JPH01276184A - Formation of image - Google Patents

Abstract

PURPOSE:To obtain an excellent image which has neither fogging nor a decrease in density by applying a minus DC voltage which has the opposite polarity from that in electrostatic charging operation to an organic photoconductive belt which is charged positively in a destaticizing process. CONSTITUTION:A drum-shape photosensitive body 10 is made of an organic photoconductor which is charged positively. When copying operation is started, the photosensitive body 10 is rotated as shown by an arrow (x) and charged uniformly and positively by an electrostatic charger 13 to enter an exposure process. Then the photosensitive body 10 forms a copy image on sheet paper through a developing device 16, a transfer charger 17, and a separation charger 18. Then the paper reaches a destaticizing device 21 through a cleaning device 20 and is destaticized here by being given negative charges without any optical fatigue, and next copying operation is made ready.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an electrophotographic device that forms images using a positively charged organic photoconductor, The present invention relates to an image forming method that prevents deterioration of characteristics.

(Prior Art) Photoreceptor materials for conventional electrophotographic devices such as copying machines and laser printers include selenium [Se] and selenium-tellurium (S).
e-Te) alloy, arsenic selenium [As2Se3].

Inorganic materials such as zinc oxide (ZnO) are mainly used. However, selenium (Se) and arsenic selenium [
As2Se3] is harmful to the human body, so the used photoreceptor must be collected after use.

In addition, in the case of selenium [Se], the crystallization temperature is 50 to 6
Because it has a low characteristic of 0 ('C), it easily crystallizes, and during repeated copying, a residual charge is generated in the crystallized part, deteriorating the image quality, and the low hardness makes it long lasting. On the other hand, there is the problem that arsenic selenium (A
s2Se3) has the problem that photoreceptor characteristics such as charging ability and sensitivity change significantly due to optical fatigue, and temperature characteristics are also poor. And for zinc oxide (ZnO),
The problem is that a long life cannot be achieved because the surface is soft and easily scratches.

For this reason, in recent years, as a solution to the above problems, photoreceptor materials such as amorphous silicon (hereinafter referred to as a-5i) and organic photoconductor (hereinafter referred to as OPC), which are non-polluting and do not require recovery processing, have been developed. It is being considered to apply it to A-5i has excellent printing durability and impact resistance, and has the advantage of having high spectral sensitivity in a wide wavelength range from the entire visible light region to the near-infrared region. It has the disadvantage of easily causing flow. Furthermore a-5
i has excellent printing durability due to its high Vickers hardness,
Although it is mainly used for high-speed devices, the high manufacturing cost makes it impossible to apply it to medium- to low-speed devices that require lower prices. On the other hand, in OPC, a-8
It is cheaper than OPC i, and can be applied to medium- and low-speed equipment. Moreover, depending on the selection of materials, printing durability and sensitivity characteristics can be greatly improved compared to conventional ones, and negatively charged OPC
Because it is easier to obtain toner compared to conventional OPCs, the development of positively charged OPC in which a charge transport layer (hereinafter referred to as CTL) and a charge generation layer (hereinafter referred to as CGL) are sequentially laminated on a conductive support is particularly important. It is progressing. However, such positive charging O
In the case of PCs, optical fatigue caused by exposure to light or charge removal causes an increase in accumulated charge during repeated copying, a decrease in charging ability, the generation of pinholes, and an increase in exposure sensitivity, resulting in fogging of images. In addition, white spots may appear in the image, and the density of halftone areas may decrease, resulting in a deterioration of image quality.

(Problems to be Solved by the Invention) In conventional positively charged OPCs, residual potential increases due to optical fatigue during repeated image forming steps, reducing charging ability and causing fogging on images. This may cause a decrease in concentration, etc.
This has the problem that the image quality is significantly degraded.

Therefore, the present invention aims to eliminate the above problem, and is aimed at eliminating the above-mentioned problem.
An object of the present invention is to provide an image forming method capable of obtaining a good image without fogging or loss of density even if the image forming step is repeated using C.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention applies a negative polarity DC voltage, which is the opposite polarity to that during charging, to the positive band '11tOPC in the static elimination step without using exposure. This method aims to improve image quality by reducing the number of exposures compared to the conventional method.

(Function) By the above-mentioned means, the present invention eliminates positive charge during the conventional static elimination process.
This prevents the optical fatigue that occurs in C, prevents an increase in accumulated charge and a decrease in charging ability, and provides good images without fogging or decrease in density.

(Example) First, the principle of generation of accumulated charge and reduction of charging ability of positively charged OPC will be explained. That is, positively charged OPC generally has a layered structure in which CTL and CGL are sequentially laminated on a conductive support. Then, during image exposure, hole/'ichiko pairs are generated in the CGL by light irradiation, and among these, electrons reach the surface, neutralize the positive charges on the positively charged surface of 020, and move onto the positively charged O20. While forming an electrostatic latent image, holes reach the conductive support via the CTL. However, at this time, some of the holes are trapped at the boundary between CGL and CTL. Such hole traps are also generated during static elimination exposure, and while copying is repeated, these trapped holes are sequentially increased and become the accumulated charge of the positively charged OPC. Furthermore, CGL, C
The charging ability of both TI and TI is significantly reduced due to optical fatigue.

Next, one embodiment of the present invention will be described with reference to FIGS. 1 and 2. (10) is a drum-shaped photoreceptor made of positively charged OPC, and the conductive substrate is aluminum [A2
] on the support (11) by the manufacturing method described below.
L (12a) and CGL (12b) are sequentially stacked. That is, first, hydrazone represented by the formula is mixed with a binder resin, phenoxy represented by the formula, and the support (11) is immersed in a liquid in which these are dissolved in a cyclohexane solvent, and this is dried. Form CTL (12a).

Next, the azo pigment represented by the formula, the hydrazone represented by the (1st formula), and the phenoxy represented by the (3rd formula) are mixed, and these are dissolved in a solvent of 1,1,2-trichloroethane to create a liquid. A support (11) having CTL (12a) is immersed therein and further dried to form CGL (12b).

Furthermore, around the photoreceptor (10), about 7
00 (V) charging charger (13), exposure device (1, 4), developing device (16), transfer charger (17), peeling charger (18), cleaning device (20), static eliminator (21) Image forming apparatuses such as the following are provided. And the static eliminating bag [(21) is the power supply (21
It consists of a charger to which a DC voltage of -5 (KV) is applied by a).

When copying is started, the photoreceptor (10) is rotated in the direction of the arrow, and the charger (13) is rotated in the direction of the arrow.
), and then an exposure process is performed. Thereafter, the photoreceptor (10) passes through a developing device 1 (16), a transfer charger (17), and a peeling charger (18) to form a copy image on a sheet paper (not shown), and then passes through a cleaning device (20) and a static eliminator. (21) is reached,
Here, a negative charge is applied and the charge is removed without being subjected to optical fatigue, and the next copy is made possible.

Furthermore, when copying was repeated in this manner, fogging and density loss due to light fatigue appeared after continuous use of about 5000 sheets, whereas with 15000
Good copy images could be obtained even after continuous use of more than (1) copies.

With this configuration, the photoreceptor (10) is not exposed to light during the static elimination process, and light fatigue during the copy cycle is less than in the past, so the accumulated charge due to repeated copying is reduced. At the same time, it is possible to prevent a decrease in charging ability, and it is possible to obtain a good image without fogging or decrease in density.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be modified in various designs. For example, the DC voltage application device may be a conductive brush etc. that slides into positive contact with the positively charged OPC and applies a negative polarity DC voltage. However, the magnitude of the applied voltage may be about -1 [KV] to -7 (KV), and more preferably -2 (KV) to -5 (
KV). Further, the image forming process performed on the positively charged OPC is not limited, and after the development process is completed, a static elimination process may be performed before the transfer process to erase excess charge, or
Alternatively, a static elimination process for eliminating residual toner may be performed before the cleaning process. Furthermore, during image exposure 4
Although the type of light source used for
Even though OPC has spectral sensitivity in the long wavelength region, the reproducibility of images of red parts of stamps and the like is also improved. Although an AC voltage application device can be considered as a static elimination method that does not depend on the dew point, a DC voltage application device has better static elimination efficiency because it does not apply a positive charge during static elimination, and the applied voltage can therefore be reduced, making it possible to use a smaller power supply. This makes it possible to make the entire device smaller and lighter.

〔Effect of the invention〕

As explained above, according to the present invention, the static elimination process can be performed by applying a negative charge without irradiation with light, and the optical fatigue of the positively charged OPC can be reduced compared to the conventional method, and the image forming process can be improved. There is no fear that the stored Vt charge will increase or the charging ability will be reduced even after repeated use, and good images without fogging or density reduction can be obtained, and positive charging is possible.
It is possible to extend the life of C.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the present invention, FIG. 1 being a schematic sectional view thereof, and FIG. 2 being a partial sectional view showing the photoreceptor thereof. 10... Photoreceptor, 11... Support, 12
a-CTL, 12b...cGL, 13
...electrostatic charger, 21...device, agent: patent attorney Norio Ogo 7361

Claims (1)

[Claims] An image forming method in which an image forming step is performed on a positively charged organic photoconductor, characterized in that a static elimination step is performed using a negative polarity DC voltage applying device.