JPH08339091A - Image forming method - Google Patents

Abstract

PURPOSE: To form an image having high gradation and high resolution and having no surface fogging by using aqueous developer in which coloring material and toner particles are dispersed and specifying the electric resistance of a photoreceptor. CONSTITUTION: The conductive layer of the photoreceptor 1 is grounded and developing bias potential is impressed on a developing electrode 2. Then, the back surface of the photoreceptor 1 is irradiated with light having image information. The exposed photoreceptor 1 becomes conductive, so that charge is moved in accordance with the bias potential and simultaneously the migration of the toner particles in the developer is guided. The charge having equivalent weight and reverse polarity to the charge moved in the photoreceptor 1 is carried to the surface of the photoreceptor 1 by the carrier liquid and the toner particles. The toner particles are held, and the charge is maintained at a part which does not directly come in contact with the photoreceptor, then the toner particles are held on the photoreceptor. In this image forming method, the developer obtained by dispersing at least a coloring agent and toner particles consisting of binder in the carrier liquid principally composed of water is used as the developer and the photoreceptor whose electric resistance is <=1×10<7> Ωcm is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method by a back exposure method using light.

[0002]

2. Description of the Related Art A method of forming an electrostatic charge image on an electrophotographic photosensitive member and visualizing it with a liquid developer is generally used as a liquid developing system. By the way, generally, in a developing method using an aqueous liquid developer, a very large amount of electric current is required at the time of development, but a photoconductor used in a conventional electrophotographic method called PPC is used for developing with an aqueous liquid developer. If so, only a few microamperes (A) of current can flow. However, according to the study by the present inventor,
In an image forming method using an aqueous liquid developer, a current of at least several hundred microamperes is required at the time of development, and preferably several milliamperes or more. It is considered that the large amount of the electric current is to prevent water, which is the carrier liquid of the aqueous liquid developer, from leaking the charges that have moved to the surface of the photoconductor and not contributing to the development. However, in the conventional electrophotographic method, the amount of electric charge held by the photoconductor is very small, and it is impossible to flow such a large amount of current.

As a result of reexamination of the developing method in the electrophotographic method from various angles, the present inventor has found that the developing means capable of supplying a large current constantly uses a liquid developer and uses the light back exposure method. It was found that this was possible. However, it is known that a conventional dry back exposure method uses a dry two-component developer or a dry one-component developer (toner only) for its development (Japanese Patent Publication No. 60-5).
9592, JP-A-5-127466). That is,
The conventional concept of the optical back exposure method presupposes the use of dry toner. However, in this conventional optical backside exposure method, it is necessary to make a place for hard carrier particles to accumulate and to charge the photoconductor with a magnetic brush, so that the photoconductor and carrier particles are in strong contact with each other and the photoconductor is damaged. Wear out. Further, even when a single-component toner is used, the photoconductor comes into contact with hard toner particles mainly composed of a pulverized product of a mixture of a colorant and a binder resin, so that the surface thereof may be damaged.

As has been seen so far, there have been almost no studies on the optical backside exposure method using a liquid developer. Especially in the water-based development method, it is a common theory that when the photoconductor comes into contact with water, the charge on the photoconductor leaks and development cannot be performed. The only means was to use a mist or a pouring liquid. For this reason, the original high resolution of the liquid developer cannot be obtained, and the utility value is low. The fact is that little consideration has been given to the use of a liquid developer, especially an aqueous developer, in the back exposure method.

A liquid developer, in which at least a colorant is dispersed in a carrier liquid mainly composed of water, is used, and the liquid developer is brought into contact with an optical semiconductor, which is generally called a photoconductor, to the photoconductor. By applying light to make it conductive and forming an electric field in the developing solution, toner particles can be attached and developed on the surface of the photoconductor on which current flows in and out to form a visible image.

On the other hand, regarding the photosensitive member used in the back exposure method, "Electrophotographic Society", Vol. 33, No. 2 (199).
In 2), the carrier mobility is small in the conventional OPC, so
It is pointed out that it cannot be used for the optical back exposure method. In fact, it is very difficult to carry out the development by the optical back exposure method, especially the development of the aqueous developer with the commercially available OPC. These facts
This is caused by the leakage of electric charge into the developer carrier liquid. If aqueous development is to be carried out by the light backside exposure method, it is necessary to supply a current that contributes to the development in addition to the current flowing in the carrier. However, conventional commercial OPC
It is difficult to supply enough current.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to provide an image formation having a high gradation and a high resolution by an optical backside exposure method and having no background fog. A second object of the present invention is to provide a pollution-free and safe image forming method.

[0008]

The inventors of the present invention have found that a developing means capable of steadily supplying a large current is possible by using the optical backside exposure method depending on the performance of the photoreceptor. . The present invention has been made based on this.

According to the present invention, (1) when an image is formed by a back exposure method using light, an aqueous liquid developing method in which toner particles composed of at least a colorant and a binder are dispersed in a carrier liquid mainly containing water as a developing solution. And the electrical resistance (volume resistance) in the dark as a photoconductor is 1 × 10.
There is provided an image forming method characterized by using a photoconductor of ⁷ Ωcm or less. According to the present invention, (2) an aqueous liquid developer in which toner particles composed of at least a colorant and a binder are dispersed in a carrier liquid mainly containing water as a developer when an image is formed by a back exposure method using light. When the strongest absorption amount of the photoconductor is set to 100, the wavelength range showing 90 or more absorption is continuous or discontinuous 1
There is provided an image forming method characterized by using a photoreceptor having a width of 00 nm or more. Further, according to the present invention, (3) an aqueous liquid developer having toner particles composed of at least a colorant and a binder dispersed in a carrier liquid mainly containing water as a developing liquid when an image is formed by a light back exposure method. As a photoreceptor, the electric resistance (volume resistance) in the dark is 1 × 10 ⁷ Ωcm or less, and the wavelength range showing 90 or more absorption when the strongest absorption amount is 100 is a width of 100 nm or more continuously or discontinuously. An image forming method is provided, which comprises using a photoconductor having

The present invention will be described in more detail below. FIG. 1 is a schematic view of an image forming apparatus using the optical back exposure method,
1 is a photoconductor, 2 is a developing electrode, 3 is a developing solution or its moving direction, 4 is a light source housed in the photoconductor, 5 is a transfer roller, and 6 is a squeeze roller. Here, the photoreceptor 1 has a transparent conductive layer provided on a transparent substrate,
Further, it has a structure in which a photosensitive layer is provided thereon. A protective layer may be provided on the photosensitive layer if necessary. Developing electrode 2 with a certain distance from photoconductor 1,
The squeeze roller 6 is arranged, and the liquid developer is connected between these to be supplied, held, and collected.

The conductive layer of the photoreceptor 1 is grounded, and the developing electrode 2
Is applied with a developing bias potential. Light having image information is emitted from the back surface of the photoconductor as the photoconductor moves. The exposed photoreceptor becomes conductive and transfers charge according to the bias potential. The charge transfer also induces migration of toner particles in the developer. Charges of opposite polarity, which are the same as the charges moving in the photoreceptor, are carried to the photoreceptor surface by the carrier liquid and the toner particles. The carried charges cancel each other on the surface of the photoconductor, but the toner particles retain the charge, and the portions not in direct contact with the photoconductor maintain the charge, and as a result, the toner particles are held on the photoconductor by the electrostatic force.

After the series of developing operations are completed, the excess developing solution is removed and the toner layer is transferred and fixed on the transfer paper. As the transfer method, transfer may be performed by simply pressing the transfer paper against the toner layer on the photoconductor 1, or electrostatically attracted by applying a voltage having a polarity opposite to that of the developing electrode. If necessary, the toner layer portion may be exposed from the back surface of the photoreceptor at the same time as or before or after the transfer step. This exposure makes it easier to eliminate the charges held on the photoconductor side, improve the transfer efficiency, and prevent development obstacles in the next development process. The fixing method may be carried out depending on the situation. In particular, if it is not necessary to form a large number of images at high speed, the carrier liquid can be dried and fixed by leaving it alone, and if high-speed image formation is required, heat it to evaporate the carrier liquid. You may accelerate | stimulate or you may fuse | melt and harden the adhesive component contained in the toner particle.

For the toner particles in the liquid developer of the present invention, a resin (binder resin) is used together with a colorant (carbon black, various pigments, etc.) that is insoluble or hardly soluble in water. Additives such as wax may be appropriately mixed with this resin, and by doing so, the wax can be melted by a slight heat drying after being transferred to the transfer paper and firmly adhered to the fibers of the transfer paper.

To produce toner particles, a colorant is dispersed by a disperser such as a ball mill or a sand mill, a resin,
A method such as redispersion with a carrier liquid or kneading into a resin can be adopted. By adding wax or the like to the resin, the toner particles can be transferred to the transfer paper, and then the wax can be melted by a slight heat drying to firmly adhere the toner to the fibers of the transfer paper.

The colorants usable in the present invention include Printex V, Printex U, Printex G,
Special Black 15, Special Black 4, Special Black 14-B (all manufactured by Degussa), Mitsubishi # 4
4, # 30, MR-11, MA-100 (manufactured by Mitsubishi Kasei), Raven 1035, Raven 1252, News Spect II (manufactured by Columbia Carbon), Regal 400, 660, Black Pearl 900, 110.
No. 0, No. 1300, inorganic pigments such as Mogar L (all manufactured by Cabot) and phthalocyanine blue, phthalocyanine green, sky blue, rhodamine lake, malachite green lake, methyl violet lake, peacock blue lake, naphthol green B, naphthol green Y, Naphthol Yellow S, Naphthol Red, Resor Fast Yellow 2G, Permanent Red 4R, Brilliant First Scarlet, Hansa Yellow, Benzidine Yellow, Resor Red,
Organic pigments such as Lake Red C, Lake Red D, Brilliant Carmine 6B, Permanent Red F5R, Pigment Scarlet 3B Indigo, Thioindigo Oil Pink and Bordeaux 10B are listed.

As a resin, Eastman Chemical (Eastman Chemical)
al) (N-10, N-11, N-12, N-14, N-3
4, N-45, C-10, C-13, C-15, C-1
6, E-10, E-11, E-12, E-14, E-1
5) Mitsui Petrochemical Co., Ltd. (110P, 220P, 220MP, 820MP, 41
0MP, 210MP, 310MP, 405MP, 200
P, 4202E, 4053E) Sanyo Chemical Co., Ltd. (131P, 151P, 161P, 171P, E30
0, E250P) manufactured by Sazol (H1, H2, A1, A2, A3, A4) manufactured by BASF (OA WAX, A WAX) manufactured by Petrolite (BARECO) 500, 2000, E-7
30, E-2018, E-2020, E-1040, Petronaba C, the same C-36, the same C
-400, C-7500) Hoechst (PE580, PE130, PED121, PED13)
6, PED153, PED521, PED522, PE
D534) Union Carbide (DYN1, DYNF, DYNH, DYNJ, DYN
K) Monsanto (ORUZON 805, 705, 50) DuPont (ALATHON 3, 10, 12, 14,
16, 20, 22, 23) Allied Chemicals (AC polyethylene 6,6A, 615) Mitsui Polychemicals (Evaflex 150, 210, 220, 250, 2
60, 310, 360, 410, 420, 450, 46
0,550,560) and other synthetic polyesters, polypropylene and modified products thereof, natural waxes such as carnauba wax, montan wax, candelilla wax, sugar cane wax, occuri wax, beeswax, wood wax, nuka wax, ester gum, Natural resin such as cured rosin, natural resin modified maleic acid resin, natural resin modified phenolic resin,
A natural resin modified polyester resin, a natural resin modified pentaerythritol resin, a natural resin modified cured resin such as an epoxy resin, or the like can be used in combination.

Examples of the dispersant include the following. (Anionic surfactant) fatty acid soap, N-acyl amino acid and its salt, alkyl ether carboxylate, acylated peptide, alkylbenzene sulfonate (AB
S) (LAS), alkylnaphthalene sulfonate, dialkyl sulfosuccinate ester salt, alkyl sulfoacetate salt, α-olefin sulfonate salt, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate ester salt,
Alkyl ether sulphate, polyoxyethylene alkyl phenyl ether sulphate, monoglycer sulphate, alkyl ether phosphate ester salt, alkyl phosphate ester salt, (cationic surfactant) aliphatic amine salt, benzalkonium salt, benzethonium chloride , Pyridinium salt, imidazolinium salt, (amphoteric surfactant) carboxybetaine acid, aminocarboxylic acid salt, imidazolinium betaine, lecithin, (nonionic surfactant) polyoxyethylene alkyl ether, single chain length polyoxy Ethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative, ethylene oxide derivative of alkylphenol formalin condensate, polyoxyethylenepolyol Cypropylene block polymer, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil and hydrogenated castor oil, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, Fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester.

On the other hand, the carrier liquid mainly contains water, but a water-soluble liquid such as ethylene glycol may be appropriately mixed. Others, polymer electrolyte, thickener, rust preventive agent,
Additives such as preservatives may be added as needed, but it is preferable not to add them.

The particle size distribution of the toner particles is preferably 0.1 μm or more and 3.0 μm or less. If the particle size of the toner is too small, the adhesion to the photoconductor becomes too strong and the transfer and cleaning properties are poor, and if it is too large, the amount of development adhesion tends to increase and the resolution tends to decrease.

The photosensitive member used in the present invention has an electric resistance (volume resistance) in the dark of 1 × 10 ⁷ Ωcm or less, preferably 1 × 10 ⁵ Ωcm or less. Such a specific value is determined by what kind of conductive polymer or conductive material is used and to what extent. The desired electric resistance can be obtained, for example, by using a conductive polymer such as an ionic complex of polyaniline or crown ether or polyethylene oxide for the binder resin. It can also be obtained by finely pulverizing and dispersing a conductive substance such as tin oxide in a resin.

In addition to the X-type metal-free phthalocyanine, the single-layer type photosensitive layer of the photoreceptor may be, for example, α-S.
e, α-As ₂ Se ₃ , amorphous chalcogenides such as α-SeAsTe, and amorphous silicon (α-Si)
Powders of semiconductor materials such as ZnO, CdS, etc .; II-VI group microcrystals; pyrylium salts; aluminum phthalocyanines, copper phthalocyanines having crystal forms such as α-type, β-type, and γ-type,
Phthalocyanine compounds such as titanyl phthalocyanine,
If necessary, a charge generating material such as an anthuron compound, an indigo compound, a triphenylmethane compound, a zulene compound, a toluidine compound, a pyrazoline compound, a quinacridone compound, a pyropyrrole compound, or the like can be used in combination.

As the charge generating material for forming the single-layer type or laminated type photosensitive layer in the photoconductor, for example, CI Pigment Blue 25 (color index (CI) 2118) is used.
0), CI Pigment Red 52 (CI4510
0), CI Basic Red 3 (CI45210)
In addition to the above, a phthalocyanine-based pigment having a porphyrin skeleton and an azo pigment having a carbazole skeleton (Japanese Patent Laid-Open Publication No.
3-95033), an azo pigment having a stilbene skeleton (described in JP-A-53-138229), and an azo pigment having a distyrylbenzene skeleton (JP-A-53-13).
3455), an azo pigment having a triphenylamine skeleton (described in JP-A-53-132547), and an azo pigment having a dibenzothiophene skeleton (JP-A-54-2).
1728), an azo pigment having an oxadiazole skeleton (described in JP-A-54-12742), an azo pigment having a fluorenone skeleton (described in JP-A-54-22834), an azo having a bisstilbene skeleton. Pigments (described in JP-A-54-17733), azo pigments having a distyryl oxadiazole skeleton (described in JP-A-54-2129), azo pigments having a distyryl carbazole skeleton (JP-A-54-17734). No.), a trisazo pigment having a carbazole skeleton (JP-A-57-19576).
No. 7, No. 57-195758), etc., and further phthalocyanine pigments such as SI MIGMENT BLUE 16 (CI74100), SI BAT Brown 5 (CI
173410), CI Bat Die (CI7303)
0) and the like, indigo pigments such as Argos Scarred B (manufactured by Violet), perylene-based pigments such as Indanthren Scarlet R (manufactured by Bayer), organic pigments such as square pigments: Se, Se alloys, CdS, amorphous Si.
Inorganic pigments such as can be used.

Further, as the charge transporting material for forming the single-layer type or multi-layer type photosensitive layer in the photoreceptor, tetracyanoelene; fluorenone compounds such as 2,4,7-trinitro-9-fluorenone; 9-carbazolyl Fluorene-based compounds such as ruiminofluorene; nitrated compounds such as dinitroanthracene; succinic anhydride; maleic anhydride; dibromomaleic anhydride; triphenylmethane-based compounds;
2,5-di (4-dimethylaminophenyl) -1,3
Oxadiazole compounds such as 4-oxadiazole;
Styryl compounds such as 9- (4-diethylaminostyryl) anthracene; carbazole compounds such as poly-N-vinylcarbazole; pyrazoline compounds such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline; 4,4 ′, 4 ″ -Tris (N, N-diphenylamino) triphenylamine, 3,3′-dimethyl-N,
Amine derivatives such as N, N ', N'-tetrakis-4-methylphenyl (1,1'-biphenyl) -4,4'-diamine; 1,1-bis (4-diethylaminophenyl) -4,4- Conjugated unsaturated compounds such as diphenyl-1,3-butadiene; hydrazone compounds such as 4- (N, N-diethylamino) benzaldehyde-N, N-diphenylhydrazone; indole compounds, oxazole compounds, isoxazole compounds, Thiazole compounds, thiadiazole compounds, imidazole compounds,
Nitrogen-containing cyclic compounds such as pyrazole compounds, pyrazoline compounds and triazole compounds; condensed polycyclic compounds and the like. Among the above charge transport materials,
A polymer material having photoconductivity such as poly-N-vinylcarbazole can also be used as a binder resin for the photosensitive layer.

Examples of the binder resin constituting the photosensitive layer include thermosetting silicone resin; curable acrylic resin; alkyd resin; unsaturated polyester resin; diallyl phthalate resin; phenol resin; urea resin; benzoguanamine resin; melamine resin; Styrene polymer; acrylic polymer; styrene-acrylic copolymer; olefin polymers such as polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polypropylene and ionomer; polyvinyl chloride; vinyl chloride-acetic acid Vinyl copolymer; polyvinyl acetate; saturated polyester; polyamide;
Thermoplastic urethane resin; polycarbonate; polyarylate; polysulfone; ketone resin; polyether and the like.

In the photosensitive layer composed of the above components, the content of the charge generating material is 2 to 100 parts by weight of the binder resin.
It is preferably in the range of 20 parts by weight, particularly preferably in the range of 3 to 15 parts by weight. Also. The content of the other charge transport material with respect to 100 parts by weight of the binder resin is preferably in the range of 40 to 200 parts by weight, particularly preferably in the range of 50 to 100 parts by weight. If the content of the charge generating material is less than 2 parts by weight or the content of the charge transporting material is less than 40 parts by weight, the sensitivity of the photoconductor may be insufficient or the residual potential may be large. On the other hand, when the content of the charge generation material exceeds 20 parts by weight, or when the content of the charge transport material is 2
If it exceeds 100 parts by weight, the abrasion resistance of the photoreceptor may be insufficient.

By using an antioxidant together with the above-mentioned photosensitive layer, it is possible to prevent deterioration due to oxidation of functional components such as a charge transport material having a structure susceptible to oxidation. As the above-mentioned antioxidant, 2,6-di-tert-butyl-p
-Cresol, triethylene glycol-bis [3-
(3-tert-Butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-]
Hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate],
2,2-thio-diethylenebis [3- (3,5-di-t
ert-Butyl-4-hydroxyphenyl) propionate], 2,2-thiobis- (4-methyl-6-ter
t-butylphenol), N, N'-hexameethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl-
2,4,6-Tris (3,5-di-tert-butyl-
Examples include phenolic antioxidants such as 4-hydroxybenzyl) benzene.

As the solvent used here, tetrahydrofuran, cyclohexanone, dioxane, dichloroethane, cyclohexane, methyl ethyl ketone, 1,1,1,
A single solvent or a mixed solvent such as 2-trichloroethane, 1,1,2,2, -tetrachloroethane, dichloromethane and ethyl cellosolve is preferable. Further, the conductive base material on the surface of which the photosensitive layer is formed is formed in an appropriate shape such as a sheet shape or a drum shape according to the mechanism and structure of the image forming apparatus in which the electrophotographic photosensitive member is incorporated. .

When a photoconductor (preferably an organic photoconductor) having such a binder is used in the above-mentioned photo-back exposure method, the electric resistance of the entire photoconductive layer is lowered. In particular, the transfer resistance of electric charges generated in the exposed portion is reduced, and the ability to transport electric charges is greatly increased. Therefore, a larger developing current can be obtained with the same developing bias, and sufficient charges can be supplied to the surface of the photosensitive layer and the developer even when the exposure is performed for a short time or the exposure intensity is weak. . When such a photoreceptor is used, the current at the time of non-exposure becomes too large, which may cause background fog. If there is a certain degree of difference and the current value during non-exposure does not exceed a specific value, problems such as background fog will not occur. The resistance value of the binder may be adjusted by the image forming device so that the binder has an appropriate resistance.

Another feature of the present invention is that the wavelength range (peak width) at which the photoconductor absorbs 90 or more when the strongest absorption amount is 100 in the absorption spectral distribution of the photoconductor is continuous or non-continuous. It has a continuous width of 100 nm or more.
Further preferably, in addition to this, the photoreceptor has an electric resistance (volume resistance) in the dark of 1 × 10 ⁷ Ωcm or less, preferably 1 × 10 ⁵ Ωcm or less. The available light sources generally have a broad emission distribution, unless a light source such as a wavelength laser oscillator is used. On the other hand, the light-sensitive material in the photoconductor has a limit in quantum efficiency and may not be able to generate a sufficient amount of charges. In some cases, it was found that holding a plurality of photosensitive materials rather than having a large amount of photosensitive material of a specific wavelength makes it possible to obtain a larger current without increasing the total amount of photosensitive material. Details of the occurrence of this phenomenon are currently under consideration.

As described above, it is possible to obtain a larger developing current by using a plurality of photosensitive materials or a photosensitive body having a wide range of absorption sensitivity. The absorption spectral distribution of the photoconductor was obtained as follows. Ushio Electric xenon lamp U
Nikon Monochromator G with I-501C as light source
The 250 type was used to perform spectral analysis, and the light was applied to the photoconductor.
The surface of the photoreceptor was charged before light irradiation, the amount of change in surface potential before and after light irradiation was measured, and the change rate was used as the absorption spectral distribution.

In the present invention, image formation is carried out by the photo-rear exposure method with a combination in which the contact angle between the photoconductor used and the liquid developer is 30 degrees or more, preferably 45 degrees or more. According to a study made by the present inventor, when image formation is performed under such conditions, background stain and fogging can be suppressed to a very low level. Background fogging in the light back exposure method is caused by toner particles contained in the excess developer remaining on the surface of the photoconductor. It is necessary to remove these residual toner particles, but it is not possible to use a reverse bias such as the Carlson process that moves the toner in the background portion toward the developing roller during development.

An electric field can be formed in the developing solution only in a portion where the photoconductor is exposed to light and has a high dielectric constant.
To apply a reverse bias, it is necessary to separately install the exposure and squeeze power supplies. For example, the reverse roller is used to squeeze the excess developer, and the entire surface is exposed at the same time. At this time, a voltage having a polarity opposite to that of the developing roller may be applied to the roller. However, it is preferable to prevent the background fog from occurring without adding an exposure light source and a power source in this way. It is also preferable that the amount of excess developer remaining on the background is small.

It is preferable that the entire excess developer can be removed. The present inventor has found that it is possible to reduce the adhesion amount of the entire excess developing solution by using the one having a weak adhesion and adhesion between the photoreceptor and the developing solution. Further, in order to obtain such a condition, it is easy to obtain when the hydrogen bonding component of the surface tension of the developer is 10 dyn / cm or more, and preferably 2
It is 0 dyn / cm or more. Resins such as those used as binders in the photosensitive layer usually have very few hydrogen bonding components,
The hydrogen-bonding component of the developer is one that does not exhibit adhesiveness. The same applies to an inorganic photoconductor.

[0034]

EXAMPLES Next, the present invention will be specifically described with reference to examples. A contact angle measuring instrument manufactured by Kyowa Chemical Co., Ltd. was used to measure the contact angle between the photoconductor and the liquid developer. The surface tension was determined from the ZISMAN plot using the same measuring device.

Example 1 An image forming apparatus as shown in FIG. 2 was prepared by modifying the photoreceptor and its peripheral portion of a wet copying machine (CT-5085) manufactured by Ricoh Company. The developing section was used as it was. However, the developing bias is a DC power supply connected externally (Kikusui Electronics Co., Ltd.
PAD-600-15L) was used. All cleaning members and corona chargers were removed. A transfer roller using a conductive rubber was attached to the removed portion of the transfer corona charger. A direct current power supply was connected to this transfer roller to provide a transfer bias. A high-intensity LED for image information exposure was arranged inside the photoconductor at a position where the developing roller was irradiated through the photoconductor, and the focus was near the back surface of the photoconductor. By adjusting the power supply, motor, clock counter, etc., the image forming speed can be adjusted from 1 to 40 sheets per minute.

(Preparation of developer) 20 parts by weight of carbon black, 20 parts by weight of polyacrylic acid alkyl ester (number average molecular weight of 5000), and 10 parts by weight of low molecular weight polyethylene (131P manufactured by Sanyo Kasei Co., Ltd.) are ion-exchanged water. 20
The mixture was mixed with 0 parts by weight and dispersed and mixed with a ball mill for 40 hours. In the mixed solution, the polymerization ratio of styrene, N-butyl acrylate and ethylene glycol dimethacrylate was set to 1
The polymerization composition of 0: 90: 1 was changed to 2,2azobis-
Polymerization was carried out by a usual suspension polymerization method using (2,4-dimethylvaleronitrile) as an initiator to obtain a crosslinked copolymer in which 70% was uncrosslinked. This copolymer in a ball mill,
The toner was obtained by dispersing and mixing for 16 hours. Ion-exchanged water was added to the obtained developer to adjust the toner concentration to 3.0% by weight, and the toner was put into the image forming device and used for image formation. The water content of the obtained toner was 60% by weight. Also,
The contact angle with the photoconductor was 65 degrees, and the hydrogen bonding component of the surface tension was 25 dyn / cm.

(Production of Organic Photoreceptor) 20 parts by weight of copper phthalocyanine pigment was added to n-methyl-2-pyrrolidone (NMP).
It was put into a ball mill together with 100 parts by weight and dispersed for 96 hours. 100 parts by weight of polyaniline and NM were added to this dispersion.
100 parts by weight of P were mixed and dispersed in a ball mill for 48 hours. Poly-N-vinylcarbazole was added to this dispersion 6 times.
0 parts by weight was added, and the mixture was further dispersed for 12 hours to prepare an OPC material. The surface of the photoconductor is a transparent acrylic pipe.
A TO layer was coated and a photoreceptor of the OPC material was molded to a thickness of 5 μm. When the electric resistance of the obtained OPC was measured, it was 1.0 × 10 ⁵ Ωc during non-exposure.
m, the exposure time of the LED was 1.0 × 10 ³ Ωcm.

An image forming experiment was conducted with such an image forming device.
As a result, the obtained image has no background fog, shows an image density of 1.3 or more at an image forming speed of 1 to 40 sheets per minute, has a high sharpness, and is a good image without crushed characters and blurred images. Was given.

Example 2 In Example 1, instead of polyaniline, a mixture of polycarbonate with 5% by weight of tin oxide was used. This OPC has an electric resistance of 1.0 × 10 ⁶ when the LED is not exposed.
Ωcm, and 1.0 × 10 ⁴ Ωcm at the time of exposure. When the same image formation as in Example 1 was performed, similarly good images were obtained.

Example 3 In Example 1, polycarbonate was used instead of polyaniline, 10 parts by weight of copper phthalocyanine and 10 parts by weight of CI Pigment Blue were used.
Further, a halogen lamp is arranged instead of the LED in the image forming device, and a liquid crystal shutter is arranged between the photoconductor and the halogen lamp so that image information can be displayed. The absorption distribution of this photoconductor has a width of 220 nm almost continuously. When images were formed using such an apparatus, an image having an image density of 1.4 or more and a high contrast could be obtained.

Comparative Example 1 In Example 1, a polyaniline was replaced with a polycarbonate to fabricate an OPC as a prototype. The electrical resistance of this OPC is
1.0 × 10 ¹¹ Ωcm when not exposed and 1.
It was 0 × 10 ⁹ Ωcm. The absorption distribution of this photoconductor has a width of 75 nm almost continuously. When an image was created with this device, the maximum image density was low, and only characters with faint text were obtained. In addition, the printing speed was low, and the characters could not be discriminated at 20 sheets per minute or more.

Comparative Example 2 OPC was prepared by mixing various kinds of phthalocyanine pigments having different skeletons in place of SI Pigment Blue in Example 3. When the absorption distribution of the obtained OPC was measured, peak widths of 88 nm and 150 nm including the peak of copper phthalocyanine were obtained. When an image was formed using these photoconductors,
In the case of a sheet having a width of nm, when the printing speed exceeds 20 sheets, the print density is rapidly lowered, and the faintness of fine characters starts to stand out. With the photoconductor of 150 nm, good images could be formed up to 30 sheets per minute, and 9-point characters could be read even when the number of sheets reached 40.

[0043]

According to the invention of claim 1, by keeping the resistance of the binder of the photosensitive member low, a large developing current can be secured, and a high image density and a high printing speed can be obtained. According to the second or third aspect of the present invention, by widening the absorption distribution of the photoconductor, a large developing current can be secured, and a high image density and a high printing speed can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the method of the present invention.

FIG. 2 is a schematic diagram of an apparatus useful in practicing the present invention.

FIG. 3 is a spectral distribution diagram of the photoconductor used in the examples.

[Explanation of symbols]

 1 Photoreceptor 2 Development Electrode 3 Moving Direction of Developer 4 Light Source 5 Transfer Roller 6 Squeeze Roller

Claims (3)

[Claims] 1. When an image is formed by a back exposure method using light, an aqueous liquid developer in which toner particles composed of at least a colorant and a binder are dispersed in a carrier liquid containing water as a developer is used as a developer. As the image forming method, a photosensitive member having an electric resistance (volume resistance) in the dark of 1 × 10 ⁷ Ωcm or less is used. 2. A photosensitive member comprising an aqueous liquid developer in which toner particles consisting of at least a colorant and a binder are dispersed in a carrier liquid containing water as a developer when an image is formed by a photo back exposure method. As an example, an image forming method is characterized in that a photosensitive member having a wavelength range showing absorption of 90 or more with continuous or discontinuous width of 100 nm or more is used. 3. An image forming apparatus using an aqueous liquid developer in which toner particles composed of at least a colorant and a binder are dispersed in a carrier liquid containing water as a developer when an image is formed by a back exposure method. As a photoreceptor having an electric resistance (volume resistance) in the dark of 1 × 10 ⁷ Ωcm or less and exhibiting an absorption of 90 or more when the strongest absorption amount is 100, the wavelength region has a width of 100 nm or more continuously or discontinuously. An image forming method characterized by using.