COATED FIXING ROLLER

Abstract: Reprographic fixing roller in which the metal surface of the roller (1) is covered with a non-stick perfluorocarbon polymer coating (2) containing metal flakes (3).

Description: TITLE COATED FIXING ROLLER BACKGROUND OF THE INVENTION The present invention concerns a fixing roller used to thermally fix an unfixed toner image that has been formed on a transfer paper with an electronic photocopier or similar device. In copiers and printers that make use of electronic photograpy, when a thermal fixing method is employed, an unfixed toner image that has been formed on a transfer paper is generally thermally fixed by means of a fixing apparatus that combines a fixing roller and pressure roller. The fixing roller used here is ordinarily one in which the surface of a metal roller that houses a heater is covered with polytetrafluoroethylene (PTFE) or other such non-stick mold-releasing type of resin layer. However, because the thermal conductivity of the surface layer of this fixing roller is low (the thermal conductivity of the metal roller is 200 to 300 xlO 4 cal • cm" *1 • sec" 1 • deg -1 , while the thermal conductivity of the resin layer is only 2 to 8 xlO 4 cal • cm" 1 • sec -1 deg -1 ) , a width of the nip formed between the fixing roller and the pressure roller had to be kept wide in order to attain the thermal efficiency needed for the desired fixing rate, and as a result, the nip pressure (the roller pressure used to form the nip) went up and the load torque increased, and this in turn led to accelerated deterioration of the parts of the appartus. Previously, it has been proposed that particles of carbon, aluminum, copper, silicon nitride, boron nitride, or other such materials with high thermal conductivity be added to the mold-releasing resin layer in an effort to ameliorate the problematic areas, for example Japanese Laid-Open Patent Applications 55-17946 (1980) , 60-80883 (1985) , and 64- 72185 (1989) . With the proposed fixing rollers, however, the addition of highly thermally conductive particles brought about a different problem in that the mold- releasing performance of the surface layer was diminished, which produced offset, etc. The present invention offers a fixing roller in which those above-mentioned problems inherent in prior art are eliminated, the fixing performance is enhanced by raising the thermal conductivity without decreasing the mold-releasing performance of the surface layer, and the load torque is reduced, thereby allowing the life of the parts to be extended. SUMMARY OF THE INVENTION The present invention provides a coated fixing roller in which the surface of a metal roller is covered with a non-stick mold-releasing type of resin layer, wherein said fixing roller is characterized by the fact that the above-mentioned resin layer contains a flake-form metal. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is one example of the fixing roller of the present invention. Figure 2 is a detail of A in Figure 1. And Figure 3 is a graph showing the results of the fixing test performed in the practical examples. In Figure 1 and 2, 1 is a metal roller, 2 is a non-stick mold-releasing resin layer that contains a flake-form metal, and 3 is a flake-form metal. In Figure 3, a is a conventional fixing roller, b is a fixing roller of the present invention, which contained 15% stainless steel flake in the coating, and c is a fixing roller of the present invention, which contained 30% stainless steel flake in the coating. DETAILED DESCRIPTION One example of the structure of the fixing roller of the present invention is shown in Figure 1. In the figure, 1 is the metal roller that makes up the core (in a pipe form) and 2 is the non-stick mold- releasing resin layer that contains flake-form metal. Although not depicted in the figure, a heater is housed in the metal roller 1. Figure 2 shows a detail of A in Figure l. In the figure, 3 is the flake-form metal. Here, since there is a chance that the mold-releasing performance of the fixing roller surface will be diminished if the flake-form metal 3 appears on the surface of the resin layer 2, this flake-form metal should be positioned nearly parallel to the surface of the metal roller 1 as to be present as much as possible in the interior of the resin layer 2, as shown in Figure 2. Examples of this flake-form metal include stainless steel, aluminum and alloys thereof, nickle, titanium, and silver, with stainless steel being particularly desirable. Alloys based on or containing at least 50% by weight of any of such metals may be used. Preferably the stainless steel contains 15-25% chromium, optionally also 7-16% nickel and further optionally 1.5-4% molybdenum. Compositions are given below. The content of the flake-form metal should be approximately 5 to 55 % with respect to the resin layer. Percentages herein are by weight except where indicated otherwise. Types of stainless steel used with the invention include flakes of Japanese steel alloys SUS304, SUS430 and SUS316L. The composition of the alloys are in Table I. Table 1 SUS304 SUS430 SUS316L C <0.080 < 0.12 <0.030 Si < 1.00 < 0.75 < 1.00 Mn < 2.00 <1.00 < 2.00 P < 0.045 < 0.040 < 0.045 S < 0.030 < 0.03 <0.030 Cr 18.00-20.00 16.00-18.00 16.00-18.00 Ni 8.00-10.50 < 0.60 12.00-15.00 Mo - - 2.00-3.00 Examples of non-stick mold-releasing resins include PTFE, tetrafluoroethylene resins that have —-= perfluoroalkoxy groups (PFA) , and mixtures of these. A conventional metal roller that houses a heater can be used without modification in the present invention. Examples of the types of materials that can be used for this metal include aluminum and alloys thereof, iron, and copper. To create the fixing roller of the present invention, either the surface of the metal roller is coated with a non-stick mold-releasing resin that has been blended with a flake-form metal, or this resin is made into a film and stuck onto the roller surface, or a resin layer is formed by means of thermal absorption. To position the flake-form metal in the resin layer so that it is nearly parallel to the surface of the metal roller, for example, the viscosity of an undiluted solution of PTFE should be lowered slightly, the spray pressure raised to 4 kg/cm 2 (57 PSI) , and this solution sprayed on during the manufacture. In any case, the thickness of this resin layer should be approximately 5 urn to 40 urn. When an unfixed toner image is thermally fixed with a combination of a pressure roller and the fixing roller of the present invention, because the surface resin layer contains a flake-form metal, the fixing performance is enhanced without diminishing the mold-releasing performance of the surface. In particular, when the flake-form metal is positioned in the resin layer nearly parallel to the surface of the metal roller, an even better effect is achieved. The present invention will now be described by giving practical examples. The fixing roller of the present invention was created by covering the surface of a metal roller made from an aluminum alloy with a PFA resin layer containing flake-form stainless steel and with a thickness of 25 urn and the change in the fixing rate due to the surface temperature of the fixing roller was examined by conducting a fixing test. Two different stainless steel contents in the resin layer were produced - 15% and 30% (weight percent, the same for all further references) . Also, a test was performed for a conventional product produced in the same manner except that there was no stainless steel in the resin layer. These results are shown in Figure 1. Curve a in the figure is the conventional product, which contained 0% stainless steel, and Curves b and c are the products of the present invention, which contained 15% and 30% stainless steel respectively. It can be seen from this figure that the fixing rate of the fixing roller b of the present invention, which contained 15% stainless steel, and that of the fixing roller c of the present invention, which contained 30% stainless steel, were enhanced approximately 10% and approximately 30%, respectively, over that of the conventional fixing roller a, which did not contain stainless steel or other such metal. Similar effects were confirmed for the use of aluminum or alloys thereof and nickel in place of the stainless steel, and for the use of a mixed system of PFA and PTFE containing 5-25% PFA (preferably about 15% PFA) , or PTFE alone. Because the fixing roller of the present invention contains a flake-form metal in the surface resin layer, the thermal conductivity can be enhanced without diminishing the mold-releasing performance of the surface, and as a result, the fixing performance is enhanced, thereby eliminating the occurrence of offset and other related problems. This effect is particularly pronounced when the flake-form metal is positioned in the resin layer nearly parallel to the surface of the metal roller. And when a fixing rate is obtained that is equivalent to that of a conventional fixing roller that contains no stainless steel or other such metal, because, for the same reason, the nip width can be made narrower with the fixing roller of the present invention than with a coventional product, the nip pressure can be reduced, and as a result, the load torque can be decreased, thereby extending the life of the parts of the apparatus, among other benefits.

Claims: Claims 1. A fixing roller in which the surface of a metal roller is covered with a perfluorocarbon polymer layer, wherein said fixing roller is characterized by the fact that said polymer layer contains a flake-form metal. 2. The fixing roller of claim 1 in which the flake-form metal is selected from stainless steel, aluminum, nickel, titanium, silver, and alloys based on any of said metals. 3. The fixing roller of claim 2 in which the flake-form metal is stainless steel. 4. The fixing roller of claim 3 in which the stainless steel contains, by weight, 15-25% chromium and, optionally, 7-16% nickel and 1.5-4% molybdenum. 5. The fixing roller of claim 2 in which 5- 55% by weight of the coating is flake-form metal. 6. The fixing roller of claim 5 in which 15-30% by weight of the coating is stainless steel. 7. The fixing roller of claim 6 in which about 30% by weight of the coating is stainless steel. 8. The fixing roller of claim 2 wherein the perfluorocarbon polymer is at least one of polytetrafluoroethylene and a copolymer of tetrafluoroethylene and perfluoroalkoxy monomers.

Inventors: AMITA AKIYASU, HAGIWARA MINORI, HIGAYA TOSHIAKI, AMITA, AKIYASU, HAGIWARA, MINORI, HIGAYA, TOSHIAKI
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1991
Main classification: B32B5
IPC codes: B05D5, G03G15