Claims
- 1. A roller fixing device comprsiing a plurality of rollers in which adjacent rollers are in contact under pressure with respect to each other, at least one of said rollers being provided with a resilient material and its outer surface with a thin non-adhesive coating layer of expanded porous polytetrafluoroethylene (PTFE) film, said coating layer rendered nonporous near the region of its external surface but otherwise porous, said coating layer wrapped along axial direction of said roller and copy paper carrying toner images thereon can be passed between said plurality of rollers to thereby fix the toner images on paper.
- 2. The roller fixing device of claim 1 wherein said coating layer is wrapped helically about said roller.
- 3. The roller fixing device of claim 1 wherein said coating layer is wrapped longitudinally along axial direction of said roller.
- 4. The roller fixing device of claim 1 wherein said coating layer contains an electroconductive filler material.
- 5. The roller fixing device of claim 1 wherein said coating layer is an oriented film.
- 6. The roller fixing device of claim 1 wherein said coating layer has thickness less than 0.15 millimeters.
- 7. A method of making a roller fixing device having a plurality of rollers comprising wrapping at least one of said rollers at its outer surface with a non-adhesive coating layer of a porous film of expanded polytetrafluoroethylene where copy paper carrying toner images pass between said plurality of rollers to fix the toner images on the paper.
- 8. A method as described in claim 7 comprising helically wrapping at least one of said rollers with a non-adhesive coating layer of a porous film of expanded PTFE.
- 9. A method as described in claim 7 comprising longitudinally wrapping at least one of said rollers with a non-adhesive coating layer of a porous film of expanded PTFE.
BACKGROUND OF THE INVENTION
This is a continuation of application Ser. No. 585,277, filed Mar. 1, 1984, now abandoned.
This invention concerns a roller fixing device for use in an electronic copying machine, particularly adapted to prevent the occurrence of off-set phenomena due to the migration of toner images on a heat fixing roller of the electronic copying machine, and enables the efficient fixing of toner by reducing the temperature rise time of the heating roller, as well as enabling one to obtain a clear copy product with little or no luster in the toner images after fixing.
In an electronic copying machine intended for dry reproduction, a fixing method has generally been employed in which toner images formed electrostatically or magnetically on copy paper are passed between two rotating rollers in contact with each other under pressure, and one or both of the rollers is heated from the inside.
This fixing process using the above-mentioned method has various advantages such as ease in the rapidity and high heat efficiency compared with other types of fixing methods and, accordingly, this roller-fixing method has been utilized in most electronic copying machines presently in use. However, because toner images on copy paper are compression-contacted in a heat-fused stated to the circumferential surface of the heated roller, a so-called "off-set phenomenon" results, wherein toner images may partially be deposited and caused to migrate on the circumferential surface of the roller, or the deposited toner images migrate to the other roller and can be retransferred to develop on the next copy paper, thereby contaminating the same. In order to prevent such a deposition on the toner images, the heat and/or press roller, which generally are made of metals such as stainless steel and aluminum, are coated at their surfaces with a non-adhesive thin film made of a material which has excellent release characteristics with respect to the toner images. For example, fluoro resins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) have been used, or silicone resins, which are coated directly on the metal roller, or after previously coating the roller with rubber-like elastic material such as synthetic rubber as a buffer layer.
Conventional methods of forming the non-adhesive thin film on the roller surface includes a method of preparing a heat-shrinkable tube made of the foregoing FEP resin, fitting the heat-shrinkable tube over the roller, and then shrinking the same under heating to apply a coating. A method of coating the above-mentioned PTFE resin by applying a liquid dispersion, solution or powder to the roller, carrying out baking the applied coating and, thereafter, forming a non-adhesive thin film by means of surface lapping or the like.
In the case where the thin film is formed by such a method, it generally results in a problem, in that the heat conductivity of the heated roller is reduced thereby lessening the stability in the temperature on the roller surface. The roller may not function well as a fixing roller in view of the non-adhesiveness, luster may be produced on the copy products affecting their appearance, or clear copies can not be obtained.
The method using a heat-shrinkable tube suffers from the problem that there is a limit in the thickness of the heat shrinkable tube as a result of the method of its production to render it difficult to further reduce the film thickness and, accordingly, the heat conductivity of the heat roller is lessened requiring a much greater time for the temperature to increase on the roller surface, thereby retarding the fixing. This also provides the drawback of increased production costs due to the use of the heat-shrinkable tube.
If the surface hardness of the fixing roller (heat and/or press roller) is high, fused toners are liable to be compressed excessively upon pressurization resulting in luster in the toner images, thereby affecting the appearance of the copy or, in an extreme case, the profile of the toner images is blurred. In view of the above, although it has been attempted to dispose a resilient material such as a silicone rubber as a buffer layer between the metal roller and the heat-shrinkable tube, such a combination has not yet provided fully acceptable results effect because of the large minimum thickness of the heat-shrinkable tube, leaving room for further improvement.
In the other case where the above-mentioned PTFE resin is coated as a liquid dispersant, solution or powder onto the roller to form a thin, non-adhesive film through baking or the like, the inherent non-adhesiveness of the resin is significantly reduced on baking and, therefore, there is a problem in view of the lessened releasability of the toner during long use and it suffers from lessened durability.
A roller fixing device is provided having a plurality of rollers in which adjacent rollers are in contact under pressure with respect to each other, at least one of the rollers being provided at the outer surface thereof with a nonadhesive coating layer, and copy paper carrying toner images thereon can be passed between this plurality of rollers to thereby fix toner images on the paper, wherein the coating layer is a porous film of open cell cellular plastic wrapped about at least one of the rollers. The coating layer can be helically wrapped about the roller or longitudinally wrapped along the axial direction of the roller. The plastic film may contain electroconductive filler material. The open cellular plastic film is preferably an oriented film of porous, expanded polytetrafluoroethylene. The coating layer can be rendered non-porous near the region of its external surface but otherwise be porous or it can be rendered nonporous throughout. The coating layer preferably has a thickness of less than 0.15 millimeters.
US Referenced Citations (12)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 0165719 |
Dec 1985 |
EPX |
Continuations (1)
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Number |
Date |
Country |
| Parent |
585277 |
Mar 1984 |
|
Patent Grant
4796046
