JP2003255800A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the rear side of a recording material from becoming dirty, to suppress staining of an edge occurring at the end of a printed recording material, and to suppress the wasteful consumption of toner. <P>SOLUTION: After the finish of image forming (time T3), application of charging bias is stopped (time T4). With the timing that a part to which application of the charging bias by a charging roller is not performed arrives at an exposing part, an exposing device performs exposure of a maximum exposure width for exposing all of an effective exposing width (time T5). After that, with the timing that the part to which application of the charging bias is not performed arrives at a developing nip part, the developing bias of +200 V is applied to a development roller (time T6). The exposure of the maximum exposure width is performed to the part of one or more rounds of the photoreceptor drum. As for the maximum exposure width in this case, the exposure width in the main scanning direction on the photoreceptor drum by the exposing device is made to be wider than a developer application width on the photoreceptor by the development roller. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus, an image forming apparatus using a contact charging means as a charging means and a non-magnetic one-component contact developing means as a developing means is known.

FIG. 8 schematically shows a sectional view of a main part of such an image forming apparatus. This image forming apparatus is a monochrome image forming apparatus including a photosensitive drum 10 as an image carrier. Then, a surface of the photosensitive drum 10 is uniformly charged by applying a predetermined charging bias to the charging roller 11 that is in contact with and is rotated by the charging bias applying power source (not shown). Next, an electrostatic latent image is formed on the surface of the photosensitive drum 10 by the exposure device 12. Then, the photosensitive drum 10
The electrostatic latent image formed above is developed by the developing device 13 to be visualized as a toner image.

The developing device 13 will be described below.
Reference numeral 20 in FIG. 8 represents a toner container. Toner container 20
Toner 21 is filled in the inside. The toner 21 is supplied onto the developing roller 16 by the toner supply roller 18 coming into contact with the developing roller 16, and is regulated by the developing blade 17 to have an optimum layer thickness and charged. Then, when a developing bias is applied to the developing roller 16 by a developing bias applying power source (not shown) and the developing roller 16 and the photosensitive drum 10 come into contact with each other, the toner on the developing roller 16 is electrostatically latent on the photosensitive drum 10. A toner image is formed by adhering to the image.

A transfer bias applying power source (not shown)
As a result, a predetermined transfer bias is applied to the transfer roller 26, the toner image formed on the photosensitive drum 10 is transferred onto the recording material P conveyed from the paper feed cassette 37, and an unfixed image is formed. To be done. Then, the fixing device 27
And the unfixed image is fixed on the recording material P by
The sheet is discharged to the sheet discharge tray 28, and the image formation is completed.

Further, the photosensitive drum 1 is not transferred at the time of transfer.
The toner remaining on 0 (transfer residual toner) is collected by the cleaning blade 14 into the waste toner container 15, and the surface of the photosensitive drum 10 is cleaned.

FIG. 9 is a sectional view of a conventional color image forming apparatus. This color image forming apparatus includes four sets of image forming units C for cyan, yellow, magenta, and black (Bk) on the intermediate transfer belt 30.
This is called a tandem system in which Y, M and Bk are arranged.

In this image forming apparatus, the first to the first for forming an image of each color of cyan, yellow, magenta and black.
The fourth image forming units are provided with photosensitive drums 10C, 10Y, 10M, and 10Bk as image bearing members, respectively. Then, a predetermined charging bias is applied by a charging bias applying power source (not shown) to the charging rollers 11C, 11Y, 11M, and 11Bk that rotate following the photosensitive drums, so that the surface of the photosensitive drum is uniformly charged. To be done. Next, the photosensitive drums 10C, 10Y, 10M of the respective colors,
Exposure devices 12C, 12Y, 12M, 1 on the 10Bk surface
An electrostatic latent image is formed by 2Bk. The electrostatic latent images formed on the photosensitive drums 10C, 10Y, 10M, and 10Bk are transferred to the developing devices 13C, 13Y, 13M, and 1C, respectively.
By being developed with 3Bk, it is visualized as a toner image.

Here, the developing devices 13C, 13Y, 13
M and 13Bk will be described. FIG. 10 is a sectional view of the developing device 13C for cyan. Since the other yellow, magenta, and black developing devices 13Y, 13M, and 13Bk have the same configuration, the cyan developing device 13 is used.
Only C will be described. Reference numeral 20C indicates a toner container, and cyan toner 21C is contained in the toner container 20C.
Is filled. The cyan toner 21C is sent to the toner supply roller 18C by rotating the toner carrying sheet 19C. The toner supply roller 18C and the developing roller 16C come into contact with each other, toner is supplied onto the developing roller 16C, and the developing blade 17C regulates and charges the layer to an optimum layer thickness. Then, when a developing bias is applied to the developing roller 16C by the developing bias applying power source and the developing roller 16C and the photosensitive drum 10C come into contact with each other,
The toner on the developing roller 16C is attached to the electrostatic latent image on the photosensitive drum 10C to form a toner image. In addition,
Reference numerals B ′, C ′, D ′, E ′, and F ′ in FIG. 10 denote the photosensitive drum 10C, the charging roller 11C, the developing roller 16C, the toner supply roller 18C, and the toner transport sheet 1 in this order.
9C shows the rotation direction.

By a primary transfer bias applying power source (not shown), each primary transfer roller 26C, 26Y, 2 shown in FIG.
A predetermined primary transfer bias is applied to 6M and 26Bk, and the toner images of the respective colors on the photosensitive drums 10C, 10Y, 10M, and 10Bk are sequentially and multiple-transferred onto the intermediate transfer belt 30 rotating in the arrow A'direction. , A full-color image is formed. Then, a predetermined secondary transfer bias is applied to the secondary transfer roller 32 by a secondary transfer bias applying power source (not shown), and the recording material P is transferred from the intermediate transfer belt 30.
The secondary transfer to is performed. Then, the unfixed image is conveyed to the fixing device 35, the unfixed image is fixed on the recording material P, and is discharged to the paper discharge tray 36, and the image formation is completed.

Further, during the primary transfer, the photosensitive drums 10C, 10Y, 10M, 10 are not transferred to the intermediate transfer belt 30.
The primary transfer residual toner remaining on Bk is collected in the waste toner containers 15C, 15Y, 15M and 15Bk by the cleaning blades 14C, 14Y, 14M and 14Bk.
The photosensitive drums 10C, 10Y, 10M, and 10Bk are cleaned. Further, the secondary transfer residual toner remaining on the intermediate transfer belt 30 without being transferred to the recording material P during the secondary transfer is collected by the intermediate transfer belt cleaning blade 33 into the intermediate transfer belt waste toner container 34, and the intermediate transfer belt waste toner container 34 is transferred. The belt 30 is cleaned.

Before image formation, the photosensitive drums 10, 10C, 10Y, 10M, and 10Bk and the charging rollers 11, 11C, 11Y, 11M, and 11Bk are used in both monochrome and color image forming apparatuses. From the contacting position to the photosensitive drums 10, 10C, 10Y, 1
0M, 10Bk and developing devices 13, 13C, 13Y, 13
The photosensitive drum 1 in a section up to a position where the developing rollers 16 and 16C of M and 13Bk are in contact with each other (see FIG. 10).
The surface potentials of 0, 10C, 10Y, 10M, and 10Bk are
As a result of dark decay, it is almost 0V.

Therefore, the photosensitive drums 10, 10C,
When the section having the surface potential of 0V on 10Y, 10M, and 10Bk passes in front of the developing rollers 16 and 16C, the negatively charged toner is discharged to the photosensitive drums 10 and 10C in the section of 0V.
Adhesion to 10Y, 10M, and 10Bk results in fog. After that, the fog toner adheres to the transfer roller 26, which is the transfer means, the intermediate transfer belt 30, and the like when coming into contact with the transfer means, and the toner adhered to the transfer roller 26 is used in the case of a monochrome image forming apparatus. Has a problem that the first first recording material P is transferred to the back side of the first recording material P when passing through the transfer roller 26, and back stain occurs on the first recording material P. Have Further, in the case of a color image forming apparatus, the toner attached to the intermediate transfer belt 30 is attached to the secondary transfer roller 32, so that the first recording material P of the first sheet passes through the secondary transfer roller 32. At that time, there is a problem that the back side of the first recording material P is transferred and the back side stain is generated on the first recording material P.

The backside of the recording material P is transferred to the transfer roller 26.
Depending on the degree of contamination such as, the first sheet does not disappear, but when a considerable amount of toner adhering to the uncharged area on the photosensitive drum 10 is repeatedly transferred to the transfer roller 26 or the like each time an image is formed, the transfer roller 26 Stains on the back side also progress, and the back stain cannot be eliminated only by the first recording material P, and the back stain occurs on a plurality of recording materials P.

Further, in the case of a color image forming apparatus using the intermediate transfer belt 30, if a large amount of fog toner reaches the intermediate transfer belt cleaning device 33, the cleaning ability will be exceeded, resulting in cleaning failure. A dirty image may be output on the surface of the recording material P, or the waste toner container 34 for the intermediate transfer belt 30 may be filled up quickly, and the waste toner container 34 may be frequently replaced.

Particularly in the case of the contact developing system, the photosensitive drums 10, 10C, 10Y, 10M, 10Bk and the developing device 1 are used.
3, 13C, 13Y, 13M, 13B are in contact with each other, so that the photosensitive drum 10,
10C, 10Y, 10M, 10Bk and developing device 13, 1
Even if the potential difference between 3C, 13Y, 13M, and 13Bk is small, the photosensitive drums 10, 10C, 10Y, 10
More toner adheres on M and 10Bk.

Further, the above-mentioned fog is a cause of wasting toner, leading to an increase in toner consumption.

Therefore, in the case of the conventional contact developing device, the separating means is provided so as to separate the photosensitive drum and the developing roller. However, in order to separate the photosensitive drum and the developing roller, a separating motor or the like is used. Was necessary, which hindered cost increase and miniaturization.

Therefore, at the start of image formation, a developing bias of +200 V is applied to the developing roller so that the developing bias is used for normal image formation when the charging portion of the photosensitive drum reaches the developing position by the charging means. That is, it is changed to -300V.

At the start of image formation, in order to bring the surface of the photosensitive drum into a dark decay state, the application of the charging bias is stopped after the image formation is completed, and the photosensitive drum is irradiated with laser light by the exposure device. The rotation of the photosensitive drum is stopped after the surface potential becomes 0V.

By the way, in a normal image formation, when the user mistakenly tries to output an image wider than the sheet passing width of the recording material, if the exposure width is wider than the sheet passing width of the recording material P, The edges of the recording material may become dirty. For this reason, a mask is applied at the time of exposure in accordance with the paper passing width of the recording material so that the exposure width is not wider than the paper passing width of the recording material.

[0022]

However, at the start of image formation, if there is a region where the masked region and the developable region overlap, the exposure from the previous image is not performed because the region is not exposed. When it is short, the potential on the surface of the photosensitive drum may be close to −500V instead of 0V. At that portion, if +200 V is applied to the developing roller at the start of image formation, the potential difference between the developing roller and the surface of the photosensitive drum becomes large, so reversal fog occurs and toner adheres to the developable area. The end of the intermediate transfer belt or the end of the transfer roller may be soiled, and thus the end of the output recording material may be soiled.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to prevent back stains on the recording material and to prevent edge stains on the edges of the printed recording material, which is wasteful. An object of the present invention is to provide an image forming apparatus capable of suppressing toner consumption.

[0024]

The invention according to claim 1 is
A rotatable image carrier, a charging unit that charges the surface of the image carrier, an exposing unit that forms an electrostatic latent image on the surface of the image carrier after charging, and a developer attached to the electrostatic latent image. In the image forming apparatus including a developing unit configured to develop as a developer image, before the rotation of the image bearing member is stopped after the image formation, the developing agent application width on the image bearing member by the developing unit is less than The image carrier is exposed for at least one revolution in a state where the exposure width of the image carrier in the main scanning direction by the exposure unit is widened.

According to a second aspect of the present invention, a rotatable image carrier, a charging unit that charges the surface of the image carrier, and an exposure unit that forms an electrostatic latent image on the surface of the image carrier after charging. ,
An image forming apparatus comprising: a developing unit that adheres a developer to the electrostatic latent image to develop the electrostatic latent image as a developer image, and at the start of rotation of the image carrier, develops on the image carrier by the developing unit. In a state where the exposure width in the main scanning direction on the image carrier by the exposure means is wider than the agent coating width,
With respect to the rotation direction of the image bearing member, from the portion of the image bearing member exposed by the exposing unit to the portion of the image bearing member to which the developer is attached by the developing unit is exposed, Before the rotation of the image carrier is stopped after the image formation, the exposure width in the main scanning direction on the image carrier by the exposing device is made wider than the developer coating width on the image carrier by the developing device. In this state, at least with respect to the rotation direction of the image carrier, at least a portion of the image carrier that is charged by the charging unit to a portion of the image carrier that is exposed by the exposing unit are exposed. It is characterized by:

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, during the image formation, the exposing unit does not perform the exposure in the main scanning direction which is equal to or larger than the maximum sheet passing width of the recording material. , Is characterized.

The invention according to claim 4 relates to claims 1 to 3.
In the image forming apparatus according to any one of items 1 to 3, before the rotation of the image carrier is stopped and when the rotation of the image carrier is started, the developer application width on the image carrier is more than The portion where the exposure width of the image carrier in the main scanning direction is widened by the exposing means is the portion to which the charging bias is not applied by the charging means or the portion to which the charging bias equal to or lower than the discharge start voltage is applied. , Is characterized.

The invention according to claim 5 relates to claims 1 to 4.
In the image forming apparatus described in any one of 1 above, the charging unit has a contact charging member that is in contact with the surface of the image carrier.

The invention according to claim 6 is the invention according to claims 1 to 5.
The image forming apparatus described in any one of 1 to 3, wherein the developing unit has a contact developing member that is in contact with the surface of the image carrier, and develops with a non-magnetic one-component developer. .

The invention according to claim 7 relates to claims 1 to 6.
In the image forming apparatus according to any one of items 1 to 3, the image carrier, the charging unit, the developing unit, and a cleaning unit for cleaning the surface of the image carrier are integrally incorporated in a cartridge container, A process cartridge that is detachable from the main body of the image forming apparatus is configured.
It is characterized by

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In addition, in each of the drawings, components denoted by the same reference numerals have similar configurations or actions, and repeated description thereof will be appropriately omitted.

<First Embodiment> FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
This is an electrophotographic laser printer, which is a vertical cross-sectional view showing a schematic configuration thereof. Note that the same components as those of the image forming apparatus of FIG. 8 described in the conventional example are denoted by the same reference numerals.

The image forming apparatus shown in FIG. 1 of the present embodiment includes a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") as an image bearing member. Photosensitive drum 1
In No. 0, an OPC (organic optical semiconductor) photosensitive layer is applied to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm over a longitudinal width of 250 mm. In addition, instead of OPC, a-Si,
CdS, Se or the like may be applied. The photosensitive drum 10 is
It is rotationally driven in the direction of arrow B1 by a driving means (not shown) at a process speed (peripheral speed) of 100 mm / sec. The photosensitive drum 10 is uniformly charged to a predetermined polarity and potential by the charging roller 11 that is brought into contact with the photosensitive drum 10 and rotates following the arrow C1.

The charging roller 11 as a charging means is a roller-shaped member having a diameter of 12 mm and an effective charging width of 23.
It is 5 mm. In addition, an elastic layer made of urethane rubber as the base layer 11b and a fluorine resin as the surface layer 11c is provided around the stainless steel cylinder as the core 11a. Instead of this, a metal such as aluminum or an aluminum alloy may be used as the material of the core metal 11a, and NB may be used as the base layer 11b of the elastic layer.
A rubber material such as R, EPDM, or silicone rubber may be used, or ether urethane, nylon, or the like may be used as the surface layer 11c of the elastic layer. The charging roller 11 is pressed against the surface of the photosensitive drum 10 with a predetermined contact pressure, and
A charging nip portion N1 is formed between 0 and 0. A charging bias applying power supply 24 is connected to the charging roller 11, and by this charging bias applying power supply 24, -100
A DC charging bias of 0 V is applied.

Next, an electrostatic latent image is formed on the surface of the photosensitive drum 10 by the exposure device 12 as an exposure means. A semiconductor laser (not shown) emits light according to an image signal corresponding to the input signal, the laser light is reflected by a polygon mirror (not shown) that rotates at high speed, and passes through an imaging lens group (not shown). Then, the photosensitive drum 10 is irradiated. Here, the effective exposure width in the main scanning direction by the exposure device 12 is 230 mm, and the toner application width (developer application width) and the maximum sheet passing width of the recording material P (direction orthogonal to the conveying direction) described later. Is wider than. The electrostatic latent image formed on the photosensitive drum 10 by the laser light irradiation is developed by the developing device 13 to be visualized as a toner image.

Now, the developing device 13 as the developing means will be described. In this embodiment, a non-magnetic one-component contact developing method is used as the developing method. Developing device 13
Includes a toner container 20. The toner container 20 is filled with 150 g of non-magnetic one-component toner. The toner supply roller 18 rotating in the direction of the arrow E1 is a sponge roller having a diameter of 16 mm in which urethane foam is provided around a cylindrical body made of metal such as aluminum, aluminum alloy, and stainless. The toner supply roller 18 and the developing roller 16 serving as a developer carrier come into contact with each other, and the toner is attached from the toner supply roller 18 to the developing roller 16, whereby the toner is supplied onto the developing roller 16.

The developing roller 16 is a roller-shaped member having a diameter of 16 mm, and has a multi-layered structure composed of urethane rubber as a base layer around a stainless steel cylindrical body and urethane rubber in which carbon is mixed as a surface layer thereon. did. Instead of this, a metal cylinder such as aluminum, aluminum alloy or stainless steel is used as the core metal, NBR, EPDM, silicone rubber, urethane rubber or other rubber material is used as the base layer of the elastic layer, and a surface layer is used. You may use ether urethane or nylon. Developing roller 16
Is driven in the direction of arrow D1 by a driving means (not shown).
It is rotationally driven at a peripheral speed (surface speed) of mm / sec.

Then, the toner on the developing roller 16 is regulated and charged by the developing blade 17 to an optimum layer thickness over the toner application width 215 mm. The developing blade 17 of the present embodiment is a straight-shaped phosphor bronze plate having spring elasticity, and a nylon surface is coated on the contact surface with the developing roller 16. Instead of this, the contact surface may have no coating material, a stainless steel plate may be used as the material of the plate, the shape of the tip of the plate may be L-shaped, or the developing blade 17 may be used. And developing roller 16
Instead of nylon, a rubber material or the like may be adhered or coated on the contact surface with the metal plate.

Then, a DC developing bias of -300 V is applied to the developing roller 16 by the developing bias applying power source 23, and the toner on the developing roller 16 is exposed at the developing nip portion N2 where the developing roller 16 and the photosensitive drum 10 are in contact with each other. It is attached to the electrostatic latent image on the drum 10 to develop the electrostatic latent image as a toner image.

On the other hand, the recording material P is fed from the paper feed cassette 37 in synchronization with the formation of the toner image on the photosensitive drum 10. The transfer roller 26 is brought into contact with the photosensitive drum 10 from below to form a transfer nip portion N3.
The transfer roller 26 is rotationally driven in the direction of arrow A1. A predetermined transfer bias is applied to the transfer roller 26 by a transfer bias applying power source (not shown). This allows
The toner image on the photosensitive drum 10 is transferred to the recording material P, and an unfixed image is formed on the surface of the recording material P.

The transfer material P after the toner image transfer is fixed by the fixing device 2.
It is transported to 7. The transfer material P is heated and pressurized here to fix the unfixed toner image on the surface, and then discharged onto the paper discharge tray 28. This completes the image formation.

The transfer residual toner remaining on the surface of the photosensitive drum 10 without being transferred to the recording material P during the transfer process is collected in the waste toner container 15 by the cleaning blade 14 as a cleaning means. As a result, the photosensitive drum 10 is cleaned, and the above-described image formation is repeated again.

Here, with respect to the operation from the start of rotation of the photosensitive drum to the start of image formation and the operation from the end of image formation to the stop of drum rotation in this embodiment, mainly referring to FIG.
A detailed description will be given with reference to FIG. 1 as appropriate.

First, regarding the operation from the start of rotation of the photosensitive drum to the start of image formation, the developing roller 16 is rotated simultaneously with the start of rotation of the photosensitive drum 10, and the charging roller 11 is rotated.
-1000 V charging bias is applied to the photosensitive drum 1
The surface potential of 0 is set to -500V, and +2 is applied to the developing roller 16.
A developing bias of 00V is applied (time T0). Then, at the timing when the surface of the photosensitive drum 10 charged to the surface potential of -500V by the charging roller 11 reaches the developing nip portion N2, the developing bias is changed from + 200V to -200V.
The voltage is changed to 300V (time T1), and then image formation is started (time T2). At this time, a mask is applied in the main scanning direction of the exposure device 12 according to the size of the recording material P so that the toner is not developed outside the range of the recording material P.

After the image formation is completed (time T
3) The application of the charging bias to the charging roller 11 is stopped (time T4). Then, at the timing when the portion to which the charging bias is not applied by the charging roller 11 reaches the exposure portion, the exposure device 12 performs the maximum exposure width exposure for exposing the entire effective exposure width (time T5). After that, a developing bias of +200 V is applied to the developing roller 16 at the timing when the portion to which the charging bias is not applied by the charging roller 11 reaches the developing nip portion N2 (time T6). When the maximum exposure width exposure reaches one round of the photosensitive drum, the rotation of the photosensitive drum 10 and the developing roller 16 is stopped, the maximum exposure width exposure is stopped, and the application of the developing bias is stopped (time T7).

Printing (image formation) by executing the above operation
As a result of the test, it was confirmed that the fog on the photosensitive drum 10 when the photosensitive drum 10 was started was eliminated, the transfer roller 26 was not stained, and the output recording material P was not stained. did it. It was also confirmed that the edge stains on the printed recording material P were eliminated, and that wasteful toner consumption was suppressed.

As described above, after the image formation is completed and before the rotation of the photosensitive drum is stopped, the maximum exposure width exposure for exposing the entire effective exposure width is performed, so that the backside stain of the recording material P does not occur and printing is performed. The edge stain of the recording material P can be suppressed, and wasteful toner consumption can be suppressed.

<Second Embodiment> In the present embodiment, the developing bias immediately after the photosensitive drum starts rotating and immediately before the photosensitive drum stops rotating, the charging bias application timing and the maximum exposure width exposure timing, the photosensitive drum, and the developing roller. The description is omitted for the image forming apparatus, since it is the same as the case of the above-described first embodiment except that the rotation timing of No. 1 is different.
FIG. 3 shows the photosensitive drum, the rotation of the developing roller, the charging of the developing roller, the application timing of the developing bias, and the exposure timing of the photosensitive drum between after the photosensitive drum starts rotating and before the image forming starts and after the image forming ends and the drum stops rotating. Will be described in detail mainly with reference to FIG.

First, regarding the period from the start of rotation of the photosensitive drum 10 to the start of image formation, the developing roller 16 is rotated at the same time as the start of rotation of the photosensitive drum 10, and a charging bias of -1000 V is applied to the charging roller 11. Then, the surface potential of the photosensitive drum 10 is set to -500V, and
Then, the maximum exposure width exposure for exposing the entire effective exposure width is performed, and a developing bias of +200 V is applied to the developing roller 16 (time T10). Then, at the timing when the photosensitive drum 10 charged to the surface potential of -500V by the charging roller 11 reaches the exposure portion, the exposure device 12 stops the maximum exposure width exposure (time T11). And
At the timing when the surface of the photosensitive drum 10 charged to the surface potential of -500V by the charging roller 11 reaches the developing nip portion N2, the developing bias is changed from + 200V to -30.
The voltage is changed to 0V (time T12), and then image formation is started (time T13). At this time, a mask is applied in the main scanning direction of the exposure device 12 according to the size of the recording material P so that the toner is not developed outside the range of the recording material P.

After the image formation is completed (time T1
4) Stop applying the charging bias to the charging roller 11 (time T15). Then, at the timing when the portion to which the charging bias is not applied by the charging roller 11 reaches the exposure portion, the exposure device 12 performs the maximum exposure width exposure (time T16). Then, at the timing when the portion to which the charging bias is not applied by the charging roller 11 reaches the developing nip portion N2, the photosensitive drum 10,
The rotation of the developing roller 16 is stopped, and the maximum exposure width exposure and the application of the developing bias are also stopped (time T17).

Printing by performing the above operations (image formation)
As a result of the test, it was confirmed that the fog on the photosensitive drum 10 when the photosensitive drum 10 was started was eliminated, the transfer roller 26 was not stained, and the output recording material P was not stained. did it. It was also confirmed that the edge stains on the printed recording material P were eliminated, and that wasteful toner consumption was suppressed.

As described above, the maximum exposure width exposure for exposing the entire effective exposure width is performed immediately after the rotation of the photosensitive drum before the image formation is started and before the rotation of the photosensitive drum is stopped after the image formation is completed. It was possible to suppress the edge stain of the printed recording material, and to suppress the wasteful toner consumption. Further, the number of rotations of the photosensitive drum can be reduced as compared with the case of the first embodiment.

<Third Embodiment> In this embodiment, an example in which the present invention is applied to a color image forming apparatus will be described.

FIG. 4 is a vertical sectional view of a color image forming apparatus. FIG. 5 is a vertical sectional view of the developing device 13C for cyan. The same components as those of the image forming apparatus of FIG. 9 described in the conventional example are designated by the same reference numerals.

The image forming apparatus according to the present embodiment has four sets of image forming units C, Y and M, which are arranged in parallel along the intermediate transfer belt 30 as an intermediate transfer member, for cyan, yellow, magenta and black. , Bk, a so-called tandem full-color printer. In the present embodiment, a photosensitive drum as an image carrier, a charging roller as a charging unit, a developing device as a developing unit, and a cleaning blade as a cleaning unit are integrally incorporated in a cartridge container. , The process cartridge 2 which is detachable from the image forming apparatus main body 1
C, 2Y, 2M, and 2Bk are configured.

The image forming apparatus shown in FIG. 4 serves as an image bearing member in each of the first, second, third and fourth image forming portions for forming images of cyan, yellow, magenta and black. Photosensitive drums 10C, 10Y, 10M, 10
It has Bk. Photosensitive drums 10C, 10Y, 10
In M and 10Bk, an OPC (organic optical semiconductor) photosensitive layer is applied to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm over a longitudinal width of 250 mm. In addition, instead of OPC,
You may apply a-Si, CdS, Se, etc. The photosensitive drums 10C, 10Y, 10M, and 10Bk are rotationally driven in the arrow direction at a process speed (peripheral speed) of 100 mm / sec by a driving unit (not shown). Photosensitive drum 1
0 is a charging roller 11C, 11Y, 1 which is in contact with the photosensitive drum 10 and is driven to rotate in the direction of arrow C2 (see FIG. 5)
By 1M and 11Bk, it is uniformly charged to a predetermined polarity and potential.

Charging rollers 11C, 11Y, 11M, 11
Bk is a roller-shaped member having a diameter of 12 mm and an effective charging width of 235 mm. In addition, a multilayer structure is provided in which a urethane rubber is provided as a base layer and an elastic layer made of a fluorine-based resin is provided as a surface layer around a stainless steel cylinder as a core. A metal such as aluminum or an aluminum alloy may be used as the material of the core metal, a rubber material such as NBR, EPDM or silicone rubber may be used as the base layer of the elastic layer, and ether may be used as the surface layer of the elastic layer. Urethane or nylon may be used.

The same charging bias applying power source (not shown) is applied to each of the charging rollers 11C, 11Y, 11M and 11Bk for forming a cyan image, forming a yellow image, forming a magenta image and forming a black image. ) Is connected,
A predetermined charging bias is applied. Here, in the present embodiment, cyan, yellow, magenta,
Black photosensitive drums 10C, 10Y, 10M, 10
The applied voltage value of the charging bias applying power source is set to Bk so that the surface potential on the photosensitive drum becomes −500 V, and the charging bias applying power source has a direct current of −1000 V.
Was applied. In this embodiment, the DC bias is used as the charging bias, but a bias in which an AC component is superimposed on a DC component may be used as the charging bias.

Next, the photosensitive drums 10C, 10Y, and
Exposure devices 12C, 12Y, 1 are provided on the surfaces of 10M and 10Bk.
An electrostatic latent image is formed by 2M and 12Bk. A semiconductor laser (not shown) emits light according to an image signal that is separated into colors according to an input signal, and the laser light is reflected by a polygon mirror (not shown) that rotates at a high speed to form an imaging lens. Each of the photosensitive drums 10C and 10C is passed through (not shown).
It is designed to irradiate Y, 10M, and 10Bk. Here, the effective exposure width is 230 mm, which is wider than the toner application width described later. The semiconductor lasers are connected to the photosensitive drums 10C, 10Y, 10M, 10
The laser light amount is set so that the potential of the image portion on Bk becomes −100 V, and each semiconductor laser has 0.5 μJ /
The light quantity was set to cm ² . The electrostatic latent images formed on the photosensitive drums 10C, 10Y, 10M, and 10Bk by laser light irradiation are transferred to the developing devices 13C and 13Y,
By being developed by 13M and 13Bk, it is visualized as a toner image.

Here, the developing devices 13C, 13Y, 13
M and 13Bk will be described using a cyan developing device as an example. The other yellow, magenta, and black developing devices 13Y, 13M, and 13Bk have the same configuration. In this embodiment, a non-magnetic one-component contact developing method is used as the developing method. 20C is a toner container,
The cyan toner 21C in the toner container 20C is a non-magnetic one-component toner, and is filled with 200 g. The cyan toner 21C is indicated by the arrow F on the toner carrying sheet 19C.
By rotating in the direction of 2, the toner supply roller 1
Sent to 8C.

The toner supply roller 18C is rotating in the direction of arrow E2. The toner supply roller 18C is an elastic roller having a diameter of 14 mm in which urethane foam is provided around a cylindrical body made of metal such as aluminum, aluminum alloy, and stainless. The toner supply roller 18C and the developing roller 16C come into contact with each other, and the toner is attached from the toner supply roller 18C to the developing roller 16C, whereby the toner is supplied onto the developing roller 16C.

The developing roller 16C is rotated at 170 mm / sec in the direction of arrow D2 by a driving means (not shown). The developing roller 16C has a diameter of 14 mm and has a multi-layered structure composed of urethane rubber as a base layer around a stainless steel cylindrical body and urethane rubber in which carbon is mixed as a surface layer on the base layer. ,
A cylindrical body made of a metal such as aluminum, an aluminum alloy, or stainless is used as the core metal, and the base layer of the elastic layer is NBR,
It may be made of a rubber material such as EPDM, silicone rubber or urethane rubber, and the surface layer may be made of ether urethane or nylon.

Then, the toner on the developing roller 16C is regulated and charged by the developing blade 17C to the optimum layer thickness over the toner application width 215 mm. The developing blade 17C of the present embodiment is a straight-shaped phosphor bronze plate having spring elasticity, but is not limited to this, and a stainless plate may be used as the material, or the shape may be an L-shape, and A rubber material, nylon, or the like may be adhered or coated on a metal plate on the contact surface between the blade and the developing roller.

A developing bias applying power source (not shown)
A developing bias of -400 V is applied to the developing roller 16C by the developing roller 16C, and the toner on the developing roller 16C is attached to the electrostatic latent image on the photosensitive drum 10C at the developing nip portion where the developing roller 16C and the photosensitive drum 10C contact each other. The electrostatic latent image is developed as a toner image.

As shown in FIG. 4, each photosensitive drum 10C,
Primary transfer rollers 26C, 26Y, and 26 that face the 10Y, 10M, and 10Bk with the intermediate transfer belt 30 interposed therebetween.
M, 26Bk are installed, and each photosensitive drum 10C,
The toner images of the respective colors on 10Y, 10M, and 10Bk are transferred to the intermediate transfer belt 30 by applying a predetermined primary transfer bias to the primary transfer rollers 26C, 26Y, 26M, and 26Bk, and a full-color image is obtained. Is formed.

The intermediate transfer belt 30 is 100 mm / sec.
The driving device (not shown) moves in the direction of arrow A2 at the process speed of. Then, the secondary transfer roller 32
By applying a predetermined secondary transfer bias by a secondary transfer bias applying power source (not shown), the full-color image on the intermediate transfer belt 30 is transferred to the recording material P and is conveyed to the fixing device 35 as it is. . In the fixing device 35, the unfixed image is fixed on the recording material P, and then the recording material P having the fixed image is discharged onto the paper discharge tray 36, and the image formation is completed.

On the other hand, during transfer, the photosensitive drums 10C, 10Y, 10M, 10Bk are not transferred to the intermediate transfer belt 30.
The transfer residual toner remaining on the cleaning blade 14
Waste toner container 1 by C, 14Y, 14M, 14Bk
5C, 15Y, 15M, and 15Bk are collected, and the photosensitive drums 10C, 10Y, 10M, and 10Bk are cleaned. The transfer residual toner remaining on the intermediate transfer belt 30 after the secondary transfer is collected by the intermediate transfer belt cleaning blade 33, and the waste toner is conveyed to the intermediate transfer belt waste toner container 34, and the above image formation is repeated again. .

Here, with respect to the operation from the start of the rotation of the photosensitive drum to the start of the image formation and the operation from the end of the image formation to the stop of the drum rotation in the present embodiment, mainly referring to FIG.
Details will be described with reference to FIG. 4 as appropriate. The present embodiment deals with the case of a color image forming apparatus, but is basically the same as that of the first embodiment.

First, regarding the operation from the start of rotation of the photosensitive drum to the start of image formation, the photosensitive drums 10C and 10C will be described.
At the same time when Y, 10M, and 10Bk start to rotate, the developing roller 1
6C, 16Y, 16M, 16Bk and intermediate transfer belt 3
0 to rotate the charging rollers 11C, 11Y, 11M, 1
The surface potential of the photosensitive drums 10C, 10Y, 10M, and 10Bk is set to -5 by applying a charging bias of -1000V to 1Bk.
00V, developing rollers 16C, 16Y, 16M, 16
A development bias of +200 V is applied to Bk (time T2
0).

Then, the charging rollers 11C, 11Y, 11
The developing bias is changed from + 200V to -300V at the timing when the surfaces of the photosensitive drums 10C, 10Y, 10M, 10Bk charged to the surface potential of -500V by M and 11Bk reach the developing nip portion (time T21).
After that, cyan image formation is started (time T22),
Images of yellow, magenta, and black are sequentially formed (time T22 to T23). At this time, a mask is applied in the main scanning direction of the exposure device 12 according to the size of the recording material P so that the toner is not developed outside the range of the recording material P.

After the image formation is completed (time T2
3) The application of the charging bias to the charging rollers 11C, 11Y, 11M and 11Bk is stopped (time T24). Then, the exposure devices 12C, 12Y, and 1 are arranged at the timing when the portions to which the charging bias is not applied by the charging rollers 11C, 11Y, 11M, and 11Bk reach the exposure portion.
The maximum exposure width exposure for exposing the entire effective exposure width is performed by 2M and 12Bk (time T25). After that, the developing rollers 16C, 16Y, 16Y are fed at the timing when the portion to which the charging bias is not applied by the charging rollers 11C, 11Y, 11M, 11Bk reaches the developing nip portion.
A developing bias of +200 V is applied to M and 16 Bk (time T26). When the maximum exposure width exposure reaches one round of the photosensitive drum, the photosensitive drums 10C, 10Y, 10
M, 10Bk and developing rollers 16C, 16Y, 16M,
The rotation of 16Bk and the intermediate transfer belt 30 is stopped, the maximum exposure width exposure is stopped, and the application of the developing bias is also stopped (time T27).

When the printing test was performed by executing the above operation, the photosensitive drums 10C, 10Y, 10M, 10B
There is no fog on the photosensitive drum when k starts,
The toner did not adhere to the intermediate transfer belt 30, the secondary transfer roller 32 did not stain, and the output recording material P did not stain the back. In addition, the edge stains generated at the edges of the printed recording material P are eliminated. Further, since the toner on the end portion of the intermediate transfer belt cleaning blade 33 is reduced, the cleaning failure of the intermediate transfer belt cleaning blade 33 is eliminated, and the image contamination due to the cleaning failure occurring on the second and third sheets can be eliminated. It was Further, wasteful toner consumption can be suppressed.

As described above, after the image formation is completed and before the rotation of the photosensitive drum is stopped, the maximum exposure width exposure for exposing the entire effective exposure width is performed, so that the recording material is printed without back stain. It is possible to suppress the edge stains generated at the end portions of the recording material, prevent image stains due to poor cleaning of the intermediate transfer belt cleaning blade, and reduce wasteful toner consumption.

<Embodiment 4> In the present embodiment, immediately after the start of rotation of the photosensitive drum and immediately before stop of rotation of the photosensitive drum, the application timing of the developing bias and the charging bias, the timing of performing the maximum exposure width exposure, the photosensitive drum, the developing roller, The image forming apparatus is the same as the above-described third embodiment except that the rotation timing of the intermediate transfer belt is different. Therefore, the description of the image forming apparatus will be omitted and the image forming apparatus will be described after the rotation of the photosensitive drum is started and before the image forming is started. Regarding the intermediate transfer belt, the photosensitive drum, the rotation of the developing roller, the charging, the application timing of the developing bias, and the photosensitive drum exposure timing between after and during the rotation stop of the drum, detailed description will be given mainly with reference to FIG. To do.

First, the photosensitive drums 10C, 10Y and 10
Regarding the period from the start of rotation of M and 10Bk to the start of image formation, the photosensitive drums 10C, 10Y, 10M, 1
Simultaneously with the start of rotation of 0Bk, the developing roller 16C and the intermediate transfer belt 30 are rotated, and the charging rollers 11C, 11
A charging bias of -1000V is applied to Y, 11M, and 11Bk, and the photosensitive drums 10C, 10Y, 10M, and 10Bk are applied.
Surface potential of -500V, and the photosensitive drums 10C, 1
Exposure devices 12C and 12 for 0Y, 10M and 10Bk
The maximum exposure width exposure for exposing the entire effective exposure width is performed by Y, 12M, and 12Bk, and the developing rollers 16C and 16C are used.
A developing bias of +200 V is applied to Y, 16M, and 16Bk (time T30).

The charging rollers 11C, 11Y, 11
At the timing when the photosensitive drums 10C, 10Y, 10M, and 10Bk charged to the surface potential of −500V by M and 11Bk reach the exposure unit, the exposure devices 12C and 12Y,
12M and 12Bk stop the maximum exposure width exposure (time T3
1). Then, the charging rollers 11C, 11Y, 11M, 1
When the surface of the photosensitive drum 10C, 10Y, 10M, 10Bk charged to the surface potential of -500V by 1Bk reaches the developing nip portion, the developing bias is set to +2.
The voltage is changed from 00V to -300V (time T32), then the cyan image formation is started (time T33), and the yellow, magenta, and black image formations are sequentially performed (time T33 to T34). At this time, a mask is applied in the main scanning direction of the exposure device 12 according to the size of the recording material P so that the toner is not developed outside the range of the recording material P.

After the black image formation is completed (time T34), the charging rollers 11C, 11Y and 11 are charged.
The application of the charging bias to M and 11 Bk is stopped (time T3
5). Then, the charging rollers 11C, 11Y, 11M, 1
At the timing when the portion to which the charging bias is not applied by 1Bk reaches the exposure unit, the exposure device 12C,
Maximum exposure width exposure is performed with 12Y, 12M, and 12Bk (time T36).

After that, the charging rollers 11C, 11Y, 11
Rotation of the photosensitive drums 10C, 10Y, 10M, 10Bk, the developing rollers 16C, 16Y, 16M, 16Bk and the intermediate transfer belt 30 at the timing when the portion to which the charging bias is not applied by M and 11Bk reaches the developing nip portion. To stop exposure of the maximum exposure width and application of the developing bias (time T37).

When the printing test was performed by executing the above operation, the photosensitive drums 10C, 10Y, 10M, 10B
There is no fog on the photosensitive drum when k starts,
The toner did not adhere to the intermediate transfer belt 30, the secondary transfer roller 32 did not stain, and the output recording material P did not stain the back. Further, the edge stains generated on the edges of the printed recording material P are eliminated. Further, since the toner on the end portion of the intermediate transfer belt cleaning blade 33 is reduced, the cleaning failure of the intermediate transfer belt cleaning blade 33 is eliminated, and the image contamination due to the cleaning failure occurring on the second and third sheets can be eliminated. It was In addition, wasteful toner consumption could be suppressed.

As described above, the maximum exposure width exposure for exposing the entire effective exposure width is performed immediately after the rotation of the photosensitive drum before the start of image formation and before the stop of the rotation of the photosensitive drum after the end of image formation. It is possible to prevent edge stains on the edges of the printed recording material without causing stains on the back side of the print medium, to prevent image stains due to poor cleaning of the intermediate transfer belt cleaning blade, and to suppress wasteful toner consumption. did it.

[0081]

As described above, according to the present invention,
The maximum exposure width exposure that exposes the image carrier on the effective exposure width by making the effective exposure width wider than the toner application width,
When the rotation of the image carrier is stopped after the image formation is completed, or immediately after the rotation of the image carrier is started before the image formation is started and before the rotation of the photosensitive drum is stopped after the image formation is completed, back stain of the recording material may occur. In addition, it is possible to suppress the edge contamination of the printed recording material at the end portion, and it is possible to suppress wasteful toner consumption.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a timing chart showing operations of the rotation of the photosensitive drum, the rotation of the developing roller, the charging bias, the exposure device, and the developing bias from the start of the rotation of the photosensitive drum to the end of the rotation of the photosensitive drum in the first embodiment.

FIG. 3 is a timing chart showing operations of the rotation of the photosensitive drum, the rotation of the developing roller, the charging bias, the exposure device, and the developing bias from the start of the rotation of the photosensitive drum to the end of the rotation of the photosensitive drum according to the second embodiment.

FIG. 4 is a vertical sectional view showing a schematic configuration of a full-color image forming apparatus according to a third embodiment.

FIG. 5 is a vertical sectional view showing a schematic configuration of a cyan developing device according to a third embodiment.

FIG. 6 is a timing chart showing the operations of the rotation of the intermediate transfer belt, the rotation of the photosensitive drum, the rotation of the developing roller, the charging bias, the exposure device, and the developing bias from the start of the rotation of the photosensitive drum to the end of the rotation of the photosensitive drum in the third embodiment. It is a chart.

FIG. 7 is a timing chart showing the operations of the rotation of the intermediate transfer belt, the rotation of the photosensitive drum, the rotation of the developing roller, the charging bias, the exposure device, and the developing bias from the start of the rotation of the photosensitive drum to the end of the rotation of the photosensitive drum in the fourth embodiment. It is a chart.

FIG. 8 is a vertical sectional view showing a schematic configuration of a conventional image forming apparatus.

FIG. 9 is a vertical cross-sectional view showing a schematic configuration of a conventional full-color image forming apparatus.

FIG. 10 is a vertical cross-sectional view showing a schematic configuration of a conventional cyan developing device.

[Explanation of symbols]

1 image forming apparatus main body 10, 10C, 10Y, 10M, 10Bk image carrier (photosensitive drum) 11, 11C, 11Y, 11M, 11Bk charging means (contact charging member, charging roller) 12, 12C, 12Y, 12M, 12Bk exposure Means (exposure device) 13, 13C, 13Y, 13M, 13Bk Developing means (developing device) 14, 14C Cleaning means (cleaning blade) 16, 16C Contact developing member (developing roller)

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H027 ED04 ED06 EE01 EF07 EF11                 2H076 AB05 AB12 AB67 EA01                 2H200 FA08 GA03 GA12 GA23 GA34                       GA44 GA47 GB12 GB25 GB41                       HA02 HA28 HB12 HB20 HB22                       JA02 JB10 JC03 LA11 LA12                       LA13 LA38

Claims (7)

[Claims] 1. A rotatable image carrier, charging means for charging the surface of the image carrier, exposure means for forming an electrostatic latent image on the surface of the image carrier after charging, and the electrostatic latent image. In an image forming apparatus provided with a developing unit that develops a developer image by adhering a developer to, before stopping rotation of the image carrier after image formation,
The image carrier is exposed for at least one revolution in a state in which the exposure width in the main scanning direction on the image carrier by the exposing unit is wider than the developer coating width on the image carrier by the developing unit. An image forming apparatus characterized by the above. 2. A rotatable image carrier, charging means for charging the surface of the image carrier, exposure means for forming an electrostatic latent image on the surface of the image carrier after charging, and the electrostatic latent image. An image forming apparatus comprising: a developing unit configured to develop a developer image by depositing a developer on the image carrier at the start of rotation of the image carrier; In a state in which the exposure width in the main scanning direction on the image carrier by the exposure unit is widened, the image from the portion of the image carrier exposed by the exposure unit with respect to the rotation direction of the image carrier. By exposing up to a portion of the carrier on which the developer is attached by the developing means, before the rotation of the image carrier is stopped after the image formation,
At least with respect to the rotation direction of the image carrier, with the exposure width in the main scanning direction on the image carrier by the exposing device being wider than the developer coating width on the image carrier by the developing device, An image forming apparatus, wherein a portion of the image carrier that is charged by the charging unit to a portion of the image carrier that is exposed by the exposing unit is exposed. 3. The image forming apparatus according to claim 1, wherein during the image formation, the exposing unit does not perform the exposure in the main scanning direction which is equal to or larger than the maximum sheet passing width of the recording material. 4. Before the rotation of the image bearing member is stopped and before the rotation of the image bearing member is started, the amount of the developer applied on the image bearing member by the exposing unit is larger than the developer coating width of the developing unit on the image bearing member. The part that widened the exposure width in the main scanning direction of
The image formation according to any one of claims 1 to 3, wherein the charging unit is a part to which a charging bias is not applied or a part to which a charging bias equal to or lower than a discharge start voltage is applied. apparatus. 5. The image forming apparatus according to claim 1, wherein the charging unit has a contact charging member that is in contact with the surface of the image carrier. 6. The developing unit has a contact developing member that is in contact with the surface of the image bearing member, and develops with a non-magnetic one-component developer. The image forming apparatus according to item 1. 7. An image carrier, the charging device, the developing device, and a cleaning device for cleaning the surface of the image carrier are integrally incorporated in a cartridge container, and are attached to and detached from the main body of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus comprises a flexible process cartridge.