JP3106015B2 - Electrophotographic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In an electrophotographic apparatus provided with a contact transfer member for transferring a toner image to a transfer material, the transfer member must be cleaned in order not to cause back contamination of the transfer material. When the transfer member is electrically cleaned, a voltage for cleaning is applied to the transfer member during non-sheet passing such as during pre-rotation at the beginning of operation, before and after sheet passing (including between sheets during continuous sheet passing). By doing so, it is common practice to prevent the toner from adhering to the transfer member, and to clean the transfer member by returning the toner adhered to the transfer member to the image carrier during transfer. Also, in order to cope with a small amount of poorly charged toner leaking from the developing tank and a reversely charged toner whose polarity has been reversed by a transfer electric field or current, the above-described cleaning is performed on normally charged toner in the opposite direction to that on transfer. It has been proposed to apply a voltage having a polarity to a transfer member for a reversely charged toner and a voltage having the same polarity as during transfer. FIG. 6 is an outline of a sequence showing a state in this case, and a case of regular development will be described as an example.

In order to prevent residual toner on the surface of the image carrier from adhering to the transfer member during pre-rotation and paper passing, a bias voltage of the same polarity as the normally charged toner (hereinafter referred to as + cleaning voltage), for example, +1. 5 KV is applied (a
Section), followed by a bias voltage having the same polarity as that of the oppositely charged toner (hereinafter referred to as “cleaning voltage”), for example, −1.5
KV is applied (section b). This is repeated at an appropriate cycle, and a reverse bias voltage (hereinafter, referred to as a normal transfer voltage), for example, −2 KV, is applied to the normally charged toner to perform predetermined transfer at the next sheet passing (section c). The cleaning voltage of the toner is applied to prevent the toner from adhering to the transfer member and return the adhered toner to the image carrier side (including the paper interval during continuous paper feeding) (d)
section).

[0004]

[0005]

When the transfer member is electrically cleaned by the conventional technique, there are some problems.

[0006] Since the image carrier made for charging is weak to the application of the + voltage, if the amount of time for applying the + voltage is large as described above, the fatigue of the image carrier is accelerated and the life is shortened. In addition, since the + charge is hardly subjected to light elimination, when a contact charging member that contacts the image carrier is used as a charger, when the image carrier is positively charged by the cleaning voltage at the transfer position, the charge is performed at the next charging position. At the time of charging, the point at which the charging potential fluctuates according to this + charging potential, and-at the transfer position, if there is no light elimination, an optical memory occurs and the image quality deteriorates. that must be avoided, further, the transfer when the current of about 0.5 .mu.A flows through the transfer roller 6 a toner roller surface to return to the photoreceptor, satisfies the above condition because the cleaning effect is maximized In order to obtain a good cleaning effect, there is such a point that must be the volume resistivity of the transfer roller 6 below 1.0 × 10 ⁹ Ωcm.

[0007] The present invention solves the above-mentioned problems, and when generating an electric field in the transfer portion, minimizes the cause of photoreceptor fatigue, performs stable charging, stains the transfer member, and fixes the back of the transfer material.
It is an object of the present invention to provide an electrophotographic apparatus capable of suppressing contamination .

[0008]

An electronic photographing apparatus according to claim 1, wherein :
The true device is charged to a first polarity and a toner image is formed.
Image carrier and transferring the toner image on the image carrier
Transfer to materials and cleaning of attached toner
A contact transfer member for performing
A first voltage applied to the contact transfer member during cleaning.
Voltage of the opposite polarity to the image carrier-contact transfer member
It is characterized in that it is set to be equal to or lower than the discharge start voltage between the electrodes .

According to a second aspect of the present invention, there is provided an electrophotographic apparatus comprising:
An image carrier on which a toner image is formed, which is charged to a polarity;
When the toner image on the image carrier is transferred to a transfer material,
In both cases, contact transfer that cleans the adhered toner
Cleaning in an electrophotographic apparatus comprising:
Sometimes the first polarity applied to the contact transfer member and vice versa
Voltage between the image carrier and the contact transfer member.
The discharge starting voltage is set to be equal to or lower than the discharge starting voltage .

[0010]

[0011]

[Action] In electrophotography having a contact transfer member abuts against the image bearing member, a voltage applied to the transfer member during cleaning, the image carrier - more to below the discharge starting voltage between the transfer member, the image bearing member it is possible to reduce the fatigue.
In particular, marks for cleaning due to the polarity opposite to the charging polarity
By controlling the applied voltage below the firing voltage, fatigue can be suppressed.
It can be done effectively . Further, the cleaning of the transfer member is not performed during the pre-rotation and between the sheets, or a cleaning step is provided separately from the copy cycle, and the transfer member is cleaned only when the transfer member is contaminated by toner adhesion. It can prevent stains and back stains on the transfer material.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic apparatus of the type shown in FIG. 3 will be described with reference to this embodiment. Figure 3 is charged to the charging unit roller 2, a configuration view of a copying machine using a transfer roller 6 to the transfer means has an axis in a direction perpendicular to the paper surface, to rotate in the direction indicated by an arrow - polarity (first pole
The OPC photosensitive layer on the surface of the image carrier 1 (hereinafter, referred to as a photosensitive member) charged to -700 V
, And the charged surface is irradiated with the reflected light 3 from the original to form an electrostatic latent image.

When the latent image arrives at a developing site facing the developing device 4, the positively charged toner adheres to the latent image portion via the developing sleeve 4a to form a toner image. A power supply 12 constantly applies a developing bias of −250 V to the developing sleeve 4 a.

Next, when the toner image reaches a transfer portion where the transfer roller 6 is pressed against the photosensitive member 1, the transfer material 5 is supplied to the transfer portion at the same time, and at the same time, -2 KV is applied to the transfer roller 6. The normal transfer voltage of
The toner image on the photoconductor is transferred to a transfer material.

After that, the transfer material carrying the toner image is conveyed to the fixing device 7. The toner remaining on the photoreceptor without being transferred at the transfer portion is eliminated by the cleaner 8, and the residual charge on the photoreceptor is eliminated by the discharging lamp 9, and the photoreceptor enters the next step.

Next, the operation of the above electrophotographic apparatus according to the present invention will be described with reference to the timing chart of FIG. When the photosensitive member is used, when the potential difference between the nip portion of the photosensitive member and the transfer roller becomes 550 V, the discharge is started.

When the transfer charge is not present at the transfer position when the transfer material is not present at the transfer position during transfer or when the transfer material is not present at the transfer position, the nip portion between The oppositely charged toner whose polarity has been reversed due to the discharge electric field formed before and after the nip portion between the photoconductor and the transfer roller and the transfer current flowing through the transfer roller, before the transfer to the image area. Cleaning is performed by applying -500 V to the transfer roller at the portion (section A). Since the amount of the poorly charged toner and the oppositely charged toner when the toner adheres to the transfer roller is considerably smaller than that of the normally charged toner in the same case, the cleaning time required for one rotation of the transfer roller is sufficient.

Here, the cleaning must be a part before connecting to the image area. The reason is that the normally charged toner adheres to the transfer roller only at a specific time, but the developing bias voltage does not work effectively for the poorly charged toner, and the oppositely charged toner has already adhered to the transfer roller. Or, as described above, the toner that has just started to adhere is a reverse-charged toner whose polarity has been inverted due to the transfer current flowing through the transfer roller. is there.

Here, if the image area is transferred without cleaning at a portion before the image area is connected, the voltage applied to the transfer roller is applied to the transfer roller surface just before the image area is transferred. Since the toner has the same polarity as that of the toner, the toner is transferred to the back surface of the transfer material, that is, the transfer material back stain occurs.

Next, the transfer of the image area starts, and a normal transfer voltage of, for example, -2 KV is applied. (Section B) For the normally charged toner adhering to the transfer roller when the width of the transfer material is smaller than the width of the original, + cleaning is performed by applying +500 V to the transfer roller after the transfer is completed and before the post-rotation is stopped (C). section). From FIG. 2, the + cleaning time is sufficient for the rotation of the transfer roller 2 to 3 times, and the same + cleaning voltage as described above is applied to the normally charged toner at the time of paper jam and at the time of warm-up rotation after the jam processing. . In this embodiment, the transfer roller was set to have a volume resistance of 10 × 10 ⁹ Ωcm or less.

(Modification) In order to reduce the chance of performing cleaning, an example in which an optical sensor or mechanism for detecting dirt on the transfer roller is provided and a cleaning process is provided separately from the copy process when dirt is detected. Show.

FIG. 4 shows an example in which the reflection type photo interrupter 10 is installed at a position facing the transfer roller. The output of this sensor is monitored by the control unit 11, and when the level of the transfer material reaches the level at which the back of the transfer material becomes dirty, a cleaning voltage is applied to the transfer roller 6 by the power supply 12 after the transfer of the copy process is completed and before the post rotation is stopped. Then, transfer roller cleaning is performed. The cleaning process requires +
As cleaning, +500 V is applied for a time required for two or three rotations of the transfer roller. As an example having a mechanism for detecting dirt on the transfer roller, when toner adheres to the surface of the transfer roller, the resistance component and the capacity component of the toner enter serially between the roller photoreceptor and the ground. In this case, the current value flowing through the transfer roller changes, and when the current value is constant, the voltage value changes according to the amount of adhered toner. Thus, the transfer current or the transfer voltage is monitored, and when the transfer material reaches a level at which the back surface of the transfer material becomes dirty, the cleaning step described in the above embodiment is activated. The monitoring of the current value or the voltage value may be performed by applying a predetermined voltage or current before or after the transfer material exists at the transfer position in order to avoid the influence of the change in the resistance value of the transfer material. Further, as another example, by making it possible to arbitrarily start the above-mentioned cleaning process on the operation panel, the chance of + cleaning can be reduced.

Even in the case where a cleaning step is provided separately from the above-described copying process, for the above-mentioned reason, for the cleaning, the time required for one rotation of the -500 V transfer roller in the portion before the transfer of the image area is applied. By doing.

[0024]

As described above, according to the present invention, stable
Charging, and also reduces the back contamination of the transfer material.
Thus, a high quality image can be obtained .

[Brief description of the drawings]

FIG. 1 is a sequence diagram illustrating an operation of applying a voltage during cleaning of a transfer member according to the present invention.

FIG. 2 is a relationship diagram between a cleaning time and a cleaning effect.

FIG. 3 is a schematic side view of a main part of an electrophotographic apparatus suitable for employing the present invention.

FIG. 4 is a schematic side view of an embodiment having an optical sensor.

FIG. 5 is a diagram illustrating the relationship between the residual charge before charging of the photoconductor at the transfer position and the surface potential of the photoconductor after regular charging.

FIG. 6 illustrates a conventional voltage application during cleaning of a transfer member.
FIG. 4 is a sequence diagram showing the operation of the embodiment .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging roller 3 Light reflected from a document 4 Developing device 4a Developing sleeve 5 Transfer material 6 Transfer roller 7 Fixing device 8 Cleaner 9 Static elimination lamp 10 Reflection type photo interrupter 11 Control unit 12 Power supply

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiaki Kagawa 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Hiroshi Ishii 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Sharp (72) Inventor Shogo Yokota 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-5-313521 (JP, A) JP-A-3-69978 (JP, A) JP-A-6-51654 (JP, A)

Claims (2)

(57) [Claims] An image carrier, which is charged to a first polarity and on which a toner image is formed, and a contact transfer member for transferring the toner image on the image carrier to a transfer material and cleaning the adhered toner In the electrophotographic apparatus, the voltage of the polarity opposite to the first polarity applied to the contact transfer member at the time of cleaning is set to be equal to or lower than the discharge starting voltage between the image carrier and the contact transfer member. An electrophotographic apparatus characterized by the following. 2. An image carrier on which a toner image is formed by being charged to a first polarity, and a contact transfer member for transferring the toner image on the image carrier to a transfer material and cleaning the adhered toner. Wherein both the voltage of the first polarity and the voltage of the opposite polarity applied to the contact transfer member at the time of cleaning are set to be equal to or lower than the discharge starting voltage between the image carrier and the contact transfer member. An electrophotographic apparatus, characterized in that: