Electrostatic charge developing toner and image forming...

Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...

Reexamination Certificate

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C430S108800, C430S110100

Reexamination Certificate

active

06696210

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrostatic charge developing toner for visualizing an electrostatic charge latent image formed in an electrophotographic method, an electrostatic printing method, an electrostatic recording method, or the like, and an image forming method using the electrostatic charge developing toner.
2. Description of the Related Art
Of the recording methods, for example, in the electrophotographic method, a photoconductive photosensitive body is charged and exposed so that an electrostatic charge latent image is formed on the photosensitive body. This electrostatic charge latent image is developed with fine-grained toner containing a coloring agent and so on, while using resin as a binder. The obtained toner image is transferred and fixed onto recording paper to thereby obtain a recorded image. Particularly, in such an electrostatic image recording process, development of an electrostatic charge latent image with fine-grained toner, and fixing of a toner image onto recording paper are important steps.
In the related art, a magnetic brush developing method using a binary developer composed of toner capable of high-speed and high-picture-quality development and magnetic carrier is generally used as a method for developing an image with toner.
In addition, a heat roller fixing method which is high in thermal efficiency and capable of high-speed fixing is often used as a method for fixing the toner.
On the other hand, recently, with the development of information apparatus, laser beam printers have made progress. In such a layer beam printer, a laser beam is used for exposing a photoconductive photosensitive body so as to reproduce every dot for a recorded image by a modulating signal based on instructions from a computer. Particularly, in a recent laser beam printer, the diameter of a laser beam is narrowed down to increase the dot density to 600 to 1,200 dpi (dots/inch) in order to meet the demand for producing an image with a higher picture quality.
With the increase of the dot density, the particle sizes of toner and carrier become smaller to develop a fine electrostatic charge latent image. Thus, application of fine-grained toner having a volume average particle size of not larger than 10 &mgr;m, and application of fine-grained carrier having a weight average particle size of not larger than 100 &mgr;m have been advanced.
On the other hand, heat roller fixing as described above is often used for the fixing. However, from the following points of view, development of high-performance toner which can be fixed with reduced power consumption of a fixing heater and a driving motor and with lower temperature and lower pressure of a heat roller has been desired.
1) To restrain the printer from being deteriorated due to overheating, and to prevent parts in the printer from producing thermal deterioration;
2) To shorten warm-up time from the time when a developing unit is actuated to the time when fixing becomes possible;
3) To prevent a failure in fixing due to heat absorption into recording paper, so as to make it possible to keep picture quality while feeding the paper continuously;
4) To prevent the recording paper from being curled and fired due to overheating; and
5) To reduce a load on the heat roller, and to simplify and miniaturize the structure of the fixing unit.
On the other hand, when the toner is formed into fine particles not larger than 10 &mgr;m in such a manner as described above, there arise problems as follows.
That is, fine-grained toner used in the developing step indeed brings about an image having a high picture quality, but easily causes toner adhesion (fogging) to a non-image area and toner flying. Accordingly, the handing properties in toner shipping or the like are also easily degraded due to the lowering of fluidity. Further, due to the strength of adhesion and the weakness in impact resistance of the fine-grained toner, carrier pollution (carrier spent) with the toner is easily produced so that the life of developer is easily reduced.
In addition, as for fixing, in order to obtain the same fixing strength, more energy is required than in the case where toner larger in particle size is used. Further, the yield in the steps of pulverizing and classifying in manufacturing the toner is reduced so that the cost of the toner increases.
Such a large number of problems are produced in fine-grained toner. It is usually difficult to put toner smaller than 4 &mgr;m into practical use. Therefore, toner classified to have an average particle size from 4 &mgr;m to 10 &mgr;m is used with the fluidity of the toner being enhanced by the improvement of external additives to the toner and the recipe for the external additives.
On the other hand, the weight average particle size of the carrier is set to be not larger than 100 &mgr;m with the reduction in particle size of the toner. Thus, the specific surface area of the carrier is increased to improve the frictional charging property with the toner. However, when the carrier is smaller than 30 &mgr;m, the magnetic force of the carrier is reduced to easily adhere onto an electrostatic charge image holding member due to electrostatic attraction force. Therefore, carrier classified to have an average particle size in a range of from 30 &mgr;m to 100 &mgr;m is used, and the surface of the carrier is coated with resin in accordance with necessity.
As a result of these improvements in the particle size distribution and in the fluidity and the charging property, fine-grained toner and developer have been able to be put into practical use in copying machines, printers, etc.
However, when printing is performed with real apparatus, particularly when printing at a high speed not lower than 10 pages per minute is repeated, the fine-grained toner has its own peculiar problem. The life of developer is reduced easily due to carrier spent by the toner, and the life of a photosensitive body is reduced easily due to filming of the photosensitive body with the toner.
In addition, it is difficult to obtain fixing strength of an image. Particularly in the fixing step, it is necessary to increase the temperature and pressure of a heat roller. Therefore, there has been a problem that it is difficult to make a fixing unit reliable, simple, small in size and low in cost.
In order to improve the fixing performance of toner, it has been known to add wax to fixing resin. For example, such techniques are disclosed in Japanese Patent Laid-Open No. 3304/1977, No. 3305/1977 and No. 52574/1982.
Such waxes are added to prevent toner from adhering to a heat roller at a low temperature or at a high temperature, that is, to prevent a so-called offset phenomenon.
For example, Japanese Patent Laid-Open No. 313413/1993 discloses that ethylene- or propylene-&agr;-olefin copolymer having viscosity of not higher than 10,000 poises at 140° C. is added to vinyl-based copolymer having a particular molecular weight distribution in order to improve the low-temperature fixing property, the offset resistance and the non-aggregability of toner.
In addition, for the similar purpose, Japanese Patent Laid-Open No. 287413/1995 discloses that paraffin wax showing a peak (melting point) at 75° C. to 85° C. in the amount of heat absorption measured by a differential scanning calorimeter (DSC) is added, and Japanese Patent Laid-Open No. 314181/1996, No. 179335/1997 and No. 319139/1997 disclose that natural-gas-based Fischer-Tropsch wax having a melting point in a range of from 85° C. to 100° C. measured by a DSC is added.
In addition, Japanese Patent Laid-Open No. 324513/1994 discloses that polyethylene wax having a melting point in a range of from 85° C. to 110° C. measured by a DSC is added, and Japanese Patent Laid-Open No. 36218/1995 discloses that polyethylene-based wax, in which any component having a melting point not higher than 50° C. has been eliminated by a distillation method or the like so as to make the melting point of the polyethylene-based wax be set in a range of from 70° C. to 120° C. mea

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