JP2001066801A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electrophotographic photoreceptor low in tendency to cause dielectric breakdown even in the case of using it in a contact charging system and capable of obtaining an image high in quality. SOLUTION: The electrophotographic photoreceptor is provided on a conductive substrate 1a with a charge generating layer 1b and a charge transfer layer 1c in this order, and the charge transfer layer 1c contains mainly an organic charge transfer material and a binder resin of a polycarbonate having number average molecular weight of >=20,000, and this layer 1c contains the binder resin in an amount of 40 weight % of the layer 1c and the charge transfer material is made of >=2 kinds and its layer thickness is >=25 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member, and more particularly, to an organic electrophotographic photosensitive member suitably used for a contact charging type electrophotographic apparatus.

[0002]

2. Description of the Related Art In an electrophotographic apparatus such as a copying machine or a printer using an electrophotographic technique, a corona charging method has been frequently used for charging an electrophotographic photosensitive member during image formation. Incidentally, there is an environmental problem that ozone is generated in corona discharge. In recent years, organic photoconductors have become widespread, but the organic photoconductors currently in practical use are usually function-separated stacked photoconductors, and a charge generation layer made of an organic material and a charge transport layer are formed on a conductive substrate. The layers are stacked in this order and function in negative charge.Charge is performed by negative corona discharge.Negative corona discharge generates one or more orders of magnitude more ozone than positive corona discharge. So it is a bigger problem. In recent years, the problem of environmental pollution has been emphasized, and as a countermeasure, a contact charging method that generates less ozone, that is, a method in which a charging member to which a voltage is applied is brought into contact with the surface of the electrophotographic photosensitive member to charge the photosensitive member has attracted attention. Practical application is underway.

FIG. 2 is an explanatory view of a main part of an example of an electrophotographic copying apparatus employing such a contact charging system, in which a contact charging system is arranged around a drum-shaped photosensitive member 1 rotatably mounted in the direction of arrow A. Charging mechanism 2, an exposure mechanism for forming an electrostatic latent image, a developing mechanism for visualizing the electrostatic latent image as a toner image 4, and a developed toner image on a transfer image support 6 such as paper. A transfer mechanism 5 for transferring is sequentially arranged, and the transferred toner image is transferred to a support 6 by a fixing unit (not shown).
An image is obtained by being fixed thereon. On the other hand, the residual toner is removed from the photosensitive member 1 by the cleaning mechanism 7, and then the memory of the electrostatic latent image remaining on the photosensitive member 1 is removed by the pre-exposure mechanism 8, and then subjected to the next image forming process. Can be

[0004]

In the contact charging method, the charging member to which a high voltage is applied is in direct contact with the photoreceptor. Therefore, the photoreceptor needs to hold a charge for a high applied voltage for a certain period of time. However, depending on the layer structure, material, and film thickness of the photoreceptor, there is one that easily causes dielectric breakdown. Also, if there is a defect such as a pinhole in the photoreceptor, current concentrates there, causing dielectric breakdown. When such a phenomenon occurs, a high-quality image cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been developed to provide an organic electrophotographic photoreceptor which can hardly cause dielectric breakdown even when used in a contact charging system and can obtain a high quality image. The purpose is to provide.

[0006]

According to the present invention, there is provided a function-separated laminated electrophotographic photosensitive member having a charge generation layer and a charge transport layer laminated in this order on a conductive substrate. The charge transport layer mainly comprises an organic charge transport material and a binder resin, wherein the binder resin is a polycarbonate resin having a number average molecular weight of 20,000 or more, and the weight ratio of the binder resin in the charge transport layer is 40%.
And the organic charge transport material is composed of two or more charge transport materials, and the charge transport layer has a thickness of 25 μm.
The problem is solved by setting the layer to be at least m.

It is more preferable that the weight ratio of the binder resin in the charge transport layer is in the range of 50% or more and 60% or less. It is more preferable that the charge transporting material contains an indole compound represented by the following general formula (I).

[0008]

Embedded image

[In the formula (I), R ₁ , R ₂ , R ₅ , R ₆ are a hydrogen atom, an alkyl group having 1 to 9 carbon atoms, an aralkyl group having 1 to 9 carbon atoms, and a 1 to 9 carbon atom. 9 represents any one of the aryl groups, wherein R ₁ ＲR ₆ and R ₂ ＲR ₅
And R ₃ and R ₄ represent any of a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a halogen atom, wherein R ₃ = R ₄ . ]

[0010]

The charge transport layer is made of a polycarbonate resin having a number average molecular weight of 20,000 or more. The thickness of the charge transport layer is increased to 25 μm or more, and the weight ratio of the binder resin in the layer is 40% or more. More preferably in the range of 50% or more and 60% or less,
In the contact charging method, a photoreceptor which hardly causes dielectric breakdown and has few pinholes and can obtain a good image can be obtained.
Further, it is preferable to include an indole compound represented by the above general formula (I) as a charge transporting material, since dielectric breakdown is less likely to occur.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments as long as the gist of the present invention is not impaired. The parts in the examples are parts by weight. FIG. 1 is a schematic sectional view showing one embodiment of the photoreceptor of the present invention, in which a charge generation layer 1 is formed on a conductive substrate 1a.
b, a photoreceptor having a structure in which the charge transport layer 1c is sequentially formed.

Example 1 A compound I represented by the following structural formula as a charge generating material was formed on a cylindrical substrate made of an aluminum alloy as a conductive substrate.
2 parts of bisazo pigment I, 2 parts of a polyester resin (manufactured by Toyobo Co., Ltd .; Byron 200) and 90 parts of cyclohexanone were mixed and dispersed by a sand grinder for 6 hours. A coating liquid diluted by adding 60 parts of tetrahydrofuran to this dispersion was applied by dip coating, and dried at 90 ° C. for 20 minutes to form a 0.4 μm-thick charge generating layer.

[0013]

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Next, as the charge transporting material, the above-mentioned general formula (I)
A compound I-1 having the following structural formula, which is a specific example of the indole compound, and a benzidine compound, which is a compound III-1 represented by the following structural formula, are mixed at a weight ratio of 1: 1. (Number average molecular weight: 50,000) to 30% by weight based on the total solid content,
What was prepared so as to be 40% by weight, 50% by weight, 60% by weight, and 70% by weight was dissolved in tetrahydrofuran to prepare five kinds of coating liquids, and these coating liquids were immersed on the charge generating layer. And dried at a temperature of 100 ° C. for 20 minutes so that the film thickness is 10 μm, 15 μm, 20 μm, and 2 μm, respectively.
By forming charge transport layers of 5 μm and 30 μm, 25 types of photoconductors were produced.

[0015]

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Example 2 The procedure of Example 1 was repeated, except that the benzidine compound as the charge transport material was changed from the compound III-1 shown in the above structural formula to the compound III-2 shown in the following structural formula. Thus, 25 types of photoconductors were produced.

[0017]

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Example 3 In Example 1, the indole compound as the charge transport material was changed from the compound I-1 of the above structural formula to the compound I-2 of the following structural formula, and the benzidine compound was replaced by the compound III- 1 to a compound III-3 represented by the following structural formula
25 types of photoreceptors were produced in the same manner as in Example 1 except that the photoreceptor was changed.

[0019]

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Comparative Example 1 In the same manner as in Example 1 except that the indole compound was not used as the charge transporting material, and only the benzidine compound which is the compound III-4 represented by the following structural formula was used. 25 types of photoconductors were produced.

[0021]

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Comparative Example 2 The procedure of Example 1 was repeated, except that the indole compound was not used as the charge transporting material, and only the benzidine compound, compound III-5 represented by the following structural formula, was used. 25 types of photoconductors were produced.

[0023]

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Each of the photoreceptors produced as described above was attached to a contact charging type copying machine as shown in FIG. 2 with the thickness of the charge transport layer and the binder resin content ratio, and was supplied with a charging mechanism of about -5 kv. Was applied to the surface of the photoreceptor to about -1 kv, and the relationship with the amount of pinholes generated was examined. Further, the image quality of each was evaluated using a contact charging type copying machine as shown in FIG. The results are shown in Table 1, Table 2, Table 3, Table 4, and Table 5 in the order of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2, respectively. In each table, the amount of pinholes was indicated by ○ when no pinhole was generated, Δ when a small amount was generated, and x when a large amount was generated.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

[Table 5]

As can be seen from the above results, the binder resin content of the charge transport layer is 40% by weight or more, and the film thickness is 25%.
When the thickness is at least μm, a photoconductor having few pinholes and good image quality can be obtained. However, as can be seen in Tables 4 and 5, the binder resin content was 70%.
When the content is less than 50% by weight, there is a problem that the characteristics of the photoreceptor deteriorate and the problem becomes a practical problem. When the content is less than 50% by weight, there is a problem that the film thickness needs to be large. Is more preferably in the range of 50% by weight or more and 60% by weight or less. Further, from the results of Tables 1, 2, 3 and Tables 4 and 5, the effect of including the indole compound represented by the general formula (I) as a charge transport material in the charge transport layer is apparent.

In the above embodiments, a polycarbonate resin having a number average molecular weight of 50,000 was used as a binder resin for the charge transport layer. However, any resin having a number average molecular weight of 20,000 or more is similarly effective.

[0032]

According to the present invention, in a function-separated laminated electrophotographic photosensitive member in which a charge generation layer and a charge transport layer are laminated on a conductive substrate in this order, the charge transport layer is made of an organic charge A binder comprising a transport material and a binder resin, wherein the binder resin is a polycarbonate resin having a number average molecular weight of 20,000 or more, wherein the weight ratio of the binder resin in the charge transport layer is 40% or more, and the organic charge is The transport material is a layer composed of two or more types of charge transport materials, and the thickness of the charge transport layer is 25 μm or more. By using such a charge transport layer, it is possible to obtain an organic electrophotographic photoreceptor which is less likely to cause dielectric breakdown even when used in a contact charging system and can obtain a high quality image.

It is more preferable that the weight ratio of the binder resin in the charge transport layer is in the range of 50% to 60%. Furthermore, it is more preferable that the charge transporting material contains the indole compound represented by the general formula (I).

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one embodiment of a photoreceptor of the present invention.

FIG. 2 is an explanatory view of a main part of a contact charging type electrophotographic copying machine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 1 a conductive substrate 1 b charge generation layer 1 c charge transport layer 2 charging mechanism 3 exposure mechanism 4 development mechanism 5 transfer mechanism 6 transfer image support 7 cleaning mechanism 8 pre-exposure mechanism

Claims (3)

[Claims] 1. A function-separated layered electrophotographic photosensitive member used in a contact charging type electrophotographic apparatus, wherein a charge generation layer and a charge transport layer are laminated on a conductive substrate in this order. The layer mainly comprises an organic charge transport material and a binder resin, wherein the binder resin is a polycarbonate resin having a number average molecular weight of 20,000 or more, and the weight ratio of the binder resin in the charge transport layer is 40% or more; and An electrophotographic photoreceptor, wherein the organic charge transport material comprises two or more types of charge transport materials, and the thickness of the charge transport layer is 25 μm or more. 2. The electrophotographic photosensitive member according to claim 1, wherein the weight ratio of the binder resin in the charge transport layer is in a range of 50% or more and 60% or less. 3. The electrophotographic photoreceptor according to claim 1, wherein the charge transport layer contains an indole compound represented by the following general formula (I) as the charge transport material. Embedded image [In the formula (I), R ₁ , R ₂ , R ₅ and R ₆ are a hydrogen atom, an alkyl group having 1 to 9 carbon atoms, an aralkyl group having 1 to 9 carbon atoms, and an aryl having 1 to 9 carbon atoms. R ₁ = R ₆ , R ₂ = R ₅ ,
R ₃ and R ₄ represent any of a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a halogen atom, and R ₃ = R ₄ . ]