Patent Publication Number: US-9414440-B2

Title: Heating roller, thermal fixing apparatus and method for producing heating roller

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2013-242697 filed on Nov. 25, 2013 the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heating roller provided on an image forming apparatus adopting the electro-photographic system, a thermal fixing apparatus provided with the heating roller, and a method for producing a heating roller. 
     2. Description of the Related Art 
     A printer adopting the electro-photographic system is provided with a fixing apparatus configured to fix an image of toner (toner image) transferred from a photosensitive drum to a paper (paper sheet). The fixing apparatus is provided with a heating roller and a pressing roller which is brought into pressurized contact with the heating roller. 
     As an example of such a heating roller, there is proposed a heating roller provided with a hollow roller core bar (mandrel), an elastic layer arranged on a surface of the hollow roller core bar, and a fluororesin tube arranged on the elastic layer (see, for example, Japanese Patent Application Laid-open No. H09-304964). 
     Further, the heating roller as described above is heated by a heater arranged inside the heating roller. When a paper onto which a toner image has been transferred passes between the heating roller and the pressing roller, this heating roller heats the toner image so as to fix the toner image to the paper. 
     SUMMARY OF THE INVENTION 
     With respect to the heating roller described in Japanese Patent Application Laid-open No. H09-304964, when the heating roller is heated by the heater, minute particles (fine particles) of which mean particle size is not more than 300 nm scatter (drift) from the elastic layer in some cases. In the recent years, the scattering of such minute particles is desired to be suppressed. 
     In view of such a situation, an object of the present teaching is to provide a heating roller capable of suppressing the scattering of minute particles of which mean particle size is not more than 300 nm, a thermal fixing apparatus provided with the heating roller, and a method for producing the heating roller. 
     According to a first aspect of the present teaching, there is provided a heating roller including: a core bar having a cylindrical shape; a rubber layer arranged on an outer circumferential surface of the core bar to cover the core bar; and a release layer arranged on an outer circumferential surface of the rubber layer, wherein in a case that a developer is thermally fixed on a recording medium, the heating roller is heated to a temperature within a fixing temperature range including a minute particle-scattering start temperature at which minute particles having mean particle diameter of not more than 300 nm start to scatter from the rubber layer; and density of the minute particles measured by a test is less than 2,000 pieces/cm 3 , the test being executed by: arranging the heating roller inside a casing of which inner volume is 0.175 m 3  and which is connected to a minute particle density measuring device configured to measure the density of the minute particles; then performing heating of the core bar of the heating roller inside the casing to 230° C. by a heater; and then measuring the density of the minute particles inside the casing after elapse of 20 minutes since start of the heating of the core bar. 
     According to such a configuration, the density of the minute particles of which mean particle size is not more than 300 nm, measured by the test is less than 2,000 pieces/cm 3 , which makes it possible to suppress the scattering of the minute particles from the rubber layer in a case that the heating roller is heated to a temperature within the fixing temperature range so as to thermally fix the developer to the recording medium. 
     According to a second aspect of the present teaching, there is provided a thermal fixing apparatus including: a heating roller including: a core bar having a cylindrical shape; a rubber layer arranged on an outer circumferential surface of the core bar to cover the core bar; and a release layer arranged on an outer circumferential surface of the rubber layer; and a heating member arranged inside the core bar of the heating roller and configured to heat the heating roller to a temperature of less than 230° C., wherein in a case that a developer is thermally fixed on a recording medium, the heating roller is heated to a temperature within a fixing temperature range including a minute particle-scattering start temperature at which minute particles having mean particle diameter of not more than 300 nm start to scatter from the rubber layer; and density of the minute particles measured by a test is less than 2,000 pieces/cm 3 , the test being executed by: arranging the heating roller inside a casing of which inner volume is 0.175 m 3  and which is connected to a minute particle density measuring device configured to measure the density of the minute particles; then performing heating of the core bar of the heating roller inside the casing to 230° C. by a heater; and then measuring the density of the minute particles inside the casing after elapse of 20 minutes since start of the heating of the core bar. 
     According to such a configuration, since the thermal fixing apparatus is provided with the heating roller, it possible to suppress the scattering of the minute particles from the rubber layer of the heating roller in a case that the heating roller is heated by the heating member to a temperature within the fixing temperature range so as to thermally fix the developer to the recording medium. 
     According to a third aspect of the present teaching, there is provided a method for producing a heating roller, the method including the steps of: preparing a core bar; forming a resin composite layer formed of a resin composite on an outer circumferential surface of the core bar so as to cover the core bar; performing primary curing of the resin composite layer at a temperature in a range of not less than 25° C. to not more than 150° C. for a duration of time in a range of not less than 0.5 hours to not more than 4 hours; preparing a rubber layer based on the resin composite layer by performing secondary curing of the resin composite layer, after the primary curing, at a temperature in a range of not less than 150° C. to not more than 230° C. for a duration of time in a range of not less than 0.5 hours to not more than 10 hours; forming a release layer on an outer circumferential surface of the rubber layer to cover the rubber layer to thereby obtain a roller member including the core bar, the rubber layer and the release layer; and heating the roller member at a temperature in a range of not less than 200° C. to not more than 250° C. for a duration of time in a range of not less than 1 hour to not more than 20 hours to thereby obtain the heating roller. 
     According to such a configuration, the resin composite layer is subjected to the second curing so as to prepare the rubber layer; and then the roller member provided with the core bar, the rubber layer and the release layer is heated at a temperature in a range of not less than 200° C. to not more than 250° C. for a duration of time in a range of not less than 1 hour to not more than 20 hours. In this case, the minute particles of which mean particles size is not more than 300 nm are scattered from the rubber layer when the roller member is heated. 
     Namely, in the method for producing the heating roller, the minute particles of which mean particles size is not more than 300 nm are scattered in advance from the rubber layer in the production step of the heating roller. Thus, in the heating roller produced by this production method, the scattering of the minute particles from the rubber layer is suppressed when the heating roller is heated to a temperature within the fixing temperature range. 
     Thus, according to the method for producing the heating roller of the present teaching, it is possible to produce the heating roller wherein the scattering of minute particles of which mean particle size is not more than 300 nm is suppressed when the heating roller is heated to a temperature within the fixing temperature range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a central cross-sectional view of a printer provided with a heating roller as an embodiment of the present teaching. 
         FIG. 2  is a front view of a heating unit shown in  FIG. 1 . 
         FIG. 3  is a front cross-sectional view of the heating unit shown in  FIG. 2 . 
         FIGS. 4A to 4C  are process views for explaining a method for producing a heating roller shown in  FIG. 3 , wherein  FIG. 4A  illustrates a step of preparing a metal raw pipe (metal pipe stock);  FIG. 4B  illustrates a step of forming a resin composite layer on the outer circumferential surface of the metal raw pipe; and  FIG. 4C  illustrates a step of curing the resin composite layer to thereby prepare a rubber layer. 
         FIGS. 5A and 5B  are process views for explaining the method for producing the heating roller, continued from that of  FIG. 4C , wherein  FIG. 5A  illustrates a step of forming a coating layer on the outer circumferential surface of the rubber layer, to thereby obtain a roller member provided with the metal raw pipe, the rubber layer and the coating layer; and  FIG. 5B  illustrates a step of heating the roller member. 
         FIG. 6  is a view for explaining a heating test for the heating roller shown in  FIG. 2 . 
         FIG. 7A  is a graph showing the scattering density of minute particles with respect to the time, in Example and Comparative Example; and  FIG. 7B  is a graph showing values of the scattering density of minute particles shown in  FIG. 7A , measured after elapse of 20 minutes since the start of heating, in Example and Comparative Example. 
         FIG. 8  is a graph showing the scattering density of minute particles with respect to the heating temperature, in Comparative Example. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     &lt;Overall Configuration of Printer&gt; 
     As shown in  FIG. 1 , a printer  1  is a direct-tandem type horizontal color printer. 
     The printer  1  is provided with a body casing  2 , a process unit  5 , a scanner unit  6 , a transfer unit  7  and a fixing unit  8 . 
     The body casing  2  has a box-like shape that is substantially rectangular in a side view, and accommodates the process unit  5 , the scanner unit  6 , the transfer unit  7  and the fixing unit  8  inside the body casing  2 . 
     Further, the body casing  2  has an opening  3 , a front cover  4 , a paper supply tray  10  and a paper discharge tray  22 . 
     Note that in the following explanation, the front/rear direction is defined with reference to that a side on which the front cover  4  of the printer  1  is provided is the near side (front side), and the left/right direction is defined with reference to that the printer  1  is viewed from the near side (front side). Namely, in  FIG. 1 , the left side of the sheet surface of  FIG. 1  is the front side, the right side of the sheet surface is the rear side, and the near side of the sheet surface is the right side and the far side of the sheet surface is the left side. Specifically, the respective directions are indicated by arrows in each of the drawings. Further, the up/down direction is the vertical direction, and the front/rear direction and the left/right direction are each the horizontal direction. 
     The opening  3  is formed at a front end portion of the body casing  2 . The front cover  4  is pivotably supported by a lower end portion of the front wall of the body casing  2  with a lower end portion of the front cover  4  as the pivot point. The front cover  4  opens or closes the opening  3 . 
     The paper supply tray  10  is detachably provided inside the body casing  2  on a bottom portion of the body casing  2 . The paper feed tray  10  is configured to accommodate a paper P, as an example of the recording medium, in the paper feed tray  10 . 
     The paper discharge tray  22  is arranged at the upper wall of the body casing  2 . The paper discharge tray  22  is recessed downward from the upper wall of the body casing  2  so that a paper P is placed on the paper discharge tray  22 . 
     The process unit  5  is arranged inside the body casing  2  at a substantially central location in the up/down direction of the body casing  2 . The process unit  5  is configured to be installable or removable with respect to the body casing  2  via the opening  3 . 
     The process unit  5  is provided with a drawer unit  9  and a developing cartridge  14 . 
     The drawer unit  9  is provided with a drawer frame  11 , a photosensitive drum  12  and a scorotron charger  13 . 
     The drawer frame  11  has a frame-like shape which is substantially rectangular in a plane view. 
     The photosensitive drum  12  is provided as a plurality of photosensitive drums  12  corresponding to a plurality of colors, respectively. Specifically, four photosensitive drums  12  are provided corresponding to four colors that are yellow, magenta, cyan and black colors, respectively. The four photosensitive drum  12  are arranged in parallel inside the drawer frame  11  at a lower end portion thereof, with a spacing distance between the photosensitive drums  12  in the front/rear direction. 
     Each of the photosensitive drums  12  has a substantially cylindrical shape extending in the left/right direction. The photosensitive drums  12  are rotatably supported by lower end portions in the both side walls of the drawer frame  11  such that a lower end portion of each of the photosensitive drums  12  is exposed from the drawer frame  11 . 
     The scorotron charger  13  is provided as a plurality of, specifically four pieces of, scorotron chargers  13  corresponding to the plurality of photosensitive drums  12 , respectively. The scorotron chargers  13  are arranged, with a spacing distance therebetween, on the upper rear side with respect to the photosensitive drums  12  corresponding thereto, respectively. 
     The developing cartridge  14  is provided as a plurality of, specifically four pieces of, developing cartridges  14  corresponding to the plurality of photosensitive drums  12 , respectively. Each of the developing cartridges  14  is configured to be installable or removable with respect to the drawer frame  11 . 
     The developing cartridges  14  are arranged at positions above and in front of the photosensitive drums  12  corresponding thereto, respectively, in a state that the developing cartridges  14  are installed to the drawer frame  11 . 
     Each of the developing cartridges  14  is provided with a developing frame  15 , a developing roller  25 , a supply roller  23  and a layer-thickness regulating blade  24 . 
     The developing frame  15  has a substantially box-like shape extending in the left/right direction. A rear side portion of the lower end portion of the developing frame  15  is open in a downward and rearward direction. The developing frame  15  is configured to accommodate a toner as an example of the developer. Such a toner is exemplified by a non-magnetic one-component polymerized toner, etc. 
     The developing roller  25  is arranged inside the developing frame  15  at a lower end portion of the developing frame  15 , and is rotatably supported by the developing frame  15 . A rear side portion of the lower end portion of the developing roller  25  is exposed from the developing frame  15  and makes contact with a front side portion of the upper end portion of the photosensitive drum  12 . 
     The supply roller  23  is arranged at a position above and in front of the developing roller  25 . A rear side portion of the lower end portion of the supply roller  23  makes contact with a front side portion of the upper end portion of the developing roller  25 . 
     The layer-thickness regulating blade  24  is arranged at a position above the developing roller  25 . A front end portion of the layer-thickness regulating blade  24  makes contact with an upper end portion of the developing roller  25 . 
     The scanner unit  6  is arranged to be located above the process unit  5 , in the body casing  2 . The scanner unit  6  is configured to emit a laser beam based on data of an image toward each of the photosensitive drums  12 . 
     The transfer unit  7  is arranged to be located below the process unit  5 , in the body casing  2 . The transfer unit  7  is provided with a driving roller  18 , a driven roller  19 , a transport belt  16  and a transfer roller  17 . 
     The driving roller  18  and the driven roller  19  are arranged in the front/rear direction with a spacing distance therebetween. The transport belt  16  is wound around and stretched between the driving roller  18  and the driven roller  19  such that a portion (upper portion) of the transport belt  16 , which is located on the upper side during the below-described circulating movement of the transport belt  16 , makes contact with the plurality of photosensitive drums  12  from therebelow. Further, the transport belt  16  makes circulating movement by the driving of the driving roller  18  and the driven motion of the driven roller  19  such that the upper portion, of the transport belt  16  contacting with the photosensitive drums  12 , moves in the front-to-rear side direction. 
     The transfer roller  17  is provided as a plurality of, specifically four pieces of, transfer rollers  17  corresponding to the plurality of photosensitive drums  12 , respectively. Each of the transfer rollers  17  is arranged to be below one of the photosensitive drums  12  corresponding thereto such that the transfer roller  17  pinches the upper portion of the transport belt  16  with the photosensitive drum  12  corresponding thereto. 
     The fixing unit  8  is arranged at a position above and behind the transfer unit  7  and behind the process unit  5 . The fixing unit  8  is provided with a heating unit  33  as an example of the thermal fixing apparatus and a pressing roller  21 . 
     The heating unit  33  is provided with a heating roller  20 , as will be described in detail later on. 
     As shown in  FIG. 1 , the pressing roller  21  is arranged at a position below and behind the heating roller  20  such that a front side portion of the upper end portion of the pressing roller  21  makes contact with a rear side portion of the lower end portion of the heating roller  20 . 
     &lt;Image-Forming Operation of Printer  1 &gt; 
     Next, an image forming operation of the printer  1  will be explained. Note that in the image forming operation as follows is executed under the control of an unillustrated controller. 
     &lt;Developing Operation&gt; 
     When the printer  1  starts the image forming operation, each of the scorotron chargers  13  uniformly charges the surface of one of the photosensitive drums  12  corresponding thereto and then the scanner unit  6  exposes the charged surfaces of the photosensitive drums  12 , based on a predetermined image data. With this, an electrostatic latent image based on the image data is formed on the surface of each of the photosensitive drums  12 . 
     Further, the toner inside the developing frame  15  is supplied to the supply rollers  23 . Each of the supply rollers  23  supplies the toner to one of the developing rollers  25  corresponding thereto. Then, the supply roller  23  and the developing roller  25  frictionally charge the toner supplied therebetween to the positive polarity. Next, the layer-thickness regulating blade  24  regulates the thickness of the toner supplied to the developing roller  25  to a predetermined (constant) thickness. Then, the developing roller  25  rotates to thereby supply the toner held on the developing roller  25  to the electrostatic latent image formed on the circumferential surface of the photosensitive drum  12 . With this, an image of the toner (toner image) is held on the circumferential surface of the photosensitive drum  12 . 
     &lt;Paper Supplying Operation and Transferring Operation&gt; 
     By the rotation of the respective rollers, papers P accommodated in the paper feed tray  10  are supplied one by one from the paper feed tray  10 , at a predetermined timing, to a space between the photosensitive drum  12  and the transport belt  16 . 
     Next, the transport belt  16  transports a paper P supplied between the photosensitive drum  12  and the transport belt  16  in the front-to-rear side direction. At this time, each of the photosensitive drums  12  and one of the transport rollers  17  corresponding thereto transport one of toner images of the respective colors onto the paper P passing therebetween and therethrough so that the toner images of the respective colors are formed on the paper P in a sequential manner. With this, a color image is formed on the paper P. 
     &lt;Fixing Operation and Paper Discharge Operation&gt; 
     Next, the paper P on which the color image is formed reaches a space between the heating roller  20  and the pressing roller  21  by the circulating movement of the transport belt  16 . The heating roller  20  and the pressing roller  21  heat and press (apply pressure to) the paper P passing therebetween and therethrough. With this, the color image transferred to the paper P is thermally fixed to the paper P. Afterwards, the respective rollers transport the paper P so that the paper P makes a U-turn frontward and upward, thereby discharging the paper P to the paper discharge tray  22 . 
     &lt;Details of Heating Unit&gt; 
     The heating unit  33  is provided with the heating roller  20 , a halogen lamp  31  as an example of the heating member, as shown in  FIG. 3 , and an unillustrated temperature controller. 
     The heating roller  20  is provided with a metal raw pipe (metal pipe stock)  26  as an example of the core bar, a heat absorbing layer  29 , a rubber layer  27  and a coating layer  28  as an example of the release layer. 
     The metal raw pipe  26  is formed of a metal material such as aluminum, etc., and has a substantially cylindrical shape extending in the left/right direction. The size in the left/right direction of the metal raw pipe  26  is, for example, in a range of not less than 220 mm to not more than 300 mm, preferably in a range of not less than 240 mm to not more than 280 mm. 
     The heat absorbing layer  29  is formed, for example, of a black paint, etc., and is arranged on the inner circumferential surface of the metal raw pipe  26 . The thickness of the heat absorbing layer  29  is, for example, in a range of not less than 5 μm to not more than 50 μm, preferably in a range of not less than 5 μm to not more than 20 μm. Further, the size in the left/right direction of the heat absorbing layer  29  is smaller than the size in the left/right direction of the metal raw pipe  26 . Furthermore, the heat absorbing layer  29  covers the inner circumferential surface of the metal raw pipe  26  such that the both end portions in the left/right direction of the inner circumferential surface of the metal raw pipe  26  are exposed (are not covered by the heat absorbing layer  29 ). 
     The rubber layer  27  is formed, for example, of a rubber material such as silicone rubber, fluoro rubber, etc., and is preferably formed of silicone rubber in view of the heat-resisting property. The rubber layer  27  is arranged on the outer circumferential surface of the metal raw pipe  26 , and has a substantially cylindrical shape extending in the left/right direction. The thickness of the rubber layer  27  is, for example, in a range of not less than 0.1 mm to not more than 1.0 mm, preferably in a range of not less than 0.3 mm to not more than 0.8 mm. Further, the size in the left/right direction of the rubber layer  27  is smaller than the size in the left/right direction of the metal raw pipe  26 , and is, for example, in a range of not less than 210 mm to not more than 260 mm, preferably in a range of not less than 220 mm to not more than 250 mm. Furthermore, the rubber layer  27  covers the outer circumferential surface of the metal raw pipe  26  such that the both end portions in the left/right direction of the outer circumferential surface of the metal raw pipe  26  are exposed (are not covered by the rubber layer  27 ). 
     The coating layer  28  is formed, for example, of a resin material such as fluororesin, silicone resin, etc. The fluororesin is preferred among such resin materials. Specific examples of the fluororesin includes polytetrafluoroethylene (PTFE), tetrafluoroethylen-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoroethylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), difluoroethylene polymer (PVdF), etc., among which the PFA is preferred. Such a resin material may be used singly, or two or more kinds of the resin material may be used in combination. 
     The coating layer  28  is arranged on the outer circumferential surface of the rubber layer  27  and has a substantially cylindrical shape extending in the left/right direction. The thickness of the coating layer  28  is, for example, in a range of not less than 20 μm to not more than 100 μm, preferably in a range of not less than 30 μm to not more than 90 μm. Further, the size in the left/right direction of the coating layer  28  is substantially same as the size in the left/right direction of the rubber layer  27 . Furthermore, the coating layer  28  covers the outer circumferential surface of the rubber layer  27  such that the rubber layer  27  is entirely covered by the coating layer  28  in the left/right direction. 
     The halogen lamp  31  has a substantially cylindrical shape extending in the left/right direction. The size in the left/right direction of the halogen lamp  31  is greater than the size in the left/right direction of the metal raw pipe  26 , and the outer diameter of the halogen lamp  31  is smaller than the inner diameter of the metal raw pipe  26 . Further, the halogen lamp  31  is arranged inside the metal raw pipe  26  such that the both end portions in the left/right direction of the halogen lamp  31  project from the metal raw pipe  26  in the left/right direction. 
     Furthermore, the halogen lamp  31  is provided with a filament  32 . The filament  32  is arranged inside the halogen lamp  31  in the left/right direction such that the filament  32  is overlapped with the heat absorbing layer  29  when the filament  32  is projected in the radial direction of the metal raw pipe  26 . 
     The unillustrated temperature controller is configured to be capable of detecting the surface temperature of the heating roller  20 , and of controlling the output of the halogen lamp  31 . 
     &lt;Minute Particle Scattering Test of Heating Roller&gt; 
     As shown in  FIG. 6 , the heating roller  20  is subjected to measurement for measuring the scattering density of the minute particles by a minute particle scattering test as an example of the test; and the measured scattering density of the minute particles is, for example, in a range of not less than 100 pieces/cm 3  to less than 2,000 pieces/cm 3 , preferably in a range of not less than 100 pieces/cm 3  to less than 1,900 pieces/cm 3 , more preferably in a range of not less than 100 pieces/cm 3  to less than 1,700 pieces/cm 3 . 
     The term “minute particles” referred herein means minute particles which scatter (fly or drift) from the rubber layer  27  when the heating roller  20  is heated and of which mean particle size is not more than 300 nm. Note that in the following explanation, the minute particles which scatter from the rubber layer  27  and of which mean particle size is not more than 300 nm is simply described as “minute particles”. 
     More specifically, the mean particle size of the minute particles is in a range of not less than 5 nm to not more than 300 nm, preferably in a range of not less than 10 nm to not more than 250 nm. The mean particle size of such minute particles can be measured by a fast-response particle sizer (model name: FMPS (Fast Mobility Particle Sizer), manufactured by TOKYO DYLEC CORPORATION). 
     The scattering density (piece/cm 3 ) of such minute particles is the number of pieces of the minute particles which are present in a space of 1 cm 3 , and is measured, for example, by a measuring unit  38 . 
     The measuring unit  38  is provided with a casing  40 , a particle density measuring device  39  as an example of the minute particle density measuring device, a communicating tube  41 , a hot plate  42  as an example of the heater, and an air cleaner  43 . 
     The casing  40  has a box-like shape that is substantially rectangular in a side view. The size in the left/right direction of the casing  40  is, for example, in a range of not less than 40 cm to not more than 80 cm, specifically 50 cm; the size in the front/rear direction of the casing  40  is, for example, in a range of not less than 60 cm to not more than 100 cm, specifically 70 cm; the size in the up/down direction of the casing  40  is, for example, in a range of not less than 40 cm to not more than 80 cm, specifically 50 cm. Further, the internal cubic volume of the casing  40  is 0.175 m 3 . 
     The particle density measuring device  39  is configured to measure the scattering density of minute particles (piece/cm 3 ) inside the casing  40 . As the above-described particle density measuring device  39 , it is possible to use any commercially available device which is exemplified by, for example, a portable condensed particle counter: model name “CPC 3007” manufactured by TOKYO DYLEC CORPORATION, and the like. 
     The communicating tube  41  has a tubular shape, and communicates the particle density measuring device  39  and the casing  40 . Specifically, an end portion of the communicating tube  41  is connected to the casing  40  so as to face the inside of the casing  40 , and the other end portion of the communicating tube  41  is connected to the particle density measuring device  39 . In such a manner, the casing  40  is connected to the particle density measuring device  39  via the communicating tube  41 . 
     The hot plate  42  is arranged inside the casing  40  at a bottom portion of the casing  40 . The hot plate  42  is configured such that the upper surface of the hot plate  42  is heated to a temperature within a temperature range, for example, of not less than 25° C. to not more than 300° C. 
     The air cleaner  43  is arranged on the upper surface of the upper wall of the casing  40 , and is configured to remove the minute particles inside the casing  40 . As the above-described air cleaner  43 , it is possible to use any commercially available device which is exemplified by, for example, PURE SPACE model name PS01-A manufactured by TANAKA SEIKI CO., LTD. 
     In order to measure the scattering density of minute particles (piece/cm 3 ) from the heating roller  20  with this measuring unit  38 , an operator at first activates the air cleaner  43  and adjusts the scattering density of the minute particles inside the casing  40  to, for example, not less than 0 pieces/cm 3 , and for example, not more than 100 pieces/cm 3 , preferably not more than 5 pieces/cm 3 . The scattering density of the minute particles in this situation is referred to as “initial scattering density of minute particles”. Note that the scattering density of the minute particles inside the casing  40  is measured by the particle density measuring device  39 . 
     Afterwards, the operator stops the air cleaner  43 . 
     Further, the operator activates the hot plate  42  and heats the upper surface of the hot plate  42  to 230° C. 
     Then, the operator arranges the heating roller  20  on the hot plate  42  so that the axial direction of the heating roller  20  is along the up/down direction and an end surface in the axial direction of the metal raw pipe  26  makes contact with the heated upper surface of the hot plate  42 . 
     With this, the metal raw pipe  26  of the heating roller  20  is heated to approximately 230° C. by the hot plate  42 , and the rubber layer  27  of the heating roller  20  is also heated to approximately 230° C. via the metal raw pipe  26 . 
     Next, when 20 minutes has elapsed since the start of the heating with respect to the heating roller  20 , the scattering density of minute particles (piece/cm 3 ) inside the casing  40  is measured by the particle density measuring device  39 . The scattering density of the minute particles inside the casing  40  in this situation is referred to as “after-heating scattering density of minute particles”. 
     Then, the after-heating scattering density of minute particles is corrected by the initial scattering density of minute particles. Specifically, the initial scattering density of minute particles is subtracted from the after-heating scattering density of minute particles. 
     In the manner described above, the scattering density of minute particles (piece/cm 3 ) from the heating roller  20  is calculated. 
     &lt;Method for Producing Heating Roller&gt; 
     In order to produce such a heating roller  20 , at first, a metal raw pipe  26  having a heat absorbing layer  29  arranged on the inner circumferential surface thereof is prepared, as shown in  FIG. 4A . 
     Next, a resin composite layer  30  is formed on the outer circumferential surface of the metal raw pipe  26  so as to cover the metal raw pipe  26  with the resin composite layer  30  as shown in  FIG. 4B . 
     In order to form such a resin composite layer  30 , for example, an unillustrated forming die is arranged so as to cover the outer circumferential surface of the metal raw pipe  26 , and a resin composite is poured into the unillustrated forming die. 
     The resin composite contains at least a resin. 
     The resin is exemplified, for example, by a silicone resin, a fluororesin, a styrene-butadiene resin, a nitrile resin, an ethylene-propylene resin, etc. Among these, the silicone resin is preferred. 
     As the silicone resin, it is possible to use any commercially available product which is exemplified, for example, by a silicone rubber produced by SHIN-ETSU CHEMICAL CO., LTD., and the like. 
     Next, as shown in  FIG. 4C , the metal raw pipe  26  having the resin composite layer  30  formed on the outer circumferential surface thereof is heated by a first heater  35 . 
     The first heater  35  is provided with a first casing  44  which has substantially box-like shape, and is configured to heat the inside of the first casing  44 . 
     Accordingly, the metal raw pipe  26  is accommodated inside the first casing  44  and is heated by the first heater  35 . 
     The heating temperature by the first heater  35  is, for example, a temperature in a range of not less than 25° C. to not more than 150° C., preferably in a range of not less than 30° C. to not more than 100° C.; the heating time (duration of heating time) by the first heater  35  is, for example, in a range of not less than 0.5 hours to not more than 4 hours, preferably in a range of not less than 1.0 hour to not more than 2 hours. 
     With this, the resin composite layer  30  undergoes primary curing. After that, the unillustrated forming die is removed. 
     Next, the metal raw pipe  26  in which the primary cured resin composite layer  30  is arranged on the outer circumferential surface of the metal raw pipe  26  is heated by a second heater  36 , as shown in  FIG. 4C . Note that although the second heater  36  may be same as or different from the first heater  35 , it is preferable that the second heater  36  is different from the first heater  35  from the viewpoint of lowering the scattering density of the minute particles. 
     The second heater  36  is provided with a second casing  45  which has substantially box-like shape, and is configured to heat the inside of the second casing  45 . 
     Accordingly, the metal raw pipe  26  is accommodated inside the second casing  45  and is heated by the second heater  36 . 
     The heating temperature by the second heater  36  is, for example, in a range of not less than 150° C. to not more than 230° C., preferably in a range of not less than 200° C. to not more than 220° C.; the heating time (duration of heating time) by the second heater  36  is, for example, in a range of not less than 0.5 hours to not less than 10 hours, preferably in a range of not less than 2.0 hours to not more than 8 hours. 
     With this, the resin composite layer  30  after having undergone the primary curing is heated and undergoes secondary curing, and is prepared as a rubber layer  27 , as shown in  FIG. 5A . 
     Next, a coating layer  28  is formed on the outer circumferential surface of the rubber layer  27  so as to cover the rubber layer  27  with the coating layer  28 . 
     In order to form the coating layer  28 , at first, a coating layer  28  having a substantially cylindrical shape extending in the left/right direction is prepared separately. Then, the coating layer  28  is attached to the outer circumferential surface of the rubber layer  27  so that the coating layer  28  covers the rubber layer  27 . 
     With this, a roller member  34  provided with the metal raw pipe  26 , the rubber layer  27 , the coating layer  28  and the heat absorbing layer  29  is prepared. 
     Next, the roller member  34  is heated as shown in  FIG. 5B  to a temperature that is not less than a minute particle-scattering start temperature at which the minute particles start to scatter. Namely, the roller member  34  is a heating roller  20  before being subjected to the heating process at a temperature that is not less than the minute particle-scattering start temperature. 
     Here, the term “minute particle-scattering start temperature” means a temperature at which the minute particles having the mean particle size of not more than 300 nm start to scatter in not less than predetermined amount from the rubber layer  27  of the roller member  34 , and is measured, for example, by the measuring unit  38  as shown in  FIG. 6 . 
     In order to measure the minute particle-scattering start temperature by the measuring unit  38 , the scattering density of the minute particles inside the casing  40  is adjusted preferably to not more than 5 pieces/cm 3 , in a similar manner in the above-described minute particle scattering test. Then, the upper surface of the hot plate  42  is heated to a predetermined initial temperature, for example, a temperature in a range of not less than 140° C. to not more than 200° C., preferably in a range of not less than 170° C. to not more than 190° C. 
     Next, the roller member  34  is arranged on the hot plate  42  so that the axial direction of the roller member  34  is along the up/down direction and an end surface in the axial direction of the metal raw pipe  26  makes contact with the heated upper surface of the hot plate  42 , followed by being stood still for 20 minutes. After 20 minutes has elapsed, the scattering density of minute particles (piece/cm 3 ) inside the casing  40  is measured by the particle density measuring device  39 . 
     At this time, in a case that the scattering density of the minute particles is less than 5,000 pieces/cm 3 , the temperature of the upper surface of the hot plate  42  is raised by a predetermined value, for example by 20° C., and the above-described operation is repeated. 
     Then, in a case that the scattering density of the minute particles exceeds 5,000 pieces/cm 3 , a temperature obtained by subtracting a predetermined value (for example, 20° C.) from the temperature of the upper surface of the hot plate  42  at a point of time when the scattering density has exceeded 5,000 pieces/cm 3  is set to be the minute particle-scattering start temperature. 
     With this, the minute particle-scattering start temperature is measured by the measuring unit  38 . 
     More specifically, the minute particle-scattering start temperature is, for example, in a range of not less than 150° C. to less than 230° C., preferably in a range of a temperature exceeding 150° C. to less than 230° C., more preferably in a range of not less than 200° C. to less than 220° C. 
     In order to heat the roller member  34  to a temperature not less than the minute particle-scattering start temperature, the roller member  34  is heated by a third heater  37  as shown in  FIG. 5B . 
     The third heater  37  is provided with a third casing  46  which has substantially box-like shape, and is configured to heat the inside of the third casing  46 . Note that although the third heater  37  may be same as or different from the second heater  36 , it is preferable that the third heater  37  is different from the second heater  36  from the viewpoint of lowering the scattering density of the minute particles. 
     Accordingly, the roller member  34  is accommodated inside the third casing  46  and is heated by the third heater  37 . 
     The heating temperature by the third heater  37  is, for example, in a range of not less than 160° C. to not more than 250° C., preferably in a range of not less than 200° C. to not more than 240° C., more preferably 230° C.; the heating time (duration of heating time) by the third heater  37  is, for example, in a range of not less than 1 hour to not more than 20 hours, preferably in a range of not less than 4 hour to not more than 10 hours. 
     In such a manner described above, the heating roller  20  is produced. 
     Note that although the roller member  34  is prepared and then the heating roller  20  is produced from (based on) the roller member  34  in the method for producing the heating roller as described above, there is no limitation to this. It is allowable to produce the heating roller  20  from a commercially available roller member  34 . Examples of the commercially available roller member  34  include a roller manufactured by SYNZTEC CO., LTD., etc. 
     &lt;Details of Fixing Operation&gt; 
     The heating roller  20  as described above is heated to a temperature within the fixing temperature range in the above-described fixing operation by the unillustrated temperature controller and the halogen lamp  31 . 
     The fixing temperature range is, for example, in a range of not less than 150° C. to not more than 250° C., preferably in a range of not less than 200° C. to not more than 240° C., more preferably in a range of a temperature exceeding 200° C. to less than 230° C. Namely, the fixing temperature range includes the minute particle-scattering start temperature. 
     [Effect of Operation] 
     In the heating roller  20 , the density, of minute particles having the mean particle size of not more than 300 nm, measured by the minute particle scattering test as shown in  FIG. 6  is less than 2,000 pieces/cm 3 . Accordingly, it is possible to suppress the scattering of the minute particles from the rubber layer  27  when the heating roller  20  is heated to a temperature within the fixing temperature range for the purpose of thermally fixing the toner (toner image) onto a paper P. 
     The fixing temperature range preferably is of more than 200° C. to less than 230° C. Namely, the fixing temperature range is lower than 230° C. that is the heating temperature in the minute particle scattering test. Accordingly, it is possible to assuredly suppress the scattering of the minute particles from the rubber layer  27  in a case that the heating roller  20  is heated to a temperature within the fixing temperature range. 
     Further, the rubber layer  27  shown in  FIG. 3  is formed preferably of a silicone rubber. Accordingly, it is possible to improve the heat resisting property of the rubber layer  27 . 
     Furthermore, the heat absorbing layer  29  is arranged on the inner circumferential surface of the meal raw pipe  26 , as shown in  FIG. 3 . Accordingly, when the halogen lamp  31  heats the metal raw pipe  26  from the inside of the metal raw pipe  26 , the heat absorbing layer  29  absorbs the heat beam (heat ray) efficiently. As a result, the heat absorbing layer  29  can be heated efficiently, consequently thereby heating the metal raw pipe  26  efficiently. 
     The heating unit  33  is provided with the heating roller  20  and the halogen lamp  31 , as shown in  FIG. 3 . Accordingly, it is possible to suppress the scattering of minute particles from the rubber layer  27  of the heating roller  20 , when the halogen lamp  31  heats the heating roller  20  to a temperature within the fixing temperature range to thereby thermally fix the toner (toner image) onto a paper P. 
     In the method for producing the heating roller  20 , the resin composite layer  30  is subjected to the secondary curing to thereby prepare the rubber layer  27  as shown in  FIGS. 4B and 4C , and then the roller member  34  provided with the metal raw pipe  26 , the rubber layer  27  and the coating layer  28  is heated by the third heater  37  preferably at a temperature in a range of not less than 200° C. to not more than 250° C. for a duration of time ranging from not less than 1 hour to not more than 20 hours, as shown in  FIGS. 5A and 5B . Accordingly, the minute particles of which mean particles size is not more than 300 nm scatter from the rubber layer  27  when the third heater  37  heats the roller member  34 . 
     In other words, in the method for producing the heating roller  20 , the minute particles of which mean particle size is not more than 300 nm are caused to scatter from the rubber layer  27  in advance in the production step of the heating roller  20 . Accordingly, in the heating roller  20  produced by this production method, the scattering of the minute particles from the rubber layer  27  is suppressed, when the heating roller  20  is heated to a temperature within the fixing temperature range. 
     Namely, according to the method for producing the heating roller  20 , it is possible to produce a heating roller  20  capable of suppressing the scattering of minute particles of which mean particle diameter is not more than 300 nm when being heated to a temperature within the fixing temperature range. 
     In the following, an example and a comparative example are shown for explaining the present teaching in further detail. The present teaching, however, is not limited to the example and the comparative example. Note that the numerical values in the example can be substituted with the upper limit value or the lower limit value of any portions described in the above-described embodiment and corresponding to those in the example. 
     Example 1 
     At first, a metal raw pipe provided with a heat absorbing layer formed of a black paint (coating) arranged on the inner circumferential surface of the metal raw pipe was prepared. 
     Note that the metal raw pipe was made of aluminum, and size in the left/right direction of the metal raw pipe was 270 mm. Further, the thickness of the heat absorbing layer was 10 μm. 
     Subsequently, an unillustrated forming die was arranged so as to cover the outer circumferential surface of the metal raw pipe, and a resin composite was poured into the unillustrated forming die. Note that the resin composite contained a silicone resin and was in liquid form. 
     In such a manner, a resin composite layer was formed on the outer circumferential surface of the metal raw pipe. 
     Next, the metal raw pipe having the resin composite layer formed thereon was accommodated and heated inside the first casing  44  of the first heater  35  shown in  FIG. 4C . 
     Note that the heating temperature by the first heater  35  was in a range of 30° C. to 60° C., and the duration of heating time by the first heater  35  was in a range of 1 hour to 2 hours. 
     With this, the resin composite layer underwent the primary curing. Afterwards, the unillustrated forming die was removed. 
     Next, the metal raw pipe provided with the primary cured resin composite layer thereon was accommodated and heated inside the second casing  45  of the second heater  36  shown in  FIG. 4C . 
     Note that the heating temperature by the second heater  36  was in a range of 200° C. to 240° C., and the duration of heating time by the second heater  36  was in a range of 4 hours to 8 hours. 
     With this, the resin composite layer underwent the secondary curing to thereby prepare a rubber layer. Further, the size in the left/right direction of the rubber layer was 240 mm and the thickness of the rubber layer was 0.5 mm. 
     Next, a coating layer having a substantially cylindrical shape was attached to the outer circumferential surface of the rubber layer so as to cover the rubber layer. Note that the coating layer was formed of PFA, and the size in the left/right direction of the coating layer was 240 mm and the thickness of the coating layer was 50 μm. 
     With this, a roller member provided with the metal raw pipe, the rubber layer, the coating layer and the heat absorbing layer was prepared. 
     Next, the roller member was accommodated and heated inside the third casing  46  of the third heater  37  shown in  FIG. 5B . 
     Note that the heating temperature by the third heater  37  was in a range of 200° C. to 250° C., and the duration of heating time by the third heater  37  was in a range of 4 hours to 8 hours. 
     In the manner described above, the heating roller was produced. 
     &lt;Evaluations&gt; 
     (1) Scattering Density of Minute Particles 
     With respect to the heating roller of Example 1, the scattering density of minute particles was measured with the measuring unit  38  shown in  FIG. 6 . 
     At first, the air cleaner  43  was activated and the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was adjusted to not more than 5 pieces/cm 3 . Further, the hot plate  42  was activated to heat the upper surface of the hot plate  42  to 230° C. 
     Next, the air cleaner  43  was stopped, and then the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was measured every 1 second and the measured values were stored (logging or data log) by the particle density measuring device  39 . 
     After elapse of 20 minutes since the start of the measuring, the logging by the particle density measuring device  39  was stopped. By doing so, the background data was obtained. 
     Subsequently, the air cleaner  43  was activated again, and the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was adjusted to not more than 5 pieces/cm 3 . 
     Next, the air cleaner  43  was stopped, and then the heating roller was arranged on the hot plate  42  so that the axial direction of the heating roller was along the up/down direction and an end surface in the axial direction of the metal raw pipe made contact with the heated upper surface of the hot plate  42 . 
     Then, the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was measured every 1 second and the measured values were stored (logging) by the particle density measuring device  39 . 
     After elapse of 20 minutes since the start of the heating of the heating roller, the logging by the particle density measuring device  39  was stopped, and the obtained measurement data was corrected by the background data. The result of the correction is shown in  FIG. 7A . Further, the scattering density of minute particles (piece/cm 3 ) measured at a point of time after elapse of 20 minutes since the start of heating of the heating roller is shown in  FIG. 7B . 
     COMPARATIVE EXAMPLE 1 
     A roller member was prepared in a similar manner as in Example 1 described above. 
     &lt;Evaluations&gt; 
     (1) Scattering Density of Minute Particles 
     With respect to the roller member of Comparative Example 1, the scattering density of minute particles was measured with the measuring unit  38  shown in  FIG. 6 . 
     At first, the background data was obtained in a similar manner as the measurement of scattering density of minute particles in Example 1. 
     Subsequently, the air cleaner  43  was activated again, and the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was adjusted to not more than 5 pieces/cm 3 . 
     Next, the air cleaner  43  was stopped, and then the roller member was arranged on the hot plate  42  so that the axial direction of the roller member was along the up/down direction and an end surface in the axial direction of the metal raw pipe made contact with the heated upper surface of the hot plate  42 . 
     Then, the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was measured every 1 second and the measured values were stored (logging) by the particle density measuring device  39 . 
     After elapse of 20 minutes since the start of the heating of the roller member, the logging by the particle density measuring device  39  was stopped, and the obtained measurement data was corrected by the background data. The result of the correction is shown in  FIG. 7A . Further, the scattering density of minute particles (piece/cm 3 ) measured at a point of time after elapse of 20 minutes since the start of heating of the roller member is shown in  FIG. 7B . 
     (2) Minute Particle-Scattering Start Temperature 
     With respect to the roller member of Comparative Example 1, the minute particle-scattering start temperature was measured with the measuring unit  38  shown in  FIG. 6 . 
     At first, the air cleaner  43  was activated and the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was adjusted to not more than 5 pieces/cm 3 . Further, the hot plate  42  was activated to heat the upper surface of the hot plate  42  to 180° C. 
     Next, the air cleaner  43  was stopped, and then the roller member was arranged on the hot plate  42  so that the axial direction of the roller member was along the up/down direction and an end surface in the axial direction of the metal raw pipe made contact with the heated upper surface of the hot plate  42 . 
     Subsequently, the roller member was heated for 10 minutes, and then the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was measured by the particle density measuring device  39 . The scattering density of the minute particles at this point of time was 1,913 pieces/cm 3 . 
     Next, the temperature of the upper surface of the hot plate  42  was raised by 20° C. (predetermined value) so that the upper surface was heated to 200° C., and was made to stand still for 10 minutes. 
     Afterwards, the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was measured again by the particle density measuring device  39 . The scattering density of the minute particles at this point of time was 544 pieces/cm 3 . 
     Next, the temperature of the upper surface of the hot plate  42  was raised further by 20° C. so that the upper surface was heated to 220° C., and was made to stand still for 10 minutes. 
     Afterwards, the scattering density of minute particles (piece/cm 3 ) inside the casing  40  was measured again by the particle density measuring device  39 . The scattering density of the minute particles at this point of time was 35,803 pieces/cm 3 . 
     At this point of time, since the scattering density of the minute particles exceeded 5,000 pieces/cm 3 , the temperature of 200° C., obtained by subtracting 20° C. (predetermined value) from 220° C. that was the temperature of the upper surface of the hot plate  42 , was confirmed as the minute particle-scattering start temperature. 
     The result of the above is shown in  FIG. 8 .