JPH0357470B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a photoreceptor, particularly an electrophotographic photoreceptor. B. Prior art In general, it is difficult for substances that absorb visible light to generate carriers to form a film on their own, with the exception of a few substances such as amorphous selenium. It has the disadvantage of poor retention of a given charge. On the contrary, materials that have excellent film-forming ability and can retain a charge of 500 V or more for a long time with a thickness of about 10 μm generally have the disadvantage of not having sufficient photoconductivity due to absorption of visible light. have. For this reason, as shown in Figure 8, Al
A carrier generation layer 2 containing a substance that absorbs visible light and generates charge carriers is provided on a conductive substrate 1 such as the like with a subbing layer 5 interposed therebetween. It has been proposed that a carrier transport layer 3 for one or both types of transport is provided to form a laminate 4, and that this laminate constitutes a photosensitive layer. In this way, by assigning charge carrier generation and transport to separate materials, the range of material selection is widened and the properties required in the electrophotographic process, such as charge retention, surface strength, and visible It has become possible to improve sensitivity to light and stability during repeated use. In addition, in FIG. 6A, the carrier generation layer 2 may be provided on the carrier transport layer 3. In such photoreceptors, it is known to use a brominated anthanthrone pigment as a high-grade organic pigment in the photosensitive layer, particularly in the chiaria generation layer. This pigment has higher sensitivity than conventional inorganic particles or perylene pigments, and can provide a uniform photosensitive layer with good scratchability. However, in order to use this pigment as an electrophotographic photoreceptor, it is necessary to improve both its crystallinity and purity, and the sublimation purification method is effective in achieving this. However, the present inventor has investigated and found that when using the conventional method, when the obtained pigment is crushed and dispersed to make a paint for the photosensitive layer, if the shear stress applied to the pigment is large, crystallization may occur. It is easy for the lattice to become distorted or for impurities to enter from the dispersion container. For this reason, charging ability and sensitivity tend to decrease, and the amount of repeated potential decrease tends to increase. On the other hand, if the shear stress applied to the pigment is small, the electrophotographic properties will deteriorate, making it unsuitable. C. Objective of the Invention An object of the present invention is to provide a photoreceptor that exhibits a high charging potential and has good repeat stability. D. Structure and effects of the invention That is, the present invention provides a photosensitive layer containing a brominated anthanthrone pigment, which is represented by the following structural formula, has an average particle size of 2 μm or less, and has been purified by a chemical refining method, and When the half width of the diffraction intensity at 2θ = 18.4° and 26.7° of the X-ray diffraction spectrum of the brominated anth-anthrone pigment is respectively Δθ (18.4°) and Δθ (26.7°), {Δθ (18.4°) ≦0.8°｜} and/or {Δθ (26.7°)≦1°}. Structural formula: In the process of arriving at the present invention, the present inventor discovered that pulverization of the pigment as described above increases its crystal defect density and deteriorates its properties, and that this crystal defect density The half width of the diffraction intensity at the diffraction angles 2θ = 18.4° and 26.7° of the diffraction spectrum (i.e., the spectral width at half the intensity of the peak of the diffraction intensity spectrum) is closely related to Δθ. I discovered that. The spectrum of the brominated anth-anthrone pigment obtained by the conventional sublimation purification method is shown in the seventh column.
As shown in the figure, when this is ground with a ball mill, the 8th
As shown in the figure, the peak at 2θ = 18.4° is blunted,
Δθ (18.4°) and Δθ (26.7°) become larger. These Δθ become larger depending on the grinding time as described later. On the other hand, an attempt was made to produce a brominated anthanthrone pigment by the following method. That is, anthanthrone shown by the following structural formula is brominated in sulfuric acid, drained, and separated by filtration to obtain brominated anthurone having the same structural formula as that used in the present invention, which is then washed and dried. did. However, in this case, as shown in FIG. 9, Δθ becomes too large and only amorphous, non-crystalline particles are obtained. Also, increasing the degree of bromination, the 10th
As shown in the figure, the peak at 2θ = 18.4° disappears, and Δθ (26.7°) becomes large. However, the crude raw material containing the brominated sample as a main component by the above method is treated with a nonionic organic solvent (preferably, this organic solvent) selected from monochlorobenzene, nitrobenzene, β-naphthol, 1-chloronaphthalene, etc. and an ionic solvent consisting of an acid such as H ₂ SO ₄ or an alkali such as NaOH) to ripen the crystals, wash, and separate by filtration, resulting in highly crystalline brominated It has been found that ance anthrone pigments are obtained. This pigment was found to be highly crystalline and highly pure, exhibiting high charging potential, high sensitivity, and good repeat stability, and is very suitable for use in photoreceptors. Figure 1 shows the case where a mixed solvent of the above ionic organic solvent and an acid is used, Figure 2 shows the case when a mixed solvent of the above nonionic organic solvent and an alkali is used, and Figure 3 shows the case where the above nonionic organic solvent and an alkali are used. The spectra obtained when organic solvents are used are shown, and it can be seen that the half-width Δθ is small and the peaks are large, that is, the crystallinity and purity are good (especially the examples in Figures 1 and 2). In addition, it was found that by this so-called chemical refining method, a purified product with clean crystallinity shown in Figure 5 can be obtained from the amorphous raw material shown in Figure 4. When using this method, the pigment does not decompose and there is no corrosion due to the removal of Br.
The target product can be obtained in good yield. The brominated anthanthrone pigment produced by the chemical purification method described above is actually pulverized and dispersed to obtain a desired particle size. At this time, Δθ changes depending on the grinding time, and especially depending on the selection of the grinding time,
{Δθ(18.4°)≦0.8°} and/or {Δθ(26.7°)≦1°}
I found out what I can do. As is clear from the data described below, this half-width range reduces the crystal defect density of the pigment particles and greatly improves the electrophotographic properties. Regarding the particle shape of the brominated anth-anthrone pigment, the short axis length is a, and the long axis length is b.
Therefore, it is desirable that b/a≧1.1. That is, it was found that excellent characteristics could be obtained by this ratio. However, as the particles become finer, not only does Δθ improve, but also the strength (absolute value) decreases, so Δθ≦
Even if 1° is satisfied, there may be cases where there are not enough crystals. In other words, even if Δθ≦1°,
When b/a<1.1, the crystallinity of the particles tends to decrease, so it is effective to set b/a≧1.1, and more preferably 1.1≦b/a≦20. Here, the long axis length b indicates the length of the axis (long axis) having the longest distance in an arbitrarily selected crystal in an electron micrograph. The short axis length a indicates the length of the axis (short axis) that passes through the bisecting point of the long axis and has the shortest distance. As a method for arbitrarily selecting crystals in an electron micrograph, for example, in the present invention, five vertical and horizontal lines are drawn on the photograph at 1 cm intervals, and crystals located at the intersections of the lines are selected. The major axis length b and minor axis length a of these crystals were measured, and b/a of each crystal was calculated. In the present invention, b/a refers to the average value of b/a of each of the above-mentioned crystals. The average particle diameter (here, means the average value of the major axis length b) of the brominated anth-anthrone pigment particles should be 2 μm or less. That is, 2μm
By making the particle size as fine as the following, it is possible to prevent the influence of the particle size on the surface of the photoreceptor, to make the surface of the photoreceptor smooth, and to stabilize the pigment dispersion.
When the average particle size exceeds 2 μm, convex portions tend to form on the surface, but when the average particle size is less than 2 μm, such convex portions can be virtually eliminated and a flat surface can be achieved, while sedimentation in the dispersion can be reduced and the liquid stabilized. You can aim for As a result, it is possible to obtain a photoreceptor that does not suffer from discharge breakdown or toner filming. The average particle size of the pigment is
It should be 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less.
However, if the average grain size is too small, crystal defects will increase and repeatability will deteriorate, and there will be a limit to miniaturization, so it is desirable to set the lower limit of the average grain size to 0.01 μm or less. Examples of binder resins that can be used in the photoreceptor of the present invention include polyethylene, polypropylene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, epoxy resin, polyurethane resin, phenolic resin, polyester resin, alkyd resin, Addition polymerization resins such as polycarbonate resin, silicone resin, melamine resin,
Polyaddition type resins, polycondensation type resins, and copolymer resins containing two or more of the repeating units of these resins, such as vinyl chloride-vinyl acetate copolymer resins, vinyl chloride-vinyl acetate-maleic anhydride copolymer resins, etc. Examples include polymer resins. However, binder resins are not limited to these,
All resins commonly used for such applications can be used. Carrier transport substances used in the carrier transport layer in the present invention include osisazole derivatives, oxdiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, pyrazoline derivatives, and oxazolone derivatives. , benzothiazole derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, hydrazone derivatives, biphenylamine derivatives, triphenylamine derivatives, poly-N-vinylcarbazole, poly-1-vinylpyrene, poly -9-vinylanthracene, 2,4,7-trinitrofluorenone, 2,4,5,7-tetranitrofluorenone, 2,7-dinitrofluorenone and the like. Examples of organic solvents used for forming the photosensitive layer of the present invention include methylene chloride, methylene bromide, 1,2-dichloroethane, sym-
Tetrachloroethane, cis-1,2-dichloroethylene, 112-trichloroethane, chloroform,
Examples include single solvents such as bromoform, dioxane, tetrahydrofuran, and pyridine, and various mixed solvents containing these as main components. E. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Example 1 After brominating ansuanthrone in sulfuric acid,
50 g of the brominated anthurone fine powder obtained by draining the water was added to a borderline solvent consisting of 100 ml of nitrobenzene and 2 ml of H ₂ SO ₄ , and the mixture was slowly stirred at 100° C. for 10 hours and then allowed to cool. The mixture was then filtered and washed to obtain 47.4 g of highly crystalline brominated anth-anthrone pigment. The X-ray diffraction spectrum of the purified pigment (JDX10RA OuKd1.541, manufactured by JEOL Ltd.) is shown in Figure 1. 40 g of the obtained purified pigment was packed into a porcelain ball mill and pulverized for 1 hour at 40 revolutions per minute (the critical number of revolutions giving maximum pulverization energy was 70 revolutions). Next, polycarbonate resin “Pantolite L-
A solution prepared by dissolving 20 g of "1250" (manufactured by Teijin Chemicals) in 1300 m of 1,2-dichloroethane was added and subjected to dispersion treatment for 24 hours to obtain a coating solution for forming a carrier generation layer. The pigment was separated by filtration using a portion of the obtained coating liquid, and the half width of the X-ray diffraction spectrum was measured. The results are shown in Table 1. Moreover, as a result of observation with an electron microscope, b/a =
2.8, b =0.8μ needle-like crystals were confirmed. Example 2 In Example 1, 1.0 g of NaOH was used instead of H ₂ SO ₄
48.2 g of highly crystalline brominated anth-anthrone pigment was obtained in the same manner as in Example 1, except that the crystals were grown at 90° C. for 48 hours. Figure 2 shows the measurement results of the X-ray diffraction spectrum. Table 1 shows the half width of the X-ray spectrum of the coating liquid obtained in the same manner as in Example 1. It was confirmed by electron microscopy that b/a = 2.9 and b = 0.8μ. Example 3 490 g of highly crystalline brominated anth-anthrone pigment was prepared in the same manner as in Example 1 except that H ₂ SO ₄ was not used and the crystals were grown at 150° C. for 8 hours.
Obtained. The measurement results of the X-ray diffraction spectrum are shown in FIG. Further, the half width of the X-ray diffraction spectrum of the coating liquid obtained in the same manner as in Example 1 is shown in Table 1. It was confirmed by electron microscopy that b/a = 2.4 and b = 0.6μ. Comparative Example 1 The X-ray diffraction spectrum of the raw material used in Example 1 and not subjected to crystallization treatment is shown in FIG. The b/a=1.06 and b =0.3μ. Comparative Example 2 The brominated anthanthrone pigment of Example 1 before the crystallization treatment was filled into a graphite evaporation source placed in a vacuum evaporation apparatus, sublimated at a temperature of 370°C for 60 minutes, and placed 50 cm above the evaporation source. was deposited on a substrate placed on the substrate. FIG. 7 shows the X-ray diffraction spectrum of the sublimation-purified pigment. 40 g of the obtained purified pigment was packed into a magnetic ball mill and pulverized for 12 hours at 40 revolutions per minute (the critical number of revolutions providing maximum pulverization energy was 70 revolutions). Next, the mixture was dispersed for 24 hours in the same manner as in Example 1 to obtain a carrier generation layer forming coating solution. The measurement results of the X-ray diffraction spectrum of the coating liquid were
As shown in the figure. It was confirmed by electron microscopy that b/a = 2.9 and b = 0.9μ. Comparative Example 3 In Comparative Example 2, a coating solution for forming a chiaria generation layer was prepared in the same manner as in Comparative Example 3, except that the ball mill grinding time was changed to 24 hours. Table 1 shows the measured half width of the X-ray diffraction spectrum. In addition, as a result of electron microscopy, b/a = 2.0, b =
It was 0.4μ. Comparative Example 4 In Comparative Example 3, the ball mill grinding time was 36 hours. Table 1 shows the measured half width of the X-ray diffraction spectrum. b/a = 1.3, b = 0.3μ. Comparative Example 5 In Comparative Example 2, the ball mill grinding time was set to 6 hours. The half width is shown in Table 1. b/a = 3.8, b = 1.8μ. Comparative Example 6 In Comparative Example 3, the ball mill grinding time was 48 hours. The half width is shown in Table 1. b/a = 1.2, b = 0.2μ. Comparative Example 7 In Comparative Example 3, the ball mill rotation speed was 55 rpm,
The grinding time was 24 hours. The half width is shown in Table 1. b/a = 2.3, b = 0.5μ. Comparative Example 8 In Comparative Example 2, the ball mill rotation speed was 70 rpm,
The grinding time was 6 hours. The half width is shown in Table 1. b/a = 1.08, b = 0.4. Comparative Example 9 In Comparative Example 1, the ball mill rotation speed was 70 rpm,
The grinding time was 12 hours. The half width is shown in Table 1. b/a = 1.05, b = 0.2μ. The parameter values of the samples obtained above and the comparative samples are summarized in Table 1. In the table, "actual" indicates an example, and "ratio" indicates a comparative example. [Table] Electrophotographic photoreceptor drums were prepared in the following manner using the carrier generation layer forming coating liquids obtained in the above Examples and Comparative Examples. 100φ aluminum drum, dry weight 0.1g/m ²
After forming an intermediate layer consisting of a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin "Eslec MF-10" (manufactured by Integral Chemical Industry Co., Ltd.) by a dip coating method, the carrier generation layer forming coating solution was applied. A carrier generating layer having a dry weight of 2.1 g/m ² was obtained by coating on the intermediate layer by the same dip coating method. On the other hand, 225 g of a carrier transport substance represented by the following structural formula, 2,4,6-trinitro-1-chlorobenzene
0.225g, 300g of polycarbonate resin 1,2-
A coating solution for forming a carrier transport layer obtained by dissolving in 2000 ml of dichloroethane was applied onto the carrier generation layer by a dip coating method to obtain a dry weight of 19.
A carrier transport layer of g/m ² was formed, and electrophotographic photoreceptors of the present invention and a comparative example (FIG. 6A) were prepared. Note that instead of the above, a carrier transport layer may be formed first, and a carrier generation layer may be formed thereon (FIG. 6B). It was attached to a testing machine (manufactured by Konishiroku Photo Industry), and the electrostatic potential was measured using a surface electrometer "Electrostatic Voltmeter Model 144D-1D" (manufactured by Monroe Electronics Inc.).
Vo (V), the exposure amount E ⁶⁰⁰ ₁₀₀ (lx・sec) required to reduce the surface potential from -600V to -100V, and the potential retention rate DD (%) after 5 seconds with the surface potential at -600V were investigated. . In addition, we conducted a 5000-cycle test to examine the stability of the electrostatic potential. For samples whose charging potential is less than 600V, increase the charging current from the standard value to E ⁶⁰⁰ ₁₀₀ and
DD was measured. The results are shown in Table 2 (sample numbers in Table 2 are shown in Table 2).
(corresponds to Example No. 1 and Comparative Example No. 1). [Table] From Tables 1 and 2, it can be seen that the samples according to the present invention have good potential holding performance without decreasing sensitivity.

[Brief explanation of drawings]

The drawings are for explaining the present invention, and
Figure 1, Figure 2, Figure 3, Figure 7, Figure 8, Figure 9
Figure 10 is an X-ray diffraction spectrum diagram of each carrier-generating substance, Figure 4 is a micrograph showing the particle structure of the raw material of the carrier-generating substance, Figure 5 is a micrograph showing the particle structure of the carrier-generating substance, FIGS. 6A and 6B are cross-sectional views of the electrophotographic photoreceptor.
In addition, in the symbols shown in the drawings, 1... conductive substrate, 2... carrier generation layer, 3
...This is the carrier transport layer.

Claims (1)

[Claims] 1. Represented by the following structural formula and having an average particle size of 2 μm
A brominated anthanthrone pigment purified by a chemical purification method is contained in the photosensitive layer, and the diffraction intensity at 2θ=18.4° and 26.7° of the X-ray diffraction spectrum of the brominated anthancerone pigment is half of the When the price ranges are Δθ (18.4°) and Δθ (26.7°), respectively, {Δθ (18.4°)≦0.8°} and/or {Δθ
(26.7゜)≦1゜｝photoreceptor. Structural formula: