Patent Publication Number: US-9841713-B2

Title: Fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-045682 filed Mar. 9, 2016. 
     TECHNICAL FIELD 
     The present invention relates to a fixing device where lubricant is applied to an inner circumferential surface of a fixing belt and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the embodiments of the present invention, there is provided a fixing device comprising: an endless fixing belt that has an inner circumferential surface to which lubricant is applied and that is rotated; a first plate-shaped body that is disposed along the inner circumferential surface and is in contact with the inner circumferential surface; a second plate-shaped body that is disposed along the first plate-shaped body at a distance to cause a capillary phenomenon in the lubricant; and a bent portion that is provided in an end portion of the second plate-shaped body in a rotating direction of the fixing belt and is bent on an inner circumferential surface side on a downstream side of an end portion of the first plate-shaped body in the rotating direction of the fixing belt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detailed based on the following figures, wherein: 
         FIG. 1  is a schematic configuration diagram illustrating an image forming apparatus according to a first exemplary embodiment; 
         FIG. 2  is a sectional view illustrating a configuration of a fixing device illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged view illustrating a main portion of  FIG. 2 ; 
         FIG. 4  is a schematic diagram corresponding to a cross section that is taken along line A-A in  FIG. 3 ; 
         FIG. 5  is a graph illustrating an outflow amount of oil with respect, to a temperature; 
         FIG. 6  is a view illustrating a fixing device according to a second exemplary embodiment and an enlarged view corresponding to a main portion of  FIG. 2 ; and 
         FIG. 7  is an enlarged view illustrating a main portion of a fixing device according to a third exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
     Hereinafter, a first exemplary embodiment of the present invention will be described with reference to the drawings.  FIG. 1  is a schematic configuration diagram illustrating an image forming apparatus  100  according to the first exemplary embodiment. The image forming apparatus  100  configures a printer of an intermediate transfer system as an example. 
     The image forming apparatus  100  includes plural image forming units  1 Y,  1 M,  1 C, and  1 K that form respective toner images of color components by an electrophotographic system, a primary transfer portion  10  that causes the toner image of each color component formed by each of the image forming units  1 Y,  1 M,  1 C, and  1 K to sequentially transfer (primarily transfer) to an intermediate transfer belt  15 , a secondary transfer portion  20  that causes superimposed toner images transferred on the intermediate transfer belt  15  to collectively transfer (secondarily transfer) on a medium P, and a fixing device  60  that fixes the image that is secondarily transferred on the medium P. The image forming apparatus  100  also includes a controller  40  that controls an operation of each portion of each device. Here, a combination of the image forming units  1 Y,  1 M,  1 C, and  1 K, the intermediate transfer belt  15 , the primary transfer portion  10 , and the secondary transfer portion  20  corresponds to an example of an image forming portion  70  that is referred to in the exemplary embodiment. 
     The image forming apparatus  100  is a so-called tandem type printer and the image forming units  1 Y,  1 M,  1 C, and  1 K are configured such that yellow (Y), magenta (M), cyan (C), and black (K) are arranged in parallel from an upstream side of the intermediate transfer belt  15 . The image forming units  1 Y,  1 M,  1 C, and  1 K have the same configuration as each other except that colors of toners to be used are different. 
     If a representative color to the image forming unit  1 Y corresponding to yellow is described with reference to numerals, the image forming unit  1 Y has a photoconductor drum  11  that is rotated in a direction of arrow A, a charger  12  that charges the photoconductor drum  11 , a laser exposure device  13  that writes an electrostatic latent image by applying an exposure beam Bm to the photoconductor drum  11 , a developing device  14  in which toner of yellow is stored and which develops the electrostatic latent image on the photoconductor drum  11  using the toner, the primary transfer portion  10  that transfers the toner image of each color component formed on the photoconductor drum  11  to the intermediate transfer belt  15 , and a toner cleaner  17  that removes residual toner on the photoconductor drum  11 . 
     The intermediate transfer belt  15  is, for example, a film-like endless belt that is formed by a material obtained by containing an antistatic agent in resin. The intermediate transfer belt  15  is bridged between the plural rolls and circulates in a B direction illustrated in  FIG. 1 . The rolls on which the intermediate transfer belt  15  is bridged are a driving roll  31  that drives the intermediate transfer belt, a support roll  32  that supports both ends of a region in which the intermediate transfer belt  15  is extended along the arrangement of the photoconductor drums  11 , a tension roll  33  that applies a constant tension to the intermediate transfer belt  15 , a rear roll  25  that is provided in the secondary transfer portion, and a cleaning portion rear roll  34  that is provided in the cleaning portion. The driving roll  31  is driven by a motor (not illustrated) and causes the intermediate transfer belt  15  to circulate at a predetermined speed. The tension roll  33  also functions as a correction roll for preventing meandering of the intermediate transfer belt  15 . 
     The primary transfer portion  10  has a primary transfer roll  16  that is disposed to face the photoconductor drum  11  where the intermediate transfer belt  15  is interposed therebetween. The intermediate transfer belt  15  is clamped between the primary transfer roll  16  and the photoconductor drum  11 . A voltage (primary transfer bias) of a polarity opposite to a charge polarity (negative polarity in the exemplary embodiment and hereinafter, the same) of the toner is applied to the primary transfer roll  16 . 
     The secondary transfer portion  20  includes a secondary transfer roll  22  that is disposed on a toner image holding surface side of the intermediate transfer belt  15 , a rear roll  25 , and a power feeding roll  26  that applies a secondary transfer bias to the rear roll  25 . The rear roll  25  is disposed on an inner circumferential surface of the intermediate transfer belt  15 , that is, on a side opposite to the secondary transfer roll  22  where the intermediate transfer belt  15  is interposed therebetween, and forms a counter electrode of the secondary transfer roll  22 . In addition, an image density sensor  43  is disposed on a downstream side from the image forming unit  1 K of black to perform adjustment of image quality. 
     In addition, an intermediate transfer belt cleaner  35  is provided on the downstream side from the secondary transfer portion  20  of the intermediate transfer belt  15  for cleaning the surface of the intermediate transfer belt  15  by removing residual toner or paper dust on the intermediate transfer belt  15  after the secondary transfer. On the other hand, a reference sensor (home position sensor)  42  is disposed on an upstream side from the image forming unit  1 Y of yellow to generate a reference signal for taking an image formation timing in each of the image forming units  1 Y,  1 M,  1 C, and  1 K. 
     Furthermore, the image forming apparatus  100  includes a sheet accommodating portion  50  that accommodates the sheet P, a pickup roll  51  that delivers the medium P integrated in the sheet accommodating portion  50 , a transport roll  52  that transports the medium P, a guide member  53  that guides the medium P transported by the transport roll  52  to the secondary transfer portion  20 , a transport belt  55  that transports the medium P to the fixing device  60  after the medium P is secondarily transferred by the secondary transfer roll  22 , and a fixing entry guide  56  that guides the medium P to the fixing device  60  as a sheet transport system. 
     Next, a basic process of the image forming portion  70  will be described. 
     After performing image processing on image data output from an image reading device or a personal computer (PC) (not illustrated), the image forming portion  70  converts the image data into color material tone data of four colors of Y, M, C, and K, and supplies the color material tone data on the laser exposure devices  13  of the image forming units  1 Y,  1 M,  1 C, and  1 K. The laser exposure device  13  applies the exposure beam Bm emitted, for example, from a semiconductor laser to the photoconductor drum  11  of each of the image forming units  1 Y,  1 M,  1 C, and  1 K in accordance with the supplied color material tone data. After a surface of the photoconductor drum  11  of each of the image forming units  1 Y,  1 M,  1 C, and  1 K is charged by the charger  12 , the surface is scanned and exposed by the laser exposure device  13  and the electrostatic latent image is formed on the photoconductor drum  11 . The formed electrostatic latent image is developed as the toner image of each color of Y, M, C, and K by the developing device  14  of each of the image forming units  1 Y.  1 M,  1 C, and  1 K. 
     The toner images formed on the photoconductor drums  11  of the image forming units  1 Y,  1 M,  1 C, and  1 K are transferred to be sequentially superimposed on the surface of the intermediate transfer belt  15  in the primary transfer portion  10 . After the toner images are sequentially transferred on the surface of the intermediate transfer belt  15 , the toner images are transported to the secondary transfer portion  20  in accordance with the movement of the intermediate transfer belt  15 . On the other hand, in the sheet transport system, the pickup roll  51  delivers the recording medium P accommodated in the sheet accommodating portion in accordance with timing when the toner image is transported to the secondary transfer portion  20 . The medium P that is delivered by the pickup roll  51  is transported by the transport roll  52  and reaches the secondary transfer portion  20  in accordance with moving timing of the intermediate transfer belt  15  in which the toner image is held. 
     The secondary transfer portion  20  transfers the toner image held on the intermediate transfer belt  15  on the medium P that is clamped between the intermediate transfer belt  15  and the secondary transfer roll  22 . The medium P to which the toner image is electrostatically transferred is transported to the fixing device  60  by the transport belt  55 . The fixing device  60  adds heat and pressure to the toner image on the medium P and fixes the toner image on the medium P. The medium P on which a fixed image is formed is discharged to an ejection portion (not illustrated). 
     On the other hand, residual toner remaining on the intermediate transfer belt  15  without being transferred from the intermediate transfer belt  15  to the medium P by the secondary transfer portion  20  is removed from the intermediate transfer belt  15  by the intermediate transfer belt cleaner  35 . 
     [Fixing Device] 
     Hereinafter, the fixing device  60  configuring the image forming apparatus  100  will be described. As illustrated in  FIG. 2 , the fixing device  60  is configured to include a fixing roll  82 , a fixing belt  84 , a heating member  86 , and a pressurizing roll  88 . 
     The fixing belt  84  is an endless band-shaped belt in a direction of circulation and is bridged between the fixing roll  82  and the heating member  86 . Outer circumferential surfaces of the fixing belt  84  and the pressurizing roll  88  are in contact with each other and the fixing belt  84  circulates in a belt rotating direction D in accordance with the rotation of the pressurizing roll  88  in a rotating direction C. Therefore, the fixing roll  82  is also rotated in a rotating direction E. 
     The fixing belt  84  is disposed to be pressed relative to the pressurizing roll  88 . The medium P is supplied on a nip portion formed between the fixing belt  84  and the pressurizing roll  88  via the fixing entry guide  56  (see  FIG. 1 ). Moreover, the supplied medium P is not limited to the sheet and may be, for example, a sheet such as a resin film. 
     As illustrated in  FIG. 3 , a lubricant  92  is applied to an inner circumferential surface  84 A of the fixing belt  84  and friction between the fixing belt  84  and the heating member  86  is suppressed. As the lubricant  92 , silicone oil is used, but other types of lubricant such as grease that is not a liquid lubricating agent at room temperature may be used. 
     As illustrated in  FIG. 3 , the heating member  86  is a member to heat the fixing belt  84  to a predetermined temperature by being in contact with the inner circumferential surface  84 A of the fixing belt  84 . The heating member  86  heats the fixing belt  84 , for example, to 200° C. or less. Therefore, as illustrated in  FIG. 2 , the medium P is clamped between the heated fixing belt  84  and the pressurizing roll  88  and is heated and pressed. The unfixed toner image is heated and melted by the fixing belt  84 , and then is fixed on the medium P. 
     The heating member  86  includes a first plate-shaped body  94  that is disposed along the inner circumferential surface  84 A of the fixing belt  84  and a second plate-shaped body  96  that is disposed along the first plate-shaped body  94 . Both end portions of the first plate-shaped body  94  and the second plate-shaped body  96  in a width direction are supported on a housing. A gap  97 , which is set to an interval to cause a capillary phenomenon in the lubricant  92 , is formed between an inner surface  94 A of the first plate-shaped body  94  and an external surface  96 B of the second plate-shaped body  96  from an end portion on an upstream side U to an end portion of a downstream side L. 
     The first plate-shaped body  94  is formed to have an arc-shaped cross section and a width dimension being in contact with the entire region of the fixing belt  84  in the width direction. The first plate-shaped body  94  includes a planar heat generating element and an external surface  94 B of the first plate-shaped body  94  is in contact with the inner circumferential surface  84 A of the fixing belt  84 . Therefore, the fixing belt  84  is heated from the inside. 
     The second plate-shaped body  96  is also formed to have an arc-shape in a cross section and the same width dimension as that of the first plate-shaped body  94 . The second plate-shaped body  96  has a function of homogenizing temperature distribution in the width direction when being heated in the first plate-shaped body  94  and the second plate-shaped body  96  is made of metal such as aluminum having high thermal conductivity. 
     A tip portion of the second plate-shaped body  96  on the upstream side U in the belt rotating direction D is extended outward on the upstream side U from a tip  94 C of the first plate-shaped body  94  on the upstream side U. An extended-out portion  96 C is formed by the tip portion. 
     After a base end portion of the second plate-shaped body  96  on the downstream side L in the belt rotating direction D is extended outward on the downstream side L from the first plate-shaped body  94 , the base end portion is bent on the inner circumferential surface  84 A of the fixing belt  84 . Therefore, a bent portion  96 D, which is bent on the inner circumferential surface  84 A side of the fixing belt  84  on the downstream side L from a base end  94 D of the first plate-shaped body  94 , is formed in the base end portion of the second plate-shaped body  96 . 
     A gap  97 A is formed between the bent portion  96 D and the base end  94 D of the first plate-shaped body  94 , and dimensions of the gap  97 A are set to substantially the same dimensions as those of the gap  97  between the first plate-shaped body  94  and the second plate-shaped body  96 . In addition, a gap  97 B is also formed between a tip  96 E of the bent portion  96 D and the inner circumferential surface  84 A of the fixing belt  84 . Dimensions of the gap  97 B are also set to substantially the same dimensions as those of the gap  97  between the first plate-shaped body  94  and the second plate-shaped body  96 . 
     As illustrated in  FIG. 4 , in the second plate-shaped body  96 , plural inner grooves  98  extending in the belt rotating direction D are formed at equal intervals in the external surface  96 B of the second plate-shaped body  96  facing the inner surface  94 A of the first plate-shaped body  94 . The inner grooves  98  are formed through the entire length from the end on the upstream side U to the end of the second plate-shaped body  96  on the downstream side L and the inner grooves  98  are also formed in both edge portions of the second plate-shaped body  96  in the width direction. 
     The inner groove  98  is formed to have a rectangular shape in a cross section and a depth dimension of the inner groove  98  is set such that an interval distance between a bottom surface  98 A of the inner groove  98  and the inner surface  94 A of the first plate-shaped body  94  is set not to cause the capillary phenomenon in the lubricant  92 . 
     Moreover, in the exemplary embodiment, a case where the inner grooves  98  are formed on the external surface  96 B of the second plate-shaped body  96  is described, but the invention is not limited to the exemplary embodiment. For example, outer grooves are formed on the inner surface  94 A of the first plate-shaped body  94  or the outer grooves are formed on the inner surface  94 A of the first plate-shaped body  94  and the inner grooves  98  may be provided on the external surface  96 B of the second plate-shaped body  96 . 
     In addition, the inner groove  98  may not have the rectangular shape in the cross section and may have a V-shaped cross section or a U-shaped cross section. 
     An operation of the exemplary embodiment having the above configuration will be described. In the fixing device  60 , if the fixing belt  84  is rotated, some of the lubricant  92  applied to the inner circumferential surface  84 A of the fixing belt  84  is scraped off in the tip  94 C of the first plate-shaped body  94  of the heating member  86  and is stored on the upstream side U of the first plate-shaped body  94 . 
     In this case, the gap  97  is formed between the first plate-shaped body  94  and the second plate-shaped body  96  configuring the heating member  86 , and it is possible to guide the lubricant  92  stored on the upstream side U of the first plate-shaped body  94  to the downstream side L via the gap  97  by the capillary phenomenon generated in the gap  97 . Then, the lubricant  92  guided to the downstream side L along the gap  97  is returned to the inner circumferential surface  84 A of the fixing belt  84  by the bent portion  96 D of the second plate-shaped body  96 . 
     As described above, the lubricant  92  that is scraped off on the upstream side U of the heating member  86  can be returned to the inner circumferential surface  84 A of the fixing belt  84  on the downstream side L of the heating member  86 . Then, it is possible to reduce a decrease in the lubricant  92  attaching to the inner circumferential surface  84 A of the fixing belt  84 . 
     Therefore, it is possible to suppress an increase in friction between the heating member  86  and the fixing belt  84  and to suppress an increase in rotation torque compared to a case where the lubricant  92  scraped off from the inner circumferential surface  84 A of the fixing belt  84  cannot be returned to the inner circumferential surface  84 A of the fixing belt  84 . 
     In this case, the plural inner grooves  98  extending in the belt rotating direction D are formed on the external surface  96 B of the second plate-shaped body  96 . Thus, it is possible to suppress spreading of the lubricant  92 , which is guided by the capillary phenomenon in the gap  97  between the first plate-shaped body  94  and the second plate-shaped body  96 , in the width direction by the inner grooves  98 . Therefore, the movement of the lubricant  92  delivered between the first plate-shaped body  94  and the second plate-shaped body  96  is facilitated in the belt rotating direction D. 
     Then, the interval distance between a bottom surface  98 A of the inner groove  98  and the inner surface  94 A of the first plate-shaped body  94  is set not to cause the capillary phenomenon in the lubricant  92 . Therefore, it is possible to suppress coming and going of the lubricant  92  on both sides of which a border is the inner grooves  98  and the movement of the lubricant  92  in the belt rotating direction D is facilitated compared to a case where the inner grooves  98  are not provided. 
     In addition, the inner grooves  98  are also formed in both edge portions of the second plate-shaped body  96  in the width direction. Therefore, leakage of the lubricant  92  on the side of the heating member  86  is suppressed. 
     Here,  FIG. 5  illustrates a test result indicating an effect of the inner grooves  98  provided in the second plate-shaped body  96  and illustrates an outflow amount of oil with respect to a temperature. 
     In this test, the lubricant  92  is supplied on the upstream side U of the heating member  86 , the heating member  86  is maintained at a predetermined temperature and then is left standing for 1 hour. Thereafter, the outflow amount of the lubricant  92  which flows out from the downstream side L of the heating member  86  is measured and a ratio to a supply amount is illustrated. A broken line in the figure indicates a test result of the exemplary embodiment having the inner grooves  98  in the second plate-shaped body  96  and a solid line in the figure includes a test result of a comparative example which does not have the inner grooves  98  in the second plate-shaped body  96 . 
     In the exemplary embodiment in which the inner grooves  98  are formed in the second plate-shaped body  96 , the outflow amount of the lubricant  92  is increased compared to the comparative example. Particularly, the effect is remarkable at 200° C. or less that is a heating temperature of the fixing belt  84  by the heating member  86 . 
     Moreover, in the exemplary embodiment, a case where the interval distance between the bottom surface  98 A of the inner groove  98  and the inner surface  94 A of the first plate-shaped body  94  is set not to cause the capillary phenomenon in the lubricant  92 . However, if the inner grooves  98  are formed, it is possible to suppress the operation of the capillary phenomenon compared to a case where the inner grooves  98  are not formed. Therefore, it is possible to obtain a certain effect for guiding the lubricant  92  in the belt rotating direction D. 
     In addition, in the exemplary embodiment, the inner grooves  98  are formed over the entire length from the end on the upstream side U to the end of the second plate-shaped body  96  on the downstream side L. However, even if the inner grooves  98  are partially provided in the second plate-shaped body  96 , it is possible to obtain a certain effect for guiding the lubricant  92  in the belt rotating direction D. 
     On the other hand, in the second plate-shaped body  96 , the extended-out portion  96 C, which is extended outward on the upstream side U from the tip  94 C of the first plate-shaped body  94  on the upstream side U, is formed in the tip portion on the upstream side U in the belt rotating direction D. Therefore, it is possible to guide the lubricant  92  accumulated on the upstream side U of the first plate-shaped body  94  to the gap  97  between the first plate-shaped body  94  and the second plate-shaped body  96 . 
     In addition, it is possible to suppress wraparound of the lubricant  92  on an inner surface  96 A side of the second plate-shaped body  96  by the extended-out portion  96 C. 
     Then, in the image forming apparatus  100  having such a fixing device  60 , it is possible to suppress an increase in friction between the heating member  86  and the fixing belt  84  due to a decrease of the lubricant  92 , and an increase in the rotation torque accordingly. Therefore, it is possible to reduce maintenance and management of replenishment and the like of the lubricant  92 . 
     Second Exemplary Embodiment 
       FIG. 6  is a view illustrating a second exemplary embodiment and the same reference numerals are given to the same or equivalent portions as those of the first exemplary embodiment, the description thereof will not be repeated, and only different portions will be described. 
     That is, an extension portion  96 F extending on the downstream side L is formed along an inner circumferential surface  84 A of a fixing belt  84  from a tip portion of a bent portion  96 D in a second plate-shaped body  96  of a heating member  86 . Dimensions of a gap  97 C between the extension portion  96 F and the inner circumferential surface  84 A of the fixing belt  84  is set to substantially the same dimensions as a gap  97  between a first plate-shaped body  94  and the second plate-shaped body  96 . 
     It is possible to uniformly level the lubricant  92  returning to the inner circumferential surface  84 A of the fixing belt  84  in the bent portion  96 D of the second plate-shaped body  96  by the extension portion  96 F extending along the inner circumferential surface  84 A with such a configuration compared to a case where the extension portion  96 F is not provided. 
     Moreover, in each of the exemplary embodiments, a case where the first plate-shaped body  94  and the second plate-shaped body  96  disposed on the inner side of the fixing belt configure the planar heating member  86  is described, but the invention is not limited to the exemplary embodiments. For example, it is possible to use the fixing belt  84  in a fixing device of an electromagnetic induction heating type. 
     Third Exemplary Embodiment 
     That is,  FIG. 7  is a view illustrating a third exemplary embodiment and a fixing device  110  that performs electromagnetic induction heating to a fixing belt  84  is illustrated. In the exemplary embodiment, the same reference numerals are given to the same or equivalent portions as those of the first and second exemplary embodiments, the description thereof will not be repeated, and only different portions will be described. 
     The fixing device  110  includes an IH heater  114  that performs electromagnetic induction heating to an AC magnetic field conductive layer provided in a fixing belt  84 . A first plate-shaped body  94  provided on an inside of the fixing belt  84  forms a magnetic path of an AC magnetic field generated by the IH heater  114  and includes a temperature-sensitive magnetic member that is electromagnetic-induction heated. 
     In addition, a second plate-shaped body  96 , which is provided in the first plate-shaped body  94  via a gap  97 , induces magnetic force lines H passing through the first plate-shaped body  94  and includes a guide member for diffusing heat generated by the first plate-shaped body  94 . 
     It is possible to obtain the same function and effect as those described above even with such a configuration. 
     Moreover, in each exemplary embodiment, a case where the first plate-shaped body  94  includes the planar heat generating element or the temperature-sensitive magnetic member, and the second plate-shaped body  96  includes the heat conductive member or the guide member is described, but the invention is not limited to the exemplary embodiments. It is possible to obtain the effects described above as long as it is a member that is disposed on the inside of the fixing belt  84  where the lubricant  92  is applied to the inner circumferential surface  84 A. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.