JPH0246937B2 - DENSHISHASHINFUKUSHAHOHO - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electrophotographic copying method.

By rotating a drum-shaped or belt-shaped photoreceptor and moving its circumferential surface cyclically in a fixed direction,
A copying system in which an electrostatic latent image is formed on this photoreceptor, the formed electrostatic latent image is developed, and a visible image obtained by the development is transferred onto a recording sheet is well known.

Formation of an electrostatic latent image on a photoreceptor is performed by uniformly charging the photoreceptor and exposing it to light. Exposure of the photoreceptor may be performed by irradiation with a light image of the original, or may be performed by line scanning with a laser beam or the like depending on the image information.

The recording sheet may be cut to a predetermined size in advance, or it may be wound into a roll and pulled out while being unwound, so that the recording sheet can be used before or after the transfer of the visible image. It may also be cut into sheet pieces.

In such a transfer method, if the repetition period of electrostatic latent image formation on the same part of the photoconductor is to be shortened during copying or continuous copying, a photoconductor that can quickly recover from optical fatigue should be used. There is a need.

During continuous copying, the repetition period of electrostatic latent image formation on the same part of the photoreceptor is shortened when the repetition speed of the copying process is increased to increase copying efficiency. In addition, if the repetition period is shortened during copying, the photoreceptor may be shaped like a small diameter drum, and when making one copy, the photoreceptor may rotate at an angle greater than 360 degrees during the formation of an electrostatic latent image. There may be cases where this is the case. In such a case, it is possible to downsize the copying apparatus.

In the case of conventionally known copying devices, the repetition cycle of forming an electrostatic latent image on the same part of the photoreceptor during continuous copying is around 4 seconds, and this cycle can cause problems due to light fatigue. This is sufficient for recovery time.

However, in order to improve copying efficiency, or to reduce the diameter of the drum-shaped photoreceptor, the repetition period may be reduced to 2.
When the time is around seconds or shorter, normal photoreceptors cannot sufficiently recover from optical fatigue, causing problems as described below.

In other words, if the recovery from photofatigue is not sufficient, the charged potential of the photoreceptor will decrease depending on the degree of photofatigue. , the image density of the obtained copy image decreases when the third copy is printed rather than the second copy. Furthermore, if the photoreceptor is made into a small diameter drum, the image density will gradually decrease even within the same copy image in response to the rotation of the photoreceptor. Such a decrease in image density continues until optical fatigue is saturated when the photoreceptor is used continuously. In addition, if recovery from optical fatigue is poor, the electrostatic latent image tends to be insufficiently erased, resulting in the occurrence of so-called afterimages.

To solve this problem, it is possible to increase the discharge voltage applied to the corona discharger that charges the photoreceptor in response to optical fatigue, or to fatigue the photoreceptor to the saturated state of optical fatigue in advance. Special measures are required, such as using it from scratch. Therefore, it is desired to develop a photoreceptor that can quickly recover from optical fatigue for use in the above-mentioned copying process with a short repetition period.

In view of the above-mentioned circumstances, it is an object of the present invention to use an electrophotographic photoreceptor that recovers quickly from optical fatigue and is used in a copying system in which the cycle of repeating the formation of an electrostatic latent image on the same part of the photoreceptor is short. The object of the present invention is to provide an electrophotographic copying method that allows high-speed copying with a small-sized copying device.

The present invention will be explained below.

Here, first, the mechanism of optical fatigue in electrophotographic photoreceptors will be briefly mentioned.

As is well known, when a photoreceptor is irradiated with light, carrier pairs of electrons and holes are generated in the photoconductive layer. The carriers generated in this way have their own mobility depending on whether they are electrons or holes, and when an electric field acts on the photoconductive layer, the carriers change their mobility. Move accordingly.
By the way, when the above-mentioned carrier is generated inside the photoconductive layer and the mobility differs depending on the polarity of the carrier, for example, when the mobility of electrons is significantly larger than that of holes, When an electric field acts on the photoconductive layer, electrons quickly move out of the photoconductive layer due to their high mobility, but holes have low mobility and do not conduct photoconductivity for a long time. Stays inside the layer. This results in a state in which the interior of the photoconductive layer is positively charged. This residual positive carrier then prevents negative charging of the photoreceptor.

Therefore, when forming a photoreceptor by providing a single photoconductive layer on a conductive substrate, the positive and negative carriers of the photoconductive layer have approximately the same mobility;
In addition, unless a suitably large size is selected, a photoreceptor with good recovery properties from optical fatigue cannot be obtained.

The present invention is characterized in that the electrophotographic photoreceptor is configured as a so-called functionally separated photoreceptor having a conductive substrate, a charge generation layer, and a charge transfer layer, and the charge transfer layer is configured to control the drift movement of the carrier. degree μ
However, under the condition of electric field strength 2 × 10 ⁵ V/cm, 10 ^-6 cm ² /
V.sec or more, and use this as a drum-shaped or belt-shaped electrophotographic photoreceptor.The electrophotographic photoreceptor is rotated and the photoreceptor is moved cyclically in a fixed direction around the photoreceptor. In an electrophotographic copying method in which an electrostatic latent image is formed on a body, the latent image is developed, and the resulting visible image is transferred onto a recording sheet, in order to obtain a visible image transferred onto the same recording sheet. An electrophotographic copying method in which, in forming an electrostatic latent image on the photoreceptor, the photoreceptor rotates through an angle of 360 degrees or more, and the repetition period of formation on the same part of the photoreceptor is 2 seconds or less. The point is that When the photoreceptor is constructed with separate functions, the thickness of the photoconductive layer used as the charge generation layer can be made sufficiently thin, so problems caused by the difference in mobility between the positive and negative carriers can be almost ignored. There are almost no material restrictions on the photoconductive material used for the layer. Charge generating agents used in the charge generating layer include, for example, CdSSe, trigonal glassy Se, SeTe, SeGe, As, Te, Sb,
Inorganic materials such as Se or SeAs and amorphous silicon doped with atoms such as Bi and Ta: perylene pigments, polycyclic quinone pigments, indigoid pigments, cyanine dyes, quinoline pigments, styryl dyes,
Organic materials such as disazo pigments are used, and these include, for example, Japanese Patent Publications Nos. 53-14932, 53-30330, 15794-1984, 53-125031, and 54-116930.
No. 54-157745, No. 47-30330, No. 47-
No. 30331, No. 47-18544, No. 53-41230, No. 49
−1231, No. 55-5333, No. 47-37543, No.
It is proposed in various publications such as No. 53-133445. A charge generating layer is formed by coating these charge generating agents on a conductive support with or without an adhesive or by vapor deposition. The appropriate thickness of the charge generation layer is 0.1 to 5 μm, as in conventional functionally separated photoreceptors, and a barrier layer can be formed between the charge generation layer and the conductive support. It is also similar to the conventional photoreceptor. Furthermore, since there are a wide variety of materials for the charge transfer layer, there is a great deal of freedom in selecting the material.
As a result, a desired photoreceptor, that is, one with good recovery from optical fatigue, can be obtained more easily than one having a single photoconductive layer.

In the present invention, the drift mobility of the carrier is 10 ^-6 cm ² /V.sec under the condition of electric field strength of 2 × 10 ⁵ V/cm.
The material constituting the above charge transfer layer is amorphous.
Se, or JP 55-42380, JP 55-
Hydrazone compounds proposed in JP-A No. 150128, JP-A No. 55-4760, etc. are suitable, and the thickness of the charge transfer layer is preferably 7 to 50 μm.

According to the electrophotographic copying method of the present invention, high-speed copying can be performed using a small-sized copying device.

Hereinafter, description will be given based on specific examples.

Experimental Example 1 A layer of As ₂ Se ₃ was formed as a charge generation layer to a thickness of 0.5 μm by vacuum evaporation on the circumferential surface of a small-diameter aluminum drum having a diameter of 30 mm and a length of 300 mm. Incidentally, the carrier mobility of As ₂ Se ₃ is on the order of 10 ^-7 (cm ² /V.sec) for electrons and on the order of 10 ^-5 for vacancies, and both have about 100
There is a difference of twice as much.

On this charge generation layer, a charge transfer layer made of hydrazone mixed with polycarbonate as a binder was formed to a thickness of 15 μm by a dipping method. The mobility of carrier holes in this charge transfer layer is 10 ^-6 under an electric field strength of 2×10 ⁵ V/cm.
cm ² /V.sec.

Using the small-diameter drum-shaped functionally separated photoreceptor thus obtained, a copying device as shown in the figure was manufactured. In the figure, reference numeral 1 indicates a photosensitive member, reference numeral 2 a charger, reference numeral 3 a slit for slit exposure, reference numeral 4 a developing device, reference numeral 5 a transfer charger, and reference numeral 6 a cleaner.

While rotating the photoconductor 1 at a peripheral surface movement speed of 100 mm/sec (at this time, the time required for one rotation of the photoconductor 1 is 0.95 sec), the surface is charged to -700V by the charger 2, and the slit 3 , the original light image is irradiated with a slit width of 5 mm to perform slit exposure, and the electrostatic latent image formed is immediately developed with dry monocomponent magnetic toner by the developing device 4, and the visible image is transferred to the charger 5. is transferred onto plain paper S as a recording sheet, and the photoreceptor 1 after transfer is
Clean the blade with Cleaner 6,
Next, by repeating the process of performing static elimination exposure using a fluorescent lamp, a full size copy of the A4 size original was made. The original is irradiated with a 450V halogen lamp, and the visible image transferred onto the plain paper S is transferred to the plain paper S by a heated roller (not shown).
fixed on top.

To obtain one copy of the same size from an A4 size original, the photoreceptor 1 rotates a little, about two revolutions.
That is, the repetition period of electrostatic latent image formation on the same portion of the photoreceptor is 0.95 seconds as mentioned above.

As a result of copying, a good copy image with uniform image density and no afterimage was obtained. That is, the photoreceptor has good recovery properties against optical fatigue.

Experimental Example 2 As in Experimental Example 1, a 0.5 μm layer of As ₂ Se ₃ was formed as a charge generation layer on the circumferential surface of a small-diameter aluminum drum with a diameter of 30 mm and a length of 300 mm using a vacuum evaporation method.
On this layer, a 50 μm thick layer of amorphous Se was deposited as a charge transport layer. This is incorporated into a copying machine as shown in the figure as a photoreceptor 1, and instead of being exposed by irradiation with a light image of an original, helium
He-Ne laser light, which performs exposure by line scanning with neon laser light, has a diameter of 632.8 μm.
Since Se is not sensitive to light of this wavelength, the writing laser light passes through the charge transfer layer and generates carriers in the charge generation layer.

The photoreceptor 1 was negatively charged by the charger 2, and a copying process was performed. The circumferential speed of photoreceptor 1 is
I set it to 200mm/sec and got an A4 size image, but
It was a good image with uniform image density and no afterimage. In this case, the repetition period of electrostatic latent image formation on the same part of the photoreceptor is extremely short, 0.5 seconds or less, but the recovery property against optical fatigue is extremely good. This is thought to be because the amorphous Se layer, which is the charge transfer layer, has an extremely large drift mobility of 0.16 cm ² /V.sec with respect to the carrier vacancies under an electric field strength of 2 × 10 ⁵ V/cm. It will be done.

Further, as a comparative example, a small drum-shaped photoreceptor as described above was used as a charge transfer layer of polyN-vinylcarbazole, 2,5-bis(P-diethylaminophenyl)-1,3,4-oxadiazole, and triallylpyra. Three types of zolin were formed, and the same experiment as in Experimental Example 1 was conducted using these. The result is
In both cases, image density clearly appeared as the photoreceptor rotated. Incidentally, the carrier drift mobility in these charge transfer layers is on the order of 10 ^-7 . Even if the repetition period of forming an electrostatic latent image on the same part of the photoconductor was set to 2 seconds or more, recovery from optical fatigue was still insufficient, and changes in image density and afterimages appeared. From this, it is considered that the limit of recovery is that the carrier mobility in the charge transfer layer is 10 ^-6 cm ² /V.sec or more.

[Brief explanation of the drawing]

The figure is a diagram schematically showing the main parts of an example of an apparatus for carrying out the electrophotographic copying method of the present invention. 1... Photoreceptor, 2... Charger, 4... Developing device, 5... Transfer charger, 6... Cleaner.

Claims (1)

[Claims] 1. An electrostatic latent image is formed on the photoconductor by rotating a drum-shaped or belt-shaped electrophotographic photoconductor and moving the circumference cyclically in a fixed direction. In an electrophotographic copying method in which an image is developed and the resulting visible image is transferred onto a recording sheet, an electrophotographic photoreceptor has a conductive substrate, a charge generation layer, and a charge transfer layer, and the charge transfer layer The drift mobility μ of the kyalid at is the electric field strength 2・
10 ^-6 cm ² /V·sec or more under the condition of 10 ⁵ V/cm, and in forming an electrostatic latent image on the photoconductor to obtain a visible image transferred onto the same recording sheet, An electrophotographic copying method characterized in that the photoreceptor rotates at an angle of 360 degrees or more, and the repetition period of forming an electrostatic latent image on the same part of the photoreceptor is 2 seconds or less.