JPH0374830B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an electrophotographic photoreceptor having high sensitivity in the long wavelength range, which is formed by forming a charge generation layer and a charge transport layer on a conductive support, and particularly relates to an electrophotographic photoreceptor having high sensitivity in the long wavelength range. The present invention relates to an electrophotographic photoreceptor having properties. [Background of the Invention] An electrophotographic photoreceptor has an inorganic or organic photoconductor layer provided on a conductive support. Organic photoconductors generally have lower photosensitivity than inorganic photoconductors, so various sensitization methods have been devised, but the most effective method is to create a charge-generating layer that generates charges when the photoreceptor is irradiated with light. and a charge transport layer that efficiently transports the charges generated in the charge generation layer. Conventionally, charge-generating substances for composite electrophotographic photoreceptors include monoazo dyes, disazo dyes, and squaric acid derivative dyes soluble in organic primary amines as disclosed in JP-A No. 52-55643, and squaric acid derivative dyes. Showa 53-
A large number of organic substances have been proposed, such as quinocyanine pigments shown in JP-A No. 42830 and JP-A-53-41230, and copper phthalocyanine pigments shown in JP-A-51-11763. In addition, tellurium-arsenic-glassy selenium series shown in Japanese Patent Publication No. 50-15137,
Japanese Patent Publication No. 49-14272 discloses polymers having imide bonds and inorganic substances such as amorphous selenium. On the other hand, as a charge transport material, JP-A-52-
Poly-N-vinylcarbazole series disclosed in JP-A No. 77730, JP-A-52-753929, etc.;
Pyrazoline derivatives shown in JP-A-105537, trinitrofluorenone shown in JP-A-46-4484, various nitro- and cyano-substituted compounds shown in JP-B-53-301, and the like. Electrophotographic photoreceptors using these materials all have good electrophotographic properties, but they exhibit high sensitivity to visible light in the wavelength range of 400 to 700 nm.
There is no sensitivity at all to near-infrared light (750 nm or more), or even if there is sensitivity, the sensitivity is low.
It has the disadvantage that it cannot be used as an electrophotographic photoreceptor that uses near-infrared light as a light source (for example, a semiconductor laser). Incidentally, in an electrophotographic copying machine using such a photoreceptor, first, the surface of the photoreceptor is charged by corona irradiation, and then imagewise exposure is performed to create an electrostatic latent image. Copying is performed by attaching toner to the electrostatic latent image to create a toner powder image, which is then transferred to paper or the like. Therefore, photoreceptors are required to have charging properties, sensitivity, resolution, optical properties, etc. depending on the process, as well as stability of these properties, toner cleanability, and abrasion resistance. In recent years, as a type of high-speed printer, a method of printing using an electrophotographic method using a laser as a light source has been devised. In particular, when a semiconductor laser is used as a light source, the light source section can be made very small, making it possible to miniaturize the printer, significantly reduce power consumption, and increase functionality.
It is attracting a lot of attention. Since the oscillation wavelength of a semiconductor laser is a long wavelength of 770 nm or more, conventional charge transport materials as described above cannot be used in electrophotographic photoreceptors. Therefore, it is desired to develop an electrophotographic photoreceptor that has high sensitivity to specific wavelengths. On the other hand, some methods have been put into practical use, although the sensitivity is still not sufficient. However, the lifespan is still insufficient, and there is a strong desire for an even longer lifespan. As a result of intensive studies aimed at providing an electrophotographic photoreceptor with excellent various electrophotographic properties and characteristics sufficient for practical use, the inventors of the present invention discovered that charge transport is possible either alone or in a thermosetting resin. Charge transport layers containing a charge transport layer and a thermoplastic resin are formed above and below through an intermediate layer containing a substance, and the concentration of the charge transport substance in the charge transport layer formed on the intermediate layer is determined by controlling the concentration of the charge transport substance in the charge transport layer formed on the intermediate layer. It has been found that this problem can be solved by making the charge transport layer smaller than the underlying charge transport layer. [Object of the Invention] An object of the present invention is to overcome the drawbacks of conventional composite type electrophotographic photoreceptors and, in particular, to provide an electrophotographic photoreceptor having extremely excellent resolution and durability. [Summary of the Invention] In general, factors that determine the life of a composite electrophotographic photoreceptor include deterioration due to corona discharge of the charge transport material and light, as well as external damage due to friction with paper (transfer paper) and developer. Examples include the occurrence of physical scratches. In particular, in the case of a composite type electrophotographic photoreceptor, the structure of the charge transport material layer on the surface is mainly charge transport material/binder resin = 1/4 or more (weight ratio).
Compared to inorganic selenium photoreceptors, these photoreceptors are significantly softer, and the charge transport material has poor corona resistance. In order to improve the surface hardness, there are conventional methods such as providing a surface protective layer or reducing the content of a charge transporting substance. However, all of these methods cause a decrease in electrophotographic properties, particularly an increase in residual potential and a decrease in sensitivity, making it difficult to achieve both electrophotographic properties and durability. As a result of various studies based on this fact, the present inventors found that in a composite electrophotographic photoreceptor comprising a layer containing a charge generating substance and a layer containing a charge transporting substance, the charge transporting layer is The charge transport layer contains a transport substance and a thermoplastic resin, and the charge transport layer is separated into two layers with an intermediate layer containing a thermosetting resin, and the charge transport substance concentration in the charge transport layer is equal to that of the charge generation layer. The nearby charge transport layer () is
20~83% layer near the surface charge transport layer () 10~
It has been found that the above-mentioned problems can be overcome by setting the amount to less than 20%, leading to the present invention. Generally, the wavelength range to which a photoreceptor is sensitive depends on the absorption wavelength range of the charge-generating material, as long as the charge transport layer used does not interfere with the light absorbed by the charge-generating material. Many studies have been carried out on long-wavelength absorbing charge-generating substances, and for example, for Se, CDS, etc., a method has been found to increase the sensitivity in the long wavelength range by adding a sensitizer. Among organic photoconductive materials, various phthalocyanine compounds have relatively good sensitivity in a long wavelength range. Generally, a charge generating substance generates charges by light passing through a charge transport layer, and the generated charges must be efficiently transferred into the charge transport layer by an electric field. Therefore, it is necessary to disperse the charge generating substance on the conductive support in such a form that the generated charges are efficiently transferred to the charge transport layer. This dispersion form is a major controlling factor for various electrophotographic properties of an electrophotographic photoreceptor, and particularly has a great influence on sensitivity, sharpness, and gradation. Therefore, it is important for electrophotographic photoreceptors to more appropriately control the dispersion form of the charge generating substance on the conductive support. The charge transport layer in the composite electrophotographic photoreceptor of the present invention has the following structure. That is, the charge transport layer formed on the charge generation layer supported on the conductive support is formed above and below the intermediate layer that can transfer charges, and is formed below the intermediate layer. The charge transport material concentration in the charge transport layer () is 20% or more, preferably
It is 40-75%. The charge transporting material concentration in the charge transporting layer ( ) formed on the intermediate layer is 20% or less. The intermediate layer consists of a thermosetting resin alone or a charge transport substance concentration in the thermosetting resin of 30% or less,
It is preferably 20% or less. Furthermore, the thickness of the intermediate layer is preferably 5 μm or less, preferably 2 μm or less. The thickness of the charge transport layer () and the charge transport layer () can be changed as desired, and are not particularly limited. Also, a film-forming aid to improve film-forming properties when forming a charge generation layer. Alternatively, various auxiliary agents can be used to improve the properties of electrophotographic photoreceptors, such as the addition of adhesion-enhancing agents or sensitizing agents to improve the adhesion between the charge-generating substance and the conductive support or charge-transporting layer. There are no restrictions on the addition of. Furthermore, conventionally known techniques can be used to form a protective film or the like on the charge transport layer. In the present invention, the charge transport layer containing a charge transport material and a thermoplastic resin is divided into () and () through an intermediate layer containing a thermosetting resin and a charge transport material, and the charge transport layer in each layer is divided into () and (). The limitation on the concentration of transported substances is based on the following reasons. First, it is preferable that the intermediate layer has a thickness of 5 μm or less; if the thickness exceeds 5 μm, the residual potential becomes large and desired electrophotographic characteristics cannot be obtained. In addition, it is preferable that the concentration of the charge transport layer substance in the intermediate layer is 20% or less, but if it exceeds 30%, the concentration of the charge transport layer () formed on the intermediate layer may be affected by the coating solvent. As the elution amount of the charge transporting substance in the intermediate layer increases, it becomes impossible to control the viscosity of the coating liquid, and it also becomes impossible to control the concentration of the charge transporting substance in the intermediate layer and the charge transporting layer (2), as well as the film thickness. , a photoreceptor with stable characteristics cannot be obtained, and mass productivity becomes poor. On the other hand, the charge transport layer ()
It is preferable that the concentration of the charge transport substance in the charge generation layer is 20% or more, but if it is less than that, the charges generated in the charge generation layer cannot be efficiently transported, resulting in an increase in residual potential and a decrease in sensitivity. Electrophotographic properties cannot be obtained. Furthermore, if the concentration of the charge transporting substance exceeds 83%, the film strength of the charge transporting layer () will be significantly reduced, making it unsuitable for practical use. On the other hand, the charge transport material concentration in the charge transport layer () is less than 10-20%. 20%
At higher concentrations, corona deterioration will be significant, resolution changes will be large, and resolution durability will be lost. Therefore, the charge generation layer, the charge transport layer (),
If ( ) and the intermediate layer are formed as described above, the surface hardness of the charge transport layer ( ) will be improved and the occurrence of external scratches will be reduced. On the other hand, regardless of the type of charge-generating substance, the type of charge-transporting substance, the type of intermediate layer material, or the method of forming these layers, sufficient electrophotographic properties and long-term durability can be achieved as a photoreceptor for electrophotography. It has characteristics that allow it to withstand repeated use. Next, a method for forming the charge generation layer and charge transport layer on the conductive support will be described. First, the charge generation layer is prepared by thoroughly mixing and stirring an organic solvent such as tetrahydrofuran, ethyl acetate, acetone, methyl ethyl ketone, halogenated hydrocarbon, etc. that can disperse the charge generation substance well or dissolve the resin and additives used as necessary. Adjust the coating liquid of the charge generating material. The conductive support is immersed in this liquid, or this liquid is dropped onto the conductive support and coated using a bar coater, roll coater, applicator, casting method, etc., and the solvent is removed by heating and cured. , or three-dimensionally cured to form a film. As the resin, a known three-dimensional curing resin or thermoplastic resin can be used. The charge transport layer and intermediate layer are prepared by mixing and stirring a charge transport substance and a resin or a resin alone in a solvent such as tetrahydrofuran, halogenated hydrocarbon, benzene, dioxane, dimethyl formamide, or alcohol, and then dissolving the charge transport material. Adjust the liquid. Using this solution, a charge transport layer (), an intermediate layer, and a charge transport layer () are sequentially formed on the charge generation layer by the same method as for forming the charge generation layer. The charge generating substance used in the present invention includes, for example, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, anthraquinone pigments,
Known pigments such as indigoid pigments, quinacrivan pigments, berylene pigments, polycyclic quinone pigments, and methine squaritate pigments can be used, and these pigments can be used alone or in combination of two or more. Examples of the charge transport substance used in the present invention include oxadiazole, triazole, imidazolone, oxazole, pyrazoline, imidazole, imidazolidine, benzothiazole, benzoxazole, triphenylamine, and derivatives of these substances. These charge transport substances can be used alone or in combination of two or more. Examples of the fixing agent resin and intermediate layer resin used in the present invention include silicone resin, phenolic resin, urea resin, melamine resin, furan resin, epoxy resin, silicone resin, vinyl chloride-vinyl acetate copolymer, and xylene resin. , toluene resin, urethane resin, vinyl acetate-methacrylic copolymer, acrylic resin, phenoxy resin, polycarbonate resin, polyester resin, polyarylate resin, etc. Among these, the fixing agent resin for the charge transport layer can be used. thermoplastic resin,
Further, a thermosetting resin may be selected as the resin for the intermediate layer. Further, these resins can be used alone or in combination of two or more. Further, as the conductive support for the composite electrophotographic photoreceptor of the present invention, in addition to metals such as aluminum, aluminum to other metal alloys, steel, iron, and copper, conductive plastics and plastics,
It is possible to use paper, glass, etc., which have been imparted with electrical conductivity, and these supports may be cylindrical, sheet, etc., and are not limited to any shape. [Examples of the Invention] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these in any way. Examples 1 to 6 The substances shown in Table 1 were weighed and placed in a glass container, and stirred using an ultrasonic vibrator for 15 hours to prepare a charge generation layer coating liquid. Table 2 shows the composition of the charge transport layer (2), and Table 3 shows the composition of the charge transport layer (2).

【table】

【table】

[Table] In each case, the component substances were weighed and placed in a glass container, and stirred until the contents were completely dissolved. The charge transport substance is an oxazole compound represented by the structural formula below. was used. All layers were coated by dipping. First, a charge generation layer was formed on an aluminum plate having a thickness of 100 μm, and then dried and cured by heating at 140° C. for 2 hours. The thickness of the charge generation layer is 1 μm or less. Next, a charge transport layer (2) was coated thereon and dried by heating at 110° C. for 2 hours. moreover,
A 5% by weight neopentyl glycol diacrylate/ethanol solution was applied thereon as an intermediate layer, and dried and cured by heating at 150° C. for 30 minutes.
The film thickness is 1 μm or less. Next, a charge transport layer () was applied thereon and dried at 110° C. for 2 hours to form a composite electrophotographic photoreceptor. The thickness of the charge transport layer () is 3 to 45 μm, the charge transport layer ()
The film thickness is 3 to 25 μm. Measurement of electrophotographic properties was carried out using an electrostatic recording paper tester (manufactured by Kawaguchi Electric, SP-428).
I did it using In this case, perform a corona discharge of -5 kV for 10 seconds to charge the surface (the initial potential is the surface potential V ₀ (V) immediately after charging for 10 seconds), and leave it in a dark place for 30 seconds (the potential at this time is set to V _{30 )} . (V), expose the surface with a tungsten lamp so that the illuminance becomes _2X , record the attenuation of the surface potential at this time and the time, and calculate the time t required for V ₃₀ to decrease to 1/2. Sensitivity (half-decreased exposure, _{E 50} (
was evaluated using a homemade resolution evaluation device. These results are summarized in Table 4 and Section 1.
Note that the resolution is the value obtained by accelerating for 3 hours and reducing the resolution.

[Table] Comparative Examples 1 to 4 The same compositions as the charge generation layer, charge transport layer (2), intermediate layer, and charge transport layer (2) used in Examples 1 to 6 were used, and the film thickness of the charge transport layer (2) was A composite type electrophotographic photoreceptor was created with only the following changes. Electrophotographic characteristics and resolution evaluation were performed in the same manner as in Example 1. The results are shown in Table 5.

[Table] Examples 7 to 11 A charge transport layer () having the composition shown in Table 6 and a charge transport layer () having the composition shown in Table 3 were coated in the same manner as in Example 1 to form a composite type. A photoreceptor for electrophotography was produced. The film thickness is 15 μm for the charge transport layer ().
The charge transport layer () is 5 μm. The results are shown in the curve (-○-) in Figure 1.

[Table] Comparative Examples 5 and 6 The same charge generation layer as in Example 1 was used, and the oxazole compound concentration in the charge transport layer () was 15%.
A charge transport layer (2) and an intermediate layer were formed in the same manner as in Example 1 using a 10% coating solution. The charge transport layer (2) was formed in the same manner as in Example 1 using a composition shown in Table 3. The results are shown in the curve (-●-) in Figure 1. Examples 12 to 16 A charge transport layer () having the composition shown in Table 2 was formed on the charge generation layer used in Example 1, and an intermediate layer was also formed in the same manner as in Example 1. A charge transport layer () was formed in the same manner as in Example 1 with the composition shown in Table 7. The film thickness is 15 μm for the charge transport layer ( ) and 5 μm for the charge transport layer ( ). The results are shown in the curve in Figure 2.

[Table] Comparative Examples 7 to 9 The charge generation layer and intermediate layer were formed in the same manner as in Example 1. The charge transport layer () was formed with a composition shown in Table 2. The charge transport layer (2) was formed by setting the oxazole compound concentration in the charge transport layer (2) to 33%, 35%, and 40%. The film thickness is the charge transport layer ()
15 μm, and the charge transport layer () is 5 μm. The results are shown in the curve in Figure 2. Examples 17 to 21 Using the coating liquids for the charge generation layer, charge transport layer (), (), etc. used in Example 1, the respective layers were formed. The intermediate layer was formed using the resin shown in Table 8, and the charge transport layer () was formed thereon. Coating was done with an applicator. A mixed solvent of methanol and tetrahydrofuran was used as the solvent. The results are shown in the curve in Figure 3.

[Table] Comparative Example 10 The same charge generation layer and charge transport layer () and () as in Example 1 were used and formed in the same manner. The intermediate layer was formed by using tetramethylolmethane triacrylate and adding 20% of an oxazole compound. A mixture of methanol and tetrahydrofuran was used as the solvent, and the thickness of the intermediate layer was 7.0 μm.
The results are shown in the curve in Figure 3. Examples 22 to 24 Charge transport layers () and () were formed using the binder resins shown in Table 9. The binder resin/charge transport material ratio is 1/1 for the charge transport layer () and 7/1 for the charge transport layer (). The middle layer is Example 1
The same material used in was used, and the film thickness was 1 μm or less. Only the middle layer was applied by dipping, and the rest were applied using an applicator. Various drying and curing conditions, solvents, etc. are the same as in Example 1. The oxazole compound used in Example 1 was used as the charge transport substance. The results are shown in Table 10.

【table】

[Table] Examples 25 to 27 The charge generation layer, charge transport layer, and intermediate layer used in Example 1 were used. These layers were applied by dipping. The charge transport layer (2) had a composition shown in Table 11 and was formed by coating with an applicator. The thickness of the charge transport layer ( ) is 5, 10, and 17 μm. The charge transport material used in the charge transport layer (2) is a naphthothiazole compound having the following structure. The results are shown in Figure 4.

〔Effect of the invention〕

The above results show that the electrophotographic photoreceptor of the present invention has excellent electrophotographic properties that are practically sufficient.

[Brief explanation of drawings]

1, 3 and 4 are electrophotographic sensitivity characteristic diagrams of a composite type electrophotographic photoreceptor, FIG. 2 is an electrophotographic resolution characteristic diagram, and FIG. 5 is a composite type electrophotographic photoreceptor according to an embodiment of the present invention. FIG. 6 is a sectional view of a conventional composite electrophotographic photoreceptor. DESCRIPTION OF SYMBOLS 1... Conductive support, 2... Charge generation layer, 3...
...Charge transport layer, 4...Charge transport layer (A), 5...Charge transport layer (B), 6...Intermediate layer.

Claims (1)

[Scope of Claims] 1. A composite electrophotographic photoreceptor in which a charge generation layer is provided on a conductive support and a charge transport layer is provided thereon, wherein the charge transport layer includes a charge transport layer material and a thermoplastic resin. , the charge transport layer is separated into two layers via an intermediate layer containing a thermosetting resin and a charge transport substance, and the concentration of the charge transport substance in the charge transport layer is equal to the charge of the layer near the charge generation layer. Transport layer () is 20
~83% and the charge transport layer in the layer near the surface ()
10 to less than 20%, and an intermediate layer is 20% or less. 2 The thickness of the charge transport layer is charge transport layer ()/
2. The composite electrophotographic photoreceptor according to claim 1, wherein the charge transport layer () has a ratio of 1/0.05 to 1/5. 3. The composite electrophotographic photoreceptor according to claim 1, wherein the intermediate layer has a thickness of 5 μm or less.