JP2006234925A - Organic photoreceptor, and image forming method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic photoreceptor with which an electrophotographic image can be produced at a high speed of ≥400 mm per second and to provide an organic photoreceptor having stable potential characteristics of a high potential by using a non-halogen solvent, and to provide an image forming method and image forming apparatus using the organic photoreceptor. <P>SOLUTION: The organic photoreceptor is used for the image forming method of applying a uniform electrostatic charge in an electrostatic charging process onto the organic photoreceptor at a process speed of ≥400 mm per second, forming the electrostatic latent image in an image exposure process, and visualizing the electrostatic latent image to the toner image under conditions of an unexposed part potential (¾VH¾) of 600 to 1,000 V in a developing process. The organic photoreceptor has a charge generating layer and a plurality of charge transfer layers on a conductive support and the charge transfer layer adjacent to the charge generating layer contains a plurality of charge transfer substances of <0.05 eV in the difference of an ionization potential and the charge transfer layer is formed by using the non-halogen solvent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic photoreceptor, an image forming method and an image forming apparatus that can be applied to an electrophotographic copying machine and printer, and an organic photoreceptor and an image forming method capable of producing an electrophotographic image at a high speed of 400 mm / second or more. And an image forming apparatus.

  2. Description of the Related Art Conventionally, in a copying machine using the Carlson method, which is the most typical electrophotographic method, after a photoreceptor is uniformly charged, charges are erased imagewise by exposure to form an electrostatic charge latent image. This electrostatic charge latent image is developed and visualized with toner, and then the toner is transferred to paper or the like and then fixed to form an image.

  Conventionally, as an electrophotographic photoreceptor, an inorganic photoreceptor having an inorganic photoconductive substance such as selenium, zinc oxide, cadmium or the like as a main component of a photosensitive layer has been widely used. However, these inorganic photoreceptors are often harmful and have problems in terms of environmental measures.

  Therefore, in recent years, organic photoreceptors using non-polluting organic substances have been actively developed and widely used. In particular, a function-separated type photoconductor, in which a charge generation function and a charge transport function are assigned to different substances and a compound having desired characteristics can be selected from a wide range, has been actively developed.

  In recent years, the image forming method using the electrophotographic method has been accelerated by writing by digital signal processing, and a copying machine or printer using a cut sheet has a printing speed of 100 sheets per second or more. A printer has been developed.

  However, an organic photoreceptor applied to such a copying machine or printer is required to have, for example, electrophotographic characteristics capable of printing 1 million sheets, that is, charging stability and stability of sensitivity, and is compatible with high-speed development. Therefore, potential stability at a high potential is required during development.

  In order to achieve stable potential characteristics at such a high potential, a technique for forming a surface layer of an organic photoreceptor with a highly durable binder resin, curable silicon resin, or the like has been disclosed (Patent Document 1 and Patent). Reference 2).

  On the other hand, halogen solvents with high binder resin solubility are generally widely used in the production of organic photoreceptors. These halogen solvents may be changed to non-halogen solvents from the viewpoint of environmental problems in recent years. desirable.

However, if the above-mentioned highly durable binder resin, curable silicone resin, or the like is dissolved using a non-halogen solvent to form a photosensitive layer such as a charge transport layer, the above-described potential stability deteriorates. ing. That is, when an organophotoreceptor is produced by changing from a halogen solvent to a non-halogen solvent, the residual potential increases due to repeated use and the image density gradually decreases. There is a problem that is likely to rise.
Japanese Patent Application Laid-Open No. 60-172044 JP 2000-221723 A

  An object of the present invention is to provide an organic photoreceptor capable of producing an electrophotographic image at a high speed of 400 mm or more per second, and to provide an organic photoreceptor capable of printing 1 million sheets at a high speed, Another object of the present invention is to provide an organic photoreceptor having a stable high potential characteristic using a non-halogen solvent, and to provide an image forming method and an image forming apparatus using the organic photoreceptor.

As a result of examining the above problems in detail, the present inventors have found that in order to obtain an organic photoreceptor having a high potential potential stable and capable of printing at high speed using a non-halogen solvent, Considering that it is effective to invalidate the trap site of the charge generated due to the aggregation of the solvent remaining in the body and the binder resin, etc., the charge transport layer is composed of upper and lower two layers, the lower layer charge transport The layer is used in combination with a charge transport material having a high charge mobility and a charge transport material that facilitates charge injection or delivery to prevent trapping of charges at the trap site. Thus, the present inventors have found that stable potential characteristics can be maintained at a high process speed by making the concentration of the charge transport material lower than that of the lower charge transport layer. That is, the above object of the present invention is achieved by using the following configuration.
(Claim 1)
The process speed is 400 mm / sec or more, a uniform charge is imparted to the organic photoreceptor in the charging process, an electrostatic latent image is formed in the image exposure process, and the unexposed potential (| VH |) in the development process is 600 V to An organic photoreceptor used in an image forming method for developing an electrostatic latent image into a toner image under a condition of 1000 V, comprising a charge generation layer and a plurality of charge transport layers on a conductive support, An organic photoreceptor, wherein the charge transport layer adjacent to the substrate contains a plurality of charge transport materials having an ionization potential difference of less than 0.5 eV, and the charge transport layer is formed using a non-halogen solvent.
(Claim 2)
The organophotoreceptor according to claim 1, wherein the charge transport layer contains an antioxidant.
(Claim 3)
3. The charge mobility (electric field strength: at 3.2 × 10 ⁵ V / cm) of the organic photoreceptor is 5.0 × 10 ⁻⁶ cm ² / V · sec or more. The organic photoreceptor described in 1.
(Claim 4)
The organophotoreceptor according to claim 1, wherein the charge generation layer contains an oxytitanyl phthalocyanine pigment as a charge generation substance.
(Claim 5)
The organophotoreceptor according to claim 1, wherein the charge generation layer contains a perylene pigment as a charge generation substance.
(Claim 6)
The process speed is 400 mm / sec or more, a uniform charge is imparted to the organic photoreceptor in the charging process, an electrostatic latent image is formed in the image exposure process, and the unexposed potential (| VH |) in the development process is 600 V to In an image forming method in which an electrostatic latent image is visualized as a toner image under a condition of 1000 V, the organic photoreceptor has a charge generation layer and a plurality of charge transport layers on a conductive support, and the charge generation layer includes An image forming method, wherein adjacent charge transport layers contain a plurality of charge transport materials having a difference in ionization potential of less than 0.5 eV, and the charge transport layers are formed using a non-halogen solvent.
(Claim 7)
The process speed is 400 mm / sec or more, an organic photoreceptor, a charger for applying uniform charge on the organic photoreceptor, an image exposure unit for forming an electrostatic latent image on the organic photoreceptor, and an unexposed on the organic photoreceptor. In an image forming apparatus having a developing unit that visualizes an electrostatic latent image into a toner image under an exposure potential (| VH |) of 600 V to 1000 V, the organic photoreceptor is a charge generation layer on a conductive support. And the charge transport layer adjacent to the charge generation layer contains a plurality of charge transport materials having a difference in ionization potential of less than 0.5 eV, the charge transport layer using a non-halogen solvent. An image forming apparatus formed.

  By using the organophotoreceptor of the present invention, it is possible to provide an organophotoreceptor exhibiting potential characteristics that can be sufficiently adapted to a high-speed copying machine having a process speed of 400 mm / sec or more even when the organophotoreceptor is produced with a non-halogen solvent. An electrophotographic image with sufficient image density and good sharpness can be provided, and an image forming method and an image forming apparatus using the organic photoreceptor can be provided.

  The organic photoreceptor of the present invention has a process speed of 400 mm / sec or more, imparts uniform charge to the organic photoreceptor in the charging step, forms an electrostatic latent image in the image exposure step, and unexposed potential in the development step. An organic photoreceptor for use in an image forming method for developing an electrostatic latent image into a toner image under a condition of (| VH |) of 600V to 1000V, a charge generation layer and a plurality of charge transport layers on a conductive support. The charge transport layer adjacent to the charge generation layer contains a plurality of charge transport materials having an ionization potential difference of less than 0.5 eV, and the charge transport layer is formed using a non-halogen solvent. Features.

  Since the organic photoreceptor has the above-described configuration, the process speed is 400 mm / sec or more, a uniform charge is imparted on the organic photoreceptor in the charging step, an electrostatic latent image is formed in the image exposure step, and development is performed. When used in an image forming method in which an electrostatic latent image is visualized as a toner image under a condition where the unexposed potential (| VH |) in the process is 600V to 1000V, The increase in residual potential is small and stable potential characteristics are exhibited, and the initial image characteristics such as image density and sharpness are stably achieved even after printing and copying 1 million sheets.

  Hereinafter, the constitution of the organic photoreceptor of the present invention will be described.

  In the present invention, the organic photoconductor means an electrophotographic photoconductor configured to have an organic compound having either a charge generation function or a charge transport function essential for the configuration of the electrophotographic photoconductor, It contains all known organic electrophotographic photoreceptors such as a photoreceptor composed of a known organic charge generating material or organic charge transport material, a photoreceptor composed of a polymer complex with a charge generating function and a charge transport function.

  The layer structure of the organic photoreceptor of the present invention preferably has a charge generation layer and a charge transport layer on a conductive support, and the charge transport layer is preferably formed of a plurality of layers. Moreover, it is preferable to provide an intermediate layer between the conductive support and the charge generation layer, which can block the entry of free carriers from the support. Hereinafter, preferred configurations of the organic photoreceptor of the present invention are shown.

Conductive Support The conductive support used in the photoreceptor of the present invention may be either a sheet or a cylinder, but in order to design an image forming apparatus in a compact manner, a cylindrical conductive support is used. Is preferred.

  Cylindrical conductive support means a cylindrical support necessary for forming an endless image by rotating. Conductivity is within a range of 0.1 mm or less in straightness and 0.1 mm or less in deflection. A support is preferred. Exceeding the roundness and shake range makes it difficult to form a good image.

As the conductive material, a metal drum such as aluminum or nickel, a plastic drum deposited with aluminum, tin oxide, indium oxide or the like, or a paper / plastic drum coated with a conductive substance can be used. The conductive support preferably has a specific resistance of 10 ³ Ωcm or less at room temperature.

  As the conductive support used in the present invention, one having an alumite film that has been sealed on the surface thereof may be used. The alumite treatment is usually performed in an acidic bath such as chromic acid, sulfuric acid, oxalic acid, phosphoric acid, boric acid, sulfamic acid, etc., but anodizing treatment in sulfuric acid gives the most preferable result. In the case of anodizing treatment in sulfuric acid, the sulfuric acid concentration is preferably 100 to 200 g / L, the aluminum ion concentration is 1 to 10 g / L, the liquid temperature is about 20 ° C., and the applied voltage is preferably about 20 V. It is not limited. The average film thickness of the anodized film is usually 20 μm or less, particularly preferably 10 μm or less.

Intermediate Layer In the present invention, it is preferable to provide an intermediate layer that can block the entry of free carriers from the support between the conductive support and the photosensitive layer.

  In the present invention, in order to improve the adhesion between the conductive support and the photosensitive layer, or to prevent charge injection from the support, an intermediate layer (including an undercoat layer) is provided between the support and the photosensitive layer. Including) can also be provided. Examples of the material for the intermediate layer include polyamide resins, vinyl chloride resins, vinyl acetate resins, and copolymer resins containing two or more of these resin repeating units. Of these subbing resins, a polyamide resin is preferable as a resin capable of reducing the increase in residual potential due to repeated use. The film thickness of the intermediate layer using these resins is preferably 0.01 to 0.5 μm.

  Examples of the intermediate layer preferably used in the present invention include an intermediate layer using a curable metal resin obtained by thermosetting an organic metal compound such as a silane coupling agent or a titanium coupling agent. As for the film thickness of the intermediate | middle layer using curable metal resin, 0.1-2 micrometers is preferable.

  An intermediate layer preferably used in the present invention includes an intermediate layer in which inorganic particles are dispersed in a binder resin. The average particle diameter of the inorganic particles is preferably 0.01 to 1 μm. In particular, an intermediate layer in which N-type semiconductive fine particles subjected to surface treatment are dispersed in a binder is preferable. For example, an intermediate layer in which titanium oxide having an average particle size of 0.01 to 1 μm, which has been surface-treated with silica / alumina treatment and a silane compound, is dispersed in a polyamide resin. The film thickness of such an intermediate layer is preferably 1 to 20 μm.

  The N-type semiconducting fine particles are fine particles having the property of using conductive carriers as electrons. That is, the property that the conductive carrier is an electron is that the N-type semiconducting fine particles are contained in an insulating binder to effectively block hole injection from the substrate, and to convert electrons from the photosensitive layer into electrons. On the other hand, it has the property which does not show blocking property.

Specific examples of the N-type semiconductive fine particles include fine particles such as titanium oxide (TiO ₂ ) and zinc oxide (ZnO). In the present invention, titanium oxide is particularly preferably used.

  The average particle diameter of the N-type semiconducting fine particles used in the present invention is preferably in the range of 10 nm to 500 nm in the number average primary particle diameter, more preferably 10 nm to 200 nm, and particularly preferably 15 nm to 50 nm. .

  The intermediate layer using N-type semiconducting fine particles whose number average primary particle size is within the above range can be finely dispersed in the layer, has sufficient potential stability, and generates black spots. Has a prevention function.

  For example, in the case of titanium oxide, the number-average primary particle size of the N-type semiconducting fine particles is magnified 10,000 times by observation with a transmission electron microscope, and 100 particles are randomly observed as primary particles. It is measured as the number average diameter.

  The shape of the N-type semiconducting fine particles used in the present invention includes dendritic, needle-like, and granular shapes. For example, in the case of titanium oxide particles, the N-type semiconductive fine particles have a crystalline form. There are anatase type, rutile type and amorphous type, but any crystal type may be used, or two or more crystal types may be mixed and used. Of these, the rutile type is the best.

  One of the hydrophobizing surface treatments performed on the N-type semiconducting fine particles is a plurality of surface treatments, and the last surface treatment is a surface treatment with a reactive organosilicon compound. Is to do. In addition, at least one of the surface treatments is at least one surface treatment selected from alumina, silica, and zirconia, and finally the surface treatment of the reactive organosilicon compound is performed. It is preferable.

  Alumina treatment, silica treatment, and zirconia treatment are treatments for depositing alumina, silica, or zirconia on the surface of the N-type semiconducting fine particles. Alumina, silica, and zirconia deposited on these surfaces include alumina, silica, Zirconia hydrates are also included. The surface treatment of the reactive organosilicon compound means using a reactive organosilicon compound in the treatment liquid.

  In this way, the surface treatment of the N-type semiconductive fine particles such as titanium oxide particles was performed at least twice, so that the surface of the N-type semiconductive fine particles was uniformly coated (treated), and the surface treatment was performed. When N-type semiconducting fine particles are used in the intermediate layer, a good photoconductor having good dispersibility of N-type semiconductive fine particles such as titanium oxide particles in the intermediate layer and causing no image defects such as black spots. You can get it.

Photosensitive layer The photosensitive layer structure of the photoconductor of the present invention has a charge generation layer (CGL) and a plurality of charge transport layers (CTL) on a conductive support, and the charge transport layer adjacent to the charge generation layer has an ionization potential. A plurality of charge transport materials having a difference of less than 0.5 eV are contained, and the charge transport layer is formed using a non-halogen solvent.

  Hereinafter, the most preferred photosensitive layer structure of the present invention will be described.

Charge generation layer Charge generation layer: The charge generation layer contains a charge generation material (CGM). Other substances may contain a binder resin and other additives as necessary.

  A known charge generation material (CGM) can be used as the charge generation material (CGM). For example, a phthalocyanine pigment, an azo pigment, a perylene pigment, an azulenium pigment, or the like can be used. Among these, the CGM that can minimize the increase in residual potential due to repeated use has a three-dimensional and potential structure that can form a stable aggregate structure among a plurality of molecules. Specifically, a phthalocyanine having a specific crystal structure. CGM of pigments and perylene pigments. For example, CGMs such as titanyl phthalocyanine having a maximum peak at a Bragg angle 2θ of 27.2 ° with respect to Cu—Kα rays and benzimidazole perylene having a maximum peak at 2θ of 12.4 have little deterioration due to repeated use. Potential increase can be reduced.

  When a binder is used as the CGM dispersion medium in the charge generation layer, a known resin can be used as the binder, but the most preferred resins include formal resin, butyral resin, silicone resin, silicone-modified butyral resin, phenoxy resin, and the like. Can be mentioned. The ratio of the binder resin to the charge generating material is preferably 20 to 600 parts by mass with respect to 100 parts by mass of the binder resin. By using these resins, the increase in residual potential associated with repeated use can be minimized. The thickness of the charge generation layer is preferably 0.01 μm to 2 μm.

Charge transport layer The charge transport layer according to the present invention has a plurality of charge transport layers, the charge transport layer adjacent to the charge generation layer contains a plurality of charge transport materials having a difference in ionization potential of less than 0.5 eV, The charge transport layer is formed using a non-halogen solvent.

  A known charge transport material (CTM) can be used as the charge transport material (CTM). For example, a triphenylamine derivative, a hydrazone compound, a styryl compound, a benzidine compound, a butadiene compound, or the like can be used.

  A plurality of charge transport materials in which the charge transport layer adjacent to the charge generation layer has an ionization potential difference of less than 0.5 eV will be described. At least one of the plurality of charge transport materials is preferably a charge transport material having high charge mobility (high mobility charge transport material) that can increase the charge mobility of the organic photoreceptor. The difference in ionization potential is less than 0.5V, preferably less than 0.3 eV.

  The charge transport material used together with the high mobility charge transport material preferably has a difference in ionization potential from the high mobility charge transport material of less than 0.5 V, more preferably less than 0.3 eV. By using a charge transport material having a high mobility in the charge transport layer adjacent to the charge generation layer and using a charge transport material having an ionization potential difference of less than 0.5 V with respect to the charge transport material having the high mobility. Even in a high-speed process of 400 mm / sec or more, an increase in residual potential can be suppressed to a small level, and an electrophotographic image with high density and good sharpness can be produced.

  Incidentally, the ionization potential (hereinafter also simply referred to as IP) of the charge generation material and the charge transport material can be measured with a surface analyzer AC-1 (manufactured by Riken Keiki Co., Ltd.).

  As the high-transport charge transporting material, styryl triphenylamine-based compounds exemplified below are preferably used, but the present invention is not limited to these exemplified compounds.

The charge mobility (at electric field strength: 3.2 × 10 ⁵ V / cm) of the organic photoreceptor of the present invention is preferably 5.0 × 10 ⁻⁶ cm ² / V · sec or more. That is, since the charge mobility of the entire organic photoreceptor is 5.0 × 10 ⁻⁶ cm ² / V · sec or more, an increase in residual potential is suppressed to a small level even in a high-speed process of 400 mm / sec or more. An electrophotographic image having good density and sharpness can be produced.

  The charge mobility is defined as the charge transfer rate per unit electric field strength, and the charge mobility can be measured by the TOF (Time Off Flight) method. This measurement method is performed with a sandwich structure in which both sides of the photosensitive layer are sandwiched between electrodes. First, a voltage is applied between the electrodes, and the sample is irradiated with pulsed light through the electrodes, and the generated charges are transferred from one side of the sample. In the process of moving to the opposing surface, the waveform of the current flowing between the electrodes is observed, and the point where the waveform falls sharply becomes the flight time τ (the current waveform is modified with an oscilloscope to obtain the flight time τ). The mobility can be obtained from the following relational expression.

Flight time τ = (sample film thickness) / (speed)
Speed = (mobility) x (electric field)
As a sample for measuring the charge mobility, a sample prepared by laminating a charge generation layer and a plurality of charge transport layers similar to those of the example on a conductive support obtained by vapor-depositing aluminum on a polyethylene phthalate film was used. The voltage at the time of measurement is generated by applying a voltage so that the electric field strength is 3.2 × 10 ⁵ V / cm, and then generating a charge from the charge generation layer by irradiating pulsed light with a laser diode having a wavelength of 680 nm. The transient current waveform was measured using a high-speed current amplifier (keithley 428) and a digital storage oscilloscope (Hewlett Packard 54111D). For determination of the transit time, a method (Scher-Control method) in which the relationship between the current (i) and the time (t) is logarithmically converted and obtained from the bending point of the obtained waveform is used.

  The charge transport layer according to the present invention preferably contains an antioxidant. Examples of the antioxidant preferably used include the following compounds.

  The charge transport layer according to the present invention is preferably composed of two upper and lower layers. When the charge transport layer is composed of two layers, the first charge transport layer adjacent to the lower charge generation layer contains a plurality of charge transport materials. The content of the charge transport material in the first charge transport layer is preferably 50 to 200 parts by weight with respect to 100 parts by weight of the binder resin. On the other hand, the content of the charge transport material in the second charge transport layer is preferably lower than that in the first charge transport layer. The content is preferably 30 to 150 parts by mass with respect to 100 parts by mass of the binder resin.

  By forming the charge transport layer with such a two-layer structure, when the charge transport layer is formed using a non-halogen solvent, the residual potential rise and potential fluctuation at high temperature and high humidity are improved, and high speed and proper An organic photoreceptor having excellent and stable potential characteristics can be formed.

  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 1 to 10 μm.

  When preparing the charge transport layer according to the present invention, a dispersion of the charge transport layer is prepared. As a solvent for the charge transport layer dispersion, a non-halogen solvent having a small environmental load is used. Non-halogen solvents include acetone, methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, benzene, toluene, xylene, tetrahydrofuran, dioxolane, dioxane, methanol, ethanol, butanol, isopropanol, ethyl acetate, butyl acetate, dimethyl sulfoxide, methyl cellosolve, etc. Can be mentioned.

  The solvent for the charge transport layer dispersion is not limited to these, but toluene, tetrahydrofuran (THF), dioxolane and the like are particularly preferably used. These solvents may be used alone or as a mixed solvent of two or more.

  As a coating processing method for producing the organic photoreceptor of the present invention, a coating processing method such as dip coating, spray coating, circular amount regulation type coating or the like is used, but the upper layer side coating processing of the photosensitive layer is a lower layer film. In order to achieve a uniform coating process, it is preferable to use a coating process method such as spray coating or circular amount regulation type (a circular slide hopper type is a typical example). The spray coating is described in detail in, for example, JP-A-3-90250 and JP-A-3-269238, and the circular amount-regulating coating is described in detail in, for example, JP-A-58-189061. Yes.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be specifically described below with reference to the accompanying drawings, and specific examples of forming an image using the image forming apparatus and the developing device of the embodiments will be given. As will be described, it is clarified that the developing method of the present invention can provide a good image with sufficient gradation and image density without black spots and fog.

  FIG. 1 is a cross-sectional view of an image forming apparatus as an example of the image forming method of the present invention.

  In FIG. 1, reference numeral 50 denotes a photosensitive drum (photosensitive member) which is an image bearing member, and is a photosensitive member of the present invention in which an organic photosensitive layer is coated on the drum, which is grounded and rotated clockwise. Reference numeral 52 denotes a scorotron charger, which uniformly charges the circumferential surface of the photosensitive drum 50 by corona discharge. Prior to the charging by the charger 52, the peripheral surface of the photosensitive member may be discharged by performing exposure by the pre-charging exposure unit 51 using a light emitting diode or the like in order to eliminate the history of the photosensitive member in the previous image formation.

  After uniform charging of the photoreceptor, image exposure based on the image signal is performed by the image exposure unit 53. The image exposure unit 53 in this figure uses a laser diode (not shown) as an exposure light source. Scanning on the photosensitive drum is performed by the light whose optical path is bent by the reflection mirror 532 through the rotating polygon mirror 531 and the fθ lens, and an electrostatic latent image is formed.

  Here, the unexposed portion potential of the photoreceptor of the present invention means the photoreceptor surface potential in a region where the surface of the photoreceptor is uniformly charged by the charger 52 and image exposure is not performed. The exposed portion potential means the photoreceptor surface potential in a region where image exposure has been performed. The potential is measured by providing a potential sensor 547 at the development position as shown in FIG.

The electrostatic latent image is then developed using a developing device 54 in a development process. A developing device 54 containing a developer composed of toner and carrier is provided on the periphery of the photosensitive drum 50, and development is performed by a developing sleeve 541 that contains a magnet and rotates while holding the developer. The inside of the developing device 54 is composed of developer agitating / conveying members 544 and 543, a conveying amount regulating member 542, and the like, and the developer is agitated and conveyed and supplied to the developing sleeve. Controlled by member 542. The amount of the developer transported varies depending on the linear velocity of the applied organic electrophotographic photosensitive member and the specific gravity of the developer, but is generally in the range of ^{20 to} 200 mg / cm ² .

  The developer includes, for example, a carrier in which the above ferrite is used as a core and an insulating resin is coated around the carrier, a colorant such as carbon black, a charge control agent, and the low molecular weight polyolefin of the present invention, which is mainly composed of the above styrene acrylic resin. The developer is made up of a toner obtained by externally adding silica, titanium oxide or the like to the colored particles, and the developer is transported to the development zone with the layer thickness regulated by the transport amount regulating member, and development is performed. At this time, development is usually performed by applying a DC bias voltage to the developing sleeve 541 and, if necessary, an AC bias voltage. Further, the developer is developed in contact with or not in contact with the photoreceptor.

  The recording paper P is fed to the transfer area by the rotation operation of the paper feed roller 57 when the transfer timing is ready after the image formation.

  In the transfer area, a transfer electrode (transfer device) 58 is pressed against the peripheral surface of the photosensitive drum 50 in synchronization with the transfer timing, and the fed recording paper P is sandwiched and transferred.

  Next, the recording paper P is neutralized by a separation electrode (separator) 59 brought into a pressure contact state almost simultaneously with the transfer roller, separated by the peripheral surface of the photosensitive drum 50, conveyed to the fixing device 60, and pressure-bonded to the heat roller 601. After the toner is welded by heating and pressurizing the roller 602, the toner is discharged to the outside of the apparatus via the discharge roller 61. The transfer electrode 58 and the separation electrode 59 are retracted away from the peripheral surface of the photosensitive drum 50 after the recording paper P has passed to prepare for the next toner image formation.

  On the other hand, after the recording paper P is separated, the photosensitive drum 50 is subjected to removal and cleaning of residual toner by pressure contact of the blade 621 of the cleaning device 62, and after receiving charge removal by the pre-charge exposure unit 51 and charging by the charger 52 again. The image forming process is entered.

  Reference numeral 70 denotes a detachable process cartridge in which a photoconductor, a charger, a transfer device, a separator, and a cleaning device are integrated.

  FIG. 2 is an enlarged view of the configuration of charge potential control of the photosensitive drum 50 of FIG.

  Hereinafter, a method of measuring the unexposed portion potential and a charging potential adjustment process for the purpose of correcting the unexposed portion potential will be described with reference to FIG.

  First, the photosensitive member 50 is uniformly charged by a charger (charging step) 52. An unexposed area that is not digitally exposed is formed on the charged photosensitive member by an image exposure device (image exposure step) 53 of a laser diode. The surface potential (unexposed portion potential) of the unexposed region is detected by the potential sensor 547, and the detected potential signal is transmitted to the process control unit 63 in FIG. The process control unit 63 is a process controller that controls the band electrode based on the potential signal from the potential sensor 547. The controller compares the potential signal from the potential sensor with the target potential signal, corrects the difference, and determines a correction signal that achieves the target potential. The high-voltage control unit 64 is a high-voltage control unit that receives a control signal from the process control unit 63 and supplies current and voltage to the charger 52. Based on the determined correction signal, a correction signal for charging current and charging grit voltage is output from the process controller to the high voltage control unit, and then corrected from the high voltage control unit to the corona wire 521 and scorotron grit 522 of the charger 52, respectively. The charged current and charged grit voltage are output. By repeating this process several times, the photosensitive member potential (unexposed portion potential) at the potential sensor position can be corrected to the target potential.

  In order to accurately measure the unexposed portion potential at the development position of the photosensitive member, it is preferable to measure the potential sensor by attaching the potential sensor to the development position (with the developing device removed if necessary). When the attachment position is away from the development position, the potential dark attenuation amount of the photoconductor from the potential sensor to the development position may be calculated and corrected accordingly.

  Here, the development position indicates a position where the latent image on the photoreceptor is developed by the developer in the development process. Specifically, the position where the photoreceptor and the development sleeve are closest to each other is regarded as the center of the development position. . That is, in the present invention, the unexposed portion potential at the developing position indicates the surface potential of the unexposed portion when the photoreceptor is closest to the developing sleeve.

  Although there are various methods for setting the unexposed portion target potential, the reversal development method used in the present invention is preferably the following unexposed portion target potential setting method (described with reference to FIG. 3). Used.

  That is, as shown in FIG. 3, the photosensitive member is charged and image exposed at the start of daily use of the printer or copying machine or every predetermined number of prints, and the exposed portion potential (VL) after image exposure is measured by a potential sensor. Detect by. The unexposed portion target potential (VH) for preventing the occurrence of fogging is set with reference to the development bias potential that controls the image density and then the development bias potential with reference to the VL.

  The reversal development conditions of the present invention are such that the unexposed portion potential (| VH |) at the development position of the photoreceptor is 600 to 1000 V in absolute value. The difference (development bias) between the DC bias potential (| VDC |) applied to VH and the developing sleeve is 50 to 300V, more preferably 70 to 280V. Even when such a high voltage is applied, when reversal development is performed using the photoconductor of the present invention, black spots peculiar to reversal development are few, and an image with high density and high gradation is achieved. The When | VH | is lower than 600V, the gradation is liable to be lowered, and when it exceeds 1000V, electrostatic breakdown of the photosensitive layer is likely to occur, and image defects such as black spots are likely to occur. If the difference of | VH | − | VDC | is smaller than 50V, image defects such as black spots are likely to occur, and if it exceeds 300V, the occurrence of weakly charged toner and carrier adhesion increases.

  In the present invention, the distance (Dsd) between the organic photoreceptor and the developing sleeve carrying the developer is preferably 350 to 800 μm, and the linear speed ratio between the photoreceptor and the developing sleeve is preferably in the range of 1: 1 to 1: 3.5. . When the Dsd exceeds 800 μm, the developing electric field becomes weak and the developability deteriorates.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this. However, “part” in the following text indicates “part by mass”.

Examples Photoconductors used for evaluation were produced as follows.

Preparation of photoreceptor 1 Intermediate layer The following intermediate layer coating solution is applied by a dip coating method onto a cleaned cylindrical aluminum substrate (10-point surface roughness Rz defined by JISB-0601 by cutting): 0.81 μm) And dried at 120 ° C. for 30 minutes to form an intermediate layer having a dry film thickness of 1.0 μm.

  The following intermediate layer dispersion is diluted twice with the same mixed solvent, and is allowed to stand overnight and then filtered (filter; rigesh mesh filter made by Nippon Pole Co., Ltd., nominal filtration accuracy: 5 microns, pressure: 50 kPa). Produced.

(Preparation of intermediate layer dispersion)
Binder resin: (Exemplary polyamide N-1) 1 part (1.00 volume part)
2. Rutile-type titanium oxide A1 (primary particle size 35 nm; a surface treatment using a copolymer of methylhydrogensiloxane and dimethylsiloxane (molar ratio 1: 1) in an amount of 5% by mass of the total mass of titanium oxide) 5 parts (1.0 part by volume)
Ethanol / n-propyl alcohol / THF (= 45/20/30 mass ratio) 10 parts The above components were mixed and dispersed in a batch system for 10 hours using a sand mill disperser to prepare an intermediate layer dispersion. .

Charge generation layer The following components were mixed and dispersed using a sand mill disperser to prepare a charge generation layer coating solution. This coating solution was applied by a dip coating method to form a charge generation layer having a dry film thickness of 0.3 μm on the intermediate layer.

Titanyl phthalocyanine pigment (a titanyl phthalocyanine pigment having a maximum diffraction peak at 27.3 ° at the Bragg angle (2θ ± 0.2 °) of the characteristic X-ray diffraction spectrum of Cu-Kα) 20 parts Silicone-modified polyvinyl butyral 10 parts 4 -Methoxy-4-methyl-2-pentanone 700 parts t-butyl acetate 300 parts <Charge transport layer 1 (CTL1)>
Charge transport material A (CT-4) 33 parts Charge transport material B (CT-7) 67 parts Polycarbonate (Z300: manufactured by Mitsubishi Gas Chemical Company) 100 parts Antioxidant (exemplary compound AO2-1) 6 parts THF / toluene ( Mass ratio: 7/3) 1000 parts Silicon oil (KF-54: manufactured by Shin-Etsu Chemical Co., Ltd.) 1 part was mixed and dissolved to prepare a charge transport layer coating solution 1. This coating solution was applied onto the charge generation layer by a dip coating method and dried at 110 ° C. for 70 minutes to form a charge transport layer 1 having a dry film thickness of 18.0 μm.

<Charge transport layer 2 (CTL2)>
Charge transport material (CT-4) 25 parts Polycarbonate (Z300: manufactured by Mitsubishi Gas Chemical Company) 50 parts Antioxidant (Exemplary Compound AO1-1) 2 parts THF / Toluene (mass ratio: 7/3) 1200 parts Silicon oil ( KF-54: manufactured by Shin-Etsu Chemical Co., Ltd.) 4 parts were mixed and dissolved to prepare a charge transport layer coating solution 2. This coating solution is applied onto the charge transport layer 1 with a circular slide hopper type coater, dried at 110 ° C. for 70 minutes to form a charge transport layer 2 (surface layer) having a dry film thickness of 7.0 μm, Photoconductor 1 was produced.

Production of Photoconductors 2 to 14 Photoconductors 2 to 14 were produced in the same manner as Photoreceptor 1 except that the types and addition amounts of the charge transport materials in charge transport layers 1 and 2 were changed as shown in Table 1.

  In Table 1, CT-11 and CT-12 represent the following compounds.

<< Evaluation 1 >>
A digital copying machine Konica “Sitos” 7085 (manufactured by Konica Minolta Business Technologies, Inc.) having a structure as shown in FIG. 1 and FIG. A copy experiment was conducted. In this experiment, the program of the unexposed portion target potential was incorporated in the memory of the process control portion of FIG. 2, and the digital copying machine was modified so that the unexposed portion target potential at the development position was automatically set. In the image formation of this copying experiment, the unexposed portion potential is measured by the potential sensor, and when the unexposed portion potential of the target value is not obtained, to achieve the unexposed portion target potential through the control unit, The output value of the charging means was controlled.

《Image evaluation》
Each photoconductor is attached to the digital copying machine, and at the start of copying, the unexposed area potential (| VH |) at the development position is set as shown in Table 2, and A4 paper is used in a high temperature and high humidity (30 ° C., 80% RH) environment. An original image having 1 million character images, white solid images, and black solid images was copied, and the copied images were taken out at the start and every 100,000 copies, and the following image evaluation was performed.

Other conditions for image formation Process speed: 420 mm / sec
Developer: A two-component developer containing carrier and toner was used.

(Image density)
A black solid image of a copied image was measured using a Macbeth RD-918. Measured with relative reflection density with paper reflection density set to “0” (Image density)
A: From the start to 1 million sheets, the black solid image density is 1.3 or higher and the image density is high.

  ○: From the start to 1 million sheets, the black solid image density is 1.0 or more, which is a practically sufficient image density.

Δ: Black solid image density of 0.7 to less than 1.0 occurred between 1 million sheets from the start (re-examination required for practical use)
×: Black solid image density of less than 0.7 occurs between 1 million sheets from the start (There is a problem in practical use)
(Fog)
Using a Macbeth reflection densitometer “RD-918”, the density of copy paper (white paper) is measured at 20 locations at absolute image density, and the average value is defined as the white paper density. Next, 20 white solid images of the copied image were similarly measured at the absolute image density, and the value obtained by subtracting the white paper density from the average density was evaluated as the fog density.

A: From the start to 1 million sheets, white solid image density is 0.005 or less (good)
○: From the start to 1 million sheets, the white solid image density is 0.01 or less (a level that is not a problem for practical use)
×: fogging with a solid white image density greater than 0.01 between the start and 1 million sheets (obviously, there is a practical problem)
(Sharpness)
Sharpness was evaluated with a character image. Evaluation was made according to the following criteria using 3 point and 5 point kanji character images of the copied image.

◎: From the start to 1 million sheets, 3 points and 5 points are clear and easy to read (good)
○: Between 1 million sheets from the start, 3 points are partially illegible copy images, but 5 points are clear and easily readable (practically acceptable level)
X: Between the start and 1 million sheets, 3 points were almost unreadable and 5 points were partially or completely unreadable (apparently, there was a practical problem).

  In Table 2, VL represents an exposure portion potential, and ΔVH and ΔVL represent potential increase values after 1 million sheets of VH and VL (a minus sign indicates a decrease value), respectively. In Table 2, the charge mobility of the photoconductor and the difference in ionization potential between CTM-A and CTM-B are values measured by the method described above.

  As is apparent from Table 2, even when the charge transport layer is formed using a non-halogen solvent, the conditions of the present invention are satisfied, that is, the charge generation layer has a charge generation layer and a plurality of charge transport layers. Photoreceptors 1 to 11 containing a plurality of charge transport materials whose adjacent charge transport layers have an ionization potential difference of less than 0.5 eV have a small potential fluctuation even after 1 million copies have been printed. Both evaluations of fog and sharpness have obtained good results. However, in the photoconductor 12 having a difference in ionization potential of 0.5 eV, VH decreases, resulting in fogging and deterioration of sharpness. ing. Further, in the photoreceptors 13 and 14 in which the charge transport layer adjacent to the charge generation layer is composed of a single charge transport material, the increase in VL is large, the image density is lowered, and the sharpness is deteriorated. It is not suitable for high speed when the speed is 420 mm / sec or more.

<< Evaluation 2 >>
Evaluation was performed under the same conditions as in Evaluation 1, except that the process speed was changed from 420 mm / sec to 350 mm / sec.

  As a result, even in the photoconductors 12, 13, and 14, the potential fluctuation was small, the difference from the photoconductors 1 to 11 was not small, and no reduction in image density or occurrence of fog was observed.

1 is a cross-sectional view of an image forming apparatus as an example of an image forming method of the present invention. FIG. 2 is an enlarged view of a configuration of charge potential control of the photosensitive drum in FIG. 1. The figure explaining the setting method of an unexposed part target electric potential.

Explanation of symbols

50 photoconductor drum (or photoconductor)
DESCRIPTION OF SYMBOLS 51 Pre-charge exposure part 52 Charging device 53 Image exposure device 54 Developer 541 Development sleeve 542 Conveyance amount regulating member 543 Developer agitation conveyance member 544 Developer agitation conveyance member 547 Potential sensor 57 Feed roller 58 Transfer electrode 59 Separation electrode (separation) vessel)
60 Fixing device 61 Paper discharge roller 62 Cleaning device 70 Process cartridge

Claims (7)

The process speed is 400 mm / sec or more, a uniform charge is imparted to the organic photoreceptor in the charging process, an electrostatic latent image is formed in the image exposure process, and the unexposed potential (| VH |) in the development process is 600 V to An organic photoreceptor used in an image forming method for developing an electrostatic latent image into a toner image under a condition of 1000 V, comprising a charge generation layer and a plurality of charge transport layers on a conductive support, An organic photoreceptor, wherein the charge transport layer adjacent to the substrate contains a plurality of charge transport materials having an ionization potential difference of less than 0.5 eV, and the charge transport layer is formed using a non-halogen solvent. The organophotoreceptor according to claim 1, wherein the charge transport layer contains an antioxidant. 3. The charge mobility (electric field strength: at 3.2 × 10 ⁵ V / cm) of the organic photoreceptor is 5.0 × 10 ⁻⁶ cm ² / V · sec or more. The organic photoreceptor described in 1. The organophotoreceptor according to claim 1, wherein the charge generation layer contains an oxytitanyl phthalocyanine pigment as a charge generation substance. The organophotoreceptor according to claim 1, wherein the charge generation layer contains a perylene pigment as a charge generation substance. The process speed is 400 mm / sec or more, a uniform charge is imparted to the organic photoreceptor in the charging process, an electrostatic latent image is formed in the image exposure process, and the unexposed potential (| VH |) in the development process is 600 V to In an image forming method in which an electrostatic latent image is visualized as a toner image under a condition of 1000 V, the organic photoreceptor has a charge generation layer and a plurality of charge transport layers on a conductive support, and the charge generation layer includes An image forming method, wherein adjacent charge transport layers contain a plurality of charge transport materials having a difference in ionization potential of less than 0.5 eV, and the charge transport layers are formed using a non-halogen solvent. The process speed is 400 mm / sec or more, an organic photoreceptor, a charger for applying uniform charge on the organic photoreceptor, an image exposure unit for forming an electrostatic latent image on the organic photoreceptor, and an unexposed on the organic photoreceptor. In an image forming apparatus having a developing unit that visualizes an electrostatic latent image into a toner image under an exposure potential (| VH |) of 600 V to 1000 V, the organic photoreceptor is a charge generation layer on a conductive support. And the charge transport layer adjacent to the charge generation layer contains a plurality of charge transport materials having a difference in ionization potential of less than 0.5 eV, the charge transport layer using a non-halogen solvent. An image forming apparatus formed.

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