EP0564655A1

EP0564655A1 - Electrophotographic photoreceptor

Info

Publication number: EP0564655A1
Application number: EP92920384A
Authority: EP
Inventors: Akihiko Idemitsu Petrochemical Co. Kurahashi
Original assignee: Idemitsu Petrochemical Co Ltd
Current assignee: Idemitsu Petrochemical Co Ltd
Priority date: 1991-09-30
Filing date: 1992-09-29
Publication date: 1993-10-13
Also published as: JPH0588382A; WO1993007540A1; EP0564655A4

Abstract

An electrophotographic photoreceptor having a photoconductive layer formed on a conductive substrate and coated with a protective layer prepared from a composition comprising a reactive (di)pentaerythritol compound, a reactive phosphazene compound and a reactive siloxane compound. The photoreceptor is excellent in abrasion resistance, surface smoothness, heat resistance, moisture resistance and so forth.

Description

TECHNICAL FIELD

The present invention relates to an electrophotographic photoreceptor. More particularly it relates to an electrophotographic photoreceptor which comprises coating the surface thereof with a protective layer made of a specific composition or incorporating said composition into an outermost photoconductive layer, having the markedly improved abrasion resistance, surface slip properties, heat resistance, moisture resistance and the like.

BACKGROUND ART

Generally, in Carlson system electrophotographic printers wherein electrophotographic photoreceptors are incorporated, for example copying machine, laser beam printer and light-emitter diode printer, the surface of an electrophotographic photoreceptor is charged with a corona discharge at first. Necessary parts of the charged photoreceptor are exposed and the surface charge of the exposed parts is selectively destaticized to form an electrostatic latent image. Then, a developer, i.e. a toner is adhered to said electrostatic latent image. The developer is transferred to and fixed in a paper to provide an electrophotographic picture.
A conventional electrophotographic photoreceptor comprises a single-ply photoconductive layer formed on the surface of a conductive substrate. The electrophotographic photoreceptor is required to have various properties: (1) it should be charged at a desired potential in a dark place (the charging properties), (2) it should not be accompanied by a leakage surface potential in a dark place (the ability to retain the charge), (3) its surface potential is quickly attenuated when a light is irradiated (the optical responsivity) and the like. Thus, in recent years, studies have been organized in an attempt to meet these requirements, resulting in an electrophotographic photoreceptor having a photoconductive layer made of a plurality of plies to carry out the function of charge generation in one ply and that of charge transfer (carrying) in another.
The printing speed of these such apparatuses has for years been made unusually faster, whether the photoconductive layers are single-ply or multi-ply. There has been a tendency that the apparatuses are miniaturized and that the processing time per print is made shorter (to deal with charging, exposing, developing and destaticizing). Thus, the photoconductive layers have come to take a high mechanical load. This mechanical load is generated as the electrophotographic photoreceptors come into contact with a blade or a brush of a cleaning device operated to scavenge the developer, the toner and a small amount of toner adhered to the surface of papers and electrophotographic photoreceptors. The electrophotographic photoreceptors bear higher mechanical loads, the greater is the speed to repeat the process of charging, exposing, developing and destaticizing. The electrophotographic photoreceptors wear out on the surface quickly, resulting in a reduction of their useful life.
Now, it is expected that the printing speed will be made even faster and therefore that a greater number of copies will be printed per sheet of electrophotographic photoreceptor. Accordingly it is necessary to improve the abrasion resistance of the electrophotographic photoreceptors to keep them useful as long as possible.
In fact, it has been proposed to provide an abrasion resistant protective layer as the outermost layer of the electrophotographic photoreceptors. For example, a silicone resin (Japanese Patent Application Laid-Open No. 75460/1987), an epoxy resin (Japanese Patent Application Laid-Open No. 103741/1978), a melamine resin (Japanese Patent Application Laid-Open No. 217052/1986), a fluororesin (Japanese Patent Application Laid-Open No. 115944/1985), an acrylic resin (Japanese Patent Application Laid-Open No. 3538/1979) and the like have been proposed as the resin for use in the formation of the protective layer.
However, it has been found that these known techniques are not capable of providing a sufficiently high abrasion resistance as desired but are liable to degrade the electrophotographic properties, attenuate the concentration or develop the fogging. Furthermore, the performance of the electrophotographic photoreceptors is susceptible to changes in environment, particularly atmospheric moisture, often blamed for an untidy printing or a defective image such as fogging.
Other than those mentioned above, several polycarbonates or curable resins have been proposed as the bonding resin for use in the formation of the protective layer in Japanese Patent Application Laid Open No. 89764/1982. But it has been found that they are not satisfactory to the full extent, with respect to the adhesiveness, the strength, the surface hardness and the like.
On the other hand, the Japanese Patent Application Laid-Open Nos. 30856/1988 and 56658/1988 have proposed el ectrophotographic photoreceptors comprising a protective layer combining a polycarbonate, a polyester or the like with a fluorine-containing resin powder. According to these proposals, the electrophotographic photoreceptors have the much improved slip properties but are poorer in the film strength and the surface hardness.

DISCLOSURE OF THE INVENTION

Under the circumstances, the present inventors have made intensive studies with a view to overcoming said shortcomings of the related arts. As a result, it has been found that the objectives can be achieved by forming a protective layer on an electrophotographic photoreceptor with a composition comprising (1) a reactive pentaerythritol compound or a reactive dipentaerythritol compound, (2) a reactive phosphazene compound and (3) a reactive siloxane compound or incorporating said composition into an outermost layer of said electrophotographic photoreceptor instead of forming said protective layer. The present invention has been completed on the basis of this finding.
Accordingly, the present invention provides an electrophotographic photoreceptor wherein a photoconductive layer formed on a conductive substrate is coated with a protective layer comprising a composition containing 100 parts by weight of a mixture of (1) 90 to 40 mole% of a reactive pentaerythritol compound or a reactive dipentaerythritol compound and (2) 10 to 60 mole% of a reactive phosphazene compound; and (3) 0.1 to 50 parts by weight of a reactive siloxane compound. The present invention also provides an electrophotographic photoreceptor wherein said photoconductive layer (particularly an outermost layer thereof) contains said composition instead of forming said protective layer.

BEST MODE FOR CARRYING OUT THE INVENTION

In an electrophotographic photoreceptor of the present invention, a protective layer is prepared from said composition or the surface of the other protective layer is coated with said composition on the surface of a photoconductive layer. If such a protective layer is not intended, said composition is incorporated into the photoconductive layer (particularly, the outermost ply thereof).
As stated above, the composition to be used in the present invention comprises (1) a reactive pentaerythritol compound or a reactive dipentaerythritol compound, (2) a reactive phosphazene compound and (3) a reactive siloxane compound. Meanwhile, this composition is a cured product resulting from the mutual reaction among the reactive (di)pentaerythritol compound (1), the reactive phosphazene compound (2) and the reactive siloxane compound (3) or the reaction between these three and the other compounds. To put it another way, said composition of the present invention is a composition containing a group derived from the reactive (di)pentaerythritol (1), a group derived from the reactive phosphazene compound (2) and a group derived from the reactive siloxane compound (3), or particularly a cured product thereof.
The reactive pentaerythritol compound (1) is a compound represented by the following general formula:

wherein R¹ to R⁴ are each -H, -OH, -R (R is an alkyl group having 1 to 10 carbon atoms), -OR (R is as defined above) or an organic group containing -OCCH=CH₂ or -OCC(CH₃)=CH₂, provided that at least one of R¹ to R⁴ is the organic group containing - OCCH=CH₂ or -OCC(CH₃)=CH₂. Preferred among them is a compound wherein two or more, particularly three or more of R¹ to R⁴ are the organic group containing -OCCH=CH₂ or -OCC(CH₃)=CH₂, since the compound is highly reactive.
Moreover, the reactive dipentaerythritol compound is a compound represented by the following general formula:

wherein R⁵ to R¹⁰ are each -H, -OH, -R (R is an alkyl group having 1 to 10 carbon atoms), -OR (R is as defined above) or an organic group containing -OCCH=CH₂ or -OCC(CH₃) =CH₂, provided that at least one of R⁵ to R¹⁰ is the organic group containing - OCCH=CH₂ or -OCC(CH₃)=CH₂. Preferred among them is a compound wherein two or more, particularly three or more of R⁵ to R¹⁰ are the organic group containing -OCCH=CH₂ or -OCC(CH₃)=CH₂, since the compound is highly reactive.
Representative examples of the organic group containing - OCCH=CH₂ or -OCC(CH₃)=CH₂ include
- OOCCH=CH₂, -OOCC(CH₃)=CH₂,

These reactive pentaerythritol compounds or reactive dipentaerythritol compounds can be used singly or in their mixture. They may partially include a (di)pentaerythritol compound without having a reactive group to such an extent that hardness of said composition remains adversely unaffected. Ordinarily, 90% or more of them are the reactive (di) pentaerythritol.
Next, the reactive phosphazene compound (2) is preferably a compound having a structure represented by the general formula (I):

[ NP(A)_a(B)_b ]_n (I)

wherein A is a curable group; B is a non-curing group; a and b are each a real number simultaneously satisfying the relations a>b, b≧0 and $a+b=2$
; and n is an integer of 3 or more. The general formula (I) does not represent a single compound but is expressed in terms of a mean value of several compounds. Therefore, a and b representing the number of two different groups are each not limited to an integer but may as well be a real number including a decimal. n is 3 or more, ordinarily in a range of 3 to 18, preferably 3 to 4 and each of these numbers is not limited to an integer but may as well be a real number including a decimal. There are many different phosphazene compounds having the repeating unit represented by the general formula (I), depending upon the kind of substituent groups.
In the general formula (I), A is a curable group. The curable group is a functional group which is cured due to the reaction in response to the irradiation of an ultraviolet ray, a visible ray, an electron beam, the use of a chemically curable agent, the application of heat or the like. Ordinarily it has a reactive double bond. Various groups having the reactive double bond can be used in the present invention and their examples are a functional group containing an acryloyl group (-OCCH=CH₂), a methacryloyl group (-OCC(CH₃)=CH₂) or an ally] group (-CH₂CH=CH₂).
Examples of said functional group containing the acryloyl group or the methacryloyl group are an acryloyloxy group, a methacryloyloxy group and further a group represented by the general formula (II):

wherein R¹³ is a hydrogen atom or a methyl group; R¹⁴ is an alkylene group having 1 to 12 (preferably 1 to 5) carbon atoms (including a branched chain alkylene group).
Specific examples of the group represented by the general formula (II) include a 2-hydroxyethyl methacrylate; a 2-hydroxypropyl methacrylate; a 3-hydroxypropyl methacrylate; a 2-hydroxybutyl methacrylate; a 3-hydroxybutyl methacrylate; a 4-hydroxybutyl methacrylate; a 5-hydroxypentyl methacrylate; a 6-hydroxy-3-methylhexyl methacrylate; a 5-hydroxyhexyl methacrylate; a 3-hydroxy-2-t-butylpropyl methacrylate; a 3-hydroxy-2,2-dimethylhexyl methacrylate; a 3-hydroxy-2-methyl-2-ethylpropyl methacrylate and a residue obtained by removing hydrogen atoms from the hydroxyl groups of the methacrylates such as 12-hydroxydodecyl methacrylate; as well as a 2-hydroxyethyl acrylate; a 2-hydroxypropyl acrylate; a 3-hydroxypropyl acrylate; a 2-hydroxybutyl acrylate; a 3-hydroxybutyl acrylate; a 4-hydroxybutyl acrylate; a 5-hydroxypentyl acrylate; a 6-hydroxy-3-methylhexyl acrylate; a 5-hydroxyhexyl acrylate; a 3-hydroxy-2-t-butylpropyl acrylate; a 3-hydroxy-2,2-dimethylhexyl acrylate; a 3-hydroxy-2-methyl-2-ethylpropyl acrylate and a residue obtained by removing hydrogen atoms from the hydroxyl groups of the acrylates such as 12-hydroxydodecyl acrylate. Preferred among them are the residue of 2-hydroxyethyl methacrylate and that of 2-hydoxyethyl acrylate.
Besides those represented by the general formula (II), examples of the functional group containing the acryloyl group or the methacryloyl group include a functional group represented by the general formula (III):

wherein R¹³ and R¹⁴ are as defined above, i.e. a residue obtained by removing hydrogen atoms from the hydroxyl groups of a hydroxyalkyl-substituted acrylamide or a hydroxyalkyl-substituted methacrylamide, and further a functional group represented by the general formula (IV):

wherein R¹³ is as defined above, i.e. a residue obtained by removing a hydrogen atom from an amino group of an acrylamide or a methacrylamide.
Furthermore, the functional group containing the allyl group is, for example an allyloxy group (CH₂=CH-CH₂O-), in addition to the allyl group per se. Other than this allyloxy group, their examples include functional groups represented by the general formulae (V) to (VII):

wherein R¹³ is as defined above; R¹⁵ and R¹⁶ are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, i.e. a residue obtained by removing the hydrogen atoms from an only hydroxyl group of an allyl compound. Specific examples of the functional groups represented by the general formulae (V) to (VII) include residues obtained by removing hydrogen atoms from the hydroxyl group of the allyl compounds such as:

On the other hand, B of the general formula (I) is not particularly limited but is, for example groups represented by the following general formulae:

R¹⁷M- (VIII)

or

In the general formula (VIII), M is an oxygen atom, a sulfur atom or an imino group; R¹⁷ is an alkyl group having 1 to 18 carbon atoms or a halogenated alkyl group having 1 to 18 carbon atoms. Their specific examples include an alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, and an octyloxy group; a halogen (for example, fluorine, chlorine, bromine and the like)-substituted alkoxy group of the same kind; an alkylthio group such as a methylthio group, an ethylthio group, a propylthio group, a butylthio group, a pentylthio group, a heptylthio group, and an octylthio group; a halogen (for example, fluorine, chlorine, bromine and the like) -substituted alkylthio group of the same kind; an alkylimino group such as a methylimino group, an ethylimino group, a propylimino group, a butylimino group, a pentylimino group, a hexylimino group, a heptylimino group, and an octylimino group; a halogen (for example, fluorine, chlorine, bromine and the like)-substituted alkylimino group of the same kind and the like. In the general formula (IX), M is as defined above; R¹⁸ to R²² are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms or a halogenated alkyl group having 1 to 4 carbon atoms. Specifically, the groups of the general formula (IX) are a phenoxy group, a thiophenyl group, a halogenated phenoxy group (2, 4, 6-tribromophenoxy group, 4-bromophenoxy group, 2-chlorophenoxy group, 2, 4-dichlorophenoxy group and the like) and a halogenated thiophenyl group (4-chlorophenylthio group and the like), as well as a residue obtained by removing hydrogen atoms from an amino group of an aniline or a halogenated aniline (2-chloroaniline, 2, 4-dichloroaniline, 2, 4, 6-tribromoaniline and the like).
In said general formula (I), a and b are each a real number satisfying a relation of $a+b=2$
, preferably additional relations 0<a≦2 and 0≦b<2 to represent a compound having 2 curable groups or more.
Furthermore, the substituent group A is meant to act when a film containing the phosphazene compound of the general formula (I) is cured. The substituent group B is to adjust the physical properties of said cured film, along with the action to control the curing performance thereof. Thus, the various physical properties of the cured film containing this phosphazene compound are determined, depending upon the optional choice of a and b; provided that a phosphazene compound entirely free from the curable group A is not curable and should be excluded as the component to be incorporated into the composition of the present invention. However, a phosphazene compound having a repeating unit represented by the relations a=2 and b=0, i.e. by the general formula (I'):

⁅NP(A)₂⁆_n (I')

can be used as the component of the composition of the present invention.
The phosphazene compounds of the present invention has the repeating units represented by said general formula (I) wherein n is in a range of 3 to 18. Particularly, the phosphazene compounds wherein n is 3 to 4 and a mixture of them are best suitable. The repeating units represented by the general formula (I) may be bonded in the form of a chain. But those bonded in a cyclic form are preferred.
A variety of reactive siloxane compounds (3) can be used in the present invention. Preferred among them are a compound represented by the following general formula:

wherein R¹¹ and R¹² are each an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 12 carbon atoms; Z¹ and Z² are each a hydrogen atom or an organic residue, provided that at least one of Z¹ and Z² is a group containing -OCCH=CH₂ or -OCC(CH₃)=CH₂; and m is a positive integer.
Likewise suitable are compounds represented by the following general formulae:

For convenience's sake, a block copolymer is illustrated by the above general formulae but a random copolymer may as well be used. In these general formulae, k and p are each an integer of 0 to 4000; q is an integer of 10 to 1000; r is an integer of 2 to 100; Y is a group derived from a diisocyanate compound, for example a group derived from a 2, 4-tolylene diisocyanate or a group derived from a methylene diphenyl diisocyanate; X is a (meth)acrylate-containing group, for example groups derived from a 2-hydroxyethyl (meth)acrylate, a pentaerythritolmonohydroxy tri(meth)acrylate and a dipentaerythritolmonohydroxy penta(meth)acrylate; R²³ is a straight chain or branched chain alkyl group or a single bond (wherein O and Si are bonded directly); R²⁴ and R²⁵ are each an alkyl group or phenyl group having 1 to 4 carbon atoms. The reactive siloxane compound either synthesized elsewhere or formed in the reaction system hereof can be used in the present invention.
These reactive siloxane compounds can be used singly or in their mixture. They may partially include a siloxane compound without having the reactive group to such an extent that hardness of said composition remain adversely unaffected. Ordinarily, 90% or more of the compounds are a reactive siloxane compound.
As stated above, the composition of the present invention contains a reactive pentaerythritol compound or a reactive dipentaerythritol compound (1), a reactive phosphazene compound (2) and a reactive siloxane compound (3) as the essential components. These components (1) to (3) are mixed in the composition, as follows: the reactive (di)pentaerythritol compound (1) and the reactive phosphazene compound (2) are mixed at a ratio of 90 to 40 mole% of (1) to 10 to 60 mole% of (2), preferably 80 to 50 mole% of (1) to 20 to 50 mole% of (2), based on the total of these two. Then, the ratio of the reactive siloxane compound (3) is adjusted to 0.1 to 50 parts by weight, preferably 0.5 to 30 parts by weight, based on 100 parts by weight of a total of the reactive (di)pentaerythritol compound (1) and the reactive phosphazene compound (2).
The reactive (di)pentaerythritol compound (1) is effective to provide higher hardness to the protective layer to be formed, contributing to the improvement of the abrasion resistance. If it is mixed too much, the protective layer is cured too fast, liable to develop cracks. It is not unlikely that the so formed protective layer is poor in the release properties when used as the electrophotographic photoreceptor.
The reactive phosphazene compound (2) is effective to prevent these cracks. The reactive siloxane compound (3) acts to improve the slip properties and the release properties effectively. Therefore, the electrophotographic photoreceptor using the composition mixing the components (1) to (3) at said ratio can have a well balanced combination of the abrasion resistance, the slip properties, the release properties, the heat resistance, the moisture resistance and the like.
Various conductive substrates can be used to build the electrophotographic photoreceptor of the present invention if they are electrically conductive and can ground the photoconductive layer. Specific examples of the conductive substrate include an aluminum, an aluminum alloy, a copper, a zinc, a stainless steel, a vanadium, a molybdenum, a chromium, a titanium, a nickel, an indium, a gold, a platinum and the like. Examples of the other conductive substrate include:

(1) a plastic (for example, a polyethylene, a polypropylene, a polyvinyl chloride, a polyethylene terephthalate, an acrylic resin, a polyethylene fluoride and the like) having a film layer formed by the vacuum deposition with one of various metals and compounds (for example, an aluminum, an aluminum alloy, an indium oxide, a tin oxide, an indium oxide alloy, a tin oxide alloy).
(2) a substrate made of a plastic incorporating conductive particles (an aluminum powder, a titanium oxide, a tin oxide, a zinc oxide, a carbon black and the like) along with an appropriate binder or a structure formed by building up a coat on a substrate which is made by using the materials of said conductive substrate.
(3) a plastic or a paper impregnated with conductive particles, or
(4) a plastic having a conductive polymer.

Furthermore, an undercoat layer having the barrier function and the undercoating function (an adhesive layer) may as well be provided on the surface of said substrate. This undercoat layer can be used for the various purposes, e.g. to improve the adhesiveness of the photoconductive layer, to improve the coating properties, to protect the substrate, to cover the defects on the substrate, to improve the properties of injecting the charge from the substrate and to protect the photoconductive layer from the electrical destruction. The undercoat layer is made from a polyvinyl alcohol, a poly-N-vinylimidazole, a polyethylene oxide, an ethyl cellulose, a methyl cellulose, an ethylene acrylate copolymer, a casein, a polyamide, a copolymerized nylon, a glue, a gelatin and the like. The undercoat layers are formed according to the known methods.
The electrophotographic photoreceptor comprises a photoconductive layer formed on a conductive substrate as described above. The photoconductive layer is either single-ply or multi-ply.
A single-ply photoconductive layer is made of a deposited film of Se, Se-Te alloy, Se-As alloy, Se-Sb alloy and Se-Bi alloy or an organic photoreceptor comprising a polyvinyl carbazole and a trinitrofluorene, or an amorphous silicone.
When the organic photoreceptor (photoconductive layer) is formed of the polyvinyl carbazole, the trinitrofluorene and the like, the cured product of said composition (i.e., the composition containing the reactive (di)pentaerythritol compound (1), the reactive phosphazene compound (2) and the reactive siloxane compound (3)) is preferably used as a binder.
When the photoconductive layer is formed of the cured product of this composition, the content of said organic photoreceptor in the photoconductive layer is optionally determined in proportion to the desired photosensitivity. Furthermore, the photoconductive layer made of said composition may be added with a monofunctional monomer or a multifunctional monomer if necessary.
Moreover, this composition can be used in the form of a mixture with a solvent, if necessary. Examples of the solvent to be used herein include organic solvents including ketones such as methylethyl ketone, methylisobutyl ketone and cyclohexanone, an aromatic hydrocarbon such as benzene, toluene and xylene, a halogenated hydrocarbon such as chloroform and methylene chloride, alcohols such as methanol, ethanol, propanol and butanol, ethers such as tetrahydrofuran and dioxane, or cellosolves such as ethylcellosolve and butylcellosolve and the like. These solvents can be used singly or in their two or more mixture.
Preferred among them is a mixed solvent of ketones, alcohols or these two. Particularly, a mixed solvent containing a methylisobutyl ketone or an isopropyl alcohol or a butyl alcohol is more preferred.
Said composition is meant to protect the photoconductive layer in the form of a cured product. The method for curing the composition is selected from the irradiation (photo-setting) of an activation energy ray (visible ray, ultraviolet ray, electron beam, Xray, γ ray and the like), the heat curing, the cold curing and the like. When an organic photoreceptor is used as the photoconductive layer, the composition is preferably cured with an activation energy ray to prevent changes in the properties of the organic substances.
When the composition is subjected to photo-setting, i.e. the method for curing by the use of an ultraviolet ray or a visible ray, it is preferable to add a photopolymerization initiator such as 1-hydroxycyclohexyl phenylketone, dibenzoyl, benzoylmethyl ether, benzoylethyl ether, p-chlorobenzophenone, p-methoxybenzophenone, benzoyl peroxide, di-tert-butyl peroxide, camphorquinone and the like. These photopolymerization initiators can be used singly or in their two or more mixture.
Ordinarily the cure promoter of this kind is used in an amount selected from a range of 0.05 to 10.0 parts by weight, based on 100 parts by weight of the composition.
Furthermore, when the composition is subjected to heat setting, i.e. the method for heat curing or cold curing, it is preferable to use a peroxide-based compound and an amine-based compound singly or in combination as the polymerization initiator. Examples of the peroxide-based compound include a benzoylperoxide; a p-chlorobenzoylperoxde; a 2, 4,-dichlorobenzoylperoxide; a t-butylhydroperoxide; a di-t-butylperoxide; a dicumylperoxide; a t-butylperoxyacetate; a diacetate; a t-butylperoxybenzoate and the like. Examples of the amine-based compound include a N, N-diethanol-p-toluidine; a dimethyl-p-toluidine; a p-toluidine; a methylamine; a t-butylamine; a methylethylamine; a diphenylamine; a 4, 4'-dinitrodiphenylamine; an o-nitroaniline; a p-bromoaniline; a 2, 4, 6-tribromoaniline and the like.
In these such cases, the peroxide-based compound and the amine-based compound are used in a total amount selected from a range of 0.05 to 5.0 parts by weight, based on 100 parts by weight of the composition.
The composition of the present invention is cured to form a photoconductive layer, as follows: at first, a photoconductive layer composition is prepared by mixing said composition, a monofunctional or multifunctional monomer if necessary, said organic photoreceptor, a solvent and a cure initiator. The so prepared composition is coated on the surface of the conductive substrate directly or via the undercoat layer. Then, the coated composition is cured.
The coating is carried out according to known conventional methods such as spinner method, spray method, roll coater method, dipping method and brushing method and if a solvent is used together, it is removed after the coating is over.
Thereafter, said curable composition is cured to form a cured film by means of cold curing or heat curing or by irradiating an ultraviolet ray, an electron beam, an X ray, a γ ray or the like.
The photoconductive layer comprising the composition of the present invention ordinarily has a thickness of 0.01 to 100µm.
Meanwhile, this single-ply photoconductive layer can be formed by using a binder resin other than the cured product of said composition. In such a case, a protective layer comprising the cured product of the composition of the present invention is preferably provided on top of the photoconductive layer.
Next, the multi-ply photoconductive layer is a sectionalized function type photoconductive layer. This multi-ply, sectionalized function type photoconductive layer comprises a charge generation layer and a charge transfer layer (a charge carrying layer). The charge generation layer and the charge transfer layer are laminated one after another on the conductive substrate (i.e. in the order of the substrate, the charge generation layer and the charge transfer layer), but they may be laminated the other way around (i.e. in the order of the substrate, the charge transfer layer and the charge generation layer). Herein, the charge generation layer contains a charge generating substance such as organic or inorganic pigment and a binder resin. This charge generating substance is, for example pigments and coloring matters which are known as the source of electric charge, including those of an azoxybenzene series, a diazo series, a trisazo series, a benzimidazole series, a polycyclic quinoline series, an indigoid series, a quinacridone series, a phthalocyanine series, a perylene series, a perinone series, a cyanine pigment, a (thio)pyrylium salt, a squarylium pigment and the like. Those pigments are illustrated, for example in Japanese Patent Application Laid Open Nos. 37543/1972, 37544/1972, 185453/1972, 18544/1972, 43942/1973, 70538/1973, 1231/1974, 105536/1974, 75214/1975 and 92738/1975. Preferred among them is a pigment of the phthalocyanine series. Particularly preferred among the phthalocyanine pigments is a τ , τ', η or η' type metal-free phthalocyanine pigment described in Japanese Patent Application Laid Open No. 182640/1983 and EP-A-0 92,255. The pigment has high sensitivity even to long wavelengths. Besides the above-mentioned pigments, there can be optionally used a pigment capable of generating a carrier for charge with the irradiation of a light.
Examples of the binder resin include a polycarbonate resin, a polyester resin, an acrylic resin, a polyvinyl formal, a polyvinyl butyral, an epoxy resin and a urethane resin.
The binder resin is mixed in a charge generation layer at a ratio of 5 to 400 parts by weight, preferably 10 to 300 parts by weight, based on 100 parts by weight of the charge generator. If the ratio is less than 5 parts by weight, the adhesiveness between the charge generation layer and the conductive substrate is poor, often causing the charge generation layer to have an uneven film and the picture quality to deteriorate. If it exceeds 400 parts by weight, there is a tendency of a low sensitivity and a high residual potential.
Meanwhile, the charge generation layer may as well be added with an additive such as plasticizer, defoaming agent, liquidity improver, pinhole control agent, coupling agent and antioxidant, if necessary.
The charge generation layer is prepared as follows: at first a dispersant is prepared by dispersing said charge generator and a binder resin and an additive to be added if necessary in a solvent. The so prepared dispersant is coated on the conductive substrate according to dip coating, roller coating, applicator coating, wire wound bar coating and the like.
Examples of said solvent include an acetone; a methyletylketone; a tetrahydrofuran; a toluene; a xylene; a dichloromethane; a 1, 2-dichloroethane; a 1, 1, 2-trichloroethane; a methanol; an isopropylalcohol and the like.
The said charge generation layer has a thickness of 0.001 to 10µm, preferably 0.01 to 5µm. If it is less than 0.001µm, a uniform charge generation layer cannot be obtained. If it exceeds 10µm, the electrifying properties and the like are often poor.
The charge transfer layer (the charge carrying layer) is formed from a charge transferring substance (a charge carrying substance) and a binder resin. Examples of the charge transferring substance include a fluorene; a fluorenone; a 2, 7-dinitro-9-fluorenone; a 3, 7-dinitro-dibenzothiophene-5-oxide; a 1-bromopyrene; a 2-phenylpyrene; a carbazole; a 3-phenylcarbazole; a 2-phenylindole; a 2-phenylnaphthalene; an oxazole; an oxadiazole; an oxatriazole; a triphenylamine; an imidazole; a chrysene;a tetraphene; an acridine; various hydrazones; a styryl compound; a 1, 1-bis(p-diethylaminophenyl) -4, 4-diphenyl-1, 3-butadiene; a 1-phenyl-3-(4-d iethylaminostyryl)-5-(4-diethylaminophenyl) pyrazoline; a 2-phenyl-4-(4-diethylaminophenyl)-5-phenyloxazole; a poly-N-vinylcarbazole; a halogenated poly-N-vinylcarbazole; a polyvinylpyrene; a polyvinylindolequinoxaline; a polyvinylbenzothiophene; a polyvinylanthracene; a polyvinylacridine; a polyvinylpyrazoline and the like. These compounds can be used singly or in their two or more mixture.
The composition of the present invention is suitable as the binder resin in the charge transfer layer just as it is suitable in the single-ply photoconductive layer.
However, the composition of the present invention and the charge transferring substance are mixed at a ratio selected to permit the charge transferring substance to have the content of ordinarily 20 to 80 parts by weight, based on the total amount of these two. Furthermore, the charge transfer layer formed of the cured product of said composition ordinarily has a thickness of 5 to 50µm, preferably 8 to 30µm. If it is less than 5µm, the charging properties often are poor. If it exceeds 50µm, there is a tendency of a low sensitivity and a poor optical responsivity.
The charge transfer layer comprising the composition of the present invention can be formed by repeating the procedure for preparing the single-ply photoconductive layer. The charge transfer layer comprising the composition of the present invention ordinarily has a thickness of 5 to 50µm, preferably 8 to 30µm. If it is less than 5µm, the charging properties often are poor. If it exceeds 50µm, there is a tendency of a low sensitivity and a poor optical responsivity.
When it is intended not to use the composition of the present invention as the binder resin to form the charge transfer layer, it is preferable to use binder resins as described hereunder. On the surface of the charge transfer layer prepared with the binder resins as set forth below, there is preferably provided a protective layer formed of the composition of the present invention (will be described later).
Examples of the binder resin other than the composition of the present invention include a polycarbonate resin, a polyestercarbonate resin, a styrene resin, an acrylic resin, a silicone resin, a polyester resin, a phenoxy resin, a polyarylate resin, a polysulfone resin, a polyetherimide resin, a vinyl acetate-vinyl chloride copolymer resin, a poly-N-vinylcarbazole resin and the like. They can be used singly or in their two or more mixture.
The binder resin is mixed in an amount of ordinarily 20 to 80% by weight, based on the total of the charge transferring substance and the binder resin. If the mixed amount is less than 20% by weight, the optical responsivity is poor. If it exceeds 80% by weight, the durability often is poor.
Meanwhile, this charge transfer layer may as well be added with an additive such as plasticizer, defoaming agent, liquidity improver, pinhole control agent, coupling agent and antioxidant if necessary.
The charge transfer layer is prepared, as follows: at first a dispersant is prepared by dispersing said charge transferring agent and the binder resin and an additive to be added if necessary in a solvent. The so obtained dispersant is coated on top of said charge generation layer according to the dip coating, the roll coating, the applicator coating, the wire wound bar coating and the like.
As the solvent herein, those used to form said charge generation layer can be used.
The said charge transfer layer has ordinarily a thickness of 5 to 50µm, preferably 8 to 30µm. If it is less than 5µm, the charging properties often are poor. If it exceeds 50µm, there is a tendency of a low sensitivity and a poor optical responsivity.
In the present invention, the protective layer is not always necessary but should be situated on the surface of the photoconductive layer when it is needed; provided, however, that the composition of the present invention must be incorporated into the photoconductive layer (particularly the outermost layer thereof), if the protective layer is not provided.
The protective layer can be formed of the cured product of said composition of the present invention. It also can be formed by combining a film of other material and a cured layer of said composition provided on the surface of said film.
The procedure for forming a protective layer from the cured product of said composition will be described in detail below. With respect to this procedure, same as above are the kind and mixed ratio of the components of said composition, or the kind of the monofunctional or multifunctional monomer to be mixed with said composition if necessary, the solvent and the cure initiator and the like. Furthermore, a lubricant such as silicone oil is suitably added to improve the slip properties even more. A further additive can also be added, properly chosen from those which are illustrated with respect to said charge transferring substance and charge transfer layer.
Moreover, when the protective layer is formed from the cured product of the composition of the present invention, a powder of metal or metal oxide can suitably be dispersed in the protective layer. The metal to be dispersed in the protective layer is, for example an aluminum, an aluminum alloy and the like. The metal oxide to be dispersed in the protective layer is, for example a tin dioxide, an antimony dioxide, a zinc oxide, a titanium oxide, a tin oxide, an indium oxide, a bismuth oxide and the like.
Preferably these metal powders and metal oxide powders have a mean particle size of 0.3µm or less. The content of these metals or metal oxides is ordinarily 80% by weight or less, preferably 60% by weight or less. The addition of these metal or metal oxide powders is effective in the destaticization, improving the electrophotographic properties.
Furthermore, a fluorine-containing resin powder or the like is suitably contained as the lubricant in the protective layer formed of the cured product of the composition of the present invention. Specific examples of the fluorine-containing resin powder are powders each comprising an ethylene tetrafluoride, an ethylene trifluoride chloride, a propylene hexafluoride, a vinyl fluoride, a vinylidene fluoride, an ethylene difluoride dichloride, a polymer such as trifluoropropyl methyldichlorosilane or a copolymer thereof, a copolymer resin comprising a vinyl chloride and the like. When the protective layer per se is formed of the cured product of the composition of the present invention, the protective layer can be adjusted to have a thickness of 0.01 to 100µm, preferably 0.5 to 15µm and more preferably 1.5 to 10µm according to the need. If the thickness is less than 0.01µm, there cannot be developed a sufficiently high function as the protective layer, resulting in a low abrasion resistance. On the other hand, if it exceeds 100µm, the sensitivity and optical reponsivity are poor, along with the residual potential at a high side. Furthermore, the protective layer formed of the cured product of said composition may as well be a laminate comprising a plurality of plies.
It also is acceptable that the protective layer of the present invention is a combination of a film made from the other materials and a cured layer of the composition of the present invention which is situated on the surface of said film.
This protective layer will be described in detail below.
The other materials for use in preparing said film are, for example a polyurethane resin, a polycarbonate resin, a polyacrylate resin, a polymethacrylate resin, a polyisodcyanate, a reaction product between a polyisodcyanate and a hydroxyl group-containing polyester or polyether, a reaction product between a polyisocyanate and a hydroxyl group-containing acrylate or epoxy resin, a reaction product between a polyisocyanate and a polyisocyanate prepolymer containing an isocyanate group with a transient masking and the like.
The film can be formed according to the application method, the dipping method, the spraying method, the after-drying method, the curing method and the like. Ordinarily the film has a thickness of 0.5 to 10µm. This film layer may as well contain said metals or metal oxides.
A cured layer to be situated on the surface of the film can be prepared by repeating the procedure for preparing the protective layer per se from the cured product of the composition of the present invention, provided that the cured layer of said composition has a thickness of 0.2 to 10µm, preferably 0.5 to 5µm.
The electrophotographic photoreceptor of the present invention as described above is not particularly limited relative to the form thereof. Usually it takes the form of a drum, however.
The present invention will be described in detail below with reference to the synthesis examples, the examples and the comparative examples.

Synthesis Example 1

Preparation of the Reactive Phosphazene Compound

58.0g (0.167mole) of a hexachlorocyclotriphosphazene (a cyclic compound represented by the general formula (NPCl₂)₃), 50ml of a toluene and 168g (2.0mole) of a pyridine were introduced into a 1 liter flask equipped with a thermometer, a stirrer, a dropping funnel and a condenser, and the resultant mixture was stirred.
Then, 14.3g (1.1mole) of a 2-hydroxyethylmethacrylate was slowly dropped thereon from the dropping funnel. The mixture was heated to 60°C on a hot water bath and the reaction was carried out for 8 hours with stirring. The precipitated crystals were filtered, the solvent was removed from the so obtained filtrate by distilling it under reduced pressure and the residue was dried well to obtain 138g of a yellow liquid substance. The yield was 91%. The so obtained substance was analyzed, with the resultant finding that it was a viscous compound whose chemical name is 1, 1, 3, 3, 5, 5-hexa(methacryloylethylenedioxy) cyclotriphosphazene (a cyclic phosphazene compound represented by the general formula [NP(OC₂H₄O₂CC(CH₃)=CH₂)₂] ₃).

Synthesis Example 2

Preparation of the Reactive Siloxane Compound

50g (18mmole) of a polydimethylsiloxane having a hydroxyl value of 1400 (a terminal alcohol) and 10g (57mmole) of a 2, 4-tolylene diisocyanate (TDI) were introduced into a 500cc flask equipped with a thermometer and a stirrer, and the resultant mixture was reacted at 60°C for 8 hours to obtain a reaction mixture. The so obtained reaction mixture was analyzed with the resultant finding that it contained a polydimethylsiloxane having a TDI bonded to a terminal thereof without having hydroxyl groups.

Synthesis Example 3

Preparation of the Reactive Siloxane Compound

50g (18mmole) of a polydimethylsiloxane having a hydroxyl value of 1400 (a terminal alcohol) and 7g (42mmole) of a hexamethylenediisocyanate (HMDI) were introduced into a 500cc flask equipped with a thermometer and a stirrer, and the resultant mixture was reacted at 60°C for 8 hours to obtain a reaction mixture. The so obtained reaction mixture was analyzed with the resultant finding that it contained a polydimethylsiloxane having a HMDI bonded to a terminal thereof without having hydroxyl groups.

Comparative Example 1

Preparation of the Electrophotographic Photoreceptor

6.0 parts by weight of a polyamide resin (brandname: M995(having a solid content of 100% by weight), supplied by Nippon Rilsan Co., Ltd.) was completely dissolved in 94 parts by weight of a solvent mixing a methanol and a dichloromethane at a ratio of 1:1. The so obtained solution was dip-coated on an aluminum plate having a thickness of 0.1mm. It was dried at 120°C over 40 minutes to form an interlayer having a thickness of 0.2µm.
Then, 2.5 parts by weight of a τ type metal-free phthalocyanine, 5.0 parts by weight of a silicone resin (brandname: KR-255 (having a solid content of 50% by weight), supplied by Shin-Etsu Chemical CO., LTD.) and 92.5 parts by weight of a methylethylketone were mixed to obtain a mixed solution. The mixed solution was introduced into a ball mill (a pot mill supplied by Nippon Kagaku Togyo Co., Ltd.), kneaded and dispersed over 24 hours to obtain a dispersant intended for use in the formation of a charge generation layer. This dispersant was dip-coated on said interlayer and dried at 120°C over 60 minutes and a charge generation layer having a thickness of 0.3µm was formed.
Next, 6.0 parts by weight of a p-diethylaminobenzaldehyde-diphenylhydrazone, 14.0 parts by weight of a polycarbonate resin (viscosity average molecular weight: 27,000, having a solid content of 100% by weight), 50 parts by weight of a dichloromethane and 30 parts by weight of a 1, 1, 2-trichloroethane were mixed and dissolved to obtain a solution intended for use in the formation of a charge transfer layer. This solution was dip-coated on the surface of said charge generation layer. It was dried at 110°C over 60 minutes to form a charge transfer layer having a thickness of 16µm. Thus, a photoreceptor (No. R1) was obtained.
The properties of this photoreceptor were determined according to the methods as set forth below. The results thereof are given in Table 1.

Comparative Example 2

Preparation of the Electrophotographic Photoreceptor

To 10g of a multifunctional acrylate (Kayarad DPHA, supplied by Nippon Kayaku Co., Ltd.), 1g of a photo-initiator (Darocur 1173, supplied by Merck Japan Limited), 5g of a conductive powder (a titanium oxide), 20g of a methylethylketone and 30g of an isobutanol were added to obtain a coating composition.
The coating composition was applied to the surface of the charge transfer layer of said photoreceptor (No. R1) and the solvent was removed, followed by the irradiation of a UV ray (for 30 seconds). Thus a protective layer having a thickness of 4µm was formed.
A photoreceptor having this protective layer was analyzed by repeating the procedure of said Comparative Example 1 and the results are given in Table 1.

(1) Evaluation of the Electrophotographic Properties

The following evaluation was carried out with an electrostatic recording chart test apparatus (SP-428, supplied by Kawaguchi Electric Co., Ltd.) using a rectangular photoreceptor sample having a size of 60×70mm.
The sample was rotated at a rate of 1000rpm, a corona of - 5kV was irradiated to the sample for 10 seconds and the attenuation of the potential was calculated from an equation of Vk=V₃₀/V₀, wherein V₀ is the initial potential, V_k is the attenuation of the potential and V₃₀ is the potential 30 seconds after the irradiation. Thereafter, 10lux of a white light was irradiated to the sample. E₅₀ is the half exposure representing a quantity of light responsible for reducing the potential to 1/2 and V_R is the residual potential after the white light is irradiated for 60 seconds.

(2) Durability Test

The durability test was conducted by using the sample which was used in the evaluation of the electrophotographic properties as set forth in (1) above. A sample was charged with a corona discharge (a surface potential: -1,000±100V) and destaticized (a destaticizing light wave length of 500nm, and an exposure of 50mJ/m²) 10,000 times, then the electrophotographic properties were determined and the results thereof were compared with the initial values.

(3) Surface Hardness

A steel wool (#0000) at a load of 500g/cm² was caused to go and come back over the surface of a sample 100 times on a HEIDON surface scanner supplied by Shinto Scientific Co., Ltd. and then the results were analyzed with eye.

(4) Abrasion Test

The abrasion test was conducted by using the sample which was used in the evaluation of the electrophotographic properties as set forth in (1) above and an abrasion test machine supplied by Hitachi Chemical Co., Ltd. A urethane rubber blade having a rubber hardness of 70 (at a load of 200g) was caused to abrade the surface of a sample at a rate of 200 times per minute for 20 minutes and the weight of the so abraded photoreceptor sample was measured.

(5) Release Properties Test

The contact angle of water was obtained by measurement with a contact angle meter CA-D model supplied by Kyowa Surface Chemistry Co., Ltd.

(6) Adhesive Properties

A peel test was conducted by the use of a checkered cellophane tape according to JIS K5400

Example 1

232g (255mmole) of a reactive phosphazene compound obtained in said Synthesis Example 1 (1, 1, 3, 3, 5, 5-hexa(methacryloylethylenedioxy) cyclotriphosphazne), 250g (839mmole) of a pentaerythritol triacrylate and 10g of a reaction mixture obtained in said Synthesis Example 2 were introduced into a 1 liter flask. The resultant mixture was heated over a hot water bath to 60°C and reacted for 24 hours with stirring to obtain a viscous product. This viscous product was found not to contain isocyanate groups. To 10g of this viscous product, 1g of a photo-initiator (Darocur 1173, supplied by Merck Japan Limited), 5g of a conductive powder (a titanium oxide), 20g of a methylethylketone and 30g of an isobutanol were added to obtain a coating composition.
The so obtained coating composition was applied to the surface of the charge transfer layer of said photoreceptor (No. R1), the solvent was removed from the coating composition and an UV ray was irradiated thereto to form a protective layer having a thickness of 4µm. A code No. 1 was assigned to the photoreceptor having this protective layer.
The properties of this photoreceptor No. 1 were evaluated by repeating the procedure of said Comparative Example 1. The results thereof are given in Table 1.

Example 2

232g (255mmole) of a reactive phosphazene compound obtained in said Synthesis Example 1 (1, 1, 3, 3, 5, 5-hexa (methacryloylethylenedioxy) cyclotriphosphazne), 150g (260mmole) of a dipentaerythritol hexaacrylate and 100g (189mmole) of a dipentaerythritol monohydroxypentaacrylate and 50g of a reaction mixture obtained in said Synthesis Example 3 were introduced into a 1 liter flask. The resultant mixture was heated over a hot water bath to 60°C and reacted over 24 hours with stirring to obtain a viscous product. This viscous product was found not to contain NCO groups.
To 10g of the viscous product, 1g of a photo-initiator (Irgacure 907, supplied by Ciba Geigy), 3g of a conductive powder (a titanium oxide), 20g of a methylethylketone and 30g of an isobutanol were added to obtain a coating composition.
A photoreceptor having a protective layer No. 2 was obtained by using this coating composition and repeating the procedure of said Example 1.
The properties of this photoreceptor No. 2 were evaluated by repeating the procedure of said Comparative Example 1. The results thereof are given in Table 1.

INDUSTRIAL APPLICABILITY

As stated above, when the electrophotographic photoreceptor of the present invention has a protective layer, said protective layer is free from peeling and flaws, has a sufficiently high strength though it is made of a thin film and further is not liable to have strains to provide the excellent electrophotographic properties.
Furthermore, when the photoconductive layer is formed by incorporating the composition of the present invention, said photoconductive layer is flaw-free, has a sufficiently high strength though it is made of a thin film and further is not liable to have strains.
Accordingly, the abrasion resistance, the surface slip properties, the heat resistance, the moisture resistance and the like are markedly improved relative to the electrophotographic photoreceptor of the present invention. It has been found highly useful in relevant industrial segments.

Claims

An electrophotographic photoreceptor wherein a photoconductive layer formed on a conductive substrate is coated with a protective layer comprising a composition containing 100 parts by weight of a mixture of (1) 90 to 40 mole% of a reactive pentaerythritol compound or a reactive dipentaerythritol compound and (2) 10 to 60 mole% of a reactive phosphazene compound; and (3) 0.1 to 50 parts by weight of a reactive siloxane compound.
An electrophotographic photoreceptor wherein a photoconductive layer formed on a conductive substrate comprises said composition as set forth in Claim 1.
An electrophotographic photoreceptor wherein a charge generation layer and a charge transfer layer are laminated on a conductive substrate and said protective layer as set forth in Claim 1 is formed as the outermost layer thereof.
The electrophotographic photoreceptor according to Claim 1 wherein the reactive pentaerythritol compound or the reactive dipentaerythritol compound contains at least three organic groups selected from -OCCH=CH₂ and -OCC(CH₃)=CH₂.
The electrophotographic photoreceptor according to Claim 1 wherein the reactive phosphazene compound is represented by the general formula (I):

[ NP(A)_a(B)_b ]_n (I)

wherein A is a curable group; B is a non-curing group; a and b are each a real number simultaneously satisfying the relations a>0, b≧0 and $a+b=2$
; and n is an integer of 3 or more.
The electrophotographic photoreceptor according to Claim 1 wherein the reactive siloxane compound is represented by the general formula:
wherein R¹¹ and R¹² are each an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 12 carbon atoms; Z¹ and Z² are each a hydrogen atom or an organic reside, provided that at least one of them is a group containing -OCCH=CH₂ or - OCC(CH₃)=CH₂; and m is an positive integer.
The electrophotographic photoreceptor according to Claim 1 wherein the photoconductive layer comprises a conductive substrate, a charge generation layer and a charge transfer layer in this order.
The electrophotographic photoreceptor according to Claim 1, wherein the photoconductive layer comprises a conductive substrate, a charge transfer layer and a charge generation layer in this order.