GB2100743A - Trisazo compounds and the preparation thereof - Google Patents

Abstract

Trisazo compounds, suitable for use as charge carrier generating materials in electrophotographic elements, have the formula: <IMAGE> in which Ar is a phenyl, o-methylphenyl, p-methylphenyl, o-ethylphenyl, p- ethylphenyl, o-ethoxyphenyl, 2,4-dimethylphenyl, 2,5-dimethyl phenyl or 5- chloro-2-methyl-phenyl group. The compounds are prepared by diazotizing 4,4', 4''-triaminotriphenylamine to obtain a corresponding hexazonium salt and reacting this with an appropriate 2-hydroxy-3-phenylcarbamoyl[a]carbazole of the formula: <IMAGE> in which Ar has the meaning defined above.

Description

SPECIFICATION Trisazo compounds and the preparation thereof This invention relates to trisazo compounds, useful as charge carrier generating materials in electrophotographic elements, and to the preparation thereof.

It is known that trisazo or disazo compounds may be used as charge carrier generating pigments in the charge carrier generating layers of multilayer-type electrophotographic elements for use in electrophotographic processes. The term "multilayer-type electrophotographic element" as used herein means an element comprising (1) an electrically conductive substrate; (2) a charge carrier generating layer which contains a charge carrier generating pigment capable of generating charge carriers when exposed to light radiation and which is formed in the form of a thin film on the electrically conductive substrate (for example by vacuum deposition of the pigment, application of a solution of the pigment, or application of a resin-containing solution having dispersed therein fine particles ofthe pigment); and (3) a charge transfer layer capable of accepting the charge carriers generated in the charge carrier generating layer and transferring them, which charge transfer layer is formed on the charge carrier generating layer and usually contains a charge transfer substance and a binder.

Disazo and trisazo compounds which have been proposed for use in multilayer-type electrophotographic elements include benzidine type disazo pigments, as disclosed in Japanese Laid Open Patent Applications Nos. 37543/1972 and 55643/1977, and triphenylamine type trisazo pigments (see Japanese Laid-Open Patent Application No. 132547/1978).

However, multilayer-type electrophotographic elements using conventional disazo ortrisazo compounds as charge carrier generating substances suffer from the defect that they have a lower sensitivity than those using inorganic substance such as arsenic selenide (As2Se3) alloy as photosensitive material and are thus unsuitable for high speed copying machines. In addition, the demand for elements for use in laser printers has been growing, and with it the requirement for elements capable of exhibiting high sensitivity especially to the wavelength region of semi-conductor lasers.

It is an object of the present invention to provide trisazo compounds which are sensitive to the wavelength region of semiconductor lasers as well as to the visible spectrum and can be used as the charge carrier generating substance in a multilayer-type electrophotographic element.

It has now been found, in accordance with the present invention, that certain trisazo compounds, as hereinafter defined, are highly sensitive and also have a substantially flat sensitivity throughout the total visible region and the wavelength region of semiconductor lasers.

According to the invention there are provided, as new capsules trisazo compounds of the formula:

in which Ar is a phenyl, o-methylphenyl, p-methylphenyl, o-ethylphenyl, p-ethylphenyl, o-ethoxyphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl or 5-chloro-2-methyl-phenyl group.

It has been found that the characteristics of compounds of the general structure of the compounds of formula (I) vary widely depending upon the nature of the Ar group attached to the terminal -CON H- groups and that the compounds in which Ar is as defined above have particularly good characteristics.

The trisazo compounds of formula (I) are black crystals at room temperature.

An electrophotographic element incorporating a trisazo compound of the invention has good sensitivity even as compared with an element incorporating an inorganic photosensitive material, and exhibits rapid response to light having a wavelength as long as 800 nm.

In the following description, the individual compounds of formula (I) will be referred to by the numbers as given in the following Table 1.

TABLE 1 Compounds of Formula I

Compound No. Ar 1-1 phenyl 1-2 o-methylphenyl 13 p-methylphenyl 1-4 o-ethylphenyl I-5 pethylphenyl 16 o-ethoxyphenyl 1-7 2,4-dimethylphenyl 1-8 2,5-dimethylphenyl 1-9 5-chl orn-2-methyl-phenyl The trisazo compounds of formula (I) may be prepared by the steps of (a) diazotizing 4,4',4"triaminotriphenylamine of the formula:

to obtain a hexazonium salt of the formula::

(in which X represents an anionic functional group), and (b) reacting the hexazonium salt of formula (III) with a 2-hydroxy-3-phenylcarbamoylbenzo[a]carbazole derivative of the formula:

in which Ar has the meaning defined above.

The diazotization of 4,4',4"-triaminotriphenylamine may be effected by adding thereto an aqueous solution of sodium nitrite in a dilute inorganic acid, such as dilute hydrochloric acid or dilute sulphuric acid, at a temperature of -1 00C to 1 OOC. This reaction goes to completion in 30 minutes to 3 hours. Further it is desirable to precipitate the hexazonium salt by adding borofluoric acid or the like to the reaction mixture and then recovering the salt, for example by filtration.

Subsequently, by adding the 2-hydroxy-3-phenylcarbamoyibenzo[a]carba derivative of formula (IV) (coupler) to the hexazonium salt, a coupling reaction is effected between the hexazonium salt and the coupler. In practice, this reaction may be carried out by a solution by mixing the hexazonium salt and coupling ingredient with an organic solvent, such as N,N-dimethylformamide etc, and adding dropwise to the solution an aqueous solution of an alkali such as sodium acetate at a temperature of about -10"C to 1 OOC. This reaction goes to completion in 5 minutes to 3 hours.

The resultant crystals are recovered and purified by conventional procedures, for example by filtration, washing with water and/or an organic solvent, and recrystallization.

In the following description reference will be made to the accompanying drawings in which: Figure 1-1,1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8 and 1-9 show the infrared absorption spectra (according to KBr Tablet method) of trisazo compounds Nos. 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, and 1-9, respectively.

Figures 2-1, 2-2, 2-3, 2-4, 2-5, 2-6, 2-7, 2-8 and 2-9 show the X-ray diffraction diagrams of the trisazo compounds Nos. 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, and 1-9, respectively; and Figure 3 is a schematic cross-sectional view through an electrophotographic element in which the trisazo compounds of the invention may be employed.

As shown in Figure 3, an electrophotographic element in which the trisazo compounds of the invention may be employed comprises an electrically conductive substrate 1 comprising a film of aluminium 3 deposited upon a polyester base 2. A charge carrier generating layer 4 (containing a trisazo compound of the invention as charge carrier generating material) is deposited on aluminium film 3 and a charge transfer layer 5 is deposited on charge carrier generating layer 4.

In order that the invention may be well understood the following examples are given by way of illustration only.

EXAMPLE 1 4,41,411-triaminotriphenylamine (8.7 g) was added to dilute hydrochloric acid prepared from conc.

hydrochloric acid (1 50 ml) and water (130 ml), and the mixture was agitated at room temperature for about 30 minutes. The mixture was then cooled to about OOC and a solution obtained by dissolving sodium nitrite (7.7 g) in water (30 ml) was added dropwise thereto at a temperature of --3 OC to +20C over about 20 minutes. The mixture was then stirred at that temperature for about one-hour, trace of insoluble matters filtered off, and a 42% aqueous solution of borofluoric acid (60 ml), added to the filtrate. The reaction mixture was then filtered to recover the resulting precipitate which was washed with water and dried, to give hexazonium trifluoroborate (15.3 g, Yield: 87%) in the form of yellow crystals (decomposition point: about 129"C).

The hexazonium salt (1.2 g) and 2-hydroxy-3-phenylcarbamoylbenzo[a]carbazole (2.5 g) were dissolved in DMF (210 ml) and to the resulting solution was added dropwise, at room temperature over about 5 minutes, a solution obtained by dissolving sodium acetate (2.9 g) in water (30 ml). The mixture was stirred at that temperature for 3 hours and then filtered to recover precipitated crystals.

The raw crystalline cake thus obtained was dispersed in DMF (300 ml) and the resulting dispersion was stirred at room temperature for about one hour and again filtered to recover crystals. This procedure was repeated four times. The resulting crystals were washed with water and dried to obtain a trisazo compound (No. l-1) of the present invention (1.5 g, yield 53%) in the form of black crystals Decomposition point: 3000C or higher Elementary analysis values: Observed values Calculated values C% 75.53 75.69 H% 3.98 4.16 N% 12.85 13.19 Infrared absorption spectrum (according to KBrtablet method): Pc=o (secondary amide) 1 670 cm- EXAMPLE 2 The procedure of Example 1 was repeated except that the 2-hydroxy-3phenylca rbamoylbenzo[a]carbazole was replaced by 2-hydroxy-3-(2-methylphenylcarbamoyl)- benzo[a]carbazole (2.7 g) to give trisazo compound No. 1-2 (2.1 g, yield 72%) in the form of black crystals.

Decomposition point: 3000C or higher Elementary analysis values: Observed values Calculated values C% 75.68 75.99 H% 4.23 4.46 H% 12.52 12.80 Infrared absorption spectrum (according to KBr tablet method): Pc=o (secondary amido) 1 670 cm- EXAMPLE 3 The procedure of Example 1 was repeated except that the 2-hydroxy-3phenylcarbamoylbenzo[a]carbazole was replaced by 2-hydroxy-3-(4methylphenylcarbamoyl)benzo[a]carbazole (2.7 g), to give trisazo compound No. 1-3 (2.0 g, yield 69%) in the form of black crystals.

Decomposition point: 3000C or higher Elementary analysis values: Observed values Calculated values C% 75.71 75.99 H% 4.26 4.46 N% 12.54 12.80 Observed values Calculated values C% 75.71 75.99 H% 4.26 4.46 N% 12.54 12.80 Infrared absorption spectrum (according to KBr tablet method): Pc=o (secondary amido) 1 670 cm- EXAMPLE 4 The procedure of Example 1 was repeated except that the 2-hydroxy-3phenylcarbamoylbenzo[a]carbazole was replaced by 2-hydroxy-3-(2 ethylphenylcarbamoyl)benzo[a]carbazole (2.8 g), to give trisazo compound No. 1-4 (1.5 g, yield 50%) in the form of black crystals.

Decomposition point: 3000C or higher Elementary analysis values Observed values Calculated values C% 75.93 76.26 H% 4.58 4.75 N% 12.50 12.43 Infrared absorption spectrum (according to KBr tablet method): Vac=0 (secondary amido) 1670 cm-' EXAMPLE 5 The procedure of Example 1 was repeated except that the 2-hydroxy-3 phenylcarbamoylbenzo[a]carbazole was replaced by 2-hydroxy-3-(4 ethylphenylcarbamoyl)benzo[a]carbazole (2.8 g), to give trisazo compound No. 1-5(1.9 g, yield 64%) in the form of black crystals.

Decomposition point: 3000C or higher Elementary analysis values Observed values Calculated values C% 76.41 76.26 H% 4.48 4.75 N% 12.16 12.43 Infrared absorption spectrum (according to KBr tablet method): Pc=o (secondary amido) 1 670 cm- EXAMPLE 7 The procedure of Example 1 was repeated except that the 2-hydroxy-3 phenylcarbamoylbenzo[a]carbazole was replaced by 2-hydroxy-3-(2,4dimethylphenylcarbamoyl)benzo[a]carbazole (2.7 g), to give trisazo compound No. 1-7 of (2.0 g, yield 68%) in the form of black crystals.

Decomposition point: 3000C or higher Elementary analysis values: Observed values Calculated values C% 76.41 76.26 H% 4.46 4.75 N% 11.93 12.43 Infrared absorption spectrum (according to KBr tablet method): Pc=o (secondary amido) 1 680 cm- EXAMPLE 8 The procedure of Example 1 was repeated except that the 2-hydroxy-3phenylcarbamoylbenzo[a]carbazole was replaced by 2-hydroxy-3-(2,5dimethylphenylcarbamoyl)benzo[a]carbazole (2.7 g), to give trisazo compound No. 1-8 (1.9 g, yield 65%) in the form of black crystals.

Decomposition point: 3000C or higher Elementary analysis values: Observed values Calculated values C% 76.09 76.26 H% 4.61 4.75 N% 11.93 12.43 Infrared absorption spectrum (according to KBr tablet method): Pc=o (secondary amido) 1 680 cm-' EXAMPLE 9 The procedure of Example 1 was repeated except that the 2-hydroxy-3phenylcarbamoylbenzo[a]ca rbazole was replaced by 2-hyd roxy-3-(2-methyl-5- chlorophenylcarbamoyl)benzo[a]carbazole (2.9 g), to give trisazo compound No. 1-9 (2.4 g, yield 78%) in the form of black crystals.

Decomposition point: 3000C or higher.

Elementary analysis values: Observed values Calculated values C% 70.50 70.84 H% 3.76 3.96 N% 11.92 11.93 Infrared absorption spectrum (according to KBr tablet method): Pc=o (secondary amido) 1 680 cm-' The trisazo compounds of the present invention are effective as charge generating-pigments for the electrophotographic elements of the multilayer type, as described above, as evidenced by the following tests.

EXAMPLE 9 A trisazo compound (No. I-I) of the present invention (76 parts by weight), a tetrahydrofuran solution (1 ,260 parts by weight) of a polyester resin (Vylon 200, tradename of product manufactured by Toyo Boseki K.K.) solid concentration: 2%), and tetrahydrofuran (3,700 parts by weight) were mixed together by milling in a ball mill.The resulting dispersion was applied onto the aluminium surface of an aluminium-coated polyester base (an electrically conductive substrate) by means of a doctor blade, followed by natural drying, to form a charge carrier generating layer about 1 micrometre thick. 1 - Phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)-pyrazoline (one part by weight), as a charge transfer substance, a polycarbonate resin (Panlite K 1300, tradename of product manufactured by Teijin Kasei K.K.) (one part by weight) and tetrahydrofuran (8 parts by weight) were mixed and dissolved to form a solution.This solution was applied onto the charge carrier generating layer prepared above, by means of a doctor blade, followed by drying at 800C for 2 minutes and then at 1000C for 5 minutes, to form a charge transfer layer about 20 micrometres thick. Thus, an electrophotographic element Il-I, which is of the multilayer type as shown in Figure 4 was prepared.

Electrophotographic elements 11-2 to 11-8 were prepared by repeating the above procedure except that combinations of charge carrier generating pigment (trisazo compound) and charge transfer substances shown in the following Table 2 were employed. In the column "charge transfer substance", D-1 means 1 -phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)-pyrazoline, D-2 means 9 ethylcarbazole-3-carboxyaldehyde l-methyl-l-phenylhydrazone and D-3 means 9-(4diethylaminophenyl)anthracene.

TABLE 2

Electrophotographic Tri salt Charge transfer element No. compound substance 11-2 1-2 D-1 11-3 1-3 D-1 11-4 1-4 D-2 11-5 1-5 D-2 11-6 16 D-1 11-7 1-7 D-1 116 16 D-1 11-9 1-9 D-3 The following electrophotographic elements were prepared for comparison.

COMPARATIVE EXAMPLE 1 The procedure of Example 9 was repeated except that the trisazo compound of the present invention was replaced by 4,4',4"-tris(2-hydroxy-3-phenylcarbamoyl-1 -naphthylazo)triphenylamine which is a trisazo pigment of the triphenylamine group, disclosed in Japanese Laid-open Patent Application No. 132547/1978, and 9-(4-diethylaminophenyl)anthracene was used as a charge transfer substance, to prepare comparative electrophotographic element 111-1.

COMPARATIVE EXAMPLE 2 The procedure of Comparative Example 1 was repeated except that the charge transfer substance of Comparative Example 1 was replaced by 1-phenyl-3-(4-diethylaminostyryl)-5-(4- diethylaminophenyl)pyrazoline, to prepare comparative electrophotographic element 111-2.

COMPARATIVE EXAMPLE 3 The procedure of Comparative Example 1 was repeated except that the charge transfer substance of Comparative Example 1 was replaced by 9-ethylcarbazole-3-carboxyaldehyde 1 -methyl-1 - phenylhydrazone, to prepare comparative electrophotographic element 111-3.

COMPARATIVE EXAMPLE 4 A polyester resin (10 parts by weight) 2,4,7-trinitro-9-fluorenone (10 parts by weight), a trisazo compound of the general formula (I) of the present invention but wherein Ar represents a 2-methyl-4methoxyphenyl group, as disclosed in Japanese Laid-open Patent Application No. 1 32347/1 978, (2 parts by weight) and tetrahydrofuran (198 parts by weight) were mixed together by milling in a ball mill, and the resulting dispersion was applied onto an aluminium-coated polyester film by means of a doctor blade, followed by drying at 1 000C for 10 minutes, to prepare comparative electrophotographic element 111-4, having a photosensitive layer 10 micrometres thick (111-4).

COMPARATIVE EXAMPLE 5 4,4'-bis(2-hydroxy-3-phenylca rba moyl-1 -naphthylazo)-3,3'-dichlorodiphenyl (1.08 part by weight) which is a benzidine disazo pigment, as disclosed in Japanese Laid-open Patent Application No.

37543/1972 or Japanese Laid-open Patent Application No. 55643/1 977, was dissolved in ethylene diamine (24.46 parts by weight). To the resulting solution was added n-butylamine (20.08 parts by weight) with stirring, and further added tetrahydrofuran (54.36 parts by weight), to prepare a coating solution for a charge carrier generating layer, which was then applied onto an aluminium coated polyester film by means of a doctor blade and dried at 800C for 5 minutes to form a charge carrier generating layer about 0.5 micrometres thick.Onto this charge carrier generating layer was applied a solution consisting of 1-phenyl-3-(4-diethylaminostyryl-5-(4-diethylaminophenyl)-pyrazoline (one part by weight, a polycarbonate resin (Panlite K-i 300) (one part by weight), and tetrahydrofuran (8 parts by weight), by means of a doctor blade, followed by drying at 80"C for 2 minutes and then at 1 000C for 5 minutes, to form a charge transfer layer about 20 micrometres thick. Thus, comparative electrophotographic element 111-5 was prepared.

COMPARATIVE EXAMPLE 6 A Se-As alloy (As: 40% by weight) as a depositing raw material was deposited onto an aluminium base at base temperature of 2000C at a depositing source temperature of 41 00C to 41 50C and under a vacuum of 1 0-6 Torr to prepare an As2Se3 electrophotographic element having a photosensitive layer about 60 micrometres thick. (Comparative inorganic electrophotographic element 111-6).

The static characteristics of the 1 5 electrophotographic elements prepared as described above, were measured by means of a commercially available electrostatic copying paper tester (SP-428 type, tradename of apparatus manufactured by Kawaguchi Denki Seisakusho).

First, a corona discharge of -6 KV (or +6 KV) was applied to each of the respective electrophotographic elements for 20 seconds whereby it was negatively (or positively) charged, followed by allowing it to stand for 20 seconds in a dark place wherein the surface potential Vpo (V) thereof at that time were measured. The elements were then each irradiated by light emitted from a tungsten lamp so that illuminance of 20 luxes was applied to their surfaces, and the period of time (second) until the surface potential reached 1/2 and 1/10 of Vpo was measured, to calculate quantities of exposure to light, E1/2 and E'/10 (lux.sec). The results are shown in Table 3.

TABLE 3

Electrophotographic Vpo E 1/2 E 1, 10 element No. (volt) (lux-sec.) (lux sec.) ll-1 643 ' 2.3 7.G 11-2 -353 2.1 4.8 11-3 -804 1.0 1.8 11-4 -917 0.9 1.8 Il-S -687 2.5 5.8 11-6 469 1.0 2.3 11-7 -526 2.0 4.3 116 -513 1.3 3.7 11-9 677 0.7 1.7 111-1 -915 9.1 39 III-2 -385 7.7 29 III-3 -785 8.1 33 III-4 -650 27.4 83 TABLE 3 - continued

Electrophotographic Vpo E 1/2 El, 2 10 element No. (volt) (lux sec.) (lux.sec.) 111-5 603 1.9 4,1 111-6 -1198 1.3 2.3 Further, in order to show that the electrophotographic elements of the present invention have good sensibility to light of long wavelengths, the following tests were carried out: First, the electrophotographic elements were electrically charged by corona discharge in a dark place (electrophotographic elements ll-1 to 11-9 and 111-1 to 111-5 were negatively charged and electrophotographic element 111-6 was positively charged) to measure the respective surface potentials, followed by irradiation with spectral monochrome light of 1 microwatt/cm3.The period of time (seconds) till the surface potential thereof decayed to half its original value was measured (wherein, the dark-decayed portion of the surface potential has been compensated), and also the amount of exposure {microwatts sec/cm2) was measured, to calculate the light decay speed (volt.cm2. uW-'.sec-l) at wavelength of 780 nm and 800 nm. The results are shown in Table 4.

TABLE 4

Wavelength of Electrophotographic irradiation light Surface potential Light decay speed element No. (nm) (volt) (volt#cm# W-1#sec.) 780 -600 170 II-1 800 -600 160 780 -400 180 II-2 800 -400 150 780 -800 950 11-3 800 -800 830 780 00 1100 11-4 800 -800 990 780 -700 130 11-5 800 -700 120 780 -700 590 11-6 800 -700 560 780 800 200 11-7 800 -600 150 780 -600 320 11-8 800 800 270 780 -800 880 II-9 800 800 730 780 -800 10 or less 111-1 800 -800 10 or less TABLE 4 (Continued)

Wavelength of Electrophotographic irradiation light Surface potential Light decay speed element No. (nm) (volt) (volt.cm2 llW~le sec.) 780 -400 10 or less 111-2 1 800 -400 10 or less 780 -700 10 or less 111-3 800 -700 10 or less 780 800 10 or less 111-4 800 -800 10 or less 780 600 10 or less 111-5 800 -600 10 or less 780 +800 50 111-6 800 +800 15 As is apparent from the results given in Tables 3 and 4, the electrophotographic elements derived from the present invention 11-1 to 11-9 are not inferior, in their sensitivity within visible light region, to other electrophotographic elements, and have a sensitivity of several tens of times or more those of other electrophotographic elements, particularly in the wavelength regions of semiconductor lasers.

As described above, the trisazo compounds of the present invention are useful materials, for electrophotographic elements, and have a number of advantages such as light weight, low cost, etc.

since the compounds are organic.

Claims (12)

1. Trisazo compounds of the general formula:

in which Ar is a phenyl, o-methylphenyl, p-methylphenyl, o-ethylphenyl, p-ethylphenyl, o-ethoxyphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl or 5-chloro-2-methyl-phenyl group.

2. A trisazo compound as claimed in Claim 1 in which Ar is a phenyl group.

3. A trisazo cdmpound as claimed in Claim 1 in which Ar is an o-methylphenyl group.

4. A trisazo compound as claimed in Claim 1 in which Ar is a p-methylphenyl group.

5. A trisazo compound as claimed in Claim 1 in which Ar is an o-ethylphenyl group.

6. A trisazo compound as claimed in Claim 1 in which Ar is a p-ethylphenyl group.

7. A trisazo compound as claimed in Claim 1 in which Ar is an o-ethoxyphenyl group.

8. A trisazo compound as claimed in Claim 1 in which Ar is a 2,4-dimethylphenyl group.

9. A trisazo compound as claimed in Claim 1 in which Ar is 2,5-dimethylphenyl group.

10. A trisazo compound as claimed in Claim 1 in which Ar is as 5-chloro-2-methyl-phenyl group.

11. A process for the preparation of a trisazo compound as claimed in claim 1 which comprises diazotising 4,4',4"-triaminotriphenylamine to yield a hexazonium salt of the formula:

(in which X represents an anionic functional group), and reacting the hexazonium salt of formula (Ill) with a 2-hydroxy-3-phenylcarbamoylbenzo[a]ca rbazole derivative of the formula:

in which Ar has the meaning defined above.

12. A process as claimed in claim 12 substantially as hereinbefore described with reference to the Examples.