Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-11-22
2002-04-09
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Fixing
C399S329000
Reexamination Certificate
active
06370352
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to Japanese patent application No. JPAP11-332716 filed on Nov. 24, 1999 in the Japanese Patent Office, the entire contents of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that is capable of effectively performing an image fixing process.
2. Discussion of the Background
An image forming apparatus that forms an image with toner based on an electrophotographic printing method has come into widespread usage in a variety of products, such as a copying machine, a printing machine, a facsimile machine, etc. In the electrophotographic printing method, a latent image formed with an electrostatic force is dusted with toner so that a toner image is generated and which is then transferred onto a recording sheet. The toner image thus placed on the recording sheet is then subjected to a fixing process in which the toner image is fixed onto the recording sheet, generally, by applications of heat and pressure using rollers, so that an image is firmly formed on the recording sheet.
The toner used in the above-mentioned image forming apparatus generally has a property of an extremely high viscosity as a plastic within a range of from a softening state to a state before a perfectly melted state (i.e., often referred to as a rubber-like-state range). Such toner thereby has a relatively high self-condensing force. Therefore, such toner is not prone to cause an offset problem in which the toner makes a deposition on a part of a fixing member, such as a roller for applying heat and pressure to the toner and the recording sheet.
In the perfectly melted state, however, the toner greatly decreases the viscosity of the plastic, which accordingly decreases the self-condensing force. As a result, the toner is likely to cause the above-mentioned offset problem. Therefore, an actual fixing process by heat is conducted with the toner in the rubber-like-state.
A melting point of the plastic used for the toner requiring a relatively high viscosity in the rubber-like-state is relatively high and, therefore, the fixing temperature is necessarily increased. Thereby, the fixing process in the image forming apparatus consumes relatively great heat energy.
In response to a recent increasing movement of saving energy and natural resources for a global environmental conservation, efforts for reducing electric power consumption have been put into practice, even in an image forming apparatus. The fixing process particularly requiring a high electric power consumption, as described above, is under a process to change into a low-temperature fixing process. To put it this concept into practice, the toner is required to have a relatively low softening point or melting point. With such a lowered softening point or melting point, the thermoplastic resin used in the toner characteristically shows a relatively low melting viscosity.
The melting viscosity in this case is referred to be as the one either at a temperature of the softening point or at a temperature higher than the melting point. More specifically, such softening and melting points correspond to softening and flow-start temperatures, respectively, for example, as specified by Shimadzu Corporation, Japan, for a measurement with a flow-tester manufactured by Shimadzu Corporation. In addition, the rubber-like-state corresponds to a range of from a softening temperature to a flow-start temperature.
The above-mentioned characteristics of the thermoplastic resin are determined by various factors, such as a softening point or a melting point, a molecular weight of the resin, a distribution of the molecular weight, an extent of crystallization, an extent of bridging between the molecules, an intermolecular force, etc. Among these factors, it is possible to lower the softening point or melting point of a resin having the same structure by lowering the molecular weight or the extent of bridging or by narrowing the distribution of the molecular weight. The distribution of the molecular weight, however, has a lower limit defined by a life limit of the resin and, if the molecular weight itself is lowered, the distribution of the molecular weight is necessarily narrowed. In general, a reduction of a molecular weight makes chains of the molecules shorter, which then causes relatively loose connections between the molecules, so that the melting viscosity is lowered. If the distribution of the molecular weight is narrowed, the connections between the molecules are loosened and as a result, the melting viscosity is also lowered. Further, if the extent of bridging between the molecules is lowered, each molecule is made more mobile and as a result, the melting viscosity is lowered.
For example, Japanese Laid-Open unexamined application, publication number 51-29825, describes a fixing method of electrophotography, which uses a fixing station using a film sheet as a part of a fixing member. In this method, after applying heat to a recording sheet, the fixing station conducts a cooling process for cooling the film sheet and the recording sheet, while holding them in close contact with each other. Upon completion of the cooling process, by which time the toner is hardened, the fixing station removes the film sheet from the recording sheet. This method includes a forced cooling process, such as cooling with a fan and cooling with water.
Japanese Laid-Open unexamined applications, publication numbers 63-118291, 63-118292, and 63-118293, describe a thermal transfer recording method. This method fixes a hot-melt print medium, which includes wax as a main component and therefore has a relatively low viscosity, relative to a film, even during a continuous print operation, avoiding the offset problem. In general, the print medium used in the thermal transfer recording includes wax as a main component thereof and the viscosity of such wax is in the range of approximately between 10-10
4
[c poise], which assures relief of the offset problem.
The above thermal transfer recording method uses a technique, which removes a film sheet from a recording sheet after a temperature of the hot-melt print medium, measured with a differential scanning calorimeter (DSC), is reduced below a temperature of a top peak value, after the hot-melt print medium is applied with heat and is melted. Specifically, Japanese Laid-Open unexamined application, publication number 63-118291, describes a forced cooling method, such as with cool blown air using a refrigerant, such as water, Freon gas, etc. Japanese Laid-Open unexamined application, publication number 63-118292, describes a method for transporting a film sheet and a recording sheet together in close contact through a cooling station. Japanese Laid-Open unexamined application, publication number 63-118293, describes a mechanism for separating a film sheet from a recording sheet and also a mechanism for holding the film sheet and the recording sheet together in close contact until the film sheet is separated from the recording sheet.
The above techniques used in the above-mentioned thermal transfer recording methods solve a problem of print medium deposition on the film sheet and which is deemed to be similar to the above-mentioned offset problem in the electrophotography fixing process. Hence, an electrophotography image forming apparatus utilizing the above-mentioned techniques has been developed, which can therefore fix a toner image with a toner of a comparatively lower melting viscosity. Such an electrophotography image forming apparatus can use a toner of the melting viscosity at the conventional level, such as the one greater than 10
13
[c poise], without a problem. This image forming apparatus does not cause the offset problem, but creates another problem when using a toner of the melting viscosity smaller than 10
13
[c poise].
Specifically, toner having melting visc
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pendegrass Joan
Ricoh & Company, Ltd.
LandOfFree
Method and apparatus for image forming capable of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for image forming capable of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for image forming capable of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2843181