JPS6215860B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a two-color image forming method, and more specifically,
The present invention provides a two-color image forming method using an electrophotographic photoreceptor that can copy a two-color original in one copying process. In the conventional Carlson method, the surface potential of the electrophotographic photoreceptor corresponding to the electrostatic latent image formed on the electrophotographic photoreceptor through a charging-exposure process maintains a single polarity, either positive or negative. While it is sufficient to obtain
In the two-color electrophotographic copying system of the present invention, similar surface potentials are used to distinguish two types of electrostatic latent images, color A (for example, red) and color B (for example, non-red).
Correspondingly, both positive and negative polarities must be maintained. Therefore, 2 formed by the method of the present invention
The color image has a latent image whose surface potential is divided into positive, negative, and zero, which is different from the conventional Carlson process. A two-color image forming method using the electrophotographic photoreceptor (electrophotographic composite photoreceptor) of the present invention includes at least a first photoconductive layer on a conductive substrate, and a second photoconductive layer laminated on the photoconductive layer. A photoreceptor consisting of a first photoconductive layer and a second photoconductive layer is primarily charged with negative polarity, and positive charges induced in the conductive substrate by charge injection or uniform irradiation with light A are transferred to the first photoconductive layer and the second photoconductive layer. The photoreceptor is transferred to the interface with the photoconductive layer of No. 2, and then subjected to image exposure after being positively charged, or by performing image exposure at the same time as the secondary charging and uniformly irradiating the photoreceptor with light A. A method of forming an electrostatic latent image in which the surface potential is divided into positive, negative, and zero, and developing this image with two types of different polarity and different color developers, as the composite photoreceptor (a) The first photoconductive layer is sensitive to light A under positive charging when it is alone, and the surface of the formed composite photoreceptor is subjected to primary charging, secondary charging, and image exposure. (b) The second photoconductive layer has a potential holding ability (potential acceptance ability and potential maintenance ability) that can sufficiently contribute to the formation of a surface potential in the image area of the composite photoreceptor when Consisting of a conductor and a sensitizing dye, this layer alone is sensitive to light B in the negative band, but has almost no sensitivity to light A, and furthermore, the formed composite photoreceptor A material that has a potential holding ability (potential receiving ability and maintaining ability) that can sufficiently contribute to the formation of a surface potential in the image area of the composite photoreceptor when its surface is subjected to primary charging, secondary charging, and image exposure. It is characterized by its use. “Light A” or “Color A” mentioned here or later
"Light of color B" means, for example, red light (wavelength of about 600 to 800 nm), and "light B" or "light of color B" mentioned here or later refers to visible light other than red light (wavelength of about 400 nm). ~600nm). A statement such as "sensitive to light of color A (or light of color B) under positive charge (or under negative charge)" refers to the state in which each layer is positively charged (or negatively charged). Light of color A (or light of color B)
This means that the photoconductive layer becomes conductive when irradiated with . Furthermore, the electrophotographic composite photoreceptor itself, which is made by laminating photoconductive layers with different photosensitive wavelength ranges, was developed by the Special Publication Act in 1974.
It is publicly known from Publication No. 26290, Japanese Patent Publication No. 49-25218, etc. However, the composite photoreceptor described in the former of these documents is made by laminating two or more photoconductive layers, each sensitized, in order to have sensitivity over the entire visible light range. The composite photoreceptor described in the latter is used to perform image exposure at the same time as AC corona charging after positive or negative primary charging to form an electrostatic latent material with either positive or negative electrostatic contrast. This is used to form an image, and both methods are different from the electrophotographic two-color image forming method in which the electrostatic latent image is divided into positive, negative, and zero potentials as in the method of the present invention. . The present invention will be explained in more detail below with reference to the drawings. FIG. 1 shows the structure of a photoreceptor (composite photoreceptor) used in the method of the present invention. Reference numeral 1 indicates a photoreceptor, and this photoreceptor 1 has a three-layer structure, consisting of a conductive support (conductive substrate) 11, a first photoconductive layer 12 provided thereon, and a photoconductive layer 12 provided thereon. A second photoconductive layer 13 is provided. The electrophotographic process (two-color image forming method) related to the present invention starts by uniformly negatively charging the photoreceptor 1 with the charger 2 (second
(See Figure and Figure 3). This charging by the charger 2 is called primary charging. This primary charge is the first
When the photoconductive layer 12 has a rectifying property, this may be carried out in the dark, but it may also be carried out while uniformly irradiating the photoreceptor 1 with light of color A (for example, red light). In terms of a model explanation, it seems easier to understand if primary charging is performed at the same time as light irradiation, so here we will explain it assuming uniform irradiation with light of color A (hν _A ). (Figure 2-1). Now, while the photoreceptor 1 is uniformly irradiated with light of color A (hν _A ), the conductive support 11 is used as a counter electrode.
When the next charging is performed, the negative charge imparted from the charger 2 uniformly charges the surface of the photoconductive layer 13, while the irradiated light of color A causes physical changes in the second photoconductive layer 13. The light of color A (hν _A ) is absorbed by the sensitive first photoconductive layer 12 and becomes a conductor. At the interface between the second photoconductive layer 13 and the first photoconductive layer 13, positive charges having a polarity opposite to the primary charge are uniformly distributed (the positive charges induced in the conductive substrate 11 are connected to the first photoconductive layer 12). (moves to the interface with the second photoconductive layer 13). Of course, at this time, the surface potential of the photoreceptor 1 is uniform and negative. Next, the charger 3 applies a positive charge.
This charging by the charger 3 is called secondary charging (Figure 2-2). When white image exposure is performed after secondary charging (Figure 2-3), light of color A and color B are reflected as reflected light in the area corresponding to the white background of the original (original with red and black images on a white background) 4. The photoreceptor is irradiated, and the first photoconductive layer is made conductive by the color A light, and the second photoconductive layer is made conductive by the color B light, and the charges accumulated in both layers are neutralized. The surface potential of the photoreceptor becomes approximately 0 as shown in FIG. 3. The unexposed area (black image area of the original 4) retains a positive surface potential due to secondary charging as shown in FIG. In the area corresponding to the color A of the original (red image area of the original), only the first photoconductive layer is made conductive by the reflected light of light A, and in order to cancel the secondary charging, the state after the primary charging is changed. , and for this reason the third
As shown in the figure, a negative surface potential appears. Figure 2-4 shows a visualized state of the latent image obtained in this way, where (-), (+)
represents color A of the original, the surface potential of the electrostatic latent image corresponding to the black image area, and are developer (electrostatic particles) T _A , developer (electrostatic particles)
It represents T _BL . Fig. 6 is slightly different from the image forming process explained in accordance with Figs. 2 and 3 above, in which after primary charging, white image exposure is performed at the same time as secondary charging, and the uniform irradiation of the halo A is performed. A latent image is formed by changing the surface potential of the photoreceptor to positive, negative, or zero. That is, Figure 6-1 shows the same primary charging as in Figure 2-1, which causes negative charging to occur on the second photoconductive layer 13 and
Positive charges appear at the interface between photoconductive layer 2 and second photoconductive layer 13. Next, the polarity opposite to the primary charge (positive polarity)
When image exposure is performed at the same time as the secondary charging, the surface potential of the photoreceptor changes because the first photoconductive layer 12 and the second photoconductive layer 13 become conductive in the area corresponding to the white background of the original 4. It becomes almost zero. In the area corresponding to the black image of document 4 (unexposed area), the first
The entire photoconductive layer 12 and second photoconductive layer 13 are charged, and negative charges are generated on the substrate 11 due to secondary charging. has the opposite polarity. Also,
In the area corresponding to the red image of the original 4, the negative charge of the second photoconductive layer 13 neutralizes a part of the positive charge during secondary charging, and at the same time, the first photoconductive layer 12 and the second photoconductive layer
The positive charges at the interface with the photoconductive layer 13 are neutralized with a part of the negative charges induced in the substrate 11 due to secondary charging, and the surface potential in this area eventually becomes lower than that in the unexposed area. is almost the same as the surface potential of . Therefore, the amount of charge charged in the secondary charging simultaneous image exposure is different between the unexposed area and the red image area (Figure 6-2). Incidentally, it is possible to easily make the surface potentials of the area corresponding to the red image and the area corresponding to the black image of the document substantially the same by setting the discharge conditions of the charger 3. Subsequently, when the first photoconductive layer 12 is uniformly exposed to light A, the first photoconductive layer 12 becomes a conductor, and a portion of the positive charge of the first photoconductive layer 12 corresponding to the unexposed area becomes conductive. The negative charge of the sexual substrate 11 is neutralized, and (6-3
As a result, the surface potential of the area corresponding to the unexposed area becomes negative. On the other hand, since the surface potential corresponding to the red image area has already been irradiated with light A (light from the red image) at the same time as secondary charging, the surface potential remains positive with almost no change (Figure 6-3). ). Such changes in the surface potential of the photoreceptor are as shown in FIG. Therefore, if the latent image thus formed is visualized using two types of different polarity and different color developers in the same manner as in Fig. 2-4, a two-color image is obtained (Fig. 6-4). FIG. 7 shows how the surface potential of the photoreceptor changes in the two-color image formation explained in FIG. The conductive substrate has a conductive layer having a volume resistance of 10 ¹⁰ Ωcm or less (1-11 in Figure 1), such as a metal plate such as Al, Cu, or PB, or SnO ₂ ,
Examples include a plate made of a metal compound such as In ₂ O ₃ , CuI, CrO ₂ or the like, or a plastic film (for example, polyester film) or paper whose surface is coated with the above compound by vapor deposition or sputtering. The thickness range of the first P-type photoconductive layer indicated by 12 of the photoreceptor 1 in FIG. 1 is suitably 3 .mu.m to 100 .mu.m, preferably 5 .mu.m to 70 .mu.m, and the materials include the following. Amorphous Se and spectral sensitizers such as AS and Te are included in the binder; inorganic types such as trigonal Se; organic types such as Sudan Red, Diane Blue, and Jenas Green. Azo pigments such as B, quinone pigments such as pyrenequinone and indanthrene brilliant violet RRP, indigo pigments such as indigo and thioindigo, bisbenzimidazole pigments such as India First Orange Toner, phthalocyanine pigments such as copper phthalocyanine, quinacridone pigments, etc. Any type of photoconductive material in which colored photoconductive particles are dispersed can be used. Binders for the first photoconductive layer dispersed in the binder include polyethylene, polystyrene, polybutadiene, styrene-butadiene copolymers, polymers and copolymers of acrylic esters or methacrylic esters, and polyesters. ,polyamide,
All materials usable for electrophotography such as polycarbonate, epoxy resin, urethane resin, silicone resin, alkyd resin, cellulose resin, and blends thereof can be used. When using a binder as a component of the first photoconductive layer, it is desirable not to form a continuous layer at the boundary between the two photoconductive layers. When forming,
Care must be taken in selecting a binder so that the first photoconductive layer is insoluble in the solvent used to form the second photoconductive layer, that is, polyvinylcarbazole and its derivatives. be. Also, if necessary, crystal violet,
Triphenylmethane dyes such as malachite green, xanthene dyes such as fluorescein, rose bengal, and rhodamine B, acridine dyes such as acridine orange, azine dyes such as phenosafranine and methylene violet, thiazine dyes such as phenothiazine, methylene blue, etc. ，
Pyrylium salts such as 3,5-triphenylpyrylium perchlorate, thiapyrylium salts such as 1,3,5-triphenylthiapyrylium perchlorate, etc. can be used as spectral sensitizers, and furthermore, chemical sensitizers can be used. A compound containing at least one of an alkyl group such as a methyl group, an alkoxy group, an amino group, an imino group, and an imido group as a sensitizer, or a polycyclic aromatic group such as anthracene, pyrene, phenanthrene, coronene, etc. in the main chain or side chain. compounds or low molecular weight electron-donating compounds having nitrogen-containing cyclic compounds such as indole, carbazole, oxazole, isoxazole, thiazole, imidazole, pyrazole, oxadiazole, thiadiazole, triazole, specifically hexamethylenediamine, N- (4-aminobutyl)cadaverine,
as-didodecylhydrazine, p-toluidine, 4
-amino-o-xylene, N,N'-diphenyl-1,2-diaminoethane, o-, m- or p-
Ditolylamine, triphenylamine, diurene, 2-bromo-3,7-dimethylnaphthalene,
2,3,5-trimethylnaphthalene, N'-(3
-Bromphenyl)-N-(β-naphthyl)urea, N'-methyl-N-(α-naphthyl)urea,
N,N'-diethyl-N-(α-naphthyl)urea, 2,6-dimethylanthracene, anthracene, 2-phenylanthracene, 9,10-diphenylanthracene, 9,9'-bianthranil, 2
-dimethylaminoanthracene, phenanthrene, 9-aminophenanthrene, 3,6-dimethylphenanthrene, 5,7-dibromo-2-phenylindole, 2,3-dimethylindoline,
3-indolylmethylamine, carbazole, 2
-Methylcarbazole, N-ethylcarbazole, 9-phenylcarbazole, 1,1'-dicarbazole, 3-(p-methoxyphenyl)oxazolidine, 3,4,5-trimethylisoxazole, 2-anilino-4, 5-diphenylthiazole, 2,4,5-trinitrophenylimidazole, 4-amino-3,5-dimethyl-1-phenylpyrazole, 2,5-diphenyl-1,3,
4-oxadiazole, 1,3,5-triphenyl-1,2,4-triazole, 1-amino-5
-Phenyltetrazole, bis-diethylaminophenyl-1,3,6-oxadiazole, etc. can be used, and compounds having an electron-accepting host structure such as carboxylic acid anhydride, ortho or paraquinoid structure, Nitro group, nitroso group,
Electron-accepting compounds such as aliphatic cyclic compounds, aromatic compounds, and heterocyclic compounds having an electron-accepting substituent such as a cyano group; more specifically, maleic anhydride, phthalic anhydride, tetrachlorophthalic anhydride, Tetrabromophthalic anhydride, naphthalic anhydride, pyromellitic anhydride, chlor-p-benzoquinone, 2,5-dichlorobenzoquinone, 2,6-
Dichlorobenzoquinone, 5,8-dichlornaphthoquinone, o-chloranil, o-bromoanil,
p-Chloranil, p-bromoanil, p-iodoanil, tetracyanokydimethane, 5,6-quinolinedione, coumarin-2,2-dione, oxindirubin, oxyindico, 1,2-dinitroethane, 2,2-dinitro Propane, 2-nitro-2-nitrosopropane, iminodiacetonitrile, succinonitrile, tetracyanoethylene, 1,1,3,3-tetracyanopropenide,
o-, m- or p-dinitrobenzene, 1,2,
3-trinitrobenzene, 1,2,4-trinitrobenzene, 1,3,5-trinitrobenzene,
Dinitrodibenzyl, 2,4-dinitroacetophenone, 2,4-dinitrotoluene, 1,3,5
-trinitrobenzophenone, 1,2,3-trinitroanisole, α,β-dinitronaphthalene, 1,4,5,8-tetranitronaphthalene,
3,4,5-trinitro-1,2-dimethylbenzene, 3-nitroso-2-nitrotoluene, 2-
Nitroso-3,5-dinitrotoluene, o-,m
- or p-nitronitrosobenzene, phthalonitrile, terephthalonitrile, isophthalonitrile, benzoyl cyanide, bromobenzyl cyanide, quinoline cyanide, o-xylylene cyanide, o-, m- or p-nitrobenzyl cyanide , 3,5-dinitropyridine, 3-nitro-2
-Pyridone, 3,4-dicyanopyridine, α-,
β- or γ-cyanopyridine, 4,6-dinitroquinone, 4-nitroxanthone, 9,10-dinitroanthracene, 1-nitroanthracene, 2-
Nitrophenanthrenequinone, 2,5-dinitrofluorenone, 2,6-dinitrofluorenone,
3,6-dinitrofluorenone, 2,7-dinitrofluorenone, 2,4,7-trinitrofluorenone, 2,4,5,7-tetranitrofluorenone, 3,6-dinitrofluorenone mandenonitrile, 3-nitrofluorenone Fluorenone mandenonitrile, tetracyanopyrene, etc. can be used. Note that a plasticizer can be used in combination with the resin binder. Dibutyl phthalate as a plasticizer,
Those commonly used as plasticizers for resins, such as dioctyl phthalate, can be used as they are. The appropriate amount to be used is about 5 to 30% by weight based on the resin. The proportion of the colored photoconductive particles to the entire first photoconductive layer constituent material is 1 to 70% by weight, preferably 5 to 70% by weight.
The appropriate amount is 40% by weight, and the amount of the spectral sensitizer and chemical sensitizer to be added is determined as necessary. It can be used until it becomes approximately 70% by weight or less based on the total weight. Figure 1, 1, 13, 2
The thickness range of the photoconductive layer is suitably 3 μm to 30 μm, preferably 5 to 15 μm, and the materials include the following. Transparent photoconductors include poly-N-vinylcarbazole and its derivatives (for example, those having a halogen such as chlorine or bromine, or a substituent such as a methyl group or an amino group in the carbazole core), polyvinylpyrene, polyvinylanthracene, Pyrene-formaldehyde condensation polymers and derivatives thereof (for example, those having a halogen such as bromine or a substituent such as a nitro group in the pyrene skeleton), or low-molecular electron-donating compounds or electron-accepting compounds already in the first photoconductive layer. Compounds etc. may also be used. As the sensitizing dye (spectral sensitizer), among the already described spectral sensitizers, diphenylmethane dyes such as auramine, acridine dyes such as acridine yellow, etc., the second one is used for forming the first photoconductive layer. The photoconductive layer has almost no sensitivity to color A light, and the photoconductive layer satisfies the purpose of improving the sensitivity to color B light;
As in the case of forming the photoconductive layer, it is also possible to use a binder, a plasticizer, a chemical sensitizer, etc. in combination. As described above, the first photoconductive layer having such a structure is sensitive to light A under positive charging when this layer alone is charged, and the surface of the composite photoreceptor formed is primarily charged. , has a potential receiving ability and a potential retaining ability that can sufficiently contribute to the formation of a surface potential in the image area of the composite photoreceptor when subjected to secondary charging with a polarity opposite to this primary charging and imagewise exposure. Further, the second photoconductive layer having such a configuration allows light A to pass through, and when this layer alone is negatively charged, it has sensitivity to light B and almost no sensitivity to light A. ,
Furthermore, the surface of the formed composite photoreceptor is charged with a primary charge, a secondary charge with a polarity opposite to this primary charge, and a potential that can sufficiently contribute to the formation of a surface potential in the image area of the composite photoreceptor when subjected to image exposure. It has the ability to accept and hold electric potential. Example A smooth aluminum plate was used as the conductive substrate corresponding to 11 in Fig. 1, and amorphous selenium sensitized with tellurium with a thickness of 70 μm was used as the first photoconductive layer corresponding to 12 in Fig. 1. there was. A second photoconductive layer corresponding to that shown in FIG. 13 was formed on this as follows. Poly-N-vinylcarbazole 10g (transparent photoconductor) Polyester resin (polymer plasticizer) 1g

[Formula] Add 189 ml of 1,2-dichloroethane to 2.2 mg and dissolve it, cast this coating solution on the first photoconductive layer, air dry for 5 minutes, and then heat in an air bath at 50°C for 1 hour. Drying was carried out to obtain a second photoconductive layer having a thickness of approximately 5 μm. Further, photoreceptors having approximately the same film thickness were obtained by applying the same coating solution onto an aluminum vapor-deposited Mylar film in the same manner. Approximately 5 μm thick with only the second photoconductive layer
-6KV corona discharge is applied to a photosensitive plate in a dark place for 20 minutes.
The photoconductive layer was charged negatively for 2 seconds. The surface potential ^U V _S at this time, the surface potential ^U V _O when left in the dark for 20 seconds after charging, and then irradiation using a 20 lux white tungsten lamp to determine the surface potential.
The exposure amount ^UE required for attenuation to 1/2 was measured. The values measured in this way are shown in Table 1. In addition, the light attenuation curve at this time and the light attenuation curve when Kodatsu Klatzten Filter No. 25 (Red) was used under similar measurement conditions are shown in Figure 4. The transmission characteristics are shown in FIG. From Figures 4 and 5, the second photoconductive layer has approximately
It shows that the sensitivity is sufficient to sufficiently attenuate B light with a wavelength shorter than 580 nm, but the sensitivity is much lower than this with respect to A light with a longer wavelength than the same wavelength. Furthermore, the photoreceptor having the composite layer of the first and second photoconductive layers was negatively charged by primary charging.
At this time, a discharge voltage of -6.2 KV was applied to the charger. Next, add red ink to plain white paper.
A two-color document with a red information image written on it using a red pencil and a red ink ballpoint pen, and a black information image written on it using black ink, a black pencil, and a black ink ballpoint pen is irradiated with white light, and the reflected light is reflected by an imaging lens system. The photoreceptor was subjected to secondary charging while being irradiated with a light image of the document by forming an image on the photoreceptor. At this time, a discharge voltage of 5.4 KV was applied to the charger. In this state, the surface potential of the photoreceptor was +1000V in the red corresponding area, +1070V in the black corresponding area, and approximately 0V in the white background area. Next, the above photoreceptor was uniformly irradiated with a 10W red fluorescent lamp, and as a result, the photoreceptor surface potential distribution was +980V in the red area, -740V in the black area, and -740V in the white area.
It became 0V. The electrostatic latent image thus formed is visualized using a developer in which a positively charged black toner and a negatively charged red toner are mixed and dispersed in a dispersion medium, and a visible image is obtained. When the image was transferred and fixed onto a recording sheet, a clear red/black two-color image with high brightness and no color mixture was obtained.

【table】 [Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a photoreceptor used in the method of the present invention. Figures 2, 3, 6 and 7
The figure is a diagram for explaining the two-color image forming method of the present invention. FIGS. 4 and 5 are diagrams for explaining the characteristics of the photoreceptor used in the present invention. 1... Photoreceptor, 2, 3... Charger, 4...
... Original document, 11 ... Conductive substrate, 12 ... First photoconductive layer, 13 ... Second photoconductive layer.

Claims (1)

[Claims] 1. At least a first photoconductive layer on a conductive substrate,
It is constructed by sequentially laminating a second photoconductive layer, and the first
The photoconductive layer has sufficient surface potential acceptance and maintenance ability to enable color development with electrostatic particles under positive charge when used alone, and sufficiently attenuates the surface potential against light A. The second photoconductive layer is composed of at least a transparent photoconductor and a sensitizing dye, and when used alone, it can be imaged and developed with electrostatic particles under negative charge. Using an electrophotographic composite photoreceptor that has extremely sufficient surface potential acceptance and maintenance ability, and sensitivity that can sufficiently attenuate light B, it has almost no sensitivity to light A. (i) Primary charging of negative polarity is performed on the photoreceptor, and positive charges induced on the conductive substrate by charge injection or uniform irradiation of light A are transferred to the first photoconductive layer and the second photoconductive layer. (ii) By performing imagewise exposure after applying positive secondary charging, or by performing imagewise exposure at the same time as the secondary charging and further irradiating uniformly with light A, the surface potential is increased. forms an electrostatic latent image divided into positive, negative, and zero potentials, and then (iii) visualizes this electrostatic latent image with two types of electrostatic particles of different polarities and different colors. Characteristic two-color image forming method.