JP2012118449A - Charging member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging member capable of uniformly charging a surface of a photosensitive body without using an additional member and without being affected by residual potential.SOLUTION: A conductive elastic layer 72 and a surface layer 73 are provided in this order on a circumference of a conductive base 71. Fine particles 74 in the shape of a spindle, a cylinder or a needle are involved in the surface layer 73 so as to cause irregularities derived from the fine particles 74, and the fine particles 74 are aligned so as to have their major axis direction substantially according with the normal direction of the conductive base 71. From the viewpoint of further improvement of uniform charging properties, the fine particles 74 have a major axis of preferably 15 μm to 20 μm, a minor axis of preferably 3 μm to 6 μm, and an aspect ratio (major axis/minor axis) of preferably 5 or less. Furthermore, the surface layer 73 has ten-point surface roughness Rz of preferably 10 μm to 20 μm, and an average distance Sm between the irregularities is preferably 10 μm to 20 μm.

Description

  The present invention relates to a charging member, and more particularly to a charging member that is in pressure contact with an electrostatic latent image carrier such as a photoconductor and uniformly charges the surface of the electrostatic latent image carrier by applying a predetermined voltage. .

  In an image forming apparatus using an electrophotographic system such as a facsimile, a printer, or a copying machine, the surface of a photoconductor (electrostatic latent image carrier) is uniformly charged to a predetermined potential, and then the photoconductor surface is exposed to form an image. An electrostatic latent image corresponding to the information is formed. The formed electrostatic latent image is developed with toner by a developing device to form a visible image. Next, after the toner image on the surface of the photoreceptor is transferred onto the paper directly or via an intermediate transfer mechanism, the toner image is melted and fixed on the paper by heating and pressing.

  Here, the charging member that uniformly charges the surface of the photosensitive member is roughly classified into a contact charging method that contacts and charges the photosensitive member and a non-contact method that charges the photosensitive member by corona discharge. In recent years, the contact charging method has been widely used due to the small amount of ozone generation and low power consumption.

  In the contact charging method, a voltage is applied to the conductive substrate using a charging roller in which a conductive elastic layer and a resistance layer are laminated in this order on the outer periphery of a conductive support, and the nip between the charging roller and the photosensitive member is used. In this method, the surface of the photosensitive member is charged by causing a minute discharge in the vicinity of the portion. The voltage application method to the charging roller includes an alternating voltage application and a direct current voltage application. The direct current voltage application method is attracting attention because it consumes less power and can be miniaturized.

  However, in the DC voltage application method, it is important to complete charging at the upstream side in the rotation direction of the charging roller at the nip portion between the charging roller and the photosensitive member. However, the DC voltage application method is different from the AC voltage application method. The discharge area is narrow, and the surface potential of the photoreceptor may not reach the desired potential. If the surface potential of the photoconductor does not reach the desired potential on the upstream side in the rotation direction of the charging roller at the nip portion between the charging roller and the photoconductor, abnormal discharge occurs on the downstream side in the rotation direction of the charging roller in the nip portion. It became easy and uniform charge could not be obtained. In addition, the DC voltage application method is easily affected by the residual potential difference between the image area after image transfer and the non-image area on the surface of the photoconductor, and the photoconductor may be charged unevenly by the charging roller. In order to eliminate the influence of the residual potential difference on the surface of the photoconductor, it is sufficient to irradiate the entire photoconductor with light before charging by the charging roller to reduce the overall surface potential. This is newly required and goes against the reduction in size and weight of the device and power saving.

  Thus, for example, a technique has been proposed in which fine unevenness is provided on the surface of the charging roller to make the surface of the photosensitive member uniform (see, for example, Patent Documents 1 and 2).

JP 2009-9057 A JP 2009-9029 A

  However, even with the proposed technique, the charging performance of the charging roller that is still satisfactory cannot be obtained.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a charging member that can uniformly charge the surface of the photoreceptor without being affected by the residual potential without adding a new member. There is to do.

  The charging member according to the present invention that achieves the above object includes a conductive substrate, a conductive elastic layer formed on the conductive substrate, and a surface layer formed on the conductive elastic layer, and the surface layer is a spindle. Containing fine particles in the shape of a cylinder, cylinder, or needle, having irregularities derived from the fine particles, and the fine particles are oriented so that the major axis direction thereof is substantially normal to the conductive substrate It is characterized by. In the present specification, the “substantially normal direction” refers to a direction including a range of ± 5 ° from the normal direction.

  Here, from the viewpoint of further improving the uniform chargeability, the major axis of the fine particles is in the range of 15 μm to 20 μm, the minor axis is in the range of 3 μm to 6 μm, and the aspect ratio (major axis / minor axis) is 5 or less. Preferably there is.

  Further, the ten-point surface roughness Rz of the surface layer is preferably in the range of 10 μm to 20 μm, and the average interval Sm of the irregularities is preferably in the range of 10 μm to 20 μm.

  In addition, according to the present invention, there is provided an image forming apparatus comprising any one of the charging members described above.

  In the charging member according to the present invention, spindle-shaped, columnar, or needle-shaped microparticles are included in the surface layer to form irregularities derived from the microparticles, and the major axis direction of the microparticles is substantially the same as that of the conductive substrate. Since the fine particles are oriented in the linear direction, the surface of the photoreceptor can be uniformly charged without being affected by the residual potential even when a DC voltage is applied.

  According to the image forming apparatus of the present invention, it is possible to reduce the size and weight and save power, and to obtain a high-quality image free from density unevenness and minute noise over a long period of time.

1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. It is a vertical sectional view showing an example of a charging roller according to the present invention. FIG. 3 is an enlarged cross-sectional view of a surface layer portion of the charging roller in FIG. 2.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention. The image forming apparatus D in FIG. 1 is a so-called tandem color printer. Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. Further, the image forming method is not limited to the tandem method, and other methods, for example, four developing devices are arranged around the rotation shaft, and these are sequentially opposed to the electrostatic latent image carrier to be full color. A so-called four-cycle method of creating an image or a monochrome method of creating a monochrome image with one developing device may be used.

  The image forming apparatus D includes an endless intermediate transfer belt 33 having conductivity. The intermediate transfer belt 33 is hung on a pair of rollers 31 and 32 disposed on both the left and right sides in the drawing. The roller 32 is connected to a motor (not shown), and the roller 32 rotates counterclockwise by driving the motor, whereby the intermediate transfer belt 33 and the roller 31 in contact therewith are driven to rotate. A secondary transfer roller 34 is in pressure contact with the outside of the belt portion supported by the roller 32. The toner image formed on the intermediate transfer belt 33 at the nip portion (secondary transfer region) between the secondary transfer roller 34 and the intermediate transfer belt 33 is transferred onto the conveyed paper P.

  A cleaning blade 92 that cleans the surface of the intermediate transfer belt 33 is provided outside the belt portion supported by the roller 31. The cleaning blade 92 removes and collects untransferred residual toner at a contact portion with the intermediate transfer belt 33.

  Below the intermediate transfer belt 33 suspended between the rollers 31 and 32, yellow (Y), magenta (M), cyan (C), black ( K) four image forming units 2Y, 2M, 2C, and 2K (hereinafter may be collectively referred to as “image forming unit 2”) are detachably arranged with respect to the apparatus main body 10. In these image forming units 2, corresponding color toner images are created using the respective color developers.

  The image forming unit 2 includes a cylindrical photoconductor 20 as an electrostatic latent image carrier. Around the photoreceptor 20, a charging roller (charging member) 7, a developing device 23, a primary transfer roller 24, and a cleaning blade 62 are arranged in this order along the rotation direction (clockwise direction). Then, one end side of the cleaning blade 62 comes into contact with the outer peripheral surface of the photoconductor 20, and the toner remaining on the surface of the photoconductor 20 is removed and collected. The primary transfer roller 24 is in pressure contact with the photoconductor 20 with the intermediate transfer belt 33 interposed therebetween to form a nip portion (primary transfer region). An exposure device 22 is disposed below the image forming unit 2. As will be described later, the charging roller 7 is a roller charging system.

  Above the intermediate transfer belt 33, hoppers 4Y, 4M, 4C, and 4K (hereinafter sometimes collectively referred to as “hopper 4”) containing toner to be supplied to the developing devices 23 of the respective colors are arranged. A paper feed cassette 50 is detachably disposed as a paper feed device below the exposure device 22. The sheets P stacked and accommodated in the sheet cassette 50 are sent out one by one to the conveyance path in order from the uppermost sheet by the rotation of the sheet feed roller 51 disposed in the vicinity of the sheet cassette 50. The paper P sent out from the paper feed cassette 50 is conveyed to the registration roller pair 52 and is sent out to the secondary transfer area at a predetermined timing.

  The image forming apparatus D can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners.

  An image forming operation example in the color mode will be briefly described. First, in each image forming unit 2, the outer peripheral surface of the photoconductor 20 that is rotationally driven at a predetermined peripheral speed is charged by the charging roller 7. Next, light corresponding to image information is projected from the exposure device 22 on the surface of the charged photoconductor 20 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by toner as a developer supplied from the developing device 23. When the toner image of each color formed on the surface of the photoreceptor 20 in this way reaches the primary transfer region by the rotation of the photoreceptor 20, the toner image is transferred from the photoreceptor 20 to the intermediate transfer belt in the order of yellow, magenta, cyan, and black. 33 is transferred (primary transfer) and superimposed.

  Residual toner remaining on the photoconductor 20 without being transferred to the intermediate transfer belt 33 is scraped off by the cleaning blade 62 and removed from the outer peripheral surface of the photoconductor 20.

  The superimposed four color toner images are conveyed to the secondary transfer region by the intermediate transfer belt 33. On the other hand, the paper P is conveyed from the registration roller pair 52 to the secondary transfer area in accordance with the timing. Then, the four color toner images are transferred (secondary transfer) from the intermediate transfer belt 33 to the paper P in the secondary transfer region. The paper P on which the four color toner images are transferred is conveyed to the fixing device 1. In the fixing device 1, the paper P passes through the nip portion between the fixing roller 11 and the pressure roller 12. During this time, the paper P is heated and pressurized, and the toner image on the paper P is melted and fixed on the paper P. The paper P on which the toner image is fixed is discharged to a paper discharge tray 54 by a discharge roller pair 53.

  On the other hand, residual toner remaining on the intermediate transfer belt 33 without being transferred onto the paper P is scraped off by the cleaning blade 92 and removed from the outer peripheral surface of the intermediate transfer belt 33. Thereafter, the rotational drive of each photoconductor 20 and the intermediate transfer belt 33 is stopped.

  FIG. 2 shows a cross-sectional configuration diagram of the charging roller 7. The charging roller 7 in this figure includes a cylindrical conductive substrate 71, a conductive elastic layer 72 formed on the outer periphery thereof, and a surface layer 73 formed on the outer periphery of the conductive elastic layer 72.

  The material of the conductive substrate 71 may be conductive, and examples thereof include metal materials such as iron, copper, stainless steel, aluminum, and nickel. In addition, the conductive substrate 71 may be subjected to a surface treatment such as plating that enhances scratch resistance and rust prevention as long as the conductivity is not impaired. The shape of the conductive substrate 71 is not limited to a columnar shape, and may be a cylindrical shape or an endless belt shape.

  The conductive elastic layer 72 has conductivity and elasticity. For example, a conductive elastic layer dispersed in a polymer elastic body is preferably used. Examples of the polymer elastic body include EPDM rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, chloroprene, silicone rubber, acrylic rubber, nitrile rubber, urethane rubber, acrylonitrile-butadiene rubber, and epichlorohydrin rubber. Examples of the conductive agent include carbon black, graphite, conductive titanium oxide, conductive tin oxide, copper powder, silver powder, and conductive fiber.

The volume resistivity of the conductive elastic layer 72 is usually preferably in the range of 10 ² Ω · cm to ^{10 10} Ω · cm, and the volume resistivity can be adjusted depending on the type and amount of the conductive agent to be dispersed.

  The hardness of the conductive elastic layer 72 is preferably in the range of 30 to 80 degrees, and can be adjusted by the amount of softening oil or plasticizer added.

  Although there is no limitation in particular as the layer thickness of the electroconductive elastic layer 72, Usually, the range of 0.5 mm-5 mm is suitable.

  The conductive elastic layer 72 may be formed, for example, by coating the outer periphery of the conductive substrate after mixing raw materials such as a polymer elastic body and a conductive agent. Alternatively, the conductive elastic layer may be separately formed by extrusion molding or the like and then fitted into the conductive substrate.

  The conductive elastic layer 72 may be blended with additives such as fillers, softeners, plasticizers, and vulcanization retarders as long as the above properties are not impaired.

  In FIG. 3, the partial expanded sectional view of the surface layer 73 is shown. The surface layer 73 is formed by dispersing and mixing fine particles 74 in a binder resin. Unevenness derived from fine particles is formed on the surface of the surface layer. As the binder resin, for example, those having a surface protection function such as a fluororesin, a silicone resin, an acrylic resin, and an amide resin are preferably used.

  The fine particles 74 are either spindle-shaped, cylindrical, or needle-shaped. The major axis is preferably in the range of 15 μm to 20 μm, the minor axis is preferably in the range of 3 μm to 6 μm, and the aspect ratio (major axis / minor axis) is 5 or less. Is preferred. The material of the fine particles 74 may be any of an organic material, an inorganic material, and a metal material.

  In the charging roller according to the present invention, it is important that the fine particles 74 contained in the surface layer 73 are oriented so that the major axis direction is substantially normal to the conductive substrate 71. As a result, the discharge point of the charging roller 7 can be increased, and the photosensitive member 20 can be charged not only on the upstream side in the charging roller rotation direction but also on the downstream side of the nip portion between the charging roller 7 and the photosensitive member 20, At the same time, abnormal discharge can be suppressed.

  In order to align the fine particles 74 such that the major axis direction is substantially normal to the conductive substrate 71, a conventionally known method can be used. For example, after applying a magnetic material to the tip of one side in the major axis direction of the fine particles 74, a paint mixed with the fine particles 74 and a binder resin is applied to the outer periphery of the conductive elastic layer 72 and simultaneously applied to the conductive substrate 71. Magnetic field lines are formed so as to be in the normal direction, and the long diameter direction of the fine particles 74 is oriented so as to be substantially normal to the conductive substrate 71. Alternatively, the fine particles 74 are used as a dielectric, an electric field is formed so as to be in a normal direction with respect to the conductive substrate 71, and the long diameter direction of the fine particles 74 is aligned in a substantially normal direction with respect to the conductive substrate 71. To do.

  The surface layer 73 is formed by, for example, preparing a paint by dispersing fine particles 74 in a binder resin and forming it on the outer periphery of the conductive elastic layer 72 by a conventionally known method such as a dipping method or a coating method. As a layer thickness of the surface layer 73, the range of 15 micrometers-100 micrometers is preferable normally, and the range of 20 micrometers-50 micrometers is more preferable. The layer thickness of the surface layer 73 refers to the length from the boundary surface with the conductive elastic layer 72 to the apex of the convex portion of the surface layer 73.

  The ten-point surface roughness Rz of the surface layer 73 is preferably in the range of 10 μm to 20 μm. By adjusting the convex portion of the surface layer 73 to a height in this range by the fine particles 74, discharge can be effectively generated and the surface of the photoreceptor 20 can be uniformly charged. Moreover, the average interval Sm of the irregularities is preferably in the range of 10 μm to 20 μm. By adjusting the concave / convex formation interval Sm within this range, a sufficient number of discharge points and a space necessary for discharge are secured, and the surface of the photoconductor 20 can be uniformly charged. The 10-point surface roughness Rz is a value measured according to JIS B0601.

Examples 1-6
A charging roller having the structure shown in FIG. 2 and having spindle-shaped fine particles having a major axis and a minor axis shown in Table 1 oriented on the surface layer of the charging roller so that the major axis direction is normal to the conductive substrate. Were used to apply an AC voltage (maximum 1 kV, amplitude 1 kV, frequency 1 kHz) and DC voltage (1 kV) to charge the photoconductor in contact. Then, a halftone (halftone dot) electrostatic latent image was formed by an exposure device and developed with toner. Next, the developed image was compared with a predetermined reference sample to evaluate its roughness. The results are shown in Table 1.

  As can be understood from Table 1, in the charging rollers of Examples 1 to 5 which are charging members according to the present invention, not only when an AC voltage is applied, but also when a DC voltage is applied, the photosensitive member is used. Uniform charging was possible.

  The charging member of the present invention is useful because the surface of the photoreceptor can be uniformly charged without being affected by the residual potential without adding a new member.

7 Charging roller (charging member)
D Image forming apparatus 71 Conductive substrate 72 Conductive elastic layer 73 Surface layer 74 Fine particles

Claims (4)

A conductive base, a conductive elastic layer formed on the conductive base, and a surface layer formed on the conductive elastic layer;
The surface layer contains spindle-shaped, columnar, or needle-shaped microparticles, has irregularities derived from the microparticles, and the microparticles are oriented so that the major axis direction is substantially normal to the conductive substrate. A charging member.   2. The charging member according to claim 1, wherein the fine particles have a major axis in the range of 15 μm to 20 μm, a minor axis in the range of 3 μm to 6 μm, and an aspect ratio (major axis / minor axis) of 5 or less.   3. The charging member according to claim 1, wherein a ten-point surface roughness Rz of the surface layer is in a range of 10 μm to 20 μm, and an average interval Sm of unevenness is in a range of 10 μm to 20 μm.   An image forming apparatus comprising the charging member according to claim 1.