JP7031196B2 - Image forming device - Google Patents

Description

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

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

The exposure apparatus forms a screen image on the photoconductor drum in which latent image dots are arranged adjacent to each other according to the image data. The number of screen lines and the screen angle of the screen image are set according to the required image quality.

On the other hand, the developing device that supplies the developing agent to the photoconductor drum has a developing roller. The developing roller has a sleeve that is rotated about a predetermined axis of rotation. Patent Document 1 discloses, as a method for manufacturing the sleeve, a technique in which the peripheral surface of a drawn aluminum tube is cut and then anodized or resin-coated on the peripheral surface. By these treatments, the developer is easily supported on the sleeve, and the toner is stably supplied from the developing roller to the photoconductor drum.

Japanese Patent No. 6053669

In the technique described in Patent Document 1, the peripheral 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. .. At this time, minute irregularities (cutting marks) with a cutting pitch are formed on the peripheral surface of the aluminum tube according to the rotation cycle of the aluminum tube and the moving speed of the cutting blade. Then, when the cutting pitch on the developing roller and the dot-to-dot pitch in the main scanning direction in the screen image of the exposure apparatus 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 above-mentioned problems, and is an image forming apparatus that suppresses the generation of diagonal streaks on an image based on the interference between the screen image and the cutting pitch of the developing roller. The purpose is to provide.

The image forming apparatus according to one aspect of the present invention has a surface on which an electrostatic latent image is formed, and has a photoconductor drum carrying a developer image on the surface and a predetermined potential on the surface of the photoconductor drum. An exposure device that forms an electrostatic latent image by irradiating the surface of the photoconductor drum charged to the predetermined potential with exposure light according to the image data, and a developing agent. It has a developing roller that includes a peripheral surface that carries the surface and is rotated around a predetermined axis of rotation, and by supplying the developing agent to the surface of the photoconductor drum, the electrostatic latent image is manifested in the developing agent image. The exposure apparatus is provided with a developing apparatus for processing, and the exposure apparatus is a screen image inclined with a predetermined screen angle θ with respect to the main scanning direction, and has a predetermined number of screen lines X per inch in the main scanning direction. The formed screen image forms the electrostatic latent image, and the developing roller extends along the circumferential direction in the rotation of the developing roller on the peripheral surface and in the axial direction of the rotating shaft. It has cutting marks formed at a predetermined pitch along the screen, and the screen angle θ (degrees) and the number of screen lines X (lines) satisfy the relational expression of 25.4 / X × cos θ> 0.10. The pitch of the cutting marks is 100 μm or more, and the surface roughness Rz along the axial direction on the peripheral surface of the developing roller is 2.0 μm or less.

According to this configuration, it is possible to prevent diagonal streaks from being generated on the image 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 material and a resin coating layer formed on the base material.

According to this configuration, the resin coating layer stably forms a developing electric field between the developing roller and the photoconductor drum. Further, even when the cutting marks formed on the peripheral surface of the base material remain on the peripheral 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. Is deterred.

In the above configuration, the substrate of the developing roller is made of aluminum, the developing roller further has 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, the alumite layer suppresses the peeling of the resin coating layer.

In the above configuration, the developing apparatus is rotated around a predetermined rotation axis and a developer storage unit that stores the developer including toner and a magnetic carrier, and receives the toner and the carrier from the developer storage unit. It is desirable to have a magnetic roller and a developing roller that receives the toner from the magnetic roller and supplies the toner to the photoconductor drum.

According to this configuration, even when the developing apparatus has a magnetic roller and a developing roller and a touch-down developing method is adopted, it is displayed on the image based on the interference between the screen image and the cutting pitch of the developing roller. Occurrence of diagonal streaks is suppressed.

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

According to this configuration, the toner layer on the developing roller that has passed through the developing nip is magnetic from the developing roller due to 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 collected on the roller side. Therefore, it is suppressed that a large cohesive force is applied to the developer in the facing region as compared with the case where the magnetic roller and the developing roller are rotated in the same direction in the regions facing each other. On the other hand, in such a case, the cutting marks formed on the peripheral surface of the developing roller are difficult to be polished by the developing agent in the facing region, and are likely to remain even after long-term use. Even in such a case, since the surface roughness Rz along the axial direction on the peripheral surface of the developing roller is set to 2.0 μm or less, the image is based on the interference between the screen image and the cutting pitch of the developing roller. The generation of diagonal streaks on the top is suppressed.

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

According to this configuration, the developer layer on the developing roller is not in contact with the surface of the photoconductor drum as in the known contact developing 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 photoconductor drum. Even in such a case, since the surface roughness Rz along the axial direction on the peripheral surface of the developing roller is set to 2.0 μm or less, the image is based on the interference between the screen image and the cutting pitch of the developing roller. The generation of diagonal streaks on the top is suppressed.

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

It is sectional drawing which shows the internal structure of the image forming apparatus which concerns on one Embodiment of this invention. It is sectional drawing of the developing apparatus which concerns on one Embodiment of this invention. It is a schematic diagram which shows the state that the base material of the developing roller which concerns on one Embodiment of this invention is cut. It is a graph which shows the measurement result of the surface roughness of the peripheral surface of the developing roller which concerns on one Embodiment of this invention. It is a schematic diagram which showed the development operation which concerns on one Embodiment of this invention. It is an enlarged schematic diagram of the electrostatic latent image on the photoconductor drum which concerns on one Embodiment of this invention. It is an enlarged schematic diagram of the electrostatic latent image on the photoconductor drum which concerns on one Embodiment of this invention. It is a schematic diagram which shows the appearance of the oblique streak which is the subject of this invention on an image. It is a graph which shows the generation state of the diagonal streak with respect to the cutting pitch and the surface roughness of the peripheral surface of a developing roller.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 1 according to the embodiment of the present invention. Here, as the image forming apparatus 1, a multifunction device having a printer function and a copying function is illustrated, but the image forming apparatus may be a printer, a copying machine, or a facsimile apparatus.

<Explanation 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 feeding device 20 arranged on the apparatus main body 10. Inside the main body 10 of the apparatus, a reading unit 25 that optically reads the original image to be copied, an image forming unit 30 that forms a toner image on the sheet, a fixing unit 60 that fixes the toner image on the sheet, and an image forming unit. The paper feed unit 40 for storing the sheets to be conveyed to the unit 30, and the transfer path 50 for transporting the sheets from the paper feed unit 40 or the paper feed 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 that constitutes a part of the transport path 50 inside.

The automatic document feeding device (ADF) 20 is rotatably attached to the upper surface of the device main body 10. The ADF 20 automatically feeds the document sheet to be copied toward a predetermined document reading position on the apparatus main body 10. On the other hand, when the user manually places the document sheet in a predetermined document reading position, the ADF 20 is opened upward. The ADF 20 includes a document tray 21 on which a document sheet is placed, a document transfer unit 22 for transporting the document sheet via an automatic document reading position, and a document ejection tray 23 for ejecting the scanned document sheet. ..

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 placed by hand. A scanning mechanism including a light source, a moving carriage, a reflection mirror, and the like, and an image pickup device are housed in the reading unit 25 (not shown). The scanning mechanism irradiates the original sheet with light and guides the reflected light to the image pickup device. The image sensor photoelectrically converts the reflected light into an analog electric signal. The analog electric signal is converted into a digital electric signal by the 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 it onto a sheet. Yellow (Y), magenta (M), cyan (C), and black (Bk) arranged in tandem. An image forming unit 32 including four units 32Y, 32M, 32C, and 32Bk forming each toner image of the above, an intermediate transfer unit 33 arranged adjacently on the image forming unit 32, and an intermediate transfer unit 33. Includes a toner supply unit 34 arranged in.

Each image forming unit 32Y, 32M, 32C, 32Bk has a photoconductor drum 321 (image carrier) and a charging device 322, an exposure device 323, a developing device 324, and a primary transfer arranged around the photoconductor drum 321. Includes rollers 325 and cleaning device 326.

The photoconductor drum 321 is a cylindrical member that rotates around its axis, and an electrostatic latent image is formed on the surface thereof, and a toner image (developer image) is supported on the surface of the photoconductor drum 321. The charging device 322 uniformly charges the surface of the photoconductor drum 321 to a predetermined potential. The exposure device 323 has a laser light source and optical equipment such as a mirror and a lens, and forms an electrostatic latent image by irradiating the surface of the photoconductor drum 321 with exposure light based on the image data of the original image. do.

The developing device 324 supplies toner (developer) to the peripheral surface of the photoconductor drum 321 in order to develop (explicit) the electrostatic latent image formed on the photoconductor drum 321 into a toner image. In this 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 portion with the photoconductor drum 321 by sandwiching the intermediate transfer belt 331 provided in the intermediate transfer unit 33, and transfers the toner image on the photoconductor drum 321 to the intermediate transfer belt 331. do. The cleaning device 326 has a cleaning roller or the like, and cleans the peripheral surface of the photoconductor drum 321 after the toner image is transferred.

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 spanned by a drive roller 332 and a driven roller 333, and toner images from a plurality of photoconductor drums 321 are superimposed on the outer peripheral surface of the intermediate transfer belt 331 at the same location. Is transcribed. The intermediate transfer unit 33 is rotated counterclockwise in FIG.

The secondary transfer roller 35 is arranged so as to face the peripheral 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 that transfers a full-color toner image overlaid on the intermediate transfer belt 331 to the sheet. A secondary transfer bias potential having a polarity opposite to that of the toner image is applied to either the drive roller 332 or the secondary transfer roller 35, and the other roller is grounded. Further, the density sensor 35A is arranged to face the peripheral surface of the intermediate transfer belt 331 at a position on the upstream side in the rotation direction of the intermediate transfer belt 331 with respect to the drive roller 332. The density sensor 35A outputs an electric signal according to the density of the image formed on the intermediate transfer belt 331.

The toner supply unit 34 includes a yellow toner container 34Y, a magenta toner container 34M, a cyan toner container 34C, and a black toner container 34Bk. These toner containers 34Y, 34C, 34M, and 34Bk each store toner of each color, and pass through a supply path (not shown) to the developing apparatus 324 of the image forming unit 32Y, 32M, 32C, 32Bk corresponding to each color of YMCBk. Supply toner of each color.

The paper feed unit 40 includes two stages of paper feed cassettes 40A and 40B for accommodating sheets to be image-formed. These paper cassettes 40A and 40B can be pulled out from the front of the apparatus main body 10 toward the front.

The fixing unit 60 is an induction heating type fixing device that performs a fixing process for fixing 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 pressed against the fixing roller 62 to form a fixing nip portion. The heating roller 61 and the fixing belt 64 are induced and heated by the induction heating unit 65, and the heat is applied to the fixing nip portion. When the sheet passes through the fixing nip portion, the toner image transferred to the sheet is fixed to the sheet.

<Structure 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. In addition, in FIG. 2, the developing apparatus 324 of FIG. 1 is shown inverted in the left-right direction. The developing device 324 includes a developing housing 80 that defines the internal space of the developing device 324. The developing housing 80 is provided with a developing agent storage unit 81 for storing a developing agent containing a non-magnetic toner and a carrier of the magnetic material. Further, inside the developing housing 80, a magnetic roller 82 arranged above the developer storage unit 81, a developing roller 83 arranged diagonally above the magnetic roller 82 and facing the magnetic roller 82, and a magnetic roller 82. A developer regulating blade 84, which is arranged so as to face each other, is arranged.

The developer storage unit 81 includes two adjacent developer storage chambers 81a and 81b extending in the longitudinal direction of the developing device 324. The developing agent storage chambers 81a and 81b are integrally formed with the developing housing 80 and are partitioned from each other by a partition plate 801 extending in the longitudinal direction, but at both ends in the longitudinal direction orthogonal to the paper surface of FIG. 2, a communication (not shown) is shown. They are communicated with each other by passages. The developer storage chambers 81a and 81b contain screw feeders 85 and 86 that agitate and convey the developer by rotating around an axis. The screw feeders 85 and 86 are rotationally driven by a drive mechanism (not shown), but their rotational directions are set to be opposite to each other. As a result, the developer is circulated and conveyed between the developer storage chamber 81a and the developer storage chamber 81b while being agitated. By this stirring, the toner and the carrier are mixed, and the toner is positively charged, for example.

The magnetic roller 82 is arranged along the longitudinal direction of the developing device 324, and is rotated clockwise around a predetermined rotation axis in FIG. 2. A fixed so-called magnet roll (not shown) is arranged inside the magnetic roller 82. The magnet roll has a plurality of magnetic poles, and in this embodiment, it has a pumping pole 821, a regulating pole 822, and a main pole 823. The pumping pole 821 faces the developer storage section 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 unit 81 onto the peripheral surface 82A by the magnetic force of the pumping electrode 821. The pumped developer is magnetically held as a developer layer (magnetic brush layer) on the peripheral surface 82A of the magnetic roller 82, and is conveyed toward the developer control blade 84 as the magnetic roller 82 rotates. ..

The developer regulating blade 84 is arranged on the upstream side of the developing roller 83 when viewed from the rotation direction of the magnetic roller 82, and regulates the layer thickness of the developer layer magnetically adhered to the peripheral surface 82A of the magnetic roller 82. The developer regulating blade 84 is a plate member made of a magnetic material extending along the longitudinal direction of the magnetic roller 82, and is supported by a predetermined support member 841 fixed in place of the developing housing 80. Further, the developer regulating blade 84 has a regulating surface 842 (that is, a tip surface of the developer regulating blade 84) that forms a regulating gap G having a predetermined size with the peripheral surface 82A of the magnetic roller 82.

The developer control blade 84 formed of a magnetic material is magnetized by the control pole 822 of the magnetic roller 82. As a result, a magnetic path is formed between the regulating surface 842 of the developer regulating blade 84 and the regulating electrode 822, that is, in the regulating gap G. When the developer layer adhered to the peripheral surface 82A of the magnetic roller 82 by the pumping electrode 821 is conveyed 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. Will be done. As a result, a uniform developer layer having a predetermined thickness is formed on the peripheral surface 82A.

The developing roller 83 is arranged so as to extend along the longitudinal direction of the developing device 324 and parallel to the magnetic roller 82, and is rotated clockwise around a predetermined rotation axis in FIG. 2. The developing roller 83 has a peripheral surface 83A that receives toner from the developer layer and supports the toner layer while rotating in contact with the developer layer held on the peripheral surface 82A of the magnetic roller 82. At the time of development in which the development operation is performed, the toner of the toner layer is supplied to the peripheral surface of the photoconductor drum 321.

The developing roller 83 and the magnetic roller 82 are rotationally driven by the driving unit 962 of FIG. A gap S having a predetermined dimension is formed between the peripheral surface 83A of the developing roller 83 and the peripheral surface 82A of the magnetic roller 82. The gap S is set to, for example, about 130 μm. The developing roller 83 is arranged so as to face the photoconductor drum 321 through an opening formed in the developing housing 80, and a gap having a predetermined size is also formed between the peripheral surface 83A and the peripheral surface of the photoconductor drum 321. There is. The magnetic roller 82 and the developing roller 83 are rotated in opposite directions in regions facing each other. Further, the distance between the magnetic roller 82 and the developing roller 83 is set to be narrower than the distance between the developing roller 83 and the photoconductor 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 cut.

In this embodiment, the developing roller 83 is mainly made of aluminum. Specifically, the circular tubular base material 830 is formed by drawing out the aluminum material. Then, as shown in FIG. 3, the peripheral surface of the base material 830 is cut by the cutting device 100 while the base material 830 is rotated around the axis SL. At this time, the cutting blade 101 cuts the peripheral surface of the base material 830 while being moved along the axial direction (arrow DK in FIG. 3) in the rotation of the base material 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. After that, the peripheral surface of the base material 830 is anodized. The alumite treatment can be stably performed by the above-mentioned cutting process. Then, the developing roller 83 is manufactured by forming a resin coating layer on the alumite layer formed by the alumite treatment.

The resin coating layer contains, for example, a layer of alcohol-soluble nylon and a conductive powder distributed therein. In this case, the conductive powder is powdery titanium oxide or the like. A dipping step for forming a conductive resin coating layer is performed on the base material 830 on which the alumite layer is formed. For example, in this dipping step, the base material 830 is immersed in a mixed liquid containing a binder resin and a conductive powder in a posture such that the axial direction is along the vertical direction. The dispersion medium of the mixture is, for example, methanol 800 [parts by weight]. In this case, the mixture is obtained by mixing the nylon, the titanium oxide, and 800 [parts by weight] of methanol together with, for example, zirconia beads having a diameter of 1.0 mm.

FIG. 4 is a graph showing the distribution (measurement result) of the surface roughness of the peripheral surface of the developing roller 83 according to the present embodiment. In FIG. 4, the horizontal axis indicates the measured length, and the vertical axis indicates the surface roughness Rz. Here, the surface roughness of the developing roller 83 in the axial direction (longitudinal direction) is measured using a contact type surface roughness meter Surfcom1500DX manufactured by Tokyo Seimitsu Co., Ltd. At this time, the measurement length is 4 mm. As described above, in the cutting process of the base material 830, the cutting blade 101 is moved in the axial direction at a predetermined pitch. Therefore, on the surface of the base material 830, a cutting mark is formed at a predetermined pitch Sm (Y) along the axial direction of the rotation axis (SL) while extending along the circumferential direction in the rotation of the developing roller 83. .. The cutting marks also remain on the peripheral surface of the developing roller 83 after being subjected to the alumite treatment and the resin coating treatment.

FIG. 5 is a schematic diagram 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 is composed of 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 is composed of 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 the control signal from the control unit.

The first application unit 88 has a DC voltage source 881 and an AC voltage source 882 connected in series, and is connected to the magnetic roller 82. A voltage obtained by superimposing the AC bias output from the AC voltage source 882 on the DC bias output from the DC voltage source 881 is applied to the magnetic roller 82. The second application unit 89 has a DC voltage source 891 and an AC voltage source 892 connected in series, and is connected to the developing roller 83. A voltage obtained by superimposing the AC bias output from the AC voltage source 892 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 are determined by the developing operation in which the developing device 324 supplies toner (develops an electrostatic latent image) on the peripheral surface of the photoconductor drum 321. It is changed according to the chargeability of the supplied toner. Further, in the recovery operation for recovering the toner adhering to the developing roller 83 to the magnetic roller 82 after the development operation is completed, further different bias values are applied to the magnetic roller 82 and the developing roller 83.

The magnetic brush layer on the peripheral surface 82A of the magnetic roller 82 is uniformly regulated in layer thickness by the developer regulating blade 84, and then is conveyed toward the developing roller 83 as the magnetic roller 82 rotates. Then, in the region of the gap S (FIG. 2), a large number of magnetic brush DBs in the magnetic brush layer come into contact with the peripheral surface 83A of the rotating developing roller 83.

At this time, the bias control unit 90 controls the first application unit 88 and the second application unit 89 to apply predetermined DC bias and AC bias to each of the magnetic roller 82 and the developing roller 83. As a result, a predetermined potential difference (development potential difference) is generated between the peripheral surface 82A of the magnetic roller 82 and the peripheral surface 83A of the developing roller 83. Due to this potential difference, only the toner T moves from the magnetic brush DB to the peripheral surface 83A at the position where the peripheral surface 82A and the peripheral surface 83A face each other (at the position where the main pole 823 (FIG. 2) faces the peripheral surface 83A). The carrier C of the magnetic brush DB and some of the remaining toner remain on the peripheral surface 82A. As a result, the toner layer TL having a predetermined thickness is supported on the peripheral surface 83A of the developing roller 83.

The toner layer TL on the peripheral surface 83A is conveyed toward the peripheral surface of the photoconductor drum 321 as the developing roller 83 rotates. A superposed 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 peripheral surface of the photoconductor drum 321 having a potential on the surface according to the electrostatic latent image and the peripheral surface 83A of the developing roller 83. Due to this potential difference, the toner T of the toner layer TL moves to the peripheral surface of the photoconductor drum 321. As a result, the electrostatic latent image on the peripheral surface of the photoconductor drum 321 is developed and a toner image is formed.

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

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

The cutting marks formed on the peripheral surface of the developing roller 83 also cause a minute streak-like distribution difference in the toner layer supported on the peripheral surface of the developing roller 83. Therefore, the toner supply capacity (toner scattering amount) from the developing roller 83 to the photoconductor drum 321 also has minute peaks and valleys along the axial direction.

The inventor of the present invention has the pitch of the cutting marks on the developing roller 83 and the pitch between dots W of the screen image formed on the photoconductor drum 321 (pitch between virtual straight lines in FIGS. 6 and 7). It was newly found that diagonal streaks that can be discerned with the naked eye are generated on the image when they interfere with each other. FIG. 8 is a schematic view showing how the diagonal 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 diagonal muscle IL is exaggerated for the sake of explanation. Such an oblique streak IL appears prominently on the halftone image HT.

Here, when the pitch of the cutting marks of the developing roller 83 is 100 μm or more, and the screen angle θ (degrees) and the number of screen lines X (lines) in the screen image satisfy the following equation 2, diagonal streaks occur. Further, when the surface roughness Rz of the developing roller 83 is 2.0 μm or less, it is possible to suppress the generation of diagonal streaks.
25.4 / X × cosθ> 0.10 ・ ・ ・ (Equation 2)
In other words, when the inter-dot pitch W in the main scanning direction of the screen image is set to be larger than 100 μm, diagonal streaks are likely to occur.

According to such a configuration, the minute distribution of the toner layer on the developing roller 83 based on the cutting marks, which both appear in a streak pattern along the main scanning direction, and the virtual straight line between the dots in the screen image interfere with each other. This makes it possible to suppress the oblique muscle image that is visible to the naked eye.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The experimental conditions in each of the conducted experiments are as follows.
-Photoreceptor drum 321: Amorphous silicon photoconductor-Toner: Volume average particle diameter 6.8 μm, Positive chargeability-Development method: Touch-down development (magnetic roller + developing roller)
-Developing roller: outer diameter φ20 mm, resin coating layer (nylon + titanium oxide), surface resistance 1.0E + 07-1.0E + 09
-Development conditions: Toner transfer amount on the developing roller 0.25 to 0.45 mg / cm ²
Gap between the developing roller 83 and the photoconductor drum 321: 75 to 150 μm
-Gap between the developing roller 83 and the magnetic roller 82: 170-350 μm
Peripheral speed ratio between the developing roller 83 and the photoconductor drum 321: 1.2 to 2.0
Development bias (maximum amplitude 1500 to 1800 (V) of AC voltage applied between the developing roller 83 and the photoconductor drum 321 and potential difference of the same DC voltage 30 to 100 (V).

Table 1 shows the measurement results of the surface shape of the developing roller 83 with respect to the base material 830 under the cutting conditions (1 to 20), and the evaluation results of the diagonal streaks in each screen image. The surface shape of the developing roller 83 was measured along the longitudinal direction of the developing roller 83 using the contact type surface roughness meter Surfcom1500DX manufactured by Tokyo Seimitsu Co., Ltd. under the following conditions.
・ Measurement length: 4 mm
-Measured value: Mean value of a total of 12 measurement points (3 points in the longitudinal direction x 4 points in the circumferential direction) In addition, the following values were measured for each measurement parameter according to the JIS B0601 standard.
Measurement pitch Sm: Average length Surface roughness Rz: 10-point average roughness Surface roughness Ra: Arithmetic mean roughness

なお、表１の斜め筋評価では、斜め筋が、画像上に現れていないものが「０」、画像上に僅かに現れているものが「１」、画像上に顕著に現れているものが「２」として示されている。また、図９は、表１の評価結果をグラフ化したものであり、現像ローラー８３の周面の切削ピッチＳｍおよび表面粗さＲｚに対する斜め筋の発生状況を示すグラフである。図９では、画像上に現れていないものが「○（表１の０）」、画像上に僅かに現れているものが「△（表１の１）」、画像上に顕著に現れているものが「×（表１の２）」として示されている。

In the diagonal streak evaluation in Table 1, the diagonal streaks that did not appear on the image were "0", those that appeared slightly on the image were "1", and those that appeared prominently on the image. It is shown as "2". Further, FIG. 9 is a graph showing the evaluation results of Table 1 and shows the state of occurrence of diagonal streaks with respect to the cutting pitch Sm and the surface roughness Rz of the peripheral surface of the developing roller 83. In FIG. 9, those not appearing on the image are “○ (0 in Table 1)”, those slightly appearing on the image are “Δ (1 in Table 1)”, and are prominently appearing on the image. The thing is shown as "x (2 in Table 1-2)".

With reference to Table 1 and FIG. 9, under the conditions of 212 screen lines and a screen angle of 45 degrees and 127 screen lines and a screen angle of 65 degrees, when the cutting pitch is Sm ≧ 100 (μm), diagonal streaks are formed. Was not generated. Further, under the conditions of 141 screen lines and 45 degrees screen angle, 178 screen lines and 27 degrees screen angle, 106 screen lines and 45 degrees screen angle, 134 screen lines and 27 degrees screen angle, When the surface roughness Rz along the axial direction on the peripheral surface of the developing roller 83 was less than 2.0 μm, the result was that no diagonal streaks were generated (cutting conditions 4, 9, 10, 11, 18 in Table 1). ..

In other words, when the dot-to-dot pitch (dot-to-dot distance) of the screen image is 85 (μm), 127 (μm) or 169 (μm), the screen angle θ (degrees) in the screen image and the screen. When the number of lines X (lines) and the pitch Y (μm) of the cutting marks of the developing roller 83 satisfy the above-mentioned equation 2, the result is that no diagonal streaks are generated. In addition, referring to Table 1, when the pitch Sm of the cutting mark is 100 μm or more, diagonal streaks are likely to occur in the range where the inter-dot pitch of the screen image is 100 μm or more. Even when the pitch of the cutting marks easily interferes with the screen image in this way, the surface roughness Rz along the axial direction on the peripheral surface of the developing roller 83 is set to 2.0 μm or less on the image. The occurrence of diagonal streaks is suppressed.

As described above, according to the present embodiment, the screen angle θ (degrees) and the number of screen lines X (lines) satisfy the predetermined relational expressions, based on the interference between the screen image and the cutting pitch of the developing roller. The occurrence of diagonal streaks on the image is suppressed.

Further, in the present embodiment, the developing roller 83 has a circular tubular base material 830 and a resin coating layer formed on the base material 830. Therefore, the resin coating layer stably forms a developing electric field between the developing roller 83 and the photoconductor drum 321. Further, even when the cutting marks formed on the peripheral surface of the base material 830 remain on the peripheral surface of the resin coating layer, diagonal streaks are formed on the image based on the interference between the screen image and the cutting pitch of the developing roller. It is suppressed from occurring.

Further, the base material 830 of the developing roller 83 is made of aluminum, the developing roller 83 further has an alumite layer formed on the base material 830, and the resin coating layer is formed on the alumite layer. Therefore, the alumite layer suppresses the peeling of the resin coating layer.

Further, the developer 324 includes a developer storage unit 81 that stores a developer containing toner and a magnetic carrier, and a magnetic roller 82 that is rotated around a predetermined axis of rotation and receives toner and carriers from the developer storage unit 81. It has a developing roller 83 that receives toner from the magnetic roller 82 and supplies toner to the photoconductor drum 321. According to this configuration, even when the developing device 324 has a magnetic roller 82 and a developing roller 83 and a touch-down developing method is adopted, it is based on the interference between the screen image and the cutting pitch of the developing roller. The occurrence of diagonal streaks on the image is suppressed.

Further, the magnetic roller 82 and the developing roller 83 are rotated in opposite directions in the regions facing each other. According to this configuration, the toner layer on the developing roller 83 that has passed through the developing nip is due to 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. Therefore, it is suppressed that a large cohesive force is applied to the developer in the facing region as compared with the case where the magnetic roller 82 and the developing roller 83 are rotated in the same direction in the regions facing each other. On the other hand, in such a case, the cutting marks formed on the peripheral surface of the developing roller 83 are difficult to be polished by the developing agent in the facing region, and are likely to remain even after long-term use. Even in such a case, the screen angle θ (degrees) and the number of screen lines X (lines) satisfy a predetermined relational expression, and the surface roughness Rz along the axial direction on the peripheral surface of the developing roller 83 is 2. Since it is set to 0.0 μm or less, it is possible to prevent diagonal streaks from being generated on the image based on the interference between the screen image and the cutting pitch of the developing roller.

Further, in the present embodiment, the developer layer on the developing roller 83 is not in contact with the surface of the photoconductor drum 321. In this case, the developer layer (toner layer) on the developing roller 83 is not in contact with the surface of the photoconductor drum 321 unlike the known contact developing method. Therefore, the minute distribution of the developer layer according to the cutting marks of the developing roller 83 greatly affects the amount of toner flying to the photoconductor drum 321. Even in such a case, the screen angle θ (degrees) and the number of screen lines X (lines) satisfy the predetermined relational expressions, so that the screen image and the cutting pitch of the developing roller are on the image based on the interference. Occurrence of diagonal streaks is suppressed. In other words, when the developer layer on the developing roller 83 is in contact with the surface of the photoconductor drum 321 as in a known contact developing 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), the oblique streak image that is remarkably likely to occur in the touch-down developing method is suppressed. .. The cutting marks of the base material 830 tend to remain on the peripheral surface of the developing roller 83 even after the subsequent alumite treatment and resin coating layer forming treatment. Further, the cutting marks appearing on the developing roller 83 (resin coating layer) appear as the distribution of the toner layer. As a result, on the photoconductor drum 321 the distribution of the toner layer due to the cutting marks (distribution of the amount of toner that can fly) may interfere with the inter-dot pitch (distance between dots) in the screen image. Was newly discovered. Then, by setting the surface roughness Rz along the axial direction on the peripheral surface of the developing roller 83 to 2.0 μm or less, diagonal streaks are formed on the image based on the interference between the screen image and the cutting pitch of the developing roller. Although it is suppressed from occurring, it is newly discovered.

It should be noted that the above effect is further confirmed even when the pitch between dots (distance between dots) of the screen image is in the range of 30 (μm) to 250 (μm) and the number of screen lines is in the range of 100 to 300 lines. rice field.

The present invention is not limited to the above aspect. Even in the two-component development method, magnetic or non-magnetic one-component development method, if a streak-like developer distribution due to cutting marks is likely to occur on the developing roller, the screen angle θ (degrees) and the number of screen lines X. When the above formula 2 is satisfied, the surface roughness Rz along the axial direction of the peripheral surface of the developing roller 83 is set to 2.0 μm or less, so that diagonal streaks are generated on the image. Is deterred. Further, the image forming apparatus 1 is not limited to the one that forms a color image, and may be one that forms a monochromatic (monochrome) image.

1 Image forming device 10 Device body 30 Image forming unit 32 Image forming unit 33 Intermediate transfer unit 321 Photoconductor drum 322 Charging device 323 Exposure device 324 Developing device 80 Developing housing 81 Developing agent storage 82 Magnetic roller 83 Developing roller 830 Base material 84 Developer control blade

Claims (6)

A photoconductor drum having a surface on which an electrostatic latent image is formed and carrying a developer image on the surface,
A charging device that charges the surface of the photoconductor drum to a predetermined potential,
An exposure device that forms an electrostatic latent image by irradiating the surface of the photoconductor drum charged with the predetermined potential with exposure light corresponding to the image data.
It has a developing roller that includes a peripheral surface that carries a developing agent and is rotated around a predetermined rotation axis, and by supplying the developing agent to the surface of the photoconductor drum, the electrostatic latent image is converted into the developing agent image. With the developing equipment that becomes apparent in
Equipped with
The exposure apparatus is a screen image inclined with a predetermined screen angle θ with respect to the main scanning direction, and the static screen image formed by a predetermined number of screen lines X per inch in the main scanning direction. It forms an electro-latent image,
The developing roller has cutting marks formed on the peripheral surface along the circumferential direction in the rotation of the developing roller and at a predetermined pitch along the axial direction of the rotating shaft.
The screen angle θ (degrees) and the number of screen lines X (lines) satisfy the relational expression of 25.4 / X × cos θ> 0.10, the pitch of the cutting marks is 100 μm or more, and further, the above. An image forming apparatus having a surface roughness Rz of 2.0 μm or less along the axial direction on the peripheral surface of a developing roller. The image forming apparatus according to claim 1, wherein the developing roller has a circular tubular base material and a resin coating layer formed on the base material. The substrate of the developing roller is made of aluminum.
The developing roller further has an alumite layer formed on the substrate, and the developing roller further has an alumite layer.
The image forming apparatus according to claim 2, wherein the resin coating layer is formed on the alumite layer. The developing device
A developer storage unit that stores the developer containing toner and a magnetic carrier, and a developer storage unit.
A magnetic roller that is rotated about a predetermined axis of rotation and receives the toner and the carrier from the developer reservoir.
The developing roller that receives the toner from the magnetic roller and supplies the toner to the photoconductor drum.
3. The image forming apparatus according to claim 3. The image forming apparatus according to claim 4 , wherein the magnetic roller and the developing roller are rotated in opposite directions in regions 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 photoconductor drum.

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