JP2020115169A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can prevent the image defect at the transfer with the charging of a sheet.SOLUTION: An image formation apparatus 100 includes: a development part 33 which forms a toner image on a photoreceptor drum 30; and a transfer part 50 which directly transfers the toner image from the photoreceptor drum 30 to a sheet. The image formation apparatus 100 also includes a pre-transfer paper guide 60 which guides the sheet conveyance to a transfer nip part N between a transfer roller 51 and the photoreceptor drum 30 from a register roller 20 and is held by the development part 33. A conductive suede 62 as a static elimination member is arranged on the guide surface of the pre-transfer paper guide 60.SELECTED DRAWING: Figure 3

Description

The present invention relates to an electrophotographic image forming apparatus.

In an electrophotographic image forming apparatus, when a toner image formed on a photoconductor drum or the like is transferred to a sheet, the sheet is temporarily held by a resist roller and the sheet is transferred to a transfer nip portion in synchronization with the rotation timing of the photoconductor drum. Transport. Further, in order to smoothly feed the paper to the transfer nip portion, a pre-transfer paper guide is provided between the registration roller and the transfer nip portion, but in the conventional image forming apparatus, the pre-transfer paper guide is an independent member. It is generally provided (for example, Patent Document 1).

However, the configuration in which the pre-transfer paper guide is provided as an independent member is disadvantageous in reducing the number of parts and downsizing the apparatus. For this reason, particularly in an image forming apparatus which is downsized, there is a structure in which the pre-transfer paper guide function is given to the developing unit. As such an image forming apparatus, for example, there is one in which the housing of the developing unit itself is used as a pre-transfer paper guide on the paper printing surface side, or the housing of the developing unit carries the pre-transfer paper guide. ..

Since the developing unit needs to be arranged with high accuracy with respect to the photosensitive drum, if the developing unit is provided with the pre-transfer paper guide, the positional accuracy between the photosensitive drum and the front end position of the pre-transfer paper guide is also secured. it can. Further, the space for passing the sheet metal, which is the conventional paper guide, can be eliminated, and the image forming apparatus can be downsized.

JP, 2007-62917, A

When the housing of the developing unit is used as the pre-transfer paper guide, the pre-transfer paper guide is made of resin such as PC+ABS (polycarbonate-acrylonitrile-butadiene-styrene mixture).

If the pre-transfer paper guide is made of resin, the paper will be charged by rubbing against the pre-transfer paper guide, causing an image defect due to a discharge phenomenon between the photoconductor drum and the paper during transfer. There is. Further, the sheet conveyed from the registration roller may not be fully discharged due to the charging phenomenon generated by the sliding friction with the registration roller, and may be conveyed in a charged state. With the pre-transfer paper guide formed of resin, it is not possible to eliminate the charge on the charged paper in this way, and it is not possible to prevent image defects due to the charging of the paper.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of preventing image defects during transfer due to electrification of paper.

In order to solve the above-mentioned problems, the present invention is an image forming apparatus having a transfer unit for transferring a toner image formed on a photosensitive drum by a developing unit from a photosensitive drum to a sheet, and comprising Guides the sheet conveyance to the transfer nip portion between the transfer member and the photoconductor drum in the transfer section, and the pre-transfer paper guide held by the developing section and the guide surface of the pre-transfer paper guide. It is characterized in that it is provided with a static elimination member arranged.

According to the above configuration, by holding the pre-transfer paper guide by the developing unit, it is possible to improve the positional accuracy between the photosensitive drum and the front end position of the pre-transfer paper guide, and suppress streaks and banding due to paper collision, It also contributes to downsizing of the image forming apparatus. In addition, by holding the pre-transfer paper guide by the developing unit, even if the pre-transfer paper guide itself does not have the function of discharging the paper, the static-eliminating member disposed on the guide surface of the pre-transfer paper guide can be used to remove the paper. It is possible to eliminate static electricity, and it is possible to prevent image defects during transfer due to electrification of paper.

Further, in the image forming apparatus, the charge removing member may be a non-woven fabric made of a conductive fiber, and the surface thereof may be a conductive suede that is raised.

According to the above configuration, the conductive suede having a raised surface can be naturally discharged into the air from the conductive fibers on the raised surface, and the conductive suede itself can be prevented from being charged. Therefore, the conductive suede does not need to be grounded, and the static elimination effect can be maintained even if the conductive suede is arranged in a floating state.

Further, the image forming apparatus may be configured such that a step portion is provided on the guide surface of the pre-transfer paper guide, and the conductive suede is arranged in the step portion.

According to the above configuration, the leading edge of the paper is less likely to come into contact with the conductive suede, and it is possible to suppress a conveyance jam that occurs when the paper is caught by the conductive suede whose surface is raised.

Further, the image forming apparatus may be configured to have a comb-shaped rib member that covers the conductive suede.

According to the above configuration, even when the curled paper is conveyed from the registration rollers, the contact between the leading end of the paper and the conductive suede is reduced by the rib member, and the effect of suppressing the conveyance jam of the paper is obtained. improves.

Further, the image forming apparatus may be configured to have a perforated sheet member that covers the conductive suede.

According to the above configuration, even when the curled paper is conveyed from the registration rollers, the perforated sheet member reduces the contact between the leading edge of the paper and the conductive suede and suppresses the conveyance jam of the paper. The effect is improved.

Further, in the image forming apparatus, the registration roller is composed of a plurality of rollers divided in the paper width direction, and the static eliminator is arranged only at a position corresponding to the registration roller in the paper width direction. Can be configured.

According to the above configuration, by disposing the charge removing member only at a position corresponding to the registration roller, it is possible to perform charge removal at a position where an image defect is likely to occur.

In the image forming apparatus of the present invention, the pre-transfer paper guide is held by the developing unit to improve the positional accuracy between the photosensitive drum and the front end position of the pre-transfer paper guide. By removing the charge of the paper by the charge removing member arranged on the guide surface, it is possible to prevent an image defect at the time of transfer due to the charge of the paper.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an enlarged image forming unit in the image forming apparatus of FIG. FIG. 3 is a schematic cross-sectional view showing an enlarged structure of a pre-transfer paper guide and its surroundings in the image forming apparatus according to the first embodiment. 9 is an enlarged schematic cross-sectional view showing a pre-transfer paper guide and a structure around the paper guide in the image forming apparatus according to the second embodiment. FIG. FIG. 9 is a perspective view showing a pre-transfer paper guide held by a developing unit in the image forming apparatus according to the second embodiment. FIG. 9 is a schematic cross-sectional view showing an enlarged structure of a pre-transfer paper guide and its surroundings in the image forming apparatus according to the third embodiment. FIG. 13 is a perspective view showing a pre-transfer paper guide held by a developing unit in the image forming apparatus according to the third embodiment.

[Embodiment 1]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an enlarged image forming unit 3 in the image forming apparatus 100.

The image forming apparatus 100 according to the present embodiment is an electrophotographic image forming apparatus, and as shown in FIG. 1, the image reading unit 1, the image forming unit 3 disposed below the image reading unit 1, and the image forming unit 3. The sheet feeding unit 2 is provided below the forming unit 3.

The image reading unit 1 includes a document placing table 11 made of transparent glass, an automatic document feeder 12 (ADF: Auto Document Feeder) for automatically feeding a document onto the document placing table 11, and a document placing table 11. A document image reading unit 13 for scanning and reading an image of a placed document is provided. The image forming unit 3 is provided in the image forming apparatus main body 110. The image forming section 3 is provided with various components that perform an electrophotographic process centered on the photosensitive drum 30 (image carrier).

The image forming unit 3 includes a photosensitive drum 30, a charging unit 31, an exposing unit 32 (not shown in FIG. 2, see FIG. 1), a developing unit 33, a transfer unit 50, a charge removing unit 34, and a cleaning unit. And a part 35.

Around the photosensitive drum 30, a charging unit 31, an exposure unit 32, a developing unit 33, a transfer unit 50, a charge eliminating unit 34, and a cleaning unit 35 are provided in this order.

The charging unit 31 is of a DC voltage application type and uniformly charges the surface of the photoconductor drum 30 to a predetermined potential. The charging unit 31 includes a charging roller 31a and a charging cleaning roller 31b (see FIG. 2). Only the DC voltage component not including the AC voltage component is applied to the charging roller 31a. The charging roller 31 a rotates while being in contact with the surface of the photoconductor drum 30 as the photoconductor drum 30 rotates (moves on the surface). The charging cleaning roller 31b cleans the surface of the charging roller 31a. The charging cleaning roller 31b rotates while being in contact with the surface of the charging roller 31a as the charging roller 31a rotates (moves on the surface).

The exposure unit 32 emits image writing light L (laser light) (see FIG. 2) modulated based on image data from a laser light source 32a (see FIG. 1). The exposure unit 32 irradiates the surface of the photosensitive drum 30 that is uniformly charged with a predetermined potential and is rotated, with the image writing light L while scanning in the main scanning direction. As a result, the exposure unit 32 can write a latent image (electrostatic latent image) on the photoconductor drum 30.

The developing unit 33 visualizes the latent image formed on the photosensitive drum 30 with toner. The developing unit 33 attaches the charged toner to the latent image formed on the photosensitive drum 30 by the exposure unit 32. As a result, the developing unit 33 can visualize the latent image on the photosensitive drum 30 to form a toner image. As shown in FIG. 2, the developing unit 33 is provided with a toner storage unit 41 that supplies toner to the developing tank 33 a of the developing unit 33.

The transfer unit 50 electrostatically transfers the toner image formed on the photosensitive drum 30 onto a sheet P such as a transfer sheet. The transfer unit 50 includes a transfer roller 51 (transfer member). The transfer roller 51 is driven by the rotation (movement of the surface) of the photosensitive drum 30 while being in contact with the surface of the photosensitive drum 30. A transfer bias (voltage) is applied to the transfer roller 51.

The charge removing unit 34 removes the residual potential remaining on the photosensitive drum 30 after the transfer. The charge removing unit 34 is located downstream of the transfer unit 50 and upstream of the charging unit 31 in the rotation direction R (see FIG. 2) of the photoconductor drum 30, and in this example, between the transfer unit 50 and the cleaning unit 35. It is arranged. The static elimination unit 34 includes a static elimination light source 34a and a static elimination light guide plate 34b. The static elimination light source 34a emits light toward the static elimination light guide plate 34b. As the static elimination light source 34a, for example, a light emitting element such as an LED can be exemplified. The static elimination light guide plate 34b guides the light from the static elimination light source 34a to the surface of the photosensitive drum 30.

The cleaning unit 35 includes a cleaning blade 36 and a waste toner carrying screw 37. The cleaning blade 36 removes transfer residual toner remaining on the photosensitive drum 30 without being transferred by the transfer unit 50. The waste toner carrying screw 37 carries the transfer residual toner removed from the photoconductor drum 30 by the cleaning blade 36 in the direction perpendicular to the drawing (upward). As a result, the image forming apparatus 100 causes the transfer residual toner conveyed by the waste toner conveying screw 37 to be stored in a waste toner collecting container (not shown) installed between the front cabinet of the image forming apparatus 100 and the image forming unit 3. Can be recovered.

As shown in FIG. 1, the image forming unit 3 includes a fixing unit 38. The fixing unit 38 heat-fixes the toner image transferred onto the paper P by the transfer unit 50 onto the paper P. The fixing unit 38 includes a heating roller 39 and a fixing roller 40. The heating roller 39 is heated to a predetermined fixing temperature. The fixing roller 40 is pressed against the heating roller 39 at a predetermined fixing pressure. As a result, the fixing unit 38 can fix the toner image on the sheet P to the sheet P with the fixing pressure of the fixing roller 40 to the heating roller 39 by melting the toner image on the sheet P by the heat of the heating roller 39.

The image forming apparatus 100 further includes a paper feed unit 2 and a transport unit 4. The paper feeding unit 2 includes a paper feeding cassette 21 and a manual paper feeding tray 22 as a plurality of paper feeding devices. The image forming apparatus 100 selects one of the paper feed cassette 21 and the manual paper feed tray 22. Further, the image forming apparatus 100 separates the sheets P one by one by the pickup roller 23 provided in the selected sheet feeding device and conveys the sheets P toward the conveying unit 4. The transport unit 4 includes a registration roller 20, a discharge roller 25, and a transport roller 26. The registration roller 20 conveys the paper P fed from the paper feed unit 2 toward the transfer nip portion N in the conveyance direction Y. The registration roller 20 is stationary before the paper P is fed. The registration roller 20 rotates so that the electrostatic latent image on the photosensitive drum 30 and the image forming area [area excluding the void (blank space) area] on the paper P coincide with each other when the paper P hits the transfer nip portion N. Driving is started.

The image forming apparatus 100 includes transport paths S1 and S2, a reverse transport path S3, and a discharge tray 24. The transport paths S1 and S2 transport the paper P from the paper feeding unit 2 to the image forming unit 3, and transport the paper P on which the toner image is fixed to the discharge tray 24. The reverse transport path S3 is used during double-sided printing. The reverse conveyance path S3 reverses the front and back surfaces of the paper P which has a toner image printed on its surface and is switched back by the discharge roller 25, and guides it to the registration roller 20 again. This allows the image forming apparatus 100 to form a toner image on the back surface as well as the front surface of the paper P during double-sided printing. In the vicinity of the transport paths S1 and S2 and the reverse transport path S3, transport rollers for transporting the paper P are appropriately arranged.

The image forming apparatus 100 according to the present embodiment has pre-transfer paper guides 60 and 61 between the registration roller 20 and the transfer nip portion N, and guides the print surface side of the paper P to the pre-transfer paper guide. The developing unit 33 is held by the developing unit 33. Here, “the pre-transfer paper guide 60 is held by the developing unit 33” means that the housing itself of the developing unit 33 is used as the pre-transfer paper guide 60 and that the housing of the developing unit 33 is a separate member. This includes both the concept of carrying the pre-transfer paper guide 60. In this way, by holding the pre-transfer paper guide 60 by the developing unit 33, it is possible to improve the positional accuracy between the photoconductor drum 30 and the front end position of the pre-transfer paper guide 60, and suppress streaks and banding due to collision. it can. Further, it contributes to downsizing of the image forming apparatus 100.

When the housing itself of the developing unit 33 is used as the pre-transfer paper guide 60, the pre-transfer paper guide 60 is made of resin (for example, PC+ABS resin) like the housing of the developing unit 33. Further, even when the case of the developing unit 33 carries a pre-transfer paper guide which is a separate member, the pre-transfer paper guide 60 is preferably made of resin. Here, the pre-transfer paper guide 60 is assumed to be made of resin.

When the pre-transfer paper guide 60 is made of resin, as described above, the charged paper P is fed into the transfer nip portion N, and an image defect may occur due to a discharge phenomenon between the photoconductor drum 30 and the paper P. There is. The image forming apparatus 100 according to the present embodiment is characterized in that the pre-transfer paper guide 60 is provided with a function of removing electricity from the paper P in order to prevent such image defects. Hereinafter, this characteristic point will be described in detail with reference to FIG. FIG. 3 is an enlarged schematic cross-sectional view showing the pre-transfer paper guide 60 and the structure around it in the image forming apparatus 100 according to the first embodiment.

As shown in FIG. 3, the pre-transfer paper guide 60 has a guide surface 60a, and the guide surface 60a is provided with a conductive suede 62 as a charge eliminating member. The conductive suede 62 is a non-woven fabric made of conductive fibers, and its surface is raised (fluffed). Further, the conductive suede 62 is preferably provided near the upstream end in the transport direction Y so as not to get too close to the transfer nip portion N.

Since the pre-transfer paper guide 60 is provided with the conductive suede 62, the image forming apparatus 100 according to the present embodiment can perform static elimination on the paper P before being conveyed to the transfer nip portion N. As a result, it is possible to prevent image defects due to the conveyance of the charged paper P to the transfer nip portion N.

However, since the surface of the conductive suede 62 is raised, if the leading edge of the paper P conveyed to the conductive suede 62 hits, the paper P may be caught by the conductive suede 62 and a conveyance jam may occur. .. Therefore, in the pre-transfer paper guide 60, in order to prevent the paper P from being caught by the conductive suede 62, the guide surface 60a is provided with the recessed stepped portion (stepped portion) 60b, and the recessed stepped portion 60b is provided with the conductive suede. 62 is arranged. With this configuration, the leading edge of the paper P is less likely to contact the conductive suede 62, and the conveyance jam of the paper P can be suppressed. Incidentally, the conductive suede 62 having a raised surface can obtain the static elimination effect only by coming close to the paper P even if it is not in contact with the paper P.

Further, the conductive suede 62 need not be grounded and may be arranged in a floating state. When the conductive suede 62 itself is charged, the charge removing effect of the conductive suede 62 naturally decreases. However, the conductive suede 62 having a raised surface can be naturally discharged into the air from the conductive fibers on the raised surface, and the conductive suede 62 itself can be prevented from being charged. Therefore, even if the conductive suede 62 is arranged in a floating state, the static elimination effect is maintained without deterioration.

[Embodiment 2]
FIG. 4 is an enlarged schematic sectional view of the pre-transfer paper guide 60 and its surrounding structure in the image forming apparatus 100 according to the second embodiment. FIG. 5 is a perspective view showing the pre-transfer paper guide 60 held by the developing unit 33.

As shown in FIG. 4, also in the second embodiment, the pre-transfer paper guide 60 has the guide surface 60a, and the conductive suede 62 as the charge removing member is arranged on the guide surface 60a.

Further, in the second embodiment, not only the conductive suede 62 but also the comb tooth-shaped rib member 63 (see FIG. 5) covers the conductive suede 62 in the recessed stepped portion 60b provided in the pre-transfer paper guide 60. It is arranged to cover. The conductive fibers raised on the surface of the conductive suede 62 are exposed from between the ribs of the rib member 63 so that the paper P can be discharged.

In this configuration, even when the curled paper P is conveyed from the registration roller 20, the contact between the leading end of the paper P and the conductive suede 62 is reduced by the rib member 63, and the conveyance jam of the paper P is prevented. The suppression effect is improved. Further, the presence of the rib member 63 allows the sheet P to be guided to the transport path more accurately.

[Embodiment 3]
FIG. 6 is an enlarged schematic sectional view of the pre-transfer paper guide 60 and its surrounding structure in the image forming apparatus 100 according to the third embodiment. FIG. 7 is a perspective view showing the pre-transfer paper guide 60 held by the developing unit 33.

As shown in FIG. 6, also in the second embodiment, the pre-transfer paper guide 60 has the guide surface 60a, and the conductive suede 62 as the charge removing member is arranged on the guide surface 60a.

Further, in the third embodiment, not only the conductive suede 62 but also the perforated sheet member 64 (see FIG. 7) having a large number of small holes is made conductive in the recessed step portion 60b provided in the pre-transfer paper guide 60. It is arranged so as to cover the sex suede 62. The conductive fibers raised on the surface of the conductive suede 62 are exposed through the small holes provided in the perforated sheet member 64, so that the paper P can be discharged. The perforated sheet member 64 does not need to be conductive, and the cost can be suppressed by using a resin sheet such as PET. However, the material of the perforated sheet member 64 is not particularly limited, and for example, a polymer sheet having conductivity may be used.

In this configuration, even when the curled paper P is conveyed from the registration rollers 20, the perforated sheet member 64 reduces the contact between the leading end of the paper P and the conductive suede 62, and thus the conveyance of the paper P. The effect of suppressing jams is improved.

Further, the small holes provided in the perforated sheet member 64 may be different in size and number depending on the position of the perforated sheet member 64. As a result, it is possible to realize a shape in which the portion of the sheet where the electricity is desired to be eliminated (e.g., the feeding roller portion) is concentrated.

(Modification)
Hereinafter, modified examples of the image forming apparatus 100 described in the first to third embodiments will be described.

In the image forming apparatus 100 described above, the configuration using the conductive suede 62 as the charge removing member provided in the pre-transfer paper guide 60 is illustrated, but as the charge removing member, a conductive member such as a charge removing brush or an aluminum tape may be used. You may use. However, when a conductive member other than the conductive suede 62 is used as the charge removing member, it is preferable that the charge removing member is grounded because these do not have a spontaneous discharge action unlike the conductive suede 62.

Further, in the above-described image forming apparatus 100, the pre-transfer paper guide 60 is made of resin, but if the pre-transfer paper guide 60 of another member is carried in the housing of the developing unit 33, the pre-transfer paper guide 60 is provided. Does not have to be made of resin, and may be made of metal such as sheet metal. However, in this case, the conductive suede 62 is used as the charge removing member provided in the pre-transfer paper guide 60. When the pre-transfer paper guide 60 is made of metal, if the pre-transfer paper guide 60 is grounded, the static electricity removal effect of the paper P can be obtained only by the pre-transfer paper guide 60. However, by providing the conductive suede 62, the pre-transfer paper guide 60 is provided. The static elimination effect can be maintained without grounding 60. Therefore, the process of assembling the image forming unit 3 in the image forming apparatus 100 can be simplified.

Further, although the image forming apparatus 100 described above is illustrated as a monochrome machine, the present invention is also applicable to a color machine. However, the color machine to which the present invention is applicable does not have an intermediate transfer unit like a tandem type color machine, and the toner image formed on the photoconductor drum is directly transferred from the photoconductor drum to the paper P. It is assumed that it is a configuration. Therefore, the color machine to which the present invention can be applied is a four-cycle type color machine that performs color printing using one photoconductor drum, and in this case, the pre-transfer paper guide is held in the developing section closest to the transfer section. Will be done.

Further, the charge eliminating member (for example, the conductive suede 62) in the above-described image forming apparatus 100 is arranged in the entire sheet width direction (direction orthogonal to the sheet conveying direction) in order to surely remove the charge on the sheet P. Preferably. However, the present invention is not limited to this, and the static eliminator may be arranged in at least a part of the paper width direction. For example, in an inexpensive image forming apparatus, the registration roller 20 may be composed of a plurality of rollers divided in the paper width direction, and an image defect due to the charging of the paper may occur only at a portion receiving the conveyance force of the registration roller 20. There are cases. In such a case, the static elimination member may be arranged only in a portion corresponding to the registration roller 20 in the paper width direction, and the static elimination may be performed only in a portion where an image defect is likely to occur.

The embodiment disclosed this time is an example in all respects, and is not a basis for a limited interpretation. Therefore, the technical scope of the present invention should not be construed only by the above-described embodiments, but should be defined based on the claims. Also, the meaning equivalent to the scope of claims and all modifications within the scope are included.

3 Image Forming Section 20 Registration Roller 30 Photosensitive Drum 31 Charging Section 32 Exposure Section 33 Developing Section 34 Electrification Section 35 Cleaning Section 38 Fixing Section 50 Transfer Section 51 Transfer Roller (Transfer Member)
60 Pre-Transfer Paper Guide 60a Guide Surface 60b Depression Step (Step)
62 Conductive suede (static elimination member)
63 rib member 64 perforated sheet member 100 image forming apparatus P sheet N transfer nip portion

Claims (6)

An image forming apparatus having a transfer unit configured to transfer a toner image formed on a photoconductor drum by a developing unit from a photoconductor drum to a sheet,
A pre-transfer paper guide that guides the sheet conveyance from the registration roller to the transfer nip portion between the transfer member and the photosensitive drum in the transfer unit, and the pre-transfer paper guide held by the developing unit;
An image forming apparatus comprising: a static eliminating member disposed on a guide surface of the pre-transfer paper guide. The image forming apparatus according to claim 1, wherein
The image forming apparatus, wherein the charge removing member is a non-woven fabric made of a conductive fiber and is a conductive suede whose surface is raised. The image forming apparatus according to claim 2, wherein
An image forming apparatus, wherein a step portion is provided on a guide surface of the pre-transfer paper guide, and the conductive suede is disposed on the step portion. The image forming apparatus according to claim 2 or 3, wherein
An image forming apparatus having a comb-shaped rib member covering the conductive suede. The image forming apparatus according to claim 2 or 3, wherein
An image forming apparatus comprising a perforated sheet member that covers the conductive suede. The image forming apparatus according to any one of claims 1 to 5, wherein:
The registration roller is composed of a plurality of rollers divided in the paper width direction,
The image forming apparatus, wherein the charge removing member is arranged only at a position corresponding to the registration roller in the sheet width direction.

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