JP2018112581A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can effectively reduce the occurrence of fogging when a developer carrier with a small surface roughness is used in a developing device employing a magnetic one-component developing system.SOLUTION: An image forming apparatus comprises an image carrier and a developing device. The image carrier has a base material and an amorphous silicon photosensitive layer formed on the surface of the base material. The developing device has a developer carrier that is arranged opposite to the image carrier and carries a magnetic one-component developer consisting only of a magnetic toner, and a metallic regulating member that is arranged with respect to the developer carrier at a predetermined interval and regulates the layer thickness of the magnetic one-component developer carried on the developer carrier. The arithmetic average roughness Ra of the surface of the photosensitive layer at an initial stage of use is within a range of 40 nm or more and 70 nm or less, and the arithmetic average roughness Ra of the surface of the developer carrier is within a range of 20 nm or more and 100 nm or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus including an image carrier on which a toner image is formed on a surface and a developing device that develops an electrostatic latent image on the image carrier.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, etc., a powder developer is mainly used, and an electrostatic latent image formed on an image carrier such as a photosensitive drum is used as a developer. A general process is to perform a fixing process after visualizing and transferring the toner image onto a recording medium.

  Developers are broadly divided into two-component developers consisting of toner and magnetic carrier, and one-component developers consisting only of magnetic toner, and are carried on a developing roller (developer carrier) by a magnetic regulating blade. The triboelectric charge of the developed developer is promoted. Further, the regulating blade serves as a regulating unit that regulates the layer thickness of the developer layer formed on the developing roller, and the gap (gap) between the regulating blade and the developing roller needs to be strictly adjusted. .

  In a magnetic one-component development method using a one-component developer, if a developing roller having a small surface roughness is used, friction between the developing roller and the developer is likely to occur, and the required charge amount is easily obtained by the rotation of the developing roller. Have advantages. Further, since a short magnetic brush can be formed, there is an advantage that a high-definition image can be formed.

  For example, in Patent Document 1, a developing sleeve having an average surface roughness Ra of 0.3 μm or more and 5.0 μm or less is used so that there is no density unevenness or density reduction due to fine powder toner caused by the use of a small diameter toner. An image forming apparatus capable of forming an image is disclosed.

JP-A-6-289724

  However, when a developing roller having a small surface roughness is used, since the toner transportability is low, the friction frequency between the developing roller and the toner increases as described above. As a result, there is a problem that the toner is overcharged and fog is likely to occur.

  In view of the above problems, the present invention provides an image forming apparatus capable of effectively suppressing the occurrence of fog when a developer carrying member having a small surface roughness is used in a magnetic one-component developing type developing apparatus. With the goal.

  In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including an image carrier and a developing device. The image carrier has a support and an amorphous silicon photosensitive layer formed on the surface of the support. The developing device is disposed opposite to the image carrier, and carries a developer carrier that carries a magnetic one-component developer composed of only magnetic toner, and is disposed at a predetermined interval with respect to the developer carrier. And a metal regulating member that regulates the layer thickness of the magnetic one-component developer carried on the body. The arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use is in the range of 40 nm to 70 nm, and the arithmetic average roughness Ra of the surface of the developer carrying member is in the range of 20 nm to 100 nm.

  The “arithmetic mean roughness Ra” in this specification is based on the surface roughness defined in 1994 edition of JISB0601.

  According to the first configuration of the present invention, a developer carrier having a surface roughness Ra of 20 nm to 100 nm and an image carrier having an arithmetic surface roughness Ra of the photosensitive layer of 40 nm to 70 nm are used in combination. The contact area of the toner with the surface of the photosensitive layer is reduced, and the adhesion force of the toner to the image carrier can be reduced. As a result, excess toner on the image carrier can be efficiently collected by the developer carrier, and fogging can be effectively suppressed.

1 is a side sectional view showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. The elements on larger scale which show the structure of the image formation part P in FIG. Side surface sectional view of the developing device 8 mounted in the image forming apparatus 100 of the present embodiment. The top view of the developing device 8 mounted in the image forming apparatus 100 of this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view of an image forming portion P in FIG. In the image forming apparatus (in this case, a monochrome printer) 100, an image forming portion P that forms a monochrome image by each process of charging, exposure, development, and transfer is disposed. In the image forming section P, along the rotation direction of the photosensitive drum 1 (counterclockwise direction in FIG. 1), the charging device 4, the exposure unit (laser scanning unit, etc.) 7, the developing device 8, the transfer roller 14, and the cleaning A device 19 and a static elimination device 6 are provided.

  When an image forming operation is performed, the photosensitive drum 1 rotating in the counterclockwise direction is uniformly charged by the charging device 4, and electrostatically is applied on the photosensitive drum 1 by the laser beam from the exposure unit 7 based on the document image data. A latent image is formed, and a developer (toner) is attached to the electrostatic latent image by the developing device 8 to form a toner image.

  The toner is supplied to the developing device 8 from the toner container 9. Note that the image data is transmitted from a host device such as a personal computer (not shown). Further, a static elimination device 6 that removes residual charges on the surface of the photosensitive drum 1 is provided on the downstream side of the cleaning device 19 with respect to the rotation direction of the photosensitive drum 1.

  A sheet is conveyed from the sheet cassette 10 or the manual sheet feeder 11 via the sheet conveyance path 12 and the registration roller pair 13 toward the photosensitive drum 1 on which the toner image is formed as described above, and the transfer roller 14. The toner image formed on the surface of the photosensitive drum 1 is transferred onto the sheet by (image transfer unit). The sheet on which the toner image has been transferred is separated from the photosensitive drum 1 and conveyed to the fixing device 15 to fix the toner image. The sheet that has passed through the fixing device 15 is conveyed to the upper part of the apparatus through the sheet conveying path 16, and is discharged to the discharge tray 18 by the discharge roller pair 17 when an image is formed on only one side of the sheet (during single-sided printing).

  The photosensitive drum 1 includes a metal cylindrical element tube (support) 1a and a photosensitive layer 1b formed on the surface of the element tube 1a. Examples of the metal forming the raw tube 1a include aluminum, iron, titanium, and magnesium. As the photosensitive layer 1b, an organic photosensitive layer using an organic photoconductor, an inorganic photosensitive layer using an inorganic photoconductor, or the like can be used, but amorphous silicon formed by vapor deposition of silane gas or the like because of its high durability. A photosensitive layer is preferred. The characteristics of the photosensitive layer 1b of the photosensitive drum 1 will be described later.

  The charging device 4 includes a charging roller 41 that contacts the photosensitive drum 1 and applies a charging bias to the drum surface and a charging cleaning roller 42 for cleaning the charging roller 41 in the charging housing.

  The charging roller 41 is made of, for example, conductive rubber, and is disposed so as to contact the photosensitive drum 1. As shown in FIG. 2, when the photosensitive drum 1 rotates in the counterclockwise direction, the charging roller 41 that contacts the surface of the photosensitive drum 1 is rotated in the clockwise direction. At this time, the surface of the photosensitive drum 1 is uniformly charged by applying a predetermined voltage to the charging roller 41. Further, as the charging roller 41 rotates, the charging cleaning roller 42 that contacts the charging roller 41 is driven to rotate counterclockwise to remove the foreign matter attached to the surface of the charging roller 41.

  The cleaning device 19 includes a cleaning blade 51 and a collection spiral 52. The cleaning blade 51 is made of urethane rubber or the like. The tip of the cleaning blade 51 is in contact with the rotation direction of the photosensitive drum 1 (see the arrow in FIG. 2) in the counter direction. The collecting spiral 52 is disposed near the lower part of the housing and rotates to convey the collected toner in one of the longitudinal directions of the housing (the direction perpendicular to the paper surface of FIG. 2) to a waste toner container (not shown). And send it out.

  3 and 4 are a side sectional view and a plan view of the developing device 8 mounted on the image forming apparatus 100. FIG. FIG. 3 shows the developing device 8 as viewed from the back side of FIG. For the sake of convenience, FIG. 4 shows a state in which the top cover is removed and the inside of the developing device 8 can be seen. As shown in FIGS. 3 and 4, the developing device 8 includes a developing container 22 that contains a magnetic one-component developer (hereinafter simply referred to as a developer) made of only magnetic toner, and a first container that agitates and conveys the developer. A stirring screw 23 and a second stirring screw 24, a developing roller 25, and a regulating blade 29 are provided.

  The inside of the developing container 22 is divided into a first transfer chamber 22b and a second transfer chamber 22c by a partition wall 22a formed integrally with the developing container 22. The partition wall 22a extends in the longitudinal direction of the developing container 22 and partitions the first transfer chamber 22b and the second transfer chamber 22c in parallel. As shown in FIG. 3, the partition wall 22 a does not exist at both ends in the longitudinal direction of the developing container 22, and the right end in the longitudinal direction of the partition wall 22 a is connected to the first communication together with the side wall of the developing container 22. On the other hand, the left end portion in the longitudinal direction of the partition wall 22a forms a second communication portion 22f together with the side wall portion of the developing container 22. The first and second communication portions 22e and 22f are opened so that the developer can be transferred between the first transfer chamber 22b and the second transfer chamber 22c.

  A first stirring screw 23 is disposed in the first transfer chamber 22b, and a second stirring screw 24 is disposed in the second transfer chamber 22c. The first and second stirring screws 23 and 24 include spiral blades that are spirally formed in the axial direction. The first agitating screw 23 conveys the developer in the first conveying chamber 22b in the direction of arrow P while agitating the developer, and conveys it to the second conveying chamber 22c, and the second agitating screw 24 moves to the second conveying chamber 22c. The developer that has been conveyed is conveyed in the direction of arrow Q while being agitated and supplied to the developing roller 25. That is, a developer circulation path is formed in the developing container 22 by the first transfer chamber 22b, the first communication portion 22e, the second transfer chamber 22c, and the second communication portion 22f. The first stirring screw 23 and the second stirring screw 24 stir and mix the developer to frictionally charge the developer.

  The developing roller 25 is formed in a cylindrical shape with a nonmagnetic material such as aluminum and incorporates a magnetic pole member 26. Further, the developing roller 25 is rotatably supported in the developing container 22 at a position adjacent to the second stirring screw 24. Further, the developing roller 25 is exposed from the opening of the developing container 22 and is opposed to the photosensitive drum 1 that is an image carrier with a certain interval. Then, the toner is supplied to the photosensitive layer 1b of the photosensitive drum 1 by rotating according to the rotation of the photosensitive drum 1 (see FIG. 1). The detailed configuration of the developing roller 25 will be described later.

  A magnetic pole member 26 made of a permanent magnet having a plurality of magnetic poles is fixed inside the developing roller 25. A magnetic brush is formed by attaching (carrying) developer to the surface of the developing roller 25 by the magnetic force of the magnetic pole member 26. The developing roller 25 is rotatably supported by the developing container 22 in a state parallel to the first stirring screw 23 and the second stirring screw 24. The first stirring screw 23, the second stirring screw 24, and the developing roller 25 are rotationally driven by a motor (not shown). Further, magnetic seal members 27 for preventing leakage of the developer from the gap between the developing container 22 and the developing roller 25 are disposed at both ends of the developing roller 25.

  The regulating blade 29 is formed such that its longitudinal direction (left-right direction in FIG. 4) is larger than the maximum developing width of the developing roller 25, and is arranged at a predetermined interval from the developing roller 25, whereby the photosensitive drum. The amount of toner supplied to 1 is regulated. As the material of the regulating blade 29, magnetic SUS (stainless steel) or the like is used. Note that magnetism may be imparted by attaching a permanent magnet to the non-magnetic regulating blade 29.

  DS rollers 31 a and 31 b are rotatably inserted on the rotation shaft of the developing roller 25. The DS rollers 31 a and 31 b strictly regulate the distance between the developing roller 25 and the photosensitive drum 1 by contacting both end portions of the outer peripheral surface of the photosensitive drum 1. The DS rollers 31a and 31b have built-in bearings, and the drum surface can be prevented from being worn by being rotated by being driven by the photosensitive drum 1.

  The developer supplied from the second stirring screw 24 is carried on the surface of the developing roller 25 to form a magnetic brush. The magnetic brush is regulated to a constant layer thickness by the regulating blade 29 and is further conveyed toward the opposing area (developing area) between the developing roller 25 and the photosensitive drum 1 by the rotation of the developing roller 25. When a predetermined developing bias is applied to the developing roller 25, a potential difference is generated between the developing roller 25 and the photosensitive drum 1, and the toner in the magnetic brush formed on the developing roller 25 is photosensitive in the developing region. The electrostatic latent image supplied to the photosensitive drum 1 and developed on the photosensitive drum 1 is developed into a toner image. Further, when the magnetic brush is separated from the photosensitive drum 1 as the developing roller 25 rotates, excess developer on the photosensitive drum 1 is collected by the magnetic brush by the alternating current component of the developing bias.

  When the toner in the developing container 22 is reduced by development, the toner (developer) stored in the toner container 9 (see FIG. 1) passes through the toner supply port 22d and reaches the upstream end of the first transfer chamber 22b. (See FIG. 4).

(Characteristics of the photosensitive layer 1b of the photosensitive drum 1)
Hereinafter, characteristics of the photosensitive layer 1b, which is a characteristic part of the photosensitive drum 1 of the present embodiment, will be described. The photosensitive drum 1 of the present embodiment has a surface roughness in which the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial stage of use is in the range of 40 [nm] to 70 [nm]. The surface state may be at least in the initial use of the photosensitive drum 1 (the state at the start of use, in other words, the state after factory shipment). In addition, the arithmetic average roughness Ra, the ten-point average roughness Rz described later, and the average interval Sm are measured by a surface roughness measuring method defined in 1994 edition of JIS B0601 using a stylus type two-dimensional roughness measuring instrument. Is done.

  When the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial stage of use is smaller than 40 [nm], the friction between the cleaning blade 51 and the photosensitive drum 1 increases, so that the cleaning blade 51 is worn or worn by long-term use. The amount of the external additive that is lost and slips through the gap between the cleaning blade 51 and the photosensitive drum 1 increases. When the arithmetic average roughness Ra is larger than 70 [nm], the gap between the cleaning blade 51 and the surface of the photosensitive layer 1b becomes large. Therefore, the amount of external additive that slips through the gap between the cleaning blade 51 and the photosensitive drum 1 at a relatively early stage of durable printing increases.

  That is, if the arithmetic average roughness Ra of the surface of the photosensitive layer 1b is too small or too large, the external additive slips through and the resulting charging roller 41 is contaminated, and the surface of the photosensitive drum 1 is charged. Image defects such as vertical stripes due to unevenness occur. Accordingly, the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is preferably in the range of 40 [nm] to 70 [nm], and is 40 [nm] to 55 [nm]. It is more preferable to be within the following range.

  When the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] to 70 [nm], the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 The ten-point average roughness Rz is preferably in the range of 0.4 [μm] to 0.9 [μm].

  This is because, even if the arithmetic average roughness Ra is within the above range, if there are large irregularities, the cleaning blade 51 cannot follow the surface shape of the photosensitive drum 1 although it deforms to some extent, and the photosensitive drum 1 and the cleaning blade. This is a rule for preventing the gap between the gap 51 and the gap 51 from increasing. Note that when the gap between the photosensitive drum 1 and the cleaning blade 51 becomes large, slipping of an external additive or the like occurs.

  In other words, if a large convex portion exists on the surface of the photosensitive drum 1 and the tip of the convex portion comes into contact with the cleaning blade 51, the concave portion located between the large convex portions contacts the cleaning blade 51. This is because it does not make sense to define the magnitude of the arithmetic average roughness Ra. In other words, it is preferable that the surface of the photosensitive drum 1 has no irregularities and has minute irregularities, and this condition is defined by the ten-point average roughness Rz and the arithmetic average roughness Ra. . Note that the ten-point average roughness Rz defines that there are no sudden irregularities.

  The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] or more and 70 [nm] or less, and the ten-point average roughness Rz is 0.4 [μm] or more and 0. When it is in the range of .9 [μm] or less, the average interval Sm of the unevenness is preferably 14 [μm] or less.

  This is due to the following reason. Even when the arithmetic average roughness Ra and the ten-point average roughness Rz are within the above ranges, when the large convex portion exists apart, the cleaning blade 51 contacts (supports) the large convex portion. Here, the average interval Sm of the unevenness is used for determining whether or not the large convex portion is separated.

  The cleaning blade 51 is elastically deformable, and is deformed so as to come into contact with the photosensitive drum 1 between large protrusions (portions). In particular, when the interval between the convex portions is wide, the contact area between the cleaning blade 51 and the photosensitive drum 1 increases. When the contact area increases, the driving torque of the photosensitive drum 1 increases due to friction with the cleaning blade 51 and the wear of the cleaning blade 51 becomes severe, eventually causing the sticking slip of the cleaning blade 51 and slipping of the external additive. Or the edge of the cleaning blade 51 is lost. Needless to say, if the edge of the cleaning blade 51 is lost, a good image cannot be obtained.

  Further, when the average interval Sm is increased, the protruding portion (mountain) is increased (the crest of the peak is wide), and when the top portion of the protruding portion is worn due to long-term use, a wide flat portion is generated at the top portion and contact with the cleaning blade 51 The area increases.

  The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] to 70 [nm], and the ten-point average roughness Rz is 0.4 [μm] or more. When it is in the range of 0.9 [μm] or less, the skewness Rsk is preferably 0.3 or more.

Here, the skewness Rsk is one of the parameters representing the strength of the surface roughness, and represents the symmetry (degree of distortion of the irregularities) between the peak and valley when the average line is the center, and the following formula ( In the reference length made dimensionless by the cube of the root mean square height Rq as in 1), it is represented by the root mean square of Z (x).

  When Rsk is larger than 0, the unevenness is a shape that is biased downward with respect to the average line. On the other hand, when Rsk is smaller than 0, the unevenness has a shape biased upward with respect to the average line. In other words, it is considered that when the skewness Rsk of the photosensitive layer is larger than 0, the contact area is reduced because the point of contact with the cleaning blade 51 is more pointed. In the present embodiment, by satisfying Rsk ≧ 0.3, the contact area between the photosensitive drum 1 and the cleaning blade 51 is reduced, and friction is effectively reduced.

  The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] to 70 [nm], and the ten-point average roughness Rz is 0.4 [μm] or more. When it is in the range of 0.9 [μm] or less, the ratio (Ra [nm] / Sm [μm]) of the arithmetic average roughness Ra [nm] to the average interval Sm [μm] of the unevenness is 3 or more. Is preferred.

  By forming irregularities with a surface roughness satisfying the above range irregularly on the surface of the photosensitive layer 1 b in the axial direction and the circumferential direction of the photosensitive drum 1, the friction between the photosensitive drum 1 and the cleaning blade 51. This can reduce the driving torque of the photosensitive drum 1 and the wear of the edge of the cleaning blade 51. In particular, by satisfying Ra [nm] / Sm [μm] ≧ 3, an uneven shape having a height (depth) of three times or more with respect to the average interval Sm is obtained, so that the photosensitive drum 1 and the cleaning blade 51 are provided. The contact area is reduced, and friction is effectively reduced.

  The irregularities on the surface of the photosensitive layer 1b of the photosensitive drum 1 are preferably present irregularly. Irregular means that the irregularity does not have a certain regularity when the irregularity is seen in any one direction within a certain plane. When there is no unevenness in a certain direction (there is no unevenness in design, but the case where there is actually a minute unevenness corresponds to an example where there is no unevenness) is irregular.

  In addition, the arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are preferably in the above ranges over the entire image forming area on the surface of the photosensitive drum 1.

(Configuration of the developing roller 25 used in the developing device 8)
Next, the developing roller 25 used in the developing device 8 will be described in detail. The developing roller 25 is formed in a hollow cylindrical shape with a metal such as aluminum or SUS. A magnetic pole member 26 (see FIG. 3) is included in the developing roller 25. When the developing roller 25 is made of aluminum, the surface of the developing roller 25 may be subjected to nickel (Ni) -chromium (Cr) plating treatment. By performing the plating treatment, the surface strength of the developing roller 25 is increased, and the generation of scratches and the scraping of the roller surface can be suppressed. In addition, it is possible to suppress the development history (ghost) from appearing as the afterimage of the immediately preceding image.

  Fine irregularities are formed by blasting on the outer peripheral surface of the developing roller 25 carrying the developer, and the surface roughness Ra of the developing roller 25 is a value that satisfies the relational expression of 20 nm ≦ Ra ≦ 100 nm. . By using the developing roller 25 having a relatively small surface roughness Ra of 20 nm ≦ Ra ≦ 100 nm, friction between the developing roller 25 and the developer is likely to occur, and the developer is brought to a necessary charge amount by the rotation of the developing roller 25. It can be charged quickly. Further, since a short magnetic brush can be formed on the developing roller 25, a high-definition image can be formed. The surface roughness Ra (nm) of the developing roller 25 can be measured using, for example, Surfcom 5000DX manufactured by Tokyo Seimitsu Co., Ltd.

  By the way, when the developing roller 25 having a small surface roughness Ra is used, since the toner transportability is low, the friction frequency between the developing roller 25 and the toner increases. As a result, the toner is overcharged and fog is likely to occur.

  Therefore, in the image forming apparatus 100 of the present embodiment, the developing roller 25 having a surface roughness Ra of 20 nm ≦ Ra ≦ 100 nm is used in combination with the photosensitive drum 1 having an arithmetic surface roughness Ra of the photosensitive layer 1b of 40 nm to 70 nm. Thus, the contact area of the toner with respect to the surface of the photosensitive layer 1b is reduced, and the adhesion force of the toner to the photosensitive drum 1 can be reduced. As a result, surplus developer (fogging toner) on the photosensitive drum 1 can be efficiently collected on the developing roller 25 by the AC bias applied to the developing roller 25, and the generation of fog can be effectively suppressed. it can.

  In the magnetic one-component development method, the method of regulating the thickness of the toner layer on the developing roller 25 uses a magnetic metal member as the regulating blade 29 as in the present embodiment, and faces the developing roller 25 in a non-contact manner. And a method of using a rubber member as the regulating blade 29 and bringing it into contact with the developing roller 25. When a configuration in which the magnetic metal regulating blade 29 is opposed to the developing roller 25 in a non-contact manner, electric charges are injected from the regulating blade 29 to the toner.

  In the case of the magnetic one-component development method, since the magnetic pole member 26 in the developing roller 25 has no separation pole, the charged toner is not separated from the developing roller 25 and the overcharged toner continues to exist on the developing roller 25. . Therefore, the present invention is particularly effective in a magnetic one-component developing system using a magnetic metal regulating blade 29.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, a monochrome printer has been described as an example of the image forming apparatus 100. However, the image forming apparatus 100 can be applied to, for example, a tandem type or rotary type color printer. Further, the present invention can also be applied to an image forming apparatus such as a copying machine, a facsimile, or a multifunction machine having these functions. However, it is necessary to include the photosensitive drum 1 and the one-component developing type developing device 8. Further, it is preferable to have a cleaning blade 51 as a means for cleaning the photosensitive drum 1.

  The photosensitive drum 1 in the above embodiment uses the cylindrical element tube 1a as a support, but may use a support of another shape. Other shapes may be a plate shape or an endless belt shape. In the above-described embodiment, the photosensitive drum 1 uses amorphous silicon as the photosensitive layer 1b. However, for example, the photosensitive drum 1 may include a charge injection blocking layer that blocks injection of charges from the support. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

  The relationship between the surface roughness of the photosensitive drum 1 and the developing roller 25 and the cleaning property was investigated. As a test method, the arithmetic average roughness Ra of the photosensitive layer 1b and the Ra of the developing roller 25 are changed, and a test image (half image) with a printing rate of 20% in a low temperature and low humidity environment (10 ° C., 10%) is 100 k. Printed continuously. The image was observed visually for the occurrence of vertical streaks due to slipping of the external additive, and when vertical streaks were observed, it was confirmed by collating with the attachment position of the external additive on the surface of the charging roller 41. The observation was performed every predetermined number of sheets, and the final judgment was made at the end of printing 100k sheets. The case where slip-through of the external additive was not recognized was evaluated as ◯, and the case where slip-through was observed was rated as x.

  The test conditions were a photosensitive drum 1 in which an amorphous silicon photosensitive layer was formed as a photosensitive layer 1b on the outer peripheral surface of an aluminum tube 1a, and Ra of the photosensitive layer 1b was 30 nm, 40 nm, 55 nm, 70 nm, and 80 nm. . Further, the developing roller 25 having the surface of the aluminum sleeve subjected to Ni—Cr plating treatment is used. / Sec. Further, a positively chargeable toner having an average particle diameter of 6.8 μm and a charge attenuation coefficient of 0.05 was used. As the cleaning blade 51, a urethane rubber blade having a length (free length) from the base end portion to the tip end portion of 11.0 mm and a thickness of 2.0 mm is used, and the angle with respect to the outer peripheral surface of the photosensitive drum 1 is 24. °, the biting amount was set to 1.2 mm, and the linear pressure was set to 20.0 N / m. The results are shown in Table 1.

  As is apparent from Table 1, the external additive slipped out when the Ra of the photosensitive layer 1b was 30 nm and 80 nm, regardless of the size of Ra of the developing roller 25. This is because when the Ra of the photosensitive layer 1b is 30 nm or less, the frictional force between the cleaning blade 51 and the photosensitive layer 1b increases, so that the cleaning blade 51 is worn or lost due to long-term use. It is thought that the amount of the external additive slipping through the gap with 1 increases. On the other hand, when the Ra of the photosensitive layer 1b is 80 nm or more, the external additive enters the concave portion of the photosensitive layer 1b, so that it is considered that the amount of the external additive slipping through the gap between the cleaning blade 51 and the photosensitive drum 1 increases.

  The relationship between the surface roughness of the photosensitive drum 1 and the developing roller 25 and the occurrence of fog was investigated. As a test method, Ra of the photosensitive layer 1b and Ra of the developing roller 25 were changed, and 100k test images (half images) having a printing rate of 8% were continuously printed in a low temperature and low humidity environment (10 ° C., 10%). . The density (FD; fog density) of the white background portion was measured using a reflection densitometer, and it was determined that fog occurred when the density was equal to or higher than the target value (0.1). Other test conditions were the same as in Example 1. The results are shown in Table 2.

  As is apparent from Table 2, the fog density (FD) becomes 0.1 or more when the Ra of the developing roller 25 is 15 nm and 105 nm regardless of the Ra size of the photosensitive layer 1b, and fog occurs. did. This is because when the Ra of the developing roller 25 is less than 20 nm, the toner holding force by the developing roller 25 increases. As a result, the friction frequency between the toner and the developing roller 25 when the magnetic brush passes through the regulating blade 29 is increased, and the ratio of the overcharged toner is increased, so that fog is likely to occur. On the other hand, when the Ra of the developing roller 25 exceeds 100 nm, the toner holding force by the developing roller 25 becomes small. As a result, the friction between the toner and the developing roller 25 when the magnetic brush passes the regulating blade 29 is reduced, and the ratio of the toner having a low charge amount or the reversely charged toner is increased, so that fog is likely to occur. .

  From the results of Tables 1 and 2, the Ra of the photosensitive layer 1b of the photosensitive drum 1 is set to 40 nm to 70 nm and the Ra of the developing roller 25 is set to 20 nm to 100 nm, thereby causing fogging and slipping of the external additive. It was confirmed that both of the image defects due to the image can be effectively suppressed.

  The present invention can be used in an image forming apparatus including a magnetic one-component developing system using magnetic toner. To provide an image forming apparatus capable of suppressing occurrence of fog due to overcharging or insufficient charging of toner regardless of the use environment, and suppressing image defects caused by slipping of external additives, regardless of the use environment. Can do.

1 Photosensitive drum (image carrier)
1a Element tube (support)
1b Photosensitive layer 8 Developing device 25 Developing roller (developer carrier)
29 Regulation blade (regulation member)
41 Charging roller (charging member)
51 Cleaning blade (cleaning member)
90 Magnetic toner 100 Image forming apparatus

Claims (3)

An image carrier having a support and an amorphous silicon photosensitive layer formed on the surface of the support;
A developer carrier that is disposed opposite to the image carrier and carries a magnetic one-component developer composed of only a magnetic toner; and a developer carrier that is disposed at a predetermined interval with respect to the developer carrier. A metal regulating member for regulating the layer thickness of the magnetic one-component developer carried on the developing device, and a developing device having
In an image forming apparatus comprising:
The arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use is in the range of 40 nm to 70 nm, and the arithmetic average roughness Ra of the surface of the developer carrying member is in the range of 20 nm to 100 nm. An image forming apparatus.   The image forming apparatus according to claim 1, further comprising a cleaning member that is disposed in contact with the surface of the image carrier and that cleans the surface of the image carrier.   The image forming apparatus according to claim 1, further comprising a charging member that is disposed in contact with or close to the surface of the image carrier and charges the image carrier.

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