EP0061091B1 - Electrophotographic recording material - Google Patents

Description

The invention relates to an electrophotographic recording material consisting of an electrically conductive carrier material and a photoconductive double layer made of organic materials, as well as a method for producing these electrophotographic recording materials and their use for reprographic purposes.

In electrophotography, the surface of an electrophotographic element, which contains a photo-semiconducting layer, is first charged uniformly electrostatically for the purpose of image formation. During imagewise exposure to actinic radiation, ie the photo-semiconductor induction radiation, the photo-semiconductor layer becomes electrically conductive on the irradiated surfaces, as a result of which the electrostatic surface charge flows off at these points if the electrically conductive carrier material is grounded. The unexposed areas, on the other hand, retain their surface charge, so that a charge image corresponding to the original remains after the exposure. If this charge image is treated with fine pigment pigment particles which have previously been charged in the opposite way to the surface charge of the electrophotographic element, these color pigment particles are deposited in the unexposed areas of the electrophotographic element and thus develop the invisible charge image into a visible image of the original. The image created in this way is then transferred to another surface, for example on paper, and fixed on it.

The electrophotographic element can either be composed of a homogeneous layer of a photo semiconductor on an electrically conductive carrier material or of several layers arranged one above the other on the carrier. Electrophotographic recording materials with a multi-layer, so-called composite structure are described. For example, DE-OS 2 220 408 discloses such materials comprising a conductive carrier, a first layer which contains charge carrier-producing compounds and a second layer with charge carrier transporting substances which is arranged in addition.

In addition to the inorganic photo semiconductors, which are usually based on selenium, a number of organic photo semiconductors are also known for the layers which generate charge carriers. However, a large number of the described organic dyes, which are suitable for generating charge carriers when irradiated with actinic light, must be deposited on the carrier material in a high vacuum and at temperatures above 300 ° C. by evaporation or sublimation (e.g. DE-OS 2 220 408, 2 239 924). However, such processes are not very economical and often not very reproducible. In addition, only thermally extremely stable dyes can be used. In the field of electrophotography, however, it is desirable to have as many dyes as effective components available.

Another group of charge-generating photoconductive organic materials is dispersed in the form of pigment particles in a matrix binder and applied to a support in a layer which contains the individual photoconductive particles. These are the electrophotographic elements described in the literature, which contain monoazo, disazo and squaric acid dye derivatives as coloring materials (inter alia US Pat. No. 3,775,105, US Pat. No. 3,824,099, US Pat. No. 3,898,084).

It has also been proposed to dissolve monoazo or disazo dyes or also the dye derivatives of squaric acid in a solvent containing primary organic amines and to apply the charge-generating layer from the solution (DE-OS 2 635 887). A disadvantage of this procedure, however, is that amines are both extremely polluting and troublesome for the processor.

There has been no shortage of attempts to achieve the production of the individual layers of the composite structure of an electrophotographic element as simply as possible. However, this requires the use of new dyes as charge-generating components.

The object of the invention was therefore to create extremely light-sensitive electrophotographic layers by means of organic photo semiconductors, which can be produced as simply as possible from a dye dispersion. The electrophotographic element should continue to be flexible, elastic and abrasion-resistant, the surface of which, if possible, should be smooth and free of striations without aftertreatment.

• a) aus einem elektrisch leitfähigen Trägermaterial,
• b) einer ersten Schicht, die Ladungsträger erzeugende Farbstoffe bestimmter Art enthält, mit einer Dicke von 0,005 bis 5 !J.m und
• c) einer zweiten, für das aktinische Licht weitgehend transparenten Schicht aus isolierenden organischen Materialien mit mindestens einer, im Licht Ladungen transportierenden Verbindung zusammensetzt.

The solution to the problem is based on an electrophotographic recording material

• a) made of an electrically conductive carrier material,
• b) a first layer, which contains charge-generating dyes of a certain type, with a thickness of 0.005 to 5 μm and
• c) a second layer, which is largely transparent to actinic light, is composed of insulating organic materials with at least one compound which transports charges in the light.

The invention accordingly relates to dyes which are active in the first layer of the electrophotographic recording material as components which generate charge carriers.

in der R¹ bis R⁴ Wasserstoff, Halogen, Methyl oder Methoxy, einer oder zwei der Reste R¹ bis R⁴ C₂- bis C₆-Alkyl, Phenyl, Phenoxy, Phenylthio, Nitro, Amino, N₁N-C₁- bis C₄-Dialkylamino ; einen Rest der Formel

einem Rest der Formel -NHCOR^S, wobei R⁵ für C₁- bis C₆-Alkyl oder gegebenenfalls substituiertes Phenyl steht, und die übrigen Reste R¹ bis R⁴ Wasserstoff, X den Rest einer methylenaktiven Verbindung oder der Formel = N-R⁶', wobei R⁶' der Rest eines aromatischen oder heterocyclischen Amins oder Hydrazins ist, und Z Wasserstoff, Methyl oder Phenyl, vorzugsweise Wasserstoff bedeuten.It was surprising that, as color-covering, charge carrier-generating layers for the electrophotographic recording materials, layers with dyes of the dye class explained below meet the requirements. Dyes of the general formula I are suitable for this

in which R ¹ to R ^{4 are} hydrogen, halogen, methyl or methoxy, one or two of the radicals R ¹ to R ^{4 are} C ₂ -C ₆ -alkyl, phenyl, phenoxy, phenylthio, nitro, amino, N ₁ NC ₁ -bis C ₄ dialkylamino; a remainder of the formula

a radical of the formula -NHCOR ^S , where R ^{5 is} C ₁ -C ₆ -alkyl or optionally substituted phenyl, and the remaining radicals R ¹ to R ^{4 are} hydrogen, X is the radical of a methylene-active compound or the formula = NR ⁶ ' , wherein R ⁶ 'is the residue of an aromatic or heterocyclic amine or hydrazine, and Z is hydrogen, methyl or phenyl, preferably hydrogen.

in der R¹ bis R⁴ Wasserstoff oder Halogen oder einer oder zwei der Reste R¹ bis R⁴ Phenyl, Phenoxy, Phenylthio, Nitro und die übrigen Wasserstoff, R⁶ Cyano, Nitro, 4-Halogenphenyl, 4-Cyanphenyl, 4-Nitrophenyl, C₁- bis C₈-Alkoxycarbonyl, Phenoxycarbonyl, Carbamoyl, N-Phenylcarbamoyl, das gegebenenfalls durch 1 bis 3 Chlor, Brom, Methyl, und/oder Methoxy substituiert ist, N-C₁- bis C₄-Alkylcarbamo- yl, ein durch Cyan, Nitro oder CF₃ in 4-Stellung substituiertes Phenyl, Phenylsulfonyl, das im Phenyl durch bis zu 3 Chlor, Brom und/oder C₁- bis C₄-Alkyl im Phenylkern substituiert ist ; einen Rest der Formel

in der A für -0-, ―S― oder N-R, R für Wasserstoff oder C₁- bis C₄-Alkyl und R⁷ und R⁸ für Wasserstoff oder Halogen, C₁- bis C₄-Alkyl oder C₁- bis C₄-Alkoxy stehen ; 1 H-Naphth [2,3-d] imidazolyl, Pyridyl, 4-Thiazolyl, 2-Methyl-4-Thiazolyl, 2-Phenyl-1,3,4-thiadiazolyl-(5), 2-Chinolinyl, 3-Indolyl oder 3-Benzthiazolyl bedeuten.Compounds of the formula II are preferred

in which R ¹ to R ^{4 are} hydrogen or halogen or one or two of the radicals R ¹ to R ^{4 are} phenyl, phenoxy, phenylthio, nitro and the remaining hydrogen, R ^{6 is} cyano, nitro, 4-halophenyl, 4-cyanophenyl, 4-nitrophenyl , C ₁ - to C ₈ -alkoxycarbonyl, phenoxycarbonyl, carbamoyl, N-phenylcarbamoyl, which is optionally substituted by 1 to 3 chlorine, bromine, methyl, and / or methoxy, NC ₁ - to C ₄ -alkylcarbamoyl, a by Cyan, nitro or CF ₃ in the 4-position substituted phenyl, phenylsulfonyl which is substituted in the phenyl by up to 3 chlorine, bromine and / or C ₁ - to C ₄ -alkyl in the phenyl nucleus; a remainder of the formula

in the A for -0-, ―S― or NR, R for hydrogen or C ₁ - to C ₄ -alkyl and R ⁷ and R ⁸ for hydrogen or halogen, C ₁ - to C ₄ -alkyl or C ₁ - bis C ₄ alkoxy; 1 H-naphth [2,3-d] imidazolyl, pyridyl, 4-thiazolyl, 2-methyl-4-thiazolyl, 2-phenyl-1,3,4-thiadiazolyl- (5), 2-quinolinyl, 3-indolyl or 3-benzothiazolyl.

in der A, R⁷ und R⁸ die obengenannte Bedeutung haben, bedeuten.Compounds of the formula 11 in which R ¹ to R ^{4 are} hydrogen or chlorine atoms or one or two of the radicals R ¹ to R ^{4 are} phenyl, phenoxy, phenylthio or nitro and the other hydrogen atoms and R ^{6 are} cyano, methylcarbonyl, phenylcarbonyl, 4 -Nitrophenyl, 4-cyanophenyl, C ₁ - to C _e -alkoxycarbonyl, phenoxycarbonyl, phenylsulfonyl, a radical of the formula

in which A, R ⁷ and R ^{8 have} the meaning given above.

in der R¹ Wasserstoff oder Halogen oder einer oder zwei der Reste R¹ bis R⁴ Phenyl, Phenoxy, Phenylthio, Nitro und die übrigen Wassertoff, B die Ergänzung zu einem Pyrazolon-, Oxazolon-, Isoxazolon-, Imidazolon-, Cyclohexandion-, Dimedon-, Pyridon- oder 4-Hydroxy-Cumarinrest oder

einen Rest der Formel

bedeuten.Compounds of the formula III are also preferred

in which R ^{1 is} hydrogen or halogen or one or two of the radicals R ¹ to R ⁴ phenyl, phenoxy, phenylthio, nitro and the other water substances, B the addition to a pyrazolone, oxazolone, isoxazolone, imidazolone, cyclohexanedione, Dimedone, pyridone or 4-hydroxy-coumarin residue or

a remainder of the formula

mean.

in der R¹ bis R⁴ Wasserstoff oder Halogen oder einer oder zwei der Reste R¹ bis R⁴ Phenyl, Phenoxy, Phenylthio, Nitro und die übrigen Wasserstoff und R⁹ einen Rest der Formel

in der R¹⁰, R" und R¹², die gleich oder verschieden sein können, für Halogen, C_l- bis C₄-Alkyl C_l- bis C₄-Alkoxy, R¹⁰ für Nitro oder Cyano und R" und R¹² für Wasserstoff, Halogen, C₁- bis C₄-Alkyl oder C₁- bis C₄-Alkoxy stehen ; oder den Rest eines heterocyclischen Amins bedeuten, beispielsweise 2-Oxazolyl, 2-Thiazolyl, 2_-lmidazolyl-, 2-(4-Phenylthiazolyl), 2-(4-Methyl-5-Carboethoxythiazolyl, 2-Benzthiazolyl, 2-(6-Ethoxybenzthiazolyl), 2-Benzimidazolyl, 2-(1-Methylbenzimidazolyl), 2-(5-Phenyl-1,3,4-thiadiazolyl oder 3-Indazolyl.Compounds of the formula IV are also preferred

in which R ¹ to R ^{4 are} hydrogen or halogen or one or two of the radicals R ¹ to R ^{4 are} phenyl, phenoxy, phenylthio, nitro and the remaining hydrogen and R ^{9 is} a radical of the formula

in which R ¹⁰ , R "and R ¹² , which may be the same or different, for halogen, C ₁ -C ₄ -alkyl C ₁ -C ₄ -alkoxy, R ¹⁰ for nitro or cyano and R" and R ¹² represent hydrogen, halogen, C ₁ -C ₄ -alkyl or C ₁ -C ₄ -alkoxy; mean or the radical of a heterocyclic amine, for example 2-oxazolyl, 2-thiazolyl, 2 _- imidazolyl, 2- (4-phenylthiazolyl), 2- (4-methyl-5-Carboethoxythiazolyl, 2-benzothiazolyl, 2- (6- Ethoxybenzthiazolyl), 2-benzimidazolyl, 2- (1-methylbenzimidazolyl), 2- (5-phenyl-1,3,4-thiadiazolyl or 3-indazolyl.

Some of the compounds mentioned are described in the literature. For example, according to the methods described in Chem. Ber. 100, 2261 (1967) or processes described in DE-OS 2 525 587.

To produce the electrophotographic recording materials according to the invention, the first charge carrier-producing layer is applied to the electrically conductive layer carrier in the form of a dispersion. The dispersion for the first layer is produced by rolling together about 20 to 85 percent by weight of the solids content of the dispersion in one or more of the dyes suitable according to the invention and 80 to 15 percent by weight in a binder which is customary for this purpose and which may have barrier properties, in the form of a Solution in an organic, easily evaporable solvent.

The first layer is cast in a thickness of approximately 0.005 to 5 μm, preferably 0.08 to 1.5 μm, which is to be understood as the solid layer thickness.

Between the support and the first layer there can be an adhesive layer in a thickness of about 0.05 to 5 wm, preferably 0.1 to 0.8 microns are arranged.

The transparent second layer is also arranged over the first layer by casting from a solution. The thickness of the second layer is preferably between 0.8 and 90, preferably between 2 and 40 μm. It consists of 30 to 60 percent by weight of one or more charge-transporting compounds, 65 to 35 percent by weight of one or more binders customary for this, 0.1 to 4 percent by weight of additives that improve the mechanical properties and optionally up to 5 percent by weight of sensitizing or activating agents Connections together. The casting process is carried out from a low-boiling solvent.

Between the first and the second layer, a barrier layer of about 0.05 to 1.5 μn1, preferably 0.1 to 0.5 μm, is optionally arranged, while it may be appropriate, depending on the intended use of the electrophotographic recording material, and the protective layer acting inactive layer on the charge carrier transporting layer.

Aluminum foils, aluminum foils, nickel foils or plastic foils coated with aluminum, tin, lead, bismuth or similar metals, preferably polyester foils, are suitable as the electrically conductive carrier material. The choice is determined by the area of application of the electrophotographic element.

The barrier layers between the conductive carrier material and the first layer or between the same and the second layer usually consist of metal oxide layers, e.g. B. alumina layers, polymers such. B. polyamide, polyvinyl alcohol, polyacrylates, polystyrene or similar systems. If necessary, the binder of the first layer can also serve as a barrier layer material at the same time.

Polyacrylates, polymethacrylates, polyesters, polyphthalic esters, polyvinyl chlorides, styrene-maleic acid copolymers, epoxides and other generally customary resins are suitable as binders for the absorption of the dyes according to the invention for producing the charge-generating layer of the electrophotographic recording materials according to the invention.

• a) niedermolekulare Verbindungen, insbesondere heterocyclische Verbindungen, wie Pyrazolinderivate, Oxazole, Oxdiazole, Phenylhydrazone, Imidazole, Triphenylaminderivate, Carbazolderivate, Pyrenderivate und weitere, kondensierte Aromaten sowie
• b) polymere Materialien, wie Polyvinylpyrene, Poly (N-vinylcarbazol), Copolymerisate aus Carbazol und Styrol, bzw. Vinylacetat und/oder Vinylchlorid.

Particularly suitable binders for the second layer transporting the charge carriers are polyvinyl chloride, polyester resins, polyacetal resins, polycarbonates, polystyrene, polyurethanes, ie those binders which have special electrical properties and are known to the person skilled in the art for this purpose. Silicone resins, polyvinyl acetate, chlorinated rubber, cellulose esters, ethyl cellulose and the like are also available. Suitable charge transport compounds which are contained in this layer are compounds which do not impair transparency for visible light, such as

• a) low molecular weight compounds, especially heterocyclic compounds, such as pyrazoline derivatives, oxazoles, oxdiazoles, phenylhydrazones, imidazoles, triphenylamine derivatives, carbazole derivatives, pyrene derivatives and other condensed aromatics and
• b) polymeric materials, such as polyvinylpyrene, poly (N-vinylcarbazole), copolymers of carbazole and styrene, or vinyl acetate and / or vinyl chloride.

Of the polymeric type, poly (N-vinylcarbazole) is particularly suitable.

The electrophotographic recording materials according to the invention can also contain further constituents to improve their mechanical properties. So wetting agents like silicone oils can improve the surface quality. Sensitizers or activators of the upper second layer can also be incorporated. As sensitizers, which can be solved in disperse form, are, for. B. triphenylmethane dyes, xanthone dyes, soluble perylene derivatives such as perylene tetracarboxylic acid esters and a number of other compounds are known. Compounds with high electron affinity, e.g. B. nitro compounds such as 2,4,7-trinitrofluorenone-9.

The electrophotographic recording material according to the invention contains highly light-sensitive photoconductive double layers which have a high mechanical stability and can, for example, be arranged on a cylindrical drum or circulate as an endless belt without any signs of wear occurring. Accordingly, they are very suitable for use for reprographic purposes, e.g. B. as copy layers, electrophotographic offset printing plates.

The invention is illustrated by the following examples.

Examples 1 to 9

5 g each of dyes 1 to 9 are mixed with 3 g each of a copolymer of vinyl chloride, acrylic acid and a maleic diester and 25 g of tetrahydrofuran and rolled on a roller mill for 12 hours. Then 75 g of tetrahydrofuran and 25 g of toluene are added. The mixture is homogenized on the roller mill for one hour.

This dispersion is then applied with a squeegee to an untreated aluminum carrier sheet 175 µm thick. The casting gap is 60 µm. The doctor blade is pulled off at a speed of 260 mm / min. After flashing off and drying for 30 minutes at 90 ° C., a dry layer thickness of 0.75 to 0.8 p.m. remains.

A solution of 47.75 g of poly (N-vinylcarbazole), 5.2 g of phthalic acid dihexyl ester and 5.75 g of a polycarbonate with a melting temperature of 220 to 230 ° C. in a solvent mixture of 287.5 is in each case on this first, covering layer g of tetrahydrofuran and 74.2 g of toluene. The casting gap is 140 pm each; the doctor blade is pulled off at 260 mm / min. After ventilation and drying for 30 minutes at 90 ° C leaves a dry layer of 8 to 8.5 µm in thickness.

The electrophotographic element prepared in this way is then loaded with a high voltage of −7.40 kV on a corona wire at a distance of 10 mm above the layer surface. After 20 seconds of loading, the maximum surface potential in volts is determined. These surface potentials are based on the surface potential of a completely similarly produced plate, equal to 100%, which according to DE-OS 2 237 539 N contains N'-dimethylperylene-3,4,9,10-tetracarboxylic acid diimide. After a further 20 seconds in the dark, the percentage drop in potential, based on the maximum potential, is determined. Then the electrophotographic element is irradiated with the light of a xenon lamp with a power consumption of 150 watts. The light-induced percentage potential drop, based on the potential after the dark drop, is measured.

The measurement results are summarized in Table 1.

Examples 10 to 18

Analogous to Examples 1 to 9, the same electrophotographic elements are produced which, instead of an untreated aluminum sheet, contain an anodized aluminum sheet with an anodized layer of approximately 0.25 μm thick.

The same measurement results as those listed in Table 1 are thus largely obtained.

Claims (7)

1. An electrophotographic recording material which consists essentially of an electrically conductive base, a first layer containing charge carrier-producing dyes, and a second layer which is substantially transparent to actinic light and is composed of an insulating organic material containing at least one compound which is charge carrier-transporting when exposed to light, wherein the charge carrier-producing dye is of the general formula I

where R¹, R², R³ and R⁴ are each hydrogen, halogen, methyl or methoxy, or one or two of the radicals R¹, R², R³ and R⁴ are C₂-C₆-alkyl, phenyl, phenoxy, phenylthio, nitro, amino, N,N-C_l-C₄-dialkylamino, radical of the formula

or a radical of the formula -NHCOR⁵, where R⁵ is C_l-C₅-alkyl or unsubstituted or substituted phenyl, and the remaining radicals R¹, R², R³ and R⁴ are each hydrogen, X is the radical of a methylene-active compound or a radical of the formula = N-R⁶', where R^6' is the radical of an aromatic or heterocyclic amine or hydrazine, and Z is hydrogen, methyl or phenyl.

2. An electrophotographic recording material as claimed in claim 1, wherein the charge carrier-producing dye is of the general formula II

where R¹, R², R³ and R⁴ are each hydrogen or halogen, or one or two of the radicals R¹, R², R³ and R⁴ are phenyl, phenoxy, phenylthio or nitro, and the remaining radicals R¹, R², R³ and R⁴ are each hydrogen, R⁶ is cyano, nitro, 4-halophenyl, 4-cyanophenyl, 4-nitrophenyl, C₁-C₈-alkoxycarbonyl, phenoxycarbonyl, carbamyl, or N-phenylcarbamyl which is unsubstituted or monosubstituted to trisubstituted by chlorine, bromine, methyl and/or methoxy, or is N―C₁―C₄-alkylcarbamyl, or phenyl which is substituted in the 4-position by cyano, nitro or CF_s, or phenylsulfonyl which is monosubstituted to trisubtituted in the phenyl nucleus by chlorine, bromine and/or C₁―C₄-alkyl, or is a radical of the formula

where A is ―0―, -S- or N-R, R is hydrogen or C₁-C₄-alkyl, and R⁷ and R⁸ are each hydrogen, halogen, C₁―C₄-alkyl or C₁―C₄-alkoxy, or R⁶ is 1H-naphth-[2,3-dJ-imidazolyl, pyridyl, thiazol-4-yl, 2-methylthiazol-4-yl, 2-phenyl-1,3,4-thiadiazol-5-yl, quinolin-2-yl, indol-3-yl or benzthiazol-3-yl.

3. An electrophotographic recording material as claimed in claim 2, wherein in the formla of the dye, R¹, R², R³ and R⁴ are each hydrogen or chlorine, or one or two of the radicals R¹, R², R³ and R⁴ are phenyl, phenoxy, phenylthio or nitro, and the remaining radicals R¹, R², R³ and R⁴ are each hydrogen, and R⁶ is cyano, methylcarbonyl, phenylcarbonyl, 4-nitrophenyl, 4-cyanophenyl, C_l-C₆-alkoxycarbonyl, phenoxycarbonyl, phenylsulfonyl or a radical of the formula

where A is -0-, ―S― or N-R, R is hydrogen or C₁―C₄-alkyl, and R⁷ and R⁸ are each hydrogen, halogen, C₁―C₄-alkyl or C₁―C₄-alkoxy, or R⁶ is 1H-naphth-[2,3-d]-imidazolyl, pyridyl, thiazol-4-yl, 2-methylthiazol-4-yl, 2-phenyl-1,3,4-thiadiazol-5-yl, quinolin-2-yl, indol-3-yl or benzthiazol-3-yl.

4. An electrophotographic recording material as claimed in claim 1, wherein the charge carrier-producing dye is of the general formula III

where R' is hydrogen or halogen, or one or two of the radicals R¹, R², R³ and R⁴ are phenyl, phenoxy, phenylthio or nitro, and the remaining radicals R¹, R², R³ and R4 are each hydrogen, and B is the complement needed to form a pyrazolone, oxazolone, isooxalone, imidazolone, cyclohexanedione, dimedone, pyridone or 4-hydroxycoumarin radical or

is a radical of the formula

5. An electrophotographic recording material as claimed in claim 1, wherein the charge carrier-producing dye is of the general formula IV

where R^l, R², R³ and R⁴ are each hydrogen or halogen, or one or two of the radicals R¹, R², R³ and R⁴ are phenyl, phenoxy, phenylthio or nitro, and the remaining radicals R¹, R², R³ and R⁴ are each hydrogen, and R⁹ is a radical of the formula

where R¹⁰, R" and R¹² may be identical or different and each is halogen, C₁―C₄-alkyl or C₁―C₄- alkoxy, or R¹⁰ is nitro or cyano and R" and R¹² are each hydrogen, halogen, C₁―C₄-alkyl or C₁―C₄- alkoxy, or R⁹ is the radical of a heterocyclic amine.

6. An electrophotographic recording material as claimed in claim 1, wherein in the second layer, which is substantially transparent to actinic light, the compound which is charge carrier-transportin when exposed to light is poly-(N-vinylcarbazole).

7. The use of an electrophotographic recording material as claimed in any of claims 1 to 6 for reprographic purposes.