JP2017156518A - Sheet-like electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-like electrophotographic photoreceptor that exhibits satisfactory solvent resistance to a liquid toner and electrical characteristics for a long period even when used for an image forming apparatus of a wet developing system.SOLUTION: In a sheet-like electrophotographic photoreceptor having at least a conductive layer, a charge generating layer, and a charge transport layer laminated in this order on a resin sheet substrate, and is used for a wet developing system, the charge transport layer includes at least a first charge transport layer that contains a charge transport material and a binder resin (A), and a second charge transport layer that contains a charge transport material and a binder resin (B); the first charge transport layer faces the charge generating layer, and the second charge transport layer is an outermost surface layer.SELECTED DRAWING: None

Description

  The present invention relates to a sheet-like electrophotographic photosensitive member used in an image forming apparatus of a wet development type, a manufacturing method thereof, and an image forming apparatus equipped with the same.

  Electrophotographic technology is widely used in fields such as light printing machines, copiers, and various printers because of its immediacy and high-quality images. As a photoreceptor that is the core of the electrophotographic technology, an organic photoreceptor having advantages such as non-pollution, easy film formation, and easy manufacture is used. As the organic photoconductor, a function-separated type multi-layer photoconductor using a charge generation layer containing a charge generation material, a charge transport material containing a charge transport material and a resin in a stacked manner is currently most common.

  Multilayered photoreceptors can be obtained by combining highly efficient charge generating substances and charge transporting substances to obtain highly sensitive photoreceptors, having a wide material selection range, and providing highly safe photoreceptors. The layer can be easily formed by coating, has high productivity, and is advantageous in terms of cost. Therefore, it is the mainstream of photoreceptors, and has been developed and put into practical use. Among them, an endless belt-like photoreceptor in which a sheet-like photoreceptor is joined at the end is preferred because of its flexible nature and a high degree of freedom when being arranged in the apparatus, and also has a wide area. For example, a photosensitive member in a form in which a sheet-like photosensitive member is wound around a drum is preferably used because it can be easily manufactured, is inexpensive, and can be easily replaced (see, for example, Patent Documents 1 and 2).

  In addition, the development method in the image forming apparatus is roughly classified into a dry development method and a wet development method. According to the wet development method, the toner particles in the solvent of the liquid developer are charged with a resin or a charge constituting the toner particles. The control agent is charged to a predetermined polarity and is characterized by being easily dispersed stably in a solvent. Therefore, the wet development method can form an image with high resolution by using fine toner particles, and is advantageous in stably realizing high-quality image formation, as compared with the dry development method.

  However, in carrying out the wet development method, the liquid developer solvent is required to have high electrical insulation, and therefore, hydrocarbon solvents having high solubility such as isoparaffin are frequently used. Therefore, since such a hydrocarbon solvent and the photosensitive layer are in contact with each other for a long time, a defect called a crack is generated on the surface of the photosensitive member, which appears as a streak defect on the printed image, thereby improving durability. May interfere. Accordingly, for example, it has been proposed to prevent elution of the charge transport agent by using an organic photoreceptor having an overcoat layer made of a thermosetting resin on the surface of the organic photoreceptor. (For example, refer to Patent Document 3). In addition, it has been proposed that a charge transport polymer is provided to impart a charge transport function to the binder resin itself, and that the solvent resistance is expressed by reducing the content of the charge transport agent. (For example, refer to Patent Document 4).

Japanese Utility Model Publication No. 6-16966 JP 2000-10315 A Japanese Patent Laid-Open No. 10-221875 JP 2003-57856 A

  However, the electrophotographic photoreceptor for wet development described in Patent Document 3 has a new problem that sensitivity is remarkably deteriorated and a manufacturing cost is increased by newly forming an overcoat layer. In addition, the electrophotographic photoreceptor for wet development described in Patent Document 4 has a problem that the molecular design of the charge transport polymer is not easy and it is difficult to stably produce it. That is, the physical properties of the binder resin varied, and as a result, there were problems such as variations in sensitivity characteristics and elution amount in the photosensitive layer.

  That is, an object of the present invention is to provide a sheet-like electrophotographic photosensitive member that has good solvent resistance and electrical characteristics for a liquid toner over a long period of time even when used in an image forming apparatus of a wet development type.

In the sheet-like photoreceptor that is used in an image forming apparatus of a wet development type, the present inventors have a plurality of charge transport layers, and each layer contains a specific binder resin, thereby preventing liquid toner. It has been found that both solvent resistance and electrical characteristics can be achieved. That is, the gist of the present invention resides in the following (1) to (5).
(1) In a sheet-like electrophotographic photosensitive member used in a wet development method in which at least a conductive layer, a charge generation layer, and a charge transport layer are laminated in this order on a resin sheet substrate, the charge transport layer is at least a charge transport layer. A first charge transport layer containing a substance and a binder resin (A), and a second charge transport layer containing a charge transport material and a binder resin (B), wherein the first charge transport layer comprises the charge A sheet-like electrophotographic photosensitive member, facing the generation layer, wherein the second charge transport layer is an outermost layer.

  Binder resin (A): A film containing 35 parts of a charge transport material represented by the following formula (1) and 4 parts of an antioxidant represented by the following formula (2) with respect to 100 parts of the binder resin (A). A resin satisfying a bright portion potential of 100 V or less when a charge transport layer having a thickness of 18 μm is measured by a dynamic measurement method.

Binder resin (B): A resin having an elastic deformation rate of 42% or more.
(2) The sheet-like electrophotographic photosensitive member according to (1), wherein the binder resin (A) is a polycarbonate resin and the binder resin (B) is a polyarylate resin.
(3) The sheet-like electrophotographic photosensitive member according to (1) or (2), wherein the film thickness of the first charge transport layer is larger than the film thickness of the second charge transport layer.
(4) The sheet-like electrophotographic photosensitive member according to any one of (1) to (3), wherein an end portion of the first charge transport layer is exposed.
(5) An image forming apparatus comprising the electrophotographic photosensitive member according to any one of (1) to (4) and a liquid toner.

  According to the present invention, when used in an image forming apparatus of a wet development system, a photoreceptor that has good solvent resistance over a long period of time, does not generate cracks, and does not peel off from the end face of the photosensitive layer. Can be obtained.

1 is a conceptual diagram illustrating an example of an image forming apparatus using an electrophotographic photosensitive member of the present invention. 1 is an X-ray diffraction pattern of oxytitanium phthalocyanine used in an example of the present invention. It is the schematic of the photoreceptor sheet | seat used in the Example of this invention. It is an X-ray diffraction pattern of phthalocyanine used in the examples. It is an X-ray diffraction pattern of phthalocyanine used in the examples.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

[Sheet electrophotographic photoreceptor]
The electrophotographic photosensitive member of the present invention is a sheet-like electrophotographic photosensitive member used in a wet development method in which at least a conductive layer, a charge generation layer, and a charge transport layer are laminated in this order on a resin sheet substrate. The layer comprises at least a first charge transport layer containing a charge transport material and a binder resin (A), and a second charge transport layer containing a charge transport material and a binder resin (B), The charge transport layer faces the charge generation layer, and the second charge transport layer is the outermost layer. An undercoat layer may be provided between the sheet substrate and the charge generation layer. Another layer may be further included between the first charge transport layer and the second charge transport layer.

  The sheet-like electrophotographic photoreceptor preferably has a sheet-like conductive support, and has a photosensitive layer and an uncoated region of the photosensitive layer in the sheet surface. The uncoated area of the photosensitive layer can be produced by regulating the coating width of the photosensitive layer. Restricting the coating width means that when a photosensitive layer is applied on a sheet-like conductive support, the width to which the photosensitive layer is to be applied is set and applied.

The continuity necessary for the electrophotographic photosensitive member to exhibit desired electrical characteristics is ensured by a conductive support in an uncoated area (for example, an aluminum layer deposited on a PET film). Although the production position of the uncoated region is not particularly limited, it is usually produced at the end of the sheet and preferably produced at the end in the major axis direction, and is produced at either one of the major axis directions. It is particularly preferred. Moreover, it is preferable to produce the support body part which excluded electroconductivity in the place different from the non-application area | region for ensuring conduction | electrical_connection. In that case, an insulating part can be obtained, for example, by peeling the aluminum layer with a sodium hydroxide solution or by forming an undeposited portion by masking during deposition. The insulating region thus produced makes it easy to wind the photoreceptor sheet around the drum base with electrostatic force. Although the production position is not particularly limited, it is usually produced at the end of the sheet and preferably produced at the end in the major axis direction, particularly preferably produced at either one of the major axis directions. .

<Conductive support>
The conductive support of the present invention is preferably a resin or paper, in particular, a biaxially stretched film laminated with a metal layer, and the biaxially stretched film is made of polyethylene terephthalate, polybutylene terephthalate or the like. Polyester resins, polyolefin resins such as polyethylene and polypropylene, polyvinyl chloride resins, and the like, and linear polyester resins, particularly polyethylene terephthalate are preferable from the viewpoint of mechanical strength and dimensional stability. In addition, the thickness of a film is 30-150 micrometers normally, Preferably it is 50-120 micrometers, More preferably, it is 70-100 micrometers.

  Moreover, as a metal of the metal vapor deposition layer which comprises an electroconductive support body, copper, nickel, zinc, aluminum, ITO (indium-tin oxide) etc. are mentioned, Among these, aluminum is preferable. The thickness of the metal vapor deposition layer is usually about 40 to 100 nm, and the vapor deposition onto the resin film is performed by a known vapor deposition method such as electrothermal heating melt vapor deposition, ion beam vapor deposition, or ion plating. Made in As the metal layer, a metal foil such as an aluminum foil or a nickel foil, or a laminate film obtained by laminating these metals can be used. In this case, the metal foil is preferably 5 μm or less. Further, a conductive material having an appropriate resistance value can be laminated on the metal foil. The support surface may be smooth, or may be roughened by mixing particles having a large particle diameter during resin film formation.

<Underlayer>
An undercoat layer may be provided between the conductive support and the photosensitive layer in order to improve adhesion and blocking properties. As the undercoat layer, a resin, a resin in which particles such as a metal oxide are dispersed, or the like is used. Examples of metal oxide particles used for the undercoat layer include metal oxide particles containing one metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, iron oxide, calcium titanate, titanium Examples thereof include metal oxide particles containing a plurality of metal elements such as strontium acid and barium titanate. Only one type of particles may be used, or a plurality of types of particles may be mixed and used. Among these metal oxide particles, titanium oxide and aluminum oxide are preferable, and aluminum oxide is particularly preferable when the conductive layer of the conductive support is a thin film. The surface of the aluminum oxide particles may be treated with an inorganic substance such as tin oxide, titanium oxide, antimony oxide, zirconium oxide, or silicon oxide, or an organic substance such as stearic acid, polyol, or silicone. The crystal form of the aluminum oxide particles is not limited.

In addition, various particle diameters of the metal oxide particles can be used. Among these, from the viewpoint of characteristics and liquid stability, the average primary particle diameter is preferably 10 nm to 100 nm, particularly preferably 10 nm to 50 nm. It is as follows.
The undercoat layer is preferably formed in a form in which metal oxide particles are dispersed in a binder resin. As binder resin used for the undercoat layer, phenoxy, epoxy, polyvinylpyrrolidone, polyvinyl alcohol, casein, polyacrylic acid, celluloses, gelatin, starch, polyurethane, polyimide, polyamide, etc. are used alone or in a cured form together with a curing agent. Among them, alcohol-soluble copolymerized polyamides, modified polyamides and the like are preferable because they exhibit good dispersibility and coating properties.

  The addition ratio of the inorganic particles to the binder resin is preferably in the range of 10% by mass to 500% by mass in terms of stability of the dispersion and coatability. The film thickness of the undercoat layer is preferably from 0.1 to 25 μm from the viewpoint of photoreceptor characteristics and applicability. Moreover, you may add a well-known antioxidant etc. to an undercoat layer.

<Charge generation layer>
The charge generation layer contains a charge generation material and also contains a binder resin and other components used as necessary. Specifically, such a charge generation layer is prepared by, for example, dissolving or dispersing a charge generation substance or the like and a binder resin in a solvent to prepare a coating solution (coating solution for forming a charge generation layer). (When an undercoat layer is provided, on the undercoat layer) and dried.

  Examples of charge generation materials include selenium and its alloys, cadmium sulfide, and other inorganic photoconductive materials; phthalocyanine pigments, azo pigments, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, anthanthrone pigments, benzimidazole pigments Various photoconductive materials such as organic pigments; In particular, organic pigments are preferable, and phthalocyanine pigments and azo pigments are particularly preferable. Note that one type of charge generation material may be used, or two or more types may be used in any combination and in any ratio. When a phthalocyanine compound is used as the charge generation material, specific examples thereof include metal-free phthalocyanine; metals such as copper, indium, gallium, tin, titanium, zinc, vanadium, silicone, germanium, or oxides, halides thereof, and the like Coordinated phthalocyanines; etc. are used. Examples of the ligand to the trivalent or higher metal atom include a hydroxyl group and an alkoxy group in addition to the oxygen atom and chlorine atom shown above. Particularly preferred are X-type, τ-type metal-free phthalocyanine, titanyl phthalocyanine such as A-type, B-type, and D-type, vanadyl phthalocyanine, chloroindium phthalocyanine, chlorogallium phthalocyanine, and hydroxygallium phthalocyanine. Incidentally, the D type is a metastable type also called Y type, and in the powder X-ray diffraction using CuKα ray, the crystal has a diffraction angle 2θ ± 0.2 ° showing a clear peak at 27.3 °. It is a type.

  The phthalocyanine compound may be a single compound or may be in some mixed state. As a mixed state in a phthalocyanine compound or in a crystalline state, each component may be mixed and used later, or a mixed state is produced in the production and processing steps of phthalocyanine compounds such as synthesis, pigmentation, crystallization, etc. But you can. As such treatment, acid paste treatment, grinding treatment, solvent treatment and the like are known.

  As binder resin, polyester resin, polyvinyl acetate resin, polyacrylate resin, polymethacrylate resin, polyester resin, polycarbonate resin, polyvinyl acetoacetal resin, polyvinyl propional resin, polyvinyl butyral resin, phenoxy resin, epoxy resin, Used in a form bound with various binder resins such as urethane resin, cellulose ester, and cellulose ether. In this case, the polyester resin according to the present invention may be used as the binder resin. Moreover, 1 type may be used for binder resin and it may use 2 or more types together by arbitrary combinations and arbitrary ratios.

The use ratio of the charge generation material in the charge generation layer is usually 30 parts by mass or more, preferably 50 parts by mass or more, and usually 500 parts by mass or less, preferably 300 parts by mass or less with respect to 100 parts by mass of the binder resin. . The thickness of the charge generation layer is usually 0.1 μm or more, preferably 0.15 μm or more, and usually 1 μm or less, preferably 0.6 μm or less.
The charge generation layer may contain components other than those described above as long as the effects of the present invention are not significantly impaired. Plasticizers, antioxidants, ultraviolet absorbers, electron withdrawing compounds, dyes, pigments used to improve film-forming properties, flexibility, coating properties, stain resistance, gas resistance, light resistance, etc. , Leveling agents, residual potential inhibitors, dispersion aids, visible light shading agents, sensitizers, surfactants, and the like.

<Charge transport layer>
The charge transport layer includes at least a first charge transport layer containing a charge transport material and a binder resin (A), and a second charge transport layer containing a charge transport material and a binder resin (B). The first charge transport layer faces the charge generation layer, and the second charge transport layer is the outermost surface layer. Each layer of the plurality of charge transport layers contains a charge transport material, and also contains a binder resin and other components used as necessary. Specifically, such a charge transport layer is prepared by, for example, dissolving or dispersing a charge transport material and a binder resin in a solvent to prepare a coating liquid (coating liquid for forming a charge transport layer), which is used as the charge generation layer. It can be obtained by coating and drying on top.

  The charge transport material is not particularly limited, and any material can be used. Examples of known charge transport materials include aromatic nitro compounds such as 2,4,7-trinitrofluorenone, cyano compounds such as tetracyanoquinodimethane, electron withdrawing materials such as quinone compounds such as diphenoquinone, and carbazole derivatives. , Indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, heterocyclic compounds such as benzofuran derivatives, aniline derivatives, hydrazone derivatives, aromatic amine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives and multiple types of these compounds Or an electron donating substance such as a polymer having a group composed of these compounds in the main chain or side chain. Among these, carbazole derivatives, aromatic amine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, and those in which a plurality of these compounds are bonded are preferable. Any one of these charge transport materials may be used alone, or two or more thereof may be used in any combination. The following specific examples are given for illustrative purposes, and any known charge transport material may be used as long as it does not contradict the spirit of the present invention.

  As for the ratio of the binder resin and the charge transport material in the charge transport layer, the charge transport material is usually used at a ratio of 10 parts by weight or more with respect to 100 parts by weight of the binder resin in each charge transport layer. Among these, 20 parts by mass or more is preferable from the viewpoint of residual potential reduction, and more preferably 30 parts by mass or more from the viewpoint of stability and charge mobility when repeatedly used. On the other hand, from the viewpoint of thermal stability of the photosensitive layer, the charge transport material is usually used at a ratio of 120 parts by mass or less. Among these, 100 parts by mass or less is preferable from the viewpoint of compatibility between the charge transport material and the binder resin, 70 parts by mass or less is more preferable from the viewpoint of printing durability, and 50 parts by mass or less is particularly preferable from the viewpoint of scratch resistance. From the viewpoint of crack resistance, it is preferable that the content of the charge transport material is smaller in the second charge transport layer than in the first charge transport layer.

  The binder resin (A) contains 35 parts of a charge transport material represented by the following formula (1) and 4 parts of an antioxidant represented by the following formula (2) with respect to 100 parts of the binder resin (A). This resin satisfies the absolute value of the bright part potential of 100 V or less when a charge transport layer having a thickness of 18 μm is measured by a dynamic measurement method. From the viewpoint of electrical characteristics, it is preferably 80 V or less, more preferably 60 V or less. A polycarbonate resin is preferable as the resin that satisfies this characteristic. Specific examples of suitable structures are shown below.

  Other binder resins may be mixed and used together. In that case, the content of the binder resin (A) is 50 parts by mass or more, preferably 100 parts by mass of the total resin in the first charge transport layer. 70 parts by mass or more is preferable from the viewpoint of electrical characteristics. Other resins used in combination include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, thermoplastic resins such as polycarbonate, polyester, polyester polycarbonate, polysulfone, phenoxy, epoxy, and silicone resin. And various thermosetting resins.

The binder resin (B) is a resin having an elastic deformation rate of 42% or more. From the viewpoint of crack resistance, it is preferably 43% or more, more preferably 44% or more. The upper limit is not particularly limited, but is usually 60% or less, preferably 55% or less. The elastic deformation rate of the resin was measured under an environment of a temperature of 25 ° C. and a relative humidity of 50% by using a microhardness meter FISHERSCOPE H100C (or HM2000 having the same performance as its successor) manufactured by Fischer. A measurement sample was measured by drying a resin solution on a glass plate and having a film thickness of 25 μm. For the measurement, a Vickers square pyramid diamond indenter having a facing angle of 136 ° is used. The measurement conditions are set as follows, the load applied to the indenter and the indentation depth under the load are continuously read, and profiles as shown in FIG. 3 plotted on the Y axis and the X axis are obtained.

<Measurement conditions>
Maximum indentation load 5mN
Load time 10 seconds
Unloading time 10 seconds
The elastic deformation rate is a value defined by the following formula, and is a ratio of work that the film performs by elasticity at the time of unloading with respect to the total work amount required for pushing.

Elastic deformation rate (%) = (We / Wt) × 100
In the above formula, the total work Wt (nJ) indicates the area surrounded by A-B-D-A in FIG. 2, and the elastic deformation work We (nJ) is the area surrounded by C-B-D-C. Indicates. As the elastic deformation rate is larger, the deformation with respect to the load is less likely to remain, and when the elastic deformation rate is 100, it means that no deformation remains. Polyarylate resin is preferable as the resin that satisfies this characteristic. Specific examples of suitable structures are shown below.

  Other binder resins may be mixed and used together. In that case, the content of the binder resin (B) is 50 parts by mass or more with respect to 100 parts by mass of the total resin in the second charge transport layer, preferably 70 parts by mass or more is preferable from the viewpoint of crack resistance. Other resins used in combination include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, thermoplastic resins such as polycarbonate, polyester, polyester polycarbonate, polysulfone, phenoxy, epoxy, and silicone resin. And various thermosetting resins.

  The thickness of each layer of the charge transport layer is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more for each layer from the viewpoint of long life, image stability, ensuring electrical characteristics, and crack resistance. Compared to the ratio of the first charge transport layer thickness required to ensure good electrical properties, the ratio of the second charge transport layer thickness required to ensure crack resistance performance Since the crack resistance performance is good even when the thickness is low, the film thickness of the first charge transport layer is preferably thicker than the film thickness of the second charge transport layer. From the viewpoint of the relationship between the thickness of each layer and the stability of image quality, the total thickness of the charge transport layer is preferably 10 μm or more and 40 μm or less. The film thickness of the first charge transport layer is preferably 5 to 25 μm, and the film thickness of the second charge transport layer is preferably 5 to 15 μm. The film thickness can be measured by a contact-type film thickness meter using eddy current or an optical non-contact film thickness meter using light interference.

[Method of applying each layer]
There is no restriction | limiting in the formation method of a photosensitive layer, Arbitrary methods can be used. For example, a coating solution obtained by dissolving or dispersing a substance to be contained in each layer in a solvent (charge generating layer forming coating solution, charge transport layer forming coating solution, dispersion type photosensitive layer forming coating solution, etc.) sequentially. It is formed by applying and drying. The coating method is not particularly limited, but as a coating method in the case of a photoreceptor (sheet-like photoreceptor) provided with a sheet-like support, a known die coating method, reverse coating method, gravure coating method, bar coating method, etc. It is formed by applying a coating solution on a support.

The coated photoreceptor is usually subjected to a drying process until the solvent of the coating film is substantially removed by evaporation. As a drying method, a conventionally known method can be applied. For example, it is performed by at least one of a heating roller, a hot air dryer, a steam dryer, an infrared dryer, a far infrared dryer and the like. The drying temperature is usually in the range of 60 ° C to 140 ° C.

When the photoreceptor of the present invention is a sheet-like photoreceptor, for example, both end portions thereof are joined by a known method such as ultrasonic fusion, and used as an endless belt. Further, for example, the sheet-like photoconductor can be used by being wound around a drum as it is. In the case of winding around a drum, for example, a thin roll may be held inside the drum for unwinding, or a single sheet may be wound.

  As a preferred embodiment, an aluminum vapor deposition layer is formed on the film so that the surface of one end of the film is exposed, and an end portion where the aluminum vapor deposition layer is exposed and the other end portion where the film is exposed are formed on the aluminum vapor deposition layer. Examples thereof include a sheet-like electrophotographic photoreceptor in which an undercoat layer, a charge generation layer, a first charge transport layer, and a second charge transport layer are formed. From the viewpoint of adhesiveness, it is preferable that the first charge transport layer is applied so that the end portion is exposed.

[Image forming apparatus]
Next, an embodiment of an image forming apparatus using the photosensitive member of the present invention will be described with reference to the drawings. However, the embodiment of the present invention is not limited to the following description, and can be arbitrarily modified and implemented without departing from the gist of the present invention.
FIG. 1 is a diagram schematically showing a main configuration of an image forming apparatus as an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus according to the present embodiment includes a photoreceptor 1, a charging device 2 as a charging unit, an exposure device 3 as an exposure unit, and a developing device 4 as a developing unit. Further, a transfer device 5 as a transfer unit, a cleaning device 6 as a cleaning unit, and a fixing device (not shown) as a fixing unit are provided as necessary.

The shape of the photoreceptor 1 is not particularly limited as long as it is the photoreceptor of the present invention described above. In FIG. 1, as an example, the above-described photosensitive layer is formed on the surface of a sheet-like support, and ultrasonic welding is performed. An endless belt-shaped photoconductor is shown.
The charging device 2 charges the photoreceptor 1 and is a device that uniformly charges the surface of the photoreceptor 1 to a predetermined potential. In FIG. 1, a corona discharge type charging device (corotron) is shown as an example of the charging device 2. However, for example, a corona charging device such as a scorotron or a contact type charging device such as a charging roller or a charging brush is often used. Used.

  In many cases, the photoreceptor 1 and the charging device 2 are designed to be removable from the main body of the image forming apparatus as a cartridge including both of them (hereinafter referred to as “photosensitive cartridge” as appropriate). For example, when the photoreceptor 1 or the charging device 2 deteriorates, the photoreceptor cartridge can be detached from the image forming apparatus main body, and another new photoreceptor cartridge can be mounted on the image forming apparatus main body. . In addition, the developer described later is often stored in a cartridge and designed to be removable from the main body of the image forming apparatus. It can be removed from the main body of the forming apparatus and another new cartridge can be mounted. Further, a cartridge provided with all of the photosensitive member 1, the charging device 2, and the developer may be used.

  The type of the exposure device 3 is not particularly limited as long as it can expose the photosensitive member 1 to form an electrostatic latent image on the photosensitive surface of the photosensitive member 1. Specific examples include halogen lamps, fluorescent lamps, lasers such as semiconductor lasers and He—Ne lasers, LEDs, and the like. Further, the support of the photoconductor may be made light transmissive, and exposure may be performed by a photoconductor internal exposure method.

The light used for the exposure is arbitrary. For example, the exposure may be performed using monochromatic light with a wavelength of 780 nm, monochromatic light with a wavelength slightly shorter than 600 nm to 700 nm, or monochromatic light with a short wavelength of 380 nm to 500 nm. . In particular, when light having a wavelength of 380 nm to 500 nm is used, the photoconductor can be exposed with light having a smaller spot size, and a high quality image having high resolution and high gradation can be formed. This is preferable when an image is desired.

  The developing device 4 represents a liquid developing device. The developer to be used is usually a toner obtained by dispersing a charged pigment and resin in a developing solvent (usually an organic solvent) having a high insulating property. Since the toner charged in the liquid is electrophoresed in response to the development electric field, the mobility of the toner in the developing solvent with viscosity is related, but the basic electric field model is the same as dry development. It is.

  2A and 2B schematically show an example of the unit configuration of the liquid developing device 4. FIG. The liquid developing device 4 shown in FIG. 2A includes a developing roller 7 and a squeeze roller 8 that are close to or in contact with the photoconductor 1 in this order along the transfer direction of the photoconductor 1. First, a developing solution having a low density is transferred from the developing roller 7 to the photosensitive member, and development is performed. Subsequently, excess developing solvent on the photosensitive member 1 is squeezed out with the squeeze roller 8 while borrowing the power of the electric field. A thin, uniform and high density toner image can be formed on the body 1.

  On the other hand, the liquid developing device 4 shown in FIG. 2B includes a developing roller 7 that is close to the photoreceptor 1 and a squeeze roller 8 that is in contact with the developing roller 7. Then, a thin toner layer having a high density and high charge is formed in advance on the developing roller 7 by an electric field and pressure between the developing roller 7 and the squeeze roller 8 before development, and then this toner layer is developed with the photoreceptor 1. By developing with an electric field between the rollers 7, a high-density toner image can be formed. If necessary, the liquid developing device 4 may be provided with a cleaning roller 9 for removing the developer remaining on the developing roller 7 and the squeeze roller 8.

  The type of the transfer device 5 is not particularly limited. For example, an apparatus using an arbitrary system such as an electrostatic transfer method such as corona transfer, roller transfer, or belt transfer, a pressure transfer method, or an adhesive transfer method may be used. it can. Here, it is assumed that the transfer device 5 includes a transfer charger, a transfer roller, a transfer belt, and the like disposed so as to face the photoreceptor 1. The transfer device 5 applies a predetermined voltage value (transfer voltage) having a polarity opposite to the charging potential of the toner, and transfers the toner image formed on the photoreceptor 1 onto a recording paper (paper, medium, transfer material) P. Is. FIG. 1 shows a direct transfer method from the photosensitive member to the recording paper P. However, the toner image is transferred from the photosensitive member to an intermediate transfer member such as an intermediate transfer belt and an intermediate transfer roller, and then transferred to the recording paper P. An intermediate transfer method can also be used.

There is no restriction | limiting in particular about the cleaning apparatus 6, For example, arbitrary cleaning apparatuses, such as a brush cleaner, a magnetic brush cleaner, an electrostatic brush cleaner, a magnetic roller cleaner, a blade cleaner, can be used. The cleaning device 6 is for scraping off residual toner adhering to the photoreceptor 1 with a cleaning member and collecting the residual toner.

When the toner transferred onto the recording paper P normally passes through a fixing device (not shown), the toner is heated and heated to a molten state, and is cooled after passing through to fix the toner on the recording paper P. The type of the fixing device is not particularly limited. For example, a fixing device of an arbitrary method such as heat roller fixing, flash fixing, oven fixing, pressure fixing, or the like can be provided.

  In the image forming apparatus configured as described above, an image is recorded as follows by a liquid developing type image forming method using a developer. That is, as shown in FIG. 1, first, the surface (photosensitive surface) of the photoreceptor 1 is charged to a predetermined potential (for example, −600 V) by the charging device 2 (charging process). At this time, charging may be performed by a DC voltage, or charging may be performed by superimposing an AC voltage on the DC voltage.

Subsequently, the photosensitive surface of the charged photoreceptor 1 is exposed by the exposure device 3 according to the image to be recorded, and an electrostatic latent image is formed on the photosensitive surface (exposure process). Then, development of the electrostatic latent image formed on the photosensitive surface of the photoreceptor 1 is performed by the developing device 4 (developing process).
As shown in FIGS. 2A and 2B, when the charged toner carried on the developing roller 7 of the developing device 4 is in contact with or close to the surface of the photoreceptor 1, a toner image corresponding to the electrostatic latent image is formed on the photoreceptor. 1 is formed on the photosensitive surface. This toner image is transferred onto the recording paper P by the transfer device 5 (manual printing process). Thereafter, toner remaining on the photosensitive surface of the photoreceptor 1 without being transferred is removed by the cleaning device 6 (cleaning step). After the transfer of the toner image onto the recording paper P, the final image is obtained by passing the toner image through the fixing device and thermally fixing the toner image onto the recording paper P (fixing step).

  Note that the image forming apparatus may have a configuration capable of performing the static elimination process in addition to the above-described configuration. The neutralization step is a step of canceling excess charged charges on the photosensitive member by exposing the photosensitive member or applying an alternating voltage. As the charge removal device, for example, an exposure device such as a fluorescent lamp or LED, a wire capable of applying an alternating current, or the like is used. When exposure is used in the static elimination process, the light intensity is often light having an exposure energy that is three times or more that of exposure light.

Further, the image forming apparatus may be further modified. For example, the image forming apparatus may have a configuration capable of performing processes such as a pre-exposure process and an auxiliary charging process, or a full color system configuration using a plurality of types of toner. Further, for example, instead of the endless belt-like photoconductor, a sheet-like photoconductor may be attached on a metal drum by electrostatic force or the like.
Note that the photosensitive member 1 can be combined with one or more of a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, a cleaning device 6 and a fixing device, as required. It may be configured as an (electrophotographic cartridge), and the electrophotographic cartridge may be detachable from a main body of an electrophotographic apparatus such as a copying machine or a laser beam printer. In this case, similarly to the cartridge described in the above embodiment, for example, when the photosensitive member 1 or other member deteriorates, the electrophotographic cartridge is removed from the image forming apparatus main body, and another new electrophotographic cartridge is replaced with the image forming apparatus. By attaching to the main body, maintenance and management of the image forming apparatus are facilitated.

[toner]
Liquid toner suspends toner particles mainly composed of a resin colored with a pigment or dye having a color such as carbon black, cyan, magenta, yellow, etc., in a solvent with high electrical resistivity, and further, as a charge control agent. What added metal soaps, such as a lecithin and a barium stearate, can be used. As the solvent having a high electrical resistivity, a hydrocarbon solvent is used, and a liquid toner in which C10 to C13 hydrocarbons occupy 80% or more of the solvent is preferable from the viewpoints of affinity with the pigment and drying property. In general, liquid toner is smaller in particle diameter than dry toner, which is advantageous in terms of high resolution image quality.

<Example 1>
Aluminum oxide particles having an average primary particle diameter of 13 nm (Alμmin manufactured by Nippon Aerosil Co., Ltd.)
μm Oxide C) was dispersed by ultrasonic waves in a mixed solvent of methanol / 1-propanol to obtain a dispersion slurry of aluminum oxide. The dispersion slurry, a mixed solvent of methanol / 1-propanol (mass ratio 7/3), and ε-caprolactam [compound represented by the following formula (A)] / bis (4-amino-3-methylcyclohexyl) methane [Compound represented by the following formula (B)] / hexamethylenediamine [compound represented by the following formula (C)] / decamethylene dicarboxylic acid [compound represented by the following formula (D)] / octadecamethylene dicarboxylic acid [following Copolymer polyamide pellets having a composition molar ratio of the compound represented by formula (E) of 60% / 15% / 5% / 15% / 5% are stirred and mixed while heating to obtain polyamide pellets. After dissolution, ultrasonic dispersion treatment is performed to obtain a solid content concentration of 8.0% containing aluminum oxide / copolymerized polyamide at a mass ratio of 1/1. It was a gas layer for dispersion.

The coating solution for forming the undercoat layer thus obtained was applied on a polyethylene terephthalate sheet (thickness 75 μm) vapor-deposited on the surface with a wire bar so that the film thickness after drying was 1.2 μm, and dried. Thus, an undercoat layer was provided.
As a charge generation material, 20 parts of titanium oxyphthalocyanine having a powder X-ray diffraction spectrum pattern with respect to CuKα characteristic X-ray shown in FIG. 4 and 280 parts of 1,2-dimethoxyethane are mixed and pulverized in a sand grind mill for 2 hours to form fine particles Dispersion processing was performed. Subsequently, 400 parts of a 2.5% 1,2-dimethoxyethane solution of polyvinyl butyral (trade name “Denkabutyral” # 6000C, manufactured by Denki Kagaku Kogyo Co., Ltd.) and 170 parts of 1,2-dimethoxyethane were mixed. Dispersion 1) was thus prepared. Next, the same operation was performed on titanium oxyphthalocyanine having a powder X-ray diffraction spectrum pattern with respect to CuKα characteristic X-ray shown in FIG. 5 to prepare dispersion 2). A mixture obtained by mixing and stirring these dispersions at a ratio of 1: 1 was applied onto the undercoat layer with a bar coater to form a charge generation layer so that the film thickness after drying was 0.4 μm.

  Next, on this film, polycarbonate resin (1A) (viscosity average molecular weight: 35,000, elastic deformation rate: 38%) is 100 parts, charge transport material (W) having the following structure is 35 parts, and has the following structure. A solution prepared by dissolving 4 parts of antioxidant (V) and 0.1 part of silicone oil as a leveling agent in 640 parts of a tetrahydrofuran / toluene (8/2) mixed solvent was applied and dried at 25 ° C. for 5 minutes. The first charge transport layer was provided so as to face the charge generation layer so that the typical film thickness was 9 μm.

  Next, 100 parts of polyarylate resin (1B) (viscosity average molecular weight: 37,000, elastic deformation rate: 47%), 35 parts of charge transport material (W), 4 parts of antioxidant (V), and A liquid in which 0.1 part of silicone oil as a leveling agent was dissolved in 640 parts of a tetrahydrofuran / toluene (8/2) mixed solvent was applied from above the first charge transport layer, and the charge transport layer on the outermost surface side was coated. The photoconductor X1 was obtained by providing the photoconductor with a second charge transport layer so that the film thickness was dried at 125 ° C. for 20 minutes, and the film thickness after drying was 9 μm.

<Example 2>
In the same manner as in Example 1, except that the polycarbonate resin was changed to polycarbonate resin (2A) (viscosity average molecular weight: 40,000, elastic deformation rate: 38%) having the following repeating structure in Example 1, Photoreceptor X2 Got.

<Example 3>
A photoconductor in the same manner as in Example 1 except that the polyarylate resin in Example 1 was changed to the polyarylate resin (2B) (viscosity average molecular weight: 40,000, elastic deformation rate: 44%) having the following repeating structure: X3 was obtained.

<Example 4>
In Example 1, except that the first charge transport layer was applied to a film thickness of 13 μm and the second charge transport layer was applied to a film thickness of 5 μm, the same as in Example 1, Photoconductor X4 was obtained.
<Example 5>
In Example 1, except that the first charge transport layer was applied to a film thickness of 16 μm and the second charge transport layer was applied to a film thickness of 2 μm, the same as in Example 1, Photoconductor X5 was obtained.

<Example 6>
In Example 1, except that the first charge transport layer was applied to a thickness of 5 μm and the second charge transport layer was applied to a thickness of 13 μm, the same as in Example 1, Photoconductor X6 was obtained.
<Example 7>
In Example 1, except that the first charge transport layer was applied to have a thickness of 2 μm and the second charge transport layer was applied to have a thickness of 16 μm, the same as in Example 1, Photoconductor X7 was obtained.

<Comparative Example 1>
In Example 1, the first charge transport layer was applied, dried at 125 ° C. for 20 minutes so that the film thickness after drying was 18 μm, the second charge transport layer was not applied, and the charge transport layer was A photoconductor Y1 was obtained in the same manner as in Example 1 except that one layer was used.
<Comparative example 2>
In Example 1, the first charge transport layer was not applied, but the second charge transport layer was applied so as to have a film thickness of 18 μm, and all the steps were performed except that the charge transport layer became one layer. In the same manner as in Example 1, a photoreceptor Y2 was obtained.

<Comparative Example 3>
In Example 1, a photoconductor Y3 was obtained in the same manner as in Example 1 except that the stacking order of the first charge transport layer and the second charge transport layer was reversed.
About the manufactured photoreceptor sheet | seat X1-X6, Y1-Y5, evaluation of the electrical property (bright part electric potential measurement) and the crack test were done. These results are summarized in Table 1.

<Light area potential measurement>
The photoreceptor sheet was affixed on an aluminum base tube (outer diameter 80 mmφ), and its bright part potential was measured under conditions of a temperature of 25 ° C. and a relative humidity of 50%. First, the angle between the static eliminator and the exposure position is set to 180 °, the angle between the charger and the exposure position is set to 70 °, the angle between the exposure position and the bright part potential measurement probe is set to −36 °, and the photosensitive member is rotated. The scorotron charging conditions were set so that the surface potential was -700 V when rotating at a speed of 60 revolutions / minute and not exposed. Under these conditions, the potential (bright part potential) of each photosensitive member when exposed to 1.2 μJ / cm 2 of 780 nm light was measured.

<Crack test>
The produced photoreceptor sheet was cut into 1 cm × 20 cm strips, and the solvent; Isopar L was thinly applied to the photoreceptor surface and left for about 3 hours. Attach this strip to Tensilon Universal Materials Testing Machine TENSILON RTM100 (A & D Co., Ltd.), reapply Isopar L and pull it with a force of 30 Newton, and measure the time until cracks occur on the surface of the photoconductor did. From the knowledge so far, it has been found that if the occurrence of cracks is 20 seconds or longer under these conditions, there are few problems in practical use.

From the above results, the photoreceptors of the examples have both electrical characteristics and crack resistance, and the thickness of the constituent layer facing the charge generation layer is larger than the thickness of the constituent layer on the surface side of the photoreceptor. It is understood that is preferred.
<Example 8>
In Example 1, when the second charge transport layer was applied, it was applied so that the area where only the first charge transport layer was applied was 2 mm, to obtain a photoreceptor X8.

<Example 9>
In Example 1, when the second charge transport layer was applied, it was applied to the same region as the first charge transport layer to obtain a photoreceptor X9.
<Example 10>
In Example 1, when the second charge transport layer was applied, the photoconductor X10 was obtained by coating so that the area where only the second charge transport layer was applied was 2 mm.

A film peeling test was performed on the manufactured photoreceptor sheets, photoreceptors of X8, X9, Y4, and Y2. These results are summarized in Table 2.
<Film peeling test>
A cellophane tape (TANOSEE Model No. TSCT-18) is affixed to the sheet-like photoconductor so as to include both the area where the charge transport layer is applied and the area where the charge transport layer is not applied. The degree of peeling of the photosensitive layer when peeled from was observed.

  From the above results, even when a polyarylate resin having excellent solvent resistance but poor adhesion is used, a polycarbonate resin is used for the layer facing the charge generation layer among the plurality of charge transport layers. By using polyarylate for the side layer, each charge transport layer is applied so that there is no area where only the surface side layer is applied, so that a photoreceptor having good solvent resistance and adhesion can be obtained. I found that I could provide it.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device (charging roller; charging part)
3 Exposure equipment (exposure section)
4 Development device (development unit)
5 Transfer device P Recording paper (paper, medium)

Claims (5)

In a sheet-like electrophotographic photoreceptor used in a wet development system in which at least a conductive layer, a charge generation layer, and a charge transport layer are laminated in this order on a resin sheet substrate, the charge transport layer includes at least a charge transport material and a binder. A first charge transport layer containing a resin (A), and a second charge transport layer containing a charge transport material and a binder resin (B), wherein the first charge transport layer is formed on the charge generation layer. The sheet-like electrophotographic photosensitive member is characterized in that the second charge transport layer is an outermost surface layer.
Binder resin (A): A film containing 35 parts of a charge transport material represented by the following formula (1) and 4 parts of an antioxidant represented by the following formula (2) with respect to 100 parts of the binder resin (A). A resin satisfying a bright portion potential of 100 V or less when a charge transport layer having a thickness of 18 μm is measured by a dynamic measurement method.

Binder resin (B): A resin having an elastic deformation rate of 42% or more.   The sheet-like electrophotographic photosensitive member according to claim 1, wherein the binder resin (A) is a polycarbonate resin and the binder resin (B) is a polyarylate resin.   3. The sheet-like electrophotographic photoreceptor according to claim 1, wherein the film thickness of the first charge transport layer is larger than the film thickness of the second charge transport layer.   The sheet-like electrophotographic photosensitive member according to claim 1, wherein an end portion of the first charge transport layer is exposed.   An image forming apparatus comprising the electrophotographic photosensitive member according to claim 1 and a liquid toner.

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