JPH0550741B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to electrophotography, and more particularly to a method for forming photoreceptor memory images using new principles.

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 viewpoint of ease of operation. A typical example of this multi-sheet copying electrophotographic method is so-called retention type electrostatic printing, in which the steps of charging, development, transfer, and cleaning are repeated after a photoconductive photosensitive layer having a photomemory effect is imagewise exposed. The law is known. 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 and others have developed poly-N-vinylcarbazole (PVK), 2,4,7-trinitrofluorenone (TNF ) and a mixed solution of leuco dye coated on an aluminum electrode, or a multilayer photoreceptor with a layer of a composition of PVK and TNF on the layer coated with the above mixed solution. Research has been conducted to form a memory image (decreased charge receptivity in the exposed area) on the photoreceptor by exposing the image twice, 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, 2)
No. 104-117 (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 image is provided in which a memory image is formed by a principle completely different from the memory effect caused by a photoinduced chemical reaction.

Further, according to the present invention, there is provided a photographic method using an electrophotographic photoreceptor having a novel multilayer structure completely different from that of 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. An electrophotographic photoreceptor comprising an element layer and a charge generation/transport layer or charge receiving layer provided on the switching element is charged and image exposed to form a memory image on the photoreceptor. Concerning the characteristic electrophotographic method.

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

In FIG. 1 showing the cross-sectional structure of a photoreceptor used in the present invention, a switching element layer 2 is provided on a conductive substrate 1, and a charge generation transport layer or a charge acceptance layer 3 is further provided on this layer 2. It is provided. 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 principle of forming the memory layer and the electrostatic image of the photoreceptor according to 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, which shows the electrostatic image forming process, in a portion L that has been exposed once, electrons (-), which are easily injected against subsequent positive charging, are transferred through the switching layer 2 in a highly conductive state. The charge image is formed by being injected into the charge-receiving layer 3, passing through the layer 3 to the surface, and erasing the positive charges (+) on the surface. Although not shown, a copy or printed matter can be obtained by developing this charge image with toner by a method known per se and transferring the formed toner image onto paper or the like. Thus,
By performing the charging process a desired number of times as shown in FIG. 2-D after one memory image formation shown in FIGS. 2-A to 2-C, a desired number of copies can be made.

In the present invention, as is clear from the above description,
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. In this case, the charge generation transport layer 1 contains charges (carriers) in the charge acceptance layer.
Since it is only required to generate , it is possible to achieve the advantage that a memory image can be formed with a significantly smaller exposure amount than the conventional method.

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 from curve 2, once the switching element layer is in a high conductivity state (ON STATE), , it is clear that the high resistance state A has almost disappeared.

FIG. 4 is a diagram showing the relationship between the surface potential and time of a photoreceptor in which Cu.TCNQ, which will be described later, is used as a switching element layer, and a PVK/TNF complex is used as a charge generation transport layer or a charge acceptance layer. 1 is the surface charging potential of an untreated photoreceptor, curve 2 is the surface charging potential after the start of exposure, and curve 3 is the surface charging potential when the photoreceptor whose switching element layer has become highly conductive due to charging exposure is recharged. show. In Figure 4, V ₀ is the initial saturation charging potential of the photoreceptor with the switching layer in the high resistance state (OFF STATE), and V ₁ is the initial saturation charging potential of the photoreceptor with the switching layer in the high conductivity state (ON STATE). It is the saturation charging potential of the body, and the memory effect (F) is expressed by the following formula: F=V ₀ −V ₁ /V ₀ =ΔV/V ₀ .

The switching element layer used in the present invention has a high resistance state (OFF STATE) electrical resistance (R _H ) in the range 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.

The aforementioned characteristic switching elements include tetracyanoethylene (TCNE), tetracyanoquinodimethane (TCNQ), tetracyanonaphthoquinodimethane (TNAP), and 2,3,5,6-tetrafluoro-7,7,8. , 8-tetracyaquinodimethane (TCNQF ₄ ) and a complex of copper or silver is 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. . As the resin binder, electrically insulating resins such as 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-diethylaminophenyl)-1,3,4-oxadiazole, bis-diethylaminophenyl-1,3,
6-oxadiazole, 4,4'-bis(diethylamino-2,2'-dimethyltriphenylmethane,
2,4,5-triaminophenyl imidazole,
2,5-bis(4-dimethylaminophenyl)-
1,3,4-triazole, 1-phenyl-3-
(4-diethylaminostyryl)-5-(4-diethylaminophenyl)-2-pyrazoline, 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-fluoreno, 2,4,5,7-tetranitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8 - trinitrothioxanthone, dinitroanthracene, dinitroacridine, dinitroanthraquinone, tetracyanoquinodimethane, etc.

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 used in the present invention, the thickness of the switching element layer is generally in the range of 1 to 5 μm, particularly 1.5 to 3.5 μm, and the thickness of the charge generation and transport layer is generally in the range of 6 to 2 μm, particularly 7 to 3.5 μm.
The thickness is preferably in the range of 12 μm in order to maintain the surface potential at a high level during charging and to utilize the memory effect to the fullest.

In the electrophotographic method of the present invention, by selecting the combination of the switching element layer and the charge generation/transport layer or the charge acceptance layer, or the thickness or thickness ratio thereof,
A memory effect (F) of 40% or more, especially 60% or more can be obtained.

In the electrophotographic method of the present invention, the photoreceptor is generally charged using a positive corona charger.
Charging is performed such that the saturation charging potential is 500 to 700 volts.

Next, the charged photoreceptor is imagewise exposed. It is a feature of the invention that a conventional electrophotographic light source such as a tungsten halogen lamp can be used as the light source. The required exposure amount varies depending on the layer structure of the photoreceptor, but in general, it is 0.1 to 100m.
It is best to select from the range of W/cm ² . Of course, a laser beam such as a gas laser or a semiconductor laser can be used as the light source.

The photoreceptor on which the memory image has been formed is charged directly or by means similar to those described above, and the electrostatic latent image formed is brought into contact with a known one-component or two-component developing toner. A toner image is formed, transferred to a transfer sheet such as paper, and fixed as necessary to produce a copy or printed matter. After the toner has been transferred, the photoreceptor is electrostatically or mechanically cleaned, and then the above-described charging, development, transfer, and cleaning are repeated as many times as necessary.

When forming a new memory image, the switching element layer in the photoreceptor is heated by means such as infrared lamp irradiation, Joule thermal heating, strong laser light irradiation, hot air blowing, or contact with a heated roller. ,
The switching element layer is placed in a high resistance state (OFF
STATE) and then perform the operations described above. An appropriate heating temperature is selected from the range of 50 to 200°C.

The invention is illustrated by the following example.

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 (Luvican M
−170BASF) 10 parts by weight of tetrahydrofuran
In addition to 90 parts by weight, a 10% PVK solution was prepared. To 10 parts by weight of this 10% PVK solution, 0.6 parts by weight of 2,4,5,7-tetranitro-9-fluoreno and 2.0 parts by weight of tetrahydrofuran were added 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 with a thickness 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, the photoreceptor drum of a commercially available electrostatic photocopier (TC-162: manufactured by Sanda Kogyo Co., Ltd.) was replaced with an alumite drum, the photoreceptor after exposure was pasted there, and the copper substrate was grounded, followed by positive corona. 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. 2-A to 2-D show the principle of forming a memory image and the principle of electrostatic image formation of the photoreceptor used in the present invention, and FIG. 1 shows the relationship between applied voltage and current for the switching element layer used in the present invention. FIG. 4 shows the relationship between the surface potential of the photoreceptor used in the present invention and time. 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 method characterized by forming a memory image on an electrophotographic photoreceptor comprising a receptor layer by charging and imagewise exposing the photoreceptor.