JP6233426B2 - Charging device - Google Patents

Description

  The present invention relates to a charging device that charges the surface of an image carrier.

  An image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic system charges a surface of a photoconductor as an image carrier, and then supplies toner to an electrostatic latent image formed by exposure. Form an image. Thereafter, the toner image is transferred onto a transfer material (for example, recording paper), and the transfer material onto which the toner image has been transferred is pressurized and heated to fix the toner image on the transfer material, thereby forming an image. After the toner image is transferred, foreign matters such as toner and external additives remaining on the photosensitive member are removed from the photosensitive member by a cleaning device.

  As a device for charging the surface of the photosensitive member, a charging device including a charging roller disposed in contact with the surface of the photosensitive member is known. Most of the foreign matter remaining on the photoconductor is removed by a cleaning device arranged upstream of the charging device, but foreign matter with a small particle size such as an external additive passes through the cleaning device and reaches the charging device. There is also. If foreign matter adheres to the charging roller, it accumulates as dirt. Due to accumulation of dirt on the charging roller, uneven charging of the photosensitive member may occur, which causes unevenness of the printed image.

  Therefore, a charging device including a cleaning roller that cleans the surface of the charging roller by contacting the charging roller and rotating in synchronization (following) with the charging roller is known. For example, in Patent Document 1, a foam material, which is a porous material that has a plurality of cells (cells) inside and is elastically deformable, is formed in a strip shape, and the foam material is wound around a shaft portion in a spiral shape. A cleaning body (cleaning roller) is disclosed. And the foreign material of a charging roll is wiped off by contacting a cleaning body with a charging roll (charging roller).

  And in the cleaning body of patent document 1, the cell is formed as a long hole shape long in the pressing direction, ie, the radial direction of the cleaning body. Thereby, the density of parts other than the cell of a foaming material becomes high, the rigidity of a pressing direction is improved, and the cleaning capability of the cleaning body becomes high. In addition, the cleaning body wipes out foreign matter on the charging roll by elastic deformation of the foaming material when the foaming material is pressed against the charging roll, and the rigidity in the pressing direction is increased. The pressing force on the roll is large.

JP 2011-145410 A

  However, in Patent Document 1, since the strength of the foam material that comes into contact with the charging roll is increased and is strongly pressed against the charging roll, a strong reaction force acts on the shaft portion through the foam material, and the shaft The part may be bent by the reaction force, and the cleaning state of the charging roll may not be kept uniform.

  In addition, the cleaning body operates to repeatedly rub the surface of the charging roll while pressing a foam material having high rigidity with a strong force, so the surface of the charging roll may be damaged or worn. It may cause uneven charging of the body.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a charging device that can suppress accumulation of dirt on a charging roller over a long period of time and suppress uneven charging of a photoreceptor.

  In order to achieve the above object, the present invention relates to a charging roller that rotates in contact with the surface of an image carrier and charges the image carrier, and rotates in contact with the surface of the charging roller. A cleaning roller that cleans the surface, and the cleaning roller has a foamed elastic body that forms a nip portion with the charging roller, and at least the cell exposed to the surface of the foamed elastic body The rate of change of the average diameter at the center of the nip portion with respect to the average diameter immediately before entering the nip portion is 1.4 or more and 3.0 or less.

  According to this configuration, it is possible to wipe off the dirt on the surface of the charging roller without strongly pressing the foamed elastic body against the charging roller. In addition, damage such as tearing of the foamed elastic body can be suppressed. Thereby, accumulation of dirt on the charging roller can be suppressed over a long period of time, and uneven charging of the image carrier can be suppressed.

  In the above configuration, the foamed elastic body may be more easily elastically deformed in the rotational direction than in the direction orthogonal to the rotational direction of the cleaning roller. Thereby, since it is easy to deform | transform in the rotation direction of the said cleaning roller strongly related to the wiping of the dirt of a charging roller, accumulation | storage of the dirt of the said charging roller can be suppressed.

  In the above configuration, the cell may have a shape in which a length in a direction intersecting a rotation direction of the cleaning roller is longer than a length in the rotation direction.

  The said structure WHEREIN: The notch may be provided in the part which cross | intersects the rotation direction of the said cleaning roller of the inner wall of the said cell exposed on the surface.

  The said structure WHEREIN: The said foaming elastic body may be provided with the notch extended on the surface in the direction which cross | intersects the rotation direction of the said cleaning roller.

  The said structure WHEREIN: As for the said foaming elastic body, the average diameter of the said cell of the surface side may be larger than the average diameter of the said cell inside.

  The said structure WHEREIN: The said foaming elastic body may be wound helically around the column-shaped shaft member.

  According to the present invention, it is possible to provide a charging device that can suppress accumulation of dirt on the charging roller over a long period of time and suppress uneven charging of the image carrier.

1 is a diagram illustrating an example of an image forming apparatus including a charging device according to the present invention. FIG. 2 is a schematic layout diagram of image forming units used in the image forming apparatus shown in FIG. 1. 1 is a schematic perspective view of a charging device according to the present invention. It is a side view of a cleaning roller. It is a figure which shows the state of the nip part of a charging roller and a cleaning roller, and a cell. It is a figure which shows the experimental apparatus which judges the cleaning performance of a cleaning roller. It is an enlarged view of the cleaning roller used for the charging device according to the present invention. It is an enlarged view of the cleaning roller used for the charging device according to the present invention. It is a side view of the cleaning roller used for the charging device according to the present invention. It is sectional drawing of the cleaning roller used for the charging device which concerns on this invention. It is a perspective view of the further another example of the cleaning roller used for the charging device which concerns on this invention. It is a graph which shows the change by the frequency | count of printing of the cleaning performance of a cleaning roller. It is a figure which shows the shape of the cell in the nip part vicinity of the cleaning roller of Example 1 and Example 2. FIG.

  The configuration of the present invention will be described with reference to the drawings.

  FIG. 1 is a view showing an example of an image forming apparatus provided with a charging device according to the present invention. In the following description, there are cases where directions such as up / down / left / right or clockwise counterclockwise are described, but FIG. 1 is used as a reference unless otherwise specified.

  An image forming apparatus A shown in FIG. 1 is a tandem color digital copier, and includes an image reader unit 20 that reads an original image, a printer unit 10 that prints the read image on a transfer material such as a recording sheet, and a printer unit 10. On the other hand, a paper feeding unit 30 for supplying a transfer material (here, recording paper) and photoconductor drums 11Y, 11M, 11C, and 11K (hereinafter referred to as “photosensitive drum 11”, which will be described later) of the printer unit 10. The image forming units 40Y, 40M, 40C, and 40K that form electrostatic latent images are provided on the surface. In addition, the image forming apparatus A includes a control unit Cont, and the printer unit 10, the image reader unit 20, and the paper feeding unit 30 are controlled by the control unit Cont.

  The image reader unit 20 reads a document placed on a document glass plate (not shown) by moving a scanner, and has a known configuration. The image reader unit 20 separates the original image into three colors of red (R), green (G), and blue (B), converts them into electrical signals using an image sensor such as a CCD (not shown),・ G / B image data is acquired. The image data for each color (R, G, B) acquired by the image reader unit 20 is subjected to various processes by the control unit Cont, and then yellow (Y), magenta (M), cyan (C), black ( K) is converted into image data of each reproduction color and stored in a recording unit (memory) provided in the control unit Cont. The image data of each reproduction color stored in the memory in the control unit Cont is subjected to positional deviation correction, and then read out for each scanning line to become a drive signal.

  The printer unit 10 forms an image on a recording medium such as a recording sheet by an electrophotographic method. The printer unit 10 includes photosensitive drums 11Y, 11M, 11C, and 11K corresponding to reproduction colors of yellow (Y), magenta (M), cyan (C), and black (K).

  The printer unit 10 includes image forming units 40Y, 40M, 40C, and 40K that form toner images of corresponding reproduction colors on the photosensitive drums 11Y, 11M, 11C, and 11K, respectively. The printer unit 10 also includes toner hoppers 12Y, 12M, 12C, and 12K and toner bottles 13Y, 13M, 13C, and 13K for supplying toner to the image forming units 40Y, 40M, 40C, and 40K. . Details of the image forming units 40Y, 40M, 40C, and 40K will be described later.

  The toner hoppers 12Y, 12M, 12C, and 12K temporarily store yellow (Y), magenta (M), cyan (C), and black (K) toners. When the toner amount (toner density) in the developing device 42 (shown in FIG. 2) of the image forming units 40Y, 40M, 40C, and 40K decreases, the corresponding image forming units 40Y, 40M are connected via a cylindrical joint (not shown). , 40C, 40K to supply toner.

  The toner bottles 13Y, 13M, 13C, and 13K are disposed above the toner hoppers 12Y, 12M, 12C, and 12K. Each of the toner bottles 13Y, 13M, 13C, and 13K contains toner of yellow (Y), magenta (M), cyan (C), and black (K), and toner hoppers 12Y, 12M, 12C, and 12K. Toner is supplied. By replacing the toner bottles 13Y, 13M, 13C, and 13K, new toner can be supplied. Examples of the toner bottles 13Y, 13M, 13C, and 13K include those in which a spiral protrusion is formed on the inner peripheral surface of a cylindrical bottle. By rotating the toner bottles 13Y, 13M, 13C, and 13K, the toner in the toner bottles 13Y, 13M, 13C, and 13K falls from the discharge port and flows into the toner hoppers 12Y, 12M, 12C, and 12K.

  The printer unit 10 superimposes yellow (Y), magenta (M), cyan (C), and black (K) toner images formed on the photoconductive drums 11Y, 11M, 11C, and 11K, and intermediate transfer belts. After transferring to 14 (primary transfer), it is transferred (secondary transfer) to a recording sheet as a transfer material. The toner transferred onto the recording paper is heated and pressurized to print a color image. In order to enable such a procedure, the printer unit 10 includes an intermediate transfer belt 14, primary transfer rollers 15Y, 15M, 15C, and 15K, a secondary transfer roller 16, a fixing unit 17, and a cleaning blade 18. Have.

  The intermediate transfer belt 14 is an endless belt, and is stretched between the driving roller 141, the driven roller 142, and the tension roller 143. As shown in FIG. 1, the tension roller 143 is disposed at a position higher than the driving roller 141 and the driven roller 142. The tension roller 143 is configured to be biased upward by an unillustrated biasing member (for example, a spring), and the tension roller 143 is biased upward, whereby tension is applied to the intermediate transfer belt 14. Is given. Note that the tension roller 143 may be omitted in a configuration in which at least one of the driving roller 141 or the driven roller 142 can be urged away.

  In the printer unit 10, photosensitive drums 11Y, 11M, 11C, and 11K are arranged below the intermediate transfer belt 14 in order from the left with a predetermined interval. The photoconductive drums 11Y, 11M, 11C, and 11K are arranged so that the rotation axis thereof is orthogonal to the moving direction of the intermediate transfer belt 14. Further, primary transfer rollers 15Y, 15M, 15C, and 15K are arranged so as to sandwich the intermediate transfer belt 14 with each of the photosensitive drums 11Y, 11M, 11C, and 11K.

  The primary transfer rollers 15Y, 15M, 15C, and 15K are rollers for transferring the toner images formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K to the intermediate transfer belt 14. The primary transfer rollers 15Y, 15M, 15C, and 15K suck toner from the photosensitive drums 11Y, 11M, 11C, and 11K by applying a charge (transfer bias) opposite to that of the toner. As a result, the toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11K are transferred to the intermediate transfer belt 14.

  The intermediate transfer belt 14 is rotated counterclockwise by the driving roller 141. By transferring toner images from the photosensitive drums 11Y, 11M, 11C, and 11K in synchronization with the intermediate transfer belt 14, yellow (Y), magenta (M), cyan (C), black ( The toner images K) are accurately superimposed and transferred (primary transfer) to the intermediate transfer belt 14. As a result, a color toner image (referred to as a primary transfer image) is formed on the surface of the intermediate transfer belt 14.

  The secondary transfer roller 16 is in pressure contact with the drive roller 141 with the intermediate transfer belt 14 interposed therebetween. A secondary transfer bias is applied to the secondary transfer roller 16 to attract toner from the primary transfer image of the intermediate transfer belt 14. Here, recording paper is supplied from the paper feeding unit 30 between the secondary transfer roller 16 and the intermediate transfer belt 14 (nip portion), and the recording paper passes through the nip portion between the driving roller 141 and the secondary transfer roller 16. When passing, the recording paper comes into contact with the intermediate transfer belt 14. At this time, by applying a secondary transfer bias to the secondary transfer roller 16, the toner image on the intermediate transfer belt 14 is transferred (secondary transfer) to the recording paper. The recording sheet on which the toner image is transferred is then conveyed to the fixing unit 17. The fixing unit 17 fixes the toner image on the recording paper by heating and pressurizing the conveyed recording paper.

  The recording paper on which the toner image is fixed is discharged to the outside of the apparatus. On the other hand, residual toner remaining without being transferred on the intermediate transfer belt 14 is collected by the cleaning blade 18 and stored in a waste toner box. The cleaning blade 18 is a plate-like member such as rubber, and is pressed toward the driven roller 142 with the intermediate transfer belt 14 interposed therebetween.

  As described above, the printer unit 10 forms a color image on the recording paper that is a transfer material.

  Next, the paper feeding unit 30 that supplies recording paper to the printer unit 10 will be described. The paper feed unit 30 includes a paper feed cassette 31, a paper feed roller 32, and a registration roller 33. The paper feed cassette 31 is a storage unit for storing recording paper. The paper feed cassette 31 is detachable and can be replenished with recording paper. In the image forming apparatus A, one sheet feeding cassette 31 is shown, but the present invention is not limited to this, and a plurality of sheet feeding cassettes may be provided. When a plurality of paper feeding cassettes are provided, for example, recording papers having different sizes and colors may be stored for each paper feeding cassette, or the arrangement directions of the recording papers may be different.

  The paper feed roller 32 pulls out the recording paper disposed at the top of the paper feed cassette 31 to the transport path (indicated by a broken line) and transports it to the registration roller 33. In the case where a plurality of paper feed cassettes 31 are provided, a paper feed roller 32 may be provided for each paper feed cassette 31.

  The registration roller 33 operates in synchronization with the rotation of the intermediate transfer belt 14, and sends the recording paper to the nip portion between the driving roller 141 and the secondary transfer roller 16. Since the registration roller 33 is synchronized with the intermediate transfer belt 14, the primary transfer image of the intermediate transfer belt 14 is accurately transferred (secondary transfer) to a predetermined position on the recording paper.

  Next, the image forming units 40Y, 40M, 40C, and 40K that form toner images on the photosensitive drums 11Y, 11M, 11C, and 11K will be described with reference to the drawings. FIG. 2 is a schematic layout diagram of image forming units used in the image forming apparatus shown in FIG. In the following description, the image forming units 40Y, 40M, 40C, and 40K are described as the image forming unit 40, and a configuration for forming a toner image on the photosensitive drum 11 is shown. Similarly, the primary transfer rollers 15Y, 15M, 15C, and 15K will be described as the primary transfer roller 15 as a representative.

  The image forming units 40Y, 40M, 40C, and 40K form toner images on the photosensitive drums 11Y, 11M, 11C, and 11K, respectively, and primarily transfer the toner images to the transfer belt 14. As shown in FIG. 2, the image forming unit 40 includes a photoreceptor 11, a charging device 50, an exposure device 41, a developing device 42, a primary transfer roller 15, and a cleaning device 43.

  The charging device 50 is a device for charging the surface of the photoconductive drum 11. Here, the charging device 50 is a contact type charging device provided with a charging roller 51 that is charged in contact with the photoconductive drum 11. Details of the charging device 50 will be described later.

  The photosensitive drum 11 is an insulator in a dark place (dark place), and has a property that when irradiated with light (when exposed), the irradiated portion becomes a conductor. The exposure device 41 forms an electrostatic latent image by irradiating the charged photosensitive drum 11 with a light beam for exposure. Note that the exposure device 41 exposes the charging drums 11Y, 11M, 11C, and 11K in synchronization.

  The developing device 42 supplies toner having a charge to the photosensitive drum 11 on which the electrostatic latent image is formed, thereby adsorbing the toner on the surface of the photosensitive drum 11 to form a toner image. As a method for forming a toner image, a method in which toner having a charge opposite to the charge charged on the photosensitive drum 11 is adsorbed to a portion where the charge was not lost by exposure (regular development) or the charge is lost. A method (reversal development) in which toner is pushed into the broken portion can be mentioned.

  The cleaning unit 43 removes charges on the surface of the photosensitive drum 11 and further removes foreign matters such as toner and / or external additives remaining on the photosensitive drum 11. The neutralization can be performed by using a neutralization lamp that is performed by irradiating the photosensitive drum 11 with light, but is not limited thereto. Examples of a method for removing the toner remaining on the photosensitive drum 11 include, but are not limited to, a method of adsorbing with a charging brush and a method of scraping with a blade formed of rubber or the like. If the developing device 42 can clean the photosensitive drum 11, the cleaning unit 43 may be omitted. Moreover, you may clean using the cleaning roller which concerns on this invention.

(First embodiment)
Next, details of the charging device 50, which is a main part of the present invention, will be described with reference to the drawings. FIG. 3 is a schematic perspective view of the charging device according to the present invention, and FIG. 4 is a side view of the cleaning roller. The charging device 50 shown in FIG. 3 includes the photosensitive drum 11.

The charging roller 51 is in contact with the photosensitive drum 11 to charge the photosensitive drum 11. Since the charging device 50 is disposed on the downstream side of the cleaning unit 43, residual toner or the like on the surface of the photosensitive drum 11 is removed by the cleaning unit 43. However, the toner often contains an external additive such as silica (SiO ₂ ), titanium (Ti), calcium (Ca), and the like, and the external additive has a small particle diameter. May reach the charging device 50. When such an external additive is accumulated as dirt, it causes uneven charging of the photosensitive drum 11, and image noise may be formed in the printed image.

  Therefore, the charging device 50 according to the present invention includes a charging roller 51 and a cleaning roller 60. The charging roller 51 is disposed so as to be parallel to and in contact with the photosensitive drum 11. The charging roller 51 charges the surface of the photosensitive drum 11 when rotating in synchronization with the photosensitive drum 11, and has a known configuration. As shown in FIG. 3, the charging roller 51 has a length that can reliably charge the portion of the surface of the photosensitive drum 11 where the electrostatic latent image is formed.

  As shown in FIGS. 3 and 4, the cleaning roller 60 is disposed so as to be parallel to the charging roller 51 and pressed against the charging roller 51, and rotates following the rotation of the charging roller 51. The cleaning roller 60 includes a shaft member 61 and a foamed elastic body 62. The shaft member 61 is a columnar member and serves as a rotating shaft of the cleaning roller 60. Note that the end of the shaft member 61 is rotatably supported by a bearing (not shown), and the cleaning roller 60 is pressed against the charging roller 51 by urging the bearing.

  The foamed elastic body 62 is a cylindrical member, and the shaft member 61 is provided so as to penetrate the center and is fixed to the shaft member 61. The foamed elastic body 62 has a structure in which a plurality of cells 63 are included. Further, the foamed elastic body 62 forms a nip portion with the charging roller 51 and has a configuration capable of elastic deformation. Examples of the foamed elastic body 62 include elastic materials such as urethane rubber, silicon rubber, EPDM rubber, acrylic rubber, nitrile rubber, hydrin rubber, and fluorine rubber, inorganic foaming agents such as sodium hydrogen carbonate, sodium carbonate, ammonium carbonate, and nitroso. Examples include, but are not limited to, those obtained by blending an organic foaming agent such as a compound, azo compound, or sulfonyl hydrazide compound.

  Moreover, although the foamed elastic body 62 illustrated in the present embodiment has a configuration in which the cells 63 are independent, the configuration is not limited thereto, and a configuration in which the cells 63 communicate with each other may be used. For example, the cell 63 may be one having an average diameter of about 200 μm, but the average diameter can be adjusted during manufacture.

  A mechanism for cleaning the surface of the charging roller 51 by the cleaning roller 60 will be described with reference to the drawings. FIG. 5 is a diagram illustrating the state of the nip portion and the cell between the charging roller and the cleaning roller. FIG. 5 shows a cross section obtained by cutting a nip portion, which is a contact portion between the charging roller 51 and the foaming elastic body 62 of the cleaning roller 60, perpendicular to the axial direction. A cell 63 shown in FIG. 5 is a cross section of the cell 63 when cut along a cross section perpendicular to the axis of the cleaning roller 60. For convenience, the cell 63 is shown by a cross-sectional circle.

  The cleaning roller 60 is pressed toward the charging roller 51, and the foamed elastic body 62 is pressed against the charging roller 51 to be elastically deformed to form a planar nip portion. The charging roller 51 and the elastic foam body 62 are moved from the left to the right in the drawing at the nip portion, the elastic foam body 62 is deformed at the nip portion, and the cells 63 included in the elastic foam body 62 are also deformed at the nip portion.

  As shown in FIG. 5, immediately before the cell 63 enters the nip portion, the cell 63 is pulled by the nip portion and contracted and deformed to have an average diameter d1. When the charging roller 51 and the cleaning roller 60 rotate and the cell 63 moves to the center of the nip portion, the cell 63 expands and the average diameter changes from d1 to d2. As described above, when the cell 63 is deformed at the nip portion, the dirt adhering to the surface of the charging roller 51 is wiped away, that is, cleaned.

  As a result of diligent research, the present inventors have found that the cleaning effect on the surface of the charging roller 51 becomes higher as the rate of change of the average diameter of the cell 63 at the center of the nip portion relative to the average diameter of the cell 63 immediately before entering the nip portion increases. I got the knowledge. The inventor has also obtained knowledge about an appropriate range of the change rate.

  An experiment conducted by the inventor will be described. The details of the experiment and the results are described below. FIG. 6 is a schematic view of a test apparatus used in the experiment. In this experiment, a cleaning roller 60 is prepared in which the rate of change in average diameter immediately before entering the nip portion of the cell 63 and the center of the nip portion are different. Then, the quality of the cleaning roller was judged by confirming image noise and tearing of the cleaning roller 60 when printing was performed by the image forming apparatus A including the charging device 50 including the cleaning rollers 60.

  With the measuring device Sp shown in FIG. 6, the change rate of the average diameter between the point just before entering the nip portion of the cell 63 and the center of the nip portion was measured. Here, the measuring apparatus Sp of FIG. 6 will be described. As shown in FIG. 6, the measuring device Sp includes a stage St on which the cleaning roller 60 to be measured is placed, and a glass plate Gs for pressing the cleaning roller 60. A VHX microscope (manufactured by Keyence Corporation) for observing the cell 63 of the foamed elastic body 62 of the cleaning roller 60 is provided.

  Then, the surface of the cleaning roller 60 (the foamed elastic body 62) placed on the stage St is observed with a VHX microscope, and at this time, the area of the openings of an arbitrary number of cells 63 is calculated. Then, from the area, the diameter when the opening of the surface of the cell 63 is assumed to be circular is calculated, and the average value of the diameters is taken as the average diameter of the cell 63. This average diameter is defined as the average diameter d1 of the cell 63 immediately before entering the nip portion.

  Thereafter, the foamed elastic body 62 of the same cleaning roller 60 is pressed from the outer peripheral side with the glass plate Gs. At this time, the amount of biting into the glass plate Gs of the foamed elastic body 62 is adjusted to be 0.7 mm. And it observes with a VHX microscope similarly to before pressing with the glass plate Gs, and calculates the average diameter of the cell 63 after a deformation | transformation. This average diameter is defined as an average diameter d2 of the cells 63 at the center of the nip portion. Then, the rate of change of the average diameter d2 of the cell 63 at the center of the nip portion with respect to the average diameter d1 of the cell 63 immediately before entering the nip portion is calculated.

  In this experiment, the rate of change of the average diameter of the cell 63 at the center of the nip portion relative to the average diameter of the cell 63 immediately before entering the nip portion is 1.1, 1.2, 1.3, as described above. 13 types of cleaning rollers 60 provided with foamed elastic bodies 62 of 1.4, 1.5, 2.0, 2.5, 2.9, 3.0, 3.1, 3.2, 3.3, A charging device was made by pressing against the charging roller so that the amount of biting was 0.7 mm. And the image noise at the time of printing 50,000 sheets, 100,000 sheets, 150,000 sheets, 200,000 sheets, and 250,000 sheets was confirmed by the image forming apparatus A including the charging device 50 provided with each cleaning roller 60.

  Note that if the cleaning of the charging roller 51 by the cleaning roller 60 is insufficient, image noise is generated. Therefore, when there is image noise in the printed image, it was determined that the cleaning performance is not sufficient. Further, by confirming image noise when printing 50,000 sheets, 100,000 sheets, 150,000 sheets, 200,000 sheets, and 250,000 sheets, it was also judged whether the cleaning performance was deteriorated depending on the number of printed sheets (number of times of printing).

  Similarly, tearing of the foamed elastic body 62 at the end of printing 50,000 sheets, 100,000 sheets, 150,000 sheets, 200,000 sheets, and 250,000 sheets was confirmed, and three ranks were classified according to the state of tearing. Thereby, the durability of the foamed elastic body 62 was determined.

  The results of the experiments conducted as described above are shown in Tables 1 and 2. Table 1 is a table showing experimental results for judging the cleaning performance of the cleaning roller, and Table 2 is a table showing experimental results for judging the durability of the cleaning roller. In the following description, the change rate of the average diameter of the cell 63 at the center of the nip portion with respect to the average diameter of the cell 63 immediately before entering the nip portion may be simply referred to as a change rate of the average diameter.

Table 1 is a table showing experimental results of changes in cleaning performance due to an increase in the number of prints of the cleaning roller. Table 1 shows 50,000, 100,000, 150,000, 200,000, and 250,000 sheets for each change rate of the average diameter of the cell 63 at the center of the nip with respect to the average diameter of the cell 63 just before entering the nip. It shows the presence or absence of image noise during printing. It should be noted that “◯” is displayed as good when the captured image has no image noise. On the other hand, “x” is displayed as a defective image noise.

  As shown in Table 1, no image noise is generated at the rate of change of all average diameters in the printed image when printing 50,000 sheets. When the cleaning roller 60 having an average diameter change rate of 1.0 was used for the printed image when printing 100,000 sheets, image noise was confirmed. Further, image noise was confirmed even when the cleaning roller 60 having 1.1 in addition to the average diameter change rate of 1.0 was used for the printed image at the time of printing 150,000 times. Further, at the time of printing 200,000 times, image noise was confirmed even with the cleaning roller 60 having an average diameter change rate of 1.2. When printing 250,000 times, image noise was confirmed even with the cleaning roller 60 having an average diameter change rate of 1.3. It can be seen that the average diameter change rate of the foamed elastic body 62 is preferably 1.4 or more from the viewpoint of the performance deterioration of the cleaning roller 60 due to the number of printings.

If the rate of change of the average diameter of the cells 63 is increased, the foamed elastic body 62 is softened and the durability is considered to be lowered. Therefore, an experiment for confirming durability was performed. Table 2 is a table showing experimental results of changes in durability due to an increase in the number of printed cleaning rollers. Table 2 shows 50,000, 100,000, 150,000, 200,000, and 250,000 sheets for each change rate of the average diameter of the cell 63 at the center of the nip portion with respect to the average diameter of the cell 63 immediately before entering the nip portion. The confirmation result of the tearing of the foamed elastic body 62 at the end of printing is shown. The foamed elastic body 62 that is not torn is marked with “◯” as good. Further, “△” indicates that the foamed elastic body 62 has been confirmed to be broken but the foamed elastic body 62 has not been removed. "X" is attached.

  As shown in Table 2, after printing 50,000 sheets, no tearing was confirmed by the cleaning roller 60 having a change rate of all average diameters. After printing 100,000 sheets, it was confirmed that the foamed elastic body 62 was torn and detached by the cleaning roller 60 having an average diameter change rate of 3.3. Further, after printing 150,000 times, it was confirmed that the foam elastic body 62 was torn and detached by the cleaning roller 60 of 3.2 in addition to the average diameter change rate of 3.3. Further, after printing 200,000 times and after printing 250,000 times, tearing of the foamed elastic body 62 was confirmed with the cleaning roller 60 having an average diameter change rate of 3.1, but no detachment was confirmed. From the viewpoint of deterioration of the foamed elastic body 62 of the cleaning roller 60 depending on the number of printings, it is understood that the average elastic diameter change rate of the foamed elastic body 62 is preferably 3.0 or less.

  From the above, in the cleaning roller 60 according to the present invention, the foaming elasticity in which the change rate of the average diameter at the center of the nip portion with respect to the average diameter immediately before entering the nip portion of the cell 63 is 1.4 or more and 3.0 or less. It has been found that by providing the body 62, the charging roller 51 can be cleaned while having durability for a long period of time.

  By providing the cleaning roller 60 having such a configuration, accumulation of dirt on the surface of the charging roller 51 can be suppressed over a long period of time. In addition, the force for pressing the cleaning roller 60 against the charging roller 51 can be suppressed to reduce energy (electric power) required for driving, and wear of the charging roller 51 and the cleaning roller 60 can be suppressed. From the above, it is possible to uniformly charge the photosensitive drum 11 over a long period of time and suppress image deterioration.

(Second Embodiment)
As shown in the first embodiment, in the cleaning roller 60 having the foamed elastic body 62, the rate of change of the average diameter of the cell 63 at the center of the nip portion relative to the average diameter of the cell 63 immediately before entering the nip portion is 1. The durability can be ensured while maintaining the cleaning performance by setting it to 4 or more and 3.0 or less.

  As a result of further research, the inventor has found that the cleaning performance with the foamed elastic body increases as the rate of change in the rotational direction increases, that is, the cleaning performance can be maintained even when the number of printed sheets increases. I understood. Such a cleaning roller capable of increasing the rate of change in the cell rotation direction will be described with reference to the drawings.

  FIG. 7 is an enlarged view of a cleaning roller used in the charging device according to the present invention. FIG. 7 is an enlarged view of one end of the cleaning roller 60A in the axial direction. The cleaning roller 60A shown in FIG. 7 has the same configuration as the cleaning roller 60 except that the cells 64 formed on the foamed elastic body 62A are different. For this reason, the same parts as those of the cleaning roller 60 are denoted by the same reference numerals, and detailed description of the same parts is omitted.

  As shown in FIG. 7, the foamed elastic body 62A of the cleaning roller 60A has a configuration including a plurality of cells 64 extending in the direction orthogonal to the rotation direction, that is, in the axial direction. When the cleaning roller 60A is pressed against the charging roller 51 to form the nip portion, the cell 64 is deformed so as to spread in the short direction, that is, the rate of change in the rotation direction becomes large.

  As described above, the cleaning roller 60A is provided with a cell 64 that extends in a direction orthogonal to the rotation direction of the cleaning roller 60A, that is, the longitudinal direction is orthogonal to the rotation direction of the cleaning roller 60A. And the charging roller 51 can be cleaned. Accumulation of dirt on the surface of the charging roller 51 can be suppressed over a long period of time.

  Further, since the cell 64 is formed so as to be easily deformed, the force for pressing the cleaning roller 60A against the charging roller 51 can be kept low, energy (electric power) required for driving is reduced, and the charging roller 51 and the cleaning roller 60A are reduced. Wear can be suppressed. From the above, it is possible to uniformly charge the photosensitive drum 11 over a long period of time and suppress image deterioration.

  In the present embodiment, the cell 64 has a shape extending in a direction orthogonal to the rotation direction of the cleaning roller 60A, that is, in a direction parallel to the axial direction, but is not limited thereto. A direction that intersects with the rotation direction of the cleaning roller 60A may be used, but in order to increase the rate of change in the rotation direction of the cell 64, a shape extending in a direction orthogonal to the rotation direction of the cleaning roller 60A is preferable.

(Third embodiment)
Another example of the cleaning roller used in the charging device according to the present invention will be described with reference to the drawings. FIG. 8 is an enlarged view of a cleaning roller used in the charging device according to the present invention. FIG. 8 is an enlarged view of one end of the cleaning roller 60B in the axial direction. The cleaning roller 60B shown in FIG. 8 has the same configuration as the cleaning roller 60 except that the cells 63 formed in the foamed elastic body 62B are provided with cuts 631. For this reason, the same parts as those of the cleaning roller 60 are denoted by the same reference numerals, and detailed description of the same parts is omitted.

  The cleaning roller 60B shown in FIG. 8 includes a notch 631 formed so as to be orthogonal to the rotation direction at an end portion orthogonal to the rotation direction of the inner wall of the cell 63 in order to increase the rate of change of the cell 63 in the rotation direction. ing. By providing such a notch 631, even if the circumferential cross section is circular like the cell 63, the notch 631 is opened, so that the rate of change in the rotation direction of the cell 63 can be increased.

  Thus, by providing the notch 631 extending in the direction perpendicular to the rotation direction of the cleaning roller 60B on the inner wall of the cell 63, the cleaning roller 60B has durability over a long period of time and cleans the charging roller 51. Is possible. Accumulation of dirt on the surface of the charging roller 51 can be suppressed over a long period of time.

  In addition, since the cells 63 are easily deformed, the force for pressing the cleaning roller 60B against the charging roller 51 can be kept low, reducing the energy (electric power) required for driving, and the charging roller 51 and the cleaning roller 60B. Wear can be suppressed. From the above, it is possible to uniformly charge the photosensitive drum 11 over a long period of time and suppress image deterioration.

  In this embodiment, the notch 631 is provided on the inner wall of the cell 63 exposed on the surface of the foamed elastic body 62B, but may be formed on the inner wall of the cell 63 inside. Moreover, although provided in the edge part of the direction orthogonal to the rotation direction of the cleaning roller 60B of the inner wall of the cell 63, it is not limited to this. An end portion in a direction intersecting with the rotation direction of the inner wall of the cell 63 can be widely used. Also, the direction in which the notch 631 extends is not limited to being orthogonal to the rotation direction, and may be any direction that intersects the rotation direction. In order to increase the amount of change in the cell 63, a shape extending at the end in the direction orthogonal to the rotation direction of the inner wall of the cell is preferable. In addition, the notches 631 are a pair with the center in between, but the present invention is not limited to this, and the number of notches may be larger. Moreover, it does not need to be formed to make a pair.

  As a manufacturing method of the cleaning roller 60B of the present embodiment, for example, the following can be considered. A foamed elastic body 62 is wound around the shaft member 61 and fixed. Then, a roller having the foamed elastic body 62 wound around the shaft member 61 is rolled onto a plane in which a plurality of blades are juxtaposed to form a cut 631 on the inner wall of the cell 63 exposed on the surface of the foamed elastic body 62. be able to.

(Fourth embodiment)
Another example of the cleaning roller used in the charging device according to the present invention will be described with reference to the drawings. FIG. 9 is a side view of a cleaning roller used in the charging device according to the present invention. The cleaning roller 60C shown in FIG. 9 has the same configuration as the cleaning roller 60 except that a cut 65 is provided on the surface of the foamed elastic body 62C. For this reason, the same parts as those of the cleaning roller 60 are denoted by the same reference numerals, and detailed description of the same parts is omitted.

  As shown in FIG. 9, in the cleaning roller 60C, the surface of the foamed elastic body 62C is provided with a notch 65 extending in the direction orthogonal to the rotational direction, that is, in the axial direction. The notches 65 are provided at equal intervals in the rotational direction of the foamed elastic body 62C. Thus, by providing the notch 65, the foamed elastic body 62C can weaken the restraining force in the rotational direction. Thereby, the rate of change of the average diameter in the rotation direction of the cell 63 can be increased.

  Thus, by providing the notch 65 extending in the direction orthogonal to the rotation direction on the surface of the cleaning roller 60C, the cleaning roller 60C has durability over a long period of time and can clean the charging roller 51. is there. Accumulation of dirt on the surface of the charging roller 51 can be suppressed over a long period of time. Further, the notch 65 itself has an effect of wiping off the dirt on the surface of the charging roller 51, so that it has a synergistic effect, and the cleaning performance becomes higher.

  In addition, since the cell 63 is formed so as to be easily deformed, the force for pressing the cleaning roller 60C against the charging roller 51 can be kept low, energy (power) required for driving is reduced, and the charging roller 51 and the cleaning roller 60C are reduced. Wear can be suppressed. From the above, it is possible to uniformly charge the photosensitive drum 11 over a long period of time and suppress image deterioration.

  As described above, the notch 65 of the present embodiment is formed on the surface of the foamed elastic body 62C regardless of the position and shape of the cell 63, and is easy to manufacture. In this embodiment, the cut 65 extends in a direction orthogonal to the rotation direction of the cleaning roller 60C. However, the present invention is not limited to this, and any direction that intersects the rotation direction may be used. In addition, although a plurality are provided, one may be provided.

  As described above, in the second embodiment, the third embodiment, and the fourth embodiment, the rate of change of the cell in the rotational direction of the foamed elastic body is increased by the cells formed in the foamed elastic body and the portions (notches and cuts) associated therewith. I was trying to do it. However, the present invention is not limited to this, and a foamed elastic body having different ease of deformation depending on the deformation direction is prepared by blending materials or other materials, and the foamed elastic body is orthogonal to the rotation direction. You may make it attach so that it may deform | transform easily in a rotation direction compared with a direction. With such a configuration, it becomes easy to deform in the rotation direction regardless of the shape of the cell. Moreover, since it is hard to deform | transform in the direction orthogonal to a rotation direction, distortion of the part fixed to a shaft member is made small, and damage is suppressed.

(Fifth embodiment)
In the charging device of the present invention, the rate of change of the average diameter of the cell at the portion of the charging roller that comes into contact with the charging roller of the cleaning roller is 1.4 or more and 3.0 or less at the center of the nip portion immediately before the nip portion. A foamed elastic body satisfying such conditions tends to have a large average diameter, that is, a low density, and as a cleaning roller, the pressing pressure of the foamed elastic body against the charging roller tends to be low. Therefore, in the present embodiment, a cleaning roller is shown that is pressed with sufficient pressure and has the cleaning performance and durability of the cleaning roller secured.

  FIG. 10 is a sectional view of a cleaning roller used in the charging device according to the present invention. FIG. 10 shows only 1/4 in the axial direction of the cross section perpendicular to the axial direction of the cleaning roller 60D. The cleaning roller 60D shown in FIG. 10 has the same configuration as the cleaning roller 60 except that the cell 66 of the foamed elastic body 62D is different. For this reason, the same parts as those of the cleaning roller 60 are denoted by the same reference numerals, and detailed description of the same parts is omitted.

  As shown in FIG. 10, in the cleaning roller 60 </ b> D, the cell 66 of the foamed elastic body 62 </ b> D has the smallest average diameter near the shaft member 61, and the average diameter increases toward the outer peripheral portion. By setting it as such a structure, in the part near the axis | shaft of foaming elastic body 62D, the average diameter of the cell 66 is small and a density is high. Therefore, the strength is high in the portion close to the axis of the foamed elastic body 62D. On the outer peripheral side, the average diameter of the cells 66 is increased and the density is decreased. For this reason, the restraining force acting on the cell 66 exposed on the surface of the foamed elastic body 62D is weak and easily deformed.

  As described above, the foamed elastic body 62D of the cleaning roller 60D has a structure with the cells 66 having a large average diameter on the radially outer side, so that the strength of the foamed elastic body 62D is secured and the nip between the charging roller 51 and the nip. The change rate of the average diameter at the portion can be made to fall within the above range. Thereby, it can suppress that the pressure of a nip part falls.

  Therefore, the cleaning roller 60D has durability for a long period of time and can clean the charging roller 51. Accumulation of dirt on the surface of the charging roller 51 can be suppressed over a long period of time.

  From the above, it is possible to uniformly charge the photosensitive drum 11 over a long period of time and suppress image deterioration.

  In the present embodiment, the cells 66 are configured such that the average diameter thereof is larger on the radially outer side of the foamed elastic body 62D. However, the present invention is not limited to this, and the cell 66 in the range of a certain depth from the outermost side or the outermost side is formed with an average diameter that satisfies the condition of the average diameter change rate immediately before and in the middle of the nip portion. The inner diameter may be an average diameter smaller than the outer diameter. In other words, the formation may be such that the average diameter does not increase stepwise but changes abruptly at a certain position. Further, in the portion close to the shaft member 61, there may be a portion where the cell 66 is not provided. Further, the foamed elastic body 62D may be formed of one layer or may be divided into multiple layers.

(Sixth embodiment)
Another example of the cleaning roller used in the charging device according to the present invention will be described with reference to the drawings. FIG. 11 is a perspective view of still another example of the cleaning roller used in the charging device according to the present invention.

  A cleaning roller 70 shown in FIG. 11 includes a shaft member 71 and a foamed elastic body 72. The shaft member 71 is a columnar member, and is used as a rotating shaft, like the shaft member 61. The foamed elastic body 72 is fixed by winding a strip-shaped member around the shaft member 71 in a spiral shape. The foamed elastic body 72 includes a cell 73.

  The foamed elastic body 72 has the same characteristics as the foamed elastic body 62. That is, the rate of change of the average diameter of the cell 73 at the center of the nip portion with respect to the average diameter of the cell 73 immediately before the nip portion with the charging roller 51 is within the range of 1.4 to 3.0.

  With this configuration, the cleaning roller 70 has durability for a long period of time and can clean the charging roller 51. Accumulation of dirt on the surface of the charging roller 51 can be suppressed over a long period of time.

  Further, since the cell 73 is easily deformed and the total area of the nip portion is small, the force for pressing the cleaning roller 70 against the charging roller 51 can be kept low, and the energy (electric power) required for driving can be reduced. In addition, wear of the charging roller 51 and the cleaning roller 70 can be suppressed. From the above, it is possible to uniformly charge the photosensitive drum 11 over a long period of time and suppress image deterioration.

(Example)
An experiment was conducted on the characteristics of the cleaning roller having such a configuration. The experiment will be described. In this experiment, the rate of change of the average diameter of the cell at the center of the nip portion with respect to the average diameter of the cell immediately before the nip portion between the urethane resin (EP-70S, manufactured by Inoac Corporation) and the charging roller is 1.4. The first embodiment in which the foamed elastic body formed so as to fall within the range of 3.0 or less is wound around the shaft member in a cylindrical shape and the second embodiment in which the foamed elastic body is wound in a spiral shape are facilitated. In addition, Example 2 is a structure which a volume becomes a half with respect to Example 1. FIG.

  Further, as a comparative example, a comparative example 1 was prepared in which a foamed elastic body in which a urethane resin (EPS, manufactured by Inoac Corporation) was formed so that the cell was not easily deformed was spirally wound around a shaft member. Comparative Example 1 has the same shape as Example 2.

In the experiment, the cleaning performance of the cleaning roller was confirmed by confirming the degree of adhesion of the toner external additive to the charging roller. Specifically, using a charging roller having a black surface, the photosensitive drum was charged for printing, the number of rotations of the photosensitive drum was counted, and the brightness of the charging roller was measured. As described above, the external additive is white particles such as silica (SiO ₂ ), titanium (Ti), calcium (Ca), and the like, and when accumulated as dirt on the charging roller, the surface of the charging roller becomes whitish due to the dirt. The brightness becomes higher. In this experiment, the fact that the brightness of the charging roller is increased by such contamination is utilized.

  The experimental results are shown below. FIG. 12 is a graph showing a change in the cleaning performance of the cleaning roller depending on the number of printings. In FIG. 12, the horizontal axis represents the number of rotations of the photosensitive drum, and the vertical axis represents the lightness (ΔL *) of the charging roller as external additive contamination.

  As shown in FIG. 12, when the cleaning rollers of Example 1 and Example 2 were used, the lightness of the charging roller gradually increased until the rotational speed of the photosensitive drum increased to about 230,000. The brightness is substantially constant. That is, in Example 1 and Example 2, it turns out that the stable cleaning performance is exhibited over a long period of time.

  On the other hand, in Comparative Example 1, the brightness of the charging roller is a little larger than that of Example 1 and Example 2 until about 230,000 revolutions, but the brightness increases rapidly after exceeding about 230,000 revolutions. It has become. That is, it can be seen that the cleaning performance of Comparative Example 1 is drastically reduced as compared with Example 1 and Example 2 when the service period is long.

  From the above, in the charging device according to the present invention, accumulation of dirt on the charging roller can be suppressed over a long period of time. As a result, it is possible to suppress the charging unevenness of the photosensitive drum and suppress the deterioration of the printed image.

  Next, Example 1 and Example 2 are compared. In conventional cleaning apparatuses, it has been considered that a cleaning roller having a foamed elastic body formed in a spiral shape has a lower cleaning performance than a cleaning roller having the same outer diameter and a foamed elastic body formed in a cylindrical shape. This is because the area of the nip portion is reduced by forming the foamed elastic body in a spiral shape, and the cleaning performance is thereby lowered.

  As shown in FIG. 12, in the charging device according to the present invention, there is almost no difference in cleaning performance between Example 1 having a cylindrical foamed elastic body and Example 2 having a spiral foamed elastic body. The cleaning performance of Example 1 and Example 2 will be described below. FIG. 13 shows the shape of the cell in the vicinity of the nip portion of the cleaning roller according to the first and second embodiments. In the following description, Example 1 and Example 2 use foamed elastic bodies having the same configuration.

  As shown in FIG. 13, in the non-nip portion that is not close to the nip portion (not affected by the nip portion), the cells of both the cleaning rollers of Example 1 and Example 2 have the average diameter d0. In Example 1, when reaching just before the nip portion, the cell is deformed to an average diameter d1 (> d0). In the case of the cylindrical shape, since a strong restraining force is applied from the portion reaching the nip portion, it is considered that the deformation of the cell has started immediately before the nip portion.

  On the other hand, in Example 2, even when it reached immediately before the nip portion, the cell was hardly changed, and the average diameter d11 of the cell was the same as or substantially the same as the average diameter d0. This is considered to be because the restraint force from the portion reaching the nip portion is weak because the spiral shape is formed, and deformation immediately before the nip portion is suppressed.

  When the cell reaches the center of the nip portion, the cell of Example 1 has an average diameter d2. Further, the cell of Example 2 has an average diameter d21. The average cell diameter d2 at the center of the nip portion of Example 1 and the average cell diameter d21 at the center of the nip portion of Example 2 are substantially the same or the average diameter of the cell of Example 2 is somewhat larger. This is because the restraining force of Example 2 is smaller than that of Example 1 where a strong restraining force acts.

  Thus, even when using the foamed elastic body having the same configuration, the average diameter of the cell immediately before the nip portion and the change rate of the average diameter of the cell at the center of the nip portion are different between the first embodiment and the second embodiment. Example 1 becomes smaller. For this reason, even if the foamed elastic bodies have different shapes, it is considered that the same cleaning performance can be exhibited.

In the charging device according to the present invention, it was found that even when a foamed elastic body formed in a spiral shape is used, adhesion of dirt on the charging roller can be suppressed over a long period of time.
As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the spirit of the invention.

11Y, 11M, 11C, 11K Photosensitive drums 12Y, 12M, 12C, 12K Toner hoppers 13Y, 13M, 13C, 13K Toner bottle 14 Intermediate transfer belt 141 Drive roller 142 Driven roller 143 Tension roller 15Y, 15M, 15C, 15K Transfer roller 16 Secondary transfer roller 17 Fixing unit 18 Cleaning blade 20 Image reader unit 30 Paper feeding unit 31 Paper feeding tray 32 Paper feeding roller 33 Registration roller 40 Image forming unit 41 Developing device 42 Exposure device 43 Cleaning unit 50 Charging device 51 Charging roller 60 60A, 60B, 60C, 60D Cleaning roller 61 Shaft member 62, 62A, 62B, 62C, 62D Foam elastic body 63 Cell 631 Notch 64 Cell 65 Notch 70 Cleaning roller 71 Shaft member 72 Foam elasticity 73 cell

Claims (7)

A charging roller that rotates in contact with the surface of the image carrier and charges the image carrier;
A cleaning roller that rotates in pressure contact with the surface of the charging roller and cleans the surface of the charging roller;
The cleaning roller is
It has a foamed elastic body that forms a nip portion with the charging roller,
2. The rate of change of the average diameter at the center of the nip portion with respect to the average diameter immediately before entering the nip portion of at least the cells exposed on the surface of the foamed elastic body among the cells of the foamed elastic body is 1.4 or more. A charging device characterized by being 0 or less.   The charging device according to claim 1, wherein the foamed elastic body is more easily elastically deformed in a rotation direction than in a direction orthogonal to the rotation direction of the cleaning roller.   The charging device according to claim 1, wherein the cell has a shape in which a length in a direction intersecting a rotation direction of the cleaning roller is longer than a length in the rotation direction.   The charging device according to any one of claims 1 to 3, wherein a notch is provided in a portion of the inner wall of the cell exposed on the surface that intersects a rotation direction of the cleaning roller.   5. The charging device according to claim 1, wherein the foamed elastic body has a notch extending on a surface thereof in a direction intersecting with a rotation direction of the cleaning roller.   The charging device according to any one of claims 1 to 5, wherein the foamed elastic body has an average diameter of the cells on the surface side larger than an average diameter of the cells on the inside.   The charging device according to any one of claims 1 to 6, wherein the foamed elastic body is spirally wound around a cylindrical shaft member.