JP4315092B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, and an image forming method. In particular, the present invention relates to an image forming apparatus and an image forming method using an intermediate transfer member.

  Conventionally, as an electrophotographic image forming apparatus using an intermediate transfer member, a toner image formed on an image carrier as a photosensitive member is transferred to the intermediate transfer member, and the toner image on the intermediate transfer member is transferred to transfer paper. What is transferred to a transfer material such as (recording paper) is known. That is, after a toner image formed on an image carrier charged to a predetermined polarity is transferred to an intermediate transfer member using electrostatic force, the toner image on the intermediate transfer member is transferred using electrostatic force. Transfer onto the transfer material.

  An image forming apparatus using such an intermediate transfer member can superimpose a toner image formed on an image carrier on the intermediate transfer member, so that a color image forming apparatus for forming a color image on a transfer material is used. Widely used. In the color image forming apparatus, after superposed and transferred on the image carrier, the superposed toner image is collectively transferred onto a transfer material using electrostatic force.

  Here, if the toner image after passing through the primary transfer portion for transferring the toner image from the image carrier to the intermediate transfer member includes a portion having a different toner adhesion amount, the toner image on the intermediate transfer member is charged. Variations in quantity occur. For example, when the toner image on the intermediate transfer member has a solid portion and a halftone portion, the charge amount of the solid portion is smaller than that of the halftone portion. Further, for example, in the case of a color image forming apparatus, the charge amount of a part where toners of a plurality of colors are superimposed on the toner image on the intermediate transfer member is smaller than that of a part where only one color toner is attached. . Furthermore, since the toner charge amount on the intermediate transfer member changes depending on the number of times of primary transfer and the environment, image defects such as uneven transfer and toner scattering are likely to occur during secondary transfer from the intermediate transfer member to the transfer material. Become.

  In order to suppress such a variation in charge amount, there is known an image forming apparatus provided with a charging unit that charges a toner image of an intermediate transfer body before being transferred onto a transfer material (for example, Patent Document 1 and Patent Document 2). ). In the image forming apparatus according to this prior art, a potential having the same polarity as that of the toner image on the intermediate transfer member is applied to the discharge electrode and controlled so that the potential of the toner image is more charged by corona discharge. It is uniform.

JP-A-10-274892 Japanese Patent Laid-Open No. 11-143255

  In such an image forming apparatus, when a visible image is formed on a transfer material, if the transfer voltage is increased, air layer discharge may occur in the transfer material, and a white bubble-like image defect may occur (so-called “ Occurrence of “white petit phenomenon”). On the other hand, if the transfer voltage is lowered, sufficient transfer charge cannot be applied to the transfer material, and as a result, “transfer unevenness” occurs in the transfer material.

  On the other hand, in order to lower the potential of the toner image on the intermediate transfer body before the secondary transfer, neutralization by corona discharge is performed to reduce the potential of the toner image on the intermediate transfer body, thereby The occurrence of “unevenness” can be suppressed. In this way, by controlling the charge of the toner image to be neutralized, the potential of the toner image can be controlled to be equal to or lower than the potential at which “transfer unevenness” occurs.

  Further, when the toner image is excessively charged, there is a problem that transfer (so-called “toner scattering phenomenon”) occurs on the transfer material on the front side of the transfer nip due to a decrease in the adhesion force with the intermediate transfer member. If the toner image is excessively charged, the toner is separated from the intermediate transfer member and scattered before the secondary transfer from the intermediate transfer member to the transfer material. As a result, it is not normally transferred to the position to be transferred, and a visible image cannot be satisfactorily formed on the transfer material. Therefore, it is necessary to determine the static elimination conditions so that uneven transfer and toner scattering do not occur.

  On the other hand, the charge amount of toner on the intermediate transfer member varies depending on the environment, the toner concentration in the developer, the number of times of image output, etc .. It is necessary to control according to the charge amount of the toner. Further, even if corona discharge is performed on the same transfer condition with the same toner charge amount, the toner charge amount after corona discharge varies depending on the environment and the state of the toner. Therefore, it is necessary to change the static elimination conditions each time the environment changes.

  The present invention solves the above problem, and even if the environment or the like changes, the potential of the toner image on the intermediate transfer member before the secondary transfer can be controlled to a potential suitable for the secondary transfer. An object is to provide an image forming apparatus and an image forming method.

  According to the first aspect of the present invention, primary transfer means for primary transfer of a toner image formed on an image carrier to an intermediate transfer member, and secondary transfer for secondary transfer of the toner image on the intermediate transfer member to a transfer material And a charge eliminating unit that is provided between the primary transfer unit and the secondary transfer unit, and reduces the potential of the toner image on the intermediate transfer member after the primary transfer unit by performing the charge removal. And a potential measuring unit that measures the potential of the toner image on the intermediate transfer body when the neutralization is performed and the neutralization unit includes the potential of the toner image measured by the potential measurement unit. The image forming apparatus is characterized in that the charge removal is carried out by changing the charge removal condition based on the above, and the potential of the toner image on the intermediate transfer member is lowered.

  The present invention measures the potential of the toner image on the intermediate transfer member after the primary transfer and before the discharging by the discharging unit, and further the toner image on the intermediate transfer member after the discharging by the discharging unit. Is measured, and the measurement results are fed back to obtain appropriate static elimination conditions. Appropriate charge removal conditions are conditions for lowering the potential of the toner image to a level that does not cause uneven transfer or toner scattering even after secondary transfer. If the potential of the toner image on the intermediate transfer member is lowered under the static elimination conditions thus obtained, the potential of the toner image can be lowered to a level at which no transfer unevenness occurs, and secondary transfer can be performed in this state. As a result, it is possible to form a good image on the transfer material that does not cause uneven transfer. Note that the charge removal in the present invention does not completely reduce the potential of the toner image to 0 [V], but means that the potential of the toner image is lowered to a certain level.

According to a second aspect of the invention, an image forming apparatus according to claim 1, measured by the potential measuring means, when the divided conductive at a preset neutralization condition is performed by the charge eliminating means The image forming apparatus further includes a determination unit that determines whether or not the potential of the toner image on the intermediate transfer member falls within a preset potential range, and the toner image on the intermediate transfer member after the charge removal by the determination unit. Is determined to be included in the preset potential range, the subsequent static elimination is performed without changing the preset static elimination conditions, and the intermediate transfer member after the static elimination is performed by the judgment means. If it is determined that the potential of the upper toner image is not included in the preset potential range, the neutralizing unit causes the potential of the toner image on the intermediate transfer member after the neutralization to be equal to the preset potential. Change the static elimination conditions so that they are included in the range. Perform neutralization after Te, it is characterized in lowering the potential of the toner image on the intermediate transfer body.

  In the present invention, the preset potential range refers to a potential range of a toner image that can satisfactorily form an image on a transfer material without causing uneven transfer or toner scattering even after secondary transfer. The potential range is obtained in advance. If the potential of the toner image neutralized by the neutralizing means is included within the preset potential range, it can be determined that transfer unevenness does not occur even if the secondary transfer is performed. I do.

  On the other hand, if the potential of the discharged toner image is not within the preset potential range, secondary transfer with this potential will cause uneven transfer, and the image will be satisfactorily used as a transfer material. Cannot be formed. In such a case, the neutralization means changes the neutralization conditions so that the potential of the toner image after neutralization drops to a level (preset range) that does not cause uneven transfer even after secondary transfer. The image potential is neutralized.

  In this way, it is determined whether or not the potential of the toner image after charge removal is included in a preset potential range (a potential range in which an image can be satisfactorily formed on a transfer material). By performing the charge removal by feeding back the result and changing the charge removal conditions, the potential of the toner image after charge removal can be lowered to the range of the potential at which an image can be satisfactorily formed on the transfer material. When the secondary transfer is performed, it is possible to form a good image with no transfer unevenness on the transfer material.

  A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the potential measuring means is provided between the charge eliminating means and the secondary transfer means. It consists of a single electrometer.

  A fourth aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the potential measuring unit is provided between the primary transfer unit and the charge eliminating unit. A first electrometer, and a second electrometer provided between the charge eliminating unit and the secondary transfer unit, and the first electrometer is removed after the primary transfer and by the charge eliminating unit. The second electrometer measures the potential of the toner image on the intermediate transfer member after the charge removal by the charge removing means. It is a feature.

  A fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the charge eliminating unit is disposed between the discharge electrode, the discharge electrode, and the intermediate transfer member. A control electrode to which a voltage for controlling discharge of the provided discharge electrode is applied, and the voltage applied to the discharge electrode is changed on the intermediate transfer member based on the potential measured by the potential measuring means. It is characterized in that the potential of the toner image is lowered.

  A sixth aspect of the present invention is the image forming apparatus according to the fifth aspect, wherein a voltage having a polarity opposite to the polarity of the potential of the toner image is applied to the discharge electrode, and the control electrode is applied to the control electrode. A voltage having the same polarity as the polarity of the potential of the toner image is applied.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the charge removing unit has a potential of a toner image when a charge is removed by the charge removing unit. When the potential is higher than a predetermined first potential, the voltage applied to the discharge electrode is increased to perform static elimination, the potential of the toner image on the intermediate transfer member is lowered, and the static elimination is performed by the static elimination means. If the potential of the toner image is smaller than the first potential and smaller than the predetermined second potential, the voltage applied to the discharge electrode is reduced to eliminate the charge, It is characterized in that the potential of the toner image on the intermediate transfer member is lowered.

  In the present invention, the first potential is a level at which uneven transfer occurs when secondary transfer is performed when the potential of the toner image is larger than the first potential in absolute value. The second potential is a level at which toner scattering occurs when secondary transfer is performed when the potential of the toner image is absolute and smaller than the second potential. The first potential is larger in absolute value than the second potential.

When the potential of the toner image after neutralization is greater than the first potential in absolute value, divided collector is insufficient, transfer unevenness. Therefore, in order to enhance the charge removal effect, the charge is removed by increasing the voltage value applied to the discharge electrode. On the other hand, when the potential of the toner image after neutralization is smaller than the second potential in absolute value, divided collector becomes excessive, the toner scattering occurs. Therefore, in order to reduce the charge removal effect, the voltage applied to the discharge electrode is reduced to perform charge removal. In this way, by changing the voltage value applied to the discharge electrode based on the potential of the toner image when static elimination is performed, it is possible to satisfactorily form an image on the transfer material during secondary transfer. It becomes.

  An eighth aspect of the present invention is the image forming apparatus according to any one of the fifth to seventh aspects, wherein the voltage applied to the control electrode is a toner image transferred onto the intermediate transfer member. Among these, the potential is smaller than the potential of the portion where the toner is adhered to the maximum and larger than the potential of the portion where the toner is not adhered.

  A ninth aspect of the present invention is the image forming apparatus according to any one of the fifth to eighth aspects, wherein a DC voltage is applied to the discharge electrode.

  A tenth aspect of the present invention is the image forming apparatus according to any one of the fifth to ninth aspects, wherein the discharging means includes the discharge electrode made of a discharge wire and the control electrode made of a grid electrode. It consists of a scorotron static eliminator.

  According to an eleventh aspect of the present invention, there is provided a primary transfer step in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer member, and a potential of the toner image on the intermediate transfer member after the primary transfer is measured. After the first potential measurement step, after the first potential measurement step, the charge removal step of lowering the potential of the toner image on the intermediate transfer body after the primary transfer by performing charge removal, A second potential measuring step for measuring the potential of the toner image on the intermediate transfer member after the potential has been lowered; and the toner image measured in the first potential measuring step and the second potential measuring step. A second charge eliminating step for reducing the potential of the toner image on the intermediate transfer member by changing the charge removal condition based on the potential, and a secondary transfer step for secondary transfer of the toner image on the intermediate transfer member to the transfer material. When an image forming method, which comprises a.

  According to a twelfth aspect of the present invention, in the image forming method according to the eleventh aspect, the potential of the toner image is lowered under preset static elimination conditions measured in the second potential measurement step. A determination step for determining whether or not the potential of the toner image on the intermediate transfer member after being included in a preset potential range, and the potential of the toner image on the intermediate transfer member after the charge removal Is determined to be included in the preset range, the subsequent neutralization is performed without changing the preset neutralization condition, and the potential of the toner image on the intermediate transfer member after the neutralization is If it is determined that it is not included in the preset range, in the second charge eliminating step, the potential of the toner image on the intermediate transfer member after the charge removal is included in the preset potential range. Change the static elimination conditions and perform static elimination afterwards. It is characterized in lowering the potential of the toner image on the serial intermediate transfer member.

  A thirteenth aspect of the present invention is the image forming method according to the eleventh aspect or the twelfth aspect of the present invention, wherein in the first neutralization step and the second neutralization step, a discharge electrode and the discharge A potential of a toner image on the intermediate transfer member is lowered by a charge eliminator including a control electrode to which a voltage for controlling discharge of the discharge electrode provided between the electrode and the intermediate transfer member is applied. It is what.

  A fourteenth aspect of the present invention is the image forming method according to the thirteenth aspect, wherein a voltage having a polarity opposite to the polarity of the potential of the toner image is applied to the discharge electrode, and the control electrode is applied to the control electrode. A voltage having the same polarity as the polarity of the potential of the toner image is applied.

The invention of claim 15 is an image forming method according to any one of claims 13 or claim 14, wherein in the second neutralization step, divided conductive by the first neutralization step is performed If the potential of the toner image in this case is greater than the preset first potential, the voltage value applied to the discharge electrode is increased to eliminate the charge, and the potential of the toner image on the intermediate transfer member is lowered. The voltage applied to the discharge electrode when the potential of the toner image when the charge is removed by the first charge removal step is smaller than the first potential and smaller than the predetermined second potential. The discharge is performed by decreasing the value, and the potential of the toner image on the intermediate transfer member is lowered.

  A sixteenth aspect of the present invention is the image forming method according to any one of the thirteenth to fifteenth aspects, wherein the voltage applied to the control electrode is a toner image transferred onto the intermediate transfer member. Among these, the potential is smaller than the potential of the portion where the toner is adhered to the maximum and larger than the potential of the portion where the toner is not adhered.

  A seventeenth aspect of the present invention is the image forming method according to any one of the thirteenth to sixteenth aspects, wherein a DC voltage is applied to the discharge electrode.

  According to an eighteenth aspect of the present invention, in the image forming method according to any one of the thirteenth to seventeenth aspects, the discharger includes the discharge electrode made of a discharge wire, and the control electrode made of a grid electrode. It consists of a scorotron static eliminator.

  According to the first and eleventh aspects of the present invention, the condition of the neutralization before the secondary transfer is performed by measuring the potential of the toner image with and without the neutralization by the neutralization unit and feeding back the measurement result. Therefore, it is possible to control the charge of the toner before the appropriate secondary transfer. As a result, a good image can be formed on the transfer material in the secondary transfer process. Since the conditions for static elimination to be performed before secondary transfer are determined by feedback control in this way, it is possible to satisfactorily form images with various adhesion amounts on the transfer material even if the toner state or environment changes. It becomes.

  According to the second and the twelfth aspects of the present invention, it is determined whether or not the potential of the toner image after charge removal is included in the range of potential that can satisfactorily form an image in the secondary transfer process. Then, according to the determination result, the charge removal is performed under different charge removal conditions, so that a good image can be formed on the transfer material even if the toner state or environment changes.

  According to the third aspect of the present invention, the potential of the toner image when the charge is eliminated and the potential of the toner image when the charge is not eliminated are measured with one electrometer, so that the influence of an error caused by the electrometer can be taken into consideration. Therefore, it is possible to perform the charge removal control without any change.

  According to the invention described in claims 6 and 14, it is possible to lower the potential of the toner image (to eliminate the charge) by applying a voltage having a polarity opposite to that of the toner image to the discharge electrode. Furthermore, by applying a voltage having the same potential as the toner image to the control electrode, it is possible to control the charge removal effect of the discharge electrode.

  According to the seventh and fifteenth aspects of the present invention, the potential of the toner image is appropriately reduced by determining the voltage to be applied to the discharge electrode based on the potential of the toner image when the charge is removed ( Can be eliminated). This makes it possible to form a good image on the transfer material even if the toner state or environment changes during secondary transfer.

  According to the invention described in claims 8 and 16, the potential of the toner image can be lowered (discharged) by applying to the control electrode a voltage smaller than the potential of the portion where the toner adheres to the maximum. It becomes possible.

  Hereinafter, an image forming apparatus and an image forming apparatus control method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.

(Constitution)
A configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a circuit configuration of the image forming apparatus according to the embodiment of the present invention. In FIG. 1, a primary transfer unit and a secondary transfer unit, which are main parts of the image forming apparatus, are shown. FIG. 2 mainly shows the static eliminator 2 and a control unit that controls the static eliminator 2.

  This image forming apparatus includes an endless belt-like intermediate transfer member 10 (hereinafter referred to as an intermediate transfer belt 10) that is an image carrier, and is arranged in a stretched state by a plurality of support roller groups. Yes. The intermediate transfer belt 10 can be rotated by a plurality of support roller groups. Along the outer peripheral surface of the intermediate transfer belt 10, four toner image forming units 20Y, 20M, 20C, and 20Bk that form toner images of different colors are arranged at predetermined intervals. Further, an intermediate point transfer member cleaning unit that removes toner remaining on the intermediate transfer belt 10 and a separation unit that separates the transfer material P from the intermediate transfer belt 10 are provided.

  The toner image forming units 20Y, 20M, 20C, and 20Bk are all arranged in the order of operation with respect to the rotating direction of the photosensitive member 21 along the rotating photosensitive member 21 and the outer peripheral surface of the photosensitive member 21. The charging unit 22, the exposure unit 23, the developing unit 24, the primary transfer unit 25, and the cleaning unit 26 are provided.

  The toner image on the photosensitive member 21 is transferred to the intermediate transfer belt 10 by applying a transfer bias voltage controlled to an appropriate magnitude to the primary transfer means 25 in each toner image forming unit to form a transfer electric field. A primary transfer roller 25A is provided. The primary transfer roller 25A is provided so as to be pressed against the photoconductor 21 via the intermediate transfer belt 10 to form a primary transfer region T1. Accordingly, the intermediate transfer belt 10 is configured to be circulated while being in contact with each of the photoreceptors 21.

The intermediate transfer belt 10 has, for example, a single layer structure composed of a belt base having semiconductivity having a volume resistivity of 1 × 10 ⁴ to 1 × 10 ¹² [Ω · cm]. Examples of the material constituting the belt substrate of the intermediate transfer belt 10 include resin materials such as thermosetting polyimide and modified polyimide, ethylene-propylene rubber (EPDM), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), and polyurethane. Examples thereof include a rubber material such as rubber, a material in which a conductive filler such as carbon is dispersed, a material in which an ionic conductive material is contained, and the like.

  A secondary transfer roller 16 to which a bias voltage applying unit 17 for applying a transfer bias voltage is connected is provided at a position downstream of the toner image forming unit arrangement region in the moving direction of the intermediate transfer belt 10. The secondary transfer roller 16 is provided so as to be pressed by the backup roller 11 constituting the support roller group via the intermediate transfer belt 10 to form the secondary transfer region T2. Thereby, the secondary transfer means 15 is comprised.

The backup roller 11 is configured by forming a semiconductive elastic layer made of, for example, an elastic body on an outer peripheral surface of a cylindrical conductive core made of, for example, stainless steel, and the resistance value of the elastic layer is, for example, 1 × 10 ⁵ to 1 × 10 ⁷ [Ω].

  The static eliminator 2 is installed between the primary transfer unit 25 and the secondary transfer unit 15, and before transferring the toner image transferred to the intermediate transfer belt 10 by the primary transfer unit 25 onto a transfer sheet as a transfer material ( Used to reduce the potential of the toner image before secondary transfer). The static eliminator 2 corresponds to the “static elimination means” of the present invention.

  The static eliminator 2 includes a discharge wire 2a, a grid electrode 2b interposed between the discharge wire 2a and the intermediate transfer belt 10, and a casing made of a conductive member surrounding the discharge wire 2a. A direct current high voltage having a polarity opposite to the charging polarity of the toner image on the intermediate transfer belt 10 is applied to the discharge wire 2a by the wire power source 2d, and corona discharge occurs. Further, the grid power supply 2e applies a DC voltage having the same polarity as the charging electrode of the toner image on the intermediate transfer belt 10 to the grid electrode 2b, thereby controlling the output of the static eliminator 2.

  The electrometer 3 a is installed between the primary transfer unit 25 and the static eliminator 2 and measures the potential of the toner image transferred onto the intermediate transfer belt 10 by the primary transfer unit 25. That is, the potential of the toner image on the intermediate transfer belt 10 before the potential is lowered by the static eliminator 2 (before static elimination) is measured. The electrometer 3 a is connected to the control unit 4 and outputs the measured potential of the toner image to the control unit 4.

  The electrometer 3b is installed between the static eliminator 2 and the secondary transfer unit 15, and measures the potential of the toner image on the intermediate transfer belt 10 after the potential is lowered by the static eliminator 2 (after static elimination). . The electrometer 3 b is connected to the control unit 4, and outputs the measured potential of the toner image to the control unit 4. The electrometer 3a corresponds to the “first electrometer” of the present invention, the electrometer 3b corresponds to the “second electrometer” of the present invention, and the electrometer 3a and the electrometer 3b of the present invention “ It corresponds to “potential measuring means”.

  The control unit 4 controls the entire image forming apparatus. In particular, in this embodiment, the control unit 4 controls the static elimination effect of the static eliminator 2. The control unit 4 is connected to an electrometer 3a, an electrometer 3b, a wire power source 2d of the static eliminator 2, and a grid power source 2e. The controller 4 receives the potential of the toner image before neutralization measured by the electrometer 3 a and the potential of the toner image after neutralization measured by the electrometer 3.

  Further, the control unit 4 determines the potential of the solid portion where the toner is attached to the maximum and the potential of the portion where the toner is not attached from the potential of the toner image before the charge removal processing, and applies it to the grid electrode 2b. Determine the voltage range to be used. Further, the condition of charge removal before secondary transfer (voltage value to be applied from the wire power supply 2d to the discharge wire 2a) is obtained from the potential of the toner image before charge removal and after charge removal. Further, it is determined whether or not the potential of the toner image has been lowered to a predetermined value from the potential of the toner image after charge removal. Further, when the potential of the toner image is not lowered to a predetermined value, the charge removal condition (voltage value to be applied from the wire power source 2d to the discharge wire 2a) is changed, and the changed voltage is discharged from the wire power source 2d. Apply to the wire 2a. The control unit 4 corresponds to “determination means” of the present invention.

  Further, the image forming apparatus is provided with a storage unit including a ROM 5 a and a RAM 5 b, and these are connected to the control unit 4. The RAM 5b forms a temporary storage area for programs, input or output data, parameters, and the like read from the ROM 5b in various processes executed and controlled by the control unit 4. The ROM 5b stores various programs that can be executed by the image forming apparatus, setting contents according to functions, and the like.

  Further, the image forming apparatus has an operation unit (not shown). The operation unit includes an input unit and a display unit. The input unit includes a keyboard having cursor keys, numeric input keys, various function keys, and the like, and outputs a pressing signal corresponding to the key pressed on the keyboard to the control unit 4. The display unit is configured by a liquid crystal display, an EL display, or the like, and displays image data, text data, or the like on the screen in accordance with an instruction of a display signal input from the control unit 4. Note that a touch panel method may be adopted for the display unit, and the display unit may be provided integrally with the input unit.

(Operation)
Next, the operation of the image forming apparatus according to this embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing operations of the image forming apparatus according to this embodiment in order. With reference to the flowchart of FIG. 3, control for obtaining a charge removal condition from the potential of the intermediate transfer belt 10 before and after the charge removal will be described.

  First, in each of the toner image forming units 20Y, 20M, 20C, and 20Bk, a charging process by the charging unit 22, an exposure process by the exposing unit 23, and a developing process by the developing unit 24 are sequentially performed, and a toner image is formed on the photoreceptor 21. Is formed. Then, primary transfer processing by the primary transfer unit 25 is performed, and the respective color toner images are sequentially superimposed on the intermediate transfer belt 10 to be primarily transferred to form a toner image on the intermediate transfer belt 10 (step). S01). As described above, the Y, M, C, and Bk toner images sequentially formed on the photosensitive member 21 are transferred onto the intermediate transfer belt 10 while being aligned on the same surface. As a result, a toner image in which a maximum of four colors are superimposed is formed on the intermediate transfer belt 10. In the case of duplex copying, after an image is formed on one side, the transfer material P is conveyed again to the transfer position.

  The potential of the superimposed toner image on the intermediate transfer belt 10 is measured by an electrometer 3a provided between the primary transfer means 25 and the static eliminator 2, and the potential is output to the control unit 4 (step). S02). FIG. 6 shows the potential of the toner image on the intermediate transfer belt 10. In FIG. 6, the horizontal axis indicates the position on the intermediate transfer belt 10, and the vertical axis indicates the potential of the toner image on the intermediate transfer belt 10 before the charge removal process.

  As shown in FIG. 6, the potential of the toner image on the intermediate transfer belt 10 is a negative potential. For example, when the toner image on the intermediate transfer belt 10 has a solid portion and a halftone portion, the solid portion adheres to the toner. Since the amount is large, the charging potential (absolute value) becomes larger than that of the halftone portion.

The controller 4 calculates a grid voltage to be applied to the grid electrode 2b from the potential of the toner image before neutralization. The range of the grid voltage applied to the grid electrode 2b is as follows.
Of the toner image transferred onto the intermediate transfer belt 10, the potential (absolute value) of the portion where the toner adheres to the maximum> grid voltage (absolute value) to be applied to the grid electrode 2b> no toner adheres. Partial potential (absolute value)
That is, even if a voltage that is higher in absolute value than the potential of the portion where the toner adheres to the maximum is applied to the grid electrode 2b, the neutralization effect cannot be obtained. Therefore, the voltage value in the above range is applied to the grid electrode 2b.

  Then, by applying a positive voltage having a polarity opposite to the potential of the toner image from the wire power source 2d to the discharge wire 2a which is a discharge electrode under the control of the control unit 4, the toner on the intermediate transfer belt 10 is subjected to corona discharge. The potential of the image is decreased by an absolute value. At the same time, a negative potential voltage equal to the potential of the toner image is applied from the grid power source 2e to the grid electrode 2b, which is a control electrode, under the control of the control unit 4 to control the charge removal effect of the discharge wire 2a (step). S03).

  Then, the potential of the toner image after the charge removal process by the charge remover 2 is measured by the electrometer 3b installed between the charge remover 2 and the secondary transfer unit 15 (step S04). The potential of the toner image measured by the electrometer 3 b is output to the control unit 4.

  The control unit 4 receives the potential of the toner image after charge removal from the electrometer 3b, and determines whether or not the potential of the toner image has dropped to a preset potential range (step S05). Here, the preset potential range is a potential range in which, even when a visible image is formed on the transfer material P by the secondary transfer unit 15, transfer unevenness, toner scattering, and the like do not occur. In addition, it means a potential range in which an image can be formed on a transfer material. The control unit 4 determines whether or not the potential of the toner image has decreased to a potential at which no transfer unevenness or toner scattering occurs.

  The range of the potential of the toner image that can satisfactorily form an image on the transfer material will be described with reference to FIG. FIG. 4 is a graph for explaining the static elimination effect. In FIG. 4, the horizontal axis represents the potential of the toner image after the primary transfer process and before being neutralized by the neutralizer 2, and the vertical axis represents the potential of the toner image after neutralization by the neutralizer 2.

For example, the potential of the previous toner image is discharged by the discharger 2 after the primary transfer and V _1. The potentials V _a and V _b represent the potential of the toner image after neutralization. When the potential of the toner image after charge removal is included in the range of potentials V _{a to} V _b , transfer unevenness and toner scattering do not occur. However, it is the excessive neutralization by discharger 2, the potential of the toner image after neutralization is less than V _a at the absolute value, the toner scattering occurs. Further, when the charge removal by the charge remover 2 is insufficient and the potential of the toner image after charge removal becomes larger than _{Vb in} absolute value, uneven transfer occurs.

The controller 4 determines whether or not the potential of the toner image after charge removal is included in the range of potentials V _{a to} V _b . The range of the potentials V _{a to} V _b corresponds to the “predetermined potential range” of the present invention, the potential V _a corresponds to the “first potential” of the present invention, and the potential V _b corresponds to the present invention. Corresponds to the “second potential”.

For example, as shown in FIG. 4B, when the toner image having the potential of the toner image before neutralization is V _{1 under} a predetermined condition, the potential of the toner image after neutralization is V ₃ . Suppose. In this case, since it is not included in the range of the potentials V _{a to} V _b , an image cannot be favorably formed on the transfer material. In this case, as shown in FIG. 4B, since the absolute value is larger than _Vb , uneven transfer occurs. That is, when neutralization is performed under this neutralization condition, the potential relationship of the toner image before and after neutralization is represented by a straight line B represented by a broken line, and uneven transfer occurs.

The potential of the toner image (potential range V _{a to} V _b ) that does not cause uneven transfer or toner scattering is obtained in advance, and the potential range of the toner image (potential V _{a to} V _b ) is stored in the ROM 5a or the like. Store it in the department. The control unit 4 can refer to the potential range (potential range V _{a to} V _b ) of the toner image stored in the storage unit, and can form an image with a favorable potential of the toner image after the charge removal process. It is determined whether or not the toner image is included in the potential range V _{a to} V _b of the toner image.

When it is determined by the control unit 4 that the potential of the toner image after static elimination has not decreased until it is included in the potential range V _{a to} V _b where an image can be satisfactorily formed (step S05, No) However, even if the secondary transfer is performed, transfer unevenness, toner scattering, and the like occur. Therefore, the primary transfer is performed again by the primary transfer unit 25 without performing the secondary transfer (step S06).

On the other hand, since the potential of the toner image cannot be lowered to a predetermined potential range (potentials V _{a to} V _b ) under the same static elimination conditions as the static elimination performed in step S03, the control unit 4 performs the static elimination conditions (discharge wires). The wire voltage applied to 2a is changed (step S07). For example, when the charge removal amount is insufficient, the voltage value applied to the discharge wire 2a is increased, and when the charge removal is excessive, the voltage value applied to the discharge wire 2a is decreased.

  Then, the wire voltage after being changed by the control unit 4 is applied from the wire power source 2d to the discharge wire 2a, and the potential of the toner image is lowered (step S08).

Thereafter, the potential of the toner image after being neutralized by the static eliminator 2 is measured by the electrometer 3 (step S04), and the control unit 4 includes the potential of the toner image after neutralization in the potentials V _{a to} V _b. It is determined whether or not it has dropped to (step S05).

When it is determined by the control unit 4 that the potential of the toner image after charge removal has decreased to be included in the potentials V _{a to} V _b that can form an image satisfactorily (step S05, Yes) In this state, secondary transfer is performed to form a visible image on the transfer material P (step S09).

For example, when the charge elimination while changing the neutralization condition, the potential of the toner image after neutralization is to become V _2. Since the potential V ₂ is included in the potentials V _{a to} V _b , it is possible to form an image satisfactorily. That is, when the charge is removed under the changed charge removal condition, the potential relationship of the toner image before and after the charge removal is represented by a straight line A.

  In this way, the potential of the toner image can be satisfactorily lowered by measuring the potential of the toner image before and after neutralization to determine whether a good image can be formed and feeding back the determination result to the neutralization process. Is possible. As a result, even if the toner state or environment changes, it is possible to control the charge of the toner before the secondary transfer stably and appropriately for images with various toner adhesion amounts, which is favorable. An image can be obtained.

  After the neutralization process is performed by the static eliminator 2, a transfer bias voltage controlled to an appropriate magnitude by the bias voltage application unit 17 is applied to the secondary transfer roller 16, and a transfer electric field is formed in the secondary transfer region T2. Due to the action of the transfer electric field, the color toner image on the intermediate transfer belt 10 is secondarily transferred to the transferred transfer material P, and thereafter, fixing processing by a fixing means (not shown) is performed. An image is formed. Further, the toner is removed together with the residual toner remaining on the intermediate transfer belt 10 by the intermediate transfer body cleaning unit 12. After a fixing process is performed by a fixing unit (not shown), the transfer material P is discharged to a discharge tray (not shown).

On the other hand, when it is determined again by the control unit 4 that the potential of the toner image after charge removal has not decreased until it is included in the potentials V _{a to} V _b that can satisfactorily form an image on the transfer material ( In step S05, No), secondary transfer is not performed, and the above-described processing (steps S06 to S08) is repeated until the potential of the toner image falls within a predetermined potential range. Then, when the potential of the toner image decreases until it is included in the potentials V _{a to} V _b , secondary transfer is performed and an image is formed on the transfer material P (step S09).

Next, specific examples will be described with reference to the table shown in FIG. Various conditions of the image forming apparatus in this specific example are shown below.
Distance between intermediate transfer belt 10 and grid electrode 2b: 1 [mm]
Roller facing the grid electrode: grounded to GND.
Side plate of the static eliminator: the same potential as the grid electrode 2b.
Intermediate transfer belt 10: Polyimide Volume resistance of the intermediate transfer belt 10: 10 ⁹ [Ω · cm]
The static elimination effect under the above conditions will be described.

[Low humidity environment (humidity 20%, temperature 10 ° C)]
First, the result of image forming processing in a low humidity environment (humidity 20%, temperature 10 ° C.) will be described. A toner image is formed on the intermediate transfer belt 10 by primary transfer (step S01), and the potential of the toner image on the intermediate transfer belt 10 before static elimination is measured by the electrometer 3a (step S02). For example, the potential of the toner image before static elimination is set to −170 [V].

  Then, the potential of the toner image is lowered by the static eliminator 2 before the secondary transfer. At this time, a voltage of +4 [kV] is applied to the discharge wire 2a, and a potential of −50 [V] is applied to the grid electrode 2b to remove the toner image (step S03).

After neutralization, before the secondary transfer, the potential of the toner image on the intermediate transfer belt 10 after neutralization is measured by the electrometer 3b (step S04). When neutralization is performed under the above conditions, the potential of the toner image after neutralization is −135 [V]. The control unit 4 determines whether or not the potential -135 [V] of the toner image after the charge removal processing is included in the range of potentials V _{a to} V _b that can satisfactorily form an image (step S05). At this potential, the charge removal is not sufficient, and if the secondary transfer is performed in this state, uneven transfer occurs, so the control unit 4 changes the charge removal condition (step S07).

  Since the charge removal is insufficient, the voltage applied to the discharge wire 2a is increased, a voltage of +5 [kV] is applied, and a voltage of −50 [V] is applied to the grid electrode 2b without changing the grid voltage. The toner image is neutralized and the potential of the toner image is lowered (step S08).

After the charge removal, the potential of the toner image on the intermediate transfer belt 10 is measured again (step S04). If neutralization is performed under the changed conditions, the potential of the toner image after neutralization becomes −110 [V], and even if secondary transfer is performed, a good image can be formed without causing uneven transfer or toner scattering. It is included in the range of possible potentials V _{a to} V _b . When secondary transfer is performed in this state, it is possible to form a good image without transfer unevenness on the transfer material P.

[High humidity environment (humidity 80%, temperature 30 ° C)]
Next, the result of the image forming process in a high humidity environment (humidity 80%, temperature 30 ° C.), which is an environment different from the low humidity environment, will be described. A toner image is formed on the intermediate transfer belt 10 by primary transfer (step S01), and the potential of the toner image on the intermediate transfer belt 10 before static elimination is measured by the electrometer 3a (step S02). For example, the potential of the toner image before static elimination is set to −140 [V].

  Then, the potential of the toner image is lowered by the static eliminator 2 before the secondary transfer. At this time, a voltage of +4 [kV] is applied to the discharge wire 2a, and a potential of −50 [V] is applied to the grid electrode 2b to remove the toner image (step S03).

After neutralization, before the secondary transfer, the potential of the toner image on the intermediate transfer belt 10 after neutralization is measured by the electrometer 3b (step S04). When neutralization is performed under the above conditions, the potential of the toner image after neutralization is −85 [V]. The controller 4 determines whether or not the potential −85 [V] of the toner image after charge removal is included in the range of potentials V _{a to} V _b that can form an image satisfactorily (step S05). At this potential, the charge is excessively removed, and if secondary transfer is performed in this state, toner scattering occurs, so the control unit 4 changes the charge removal condition (step S07).

  Since the charge removal is excessive, the voltage applied to the discharge wire 2a is lowered, a voltage of +3.5 [kV] is applied, and the grid voltage is not changed, and the grid electrode 2b is set to −50 [V]. The toner image is neutralized by applying a voltage (step S08).

After the charge removal, the potential of the toner image on the intermediate transfer belt 10 is measured again (step S04). If neutralization is performed under the changed conditions, the potential of the toner image after neutralization becomes −100 [V], and even if secondary transfer is performed, an image can be formed satisfactorily without causing uneven transfer or toner scattering. It is included in the range of possible potentials V _{a to} V _b . If secondary transfer is performed in this state, it is possible to form a good image without uneven transfer.

  As described above, the potential of the toner image on the intermediate transfer belt 10 before and after the charge removal is measured, and the charge removal conditions are determined from the measurement result. Therefore, it is possible to control the charge of the toner before the secondary transfer stably and appropriately with respect to an image with a large amount of adhesion. By performing secondary transfer in that state, it is possible to form a good image on the transfer material.

[Modification]
The present invention is not limited to the embodiment described above. In the embodiment described above, using the electrometer 3a and the electrometer 3b, the potential of the toner image before neutralization and the potential of the toner image after neutralization by the static eliminator 2 are measured, and the measurement result is fed back. The static elimination conditions are determined. Thus, the two electrometers 3a and 3b may be used, but instead of using the two electrometers, the potential of the toner image may be measured using only one electrometer.

  For example, the electrometer 3 b is installed only between the static eliminator 2 and the secondary transfer unit 15 without installing the electrometer 3 a between the primary transfer unit 25 and the static eliminator 2. The control when the electrometer 3b is installed in this way will be described.

  First, a primary transfer process by the primary transfer unit 25 is performed, and a toner image is formed on the intermediate transfer belt 10. After the primary transfer process, the neutralization is not performed by the static eliminator 2, and the electric potential of the toner image when the neutralization is not performed is measured by the electrometer 3b after passing through the static eliminator 2. The potential of the toner image measured at this time is “the potential of the toner image when no charge removal is performed”. “The potential of the toner image when no charge removal is performed” measured by the electrometer 3 b is output to the control unit 4.

  Then, after the potential of the toner image is measured by the electrometer 3b, the secondary transfer unit 15 does not perform the secondary transfer process, and passes through the secondary transfer unit 15 as it is, and further passes through the primary transfer unit 25, The static eliminator 2 neutralizes the toner image under predetermined static elimination conditions.

  After neutralization is performed by the static eliminator 2, the potential of the toner image is measured by the electrometer 3b. The potential of the toner image measured at this time is “the potential of the toner image when the charge is removed”. The “potential of the toner image when static elimination is performed” measured by the electrometer 3 b is output to the control unit 4.

The control unit 4 determines whether or not “the potential of the toner image when the charge is removed” is included in the range of potentials V _{a to} V _b that can form an image satisfactorily. When the control unit 4 determines that “the potential of the toner image when the charge removal is performed” is not included in the range of the potentials V _{a to} V _b , the charge removal condition is changed by the control unit 4.

For example, if “the potential of the toner image when static elimination is performed” is larger than _{Vb in} absolute value, uneven transfer may occur if the secondary transfer process is performed at this potential. Accordingly, since the charge removal is insufficient, the wire voltage applied to the discharge wire 2a is increased. Conversely, when "the potential of the toner image in the case of performing neutralization" is V _a smaller absolute value, the toner scattering occurs when performing secondary transfer process in the state of the potential. Accordingly, since the charge removal is excessive, the wire voltage applied to the discharge wire 2a is lowered.

  Then, a primary transfer process is performed again by the primary transfer unit 25, and a toner image is formed on the intermediate transfer belt 10. After the primary transfer process, the charge of the toner image is not measured by the charge eliminator 2 but passes through the charge eliminator 2 and is again measured by the electrometer 3b.

  Then, after the potential of the toner image is measured by the electrometer 3 b, the secondary transfer process by the secondary transfer unit 15 is not performed, but the secondary transfer unit 15 and the primary transfer unit 25 are passed through and are changed by the static eliminator 2. The toner image is neutralized under the subsequent neutralization conditions.

After neutralization is performed by the static eliminator 2, the “potential of the toner image when neutralization is performed” is measured by the electrometer 3b. Then, the control unit 4 determines whether or not the potential of the toner image when the charge is removed is included in the range of potentials V _{a to} V _b that can form an image satisfactorily.

When it is determined that the potential of the toner image when the charge is removed is included in the range of potentials V _{a to} V _b , secondary transfer processing is performed in the state of the potential to form an image on the transfer material. In this way, by measuring the potential of the toner image in the case of not performing neutralization and the potential of the toner image in the case of performing neutralization, and feeding back the measurement result to change the neutralization conditions, the same as in the above-described embodiment. Even if the toner state or environment changes, it becomes possible to control the charge of the toner before the secondary transfer stably and appropriately. As a result, a good image can be formed on the transfer material.

  In addition, by measuring the potential of the toner image when neutralization is not performed and the potential of the toner image when neutralization is performed with one electrometer 3b, and feeding back the measurement result to change the neutralization conditions, There is no need to consider the influence of errors between the electrometers, and there is no need to secure a space for installing the electrometer 3a in the image forming apparatus. Since there is no error between the electrometers, it is possible to stably measure the potential of the toner image, thereby enabling stable feedback control. Further, since it is not necessary to secure an installation space for the electrometer 3a, there is no possibility that the image forming apparatus is increased in size, and the image forming apparatus can be reduced in size by the electrometer 3a.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram showing a circuit configuration of an image forming apparatus according to an embodiment of the present invention. 3 is a flowchart illustrating operations of the image forming apparatus according to the embodiment of the present invention in order. It is a graph for demonstrating the static elimination effect. 6 is a table for explaining an operation result of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram for explaining a potential of a toner image on an intermediate transfer member.

Explanation of symbols

2 Static eliminator 2a Discharge wire 2b Grid electrode 3a, 3b Electrometer 4 Control unit

Claims (18)

Primary transfer means for primarily transferring a toner image formed on the image carrier to an intermediate transfer member;
Secondary transfer means for secondary transfer of the toner image on the intermediate transfer member to a transfer material;
A neutralization unit that is provided between the primary transfer unit and the secondary transfer unit, and reduces the potential of the toner image on the intermediate transfer member after the primary transfer unit by performing neutralization;
A potential measuring means for measuring the potential of the toner image on the intermediate transfer body when the static elimination is performed by the static elimination means;
With
The image forming apparatus is characterized in that the charge removing unit performs charge removal while changing the charge removing condition based on the potential of the toner image measured by the potential measuring unit, and reduces the potential of the toner image on the intermediate transfer member. . Measured by the potential measuring means, or the potential of the toner image on the intermediate transfer member when the divided conductive at a preset neutralization condition is performed by the charge removing means is included in the range of a preset potential A determination means for determining whether or not,
If it is determined by the determination means that the potential of the toner image on the intermediate transfer member after the neutralization is included in the preset potential range, the preset neutralization conditions are not changed and the subsequent neutralization conditions are changed. Perform static elimination,
If it is determined by the determination means that the potential of the toner image on the intermediate transfer member after the charge removal is not included in the preset potential range, the charge removal means determines the toner on the intermediate transfer member after the charge removal. 2. The potential of the toner image on the intermediate transfer member is lowered by changing the static elimination conditions so that the potential of the image is included in the preset potential range and performing subsequent static elimination. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the potential measuring unit includes a single electrometer provided between the charge eliminating unit and the secondary transfer unit. The potential measuring means includes a first electrometer provided between the primary transfer means and the static elimination means, and a second electrometer provided between the static elimination means and the secondary transfer means, Consists of
The first electrometer measures the potential of the toner image on the intermediate transfer member after the primary transfer and before the neutralization by the neutralization unit,
3. The image formation according to claim 1, wherein the second electrometer measures the potential of the toner image on the intermediate transfer member after the charge removal by the charge removal unit. apparatus.   The charge eliminating means includes a discharge electrode and a control electrode to which a voltage for controlling discharge of the discharge electrode provided between the discharge electrode and the intermediate transfer member is applied, and is measured by the potential measuring means. 5. The image forming apparatus according to claim 1, wherein the voltage applied to the discharge electrode is changed based on the determined potential to reduce the potential of the toner image on the intermediate transfer member.   A voltage having a polarity opposite to the polarity of the potential of the toner image is applied to the discharge electrode, and a voltage having the same polarity as the polarity of the potential of the toner image is applied to the control electrode. The image forming apparatus according to claim 5. The neutralization unit performs neutralization by increasing the voltage value applied to the discharge electrode when the potential of the toner image when the neutralization is performed by the neutralization unit is greater than a predetermined first potential, Reducing the potential of the toner image on the intermediate transfer member;
If the potential of the toner image when the neutralization is performed by the neutralizing unit is smaller than the first potential and smaller than the predetermined second potential, the voltage value applied to the discharge electrode is decreased. 7. The image forming apparatus according to claim 5, wherein static elimination is performed to reduce a potential of the toner image on the intermediate transfer member.   The voltage applied to the control electrode is smaller than the potential of the portion of the toner image transferred onto the intermediate transfer member where the toner is attached to the maximum, and more than the potential of the portion where the toner is not attached. The image forming apparatus according to claim 5, wherein the image forming apparatus is large.   9. The image forming apparatus according to claim 5, wherein a DC voltage is applied to the discharge electrode.   10. The image forming apparatus according to claim 5, wherein the static elimination unit includes a scorotron static eliminator in which the discharge electrode is a discharge wire and the control electrode is a grid electrode. A primary transfer step in which a toner image formed on the image carrier is primarily transferred to an intermediate transfer member;
A first potential measuring step for measuring a potential of a toner image on the intermediate transfer member after the primary transfer;
After the first potential measurement step, a charge removal step of reducing the potential of the toner image on the intermediate transfer body after the primary transfer by performing charge removal;
A second potential measuring step for measuring the potential of the toner image on the intermediate transfer member after the potential of the toner image has been lowered by the charge eliminating step;
A second charge eliminating step of changing the charge removal condition based on the toner image potential measured in the first potential measurement step and the second potential measurement step to lower the potential of the toner image on the intermediate transfer member. When,
A secondary transfer step of secondarily transferring the toner image on the intermediate transfer member to a transfer material;
An image forming method comprising: The potential of the toner image on the intermediate transfer member after the potential of the toner image is lowered under preset static elimination conditions measured in the second potential measurement step is within a preset potential range. And further comprising a determination step of determining whether or not it is included,
When it is determined that the potential of the toner image on the intermediate transfer body after the charge removal is included in the preset range, the subsequent charge removal is performed without changing the preset charge removal condition,
When it is determined that the potential of the toner image on the intermediate transfer member after the charge removal is not included in the preset range, the second charge removal step includes the step of removing the toner image on the intermediate transfer member after the charge removal. 12. The toner image on the intermediate transfer member is lowered by changing the static elimination conditions so that the potential is included in the preset potential range, thereby lowering the potential of the toner image on the intermediate transfer member. Image forming method.   In the first static elimination step and the second static elimination step, a discharge electrode and a control electrode to which a voltage for controlling the discharge of the discharge electrode provided between the discharge electrode and the intermediate transfer member is applied. The image forming method according to claim 11, wherein the potential of the toner image on the intermediate transfer member is lowered by the static eliminator.   A voltage having a polarity opposite to the polarity of the potential of the toner image is applied to the discharge electrode, and a voltage having the same polarity as the polarity of the potential of the toner image is applied to the control electrode. The image forming method according to claim 13. Wherein in the second neutralization step, when the first potential higher than the potential of the toner image when the divided conductive by the first neutralization step is performed is set in advance, the voltage applied to the discharge electrode Removing the charge by enlarging, lowering the potential of the toner image on the intermediate transfer member,
The voltage applied to the discharge electrode when the potential of the toner image when the charge is removed by the first charge removal step is smaller than the first potential and smaller than the predetermined second potential. 15. The image forming method according to claim 13, wherein discharging is performed with a reduced value to reduce the potential of the toner image on the intermediate transfer member.   The voltage applied to the control electrode is smaller than the potential of the portion of the toner image transferred onto the intermediate transfer member where the toner is attached to the maximum, and more than the potential of the portion where the toner is not attached. The image forming method according to claim 13, wherein the image forming method is large.   The image forming method according to claim 13, wherein a DC voltage is applied to the discharge electrode.   18. The image forming method according to claim 13, wherein the static eliminator is a scorotron static eliminator in which the discharge electrode is made of a discharge wire and the control electrode is a grid electrode.

Images