JPH0554672B2 - - 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. 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 in which a mixed solution of leuco dye and leuco dye is coated on an aluminum electrode, or a multilayer photoconductor in which a layer of a composition of PVK and TNF is provided 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 memory effect caused by a photochemical reaction. 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, according to the present invention, the switching element layer comprises a conductive substrate, a switching element layer formed on the conductive substrate, and a charge generation/transport or charge acceptance layer formed on the switching element layer. Microcrystalline particles consisting of a complex of a cyano group-containing electron-accepting compound and copper or silver have a molecular weight of 600 to
Provided is an electrophotographic multilayer photoreceptor comprising a composition in which a polyalkylene polyol of 10,000 is dispersed in a polyarylate resin as a dispersion medium. 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, as the switching element layer, microcrystalline particles made of a complex of a cyano group-containing electron-accepting compound and copper or silver are dispersed in a polyarylate resin using a polyalkylene polyol as a dispersion medium. The point is that a composition is used. This composition, particularly the complex, has a switching function and a memory function in which it becomes highly conductive in a high electric field and maintains this highly conductive state. The principle of forming a memory image and the principle of forming an electrostatic image on the photoreceptor of the present invention will be explained below with reference to Figures 2-A to 2-D. First, in the charged 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 exposed to image light 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 a positive 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 the bright area 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 against subsequent positive charging, form a highly conductive switching layer 2. 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,
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 high charge transport layer or charge receiving layer to cause a photochemical change in the memory forming layer. Since the invention requires only the generation of charges (carriers) in the charge generation transport layer or the charge transport 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 resistance state A almost disappears in the switching element layer once it becomes 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 ) 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 −
The ratio of 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), tetracyanodimethylquinomethane (TCNQ(Me) ₂ ), and tetracyanoquinodimethane (TCNQ). Cyanodimethoxyquinomethane (TCNQ(OMe) ₂ ), 2,3,
A complex of an electron-accepting substance such as 5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF ₄ ) and copper or silver is preferably used. In the present invention, microcrystalline particles of the above complex are dispersed in polyarylate using polyalkylene polyol as a dispersion medium, and this dispersion is used as a switching element layer. Polyarylate has the following structure It is a thermoplastic resin based on U-Polymer and is commercially available in Japan from Unitika Co., Ltd. under the trade name U-Polymer. This resin has a high density of aromatic rings in its main chain, so it has excellent heat resistance and has a high heat distortion temperature (approx.
175℃) and high volume resistivity (approximately 2
×10 ¹⁶ Ω-cm) and withstand voltage (approximately 400 KV/cm). In the photoreceptor of the present invention, a high electric field is applied to the switching element layer, but by using polyarylate having a high withstand voltage as the resin binder, problems such as dielectric breakdown of the switching element layer can be solved. In addition, the above-mentioned complex salt exhibits a switching function between a high resistance state and a high conductivity state, for example, by the following formula [(u ⁺ (TCNQ・−]nCuxΓ+[Cu ⁺ (TCN
Q・−)]n−x+(TCNQ°)x, the low conductivity simple salt on the left side partially generates neutral molecules when a voltage higher than the threshold is applied, and becomes the so-called high conductivity simple salt. It is understood that this is due to changes in conductivity due to the formation of complex salts, but in order to restore this highly conductive complex salt to a high resistance simple salt, it is necessary to heat the salt to a high temperature. become. According to the present invention, by using polyarylate as the binder resin, there is an advantage that it can withstand high temperature heating. Furthermore, the microcrystalline particles of the complex salt described above are difficult to disperse in polyarylate, and it is difficult to form a homogeneous dispersed phase in a dispersed state. However, according to the present invention, polyalkylene polyol can be used as a dispersion medium. By doing so, it becomes possible to form a switching element layer whose composition is homogeneous throughout. This is because hydrophilic polymers such as polyalkylene polyols, e.g. polyethylene glycol (PEG), are combined with ionic additives such as copper or silver complexes, e.g. Cu.TCNQ, of electron-accepting compounds containing cyano groups used as switching element layers. This is thought to be because when acting as a dispersant for substances, the hydrophilic polymer itself plays the role of a surfactant and disperses the complex particles more finely. Furthermore, for this purpose, at the interface between the switching element layer and the charge generation/transport layer or the charge acceptance layer, the contact area between the electron transport substance in the charge generation/transport layer or the charge acceptance layer, such as tetranitrofluorenone molecules, and the complex particles is reduced. As a result, the electron transfer process from the switching element layer to the charge generation/transport layer or the charge acceptance layer can be carried out more efficiently. The microcrystalline complex and polyarylate are preferably used in a weight ratio of 1:4 to 4:1, particularly 2:3 to 3:2. FIG. 3 shows the electric field threshold (V/cm) of the switching function and the volume resistance of the switching element layer in a high resistance state and a high conductivity state when the complex content in the switching element layer is changed. From these results, it will be understood that stable functionality is achieved within the above range. Examples of polyalkylene polyols include polyethylene glycol, polypropylene glycol, poly(ethylene glycol/propylene glycol), and polybutylene glycol, as well as adducts of polyhydric alcohols such as glycerin, sorbitan, and mannitol with ethylene oxide or propylene oxide. used. The weight average molecular weight of these polyalkylene polyols is 600 to 600.
Preferably in the 10000 range. The molecular weight is as shown in the comparative example described later, and if the molecular weight is too large, the hydrophilicity of the polyalkylene polyol will decrease, the dispersion effect will decrease, and the memory effect will tend to decrease. The amount of polyalkylene polyol blended is preferably 2 to 10% by weight, particularly 4 to 7% by weight, based on the binder resin, from the viewpoint of dispersibility. The binder described above is dissolved in a suitable solvent such as tetrahydrofuran, chloroform, dioxane,
dimethylacetamide, dimethylformamide,
It is dissolved in a solvent such as dimethyl sulfoxide to disperse the microcrystalline complex, applied onto a conductive substrate, and dried to form a switching element layer. The charge generation transport layer or charge receiving layer used in the present invention generates charges (carriers: holes) by light irradiation and transports them to the interface, and also transports the charges (electrons) injected from the switching element to the surface. It must be something that does. 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-diethylaminophenyl)-
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-fluorenone, 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 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 transport layer or the charge transport layer is generally 6 to 20 μm, particularly 7 to 12 μm.
It is preferable for the surface potential to be within this range to maintain the surface potential at a high level during charging and to utilize the memory effect to the fullest. 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 was mixed with polyaryate resin (U-polymer 8000 manufactured by Unitika).
10 parts by weight, polyethylene glycol (PEG1000
Sanyo Chemical Industries, Ltd.) 0.5 parts by weight, chloroform 90
After mixing with a solution consisting of parts by weight and ultrasonic dispersion for 30 minutes, it was placed on a copper substrate by a wire bar.
Apply and dry. Drying was performed at 80℃ for 15 minutes, and if necessary, vacuum drying for 6 hours until the film thickness was 2μ.
m switching element layers were formed. Measurement of switching development 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. V-I at the first voltage application
The curve is shown as curve 1 in FIG. Furthermore, the VI curve in the second and subsequent voltage applications is shown in Curve 2. Production of Example 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 (manufactured by BASF) and 90 parts by weight of tetrahydrofuran to prepare a 10% PVK solution.
2,4,5,7- to 10 parts by weight of this 10% PVK solution.
0.6 parts by weight of tetranitro-9-fluorenone 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 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 hour using a tungsten lamp (14 mW/cm ² ) as the irradiation light. Next, the photoreceptor drum of a commercially available electrophotographic copying machine (DC-162: manufactured by Sanda Kogyo Co., Ltd.) was replaced with an alumite drum, the exposed photoreceptor was attached thereto, the copper substrate was grounded, and a positive corona discharge was applied. (+6KV), toner development, transfer to plain paper and cleaning cycles were continuously repeated to perform electrostatic printing. 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. Comparative example No polyethylene glycol (PEG) was added in the switching element layer in the example, and the weight average molecular weight was 600, 1000, 2000, 20000, 100000.
Six types of photoreceptors were produced in the same manner as in the examples. Next, positive corona discharge (+6.0 KV) was performed on these six types of photoreceptors, and the initial surface potential (Vo) was measured. Furthermore, the photosensitive pair after corona discharge was exposed to light for about 1 minute using a tungsten lamp (14 mW/cm ² ). Thereafter, positive corona discharge (+6.0 KV) was performed again, and the surface potential (V ₁ ) was measured. From these results, the memory effect (F=
Vo−Vl/Vo×100) was calculated. The results are shown in Table 1 below. Note that a commercially available surface electrometer (Trek Co Model 360) was used to measure the surface potential.

[Table] From the results in Table 1, the lower the molecular weight of PEG, the more significant the memory effect was.

[Brief explanation of the drawing]

FIG. 1 shows the cross-sectional structure of the photoreceptor of the present invention,
2-A to 2-D show the principle of forming a memory image and the principle of forming an electrostatic image of the photoreceptor of the present invention,
FIG. 3 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 Consists of a conductive substrate, a switching element layer formed on the conductive substrate, and a charge generation transport or charge acceptance layer formed on the switching element layer, and the switching element layer is made of a cyano group-containing electron-accepting compound. 1. An electrophotographic multilayer photoreceptor comprising a composition in which microcrystalline particles consisting of a complex of copper or silver are dispersed in a polyarylate resin using a polyalkylene polyol having a molecular weight of 600 to 100,000 as a dispersion medium.