JP2010079234A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a monolayer photoreceptor that gives a latent image with high resolution, and reducing production of defective images such as a memory image. <P>SOLUTION: An electrophotographic image forming apparatus is equipped with at least: an electrophotographic photoreceptor having a monolayer photosensitive layer on a conductive substrate having a light transmitting property for destaticizing light, the photosensitive layer containing a charge generating substance having an electron transporting ability and a hole transporting substance, or a charge generating substance, an electron transporting substance and a hole transporting substance; a charging means charging the electrophotographic photoreceptor into negative charges; an exposing means irradiating the electrophotographic photoreceptor with exposure light to form an electrostatic latent image corresponding to image information; a developing means developing the electrostatic latent image to form a toner image; a transfer means transferring the toner image; and a destaticizing means irradiating the electrophotographic photoreceptor through the conductive substrate side with destaticizing light to destaticize the residual charges of the electrophotographic photoreceptor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic high-resolution image forming apparatus and a high-resolution image forming method.

  In recent years, in order to improve the image quality of an output image of an electrophotographic apparatus, an increase in 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. Scattering of exposure light in the layer and diffusion of holes are extremely small, and high resolution can be realized (Patent Document 1).

  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 very slow compared to hole conduction, and therefore accumulates as a space potential in the photosensitive layer. For this reason, the single-layer type photoconductor can only be put into practical use as a positively charged type photoconductor that requires a short movement distance of electrons, and negatively charged toner that occupies most of the market cannot be used.

  Even when used as a positively charged photoreceptor, the mobility of electrons is very slow compared to the conduction of holes, so that the electrons separated in the deep part of the single-layer photoreceptor by the exposure light incident to the inside are It cannot reach the surface layer within a predetermined process 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). )).

  In order to solve this problem, a method has been proposed in which the space potential is neutralized separately from the surface charge by charging the photoconductor with a polarity opposite to that of charging by the charging means (Patent Document 2). According to the method, since the photosensitive member is charged with a reverse polarity to the surface charge, abnormal discharge may occur during the charging and damage of the photosensitive member may occur.

JP-A-6-202349 Japanese Patent Laid-Open No. 9-90833

  SUMMARY OF THE INVENTION An object of the present invention is to provide a negatively charged image forming apparatus that includes a single-layer type photoconductor that can obtain a high-resolution latent image and that reduces the occurrence of defective images such as memory images.

  In order to achieve the above object, charge separation by exposure light occurs in the surface layer of the photosensitive member, charge movement in the photosensitive layer is performed in sufficiently fast holes, and the space potential that can remain in the photosensitive layer is improved. An electrophotographic image forming apparatus that can be removed has been devised.

  That is, the present invention provides a charge generating substance and a hole transporting substance having an electron transporting ability, or a single substance containing a charge generating substance, an electron transporting substance and a hole transporting substance on a conductive substrate that is transparent to static elimination light. An electrophotographic photosensitive member having a layer-type photosensitive layer; a charging means for charging the electrophotographic photosensitive member to a negative charge; and exposing the electrophotographic photosensitive member to exposure light to form an electrostatic latent image corresponding to image information. An exposure unit for forming, a developing unit for developing the electrostatic latent image to form a toner image, a transfer unit for transferring the toner image, and the charge removing light from the conductive substrate side of the electrophotographic photosensitive member. Then, an electrophotographic image forming apparatus is provided, comprising at least a neutralizing unit that neutralizes residual charges of the electrophotographic photosensitive member.

  According to the present invention, a high-sensitivity and high-resolution single-layer type photoconductor is provided, and it is possible to provide a high-quality image that can easily remove a spatial potential without applying a load to the photoconductor. A high image forming apparatus can be realized.

  The image forming apparatus of the present invention contains a charge generating material and a hole transporting material having an electron transporting ability, or a charge generating material, an electron transporting material and a hole transporting material on a conductive substrate that is transparent to static elimination light. An electrophotographic photosensitive member having a single-layer type photosensitive layer, a charging means for negatively charging the electrophotographic photosensitive member, and the charge removing light from the conductive substrate side of the electrophotographic photosensitive member. It is characterized by comprising at least a charge eliminating means for eliminating the residual charge on the photoreceptor.

In the image forming apparatus of the present invention, a single-layer type photosensitive member that can only be used for positive charging in the past is provided by including a static elimination system composed of a combination of the electrophotographic photosensitive member and the static elimination means as described above. Used with negative charge.
That is, by exposing the negatively charged photosensitive layer, charge separation occurs in the charge generation material in the photosensitive layer, and the holes reach the surface layer according to the electric field and recombine with the surface negative charge to form a latent image. . On the other hand, although electrons are attracted to the substrate side in accordance with the electric field, they move in the photosensitive layer because of their slow moving speed. However, the induction effect of the photosensitive layer, the interaction with the charge generating substance, or the generation of charges It can move in the photosensitive layer by the interaction between the substance and the electron transport substance, and can be separated to a distance at which a latent image having a surface potential sufficient for development can be formed.

On the other hand, in the static elimination process, the static elimination light irradiated from the conductive substrate side passes through the transparent conductive substrate and causes charge separation mainly under the photosensitive layer, and the generated holes pass through the inside of the photosensitive layer. In the process, the electrons held in the photosensitive layer are removed, and the surface negative charge is eliminated by reaching the surface.
In this way, the static elimination system easily erases the spatial potential inside the photosensitive layer when the single-layer type photosensitive member is used with a negative charge, together with the remaining surface potential, without applying a load to the photosensitive member.

  As a result of using a single-layer type photoreceptor with negative charging, it is possible to form an image by a negative charging process in which the charging potential is stable compared to positive charging. Further, as the toner, negatively charged toners that are widely available in the same market as the laminated photoreceptor can be used, so that the selectivity is widened and a highly functional toner can be used. In addition, since charge separation due to exposure light occurs on the surface layer of the photoreceptor, it is possible to perform exposure at extremely high resolution and high speed.

Moreover, since holes that can move at a very high speed compared to electrons are used for static elimination, it is possible to handle high-speed processes.
Further, by irradiating the neutralization light from the conductive substrate side, absorption of the neutralization light by the surface layer portion of the photosensitive layer can be avoided, and the neutralization light can be irradiated to the lower part of the photosensitive layer with lower irradiation energy. It is also possible to reduce deterioration of the charge generation material (and sensitizer) and the charge transport material in the surface layer portion of the photosensitive layer due to the neutralizing light irradiation. Since the means for irradiating the neutralizing light can be installed on the conductive substrate side, it can contribute to downsizing of the apparatus.

Furthermore, if the charge is removed from the photoconductor after development and before transfer, the charge removal process previously performed after transfer can be performed in parallel with the development to transfer process, so the speed of the entire process can be improved and faster. An image forming apparatus can be realized.
That is, in the image forming apparatus of the present invention, since the discharge light is irradiated from the back surface (conductive substrate side), even if a toner image is formed on the surface of the photosensitive layer, the discharge light is irradiated to the entire surface without being blocked by the toner. Thus, the entire photosensitive layer can be discharged efficiently.
On the other hand, since a certain amount of time is required until the charge generated in the lower part of the photosensitive layer due to the irradiation of the static elimination light reaches the surface of the photosensitive member, the toner image formed on the surface of the photosensitive member is transferred before destruction and exposed to light after transfer. It is possible to neutralize the body surface.
In this way, the image forming process can be speeded up.
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.

The present invention will be specifically described below with reference to the drawings.
It should be noted that the image forming apparatus of the present invention is not limited to the form specifically 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. For example, although the photoconductor is shown as a drum shape in FIG. 1, other shapes (for example, a belt shape) may be used, and a specific form of the image forming apparatus in that case can be easily understood by those skilled in the art. .

FIG. 1 is a schematic side cross-sectional view showing the configuration of an embodiment of the image forming apparatus of the present invention.
FIG. 4 is a schematic side sectional view showing the configuration of another embodiment of the image forming apparatus of the present invention.
An image forming apparatus 20 shown in FIGS. 1 and 4 includes an electrophotographic photoreceptor 21 (for example, the photoreceptor shown in FIGS. 2 and 3), a charging unit (charger) 24, an exposure unit 28, and a developing unit. The unit (developing unit) 25, the transfer unit (transfer unit) 26, the cleaner 27, the fixing unit (fixing unit) 31, and the charge eliminating unit 29 are configured. Reference numeral 30 indicates a transfer sheet.

The charger 24, the exposure unit 28, the developing unit 25, the transfer unit 26, and the cleaner 27 are provided in this order from the upstream side to the downstream side in the rotation direction along the outer peripheral surface of the photoconductor 21.
The neutralizing means 29 is provided facing the conductive substrate of the photoconductor 21 (inside the photoconductor in FIGS. 1 and 4), and in the form shown in FIG. 1, between the cleaner 27 and the charger 24, FIG. In the illustrated form, the photosensitive member is irradiated with static elimination light from the side of the conductive substrate between the developing unit 25 and the transfer unit 26.

<Electrophotographic photoreceptor>
The electrophotographic photosensitive member that can be used in the image forming apparatus of the present invention includes a charge generating substance and a hole transporting substance having an electron transporting ability, or a charge generating substance and an electron on a conductive substrate that is transparent to static elimination light. It has a single-layer type photosensitive layer containing a transport material and a hole transport material.
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 substrate constituting the core of the photoconductor 21, thereby rotating the photoconductor 21 at a predetermined peripheral speed.

2 and 3 are partial cross-sectional views schematically showing the configuration of an embodiment of an electrophotographic photosensitive member that can be used in the image forming apparatus of the present invention.
The photosensitive member partially shown in FIG. 2 has a charge generating substance (7), a hole transporting substance (5), and an electron transporting substance (6) on a conductive substrate (1) having a predetermined translucency. A single-layer type photosensitive layer (4) is provided. In addition, when a charge generation material has an electron transport ability, an electron transport material (6) can be omitted.
The photoconductor partially shown in FIG. 3 has a structure in which an intermediate layer (2) is further provided directly on the conductive substrate (1), and other configurations are the same as those of the photoconductor shown in FIG. . Similarly, when the charge generation material has an electron transport ability, the electron transport material (6) can be omitted.

[Conductive substrate]
The conductive substrate (1) has a role as an electrode of a photoreceptor and a function as a support member for other layers. In addition, in the present invention, the conductive substrate is translucent to static elimination light.

  As the conductive substrate used in the present invention, those known in the art can be used as long as they have the predetermined translucency. Examples include polyethylene terephthalate, polycarbonate, acrylic resin, epoxy resin, polyurethane, polyester, polyethylene, polyamide, polyamideimide, polystyrene, polyacetal, polyolefin, vinylon, and other polymer materials, and glass, quartz, sapphire, and other inorganic materials. A light-transmitting conductive compound such as conductive polymer, tin oxide, indium oxide, indium-tin oxide (ITO), lead oxide, copper iodide, Ti, Al, Ni, Au, What formed the translucent conductive layer containing metals, such as Ag and Cu, by vapor deposition, application | coating, sputtering, etc. is mentioned.

  The shape of the conductive substrate is not particularly limited, and may be a drum, a sheet, a seamless belt, or the like.

  The translucent conductive substrate has a transmissivity for static elimination light as measured by a spectrophotometer (for example, U-3410 manufactured by Hitachi, Ltd.), for example, 50% or more, preferably 60% or more. Preferably it may be 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more.

[Single-layer type photosensitive layer]
The single-layer type photosensitive layer (4) comprises at least a charge generation material (7) and a hole transport material (5) having an electron transport ability, or a charge generation material (7), a hole transport material (5) and an electron transport material (6). And has a function of generating holes (and electrons) by charge separation with a charge generating material contained in the photosensitive layer (mainly the surface layer portion) upon exposure to exposure light. 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. Electrons generated at the same time as the holes are once held in the photosensitive layer, but as described above, they are erased by holes generated mainly (under the photosensitive layer) by the static elimination light irradiated from the conductive substrate side. .

As the charge generation material in the single-layer type photosensitive layer, any material can be used as long as it is generally used as a charge generation material in an electrophotographic photosensitive member. For example, monoazo, bisazo, trisazo pigments, etc. Azo pigments, perylene-type, coumarin-type, polycyclic condensation-type pigments represented by polycyclic quinone-type dyes, phthalocyanine-type dyes such as metal and metal-free phthalocyanine, metal-free and metal naphthalocyanine, indigo-type pigments, squarylium dyes , Organic materials represented by pyrylium compounds, thiopyrylium compounds, and triphenylmethane dyes. Inorganic materials can also be used, but preferably organic materials are used.
These charge generation materials may be used alone or in combination of two or more. Specific (non-limiting) examples of each 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, 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.
Examples of the coumarin pigments include compounds described in JP-A-3-1148, JP-A-4-46348, JP-A-4-225364, and the like.

  Specific examples of the polycyclic quinone dye include anthraquinone, pyrenequinone, compounds described in JP-A No. 1-219841, JP-A No. 3-95562, JP-A No. 5-23725, and the like.

  Specific examples of phthalocyanine dyes 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, metal-free naphthalocyanines, titanyloxynaphthalocyanines , Copper naphthalocyanines, hydroxygalli Muna phthalocyanines, include vanadyl oxy naphthalocyanine, and the like, these compounds are further optimized by the crystal structure.

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.
Among these charge generation materials, polycyclic condensed pigments and phthalocyanine dyes are preferable because of their high sensitivity and electron transport ability.

  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, stilbene compounds, hydrazones. Compound, butadiene compound, enamine compound, polycyclic aromatic compound, indole derivative, pyrazoline derivative, oxazolone derivative, benzimidazole derivative, quinazoline derivative, benzofuran derivative, acridine derivative, phenazine derivative, aminostilbene derivative, triarylamine derivative, triaryl Examples include methane derivatives, phenylenediamine derivatives, and benzidine derivatives.

Moreover, the polymer which has the group which arises from these compounds in a principal chain or a side chain, for example, poly-N-vinyl carbazole, poly-1-vinyl pyrene, poly-9-vinyl anthracene, etc. are mentioned.
The above hole transport materials may be used alone or in admixture of two or more.
Among these hole transport materials, aminostilbene derivatives, hydrazone compounds, butadiene compounds, enamine compounds, and benzidine derivatives are preferable because of high hole mobility and stability.

  The single-layer type photosensitive layer may contain a sensitizer. By containing 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.

Examples of the electron transport material (6) include perylene dyes, 1,4,5,8-naphthalenetetracarboxydiimide derivatives, quinones such as diphenoquinone and naphthoquinone derivatives, and cyano compounds such as tetracyanoethylene and terephthalmalondinitrile. Aldehydes such as 4-nitrobenzaldehyde, anthraquinones such as anthraquinone and 1-nitroanthraquinone, and polycyclic or heterocyclic nitro such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitrofluorenone A compound or a material obtained by polymerizing these electron-withdrawing materials can be used.
Among these electron transport materials, perylene dyes and quinones are preferable because they have high electron transport ability and no toxicity.

  If the charge generating material has an electron transporting ability, it can also act as an electron transporting material. Therefore, if such a charge generating material is used in a single-layer type photosensitive layer, the addition of the electron transporting material can be omitted or added. The amount can be kept small.

As the binder resin for the single-layer type photosensitive layer, a resin having compatibility with the charge transport material contained in the photosensitive layer is selected. For example, vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and co-polymers thereof. Polymer, polycarbonate, polyester, polyester carbonate, polysulfone, phenoxy, epoxy, silicone resin, polyarylate, polyamide, polyester, polyketone, polyurethane, polyacrylamide, phenol resin, etc. are mentioned, these are used alone or in combination of two or more Or a partially crosslinked thermosetting resin may 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.

The blending ratio of the charge generating material to the binder resin is 2 to 30% by weight. When the amount is less than this range, sufficient sensitivity cannot be obtained, and when the amount is larger, not only the film strength of the photosensitive layer is lowered, but also dispersibility is lowered and coarse particles are increased, which causes image defects.
When the photosensitive layer contains a sensitizer, the sensitizer is preferably in the range of 0.1 wt% to 20 wt% with respect 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.

The compounding ratio of the hole transport material to the binder resin is 40 to 100% by weight. 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 compounding ratio of the electron transport material to the binder resin is 0 to 100% by weight. When the amount is larger than this range, the film strength of the photosensitive layer is lowered and the printing durability is deteriorated.

  In the present invention, the hole transport material needs to move carriers during exposure and charge removal, in particular, holes must pass through the photosensitive layer during charge removal. On the other hand, as described above, the electron transport material contains charge-separated electrons. The content of the electron transporting material in the photosensitive layer may be the same as or less than the content of the hole transporting material, as long as it has a function of carrying it to some extent inside the photosensitive layer and stably holding it until static elimination. The electron transport material may be, for example, 100% by weight or less, 60% by weight or less, or 50% by weight or less based on the hole transport material. The lower limit is not particularly limited, and may be, for example, 1% by weight or more, 5% by weight or more, and 10% by weight or more, but may be 0% by weight when the charge generation material has an electron transporting ability.

  For single-layer type photosensitive layers, known plasticizers such as dibasic acid esters, fatty acid esters, phosphoric acid esters, phthalic acid esters, chlorinated paraffins and epoxy type plasticizers, and silicone leveling are used as necessary. An agent may be added to impart processability and flexibility to the photosensitive layer, or to improve surface smoothness. Further, fine particles of inorganic and organic compounds can be added to increase mechanical strength and improve electrical characteristics.

The single-layer type photosensitive layer may also contain various additives such as an antioxidant as necessary.
As the antioxidant, a phenolic antioxidant typified by 2,6-di-t-butyl-4-methyl-phenol is suitable. The antioxidant is preferably contained in an amount of 0.1% by weight to 50% by weight with respect to 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 single-layer type photosensitive layer is, for example, 10 to 100 μm, preferably 10 to 50 μm. If the film thickness of the photosensitive layer is smaller than 10 μm, the charge holding ability may be lowered. On the other hand, if it exceeds 100 μm, the static elimination process takes a long time and the process speed becomes slow.

The single-layer type photosensitive layer can be formed by dispersing a charge generating material, a hole transport material, a binder resin, and, if necessary, an electron transport material and other additives in a suitable organic solvent and applying them. .
The single-layer type photosensitive layer is applied using 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, or a blade coating method, as in the case of the intermediate layer described later. It can be carried out.

  Suitable organic solvents include aromatic hydrocarbons such as benzene, toluene, xylene and monochlorobenzene, halogenated hydrocarbons such as dichloromethane and dichloroethane, single solvents of solvents such as tetrahydrofuran, dioxane, dimethoxymethyl ether and dimethylformamide, or 2 A mixed solvent of more than one species, or a solvent such as alcohol, acetonitrile, methyl ethyl ketone or the like can be further added and used as necessary.

[Middle layer]
The intermediate layer covers defects on the surface of the conductive substrate, prevents carrier injection from the conductive substrate to the photosensitive layer, improves chargeability and ensures appropriate charge retention performance, and adheres to the photosensitive layer. Image defects can be prevented by improving the coating properties and / or improving the coating properties of the photosensitive layer.

  In particular, when an image is formed using the reversal development method, 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 (e.g., a conductive substrate or (When chargeability is reduced in a small area due to a defect in the photosensitive layer), the image quality is significantly deteriorated due to the occurrence of fogging of an image called a black spot where toner adheres to a white background and a minute black spot is formed. Such image defects can be prevented by providing an intermediate layer.

  Therefore, in the electrophotographic photoreceptor used in the image forming apparatus of the present invention, it is preferable to provide the intermediate layer (2) directly on the conductive substrate (1).

When used in the image forming apparatus of the present invention, the intermediate layer is also translucent to static elimination light, like the conductive substrate.
The translucent intermediate layer has a transmissivity with respect to static elimination light as measured by a spectrophotometer (for example, U-3410 manufactured by Hitachi, Ltd.), for example, 50% or more, preferably 60% or more, more preferably. May be 70% or more, more preferably 80% or more, more preferably 90% or more, and more preferably 95% or more. The light transmittance of the conductive substrate and the intermediate layer combined (the light transmittance of the conductive substrate × the light transmittance of the intermediate layer) is, for example, 50% or more, preferably 60% or more, more preferably 70% or more, and more. Preferably it is 80% or more, More preferably, it is 90% or more, More preferably, it is 95% or more.

  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, silicon resin, polyvinyl butyral resin, polyamide resin, and repeating units thereof. Among them, a copolymer resin containing two or more of them, 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.

  In order to adjust the volume resistance value of the intermediate layer, to prevent carrier injection from the conductive substrate to the photosensitive layer, and to maintain the electrical characteristics of the photoreceptor in various environments, a metal oxide such as titanium oxide is used. It can be included.

  The ratio P / R between the metal oxide (P) and the resin (R) in the intermediate layer is preferably in the range of 0/10 to 9/1 by weight. When the P / R ratio exceeds 9/1, the dispersibility of the inorganic oxide fine particles decreases and the possibility of forming an aggregate increases, so the transparency of the coating film decreases and the adhesion to the conductive substrate. And the possibility that image defects such as black spots will occur increases.

  The intermediate layer contains the above resin with water or various organic solvents, particularly methanol, ethanol, butanol alone, or water / alcohols, a mixed solvent of two or more alcohols, or acetone, dioxolane, etc./alcohols. It can be formed by applying a coating solution for an intermediate layer dissolved in a mixed solvent or a mixed solvent of a chlorinated solvent / alcohol such as dichloroethane, chloroform, trichloroethane or the like on a conductive substrate.

  When a metal oxide is contained in the intermediate layer, an intermediate layer coating solution in which the metal oxide is dispersed in a solution obtained by dissolving the above-described resin in various solvents as described above can be used. At this time, as a method for dispersing the metal oxide, a general method such as a ball mill, a sand mill, an attritor, a vibration mill, or 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 the physical properties and productivity of the coating liquid. In particular, the dip coating method is a method in which an intermediate layer is formed by immersing a conductive substrate in a coating tank filled with a coating solution and then pulling it up at a constant rate or a rate that changes sequentially. It is more preferable because of its excellent properties and cost. 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 0.1 μm to 10 μm, more preferably 0.5 μm to 6 μm. If the thickness of the intermediate layer is less than 0.1 μm, it will not function as an intermediate layer substantially, and defects in the conductive substrate will not be covered to provide a uniform surface property, preventing carrier injection from the conductive substrate. May not be able to be performed, and chargeability may be reduced. Increasing the thickness above 10 μm is not preferable because the translucency of the intermediate layer is lowered, and when the intermediate layer is applied by dip coating, it becomes difficult to produce the photoreceptor and the sensitivity of the photoreceptor is lowered.

[Protective layer]
Although not shown in FIGS. 2 and 3, the electrophotographic photosensitive member may be provided with a protective layer 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. For 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 for 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 translucency 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 material or an organic material for reasons such as improving dispersibility and modifying surface properties. In general, examples of the water-repellent treatment include 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 the charging property, 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 or oligomers having a perfluoroalkyl group in the side chain 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 binder 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 ketone, 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 step, 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 subjected to a crosslinking reaction 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.
If 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 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 formation process on photoconductor]
Hereinafter, an image forming process on the photoreceptor will be described.
Here, since the photoreceptor is negatively charged, the surface of the single-layer photoreceptor is first negatively charged by the charging means.

  Next, when the surface of the photoreceptor is exposed by the exposure unit, charge separation occurs in the charge generation material in the single-layer type photosensitive layer (mainly the surface layer portion). The holes generated by the charge separation reach the surface layer according to the electric field formed by charging and recombine with the negative charges on the surface of the photoreceptor to form a high-resolution latent image. On the other hand, the electrons generated simultaneously by the charge separation are attracted to the conductive substrate side by the electric field, but the electron transporting ability of the electron transporting substance is generally low, and the electron transporting substance may not be contained in the present invention. (In this case, since the charge generating material is responsible for electron transport), it remains in the photosensitive layer without reaching the conductive substrate (particularly in a high-speed process).

  The latent image on the surface of the photoconductor is developed as a toner image by a reversal development method in the same manner as a general photoconductor, and the toner image is transferred to paper. Thereafter, residual toner on the surface of the photoreceptor is removed by a cleaner.

Finally, the residual charge inside the photosensitive layer and on the surface of the photosensitive member is removed by irradiating the photosensitive member with the removing light from the translucent conductive substrate side. That is, the charge generation material in the photosensitive layer (mainly in the lower part) separates charges from holes and electrons, and the electric field causes the electrons to flow into the conductive substrate, the holes move to the surface layer side, and reach the surface of the photosensitive layer. The electrons remaining in the photosensitive layer are erased, and the surface charge is erased when the surface layer is reached.
The charge removal light can be irradiated from the conductive substrate side below the photosensitive member before the toner image formed by the developing unit is transferred by the transfer unit. In this case, the timing of charge removal is adjusted so that charge separation occurs at the bottom of the photosensitive layer between the development and transfer processes, and the generated charge removal holes reach the surface of the photoconductor after the transfer is completed to remove the surface charge. Is done.

  By the above-described operation, formation of a very high resolution latent image (and therefore a toner image) and removal of residual electrons inside the photosensitive layer (and therefore avoidance of the memory phenomenon) are realized.

<Charging means>
The charger 24 is a charging unit that charges the outer peripheral surface of the photoconductor 21 to a predetermined negative potential. Examples of the charger 24 include a corona discharge charger such as a corotron and a scorotron (for example, a charger wire), and a contact charger using a charging roller or a charging brush. Since the contact type charger generates very little ozone and acid gas compared to the charger of the corona discharge type charger, the single layer type photosensitive material in which the charge generating material is present on the surface layer as in the present invention. Suitable for use on the body.

<Exposure means>
The exposure unit 28 includes, for example, a semiconductor laser as a light source, and irradiates light output from the light source according to image information between the charger 24 and the developing unit 25 of the photoreceptor 21 (from the surface layer side). Thus, the outer peripheral surface of the charged photoconductor 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, a single-layer type photoreceptor is used, and it is sufficient that charge separation by exposure occurs in the surface layer region. Therefore, a light source capable of irradiating light with a short wavelength is used as the exposure unit. be able to.

  In one embodiment, the exposure means 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.

In addition, the following points were problems when using a short wavelength laser to improve resolution in a conventional function-separated type photoreceptor:
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 the image forming apparatus of the present invention uses a single-layer type photoreceptor, and charge separation occurs on the surface of the photoreceptor in the single-layer type photoreceptor, so that it is not necessary for the laser light to reach the lower layer. This is because the deterioration proceeds only on the surface layer, and the deteriorated portion peels off with the wear of the photoreceptor.

<Developing means>
The developing device 25 is a developing unit that develops the electrostatic latent image formed on the surface of the photoconductor 21 by exposure into a toner image that is a visible image with a developer, and is provided facing the photoconductor 21. The developing device includes, for example, a developing roller that supplies toner to the outer peripheral surface of the photoconductor 21, and supports the developing roller so as to be rotatable about a rotation axis parallel to the rotation axis of the photoconductor 21, and includes toner in an internal space thereof. And a casing for containing the developer.

<Transfer means>
The transfer unit 26 is a transfer sheet 30 that is a recording medium for supplying a toner image formed on the outer peripheral surface of the photoconductor 21 by development from the direction of the arrow between the photoconductor 21 and the transfer unit 26 by a conveying unit (not shown). It is a transfer means to transfer on. The transfer device 26 may be, 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.

<Static removal means>
The neutralization means 29 includes a light source such as a semiconductor laser or a lamp, and generates charges in the single-layer type photosensitive layer (mainly the lower part) by irradiating the neutralizing light output from the light source from the conductive substrate side of the photoreceptor 21. Charge separation is caused by the substance to generate holes, thereby removing space electrons and surface charges inside the photosensitive layer.
In the image forming apparatus of the present invention, the discharging operation by the discharging unit may be started after the toner image formed on the surface by the developing unit is transferred by the transferring unit (residual toner is removed by the cleaner). Or before or after the toner image is transferred by the transfer means.

In one embodiment, the static elimination means is a static elimination lamp. Since the neutralizing lamp can irradiate the entire surface under the photosensitive layer in the region to be neutralized, it is possible to efficiently neutralize the photosensitive member.
The static eliminator is preferably a static elimination lamp. Examples of the static elimination lamp include a halogen lamp, a tungsten lamp, a xenon lamp, a krypton lamp, a fluorescent lamp, and a light emitting diode (LED and LED array).
In addition, when the static elimination light is irradiated between the development and transfer process, if the static elimination light reaches the surface layer of the photosensitive layer, the surface charge is eliminated before transfer, and as a result, the possibility of causing image defects increases. Needs to be irradiated with an intensity that does not reach the surface layer of the photosensitive layer. In the image forming apparatus of the present invention, as described above, the holes generated in the lower part of the photosensitive layer neutralize the charge inside and on the surface of the photosensitive layer. Therefore, it is not necessary for the neutralizing light to reach the surface of the photosensitive layer. If it reaches the lower part, a sufficient static elimination effect can be obtained.

<Cleaner>
The image forming apparatus 20 may be provided with a cleaner 27 that is a cleaning unit that removes and collects toner remaining on the outer peripheral surface of the photoreceptor 21 after the toner image is transferred. The cleaner 27 may include, for example, a cleaning blade that is pressed against the outer peripheral surface of the photoconductor 21 and peels off the remaining toner, and a recovery casing that stores the toner peeled off by the cleaning blade.

<Fixing means>
The image forming apparatus 20 may be provided with a fixing device 31 that is a fixing unit for fixing the transferred image on the downstream side where the transfer paper 30 that has passed between the photosensitive member 21 and the transfer device 26 is conveyed. Good. The fixing device 31 is a fixing unit that fixes the transferred image. The fixing device may include, for example, a heating roller 31a having a heating unit (not shown), and a pressure roller 31b that is provided to face the heating roller 31a and is pressed by the heating roller 31a to form a contact portion.

<Operation of Image Forming Apparatus>
The image forming operation by the image forming apparatus 20 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 a corresponding to image information is irradiated from the exposure means 28 to the surface of the photoreceptor 21. By this exposure, the surface charge of the exposed portion of the photoreceptor 21 is removed, and a difference in surface potential occurs between the exposed portion and the non-exposed portion, whereby an electrostatic latent image is formed.
A semiconductor laser is generally used as the light source of the exposure means 28.

  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 to which the toner image has been transferred is conveyed to a fixing device 31 by a conveying means, and is heated and pressurized when passing through a contact portion between a heating roller 31a and a pressure roller 31b of the fixing device 31, and toner 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 20 by a conveying unit (not shown).

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 by the cleaner 27 and collected.
The surface charge of the photoreceptor 21 from which the toner has been removed in this way and the residual electrons inside the single-layer type photosensitive layer are generated by charge removal from the conductive substrate side, thereby generating charges below the single-layer type photosensitive layer. The electrostatic latent image on the surface of the photoreceptor 21 disappears due to erasing by holes generated in the material. 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 image forming apparatus of the present invention together with comparative examples. However, the present invention is not limited to the following examples.

(Example 1)
An ITO film was deposited on a glass tube having a thickness of 1.8 mm (t), a diameter of 30 mm (φ), and a length of 300 mm to produce a translucent conductive substrate.

  Next, 1 part by weight of metal-free phthalocyanine as a charge generating substance, 16 parts by weight of a polycarbonate resin (Mitsubishi Gas Chemical Co., Ltd .: Z-400), 10 parts by weight of a hole transport material represented by the following structural formula (1), , 5 parts by weight of 3,5-dimethyl-3 ′, 5′-di-t-butyldiphenoquinone, which is an electron transporting substance, and 0.5 parts by weight of 2,6-di-t-butyl-4-methylphenol And 130 parts by weight of tetrahydrofuran (THF) were dispersed with a ball mill for 12 hours to prepare a photosensitive layer coating solution. This coating solution was applied onto the conductive substrate by dip coating and then dried with hot air at a temperature of 110 ° C. for 1 hour to form a single-layer type photosensitive layer having a thickness of 25 μm.

Thus, an electrophotographic photosensitive member having the layer structure of FIG. 2 was produced.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(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 ) as an intermediate layer material And 9 parts by weight of a copolymer nylon resin (Toray Industries, Inc .: CM8000) are 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. An intermediate layer coating solution was prepared. The prepared coating solution was applied onto the same light-transmitting conductive substrate as in Example 1 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 photosensitive member having the layer structure of FIG. 3 was produced.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

Example 3
An electrophotographic photoreceptor in the same manner as in Example 2, except that metal-free naphthalocyanine is used as the charge generation material of the single-layer type photosensitive layer and a naphthoquinone compound represented by the following structural formula (2) is used as the electron transport material. Was made.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

Example 4
Except that hydroxygallium phthalocyanine (manufactured by Nippon Materials Co., Ltd.) was used as the charge generation material of the single-layer type photosensitive layer, and a compound represented by the following structural formula (3) was used as the electron transport material, the same as in Example 2. An electrophotographic photosensitive member was produced.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Example 5)
Except for using 5 parts by weight of a coumarin dye represented by the following structural formula (4) as the charge generation material of the single-layer type photosensitive layer and using a quinone compound represented by the following structural formula (5) as the electron transporting material, An electrophotographic photosensitive member was produced in the same manner as in Example 2.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

Example 6
Except that 5 parts by weight of an azo dye represented by the following structural formula (6) was used as the charge generation material of the single-layer type photosensitive layer, and the compound represented by the structural formula (3) was used as the electron transporting material. In the same manner as in Example 2, an electrophotographic photosensitive member was produced.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Example 7)
In the same manner as in Example 2, an intermediate layer was formed, and on the upper part, 5 parts by weight of a perylene dye represented by the following structural formula (7) as a charge generating substance and a polycarbonate resin (manufactured by 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 (1), 5 parts by weight of the compound represented by the structural formula (3) as an electron transport material, and 2,6-di- After dip-coating a photosensitive layer coating solution in which 0.5 parts by weight of t-butyl-4-methylphenol and 120 parts by weight of THF are dispersed by a ball mill for 12 hours, the film is dried in hot air at a temperature of 110 ° C. for 1 hour. A 25 μm single layer type photosensitive layer was formed to prepare an electrophotographic photosensitive member.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Example 8)
Using 5 parts by weight of a perylene dye represented by the following structural formula (8) as the charge generation material of the single-layer type photosensitive layer, using a compound represented by the following structural formula (9) as the hole transport material and alizarin as the electron transport material. An electrophotographic photosensitive member was produced in the same manner as in Example 7 except that.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

Example 9
An electrophotographic photosensitive member is produced in the same manner as in Example 8, except that a single-layer type photosensitive layer is formed using a coating solution obtained by removing the electron transport material alizarin from the coating solution for the photosensitive layer used in Example 8. did.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Example 10)
On the photoreceptor of Example 7, 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) Parts are mixed and subjected to a hydrolysis reaction at room temperature for 16 hours, followed by 1 part by weight of an antioxidant (manufactured by Sankyo Co., Ltd .: Sanol LS2626), a compound having a charge transporting structural unit represented by the following structural formula (10) After applying 5 parts by weight, colloidal silica (methanol dispersion, solid content 30% by weight) 20 parts by weight, and adding 1 part by weight of aluminum acetylacetonate as a curing catalyst and applying the coating solution for forming a protective layer by a ring coating method Then, it was cured and dried at a temperature of 120 ° C. for 2 hours to produce an electrophotographic photoreceptor having a protective layer having a thickness of 1 μm.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Comparative Example 1)
Except that a single-layer type photosensitive layer was formed using a coating solution obtained by removing the compound represented by the structural formula (1) as the hole transport material from the coating solution for the photosensitive layer used in Example 2, Similarly, an electrophotographic photosensitive member was produced.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Comparative Example 2)
Except that a single-layer type photosensitive layer was formed using a coating solution obtained by removing the compound represented by the structural formula (3), which is an electron transport material, from the coating solution for the photosensitive layer used in Example 6, and Similarly, an electrophotographic photosensitive member was produced.
The produced photoreceptor was used in the following evaluation test in combination with a charge eliminating means capable of irradiating from the conductive substrate side.

(Comparative Example 3)
Example 2 except that the translucent conductive substrate was replaced with a (non-translucent) aluminum cylindrical tube having a thickness of 0.8 mm (t) × diameter 30 mm (φ) × length 300 mm. In the same manner as above, an electrophotographic photosensitive member was produced.
The produced photoreceptor was subjected to the following evaluation test in combination with a charge eliminating means capable of irradiating from the surface of the photoreceptor.

(Comparative Example 4)
In Example 7, the electrophotographic photosensitive substrate was changed in the same manner as in Example 7 except that the translucent conductive substrate was replaced with an aluminum cylindrical tube having a thickness of 0.8 mm (t) × diameter 30 mm (φ) × length 300 mm. The body was made.
The produced photoreceptor was subjected to the following evaluation test in combination with a charge eliminating means capable of irradiating from the surface of the photoreceptor.

(Comparative Example 5)
An intermediate layer was formed in the same manner as in Example 2 on an aluminum cylindrical tube having a thickness of 0.8 mm (t) × diameter 30 mm (φ) × length 300 mm.
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 THF, 2 parts by weight of oxotitanium phthalocyanine was added and dispersed with a paint shaker for 2 hours. A coating solution for charge generation layer was prepared. This coating solution was dip-coated on the previously formed intermediate layer and then dried to form a charge generation layer having a thickness of 0.3 μm.

Next, 10 parts by weight of the hole transport material represented by the structural formula (1), 16 parts by weight of a polycarbonate resin (Mitsubishi Gas Chemical Co., Ltd .: Z400), and 2,6-di-t-butyl-4-methyl A hole transport layer coating solution was prepared by dissolving 0.5 parts by weight of phenol in 90 parts by weight of THF. This coating solution was dip-coated on the previously formed charge generation layer and then dried to form a hole transport layer having a thickness of 25 μm. This photoreceptor is a so-called general laminated photoreceptor.
The produced photoreceptor was subjected to the following evaluation test in combination with a charge eliminating means capable of irradiating from the surface of the photoreceptor.

Table 1 shows a summary of the structures of the photoreceptors used in Examples 1 to 10 and Comparative Examples 1 to 5.

[Evaluation 1]
Each electrophotographic photosensitive member produced as described above was charged at −6.5 kV by a contact roller method at a temperature / humidity of 25 ° C./50%, and a charging potential V ₀ [V] which is a surface potential immediately after charging. And the surface potential V _L [V] of the electrophotographic photosensitive member at 80 msec after exposure with light of the wavelength shown in Table 2 obtained by spectroscopy with a monochromator is removed from the conductive substrate side of the photosensitive member. The measurement was performed in a test apparatus (Gentech Co., Ltd .: CYNTHIA56SN) remodeled so that it could be irradiated with light.

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 neutralizing with the light of the wavelength shown in Table 2 obtained by spectroscopy with a monochromator and repeating the charge-exposure-discharge process (one process 750 msec) 100 times continuously. V ₀ [V] and the surface potential V _L [V] after exposure were also measured.
A spectrophotometer is used to measure the transmittance of the conductive substrate (Example 1) with respect to static elimination light or the combined transmittance of the conductive substrate and the intermediate layer (Examples 2 to 10, Comparative Examples 1 and 2). U-3410 (manufactured by Hitachi, Ltd.) was used.

The results are shown in Table 2.
In Comparative Examples 3 to 5, the static elimination light was applied from the surface of the photoreceptor (photosensitive layer surface side) as usual.

  As shown in Table 2, in Examples 1 to 10, the electrical characteristics of the photoreceptor were stable even when repeatedly used with negative charging. In Example 9 in which a perylene dye having an electron transporting capability was used in the photosensitive layer, the photoreceptor had sufficient electrical characteristics even without the addition of an electron transporting substance.

  On the other hand, if the hole transport material is not added to the photosensitive layer as in Comparative Example 1, the initial sensitivity is lowered. At the time of repetition, it was confirmed that the surface potential of the photoreceptor rose to −850 to −900 V, and the potential did not drop sufficiently even after exposure. This is presumably because holes (particularly generated in the lower part of the photosensitive layer during static elimination) cannot move in the photosensitive layer.

  When an azo dye having an extremely low electron transport ability was used in the photosensitive layer without adding an electron transport material as in Comparative Example 2, the surface potential was hardly lowered even after exposure, and the sensitivity was not high from the beginning. .

As in Comparative Examples 3 and 4, when neutralizing light was irradiated from the surface layer side of the single-layer type photoreceptor, it was confirmed that the surface potential of the photoreceptor increased during repetition, and the potential did not decrease even when exposed. This is presumably because the charge removal is insufficient and electrons stay in the photosensitive layer.
In Comparative Example 5 using a laminated photoreceptor, there was no problem with respect to sensitivity.

  Comparing Examples 1 and 2, it can be seen that the chargeability of the photoconductor is slightly increased when the photoconductor includes the intermediate layer.

[Evaluation 2]
Each electrophotographic photosensitive member produced in Examples 2, 5, 7, and 9 and Comparative Examples 1 and 2 was mounted on a Sharp copier AR-F330 (with a semiconductor laser having an oscillation wavelength shown in Table 3 as an exposure light source and charged) The container is remodeled into a contact roller type, and a standard image with text and photographs is repeated 100 times by remodeling so that it can irradiate static electricity (using a static elimination lamp) from the conductive substrate side; see Fig. 1) Output and confirmed the presence of memory phenomenon.
The results are shown in Table 3.

  As shown in Table 3, a memory image did not appear in the image forming apparatus of the example of the present invention, whereas a memory image appeared in the image forming apparatus of the comparative example.

[Evaluation 3]
A contact roller type charger, an exposure unit (laser oscillation wavelength is shown in Table 4) that can variably control the laser beam diameter from 300 to 6000 dpi by controlling the aperture diameter, and a liquid toner having a toner with a particle diameter of 0.2 μm. In an experimental machine having a developing section capable of developing, each electrophotographic photosensitive member of Examples 2, 5, 7 and Comparative Example 5 was used, and a cycle of 1 dot line with 1 dot and 1 dot line and 1 blank space repeated. These 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 image forming apparatus of the example of the present invention had 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 5 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 a periodic 1 dot line is blurred and unclear as a line cannot be recognized. Only a good image was obtained. This is because holes generated by charge separation in the charge generation layer inside (in the deep part) of the photoreceptor diffuse in the surface direction while moving through the charge transport layer to the surface layer.

(Examples 11 and 12)
A semiconductor laser having the oscillation wavelength shown in Table 5 is mounted as the exposure light source, the time between the exposure and development process is adjusted to 100 msec, the time between the exposure and transfer process is adjusted to 150 msec, and the time between the exposure and the discharge process is 150 msec. The same electrophotographic photosensitive member as in Examples 2 and 5 is mounted on the remodeling machine (see FIG. 4), and the charging potential V ₀ [V] immediately after charging (−6.5 kV) is shown in Table 5. The surface potential V _L [V] at 100 msec after exposure with light, the surface potential V ₀ [V] immediately after charging after repeating 100 times continuously, and the surface potential V _L [V] after exposure were measured. .
The results are shown in Table 5.

(Examples 13 and 14)
The measurement was performed in the same manner as in Examples 11 and 12 except that the time between the exposure and the charge removal process was arranged at a position of 400 msec (see FIG. 1).
The results are shown in Table 5.

By comparing the results of Examples 11 and 12 with the results of Examples 13 and 14, the image forming apparatus whose discharge position is before the transfer position is almost equivalent to the image forming apparatus whose discharge position is after the transfer position. It can be understood that electrical characteristics can be obtained.
Therefore, according to the image forming apparatus of the present invention, it is possible to simultaneously improve the process speed and reduce the diameter of the photosensitive member (miniaturization of the apparatus).

1 is a schematic side view illustrating a configuration of an embodiment of an image forming apparatus of the present invention. FIG. 2 is a schematic enlarged cross-sectional view showing a configuration of a main part in one embodiment of a photoreceptor that can be used in the image forming apparatus of the present invention. It is a model expanded sectional view which shows the structure of the principal part in another one form of the photoreceptor which can be used for the image forming apparatus of this invention. It is a model side view which shows the structure of another one form of the image forming apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductive substrate 2 Intermediate layer 4 Single layer type photosensitive layer 5 Hole transport material 6 Electron transport material 7 Charge generation material

20 Image forming apparatus 21 of the present invention Electrophotographic photosensitive member 24 Charger 25 Developer 26 Transfer device 27 Cleaner 28 Exposure means 28a Exposure light 29 Neutralization means 30 Transfer paper 31 Fixing device 31a Heating roller 31b Pressure roller

Claims (11)

  A single layer type photosensitive layer containing a charge generating substance and a hole transporting substance having electron transporting ability or a charge generating substance, an electron transporting substance and a hole transporting substance is provided on a conductive substrate that is transparent to static elimination light. An electrophotographic photoreceptor, charging means for negatively charging the electrophotographic photoreceptor, exposure means for irradiating exposure light on the electrophotographic photoreceptor to form an electrostatic latent image corresponding to image information, A developing unit that develops the electrostatic latent image to form a toner image, a transfer unit that transfers the toner image, and the electrophotographic photosensitive member that is irradiated with the charge-removing light from the conductive substrate side of the electrophotographic photosensitive member. An electrophotographic image forming apparatus comprising: at least a charge removing unit that removes residual charges on the body.   The electrophotographic image forming apparatus according to claim 1, wherein the charge generation material is a phthalocyanine dye or a polycyclic condensation pigment.   The electrophotographic image forming apparatus according to claim 1, wherein the electron transport material is a quinone dye or a perylene dye.   The electrophotographic image forming apparatus according to claim 1, wherein the single-layer type photosensitive layer contains 60% by weight or less of an electron transport material with respect to the hole transport material.   The electrophotographic image forming apparatus according to any one of claims 1 to 4, wherein the charge generation material has an electron transporting ability, and the single-layer type photosensitive layer does not contain another electron transporting material.   The electrophotographic image forming apparatus according to claim 1, wherein the electrophotographic photosensitive member further includes an intermediate layer directly on the conductive substrate.   The electrophotographic image forming apparatus according to claim 1, wherein the charging unit is a contact charging method.   The electrophotographic image forming apparatus according to claim 1, wherein the exposure unit includes a semiconductor laser having an oscillation wavelength in a range of 380 to 650 nm as an exposure light source.   The electrophotographic image forming apparatus according to claim 1, wherein the charge eliminating unit is a charge eliminating lamp.   The electrophotographic image forming apparatus according to claim 9, wherein the charge eliminating unit irradiates the charge eliminating light before the toner image formed by the developing unit is transferred by the transfer unit.   The electrophotographic image forming apparatus according to claim 1, wherein a reversal development method is used.

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