JP2002132068A - Image forming machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve various problems concerning toner being stuck to both sides of the effective chargeable width (W1) of an image carrying means (14a), in an image forming machine equipped having a reversal developing means (32a). SOLUTION: A transfer means (4) includes a transfer belt (12), driven to be rotated and a transfer voltage applying means (72a) for applying transfer voltage to the back surface of the transfer belt. The transfer voltage applying means applies the transfer voltage to the transfer belt in a prescribed effective transfer width (W12), and the surface of the transfer belt is brought into direct contact with the image carrying means in specified effective contact width (W13) and via an image receiving member. The effective contact width (W13) is larger than the effective chargeable width (W1) and is also larger than the effective transfer width (W12).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic image forming machine such as an electrostatic copying machine, a printing machine and a facsimile, and more particularly, an image bearing means which may be in the form of a rotating drum or an endless belt, and an image bearing means. Charging means for charging the electrostatic latent image to a predetermined polarity, an exposing means for selectively discharging the charged image bearing means to form an electrostatic latent image, and developing the electrostatic latent image on the image bearing means into a toner image A reversal developing unit, a transfer unit for transferring the toner image on the image carrying unit to an image receiving member which may be plain paper, and a cleaning unit for removing toner remaining on the image carrying unit after the transfer. To an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming machine of the above-mentioned embodiment, a charging means which can be constituted by a corona discharger charges an image bearing means to a specific polarity with a predetermined effective charging width. The width of the image bearing means is larger than the effective charging width, and on both sides of the effective charging width, the surface of the image bearing means is not stably charged to a predetermined potential, and is substantially lower than the predetermined potential. It can be at zero potential or opposite polarity. In the development by the reversal developing means, the toner does not adhere to the portion where the charged potential remains, but adheres to the charge eliminating portion where the charged potential has disappeared. Therefore, in an image forming apparatus employing the reversal developing means, toner tends to adhere to and be contaminated on both sides of the effective charging width on the surface of the image bearing means. Even if the effective developing width by the developing means is substantially the same as or slightly smaller than the effective charging width, the floating toner such as toner repelled by the charging potential on the image bearing means forms an image on both sides of the effective charging width. It can be deposited on the carrying means.

On the other hand, as a transfer means in the image forming machine of the above-mentioned form, recently, instead of a transfer corona discharger, a transfer roller to which a transfer voltage is applied is used, or a transfer drive is performed. A form including an endless transfer belt and a transfer voltage applying means for applying a transfer voltage to the back surface of the transfer belt has been proposed and put to practical use. The transfer roller or the transfer belt is brought into direct contact with the image bearing means via the image receiving member over the entire width thereof. The transfer voltage applying means is usually composed of a voltage applying roller formed of a conductive material and to which a transfer voltage is applied. The width of the voltage applying roller is substantially the same as the width of the transfer belt, so that the transfer belt is brought into contact with the image bearing means over its entire width and a transfer voltage is applied over its entire width.

When the width of the transfer roller or the transfer belt is larger than the effective charging width, the maximum image receiving member is usually somewhat smaller than the effective charging width. The transfer roller or the transfer belt is brought into direct contact with the image bearing means without transferring the toner adhered to the image bearing means onto the transfer roller or the transfer belt, whereby the surface of the transfer roller or the transfer belt is transferred by the toner. It will be polluted. When both sides of the surface of the transfer roller or the transfer belt are contaminated with the toner, the contact state between the image bearing unit and the transfer roller or the transfer belt is deteriorated, and poor transfer is generated. The surface of the image bearing unit is damaged. And other problems occur. To solve such a problem, Japanese Patent No. 25975 is disclosed.
No. 40 proposes to make the width of the transfer roller (or the transfer belt) smaller than the effective charging width.

[0005]

If the width of the transfer roller or the transfer belt is made smaller than the effective charging width, toner adhering to the image bearing means on both sides of the effective charging width is transferred to the transfer roller or the transfer belt. Although this is prevented, a separate problem arises: Primarily,
If the width of the transfer roller or the transfer belt is made smaller than the effective charging width, the width of the transfer roller or the transfer belt becomes substantially the same as or smaller than the maximum image receiving member, and the transferability of the image receiving member by the transfer roller or the transfer belt decreases. However, the image receiving member tends to skew or jam.
Second, especially when the effective cleaning width of the cleaning means is substantially the same as or smaller than the effective charging width, the toner attached to both sides of the effective charging width on the surface of the image bearing means is accumulated without being removed. In many cases, such toner accidentally floats and contaminates the inside or the periphery of the image forming apparatus. In particular, floating toner adheres to the bearing mechanism of the transfer roller or the bearing mechanism of the support roller for the transfer belt, the means for applying the transfer voltage to the transfer roller or the transfer belt, and not only contaminates them but also impairs their functions. Tend to do so.

The present invention has been made in view of the above-mentioned facts, and its main technical problem is to solve various problems as described above relating to toner adhering to both sides of the effective charging width on the surface of the image bearing means. The problem is solved by adopting a unique configuration for the transfer means.

[0007]

Means for Solving the Problems As a result of earnest studies, the present inventors have developed a transfer belt which rotates a transfer means and a transfer voltage applying means for applying a transfer voltage to the back surface of the transfer belt. The transfer voltage applying means applies a transfer voltage to the transfer belt with a predetermined effective transfer width, and the surface of the transfer belt is brought into direct contact with the image bearing means via the image receiving member with a predetermined effective contact width, and It has been found that the main technical problem can be achieved by setting the contact width larger than the effective charging width of the charging means and larger than the effective transfer width.

That is, according to the present invention, there is provided an image forming apparatus which achieves the above-mentioned main technical problems, comprising an image carrying means which can be sequentially moved through a charging area, an exposure area, a development area, a transfer area and a cleaning area. A charging means for charging the image bearing means in the charging area; and an exposure means for selectively discharging the image bearing means in the exposure area to form an electrostatic latent image on the image bearing means. Reversal developing means for developing the electrostatic latent image into a toner image in the development area; transfer means for transferring the toner image on the image carrying means to an image receiving member in the transfer area; Cleaning means for removing toner remaining on the image bearing means after transfer in the cleaning area, wherein the transfer means applies a transfer voltage to a transfer belt driven to rotate and a back surface of the transfer belt. Transfer means for charging the image bearing means with a predetermined effective charge width, and the transfer voltage application means charges the transfer belt with a predetermined effective transfer width. Applying the transfer voltage, the surface of the transfer belt is brought into direct contact with the image bearing means via the image receiving member with a predetermined effective contact width,
An image forming apparatus is provided, wherein the effective contact width is larger than the effective charging width and larger than the effective transfer width.

Preferably, the effective contact width is larger than the maximum image receiving member width. In a preferred embodiment, the transfer unit includes a belt cleaning unit for removing adhered toner from the surface of the transfer belt, and an effective cleaning width of the belt cleaning unit is larger than the effective contact width. Preferably, the effective transfer width is smaller than the effective charge width. The transfer voltage applying means can be formed of a voltage applying roller formed of a conductive material and to which a transfer voltage is applied. Pressing rollers may be provided which are respectively disposed on both sides of the voltage applying roller and which act on the back surface of the transfer belt to press the surface of the transfer belt against the image bearing means. Conveniently, the pressing roller is concentric with the voltage applying roller. The voltage applying roller and the pressing roller are fixed to a conductive common support shaft rotatably mounted, and a transfer voltage is applied to the voltage applying roller via the common supporting shaft, and the pressing roller is It is preferably formed from an insulating material.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an image forming machine constructed according to the present invention will be described below in more detail with reference to the accompanying drawings.

FIG. 1 schematically shows the main components of a preferred embodiment of an image forming machine constructed according to the present invention. The illustrated image forming machine includes four image forming units arranged in tandem, namely, a black toner image forming unit 2a, a magenta toner image forming unit 2b, a cyan toner image forming unit 2c, and a yellow toner image forming unit 2d and one transfer unit. And a belt unit 4 for forming a color image. The transfer belt unit 4 includes a driven roller 6, a driven roller 8, a tension roller 10, and an endless transfer belt 12 wound around these (the transfer belt unit 4 further includes four voltage applying units. And a pressure roller attached to the voltage applying roller, which will be described later in detail). The driven roller 6 and the driven roller 8 are arranged at predetermined intervals in the left-right direction in FIG. The transfer belt 12 can be formed from a flexible material having conductivity such as conductive synthetic rubber. The driven roller 6 is driven to rotate in the direction indicated by the arrow 14, whereby the transfer belt 12 is driven to rotate in the direction indicated by the arrow 14. Black toner image forming unit 2a, magenta toner image forming unit 2b, cyan toner image forming unit 2c, and yellow toner image forming unit 2
“d” is arranged in tandem with an upper running portion of the transfer belt 12 in the transfer belt unit 4.

Each of the black toner image forming unit 2a, the magenta toner image forming unit 2b, the cyan toner image forming unit 2c, and the yellow toner image forming unit 2d forms a toner image of a different color (accordingly, each developing (The color of the toner used in the means is different). Therefore,
Hereinafter, the configuration of the black toner image forming unit 2a will be described in detail.
b, the details of the configurations of the cyan toner image forming unit 2c and the yellow toner image forming unit 2d are omitted to avoid duplication. The black toner image forming unit 2a includes a rotating drum 14 constituting an image bearing unit.
a. An electrophotographic photosensitive member is arranged on the outer peripheral surface of the rotating drum 14a. Rotating drum 14a
Is rotated in the direction indicated by the arrow 16a, and its outer peripheral surface has a charging area 18a, an exposure area 20a, a developing area 22a,
4a and the cleaning area 26a are sequentially moved. In the charging area 18a, the outer peripheral surface of the rotating drum 14a is charged to a specific polarity by the charging means 28a, and in the exposure area 20a, the outer peripheral surface of the rotating drum 14a is selectively exposed and discharged by the exposing means 30a. As a result, an electrostatic latent image is formed on the outer peripheral surface of the rotating drum 14a. In the developing area 22a, black toner is applied to the electrostatic latent image on the outer peripheral surface of the rotating drum 14a by the reversal developing means 32a, and the electrostatic latent image is developed into a black toner image. The reversal developing means 32a develops the electrostatic latent image into a toner image by a so-called reversal developing method, that is, the toner charged to the same polarity as the charging of the outer peripheral surface of the rotating drum 14a by the charging means 28a is applied to the outer peripheral surface of the rotating drum 14a. The electrostatic latent image is developed into a toner image by selectively adhering to the region where the charge has been removed. In a region of the outer peripheral surface of the rotating drum 14a where the charge remains without being neutralized, the adhesion of the toner is prevented by the electrostatic repulsion. In the transfer area 24, the black toner image on the outer peripheral surface of the rotary drum 14a is transferred onto an image receiving member conveyed through the transfer area 24 by the operation of a transfer unit described in detail later. The image receiving member may be a plain paper sheet.
In the cleaning area 26a, the cleaning means 3
By 4a, the toner remaining on the outer peripheral surface of the rotary drum 14a is removed.

FIG. 2 shows the charging means 28a in the black toner image forming unit 2a. The charging means 28a in the illustrated embodiment is constituted by a corona discharger, and has a shield case 36a extending in the axial direction of the rotating drum 14a. Shield case 36a
Has an elongated box shape with a surface facing the rotating drum 14a, that is, a lower surface opened, and a conductive wire 38a extending in the axial direction of the rotating drum 14a is stretched inside the shield case 36a. A grid 40a is provided on the lower surface of the shield case 36a. A large number of slits are formed in a main portion of the grid 40a except for both end portions thereof. Corona discharge is applied to the outer peripheral surface of the rotary drum 14a in a region of a width W1 where the multiple slits are formed, and the rotary drum is formed. The outer peripheral surface of 14a is charged to a specific polarity. At both ends of the grid 40a, the grid 40a
This blocks the corona discharge. Therefore, the charging means 28
a charges the outer peripheral surface of the rotary drum 14a in the area of the width W1. On both sides of the width W1, the outer peripheral surface of the rotary drum 14a is not substantially charged. Therefore, the width W1 is nothing but the effective charging width of the charging means 28a. The illustrated charging means 28a further includes a spacing roller 42a rotatably mounted on the shield case 36a on both sides of the grid 40a. The outer peripheral surface of the interval setting roller 42a projects beyond the lower surface of the shield case 36a.
The gap between the outer peripheral surface of the rotating drum 14a and the grid 40a of the charging means 28a is set to a predetermined value by bringing the outer peripheral surface of the rotating drum 14a into contact with the outer peripheral surface of the rotating drum 14a. The length between the widthwise outer ends of the pair of interval setting rollers 42a is W2, which is larger than the effective charging width W1.

The exposure means 30a may have a well-known form in which a large number of light emitting elements are arranged in the axial direction of the rotary drum 14a. The exposure means 30a has a maximum exposure width W3
In FIG. 8, the peripheral surface of the rotary drum 14a is selectively exposed to form a required electrostatic latent image.

Referring to FIG. 3 together with FIG. 1, the reversal developing means 32a, which may be a known form per se, includes a developing housing 4 containing a developer (not shown).
4a. The developer may be a two-component developer composed of toner and carrier particles or a one-component developer composed of only toner. The rotating drum 1 is provided in the developing housing 44a.
An opening is formed at a portion facing the outer peripheral surface of 4a. A developer applying means 46a is provided in the developing housing 44a, and the developer applying means 46a
and a sleeve member 48a extending in the axial direction of FIG.
The outer peripheral surface of the sleeve member 48a is
Partially project through the opening. A stationary magnet (not shown) is provided in the sleeve member 48a, and the sleeve member 48a is driven to rotate in a direction indicated by an arrow 50a. The developer is held on the outer peripheral surface of the sleeve member 48a by the magnetic attraction force of the stationary magnet,
The developer is applied to the electrostatic latent image formed on the outer peripheral surface of the rotating drum 14a. In the illustrated embodiment,
The stationary magnet is arranged in the region of the width W4, and the sleeve member 48a holds the developer on the outer peripheral surface in the region of the width W4 and applies the developer to the outer peripheral surface of the rotary drum 14a. Therefore, the width W4 is the effective developing width of the reversal developing means 32a. On both sides of the sleeve member 48a, interval setting rollers 52a are rotatably disposed. The outer diameter of the interval setting roller 52a is larger than the outer diameter of the sleeve member 48a by a predetermined amount, and the outer circumference of the sleeve member 48a and the outer circumference of the rotary drum 14a are brought into contact by bringing the interval setting roller 52a into contact with the outer peripheral surface of the rotary drum 14a. The distance from the surface is set to a predetermined value.
The length between the outer ends of the pair of interval setting rollers 52a is W5 larger than the effective development width W4. The developing housing 44a has an upstream seal member 5 associated with the opening.
4a and a pair of side seal members 56a are provided.
The upstream seal member 54a, which can be formed from an appropriate synthetic resin film, has a strip shape extending in the axial direction of the rotary drum 14a, and its free edge is located on the outer periphery of the rotary drum 14a on the upstream side of the developing area 22a. It is touching the surface. A pair of side seal members 56a, which can be formed from a flexible material such as a pile sheet,
The rotary drum 14a is provided on both sides of the developer applying means 46a.
Is brought into contact with the outer peripheral surface of the main body. Upstream seal member 54
a and the pair of side seal members 56 a
It is provided to prevent the toner in the developer contained in 4a from scattering around. The upstream seal member 54a has a width W6 larger than the effective development width W4. The length between the outer ends of the pair of side seal members 56a is also W7 which is larger than the effective development width W4.

Continuing the description with reference to FIG. 4 in conjunction with FIG.
a includes a cleaning housing 58a. An opening is formed in a portion of the cleaning housing 58a facing the outer peripheral surface of the rotating drum 14a. The cleaning housing 58a includes a cleaning blade 6
0a and a cleaning brush 62a are mounted.
The cleaning blade 60a is formed of a flexible material such as synthetic rubber, and its leading edge has a rotating drum 14a.
a. Cleaning brush 6
2a is rotated in the direction indicated by the arrow 63a, and a flexible brush disposed on the outer peripheral surface acts on the outer peripheral surface of the rotating drum 14a. The cleaning brush 62a partially removes the toner remaining on the peripheral surface of the rotating drum 14a after the transfer and applies a so-called loosening action to the remaining toner. The cleaning blade 60a removes the toner subjected to the loosening action from the outer peripheral surface of the rotating drum 14a.
The cleaning blade 60a is elongated in the axial direction of the rotary drum 14a over a width W8, and the width W8 is an effective cleaning width of the cleaning unit 34a. The width of the cleaning brush 62a is also substantially the same as the width W8, and both ends of the cleaning brush 62a are substantially aligned with both ends of the cleaning blade 60a. The cleaning housing 58a is also provided with an upstream seal member 64a and a pair of side seal members 66a in relation to the opening. Upstream seal member 64a that can be formed from an appropriate synthetic resin film
Has a strip shape elongated in the axial direction of the rotating drum 14a, and its free edge is the cleaning area 26.
a and is brought into contact with the outer peripheral surface of the rotary drum 14a on the upstream side of the rotating drum 14a. A pair of side seal members 66a, which can be formed from a flexible material such as a pile sheet, are brought into contact with the outer peripheral surface of the rotary drum 14a on both sides of the cleaning blade 60a and the cleaning brush 62a. The upstream seal member 64a and the pair of side seal members 66a are provided to prevent the toner removed from the outer peripheral surface of the rotary drum 14a and contained in the cleaning housing 58a from scattering around. The upstream seal member 64a has a width W9 larger than the effective cleaning width W8. Also, a pair of side seal members 66a
Is also a width W10 larger than the effective cleaning width W8. Cleaning housing 58a
Is further provided with a static elimination means 68a on the lower surface thereof. The static elimination means 68a is, for example, a rotary drum 14a.
Of the rotary drum 14a by irradiating the outer peripheral surface of the rotary drum 14a between the transfer area 24a and the cleaning area 26a.
The residual charge on the outer peripheral surface of a is eliminated. Static elimination means 68
a irradiates the outer peripheral surface of the rotating drum 14a with an effective charge removing width W11 larger than the effective cleaning width W8.

Transfer belt unit 4 constituting transfer means
Includes a support frame 70 (a part of which is indicated by a two-dot chain line in FIG. 5) disposed at a predetermined position in a housing (not shown) of the image forming machine. 6. The driven roller 8 and the tension roller 10 are rotatably mounted on the support frame 70. The illustrated transfer belt unit 4 includes the four image forming units described above, that is, the black toner image forming unit 2a, the magenta toner image forming unit 2b, and the cyan toner image forming unit 2c.
And transfer voltage applying means 72a, 72b, 72c and 72d provided in association with the transfer areas 24a, 24b, 24c and 24d of the yellow toner image forming unit 2d. 5 and 6, which illustrate the transfer voltage applying means 72a.
1 and 6, both ends of a common support shaft 74a extending in a direction perpendicular to the plane of FIG. 1 and FIG. 6 are supported by a support frame 70 via a shaft support mechanism 76a (FIG. 6). The common support shaft 74a can be formed from a suitable conductive metal material such as steel. The support frame 70 has both side plate portions spaced apart in the left-right direction in FIG.
8a is fixed. Each of the shaft support mechanisms 76a includes an inverted L-shaped revolving plate 80a rotatably mounted on each of the supporting short shafts 78a, and one end of a common support shaft 74a rotates at one end of each of the revolving plates 80a. It is freely attached. A tension spring 82a is provided between the other end of the revolving plate 80a and the support frame 70, and the revolving plate 80a is elastically biased clockwise in FIG.

As clearly shown in FIG. 5, the common support shaft 7
A voltage applying roller 84a constituting the voltage applying means 72a is fixed to 4a. Further, a pair of pressing rollers 86a arranged on both sides of the voltage applying roller 84a are also fixed to the common support shaft 74a. The voltage applying roller 84a is conveniently formed of a relatively flexible material having conductivity, for example, conductive synthetic rubber. On the other hand, the pressing roller 84a is conveniently formed of an insulating relatively soft material, for example, insulating synthetic rubber. A required transfer voltage is applied to the voltage applying roller 84a via the common support shaft 74a and the revolving plate 80a. FIG.
6, the pivot plate 80a is resiliently biased clockwise in FIG. 6 by a tension spring 82a, so that the voltage applying roller 84a and the pressing roller 86a are moved upward in FIG. Is resiliently biased. Thus, the voltage applying roller 84a and the pressing roller 86a are elastically pressed via the transfer belt 12 against the outer peripheral surface of the rotating drum 14a in the black toner image forming unit 2a. The transfer voltage applied to the voltage applying roller 84a is transmitted to the transfer belt 12, so that in the transfer area 24a, the outer peripheral surface of the rotary drum 14a and the transfer belt in the area where the voltage applying roller 84a extends, that is, the area of the width W12. 1
A transfer voltage is applied to an image receiving member (not shown) conveyed between the rotating drum 14a and the transfer roller 2, and a black toner image is transferred from the outer peripheral surface of the rotating drum 14a to the image receiving member in the area of the width W12. The width W
Reference numeral 12 denotes an effective transfer width. Since the pressing roller 86a is insulative, no effective transfer voltage is applied to the transfer belt 12 at a portion outside the width W12.
However, due to the presence of the pair of pressing rollers 86a, the transfer belt 12 is pressed against the outer peripheral surface of the rotary drum 14a in a region having a width W13 larger than the effective transfer width.
Accordingly, the width W13 is an effective contact width in which the transfer belt 12 is brought into direct contact with the outer peripheral surface of the rotary drum 14a via the image receiving member at a portion where the image receiving member is not present. As clearly shown in FIG. 5, in the illustrated embodiment, the transfer belt 1
2 has a width W14 which is larger than the effective contact width W13.
There is a non-contact portion that does not come into sufficiently close contact with the outer peripheral surface of 4a. In such a non-contact portion, the transfer belt 12
A projection 88 having a width W15 is formed on the inner surface of the substrate (the projection 88 will be further described later).
The width of the rotating drum 14a may be substantially the same as or slightly larger than the width W14 of the transfer belt 12.

In the illustrated embodiment, the voltage applying roller 84a and the pressing roller 86a are fixed to the common support shaft 74. However, when viewed in the moving direction of the transfer belt 12, the voltage applying roller 84a and / or A separate support shaft is rotatably mounted on the downstream side, and a pressing roller 86a is attached to the support shaft.
Can also be fixed. In this case, the pressing roller 8
6a may be a form extending continuously over the effective contact width W14.

Although the transfer voltage applying means 72a and its related components arranged in relation to the transfer area 24a of the black toner image forming unit 2a have been described, the magenta toner image forming unit 2b, the cyan toner image forming unit 2c and the yellow Toner image forming unit 2
The transfer voltage applying means 72b, 72c and 72d disposed in relation to the transfer areas 24b, 24c and 24d of d, and their related components are also substantially the same, and therefore a detailed description thereof will be omitted. I do.

Referring to FIG. 7 together with FIGS. 1 and 5, the support frame 70 has a support shaft 90 extending in the left-right direction in FIG. 5 and the direction perpendicular to the plane of FIG.
Are mounted rotatably, and the driven roller 6 is fixed to the support shaft 90. One end of the support shaft 90 projects beyond one side plate of the support frame 70, and an input gear (not shown) is fixed to the projecting end. The input gear is connected to a rotary drive source (not shown), which may be an electric motor, via a suitable transmission means.
Is rotated in the direction indicated by the arrow 14.
As clearly shown in FIG. 7, the driven roller 6 has a central main part 94 and small diameter parts 96 arranged on both sides. The entire width W16 of the driven roller 6 is substantially the same as the entire width W14 of the transfer belt 12, and the width W17 of the small-diameter portion 96 is the width W1 of the protruding portion 88 formed on both sides of the transfer belt 12.
5 and substantially the same. Central main portion 94 of driven roller 6
The difference in radius between the small diameter portion 96 and the small diameter portion 96 may be substantially the same as the projection thickness of the projection portion 88 on the transfer belt 12. Accordingly, as shown in FIG. 7, the transfer belt 12 has a central main portion 9 of the driven roller 6 in a region between the protrusions 88 on both sides thereof.
4, the protrusions 88 on both sides of the transfer belt 12 are small-diameter portions 96 on both sides of the driven roller 6.
It is located in. The driven roller 8 and the tension roller 10 also have substantially the same configuration as the driven roller 6, and the protrusions 88 formed on both sides of the transfer belt 12 are provided on both sides of the driven roller 6, the driven roller 8 and the tension roller 10. By being located at the formed small diameter portion, meandering of the transfer belt 12 is prevented.

As shown in FIGS. 1 and 7, below the portion where the driven roller 6 is provided, a belt cleaning means 98 is provided. The belt cleaning unit 98 includes a cleaning case 100 and a cleaning blade 102. The cleaning blade 102, which can be formed from a flexible material such as synthetic rubber, is fixed at a predetermined position, and its free edge is pressed against the surface of the transfer belt 12. The cleaning case 100 fixed at a required position may have a box shape surrounding the cleaning blade 102. As will be further described later, although toner may adhere to the surface of the transfer belt 12, the cleaning blade 102 has its free edge pressed against the driven roller 6 via the transfer belt 12,
Thus, the toner adheres to the surface of the transfer belt 12 and is removed therefrom. The removed toner is stored in the cleaning case 100. Cleaning blade 10
2 is a width W18 substantially the same as the width W14 of the transfer belt 12.
And removes the adhered toner from the surface of the transfer belt 12 over the entire area of the width W18. Therefore, the width W18
Is the effective cleaning width of the belt cleaning means 98. On the inner surface of both side walls of the cleaning case 100 extending upward beyond the lower surface of the driven roller 6, there are provided side seals that are in close contact with the end surface of the driven roller 6, the side surface of the transfer belt 12, and the side surface of the cleaning blade 102. A piece 104 can be provided. The sealing piece 104 can be formed from a flexible material such as a pile sheet. If desired, upstream and downstream seal pieces, conveniently formed of a synthetic resin film, which are brought into close contact with the surface of the transfer belt 12 upstream and downstream of the cleaning case 100 as viewed in the direction of movement of the transfer belt 12. (Not shown) can also be provided.

Referring to FIG. 8, in the image forming machine constructed according to the present invention, the transfer belt 1
2, the effective contact width W13 is larger than the effective transfer width W12 defined by the extension width of the voltage applying roller 84a, and the effective charging width W12 of the charging unit 18a is also larger.
It is important that it is greater than one. As described above, in a region outside the effective charging width W1, the peripheral surface of the rotating drum 14a may be at a potential substantially lower than a predetermined potential, substantially zero potential, or the opposite polarity. May adhere to the peripheral surface of the toner. The toner attached to the peripheral surface of the rotating drum 14a outside the effective charging width W1 is transferred from the rotating drum 14a in the transfer area 24a because the effective contact width W13 of the transfer belt 12 is larger than the effective charging width W1. It is transferred to the surface of the belt 12. Then, the toner transferred to the surface of the transfer belt 12 is removed from the surface of the transfer belt 12 by the action of the cleaning blade 102 of the belt cleaning unit 98. Accordingly, while the toner adhering to the peripheral surface of the rotating drum 14a on both sides of the effective charging width W1 is attached to the peripheral surface of the rotating drum 14a and moved along with the rotation of the rotating drum 14a, the rotating drum 14a Floating from the peripheral surface of the image forming apparatus and contaminating the inside or surroundings of the image forming apparatus can be sufficiently and effectively prevented. In addition, the maximum image receiving member width W19
Is generally substantially the same as or slightly larger than the effective transfer width W12, but the effective contact width W
13 and therefore the image receiving member is
By the cooperation of the rotary drum 14a and the rotary drum 14a, the sheet can be sufficiently satisfactorily conveyed therebetween. The effective transfer width W12 itself may be enlarged to substantially set the effective contact width W13 to omit the pressing roller 84a. However, in this case, the transfer belt 12 can be moved without an image receiving member. A transfer voltage is applied to the transfer belt 12 in a region outside the maximum image receiving member width W19 that is brought into direct contact with the rotating drum 14a, and as a result, a relatively large amount of current flows into the rotating drum 14a. Rotating drum 14a
May be deteriorated early. The transfer belt 12 has a rotating drum 14 over the range of its effective contact width W12.
a, the toner is transferred from the transfer belt 12
The effective cleaning width W18 of the belt cleaning means 98 may be adjusted to sufficiently remove toner adhering to the surface of the transfer belt 12 because the toner may move outward in the width direction on the surface of the transfer belt 12. It is preferably somewhat larger than the effective contact width W13, and may be substantially the same as the transfer belt width W14, for example. The effective charging width W1 of the charging unit 28a may be somewhat larger than the effective transfer width W12 defined by the extension width of the voltage applying roller 84a.

Continuing the description with reference to FIG. 8, in the illustrated embodiment, the effective charging width W
1, not only the effective transfer width W12 defined by the maximum image receiving member width W19 and the extension width of the voltage application roller 84a, but also the effective charge removal width W in the cleaning unit 34a.
11, the effective cleaning width W8, and the reversal developing means 3
2a and the maximum exposure width W3 of the exposure unit 30a are also equal to the effective contact width W13 of the transfer belt 12.
The relationship between these various widths is set to W13>W11>W8>W4>W19> W3.

The width W2 of the pair of interval setting rollers 42a in the charging means 28a and the width W of the pair of interval setting rollers 52a in the reversal developing means 32a.
5. Upstream seal member 54a in reversal developing means 32a
The width W6 of the pair of side seal members 56a in the reversal developing unit 32a, the width W9 of the upstream seal member 64a in the cleaning unit 34a, and the width W10 of the pair of side seal members 66a in the cleaning unit 34a. Each also has a transfer belt 12
Is preferably smaller than the effective contact width W13.
When set as such, the widths W2, W5,
In the range of W6, W7, W9 and W10, the toner adhered to the outer peripheral surface of the rotating drum 14a is
And the toner does not remain on the outer peripheral surface of the rotating drum 14a. Therefore, it is possible to sufficiently reliably prevent the toner from being accumulated between the interval setting rollers 42a and 52a and the outer peripheral surface of the rotating drum 14a, thereby damaging the interval setting. Also, the sealing members 54a, 5a
The toner accumulates between the outer peripheral surfaces of the rotary drum 14a and the seal members 54a, 56a, 6a.
The deterioration of the sealing effect by 4a and 66a is also sufficiently avoided.

[0026]

According to the image forming apparatus of the present invention, the above-mentioned various problems of the toner adhering to both sides of the effective charging width on the surface of the image carrying means, which exist in the conventional image forming apparatus, are solved. .

[Brief description of the drawings]

FIG. 1 is a simplified diagram showing main components of a preferred embodiment of an image forming machine configured according to the present invention.

FIG. 2 is a simplified partial sectional view showing a charging unit in the image forming apparatus shown in FIG.

FIG. 3 is a simplified partial sectional view showing a developing unit in the image forming machine shown in FIG.

FIG. 4 is a simplified partial sectional view showing a cleaning unit in the image forming apparatus shown in FIG.

FIG. 5 is a simplified partial sectional view showing a transfer unit in the image forming machine shown in FIG.

FIG. 6 is a simplified diagram showing a mounting mode of a voltage applying roller and a pressing roller in a transfer unit of the image forming machine shown in FIG.

FIG. 7 is a simplified partial cross-sectional view showing a belt cleaning unit in the transfer unit of the image forming machine shown in FIG.

FIG. 8 is a schematic diagram showing a relative relationship between various widths in the image forming apparatus shown in FIG.

[Explanation of symbols]

 2a: Black toner image forming unit 2b: Magenta toner image forming unit 2c: Cyan toner image forming unit 2d: Yellow toner image forming unit 4: Transfer belt unit (transfer unit) 12: Transfer belt 14a: Rotating drum (image bearing unit) 18a: charging area 20a: developing area 22a: developing area 24a: transfer area 26a: cleaning area 28a: charging means 30a: exposure means 32a: reversal developing means 72a: voltage applying means 74a: common support shaft 84a: voltage applying roller 86a: Press roller 98: Belt cleaning means W1: Effective charging width W4: Effective developing width W12: Effective transfer width W13: Effective contact width W14: Transfer belt width W18: Effective cleaning width of belt cleaning means W19: Maximum image receiving member width

Claims (8)

[Claims] An image bearing means for sequentially moving through a charging area, an exposure area, a developing area, a transfer area, and a cleaning area; a charging means for charging the image bearing means in the charging area; Exposure means for selectively discharging the image bearing means in the exposure area to form an electrostatic latent image on the image bearing means; and developing means for developing the electrostatic latent image into a toner image in the development area. Reversal developing means, transfer means for transferring the toner image on the image bearing means on the image receiving member in the transfer area, and removing toner remaining on the image bearing means after transfer in the cleaning area. An image forming machine, comprising: a transfer belt that is driven to rotate; and a transfer voltage application unit that applies a transfer voltage to the back surface of the transfer belt. The step charges the image bearing means with a predetermined effective charging width, the transfer voltage applying means applies the transfer voltage to the transfer belt with a predetermined effective transfer width, and the surface of the transfer belt receives the image with a predetermined effective contact width. An image forming machine which is brought into contact with said image bearing means directly and via a member, wherein said effective contact width is larger than said effective charging width and larger than said effective transfer width. 2. The image forming apparatus according to claim 1, wherein said effective contact width is larger than a maximum image receiving member width. 3. The transfer device according to claim 1, wherein the transfer device includes a belt cleaning device for removing adhered toner from a surface of the transfer belt, and an effective cleaning width of the belt cleaning device is larger than the effective contact width. Or the image forming machine according to 2. 4. The image forming apparatus according to claim 1, wherein said effective transfer width is smaller than said effective charge width. 5. The image forming apparatus according to claim 1, wherein said transfer voltage applying means is formed of a conductive material and comprises a voltage applying roller to which a transfer voltage is applied. 6. The transfer unit includes a pressing roller disposed on each side of the effective transfer width and acting on the back surface of the transfer belt to press the surface of the transfer belt against the image bearing unit. The image forming apparatus according to claim 1. 7. The transfer voltage applying means comprises a voltage applying roller formed of a conductive material and to which a transfer voltage is applied, wherein the transfer means is concentric with the voltage applying roller. The image forming apparatus according to any one of claims 1 to 4, further comprising a pressing roller disposed on each side and acting on a back surface of the transfer belt to press the front surface of the transfer belt against the image bearing means. . 8. The voltage applying roller and the pressing roller are fixed to a rotatable conductive common support shaft, and a transfer voltage is applied to the voltage applying roller via the common support shaft. The image forming apparatus according to claim 7, wherein the pressing roller is formed of an insulating material.