JPH0784568B2 - Method for producing highly crystalline brominated anthanthrone pigment for photoconductor - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a method for producing a highly crystalline brominated anthanthrone pigment for a photoreceptor, particularly an electrophotographic photoreceptor.

B. BACKGROUND ART Generally, substances that absorb visible light and generate carriers are
Except for a very small amount of amorphous selenium and the like, it is difficult to form a film by itself, and it has a drawback that it lacks in holding power for the electric charge given to its surface. On the contrary, a substance that has excellent film-forming ability and can hold a charge of 500 V or more for a long time with a thickness of about 10 μm does not generally have sufficient photoconductivity due to absorption of visible light. have.

For this reason, as shown in FIG. 6A, a carrier generation layer 2 containing a substance that absorbs visible light to generate charge carriers is provided on a conductive substrate 1 such as Al via a subbing layer 5. Further, it has been proposed that a carrier transport layer 3 for transporting either or both of positive and negative charge carriers generated in the carrier generation layer is provided to form a laminate 4, and the photosensitive layer is constituted by the laminate. In this way, by sharing the generation and transport of charge carriers by separate substances, the selection range of materials is widened, and various properties required in the electrophotographic process, such as charge retention, surface strength, and visible light, are reduced. It has become possible to improve or improve sensitivity and stability upon repeated use.

Note that, as shown in FIG. 6B, the carrier generation layer 2 may be provided on the carrier transport layer 3.

In such a photoreceptor, it is known to use a brominated anthanthrone pigment as a higher organic pigment in the photosensitive layer, particularly in the carrier generation layer. This pigment has higher sensitivity than the case of conventional inorganic particles or perylene pigment,
It is possible to obtain a photosensitive layer that is uniform and has good scratch resistance.

However, in order to use this pigment as an electrophotographic photoreceptor, it is necessary to enhance both its crystallinity and purity, and the sublimation purification method is effective in achieving this.
However, as a result of examination by the present inventor, in the case of the conventional method, when the obtained pigment is pulverized and dispersed into a coating material for a photosensitive layer, a shear stress (Share Stre
When ss) is large (when the substrate temperature is high, the pigment particles are large and highly crystalline), the crystal lattice is distorted or impurities are easily mixed from the dispersion container. As a result, the charging ability and sensitivity decrease,
The amount of repeated potential decrease tends to increase. On the contrary, when the shear stress applied to the pigment is small (in this case, the substrate temperature is low, the pigment particles are small and the crystal is low), the electrophotographic characteristics are deteriorated, which is unsuitable.

C. OBJECT OF THE INVENTION It is an object of the present invention to provide a method for producing a highly crystalline brominated anthanthrone pigment suitable for obtaining a photoreceptor exhibiting a high charging potential and sensitivity and having good repeated stability.

D. Structure of the Invention and Effect of the Invention That is, the present invention has the following structural formula: The raw material containing brominated anthanthrone represented by as a main component is treated with a mixed solution of a nonionic solvent (particularly an aromatic organic solvent) and an ionic solvent (particularly an acid or alkali) to crystallize the crystals. After the steps of washing and separation by filtration,
The full width at half maximum of the diffraction intensity at 2θ = 18.4 ° and 26.7 ° of the X-ray diffraction spectrum is Δθ (18.4 °) and Δθ, respectively.
Highly crystalline bromination for a photoreceptor for obtaining the above-mentioned brominated anthanthrone in which {Δθ (18.4 °) ≦ 0.8 °} and / or {Δθ (26.7 °) ≦ 1 °} when (26.7 °) The present invention relates to a method for producing anthanthrone pigment.

In the process of reaching the present invention, the present inventor increased the crystal defect density by pulverizing the pigment as described above and deteriorated the characteristics, and this crystal defect density was the characteristic X-ray of the brominated anthanthrone pigment. It was found that it is closely related to the full width at half maximum of the diffraction intensity at the diffraction angles 2θ = 18.4 ° and 26.7 ° of the diffraction spectrum (that is, the spectrum width at the intensity half of the peak of the diffraction intensity spectrum) Δθ. . The spectrum of the brominated anthanthrone pigment obtained by the conventional sublimation purification method is
As shown in the figure, when this is crushed with a ball mill, the peak at 2θ = 18.4 ° becomes blunt as shown in Fig. 8, and Δθ (18.4
) And Δθ (26.7 °) increase. These Δθ
Is further increased depending on the crushing time as described later.

On the other hand, an attempt was made to produce a brominated anthanthrone pigment by the following method.

That is, the anthanthrone represented by the following structural formula is brominated in sulfuric acid and then poured into water, and separated by filtration to obtain a brominated anthurone of the same structural formula as that produced in the present invention,
This was washed and dried.

However, in this case, Δθ becomes too large as shown in FIG. 9, and only amorphous amorphous particles are obtained. Moreover, when the degree of bromination is increased, 2θ = 18.4 as shown in Fig. 10.
The peak at ° disappears and Δθ (26.7 °) becomes large.

However, a sample brominated by the above method, that is, the above-mentioned brominated anthurone is separated by filtration, and a crude raw material containing this as a main component is selected from monochlorobenzene, nitrobenzene, β-naphthol, 1-chloronaphthalene, etc. Nonionic organic solvents and ionic solvents (acids selected from sulfuric acid, fuming sulfuric acid, sulfuric anhydride, acetic acid and its halogen derivatives, phosphoric acid; or lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide) , A strontium hydroxide, an alkali selected from barium hydroxide) are treated with a borderline solvent mixed with a crystal, the crystals are matured, washed, and separated by filtration to obtain a highly crystalline brominated anthanthrone pigment. There was found. It has been found that this pigment is highly suitable for use as a photoreceptor having high crystallinity, high purity, high charging potential, high sensitivity, and good repeated stability. FIG. 1 shows each spectrum when a mixed solvent of the above nonionic organic solvent and an acid is used, and FIG. 2 shows each spectrum when a mixed solvent of the above nonionic organic solvent and an alkali is used. It can be seen that the full width at half maximum Δθ is small and the peak is large, that is, the crystallinity and purity are good. In this case, it is effective that the above acid or alkali, in addition to the above nonionic organic solvent, further promotes the dissolving action.

In the above, the mixing ratio of the nonionic organic solvent and the acid (or alkali) is (100: 0.1) to (100: 50) in volume ratio.
Is preferred, and (100: 1) to (100: 20) is even better.

Further, it has been found that such a so-called chemical refining method can obtain a clean crystalline product shown in FIG. 4 from the amorphous raw material shown in FIG. Further, when this chemical refining method is used, the pigment is not decomposed, corrosion due to deBr is not caused, and the target product is obtained in good yield.

That is, the manufacturing method of the present invention described above has the following advantages.

(1) Since it is a chemical manufacturing method, it is easy to control the operating conditions even if the raw material is easily decomposed by heat.

(2), yield and yield are high.

(3) The acid is not generated by the debromination reaction and the device is not corroded.

(4) The refining cost is low.

(5) The crystallinity and purity are significantly enhanced, and a pigment that can be sufficiently used as a raw material for organic semiconductors is obtained.

(6) It is possible to realize an electrophotographic photosensitive member having low manufacturing cost, high sensitivity, and repeated stability.

In the method of the present invention, it is desirable that the nonionic solvent used (especially aromatic organic solvent) has a dipole moment of 1.0 to 5.0 (Debye unit). Thus, an aromatic solvent having a high boiling point in addition to being polar (that is, having a polar substituent such as OH, Cl or No ₂ ) is preferable.
That is, such a solvent not only withstands high-temperature treatment, but also has an action of affinity with anthanthrone and loosening its crystal lattice.

The nonionic solvent used in the present invention is preferably a polar solvent having an oxygen atom, a nitrogen atom, a halogen atom or the like, for example, chlorine, bromine, iodine,
Halogen atom such as fluorine, nitro group, alkoxy group,
Phenoxy group, carboxyl group, hydroxy group, ester group, amide group, nitrile group, formyl group, amino group,
Examples thereof include aromatic hydrocarbons and heterocyclic compounds having a substituent such as a mercapto group, a sulfo group and a sulfonamide group. Organic solvents having a dipole moment of 1.0 to 5.0 (Debye unit) are, for example, TECHNIQUE OF ORGANIC CHEMISTRY vol VI
I, 1955 edition InterScience Publisher,
It is listed in'New York '.

Specific examples of the solvent effective in the present invention include the following.

Phenetol, anisole, o-cresol, m-toluidine, fluorobenzene, m-dichlorobenzene, aniline, p-toluidine, m-cresol, p-cresol, monochlorobenzene, 1-chloronaphthalene, β
-Naphthol, o-toluidine, benzyl alcohol,
Phenol, bromobenzene, benzyl acetate, o
-Chloroaniline, m-fluorotoluene, methylbenzoate, benzylbenzoate, ethylbenzoate, p-fluorotoluene, pyridine, o-dichlorobenzene, dibutylphthalate, methylsalicylate, benzaldehyde, phenylacetonitrile, nitrobenzene, benzonitrile, o -Nitroanisole.

The brominated anthanthrone pigment obtained by the chemical refining method described above is actually pulverized and dispersed to have a desired particle size. At that time, as shown in Fig. 5 (however, the data of the sample chemically purified with sulfuric acid + nitrobenzene), the grinding time (40
Δθ changes depending on the rotation / minute ball mill used)
In particular, depending on the selection of the grinding time, {△ θ (18.4 ° ≤0.8
)} And / or {Δθ (26.7 °) ≤ 1 °}. With such a half-width range, as is apparent from the data described below, the crystal defect density of the pigment particles is lowered, and the electrophotographic characteristics are greatly improved.

Further, regarding the particle shape of the brominated anthanthrone pigment, if the minor axis length is a and the major axis length is b, then b /
It is desirable that a ≧ 1.1. That is, it was found that excellent characteristics were obtained by this ratio. However, along with the atomization, Δθ increases and the strength (absolute value) also decreases. Therefore, even if Δθ ≦ 1 ° is satisfied, sufficient crystallinity may not occur. In other words, even if Δθ ≦ 1 °, if b / a <1.1, the crystallinity of the particles tends to decrease, so
It is effective that b / a ≧ 1.1, and further 1.1 ≦ b / a ≦ 20. Here, the major axis length b indicates the length of the axis (long axis) having the longest distance in the crystal arbitrarily selected in the electron micrograph. The minor axis length a is 2 of the major axis.
It indicates the length of the axis that passes through the equal points and has the shortest distance (short axis).

As a method for arbitrarily selecting a crystal in an electron micrograph, for example, in the present invention, a line is drawn on the photo at intervals of 1 cm, 5 lines each in the vertical and horizontal directions, and the crystal at the intersection is selected. The major axis length b and the minor axis length a of these crystals are measured,
The b / a of each crystal was calculated.

The term “b / a” as used in the present invention refers to the average value of b / a of each of the crystals.

The average particle size of the brominated anthanthrone pigment particles (here, the average value of the major axis length b) is 2.
It is desirable that the thickness be less than or equal to μm. That is, by making it finer to 2 μm or less, the influence of the particle size on the surface of the photoconductor can be prevented, the surface of the photoconductor can be made smooth, and the pigment dispersion can be stabilized. If the average particle size exceeds 2 μm,
Convex portions are likely to occur on the surface, but if it is 2 μm or less, such a convex portion can be substantially eliminated and a flat surface can be realized, and settling of particles in the dispersion liquid can be reduced to stabilize the liquid. As a result, it is possible to obtain a photoconductor in which discharge breakdown or toner filming does not occur. The average particle size of the pigment is preferably 2 μm or less, more preferably 1 μm or less, further preferably 0.5 μm or less. However, if the average particle size is too small, the crystal defects are rather increased, the sensitivity and repeatability are deteriorated, and there is a limit in miniaturization. Therefore, it is desirable to set the lower limit of the average particle size to 0.01 μm.

Examples of the binder resin 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, phenol resin, polyester resin, alkyd resin, Addition polymerization type resins such as polycarbonate resin, silicone resin, melamine resin, polyaddition type resin, polycondensation type resin and copolymer resin containing two or more of repeating units of these resins, for example, vinyl chloride-vinyl acetate Examples thereof include a copolymer resin and a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin. However, the binder resin is not limited to these, and any resin generally used for such an application can be used.

As the carrier transporting material used in the carrier transporting layer in the present invention, an oxazole derivative, an oxadiazole derivative, a thiazole derivative, a thiadiazole derivative, a triazole derivative, an imidazole derivative, an imidazolone derivative, an imidazolidine derivative, a bisimidazolidine derivative, a pyrazoline derivative, Oxazolone derivative, benzothiazole derivative, benzimidazole derivative, quinazoline derivative, benzofuran derivative, acridine derivative,
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 the organic solvent used for forming the photosensitive layer of the present invention include methylene chloride, methylene bromide,
1,2-dichloroethane, sym-tetrachloroethane, cis
-1,2-dichloroethylene, 1,1,2-trichloroethane,
Specific solvents include chloroform, bromoform, dioxane, tetrahydrofuran, pyridine and the like, or various mixed solvents containing these as the main components.

E. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

Example 1 50 g of brominated anthurone fine powder obtained by brominating anthanthrone in sulfuric acid and then pouring in 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 heated at 100 ° C. for 10 hours. After slowly stirring, the mixture was allowed to cool. Then, filtration and washing were performed to obtain 47.4 g of highly crystalline brominated anthurone pigment. The X-ray diffraction spectrum (JDX10RA CuKα1.541Å manufactured by JEOL Ltd.) of the purified pigment is shown in FIG. 40 g of the obtained purified pigment was filled in a porcelain ball mill,
40 revolutions per minute (the critical rotation speed that gives the maximum grinding energy is
It was crushed for 1 hour at 70 rpm. Next, a solution prepared by dissolving 20 g of polycarbonate resin "Panlite L-1250" (manufactured by Teijin Chemicals Ltd.) in 1300 ml of 1,2-dichloroethane was added and dispersed for 24 hours to obtain a carrier generation layer forming coating solution. The pigment is separated by filtration using a part of the obtained coating liquid, and the half value width of the X-ray diffraction spectrum is measured. Also, as a result of observing with an electron microscope, ▲ ▼ = 2.8, = 0.8μ
It was confirmed to be a needle-shaped crystal.

Example 2 In Example 1, 1.0 g of NaOH was used instead of H ₂ SO ₄ , and 90
Highly crystalline brominated anthanthrone pigment (48.2 g) was obtained in the same manner as in Example 1 except that the crystal was grown at 48 ° C. for 48 hours. The measurement result of the X-ray diffraction spectrum is shown in FIG. Table 1 shows the full width at half maximum of the X-ray diffraction spectrum of the coating liquid obtained in the same manner as in Example 1. By electron microscope
It was confirmed that ▼ = 2.3 and = 0.6μ.

Comparative Example 1 The X-ray diffraction spectrum of the raw material used in Example 1 which was not subjected to the crystallization treatment is shown in FIG.

▲ ▼ = 1.06, = 0.3μ.

Example 3 A coating liquid for forming a carrier generating layer was prepared in the same manner as in Example 1 except that the ball mill grinding time was changed to 20 hours. Table 1 shows the measured values of the full width at half maximum of the X-ray diffraction spectrum. Also, as a result of electron microscope observation, ▲ ▼ =
1.7, = 0.6μ.

Example 4 In Example 1, the ball mill grinding time was set to 2 hours.
Table 1 shows the measured values of the full width at half maximum of the X-ray diffraction spectrum. ▲
▼ = 2.5, = 0.7μ.

Example 5 In Example 1, the ball mill rotation speed was 55 rpm, and the grinding time was 10 hours. The full width at half maximum is shown in Table-1. ▲ ▼
= 1.9 and = 0.5μ.

Comparative Example 2 In Example 1, the ball mill grinding time was set to 48 hours.
The full width at half maximum is shown in Table-1. ▲ ▼ ＝ 1.6 、 ＝ 0.3μ
Met.

Example 6 In Example 1, the ball mill rotation speed was 70 rpm and the grinding time was 5 hours. The full width at half maximum is shown in Table-1. ▲ ▼
= 1.04 and = 0.3μ.

Comparative Example 3 In Example 1, the ball mill rotation speed was 70 rpm and the grinding time was 10 hours. The full width at half maximum is shown in Table-1. ▲ ▼
= 1.03 and = 0.3μ.

The parameter values of the samples and comparative samples obtained above are summarized in Table 1. In the table, "actual" indicates an example and "ratio" indicates a comparative example.

An electrophotographic photosensitive drum was prepared by the following method using the carrier generation layer forming coating liquids obtained in the above Examples and Comparative Examples.

An intermediate layer made of vinyl chloride-vinyl acetate-maleic anhydride copolymer resin "S-REC MF-10" (manufactured by Sekisui Chemical Co., Ltd.) having a dry weight of 0.1 g / m ² is dip-coated on a 100φ aluminum drum. Then, the coating liquid for forming a carrier generating layer was applied onto the intermediate layer by the same dip coating method to obtain a carrier generating layer having a dry weight of 2.1 g / m ² .

On the other hand, 225 g of a carrier transport material represented by the following structural formula, 0.24 g of 2,4,6-trinitro-1-chlorobenzene and 300 g of polycarbonate resin were dissolved in 2000 ml of 1,2-dichloroethane to obtain a carrier-transporting layer-forming coating solution on the carrier generating layer by dip coating. After coating, a carrier transport layer having a dry weight of 19 g / m ² was formed to prepare electrophotographic photoreceptors of the present invention and comparison (FIG. 6A).

Instead of the above, the carrier transport layer may be first formed and then the carrier generation layer may be formed thereon. (Fig. 6B) The samples and comparative samples obtained in the above examples and comparative examples were mounted on a photoconductor tester (manufactured by Konishi Rokusha Kogyo Co., Ltd.), and a surface electrometer "electrostatic voltmeter 144D-1D type" was installed.
(Made by Monroe Electronics Incorporated)
, The charging potential V ₀ (V) and the surface potential from -600V to-
Exposure required to reduce to 100V ▲ E ⁶⁰⁰ ₁₀₀ ▼ (lx ・ se
c) and the surface potential is -600 V and the potential holding ratio DD after 5 seconds
(%) Was investigated.

In addition, the stability of the charging potential was examined by repeating the test 5000 times.

For samples whose charging potential was less than 600 V, the charging current value was increased from the standard value and the E ⁶⁰⁰ ₁₀₀ and DD were measured. The results are shown in Table-2 (Sample No. in Table-2 corresponds to Example No. and Comparative Example No. in Table-1).

It can be seen from Tables 1 and 2 that the samples according to the present invention have good sensitivity and potential holding performance.

[Brief description of drawings]

The drawings are for explaining the present invention, and FIG. 1, FIG. 2, FIG. 7, FIG. 8, FIG. 9, and FIG. FIG. 3 is a micrograph showing the particle structure of the raw material of the carrier-generating substance, FIG. 4 is a micrograph showing the particle structure of the carrier-generating substance, FIG. 5 is a graph showing the change in half-width with crushing time, FIG. 6A and FIG. FIG. 6B is each sectional view of the electrophotographic photosensitive member. In the drawings, reference numerals 1 ... Conductive substrate 2 ... Carrier generation layer 3 ... Carrier transport layer.

Front page continuation (72) Inventor Hiroyuki Nomori 2970 Ishikawa-cho, Hachioji-shi, Tokyo Within Konishi Rokusha Shin Kogyo Co., Ltd. (56) Reference JP-A-57-67934 (JP, A) JP-A-57-180666 (JP, A) Japanese Patent Publication 3-57470 (JP, B2)

Claims (1)

[Claims] 1. The following structural formula: The raw material containing brominated anthanthrone as the main component is treated with a mixed solution of a nonionic solvent and an ionic solvent to crystallize, and the crystals are washed, separated by filtration and separated by X-ray diffraction. When the half-value width of the diffraction intensity at 2θ = 18.4 ° and 26.7 ° of the spectrum is Δθ (18.4 °) and Δθ (26.7 °) respectively, {Δθ (18.4 °) ≦ 0.8
°} and / or {Δθ (26.7 °) ≦ 1 °}, wherein the brominated anthanthrone is highly crystalline.