JP2009186496A - Coating liquid for charge generation layer and manufacturing method of electrophotographic photoreceptor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of electrophotographic photoreceptor in which a photosensitive layer can be formed without causing coating omission or coating unevenness and which can obtain an image of satisfactory image quality. <P>SOLUTION: This invention relates to a coating liquid for a charge generation layer used for forming a charge generation layer of a layered electrophotographic photoreceptor with at least the charge generation layer and a charge transport layer disposed on a conductive support, wherein the coating liquid for the charge generation layer contains at least two kinds of solvents and has such properties that a difference between boiling points of the solvents is larger than 35°C and a dielectric constant of at least one solvent is 6 or smaller. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating solution for a charge generation layer and a method for producing an electrophotographic photoreceptor. More specifically, the present invention relates to a charge generation layer coating solution that defines a solvent that constitutes a charge generation layer coating solution used in the production of an electrophotographic photosensitive member, and a method for producing an electrophotographic photosensitive member.

Inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide are known as materials constituting the photosensitive layer of an electrophotographic photoreceptor (hereinafter also simply referred to as a photoreceptor). A photoreceptor using these inorganic photoconductive materials can be charged to an appropriate potential in a dark place, has little charge dissipation in the dark place, and can quickly dissipate charge by light irradiation, etc. Have advantages.
However, this photoreceptor also has various drawbacks. For example, a photoconductor using selenium has a high manufacturing cost because the manufacturing conditions are difficult. In addition, it is sensitive to heat and mechanical shock, so it needs to be handled with care.

In a photoreceptor using cadmium sulfide and zinc oxide, stable sensitivity cannot be obtained in a humid environment. For this reason, the dye added as a sensitizer causes charging deterioration due to corona charging and photobleaching due to exposure, so that stable characteristics cannot be given over a long period of time.
For such inorganic photoconductive materials, various organic photoconductive materials such as polyvinyl carbazole have been proposed. Organic photoconductive materials are superior to inorganic photoconductive materials in terms of film-forming properties and light weight. However, it is inferior in terms of sensitivity, durability, and stability due to environmental changes. Therefore, in recent years, various research and development have been conducted in order to solve these drawbacks, and a layer in which the charge generation function and the charge transport function in the photoconductive function of the photosensitive member are assigned to separate substances, respectively. A function-separated type photoreceptor that is a mold or a dispersion type has been proposed.

  The functional separation type photoconductor has a wide selection range of each substance, and a high-performance photoconductor by combining the best materials in electrophotographic characteristics such as charging characteristics, sensitivity, residual potential, repeat characteristics and printing durability. Can provide. Further, since it can be produced by a coating method, it is possible to provide a photoconductor that is extremely productive and inexpensive, and the photosensitive wavelength range can be freely controlled by appropriately selecting a charge generating material.

  Recently, in order to obtain a higher quality image and to store an input image or freely edit it, digitization of image formation is rapidly progressing. Until now, digital image forming apparatuses have been limited to laser processors, LED printers and some color laser copiers (registered trademark), which are output devices of word processors and personal computers. However, digitization is also progressing in the field of copying machines where analog image formation has been the mainstream.

  In such digital image formation, when computer information is used, the electrical signal is converted into an optical signal. In the case of inputting information from a document, after the document information is read as optical information, it is once converted into a digital electric signal and then converted into an optical signal again. The converted optical signal is input to the photoreceptor.

  In any case, an optical signal is input to the photoconductor, but laser light or LED light is mainly used for optical input of such a digital electric signal. Currently, the oscillation wavelengths of input light that are most often used are near-infrared light of 780 nm and 660 nm and long-wavelength light close thereto. The first requirement for a photoreceptor used for digital image formation is sensitivity to these long-wavelength light. For this reason, a wide variety of materials have been studied as materials for constituting the photoreceptor. In particular, since phthalocyanine compounds are relatively easy to synthesize and many are sensitive to long wavelength light, they are widely used in practical use.

  For example, JP-B-5-55860 (Patent Document 1) discloses a photoreceptor using oxotitanium phthalocyanine, and JP-A-59-155551 (Patent Document 2) discloses a photoreceptor using β-type indium phthalocyanine. However, JP-A-2-233769 (Patent Document 3) discloses a photoconductor using an X-type metal-free phthalocyanine, and JP-A-61-28575 (Patent Document 4) uses a vanadyloxyphthalocyanine. Each body is disclosed.

  It has also been found that oxotitanium phthalocyanine having a specific crystal type is particularly sensitive. For example, Japanese Patent No. 2285593 (Patent Document 5) has a maximum diffraction peak at a Bragg angle (2θ ± 2 °) of 27.3 ° in an X-ray diffraction spectrum, and includes 7.4 °, 9.7 ° and Oxotitanium phthalocyanine having a peak at 24.2 ° is disclosed in Japanese Patent No. 2700859 (Patent Document 6) as Bragg angles (2θ ± 2 °) of 9.5 °, 9.7 °, 11 in the X-ray diffraction spectrum. Oxotitanium phthalocyanines having peaks at .7 °, 15.0 °, 23.5 °, 24.1 ° and 27,3 ° are disclosed, respectively.

  However, phthalocyanine is generally unstable in crystal form. Therefore, when producing the coating solution for the photosensitive layer, there is a problem that the crystal form changes in the dispersion step and the performance cannot be sufficiently extracted. In order to solve such drawbacks, various dispersion solvents have been studied, but the solvent that stabilizes the crystal form is not necessarily excellent in coating property, productivity, and dispersion stability. In many cases, a mixed solvent is used in order to achieve both productivity and the like. In addition, in an azo pigment that exhibits sensitivity to long-wavelength light, as disclosed in JP-A No. 7-110587 (Patent Document 7), in order to improve the dispersion stability of the coating liquid, two or more kinds are used. Increasing use of solvents as dispersion solvents.

  From the viewpoint of preventing charge injection from the conductive support to the photosensitive layer during charging of the photosensitive layer and preventing light reflection of the conductive support, at least a binder resin and metal oxide particles or resin fine particles are used. A structure in which an undercoat layer to be contained is further provided between a conductive support and a photosensitive layer has come to dominate.

  Here, since the film thickness of the charge generation layer is usually several μm or less, if there is even a concavo-convex portion on the surface to be coated of the undercoat layer, the entire surface to be coated is applied even if the coating liquid is applied. It has been extremely difficult to completely cover the film with a liquid film. Specifically, when the coating liquid is applied to the surface to be coated or in the subsequent drying process, the liquid film made of the coating liquid is dried in the uneven portions, and the holes that are not covered with the uneven portions are exposed. There is a problem that the “coating missing” that occurs. When using a photosensitive member having a photosensitive layer in which such coating is removed, image defects such as white spots and black spots appear in the obtained image, and the image quality deteriorates.

  In addition, when forming a photosensitive layer in the conventional manufacturing method, the film thickness of the photosensitive layer obtained over the entire area where the coating solution is applied is not uniform, and so-called “coating unevenness” is generated. There was also a problem of doing. The cause of this is due to the effect that the drying speed of the coating liquid is locally different in the coated surface of the coated surface. The coating unevenness is particularly likely to occur when the coating liquid contains two or more kinds of solvents having different evaporation rates. When a photoreceptor having a photosensitive layer with coating unevenness is used, density unevenness appears in the resulting image, leading to a reduction in image quality. For this reason, technological development for preventing the above-mentioned coating leakage and coating unevenness and uniformly coating the coating solution on the undercoat layer has been actively promoted.

  As such a technique, for example, Japanese Patent Laid-Open No. 3-260657 (Patent Document 8) discloses a coating for a charge generation layer intended to prevent coating unevenness by using at least one chlorine-based solvent as a solvent. Liquid has been proposed. Japanese Patent Application Laid-Open No. 4-14053 (Patent Document 9) discloses that a photosensitive layer is obtained by using a coating solution for a charge generation layer prepared using a solvent that is not compatible with the intermediate layer (undercoat layer). There has been proposed a method for producing an electrophotographic photosensitive member intended to prevent elution of an intermediate layer (undercoat layer) during the formation process. Japanese Patent Application Laid-Open No. 2004-29242 (Patent Document 10) proposes prevention of coating leakage and coating unevenness by using a charge generation layer coating liquid in which the difference in boiling point between two kinds of solvents is 35 ° C. or less. Has been.

Japanese Patent Publication No. 5-55860 JP 59-155851 A JP-A-2-233769 JP 61-28557 A Japanese Patent No. 2218593 Japanese Patent No. 2700859 Japanese Patent Laid-Open No. 7-110587 JP-A-3-260657 Japanese Patent Laid-Open No. 4-14053 JP 2004-29242 A

  However, the occurrence of coating leakage is not limited to the unevenness of the surface to be coated, but can also occur when there is no unevenness. For example, when the conductive support is not sufficiently cleaned, or oily substances that do not appear on the unevenness are adhered. The adhesion of oil may be mixed from the coating device or contamination of silicone oil in the coating solution. For this reason, it is extremely difficult to completely prevent coating leakage and coating unevenness with these conventional techniques. Therefore, an electrophotographic photosensitive member that can prevent coating defects and coating unevenness and maintains image quality without image defects is desired.

The inventors of the present invention can form a photosensitive layer without incurring coating defects or uneven coating by selecting a solvent contained in the coating solution for the charge generation layer, and obtain an image with good image quality. The present inventors have found a method for producing an electrophotographic photosensitive member that can be produced and have arrived at the present invention.
Thus, according to the present invention, there is provided a coating solution for a charge generation layer used for forming a charge generation layer of a laminated electrophotographic photosensitive member provided with at least a charge generation layer and a charge transport layer on a conductive support, The coating solution for charge generation layer contains at least two kinds of solvents, and the two kinds of solvents have a property that the difference in boiling point between each other is larger than 35 ° C. and the dielectric constant of at least one of the solvents is 6 or less. A coating liquid for a charge generation layer is provided.

  Furthermore, according to the present invention, there is provided a method for producing a laminated electrophotographic photosensitive member in which at least a charge generation layer and a charge transport layer are provided on a conductive support, wherein the charge generation layer is contained in a charge generation layer coating solution. The conductive support is formed by dip coating, and the charge generation layer coating solution contains at least two types of solvents, and the difference between the boiling points of the two types of solvents is greater than 35 ° C. And the manufacturing method of the electrophotographic photoreceptor characterized by having the property that the dielectric constant of at least one solvent is 6 or less.

According to the coating solution for charge generation layer of the present invention, it is possible to prevent coating unevenness and coating unevenness due to adhesion of an oily substance having small unevenness in addition to unevenness on the surface to be coated. As described above, the charge generation layer coating liquid of the present invention has improved coating properties on the coated surface. By using this coating solution for charge generation layer, a photoreceptor capable of obtaining a higher quality image can be obtained with a high yield.
Moreover, since the coating liquid contains a silicone oil having a specific viscosity, it is possible to further prevent coating leakage and coating unevenness. In particular, coating unevenness that occurs when the conductive support is pulled up from the coating solution can be prevented.

According to the production method of the present invention, it is possible to produce a photoreceptor free from coating defects and coating unevenness.
According to the photoreceptor of the present invention, it is possible to provide an image quality free from blurring and unevenness. In addition, by having the undercoat layer at a specific position, it is possible to provide a photoreceptor that is stable in electrical characteristics and has high image quality.

The present invention will be described below.
(Charge generation layer)
In the present invention, a charge generation layer coating solution containing at least two kinds of solvents is used for forming the charge generation layer. The two types of solvents have the property that the difference in boiling point between each other is greater than 35 ° C., and the dielectric constant of at least one of the solvents is 6 or less.
In the process in which the solvent evaporates from the liquid film obtained by applying the charge generation layer coating liquid onto the surface to be coated and the drying of the liquid film proceeds, the coating has been lost due to the low boiling point solvent having a high evaporation rate. It becomes easy to do. However, by making the difference in boiling point greater than 35 ° C., it is possible to prevent the occurrence of coating leakage due to the high boiling point solvent.

The upper limit of the difference in boiling point is not particularly limited as long as the charge generation layer coating solution can be applied onto the surface to be coated. For example, it can be 180 degreeC. Moreover, a preferable difference in boiling points is 40 to 80 ° C.
In addition, the dielectric constant of one of the two types of solvents is 6 or less. The measurement temperature of the dielectric constant is 20 ° C. By using a solvent having a dielectric constant of 6 or less, it is possible to prevent the coating surface from being uneven due to unevenness on the surface to be coated, or small unevenness formed by the adhesion of oily substances. The cause of the adhesion of the oily substance is a small amount of cutting oil remaining during cutting of the conductive support due to poor cleaning of the conductive support, a small amount of contamination from the coating device, contamination of silicone oil in the coating liquid, etc. Conceivable. Usually, oily substances are nonpolar and have a dielectric constant of about 2. Therefore, it is very easy to dissolve in a nonpolar solvent having a low dielectric constant, but difficult to dissolve in a polar solvent. Therefore, it can be said that the compatibility with the polar solvent is poor. The coating solution for charge generation layer of the present invention can be dissolved in a solvent or infiltrated with a solvent during coating, so that it can be applied to the coating solution for charge generation layer. As a result, the occurrence of coating leakage can be prevented.

By including at least a solvent having a dielectric constant of 6 or less and including two types of solvents having a difference in boiling point greater than 35 ° C., it is possible to more effectively prevent the occurrence of coating leakage.
Examples of the solvent that can be used for the coating solution for the charge generation layer include halogenated hydrocarbons such as methylene chloride (40 ° C., 9.1) and 1,2-dichloroethane (84 ° C., 10.4), acetone (56 ° C. 21), ketones such as cyclohexanone (156 ° C., 18.3), esters such as ethyl acetate (77 ° C., 6.0), n-butyl acetate (127 ° C., 6.1), 1,2- Ethers such as dimethoxyethane (85 ° C., 5.5), tetrahydrofuran (66 ° C., 7.5) and 1,3-dioxolane (76 ° C., 7.1), benzene (80 ° C., 2.3), toluene Aromatic hydrocarbons such as (111 ° C., 2.4), methyl isobutyl ketone (116 ° C., 13.5) and o-, m-, p-xylene (144-138, 1.1), and N, N-dimethylformamide (1 0 ° C., 38) and N, N- dimethylacetamide (166 ° C., include aprotic polar solvents 47) or the like. In the parentheses, the former means boiling point and the latter means dielectric constant.

  Among the above specific examples, methylene chloride, diethane, acetone, ethyl acetate, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, benzene, etc. can be used as the low boiling point solvent, and the high boiling point solvent can be used. , Cyclohexanone, n-butyl acetate, toluene, o-, m-, p-xylene, N, N-dimethylformamide, N, N-dimethylacetamide and the like can be used. These low-boiling and high-boiling solvents are selected such that the difference between the boiling points is greater than 35 ° C.

The two types of solvents can be selected from any combination of 1,2-dimethoxyethane and cyclohexanone, acetone and toluene, methylene chloride and toluene.
Among the two kinds of solvents, the weight ratio of the high boiling point solvent to the low boiling point solvent can be in the range of 1: 2 to 10. By setting it within this range, it is possible to further prevent coating leakage and coating unevenness due to the photoreceptor. A preferred weight ratio is 1: 3-9.
The charge generation layer coating solution may contain other solvents as long as the two kinds of solvents are contained. From the standpoint of preventing coating removal and coating unevenness due to the photoreceptor, the ratio of the above two solvents to the total solvent is preferably 80% by weight or more.

The charge generation layer coating solution can be prepared, for example, by mixing and dispersing a charge generation material in a solution obtained by dissolving a binder resin in a solvent.
The binder resin is not particularly limited, and all resins generally used for the charge generation layer can be used alone or in admixture of two or more. For example, insulating materials such as melamine resin, epoxy resin, silicon resin, polyurethane resin, acrylic resin, polycarbonate resin, polyarylate resin, phenoxy resin, butyral resin, vinyl chloride-vinyl acetate copolymer and acrylonitrile-styrene copolymer A copolymer resin may be mentioned.
The binder resin can be used in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the total solvent. A preferred use range is 5 to 10 parts by weight.

  The charge generation material is not particularly limited, and all charge generation materials generally used for the charge generation layer can be used alone or in combination of two or more. Examples thereof include bisazo compounds such as chlorodian blue, polycyclic quinone compounds such as dibromoanthanthrone, perylene compounds, quinacridone compounds, phthalocyanine compounds, and azulenium salt compounds.

  Of these charge generation materials, phthalocyanine compounds are preferred. Among the phthalocyanine compounds, Bragg angles (2θ ± 0.2 °) of 7.3 °, 9.4 °, 9.6 °, 11.6 °, 13 in the X-ray diffraction spectrum using CuKα ray. Main diffraction peaks at 3 °, 17.9 °, 24.1 ° and 27.2 °, and a peak bundle of 9.4 ° and 9.6 ° of which shows the maximum diffraction peak, In addition, crystalline oxotitanium phthalocyanine in which the peak at 27.2 ° shows the second largest peak is more preferable. Further, the crystalline oxotitanium phthalocyanine is preferably X-type metal-free phthalocyanine.

The charge generation material can be used in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the total solvent. A preferred use range is 5 to 15 parts by weight.
The coating solution for charge generation layer may contain silicone oil. When two types of solvents are used, when the conductive support is pulled up from the coating solution, ring-shaped coating unevenness of several mm to several cm, that is, liquid rising may occur at the lower end of the support. This is because the surface tension and evaporation rate between solvents are different. Specifically, the liquid rising is a process of natural drying immediately after application, and the difference in surface tension between the relatively quickly dried portion and the slowly dried portion becomes large, and the undried liquid at the lower end of the support is increased. Is caused to be pulled upward by the surface tension. In order to prevent the liquid from rising, it is effective to include silicone oil in the coating solution.

  The silicone oil preferably has a viscosity in the range of 5 to 50 mPa · s. If the viscosity of the silicone oil is too high, the compatibility with the coating solution may be reduced. When the compatibility is lowered, the silicone oil is localized on the surface, and the proportion of the silicone oil consumed together with the coating solution at the time of dip coating increases. As a result, the sustainability of the liquid overflow prevention effect may deteriorate. If the viscosity of the silicone oil is too small, the effect of preventing the liquid from rising may be reduced. In order to ensure the prevention effect, it is necessary to add a large amount of silicone oil, which may adversely affect the electrostatic characteristics of the electrophotographic photosensitive member. A more preferable viscosity is 10 to 30 mPa · s.

  Moreover, it is preferable that a silicone oil is contained in 1-20 weight% with respect to solid content of the coating liquid for charge generation layers. If the amount of silicone oil added is small, the effect of preventing the liquid from rising may be reduced. If the amount added is large, the electrostatic characteristics of the electrophotographic photosensitive member may be adversely affected. A more preferable addition amount is 0.01 to 2% by weight with respect to the coating solution.

As the silicone oil that can be contained in the coating solution, generally, any oil that has an effect of reducing the surface tension can be used. For example, the KF series manufactured by Shin-Etsu Chemical Co., Ltd. can be mentioned. Of these, dimethyl silicone oil is preferable because it does not deteriorate the characteristics of the electrophotographic photosensitive member.
The method for forming the charge generation layer is not particularly limited as long as the coating liquid of the present invention is used, and examples thereof include a dip coating method, a spray method, a bead method, and a nozzle method. Of these, the dip coating method is common because of its high mass productivity and low equipment costs.

  The charge generation layer can be formed, for example, by a dip coating method using the dip coating apparatus 10 shown in FIG. In the dip coating apparatus 10, the charge generation layer coating liquid 12 is accommodated in the coating liquid tank 11. In addition, the conductive support 2 is fixed to the arm 14. The arm 14 moves up and down by driving the motor 15 of the lifting device 13. The conductive support 2 fixed to the arm 14 is immersed in the charge generation layer coating solution 12 by the lifting device 13 and then pulled up. A charge generation layer can be formed on the conductive support 2 by evaporating the solvent from the charge generation layer coating solution 12 applied to the conductive support 2.

  The thickness of the charge generation layer is preferably in the range of 0.05 to 5 μm, particularly preferably in the range of 0.1 to 1 μm. If the charge generation layer is thinner than 0.05 μm, light absorption is reduced and sensitivity may be lowered. On the other hand, if it is thicker than 5 μm, the generation of heat carriers increases and the chargeability may decrease.

(Conductive support)
The charge generation layer is provided on the conductive support. Usable conductive supports include, for example, drums and sheets made of metal such as aluminum, aluminum alloy, copper, zinc, nickel, stainless steel and titanium. In addition, polymer materials such as polyethylene terephthalate, phenolic resin, nylon and polystyrene, glass and hard paper drums, sheets and seamless belts, metal foil laminated, metal deposited, titanium oxide, Examples thereof include those obtained by conducting a conductive treatment by applying a conductive material such as tin oxide, indium oxide and carbon black together with an appropriate binder resin.

(Charge transport layer)
A charge transport layer is provided on the charge generation layer.
The charge transport layer usually contains a charge transport material and a binder resin. Examples of the charge transport material include hydrazone compounds, pyrazoline compounds, triphenylamine compounds, triphenylmethane compounds, stilbene compounds, oxadiazole compounds, enamine compounds, and the like. These may be used alone or in combination of two or more.

As the binder resin, one or a mixture of two or more binder resins listed in the column of the charge generation layer can be used. The binder resin can be used in the range of 5 to 200 parts by weight with respect to 100 parts by weight of the charge transport material.
The thickness of the charge transport layer is preferably in the range of 5 to 50 μm, particularly preferably in the range of 10 to 40 μm. If the thickness of the charge transport layer is smaller than 5 μm, the charge holding ability may be lowered. On the other hand, when the film thickness is larger than 50 μm, it is difficult to form a film having a uniform thickness, and productivity may be lowered.

The method for forming the charge transport layer is not particularly limited, and examples thereof include a dip coating method, a spray method, a bead method, and a nozzle method. Of these, the dip coating method is common because of its high mass productivity and low equipment costs. Moreover, the dip coating method shown in FIG. 1 can be used for the dip coating method.
The charge transport layer coating solution is prepared by dissolving the charge transport material in a solution obtained by dissolving the binder resin in a solvent. Examples of the solvent that can be used include dichloromethane, tetrahydrofuran, dioxane, dioxolane, and the like. These may be used alone or in combination of two or more.

(Photosensitive layer)
A laminate of the charge generation layer and the charge transport layer is generally referred to as a photosensitive layer.
An electron-accepting substance may be added to the photosensitive layer (charge generation layer and / or charge transport layer) for the purpose of improving sensitivity and reducing residual potential and fatigue during repeated use.

Examples of the electron-accepting substance include quinone compounds such as parabenzoquinone, chloranil, tetrachloro1,2-benzoquinone, hydroquinone, 2,6-dimethylbenzoquinone, methyl 1,4-benzoquinone, α-naphthoquinone and β-naphthoquinone, Nitro such as 2,4,7-trinitro-9-fluorenone, 1,3,6,8-tetranitrocarbazole, p-nitrobenzophenone, 2,4,5,7-tetranitro-9-fluorenone and 2-nitrofluorenone Compounds, and tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane, 4- (p-nitrobenzoyloxy) -2 ', 2'-dicyanovinylbenzene and 4- (m-nitrobenzoyloxy) Cyano compounds such as -2 ', 2'-dicyanovinylbenzene, Ruorenon compounds, quinone compounds, and Cl, benzene derivatives having an electron attractive substituent ₂ such CN and NO like. These may be used alone or in combination of two or more.

The photosensitive layer contains ultraviolet absorbers and antioxidants such as benzoic acid, stilbene compounds and derivatives thereof, nitrogen-containing compounds such as triazole compounds, imidazole compounds, oxadiazole compounds, thiazole compounds, and derivatives thereof. It does n’t matter.
Furthermore, the photosensitive layer is mixed with a plasticizer such as dibasic acid ester, fatty acid ester, phosphoric acid ester, phthalic acid ester and chlorinated paraffin as necessary, to give processability and flexibility. Mechanical properties may be improved.

(Underlayer)
An undercoat layer may be provided between the conductive support and the charge generation layer. The undercoat layer is provided for improving the adhesion of the photosensitive layer to the conductive support and the charge blocking property from the conductive support.
The undercoat layer generally contains a resin as a main component. Considering that the photosensitive layer is formed on the undercoat layer using a solvent, the resin preferably has a high solvent resistance with respect to a general organic solvent. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, acrylic resins, polyurethane, melamine resins, phenol resins and epoxy resins. And a curable resin that forms a three-dimensional network structure.

For the purpose of preventing moire and reducing residual potential, fine powder pigments of metal oxides such as titanium oxide, silica, alumina, zirconium oxide, tin oxide and indium oxide may be added to the undercoat layer.
The thickness of the undercoat layer is preferably in the range of 0.1 to 20 μm, particularly preferably in the range of 1 to 5 μm. If the thickness of the undercoat layer is smaller than 0.1 μm, the function of the undercoat layer may be reduced, and it becomes difficult to obtain a uniform surface by covering the defects of the conductive support. The chargeability may be reduced due to a decrease in the function of preventing the injection of charges from the surface. On the other hand, if the film thickness is larger than 20 μm, it is difficult to form the undercoat layer by a dip coating method, and the mechanical strength of the coating film may be lowered.

A method for forming the undercoat layer is not particularly limited, and examples thereof include a dip coating method, a spray method, a bead method, and a nozzle method. Of these, the dip coating method is common because of its high mass productivity and low equipment costs. Moreover, the dip coating method shown in FIG. 1 can be used for the dip coating method.
The undercoat layer coating solution can be prepared by dissolving a resin in a solvent and dispersing a fine powder pigment of a metal oxide in the obtained solution as necessary. Examples of the solvent include alcohol solvents such as methanol and ethanol, ketone solvents such as methyl ethyl ketone and cyclohexanone, and ether solvents such as tetrahydrofuran.
For the dispersion of the fine powder pigment, a ball mill, a sand mill, an attritor, a vibration mill, a colloid mill, an ultrasonic disperser, or the like can be used.

(Surface protective layer)
If necessary, a surface protective layer for protecting the surface of the photosensitive layer may be provided on the photosensitive layer. A thermoplastic resin, light, or a thermosetting resin can be used for the surface protective layer. The surface protective layer may contain the above-described inorganic materials such as ultraviolet ray inhibitors, antioxidants, metal oxides, organometallic compounds, electron accepting substances, plasticizers, and the like.
The method for forming the surface protective layer is not particularly limited, and examples thereof include a dip coating method, a spray method, a bead method, and a nozzle method. Of these, the dip coating method is common because of its high mass productivity and low equipment costs. Moreover, the dip coating method shown in FIG. 1 can be used for the dip coating method.

(Configuration of photoconductor)
Examples of the structure of the photoreceptor are shown in FIGS. 2 and 3 are schematic sectional views of the photoreceptor.
FIG. 2 shows a function-separated type photoreceptor 1 which includes an undercoat layer (intermediate layer) 3 on a conductive support 2 and a photosensitive layer 6 on the undercoat layer 3. The photosensitive layer 6 is formed by laminating the charge generation layer 4 and the charge transport layer 5 from the undercoat layer 3 side.
FIG. 3 includes a photosensitive layer 6 on the conductive support 2. The photosensitive layer 6 is formed by laminating the charge generation layer 4 and the charge transport layer 5 from the conductive support 2 side.

(Image forming device)
FIG. 4 is a schematic configuration diagram of the image forming apparatus 21 on which the photosensitive member 1 is mounted. The image forming apparatus 21 includes at least a charging device 22, an exposure device 23, a developing device 24, a transfer device 26, a fixing device 27, a cleaning device 28, and a charge eliminating device 29 around the photosensitive member 1 that is rotatably arranged. .

A procedure for forming an image using the image forming apparatus 21 will be described.
First, after the surface of the photoreceptor 1 is charged to a predetermined potential by the charging device 22, a latent image is formed on the surface of the photoreceptor 1 by exposure of the exposure device 23. The formed latent image is developed with a developer by the developing device 24, and a visible image is thus formed on the surface of the photoreceptor 1. The formed visible image is transferred to the recording paper 25 conveyed to the transfer position by the transfer device 26 and fixed by the fixing device 27 to form an image on the recording paper 25. The developer remaining on the photoreceptor 1 after the transfer is cleaned by the cleaning device 28, and the remaining charge is neutralized by the neutralization device 29. By repeating the above steps, images can be formed continuously.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the following, “part” means “part by weight”. The main materials used for each layer used in this example are specifically as follows.
[Titanium oxide]
Product name: Dendritic rutile titanium oxide surface-treated with TTO-MI-1, Al ₂ O ₃ and ZrO ₂ , 85% titanium component, manufactured by Ishihara Sangyo Co., Ltd. [Alcohol-soluble nylon resin]
Product name: CM8000, manufactured by Toray Industries, Inc. [Butyral resin]
Product name: S-LEC BX-1, manufactured by Sekisui Chemical Co., Ltd. [silicone oil]
Product name: KF96, viscosity 10 mPa · s, manufactured by Shin-Etsu Chemical Co., Ltd. [Polycarbonate resin]
Product name: GH-503, manufactured by Idemitsu Kosan Co., Ltd. Product name: TS2040, manufactured by Teijin Chemicals Ltd. [Antioxidant]
Product name: Irganox 1010, manufactured by Ciba Specialty Chemicals

Example 1
3 parts of titanium oxide (TTO-MI-1) and 3 parts of alcohol-soluble nylon resin (CM8000) are added to a mixed solvent of 60 parts of methyl alcohol and 40 parts of 1,3-dioxolane, and dispersed for 10 hours with a paint shaker. The undercoat layer coating solution was prepared by processing. The coating solution was filled in the coating tank, and the aluminum cylindrical conductive support 2 (diameter: 30 mm, length: 346 mm) was dipped and pulled up and dried naturally to form an undercoat layer 3 having a layer thickness of 0.9 μm. .
Next, 15 parts of titanyl phthalocyanine represented by the following structural formula (1), 10 parts of butyral resin (S-LEC BX-1), 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5) 5) 1260 parts, 140 parts of cyclohexanone (boiling point: 156 ° C., dielectric constant: 18.3) and KF96 (viscosity: 10 mPa · s) were dispersed in a ball mill for 72 hours to prepare a charge generation layer coating solution. This coating solution was applied onto the above-described undercoat layer by the same application method as in the case of the undercoat layer, and then naturally dried to form a charge generation layer 4 having a layer thickness of 0.4 μm.

FIG. 5 is a diagram showing an X-ray diffraction spectrum of the titanyl phthalocyanine crystal, and the X-ray diffraction spectrum is a result of measurement under the following conditions.
X-ray source CuKα = 1.54050Å
Voltage: 30kV
Current: 50 mA
Start angle: 5.0 deg.
Stop angle: 35.0 deg.
Step angle: 0.01 deg.
Measurement time: 1 deg. / Min.
Measuring method: θ / 2θ scanning method Measuring device: RINT-TTR III manufactured by Rigaku
From FIG. 5, the titanyl phthalocyanine crystal has a Bragg angle (2θ ± 0.2 °) of 7.3 °, 9.4 °, 9.6 °, 11.6 °, 13.3 °, 17.9 °, Major diffraction peaks are shown at 24.1 ° and 27.2 °, of which the peak bundle of 9.4 ° and 9.6 ° is the maximum diffraction peak, and the peak at 27.2 ° is 2 It can be seen that it shows the second largest peak.

  Next, 100 parts of an enamine compound represented by the following structural formula (2), 100 parts of a polycarbonate resin (GH-503), 80 parts of a polycarbonate resin (TS2040) and 3 parts of an antioxidant (Irganox 1010) as a charge transport material are added to 950 tetrahydrofuran. A charge transport layer coating solution was prepared by mixing with the part and dissolving. This coating solution is applied onto the charge generation layer by the same coating method as that for the undercoat layer and the charge generation layer, and dried at 130 ° C. for 60 minutes to form the charge transport layer 5 having a layer thickness of 22 μm. A photoreceptor was obtained.

(Example 2)
A photoconductor was prepared in the same manner as in Example 1 except that 10 parts of titanyl phthalocyanine represented by the structural formula (1) and 5 parts of X-type metal-free phthalocyanine were used as the charge generation material.
(Example 3)
Example 1 except that 1260 parts of acetone (boiling point: 56 ° C., dielectric constant: 21) and 140 parts of toluene (boiling point: 111 ° C., dielectric constant: 2.4) were used as the solvent for the charge generation layer coating solution. A photoreceptor was prepared in the same manner as described above.
Example 4
A photoconductor was prepared in the same manner as in Example 3 except that 10 parts of titanyl phthalocyanine represented by the structural formula (1) and 5 parts of X-type metal-free phthalocyanine were used as the charge generation material.

(Comparative Example 1)
1400 parts of 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5.5) is used as a solvent for the charge generation layer coating solution, and KF96 (viscosity: 10 mPa · s) is not used for the charge generation layer coating solution. Except for this, a photoconductor was prepared in the same manner as in Example 1.
(Comparative Example 2)
1260 parts of 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5.5) and 140 parts of hexane (boiling point: 69 ° C., dielectric constant: 1.8) were used as the solvent for the coating solution for the charge generation layer. Except for this, a photoconductor was prepared in the same manner as in Example 2.
(Comparative Example 3)
1260 parts of 1,3-dioxolane (boiling point: 76 ° C., dielectric constant: 7.1) and 140 parts of hexane (boiling point: 69 ° C., dielectric constant: 1.8) were used as the solvent for the charge generation layer coating solution. A photoreceptor was prepared in the same manner as Example 2 except for the above.

(Example 5)
A photoconductor was prepared in the same manner as in Example 1 except that the undercoat layer was not formed and the charge generation layer coating solution was formed on an aluminum cylindrical conductive support.
(Example 6)
A photoconductor was prepared in the same manner as in Example 1 except that the charge generation layer coating solution did not contain KF96 (viscosity: 10 mPa · s).
(Example 7)
A photoconductor was prepared in the same manner as in Example 5 (no undercoat layer) except that the charge generation layer coating solution did not contain KF96 (viscosity 10 mPa · s).

(Comparative Example 4)
1260 parts of 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5.5) and 140 parts of hexane (boiling point: 69 ° C., dielectric constant: 1.8) were used as the solvent for the coating solution for the charge generation layer. Except for this, a photoconductor was prepared in the same manner as in Example 1.
(Comparative Example 5)
1260 parts of 1,3-dioxolane (boiling point: 76 ° C., dielectric constant: 7.1) and 140 parts of hexane (boiling point: 69 ° C., dielectric constant: 1.8) were used as the solvent for the charge generation layer coating solution. A photoreceptor was prepared in the same manner as in Example 1 except for the above.

(Example 8)
As the solvent for the coating solution for the charge generation layer, 1120 parts of 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5.5) and 280 parts of cyclohexanone (boiling point: 156 ° C., dielectric constant: 18.3) were used. Except for this, a photoconductor was prepared in the same manner as in Example 1.
Example 9
As a solvent of the coating solution for the charge generation layer, 980 parts of 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5.5) and 420 parts of cyclohexanone (boiling point: 156 ° C., dielectric constant: 18.3) were used. Except for this, a photoconductor was prepared in the same manner as in Example 1.
(Example 10)
As a solvent for the charge generation layer coating solution, 700 parts of 1,2-dimethoxyethane (boiling point: 85 ° C., dielectric constant: 5.5) and 700 parts of cyclohexanone (boiling point: 156 ° C., dielectric constant: 18.3) were used. Except for this, a photoconductor was prepared in the same manner as in Example 1.

The coating leakage and liquid rise of each photoconductor in Examples 1 to 10 and Comparative Examples 1 to 5 were evaluated. The evaluation criteria are as follows.
[Coating missing]
Twenty photoconductors of each of Examples 1 to 10 and Comparative Examples 1 to 5 were prepared and visually confirmed. The number of coating spots out of 20 was judged as 0 for ◯, 1-5 for Δ, and 6 or more for x.
[Liquid finish (uneven coating)]
The length from the end surface of the support at the end of coating was evaluated as 0 to 5 mm, Δ from 5 mm to less than 10 mm, and Δ from 10 mm or more.
[Comprehensive evaluation]
When the coating leakage and the liquid rise were both “good”, it was evaluated as “good”, when there was Δ in one side, “△” when there was “×”, and “x” when there was “×” in one side. The evaluation results are shown in Table 1.

The charge generation layer coating liquids of Examples 1 to 10 containing two kinds of solvents having a boiling point difference of greater than 35 ° C., and at least one of the solvents having a dielectric constant of 6 or less, are suppressed from being coated and spilled. In particular, when the ratio of the low boiling point solvent to the high boiling point solvent is twice or more, it can be said that the coating property is excellent.
The photoconductor of Comparative Example 1 had one type of solvent for the charge generation layer coating solution, and the coating could not be eliminated. Further, in the photoconductors of Comparative Examples 2 to 5, the solvent of the coating solution for the charge generation layer was a combination that did not satisfy the difference in boiling point and the dielectric constant of the present invention, and the coating was not eliminated.

Examples 5 and 7 are photoconductors without an undercoat layer, and it can be seen that coating removal can be improved by having an undercoat layer as compared with other examples. Furthermore, Examples 6 and 7 are photoconductors that do not contain silicone oil in the coating solution for charge generation layer, and it can be seen that the addition of silicone oil can improve liquid rise by comparing with other examples. .
From Examples 1, 8 and 9 and Example 10, it can be seen that the coating leakage can be further improved by increasing the content of the solvent having a low boiling point 2 to 10 times the content of the solvent having a high boiling point. .

It is the schematic of a dip coating apparatus. It is a schematic sectional drawing of a photoreceptor. It is a schematic sectional drawing of a photoreceptor. 1 is a schematic diagram of an image forming apparatus. It is a X-ray-diffraction spectrum figure of the titanyl phthalocyanine crystal used for the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrophotographic photosensitive member, 2 Conductive support body, 3 Undercoat layer, 4 Charge generation layer 5 Charge transport layer, 6 Photosensitive layer, 10 Immersion coating apparatus, 11 Coating liquid tank 12 Coating liquid for charge generation layer, 13 Lifting device , 14 arm, 15 motor 21 image forming device, 22 charging device, 23 exposure device, 24 developing device 25 recording paper, 26 transfer device, 27 fixing device, 28 cleaning device 29 static eliminating device

Claims (8)

A charge generation layer coating solution used for forming a charge generation layer of a laminated electrophotographic photosensitive member provided with at least a charge generation layer and a charge transport layer on a conductive support, wherein the charge generation layer coating solution is A charge comprising: at least two kinds of solvents, wherein the two kinds of solvents have a property that a difference in boiling point between them is larger than 35 ° C. and a dielectric constant of at least one of the solvents is 6 or less. Generation layer coating solution. The two types of solvents are methylene chloride, dichloride ethane, acetone, ethyl acetate, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane and benzene as low-boiling solvents, and cyclohexanone as high-boiling solvents. , N-butyl acetate, toluene, o-, m-, p-xylene, methyl isobutyl ketone, N, N-dimethylformamide and N, N-dimethylacetamide are selected so that the difference in boiling point is greater than 35 ° C. The coating solution for a charge generation layer according to claim 1. 3. The charge generation layer coating solution according to claim 2, wherein the two types of solvents are selected from any combination of 1,2-dimethoxyethane and cyclohexanone, acetone and toluene, and methylene chloride and toluene. The charge generating layer coating solution according to any one of claims 1 to 3, wherein the two types of solvents include a low-boiling solvent having a content 2 to 10 times that of the high-boiling solvent. The charge generation layer coating solution contains a silicone oil, the silicone oil has a viscosity in the range of 5 to 50 mPa · s, and is 1 to 20% by weight based on the solid content of the charge generation layer coating solution. The charge generation layer coating solution according to any one of claims 1 to 4, which is added in a range. In the X-ray diffraction spectrum using CuKα rays, the charge generation layer coating solution has Bragg angles (2θ ± 0.2 °) of 7.3 °, 9.4 °, 9.6 °, 11.6 °, Major diffraction peaks are shown at 13.3 °, 17.9 °, 24.1 °, and 27.2 °, and the peak bundle of 9.4 ° and 9.6 ° of which shows the maximum diffraction peak. The charge generation layer coating solution according to any one of claims 1 to 5, further comprising a crystalline oxotitanium phthalocyanine having a peak at 27.2 ° which is the second largest peak. The charge generation layer coating solution according to claim 6, wherein the charge generation layer coating solution contains X-type metal-free phthalocyanine. A method for producing a laminated electrophotographic photosensitive member having at least a charge generation layer and a charge transport layer provided on a conductive support, wherein the charge generation layer immerses the conductive support in a coating solution for a charge generation layer. The charge generation layer coating solution is formed by coating, and includes at least two types of solvents, and the two types of solvents have a difference in boiling point between 35 ° C. and a dielectric of at least one of the solvents. A method for producing an electrophotographic photosensitive member, wherein the rate is 6 or less.

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