JP5803343B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus capable of forming a color image.

  Conventionally, as an image forming apparatus such as a color printer, a tandem type is known in which photosensitive drums corresponding to yellow, magenta, cyan, and black are arranged side by side along a sheet conveyance direction (Patent Document). 1). In the tandem type image forming apparatus, a transfer roller is provided corresponding to each photosensitive drum, and when a transfer bias is applied to the transfer roller, when conveying a sheet between the photosensitive drum and the transfer roller, The toner on the photosensitive drum is transferred onto the paper.

JP 2007-102084 A

  By the way, in the technique described above, as shown in FIG. 6A, for example, when the first color toner T1 transferred to the paper P is aggregated in one place, the potential of the first color toner T1 is increased. There is. In this case, as shown in FIG. 6B, when the toner T2 of the other color is superimposed on the toner T1 of the first color, the other color of the toner T1 having a high potential is transferred. There is a problem that the toner T2 is repelled and scattered. This scattering problem is caused by the fact that the charge amount increases by the transfer bias when the first color toner passes between the photosensitive drums of the second and third colors and the transfer roller (hereinafter also referred to as “charge-up”). This occurs remarkably when the fourth color toner is placed on the first color toner.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of satisfactorily superimposing toners of other colors on toner (developer) transferred onto a sheet (transfer medium).

In order to solve the above problems, an image forming apparatus according to the present invention includes a first image forming unit and a second image forming unit.
The first image forming unit includes a first photosensitive member, a first developing roller that supplies a developer to the first photosensitive member, and development of a first color supplied to the first developing roller. A first developer container in which a developer is accommodated, and a first developer container disposed opposite to the first photosensitive member and transferring the developer to a transfer medium between the first photosensitive member and the first photosensitive member; And a transfer member.
The second image forming unit includes a second photosensitive member, a second developing roller that supplies a developer to the second photosensitive member, and a second color developing member that is supplied to the second developing roller. A second developer container in which the developer is accommodated, and a second developer container disposed opposite to the second photoconductor to transfer the developer to the transfer medium between the second photoconductor and the second photoconductor. And a transfer member.
The first photoconductor is disposed upstream of the second photoconductor in the transport direction of the transfer medium.
The first image forming unit is located at a position downstream of the first developing roller and upstream of the first transfer member in the rotation direction of the first photoconductor. A first pre-transfer exposure member for exposing the surface of the photoconductor.
The first pre-transfer exposure member is configured to emit light that can be absorbed by the developer of the first color, and the first photoconductor is exposed by the first pre-transfer exposure member. In addition, the second photoconductor is not exposed at a position downstream of the second developing roller in the rotation direction of the second photoconductor and upstream of the second transfer member. It is configured as follows.

  According to the present invention, when the first photoconductor is exposed with the first pre-exposure exposure member, the portion of the surface of the first photoconductor on which the developer of the first color is attached is light. By absorbing, the potential is unlikely to decrease, and the potential of the portion where the developer is not adhered is decreased. As a result, the developer of the first color scatters to the surrounding area, so that an increase in potential due to the aggregation of the developer when transferred onto the paper can be suppressed, and the developer of the second color on the downstream side can be suppressed. It is possible to accurately overlay the first color developer. Further, since the pre-transfer exposure (exposure on the downstream side of the developing roller and the upstream side of the transfer member) is not performed on the second photosensitive member, the second photosensitive member is exposed on the second photosensitive member. Since the second color developer is not scattered, the second color developer can be superimposed on the first color developer without bleeding.

  In the present invention, an image forming unit different from the first image forming unit and the second image forming unit may be connected to the first image forming unit and the second image forming unit in the transport direction. At least one of them may be arranged so that the second color is black, and the first image forming unit may be provided on the most upstream side in the transport direction.

  According to this, in a situation where another image forming unit is provided between the first image forming unit and the second image forming unit, the first color developer is charged up and the black developer is supplied. Although it is difficult to be placed on the first color developer, the effect of charge-up is reduced by dispersing the first color developer in the first image forming unit, and the black developer is changed to the first color developer. It is possible to overlay the developer accurately.

  In the present invention, it is desirable that the first color is yellow and the second color is black.

  According to this, since the color of the developer to be scattered is yellow that is not conspicuous, the image quality can be maintained. Further, since the black developer with a conspicuous color does not scatter on the yellow developer, the image quality can be improved.

  In the present invention, a third image forming unit having a third photoconductor to which a magenta developer is supplied and a fourth image forming unit having a fourth photoconductor to which a cyan developer is supplied. And the third photoconductor and the fourth photoconductor may be disposed between the first photoconductor and the second photoconductor.

  According to this, the least noticeable yellow developer is scattered on the most upstream side, whereby the influence on the image quality due to the scattering can be minimized.

  In the present invention, the third image forming unit is disposed opposite to the third developing roller for supplying a developer to the third photosensitive member, and the third photosensitive member. A third transfer member for transferring the developer to the transfer medium with respect to the photosensitive member, and a downstream side of the third developing roller in the rotational direction of the third photosensitive member, and the first photosensitive member. A third pre-transfer exposure member that exposes the surface of the third photosensitive member at a position upstream of the third transfer member, and the fourth image forming unit is disposed on the fourth photosensitive member. A fourth developing roller for supplying the developer, and a fourth transfer member which is disposed to face the fourth photosensitive member and transfers the developer to the transfer medium between the fourth photosensitive member and the fourth photosensitive member; In the rotational direction of the fourth photoconductor, downstream of the fourth developing roller and upstream of the fourth transfer member. And a fourth pre-transfer exposure member that exposes the surface of the fourth photoconductor at the position, the light emitted from the first pre-transfer exposure member is the first photoconductor. The ratio of light absorbed by the upper developer is that the light emitted from the third pre-transfer exposure member and the fourth pre-transfer exposure member is developed on the third photoconductor and the fourth photoconductor. You may comprise so that it may become larger than the ratio absorbed by an agent.

  According to this, in the third photoconductor and the fourth photoconductor, light is not easily absorbed by the developer as compared with the first photoconductor, so that development on the third photoconductor and the fourth photoconductor is performed. The scattering of the agent can be reduced. In addition, since the pre-transfer exposure is performed on the third photoconductor and the fourth photoconductor, the potential of the entire third photoconductor and the fourth photoconductor can be lowered. It is possible to suppress the charge-up of the first color developer when the first color developer passes through the third photoconductor and the fourth photoconductor. Transferability can be improved.

  In the present invention, it is desirable that the peak wavelength of the light emitted from the first pre-transfer exposure member is longer than the wavelength region of ultraviolet rays.

  According to this, deterioration of the photoconductor can be suppressed as compared with the case where light having a peak wavelength in the ultraviolet wavelength region is emitted to the photoconductor.

  According to the present invention, it is possible to satisfactorily superimpose other color toners on the developer transferred onto the transfer medium.

It is explanatory drawing which simplifies and shows the color printer which concerns on one Embodiment of this invention. It is explanatory drawing which shows the 1st pre-transfer exposure member. FIG. 4 is an explanatory diagram (a) to (d) showing a state in which toner supplied onto a photosensitive drum is scattered by pre-transfer exposure. 4A and 4B are explanatory views showing a state in which black toner is superimposed on scattered yellow toner. It is explanatory drawing which shows the form which provides the 3rd and 4th pre-transfer exposure member in the 3rd and 4th image formation part, and radiate | emits light from each pre-transfer exposure member. FIG. 6 is an explanatory diagram for explaining a problem that occurs when a toner of another color is superimposed on a first color toner.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, an overall configuration of a color printer as an example of an image forming apparatus will be described, and then details of characteristic portions of the present invention will be described.

  In the following description, the direction will be described with reference to the user when using the color printer. That is, in FIG. 1, the left side toward the paper surface is “front side (front side)”, the right side toward the paper surface is “rear side (back side)”, the back side toward the paper surface is “left side”, and it faces the paper surface. Let the near side be the “right side”. In addition, the vertical direction toward the page is defined as the “vertical direction”.

  As shown in FIG. 1, the color printer 1 includes a paper supply unit 20 that supplies a sheet P as an example of a transfer medium and an image forming unit that forms an image on the fed sheet P in the apparatus main body 10. 30 and a paper discharge unit 90 for discharging the paper P on which an image is formed.

  The paper feed unit 20 includes a paper feed tray 21 that accommodates the paper P and a paper transport device 22 that transports the paper P from the paper feed tray 21 to the image forming unit 30.

  The image forming unit 30 includes a scanner unit 40, a process unit 50, a transfer unit 70, and a fixing unit 80.

  The scanner unit 40 is provided in an upper part of the apparatus main body 10 and includes a laser light emitting unit, a polygon mirror, a lens, a reflecting mirror, and the like (not shown). In the scanner unit 40, the laser beam is irradiated at a high speed on the surface of a photosensitive drum 51 as an example of a photosensitive member to be described later through a path indicated by a two-dot chain line in the drawing.

  The process unit 50 can be attached to and detached from the apparatus main body 10 through an opening 10 </ b> A formed by opening the front cover 11 disposed on the front surface of the apparatus main body 10. The process unit 50 includes a drawer 60, four photosensitive drums 51 that are rotatably supported by the drawer 60, and four developing cartridges 52 that are detachably provided on the drawer 60 so as to correspond to the photosensitive drums 51. ing.

  In the present specification and drawings, when specifying the photosensitive drum 51 and the developing cartridge 52 corresponding to the color of the toner (developer), Y, m, magenta, cyan, black are respectively associated with Y, The symbols M, C, and K are attached. In addition, when describing the photosensitive drum 51 and the like regardless of the toner color, the symbols Y, M, C, and K as described above are omitted.

  The respective photosensitive drums 51 are arranged along the front-rear direction (predetermined direction) in a state where the process unit 50 is mounted on the apparatus main body 10. The drawer 60 is appropriately provided with four chargers 55 for exposing each photosensitive drum 51. The developing cartridge 52 is provided with a developing roller 53 that supplies toner to the photosensitive drum 51, a toner container 54 that stores toner therein, a known layer thickness regulating blade, a supply roller, and the like.

  The transfer unit 70 is provided between the paper feeding unit 20 and the process unit 50, and includes a known driving roller 71, a driven roller 72, a conveying belt 73, and a transfer roller 74 as an example of a transfer member.

  The driving roller 71 and the driven roller 72 are arranged in parallel in a spaced manner 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 between the photosensitive drums 51 are arranged inside the conveyor belt 73 so as to face the photosensitive drums 51. A transfer bias is applied to the transfer roller 74 by constant current control during transfer.

  The fixing unit 80 is disposed on the back side of the process unit 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, first, the surface of each photosensitive drum 51 is uniformly charged by the charger 55 and then exposed by the scanner unit 40. 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. Thereafter, the toner in the developing cartridge 52 is supplied to the electrostatic latent image on the photosensitive drum 51 by the developing roller 53 rotatably supported by the developing cartridge 52, so that the toner image is carried on the photosensitive drum 51. Is done.

  Next, the paper P supplied onto the conveyance belt 73 passes between each photosensitive drum 51 and each transfer roller 74, so that the toner image formed on each photosensitive drum 51 is transferred onto the paper P. The Then, as the paper P passes between the heating roller 81 and the pressure roller 82, the toner image transferred onto the paper P is thermally fixed.

  The paper discharge unit 90 mainly includes a plurality of transport rollers 91 that transport the paper P. The sheet P on which the toner image has been transferred and heat-fixed is transported by the transport roller 91 and discharged outside the apparatus main body 10.

<Detailed Structure of Image Forming Unit 30>
The image forming unit 30 is divided into four image forming units 30Y, 30M, 30C, and 30K in order to form yellow, magenta, cyan, and black images on the paper P, respectively. Specifically, the image forming unit 30Y for forming a yellow image on the paper P includes each member such as the photosensitive drum 51Y indicated with a symbol Y in the drawing, a light source for yellow in the scanner unit 40, and the like. It is composed of yellow optical components for guiding light from the light source to the photosensitive drum 51Y.

  The four image forming units 30Y, 30M, 30C, and 30K are arranged in order of yellow, magenta, cyan, and black from the upstream side to the downstream side in the conveyance direction of the paper P. That is, in the present embodiment, the yellow image forming unit 30Y corresponds to the first image forming unit, the black image forming unit 30K corresponds to the second image forming unit, and the magenta image forming unit. 30M corresponds to the third image forming unit, and the cyan image forming unit 30C corresponds to the fourth image forming unit. In the following description, as necessary, members corresponding to yellow are prefixed with “first” and members corresponding to magenta are prefixed with “third” to correspond to cyan. “4th” is attached to the member to be attached, and “second” is attached to the member corresponding to black.

  The first image forming unit 30Y located on the most upstream side is provided with a first pre-transfer exposure member 100, and the other image forming units 30M, 30C, and 30K are not provided with a pre-transfer exposure member. It has become. That is, only the first photosensitive drum 51Y is subjected to pre-transfer exposure (exposure at a position downstream of the developing roller 53 and upstream of the transfer roller 74), and the other photosensitive drums 51M and 51C. , 51K is not subjected to pre-transfer exposure.

  The first pre-transfer exposure member 100 is disposed at a position downstream of the developing roller 53Y and upstream of the transfer roller 74Y in the rotation direction of the photosensitive drum 51Y, and the surface of the photosensitive drum 51Y is disposed at the position. It is exposed. Specifically, as shown in FIG. 2, the first pre-transfer exposure member 100 is emitted from one light source 110 such as a cold cathode tube or a light emitting diode and the light source 110 along the axial direction of the photosensitive drum 51Y. And a light guide plate 120 that deflects light at substantially right angles and emits the light to substantially the entire axial direction of the surface of the photosensitive drum 51Y. The light emission range to the photosensitive drum 51Y may be equal to or greater than the image formation range (the maximum width of the image formed on the paper P).

  The first pre-transfer exposure member 100 is configured to emit light that can be absorbed by yellow toner. Specifically, the first pre-exposure exposure member 100 is configured to emit light having a peak wavelength of light of 380 nm to 480 nm that is longer than the wavelength region of ultraviolet rays. In particular, in the present embodiment, the center wavelength is 470 nm. It is configured to emit blue light.

  Thereby, it is possible to suppress the deterioration of the photosensitive drum 51Y as compared with the case where light having a peak wavelength in the ultraviolet wavelength region is emitted to the photosensitive drum 51Y.

  As shown in FIG. 1, the apparatus main body 10 is provided with a control device 200 for controlling the first pre-transfer exposure member 100. Upon receiving the print command, the control device 200 controls the first pre-transfer exposure member 100 so that light is emitted from the first pre-transfer exposure member 100 to the photosensitive drum 51Y during the print control. ing.

<Operation of First Pre-transfer Exposure Member 100>
Next, the operation of the first pre-transfer exposure member 100 will be described.
As shown in FIGS. 3A and 3B, when the surface of the photosensitive drum 51Y charged by the charger 55Y is exposed by the laser beam from the scanner unit 40, the potential of the portion exposed by the laser beam is lowered.

  As shown in FIG. 3C, when the yellow toner TY is supplied from the developing roller 53Y to the portion exposed by the scanner unit 40, a toner image is formed by the yellow toner TY on the photosensitive drum 51Y. The Thereafter, when the surface of the photosensitive drum 51Y is exposed by the first pre-transfer exposure member 100, the portion of the surface of the photosensitive drum 51Y to which the yellow toner TY is attached as shown in FIG. Since the toner TY absorbs blue light, the potential hardly decreases. Therefore, the potential of the portion where the toner TY is not adhered is lower than the portion where the toner TY is adhered.

  As a result, the yellow toner TY is scattered in the surrounding area, so that an increase in potential due to aggregation of the toner TY can be suppressed.

  Thereafter, as shown in FIG. 4A, the yellow toner TY scattered on the photosensitive drum 51Y is transferred to the paper P, so that the potential of the yellow toner TY is also maintained on the paper P. Then, as shown in FIG. 4B, when the black toner TK is transferred onto the yellow toner TY on the paper P, the black toner TK is not repelled by the yellow toner TY. Therefore, the black toner TK can be accurately superimposed on the yellow toner.

As described above, according to the present embodiment, in addition to the effects described above, the following effects are also achieved.
Since the black photosensitive drum 51K is not subjected to the pre-transfer exposure, the black toner TK is not scattered on the black photosensitive drum 51K. Therefore, the black toner TK is not smeared on the yellow toner TY. Can be stacked.

  In a situation where another image forming unit 30M, 30C is provided between the first image forming unit 30Y and the second image forming unit 30K, the yellow toner is charged up and the black toner TK is replaced with the yellow toner TY. Although it is difficult to be placed on top, by dispersing the yellow toner TY in the first image forming unit 30Y, the influence of the charge-up can be reduced, and the black toner TK can be accurately superimposed on the yellow toner TY. As a result, a change in color tone due to the appearance of yellow toner as a base can be reduced.

  Since the color of the toner scattered by the pre-transfer exposure is yellow, the image quality can be maintained. Further, since the conspicuous black toner TK is not scattered, the image quality can be improved.

  In particular, in this embodiment, the least noticeable yellow toner is scattered on the most upstream side by the pre-transfer exposure, so that the influence on the image quality due to the scattering can be minimized.

  In addition, this invention is not limited to the said embodiment, It can utilize with various forms so that it may illustrate below. In the following description, the same reference numerals are given to members having substantially the same structure as in the above embodiment, and the description thereof is omitted.

  In the embodiment, the first pre-transfer exposure member 100 is provided only in the first image forming unit 30Y. However, the present invention is not limited to this. For example, as shown in FIG. 5, the third image forming unit 30M and the fourth image forming unit 30C are also provided with a third pre-transfer exposure member 300 and a fourth pre-transfer exposure member 400, and before each transfer. Blue light similar to that in the above embodiment may be emitted from the exposure members 100, 300, and 400. That is, light may be emitted from the pre-transfer exposure members 100, 300, and 400 toward the photosensitive drums 51Y, 51M, and 51C by the control device 200. In other words, the proportion of the light emitted from the first pre-transfer exposure member 100 absorbed by the yellow toner on the first photosensitive drum 51Y is determined by the third pre-transfer exposure member 300 and the fourth pre-transfer exposure. When the light emitted from the member 400 is configured to be larger than the ratio of light absorbed by magenta or cyan toner on the third photosensitive drum 51M and the fourth photosensitive drum 51C, each transfer is performed. Light may be emitted from the pre-exposure members 100, 300, and 400 toward the photosensitive drums 51Y, 51M, and 51C.

  Accordingly, the third photosensitive drum 51M and the fourth photosensitive drum 51C are less likely to absorb light by the toner than the first photosensitive drum 51Y. Therefore, the third photosensitive drum 51M and the fourth photosensitive drum 51C are used. The scattering of the toner on 51C can be reduced. Further, since the potential of the entire third photosensitive drum 51M and the fourth photosensitive drum 51C can be lowered by the pre-transfer exposure, the yellow toner on the paper P is transferred to the third photosensitive drum 51M and the fourth photosensitive drum. It is possible to suppress the charge-up of the yellow toner when passing through 51C, and it is possible to improve the transferability in the second image forming unit 30K.

  In the embodiment, the first image forming unit is the yellow image forming unit 30Y, the second image forming unit is the black image forming unit 30K, the third image forming unit is the magenta image forming unit 30M, Although the fourth image forming unit is the cyan image forming unit 30C, the present invention is not limited to this, and the relationship between each image forming unit and the color may be changed as appropriate.

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

  In the embodiment, the paper P such as a thick paper, a postcard, and a thin paper is used as an example of the transfer medium. However, the present invention is not limited to this, and may be an OHP sheet, an intermediate transfer belt, or the like. There may be.

  In the above embodiment, the transfer roller 74 is used as the transfer member. However, the present invention is not limited to this, and any transfer bias is applied, such as a conductive brush or a conductive leaf spring. Also good.

  In the above embodiment, the present invention is applied to the color printer 1. However, the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses such as a copying machine and a multifunction machine.

DESCRIPTION OF SYMBOLS 1 Color printer 30Y 1st image formation part 30K 2nd image formation part 51Y 1st photosensitive drum 53Y 1st developing roller 54 Toner container 55Y Charger 74Y Transfer roller 100 1st pre-transfer exposure member P Paper

Claims (5)

A first photosensitive member, a first developing roller that supplies developer to the first photosensitive member, and a first color developer that is supplied to the first developing roller are accommodated therein. And a first transfer member disposed opposite to the first photosensitive member and transferring the developer to the transfer medium between the first photosensitive member and the first photosensitive member. 1 image forming unit;
A second photosensitive member, a second developing roller that supplies developer to the second photosensitive member, and a second color developer that is supplied to the second developing roller. And a second transfer member that is disposed to face the second photosensitive member and transfers the developer to the transfer medium between the second photosensitive member and the second photosensitive member. Two image forming units;
A third photosensitive member, a third developing roller that supplies developer to the third photosensitive member, and a third color developer that is supplied to the third developing roller are accommodated therein. And a third transfer member that is disposed to face the third photosensitive member and transfers the developer to the transfer medium between the third photosensitive member and the third photosensitive member. 3 image forming units;
A fourth photosensitive member, a fourth developing roller that supplies developer to the fourth photosensitive member, and a fourth color developer that is supplied to the fourth developing roller are accommodated therein. And a fourth transfer member disposed opposite to the fourth photosensitive member and transferring the developer to the transfer medium between the fourth photosensitive member and the fourth photosensitive member. An image forming apparatus comprising: 4 image forming units ;
The first color is yellow, and the first photoconductor is disposed on the most upstream side in the transport direction of the transfer medium,
The first image forming unit is located at a position downstream of the first developing roller and upstream of the first transfer member in the rotation direction of the first photoconductor. A pre-transfer exposure member that exposes the surface of the photoconductor,
The pre-transfer exposure member is configured to emit light that can be absorbed by the yellow developer,
The first photoconductor is exposed by the pre-transfer exposure member , and the second photoconductor is downstream of the second developing roller in the rotation direction of the second photoconductor, and The third photosensitive member is not exposed at a position upstream of the second transfer member, and the third photosensitive member is downstream of the third developing roller in the rotation direction of the third photosensitive member, and the No exposure is performed at a position upstream of the third transfer member, and the fourth photoconductor is downstream of the fourth developing roller in the rotation direction of the fourth photoconductor and the fourth photoconductor An image forming apparatus configured to prevent exposure at a position upstream of a transfer member . Before Symbol image forming apparatus of claim 1, wherein the second color is characterized by a black der Turkey.   The image forming apparatus according to claim 1, wherein the third color is magenta, and the fourth color is cyan. Wherein the front Symbol third photoreceptor fourth photoreceptors, any of claims 1 to 3, characterized in that it is arranged between the second photosensitive member and said first photoreceptor whether the image forming apparatus according to (1). The peak wavelength of light emitted from the pre-transfer exposure member, the image forming apparatus according to any one of claims 1 to 4, wherein longer than the wavelength region of the ultraviolet.

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