Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1995-08-30
2003-10-14
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109300, C430S109400, C430S109100, C430S111400, C430S108100, C430S108800
Reexamination Certificate
active
06632577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to an image forming method carried out by developing an electrostatic latent image to form a toner image and transferring the toner image to a recording medium, followed by fixing. More particularly, it relates to an image forming method in which untransferred toner having remained on an electrostatic latent image bearing member after transfer is collected by a cleaning means and again used in the development of electrostatic latent images.
2. Related Background Art
A number of methods as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publications No. 42-23910 and No. 43-24748 and so forth are conventionally known for electrophotography. In general, copies are obtained by forming an electrostatic latent image on a photosensitive member by utilizing a photoconductive material and by various means, subsequently developing the latent image by the use of a toner, and transferring the toner image to a transfer medium such as paper if necessary, followed by fixing by the action of heat, pressure, heat-and-pressure or solvent vapor.
Various methods or apparatus have been developed in relation to the above final step, i.e., the step of fixing the toner image to a sheet such as paper. A method most commonly available at present is the pressure heating system making use of a heating roller.
The pressure heating system making use of a heating roller is a method of carrying out fixing by causing an image-receiving sheet to pass over a heating roller whose surface is formed of a material having a releasability to toner while a toner image surface of the former is brought into contact with the surface of the latter under application of a pressure. Since in this method the surface of the heating roller comes into contact with the toner image of the image-receiving sheet under application of a pressure, a very good thermal efficiency can be achieved when the toner image is melt-adhered onto the image-receiving sheet, so that fixing can be carried out rapidly. This method is therefore very effective in high-speed electrophotographic copying machines. In this method, however, since the surface of the heating roller comes into contact with the toner image in a molten state under application of a pressure, part of the toner image may sometimes adhere and transfer to the surface of the fixing roller, which may re-transfer to the subsequent image-receiving sheet to cause an offset phenomenon, resulting in a contamination of the image-receiving sheet. Thus, it is one of important requirements in the heating roller fixing method to cause no toner to adhere to the surface of the heat-fixing roller.
For the purpose of causing no toner to adhere to the surface of a fixing roller, it has been attempted, for example, to form the surface of a roller by the use of a material having a good releasability to the toner, such as silicone rubber or fluorine resin, and further covering the roller surface with a thin film of a fluid having a good releasability, such as silicone oil in order to prevent offset to its surface and to prevent roller surface fatigue. Although this method is very effective for preventing the toner offset, it requires a device for feeding an offset preventing fluid, and hence has the problem that a fixing assembly becomes complicated.
Moreover, under the influence of such a device, the machine inside may be contaminated because of the evaporation of silicone oil by heat. Accordingly, from the thought that no device for feeding silicone oil should be used and instead the offset preventing fluid should be fed from the interior of the toner at the time of heating, a method is proposed in which a release agent such as low-molecular weight polyethylene or low-molecular weight polypropylene is added in the toner. When such an additive is used in a large quantity to make its addition very effective, it causes filming on the photosensitive member or contaminates the surface of a carrier or a toner carrying member such as a sleeve. As a result, deterioration of images is caused and there are problems in practical use. Accordingly, the release agent is added in toner in an amount small enough not to cause deterioration of images, and a releasing oil is fed a little or a cleaning device for removing the toner having offsetted is used in combination. The cleaning unit is a device comprising a cleaning means making use of a wind-up type member such as a web.
It is also known to incorporate a wax into toner as a release agent. For example, Japanese Patent Applications Laid-open No. 52-3304, No. 52-3305 and No. 57-52574 disclose such techniques.
Japanese Patent Applications Laid-open No. 3-50559, No. 2-79860, No. 1-109359, No. 62-14166, No. 61-273554, No. 61-94062, No. 61-138259, No. 60-252361, No. 60-252360 and No. 60-217366 disclose techniques by which waxes are incorporated into toners.
The waxes are used to improve anti-offset properties of toner in low-temperature fixing or high-temperature fixing or to improve fixing performance in low-temperature fixing.
In practice, however, good high-temperature anti-offset properties have been achieved but no satisfactory low-temperature fixing performance results, or good low-temperature anti-offset properties and low-temperature fixing have been achieved but unsatisfactory high-temperature anti-offset properties result. Thus, good low-temperature anti-offset properties and good high-temperature anti-offset properties have not been simultaneously achieved.
Now, as other methods, various attempts are made on techniques to improve of binder resins.
For example, in order to prevent the offset of toner, a method is known in which the glass transition point (Tg) or molecular weight of a binder resin in a toner is made higher to improve melt elasticity of the toner. If, however, such a method is used to improve anti-offset properties, the fixing performance may become unsatisfactory to cause the problem that fixing performance in low-temperature fixing (i.e., low-temperature fixing performance) becomes poor which is required when high-speed copying machines are used or energy saving is intended.
On the other hand, in order to improve the fixing performance of a toner, the viscosity of the toner at the time of melting must be decreased to increase the area in which the toner adheres to a fixing substrate. For this reason, it is required to make the Tg or molecular weight of the binder resin lower.
Since the low-temperature fixing performance and the anti-offset properties conflict each other in one aspect, it is very difficult to make an improvement in toners that can simultaneously satisfy these functions.
As proposals to solve these problems, for example, Japanese Patent Publication No. 51-23354 discloses a toner comprising a vinyl polymer appropriately cross-linked by adding a cross-linking agent and a molecular weight modifier, and Japanese Patent Publication No. 55-6895 discloses a toner comprising an &agr;,&bgr;-unsaturated ethylene monomer as a component unit and whose molecular weight distribution has been broadened so that the ratio of weight average molecular weight to number average molecular weight comes to be 3.5 to 40. Another proposal is made for a toner comprising a vinyl polymer in which a blended resin having specific Tg, molecular weight, gel content and so forth is used.
It is true that these toners proposed can achieve a broader fixing temperature range between lowest fixing temperature (the lowest temperature at which fixing can be carried out) and offset temperature (the temperature at which the offset begins to occur) than a toner comprising a single-component resin having a narrow molecular weight distribution, but it is difficult to make the fixing temperature sufficiently low when a satisfactory offset preventing performance is imparted. On the contrary, there is a problem that the offset preventing performance becomes unsatisfactory when importance is attached to low-temperature fixing performance.
For example, a toner comprising a binder resin comp
Akashi Yasutaka
Mikuriya Yushi
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