JP2010002721A - Negative charge type high resolution photoreceptor and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-resolution electrophotographic photoreceptor which makes electrical charge separation due to exposure light occur on its surface layer and also makes electrical charges in a photosensitive layer move in a hole with sufficiently high speed. <P>SOLUTION: The electrophotographic photoreceptor has, on a conductive base material, an electrical charge generating layer which contains an electrical charge generating substance, and an organic photosensitive layer which contains at least an electrical charge generating substance and a hole transfer substance, in this order. In this case, the main electrical charge generating substance in the electrical charge generating layer is different from the main electrical charge generating substance in the organic photosensitive layer. The above problem can be solved by this electrophotographic photoreceptor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic high-resolution photoreceptor and a high-resolution image forming apparatus using the same.

  In the electrophotographic photosensitive member, organic photoconductive materials have come to be used more generally than inorganic photoconductive materials that have been used in the past due to development progress. This is because an electrophotographic photoreceptor using an organic photoconductive material has some problems in sensitivity, durability, environmental stability, etc., but it is inorganic in terms of toxicity, cost, freedom of material design, etc. This is because it has many advantages compared to the system photoconductive materials.

  An organic photoreceptor using such an organic photoconductive material includes a single-layer photoreceptor in which a charge transport material (a hole transport material, an electron transport material) is dispersed together with a charge generation material in the same photosensitive layer. And a laminate type photoreceptor in which a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material are laminated, and an organic photoreceptor currently in common use is a laminate type photoreceptor. is there. This is because the multilayer photoconductor has a wide selection range of materials that can be used in each layer, and by combining the best materials among them, the electrophotographic characteristics such as charging characteristics, sensitivity, residual potential, repeat characteristics, printing durability, etc. This is because a high-performance photoconductor can be provided.

  On the other hand, in recent years, in order to improve the image quality of the output image of the electrophotographic apparatus, higher resolution of the image quality has been studied. There are several means to achieve high resolution image quality with high recording density, but the simplest means is to use a single layer type photoreceptor. In single-layer photoconductors, charge transport materials and charge generation materials are dispersed in the same photoconductive layer, so that exposure light absorption and charge separation occur on the surface of the photoconductive layer, resulting in charge transport found in multilayer photoconductors. High resolution can be realized with very little exposure light scattering and hole diffusion in the layer.

Japanese Patent Laid-Open No. 9-90833

  However, in a single-layer type photoreceptor, charge separation occurs on the surface layer of the photoreceptor. Therefore, when used as a negatively charged photoreceptor, surface charge can be patterned with holes generated by exposure light. Is slower by about two orders of magnitude compared to hole conduction, and therefore accumulates as a space potential in the photosensitive layer. For this reason, the single-layer type photosensitive member can only be put into practical use as a positively charged type photosensitive member that requires only a short moving distance of electrons, and negatively charged toner that occupies most of the market cannot be used.

  Further, even when used as a positively charged photoreceptor, the electron mobility is extremely slow as described above, so that the electrons separated in the deep part of the photoreceptor by the exposure light incident to the inside are within a predetermined process. It cannot reach the surface layer and accumulates as a space potential inside. Due to the effect of this accumulated space charge, even if it is positively charged in the next charging step, the potential decreases on the surface of the photosensitive member, and further appears as a difference in sensitivity in the developing step, and this portion becomes black in the image (memory image). There was also the problem of the occurrence of

  In order to realize a high-resolution photoconductor that overcomes the above problems, an electrophotographic photoconductor in which charge separation by exposure light occurs on the surface of the photoconductor, and the movement of charges in the photoconductive layer is performed in sufficiently fast holes, and the same Devised an image forming system using

  That is, the present invention comprises, on a conductive substrate, a charge generation layer containing a charge generation material and an organic photosensitive layer containing at least a charge generation material and a hole transport material in this order. An electrophotographic photosensitive member is provided wherein the charge generating material is different from the main charge generating material in the organic photosensitive layer.

  The present invention also provides the electrophotographic photosensitive member, a charging unit for charging the electrophotographic photosensitive member, an exposure unit for exposing the charged electrophotographic photosensitive member, and an electrostatic latent image formed by the exposure. An image forming apparatus comprising: a developing unit that develops an image; a transfer unit that transfers a developed toner image; and a static elimination unit that neutralizes the surface charge of the electrophotographic photosensitive member by using static elimination light. provide.

According to the electrophotographic photosensitive member of the present invention, it is possible to realize a photosensitive member having high sensitivity and high resolution equivalent to those of a single layer type photosensitive member and being charged by negative charging.
Further, according to the image forming apparatus of the present invention, it is possible to realize a highly reliable image forming apparatus that is provided with a high-sensitivity and high-resolution negatively charged photoreceptor and can provide a high-quality image.

<Electrophotographic photoreceptor>
The electrophotographic photoreceptor of the present invention comprises, on a conductive substrate, a charge generation layer containing a charge generation material and an organic photosensitive layer containing at least a charge generation material and a hole transport material in this order. The main charge generation material therein is different from the main charge generation material in the organic photosensitive layer.

  Since the organic photosensitive layer contains at least a charge generation material and a hole transport material, charges (holes) generated in the charge generation material in the photosensitive layer by exposure light move through the photosensitive layer at a high speed by the hole transport material. An electrostatic latent image is formed on the surface of the photosensitive member and does not accumulate inside the photosensitive layer. In addition, since charge separation occurs in the surface layer portion, the moving distance to the surface of the photoreceptor is short, and there is no fear of diffusion. As a result, a high-speed and high-sensitivity exposure process becomes possible, and in addition, a memory phenomenon due to the internal accumulation of electric charges does not occur.

  On the other hand, in the exposure process, electrons generated at the same time as the holes are held inside the photosensitive layer because of their slow moving speed. However, by providing a charge generating layer containing a charge generating material below the organic photosensitive layer, This electron inside the layer is quickly and reliably erased in the static elimination process and does not accumulate as a space potential. That is, the holes generated in the charge generation material in the charge generation layer due to the static elimination light not only erase the residual charge on the surface as in the conventional laminated photoreceptor, but also when moving at high speed in the organic photosensitive layer. It recombines with the held electrons and disappears. For this reason, the deterioration of the electrical characteristics of the photoreceptor due to repeated use is suppressed.

The main charge generation material in the charge generation layer is different from the main charge generation material in the organic photosensitive layer, so that charge separation occurs mainly in the organic photosensitive layer in the exposure process, and charge separation occurs mainly in the charge generation layer in the charge removal process. This can provide the above advantages.
In the present invention, the “main charge generation material” in the charge generation layer or the organic photosensitive layer means that the charge generation layer contains only one type of charge generation material in the charge generation layer or the organic photosensitive layer. This refers to a substance, and when a plurality of types of charge generating substances are contained, it means the charge generating substance having the highest content.

The main charge generation material in the charge generation layer preferably has an absorption wavelength characteristic different from that of the main charge generation material in the photosensitive layer, and has absorption on the longer wavelength side than the main charge generation material in the photosensitive layer. It is more preferable. More preferably, the absorption spectrum of the main charge generation material in the charge generation layer and the absorption spectrum of the main charge generation material in the photosensitive layer do not overlap in the irradiation wavelength region of the static elimination light.
More specifically, the main charge generation material in the charge generation layer has an absorption peak at a wavelength that is 50 nm or more (more preferably 100 nm or more) away from the wavelength of the absorption peak on the longest wavelength side in the organic photosensitive layer. It is preferable to have.

One example of a preferred combination of the main charge generating material in the organic photosensitive layer and the main charge generating material in the charge layer is one in which the main charge generating material in the charge generating layer has an absorption in the range of 700 to 900 nm. This is a combination in which the main charge generating substance in the photosensitive layer has absorption in the range of 380 to 650 nm.
The above combinations include, for example, bisazo dyes, polycyclic quinone dyes (more preferably anthraquinone dyes), coumarin dyes, perylene dyes, triphenylmethane dyes as main charge generating substances in the organic photosensitive layer. And a main charge generation material in the charge generation layer for charge removal can be realized by selecting from phthalocyanine dyes, squarylium dyes, and trisazo dyes.

(Embodiment)
Hereinafter, embodiments of the electrophotographic photosensitive member of the present invention will be described with reference to the accompanying drawings. The electrophotographic photosensitive member of the present invention is not limited to the embodiments described below, and can of course include other forms with various modifications without departing from the gist of the present invention. Such other forms are easily understood by those skilled in the art based on the description of the specification and the drawings.

(Embodiment 1)
FIG. 1 is a partial cross-sectional view schematically showing the configuration of one embodiment of the electrophotographic photosensitive member of the present invention. The photoconductor of this embodiment comprises a charge generation layer (3) for charge removal, in which an intermediate layer (2), a charge generation material B (8) are dispersed in a binder resin on a conductive support (1), and a charge generation material. An organic photosensitive layer (4) in which A (7), a hole transport material (5) and an electron transport material (6) are dispersed in a binder resin is provided in this order. That is, this electrophotographic photosensitive member has a structure in which a charge generation layer (3) for static elimination is provided below the photosensitive layer of a so-called single layer type organic photosensitive member (between the photosensitive layer (4) and the intermediate layer (2)). It has become.

[Conductive support]
The conductive support (1) is not particularly limited as long as it has a role as an electrode of the photoreceptor and a function as a support member for other layers and can be used in this field.
For example, as a conductive support, a metal drum and sheet made of aluminum, aluminum alloy, copper, zinc, stainless steel, titanium or the like; or a polymer material such as polyethylene terephthalate, nylon or polystyrene, metal on hard paper or glass Examples include a laminate of foil, a metal material vapor-deposited, a drum, a sheet, and a seamless belt on which a layer of a conductive compound such as a conductive polymer, tin oxide, or indium oxide is vapor-deposited or applied.

If necessary, the surface of the conductive support is irregularly reflected within a range that does not affect the image quality, such as anodic oxide coating, surface treatment with chemicals or hot water, coloring treatment, or roughening the surface. Processing may be performed.
In an electrophotographic process using a laser as an exposure light source, the wavelengths of the laser light are uniform, so the laser light reflected on the surface of the photoconductor and the laser light reflected inside the photoconductor cause interference, and the interference due to this interference. Stripes may appear on the image and cause image defects. By performing the above-described treatment on the surface of the conductive support 1, image defects due to interference of laser light having the same wavelength can be prevented.

[Charge generation layer]
The charge generation layer (3) (the charge generation layer for charge removal) contains at least the charge generation material B (8), and upon irradiation with charge removal light, holes ( And electrons). The generated holes reach the surface of the photoreceptor through the organic photosensitive layer and erase surface charges, or erase electrons held in the photosensitive layer. On the other hand, if the above effect is exerted also on exposure light, formation of an electrostatic latent image on the surface of the photoreceptor is hindered. For this reason, the main charge generation material contained in the present (charge eliminating) charge generation layer needs to be different from the main charge generation material contained in the organic photosensitive layer.

  Examples of charge generation materials that can be contained in the charge generation layer include azo pigments such as monoazo, bisazo, and trisazo pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, metal phthalocyanines, and metal-free phthalocyanines , Squarylium dyes, pyrylium compounds, thiopyrylium compounds, triphenylmethane dyes (methine dyes), and inorganic materials. These charge generation materials may be used alone or in combination of two or more. However, since these compounds vary greatly in absorption wavelength range, extinction coefficient, and quantum efficiency depending on substituents, conjugate structures, crystal structures, etc., select a dye having a compound structure / crystal system having the required absorption wavelength. There is a need. Specific examples of these compounds include the following compounds.

  Examples of the azo pigment include JP-A-1-200277, JP-A-1-202757, JP-A-1-319754, JP-A-2-72372, JP-A-2-254467, JP-A-3-27863, 4-96068, JP-A-4-96069, JP-A-4-147265, JP-A-5-142841, JP-A-5-303226, JP-A-6-324504, and JP-A-7-168379. Compounds. Moreover, the structure of the coupler component used for these azo pigments varies widely. Examples thereof include compounds described in JP-A-2-11069, JP-A-4-149448, JP-A-6-27705, and JP-A-6-348047.

  Specific examples of indigo pigments include indigo, thioindigo, JP-A-1-109352, JP-A-5-2277, JP-A-5-23725, JP-A-6-222591, JP-A-9-15888, Examples thereof include compounds described in Kaihei 9-152728 and JP-A No. 2002-123015.

  Examples of perylene pigments include perylene imide and perylene acid anhydride. For example, JP-A-1-88461, JP-A-1-118143, JP-A-1-118144, JP-A-1-118145, and JP-A-1-118146. JP-A-1-118147, JP-A-1-159660, JP-A-2-228670, JP-A-2-228671, JP-A-2-251858, JP-A-3-1-1150, JP-A-4-186363 JP-A-4-186364, JP-A-4-264451, JP-A-5-6015, JP-A-5-232726, JP-A-5-249718, JP-A-5-249719, JP-A-6-32789, Examples thereof include compounds described in JP-A-7-89962, JP-A-7-319189, JP-A-2005-23322, and the like.

  Specific examples of the polycyclic quinone pigment include anthraquinone, pyrenequinone, compounds described in JP-A Nos. 1-219841, JP-A-3-95562, JP-A-5-23725, and the like.

  Specific examples of phthalocyanine compounds include metal-free phthalocyanines, titanyloxyphthalocyanines, copper phthalocyanines, aluminum phthalocyanines, germanium phthalocyanines, chlorogallium phthalocyanines, chloroindium phthalocyanines, magnesium phthalocyanines, chloroaluminum phthalocyanines, tin Phthalocyanines, vanadyloxyphthalocyanines, gallium phthalocyanines, zinc phthalocyanines, cobalt phthalocyanines, nickel phthalocyanines, hydroxygallium phthalocyanines, dichlorotitanyl phthalocyanines, diphenoxygermanium phthalocyanines, etc. Has been further optimized by.

Specific examples of the pyrylium compound and the thiopyrylium compound include compounds described in JP-A-1-259365, JP-A-4-19556, and the like.
Specific examples of the squarylium dye include JP-A-1-146845, JP-A-1-14684, JP-A-1-146847, JP-A-1-146864, JP-A-1-147552, JP-A-1-147553, JP-A-1-147554, JP-A-1-159663, JP-A-1-228960, JP-A-1-23074, JP-A-5-339233, JP-A-6-184109, JP-A-6-263732, Examples thereof include compounds described in Kaihei 8-245895, JP-A 2000-265077, and the like.
Specific examples of the inorganic material include selenium, CdS, amorphous silicon, polysilicon, and the like.

As the charge generation material of the charge generation layer for charge removal, it is necessary to be sensitive to light transmitted through the organic photosensitive layer. As will be described later, in addition to the charge generation material, the photosensitive layer includes at least a binder resin,
-Many hole transport materials having absorption up to about 400-450 nm, some up to about 500 nm,
-Most of them contain an electron transport material having absorption up to around 550 nm, so that the wavelength is longer than the charge generation material of the photosensitive layer (for example, longer than 600 nm, preferably longer than 700 nm; upper limit is not particularly limited) However, a compound having absorption (for example, at 900 nm; more specifically at 780 nm) is preferable.
Accordingly, phthalocyanine dyes, squarylium dyes, and trisazo compounds are preferred as the charge generation material for the charge generation layer because they have an absorption wavelength on the long wavelength side. Among these, phthalocyanine dyes are particularly durable and are most suitable because they are mainstream as charge generating materials for current digital photoreceptors.

  In order for the charge generation layer to fully exhibit the charge removal effect, the main charge generation material in the charge generation layer must generate charges in the wavelength region of light that transmits through the organic photosensitive layer with a transmittance of 50% or more. It is preferable to have an absorption peak capable of

  A sensitizing dye may be added to the charge generation layer for charge removal. By adding the sensitizer, the charge separation efficiency in the charge generation material is increased. Represented by triphenylmethane dyes typified by chill violet, crystal violet, night blue, victoria blue, etc., erythrosine, rhodamine B, rhodamine 3R, acridine dyes typified by acridine orange, frappeosin, methylene blue, methylene green, etc. Thiazine dyes, oxazine dyes typified by capri blue, meldra blue, etc., other cyanine dyes, styryl dyes, pyrylium salt dyes, thiopyrylium salt dyes and the like.

  The charge generation layer may contain a binder resin in order to improve the binding property. Examples of the binder resin include polyester resin, polystyrene resin, polyurethane resin, phenol resin, alkyd resin, melamine resin, epoxy resin, silicon resin, acrylic resin, methacrylic resin, polycarbonate resin, polyarylate resin, phenoxy resin, and polyvinyl butyral resin. , Polyvinyl formal resin and the like, and copolymer resins containing two or more repeating units.

Specific examples of the copolymer resin include, for example, insulating resins such as vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, and acrylonitrile-styrene copolymer resin. Can be mentioned.
The binder resin is not limited to those described above, and any resin generally used in this field can also be used. Binder resin may be used individually by 1 type, or 2 or more types may be used together.

The weight ratio of the charge generation material to the binder resin in the charge generation layer for charge removal is preferably in the range of 0.1: 1 to 4: 1. If the ratio of the charge generation material is less than this range, the charge removal cannot be completed, resulting in a decrease in charging ability and a memory phenomenon. If the ratio is large, not only the film strength of the charge generation layer is decreased but also the dispersibility is decreased. Since coarse particles increase, uniform charge removal cannot be performed.
The sensitizing dye is preferably in the range of 0.1% to 20% by weight relative to the charge generating material. When the amount is less than this range, sensitization cannot be performed, and when the amount is larger, dispersibility is affected.

  As a method for forming the charge generation layer for static elimination, a vacuum deposition method in which the charge generation material (and sensitizing dye) is vacuum-deposited on the surface of a conductive support or an intermediate layer (described later), the charge generation material ( And a coating method for coating the surface of the conductive support or the intermediate layer with a coating solution for a charge generation layer containing a sensitizing dye). In general, a simple coating method is preferable among these. The charge generation layer coating solution is prepared, for example, by adding the above-described charge generation material (and sensitizing dye) and, if necessary, the above-described binder resin in a suitable solvent, and dispersing by a conventionally known method. Can do.

  Examples of the solvent used in the coating solution for the charge generation layer include halogenated hydrocarbons such as methylene chloride and ethane dichloride, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, Ethers such as tetrahydrofuran and dioxane, cellosolves such as dimethoxyethane, aromatic hydrocarbons such as benzene, toluene and xylene, aprotic polar solvents such as N, N-dimethylformamide and N, N-dimethylacetamide Can be mentioned. One of these solvents may be used alone, or two or more thereof may be mixed and used as a mixed solvent.

The charge generation material may be pulverized in advance by a pulverizer before being dispersed in the solvent. Examples of the pulverizer used for the pulverization treatment include a ball mill, a sand mill, an attritor, a vibration mill, and an ultrasonic disperser.
Examples of the disperser used when the charge generating substance is dispersed in the solvent include a paint shaker, a ball mill, and a sand mill. As a dispersion condition at this time, an appropriate condition is selected so that impurities are not mixed due to wear of a container and a member constituting the disperser.

  Examples of the coating method of the charge generation layer coating liquid include a spray method, a bar coating method, a roll coating method, a blade method, a ring method, and a dip coating method. Among these coating methods, in particular, the dip coating method is a method of forming a layer on the surface of the substrate by immersing the substrate in a coating tank filled with a coating solution and then pulling it up at a constant speed or a sequentially changing speed. It is relatively simple and excellent in terms of productivity and cost, and is therefore preferably used.

In order to stabilize the dispersibility of the coating liquid, the apparatus used for the dip coating method may be provided with a coating liquid dispersing apparatus represented by an ultrasonic generator. Note that the coating method is not limited to these, and an optimum method can be appropriately selected in consideration of physical properties and productivity of the coating solution.
The film thickness of the charge generation layer is preferably in the range of 0.05 μm to 5 μm, more preferably 0.1 μm to 1 μm.

[Organic photosensitive layer]
The organic photosensitive layer (4) contains at least a charge generating substance A (7) and a hole transporting substance (5). Upon exposure to exposure light, holes are generated by charge separation with the charge generating substance contained in the layer. (And electrons). The generated holes are conveyed to the surface of the photosensitive member charged at high speed by the hole transport material, and form an electrostatic latent image there. The electrons generated at the same time as the holes are once held in the photosensitive layer, but are erased by the holes generated in the charge generation layer by the charge removal light as described above.
In addition, the photosensitive layer (4) needs to be sufficiently transparent to the charge removal layer in order to allow the charge removal light to reach the charge generation layer (3) for charge removal. Here, “sufficiently transparent to static elimination light” means that the transmittance is 40% or more (preferably 50% or more, more preferably 60% or more, more preferably 70% or more, more preferably 80%. % Or more).

  For the above-described action, the main charge generation material contained in the organic photosensitive layer needs to be different from the main charge generation material contained in the charge generation layer (for neutralization). Preferably, the main charge generation material in the organic photosensitive layer has an absorption peak on the shorter wavelength side than the main charge generation material in the charge generation layer.

  As the main charge generating substance in the organic photosensitive layer, the same kind (but different) compound as the compound used in the charge generating layer described above can be used, and among them, azo dyes, polycyclic quinone type (more preferably Anthraquinone dyes, coumarin dyes, and perylene dyes are preferred because they have an absorption wavelength on the relatively short wavelength side. In particular, a perylene dye having a high stability and an electron transporting ability, and a bisazo dye having a proven record in an analog photoreceptor are optimal.

In the photoreceptor of the present invention, one of the preferred combinations of the main charge generating material in the organic photosensitive layer and the main charge generating material in the charge layer is, for example, as described above, if the main charge generating material in the charge generating layer is The combination has absorption in the range of 700 to 900 nm, and the main charge generation material in the organic photosensitive layer has absorption in the range of 380 to 650 nm.
Preferred specific combinations are: perylene dye-phthalocyanine dye, perylene dye-trisazo dye, bisazo dye-trisazo dye, bisazo dye -It is a phthalocyanine pigment.

  The photosensitive layer is, for example, 50% or more with respect to static elimination light (for example, light having a wavelength or wavelength range absorbed by the main charge generation material in the charge generation layer: for example, light having a wavelength in the range of 700 to 900 nm). The transmittance is preferably 60% or more, more preferably 70% or more, more preferably 80% or more, and more preferably 90% or more.

  Examples of the hole transport material (5) include carbazole derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazones. Compounds, polycyclic aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives And stilbene derivatives and benzidine derivatives.

  Also included are polymers having groups derived from these compounds in the main chain or side chain, such as poly-N-vinylcarbazole, poly-1-vinylpyrene, and poly-9-vinylanthracene.

The photosensitive layer preferably contains an electron transport material (6).
By containing an electron transport material in the photosensitive layer, electrons generated by charge separation can be stably held by the photosensitive layer.
Electron transport materials include perylene dyes, quinones such as diphenoquinone and naphthoquinone derivatives, cyano compounds such as tetracyanoethylene and terephthalmalondinitrile, aldehydes such as 4-nitrobenzaldehyde, anthraquinone, 1-nitroanthraquinone, etc. Anthraquinones, polycyclic or heterocyclic nitro compounds such as 2,4,7-trinitrofluorenone, 2,4,5,7-tetranitrofluorenone, etc., or those obtained by polymerizing these electron-withdrawing materials it can.

Since the electron transport material in the photosensitive layer only needs to have a function of temporarily maintaining the charge-separated electrons until static elimination, the electron transport material may be a phenol or phosphate electron accepting antioxidant as an electron transport material. Alternatively, electron-accepting substances such as conjugated compounds such as terphenyl and anthracene, and acid anhydrides such as succinic anhydride, maleic anhydride, phthalic anhydride, and 4-chloronaphthalic anhydride can also be used.
A charge generating material can also act as an electron transporting material if it has an electron transporting ability. Therefore, if such a charge generating material is used in an organic photosensitive layer, it is not necessary to add an additional electron transporting material in the photosensitive layer. Electrons can be held stably.

As the binder resin of the photosensitive layer, those having compatibility with the charge transporting substance contained in the organic photosensitive layer are selected, for example, vinyl polymers such as polymethyl methacrylate, polystyrene, polyvinyl chloride, and copolymers thereof, Examples include polycarbonate, polyester, polyester carbonate, polysulfone, phenoxy, epoxy, silicone resin, polyarylate, polyamide, polyester, polyketone, polyurethane, polyacrylamide, and phenol resin. These can be used alone or in combination. Alternatively, a partially cross-linked thermosetting resin may also be used. Among these, resins such as polystyrene, polycarbonate, polyarylate, and polyphenylene oxide are preferable because they have a volume resistance of 10 ¹³ Ω or more and are excellent in film property and potential characteristics.

Regarding the blending ratio of the above substances, the charge generating substance is 2 to 30% by weight with respect to the binder resin. If it is less than this range, sufficient sensitivity cannot be obtained, and if it is more, the film strength of the photosensitive layer is lowered.
The blending ratio of the charge generating material to the binder resin does not need to be constant throughout the organic photosensitive layer (in the thickness direction) and may be higher on the surface layer side than on the conductive substrate side. In this case, for example, it is 0 to 10% by weight on the conductive substrate side and 5 to 60% by weight on the surface layer side.

The hole transport material is 40 to 100% by weight based on the binder resin. If the amount is less than this range, sufficient sensitivity cannot be obtained. If the amount is more than this range, the film strength of the photosensitive layer is lowered and printing durability is deteriorated.
The electron transport material is 0 to 100% by weight based on the binder resin. When the amount is larger than this range, the film strength of the photosensitive layer is lowered and the printing durability is deteriorated.
As described above, the electron transport material only needs to have a function of temporarily and stably holding the charge-separated electrons until static elimination, but the hole transport material is capable of moving carriers during exposure and static elimination, in particular, hole elimination during static elimination. Since it is necessary to pass through the photosensitive layer, it is preferred that the photosensitive layer contains more hole transport material than electron transport material. Specifically, the hole transport material is preferably contained in an amount of 1.5 times or more, more preferably 2 times or more, relative to the electron transport material.

  If necessary, known plasticizers such as dibasic acid esters, fatty acid esters, phosphate esters, phthalate esters, plasticizers such as chlorinated paraffins and epoxy type plasticizers, and silicone leveling agents are added to the photosensitive layer. Thus, processability and flexibility of the photosensitive layer can be imparted and surface smoothness can be improved. Further, fine particles of inorganic and organic compounds can be added to increase mechanical strength and improve electrical characteristics.

  The photosensitive layer may also contain various additives such as an antioxidant and a sensitizer as necessary. In particular, α-tocopherol and 2,6-di-t-butyl-4-methyl-phenol are suitable as antioxidants, and α-tocopherol is 0.1 wt% or more and 5 wt% based on the charge transport material. Preferably, 2,6-di-t-butyl-4-methyl-phenol is contained in an amount of 0.1% by weight or more and 50% by weight or less based on the charge transport material. As a result, the potential characteristics are excellent, and the stability as a coating liquid is increased.

  The film thickness of the photosensitive layer is, for example, 10 to 60 μm, preferably 10 to 40 μm.

The photosensitive layer can be formed by dispersing and applying a charge generating material, a hole transporting material, a binder resin, and, if necessary, an electron transporting material and other additives in a suitable organic solvent.
The photosensitive layer is applied in the same manner as the charge generation layer and the intermediate layer described below, for example, a coating method such as a dip coating method, a spray coating method, a spinner coating method, a roller coating method, a Meyer bar coating method, a blade coating method, Can be used.

  Suitable organic solvents include aromatic hydrocarbons such as benzene, toluene, xylene and monochlorobenzene, halogenated hydrocarbons such as dichloromethane and dichloroethane, and solvents such as tetrahydrofuran, dioxane, dimethoxymethyl ether and dimethylformamide alone or in combination. The above mixed solvent or, if necessary, a solvent such as alcohols, acetonitrile, or methyl ethyl ketone can be further added and used.

  The photosensitive layer having a higher ratio of the charge generation material to the binder resin on the conductive substrate side than the surface layer side is formed by preparing two or more coating liquids having different mixing ratios and sequentially recoating them. It is also possible to form two or more coating liquids having different blending ratios by setting them in separate spray coating apparatuses and controlling the spray amount of each spray. In this case, the concentration of the charge generating substance is continuously increased. It is also possible to change it.

[Middle layer]
It is preferable to provide an intermediate layer (2) between the conductive support (1) and the charge generation layer (3).
The intermediate layer covers defects on the surface of the conductive support, improves chargeability by preventing carrier injection from the conductive support to the photosensitive layer, improves the adhesion of the charge generation layer, and Image defects can be prevented by improving the coating property of the charge generation layer.
In particular, when an image is formed using a reversal development process, a toner image is formed in a portion where the surface charge has decreased due to exposure, so if the surface charge decreases due to factors other than exposure (for example, a conductive support) Image quality deterioration due to the occurrence of image fogging called black spots where toner adheres to a white background and minute black spots are formed. (Image defects) may occur, and such image defects are prevented by providing the intermediate layer.

  As the material for the intermediate layer, various resin materials and those containing metal particles or metal oxide particles such as titanium oxide, aluminum oxide, tin oxide, zinc oxide, antimony oxide, barium sulfate and the like are used.

  Examples of resin materials include polyethylene, polypropylene, polystyrene, acrylic resin, vinyl chloride resin, vinyl acetate resin, polyurethane resin, epoxy resin, polyester resin, melamine resin, silicon resin, polyvinyl butyral resin, polyamide resin, etc. Copolymer resins containing two or more of these repeating units, casein, gelatin, polyvinyl alcohol, ethyl cellulose and the like can be mentioned. Of these, polyamide resins are preferred. Of the polyamide resins, more preferably, an alcohol-soluble nylon resin can be used. For example, 6-nylon, 6,6-nylon, 6,10-nylon, 11-nylon, 12-nylon, etc. copolymerized so-called copolymer nylon, N-alkoxymethyl modified nylon, N-alkoxyethyl modified Those obtained by chemically modifying nylon such as nylon are preferred.

  Metal oxides such as titanium oxide to adjust the volume resistance value of the intermediate layer to prevent carrier injection from the conductive support to the photosensitive layer and to maintain the electrical properties of the photoreceptor in various environments Can be contained.

When the intermediate layer contains a metal oxide, the above-mentioned resin may be water and various organic solvents, particularly water, methanol, ethanol, butanol alone, or water / alcohol, a mixed solvent of two or more alcohols, or Intermediate layer in which metal oxides such as titanium oxide are dispersed in a solution dissolved in a mixed solvent with acetone, dioxolane, etc./alcohol, or a chlorinated solvent / alcohol, such as dichloroethane, chloroform, trichloroethane, etc. An application liquid can be prepared. An intermediate layer can be formed by applying the dispersion onto a conductive support.
The content of the resin and the metal oxide in the coating solution for the intermediate layer is a ratio of 3/97 wt% to 20/80 wt% with respect to the content of the organic solvent used in the coating solution for the intermediate layer. It is preferable.

  As a method for dispersing the coating liquid for the intermediate layer, general methods such as a ball mill, a sand mill, an attritor, a vibration mill, and an ultrasonic disperser can be applied.

  Examples of the coating method include a blade coating method, a wire bar coating method, a spray coating method, a dip coating method, a bead coating method, and a curtain coating method. Among these application methods, an optimum method can be selected in consideration of physical properties and productivity of the coating liquid. In particular, the dip coating method is a method of forming an intermediate layer by immersing the conductive support in a coating tank filled with a coating solution and then pulling it up at a constant speed or a speed that changes sequentially, and is relatively simple, Since it is excellent in terms of productivity and cost, it is more preferable. In order to stabilize the dispersibility of the coating liquid, a coating liquid dispersing device (represented by an ultrasonic generator) may be provided.

  The thickness of the intermediate layer is preferably in the range of 0.01 μm to 20 μm, more preferably 0.05 μm to 10 μm. If the film thickness of the intermediate layer is smaller than 0.01 μm, it will not substantially function as an intermediate layer, and a uniform surface property cannot be obtained by covering defects of the conductive support, and carriers are injected from the conductive support. May not be prevented, and the chargeability may be reduced. When the intermediate layer is applied by dip coating, it is difficult to produce the photoreceptor and the sensitivity of the photoreceptor is lowered, which is not preferable.

(Embodiment 2)
Further, since the electrophotographic photosensitive member of the present invention uses holes as carriers, it can be provided with the configuration shown in FIG. In this embodiment, a hole transport layer containing only the hole transport material (5) as a charge transport material is disposed between the photosensitive layer and the charge transport layer.

  Such a configuration can be adopted because it is sufficient that the charge separation by exposure occurs in the surface layer region, and it is not necessary that the charge generating substance exists deep in the photoreceptor, This is because the movement of carriers (charges) in the process only needs to be able to move holes, and it is sufficient that a hole transport material is present between the charge generation layer and the photosensitive layer.

[Hole transport layer]
A hole transport layer containing only the hole transport material (5) as a charge transport material may be provided between the organic photosensitive layer and the charge generation layer. By arranging a layer containing only a hole transport material as a charge transport material and no electron transport material (including a charge generating material having an electron transport capability) below the photosensitive layer, the movement of electrons across this layer is suppressed. In addition, the dark decay of the photoconductor is reduced, and the charging performance can be improved.

  Examples of the hole transport material include carbazole derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, many Ring aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives, stilbene derivatives And benzidine derivatives.

Also included are polymers having groups derived from these compounds in the main chain or side chain, such as poly-N-vinylcarbazole, poly-1-vinylpyrene, and poly-9-vinylanthracene.
The hole transport material used in the hole transport layer may be the same (or the same combination) as or different from the hole transport material contained in the organic photosensitive layer.

  As the binder resin for forming the charge transport layer, a resin having excellent compatibility with the charge transport material is selected. Specific examples of such binder resins include, for example, vinyl polymer resins and copolymer resins such as polymethyl methacrylate resins, polystyrene resins, and polyvinyl chloride resins, and polycarbonate resins, polyester resins, polyester carbonate resins, and polysulfone resins. Phenoxy resin, epoxy resin, silicone resin, polyarylate resin, polyamide resin, polyether resin, polyurethane resin, polyacrylamide resin and phenol resin. Moreover, the thermosetting resin which partially bridge | crosslinked these resin is also mentioned. One of these resins may be used alone, or two or more thereof may be mixed and used.

Among the above resins, polystyrene resin, polycarbonate resin, polyarylate resin or polyphenylene oxide has a volume resistivity of 10 ¹³ Ω · cm or more, excellent electrical insulation, and also has film property and potential characteristics. Since it is excellent, it is preferably used.

  The compounding ratio of the hole transport material to the binder resin in the hole transport layer is 40 to 120% by weight. When the amount is less than this range, sufficient sensitivity cannot be obtained, and when the amount is more, the possibility that the charge transport material is crystallized increases.

An additive such as a plasticizer and / or a leveling agent may be added to the hole transport layer as necessary in order to improve film formability, flexibility, and surface smoothness.
Examples of the plasticizer include dibasic acid esters such as phthalate esters, fatty acid esters, phosphate esters, chlorinated paraffins, and epoxy type plasticizers.
Examples of the leveling agent include silicone-based leveling agents such as dimethyl silicone, diphenyl silicone, and phenylmethyl silicone.

  The hole transport layer may also contain fine particles of an inorganic compound and / or an organic compound in order to increase mechanical strength and improve electrical characteristics. Specific examples of such an inorganic compound include fine metal oxide particles such as titanium oxide. Specific examples of organic compound fine particles include fine particles of fluorine atom-containing polymers such as tetrafluoroethylene polymer fine particles.

  The hole transport layer may contain various additives such as an antioxidant and / or a sensitizer as necessary. As a result, the potential characteristics are improved, the stability as a coating solution is increased, fatigue deterioration when the photoreceptor is repeatedly used can be reduced, and durability can be improved.

  As the antioxidant, a hindered phenol derivative or a hindered amine derivative is preferably used. The hindered phenol derivative and the hindered amine derivative may be used by mixing at an arbitrary ratio.

  The film thickness of the hole transport layer is, for example, 1 to 20 μm, preferably 5 to 15 μm.

  For example, as in the case of forming the organic photosensitive layer described above, the hole transport layer is used for the charge transport layer by dissolving or dispersing the hole transport material and the binder resin and, if necessary, the above-described additives in an appropriate solvent. By preparing a coating solution and applying this coating solution on the charge generation layer by dip coating, spray coating, spinner coating, roller coating, Meyer bar coating, blade coating, etc. It is formed. Among these coating methods, the dip coating method is particularly excellent in various respects as described above, and can be used when forming a hole transport layer.

[Protective layer]
Although not shown in FIGS. 1 and 2, in the electrophotographic photoreceptor of the present invention, a protective layer may be provided as the outermost layer.
By providing a protective layer, the printing durability of the photosensitive layer can be improved, and chemical adverse effects on the photosensitive layer such as ozone or nitrogen oxides generated by corona discharge when the surface of the electrophotographic photosensitive member is charged. Can be prevented. As the protective layer, for example, a layer made of a binder resin, an inorganic filler-containing resin, an inorganic oxide, or the like is used.

  The binder resin used in the protective layer is ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, phenol resin, polyacetal, polyamide, polyamideimide, polyacrylate, polyallylsulfone, polybutylene. , Polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethyl bentene, polypropylene, polyphenylene oxide, polysulfone, polystyrene, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, Examples of the resin include polyvinylidene chloride and epoxy resin.

  For the purpose of improving the wear resistance, the protective layer may contain a fluororesin such as polytetrafluoroethylene, a silicone resin, and an inorganic filler or organic filler having high hardness to these resins. These fillers preferably have an average particle size of 0.02 to 3 μm, more preferably 0.05 to 1 μm. When the average particle size is less than 0.02 μm, the wear resistance of the surface protective layer becomes weak, and the life of the electrophotographic photosensitive member is shortened. When the average particle diameter exceeds 3 μm, light is likely to be scattered by the protective layer, causing a reduction in resolution.

  The filler content in the protective layer is 5 to 50% by weight, preferably 10 to 40% by weight. If it is less than 5% by weight, the abrasion resistance is not sufficient, and if it exceeds 50% by weight, the transparency of the protective layer is impaired and the sensitivity is lowered.

  Specific examples of fillers added to the protective layer include titanium oxide, tin oxide, zinc oxide, zirconium oxide, indium oxide, silicon nitride, calcium oxide, barium sulfate, ITO, silica, colloidal silica, alumina, carbon black, fluorine. Examples thereof include one or a mixture of two or more selected from a resin fine powder, a polysiloxane resin fine powder, and a polymer charge transport material fine powder. These fillers may be surface-treated with an inorganic substance or an organic substance for reasons such as improving dispersibility and modifying surface properties. In general, water-repellent treatment includes those treated with a silane coupling agent, those treated with a fluorinated silane coupling agent, those treated with a higher fatty acid treatment or a polymer material, etc. Examples of the surface include alumina, zirconia, tin oxide, and silica treated.

  A charge transport material (for example, the above-described hole transport material or electron transport material) may be added to the protective layer for the purpose of efficiently transporting holes or electrons. For the purpose of improving charging properties, a phenol compound, a hydroquinone compound, a hindered phenol compound, a hindered amine compound, a compound in which a hindered amine and a hindered phenol are present in the same molecule, and the like can be added.

  A plasticizer and / or a leveling agent may also be added to the protective layer. As a plasticizer, what is used as a plasticizer of general resin, such as a dibutyl phthalate and a dioctyl phthalate, can be used, and the usage-amount is about 0 to 30 weight% with respect to binder resin. As the leveling agent, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, polymers having a perfluoroalkyl group in the side chain, or oligomers are used, and the amount used is 0 to 1% by weight based on the binder resin. Is appropriate.

  The filler is pulverized with a resin and / or a charge transport material or other additives, or is dispersed in a dispersion solvent as it is and applied as a protective layer.

Dispersing solvents include methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone ketones, ethers such as dioxane, tetrahydrofuran and ethyl cellosolve, aromatics such as toluene and xylene, halogens such as chlorobenzene and dichloromethane, ethyl acetate and butyl acetate Esters such as are used.
When adding a pulverization process, a ball mill, a sand mill, a vibration mill or the like is used.

  When the protective layer is composed of at least a layer made of a curable resin, various crosslinking reactions known in the field of materials, such as radical polymerization, ionic polymerization, thermal polymerization, photopolymerization, radiation polymerization, etc. can be used. . In order to realize a cured protective layer having a low surface energy, a material having a silicone structure, a perfluoroalkyl structure, a long-chain alkyl structure, or the like may be cross-linked by a known method.

  As described above, in order to provide the protective layer with a charge transport function, a substance having a charge transport function or a polymer charge transport substance may be subjected to a crosslinking reaction. For example, by combining a crosslinkable organopolysiloxane resin and a compound containing a structural unit that can be bonded to it and has a charge transporting property, and curing it, a polysiloxane resin is realized with excellent durability and electrical characteristics. Is done.

The thickness of the protective layer is preferably from 0.5 μm to 5 μm, more preferably from 1 μm to 3 μm.
When the thickness of the protective layer is less than 0.5 μm, the protective layer is easily peeled off from the interface with the underlying photosensitive layer when subjected to an external force such as contact with a blade or a charging roller. This is because when the protective layer is thin, when the external force is applied, the protective layer itself is not resisted and a force is constantly applied to the interface with the photosensitive layer. This is thought to be because the interface is likely to shift. Further, the entire protective layer may be lost before the lifetime of the electrophotographic photosensitive member due to wear.

  If the thickness of the protective layer is greater than 5 μm, carriers are diffused in the process of moving through the protective layer, so that character thickening or the like is likely to occur, and sensitivity decreases and a residual potential increases due to repetition.

<Image forming operation using electrophotographic photosensitive member>
A series of flow of image formation using the electrophotographic photosensitive member of the present invention will be briefly described.
First, the surface of the organic photoreceptor is negatively charged by corona charging, contact charging, or the like. Next, the photoconductor is exposed to exposure light in accordance with an image, whereby charge separation is performed by the charge generation material A in the photosensitive layer. The holes reach the surface layer according to the electric field and recombine with the negative charges on the surface of the photoreceptor to form a latent image. Although the electrons move to the substrate side, the moving speed of the electrons is extremely slow, so that they remain in the photosensitive layer. The latent image on the surface of the photoreceptor is developed as a toner image by a reversal development process in the same manner as a general photoreceptor, and the toner is transferred to paper. Thereafter, residual toner on the surface of the photoreceptor is removed by a cleaner.

  Finally, the charge removal layer provided under the photosensitive layer is irradiated with charge removal light, thereby removing the residual charge in the photosensitive layer and on the surface of the photoreceptor. In other words, holes and electrons are separated by the charge generation material B of the charge generation layer for charge removal by the charge removal light, the electrons move to the substrate side, the holes move to the surface layer side by the electric field, and the holes reach the photosensitive layer surface layer. The electrons remaining in the photosensitive layer by the exposure are erased, and the holes reaching the surface layer erase the remaining surface charge.

  The above-described image formation is considered to correspond to the case where a general single-layer type photoreceptor is negatively charged and holes are used as carriers from charging to transfer, so that the resolution is very high as with a single-layer photoreceptor. realizable. On the other hand, neutralization is performed in exactly the same way as a general laminated photoconductor, and residual electrons inside the photosensitive layer can also be removed. The phenomenon can also be avoided.

<Image forming apparatus>
The image forming apparatus of the present invention is not limited to a specific one as long as the above-described electrophotographic photosensitive member according to the present invention is used as the photosensitive member, and is known as a configuration of an electrophotographic image forming apparatus. Can be adopted.

For example, the image forming apparatus of the present invention includes an electrophotographic photosensitive member, a charging unit (charging device) that charges the electrophotographic photosensitive member, and an exposure unit (exposure device) that performs exposure on the charged electrophotographic photosensitive member. A developing means (developing apparatus) for developing the electrostatic latent image formed by exposure, a transferring means (transfer apparatus) for transferring the developed toner image, and a surface charge of the electrophotographic photosensitive member using static electricity. It is possible to provide a configuration including a static elimination means (static elimination device) for eliminating static electricity.
The image forming apparatus of the present invention may be, for example, an electrophotographic copying machine, a printer, a facsimile machine, or a complex machine thereof.

According to one embodiment of the image forming apparatus of the present invention, the exposure unit includes a semiconductor laser having an oscillation wavelength in the range of 380 to 650 nm as an exposure light source. In this embodiment, the spot diameter of the laser can be narrowed down, and a higher resolution image can be provided. Particularly in recent years, a 405 nm semiconductor laser has been realized as a semiconductor laser for Blu-ray Disc, and a laser having a spot diameter about half that of a conventional near infrared 780 nm laser has been commercialized.

Further, in the conventional function-separated type photoconductor, the following points have been a problem when the resolution is improved by using such a short wavelength laser, particularly a laser having an oscillation wavelength of about 400 nm for a Blu-ray laser:
The charge transport layer must be transparent to the laser wavelength because it is necessary to transmit the short wavelength laser light to the charge generation layer;
-Since a high-energy short wavelength laser is used, deterioration is quick, but this embodiment does not cause a problem. This is because, in the photoconductor according to the present invention, charge separation occurs on the surface of the photoconductor, so there is no need for the laser light to reach the lower layer, and further deterioration proceeds only on the surface, and the deteriorated portion peels off as the photoconductor wears. Because.

  According to another embodiment of the image forming apparatus of the present invention, the static eliminator includes a semiconductor laser having an oscillation wavelength in the range of 700 to 900 nm as a static elimination light source. In this embodiment, since light having a longer wavelength is used as the charge removal light, it can reach the charge generation layer for charge removal without being absorbed by the photosensitive layer.

According to another embodiment of the image forming apparatus of the present invention, it is possible to provide an apparatus having a high resolution (for example, 2000 dpi or more) in which the developing unit includes liquid toner.
According to another embodiment of the image forming apparatus of the present invention, an image forming apparatus using a reversal development process is provided.

  According to another embodiment of the image forming apparatus of the present invention, an image forming apparatus having a resolution of 2000 dpi or more is provided. According to a more preferred embodiment, the image forming apparatus can be provided as an image forming apparatus having a resolution of 2500 dpi or more, and more preferably 5000 dpi or more.

The image forming apparatus of the present invention will be specifically described with reference to the drawings.
FIG. 3 is a schematic side view showing the configuration of an embodiment of the image forming apparatus of the present invention.
The image forming apparatus shown in FIG. 3 includes a photoreceptor 21 (for example, the photoreceptor shown in FIG. 1 or 2) according to the present invention, a charging unit (charger) 24, an exposure unit 28, and a developing unit (developing). ) 25, transfer means (transfer device) 26, cleaner 27, fixing means (fixing device) 31, and static elimination means 29. Reference numeral 30 indicates a transfer sheet.

  The photosensitive member 21 is rotatably supported by an image forming apparatus main body (not shown), and is driven to rotate in the direction of an arrow around a rotation axis by a driving unit (not shown). The drive means includes, for example, an electric motor and a reduction gear, and transmits the driving force to a conductive support constituting the core of the photoconductor 21, thereby rotating the photoconductor 21 at a predetermined peripheral speed. .

  A charger 24, an exposure unit 28, a developing unit 25, a transfer unit 26, a cleaner 27, and a charge eliminating unit 29 are arranged in this order from the upstream side to the downstream side in the rotation direction of the photoconductor 21 along the outer peripheral surface of the photoconductor 21. It is provided facing.

  The charger 24 is a charging unit that charges the outer peripheral surface of the photoconductor 21 to a predetermined potential. The charger 24 can use a charger wire such as a corotron or a scorotron. Although a contact-type charging roller can be used as the charging means, the use of a contact-type charging roller is preferable for the photoconductor 21 on which a surface protective layer is formed because high wear resistance of the surface of the photoconductor is required.

  The exposure unit 28 includes, for example, a semiconductor laser as a light source, and irradiates light such as a laser beam output from the light source according to image information between the charger 24 and the developing unit 25 of the photosensitive member 21. Then, the outer peripheral surface of the charged photoreceptor 21 is exposed. The exposure light is repeatedly scanned in the main scanning direction in the direction in which the rotation axis of the photoconductor 21 extends, and accordingly, electrostatic latent images corresponding to image information are sequentially formed on the surface of the photoconductor 21.

In the image forming apparatus of the present invention, the above-described photoreceptor according to the present invention is used, and it is sufficient that the charge separation by exposure occurs in the surface layer region. Therefore, it is possible to use short wavelength light as the exposure light. it can. The exposure light preferably has a shorter wavelength than the charge removal light.
Preferably, a semiconductor laser having an oscillation wavelength at a short wavelength (for example, in the range of 380 to 650 nm) is preferably used as the exposure light source.

  The developing unit 25 is a developing unit that develops an electrostatic latent image formed on the surface of the photoreceptor 21 by exposure with a developer. The developing unit 25 is provided facing the photoreceptor 21, and applies toner to the outer peripheral surface of the photoreceptor 21. A developing roller to be supplied, and a casing for supporting the developing roller so as to be rotatable around a rotation axis parallel to the rotation axis of the photosensitive member 21 and accommodating a developer containing toner in the internal space thereof. As the developing toner, either a dry toner or a liquid toner can be used, but a liquid toner is preferable in that it can provide a higher resolution (2000 dpi or more) image.

  The transfer device 26 is a recording medium in which a toner image, which is a visible image formed on the outer peripheral surface of the photoconductor 21 by development, is supplied between the photoconductor 21 and the transfer device 26 from the direction of the arrow by a conveying unit (not shown). Transfer means for transferring onto the transfer paper 30. The transfer unit 26 is, for example, a non-contact type transfer unit that includes a charging unit and transfers the toner image onto the transfer paper 30 by applying a charge having a polarity opposite to that of the toner to the transfer paper 30.

  The cleaner 27 is a cleaning unit that removes and collects toner remaining on the outer peripheral surface of the photoconductor 21 after the transfer operation by the transfer device 26, and is physically performed by a cleaning blade that peels off toner remaining on the outer peripheral surface of the photoconductor 21. The remaining toner is scraped off.

  The neutralizing unit 29 includes a light source such as a semiconductor laser or a lamp with a filter that cuts a predetermined wavelength, and irradiates the neutralizing light output from the light source between the cleaner 27 of the photosensitive member 21 and the charger 24. Thus, holes are generated in the charge generation material in the charge generation layer for charge removal, and space electrons and surface charges inside the photosensitive layer are removed.

  The charge removal light can pass through the photosensitive layer of the photoreceptor (transmittance: for example, 50% or more, preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more). In addition, light having a wavelength or a wavelength region that can cause charge separation with a charge generation material (particularly a main charge generation material) contained in the charge generation layer can be used. The neutralizing light preferably has a longer wavelength than the exposure light.

  As the static elimination light source, it is preferable to use, for example, a semiconductor laser having an oscillation wavelength at a predetermined wavelength (for example, a range of 700 to 900 nm) or various lamps with a filter for cutting a short wavelength component (for example, 700 nm or less). However, as long as it is possible to irradiate light in a wavelength region where charge generation is greater in the charge generation layer for discharging than in the photosensitive layer, a general light source can be used as it is.

  Prior to the cleaner 27, a primary charge eliminating means for removing surface charges may be provided. In addition, a charging unit may be provided before the charge eliminating unit 29 in order to adjust the electric field of the photosensitive layer disturbed by the transfer.

  Further, the image forming apparatus 20 is provided with a fixing device 31 as fixing means for fixing the transferred image on the downstream side where the transfer paper 30 that has passed between the photoreceptor 21 and the transfer device 26 is conveyed. . The fixing device 31 includes a heating roller having a heating unit (not shown), and a pressure roller that is provided to face the heating roller and is pressed by the heating roller to form a contact portion.

The image forming operation by this image forming apparatus is performed as follows.
First, when the photosensitive member 21 is rotated in the direction of the arrow by the driving unit, the photosensitive member 21 is provided by the charger 24 provided on the upstream side in the rotational direction of the photosensitive member 21 with respect to the imaging point of the exposure light from the exposing unit 28. Is uniformly charged to a predetermined negative potential.

  Next, exposure light 28 corresponding to the image information is irradiated from the exposure means 28 to the surface of the photoreceptor 21. With this exposure, the surface charge of the portion irradiated with the exposure light is removed from the photosensitive member 21, and a difference occurs between the surface potential of the portion irradiated with the exposure light and the surface potential of the portion not irradiated with the exposure light. An electrostatic latent image is formed.

  Toner is supplied to the surface of the photosensitive member 21 on which the electrostatic latent image is formed from a developing unit 25 provided on the downstream side in the rotation direction of the photosensitive member 21 with respect to the imaging point of the exposure light from the exposure unit 28. The latent image is developed to form a toner image.

  In synchronization with the exposure of the photoconductor 21, the transfer paper 30 is supplied between the photoconductor 21 and the transfer device 26. The transfer device 26 applies a charge having a polarity opposite to that of the toner to the supplied transfer paper 30, and the toner image formed on the surface of the photoreceptor 21 is transferred onto the transfer paper 30.

  The transfer paper 30 onto which the toner image has been transferred is conveyed to a fixing device 31 by a conveying means, and is heated and pressed when passing through a contact portion between a heating roller and a pressure roller of the fixing device 31, so that the toner image is transferred. The image is fixed on the transfer paper 30 and becomes a robust image. The transfer paper 30 on which the image is formed in this manner is discharged to the outside of the image forming apparatus by the conveying means.

  On the other hand, the toner remaining on the surface of the photoconductor 21 even after the transfer of the toner image by the transfer unit 26 is separated from the surface of the photoconductor 21 by the cleaner 27 and collected. The surface charge of the photosensitive member 21 from which the toner has been removed in this manner and the remaining electrons inside the photosensitive layer are removed by holes generated by irradiating the charge removal layer 29 with the charge removal light 29, and The electrostatic latent image on the surface disappears. Thereafter, the photosensitive member 21 is further driven to rotate, and a series of operations starting from charging again is repeated to continuously form images.

  Hereinafter, the present invention will be described more specifically by showing examples of the electrophotographic photoreceptor of the present invention and an image forming apparatus using the same, but the present invention is limited to the following examples. is not.

(Example 1)
After adding 2 parts by weight of oxotitanium phthalocyanine as a charge generating substance to a resin solution obtained by dissolving 1 part by weight of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd .: BX-1) in 97 parts by weight of tetrahydrofuran (THF) Then, the mixture was dispersed for 10 hours with a paint shaker to prepare a coating solution for a charge generation layer. The charge generation layer coating solution is applied to a conductive support made of aluminum and having a thickness of 0.8 mm (t) × diameter 30 mm (φ) × length 300 mm using a dip coating apparatus, followed by drying to obtain a film thickness. A charge generation layer for charge removal of 0.3 μm was formed.

  Next, 1 part by weight of an azo dye represented by the following structural formula (1), 18 parts by weight of a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Inc .: Z-400) as a charge generation material, and the following structural formula (2) Hole transport material 10 parts by weight, electron transport material 3,5-dimethyl-3 ′, 5′-di-t-butyldiphenoquinone 5 parts by weight, 2,6-di-t-butyl-4 -0.5 parts by weight of methylphenol and 130 parts by weight of THF were dispersed with a ball mill for 12 hours to prepare a coating solution for a photosensitive layer. This photosensitive layer coating solution was applied onto the previously formed intermediate layer with a baker applicator and then dried with hot air at a temperature of 110 ° C. for 1 hour to form a photosensitive layer having a thickness of 25 μm. Thus, an electrophotographic photosensitive member having the layer structure of Example 1 was produced.

(Example 2)
9 parts by weight of dendritic titanium oxide (Ishihara Sangyo Co., Ltd .: TTO-D-1) surface-treated with aluminum oxide (Al ₂ O ₃ ) and zirconium dioxide (ZrO ₂ ), copolymer nylon resin (Toray Industries, Inc.) 9 parts by weight (manufactured by Co., Ltd .: CM8000) was added to a mixed solvent of 41 parts by weight of 1,3-dioxolane and 41 parts by weight of methanol and dispersed for 12 hours using a paint shaker to prepare a coating solution for an intermediate layer. . The prepared coating solution for intermediate layer was applied to the conductive support used in Example 1 by using a dip coating apparatus and then dried to form an intermediate layer having a thickness of 1 μm.
Thereafter, in the same manner as in Example 1, an electrophotographic photoreceptor of Example 2 having the layer configuration of FIG. 1 was produced.

Example 3
An electrophotographic photosensitive member of Example 3 was produced in the same manner as in Example 2 except that an anthraquinone dye (MACROLEX Green 5B Gran) was used as the charge generation material for the photosensitive layer.

Example 4
An electrophotographic photosensitive member of Example 4 was produced in the same manner as in Example 2 except that 4 parts by weight of a coumarin dye represented by the following structural formula (3) was used as the charge generation material for the photosensitive layer.

(Example 5)
In the same manner as in Example 2, a charge generation layer for static elimination was formed, and on top of that, 2 parts by weight of a perylene dye represented by the following structural formula (4) as a charge generation material and an electron transport material, and a polycarbonate resin (Mitsubishi Gas) Chemical Co., Ltd .: Z-400) 18 parts by weight, 10 parts by weight of the hole transport material represented by the structural formula (2), and 0.5 parts by weight of 2,6-di-t-butyl-4-methylphenol Then, 120 parts by weight of THF was dip-coated with a ball mill for 12 hours, and then dried with hot air at a temperature of 110 ° C. for 1 hour to form a photosensitive layer having a thickness of 25 μm. Thus, the electrophotographic photosensitive member of Example 5 was produced.

Example 6
The electron of Example 6 was used in the same manner as in Example 2 except that 1 part by weight of the azo dye represented by the above structural formula (1) and 0.0076 part by weight of oxotitanium phthalocyanine were used as the charge generation material for the photosensitive layer. A photographic photoreceptor was prepared.

(Example 7)
The electron of Example 7 was obtained in the same manner as in Example 2 except that 1 part by weight of the azo dye represented by the structural formula (1) and 0.0001 part by weight of oxotitanium phthalocyanine were used as the charge generation material for the photosensitive layer. A photographic photoreceptor was prepared.

(Example 8)
The electrophotography of Example 8 was prepared in the same manner as in Example 2 except that a coating liquid excluding the electron transport material was prepared from the coating liquid for photosensitive layer of Example 2 and the photosensitive layer was applied with the coating liquid. A photoconductor was prepared.

Example 9
In the same manner as in Example 2, a charge generation layer for static elimination was formed, and on that, 0.2 part by weight of an azo dye represented by the structural formula (1) and a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Inc .: Z -400) 18 parts by weight, 12 parts by weight of a charge transport material represented by the following structural formula (2), and 3,5-dimethyl-3 ′, 5′-di-t-butyldiphenoquinone as an electron transport material A coating solution in which 1 part by weight, 0.2 part by weight of 2,6-di-t-butyl-4-methylphenol and 125 parts by weight of THF are dispersed by a ball mill is applied by dip coating, and then dried to form a film. A lower layer of a photosensitive layer having a thickness of 15 μm was formed (CGM / binder resin = 1/90). Furthermore, 2 parts by weight of the azo dye represented by the structural formula (1), 20 parts by weight of a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Inc .: Z-400), and the following structural formula (2) Charge transport material 10 parts by weight, electron transport material 3,5-dimethyl-3 ′, 5′-di-t-butyldiphenoquinone 5 parts by weight, 2,6-di-t-butyl-4 -0.5 parts by weight of methylphenol and 140 parts by weight of THF were dispersed with a ball mill for 12 hours, and the coating solution was applied onto the lower layer of the photosensitive layer previously formed by the ring coating method, and then at a temperature of 110 ° C for 1 hour. The film was dried with hot air to form a photosensitive layer having a thickness of 10 μm (CGM / binder resin = 1/10). Thus, the electrophotographic photosensitive member of Example 9 was produced.

(Example 10)
In the same manner as in Example 2, the charge generation layer for charge removal was formed, and on that, 12 parts by weight of the hole transport material represented by the structural formula (2) and polycarbonate resin (Mitsubishi Gas Chemical Co., Ltd .: Z200) 18 were formed. A coating solution prepared by dissolving 120 parts by weight of THF with 0.2 part by weight of 2,6-di-t-butyl-4-methylphenol dissolved in 120 parts by weight of THF is dried and dried to transport a hole with a thickness of 15 μm. A layer was formed. In addition, 6 parts by weight of a perylene dye represented by the structural formula (4) as a charge generating material and an electron transporting material, 18 parts by weight of a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Inc .: Z-400), and the above structure A coating solution in which 10 parts by weight of the charge transporting material represented by the formula (2), 0.5 part by weight of 2,6-di-tert-butyl-4-methylphenol, and 120 parts by weight of THF are dispersed by a ball mill for 12 hours. Was applied by a ring coating method and then dried with hot air at a temperature of 110 ° C. for 1 hour to form a photosensitive layer having a thickness of 10 μm. Thus, an electrophotographic photosensitive member of Example 10 having the layer configuration of FIG. 2 was produced.

Example 11
On the photoreceptor of Example 10, 30 parts by weight of methyltrimethoxysilane, 5 parts by weight of dimethyldimethoxysilane, 20 parts by weight of 2.5% acetic acid aqueous solution, 100 parts by weight of 2-methoxyethanol, 50 parts by weight of methyl isobutyl ketone (MIBK) After mixing parts and hydrolyzing at room temperature for 16 hours, 1 part by weight of an antioxidant (manufactured by Sankyo Co., Ltd .: SANOL LS2626), a charge transporting structural unit-containing compound 5 represented by the following structural formula (5) After applying a ring coating method, a coating solution for forming a protective layer in which 20 parts by weight of colloidal silica (methanol dispersion, solid content of 30% by mass) and 1 part by weight of aluminum acetylacetonate as a curing catalyst are added and dissolved. Then, it was cured and dried at a temperature of 120 ° C. for 2 hours to produce an electrophotographic photoreceptor of Example 11 having a protective layer having a thickness of 1 μm.

(Comparative Example 1)
An electrophotographic photosensitive member was produced in the same manner as in Example 2 except that the same oxotitanium phthalocyanine as that of the charge generation layer for charge removal was used as the charge generation material for the photosensitive layer.

(Comparative Example 2)
An electrophotographic photosensitive member excluding the charge generation layer for charge removal in Example 2 was prepared. This photoreceptor is a so-called general single layer type photoreceptor.

(Comparative Example 3)
In the same manner as in Example 2, a charge generating layer for static elimination (here, used as a charge generating layer of a function-separated type laminated photosensitive layer) is formed, and on that, a hole transport material represented by the structural formula (2) is formed. 10 parts by weight, 16 parts by weight of a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Ltd .: Z200) and 0.2 parts by weight of 2,6-di-t-butyl-4-methylphenol are dissolved in 90 parts by weight of THF. The coating liquid was applied by dip coating and dried to form a hole transport layer having a film thickness of 25 μm (here, used as a charge transport layer of the function-separated type laminated photosensitive layer). This photoreceptor is a so-called general laminated photoreceptor.

(Comparative Example 4)
An electrophotographic photosensitive member was produced in the same manner as in Comparative Example 3 except that the coumarin dye represented by the above structural formula (3) was used as the charge generation material of the charge generation layer.

The structures of the above photoreceptors are summarized in Table 1 below.

[Evaluation 1]
The electrophotographic photosensitive members of Examples 1 to 11 and Comparative Examples 1 to 4 manufactured as described above were subjected to corona discharge at −6.5 kV by a scorotron method, and a charging potential V ₀ [surface potential immediately after charging] V] and the surface potential V _L [V] of the electrophotographic photosensitive member at 80 msec after exposure with the light having the wavelength shown in Table 2 obtained by spectroscopy with a monochromator were tested using a test apparatus (manufactured by Gentec Corporation). : CYNTHIA56SN).

At the same time, sensitivity E _1/2 [mJ / cm ² ] was also measured based on the exposure amount required to halve the charged potential of the photoreceptor. Thereafter, the surface potential immediately after charging after static electricity was removed with light of the wavelength shown in Table 2 obtained by spectroscopy with a monochromator, and the charge-exposure-charge removal process (one process 150 msec) was repeated 100 times continuously. V ₀ [V] and the surface potential V _L [V] after exposure were also measured. The results are shown in Table 2.

As shown in Table 2, the photoconductors of the present invention (Examples 1 to 5) are negatively charged and have stable electrical characteristics even when used repeatedly. The photoreceptor that did not reach it was confirmed that electrons stay in the photosensitive layer, the surface potential is saturated at -850 to 900 V, and the potential does not drop even when exposed.
Further, in the photoconductors of Examples 6 and 7, the oxotitanium phthalocyanine was intentionally added so that a part of the static elimination light was absorbed by the photosensitive layer, but when the transmittance of the static elimination light was lower than 50%. An increase in the charging potential after repetition and an increase in the potential after exposure were observed. A spectrophotometer U-3410 (manufactured by Hitachi, Ltd.) was used for the measurement of transmittance.

Further, comparing the photoconductors of Examples 1 and 2, it can be seen that the chargeability is slightly increased by employing the intermediate layer.
In addition, the laminated type photoconductor of Comparative Example 3 had no problem in sensitivity, but the laminated type photoconductor of Comparative Example 4 had no sensitivity because exposure light did not reach the charge generation layer. Electrical characteristics could not be measured.
Further, the photoreceptor of Example 5 using a perylene dye having an electron transporting ability had sufficient electric characteristics even without adding an electron transporting substance. On the other hand, in the photoconductor of Example 8 using an azo dye, since the electron transporting ability of the dye is low, the injection efficiency of charges separated by the dye is lowered when the electron transport material is not contained. However, a decrease in sensitivity was observed.
Furthermore, the photoconductors of Examples 9 to 11 in which a large amount of charge generating material was present on the surface layer exhibited extremely good sensitivity.

[Evaluation 2]
Each of the electrophotographic photosensitive members of Examples 2 to 4 and Comparative Example 2 is a Sharp copier AR-F330 remodeling machine (a filter having a semiconductor laser having an oscillation wavelength shown in Table 3 as an exposure light source and cutting a wavelength of 700 nm or less to a static elimination lamp. In the case of Comparative Example 2, a standard image mixed with characters and photos was repeatedly output 100 times in order to confirm the presence or absence of the memory phenomenon. The results are shown in Table 3.

  As shown in Table 3, a memory image did not appear on the photoreceptor of the present invention, whereas a memory image appeared on the single-layer photoreceptor of the comparative example.

[Evaluation 3]
Scorotron charger, exposure unit capable of variably controlling the laser beam diameter from 300 to 6000 dpi by controlling the aperture diameter (laser oscillation wavelength is shown in Table 4), and development with liquid toner having toner with a particle diameter of 0.2 μm In an experimental machine having a developing unit, each of the electrophotographic photosensitive members of Examples 2 to 4 and Comparative Examples 2 to 4 was used to repeat 1 isolated dot and 1 dot line minus 1 dot blank. Images were output to check the resolution of each photoconductor. The results are shown in Table 4.

  As shown in Table 4, it was confirmed that the photoreceptor of the present invention and the photoreceptor of Comparative Example 2 which is a single-layer photoreceptor have a resolution of 5000 dpi or more. This well represents the characteristics of a single-layer photoconductor in which charge separation by exposure light occurs near the surface.

  On the other hand, the photoconductor of Comparative Example 3 which is a laminated type photoconductor can output an image of 600 dpi, but if it exceeds 2500 dpi, an isolated 1 dot cannot be output and an image of a periodic 1 dot line is blurred and cannot be recognized as a line. Only a good image was obtained. This is because holes generated by charge separation in the charge generation layer inside the photoreceptor diffuse in the surface direction while moving through the charge transport layer to the surface layer.

  Further, in the photoconductor of Comparative Example 4, since the exposure light was absorbed by the charge transport layer and did not reach the charge generation layer, even an image could not be obtained.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of a main part in one embodiment of the photoreceptor of the present invention. FIG. 6 is a schematic cross-sectional view showing a configuration of a main part in another embodiment of the photoconductor of the present invention. 1 is a schematic side view illustrating a configuration of an image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductive support body 2 Intermediate | middle layer 3 (For static elimination) Charge generation layer 4 Organic photosensitive layer 5 Hole transport material 6 Electron transport material 7 Charge generation material A
8 Charge generation material B
DESCRIPTION OF SYMBOLS 10 Hole transport layer 21 Photoconductor 24 of this invention Charging means 25 Developing means 26 Transfer means 27 Cleaner 28 Exposure means 29 Light removal means 30 Transfer paper 31 Fixing means

Claims (19)

  On a conductive substrate, a charge generation layer containing a charge generation material and an organic photosensitive layer containing at least a charge generation material and a hole transport material are provided in this order, and the main charge generation material in the charge generation layer is an organic photosensitive layer. An electrophotographic photosensitive member characterized by being different from a main charge generating substance in the layer.   The electrophotographic photosensitive member according to claim 1, wherein the main charge generation material in the charge generation layer has absorption at a longer wavelength than the main charge generation material in the organic photosensitive layer.   The electrophotographic photosensitive member according to claim 1 or 2, wherein the main charge generating material in the charge generating layer has an absorption peak at a wavelength that is 50 nm or more away from the wavelength of the absorption peak on the longest wavelength side in the organic photosensitive layer. .   The electrophotographic photosensitive member according to any one of claims 1 to 3, wherein a main charge generation material in the charge generation layer is selected from phthalocyanine dyes.   The electrophotography according to any one of claims 1 to 4, wherein the main charge generating substance in the organic photosensitive layer is selected from the group consisting of azo dyes, polycyclic quinone dyes, coumarin dyes, and perylene dyes. Photoconductor.   The main charge generation material in the charge generation layer has an absorption peak capable of generating charge in a wavelength region of light that transmits the organic photosensitive layer with a transmittance of 50% or more. The electrophotographic photosensitive member according to any one of the above.   The electrophotographic photosensitive member according to claim 1, wherein the organic photosensitive layer contains an electron transport material.   The electrophotographic photosensitive member according to claim 7, wherein the organic photosensitive layer contains more hole transport material than electron transport material.   The electrophotographic apparatus according to any one of claims 1 to 8, wherein the organic photosensitive layer further contains a binder resin, and a mixing ratio of the charge generating material in the organic photosensitive layer to the binder resin is higher on the surface layer side than on the conductive substrate side. Photoconductor.   The electrophotographic photosensitive member according to claim 1, further comprising a hole transport layer containing only a hole transport material as a charge transport material between the organic photosensitive layer and the charge generation layer.   The electrophotographic photosensitive member according to claim 1, wherein the charge generating material has an electron transporting ability in the organic photosensitive layer.   The electrophotographic photosensitive member according to claim 1, further comprising a protective layer as an outermost surface layer.   The electrophotographic photosensitive member according to claim 1, further comprising an intermediate layer between the conductive substrate and the charge generation layer.   The electrophotographic photosensitive member according to claim 1, a charging unit for charging the electrophotographic photosensitive member, an exposure unit for exposing the charged electrophotographic photosensitive member, and an exposure unit. Development means for developing the electrostatic latent image to be developed, transfer means for transferring the developed toner image, and static elimination means for eliminating the surface charge of the electrophotographic photosensitive member using static elimination light. Image forming apparatus.   The neutralizing means is a light source that irradiates light including a wavelength having an absorption peak at which a main charge generating substance in the organic photosensitive layer of the photoreceptor can generate charges, and the light has a transmittance of 50% or more through the organic photosensitive layer. The image forming apparatus according to claim 14, wherein the image forming apparatus transmits the light.   The image forming apparatus according to claim 14, wherein the exposure unit includes a semiconductor laser having an oscillation wavelength in the range of 380 to 650 nm as an exposure light source.   The image forming apparatus according to any one of claims 14 to 16, wherein the static elimination means includes a semiconductor laser having an oscillation wavelength in a range of 700 to 900 nm as a static elimination light source.   The image forming apparatus according to claim 14, wherein the developing unit includes liquid toner and has a resolution of 2000 dpi or more.   The image forming apparatus according to claim 14, wherein a reversal development process is used.

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