JP3695136B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer, a facsimile, or a copying machine that forms an image using electrophotographic technology. In particular, the present invention relates to the intermediate transfer belt.
[0002]
[Prior art]
In general, an image forming apparatus using an electrophotographic technique includes a photosensitive member having a photosensitive layer on the outer peripheral surface of a conductive layer, a charging unit that uniformly charges the photosensitive layer of the photosensitive member, and the charging unit uniformly. An exposure unit that selectively exposes the charged photosensitive layer to form an electrostatic latent image, and a toner that is a developer is applied to the electrostatic latent image formed by the exposure unit to form a visible image (toner And a transfer device for transferring the toner image developed by the developing means onto a recording medium such as paper.
[0003]
As a transfer device for transferring the toner image developed on the photoconductor to a recording medium such as paper, conventionally, the toner image formed on the photoconductor is transferred (primary transfer), and this toner image is further recorded. A belt having an intermediate transfer belt for transferring (secondary transfer) to a medium is known.
[0004]
4A and 4B are conceptual views showing an example of an image forming apparatus provided with such an intermediate transfer belt. FIG. 4A is a schematic perspective view, and FIG. 4B is a partial cross-sectional view along line bb in FIG.
[0005]
In the figure, reference numeral 1 denotes a photoreceptor, which has a conductive layer 1a and a photosensitive layer 1b formed on the conductive layer 1a. The conductive layer 1a is grounded.
[0006]
Reference numeral 2 denotes an intermediate transfer belt, which is composed of a dielectric (medium resistance layer) having a resistance value of approximately 10 ⁷ to 10 ¹⁴ Ωcm, for example. Such an intermediate transfer belt 2 can be prepared by kneading conductive carbon in synthetic resin or the like.
[0007]
The intermediate transfer belt 2 is in contact with the photoreceptor 1 at least during image formation, and the contact portion T1 forms a transfer portion (in this case, a primary transfer portion). A primary transfer roller 3 is disposed from the inside of the intermediate transfer belt 2 in the primary transfer portion T1, and a primary transfer voltage is applied to the intermediate transfer medium 2 by the primary transfer roller 3.
[0008]
Further, a secondary transfer roller 4 that applies a secondary transfer voltage is pressed against the intermediate transfer belt 2, and the pressure contact portion forms a secondary transfer portion T <b> 2. A backup roller 5 is disposed from the inner side of the intermediate transfer belt 2 in the secondary transfer portion T2.
[0009]
At the time of image formation, first, the photosensitive member 1 and the intermediate transfer belt 2 are rotationally driven, and the photosensitive layer 1b of the photosensitive member 1 is uniformly charged by a charging unit (not shown), and then an exposure unit (not shown). To selectively form an electrostatic latent image. Next, toner as a developer is applied to the electrostatic latent image by developing means (not shown) to become a visible image (toner image), and this toner image is transferred onto the intermediate transfer belt 2 in the primary transfer portion T1. Then, in the secondary transfer portion T2, the image is transferred to a recording medium such as paper supplied to the secondary transfer portion T2.
[0010]
The recording medium onto which the toner image has been transferred passes through a fixing device (not shown) to fix the toner image.
[0011]
[Problems to be solved by the invention]
The intermediate transfer body 2 in the conventional image forming apparatus described above has a single layer structure formed by kneading conductive particles such as conductive carbon in a synthetic resin or the like, and the conductive particles are uniform in the resin. It was difficult to disperse in the film, and the resistance value was likely to be uneven.
[0012]
Therefore, there is a problem that unevenness is easily generated in the electric field in the transfer portion, and as a result, transfer unevenness is easily generated.
[0013]
In addition, local protrusions on the surface of the intermediate transfer member due to gelling components in the resin and aggregates of conductive particles are likely to occur, and therefore, the contact portion between the photosensitive member and the intermediate transfer member, the intermediate transfer member, and the back surface thereof. At the abutting portion with the arranged roller, the abutting becomes locally unstable, and there is a problem that transfer unevenness is likely to occur.
[0014]
An object of the present invention is to provide an image forming apparatus that solves the above-described problems, is less likely to cause uneven transfer, and can form a good image.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to claim 1, wherein a transfer part is formed between a photoreceptor on which an image is formed on the surface of the photosensitive layer formed on the conductive layer and the surface of the photoreceptor. And an intermediate transfer belt to which the image is transferred in the transfer unit,
The intermediate transfer belt is formed on the conductive layer, a resistance layer formed on the conductive layer, and the image is transferred. The intermediate transfer belt is exposed on the surface of the end of the intermediate transfer belt and supplies a transfer voltage to the conductive layer. While having an electrode part and a bead provided along the back end part of the belt,
A taper surface is formed at the end of at least one of the rollers on which the intermediate transfer belt is stretched, and the meandering of the intermediate transfer belt is regulated by bringing a bead into contact with the taper surface. And
An annular rib-shaped gap member that forms a gap between the electrode portion and the photosensitive member is provided on or near the extension line of the inner surface of the bead in the intermediate transfer belt.
[0016]
The image forming apparatus according to claim 2 is the image forming apparatus according to claim 1, wherein the gap member is made of a material having a resistance value higher than that of the resistance layer of the intermediate transfer medium. .
[0017]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the gap member is made of an insulating material.
[0018]
An image forming apparatus according to a fourth aspect is the image forming apparatus according to the first, second, or third aspect, wherein the gap member has a trapezoidal cross-sectional shape.
[0019]
[Function and effect]
According to the image forming apparatus of the first aspect, the following effects can be obtained.
[0020]
(A) Intermediate transfer in which a transfer part is formed between a photoreceptor on which an image is formed on the surface of the photosensitive layer formed on the conductive layer and the surface of the photoreceptor, and the image is transferred in the transfer part Therefore, the image formed on the surface of the photoreceptor is transferred to the intermediate transfer belt at the transfer portion.
[0021]
The intermediate transfer member has a multilayer structure including a conductive layer and a resistance layer formed on the conductive layer to which the image is transferred. For example, the resistance layer disperses conductive particles. It is possible to form by applying the cured resin solution, curing and drying. Thus, when conductive particles are dispersed in a resin solution in which a resin is dissolved in a solvent, the dispersibility of the conductive particles becomes better than when conductive particles are kneaded in a heat-melted resin. . Therefore, resistance unevenness of the resistance layer itself can be made difficult to occur. In addition, since the dispersibility of the conductive particles becomes good, local protrusions on the surface of the resistance layer can be hardly generated, and it is possible to stabilize the contact with the photoconductor and prevent transfer defects. It becomes.
[0022]
In addition, since the resistance layer is integrally formed on the conductive layer, when a transfer voltage is supplied to the conductive layer by the electrode portion, the potential on the back side of the resistance layer becomes substantially uniform, and over the entire transfer region. A substantially uniform transfer electric field is formed.
[0023]
Therefore, according to the image forming apparatus of the first aspect, unevenness in the electric field in the transfer portion is less likely to occur and image displacement is less likely to occur, and as a result, a good image with less transfer unevenness and displacement is formed. It becomes possible to do.
[0024]
In addition, since the electrode portion for supplying the transfer voltage to the conductive layer is exposed on the surface of the end portion of the intermediate transfer belt, the transfer voltage can be easily supplied to the conductive layer.
[0025]
By the way, the intermediate transfer belt is configured as described above, that is, the resistance layer is formed on the conductive layer, and the electrode portion for supplying a transfer voltage to the conductive layer is exposed on the surface of the end portion of the intermediate transfer belt. It has been found that the following problems occur when the bead is provided along the back end.
[0026]
As shown in FIG. 5A, a pinhole 1c may exist in the photosensitive layer 1b of the photoreceptor 1, and the pinhole 1c exists at the end of the photoreceptor 1 as shown. There is.
[0027]
In such a situation, as shown in FIG. 5B, the structure of the intermediate transfer belt 20 is such that the resistance layer 22 is formed on the conductive layer 21 and the electrode for supplying the transfer voltage V1 to the conductive layer 21. If the portion 23 is exposed on the surface of the end portion of the intermediate transfer belt 10, the flow from the electrode portion 23 to the conductive layer 1a of the photoreceptor 1 via the pinhole 1c is achieved if no measures are taken. It was found that a discharge current E was generated, and transfer voltage V1 was not properly applied, resulting in transfer failure.
[0028]
Further, for example, as shown in FIG. 6, a tapered surface 15a is formed at the end of at least one roller (for example, the primary transfer roller 15) among the rollers on which the intermediate transfer belt 20 is stretched, and the tapered surface 15a. When the meandering of the intermediate transfer belt 20 is regulated by bringing the bead 26 into contact with the bead 26, the electrode portion 23 is an extension of the inner side surface 26a of the bead 26 when the bead 26 comes into contact with the tapered surface 15a. Since it bends on or in the vicinity of the line, electric discharge is likely to occur between the bent portion 23b and the conductive layer 1a of the photosensitive member 1, and the transfer voltage V1 is not properly applied, and transfer defects are likely to occur. Do you get it. Note that the discharge in this case may occur even if the pinhole 1c described above is not necessarily provided. Even if the primary transfer roller 15 is not provided, if the tapered surface is formed on the other rollers, the bent portion 23b is formed. Since it may remain, there is a possibility that the discharge is likely to occur.
[0029]
On the other hand, according to the image forming apparatus of the first aspect, since the annular and rib-like gap member is provided between the electrode portion of the intermediate transfer belt and the photosensitive member. With the gap member, it is possible to form an appropriate distance between the surface of the conductive layer of the photoconductor in the transfer portion and the surface of the electrode portion of the intermediate transfer belt.
[0030]
In addition, since the gap member is provided on or in the vicinity of the extension line of the inner side surface of the bead in the intermediate transfer belt, the bending of the electrode portion hardly occurs.
[0031]
Therefore, according to the image forming apparatus of the first aspect, even if the intermediate transfer belt has the above-described configuration, the discharge current is not generated even if there is a pinhole at the end of the photoreceptor. Accordingly, transfer defects do not occur.
[0032]
If the intermediate transfer belt has a single-layer structure as in the prior art, the above-described problem occurs even if there is a pinhole 1c at the end of the photoreceptor 1, as shown in FIG. Absent.
[0033]
(B) Since the gap member is provided in an annular rib shape on or near the extension line of the inner surface of the bead in the intermediate transfer belt, the gap member serves as a partition wall for the toner, and the toner on the resistance layer Thus, movement across the entire surface of the electrode portion is prevented.
[0034]
Accordingly, it is possible to prevent power feeding failure that may occur when the toner on the resistance layer moves to the entire surface of the electrode portion and adheres to the surface of the electrode portion.
[0035]
In addition, since the bending position of the electrode portion that would occur without the gap member is reinforced by the gap material, the durability of the electrode portion is also improved.
[0036]
(C) Since the gap member is formed in a rib shape, when the gap member having the same width as that of the electrode portion is provided at the end of the photosensitive member, or the sliding member having the same width as that of the electrode portion is photosensitive. The contact area between the gap member and the photosensitive member or the intermediate transfer belt is reduced as compared with the case where the belt and the intermediate transfer belt are slidably interposed between the two. Accordingly, an increase in rotational load, twisting, and meandering (one-sided) due to the force applied to a part of the width direction (axial direction) of the photoreceptor and the intermediate transfer belt is reduced.
[0037]
According to the image forming apparatus of the second aspect, in the image forming apparatus of the first aspect, the gap member is made of a material having a higher resistance value than the resistance layer of the intermediate transfer medium. The generation of the discharged current is more reliably prevented, and the transfer failure is surely prevented.
[0038]
According to the image forming apparatus of claim 3, in the image forming apparatus of claim 2, since the gap member is made of an insulating material, the generation of the above-described discharge current is more reliably prevented, Transfer defects can be prevented more reliably.
[0039]
According to the image forming apparatus of claim 4, in the image forming apparatus of claim 1, 2, or 3, the gap member has a trapezoidal cross section, so that the strength of the gap member is improved. Become.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0041]
1A and 1B are diagrams showing an embodiment of an image forming apparatus according to the present invention. FIG. 1A is a schematic perspective view, and FIG. 1B is a partial cross-sectional view taken along line bb in FIG.
[0042]
In the figure, reference numeral 10 denotes a photoreceptor, which has a conductive layer 10a and a photosensitive layer 10b formed on the conductive layer 10a. The conductive layer 10a is grounded.
[0043]
An intermediate transfer belt 20 is exposed to the conductive layer 21, the resistance layer 22 formed on the conductive layer 21, and the end surface of the intermediate transfer belt, and supplies the transfer voltage V1 to the conductive layer 21. And a bead 26 provided along the back end of the belt. In this embodiment, the conductive layer 21 is formed on an insulating substrate 24 made of a synthetic resin, and the resistance layer 22 is formed on the conductive layer 21. The conductive layer 21 is exposed in a strip shape because the resistance layer 22 is removed in a strip shape at one side edge of the intermediate transfer belt 20 or is not formed in advance in a strip shape, and an electrode portion 23 is formed in the exposed portion. . In addition, it is also possible to form an electrode part by the strip | belt-shaped exposed part itself of the conductive layer 21. FIG. The bead 26 is formed integrally with the insulating substrate 24 or by being attached to the back surface of the insulating substrate 24.
[0044]
The intermediate transfer belt 20 is in contact with the photoreceptor 10 at least during image formation, and the contact portion T1 forms a transfer portion (in this case, a primary transfer portion). Although the primary transfer roller 15 is disposed from the inner side of the intermediate transfer belt 20 in the primary transfer portion T1, the primary transfer roller 15 is not necessarily provided.
[0045]
As shown in FIG. 1A, an electrode roller 37 is disposed in contact with the electrode portion 23 of the intermediate transfer belt 20, and the conductive layer 21 is interposed via the electrode roller 37 and the electrode portion 23. A primary transfer voltage V1 is applied.
[0046]
Further, a secondary transfer roller 38 to which a secondary transfer voltage V2 is applied is pressed against the intermediate transfer belt 20, and the pressure contact portion forms a secondary transfer portion T2. A backup roller 33 is disposed from the inner side of the intermediate transfer belt 20 in the secondary transfer portion T2.
[0047]
The tapered surface that abuts the bead 26 and restricts the meandering of the intermediate transfer belt 20 may be provided on at least one of the rollers on which the intermediate transfer belt 20 is stretched. In this embodiment, primary transfer is performed. A tapered surface 15a is formed at the end of the roller 15 (see FIG. 2). When the primary transfer roller 15 is not provided, the tapered surface 15 a is formed on the backup roller 33.
[0048]
At the time of image formation, first, the photosensitive member 10 and the intermediate transfer belt 20 are rotationally driven, and the photosensitive layer 10b of the photosensitive member 10 is uniformly charged by a charging unit (not shown), and then an exposure unit (not shown). To selectively form an electrostatic latent image. Next, toner as a developer is applied to the electrostatic latent image by developing means (not shown) to become a visible image (toner image), and this toner image is transferred onto the intermediate transfer belt 20 in the primary transfer portion T1. Then, in the secondary transfer portion T2, the image is transferred to a recording medium such as paper supplied to the secondary transfer portion T2.
[0049]
The recording medium onto which the toner image has been transferred passes through a fixing device (not shown) to fix the toner image.
[0050]
Incidentally, as described above, the pinhole 10c may exist in the photosensitive layer 10b of the photoconductor 10, and the pinhole 10c exists at the end of the photoconductor 10 as shown in FIG. There is.
[0051]
In such a situation, as described above, the intermediate transfer belt 20 is configured such that the resistance layer 22 is formed on the conductive layer 21 and the electrode portion 23 for supplying the transfer voltage V1 to the conductive layer 21 is the intermediate transfer. If no measures are taken when the structure is exposed on the surface of the end portion of the belt 10, a discharge current flows from the electrode portion 23 to the conductive layer 10a of the photoreceptor 10 through the pinhole 10c. As described above, the transfer voltage V1 is not properly applied and a transfer failure occurs.
[0052]
Therefore, in this embodiment, an annular rib-shaped gap member 25 that forms a gap between the electrode portion 23 and the photoconductor 10 is provided on an extension line of the inner side surface 26 a of the bead 26 in the intermediate transfer belt 20. It is. The gap member 25 may be provided in the vicinity of an extension line of the inner side surface 26 a of the bead 26. The cross-sectional shape of the gap member 25 can be formed in a trapezoidal shape as indicated by an imaginary line 25 ′. The gap member 25 is formed of a material having a higher resistance value than the resistance layer 22 of the intermediate transfer medium 20, more preferably an insulating material.
[0053]
According to the image forming apparatus as described above, the following effects can be obtained.
[0054]
(A) A transfer portion T1 is formed between the photoreceptor 10 on which the image is formed on the surface of the photosensitive layer 10b formed on the conductive layer 10a and the surface of the photoreceptor, and the image is transferred to the transfer portion T1. Therefore, the image formed on the surface of the photoconductor 10 is transferred to the intermediate transfer belt at the transfer portion T1.
[0055]
The intermediate transfer body 20 has a multilayer structure including a conductive layer 21 and a resistance layer 22 formed on the conductive layer 21 to which the image is transferred. It can be formed by applying a resin solution in which conductive particles are dispersed, curing, and drying. Thus, when conductive particles are dispersed in a resin solution in which a resin is dissolved in a solvent, the dispersibility of the conductive particles becomes better than when conductive particles are kneaded in a heat-melted resin. . Therefore, resistance unevenness of the resistance layer 22 itself can be made difficult to occur. Further, since the dispersibility of the conductive particles becomes good, local protrusions on the surface of the resistance layer 22 can be hardly generated, and the contact with the photoreceptor 10 and the like can be stabilized to prevent transfer failure. Is possible.
[0056]
Further, since the resistance layer 22 is integrally formed on the conductive layer 21, when a transfer voltage is supplied to the conductive layer 21 by the electrode portion 23, the potential on the back side of the resistance layer 22 becomes substantially uniform, and the transfer region A substantially uniform transfer electric field is formed over the entire surface.
[0057]
Therefore, according to the image forming apparatus of this embodiment, unevenness in the electric field in the transfer portion T1 is less likely to occur and image misalignment is less likely to occur, and as a result, a good image with less transfer unevenness and misalignment is formed. It becomes possible to do.
[0058]
Moreover, since the electrode portion 23 for supplying the transfer voltage V1 to the conductive layer 21 is exposed on the surface of the end portion of the intermediate transfer belt 20, the transfer voltage V1 can be easily applied by the electrode roller 37 as shown in the figure, for example. Power can be supplied to the conductive layer 21.
[0059]
(B) An annular rib-shaped gap member 25 that forms a gap between the electrode portion 23 of the intermediate transfer belt 20 and the photosensitive member 10 is on an extension line of the inner side surface 26a of the bead 26 in the intermediate transfer belt 20 (or The gap member 25 forms an appropriate gap G between the surface of the conductive layer 10a of the photoreceptor 10 and the surface of the electrode portion 23 of the intermediate transfer belt 20 in the transfer portion T1. Is possible.
[0060]
In addition, since the gap member 25 is provided on (or in the vicinity of) the extension line of the inner surface 26a of the bead 26 in the intermediate transfer belt 20, the above-described bending of the electrode portion 23 hardly occurs as shown in FIG. Become. Even if the primary transfer roller 15 is provided, an appropriate gap G ′ is provided between the surface of the conductive layer 10a of the photoreceptor 10 and the surface of the electrode portion 23 of the intermediate transfer belt 20 by the gap member 25 in the transfer portion T1. Will be formed.
[0061]
Therefore, even if the intermediate transfer belt 20 has the above-described configuration, even if the pinhole 10c is present at the end of the photoconductor 10, the occurrence of the discharge current can be prevented and the occurrence of transfer failure can be prevented. it can. It should be noted that the gaps G and G ′ are preferably configured to be 20 μm or more. It has been confirmed by an experiment by the present inventors that the discharge current is not generated at a transfer voltage adopted in this type of image forming apparatus if the gaps G and G ′ are 20 μm or more.
[0062]
In addition, even if the photosensitive layer 10b at the portion facing the electrode portion 23 has a partially thin portion, generation of a new pinhole due to a discharge phenomenon is prevented.
[0063]
(C) Since the gap member 25 is provided in an annular and rib shape on (or in the vicinity of) the extended surface of the inner surface 26a of the bead 26 in the intermediate transfer belt 20, it functions as a partition wall for the toner and resists. The toner on the layer 22 is prevented from moving over the entire surface of the electrode portion 23.
[0064]
In particular, a cleaning member that collects waste toner remaining on the resistance layer 22 is generally disposed on the resistance layer 22 of the intermediate transfer belt 20. Toner may spill or may not be completely recovered.
[0065]
In contrast, according to this embodiment, the gap member 25 serves as a partition wall for the toner, thereby preventing the waste toner from moving over the entire surface of the electrode portion 23. Become.
[0066]
Accordingly, it is possible to prevent power supply failure that may occur when the toner on the resistance layer 22 moves to the entire surface of the electrode portion 23 and adheres to the surface of the electrode portion 23.
[0067]
Moreover, since the bending position of the electrode part 23 that would occur without the gap member 25 is reinforced by the gap material 25, the durability of the electrode part 23 is also improved.
[0068]
(D) When the cross-sectional shape of the gap member 25 is formed in a trapezoidal shape as indicated by a virtual line 25 ′, the strength of the gap member 25 itself is further improved.
[0069]
(E) Since the gap member 25 is formed in a rib shape, when the gap member having the same width as that of the electrode portion 23 is provided at the end of the photosensitive member, or the sliding member having the same width as that of the electrode portion. Compared with the case where the gap member 25 is slidably interposed between the photosensitive member and the intermediate transfer belt, the contact area between the gap member 25 and the photosensitive member 10 or the intermediate transfer belt 20 is reduced. . Therefore, an increase in rotational load, twisting, and meandering (one-sided) due to the force applied to a part of the width direction (axial direction) of the photoreceptor 10 and the intermediate transfer belt 20 is reduced.
[0070]
(F) Since the gap member 25 is made of a material having a higher resistance value than that of the resistance layer 22 of the intermediate transfer medium 20, the above-described discharge current can be prevented more reliably. When the gap member 25 is made of an insulating material, the above-described discharge current can be prevented more reliably.
[0071]
【Example】
FIG. 3 is a schematic diagram showing an example of an image forming apparatus to which the above embodiment can be applied. In FIG. 3, the same reference numerals are given to the same or corresponding parts as those of the above-described embodiment.
[0072]
This image forming apparatus is an apparatus capable of forming a full-color image using a developing device using toners of four colors of yellow, cyan, magenta, and black.
[0073]
In FIG. 3, reference numeral 10 denotes a photoconductor, which can be driven to rotate in the direction indicated by an arrow by an appropriate driving means (not shown).
[0074]
A charging roller 11 as a charging unit, a developing roller 17 (Y, M, C, K) as a developing unit, an intermediate transfer device 30, and a cleaning unit 12 are arranged around the photoconductor 10 along the rotation direction. Has been placed.
[0075]
The photoreceptor 10 includes a cylindrical conductive substrate 10a and a photosensitive layer 10b formed on the surface thereof.
[0076]
The charging roller 11 is in contact with the outer peripheral surface of the photoconductor 10, and can uniformly charge the photosensitive layer 10b (for example, can be charged to about -600V). On the outer peripheral surface of the uniformly charged photoconductor 10, selective exposure L corresponding to desired image information is performed by an exposure unit (not shown), and an electrostatic latent image is formed on the photoconductor 10 by this exposure L. The The potential of the exposed portion, that is, the portion where the electrostatic latent image is formed can be set to about −100 V, for example.
[0077]
The electrostatic latent image is developed by the developing roller 17 with toner charged to “−” applied thereto.
[0078]
As the developing rollers, a yellow developing roller 17Y, a cyan developing roller 17C, a magenta developing roller 17M, and a black developing roller 17K are provided. These developing rollers 17Y, 17C, 17M, and 17K can selectively contact the photoreceptor 10, and when contacted, toner of any one of yellow, cyan, magenta, and black is applied to the photoreceptor. The electrostatic latent image on the photoconductor 10 is developed by applying to the surface 10.
[0079]
The developed toner image is transferred onto an intermediate transfer belt 20 as an intermediate transfer belt described later.
[0080]
The cleaning unit 12 includes a cleaner blade 13 that scrapes off the toner remaining and adhered to the outer peripheral surface of the photoreceptor 10 after the transfer, and a receiving portion 14 that receives the toner scraped off by the cleaner blade 13. Yes.
[0081]
The intermediate transfer device 30 includes a drive roller 31, four driven rollers 32, 33, 34, and 35, and an intermediate transfer belt 20 that is stretched around each of these rollers.
[0082]
The driving roller 31 is rotationally driven at substantially the same peripheral speed as that of the photosensitive member 10 because a gear (not shown) fixed to the end of the driving roller 31 meshes with a driving gear (not shown) of the photosensitive member 10. Accordingly, the intermediate transfer belt 20 can be driven to circulate in the direction indicated by the arrow at substantially the same peripheral speed as the photoconductor 10.
[0083]
The driven roller 35 is disposed at a position where the intermediate transfer belt 20 is pressed against the photoconductor 10 by its own tension between the driven roller 35 and the primary roller at the press-contact portion between the photoconductor 10 and the intermediate transfer belt 20. A transfer portion T1 is formed. Therefore, the primary transfer roller 15 is not provided. The driven roller 35 is disposed near the primary transfer portion T1 on the upstream side of the intermediate transfer belt 20 in the circulation direction.
[0084]
The driving roller 31 is provided with the electrode roller 37 via the intermediate transfer belt 20. As described above, the conductive layer 21 of the intermediate transfer belt 20 is charged with the photosensitive member 10 via the electrode roller 37. A transfer voltage V1 having a polarity opposite to the polarity (a primary transfer voltage, for example, a voltage of about +500 V) can be applied.
[0085]
The driven roller 32 is a tension roller, and biases the intermediate transfer belt 20 in the tension direction by a biasing means (not shown).
[0086]
The driven roller 33 is a backup roller that forms the secondary transfer portion T2. A secondary transfer roller 38 is opposed to the backup roller 33 with the intermediate transfer belt 20 interposed therebetween. The secondary transfer roller 38 can be brought into contact with and separated from the intermediate transfer belt 20 by a contact and separation mechanism (not shown). A secondary transfer voltage V2 (a voltage higher than the primary transfer voltage, for example, a voltage of about +1000 V) is applied to the secondary transfer roller 38.
[0087]
The driven roller 34 is a backup roller for the belt cleaner 39. The belt cleaner 39 includes a cleaner blade 39a that contacts the intermediate transfer belt 20 and scrapes off toner adhering to the outer peripheral surface thereof, and a receiving portion 39b that receives the toner scraped off by the cleaner blade 39a. ing. The belt cleaner 39 can be brought into and out of contact with the intermediate transfer belt 20 by a contact and separation mechanism (not shown).
[0088]
In the intermediate transfer belt 20 in this embodiment, the insulating base 24 is made of a sheet-like transparent PET, and the conductive layer 21 is formed on the insulating substrate 24 by vapor deposition of AL, and a urethane base (binding) is formed thereon. Resin) Fluorine fine particles and conductive agent SnO dispersed paint is applied in a thickness of about 10 to 100 μm and the resistance layer 22 is formed by welding both ends of the belt by ultrasonic fusion to form an endless shape. It is. The surface resistance of the resistance layer 22 is about 10 ⁸ to 10 ¹⁵ Ω / □, and the volume resistivity is about 10 ⁷ to 10 ¹⁴ Ωcm. The resistance value of the conductive layer 21 is desirably 10 6 Ωcm or less. The coating is applied leaving the belt at one side edge to expose the conductive layer 21 in the form of a strip, and the exposed portion forms the electrode portion 23 or the exposed portion forms the electrode portion 23. The electrode roller 37 is brought into contact with the electrode portion 23. The gap member 25 is made of urethane. The gap member 25 is formed by silk printing or pasting a tape. When formed by silk printing, it is possible to form a pattern without variation in height. When formed by attaching a tape, there is no possibility that the intermediate transfer belt 20 will be altered because a process such as heating during manufacturing is unnecessary. The beads 26 are affixed to both ends of the back surface of the insulating base 24. Silicon rubber is used as the bead 26, and its thickness (projection height) is about 1.5 mm and the width is about 4 mm. The elastic strength of the bead 26 is about E = 2.0 to 8.0 MPa.
[0089]
Tapered surfaces that abut the bead 26 and restrict the meandering of the intermediate transfer belt 20 are provided at both ends of the tension roller 32.
[0090]
The electrode roller 37 is composed of an elastic roller made of a single foam foam having conductivity.
[0091]
In the process in which the intermediate transfer belt 20 is circulated, the toner image on the photoconductor 10 is transferred onto the intermediate transfer belt 20 at the primary transfer portion T1, and the toner image transferred onto the intermediate transfer belt 20 is transferred to the secondary transfer belt T20. In the transfer portion T2, the image is transferred to a recording medium S such as paper supplied between the secondary transfer roller 38 and the transfer portion T2. The recording medium S is fed from a sheet feeding device (not shown) and is supplied to the secondary transfer portion T2 by the gate roller pair 40 at a predetermined timing.
[0092]
The basic operation of the entire image forming apparatus as described above is as follows.
[0093]
(I) When a print command signal (image formation signal) from a host computer or the like (not shown) is input to the control unit of the image forming apparatus, the photosensitive member 10, the developing roller 17, and the intermediate transfer belt 20 are Driven by rotation.
[0094]
(Ii) The outer peripheral surface of the photoconductor 10 is uniformly charged by the charging roller 11.
[0095]
(Iii) On the outer peripheral surface of the uniformly charged photoreceptor 10, selective exposure L corresponding to image information of the first color (for example, yellow) is performed by an exposure unit (not shown), and an electrostatic latent image for yellow is formed. It is formed.
[0096]
(Iv) Only the developing roller 17Y for the first color (for example, yellow) is in contact with the photosensitive member 10, whereby the electrostatic latent image is developed, and the first color (for example, yellow) toner image is transferred to the photosensitive member. 10 is formed.
[0097]
(V) A primary transfer voltage V1 having a polarity opposite to the charging polarity of the toner is applied to the intermediate transfer belt 20, and a toner image formed on the photosensitive member 10 is transferred to a primary transfer portion, that is, the photosensitive member 10 and the intermediate transfer belt. Then, the toner image is transferred onto the intermediate transfer belt 20 at the press-contact portion T1 with 20. At this time, the secondary transfer roller 38 and the belt cleaner 39 are separated from the intermediate transfer belt 20.
[0098]
(Vi) After the toner remaining on the photoconductor 10 is removed by the cleaning unit 12, the photoconductor 10 is neutralized by neutralizing light from a neutralizing unit (not shown).
[0099]
(Vii) The operations (ii) to (vi) are repeated as necessary. That is, the second color, the third color, and the fourth color are repeated according to the content of the print command signal, and the toner images according to the content of the print command signal are superimposed on the intermediate transfer belt 20 to be intermediate. It is formed on the transfer belt 20.
[0100]
(Viii) The recording medium S is supplied at a predetermined timing, immediately before or after the leading end of the recording medium S reaches the second transfer portion T2 (in short, on the intermediate transfer belt 20 at a desired position on the recording medium S). The secondary transfer roller 38 is pressed against the intermediate transfer belt 20 and the secondary transfer voltage V2 is applied to the toner image on the intermediate transfer belt 20 (basically a full-color image). Is transferred onto the recording medium S. Further, the belt cleaner 39 contacts the intermediate transfer belt 20, and the toner remaining on the intermediate transfer belt 20 after the secondary transfer is removed.
[0101]
(Ix) When the recording medium S passes through a fixing device (not shown), the toner image is fixed on the recording medium S, and then the recording medium S is discharged out of the apparatus.
[0102]
According to the image forming apparatus as described above, since the intermediate transfer belt 20 is pressed against the photoreceptor 10 between the rollers 31 and 35, the intermediate transfer belt 20 at the press contact portion (primary transfer portion) T1 is It is pressed against the photoreceptor 10 by its own tension.
[0103]
Therefore, the visible image on the photoconductor 10 is transferred onto the intermediate transfer belt 20 without providing a pressure roller (primary transfer roller) for pressing the intermediate transfer belt 20 against the photoconductor 10 at the pressure contact portion T1. Can do.
[0104]
Further, the intermediate transfer belt 20 is composed of a multilayer belt having a conductive layer 21 and a resistance layer 22 formed on the conductive layer 21 and pressed against the photoconductor 10. The potential on the back side of the resistance layer 22 of the intermediate transfer belt 20 becomes substantially uniform over the entire area of the pressure contact portion (ie, primary transfer portion) T1 with the intermediate transfer belt 20, and as a result, transfer with less toner scattering is obtained. Will be.
[0105]
Therefore, it becomes difficult to be affected by the unevenness of the surface resistance of the intermediate transfer belt 20, and the unevenness of density is further less likely to occur. In addition, since the potential on the back side of the resistance layer 21 of the intermediate transfer belt 20 is substantially uniform over the entire area of the pressure contact portion (that is, the primary transfer portion) T1 between the photosensitive member 10 and the intermediate transfer belt 20, the necessary minimum Transfer with a limited voltage is possible.
[0106]
Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above-described embodiments and examples, and can be appropriately modified within the scope of the gist of the present invention.
[0107]
【The invention's effect】
The image forming apparatus according to any one of claims 1 to 4, in which unevenness in the electric field in the transfer portion is less likely to occur and image misalignment is less likely to occur, and as a result, a good image with less transfer unevenness and misalignment is formed. It becomes possible to do. In addition, the transfer voltage can be supplied easily and reliably, and no transfer failure occurs. The electrode part is also reinforced.
[0108]
further,
According to the image forming apparatus of the second aspect, transfer defects can be prevented more reliably.
[0109]
According to the image forming apparatus of the third aspect, the transfer failure can be prevented more reliably.
[0110]
According to the image forming apparatus of the fourth aspect, the strength of the gap member is improved.
[0111]
[Brief description of the drawings]
1A and 1B are diagrams illustrating an image forming apparatus according to an embodiment of the present invention, in which FIG. 1A is a schematic perspective view, and FIG. 1B is a partial cross-sectional view along line bb in FIG.
FIG. 2 is a view corresponding to the bb partial cross-sectional view in FIG.
FIG. 3 is a schematic diagram showing an example of an image forming apparatus to which the above embodiment is applied.
4A and 4B are diagrams illustrating an example of a conventional image forming apparatus, in which FIG. 4A is a schematic perspective view, and FIG. 4B is a partial cross-sectional view taken along line bb in FIG.
5A and 5B are cross-sectional views for explaining a problem.
FIG. 6 is a cross-sectional view for explaining a problem.
[Explanation of symbols]
10 Photoconductor 10a Conductive layer 10b Photosensitive layer T1 Primary transfer portion T1 (transfer portion)
20 Intermediate transfer belt 21 Conductive layer 22 Resistive layer 23 Electrode portion G Spacing 25 Gap member 26 Bead

Claims (4)

A photosensitive member on which an image is formed on the surface of the photosensitive layer formed on the conductive layer, and an intermediate transfer belt on which a transfer portion is formed between the photosensitive member surface and the image is transferred at the transfer portion. An image forming apparatus having
The intermediate transfer belt is formed on the conductive layer, a resistance layer formed on the conductive layer, and the image is transferred. The intermediate transfer belt is exposed on the surface of the end of the intermediate transfer belt and supplies a transfer voltage to the conductive layer. While having an electrode part and a bead provided along the back end part of the belt,
A taper surface is formed at the end of at least one of the rollers on which the intermediate transfer belt is stretched, and the meandering of the intermediate transfer belt is regulated by bringing a bead into contact with the taper surface. And
An annular rib-shaped gap member that forms a gap between the electrode portion and the photosensitive member is provided on or near an extension line of the inner surface of the bead in the intermediate transfer belt. Forming equipment.   The image forming apparatus according to claim 1, wherein the gap member is made of a material having a higher resistance value than the resistance layer of the intermediate transfer medium.   The image forming apparatus according to claim 2, wherein the gap member is made of an insulating material.   The image forming apparatus according to claim 1, wherein a cross-sectional shape of the gap member is a trapezoid.

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