JP2013097092A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of providing a recording sheet which is hardly creased and successfully transferring a developer image.SOLUTION: There is provided an image forming apparatus comprising: a plurality of photoreceptor drums arranged in parallel along the conveyance direction of a recording sheet; and a plurality of transfer rollers 74 which have a straight shape or a crown shape, are arranged corresponding to the photoreceptor drums respectively and biased toward each photoreceptor drum, both ends of which correspond to each other. Among the plurality of transfer rollers 74, a transfer roller for black 74K disposed on the uppermost stream side in the conveyance direction of the recording sheet has a straight shape, and among the plurality of transfer rollers 74, at least one transfer roller except for the transfer roller for black 74K has a crown shape.

Description

  The present invention relates to an image forming apparatus including a plurality of photoconductors and a plurality of transfer rollers.

  2. Description of the Related Art Generally, an electrophotographic image forming apparatus is known that includes a photoreceptor that carries a toner image, and a transfer roller that sandwiches the paper between the photoreceptor and transfers the toner image on the photoreceptor to the paper. It has been. Specifically, in such an image forming apparatus, both ends of the transfer roller are pressed toward the photoconductor. Further, a transfer current for transferring the toner image to the paper flows between the transfer roller and the photosensitive member.

  By the way, in the image forming apparatus described above, when the transfer roller is formed in a straight shape with a constant diameter, a difference occurs in the pressing force of the transfer roller to the photosensitive member at both ends and the center in the axial direction of the transfer roller, The nip width between the transfer roller and the photosensitive member becomes non-uniform, causing a problem that a uniform transfer current does not flow.

  Therefore, an image forming apparatus in which a transfer roller has a crown shape is conventionally known (see, for example, Patent Document 1). In this way, by forming the transfer roller in a crown shape, when the both ends of the transfer roller are pressed toward the photoconductor, the pressing force on the photoconductor is substantially uniform at the center and both ends of the transfer roller. Therefore, the nip width between the transfer roller and the photosensitive member becomes substantially uniform, and the transfer current can be made substantially uniform.

JP-A-4-22980

  However, the transfer roller having the crown shape described above may have variations in the pressing force against the photosensitive member at both ends of the transfer roller due to a shape error or the like. When the transfer roller having such a crown shape is employed in a tandem color printer in which a plurality of photoconductors are arranged in parallel along the recording sheet conveyance direction, for example, a western envelope (on the long side) When printing is performed on an envelope having a lid, the folds of the lid portion of the envelope cannot be firmly pressed by the transfer roller, and the lid may be lifted from the envelope body and may be wrinkled. Also, the wrinkles on the envelope caused unevenness in the transfer current, so that sufficient transfer was not performed in a portion where the transfer current was weak, and so-called white spots were formed in which the base (paper) was visible.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that is less likely to wrinkle a recording sheet and can transfer a developer image satisfactorily.

In order to achieve the above object, an image forming apparatus of the present invention has a plurality of photoconductors arranged in parallel along the recording sheet conveyance direction, and a straight shape or a crown shape, and corresponds to each photoconductor. And a plurality of transfer rollers that are urged toward the corresponding photoreceptors at both ends.
Of the plurality of transfer rollers, the first transfer roller disposed on the most upstream side in the recording sheet conveyance direction has a straight shape, and at least one of the plurality of transfer rollers other than the first transfer roller. One has a crown shape.

  According to the image forming apparatus configured as described above, since the first transfer roller disposed on the most upstream side has a straight shape, the both ends in the width direction of the recording sheet are firmly disposed between the transfer roller and the photosensitive member. Since the recording sheet can be transported satisfactorily while pressing, it is difficult for the recording sheet to wrinkle. In addition, since the crown-shaped transfer roller is disposed downstream of the first transfer roller in the recording sheet conveyance direction, the developer image can be transferred favorably on the downstream side.

  In the image forming apparatus described above, it is desirable that all of the plurality of transfer rollers other than the first transfer roller have a crown shape.

  According to the image forming apparatus configured as described above, it is possible to transfer the developer image more favorably while transporting the recording sheet favorably.

  In the above-described image forming apparatus, it is desirable that the transfer roller having a crown shape has a smaller crown amount as it is closer to the first transfer roller.

  According to the image forming apparatus configured as described above, the recording sheet can be conveyed by firmly pressing both ends in the width direction of the recording sheet toward the upstream side in the recording sheet conveyance direction. While suppressing, the transfer of the developer image can be performed well.

  In the image forming apparatus described above, all the transfer rollers having a crown shape may be formed with substantially the same crown amount.

  According to the image forming apparatus configured as described above, the cost can be reduced as compared with the case where the plurality of transfer rollers have all different shapes.

  Further, in the above-described image forming apparatus, only the transfer roller disposed on the most downstream side in the recording sheet conveyance direction among the plurality of transfer rollers may have a crown shape.

  According to the image forming apparatus configured as described above, the recording sheet can be conveyed more favorably.

  In the above-described image forming apparatus, it is desirable that a bias having a larger absolute value is applied to the plurality of transfer rollers as they are arranged on the downstream side in the recording sheet conveyance direction.

  According to the image forming apparatus configured as described above, the potential of the recording sheet to which the developer is transferred increases as it goes downstream in the recording sheet conveyance direction, and the developer moves from the photoreceptor to the recording sheet. Since it is difficult, the transfer can be reliably performed by increasing the transfer bias.

  According to the present invention, among the plurality of transfer rollers, the first transfer roller disposed on the uppermost stream side in the recording sheet conveyance direction has a straight shape, so that the recording sheet can be conveyed satisfactorily. it can. Since at least one of the transfer rollers disposed on the downstream side of the first transfer roller has a crown shape, the developer image can be transferred satisfactorily.

1 is a side sectional view of a color printer according to an embodiment of the present invention. It is a figure which shows the power supply device connected to each transfer roller. It is a figure which shows four transfer rollers. It is a figure explaining the crown amount of a transfer roller. It is the table | surface which put together the result of experiment.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, the overall configuration of the color printer 1 (image forming apparatus) will be briefly described, and then the details of the features of the present invention will be described.

  Further, in the following explanation, explanation will be given in the direction based on the user when the color printer 1 is used. That is, in FIG. 1, the left side is the “front (front) side”, the right side is the “rear (back) side”, the back side in the vertical direction of the paper is the “left side”, and the front side in the vertical direction of the paper is “Right side”. In addition, the vertical direction toward the page is defined as the “vertical direction”.

<Overall structure of color printer>
As shown in FIG. 1, a color printer 1 includes, in an apparatus main body 2, a paper feeding unit 20 that feeds a sheet S as an example of a recording sheet, and an image forming unit that forms an image on the fed sheet S. 30 and a paper discharge unit 90 for discharging the paper S on which an image is formed.

  An opening 2 </ b> A is formed in the upper part of the apparatus main body 2. The opening 2A is opened and closed by an upper cover 3 that is rotatably supported by the apparatus main body 2. An upper surface of the upper cover 3 serves as a paper discharge tray 4 that accumulates the paper S discharged from the apparatus main body 2.

  The paper feeding unit 20 is provided at a lower portion in the apparatus main body 2, and a paper feeding tray 21 that is detachably attached to the apparatus main body 2, and a paper supply mechanism that conveys the paper S from the paper feeding tray 21 to the image forming unit 30. 22 is provided. The paper supply mechanism 22 is provided on the front side of the paper feed tray 21 and includes a paper feed roller 23, a separation roller 24, and a separation pad 25.

  In the paper feed unit 20 configured in this way, the paper S in the paper feed tray 21 is separated one by one and sent upward, and passes through between the paper dust removal roller 26 and the pinch roller 27 in the process. After the powder is removed, the direction is changed backward through a conveyance path (not shown), and the paper passes through the pair of registration rollers 28 and is supplied to the image forming unit 30.

  The image forming unit 30 includes four LED units 40, four process cartridges 50, a transfer unit 70, and a fixing unit 80.

  The LED unit 40 is swingably connected to an LED mounting member (not shown) provided at the lower portion of the upper cover 3, and is appropriately positioned and supported by a positioning member (not shown) provided on the apparatus body 2. Yes.

  The process cartridge 50 is arranged in parallel in the front-rear direction between the upper cover 3 and the paper feed unit 20, and includes a drum cartridge 58 and a developing cartridge 56 that can be attached to and detached from the drum cartridge 58.

  The developing cartridge 56 mainly includes a developing roller 53, a supply roller 54, a layer thickness regulating blade 57, and a toner accommodating portion 55 that accommodates toner as an example of a developer.

  Further, in the normal state, the developing cartridge 56 is indicated by reference numerals 56K, 56Y, 56M, and 56C containing toners for black, yellow, magenta, and cyan from the upstream side in the transport direction of the paper S. They are arranged in this order.

  The drum cartridge 58 includes a photosensitive drum 51 as an example of a photosensitive member, a scorotron charger 52, and the like. In the present specification and drawings, when the photosensitive drum 51 corresponding to the color of toner is specified, the symbols K, Y, M, and C are assigned to black, yellow, magenta, and cyan, respectively. It will be attached. The four drum cartridges 58 are arranged side by side so that four (a plurality of) photosensitive drums 51 are arranged in parallel along the paper transport direction, that is, the front-rear direction.

  The transfer unit 70 is provided between the paper feeding unit 20 and each process cartridge 50, and includes a driving roller 71, a driven roller 72, a conveyance belt 73, and a transfer roller 74.

  The driving roller 71 and the driven roller 72 are arranged in parallel with a space in the front-rear direction, and a conveyance belt 73 formed of an endless belt is stretched between them. The outer surface of the conveyance belt 73 is in contact with each photosensitive drum 51. In addition, four transfer rollers 74 that sandwich the conveyor belt 73 with the respective photosensitive drums 51 are arranged inside the conveyor belt 73 so as to face the respective photosensitive drums 51. The transfer roller 74 is applied with a transfer bias (transfer voltage) having a polarity different from the charging polarity of the toner by constant current control during transfer.

  In the present specification and drawings, when specifying the transfer roller 74 corresponding to the color of the toner, symbols K, Y, M, and C are assigned to each of black, yellow, magenta, and cyan. I decided to. A detailed configuration of the transfer roller 74 will be described later.

  The fixing unit 80 is disposed on the rear side of each process cartridge 50 and the transfer unit 70, and includes a heating roller 81 and a pressure roller 82 that is disposed to face the heating roller 81 and presses the heating roller 81.

  In the image forming unit 30 configured as described above, for example, in the case of the color printing mode, first, the surface of each photosensitive drum 51 is uniformly charged by each scorotron charger 52, and then the LED unit 40 Exposed. As a result, the potential of the exposed portion is lowered, and an electrostatic latent image based on the image data is formed on each photosensitive drum 51. The toner in the toner container 55 is supplied to the developing roller 53 via the supply roller 54 and enters between the developing roller 53 and the layer thickness regulating blade 57 to form a thin layer having a certain thickness. Supported on. Note that the toner in the toner container 55 is agitated by an agitator (not shown) when the developing roller 53 rotates.

  The toner carried on the developing roller 53 is supplied from the developing roller 53 to the electrostatic latent image formed on the photosensitive drum 51 as the developing roller 53 rotates in contact with the photosensitive drum 51. As a result, the electrostatic latent image is visualized and a toner image is formed on the photosensitive drum 51.

  Then, the sheet S supplied onto the conveyor belt 73 passes between each photosensitive drum 51 and each transfer roller 74 disposed inside the conveyor belt 73, so that the sheet S is formed on each photosensitive drum 51. The transferred toner image is transferred onto the paper S. Further, as the sheet S passes between the heating roller 81 and the pressure roller 82, the toner image transferred onto the sheet S is thermally fixed.

  The paper discharge unit 90 includes a paper discharge-side transport path 91 formed so as to extend upward from the exit of the fixing unit 80 and reverse forward, and a plurality of pairs of transport rollers 92 that transport the paper S. . The sheet S on which the toner image has been transferred and heat-fixed is transported along a paper discharge side transport path 91 by a transport roller 92, discharged outside the apparatus main body 2, and accumulated in the paper discharge tray 4.

<Detailed configuration of transfer roller>
Next, a detailed configuration of the transfer roller 74, which is a characteristic part of the present invention, will be described.

  As shown in FIG. 2, the four transfer rollers 74 are provided corresponding to the respective photosensitive drums 51, and in order from the most upstream side in the paper transport direction, a black transfer roller 74 </ b> K as an example of a first transfer roller. A yellow transfer roller 74Y, a magenta transfer roller 74M, and a cyan transfer roller 74C are provided. Both ends of each transfer roller 74 are urged toward the corresponding photosensitive drum 51 by urging means (not shown).

  Each transfer roller 74 is connected to a power supply device 100 provided in the apparatus main body 2 so that a transfer bias is applied. Specifically, as the four transfer rollers 74 are arranged on the downstream side in the sheet conveyance direction, a bias having a larger absolute value is applied. Since the potential of the sheet S on which the toner is transferred increases as it goes downstream in the sheet conveyance direction, and the toner hardly moves from the photosensitive drum 51 to the sheet S, the absolute value of the transfer bias is set to the sheet as described above. By increasing the size toward the downstream side in the transport direction, the transfer can be reliably performed.

  The four transfer rollers 74 have a straight shape or a crown shape as shown in FIG. Specifically, the black transfer roller 74K disposed on the most upstream side in the paper transport direction has a straight shape, and the transfer rollers 74Y and 74M other than the black transfer roller 74K among the four transfer rollers 74 are provided. 74C all have a crown shape.

  More specifically, the transfer roller 74Y, 74M, 74C having a crown shape has a smaller crown amount as it is closer to the black transfer roller 74K. Of the transfer rollers 74Y, 74M, and 74C having the crown shape, the crown amount of the cyan transfer roller 74C that is disposed at the position farthest from the black transfer roller 74K, that is, the crown amount is the largest. It is desirable that the crown amount is optimal so that the pressing force against the photosensitive drum 51 at both ends and the center in the axial direction is substantially uniform when both ends in the direction are urged toward the photosensitive drum 51. .

Here, the crown amount in the present embodiment will be described with reference to FIG.
The crown amount X is such that X = φB− (φA + φC) when the outer diameters at both ends of the sheet passing range of the transfer roller 74 are φA and φC and the outer diameter at the center of the sheet passing range of the transfer roller 74 is φB. Defined by / 2. The crown amount X given to each transfer roller 74 is determined through experiments and the like.

  For example, the transfer roller 74 includes a metal shaft 74A (diameter 5 mm, length 240 mm) and rubber 74B (diameter 12.5 mm in the axial center, length 220 mm, rubber hardness Asker-C 30) covering the shaft 74A. The optimum crown amount X of the transfer roller 74 is 0.3 mm when both ends of the transfer roller 74 are pressed toward the photosensitive drum 51 with a pressure of 500 gf.

  That is, when the transfer roller having the above dimensions is employed, the crown amount X of the cyan transfer roller 74C is preferably 0.30 mm. For example, the crown amount X of the magenta transfer roller 74M can be set to 0.25 mm, and the crown amount X of the yellow transfer roller 74Y can be set to 0.20 mm. In addition, the straight shape in this embodiment is that whose crown amount X is less than 0.1 mm.

According to the above, the following operations and effects can be obtained in the present embodiment.
Of the four transfer rollers 74, the black transfer roller 74 </ b> K disposed on the most upstream side in the sheet conveyance direction has a straight shape, and thus the sheet S is firmly sandwiched between the photosensitive drum 51. Can be transported. As a result, even when printing is performed on a Western-style envelope, the lid does not rise, so that wrinkles on the envelope can be suppressed.

  Of the four transfer rollers 74, the transfer rollers 74Y, 74M, and 74C other than the black transfer roller 74K have a crown shape. Therefore, when printing is performed on plain paper, the transfer rollers 74Y, 74M, and 74C have a crown shape. However, the toner image can be well transferred on the downstream side in the paper conveyance direction. Even when printing is performed on a western envelope, the transfer rollers 74Y, 74M, and 74C other than the black transfer roller 74K have a crown shape because both ends in the width direction are firmly pressed by the black transfer roller 74K. Even if it is present, the toner image can be transferred satisfactorily.

  Further, since the crown amount of the transfer rollers 74Y, 74M, and 74C having the crown shape is smaller as the distance is closer to the black transfer roller 74K, the both ends in the width direction of the sheet S are firmly attached toward the upstream side in the sheet conveyance direction. Since the sheet can be conveyed while being pressed, the toner image can be transferred well while further suppressing the wrinkles on the sheet S.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. About a concrete structure, it can change suitably in the range which does not deviate from the meaning of this invention.

  In the above-described embodiment, among the four transfer rollers 74, all the transfer rollers 74Y, 74M, and 74C other than the black transfer roller 74K have a crown shape, but the present invention is not limited to this. Of the four transfer rollers 74, at least one of the transfer rollers 74Y, 74M, and 74C other than the black transfer roller 74K may have a crown shape. For example, of the four transfer rollers 74, only the cyan transfer roller 74C disposed on the most downstream side in the paper conveyance direction may have a crown shape.

  As described above, the transfer of the transfer roller 74 disposed on the most downstream side in the sheet conveyance direction is crowned, whereby the conveyance of the sheet is further improved.

  In the embodiment, the transfer rollers 74Y, 74M, and 74C having the crown shape are set such that the closer to the black transfer roller 74K, the smaller the crown amount, but the present invention is not limited to this. . For example, the transfer rollers 74Y, 74M, and 74C having a crown shape may all be formed with substantially the same crown amount.

  With this configuration, the cost can be reduced as compared to the case where the transfer rollers 74Y, 74M, and 74C are all different shapes.

  In the above-described embodiment, the photosensitive drum 51 is used as the image carrier. However, the present invention is not limited to this, and for example, a belt-shaped photosensitive member may be used.

  In the above embodiment, the color printer 1 is exemplified as the image forming apparatus. However, the present invention is not limited to this, and the present invention can also be applied to a multifunction machine or a copier.

  Next, an experiment comparing the printing state and the transportability due to the difference in the shape of the transfer roller will be described.

1. Print test Developer cartridges are arranged in the order of black (K), yellow (Y), magenta (M), and cyan (C) from the upstream side in the paper conveyance direction. An image was printed.

(1) Evaluation of printing results By observing plain paper and Western-style envelopes on which printing was completed, it was confirmed whether or not white spots had occurred at locations where printing should be performed.

(2) Evaluation of envelope transportability It was confirmed whether or not wrinkles approached the envelope after printing.

2. Conditions for each example and comparative example The conditions for each example and comparative example were as described below.
[Example 1]
The transfer roller corresponding to each color has the following shape.
Black (K): Straight Yellow (Y): Straight Magenta (M): Straight Cyan (C): Crown

[Example 2]
The transfer roller corresponding to each color has the following shape.
Black (K): Straight Yellow (Y): Straight Magenta (M): Crown Cyan (C): Crown

[Example 3]
The transfer roller corresponding to each color has the following shape.
Black (K): Straight Yellow (Y): Crown Magenta (M): Crown Cyan (C): Crown

[Comparative Example 1]
All transfer rollers were straight.

[Comparative Example 2]
All transfer rollers have a crown shape.

3. Results FIG. 5 shows a summary of the print test results in Examples 1 to 3 and Comparative Examples 1 and 2.
When printing was performed on plain paper, white spots were noticeable in Comparative Example 1, and white spots were not seen in Comparative Example 2. In Examples 1 to 3, white spots with no problem in printing were observed.

  When printing was performed on the envelope, white spots were not seen in Comparative Example 1, and white spots were noticeable in Comparative Example 2. In Examples 1 to 3, white spots with no problem in printing were observed.

  In addition, when printing was performed on the envelope, in Comparative Example 1, no wrinkles were observed on the envelope, and in Comparative Example 2, clear wrinkles were confirmed in the lid portion and the central portion of the envelope in the paper conveyance direction. And in Examples 1-3, it was confirmed that the small wrinkle has approached the back end side of the envelope in a paper conveyance direction.

  From the above results, in order to achieve both transferability to plain paper, transferability to envelopes, and envelope transportability, straight transfer rollers are disposed at least on the most upstream side as in Examples 1-3. In addition, it has been found that a configuration in which a crown-shaped transfer roller is disposed on any of the downstream sides is desirable.

1 Color Printer 51 Photosensitive Drum 74 Transfer Roller 74C Cyan Transfer Roller 74K Black Transfer Roller 74M Magenta Transfer Roller 74Y Yellow Transfer Roller S Paper X Crown Amount

Claims (6)

A plurality of photoconductors arranged in parallel along the recording sheet conveyance direction;
An image forming apparatus comprising: a plurality of transfer rollers each having a straight shape or a crown shape, provided corresponding to each of the photoconductors, and having both ends biased toward the corresponding photoconductors; There,
Among the plurality of transfer rollers, the first transfer roller disposed on the most upstream side in the recording sheet conveyance direction has a straight shape,
At least one of the plurality of transfer rollers other than the first transfer roller has a crown shape.   2. The image forming apparatus according to claim 1, wherein, of the plurality of transfer rollers, all but the first transfer roller have a crown shape.   The image forming apparatus according to claim 1, wherein the transfer roller having a crown shape has a smaller crown amount as it is closer to the first transfer roller.   The image forming apparatus according to claim 2, wherein all of the transfer rollers having a crown shape are formed with substantially the same crown amount.   2. The image forming apparatus according to claim 1, wherein, of the plurality of transfer rollers, only the transfer roller disposed on the most downstream side in the recording sheet conveyance direction has a crown shape.   6. The bias having a larger absolute value is applied to the plurality of transfer rollers arranged closer to the downstream side in the recording sheet conveyance direction. 6. Image forming apparatus.

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