JPH0642101B2 - Electrophotographic recording device - Google Patents

Description

The present invention relates to a transfer type electrophotographic recording apparatus.

2. Description of the Related Art FIG. 3 shows an example of a conventional transfer type electrophotographic recording apparatus. A photoconductive insulating layer is formed on the surface of the drum-shaped photoreceptor 1. Around the photoconductor 1, along the clockwise rotation direction, a charging charger 2, an exposure device 3, a developing device 4, a transfer charger 5, a separation charger 6, a cleaning device 7, a charge eliminating device 8 and the like are arranged. There is.

The photoconductive surface of the photoconductor 1 is uniformly charged in advance to a predetermined polarity by the charging charger 2. Then, when the exposure device 3 projects light reflected from the document or light according to the image signal, the charged charges on the photoconductor 1 are selectively erased, and the electrostatic latent image of the image to be reproduced is reproduced there. An image is formed. This electrostatic latent image is developed by supplying the developer 9 containing colored fine particles called toner from the next developing device 4. The developing device 4 includes a magnet roller 4a and a non-magnetic sleeve 4b around the magnet roller 4a, and the relative rotation of the two conveys the developer 9 on the surface of the non-magnetic sleeve 4b. Due to friction with the magnetic carrier in the developer 9, the toner is triboelectrically charged to the polarity opposite to the latent image polarity in the case of regular development and to the same polarity as the latent image in the case of reversal development. Adheres to the image area. The recording sheet 10 is superposed on the developed toner image 9a, and by being charged from the back thereof with a polarity opposite to that of the toner by the transfer charger 5,
The toner image 9a is transferred to the recording sheet 10. The recording sheet 10 is separated from the surface of the photoconductor 1 by being discharged by the separation charger 6, and is conveyed toward a fixing device (not shown). The cleaning device 7 removes the residual toner on the surface of one of the photoconductors 1 and the static eliminator 8 removes the residual potential.

Problems to be Solved by the Invention In such a transfer type electrophotographic recording apparatus, the transfer characteristics depend on the humidity condition of the outside air. In particular,
When the humidity is high, the transferred image density is lowered or the transferred image is disturbed. This is because when the humidity becomes high, the recording sheet absorbs moisture and the electric resistance value decreases, so that the charge leaks when charged by the transfer charger, and the charge is sufficient to attract the toner on the photoconductor. Is not accumulated on the recording sheet and the adhesion of the recording sheet to the surface of the photoconductor is weakened.

In order to prevent such transfer failure due to moisture, a heat roll is provided in the recording sheet feeding section, and when the humidity is high, the heat roll heats the recording sheet to raise its electric resistance value to the value at normal times. Doing is one way. However, heating with a heat roll requires a rising time to reach a constant temperature, and constant heating increases power consumption, and there is a risk of overheating. It is also possible to increase the charge holding amount of the recording sheet by increasing the charging voltage by the transfer charger, but in the device that performs reversal development, the charging polarity by the transfer charger is opposite to the charging polarity of the photoconductor by the charging charger. Therefore, the electrostatic characteristics of the photoconductor are adversely affected in various ways.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an improved electrophotographic recording apparatus capable of eliminating transfer failure at high humidity by a simple method.

The electrophotographic recording apparatus according to the present invention has a means for directly or indirectly detecting the humidity of the outside air, and a charging potential (exposure to the photoreceptor before exposure to light when the humidity exceeds a certain value). Hereinafter, it will be referred to as an initial charging potential.) A means for switching to a higher value than in the normal case.

When the working humidity detecting means detects high humidity, the initial charge amount on the photoconductor is increased manually or automatically, and the recording sheet is brought into close contact with the surface of the photoconductor to perform good transfer.

Embodiment FIG. 1 shows an embodiment of the present invention. Third
The reference numerals used in the description of the drawings are used for similar members. In this embodiment, the reversal development method is adopted. The exposure device 3 irradiates the surface of the photoconductor 1 uniformly charged with a predetermined polarity by the charging charger 2 with light corresponding to an image signal. This image signal is obtained by scanning the document image, and the image portion of the document image is the output signal. Therefore, when light is emitted from the exposure device 3 in response to the image portion signal, the charged electric charge of the light-exposed portion is erased, and the non-imaged portion remains as the non-image portion. In such an electrostatic latent image, the potential of the image portion is near zero volt, so that toner is attached to the non-image portion to form a negative image if the regular development is performed. Therefore, the bias power source 11 is connected to the non-magnetic sleeve 4b of the developing device 4 so that the developing bias potential, that is, the potential of the sleeve 4b is set to be slightly lower than the potential of the non-image portion of the latent image, and the developer 9 is used. The toner inside is charged to the same polarity as the latent image polarity. By doing so, the potential difference from the sleeve 4b becomes larger in the image portion than in the non-image portion of the latent image, so that the toner adheres to the image portion due to this potential difference and a positive image is obtained.

The recording sheet 10 is superposed on the toner image 9a on the photoconductor 1, and the toner image 9a is transferred onto the recording sheet 10 by being charged from the transfer charger 5 with a polarity opposite to that of the toner image. . The recording sheet 10 is separated from the surface of the photoconductor 1 after the charge is removed by the separation charger 6, and the surface of the photoconductor 1 is cleaned by the cleaning device 7 and then removed by the charge removal device 8.

The transfer charger 5 transfers the toner image 9a onto the recording sheet 10, that is, the force with which the toner is attracted to the recording sheet.
Is proportional to the amount of charge held by the recording sheet 10 due to the charging, and is inversely proportional to the square of the distance between the toner and the recording sheet 10. Therefore, the transfer efficiency can be improved by increasing the charge amount by the transfer charger 5 or by bringing the recording sheet 10 into close contact with the surface of the photoconductor 1.

Therefore, in the present invention, the initial charging potential is increased at the time of high humidity where the transfer efficiency is deteriorated, and the recording sheet is brought into close contact with the surface of the photoreceptor as much as possible to prevent the transfer efficiency from being deteriorated. Therefore, the humidity detecting means 12 and the means 13 for switching the voltage applied to the charging charger 2 are provided. The humidity detecting means 12 may directly detect the humidity of the outside air or may indirectly detect the outside air humidity by measuring the electric resistance of the recording sheet 10. When the humidity detecting means 12 detects a certain humidity or more, the applied voltage switching means 13 switches the voltage applied to the charger 2 to a higher voltage than the voltage applied at the normal time by the signal. As a result, the photoconductor 1
The initial charging potential to the surface increases, the recording sheet 10 strongly adheres to the surface of the photoconductor 1 during transfer, and the decrease in transfer efficiency is prevented. FIG. 2 schematically shows such a potential relation of each part. The polarities of the potentials may be generally opposite.

When reversal development is performed, the ratio of the image portion in the electrostatic latent image is often about 10% in area ratio, so the potential of the non-image portion, which accounts for the remaining 90%, is increased to the initial charging potential. It is particularly preferable to increase the amount in order to strongly adhere the recording sheet to the surface of the photoconductor. Also,
The initial charging potential influences the fog or background stain of the non-image area, and increasing the initial charging potential tends to reduce the fog or background stain. Therefore, increasing the initial charging potential at high humidity does not lead to deterioration of image characteristics when reversal development is performed. Further, increasing the initial charging potential is also expected to increase the exposed portion potential, but for this purpose, for example, the exposure amount is increased to suppress the rise of the exposed portion potential, or the developing bias potential is set to the exposed portion. By raising the potential in proportion to the rise in the potential, the potential difference between the developing bias potential and the exposed portion potential can be made constant to prevent the image density from decreasing.

By the way, there is an upper limit in increasing the initial charging potential of the surface of the photoconductor 1, and if the charging potential near the upper limit is continuously used at high humidity, the photoconductor 1 may be fatigued and its life may be shortened. Also, the recording sheet 1 at high humidity
When the recording sheets 10 are laminated, it is considered that the electric resistance value of 0 decreases from the uppermost sheet which is in contact with the outside air or from there to several lower layers. In this case, the roll is considered to be the first roll or a few rolls from the first roll and the part fed from the roll. Therefore, when increasing the initial charging potential of the surface of the photoconductor 1, the number or the number of recording sheets 1
You may make it detect 0 and raise only these.

In the above embodiment, high humidity is detected directly or indirectly by some sensor, and the initial charging potential is automatically increased by the signal from these,
In the case of a normal electrophotographic copying machine, a person directly activates the apparatus so that the apparatus operates. Therefore, if a person detects high humidity by any means, for example, a manual switch is used. The applied voltage may be switched to a higher voltage by.

As described above, in the electrophotographic recording apparatus according to the present invention, the initial charging potential with respect to the surface of the photoconductor is increased when the humidity is high. Therefore, the recording sheet strongly adheres to the surface of the photoconductor and absorbs moisture from the recording sheet. It is possible to prevent the transfer failure due to the phenomenon, and it is possible to obtain a good transferred image under any environment.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic recording apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing potential relations of respective parts associated therewith, and FIG. 3 is a schematic configuration diagram of a conventional electrophotographic recording apparatus. Is. 1 ... Photosensitive member, 2 ... Charging charger, 3 ... Exposure device, 4 ... Developing device, 5 ... Transfer charger, 6 ... Separation charger, 7 ... Cleaning device, 8 ... Static elimination device, 9 ... ... developer, 10 ... recording sheet.

Claims (1)

[Claims] 1. A toner image is formed on a recording sheet by exposing the surface of a photoconductor to an electrostatic latent image to form an electrostatic latent image and adhering toner having the same polarity as the electrostatic latent image. An electrophotographic recording apparatus by a reversal development method by transferring, detecting means for directly or indirectly detecting humidity of outside air, charging means for charging the photoconductor, and humidity of the detecting means exceeds a predetermined value. An electrophotographic recording apparatus comprising: a control unit that controls the charging unit to increase an initial charging potential on the photoconductor.