JP2019061103A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that prevents the occurrence of oblique stripes on an image on the basis of the interference between a screen image and the cutting pitch of a developing roller.SOLUTION: An exposure device 323 forms an electrostatic latent image on a photoreceptor drum 321 with a screen image that is inclined with respect to a main scanning direction at a predetermined screen angle θ, the screen image formed with a predetermined screen line number X per one inch in the main scanning direction. A developing roller of a developing device 324 has cutting traces that extend along the circumferential direction and are formed at a predetermined pitch Y along the axial direction. The screen angle θ (degrees), the screen line number X (number of lines), and the pitch Y (μm) of the cutting traces satisfy the following relational expression: 25.4/X×0.9×cosθ<Y or Y>25.4/X×1.1×cosθ.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus for forming an image on a sheet.

  An image forming apparatus such as a copying machine, a printer, or a facsimile that uses an electrophotographic method includes a photosensitive drum, an exposure device, a developing device, and a transfer device. An electrostatic latent image is formed on the photosensitive drum, which has been charged to a predetermined potential in advance, by the exposure device irradiating exposure light corresponding to the image data. Further, a developer is supplied to the electrostatic latent image from the developing device to form a toner image on the image carrier.

  The exposure device forms, on the photosensitive drum, a screen image in which latent image dots are arranged adjacent to each other according to the image data. The screen ruling of the screen image and the screen angle are set in accordance with the required image quality.

  On the other hand, the developing device for supplying the developer to the photosensitive drum has a developing roller. The developing roller has a sleeve that is rotated about a predetermined rotation axis. Patent Document 1 discloses, as a method for manufacturing the sleeve, a technique in which the circumferential surface of a drawn aluminum tube is cut and then the circumferential surface is subjected to an alumite treatment or a resin coating treatment. By these processes, the developer is easily supported on the sleeve, and the toner is stably supplied from the developing roller to the photosensitive drum.

Patent No. 6053669

  In the technique described in Patent Document 1, the circumferential surface of the aluminum tube is cut by the cutting blade by moving the cutting blade in the axial direction at a predetermined speed while the aluminum tube is rotated at a predetermined rotation speed. . Under the present circumstances, according to the rotation period of an aluminum pipe, and the moving speed of a cutting blade, the unevenness (cutting mark) of minute cutting pitch is formed on the peripheral surface of an aluminum pipe. Then, when the cutting pitch on the developing roller and the pitch between dots in the main scanning direction in the screen image of the exposure device interfere with each other, there is a problem that an oblique streak image (interference fringe) is generated on the image.

  The present invention has been made to solve the problems as described above, and an image forming apparatus in which the generation of oblique streaks on an image is suppressed based on the interference between the screen image and the cutting pitch of the developing roller. Intended to be provided.

  An image forming apparatus according to one aspect of the present invention has a surface on which an electrostatic latent image is formed, and a photosensitive drum carrying a developer image on the surface, and the surface of the photosensitive drum having a predetermined potential. An exposure device for forming the electrostatic latent image by irradiating the surface of the photosensitive drum charged to the predetermined potential with exposure light according to image data; And a developing roller including a peripheral surface carrying the toner and rotated about a predetermined rotation axis, and supplying the developer to the surface of the photosensitive drum brings the electrostatic latent image to the developer image The exposure device is a screen image inclined at a predetermined screen angle θ with respect to the main scanning direction, and has a predetermined number X of screen lines per inch in the main scanning direction. Formed The electrostatic latent image is formed by a screen image, and the developing roller extends along the circumferential direction in the rotation of the developing roller on the circumferential surface and is predetermined along the axial direction of the rotation axis. That the screen angle θ (degree), the screen line number X (pieces) and the pitch Y (μm) of the cutting mark satisfy the following relational expression Image forming apparatus characterized by 25.4 / X × 0.9 × cos θ <Y or Y> 25.4 / X × 1.1 × cos θ

  According to this configuration, the generation of oblique streaks on the image is suppressed based on the interference between the screen image and the cutting pitch of the developing roller.

  In the above configuration, it is desirable that the developing roller has a circular tubular base and a resin coating layer formed on the base.

  According to this configuration, the development electric field is stably formed between the developing roller and the photosensitive drum by the resin coating layer. In addition, even when cutting marks formed on the circumferential surface of the substrate remain on the circumferential surface of the resin coating layer, diagonal streaks are generated on the image based on the interference between the screen image and the cutting pitch of the developing roller. It is deterred to do.

  In the above configuration, the substrate of the developing roller is made of aluminum, and the developing roller further includes an alumite layer formed on the substrate, and the resin coating layer is formed on the alumite layer. It is desirable that it is done.

  According to this configuration, peeling of the resin coating layer is suppressed by the alumite layer.

  In the above configuration, the developing device is rotated about a predetermined rotation axis with a developer storage portion storing the developer containing toner and a magnetic carrier, and receives the toner and the carrier from the developer storage portion. It is preferable to have a magnetic roller, and the developing roller that receives the toner from the magnetic roller and supplies the toner to the photosensitive drum.

  According to this configuration, even if the developing device has the magnetic roller and the developing roller and the touch-down developing method is adopted, the image is formed on the image based on the interference between the screen image and the cutting pitch of the developing roller. The occurrence of oblique streaks is suppressed.

  In the above configuration, it is desirable that the magnetic roller and the developing roller be rotated in opposite directions in the area facing each other.

  According to this configuration, the toner layer on the developing roller which has passed through the developing nip is separated from the developing roller by the mechanical scraping force of the magnetic brush on the magnetic roller and the potential difference between the magnetic roller and the developing roller. It is easily recovered on the roller side. For this reason, compared with the case where the magnetic roller and the developing roller are rotated in the same direction in the area facing each other, it is suppressed that a large cohesive force is given to the developer in the opposite area. On the other hand, in such a case, the cutting marks formed on the circumferential surface of the developing roller are not easily polished by the developer in the opposite region, and easily remain even after long-term use. Even in such a case, since the screen angle θ (degree), the number of screen lines X (pieces) and the pitch Y (μm) of cutting marks satisfy the predetermined relational expression, the cutting pitch of the screen image and the developing roller Generation of oblique streaks on the image based on the interference with

  In the above configuration, the developer layer on the developing roller may be in non-contact with the surface of the photosensitive drum.

  According to this configuration, the developer layer on the developing roller is not in contact with the surface of the photosensitive drum as in the known contact development method. Therefore, the minute distribution of the developer layer according to the cutting marks of the developing roller greatly affects the amount of toner flying to the photosensitive drum. Even in such a case, since the screen angle θ (degree), the number of screen lines X (pieces) and the pitch Y (μm) of cutting marks satisfy the predetermined relational expression, the cutting pitch of the screen image and the developing roller Generation of oblique streaks on the image based on the interference with

  According to the present invention, it is possible to provide an image forming apparatus in which the generation of oblique streaks on an image is suppressed based on the interference between the screen image and the cutting pitch of the developing roller.

FIG. 1 is a cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a developing device according to an embodiment of the present invention. It is a schematic diagram which shows a mode that cutting processing is given to the base material of the development roller which concerns on one Embodiment of this invention. It is a graph which shows the measurement result of the surface roughness of the surrounding surface of the development roller which concerns on one Embodiment of this invention. FIG. 7 is a schematic view showing a developing operation according to an embodiment of the present invention. FIG. 2 is an enlarged schematic view of an electrostatic latent image on a photosensitive drum according to an embodiment of the present invention. FIG. 2 is an enlarged schematic view of an electrostatic latent image on a photosensitive drum according to an embodiment of the present invention. It is a schematic diagram which shows a mode that the oblique line which is the subject of this invention appeared on the image.

  Hereinafter, embodiments of the present invention will be described in detail based on the drawings. FIG. 1 is a cross-sectional view showing an internal structure of an image forming apparatus 1 according to an embodiment of the present invention. Here, as the image forming apparatus 1, a complex machine provided with a printer function and a copying function is exemplified, but the image forming apparatus may be a printer, a copier, or a facsimile machine.

<Description of Image Forming Apparatus>
The image forming apparatus 1 includes an apparatus main body 10 having a substantially rectangular parallelepiped housing structure, and an automatic document feeder 20 disposed on the apparatus main body 10. Inside the apparatus body 10, a reading unit 25 for optically reading an original image to be copied, an image forming unit 30 for forming a toner image on a sheet, a fixing unit 60 for fixing the toner image on a sheet, and image formation A sheet feeding unit 40 for storing sheets conveyed to the unit 30 and a conveyance path 50 for conveying a sheet from the sheet feeding unit 40 or the sheet feeding tray 46 to the sheet discharge port 10E via the image forming unit 30 and the fixing unit 60 And a transport unit 55 having a sheet transport path forming a part of the transport path 50 therein.

  An automatic document feeder (ADF) 20 is rotatably attached to the upper surface of the apparatus main body 10. The ADF 20 automatically feeds a document sheet to be copied toward a predetermined document reading position in the apparatus main body 10. On the other hand, when the user manually places the document sheet at a predetermined document reading position, the ADF 20 is opened upward. ADF 20 includes a document tray 21 on which a document sheet is placed, a document conveyance unit 22 for conveying the document sheet via an automatic document reading position, and a document discharge tray 23 for discharging the document sheet after reading .

  The reading unit 25 optically reads an image of a document sheet automatically fed from the ADF 20 on the upper surface of the apparatus main body 10 or a document sheet manually placed. In the reading unit 25, a scanning mechanism including a light source, a movable carriage, a reflection mirror, and the like, and an imaging device are accommodated (not shown). The scanning mechanism irradiates the document sheet with light and guides the reflected light to the imaging device. The imaging device photoelectrically converts the reflected light into an analog electrical signal. The analog electrical signal is converted into a digital electrical signal by an A / D conversion circuit, and then input to the image forming unit 30.

  The image forming unit 30 generates a full color toner image and transfers the image onto a sheet, and the yellow (Y), magenta (M), cyan (C) and black (Bk) arranged in tandem are formed. Image forming unit 32 including four units 32Y, 32M, 32C, and 32Bk for forming respective toner images, an intermediate transfer unit 33 disposed adjacent to the upper side of the image forming unit 32, and the intermediate transfer unit 33. And a toner replenishing unit 34 disposed in FIG.

  Each of the image forming units 32Y, 32M, 32C, 32Bk includes a photosensitive drum 321 (image carrier) and a charging device 322, an exposing device 323, a developing device 324, and a primary transfer, which are disposed around the photosensitive drum 321. A roller 325 and a cleaning device 326 are included.

  The photosensitive drum 321 is a cylindrical member which rotates about its axis, and forms an electrostatic latent image on the surface thereof and carries a toner image (developer image). The charging device 322 uniformly charges the surface of the photosensitive drum 321 to a predetermined potential. The exposure device 323 includes a laser light source and an optical system device such as a mirror and a lens, and forms an electrostatic latent image by irradiating the surface of the photosensitive drum 321 with exposure light based on image data of an original image. Do.

  The developing device 324 supplies toner (developer) to the circumferential surface of the photosensitive drum 321 in order to develop the electrostatic latent image formed on the photosensitive drum 321 into a toner image. In the present embodiment, the developing device 324 is for a two-component developer, and includes a screw feeder, a magnetic roller, and a developing roller as described later.

  The primary transfer roller 325 forms a nip with the photosensitive drum 321 across the intermediate transfer belt 331 provided in the intermediate transfer unit 33, and the toner image on the photosensitive drum 321 is primarily transferred onto the intermediate transfer belt 331. Do. The cleaning device 326 has a cleaning roller and the like, and cleans the circumferential surface of the photosensitive drum 321 after transferring the toner image.

  The intermediate transfer unit 33 includes an intermediate transfer belt 331, a drive roller 332 and a driven roller 333. The intermediate transfer belt 331 is an endless belt bridged around the drive roller 332 and the driven roller 333. On the outer peripheral surface of the intermediate transfer belt 331, toner images from a plurality of photosensitive drums 321 overlap in the same place. Is transferred. The intermediate transfer unit 33 is rotated counterclockwise in FIG.

  The secondary transfer roller 35 is disposed to face the circumferential surface of the drive roller 332. The nip portion between the drive roller 332 and the secondary transfer roller 35 is a secondary transfer portion for transferring the full color toner image superimposed on the intermediate transfer belt 331 onto a sheet. A secondary transfer bias potential opposite in polarity to the toner image is applied to either the drive roller 332 or the secondary transfer roller 35, and the other roller is grounded. A density sensor 35A is disposed opposite to the circumferential surface of the intermediate transfer belt 331 at a position upstream of the driving roller 332 in the rotational direction of the intermediate transfer belt 331. The density sensor 35A outputs an electrical signal corresponding to the density of the image formed on the intermediate transfer belt 331.

  The toner replenishing unit 34 includes a yellow toner container 34Y, a magenta toner container 34M, a cyan toner container 34C, and a black toner container 34Bk. The toner containers 34Y, 34C, 34M, 34Bk store toners of the respective colors, and are supplied to the developing devices 324 of the image forming units 32Y, 32M, 32C, 32Bk corresponding to the respective colors YMCBk through supply paths (not shown). Supply toner of each color.

  The sheet feeding unit 40 includes two-stage sheet feeding cassettes 40A and 40B that store sheets subjected to image forming processing. The paper feed cassettes 40A and 40B can be pulled out from the front of the apparatus main body 10 in the front direction.

  The fixing unit 60 is an induction heating type fixing device that performs a fixing process to fix a toner image on a sheet, and includes a heating roller 61, a fixing roller 62, a pressure roller 63, a fixing belt 64, and an induction heating unit 65. The pressure roller 63 is in pressure contact with the fixing roller 62 to form a fixing nip portion. The heating roller 61 and the fixing belt 64 are induction-heated by the induction heating unit 65 to apply the heat to the fixing nip portion. As the sheet passes through the fixing nip portion, the toner image transferred to the sheet is fixed to the sheet.

<Configuration of Developing Device>
Subsequently, the developing device 324 will be described in detail. FIG. 2 is a vertical sectional view schematically showing the internal structure of the developing device 324. As shown in FIG. Note that FIG. 2 shows the developing device 324 of FIG. 1 while being horizontally reversed. The developing device 324 includes a developing housing 80 which defines an internal space of the developing device 324. The developing housing 80 is provided with a developer storage portion 81 for storing a developer including a nonmagnetic toner and a magnetic carrier. Further, inside the development housing 80, a magnetic roller 82 disposed above the developer storage portion 81, a development roller 83 disposed opposite to the magnetic roller 82 at a position obliquely above the magnetic roller 82, and a magnetic roller 82 And a developer regulating blade 84 disposed opposite to the toner.

  The developer storage portion 81 includes two adjacent developer storage chambers 81 a and 81 b extending in the longitudinal direction of the developing device 324. The developer storage chambers 81a and 81b are formed integrally with the developing housing 80 and are separated from each other by a partition plate 801 extending in the longitudinal direction, but are not continuous at both ends in the longitudinal direction orthogonal to the sheet of FIG. The channels communicate with each other. In each of the developer storage chambers 81a and 81b, screw feeders 85 and 86 that agitate and transport the developer by rotating around the axis are accommodated. The screw feeders 85 and 86 are rotationally driven by a drive mechanism (not shown), but their rotational directions are set opposite to each other. As a result, the developer is circulated and conveyed while being stirred between the developer storage chamber 81a and the developer storage chamber 81b. By this stirring, the toner and the carrier are mixed, and the toner is, for example, positively charged.

  The magnetic roller 82 is disposed along the longitudinal direction of the developing device 324, and is rotated clockwise around a predetermined rotation axis in FIG. Inside the magnetic roller 82, a fixed so-called magnet roll (not shown) is disposed. The magnet roll has a plurality of magnetic poles, and in the present embodiment, it has an upper pole 821, a control pole 822 and a main pole 823. The scooping pole 821 faces the developer storage portion 81, the regulating pole 822 faces the developer regulating blade 84, and the main pole 823 faces the developing roller 83.

  The magnetic roller 82 magnetically pumps (receives) the developer from the developer storage portion 81 onto the circumferential surface 82A by the magnetic force of the suction pole 821. The pumped developer is magnetically held as a developer layer (magnetic brush layer) on the circumferential surface 82A of the magnetic roller 82, and is conveyed toward the developer regulation blade 84 as the magnetic roller 82 rotates. .

  The developer regulating blade 84 is disposed on the upstream side of the developing roller 83 as viewed in the rotational direction of the magnetic roller 82, and regulates the thickness of the developer layer magnetically attached to the circumferential surface 82A of the magnetic roller 82. The developer regulation blade 84 is a plate member made of a magnetic material extending in the longitudinal direction of the magnetic roller 82, and is supported by a predetermined support member 841 fixed to an appropriate position of the development housing 80. Further, the developer regulation blade 84 has a regulation surface 842 (that is, the tip surface of the developer regulation blade 84) which forms a regulation gap G of a predetermined dimension with the circumferential surface 82A of the magnetic roller 82.

  The developer regulation blade 84 formed of a magnetic material is magnetized by the regulation pole 822 of the magnetic roller 82. Thus, a magnetic path is formed between the control surface 842 of the developer control blade 84 and the control pole 822, that is, in the control gap G. When the developer layer deposited on the circumferential surface 82A of the magnetic roller 82 by the scooping pole 821 is transported into the regulation gap G with the rotation of the magnetic roller 82, the layer thickness of the developer layer is regulated in the regulation gap G Be done. Thus, a uniform developer layer of a predetermined thickness is formed on the circumferential surface 82A.

  The developing roller 83 is disposed to extend along the longitudinal direction of the developing device 324 and in parallel to the magnetic roller 82, and is rotated clockwise around a predetermined rotation axis in FIG. The developing roller 83 has a circumferential surface 83A that receives the toner from the developer layer and carries the toner layer while rotating in a state of being in contact with the developer layer held on the circumferential surface 82A of the magnetic roller 82. At the time of development in which a developing operation is performed, the toner of the toner layer is supplied to the circumferential surface of the photosensitive drum 321.

  The developing roller 83 and the magnetic roller 82 are rotationally driven by the drive unit 962 of FIG. Between the circumferential surface 83A of the developing roller 83 and the circumferential surface 82A of the magnetic roller 82, a gap S having a predetermined dimension is formed. The gap S is set to, for example, about 130 μm. The developing roller 83 is disposed to face the photosensitive drum 321 through an opening formed in the developing housing 80, and a gap of a predetermined size is also formed between the circumferential surface 83A and the circumferential surface of the photosensitive drum 321. There is. The magnetic roller 82 and the developing roller 83 are rotated in opposite directions in the area facing each other. Further, the distance between the magnetic roller 82 and the developing roller 83 is set smaller than the distance between the developing roller 83 and the photosensitive drum 321.

  FIG. 3 is a schematic view showing how the base material 830 of the developing roller 83 according to the present embodiment is subjected to cutting.

  In the present embodiment, the developing roller 83 is mainly made of aluminum. Specifically, a tubular base 830 is formed by drawing of an aluminum material. Thereafter, as shown in FIG. 3, the circumferential surface of the substrate 830 is cut by the cutting device 100 while the substrate 830 is rotated about the axis SL. At this time, the cutting blade 101 cuts the circumferential surface of the base 830 while being moved along the axial direction (arrow DK in FIG. 3) in the rotation of the base 830. The cutting blade 101 is moved at a predetermined pitch Sm (Y) in the axial direction each time the base material 830 is rotated once. Thereafter, the peripheral surface of the substrate 830 is subjected to an alumite treatment. In addition, the said alumite process can be performed stably by said cutting. Then, the resin coating layer is formed on the alumite layer formed by the alumite treatment, whereby the developing roller 83 is manufactured.

  The resin coating layer includes, for example, a layer of alcohol soluble nylon and conductive powder distributed therein. In this case, the conductive powder is powdery titanium oxide or the like. The substrate 830 on which the alumite layer is formed is subjected to a dipping process for forming a conductive resin coating layer. For example, in this dipping step, the base material 830 is immersed in a mixed solution containing a binder resin and a conductive powder in a posture in which the axial direction is along the vertical direction. The dispersion medium of the mixed solution is, for example, 800 parts by weight of methanol. In this case, the mixed solution is obtained by mixing the nylon, the titanium oxide, and the methanol (800 parts by weight) with zirconia beads having a diameter of, for example, 1.0 millimeter.

  FIG. 4 is a graph showing the distribution (measurement result) of the surface roughness of the circumferential surface of the developing roller 83 according to the present embodiment. In FIG. 4, the horizontal axis indicates the measurement length, and the vertical axis indicates the surface roughness Rz. Here, the surface roughness in the axial direction (longitudinal direction) of the developing roller 83 is measured by using a contact type surface roughness meter Surfcom 1500 DX manufactured by Tokyo Seimitsu Co., Ltd. At this time, the measurement length is 4 mm. As described above, in cutting of the base 830, the cutting blade 101 is moved in the axial direction at a predetermined pitch. Therefore, cutting traces are formed on the surface of the base material 830 along the circumferential direction in the rotation of the developing roller 83 and at a predetermined pitch Sm (Y) along the axial direction of the rotation axis (SL) . The cutting marks remain on the circumferential surface of the developing roller 83 after the alumite treatment and the resin coating treatment.

  FIG. 5 is a schematic view showing a developing operation according to the present embodiment. The developing device 324 further includes a first application unit 88 (bias application unit) and a second application unit 89 (bias application unit).

  The first application unit 88 includes a DC power supply and an AC power supply, and applies a bias to the magnetic roller 82 in the developing device 324 based on a control signal from a control unit (not shown). Similarly, the second application unit 89 includes a DC power supply and an AC power supply, and applies a bias to the developing roller 83 in the developing device 324 based on a control signal from the control unit.

  The first application unit 88 includes a DC voltage source 881 and an AC voltage source 882 connected in series, and is connected to the magnetic roller 82. A voltage in which the AC bias output from the AC voltage source 882 is superimposed on the DC bias output from the DC voltage source 881 is applied to the magnetic roller 82. The second application unit 89 includes a DC voltage source 891 and an AC voltage source 892 connected in series, and is connected to the developing roller 83. A voltage in which the AC bias output from the AC voltage source 892 is superimposed on the DC bias output from the DC voltage source 891 is applied to the developing roller 83.

  The values of the DC bias and the AC bias applied to the magnetic roller 82 and the developing roller 83 cause the developing device 324 to supply toner on the circumferential surface of the photosensitive drum 321 (develop the electrostatic latent image), It changes according to the chargeability of the supplied toner. Further, after the completion of the developing operation, in the collecting operation for collecting the toner attached to the developing roller 83 to the magnetic roller 82, different bias values are applied to the magnetic roller 82 and the developing roller 83.

  The magnetic brush layer on the circumferential surface 82 A of the magnetic roller 82 is conveyed toward the developing roller 83 as the magnetic roller 82 rotates after the layer thickness is regulated uniformly by the developer regulating blade 84. Thereafter, in the region of the gap S (FIG. 2), the large number of magnetic brushes DB in the magnetic brush layer contact the circumferential surface 83A of the developing roller 83 in rotation.

  At this time, the bias control unit 90 controls the first applying unit 88 and the second applying unit 89 to apply predetermined DC bias and AC bias to the magnetic roller 82 and the developing roller 83, respectively. As a result, a predetermined potential difference (development potential difference) is generated between the circumferential surface 82A of the magnetic roller 82 and the circumferential surface 83A of the developing roller 83. Due to this potential difference, only the toner T moves from the magnetic brush DB to the circumferential surface 83A at the facing position between the circumferential surface 82A and the circumferential surface 83A (at the facing position of the main pole 823 (FIG. 2) and the circumferential surface 83A) The carrier C of the magnetic brush DB and a part of the remaining toner remain on the circumferential surface 82A. Thus, the toner layer TL of a predetermined thickness is carried on the circumferential surface 83A of the developing roller 83.

  The toner layer TL on the circumferential surface 83A is transported toward the circumferential surface of the photosensitive drum 321 as the developing roller 83 rotates. A superimposed voltage of a DC voltage and an AC voltage is applied to the developing roller 83. Therefore, a predetermined potential difference is generated between the circumferential surface of the photosensitive drum 321 having a potential on the surface according to the electrostatic latent image and the circumferential surface 83A of the developing roller 83. Due to this potential difference, the toner T of the toner layer TL moves to the circumferential surface of the photosensitive drum 321. Thus, the electrostatic latent image on the circumferential surface of the photosensitive drum 321 is developed to form a toner image.

6 and 7 are enlarged schematic views of the electrostatic latent image formed on the photosensitive drum 321 by the exposure device 323 according to the present embodiment. The exposure device 323 is a screen image inclined at a predetermined screen angle θ at an acute angle with respect to the main scanning direction Dh (the axial direction of the photosensitive drum 321), and a predetermined screen per inch in the main scanning direction Dh. The electrostatic latent image is formed by the screen image formed with the number of lines X. In FIG. 6 and FIG. 7, Df indicates the sub-scanning direction. By selectively arranging the dots DI at the screen angle θ on the circumferential surface of the photosensitive drum 321, an electrostatic latent image corresponding to the image data is formed. At this time, the dots DI are arranged at predetermined intervals on an imaginary straight line extending in parallel with the sub scanning direction Df. In FIG. 6, the screen line number X is 212 lines, the screen angle θ is 45 degrees, and the interval W (dot pitch) in the main scanning direction Dh of the virtual straight line is set to 0.085 mm. Further, in FIG. 7, the screen line number X = 141 line, and the screen angle θ = 45 degrees, and the interval W in the main scanning direction Dh of the virtual straight line is set to 0.127 mm. The inter-dot pitch W is calculated by the following equation 1.
W = 25.4 / X × cos θ (Equation 1)

  As described above, the developing roller 83 extends along the circumferential direction in the rotation of the developing roller 83 on the circumferential surface, and at a predetermined pitch Sm (= Y) along the axial direction of the rotation axis of the developing roller 83 It has a formed cutting mark. The cutting marks extend spirally and continuously on the circumferential surface of the developing roller 83 on the premise of the cutting method of FIG. 3.

  Due to the above-described cutting marks formed on the circumferential surface of the developing roller 83, a micro streak of distribution difference is also caused in the toner layer carried on the circumferential surface of the developing roller 83. For this reason, the toner supply capability (toner scattering amount) from the developing roller 83 to the photosensitive drum 321 also has minute peaks and valleys along the axial direction.

  The inventor of the present invention found that the pitch of the cutting marks on the developing roller 83 and the pitch W between dots of the screen image formed on the photosensitive drum 321 (the pitch between the virtual straight lines in FIGS. 6 and 7). When they interfere with one another, it has been newly found that an oblique muscle which can be identified with the naked eye occurs on the image. FIG. 8 is a schematic view showing a state where oblique muscle IL, which is the subject of the present invention, appears on the image of the sheet S. In FIG. 8, the pitch of the oblique muscle IL is exaggerated for the purpose of explanation. Such oblique muscle IL appears notably on the halftone image HT.

Here, when the screen angle θ (degrees) in the screen image, the screen line number X (pieces) and the pitch Y (μm) of the cutting trace of the developing roller 83 satisfy the following equation 2 or equation 3, diagonal stripes It is possible to suppress the occurrence.
25.4 / X × 0.9 × cos θ <Y (Equation 2)
Y> 25.4 / X × 1.1 × cos θ (Equation 3)
In other words, it is desirable that the cutting pitch Y on the developing roller 83 is not included in the range of ± 10% of the dot pitch W in the main scanning direction of the screen image.

  According to such a configuration, the minute distribution of the toner layer on the developing roller 83 based on the cutting marks and the virtual straight line between the dots in the screen image interfere with each other, which both appear as streaks along the main scanning direction. Thus, it is possible to suppress oblique muscle images visually recognized by the naked eye.

Hereinafter, the embodiment of the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. In addition, the experimental conditions in each implemented experiment are as follows.
Photosensitive drum 321: Amorphous silicon photosensitive member Toner: Volume average particle diameter 6.8 μm, Positive charging property Development method: Touch down development (magnetic roller + development roller)
· Developing roller: outer diameter φ 20 mm, resin coating layer (nylon + titanium oxide), surface resistance 1.0E + 07 ~ 1.0E + 09
Development conditions: Toner conveyance amount on development roller 0.25 to 0.45 mg / cm ²
· Gap between developing roller 83 and photosensitive drum 321: 75 to 150 μm
· Gap between developing roller 83 and magnetic roller 82: 170 to 350 μm
The circumferential speed ratio between the developing roller 83 and the photosensitive drum 321: 1.2 to 2.0
· Development bias (maximum amplitude 1500 to 1800 (V) of AC voltage applied between development roller 83 and photosensitive drum 321, potential difference 30 to 100 (V) of the DC voltage

Table 1 shows the measurement results of the surface shape under the cutting conditions (1 to 20) of the developing roller 83 with respect to the base material 830 and the evaluation results of the oblique streaks in each screen image. The surface shape of the developing roller 83 was measured along the longitudinal direction of the developing roller 83 under the following conditions using a contact-type surface roughness meter Surfcom 1500 DX manufactured by Tokyo Seimitsu Co., Ltd.
・ Measurement length: 4 mm
Measured value: Average value of a total of 12 measurement points (3 points in the longitudinal direction × 4 points in the circumferential direction) Further, each measurement parameter was measured according to JIS B 0601 standard, and the following values were measured.
Measurement pitch Sm: average length surface roughness Rz: 10 point average roughness surface roughness Ra: arithmetic average roughness

In the evaluation of oblique lines in Table 1, those which are not shown in the image are oblique lines “0”, those slightly appearing on the image “1”, and those notably appearing on the image It is shown as "2".

  With reference to Table 1, under the conditions of 212 screen lines, 45 screen angles, 127 screen lines and 65 angle screen angles, diagonal streaks do not occur in the case of cutting pitch Sm (100 (μm) It became a result. In addition, under the conditions of 141 screen lines, 45 screen angles, 178 screen lines, and 27 screen angles, diagonal streaks occur when the cutting pitch Sm 100 100 (μm) or Sm 142 142 (μm). It did not occur. Furthermore, under the conditions of 106 screen lines, 45 ° screen angle, 134 screen lines and 27 ° screen angle, diagonal streaks are not generated in the case of cutting pitch Sm ≦ 150 (μm). The

  In other words, the screen angle θ (degrees) in the screen image, the screen, in all cases where the inter-dot pitch (distance between dots) of the screen image is 85 (μm), 127 (μm) and 169 (μm) In the case where the number of lines X (number) and the pitch Y (μm) of the cutting trace of the developing roller 83 satisfy the equation 2 or 3 described above, the result is that no oblique streaks are generated.

  As described above, according to the present embodiment, since the screen angle θ (degree), the screen line number X (pieces) and the pitch Y (μm) of the cutting marks satisfy the predetermined relational expression, the screen image and the developing roller Generation of oblique streaks on the image based on the interference with the cutting pitch.

  Further, in the present embodiment, the developing roller 83 has a circular tubular base 830 and a resin coating layer formed on the base 830. Therefore, a developing electric field is stably formed between the developing roller 83 and the photosensitive drum 321 by the resin coating layer. In addition, even when cutting marks formed on the circumferential surface of the substrate 830 remain on the circumferential surface of the resin coating layer, diagonal streaks appear on the image based on the interference between the screen image and the cutting pitch of the developing roller. Occurrence is suppressed.

  The base 830 of the developing roller 83 is made of aluminum, and the developing roller 83 further has an alumite layer formed on the base 830, and the resin coating layer is formed on the alumite layer. For this reason, peeling of the resin coating layer is suppressed by the alumite layer.

  The developing device 324 further includes a developer storage portion 81 for storing a developer containing toner and a magnetic carrier, and a magnetic roller 82 which is rotated about a predetermined rotation axis and receives the toner and the carrier from the developer storage portion 81. And a developing roller 83 which receives toner from the magnetic roller 82 and supplies the toner to the photosensitive drum 321. According to this configuration, even if the developing device 324 has the magnetic roller 82 and the developing roller 83 and the touch-down developing method is adopted, based on the interference between the screen image and the cutting pitch of the developing roller. The occurrence of oblique streaks on the image is suppressed.

  In addition, the magnetic roller 82 and the developing roller 83 are rotated in opposite directions in the area facing each other. According to this configuration, the toner layer on the developing roller 83 which has passed through the developing nip is affected by the mechanical scraping force of the magnetic brush on the magnetic roller 82 and the potential difference between the magnetic roller 82 and the developing roller 83. It is easily collected from the developing roller 83 to the magnetic roller 82 side. For this reason, compared with the case where the magnetic roller 82 and the developing roller 83 are rotated in the same direction in the area facing each other, application of a large cohesive force to the developer in the facing area is suppressed. On the other hand, in such a case, the cutting marks formed on the circumferential surface of the developing roller 83 are less likely to be polished by the developer in the opposing area, and easily remain even after long-term use. Even in such a case, since the screen angle θ (degree), the number of screen lines X (pieces) and the pitch Y (μm) of cutting marks satisfy the predetermined relational expression, the cutting pitch of the screen image and the developing roller Generation of oblique streaks on the image based on the interference with

  Further, in the present embodiment, the developer layer on the developing roller 83 is not in contact with the surface of the photosensitive drum 321. In this case, the developer layer (toner layer) on the developing roller 83 is not in contact with the surface of the photosensitive drum 321 as in the known contact developing method. Therefore, the minute distribution of the developer layer according to the cutting marks of the developing roller 83 largely affects the amount of toner flying to the photosensitive drum 321. Even in such a case, since the screen angle θ (degree), the number of screen lines X (pieces) and the pitch Y (μm) of cutting marks satisfy the predetermined relational expression, the cutting pitch of the screen image and the developing roller Generation of oblique streaks on the image based on the interference with In other words, when the developer layer on the developing roller 83 is in contact with the surface of the photosensitive drum 321 as in the known contact development method, the developer layer can move along the axial direction at the developing nip. Therefore, the minute distribution of the developer layer according to the cutting marks is easily relaxed.

  As described above, the inventor of the present invention has newly found that, due to the cutting marks of the developing roller 83 (base material 830), it is newly possible to suppress the oblique streak image which is significantly generated in the touch-down developing method. . The cutting marks of the substrate 830 are likely to remain on the circumferential surface of the developing roller 83 even after the alumite treatment and the formation of the resin coating layer. Further, the cutting marks appearing on the developing roller 83 (resin coating layer) appear as a distribution of the toner layer. As a result, on the photosensitive drum 321, the distribution of the toner layer (distribution of the toner flyable amount) caused by the cutting marks may interfere with the inter-dot pitch (inter-dot distance) in the screen image. Was newly discovered. Then, the screen image and the developing roller are cut when the screen angle θ (degrees), the screen line number X (numbers) and the pitch Y (μm) of the cutting marks satisfy the predetermined relational expression (Expression 2 or Expression 3) It has been newly found that generation of oblique streaks on the image is suppressed based on the interference with the pitch.

  In addition, the above effect is further confirmed in the range of 30 (μm) to 250 (μm) in the inter-dot pitch (distance between dots) of the screen image and the number of screen lines of 100 to 300. The

  The present invention is not limited to the above embodiment. Even in the two-component developing method or the magnetic or non-magnetic one-component developing method, when streaky developer distribution caused by cutting marks is easily generated on the developing roller, the screen angle θ (degrees), the number of screen lines X When (pitch) and the pitch Y (μm) of the cutting marks satisfy the above-mentioned Formula 2 or Formula 3, it is suppressed that an oblique streak is generated on the image. Further, the image forming apparatus 1 is not limited to one that forms a color image, and may form a single color (monochrome) image.

Reference Signs List 1 image forming apparatus 10 apparatus main body 30 image forming unit 32 image forming unit 33 intermediate transfer unit 321 photosensitive drum 322 charging device 323 exposure device 324 developing device 80 developing housing 81 developer storage portion 82 magnetic roller 83 developing roller 830 substrate 84 Developer regulation blade

Claims (6)

A photosensitive drum having a surface on which an electrostatic latent image is formed and carrying a developer image on the surface;
A charging device for charging the surface of the photosensitive drum to a predetermined potential;
An exposure device that forms the electrostatic latent image by irradiating the surface of the photosensitive drum charged to the predetermined potential with exposure light according to image data;
The image forming apparatus has a developing roller including a circumferential surface carrying a developer and rotated about a predetermined rotation axis, and supplying the developer to the surface of the photosensitive drum to form the electrostatic latent image as the developer image A developing device that
Equipped with
The exposure apparatus is a screen image inclined at a predetermined screen angle θ with respect to the main scanning direction, and the screen image formed by a predetermined number of screen lines X per inch in the main scanning direction. Forming an electrostatic latent image,
The developing roller has cutting marks formed along the circumferential direction of rotation of the developing roller on the circumferential surface and formed at a predetermined pitch Y along the axial direction of the rotation shaft.
An image forming apparatus, wherein the screen angle θ (degrees), the number of screen lines X (pieces), and the pitch Y (μm) of the cutting marks satisfy the following relational expression.
25.4 / X × 0.9 × cos θ <Y
Or
Y> 25.4 / X × 1.1 × cos θ   The image forming apparatus according to claim 1, wherein the developing roller has a circular tubular base, and a resin coating layer formed on the base. The substrate of the developing roller is made of aluminum,
The developing roller further comprises an alumite layer formed on the substrate,
The image forming apparatus according to claim 2, wherein the resin coating layer is formed on the alumite layer. The developing device is
A developer storage portion for storing the developer containing toner and magnetic carrier;
A magnetic roller which is rotated about a predetermined rotation axis and receives the toner and the carrier from the developer storage portion;
The developing roller that receives the toner from the magnetic roller and supplies the toner to the photosensitive drum;
The image forming apparatus according to any one of claims 1 to 3, further comprising:   The image forming apparatus according to claim 4, wherein the magnetic roller and the developing roller are rotated in opposite directions in areas facing each other.   The image forming apparatus according to any one of claims 1 to 5, wherein the developer layer on the developing roller is not in contact with the surface of the photosensitive drum.