JPH0784468A - Image forming device - Google Patents

Abstract

PURPOSE:To form an excellent quality image on both surfaces of a paper sheet by preventing fogging toner from being transferred on the surface of a roller, in an image forming device provided with the roller guiding a transfer paper in the vicinity of a position where an electrostatic latent image holder faces a transfer device. CONSTITUTION:The large diameter parts 17a and 17b abutted on the surface of the nonimage part of the electrostatic latent image holder are provided on both end parts of a conductive roller 15 and the outside diameter of the large diameter part 17b located opposite to the side of a side resist is set larger than that of the other large diameter part 17a. Moreover, the large diameter part 17a of the side resist side is constituted of a member whose friction against the surface of the electrostatic latent image holder is smaller than that of the large diameter part 17b of the opposite side. Thus, when a small-sized paper is used, the gap of the side where the paper does not pass is adjusted slightly wider than that of the opposite side, the transfer of the fogging toner can be prevented and simultaneously, the abrasion of the large diameter part 17a of the side resist side can be prevented as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a toner image formed on an electrostatic latent image holding member onto a transfer sheet to form an image, and particularly to a transfer sheet near a transfer section. The present invention relates to an image forming apparatus including a roller that holds a sheet.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus such as an electrophotographic copying machine, a laser printer, and a facsimile, there is known one shown in FIG. In this image forming apparatus, an electrostatic latent image holder 102 made of a cylindrical photosensitive member is provided in a housing 101 of the apparatus main body, and the electrostatic latent image holder 102 is provided around the electrostatic latent image holder 102. A charger 103 for uniformly charging, an exposure device 109 for irradiating image light to form an electrostatic latent image, a developing device 104 for developing the electrostatic latent image by adhesion of toner, and a developed toner image. It has a transfer device 106 for transferring onto a transfer sheet and a cleaning device 108 for removing the toner remaining on the electrostatic latent image holding member 102 after transfer. Further, in the housing 101, a paper tray 110 for accommodating transfer paper, a paper conveyance path 111 for conveying the transfer paper to the transfer portion, a pair of registration rollers 113 and a registration guide 116 for holding the transfer paper at the transfer portion. It also has a peeling device 107 that removes static electricity and peels off the transfer paper on which the toner image has been transferred, and a fuser roll 112 that fixes the toner on the transfer paper.

As the transfer device 106, a transfer charger having a wire stretched in a shield case is used. In the transfer step, a high voltage is applied to the wire to cause corona discharge from the back surface of the transfer sheet, so that the toner image on the electrostatic latent image holder is transferred onto the transfer sheet. In such an image forming apparatus, the developing device 104 develops the electrostatic latent image formed on the electrostatic latent image holding member by the exposure of the image light, and the developed toner image is transferred from the paper conveyance path 111 to the transfer portion. The transfer device 106 transfers the transferred transfer paper onto the fuser roll 112.
The toner is further fixed, and one print image is formed.

The transfer device 106 used in the image forming apparatus as described above, and the registration roller pair 113 and the registration guide 116 arranged near the transfer device are, for example, an image forming apparatus for forming an image on both sides of a transfer sheet. It is also widely used in. In general, when forming a double-sided image, the transfer device 106 is generally set to the same voltage without changing the state or the like between the printing of the first side and the printing of the second side. Recently, an attempt has been made to obtain the optimum transfer image quality by switching the output level of the transfer current applied to the transfer charger in consideration of the image quality. However, even with such a method, it has not been possible to satisfy all print image quality in double-sided printing. Especially during double-sided printing, the curl of the transfer paper after single-sided printing often causes transfer defects such as image blur, double image, and image loss at the front and rear edges of the paper. There was a drawback that defects were likely to occur.

In order to improve such a defect, rollers which are supported at a constant interval in the axial direction of the electrostatic latent image holding member are arranged near the transfer portion, and the transfer sheet is electrostatically latently transferred at the transfer portion. There has been proposed a device for guiding the surface of the image carrier so as to contact it. In such an image forming apparatus, even if the transfer paper is curled during double-sided printing, the transfer paper can be stably held at the transfer unit, and it is possible to prevent occurrence of transfer failure due to paper blur or the like. . As an image forming apparatus provided with the roller as described above, for example, Japanese Patent Application Laid-Open No. 4-15
3682, Actual Kaihei 4-59861, Actual Kaihei 4-5986
2, Japanese Utility Model Laid-Open No. 4-59863 and Japanese Utility Model Laid-Open No. 2-123962.

[0006]

However, in the image forming apparatus as described above, after the development of the electrostatic latent image, the surface of the electrostatic latent image holding member other than the region where the electrostatic latent image is formed is slightly left. Toner is attached (so-called fog toner), and when using a small size transfer paper, the fog toner existing in the area where the paper does not face the electrostatic latent image carrier is transferred onto the roller during the transfer process. I will end up. Therefore, when a large-sized transfer sheet is used after a small-sized transfer sheet is used, the toner transferred onto the roller adheres to the back side of the transfer sheet, and the transfer sheet is contaminated. The present invention has been made in view of the above problems, and an object thereof is to prevent the fog toner on the electrostatic latent image holding member from transferring to the surface of the roller, and to improve both sides of the paper. An image forming apparatus capable of obtaining various images.

[0007]

In order to solve the above-mentioned problems, the present invention relates to an electrostatic latent image holder on which an electrostatic latent image is formed on the surface by irradiation of image light after uniform charging, A transfer device for transferring a toner image formed by adhering toner to the electrostatic latent image onto a transfer sheet conveyed along a side resist provided on one side of a sheet conveying path; An image forming apparatus, comprising: a cylindrical conductive roller that is disposed in the vicinity of the electrostatic latent image holder and is in proximity to the transfer sheet and guides the transfer sheet to the surface of the electrostatic latent image holder. A large-diameter portion that comes into contact with the surface of the non-image portion of the electrostatic latent image holding member is provided at both ends of, and the outer diameter of the large-diameter portion located opposite to the side resist side is larger than that of the other large-diameter portion. It shall be set larger than the outer diameter.

In the image forming apparatus, the large-diameter portion is a member that causes friction to such an extent that a rotational driving force can be transmitted to the conductive roller by contacting the surface of the electrostatic latent image holding member. It is desirable that the large-diameter portion on the side resist side is formed of a member having less friction with the surface of the electrostatic latent image holding member than the large-diameter portion on the opposite side.

The large diameter portion can be appropriately set as long as it has a structure in which both ends are larger than the diameter of the conductive roller. For example, a structure in which a coating layer is provided on both ends of the conductive roller, or a conductive roller is used. A cylindrical member having an outer diameter larger than that of the conductive roller can be fitted into both ends of the conductive roller.

The outer diameter of the large-diameter portion may be such that the transfer sheet is sandwiched between the conductive roller and the electrostatic latent image holder and held so that the transfer sheet contacts the surface of the electrostatic latent image holder. The dimensions are set so that it can be done. Also, by adjusting the outer diameters of the large-diameter portion on the side resist side and the large-diameter portion on the opposite side, the gap between the conductive roller and the electrostatic latent image holding member is set on the opposite side of the side resist in the axial direction of the roller. The gap is set to be slightly larger than that on the side resist side, and at least in the vicinity of the end portion on the side opposite to the side resist, a gap is secured so that the fog toner on the electrostatic latent image holder does not transfer to the conductive roller.

It is desirable that the large-diameter portion on the side resist side and the large-diameter portion on the opposite side are made of appropriate members having different friction coefficients. For example, the large-diameter portion on the side resist side is made of synthetic resin. It is preferable that the large-diameter portion on the opposite side is made of a material such as rubber having a large friction with the surface of the electrostatic latent image holding member.

[0012]

In the image forming apparatus having the above-described structure, the large diameter portion that contacts the surface of the electrostatic latent image holding member is provided at both ends of the conductive roller, and the outer diameter of the large diameter portion opposite to the side resist is provided. Is set to be larger than the outer diameter of the large-diameter portion on the side resist side, so that the gap between the surface of the conductive roller and the surface of the electrostatic latent image holding member is in the roller axial direction and is larger than that on the side resist side. The opposite side is adjusted to be slightly wider.
Therefore, even when using a small-sized transfer sheet, the fog toner on the electrostatic latent image holding member existing on the side of the wide gap (the side opposite to the side resist) where the sheet does not pass through is transferred to the conductive roller during the transfer process. Transfer to the surface is prevented.
Therefore, even if a large-sized transfer paper is used after a small-sized transfer paper is used, toner does not adhere to the back surface of the transfer paper to stain the paper, and an image defect due to the adhered toner does not occur and a good image is obtained. Can be obtained.

Further, by forming the large-diameter portion of the large-diameter portion on the side opposite to the side resist with a member having a larger friction coefficient than the large-diameter portion of the side resist side, the outer diameters of the large-diameter portions are different from each other. Even if the size is set, it is possible to prevent the large diameter portion on the side of the side resist having a small outer diameter from being worn by friction during rotation. Therefore, the gap between the conductive roller and the electrostatic latent image carrier is kept constant in the initial state, and it is possible to prevent the transfer of the toner to the conductive roller due to the gap.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the present invention. This image forming apparatus has, in a housing 1, an electrostatic latent image holder 2 on the surface of which an electrostatic latent image is formed by irradiation of image light.
A charging device 3, an exposure device 9, a developing device 4, a transfer auxiliary charging device 5, a transfer device 6, a peeling device 7, and a cleaning device 8 are arranged around the area. Further, in the housing 1, as in the conventional image forming apparatus, a paper tray 10, a paper transport path 11, a fuser roll 12 and the like are arranged. 2 is a perspective view showing an outline of the transfer device 6,
FIG. 3 is a view showing a cross section perpendicular to the axial direction of the metal roller of the transfer device 6.

As shown in FIG. 3, the transfer device 6 includes a peeling device 7 for peeling the transfer sheet from the electrostatic latent image carrier.
And a transfer charger in which a wire 24 is stretched in a shield case 20, and an electrostatic latent image on the upper side of the transfer charger in the rotation direction of the electrostatic latent image holder 2 at the upper side. It has a holder and a metal roller 15 supported such that their axes are substantially parallel and their surfaces are close to each other. In addition, at a position adjacent to the metal roller 15,
A plate-shaped halo baffle 16 for introducing a transfer sheet is installed in the gap between the metal roller 15 and the electrostatic latent image holder 2 over the entire length. As shown in FIG. 2, the metal roller 15 has a coating portion 17a in which both ends of a cylindrical conductive member are coated with a semi-conductive or insulating material so as to have a diameter larger than the outer diameter of the conductive member. , 17b, and as shown in FIG. 3, the covering portions 17a, 17b are in contact with and supported by both end portions of the surface of the electrostatic latent image holding member 2. Reference numeral 21 shown in the drawing is a shield case of the peeling device 7, reference numeral 2
Reference numeral 5 is a peeling wire.

The thickness of the covering portions 17a and 17b is as shown in FIG.
2, the outer diameter of the covering portion 17a on the side closer to the side resist 22 (the front side in FIG. 2) which is brought into contact with one of the side edges of the transfer sheet is smaller than the outer diameter of the other covering portion 17b. Is also set to be small. More specifically, the covering portion 17a is larger than the diameter of the metal roller 15 by 0.3 mm, and the covering portion 17b is larger than the diameter of the metal roller 15 by 0.6 m.
It is getting bigger. The covering portion 17a is made of synthetic resin, and the covering portion 17b is made of rubber material. The rotational driving force of the electrostatic latent image holding member is transmitted through the covering portion 17b, and the metal roller 15 is electrostatically latent. The image carrier 2 is adapted to rotate.

As shown in FIGS. 2 and 3, the metal roller 15 is supported by conductive bearings 19 arranged at both ends of the transfer device 6, and when mounted on the main body of the image forming apparatus, it is a spring. The metal roller 15 is pressed in the direction of the electrostatic latent image holder 2 by 18. As a result, the coating portions 17a and 17b come into contact with the surface of the electrostatic latent image holding member 2 with a constant contact pressure, and as shown in FIG. 4, the coating portions 17a and 17b.
The surface of the electrostatic latent image holder 2 and the surface of the metal roller are supported via b via a predetermined gap. At this time, the covering part 1
Due to the difference in outer diameter between 7a and 17b, a gap width is generated in the axial direction of the electrostatic latent image holding member, and the gap A on the side resist side is adjusted to be narrower than the gap B on the opposite side (FIG. 4).
Medium, A = 0,15 mm, B = 0,30 mm). In the image forming apparatus according to the present exemplary embodiment, the gap is set to 0.2 mm or more at a portion where the sheet does not pass, and the gap is 0.2 mm.
If it exceeds, it is possible to prevent the toner from adhering to the surface of the metal roller. Note that this gap is the rotational speed of the electrostatic latent image carrier,
It is desirable to select an appropriate size according to the properties of the toner used.

The metal roller 15 is a conductive bearing 1.
It is electrically grounded via 9 and prevents electric charges from accumulating on the roller 15 when a transfer current is applied to the wire 24. The hello baffle 16 is
The plate-shaped member is connected to the paper transport path 11 in the tangential direction of the metal roller 15.
Of the metal roller 15 and the sheet conveying path 1
1 is connected to guide the transfer sheet between the electrostatic latent image holder 2 and the metal roller 15.

The transfer charger disposed in the transfer device 6 has a structure in which a wire 24 to which a transfer current is applied is stretched in a shield case 20, and is used in the conventional image forming apparatus shown in FIG. It has the same structure as The metal roller 15 is supported so as to be located above the shield case 20 in the field of view of the wire 24 as shown in FIG. 3, and when a transfer current is applied to the wire 24, the metal roller 15 is also transferred. The position is such that the beam extends. The other configurations of the image forming apparatus are the same as those of the conventional image forming apparatus.

Next, the operation of the image forming apparatus of this embodiment will be described. The electrostatic latent image holder 2 is uniformly charged by the charger 3, and when the exposure device 9 irradiates image light, an electrostatic latent image due to a difference in charging potential is formed on the surface of the electrostatic latent image holder 2. It is formed. At this time, the image light illuminates the image portion, and has the same polarity charge as the surface potential polarity of the electrostatic latent image holder 2 at the position where the developing device 4 and the electrostatic latent image holder 2 face each other. The toner is transferred to the exposed area and the electrostatic latent image is developed. The developed toner image passes through a position facing the auxiliary transfer charger 5 by the rotation of the electrostatic latent image holding member 2, is adjusted to an appropriate potential, and is conveyed to a transfer unit facing the metal roller 15 and the wire 24. To be done.

On the other hand, the transfer sheets accommodated in the sheet tray 10 are drawn out one by one by the feed roller 11a and conveyed to the registration roll 13 through the sheet conveying path 11. At this time, the transfer sheet is set so that it is fed to the transfer section at the timing when the toner image arrives at the transfer section by the registration roll 13, and the transfer sheet is fed with the hello baffle 16 at a predetermined timing. Then, it is guided to the side resist 22 and passes through the position where the metal roller 15 and the electrostatic latent image holding member 2 face each other, and is conveyed to the transfer portion.

At this time, since the metal roller 15 and the electrostatic latent image carrier 2 rotate in the same direction while holding a predetermined gap,
The transfer sheet comes into contact with the surface of the electrostatic latent image holder 2 and is guided to a region where the wire 24 and the electrostatic latent image holder 2 face each other while maintaining the contact state. At this time, in the case of transferring to the second surface of the paper, even if the paper is rolled at the time of transferring the first surface, the contact state is maintained up to near the rear end. At the transfer portion, a transfer current is applied to the wire 24, and the toner image on the electrostatic latent image carrier is transferred to a predetermined position on the transfer paper. At this time, the side edge of the transfer paper is the side resist 2
Since the sheet is conveyed so as to be in contact with the sheet 2, when a small-sized sheet is used, the sheet does not exist at the opposite end of the metal roller 15, that is, near the covering portion 17b side. However,
The gap between the electrostatic latent image holder 2 and the metal roller 15 is the covering portion 1
Since the area near the covering portion 17b is set to be larger than the area near the side 7a, the fog toner on the surface of the electrostatic latent image holding member 2 is not covered by the metal roller 1.
5 can be prevented from being transferred to the surface.

For this reason, the fog toner is transferred to the metal roller 15.
It is possible to prevent the transfer sheet from becoming dirty and from having image quality defects caused by the adhesion to the surface. The transfer sheet on which the toner image has been transferred in the above-described steps is destaticized and peeled by the peeling device 7, and is transported on the transport belt 14. Further, the toner image is fixed on the transfer paper by the fuser roll 12 to form one copy image. The copied image thus obtained is a good image without any image quality defect, and even if a large size paper is used after a small size paper is used, toner does not adhere to the back surface of the paper. It was also possible to eliminate the occurrence of stains on the paper.

Table 1 shows the degree of wear of the covering portions 17a and 17b when a predetermined number of copies are made in the image forming apparatus of the present embodiment through the above-mentioned steps, and the covering portions on both sides are examined. It is shown in comparison with the one using a rubber material. Further, FIG. 5 is a graph showing this result. (Hereafter, margin)

[0025]

[Table 1]

In Table 1 and FIG. 5, when the coating portion 17a on the side resist side is made of synthetic resin as in this embodiment, the friction amount is smaller than that when the coating portion is made of rubber material. It was confirmed that, when the transfer amount of the rubber material was 150 × 10 ³ sheets, the wear amount was 0.33 mm, whereas that of the synthetic resin was 0 mm, and the wear amount was hardly worn even when used for a long period of time. Therefore, the gap setting between the metal roller and the electrostatic latent image holder can be maintained in the initial state, and the maintainability of the apparatus can be improved.

[0027]

As described above, according to the image forming apparatus of the present invention, even when the toner images are transferred to both sides, it is possible to clearly transfer the toner images to both ends by the action of the conductive roller, and the conductive image is formed. Since the gap between the electrostatic roller and the electrostatic latent image holder is set to be wider on the opposite side than on the side resist side, the fog toner on the electrostatic latent image holder is conductive at a position where the gap is wide. It is possible to prevent the transfer to the surface of the elastic roller. Therefore, even when a large-sized transfer sheet is used after a small-sized transfer sheet is used, adhesion of toner to the back surface of the sheet is prevented, and a good image can be obtained. Further, by forming the member having a smaller outer diameter of the thick shaft portion with a member having a smaller friction coefficient than the other thick shaft portions, wear during rotation is prevented and the maintainability of the device can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus that is an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a transfer device used in the image forming apparatus.

FIG. 3 is a schematic sectional view showing a transfer device used in the image forming apparatus.

FIG. 4 is a diagram showing a contact state of a metal roller used in the image forming apparatus with an electrostatic latent image holder.

FIG. 5 is a diagram showing an amount of wear of a coating portion of a metal roller used in the image forming apparatus.

FIG. 6 is a schematic configuration diagram showing a conventional image forming apparatus.

[Explanation of symbols]

 1 Image Forming Device 2 Electrostatic Latent Image Holder 3 Charging Device 4 Developing Device 5 Transfer Auxiliary Charger 6 Transfer Device 7 Peeling Device 8 Cleaning Device 9 Exposure Device 10 Paper Tray 11 Paper Conveying Path 12 Fuser Roll 13 Registration Roll 14 Conveying Belt 15 Metal Roller 16 Halo Baffle 17 Cover 18 Spring 19 Bearing 20 Shield Case 22 Side Resist 24 Wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Shiina 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (2)

[Claims] 1. An electrostatic latent image holder on which an electrostatic latent image is formed by irradiation of image light after uniform charging, and a toner image formed by adhering toner to the electrostatic latent image. A transfer device that transfers the image onto a transfer sheet that is conveyed along a side resist provided on one side of the sheet conveyance path; and a transfer sheet that is disposed near the transfer device and in the vicinity of the electrostatic latent image holder. An image forming apparatus including a cylindrical conductive roller for guiding the electrostatic latent image holder so that the electrostatic latent image holder is brought into contact with the surface of the electrostatic latent image holder. An image forming apparatus characterized in that a large-diameter portion that abuts is provided, and an outer diameter of the large-diameter portion located opposite to the side resist side is set to be larger than an outer diameter of the other large-diameter portion. . 2. The image forming apparatus according to claim 1, wherein the large-diameter portion is in contact with the surface of the electrostatic latent image holding member to transmit the rotational driving force to the conductive roller. And a large-diameter portion on the side resist side has a smaller friction with the surface of the electrostatic latent image holding member than the large-diameter portion on the opposite side. An image forming apparatus characterized by.