JPH0550740B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor for repeatedly forming electrostatic images by utilizing the memory effect of the photoreceptor. It is.

BACKGROUND ART Conventionally, in addition to printing technology, multi-sheet copying technology based on electrophotography has been used to reproduce multiple copies of manuscripts from the standpoint of ease of operation. As a typical example of this multi-copy electrophotographic method,
A so-called retention type electrostatic printing method is known in which the steps of charging, development, transfer and cleaning are repeated after imagewise exposing a photoconductive photosensitive layer having a photomemory effect. This method uses the principle that the exposed part of the photosensitive layer becomes conductive due to the photomemory effect, making it difficult for electric charge to be deposited on this part. The sensitivity of the photoreceptor is low, and the photoreceptor must be image-exposed using a high-output light source, which is inconvenient.

Recently, photoreceptors that utilize the optical memory effect have been developed; for example, Professor Inoue et al.
2,4,7-trinitrofluorenone (TNF)
A photoconductor coated with a mixed solution of leuco dye and leuco dye on an aluminum electrode, or a multilayer photoconductor with a layer of a composition of PVK and TNF on the layer coated with the above mixed solution, is used. Research is being conducted to form a memory image (decreased charge acceptance in the exposed area) on the photoreceptor through image exposure, and to obtain a large number of copies by repeating the process of charging, developing, and transferring. (Journal of the Photographic Society of Japan Vol. 44 No. 2 No. 104
(See pages 117-117 (1981)). Memory formation in these photoreceptors is said to result from a chemical reaction after light absorption between a charge transfer complex formed by TNF and a leuco dye.

Structure of the Invention According to the present invention, an electrophotographic photoreceptor is provided in which a memory image is formed based on a principle completely different from the photo-induced memory effect.

Further, according to the present invention, there is provided an electrophotographic photoreceptor having a novel multilayer structure that is completely different from conventional photoreceptors.

That is, the present invention provides a switching device comprising a conductive substrate, a complex of an electron-accepting substance and copper or silver provided on the conductive substrate, and which becomes and maintains a high conductivity state in a high electric field. The present invention relates to an electrophotographic photoreceptor comprising an element layer and a charge generation/transport layer or a charge acceptance layer provided on the switching element layer.

The invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1 showing the cross-sectional structure of this photoreceptor,
A switching element layer 2 is provided on the electrically conductive substrate 1, and a charge generation/transport layer or a charge acceptance layer 3 is provided on top of this layer 2. Although not shown, a charge injection barrier layer or an under layer for increasing adhesive strength may be provided between the conductive substrate 1 and the switching element layer 2, if desired.

An important feature of the present invention is that the switching element layer 2 is a switching element layer that becomes highly conductive in a high electric field and maintains this highly conductive state.

The principles of forming the memory layer and the electrostatic image of the photoreceptor of the present invention will be explained below with reference to Figures 2-A to 2-D.

First, in the charging-image exposure step shown in FIG. 2-A, the surface of the photoreceptor 4 is charged to a constant polarity by the corona charger 5, and then the surface is image-wise exposed by the light source 6. In the example shown in the figure,
The surface of the charge-accepting layer 3 is positively charged, and a negative charge is induced in the conductive substrate 1.

In Fig. 2-B showing the first stage of memory image formation, the surface charge remains unchanged in the dark area D, but in the bright area L, charges (carriers) are generated in the charge receiving layer 3, and holes ( +) is the lamination interface,
That is, it moves to the interface with the switching element layer 2,
As a result, a high electric field is applied to the switching element layer 2 in bright and dark L.

In Figure 2-C showing the second stage of memory image formation, the bright area L of the switching element layer 2 is in a high conductivity state (ON) due to the high electric field applied.
STATE), that is, induced into a low resistance state. The dark region D of the switching element layer 2 remains in a high resistance state (OFF STATE), and the switching element layer 2 continues to maintain the above-mentioned state, and as a result, in the bright region L, the conductive substrate 1 This makes it easy to inject electrons.

In FIG. 2-D showing the electrostatic image forming process, in a portion L that has been exposed once, electrons (-), which are easily injected in response to subsequent positive charging, contact the switching layer 2 in a highly conductive state. The charge image is formed by being injected into the charge-receiving layer 3 through the charge receiving layer 3, reaching the surface through the layer 3, and erasing the positive charges (+) on the surface. Although not shown, this charge image is
By developing with toner and transferring the formed toner image to paper etc. by a method known per se,
Copies or printed materials can be obtained. Thus, by performing the charging process a desired number of times as shown in FIG. 2-D after forming the memory image once shown in FIGS. 2-A to 2-C, it is possible to make a desired number of copies.

In the present invention, as is clear from the above description,
The light is characterized in that it is used only for the purpose of generating charges in the charge generation transport layer or the charge receiving layer 3, in other words, for applying a high electric field to the switching element layer 2. That is, in conventional multilayer photoreceptors, it was necessary to also expose the memory forming layer to light through the charge transport layer or the charge receiving layer to cause a photochemical change in the memory forming layer. Since this method only requires the generation of charges (carriers) in the charge generation transport layer or charge receiving layer, it is possible to form a memory image with a significantly lower exposure amount than in conventional methods. This advantage is achieved.

FIG. 3 shows a certain switching element layer (Cu/TCNQ to be described later) used in the present invention.
Curve 1 shows the relationship between applied voltage and current; curve 1 is the relationship between voltage and current for an untreated switching element layer, and curve 2 is a similar relationship for the switching element layer after high voltage application. It is something. From curve 1, it can be seen that this switching element layer has a high resistance state A with a gentle slope and a low resistance state B with an extremely large slope, and curve 2
It is clear that the high-low resistance state A almost disappears in the switching element layer once it is in a high conductivity state (ON STATE).

The switching element layer used in the present invention has a high resistance state (OFF STATE) electrical resistance (R _H ) of 10 ⁸ to 10 ¹⁴ Ω-cm, particularly 10 ⁹ to 10 ¹¹ Ω-cm, for charge retention. On the other hand, R _H and low resistance state (ON STATE) electrical resistance (R _L −
Ω-cm) (R _H /R _L ) is 1×10 ¹ to 1×
A value within the range of 10 ⁵ is desirable in terms of contrast.

Examples of switching elements having the above characteristics include tetracyanoethylene (TCNE), tetracyanoquinodimethane (TCNQ), tetracyanonaphthoquinodimethane (TNAP), and 2,3,5,6-tetrafluoro-7,7. , 8,8-tetracyanomonodimethane (TCNLF ₄ ) and other electron-accepting substances;
Complexes with copper or silver are preferably used.

These complexes can be directly formed in the form of a thin crystalline film on a conductive substrate by means such as vapor deposition, or microcrystals can be dispersed in a resin binder and provided on the conductive substrate. . Examples of resin binders include electrically insulating resins, standing polyester resins, acrylic resins, styrene resins, polycarbonate resins, vinyl chloride-vinyl acetate copolymers, phenoxy resins, epoxy resins,
Silicone resin, alkyd resin, etc. are used.
The microcrystalline complex and resin binder are used in a weight ratio of 1:4 to 4:1. These resin binders can be mixed with tetrahydrofuran, chloroform,
The microcrystalline complex is dispersed by dissolving in a solvent such as dioxane, dimethylacetamide, dimethylformamide, dimethylsulfoxide, etc., coated on a conductive substrate, and dried to form a switching element layer.

The charge generating transport layer or charge receiving layer used in the present invention must be capable of generating charges (carriers) upon irradiation with light, transporting the charges to the interface, and transporting the charges injected from the switching element to the surface. . From this point of view, this layer must be capable of transporting both holes and electrons.

For this purpose, mixtures of hole transporters and electron transporters or charge transport complexes are preferably used.

Examples of suitable hole transport materials are poly-N-vinylcarbazole, phenanthrene, N-ethylcarbazole, 2,5-diphenyl-1,3,4-oxadiazole, 2,5-bis-(4-diethylamino). phenyl)-1,3,4-oxydiazole, bis-diethylaminophenyl-1,3,6
-oxadiazole, 4,4'-bis(diethylamino-2,2'-dimethyltriphenylmethane,
2,4,5-triaminophenyl imidazole,
2,5-bis(4-diethylaminophenyl)-
1,3,4-triazole, 1-phenyl-3-
(4-diethylaminostyryl)-5-(4-diethylaminophenyl)-2-pyrizoline, p-diethylaminobenzaldehyde-(diphenylhydrazone), etc. Examples of suitable electron transport materials are 2-nitro-9- Fluorenone, 2,7-dinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone,
These include dinitroanthracene, dinitroacridine, dinitroanthraquinone, and tetracyanoquinodimethane.

When these mixtures or complexes have film-forming properties, they can be applied as a solution of an organic solvent onto the switching element layer, and when they do not have film-forming properties, they can be coated with the resin binder exemplified above. The above-mentioned combined substance may be dispersed in a solution of the above-mentioned material and applied to form a charge generation/transport layer or a charge receiving layer.

In the present invention, conductive metal substrates such as copper, aluminum, tinplate, etc., conductive treated paper, NESA glass, etc. are used as the conductive substrate, and these are used in the form of a sheet or a drum.

In the photoreceptor of the present invention, the thickness of the switching element layer is generally 1 to 5 μm, particularly 1.5 to 3.5 μm.
The thickness of the charge generation and transport layer is generally in the range of 6 to 2 μm, particularly in the range of 7 to 12 μm, to maintain the surface potential at a high level during charging and to prevent the memory effect. Preferred for maximum utilization.

The photoreceptor of the present invention is useful as an electrophotographic photoreceptor for making multiple copies with one exposure, and is also useful as a readable electronic recording medium.

Reference Example Formation of Switching Element Layer 10 parts by weight of copper-tetracyanoquinodimethane complex (Cu/TCNQ) ground by a ball mill, 10 parts by weight of polyacrylate resin (U-polymer8000 manufactured by Unitika), polyethylene glycol (PEG
The mixture was mixed with a solution consisting of 0.5 parts by weight of 1000 (manufactured by Sanyo Chemical Industries, Ltd.) and 90 parts by weight of chloroform, subjected to ultrasonic dispersion for 30 minutes, and then applied onto a copper substrate using a wire bar and dried. Drying is performed at 80℃ for 15 minutes, and if necessary vacuum drying for 6 hours to reduce the film thickness.
A switching element layer of 2 μm was formed.

Measurement of switching phenomenon Al was vacuum-deposited on the above switching element layer,
A sandwich-type cell was formed using an Al deposited film and a copper substrate as electrodes.

Next, a voltage of +3.0V to -3.0V was applied to the copper substrate side. The VI curve in the first voltage application is shown in curve 1 in FIG. Furthermore, the VI curve in the second and subsequent voltage applications is shown in Curve 2.

Example Production of photoreceptor A switching element layer was formed on a copper substrate by the same method as in the reference example.

Next, polyvinylcarbazole (LuvicanM-
170 BASF) 10 parts by weight and 90% tetrahydrofuran
In addition to parts by weight, a 10% PVK solution was prepared. this
0.5 parts by weight of 2,4,7-trinitro-9-fluoreno and 2.0 parts by weight of tetrahydrofuran were added to 10 parts by weight of 10% PVK solution and sufficiently dissolved using an ultrasonic disperser to prepare a photosensitive layer coating solution.

This coating solution was applied onto the previously formed switching layer using a wire bar and dried to form a layer of 7 μm.
A photosensitive layer was formed to obtain a photoreceptor.

Copying Test The photoreceptor prepared above was set in a surface potential light attenuator, and after positive corona discharge (+6.0 KV) was applied for about 30 seconds, the original was exposed. Note that exposure was performed for about 1 minute using a tungsten lamp (14 mW/cm ² ) as the irradiation light.

Next, replace the photoreceptor drum of a commercially available electrophotographic copying machine (TC-162: manufactured by Sanda Kogyo Co., Ltd.) with an alumite drum, attach this photoreceptor after exposure to it, and ground the copper substrate. Electrostatic printing was performed by continuously repeating the cycle of discharge (+6KV), toner development, and transfer cleaning to plain paper.

When printing was performed up to 50 cycles, almost no image noise or contrast disturbance was observed when compared with the initial image, and clear printed matter was obtained.

[Brief explanation of the drawing]

Fig. 1 shows the cross-sectional structure of the photoreceptor of the present invention, Figs.
The figure shows the relationship between applied voltage and current for the switching element layer used in the present invention. 1... Conductive substrate, 2... Switching element layer, 3... Charge generation transport or charge receiving layer.

Claims (1)

[Claims] 1. A conductive substrate, provided on the conductive substrate,
A switching element layer made of a complex of an electron-accepting substance and copper or silver, which becomes and maintains a high conductivity state in a high electric field, and a charge generation transport layer or charge provided on the switching element layer. An electrophotographic photoreceptor consisting of a receptor layer. 2. The photoreceptor according to claim 1, wherein the charge generating transport layer or the charge receiving layer comprises a mixture or a charge transport complex of a hole transporting material and an electron transporting material.