Patent Publication Number: US-6709373-B2

Title: Pressure roller for fixing device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of Applicant&#39;s Ser. No. 09/982,754 filed in the U.S. Patent &amp; Trademark Office on Oct. 22, 2001, and assigned to the assignee of the present invention. 
    
    
     CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 and § 120 from my application PRESSURE ROLLER FOR FIXING DEVICE AND A MANUFACTURING METHOD OF THE SAME filed with the Korean Industrial Property Office on Feb. 20, 2001 and there duly assigned Serial No. 8505/2001. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a pressure roller for a fixing device in a printer and a method for manufacturing the pressure roller. More particularly, the present invention relates to a pressure roller used for a fixing device and configured to achieve an improved elastic strain, and a method for manufacturing the pressure roller. 
     2. Related Art 
     Generally, a printer includes a photosensitive medium, a light scanning device, a developing device, and a fixing device. A latent image is formed on the photosensitive medium by the light scanning device, and is then developed into a toner image by the developing device. The toner image is then transferred to a sheet. The fixing device serves to firmly fix the toner image to the sheet. Typically, such a fixing device includes a transfer roller arranged to rotate while contacting the photosensitive medium, and a pressure roller arranged to rotate while contacting the transfer roller. The transfer roller is internally or externally provided with a heater which serves to maintain the transfer roller at a high temperature in order to obtain an improved transfer of the toner image from the photosensitive medium to the sheet. The pressure roller, which rotates while contacting the transfer roller at a desired pressure, is made of a material exhibiting a thermal stability and a resistance against compression. 
     Exemplars of recent efforts include the FIXING APPARATUS OF Ota et al., U.S. Pat. No. 6,266,509; THE IMAGE HEATING APPARATUS of Kitamura et al., U.S. Pat. No. 6,173,131 and; FIXING APPARATUS of Haneda et al., U.S. Pat. No. 6,157,805. 
     The pressure roller typically includes a shaft and a resin tube. A silicone rubber layer is interposed between the resin tube and the shaft. 
     In order to manufacture a pressure roller having the above mentioned configuration, the resin tube is fitted in a mold having the shape of a pipe with a circular cross section. The shaft is then concentrically arranged in the resin tube in a fixed state. That is, the shaft is supported by the mold so that it is maintained in a fixed state. The shaft has an outer diameter which is less than the inner diameter of the resin tube by a desired amount. 
     Under a condition in which the shaft is maintained in a fixed state in the resin tube, liquid-phase silicone rubber is injected between the inner surface of the resin tube and the outer surface of the shaft. As moisture contained in the liquid-phase silicone rubber is vaporized, a porous silicone rubber layer is formed. In order to allow the silicone rubber layer to come into tight contact with the resin tube, the entire inner surface of the resin tube is subjected to an etching treatment. An adhesive is also coated on the etched inner surface of the resin tube. 
     After completion of the formation of the silicone rubber layer, the molded product is removed from the mold. Thus, manufacture of the pressure roller is completed. 
     The silicone rubber layer interposed between the inner surface of the resin tube and the outer surface of the shaft should have a porous structure which is formed by vaporization. To this end, a low temperature vulcanizing (LTV) silicone rubber is used as the material of the silicone rubber layer in order to achieve formation of pores in a temperature range not causing deformation of the resin tube. However, such LTV silicone rubber is expensive as compared to high temperature vulcanizing (HTV) silicone rubber which is foamed at a high temperature of about 120° C. to form pores. 
     Furthermore, the pressure roller described above has a high manufacturing cost because the entire inner surface of the resin tube must be subjected to an etching treatment in order to allow the silicone rubber layer to come into tight contact with the resin tube. 
     In addition, the pressure roller should exhibit an elastic strain sufficient to reduce the pressure of the pressure roller against the transfer roller while allowing the pressure roller to have a contact surface with superior flatness. However, the silicone rubber layer described above exhibits a high degree of hardness. As a result, there is a disadvantage in that it is necessary to increase the pressure to be applied to the transfer roller. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in view of the above mentioned problems, and an object of invention is to provide an improved pressure roller and method of manufacturing such a pressure roller for a fixing device. 
     It is also an object to provide a pressure roller for a fixing device and a method of manufacturing such a pressure roller which uses HTV silicone rubber exhibiting a foamability at a high temperature, thereby reducing manufacturing cost while exhibiting a desired elastic strain at a low pressure. 
     In accordance with one aspect, the present invention provides a pressure roller for a fixing device, that may be constructed with a shaft; a first silicone rubber layer formed on the shaft as an axially elongate cylindrical layer so as to surround the shaft and the first silicone rubber layer; a resin tube formed on the first silicone rubber layer so as to surround the shaft, the resin tube having extensions at opposite ends thereof, each extension extending beyond an opposite end of the first silicone rubber layer; and second silicone rubber layers, each formed at a respective axially opposite end of the first silicone rubber layer between the extensions of the resin tube and the shaft, the second silicone rubber layers serving to couple the first silicone rubber layer to the resin tube. 
     In accordance with another aspect, the present invention provides a pressure roller for a fixing device, that may be constructed with a shaft; a silicone rubber layer extruded on the shaft as an axially elongate cylindrical layer using an extruder so as to surround the shaft, and foamed so as to have a number of pores; and a resin tube bonded by adhesive to the silicone rubber layer while surrounding the silicone rubber layer. 
     In accordance with another aspect, the present invention provides a method for manufacturing a pressure roller for a fixing device by forming a silicone rubber layer by extruding silicone rubber on a shaft with an extruder, and curing the extruded silicone rubber to foam the silicone rubber, thereby forming a silicone rubber layer having a number of pores. A resin tube forms a cylindrical sheath that surrounds and encases the silicone rubber layer. The resin tube is bonded to the silicone rubber layer with an adhesive while surrounding the silicone rubber layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference numerals indicate the same or similar components, and wherein: 
     FIGS. 1 a  and  1   b  are side and sectional views, respectively, of a pressure roller used for a fixing device; 
     FIGS. 2 a  and  2   b  are side and sectional views, respectively, of a pressure roller used for a fixing device in accordance with a first embodiment of the present invention; 
     FIGS. 3 a  and  3   b  are partially-sectioned views of a resin tube and a first silicone rubber layer formed on a shaft, respectively, in the pressure roller shown in FIGS. 2 a  and  2   b;    
     FIGS. 4 a  and  4   b  are side and sectional views, respectively, of a pressure roller used for a fixing device in accordance with a second embodiment of the present invention; 
     FIGS. 5 a  and  5   b  are partially-sectioned views of a resin tube and a foamed silicone rubber layer formed on a shaft in accordance with an extrusion process, respectively, in the pressure roller shown in FIGS. 4 a  and  4   b;    
     FIG. 6 is a flow chart illustrating a method for manufacturing the pressure roller according to the first embodiment of the present invention; and 
     FIG. 7 is a flow chart illustrating a method for manufacturing the pressure roller constructed as a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 a  and  1   b  are side and sectional views, respectively, of a pressure roller used for a fixing device. Referring to FIG. 1, the pressure roller includes a shaft  11 , a resin tube  15 , and a silicone rubber layer  13  interposed between the resin tube  15  and the shaft  11 . 
     In order to manufacture the pressure roller having such a configuration, the resin tube  15  is fitted in a mold having the shape of a pipe with a circular cross section. The shaft  11  is then concentrically disposed in the resin tube  15  in a fixed state. The shaft  11  is supported by the mold so that it is maintained in a fixed state. The shaft  11  has an outer diameter which is less than the inner diameter of the resin tube  15  by a desired amount. 
     Under a condition in which the shaft  11  is maintained in a fixed state in the resin tube  15 , liquid-phase silicone rubber is injected between the inner surface of the resin tube  15  and the outer surface of the shaft  11 . As moisture contained in the liquid-phase silicone rubber is vaporized, a porous silicone rubber layer  13  is formed. In order to allow the silicone rubber layer  13  to come into tight contact with the resin tube  15 , the entire inner surface of the resin tube  15  is subjected to an etching treatment. An adhesive is also coated on the etched inner surface of the resin tube  15 . 
     After completion of the formation of the silicone rubber layer  13 , the molded product is removed from the mold. Thus, manufacture of the pressure roller is completed. 
     The silicone rubber layer  13  interposed between the inner surface of the resin tube  15  and the outer surface of the shaft  11  should have a porous structure which is formed by vaporization. To this end, a low temperature vulcanizing (LTV) silicone rubber is used as the material of the silicone rubber layer  13  in order to achieve formation of pores in a temperature range not causing deformation of the resin tube  15 . However, such LTV silicone rubber is expensive as compared to high temperature vulcanizing (HTV) silicone rubber which is foamed at a high temperature of about 120° C. to form pores. 
     Furthermore, the pressure roller described above has a high manufacturing cost because the entire inner surface of the resin tube  15  must be subjected to an etching treatment in order to allow the silicone rubber layer  13  to come into tight contact with the resin tube  15 . 
     FIGS. 2 a  and  2   b  are side and sectional views, respectively of a pressure roller used for a fixing device in accordance with a first embodiment of the present invention. Referring to FIGS. 2 a  and  2   b , the pressure roller includes a shaft  21 , a first silicone rubber layer  23 , a resin tube  25 , and second silicone rubber layers  27 . The first silicone rubber layer  23  is formed on the shaft  21  in accordance with an extrusion process using an extruder. The first silicone rubber layer  23  is also foamed to have a porous structure. The resin tube  25  has extensions  25   a  and  25   b  at respective opposite ends thereof, each extension  25   a ,  25   b  extending beyond an associated one of the opposite ends of the first silicone rubber layer  23 . Each extension  25   a ,  25   b  of the resin tube  25  is etched to a desired depth in order to obtain a desired surface roughness. Each of the second silicone rubber layers  27  is formed at a space defined at an associated end of the first silicone rubber layer  23  between an inner surface of the associated extension  25   a  or  25   b  of the resin tube  25  and the outer surface of the shaft  21 . The second silicone rubber layers  27  serve to fix the first silicone rubber layer  23  to the resin tube  25 . 
     FIGS. 3 a  and  3   b  are partially-sectioned views of the resin tube and the first silicone rubber layer formed on the shaft, respectively, in the pressure roller shown in FIGS. 2 a  and  2   b . In FIGS. 3 a  and  3   b , elements corresponding to those in FIGS. 2 a  and  2   b  are denoted by the same reference numerals. 
     Referring to FIGS. 2 a  thru  3   b , the resin tube  25  has a cylindrical structure having a desired inner diameter, a desired outer diameter, and a desired longitudinal length. The resin tube  25  is provided with etched portions  25   c  and  25   d  at respective opposite longitudinal ends thereof. Preferably, the resin tube  25  is made of polytetrafluoroethylene (PTFE) or perfluoroalkyl vinyl ether (PFA) exhibiting a high heat resistance and a high compression resistance while being effective to avoid surface contamination resulting from surface friction against a sheet. 
     The procedure for manufacturing the pressure roller having the above mentioned configuration will now be described. As shown in FIG. 3 b , the shaft  21  is prepared by being machined to have a desired outer diameter. Thereafter, a silicone rubber material augmented with a foaming agent is extruded on the shaft  21  using an extruder, thereby forming a silicone rubber layer  23 . For the silicone rubber material, an inexpensive HTV silicone rubber is used. Since HTV silicone rubber can be cured at a high temperature, the silicone rubber layer  23  extruded on the shaft  21  is subjected to a curing process in a chamber maintained at about 120° C. In accordance with this curing process, the silicone rubber layer  23  is foamed so as to have a number of pores. 
     The silicone rubber layer  23 , which has a porous structure in accordance with the curing process, is then subjected to a primary heat treatment in a chamber maintained at about 200° C. During the primary heat treatment, vapors are generated at the silicone rubber layer  23 . Those vapors are diffused around pores present on the surface of the silicone rubber layer  23  by virtue of migration and permeation phenomena resulting from intrinsic characteristics of the silicone rubber. Thus, undesirable vapors can vent from the silicone rubber layer  23  in accordance with the primary heat treatment. 
     The silicone rubber layer  23  subjected to the primary heat treatment is then subjected to a secondary heat treatment in a chamber maintained at a temperature of 180 to 200° C. The secondary heat treatment is carried out under a condition in which ambient air is forcibly circulated. By virtue of such a forced circulation of ambient air, the odor of silicone rubber can be removed. After completion of the secondary heat treatment, the silicone rubber layer  23  is polished so as to have an outer diameter corresponding to the inner diameter of the resin tube  25  so that it can be disposed in the resin tube  25 . The silicone rubber layer  23  is also subjected to a cutting process so that it has a longitudinal length less than that of the resin tube  25  at respective opposite ends thereof. Thus, the first silicone rubber layer  23  is completely formed. 
     After the formation of the first silicone rubber layer  23 , the resin tube  25  is fitted around the first silicone rubber layer  23 . The fitting process is carried out in such a fashion that the resin tube  25  is provided at opposite ends thereof with extensions  25   a  and  25   b , respectively, extending beyond respective ends of the first silicone rubber layer  23  and corresponding to respective etched portions  25   c  and  25   d . A liquid-phase silicone rubber is then injected into a space defined by each etched portion  25   c ,  25   d  of the resin tube  25 . As the liquid-phase silicone rubber is subjected to a vaporization process, the second silicone rubber layer  27  is formed. Since the second silicone rubber layer  27  should exhibit the same compressibility as the first silicone rubber layer  23 , it is preferred that the second silicone rubber layer  27  be made of a silicone rubber material exhibiting a degree of hardness less than that of the first silicone rubber layer  23 . Since the formation of pores in the second silicone rubber layer  27  in accordance with the vaporization is carried out under a condition in which the second silicone rubber layer  27  is applied to the resin tube  25 , it is preferred that the second silicone rubber layer  27  be made of LTV silicone rubber in order to conduct the vaporization without any deformation of the resin tube  25 . 
     Thus, the manufacture of the pressure roller of FIGS. 2 a  and  2   b  according to the first embodiment of the present invention is complete. As is apparent from the above description, the pressure roller according to the first embodiment achieves a reduction in material costs because it mainly uses inexpensive HTV silicone rubber in accordance with the application of an extrusion process, while partially using an expensive liquid-phase silicone rubber only for a small part thereof which requires application of an injection process. Also, it is possible to achieve a reduction in treatment costs in that only a part of the resin tube is subjected to the etching treatment. 
     FIGS. 4 a  and  4   b  are side and sectional views, respectively, of a pressure roller used for a fixing device in accordance with a second embodiment of the present invention. Referring to FIGS. 4 a  and  4   b , the pressure roller includes a shaft  41 , a silicone rubber layer  43  formed on the shaft  41  in accordance with an extrusion process using an extruder and foamed to have a number of pores, and a resin tube  45  disposed around the silicone rubber layer  43  and coated with adhesive at an inner surface thereof facing the outer surface of the silicone rubber layer  43  so that it is coupled with the silicone rubber layer  43 . 
     FIGS. 5 a  and  5   b  are partially-sectioned views of the resin tube and the foamed silicone rubber layer formed on the shaft in accordance with an extrusion process, respectively, in the pressure roller of FIGS. 4 a  and  4   b . In FIGS. 5 a  and  5   b , elements corresponding to those in FIGS. 4 a  and  4   b  are denoted by the same reference numerals. 
     Referring to FIGS. 4 a  thru  5   b , the resin tube  45  has the same structure as the resin tube  25  according to the first embodiment shown in FIG. 3 a . The resin tube  45  is provided with etched portions  45   a  and  45   b  in the same fashion as in the first embodiment. It is preferred that the resin tube  45  be made of PTFE, as in the first embodiment. 
     As shown in FIG. 5 b , the shaft  41  is prepared by being machined to have a desired outer diameter. Thereafter, a silicone rubber material augmented with a foaming agent is extruded on the shaft  41  using an extruder, thereby forming a silicone rubber layer  43 . For the silicone rubber material, inexpensive HTV silicone rubber is used. The silicone rubber layer  43  is cured, and then sequentially subjected to a primary heat treatment and a secondary heat treatment. The curing process, the primary heat treatment and the secondary heat treatment are carried out in the same fashion as in the first embodiment. 
     After completion of the secondary heat treatment, the silicone rubber layer  43  is subjected to a cutting process so that it has the same longitudinal length as the resin tube  45 . The silicone rubber layer  43  is also polished so as to have an outer diameter corresponding to the inner diameter of the resin tube  45  so that it can be fitted in the resin tube  45 . Thus, the silicone rubber layer  43  is completed formed. In order to bond the silicone rubber layer  43  to the resin tube  45 , adhesive (for example, S-33-156-1 manufactured by Shinetsu Chemical Co.) is coated over each etched portion  45   a  and  45   b  of the resin tube  45 . In accordance with the adhesive used, it may be unnecessary to provide the etched portions  45   a  and  45   b , in which case the etching process may be omitted. The shaft  41  with the polished silicone rubber layer  43  is then disposed in the resin tube  45 . The silicone rubber layer  43  is then bonded to the resin tube  45 , and the manufacture of the pressure roller is complete. 
     As is apparent from the above description, the pressure roller according to the second embodiment can achieve a reduction in material costs because it only uses inexpensive HTV silicone rubber in accordance with application of extrusion and foaming processes. Also, it is possible to achieve a reduction in treatment costs in that only a part of the resin tube is subjected to the etching treatment, or the resin tube is not subjected to etching treatment at all. 
     FIG. 6 is a flow chart illustrating a method for manufacturing the pressure roller according to the first embodiment of the present invention. 
     In accordance with this method, HTV silicone rubber augmented with a foaming agent is extruded on the shaft  21  using an extruder, thereby forming silicone rubber layer  23  (Step S 110 ). The silicone rubber layer  23  is then subjected to a curing process in a chamber maintained at about 120° C. so that it is foamed in order to form a number of pores (Step S 112 ). The foamed silicone rubber layer  23  is then subjected to a primary heat treatment in a chamber maintained at about 200° C. (Step S 114 ). During the primary heat treatment, undesirable vapors are removed from the silicone rubber layer  23 . The silicone rubber layer  23  subjected to the primary heat treatment is then subjected to a secondary heat treatment in a chamber maintained at a temperature of 180 to 200° C. (Step S 116 ). The secondary heat treatment is carried out under a condition in which ambient air is forcibly circulated. By virtue of such a forced circulation of ambient air, the odor of silicone rubber is removed. After completion of the secondary heat treatment, the silicone rubber layer is polished so as to have an outer diameter corresponding to the inner diameter of the resin tube  25  so that it can be disposed in the resin tube  25  (Step S 118 ). The polishing process is continued until the silicone rubber layer has an outer diameter which allows the silicone rubber layer  23  to be tight-fitted in the resin tube  25  (Step S 120 ). 
     After completion of the polishing process, the silicone rubber layer  23  is subjected to a cutting process so that it has a longitudinal length less than that of the resin tube  25  at opposite ends thereof (Step S 122 ). Accordingly, the resin tube  25  may have, at opposite ends thereof, extensions  25   a ,  25   b  extending beyond respective ends of the silicone rubber layer  23  so as to have the same length when the silicone rubber layer  23  is disposed in the resin tube  25 . Thereafter, the extensions  25   a ,  25   b  of the resin tube  25  are etched so as to form etched portions  25   c ,  25   d  to which a liquid-phase silicone rubber is to be applied (Step S 124 ). The cut silicone rubber layer  23  is then disposed in the resin tube  25  in such a fashion that the resin tube  25  has, at opposite ends thereof, extensions  25   a ,  25   b  extending beyond respective ends of the silicone rubber layer  23  by the same length (Step S 126 ). Thus, the first silicone rubber layer  23  is completed formed. After the fitting of the first silicone rubber layer  23 , a liquid-phase silicone rubber is injected into a space defined by each extension  25   a ,  25   b  of the resin tube  25  (Step S 128 ). In this case, it is preferable to use LTV silicone rubber exhibiting a degree of hardness less than that of HTV silicone rubber because the resultant layer can exhibit the same compressibility as the first silicone rubber layer  23 , and can be subjected to a desired vaporization without any deformation of the resin tube  25 . 
     The injected liquid-phase silicone rubber is maintained at ambient temperature as it is, or is subjected to vaporization in a temperature range not causing any deformation of the resin tube  25  so that it has a number of pores. That is, the injected liquid-phase silicone rubber is formed into the second silicone rubber layer  27 . Thus, the procedure for manufacturing the pressure roller according to the first embodiment of the present invention is complete. 
     FIG. 7 is a flow chart illustrating a method for manufacturing the pressure roller according to the second embodiment of the present invention. 
     In this method, steps for extruding silicone rubber on the shaft  41  (Step S 210 ), foaming the extruded silicone rubber (Step S 212 ), subjecting the foamed silicone rubber to primary and secondary heat treatments (Steps S 214  and S 216 ), and polishing the heat-treated silicone rubber (Step S 218 ) are carried out in the same fashion as those of FIG. 6 associated with the first embodiment of the present invention. In accordance with this method, the polishing process is continued until the silicone rubber layer  43  has an outer diameter which allows the silicone rubber layer  43  to be tight-fitted in the resin tube  45  (Step S 220 ). 
     After completion of the polishing process, the silicone rubber layer  43  is subjected to a cutting process so that it has the same longitudinal length as the resin tube  45  (Step S 222 ). The silicone rubber layer  43  is also subjected to an etching process so that it has etched portions  45   a  and  45   b  which have the same length at respective opposite ends thereof (Step S 224 ). An adhesive then is coated over each etched portion  45   a  of the resin tube  45  (Step S 226 ). In accordance with the adhesive used, it may be unnecessary to provide the etched portions  45   a  and  45   b , in which case the etching process may be omitted. The cut silicone rubber layer  43  is then disposed in the resin tube  45 , and the cut silicone rubber layer  43  is bonded to the resin tube  45  (Step S 228 ). Thus, the cut silicone rubber layer  43  is formed, and the procedure for manufacturing the pressure roller according to the second embodiment of the present invention is complete. 
     Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the invention, as disclosed in the accompanying claims.