ELASTIC ROTATABLE MEMBER AND FIXING APPARATUS USING SAME

Abstract: An elastic rotatable member (1) conveniently usable as an image fixing member has a base member, a first primer layer (3), an elastic layer (4), a second primer layer (5) and a resin layer (6) in the order named. The first primer layer (3) has a thermal conductivity higher than that of the second primer layer (5). Using the elastic rotatable member (1), the sheet conveying property, releasability, wear resistance and durability are improved.

Description: The present invention relates to an elastic rotatable member usable in various image forming apparatuses such as an electrophotographic copying machine and laser beam printer, more particularly to an elastic rotatable member conveniently usable for a conveying roller for conveying transfer sheets or recording materials in the image forming apparatuses and an image fixing roller for fixing a toner image on the transfer sheets or recording materials in the image forming apparatuses. The present invention also relates to an image fixing apparatus using such an elastic rotatable member. Since the elastic rotatable member according to the present invention is most conveniently usable as an image fixing roller in an image fixing apparatus, the following description will be mainly directed to an image fixing roller or an image fixing device. In the field of image forming apparatus such as an electrophotographic copying machine, a conveying roller for conveying, along a predetermined passage, a transfer sheet or recording material which is usually a paper sheet is required to have conveying property, releasability and durability. Among various conveying rollers, an image fixing roller is required to have those properties and wear resistance and image fixing property under more severe conditions, since it has to apply heat to an unfixed toner image on the transfer sheet and has to convey the transfer sheet to a predetermined passage while preventing toner off-set. In the field of the image fixing technique, it is general that a heat-fixing roller for contacting directly to the toner image comprises a core metal coated with a resin layer such as tetrafluoroethylene resin or the like, and that a pressing roller press-contacted to the heat-fixing roller to increase the heating period for the toner image comprises a roller coated with a rubber layer. The recording material such as paper supporting a toner image is passed through a nip region established by the couple of rollers. However, since the surface of the heat-fixing roller contactable to the toner image is almost a rigid body, it does not follow an unsmoothness of the paper surface or the toner image, with the result that the heat is not transferred efficiently when the toner image is pressed. The fixing ability and the image quality are worse than when a rubber roller is used at the toner contacting side. Additionally, there is recognized more low temperature off-set because of the worse fixing ability. Further, curling and wrinkles of the paper by the toner image fixing under high humid conditions are more remarkable than when the rubber roller is used at the toner image contacting side. Where, however, a rubber roller is used as a roller for contacting the toner image, the releasability property of the surface of the roller easily changes with time, and therefore, it can exhibit good property with a very little toner off-set at an initial stage of use, but the releasability is gradually deteriorated with the number of operations. Once the roller is contaminated by the toner, it is difficult to remove it from the roller by a cleaning member, so that the off-set rapidly increases. Also, when a rubber roller is used, the roller surface is easily worn by a member or members disposed in contact with a sheet separation pawl and a temperature sensor, because the wear resistance thereof is low. If this occurs, localized insufficient image fixing and localized toner off-set are increased. As described above, the rubber roller and the resin roller have their own advantages and also the corresponding disadvantages. An elastic roller having the advantages of the rubber roller and the resin roller is desired. To meet the desire, proposals have been made as to a roller having an elastic rubber layer and a resin layer thereon in U.S. Serial Nos. 793,546 filed on October 31, 1985, 831,729 filed on February 21, 1986 and 877,849 filed on June 24, 1986. The rollers disclosed in those applications exhibit surface resin property, a sufficient total elasticity, a fixing ability, wear resistance and releasability, which are better than those in the prior art. Still, an improvement of such a roller is desired in the bonding strength between the elastic rubber layer and the resin layer and in the thermal deterioration resulting when the resin layer is formed on the elastic rubber layer by sintering. From the JP-A 61-83 567 an elastic rotatable member is known comprising a basic member, a primer layer, an elastic material layer, a mixed layer and an internal surface part containing a fluorine rubber and a resin component layer at the external surface side. The subject matter of the application is based on the object, to provide an elastic rotatable member and an image fixing apparatus using the same according to which the bonding strength between the elastic material layer and the resin layer is improved wherein the elastic material layer does in no way suffer any damage from the thermal treatment. This object is solved by the features of claim 1 and 11, respectively. The design of a second primer layer between the resin layer and the elastic material layer allows an increase of the bonding strength between the elastic material layer and the resin layer and, besides, guarantees that, when producing the resin layer which is a process requiring a relatively high heat, there is no negative impact on the properties of the heat sensitive elastic material layer. The present invention will become more apparent upon a consideration of the following description of the preferred embodiments taken in conjunction with the accompanying drawings, in which: Figure 1 is a sectional view of an image fixing apparatus using the elastic rotatable member according to an embodiment of the present invention; Figure 2 is a sectional view of rollers and Figure 3 is a sectional view of an example of apparatus for manufacturing the image fixing roller. Referring to Figure 1, there is shown an electrophotographic copying machine as an example of an image forming apparatus, which includes an image fixing device for heat-fixing a toner image, using an elastic rotatable member according to this invention. As shown in Figure 1, the image fixing device includes a heat-fixing roller 1 which contains therein a heating source H and which is adapted to contacting the toner image T supported on a transfer sheet P (an image bearing member) and a pressing roller 10 for pressing the transfer sheet P supporting the toner image T to the heat-fixing roller 1. In this embodiment, the heat-fixing roller 1 and the pressing roller 10 have generally the same layer structure. More particularly, each of them includes a core metal 2 (12), a first primer layer 3 (13), an elastic material layer 4 (14), a second primer layer 5 (15) and a surface resin layer 6 (16) which is a surface releasing layer, in the order named. Both the first and the second primer layer serves as a bonding layer. The elastic layer 4 (14) is of a material having a relatively high thermal conductivity. Also, the first primer layer 3 (13) inside the elastic layer 4 (14) is of a material having a relatively high thermal conductivity. On the other hand, the second primer layer 5 (15) outside the elastic layer 4 (14) is of a material having a good thermal insulation property, that is, a relatively low thermal conductivity. The thermal conductivity of the first primer layer 3 (13) is larger than the thermal conductivity of the second primer layer 5 (15). Preferably, the thermal conductivity of the elastic layer 4 (14) is larger than the thermal conductivity of the first primer layer 3 (13). The structures and thermal conductivities will be described in more detail hereinafter. In this embodiment, the heat fixing roller 1 and the pressing roller 10 have the same structure of layers, but the above structure may be incorporated into at least one of those rollers, preferably into the heat-fixing roller 1 contacting the toner image, leaving the pressing roller 10 having a conventional structure. The fixing device is provided with a temperature sensor G for detecting the surface temperature of the heat-fixing roller 1 so as to maintain the surface temperature at an optimum temperature to fuse the toner, 160 - 200 °C, for example and is also provided with an off-set preventing liquid applying and cleaning means C for applying off-set preventing liquid such as silicone oil or the like onto the surface of the heat-fixing roller 1 and for cleaning the surface of the heat-fixing roller 1. The layer structures will be described in detail. The surface of the heat-fixing roller 1 has a core metal 2 of aluminum or the like which has a relatively high thermal conductivity and the first primer layer 3 of a silicon material which has a relatively good or high thermal conductivity, preferably has a thermal conductivity not less than 0.6x10³ cal.cm/(sec.cm².°C), and preferably has a layer thickness 2 - 30 µm. On the first primer layer 3 is formed an elastic layer 4 of a fluorine or silicone rubber which has a relatively high thermal conductivity, preferably has a thermal conductivity not less than 0.8x10⁻³ cal.cm/(sec.cm².°C), and preferably has a layer thickness of 0.3 - 2.0 mm. On the elastic layer 4 is formed the second primer layer 5 of a silicone or fluorine material which has a relatively good thermal insulation property, preferably has a thermal conductivity not more than 0.4x10⁻³ cal.cm/(sec.cm².°C), and preferably has a layer thickness of 5 - 60 µm. On the second primer layer 5 is formed a resin layer 6 of a PFA resin (tetrafluoroethyleneperfluoroalkoxyethylene copolymer resin), PTFE resin (tetrafluoroethylene resin) or another fluorine resin which has a layer thickness of 5 - 35 µm and has a film strength of not less than 50 kg/cm². The pressing roller 10 has the core metal 12 of stainless steel or iron or the like and the first primer layer 13 of a silicone material having a relatively high heat conductivity, preferably having a thermal conductivity not less than 0.6x10⁻³ cal.cm/(sec.cm².°C) and has a layer thickness of 2 - 30 µm. On the first primer layer 13 is formed an elastic layer 14 of fluorine rubber or silicone rubber which has a relatively high thermal conductivity, preferably has a thermal conductivity of not less than 0.8x10⁻³ cal.cm/(sec.cm².°C), and preferably has a layer thickness of 3 - 10 mm. On the elastic layer 14 is formed the second primer layer 15 of a silicone or fluorine material which has a relatively high thermal insulating property, preferably has a thermal conductivity not more than 0.4x10⁻³ cal.cm/(sec.cm².°C). and preferably has a layer thickness of 5 - 60 µm. On the second primer layer 15 is formed a resin layer 16 of the PFA resin, PTFE resin or another fluorine resin, which preferably has a layer thickness of 5 - 35 µm and preferably has a film strength of not less than 50 kg/cm². Each of the heat-fixing roller 1 and the pressing roller 10 has a symmetricity about a center line between longitudinal ends, and preferably, the heat-fixing roller 1 (or the pressing roller 10) is reversely crowned, that is, the diameter in the middle between the longitudinal ends is slightly smaller than the diameters at the opposite ends. The description will be made with respect to the method of manufacturing the above-described heat-fixing roller 1 and the pressing roller 10. As for the manufacturing of the heat-fixing roller 1, an aluminum core metal 2 is prepared so as to have a finished surface and have the center diameter of 58.3 mm (6.5 mm in thickness and 150 µm of the reverse-crown). The surface then is degreased by sandblasting and is dried. On the core metal 2, a silicone primer is applied in the thickness of 7 µm and is air-dried, the primer having the thermal conductivity of 0.8x10⁻³ cal.cm/(sec.cm².°C)(after the air drying). Then, a heat curing type silicone rubber sheet having a relatively high thermal conductivity (1.5x10⁻³ cal.cm/(sec.cm².°C)) is wrapped thereon and is press-vulcanized at 160 °C for 30 minutes. Thereafter, the surface is machined to provide the rubber thickness of 0.5 mm, whereby a silicone rubber roller is manufactured. On the silicone rubber roller, a fluorine primer having a good thermal insulation property is applied in the thickness of 15 µm and is air-dried (thermal conductivity thereof is 0.2x10⁻³ cal.cm/(sec.cm².°C)(after the air drying)). PFA powder is sprayed thereon into the thickness of 20 µm. The core metal is masked with a thermal insulation member. The surface of the PFA resin is heated by infrared heating at a temperature not less than crystal fusing melting, 340 °C for example for 30 minutes to sinter the PFA coating, while cooling the inside of the core metal by air. Then, it is cooled quickly. By the cooling or quenching, the sintered fluorine resin surface layer has resin properties including a crystallinity not more than 95 %, the tensile strength not less than 50 kg/cm² and contact angle with respect to water not less than 100 degrees. Further, the sintered resin layer having a sufficient thickness is strongly bonded to the rubber roller. The sintering of the surface fluorine resin layer may be effected by using dielectric heating method. As shown in Figure 3, a dielectric heating device uses both of dielectric heating and external infrared heating. It includes a magnetron 105, a waveguide 106 for propagating high frequency wave (950 - 2450 MHz) produced by the magnetron 105, an openable resin container 102 communicating with the waveguide 106 and having a metal plate 103 for reflecting the high frequency wave, and two top and two bottom infrared lamps 111 with shades for externally heating it by infrared rays. In the resin container 102, there are provided a fan 100 for producing air flow in the inside of the hollow heat-fixing roller 1 and a fan 101 for producing air flow in the container 102, both of the fans being driven by external driving means. The container is openable by rotating an upper half thereof about a pivot 108. The upper frame is provided with a grip 109, while the lower half is provided with an arm 107 for positioning a flange 1A of the roller 1. Control means 110 controls operations of the driving means 104, the magnetron 105 and the infrared lamp 111. Since the heat-fixing roller 1 has an inside silicone rubber layer 4 and a surface fluorine resin layer 6, the high frequency wave is mainly absorbed by the fluorine resin layer 6 since it has a larger dielectric constant than the silicone rubber layer 4. Therefore, the fluorine resin layer 6 is quickly heated by the high frequency wave and the infrared rays and also by the heat accumulated in the constant temperature oven, and is completely sintered at the temperature not lower than the crystal melting temperature of the fluorine resin, at 340 °C for example, for 15 minutes. After the sintering, the roller is quenched. In this embodiment, the surface fluorine resin is preferably PTFE dispersion, such as those available from Daikin Kabushiki Kaisha, Japan as tetrafluoroethylene resin dispersion D-1. By using the dielectric heating technique, the loss of energy is minimized, and in addition, the heat attack to the elastic layer is minimized. What should be considered in the manufacturing of the elastic rotatable member of the present invention is that when the unsintered resin material is heated and sintered after it is applied on the second primer layer, the elastic layer under the second primer layer is to be maintained below the temperature at which the material constituting the elastic layer is durable. On the other hand, the pressing roller 10 is manufactured in the similar manner. The core metal 12 is of iron, but the materials of the elastic layer 14, the first and second primer layers 13 and 15 and the resin layer 16 are of the same materials as of the heat-fixing roller 1. However, the layer thicknesses of the first primer layer 13, the elastic layer 14, the second primer layer 15 and the resin layer 16 are, 7 µm, 6 mm, 15 µm and 20 µm, respectively. The outer diameter of the pressing roller 10 is the same as that of the heat-fixing roller. For both of the heat-fixing roller 1 and the pressing roller 10, the first primer is, for example, of silane coupling agent, silane compound having a molecular weight larger than that of the silane coupling agent, catalyser, metal powder and red ion oxide diluted by solvent available from SHIN'ETSU KAGAKU KOGYO KABUSHIKI KAISHA. And, it is sprayed on the core metal and is air-dried. For both of the heat-fixing roller 1 and the pressing roller 10, the second primer is, for example, of amine silane coupling agent, PTFE powder diluted by solvent available from SHIN'ETSU KAGAKU KOGYO KABUSHIKI KAISHA. It is sprayed on the elastic rubber layer and is air-dried. The elastic rubber layers 4 and 14 of the heat-fixing roller 1 and the pressing roller 10 are not deteriorated by heat during the fluorine resin layer being heat-sintered, and the rubber properties thereof such as impact resilience are substantially the same as those before the sintering, which are desirable. Also, the surface layer 6(16) of the fluorine resin is completely sintered and shows very good releasability, wear resistance and the bonding strength with the elastic rubber layers 4(14). The reason is considered as follows. According to this embodiment, the first primer layer 3(13) below the elastic layer 4(14) has a relatively high thermal conductivity, while the second primer layer 5(15) on the elastic layer 4(14) has a relatively low thermal conductivity, that is, a higher insulating property. Therefore, when the surface resin is sintered at a temperature not less than the resin crystal melting point to form a sintered resin layer 6(16), the second primer layer 5(15) is attacked by heat, but the heat transmission to the elastic layer 4(14) is retarded or substantially prevented due to the relatively higher insulation property of the second primer. Moreover, even if the heat is transmitted to the elastic layer 4(14) so that the elastic layer 4(14) is attacked slightly by heat, the heat is released without difficulty to the core metal 2(12) through the first primer layer 3(13) since the first primer layer 3(13) under the elastic layer 4(14) has a relatively high thermal conductivity, whereby the heat is not accumulated in the elastic layer 4(14). It is considered that the elastic layer 4(14) is protected from deterioration by heat in this manner. On the other hand, the second primer layer 5(15) having a relatively higher insulating property is effective to prevent transmission of heat, and therefore, sufficient thermal energy is applied to the surface resin material, whereby the resin material is completely sintered with the result of sufficient resin property. Together with the sintering of the resin material, and with the bonding function of the second primer layer 5(15), a strong bonding strength is provided between the elastic layer 4(14) and the resin layer 6(16), and therefore, the surface resin layer 6(16) is not peeled off easily. Endurance tests have been conducted using the heat-fixing roller 1 and the pressing roller 10 of this embodiment under the following conditions: surface temperature of the heat-fixing roller 1: 180 °C sheet speed: 200 m/sec sheet feed: 30/(A4 size.min) Under the condition of 15 °C, the fixing ability was good, and the occurrences of toner off-set were reduced down to not more than one fifth of those in conventional devices. Further, the period between necessities of exchanging the cleaning member was increased up to not less than 5 times. Under the conditions of 32.5 °C and the relative humidity of 85 %, the transfer sheets were not wrinkled, and very few curling was recognized so that the sheets were stacked in a sorter or the like in good order. Additionally, the image was hardly crushed, and the image quality was satisfactory. Those good results were maintained even after 300,000 sheets were passed through the nip between the heat-fixing roller 1 and the pressing roller 10, and even after 500,000 sheets were passed therethrough. As described, when the elastic rotatable member 1(10) is used as a heat-fixing roller 1 of an image fixing device, the good thermal conductivity of the first primer layer 3 and the elastic layer 4 is effective to reduce the thermal resistance against the heat from the roller inside to the outside so that the fixing ability and the durability are improved. Moreover, the second primer layer 5 having a relatively low thermal conductivity is effective to provide a heat-resistance and producing a properly controlled heat flow. Therefore, in the case that a number of copies are produced continuously, the heat application to the sheets can be made uniform over the number of the copies. Without the present invention, a great amount of heat is applied to the first or first several sheets, whereas only a small amount of heat is applied to the last sheets. This is eliminated using the fixing roller 1 according to the present invention. According to various inventors' experiments, it has been found that it is particularly preferable in order to provide good results that the thermal conductivity of the first primer layer 3(13) is not less than 0.6x10⁻³ cal.cm/(sec.cm².°C); the thermal conductivity of the elastic layer 4(14) is not less than 0.8x10⁻³ cal.cm/(sec.cm².°C), further preferably, not less than 1.2x10⁻³ cal.cm/(sec.cm².°C); the thermal conductivity of the second primer layer 5(15) is not more than 0.4x10⁻³ cal.cm/(sec.cm².°C), further preferably, not more than 0.25x10⁻³ cal.cm/(sec.cm².°C); and, in addition, the thickness of the elastic layer 4(14) is larger than that of the second primer layer 5(15) which is in turn larger than the first primer layer 3(13), and the thickness of the elastic layer 4(14) is larger than 6 times the resin layer 6(16). The thermal conductivities of the first and second primers, remain unchanged during the air-drying. The elastic rotatable member 1(10) according to the present invention is applicable in addition to the rollers for image fixing described above, to a conveying roller, a cleaning roller and a releasing agent applying roller or the like. In any application, the releasability of the surface resin layer 6(16) together with the resilience provided by the elastic layers 4(14) are advantageously utilized. The elastic rotatable 1(10) member of the present invention is not limited to the form of the roller and may be in the form of a belt. As described hereinbefore, in the elastic rotatable member according to this embodiment, the elastic layer 4(14) is made of a high thermal conductivity material; the first primer layer 3(13) inside the elastic layer 4(14) has a high thermal conductivity; the second layer 4(14) has a high thermal conductivity; the second primer layer 5(15) outside the elastic layer 4(14) has a good thermal insulation property; and the surface resin layer 6(16) is formed outside the second primer layer 5(15). The surface resin layer 6(16) provides desirable conveying property, releasability and wear resistance and durability, while simultaneously the inside elastic layer 4(14) and the first and second primer layers 3(13), 5(15) provide an appropriate elasticity and proper heat transmitting speed. Therefore, when it is used as a rotatable member or members for image fixing, good image fixing ability and image quality are assured with the advantage of remarkably reducing occurrences of curling and wrinkle. Further, the elastic rotatable member 1(10) of the present invention has the first primer layer 3(13) having the thermal conductivity larger than that of the second primer layer 5(15), whereby the elastic layer 4(14) inside the second primer layer 5(15) is substantially released from the thermal damage due to the thermal insulating property of the second primer layer 5(15), in addition, between the elastic layer 4(14) and the surface resin layer 6(16) to which sufficient heat is applied, there is provided a high bonding strength to provide sufficient durability together with excellent surface releasability and surface wear resistance. Additionally, the elastic rotatable member 1(10) according to the present invention is substantially free from the deterioration of the elastic layer 4(14) by heat during the sintering of the resin layer 6(16) in manufacturing. Therefore, the desired and appropriate elasticity can be maintained.

Claims: An elastic rotatable member (1,10), comprising a basic member (2,12), an elastic material layer (4,14) outside said basic member (2,12), a first primer layer (3,13) between said basic member (2,12) and said elastic material layer (4,14), and a resin layer (6,16) outside said elastic material layer (4,14), characterized by a second primer layer (5,15) disposed between said elastic material layer (4,14) and said resin layer (6,16), wherein said first primer layer (3,13) has a thermal conductivity which is larger than that of said second primer layer (5,15). A member according to claim 1, wherein said elastic material layer (4,14) is of silicone rubber. A member according to claim 2, wherein said first primer layer (3,13) is of a silicone primer. A member according to claim 2, wherein said resin layer (6,16) is of a fluorine resin. A member according to claim 4, wherein said second primer layer (5,15) is of a silicone or fluorine primer. A member according to claim 4, wherein said resin layer (6,16) is of PFA resin (tetrafluorethylene-perfluoroalkoxyethylene copolymer resin) or of PTFE resin (tetrafluoroethylene resin). A member according to claim 1, wherein said elastic material layer (4,14) is of an elastic material having a relatively high thermal conductivity, and the elastic material layer (4,14) has a thermal conductivity which is higher than that of the first primer layer (3,13). A member according to claim 1, wherein said elastic rotatable member (1,10) is an image fixing rotatable member for fixing an unfixed image. A member according to claim 1, wherein said resin layer (6,16) is formed, after unsintered fluorine resin material is applied on the second primer layer (5,15), by heating and sintering said resin material at a temperature not lower than a crystal melting point of the fluorine resin material, the heat being not applied to said resin material through the other layers of said member. A member according to claim 9, wherein the fluorine resin material applied on said second primer layer (5,15) is of a type wherein the fluorine resin material is dispersed. An image fixing apparatus, comprising: first and second rotatable members (1,10) press-contacted to each other to form a nip to which an image bearing member (P) supporting an unfixed image (T) is passed through, during which the image is fixed; wherein at least one of said first and second rotatable members (1,10) is as claimed in any preceding claims. An apparatus according to claim 11, wherein said at least one of the rotatable members (1,10) is adapted to contacting directly to the unfixed image and is provided with heating means (H) therein.

Inventors: GOTO, MASAHIRO, KUGE, TSUKASA, SAKURAI, MASAAKI, SHIGENOBU, MICHIO, YAMAMOTO, IICHIRO
Applicants: CANON KABUSHIKI KAISHA, KABUSHIKI KAISHA I.S.T.
Application year: 1987
Main classification: G03G15
IPC codes: G03G15, G03G21, F16C13, B05C1