JP2000010383A - Electrophotographic printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of reducing a printing grade by the degradation of the surface of a photoreceptor by contact of an electrifier and the photoreceptor. SOLUTION: In an electrophotographic printer for performing printing by an electrophotographic process by electrifying a photoreceptor 1 by an electrifier 2 contacting with the photoreceptor 1, a nonelectrified part is formed in the photoreceptor 1 at nonprinting time, a toner layer is stuck to this nonelectrified part, this toner layer is moved up to the electrifier 2, and the toner layer is interposed between the photoreceptor 1 and the electrifier 2 to put the photoreceptor 1 and the electrifier 2 in a noncontact state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic printer, and more particularly, to an electrophotographic printer that charges a photosensitive member by a charger in contact with the photosensitive member and performs printing by an electrophotographic process.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic printer has a fixing device for fixing a toner to a medium by arranging a charging device, an exposing device, a developing device, and a transferring device around a photosensitive member. To perform printing, first rotate the photoconductor, uniformly charge the surface of the photoconductor with a charger, and then apply light energy to the charged photoconductor surface with an exposure device to form an electrostatic latent image. It is formed. Toner is attached to the electrostatic latent image by a developing device, and then the toner is transferred from the photoconductor to a printing medium by a transfer device. The print medium is transported to the fixing device, and the toner transferred to the print medium is fixed by the fixing device.

[0003]

However, in the above-mentioned conventional electrophotographic printer, the charging device and the developing device have a unit structure integral with the photosensitive member, the charging device comprises a charging roller, and the charging roller comprises the photosensitive member. Is in constant contact with When the contact state of the charging roller with the photoconductor is long, a component of the charging roller causes a chemical change in a contact portion of the photoconductor. The chemical change and the mechanical pressure of the charging roller on the photoconductor degrade the surface of the photoconductor. When the surface of the photoconductor is partially deteriorated, the charge distribution on the surface of the photoconductor at the time of printing becomes nonuniform, and the electrostatic latent image formed on the surface is disturbed, thereby deteriorating the print quality.

As a countermeasure against this, when the product is shipped, direct contact can be avoided by sandwiching the paper between the charging roller and the photosensitive member, but this cannot be done after the start of use. As a countermeasure, provision of a mechanism for forcibly separating the charging roller from the photosensitive member when not in use is considered as a countermeasure. However, in this case, the configuration of the separation mechanism becomes complicated, which leads to an increase in the cost of the apparatus.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an electrophotographic printer that charges a photoconductor by a charger in contact with the photoconductor and performs printing by an electrophotographic process. The present invention is characterized in that the photoconductor and the charger are brought into a non-contact state by interposing a toner layer between the photoconductor and the charger.

[0006] The toner layer may be formed by adhering toner to a portion where the photoconductor is not charged by the charger, or may be formed by exposing the photoconductor by exposure means.

According to the present invention having the above-described structure, by interposing the toner layer between the photoreceptor and the charger, the photoreceptor and the charger can be separated even when not in use. Degradation of print quality due to deterioration of the print quality can be prevented.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals. FIG. 1 is a configuration diagram showing a main part of an embodiment of the present invention.

In FIG. 1, an electrophotographic printer according to an embodiment includes a rotatable photosensitive member 1 for forming an electrostatic latent image on a surface, a charger 2 for uniformly charging the surface of the photosensitive member 1, and a photosensitive member. An exposure unit 3 for irradiating light energy to one surface to expose the surface;
The image forming apparatus includes a developing device 4 for developing an electrostatic latent image on the photoconductor 1 and a transfer device 5 for transferring toner from the photoconductor 1 to a printing medium. The charger 2, the developing device 4 and the transfer device 5 are formed by rollers and rotate together with the photoconductor 1, and the charger 2 and the developing device 4 are in contact with the photoconductor 1.

The charger 2, the developing device 4 and the transfer device 5 are connected to a high-voltage power supply 6, and a predetermined voltage is applied from the high-voltage power supply 6. High-voltage power supply 6 is a control unit (microprocessor)
7 is controlled. The control unit 7 controls the exposure unit 3 and controls the operation of the entire printer.

Next, the operation will be described. FIG. 2 is a time chart showing an operation when the printing is completed and the photosensitive member is stopped. First, when printing is completed and the photosensitive member 1 is to be stopped, a negative voltage is still applied to the charger 2, a negative voltage is also applied to the developing device 4, and a positive voltage is applied to the transfer device 5. In the state where the voltage is applied or the voltage is zero, the control unit 7 turns off the voltage applied to the charger 2 for a certain period of time via the high voltage power supply 6. Thus, an uncharged portion is formed on the surface of the photoconductor 1. At this time, the exposure device 3 is not driven.

When the photosensitive member 1 rotates and an uncharged portion reaches the developing device 4, toner is attached to the uncharged portion by the developing device 4. FIG. 3 shows the photoconductor 1 to which the toner is attached. As shown in FIG. 3, the toner 10 is attached with a certain width in the axial direction of the photoconductor 1.

The toner 10 adhered to the photoreceptor 1 is transferred to the transfer unit 5
Before the control reaches, the control unit 7 applies a negative voltage to the transfer device 5 via the high-voltage power supply 6. The time for applying the negative voltage is set so that the toner 10 passes through the contact portion with the transfer device 5. As a result, the toner 10 on the photoconductor 1 is not transferred to the transfer device 5 but remains on the photoconductor 1.

The photosensitive member 1 further rotates, and the toner 10 reaches the charger 2. At this point, the rotation of the photoconductor 1 is stopped. That is, after the applied voltage of the charger 2 is turned off, the photosensitive member 1
Rotates once, and when the toner 10 enters between the charger 2 and the photoconductor 1, the rotation of the photoconductor 1 is stopped. When the toner 10 enters between the charger 2 and the photoconductor 1, the charger 2 and the photoconductor 1 are kept out of contact. This state is shown in FIG.
Shown in The width of the toner 10 is determined by the time when the voltage of the charger 2 is turned off. This width is set to be slightly larger than the nip amount at which the charger 2 and the photosensitive member 1 come into contact.

Thereafter, when printing is started, as shown in FIG. 5, the controller 1 sets the voltage applied to the charger 2 and the developing device 4 to a negative voltage. At this time, the potential of the developing device 4 is set lower than the potential of the charging device 2. At the same time, the photoconductor 1 is rotated. As the photoconductor 1 rotates, the toner 10 separates from the charger 2 and reaches the developing unit 4 on the photoconductor 1, and is moved from the photoconductor 1 to the developing unit 4 by the developing unit 4. Thus, the toner 10 is collected by the developing unit 4 and does not affect the subsequent printing. FIG. 5 is a time chart showing the operation at the start of printing.

An exposure device 3 may be used as a method for attaching toner to the photoreceptor 1. The operation in this case will be described below. When the printing is completed and the photosensitive member 1 is to be stopped, a negative voltage is still applied to the charger 2, a negative voltage is also applied to the developing device 4, and a positive voltage is applied to the transfer device 5. In a state where the voltage is zero or the voltage is zero, the control unit 7 drives the exposure unit 3 to expose a part of the photoconductor 1. As a result, the potential of the exposed portion of the photoconductor 1 decreases. The exposed portion is formed in a linear shape parallel to the axis of the photoconductor 1.

The photosensitive member 1 is rotated, and the exposed portion is
, The toner is attached to the exposed portion by the developing device 4. The photoreceptor 1 to which the toner has been attached is as shown in FIG.

The toner 10 attached to the photosensitive member 1 is transferred to the transfer device 5
Before the control reaches, the control unit 7 applies a negative voltage to the transfer device 5 via the high-voltage power supply 6. The time for applying the negative voltage is set so that the toner 10 passes through the contact portion with the transfer device 5. As a result, the toner 10 on the photoconductor 1 is not transferred to the transfer device 5 but remains on the photoconductor 1.

The photoconductor 1 further rotates, and the toner 10 reaches the charger 2. At this point, the rotation of the photoconductor 1 is stopped. When the toner 10 enters between the charger 2 and the photoconductor 1, the charger 2 and the photoconductor 1 are kept in non-contact as shown in FIG.

In this case, the thickness of the toner 10 can be freely changed by controlling the exposure time or the exposure pattern of the exposure unit 3 by the control unit 7. That is, by increasing the exposure time and increasing the density of the exposure pattern, the thickness of the toner 10 increases. For example, in a period shortly after the start of use of the printer, the charger 2
At this time, the layer of the toner 10 adhering to the photoreceptor 1 is thickened, and after a long use of the printer, the toner adhering to the surface of the charger 2 is very small. In this case, the layer of the toner 10 can be made thinner. However, it is necessary that the exposure pattern be such that the toner layer is formed over the entire photoconductor 1 in the axial direction.
Note that as the exposure device, a light emitting diode or a laser light emitting device may be used.

[0021]

As described above in detail, according to the present invention, the toner layer is interposed between the photoreceptor and the charger so that the photoreceptor and the charger can be directly used even when not in use. Since contact can be avoided, it is possible to prevent a decrease in print quality due to deterioration of the photoconductor. In addition, since a mechanism for separating the charger from the photoconductor is not required, it does not lead to an increase in the size of the apparatus or an increase in cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a main part of an embodiment.

FIG. 2 is a time chart showing the operation of the embodiment.

FIG. 3 is an explanatory diagram illustrating a photoconductor to which toner is attached.

FIG. 4 is an explanatory diagram illustrating toner between a photoconductor and a charger.

FIG. 5 is a time chart showing an operation at the start of printing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charger 3 Exposure device 7 Control part 10 Toner

Claims (3)

[Claims] 1. An electrophotographic printer that charges a photosensitive member by a charger in contact with the photosensitive member and performs printing by an electrophotographic process, wherein a toner layer is interposed between the photosensitive member and the charger during non-printing. An electrophotographic printer wherein the photoconductor and the charger are brought into a non-contact state by causing the photosensitive member and the charger to be in non-contact state. 2. The electrophotographic printer according to claim 1, wherein the toner layer is formed by attaching toner to a portion of the charging device where the photoconductor is not charged. 3. The electrophotographic printer according to claim 1, wherein the toner layer is formed by exposing the photoreceptor to light by an exposing unit and attaching toner to the exposed portion.