Image fixing roller with perforate outer layer

Abstract: An image fixing elastic roller includes a metal core (1), a sponge layer (2) provided around the metal core, and a fluoroplastic layer (3) provided around the sponge layer (2), in which the fluoroplastic layer (3) is formed with a plurality of holes (A, B) in a predetermined distribution for suppressing paper wrinkles. The fluoroplastic layer (3) is preferably formed with a higher distribution density of holes (A, B) at a central portion thereof than at end portions thereof.

Description: The present invention relates to a roller for fixing electrophotographic images, and more specifically, to an image fixing roller which is used as a pressure roller for uniformly pressing an image support sheet relative to an image fixing heating roller. In general, fixing devices conventional of electrophotographic copying machines or the like are structured such that a non-fixed toner image transferred onto an image support sheet, such as a paper sheet, is heat-pressed between a non-adhesive heating roller and an elastic pressure roller so as to be melted and fixed thereon. Conventional toner image devices are generally formed by providing a heat-resisting resilient layer, e.g., silicone sponge, around a metal core, and further providing a non-adhesive layer, e.g., fluoroplastic on the outer periphery of the resilient layer to prevent the adhesion of toner to the pressure roller. Since it is common to operate such a fixing device intermittently, it is desired that the heating roller rapidly increases its surface temperature to start the fixing operation within a short period of time after the fixing device is brought into operation. Similarly, it is also desired that the pressure roller approaches the surface temperature of the heating roller within a short period of time after the fixing device is brought into operation. In view of this, the resilient layer of the pressure roller is generally formed of a sponge layer having a relatively low heat capacity and low heat conductivity. However, there has been a problem such that it has been difficult to fix high-quality images on a number of paper sheets continuously in accordance with the prior art fixing devices, since paper wrinkles are easily formed with a lapse of operating time after the activation of the fixing device. It is, therefore, an object of the present invention to provide an improved image fixing roller capable of suppressing or limiting generation of paper wrinkles, notwithstanding the continuous fixing of images, thereby providing a large number of high-quality fixed images in a successive manner. According to an aspect of the present invention, an image fixing elastic roller for uniformly pressing an image support member with a heated fixing roller comprises a metal core; a sponge layer provided around the metal core; and a fluoroplastic layer provided around the sponge layer, wherein the fluoroplastic layer is provided with a plurality of distributed holes, so arranged as to substantially equalise the temperature along the length of the roller. Optionally, the distribution density of the holes in the fluoroplastic layer is larger at a central portion of the roller than at end portions thereof. The present invention will be more fully understood from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the present invention, which are given by way of example only. and are not intended to limit the present invention. Fig. 1A is a front view of an image fixing roller for illustrating first and second preferred embodiments of the present invention, as compared with a comparative example; and Fig. 1B is a side view of the image fixing roller of Fig. 1A. Preferred embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In Figs. 1A and 1B, there are shown the front and side views of an image fixing roller for explaining first and second preferred embodiments of the present invention and also a comparative example. Figs. 1A and 1B therefore illustrate a resilient image fixing roller having an outer layer provided with a plurality of holes in a predetermined distribution. First, the comparative example will be described. Referring to Fig. 1B, an iron core 1 having a diameter of 12mm was applied with a primer. Thereafter, the primed iron core 1 was coated with a foaming silicone rubber composition by extrusion. The silicone rubber composition was then heated to expand it and vulcanised so as to form a foamed silicone rubber sponge layer 2. In the illustrated embodiment the sponge layer 2 has 32 degrees of Asker C-type hardness (load = 300g) with an expansion ration of 170% and a thickness of approximately 6mm. Subsequently, the surface of the sponge layer 2 was abraded and had a bridged type adhesive applied thereto, and then was coated with a fluoroplastic layer. In this embodiment the sponge layer 2 was coated with a PFA (perfluoroalkoxyl) plastic tube, which was made adhesive at the inner side and had a thickness of 50µm; heat was then applied for adhesion of the fluoroplastic. Hence an elastic roller having an outer diameter of 20mm and a length of 225mm with fluoroplastic layer 3 at its periphery and an Asker C-type hardness (load = 300g) of 45 degrees was produced. The first preferred embodiment will be described hereinbelow. Embodiment 1 The surface of the elastic roller of the sample was pricked with a needle, which in this embodiment had a length of 3mm and a diameter of 0.6mm, at intervals along straight lines at angle to the longitudinal axis of the roller. A margin was provided at the ends of the roller. In the illustrated embodiment the holes were formed at intervals of 10mm along 8 straight lines, which are in parallel and at an angle of 45 degrees with respect to the longitudinal centre axis of the elastic roller with a margin of 12.5mm from both ends of the elastic roller. As a result, an elastic roller of the first preferred embodiment was produced having the fluoroplastic layer 3 provided with 21 holes A aligned on each of 8 straight lines, a total of 168 holes. The second preferred embodiment will now be described hereinbelow. Embodiment 2 The surface of the elastic roller of the first embodiment was further pricked with a needle, which in this embodiment had a length of 3mm and a diameter of 0.6 mm, at intervals along straight lines at an angle to the longitudinal axis of the roller and between the straight lines of the first embodiment. In the illustrated embodiment holes were formed at intervals of 10mm for providing 10 holes on each of 8 additional straight lines between the 8 straight lines of the first embodiment with a margin of 67.5mm from both ends of the elastic roller. A total of 80 holes B were formed. As a result, an elastic roller of the second preferred embodiment was produced having the fluoroplastic layer 3 provided with 10 additional holes B aligned on each of 8 additional straight lines. There were thus arranged 248 holes (A and B) in total in a zigzag fashion at the central portion of the roller for providing a higher distribution density of the holes at a central portion than at end portions thereof. A test has been carried out with an electrophotograph fixing device incorporating the fixing elastic rollers of the present invention. By activating the device, electrophotographic copying was successively performed in the following order: a: copied black solid images on 2 sheets of copying paper of 60g; b: copied character images on 30 sheets of copying paper of 60g; and c: copied black solid images on 2 sheets of copying paper of 60g. The copying operation was repeated with respect to 5 rollers for each of the examples, for the first preferred embodiment and second preferred embodiment. Evaluation of the copying was implemented by utilising the copied black solid images whether or not there were any paper wrinkles. The first sheet of the black solid image copied by step a was designated a1 and the second sheet a2; the first sheet of the black solid image copied by step c was designated c1 and the second sheet c2. The results of the evaluation are given in Table 1, wherein each Figure represents the total points for each of the 5 elastic rollers. A score of 2 was given for sheets with no paper wrinkles, a score of 1 for sheets with earthworm-like wrinkles and a score of 0 for sheets with paper wrinkles. elastic roller a1 a2 c1 c2 comparative example 10 10 3 3 embodiment 1 10 10 5 8 embodiment 2 10 10 10 8 As will be appreciated from Table 1, according to the preferred embodiments of the invention, wherein the image fixing elastic rollers are provided with holes provide considerably improved image quality after repeated of copying vis-à-vis the comparative example. Thus, the present invention suppresses the formation of paper wrinkles. Accordingly, in the fixing device incorporating the elastic rollers of the preferred embodiments of the present invention, a stable fixing operation can be performed immediately after the heating roller is warmed to a required temperature. In addition, the paper wrinkles are suppressed even when the fixing of images is successively performed. Further, in accordance with the present invention, the stable fixing operation can be continued reliably for a large number of high-quality images on copying paper. As will be further appreciated from Table 1, according to the second preferred embodiment, the image fixing elastic roller having concentrated holes A and B at the central portion further improves the image quality after repeated vis-à-vis the comparative example. It is to be understood that this invention is not to be limited to the preferred embodiments and modifications described above, and that various changes and modifications may be made without departing from the scope of the invention as claimed.

Claims: An image fixing elastic roller for uniformly pressing an image support member with a heated fixing roller, which image fixing elastic roller comprises: a metal core; a sponge layer provided around the metal core: and a fluoroplastic layer provided around the sponge layer characterised in that the fluoroplastic layer is formed with a plurality of holes so arranged as to substantially equalise the temperature along the length of the roller. The image fixing elastic roller as defined in claim 1, wherein the distribution density of the holes in the fluoroplastic layer is larger at a central portion of the roller than at end portions thereof. The image fixing elastic roller as defined in claim 1, wherein the holes are provided along 8 straight lines, which are in parallel and 45 degrees apart with respect to the longitudinal centre axis of the elastic roller. The image fixing elastic roller as defined in claim 3, wherein the holes are provided at intervals of 10mm along the 8 straight lines with a margin of 12.5mm from both ends of the elastic roller. The image fixing elastic roller as defined in claim 2, wherein a first group of holes are provided along 8 straight lines, which are in parallel and 45 degrees apart with respect to the longitudinal centre axis of the elastic roller and a second group of holes are provided along 8 straight lines between said 8 straight lines. The image fixing elastic roller as defined in claim 5, wherein the first group of holes are provided at intervals of 10mm along the 8 straight lines with a margin of 12.5mm from both ends of the elastic roller and the second group of holes are provided at intervals of 10mm along the 8 additional straight lines with a margin of 67.5mm from both ends of the elastic roller. The image fixing elastic roller as defined in any of claims 1 to 6, wherein the diameter of each hole is substantially 0.6mm. The use of a roller as defined in any of claims 1 to 7 to control wrinkling of paper in an electrophotographic copying machine. An electrophotographic copying machine comprising a roller as defined in any of claims 1 to 7.

Inventors: SAITO SHINJI, SUGIZAKI AKIHIKO, UCHIDA YUJI, SAITO, SHINJI, SUGIZAKI, AKIHIKO, UCHIDA, YUJI
Applicants: NITTO KOGYO KK, NITTO KOGYO CO., LTD.
Application year: 1995
Main classification: G03G15
IPC codes: F16C13, C09D127, G03G15