Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-02-18
2002-04-23
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Fixing
C399S331000, C399S333000
Reexamination Certificate
active
06377777
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a pressure roller and a heat-fixing device including such a pressure roller for use in an electrophotographic image forming apparatus. More specifically, the present invention relates to a roller for nipping a recording material for conveying the recording material, and particularly a pressure roller used in a heat-fixing device for permanently fixing a toner image onto a recording material in a recording system according to, e.g., electrophotography or electrostatic recording.
Many of conventional electrophotographic copying machines and printers have adopted, as fixing means, those of the heat-fixing type including a contact-heating hot roller fixing device exhibiting good heat efficiency and safeness and a film-heating type fixing devices requiring less energy consumption.
A heat-fixing device of the hot roller type includes a heating roller (fixing roller) as a rotating member for heating and an elastic pressure roller as a rotating member for pressurization pressed against the heating roller as basic members. A pair of the rollers are rotated, and a recording material (such as transfer paper, electrostatic recording paper, electrofax paper or printing paper) carrying a yet-unfixed toner image conveyed to a pressure nip (fixing nip) between the rollers is nipped and passed between the rollers, whereby the toner image is heat-fixed to form a permanently fixed image on the recording material surface under the action of a heat from the heating roller and a pressure at the pressing nip.
A typical of the elastic pressure roller used for the above purpose comprises a solid or hollow cylindrical core metal or metal substrate, an elastic layer formed on the metal substrate, and a toner release layer of a fluorine-containing resin formed on the outer peripheral surface of the elastic layer. In order to ensure a sufficient contact area between the recording material and the heating roller, the pressure roller is required to exhibit a sufficient elasticity so that the elastic layer is formed in a relatively large thickness. The elastic layer frequently comprises silicone rubber in view of the heat resistance.
Fixing devices of the film-heating type are disclosed, e.g., in Japanese Laid-Open Patent Application (JP-A) 63-313182, JP-A 2-157878, JP-A 4-44075 to 4-44083 and JP-A 4-204980 to 4-204984. In a typical film-heating type fixing device, a heat-resistant film (fixing film) as a rotating member for heating is pressed against a heating member (heat-generating member) while being moved in contact with the heat-generating member by the action of a rotation member (elastic roller) for pressurization, and a recording material carrying a yet-unfixed toner image is conveyed to a pressure nip formed between the heating member and the elastic roller pressed against each other via the heat-resistant film and moved together with the heat-resistant film, thereby fixing the yet-unfixed toner image to provide a permanently fixed image on the recording material under the action of a heat imparted from the heating member via the heat-resistant film and a pressure at the pressure nip.
Such a film-heating type fixing device allows economization of electricity and shortening of a waiting time (i.e., an improved quick-start performance) as the heating member can comprise a low-heat capacity linear heating member and the heat-resistant film comprises a film of a low-heat capacity.
As fixing devices of this type, there are known those according to a scheme wherein a drive roller is disposed in contact with an inner surface of the fixing film to drive the fixing film under tension and also those according to a scheme wherein a fixing film is wound loosely about a film guide and a rotating member for pressurization is primarily driven to drive the fixing film in rotation following the rotation of the rotating member. In recent years, the latter pressure rotation member (pressure roller) drive-type devices are more frequently adopted in view of a smaller number of parts required therein.
The elastic roller used for the above purpose may frequently comprise a solid or hollow core metal or metal substrate, a silicone rubber elastic layer or a silicone sponge layer formed on the metal substrate, and further a toner release layer of a fluorine-containing resin formed directly or via an adhesive layer thereon. In the commercial devices, the fluorine-containing resin layer has been given as a coating formed of a tube of fluorine-containing resin or formed by applying and baking a paint of fluorine-containing resins. In order to ensure a sufficient contact area between the recording material and the heating member, the pressure roller is required to exhibit a sufficient elasticity so that the elastic layer is formed in a relatively large thickness.
In recent years, not only in the above-mentioned pressure roller-drive type film-heating fixing device, but also in the hot roller fixing device and the fixing film-drive type film-hating fixing device, a higher-speed operation is strongly desired and also the adaptability to providing a smaller-size image forming apparatus is demanded. Further, for realizing economization of electricity, the demand for a heat-fixing device exhibiting an improved heat efficiency without requiring a standby temperature control is also increasing.
For complying with such demands for fixing devices, it is inevitably required to use a fixing roller and a pressure roller of relatively smaller diameters and operated at a relatively low pressure. Accordingly, in the case of an image forming apparatus operated at a high recording material-conveying speed, it becomes necessary to provide a broader pressure nip between the fixing roller or fixing film and the pressure roller at a low pressure in order to supply a sufficient heat to the recording material. For this reason, it has been tried to develop a pressure roller having a lower roller hardness.
For example, as a low-hardness fixing pressure roller, JP-A 7-271233 has proposed a fixing pressure roller comprising a silicone rubber layer formed from liquid silicone and having hollow pores continuous in its longitudinal direction, and also a fluorine-containing resin layer formed on the silicone rubber layer and having a surface hardness of at most 60 deg. as measured by an Asker-C hardness meter (1 kg-f).
JP-A 7-271233 has proposed a pressure roller having an elastic layer comprising a porous silicone rubber sponge layer having a hardness of 35-50 deg. (Asker-C) and a tube of PFA (tetrafluoroethyleneperfluoroalkyl vinyl ether copolymer) coating the sponge layer, thus providing an entire roller hardness (Asker-C) of 45-60 deg. so as to exhibit a good fixing performance while preventing the occurrence of paper wrinkles.
The above-mentioned JP-A 63-313182 and JP-A 2-157878 disclose a film-heating fixing device including a heating unit comprising at least a fixedly supported heating member (heater) and a cylindrical heat-resistant film for fixation conveyed while being pressed against the heating member, and a pressing member for pressing a recording material against the heating member, so as to transmit a heat from the heating member to the recording material via the film, thereby heat-fixing a yet-unfixed toner image carried on the recording material onto the recording material surface.
An example of such a heat-fixing device is illustrated in FIG.
3
. Referring to
FIG. 3
, the fixing device includes a cylindrical film
101
comprising a 40 to 60 &mgr;m-thick polyimide base film and a 40 to 60 &mgr;m-thick release layer of PFA (tetrafluoroethylene-alkyl vinyl ether copolymer) alone or in mixture with PTFE (polytetrafluoroethylene) dispersed in PFA formed thereon for constituting an outer layer contacting a recording material P and a toner image T thereon.
The fixing device also includes a heating member (heater)
102
, which basically comprises an insulating, heat-resistant and low-heat capacity ceramic substrate extends in a longitudinal direction perpendicular to the con
Hayakawa Akira
Karashima Kenji
Kawamoto Hideo
Kishino Kazuo
Kitano Yuji
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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