JP2020012965A - Developing device and image forming apparatus - Google Patents

Abstract

To reduce a difference in surface potential between an exposure area and a non-exposure area.SOLUTION: An image forming apparatus 100 comprises: a photoreceptor drum 42; a charging roller 44; an exposure unit 41; a developing roller 431; and a first static eliminator 45. The charging roller 44 charges a peripheral surface of the photoreceptor drum 42. The exposure unit 41 exposes the photoreceptor drum 42 to form an electrostatic latent image. The first static eliminator 45 eliminates static electricity on the peripheral surface of the photoreceptor drum 42. An actual contact area ratio Z, and the quotient X obtained by dividing the static eliminating light quantity L2 of the first static eliminator 45 by the exposure light quantity L1 satisfy the following formula (A). The actual contact area ratio Z indicates the quotient obtained by dividing the actual contact area SR by the nip area SN. The actual contact area SR indicates the area in which the photoreceptor drum 42 is in contact with a surface of the charging roller 44. The nip area SN indicates the product of a nip width NB and a contact length NL. Formula (A) is Z≤C1×X-C2, wherein the constant C1 and the constant C2 are preset.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a developing device and an image forming device.

  In an image forming apparatus, various techniques for suppressing a decrease in image quality have been disclosed.

  For example, the image forming apparatus described in Patent Literature 1 includes a charging device and a photosensitive drum. The charging device has a charging roller and a suspension device. The charging roller is in contact with the surface of the photosensitive drum, and forms a nip with the photosensitive drum by elastic deformation. The charging roller charges the surface of the photosensitive drum while rotating. The suspension device changes the state of the elastic deformation according to the peripheral speed of the photosensitive drum, thereby changing the area of the surface of the charging roller. The area of the charging roller surface indicates an area contributing to air discharge. Air discharge occurs between the surface of the charging roller and the surface of the photosensitive drum near the nip.

JP 2012-181407 A

  However, in the image forming apparatus described in Patent Literature 1, there is a possibility that a surface potential difference of the photosensitive drum occurs between the exposed area and the non-exposed area. The exposure region indicates a region where an electrostatic latent image is formed by the exposure device before the peripheral surface of the photosensitive drum is charged by the charging roller. The non-exposed area indicates an area where an electrostatic latent image is not formed by the exposure device before the peripheral surface of the photosensitive drum is charged by the charging roller. This surface potential difference may cause a density difference of an image formed on a sheet.

  The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of reducing a surface potential difference between an exposed area and a non-exposed area.

The developing device according to the present invention includes a photosensitive drum, a charging roller, an exposing device, a developing roller, and a first static eliminator. The charging roller charges the peripheral surface of the photoconductor drum. The exposure device exposes the photosensitive drum to form an electrostatic latent image. The developing roller supplies a toner to the electrostatic latent image to form a toner image. The first static eliminator neutralizes the peripheral surface of the photosensitive drum. The actual contact area ratio Z and the quotient X obtained by dividing the light amount of the first static eliminator by the exposure light amount satisfy Expression (A). The actual contact area ratio Z indicates a quotient obtained by dividing the actual contact area by the nip area. The actual contact area indicates an area where the photosensitive drum is in contact with the surface of the charging roller. The nip area indicates a product of a nip width and a contact length. The contact length indicates a length in which the charging roller contacts the photosensitive drum in the longitudinal direction of the charging roller.
Z ≦ C1 × X−C2 Formula (A)
However, the constant C1 and the constant C2 are set in advance.

An image forming apparatus according to the present invention includes a photosensitive drum, a charging roller, an exposing device, a developing roller, a transfer unit, and a first static eliminator. The charging roller charges the peripheral surface of the photoconductor drum. The exposure device exposes the photosensitive drum to form an electrostatic latent image. The developing roller supplies a toner to the electrostatic latent image to form a toner image. The transfer unit transfers the toner image to a recording medium. The first static eliminator neutralizes the peripheral surface of the photosensitive drum. The actual contact area ratio Z and the quotient X obtained by dividing the light amount of the first static eliminator by the exposure light amount satisfy Expression (A). The actual contact area ratio Z indicates a quotient obtained by dividing the actual contact area by the nip area. The actual contact area indicates an area where the photosensitive drum is in contact with the surface of the charging roller. The nip area indicates a product of a nip width and a contact length. The contact length indicates a length in which the charging roller contacts the photosensitive drum in the longitudinal direction of the charging roller.
Z ≦ C1 × X−C2 Formula (A)
However, the constant C1 and the constant C2 are set in advance.

  According to the developing device and the image forming apparatus of the present invention, the surface potential difference between the exposed region and the non-exposed region can be reduced.

FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of a configuration of an image forming unit according to the embodiment of the present disclosure. It is a figure showing an example of a measuring device of an actual contact area. It is a figure showing an example of a measurement result of an actual contact area. 9 is a graph showing an example of an effect of an actual contact area ratio on a change in dark potential. FIG. 3 is a conceptual diagram illustrating a phenomenon in which internal carriers of a photoconductor layer are drawn out to a charging roller. 4 is a chart showing an example of a relationship between an actual contact area ratio, a quotient obtained by dividing a light amount of a first static eliminator by an exposure light amount, and a surface potential difference. 6 is a graph showing an example of a relationship between an actual contact area ratio, a quotient obtained by dividing a charge removal light amount by an exposure light amount, and an evaluation result. It is a figure showing an example of arrangement of the 2nd static eliminator.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings (FIGS. 1 to 9). In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

  First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of the image forming apparatus 100. The image forming apparatus 100 is a color MFP.

  As shown in FIG. 1, the image forming apparatus 100 includes an image forming unit 1, an image reading unit 2, and a document conveying unit 3. The image forming unit 1 forms an image on a sheet P. The image reading unit 2 reads an image formed on the document R and generates image information. The document transport unit 3 transports the document R to the image reading unit 2.

  The image forming unit 1 includes a feeding unit 12, a conveyance unit LP, a toner supply unit 13, an image forming unit 4, a fixing unit 16, and a discharging unit 17. The image forming unit 4 includes a transfer unit 5.

  The feeding section 12 supplies the sheet P to the transport section LP. The transport unit LP transports the sheet P to the discharge unit 17 via the transfer unit 5 and the fixing unit 16. The sheet P corresponds to an example of a “recording medium”.

  A toner container 131, a toner container 132, a toner container 133, and a toner container 134 are mounted on the toner supply unit 13. The toner container 131 stores cyan toner TN1. The toner container 132 stores magenta toner TN2. The toner container 133 stores yellow toner TN3. The toner container 134 stores black toner TN4. In the following description, each of the toner containers 131 to 134 may be collectively referred to as a toner container 130. Further, each of the toners TN1 to TN4 may be collectively referred to as a toner TN. The toner container 130 supplies the toner TN to the image forming unit 4. The image forming unit 4 forms an image on the sheet P. The configuration of the image forming unit 4 will be described later in detail with reference to FIG.

  The transfer unit 5 includes an intermediate transfer belt 54. The image forming unit 4 transfers the cyan, magenta, yellow, and black toner images onto the intermediate transfer belt 54. A plurality of color toner images are superimposed on the intermediate transfer belt 54, and an image is formed on the intermediate transfer belt 54. The transfer unit 5 transfers the image formed on the intermediate transfer belt 54 onto the paper P. As a result, an image is formed on the sheet P.

  The fixing unit 16 heats and pressurizes the sheet P, and fixes an image formed on the sheet P to the sheet P. The discharge unit 17 discharges the sheet P to the outside of the image forming apparatus 100.

  Next, the configuration of the image forming unit 4 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram illustrating an example of the configuration of the image forming unit 4. As shown in FIG. 2, the image forming unit 4 includes an image forming unit 4c, an image forming unit 4m, an image forming unit 4y, and an image forming unit 4k.

  Each of the image forming unit 4c, the image forming unit 4m, the image forming unit 4y, and the image forming unit 4k controls the exposure unit 41, the photosensitive drum 42, the developing unit 43, the charging roller 44, the first static eliminator 45, and the cleaning blade 46. Prepare. The developing unit 43 has a developing roller 431. The configuration of each of the image forming unit 4c, the image forming unit 4m, the image forming unit 4y, and the image forming unit 4k is substantially the same except for the color of the supplied toner TN. Therefore, in the following description, the configuration of the image forming unit 4c to which the cyan toner TN1 is supplied will be described, and the configurations of the image forming units 4m, 4y, and 4k other than the image forming unit 4c will be described. Description is omitted.

  The image forming unit 4c includes an exposure unit 41c (41), a photosensitive drum 42c (42), a developing unit 43c (43), a charging roller 44c (44), a first static eliminator 45c (45), and a cleaning blade 46c (46). Having.

The charging roller 44c charges the photosensitive drum 42c to a predetermined potential. The electric resistance of the charging roller 44c is, for example, not less than 1 × 10 ⁴ Ω and not more than 1 × 10 ⁹ Ω. The exposing device 41c irradiates the photosensitive drum 42c with laser light to expose the photosensitive drum 42c to form an electrostatic latent image on the photosensitive drum 42c. The developing unit 43c has a developing roller 431c (431). The developing roller 431c supplies the cyan toner TN1 to the photosensitive drum 42c and develops the electrostatic latent image to form a toner image. Thus, a cyan toner image is formed on the peripheral surface of the photosensitive drum 42c.

  The transfer unit 5 transfers the toner image onto the paper P. The transfer unit 5 includes a primary transfer roller 51, a secondary transfer roller 52, a driving roller 53, an intermediate transfer belt 54, a driven roller 55, and a blade 56. The primary transfer roller 51 transfers the cyan, magenta, yellow, and black toner images from the photosensitive drum 42 to the intermediate transfer belt 54. The primary transfer roller 51 includes a primary transfer roller 51c, a primary transfer roller 51m, a primary transfer roller 51y, and a primary transfer roller 51k.

  The drive roller 53 drives the intermediate transfer belt 54. The intermediate transfer belt 54 is an endless belt stretched around the primary transfer roller 51, the driving roller 53, and the driven roller 55. The intermediate transfer belt 54 is driven to rotate counterclockwise by the drive roller 53 as indicated by arrows DR1 and DR2. The driven roller 55 is driven to rotate as the intermediate transfer belt 54 rotates. The blade 56 removes the toner TN remaining on the surface of the intermediate transfer belt 54.

  The secondary transfer roller 52 is pressed by the drive roller 53, and a nip portion NQ is formed between the secondary transfer roller 52 and the drive roller 53. The secondary transfer roller 52 transfers the toner image on the intermediate transfer belt 54 to the sheet P when the sheet P passes through the nip NQ.

  The first static eliminator 45c irradiates the surface of the photoconductor drum 42c with static elimination light to neutralize the surface of the photoconductor drum 42c. The static elimination light is, for example, laser light. The first static eliminator 45 c is disposed downstream of the primary transfer roller 51 in the rotation direction of the photosensitive drum 42. That is, the first static eliminator 45c neutralizes the surface of the photosensitive drum 42 after the toner image is transferred from the photosensitive drum 42 to the intermediate transfer belt 54 by the primary transfer roller 51.

  The tip (upper end in FIG. 2) of the cleaning blade 46c is in sliding contact with the peripheral surface of the photosensitive drum 42c. The cyan toner TN1 remaining on the peripheral surface of the photosensitive drum 42c is removed by the sliding contact between the peripheral surface of the photosensitive drum 42c and the tip of the cleaning blade 46c.

  Note that the photosensitive drum 42, the charging roller 44, the exposing device 41, the developing roller 431, and the first static eliminator 45 correspond to an example of a “developing device”.

  Next, the measuring device 6 for measuring the actual contact area SR between the charging roller 44 and the photosensitive drum 42 will be described with reference to FIGS. FIG. 3 is a diagram illustrating an example of the measuring device 6 for the actual contact area SR. The actual contact area SR indicates an area where the charging roller 44 and the photosensitive drum 42 are in contact. Specifically, the actual contact area SR indicates the total area of the area RED where the surface of the charging roller 44 and the surface of the photosensitive drum 42 are actually in contact. The area RED will be described later in detail with reference to FIG.

  As shown in FIG. 3, the measuring device 6 includes a prism 61, a light source 62, a light receiving unit 63, and an electronic balance 64.

  The prism 61 is formed of triangular prism glass. The prism 61 is mounted on the two charging rollers 44. A pressing force F acts on the upper end of the prism 61 downward. The prism 61 guides the light beam LB from the light source 62 to the charging roller 44. The prism 61 guides the light reflected on the lower surface of the prism 61 to the light receiving unit 63.

  The light source 62 emits the light beam LB toward the prism 61. The light source 62 includes, for example, an LED (Light Emitting Diode). That is, the light beam LB is, for example, a laser beam.

  The light receiving section 63 receives light reflected from the lower surface of the prism 61. The light receiving unit 63 includes a lens and a camera. The lens focuses the reflected light on the camera. The camera includes, for example, a CCD (Charge Coupled Device) and detects reflected light.

  In a region RED where the surface of the charging roller 44 is in contact with the surface of the prism 61, the light beam LB is irregularly reflected on the surface of the charging roller 44. Therefore, when the light beam LB is reflected on the area RED, the light receiving unit 63 does not receive the light beam LB. On the other hand, in a region RFD where the surface of the charging roller 44 does not contact the surface of the prism 61, the light beam LB is regularly reflected at the bottom surface of the prism 61. Therefore, when the light beam LB is reflected by the region RFD, the light receiving unit 63 receives the light beam LB. The region RFD will be described later in detail with reference to FIG.

  The electronic balance 64 detects the pressing force F.

  Next, a measurement result of the actual contact area SR will be described with reference to FIGS. FIG. 4 is a diagram illustrating an example of a measurement result of the actual contact area SR. In FIG. 4, the upper diagram shows an example of an image captured by the camera of the light receiving unit 63. The width NB indicates a nip width between the charging roller 44 and the prism 61. The lower diagram in FIG. 4 is an enlarged view of the area AR in the upper diagram.

  As shown in FIG. 4, the area AR includes an area RED and an area RFD. The region RED is shown in black, and the region RFD is shown in white. The region RED indicates a region where the light beam LB does not enter. That is, the region RED indicates a region where the surface of the charging roller 44 and the surface of the prism 61 are in contact. The region RFD indicates a region where the light beam LB is incident. That is, the region RFD indicates a region where the surface of the charging roller 44 and the surface of the prism 61 are not in contact.

  In the nip area between the charging roller 44 and the photosensitive drum 42, the actual contact area SR is obtained by calculating the total area of the area RED.

  The actual contact area SR increases or decreases according to the surface roughness Rz of the charging roller 44. The actual contact area SR increases as the surface roughness Rz decreases. Further, the surface roughness Rz of the charging roller 44 can be adjusted by adjusting at least one of the filler particle diameter and the content of the filler particles contained in the surface layer of the charging roller 44.

  Next, the effect of the actual contact area ratio Z on the change in the dark potential DP will be described with reference to FIGS. FIG. 5 is a graph showing an example of the effect of the actual contact area ratio Z on the change in the dark potential DP. The actual contact area ratio Z indicates a quotient obtained by dividing the actual contact area SR by the nip area SN. The nip area SN is calculated by the product of the nip width NB and the contact length NL. The contact length NL indicates the length of contact of the charging roller 44 with the photosensitive drum 42 in the longitudinal direction of the charging roller 44.

  The horizontal axis in FIG. 5 indicates time T, and the vertical axis in FIG. 5 indicates dark potential DP. A graph G11 indicated by a solid line indicates a change in the dark potential DP when the actual contact area ratio Z is small (for example, when the actual contact area ratio Z is 0.1). A graph G12 indicated by a broken line shows a change in the dark potential DP when the actual contact area ratio Z is large (for example, when the actual contact area ratio Z is 0.5).

  As shown in FIG. 5, when the actual contact area ratio Z is large, the dark decay is greater than when the actual contact area ratio Z is small. The dark decay indicates the amount of decay of the dark potential DP. Specifically, the dark decay increases as the actual contact area ratio Z increases. The cause will be described below.

  As the actual contact area ratio Z increases, the electric field intensity at the nip between the charging roller 44 and the photosensitive drum 42 increases. In addition, as the electric field intensity at the nip is higher, the amount of the internal carrier INC drawn from the photoconductor layer 421 on the surface of the photoconductor drum 42 increases. Furthermore, the dark decay increases as the amount of internal carrier INC extracted from the photoconductor layer 421 increases. In this way, the dark decay increases as the actual contact area ratio Z increases.

  Next, a phenomenon in which the internal carrier INC of the photoconductor layer 421 is drawn out to the charging roller 44 will be described with reference to FIGS. FIG. 6 is a conceptual diagram illustrating a phenomenon in which the internal carrier INC of the photoconductor layer 421 is drawn out to the charging roller 44. The internal carrier INC indicates charged particles existing inside the photoconductor layer 421.

  Since the diameter of the photoconductor drum 42 is larger than the diameter of the charging roller 44, in FIG. 6, the upper surface of the photoconductor layer 421 of the photoconductor drum 42 is illustrated as a plane for convenience.

  In the embodiment of the present invention, the photoconductor layer 421 is formed of a single-layer OPC (Organic Photoconductor). Extraction of the internal carrier INC is more likely to occur when the photoconductor layer 421 is formed by a single layer of OPC than when the photoconductor layer 421 is formed by a laminated OPC. This is because, in a single-layer OPC, materials having functions such as a charge generation material and a charge transport material are distributed over the entire surface of the photoconductor layer 421, so that the extraction of internal carriers INC is increased. Is attributed to

<Example 1>
Next, the relationship between the actual contact area ratio Z and the quotient X and the surface potential difference ΔV will be described with reference to FIGS. The quotient X indicates a quotient obtained by dividing the light elimination light amount L2 of the first static eliminator 45 by the exposure light amount L1. FIG. 7 is a chart showing an example of the relationship between the actual contact area ratio Z, the quotient X obtained by dividing the light elimination light amount L2 of the first charge eliminator 45 by the exposure light amount L1, and the surface potential difference ΔV. FIG. 7 shows the results of the experiment. The experimental conditions are shown below.

<Experiment conditions>
As the image forming apparatus 100, TASKalfa406ci (product name) manufactured by Kyocera Document Solutions Inc. was used. The photoconductor layer 421 was a single-layer OPC. The linear velocity VL of the photosensitive drum 42 was 210 mm / sec. The diameter of the charging roller 44 was 12 mm, and the electric resistance of the charging roller 44 was 1.0 × 10 ⁵ Ω.

  As the light source of the first static eliminator 45, eight red LED chips were arranged at an interval of 15 mm along the axial direction of the photosensitive drum. The wavelength of the light emitted from the red LED chip was 780 nm.

<Evaluation items>
The surface potential difference ΔV of the photosensitive drum 42 was measured. The surface potential difference ΔV indicates a difference between the surface potential of the photosensitive drum 42 in the exposed area and the surface potential of the photosensitive drum 42 in the non-exposed area. The exposure region indicates a region where the electrostatic latent image is formed by the exposure device 41 before the peripheral surface of the photosensitive drum 42 is charged by the charging roller 44. The non-exposure area indicates an area where an electrostatic latent image is not formed by the exposure device 41 before the charging roller 44 charges the peripheral surface of the photosensitive drum 42.

<Experimental results>
As shown in FIG. 7, the experiment was performed at ten levels from level A to level J. At the level A, the surface roughness Rz of the charging roller 44 was 1.0 μm, and the surface roughness Rz increased from the level A to the level J. For example, at the level G, the surface roughness Rz was 17.8 μm, at the level H, the surface roughness Rz was 18.4 μm, and at the level J, the surface roughness Rz was 28.5 μm.

  The actual contact area ratio Z decreased from the level A toward the level J. For example, at the level A, the actual contact area ratio Z was 98%, at the level B, the actual contact area ratio Z was 72%, and at the level C, the actual contact area ratio Z was 58%. .

In each of the ten levels from level A to level J, the exposure light amount L1 was 1.1 μJ / cm ² . The exposure light amount L1 indicates the amount of light emitted from the exposure device 41 to the peripheral surface of the photosensitive drum 42. Further, in each of ten levels from level A to level J, the amount of static elimination light L2 was changed in nine steps from 0.52 μJ / cm ² to 4.67 μJ / cm ² . Specifically, the light elimination light amount L2 is set to 0.52 μJ / cm ² , 1.04 μJ / cm ² , 1.56 μJ / cm ² , 2.08 μJ / cm ² , 2.59 μJ / cm ² , 3.11 μJ / cm. ² , 3.63 μJ / cm ² , 4.15 μJ / cm ^2, and 4.67 μJ / cm ² . The light elimination light amount L <b> 2 indicates the amount of light emitted from the first static eliminator 45 to the peripheral surface of the photosensitive drum 42.

The surface potential difference ΔV decreased from the level A toward the level J. For example, when the light elimination light amount L2 is 0.52 μJ / cm ² , at the level A, the surface potential difference ΔV is 15.9 V, and at the level B, the surface potential difference ΔV is 15.0 V. At level I, the surface potential difference ΔV was 8.8 V, and at level J, the surface potential difference ΔV was 8.6 V. That is, as the actual contact area ratio Z decreased, the surface potential difference ΔV decreased. This is because the difference between the extraction amount of the internal carrier INC in the exposed region and the extraction amount of the internal carrier INC in the non-exposed region decreases as the actual contact area ratio Z decreases.

In addition, the surface potential difference ΔV decreased with an increase in the charge elimination light amount L2. For example, the levels A, neutralizing amount L2 is in 0.52μJ / cm ^2, the surface potential difference ΔV is 15.9V, neutralizing amount L2 is in 1.04μJ / cm ^2, the surface potential difference ΔV was 11.2V . When the light elimination light amount L2 was 3.30 μJ / cm ² , the surface potential difference ΔV was 5.6 V, and when the light elimination light amount L2 was 3.77 μJ / cm ² , the surface potential difference ΔV was 5.0 V. That is, the surface potential difference ΔV decreased with an increase in the quotient X obtained by dividing the light elimination light amount L2 by the exposure light amount L1.

<Evaluation results>
It was visually determined whether there was a density difference between the exposed area and the non-exposed area. When there was a density difference, it was determined to be defective, and when there was no density difference, it was determined to be good. In FIG. 7, the evaluation result is poor in the region on the left (or upper side) of the boundary line BL, and the evaluation result is good in the region on the right side (or lower side) of the boundary line BL. In other words, it was found that the evaluation result was good if the surface potential difference ΔV was less than 6.5 V.

  FIG. 8 is a graph showing an example of the relationship between the actual contact area ratio Z, the quotient X, and the evaluation result. The quotient X indicates a quotient obtained by dividing the light elimination light amount L2 by the exposure light amount L1. The vertical axis of FIG. 8 indicates the actual contact area ratio Z, and the horizontal axis of FIG. 8 indicates a quotient X obtained by dividing the charge elimination light amount L2 by the exposure light amount L1. In FIG. 8, a circle indicates that the evaluation result is good, and a cross indicates that the evaluation result is bad.

As shown in the graph G2 in FIG. 8, when the following expression (1) was satisfied, the evaluation result was good.
Z ≦ 46.3 × X-31.2 (1)
The quotient X is represented by the following equation (2).
X = L2 / L1 (2)

  As described above with reference to FIGS. 2 to 8, in the embodiment of the present invention, the actual contact area ratio Z and the quotient X obtained by dividing the charge removal light amount L2 by the exposure light amount L1 satisfy Expression (1). In this case, it was found that there was no difference in density between the exposed area and the non-exposed area. That is, it has been found that the surface potential difference ΔV between the exposed region and the non-exposed region can be reduced by adjusting at least one of the actual contact area ratio Z and the charge removal light amount L2 so as to satisfy Expression (1).

  Further, in the embodiment of the present invention, since the photoconductor layer 421 is formed by single-layer OPC, the extraction of the internal carrier INC occurs as compared with the case where the photoconductor layer 421 is formed by stacked OPC. easy. Therefore, a large surface potential difference ΔV is generated depending on whether or not the exposure is performed. On the other hand, by satisfying the expression (1), it is possible to reduce the amount of the internal carrier INC extracted from the photoconductor layer 421. Therefore, the difference in image density can be effectively reduced.

In the embodiment of the present invention, the condition for forming an image having a small density difference between the exposed area and the non-exposed area is represented by Expression (1), but the present invention is not limited to this. The following equation (3) should be satisfied.
Z ≦ C1 × X-C2 (3)
However, the constant C1 and the constant C2 are set in advance, for example, by experiments. In the embodiment of the present invention, for example, the constant C1 is 46.3 and the constant C2 is 31.2.

  Next, with reference to FIGS. 2 to 9, the effect of the light elimination light amount L3 of the second static eliminator 47 will be described. FIG. 9 is a diagram illustrating an example of an arrangement of the second static eliminator 47. As shown in FIG. 9, the image forming unit 4 further includes a second static eliminator 47. The second static eliminator 47 is arranged upstream of the primary transfer roller 51 in the rotation direction of the charging roller 44.

  The second static eliminator 47 irradiates the surface of the photoconductor drum 42 with static elimination light to neutralize the surface of the photoconductor drum 42. The static elimination light is, for example, laser light. The first static eliminator 45 is different from the first static eliminator 47 in that the surface of the photosensitive drum 42 after the transfer is neutralized, whereas the second static eliminator 47 is to neutralize the surface of the photosensitive drum 42 before the transfer. The second static eliminator 47 forms a “developing device”.

For example, when the light elimination light amount L3 of the second static eliminator 47 is set to 0.5 μJ / cm ² , it has been found that the evaluation results described with reference to FIGS. 7 and 8 are improved. This is a result showing that the surface potential difference ΔV between the exposed region and the non-exposed region is reduced. This is because when pre-transfer static elimination is performed by the second static eliminator 47, the toner TN adheres to the exposed area. Therefore, the second static eliminator 47 can eliminate only the non-exposed area. Therefore, it is possible to reduce the difference between the extraction amount of the internal carrier INC in the exposure region and the extraction amount of the internal carrier INC in the non-exposure region. As a result, the surface potential difference ΔV can be reduced.

Specifically, in order to form an image having a small density difference between the exposed region and the non-exposed region, the actual contact area ratio Z and the quotient Y may satisfy the following expression (4). The quotient Y indicates a quotient obtained by subtracting the charge elimination light amount L2 of the first charge eliminator 45 by a difference obtained by subtracting the charge elimination light amount L3 of the second charge eliminator 47 from the exposure light amount L1.
Z ≦ 46.3 × Y-31.2 (4)
The quotient Y is represented by the following equation (5).
Y = L2 / (L1-L3) (5)

  As described above with reference to FIGS. 2 to 9, in the embodiment of the present invention, when Expression (4) is satisfied, the image of the image accompanying the surface potential difference ΔV between the exposed region and the non-exposed region is determined. Experiments have shown that concentration differences can be reduced. That is, by setting conditions so as to satisfy Expression (4), the difference in image density can be reduced.

In the embodiment of the present invention, the condition for forming an image having a small density difference between the exposed area and the non-exposed area is represented by Expression (4), but the present invention is not limited to this. The following equation (6) should be satisfied.
Z ≦ C1 × Y−C2 (6)
However, the constant C1 and the constant C2 are set in advance, for example, by experiments. In the embodiment of the present invention, for example, the constant C1 is 46.3 and the constant C2 is 31.2.

  The embodiment of the invention has been described with reference to the drawings. However, the present invention is not limited to the above embodiment, and can be implemented in various modes without departing from the gist thereof (for example, (1) and (2) shown below). The drawings schematically show each component in order to make it easy to understand, and the thickness, length, number, etc. of each component shown in the drawings are different from actual ones for convenience of drawing. There are cases. Further, the shapes, dimensions, and the like of the respective constituent elements shown in the above-described embodiment are merely examples, and are not particularly limited, and various changes can be made without substantially departing from the configuration of the present invention.

  (1) As described with reference to FIG. 1, in the embodiment of the present invention, the image forming apparatus 100 is a color MFP, but the present invention is not limited to this. The image forming apparatus 100 may form an image on the sheet P. The image forming apparatus 100 may be, for example, a color printer. Further, the image forming apparatus 100 may be, for example, a monochrome copying machine.

  (2) As described with reference to FIGS. 2 to 6, the photoconductor layer 421 is a single-layer OPC in the embodiment of the present invention, but the present invention is not limited to this. For example, the photoconductor layer 421 may be amorphous silicon. Further, for example, the photoconductor layer 421 may be a laminated OPC.

  INDUSTRIAL APPLICATION This invention is applicable to the field of a developing device and an image forming apparatus.

REFERENCE SIGNS LIST 100 image forming apparatus 1 image forming unit 4 image forming section 41, 41c, 41m, 41y, 41k Exposure device (part of developing device)
42, 42c, 42m, 42y, 42k Photoconductor drum (part of the developing device)
421 Photoconductor layer 43, 43c, 43m, 43y, 43k Developing section 431, 431c, 431m, 431y, 431k Developing roller (part of developing device)
44, 44c, 44m, 44y, 44k Charging roller (part of the developing device)
45, 45c, 45m, 45y, 45k First static eliminator (part of the developing device)
47, 47c, 47m, 47y, 47k Second static eliminator (part of the developing device)
5 Transfer unit 54 Intermediate transfer belt Z Actual contact area ratio SR Actual contact area SN Nip area NB Nip width NL Contact length DP Dark potential INC Internal carrier ΔV Surface potential difference Rz Surface roughness VL Linear velocity L1 Exposure light amount L2 Static electricity removal amount L3 Light removal amount

Claims (4)

A photosensitive drum,
A charging roller for charging the peripheral surface of the photoconductor drum,
An exposure device that exposes the photosensitive drum to form an electrostatic latent image;
A developing roller that supplies toner to the electrostatic latent image and forms a toner image;
A first static eliminator for neutralizing the peripheral surface of the photosensitive drum,
The actual contact area ratio Z and a quotient X obtained by dividing the light amount of the first static eliminator by the exposure light amount satisfy Expression (A);
The actual contact area ratio Z indicates a quotient obtained by dividing the actual contact area by the nip area,
The actual contact area indicates an area where the photosensitive drum and the surface of the charging roller are in contact with each other,
The nip area indicates a product of a nip width and a contact length,
The developing device, wherein the contact length indicates a length of contact of the charging roller with the photosensitive drum in a longitudinal direction of the charging roller.
Z ≦ C1 × X−C2 Formula (A)
However, the constant C1 and the constant C2 are set in advance. A second static eliminator for neutralizing the peripheral surface of the photosensitive drum before the transfer;
2. The method according to claim 1, wherein the actual contact area ratio Z and a quotient Y obtained by dividing a light amount of the first static eliminator by a difference obtained by subtracting a light amount of the second static eliminator from the exposure light amount satisfy formula (B). 3. The developing device as described in the above.
Z ≦ C1 × Y−C2 Formula (B) The photoconductor drum includes a photoconductor,
The developing device according to claim 1, wherein the photoconductor is a single-layer organic photoconductor. A photosensitive drum,
A charging roller for charging the peripheral surface of the photoconductor drum,
An exposure device that exposes the photosensitive drum to form an electrostatic latent image;
A developing roller that supplies toner to the electrostatic latent image and forms a toner image;
A transfer unit that transfers the toner image to a recording medium,
A first static eliminator for neutralizing the peripheral surface of the photosensitive drum,
The actual contact area ratio Z and a quotient X obtained by dividing the light amount of the first static eliminator by the exposure light amount satisfy Expression (A);
The actual contact area ratio Z indicates a quotient obtained by dividing the actual contact area by the nip area,
The actual contact area indicates an area where the photosensitive drum and the surface of the charging roller are in contact with each other,
The nip area indicates a product of a nip width and a contact length,
The image forming apparatus according to claim 1, wherein the contact length indicates a length of contact of the charging roller with the photosensitive drum in a longitudinal direction of the charging roller.
Z ≦ C1 × X−C2 Formula (A)
However, the constant C1 and the constant C2 are set in advance.