Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2001-11-30
2004-03-02
Braun, Fred L. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C219S216000, C399S330000
Reexamination Certificate
active
06701102
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a fixing device for heating and fixing an unfixed image formed and borne on a recording material, and an image forming apparatus such as a printer, a copier or a facsimile apparatus using the fixing device. More particularly, the invention relates to a fixing device of the film heating type or the pressure rotary member driving type, and an image forming apparatus provided with the fixing device. The fixing device of the film heating type will hereinafter be sometimes referred to as a film type fixing device.
2. Description of Related Art
In image forming apparatuses such as a printer, a copier and a facsimile apparatus using the image forming technique such as the electrophotographic process or the electrostatic recording process, heat roller fixing devices of the contact heating type good in heat efficiency and safety and energy saving type and on-demand type fixing devices of the film heating type have heretofore been widely adopted as fixing devices for fixing an unfixed image formed and borne on a recording material.
A fixing device of the film heating type is proposed, for example, in Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Application Laid-Open Nos. 4-44075 to 44083, Japanese Patent Applications Laid-Open Nos. 4-204980 to 204984, etc., and is a device having a heater (heating member), heat-resistant film (fixing film) frictionally sliding relative to this heater, and a pressure member being in pressure contact with the heater with the film interposed therebetween and forming a fixing nip portion, and in which a recording material having an unfixed image formed thereon is nipped and conveyed between the film and the pressure member in the fixing nip portion, whereby the unfixed image on the recording material is a fixed as a permanent image by heat imparted from the heater through the film and the pressure force of the fixing nip portion.
Such a fixing device of the film heating type can use a low heat capacity linear heating member as the heater, and use thin film of low heat capacity as the film and therefore, the saving of electric power and the shortening of waiting time (the quick starting property) are possible.
Also, in the fixing device of this film heating type, as driving systems for the fixing film, there are a system using a conveying roller and a driven roller exclusively for the conveyance of the film and conveying the fixing film between the conveying roller and a pressure roller as the pressure member while applying tension, and a tensionless system for rotatively driving the pressure roller as the pressure member to thereby drive cylindrical fixing film by the conveying force of the pressure roller. The former has the advantage that the conveying property of the fixing film can be heightened, and the latter has the advantage that the construction of the device can be simplified to thereby realize a low-cost device. In recent years, the latter rotary member driving system for pressurization has often been adopted because of the small number of parts required in it.
Also, with the recent development of the computer industry, the demand for printers has been on the rise and printers have come to be used in various countries of the world. Thus, recording materials used are rich in the variety of type, thickness, surface property, etc. and at the same, coupled with the higher speed of the image forming apparatus, the instantaneous quantity of heat given from the heater to the recording material has been increased little by little to thereby obtain a satisfactory fixing property from the viewpoints of the shortening of the printing time for the first sheet, the securement of the fixing property of the first printed sheet, etc. Further, in recent years, the user's requirement for a high quality of image has increased and printers excellent in dot reproducibility and halftone reproducibility have been announced, and the particle diameter of a toner which is a visualizing agent (developer) has been made smaller, whereby a higher image of quality has been achieved.
When use was made of developing devices of the film heating type and the pressure rotary member driving type and 50 sheets were passed in intermittent printing, “slip jam” occurred in the fixing devices.
The slip jam (hereinafter referred to as the slip) is a phenomenon which is caused by the pressure roller and a recording material (hereinafter referred to as the paper sheet) bearing an unfixed image thereon slip relative to each other when in a fixing device of the film heating type and the pressure rotary member driving type which is pressure roller driving and film driven (tensionless), the paper sheet has been conveyed to the fixing nip portion.
The result of the measurement of the rotational speed of the film effected by a laser Doppler speed meter in a state in which the slip occurred is shown in
FIG. 14
of the accompanying drawings. As shown in
FIG. 14
, it will be seen that from the moment when the paper has been nipped by the fixing nip portion, the paper slips, whereby the speed of the film becomes lower and the driving force from the pressure roller is not transmitted to the film. Therefore, the paper sheet cannot be conveyed at a constant speed and the slip occurs.
Further, when the confirmation of the slip has been made, it has been found that the slip is liable to occur under the following conditions.
Condition (i): the moisture absorbing amount of the recording material (paper sheet) is high.
Condition (ii): the temperature of the pressure roller is high.
Condition (iii): the dot percentage of the print pattern is high.
About Condition (i)
Media various in texture, basis weight, etc. are used for printing. Among these, there are media which absorb moisture when they are left under a high-temperature high-humidity environment. Therefore, when in the course of printing, the paper is conveyed to the fixing nip, the pressure roller and the film are sufficiently warmed by the heating of the heater, and when the paper sheet is nipped by the fixing nip, steam is created from the paper. The steam created at this time is present between the pressure roller and the paper sheet and therefore, the conveying force of the pressure roller is not transmitted to the film through the paper and the film slips.
The heater is heating also during the time when the film slips, and by time elapsing after the slip has occurred, the steam contained in the paper evaporates, and when the driving force from the pressure roller comes to be transmitted to the film through the paper sheet, the paper conveying speed comes to be obtained stably (FIG.
14
). However, by the slip occurring at first, paper conveyance is delayed to thereby cause jam.
Generally, as paper liable to cause slip, mention may be made of paper having the moisture content of 8.0% or greater when left under 23° C. and 70% RH, and 70 g/m
2
or less as the basis weight.
About Condition (ii)
The fixing temperature during printing (target temperature) is determined so that the fixing property can be secured and heat offset may not occur. Further, the fixing temperature (target temperature) is determined in conformity with the temperature detected by a thermistor immediately before printing is started, and is controlled so as to become a high heater temperature in a state in which the fixing device has been cooled as when a power source switch has been closed, and further, when printing is continued, the pressure roller, a film guide, a rigid pressure stay (a T-stay or a metallic stay), etc. are warmed and therefore, it is a usual practice to lower the fixing temperature in conformity with the number of printed sheets.
When intermittent printing is effected, the pressure roller is heated by the remaining heat in each printing course and the heat thereof is accumulated therein and therefore, the temperature tends to become high as compared with that in continuous printing.
Also, the heater
Hasegawa Hiroto
Izawa Satoru
Kanari Kenji
Miyamoto Toshio
Suzumi Masahiko
Braun Fred L.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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