JPH0616195B2 - Electrophotography - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrophotographic method utilizing a memory effect.

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 one of the multi-copy electrophotography, a so-called retention type electrostatic printing, in which a photoconductive photosensitive layer having an optical memory effect is image-lighted and then the charging, developing, transferring and cleaning steps are repeated. The law is known. 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.
Known photoconductors have a low sensitivity for giving a desired optical memory effect, 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.
-Vinylcarbazole (PVK), 2,4,7-trinitrofluorenone (TNF) and a leuco dye mixed solution coated on an aluminum electrode, or on the mixed solution coating layer, PVK and TNF By using a multi-layered photoconductor provided with a layer of the composition and exposing the image once, a memory image (reduction of charge acceptability in the exposed area) is formed on the photoconductor, and charging-development-transfer is performed. A study has been conducted to obtain a large number of copies by repeating the above process (see Journal of the Photographic Society of Japan, Vol. 44, No. 2, pages 104 to 117 (1981)). It is said that the memory formation in these photoconductors is caused by the chemical reaction of the charge transfer complex formed by TNF and the leuco dye after light absorption.

According to the present invention, the formation of the memory image is performed by a completely different principle from the formation of the memory image by the photochemical reaction,
Moreover, an electrophotographic method is provided in which a memory image can be formed with a relatively small exposure amount.

Further, according to the present invention, an electrophotographic apparatus which uses a multi-layered photoreceptor having a completely different layer constitution from a conventional photoreceptor and forms a memory image by combining pre-charging-exposure and main-charging-image exposure. Law is provided.

That is, the present invention provides a conductive substrate, a switching element layer provided on the conductive substrate, which is in a high conductivity state in a high electric field and maintains the high conductivity state, and charge generation provided on the switching element layer. Pre-charging and pre-uniform exposure are performed on an electrophotographic photosensitive member composed of a transport or charge-receptive layer within a limit in which a high electric field is not applied to a switching element, and then main charging and image of the same polarity as pre-charging. An electrophotographic method is provided which comprises exposing and forming a memory image on a photoreceptor.

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

In FIG. 1 showing a 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 accepting layer 3 is further provided on the layer 2. It is provided. Although not shown, conductive substrate 1
If desired, a charge injection barrier layer or an under layer for enhancing the adhesive force may be provided between the switching element layer 2 and the switching element layer 2.

One of the important features of the present invention is that, as the switching layer 2, a switching element layer which is in a high conductivity state in a high electric field and maintains this high conductivity state is used.

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

First, in the pre-charging step of FIG. 2-A, the surface of the photoconductor 4 is charged by the corona charger 5 to a constant polarity charge. 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.

Next, in FIG. 2-B showing the pre-uniform exposure step, the photoconductor 4 whose surface is charged is uniformly pre-exposed by the light source 6. By this pre-exposure, charges (carriers) are generated in the charge receiving layer 3, and the generated holes (+) move to the stacking interface, that is, the interface with the switching element layer 2 and are accumulated there.

In the present invention, the above-mentioned pre-charging and pre-uniform exposure steps are performed within the limitation that a high electric field is not applied to the switching element layer 2. Thus, although a certain amount of positive charge is accumulated at the interface between the charge receiving layer 3 and the switching element layer 2, the switching element layer 2 is still maintained in a high resistance state (OFF STATE). . In FIG. 2-C showing the main charge and image exposure process, the pre-charged and pre-exposed photoconductor 4 is charged to a constant polarity charge by a corona charger 5 ', and then this surface is charged by a light source 6'. Image exposure.

In Figure 2-D showing the first step of memory image formation,
In the dark portion D, the surface charge remains as it is, but in the light portion L, as in the case shown in FIG. 2-B, charge (carrier) is generated in the charge receiving layer 3 and the hole (+) switching element layer 2 is generated. To the interface, the charge accumulation exceeds the above-mentioned limit, and a high electric field is applied to the element layer 2.

In FIG. 2-E, in the bright portion L of the switching element layer 2, a high electric field (ON STA) is applied due to the applied high electric field.
TE), that is, a low resistance state is induced. In the dark portion D of the switching element layer 2, a high resistance state (OFF STAT
E) remains as it is, and the above-mentioned state is continuously maintained in the switching element layer 2, and as a result, in the bright portion L, the injection of electrons from the conductive substrate 1 becomes easy.

In FIG. 2-F showing the electrostatic image forming step, in the portion L which has been exposed once, the electron (−) which has become easy to be injected due to the subsequent positive charging is in the high conductivity state of the switching layer 2.
Via charge generation and transport or injection into the charge receiving layer 3,
A charge image is formed by reaching the surface through the layer 3 and erasing the positive charges (+) on the surface. Although not shown, this charge image can be obtained by a method known per se.
By developing with a toner and transferring the formed toner image onto paper or the like, a copy or a printed matter can be obtained. Thus, the desired number of copies can be made by performing the desired number of charging steps shown in FIG. 2-F after one memory image formation shown in FIGS. 2-A to 2-E.

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 as compared with the conventional method. The advantage is achieved.

Furthermore, in the present invention, prior to the main charging and the imagewise exposure, pre-charging and pre-uniform exposure are performed within a limit where a high electric field is not applied to the switching element layer, thereby switching between the charge generation transport layer or the charge receiving layer. It becomes possible to accumulate charges within the above limits at the interface with the device layer in advance, and even when the amount of charge transport to the interface performed in the subsequent image exposure process is relatively small, switching in the switching device layer is performed. The operation can be effectively and smoothly performed. This means that the exposure amount in the image exposure process is significantly saved, and as a result, the exposure operation can be easily performed by using the light source and the exposure system used in a general copying machine.

FIG. 3 shows the relationship between the applied voltage and the current for one of the switching element layers used in the present invention (Cu.TCNQ described later). Curve 1 shows the untreated switching element layer. The relationship between the voltage and the current, curve 2 is the same relationship as for the switching element layer after application of the high voltage. It can be seen from the curve 1 that the switching element layer has a high-low resistance state A with a gentle slope and a low resistance state B with a very large slope, and from the curve 2 the switching element layer once brought into a high conductivity state (ON STATE). In, 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 having Cu / TCNQ as a switching element layer and PVK / TNF complex as a charge generating / transporting layer or charge accepting layer, which will be described later. (1) is the surface charge potential of the untreated photoreceptor, curve (2) is the surface charge potential after the start of exposure, and curve (2 ') is the pre-charge-pre-uniform exposure within the limit where the switching operation is not performed. After that, the surface charging potential at the time of main charging and exposure (however, the applied voltage is adjusted so that the surface potential of the photoconductor after the main charging becomes the same), the curve (3) shows The surface charging potential when the photoconductor in which the switching element layer is in the high conductivity state is recharged is shown. In FIG. 4, V ₀ is a high resistance state (OFF STAT
E) is the initial saturation charge potential of the photoconductor having the switching layer in V), V ₁ is the saturation charge potential of the photoconductor having the switching layer in the high conductivity state (ON STATE), and the memory effect (F) Is the following formula It is represented by.

Referring to the results of FIG. 4, by performing the pre-charging and the pre-uniform exposure within the above-mentioned limits prior to the main charging-image exposure, the light attenuation after the light irradiation is rapid, and the apparent sensitivity is reduced. It will be clear that a significant rise will result.

The switching element layer used in the present invention has a high resistance state (O
The electric resistance ( _RH ) of FF STATE) is 10 ^{8 to} 10
¹⁴ Ω-cm, especially 10 ^{9 to} 10 ¹¹ Ω-cm is desirable in terms of charge retention, while R _H and low resistance (ON STATE) electric resistance ( _RL : Ω-cm) It is desirable in terms of contrast that the ratio (R _H / R _L ) to the ratio is in the range of 1 × 10 ^{1 to} 1 × 10 ⁵ .

Examples of the switching element having the above-mentioned characteristics include tetracyanoethylene (TCNE), tetracyanoquinodimethane (TCNQ), tetracyanonaphthoquinodimethane (TNAP), 2,3,5,6-tetrafluoro-7,
7,8,8-Tetracyanoquinodimethane (TCNQ
A complex of a cyano group-containing electron-accepting substance such as F ₄ ) and copper or silver is preferably used, but other switching elements having similar characteristics can also be used.

These complexes can be directly formed in the form of a crystalline thin 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. it can. 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, epoxy resin, silicone resin, alkyd resin and the like are used. The microcrystalline complex and the resin binder are used in a weight ratio of 1: 4 to 4: 1. These resin binders are dissolved in a solvent such as tetrahydrofuran, chloroform, dioxane, dimethylacetamide, dimethylformamide, dimethylsulfoxide, and the microcrystalline complex is dispersed, coated on a conductive substrate, and dried to form a switching element layer. Let

The charge-generating transport layer or charge-accepting layer used in the present invention must generate charges (carriers) by light irradiation, transfer the charges to the interface, and transfer the charges injected from the switching element to the surface. . From this perspective, this layer must be capable of transporting both holes and electrons.

For this purpose, a mixture of hole and electron transport materials or a charge transport complex is advantageously 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 Methazole, 2,
5-bis (4-diethylaminophenyl) -1,3,4
-Triazole, 1-phenyl-3- (4-diethylaminostyryl) -5- (4-diethylaminophenyl)
2-pyrazoline, p-diethylaminobenzaldehyde- (diphenylhydrazone) and the like. Examples of suitable electron-transporting substances 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 and the like.

When the mixture or complex has a film-forming property, it may be applied as a solution of an organic solvent on the switching element layer, and when the mixture or complex does not have a film-forming property, the resin binder exemplified above is used. It is sufficient to disperse the above-mentioned combination substance in the above solution and apply it to form a charge generation transport layer or a charge acceptance 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 photoconductor 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 generating / transporting layer to the charge receiving layer is generally 6 to 20 μm, especially 7 to 12 μm. It is preferable that it is in the range of (1) in order to maintain the surface potential at the time of charging at a high level and to maximize the memory effect.

In the electrophotographic method of the present invention, by selecting the combination of the switching element layer and the charge generating / transporting layer or the charge receiving layer, or the thickness and thickness ratio thereof, 40% or more, particularly 60% or more.
% Or more of the memory effect (F) can be obtained.

In the electrophotographic method of the present invention, the photoconductor is charged by using a corona charger having a positive polarity, and the saturation charge potential is 5
Charging is performed so that the voltage becomes 00 to 700 volts.

On the other hand, the pre-charging and the pre-uniform exposure of the photosensitive member are performed in the limit that the switching operation of the switching element layer is not substantially performed. For this reason, a means such as performing the amount of pre-charging less than that of main charging, performing the amount of pre-exposure less than that of image exposure, or adopting a combination of these is adopted. To do. More specifically, the charging potential of the pre-charging is within the range of 10 to 50% of the potential of the main charging,
Alternatively, the exposure amount of the pre-uniform exposure is set to 1 to 1 of that of the image exposure.
Means such as setting the range to 0% is adopted. The fact that pre-charging and pre-exposure within the limits specified in the present invention means that even if the initial saturation charging potential (V _P ) of pre-charging is higher than the charging potential (V _C ) of main charging, the difference Can be confirmed by being 50% or less.

Then, the charged photoreceptor is imagewise exposed. It is a feature of the present 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 photoconductor, but it is generally preferable to select it in the range of 0.1 to 100 mW / cm ² . Of course, as the light source, a laser beam such as a gas laser semiconductor laser can be used.

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

When newly forming a memory image, the switching element layer in the photoconductor is heated by means of infrared lamp irradiation, Joule heat heating, strong laser light irradiation, hot air blowing, contact with a heat roller, etc. The switching element layer may be returned to the high resistance state (OFF STATE), and then the above-mentioned operation may be performed. Heating temperature is 50 ~ 200 ℃
Select an appropriate temperature from the range.

The invention is illustrated by the following example.

Reference Example Formation of Switching Element Layer 10 parts by weight of a copper-tetracyanoquinodimethane complex (Cu.TCNQ) crushed by a ball mill was mixed with a polyarylate resin (U-polymer 8000 Unitika).
10 parts by weight, polyethylene glycol (PEG 100
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 copper 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 Phenomenon Al was vacuum-deposited on the switching element layer to form a sandwich type cell using the Al vapor deposition film and the 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 Preparation of Photoreceptor A switching element layer was formed on a copper substrate by the same method as in the reference example.

Next, polyvinyl cavalzole (Luvi-can M-170
90 parts by weight of tetrahydrofuran was added to 10 parts by weight of BASF) to prepare a 10% PVK solution. This 10%
0.6 part by weight of 2,4,5,7-tetranitro-9-fluorenone and 10 parts by weight of PVK solution and tetrahydrofuran
2.0 parts by weight was added and sufficiently dissolved with an ultrasonic disperser to prepare a photosensitive layer coating liquid.

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

Copy test After the photoconductor was set in the surface potential optical attenuator for the above-mentioned production and positive corona discharge (+3.0 kv) was performed for about 10 seconds, uniform exposure was performed for about 5 seconds with a tungsten lamp (14 mW / cm ² ). went. Next, positive corona discharge for about 20 seconds (+ 6.0k
After performing v), the original was exposed. A tungsten lamp (14 mW / cm ² ) was used as the irradiation light, and about 1
Exposure was performed for a minute.

Next, replace the photoconductor drum of a commercially available electrostatic photocopier (DC-162; manufactured by Mita Kogyo Co., Ltd.) with an alumite drum,
After sticking the exposed photoreceptor to it and grounding the copper substrate, positive corona discharge (+6 kv), toner development, transfer to plain paper, and cleaning cycle are repeated continuously,
Electrostatic printing was performed.

When printing was performed 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 shows the cross-sectional structure of the photoconductor used in the present invention.
FIGS. 2A to 2F show the principle of forming a memory image and the principle of forming an electrostatic image on a photoreceptor by the method of the present invention, and FIG. 3 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 photosensitive member used in the present invention and time. 1 ... Conductive substrate 2 ... Switching element layer 3 ... Charge generation / transport or charge reception layer

Claims (1)

[Claims] 1. A conductive substrate, provided on the conductive substrate,
A switching element layer is provided for an electrophotographic photosensitive member including a switching element layer which is in a high electrical conductivity state and maintains a high electrical conductivity state under a high electric field, and a charge generating / transporting or electron accepting layer provided on the switching element layer. Pre-charging and pre-uniform exposure are performed within a limit in which a high electric field is not applied to, and then main charging and image exposure having the same polarity as pre-charging are performed to form a memory image on the photoconductor. Electrophotography.