Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-01-25
2001-09-25
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...
C430S111330, C430S111410
Reexamination Certificate
active
06294304
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic carrier in powder or particle form used in electrophotographic development equipment, and, more particularly, to an environmentally benign manganese oxide, iron oxide carrier having titanium dioxide or titanium oxide added thereto to control magnetic brush properties of the carrier.
Carriers in the form of powder or particles are used to transfer toner in many types of electrophotographic development equipment or reprographic equipment. For example, such powders are used in copying machines and laser printers. Typically such carriers are ferrite powders that consist of iron oxide in combination with various metal oxides such as nickel, zinc or copper among others. Patents have been issued directed to various ferrite carrier compositions including the following: U.S. Pat. Nos. 4,623,603, Timura et al.; 4,85,162, Honjo et al.; 4,898,801, Tachibana et al.; 4,485,162, Imamura et al.; and 3,929,657, Jones. Such prior art patents teach both single component and dual component ferrite carriers. These patents also teach various crystalline structures for the carriers. These patents also teach the utilization of compositions of ferrites with various metals and various processes for the manufacture of such carriers.
The need to provide environmentally benign carriers which may be safely and easily recycled or disposed following use is a growing prerequisite design consideration for electrophotographic development equipment. Currently many compositions which are used as carriers, contain elements that might be regarded as hazardous to the environment. The proposed invention concerns a composition which does not present the environmental concerns of many currently available carriers.
It is also known that when an iron oxide carrier is selected for electrophotographic magnetic brush development, the electrical conductivity and the magnetic properties of the carrier are important and parameters are often established for desired development characteristics. Additionally, carriers are often coated with various polymer resins selected for compatibility with specific toners. Polymer coatings are known to typically reduce the conductivity or increase the resistivity of the carriers. Conductive additives such as carbon black may also be added to coatings to increase the conductivity or lower the resistivity of carriers. However, coatings on carrier surfaces wear or erode and subsequently are transferred onto the copied or printed documents along with the toner. Black toner applications typically do not show adverse effects resulting from the transfer of additives. However, the image quality from color toner applications, which are becoming more and more popular, can be adversely affected. The color toner applications for magenta, cyan and yellow thus may be adversely affected in many circumstances and so there has developed a need to provide an environmentally benign iron oxide or ferrite carrier particle or core which maintains an appropriately high conductivity prior to coating and which can simultaneously offer a range of magnetic values useful in magnetic brush developer systems particularly for color reprographics.
SUMMARY OF THE INVENTION
Briefly, the present invention comprises an improved magnetic carrier which is made from a combination of an iron oxide, e.g. ferrite (Fe
2
O
3
) and an oxide of manganese, e.g. manganese oxide or manganese dioxide with an additive of titanium dioxide in the range typically of 0.5 to 10% by weight. It has been found that such carriers are useful because of their high conductivity or low resistivity and further because their magnetic moment may be limited to less than 80 electromagnetic units per gram (emu/g). The maintenance of a magnetic moment below about 80 emu/g is especially important in color electrophotographic machines. While high moment carriers are useful for some applications (those greater than 80 emu/g), the presently available equipment for color applications preferably utilizes carriers having a lower magnetic moment, typically in the range below 80 and more desirably in the range of 60-65 emu/g. Failure to provide a lower magnetic moment carrier as described may tend to cause the formation of rigid magnetic toning brushes which can scratch the surface of a photo conductor roll thereby leading to premature failure or limited copy detail, particularly with color electrophotographic machines. Such a deficiency results from the inability of a stiff brush to effectively present toner particles to the photo conductor during the toner transfer phase of the developing process. The present invention permits widely varying magnetic moments by an environmentally benign ferrite carrier powder or particle while maintaining high electrical conductivity, typically less than 1×10
8
ohm-cm.
Thus it is an object of the invention to provide an improved electrophotographic development, carrier material which is environmentally safe and benign.
It is a further object of the invention to provide an electrophotographic carrier that is useful to the same degree as prior art carriers, particularly carriers comprising ferrites in combination with metal elements.
Another object of the invention is to provide an electrophotographic carrier core which maintains high electrical conductivity or low resistivity while simultaneously maintaining the capability of providing a wide range of magnetic properties as compared to prior art carriers.
A further object of the invention is to provide an electrophotographic development carrier comprised of an oxide of manganese, an iron oxide and titanium oxide or titanium dioxide.
Another object of the invention is to provide an electrophotographic carrier material which may be manufactured in the form of a particle and has the capability of being coated with a polymer resin which does not contain any conductive additives thus providing a powder that displays electrical resistivity or conductivity similar to or the same as prior art carriers that may have required such additives.
Another object of the invention is to provide a manganese ferrite powder for use as a carrier material in electrophotographic machines which can be used in machines already in service as well as new machines.
These and other objects, advantages and features of the invention are set forth in additional detail in the description which follows.
REFERENCES:
patent: 3567641 (1971-03-01), Ross et al.
patent: 3929657 (1975-12-01), Jones
patent: 4485162 (1984-11-01), Imamura et al.
patent: 4623603 (1986-11-01), Iimura et al.
patent: 4898801 (1990-02-01), Tachibana et al.
patent: 5199983 (1993-04-01), Katamoto
patent: 5419994 (1995-05-01), Honjo et al.
patent: 5595850 (1997-01-01), Honjo et al.
patent: 5693444 (1997-12-01), Takagi et al.
patent: 5798198 (1998-08-01), Sukovich et al.
Diamond, Arthur S. (editor) Handbook of Imaging Materials. New York: Marcel-Dekker, Inc. p. 202, 1991.*
Shambalev, V.N. et al. Self-Dissusion if Cations in the Solid Solution System of Ti-substituted Mn-Zn Ferrites, physica status solidi (a), vol. 11, No. 2, pp.K71-K74, Apr. 1989.*
Fleischer, Michael. Glossary of Mineral Species. Tucson: The Mineralogical Record, Inc. p. 225, 1987.*
Diamond, Arthur S. (editor) Handbook of Imaging Materials. New York: Marcel-Dekker, Inc. pp. 210-215, 222, and 223, 1991.
Hutcheson William R.
Sukovich Alan
Banner & Witcoff , Ltd.
Powdertech Corporation
Rodee Christopher
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