JPH07325491A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain the excellent image on both sides of a paper sheet by preventing the fog toner covering on an electrostatic latent image carrier from shifting to the surface of the auxiliary roller of transfer device and preventing the electrostatic latent image from damage, in the image forming device of an electrophotographic system. CONSTITUTION:The conductive roller 13 disposed in the vicinity of the transfer device 6 as an auxiliary roll is provided with the large diameter part on the both end part, and the conductive roller 13 is composed of the cylindrical metal member coated by elastic material. Thus, the transfer defect is prevented from causing at the time of both-face printing, the fog toner covering on the electrostatic latent image carrier 2 is prevented from shifting to the conductive roller, the paper transporting is surely performed and the electrostatic latent image carrier is prevented from damage even if the conductive roller 13 is brought into contact with the electrostatic latent image carrier 2.

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, the one shown in FIG. 10 has been known. 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, the housing 101
A paper tray 110 for accommodating the transfer paper, a paper conveyance path 111 for conveying the transfer paper to the transfer portion, a pair of registration rollers 115 and a resist guide 116 for conveying the transfer paper to the transfer portion, and a toner image It has a peeling device 107 that removes static electricity and peels off the transferred transfer paper, and a fuser roll 112 that fixes the toner on the transfer paper.

As the transfer device 106, a transfer charger having an electrode wire stretched in a shield case is used. In the transfer step, a high voltage is applied to the electrode wires 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. A transfer device 106 transfers the transferred transfer paper onto the transfer paper, and the toner is fixed by the fuser roll 112 to form one print image.

The transfer device 106 used in the image forming apparatus as described above, and the registration roller pair 115 and the registration guide 116 arranged near the transfer device are, for example, an image forming apparatus that forms an image on both sides of transfer paper. 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, a roller which is supported in the vicinity of the transfer portion in the axial direction of the electrostatic latent image holder is disposed so as to support the electrostatic latent image on the transfer sheet. Devices have been proposed for guiding the carrier surface into contact.
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 the image forming apparatus provided with the roller as described above, for example, JP-A-4-153681, JP-A-4-59861, and JP-A-4-598.
No. 62, No. 4-59863, No. 2-59863.
Those disclosed in Japanese Patent No. 123962 and the like are known.

[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. Further, the roller is formed of a conductive material in order to prevent charging, but if the roller is a metal roller, the roller bends due to vibration during transportation of the device, and the electrostatic latent image holding member is damaged, Further, since the coefficient of friction is small, there is a problem that the paper cannot be fed smoothly.

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 being transferred to the surface of the roller and to make it static. An object of the present invention is to provide an image forming apparatus capable of preventing damage to a latent image holding member and obtaining good images on both sides of a sheet.

[0008]

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 that transfers a toner image formed by attaching toner to the electrostatic latent image onto a transfer sheet, and a transfer device that is disposed in the vicinity of the transfer device and faces the electrostatic latent image holder. In an image forming apparatus including a conductive roller that guides the electrostatic latent image holder so as to come into contact with the surface of the electrostatic latent image holder, a large diameter contacting both surfaces of the conductive roller with the surface of the non-image portion of the electrostatic latent image holder. And the conductive roller is formed by coating a metal columnar member with a conductive elastic material.

Further, in the image forming apparatus, it is preferable that the conductive roller is electrically grounded.
In the image forming apparatus, the large-diameter portion is formed of a member that causes friction to the extent that a rotational driving force can be transmitted to the conductive roller by contacting the surface of the electrostatic latent image holding member. However, for example, those made of synthetic resin or rubber are preferable.

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 allows the transfer sheet to be held between the conductive roller and the electrostatic latent image holder so that the transfer sheet contacts the surface of the electrostatic latent image holder. The dimensions are set.

The elastic material is not particularly limited as long as it has conductivity, and examples thereof include synthetic rubber mixed with carbon powder, synthetic resin, etc., and the resistivity is about 10 ⁸ Ωcm or less. It is necessary to reduce the fog toner.

[0012]

In the image forming apparatus having the above-described structure, the conductive roller and the electrostatic latent image are formed because the conductive roller is provided with the large-diameter portion which is in contact with the surface of the electrostatic latent image holding member. The holding body keeps a certain distance, so even when using a small size transfer paper, the fog toner on the electrostatic latent image holding body existing in the area where the paper does not pass is transferred to the surface of the conductive roller during the transfer process. It is prevented from transferring. 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, since the conductive roller is a metal cylindrical member coated with a conductive elastic material, even if the roller bends due to vibration when the apparatus is moved or the like and comes into contact with the electrostatic latent image holding member. , Does not damage the electrostatic latent image holder. Further, the surface friction of the conductive roller is larger than that of a metal roller or the like, so that the paper can be reliably fed. Further, by electrically grounding the conductive roller, it is possible to prevent transfer of the fog toner further without excessively accumulating static electricity or electric charges flowing from the transfer charger.

[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 according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram showing a main part of the image forming apparatus. This image forming apparatus has an electrostatic latent image holder 2 on the surface of which an electrostatic latent image is formed by the irradiation of image light in a housing 1, and the electrostatic latent image holder 2 is surrounded by the electrostatic latent image holder 2. Is a charger 3, an exposure device 9, a developing device 4,
A transfer auxiliary charger 5, a transfer device 6, a peeling device 7, and a cleaning device 8 are arranged. 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.

3 is a perspective view showing the outline of the transfer device 6, and FIG. 4 is a view showing a cross section perpendicular to the axial direction of the conductive roller of the transfer device 6. As shown in FIG. As shown in FIG. 4, the transfer device 6 is integrated with a peeling device 7 for peeling the transfer sheet from the electrostatic latent image holder, and the electrode wire 24 is stretched inside the shield case 14. And a transfer charger that is supported above the transfer charger on the upstream side in the rotational direction of the electrostatic latent image holder 2 so that their axes are substantially parallel to each other and their surfaces are close to each other. And a conductive roller 13. The conductive roller 1 is provided at a position adjacent to the conductive roller 13.
A plate-shaped resist guide 16 for introducing the transfer sheet is installed in the gap between the electrostatic latent image holder 3 and the electrostatic latent image holder 2 over the entire length. Reference numeral 21 shown in the drawing is a shield case of the peeling device 7, and reference numeral 25 is an electrode wire for peeling.

As shown in FIG. 5A, the conductive roller 13 has semi-conductive or insulating properties on both ends of a cylindrical conductive member so that the conductive roller 13 has a diameter larger than the outer diameter of the conductive member. It has a coating portion 17 coated with a material, and the coating portion 1
7 is supported by abutting both ends of the surface of the electrostatic latent image holder 2. The outer diameter of the conductive roller 13 is 10 mm so as not to interfere with the transfer beam from the electrode wire 24.
Within the range, preferably 4 to 7 mm is suitable, and is electrically installed via the shield case 14. In this embodiment, the covering portion 17 is 0.3 m from the diameter of the conductive roller 13.
It was assumed to be large.

The covering portion 17 is made of synthetic resin, rubber or the like, and the rotational driving force of the electrostatic latent image holding member is transmitted through the covering portion 17 so that the conductive roller 13 is formed.
Rotate according to the electrostatic latent image holder 2. Further, as shown in FIG. 5B, the cross section of the conductive roller 13 has a central cylindrical member 13a made of metal and an outer cover layer 13b made of an elastic material. The conductive roller 13 is, as shown in FIGS.
Are supported by conductive bearings 19 disposed at both ends of the spring 1 when mounted on the main body of the image forming apparatus.
The conductive roller 13 is pressed toward the electrostatic latent image carrier 2 by 8. As a result, the covering portion 17 comes into contact with the surface of the electrostatic latent image holding body 2 with a constant contact pressure, and as shown in FIG. The surface is supported with a predetermined gap.

In the image forming apparatus of this embodiment, the gap in the area where the paper does not pass is set to 0.2 mm or more, and when it exceeds 0.2 mm, it is possible to prevent toner from adhering to the surface of the conductive roller. Incidentally, it is desirable to select an appropriate size for this gap depending on the rotation speed of the electrostatic latent image holding member, the properties of the toner used, and the like. The conductive roller 13 is electrically grounded via a conductive bearing 19 so as to prevent electric charges from accumulating on the conductive roller 13 when a transfer current is applied to the wire 24. .

The registration guide 16 has a structure in which a plate-shaped member is projected in the tangential direction of the conductive roller 13 toward the upstream side of the paper transport path 11 and the tip portion is curved downward. It is configured to be guided from the transport path 11 between the electrostatic latent image holder 2 and the conductive roller 13.
The transfer charger provided in the transfer device 6 is an electrode wire 2 to which a transfer current is applied in the shield case 14.
4 is stretched and has the same structure as that used in the conventional image forming apparatus shown in FIG.
The conductive roller 13 is supported so as to be located above the shield case 20 in the field of view of the electrode wire 24 as shown in FIG. 3, and when a transfer current is applied to the transfer corotron 24, the conductive roller 13 is supported. The position is such that the transfer beam reaches 13 as well. 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 carrier 2 is uniformly charged by the charger 3, and when the exposure device 9 irradiates the image light, an electrostatic latent image due to a difference in charging potential is generated on the surface of the electrostatic latent image carrier 2. Is formed. At this time, the image light illuminates the image portion, and the developing device 4 and the electrostatic latent image holder 2
The toner having the same polarity charge as the surface potential polarity of the electrostatic latent image holding member 2 is transferred to the exposed portion at a position facing the electrostatic latent image holding member 2 to develop the electrostatic latent image. The developed toner image passes through a position facing the transfer auxiliary charging device 5 by the rotation of the electrostatic latent image holding member 2, is adjusted to an appropriate potential, and is a transfer unit facing the conductive roller 13 and the transfer corotron 24. Be transported to.

On the other hand, the transfer sheets accommodated in the sheet tray 10 are pulled out one by one by the feed roller 11a and conveyed to the registration roller pair 15 through the sheet conveying path 11. At this time, the conveyance timing of the transfer sheet is set so that the toner image is fed to the transfer section by the registration roller pair 15 at the timing when the toner image reaches the transfer section. 16 and the side resist 22 to pass through a position where the conductive roller 13 and the electrostatic latent image holder 2 face each other,
It is transported to the transfer section.

At this time, since the conductive roller 13 and the electrostatic latent image holder 2 hold a predetermined gap and the peripheral surfaces move in the same direction, the transfer sheet comes into contact with the surface of the electrostatic latent image holder 2. Then, while maintaining this contact state, the electrode wire 24 and the electrostatic latent image holding body 2 are guided to a region facing each other. At this time, in the case of transferring to the second surface of the paper, even if the paper is curled or wavy during fixing of the first surface, the conductive roller 1
By 3, the contact state is maintained up to near the rear end. At the transfer portion, a transfer current is applied to the electrode wire 24,
The toner image on the electrostatic latent image carrier is transferred to a predetermined position on the transfer paper, and the toner image is transferred clearly because the paper is in good contact with the electrostatic latent image carrier even near the rear end. . At this time, since the transfer sheet is conveyed so that its side edge contacts the side resist 22, when a small-sized sheet is used, the sheet does not exist in a part of the conductive roller 13. However, since the gap between the electrostatic latent image holder 2 and the conductive roller 13 has a constant gap, the conductive roller 13 is formed on the surface of the electrostatic latent image holder 2 where the fog toner does not exist. Can be prevented from being transferred to the surface of.
Therefore, it is possible to prevent the transfer sheet from being contaminated and the image quality from being defective due to the fog toner adhering to the surface of the conductive roller 13.

The transfer paper on which the toner image has been transferred in the above steps is destaticized / peeled by the peeling device 7 and conveyed on the conveyor belt. Further, the toner image is fixed on the transfer paper by the fuser roll 12 to form one copy image.

Next, in the above embodiment, the conductive roller 1
Using the elastic material 13b having different electric resistance values coated on the surface of No. 3, stains on the roller during image formation,
Indicates the state of paper stains. As shown in Table 1, the resistivity is 10
^When it is ⁸ Ωcm or less, the toner is more difficult to adhere to the surface of the conductive roller, and the roller smear level and the back surface smear level of the copy are good for those having a resistivity of more than 10 ⁸ Ωcm.

The roller dirt level and the back surface dirt level are the dirt on the back surface of the conductive roller and the transfer paper after the copying of 50 sheets, which is visually observed. The one that was dirty was marked with Δ, and the one that was worrisome with dirt was marked with x. Further, the number of backside stain elimination shows the number of sheets after the stain is transferred to the sheet until the stain is eliminated, and the number of the backside stain elimination number is displayed as 0 means that the backside is almost not stained. Means (Below margin)

[Table 1]

FIG. 7 shows the degree of transfer failure (white spots) that occurs at the trailing edge of the second surface when the toner images are transferred to both surfaces in the image forming apparatus according to the above-described embodiment of the present invention. (A) Room temperature 20 ° C, humidity 50% (b) Room temperature 28
C., humidity 85% (c) 50 copies were made in an environment of room temperature 10.degree. C. and humidity 30%. On the other hand, FIG. 8 uses the conventional image forming apparatus shown in FIG. 10 (one without a conductive roller) to form toner images on both sides under the same conditions as the experiment according to the embodiment of the present invention shown in FIG. This shows a rear-end transfer defect (white spots) on the second surface when transferred.

As is apparent from FIGS. 7 and 8, according to the image forming apparatus of the present invention, the white spot width is significantly narrowed, and a good image can be obtained. Further, FIG. 9 shows the amount of white spots when the paper is moistened to the extent that it is wavy, and the toner image is transferred to one side of this paper. The image forming apparatus of the embodiment of the present invention is shown in FIG. As shown in, the amount of white spots on all sheets was 3 mm or less. On the other hand, in the conventional image forming apparatus, as shown in FIG.
About 7% or more of the transferred sheets had white spots of 7 mm or more.

Thus, the copied image obtained by the image forming apparatus of the embodiment of the present invention is
The image is good without any image quality defects, and even if you use a small size paper and then a large size paper, toner does not adhere to the back side of the paper and the stains on the paper are eliminated. We were able to.

[0029]

As described above, in the image forming apparatus of the present invention, due to the action of the conductive roller, even when the image is transferred to a paper having a corrugated surface containing moisture, or a toner image is transferred to both sides, It is possible to clearly transfer to the edge. The conductive roller has a large diameter portion, and only the large diameter portion contacts the electrostatic latent image holding member, and the other portions have a certain distance from the electrostatic latent image holding member. It is possible to prevent the fog toner on the holding body from transferring to the surface of the conductive roller. Therefore, even when a large-sized transfer paper is used after a small-sized transfer paper is used, adhesion of toner to the back surface of the paper is prevented, and a good image can be formed on both surfaces without causing dirt on the back surface. can get.

Further, since the vicinity of the surface of the conductive roller is covered with the elastic material, it is possible to prevent the surface of the electrostatic latent image carrier from being damaged even if a shock is applied during transportation of the apparatus main body.
Further, the coefficient of friction of the elastic member is larger than that of metal or the like, and the paper can be smoothly fed. Further, by grounding the conductive roller, it is possible to prevent charges from being accumulated on the conductive roller and further prevent the surface from being soiled.

[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 configuration diagram showing a main part of the image forming apparatus.

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

FIG. 4 is a schematic sectional view showing a transfer device used in the image forming apparatus.

5A and 5B are a plan view and a cross-sectional view showing a conductive roller used in the transfer device.

FIG. 6 is a diagram showing a contact state of a conductive roller used in the image forming apparatus with an electrostatic latent image holder.

FIG. 7 is a diagram showing the trailing edge whiteout amount on the second surface when the toner images are transferred to both surfaces in the image forming apparatus of the present invention.

FIG. 8 is a diagram showing a trailing edge whiteout amount on a second surface when a toner image is transferred to both surfaces in a conventional image forming apparatus.

FIG. 9 is a diagram for comparing whiteout amounts when toner is transferred to one side of a water-containing paper, showing (a) a result of the image forming apparatus of the present invention and (b) a result of a conventional image forming apparatus. It is a thing.

FIG. 10 is a schematic configuration diagram showing a conventional image forming apparatus.

[Explanation of symbols]

 1, 101 image forming apparatus 2, 102 electrostatic latent image carrier 3, 103 charging device 4, 104 developing device 5 transfer auxiliary charging device 6, 106 transfer device 7, 107 peeling device 8, 108 cleaning device 9, 109 exposure device 10, 110 Paper tray 11, 111 Paper transport path 12, 112 Fuser roll 13 Conductive roller 14 Shield case 15, 115 Register roller pair 16, 116 Register guide 17 Cover 18 Spring 19 Conductive bearing 21 Shield case 22 Side resist 24 wire

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 for transferring the transfer sheet onto a transfer sheet, and a conductive roller which is arranged in the vicinity of the transfer device so as to face the electrostatic latent image holder and guides the transfer sheet so as to contact the surface of the electrostatic latent image holder. In an image forming apparatus including, a large diameter portion that comes into contact with the non-image portion surface of the electrostatic latent image holding member is provided at both ends of the conductive roller, and the conductive roller is a metal columnar member. An image forming apparatus characterized by being coated with a conductive elastic material. 2. The image forming apparatus according to claim 1, wherein the conductive roller is electrically grounded.