Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-12-14
2003-05-27
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109400
Reexamination Certificate
active
06569592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming an image which is obtained by employing an electrophotographic apparatus utilizing an electrophotographic process such as a copying machine, a printer and a facsimile.
2. Description of the Related Art
In an electrophotographic process, multiple methods such as a method disclosed in Japanese Patent Laid-Open No. 23910/1967 have been known. Ordinarily, a fixed image is formed through plural processes in which a latent image is electrically formed by various ways on a photosensitive material utilizing a photoconductive substance, this latent image is developed using a toner, the thus-developed toner latent image on the photosensitive material is transferred onto a transfer material such as paper and a sheet to reveal a toner image either via or not via an intermediate transfer material, then, the thus-transferred image is fixed on the transfer material such as the paper and the sheet The photosensitive material is optionally cleaned to remove the toner left thereon by various types of ways and the thus-removed toner is provided again in the plural processes described above.
As for a fusing technique for fusing the transferred image which has been transferred on a surface of the transfer material, a fusing method utilizing a heat roil system in which the transfer material (herein also optionally referred to as paper or sheet) on which the toner image is transferred is inserted into between a pair of rolls including a heating roll and a pressure roll to fuse the toner image. Such fusing method can obtain a firmly fused image at a high speed compared with other fusing methods whereupon energy efficiency is high and a detrimental effect to environment to be caused by vaporization of a solvent is small.
In recent years, an effort for increasing a copying speed has been paid in a field of the copying machines for the purpose of enhancing productivity, however, when fusing is executed at a higher speed by using a fusing apparatus of a nip roll system, it is necessary that same quantities of thermal energy and pressure as those in a case at a low speed are added to the toner and the paper. For this reason, it is necessary that a width of a pressure-contact portion (hereinafter referred to as “nip”) of a roll becomes larger in proportion with a process speed. As for a method of widening a nip width, there exist a method of increasing a load between the rolls, a method of increasing a thickness of an elastic body and a method of increasing a diameter of the roll. In the method of increasing the load or the method of increasing the thickness of the elastic body, a shape of a nip along a width direction may come to be uneven derived from a strain of the roll to cause a fusing unevenness or generation of a wrinkle on paper, hence, there intrinsically is a limitation on the load to be applied and a thickness of the elastic body. Further, in the method of increasing the diameter of the roll, though there is no such a quality problem of as described above, there is a problem that a size of the apparatus becomes large whereby a time (also referred to as warm-up time) for raising a temperature of the roll from a room temperature to a fixable temperature is prolonged.
In order to solve these problems and correspond to an increase of speed in operation, a method of using an endless belt (hereinafter referred to as “belt-nip system”) disclosed in Japanese Patent Laid-Open No. 132972/1986 has been propose. A fusing apparatus of the belt-nip system has an endless belt which is tightly stretched between plural support rolls in a rotatable manner, and a heat-fixing roll which forms the nip by contacting the endless belt Paper on which an undeveloped toner image is formed is allowed to pass through the nip formed by the heat-fixing roll and the endless belt to perform fixation by a pressure and a thermal energy generated in the nip. By taking such a constitution, a width of the nip to be formed by the endless belt and the heat-fixing roll can easily be larger than that formed by an ordinary nip-roll system whereby it becomes possible to correspond to the increase of speed in operation. Further, when compared at a same process speed, the constitution can be smaller in size than that of a fusing roll of the roll-nip system.
In the fusing method by means of the roll-nip system or the belt-nip system, the toner image and the roll or the belt arc contacted with each other whereupon, at the time of fusing, a phenomenon that a portion of the toner is stuck to the roll or the belt, that is, a so-called hot offset, is likely to occur. Particularly, when a fusing temperature of the fusing apparatus is high, an agglomerating force of the toner is deceased to cause a problem that the hot offset is likely to occur.
Further, in recent years, in order to decrease an energy consumption, it is desired that fusing can be performed at a lower temperature. Particularly, in order to attain a far higher degree of energy saving, it is desired to turn off electricity to the fusing apparatus when it is not in use whereupon it is necessary to raise a temperature of the fusing apparatus to a working temperature immediately after the apparatus is excited. For this reason, it is desirous to allow a heat capacity of the fixing apparatus to be as low as possible; however, on such an occasion, the temperature of the fusing apparatus tends to be fluctuated in a larger amplitude than usual. Namely, an overshoot of a temperature after the electricity is turned on becomes large and, at the same time, a decrease of a temperature derived from passing the paper becomes large. Further, a difference between temperatures of a portion through which the paper is passed and other portions to be derived when the paper having a width narrower than that of the fusing apparatus is continuously passed therethrough also become large. Particularly, in some case in which a high speed copying machine or printer is used, a power supply capacity is likely to be short whereupon such a tendency as described above is large. Therefore, the toner which can be fused at a low temperature and does not generate the hot offset up to a range of a far higher temperature, that is, has a wide fusing latitude is desired.
In order to decrease the fusing temperature of the toner, an adoption of a crystalline resin as a binder resin is proposed in Japanese Patent Laid-Opens No. 24702/1992, No. 24703/1992, and No. 329917/1997; however, though such a method as described above can decrease the fusing temperature, the hot offset resistance is not necessarily sufficient. Namely, though there is an effect of preventing generation of the hot offset to some extent by allowing a melted toner to be penetrated in paper, the melted toner tends to be excessively penetrated in the paper to cause a problem that an image having a uniform high density can not be obtained.
On the other hand, in order to prevent the generation of the hot offset, it is known that a low molecular weight polymer and a high molecular weight polymer are blended to produce a mixture which is then used as a binder resin of the toner containing a resin having an appropriate molecular weight distribution (disclosed in Japanese Patent Laid-Open No. 134652/1975) and it is also known that a resin having a crosslink therein is used (disclosed in Japanese Patent Laid-Open No. 23354/1975). However, these methods as described above can not obtain the wide fusing latitude enough to satisfy requirements of recent years. By using a large quantity of the high molecular weight polymer or a crosslinked polymer, it becomes difficult to generate the hot offset but, instead, the fusing temperature is increased. On the other hand, when a molecular weight of the low molecular weight polymer is decreased or a quantity of this polymer is increased in order to decrease the fusing temperature, a temperature of generating the hot offset is decreased. Further, the fusing temperature can be deceased either by decreasing a glass transition
Daimon Katsumi
Fukushima Norihito
Hamano Hirokazu
Imai Takashi
Ishihara Yuka
Fuji 'Xerox Co., Ltd.
Goodrow John
Oliff & Berridge,PLC
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