JP2008299076A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus suppressing discharge that may be caused in a gap between an image carrier and a belt member, and reducing deterioration of, for example, the back of the belt member. <P>SOLUTION: When it is not necessary to apply a bias to an area of the back of the intermediate transfer belt 110, the area which is behind a transfer nip, the apparatus can separate at least one of a transfer bias roller 62 for the reverse polarity to toner or an exit bias blade 71 for the same polarity as the toner from the back of the intermediate transfer belt. This reduces wear in, for example, the back of the intermediate transfer belt, compared to the case where the transfer bias roller 62 and the exit bias blade 71 are kept in contact with the intermediate transfer belt 110. Discharge that may be caused in a gap between the photoreceptor 1 and the intermediate transfer belt 110 is thereby suppressed and deterioration of, for example, the back of the intermediate transfer belt is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to bias application in primary transfer of a color electrophotographic apparatus using an intermediate transfer member.

  In this type of image forming apparatus, a phenomenon of transfer dust may occur during the primary transfer from the photoreceptor to the intermediate transfer belt. Here, transfer dust refers to the fact that the toner image formed on the photoconductor is not transferred to the position where it should be transferred, but is diffused and transferred to the periphery during the primary transfer. It is a phenomenon that causes blurring. The cause of the transfer dust is, for example, when the photosensitive member and the intermediate transfer belt are separated from each other on the downstream side in the moving direction of the intermediate transfer belt from the transfer nip formed by the photosensitive member and the intermediate transfer belt. Some are caused by electric discharge generated in the gap with the belt.

  In order to suppress the occurrence of such a discharge, in the image forming apparatus disclosed in Patent Document 1, the toner is properly charged on the back surface portion of the intermediate transfer belt in the contact area where the photosensitive member and the intermediate transfer belt are in contact with each other. A transfer member to which a transfer voltage having a polarity opposite to that of the polarity is applied and a static elimination electrode to which a voltage having the same polarity as the normal charging polarity of the toner is applied are always in contact with each other. As a result, the charge of the reverse polarity remaining on the intermediate transfer belt after the toner image is transferred from the photosensitive member until the intermediate transfer belt is separated from the photosensitive member can be discharged by the discharging electrode. it can. Therefore, it is possible to suppress the occurrence of discharge when the intermediate transfer belt is separated from the photoreceptor, and to suppress the generation of transfer dust.

JP 2006-301577 A

  However, in the image forming apparatus of Patent Document 1, since the transfer member and the neutralization electrode are always kept in contact with the back side of the intermediate transfer belt, the back surface of the intermediate transfer belt and the contact surface of the transfer member and the neutralization electrode are easily worn. Become. When the back surface of the intermediate transfer belt is worn and deteriorated as described above, for example, the resistance value between the transfer member and the back surface of the intermediate transfer belt fluctuates, so that an appropriate transfer electric field cannot be obtained and image quality is deteriorated. Arise.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress an electric discharge generated in a gap between an image carrier and a belt member and to reduce deterioration of a belt member back surface and the like. A forming apparatus is provided.

In order to achieve the above object, the invention of claim 1 is directed to an image carrier that carries a toner image on its surface, and a front surface that is stretched endlessly by being stretched by a plurality of stretching members. An endless belt member that is in contact with the body to form a transfer nip, and a transfer bias having a polarity opposite to the charging polarity of the toner while being in contact with the back side region of the transfer nip among all regions on the back surface of the belt member. An image forming apparatus comprising: a first bias applying unit that applies; and a second bias applying unit that removes the charge of the belt member with a bias having the same polarity as the charging polarity of the toner while contacting the back side region. At least one of the first bias applying unit and the second bias applying unit is configured to be able to contact and separate from the belt member.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the first bias applying unit can be brought into contact with or separated from the belt member or a contact position can be changed. The means can be brought into contact with and separated from the belt member, and the displacement operation of the first bias applying means and the second bias means relative to the belt member is performed in conjunction with each other. To do.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the displacement operation of the first bias applying unit and the second bias unit with respect to the belt member is performed in a predetermined image forming mode. It is performed according to.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, at least one of the first bias applying unit and the second bias applying unit is a blade member. A taper is provided at a side end portion in contact with the belt member so as to form a slope facing the belt member, and an angle formed by the blade member and the belt member is substantially the same as the taper angle. It is characterized by being.
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, an angle formed by the blade member and the belt member is 10 [°] or more and 20 [°] or less, and the blade member is the belt member. The linear pressure at the time of contacting is 1 [gf / mm] or more and 10 [gf / mm] or less.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, a sliding member having an electric resistance value of 10 ⁴ [Ω] or more is provided on a contact surface of the blade member in contact with the belt member. It is characterized by being.

  In the present invention, when it is not necessary to apply a bias to the back side region of the transfer nip on the back surface of the belt member, at least one of the reverse polarity toner bias application member and the same polarity toner bias application member is connected from the back surface of the belt member. Can be separated. Accordingly, it is possible to suppress wear of the back surface of the belt member and the like as compared with the case where the bias applying member having the reverse polarity of the toner and the bias applying member having the same polarity of the toner are always kept in contact with the belt member.

  As described above, according to the present invention, there are excellent effects that the discharge generated in the gap between the image carrier and the belt member can be suppressed and the deterioration of the back surface of the belt member can be reduced.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of a tandem type color laser copier (hereinafter simply referred to as “copier”) 500 in which a plurality of photoconductors are arranged in parallel will be described.
FIG. 2 is a schematic configuration diagram of the copier 500 according to the present embodiment. The copier 500 includes a printer unit 100, a paper feeding device 200 on which the printer unit 100 is placed, a scanner 300 fixed on the printer unit 100, and the like. An automatic document feeder 400 fixed on the scanner 300 is also provided.

  The printer unit 100 forms an image including four sets of process cartridges 18Y, 18M, 18C, and 18K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). A unit 20 is provided. Y, M, C, and K attached to the numbers of the respective symbols indicate members for yellow, cyan, magenta, and black (the same applies hereinafter). In addition to the process cartridges 18Y, 18M, 18C, and 18K, an optical writing unit 21, an intermediate transfer unit 17, a secondary transfer device 22, a resist roller pair 49, a belt fixing type fixing device 25, and the like are disposed. .

  The optical writing unit 21 includes a light source (not shown), a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of a photoreceptor to be described later with laser light based on image data.

  The process cartridges 18Y, 18M, 18C, and 18K include a drum-shaped photosensitive member 1, a charger, a developing device 4, a drum cleaning device, a static eliminator, and the like. The process cartridges 18Y, 18M, 18C, and 18K can be pulled out from the printer unit 100 along guide rails (not shown) fixed to the printer unit 100. Further, by pushing the process cartridges 18Y, 18M, 18C, and 18K into the printer unit 100, the process cartridges 18Y, 18M, 18C, and 18K can be loaded at predetermined positions. Thereby, the replacement work and maintenance of the process cartridges 18Y, 18M, 18C, and 18K can be easily performed.

Hereinafter, the yellow process cartridge 18 will be described.
The surface of the photoreceptor 1Y is uniformly charged by a charger as charging means. The surface of the photoreceptor 1 </ b> Y that has been subjected to charging processing is irradiated with laser light that has been modulated and deflected by the optical writing unit 21. Then, the potential of the irradiation part (exposure part) is attenuated. By this attenuation, an electrostatic latent image for Y is formed on the surface of the photoreceptor 1Y. The formed electrostatic latent image for Y is developed by the developing device 4Y as developing means to become a Y toner image.
The Y toner image formed on the Y photoconductor 1Y is primarily transferred to an intermediate transfer belt 110 described later. The surface of the photoreceptor 1Y after the primary transfer is cleaned of the transfer residual toner by a drum cleaning device.
In the Y process cartridge 18Y, the photoconductor 1Y cleaned by the drum cleaning device is discharged by the charge eliminator. Then, it is uniformly charged by the charger and returns to the initial state. The series of processes as described above is the same for the other process cartridges (18M, C, K).

Next, a basic configuration of the intermediate transfer unit 17 will be described.
The intermediate transfer unit 17 includes an intermediate transfer belt 110, a belt cleaning device 90, and the like. Further, it also includes a tension roller 14, a driving roller 15, a secondary transfer backup roller 16, four transfer bias rollers 62Y, M, C, and K.
The intermediate transfer belt 110 is tensioned by a plurality of rollers including the tension roller 14. Then, it is endlessly moved clockwise in the drawing by the rotation of the driving roller 15 driven by a belt driving motor (not shown).
The four transfer bias rollers 62Y, 62M, 62C, and 62K are disposed so as to be in contact with the inner peripheral surface side of the intermediate transfer belt 110, and receive a primary transfer bias from a power source (not shown). Further, the intermediate transfer belt 110 is pressed toward the photoreceptors 1Y, 1M, 1C, and 1K from the back surface side that is the inner peripheral surface side to form primary transfer nips. In each primary transfer nip, a primary transfer electric field is formed between the photoreceptor 1 and the transfer bias roller 62 due to the influence of the primary transfer bias.
The above-described Y toner image formed on the Y photoconductor 1Y is primarily transferred onto the intermediate transfer belt 110 due to the influence of the primary transfer electric field and nip pressure. On the Y toner image, the M, C, K toner images formed on the M, C, K photoconductors 1M, C, K are sequentially superposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) that is a multiple toner image is formed on the intermediate transfer belt 110.
The four-color toner image superimposed and transferred onto the intermediate transfer belt 110 is secondarily transferred onto a transfer sheet (not shown) as a recording sheet at a secondary transfer nip described later. Transfer residual toner remaining on the surface of the intermediate transfer belt 110 after passing through the secondary transfer nip is cleaned by a belt cleaning device 90 that sandwiches the belt with the driving roller 15 on the left side in the drawing.

Next, the secondary transfer device 22 will be described.
Below the intermediate transfer unit 17 in the figure, a secondary transfer device 22 is disposed in which a paper conveying belt 24 is stretched by two stretching rollers 23. The paper transport belt 24 is moved endlessly in the counterclockwise direction in the drawing in accordance with the rotational drive of at least one of the stretching rollers 23. One of the two stretching rollers 23 arranged on the right side in the drawing sandwiches the intermediate transfer belt 110 and the paper transport belt 24 between the secondary transfer backup roller 16 of the intermediate transfer unit 17. It is out. By this sandwiching, a secondary transfer nip is formed in which the intermediate transfer belt 110 of the intermediate transfer unit 17 and the paper transport belt 24 of the secondary transfer device 22 are in contact with each other. A secondary transfer bias having a polarity opposite to that of the toner is applied to the one stretching roller 23 by a power source (not shown). By applying this secondary transfer bias, the four-color toner image on the intermediate transfer belt 110 of the intermediate transfer unit 17 is electrostatically moved from the belt side toward the one stretching roller 23 side in the secondary transfer nip. A next transfer electric field is formed. The transfer paper fed into the secondary transfer nip so as to synchronize with the four-color toner image on the intermediate transfer belt 110 by a registration roller pair 49 to be described later has four colors affected by the secondary transfer electric field and nip pressure. The toner image is secondarily transferred. Instead of the secondary transfer method in which the secondary transfer bias is applied to one of the stretching rollers 23 as described above, a charger for charging the transfer paper in a non-contact manner may be provided.

  In the paper feeding device 200 provided at the lower part of the copying machine 500 main body, a plurality of paper feeding cassettes 44 in which a plurality of transfer sheets can be stacked and stored in a bundle of sheets are arranged so as to overlap each other in the vertical direction. It is installed. Each paper feed cassette 44 presses the paper feed roller 42 against the uppermost transfer paper in the paper bundle. Then, by rotating the paper feed roller 42, the uppermost transfer paper is sent out toward the paper feed path 46.

  The paper feed path 46 that receives the transfer paper fed from the paper feed cassette 44 has a plurality of conveying roller pairs 47 and a registration roller pair 49 provided near the end in the path. Then, the transfer paper is conveyed toward the registration roller pair 49. The transfer sheet conveyed toward the registration roller pair 49 is sandwiched between the rollers of the registration roller pair 49. On the other hand, in the intermediate transfer unit 17, the four-color toner image formed on the intermediate transfer belt 110 enters the secondary transfer nip as the belt moves endlessly. The registration roller pair 49 sends out the transfer paper sandwiched between the rollers at a timing at which the transfer paper can be brought into close contact with the four-color toner image at the secondary transfer nip. Thereby, in the secondary transfer nip, the four-color toner image on the intermediate transfer belt 110 is in close contact with the transfer paper. Then, it is secondarily transferred onto the transfer paper and becomes a full color image on the white transfer paper. The transfer paper on which the full-color image is formed in this manner exits the secondary transfer nip as the paper transport belt 24 moves endlessly, and then is sent from the paper transport belt 24 to the fixing device 25.

  The fixing device 25 includes a belt unit that moves the fixing belt 26 endlessly while being stretched by two rollers, and a pressure roller 27 that is pressed toward one roller of the belt unit. The fixing belt 26 and the pressure roller 27 are in contact with each other to form a fixing nip, and the transfer paper received from the paper transport belt 24 is sandwiched therebetween. Of the two rollers in the belt unit, the roller that is pressed from the pressure roller 27 has a heat source (not shown) inside, and pressurizes the fixing belt 26 by the generated heat. The pressed fixing belt 26 heats the transfer paper sandwiched in the fixing nip. The full color image is fixed on the transfer paper by the influence of the heating and the nip pressure.

  The transfer paper that has been subjected to the fixing process in the fixing device 25 is stacked on a stack portion 57 that protrudes from the left side plate in the drawing of the printer housing or forms a toner image on the other surface. Therefore, it is returned to the secondary transfer nip described above.

  When a document (not shown) is copied, for example, a bundle of sheet documents is set on the document table 30 of the automatic document feeder 400. However, when the original is a single-sided original that is closed in a main form, it is set on the contact glass 32. Prior to this setting, the automatic document feeder 400 is opened with respect to the copying machine 500, and the contact glass 32 of the scanner 300 is exposed. Thereafter, the single-bound original is pressed by the closed automatic document feeder 400.

  When a copy start switch (not shown) is pressed after the document is set in this way, the document reading operation by the scanner 300 starts. However, when a sheet document is set on the automatic document feeder 400, the automatic document feeder 400 automatically moves the sheet document to the contact glass 32 prior to the document reading operation. In the document reading operation, first, the first traveling body 33 and the second traveling body 34 start traveling together, and light is emitted from a light source provided in the first traveling body 33. Then, the reflected light from the document surface is reflected by a mirror provided in the second traveling body 34, passes through the imaging lens 35, and then enters the reading sensor 36. The reading sensor 36 constructs image information based on incident light.

  In parallel with such document reading operation, each device in each process cartridge (18Y, M, C, K), the intermediate transfer unit 17, the secondary transfer device 22, and the fixing device 25 start driving. Then, based on the image information constructed by the reading sensor 36, the optical writing unit 21 is driven and controlled, and Y, M, C, K toner images are formed on the respective photosensitive members (40Y, M, C, K). Is formed. These toner images become four-color toner images superimposed and transferred on the intermediate transfer belt 110.

  Further, almost simultaneously with the start of the document reading operation, the paper feeding operation is started in the paper feeding device 200. In this paper feeding operation, one of the paper feeding rollers 42 is selectively rotated, and the transfer paper is sent out from one of the paper feeding cassettes 44 accommodated in the paper bank 43 in multiple stages. The fed transfer sheets are separated one by one by the separation roller 45 and enter the reverse feeding path 46, and then conveyed toward the secondary transfer nip by the conveyance roller pair 47. In some cases, paper feeding from the manual feed tray 51 is performed instead of such paper feeding from the paper feeding cassette 44. In this case, after the manual feed roller 50 is selectively rotated to feed the transfer paper on the manual feed tray 51, the separation roller 52 separates the transfer paper one by one and feeds it to the manual feed path 53 of the printer unit 100. Make paper.

  When forming another color image composed of two or more colors of toner, the copying machine 500 stretches the intermediate transfer belt 110 so that the upper stretched surface is substantially horizontal, and the upper stretched surface is placed on the upper stretched surface. All photoreceptors (1Y, M, C, K) are brought into contact. On the other hand, when forming a monochrome image consisting of only K toner, the intermediate transfer belt 110 is tilted to the lower left in the drawing by a mechanism (not shown) and the upper stretched surface is set to Y, M, C. The photoconductors 1Y, 1M, and 1C are separated. Of the four photoconductors 1Y, 1M, 1C, and 1K, only the K photoconductor 1K is rotated counterclockwise in the drawing to form only the K toner image. At this time, for Y, M, and C, not only the photoconductor but also the developing device 4 is stopped to prevent unnecessary consumption of the photoconductor and the developer.

  The copying machine 500 includes a control unit (not shown) including a CPU that controls the following devices in the copying machine 500, and an operation display unit (not shown) including a liquid crystal display, various key buttons, and the like. Yes. The operator sends a command to the control unit by a key input operation on the operation display unit, so that one of the three modes is selected from the three-sided print mode, which is a mode for forming an image only on one side of the transfer paper. You can choose one. The three single-sided printing modes include a direct discharge mode, a reverse discharge mode, and a reverse decal discharge mode.

FIG. 3 is an enlarged configuration diagram showing the developing device 4 and the photoreceptor 1 provided in one of the four process cartridges 18 (Y, M, C, K). The four process cartridges 18 (Y, M, C, K) have substantially the same configuration except that the colors of the toners to be handled are different from each other. Therefore, Y, M, C denoted by “4” in FIG. , K are omitted.
As shown in FIG. 3, the surface of the photosensitive member 1 is charged by a charging device (not shown) while rotating in the direction of arrow G in the drawing. The charged surface of the photoreceptor 1 is supplied with toner from the developing device 4 to a latent image on which an electrostatic latent image is formed by laser light emitted from an exposure device (not shown), thereby forming a toner image.

Next, a detailed description of the intermediate transfer unit 17 which is a characteristic part of the copying machine 500 of the present embodiment will be given.
FIG. 1 shows a case where image formation is performed in the standard mode. In this embodiment, the primary transfer frame 80 is transferred by applying a bias having a normal charging polarity (minus polarity in this embodiment) and a reverse polarity (plus polarity in this embodiment) of the toner to the intermediate transfer belt 110. A bias roller 62 is attached via a bearing (not shown). The transfer bias roller 62 is pressed against the intermediate transfer belt 110 by a compression spring 83 with a predetermined pressure.

  In the standard mode, the intermediate transfer belt 110 is disposed substantially horizontally and is driven to rotate. Further, the position at which the transfer bias roller 62 contacts the intermediate transfer belt 110 is set to contact at a position offset about 1 [mm] to 2 [mm] downstream from the center position of the photoreceptor 1. ing. This suppresses the occurrence of so-called pre-transfer, in which the toner on the photoreceptor 1 moves away from the photoreceptor 1 and moves onto the intermediate transfer belt 110 due to the action of the transfer electric field generated on the upstream side of the transfer nip portion. ing.

  A winding roller 73 is rotatably supported by the primary transfer frame 80 on the upstream side of the transfer bias roller 62 by a bearing (not shown). ing. Further, an exit bias blade 71 for applying a bias having the same polarity as the normal charging polarity of the toner (in this embodiment, a negative polarity) to the intermediate transfer belt 110, which will be described in detail later, is also applied to the intermediate transfer belt 110 in the standard mode. Evacuate to a position that does not touch.

  Note that the standard mode is used when an image such as a solid image, a line image, or a character image that is difficult to recognize image quality variation is formed. This is because a solid image, a line image, a character image, and the like cannot be expected to have a great effect due to the action of the exit bias blade 71 as described later. Therefore, by using the standard mode when forming these images, it is possible to prevent the back surface of the intermediate transfer belt 17 from being worn by the exit bias blade 71 and the winding roller 73, and the intermediate transfer belt 17 and the exit bias blade 71. Can be reduced.

  FIG. 4 shows a case where image formation is performed in the high image quality mode. In the present embodiment, the high image quality mode is used particularly when it is desired to reduce dust such as an image in which the dot gradation affects the image quality, for example, a photographic image, a halftone image, or a superimposed character image of two or more colors. Also, switching between the standard mode and the high image quality mode can be performed by the user selecting a key on the operation panel. It should be noted that the control is switched from the high image quality mode to the standard mode when a predetermined time elapses after the image formation in the high image quality mode is completed.

  As shown in FIG. 4, a transfer bias roller 62 is provided in contact with the back side of the intermediate transfer belt 110 on the upstream side of the primary transfer nip, and an exit bias blade 71 is provided on the back side of the intermediate transfer belt 110 on the downstream side. It is provided in contact. If the transfer bias roller 62 and the intermediate transfer belt 110 come into contact with each other before the photosensitive member 1 and the intermediate transfer belt 110 come into contact with each other, an electric field acts on the toner of the photosensitive member 1 so that the photosensitive member 1 becomes intermediate. The toner on the photoreceptor 1 moves to the intermediate transfer belt 110 before coming into contact with the transfer belt 110, so-called pre-transfer occurs, and the image is disturbed. Therefore, the transfer bias roller 62 is preferably brought into contact with a nip formed by winding of the photoreceptor 1 and the intermediate transfer belt 110. In this embodiment, the transfer bias roller 62 is formed by the photoreceptor 1 and the intermediate transfer belt 110. The transfer bias roller 62 is brought into contact with the intermediate transfer belt 110 with a predetermined pressure at a position offset about 1 [mm] to 2 [mm] downstream from the most upstream end of the winding belt nip.

  A toner image (not shown) formed on the photoreceptor 1 is charged positively by the transfer bias roller 62 in the primary transfer nip formed by the photoreceptor 1 and the intermediate transfer belt 110. As a result, the negative polarity toner is transferred from the photoreceptor 1 to the intermediate transfer belt 110 and transferred onto the intermediate transfer belt 110. Thereafter, the potential of the intermediate transfer belt 110 is dropped by the action of an electric field by the outlet bias blade 71 on the back surface of the intermediate transfer belt 110 in the primary transfer nip. Thereby, the discharge due to the potential difference at the time of peeling between the photoreceptor 1 and the intermediate transfer belt 110 is suppressed. In this way, the toner image once transferred from the photoconductor 1 to the intermediate transfer belt 110 is moved again to the photoconductor 1 by suppressing the discharge at the time of peeling between the photoconductor 1 and the intermediate transfer belt 110. In other words, the occurrence of so-called retransfer or the like can be suppressed and the occurrence of transfer dust can be suppressed.

  Here, the suppression of the discharge that occurs when the photoreceptor 1 and the intermediate transfer belt 110 are peeled in the nip exit region after the primary transfer will be described in more detail. In order to suppress discharge at the time of peeling between the photoreceptor 1 and the intermediate transfer belt 110, it is necessary to keep the potential of the intermediate transfer belt 110 immediately after the primary transfer within a predetermined range. Therefore, in the present embodiment, the exit bias blade 71 is brought into contact with the back side of the intermediate transfer belt 110, and the positive charge remaining on the intermediate transfer belt 110 after the primary transfer is neutralized, thereby removing the intermediate transfer belt 110 immediately after the primary transfer. Is maintained within a predetermined range.

  In addition, in order to eliminate the positive charge remaining on the intermediate transfer belt 110 after the primary transfer, the negative polarity bias applied to the intermediate transfer belt 110 by the outlet bias blade 71 is examined by the inventor based on various experiments. As a result, a range of 0 [V] to −800 [V] is desirable. Within this range, the positive charge remaining on the intermediate transfer belt is appropriately eliminated, and the potential of the intermediate transfer belt 110 immediately after the primary transfer can be maintained within a predetermined range, so that good image quality can be obtained. If the bias is smaller than this range in the negative direction, neutralization of the positive charge remaining on the intermediate transfer belt 110 is insufficient. In addition, if a negative bias larger than this range in the negative direction is excessively applied to the intermediate transfer belt 110, the intermediate transfer belt 110 is largely biased to the negative side, and a discharge occurs due to a potential difference from the photoreceptor 1. . That is, even if the charge removal is insufficient, a problem occurs even if the charge removal is excessive.

Next, the operation and action when shifting from the standard mode to the high image quality mode will be described.
In this embodiment, a transfer bias roller 62 attached to the primary transfer frame 80 via a bearing (not shown) and a winding roller 73 attached via a bearing (not shown) on the upstream side of the transfer bias roller 62 rotate. Supported as possible. The entire primary transfer frame 80 is configured to be rotatable about the photoreceptor 1 as a center by an end pin (not shown) and a groove of an intermediate transfer frame (not shown). An outlet bias blade 71 is fixed to the blade frame 81 at a predetermined angle. The entire blade frame 81 is configured to be movable in an oblique direction as indicated by an arrow in the figure by an end pin (not shown) and a groove of an intermediate transfer frame (not shown).

  When image formation is performed in the high image quality mode, the blade cam 81 moves to a predetermined position as the contact cam 82 rotates in the direction of the arrow in the figure. Further, the primary transfer frame 80 is pushed by the blade frame 81 by the movement of the blade frame 81, and is rotated in the direction of the arrow in the figure, so that the primary transfer frame 80 moves to a predetermined position.

  As described above, the primary transfer frame 80 rotates clockwise in FIG. 4, so that the winding roller 73 contacts the intermediate transfer belt 110 and the winding roller 73 pushes the intermediate transfer belt 110 upward. The winding roller 73 is grounded to GND in order to cancel the potential history of the intermediate transfer belt 110 after passing through the upstream color process cartridge (for example, the process cartridge 18Y). As a result, since there is a residual potential in the intermediate transfer belt 110, pre-transfer or the like occurs before the photoreceptor 1 and the intermediate transfer belt 110 are wound around the next color process cartridge (process cartridge 18M), and the image is distorted. Can be suppressed. Further, when the intermediate transfer belt 110 is pushed up by the winding roller 73, the winding length of the intermediate transfer belt 110 around the photoreceptor 1 is about 2 [mm] in the standard mode, whereas the high image quality is high. In the case of the mode, it is expanded from 5 [mm] to about 6 [mm].

  In addition, the transfer bias roller 62 is arranged on the most upstream side of the winding belt nip expanded by the winding roller 73 in the present embodiment in order to suppress the occurrence of pre-transfer as described above. 1 [mm] to 2 [mm] from the downstream side to the offset position and contact the back surface of the intermediate transfer belt 110 at that position with a predetermined pressure. Since the transfer bias roller 62 rotates together with the compression spring 83, the contact pressure of the transfer bias roller 62 with respect to the intermediate transfer belt 110 does not change in either the standard mode or the high image quality mode.

  The exit bias blade 71 is fixed to the blade frame 81, and the back surface of the intermediate transfer belt 110 is located downstream of the position where the transfer bias roller 62 contacts the intermediate transfer belt 110 by the rotation of the contact cam 82. Abut. In the present embodiment, the photosensitive member 1 and the intermediate transfer belt 110 are brought into contact with each other in order to suppress discharge when the photosensitive member 1 and the intermediate transfer belt 110 are separated on the downstream side of the belt nip by the outlet bias blade 71. The exit bias blade 71 is brought into contact with the back surface of the intermediate transfer belt 110 at a position offset about 1 [mm] to 2 [mm] upstream from the most downstream end of the belt nip. In this way, by suppressing discharge at the time of peeling at the downstream side of the belt nip, the toner image once transferred from the photoreceptor 1 to the intermediate transfer belt 110 as described above moves to the photoreceptor 1 again. In other words, the occurrence of so-called retransfer or the like can be suppressed, and the occurrence of transfer dust can be suppressed.

  When shifting from the high image quality mode to the standard mode, such as after the image formation in the high image quality mode is completed, the contact cam 82 rotates in the direction opposite to the arrow direction in the figure and is released as shown in FIG. Return to position. In conjunction with the rotation of the contact cam 82, the primary transfer frame 80 and the blade frame 81 are also returned to the standard mode position as shown in FIG.

  In the present embodiment, the exit bias blade 71 and the like are brought into and out of contact with the intermediate transfer belt 110 in the standard mode and the high image quality mode for the following reasons.

Since the exit bias blade 71 slides with respect to the back surface of the intermediate transfer belt 110, the intermediate transfer belt 110 and the exit bias blade 71 are worn. A small amount of wear powder is generated and accumulated over time at the contact portion between the outlet bias blade 71 and the intermediate transfer belt 110. As described above, the resistance value between the outlet bias blade 71 and the intermediate transfer belt 110 varies due to the wear and deterioration of the intermediate transfer belt 110 and the outlet bias blade 71 or accumulation of wear powder. If the resistance value between the back surface of the intermediate transfer belt 110 and the exit bias blade 71 fluctuates in this way, the current flowing between them fluctuates, and there is a possibility that good image quality cannot be stably obtained.

  For this reason, in this embodiment, the exit bias blade 71 is brought into contact with and slides on the back surface of the intermediate transfer belt 110 only in a limited condition by providing a high image quality mode, and the intermediate transfer belt 110 and the exit bias blade 71 are worn. It has a configuration that can suppress this. Thereby, the durability of the exit bias blade 71 and the intermediate transfer belt 110 can be sufficiently maintained, and the deterioration of the exit bias blade 71 and the intermediate transfer belt 110 and the generation amount of wear powder can be reduced.

  Further, the abrasion powder generated by the wear of the intermediate transfer belt 110 and the exit bias blade 71 is linked to the rotation operation of the exit bias blade 71 when shifting from the high image quality mode to the standard mode. Wear particles and foreign matters are removed by bringing a contact portion of the intermediate transfer belt 110 into contact with a cleaning member (not shown). As the cleaning member, a sheet member or a roller member provided on the surface with a member such as a nonwoven fabric, a member such as flocking, or a member such as a resin brush is suitable.

  FIG. 5 is a detailed explanatory view of the outlet bias blade 71 provided with the auxiliary blade 72 used in the present embodiment. In the present embodiment, an auxiliary blade 72 is provided at the tip of the exit bias blade 71 on the side in contact with the intermediate transfer belt 110. The outlet bias blade 71 is a metal plate made of iron, copper, stainless steel or the like and is formed of a member having a thickness of 0.05 [mm] to 0.2 [mm]. In order to reduce the sliding load on the intermediate transfer belt 110 and relax the mounting position accuracy, it is necessary to make the contact pressure of the auxiliary blade 72 as small as possible. For example, in the configuration in which the urging force is urged to the auxiliary blade 72 by the spring member, it is necessary to reduce the contact pressure as much as possible by reducing the spring constant of the spring member.

  The auxiliary blade 72 is preferably a film material, a sheet material and a belt material having a thickness of about 10 [μm] to 100 [μm]. In particular, by using a medium-resistance resin sheet material, a material equivalent to the intermediate transfer belt 110, a belt material having a thickness and electrical characteristics, or a thin resin film material having high resistance or insulation, Good slidability, adhesion and followability can be secured, and initial electrical characteristics can be satisfied. Further, a resin coating having the same characteristics as the above-described members may be applied to the tip of the exit bias blade 71.

Here, as a resin sheet material, a PFA sheet having a resistance value of about 10 ⁴ Ω is approximately 10 ⁴ Ω and a PI sheet having a resistance value of approximately 10 is approximately 10 ⁴ Ω and 50 μm to 100 μm. A resin sheet material having a resistance value of about 10 ¹⁴ Ω or the like with a PET sheet of about ⁷ Ω to 10 ⁹ Ω or 10 [μm] to 50 [μm] is preferable.

  In the present embodiment, the outlet bias blade 71 is configured to contact the intermediate transfer belt 110 in the counter direction. At this time, the angle at which the exit bias blade 71 and the intermediate transfer belt 110 abut is preferably 10 [°] or more and 20 [°] or less. If this angle is smaller than 10 [°], the outlet bias blade 71 tends to hit the surface, and a large biting amount must be taken in order to ensure a predetermined contact pressure. It is difficult to make contact evenly due to the surface accuracy of 71. On the other hand, when the angle is larger than 20 [°], the exit bias blade 71 tends to hit the edge, and the contact accuracy becomes difficult due to the edge accuracy.

  The linear pressure at which the exit bias blade 71 and the intermediate transfer belt 110 abut is preferably 1 [gf / mm] or more and 10 [gf / mm] or less. When the linear pressure is smaller than 1 [gf / mm], the surface pressure and edge accuracy of the outlet bias blade 71 are easily affected. When the linear pressure is greater than 10 [gf / mm], the friction between the outlet bias blade 71 and the intermediate transfer belt 110 increases due to the sliding between the outlet bias blade 71 and the intermediate transfer belt 110. As a result, the amount of scratches and wear on the outlet bias blade 71 and the intermediate transfer belt 110 over time increases.

  As described above, the exit bias blade 71 is a thin metal plate having a thickness of 0.05 [mm] to 0.2 [mm]. However, the edge of the surface in contact with the intermediate transfer belt 110 is die cut, wire cut or laser. Even if the auxiliary blade 72 is attached to the tip of the exit bias blade 71, the nip width between the intermediate transfer belt 110 and the auxiliary blade 72 (exit bias blade 71) is 0.1 [ mm] to 0.3 [mm] and the pressure concentrates on the edge, and a uniform electric field cannot be obtained when a bias is applied. Therefore, for example, a streak-like image is generated when a full-color image is formed.

Therefore, in this embodiment, as shown in FIGS. 5 and 6, the edge angle of the surface of the exit bias blade 71 on the side that contacts the intermediate transfer belt 110, in other words, the side that contacts the intermediate transfer belt 110 of the exit bias blade 71. When the intermediate transfer belt 110 and the outlet bias blade 71 come into contact with each other, the taper angle θ ₁ provided to form an inclined surface facing the intermediate transfer belt 110 at the end, and the outlet bias blade 71 and the intermediate transfer belt 110. the angle theta ₂ which forms in the are sharp-cut to be substantially the same. As a result, the nip width when the exit bias blade 71 is in contact with the intermediate transfer belt 110 is about 0.6 [mm] to 0.8 [mm], so that the contact state does not fall within the per-surface category. To do. As a result, a uniform electric field is obtained when a bias is applied from the exit bias blade 71 to the intermediate transfer belt 110, and a good image can be obtained even with a solid image.

As described above, according to the present embodiment, the photosensitive member 1 that is an image bearing member that carries a toner image on the surface, and the front surface of the photosensitive member 1 while being endlessly moved by being stretched by a plurality of stretching members. The intermediate transfer belt 110, which is an endless belt member that forms a transfer nip by contact, and the charging polarity of the toner while contacting the back side region of the transfer nip among all the regions on the back surface of the intermediate transfer belt 110. A transfer bias roller 62, which is a first bias applying means for applying a transfer bias having a reverse polarity, and a second for removing the charge of the intermediate transfer belt 110 with a bias having the same polarity as the charging polarity of the toner while contacting the back side region. In the copier 500, which is an image forming apparatus provided with an exit bias blade 71 serving as a bias applying means, a transfer bias roller 62 and an exit bias blade 71 One even without, are detachably configured with respect to the intermediate transfer belt 110. Thereby, it is possible to suppress the transfer bias roller 62 and the exit bias blade 71 from contacting the back surface of the intermediate transfer belt 110 more than necessary. Therefore, wear of the back surface of the intermediate transfer belt 110, the transfer bias roller 62, and the exit bias blade 71 is suppressed compared to the case where the transfer bias roller 62 and the exit bias blade 71 are kept in contact with the back surface of the intermediate transfer belt 110 over time. Deterioration of the back surface of the intermediate transfer belt 110, the transfer bias roller 62, and the exit bias blade 71 can be reduced.
Further, according to the present embodiment, the transfer bias roller 62 can be brought into contact with or separated from the intermediate transfer belt 110 or the contact position can be changed, and the outlet bias blade 71 can be brought into contact with or separated from the intermediate transfer belt 110. Thus, the displacement operation of the transfer bias roller 62 and the exit bias blade 71 with respect to the intermediate transfer belt 110 is performed in conjunction with each other. In this way, by performing the displacement operation of the transfer bias roller 62 and the exit bias blade 71 in conjunction with each other, the displacement operation can be simplified and easily performed.
Further, according to the present embodiment, the displacement operation of the transfer bias roller 62 and the exit bias blade 71 with respect to the intermediate transfer belt is performed in accordance with a standard mode and a high image quality mode that are predetermined image forming modes. Thus, only in the high image quality mode in which image formation requiring high image quality is performed, both the transfer bias roller 62 and the exit bias blade 71 are brought into contact with the intermediate transfer belt 110 to form an image that does not require high image quality. By separating at least one of the transfer bias roller 62 and the exit bias blade 71 from the intermediate transfer belt in the standard mode to be formed, the intermediate transfer belt 110, the transfer bias roller 62, the exit bias blade 71, and the like are prevented from being worn out and deteriorated. can do.
Further, according to the present embodiment, a taper is provided at the side end of the exit bias blade 71 that contacts the intermediate transfer belt 110 so as to form a slope facing the intermediate transfer belt 110. The angle θ ₂ formed with the transfer belt 110 and the taper angle θ ₁ are substantially the same. Thereby, the contact portion between the outlet bias blade 71 and the intermediate transfer belt 110 can be stabilized. Further, the frictional resistance between the exit bias blade 71 and the intermediate transfer belt 110 is reduced, and wear of the exit bias blade 71 and the intermediate transfer belt 110 can be reduced. The same effect can be obtained even when the transfer bias roller 62 is a transfer bias blade.
Further, according to the present embodiment, the angle formed between the exit bias blade 71 and the intermediate transfer belt 110 is 10 ° or more and 20 ° or less, and the line when the exit bias blade 71 contacts the intermediate transfer belt 110. The pressure is 1 [gf / mm] or more and 10 [gf / mm] or less. As a result, the exit bias blade 71 can come into contact with the intermediate transfer belt 110 in an optimum state, so that the electrical stability between the exit bias blade 71 and the intermediate transfer belt 110 can be improved.
Further, according to the present embodiment, the auxiliary blade 72 that is a sliding member having an electric resistance value of 10 ⁴ [Ω] or more is provided on the contact surface of the exit bias blade 71 that contacts the intermediate transfer belt 110. Thereby, the electrical stability between the outlet bias blade 71 and the intermediate transfer belt 110 can be further improved.

  In the present embodiment, the configuration in which the exit bias blade 71 is brought into contact with and separated from the intermediate transfer belt 110 has been described. However, the present invention is not limited to this. For example, in the case where a color image can be formed with toners of a plurality of colors as in the copying machine of the present embodiment, the transfer bias roller 62 relating to another color is used as the intermediate transfer belt when forming a black single color image. It is made to separate from 110. In this way, the transfer bias roller 62 is configured to be able to contact and separate from the intermediate transfer belt 110, and when the primary transfer is not performed, the transfer bias roller 62 is separated from the intermediate transfer belt 110, so that the intermediate transfer belt 110 It is possible to further reduce the wear and deterioration of the back surface of 110.

  In this embodiment, the outlet bias blade 71 is provided on the downstream side of the transfer bias roller 62. However, the present invention is not limited to this configuration. For example, the present invention can be applied to a configuration in which the exit bias blade 71 is provided on the upstream side of the transfer bias roller 62 and a configuration in which the exit bias blade 71 is provided on the upstream side and the downstream side of the transfer bias roller 62. is there. Also in these configurations, by applying the present invention, it is possible to reduce the deterioration of the intermediate transfer belt 110 and the like by the effects described in the present embodiment. Further, a transfer bias blade may be used instead of the transfer bias roller 62, or an exit bias roller may be used instead of the exit bias blade 71.

FIG. 4 is an enlarged schematic configuration diagram of a standard mode of an intermediate transfer unit that is a feature of the present invention. 1 is a schematic configuration diagram of a copier according to an embodiment. FIG. 2 is a schematic configuration diagram of a developing device and a photoreceptor. FIG. 3 is an enlarged schematic configuration diagram of an intermediate transfer unit in a high image quality mode. The schematic block diagram of the exit bias blade provided with the auxiliary | assistant blade. The schematic block diagram of an exit bias blade.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Developing device 5 Developing roller 6 Collection screw 7 Collection conveyance path 8 Supply screw 9 Supply conveyance path 10 Stirring conveyance path 11 Stirring screw 12 Developing doctor 14 Stretching roller 15 Driving roller 16 Secondary transfer backup roller 17 Intermediate transfer unit 18 Process Cartridge 20 Image Forming Unit 21 Optical Writing Unit 22 Secondary Transfer Device 23 Tension Roller 24 Paper Conveying Belt 25 Fixing Device 26 Fixing Belt 27 Pressure Roller 62 Transfer Bias Roller 71 Exit Bias Blade 72 Auxiliary Blade 73 Winding Roller 80 Primary transfer frame 81 Blade frame 82 Contact cam 83 Compression spring 90 Belt cleaning device 100 Printer unit 110 Intermediate transfer belt 133 First partition wall 134 Second partition wall

Claims (6)

An image carrier that carries a toner image on the surface;
An endless belt member that is stretched by a plurality of stretching members and is endlessly moved while the front surface is brought into contact with the image carrier to form a transfer nip;
A first bias applying means for applying a transfer bias having a polarity opposite to the charging polarity of the toner while being in contact with the back side region of the transfer nip among all the regions on the back surface of the belt member;
An image forming apparatus comprising: a second bias applying unit that removes the charge of the belt member with a bias having the same polarity as the charging polarity of the toner while being in contact with the back side region;
An image forming apparatus, wherein at least one of the first bias applying unit and the second bias applying unit is configured to be able to contact and separate from the belt member. The image forming apparatus according to claim 1.
The first bias applying means can be contacted / separated with respect to the belt member or the contact position can be changed, and the second bias applying means can be contacted / separated with respect to the belt member,
An image forming apparatus, wherein the displacement operation of the first bias applying means and the second bias means with respect to the belt member is performed in conjunction with each other. The image forming apparatus according to claim 1 or 2,
An image forming apparatus according to claim 1, wherein the displacement operation of the first bias applying unit and the second bias unit with respect to the belt member is performed in accordance with a predetermined image forming mode. The image forming apparatus according to claim 1, 2 or 3.
At least one of the first bias applying unit and the second bias applying unit is a blade member, and is tapered so as to form an inclined surface facing the belt member at a side end portion of the blade member in contact with the belt member. And an angle formed by the blade member and the belt member is substantially the same as an angle of the taper. The image forming apparatus according to claim 4.
The angle formed by the blade member and the belt member is 10 [°] or more and 20 [°] or less, and the linear pressure when the blade member is in contact with the belt member is 1 [gf / mm] or more and 10 [gf / mm] or less. The image forming apparatus according to claim 4 or 5,
An image forming apparatus, wherein a sliding member having an electric resistance value of 10 ⁴ [Ω] or more is provided on a contact surface of the blade member in contact with the belt member.

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