JP6350389B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus such as a multifunction peripheral, after an image of a document is read by an image reading unit, light is irradiated on the photoconductor provided in the image forming unit based on the read image, and the image is statically applied on the photoconductor. An electrostatic latent image is formed. Thereafter, a charged developer is supplied onto the electrostatic latent image formed by the developing device to form a visible image, which is then transferred to a sheet, fixed by a fixing device provided in the image forming apparatus, and discharged outside the apparatus. .

  Here, technologies related to an image forming apparatus including a developing device are disclosed in Japanese Patent Application Laid-Open No. 2007-57629 (Patent Document 1), Japanese Patent No. 399645 (Patent Document 2), Japanese Patent No. 4586635 (Patent Document 3), and Japanese Patent No. No. 5140920 (Patent Document 4).

JP 2007-57629 A Japanese Patent No. 3991645 Japanese Patent No. 4586635 Patent No. 5140920

  At the time of image formation, the surface of the photoconductor is charged to a predetermined potential, and an electrostatic latent image is formed on the surface of the photoconductor by exposure. Then, a developer is supplied to the photoconductor to obtain a visible image. The surface of the charging roller that charges the photoreceptor is contaminated by long-term use. Specifically, the external additive contained in the toner of the developer passes through the cleaning blade and adheres to the surface of the charging roller via the photosensitive member. When a large amount of external additive adheres to the charging roller, the function of charging the photoreceptor to a predetermined surface potential is reduced. As a result, when an image is formed, an image defect such as a background fog or a decrease in the density of a halftone image may occur. Further, if charging unevenness occurs due to the effect of the attached external additive when the photosensitive member is charged, unevenness in the density of a halftone image or a vertical streak-like image may occur.

  There is a method of cleaning the surface of the charging roller by providing a mechanism for cleaning the surface of the charging roller as in the techniques disclosed in Patent Documents 1 to 4. According to the cleaning mechanism, the surface of the charging roller is rubbed with a brush or sponge provided in the apparatus to remove external additives and foreign matters attached to the charging roller. However, such a mechanism becomes a large-scale apparatus configuration, and is not preferable when saving the space of the image forming apparatus.

  Further, as a cause of the generation of a vertical streak-like image, there is also a cause due to scratches generated in the circumferential direction of the photoconductor. Frequent scratches in the circumferential direction of the photoconductor are caused by a lump of external additive or foreign matter biting between the cleaning blade and the photoconductor.

  As one of the methods to reduce the influence on the image due to the biting of foreign matter, the photosensitive member is swung in the axial direction with a long period, and the biting foreign matter causes damage to the photosensitive member and the influence on the image. There is also a mechanism that attempts to reduce this. However, when the method of fixing the charging roller while swinging the photosensitive member is adopted, contamination of the charging roller is promoted by friction in the axial direction between the photosensitive member and the charging roller. In particular, such a phenomenon is remarkable when the photosensitive layer provided on the photoreceptor is a positively charged type and is made of a single layer resin.

  An object of the present invention is to provide an image forming apparatus that improves the image quality over a long period of time while simplifying the configuration of the apparatus.

In one aspect of the present invention, an image forming apparatus includes an image forming unit that forms an image. The image forming apparatus includes a photosensitive member, a charging roller, a charging bias voltage application unit, an exposure unit, a development unit, a development bias voltage application unit, a transfer unit, a cleaning blade, a control unit, and a photosensitive member swing. A moving mechanism . The photoreceptor is a positively charged type and has a single-layer resin photosensitive layer. The charging roller is a rubber charging roller that charges the photoreceptor. The charging bias voltage applying unit applies a charging bias voltage for charging the photosensitive member to the charging roller. The exposure unit exposes the photosensitive member charged by the charging roller to form an electrostatic latent image on the photosensitive member. The developing unit supplies a toner to the photoreceptor on which the electrostatic latent image is formed to form a visible image. The development bias voltage application unit applies a development bias voltage to the development unit. The transfer unit transfers the visible image formed by the developing unit to a recording medium. The cleaning blade is a rubber cleaning blade that removes toner remaining on the photoreceptor. The control unit controls the image forming apparatus. The photosensitive member swinging mechanism swings the photosensitive member in the axial direction. The rebound resilience of the cleaning blade is 35% or less. The molecular weight of the resin constituting the photosensitive layer is 50000 or more. The voltage applied by the charging bias voltage application unit is a DC voltage. The charging roller is allowed to move in the axial direction. The charging roller moves in the axial direction as the photosensitive member swings in the axial direction of the photosensitive member. The allowable movement amount of the charging roller in the axial direction is larger than the swing amount of the photosensitive member in the axial direction by the photosensitive member swinging mechanism.

  According to such an image forming apparatus, since the molecular weight of the resin constituting the photosensitive layer is 50000 or more, the surface roughness of the photoreceptor can be maintained in a somewhat smooth state over a long period of time. Further, coupled with the rebound resilience of the cleaning blade being 35% or less, it is possible to reduce the slipping of the external additive contained in the toner and reduce the contamination of the charging roller. Then, contamination of the charging roller due to adhesion of the external additive can be suppressed, and the surface of the photoreceptor can be appropriately charged. In addition, since the voltage applied by the charging bias voltage application unit is a DC voltage, contamination of the charging roller can be suppressed. Such a configuration does not complicate the device configuration. Therefore, according to such an image forming apparatus, it is possible to improve the image quality over a long period of time while simplifying the apparatus configuration.

1 is a diagram illustrating a multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the multifunction peripheral. FIG. 2 is a diagram illustrating an image forming unit provided in the multifunction machine. It is a figure which shows the structure of a yellow image formation unit. It is a graph which shows the relationship between the surface potential of a photoconductor and the contamination degree of a charging roller. It is a graph which shows the relationship between the contamination degree (DELTA) L of a charging roller at the time of changing the resilience elastic modulus of a cleaning blade, and durable sheets. It is a graph which shows the relationship between the contamination degree (DELTA) L of a charging roller, and the ten-point average roughness Rz of the surface of a photoreceptor. 4 is a graph showing the relationship between the ten-point average roughness Rz of the surface of the photoconductor after the formation of 100k images and the molecular weight of the binder resin constituting the photoconductive layer of the photoconductor. 6 is a graph showing the relationship between the contamination ΔL of the charging roller and the coefficient of friction μ of the surface of the photosensitive member after forming 100k images. It is a graph which shows the contamination degree (DELTA) L of the charging roller by the difference in the application method of the voltage by a charging bias voltage application part. 3 is a graph showing a relationship between a resistance value of a charging roller and a surface potential of a photoreceptor. It is a graph which shows the relationship between the contamination degree (DELTA) L of the charging roller after 100k image formation, and the movement tolerance of the axial direction of a charging roller. It is a graph which shows the relationship of the contamination degree (DELTA) L of a charging roller by the difference in the presence or absence of the application of the voltage by the charging bias voltage application part at the time of aging. 6 is a graph showing the relationship of the charging roller contamination degree ΔL depending on the presence or absence of toner supply during non-image formation.

  Embodiments of the present invention will be described below. FIG. 1 is a diagram illustrating a multifunction peripheral when an image forming apparatus according to an embodiment of the present invention is applied to the multifunction peripheral. FIG. 2 is a diagram illustrating the image forming unit 15 provided in the multifunction machine 11.

  Referring to FIGS. 1 and 2, the multifunction machine 11 includes a control unit 12, an operation unit 13, an image reading unit 14, an image forming unit 15, a paper setting unit 19, and a discharge tray 30.

  The control unit 12 controls the entire multifunction machine 11. The operation unit 13 includes a display screen (not shown) for displaying information transmitted from the multifunction machine 11 side and user input contents. The operation unit 13 inputs image forming conditions such as the number of copies to be printed and gradation, and power on / off. The image reading unit 14 includes an ADF (Auto Document Feeder) 22 as a document transport device that transports a document set at the set position to the read position. The image reading unit 14 reads an image of a document set on the ADF 22 or a mounting table (not shown). The paper setting unit 19 includes a manual feed tray 28 for manually setting paper and a paper feed cassette group 29 that can store a plurality of different sizes of paper. The paper setting unit 19 sets paper to be supplied to the image forming unit 15. The image forming unit 15 forms an image on the conveyed paper based on the image read by the image reading unit 14 and the image data transmitted via the network 25. The sheet on which the image is formed by the image forming unit 15 is discharged to the discharge tray 30.

  Next, the configuration of the image forming unit 15 provided in the multifunction machine 11 will be described in more detail.

  The image forming unit 15 includes a first image forming unit 41a, a second image forming unit 41b, a third image forming unit 41c, and a fourth image forming unit corresponding to four colors of yellow, magenta, cyan, and black, respectively. An image unit 41d, an LSU (Laser Scanner Unit) 31 as an exposure device, a transfer belt 32 as an intermediate transfer member, and four primary transfer rollers 33a and 33b provided corresponding to the image forming units 41a to 41d, A primary transfer unit 34 including 33c and 33d, a secondary transfer roller 35, a developing bias voltage applying unit 38, a charging bias voltage applying unit 39, and a photoreceptor swinging mechanism 40 are included. The LSU 31 is schematically indicated by a one-dot chain line. Note that the multifunction machine 11 includes a so-called four-tandem image forming unit 15.

  The first image forming unit 41a that forms a yellow visible image has a first photosensitive member 42a on which an electrostatic latent image is formed, and a first developer that supplies yellow developer to the first photosensitive member 42a. Development roller 43a and first charging roller 44a for charging first photosensitive member 42a. The second image forming unit 41b for forming a visible cyan image has a second photosensitive member 42b on which an electrostatic latent image is formed, and a second developer for supplying a cyan developer to the second photosensitive member 42b. Development roller 43b and second charging roller 44b for charging the second photoconductor 42b. The third image forming unit 41c that forms a magenta visible image has a third photosensitive member 42c on which an electrostatic latent image is formed, and a third photosensitive member 42c that supplies a magenta developer to the third photosensitive member 42c. Developing roller 43c and third charging roller 44c for charging the third photoconductor 42c. The fourth image forming unit 41d that forms a black visible image has a fourth photoconductor 42d on which an electrostatic latent image is formed, and a fourth developer that supplies black developer to the fourth photoconductor 42d. Development roller 43d and a fourth charging roller 44d for charging the fourth photoconductor 42d.

  The development bias voltage application unit 38 applies development bias voltages to the first to fourth development rollers 43a to 43d, respectively. The development bias voltage application unit 38 can apply both alternating current (AC) and direct current (DC) development bias voltages. The development bias voltage application unit 38 can apply only alternating current, or can apply direct current superimposed on alternating current. Further, the developing bias voltage application unit 38 can individually apply the developing bias voltage to each of the first to fourth developing rollers 43a to 43d. Note that a development bias voltage in which AC is superimposed on DC is effective from the viewpoint of improving image quality because the developability of toner can be precisely controlled.

  The charging bias voltage application unit 39 applies a developing bias voltage to each of the first to fourth charging rollers 44a to 44d. The charging bias voltage application unit 39 can apply both AC and DC developing bias voltages. The charging bias voltage application unit 39 can apply only a direct current, or can apply an alternating current superimposed on the direct current.

  Here, the configuration of the yellow image forming unit 41a will be described. FIG. 3 is a diagram showing the configuration of the yellow image forming unit 41a. Referring to FIG. 3, the yellow image forming unit 41a includes a first photosensitive member 42a, a first developing roller 43a, a first charging roller 44a, a first charge eliminating lamp 45a, and a first charge removing lamp 45a. A toner seal 46a and a first cleaning blade 47a are included. The first photoreceptor 42a is a positively charged type and has a single-layer resin photosensitive layer. The first photoreceptor 42a is obtained by applying a resin constituting the photosensitive layer on the surface of an aluminum tube. The photosensitive member swinging mechanism 40 can swing the first photosensitive member 42a in the axial direction at a predetermined cycle. The axial direction of the first photoconductor 42a is the front and back direction in FIG. The first developing roller 43a carries the toner constituting the developer on the surface thereof. The first developing roller 43a supplies the charged toner so as to move to the first photosensitive member 42a side by a high voltage such as a developing bias. The first charging roller 44a is a roller in which conductive rubber is provided around a metal shaft. The first charging roller 44a charges the surface of the first photoreceptor 42a by a near discharge by a charging bias voltage that is a voltage applied to the shaft. The first charging roller 44a is allowed to move in the axial direction, which is the front and back direction in FIG. The first static elimination lamp 45a neutralizes residual charges on the first photoconductor 42a after primary transfer by the primary transfer roller 33a. The first cleaning blade 47a removes the toner 50 remaining on the first photoconductor 42a by scraping after the charge removal. At the time of cleaning, the tip of the first cleaning blade 47a, that is, the portion that comes into contact with the first photoconductor 42a performs a minute movement called stick-slip. The first toner seal 46a prevents leakage of toner scraped by the first cleaning blade 47a. Note that the cyan image forming unit 41b, the magenta image forming unit 41c, and the black image forming unit 41d have the same configuration as the yellow image forming unit 41a, and thus description thereof is omitted.

First to fourth image forming units 41a~41d are yellow, cyan, magenta, in the order of black, are arranged from the upstream side in the rotation direction of the transfer belt 32 shown in the direction of arrow D ₁ of the in Fig. That is, the first image forming unit 41a, the second image forming unit 41b, the third image forming unit 41c, and the fourth image forming unit 41d are arranged in this order from the upstream side. A fourth image forming unit 41d is arranged on the most downstream side.

  The first to fourth charging rollers 44a to 44d respectively charge the first to fourth photoconductors 42a to 42d to a predetermined potential. The LSU 31 exposes the first to fourth photoconductors 42a to 42d based on the images read by the image reading unit 14, respectively. An electrostatic latent image is formed on each of the first to fourth photoconductors 42a to 42d based on the exposed light of each color component. The electrostatic latent images formed on the first to fourth photoconductors 42a to 42d are supplied with developer of each color, specifically, toner from the first to fourth developing rollers 43a to 43d, respectively. The toner of each color is supplied onto the first to fourth photoconductors 42a to 42d, respectively, and a visible image is formed with the toner of each color on the first to fourth photoconductors 42a to 42d. The visible images of the toner formed on the first to fourth photoconductors 42 a to 42 d in this way are primarily transferred to the transfer belt 32. The toner contains a small amount of an external additive such as silica, alumina, or titanium oxide, that is, a surface treatment agent. The size of the external additive is very small compared to the size of the toner.

The transfer belt 32 is endless. The transfer belt 32 is rotated in one direction by a driving roller 36a and a driven roller 36b. Rotational direction of the transfer belt 32 is indicated by an arrow D ₁ of the in Fig. That is, with respect to the rotation direction of the transfer belt 32, the lower region where the first to fourth photoconductors 42a to 42d are provided is the direction from the left side to the right side, and the opposite upper region is the right side to the left side. It is the direction toward. Among the first to fourth image forming units 41a to 41d, the first image forming unit 41a that forms a yellow visible image is disposed on the most upstream side in the rotation direction of the transfer belt 32, and the black visible image is displayed. A fourth image forming unit 41d that forms an image is arranged on the most downstream side. It is assumed that the transfer belt 32 rotates from the upstream side toward the downstream side.

  The four primary transfer rollers 33a to 33d are arranged at positions facing the photoconductors 42a to 42d of the respective colors with the transfer belt 32 interposed therebetween. By the primary transfer unit 34, the visible images of toner formed by the first to fourth image forming units 41 a to 41 d of four colors of yellow, magenta, cyan, and black are primarily transferred to the transfer belt 32. Specifically, by applying a primary transfer bias to each of the primary transfer rollers 33a to 33d, a visible image formed by the toner formed by the first to fourth image forming units 41a to 41d becomes a surface of the transfer belt 32. The primary transfer. At this time, the images of the respective colors are superimposed on the transfer belt 32, and a full-color image is formed on the transfer belt 32.

  The secondary transfer roller 35 is provided at a position facing the driven roller 36 b via the transfer belt 32. The image forming unit 15 includes a sheet conveyance path 37a for conveying a sheet as a recording medium at a position where the secondary transfer roller 35 and the surface of the transfer belt 32 abut. The image forming unit 15 also includes a sheet conveyance path 37b for conveying the second-transferred sheet to a fixing unit (not shown). A sheet is supplied from a sheet conveyance path 37a on the upstream side where the sheet feeding cassettes 23a to 23c are located to a position where the secondary transfer roller 35 and the surface of the transfer belt 32 abut. A secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 35 in accordance with the paper transport timing. By applying a secondary transfer bias to the secondary transfer roller 35, the visible image formed by the toner formed on the surface of the transfer belt 32 is electrically drawn to the supplied paper side and is secondarily transferred to the paper. . The sheet on which the visible image is transferred by the toner is conveyed to a fixing unit (not shown) using the sheet conveyance path 37b.

  Note that one image forming condition in the multifunction machine 11 is as follows. A TASKalfa 2550Ci modified machine manufactured by Kyocera Document Solutions Inc. is used as the multifunction machine 11. As for image forming conditions, the system speed is 160 mm / second, and the first to fourth photoconductors 42 a to 42 d are positively charged single layer type OPC (Organic Photoconductor) drums (φ30 mm, film thickness 30 μm, photosensitive layer binder resin). Molecular weight 55000), first to fourth charging rollers 44a to 44d made of φ12 mm epichlorohydrin rubber roller, charging voltage applied by charging bias voltage application unit 39 is DC constant voltage, surface potential is + 500V, and development method is non-contact AC + DC application Touchdown development method by development, the applied voltage by the development bias voltage application unit 38 is 180 Vdc, 1450 Vpp (peak to peak), 3.6 KHz, the cleaning blade 47 a is made of urethane rubber, and the thickness is 2.0 mm (JIS-A hardness is 75 degrees) Rebound resilience at 23 ° C There is 30%, and that of the Young's modulus of 9.5MPa).

  Next, the relationship between the surface potential of the photoreceptor 42a and the degree of contamination by the external additive of the charging roller 44a will be described using the yellow image forming unit 41a shown in FIG. The charging roller 44a is contaminated by the adhesion of the external additive contained in the toner via the photoreceptor 42a. Contamination due to the external additive of the charging roller 44a appears in the brightness difference of the surface of the charging roller 44a because the surface of the charging roller 44a, which is originally black, is contaminated by the white external additive.

  FIG. 4 is a graph showing the relationship between the surface potential Vo of the photoreceptor 42a and the degree of contamination ΔL of the charging roller 44a. In FIG. 4, the vertical axis represents the surface potential Vo (V), and the horizontal axis represents the degree of contamination ΔL of the charging roller 44a. It shows that the surface of charging roller 44a is contaminated, so that the value of contamination degree (DELTA) L is large. Regarding the contamination degree ΔL of the charging roller 44a, after the image formation of a predetermined amount, the lightness (L value) of the surface of the charging roller 44a is measured, and the difference from the lightness of the original charging roller 44a is defined as the contamination degree ΔL. It was measured. The brightness was measured with SpectroEye manufactured by GretagMacbeth.

  Referring to FIG. 4, when contamination of charging roller 44a proceeds, the value of surface potential Vo decreases. That is, although the same voltage is applied to the charging roller 44a by the charging bias voltage application unit 39, the surface potential of the charged photoconductor 42a is determined by using the charging roller 44a having a contamination degree ΔL of 30 as a boundary. , Has fallen significantly. Therefore, it can be understood that if the degree of contamination ΔL of the charging roller 44a is suppressed to 30 or less, appropriate charging of the photoreceptor 42a can be ensured.

  FIG. 5 is a graph showing the relationship between the contamination degree ΔL of the charging roller 44a and the durable number when the rebound resilience of the cleaning blade 47a is changed. In FIG. 5, the vertical axis indicates the contamination ΔL of the charging roller 44a, and the horizontal axis indicates the durable number (k (1000) sheets). Regarding the resilience elastic modulus of the cleaning blade 47a, the cases of 30%, 35% and 47% are shown. In FIG. 5, when the diamond has a rebound resilience of 30%, the square has a rebound resilience of 35%, and the triangle has a rebound resilience of 47%.

  Referring to FIG. 5, the lower the rebound resilience, the smaller the value of the contamination degree ΔL of the charging roller 44a. Regarding this factor, it is considered that the smaller the rebound resilience, the smaller the movement (stick-slip phenomenon) of the cleaning blade 47a during cleaning, and as a result, the slipping of the external additive from the cleaning blade 47a decreases. It is done. Here, when the rebound resilience of the cleaning blade 47a is 47%, the durable number is 50k and the value of the contamination ΔL is about 35. On the other hand, when the rebound resilience of the cleaning blade 47a is 35%, the contamination degree ΔL is about 30 even if the durable number is 100k. When the rebound resilience of the cleaning blade 47a is 30%, the contamination degree ΔL is about 20 even if the durable number is 100k. Therefore, the rebound resilience of the cleaning blade 47a is set to 35% or less, and the value of the contamination degree ΔL when the durable number is 100k can be set to 30 or less.

  FIG. 6 is a graph showing the relationship between the degree of contamination ΔL of the charging roller 44a and the ten-point average roughness Rz of the surface of the photoreceptor 42a after 100k images are formed. In FIG. 6, the vertical axis indicates the contamination ΔL of the charging roller 44a, and the horizontal axis indicates the surface roughness Rz of the surface of the photoreceptor 42a. For the surface roughness Rz, SURFCOM 1500DX manufactured by Tokyo Seimitsu Co., Ltd. is used, the roughness of the aluminum base tube constituting the photoreceptor 42a is changed by machining, and the value of the surface roughness Rz of the surface of the photoreceptor 42a is set. It was adjusted. The surface roughness Rz is a ten-point average roughness according to JIS (1982) standards.

  Referring to FIG. 6, the higher the value of surface roughness Rz of the surface of photoconductor 42a, the higher the value of contamination degree ΔL. Regarding this factor, it is considered that the higher the value of the surface roughness Rz of the surface of the photoconductor 42a, the more the surface of the charging roller 44a is contaminated due to slipping of the external additive from the cleaning blade 47a. Here, by setting the surface roughness Rz of the surface of the photoreceptor 42a to 3 μm or less, the value of the contamination degree ΔL can be set to 30 or less.

  FIG. 7 is a graph showing the relationship between the ten-point average roughness Rz of the surface of the photoreceptor 42a after the formation of 100k images and the molecular weight of the binder resin constituting the photosensitive layer of the photoreceptor 42a. In FIG. 7, the vertical axis represents the surface roughness Rz of the surface of the photoreceptor 42a, and the horizontal axis represents the molecular weight of the binder resin constituting the photosensitive layer of the photoreceptor 42a.

  Referring to FIG. 7, the higher the molecular weight of the binder resin constituting the photosensitive layer of the photoreceptor 42a, the lower the surface roughness Rz value of the surface of the photoreceptor 42a. Regarding this factor, it is considered that the higher the molecular weight of the binder resin, the more the wear resistance of the photoreceptor 42a is improved. If the molecular weight is 50000 or more, the surface roughness Rz of the surface of the photoreceptor 42a can be 3 μm or less.

  FIG. 8 is a graph showing the relationship between the degree of contamination ΔL of the charging roller 44a and the coefficient of friction μ of the surface of the photoreceptor 42a after 100k images are formed. In FIG. 8, the vertical axis represents the degree of contamination ΔL of the charging roller 44a, and the horizontal axis represents the friction coefficient μ of the surface of the photoreceptor 42a. The friction coefficient μ of the surface of the photoreceptor 42a was calculated by measuring a skid load in a state where a knitted cloth was laid on the photoreceptor 42a and a 2N (Newton) load was applied to the waste.

  Referring to FIG. 8, the higher the friction coefficient μ of the surface of the photoreceptor 42a, the higher the value of the contamination degree ΔL of the charging roller 44a. This is considered to be because if the friction coefficient μ on the surface of the photoreceptor 42a is low, slipping from the cleaning blade 47a is suppressed and the charging roller 44a is less likely to be contaminated. Here, by setting the friction coefficient μ of the surface of the photoreceptor 42a to 0.6 or less, the contamination degree ΔL of the charging roller 44a can be suppressed to 30 or less.

  FIG. 9 is a graph showing the degree of contamination ΔL of the charging roller 44a due to the difference in the voltage application method by the charging bias voltage application unit 39. In FIG. 9, the vertical axis represents the degree of contamination ΔL of the charging roller 44a. Note that when only a direct current (DC) voltage is used, the applied voltage is 1300 Vdc, and when the direct current (DC) voltage is superimposed on the alternating current (AC) voltage, the applied voltage is 1500 Vpp + 520 Vdc.

  Referring to FIG. 9, when the voltage applied to charging roller 44 a is only a DC voltage, contamination degree ΔL of charging roller 44 a is about 30. On the other hand, when the voltage applied to the charging roller 44a is obtained by superimposing the DC voltage on the AC voltage, the contamination degree ΔL of the charging roller 44a is 40 or more. Regarding this factor, when a DC voltage is superimposed on an AC voltage, the amount of discharge from the charging roller 44a side to the photoconductor 42a side increases and the number of discharge products on the photoconductor 42a also increases, resulting in an external additive. It is considered that the amount of slipping from the cleaning blade 47a increased due to the increase in the adhesion of the toner to the photoreceptor 42a. Therefore, if the voltage applied to the charging roller 44a is only a DC voltage, the contamination degree ΔL of the charging roller 44a can be 30 or less. As for the charging bias, if only DC is applied, it is possible to reduce the film abrasion of the photosensitive layer, that is, the photosensitive film, and to reduce the amount of ozone generated, the charging sound, and the frequency interference with the development. Since these can be eliminated, it is further advantageous in these points.

  FIG. 10 is a graph showing the relationship between the resistance value of the charging roller 44a and the surface potential of the photoreceptor 42a. In FIG. 10, the vertical axis represents the surface potential Vo (V) of the photoreceptor 42a, and the horizontal axis represents the resistance value (log Ω) of the charging roller 44a. About resistance value, the resistance value at the time of applying 500V is shown.

  Referring to FIG. 10, as the resistance value of charging roller 44a increases, the surface potential value of photoreceptor 42a decreases. Here, when the resistance value of the charging roller 44a becomes larger than 6.8 logΩ, the surface potential rapidly decreases. In other words, if the resistance value of the charging roller 44a is 6.8 logΩ or less, the influence on the surface potential is small. On the other hand, if the resistance value of the charging roller 44a is too low, the applied voltage leaks to the photoreceptor 42a, and the photosensitive layer may cause dielectric breakdown. When such dielectric breakdown occurs, the image appears as a black spot at the location where the dielectric breakdown occurs, which is not preferable. Therefore, considering the influence of dielectric breakdown of the photosensitive layer, the resistance value of the charging roller 44a is preferably set to 5.2 logΩ or more. That is, when the resistance value of the charging roller 44a is set to 5.2 log Ω or more and 6.8 log Ω or less, the surface potential of the photosensitive member 42a can be made appropriate and the influence on the photosensitive layer can be reduced.

  Regarding the surface roughness of the charging roller 44a, it is preferable that the ten-point average roughness Rz is 9 to 19 [mu] m and the average interval Sm of the unevenness is 55 to 130 [mu] m.

  In Table 1, the relationship between the value obtained by subtracting the developing bias voltage Vdc from the surface potential Vo and the image obtained under these conditions is shown. Experimentally, a roller having a contamination degree ΔL of about 40 was used in order to make the charging roller 44a partially contaminated. Then, a halftone image was formed, and the formed image was evaluated. Specifically, the level at which there is no particular problem is considered good, and the level where problems occur is inferior.

  Referring to Table 1, when the value of Vo−Vdc is 50 to 400V, a good image is obtained. On the other hand, when the value of Vo−Vdc is 0V, a vertical streak-like image at a position where the contamination degree ΔL is 40 is obtained. When the value of Vo-Vdc was -100V, a background fogging image was obtained. Further, when the value of Vo−Vdc was 450V, a so-called reverse background fogging image was obtained. The reverse background fog image is an image in which reversely charged toner adheres to the white portion. Therefore, a favorable image can be obtained by setting 50 ≦ Vo−Vdc ≦ 400V.

  Here, since the charging roller 44a is allowed to move in the axial direction, when the photosensitive member swinging mechanism 40 that swings the photosensitive member 42a is operated, the charging roller 44a is accompanied by the swinging of the photosensitive member 42a in the axial direction. Thus, the charging roller 44a moves in the axial direction. FIG. 11 is a graph showing the relationship between the degree of contamination ΔL of the charging roller 44a and the allowable movement amount in the axial direction of the charging roller 44a after 100k images have been formed. In FIG. 11, the vertical axis indicates the degree of contamination ΔL of the charging roller 44a, and the horizontal axis indicates the allowable swinging amount of the charging roller 44a in the axial direction. The swing allowable amount indicates the distance of the charging roller 44a that can move in the axial direction along with the swing motion of the photosensitive member 42a. When the photosensitive member swinging mechanism 40 is operated, the swing amount of the photosensitive member 42a in the axial direction is 1.0 mm.

  Referring to FIG. 11, as the allowable swing amount of charging roller 44a increases, contamination degree ΔL decreases. In this case, the amount of swinging of the photosensitive member 42a in the axial direction is 1.0 mm, and if the swinging allowable amount of the charging roller 44a is 1.0 mm or more, the contamination degree ΔL is 30 or less. Therefore, the contamination degree ΔL of the charging roller 44a can be suppressed to 30 or less by setting the allowable swinging amount of the charging roller 44a to be larger than the swinging amount of the photosensitive member 42a in the axial direction.

  FIG. 12 is a graph showing the relationship of the degree of contamination ΔL of the charging roller 44a depending on whether or not voltage is applied by the charging bias voltage applying unit 39 during aging. In FIG. 12, the vertical axis indicates the degree of contamination ΔL of the charging roller 44a. In addition, the applied voltage when there is an applied voltage is 1000V. Here, the time of aging is a state in which the photoconductor 42a is rotating in a state in which no image is formed, for example, during the time when toner is being replenished or in a time zone after the power to the multifunction device 11 is turned on. is there.

  Referring to FIG. 12, when a voltage is applied by charging bias voltage applying unit 39 from the control unit by control unit 12 during aging, the contamination degree ΔL of charging roller 44 a is about 20. On the other hand, when no voltage is applied during aging, the degree of contamination ΔL of the charging roller 44a is about 45. The reason for this is considered to be that when a voltage is applied during aging, the external additive attached to the charging roller 44a moves to some extent toward the photoreceptor 42a and is cleaned. Therefore, the contamination ΔL of the charging roller 44a can be reduced to 30 or less by applying a voltage from the charging bias voltage applying unit 39 during aging.

  FIG. 13 is a graph showing the relationship of the degree of contamination ΔL of the charging roller 44a with and without toner supply during non-image formation. In FIG. 13, the vertical axis represents the degree of contamination ΔL of the charging roller 44a. In the case of supplying toner, during non-image formation, an amount of toner that can form an image having a width of 10 mm is moved from the developing roller 43a side to the photoconductor 42a side, and cleaning is performed without performing transfer. The state of supply to the blade 47a side is shown. Here, the time of non-image formation is a state in which an image is not formed, and refers to, for example, a time zone between a plurality of conveyed sheets.

  Referring to FIG. 13, when toner is supplied from the control unit by control unit 12 during non-image formation, the contamination degree ΔL of charging roller 44 a is about 22. On the other hand, when no toner is supplied during non-image formation, the contamination degree ΔL of the charging roller 44a is about 32. With respect to this factor, the toner intervening at the edge of the cleaning blade 47a can be periodically replaced by supplying toner during non-image formation. Thereby, it is considered that the friction state between the photoconductor 42a and the cleaning blade 47a can be appropriately maintained, the stress caused by the toner can be reduced, and the detachment of the external additive from the toner can be reduced. Accordingly, when toner is supplied from the developing roller 43a during non-image formation, the contamination degree ΔL of the charging roller 44a can be set to 30 or less.

  As described above, according to the MFP 11 having such a configuration, it is possible to improve the image quality over a long period of time while simplifying the device configuration.

  In the above embodiment, the so-called quadruple tandem image forming method is used. However, the present invention is not limited to this, and a monochromatic image forming method including one image forming unit may be adopted. .

  In the above embodiment, an intermediate transfer member such as a transfer belt is used. However, the present invention is not limited to this, and the present invention is also used for a mechanism for transferring a visible image directly to a sheet.

  It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not restrictive in any respect. The scope of the present invention is defined by the scope of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

  The image forming apparatus according to the present invention is particularly effectively used when simplification of the apparatus configuration and improvement in image quality are required.

  DESCRIPTION OF SYMBOLS 11 MFP, 12 Control part, 13 Operation part, 14 Image reading part, 15 Image formation part, 16 Hard disk, 17 Facsimile communication part, 18 Network interface part, 19 Paper setting part, 21 Display screen, 22 ADF, 23a, 23b , 23c Paper feed cassette, 24 Public line, 25 Network, 26a, 26b, 26c Computer, 27 Image forming system, 28 Manual feed tray, 29 Paper feed cassette group, 30 Discharge tray, 31 LSU, 32 Transfer belt, 33a, 33b, 33c, 33d Primary transfer roller, 34 Primary transfer unit, 35 Secondary transfer roller, 36a Drive roller, 36b Driven roller, 37a, 37b Paper transport path, 38 Development bias voltage application unit, 39 Charging bias voltage application unit, 40 feeling Body swinging mechanism, 41a, 41b, 41c, 41d image forming unit, 42a, 42b, 42c, 42d photoconductor, 43a, 43b, 43c, 43d developing roller, 44a, 44b, 44c, 44d charging roller, 45a discharging lamp, 46a Toner seal, 47a Cleaning blade, 50 toner.

Claims (7)

An image forming apparatus including an image forming unit for forming an image,
A positively charged photosensitive body having a single-layer resin photosensitive layer;
A rubber charging roller for charging the photoreceptor;
A charging bias voltage application unit for applying a charging bias voltage for charging the photosensitive member to the charging roller;
Exposing the photosensitive member charged by the charging roller to form an electrostatic latent image on the photosensitive member; and
A developing unit for supplying a toner to the photoreceptor on which an electrostatic latent image is formed to form a visible image;
A developing bias voltage applying unit for applying a developing bias voltage to the developing unit;
A transfer unit for transferring a visible image formed by the developing unit to a recording medium;
A rubber cleaning blade for removing toner remaining on the photoreceptor;
A control unit for controlling the image forming apparatus ;
A photosensitive member swinging mechanism for swinging the photosensitive member in the axial direction ;
The rebound resilience of the cleaning blade is 35% or less,
The molecular weight of the resin constituting the photosensitive layer is 50,000 or more,
The voltage applied by the charging bias voltage application unit is a DC voltage ,
The charging roller is allowed to move in the axial direction,
The charging roller moves in the axial direction as the photosensitive member swings in the axial direction of the photoconductor,
An image forming apparatus in which an axial movement allowable amount of the charging roller is larger than an axial swing amount of the photoconductor by the photoconductor swing mechanism . The image forming apparatus according to claim 1, wherein a friction coefficient μ of the surface of the photoconductor is 0.6 or less. The image forming apparatus according to claim 1, wherein the surface roughness Rz of the surface of the photoconductor is 3 μm or less. The image forming apparatus according to claim 1, wherein a resistance value of the charging roller when a voltage of 500 V is applied is in a range of 5.2 to 6.8 logΩ. The control unit controls the charging bias voltage application unit to apply the charging bias voltage to the charging roller during aging when the photoconductor is rotating without forming an image. 5. The image forming apparatus according to any one of 4 above. The image forming apparatus according to claim 1, wherein the control unit controls the developing unit to supply a predetermined amount of the toner to the photoconductor during non-image formation. 2. The relationship of 50 ≦ Vo−Vdc ≦ 400 is satisfied, where Vo is a surface potential of the photosensitive member charged by the charging roller and Vdc is the developing bias voltage applied by the developing bias voltage applying unit. The image forming apparatus of any one of -6.

Images