JP2008292773A - Static charging roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a static charging roller which is of a double structure flexible and lightweight but does not produce white dots or black tots on halftone images. <P>SOLUTION: This charging roller 16 is composed of a first conductive elastic layer 54 consisting of foamed nitril based rubber and conductive carbon black and supported on the core metal 53, and a second conductive elastic layer 55 consisting of epichlorohydrin based rubber and conductive carbon black. Its surface is treated with a surface treatment liquid containing isocyanate, and ground for 40 seconds using a roller sandpaper (Sankyo Rikagaku Co., Ltd.: lapping film LDF3000) in a rubber roller mirror finishing machine to obtain a surface roughness represented by Ra=0.20 μm and Rz=0.98 μm. Further, it is preferable to obtain a surface roughness between Ra≤0.20 μm and Rz≤1.00 μm by changing the lapping film and the polishing time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charging roller that does not cause white spots or black spots in a halftone image formed in an electrophotographic image forming apparatus.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus (printer) that forms characters and images on a sheet by transferring and fixing a toner image formed on a photoreceptor onto the sheet is known. Usually, the above-mentioned photoreceptor is a drum type, and an electrostatic latent image is formed on the peripheral surface by an exposure head. The electrostatic latent image is converted into a toner image by a developing device, and further transferred onto a sheet by a transfer device.

  Prior to this formation of the electrostatic latent image, initialization charging by a charging device is always performed. In this initialization charging, discharge type non-contact chargers and brush type contact chargers were traditionally used. However, the discharge type generates ozone and adversely affects the surrounding environment. The brush type is uniform. Each of them has a problem in that it is difficult to realize a proper charging, and at present, a roller-type contact charger, that is, a charging roller is almost used.

  In the method using this charging roller, the roller is usually a rubber roller type composed of a conductive thick rubber layer fitted on a shaft (core metal). However, since this is expensive, the roller is configured at low cost. For this purpose, a lightweight, double-structured charging roller constructed by covering a conductive foam roller that is externally fitted to a shaft with a conductive tube and bonding them together with an adhesive in the non-image forming areas at both ends. The method used is known. (For example, refer to Patent Document 1.)

  Generally, as the conductive foam used for the charging roller, conductive foam made of polyurethane, silicone rubber, nitrile rubber or the like has been used. However, since the charging roller is required to have a non-contaminating property to the photosensitive drum and its own conductivity, various coating layers and surface treatment layers are formed on the surface of the elastic layer made of the conductive foam. Alternatively, a double structure using a coated tube or the like is employed.

  Further, in the above-described lightweight dual structure charging roller, when both ends of the charging roller are urged toward the photosensitive drum to enhance the charging property, pressure is applied to both ends rather than the center, and the center and both ends are charged. In order to eliminate the occurrence of unevenness in charging property at the portion, a method is known in which an adhesive is applied from the end portion to a predetermined range from the image forming region to increase the electrical resistance of the end portion. (For example, see Patent Document 2.)

Further, as a charging roll having a low discharge sound and excellent charging characteristics, the double layer first layer on the core metal contains nitrile rubber and conductive carbon black, and the rubber hardness is 10 to 50 in Asker C. There has been proposed a charging roller that is formed of a nitrile rubber foam having a surface treatment layer that is made of epichlorohydrin rubber and that is surface-treated with a surface treatment liquid containing isocyanate on the surface. Yes. (For example, see Patent Document 3.)
JP-A-11-125956 JP 2001-022251 A JP 2005-292600 A

  By the way, in recent years, electrophotographic printers using toner as described above have various technical aspects in which the printing speed was about 13 sheets / second when A4 size paper was laid down at the beginning. Due to the improvement, a printing speed of 29 sheets / second has become normal, and the printing speed has been increased to more than double the original printing speed.

  However, when the printing speed is increased in this way, there is no problem with the rubber roller type having a thick rubber single layer structure. However, the conductive foam roller and the conductive tube as described in Patent Documents 1 to 3 described above. When a half-tone image was printed, it was found that there was a problem that white spots and black spots were generated.

  In view of the above-described conventional situation, an object of the present invention is to provide a charging roller that does not generate white spots or black spots in a halftone image while having a lightweight and flexible double structure.

  First, the charging roller according to the first aspect of the present invention forms an electrostatic latent image on a photoconductor drum that has been charged by initialization, converts the electrostatic latent image into a toner image, and transfers the toner image onto a sheet to form an image. A first conductive elastic layer used in an image forming apparatus to be formed and supported on at least a central core metal, and a second conductive elastic layer provided on the first conductive elastic layer. A charging roller for initializing and charging the photosensitive drum, wherein the first conductive elastic layer is formed of nitrile foam rubber and conductive carbon black, and the second conductive elastic layer is formed of epichlorohydrin. And forming a surface layer that is surface-treated with a surface treatment liquid containing isocyanate on the surface, and the surface roughness of the surface layer is Ra ≦ 0.20 μm. Constitute.

  Next, a charging roller according to a second aspect of the present invention forms an electrostatic latent image on a photosensitive drum that has been charged by initialization, converts the electrostatic latent image into a toner image, and transfers the toner image onto a sheet of paper. A first conductive elastic layer supported on at least a central metal core and a second conductive elastic layer provided on the first conductive elastic layer. A charging roller for initializing and charging the photosensitive drum, wherein the first conductive elastic layer is formed of nitrile foam rubber and conductive carbon black, and the second conductive elastic layer is formed A surface layer formed by epichlorohydrin rubber and conductive carbon black and surface-treated with a surface treatment liquid containing isocyanate is formed on the surface, and the surface roughness of the surface layer is Rz ≦ 1.00 μm. Configured.

  According to the present invention, it is possible to provide a charging roller that does not cause white spots or black spots in a halftone image while having a lightweight and flexible double structure.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 is a side sectional view showing an internal configuration of an image forming apparatus provided with a charging roller in an embodiment, and shows a tandem type color image forming apparatus as an example.

  A color image forming apparatus 1 shown in FIG. 1 is a small color image forming apparatus that can be mounted on a desktop personal computer rack, for example, and is opened and closed on the front surface (right side of the figure) of the main body base 2. A paper feed tray 3 is provided, and a paper cassette 4 is detachably provided at the bottom. A large number of sheets P are placed and stored in the sheet cassette 4.

  The upper lid 5 forms a paper discharge tray 6 together with the upper surface of the rear part of the main body base 2, on which an image-formed paper discharged from the upper paper discharge port 7 is stacked. An operation panel 9 including a liquid crystal display device, a power switch, a plurality of data input keys and the like is disposed on the upper surface of the main body base 2 on the front side of the upper lid 5.

  Inside the color image forming apparatus 1, a paper transport belt (hereinafter simply referred to as a belt) 11 is arranged in a flat loop shape at the front and rear at substantially the center. The both ends of the sheet conveying belt 11 are held by the driving roller 12 and the driven roller 13 and circulate in a counterclockwise direction indicated by an arrow A in the drawing.

  In the upper circulation portion of the belt 11, four photosensitive drums 14 (14a, 14b, 14c, and 14d) are arranged in a multistage manner in the paper transport direction (from the right to the left in the drawing). Then, each of the photosensitive drums 14 is surrounded (hereinafter, only the peripheral devices around the photosensitive drum 14d are represented by reference numerals), and the cleaner 15, the charging roller 16, the writing head 17, and the developing device. 18 and a transfer sheet 19 are arranged.

  From the developing device 18 corresponding to the photosensitive drum 14a to the developing device 18 corresponding to the photosensitive drum 14d, each developing device 18 has M (magenta: red dye) and C (cyan: greenish) which are three primary colors of subtractive color mixing. Blue (with blue) and Y (yellow: yellow) toners, and K (black: black) toner dedicated to printing of black portions of characters and images are accommodated.

  The four write heads 17 are supported by the upper lid 5 via support members 21. The transfer sheet 19 is disposed as a member belonging to the belt unit. As will be described in detail later, the photosensitive drum 14, the cleaner 15, and the charging roller 16 constitute a drum sub unit, and the developing unit 18 includes members inside to constitute a developing sub unit. These sub units are combined to form an image forming unit.

  The belt 11 is always urged downward as indicated by an arrow B in the figure by a tension roller 22 that presses against the downstream side rear surface of the lower circulation portion, and maintains an appropriate tension. A suction roller 23 is pressed against the upstream end of the upper circulation portion of the belt 11 to form a paper carry-in portion.

  A standby roller pair 24 is disposed upstream of the belt 11 in the conveying direction, a paper feed guide path 25 is disposed below the standby roller pair 24, and a feed roller pair 26 is disposed at the lower end thereof. A paper feed end of the paper cassette 4 is positioned below the pair of feed rollers 26, and a paper feed roller 27 is disposed above the paper feed end.

  On the other hand, on the downstream side of the belt 11 in the sheet conveyance direction (left side in the figure), from a pressure roller, a heat roller, a separation claw, a peripheral surface cleaner, an oil application roller, a temperature measuring device and the like assembled in a heat insulating casing. A fixing device 28 is provided.

  A pair of carry-out rollers 29 is disposed behind the fixing device 28, and a paper discharge path 31 is formed above the pair of discharge rollers 28. The end of the paper discharge path 31 opens above the rear of the discharge tray 6 and is there. A paper discharge roller pair 32 is arranged.

  In addition, an electrical component 33 having an appropriate circuit board mounted thereon is disposed between the belt 11 and the paper cassette 4, and a control device composed of a plurality of electronic components is mounted on the circuit board. The control device includes a controller unit and an engine unit (not shown).

  The controller unit comprises a CPU (Central Processing Unit), ROM (Read Only Memory), EEPROM (Rewritable Read Memory), Frame Memory, Image Data Transfer Circuit, etc., and print data input from a host computer etc. Is analyzed, print data is created and transferred to the engine unit.

  The engine unit includes a CPU, a ROM, and the like. Data and command signals from the controller unit, an output of a temperature sensor (not shown), an output of a paper detection sensor, etc. are input to the input side, and a motor (not shown) is input to the output side. A motor driver that drives the motor, a clutch driver that switches a drive system that transmits the drive of the motor to each part, a print driver that drives the write head 17 based on the print data, a charging roller 16, a transfer sheet 19, and a developing roller that will be described later Are connected to a bias power supply driver for supplying a predetermined bias current.

  The engine unit drives and controls each unit based on data and command signals from the controller unit, outputs from various sensors, and the like.

  FIG. 2A is an external perspective view showing only the above-described image forming unit, and FIG. 2B is a side sectional view showing the internal configuration thereof. In FIGS. 4A and 4B, the same parts as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  As shown in FIGS. 2 (a) and 2 (b), the image forming unit 35 is constructed by assembling the developing sub unit 18 and the drum sub unit 36 integrally. One drum sub-unit 36 includes the photosensitive drum 14, the cleaner 15, and the charging roller 16 shown in FIG. 1, and further includes a drum cover 37 movably back and forth (left and right in FIG. 2B). A waste toner delivery pipe 38 is provided inside the unit.

  As the upper lid 5 (see FIG. 1) is closed, the writing head 17 descends along an arcuate locus as shown by an arrow C in FIG. The upper portion of the drum unit 36 is positioned by being fitted into a long slot 39 (see FIG. 2A) formed along the axial direction of the photosensitive drum 14.

  The other developing unit 18 includes a support portion 41 (41a, 41b) that supports the drum sub unit 36, a developing casing 42 that contains developer (toner) 40, and an opening portion of the developing casing 42 that has a circumferential surface. A developing roller 43 with an exposed portion, and a toner stirring member 44, a toner supply roller 45, a doctor blade 46, a scooping sheet 47 and the like so as to be buried in the toner 40 inside the developing casing 42. Yes. In addition, a waste toner receiving pipe 48 is disposed at the upper portion, and a collection bag 49 for storing the waste toner is attached to the waste toner receiving pipe 48.

  A bearing hole 51 (see FIG. 2 (a)) is formed in one support portion 41a of the developing sub unit 18, and the other support portion 41b is not clearly visible in the figure formed by cutting out from above. Is provided with a bearing groove. In addition, a fixing lever 52 is attached in the vicinity of the opening so as to be rotatable about 90 degrees up and down.

  One end portion of the support shaft 43-1 of the developing roller 43 protrudes from the side surface of the support portion 41a of the developing sub unit 18, and one end portion of the support shaft 14-1 of the photosensitive drum 14 extends from the bearing hole 51. It protrudes.

  Further, the other end of the support shaft 43-1 of the developing roller 43 protrudes from the side surface of the support portion 41b that cannot be seen in FIG. 2A, and other than the support shaft 14-1 of the photosensitive drum 14 from the bearing groove. The end is protruding.

  When the developing sub unit 18 and the drum sub unit 36 are assembled together and completed as the image forming unit 35 as shown in FIGS. 2A and 2B, the waste toner sending pipe 38 and the waste toner receiving pipe 48 are formed. Are connected by a transport pipe (not shown).

  Next, the operation of the tandem color image forming apparatus 1 having the above-described configuration will be described with reference to FIG. 1 and FIG. First, power is turned on to the apparatus main body 1 shown in FIG. 1, and printing (printing) is performed when the paper quality, number of sheets to be used, print mode, and other specifications are input as a key input or a signal from a connected host device. Be started.

  A sheet feeding roller 27 takes out one sheet of paper P placed and accommodated in the sheet cassette 4 and feeds the sheet P to the standby roller pair 24 through the feeding roller pair 26 and the sheet feeding guide path 25. The standby roller pair 24 temporarily stops its rotation, the front end of the paper P is brought into contact with the holding portion to stop the paper advance, the skew is corrected, and the conveyance timing is waited.

  The driving roller 12 rotates in the counterclockwise direction, and the driven roller 13 is driven to rotate in the same counterclockwise direction. As a result, the belt 11 is circulated and moved counterclockwise as a whole by the upper circulation portion coming into contact with the four photosensitive drums 14.

  At the same time, various devices arranged around the photosensitive drum 14 are sequentially driven in accordance with the printing timing. The photosensitive drum 14 rotates in the clockwise direction, and the charging roller 16 applies a uniform high negative charge to the circumferential surface of the photosensitive drum 14 to initialize the potential.

  The writing head 17 exposes the peripheral surface of the photosensitive drum 14 in accordance with the image signal to attenuate the potential. As a result, an electrostatic latent image is formed on the circumferential surface of the photosensitive drum 14 from the high negative potential portion by the initialization and the low negative potential portion attenuated by the exposure.

  The developing roller 43 transfers the toner 40 of the developing casing 42 to the low potential portion of the electrostatic latent image to form a toner image on the circumferential surface of the photosensitive drum 14 (reverse development).

  When the leading edge of the toner image on the peripheral surface of the most upstream photosensitive drum 14a is rotated and conveyed to the portion facing the belt 11, the standby roller pair is set so that the printing start position of the paper P coincides with the opposite portion. 24 starts to rotate and feeds the paper P to the paper carry-in section.

  The driven roller 13 and the suction roller 23 sandwich the conveyed paper P together with the belt 11 and convey it. The sheet P is attracted to the belt 11 and conveyed to the first transfer portion formed by the photosensitive drum 14 a and the transfer sheet 19.

  The transfer sheet 19 applies a transfer current (or transfer voltage) output from a transfer bias power source (not shown) to the paper P via the belt 11. As a result, the M (magenta) toner image on the photosensitive drum 14 a is transferred to the paper P.

  Subsequently, the C (cyan) toner image is transferred at the second transfer portion from the upstream formed by the photosensitive drum 14 b and the transfer sheet 19, and further from the upstream formed by the photosensitive drum 14 c and the transfer sheet 19. A Y (yellow) toner image is transferred at the third transfer portion.

  Further, the K (black) toner image is transferred at the most downstream transfer portion formed by the photosensitive drum 14 d and the transfer sheet 19, and the four color toner images are sequentially overlaid on the paper P.

  The paper P onto which the four color toner images have been transferred in this way is separated from the belt 11 and carried into the fixing device 28. The fixing device 28 fixes the toner image on the paper P by heat and pressure. After the image fixing, the paper P is discharged by the carry-out roller pair 29 via the paper discharge path 31 and the discharge roller pair 32 onto the paper discharge tray 6 with the toner image facing down.

  FIG. 3A is a front view showing the positional relationship between the charging roller 16 and the photosensitive drum 14 in the color image forming apparatus 1 of the present example that operates as described above, and FIG. It is sectional drawing of the diameter direction of these.

  The charging roller 16 of this example shown in FIGS. 4A and 4B includes a first conductive elastic layer 54 supported on a central core metal 53, and on the first conductive elastic layer 54. The second conductive elastic layer 55 is provided.

  The first conductive elastic layer 54 is composed of nitrile foam rubber and conductive carbon black. Further, the second conductive elastic layer 55 is composed of epichlorohydrin rubber and conductive carbon black, and a surface treatment layer is formed on the surface thereof by a surface treatment liquid containing isocyanate.

  By the way, it is considered that white spots and black spots are caused by abnormal discharge when the surface roughness of the charging roller becomes larger than a certain level. For this reason, Rz is important, but if Ra, which is the average roughness, is large, Rz generally increases. Therefore, it is necessary to consider that the average roughness Ra does not increase beyond a certain level.

  Here, the manufacturing method of the 1st electroconductive elastic layer 54 and the 2nd electroconductive elastic layer 55 as Example 1 of this embodiment is demonstrated.

  First, 100 parts by mass of a medium to high nitrile rubber (Mooney viscosity: ML1 + 4 (100 ° C.): 30) of 33% nitrile, 5 parts by mass of zinc white, 1 part by mass of stearic acid, conductive carbon (Toka Black) # 5500: manufactured by Tokai Carbon Co., Ltd., 25 parts by mass, DOP30 by mass, 1 part by mass of vulcanized material (sulfur), and 3.5 parts by mass of vulcanization aid are prepared.

  Next, a foaming agent (ADCA cell microphone CAP: manufactured by Sankyo Kasei Co., Ltd.) and 3 parts by mass of a foaming aid are added to each of these and kneaded with a roll mixer (first conductive material before foaming). The layer) is preformed by extrusion onto a core bar 53 having an outer diameter of 6 mm with a thickness of 1 mm.

  Thereafter, the first conductive elastic layer before foaming is foamed by heating in an electric furnace at 150 ° C. for 1 hour, polished so that the outer diameter D1 becomes 8.9 mm, and foamed first conductive The elastic elastic layer 54 is created.

  Subsequently, 100 parts by mass of epichlorohydrin rubber (ECO), 20 parts by mass of conductive carbon black (Toka Black # 4500, manufactured by Tokai Carbon Co., Ltd.), 5 parts by mass of zinc white, 2 parts by mass of stearic acid, and additive Add 1.5 parts by mass of the vulcanizing agent, knead with a roll mixer, and after injection molding, vulcanize at 170 ° C. for 30 minutes, thickness 0.7 mm, inner diameter D2 is 8.7 mm The rubber sleeve is formed and used as the second conductive elastic layer 55.

  Then, the second conductive elastic layer 55 is sheathed on the first conductive elastic layer 54, and the first conductive elastic layer 54 and the second conductive elastic layer 55 are separated from the both end portions of the roller by 2 mm. A mixture of a reactive hot melt adhesive (Coronate 3080 manufactured by Nippon Polyurethane Co., Ltd.) and 2 parts by mass of conductive carbon black (Tokai Carbon Co., Ltd .: Tocan Black # 4500) was applied with a dispenser. The two layers of conductive elastic rollers were bonded.

  In order to polish the surface of the two-layer conductive elastic roller, the surface was polished for 40 seconds using a roller-type polishing paper (Sankyo Rikagaku Co., Ltd .: Lapping Film LDF3000) with a rubber roller mirror finisher.

  Here, 100 parts by mass of ethyl acetate, 20 parts by mass of isocyanate compound (MDI), 4 parts by mass of acetylene black (manufactured by Denki Kagaku) and 2 parts by mass of acrylic silicone polymer (Modifier FS700: manufactured by Nippon Oil & Fats Co., Ltd.) A surface treatment solution is prepared by dispersing and mixing for 3 hours.

  Then, the polished two-layered conductive elastic roller is immersed in the surface treatment solution at 23 ° C. for 60 seconds, and then heated in an oven at 120 ° C. for 1 hour to form the second conductive elastic layer 55. Thus, a charging roller 16 (16-1) having a surface treatment layer formed thereon was obtained.

  When the surface roughness of the charging roller 16 was measured, Ra = 0.20 μm and Rz = 0.98 μm. When the charging roller 16 prepared by the above method is attached to a charging roller mounting portion of a commercially available color printer (manufactured by Casio Computer Co., Ltd .: N5300) and evaluated by printing a halftone image, a good image is obtained and evaluated. Was "○".

  Hereinafter, in addition to Example 1 described above, Examples 2 to 4 having different surface roughnesses and Comparative Example 1 in which surface treatment is not performed are prepared, and the charging rollers are classified according to the surface roughness. The degree of occurrence of white spots and black spots in the halftone image formed by using them was determined.

  FIG. 4 is a chart showing an evaluation of the degree of occurrence of white spots and black spots in halftone images formed using the charging rollers of Examples 1 to 4 and Comparative Example 1 created according to the surface roughness in the first embodiment. is there.

  In Example 2 shown in the same figure, in order to polish the surface of the two-layer conductive elastic roller, the surface of the roller is polished for 1 minute by using a roller type polishing paper (Sankyo Chemical Co., Ltd .: Lapping Film LDF4000) with a rubber roller mirror finisher. A charging roller 16 (16-2) was obtained by the same method as in Example 1 except for polishing.

  When the surface roughness of the charging roller 16-2 was measured, Ra = 0.16 μm and RZ = 0.74 μm.

  And when this charging roller 16-2 was attached to the charging roller mounting portion of a commercially available color printer (manufactured by Casio Computer Co., Ltd .: N5300) and a halftone image was printed and evaluated, a good image was obtained. ○ ”.

  Next, as Example 3 shown in FIG. 4, in order to polish the surface of the two-layer conductive elastic roller, using a roller type polishing paper (Sankyo Chemical Co., Ltd .: Lapping Film LDF4000) with a rubber roller mirror finisher for 1 minute A charging roller 16 (16-3) was obtained in the same manner as in Example 1 except that the surface was polished.

  When the surface roughness of the charging roller 16-3 was measured, Ra = 0.13 μm and RZ = 0.57 μm.

  When this charging roller 16-3 is attached to a charging roller mounting portion of a commercially available color printer (Casio Computer Co., Ltd .: N5300) and a halftone image is printed and evaluated, a good image is obtained. The evaluation was “◯”.

  Furthermore, as Example 4 shown in FIG. 4, in order to polish the surface of the two-layer conductive elastic roller, using a roller type polishing paper (Sankyo Rika Chemicals Co., Ltd .: Lapping Film LDF3000) first by a rubber roller mirror finisher, The surface was polished for 1 minute.

  Next, it was prepared and charged in the same manner as in Example 1 except that the surface was polished for 1 minute using a fine roller type polishing paper (Sankyo Rikagaku Co., Ltd .: Lapping Film LDF6000) with a rubber roller mirror finisher. A roller 16 (16-4) was obtained.

  When the surface roughness of the charging roller 4 was measured, Ra = 0.089 μm and Rz = 0 · 47 μm.

  When this charging roller 16-4 was attached to a charging roller mounting portion of a commercially available color printer (manufactured by Casio Computer Co., Ltd .: N5300) and a halftone image was printed and evaluated, a good image quality was obtained. ○ ”.

  For reference, as a comparative example 1 shown in FIG. 4, a charging roller 16 (16-5) is obtained by the same method as in the example 1 except that the surface of the two-layer conductive roller is not polished. It was.

  When the surface roughness of the charging roller 16-5 was measured, Ra = 0.27 μm and Rz = 1.30 μm.

  When this charging roller 16-5 is attached to a charging roller mounting portion of a commercially available color printer (Casio Computer Co., Ltd .: N5300) and a halftone image is printed, only an image having many white spots and black spots is obtained. X ".

  Here, in the charging roller 16-5 of Comparative Example 1 having a rough surface such as Ra = 0.27 μm and Rz = 1.3 μm, which were prepared without polishing the surface in the above test, a halftone image was obtained. White spots and black spots are generated at the time of formation, and those in which the surfaces are sequentially smoothed in Example 1, Example 2, Example 3, and Example 4 do not generate white spots and black spots at the time of halftone image formation. For Example 4, an attempt was made to further smooth the surface.

  That is, in order to polish the surface of the two-layer conductive elastic roller, the surface is first polished for 1 minute by using a roller-type polishing paper (Sankyo Chemical Co., Ltd .: Lapping Film LDF3000) with a rubber roller mirror finisher. The surface was polished for 5 minutes, 4 minutes longer than in Example 4, using a fine roller-type abrasive paper (Sankyo Rikagaku Co., Ltd .: Lapping Film LDF6000).

  Other than this, a charging roller was obtained by the same method as in Example 1, and the surface roughness of this charging roller was measured. As a result, Ra = 0.089 μm and Rz = 0.47 μm. In other words, it was found that even if the polishing time was extended for 4 minutes, the surface roughness did not change (no more smooth).

  That is, even if the polishing time is extended beyond 1 minute, the surface roughness cannot be changed (smoothed) more than when the polishing time is 1 minute, so it is useless to extend the polishing time. It turns out.

  In addition, the charging roller extended for 4 minutes in this second polishing is attached to the charging roller mounting portion of a commercially available color printer (Casio Computer Co., Ltd .: N5300), and a halftone image is formed, printed, and evaluated. As a result, it goes without saying that a good image without white spots or black spots was obtained.

  Further, even when Rz is set to 0.4 μm, a good image having no white spots or black spots can be obtained. In this case, it is necessary to polish a large number of times by using a lapping film having different eyes. Like the time extension, it is effective in that a good effect is recognized, but it is not practical because it takes time.

  In summary, when the surface of the charging roller is smooth, that is, in the surface roughness, Rz is in the range of 1 μm or less and 0.4 μm or more, and Ra is 0.2 μm or less and in the range of 0.08 μm or more. It turns out that a good image without white spots and black spots can be obtained.

  Rz is effective even if it is 0.4 μm or less, except that it takes time and costs are high, and Ra is also effective if it takes 0.08 μm or less and time is high. Therefore, it is not necessary to set a lower limit for Rz, and “Rz ≦ 1.0 μm” may be set, and it is not necessary to set a lower limit for Ra, and “Ra ≦ 0.2 μm” may be set.

FIG. 3 is a side cross-sectional view illustrating an internal configuration of a tandem type color image forming apparatus including a charging roller according to the first exemplary embodiment. FIG. 3A is an external perspective view showing only an image forming unit of a color image forming apparatus provided with a charging roller in Embodiment 1, and FIG. 2B is a side sectional view showing the internal configuration thereof. (a) is a front view showing the arrangement relationship between the charging roller and the photosensitive drum in Embodiment 1, and (b) is a sectional view in the diameter direction of the charging roller. 6 is a chart showing an evaluation of the degree of occurrence of white spots and black spots in halftone images formed using the charging rollers of Examples 1 to 4 and Comparative Example 1 created for each surface roughness in the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 2 Main body base 3 Opening / closing paper feed tray 4 Paper cassette 5 Top cover 6 Paper discharge tray 7 Upper paper discharge outlet 9 Operation panel 11 Paper conveyance belt (belt)
12 driving roller 13 driven roller 14 (14a, 14b, 14c, 14d) photosensitive drum 14-1 photosensitive drum support shaft 15 cleaner 16 (16-1, 16-2, 16-3, 16-4) charging roller 17 Write head 18 Developer (development sub-unit)
19 Transfer Sheet 21 Support Member 22 Tension Roller 23 Adsorption Roller 24 Standby Roller Pair 25 Feeding Guide Path
26 Feeding roller pair 27 Feeding roller 28 Fixing device 29 Unloading roller pair 31 Paper discharge path 32 Paper discharge roller pair 33 Electrical unit 35 Image forming unit 36 Drum sub unit 37 Drum cover 38 Waste toner delivery pipe 39 Long groove hole 40 Development Agent (toner)
41 (41a, 41b) Support section 42 Developing casing 43 Developing roller 43-1 Developing roller support shaft 44 Toner stirring member 45 Toner supply roller 46 Doctor blade 47 Scoop sheet 48 Waste toner receiving pipe 49 Collection bag 53 Core metal 54 First core 54 Conductive elastic layer 55 Second conductive elastic layer

Claims (2)

Used in an image forming apparatus that forms an electrostatic latent image on a photosensitive drum that has been charged by initialization, converts the electrostatic latent image into a toner image, and transfers the toner image onto a sheet to form an image. A charge comprising initializing and charging the photosensitive drum comprising a first conductive elastic layer supported on the core metal and a second conductive elastic layer provided on the first conductive elastic layer. Laura,
The first conductive elastic layer is formed of nitrile foam rubber and conductive carbon black,
Forming the second conductive elastic layer with epichlorohydrin rubber and conductive carbon black, and forming a surface layer surface-treated with a surface treatment liquid containing isocyanate on the surface;
A charging roller having a surface roughness Ra ≦ 0.20 μm. Used in an image forming apparatus that forms an electrostatic latent image on a photosensitive drum that has been charged by initialization, converts the electrostatic latent image into a toner image, and transfers the toner image onto a sheet to form an image. A charge comprising initializing and charging the photosensitive drum comprising a first conductive elastic layer supported on the core metal and a second conductive elastic layer provided on the first conductive elastic layer. Laura,
The first conductive elastic layer is formed of nitrile foam rubber and conductive carbon black,
Forming the second conductive elastic layer with epichlorohydrin rubber and conductive carbon black, and forming a surface layer surface-treated with a surface treatment liquid containing isocyanate on the surface;
A charging roller, wherein the surface roughness of the surface layer is Rz ≦ 1.00 μm.