerium dioxide rich polishing aids are commercially available from Ferro Electronic Materials. Strontium Titanate (99% pure) is available from Sigma-Aldrich. Milling or classification of the IFP or combinations of milled and classified IFPs can also be accomplished to produce the desired particle size distribution. SRS135 from Ferro Electronic materials is a milled version of their SRS123. SRS123C was classified by CCE technologies from SRS123. A useful composition is a mixture of SRS 123C and SRS 135 in the ratio 30:70 to 70:30 by weight.
The inorganic fine powder (IFP) added to the developer can be a pure material or mixtures of materials. Cerium dioxide or mixtures of cerium dioxide may be used advantageously as cleaning aids to ensure that the photoconductive element is not contaminated and to ensure that the surface of the developer roll sleeve is not scummed or otherwise contaminated. The positively chargeable inorganic fine powder is attracted to the vicinity of the surface of the developer roll sleeve during the development process. The cerium dioxide effectively cleans the surface of the developer roll sleeve and removes any toner or other contaminates.
Contamination of the surface of the developer roll sleeve degrades image quality. Toner or other materials that become physically attached to the surface of the developer roll sleeve will result in decreasing the charge-to-mass of the toner by interfering with the triboelectric interaction between the surface of the toner particle and the surface of the developer roll sleeve. The poorly charged toner particles will not develop onto the image areas of the photoconductor and image reflection density will be lowered and background increased. In addition, the presence of attached (scummed) toner on the surface of the developer roll sleeve will cause localized irregularities in the surface of the toner on the developer roll sleeve. These surface irregularities may in some cases result in reproduction of non-uniform solid area density particularly for low-density originals.
To avoid image quality degradation due to contamination of the developer roll sleeve, appropriate positively chargeable inorganic fine powder (IFP) cleaning aids must be employed.
Contois Robert E.
Marsh Dana G.
Putnam David Daniel
Goodrow John
Nexpress Solutions LLC
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