JPH0668627B2 - Electrophotographic photoreceptor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member for repeatedly forming an electrostatic image by utilizing a memory effect of the photosensitive member.

2. Description of the Related Art Conventionally, in order to reproduce a large number of originals, in addition to the printing technique, the technique of copying a large number of sheets by electrophotography has been adopted from the viewpoint of ease of operation.

As a typical example of this multi-copy electrophotography, after image-exposing a photoconductive photosensitive layer having an optical memory effect,
There is known a so-called retention type electrostatic printing method in which various steps of charging, developing, transferring and cleaning are repeated. This method uses the principle that the exposed portion of the photosensitive layer becomes conductive due to the optical memory effect, and it becomes difficult for electric charges to be transferred to this portion. However, the known photosensitive member provides a desired optical memory effect. The sensitivity is low, and there is an inconvenience that the photoconductor must be image-exposed using a high-power light source.

Recently, a photoconductor utilizing the optical memory effect has also been developed. For example, Professor Inoue et al.
A photoconductor obtained by coating a mixed solution of vinylcarbazole, 2,4,7-trinitrofluorenone (TNF) and a leuco dye on an aluminum electrode, or a layer of a composition of PVK and TNF on the mixed solution coating layer. By using a multi-layered photoconductor provided with a single imagewise exposure, a memory image (reduction in charge acceptability of the exposed part) is formed on the photoconductor, and the process of charging-developing-transfer is repeated. Therefore, many studies have been conducted to obtain many copies (Journal of the Photographic Society of Japan, No. 44).
Vol. 2, pp. 104-117 (1981)). The memory formation in these photoconductors is said to be due to the chemical reaction of the charge transfer complex formed by TNF and the leuco dye after light absorption.

According to the present invention, there is provided an electrophotographic photosensitive member on which a memory image is formed on the principle completely different from a photochemical reaction, and moreover, a memory image and a charge image by charging thereafter are efficiently formed. .

The present invention further provides an electrophotographic multilayer photoreceptor having a novel multilayer structure.

That is, the present invention provides a conductive substrate, a switching element layer containing a copper-tetracyanoquinodimethane complex formed on the conductive substrate, and a surface containing a charge transfer complex of a polyvinylcarbazole-based polymer and tetranitrofluorenone. The present invention relates to an electrophotographic photosensitive member characterized by comprising layers.

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

In FIG. 1 showing the sectional structure of this photoreceptor, a switching element layer 2 is provided on a conductive substrate 1, and a charge generation / transport layer or a charge receiving layer 3 is further provided on this layer 2. Although not shown, a charge injection barrier layer or an under layer for enhancing the adhesive force may be provided between the conductive substrate 1 and the switching element layer 2 as desired.

According to the present invention, as the switching element layer 2, one containing a copper-tetracyanoquinodimethane complex is used. This copper-tetracyanoquinodimethane complex (Cu ・ TC
NQ) has a switching function in which it is in a high conductivity state in a high electric field and this high conductivity state is maintained. Further, according to the present invention, as the charge generating / transporting layer or the charge accepting layer 3, a charge transfer complex of polyvinylcarbazole (PVK) or its homolog and tetranitrofluorenone (TeNF) is used.

The principle of forming a memory image and the principle of forming an electrostatic image on the photoconductor of the present invention will be described below with reference to FIGS. 2-A to 2-D.

First, in the charged image exposure step of FIG. 2-A, the surface of the photoconductor 4 is charged with a charge of a constant polarity by the corona charger 5, and then the surface is imagewise exposed by the light source 6. In the specific example shown in the figure, the surface of the charge receiving layer 3 is positively charged, and the conductive substrate 1 is negatively charged.

In Figure 2-B showing the first step of memory image formation,
In the dark portion D, the surface charge remains unchanged, but in the light portion L, charge (carrier) is generated in the charge receiving layer 3, and the generated hole (+) moves to the stacking interface, that is, the interface with the switching element layer 2. In the bright part L, a high electric field is applied to the switching element layer 2 as a result.

In Figure 2-C showing the second stage of memory image formation,
In the bright portion L of the switching element layer 2, the high electric field applied induces a high electric conduction state (ON STATE), that is, a low resistance state. In the dark portion D of the switching element layer 2, the high resistance state (OFF STATE) remains and the switching element layer 2
In the above, the above-mentioned state is continuously maintained, and as a result, in the bright portion L, electrons can be easily injected from the conductive substrate 1.

In FIG. 2-D showing the electrostatic image forming step, in the portion L which has been exposed once, the electron (−), which has become easy to be injected with respect to the subsequent positive charging, is in the high conductivity state of the switching layer 2.
By being injected into the charge-receiving layer 3 through the layer, reaching the surface through the layer 3, and erasing the positive charge (+) on the surface,
A charge image is formed. Although not shown, the charge image is developed with a toner by a method known per se, and the formed toner image is transferred to paper or the like, whereby a copy or a printed matter can be obtained. Thus, after one memory image formation shown in FIGS. 2-A to 2-C,
By carrying out the desired number of charging steps shown in FIG. D, the desired number of copies can be made.

In the present invention, as is apparent from the above description, light is used only for the purpose of generating charges in the charge generating / transporting layer or the charge receiving layer 3, in other words, for applying a high electric field to the switching element layer 2. There is. That is, in the conventional multilayer photoreceptor, it is necessary to expose the memory forming layer through the charge transport layer or the charge receiving layer to cause photochemical change in the memory forming layer. In this case, since it is only required to generate charges (carriers) in the charge generating / transporting layer or the charge receiving layer, it is possible to form a memory image with a significantly smaller exposure amount than in the conventional method. The advantage is achieved.

FIG. 3 shows the switching element layer (Cu.
TCNQ) shows the relationship between the applied voltage and the current, curve 1 shows the relationship between the voltage and the current for the untreated switching element layer, and curve 2 shows the same for the switching element layer after the high voltage application. It is a study of relationships.
From curve 1, this switching element layer has a high resistance state A with a gradual slope and a low resistance state B with an extremely large slope, and from curve 2 a high conductivity state (ON ST).
ATE) switching element layer, high resistance state A
Is almost disappeared.

Tetracyanoquinodimethane (TCNQ) has the following structural formula Having a compound, its copper complex that shows the switching function of the high-resistance state and high conductivity state, the following formula [Cu ⁺ (TCNQ ^- ·)] _{^{n Cu o x + (TCNQ o}} ) x + [Cu ⁺ (TCNQ
^-・)] As represented by _nx , the low-conductivity simple salt on the left-hand side partially generates neutral molecules when a voltage higher than the threshold is applied, so that a so-called high-conductivity complex salt is formed. It is understood that it is due to the degree change.

The Cu.TCNQ complex used in the present invention has several advantages for the purposes of the present invention over other complexes of the same type. For example, Cu-TCNQ complex is superior in stability and reproducibility to silver salt. Furthermore, this Cu / TCNQ complex is superior to other complexes in that it has both a switching function and a memory function (retention).

The Cu-TCNQ complex can be formed directly on the conductive substrate in the form of a crystalline thin film by means such as vapor deposition, or microcrystals can be dispersed in a resin binder and provided on the conductive substrate. it can. In terms of easiness of production, it is preferable to disperse the microcrystalline complex in a resin binder before use.

As the resin binder, an electrically insulating resin such as polyester resin, acrylic resin, styrene resin, polycarbonate resin, vinyl chloride-vinyl acetate copolymer, phenoxy resin or alkyd resin is used. The microcrystalline complex and the resin binder are in a weight ratio of 1: 4 to 4: 1, especially 2: 2.
It is preferred to use it in a weight ratio of 3 to 3: 2.

FIG. 4 shows the electric field threshold value (V / cm) of the switching function and the volume resistance of the switching element layer in the high resistance state and the high conductivity state when the complex content in the switching element layer was changed. From these results,
It will be understood that stable functions are achieved in the above range.

The above-mentioned binder is dissolved in a suitable solvent such as tetrahydrofuran, chloroform, dioxane, dimethineacetamide, dimethylformamide, dimethylsulfoxide, etc. to disperse the microcrystalline complex, coated on a conductive substrate, dried and switched. An element layer is formed.

The charge generating / transporting layer or charge receiving layer used in the present invention generates charges (carriers: holes) by specific irradiation, transfers these to the surface, and transfers charges (electrons) injected from the switching element to the surface. Must be one.

The PVK-TeNF charge transfer complex used in the present invention is particularly excellent in the above-mentioned properties. That is, a wide variety of substances are conventionally known as hole transporting substances and electron transporting substances, and there are various combinations of their complexes, but the electron injection barrier from the switching element layer is about 0.4 eV, The value is about 0.25 eV lower than that of the most typical PVK-TNF complex, which is an advantage that electron injection is easily performed.

In the present invention, polyvinylcarbazole (PVK, monomer unit basis) and tetranitrofluorenone (TeNF) are preferably used in a molar ratio of 1: 0.4 to 1: 1, particularly 1: 0.6 to 1: 0.7.

Fig. 5 shows that the molar ratio of TeNF: PVK was changed to 5.0 × 10 ⁵ V / c.
Shows the mobility of electrons and holes measured in an electric field of m. According to this result, at the above-mentioned molar ratio, the movement of holes is controlled, so that the charging potential in the dark portion (D) is maintained, and the movement of the injected electrons is actively performed in the bright portion (L). It can be seen that a charge image having a large contrast is formed in the charging step shown in FIG. 2-D.

FIG. 6 is a diagram showing the relationship between the surface potential and time of a photoconductor having Cu / TCNQ as a switching element layer and PVK / TeNF complex as a charge generating / transporting layer or charge receiving layer, which will be described later. (1) is the surface charge potential of the untreated photoconductor, curve (2) is the surface charge potential after the start of exposure, and curve (3) is the recharge of the photoconductor in which the switching element layer has become highly conductive due to charging-exposure. The surface charging potential at the time of performing is shown. In FIG. 6, Vo is the initial saturation charging potential of the photoconductor provided with the switching layer in the high resistance state (OFF SRATE), and V ₁ is the photoconductor provided with the switching layer in the high conductivity state (ON STATE). Is the saturated charge potential of, and the memory effect (F) is It is represented by.

FIG. 7 shows the results of examining the relationship between the initial saturated charging potential and the memory effect (F) by changing the molar ratio of TeNF: PVK. From the results shown in FIG. 7, it is understood that a remarkable memory effect can be obtained when the molar ratio of the two is within the above range.

The layer of PVK-TeNF complex can be easily formed by, for example, dissolving these in an organic solvent and applying the solution on the switching element layer.

In the present invention, as the conductive substrate, a conductive metal substrate such as copper, aluminum or tin plate, conductive treated paper, NESA glass or the like is used, 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 in the range of 1 to 5 μm, particularly 1.5 to 3.5 μm, and the thickness of the charge generation / transport or charge transport layer is generally 6 to
It is preferable that the thickness is in the range of 20 μm, particularly 7 to 12 μm in order to keep the surface potential at the time of charging at a high level and to maximize the memory effect.

INDUSTRIAL APPLICABILITY The photoconductor of the present invention is useful as an electrophotographic photoconductor for copying a large number of sheets in a single exposure and also as a readable electronic recording medium.

Reference example Formation of switching element layer 10 parts by weight of copper-tetracyanoquinodimethane complex (Cu / TCNQ) crushed by a ball mill, 10 parts by weight of polyarylate resin (U-polymer 8000 Unitika), polyethylene glycol (PEG1000 Sanyo) 0.5 parts by weight and 90 parts by weight of chloroform were mixed and ultrasonically dispersed for 30 minutes, and then coated on a steel substrate with a wire bar and dried. Vacuum drying was carried out at 80 ° C. for 15 minutes, and if necessary, for 6 hours to form a switching element layer having a film thickness of 2 μm.

Measurement of Switching Development A was vacuum-deposited on the switching element layer to form a sandwich type cell using the A vapor deposition film and a copper substrate as electrodes.

Next, a voltage of +3.0 V to -3.0 V was applied to the copper substrate side. The VI curve in the first voltage application is shown by the curve (1) in FIG. Further, the VI curve in the second and subsequent voltage application is shown in the 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-170 BA
90 parts by weight of tetrahydrofuran was added to 10 parts by weight of SF company) to prepare a 10% PVK solution. To 10 parts by weight of this 10% PVK solution was added 2,4,5,7-tetranitro-9-fluorenone 0.6.
1 part by weight and 2.0 parts by weight of tetrahydrofuran are sufficiently dissolved with an ultrasonic disperser, and the photosensitive layer coating liquid is applied on the switching layer previously formed with a wire bar and dried to form a photosensitive layer of 7 μm. To obtain a photoconductor.

Copy Test The above-prepared photoconductor was set in a surface potential light attenuator, and after positive corona discharge (+6.0 KV) for about 30 seconds, document exposure was performed. A tungsten lamp (14 mW / cm ² ) was used as irradiation light, and exposure was performed for about 1 minute.

Next, replace the photoconductor drum of a commercially available electrostatographic copying machine (DC-162: manufactured by Mita Kogyo Co., Ltd.) with an alumite drum, attach the exposed photoconductor there, and ground the copper substrate, and then positive corona discharge (+ 6KV), toner phenomenon, transfer to plain paper, and cleaning cycle were repeated continuously to perform electrostatic printing.

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

[Brief description of drawings]

FIG. 1 is a diagram showing a sectional structure of a photoconductor of the present invention, FIG. 2 is a principle diagram showing formation of a memory image and electrostatic image using the photoconductor of the present invention, and FIG. 3 is a diagram showing the present invention. FIG. 4 is a diagram showing the relationship between the applied voltage and current of the switching element layer used, FIG. 4 is a diagram showing the relationship between the volume resistance and electric field threshold value of the switching element layer, and the Cu / TCNQ content, and FIG. 5 is used in the present invention. FIG. 6 is a diagram showing the mobility of electrons and holes in the charge generating / transporting or charge accepting layer, FIG. 6 is a diagram showing the time change of the surface potential of the photoreceptor of the present invention, and FIG. 7 is the charge generating / transporting layer or charge It is a figure which shows the initial saturation potential of a receptive layer, and a memory effect, and the relationship of the molar ratio of TeNF: PVK. 1 ... Conductive substrate, 2 ... Switching element layer 3 ... Charge generation / transport or charge acceptance layer

Claims (1)

[Claims] 1. A conductive substrate, a switching element layer containing a copper-tetracyanoquinodimethane complex formed on the conductive substrate, and a surface layer containing a charge transfer complex of a polyvinylcarbazole polymer and tetranitrofluorenone. An electrophotographic photosensitive member comprising: