Patent Publication Number: US-8977182-B2

Title: Loop brush roller and image forming apparatus

Description:
This application is based on Japanese Patent Application No. 2011-134962 filed with the Japan Patent Office on Jun. 17, 2011, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a loop brush roller as well as an image forming apparatus such as a copying machine, a printer, a facsimile machine or a combination machine thereof that has a loop brush roller and uses an electrophotographic method. 
     2. Description of the Related Art 
     A general image forming apparatus performs image formation, and has a cylindrical and rotatable image carrier, charging means for uniformly charging a surface of the image carrier, exposing means for exposing the image carrier to form an electrostatic latent image, developing means for developing the electrostatic latent image to form a toner image by a potential difference between a voltage applied to a developing unit and the electrostatic latent image, transferring and transporting means that is arranged to face a photosensitive drum for receiving a voltage opposite in polarity to the toner image, thereby transferring the toner image on the image carrier onto a transfer member such as a paper sheer and simultaneously transporting it, cleaning means that is in contact with the photosensitive drum for scraping untransferred residual toner that remains on the photosensitive drum without being transferred onto the transfer member, and fixing means for fixing the toner image onto the transfer member by applying heat and pressure to the toner image transferred onto the transfer member. 
     As the cleaning means, the apparatus uses a cleaning blade that scrapes the untransferred residual toner by pressing a strip of polyurethane against the image carrier. 
     In recent years, brush rollers have been used in various positions in the image forming apparatus. As the brush rollers, there have been a loop brush roller in which bundles of fibers extend through a base member formed by weaving warps and wefts together to form loop forms on one of the surfaces, as well as a straight-bristle brush roller having fiber bundles protruding from a base member. 
     Conventionally, the straight-bristle brush rollers having simple structures have been used in many cases, but use of the loop brush rollers is now spreading because the loop brush roller applies a lower pressure to a contact target and thus applies less damage thereto. A range of use thereof contains an electrically charging brush roller, a cleaning brush roller, a lubricant application brush roller, a paper dust removing brush roller and others. The case where it is used as the loop brush roller for applying the lubricant will be primarily described below. 
     When the loop brush roller is used, a manner of handling it must be different from that for the straight-bristle brush roller. For example, Japanese Laid-Open Patent Publication No. 2010-107683 (reference 1) has proposed a structure in which an angle formed by rotation directions of a loop brush roller and a brush roller is set in a predetermined fashion to reduce a frictional force between an end of a cleaning blade end and a surface of an image carrier member and thereby to allow a long-term use of the cleaning blade and the image carrier. 
     Further, Japanese Laid-Open Patent Publication No. 2010-097234 (reference 2) has made such a proposal that an angle of a line of intersection between a flat plane containing a loop and a base member surface is set to a predetermined angle, and thereby uniform scraping of solid lubricant as well as lubricant dropping by shaking it by flicker are achieved. 
     Japanese Laid-Open Patent Publication No. 06-289759 (reference 3) has disclosed a fur brush roller that is slidably in contact with a surface of an image carrier to clean the surface. This fur brush roller has looped fur members to be in contact with the surface of a latent image carrier, and the looped fur member has a space of at least 3 mm between opposite leg base ends of each member. 
     However, due to such a structure that the base member into which the loops are woven is spirally wound around a core roller, the loop brush roller suffers from a problem that the loops may fray when they receive a strong tensile force. 
     When fraying occurs in the loop brush roller that is used as the lubricant applying brush roller, the frayed fiber bundles are wound around the surface of the brush roller so that the leading end portion of the brush roller having a high lubricant-scraping ability is covered with the fiber bundles to lower its lubricant-scraping ability. 
     This reduces an amount of the lubricant that is supplied to the image carrier from the lubricant-supplying loop brush roller, and increases a friction that occurs between the cleaning blade and the image carrier, and the cleaning blade and the image carrier will become unusable due to wearing within a short term. 
     SUMMARY OF THE INVENTION 
     A loop brush roller according to the invention includes a core roller and a ribbon brush spirally wound around the core roller. The ribbon brush includes a base member formed by weaving warps extending in the same direction as a weaving direction and wefts extending perpendicularly to the weaving direction together, and fiber bundles extending in the base member and between the warps in parallel with the warp. Each of the fiber bundles forms loops protruding beyond a surface side of the base member with constant spaces therebetween. In at least one of the opposite ends located in a direction perpendicular to the weaving direction of the ribbon brush, when the surface side is assumed as an upper side, the weft extending between the neighboring loops passes under the warp, and the weft extending through the loop passes above the warp. 
     The image forming apparatus according to the invention includes an image carrier, and a loop brush roller arranged in rotatable contact with the image carrier, and including core roller and a ribbon brush spirally wound around the core roller, and has a following structure. 
     The ribbon brush includes a base member formed by weaving warps extending in the same direction as a weaving direction and wefts extending perpendicularly to the weaving direction together, and fiber bundles extending in the base member and between the warps in parallel with the warp. The fiber bundle forms loops protruding beyond a surface side of the base member with constant spaces therebetween. In at least one of the opposite ends located in a direction perpendicular to the weaving direction of the ribbon brush, when the surface side is assumed as an upper side, the weft extending between the neighboring loops passes under the warp, and the weft extending through the loop passes above the warp. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a whole structure of an image forming apparatus in an embodiment. 
         FIG. 2  shows a schematic structure of lubricant supplying means in the embodiment. 
         FIG. 3  shows a whole structure of a loop brush roller in the embodiment. 
         FIG. 4  is a plan of a ribbon brush in the embodiment. 
         FIG. 5  shows a structure of an end viewed in a direction perpendicular to a weaving direction (W) indicated by V in  FIG. 4 . 
         FIG. 6  is a first schematic view showing a case where a tensile force is applied to a loop of the ribbon brush in the embodiment. 
         FIG. 7  is a second schematic view showing a case where the tensile force is applied to the loop of the ribbon brush in the embodiment. 
         FIG. 8  is a corresponding view showing a structure of an end portion in a comparison example viewed in a direction perpendicular to the weaving direction (W) indicated by V in  FIG. 4 . 
         FIG. 9  is a first schematic view showing a case where a tensile force is applied to a loop of a ribbon brush in the comparison example. 
         FIG. 10  is a second schematic view showing a case where the tensile force is applied to the loop of the ribbon brush in the comparison example. 
         FIG. 11  shows a relationship between a position and a fraying-causing load value of the loop brush roller in the embodiment and the loop brush roller in the comparison example. 
         FIG. 12  is a plan of a ribbon brush of another embodiment. 
         FIG. 13  is a perspective view showing a state in which the ribbon brush is spirally wound around a core roller. 
         FIG. 14  schematically shows an external force occurring at a seam of the ribbon brush of the loop brush roller. 
         FIG. 15  is a plan showing a ribbon brush of a still another embodiment. 
         FIG. 16  shows a result of evaluation of experimental examples  1  to  5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An image forming apparatus in an embodiment according to the invention will be described below with reference to the drawings. Numbers of items, amounts and the like that may be referred to in the following description of the embodiment do not restrict scopes of the invention, unless otherwise specified. Further, the same or corresponding parts and portions bear the same reference numbers, and description thereof may not be repeated 
     (Image Forming Apparatus  100 ) 
       FIG. 1  shows an image forming apparatus  100  in an embodiment. As shown in  FIG. 1 , image forming apparatus  100  includes four photosensitive drums  10  that serve as image carriers and correspond to four developing devices containing toner of different colors, i.e., yellow, magenta, cyan and black, respectively. 
     For performing full-color image formation in image forming apparatus  100 , each photosensitive drum  10  rotates to charge a surface of each photosensitive drum  10  by a charging device  12  that performs corona charging. An exposing device  13  performs exposure on each photosensitive drum  10  thus charged according to image data, and thereby forms an electrostatic latent image on the surface of each photosensitive drum  10 . 
     A developing device  11  corresponding to each photosensitive drum  10  bearing the electrostatic latent image performs developing by supplying toner of a predetermined color to the electrostatic latent image on photosensitive drum  10 , and thereby forms a toner image of the color on the surface of corresponding photosensitive drum  10 . 
     Primary transfer devices  16  each having a roller-like form successively performs a primary transfer operation of transferring the toner images of the predetermined colors formed on the corresponding photosensitive drums  10  onto an intermediate transfer member  15  of an endless belt form arranged around and driven by rollers  14 . Thereby, a full-color toner image is formed on intermediate transfer member  15 . 
     Intermediate transfer member  15  leads the full-color toner image formed on intermediate transfer member  15  to a position opposed to a secondary transfer device  17  of a roller-like form. Simultaneously, a record sheet S accommodated in a lower portion of image forming apparatus  100  is led by feed rollers  18  to a position between intermediate transfer member  15  and secondary transfer device  17 , which performs secondary transfer by transferring the full-color toner image thus formed on intermediate transfer member  15  onto record sheet S. 
     Record sheet S onto which the full-color toner image is transferred is led to a fixing device  19 , which fixes the transferred full-color toner image to record sheet S. Thereafter, record sheet S bearing the full-color toner image thus fixed is discharged. Also, the toner that was not transferred onto record sheet S and remains on intermediate transfer member  15  is removed from intermediate transfer member  15  by a first cleaning blade  21  arranged in a first cleaning device  20 . 
     In this image forming apparatus  100 , lubricant supplying means  30  supplies the lubricant to the surface of each photosensitive drum  10  as shown in  FIG. 1  after the toner image is transferred to intermediate transfer member  15 . Thereafter, an edge of a second cleaning blade  40  is pressed against the surface of each photosensitive drum  10  to remove the toner remaining on the surface of each photosensitive drum  10 . Also, leveling means  41  applies the lubricant supplied to the surface of each photosensitive drum  10  over the surface of each photosensitive drum  10 . 
     As shown in  FIG. 2 , for supplying the lubricant by lubricant supplying means  30  onto the surface of photosensitive drum  10  after the above transferring, this embodiment employs a loop brush roller  31  that rotates in contact with the surface of photosensitive drum  10  and is arranged in an axial direction of photosensitive drum  10 . 
     Further, pressing means  33  formed of a spring member is configured to press a solid lubricant  32  arranged in the axial direction of photosensitive drum  10  against loop brush roller  31  so that a ribbon brush  31   a  in loop brush roller  31  may scrape the lubricant off solid lubricant  32  to supply it to the surface of photosensitive drum  10 . 
     Loop brush roller  31  performs a counter rotation, i.e., rotation in the same direction as photosensitive drum  10  to attain a linear speed that is substantially equal to or larger (i.e., 1.3 times larger in this embodiment) than that of photosensitive drum  10 . It is made of electrically conductive polyester and has a resistance value of 10 6 Ω-10 8 Ω. 
     It is made of bundles of fibers having a fiber thickness of  4  deniers and a fiber density of 150 kF/inch 2 . A core roller of loop brush roller  31  is made of iron and has a diameter of 6 mm. Loop brush roller  31  has an outer diameter of 12 mm. The fiber bundles are woven on the base member of 0.5 mm in thickness so that the fiber bundles have a height of about 2.5 mm. 
     Solid lubricant  32  is formed by melting and forming powder of zinc stearate. If it were used as it is, it would be fragile to break. Therefore, it is adhered to a holding member made of a metal plate by a double-side adhesive tape. Pressing means  33  formed of a compressive spring holds and presses this solid lubricant  32  against loop brush roller  31 . 
     Solid lubricant  32  is shaved to return to a powder form by the rotation of loop brush roller  31  and the pressing force of pressing means  33 , and is transferred to a portion, where it comes in contact with photosensitive drum  10  and is applied to photosensitive drum  10 . Photosensitive drum  10  is a layered type of organic photosensitive drum having a charge generating layer and a charge transporting layer, and is provided at its outermost surface with an overcoat layer (OCL) of about 2 μm in thickness. 
     The OCL contains fine particles of SiO 2  of 50 nm in particle diameter, and these particles form irregular roughness at the surface of photosensitive drum  10 . The irregular forms improve properties of taking in and holding the zinc stearate. 
     Leveling means  41  that is located downstream, in the rotation direction of photosensitive drum  10 , from loop brush roller  31  is made of polyurethane rubber, has a sheet-like form and is arranged in a trailing direction so that its leading end portion may come into contact with photosensitive drum  10 . 
     The powder of solid lubricant  32  that was applied to photosensitive drum  10  by loop brush roller  31  and was transported to the contact portion between leveling means  41  and photosensitive drum  10  forms a film of solid lubricant  32  over photosensitive drum  10 . The film of solid lubricant  32  has a low friction coefficient, and can offer an effect of reducing a force that acts between photosensitive drum  10  and second cleaning blade  40  so that it can reduce the friction between photosensitive drum  10  and second cleaning blade  40  to increase a life of photosensitive drum  10 . 
     (Loop Brush Roller  31 ) 
       FIG. 3  shows a whole structure of loop brush roller  31  in the embodiment. As shown in  FIG. 3 , loop brush roller  31  is formed of a core roller  34  made of metal and ribbon brush  31   a  wound around core roller  34 . Ribbon brush  31   a  is a ribbon of a strip form having a predetermined width, and is formed by passing the fiber bundles through the base member formed by weaving the warps and wefts together and thereby forming loop forms on one of the surfaces. 
     A generally used iron shaft is used as core roller  34 . It is desirable that core roller  34  has an outer diameter of 6 mm or more from a viewpoint of preventing bending. Since ribbon brush  31   a  is wound around core roller  34 , this structure produces a seam B 1  where opposite ends of ribbon brush  31   a  are in contact with each other. 
     (Structure of Ribbon Brush  31   a ) 
       FIG. 4  shows a schematic structure of ribbon brush  31   a  in the embodiment, and  FIG. 5  shows a structure of an end portion viewed in a direction perpendicular to a weaving direction (W) indicated by V in  FIG. 4 . As shown in  FIG. 4 , ribbon brush  31   a  in the embodiment has a base member  310  that is formed by weaving warps  31   a   1  running in the same direction as the weaving direction (W) and wefts  31   a   2  running perpendicularly to the weaving direction (W) together, and fiber bundles  31   a   3  extending parallel to warp  31   a   1  through base member  310  protrude at regularly spaced positions on the front surface (one of the surfaces) of base member  310  to form loops  310 R. 
     In this embodiment, sixteen warps are used, and fiber bundle  31   a   3  is not arranged between #2 and #3, between #4 and #5, between #6 and #7, between #8 and #9, between #10 and #11, between #12 and #13, and between #14 and #15. 
     As shown in  FIG. 5 , in fiber bundle  31   a   3  located in each end portion and extending between #1 and #2 or between #15 and #16, weft  31   a   2  extending between neighboring loops  310 R passes under warp  31   a   1  , and weft  31   a   2  extending through loop  310 R passes above warp  31   a   1 . 
     Referring to  FIGS. 5 to 7 , the case where a tensile force F 1  acts on loop  310 R will be described below.  FIGS. 6 and 7  schematically show forces that occur in warp  31   a   1  and weft  31   a   2  when tensile force F 1  acts on loop  310 R, and correspond to a view taken in a direction of arrow VI in  FIG. 5 . 
     As shown in  FIG. 6 , when tensile force F 1  acts on each of neighboring loops  310 R, a tension of f 1  acts on fiber bundle  31   a   3 , and a force acts to pull up weft  31   a   2  located between neighboring loops  310 R. 
     As shown in  FIG. 7 , however, warp  31   a   1  is present above weft  31   a   2  in a region between neighboring loops  310 R, and therefore prevents upward movement of weft  31   a   2 . Consequently, in the opposite ends of ribbon brush  31   a  in this embodiment, even when the tensile force acts on loops  310 R, fraying at the opposite ends of ribbon brush  31   a  can be suppressed. 
     Referring to  FIGS. 8 to 10 , the case where the opposite ends of ribbon brush  31   a  are liable to fray will be described below.  FIG. 8  shows a structure corresponding to the end viewed perpendicularly to the weaving direction (W) similarly to  FIG. 5 .  FIGS. 9 and 10  schematically show forces that occur in warp  31   a   1  and weft  31   a   2  when tensile force F 1  acts on loop  310 R, and correspond to a view taken in a direction of arrow IX in  FIG. 8 . 
     In  FIG. 8 , weft  31   a   2  extending between neighboring loops  310 R passes above warp  31   a   1  , and weft  31   a   2  extending through loop  310 R passes under warp  31   a   1  . The manner of weaving warps  31   a   1  and wefts  31   a   2  is opposite to that in  FIG. 5 . 
     When tensile force F 1  acts on each of neighboring loops  310 R, the tension of f1 acts on fiber bundle  31   a   3  to act as a force pulling up weft  31   a   2  located between neighboring loops  310 R. 
     Since warp  31   a   1  is present under weft  31   a   2  between neighboring loops  310 R as shown in  FIG. 9 , warp  31   a   1  does not prevent the upward movement of weft  31   a   2 . Consequently, warp  31   a   1  can be easily lifted upward to cause fraying at the end of ribbon brush  31   a.    
     When the fraying occurs at the end of ribbon brush  31   a , fluffing is observed at seam B 1  (see  FIG. 3 ) in the brush roller. When the brush roller having the frayed portion is continuously used, the frayed portion becomes long and will be wound around the brush roller to cover the surface of the brush roller. 
     In this state, the frayed fiber bundles  31   a   3  cover the leading end portion of the brush roller that has a large ability of scraping off solid lubricant  32 , which reduces the ability of scraping off solid lubricant  32 . This causes a failure in film formation of solid lubricant  32  to increase the friction between photosensitive drum  10  and second cleaning blade  40 . This results in decrease in life of photosensitive drum  10  so that image noises will occur early. 
     For evaluating loop brush roller  31  in this embodiment, the possibility of causing the fraying was evaluated in connection with loop brush roller  31  in the embodiment and the brush roller of the structure shown in  FIG. 8 .  FIG. 11  shows the result of the evaluation. 
     For the evaluation, such a method was employed that a hook attached to a portion of a measurement probe portion of a push-pull gauge was hooked to the loop of the brush roller and a tensile force was applied thereto to measure a load value causing the fraying. The loop that is liable to cause the fraying causes the fraying even when the load is small, and the loop that is resistant to fraying does not fray until a large load is applied. 
     The load value which caused the fraying of the loop in the longitudinal direction of the brush roller was measured. Owing to the structure of the brush roller in which the ribbon brush is spirally wound around the core roll, the brush roller in the embodiment differs from the comparison brush roller in load value causing the fraying at the seam where the ribbon brush ends continue. 
     In the comparison brush roller, the end of the ribbon brush exhibited the fraying-causing load value between 1 N and 1.3 N, and thus was frayed by a tensile force lower than the fraying-causing load value of 1.5 N or more of the other regions. 
     In the brush roller in the embodiment, the end portion of the ribbon brush exhibited the fraying-causing load value of 1.5 N or more, and it was confirmed that the end potion has substantially the same resistance against the fraying as the regions other than the end. 
     Referring to  FIG. 4  again, description about fiber bundle  31   a   3  forming the loop will be given particularly in connection with a relationship between the number of warps  31   a   1  passing between neighboring fiber bundles  31   a   3 , the number of fiber bundles  31   a   3  located on or between one and the other ends of ribbon brush  31   a  and the direction in which ribbon brush  31   a  is wound around core roller  34 . 
     The case where warps  31   a   1  extending between neighboring fiber bundles  31   a   3  are even in number, and fiber bundles  31   a   3  on or between one and the other ends of ribbon brush  31   a  are even in number will be discussed below. 
     As shown in  FIG. 12 , when warps  31   a   1  between neighboring fiber bundles  31   a   3  are two in number and fiber bundles  31   a   3  on or between one and the other ends of ribbon brush  31   b  are eight in number, the end to which the embodiment of the invention is applied can be formed in each of ends A and B of ribbon brush  31   b.    
     Accordingly, ribbon brush  31   b  of the above structure has a uniform resistance against the fraying regardless of the winding direction of the ribbon around core roller  34 , and it is most desirable to use this ribbon brush  31   b  as the structure of the brush roller. 
     Then, a ribbon brush  31   c  shown in  FIG. 13  will be discussed. In ribbon brush  31   c , when warps  31   a   1  passing between neighboring fiber bundles  31   a   3  are even (e.g., two) in number, and fiber bundles  31   a   3  located on or between the opposite ends are odd (e.g., seven) in number, the end surface to which the embodiment of the invention is applied can be formed on one end (end A), but the other end (end B) has a structure shown in  FIG. 8  that is liable to fray. 
     Accordingly, in the case where ribbon brush  31   c  is to be spirally wound around core roller  34  as shown in  FIGS. 13 and 14 , it is wound such that an end portion E 1  having end A is located downstream (on the rear side in the moving direction of ribbon brush  31   c ) in a rotation direction R of loop brush roller  31 . Thereby, an end portion E 2  having end B that is liable to fray is located on the upstream side (forward side in the moving direction of ribbon brush  31   c ) in rotation direction R. 
     Consequently, as shown in  FIG. 14 , force F 1  in the tensile direction acts on end A resistant to the fraying, and a force F 2  in the compression direction acts on end B that is liable to fray so that it is possible to suppress occurrence of the fraying at seam B 1 . 
     Through  FIGS. 4 to 12 , the example where warps  31   a   1  passing between neighboring fiber bundles  31   a   3  are two in number has been described. However, the same is true with respect to the cases where the number increases to 4, 6 or others provided it is even. 
     Likewise, the cases where fiber bundles  31   a   3  on or between the opposite ends of the ribbon brush are four in  FIG. 4  or seven in  FIG. 12  have been described. However, the fiber bundles may be even or odd in number. 
     Referring to  FIG. 15 , a ribbon brush  31   d  in the case where warps  31   a   1  extending between neighboring fiber bundles  31   a   3  is odd (one) in number will be described below. When the end surface employing the embodiment of the invention is applied is formed at end A, end B has the end structure that is liable to fray and is shown in  FIG. 8  regardless of the number of the loops located on or between the opposite ends of ribbon brush  31   d.    
     Therefore, in the process of spirally winding ribbon brush  31   d  around core roller  34 , it is effective to perform the winding such that end A employing the embodiment of the invention is located downstream in the rotation direction of the brush roller. Although it has been described that warp  31   a   1  passing between neighboring fiber bundles  31   a   3  is one in number, the same is true with respect to the cases where the number increases to 3, 5 or others provided it is odd. 
     Experimental Example 
     Durability tests were performed on experimental examples 1, 2 and 3 using brush rollers employing the embodiment of the invention as the brush rollers for the lubricant application, as well as an experimental example 4 using a brush roller having the end structures shown in  FIG. 8  in opposite ends, respectively. 
     Machines used in the durability tests were prepared by modifying imaging units “bizhub PRO C6501P” (A4 65 sheets/min, 600 dpi) manufactured by Konica Minolta Business Technologies, Inc. into structures of the experimental examples. The test used lubricant supplying means  30 , solid lubricant  32  and photosensitive drum  10  already illustrated in  FIGS. 1 and 2 . 
     Pressing means  33  pushed solid lubricant  32  against loop brush roller  31  at 2 N/m. Second cleaning blade  40  was made of polyurethane rubber, and its pressing force and contact angle were 25 N/m and 15 degrees, respectively. The pressing force and the contact angle of leveling means  41  were 25 N/m and 45 degrees, respectively. 
     Developing device  11  performed two-component developing using developer made of a mixture of carrier and toner, and the toner had a negative charging property. Such endurance conditions were used that charts of colors each having an image density of 5% were continuously printed under an environment of 23 deg. C. and 65% R/H. 
     An amount of wearing of the film thickness of photosensitive drum  10 , a width of a worn portion of second cleaning blade  40  and image noise were determined as evaluation items after passing the sheets of 100 k (k is 1000 (third power of 10)), 400 k, 800 k and 1200 k in number. 
       FIG. 16  shows results of the determination. In  FIG. 16 , “A” in “FRAYING” represents “no fraying”, “B” represents that the frayed loop had a length equal to or smaller than ((loop height)×2), and “C” represents that the frayed loop had a length larger than ((loop height)×2). 
     In connection with the amount of wearing of the film thickness of photosensitive drum  10  (“PHOTOSENSITIVE DRUM WEARING”), “A”, “B” and “C” represent an amount equal to or smaller than 1.0 μm, an amount smaller than 1.4 μm and an amount equal to or larger than 1.4 μm, respectively. 
     In “CLEANING BLADE WEARING”, “A” represents the width of wearing observed by a microscope that is equal to or smaller than 20 μm, “B” represents the width between 20 μm and 30 μm, and “C” represents the width of 30 μm or more. 
     In connection with the “IMAGE NOISE”, such an A3-size chart in portrait format was prepared that bears a solid belt-like image between positions of 0 mm and 100 mm from an edge thereof and a while solid image between positions of 100 mm and 420 mm. Using this image, evaluation about a cleaning failure and fogging was performed. “A” represents that neither cleaning failure nor fogging occurred. “B” represents that slight fogging occurred and “C” represents that the cleaning failure or serious fogging occurred. 
     The brush roller used in the above has a structure shown in  FIGS. 13 and 14 . The experimental example 1 used a ribbon brush provided at its opposite ends with the structures according to the present invention shown in  FIGS. 5 to 7 . In each of the ribbon brushes used in the experimental examples 2 and 3, one end portion is based on the invention, but the other end portion is the “frayed end” shown in  FIGS. 8 to 10 . In the experimental example 2, the ribbon brush is wound such that the frayed end may be located on the upstream side in rotation direction R in  FIG. 13  (i.e., on the forward side in the moving direction of the ribbon brush). Conversely, in the experimental example 3, the ribbon brush is wound such that the frayed end may be located on the downstream side in rotation direction R (i.e., on the rearward side in the moving direction of the ribbon brush). The experimental example 4 uses a ribbon brush having the “frayed end” at its opposite end portions, respectively. 
     As described above, in the brush roller in the embodiment and the image forming apparatus using the brush roller, even when the loop in the brush roller receives a tensile force, the warps passing between the loops interfere with the wefts so that fraying of the loops can be suppressed. 
     Thereby, it is possible to prevent disadvantages caused by fraying of the ribbon brush. For example, when the loop brush is used as the brush roller for lubricant application, it is possible to prevent occurrence of the image noises due to wearing of the cleaning blade and the photosensitive drum within a short period due to reduction in amount of the lubricant applied to the image carrier. 
     Although the embodiment has been described in connection with the case where the brush roller is used as the brush roller for lubricant application, similar effects can be achieved even in the case where it is used as a charging brush roller, a cleaning brush roller, a paper powder removing brush roller or the like. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.