JPH11344816A - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positively chargeable single-layer type organic electrophotographic photoreceptor used for an electrophotographic printer, a copying machine or the like.

[0002]

2. Description of the Related Art A photoconductor for electrophotography has a structure in which a photoconductor layer having a photoconductive function is provided on a conductive substrate. Among these, in an organic electrophotographic photoreceptor (OPC) containing an organic compound as a functional component responsible for charge generation and transport, functional layers such as a charge generation layer (CGL) and a charge transport layer (CTL) are laminated. And a single-layer type that performs these functions in a single layer.

[0003] Most of the organic electrophotographic photoreceptors that are widely used at present are of the stacked type in which the surface is negatively charged. In contrast, a positively charged organic electrophotographic photoreceptor has features such as low ozone generation during use and a large margin for film shaving, but generally, organic substances are difficult to transport negative charges. It is difficult to use a stacked type with separate functions, and a single-layer type is often used. The single-layer type is higher in productivity and more advantageous in cost than the stacked type.

[0004]

However, a positively-charged single-layer type organic photoreceptor does not always sufficiently satisfy all the required performances required for an electrophotographic photoreceptor.

In particular, a memory phenomenon in which the previous history of a printed image appears in the next printed image is a serious image disorder,
This is a serious problem in practical use. As the memory phenomenon, there are a positive memory in which the density of the previous image appears in the next image as it is, and a negative memory in which the density is inverted.

The details of the mechanism of the image memory phenomenon are described in
Although there are still many unclear points and no complete elucidation has been made, in particular, the single-layer type organic photoreceptor is subjected to reverse charging (negative charging in the case of positive charging type) during the transfer process during the copying process. In this case, it is considered that one of the factors is the injection of charges from the conductive substrate to the photosensitive layer.

In view of the above situation, an object of the present invention is to provide a positively charged single-layer type organic electrophotographic photoreceptor in which a memory phenomenon caused by a transfer process in an electrophotographic system is reduced. .

[0008]

In order to solve the above-mentioned problems, an electrophotographic photoreceptor of the present invention comprises a positively-charged single-layer type photosensitive member having a photosensitive layer containing a charge generating material and a charge transporting material. In the organic electrophotographic photoreceptor, the charge transport material has an ionization potential (lpT) of 5.5 eV or less.

The inside of the photosensitive layer has a structure in which a charge generating material is dispersed as particles in a charge transporting material and a binder.
By the light irradiation, positive charges (holes) and negative charges (electrons) are generated inside the charge generating material. Some of the generated charges disappear by recombination, but most of the holes are injected into the charge transporting material by an electric field applied to the photosensitive layer, thereby canceling the surface charge as a photocurrent. With this process,
An electric latent image is formed by lowering the potential of a portion of the photoreceptor surface that has been irradiated with light and keeping a high potential in a portion that has not been irradiated with light. In this state, when the toner positively charged to the intermediate potential adheres to the surface of the photoreceptor, the toner selectively adheres to the portion irradiated with the light whose potential has decreased (developing process).

The transfer process is a process for transferring the toner adhered to the surface of the photoreceptor to paper. The paper is negatively charged and brought into contact with the surface of the photoreceptor to transfer the toner by electrostatic force. The present inventors have made the following speculation about the mechanism of memory development caused by this process. That is, positive charge is injected into the photosensitive layer from the conductive substrate due to negative charge, but it is presumed that the effective negative charge position applied to the photosensitive layer differs depending on the presence or absence of toner on the surface of the photosensitive member. In other words, the negative voltage applied to the photosensitive layer by the positive charge of the toner is reduced in the portion where the toner is present, so that the injected positive charge is smaller than the portion where the toner is not present. Due to this difference in history, during the next charging process, the charging potential in the portion where the toner was present (the black portion in the image) is higher than the charging potential in the portion where the toner was absent (the white portion in the image). A negative memory phenomenon in which the density in the next image decreases appears.

In order to suppress the memory phenomenon caused by the above mechanism, it is important to suppress the injection of positive charges from the conductive substrate into the photosensitive layer due to negative charging. As this means, the present inventors have found that it is effective to lower the ionization potential of the charge transport material in the photosensitive layer. That is, the injection of positive charges from the conductive substrate
It is affected by the difference in ionization potential between the conductive substrate and the charge transport material. The ionization potential of aluminum, which is often used as a conductive substrate material, varies depending on the alloy composition and surface state of aluminum, but is about 3.8 to
4.3 eV. In addition, the ionization potential of a commonly used charge transporting material is generally in the range of 4.5 to 6.0 eV. As a result of the inventor's intensive studies on these ionization potentials, as a result of suppressing the positive charge injection, the smaller the ionization potential value of the charge transporting material, the better, and practically 5.5 eV or less, preferably It was found that it was 5.2 eV or less.

[0012]

FIG. 1 schematically shows the structure of a positively charged single-layer type photosensitive member according to an embodiment of the present invention. This single-layer type photoreceptor comprises a conductive substrate 1, an intermediate layer 2, a photosensitive layer 3
It is comprised by these.

The intermediate layer 2 is provided, if necessary, mainly in this photosensitive member in order to improve the adhesion between the photosensitive layer 3 and the substrate 1. For this purpose, the thickness of the intermediate layer 2 is preferably about 0.5 μm or less. By increasing the thickness of the intermediate layer 2, it is possible to suppress the injection of positive charges from the substrate 1 to the photosensitive layer 3 in the transfer process.
The transfer of the positive charge from the photosensitive layer 3 to the substrate 1 required in the developing process at the time of the positive charge is also suppressed, and as a result, a problem that the residual potential is increased occurs.
Cannot be given a thickness of 0.5 μm or more, so that the intermediate layer cannot have the function of suppressing positive charge injection. Therefore, this intermediate layer 2 has a small problem of adhesion,
Alternatively, it may not be provided if it can be solved by another means.

As the conductive substrate 1, a cylinder made of various metals (such as aluminum) or a conductive plastic film can be used.

In the intermediate layer 2, as a material of the polymer dispersed coating, insulating polymers such as casein, polyvinyl alcohol, polyvinyl acetal, nylon, melamine, and cellulose, or conductive polymers such as polythiophene, polypyrrole, and polyaniline; Those containing a metal oxide powder such as titanium dioxide and zinc oxide in these polymers can be used. Alternatively, an alumite-treated surface of the conductive substrate or a surface-modified one with an undercoating layer such as a resin film can be used.

The photosensitive layer 3 is mainly composed of a charge generating material, a charge transporting material, and a resin binder. As the charge generating material, various phthalocyanine compounds, azo compounds, polycyclic quinone compounds, derivatives thereof, and the like shown in the following specific examples I-1 to I-4 can be used.

[0017]

Examples of the charge transport material having an ionization potential value of 5.5 eV or less include various hydrazone compounds, styryl compounds, diamine compounds, butadiene compounds, indole compounds, and mixtures thereof of the following specific examples II-1 to II-7. Can be used.

The above-described charge transporting material is mainly a positive charge transporting material. However, a negative charge transporting material such as a diphenoquinone derivative, a benzoquinone derivative, an anthraquinone derivative, a stilbenequinone derivative or the like can also be used. .

[0020]

[0021]

As the binder resin for the photosensitive layer, polycarbonate is currently widely used as the most excellent material system in terms of film strength and printing durability. Examples of this polycarbonate include bisphenol A type, bisfuphenol Z type and the like and various copolymers as shown in the following specific examples III-1 and III-2.

[0023]

The optimum average molecular weight range of such a polycarbonate resin is 10,000 to 100,000. In addition, polystyrene, polyphenylene ether acrylic, polyester,
Polyamide, polyurethane, epoxy polyvinyl butyral, polyvinyl acetal, phenoxy resin, silicone resin, acrylic resin, vinyl chloride resin, vinylidene chloride resin, vinyl acetate resin, formal resin, cellulose resin, or copolymers thereof, and halides thereof And a cyanoethyl compound.

Further, as the antioxidant to be added to the photosensitive layer, the following specific examples IV-1 to IV-4 can be used alone or in an appropriate combination.

[0026]

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Example 1 A polyvinyl acetal resin having a thickness of 0.1 μm was formed as an intermediate layer on an Al substrate. Further, as the charge generating material, the metal-free phthalocyanine (X-type,
3.0% by weight), and the specific example II-1 was used as the charge transport material.
(42% by weight) and bisphenol Z-type polycarbonate (50% by weight of the antioxidant of the specific example IV-1) as a binder resin were dissolved and dispersed in a tetrahydrofuran solvent to obtain a 25 μm-thick photosensitive film. The layer was formed by dip coating to form a photoreceptor. Using this photoreceptor, electrical characteristics were evaluated.

Example 2 A photoconductor was produced using the same materials and under the same conditions as in Example 1 except that the specific example II-2 was used instead of the specific example II-1 as the charge transporting material.

Example 3 A photoconductor was prepared by using the same materials and under the same conditions as in Example 1 except that the specific example II-3 was used instead of the specific example II-1 as the charge transporting material.

Example 4 A photoconductor was prepared by using the same materials and under the same conditions as in Example 1 except that the specific example II-4 was used instead of the specific example II-1 as the charge transporting material.

Example 5 A photoconductor was prepared by using the same materials and under the same conditions as in Example 1 except that the specific example II-5 was used instead of the specific example II-1 as the charge transporting material.

Example 6 A photoconductor was produced using the same materials and under the same conditions as in Example 1 except that the specific example II-6 was used instead of the specific example II-1 as the charge transporting material.

Example 7 A photoconductor was produced by using the same materials and under the same conditions as in Example 1 except that the specific example II-7 was used instead of the specific example II-1 as the charge transporting material.

Comparative Example 1 A styryl compound A having an ionization potential of 5.52 eV was used in place of the specific example II-1 as a charge transport material. A photoreceptor was manufactured using the same materials and under the same conditions as in Example 1 except for using.

COMPARATIVE EXAMPLE 2 An amine compound B having an ionization potential of 5.60 eV instead of the specific example II-1 as a charge transport material A photoreceptor was manufactured using the same materials and under the same conditions as in Example 1 except for using.

The ionization potential of the charge transport material was measured using an atmospheric ultraviolet photoelectron analyzer AC-1 manufactured by Riken Keiki Co., Ltd.
Measured by mold. At this time, the energy of the exposure light source is 5
0 nW.

Evaluation of the photoreceptor characteristics was performed by mounting various photoreceptors on a laser beam printer having fixed outputs of a charging mechanism, an exposure mechanism, and a static elimination mechanism, and at room temperature and normal humidity (20 ° C., 50 RH).
It carried out under the atmosphere of. 780n wavelength as an exposure light source
A monochromatic laser beam of 1 μJ / cm ^{2 at} m was used. After setting the initial charging potential to 600 V, the monochromatic light was exposed, and the image was evaluated at the initial stage and after printing 1,000 sheets. The results are shown in Table 1 below.

[0038]

[Table 1] * Evaluation of the memory was made into 5 levels. 1>2>3>4> 5 in the order of memory strength.

As can be seen from Table 1, the ionization potential and the strength of the memory after running are well correlated, and especially when a charge transport material larger than 5.5 eV is used, it is at a level that is a practical obstacle. .

[0040]

According to the present invention, it is possible to obtain a positively charged single-layer type electrophotographic photoreceptor in which a memory phenomenon caused by an electrophotographic transfer process is reduced. Could be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of one example of a single-layer type electrophotographic photoconductor of the present invention.

[Explanation of symbols]

 Reference Signs List 1 conductive substrate 2 intermediate layer 3 photosensitive layer

Claims (1)

[Claims] 1. A positively-charged single-layer type organic electrophotographic photoreceptor comprising a photosensitive layer containing a charge generating material and a charge transporting material on a conductive substrate, wherein the ionization potential of the charge transporting material ( lpT) is 5.5 eV or less.