JPS60143346A - Composite type photosensitive body for electrophotography - Google Patents

Abstract

PURPOSE:To improve the resolution and durability of a composite type photosensitive body for electrophotography provided with an electric charge generating layer and an electric charge transfer layer on a conductive base by forming separately the charge transfer layer of the specific two layers having different concns. of the charge transfer material. CONSTITUTION:An electric charge generating layer 2 contg. an electric charge generating material (e.g.; non-metallic phthalocyanine) is formed on a conductive base 1 consisting of an aluminum sheet or the like. The 1st electric charge transfer layer 4 contg. an electric charge transfer material (e.g.; oxadiazole) at >=20% concn. is provided thereon and an intermediate layer 6 is formed thereon; further the 2nd charge transfer layer 5 contg. the charge transfer material at <=20% concn. is formed on the layer 6, by which the intended composite type photosensitive body for electrophotography is obtd. The resulted photosensitive body has a substantial electrophotographic characteristic and since the surface hardness of the layer 5 is improved, less external damages are generated.

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 and comprising a charge generation layer and a charge transport layer formed on a conductive support. In particular, the present invention relates to an electrophotographic photoreceptor having high resolution and excellent durability.

[Background of the invention]

An electrophotographic photoreceptor has an inorganic or organic photoconductor layer provided on a conductive support.

In general, organic photoreceptors have lower photosensitivity than inorganic conductors, so various sensitization methods have been devised, but the most effective method is charge generation, which generates charges by irradiating the photoreceptor with light. The charge transport layer efficiently transports the charges generated in the charge generation layer.

Conventionally, as a charge generating material for a composite type electrophotographic photoreceptor, Aritsuki No.
Monoazo dyes, disazo dyes, and squaric acid derivative dyes soluble in amines, quinocyanine pigments shown in JP-A-53-42830 and JP-A-53-41230, and quinocyanine pigments shown in JP-A-51-11763 A number of organic materials have been proposed, such as the copper phthalocyanine pigments shown. In addition, the tellurium-arsenic-glassy selenium series shown in Japanese Patent Publication No. 50-15137, Japanese Patent Publication No. 49-14272
Polymers having imide bonds and inorganic substances such as amorphous selenium are also proposed.

On the other hand, as a charge transport material, Japanese Patent Application Laid-Open No. 52-77730
Poly-N-vinylcarbazole series disclosed in JP-A-52-753929, etc., JP-A-49-105
Pyrazoline derivatives disclosed in Publication No. 537, JP-A-1986
Trinitrofluorenone shown in Publication No.-4484,
Japanese Patent Publication No. 53-3011 discloses various nitro- and cyano-substituted compounds. Electrophotographic photoreceptors using these materials all have good electrophotographic properties, but these photoreceptors exhibit high sensitivity to visible light in the wavelength range of 400 to 7QQnm, and are sensitive to near-infrared light (750 nm or more). They have the disadvantage that they cannot be used as electrophotographic photoreceptors that use near-infrared light as a light source (e.g., semiconductor lasers) because they have no sensitivity at all, or have low sensitivity even if they have sensitivity. Ta.

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. Toner is attached to the electrostatic latent image to create a toner powder image, which is then transferred to paper or other paper for printing. Therefore,
The photoreceptor is required to have charging properties, sensitivity, M image resolution, optical properties, etc. depending on the process, as well as stability of these properties, toner cleanability, and abrasion resistance.

In recent years, a method of printing using an electrophotographic method using a laser as a light source has been devised as one of the high-speed printers. 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 printers, significantly reduce power consumption, and increase functionality, which is attracting a lot of attention. has been done. Since the oscillation wavelength of a semiconductor laser is a long wavelength of 7701 m 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.

The inventors of the present invention have made intensive studies to provide an electrophotographic photoreceptor that has excellent various electrophotographic properties and has sufficient properties for practical use. Charge transport layers are formed above and below, and the charge transport substance concentration in the charge transport layer formed on the intermediate layer is
It has been found that the problem can be solved by making the charge transport node smaller than the charge transport node formed in the lower layer of the intermediate layer.

[Purpose 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 with extremely excellent resolution and durability.

[Summary of the invention]

In general, factors that determine the lifespan of composite electrophotographic photoreceptors include the occurrence of external scratches due to friction with paper (transfer paper) and developer, in addition to deterioration due to corona discharge and light of the charge transport material. etc.

In particular, in the case of composite type electrophotographic photoreceptors, the structure of the charge transport material layer on the surface is often mainly charge transport material/binder resin = 1/4 or more (weight ratio), and inorganic Compared to the selenium photoreceptor, there is a problem that the charge transport material is extremely soft and has poor corona resistance. In order to improve the surface hardness, there are conventionally known methods of 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 consisting of a layer containing a charge generating substance and a layer containing a charge transporting substance, the charge transporting layer does not carry charges. The charge transport substance concentration in the charge transport layer formed below the intermediate layer is lower than the charge transport substance concentration in the charge transport layer formed below the intermediate layer. It has been discovered that the above problems can be overcome by reducing the concentration of the substance, 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-transporting layer used does not interfere with the light absorbed by the charge-generating material. Many studies have been conducted on long-wavelength absorbing charge-generating materials, such as S
For e, Cds, etc., a method has been found to increase the sensitivity in the long wavelength range by adding a sensitizer, but among the above-mentioned organic photoconductive materials, various 7-talocyanine compounds have relatively long wavelengths. Sensitivity is good in the range. Generally, a charge generating material generates charges due to 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 concentration of the charge transport substance in the charge transport layer (1) is 20% or more, preferably 40 to 75%. The charge transporting layer formed on the intermediate layer (the concentration of the charge transporting substance in the former layer must be 30% or less, preferably 20% or less. The intermediate layer is made of resin alone or the concentration of the charge transporting substance is 30% or less. The thickness of the intermediate layer is preferably 20 inches or less.
The thickness is preferably 2 μm or less, preferably 2 μm or less. The thickness of the charge transport layer (1) and the charge transport layer (former layer) can be changed as desired and is not particularly limited.Furthermore, film formation aids or In order to improve the adhesion between the charge generating substance and the conductive support or charge transport layer, various auxiliary agents such as sensitizers and sensitizing agents can be added to improve the adhesion force between the charge generating substance and the conductive support or the charge transport layer. There are no restrictions on the addition.Furthermore, with regard to the formation of a charge transport layer (a protection film formed on top of the charge transport layer, etc.), it is also possible to use conventionally known techniques.

In the present invention, the reason why the charge transport layer is divided into (1) and (II) through an intermediate layer and the concentration of the charge transport substance in each layer is limited is based on the following reasons. be. It is preferable that the thickness of the intermediate layer is 10 μm or less; if the thickness is greater than that, the residual potential will become too large and the desired electrophotographic properties will not be obtained. It is still preferable that the charge transport material/Jl concentration is 30% or less, but if it exceeds 50%, the coating solution solvent may be used when coating the charge transport layer (II) formed on the intermediate layer. This increases the elution amount of the charge transport substance in the intermediate layer, making it impossible to control the viscosity of the coating solution, and making it impossible to control the concentration of the charge transport substance in the intermediate layer and the charge transport layer (formerly), as well as the film thickness. On the other hand, it is preferable that the concentration of the charge transport substance in the charge transport layer (1) is 20 or more, but if it is less than that, the charge The charge generated in the generation layer cannot be efficiently transported, resulting in an increase in residual potential and a decrease in sensitivity, making it impossible to obtain the desired electrophotographic properties. If you exceed
The film strength of the charge transport layer (1) is significantly reduced, making it unusable. On the other hand, the concentration of the charge transporting substance in the charge transporting layer (II) is preferably 30 or less, but if the concentration is higher than that, corona deterioration will be significant, resolution change will be large, and resolution durability will be lost. Therefore, if the charge generation layer, the charge transport layer (1), (II) and the intermediate layer are made as described above, the surface hardness of the charge transport layer (formerly) will be improved and the occurrence of external scratches will be reduced; , regardless of the type of charge-generating substance, the type of charge-transporting substance, the type of material of the intermediate layer, or the method of forming these layers, it has sufficient photographic properties and long-term durability 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 bath agent is removed by heating. A film is formed by curing or three-dimensional curing. As the resin, a known three-dimensional curing resin or thermoplastic resin can be used. charge transport layer,
The intermediate layer is made by mixing and stirring and dissolving a charge transport substance and a resin or a resin alone in a solvent such as tetrahydrof5:/, haC1,) 7-carbon hydrocarbon, benzene, dioxane, dimethylformamide, alcohol, etc. to transport charges. Adjust the coating liquid for the material. Using this solution, a charge transport layer (I), an intermediate layer, and a charge transport layer (It) 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 is, for example, a known pigment such as a 7-thalocyanine pigment such as a metal phthalocyanine or a metal-free phthalocyanine, an anthraquinone pigment, an indigoid pigment, a quinacrypan pigment, a perylene pigment, a polycyclic quinone pigment, or a methine squaric acid pigment. Examples include pigments, 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, imidasilone, trioxazole, 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 binder resin and intermediate layer resin used in the present invention include silicone resin, phenol resin, urea resin, melamine resin, furan resin, epoxy resin, silicone resin, vinyl chloride-vinyl acetate copolymer, and xylene resin. resins, toluene resins, urethane resins, vinyl acetate-methacrylic copolymers, acrylic resins, phenoxy resins, polycarbonate resins, polyester resins, polyarylate resins, etc., and these resins may be used alone or in combination of two
Can be used in combination with more than one species.

Examples of the conductive support for the composite electrophotographic photoreceptor of the present invention include metals such as aluminum, aluminum-other metal alloys, steel, iron, and copper, as well as conductive plastics, paper, and glass. These supports may have a cylindrical shape, a sheet, etc., and are not limited to any shape.

[Embodiments of the invention]

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto in any way.

Examples 1 to 6 The substances shown in Table 1 were weighed and placed in a glass container, and the mixture was stirred using an ultrasonic vibrator for 15 hours to prepare a coating liquid for a charge generation layer. Table 2 shows the composition of the charge transport layer (I), and Table 3 shows the composition of the charge transport layer (old).

In both Tables 2 and 3, the component materials were weighed and placed in a glass container, and stirred in a trench to completely dissolve the contents.

As the charge transport substance, an oxazole compound represented by the following structural formula 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 tl' for 2 hours. The thickness of the charge generation layer is 1 μm or less. Next, a charge transport layer (1) is coated on top of the 110C
It was heated and dried for 2 hours.

Further, an intermediate layer was applied thereon and dried and cured by heating at 150C for 30 minutes. The film thickness is 1 μm or less. Next, a charge transport layer (II) was coated thereon and dried at 110C for 2 hours to form a composite electrophotographic photoreceptor. 'The thickness of the charge transport layer (1) is 3 to 45 μm. The thickness of the charge transport layer (n) is 3 to 25 μm. The electrophotographic properties were measured using an electrostatic recording paper tester (manufactured by Kawaguchi Electric, 5P-4).
28). In this case, conduct corona discharge of minus 5 kV for 10 seconds to charge (10 seconds I1:・
The surface potential Vo (V) of Toshiro Dencho is the initial potential), 3
After leaving it in the dark for 0 seconds (the potential at this time is expressed as Vso (V), illuminate it with a tungsten lamp so that the surface illuminance is 21.0 seconds, record the decay of the surface potential and the time, The time t required for V3° to become 1/2 (
Sensitivity (half-reduced exposure amount, Eso(tx
Hs). Further, the resolution was evaluated using a homemade resolution evaluation device using the Electrophotography Society Test Chart A I-R (1975). These results are summarized in the fourth
It is shown in the table and Figure 1.

Oka, the resolution is a value obtained by accelerating for 3 hours and lowering the resolution.

Comparative Examples 1 to 4 Charge generation layer and charge transport layer (I) used in Examples 1 to 6
A composite electrophotographic photoreceptor was fabricated using the intermediate layer, charge transport layer (the same composition as the old one, and only the thickness of the charge transport layer (the old one) was changed.The electrophotographic characteristics and resolution evaluation are as shown in Example 1
I did the same thing. The results are shown in Table 5.

The transport layer (old) was formed.The film thickness was 15μ for the charge transport layer (1).
m1 charge transport layer (old was 5 μm). The results are shown in curve 1v in Figure 2.

Examples 17-21 Charge generation layer and charge transport layer (■) used in Example 1.

(Each layer was formed using a coating liquid such as Old.

The intermediate layer was formed using the resin shown in Table 8, and the charge transport layer (n) 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 curve (■) in Figure 3.

Table 8 Comparative Example 10 The charge generation layer and charge transport layers (1) and (II) were the same as in Example 1 and were formed in the same manner. The intermediate layer was formed by using tetramethylolmethane triacrylate and adding 20 units 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 curve 1v in Figure 2.

Examples 22-24 Charge transport layer (■) using the binder resin shown in Table 9.

(II) was formed. The binder resin/charge transport substance ratio is 1/1 for charge transport layer (1) and 7/1 for charge transport layer (II). The intermediate layer is the same as that used in Example 1, and its thickness is 1 μm or less. Only the middle layer was applied by dipping, and the rest were applied using an applicator. The drying and curing conditions, solvent, etc. of each layer were 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 10 Examples 25 to 27 The charge generation layer, charge transport layer, and intermediate layer used in Example 1 were used. These layers are U charge transport layer (I) coated by dipping method.
The compositions shown in Table 11 were used and formed by coating with an applicator. Charge transport layer (old film thickness was 5,10.
It is 17 μm. The charge transport material used in the charge transport layer (If) is a naphthothiazole compound having the following structure. The results are shown in Figure 4.

[Effects of the Invention] - From the above results, it can be seen that the electrophotographic photoreceptor of the present invention is an excellent electrophotographic photoreceptor having practically sufficient electrophotographic properties.

[Brief explanation of the drawing]

FIGS. 1, 3, and 4 are electrophotographic sensitivity characteristic diagrams of a composite electrophotographic photoreceptor, FIG. 2 is an ε-photo resolution characteristic diagram, and FIG. 5 is an example 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 (5), 5... Charge transport layer CB), 6 Compound (%) of charge transport J (1) 2nd section 0 10 20. 30 110 ￥Visit ゛print &shoe'ff)'s oxazol compound (pride) Figure 3 Middle class W thick compliant 躬q, Zuden 11 bow '78mi 219 (-month! IL) σ film thickness
(Continued from μm Figure 5, Page 1 @Inventor Toshikazu Narahara Inside Hitachi Wheels 3-chome

Claims (1)

[Scope of Claims] 1. In a composite electrophotographic photoreceptor in which a charge generation layer and a charge transport layer are provided on a conductive support, the charge transport layer is formed through an intermediate layer that allows charge to move. Formed separately into two layers
A composite electrophotographic photosensitive material, wherein the concentration of the charge transport substance in the charge transport layer is higher in the charge transport layer in the layer near the charge generation layer than in the charge transport layer in the layer near the surface. body. 2. The composite Kameko photograph according to claim 1, wherein the charge transporting substance concentration is 20% or more in the charge transporting layer (5) and 20% or less in the charge transporting layer (to). Photoreceptor for use. 3. A photographic photoreceptor, characterized in that the thickness of the charge transport layer has a charge transport layer (A)/charge transport layer (B) ratio of 110.05 to 115. 4. The composite electrophotographic photoreceptor according to claim 1, wherein the resin for the intermediate layer is different from the binder resin of the charge transport layer (self) and the charge transport layer (b). . 5. The composite electrophotographic photoreceptor according to claim 1, wherein the intermediate layer contains a charge transporting substance in an amount of 20% or less and has a thickness of 5 μm or less.