JPS61200545A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic sensitive body having superior photosensitivity even in environment at low temp. and humidity or at high temp. and humidity by forming a layer contg. a specified bisazo compound as a carrier generating substance in the form of fine particles having a specified particle size basing on the thickness of the layer while maintaining the crystal form. CONSTITUTION:A bisazo compound represented by the formula [where each of Ar1 and Ar2 is (substituted) phenyl or naphthyl, Ar3 is an aromatic heterocyclic or carboxylic ring having an electron withdrawing group as a substituent, and Z is a group of atoms required to form a (substituted) aromatic heterocyclic or carboxylic ring] is used as a carrier generating substance. Crystals of the compound is ground to fine powder having <=0.01mum uniform particle size, and the fine particles are dispersed in DMF as a polar org. solvent with an ultrasonic homogenizer to further reduce the particle size. A photosensitive layer contg. the bisazo compound dispersed uniformly in a binder in the form of fine particles having a particle size <=1/5 time the thickness of the layer without changing the crystal state is formed on an electrically conductive support to obtain a sensitive body having superior durability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor having a photosensitive layer containing a bisazo compound.

[Prior art and its problems]

As a photoreceptor for electrophotography (hereinafter simply referred to as photoreceptor), the required potential can be reached by corona discharge etc. in a dark place. ! F
They are required to have the capability of being able to charge, have little charge leakage, and quickly discharge when irradiated with light. Therefore, as a photoconductive material used in the photosensitive layer of a photoreceptor, it is difficult to use a photoconductive material that is large in the dark. It is required to have Ff1jL ability, have low leakage current, have the ability to generate a large amount of carriers by light irradiation, and have excellent transport ability to rapidly transport the generated carriers.

Conventionally, inorganic photoconductive materials such as amorphous selenium, amorphous selenium alloy, rR zinc oxide, and cadmium sulfide have been used as photoconductive materials having such performance, but in recent years, flexible photoconductive materials have been used.

Organic photoconductive materials have been attracting attention due to their impact resistance, thermal stability, film-forming properties, and the like.

Recently, there has been much research into functionally separated photoreceptors in which the performance of the photoreceptor is improved by assigning the carrier generation function and the carrier transport function to different substances. In such functionally separated type photoreceptors, many methods have been proposed that use organic dyes or organic pigments as carrier generating substances.1) Indigo pigments, 7-talocyanine pigments, azo pigments, etc. are known. , sufficient fastness, properties 1. ．． It is difficult to find a compound that has light resistance and excellent carrier generation ability.

Among these, bisazo compounds are known to be effective as photoconductive substances for photoreceptors (for example, Japanese Patent Laid-Open No. 47-37543).

Bisazo compounds are pigments and are not conductive to common solvents. Therefore, when producing a photoreceptor using a bisazo compound as a photoconductive material, the bisazo compound is usually made into a fine powder, and the fine powder is mixed into a synthetic resin binder, or other materials are added to the binder. A method is used in which the additives are uniformly dispersed into a coating solution, and this coating solution is uniformly applied onto a substrate. In this case, the electrophotographic properties of the resulting photoreceptor vary greatly depending on the crystalline state and agglomerated state of the fine powder of the bisazo compound.

In particular, if the crystalline state is poor, or if it is amorphous, the photoreceptor's treble TVF properties and photosensitivity will be poor.

Bisazo compounds are made from the corresponding amino compounds,
It can be easily synthesized by coupling a diazonium salt obtained by diazotizing this with a coupler in a tm medium. However, the crystal form observed differs depending on the reaction conditions during the coupling. When it becomes amorphous, it is necessary to transform it into a crystalline state by means of a vapor treatment or the like.

In addition, in order to form a uniform bisazo compound coating film during the production of a photoreceptor, it is necessary that the fine powder of the bisazo compound be uniformly fine and free of coarse particles or agglomerated clumps of fine particles. A method has been proposed in which a fine powder is obtained by washing the reaction product of a bisazo compound synthesized in the following manner with an organic solvent, further washing with water, and then drying.

However, this method also causes variations in particle size during mass production, and is still not a satisfactory method.

In an attempt to obtain bisazo compounds with fine particles of uniform particle size,
When the KFi and bisazo compounds are pulverized six times by applying mechanical strain using a ball mill, etc., the crystal form of the bisazo compound changes and the crystal state deteriorates, resulting in the formation of a photoreceptor.
The r4 problem of deterioration of characteristics and photosensitivity is that bisazo compounds whose crystal form has changed due to pulverization treatment can be changed by heat treatment at a temperature close to the melting point @°C to change the crystal form and improve its properties as a good crystal state. However, there is a problem in that the cost of improvement must be spent and the number of manufacturing steps for the photoreceptor increases. Furthermore, when trying to create a coating liquid by adding a resin binder etc. to the finely powdered bisazo compound and performing the entire dispersion process using a kneader etc., the more finely powdered the bisazo compound is, the more There is a problem in that the fine powders tend to coagulate with each other, and a new aggregate state is formed during the dispersion treatment process, making it difficult to obtain a coating liquid in which the bisazo compound is uniformly dispersed, resulting in a failure to form a uniform coating film.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a band 1 having a layer containing a bisazo compound as a carrier generating substance.
An object of the present invention is to provide an electrophotographic photoreceptor with excellent 1c characteristics and photosensitivity.

[Key points of the invention]

An object of the present invention is to provide an electrophotographic photoreceptor having a layer containing a bisazo compound as a carrier generating substance, in which the bisazo compound has the structural formula shown below, and the particle size is as thick as the layer containing the bisazo compound. This is achieved by forming fine particles with unbroken crystals that have a particle size smaller than that of a lump.

Structural formula (wherein Arλ and Ar each represent a substituted or unsubstituted nophenyl group or naphthyl group, Ar3 represents an aromatic heterocycle or aromatic carbocycle substituted with an electron-withdrawing group, (2 represents a substituted or unsubstituted aromatic complex fI!I or an atomic group that damages the aromatic carbon ring.) In order to form a thin layer with a uniform thickness, it is required that the particle size of the substance dispersed in the film is sufficiently smaller than the film thickness. In the case of a photoreceptor having a photosensitive layer containing a bisazo compound dispersed therein, if the particle size of the fine particles of the bisazo compound is less than the thickness of the film, it is practically effective in terms of the characteristics of the photoreceptor. It turns out. Of course, from the viewpoint of uniformity of film thickness, it is desirable that the particles be as fine as possible. However, if the crystal form of the bisazo compound is broken into fine particles such as tl, the properties as a photoreceptor will deteriorate, which is not preferable. That is, the particle size of the fine particles of the bisazo compound is at least smaller than the thickness of the film, and is preferably as small as possible without breaking the crystals.

The bisazo compound is 1 in the X-ray diffraction diagram of Cu-Ka.
For example, as shown in Figure 1, it is necessary that the crystal is broken to such an extent that the diffraction peak of the crystal can be clearly recognized. do not have.

Furthermore, since the bisazo compound of the present invention has a child-attracting group, if it is suspended in a polar organic solvent, the fine particles of the bisazo compound will not aggregate, making it possible to obtain a uniform coating film. It's valid.

Additionally, K for suspending the bisazo compound in a polar organic solvent
When ultrasonic dispersion treatment is applied, the crystal structure of the bisazo compound fine powder can be transformed due to the local heating effect generated by the generation of bubbles and quenching of IK during the treatment process. The broken bisazo compound fine powder can be re-crystallized to exhibit good electrophotographic properties, which is very effective.

[Embodiments of the invention]

Hereinafter, the present invention 811 will be explained based on an example.

Example 1 A bisazo compound was milled to a particle size of 0.0 using a ball mill.
Pulverized into a fine powder with a uniform particle size of 1 μm or less, the fine particles of the crushed bisazo compound, one heavy electric moiety, and N,N'-dimethylformamide (DMF), which is a polar organic solvent.
A 300-layer lid was subjected to ultrasonic dispersion treatment for 2 hours using an ultrasonic homogenizer to prepare a suspension in which fine particles of bisazotized sweet were uniformly dispersed in a polar organic solvent. When the crystalline state of the dispersed bisazo compound particles was examined using Cu-Ka X-rays, it was found that they had good crystal grains as shown in the XIfM diffraction diagram of FIG. One layer of polymethacrylic methyl polymer (PMA) and 6 parts by weight of toluene were added to this suspension and mixed well with a magnetic stirrer to prepare a uniform coating solution. Apply this coating liquid to a thickness of 75 mm.
It was coated and dried on a .mu.m aluminum vapor-deposited polyester film substrate using a wire bar so that the film thickness after drying was 0.2 .mu.m to obtain a carrier generation layer. Above this KN, N
-f ethylaminobenzaldehyde-1゜1-diphenylhydrogen 2/1 part by weight and 1 part by weight of polyester resin were well suspended in tetrahydro 7ran, and the film thickness after drying was 1.
It was coated and dried to a thickness of 5 μm to form a medium transport layer.

Kawaguchi [lA
Using Seisakusho 1llsp-428 model electrostatic paper tester,
We evaluated its electrophotographic properties. Corona discharge was performed for 10 seconds at a voltage of -6.0 KV to negatively charge the photoreceptor, and the band potential on the surface of the photoreceptor at that time was measured. After that, the electric potential Vp was determined by * when it was left in a dark place for 2 seconds, and then 2 lux of white light was applied to the surface of the photoconductor? Irradiation Vp is half ec
Measure the time until tj1. Exposure iK% was determined. As a result, V m = 1200 volts E% = 2.0 lux·sec. Fine particles of a bisazo compound having an electron-withdrawing group, having a particle size of 0.01 μm or less, which is smaller than an agglomerate with a film thickness of 0.2 μm, and having good crystallization as shown in Figure 1, are used as a carrier-generating substance. It has been found that the photoreceptor having the carrier generation layer shown in FIG.

Example 1. Using a bisazo compound showing the X-ray diffraction diagram of FIG. A photoreceptor was prepared according to the method, and its electrophotographic properties were evaluated. As a result, a value of V=-1100 volts KH=2.0 lux·sec was obtained, and it was found that a photoreceptor with excellent characteristics could be obtained even if the crystal form of the bisazo compound was different.

Comparative Example 1゜Example 1.0 A bisazo compound was pulverized in a ball mill until its crystal form was broken and the X-ray diffraction pattern shown in FIG. 3 was obtained. The bisazo compound fine particles were dispersed in toluene and Il! i! Toshimaru. Example 1. This toluene suspension was used instead of the polar organic solvent suspension of the bisazo compound in Example 1. A photoreceptor was prepared according to the method described in the following, and its electrophotographic properties were evaluated. As a result, values of VA=-1200 volts and EH=10 lux·sec were obtained, indicating that the photosensitivity deteriorates when a bisazo compound with a broken crystal form is used.

Comparative Example 2 The bisazo compound of Example was ground by a ball mill to 0.
The particle size was limited to 1 μm, and the subsequent steps were carried out as in Example 1.
．． A photoreceptor was prepared according to the method, and its electrophotographic properties were evaluated. As a result, the value was 3A = 20 lux·sec for VA--1100 holt, and it was found that the particle size of the bisazo compound powder was large compared to the film thickness, so that a uniform coating film could not be obtained and the properties deteriorated.

〔Effect of the invention〕

As mentioned above, as a carrier generating substance of the functional Jlli type photoreceptor, a bisazo compound having an electron-withdrawing group is contained in the form of fine particles, and the fine particles have a particle size smaller than the spoon of the film thickness and are crystalline. The photoreceptor of the present invention, which is made up of unbroken fine particles, is a practically excellent electrophotographic photoreceptor with good charging characteristics and photosensitivity.

[Brief explanation of drawings]

Oni diagram shows the Xl of α in Cu- of the bisazo compound of Example 1 and Comparative Example 2, FIG. 2 shows Example 2, and FIG. 3 shows Comparative Example 1. ! It is a diffraction diagram. e Tomi 1 Figure

Claims (1)

[Scope of Claims] An electrophotographic photoreceptor having a layer containing a bisazo compound as a carrier generating substance, wherein the bisazo compound has the structural formula shown below, and 1/5 of the thickness of the layer containing the bisazo compound. A photoreceptor for electrophotography characterized by having fine particles with a smaller particle size and unbroken crystals. Structural formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, in the formula, Ar_1 and Ar_2 each represent a substituted or unsubstituted phenyl group or naphthyl group, and A
r_3 represents an aromatic heterocycle or aromatic carbocycle substituted with an electron-withdrawing group, and Z represents an atomic group constituting the substituted or unsubstituted aromatic heterocycle or aromatic carbocycle . )