DE3852820T2 - Photoreceptor for electrophotography. - Google Patents

Description

Background of the invention

The present invention relates to a photoreceptor for electrophotography, particularly it relates to a high-sensitivity photoreceptor for electrophotography containing an azo compound.

Photoreceptors using inorganic photoconductors such as selenium, cadmium sulfide, zinc oxide and the like have been applied to electrophotography. Recently, however, photoreceptors using organic photoconductors (OPC), or so-called organic photoreceptors, have found applications for PPC and printers due to many advantages of OPC such as: they do not cause a pollution problem, they are easy to manufacture and handle, they can produce high-quality images, and they can be easily formed into photoreceptors in various forms such as drum, film, belt, etc., and the demand for such organic photoreceptors is increasing every year. Organic photoreceptors actually have many advantages over the conventional inorganic photoreceptors, but they are still inferior to the conventional photoreceptors in sensitivity and durability and are therefore currently mainly used only for low-speed devices.

Many attempts have been made to improve the sensitivity and durability of organic photoreceptors.

The first commercially available organic photoreceptor was the one that utilized the sensitizing effect of a charge-transfer complex containing a mixture of polyvinylcarbazole (PVK) and 2,4,7-trinitrofluorenone (TNF), which is an electron-attracting compound.

This initiated the development of many organic photoreceptors of the charge-transfer complex type, but so far there is none that surpasses the PVK-TNF type photoreceptors in terms of performance.

The organic photoreceptors that are currently commonly used in the field are the so-called "function-separated" ones, in which the function of generating the charge carrier and the function of transporting it are performed separately by two different compounds.

The function-separated photoreceptors have advantages that it is possible to combine a compound having high carrier generation efficiency and a compound having high transport efficiency, and also the range of selection of materials having excellent durability is wide, so that a photoreceptor having high sensitivity and excellent durability can be obtained.

There are two types of functionally separated receptors: the layered type in which the carrier-generating material and the carrier-transporting material form separate layers and are laminated, and the single-layer type in which both materials are contained in the same sensitive layer. In both types, the process of generating a carrier in the carrier-generating material upon absorption of light, injecting the generated carrier into the carrier-transporting material, and transporting the carrier between the molecules of the carrier-transporting material proceed in the medium. Therefore, the sensitivity of the photoreceptor depends on the carrier generation efficiency, the injection efficiency, and the transport efficiency, so that a combination of a carrier-generating material with a high carrier generation efficiency and a carrier-transporting material with a high carrier transport efficiency and the compound with a high carrier injection efficiency are selected.

Various types of photoconductive pigments have been developed as a carrier-forming material. In particular, azo pigments have been preferably investigated as a carrier-forming material for PPC because they have high sensitivity and also excellent spectral sensitivity compared with other types of pigments, and some of such azo pigments have been put into practical use.

However, conventional pigments are still unsatisfactory in terms of durability, as they show strong light fatigue or fatigue symptoms due to light irradiation.

The object of the present invention is to provide a photoreceptor improved in sensitivity and durability, both of which are unsatisfactory in conventional organic photoreceptors. In particular, this invention envisages providing an organic photoreceptor which has high sensitivity, is highly resistant to light fatigue, minimizes deterioration of electrostatic properties after repeated use, and has excellent durability.

Regarding the azo pigments used as the carrier material, bis-azo pigments containing a coupling component of the "naphthol AS" type have been studied and reported in many literatures, e.g., Japanese Patent Application Laid-Open (KOKAI) No. 47-37543. However, the azo pigments containing this type of coupling component have defects in that they have a large light fatigue as well as poor stability of electrostatic properties.

As a result of extensive studies on finding azo compounds usable as a carrier-forming material to obtain a photoreceptor for electrophotography having high sensitivity and durability, the present inventors have found that certain specific coupler-asymmetric bis-azo compounds are suitable for the purpose, and have accomplished the present invention based on this finding.

Detailed description of the invention

The present invention relates to a photoreceptor for electrophotography comprising a conductive substrate and a photosensitive layer thereon which contains an azo compound of the formula (I):

A-N=N-D-N=N-B (I)

where:

A is a coupling component derived from the following formula (II):

wherein Q represents a divalent group of an aromatic hydrocarbon which may have one or more substituents, or a divalent group of a heterocyclic ring which may have one or more substituents,

B represents another coupling component having a phenolic hydroxyl group which is different from coupling component A, and wherein

D represents a divalent group, wherein the carbon atoms bonded to the azo groups are SP² carbon atoms forming double bonds, except for a divalent group of the formula:

wherein R is a hydrogen atom, a lower alkyl group, a lower alkoxy group or a halogen atom,

characterized in that

B represents a coupling component derived from a coupler selected from the group consisting of the couplers of the following formulas (IV-a) to (IV-i):

wherein Y₁ and Y₂ independently represent hydrogen atom, halogen atom, an alkyl group which may have a substituent, aryl group, heterocyclic group, alkoxy group, aryloxy group, aralkyloxy group, carboxyl group, alkoxycarbonyl group, aryloxycarbonyl group, substituted or unsubstituted carbamoyl group, substituted or unsubstituted hydrazinecarbonyl group, acyl group or acylamino group:

wherein Y₃ represents a hydrogen atom, halogen atom, an alkyl group which may have a substituent, aryl group, heterocyclic group, alkoxy group, aryloxy group, aralalkyloxy group, carboxyl group, alkoxycarbonyl group, aryloxycarbonyl group or acyl group, and Z represents a divalent group which forms an aromatic hydrocarbon ring or heterocyclic ring by condensing with the benzene ring:

wherein R₁ and R₂ independently represent hydrogen atom, lower alkyl group which may have a substituent, aryl group or heterocyclic group, and wherein R₁ and R₂ may be bonded to each other to form a ring, and Z has the same meaning as defined with reference to the formula (IV-b);

wherein R₁, R₂ and Z are as defined above with reference to formula (IV-c);

wherein R₃ and R₄ independently represent a hydrogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, an aryl group, a heterocyclic group, a vinyl group which may have a substituent or a butadienyl group which may have a substituent, and R₃ and R₄ may be bonded to each other to form a ring, and Z is as defined above with reference to the formula (IV-b);

wherein R₁ and R₃ have the same meaning as defined above with reference to formulas (IV-c) and (IV-e);

wherein R₁ and Z have the same meaning as defined above with reference to formulas (IV-c) and (IV-b);

wherein R₅ represents an alkyl group which may have a substituent, alkenyl group which may have a substituent, alkynyl group which may have a substituent or aryl group;

wherein R₆, R₇, R₈ and R₆ independently represent a hydrogen atom, halogen atom, an alkyl group which may have a substituent, a vinyl group which may have a substituent, a substituted amino group or aryl group, and R₆ may represent, in addition to the above, -R₁₀, wherein R₁₀ represents an alkyl group which may have a substituent, an aryl group, a heterocyclic group, a vinyl group which may have a substituent, an amino group which may have a substituent or an alkoxy group which may have a substituent.

The azo compounds of the present invention are described in detail below.

In the formula (I) shown above, A and B bonded to the azo groups represent the coupling components which are different from each other. A represents a coupling component derived from the formula (II) bonded to an azo group by means of a coupling reaction with a diazonium salt. In the formula (II), Q represents a divalent group of an aromatic hydrocarbon having one or more substituents or a divalent group of a heterocyclic ring which may have one or more substituents.

Typical examples of the divalent group of aromatic hydrocarbon are divalent groups of monocyclic aromatic hydrocarbons such as o-phenylene group, and divalent groups of condensed polycyclic aromatic hydrocarbons such as o-naphthylene group, 1,8-naphthylene group, 1,2-anthraquinonylene group and 9,10-phenanthrylene group.

Examples of the divalent group of the heterocyclic ring are: 3,4-pyrazolediyl group, 2,3-pyridinediyl group, 3,4-pyridinediyl group, 4,5-pyrimidinediyl group, 6,7-indazolediyl group, 5,6-benzimidazolediyl group and 5,6-quinolinediyl group.

In the present invention, these divalent groups of the aromatic hydrocarbons and heterocyclic rings may have one or more substituents. Examples of such substituents are alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl and n-hexyl; trifluoromethyl group; alkoxy group such as methoxy, ethoxy, propoxy and butoxy; hydroxyl group; nitro group; cyano group; amino group; substituted amino groups such as dimethylamino, diethylamino and dibenzylamino groups; halogen atoms such as fluorine, chlorine, bromine and iodine; carboxyl group; alkoxycarbonyl groups such as ethoxycarbonyl; carbamoyl group; acyl groups such as acetyl and benzoyl; aryloxy groups such as phenoxy; arylalkoxy groups such as benzyloxy; and aryloxycarbonyl groups such as phenyloxycarbonyl. Among these groups alkyl groups, alkoxy groups, the nitro group, halogen atoms, hydroxyl groups and the carbamoyl group are preferred. Among these, the methyl group, methoxy group, nitro group, chlorine atom and hydroxyl group are particularly preferred.

B represents a coupling component having a phenolic hydroxyl group different from A.

"Phenolic hydroxyl group" means a hydroxyl group substituted on an aromatic hydrocarbon ring. An aliphatic hydrocarbon ring or a heterocyclic ring may be further condensed on the aromatic hydrocarbon ring.

Examples of the substituents in the above formulas (IV-a) to (IV-i) of the coupling component B are shown below.

Examples of the halogen atom are: fluorine atom, chlorine atom, bromine atom and iodine atom. Examples of the alkyl group which may have a substituent are: methyl, ethyl, n-propyl, n-butyl, isobutyl, tert-butyl, n-hexyl, n-octyl, benzyl, p-methylbenzyl, p-chlorobenzyl, 2-phenylethyl, 1-naphthylmethyl, 2-naphthylmethyl, allyl, 2-hydroxyethyl, 2-methoxyethyl, 3-morpholinopropyl, 2-diethylaminoethyl and 3-carbazolylmethyl. Among these, the lower alkyl groups are the alkyl groups having 1 to 6 carbon atoms.

Examples of the aryl group are aromatic hydrocarbon groups such as phenyl, naphthyl, anthryl, pyrenyl, phenantryl, anthrachinoryl, acenaphthyl, fluorenyl, biphenylyl, p-terphenylyl and p-styrylphenyryl. As substituents thereof, the following can be mentioned: alkyl groups such as methyl, ethyl and butyl; halogen atoms such as fluorine, chlorine, bromine and iodine; alkoxy groups such as methoxy, ethoxy and butoxy; aryloxy groups such as phenoxy; hydroxyl group; nitro group; cyano group; amino group; substituted amino groups such as dimethylamino, diethyl-substituted amino groups such as dimethylamino, diethylamino and dibenzylamino group; carboxyl group; alkoxycarbonyl groups such as ethoxycarbonyl; aryloxycarbonyl groups such as phenyloxycarbonyl; Acyloxy groups such as acetoxy and benzoyloxy; acyl groups such as acetyl and benzoyl; substituted aminocarbonyl groups such as carbamoyl, dimethylaminocarbonyl and phenylaminocarbonyl; and arylalkoxy groups such as benzyloxy and phenetyloxy.

Examples of the heterocyclic group are furyl, thienyl, thiazolyl, indolyl, pyrrolyl, carbazolyl, pyridyl, morpholino, quinolyl, imidazolyl, oxazolyl, triazolyl, piperidyl, benzoxazolyl, benzimidazolyl, benzthiazolyl, acridyl, xanthenyl, phenazinyl, phenothiazinyl and coumarinyl.

These heterocyclic groups can have the same substituents as the above-mentioned aryl groups.

Methoxy and ethoxy can be mentioned as examples of the alkoxy group, phenoxy, p-chlorophenoxy, p-methylphenoxy and 1-naphthoxy as examples of the aryloxy group, and benzyloxy and phenethyloxy as examples of the aralkyloxy group.

Methoxycarbonyl and ethoxycarbonyl can be mentioned as examples of the alkoxycarbonyl group, and phenoxycarbonyl and 1-naphthoxycarbonyl as examples of the aryloxycarbonyl group.

Z represents a divalent group forming an aromatic hydrocarbon ring or a heterocyclic ring such as a naphthalene ring, anthrazine ring, carbazole ring, benzocarbazole ring or dibenzofuran ring condensed with a benzene ring.

Examples of the groups represented by R₁ and R₂ which are bonded together to form a ring are cyclohexylidene, indenylidene, fluorenylidene and pentamethylene.

Examples of the alkenyl group are allyl, 3-butenyl and cinnamyl.

The structural formulas of examples of the couplers represented by the above-described formulas (II) and (IV-a) to (IV-i) are shown in Tables 1 and 2 below. Table 1 (Examples of A) No. Structural formula No. Structural formula No. Structural formula Table 2 (Examples of B) No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula No. Structural formula

D in the formula (I) represents a divalent group, wherein the carbon atoms bonded to the azo groups are SP² carbon atoms forming double bonds. Such divalent groups include those derived from aromatic hydrocarbon ring or aromatic heterocyclic ring; from aromatic hydrocarbon rings; aromatic heterocyclic rings and/or by direct bonding or condensation to form a condensed ring; and compounds formed by combining aromatic hydrocarbons, aromatic heterocyclic compounds or alicyclic hydrocarbons through a bonding group. As typical examples of such divalent groups, those derived from benzene, naphthalene, anthraquinone, pyrene, fluorenone, anthraquinone, phenanthrene, biphenylene, triphenylene, perylene, etc. as divalent groups of aromatic hydrocarbon rings, and those derived from N-ethylcarbazole, acridine, xanthone, phenazine, dibenzothiophene, dibenzofuran, etc. as divalent groups of aromatic heterocyclic rings can be mentioned.

Some examples of the directly bonded divalent groups of aromatic hydrocarbons or aromatic heterocyclic rings or the divalent groups of condensed rings are listed in Table 3 below. Table 3 No. Bivalent group No. Bivalent group

Examples of the bonding groups are: -O-, -S-, -S-S-, -SO-, -SO₂-, -SO₂NH-, -CH₂-, -NH-, -CO-, ,-CO-CO-, -CO₂-, -CONH-, -CH=CH-, -CH= , -CH=CH-CH=CH-, -N=N-, -CH=N-N=CH-, -NH-NH-, -CH=N-, -CONH-NH- and -NHCONH-.

Examples of the hydrocarbon ring and the heterocyclic ring are: benzene, naphthalene, acenaphthine, anthracene, pyrene, fluorene, fluorenone, phenanthrene, naphthoquinone, anthraquinone, cyclohexane, cyclohexanone, piperadine, pyrrole, furan, thiophene, oxazole, thiazole, pyrazole, pyrazoline, imidazole, imidazolidine, oxadiazole, thiadiazole, triazole, pyridine, indole, quinoline, carbazole, xanthene, coumarin, xanthone and phenothiazine. D was obtained by combining these hydrocarbon or heterocyclic rings with said bonding groups. These hydrocarbon rings and heterocyclic rings may have a substituent.

Some of the examples of D are listed in Table 4 below. Table 4 No. Bivalent group No. Bivalent group No. Bivalent group No. Bivalent group No. Bivalent group No. Bivalent group

The azo compounds according to this invention can be prepared by various methods such as those mentioned below.

In one process, one of the amino groups in a diamine of formula (V):

H₂N-D-NH₂ (V)

wherein D has the same meaning as with respect to formula (I),

protected with a protecting group or converted into a nitro group to bring the compound into a state not susceptible to a diazotization reaction, and the other amino group alone is subjected to a diazotization reaction in a usual manner, followed by a coupling reaction, followed by a coupling reaction with a coupler to synthesize a monoazo compound, after which the protecting group of the remaining amino group is removed or the nitro group is reduced to restore the original form of the amino group, followed by a diazotization reaction and a coupling reaction with a coupler different from that first used, thereby producing an azo compound of the formula (I).

In another process, a tetrazonium salt of formula (III):

X⁻N₂⁺-D-N₂⁺X⁻ (III)

with a mixture of a coupler of formula (II) and a different coupler to obtain an azo compound of formula (I):

A-N=N-D-N=N-B (I)

to produce.

It is possible to use azo compounds prepared by any possible method, but the first method described has the disadvantages that many reaction steps are involved and that the cost of preparing the compound is high. The second method is the same as the conventional method except that different types of couplers are used instead of using a single coupler, and it is advantageous over the first method in that it allows the target compound to be prepared more easily.

In the second method, however, since the reaction is carried out by mixing the couplers, it may easily happen that an azo compound having the same coupler (the compound of formula (VI) or (VII) shown below) could be prepared as well as an azo compound of formula (I) having different couplers.

A-N=N-D-N=N-B (I)

A-N=N-D-N=N-A (VI)

B-N=N-D-N=N-B (VII)

There is no problem if the proportion of the compound of formula (VI) or (VII) mixed in the product is small, but if the proportion of the compound (VI) or (VII) is high, the product will exhibit properties of the compound (VI) or (VII) rather than properties of the azo compound (I) of the invention, so that when using the second method, it becomes necessary to select the reaction conditions so that the proportion of the azo compound (I) is higher than that of the compound (VI) or (VII) as much as possible.

The studies on this matter by the present inventors revealed that the coupling reaction takes a different course depending on the molecular structure of the coupler, and an azo compound represented by formula (I) of the invention can be synthesized with higher purity by suitably selecting the reaction conditions such as the mixing ratio of the couplers.

Therefore, the azo compounds of this invention can be easily synthesized by the second method described above.

The synthesis procedure is described in more detail below.

An azo compound of formula (I):

A-N=N-D-N=N-B (I)

can be synthesized by a tetrazonium salt of formula (III):

X⁻N₂⁺-D-N₂⁺X⁻ (III)

and a mixture of couplers A-H and B-H are subjected to a coupling reaction in a known manner. In this reaction, water and/or an organic solvent such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, methanol, ethanol, isopropanol or the like is/are preferably used as a reaction solvent. The reaction is carried out in the presence of a base at a temperature below 30°C for a period of about 30 minutes to 10 hours.

Two types of couplers are mixed in equimolar amounts, or, if the couplers differ in reactivity, the coupler with lower reactivity is used in excess amount over the other coupler. It is usually preferred to carry out the reaction using the coupler with higher reactivity in a ratio of 1 to 1.5 moles to 1 mole of tetrazonium salt.

The couplers used in the invention can be sensitized by a known method.

The coupler of formula (II-a) or (II-b) can be obtained by a process which comprises heating a hydroxynaphthalic anhydride (VIII) and a diamine (IX) in an organic solvent such as acetic acid to effect dehydration condensation according to the following reaction scheme A (see Japanese Patent Publication No. 61-30265). Reaction Scheme A

The coupler synthesized by the above method is obtained as a mixture of isomers of formulas (II-a) and (II-b). In the present invention, both of these isomers can be used, but the isomers prepared from the same starting materials (the same hydroxynaphthalic anhydride (VIII) and the same diamine (IX)) in the reaction scheme A are regarded as the same couplers. Usually, the isomers prepared by the reaction are not separated and subjected to the coupling reaction in the form of a mixture.

The photoreceptor for electrophotography according to the invention has a photosensitive layer containing at least one of the azo compounds represented by formula (I). Various types of sensitive layers are known, and any of these sensitive layers can be used for the photoreceptor for electrophotography of the invention. The following types of photosensitive layer are usually used:

(1) photosensitive layer consisting of an azo compound;

(2) photosensitive layer containing an azo compound dispersed in a binder;

(3) photosensitive layer comprising an azo compound dispersed in a known charge transport material;

(4) A laminated photosensitive layer comprising a photosensitive layer of at least one of (1) to (3) serving as a charge generating layer and a charge transport layer containing a known charge carrier transport material laminated thereon.

The azo compounds of formula (I) generate a carrier with extremely high efficiency in light absorption. The generated carrier can be transported by the azo compound acting as a medium, but it is preferable to transport the carrier using a known carrier transport material.

In this regard, it is particularly preferable to construct a layered photoreceptor in which an azo compound of the invention is dispersed in a binder to form a charge generating layer and a charge transporting layer containing a known charge carrier transporting material is laminated thereon, or a single layer type photoreceptor in which a known charge carrier transporting material is added to the azo compound dispersed layer.

The azo compounds of the formula (I) according to the invention have a high carrier generation efficiency and a high carrier injection efficiency into the carrier transport material, and they have excellent characteristics as a carrier generation material for the layered or single-layered function-separated photoreceptor.

The carrier transport material used in combination with an azo compound of this invention is generally classified into two types: electron transport material and hole transport material. These two types of carrier transport material can be used, either singly or in combination, for the photoreceptor of the invention. As the electron transport material, there can be mentioned electron acceptor compounds having an electron acceptor group such as nitro group, cyano group, ester group, etc., the typical examples of such electron acceptor compounds are nitrated fluorenones such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitrofluorenone and tetracyanoquinodimethane. As the hole transport material, there can be mentioned organic photoconductive electron donor compounds, e.g. heterocyclic compounds such as carbazole, indole, imidazole, oxazole, thiazole, oxadiazole, pyrazole, pyrazoline, thiadiazole, benzoxyazole, benzothiazole and naphthothiazole, diarylalkane derivatives such as diphenylmethane, triarylalkane derivatives such as triphenylmethane, triarylamine derivatives such as triphenylamine, phenylenediamine derivatives, N-phenylcarbazole derivatives, diarylethylene derivatives such as stilbene, and hydrazone compounds. Particularly preferred are compounds having a strong electron donor characteristic, such as compounds having a substituted amino group such as a dialkylamino or diphenylamino group, an electron donor group such as an alkoxy or alkyl group, or an aromatic cyclic group substituted with the electron donor group. It is also possible to use the polymers having a group derived from the compounds in the main or side chain, such as polyvinylcarbazole, polyglycidylcarbazole, polyvinylpyrene, polyvinylphenylanthracene, polyvinylacridine and pyrene-formaldehyde resin. The most preferred are hydrazone compounds of the following formula (X):

wherein Ar¹ represents an aromatic hydrocarbon group which may bear a substituent, such as phenyl, naphthyl, anthryl, pyrenyl and styryl, or a heterocyclic group such as carbazoryl; R¹ and R² independently represent an alkyl group such as methyl and ethyl, an aryl group such as phenyl and naphthyl, or an aralkyl group such as benzyl, but at least one of R¹ and R² is an aryl group; l is a number of 1 or 2.

The photoreceptor for electrophotography according to the invention is characterized in that it has a sensitive layer containing an azo compound synthesized according to the invention on a conductive substrate, but the photoreceptor of the invention may also have an intermediate layer such as an adhesive layer or blocking layer, a protective layer or other layers for improving properties such as electrical or mechanical properties. As the conductive substrate, any of the known types used in conventional photoreceptors for electrophotography can be used, e.g., metal drums or foils made of metals such as aluminum, copper, etc., laminates of foils of such metals, and vacuum-deposited articles of such metals. It is also possible to use plastic films, plastic drums, paper, etc. which have been subjected to a conductive treatment by coating conductive materials such as metal powder, carbon black, copper iodide, conductive polymer, high molecular electrolyte or the like with a suitable binder; conductive plastic sheets and drums containing a conductive material such as metal powder, carbon black, carbon fiber, etc.; and plastic film having a layer of a conductive metal oxide such as tin oxide, indium oxide or the like on the surface.

The sensitive layer containing an azo compound according to the invention can be prepared by the conventional methods.

For example, a photoreceptor for electrophotography having a sensitive layer of the above-mentioned type (1) can be prepared by coating a solution obtained by dissolving or dispersing an azo compound of the formula (I) in a suitable solvent on a conductive substrate and drying it to form a sensitive layer having a thickness of several µm to several tens of µm. As the solvent used for this coating solution, there can be used basic solvents capable of dissolving bis-azo compounds such as butylamine and ethylamine; ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene and xylene; aprotic polar solvents such as N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone and dimethyl sulfoxide; alcohols such as methanol, ethanol and isopropanol; Esters such as ethyl acetate, methyl formate and methyl cellulose acetate; chlorinated hydrocarbons such as dichloroethane and chloroform, and other such substances which can disperse azo compounds. When solvents which disperse an azo compound are used, it is necessary to break the azo compound into fine particles of a size of not more than 5 µm, preferably not more than 1 µm, more preferably not more than 0.5 µm.

When a binder is dissolved in the coating solution used to form a sensitive layer of the above-mentioned type (1), it is possible to produce a photoreceptor for electrophotography having a sensitive layer of the type (2).

As binders, polymers or copolymers of vinyl compounds such as styrene, vinyl acetate, acrylic esters, methacrylic esters, vinyl alcohol and ethyl vinyl ether, phenoxy resins, polysulphone, polyvinyl acetal, polycarbonate, polyester, polyamide, polyurethane, cellulose ester, cellulose ether, epoxy resin, silicon resin and the like can be used.

The mixing ratio of the binder polymer to the azo compound of the invention is not particularly defined, but the binder polymer is preferably used in an amount of 5 to 500 parts by weight, more preferably 20 to 300 parts by weight, per 100 parts by weight of the azo compound.

The coating solution may contain, in addition to the said materials, a dispersion stabilizer, an agent for improving the coating properties and other additives for improving the quality, such as a dye, electron-attracting compounds, etc.

When a carrier transport material is dissolved in the coating solution used for forming a sensitive layer of the above-mentioned type (1), a single-layer photoreceptor having a separate function can be prepared. As the carrier transport material, any of those mentioned above can be used. It is preferable to use a binder polymer, except when polymeric carrier transport material such as polyvinylcarbazole and polyglycidylcarbazole is used, which itself has film-forming properties and can be used as a binder.

Any of the above mentioned polymers can be used as a binder polymer.

In this case, such a binder polymer is used in an amount of usually 10 to 1,000 parts by weight, preferably 30 to 500 parts by weight, per 10 parts by weight of azo compound. The charge carrier transport material is used in an amount of 5 to 1,000 parts by weight, preferably 20 to 500 parts by weight, per 10 parts by weight of azo compound. When a charge carrier transport material is used which itself is used as a binder Such a charge carrier transport material is used in an amount of usually 3 to 100 parts by weight per 1 part by weight of azo compound.

In this case, it is possible to use another binder polymer or other binder polymers to improve the quality of the sensitive layer such as adhesiveness, flexibility, etc. The thickness of the single layer type sensitive layer is usually 5 to 50 µm, preferably 10 to 30 µm.

When an azo compound-containing sensitive layer of the above-mentioned type (1) to (3) is used as a charge generation layer and a charge transport layer containing a charge carrier transport material as mentioned above is laminated thereon, a layered function-separated photoreceptor of the type (4) can be obtained. In this case, the thickness of the charge generation layer is in the range of 0.05 to 5 µm, preferably 0.1 to 2 µm.

Two or more different types of carrier transport material may be used in admixture. When the carrier transport material is a high molecular compound having film-forming properties, a binder polymer need not be used, but a binder polymer may be mixed for improving flexibility or for other purposes. When the carrier transport material is a low molecular compound, a binder polymer must be used to form a film. As the binder polymer, those mentioned above may be used. The amount of such a binder polymer in this case is in the range of 50 to 3,000 parts by weight, preferably 70 to 1,000 parts by weight, per 100 parts by weight of the carrier transport material.

The charge transport layer may contain other various types of additives for improving the product performance or for increasing the mechanical strength, durability, etc. of the coating film. Such additives include electron accepting compounds, coloring material, stabilizers such as UV absorbers and antioxidants, agents for improving the coating properties, plasticizers, crosslinking agents, etc.

Examples of the electron acceptor compounds are quinones such as chloranil, 2,3-dichloro-1,4-naphthoquinone, 2-methylanthraquinone, 1-nitroanthraquinone, 1-chloro-5-nitroanthraquinone, 2-chloroanthraquinone and phenanthrenequinone; aldehydes such as 4-nitrobenzaldehyde, ketones such as 9-benzoylanthracene, indandione, 3,5-dinitrobenzophenone and 3,3',5,5'-tetranitrobenzophenone; acid anhydrides such as phthalic anhydride and 4-chloronaphthalic anhydride; cyano compounds such as tetracyanoethylene, terephthalmalononitrile, 4-nitrobenzalmalononitrile, 4-benzoyloxybenzalmalononitrile and 4-(p-nitrobenzoyloxy)benzalmalononitrile; and phthalides such as 3-benzalphthalide, 3-(α-cyano-p-nitrobenzal)phthalide and 3-(α-cyano-p-nitrobenzal)-4,5,6,7-tetrachlorophthalide.

The order of laminating the charge generation layer and the charge transport layer is optional, but usually the charge transport layer is laminated on the charge generation layer because the charge generation layer is thin and easily damaged mechanically. The thickness of the charge transport layer is 5 to 50 µm, preferably 10 to 30 µm.

The photoreceptor for electrophotography containing a diazo compound according to the invention has high sensitivity and also has excellent color sensitivity. In particular, it is minimized in light fatigue so that when it is used repeatedly, little change occurs in sensitivity, charge acceptance and residual potential, and it has high stability and particularly excellent durability. The photoreceptor of the invention is not only suitable for high-speed PPC, but can also be advantageously used as a photoreceptor for printers such as laser printers, liquid crystal switch printers, LED printers, etc., where particularly high stability in performance characteristics and particularly high reliability are required.

The present invention will be described in more detail below with reference to Examples and Reference Example, but the scope of the present invention is not limited to these Examples. In the following description of Examples and Reference Example, all "parts" are parts by weight unless otherwise specified.

Short explanation of the drawings

Figs. 1 to 4 are absorption spectra of the azo compounds obtained in Preparation Example 1.

Fig. 5 is an absorption spectrum of the compound obtained in Preparation Example 2.

Fig. 6 is an absorption spectrum of the azo compound obtained in Preparation Example 3.

Fig. 7 is a graph showing the spectral sensitivity of the photoreceptor obtained in Example 36.

Fig. 8 is a graph showing the spectral sensitivity of a commercially available photoreceptor determined for comparison with Example 36.

Reference example

In a mixed solvent of 30 parts of acetic acid and 150 parts of nitrobenzene, 13.8 parts of 3-hydroxyphthalic anhydride (manufactured by Tokyo Kasei Kogyo KK) and 9.2 parts of o-phenylenediamine (manufactured by Tokyo Kasei Kogyo KK) were dissolved and reacted with stirring at the boiling point of acetic acid for 2 hours. The reaction mixture was cooled to room temperature, and the precipitated crystals were filtered off, washed well with methanol and dried. The obtained crystals were yellow and feathery and were not melted at temperatures below 320 °C. Elemental analysis and IR absorption spectroscopy of the crystals showed that they consisted of 2-hydroxy- and 5-hydroxy-7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-one.

Yield: 17.8 parts.

Analysis; calculated for C₁₈H₁₀O₂N₂:

calculated: C, 75.54%; H, 3.53%; N, 9.78%.

found: C, 75.50%; H, 3.49%; N, 9.72%.

Manufacturing example 1

In 825 parts of dimethyl sulfoxide were dissolved 2.43 parts of 2-hydroxy- and 5-hydroxy-7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-one (coupler No. A-1) and 2.24 parts of naphthol AS (coupler No. B-12). To this solution kept at 20 to 23°C was added a solution prepared by dissolving 2.92 parts of tetrazonium borofluoride obtained by diazotizing 2,5-bis-(p-aminophenyl)-1,3,4-oxadiazole. To the resulting solution was added a solution of 5 parts of sodium acetate and 15 parts of water with stirring, and the mixed solution was stirred for 3 hours. The precipitate formed was filtered off, washed successively with dimethyl sulfoxide, dilute acetic acid, water, methanol and tetrahydrofuran in the order given, and then dried. The yield was 1.74 parts (32.5%). An IR absorption spectrum of this azo compound is shown in Fig. 1.

Analysis; calculated for C₄�9H₂�9N�9C�5:

calculated: C, 71.44%; H, 3.55%; N, 15.30%.

found: C, 71.43%; H, 3.69%; N, 15.11%.

The following formula (P-1) was used as the structural formula of the azo compound for the calculation:

The elemental analysis values found were in good agreement with the calculated values of the structural formula (P-1). In this synthesis reaction, a good agreement of the elemental analysis values was also found, even when two different biazo compounds (P- 2 and P-3), formed from separate reactions of coupler types, were mixed in equimolar amounts.

(P-2 shows only one of the three different isomers formed by the reaction.)

To distinguish these two cases, the absorption spectra of the sulfuric acid solutions of the azo compounds were measured (Fig. 2-4).

Fig. 2 shows the absorption spectra of the respective azo compounds in a sulfuric acid solution. It can be seen that the absorption of the synthesized azo compound (A) shows a different spectrum from the azo compounds P-2 and P-3 (B shows the absorption spectrum of P-2 and C the absorption spectrum of P-3).

To confirm whether spectrum A is a combined version of the spectra of P-2 and P-3, spectra P-2 and P-3 were combined (absorption spectrum B) to determine the spectral curve closest to spectrum A using the least squares calculation (Fig. 3).

The results of Fig. 3 show that no good agreement was obtained.

To determine the accuracy of the combination of the spectral curves, the absorption spectrum (spectrum A) obtained for a mixture of the azo compounds of P-2 (absorption spectrum C) and P-3 (absorption spectrum D) was compared with the result of combining the absorption spectra of P-2 and P-3 (absorption spectrum B) (Fig. 4). In this case, a good agreement was obtained. This shows that the azo compound obtained from the synthesis is not a mixture of P-2 and P-3, but has its own structure. Therefore, and due to the fact that this azo compound shows a spectrum different from the combined spectrum of P-2 and P-3, conceivable from the results of elemental analysis, it was confirmed that the synthesized azo compound has the structure P-1.

Manufacturing example 2

In 825 parts of dimethyl sulfoxide, 4.86 parts of coupler A-1 and 2.24 parts of coupler B-12 were dissolved. To this solution, a solution obtained by dissolving 3.8 parts of tetrazonium borohydrofluoride obtained from 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole in 55 parts of dimethyl sulfoxide was added, and the mixed solution was subjected to a coupling reaction and other treatments in the same manner as in Preparation Example 1 to obtain an azo compound.

Yield: 4.08 parts (59.0%).

Analysis; calculated for C₄�9H₂�9N�9O�5:

calculated: C, 71.44%; H, 3.55%; N, 15.30%.

found: C, 71.55%; H, 3.66%; N, 15.15%.

An absorption spectrum of a sulfuric acid solution of this compound is shown in Fig. 5, and the mixing ratio of the two types of couplers was 1:1 (mol) in Preparation Example 1 and 2:1 in Preparation Example 2, that is, in this example, the coupling reaction was carried out by using twice the amount of Coupler A-1 as compared with Coupler B-12, However, both elemental analysis data and the absorption spectrum agreed with those of the compound of structural formula P-1. Thus, an azo compound of structure P-1 was obtained.

Manufacturing example 3

The procedure of Preparation Example 1 was followed except that 2.65 parts of Naphthol AS-TR (Coupler No. B-1) was used to obtain 2.5 parts of an azo compound.

An IR absorption spectrum of this compound is shown in Fig. 6.

The elemental analysis data were in good agreement with the calculated data obtained assuming that the structure of the azo compound was of formula P-4 shown below.

Analysis; calculated for C₅₀₀H₃₀₀N₄O₅Cl:

calculated: C, 68.85%; H, 3.47%; N, 14.45%; Cl, 4.06%.

found: C, 68.94%; H, 3.57%; N, 14.16%; Cl, 3.53%.

example 1

One part of the azo compound synthesized in Preparation Example 1 and one part of polyvinyl butyral resin (S-Lec B, manufactured by Sekisui Chemical Co., Ltd.) were ground by a sand mill and dispersed in 100 parts of tetrahydrofuran. The dispersion was coated on a 75 µm-thick polyester film on which aluminum was deposited so that the coating thickness after drying was 0.4 g/m², and the coating was dried to form a charge generation layer.

On this charge generation layer, a solution of 90 parts of N-methyl-3-carbazolecarbaldehyde diphenyl hydrazone and 100 parts of polycarbonate resin (NOVALEX 7030A, manufactured by Mitsubishi Kasei Corporation) in 1,000 parts of tetrahydrofuran was coated so that the coating thickness after drying was 13 µm, and the coating was dried to form a charge transport layer. Thus, a two-layer photoreceptor for electrophotography was obtained.

To determine the sensitivity of this photoreceptor, its half-value fall-off exposure (E½) was determined.

The half-life decay exposure was determined in the following manner using an electrostatic paper analyzer (model SP-428, manufactured by Kawaguchi Electric Works): First, the photoreceptor was charged by a -5.3 KV corona charge in a dark place and then exposed to a white light of 5 lux, and the exposure amount of light required to reduce the surface potential from -450 V to -225 V was determined.

The half-value decay exposure (E½) of the photoreceptor determined in this way was 1.2 lux s. The surface potential (residual potential) after sufficient exposure (after a 50 lux s exposure) was -1 V.

To investigate the durability of this photoreceptor, it was subjected to 2,000 repetitions of charging and exposure, and the changes in surface potential (Vo) after corona charging, sensitivity (E½) and residual potential (Vr) were determined. The exposure intensity was determined by applying 50 lux s of white light.

The sensitivity (E½) was determined by determining the half-decay exposure required to reduce the surface potential from -400 V to -200 V.

The results of the measurements are shown in Table 5. Table 5 At the beginning After 2,000 cycles

The results in Table 5 clearly show that the photoreceptor has very stable properties.

Examples 2 to 21

Photoreceptors were prepared following the same procedure as in Example 1, except that instead of using the azo compound of Example 1, the azo compounds of the following structure were used:

in which couplers A and B are those of the structures A-H and B-H shown in Tables 1 and 2, and the sensitivities of the resulting photoreceptors were determined.

The results of the measurements are shown in Table 6. Table 6 Coupler structure example

Examples 22 to 29

Photoreceptors were prepared by following the same procedure as in Example 1 except that the azo compounds of the following formula (XII) were used in place of the azo compound used in Example 1, and the sensitivities of these photoreceptors were determined.

The results are shown in Table 7. Table 7 Example

Examples 30 to 35

Photoreceptors were prepared by following the same procedure as in Example 1 except that 90 parts of 1-pyrene-carbaldehyde-diphenylhydrazone was used instead of N-methyl-3-carbazole-carbaldehyde-diphenylhydrazone as the charge transport composition, and the sensitivities of these photoreceptors were determined.

The sensitivities of the photoreceptors in other examples were also determined by changing the hydrazone compound in the charge transport layer as indicated above.

The results are shown in Table 8. Table 8 Example Example No. with the same charge generation layer

Example 36

A photoreceptor was prepared by following the same procedure as in Example 30 except that the thickness of the charge transport layer was changed to 20 µm. The sensitivity (E½) of this photoreceptor was 0.67 lux s.

The spectral sensitivity of this photoreceptor was measured using a monochromator (Shimadzu Bausch & Lomb High Intensity Grating Monochromator, by Shimadzu Corp.) as the light source of the electrostatic paper analyzer used in Example 1. The light intensity was determined by means of an optical light amplifier, Model 66XLA (manufactured by Photodyne Inc.).

The determined spectral sensitivity is shown in Fig. 7.

In the graph of Fig. 7, the abscissa shows the wavelength and the ordinate shows the sensitivity (expressed by the reciprocal of E½). For comparison, the spectral sensitivity of an organic photoreceptor for PPC (SF-750, manufactured by Sharp Corp.) is shown in Fig. 8.

As shown in Fig. 7, the photoreceptor of the invention has a high sensitivity in the wavelength range of 500 to 600 nm and is suitable for PPC.

It is also noted that the peak value of the spectral sensitivity is as high as 6.35 cm2/uJ, which is about 6 times higher than the spectral sensitivity of the practically used organic photoreceptor listed here for comparison.

Then, a photoreceptor formed by coating an aluminum drum with the same sensitive layer as the photoreceptor described above was connected to a PPC (SF-8200 from Sharp Corp.) and subjected to a durability test. After optimizing the exposure intensity in accordance with the sensitivity of the photoreceptor, the charge-exposure repeat test was conducted. The surface potential and the residual potential after corona charging are shown in Table 9. Table 9 At the beginning After 120,000 cycles

The results in Table 9 show that this photoreceptor shows practically no change in the surface potential and residual potential and maintains its high sensitivity even after 120,000 cycles of charge-exposure repetition, which demonstrates the extremely high sensitivity, stability and excellent durability of the photoreceptor of the present invention.

When this photoreceptor was used to make 120,000 copies in a continuous manner, no reduction in image density nor any fogging was observed, and clear image copies were obtained.

Claims (2)

1. Photoreceptor for electrophotography, comprising a conductive substrate and a photosensitive layer thereon which contains an azo compound of formula (I) A-N=N-D-N=N-B (I) where: A is a coupling component derived from the following formula (II): wherein Q represents a divalent group derived from an aromatic hydrocarbon which may have one or more substituents or a divalent group derived from a heterocyclic compound which may have one or more substituents, B is a coupling component with a phenolic hydroxyl group, which is different from the coupling component A, and D is a divalent group, where the carbon atoms bonded to the azo groups are SP² carbon atoms forming double bonds, except for a divalent group of the formula: wherein R is a hydrogen atom, a lower alkyl group, lower alkoxy group or a halogen atom, characterized in that B represents a coupling component derived from a coupler selected from the group consisting of the couplers of the following formulas (IV-a) to (IV-i): wherein Y₁ and Y₂ independently represent hydrogen atom, halogen atom, alkyl group which may have a substituent, aryl group, heterocyclic group, alkoxy group, aryloxy group, aralkyloxy group, carboxyl group, alkoxycarbonyl group, aryloxycarbonyl group, substituted or unsubstituted carbamoyl group, substituted or unsubstituted hydrazinocarbonyl group, acyl group or acylamino group; wherein Y₃ represents hydrogen atom, halogen atom, alkyl group which may have a substituent, aryl group, heterocyclic group, alkoxy group, aryloxy group, aralalkyloxy group, carboxyl group, alkoxycarbonyl group, aryloxycarbonyl group or acyl group, and Z represents a divalent group which forms an aromatic hydrocarbon ring or heterocyclic ring by condensing with the benzene ring; wherein R₁ and R₂ independently represent hydrogen atom, lower alkyl group which may have a substituent, aryl group or heterocyclic group, and wherein R₁ and R₂ may be bonded to each other to form a ring, and Z has the same meaning as defined with reference to the formula (IV-b); wherein R₁, R₂ and Z are as defined above with reference to formula (IV-c); wherein R₃ and R₄ independently represent hydrogen atom, alkyl group which may have a substituent, alkenyl group which may have a substituent, alkynyl group which may have a substituent, aryl group, heterocyclic group, vinyl group which may have a substituent or butadienyl group which may have a substituent, and R₃ and R₄ may be bonded to each other to form a ring, and Z is as defined above with reference to formula (IV-b); wherein R₁ and R₃ have the same meaning as defined above with reference to formulas (IV-c) and (IV-e); wherein R₁ and Z have the same meaning as defined above with reference to formulas (IV-c) and (IV-b); wherein R₅ represents an alkyl group which may have a substituent, alkenyl group which may have a substituent, alkynyl group which may have a substituent or aryl group; wherein R₆, R₇, R₈ and R₆ independently represent hydrogen atom, halogen atom, an alkyl group which may have a substituent, vinyl group which may have a substituent, substituted amino group or aryl group, and R₆ may represent, in addition to the above - -R₁₀, wherein R₁₀ represents an alkyl group which may have a substituent, aryl group, heterocyclic group, vinyl group which may have a substituent, amino group which may have a substituent, or alkoxy group which may have a substituent. 2. Photoreceptor according to claim 1, wherein the divalent group D is a divalent group derived from a compound selected from the group consisting of aromatic hydrocarbons, aromatic heterocyclic compounds, directly bonded compounds of aromatic hydrocarbons and/or aromatic heterocyclic compounds, condensed compounds of aromatic hydrocarbons and/or aromatic heterocyclic compounds, and compounds formed by combining aromatic hydrocarbons, alicyclic hydrocarbons or heterocyclic compounds through a bonding group.