EP0501455A1

EP0501455A1 - Photoconductor for electrophotography

Info

Publication number: EP0501455A1
Application number: EP92103281A
Authority: EP
Inventors: Yoichi c/o Fuji Electric Co. Ltd. Nakamura; Mikio c/o Fuji Electric Co. Ltd. Takashima; Sumitaka C/O Fuji Electric Co. Ltd. Nogami
Original assignee: Fuji Electric Co Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 1991-02-27
Filing date: 1992-02-26
Publication date: 1992-09-02
Also published as: JPH04271356A

Abstract

The photoconductor for electrophotography (1) comprises an electroconductive substrate (2) and a photosensitive layer (3) formed on the substrate. The photosensitive layer (3) comprises a charge generating layer (3a) and a charge transporting layer (3b) laminated one on another. The charge generating layer (3a) contains an organic pigment and a polyether ketone represented by general formula (I) below as the binder resin.

wherein X is a group selected from the class consisting of:

m is 0 or 1; and n is a positive integer.

Description

The present invention relates to photoconductors for electrophotography, and more particularly to a photoconductor for electrophotography which includes an electroconductive substrate having thereon a photoconductor having a charge generating layer and a charge transporting layer.
Photoconductors for electrophotography (hereafter, sometimes referred to simply as "photoconductors") each include an electroconductive substrate having thereon a photosensitive layer containing a photoconductive material. In the electrophotographic image formation system according to Carlson, a photoconductor is subjected in the dark to corona discharge to charge the photoconductor, the surface of the charged photoconductor is imagewise exposed light using a manuscript or copy bearing, e.g., letters and/or pictures to form a latent electrostatic image, the thus formed latent electrostatic image is developed with a toner to form a visible image, the developed toner image is transferred to a support such as a paper sheet to fix the toner image on the support. After the toner image transfer, the photoconductor is subjected to the steps of removal of the electric charge and removal of the remaining toner (cleaning), and the like to be ready for reuse for a prolonged period of time.
Therefore, photoconductors are required to have not only sufficient electrophotographic characteristics such as charge generating properties, surface charge maintaining properties, and light sensitivity but also sufficient resistances to abrasion, ozone, ultraviolet, or the like upon repeated use for a long time. In addition, they are required to have sufficient resistances to environmental conditions upon their use such as low temperature/low humidity, or high temperature/high humidity).
Heretofore, use has been widely made of photoconductors having photosensitive layers in which inorganic photoconductive materials composed mainly of selenium, zinc oxide, cadmium sulfide and the like. However, these inorganic photoconductors have not always been satisfactory in light sensitivity, thermal stability, durability, resistance to environmental conditions, toxicity, etc.
Photoconductors for electrophotography utilizing organic materials have recently been studied and developed. Organic photoconductors are generally less toxic than inorganic photoconductors. The organic photoconductors have attracted much attention and have been put into practical use increasingly by virtue of the advantageous features of the organic materials such as transparency, flexibility, lightness in weight, productivity, etc., as compared with the inorganic materials. For example, Japanese Patent Publication No. 10496/1975 discloses a photoconductor composed of poly-N-vinylcarbazole and 2,4,4-trinitro-o-fluorenone while Japanese Patent Publication No. 25658/1973 described a photoconductor composed of poly-N-vinylcarbazole sensitized with a pyrylium dye. However, such conventional photoconductors are not totally sufficient for their light sensitivity and durability. In later days, so-called function-separated type laminate photoconductors in which a charge generating layer and a charge transporting layer are provided separately have been developed. For example, Japanese Patent Publication No. 42380/1980 discloses a function-separated type photoconductor which uses chlorocyan blue and a hydrazone compound.
As described above, division of the photosensitive layer into a charge generating layer and a charge transporting layer, or sharing of functions by different layers, facilitated the fabrication of photoconductors with various characteristics, further development has been made with expectation to obtaining photoconductors with a high light sensitivity and a high durability.
Generally, the charge generating layer of the aforementioned type photoconductor is constructed by an organic pigment and a binder resin. The binder resin is used to obviate disadvantages of the charge generating layer composed of the organic pigment exclusively that the charge generating layer itself lacks film-forming properties and has a poor adhesion to the substrate and has a poor adhesion to the charge transporting layer. This decreases the mechanical strength of the photoconductor. Furthermore, the dispersibility and dispersion stability of the coating for forming the charge generating layer are insufficient, which prevents continuous coating on industrial scale. Examples of such binder resins include polyvinylbutyral as disclosed in Japanese Patent Application Laid-Open No. 105145/1983, acrylic resin having an acid value of 10 to 40 and a glass transition point of 70°C ore lower as disclosed in Japanese Patent Application Laid-Open No. 192040/1983, polyvinylpyrrolidone as disclosed in Japanese Patent Application Laid-Open No. 12646/1981, polyvinylpyridine as disclosed in Japanese Patent Application Laid-Open No. 60443/1981, and phenol resin as disclosed in Japanese Patent Application Laid-Open No. 17448/1983.
Generally, binders for use in charge generating layer must meet, for example, the following performances:

(1) They have good dispersibility and dispersion stability for organic pigments as the charge generating substance.
(2) They have good adhesion with the electroconductive substrate or subbing layer and with the charge transporting layer.
(3) They are not attacked by the coating liquid for forming a charge transporting layer or the coating fro forming a protective layer
(4) Their characteristics are stable with respect to temperature and humidity, thus giving no adverse influences on the electrophotographic properties of the photoconductor.
(5) They give rise to a charge generating layer with a high efficiency of charge generation and a high efficiency of transportation of generated charge.

The aforementioned performances vary greatly depending on the binder resin used, and hence selection of binder resins is one of the important factors for controlling the performances of the photoconductor.
However, there has been no valid rule for the selection of the binder resin, and at present the binder resin is selected after many experiments depending on the type of the organic pigment used as the charge generating substance. No binder resin that meets the aforementioned requirements sufficiently has been obtained yet.
Therefore, it is an object of the present invention to provide a photoconductor which has a smooth charge generating layer containing dispersed therein uniformly an organic pigment as a charge generating substance and having a uniform thickness, and which has a sufficient light sensitivity, but is free of the occurrence of inconveniences such as white points and black blots in the image formed, deteriorations after repeated use for a long time, and suffers from less variation of characteristics with changes of temperature and humidity.
As a result of intensive studies, it has now been found that the above-described object can be achieved by the use of a specified polyether ketone as a binder resin together with an organic pigment in the charge generating layer of the photoconductive layer which constitutes the photoconductor.
According to the present invention, a photoconductor for electrophotography comprises:
a substrate; and
a photosensitive layer formed on the substrate and including a charge generating layer and a charge transporting layer,
wherein the charge generating layer contains an organic pigment as a charge generating substance and a binder resin as a binder, the binder resin being represented by general formula (I):

wherein X is a group selected from the class consisting of:

m is 0 or 1; and n is a positive integer.
Here, preferably n is a positive integer satisfying:
10 ≦ n ≦ 5,000.
The binder resin may be one selected from polyether ketone resins represented by the following formulae:
The organic pigment may be an azo pigment. Preferably, the azo pigment may be a disazo pigment represented by general formula (II):

wherein R₁ is a halogen atom, an alkyl group, or an alkoxy group; R₂ is an alkyl group which is unsubstituted or substituted; R₃ is a hydrogen atom, a cyano group, a carbamoyl group, a carboxyl group, an ester group, an acyl group; and R₄ is a hydrogen atom, a halogen atom, a nitro group, an alkyl group, or an alkoxy group. The organic pigment may be a polycyclic quinone compound. The organic pigment may also be a phthalocyanine pigment.
According to the present invention, the use of the polyether ketone represented by general formula (I) above in the charge generating layer as a binder results in a charge generating layer which can contain an organic pigment dispersed therein uniformly, has a uniform thickness and is smooth, and the photoconductor having such a charge generating layer has a sufficient light sensitivity and is free of inconveniences such as white points and black blots in the image due to agglomeration of the particles of the organic pigment. The photoconductor suffers from less deterioration after repeated use for long time. Also, the photoconductor suffers from less variation of characteristics with changes of temperature and humidity.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawing.
Fig. 1 is a schematic cross sectional view showing a photoconductor in accordance with one embodiment of the present invention.
Referring to Fig. 1, a photoconductor 1 according to one embodiment of the present invention comprises an electroconductive substrate 2, and a photosensitive layer 3 provided on the substrate 1. The photosensitive layer 3 has a charge generating layer 3a and a charge transporting layer 3b.
The electroconductive substrate or support 2 acts as an electrode and supports the charge generating layer 3a and the charge transporting layer 3b. In Fig. 1, the electroconductive substrate 2 is in the form of a plate. However, it is not limited to a plate but may be in any other forms such as a cylinder, and a film. The electroconductive substrate 2 may be made of aluminum, stainless steel, electroconductive plastic or the like. If desired, an electroconductive coating may be provided on a surface of the electroconductive substrate 2 so that the smoothness of the substrate can be increased. Also a subbing layer may be provided on the electroconductive substrate 2, if desired, in order to increase adhesion between the charge generating layer 3a and the substrate 2.
The charge generating layer 3a can be formed by coating the substrate 2 with a solution composed mainly of a binder resin represented by general formula (I) above as a binder, an organic pigment as a charge generating substance, and an organic solvent, and drying it.
In general formula (I) above, n is a weight average molecular weight, which is within the range of generally 10 ≦ n ≦ 5,000, and preferably 50 ≦ n ≦ 500. In the ordinary methods, the polyether ketone represented by general formula (I) above can hardly be synthesized.
As described in Journal of Polymer Science Part A-1, 5, 2375 (1967), the polyether ketone represented by general formula (I) can be prepared with ease by condensing a disodium salt of bisphenol compound such as disodium salt of bisphenol A or 2,2-bis(p-hydroxyphenyl)hexafluoropropane with 4, 4'-difluorobenzophenone or bis(p-hydroxyphenyl)terephthaloyl, respectively, or a disodium salt of bis(p-hydroxyphenyl)sulfone with 4,4'-difluorobenzophenone or bis(p-fluorophenyl)terephthaloyl), in a solvent with heating. The product can be purified by precipitation from a mixed solvent of chloroform-methane. Preferably, the reaction may be conducted in a polar solvent such as sulfolane at a temperature of 230 to 240°C for about 4 hours. Also, reference is made to Japanese Patent Applications Laid-Open Nos. 70256/1988, 247757/1988, 259571/1988, and 169456/1989 which disclose those polyether ketones represented by formula (I) above in which m is 1 and methods for preparing them.
Specific examples of the polyether ketone represented by general formula (I) above include the following polymers:
The organic pigment which can be used as the charge generating substance in the present invention is a pigment which absorbs light and generates electrons or holes in the presence of an electric field.
Examples of such organic pigment include azo pigments, anthraquinone pigments, polycyclic quinone pigments, indigo pigments, diphenylmethane pigments, azine pigments, cyanine pigments, quinoline pigments, benzoquinone pigments, naphthoquinone pigments, naphthalkoxide pigments, perylene pigments, fluorenone pigments, squarylium pigments, azulenium pigments, quinacridone pigments, phthalocyanine pigments, naphthalocyanine pigments, porphyrin pigments, and the like.
Among these pigments particularly preferred are polycyclic quinone pigments such as 3,9-dibromo-anthoanthrone, α-, β-, ζ₋ and χ-type metal-free phthalocyanines, metal phthalocyanines, e.g., copper phthalocyanine, chloroaluminum phthalocyanine, vanadyl phthalocyanine, titanyl phthalocyanine, titanoxyphthalocyanine, and the like. Also particularly preferred are azo pigments represented by general formula (II)

wherein R₁ is a halogen atom, an alkyl group, or an alkoxy group; R₂ is an alkyl group which is unsubstituted or substituted; R₃ is a hydrogen atom, a cyano group, a carbamoyl group, a carboxyl group, an ester group, an acyl group; and R₄ is a hydrogen atom, a halogen atom, a nitro group, an alkyl group, or an alkoxy group.
The aforementioned azo pigments are known (cf. Japanese Patent Application Laid-Open No. 305362/1988).
Specific examples of the azo pigment represented by general formula (II) above include the following:
These pigments may be used singly or two or more of them may be used as mixtures in any proportions.
The organic solvent suitable for the coating for forming the charge generating layer includes cyclohexanone, dioxane, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, ethyl acetate, cellosolve, toluene, xylene, methylene chloride, and the like.
The coating for the charge generating layer which can be used in the present invention can be prepared by dispersing the polyether ketone represented by general formula (I), and optionally one or more additives such as a flow leveling agent and a surfactant in the aforementioned organic solvent using a dispersion mixer such as a ball mill, a sand mill, or an attritor. Blend ratio of the polyether ketone to the organic pigment is generally 5 to 200 parts by weight, preferably 10 to 100 parts by weight, of the polyether ketone per 100 parts by weight of the organic pigment. If the blend ratio is below 5 parts by weight of the polyether ketone per 100 parts by weight of the organic pigment, adhesion of the charge generating layer decreases while it exceeds 200 parts by weight of the polyether ketone per 100 parts by weight of the organic pigment, the light sensitivity of the resulting photoconductor decreases. Therefore, the blend ratios within the aforementioned range are preferred.
The charge generating layer is formed by coating the coating liquid to a thickness of 0.05 to 5 µm on dry basis. If the thickness is less than 0.05 µm, the film-forming properties are poor so that defects tend to occur in images. On the other hand, if the thickness exceeds 5 µm, there occurs decrease of electrophotographic properties such as charging properties. Therefore, it is preferred that the thickness of the charge generating layer is within the aforementioned range.
On the charge generating layer 3a prepared as described above is formed the charge transporting layer 3b by coating and drying in a conventional manner. The coating liquid which can be used for forming the charge transporting layer is the one which is composed mainly of a high molecular weight compound as a charge transporting substance and an organic solvent, or the one which is composed mainly of a low molecular weight compound as a charge transporting substance, a binder resin as a binder, and an organic solvent.
Examples of preferred charge transporting substance include high molecular weight compounds such as poly(N-vinylcarbazole)s, poly(vinylanthracene)s, poly(9.10-anthracenenylene-dodecanedicarboxylate)s, polysilanes, polygermanes, and poly(p-phenylene-sulfide)s, and low molecular weight compounds such as hydrazone compounds, pyrazoline compounds, enamine compounds, styryl compounds, arylmethane compounds, arylamine compounds, butadiene compounds, and azine compounds. These compounds can be used singly, or two or more of them can be used in combination.
When the low molecular weight compounds are used as the charge transporting substance, use is made of binder resins as the binder. As the binder resin, there can be used one or more of polycarbonates, polyesters, polyurethanes, epoxy resins, silicone resins, polystyrenes, and the like. A mixture of 50 to 200 parts by weight of the binder resin per 100 parts by weight of the low molecular weight compound is dissolved in an organic solvent which can dissolve both of them to form a coating solution.
The coating solution for the charge generating layer may contain stabilizers such as antioxidants, ultraviolet absorbents, and proton absorbents, if desired. Also, the coating liquid for the charge generating layer may contain a flow leveling agent, an anti-sagging agent or the like, in order to prevent defects on the coated surface upon coating.
The thickness of the charge generating layer may be set up freely depending on the charging properties, light sensitivity and durability or plate wear of the photoconductor. The thickness of the charge generating layer is usually 5 to 50 µm, and preferably 10 to 30 µm.

EXAMPLES

Hereafter, the present invention will be described in more detail by examples. However, the invention should not be construed as being limited thereto.

Preparation Example 1

Preparation of Polyether Ketone I-2

In a 2-liter three-necked reaction vessel made of glass and equipped with a stirrer, a nitrogen gas blower and a reflux condenser having an aspirator were charged the following starting materials:

4,4'-Isopropylidenediphenol 228.3 g (1 mol)

4,4'-Difluorobenzophenone 218 g (1 mol)

K₂CO₃ (anhydrous) 145 g (1.05 mol)

Sulfolane 1,400 g

and the mixture was heated to 230°C in 1 hour while blowing nitrogen gas therein. The reaction was continued at 230°C for 4 hours with stirring. After 5 hours from the initiation of the reaction, a solution of 1 g of 4,4'-difluorobenzophenone in 500 g of sulfolane was added to the reaction mixture. The resulting mixture was allowed to react for 1 hour. Then, the reaction mixture was put in a large amount of water to precipitate a solid product. The solid product was dissolved in tetrahydrofuran and precipitated with methanol. This procedure was repeated three times to obtain 377 g of a polyether ketone. Upon gel permeation chromatography, the polymer gave a molecular weight of 62,700 in terms of polystyrene, with an average degree of polycondensation n = 150 (polyether ketone I-2 above).

Preparation Example 2

Preparation of Polyether Ketone I-3

Substantially the same procedures as in Preparation Example 1 were repeated except that difluorobenzophenone was replaced by 1 mol of difluoro-p-dibenzoylbenzene to obtain polyether ketone I-3 above. The degree of polymerization, n, was controlled by the amount of a reaction controlling agent which was added to terminate the reaction.

Preparation Example 3

Preparation of Polyether Ketone I-4

Substantially the same procedures as in Preparation Example 1 were repeated except that bisphenol A used as the diphenol compound was replaced by bisphenol S to obtain polyether ketone I-4 above. The degree of polymerization, n, was controlled by the amount of a reaction controlling agent which was added to terminate the reaction.

Preparation Example 4

Preparation of Polyether Ketone I-5

Substantially the same procedures as in Preparation Example 1 were repeated except that bisphenol A used as the diphenol compound was replaced by bisphenol F to obtain polyether ketone I-5. The degree of polymerization, n, was controlled by the amount of a reaction controlling agent which was added to terminate the reaction.

Preparation Example 5

Preparation of Polyether Ketone I-6

Substantially the same procedures as in Preparation Example 1 were repeated except that bisphenol A used as the diphenol compound was replaced by bisphenol F to obtain polyether ketone I-6. The degree of polymerization, n, was controlled by the amount of a reaction controlling agent which was added to terminate the reaction.

Example 1

A mixture of 8 parts by weight of aluminum phthalocyanine chloride purified by sublimation and 563 parts by weight of chloroform was ground in a glass ball mill at room temperature for 10 hours. In the resulting dispersion were dissolved 8 parts by weight of polyether ketone I-2 above to prepare a coating liquid. On the other hand, a solution of a copolyamide (CM-4001, trade name for a product by Toray) in methanol in a concentration of 1 % by weight was coated on a 100 µm-thick aluminum sheet to a thickness of 0.1 µm (dry basis) to prepare a substrate with a subbing layer. The aforementioned coating liquid was applied on the subbing layer and dried at 100°C for 1 hour to form a charge generating layer in a thickness of 0.1 µm (dry basis) . Then, on the charge generating layer thus formed was coated a solution of 10 parts by weight of p-diethylaminobenzaldehyde (diphenylhydrazone), 10 parts by weight of polycarbonate (pcz-3000, trade name for a product by Mitsubishi Gas Chemical), and 72 parts by weight of 1,2-dichloroethane, followed by vacuum drying at room temperature to form a charge transporting layer in a thickness of 15 µm, thus producing a photoconductor.

Example 2

A photoconductor was fabricated in the same manner as in Example 1 except that the binder resin to be used in the charge generating layer was replaced by polyether ketone No. I-3

Example 3

A photoconductor was fabricated in the same manner as in Example 1 except that the binder resin to be used in the charge generating layer was replaced by polyether ketone No. I-4

Example 4

A photoconductor was fabricated in the same manner as in Example 1 except that the binder resin to be used in the charge generating layer was replaced by polyether ketone No. I-6

Comparative Example 1

A photoconductor was fabricated in the same manner as in Example 1 except that the binder resin to be used in the charge generating layer was replaced by polyvinylbutyral (BM-2, trade name for a product by Sekisui Chemical).

Comparative Example 2

A photoconductor was fabricated in the same manner as in Example 1 except that the binder resin to be used in the charge generating layer was replaced by polyester (Byron 200, trade name for a product by Toyobo).

Comparative Example 3

A photoconductor was fabricated in the same manner as in Example 1 except that the binder resin to be used in the charge generating layer was replaced by an acrylic resin (Acridic A-801, trade name for a product by Dainippon Ink and Chemical Industry).

Example 5

Eight (8) parts by weight of χ-type metal-free phthalocyanine (Dainippon Ink and Chemical Industry) and 563 parts by weight of chloroform were mixed in a glass ball mill at room temperature for 10 hours to prepare a dispersion, to which were added 8 parts by weight of the polyether ketone I-5 above to obtain a coating liquid.
The coating liquid thus obtained was applied on the same substrate as used in Example 1 and dried at 100°C for 1 hour to form a charge generating layer in a thickness of 0.4 µm. On this layer was coated a solution composed of 10 parts by weight of 4-(diethylamino)styryl-2-anthracene, 10 parts by weight of a polycarbonate (pcz-300, trade name for a product by Mitsubishi Gas Chemical), and 72 parts by weight of 1,2-dichloroethane, followed by vacuum drying at room temperature to form a charge transporting layer in a thickness of 15 µm, thus producing a photoconductor.

Comparative Example 4

A photoconductor was fabricated in the same manner as in Example 5 except that the binder resin to be used in the charge generating layer was replaced by polyester (Byron 200, trade name for a product by Toyobo).

Comparative Example 5

A photoconductor was fabricated in the same manner as in Example 5 except that the binder resin to be used in the charge generating layer was replaced by polyvinyl chloride (MR-100, trade name for a product by Nippon Zeon).

Example 6

A mixture of 3 parts by weight of the above azo pigment, 1 part by weight of the polyether ketone I-1 as the binder resin and 96 parts by weight of tetrahydrofuran was mixed in a ball mill to prepare a dispersion as a coating liquid.
The coating liquid was coated on the same substrate as used in Example 1 and dried to form a charge generating layer in a thickness of 1 µm. Then, on this layer was coated a solution composed of 10 parts by weight of p-diethylaminobenzaldehyde(phenyl, naphthylhydrazone), 10 parts by weight of a polycarbonate (pcz-300, trade name for a product by Mitsubishi Gas Chemical), and 72 parts by weight of 1,2-dichloroethane, followed by vacuum drying at room temperature to form a charge transporting layer in a thickness of 20 µm, thus producing a photoconductor.

Example 7

A photoconductor was fabricated in the same manner as in Example 6 except that the binder resin to be used in the charge generating layer was replaced by polyether ketone No. I-3

Example 8

A photoconductor was fabricated in the same manner as in Example 6 except that the binder resin to be used in the charge generating layer was replaced by polyether ketone No. I-6

Comparative Example 6

A photoconductor was fabricated in the same manner as in Example 6 except that the binder resin to be used in the charge generating layer was replaced by polyester (Byron 200, trade name for a product by Toyobo).

Comparative Example 7

A photoconductor was fabricated in the same manner as in Example 6 except that the binder resin to be used in the charge generating layer was replaced by polyvinylbutyral (BM-2, trade name for a product by Sekisui Chemical).

Example 9

A mixture of 7 parts by weight of a commercially available quinone dye, 4,10-dibromoanthanthrone (Monolite Red 2Y, trade name for a product by ICI; Color Index No. 59300), 3 parts by weight of Polymer I-1 and 19 parts by weight of cyclohexanone was dispersed in a sand mill using glass beads of 1 mm in diameter to obtain a dispersion. Additional cyclohexanone was added to the dispersion to prepare a coating liquid with a solid content of 3 % by weight. Then, a photoconductor was produced in the same manner as in Example 1 except that the coating liquid containing aluminum phthalocyanine chloride used in Example 1 was replaced by the aforementioned coating liquid containing the quinone dye and that the thickness of charge generating layer was changed to 1 µm.

Comparative Example 8

A photoconductor was produced in the same manner as in Example 9 except that Polymer I-1 used as the binder resin for the charge generating layer was replaced by polyvinylbutyral (BM-1, trade name for a product by Sekisui Chemical).
The electrophotographic characteristics of the photoconductors thus produced were measured by utilizing an electrostatic recording paper testing apparatus (Kawaguchi Denki Model SP-428).
The surface potential V₀ (volts) of each photoconductor which is an initial surface potential was measured when the surface of the photoconductor was positively charged in the dark by corona charge at -6 kV for 10 seconds. After the discontinuation of the corona discharge, the photoconductor was allowed to stand in the dark for 5 seconds, after which the surface potential V_d (volts) of the photoconductor was measured. Surface potential attenuation ratio, DDR₅ (%), was calculated from V_d. Subsequently, for the photoconductors of Examples 1 to 5 and Comparative Examples 1 to 5 which used phthalocyanine pigment as the charge generating substance and thus were sensitive to light in the longer wavelength region, a monochromatic light with a wavelength of 780 nm was irradiated to each photoconductor in an exposure amount of 3.84 µW/cm², and the time (seconds) required for the irradiation to decrease the surface potential of the photoconductor to half of the V_d was measured, from which time was calculated half decay exposure amount E_1/2 (µW/cm²) . Also, the surface potential of the photoconductor after 1.3 seconds of irradiation of the photoconductor with the aforementioned monochromatic light as a residual potential V_r (volts). On the other hand, as to the photoconductors of Examples 6 to 9 and Comparative Examples 6 to 8, which used azo pigment as the charge generating substance and were sensitive to visible light, the surface of the photoconductor was irradiated with white light from a tungsten lamp at an illuminance of 20 luxes and the time required for the irradiation to decrease the surface potential of the photoconductor to half of the V_d was measured, from which time half decay exposure amount E_1/2 (lux·seconds) was calculated. Also the surface potential of the photoconductor after 1.3 seconds of irradiation of the photoconductor with the white light was measured as a residual potential V_r (volts). After repeating the procedures of charging and exposure as mentioned above 2,500 times continuously, the characteristics of the photoconductor were measured to examine variation of characteristics.

Results obtained are shown in Tables 1 to 4, with Table 1 showing results of initial characteristics of the photoconductors in Examples 1 to 5 and Comparative Examples 1 to 5, Table 2 showing results of characteristics of the photoconductors in Examples 1 to 5 and Comparative Examples 1 to 5 after repetition of 2,500 times, Table 3 showing results of initial characteristics of the photoconductors in Examples 6 to 9 and Comparative Examples 6 to 8, and Table 4 showing results of characteristics of the photoconductors in Examples 6 to 9 and Comparative Examples 6 to 8 after repetition of 2,500 times.

Table 1

Initial Characteristics of Photoconductor
	V₀ (volts)	DDR₅ (%)	E_1/2 (µJ/cm²)	V_r (volts)
Example 1	-580	3.1	0.35	-20
Example 2	-560	3.0	0.40	-24
Example 3	-590	4.0	0.30	-29
Example 4	-570	4.4	0.35	-30
Comparative Example 1	-580	4.1	0.48	-41
Comparative Example 2	-600	5.0	0.45	-45
Comparative Example 3	-600	4.6	0.40	-32
Example 5	-560	3.9	0.35	-20
Comparative Example 4	-550	4.5	0.40	-35
Comparative Example 5	-580	4.7	0.40	-34

Table 2

Characteristics of Photoconductor After Repetition of 2,500 Times
	V₀ (volts)	DDR₅ (%)	E_1/2 (µJ/cm²)	V_r (volts)
Example 1	-570	3.9	0.32	-20
Example 2	-555	4.0	0.38	-23
Example 3	-560	7.0	0.29	-27
Example 4	-570	6.0	0.34	-29
Comparative Example 1	-500	8.9	0.40	-45
Comparative Example 2	-510	9.0	0.40	-47
Comparative Example 3	-500	11.0	0.35	-40
Example 5	-550	4.2	0.31	-20
Comparative Example 4	-500	9.2	0.35	-30
Comparative Example 5	-520	98.0	0.35	-29

Table 3

Initial Characteristics of Photoconductor
	V₀ (volts)	DDR₅ (%)	E_1/2 (lux·sec)	V_r (volts)
Example 6	-560	3.0	1.4	-20
Example 7	-570	4.1	1.3	-25
Example 8	-585	4.0	1.1	-18
Example 9	-570	3.0	1.2	-20
Comparative Example 6	-560	4.6	1.5	-25
Comparative Example 7	-570	4.7	1.6	-25
Comparative Example 8	-570	5.0	1.6	-30

Table 4

Characteristics of Photoconductor After Repetition of 2,500 Times
	V₀ (volts)	DDR₅ (%)	E_1/2 (µJ/cm²)	V_r (volts)
Example 6	-550	3.9	1.1	-20
Example 7	-560	4.6	1.0	-27
Example 8	-570	4.5	0.9	-20
Example 9	-560	3.2	1.1	-20
Comparative Example 6	-470	8.0	1.3	-35
Comparative Example 7	-490	8.7	1.5	-38
Comparative Example 8	-550	9.6	1.8	-50

The results shown in Tables 1 and 3 revealed that as compared with the corresponding photoconductors of Comparative Examples 1 to 8, the photoconductors of Examples 1 to 9 each had a small surface potential attenuation ratio and was stable, had sufficient sensitivity and low residual potential, thus showing superior initial characteristics. Comparing the results shown in Tables 1 and 3 with those shown in Tables 2 and 4, respectively, it can be seen that the photoconductors of Examples 1 to 9 were more stable than the corresponding photoconductors of Comparative Examples 1 to 8 because the photoconductors of the invention exhibited less variation of characteristics after repeated charging and exposure over the comparative photoconductors. Thus the effect of the use of the polyether ketone represented by general formula (I) above is evident.

From the photoconductors as mentioned above, those of Examples 1 and 6 and Comparative Examples 1 and 6 were selected. The photoconductors of Example 1 and Comparative Example 1 were each attached to an aluminum pipe having a diameter of 8 cm and a length of 40 cm, and then the aluminum pipes were fitted in a commercially available printer (LL-NIP, trade name for a product of Nippon Electric Corporation). On the other hand, the photoconductors of Example 6 and Comparative Example 6 were each attached onto an aluminum pipe having a diameter of 8 cm and a length of 34 cm, and the aluminum pipes were fitted in a commercially available copier (EP-490Z, trade name for a product by Minolta Camera Co., Ltd.). The printer and the copier were subjected to durability or plate wear test by repeating image outputting (printing or reproducing images) until 150,000 sheets of A4-size paper under the conditions of normal temperature (23°C)/normal humidity (relative humidity of 60 %), low temperature (7°C)/low humidity (relative humidity of 50 %), and high temperature (35°C)/high humidity (relative humidity of 80 %), respectively, with measuring the surface potential in the dark, Vd (volts), and the surface potential at illuminance, Vi (volts), of each photoconductor and evaluating the quality of the resulting images, both after initial run and after 150,000 runs. Results on the photoconductors fitted in the printer are shown in Table 5, and results on the photoconductors fitted to the copier are shown in Table 6.

Table 5

En-viron-ment	Test Item	Example 1		Comparative Example 1
		Initial	Final	Initial	Final
N/N¹)	V_d (volts)	-750	-730	-780	-750
	V_i (volts)	-170	-130	-250	-230
	Image	Good	Good	Good	Good
L/L²)	V_d (volts)	-750	-720	-780	-650
	V_i (volts)	-200	-170	-200	-350
	Image	Good	Good	Good	Poor (Fog)
H/H³)	V_d (volts)	-710	-710	-700	-500
	V_i (volts)	0	0	-200	-150
	Image	Good	Good	Good	Poor (Fog)

Notes: 1) Normal temperature (23°C)/normal humidity (relative humidity of 60 %)
2) Low temperature (7°C) /low humidity (relative humidity of 50 %)
3) High temperature (35°C)/high humidity (relative humidity of 80 %)

Table 6

En-viron-ment	Test Item	Example 6		Comparative Example 6
		Initial	Final	Initial	Final
N/N¹)	V_d (volts)	-400	-380	-400	-380
	V_i (volts)	-85	-78	-50	-80
	Image	Good	Good	Good	Good
L/L²)	V_d (volts)	-400	-390	-400	-380
	V_i (volts)	-90	-85	-70	-200
	Image	Good	Good	Good	Poor (Fog)
H/H³)	V_d (volts)	-390	-380	-420	-400
	V_i (volts)	-85	-80	-40	-190
	Image	Good	Good	Good	Poor (Fog)

Notes: 1) Normal temperature (23°C)/normal humidity (relative humidity of 60 %)
2) Low temperature (7°C)/low humidity (relative humidity of 50 %)
3) High temperature (35°C)/high humidity (relative humidity of 80 %)

From the results shown in Table 5, it can be seen that the photoconductor of Example 1 tended to showed a slight increase in V_i but gave rise to good images both after initial run and after repeated runs under the low temperature/low humidity conditions while it showed a very low V_i but no variation in characteristics, giving good images both after initial run and after repeated runs under the high temperature/high humidity conditions. On the other hand, the photoconductor of Comaparative Example 1 showed a higher V_i than the photoconductor of Example 1 but still gave a good image after initial run, showing less variation in characteristics due to repeated runs so that good images were obtained after repeated runs under the normal temperature/normal humidity conditions while it showed considerable variation in characteristics so that good images were not obtained both under the low temperature/low humidity conditions and under the high temperature/high humidity conditions.
From the results shown in Table 6, it can be seen that the photoconductor of Example 6 had good characteristics under the normal temperature/normal humidity conditions, the low temperature/low humidity conditions, and the high temperature/high humidity conditions, respectively, and showed less variation in characteristics after repeated image outputting to give good images after repeated runs. On the contrary, the photoconductor of Comparative Example 6 showed a drastic variation in V_i after repeated image outputting under the low temperature/low humidity conditions and under the high temperature/high humidity conditions, thus failing to give good images.
As mentioned above, photoconductors which suffer from less variation in characteristics upon change of the environment and having excellent durabilities can be obtained by the use of the polyether ketone represented by general formula (I) above as the binder resin in the charge generating layer.
The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the intention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention.

Claims

A photoconductor for electrophotography characterized by comprising:
a substrate; and
a photosensitive layer formed on the substrate and including a charge generating layer and a charge transporting layer,
wherein said charge generating layer contains an organic pigment as a charge generating substance and a binder resin as a binder, said binder resin being represented by general formula (I):
wherein X is a group selected from the class consisting of:
m is 0 or 1; and n is a positive integer.
A photoconductor as claimed in claim 1, characterized in that said positive integer satisfying:
10 ≦ n ≦ 5,000.
A photoconductor as claimed in claim 1, characterized in that said binder resin is represented by the following formula:
A photoconductor as claimed in claim 1, characterized in that said binder resin is represented by the following formula:
A photoconductor as claimed in claim 1, characterized in that said binder resin is represented by the following formula:
A photoconductor as claimed in claim 1, characterized in that said binder resin is represented by the following formula:
A photoconductor as claimed in claim 1, characterized in that said binder resin is represented by the following formula:
A photoconductor as claimed in claim 1, characterized in that said binder resin is represented by the following formula:
A photoconductor as claimed in claim 1, characterized in that said organic pigment is an azo pigment.
A photoconductor as claimed in claim 9, characterized in that said azo pigment is a disazo pigment represented by general formula (II):
wherein R₁ is a halogen atom, an alkyl group, or an alkoxy group; R₂ is an alkyl group which is unsubstituted or substituted with a substituent; R₃ is a hydrogen atom, a cyano group, a carbamoyl group, a carboxyl group, an ester group, an acyl group; and R₄ is a hydrogen atom, a halogen atom, a nitro group, an alkyl group, or an alkoxy group.
A photoconductor as claimed in claim 10, characterized in that said binder resin is one selected from the group consisting of:
A photoconductor as claimed in claim 1, characterized in that said organic pigment is a polycyclic quinone compound.
A photoconductor as claimed in claim 1, characterized in that said organic pigment is a phthalocyanine pigment.