JP3217109B2 - Method for preventing back contamination of transfer material in electrophotographic apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention applies a normal transfer voltage having a polarity opposite to that of normal toner when a transfer material such as paper is supplied, and a cleaning voltage having the same polarity as the normal toner when no transfer material is supplied. The present invention relates to a method for preventing back contamination of a transfer material in an electrophotographic apparatus such as a printer and a copying machine.

[0002]

2. Description of the Related Art In general, an electrophotographic apparatus includes an image carrier such as a photosensitive drum, a charging section for charging the image carrier, and irradiating the image carrier according to an image to a charged surface of an upper image carrier. An exposure unit that forms an electrostatic latent image, a developing unit that supplies a regular toner charged to the latent image to form a toner image, and a transfer roller that transfers the toner image to a transfer material such as paper are provided. The transfer roller is cleaned at the time of pre-rotation at the beginning of operation, before and after paper passing, or at the time of non-sheet passing such as between sheets during continuous sheet passing.

[0003] The cleaning of the transfer roller is a process for preventing the toner from adhering to the transfer roller and returning the regular toner adhered to the transfer roller to the image carrier side during the transfer, and has a polarity opposite to that of the transfer. (The same polarity as the normal toner) is applied to the transfer roller.

FIG. 6 is a sequence diagram showing an outline of a conventional cleaning operation. (A) is the voltage V applied to the charging unit.
c, and (b) the charged potential Vdc of the image carrier after exposure,
(C) shows the developing bias voltage Vd applied to the developing sleeve in the developing section, and (d) shows the charging potential Vd of the image carrier.
c and the potential difference Vdc−Vd between the developing bias voltage Vd
And (e) shows the voltage Vt applied to the transfer roller.

As shown in FIG. 6, during the pre-rotation, the residual toner on the surface of the image carrier is prevented from adhering to the transfer roller.
Regular toner (in this case, the developing bias voltage Vd is −
Since 250 V is applied, the regular toner has a positive polarity. ) Is applied to the transfer roller (hereinafter, referred to as a cleaning voltage). At the time of each subsequent paper passing, in order to perform predetermined transfer, a voltage having a polarity opposite to that of the normal toner (hereinafter, referred to as a normal transfer voltage) -2.
kV is applied. Also, at the time of non-sheet passing between sheets passing, a cleaning voltage of about 500 V is applied similarly to the previous rotation.

[0006]

By the way, conventionally, the voltage Vc applied to the charging unit at the time of the pre-rotation and the paper interval, that is, at the time of non-paper passing is set to 0V. Therefore, the charged potential of the image carrier after exposure when paper is not passed is the residual potential (−30).
V). At this time, since the potential difference Vdc-Vd between the image carrier and the developing sleeve is 220 V, the negatively charged toner (hereinafter, referred to as the oppositely charged toner) that is present in the normal toner is present. Attaches to body. The oppositely charged toner thus adhered to the image carrier adheres to the transfer roller due to electrostatic force and mechanical adhesive force when a cleaning voltage of about 500 V is applied to the transfer roller during non-sheet passing. .

As a result, the voltage Vt applied to the transfer roller at the time of paper passing is changed from the cleaning voltage to the normal transfer voltage (−2k).
When switching to V), there is a problem that the oppositely charged toner adhered to the transfer roller repels the transfer roller due to electrostatic force, adheres to the paper as the transfer material, and stains the back surface of the paper. FIG. 7 shows the principle of occurrence of back contamination of the transfer material.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the oppositely charged toner from adhering to a transfer member when a transfer material is not supplied in an electrophotographic apparatus, and to solve the problem of back contamination of the transfer material.

[0009]

In order to achieve the above object, a method for preventing back contamination of a transfer material according to the present invention comprises the steps of:
A charging unit that charges the image carrier, an exposure unit that irradiates the image carrier according to an image to form an electrostatic latent image on a charged surface of the image carrier, and is charged normally by a developing bias voltage. A developing unit that supplies a toner image to the electrostatic latent image to form a toner image, and a transfer member that transfers the toner image to a transfer material. When the transfer material is supplied, a normal toner having a polarity opposite to the polarity of the normal toner is provided. In an electrophotographic apparatus in which a transfer voltage is applied to the transfer member when a transfer voltage is not supplied, a cleaning voltage having the same polarity as that of the normal toner is applied to the developing member of the image carrier when the transfer material is not supplied. Charging potential Vdc
Potential difference (Vdc-V
By controlling the charging potential Vdc of the image carrier so that d) has a polarity opposite to the polarity of the normal toner,
The oppositely charged toner having a polarity opposite to that of the normal toner is prevented from adhering to the image carrier.

The charge potential of the image carrier is controlled as follows so that the potential difference between the charge potential of the image carrier and the developing bias voltage is opposite to the polarity of the normal toner. .

I) A constant voltage is always applied to the charging unit, and the amount of light irradiated on the image carrier is controlled when the transfer material is not supplied. Such control of the irradiation light amount of the image carrier, in the above-mentioned exposure unit, provided a shutter having a halftone exposure surface on the side facing the image carrier,
When the transfer material is not supplied, the shutter can be closed and the light reflected by the exposure surface can be irradiated to the image carrier.

Ii) Alternatively, the voltage applied to the charging unit may be changed between when the transfer material is supplied and when the transfer material is not supplied.

[0013]

When the transfer material is not supplied, the potential difference (Vdc-V) between the charging potential Vdc of the image carrier and the developing bias voltage Vd is obtained.
Since Vd) is opposite to the polarity of the regular toner, the regular toner adheres to the surface of the image carrier according to the degree of the potential difference. The oppositely charged toner does not adhere. At this time, since the cleaning voltage is applied to the transfer member, the toner adhered to the image carrier does not adhere to the transfer member. Therefore,
When the transfer material is conveyed, no toner adheres to the back surface of the transfer material, and no back contamination occurs.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a schematic side view of a main part of a copying machine to which a method for preventing back contamination of a transfer material according to the present invention is applied.
Reference numeral 1 denotes a photosensitive drum as an image carrier having an OPC photosensitive layer on its surface, reference numeral 2 denotes a charger for charging the photosensitive drum 1, reference numeral 3 denotes a developing device having a developing sleeve 3a therein, and reference numeral 5 denotes a developing device. Reference numeral 6 denotes a transfer roller as a transfer member, 7 denotes a fixing device, 8 denotes a cleaner for the photosensitive drum 1, and 9 denotes a lamp as a light source for exposure. The lamp 9 is also used as a static elimination lamp. Also, 1
Reference numerals 0, 11, and 12 denote power supplies for applying voltages to the charger 2, the developing device 3, and the transfer roller 6, respectively. Reference numeral 14 denotes reflected light from a document (not shown) including an image. Irradiate accordingly.

FIG. 2 shows the structure of the exposure unit. The exposure unit includes the light source 9, reflector 16, selfoc lens 17, light source cover 18, and the like. A shutter 20 is provided in the optical path of the reflected light 14 from the document in the longitudinal direction of the photosensitive drum 1. Shutter 20
As shown in FIG. 2, when taking two operating positions, that is, an open position a and a closed position b, and taking the closed position b, when the reflected light from the shutter 20 takes the open position a, The reflected light 14 from the document irradiates the photosensitive drum 1 respectively. .

The exposure surface of the shutter 20 (the surface facing the photosensitive drum 1) is halftone, so that when the reflected light from the shutter 20 irradiates the photosensitive drum 1, the photosensitive drum 1 1 is set to -300V.

As shown in FIGS. 3 and 4, the shutter 20 has a first rotating member 22 rotatably provided around an axis 21 extending in a direction perpendicular to the original scanning direction (the moving direction of the table glass 19). And rotates with the first rotating member 22 between the open position a and the closed position b as described later. The first rotating member 22 is connected to a frame (not shown) of the copying machine by a spring 24 attached to a side surface 23 (only one of which is shown).
0 is held in the open position a or the closed position b.

The first rotating member 22 is rotated by a driving mechanism shown in FIG. The drive mechanism is the table glass 1
9, a pressing projection 30 provided on the lower surface (only one pair is shown);
An engagement protrusion 25 provided below the side surface 23 of the first rotation member 22 and a second protrusion rotatably supported around a shaft 31.
And a rotating member 33. The second rotating member 33 has a first engaging portion 34 that engages with the pressing protrusion 30 of the table glass 19 and a second U-shaped second engaging member that engages with the engaging protrusion 25 of the first rotating member 22. It has a mating portion 35 and is held at the neutral position c by the spring 32. The drive mechanism having the above configuration rotates the first rotary member 22 as described below to bring the shutter 20 to the open position a or the closed position b.

Assume that the copying machine is in a state before scanning the original. At this time, the shutter 20 is closed. Here, when the table glass 19 moves to the right side of the drawing for scanning the original, the pressing protrusion 30 in the front of the scanning direction engages with the first engaging portion 34 of the second rotating member 33 and presses the second rotating member 33. The member 33 is rotated clockwise in the figure. By this rotation, the second engagement portion 35 engages with the first rotating member 22, and as a result, the first rotating member 22 also rotates clockwise. The rotation of the first rotating member 22 causes the shutter 20 to move to the open position a shown in FIG.
I come to. FIG. 3A shows a state in which the shutter 20 is opened immediately after the table glass 19 starts to move for document scanning. The shutter 20 is operated by the spring 24 until the document scanning ends. It is held at this open position a.

On the other hand, when the table glass 19 returns to the left in the drawing, the pressing projection 30 located forward of the table glass 19 in the return direction is moved to the first rotation member 33 by the first rotation member.
The first rotating member 22 is rotated in a counterclockwise direction by engaging and pressing the engaging portion 34 to rotate the second rotating member 33 in a counterclockwise direction. Position. FIG. 3B shows the shutter 20 immediately after the table glass 19 starts returning.
At this point, the shutter 20 is closed. Until the table glass 19 returns
The shutter 20 holds the closed position b.

FIG. 5 is a sequence diagram showing the operation of the copying machine having the above configuration. The operation of the copying machine will be described with reference to FIG. In the figure, (a) shows the voltage Vc applied to the charger 2 and (b) the charging potential Vdc of the photosensitive drum 1 after exposure.
(C) shows the developing bias voltage Vd applied to the developing sleeve 3a, and (d) shows the charging potential V of the photosensitive drum 1.
potential difference Vdc-Vd between dc and developing bias voltage Vd
(E) shows the voltage Vt applied to the transfer roller 6.

As shown in FIG. 5A, a voltage of -1.3 kV is always applied to the charger 2, whereby
The OPC photosensitive layer of the photosensitive drum 1 is uniformly charged to -700V. When exposing the original, the shutter 20 is used.
Are open, the reflected light 14
Irradiation forms an electrostatic latent image.

When the electrostatic latent image arrives at a developing site facing the developing device 3, the regular toner charged to the positive polarity via the developing sleeve 3a adheres to the electrostatic latent image to form a toner image. . Note that a developing bias of -250 V is constantly applied to the developing sleeve 3a by the power supply 11 (FIG. 5C).

Next, when the toner image reaches the transfer site where the transfer roller 6 is pressed against the photosensitive drum 1, the paper 5 is supplied to this transfer site in synchronization with the timing, and A normal transfer voltage of 2 kV is applied (FIG. 5E). As a result, the toner image on the photosensitive drum 1 is transferred to the paper 6.

After that, the paper 6 carrying the toner image is conveyed to the fixing device 7. On the other hand, the residual toner remaining on the photosensitive drum 1 without being transferred to the paper 6 at the transfer portion is
Accordingly, the residual charges on the photosensitive drum 1 are eliminated by the lamp 9 (however, a residual potential of about −30 V remains), and the photosensitive drum 1 enters the next step.

On the other hand, when the paper is not passed, the shutter 20 having the halftone exposure surface is closed, so that the photosensitive drum 1 is irradiated with the reflected light 12 from the exposure surface of the shutter 20. The amount of light applied to the photosensitive drum 1 by the halftone exposure surface is controlled to be slightly less than half of the total amount of light from the lamp, and the charged potential Vdc of the photosensitive drum 1 is controlled.
Becomes -300V. Therefore, the developing bias voltage −
As shown in FIG. 5D, the potential difference Vdc−Vd from 250 V is −50 V, which is the negative polarity opposite to the polarity (positive) of the normal toner. And the extent is small. Therefore, the oppositely-charged toner mixed with the regular toner does not adhere to the developing portion of the photosensitive drum 1, and the regular toner slightly adheres.

At this time, as shown in FIG. 3E, a cleaning voltage of about 500 V is applied to the transfer roller 6, so that the regular toner adhering to the photosensitive drum 1 is transferred at the transfer portion. It repels the roller 6 and does not adhere to the transfer roller 6. Therefore, the back surface of the paper 6 is not stained during the next paper passing.

Note that the potential difference Vdc-Vd between the charging potential of the photosensitive drum 1 and the developing bias voltage when paper is not passed is ideally set to a value as close to 0 V as possible from the viewpoint of economical use of toner. It is.

In the above embodiment, a roller is used as the transfer member, but a belt type may be used.

In the above-described embodiment, the shutter 20 is provided to control the amount of light irradiated to the photosensitive drum 1 in order to perform exposure and neutralization by the common lamp 9, but the exposure and neutralization are performed by separate lamps. In this case, the light amount of the exposure lamp may be changed by an appropriate method without providing the shutter 20. Alternatively, the charging voltage of the photosensitive drum 1 may be switched between when paper is passed and when paper is not passed. In this case, the light amount of the irradiation light to the photosensitive drum 1 can be kept constant. The point is that the potential difference Vd between the charging potential of the photosensitive drum 1 and the developing bias voltage when paper is not passed is
It is to control the charging potential Vdc of the photosensitive drum 1 so that c-Vd has a polarity opposite to the polarity of the normal toner.

[0031]

As is apparent from the above description, the present invention is arranged so that the potential difference between the charging potential of the image bearing member and the developing bias voltage has a polarity opposite to that of the normal toner when paper is not passed. In this case, the charging potential of the image carrier is controlled. Therefore, it is possible to prevent the oppositely charged toner from adhering to the image carrier when paper is not passed. Further, although the regular toner adheres to the image carrier, the regular toner does not adhere to the transfer member because the cleaning voltage having the same polarity as that of the regular toner is applied to the transfer member when paper is not passed.
As described above, according to the present invention, it is possible to prevent the toner from adhering to the transfer material when the paper is not passed, so that when the transfer material is sent to the transfer portion, the back surface of the transfer material can be prevented from being stained.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a main part of an electrophotographic apparatus (copier) to which a method of the present invention is applied.

FIG. 2 is a view showing an exposure unit of the electrophotographic apparatus of FIG.

3A is a diagram illustrating a shutter operation position (open position) during document exposure, and FIG. 3B is a diagram illustrating a shutter operation position (close position) during non-sheet passing.

FIG. 4 is a side view of the shutter driving mechanism.

FIG. 5 is a sequence diagram illustrating an operation according to a method of preventing back contamination of a transfer material according to an embodiment of the present invention.

FIG. 6 is a sequence diagram showing an operation of a conventional electrophotographic apparatus.

FIG. 7 is a diagram illustrating the principle of generation of back contamination on a transfer material.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photosensitive drum (image carrier), 2 charger, 3 developing device, 5 paper (transfer material), 6 transfer roller, 7 fixing device,
8 cleaner, 9 lamp, 14 reflected light for irradiating the photosensitive drum 1, 19 table glass, 20 shutter.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Ishii 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroyuki Sawai 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Shogo Yokota 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-63-247781 (JP, A) JP-A-5-53401 (JP, A) JP-A-3-156480 (JP, A) JP-A-61-277978 (JP, A) JP-A-3-69978 (JP, A) JP-A-4-348374 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/00 G03G 15/02 G03G 15/16 G03G 21/00-21/04 G03G 21/14

Claims (3)

(57) [Claims] 1. An image bearing member, a charging portion for charging the image bearing member, and an exposure portion for irradiating the image bearing member according to an image to form an electrostatic latent image on a charged surface of the image bearing member. A developing unit that supplies a regular toner charged normally by a developing bias voltage to the electrostatic latent image to form a toner image, and a transfer member that transfers the toner image to a transfer material. Sometimes, a normal transfer voltage having a polarity opposite to the polarity of the normal toner, and a cleaning voltage having the same polarity as the polarity of the normal toner is applied to the transfer member when the transfer material is not supplied. When a voltage is applied and the transfer material is not supplied, the potential difference (Vd) between the charging potential Vdc at the developing site of the image carrier and the developing bias voltage Vd is determined.
By controlling the amount of light irradiating the image carrier so that c-Vd) is opposite in polarity to the polarity of the normal toner, the charging potential Vdc of the image carrier is controlled, whereby the image carrier is controlled. A method for preventing back-side contamination of a transfer material, wherein a reversely charged toner having a polarity opposite to the polarity of regular toner is prevented from adhering to the transfer material. 2. The method according to claim 1, wherein the exposure unit is provided with a shutter having a halftone exposure surface on a side facing the image carrier, and the transfer material is supplied. If not, close the shutter,
A method for preventing back contamination of a transfer material, wherein the amount of light is controlled by irradiating the image carrier with light reflected by the exposure surface. 3. An image carrier, a charging section for charging the image carrier, and an exposure section for irradiating the image carrier according to an image to form an electrostatic latent image on a charged surface of the image carrier. A developing unit that supplies a regular toner charged normally by a developing bias voltage to the electrostatic latent image to form a toner image, and a transfer member that transfers the toner image to a transfer material. In an electrophotographic apparatus in which a normal transfer voltage having a polarity opposite to the polarity of the normal toner and a cleaning voltage having the same polarity as the polarity of the normal toner is applied to the transfer member when the transfer material is not supplied, when the transfer material is not supplied, When the transfer material is supplied, the potential difference (Vdc-Vd) between the charging potential Vdc at the developing portion of the image carrier and the developing bias voltage Vd is opposite to the polarity of the normal toner. Apply different voltages to the charging unit Applying charging potential Vd of the image carrier by
A method for preventing back-stain on a transfer material, wherein c is controlled so that oppositely charged toner having a polarity opposite to the polarity of normal toner is prevented from adhering to the image carrier.