JPH05249802A - Electrophotographic printer - Google Patents

Abstract

PURPOSE:To improve image definition by preventing sticking of remaining toner to an electrifying roll and evenly electrifying the surface of a photosensitive drum. CONSTITUTION:This printer is provided with the photosensitive drum 11, the electrifying roll 12 electrifying the surface of the photosensitive drum 11 by rotating while in a sliding contact with the photosensitive drum 11, a developing device 15 developing an electrostatic latent image and eliminating the remaining toner 16a on the photosensitive drum 11 and a transfer device 18 to transfer a toner image to paper 19. The electrifying roll 12 is provided with releasing property on its surface which is in contact with the photosensitive drum 11 and is the same polarity as the toner on the electrostatic charge string and consists of material which is electrified to the same polarity as the toner. Furthermore, the surface coming into contact with the photosensitive drum 11 is formed by fluorocarbon resin with carbon dispersed in it, the surface is on a negative side against toner on the electrostatic charge string and the fluorocarbon resin is constituted of copolymer of tetrafluoroethylene and perfluoroalkylvinylether or polytetrafluoroethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic printer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic printer, a photoconductor is provided on the surface of a cylindrical conductive base material to form a photoconductor drum, and corona discharge is performed by a corona charger while rotating the photoconductor drum. I am trying to charge it. Then, the photosensitive drum is exposed to form an electrostatic latent image on the surface of the photosensitive drum, and toner is attached to the electrostatic latent image for development. Then, the toner image formed by development is transferred and fixed on a recording medium such as paper.

By the way, during transfer, not all of the toner on the photosensitive drum is transferred to the paper, and some of the toner remains on the surface of the photosensitive drum. This residual toner (hereinafter referred to as "residual toner") needs to be removed, and therefore a cleaning device is provided. As mentioned above, around the photosensitive drum,
Each work of a charging process, an exposure process, a developing process, a transfer process and a cleaning process is performed. In the charging step among these steps, the corona charging method by corona discharge is used as described above. Instead of the corona charging method, a contact charging method in which a charging member is brought into contact with the photosensitive drum to charge the same. Is provided. In this case, for example, a charging roller is used as the charging member, a voltage is applied to the charging roller, and a potential set on the surface is formed by contacting the photosensitive drum. The residual toner after the transfer process is passed through the charging process, and then is developed and cleaned at the same time in the next developing process.

According to this type of contact charging system, the applied voltage can be made lower than that in the corona charging system, and the amount of ozone generated is small. Further, since cleaning is performed at the same time as development is performed, a dedicated cleaner is not required and the photosensitive drum can be made smaller. Therefore, the size and cost of the electrophotographic printer can be reduced, and the maintainability can be improved.

[0005]

However, in the above-mentioned conventional electrophotographic printer, when continuously charged, the residual toner on the photosensitive drum adheres to the surface of the charging roller to cause a filming phenomenon. If the adhered residual toner adheres to the charging roller, the surface becomes insulating and the charging ability deteriorates. Then, the surface of the photosensitive drum becomes non-uniformly charged, and background fog and black streaks occur, resulting in deterioration of image quality.

The present invention solves the above-mentioned problems of the conventional electrophotographic printer, prevents the residual toner from sticking to the charging roller, and uniformly charges the surface of the photosensitive drum. An object is to provide an electrophotographic printer that can improve the quality.

[0007]

Therefore, in the electrophotographic printer of the present invention, the photosensitive drum and the photosensitive drum are rubbed and rotated to charge the surface of the photosensitive drum. A charging roller, a developing device for developing the electrostatic latent image formed on the surface of the photoconductor drum and removing residual toner on the photoconductor drum after transfer, and recording the toner image formed by the development. It has a transfer device for transferring to a medium.

The charging roller has a releasable surface in contact with the photosensitive drum, is on the same polarity side as the toner on the charging train, and is made of a material that is charged to the same polarity as the toner. The surface of the charging roller in contact with the photosensitive drum is formed by dispersing carbon in a fluororesin, and the fluororesin is tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or polytetrafluoroethylene. ..

[0009]

According to the present invention, as described above, the photosensitive drum, the charging roller for charging the surface of the photosensitive drum,
A developing device for developing the electrostatic latent image formed on the surface of the photosensitive drum and removing residual toner on the surface of the photosensitive drum after transfer, and a transfer for transferring the toner image formed by the development to a recording medium. Have a vessel.

Therefore, the electrostatic latent image formed on the photosensitive drum is developed into a toner image, which is transferred to the recording medium and fixed. After the transfer, the residual toner on the surface of the photoconductor drum is temporarily separated from the photoconductor drum by the charging roller or moved on the photoconductor drum to weaken the adhesive force. Sent to. In the developing device, a developing bias potential is generated in the developing roller, and the residual toner is removed and collected in the developing device.

The charging roller rotates by rubbing the photosensitive drum. The surface of the charging roller in contact with the photosensitive drum has releasability, is on the same polarity side as the toner on the charging line, and is made of a material that is charged to the same polarity as the toner. Since the surface of the charging roller that contacts the photosensitive drum is a fluororesin in which carbon is dispersed,
On the charging column, it is on the negative side with respect to the toner and is charged to the same negative as the toner. The fluororesin is tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or polytetrafluoroethylene.

Therefore, not only is the surface of the charging roller releasable, but it is charged to the same polarity as the residual toner.
The adhesive force of the residual toner is weakened, and the residual toner is easily removed from the charging roller.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic view of an electrophotographic printer showing an embodiment of the present invention, and FIG. 2 is a sectional view of a charging roller in the embodiment of the present invention. In FIG. 1, 11 is a photosensitive drum, 12 is a charging roller disposed so as to contact the photosensitive drum 11, 13 is a conductive shaft disposed in the center of the charging roller 12, The conductive shaft 13 is connected to a high voltage power source (not shown). 14
Is an LED head for exposing the photosensitive drum 11, 15
Is a developing device for accommodating the toner 16, conveying the toner 16 to the photoconductor drum 11 by negatively charging the toner 16 by the developing roller 17 provided in the opening, and forming the photoconductor drum 11 on the photoconductor drum 11 by the development. It is a transfer device for transferring the formed toner image to a recording medium such as the paper 19. The sheet 19 is passed between the photoconductor drum 11 and the transfer device 18.

In FIG. 2, reference numeral 21 denotes the photosensitive drum 1
1 is a surface layer portion in contact with 1, and is formed of, for example, a conductive PFA resin tube formed by dispersing carbon in a fluororesin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer).
^It has a volume resistance value of ⁷ to 10 ¹¹ [Ω · cm] and a thickness of 50 [μm]. Reference numeral 22 denotes an inner layer portion having elasticity, which is made of conductive rubber such as conductive silicone rubber, conductive EPDM rubber, and conductive urethane rubber.
Further, 13 is a conductive shaft.

In the electrophotographic printer having the above structure, the photosensitive drum 11 (FIG. 1) rotates in the direction of arrow A, and the charging roller 12 rotates in the direction of arrow B. A voltage is applied to the charging roller 12 from a high-voltage power source (not shown) by the conductive shaft 13, and the charging roller 12 contacts the photosensitive drum 11 to charge the photosensitive drum 11. Since the photoconductor drum 11 is rotating, charging is performed while the contact portion with the charging roller 12 sequentially moves in plane.

Then, the charged photosensitive drum 11
The surface of the LED head 14 is rotated by the direction of arrow A.
To the position opposite to, and sequentially exposed by the LED head 14 to form an electrostatic latent image. When the electrostatic latent image on the photoconductor drum 11 moves to a position facing the developing device 15, the toner 16 on the developing roller 17 adheres to the electrostatic latent image and development is performed.

In this way, the toner image developed is opposed to the sheet 19 conveyed with the rotation of the photosensitive drum 11, and the opposing position is sequentially moved to be transferred by the transfer unit 18. In this case, all of the toner 16 is the paper 1
9 is not transferred to the surface of the photosensitive drum 11, and a part thereof remains on the surface of the photosensitive drum 11.

The residual toner 16a on the surface of the photoconductor drum 11 moves as the photoconductor drum 11 rotates in the direction of arrow A, and is carried to a position where the photoconductor drum 11 and the charging roller 12 come into contact with each other, that is, a contact portion. Here, the charging roller 1
2 is rotating in the direction of arrow B, the residual toner 16a
Does not enter between the contact portion between the photosensitive drum 11 and the charging roller 12, but is wiped off by the charging roller 12 and adheres to the outer periphery of the charging roller 12. That is, the charging roller 12 has a cleaning ability with respect to the photosensitive drum 11.

Then, the residual toner 16a adhered to the charging roller 12 is carried to the opposite side of the contact portion by the rotation of the charging roller 12, and adheres to the surface of the photosensitive drum 11 again. Here, as the surface layer portion 21 of the charging roller 12,
For example, when silicone rubber is used and the photosensitive drum 11 is rubbed through the residual toner 16a, the silicone rubber is on the same polarity side, that is, the positive side with respect to the toner (residual toner 16a) on the charging column, so that the charging roller is The surface of 12 is positively charged with a polarity opposite to that of the residual toner 16a. Therefore, the adhesive force between the charging roller 12 and the residual toner 16a increases, and the residual toner 16a remains adhered to the surface of the charging roller 12 and the photoconductor drum 11
Can not be attached to. When the charging roller 12 is continuously rotated in such a state, a filming phenomenon occurs.

On the other hand, in the electrophotographic printer of the present invention, the surface layer portion 21 of the charging roller 12 uses a material having the same polarity side as the toner on the charging column, such as PFA. Since the PFA has releasability and is on the negative side with respect to the toner on the charging line, the surface of the charging roller 12 is negatively charged with the same polarity as the residual toner 16a, and the adhesive force with the residual toner 16a. Works on the repulsive side.
Therefore, the residual toner 16a does not adhere to the surface of the charging roller 12 and can be easily attached to the surface of the photoconductor drum 11.

As described above, since the residual toner 16a does not adhere to the surface of the charging roller 12, the charging roller 12 and the photosensitive drum 11 can always be in stable contact with each other, and good charging can be performed. After being cleaned by the charging roller 12, the residual toner 16a that has adhered to the surface of the photosensitive drum 11 again normally absorbs light when exposed to light from the LED head 14 and forms a shadow on the surface of the photosensitive drum 11. Will end up. However, in reality, since the particle diameter of the residual toner 16a is small and the amount of residual toner is small, light wraps around the charge generation layer of the photosensitive drum 11 below the residual toner 16a, and exposure is performed.

Subsequently, the electrostatic latent image on the photosensitive drum 11 in the next process is developed while holding the residual toner 16a. The residual toner 16a is once separated from the photosensitive drum 11 by the charging roller 12. Therefore, the adhesive force between the photosensitive drum 11 and the photosensitive drum 11 is weak and the developing device 1
No. 5, the development is performed, and at the same time, it is easily cleaned. Then, the residual toner 16a cleaned by the developing device 15 is once collected by the developing device 15 and used again as the toner 16 for development.

Here, the material of the surface layer portion 21 of the charging roller 12 is changed, and the photosensitive drum 1 is transferred through the residual toner 16a.
A state in which the residual toner 16a is attached to the surface of the charging roller 12 when the charging is performed by rubbing 1 will be described. FIG. 3 is a comparison diagram of the toner adhesion state on the surface of the charging roller. As shown in the figure, the silicone rubber, polyamide coat, etc. constituting the surface layer portion 21 of Comparative Examples 1 to 3 are on the plus side of the toner on the charging column, and the amount of residual toner 16a adhering to the charging roller 12 is Will increase.
Further, as in Examples 1 and 2, those using a fluororesin such as PFA or PTFE (polytetrafluoroethylene) are both on the negative side of the toner on the charging column and adhere to the charging roller 12. The amount of residual toner 16a is small, and the charging is good.

Thus, the surface layer portion 2 of the charging roller 12
If the material of No. 1 which is on the negative side of the toner on the charging column and is charged to the same polarity as the residual toner 16a is selected, the amount of the residual toner 16a adhering to the charging roller 12 can be reduced, Good charging can be performed. Next, the electrophotographic process will be described with reference to FIGS.

FIG. 4 is a uniforming process diagram in the electrophotographic printer of the present invention, FIG. 5 is a charging process diagram in the electrophotographic printer of the present invention, FIG. 6 is an exposure process diagram in the electrophotographic printer of the present invention, and FIG. 7 is a book. Fig. 8 is a cleaning process diagram in the electrophotographic printer of the invention, Fig. 8 is a developing process diagram in the electrophotographic printer of the invention, Fig. 9 is a sectional view of a photosensitive drum in the electrophotographic printer of the invention, and Fig. 10 is an electrophotographic printer of the invention. 3 is a functional explanatory diagram of the photosensitive drum in FIG.

In this case, in order to simplify the electrophotographic process, a reversal development method of developing the exposed portion is adopted,
In addition, the contact development method is adopted in order to remove the residual toner 16a after the transfer at the same time as the development. First, the charging roller 12 rubs against the photosensitive drum 11,
The residual toner 16a in the two layers above is made uniform and 1
In addition to forming the layer (FIG. 4), the surface of the photosensitive drum 11 is charged to a charging potential (V ₀ ) of −700 [V] (FIG. 5). At this time, the residual toner 16a on the photosensitive drum 11
Are also charged at the same time. The residual toner 16a is once separated by the charging roller 12 and then is re-photosensitive.
Since it adheres to the upper side, the adhesion force with the photoconductor drum 11 is weakened.

Next, the photosensitive drum 11 is the LED head 1
4, the potential of the exposed portion is attenuated to form an electrostatic latent image (FIG. 6). At this time, the residual potential (V _r ) of the exposed portion becomes −100 [V]. As shown in FIG. 9, the photosensitive drum 11 is formed by sequentially coating a charge generation layer 11b and a charge transport layer 11c on an aluminum pipe 11a having an outer diameter of 30 [mm] and an inner thickness of 1 [mm]. ing. The charge transport layer 11c has a thickness of 20 μm, is transparent to visible light and LED light, and is formed on the charge generation layer 11b. Therefore,
When the photosensitive drum 11 is exposed, the particle size is 30 [μm]
Even if the following residual toner 16a adheres to the surface of the charge transport layer 11c, the charge generation layer 11b is irradiated with diffracted light or reflected / scattered light in the charge transport layer 11c as shown in FIG. The shadow of the particle 16a is hardly formed.

The potential of the portion of the photosensitive drum 11 which is not exposed by the LED head 14 and the potential of the residual toner 16a adhering thereto remain at -700 [V] (FIG. 7). Next, the electrostatic latent image on the photoconductor drum 11 is developed by the developing device 15. At this time, the developing bias potential ( _Vb ) of the developing device 15 is -400.
[V], and the residual toner 16a attached to the exposed portion of the photosensitive drum 11 is
It is directly attached on top of 1. In addition, the photosensitive drum 11
Residual toner 16 adhered to the unexposed portion of the
a is attracted to the developing device 15 by electrostatic force. That is, it is cleaned by the developing device 15 simultaneously with the development.

Next, the developed toner image on the photosensitive drum 11 is sent to the transfer device 18 and comes into contact with the paper 19 conveyed by the medium feeding means (not shown), and the paper 19 is conveyed.
Transferred on top (Fig. 8). Next, a second embodiment of the present invention will be described. FIG. 11 is a schematic diagram of an electrophotographic printer showing a second embodiment of the present invention.

In the figure, 11 is a photosensitive drum, and 12 is a charging roller. In the second embodiment, the photosensitive drum 11 rotates in the direction of arrow A as in the first embodiment, but the charging roller 12 rotates in the direction of arrow C contrary to the first embodiment. I am doing it. In this case, the surface moving speed of the charging roller 12 is set to a value different from the surface moving speed of the photosensitive drum 11, and the charging roller 12 is set to the photosensitive drum 1
1 is rubbed. By doing so, the residual toner 16a on the photoconductor drum 11 after the transfer is transferred.
Are forcibly moved on the photosensitive drum 11.

Therefore, the residual toner 16a is weakly attached to the photosensitive drum 11 and can be easily removed. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0032]

As described in detail above, according to the present invention, a photosensitive drum, a charging roller that rubs the photosensitive drum to rotate it, and charges the surface of the photosensitive drum, and an electrostatic roller. It has a developing device for developing the latent image and removing the residual toner on the photosensitive drum, and a transfer device for transferring the toner image to a recording medium.

The surface of the charging roller in contact with the photosensitive drum has releasability, is on the same polarity side as the toner on the charging line, and is made of a material that is charged to the same polarity as the toner. The surface of the charging roller that contacts the photosensitive drum is
Formed by dispersing carbon in fluorine resin,
It is on the negative side with respect to the toner on the charging line, and the fluororesin is tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or polytetrafluoroethylene.

The surface of the charging roller in contact with the photosensitive drum has releasability and is charged to the same polarity as the toner, so that the adhesive force of the residual toner is weakened and the residual toner is easily removed from the charging roller. And collected in the developing device.
Therefore, the charging ability of the charging roller does not decrease, the surface of the photoconductor drum can be always uniformly charged, and the image quality can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrophotographic printer showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a charging roller according to an exemplary embodiment of the present invention.

FIG. 3 is a comparison diagram of a toner adhesion state on a surface of a charging roller.

FIG. 4 is a uniforming process chart in the electrophotographic printer of the present invention.

FIG. 5 is a diagram illustrating a charging process in the electrophotographic printer of the present invention.

FIG. 6 is an exposure process diagram of the electrophotographic printer of the present invention.

FIG. 7 is a cleaning process diagram in the electrophotographic printer of the present invention.

FIG. 8 is a developing process diagram in the electrophotographic printer of the present invention.

FIG. 9 is a sectional view of a photosensitive drum in the electrophotographic printer of the present invention.

FIG. 10 is a functional explanatory diagram of a photosensitive drum in the electrophotographic printer of the present invention.

FIG. 11 is a schematic view of an electrophotographic printer showing a second embodiment of the present invention.

[Explanation of symbols]

 11 Photoreceptor Drum 12 Charging Roller 13 Conductive Shaft 14 LED Head 15 Developing Device 16 Toner 16a Residual Toner 17 Developing Roller 18 Transfer Device 19 Paper (Recording Medium)

Claims (4)

[Claims] 1. A photosensitive drum, comprising: (a) a photosensitive drum; (b) a charging roller that rubs and rotates the photosensitive drum to charge the surface of the photosensitive drum; and (c) a surface of the photosensitive drum. A developing device that develops the formed electrostatic latent image and removes toner remaining on the surface of the photosensitive drum after transfer,
(D) a transfer device for transferring the toner image formed by development to a recording medium, (e) the charging roller has a releasable surface in contact with the photoconductor drum, On the other hand, an electrophotographic printer that is on the same polarity side and is made of a material that is charged to the same polarity as the toner. 2. The electrophotographic printer according to claim 1, wherein a surface of the charging roller which is in contact with the photosensitive drum is formed of a fluororesin in which carbon is dispersed. 3. The electrophotographic printer according to claim 2, wherein the fluorine-based resin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. 4. The electrophotographic printer according to claim 2, wherein the fluororesin is polytetrafluoroethylene.