JP2018109720A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of forming a high-definition image by using a carrier having a small surface roughness and suppressing carrier development from a developer carrier to an image carrier. An image forming apparatus includes 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 has a developer carrying body disposed opposite to the image carrying body, and develops the image carrying body and the development using a magnetic brush formed on the developer carrying body with a two-component developer containing toner and carrier. The electrostatic latent image on the image carrier is developed into a toner image in the development area where the agent carrier is opposed. The arithmetic average roughness Ra of the photosensitive layer surface in the initial use is in the range of 40 nm to 70 nm, and the arithmetic average roughness Ra of the carrier surface is in the range of 1.0 μm to 3.0 μm. [Selection] 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 roughly classified into two-component developers composed of toner and magnetic carrier, and one-component developers composed only of magnetic toner. In the two-component development method using a two-component developer, the direction in which toner fog is suppressed (opposite polarity with respect to the toner) in a region (development region) facing the photosensitive drum (image carrier) and the development roller (developer carrier). ) Electric field. At this time, so-called carrier development in which the carrier in the magnetic brush (carrier chain) carried on the developing roller moves to the photosensitive drum is likely to occur. Since the carrier once transferred to the photosensitive drum has strong adhesion, it is output to the print image without returning to the developing roller side, and appears as a white spot or a black spot.

  On the other hand, by making the surface roughness of the carrier small and uniform, the stirring performance is improved and the magnetic brush is stably formed, so that a high-definition image can be obtained. Therefore, as described in Patent Document 1, a carrier having a surface roughness of 0.5 μm or more and 1.0 μm or less is often used.

JP 2012-168284 A

  However, when a uniform carrier having a small surface roughness as in Patent Document 1 is used, there is a problem in that the adhesion force to the photosensitive drum increases and image defects are likely to occur due to carrier development. .

  In view of the above problems, the present invention can suppress carrier development from a developer carrier to an image carrier while forming a high-definition image by using a carrier having a small surface roughness in the two-component development method. An object of the present invention is to provide a simple image forming apparatus.

  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 has a developer carrying body disposed opposite to the image carrying body, and develops the image carrying body and the development using a magnetic brush formed on the developer carrying body with a two-component developer containing toner and carrier. The electrostatic latent image on the image carrier is developed into a toner image in the development area where the agent carrier is opposed. The arithmetic average roughness Ra of the photosensitive layer surface in the initial use is in the range of 40 nm to 70 nm, and the arithmetic average roughness Ra of the carrier surface is in the range of 1.0 μm to 3.0 μm.

  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, the arithmetic average roughness Ra of the surface of the amorphous silicon photosensitive layer in the initial use is 40 nm to 70 nm, and the surface arithmetic average roughness Ra is 1.0 μm to 3 μm. By using together with a two-component developer containing a carrier of 0.0 μm or less, it is possible to suppress carrier development by reducing the adhesion of the carrier to the surface of the photosensitive layer and to maintain the chargeability of the toner. Occurrence of image defects due to slipping of the additive can also be 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. Graph showing relationship between surface roughness Ra of photosensitive layer 1b and carrier and carrier development Graph showing the relationship between carrier surface roughness and toner charge

  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 two-component developer (hereinafter simply referred to as a developer) composed of toner and a magnetic carrier, and agitates and conveys the developer. The first stirring screw 23 and the second stirring screw 24, the developing roller 25, and the regulation 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 charge the developer by stirring and mixing the developer and causing the toner and the carrier to rub. The detailed configuration of the two-component developer used in the present invention will be described later.

  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).

  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, and is arranged at a predetermined interval from the developing roller 25 so as to be supplied to the photosensitive drum 1. Regulate the amount of toner. 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.

  On the bottom surface of the second transfer chamber 22c facing the second agitating screw 24, a toner concentration sensor (see FIG. 5) for detecting the toner concentration T / C (ratio of toner to carrier) in the developer stored in the developing container 22. Not shown). In accordance with the detection result of the toner density sensor, the toner stored in the toner container 9 (see FIG. 1) passes through the toner replenishing port 22d provided in the upper part of the developing container 22, and the upstream end ( (See FIG. 4).

  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 bias voltage 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.

(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 at the initial stage of use is smaller than 40 [nm], the adhesion of the carrier to the photosensitive layer 1b increases, and image defects such as white spots and black spots due to carrier development occur. 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. For this reason, slipping of the external additive and contamination of the charging roller 41 due to the slipping of the external additive start from a relatively early stage of durable printing, and image defects such as vertical stripes due to uneven charging on the surface of the photosensitive drum 1 occur. The arithmetic average roughness Ra of the surface of the photosensitive layer 1b at the initial use of the photosensitive drum 1 is preferably in the range of 40 [nm] to 70 [nm].

  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.

(Characteristics of two-component developer used for developing device 8)
Next, the two-component developer composed of toner and carrier used in the developing device 8 will be described in detail. The toner is obtained by adding an external additive to toner base particles. The toner base particles contain a binder resin and a colorant. The toner base particles may contain a release agent, a charge control agent, magnetic powder and the like as necessary. The weight average particle diameter of the toner base particles is preferably 5 to 12 μm, and more preferably 6 to 10 μm. The weight average particle diameter of the toner base particles is measured by a particle size distribution measuring device (for example, Multisizer II type manufactured by Coulter, Inc.). The toner base particles are produced by a known method such as a pulverization classification method, a melt granulation method, a spray granulation method, or a polymerization method.

  Examples of the external additive include inorganic oxides such as silica, titanium oxide, and alumina, and metal soaps such as calcium stearate. The amount of the external additive is usually 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.

  Examples of the carrier include magnetic particles or resin particles in which a magnetic material is dispersed in a binder resin. Examples of magnetic materials include magnetic metals such as iron, nickel, cobalt, alloys thereof, alloys containing rare earths, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium Examples thereof include soft ferrites such as ferrite and lithium ferrite, iron-based oxides such as copper-zinc ferrite, and mixtures thereof.

  Examples of the binder resin include vinyl resins, polyester resins, epoxy resins, phenol resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, polyether resins, and mixtures thereof. Magnetic particles are produced by a known method such as a sintering method or an atomizing method. The surface of the carrier may be coated with a resin coating layer.

  The volume average particle diameter of the carrier is preferably 20 to 50 μm. By setting the volume average particle diameter of the carrier to 20 μm or more, a decrease in fluidity of the two-component developer is suppressed, the toner charge amount is not excessive, and density unevenness is suppressed. By setting the volume average particle size of the carrier to 50 μm or less, the specific surface area of the carrier is increased and the amount of toner that can be carried by the carrier is increased. Thereby, the toner density in the magnetic brush can be maintained in a high state, and the toner is sufficiently supplied to the developing roller 25, so that the thickness of the toner layer can be sufficiently secured. As a result, a sufficient amount of toner flying from the toner layer to the electrostatic latent image on the photosensitive drum 1 can be secured, image density reduction can be suppressed, and image density unevenness can be suppressed. Further, since the toner is sufficiently supplied to the developing roller 25, it is difficult to form a toner missing portion in the toner layer of the developing roller 25, and the occurrence of history development (ghost) is suppressed.

  The saturation magnetization of the carrier is preferably 30 eum / g to 90 eum / g. By setting the saturation magnetization of the carrier within the above range, it is possible to increase the strength of the magnetic brush and at the same time to reduce the magnetic brush resistance, and developability from the developing roller 25 to the photosensitive drum 1 and from the photosensitive drum 1. The toner recoverability to the developing roller 25 can be improved at the same time.

  In the present embodiment, a carrier having an arithmetic average roughness Ra of 1.0 μm or more and 3.0 μm or less is used. When Ra on the carrier surface is less than 1.0 μm, the adhesion force to the photosensitive drum 1 is increased and carrier development is likely to occur. When Ra on the carrier surface exceeds 3.0 μm, the coating layer formed on the carrier surface is easily peeled off, the charge amount is lowered, and the durability of the carrier is lowered.

  Ra of the carrier surface can be measured by observing the surface at a magnification of 1800 using, for example, a three-dimensional microscope (OPTELICS HYBRID MC2000, manufactured by Lasertec). A roughness curve is obtained from the observed three-dimensional shape of the carrier surface, and the absolute value (5 samples) in the reference length (7 μm) of the roughness curve is averaged.

  Further, when Ra on the carrier surface is small, the adhesion force to the photosensitive drum 1 is increased, and there is a possibility that carrier development from the developing roller 25 to the photosensitive drum 1 may occur. In this embodiment, the photosensitive layer 1b By using together with the photoreceptor drum 1 having Ra of 40 nm or more and 70 nm or less, the contact area of the carrier with the surface of the photosensitive layer 1 b is reduced, and the adhesion force of the carrier to the photoreceptor drum 1 can be reduced. As a result, even if the carrier moves from the developing roller 25 to the photosensitive drum 1, it can be easily returned to the developing roller 25 by the AC component of the developing bias, and the occurrence of carrier development is suppressed. Further, since the arithmetic surface roughness Ra of the photosensitive layer 1b is as extremely small as 40 nm or more and 70 nm or less, the cleaning failure due to the toner external additive slipping through the gap between the photosensitive layer 1b and the cleaning blade 51, and the charging roller 41 associated therewith. There is no pollution.

Further, when the photosensitive drum 1 having Ra of 40 nm or more and 70 nm or less and a carrier having an arithmetic average roughness Ra of 1.0 μm or more and 3.0 μm or less are used in combination, between the photosensitive drum and the developing roller (between DS) ) If the gap is too narrow, the texture of the image will be coarse, and if the gap between DSs is too wide, it will be easy to see pitch unevenness. Also, if the developer transport amount (magnetic brush weight per unit area) in the development area is too small, the gap between the magnetic brushes is widened and the texture of the image becomes rough. If the developer transport amount is too large, the gap between DS changes. It becomes easy to see the pitch unevenness because it is easily affected. Therefore, it is preferable that the DS gap is 200 to 500 μm and the developer transport amount in the development region is 20 to 40 mg / cm ² as development conditions.

  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 two-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 layer 1b of the photosensitive drum 1 and the surface roughness of the carrier and the carrier development was investigated. As a test method, the arithmetic average roughness Ra of the photosensitive layer 1b and the carrier was changed, and a lattice-shaped test image was developed on the photosensitive drum 1 and peeled off with an adhesive tape. The image peeled off with the tape was observed with a microscope, and the number of carriers developed on the image was measured. Then, when the number of carriers per 0.2 cm ^{2 of} the image was less than 0.85, it was evaluated as ◯, and when it was 0.85 or more, it was evaluated as x.

As test conditions, a photosensitive drum 1 having an amorphous silicon photosensitive layer formed as a photosensitive layer 1b on the outer peripheral surface of an aluminum tube 1a was used, and Ra of the photosensitive layer 1b was set to 40 nm ≦ Ra ≦ 70 nm. Further, the two-component developer comprises a positively chargeable toner having an average particle diameter of 6.8 μm, a carrier having a saturation magnetization of 30 to 90 emu / g, and an average particle diameter of 20 to 50 μm, and T / C (weight ratio of toner to carrier). ) 8% mixed and used. The developing conditions are as follows: the amount of magnetic brush in the developing region is 20 to 40 mg / cm ² , the gap between the photosensitive drum and the developing roller (between DS) is 200 to 500 μm, the DC component of the developing bias applied to the developing roller 25 is 300 V, and AC The peak-to-peak value of the component was 1500V. The results are shown in FIG.

  As is apparent from FIG. 5, when Ra on the carrier surface is less than 1.0 μm, carrier development occurred regardless of Ra of the photosensitive layer 1b. This is because when the Ra of the carrier decreases, the adhesion force of the carrier to the photosensitive drum 1 increases, and the carrier transferred to the photosensitive drum 1 is not collected by the developing roller 25. On the other hand, when Ra on the surface of the carrier exceeds 3.0 μm, the coating layer is easily peeled off, the charge amount is lowered, and the durability of the carrier is lowered. On the other hand, when the Ra of the photosensitive layer 1b is less than 40 nm, carrier development occurs even if the Ra of the carrier surface is 1.0 μm or more, and when the Ra of the photosensitive layer 1b exceeds 70 nm, the carrier development is suppressed. A problem due to slipping of the toner external additive from the cleaning blade 51 occurred. Therefore, by setting the Ra of the photosensitive layer 1b to 40 nm ≦ Ra ≦ 70 nm and the Ra of the carrier surface within the range of 1.0 μm ≦ Ra ≦ 3.0 μm (hatched region in FIG. 5), the durability of the carrier and the cleaning blade 51 are improved. It was confirmed that carrier development can be suppressed while maintaining the cleanability by the above.

  The relationship between the surface roughness of the carrier and the charge amount of the toner was investigated. As a test method, 10 k (10000) test images having a printing rate of 10% were continuously printed in a normal temperature and humidity environment (25 ° C., 50%) by changing the charge attenuation coefficient of the toner. The toner charge amount (Q / M) per unit weight after printing 10k sheets was measured with a QM meter (MODEL210HS, manufactured by TREK). When T / C * Q / M was 150 or less, it was determined that the charge amount was insufficient. . Test conditions and development conditions were the same as in Example 1. The results are shown in FIG.

  As is clear from FIG. 6, T / C * Q / M was below the target value (150) when Ra of the carrier exceeded 3.0 μm. This is because when the Ra of the carrier increases, the coat layer on the carrier surface is easily peeled off, and the charging performance decreases as the durable printing proceeds.

  The relationship between the surface roughness of the photosensitive layer 1b of the photosensitive drum 1 and the cleaning property was evaluated. As a test method, the Ra of the photosensitive layer 1b was changed to 36 μm, 45 μm, 56 μm, 64 μm, 75 μm, and 82 μm, and a test image (half image) with a printing rate of 20% in a low temperature and low humidity environment (10 ° C., 15%). 20k (20000) sheets were continuously printed. The occurrence of vertical streaks due to slipping of the external additive was visually observed, 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. Observation was performed by outputting a test image every 1k (1000) sheets, and a final judgment was made when printing of 20k sheets was completed. The case where no vertical streak occurred at the end of durable printing (after printing 20k sheets) was marked with ◯, and the case where the vertical streak occurred before the end of durable printing was marked with x. The results are shown in Table 1.

  As is apparent from Table 1, when the Ra of the photosensitive layer 1b is greater than 70 nm, vertical stripes due to poor cleaning occurred. This is because when the Ra of the photosensitive layer 1 b increases, the external additive slips through the gap between the cleaning blade 51 and the photosensitive layer 1 b, and the external additive adheres to the charging roller 41 and the surface of the photosensitive drum 1. This is because uneven charging occurs.

  From the results of Examples 1 to 3, by combining the photosensitive drum 1 in which the Ra of the photosensitive layer 1b is 40 nm or more and 70 nm or less and a two-component developer containing a carrier in which Ra is 1.0 μm or more and 3.0 μm or less. It has been confirmed that carrier development does not occur over a long period of time, the chargeability of the toner is improved, and image defects due to slipping of the external additive can be suppressed.

  The relationship between the volume average particle diameter of the carrier, the saturation magnetization, the gap between DS and the developer transport amount, the texture of the image, the pitch unevenness, and the carrier development was investigated. Regarding carrier development, carrier development was evaluated in the same manner as in Example 1. For image texture and pitch unevenness, any one of carrier volume average particle diameter, saturation magnetization, gap between DS and developer transport amount is changed, and it is in a normal temperature and humidity environment (25 ° C., 50%). The test image (half image) with a printing rate of 10% was continuously printed on 10k (10000) sheets. The pitch unevenness and fineness of the image were observed visually for every 1k (1000) sheets.

The evaluation criteria for carrier development are ◎, when the number of carriers per 0.2 cm ^{2 of} image is less than 0.1 over the entire period of durable printing, 0.1 or more and less than 0.2. The case was O, the case of 0.2 or more and less than 0.85 was Δ, and the case of 0.85 or more was ×. For the texture of the image, compare the texture of the image (with roughness) with the reference image, ◎ if the texture is very fine over the entire period of durable printing, ◎ if the texture is fine, ○ if the texture is slightly rough Δ, when the texture is rough, it was marked as x. As for pitch unevenness, ◎ indicates that no pitch unevenness has occurred over the entire period of durable printing, ◯ indicates that there is very little pitch unevenness, △ indicates that there is slight visible pitch unevenness, and Δ indicates that pitch unevenness is present. The case where it generate | occur | produced notably was set as x. The results are shown in Tables 2-5.

From the results of Example 4, when the photosensitive drum 1 having a Ra of the photosensitive layer 1b of 40 nm or more and 70 nm or less and the two-component developer containing a carrier of Ra of 1.0 μm or more and 3.0 μm or less are combined, Carrier development can be performed over a long period of time by setting the volume average particle size to 20 to 50 μm, the saturation magnetization to 30 to 90 emu / g, the DS gap to 200 to 500 μm, and the developer transport amount to 20 to 40 mg / cm ^2. It was confirmed that no toner was generated, the chargeability of the toner was good, and image defects due to slipping of the external additive could be suppressed.

  The present invention can be used for an image forming apparatus including a two-component developing type developing device using a two-component developer including a toner and a carrier. By using the present invention, an image forming apparatus capable of suppressing carrier development from a developer carrier to an image carrier while forming a high-definition image by using a carrier having a small surface roughness is provided. it can.

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

Claims (6)

An image carrier having a support and an amorphous silicon photosensitive layer formed on the surface of the support;
The image carrier and the development using a magnetic brush having a developer carrier disposed opposite to the image carrier, and formed on the developer carrier with a two-component developer including a toner and a carrier. A developing device that develops the electrostatic latent image on the image carrier into a toner image in a development region facing the agent carrier;
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 carrier surface is in the range of 1.0 μm to 3.0 μm. An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the carrier has a volume average particle diameter of 20 to 50 μm and a saturation magnetization of 30 to 90 eum / g. 3. The image forming apparatus according to claim 1, wherein a weight of the magnetic brush per unit area in the developing region is 20 to 40 mg / cm ^{2. 4} .   4. The image forming apparatus according to claim 1, wherein an interval between the image carrier and the developer carrier in the development region is 200 to 500 [mu] m.   5. 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. 6.   6. 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.