JP2002351262A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can provide good transfer characteristics by reducing the amount of reverse transfer to a photoreceptor even when a recording material having a smooth surface is used. SOLUTION: Each photoreceptor drum 5 is driven by a motor 33, and a transfer belt 21 is driven by another motor not shown. By changing the rotation speed of the motor 33, the linear velocity of the photoreceptor drum 5 is adapted to be adjustable. When a sheet of plain pair is used as a recording material, the linear velocity of the photoreceptor drum 5 is controlled to be slower than that of the transfer belt 21 by approximately 1.2%. When a transparency is used, the both linear velocities are controlled to be equal. The reverse transfer of toner from a transparency as a recording material to the photoreceptor is thereby reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art An electrophotographic copying machine, printer,
2. Description of the Related Art In an image forming apparatus such as a facsimile, a transfer device using a transfer belt as a transfer device for transferring a visible image (toner image) held on an image carrier (photoreceptor) onto a recording material (transfer paper or the like). Is well known. The belt transfer device
A transfer belt is brought into contact with a photoreceptor, which is an image carrier, and a recording material is passed through a nip portion (transfer nip), and a transfer bias voltage is applied to the transfer belt to transfer a toner image on the photoreceptor to the recording material. Transcribed to

In a transfer device using a transfer belt, the paper (recording material) is conveyed at a speed substantially equal to the speed of the surface of the transfer belt because the paper is conveyed by attracting the paper to the transfer belt. General. When the speed of the transfer belt (that is, the paper conveyed by the transfer belt) and the speed of the surface of the photosensitive drum are the same, transfer is performed only by electrostatic force, but a linear speed difference is provided between the two. in case of,
Since a mechanical peeling force (a force for peeling off the toner from the photosensitive drum) is applied in addition to the electrostatic force, the transfer rate is improved, which is effective in reducing image quality deterioration due to poor transfer.

A device in which the speed difference is provided between the surface of the transfer belt and the surface of the photoreceptor for the purpose of improving the transferability has conventionally been designed so as to maintain the speed difference between the transfer belt and the photoreceptor regardless of the type of paper. Have been.

Japanese Patent Application Laid-Open No. 1-179967 (Japanese Patent No. 2743359) discloses a transfer device in which the surface speed of a transfer member and the surface speed of a photoreceptor have a speed difference. In the publication, the peripheral speed of the transfer drum is made slightly faster than the moving speed of the photoreceptor to suppress the influence of the driving force acting on the transfer body from a plurality of photoreceptors in a tandem type image forming apparatus. It is said that there is a stabilizing effect (page 5, right column, lines 7 to 12).

[0006]

However, a tandem-type color image is obtained in which a plurality of photoconductors are arranged and a color image is obtained by sequentially transferring toner images from the respective photoconductors onto paper conveyed by a transfer belt. In the forming apparatus, there is a problem that the reverse transfer amount of the toner from the sheet to the photosensitive member increases in the photosensitive member on the downstream side in the sheet conveying direction. Conventionally, this problem has been dealt with by, for example, increasing the transfer current value to the photoconductor as it is located downstream (for example, JP-A-6-230686).

[0007] Since the surface of plain paper is rough,
The toner once transferred to the sheet is easily held on the sheet surface, and the amount of the reverse transfer to the photoreceptor located downstream is small. On the other hand, in the case of a recording material having a smooth surface such as an OHP sheet, the toner once transferred to the OHP sheet is difficult to be retained on the sheet surface, and the amount of reverse transfer to a photoconductor located downstream is large. I know. In particular, when a speed difference is provided between the transfer member and the photoconductor, there is a problem that the amount of reverse transfer to the photoconductor increases because the mechanical stripping force increases.

The present invention solves the above-mentioned problems in the conventional image forming apparatus and achieves good transferability by reducing the amount of reverse transfer to a photosensitive member even with a recording material having a smooth surface. An object of the present invention is to provide an image forming apparatus capable of performing the above.

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided an image carrier, and a visible image carried by the image carrier, the recording material being conveyed while being disposed opposite the image carrier. In a case where the image forming apparatus is provided with a transfer / transporting unit for transferring the image onto a recording material, the linear velocity of at least one of the image carrier and the transfer / conveying unit can be changed, and when a predetermined special paper is passed, By setting the linear velocity of the image carrier and the transfer / conveying means to be the same, and providing a linear velocity difference between the image carrier and the transfer / conveying means when a recording material other than the special paper is passed. Will be resolved.

According to another aspect of the present invention, a plurality of image carriers are arranged in opposition to the transfer / conveying means, and an image formed on each image carrier is conveyed by the transfer / conveyance means. It is proposed that transfer can be performed on a recording material to be overlaid.

Further, in order to solve the above-mentioned problems, the present invention proposes that the special paper is an OHP sheet.
Further, in order to solve the above-mentioned problem, the present invention proposes that a linear velocity difference is provided between the image carrier and the transfer / transporting unit by changing a linear velocity of the image carrier. .

Further, in order to solve the above-mentioned problems, the present invention proposes to provide a bias cleaning type cleaning means for cleaning the transfer / transport means.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a schematic configuration of a color laser printer as an example of an image forming apparatus according to the present invention. The color laser printer 1 has a paper feeding unit 2 provided at a lower portion of the apparatus main body, and an image forming unit 3 arranged at substantially the center of the apparatus. Above the image forming section 3, an optical writing device 4 is provided. A paper discharge tray 8 is formed on the upper surface of the apparatus. Recording paper (transfer paper,
An OHP sheet or the like is fed, the image formed by the image forming unit 3 is transferred onto a sheet, fixed by the fixing device 10 and discharged to the discharge tray 8. Paper can be fed from a manual feed tray (not shown) on the side of the apparatus, and paper can be discharged to a discharge tray (not shown) on the side of the apparatus.

The image forming section 3 is provided with a transfer / conveyance belt device 20 extending in the left-right direction in FIG. Along the upper running side of the transfer / transport belt device 20, magenta (M), cyan (C), yellow (Y), black (B
Four image forming units for k) are arranged side by side.

The construction of each image forming unit is the same, and each image forming unit has a photosensitive drum 5 as an image carrier. The photosensitive drum 5 is driven to rotate clockwise in the figure by a driving unit (not shown). Around the photoreceptor drum 5, other than the developing device 6 and the cleaning device 7, devices necessary for the electrophotographic process, such as a charging unit, are provided. The developing device 6 is a two-component developing device including a toner and a carrier, and applies the toner carried on the developing sleeve to the photosensitive drum 5. The laser beam from the optical writing device 4 irradiates the photosensitive drum 5 from between the charging roll and the developing device 6.

FIG. 2 is a schematic diagram showing the structure of the image forming section 3 centering on the transfer / conveying belt device 20 and the photosensitive drum 5. As shown in this figure, an endless loop-shaped transfer belt 2
1 is wound around a driving roller 22, a driven roller 23 and two auxiliary rollers 24 and 25. These rollers are rotatably supported by a fixed frame (not shown), and the transfer belt 21 is rotated counterclockwise in the figure. Above the driven roller 23, a paper suction roller 26 is sandwiched by the belt 21.
Is provided. The recording paper is sent out onto the belt 21 from between the driven roller 23 and the attraction roller 26, and is conveyed while being electrostatically attracted onto the transfer belt 21 by the bias voltage applied to the attraction roller 26.

The inside of the upper running side of the transfer belt 21 is
One transfer brush 29 is provided so as to contact the belt. Each transfer brush 29 is disposed at a position corresponding to each of the four photoconductor drums 5, and a predetermined transfer bias is applied to each transfer brush 29, so that the photoconductor drum 5 is transferred onto the sheet from the photoconductor drum 5. The upper toner image is transferred.

The driving roller 22 and the driven roller 23
Two rollers 27 and 28 are provided between them. The roller 27 is a fixed roller rotatably supported by a fixed frame, like the drive roller 22 and the like. Although not shown in the drawing, a movable arm that can swing around a support shaft of the roller 27 is provided, and a movable roller 28 is supported on a free end side of the movable arm. When the movable roller 28 is pushed upward, the upper running side of the transfer belt 21 contacts the four photosensitive drums 5 (5M, 5C, 5Y, 5Bk) (the state of FIG. 2). When the movable roller 28 descends, the transfer belt 21 moves between the roller 27 and the driving roller 22.
Abuts only on the photosensitive drum 5Bk for black, and the roller 2
The transfer belt in a portion between the transfer roller 7 and the driven roller 23 is separated from the photosensitive drums 5M, 5C, and 5Y for color.

That is, in the present embodiment, in the case of color printing, the transfer belt 21 has four photosensitive drums 5.
(5M, 5C, 5Y, 5Bk), and in the case of monochrome printing, the transfer belt 21 is kept in contact with only the photosensitive drum 5Bk.

A belt cleaning roller 30 is provided on the lower traveling side of the transfer belt 21 so as to be in pressure contact with the belt 21. The cleaning roller 3
Corresponding to 0, an opposing roller 32 is disposed inside the belt 21. A cleaning bias of 10 to 15 μA is applied to the cleaning roller 30 which is a metal roller. The opposing roller 32 uses a sponge roller having a low resistance and is grounded. Further, a cleaning blade 31 is in contact with the cleaning roller 30. In such a belt cleaning unit, the toner on the belt 21 is attracted to the cleaning roller 30 by the bias cleaning method, and the toner attached to the cleaning roller 30 is scraped off by the blade 31.
The cleaning roller 30 is rotationally driven in the same direction as the transfer belt 21 at a predetermined speed by a drive mechanism (not shown).

Here, the printing operation in the present embodiment will be described mainly with reference to FIG. In the image forming unit for magenta, the surface of the photosensitive drum 5M is uniformly charged to a predetermined potential by the charging roll. In the exposure device 4, a laser diode (LD) (not shown) is driven based on image data sent from a host machine such as a personal computer to irradiate the polygon mirror 9 with laser light, and the laser light is emitted through a cylinder lens, a mirror, and the like. The light is guided onto the photosensitive drum 5M, and an electrostatic latent image to be developed with magenta toner is formed on the photosensitive drum 5M. Toner is applied to this latent image from the developing device 6 to form a magenta toner visible image.

On the other hand, a sheet designated as a transfer material is fed from the sheet feeding section 2, and the fed sheet is once abutted against a pair of registration rollers 13 provided on the upstream side in the transport direction of the transfer transport belt device 20. Hit. At the time of color printing, the transfer conveyor belt device 20 uses the transfer belt 2 as described above.
1 is pushed up so as to contact the four photosensitive drums. Then, the sheet is fed onto the belt 21 in synchronization with the visible image, and reaches the transfer position facing the photosensitive drum 5M by running of the belt. At this transfer position, the visible image of the magenta toner is transferred to the sheet by the action of the transfer brush 29 disposed on the back side of the transfer belt 21.

In the same manner as in the case of magenta, a visible image of each toner is formed on the surface of each photosensitive drum 5 in other image forming units, and these visible images are conveyed by the transfer belt 21. Each time the sheet arrives at each transfer position, the sheet is overlaid and transferred. Therefore, in the color printer according to the present embodiment, a full-color image is overlaid and transferred onto a sheet in substantially the same short time as a monochrome image.

On the other hand, in the case of monochrome printing, in the transfer / conveyance belt device 20, the portion between the driven roller 23 and the fixed roller 27 of the transfer belt 21 is lowered as described above, and the photosensitive drums 5M and 5C for color are used. , 5Y are separated from the transfer belt 21. Then, only in the black image forming unit, a visible image of black toner is formed on the surface of the photosensitive drum 5Bk, and Bk is applied to the sheet fed onto the belt 21 in synchronization with the visible image. The toner image is transferred.

The sheet after the transfer of the toner image is transferred to a transfer belt 21.
And is fixed by the fixing device 10. The fixing device 10 has a pressure roller 11 and a heating roller 12, and performs fixing by passing a sheet carrying an unfixed toner image between nips where both rollers are pressed.

The sheet on which fixing has been completed is discharged to a discharge tray 8 provided on the upper surface of the apparatus main body. At this time, the sheet is inverted and discharged on the back side. For the printer, backside discharge is an almost essential condition for aligning prints in page order.

Next, the gist of the present invention will be described with reference to FIG. As shown in FIG. 2, the four photosensitive drums 5
(5M, 5C, 5Y, 5Bk) are individually driven by dedicated drive motors 33 (33M, 33C, 33Y, 33Bk). The rotation speed of each drive motor 33 can be controlled by the CPU 34. The transfer belt 21 is driven by rotating the drive roller 22 by another motor (not shown). In the present embodiment, the linear speed of the transfer belt 21 is constant and is not changed.

In this embodiment, the speed (linear speed) of the surface of the photosensitive drum 5 is 123.5 mm / sec when plain paper is used as the recording paper, and when the OHP sheet is used as the recording paper. Is controlled so that the linear velocity of the photosensitive drum 5 is 125 mm / sec. Switching of the linear speed of the photosensitive drum 5 is performed by changing the number of input pulses to each drive motor 33 by software. The control program is stored in a ROM 35 attached to the CPU 34. The speed of the surface of the transfer belt 21 is 125 mm / sec regardless of the type of recording paper. Therefore, in the present embodiment, when plain paper is used as the recording paper, there is a linear velocity difference between the photosensitive drum 5 and the transfer belt 21, and when the OHP sheet is used as the recording paper, the photosensitive drum 5 And the transfer belt 21 is driven at a constant speed.

Here, the relationship between the speed ratio between the transfer belt and the photosensitive drum and the transfer rate will be described with reference to FIG.
In the graph of FIG. 3, the vertical axis represents the transfer rate [%], and the horizontal axis represents the speed ratio [%] between the transfer belt and the photosensitive drum. The speed ratio between the transfer belt and the photosensitive drum is (photoconductor speed−transfer belt speed) ÷ photoconductor speed [%]. As can be seen from this graph, the transfer rate decreases when the speed ratio between the transfer belt and the photosensitive drum is in the range of -1% to + 1%.

Next, the relationship between the speed ratio between the transfer belt and the photosensitive drum and the amount of reverse transfer will be described with reference to FIG.
In the graph of FIG. 4, the vertical axis represents the amount of reverse transcription [mg / c].
m ² ], and the horizontal axis represents the speed ratio [%] between the transfer belt and the photosensitive drum. The speed ratio between the transfer belt and the photosensitive drum is (photoconductor speed−transfer belt speed) ÷ photoconductor speed [%]. As can be seen from this graph, the reverse transfer amount itself is not large on plain paper having a rough surface and easy to hold toner, and the reverse transfer amount greatly varies depending on the speed ratio between the transfer belt and the photosensitive drum. Never. On the other hand, in a recording medium such as an OHP sheet in which the surface of the paper is smooth and the toner is not easily retained, the amount of reverse transfer is larger than that of plain paper, and the speed ratio between the transfer belt and the photosensitive drum is in the range of -1% to + 1%. As a result, the amount of reverse transfer is greatly reduced.

From these facts, when plain paper is used as the recording paper, the reverse transfer amount itself is not large, so that FIG.
By setting the transfer rate in the range shown in (1), that is, the speed ratio between the transfer belt and the photosensitive drum to be -1% or less, or + 1% or more, a good image can be obtained. In the present embodiment, as described above, the transfer belt 21
Of the photosensitive drum 5 (5M,
5C, 5Y, 5Bk) linear velocity of 123.5 mm / sec
Is set to In this case, the speed ratio between the two is approximately -1.
2%.

When an OHP sheet is used as the recording paper, the absolute value of the reverse transfer amount is large, so the range of the reverse transfer amount in FIG. 4 is small, that is, the speed ratio between the transfer belt and the photosensitive drum is -1. By setting so as to be in the range of% to + 1%, a good image with a reduced amount of reverse transfer can be obtained although the transfer rate is low. In the present embodiment, as described above, the linear velocity of the transfer belt 21 and the linear velocity of the photosensitive drum 5 (5M, 5C, 5Y, 5Bk) are both set to 12
The constant speed is set to 5 mm / sec.

As described above, in the printer 1 of the present embodiment, when plain paper is used as recording paper, a linear velocity difference is provided between the photosensitive drum 5 and the transfer belt 21, and an OHP sheet is used as recording paper. When used, the photoreceptor drum 5 and the transfer belt 21 are driven at a constant speed, so that high transferability to plain paper is ensured, while the problem of reverse transfer, which is a problem when using an OHP sheet, is caused. It was possible to reduce blurs such as images and obtain high-quality images.

In a tandem-type apparatus as in the present embodiment, reverse transfer on a smooth surface paper such as an OHP sheet is likely to occur on a downstream photosensitive drum. In such a tandem-type apparatus, the effect of reducing image quality deterioration due to reverse transfer is great.

Then, the special paper having a smooth surface is
By limiting the photoconductor drum 5 and the transfer belt 21 at a constant speed only when the OHP sheet is used only when the OHP sheet is used, it is possible to effectively reduce the unevenness of the OHP sheet such as a bug-eating image due to reverse transfer. In addition, it is possible to ensure the transferability on other paper.

In this embodiment, when a linear velocity difference is provided between the photosensitive drum 5 and the transfer belt 21, the linear velocity of the photosensitive drum 5 is changed to provide a linear velocity difference between the two. I have to. As a result, since the linear speed of the transfer belt is the same regardless of the type of paper, there is no need to change the registration timing or the optical writing timing, which complicates control by changing the linear speed of the transfer belt and other side effects ( For example, it is possible to prevent an adverse effect due to a change in fixing property due to a change in the sheet conveyance speed.

In this embodiment, the transfer belt 2
As the cleaning means for cleaning 1, a bias cleaning type cleaning means is employed. Since the cleaning roller 30 to which the driving force is applied is brought into contact with the transfer belt 21, the pressure applied to the transfer belt can be made constant as compared with a cleaning unit using a blade method or the like. Speed unevenness can be reduced. Further, the cleaning roller 30
And the speed difference between the transfer belt 21 and the transfer belt 21 can be set to an optimum position experimentally. As a result, when plain paper is used, high image quality with less color shift can be obtained.
When a sheet is used, image quality deterioration due to reverse transfer can be avoided.

Although the present invention has been described with reference to the illustrated embodiment, the present invention is not limited to this. For example, the invention of claim 1 can be applied to an apparatus having one image carrier (photoconductor). It is also possible to use a transfer drum as the transfer / transporting means. Further, in the case where a linear velocity difference is provided between the transfer / conveying means and the image carrier, the linear velocity of the image carrier may be higher than the linear velocity of the transfer / conveying means. Also,
When a linear velocity difference is provided between the transfer / conveying means and the image carrier, it is possible to change the linear velocity of the transfer / conveying means instead of changing the linear velocity of the image carrier. Further, in the above embodiment, a part of the transfer / conveying means is configured to be able to contact / separate from a part of the image carrier. The present invention can be applied to an apparatus having such a configuration. Of course, the image forming apparatus may be a copying machine other than a printer or a facsimile.

Further, as the special paper having a smooth surface, there is a paper other than the OHP sheet, for example, a coated paper, and when these are used, the transfer conveying means and the image carrier may be driven at a constant speed. . In addition, appropriate changes can be made within the scope of the present invention.

[0040]

As described above, according to the image forming apparatus of the present invention, when a predetermined special paper is passed, the linear velocity of the image carrier and the transfer / conveying means is the same, and other recording materials are used. In the case of (1), a linear velocity difference is provided between the image carrier and the transfer / conveyance means.
It is possible to reduce blemishes such as insect-eating images due to reverse transfer, which was a problem when using sheets,
High quality images can be obtained.

According to the second aspect of the present invention, in a tandem type apparatus, reverse transfer on a smooth surface paper such as an OHP sheet is likely to occur on the downstream image carrier. This is very effective in reducing image quality deterioration due to reverse transfer.

According to the third aspect of the present invention, the special paper having a smooth surface is limited to an OHP sheet, and the image carrier and the transfer / conveying means are driven at a constant speed only when the OHP sheet is used. In this way, it is possible to effectively reduce the unevenness such as the insect-eating image due to the reverse transfer, and to ensure the transferability on another sheet.

According to the fourth aspect of the present invention, when a linear velocity difference is provided between the image carrier and the transfer / transporting means, the linear velocity of the image carrier is changed to provide a linear velocity difference between the two. Accordingly, since the linear speed of the transfer / conveying means is constant, there is no need to change the registration timing or the optical writing timing, which complicates the control by changing the linear speed of the transfer / conveying means and other side effects (for example, the paper conveying speed). Of the fixing property due to the change of the image quality) can be prevented.

According to the fifth aspect of the present invention, since the cleaning means of the bias cleaning system for cleaning the transfer and conveyance means is provided, the transfer and conveyance means can be cleaned while keeping the pressure applied to the transfer and conveyance means constant. There is no speed unevenness. further,
The relationship between the cleaning means and the transfer / conveyance means can be set at an optimum position experimentally.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a color laser printer as an example of an image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of an image forming unit of the printer.

FIG. 3 is a graph showing a relationship between a speed ratio between a transfer belt and a photosensitive drum and a transfer rate.

FIG. 4 is a graph showing a relationship between a speed ratio between a transfer belt and a photosensitive drum and a reverse transfer amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Color laser printer 2 Paper feed part 3 Image formation part 4 Optical writing device 5 Photoconductor drum (image carrier) 20 Transfer conveyance belt device 21 Transfer belt 29 Transfer brush 30 Belt cleaning roller 33 Photoconductor drive motor

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 15/00 518 G03G 15/00 518 15/16 15/16 F term (reference) 2H027 DC02 ED02 ED16 EE03 EF09 2H072 CA07 HA08 JA03 JA08 JC09 2H200 FA05 FA20 GA10 GA12 GA23 GA29 GA47 HA02 HB07 JA01 JB06 JB42 LB03 PA11 PA26 PB25 3F049 AA10 DA03 EA10 LA02 LA05 LA07 LB03 LB08 3F101 AB01 AB07 AB14 LA02 LA05 LA07 LB03 LB08

Claims (5)

[Claims] 1. An image bearing member, comprising: an image carrier; and a transfer / conveying means disposed opposite to the image carrier for conveying a recording material and transferring a visible image carried by the image carrier onto the recording material. In the image forming apparatus, a linear speed of at least one of the image carrier and the transfer / conveying means is configured to be changeable, and when a predetermined special paper is passed, the linear speed of the image carrier and the transfer / transport means is changed. An image forming apparatus comprising: a recording medium other than the special paper; and a linear velocity difference between the image carrier and the transfer conveyance unit. 2. An image forming apparatus according to claim 1, wherein a plurality of image carriers are arranged in opposition to said transfer / conveying means, and an image formed on each image carrier can be transferred onto a recording material conveyed by said transfer / conveying means. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the special paper is an OHP sheet. 4. Changing the linear velocity of the image carrier,
The image forming apparatus according to claim 1, wherein a linear velocity difference is provided between the image carrier and the transfer / conveyance unit. 5. The image forming apparatus according to claim 1, further comprising a bias cleaning type cleaning unit that cleans the transfer conveyance unit.