JPH0453428B2 - - Google Patents

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 a photoreceptor), it can be charged to the required potential by corona discharge in a dark place, has little leakage of charge, and has the ability to quickly discharge when irradiated with light. That is required. Therefore,
The photoconductive material used for the photosensitive layer of the photoreceptor must have a large charging ability in the dark, low leakage current, the ability to generate a large amount of carriers when irradiated with light, and the ability to quickly remove generated carriers. It is desired to have excellent transportation ability to transport the materials to other countries.

As a photoconductive material with such performance,
Traditionally, inorganic photoconductive materials such as amorphous selenium, amorphous aslenium alloy, zinc oxide, and cadmium sulfide have been used, but in recent years, improvements have been made in terms of flexibility, impact resistance, thermal stability, film-forming properties, etc. Organic photoconductive materials are attracting attention.

Furthermore, recently, there has been active research into functionally separated photoreceptors in which the performance of the photoreceptor is improved by assigning different substances to the aforementioned carrier generation function and carrier transport function. For such functionally separated photoreceptors, many methods have been proposed that use organic dyes or organic pigments as carrier generating substances, and indigo pigments, phthalocyanine pigments, azo pigments, etc. are known, but they do not have sufficient robustness. It is difficult to find a compound that has good properties, light resistance, and excellent carrier generation ability.

Under these circumstances, bisazo compounds are known to be effective as photoconductive materials for photoreceptors (for example, see Japanese Patent Application Laid-open No. 37543/1983).

Bisazo compounds are pigments and are insoluble in 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 the coating solution is uniformly applied onto a conductive 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. A bisazo compound can be easily synthesized by using a corresponding amino compound as a raw material and coupling the resulting diazonium salt with a coupler in a solvent. However, the crystal form obtained differs depending on the reaction conditions when coupling is performed.

In addition, in order to form a uniform bisazo compound coating film during the production of a photoreceptor, it is necessary that the bisazo compound fine powder be uniformly fine and free of coarse particles or agglomerated clumps of fine particles, such as the above-mentioned 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 in mass production, and is still not a satisfactory method.

Furthermore, when attempting to prepare a coating liquid by adding a resin binder etc. to a finely powdered bisazo compound and performing a dispersion treatment using a kneader, etc., if the bisazo compound is finely powdered, The problem is that the finer powders are more likely to coagulate with each other, and a new aggregation state is formed during the dispersion treatment process, making it difficult to obtain a coating solution in which the bisazo compound is evenly dispersed, resulting in the formation of a uniform coating film. There is.

Further, in order to obtain a uniform coating film in which the fine powder is not aggregated, there is a drawback that a special solvent must be used, as disclosed, for example, in JP-A-52-55643.

[Purpose of the invention]

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

[Key points of the invention]

The above-mentioned object of the present invention is achieved by using a specific bisazo compound in an electrophotographic photoreceptor having a layer containing a bisazo compound as a carrier generating substance, and by forming fine particles of a certain particle size. .

Therefore, the present invention provides an electrophotographic photoreceptor having a layer containing a bisazo compound as a carrier generating substance, wherein the bisazo compound has the following structural formula, and the thickness of the layer containing the bisazo compound is 1. It is a fine particle with a particle size smaller than /5 and has broken crystals, and furthermore, this fine particle is the Kα of copper.
In an X-ray diffraction diagram using rays, 2θ = 23° to 28° based on the diffraction intensity at 2θ = 40°
An electrophotographic photoreceptor, characterized in that it exhibits an X-ray diffraction diagram in which the maximum value of diffraction intensity is 4 times or less, structural formula: (In the formula, Ar ₁ and Ar ₂ each represent a substituted or unsubstituted phenyl or naphthyl group, and the substituent represents a halogen atom, a lower alkyl group, a lower alkoxy group, etc.)

By the way, in order to form the photosensitive layer of a photoconductor, especially a thin layer such as the carrier generation layer of a functionally separated photoconductor, to a uniform film thickness, the particle size of the substance dispersed in the film must be adjusted to the film thickness. It is desired that it be sufficiently small in comparison. In the case of a photoreceptor having a photoreceptor layer containing a bisazo compound dispersed therein, research has shown that if the particle size of the fine particles of the bisazo compound is 1/5 or less of the film thickness, it is practically effective in terms of the characteristics of the photoreceptor. It turns out that it is. Of course, from the viewpoint of uniformity of film thickness, it is desirable that the particles be as fine as possible.

Thus, even if the bisazo compound of the present invention having the above structural formula is pulverized by pulverization, when a resin binder is added to it and dispersion is performed using a kneader or the like, it becomes fine. It was found that a coating film in which the powder was uniformly dispersed without agglomeration was obtained.

The bisazo compound of the present invention needs to be fine particles with a particle size smaller than 1/5 of the thickness of the layer containing it and whose crystals are broken to a predetermined degree. Such pulverization can be performed by a suitable pulverizing means such as a ball mill. for example,
This can be carried out by dispersing fine particles pulverized by ball milling into tetrahydrofuran. The degree of crystal destruction can be determined by X using copper Kα rays.
It can be determined by line diffraction. The bisazo compound of the present invention preferably has crystals broken to such an extent that a crystal diffraction peak as shown in FIG. 1 is observed, for example. That is, X using Cu-Kα radiation
In the line diffraction diagram, it is preferable that the crystal be broken so that the maximum value of the diffraction intensity at 2θ=23° to 28° is 4 times or less based on the diffraction intensity at 2θ=40°. Therefore, materials that do not satisfy these conditions, such as materials exhibiting diffraction peaks as shown in FIG. 2, are not preferred.

Examples of the present invention will be described below, including a photoreceptor containing the above-mentioned bisazo compound as a carrier generating substance,
In particular, detailed description will be given in connection with the production of a functionally separated photoreceptor. Of course, the present invention is not limited to such photoreceptors.

[Embodiments of the invention]

In general, functionally separated photoreceptors, as mentioned above,
It is constructed by providing a carrier generation layer on a conductive substrate and further providing a carrier transport layer thereon, or by first providing a carrier transport layer and then providing a carrier generation layer.

As the conductive substrate, a metal plate or sheet made of aluminum, copper, zinc, etc., a plastic sheet or film made of polyester, etc., on which the above metals are deposited are used.

The carrier generation layer is formed by uniformly mixing the bisazo compound of the present invention as a carrier generation substance with a suitable resin binder, solvent, etc. to prepare a coating solution, coating this on a conductive substrate, and drying it. It is formed as a result. The binder may be any of the known resins used for this type of purpose, such as polyesters, (meth)acrylics, polyamides, polyurethanes, epoxies, polycarbonates, silicone resins, and the like. The solvent may be alcohol, ether, aromatic hydrocarbon, etc. As a coating method, an applicator method, a bar coater method, etc. can be used.

The carrier transport layer can be formed by uniformly mixing a carrier transport substance with the same binder and solvent as described above to form a coating solution, and applying the same in the same manner.
Carrier transport substances include known ones, such as aromatic tertiary amino (and diamino, triamino)
compounds, polyvinylcarobazole compounds, pyrazoline derivatives, triazine derivatives, quinazoline derivatives, oxadiazole derivatives, and the like.

The thickness of the carrier generation layer is generally 0.005 to 10 μm.
The thickness of the carrier transport layer may generally be about 5 to 100 μm.

Example 1 The following structural formula A bisazo compound represented by is ground into a fine powder with a uniform particle size of 0.01 μm or less using a ball mill, and 1 part by weight of the ground bisazo compound fine particles and 30 parts by weight of tetrahydrofuran are mixed using a mixer. A dispersion treatment was performed to prepare a suspension in which fine particles of a bisazo compound were uniformly dispersed in a solvent. The fine particles of the bisazo compound that were dispersed at this time were
When the crystalline state was examined using -Kα X-rays, a broken crystal pattern was obtained as shown in the X-ray diffraction diagram in Figure 1.

To this suspension, 1 part by weight of polymethyl methacrylate (PMMA) and 6 parts by weight of toluene were added,
A uniform coating solution was prepared by mixing well with a magnetic stirrer. This coating solution was applied onto a 75 μm thick aluminum vapor-deposited polyester film substrate using a wire bar so that the film thickness after drying was 0.2 μm, and dried to form a carrier generation layer.
On top of this, 1 part by weight of N,N-diethylaminobenzaldehyde-1,1-diphenylhydrazone,
A solution prepared by thoroughly suspending 1 part by weight of a polyester resin in tetrahydrofuran was coated to a dry film thickness of 15 μm, and dried to form a carrier transport layer.

The electrophotographic properties of the thus prepared photoreceptor were evaluated using a Kawaguchi Electric Seisakusho SP-428 electrostatic paper tester. Corona discharge was performed for 10 seconds at a voltage of -6.0 KV to negatively charge the photoreceptor, and the charging voltage VA on the surface of the photoreceptor at that time was measured. After that, calculate the charged potential Vp when discharging for 2 seconds in a dark place, then irradiate the photoreceptor surface with 2 lux white light, measure the time until Vp is halved, and calculate the halving exposure amount E _1/2 I asked for As a result, VA = -1200 volts E _1/2 = 2.0 lux-seconds.

From this result, we found that a carrier generation layer containing fine particles of a bisazo compound with a particle size of 0.01 μm or less, which is smaller than 1/5 of the film thickness of 0.2 μm, and a broken crystal shape as shown in Figure 1, is used as a carrier generation material. It can be seen that the photoreceptor having the above-mentioned structure is a photoreceptor with excellent electrophotographic properties.

Comparative Example 1 The bisazo compound of Example 1 was pulverized in a ball mill until its crystal form was broken and the X-ray diffraction pattern shown in FIG. 1 was obtained. The bisazo compound fine particles were dispersed in a solution of 1 part tetrahydrofuran and 1 part n-butylamine to form a suspension. The fine particles of the bisazo compound that were dispersed at this time were
When the crystal state was examined using X-rays, it showed a well-organized crystal pattern as shown in Figure 2.

Using the above mixed suspension instead of the tetrahydrofuran suspension of the bisazo compound of Example 1,
A photoreceptor was produced in the same manner as in Example 1 except for the following. The electrophotographic properties of the obtained photoreceptor were evaluated.
As a result, a value of VA=-1200 volts E _1/2 =20 lux·sec was obtained, and it was found that the photosensitivity deteriorates when a bisazo compound with a well-organized crystal form is used.

Comparative Example 2 The following structural formula was used instead of the bisazo compound of Example 1. A photoreceptor was produced in the same manner as in Example 1, except that the following was used. However, when this bisazo compound is used, the fine particles of the bisazo compound aggregate during the preparation of the coating solution, making it impossible to obtain a uniform coating film.

〔Effect of the invention〕

As mentioned above, as a carrier generating substance for a functionally separated photoreceptor, a bisazo compound having the above structural formula, which has a particle size smaller than 1/5 of the thickness of the layer containing this compound, and has no crystals. The photoreceptor according to the present invention, which uses a broken one, is a practically excellent electrophotographic photoreceptor with good charging characteristics and photosensitivity.

In addition, the bisazo compound used in the present invention can be used as a coating solution to create a uniform coating film without using special solvents, and can produce excellent photoelectric properties without going through the complicated process of conventional methods. A photoreceptor can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction pattern (Cu-Kα) of a broken bisazo compound in the crystalline form of the present invention. FIG. 2 is an X-ray diffraction pattern (Cu-Kα) of a bisazo compound with a well-organized crystal structure.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor having a layer containing a bisazo compound as a carrier generating substance, wherein the bisazo compound has a structural formula: (In the formula, Ar ₁ and Ar ₂ each represent a substituted or unsubstituted phenyl or naphthyl group.) and 1/1/2 the thickness of the layer containing the bisazo compound.
In addition, the bisazo compound fine particles have a particle size smaller than 5, and have broken crystals, and furthermore, in an X-ray diffraction diagram using copper Kα rays,
2θ based on the diffraction intensity at 2θ=40°
1. A photoreceptor for electrophotography, characterized in that it exhibits an X-ray diffraction pattern in which the maximum value of diffraction intensity between =23° and 28° is 4 times or less.