JPH0335258A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To eliminate the influence of a transfer charger in a previous process and to obtain sharp image without fogging by providing a switching means switching a main electrifying means and an AC voltage impressing means and turning the switching means to the AC voltage impressing means when a copy is made on paper larger than the previous copying process. CONSTITUTION:An electric charger 2 is constituted of a main electrifier 2a and an AC voltage electrifier 2b, which can be switched by a switch 2c according to necessity. Copying processes are repeated and copied images are successively obtained. For example, when copying is carried out with respect to large sized paper in a next process, the switch 2c of the charger 2 is turned onto the AC voltage electrifier 2b side and a prescribed voltage is impressed on the surface of a photosesitive drum 1, whereby residual charges applied by a transfer charger 5 in the previous process are removed, afterward, the switch is turned onto the main electrifier 2a side. Therefore, when the copy is made on the paper larger than the previous process in size, it is eliminated that the fogging arises on both edges of the paper under the influence of the transfer charger 5 in the previous process, and sharp image without fogging can be obtained for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic apparatus using an electrophotographic method, such as a printer or an electrophotographic copying machine.

(Prior Art) Generally, in an electrophotographic apparatus using an electrophotographic method, a copied image is obtained by an image forming process as described below. First, the surface of an image carrier such as a photoconductor drum having photoconductivity is uniformly charged. Next, an electrostatic latent image is formed by projecting the document image onto the photoreceptor drum. This electrostatic latent image is made visible by charging electrostatic particles such as toner and making them adhere to the electrostatic latent image. This visible image is transferred to a transfer material such as a sheet of paper by applying a charge having a polarity opposite to that of the toner from behind the transfer material using a transfer charger or the like. Further, the transferred image transferred to the transfer material is melted and fixed to the transfer material by a fixing roller, thereby obtaining a copy image.

Note that the toner remaining on the photoreceptor drum is scraped off by a cleaning device or the like, and the charge remaining on the photoreceptor drum is erased by a static elimination charger, a static elimination lamp, etc., and the next copying process begins. Thereafter, the above-described image forming process is repeated to repeatedly obtain copied images. In such electrophotographic copying machines, OPCs (organic photosensitive drums) are widely used because, compared to inorganic photosensitive drums, spectral sensitivity can be obtained by selecting materials. However, such an OPC has the disadvantage that if the tram surface becomes charged with a polarity opposite to the normal charging polarity, the static electricity cannot be completely removed only by normal static elimination means such as a static elimination lamp or a static elimination charger. For this reason, for example, A4
When passing A3 size paper after passing A3 size paper, there was a problem in that fogging occurred at both ends of the A3 size paper. This is because there is no paper on the photoreceptor drum during the transfer process when passing A4 paper, and the charge remains in the charged area of the direct transfer charger before entering the copying process for the next A3 size paper. This is because toner adheres to this area.

(Problems to be Solved by the Invention) As detailed above, in an electrophotographic apparatus that uses conventional reversal development, when passing a larger size of paper after the pre-copying process, it is necessary to There was a problem in that fogging occurred at both ends due to the influence of the transfer charger in the previous copying process.

In order to solve the above-mentioned problems, the present invention provides means for applying alternating current to the image carrier in addition to the main charging means, and when copying onto paper of a larger size than in the previous copying step, charging by the main charging means is provided. The object of the present invention is to apply alternating current to the image carrier by the alternating current voltage applying means before the step, thereby eliminating the influence of the transfer charger in the previous step and obtaining a clear image without fog.

(Means for Solving the Problems) According to the present invention, when the size of the paper is made larger than that in the previous process, an AC voltage can be applied before charging by the main charging means, The structure is such that the charge remaining on the photoreceptor in the previous process is removed. The main charging means and the AC voltage application means can be switched by a changeover switch, and the auxiliary charging means performs charging only when the size of the paper is made larger than the previous step, before the main charging means charges.

(Function) According to the present invention, when the size of paper is made larger than that in the previous process, since the AC voltage application means is provided together with the main charging means, the charging by the AC voltage application means is replaced by the charging by the main charging means. can be carried out before the process to remove residual charges caused by the transfer charger in the previous process. For this reason,
Even when copying onto paper of a larger size than that used in the previous process, fogging does not occur at both ends of the paper, and clear images can be obtained for a long time.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

First, the structure of the electrophotographic copying machine used in this embodiment will be explained with reference to FIG. An OPCP ram 1 (organic photosensitive drum 1) serving as an image carrier is installed in the center of the electrophotographic copying machine, and can rotate clockwise as shown by the arrow in the figure. Around the photosensitive drum 1, a charging charger 2, an exposure lamp 3, a reversal developing device 4, a transfer charger 5, a cleaning device 6, and a static elimination lamp 7 are arranged in this order clockwise. The charger 2 further includes a main charger 2a and an AC voltage charger 2b, which can be switched as necessary by a switch 2c. Further, a paper conveyance path 8 is formed between the photoconductor 1 and the transfer charger 5, and a pair of paper feed rollers 9 is provided at one end of the paper conveyance path 8, and a pair of fixing rollers 10 are provided at the other end of the paper conveyance path 8.
A pair of paper discharge rollers 11- is provided.

Next, the operation of this electrophotographic copying machine will be explained.

First, the switch 2c of the charger 2 is set to the main charger 2a side so that the surface of the OPCP ram 1 is uniformly charged by the charger 2. Next, an original image is projected by the exposure lamp 3 to form an electrostatic latent image on the OPCP ram 1. The electrostatic latent image is reversely developed by adhering toner particles to the electrostatic latent image. Meanwhile, in synchronization with the formation of this electrostatic latent image, an A4 size paper P is fed onto the paper conveyance path 8 by a pair of paper feed rollers 9. The formed visible image is transferred to the paper conveyed on the paper conveyance path 8 by charging of the transfer charger 5, and the transferred image is further fixed to the paper P by the fixing roller 10, thereby obtaining a copy image. O
Toner remaining on the PCP ram 1 without being completely transferred is scraped off by a cleaning device 6. The residual charge on the OPC drum 1 is almost completely removed by the static elimination lamp 7, and the next copying process begins.

Thereafter, the above-described copying process is repeated to obtain copied images one after another. For example, when copying is performed on A3 size paper P- in the next process, first set the switch 2c of the charger 2 to the AC voltage charger 2b side to remove the residual charge caused by the transfer charger in the previous process. . Thereafter, the switch is switched to the main charger 2a side, and the normal copying operation is performed.

As a result, static electricity on the photoreceptor drum 1 can be completely eliminated, so even when copying a sheet larger than that in the previous process, fogging will not occur at both ends of the paper due to the influence of the transfer charger 5 in the previous process. do not have.

[Effects of the Invention] As described in detail above, according to the present invention, in an image forming apparatus using reversal development, an AC voltage applying means is provided together with a charger, and if necessary, charging by the main charger can be stopped. Since charging is performed using an AC voltage applying means beforehand, clear images without fogging can be obtained for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of an electrophotographic apparatus used in an embodiment of the present invention. 2...Charger 2a...Main charger 2b...AC voltage charger 2C...Switch

Claims (1)

[Claims] a main charging means for charging the surface of the image carrier to a constant polarity;
an alternating current voltage applying means for applying an alternating current to the surface of the image carrier; a switching means for switching between the main charging means and the alternating current voltage applying means; an exposing means for exposing a document image onto the image carrier; An electrophotographic apparatus comprising a reversal developing means for reversing developing an electrostatic latent image formed by the reversing developing means, and a transfer means for transferring a developer image developed by the reversing developing means onto a transfer material. .