JP2005309181A - Intermediate transfer unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of an image forming apparatus using an intermediate transfer belt formed from a plurality of layers, that it is difficult for either (1) an intermediate transfer belt or a unit including it or (2) a photoreceptor drum or a unit including it to be fitted into or removed from the apparatus in the longitudinal direction of the photoreceptor drum when the other has been already fitted in the apparatus. <P>SOLUTION: A member for correcting the curvature of a belt end is added to an intermediate transfer unit in order to facilitate the fitting and removal of either the intermediate transfer belt or the unit including it or the photoreceptor drum or the unit including it. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly to an intermediate transfer unit using an intermediate transfer belt.

  In general, an electrophotographic image forming apparatus (image forming apparatus) that uses a so-called intermediate transfer belt when forming a color image using an electrophotographic process is known. This image forming apparatus has a photoconductor unit including a photoconductor drum for each color of yellow (Y), magenta (M), cyan (C), and black (BK). That is, it has a yellow photoconductor unit, a magenta photoconductor unit, a cyan photoconductor unit, and a black photoconductor unit. The electrostatic latent images formed on the four photosensitive drums are developed using yellow toner, magenta toner, cyan toner, and black toner, respectively, to obtain toner images of the respective colors. Each color toner image is sequentially primary-transferred to an intermediate transfer belt, and then the transfer image transferred to the intermediate transfer belt is secondarily transferred and fixed on a recording medium (paper) to obtain a color image.

  Each photoconductor unit includes a photoconductor drum, and around the photoconductor drum, a charger (main charger), an exposure unit, a developer, a transfer device (primary transfer device), a cleaning unit, and a charge removal unit ( Eraser) is arranged. Then, after the surface of the photosensitive drum is uniformly charged by the charger, an electrostatic latent image is formed on the surface of the photosensitive drum by the exposure unit. Thereafter, the electrostatic latent image is developed by the developing unit to form a toner image on the photosensitive drum, and the toner image on the photosensitive drum is transferred to the intermediate transfer belt by the transfer unit. The residual toner remaining on the photosensitive drum is removed by the cleaning unit.

  As described above, after the toner image is transferred as a primary transfer image to the intermediate transfer belt by each photoconductor unit, the primary transfer image is transferred onto a recording medium using, for example, a secondary transfer device, and the secondary transfer image is transferred. Get. Thereafter, a secondary transfer image on the recording medium is fixed on the recording medium by a fixing unit to obtain a color image.

  By the way, in the image forming apparatus described above, an endless belt-shaped transfer body (hereinafter referred to as an intermediate transfer belt) that rotates in a predetermined direction is generally used as an intermediate transfer belt. A photoconductor unit is arranged. The secondary transfer device described above is arranged downstream of the intermediate transfer belt in the rotation direction.

  In the above-described image forming apparatus, the toner images formed by the respective photoconductor units are sequentially transferred to the intermediate transfer belt, so that the toner images formed by the respective photoconductor units are accurately superimposed. It is difficult to cause image shift (color shift) and jitter.

  Incidentally, in the image forming apparatus described above, a conductive elastic roller is generally used as a transfer device, and a voltage is applied to the conductive elastic roller while the intermediate transfer belt is sandwiched between the photosensitive drum and the conductive elastic roller. Is applied to transfer the toner image from the photosensitive drum to the intermediate transfer belt. As described above, when a conductive elastic roller is used as the transfer device, for example, a ruled line image having a width of about 1 mm along (in parallel with) the rotation direction (conveying direction) of the intermediate transfer belt is primarily transferred to the intermediate transfer belt. The intermediate portion (middle side) of the ruled line image may not be transferred. That is, a so-called “missing” state may occur. In particular, when transferring a so-called multiple transfer image with an intermediate transfer belt, a transfer failure such as “missing” often occurs. For example, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are primarily transferred to an intermediate transfer belt in this order, and a so-called “red (R)” is formed by the yellow toner image and the magenta toner image. When an image is transferred, an image defect (transfer defect) such as “missing” may occur in the magenta image transferred upward on the intermediate transfer belt.

  This “missing” phenomenon occurs when the toner on the photosensitive drum is primarily transferred onto the intermediate transfer belt, and the toner on the photosensitive drum is fixed on the photosensitive drum by the pressure received from the intermediate transfer belt. This is a phenomenon in which force is not transferred onto the intermediate transfer belt. In particular, under high-temperature and high-humidity conditions, the toner is easily fixed, and thus this “collapse” phenomenon is likely to occur.

  To prevent this “missing” phenomenon: 1. reduce the pressure applied to the toner during transfer; 2. The toner is easy to release from the photosensitive drum. For example, the toner can be easily held on the intermediate transfer belt.

  As a specific method of 2, the surface roughness of the photoconductor may be reduced. However, since the photoconductor drum and the intermediate transfer belt are actually transferred with a speed difference, if the surface roughness is too small, Since the toner image on the photosensitive drum may be disturbed by the speed difference at the transfer nip entry portion before the transfer electric field is generated, it is not realistic. As a specific method 3, the tackiness of the intermediate transfer belt may be increased, but it becomes difficult to clean the toner remaining on the intermediate transfer belt after the secondary transfer. Further, by increasing the tackiness, heat is likely to be generated due to friction with the cleaning member, thereby causing filming in which toner is fused on the intermediate transfer belt.

  Finally, as one specific method, 1-1. Decreasing the hardness of the primary transfer roller 1-2. It may reduce the hardness of the intermediate transfer belt. As in 1-1, when the method of reducing the hardness of the primary transfer roller is used for a long period of time, the primary transfer roller creeps and becomes smaller in diameter as the same part is repeatedly used for transfer. Does not come into contact with the photosensitive drum, and transfer failure occurs. Even if the primary transfer roller is made small, if the intermediate transfer belt is thick and hard, the pressure reducing effect due to the hardness reduction of the primary transfer roller is reduced. Therefore, a method of reducing the hardness of the surface of the intermediate transfer belt as in 1-2 is desirable. In general, since the intermediate transfer belt is larger than the primary transfer roller, even when it is used for a long period of time, it is unlikely that the transfer is always performed at the same location, so that it is difficult to creep. Further, the effect of reducing the pressure applied to the toner by reducing the hardness of the surface that is in direct contact with the toner is greater than when reducing the hardness of the primary transfer roller. In addition, by reducing the hardness of the intermediate transfer belt, the gap generated between the toner, the intermediate transfer belt, and the photosensitive member can be reduced, and the discharge phenomenon that occurs in the small gap due to the electric field during primary transfer is reduced. Thus, ions generated in the air can be reduced. Due to the ion irradiation to the toner, the toner charge is less likely to be reduced or the reversal of the charge is less likely to occur, and not only “blank” in primary transfer but also transfer efficiency is improved.

  This can also be applied to the secondary transfer portion. By reducing the hardness of the intermediate transfer belt, the gap generated between the toner, the intermediate transfer belt, and the recording paper can be reduced, and the discharge phenomenon generated in the air gap due to the electric field at the time of primary transfer can be reduced. The ions generated therein can be reduced, and similarly, the toner charge is less likely to decrease or the charge reversal hardly occurs, and the transfer efficiency in the secondary transfer is improved. In particular, the transfer efficiency in a low-temperature and low-humidity environment that easily discharges in air and the transfer efficiency to a recording paper (rough paper) having a large surface roughness are greatly improved.

By the way, as a method for reducing the surface hardness of the intermediate transfer belt, an elastic rubber material is used as a material for the intermediate transfer belt, and examples thereof include urethane rubber, silicone rubber, and fluorine rubber. However, when rubber is used as a single unit, when the toner images formed on the photosensitive drums are sequentially transferred to the intermediate transfer belt, the rubber expands and contracts due to fluctuations in the tension generated on the intermediate transfer belt during printing, so that the accuracy is high. It is difficult to superimpose each color, and image misalignment (color misregistration) and jitter are likely to occur. As described above, the intermediate transfer belt has a layer of elasticity (innermost layer) in contact with the primary transfer roller and the tension roller that has a higher elastic coefficient than rubber. A large resin layer or a high hardness elastomer is desirable. Examples of the material for the resin layer include polyimide (PI), polyvinylidene fluoride (PVDF), and polycarbonate (PC).

  Furthermore, in an intermediate transfer belt having a two-layer structure of a rubber layer and a resin layer, a toner layer is formed on the surface of the rubber layer, but the rubber layer remains after the secondary transfer because of its poor release property from the toner. It becomes difficult to clean the toner. Therefore, when the outermost layer in contact with the toner layer is an intermediate transfer belt coated with a resin film (for example, a fluororesin film or a silicone resin film), the toner releasability is improved and cleaning becomes easy. However, when the coating layer is thickened, the resin layer generally has a larger elastic coefficient than the rubber layer, and therefore the effect of reducing the pressure on the toner and the effect of reducing the voids are reduced. Therefore, the thickness of the coating layer is desirably about 5 to 50 μm. Therefore, it is desirable that the outermost layer is formed of a resin film coating, the intermediate layer is a rubber layer, and the innermost layer is formed of at least three layers. This is because when the thickness of the intermediate transfer belt is large, the amount of variation in thickness increases, thereby causing color misregistration.

  As described above, as an intermediate transfer belt forming at least two layers, a surface layer of silicone rubber or the like is laminated on a plastic base made of a thermoplastic resin or a thermosetting resin (Patent Document 1), or a plastic Examples include those in which the surface of the substrate is coated with a fluororesin or the like (Patent Document 2).

  However, in an intermediate transfer belt that forms at least two layers, when silicone rubber, for example, is bonded on the innermost layer, for example, polyimide, it is usually bonded using a thermoplastic adhesive. This adhesive layer is bonded to the intermediate layer through a drying process or natural drying. However, (1) the belt end portion is in contact with air, so the cooling rate is faster and the belt shrinks faster than the belt center portion. (2) Normally, the rubber layer is hotter than the innermost resin layer. Since the expansion coefficient is large, the shrinkage of the rubber layer due to cooling is large, and the end of the outermost layer tends to warp outward. Even if the outermost layer is a resin coating, the middle layer is rubber, and the innermost layer is a resin-configured three-layer belt, the middle layer rubber layer is thicker than the outermost coating layer and has a larger thermal expansion coefficient. The belt tends to warp outward due to contraction.

To this end, (1) when the intermediate transfer belt or an intermediate transfer unit including the intermediate transfer belt is installed in the apparatus main body from the length direction of the photosensitive drum in a state where the photosensitive body unit is mounted on the apparatus main body, The belt end is in contact with the photosensitive drum or the photosensitive unit including the same due to warpage, and it is difficult to incorporate or take it out of the apparatus main body. (2) With the intermediate transfer belt attached to the apparatus main body, When a photoconductive drum or a photoconductive drum unit including a photoconductive drum is assembled into the apparatus main body from the length direction of the photoconductive drum, the belt end portion of the photoconductive drum or the photoconductive drum including the photoconductive drum is caused by the warp of the belt. There was a problem that it was difficult to incorporate into or remove from the apparatus main body by contacting the drum unit.
Japanese Patent Publication No. 1-334375 Japanese Patent Laid-Open No. 5-204255

  The problems to be solved are as follows: 1. In an image forming apparatus using an intermediate transfer belt having a plurality of layers, 1. Intermediate transfer belt or unit including the same When either one of the photosensitive drum or the unit including the photosensitive drum is incorporated in the apparatus, it is difficult to incorporate or take out the other non-integrated unit in the longitudinal direction of the photosensitive drum. It is.

In the present invention, in order to facilitate the incorporation and removal of the intermediate transfer belt, or the unit including the same, the photosensitive drum, or the unit including the same, a member that corrects the warp of the belt end is added to the intermediate transfer unit. Is the most important feature.
More specifically, it is as follows.
That is, according to the present invention, a toner image formed on an image carrier provided corresponding to each color is temporarily transferred onto an intermediate transfer belt by a conductive roller to which a voltage is applied, and then the primary transfer image is transferred. An intermediate transfer belt unit for use in an image forming apparatus for transferring image to a recording medium, wherein the intermediate transfer belt is formed by laminating at least two layers of materials having different thermal expansion coefficients, and the conductive roller is attached to the intermediate transfer belt. It is configured to be separable from each other, and a pressing member that presses the end side of the intermediate transfer belt in a direction away from the image carrier is provided so as to interlock with the conductive roller.
It is characterized by that.

  In the intermediate transfer unit of the present invention, since the intermediate transfer belt does not come into contact with the photosensitive drum or a unit including the intermediate transfer belt in order to suppress warping of the end of the intermediate transfer belt, the intermediate transfer unit, the photosensitive drum, or the As a result, it is easy to incorporate and take out the unit including the product, and there is an advantage that productivity and maintenance are improved.

  The purpose of facilitating the incorporation and removal of the intermediate transfer unit, the photosensitive drum, or a unit including the intermediate transfer unit is realized with a minimum number of parts.

  FIG. 1 shows an intermediate transfer unit 100 in the present embodiment. FIG. 2 is a partially enlarged perspective view of the primary transfer portion, in which the intermediate transfer belt is partially sectioned. FIG. 3 is a cross-sectional view of this configuration, where X is the direction in which the photoreceptor unit 200 and the intermediate transfer unit 100 are assembled or removed. The direction in which the primary transfer roller moves during transfer is defined as Y. Due to the presence of the belt pressing portion 411, the warped portion of the end portion of the intermediate transfer belt does not come into contact with the side surface of the photosensitive drum, so that the intermediate transfer unit can be easily incorporated into the apparatus. Similarly, the presence of the belt pressing portion 411 makes it easy to incorporate the intermediate transfer unit into the apparatus because the warped portion of the end of the intermediate transfer belt does not contact the side surface of the photosensitive drum.

  In FIG. 3, the photosensitive drum 5 is held by a shaft 51 that is crimped to a sheet metal. Further, the shaft 51 held by the sheet metal is fixed by the photoconductor cover 52. The intermediate transfer belt 1 is pressed against the photosensitive drum 5 by the reciprocating motion of the primary transfer roll 4, and an electric field is formed by the voltage applied to the primary transfer roll 4, and the toner image 3 on the photosensitive drum 5 is transferred. In the intermediate transfer belt 1, the outermost layer is a coating material 11 in which graphite and mica are dispersed in tetrafluoroethylene resin (PTFE), the intermediate layer is silicone rubber 12, and the innermost layer is polyimide 13. The primary transfer roll 4 is obtained by forming urethane foam around a stainless steel round bar. Bearings 41 are attached to both ends of the primary transfer roller 4, and the primary transfer roller 4 is moved up and down by the reciprocating motion of the bearing, so that the intermediate transfer belt 1 is in contact with and separated from the photosensitive drum 2. The bearing 41 reciprocates in conjunction with the reciprocating link 42.

  The bearing 41 of the primary transfer roller 4 is made of polyoxymethylene resin (POM) and includes a bearing portion 410 and a belt pressing portion 411. The bearing portion 410 slides against the stainless shaft portion of the primary transfer roller by sliding friction. Further, the belt pressing portion 411 is L-shaped, and the L portion presses the end of the intermediate transfer belt 1 in a direction away from the photosensitive drum 5. Therefore, the belt pressing portion 411 can reciprocate in synchronization with the primary transfer roller 4. For example, considering the case where the belt pressing portion 411 is attached to the main body of the intermediate transfer unit and does not reciprocate in synchronization with the primary transfer roller 410, the primary transfer roller 410 is raised during transfer, and the photosensitive drum 5 When the intermediate transfer belt 1 is pressed, the belt pressing portion 411 does not move, so that the end of the intermediate transfer belt 1 is pulled downward (in the direction opposite to the transfer pressing). Therefore, the pressing of the intermediate transfer belt 1 at both ends of the photosensitive drum 5 becomes insufficient, and transfer failure occurs.

  FIG. 4 is a front view of FIG. A is the rotating direction of the photosensitive drum, and B is the moving direction of the intermediate transfer belt. The center of the photosensitive drum 5 and the center of the primary transfer roller 4 are separated by a distance C, and the primary transfer roller 4 is located on the downstream side of the photosensitive drum 5. This is because the distance C is separated, and when the primary transfer roller 4 is lifted, an electric field is applied to the toner while the intermediate transfer belt 1 is sufficiently wound around the photosensitive drum 2. Decreases and image quality improves.

  Further, the belt pressing portion 411 of the bearing 41 is located downstream from the center line of the primary transfer roller 4. This is to prevent the belt pressing portion 411 from contacting as much as possible when the photosensitive drum or the unit including the photosensitive drum is inserted and removed. The same applies when the intermediate transfer unit is inserted and removed.

  The belt pressing portions are respectively attached to both sides of the intermediate belt of the photosensitive drums of each color of yellow (Y), magenta (M), cyan (C), and black (BK).

  FIG. 5 is a partial front view of the intermediate transfer unit in the present embodiment. The difference from the first embodiment is that the belt pressing portion 411 is provided not only on the downstream side but also on the upstream side. In this method, when the belt warpage is large, the intermediate transfer unit and the photoconductor unit can be more easily assembled than those in the first embodiment.

  FIG. 6 is a partial front view of the intermediate transfer unit in the present embodiment. The difference from the first and second embodiments is that the belt pressing portion 411 of the bearing 41 is a separate member from the bearing portion 410. The belt pressing portion 411 is interlocked with the reciprocating motion of the primary transfer roller. The primary transfer roller is reciprocated by a link through a bearing 41. Further, this link can reciprocate in conjunction with the belt presser 411.

  By adopting such a configuration, the movement amount of the primary transfer roller and the movement amount of the belt pressing portion 411 can be made different. As a result, the belt pressing amount when the primary transfer roller is raised and the belt pressing amount when the primary transfer roller is lowered can be changed. Since the belt presser when the primary transfer roller is raised can be eliminated, the transfer failure at the end due to the belt press at the end can be completely eliminated. Furthermore, by increasing the belt pressing amount when the primary transfer roller is lowered, it becomes easier to incorporate the intermediate transfer unit and the photosensitive unit than in the first and second embodiments.

  FIG. 7 is a partial front view of the intermediate transfer unit in the present embodiment. The difference from the first, second, and third embodiments is that the belt pressing portion 411 of the bearing 41 is a separate member from the bearing portion 410, and the belt pressing portion 411 is attached not only on the downstream side but also on the upstream side. . Similar to the second embodiment, since the belt presser 411 is also provided on the upstream side, the warpage can be suppressed more than the first and third embodiments when the belt warpage is large.

  Similarly to the third embodiment, since the belt pressing portion 411 of the bearing 41 is a separate member from the bearing portion 410, the moving amount of the primary transfer roller and the moving amount of the belt pressing portion 411 can be made different. The belt pressing amount when the primary transfer roller is raised and the belt pressing amount when the primary transfer roller is lowered can be changed. Since the belt presser when the primary transfer roller is raised can be eliminated, the transfer failure at the end due to the belt press at the end can be completely eliminated. Furthermore, by increasing the belt pressing amount when the primary transfer roller is lowered, it becomes easier to incorporate the intermediate transfer unit and the photosensitive unit than in the first and second embodiments.

  As described above, the intermediate transfer unit using the intermediate transfer belt according to the present invention can be used in an image forming apparatus using an electrophotographic process such as a printer or a copying machine. This configuration is not only an intermediate transfer unit, but also a paper transport unit using a paper transport belt, a fixing unit using a fixing belt, and other components of an electrophotographic process using a laminated belt. Can be applied.

Overall perspective view showing an embodiment of an intermediate transfer unit The perspective view which showed Example 1 of the intermediate transfer unit Sectional view showing Example 1 of intermediate transfer unit Front view showing Example 1 of intermediate transfer unit Front view showing Embodiment 2 of the intermediate transfer unit Front view showing Embodiment 3 of the intermediate transfer unit Front view showing Embodiment 4 of the intermediate transfer unit

Explanation of symbols

Reference Signs List 1 intermediate transfer belt 3 toner image 4 primary transfer roller 5 photoconductor drum 11 outermost layer of intermediate transfer belt 12 intermediate layer of intermediate transfer belt 13 innermost layer of intermediate transfer belt 41 bearing 51 caulking sheet metal 52 photoconductor unit housing 100 intermediate transfer Unit 200 photoconductor unit 410 bearing 411 belt presser

Claims (8)

A toner image formed on an image carrier provided for each color is temporarily transferred onto an intermediate transfer belt by a conductive roller to which a voltage is applied, and then the primary transfer image is transferred to a recording medium. An intermediate transfer belt unit used in an image forming apparatus,
The intermediate transfer belt is formed by laminating at least two layers of materials having different thermal expansion coefficients,
The conductive roller is configured to be separated from the intermediate transfer belt,
A pressing member for pressing the end side of the intermediate transfer belt in a direction away from the image carrier is provided so as to interlock with the conductive roller;
An intermediate transfer unit characterized by that. 2. The intermediate transfer unit according to claim 1, wherein the layer on the image carrier side of the intermediate transfer belt has a larger thermal expansion coefficient than other layers to be laminated. The intermediate transfer unit according to claim 1, wherein the pressing member is disposed on the downstream side of the image carrier with respect to the rotational movement direction of the intermediate transfer belt. The intermediate transfer unit according to claim 1, wherein at least one pressing member is installed on the upstream side and the downstream side of the image carrier with respect to the rotational movement direction of the intermediate transfer belt. The intermediate transfer unit according to claim 1, further comprising a bearing that supports the electrically conductive roller that can be separated, and the pressing member is provided integrally with the bearing. 6. The intermediate transfer unit according to claim 5, wherein the pressing member provided integrally with the bearing is disposed on the downstream side of the image carrier with respect to the rotational movement direction of the intermediate transfer belt. The at least one pressing member provided integrally with the bearing is disposed on the upstream side and the downstream side of the image carrier with respect to the rotational movement direction of the intermediate transfer belt. Intermediate transfer unit. 8. An image transfer body on which an electrostatic latent image is formed, an imager for forming a toner image on the image support, and an intermediate transfer unit according to claim 1, to which a toner image on the image support is transferred. An image forming apparatus.

Images