PHOTOCONDUCTIVE RECORDING MATERIAL CONTAINING CROSSLINKED BINDER SYSTEM

Abstract: A photoconductive recording material comprising a support and a charge generating layer (CGL) in contiguous relationship with a charge transporting layer (CTL) containing a p-charge transporting material (p-CTM), wherein the binder of said charge generating layer (CGL) has been made insoluble in methylene chloride by crosslinking, and said binder is composed essentially of at least one epoxy resin (1) as defined herein and/or at least one dialkanolamine-modified epoxy resin linked with at least one polyisocyanate.

Description: DESCRIPTION PHOTOCONDUCTIVE RECORDING MATERIAL CONTAINING CROSSLINKED BINDER SYSTEM The present invention relates to photosensitive recording materials suitable for use in electrophotography. 2. Background of the invention In electrophotography photoconductive materials are used to form a latent electrostatic charge image that is developable with finely divided colouring material, called toner. The developed image can then be permanently affixed to the photoconductive recording material, e.g. a photoconductive zinc oxide-binder layer, or transferred from the photoconductor layer, e.g. a selenium or selenium alloy layer, onto a receptor material, e.g. plain paper and fixed thereon. In electrophotographic copying and printing systems with toner transfer to a receptor material the photoconductive recording material is reusable. In order to permit rapid multiple printing or copying, a photoconductor layer has to be used that rapidly loses its charge on photo—exposure and also rapidly regains its insulating state after the exposure to receive again a sufficiently high electrostatic charge for a next image formation. The failure of a material to return completely to its relatively insulating state prior to succeeding charging/imaging steps is commonly known in the art as "f tigue". The fatigue phenomenon has been used as a guide in the selection of commercially useful photoconductive materials, since the fatigue of the photoconductive layer limits the copying rates achievable. A further important property which determines the suitability of a particular photoconductive material for electrophotographic copying is its photosensitivity, which must be sufficiently high for use in copying apparatuses operating with the fairly low intensity light reflected from the original. Commercial usefulness also requires that the photoconductive layer has a spectral sensitivity that matches the spectral intensity distribution of the light source e.g. a laser or a lamp. This enables, in the case of a white light source, all the colours to be reproduced in balance. Known photoconductive recording materials exist in different configurations with one or more "active" layers coated on a conducting substrate and include optionally an outermost protective layer. By "active" layer is meant a layer that plays a role in the formation of the electrostatic charge image. Such a layer may be the layer responsible for charge carrier generation, charge carrier transport or both. Such layers may have a homogeneous structure or heterogeneous structure. Examples of active layers in said photoconductive recording material having a homogeneous structure are layers made of vacuum- deposited photoconductive selenium, doped silicon, selenium alloys and homogeneous photoconducting polymer coatings, e.g. of poly(vinylcarbazole) or polymeric binder(s) molecularly doped with an electron (negative charge carrier) transporting compound or a hole (positive charge carrier) transporting compound such as particular hydrazones, amines and heteroaromatic compounds sensitized by a dissolved dye, so that in said layers both charge carrier generation and charge carrier transport take place. Examples of active layers in said photoconductive recording material having a heterogeneous structure are layers of one or more photosensitive organic or inorganic charge generating pigment particles dispersed in a polymer binder or polymer binder mixture in the presence optionally of (a) molecularly dispersed charge transport compound(s) , so that the recording layer may exhibit only charge carrier generation properties or both charge carrier generation and charge transport properties. According to an embodiment that may offer photoconductive recording materials with particularly low fatigue a charge generating and charge transporting layer are combined in contiguous relationship. Layers which serve only for the charge transport of charge generated in an adjacent charge generating layer are e.g. plasma-deposited inorganic layers, photoconducting polymer layers, e.g. on the basis of poly(N-vinylcarbazole) or layers made of low molecular weight organic compounds molecularly distributed in a polymer binder or binder mixture. Useful charge carrier generating pigments (CGM's) belong to one of the following classes : a) perylimides, e.g. C.I. 71130 (C.I. = Colour Index) described in DBP 2 237 539; b) polynuclear quinones, e.g. anthanthrones such as C.I. 59 300 described in DBP 2 237 678; c) quinacridones, e.g. C.I. 46 500 described in DBP 2 237 679; d) naphthalene 1, ,5,8-tetracarboxylic acid derived pigments including the perinones, e.g. Orange GR, C.I. 71 105 described in DBP 2 239 923; e) tetrabenzoporphyrins and tetranaphthaloporphyrins, e.g. U2~ phthalocyanine in X-crystal form (X-I^Pc) described in US-P 3,357,989, metal phthaloσyanines, e.g. CuPc C.I. 74 160 described in DBP 2 239 924, indium phthalocyanine described in US-P 4,713,312 and tetrabenzoporphyrins described in EP 428,214A; and naphthalocyanines having siloxy groups bonded to the central metal silicon described in published EP—A 243,205; f) indigo- and thioindigo dyes, e.g. Pigment Red 88, C.I. 73 312 described in DBP 2 237 680; g) benzothioxanthene derivatives as described e.g. in Deutsches Auslegungsschrift (DAS) 2 355 075; h) perylene 3,4, 9,10-tetracarboxylic acid -derived pigments including condensation products with o-diamines as described e.g. in DAS 2 314 051; i) polyazo-pigments including bisazo-, trisazo- and tetrakisazo- pigments, e.g. Chlordiane Blue C.I. 21 180 described in DAS 2 635 887, trisazo-pigments, e.g. as described in US-P 4,990 421 and bisazo-pigments described in Deutsches Offenlegungsschrift (DOS) 2 919 791, DOS 3 026 653 and DOS 3 032 117; j) squarylium dyes as described e.g. in DAS 2 401 220; k) polymethine dyes; 1) dyes containing quinazoline groups, e.g. as described in GB-P 1,416,602 according to the following general formula : in which R and R 1 are either identical or different and denote hydrogen, C- -C^ alkyl, alkoxy, halogen, nitro or hydroxyl or together denote a fused aromatic ring system; m) triarylmethane dyes; and n) dyes containing 1, 5— diamino-anthraquinone groups, o) inorganic photoconducting pigments e. g. Se, Se alloys, s2Sβ3, Ti0 2 , ZnO, CdS, etc. Organic charge carrier transporting substances may be either polymeric or non-polymeric materials. Examples of preferred polymeric positive hole charge carrier transporting substances are poly(N-vinylcarbazole) , N-vinylcarbazole copolymers, polyvinyl anthracene and the condensation products of an aldehyde with two or more 1,2-dihydroquinoline molecules as described in US-P 5,043,238. Preferred non-polymeric materials for positive charge transport are : a) hydrazones e.g. a p-diethylaminobenzaldehyde diphenyl hydrazone as described in US-P 4,150,987; and other hydrazones described in US-P 4,423,129; US-P 4,278,747, US-P 4,365,014, EP 448,843 A and EP 452,569 A, e.g. T191 from Takasago b) aromatic amines e.g. N,N'-diphenyl, N,N-bis-m-tolyl benzidine as described in US-P 4,265,990, tris (p-tolyl) mine as described in US P 3,189,730 : 1,3,5-tris (aminophenyl)benzenes as described in US-P 4,923,774 ; 3,5-diarylaniline derivatives as described in EP 534,514 A, and triphenyloxazole derivatives as described in EP 534,005 A ; c) heteroaromatic compounds e.g. N-(p-aminophenyl) carbazoles as described in USP 3,912,509 and dihydroquinoline compounds as described in US-P 3,832,171, US-P 3,830,647, US-P 4,943,502, US- P 5,043,238, EP 452 569A and EP 462 327A e.g. d) triphenylmethane derivatives as described for example in US-P 4,265,990; e) pyrazoline derivatives as described for example in US-P 3,837,851; f) stilbene derivatives as described for example in Japanese Laid Open Patent Application (JL-OP) 198,043/83. The choice of binder for the charge generating layer (CGL) for a given charge generating pigment (CGM) and a given charge transport layer (CTL) has a strong influence on the electro-optical properties of the photoreceptors. One or more of the following phenomena can have a negative influence on the electro-optical properties of the photoconductive recording material : i) interfacial mixing between the CGL and the CTL resulting in CGM-doping of the CTL and CTM-doping of the CGL causing charge trapping; ii) charge trapping in the CGL; iii) poor charge transport in the CGL; iv) poor charge transport blocking properties in the absence of a blocking layer. Interfacial mixing between the CGL and the CTL can be avoided by using a CGL-binder or binders, which is/are insoluble in the solvent used for dissolving the CTL-binders in which CTM's exhibit optimum charge transport properties is limited as is the range of solvents in which efficient CTM' s are soluble. The range of solvents in which both CTL-binders and CTM's are soluble is thus extremely narrow and often limited to chlorohydrocarbons such as methylene chloride. Methylene chloride is an extremely powerful solvent and the range of CGL-binders which is totally insoluble in methylene chloride is extremely limited, unless the CGL-binder is crosslinked in a subsequent hardening process. Hardening is here considered as a treatment which renders the binder of a charge generating layer of the photoconductive recording material insoluble in methylene chloride. 3. Summary of the invention It is an object of the present invention to provide a multiple layer photoconductive recording material with improved photosensitivity. It is a further object of the present invention to provide a photoconductive recording material wherein the interfacial mixing is avoided of a charge transporting layer with a charge generating layer during overcoating of the charge generating layer with a solution of the charge transporting layer ingredients. It is still a further object of the present invention to provide a said photoconductive recording material wherein the binder system for the charge generating layer allows efficient charge transport in the charge generating layer and efficient charge injection into the charge transporting layer which is a positive charge transporting layer. In accordance with the present invention a photoconductive recording material is provided comprising a support and a charge generating layer (CGL) in contiguous relationship with a charge transporting layer (CTL) containing a p-charge transporting material (p-CTM) , wherein the binder of said charge generating layer (CGL) has been made insoluble in methylene chloride by crosslinking, and said binder is composed essentially of at least one resin (1) and/or at least one resin (2) crosslinked with at least one polyisocyanate, said resin (1) before its crosslinking corresponding to the following general formula (I) : R 7 R 8 — C- in which : X represents S, S0 2 , -C- or R 5 -C-R , each of R 1 , R 2 , R , R 4 , R 9 and R 10 (same or different) represents hydrogen, halogen, an alkyl group or an aryl group; R-> is OH, -OCH 2 CHCH 2 OH or -OCH 2 CH-CH 2 ; OH X 0 ; each of R and R° (same or different) represents hydrogen, an alkyl group, an aryl group or together represents the necessary atoms to close a cycloaliphatic ring, e.g. cyclohexane ring, and n is zero or an integer; and said resin (2) before its crosslinking being a dialkanolamine- modified epoxy resin. 4. Detailed description of the invention The polyisocyanate may be set free in the recording layer in situ, e.g. by heat, from a blocked polyisocyanate also called a polyisocyanate precursor. The synthesis of resin (1) may proceed as described for bisphenol-epichlorhydrin resins (ref. "The Chemistry of Organic Film Formers" by D. H. Solomon, John Wiley & Sons, Inc. New York (1967), p. 179-189) using as reaction ingredients a bisphenol, e.g. bisphenol A, and epichlorhydrin. Preferred bisphenol-epichlorhydrin resins are derived from bisphenol A (4,4'-isopropylidenediphenol) and epichlorhydrin. According to one embodiment a photoconductive recording material of the present invention has a charge generating layer containing as the sole binder one or more of said polyhydroxy resins with the general formula (I) and/or at least one of said dialkanolamine- modified epoxy resins σrosslinked with at least one polyisocyanate. According to another embodiment a photoconductive recording material of the present invention has a charge generating layer containing one or more resins obtained by the crosslinking with said polyisocyanate(s) of (i) polymeric compounds according to said general formula (I) and/or of (ii) at least one said dialkanolamine- modified epoxy resin having a total free HO-group content in an equivalent ratio from 3.0:1 to 1:2.0 with respect to free isocyanate groups of said polyisocyanate(s) . According to a further embodiment a photoconductive recording material according to the present invention has a charge generating layer containing at least 30 wt% of charge generating material (s) (CΘl's) and one or more resins with the general formula (I) and/or dialkanolamine-modified epoxy resins hardened with one or more of said polyisocyanates . Resins according to said general formula (I) are e.g. phenoxy resins of UNION CARBIDE CORP., U.S.A. sold under the following tradenames : PHENOXY PKHC PHENOXY PKHH PHENOXY PKHJ and PHENOXY PKHM-301; Bisphenol A-epichlorhydrin epoxy resins from SHELL CHEMICAL Co. sold under the following tradenames : EPON 1001 EPON 1002 EPON 1004 EPON 1007 EPON 1009 EPONOL Resin 53-BH-35 EPONOL Resin 55-BH-30; Bisphenol A-epichlorhydrin epoxy resins from DOW CHEMICAL U.S.A. sold under the following tradenames : DER 667 DER 668 DER 669 DER 684 - EK40; Bisphenol A-epichlorhydrin epoxy resins from CIBA-GEIGY AG Switzerland sold under the following tradenames : ARALDITE GT 6071 ARALDITE GT7203 ARALDITE GT7097 ARALDITE GT6099, and ARALDITE GZ488 N40. Dialkanolamine-modified epoxy resins can be prepared from commercially available epoxy resins with dialkanolamines in the melt or in a solvent mixture under reflux. (A) In the melt reaction the epoxy resin is heated to its melting point in a vessel equipped with a stirrer and a thermometer and the equivalent amount of dialkanolamine quickly added with stirring. The mixture is further heated at temperatures between 100°C and 200°C depending on the chain length of the epoxy resin for two hours with inert gas being bubbled through the reaction mixture. After 2 hours the product is poured out of the vessel, allowed to cool and then broken up into small particles. The reaction is exothermic and cooling is necessary for larger quantities to avoid local overheating. (B) In the reaction in a solvent mixture a 50 wt% solution of epoxy resin in a mixture of ethylglycol acetate, methylisobutylketone and xylene (2:1:1) is added to a vessel equipped with a reflux condenser, a thermometer and a stirrer. The equivalent amount of dialkanolamine is then added with stirring and the reaction mixture heated to its boiling point. After 2 hours under reflux, the reaction mixture is cooled and a 50 wt% solution of the dialkanolamine-modified epoxy resin obtained. The polyisocyanates and blocked polyisocyanates used for hardening resins with general formula (I) and dialkanolamine- modified epoxy resins according to the present invention are derived from polyisocyanates or mixtures thereof e.g. 1,6-hexane diisoσyanate (HDI) ; toluylene diisoσyanate (TDI) ; diphenylmethane-4,4'-diisoσyanate (MDI) ; isophorondiisocyanate (IPDI) ; triphenylmethane-4,4' ,4" triisocyanate thiophosphoric acid tris (p-isocyanatophenyl ester) Bayer AG, Germany produces a large variety of polyisocyanates and blocked polyisocyanates under the tradename DESMODUR e.g. : DESMODUR N75, a 75 % solution of a biuret HDI, DESMODUR N100, a biuret HDT; DESMODUR N3200, a biuret HDI (lower viscosity than DESMODUR N100) ; DESMODUR N3300, an HDI isocyanurate; DESMODUR N3390, a 90 % solution of an HDI isocyanurate; DESMODUR L75, a 75 % solution of a TDI-adduct, DESMODUR IL, a TDI-isoσyanurate; DESMODUR IL 1351, a TDI-polyisocyanate; DESMODUR HL, a TDI/HDI-polyisocyanate; DESMODUR VL, a MDI-polyisocyanate; DESMODUR Z4370, an IPDI-isocyanurate; and blocked polyisocyanates, such as : DESMODUR BL3175, a blocked HDI-type crosslinking stoving urethane resin; and DESMODUR BL100, a blocked TDI-type crosslinking stoving urethane resin. A suitable polyisocyanate precursor, also called a blocked polyisocyanate compound, for use according to the present invention has the following structural formula P : H 3 C-CH 2 -C- -CH.-O-CO-NH-^ -CH NH -CO-O-^ Said polyisocyanate precursor has a good stability at room temperature (20 °C) and generates free polyisocyanate in the temperature range of 100 to 150 °C. The hardening reaction with polyisocyanate taking place in said temperature range is mainly based on the reaction between the isocyanate groups of the thermo-generated polyisocyanate and the free hydroxyl groups of the bisphenol-epoxy type resin, but is also based on the formation of allophanate groups in the reaction of already existing urethane groups of the resin particles with isocyanate groups of the polyisocyanate [ref. D.H. Solomon " The Chemistry of Organic Film Formers" - John Wiley & Sons, Inc. New York, (1967) p. 203] . The resins with general formula (I) and dialkanolamine-modified epoxy resins hardened with polyisocyanates may be used in combination with at least one other polymer serving as binding agent, e.g. in combination with acrylate and methacrylate resins, copolyesters of a diol, e.g. glycol, with isophthalic and/or terephthaliσ aσid, polyaσetals, polyurethanes, polyester-urethanes, aromatic polycarbonates, wherein a preferred combination contains at least 50 % by weight of said resins with general formula (I) and/or dialkanolamine-modified epoxy resins hardened with polyisocyanates or blocked polyisocyanates in the total binder content. A polyester resin particularly suitable for use in combination with said crosslinked resins is DYNAPOL L 206 (registered trade mark of Dynamit Nobel) for a copolyester of terephthaliσ aσid and isophthaliσ aσid with ethylene glyσol and neopentyl glyσol, the molar ratio of tere- to isophthaliσ aσid being 3/2) . Said polyester resin improves the adherenσe to aluminium that may form a σonduσtive σoating on the support of the reσording material. Aromatic polycarbonates that are suitable for use in admixture with said crosslinked resins can be prepared by methods such as those described by D.Freitag, U.Grigo, P.R.Muller and W.Nouvertne in the Encyclopedia of Polymer Scienσe and Engineering, 2nd ed., Vol. II, pages 648-718, (1988) published by Wiley and Sons Inc., and have one or more repeating units within the scope of following general formula : 1 2 3 4 wherein : X, R , R , R and R have the same meaning as described in general formula (I) above. Aromatic polycarbonates having a molecular weight in the range of 10,000 to 200,000 are preferred. " Suitable polycarbonates having such a high molecular weight are sold under the registered trade mark MAKROLON of Bayer AG, W-Germany. MAKROLON CD 2000 (registered trade mark) is a bisphenol A polycarbonate with molecular weight in the range of 12,000 to 25,000 1 2 3 4 7 ' 8 7 8 wherein R =R =R =R =H, X is R -C-R with R =R =CH_ . i 3 MAKROLON 5700 (registered trade mark) is a bisphenol A polyσarbonate with molecular weight in the range of 50,000 to 120,000 wherein R =R =R =R 4 =H, X is R -C-R with R7=R8=CH_ . i 3 Bisphenol Z polycarbonate is an aromatic polycarbonate containing 1 2 3 4 7 ' 8 7 recurring units wherein R =R =R =R =H, X is R -C-R , and R together 8 I with R represents the necessary atoms to close a cyσlohexane ring. Suitable electroniσally inaσtive binder resins for use in aσtive layers of the present photoσonduσtive reσording material not containing said resins hardened with polyisoσyanates are e.g. the above mentioned polyester and polyσarbonates, but also cellulose esters, aσrylate and methaσrylate resins, e.g. σyanoaσrylate resins, polyvinyl σhloride, copolymers of vinyl chloride, e.g. copolyvinyl chloride/acetate and σopolyvinyl σhloride/maleiσ anhydride. Further useful binder resins for an active layer are siliσone resins, polystyrene and copolymers of styrene and maleiσ anhydride and copolymers of butadiene and styrene. Charge transport layers in the photoconduσtors of the present invention preferably have a thickness in the range of 5 to 50 μm, more preferably in range of 5 to 30 μm. If these layers σontain low molecular weight charge transport molecules, such compounds will preferably be present in concentrations of 30 to 70 % by weight. The presence of one or more spectral sensitizing agents can have , an advantageous effect on the charge transport. In that σonneσtion reference is made to the methine dyes and xanthene dyes described in US-P 3,832,171. Preferably these dyes are used in an amount not substantially reduσing the transparenσy in the visible light region (420-750 nm) of the σharge transporting layer so that the charge generating layer still can receive a substantial amount of the exposure light when exposed through the charge transporting layer. The charge transporting layer may contain compounds substituted with electron-acceptor groups forming an intermolecular charge transfer complex, i.e. donor-acσeptor complex when electron donor charge transport compounds are present. Useful compounds having electron-accepting groups are nitrocellulose and aromatic nitro-compounds such as nitrated fluorenone-9 derivatives, nitrated 9-dicyanomethylene fluorenone derivatives, nitrated naphthalenes and nitrated naphthalic acid anhydrides or imide derivatives. The preferred conσentration range of said compounds having electron acceptor groups is such that the donor/acceptor weight ratio is 2.5:1 to 1,000:1. Compounds aσting as stabilising agents against deterioration by ultra-violet radiation, so-σalled UV-stabilizers, may also be inσorporated in said σharge transport layer. Examples of UV-stabilizers are benztriazoles. For σontrolling the visσosity and aiding deaeration of the coating compositions and σontrolling their optiσal σlarity siliσone oils may be added to the σharge transport layer. As σharge generating σompounds for use in a reσording material aσσording to the present invention any of the organiσ pigments belonging to one of the following classes and able to transfer eleσtrons to eleσtron transporting materials may be used : a) perylimides, e.g. C.I. 71 130 (C.I. = Colour Index) desσribed in DBP 2,237,539, b) polynuσlear quinones, e.g. anthanthrones suσh as C.I. 59 300 desσribed in DBP 2,237,678, σ) quinaσridones, e.g. C.I. 46 500 desσribed in DBP 2,237,679, d) naphthalene 1,4,5,8-tetraσarboxyliσ aσid derived pigments inσluding the perinones, e.g. Orange GR, C.I. 71 105 desσribed in DBP 2,239,923, e) tetrabenzoporphyrins and tetranaphthaloporphyrins, e.g. H 2 -phthaloσyanine in X-σrystal form (X-H 2 Pσ) desσribed in US-P 3,357,989, metal phthaloσyanines, e.g. CuPσ C.I. 74 160 described in DBP 2,239,924, indium phthalocyanine described in US-P 4,713,312, tetrabenzoporphyrins described in EP 428,214A, silicon naphthalocyanines having siloxy groups bonded to the central silicon as described in EP-A 0243205 and X- and β- morphology form H 2 Pσ(CN) χ , H 2 Pσ(CH3) χ and H 2 PσCl χ pigments. f) indigo- and thioindigo dyes, e.g. Pigment Red 88, C.I. 73 312 described in DBP 2,237,680, g) benzothioxanthene-derivatives as described e.g. in DAS 2,355,075, h) perylene 3,4, 9,10-tetracarboxyliσ acid derived pigments including condensation products with o-diamines as described e.g. in DAS 2,314,051, i) polyazo-pigments inσluding bisazo-, trisazo- and tetrakisazo- pigments, e.g. Chlordiane Blue C.I. 21 180 desσribed in DAS 2,635,887, and bisazopigments desσribed in DOS 2,919,791, DOS 3,026,653 and DOS 3,032,117, j) squariliu dyes as desσribed e.g. in DAS 2,401,220, k) polymethine dyes. 1) dyes σontaining quinazoline groups, e.g. as desσribed in GB—P 1,416,602 aσσording to the following general formula : wherein R' and R" have the meaning desσribed in said GB-P doσument. Inorganiσ substances suited for photogenerating negative charges in a recording material acσording to the present invention are e.g. amorphous selenium and selenium alloys e.g. selenium-tellurium, selenium-tellurium-arseniσ and selenium-arseniσ and inorganiσ photoconductive crystalline compounds such as cadmium sulphoselenide, cadmiumselenide, cadmium sulphide and mixtures thereof as disclosed in US-P 4,140,529. The thickness of the charge generating layer is preferably not more than 10 μm, more preferably not more than 5 μm. In the recording materials of the present invention an adhesive layer or barrier layer may be present between the σharge generating layer and the support or the σharge transport layer and the support. Useful for that purpose are e.g. a polyamide layer, nitroσellulose layer, hydrolysed silane layer, or aluminium oxide layer aσting as a bloσking layer preventing positive or negative charge injection from the support side. The thickness of said barrier layer is preferably not more than 1 micron. The conduσtive support may be made of any suitable σonduσtive material. Typiσal σonduσtors inσlude aluminum, steel, brass and paper and resin materials inσorporating or σoated with σonduσtivity enhanσing substances. An insulating support such as a resin support is e.g. provided with a conduσtive σoating e.g. vaσuum-deposited metal suσh as aluminium, dispersed σarbon blaσk, graphite and σonduσtive monomeriσ salts or a σonductive polymer, e.g. a polymer containing quaternized nitrogen atoms as in Calgon Conductive polymer 261 (trade mark of Calgon Corporation, Inc., Pittsburgh, Pa., U.S.A.) described in US-P 3,832,171. According to a particular embodiment the support is an insulating resin support provided with an aluminium layer forming a conduσtive σoating. The support may be in the form of a foil, web or be part of a drum. An eleσtrophotographiσ recording process acσording to the present invention comprises the steps of : (1) overall eleσtrostatically σharging, e.g. with σorona-deviσe, the photoσonduσtive layer σontaining at least one resin aσσording to general formula (I) and/or alkanolamine-modified epoxy resins hardened with at least one polyisoσyanate or bloσked polyisocyanate; (2) image-wise photo-exposing said layer thereby obtaining a latent eleσtrostatiσ image, that may be toner-developed. When applying a bilayer-system eleσtrophotographiσ recording material including on an electriσally σonduσtive support a photosensitive σharge generating layer that σontains one or more resins aσσording to general formula (I) and/or alkanolamine-modified epoxy resins hardened with one or more polyisocyanates or blocked polyisocyanates in contiguous relationship with a charge transporting layer, the photo-exposure of the charge generating layer proceeds preferably through the charge transporting layer but may be direct if the charge generating layer is uppermost or may proceed likewise through the conductive support if the latter is transparent enough to the exposure light. The development of the latent electrostatic image commonly ocσurs preferably with finely divided eleσtrostatiσally attractable material, called toner particles that are attracted by σoulomb force to the electrostatic charge pattern. The toner development is a dry or liquid toner development known to those skilled in the art. In positive-positive development toner particles deposit on those areas of the σharge σarrying surfaσe whiσh are in positive-positive relation to the original image. In reversal development, toner partiσles migrate and deposit on the recording surface areas whiσh are in negative-positive image value relation to the original. In the latter case the areas discharged by photo-exposure obtain by induction through a properly biased developing electrode a charge of opposite charge sign with respect to the charge sign of the toner particles so that the toner becomes deposited in the photo-exposed areas that were discharged in the imagewise exposure (ref. : R.M. Schaffert "Eleσtrophotography" - The Foσal Press - London, New York, enlarged and revised edition 1975, p. 50-51 and T.P. Maσlean "Eleσtroniσ Imaging" Aσademiσ Press - London, 1979, p. 231) . Aσσording to a partiσular embodiment eleσtrostatiσ σharging, e.g. by σorona, and the imagewise photo-exposure proσeed simultaneously. Residual σharge after toner development may be dissipated before starting a next σopying cycle by overall exposure and/or alternating current corona treatment. Recording materials acσording to the present invention depending on the speσtral sensitivity of the σharge generating layer may be used in σombination with all kinds of photon-radiation, e.g. light of the visible spectrum, infra-red light, near ultra-violet light and likewise X-rays when electron-positive hole pairs can be formed by said radiation in the σharge generating layer. Thus, they σan be used in σombination with inσandesσent lamps, fluoresσent lamps, laser light sourσes or light emitting diodes by proper σhoiσe of the speσtral sensitivity of the σharge generating substanσe or mixtures thereof. The toner image obtained may be fixed onto the reσording material or may be transferred to a reσeptor material to form thereon after fixing the final visible image. A reσording material aσσording to the present invention showing a partiσularly low fatigue effeσt σan be used in recording apparatus operating with rapidly following copying cyσles inσluding the sequential steps of overall σharging, imagewise exposing, toner development and toner transfer to a receptor element. The following examples further illustrate the present invention. All parts, ratios and percentages are by weight unless otherwise stated. The evaluations of electrophotographic properties determined on the recording materials of the following examples relate to the performance of the recording materials in an electrophotographic process with a reusable photoreσeptor. The measurements of the performanσe σharaσteristiσs were σarried out by using a sensitometriσ measurement in whiσh the disσharge was obtained for 16 different exposures in addition to zero exposure. The photoσonduσtive reσording sheet material was mounted with its σonduσtive baσking on an aluminium drum whiσh was earthed and rotated at a σirσumferential speed of 10 cm/s. The recording material was sequentially charged with a negative corona at a voltage of -5.7 kV operating with a grid voltae of -600 V. Subsequently the recording material was exposed (simulating image—wise exposure) with a light dose of monochromatiσ light obtained from a monoσhromator positioned at the σirσtimferenσe of the drum at an angle of 45° with respeσt to the σorona sourσe. The photo-exposure lasted 200 s. Thereupon, the exposed reσording material passed an eleσtrometer probe positioned at an angle of 180° with respect to the corona source. After effecting an overall post-exposure with a halogen lamp producing 355 mJ/m2 positioned at an angle of 270° with respect to the corona source a new copying σyσle started. Eaσh measurement relates to 80 σopying σyσles in whiσh the photoσonduσtor is exposed to the full light sourσe intensity for the first 5 σycles, then sequentially to the light source the light output of whiσh is moderated by grey filters of optiσal densities 0.2, 0.38, 0.55, 0.73, 0.92, 1.02, 1.20, 1.45, 1.56, 1.70, 1.95, 2.16, 2.25, 2.51 and 3.21, eaσh for 5 σycles and finally to zero light intensity for the last 5 cyσles. The eleσtro-optiσal results quoted in the EXAMPLES 1 to 43 and COMPARATIVE EXAMPLES 1 to 3 hereinafter refer to charging level at zero light intensity (CL) and to discharge at a light intensity corresponding to the light source intensity moderated by a grey filter to the exposure indicated to a residual potential RP. The % discharge is : -^g^ x 100 For a given corona voltage, corona grid voltage, separating distance of the corona wires to recording surface and drum cirσumferential speed the σharging level CL is only dependent upon the thiσkness of the σharge transport layer and its speσific resistivity. In practiσe CL expressed in volts should be preferably > 30 d, where d is the thickness in μm of the charge transport layer. The structures of the p-CTM's used in the examples (PI to P6) are given below : All ratios and perσentages mentioned in the Examples are by weight. EXAMPLE 1 In the produσtion of a composite layer electrophotographiσ reσording material a 175 μm thiσk polyester film pre-σoated with a vaσuum-deposited layer of aluminium was doσtor-blade σoated with a dispersion of charge generating pigment to a thickness of 0.9 μm. Said dispersion was prepared by mixing 2 g of metal-free X-phthalocyanine (FASTOGEN BLUE 812OB tradename from Dainippon Ink and Chemiσals Inσ.); 0.3 g of PHENOXY PKHH (tradename for a bisphenol A—epiσhlorhydrin phenoxy resin from Union Carbide) ; and 26.45 g of methylene chloride for 40 hours in a ball mill. 0.88 g of PHENOXY PKHH (tradename), 9.36 g of butan-2-one, 26.58 g of methylene chloride and 1.09 g of DESMODUR N75 (tradename for a a 75 % solution of a hexamethylene diisocyanate-type hardener in 1:1 xylene:l-methoxyρropylaσetate-2 from Bayer AG.), were then added to the dispersion and the dispersion mixed for a further 15 minutes. The applied layer was dried and thermally hardened for 2 hours at 100°C and then overσoated using a doσtor-blade σoater with a filtered solution σonsisting of 3 g of the CTM PI; 3 g of MAKROLON 5700 (tradename for a bisphenol A polyσarbonate from Bayer AG) ; and 44 g of methylene σhloride to a dried thiσkness of 14.1 μ . This layer was dried at 50°C for 16 hours. The eleσtro-optiσal σharaσteristiσs of the thus obtained photoσonduσtive reσording materials were determined as desσribed above. At a σharging level of —516 V and an exposure Ig60 t °^ ^ mJ/m 2 , the following results were obtained : CL = -516 V RP = -73 V % Discharge = 85.9 EXAMPLES 2 AND 3 AND COMPARATIVE EXAMPLE 1 The photoσonduσtive reσording materials of examples 2 and 3 and σomparative example 1 were produced as described for example 1 exσept that alternative hardeners were used in the materials of examples 2 and 3 and no hardener was used for the material of σomparative example 1 and the amounts of PHENOXY PKHH (tradename) and hardener were adjusted to obtain a theoretiσal degree of hardening of 100 %. The weight perσentages of the PHENOXY PKHH (tradename) and hardener in the CGL's σalσulated on the basis of the solids content of the hardener are given in Table 1 together with the CTL layer thicknesses. The electro-optiσal σharaσteristiσs of the thus obtained photoσonduσtive reσording materials were determined as desσribed above and the results summarized in Table 1 together with those for the photoσonduσtive reσording material of example 1. From this table it is evident that hardening of PHENOXY PKHH (tradename) with DESMODUR N75, N100 or N3200 (tradenames) produces a significant improvement in the eleσtro-optiσal properties of the photosensitive reσording material as σan be learned from the inσrease in % disσharge. 20 EXAMPLES 4 TO 9 AND COMPARATIVE EXAMPLE 2 The photoconductive recording materials of examples 4 to 10 and comparative example 2 were produced as described for example 1 except that DER 684 EK40 (tradename for a high molecular weight bisphenol A-epichlorhydrin epoxy resin from Dow Chemical) , was used instead of PHENOXY PKHH (tradename) with different polyisocyanate hardeners except in the case of comparative example 2 for which no hardener was used. The amounts of DER 684 EK40 (tradename) and hardener were adjusted to obtain a theoretical degree of hardening of 100 %. The weight percentages of the DER 684 EK40 (tradename) and hardener in the CGL's calculated on the basis of the solids content of the hardener are given in Table 2 together with the CTL layer thiσknesses. The eleσtro-optiσal σharaσteristiσs of the thus obtained photoσonduσtive reσording materials were determined as described above and the results summarized in Table 2. From this table it is evident that hardening of DER684 EK40 (tradename) with DESMODUR N75, N100, N3200, VL and Z4370 (tradenames) produces a signifiσant improvement in the electro-optical properties of the photosensitive recording material as can be seen from the increase in % discharge. TABLE 2 Example DER 684 Hardener Hard- I 6 60 t = 10 m / τa2 No. -EK 40 (tradenames) ener conσ. σonσ . ^CTL ^^ RP % Dis¬ [wt%] [wt%] [μm] [V] [V] charge 4 30.35 DESMODUR N75 19. 65 14 .1 -534 -94 82 .4 5 30.35 DESMODUR N100 19. 65 15 . 1 -530 -91 82 . 8 6 30.86 DESMODUR N3200 19.14 13 . 1 -537 -90 83 .2 7 30.10 DESMODUR N3300 19. 90 14 .1 -553 -127 77 . 0 8 34.22 DESMODUR VL 15 .78 14 .1 -487 -88 81 . 9 9 26.82 DESMODUR Z4370 23 .18 15 .1 -557 -108 80 . 6 Comparative Example No . 2 50 none 13 . 1 -593 -145 75 .5 EXAMPLES 10 TO 16 AND COMPARATIVE EXAMPLE 3 The photoconduσtive reσording materials of examples 11 to 16 and σomparative example 3 were produσed as desσribed for example 1 exσept that EPON 1009 (tradename for a bisphenol A-epiσhlorhydrin epoxy resin from Shell Chemiσal Co. , was used instead of PHENOXY PKHH (tradename) with different polyisoσyanate hardeners and no hardener in the σase of σomparative example 3 and in the σase of example 15 a hardening temperature of 150°C was used instead of 100°C. The amounts of EPON 1009 (tradename) and hardener were adjusted to obtain a theoretical degree of hardening of 100 %. The weight perσentages of the EPON 1009 (tradename) and hardener in the CGL's σalσulated on the basis of the solids content of the hardener are given in Table 3 together with the CTL layer thicknesses. The electro-optiσal σharaσteristiσs of the thus obtained photoσonduσtive reσording materials were determined as desσribed above and the results are summarized in Table 3. From this table it is evident that hardening of EPON 1009 (tradename) with DESMODUR N75, NlOO, N3200, BL3175 and L75 (tradenames) produσes a signifiσant improvement in the eleσtro-optiσal properties of the photosensitive recording material as can be seen from the increase in % discharge. EXAMPLES 16 TO 27 The photoconductive recording materials of examples 16 to 27 were produced as described for example 1 exσept that different bisphenol A epiσhlorhydrin epoxy resins from different suppliers with different epoxy equivalent weights were used instead of PHENOXY PKHH. The amounts of epoxy resin and DESMODUR N75 were adjusted to obtain a theoretiσal degree of hardening of 100 %. The weight perσentages of epoxy resin and DESMODUR N75 σalσulated on the basis of the solids σontent of DESMODUR N75 are given in Table 4 together with the CTL layer thiσknesses. The eleσtro-optiσal σharaσteristiσs of the thus obtained photoσonduσtive reσording materials were determined as described above and the results are summarized in Table 4 together with those for the photoconductive recording materials of examples 10 and 4. * from Ciba Geigy AG + from Shell Chemiσal Co. 0 from Dow Chemiσal EXAMPLES 28 AND 29 The photoσonduσtive reσording materials of examples 28 and 29 were produced as described for example 1 except that diethanolamine-modified ARALDITE GT 6071 (tradename) and diethanolamine-modified ARALDITE GT 6099 (tradename) were used as hydroxy group-containing resins instead of PHENOXY PKHH (tradename) . The amounts of resin and DESMODUR N75 (tradename) were adjusted to obtain a theoretical degree of hardening of 100 %. The weight percentages of the resins and DESMODUR N75 (tradename) in the CGL's calculated on the basis of the solids content of the hardener are given in Table 5 together with the CTL layer thiσknesses. The eleσtro-optiσal σharacteristics of the thus obtained photoσonductive reσording materials were determined as desσribed above and the results are summarized in Table 5. TABLE 5 Example Resin Resin DESMODUR I 660 t = ~~ m /m 2 No. N75 cone. cone. CTIj CL RP % Dis- [wt%] [wt%] [μm] [V] [V] charge 28 Diethanolamine- 17.73 32.27 14.1 -560 -111 80.2 modified ARALDITE GT 6071 29 Diethanolamine- 23.32 26.68 12.1 -605 -187 69.1 modified ARALDITE GT 6099 EXAMPLES 30 TO 33 The photoconductive recording materials of examples 31 to 34 were produced as described in example 19 except that the amounts of ARALDITE GT7203 (tradename) and DESMODUR N75 (tradename) were adjusted to obtain various theoretiσal degrees of hardening, as indiσated in Table 6. The weight percentages of ARALDITE GT7203 (tradename) and DESMODUR N75 (tradename) calσulated on the basis of the solids σontents of the reaσtants are given in Table 6 together with the CTL layer thiσknesses. The eleσtro-optiσal properties of the thus obtained photoσonduσtive reσording materials were determined as desσribed above and the results are summarized in Table 6. TABLE 6 Example ARALDITE DESMODUR Theoretical ■ 660t = 10 mJ/m 2 EXAMPLES 34 TO 39 The photoconductive recording materials of examples 34 to 39 were produced as described for example 10 except that different CTM's were used in the charge transport layer. The CTM's used together with the CTM concentrations used in the CTL and the CTL layer thicknesses are given in Table 7. The electro-optical characteristics of the thus obtained photoconductive recording materials were determined as described above and the results are summarized in Table 7 below. EXAMPLES 40 TO 43 The photoconductive recording materials of examples 40 to 43 were produced as described in example 1 except that various CGM' s with different grinding times were used. The CGM' s and grinding times used together with the CTL layer thicknesses are summarized in Table 8. 25 The characteristics of the thus obtained photoconductive recording materials were determined as described above and are given in Table 8. metal-free X-phthalocyanine (FASTOGEN Blue 8120B from Dainippon Ink and Chemicals Inc.) + CGM 2 = a mixed crystalline pigment with an X-morphology consisting of a 1.75:1 molar mixture of metal-free 1—cyano phthalocyanine to unsubstited metal-free phthalocyanine ° CGM 3 = metal-free ω-triazotetrabenzoporphyrin x CGM 4 = 4,10-dibromoanthanthrone (ICI) .

Claims: CLAIMS 1. A photoconductive recording material comprising a support and a charge generating layer (CGL) in contiguous relationship with a charge transporting layer (CTL) containing a p-charge transporting material (p-CTM) , wherein the binder of said charge generating layer (CGL) has been made insoluble in methylene chloride by crosslinking, and said binder is composed essentially of at least one resin (1) and/or at least one resin (2) crosslinked with at least one polyisoσyanate, said resin (1) before its crosslinking corresponding to the following general formula (I) : in which : X represents S, S0 eaσh of R,1, R , R , R , J an erent) represents hydrogen, halogen, an alkyl group or an aryl group; R is OH, -OCH 2 CHCH 2 OH or -OCH 2 CH-CH 2 ; OH 0 eaσh of R 7 and Rft (same or different) represents hydrogen, an alkyl group, an aryl group or together represents the neσessary atoms to σlose a σyσloaliphatiσ ring, and n is zero or an integer; and said resin (2) before its crosslinking being a dialkanolamine- modified epoxy resin. 2. Photoconduσtive reσording material aσσording to σlaim 1, wherein said charge generating layer σontains as the sole binder one or more of said polyhydroxy resins with the general formula (I) and/or at least one of said dialkanolamine-modified epoxy resins crosslinked with at least one polyisocyanate. 3. Photoconductive recording material according to claim 1, wherein said charge generating layer contains one or more resins obtained by the crosslinking with said polyisocyanate(s) of (i) polymeric compounds according to said general formula (I) and/or of (ii) at least one said dialkanolamine-modified epoxy resin having a total free HO-group content in an equivalent ratio from 3.0:1 to 1:2.0 with respect to free isocyanate groups of said polyisocyanate(s) . 4. Photoconductive recording material according to claim 1, wherein said charge generating layer contains at least 30 wt% of charge generating material (s) (CGM's) and one or more resins with the general formula (I) and/or dialkanolamine-modified epoxy resins hardened with one or more polyisocyanate. 5. Photoconductive recording material acσording to claim 1, wherein at least one of said polyisoσyanates serving as σrosslinking agent in the formation of a polyurethane resin with the above mentioned resins (1) and resins (2) is selected from the group σonsisting of : 1,6-hexane diisoσyanate, (HDI) ; toluylene diisoσyanate (TDI) ; diphenylmethane-4,4'-diisoσyanate (MDI) ; isophorondiisoσyanate (IPDI) ; triphenylmethane-4,4' ,4" triisoσyanate, and thiophosphoric acid tris (p-isocyanatophenyl ester) or is derived therefrom. 6. Photoσonduσtive reσording material acσording to σlaim 1, wherein said polyisoσyanate used in the σrosslinking reaσtion is set free in situ in the reσording layer from a bloσked polyisocyanate. 7. Photoσonduσtive reσording material according to any of the preceding claims, wherein said resins obtained by crosslinking the resins according to said general formula (I) and dialkanolamine- modified epoxy resins with polyisocyanates are used in combination with at least one other polymer serving as binding agent. 8. Photoσonductive recording material acσording to σlaim 7, wherein said other polymer is seleσted from the group σonsisting of an aσrylate resin, methaσrylate resin, σopolyester of a diol with isophthaliσ and/or terephthaliσ acid, polyacetal, polyurethane, polyester-urethane and aromatic polycarbonate. 9. Photoconductive recording material according to claim 7 or 8, wherein said other polymer is present in said combination in an amount less than 50 % by weight of the total binder content. 10. Photoconductive recording material aσσording to any of the preσeding σlai s, wherein said support σonsists of aluminium or is a resin support provided with an aluminium layer forming a σonduσtive σoating.

Inventors: DE MEUTTER STEFAAN, MONBALIU MARCEL, TERRELL DAVID, DE MEUTTER, STEFAAN, MONBALIU, MARCEL, TERRELL, DAVID
Applicants: AGFA GEVAERT NV, MEUTTER STEFAAN DE, MONBALIU MARCEL, TERRELL DAVID, AGFA-GEVAERT NAAMLOZE VENNOOTSCHAP
Application year: 1993
Main classification: G03G5
IPC codes: G03G5