JPH09106091A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor having high resistance against printing and humidity as well as a long service life by using a suitable material as a surface protection layer. SOLUTION: A charge transport layer 2 formed out of an organic substance, and a charge generation layer 3 of an organic substance are laminated on a conductive substrate 1, and the charge generation layer 3 is covered with a surface protection layer 4. In this case, the surface protection layer 4 is composed of a mixture of urethane resin and tetraethyl silicate, and the contact angle of demineralized water measured on the surface thereof in the air is equal to 70 degrees or more. The surface protection layer 4 is alternatively composed of a mixture of acryl graft copolymer containing fluorine and tetraethyl silicate and, then, the contact angle of demineralized water measured on the surface thereof in the air is taken at 75 degrees or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated type electrophotographic photoreceptor which is used in a positive charging system using an organic photoconductive substance.

[0002]

2. Description of the Related Art In recent years, organic photoconductive substances have been widely studied as photosensitive materials for electrophotographic photoconductors (hereinafter also simply referred to as photoconductors). A photosensitive material using an organic photoconductive substance has flexibility, thermal stability, film-forming properties, transparency, and transparency as compared with the case where an inorganic photoconductive substance such as selenium, which has been mainly used conventionally, is used. Although it has many advantages such as price, it has the drawback of being inferior in terms of dark resistance and light sensitivity. Therefore, taking advantage of the ease of film formation, the photosensitive layer of the photoreceptor is mainly used for the layer that contributes to charge generation and the layer that mainly contributes to the retention of surface charge in a dark place and the charge transport during photoreception. Practical application has been promoted by stacking layers separated in function, selecting and using materials suitable for the functions of each layer, and improving the electrophotographic characteristics as a whole.

This type of multi-layer photosensitive member is usually formed by sequentially stacking a charge generating layer containing an organic charge generating substance and a charge transporting layer containing an organic charge transporting substance on a conductive substrate. For example, a Carlson method is applied to image formation by electrophotography using these photoconductors. Image formation by this method is performed by corona discharge to a photoconductor in a dark place, formation of an electrostatic latent image such as characters and pictures on a document by exposure on the charged surface of the photoconductor, and electrostatic latent image formed. It is performed by developing the image with toner, transferring the developed toner image to a support such as paper, and fixing.After the toner image is transferred, the photoconductor is neutralized, residual toner is removed, and light is neutralized. Be used.

[0004]

At this time, a negative charging system is adopted for charging the photosensitive member. However, since a large amount of ozone is generated in the negative corona discharge, the surface of the photosensitive member is strongly oxidized by ozone during charging. Therefore, it is necessary to take measures against ozone deterioration by the photoconductor itself or the mechanism of the apparatus. If the positive charging method can be applied, the corona discharge is more stable than the negative charging method. Generates less ozone,
Further, it is convenient in that a suitable developer can be easily produced. However, in order to form a photoreceptor to which the positive charging method can be applied, the layer structure of the conductive substrate-charge generation layer-charge transport layer is used. No suitable organic charge generating substance or organic charge transporting substance has been found yet.

In order to enable the photoconductor to be positively charged,
It is considered that a charge generating substance and a charge transporting substance are mixed to form a single layer, or a charge generating layer is formed on the charge transporting layer. However, the former has a drawback that the charge accepting ability is low and the repetition characteristics are insufficient. On the other hand, in the latter case, it was difficult to form the charge generation layer with a thickness of 1 μm or less, preferably 0.3 μm or less, and without degrading the charge transport layer already formed on the substrate. Furthermore, recently, a photoreceptor using an organic material has been required to have the same durability as a photoreceptor such as selenium. It was extremely difficult for the photoreceptor provided with the generating layer to satisfy the requirement of durability. Therefore, in order to improve the durability of these photoconductors, various proposals have been made to provide a surface protective layer having excellent abrasion resistance and good light shielding properties on the charge generation layer. However, when such a surface protective layer is provided, there is a problem that image deletion occurs under high temperature and high humidity.

An object of the present invention is to provide a long-life electrophotographic photoreceptor having excellent printing durability and moisture resistance by using an appropriate material for the surface protective layer.

[0007]

In order to achieve the above object, the present invention provides a charge transport layer made of an organic material and a charge generation layer made of an organic material, which are laminated on a conductive substrate.
In the case where the charge generation layer is covered with a surface protective layer made of a mixture of a urethane resin and tetraethyl silicate, the contact angle of pure water measured in the air on the surface of the surface protective layer is 70 degrees or more. Alternatively, a charge transport layer made of an organic substance and a charge generation layer made of an organic substance are laminated on a conductive substrate, and the charge generation layer is formed by a surface protective layer made of a mixture of a fluorine-containing acrylic graft copolymer and tetraethyl silicate. In the thing to be covered, it is assumed that the surface protection layer has a contact angle of pure water of 70 degrees or more measured in air on the surface.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual sectional view of a photoreceptor in which the present invention is embodied. 1 is a conductive substrate, 2 is a charge transport layer, 3 is a charge generating layer, and 4 is a surface protective layer. is there. The conductive substrate 1 serves as an electrode of the photoconductor and also serves as a support for other layers, and may be cylindrical, plate-shaped, or film-shaped, and is made of aluminum, stainless steel, nickel, or the like. It may be a metal, glass, resin or the like that has been subjected to a conductive treatment.

The charge transporting layer 2 is a coating film made of a material in which an organic charge transporting substance is dispersed in a resin binder, and holds an electric charge of the photoconductor as an insulating layer in a dark place and a charge generating layer at the time of receiving light. It exerts the function of transporting electric charges injected from. As the organic charge transporting substance, derivatives such as pyrazoline, hydrazone, triphenylmethane and oxadiazole are used. As resin binder, polycarbonate, polyester, polyamide, polyurethane,
Epoxy, silicone resin, methacrylic acid polymers and copolymers are used, but compatibility with charge transporting substances is important in addition to mechanical, chemical and electrical stability and adhesion. .

The charge generating layer 3 is formed by vapor deposition of an organic photoconductive substance or by coating a material in which particles of the organic photoconductive substance are dispersed in a resin binder, and receives light to generate charges. In addition, it is important that the charge generation efficiency is high, and at the same time, the generated charge can be injected into the charge transport layer 2 and the surface protective layer 4. As the charge generating substance, phthalocyanine compounds such as metal-free phthalocyanine and titanyl phthalocyanine, various azo, quinone, and indigo pigments are used. You can Since the charge generation layer only needs to have a charge generation function, its film thickness is determined by the light absorption coefficient of the charge generation substance and is generally 5 μm or less, preferably 1 μm or less. The charge generation layer can be mainly composed of a charge generation substance and added with a charge transporting substance or the like.

The surface protective layer 4 is provided on the thin charge generating layer 3 in order to enhance the durability of the photoconductor, and is sufficiently resistant to mechanical friction such as cleaning.
In a dark place, it has the function of receiving and holding the electric charge of corona discharge, and also has the property of transmitting the light to which the charge generation layer 3 is sensitive, and transmits the light at the time of exposure to reach the charge generation layer. , Receives the injection of the generated charges and neutralizes and eliminates the surface charges.

The effects of the present invention will be described below with reference to specific embodiments.

[0013]

【Example】

Example 1 As the charge transport layer 2, 100 parts by weight of an organic charge transporting substance 1-phenyl-3- (P-diethylaminostyryl) -5- (paradiethylaminophenyl) -2-pyrazoline was added to 700 parts by weight of tetrahydrofuran (THF). An aluminum cylinder is dipped in a solution prepared by mixing a solution prepared by dissolving 100 parts by weight of polymethylmethacrylate polymer in 700 parts by weight of toluene to form a coating film, and the film thickness after drying is 1
The thickness was set to 5 μm. On the charge transport layer 2 thus obtained, copper-phthalocyanine (light absorption maximum 600-
(700 nm) 50 parts by weight together with 100 parts by weight of polyester resin and a THF solvent are kneaded by a mixer for 3 hours to prepare a coating solution, which is applied by a dipping method and the film thickness after drying is 1
The charge generation layer 3 was formed to have a thickness of μm.

On the charge generation layer 3 thus obtained, 10 parts by weight of a mixture of tetraethyl silicate and urethane resin mixed in various compounding ratios and methyl ethyl ketone 1
The coating film dissolved in 00 parts by weight has a film thickness of 0.5μ after drying.
Then, the surface protective layer 4 was formed by coating so as to have a thickness of m. On the other hand, up to the charge generation layer 3 was formed under the same conditions as in Example 1, and only the surface protection layer 4 was formed with tetraethyl silicate at 0.5 μm.
m.

A contact angle between the surface protective layer 4 and water 5 as shown in FIG. 2 and these photoconductors are mounted on an actual copying machine, and an image test is conducted in an atmosphere of a temperature of 35 ° C. and a relative humidity of 85%. The results obtained are shown in Table 1.

[0016]

[Table 1]

In the image evaluation results, ⊚ indicates that an extremely clear image was obtained, ∘ indicates that the image was good, Δ indicates that the image deletion was a little, and × indicates that the image deletion was remarkable. When the surface protective layer 4 is formed of a mixture of tetraethyl silicate and urethane resin and the contact angle is 70 degrees or more, a good image can be obtained. Example 2 Under the same conditions as in Example 1, up to the charge generation layer 3 was formed, and only the surface protective layer 4 was treated with a fluorine-containing acrylic graft copolymer (trade name: comb polymer LF-40: manufactured by Soken Chemical Co., Ltd.). It was formed with a coating solution by mixing with tetraethyl acid salt in various compounding ratios. Table 2 shows the results.

[0018]

[Table 2]

The symbols in the image evaluation column have the same meanings as in Table 1. When the results of Tables 1 and 2 and Examples 1 and 2 are summarized, it can be seen that when the contact angle θ is 70 degrees or more, a clear image without image deterioration can be obtained in high temperature and high humidity. The contact angle of 70 ° or more when only 15% of the fluorine-containing resin was mixed in Example 4 is because the C—F bond is strong and water adsorption, that is, the bond with the OH group is unlikely to occur. Conceivable. For this reason, it is preferable that the content of the fluororesin be larger than that in view of moisture resistance.

[0020]

According to the present invention, the adsorption of water to the surface protective layer for protecting the thin charge generating layer in the positive charging system and improving the printing durability is evaluated by the contact angle of pure water on the surface, By using the surface protective layer having a large contact angle, the printing durability was improved, and an organic photoconductor in which image deletion did not occur in high temperature and high humidity could be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a photoconductor embodying the present invention.

FIG. 2 is an explanatory diagram of a contact angle of water on the surface.

[Explanation of symbols]

 1 Conductive Substrate 2 Charge Transport Layer 3 Charge Generation Layer 4 Surface Protection Layer 5 Water

Claims (2)

[Claims] 1. A charge transport layer made of an organic material and a charge generation layer made of an organic material are laminated on a conductive substrate, and the charge generation layer is covered with a surface protection layer, wherein the surface protection layer is made of urethane resin. A photoreceptor for electrophotography, which is formed from a mixture with tetraethyl acid salt and has a contact angle of pure water of 70 degrees or more measured in air on the surface of the surface protective layer. 2. A charge transport layer made of an organic substance and a charge generation layer made of an organic substance are laminated on a conductive substrate, and the charge generation layer is covered with a surface protection layer, wherein the surface protection layer is a fluorine-containing acrylic resin. Formed from a mixture of a graft copolymer and tetraethyl silicate, the contact angle of pure water measured in air on the surface of the surface protective layer is 75.
A photoconductor for electrophotography, characterized by having a degree of rotation of at least one degree.