Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-11-04
2004-09-14
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108800, C430S110200
Reexamination Certificate
active
06790577
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a toner for developing an electrostatically charged image in pressure fixing type and heat roller fixing type (also referred to hereinafter as “pressure heating type” or “pressure heating system”).
More specifically, this invention relates to a practically applicable toner type developing agent of the dry one-component magnetic type, dry one-component nonmagnetic type, dry two-component type, liquid dried type, or liquid type that can be pressure fixed onto film or other substrates to be copied, has adequate fixing properties (hereinafter referred to as “fixing ability”), toner spent properties, and transparency to enable pressure fixing at a low temperature of less than 100° C. even in the case of heat roller fixing, can form sharp images, and is excellent in high-speed fixing ability and preservation stability, thereby enabling to secure an adequate temperature range in which offset phenomena will not occur (hereinafter referred to as “offset-free temperature range”).
This invention also concerns the above-mentioned toner that can be applied widely in copiers, printers, facsimile machines, color copiers, color laser copiers, color laser printers, and high speed electrophotographic printers.
BACKGROUND ART
With recent rapid spread of office automation, there have been growing demands, in electrostatically charged image developing copiers and printers, for higher resistance to mechanical impact for accommodating to high-speed printing and demands for high grade images, in other words, sharpness, low-temperature fixing ability and excellent light transmittance for accommodating to color toners.
Such needs for high speed copying and high grade images require to secure the necessary and adequate toner particle strength and a wide offset-free temperature range that enables practical applications at low temperatures. Furthermore, it is expected to realize the oil-free type copying methods, which do not require oil feeding to the fixing roll and thus bring no problem of soiling the substrates to be copied.
Under these circumstances, the present inventor found and discloses in JP-A-2000-66438 that a toner for developing a heat roller fixing type electrostatically charged image comprising a polyolefin resin having a cyclic structure as the binder resin and adopting a suitable combination of fatty acid amide wax, oxidized polyethylene wax, polyethylene wax and acid-modified polypropylene wax so as to impart various functions, can answer the above demands.
This toner, however, has limits in terms of the copying speed and fixing temperature in heat roller fixing applications. Meanwhile, the market has recently been demanding even higher copying speeds and adequate accommodations for demands for low-temperature fixing due to the need of saving electric power.
In forming full color images with three or four colors (Y: yellow, M: magenta, C: cyan, B: blue) added and mixed by the electrophotographic method, the process of transfer onto the substrate to be copied needs a toner particle which is infinitely close to sphere or true sphere and has smooth surface conditions.
However, the conventional mechanical milling method and air impact milling method using a high-velocity air flow could hardly be successful in preparing toners that were spherical and had smooth surfaces.
In heat roller fixing systems which are currently and generally used for fixing a full-color image onto paper, OHP film, or other substrates to be copied, an excessive amount of heat must be supplied to fix a three- or four-color toner, and silicone oil or the like should also be supplied to the fixing roller to prevent transfer of toner onto the heat roller (so-called “offset phenomenon”).
Performances required of a toner are diverse and include charging properties, fixing ability, wear resistance, conveyability, preservation stability (the tendency of toner particles not to agglomerate mutually and form lumps even after a long period of time), etc. However, a toner obtained by dry mixing in a conventional compounding method is not satisfactory in meeting all such needs.
In order to answer each of the above needs, a toner must be provided with various conflicting functions. In order to solve such problems, microcapsule toners having a structure in which a core material (core substance) particle called “core” is encapsulated with a shell material (shell substance) called “shell” have been being proposed. For example, a binder resin which has a good fixing ability, but tends to give rise to the offset phenomenon due to poor preservation stability may be used as the core material, and a coating resin which has good preservation stability and offset-free property may be used as the shell material, thereby satisfying the conflicting demands.
Ideas have been proposed concerning such function-separated type microcapsule toners. For example, JP-A-9-292735 discloses a film fixing heating type image forming device that uses a microcapsule toner prepared by a suspension polymerization method. JP-A-59-53856 and JP-A-59-61842 disclose examples prepared by the similar method.
Also, JP-B-56-13945 proposes a preparation method based on the spray drying method; JP-B-8-16793 proposes a preparation method based on the water-drop phase separation method; and JP-A-3-56970 proposes a preparation method in which the shell layer is formed by an in situ polymerization method and to get microparticles using a high-pressure homogenizer.
Besides the above, interfacial polymerization methods, coacervation methods, dry capsule methods, etc. have also been introduced.
However, these prior art techniques, except for the spray drying method, use water as a medium, thus rendering the drying process troublesome. Therefore, they were inadequate for producing microcapsule toners at an industrial scale.
Also, the spray drying method had a difficulty in obtaining uniform particulates of the desired average particle diameter, usually of 10 &mgr;m or less.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a microcapsule toner which can be adequately used in a low-temperature heat fixing system or in a pressure fixing system that enables high speed copying, as well as in a heat roller fixing system, solves the problems of prior-art microcapsules, and yet is excellent in preservation stability and prevention of the offset phenomenon.
The present inventor has completed this invention upon finding that the above-described problems can be solved by using two types of olefin copolymers, each having a cyclic structure but differing in glass transition temperature and number average molecular weight, one being used as a binder resin for the core and the other as a resin in the shell for coating the core (coating resin), of a microcapsule toner particle.
More specifically, this invention provides a toner for developing an electrostatically charged image which comprises a microcapsule toner particle composed of a core and a shell, the core comprising a colorant and a binder resin containing an olefin copolymer having a cyclic structure, said olefin copolymer having a glass transition temperature ranging from −20° C. to less than 60° C. and a number average molecular weight ranging from 100 to 20,000, and the shell comprising a resin for coating the core.
The invention also provides a toner for developing an electrostatically charged image which comprises a microcapsule toner particle composed of a core comprising a colorant and a binder resin; and a shell comprising a resin for coating the core containing an olefin copolymer having a cyclic structure, said olefin copolymer having a glass transition temperature ranging from 60° C. to 180° C. and a number average molecular weight ranging from 1,000 to 100,000.
The invention furthermore provides a toner for developing an electrostatically charged image which comprises a microcapsule toner particle composed of a core and a shell, the core comprising a colorant and a binder resin containing an olefin copolymer having a cyclic structure, said
Dote Janis L.
Ticona GmbH
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