Patent Publication Number: US-7594329-B2

Title: Heat insulation roller and manufacturing method thereof

Description:
FIELD OF THE INVENTION 
   The present invention relates to a heat insulation roller and a manufacturing method thereof used for various devices requiring temperature control such as a tension roller of a fixing belt of an image forming apparatus. 
   DESCRIPTION OF THE BACKGROUND 
   In an image forming apparatus such as an electro-photographic copying apparatus and a printer, in recent years, a belt type fixing apparatus has been developed. The belt type fixing apparatus can set a long fixing time, so that even in a color image composed of superimposed toners, a satisfactory fixing property can be obtained. Some belt type fixing apparatus stretches an endless fixing belt between a heating roller and a separation roller, heats the fixing belt by the heating roller, and inserts a sheet of paper through a nipper section between the fixing belt and a pressure roller to heat, pressurize, and fix a toner image. The fixing belt, to obtain high-speed and satisfactory fixing, is required to shorten the warming-up time and retain a predetermined fixing temperature. For the purpose, the separation roller is required to use a highly heat insulation roller to prevent the fixing belt from cooling when it makes contact with the fixing belt and furthermore is required to reduce the weight to realize compactness, lightweight, and energy conservation of the apparatus. 
   Conventionally, in Japanese Patent Application Publication No. 2004-109649, an apparatus having a plurality of heat pipes installed inside a central part of a core bar of a fixing roller is disclosed. 
   However, the pipes are structured so as to be installed inside the core bar and uniformly diffuse heat to the core bar. Namely, the pipes do not form a heat insulation structure between the hollows of the pipes and the core bar. Further, as a heat insulating separation roller, there are a roller composed of heat resistant silicone rubber or heat resistant sponge and a ceramic roller covered with a PFA (perfluoroalkyl vinyl ether) tube available. However, the heat resistant silicone rubber and heat resistant sponge have comparatively high thermal conductivity, thus a higher heat insulating effect cannot be obtained, and the warming-up time cannot be shortened. Furthermore, the ceramics roller produces a heat insulation effect by an air layer contained in ceramics, contributes to shortening of the warming-up time, though is difficult to ensure the manufacturing accuracy, requires a damage prevention measure, thereby is comparatively expensive. 
   Therefore, in the separation roller for driving the fixing belt, to prevent the fixing belt from loss of temperature, it is desired to use a heat insulation roller which is low in heat capacity, high in heat insulation, and light in weight, has a satisfactory fixing efficiency, and can obtain a fixed image of high image quality. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a heat insulation roller which is light in weight and has a high heat insulation property and a manufacturing method thereof. 
   According to an embodiment of the present invention, there is provided an insulation roller comprising a core roller, an outer peripheral roller coaxial with the core roller, and a plurality of hollow pipes uniformly arranged in a gap between the core roller and the outer peripheral roller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram showing the image forming unit of the color image forming apparatus of the first embodiment of the present invention; 
       FIG. 2  is a schematic perspective view showing the fixing apparatus of the first embodiment of the present invention; 
       FIG. 3  is a schematic constitution view showing the fixing apparatus of the first embodiment of the present invention; 
       FIG. 4  is a schematic constitution view showing a part of the separation roller the first embodiment of the present invention; 
       FIG. 5  is a schematic explanatory diagram showing the rolling process of the heat insulation roller base material of the first embodiment of the present invention; 
       FIG. 6  is a schematic explanatory diagram showing the cut process of the heat insulation roller base material of the first embodiment of the present invention; 
       FIG. 7  is a schematic explanatory diagram showing the removal process of the outer peripheral roller and hollow pipes at both ends of the heat insulation roller base material of the first embodiment of the present invention; 
       FIG. 8  is a schematic explanatory diagram showing the working process of the core roller of the heat insulation roller base material of the first embodiment of the present invention; and 
       FIG. 9  is a cross sectional view showing the separation roller of the second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The first embodiment of the present invention will be explained in detail with reference to the accompanying drawings.  FIG. 1  is a schematic block diagram showing image forming unit  1  and paper feed unit  10  of the color image forming apparatus of the embodiment of the present invention. Paper feed unit  10  takes out sheet of paper P by pick-up roller  7  from paper feed cassette  24  and feeds sheet of paper P toward resist roller  17  via separation roller  16  and conveying rollers  9 . 
   Around photosensitive drum  2  of image forming unit  1 , charger  5  for uniformly charging sequentially photosensitive drum  2  according to the rotation of photosensitive drum  2  in the direction of arrow s, irradiation position  4   b  of laser beam  4   a  from laser exposure apparatus  4  which is a latent image forming section for forming a latent image on charged photosensitive drum  2 , black developing apparatus  8 B, and color developing apparatus  8 A of a revolver type for rotatably supporting developing devices  8   a ,  8   b , and  8   c  for developing by developers of yellow (Y), magenta (M), and cyan (C) in the direction of arrow t. 
   Furthermore, around photosensitive drum  2 , transfer belt unit  35  having an intermediate transfer belt  3 , which is stretched and suspended by driving roller  3   c , driven roller  3   a , and tension rollers  3   b  and  3   d  and on which a toner image is primarily transferred on photosensitive drum  2  at the position of primary transfer roller  12 , and a cleaner  6  are arranged. Intermediate transfer belt  3  has belt cleaner  14 . Further, image forming apparatus  1  has secondary transfer roller  11  for secondarily transferring a toner image of a plurality of colors superimposed on intermediate transfer belt  3  onto sheet of paper P which is a recording medium, fixing apparatus  13  of a fixing belt type for fixing the toner image on sheet of paper P, paper ejection rollers  30  for ejecting sheet of paper P after fixing to paper ejection section  31 , and reverse conveyor apparatus  26  for reversing sheet of paper P at the time of forming both-side images. 
   Next, fixing apparatus  13  will be described. Fixing apparatus  13 , as shown in  FIGS. 2 to 4 , has heating section  13   a  having fixing belt  53  suspended by heating roller  51  and separation roller  54  which is a heat insulation roller and driven by separation roller  54  to rotate in the direction of arrow v. Further, fixing apparatus  13  has pressure section  13   b  having pressure roller  52  pressed to heating roller  51  by pressure arm  62  and pressure spring  63  and rotated in the direction of arrow w at the same speed as that of fixing belt  53 . By doing this, between fixing belt  53  supported by heating roller  51  and pressure roller  52 , desired nipper section  53   a  is formed. 
   Heating roller  51  is composed of an iron pipe  51   a  with an outer diameter of 40 mm and a material thickness of 0.75 mm internally including electromagnetic induction coil  51   b  and is inductively heated. Separation roller  54  uses stainless steel (SUS304) of thermal conductivity of 16 W/m-K as a material. Separation roller  54  is composed of hollow pipes  54   c  with material thickness T 2  of 0.3 mm and an outer diameter of 4.5 mm uniformly arranged between core roller  54   a  with an outer diameter of 10 mm and outer peripheral roller  54   b  with material thickness T 1  of 0.5 mm and an outer diameter of 20 mm. Separation roller  54 , since hollow pipes  54   c  are arranged between core roller  54   a  and outer peripheral roller  54   b  to provide a space, can be formed to a structural body of low heat capacity and can produce a high heat insulating effect. Separation roller  54  is pressed in the direction of arrow F so as to always give tension to fixing belt  53  and is driven to rotate by a driving motor not drawn. A 1   
   Separation roller  54  is manufactured by the processes shown in  FIGS. 5 to 8 . Firstly, core roller  54   a  and hollow pipes  54   c  are inserted into pipe  60  having an outer diameter larger than that of core roller  54   a  by about 10% and then as shown in  FIG. 5 , pipe  60  is inserted into mouthpiece  61  drawn to an outer diameter of 20 mm, which is the size of separation roller  54 , in the direction of arrow y so as to form long heat insulation roller base material  62 . By doing this, hollow pipes  54   c  are adhered and fixed to the gap between core roller  54   a  and pipe  60 . 
   Next, as shown in  FIG. 6 , long heat insulation roller base material  62  is cut to the size of separation roller  54  by a cutter or a water jet. Thereafter, as shown in  FIG. 7 , only pipe  60  and hollow pipes  54   c  at both ends  62   a  of heat insulation roller base material  62  are removed so as to leave core roller  54   a  at both ends. Next, as shown in  FIG. 8 , slits  63  are bored at both ends of core roller  54   a  to form separation roller  54 . 
   Fixing belt  53  is composed of a 3-layer belt of a nickel (Ni) substrate laminated with silicone rubber and PFA (perfluoroalkyl vinyl ether). With fixing belt  53 , oil roller  55  for feeding oil onto the surface of fixing belt  53  is in contact. With oil roller  55 , cleaning roller  56  for adhering and cleaning stains of the surface of oil roller  55  is in contact. Further, in the neighborhood of separation roller  54 , separation plate  58  for preventing sheets of paper P from wrapping is installed. 
   Pressure roller  52  is composed of roller-shaped sponge with an outer diameter of 38 mm. Around pressure roller  52 , separation pawl  57  for preventing sheets of paper P from wrapping and cleaning blade unit  59  for scraping and cleaning stains of the surface of the pressure roller are installed. 
   Next, the color image forming process by image forming unit  1  will be explained. Image forming unit  1  superimposes toner images in the order of black (BK), cyan (C), magenta (M), and yellow (Y) to form a color image. 
   When the image forming process starts, in fixing apparatus  13 , heating roller  51  is heated by electromagnetic induction coil  51   b , and fixing belt  53  is driven to rotate by separation roller  54  in the direction of arrow v, thus the warming-up is started. At this time, since separation roller  54  is a structural body of low heat capacity, fixing belt  53 , when it makes contact with separation roller  54 , is not taken greatly the heat given by heating roller  51 . Therefore, fixing roller  53  can realize warming-up at high speed. 
   When the fixing roller  53  finishes the warming-up and is put into a ready state, intermediate transfer belt  3  is rotated in the direction of arrow u in correspondence with driving by photosensitive drum  2 . Photosensitive drum  2  is uniformly charged by charger  5  according to the rotation in the direction of arrow s, is irradiated with laser beam  4   a  according to a black image signal by laser exposure apparatus  4  to form a black electrostatic latent image, which is developed by black developing apparatus  8 B moved to the developing position. 
   The black (BK) toner image on photosensitive drum  2  is primarily transferred electrostatically onto intermediate transfer belt  3  rotating in the direction of arrow u at the position of primary transfer roller  12 . After the primary transfer, photosensitive drum  2  is cleaned residual toner by cleaner  6 . 
   Hereafter, similarly to the black (BK) toner image forming process, the toner image forming processes of cyan (C), magenta (M), and yellow (Y) are sequentially repeated, and toner images of a plurality of colors are superimposed at the same position on intermediate transfer belt  3 , thus a full-color toner image is obtained on intermediate transfer belt  3 . During this period, black developing apparatus  8 B is separated from photosensitive drum  2  and color developing apparatus  8 A rotates in the direction of arrow t according to arrival of electrostatic latent images of various colors, thereby arranges sequentially cyan (C) developing device  8   c , magenta (M) developing device  8   b , and yellow (Y) developing device  8   a  opposite to photosensitive drum  2 . 
   Hereafter, the full-color toner images of black (BK), cyan (C), magenta (M), and yellow (Y) superimposed on intermediate transfer belt  3  are secondarily transferred onto sheet of paper P in a batch at the secondary transfer position opposite to secondary transfer roller  11 . Sheet of paper P is conveyed to the secondary transfer position synchronously with arrival of the full-color toner images on intermediate transfer belt  3  at the secondary transfer position. 
   Sheet of paper P on which the full-color toner images are formed moves in the direction of arrow x, is conveyed to fixing apparatus  13 , and is inserted through nipper section  53   a  between fixing belt  53  and pressure roller  52  to fully heat, pressurize, and fix the full-color toner images. Sheet of paper P passing through nipper section  53   a  is separated from fixing belt  53  by the stiffness thereof, is guided by separation plate  58 , and is ejected from paper ejection roller  30  to paper ejection section  31 . However, when sheet of paper P is wrapped in pressure roller  52 , it is separated by separation pawl  57 . 
   During this period, fixing belt  53  rotating in the direction of arrow v is heated by contact with heating roller  51  heated by electromagnetic induction coil  51   b . By doing this, fixing belt  53 , in nipper section  53   a  with pressure roller  52 , is retained at the fixable temperature. Fixing belt  53 , after passing nipper section  53   a , makes contact with separation roller  54 . However, separation roller  54  is a structural body of low heat capacity, so that fixing belt  53  is not taken greatly the heat. Therefore, fixing belt  53 , after making contact with separation roller  54 , reaches heating roller  51  once again in a state that it is almost kept in the heating state by heating roller  51  and is re-heated by heating roller  51 . Further, toner adhered onto the surface of fixing belt  53  is removed by oil roller  55  and then oil roller  55  is cleaned by cleaning roller  56 . Stains of pressure roller  52  are scraped by cleaning blade  59 . 
   As mentioned above, in fixing apparatus  13 , fixing belt  53  is not taken heat, though it makes contact with separation roller  54 . Therefore, fixing belt  53  can be warmed up at high speed and can be kept at the fixable temperature. 
   Further, when the warming-up time of fixing belt  53  is tested using fixing apparatus  13 , compared with a comparison example using a separation roller composed of a heat resistant silicone rubber roller with an outer diameter of 20 mm in an environment at a room temperature of 25° C., the warming-up time up to the fixing temperature 180° C. is improved by about 5%. Further, the weight of separation roller  54  of this embodiment is reduced by about 3% compared with comparison example 1. 
   According to the first embodiment, hollow pipes  54   c  are arranged between core roller  54   a  of separation roller  54  and outer peripheral roller  54   b , so that separation roller  54  can be formed an a structural body of low heat capacity and although it is light in weight and inexpensive, the heat insulating effect can be increased. Therefore, when fixing belt  53  of fixing apparatus  13  is given tension and driven by such separation roller  54 , although it makes contact with separation roller  54 , the temperature reduction of the fixing belt can be made smaller and the warming-up can be speeded up. Further, during fixing, the surface temperature of fixing belt  53  can be easily kept at a predetermined fixable temperature and a fixed image of high image quality can be obtained by fixing belt  53 . 
   Further, according to the first embodiment, during manufacturing of separation roller  54 , core roller  54   a  and hollow pipes  54   c  are inserted into pipe  60 , and pipe  60  is extended at both of its ends forming outer peripheral roller  54   b , thus hollow pipes  54   c  can be uniformly adhered and fixed easily between core roller  54   a  and outer peripheral roller  54   b . Thereafter, outer peripheral roller  54   b  and the ends of hollow pipes  54   c  are removed, thus forming of slit  63  which is secondary working of remaining core roller  54   a  can be executed easily, and highly heat insulating separation roller  54  can be manufactured easily. Further, material thickness T 1  of outer peripheral roller  54   b  is larger than material thickness T 2  of hollow pipes  54   c , so that there is no fear that during rolling of outer peripheral roller  54   b , the shape of hollow pipes  54   c  may adversely affect the shape of outer peripheral roller  54   b  and outer peripheral roller  54   b  having an even and smooth surface can be obtained easily. 
   Next, the second embodiment of the present invention will be explained. The second embodiment is different from the first embodiment in the material and manufacturing process of the separation roller. Therefore, in the second embodiment, the same parts as those of the explained constitution of the first embodiment are assigned the same numerals and the explanation thereof will be omitted. In this embodiment, as shown in  FIG. 9 , separation roller  70  which is a heat insulation roller is manufactured. Through stainless steel core roller  70   a  with an outer diameter of 10 mm and thermal conductivity of 16 W/m-K, stainless steel outer peripheral roller  70   b  with material thickness T 1  of 0.5 mm, an outer diameter of 20 mm, and thermal conductivity of 16 W/m-K is inserted. 
   Between core roller  70   a  and outer peripheral roller  70   b , hollow pipes  70   c  with material thickness T 2  of 0.3 mm and an outer diameter of 4.5 mm are uniformly inserted, and adhesive  70   d  is injected into the gap thereof to adhere and fix hollow pipes  70   c , thus a long heat insulation roller base material is prepared. Hereafter, the long heat insulation roller base material is cut to the size of separation roller  70 , and outer peripheral roller  70   b  and hollow pipes  70   c  at both ends are removed, and slits are bored at both ends of core roller  70   a , and separation roller  70  is formed. 
   According to the second embodiment, similarly to the first embodiment, hollow pipes  70   c  are arranged between core roller  70   a  and outer peripheral roller  70   b  of separation roller  70 , thus separation roller  70  can be formed an a structural body of low heat capacity and a heat insulation roller, although light in weight and inexpensive, realizing a high heat insulating effect can be obtained. 
   Further, the present invention is not limited to the aforementioned embodiments and can be variously changed within the scope of the present invention, and for example, the structure of an image forming apparatus loading the fixing apparatus using the heat insulation roller of the present invention is not limited, and an image forming apparatus of a tandem type arranging a plurality of photoconductor units in parallel is acceptable. Further, in the heat insulation roller, the material and material thickness thereof are not limited, and in the first embodiment, iron may be optionally used instead of stainless steel, though to retain the heat insulating property, a material of thermal conductivity of 90 W/m-K or less is preferably used. 
   Furthermore, to prevent the shape of the hollow pipes from affecting the outer peripheral roller, material thickness T 2  of the hollow pipes is preferably equal to or smaller than material thickness T 1  of the outer peripheral roller. Further, the structure of the heat insulation roller is optional, and the hollow pipes, if they are in a pipe shape, may be elliptic, and between the core roller and the outer peripheral roller, thin hollow pipes may be arranged in a plurality of stages. Furthermore, the core roller may be composed of a pipe instead of a solid roller. Further, the manufacturing process and use of the heat insulation roller are not limited. 
   As mentioned above, according to the present invention, between the core roller and the outer peripheral roller, the hollow pipes are arranged uniformly, so that a heat insulation roller which is light in weight and inexpensive can be obtained easily. Therefore, when such a heat insulation roller is used as a tension roller of the fixing belt, the fixing belt can be prevented from reduction in temperature, and the warming-up of the fixing apparatus can be speeded up, and a fixed image of high image quality can be obtained.