JPH0352625B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method of imaging that can be classified as sustained conductivity electrophotography. Persistent conductive electrophotography utilizes the phenomenon that when a certain type of photosensitive material is exposed to light, a persistent conductive image (that is, has a memory effect) is formed in the exposed area. Various types of photosensitive materials have been proposed for this purpose, but a typical one is one in which a photosensitive memory layer containing an organic photoconductive substance and a memory effect imparting agent is formed on a conductive substrate. (For example, US Pat. No. 3,879,201 and US Pat. No. 3,997,342). As the organic photoconductor, a polymeric photoconductor such as polyvinylcarbazole as it is, or a low molecular weight photoconductor such as oxydiazole dispersed in an electrically insulating binder is used.As a memory effect imparting agent, Various proton donors are known. As mentioned above, exposure of such a photosensitive memory layer results in a persistent conductive image (latent image). One drawback of the sustained conductivity electrophotographic method described above is that the amount of exposure required to obtain the desired sustained conductivity image is quite large, on the order of 10 mJ/cm ² . In order to eliminate the drawbacks of sustained conductivity electrophotography and improve exposure sensitivity, the present inventors have already developed several techniques in addition to using various sensitizers. There is. For example, Tokuko Sho 60
The specification of Publication No. 44657 (Japanese Patent Application No. 5216710) describes a method of corona charging the photosensitive memory layer before exposure, and the specification of JP-A-56-17358 describes the method of corona charging the photosensitive memory layer before exposure. Each discloses a photosensitive material in which a relatively thin photoconductive layer without a memory effect is formed. Although these techniques can provide some improvement in exposure sensitivity, they are still far from sufficient. In view of the above-mentioned circumstances, the main object of the present invention is to provide a sustained conductivity electrophotographic method with further improved exposure sensitivity. As a result of research for the above-mentioned purpose, the present inventors found that when carrying out sustained conductive electrophotography using a conventional photosensitive material (image forming material), by applying a voltage to the photosensitive memory layer at the same time as exposure. It was found that the sensitivity was significantly improved by more than 100 times compared to when no voltage was applied, and by more than 10 times compared to when corona charging was performed. The image forming method of the present invention is based on such knowledge, and more specifically, an image forming material in which a photosensitive memory layer containing an organic photoconductive substance and a memory effect imparting agent is formed on a conductive substrate. a counter electrode that contacts a surface of the photosensitive memory layer opposite to the side that is in contact with the conductive substrate when forming a persistent conductive image on the photosensitive memory layer by exposing the photosensitive memory layer to light; the photosensitive memory layer by applying a voltage across the conductive substrate and maintaining the voltage applied to the photosensitive memory layer substantially constant so as not to decay at least while the exposure is being carried out; Recording sensitivity is increased by amplifying the injection efficiency of persistent charge at or near the interface between the memory layer and the conductive substrate, thereby causing sustained conduction in the exposed portion of the photosensitive memory layer where voltage is applied. It is characterized by forming a sexual image. The reason why the sensitivity is greatly improved when exposure is performed under voltage application when forming a sustained conductive image according to the method of the present invention is not necessarily clear, but it is estimated as follows. be done. In other words, in order to provide a photosensitive memory layer with a memory function, it is basically effective to inject charges such as electrons or holes into the photosensitive memory layer by light, and by increasing the injection efficiency, the memory sensitivity can be increased. It is done. Since charge cannot be injected simply by exposure, the memory sensitivity is limited by the sensitivity of the photosensitive memory layer itself. On the other hand, if exposure is performed after corona charging, the injection efficiency of charges such as electrons or holes increases due to the applied electric field. However, in the process of sensitization by corona charging, the amount of charge injected by light is limited by the surface charge, so no further sensitization can be expected.However, as in the present invention, when voltage is applied, Exposure to light removes these limitations, thus providing a significant increase in memory sensitivity at a constant electric field strength. In particular, in the present invention, the interface between the photosensitive memory layer and the conductive substrate is improved by maintaining the voltage applied to the photosensitive memory layer substantially constant without attenuation at least while the exposure is being performed. Alternatively, the injection efficiency of persistent charges near the interface is greatly amplified, resulting in increased recording sensitivity. Furthermore, according to the method of the present invention, when forming a sustained conductive image, significant sensitization is achieved by simultaneously exposing to light and applying a voltage. It becomes possible not only to perform imagewise exposure (imagewise exposure) but also to perform image formation by applying an applied voltage (imagewise voltage application). Note that in electrophotography, the simultaneous application of voltage and exposure is also disclosed in US Pat. No. 2,825,814. However, in this case, an insulator is interposed between the photoconductive layer, which does not have a general memory function, and the transparent conductive layer, a voltage is applied, and the photoconductive layer becomes conductive by exposing it to light. An electrostatic image (latent image) is formed on an insulator near the exposed part of the photoconductive layer (but separated by a certain small distance) through the exposed part of the photoconductive layer. It's not an issue at all. That is, the photoconductive layer serves only as a kind of selective blocking layer for electric current. On the other hand, in the method of the present invention, voltage application and exposure are performed simultaneously in order to improve the memory sensitivity of the photosensitive memory layer, and since a sustained conductive image is formed, the voltage application and exposure are performed simultaneously. However, the simultaneous application of light and light in the method of the present invention is completely different from that described in the above-mentioned US patent specification. Hereinafter, the present invention will be explained in more detail with reference to the drawings. In the following description, "parts" are based on weight unless otherwise specified. FIG. 1 is a schematic diagram illustrating an embodiment of the image forming method of the present invention when viewed from the extending direction of the image forming material. Referring to FIG. 1, an image forming material 1 has a photosensitive memory layer 3 provided on a conductive substrate 2, and is not particularly different from that used in the prior art as described above. do not have. For clarity, the conductive substrate 2 can be made of any conductive material such as Al, Cu or other metal materials, but in this example, it is used to expose the photosensitive memory layer 3 through itself. , it also needs to be transparent. Such a transparent conductive substrate may be a glass plate or a sheet of transparent plastic such as polyester or polycarbonate, and a conductive metal or semiconductor having a resistivity of 10 ⁶ Ω or less, such as SnO ₂ , In ₂ O ₃ , or SiO ₂ . A layer formed with a film is preferably used (note that when such a laminate is used, it is naturally used in such a manner that the conductive film is in contact with the photosensitive memory layer, but illustration of such a laminate structure is omitted). Among these, an In ₂ O ₃ --SnO ₂ thin film having a resistivity of about 10 ⁴ Ω/hole is a preferable conductive film. The photosensitive memory layer 3 contains an organic photoconductive substance and a memory effect imparting agent. As mentioned above, the organic photoconductive substance includes a polymeric photoconductor as it is or a dispersion of a low-molecular photoconductor in an insulating binder. In addition to polyvinylcarbazole mentioned above, polymeric photoconductors include poly(N- Ethylenically unsaturated group-substituted carbazoles; polyN-ethylenically unsaturated group-substituted phenothiazines such as polyN-acrylphenothiazine and polyN-(β-acryloxy)phenothiazine; polyvinylpyrene, etc. are used. Among these, poly N-ethylenically unsaturated group-substituted carbazoles, particularly polyvinyl carbazole, are preferably used. As the low molecular weight photoconductor, oxadiazoles substituted with alkylaminophenyl groups, pyrazolines, hydrazones, thiazoles, triphenylmethane derivatives, etc. are used. These low molecular weight photoconductors contain, for example, about 1 to 10 parts of an electrically insulating binder such as silicone resin, styrene-butadiene copolymer resin, saturated or unsaturated polyester resin, or polyvinyl acetal resin. In combination with resins, it is used as a film-forming organic photoconductive material. On the other hand, examples of memory effect imparting agents include diazonium salts, acid anhydrides, o-sulfobenzimide, ninhydrins, cyano compounds, nitro compounds, sulfonyl chlorides, diphenyl or triphenylmethanes, and o-benzoylbenzoic acid. Preferred specific examples include those represented by the following chemical formula.

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[Formula] It is preferable to further add a sensitizer selected from electron-accepting substances, dyes, etc. to the photosensitive memory layer 3 in order to sensitize the above-mentioned organic photoconductive substance. Examples of electron-accepting substances include nitro-substituted benzene, diano-substituted benzene, halogen-substituted benzene, quinones, and trinitrofluorenone. Further, as the sensitizing dye, for example, triphenylmethane dye, pyrylium salt dye, xanthene dye, etc. are used. The photosensitive memory layer 3 preferably contains each of the above components in an amount of 0.1 to 0.5 mol of sensitizer per 1 mole of photoconductor (if the photoconductor is a polymer, 1 mole of its polymer unit) in the organic photoconductive material. and 0.0001 to 0.1 mol of a memory effect imparting agent, diluted with a solvent if necessary, and coated on the conductive substrate 2. The thickness of the photosensitive memory layer 3 is, for example, about 1 to 20 μm. Although not particularly shown in the drawings, as described in the specification of JP-A-56-17358, a relatively thin organic photoconductive substance and a sensitizer (particularly an electron-accepting substance) are placed in contact with the photosensitive memory layer 3. It is also possible to provide a photoconductive layer consisting of. In the example shown in FIG. 1, the image forming method of the present invention is carried out using a combination of such an image forming material 1, a rolled electrode 4, a DC power source 5, a light source 6, and a transparent original 7. The rolled electrode 4 is made of metal or the above-mentioned material on the outer periphery of the cylindrical support 4a.
A conductive film 4b made of a semiconductor such as In ₂ O ₃ is formed. When carrying out the present invention, the rolled electrode 4
The conductive film 4b is brought into contact with the photoconductive memory layer 3 of the image forming material 1 and electrically connected to the negative electrode of the DC power source 5. On the other hand, the positive pole of the DC power source 5 is electrically connected to the conductive substrate 2 of the image-forming material, thereby applying a DC voltage to the photoconductive memory layer 3. On the other hand, the contact portion of the same photoconductive memory layer 3 with the rolled electrode 4 is irradiated with light carrying image information through the light source 6 and the transparent original 7 through the transparent conductive substrate 2 (imagewise exposure). As a result, in accordance with the method of the present invention, voltage application and exposure are performed simultaneously at the contact portion of the photosensitive memory layer 3 with the rolled electrode 4, and electrons are selectively injected into the exposed portion, making it conductive. The exposed and voltage applied portion, which has once become conductive, maintains its conductivity even after the voltage is removed by movement of the rolled electrode 4 and the exposure ends due to the memory effect of the photosensitive memory layer 3. Therefore, if the rolled electrode 4 is moved while being in contact with the photosensitive memory layer 3 during uniform imagewise exposure, a persistent conductive image (latent image) corresponding to the exposure pattern is formed on the photosensitive memory layer 3. . In the above embodiment, the photosensitive memory layer 3 may be irradiated with imagewise light over the entire surface, or by using an appropriate slit, it may be selectively exposed only to the area in contact with the rolled electrode 4. . Further, the rolled electrode 4 may be a rolled rubber electrode made of rubber mixed with carbonic acid or metal powder to make it conductive, instead of being laminated as shown in FIG. 1. In the method of the present invention, the counter electrode used to apply a voltage to the photosensitive memory layer 3 in combination with the conductive substrate 2 does not necessarily need to be a rolled electrode as shown in FIG. 1, but may be a flat electrode. The method of the present invention can also be carried out by pressing the photosensitive memory layer 3. However, in this case, there is a drawback that discharge breakdown tends to occur due to pinholes or impurities on the surface of the photosensitive memory layer 3.
Therefore, it is possible to make the counter electrode a roll-shaped electrode as shown in Figure 1, and to bring the photosensitive memory layer into line contact (actually, it will be a surface contact within a certain width), thereby making it difficult for discharge damage to occur. preferable. When carrying out the method of the present invention according to the embodiment shown in FIG. 1, a sustained conductive image is formed on the photosensitive memory layer 3 at an exposure dose of 0.04 to 0.1 mJ/cm ² when the applied voltage is 100 to 200 V. be done. Note that the photosensitive memory layer 3 does not necessarily need to be exposed through the conductive substrate 2. For example, in the rolled electrode shown in FIG. 1, the photosensitive memory layer 3 may be exposed from inside the rolled electrode 4 by using a transparent conductive film such as SnO ₂ on the transparent support 4a made of cylindrical glass or the like. can. Furthermore, the imagewise light beam irradiated onto the photosensitive memory layer 3 is
Needless to say, it is not necessary to irradiate the entire surface using a transparent original or the like as shown in FIG. 1, and it can also be obtained by scanning a light beam. Laser light with a relatively high energy density per unit area is suitable as the light beam to be used.
For example, Ar laser 514nm, ruby laser
488nm, die laser, He-Ne laser, etc. are used. In this case, a sustained conductive image can be obtained with an exposure amount of about 0.01 to 0.1 mJ/cm ² . Such an exposure method using beam scanning is suitable for performing exposure from inside the roll-shaped electrode described above. Further, the line contact between the image forming material 1 and the counter electrode 4 does not necessarily have to be made by a combination of a flat sheet-like image forming material and a roll-shaped counter electrode as shown in FIG. A combination i of an image forming material 11 (for example, obtained by winding a sheet image forming material 1 around a glass drum) and a planar counter electrode 14, or a combination i of a drum shaped image forming material 11 and a roll form as shown in FIG. It can also be obtained in combination with the counter electrode 4. In either case, exposure is carried out at the contact point to form a persistent conductive image across the photosensitive memory layer of the imaging material 11 as the roll or drum rotates. Note that in FIGS. 2 and 3, the layer configurations of the image forming material and the counter electrode, and related equipment are not illustrated. In the image forming method of the present invention, a sustained conductive image is formed for the first time in the superimposed application area of light and voltage, and cannot be obtained by irradiating light alone if the intensity is up to a certain level. Therefore, it is not always necessary to add image information to the irradiation light as described above, and it may be provided by a scanning electrode for applying a voltage. For example, as shown in FIG. 4 corresponding to FIG. 1, a light source 16 emits light of an exposure intensity that does not, by itself, provide a sustained conductive image, but which, in combination with an applied voltage, provides such an image to the photosensitive memory layer. A sustained conductive image can be provided by uniformly irradiating the photosensitive memory layer 3 and scanning the photosensitive memory layer 3 with the pin electrode 24, which is a counter electrode, in contact with the photosensitive memory layer 3. When a pin electrode is used, since the contact area of the pin electrode with the photosensitive memory layer is extremely small, a connected conductive image can be formed even if exposure is performed from the pin electrode side as shown in FIG. It is also possible to use dot electrodes instead of pin electrodes as scanning electrodes, and other modifications such as winding the image forming material around a drum to form a drum shape and irradiating light through slits can be done using the above-mentioned imagewise exposure method. It can also be carried out in the same manner as in the case of image formation by. In the above, the case where a DC power source is used as the power source has been described. In the method of the present invention, a relatively high frequency such as 50 to 60 Hz/sec is disadvantageous because the injection speed of electrons into the photosensitive memory layer cannot be followed. However, it may be possible to use lower frequencies. Furthermore, when using a DC power source, whether the counter electrode in contact with the photosensitive memory layer is a negative electrode or a positive electrode has a large influence on memory sensitivity. Which one is used for a particular photosensitive memory layer depends on the type of organic photoconductive material forming the photosensitive memory layer. For example, when polyvinylcarbazoles, which generally have characteristics as p-type semiconductors, are used, it is preferable to use the counter electrode 4 as a negative electrode as shown in FIGS. 1 and 4. The sustained conductive image (latent image) obtained as described above has a persistence of about 1 to 20 hours, and can be used in various ways in the same manner as images obtained by conventional sustained conductive electrophotography. used. For example, electrostatic photography or electrostatic printing is the most effective method.
Corona discharge is applied to the photosensitive memory layer on which the persistently conductive image has been formed, and a reversed electrostatic latent image is formed in the non-image area, followed by development by adhesion of toner powder and transfer to paper, etc. Various developing methods can be applied as they are. Once a sustained conductive image is obtained by the method of the present invention, charging-
By repeating development and transfer, a large number of copies can be obtained. Furthermore, as a method that takes advantage of the memory function, it is possible to separate it from the conductive image, so it is expected to be applied as a printing plate that can be printed in parts. Of course, other methods for developing persistently conductive images such as electrolysis and electrophoresis can also be used. The present invention will be explained in more detail with reference to the following examples. Example 1 2,5-dibutoxy-4-morpholinobenzenediazonium tetrafluoroborate (memory effect imparting agent) 2 mg Polyvinylcarbazole (photoconductive substance: Tubicol manufactured by Takasago Dyes Co., Ltd.) 1 g Trinitrofluorenone (sensitizing dye) 50 mg CHCl ₃ 25g Prepare a mixed solution with the above composition in a dark place,
In ₂ O ₃ −SnO ₂ was applied to a polyester film (transparent conductive film manufactured by Teijin Ltd.) using a wire bar, and dried with ventilation at 50°C for about 1 hour to a film thickness of about
A photosensitive material (image forming material) having a 10 μm photosensitive memory layer was formed. In addition, in order to dry completely, the photosensitive memory layer was left to stand for another day, and then the entire surface of the photosensitive memory layer was made conductive in the following manner. That is, a counter electrode (negative electrode) was formed into a roll using a conductive rubber sheet (Shin-Etsu Chemical) in a manner similar to that shown in Figure 1, a DC voltage of 200 V was applied, and interference was applied from the polyester film side to the contact area with the photosensitive material. 50n using filter and halogen lamp
The entire surface of the photosensitive memory layer was made conductive by irradiating it with light of 0.1 mW/cm ² . The photosensitive memory layer was charged (-6KV) with a corona charger (manufactured by Kawaguchi Electric Co., Ltd.) before and after conductivity (voltage simultaneous exposure).
The surface potential was measured after the irradiation, and for comparison, similar measurements were also made when only exposure was performed and when only exposure was performed after corona charging treatment (-6 KV). The results are shown in Table 1.

[Table] When only exposure was performed with an exposure dose of 0.1 mJ/cm ² , the surface potential after exposure was 730V, which was the same as the surface potential before exposure, which was 730V. Furthermore, in the same manner as above, when performing simultaneous exposure to a voltage of ^200V .
6KV) and a positive polarity electrophotographic wet toner to obtain a toner image on the non-exposed area of the surface of the photosensitive material.
Its resolution was 15 lines/mm. Example 2 O-benzoylbenzoic acid 10mg Polyvinylcarbazole 1g Trinitrofluorenone 40mg THF (tetrahydrofuran) 25g A mixed solution having the above composition was prepared in the dark,
In ₂ O ₃ -SnO ₂ similar to that used in Example 1 was coated on a polyester film with a gap width of 4 mils (approximately 0.1 mm) using a doctor blade, dried completely, and exposed to a film thickness of 10 μm. A photosensitive material having a memory layer was obtained. This photosensitive memory layer
An attempt was made to form a sustained conductive image by scanning while applying a voltage of 200 V using a tungsten pin electrode while irradiating light of 500 nm and intensity of 0.1 mW/cm ² at 0.1 mJ/cm ² . It was confirmed that image formation was performed by developing toner of opposite polarity after voltage application, and the scanning speed was 10 cm/sec. Example 3 Recording was carried out in the same manner as in Example 1 except that a 514 nm Ar laser was used instead of the halogen lamp as the light source. As a result, in the case of simultaneous voltage exposure, the exposure amount
Image formation was possible at 100erg/cm ² .

[Brief explanation of drawings]

FIG. 1, FIG. 4, and FIG. 5 are schematic diagrams illustrating one embodiment of the image forming method of the present invention, respectively;
FIGS. 2 and 3 are schematic diagrams showing other examples of arrangement of the image forming material and the counter electrode, respectively. DESCRIPTION OF SYMBOLS 1, 11... Image forming material, 2... Conductive substrate, 3... Photosensitive memory layer, 4... Counter electrode (4
a... Support, 4b... Conductive layer), 5... DC power supply, 6, 16... Light source, 7... Transparent original.

Claims (1)

[Scope of Claims] 1. A photosensitive memory layer containing an organic photoconductive substance and a memory effect imparting agent is formed by exposing the photosensitive memory layer of an image forming material formed on a conductive substrate to light. When forming a persistent conductive image on the layer, a voltage is applied between the conductive substrate and a counter electrode that contacts the surface of the photosensitive memory layer opposite to the side that is in contact with the conductive substrate; persistence at or near the interface between the photosensitive memory layer and the conductive substrate by maintaining the voltage applied to the memory layer substantially constant without attenuation at least while the exposure is being performed; A method for forming an image, characterized in that charge injection efficiency is amplified to increase recording sensitivity, thereby forming a persistent conductive image in the voltage-applied and exposed portions of the photosensitive memory layer. 2. Image formation according to claim 1, wherein at least one of the conductive substrate and the conductive substrate is transparent, and the photosensitive memory layer is exposed to light through the transparent conductive substrate or the counter electrode. Method. 3 uniformly applying a voltage to the photosensitive memory layer,
The image forming method according to claim 1 or 2, wherein imagewise exposure is performed simultaneously. 4. The image forming method according to claim 1 or 2, wherein the photosensitive memory layer is uniformly exposed to light and an imagewise voltage is applied at the same time. 5. The image forming method according to any one of claims 1 to 4, wherein the counter electrode comprises a roller whose outer periphery is electrically conductive. 6. The image forming method according to claim 4, wherein the counter electrode is a pin electrode. 7. The image forming method according to claim 4, wherein the counter electrode is a dot electrode. 8. The image forming method according to any one of claims 1 to 7, wherein the applied voltage is a DC voltage. 9. The image forming method according to claim 8, wherein the counter electrode serves as a negative electrode.