Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1978-07-31
1981-05-05
Welsh, John D.
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
430109, 430137, G03G 914
Patent
active
042659922
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a one-component type developer for electrophotography. More particularly, the invention relates to an electrically conductive magnetic developer capable of development without the use of a magnetic carrier, in which fixing and electric resistance-controlling fine particles are tightly held on the surfaces of fixing magneto-sensitive particles in the substantially non-embedded state, whereby low electric resistance and good flowability, desireable for the development operation, can be maintained and contamination of the background or parts of a copying machine with the above-mentioned fine particles separated from the surfaces of the fixing magneto-sensitive particles can be drastically diminished.
(2) Description of the Prior Art
As one of methods for developing electrostatic latent images formed by electrophotography, there has heretofore been broadly adopted a so-called magnetic brush method. According to the basic magnetic brush method, toner particles comprising a pigment and a resin imparting a fixing property and desirable electric characteristics to the pigment are mixed with a magnetic carrier such as iron powder to form a developer, and an electrostatic latent image-carrying surface of a support is tightly contacted with magnetic brushes composed of this developer to visualize the latent image with the toner particles. In this method using such mixture of a toner and a magnetic carrier, only the toner particles are consumed by the development operation and the mixing ratio of the toner to the magnetic carrier is changed. Accordingly, there must be conducted a troublesome operation of supplying the toner into a developing mechanism to maintain a predetermined mixing ratio between the toner and magnetic carrier.
A so-called magnetic developer as disclosed in the specification of U.S. Pat. No. 3,639,245 or Japanese Patent Application Laid-Open Specification No. 20729/75 is known as a developer capable of development with a toner alone without the use of a particular carrier. A customarily used magnetic developer of this type is ordinarily formed by dispersing a powder of a magnetic material such as triiron tetroxide, optionally with other pigment, into a binder resin medium, forming the resulting composition into particles and embedding an electrically conductive substance such as carbon black into the surfaces of the particles to impart to the entire particles a property of being magnetically attracted and to render the surfaces of the particles electrically conductive.
This magnetic developer has an advantage that a clear and sharp image with reduced edge effects can be obtained according to the magnetic brush development method without using a magnetic carrier or the like. However, preparation of this magnetic developer involves various defects and difficulties.
Further, such known magnetic developers are still insufficient with respect to the flowability of developer particles, and because of this insufficient flowability, various troubles are caused at the developing step. More specifically, since the known magnetic developer has not a flowability sufficient to apply the developer uniformly onto a developing roller (sleeve), for example, masses of the developer are formed on the surface of the sleeve and the background is often contaminated when such masses of the developer particles fall down on a copying sheet or the like. Further, blurred images are readily formed because of non-uniform adhesion of the developer particles to the sleeve surface.
As means for improving the flowability of particles of a magnetic developer, there is known a method in which finely divided silica is incorporated as a lubricating agent in the magnetic developer particles. Since the electric resistance of the silica powder adhering around the particles of the electrically conductive magnetic developer is relatively high, the electric resistance of the developer as a whole is increased and such defects as blurring of image contour
REFERENCES:
patent: 3196032 (1965-07-01), Seymour
patent: 3239465 (1966-03-01), Rhemfrank
patent: 3558492 (1971-01-01), Proskow
patent: 3639245 (1972-02-01), Nelson
patent: 3645770 (1972-02-01), Flint
patent: 3933665 (1976-01-01), Van England
patent: 4022738 (1977-05-01), Shimada et al.
Aizawa Tatsuo
Kouchi Toshihiro
Takayama Hiroshi
Mita Industrial Company Limited
Welsh John D.
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