JP5417118B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that outputs a toner image on a photosensitive drum to an intermediate transfer member or paper.

  In this type of image forming apparatus, an electrophotographic system is used. When the charger precharges the photosensitive drum and the exposure unit irradiates light on the surface of the photosensitive drum, an electrostatic latent image is formed on the surface. It is formed. Further, the developing device carries toner, and when a developing bias voltage is applied, the toner is excited and adheres to the electrostatic latent image, and a toner image is formed on the surface of the photosensitive drum. Then, the toner image is transferred and fixed on a sheet or a sheet via an intermediate transfer member.

Here, a structure in which the surface of the photosensitive drum is irradiated with static elimination light is known (see, for example, Patent Documents 1 and 2). This is because a memory image is generated unless the exposure history of the photosensitive drum is eliminated. Therefore, the charge eliminating unit irradiates the charge eliminating light before charging, and removes the charge (residual charge) remaining on the surface of the photosensitive drum after transfer.
Note that a small amount of toner may remain on the surface of the photosensitive drum without being transferred to the sheet, and it is necessary to remove it until the next image formation. For this reason, the documents 1 and 2 also disclose that the surface of the photosensitive drum is cleaned with a cleaning blade.

JP 2001-34129 A JP 2006-234882 A

  By the way, on the surface of the photosensitive drum, the outer region of the sheet passing width in the rotational axis direction of the photosensitive drum is a range where no image is formed. This is because the transfer surface of the intermediate transfer member does not contact the paper. On the other hand, in order to enable toner images to be formed on both the left and right sides of the paper, the development width needs to be set wider than the paper passage width. The charging width is set wider than the developing width. This is because if the charge width is narrower than the development width, the toner continues to adhere to the outer region of the charge width.

  That is, although the toner (including the external additive) is directed to the inner region of the developing width by applying the developing bias voltage, the region corresponds to the inner region of the charging width. The toner itself does not adhere to the surface of the photosensitive drum and returns to the developing unit. On the other hand, the external additive itself is detached from the toner and left in the region. Thereafter, only this external additive is transferred from the surface of the photosensitive drum to the transfer surface of the intermediate transfer member or deposited on the edge of the cleaning blade.

  Here, the state of only the external additive transferred to the former transfer surface is difficult to clean with the cleaning device for the intermediate transfer member. In addition, a slight difference in linear velocity between the intermediate transfer member and the photosensitive drum is a region outside the above-described sheet passing width in the surface of the photosensitive drum that is in contact with the intermediate transfer member. The inner region of the development width is polished with an external additive. Further, there is a problem that the area is polished with an external additive by the latter cleaning blade, and the amount of wear of the photosensitive drum in this area shortens the life of the photosensitive drum.

In solving this problem, even if the conventional technology described above is applied, the amount of static elimination light with respect to the outer region of the sheet passing width is only increased compared to the inner region of the sheet passing width. The amount of discharge at the time increases, the surface of the photosensitive drum deteriorates, and wear of the outer region of the sheet passing width is further promoted.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of solving the above-described problems and suppressing the wear of the outer region of the sheet passing width of the photosensitive drum.

A first invention for achieving the above object is to form a toner image by developing a latent image formed on the surface of a photosensitive drum through charging or exposure with toner containing an external additive. Is an image forming apparatus for transferring the image to a transfer material.
Before the charging, the surface of the photosensitive drum is irradiated with static elimination light, and after the transfer, the static elimination unit for removing the charge remaining on the surface of the photosensitive drum, and the rotational axis direction of the photosensitive drum. Discharging intensity adjusting means is provided for reducing the amount of the neutralizing light in the outer region of the sheet passing width and the inner region of the developing width as compared with the inner region of the sheet passing width.

According to the first invention, a toner image obtained by developing the latent image with toner is formed on the surface of the photosensitive drum by driving the photosensitive drum, and the toner image is transferred to a transfer material.
The neutralization unit irradiates the surface of the photosensitive drum with neutralizing light before charging, and removes charges (residual charges) remaining on the surface of the photosensitive drum after transfer.

  Here, assuming that the transfer material is an intermediate transfer belt, the toner and the external additive in the inner region of the sheet passing width will be secondarily transferred to the sheet, so that the transfer surface of the transfer belt is transferred to the transfer belt. Does not remain. Even when a developing bias voltage is applied, the toner itself in the outer region of the sheet passing width and the inner region of the developing width does not adhere to the surface of the photosensitive drum. On the other hand, the external additive itself is detached from the toner and left in the region, and only this external additive is transferred from the surface of the photosensitive drum to the transfer surface of the transfer belt. This phenomenon can also be seen from the appearance of a white band along the circumferential direction on the transfer surface.

The portion that appears in the white band has high polishing performance, and the inner region of the developing width that is the outer region of the sheet passing width is polished more than the inner region of the sheet passing width.
However, according to the present invention, the static elimination intensity adjusting means determines the amount of static elimination light for the outer area of the sheet passing width and the inner area of the developing width on the surface of the photosensitive drum with respect to the inner area of the sheet passing width. The surface potential in the outer region of the sheet passing width and in the inner region of the developing width is set higher than the surface potential of the inner region of the sheet passing width.

  In other words, in the area outside the sheet passing width and inside the development width, the current flowing from the charging to the photosensitive drum decreases when the surface potential is increased during the next image formation, and the discharge amount (discharge) during charging is reduced. Less energy) than the inner area of the sheet passing width. Therefore, as a result of suppressing the deterioration of the surface of the photosensitive drum due to the generation of the discharge energy, the surface of the photosensitive drum becomes difficult to be polished with the external additive, and the life of the photosensitive drum can be extended.

According to a second aspect of the present invention, in the configuration of the first aspect of the invention, the neutralization unit irradiates the neutralization light to the outer region of the sheet passing width and the inner region of the development width.
According to the second aspect of the invention, in addition to the operation of the first aspect, the static eliminator unit completely eliminates the static elimination light with respect to the inner area of the developing width, which is the outer area of the sheet passing width on the surface of the photosensitive drum. Rather than not irradiating, the irradiation is performed while weakening the amount of light relative to the inner area of the sheet passing width. Therefore, it is possible to secure a necessary amount of light in the inner region of the sheet passing width, and the image quality is not impaired.

In addition, there is a concern that the reverse charge toner is developed if no neutralizing light is irradiated. However, since the irradiation is performed with a low amount of light as described above, the surface potential of the region does not become excessively high. In-machine contamination due to development of charged toner can also be prevented.
Furthermore, since the portion where the amount of the neutralizing light is weakened is an area outside the sheet passing width, there is no concern about the generation of a memory image.

According to a third aspect of the present invention, in the configuration of the first or second aspect of the present invention, the apparatus further comprises a charger that contacts and charges the surface of the photosensitive drum.
According to the third invention, in addition to the effects of the first and second inventions, the contact charging type charger does not generate ozone or nitrogen oxide as compared with the case of the corona discharge type charging device. Therefore, although the image quality can be improved, the voltage is also applied in direct contact with the portion of the surface of the photosensitive drum that is polished with the external additive. In other words, the leak does not endure the voltage and penetrates the photosensitive film at the location, the current escapes outward, the central portion of the surface is not charged, and an abnormal image such as a horizontal streak is caused. However, if the above-described static elimination intensity adjusting means is provided, the leakage can be avoided even if a contact charging type charger is used.

According to a fourth invention, in any one of the first to third inventions, the photosensitive drum is a photosensitive drum having an organic photosensitive layer on a surface thereof.
According to the fourth invention, in addition to the effects of the first to third inventions, the surface of the photosensitive drum having an organic photosensitive layer is particularly easily scraped, and polishing with an external additive is performed in the photosensitive drum. Although there is a concern that the drum may be greatly affected, if the static elimination intensity adjusting means is provided, the characteristics of the photosensitive drum can be maintained over a long period of time, and a particularly remarkable effect is achieved.

According to a fifth aspect of the present invention, in the configuration of any one of the first to fourth aspects, the static elimination intensity adjusting means is a light shielding member that covers the static elimination unit for the inner area of the developing width and the outer area of the sheet passing width. Features.
According to the fifth invention, in addition to the effects of the first to fourth inventions, the light shielding member reaches the inner area of the developing width and the outer area of the sheet passing width on the surface of the photosensitive drum. Since the amount of static elimination light is weakened by shielding, the generation of discharge energy can be reliably reduced.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the static elimination unit includes a plurality of light sources having substantially the same light emission characteristics along the rotation axis of the photosensitive drum. The intensity adjusting means is characterized in that the interval between the light sources that are the outer region of the sheet passing width and the inner region of the developing width is wider than that of the inner region of the sheet passing width.
According to the sixth aspect of the invention, in addition to the effects of the first to fifth aspects of the invention, the interval between the light sources that are the outer area of the sheet passing width and the inner area of the developing width is increased on the surface of the photosensitive drum. The number of the photosensitive drums per unit area is reduced to reduce the amount of static elimination light reaching the area, and in this case as well, the generation of discharge energy can be reliably reduced.

According to a seventh invention, in any one of the first to fifth inventions, the static elimination unit includes a plurality of light sources along the rotation axis of the photosensitive drum, and the static elimination intensity adjusting means has a sheet passing width. The light emission characteristic of the light source that is the outer area and that is the inner area of the development width is lower than that of the inner area of the sheet passing width.
According to the seventh invention, in addition to the effects of the first to fifth inventions, the light emission characteristics of the light source that is the outer region of the sheet passing width and the inner region of the developing width of the surface of the photosensitive drum are further provided. Even if the same current is applied, the light quantity of the static elimination light reaching the region is reduced by reducing the light quantity. In this case, the generation of discharge energy can be surely reduced.

  According to the present invention, an image forming apparatus capable of preventing excessive polishing of the photosensitive drum in the region is provided because the amount of charge removal light is weakened with respect to the region outside the sheet passing width and the region inside the developing width. Can do.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is a cross-sectional view around the image forming unit in FIG. 1. FIG. 3 is an explanatory diagram of widths of a photosensitive drum, a charging roller, and a developing roller in FIG. 2. FIG. 3 is a plan view of the eraser of FIG. 2. (A) is a top view of the eraser of 2nd Example, (b) is a top view of the eraser of 3rd Example. It is a figure explaining the relationship between static elimination energy and charging current. It is explanatory drawing of an experimental result.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 schematically shows the structure of a printer 1 capable of color printing, which is an example of an image forming apparatus. The cross section shown in the figure is seen from the left side of the printer 1. For this reason, the front surface of the printer 1 is positioned on the right side and the rear surface of the printer 1 is positioned on the left side.

As shown in the figure, a paper discharge tray 36 is provided above the apparatus main body 2 of the printer 1, and a plurality of operation keys used for various operations of the user and various types are provided near the tray 36. A front cover 5 on which a screen for displaying information is arranged is provided.
Further, a sheet feeding cassette 4 is disposed below the apparatus main body 2, and sheets of sheets are stored in the storage unit 40 in a stacked state. As shown in the figure, a roller 46 is provided on the upper right side of the accommodating portion 40.

Then, the paper is sent toward the upper right of the cassette 4 in the figure, and the sent paper is conveyed upward along the front surface of the printer 1 inside the apparatus main body 2.
Further, the cassette 4 is configured to be able to be pulled out toward the front side of the printer 1, that is, in the right direction in FIG. Can be replaced with another type of paper.

Inside the apparatus main body 2, a conveyance roller 10, a registration roller 14, an image forming unit 16, and a secondary transfer unit 30 are sequentially arranged on the downstream side when viewed in the sheet conveyance direction from the cassette 4.
The image forming unit 16 includes four image forming units 17 arranged in parallel, and each unit 17 is provided with a photosensitive drum 18 (FIGS. 1 and 2). The photosensitive drum 18 is rotatably installed and is driven clockwise in FIGS. 1 and 2 by a driving motor (not shown).

The photosensitive drum 18 of the present embodiment is an OPC drum formed with a diameter of, for example, 30 mm and having an organic photosensitive layer on the surface (OPC: Organic Photoconductor).
An exposure unit 15 is provided between the photosensitive drum 18 and the cassette 4 (FIG. 1), and laser light is emitted from the exposure unit 15 toward the photosensitive drums 18 respectively. . As shown in FIGS. 1 and 2, a charger 20, a developing device 24, an intermediate transfer roller 13, and a cleaning unit 50 are provided at appropriate positions around each photosensitive drum 18.

  As shown in FIG. 2, the charger 20 is located in the lower part of the image forming unit 17, and in the casing 70 opened upward, the charging roller 21 in contact with the photosensitive drum 18, and the charging roller 21. A rubbing roller 22 having a brush for cleaning the surface by polishing rubbing is provided to charge the surface of the photosensitive drum 18. The charging roller 21 is made of, for example, epichlorohydrin rubber and has a diameter of φ12 mm.

The developing device 24 is disposed on the left side of the unit 17 and has a developing roller 25 facing the photosensitive drum 18. The roller 25 is driven counterclockwise in the figure by a drive motor (not shown).
The reference numeral 26 in FIG. 2 is a gap regulating roller. The rollers 26 are provided at both ends of the developing roller 25 (FIG. 3), and the gap between the developing roller 25 and the photosensitive drum 18 is set with the photosensitive drum 18.

  The image forming unit 16 includes a rubber intermediate transfer belt (transfer material) 12, and the transfer belt 12 is disposed above each photosensitive drum 18, and four pieces are provided between the transfer belt 12 and the tray 36. The toner container 23 is disposed (FIG. 1). These containers 23 are arranged in the order of magenta, cyan, yellow, and black from the back side to the front side of the printer 1, and the capacity of the black container is configured to be the largest. .

The secondary transfer unit 30 includes a transfer roller 31, and the transfer roller 31 is configured to be able to press against the transfer belt 12 from obliquely below.
The transfer belt 12 and the transfer roller 31 use toner supplied from each of the four toner containers 23 to form a nip portion for transferring a toner image onto a sheet.

In addition, a fixing unit 32, a discharge branching unit 34, and a discharge tray 36 are sequentially arranged on the downstream side of the secondary transfer unit 30 when viewed in the sheet conveyance direction.
In the present embodiment, a duplex printing unit 38 is formed between the secondary transfer unit 30 and the manual feed tray 3. The duplex printing unit 38 branches from the discharge branching portion 34 on the front side of the apparatus main body 2 and extends downward, and is connected to the upstream side of the registration roller 14.

  Here, a small amount of external additives (titanium oxide, silica, alumina, etc.) are added to the toner of this embodiment. As shown in FIG. 2, the cleaning unit 50 described above has a housing 51 that opens toward the photosensitive drum 18 on the downstream side of the transfer position with the intermediate transfer roller 13 in the rotational direction of the photosensitive drum 18. And a cleaning blade 52 and a toner recovery unit 80 are provided at appropriate positions of the housing 51.

  Specifically, the cleaning blade 52 includes a main body of a galvanized steel plate fixed to the lower end of the housing 51, and a polyurethane rubber blade portion welded to the main body. It extends along the rotation axis. Then, the photoconductor edge contacts in the counter direction at a position lower than the rotation axis of the drum 18, and scrapes off residual toner and discharge products including external additives attached to the surface of the photoconductor drum 18.

Residual toner or the like scraped off from the surface of the photosensitive drum 18 by the cleaning blade 52 is recovered from the toner recovery unit 80.
Specifically, the toner recovery unit 80 has a screw 88 near the bottom surface of the housing 51. The screw 88 is installed on the right side of the cleaning blade 52 as viewed in FIG. 2, extends along the rotational axis direction of the photosensitive drum 18, and has a tip connected to a drive motor (not shown). When the drive motor is driven, residual toner and the like in the housing 51 are collected in a collection container via the screw 88.

By the way, in the image forming unit 17 of this embodiment, when the rotation axes are arranged, the widths of the developing roller 25, the charging roller 21, the photosensitive drum 18, and the like are not the same.
Specifically, as shown in FIG. 3 explaining the relationship between the widths of these components, the photosensitive layer width of the photosensitive drum 18 indicated by a broken line in this figure is the charging width indicated by a two-dot chain line in the same figure. Is set wider than. The width of the transfer belt 12 described above is set between the photosensitive layer width and the charging width or equivalent to the charging width.

Further, the charging width is set wider or equal to the developing width shown by the solid line in FIG. This is because if the charge width is narrower than the development width, the toner continues to adhere to the outer region of the charge width.
Further, the developing width is always set wider than the sheet passing width indicated by the one-dot chain line in FIG. This is because a toner image can be formed on both right and left ends of the sheet.

That is, on the surface of the photosensitive drum 18, the outer region of the sheet passing width viewed in the direction of the rotation axis of the photosensitive drum 18 does not contact the sheet even on the transfer surface of the transfer belt 12, and is in a range where no image is formed.
However, when the developing bias voltage is applied, the toner containing the external additive is in the outer region of the sheet passing width indicated by the one-dot chain line in FIG. 3, and the inner region of the developing width indicated by the solid line in FIG. In other words, it also goes to the non-image area 76 indicated by diagonal lines in FIG.

The toner itself does not adhere to the surface of the photosensitive drum 18 and returns to the developing unit 24. This is because the non-image area 76 corresponds to an inner area of the charging width indicated by a two-dot chain line in FIG.
On the other hand, the external additive itself is detached from the toner and left in the non-image area 76. After that, when only this external additive is transferred from the surface of the photosensitive drum 18 to the transfer surface of the belt 12, it contacts next time. The non-image area 76 of the photosensitive drum 18 is polished with an external additive.

Moreover, the non-image area 76 is formed on all the photosensitive drums 18 for magenta, cyan, yellow, and black.
Therefore, in this embodiment, the amount of charge removal light for the non-image region 76 is weaker than the amount of charge removal light for the inner region of the sheet passing width indicated by the one-dot chain line in FIG.

  Specifically, as shown in FIG. 2, the eraser (static elimination unit) 19 of the present embodiment performs static elimination after cleaning, that is, sensitizes the static elimination light after the cleaning process by the cleaning unit 50 through the current transfer. The surface of the photoconductive drum 18 is irradiated, and electric charges (residual electric charges) remaining on the surface of the photoconductive drum 18 until the next charging are removed.

In addition to FIG. 2, the eraser 19 includes a holder 60 extending along the rotation axis of the photosensitive drum 18 as shown in FIG. 4 as viewed from the rotation axis of the photosensitive drum 18, and a longitudinal direction of the holder 60. LED chips (light sources) 62 and 64 embedded along the direction.
The LED chip 62 is arranged on the holder 60 so as to irradiate the inner region of the sheet passing width described above in the photosensitive drum 18. The LED chips 64 are arranged on both ends, and are responsible for irradiation of the non-image area 76 and the boundary portion between the inner side and the outer side of the sheet passing width.

However, the LED chips 62 and 64 of this embodiment both have substantially the same light emission characteristics. This is because the amount of light from the LED chip 64 in this embodiment is weakened before reaching the non-image area 76 or the boundary portion.
More specifically, as shown in FIGS. 2 and 4, the side wall 72 disposed on the eraser 19 side of the casing 70 of the charger 20 does not allow the charge removal light of the LED chips 62 and 64 to enter the charging region. However, the side wall 72 is provided with a light shielding member (static elimination intensity adjusting means) 74 standing upright.

The light shielding member 74 is attached to the side wall 72 so as to cover a part of the LED chip 64 when viewed from the photosensitive drum 18.
Thereby, the light quantity to the non-image area | region 76 which the LED chip 64 bears, and the said boundary part is irradiated, being weakened compared with the light quantity to the inner side area | region of the above-mentioned paper passing width which the LED chip 62 bears.

  Returning to FIG. 1 again, when the printer 1 performs printing, the paper is separated from the cassette 4 by the roller 46 and sent out one by one. The sent paper reaches the registration roller 14. The registration roller 14 corrects the oblique feeding of the paper and measures the image transfer timing with the toner image formed by the image forming unit 16, while feeding the paper to the secondary transfer unit 30 at a predetermined paper feed timing. Send it out.

On the other hand, a controller (not shown) is configured to be able to receive image data to be printed from the outside. This image data is data in which various images such as characters, codes, figures, symbols, diagrams, and patterns are converted into data. Based on this data, the controller controls light irradiation and the like.
Specifically, the LED chips 62 and 64 of the eraser 19 are turned on to remove the charge from each photosensitive drum 18, and then the charger 20 charges the surface of the photosensitive drum 18. Subsequently, when the exposure unit 15 irradiates the surface of the photosensitive drum 18 with laser light, an electrostatic latent image is formed on the surface of each photosensitive drum 18, and a toner image of each color is formed from the electrostatic latent image. Is done.

Each toner image is secondarily transferred onto a sheet by the secondary transfer unit 30. The toner remaining on the surface of the photosensitive drum 18 is removed by the cleaning unit 50.
Subsequently, the sheet is fed toward the fixing unit 32 with an unfixed toner image carried thereon, and is heated and pressed by the fixing unit 32 to fix the toner image. Thereafter, the sheet sent from the fixing unit 32 is discharged to the discharge tray 36 via the discharge roller 35 and stacked in the height direction.

  When double-sided printing is performed on this single-sided printing, the conveyance direction of the paper discharged from the fixing unit 32 is switched by the discharge branching unit 34. That is, the sheet printed on one side is pulled back into the apparatus main body 2 and conveyed to the duplex printing unit 38. Subsequently, the sheet is sent toward the upstream side of the registration roller 14 and is sent again toward the secondary transfer unit 30. As a result, the toner image is transferred to the side of the paper that has not been printed.

By the way, in the above-described embodiment, the light amount of the LED chip 64 is weakened by using the light shielding member 74, but the configuration for weakening the light amount reaching the non-image region 76 or the like is not limited to the light shielding member 74.
Specifically, the eraser (static elimination unit) 19A shown in FIG. 5A also uses LED chips 62 and 64 having substantially the same light emission characteristics as in the above-described embodiment. The LED chip 64 bears the non-image area 76 and the boundary portion in the inner area of the paper width.

  However, in the eraser 19A of FIG. 5 (a), the holder (static charge intensity adjusting means) 60A has the distance between the LED chip 64 and the adjacent LED chip 62 compared to the distance between the other LED chips 62, 62. In this case as well, the light quantity to the non-image area 76 and the boundary portion that the LED chip 64 bears is larger than the light quantity to the inner area of the paper passing width that the LED chip 62 bears. Irradiated while being weakened.

  On the other hand, in the eraser (static elimination unit) 19B shown in FIG. 5B, the LED chip 62 and the LED chip (static elimination intensity adjusting means) 64B are embedded in the holder 60 at substantially equal intervals, and the LED chip 62 has a sheet passing width. The LED chip 64B serves as the non-image area 76 and the boundary portion as the inner area. However, as the LED chip 64B, a chip having a rank with a smaller amount of light than the LED chip 62 is selected.

Therefore, in this case as well, the amount of light to the non-image area 76 and the boundary portion that the LED chip 64B bears is irradiated while being weakened compared to the amount of light to the inner area of the above-described paper passing width that the LED chip 62 bears. Will be.
As described above, according to this embodiment, in the plurality of image forming units 17, toner images obtained by developing the latent images with the corresponding color toners are individually formed on the surfaces of the respective photosensitive drums 18. The intermediate transfer belt 12 superimposes these individual toner images on the transfer surface (primary transfer) and performs secondary transfer onto the paper.

The eraser 19 (19A, 19B) irradiates the surface of the photosensitive drum 18 with static elimination light before the next charging, and charges (residual charges) remaining on the surface of the photosensitive drum 18 after transfer. Remove.
Here, even when the developing bias voltage is applied, the toner itself in the non-image area 76 of FIG. 3, that is, the outer area of the sheet passing width and the inner area of the developing width does not adhere to the surface of the photosensitive drum 18. On the other hand, the external additive itself is detached from the toner and left in the non-image area 76, and only this external additive is transferred from the surface of the photosensitive drum 18 to the transfer surface of the belt 12. This phenomenon can also be seen from the appearance of a white band along the circumferential direction on the transfer surface.

The portion appearing in the white band has high polishing performance, and the non-image area 76 of the photosensitive drum 18 is polished more than the inner area of the paper width.
Therefore, according to the present embodiment, each static elimination intensity adjusting means applied to the eraser 19 (19A, 19B) indicates the amount of static elimination light with respect to the non-image area 76 of the photosensitive drum 18 by a one-dot chain line in FIG. It is weaker than the inner region of the sheet passing width shown, and the discharge amount (discharge energy) at the time of charging is reduced.

  This point will be described in detail. The amount of charge removal light for the non-image region 76 is weaker than the amount of charge removal light for the inner region of the sheet passing width, and as shown by the broken line in FIG. When the static elimination energy corresponding to the non-image area 76 from about 225 mm to about 250 mm is reduced, the surface potential of the non-image area 76 becomes higher than the surface potential of the inner area of the sheet passing width.

  In other words, in this non-image area 76, when the surface potential is increased to the level necessary for the next image formation, the current flowing from the charger 20 to the photosensitive drum 18 is reduced, and the amount of discharge (discharge energy) at the time of charging is equal to the sheet passing width. Less than the inner area. In other words, the surface potential of the photosensitive drum 18 can be saturated with a small charging current, as shown by the solid line in FIG.

Therefore, as a result of suppressing the deterioration of the surface of the photosensitive drum 18 due to the generation of the discharge energy, the surface of the photosensitive drum 18 becomes difficult to be polished with the external additive, and the life of the photosensitive drum 18 can be extended.
This point will also be described in detail. In the comparative example in which the amount of the neutralizing light with respect to the non-image area 76 is irradiated with substantially the same amount without being weakened as compared with the inner area of the sheet passing width, A portion corresponding to the non-image area 76 is cut off greatly.

  On the other hand, if the above-described eraser 19 (19A, 19B) is used and the amount of static elimination light for the non-image area 76 is made weaker than the inner area of the paper width, this non-image is displayed as indicated by the mark ● in FIG. The amount of wear at the portion corresponding to the region 76 can be suppressed, and a photosensitive film thickness that can maintain the pressure resistance of the photosensitive drum 18 can be secured. As a result, good image formation is performed over a long period of time, and the reliability of the printer 1 is improved.

  Next, each static elimination intensity adjusting means applied to the eraser 19 (19A, 19B) does not irradiate the non-image area 76 of the photosensitive drum 18 with static elimination light at all, but the light quantity with respect to the inner area of the sheet passing width. Irradiation while weakening compared to. Therefore, the amount of light necessary for the inner area of the sheet passing width can be kept constant, and the image quality is not impaired.

In addition, there is a concern that the reverse charge toner is developed if no neutralizing light is irradiated. However, since the irradiation is performed with a low amount of light as described above, the surface potential of the region does not become excessively high. In-machine contamination due to development of charged toner can also be prevented.
Furthermore, since the portion where the amount of the neutralizing light is weakened is an area outside the sheet passing width, there is no concern about the generation of a memory image.

Furthermore, since the contact charging type charger 20 does not generate ozone or nitrogen oxide as compared with the case of using a corona discharge type charging device, the image quality can be improved. A voltage is also applied to the non-image area 76 in direct contact with the charging roller 21.
That is, in the non-image area 76, leakage that penetrates the photosensitive film without being able to withstand the voltage occurs, the current escapes outward, the central portion of the surface of the photosensitive drum 18 is not charged, and horizontal stripes or the like are generated. Invite abnormal images. However, if the above-described static elimination intensity adjusting means is provided, the leakage can be avoided even if the contact charging type charger 20 is used.

Further, the surface of the OPC drum 18 is particularly easily scraped, and there is a concern that polishing with an external additive may have a large effect on the OPC drum 18. However, if the static elimination intensity adjusting means is provided, the characteristics of the OPC drum 18 are improved. It can be maintained over a long period of time, and has a particularly remarkable effect.
Further, as shown in the embodiment of FIGS. 2 and 4, the light shielding member 74 weakens the amount of neutralizing light reaching the non-image area 76 of the photosensitive drum 18 by shielding, thereby reliably reducing the generation of discharge energy. be able to.

Furthermore, as shown in the embodiment of FIG. 5A, the interval between the LEDs 64 that carry the non-image area 76 of the photosensitive drum 18 is made wider than the interval between the LEDs 62, and the number of the photosensitive drums 18 per unit area is reduced. Thus, the amount of static elimination light reaching the non-image area 76 is weakened, and in this case as well, the generation of discharge energy can be reliably reduced.
Further, as shown in the embodiment of FIG. 5B, the light emission characteristic of the LED 64B that bears the non-image area 76 is made lower than the light emission characteristic of the LED 62, and even if the same current is applied, the light intensity is reduced to the non-image area 76. The amount of the static elimination light that arrives is weakened, and even in this case, the generation of discharge energy can be reliably reduced.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims.
For example, in the above embodiment, the toner image is transferred to the intermediate transfer belt above the photosensitive drum, but may be transferred to the belt below the photosensitive drum.
In the above-described embodiment, the printer 1 using the intermediate transfer belt is described. However, the present invention can also be applied to a case where the toner image on the photosensitive drum 18 is directly transferred to a sheet, and the transfer material of the present invention may be a sheet.

  Specifically, even in the case of this direct transfer, the toner and the external additive in the inner region of the sheet passing width are transferred to the sheet, and thus hardly remain on the surface of the photosensitive drum. Even when the developing bias voltage is applied, the toner itself in the non-image area 76 of the photosensitive drum 18 does not adhere to the surface of the photosensitive drum 18. On the other hand, the external additive itself is detached from the toner and left in the non-image area 76, and only this external additive is deposited on the edge of the cleaning blade 52 from the surface of the photosensitive drum 18. The width of the cleaning blade 52 is substantially equal to the development width.

The portion where the external additive is deposited has a high polishing performance, and the non-image area 76 is polished more than the inner area of the paper width, resulting in the same problem as when the intermediate transfer belt is used. is there.
Further, in this embodiment, an example in which the image forming apparatus is embodied in a printer is shown. However, the image forming apparatus of the present invention is naturally applicable to a multifunction machine, a copier, a facsimile machine, and the like.

  In any of these cases, similarly to the above, there is an effect that it is possible to suppress wear in the outer region of the sheet passing width.

1 Printer (image forming device)
18 Photosensitive drum 20 Charger 12 Transfer belt (transfer material)
19, 19A, 19B Eraser (Charging unit)
60A holder (static neutralization intensity adjusting means)
62, 64 LED chip (light source)
64B LED chip (static neutralization intensity adjusting means)
74 Light-shielding member (static neutralization intensity adjusting means)
76 Non-image area

Claims (3)

An image forming apparatus that forms a toner image by developing a latent image formed on a surface of a photosensitive drum through charging or exposure with toner containing an external additive, and transfers the toner image to a transfer material,
A plurality of light sources arranged along the rotation axis of the photosensitive drum, and a developing width that is an outer region of the sheet passing width as viewed in the direction of the rotation axis on the surface of the photosensitive drum before charging. by the relative inner region irradiated with lamp light having the same emission characteristics from the plurality of light sources, a charge removing unit for removing the remaining on the surface of the photosensitive drum after a transfer charge,
The light shielding member covering said neutralization unit relative to the inner region of the developing width an outer region of the sheet width, the light intensity of the lamp light to reach the interior region of the developing width an outer region of the sheet width, an image forming apparatus characterized by comprising a charge eliminating intensity adjusting means for weaker than the light intensity of the lamp light to reach the inner region of the sheet width. The image forming apparatus according to claim 1 ,
An image forming apparatus, further comprising a charger for charging the surface of the photosensitive drum in contact with the surface. An image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the photosensitive drum is a photosensitive drum having an organic photosensitive layer on a surface thereof.

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