FIXING DEVICE

Abstract: The present invention provides a roller fixation device which uses a roller having fluororesin surface layer as a heat roller or a pressure roll of excellent durability as well as mold releasability. The fixation device may comprise a revolving body to serve as a heat roller or a pressure roller having thereon a fluororesin-mixed elastic layer such as a rubber layer, or a layer having a rubber-like elasticity, on the outside of which is a surface layer formed by coating thereon with fluororesin-coated surface layer, or a fixation device com­ prising a revolving body as a heat roller or a pressure roller having thereon a fluororesin-containing rubber layer, on which is formed a 2-to-100µm-thick fluororesin layer.

Description: BACKGROUND OF THE INVENTION The present invention relates to an improvement of the fixation device for fixing a toner image onto a recording material such as paper in image recording apparatus such as electrophotographic copying apparatus, facsimile, and the like. In electrophotographic copying apparatus, contact-type heat roller fixation devices are mostly used for fixing an unfixed image onto a recording material such as recording paper. In a process of this type, an unfixed toner image-bearing recording material is transported into between a pair of revolving bodies, a heat source-having heat roller and a pressure roller which presses thereon, to thermally fix the toner image onto the recording material. Figure 3 is a cross-sectional view of a general heat roller-type fixation device, wherein 1 is a cylindrical heat roller having thereinside such a heating means as heater 1a, which rotates clockwise in fixation; 2 is a cylindrical pressure roller which is arranged to press on the heat roller and rotates counterclockwise during fixation; a copying paper sheet P bearing a toner image consisting of unfixed toner T is transported from the right by a transport belt 3 to the heat roller 1 and pressure roller 2 thereby to be pressed and heated to be fixed and then ejected leftward; 4a and 4b are separation claws for separating copying paper P, provided so as to prevent the paper from wrapping around either heat roller 1 or pressure roller 2; 6 is a felt-like oil pad into which is impregnated a mold lubricant such as silicone oil having an appropriate viscosity; and 5 is a cleaning roller made of a brush-like fiber planted in the cylindrical form. The cleaning roller 5 revolves to remove the toner residue remaining on the circumferential surface of the heat roller and also serves to supply the mold lubricant properly to the heat roller. Those which have been used as the heat roller 1 are ones composed of an about 2-5mm-thick Aℓ pipe as a core metal and a 200-500µ-thick silicone rubber or Teflon coated therearound. And those which have been used as the pressure roller 2 are ones composed of an about 30mm⊘ cylindrical stainless steel as a core metal (a core member) covered therearound with an about 5mm-thick silicone rubber. Requirements for such roller fixation devices include functions to insure fixation without an offset phenomenon and a good mold releasability without rumpling recording paper and, when silicone oil or the like is used as a mold lubricant, high wear resistance of the surface of the rollers thereof against the silicone oil, and also against the strike by separation claws and the like. The fixation devices using the above-described conventional examples of the heat-roller were unsatisfactory for long-term use. For example, a silicone rubber-coated heat roller, although advantageous in respect that it shows a better fixability and produces less rumples on recording paper and less blurred image than does a Teflon-coated heat roller, has the disadvantage that it is poor in the mold releasability. To remove the disadvantage, an attempt has been made to coat silicone oil on the silicone rubber-coated surface to improve the mold releasability, but this tends to cause the silicone rubber to swell and to produce a compression permanent set, being accompanied by the disadvantage of a significant roller-surface wear due to the strike by separation claws or the like, when coating silicone oil on the silicone rubber surface. For this reason, fluororesin, as the roller surface material excellent in the mold releasability and not swelling even by silicone oil, has attracted attention, and thus there have been many proposals for the application of fluororesin to the surface layer of the roller. Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication)Nos.89785/1982 and 74578/1984 relate to roller fixation devices comprising a roller having a core metal provided thereon with an elastic layer, on which is further formed a fluororesin layer. Fluororesin, however, has the disadvantage that it has a high hardness and is quite different from the elastic layer thereunderneath in physical properties such as elastic modulus, and therefore, when a cardboard-type thick recording paper is fixed by a fixing device using the above roller, cracks appear on the fluororesin layer's portion corresponding to a side edge of the recording paper, and thus the resin lacks durability, because of the different level between the roller surface and the thick paper surface. Japanese Patent O.P.I. Publication Nos.135871/1982, 5770/ 1983, 27175/1983 and 90673/1983 propose roller fixation devices having a roller core metal formed thereon with an elastic layer, on which is further formed a fluororesin-containing fluororubber layer. These proposals utilize the phenomenon that, when a fluororesin-containing fluororubber is coated and burnt as the roller surface, the fluororesin comes out on the surface, whereby a fluororesin layer becomes formed. In this instance, the adherence of the surface fluororesin layer with the base material is excellent, and the thickness of the surface-deposited fluororesin layer is equal to or less than about 1µm. A fixation device which uses the thus constructed revolving body, although its mold releasability is well secured, is poor in the durability because the surface fluororesin layer is extremely thin. OBJECT AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a roller fixation device which uses a roller having a fluororesin surface layer as a heat roller or a pressure roller with excellent durability as well as mold releasability. According to the present invention there is provided a fixation device which comprises a roller comprising a fluororesin-containing rubber layer and a fluororesin surface layer from 2 to 100 micrometres thickness surrounding, and in contact with, the outside of the rubber layer. There is also provided a fixation device for fixing a recording material carrying toners of the surface thereof by pressing and transporting the recording material between two rollers characterised in that, at least one of the rollers comprises a core member, a rubber layer containing fluororesin around the core member, and a hard fluororesin layer from 2 to 100 micrometres thickness around the outer circumferential surface of the rubber layer. BRIEF DESCRIPTION OF THE INVENTION Fig. 1 ilustrates a cross-sectional view of an example of the roller-type fixation devices applicable with a revolving body relating to the invention; Fig. 2(a) and 2(b) illustrate the cross-sectional views of each example of the heat-rollers relating to the invention, respectively; and Fig. 3 illustrates an example of the pressure-rollers relating to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention relates, for example, to such a roller-type fixation device as shown in Fig. 1 in which the revolving body thereof is embodied by the invention. That is, the present invention relates to a fixation device which is such that a fluororesin-mixed rubber layer is provided between a roller core metal as the core member for the roller or an elastic layer provided on the roller core metal and a fluororesin layer as the surface layer. The fluororesin-mixed rubber layer, by being coated or burnt, is at least in the fluororesin or fluororesin-rich state at the portion thereof adhering to the fluroresin of the surface layer, so that the adherence is satisfactory, and therefore the thickness of the fluororesin layer as the surface layer can be relatively freely settled. The suitable thickness of the fluororesin layer for the roller fixation device is from 2 to 100µm, and preferably from 5 to 30µm. Since the roller core metal or the elastic layer provided on the roller core metal and the rubber layer are very well adherent to each other, a good adherence can be obtained between the layers, and since the physical properties such as elastic modulus against external pressure to the roller surface varies reasonably in order from the surface layer, the device is excellent also in durability. We have been conducting a number of experiments based on the above invention. The following Examples (1-1) and (1-2) wherein this invention is applied to the heat roller and Example (2-1) wherein this invention is applied to the pressure roller will further illustrate the present invention. EXAMPLE (1-1) This example is a heat roller having a cross-sectional form as shown in Figure 2(a), wherein 11d is a core metal in the hollow cylindrical form made of aluminum having an external diameter of 40mm⊘ and a thickness t=5mm, and 11c is an elastic layer made of a highly heat-resistant silicone rubber with t=0.3mm coated around the circumference of 11d. On the elastic layer 11c is coated and burnt a fluororesin-mixed rubber layer 11b. As the rubber layer a Daikin product Dai El Latex, CLS-213 a mixture of fluororesin with fluororubber, is used. The fluororesin-mixed rubber layer 11b is formed with a thickness t=20µm. On the rubber layer 11b is further formed a surface layer using PFA (a product of Mitsui Fluorochemical). The "PFA" is the trade name of a Teflon resin called "Teflon" PFA Fluorocarbon resin, manufactured by E.I.DuPont de Memours and Co. (Inc.). The fluororesin layer 11a consisting of PFA coated and burnt on the rubber layer 11b has a thickness t=20µm. EXAMPLE (1-2) This example is a heat roller having a cross-sectional form as shown in Figure 1(b), wherein 12d is a core metal in the hollow cylindrical form made of aluminum having an external diameter of 40mm⊘ and a thickness t=5mm, and 12b is a fluororesin-mixed rubber layer having a thickness t=300µm, coated and burnt around the circumference of 12d. As the rubber layer a fluororubber is used; a fluororesin-mixed Daikin product Dai El Latex, CLS-213 is coated and then burnt. On the rubber layer 12b is further coated and burnt a fluororesin layer 12a as the surface layer having a thickness t= 20µm, the fluororesin being PFA (a product of Mitsui Fluorochemical). EXAMPLE (2-1) This example is a pressure roller having a cross-sectional form as shown in Figure 2, wherein 21d is a core metal made of a 30mm⊘ SUS, the circumference of which is covered with an elastic layer 21c consisting of a silicone rubber (a product of Shin-etsu Chemical Industry Co., Ltd.) having a thickness t=5mm. On the surface of the elastic layer 21c is coated and burnt a rubber layer 21b comprised of a fluororesin-mixed fluororubber Daikin product, Dai El Latex, CLS-213. On the surface of the rubber layer 21b is coated and burnt a fluororesin layer 21a as the surface layer having a thickness t=10µm, the fluororesin being PFA (a product of Mitsui Fluorochemical). COMPARATIVE TEST A comparative test was made in comparison of the heat rollers (1-1) and (1-2) and the pressure roller (2-1) with those having the same external forms prepared by conventional techniques in the manner of interchanging them in a copying apparatus. The copying apparatus that was used in the test is U-Bix 3300MR (manufactured by konishiroku Photo Ind. Co., Ltd.) whose roller fixation device is of the schematic cross-sectional view shown in Figure 3. Both-side copying test was made under the following test conditions: 1. Copying speed: 33 sheets/min. (A4-size paper) 2. Transport speed: 220mm/sec. 3. Roller fixation device: 3-1. Surface temperature: 200°C (heat roller surface) 3-2. External diameter of heat roller: 40mm⊘ 3-3. External diameter of pressure roller: 40mm⊘ 3-4. Pressure force (linear pressure): 0.5kg/cm (1) Heat Roller Comparative Test The results of the comparative test of Examples (1-1) and (1-2) with those prepared by conventional techniques are given in Table 1. The test numbers (1-1) through (1-4) have fluororesin as the surface layer and have the same surface condition, but differ in the test results, which are attributed, in the cases of (1-1) and (1-2), to (1) the adaptability to external pressure due to the physical characteristic varying in stages from the surface layer toward the inside, (2) the good adherence between the layers, and (3) the slight but effective elasticity to external pressure, which functions effectively to prevent copying paper from being rumpled. The "Low-temp. run under" in the row of (1-3) of the table means that under-fixation has occurred after a run of 100-copy fixation at a room temperature of 10°C. This is due to the fact that heat is hard to be transmitted because the surface of the roller is so hard as compared to that of the other examples that the surface of the roller fails to come into close contact with recording paper or toner; that is, in (1-3), the surface fluororesin lacks elasticity. (1-5) and (1-6) are examples where fluororubber or silicone rubber is used as the surface layer, and the test results show that they are inferior in the durability to fluororesin. (2) Pressure Roller Comparative Test The results of the comparative test of Example (2-1) with those prepared by conventional techniques are given in Table 2. The heat roller that was used in this test is the one previously mentioned as (1-1). The test Nos.(2-1) and (2-2) both show good results, provided that (2-2) is one prepared by putting a silicone rubber-coated core metal into a heat-shrinkable PFA tube and heat-treating the PFA, and therefore it is to be careful in manufacture to form the external diameter of the pressure roller with its accuracy always maintained high. The above test result of (2-2) is one obtained when a specially highly accurate diameter-having roller is used. As is apparent from the results of the above-dexribed comparative test, the fixation device which uses the revolving body of this invention is excellent in the fixability and also in the durability. Particularly this effect becomes more significant when the present invention is applied to both heat roller and pressure roller. The roller surface layer consisting of fluororesin is of course not swelled by silicone oil, and therefore it insures the mold releasability and reduces wear of the surface layer. Also for this reason, silicone oil, etc., is more suitably usable. In addition, since fluororesin is elctrically insulating, if consecutive fixation operation is performed over a long period under a dry condition, the roller surface is charged to possibly cause recording paper to wrap around the roller, resulting in paper separation failure. Accordingly the combined use of a neutralizer with the roller of this invention is more effective in practicing this invention, the neutralizer being such as a metallic brush arranged so as to be grounded through the copying apparatus body and rub the roller surface. As for the abovementioned fluororesins given in the examples and those used in fluororesin-containing rubbers, tetrafluoroethylene, photopolymer of tetrafluoroethylene and hexafluoropropylene and the like which are sold under the trade name, "Teflon", as well as PFA, may be applicable, and further the other fluororesins may also be allowed to use. Also, the fluororesin layers provided over to the surface of the fluororesin-containing rubber layers may be arranged in various methods besides the coating method and the burning method, provided that no crease will occur after such a fluororesin layer is formed and the shape of a roller will not be deformed. It is needless to say that such coa tings include, for example, a spray coating and other coating methods as well as the popular coating methods. Besides the abovementioned coating methods, such fluororesin layers may be provided by molding, wetting, wrapping fluororesins around a sheet or a tube at a high temperature, or the like ways, provided that the interface between the uppermost fluororesin surface layer and the fluororesin-containing rubber layer arranged inside may be fitted well.

Claims: A fixation device which comprises a roller comprising a fluororesin-containing rubber layer and a fluororesin surface layer from 2 to 100 micrometres thickness surrounding, and in contact with, the outside of the rubber layer. The fixation device according to claim 1, characterised in that the roller comprises a core member, an elastic layer around the core member, the fluororesin-containing rubber layer around the elastic layer and the fluororesin surface layer around the fluororesin-containing rubber layer. The fixation device according to claims 1 or 2, characterised in that the fluororesin surface layer is from 5 to 30 micrometres thickness. A fixation device for fixing a recording material carrying toners on the surface thereof by pressing and transporting the recording material between two rollers characterised in that, at least one of the rollers comprises a core member, a rubber layer containing fluororesin around the core member, and a hard fluororesin layer from 2 to 100 micrometres thickness around the outer circumferential surface of the rubber layer. The fixation device according to claim 4, characterised in that both of the rollers comprise a core member, a rubber layer containing fluororesin around the core member and a fluororesin layer surrounding, and in contact with, the outside of the rubber layer. The fixation device according to claims 4 or 5, characterised in that the fluororesin surface layer is from 5 to 30 micrometres thickness.

Inventors: MOGI, MICHIO
Applicants: KONICA CORPORATION
Application year: 1985
Main classification: G03G15
IPC codes: G03G15, B32B25