JPS5835541A - Electrophotographic receptor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

An electrostatic latent image is formed on the photoreceptor by rotating a drum-shaped or belt-shaped photoreceptor and moving its peripheral surface cyclically in a fixed direction, and the formed electrostatic latent image is developed. A copying method in which a visible image obtained by 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, and the recording sheet may be used before or after the transfer of the visible image. , sometimes cut into sheet pieces.

In such a copying 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, when the above-mentioned repetition period becomes short 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 occurs.

In conventionally known copying devices, the repetition period of electrostatic latent image formation on the same part of the photoconductor is 4 times in the case of continuous copying.
The period is around seconds, and this period is sufficient for recovery from optical fatigue.

However, in order to improve copying efficiency, or by reducing the diameter of the drum-shaped photoreceptor and reducing the repetition cycle to around 2 seconds or even shorter, it is difficult to recover from photofatigue with a normal photoreceptor. However, the following problems occur.

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. On the other hand, 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 decrease stepwise 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. Furthermore, 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 photofatigue, or to fatigue the photoreceptor to the saturated state of photofatigue 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 cycle.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide an electrophotographic photoreceptor for use in a copying system with a short cycle of repeating the formation of an electrostatic latent image on the same portion of the photoreceptor, which recovers quickly from optical fatigue. It is in.

The present invention will be explained below.

First, let us briefly touch on the mechanism of photofatigue that occurs in electrophotographic photoreceptors.

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 are either electrons or
Alternatively, carriers have their own mobility depending on whether they are vacancies, and when an electric field acts on the photoconductive layer, carriers move according to their mobility. By the way, if the carriers described above are generated inside the photoconductive layer and the mobility differs depending on the polarity of the carriers, for example, if 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 remain inside the photoconductive layer for a long time. Stay. This results in a state in which the inside of the photoconductive layer is charged with positive carriers. So, this residual positive carrier is
This prevents positive charging of the photoreceptor.

Therefore, when forming a photoreceptor by providing a single photoconductive layer on a conductive substrate, the photoconductive layer should have approximately the same mobility of positive and negative carriers and be appropriately large. Unless this is selected, it will not be possible to obtain a photoreceptor with good recovery from optical fatigue.

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 carriers. The degree μ is the electric field strength 2 x 105
The point is that under the conditions of v/, , 10'ctIVV, t;m or more was selected. When the photoreceptor is configured with separate functions, the thickness of the photoconductive layer used as the charge generation layer can be made sufficiently thin, so problems caused by differences in the mobility of positive and negative carriers can be almost ignored. There are almost no material restrictions on the photoconductive material used for the layer. The charge generating agent used in the charge generating layer is, for example, Cd
55 e, trigonal glassy Sg+ sgTgl 5eG
Inorganic materials such as Sll or 73gAs doped with atoms such as e+ AS, Te+ Sh+Bi+Tα, and amorphous silicon: perylene pigments, polycyclic quinone pigments, indigoid pigments, cyanine dyes, quinoline pigments,
Organic materials such as styryl dyes and disazo pigments are used.
-30330, JP-A-53-15794, JP-A No. 53-
No. 125031, No. 54-116930, No. 54-1
No. 57745, No. 47-30330, No. 47-303
No. 31, No. 47-18544, No. 53-41230, No. 49-1231, No. 55-53333, No. 47
This method is proposed in publications such as No. 37543 and 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 thickness of the charge generation layer is suitably 0.1 to 5 μm, as in conventional functionally separated photoreceptors, and a barrier layer is formed between the charge generation layer and the conductive support. The photoreceptor is also similar to conventional photoreceptors. In addition, since there are a wide variety of materials for the charge transport layer,
There is a great deal of freedom in that choice. 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.

Amorphous S'+ or Japanese Patent Publication No. 55-42380 is used as a material constituting the charge transfer layer having a carrier drift mobility of 10', -d/V, sec or more under the conditions of electric field strength 2 x 10 V/sub. No., Japanese Patent Publication No. 55-15012
The hydrazone compound proposed in No. 8, JP-A No. 55-4760, etc. is suitable, and the thickness of the charge transfer layer is 7 to 50 μm.
m is appropriate.

The following is a description based on a specific experimental example.

Experimental Example A layer of As25g3 was formed as a charge generation layer to a thickness of 0.5 .mu.m by vacuum evaporation on the surface of a small diameter aluminum drum having a diameter of 1.degree., 3 Q mm and a length of 3 aomm. By the way,
The carrier mobility of As25g3 is 10 for electrons.
'('/y, see), and that for the vacancy is on the order of lO, and there is a difference of about 100 times between the two.

On this charge generation layer, a charge transport 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 vacancies as carriers in this charge transfer layer is 1O-6d/cm under an electric field strength of 2 x 105V/cm.
'V, g.

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 photoreceptor, 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 photoreceptor 1 at a moving speed of 100-1 (
At this time, the time required for one rotation of the photoreceptor l is 0.95 times. ), Charger 2 charges the surface to -700v.
, and performs slit exposure by irradiating the optical image of the document with a slit width of 5rrLrlL through the slit 3, and immediately develops the electrostatic latent image formed using a dry-component magnetic toner using the developing device 4. By repeating the process of transferring a visible image onto plain paper S, which is a recording sheet, using a transfer charger 5, cleaning the photoreceptor 1 after the transfer with a blade using a cleaner 6, and then performing static elimination exposure using a fluorescent lamp, an A4 I made a full size copy of the size original. The original is irradiated with a 450 cm logen lamp, and the visible image transferred onto the plain paper S is fixed onto the plain paper S by a heat roller (not shown).

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 forming an electrostatic latent image on the same portion of the photoreceptor is Q, 95 seconds as mentioned above.

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

Experimental Example The same as in Experimental Example 1 was applied as a charge generation layer on the surface of a small diameter aluminum drum with a diameter of 2° and a length of 3QQ myn.
A 0.5 μm thick layer of As25g3 was formed by vacuum evaporation, and amorphous S was formed on this layer as a charge transfer layer.

A layer with a thickness of 50 μm was formed by vapor deposition. This was 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 a document, exposure was performed by line scanning with helium-neon laser light. Hg
-Ne laser light has a wavelength 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 200 mm/se
A4 size images were obtained using the setting e, and the images were good with uniform image density and no afterimages. 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 means that the amorphous Se layer, which is a charge transfer layer, has a ratio of 2 x 1 to vacancies, which are carriers.
0.167/V under electric field strength of 05V/m, see
This is thought to be due to the extremely large drift mobility.

Furthermore, as a comparative example, a small-diameter drum-shaped photoreceptor as described above was prepared using polyN-vinyl carbazole as a charge transfer layer.
5-bis(p-diethylaminophenyl)-1,3,4-
Three types were formed using oxadiazole and triallylpyrazoline, and the same experiment as in Experimental Example 1 was conducted using these.

The result is that in each case, depending on the rotation of the photoreceptor,
The image density was clearly visible. Incidentally, the carrier drift mobility in these charge transfer layers is on the order of 10<->. Even if the repetition period of forming an electrostatic latent image on the same part of the photoreceptor 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 equal to or higher than IQ cd/V, sae.

[Brief explanation of the drawing]

FIG. 1 is a front view schematically showing the main parts of a copying apparatus using a small-diameter drum-shaped photoreceptor as one example of the photoreceptor according to the present invention. 1...7 photosensitive bodies, 2...charger, 4...
・Developing device, 5... Transfer charger, 6...
cleaner.

Claims (1)

[Scope of Claims] An electrostatic latent image is formed on the photoreceptor by rotating a drum-shaped or belt-shaped photoreceptor and moving its surface cyclically in a fixed direction. A copying method in which a visible image is developed and the resulting visible image is transferred onto a recording sheet, and
A photoreceptor used in a copying method with a short repetition cycle of forming an electrostatic latent image on the same part of a photoreceptor during copying or continuous copying, the photoreceptor comprising a conductive substrate, a charge generation layer, and a charge transfer layer. and the carrier drift mobility μ in the charge transfer layer is electric field strength 2×10. ” v7., 1O-6 under the conditions of
An electrophotographic photoreceptor having a cIV of 10.1.1 or higher.