Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-09-26
2002-10-01
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Fixing
C399S333000, C029S895320, C492S056000, C523S218000
Reexamination Certificate
active
06459878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heating assembly and an image-forming apparatus, a process for producing a silicone rubber sponge, and a process for producing a silicone rubber sponge roller usable as a press roller for an image-heating assembly of electrophotographic image-forming apparatus such as copying machines and laser beam printers.
2. Related Background Art
Heating assemblies are conventionally in wide use as, e.g., heat-fixing assemblies for fixing unfixed images onto recording mediums used in image-forming apparatus, image-heating assemblies for heating recording mediums to modify their surface properties such as gloss, and heat-treating assemblies for drying or laminating target materials by heating.
A prior-art heating assembly will be described below taking the case of a heat-fixing assembly equipped in image-forming apparatus such as electrophotographic copying machines and printers.
The heat-fixing assembly of image-forming apparatus is a unit by which an unfixed image (toner image) corresponding to intended image information, formed and carried on a recording medium (such as transfer sheet, electrostatic recording paper, electrofax paper and printing paper) by a transfer system or direct system is thermally fixed as a permanent fixed image onto the surface of the recording medium. Widely used as the heat-fixing assembly is an assembly of contact heating type in which a heating means and a pressing means are face to face brought into pressure contact to form a pressure contact nip (a fixing nip), and a recording medium to which images are to be fixed is guided into the pressure contact nip and is held and transported between them to cause the unfixed image to fix to the recording medium surface by heat and pressure, as in a heating roller system and a film heating system. These heating systems are described below.
A) Heating Roller System
This is basically constituted of a pair of rollers pressure-contacted in parallel, consisting of a heating roller (fixing roller) as the heating means and an elastic press roller as the pressing means. The pair of rollers are rotated and the recording medium to which images are to be fixed is guided into a pressure contact nip between the pair of rollers and is held and transported between them to cause the unfixed image to fix to the recording medium surface by heat and pressure, i.e., by the heat of the heating roller and the pressure at the pressure contact nip.
B) Film Heating System
The film heating system is disclosed in, e.g., Japanese Patent Applications Laid-Open No. 63-313182, No. 2-157878, No. 4-44075, No. 4-44083, No. 4-204980 and No. 4-204984. The film heating system has a heating element and a heat-resistant film (fixing film) as the fixing means and has an elastic press roller as the pressing means. The heat-resistant film is brought into pressure contact with the heating element by the aid of the elastic press roller to form a pressure contact nip, and the heat-resistant film is brought into close contact with the heating element and is transported being slidably rubbed, where a recording medium to which images are to be fixed is guided between the heat-resistant film and the elastic press roller at the pressure contact nip to allow this recording medium to be transported together with the heat-resistant film. At this stage, the unfixed image is fixed to the recording medium surface by heat and pressure, i.e., by the heat applied from the heating element to the recording medium through the heat-resistant film and by the pressure applied at the pressure contact nip. The recording medium is separated from the heat-resistant film after it has passed the pressure contact nip.
In the heating assembly of this film heating system, a linear heating element with a low heat capacity can be used and a thin film with a low heat capacity as the heat-resistant film, and hence energy can be more saved and the waiting time can be more shortened (can be started more quickly). Also, the heating assembly of this film heating system has types of a system in which an endless belt is used as the heat-resistant film and, as a means for driving the film rotatingly, a drive roller is provided on the inner peripheral side of the film to drive the film rotatingly while a tension is applied to the film, and a system in which the film is externally loosely fitted to a film guide and a pressing rotating member as a pressing means is driven to move the film to follow up the pressing rotating member. The latter pressing rotating member drive system is often used because of an advantage that component parts can be fewer.
In the heating assembly in which the heating means and the press roller are face to face provided to form the pressure contact nip as a heating target material heating zone and the heating target material is treated by heat and pressure as in the heat-fixing assembly of the heating roller system or film heating system described above, in order to make the assembly high-speed and its waiting time shorter the press roller may be formed of an elastic material and the pressure contact nip formed between the roller and the heating means on account of the former's elastic deformation may be made wider so that the time for providing a sufficient quantity of heat to the heating target material can be ensured to improve efficiency for imparting heat to the heating target material. However, only making the pressure contact nip merely wider makes the heating assembly itself larger and at the same time results in an increase in power consumption. Accordingly, the assembly must further be improved in thermal efficiency in order to make the assembly small-sized and to achieve cost reduction and low power consumption.
From the viewpoint of an improvement in thermal efficiency of the heating assembly, the quantity of heat taken away from the heating means to the pressing means side is not negligible. Accordingly, in order to make the assembly high-speed and achieve its low power consumption, it is desired to make the pressing means have a low heat capacity. As a means for making such a pressing means have a low heat capacity, it is known, as disclosed in, e.g., Japanese Patent Application Laid-Open No. 9-114281, that a pressing rotating member having superior heat insulation properties can be produced in a good mass productivity by incorporating an elastic layer of the pressing means press roller with a hollow filler.
As the hollow filler, inorganic fillers containing air in the interior such as hollow silica, alumina, glass and glass fiber are used. However, when such inorganic type hollow fillers are used, the fillers are so hard as to make the press roller's elastic layer hard, bringing about a problem that a great pressure must be applied in order to ensure a wide fixing nip.
In addition, in heating assemblies of electrophotographic image-forming apparatus, the assemblies have become more small-sized in recent years, and press rollers used therein have also become more small-sized. Making press rollers have a small diameter brings about a tendency of making the elastic layer have a low hardness in order to ensure the nip width at the time of fixing; the elastic layer being covered on the periphery of a press roller mandrel. For example, as disclosed in Japanese Patent Publication No. 4-77315, those making use of a foamed elastic material (sponge rubber) in the elastic layer are put into practical use in a large number. However, at the time a blowing agent mixed in silicone rubber is heated to cause blowing, its blowing pressure may break cell walls of silicone rubber to make some cells of the resultant foam uncovered to the surface, or make very thin the cell walls that isolate the foam cells from the atmosphere, to form virtual concavities. Also, in the case when silicone rubber is blown in a mold, the blowing pressure extends in irregular directions, and hence irregular blowing stress stands occurred in the rubber. Thus, once the silicone rubber is taken out of the mold after
Kawamoto Hideo
Kishino Kazuo
Kitano Yuji
Nakagawa Ken
Nakazono Yusuke
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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