JP2007188003A - Method for manufacturing electrophotographic photoreceptor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an organic photoreceptor free of unevenness in coating films and having a smooth surface free of pinholes and bubbles in a very short time without deteriorating characteristics as a photoreceptor. <P>SOLUTION: The method for manufacturing an electrophotographic photoreceptor includes: a step of applying a coating liquid for forming a charge transport layer ≥2 times in piles on a charge generating layer on a substrate so that the thickness of a single coating film is made ≤10 μm, wherein the coating liquid comprises at least a charge transport material having an enamine structure and a solvent having a relative evaporation rate of <1.7; and a step of obtaining a charge transport layer by drying each coating film after each application under such temperature conditions of coating film surfaces that the solvent is evaporated without deteriorating the charge transport material and surface temperatures become gradually high from the first coating film in the order of subsequently formed coating films. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an electrophotographic photoreceptor. More specifically, the present invention relates to a method for producing an electrophotographic photoreceptor including a step of forming a charge transport layer by applying and drying a coating solution two or more times.

  An electrophotographic image forming apparatus (hereinafter also referred to as an electrophotographic apparatus or simply an apparatus) used as a copying machine, a printer, a facsimile apparatus, or the like forms an image through the following electrophotographic process.

  First, the surface of an electrophotographic photoreceptor (hereinafter also simply referred to as a photoreceptor) provided in the apparatus is uniformly charged to a predetermined potential by a charger. Next, exposure is performed with light according to image information by an exposure unit, and an electrostatic latent image is formed on the surface of the photoreceptor. The formed electrostatic latent image is developed with a developer containing toner supplied from the developing means to form a visible toner image. The formed toner image is transferred from the surface of the photoreceptor to a transfer material such as recording paper by a transfer unit, and fixed by a fixing unit. Further, the surface of the photosensitive member after the toner image is transferred is cleaned by a cleaning unit, and the toner remaining on the surface of the photosensitive member without being transferred onto the transfer material and remains attached to the surface of the photosensitive member at the time of transfer. Remove foreign matter such as paper dust from the remaining recording paper. Thereafter, the surface charge of the photoreceptor is neutralized by a static eliminator or the like, and the electrostatic latent image on the surface of the photoreceptor is lost.

  A photoreceptor used in such an electrophotographic process is formed by laminating a photosensitive layer containing a photoconductive material on a conductive substrate. Conventionally, a photoreceptor using an inorganic photoconductive material (hereinafter referred to as an inorganic photoreceptor) has been used as the photoreceptor. As a typical inorganic photoreceptor, a selenium photoreceptor using a layer made of amorphous selenium (a-Se) or amorphous selenium arsenic (a-AsSe) as a photosensitive layer, zinc oxide (ZnO) or sulfide. A zinc oxide-based or cadmium sulfide-based photoconductor using a photosensitive layer in which cadmium (CdS) is dispersed in a resin together with a sensitizer such as a dye, and a layer made of amorphous silicon (a-Si) are used as the photosensitive layer. There are amorphous silicon photoconductors used (hereinafter referred to as a-Si photoconductors) and the like.

However, inorganic photoreceptors have the following drawbacks.
Selenium photoreceptors and cadmium sulfide photoreceptors have problems with heat resistance and storage stability. Selenium and cadmium are toxic to the human body and the environment. For this reason, a photoreceptor using these must be recovered after use and disposed of appropriately.

  Zinc oxide photoreceptors have the disadvantages of low sensitivity and low durability, and are rarely used today. The a-Si photoreceptor, which is attracting attention as a non-polluting inorganic photoreceptor, has advantages such as high sensitivity and high durability. On the other hand, since it is manufactured using a plasma chemical vapor deposition (abbreviation: PCVD) method, it is difficult to uniformly form a photosensitive layer and image defects are likely to occur. In addition, the a-Si photoreceptor has the disadvantages of low productivity and high manufacturing costs.

  In recent years, development of photoconductive materials used for photoreceptors has progressed, and organic photoconductive materials, that is, organic photoconductors (Organic Photoconductors), have been used in place of conventionally used inorganic photoconductive materials. (Abbreviation: OPC) is frequently used. A photoreceptor using an organic photoconductive material (hereinafter referred to as an organic photoreceptor) has some problems in sensitivity, durability, environmental stability, and the like. However, it has many advantages over inorganic photoreceptors in terms of toxicity, manufacturing cost, and freedom of material design. The organic photoreceptor also has an advantage that the photosensitive layer can be formed by an easy and inexpensive method typified by a dip coating method. Due to these advantages, organic photoreceptors have gradually become the mainstream of photoreceptors. In response to the recent demand for significant improvements in sensitivity and durability, organic photoconductors are now being used as photoconductors except in special cases.

  In particular, the performance of organic photoreceptors has been remarkably improved by the development of function-separated photoreceptors in which a charge generation function and a charge transport function are assigned to different substances. In addition to the above-mentioned advantages of the organic photoconductor, the function-separated type photoconductor has a wide material selection range of the charge generation material responsible for the charge generation function and the charge transport material responsible for the charge transport function, and has a desired characteristic. It also has the advantage that the body can be made relatively easily.

  There are two types of function-separated type photoreceptors: a laminated type and a single layer type. In the laminated type function-separated type photoreceptor, a laminated type photosensitive layer is formed by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. Generally, the charge generation layer and the charge transport layer are formed in a form in which the charge generation material and the charge transport material are dispersed in a binder resin which is a binder. In addition, in the single-layer type function dispersion type photoreceptor, a single-layer type photosensitive layer in which a charge generation material and a charge transport material are dispersed together in a binder resin is provided.

  Various materials such as phthalocyanine pigments, squarylium dyes, azo pigments, perylene pigments, polycyclic quinone pigments, cyanine dyes, squaric acid dyes, and pyrylium salt dyes are considered as charge generating materials used in functionally separated photoconductors. Various materials having high light resistance and high charge generation capability have been proposed.

  On the other hand, various compounds such as pyrazoline compounds, hydrazone compounds, triphenylamine compounds, and stilbene compounds are known as charge transport materials. Recently, pyrene derivatives, naphthalene derivatives, terphenyl derivatives and the like having condensed polycyclic hydrocarbons as a central nucleus have been developed.

Charge transport materials include
(1) being stable to light and heat;
(2) being stable against active substances such as ozone, nitrogen oxides (chemical formula: NOx) and nitric acid generated by corona discharge when charging the surface of the photoreceptor;
(3) having a high charge transport capability;
(4) High compatibility with organic solvent and binder resin,
(5) It must be easy and inexpensive to manufacture. However, although the aforementioned charge transport materials meet some of these requirements, they have not yet met all at a high level.

  Also, in recent years, electrophotographic apparatuses such as digital copying machines and printers have been miniaturized and speeded up, and high sensitivity corresponding to miniaturization and speed has been demanded as a photoreceptor characteristic. In particular, a high charge transport capability is required. In a high-speed electrophotographic process, since the time from exposure to development is short, a photoreceptor having excellent photoresponsiveness is required. If the photoresponsiveness is poor, that is, if the decay rate of the surface potential after exposure is slow, the residual potential rises, and the photoconductor is repeatedly used in a state where the surface potential of the photoreceptor is not sufficiently attenuated. For this reason, the surface charge of the portion to be erased is not sufficiently erased by exposure, resulting in an adverse effect such as an early deterioration in image quality. Since the photoresponsiveness depends on the charge transporting ability of the charge transporting substance, a charge transporting substance having a higher charge transporting ability is also required from this point.

  As a charge transport material satisfying such requirements, a charge transport material having an enamine structure, which has a higher charge transport capability than the above-described charge transport material, has been proposed (for example, JP-A-2-511162: Patent Documents). 1, Japanese Patent Laid-Open No. 6-43674: Patent Document 2, Japanese Patent Laid-Open No. 10-69107: Patent Document 3). By using these charge transport materials having an enamine structure, even if the binder resin ratio in the charge transport layer (or at least the outermost layer in the case of a charge transport layer composed of a plurality of layers) is increased, the photoresponsiveness is improved. Thus, a charge transport layer having a composition capable of simultaneously improving the photoresponsiveness and printing durability can be obtained.

The photosensitive layer is formed by applying a coating solution in which an organic functional material and an organic binder are dissolved or dispersed in a solvent to a uniform thickness on a conductive substrate by a dipping method. It is manufactured through a drying process for removing the contained solvent.
In the dipping method, one end of a cylindrical conductive substrate that is a substrate for a photoconductor is held, the cylinder axis is immersed in the coating solution in a state perpendicular to the liquid surface of the coating solution, and then the coating solution is used. This is a method of applying a photosensitive layer to the surface of a conductive substrate by pulling it up, and is often used in the production of a photoreceptor.

  However, since the film thickness of the coating film formed by the dipping method greatly depends on the pulling speed at which the conductive substrate is pulled up from the coating liquid, the viscosity of the coating liquid, the evaporation rate of the volatile components contained in the coating liquid, and so on. These must be strictly controlled. Also, since the conductive substrate is pulled up and down from the coating solution, the coating solution drips down along the surface of the conductive substrate due to the action of gravity, and the upper film thickness with respect to the pulling direction is lower than the lower film thickness. There is a problem that it becomes smaller.

  In order to eliminate such non-uniform film thickness, it is necessary to strictly control the pulling speed, but this is difficult to control. Therefore, in order to form a coating film having a uniform thickness, there is also a basic problem that the pulling speed after immersion must be slowed. Moreover, since a coating film is formed even in the inside of an electroconductive base | substrate which does not need to apply | coat and an end surface, there also exists a problem that the coating film formed in the inside and end surface of an electroconductive base | substrate must be peeled. Furthermore, since the conductive substrate is immersed in the coating solution, the tank for storing the coating solution must always contain an amount of the coating solution sufficient to immerse the entire length of the conductive substrate. As described above, since it is necessary to always prepare an amount of the coating liquid that exceeds the amount required for forming the coating film, there is a problem that the usage efficiency of the coating liquid is deteriorated.

  Therefore, in order to increase the use efficiency of the coating solution, instead of preparing a new coating solution for each coating, a newly prepared application amount is applied to the coating solution that has already been used and is stored in the storage tank. The method of adding the liquid and using the same coating liquid many times is taken. However, the viscosity and characteristics of the coating solution change with time and change with a slight difference from the newly added coating solution. Therefore, the application conditions have to be optimized every time the application work is performed, and the work efficiency is reduced.

  In particular, when applying a charge transport layer using a charge transport material having an enamine structure and increasing the ratio of the binder resin in the charge transport layer in order to achieve high photoresponsiveness and high printing durability as described above, The change with time of the viscosity of the coating solution becomes larger. Therefore, the dipping method is not suitable. Further, when two charge transport layers are formed, there is also a problem that the first charge transport layer is dissolved at the time of the second dip coating, and the second layer coating solution is changed.

As a coating method other than the dipping method, there are a spray coating method and a blade coating method.
In the spray coating method, coating is performed by ejecting the coating liquid as fine particles from a spray nozzle, so that the appearance after coating is good. However, since the thickness of the layer formed by one application is thin, in order to obtain a desired layer thickness, a plurality of applications must be repeated. In addition, when a large amount of coating solution is applied at once, the coating solution drips and a coating layer having a non-uniform thickness is formed. Furthermore, since the volatile components in the coating liquid are easily volatilized by spraying the coating liquid, the viscosity of the coating liquid is increased, and an orange peel (an orange skin-like wave on the surface) is formed on the formed coating layer. A phenomenon that occurs).

In the blade coating method, the blade is disposed at a position close to the conductive substrate, the coating solution is supplied to the blade, the coating solution is applied to the conductive substrate by the blade, and the blade is rotated once by rotating the conductive substrate. This is a coating method for retreating. With this method, high productivity can be obtained. However, when the blade is retracted, there is a problem in that a part of the coating film applied to the conductive substrate rises due to the surface tension of the coating liquid and the film thickness becomes non-uniform.
On the other hand, the drying step is generally performed by a batch method in which a certain number of conductive substrates having a coating film are charged in an oven capable of blowing hot air at a predetermined temperature, or a continuous method in which the substrate is passed through a tunnel furnace.

  However, in hot air drying, the coating surface to which the hot air is directly or indirectly applied in the drying apparatus is first dried even though the solvent remains in the film and is in an undried state. The Furthermore, since the temperature is non-uniform between the location where the hot air hits and the location where the hot air does not hit, unevenness occurs in the dry state. As the drying progresses, the surface of the coating film becomes dry and hardens, while in the film, the temperature rises and drying begins to generate a gas in which the solvent is vaporized. Since this gas is difficult to escape due to the film cured on the surface of the coating film, the time until the entire coating film is dried is made extremely long. Further, long-time drying requires not only a large continuous drying furnace and batch-type oven on a general production line, but also a large cost for operation and management. Furthermore, when the solvent evaporates from the inside of the coating film, defects such as bubbles, pinholes and coating film repelling may occur on the coating film surface.

On the other hand, if the drying is insufficient, the solvent remains in the coating film, so that the sensitivity of the photosensitive layer is poor, the repeated exposure stability is lowered, and cracks and peeling are likely to occur.
As conventional techniques for solving such problems, Japanese Patent Publication No. 5-50742 (Patent Document 4) and Japanese Patent Application Laid-Open No. 11-311871 (Patent Document 5) are far from the constituent material of the coating film by an infrared heater. A method of absorbing and heating infrared rays to dry is described. This drying method heats the coating material itself, so there is little unevenness and the coating surface is hard to harden, so the above-mentioned defects can be prevented, and since the energy supplied to the coating film is high, drying can be done in a short time. it can.

Japanese Patent Laid-Open No. 2-51162 Japanese Patent Laid-Open No. 6-43674 Japanese Patent Laid-Open No. 10-69107 Japanese Patent Publication No. 5-50742 JP-A-11-311871

However, when a coating film containing a charge transport material having an enamine structure is dried, the enamine structure is weak against heat, so that it may be deteriorated by far infrared rays having a large amount of supplied heat.
An object of the present invention is to produce an organic photoreceptor having a smooth surface with no coating unevenness and no generation of pinholes and bubbles, in a very short time and without impairing the characteristics of the photoreceptor. Is to provide a way to do.

Thus, according to the present invention, a charge transport layer forming coating solution containing at least a charge transport material having an enamine structure and a solvent having a relative evaporation rate of less than 1.7 is formed on the charge generation layer on the substrate. A step of applying two or more times so that the thickness of the coating film is 10 μm or less;
After each coating, the coating material is not deteriorated, the solvent is evaporated, and the coating surface temperature is gradually increased from the first coating to the coating formed thereafter. And a step of obtaining a charge transport layer by drying the film.

According to the present invention, the coating liquid is applied twice or more times, the coating film is dried, and the charge transport layer is formed, so that the thickness of one coating film is 10 μm or less, and a predetermined value is applied after each coating. The dried state of the lower coating film can also be made favorable by performing heat drying at a temperature of.
On the other hand, by using a charge transport material having an enamine structure, the sensitivity does not deteriorate even when used repeatedly in harsh environments such as high-temperature and high-humidity environments. Is obtained. Furthermore, in order to obtain high printing durability, it is possible to afford to increase the ratio of the binder resin in the charge transport layer. At this time, by setting the ultimate temperature to 80 ° C. to 140 ° C., drying can be sufficiently performed without deteriorating the charge transport material. In addition, it is possible to suppress deterioration of the lower coating film heated for a longer time by setting the ultimate temperature of the upper coating film surface to be sequentially higher than that of the lower coating film.

Moreover, the leveling property after application | coating can be improved by using the organic solvent whose relative evaporation rate is less than 1.7. As a result, a photoconductor having a uniform film thickness, no unevenness, no peeling and cracking, and good smoothness can be obtained.
As the coating method, the roll coating method is optimal.
Further, when the solvent having a relative evaporation rate of less than 1.7 is contained in 30% by weight or more in all the solvents, curing of the coating film surface at the initial stage of drying, which is a problem in hot air drying, can be prevented. Therefore, the internal solvent can be removed efficiently. As a result, it is possible to provide a photosensitive member with excellent smoothness free from unevenness, peeling and cracking in a very short time.

In addition, a solvent having a relative evaporation rate of less than 1.7 is present in a lower ratio in the coating liquid for forming the upper layer than the lower layer, thereby lowering the ratio of the solvent in the entire coating film as it is repeatedly applied. Can do. Therefore, the drying efficiency of the solvent can be further increased.
In addition, the charge transport material (especially longer far-infrared heating) can be achieved by increasing the arrival temperature of the upper coating surface of two adjacent coating films by 10 ° C. to 30 ° C. higher than the arrival temperature of the lower coating surface. Residual solvent can be reduced while suppressing the deterioration of the lowermost charge transport material.

  By using far-infrared heating for heating and drying, the drying time can be shortened by setting the drying time of each layer until a predetermined temperature is reached. Furthermore, the coating film is heated by absorbing far-infrared rays in the constituent material itself of the coating film. Therefore, the coating surface can be prevented from being hardened at the initial stage of drying, which has become a problem with hot air drying, and the internal solvent can be efficiently removed.

Hereinafter, a method for producing an electrophotographic photoreceptor will be described.
The photoreceptor manufactured according to the present invention is not particularly limited, and various modifications are allowed. Such a photoreceptor may have, for example, a structure including a photosensitive layer including a charge generation layer and a charge transport layer on a substrate, and includes an undercoat layer on the substrate. May have a structure including a charge generation layer and a charge transport layer.
Hereinafter, the substrate of the photoreceptor that can be produced by the production method of the present invention, the components of the photosensitive layer and the coating solution for forming each layer of the photosensitive layer will be described.

(Charge transport layer)
The present invention is characterized by a method for forming a charge transport layer. First, a method for forming this layer will be described.
The charge transport layer is made of a charge transport material having an ability to accept and transport charges generated by the charge generation material. Moreover, binder resin may be included as needed.

  In the present invention, at least two charge transport layers are provided. More preferably, it is 2-4 layers. Each charge transport layer has a thickness of 10 μm or less, more preferably 5 to 10 μm. The composition of each layer may be the same or different.

  The total film thickness of the charge transport layer is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. If the total thickness of the charge transport layer is less than 5 μm, the charge holding ability of the surface of the photoreceptor may be lowered. If the total thickness of the charge transport layer exceeds 50 μm, the resolution of the photoreceptor may be lowered.

In addition, by using a charge transport material having an enamine structure for the charge transport layer, the sensitivity does not deteriorate even when used repeatedly in a harsh environment such as a high temperature and high humidity environment. A photosensitive member having excellent photoresponsiveness can be obtained. The charge transport material having an enamine structure is used alone or in combination of two or more.
The charge transport material having an enamine structure is not particularly limited, and known materials can be used. Examples of the charge transport material having an enamine structure that can be particularly preferably used in the present invention include the following.

  The charge transport material having an enamine structure may be used by mixing with other charge transport materials. Examples of other charge transport materials used by mixing with a charge transport material having an enamine structure include a hole transport material and an electron transport material.

  Examples of hole transport materials include carbazole derivatives, pyrene derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, Polycyclic aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives, stilbene Derivatives, benzidine derivatives and the like. In addition, polymers having groups derived from these compounds in the main chain or side chain, such as poly-N-vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, poly-9-vinylanthracene And polysilane.

  Examples of the electron transport material include organic compounds such as benzoquinone derivatives, tetracyanoethylene derivatives, tetracyanoquinodimethane derivatives, fluorenone derivatives, xanthone derivatives, phenanthraquinone derivatives, phthalic anhydride derivatives, diphenoquinone derivatives, amorphous silicon, Examples include inorganic materials such as amorphous selenium, tellurium, selenium-tellurium alloy, cadmium sulfide, antimony sulfide, zinc oxide, and zinc sulfide.

The charge (hole or electron) transporting material is not limited to those described above, and can be used alone or in admixture of two or more.
Thus, when a charge transport material having an enamine structure is mixed with another charge transport material, if the ratio of the charge transport material other than the charge transport material having an enamine structure is too large, the charge transport capability of the charge transport layer Is insufficient, and the sensitivity and photoresponsiveness of the photoreceptor may not be sufficiently obtained. Therefore, it is preferable to use, as the charge transport material, a mixture containing a charge transport material having an enamine structure as a main component. Here, the main component means 50% by weight or more based on the total amount of the charge transport material.

  The charge transport layer is a coating solution for forming a charge transport layer obtained by dissolving or dispersing a charge transport material in a solvent, particularly a binder resin solution obtained by dissolving or mixing a binder resin as a binder in a solvent. In addition, a coating solution obtained by dissolving or dispersing the charge transport material by a known method can be formed by coating on the charge generation layer.

As the binder resin for the charge transport layer, a resin having excellent compatibility with the charge transport material is selected. Examples of the binder resin include vinyl polymer resins such as polymethyl methacrylate resin, polystyrene resin, and polyvinyl chloride resin, and copolymer resins thereof, polycarbonate resin, polyester resin, polyester carbonate resin, polysulfone resin, phenoxy resin, and epoxy resin. , Silicone resin, polyarylate resin, polyamide resin, methacrylic resin, acrylic resin, polyether resin, polyurethane resin, polyacrylamide resin, phenol resin, and the like. Moreover, you may use the thermosetting resin which bridge | crosslinked these resin partially. These resins may be used alone or in combination of two or more. Among the resins described above, polystyrene resin, polycarbonate resin, polyarylate resin, or polyphenylene oxide is particularly excellent because it has a volume resistance of 10 ¹³ Ω or more and excellent electrical insulation, and also has excellent film formability and electrical characteristics. preferable.

  The ratio (B / A) of the weight (B) of the binder resin to the weight (A) of the charge transport material is 12/10 or more and 30/10 or less (= 1.2) when the composition of each charge transport layer is the same. Is preferably 3.0 or less). When the ratio (B / A) exceeds 30/10 (= 3.0) and the binder resin content is increased, the viscosity of the coating solution for forming the charge transport layer increases, leading to a decrease in coating speed and productivity. May be significantly worse. Furthermore, if the amount of the solvent in the coating liquid for forming the charge transport layer is increased in order to suppress this increase in viscosity, a brushing phenomenon that causes white turbidity in the formed charge transport layer occurs. Further, when the ratio (B / A) is less than 12/10 (= 1.2) and the binder resin ratio is low, the printing durability is lowered and the charge transport is lower than when the binder resin ratio is high. Since the amount of wear of the layer increases, the endurance life may be shortened.

  However, when each charge transport layer formed in each application has a different composition, this ratio can be arbitrarily changed according to the function of each layer, thereby achieving both photoresponsiveness and printing durability. Can be achieved relatively easily. For example, among the charge transport layers having a plurality of compositions, the ratio (B / A) in the uppermost charge transport layer is made higher than the aforementioned 20/10 (= 2.0) to increase the binder resin content ratio. However, if the ratio (B / A) in the lower charge transport layer is lowered to reduce the content ratio of the binder resin, both durability and responsiveness can be achieved.

  That is, the uppermost layer of the charge transport layer is formed with a thickness that is greater than or equal to the thickness at which the photoconductor wears, and the binder resin content of the charge transport layer is extremely increased to increase wear resistance and ensure responsiveness. Therefore, the responsiveness of the entire charge transport layer can be ensured by increasing the content ratio of the charge transport material in the lower layer than the uppermost layer to increase the mobility of holes.

  The ratio (B / A) in the uppermost charge transport layer for expressing a suitable wear resistance life is 20/10 to 60/10 (= 2.0 to 6.0) by weight. If the ratio (B / A) exceeds 6.0 and the binder resin ratio becomes high, the concentration of the charge transport material becomes too low, which makes it difficult for hopping conduction to occur and the hole mobility may be extremely poor. . On the other hand, when the ratio (B / A) is less than 2.0, the printing durability may be lower than when the binder resin ratio is high, and the wear amount of the charge transport layer may increase. Therefore, a suitable ratio (B / A) is set to 2.0 or more and 6.0 or less.

  Moreover, the suitable range of the said ratio (B / A) of a lower layer is 8 / 10-20 / 10 (= 0.8-2.0) by weight ratio. When the ratio (B / A) exceeds 2.0 and the binder resin ratio increases, the hole mobility becomes slow, and the responsiveness of the entire charge transport layer may be too low. Further, when the ratio (B / A) is less than 0.8, the concentration of the charge transport material is high, so that the crystallization of the charge transport material may occur during repeated use, and the image quality may be extremely deteriorated.

Furthermore, the mobility of all of the uppermost layer and the lower layer portion, that is, the entire charge transport layer is 1.0 × 10 ⁻⁶ cm ² at an environmental temperature of 5 ° C. and an electric field strength of 2.5 × 10 ⁵ V / cm. By setting it to / Vs or more, the responsiveness of the photoreceptor required for the current image formation can be sufficiently ensured.

  The mobility of the entire charge transport layer can be controlled by adjusting the binder resin content in the upper and lower charge transport layers, adjusting the thickness of the upper and lower layers, or the material structure of the upper and lower charge transport materials. It can be realized by optimizing. That is, since the mobility is proportional to the concentration of the charge transport material, the mobility is high when the content of the charge transport material in the charge transport layer is high, and the mobility is low when the content is low. When the charge transport layer is composed of two or more layers and the mobility of each layer is different, if the layer with low mobility is thickened, the mobility of the entire charge transport layer becomes low, and conversely the layer with high mobility When the thickness is increased, the mobility of the entire charge transport layer is increased. Furthermore, the mobility of the charge transport layer can be increased by using a charge transport material having a high mobility property. In reality, by optimizing the above conditions according to the specifications required for the photoconductor, it is possible to produce a photoconductor having sufficiently high mobility of the charge transport layer and satisfying the required specifications. it can.

As an example of the case where the charge transport layer is composed of two layers, the mobility of the entire charge transport layer can be obtained by the following equation (2). Therefore, the above conditions are selected and set based on the equation (2). Thus, the desired mobility is controlled.
Mobility of the entire charge transport layer = (d1η1c1 + d2η2c2) / (d1 + d2) (2)
here,
d1: Lower layer thickness η1: Mobility of lower layer charge transport material c1: Concentration of lower layer charge transport material d2: Upper layer thickness η2: Mobility of upper layer charge transport material c2: Concentration of upper layer charge transport material It is.
The concentration c of the charge transport material is a value obtained by dividing the amount of the charge transport material by (amount of charge transport material + amount of binder resin).

  In order to improve the film formability, flexibility and surface smoothness, an additive such as a plasticizer or a surface modifier may be added to the charge transport layer as necessary. Examples of the plasticizer include biphenyl, biphenyl chloride, benzophenone, o-terphenyl, dibasic acid ester, fatty acid ester, phosphoric acid ester, phthalic acid ester, various fluorohydrocarbons, chlorinated paraffin, and epoxy type plasticizer. be able to. Examples of the surface modifier include silicone oil and fluororesin.

  In addition, fine particles of an inorganic compound or an organic compound may be added to the charge transport layer in order to increase mechanical strength and improve electrical characteristics. Furthermore, you may add various additives, such as antioxidant and a light stabilizer, as needed. As a result, deterioration of the surface layer due to adhesion of active substances such as ozone and NOx generated during charging is reduced, and durability when the photoreceptor is repeatedly used can be improved. In addition, the stability as a coating liquid for forming a charge transport layer is increased, the life of the liquid is extended, and the photoreceptor manufactured with the coating liquid is also reduced in impurities, so that the durability can be improved.

  As the antioxidant and the light stabilizer, hindered phenol derivatives or hindered amine derivatives are preferably used. The hindered phenol derivative is preferably used in a weight ratio in the range of 0.001 to 0.10 with respect to the weight of the charge transport material. The hindered amine derivative is preferably used in a weight ratio in the range of 0.001 to 0.10 with respect to the weight of the charge transport material. Further, a hindered phenol derivative and a hindered amine derivative may be mixed and used. In this case, it is preferable that the total use amount of the hindered phenol derivative and the hindered amine derivative is a weight ratio in the range of 0.001 to 0.10 with respect to the weight of the charge transport material.

  When the amount of hindered phenol derivative used or the amount of hindered amine derivative used or the total amount of hindered phenol derivative and hindered amine derivative used is less than 0.001 by weight with respect to the weight of the charge transport material, the charge transport layer is formed. In some cases, a sufficient effect cannot be exhibited in improving the stability of the coating solution and improving the durability of the photoreceptor. On the other hand, if the weight ratio exceeds 0.10, the electrical characteristics of the photoreceptor may be adversely affected.

  Further, among the plurality of charge transport layers formed by each application, the total amount of the antioxidant and the light stabilizer contained in the uppermost charge transport layer is the antioxidant contained in the lower charge transport layer. And more than the total amount of light stabilizer. Thereby, durability against deterioration of the surface layer due to adhesion of active substances such as ozone and NOx generated during charging can be efficiently improved. That is, by adding a large amount of an antioxidant and a light stabilizer only to the uppermost charge transport layer exposed to an active substance such as ozone and NOx, the active substance can be efficiently supplemented and inactivated by the uppermost layer. Therefore, the deterioration of the photoreceptor can be effectively prevented. Further, since the total amount of the antioxidant and the light stabilizer can be suppressed in the entire charge transport layer, adverse effects on the electrical characteristics of the photoreceptor can be reduced. Therefore, it is possible to provide a highly durable photoconductor.

  The charge transport layer is prepared by dissolving or dispersing the charge transport material, the binder resin, and, if necessary, the aforementioned additives in a suitable solvent to prepare a charge transport layer forming coating solution, and applying the coating solution. -It can be formed by drying.

The solvent used in the coating solution for forming the charge transport layer includes the following general formulas for preventing drying and curing at the initial stage of drying the coating surface, effectively drying the solvent inside the coating film, and ensuring coating uniformity. A solvent having a relative evaporation rate represented by (1) of less than 1.7 is used.
Relative evaporation rate = time for n-butyl acetate to evaporate / time for test solvent to evaporate (1)
That is, when only a solvent having a high evaporation rate (relative evaporation rate of 1.7 or more) is used, the coating surface is dry-cured due to an air flow in the initial stage of drying, and the solvent inside the coating becomes difficult to dry. When a solvent having a low evaporation rate (relative evaporation rate less than 1.7) is used, the surface of the coating film is not cured, and the internal solvent can be efficiently diffused and vaporized. A preferred relative evaporation rate is 0.3 to 1.7. The proportion of the solvent having a relative evaporation rate of less than 1.7 in the solvent is preferably 30% by weight or more. Table 1 shows the relative evaporation rates of typical solvents.

  Solvents that satisfy the above conditions and dissolve the charge transport material well include 1,4-dioxane (1.65), ethylene glycol monomethyl ether (0.53), diethylene glycol monomethyl ether (0.02), diethylene glycol mono Examples include butyl ether (0.004), xylene (0.76), cyclohexanone (0.32), isophorone (0.026), and n-butyl acetate (1.00). These solvents may be used alone or in admixture of two or more.

However, if a solvent having a relative evaporation rate of less than 1.7 is used alone, the evaporation rate may be too small. In that case, in order to shorten the drying time, a solvent having a relative evaporation rate of 1.7 or more may be mixed to some extent. In particular, it is preferable that the ratio of the solvent having a relative evaporation rate of less than 1.7 in the solvent composition in the coating liquid is lower in the coating liquid used for the upper charge transport layer. In other words, the proportion of the solvent that hardly evaporates in the entire charge transport layer decreases as coating is repeated, and the drying efficiency during drying of the upper charge transport layer can be further increased. The difference in the ratio of the solvent having a relative evaporation rate of less than 1.7 between the uppermost coating film and the lowermost coating film is preferably 40 to 70%, and more preferably 50 to 65%.
Furthermore, if necessary, a solvent that does not easily dissolve the charge transport material or the like by itself, such as alcohols, acetonitrile, or methyl ethyl ketone, can also be used.

  Each coating film is dried under the temperature condition of the coating film surface which does not deteriorate the charge transport material, evaporates the solvent, and gradually increases from the first coating film to the coating film formed thereafter. It is preferable to perform drying of each coating film between 80-140 degreeC. Here, the upper coating film is dried under the condition that the surface temperature is higher than the surface temperature of the lower coating film. In particular, it is preferable that the reached temperature of the upper coating film surface of two adjacent coating films is 10 ° C. to 30 ° C. higher than the reached temperature of the lower coating film surface. The drying time is not particularly limited, and may be a time required to reach a predetermined temperature.

(Substrate)
The substrate is usually conductive. As the conductive substrate, for example, a metal material such as aluminum, aluminum alloy, copper, zinc, stainless steel, or titanium can be used. The conductive substrate is not limited to these metal materials, but is a polymer material such as polyethylene terephthalate, polyester, polyoxymethylene and polystyrene, a hard paper, a surface such as glass laminated with a metal foil, metal A material obtained by vapor deposition or a material obtained by vapor deposition or application of a conductive compound layer such as a conductive polymer, tin oxide, indium oxide, carbon particles, or metal particles can also be used. In addition, the surface of the substrate is optionally treated within a range that does not affect the image quality of the image formed when used as a photoconductor, surface treatment with chemicals, hot water, etc., and color treatment. Alternatively, irregular reflection processing such as roughening the surface may be performed. In an electrophotographic process using a laser as an exposure light source, the incident laser light has the same wavelength, so that the incident laser light and the light reflected in the photosensitive member cause interference, and interference fringes due to this interference appear on the image. It may appear and image defects may occur. By performing the irregular reflection treatment as described above on the surface of the substrate, it is possible to prevent image defects due to the interference of laser light having the same wavelength.
The shape of the substrate is not particularly limited, and any known shape such as a plate shape or a cylindrical shape can be used. Of these, a cylindrical shape is preferable.

(Charge generation layer)
The charge generation layer contains, as a main component, a charge generation material that generates charges by absorbing light. Examples of charge generation materials include azo pigments such as monoazo pigments, bisazo pigments and trisazo pigments, indigo pigments such as indigo and thioindigo, perylene pigments such as perylene imide and perylene anhydride, and polycyclic quinones such as anthraquinone and pyrenequinone. Pigments, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, triphenylmethane pigments such as methyl violet, crystal violet, knight blue and victoria blue, acridine pigments such as erythrosin, rhodamine B, rhodamine 3R, acridine orange and frapposin , Thiazine dyes such as methylene blue and methylene green, oxazine dyes such as capri blue and meldra blue, squarylium dyes, pyrylium salts, thiopyrylium salts, thioindigo colors , Bisbenzimidazole dyes, quinacridone dyes, quinoline dyes, lake dyes, azo lake dyes, dioxazine dyes, azurenium dyes, triarylmethane dyes, xanthene dyes, cyanine dyes And inorganic materials such as dyes, amorphous silicon, amorphous selenium, tellurium, selenium-tellurium alloys, cadmium sulfide, antimony sulfide, zinc oxide, and zinc sulfide. These charge generation materials may be used alone or in combination of two or more.

  The thickness of the charge generation layer is preferably 0.05 μm or more and 5 μm or less, more preferably 0.1 μm or more and 1 μm or less. If the film thickness of the charge generation layer is less than 0.05 μm, the light absorption efficiency is lowered, and the sensitivity of the photoreceptor may be lowered. If the film thickness of the charge generation layer exceeds 5 μm, the charge transfer inside the charge generation layer becomes a rate-determining step in the process of erasing the charge on the surface of the photoreceptor, and the sensitivity may be lowered.

  The charge generation layer is a coating solution for forming a charge generation layer obtained by dissolving or dispersing a charge generation material in a solvent, particularly a binder resin solution obtained by dissolving or mixing a binder resin as a binder in a solvent. Further, it can be formed by applying a coating solution obtained by dispersing the charge generating material by a known method on the substrate or the undercoat layer.

  As the binder resin used in the coating solution for forming the charge generation layer, any commonly used known resin can be used. For example, polyester resin, polystyrene resin, polyurethane resin, phenol resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate resin, polyarylate resin, phenoxy resin, polyvinyl butyral resin, polyvinyl formal resin, etc. And a resin selected from the group consisting of a copolymer resin containing two or more of the repeating units constituting these resins can be used. Examples of the copolymer resin include insulating resins such as vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, and acrylonitrile-styrene copolymer resin. . These may be used individually by 1 type and may use 2 or more types together.

  Examples of the solvent used in the coating solution for forming the charge generation layer include halogenated hydrocarbons such as 1,3-dichloropropane and trichloroethane, ketones such as isophorone, methyl ethyl ketone, acetophenone, cyclohexanone, and isophorone, ethyl acetate, and benzoic acid. Esters such as methyl acid, n-butyl acetate, tetrahydrofuran, 1,4-dioxane, dibenzyl ether, ethers such as 1,2-dimethoxyethane, benzene, toluene, xylene, mesitylene, tetralin, diphenylmethane, dimethoxybenzene, Aromatic hydrocarbons such as dichlorobenzene, sulfur-containing solvents such as diphenyl sulfide, fluorine-based solvents such as hexafluoroisopropanol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, etc. Glyme solvents, N, N- dimethylformamide, N, aprotic polar solvents such as N- dimethylacetamide. These solvents can be used alone or as a mixed solvent in which two or more are mixed.

The blending ratio of the charge generation material and the binder resin is preferably such that the charge generation material is in the range of 10 wt% to 99 wt% when the weight of the entire charge generation layer is 100%. If the charge generation material is less than 10% by weight, the sensitivity of the photoreceptor may be lowered. When the charge generation material exceeds 99% by weight, not only the strength of the charge generation layer is decreased, but also the dispersibility of the charge generation material is decreased and the coarse particles are increased. Therefore, image defects, particularly image fogging called black spots where toner adheres to a white background and minute black spots are formed may occur.
As a pretreatment for dispersing the charge generation material in the binder resin solution, the charge generation material may be pulverized in advance by a pulverizer. Examples of the pulverizer used for the pulverization treatment include a ball mill, a sand mill, an attritor, a vibration mill, and an ultrasonic disperser. As a dispersion condition at this time, it is desirable to select an appropriate condition so that impurities are not mixed due to wear of members used in the container and the disperser.

Furthermore, you may add various additives, such as a hole transport material, an electron transport material, antioxidant, a dispersion stabilizer, and a sensitizer, to a charge generation layer as needed. As a result, the potential characteristics are improved, and the stability as the coating liquid can be improved. Further, it is possible to reduce fatigue deterioration when the photoreceptor is used repeatedly, and to improve durability.
Examples of the coating method for the charge generation layer forming coating solution include a spray method, a ring coating method, a roll coating method, a blade method, and a dipping method.

(Undercoat layer)
The photoreceptor may be provided with an undercoat layer between the base and the charge generation layer as described above. By providing the undercoat layer, injection of charges from the substrate to the photosensitive layer can be prevented, so that a decrease in charge holding ability of the photoreceptor can be prevented. In addition, when a photoreceptor having an undercoat layer is used for image formation, it is possible to prevent the occurrence of defects such as fogging in the image because the reduction of surface charge other than the portion to be erased by exposure is suppressed. . Furthermore, since the surface of the substrate can be smoothed by covering the defects on the surface of the substrate with the undercoat layer, the film forming properties of the charge generation layer and the charge transport layer can be improved. Further, peeling of the charge generation layer and the charge transport layer from the substrate can be suppressed, and adhesion to the substrate can be improved.

  Examples of the undercoat layer include resin layers and alumite layers made of various resin materials. The resin material for forming the resin layer is polyethylene resin, polypropylene resin, polystyrene resin, acrylic resin, vinyl chloride resin, vinyl acetate resin, polyurethane resin, epoxy resin, polyester resin, melamine resin, polycarbonate resin, polyester carbonate resin, polysulfone. Resins, phenoxy resins, polyarylate resins, silicone resins, polyvinyl butyral resins, polyamide resins and the like, copolymer resins containing two or more repeating units constituting these resins, casein, gelatin, polyvinyl alcohol, Examples include ethyl cellulose.

  The thickness of the undercoat layer is preferably 0.01 μm or more and 20 μm or less, more preferably 0.1 μm or more and 10 μm or less. If the thickness of the undercoat layer is less than 0.01 μm, it may not substantially function as the undercoat layer, and it may be difficult to obtain a uniform surface by covering defects of the conductive substrate. Further, since it becomes impossible to prevent the injection of charge from the conductive substrate to the photosensitive layer, the charging property of the photosensitive layer may be lowered. If the thickness of the undercoat layer exceeds 20 μm, it is difficult to form the undercoat layer uniformly, and the sensitivity of the photoreceptor may be lowered.

  The undercoat layer may contain metal oxide particles. By containing these particles, the volume resistance value of the undercoat layer can be adjusted, and injection of charges from the substrate to the photosensitive layer can be further suppressed. In addition, the electrical characteristics of the photoreceptor can be maintained even when there are changes in temperature, humidity, and the like. Examples of the metal oxide particles include titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide particles. In the case where particles such as metal oxide are contained in the undercoat layer, for example, a coating solution for forming an undercoat layer is prepared by dispersing these particles in a resin solution in which the aforementioned resin is dissolved. An undercoat layer can be formed by coating on a substrate.

  As the solvent for the resin solution, in addition to the solvents described in the column of the charge generation layer and the charge transport layer, alcohols such as water, methanol, ethanol and butanol, glyme solvents such as ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, etc. Can be used. Moreover, the mixed solvent which mixed 2 or more types of these solvents can also be used.

Examples of the method for dispersing the metal oxide particles in the resin solution include a general method using a ball mill, a sand mill, an attritor, a vibration mill, an ultrasonic disperser, or the like.
The total content (weight) of the resin and metal oxide in the coating solution for forming the undercoat layer is C, and the content (weight) of the solvent in the coating solution for forming the undercoat layer is D, the content The ratio of the total content C to D (C / D) is preferably 1/99 or more and 40/60 or less (= 0.01 or more and 0.67 or less), more preferably 2/98 or more and 30/70. It is below (= 0.02 or more and 0.43 or less).

  The ratio (E / F) of the resin content (weight) E to the metal oxide content (weight) F in the coating solution for forming the undercoat layer is 1/99 or more and 90/10 or less (= 0.01 or more). 9.0 or less), more preferably 5/95 or more and 70/30 or less (= 0.05 or more and 2.33 or less).

  Examples of the coating method for the coating solution for forming the undercoat layer include a spray method, a ring coating method, a roll coating method, a blade method, and a dipping method. The coating film for forming the undercoat layer may form a charge generation layer after undergoing a drying process. Further, drying of the coating film for forming the undercoat layer may be combined with drying of the coating film for forming the charge generation layer.

(Specific examples of application and drying)
Further, the present invention will be described in more detail using a specific coating / drying apparatus.
FIG. 1 is a schematic view of a coating / drying apparatus that can be suitably used in the production method of the present invention. In FIG. 1, 1 is a coating apparatus, 2 is a conductive substrate, 3 is a coating liquid, 4 is a coating roll, 5 is a coating liquid supply means, 5a is a nozzle, 6 is a scraping roll, 7 is a cleaning blade, and 8 is an infrared ray. A drying device (with a temperature detection sensor), 9 is an arm for holding a conductive substrate, and 10 is a rail for holding and moving the arm.

The coating device 1 is a coating device by a natural roll coating method,
A conductive substrate 2 rotatably supported by a shaft (not shown);
It is arranged so that its axis is parallel to the axis of the conductive substrate 2 and in contact with the coating liquid 3 (that is, arranged so as to have a specific nip pressure with the conductive substrate 2). Application roll (also called applicator roll) 4,
A coating solution supply means 5 for supplying the coating solution 3 so that the coating roll 4 has a constant film thickness;
A scraping roll 6 that is disposed so that the axis of the coating roll 4 is parallel to the axis of the coating roll 4 and abuts the coating roll 4 and scrapes off excess coating liquid that has not been applied to the conductive substrate 2;
A cleaning blade 7 for cleaning the surface of the scraping roll 6 is included.

  The coating apparatus 1 includes an attaching / detaching apparatus that attaches and detaches the conductive substrate 2 that is an object to be coated to the apparatus body, a conductive substrate driving device that rotationally drives the conductive substrate 2, and the conductive substrate 2 that is separated from the coating roll 4. Conductive substrate separation device, chuck for mounting the coating roll 4 on the apparatus main body, coating roll driving device for driving the coating roll 4 to rotate, each detecting device for detecting the operating state of each driving device, the separating device, and the like. Control means for controlling the operation of each drive device and separation device in response to the detection output may be included.

  In the case of the natural roll coating method, it is preferable that at least the surface layer portion of the coating roll 4 is made of an elastic material. Examples of elastic materials include silicone rubber, organic polysulfide rubber, nitrile / butadiene rubber, nitrosulfonated polyethylene, styrene / butadiene rubber, silicone resin, fluororesin resin, etc. A coated one is mentioned.

As the coating solution supply means 5, a known means can be used. For example, there is a means for supplying a coating film having a constant film thickness to the coating roll 4 from the nozzle 5a.
In the case of the natural roll coating method, the scraping roll 6 is provided to prevent the coating roll 4 from being damaged because at least the surface layer portion of the coating roll 4 is made of an elastic material.
The cleaning blade 7 serves to remove the coating liquid 3 on the surface of the scraping roll 6. The cleaning blade 7 is made of an elastic metal plate, resin plate, or the like, and is provided so that its free end is in contact with the surface of the scraping roll 6.

The application method is not limited to the natural roll application method of FIG. 1, and may be a reverse roll application method in which the application roll and the conductive substrate have the same rotation direction.
In the reverse roll coating method, most of the coating rolls are made of metal rolls, and are arranged in parallel with a specific gap with the conductive substrate to be coated. The film also depends on the size of the gap. Thickness can be controlled. In the case of a reverse roll coating type coating apparatus, the cleaning blade may be provided so as to directly contact the coating roll.

Hereinafter, a coating method when the coating liquid 3 is applied to the conductive substrate 2 using the coating apparatus 1 will be described.
First, in a state where the conductive substrate 2 is separated from the coating roll 4, the conductive substrate 2 is rotated at a predetermined peripheral speed in the direction of the arrow in the drawing by the conductive substrate driving device. Next, the coating liquid 3 having a constant film thickness generated by the coating liquid supply means 5 is transferred to the coating roll 4 and rotated several times to form a coating film of the coating liquid 3 having a uniform thickness on the surface of the coating roll 4. Let Thereafter, the coating film is transferred to the conductive substrate 2 by bringing the conductive substrate 2 rotating at a predetermined peripheral speed into contact with the coating roll 4.

  After the start of coating, that is, after bringing the conductive substrate 2 into contact with the coating roll 4, the conductive substrate 2 has a number of rotations (number of coatings) of 1 or more in order to make the thickness of the coating film uniform. , And rotated to be in a range of 20 times or less. The number of rotations is preferably 1.5 to 10 times, more preferably 2 to 5 times. If the number of rotations of the conductive substrate 2 is less than one, an uncoated outer peripheral surface remains, so that a coating film having a uniform thickness may not be obtained. If the number of rotations of the conductive substrate 2 exceeds 20, the work time may be long and the production efficiency may be reduced.

Excess coating film on the application roll 3 that has not been transferred to the conductive substrate 2 at the time of application is transferred to the scraping roll 6 and further discharged out of the apparatus by the cleaning blade 7.
The film thickness of the coating liquid 3 transferred to the conductive substrate 2 is adjusted by the coating liquid supply means 5 described above, the peripheral speed of the coating roll 4 and the conductive substrate 2, It can be controlled by adjusting the number of coatings, the physical properties of the coating liquid 3, the material of the surfaces of the conductive substrate 2 and the coating roll 4, the nip width between the conductive substrate 2 and the coating roll 4, the size of the gap, and the like.

Next, the infrared drying device 8 will be described.
As the infrared ray, a wavelength of 4 to 1000 μm can be used. However, a heater having a maximum energy wavelength in the region of 4 to 25 μm where the absorption is large is optimal for heating the organic compound. Such heaters include ceramic heaters, seed heaters, halogen lamp heaters, and quartz heaters. Among them, a ceramic heater that can easily change the life and the heater shape is optimal. The length of the heater is preferably slightly longer than the coating film in order to uniformly heat the entire coating film. The irradiation intensity can be controlled by controlling the distance between the coating film and the heater and the heater output. The irradiation intensity is usually optimized depending on the constituent material of the coating film, particularly the solvent type.

  Furthermore, energy efficiency can be improved by providing a reflector on the back surface of the heater (the surface opposite to the coating film). In addition, higher heating can be obtained by increasing the number of reflectors installed up and down. The infrared drying device 8 may be provided with a blower nozzle such as a blower or an air shower. In that case, it is possible to supply air current of preferably 50 ° C. or higher and 130 ° C. or lower to the coating film applied to the conductive substrate 2 and simultaneously perform drying with hot air.

  When drying begins, heating is spent on increasing the temperature of the coating. The temperature rise varies depending on the heat capacity of the coating film and the substrate. The drying time can be shortened by adjusting the output of the heating source, the temperature of the airflow, and the amount of airflow to perform heating rapidly. If the drying continues further in the output of the initial heating after reaching the predetermined temperature, the coating temperature will always rise, and the coating temperature will rise above the heat resistance temperature of the photoconductor, or the boiling point of the solvent will be exceeded. Therefore, foaming may occur. In this case, it is preferable to take out the conductive substrate from the apparatus when the temperature reaches a predetermined temperature. The infrared drying apparatus is usually provided with a temperature detection sensor, and preferably has a mechanism for automatically discharging the conductive substrate from the infrared drying apparatus when the surface temperature of the coating film reaches a predetermined temperature. . In FIG. 1, the taking-out means is omitted because it becomes complicated.

  The coating film on the cylindrical substrate is preferably dried while the cylindrical substrate is installed in the horizontal direction and rotated around the central axis of the cylinder. That is, when a cylindrical substrate on which a coating film is formed is introduced into a drying furnace, the coating film may drop in the direction of gravity because the viscosity of the coating film decreases and the fluidity increases as the temperature of the coating film increases. In this case, the film thickness in the circumferential direction becomes non-uniform. Therefore, by rotating the cylindrical substrate about the central axis of the cylinder, the influence of gravity on the coating film can be made uniform, and the film can be dried while the film thickness in the circumferential direction is kept uniform. Furthermore, since the drying method described here is also directional, for example, a portion that is not irradiated with infrared rays is not heated, so that the heating unevenness of the entire substrate can be prevented by rotating the cylindrical substrate. The number of rotations at this time is preferably 1 to 500 rpm, and most preferably 5 to 200 rpm. If it is 1 rpm or less, unevenness due to dripping of the coating film may occur, and if it is 500 rpm or more, the coating film may be scattered by the centrifugal force.

  The coating device 1 and the infrared drying device 8 may be arranged alternately and in series. In this case, since the conductive substrate 2 held by the conductive substrate holding arm 9 is moved by the rail 10 and alternately passes through the coating device 1 and the drying device 8, the coating and drying can be repeated. it can. The coating solution used in each of the coating apparatuses 1 may have the same composition or a different composition depending on the target photoreceptor.

  In the above specific example, the roll coating method is shown as the coating method, but other coating methods such as a spray coating method and a blade coating method may be adopted as long as a desired photoreceptor is obtained. Furthermore, although the infrared heating method is shown as the drying method, other drying methods such as a hot air drying method and a vacuum drying method may be adopted.

Examples of the present invention will be described below. The present invention is not limited to these examples.
Example 1
An aluminum cylindrical conductive substrate having a diameter of 40 mm and a total length of 340 mm was prepared, and each layer was applied and formed as follows.

a: Undercoat layer Titanium oxide (Ishihara Sangyo Co., Ltd .: TTO55A) 21 parts by weight and copolymer nylon resin (Toray Industries, Inc .: Amilan CM8000) 39 parts by weight, methanol 329 parts by weight and 1,4-dioxolane 611 parts by weight In addition, a coating solution for forming an undercoat layer was prepared by dispersing for 8 hours using a paint shaker. An undercoat layer having a film thickness of 1.0 μm is formed by a dip coating method in which the coating solution for forming the undercoat layer is filled in a coating tank and the conductive substrate is immersed in the coating tank and then left standing at room temperature for 1 hour. Then, the following charge generation layer was applied.

b: Charge generation layer As oxotitanium phthalocyanine, a clear diffraction peak is shown at least at a Bragg angle (2θ ± 0.2 °) of 27.2 ° in an X-ray diffraction spectrum by Cu-Kα characteristic X-ray (wavelength: 1.54Å) 2 parts by weight of oxotitanium phthalocyanine having a crystal structure, 1 part by weight of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd .: ESREC BM-S) and 97 parts by weight of methyl ethyl ketone are mixed and dispersed with a paint shaker. A coating solution for forming a charge generation layer was prepared. This charge generation layer forming coating solution was applied on the undercoat layer by the same dip coating method as that for the undercoat layer, thereby forming a charge generation layer having a thickness of 0.4 μm on the undercoat layer. After standing at room temperature for 1 hour, the next charge transport layer was applied.

c: charge transport layer 10 parts by weight of the charge transport material represented by the structural formula (1a), 18 parts by weight of a polycarbonate resin (Mitsubishi Engineering Plastics: Iupilon Z400) as a binder resin, 2,6-di-t -0.1 part by weight of butyl-4-methylphenol (BHT) was dissolved in 112 parts by weight of cyclohexanone to prepare a coating solution for forming a charge transport layer. For evaluation 2 described later, 0.1 part by weight of triphenylamine dimer (abbreviation: TPD: internal standard substance) represented by the following structural formula (2) was also added to the coating solution.

The above coating solution is applied by a roll coating method onto an aluminum cylindrical conductive substrate on which an undercoat layer and a charge generation layer are formed. Under a ceramic heater having a heater temperature of 200 ° C. (Y-1 type manufactured by Yamaki Denki Co., Ltd.) A 10 μm-thick charge transport layer was formed by drying until the surface temperature reached 100 ° C. while uniformly flowing an air flow with a temperature of 80 ° C., a wind speed of 10 m / min, and an air volume of 0.5 m ³ / min. Thereafter, the coating solution was applied again by a roll coating method and dried under the same heater until it reached 130 ° C., thereby forming an additional 10 μm charge transport layer on the first charge transport layer. The time required for drying was 1.5 minutes for the first time and 2 minutes for the second time.

(Example 2)
The same procedure as in Example 1 was performed except that the solvent of the coating solution for forming the charge transport layer was changed to xylene.

(Example 3)
The same procedure as in Example 1 was performed except that the solvent of the coating solution for forming the charge transport layer was changed to 56 parts by weight of cyclohexanone and 56 parts by weight of toluene (the solvent weight ratio was cyclohexanone: toluene = 50: 50).

Example 4
The same procedure as in Example 1 was conducted except that the solvent of the coating solution for forming the charge transport layer was changed to 40 parts by weight of cyclohexanone and 72 parts by weight of toluene (the solvent weight ratio was cyclohexanone: toluene = 36: 64).

(Example 5)
The solvent of the charge transport layer forming coating solution used for the first coating of the charge transport layer was 112 parts by weight of cyclohexanone, the solvent of the charge transport layer forming coating solution used for the second coating of 40 parts by weight of cyclohexanone, and toluene 72 The same procedure as in Example 1 was conducted except that the weight part (the weight ratio of the solvent was cyclohexanone: toluene = 36: 64) was changed.

(Example 6)
The same procedure as in Example 1 was conducted except that the first drying temperature and the second drying temperature were 125 ° C. and 130 ° C., respectively.

(Example 7)
The same procedure as in Example 1 was performed except that the final drying temperature and the final drying temperature were 105 ° C. and 110 ° C., respectively.

(Example 8)
The same procedure as in Example 1 was conducted except that the final drying temperature and the final drying temperature were 90 ° C. and 130 ° C., respectively.

Example 9
A charge transport layer having a film thickness of 8 μm is applied by applying a coating solution onto a cylindrical aluminum conductive substrate on which an undercoat layer and a charge generation layer are formed by a roll coating method and drying until the surface temperature reaches 80 ° C. Formed. Thereafter, the coating solution was again applied by a roll coating method, and then dried to 100 ° C. under the same heater to form a 6 μm charge transport layer on the first charge transport layer. The coating solution was applied again by the roll coating method, and then dried under the same heater until it reached 130 ° C. to form a charge transport layer having a thickness of 6 μm. Except for the above, the procedure was the same as in Example 1.

(Example 10)
The procedure was the same as Example 1 except that the charge transport material represented by the structural formula (1b) was used.

(Example 11)
The procedure was the same as Example 1 except that the charge transport material represented by the structural formula (1c) was used.

(Comparative Example 1)
A charge transport layer having a film thickness of 20 μm was formed by a roll coating method, and an air flow at a temperature of 80 ° C., a wind speed of 10 m / min, and an air volume of 0.5 m ³ / min was uniformly fed to the sample under a ceramic heater having a heater temperature of 240 ° C. Except this, the procedure was the same as in Example 1.

(Comparative Example 2)
Comparative Example 1 was performed except that the drying time was 15 minutes.
(Comparative Example 3)
Comparative Example 1 was performed except that the dip coating method was used.
(Comparative Example 4)
The same procedure as in Example 1 was performed except that the solvent of the coating solution for forming the charge transport layer was changed to 112 parts by weight of toluene.

(Comparative Example 5)
The same procedure as in Example 1 was conducted except that the final drying temperature and the final drying temperature were 75 ° C. and 105 ° C., respectively.
(Comparative Example 6)
The same procedure as in Example 1 was performed except that the final drying temperature and the final drying temperature were 130 ° C. and 160 ° C., respectively.
(Comparative Example 7)
The same procedure as in Example 1 was conducted except that the final drying temperature and the final drying temperature were 130 ° C. and 100 ° C., respectively.

(Evaluation 1)
With respect to each of the photoreceptors of Examples 1 to 11 and Comparative Examples 1 to 7, a temperature / humidity of 5 ° C./20% is used, and −6.5 kV by a scorotron method using a test apparatus CYNTHIA56SN manufactured by Gentec Corporation. Was exposed to light having a wavelength of 780 nm (1.0 μJ / cm ² ) obtained by spectroscopy with a monochromator and then the surface potential of the photoreceptor after 80 msec was measured.

(Evaluation 2)
A part of the coating films of Examples 1 to 11 and Comparative Examples 1 to 7 described above were cut out and extracted with acetone, and the extract was subjected to TPD with a high performance liquid chromatography apparatus (Agilent 1100 series manufactured by Yokogawa Analytical Systems). Was used as an internal standard substance to determine the amount of residual solvent. In addition, the amount of residual solvent is shown by the weight ratio of the residual solvent with respect to the solid content weight in a coating film.

Based on the above evaluation results, comprehensive evaluation was performed according to the following evaluation criteria.
○: Good state of coating film, residual potential less than −150 V, residual solvent amount less than 1% Δ: Good coating film state, residual potential of −150 V to less than −200 V, residual solvent amount of less than 1% ×: poor coating film state Table 2 shows the results of the residual potential of -200 V or higher and the residual solvent amount of 1% or higher.

  From Examples 1 and 9 to 11 and Comparative Examples 1 and 3, when the number of times the charge transport layer is applied is 1, the amount of the residual solvent and the residual potential are 2 times because the internal solvent is difficult to vaporize. Bigger than. Further, when the drying time was lengthened to reduce the residual solvent amount as in Comparative Example 2, the residual potential was further increased.

  In Examples 1 to 5 and Comparative Example 4, in the case of only a solvent having a high evaporation rate (Comparative Example 4), the surface of the coating film was dried and cured before the drying of the coating film inside was completed, and the solvent in the coating film was Since it became difficult to evaporate, a large amount of residual solvent was detected although the solvent itself easily evaporated. Moreover, since temperature was raised in a short time, foaming was also confirmed.

  Compared to Example 1 and Comparative Examples 5 to 7, when the reached temperature is low (Comparative Example 5), the amount of residual solvent is large due to insufficient drying, and conversely when the reached temperature is high (Comparative Example 6), charge transport by far infrared rays The deterioration of the substance increases and the residual potential increases. Further, when the outer reached temperature was set small (Comparative Example 7), the drying efficiency after coating the outer charge transport layer was deteriorated, and the residual solvent amount and the residual potential were also increased.

  Furthermore, from the comparison between Example 1 and Examples 6 and 7, when the difference between the reached temperature of the upper coating surface of two adjacent coating films and the reached temperature of the lower coating surface is less than 10 ° C., When the temperature reached when the outermost charge transport layer is dried (Example 6), the deterioration of the charge transport material due to far-infrared tends to be slightly larger, and conversely, when the innermost charge transport layer is dried. When the reached temperature is low (Example 7), there is a tendency that the drying becomes slightly insufficient. Further, from comparison between Example 1 and Example 8, if the difference between the arrival temperature of the upper coating surface of the two adjacent coating films and the arrival temperature of the lower coating surface is too large, drying is insufficient. There is a tendency to become. Therefore, it is desirable that the difference between the temperature reached on the upper surface of the two adjacent coatings and the temperature reached on the lower surface of the coating is 10 ° C. to 30 ° C.

1 is a schematic diagram of a coating / drying apparatus according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coating device 2 Conductive substrate 3 Coating liquid 4 Coating roll 5 Coating liquid supply means 5a Nozzle 6 Scraping roll 7 Cleaning blade 8 Infrared dryer (with temperature detection sensor)
9 Arm for holding conductive substrate 10 Rail for holding / moving arm

Claims (7)

A coating solution for forming a charge transport layer containing at least a charge transport material having an enamine structure and a solvent having a relative evaporation rate of less than 1.7 is formed on a charge generation layer on a substrate with a coating film thickness of 10 μm. A step of applying two or more times so as to be below,
After each coating, the coating material is not deteriorated, the solvent is evaporated, and the coating surface temperature is gradually increased from the first coating to the coating formed thereafter. And a step of obtaining a charge transport layer by drying the film.   The method for producing an electrophotographic photosensitive member according to claim 1, wherein each of the coating films is dried at 80 to 140 ° C.   The method for producing an electrophotographic photosensitive member according to claim 1, wherein the substrate is a cylindrical substrate, and the coating is performed by a roll coating method.   The method for producing an electrophotographic photosensitive member according to claim 1, wherein the solvent having a relative evaporation rate of less than 1.7 is contained in an amount of 30% by weight or more in all the solvents.   The method for producing an electrophotographic photosensitive member according to claim 1, wherein the solvent having a relative evaporation rate of less than 1.7 is present in a low ratio in the coating solution for forming a coating film higher than the lower layer.   The method for producing an electrophotographic photosensitive member according to claim 1, wherein the temperature reached by the upper surface of the two adjacent coatings is 10 to 30 ° C higher than the temperature reached by the lower surface of the coating.   The method for producing an electrophotographic photoreceptor according to claim 1, wherein the drying is performed by infrared heating.

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