EP0000581A2 - Electrophotographic recording material - Google Patents

Abstract

Electrophotographic recording material composed of an electrically conductive support, optionally an insulating intermediate layer and a photoconductive layer comprising at least one layer which generates charge carriers and transports charges, binders and conventional additives, in which the recording material, when the support is relatively thick, is so flexible that it is flexible it can repeatedly run over rolls of at least 18 mm in diameter without being prone to hairline cracks. The recording material contains cellulose acyl ester, preferably with 2 to 4 carbon atoms, with an acetyl content of at most 30% and a viscosity of more than 15 poises, measured according to ASTM D 817-65, formula A and D 1343-56.

Description

The invention relates to electrophotographic recording material comprising an electrically conductive layer support, optionally an insulating intermediate layer and a photoconductive layer comprising at least one charge carrier-producing and charge-transporting layer, binder and conventional additive-containing layer. The invention relates in particular to recording material, the photoconductive layer of which consists of a charge carrier generating layer and a charge transport layer.

Photoconductive layers are e.g. B. from German Offenlegungsschriften 21 08 935, 21 08 938, 21 08 944, 21 08 958, 21 08 968, 21 08 984 and 21 08 992 known. With relatively good electrophotographic properties, however, the mechanical properties are disadvantageous when the polyvinylcarbazole used and mainly described is not very flexible as a charge transport layer and, owing to its large molecular weight and its chemical nature, is only slightly compatible or miscible with binders and resins. In addition, the adhesion of such layers to the electrically conductive substrate is insufficient for practical purposes. The use of these materials is limited to photoconductor arrangements that are not mechanically resilient.

The German laid-open publications 22 20 408, 23 14 051 and 23 53 639 describe well-adhering and also flexible, photoconductive layers, but these are also sufficient when used in mechanically strong layers claimed, self-supporting recording materials such. B. photoconductor bears not yet meet all requirements. If the recording material is repeatedly guided over rollers, fine hairline cracks appear on the surface of the photoconductor. This bending stress on the photoconductor layer, which can also be located on a relatively thick substrate, causes its gradual mechanical destruction.

It was therefore an object of the present invention to provide an electrophotographic recording material which, with very good photosensitivity, has been modified in its flexibility to such an extent that it can be used safely even on relatively thick substrates, for example as a continuous photoconductor belt, under high mechanical stress and on rolls with a small amount Diameter can be performed.

The solution to this problem is based on an electrophotographic recording material comprising an electrically conductive layer support, optionally an insulating intermediate layer and a photoconductive layer comprising at least one charge carrier-generating and charge-transporting layer, binder and conventional additives, and is characterized in that the recording material contains a 75 to 250 µm thick layer support worked as a photoconductor tape is so flexible that it repeatedly leads over rolls of at least 18 mm in diameter does not tend to hairline cracks and that it contains cellulose acyl esters as a binder an acetyl content of at most 30% and a viscosity above 15 poises, measured according to ASTM D 817-65, formulas A and D 1343-56. The cellulose acyl ester preferably has an acetyl content of at most 15% with a viscosity of over 15, in particular over 50 poises. The acyl groups preferably have two to four carbon atoms.

The viscosity is determined in accordance with ASTM D 817-65, formula A and D 1343-56 by dissolving 20 parts by weight of cellulose acyl ester in 8 parts by weight of ethanol (95% by volume) and 72 parts by weight of acetone using the ball drop method at 25 ° C.

It is achieved by the invention that electrophotographic recording material can be made available which, in comparison with materials with the previously known and customary binders, has the same good photosensitivity and a low residual charge, a great flexibility.

These properties allow the materials according to the invention to be used for mechanically strong photoconductor tapes which run in a relatively fast cyclic copying process. A recording material which contains a cellulose acetobutyrate with a maximum of 15% acetyl content and a viscosity in the range of 60-110 poises, measured according to ASTM D 817-65, formulas A and D 1343-56, has proven useful for particularly strong mechanical loads . Repeated guidance takes place via roles e.g. B. in the bending stress test and usually happens 5000 times.

The arrangement of a simple photoconductive layer has the advantage of being simple to manufacture (FIG. 1). The arrangement in separate charge carrier generating layer and charge transport layer, on the other hand, has the advantage of the compact arrangement of the particles and the optimal charge carrier generation advice (FIGS. 2-4). Less thermally stable dyes, which, for example, cannot be vapor-deposited onto the electrically conductive layer support, can be used in accordance with the arrangements in FIGS. 1 and 4.

In the development of photoconductive layers, the use of cellulose acyl esters in photoconductor compositions is described, for example in the enumeration of possible binders, cellulose esters and ethers are often mentioned (eg DE-PS 12 46 407. The unusual special position found however, in terms of flexibility and photosensitivity properties, it was surprising and unexpected.

und zum anderen photoleitfähige organische Substanzen zugefügt sein. Im Hinblick auf die angeführte relativ große elektrische Leitfähigkeit und im Hinblick auf das Mischungsverhältnis mit bis zu 30 Gewichtsprozent an Photoleiter sind diese Zusammensetzungen jedoch nicht für das erfindungsgemäße Aufzeichnungsmaterial geeignet.It is known from German Offenlegungsschriften 24 52 622 and 24 52 623 to use cellulose esters in protective layers over photoconductor layers, as are known, for example, from DT-AS 15 72 347, in addition to other binders. These protective layers can contain substances that increase conductivity in a resistance range of the layer between 10 ⁷ and 10 ⁹

and be added to other photoconductive organic substances. In view of the relatively high electrical conductivity mentioned and in view of the mixing ratio with up to 30 percent by weight of photoconductor, however, these compositions are not suitable for the recording material according to the invention.

The structure of the recording material according to the invention is explained schematically in four variants with reference to the accompanying figures. Numeral 1 indicates the electrically conductive layer support, number 2 shows the charge-generating layer. Number 3 indicates the charge transport layer and number 4 indicates the insulating intermediate layer. Section 5 shows layers which represent a charge generation layer in dispersion. With number 6 a ^p hotoleitfähige layer of photoconductor as the charge-transporting compound, dye is represented as a charge carrier generating compound and binder, etc..

Aluminum foil or also transparent polyester foil coated with aluminum or aluminum-clad polyester foil with a thickness of ^S 300 μm are preferably used as the electrically conductive layer support. However, other electrically conductive substrate material can also be used. The layer support can be a flexible endless belt, e.g. B. made of nickel or steel. According to the invention, a layer support is used which worked as a band, is largely rigid across the direction of travel and is flexible and dimensionally stable along the direction of travel. In addition to a band made of metal, which already fulfills these conditions very well at thicknesses of 100-120 μm, aluminum-vapor-coated polyester films of sufficient thickness are used, mainly in the range of 75-250 μm. It has been shown that the greater thickness of this substrate is necessary for the rigidity. Accordingly, a correspondingly greater flexibility of the applied coating is required. By welding, straps can be formed with layers as layer supports, which are used in high-speed copying machines.

The insulating intermediate layer 4 can consist of organic material or optionally also a thermally, anodically or chemically produced aluminum oxide intermediate layer, and in addition to promoting adhesion, it has the aim, for example, of reducing the charge carrier injection from the layer carrier into the photoconductive layer in the dark by its arrangement. On the other hand, it does not hinder the flow of charge during the exposure process. Natural or synthetic resin binders can be used for the intermediate layer, such as, for example, polyamide resins, polyvinylphosphonic acid, polyurethanes or polyester resins. Their thickness can be up to 5 / µm, while thicknesses of aluminum oxide layers are mostly in the range of 10 ^-2 - / µm.

Such inorganic or organic substances are used as charge-generating compounds, as have been known for this purpose up to now. This subheading includes dyes or amorphous selenium. The dyes used or inorganic substances to be mixed such as. B. Tellurium determine the spectral sensitivity of the photoconductive layer to a particular degree.

The application of a homogeneous, densely packed dye layer carrier-producing substance layer as a charge carrier-generating layer is known and is obtained by evaporating the dye onto the carrier in vacuo. Depending on the vacuum setting, the dyes can be evaporated without decomposition under relatively favorable conditions of 10 ^-3 to 10 ^-5 Torr and 250 to 400 ° C heating temperature. The temperature of the carrier is below 50 ° C.

Layers with densely packed dye molecules are obtained, which has the advantage that the high extinction of the dyes enables a large concentration of excited dye molecules.

Depending on the type of use, the production of the charge carrier-producing layer with a uniform thickness can also be achieved by other coating techniques, such as, for example, by mechanically rubbing the finely powdered dye into the electrically conductive layer support, by chemical deposition of a leucase base to be oxidized, by electrolytic or electrochemical processes , by gun spray technique or by applying from a solution and drying the same.

In combination of the dyes with materials for the insulating intermediate layer 4 (FIG. 3) or as a replacement for an intermediate layer 4, homogeneous, well-covering dye layers with thicknesses of the order of magnitude of 0.01-3 μm are obtained by dispersing the dyes even in a binder according to the invention by coating of the electrically conductive layer carrier is possible (layer 5 in FIG. 41). The use of highly viscous cellulose acyl esters is particularly advantageous, since during grinding a very good distribution of the pigments (small grain size) is achieved during the coating. The ratio of charge-generating substance to binder can be achieved However, preference is given to primers with a dye content of more than 50% and a correspondingly high optical density. This also achieves the use of dyes which are not very thermally stable, such as azo or bisazo dyes. At the same time, the presence of the binder : H mediation caused.

• Perylen-3,4,9.10-tetracarbonsäureanhydrid bzw. Perylen-3,4,9,10-tetracarbonsäureimiderivate nach DT-OS 22 37 539; polynukleare Chinone nach DT-OS 22 37 678; cis- bzw. trans-Perinone nach DT-OS 22 39 923; Thioindigo-Farbstoffe nach DT-OS 22 37 680; Chinacridone nach DT-OS 22 37 679; Kondensationsprodukte aus Benzo-4 ,10-thioxanther.-3,1' -dicarbonsäureanhydrid und Aminen nach DT-OS 23 55 075; Phthalocyanin-Derivate nach DT-OS 22 39 924 und Farbstoffe, die durch Kondensation nach der Vorschrift Bull. Chem. Soc. Japan 25, 411 - 413 1952 aus Perylen-3,4,9,10-tetracarbonsäureanhydrid und o-Phenylendiamin oder 1,8-Diaminonaphthalin hergestellt. -werden

Dyes of various classes can be used as the charge carrier-producing compounds. Examples include:

• Perylene-3,4,9,10-tetracarboxylic anhydride or perylene-3,4,9,10-tetracarboximide derivatives according to DT-OS 22 37 539; polynuclear quinones according to DT-OS 22 37 678; cis or trans perinones according to DT-OS 22 39 923; Thioindigo dyes according to DT-OS 22 37 680; Quinacridones according to DT-OS 22 37 679; Condensation products from benzo-4, 10-thioxanther.-3,1'-dicarboxylic acid anhydride and amines according to DT-OS 23 55 075; Phthalocyanine derivatives according to DT-OS 22 39 924 and dyes, which by condensation according to the Bull. Chem. Soc. Japan 25, 411 - 413 1952 made from perylene-3,4,9,10-tetracarboxylic anhydride and o-phenylenediamine or 1,8-diaminonaphthalene. -become

As mentioned, thin layers of inorganic substances which generate charge carriers and are produced by vapor deposition of selenium, doped selenium, cadmium sulfide etc. are also suitable.

-Elektronensystem besitzen. Hierzu gehören sowohl monomere wie polymere aromatische carbocyclische und heterocyclische Verbindungen.In the photoconductive layer, particularly in the charge transport layer, charge transporting compounds are used as photoconductors. These are mostly organic compounds that are extensive

-Electronic system own. These include both monomeric and polymeric aromatic carbocyclic and heterocyclic compounds.

Monomers which have at least one dialkylamino group are used in particular. Heterocyclic compounds such as oxdiazole derivatives according to DT-AS 10 58 836, in particular 2,5-bis- (4'-diethylaminophonyl) -oxdiazole-1,3,4, have proven particularly useful. Other suitable monomers are, for example, triphenyl amine derivatives, more highly condensed aromatic carbocyclic compounds such as pyrene, benzo-fused heterocycles, and also pyrazoline or imidazole derivatives according to DT-PS 10 60 714 and DT-PS 11 06 599; this subheading also includes triazole, thiadiazole and oxazole derivatives, as are known from German patents 10 60 260, 12 99 296, 11 20 875.

As polymers z. B. more condensed aromatic compounds such as formaldehyde condensation products with various aromatics, such as condensates of formaldehyde and 3-bromopyrene according to DE-OS 21 37 288 particularly proven.

Without the layer generating the charge carrier, the charge transport layer has practically no photosensitivity in the visible range of approximately 420-750 nm. It preferably consists of a mixture of an electron donor compound as a photoconductor with a resin binder if the recording material is to be negatively charged. It is preferably transparent.

entsprechend angewandten Kapillaren im Bereich I - III bei 25°C (nach DIN 51 562) mindestens eine Viskosität von 20 cSt.In addition to the charge-generating and charge-transporting compounds, the added binder influences both the mechanical behavior, such as abrasion, flexibility, film formation, etc., and the electrophotographic properties, such as photosensitivity, residual charge, etc. B. according to DT-OS 23 53 639 previously film-forming compounds such as polyester resins, polyvinyl chloride / polyvinyl acetate copolymer

correspondingly used capillaries in the range I - III at 25 ° C (according to DIN 51 562) at least a viscosity of 20 cSt.

Electrophotographic recording material with these cellulose products as binders gives films with high elasticity.

Die.Celluloseacylester differ in addition to their degree of viscosity, especially with regard to their acyl radical. It was found that with increasing content of It was found that with increasing content of butyryl groups, in exchange for the acetyl groups, the photoconductor arrangement can be adjusted more light-sensitive. Therefore, it has proven to be particularly advantageous according to the invention to use cellulose acetobutyrata with at most 15 acetyl and z. B. use at least 15 butyryl content at high viscosity. This subheading also includes cellulose propionates with a high propionyl content or cellulose acetobutyrates with a large butyryl content. Mixtures of cellulose acyl esters can also be used.

The mixing ratio of the charge transporting compound to the binder can vary. However, the requirement for maximum photosensitivity, i. H. the largest possible proportion of charge-transporting compound and after avoiding crystallization thereof and increasing the flexibility, d. H. the largest possible proportion of cellulose acyl ester, relatively certain limits.

According to this, the preferred content of cellulose acyl ester for charge-transporting compound is in the range from 20 to 60 parts by weight to 80 to 40 parts by weight. Too large a proportion of monomers adversely affects flexibility, so that in particularly preferred, flexible forms of stirring, the ratio of cellulose acyl ester to charge-transporting compound is approximately 50:50 parts by weight.

When using polymeric Laduna transport compounds, the cellulose acyl ester content is in the range below 50%.

The charge transport layers with monomers such as 2,5-bis (4'-diethylaminophenyl) oxdiazole-1,3,4 are amorphous according to X-ray goniometer measurements.

The layer thickness of the photoconductive layer is in a range which corresponds to a layer weight of approximately 5 to 50 g / m ² . In the case of forming the photoconductive layer as a charge carrier generating layer and charge transport layer, layer thicknesses in the range from 0.005 to 2 _/ um, preferably 0.005 to 1 / um and in the range of 2 to 20 / m, preferably 3 to 10 _/ um, are suitable. If the charge-generating layer is in dispersion, layer thicknesses in the range of preferably 0.1-1 μm are suitable.

However, if the mechanical requirements and the electrophotographic parameters, such as charge and development station, a copier allow, the specified limits are extended up or down case by case.

Leveling agents such as silicone oils, wetting agents, in particular nonionic substances, plasticizers of different compositions, such as, for example, those based on chlorinated hydrocarbons or based on phthalic acid esters are considered to be conventional additives. If necessary, sensitizers and / or acceptors can also be added to the charge transport layer, but only to the extent that the optical transparency of the charge transport layer is not significantly impaired.

The invention is illustrated by the examples:

example 1

Beäampfte aluminum on a polyester film of 75 _/ um thickness is the pigment N, N'-dimethyl-3,4,9,10-tetracarboxylic perylene in fun Vakuumbedamp- ^g sanlage at 10 ^-4 - 10 ^-5 Torr within Evaporated at about 230 ° C for 2 minutes. The distance between the despair source and the substrate is about 20 cm. The homogeneously evaporated dye layer has a layer weight in the range of 100-200 mg / m ² . The electrically conductive substrate. is completely covered by this.

• a) Äthyl-Cellulose'mit einem Äthoxylgehält von 47,5 bis 49 %
• b) Celluloseacetat mit einem Acetylgehalt von 38, 4 % und
• c) Celluloseprcpionat mit einem Propionylgehalt von 44,7 %.

A solution of equal parts by weight of 2,5-bis (4'-diethyl- aminophenyl) -oxdiazole-1,3,4 (mp. 149-150 ° C) and one of the following cellulose derivatives spun in tetrahydrofuran:

• a) ethyl cellulose with an ethoxyl content of 47.5 to 49%
• b) cellulose acetate with an acetyl content of 38.4% and
• c) Cellulose propionate with a propionyl content of 44.7%.

To. Drying the applied solutions in a forced air drying oven at 110 ° C for about 5 minutes, the respective layer thickness is 9-10 _/ um.

• Zur Ermittlung der Heillentladungskurven bewegt sich die Meßprobe auf einem sich drehenden Teller durch eine Aufladevorrichtung hindurch zur Belichtungsstation, wo sie mit einer Xenonlampe XBO 150 der Firma Osram.kontinuierlich belichtet wird. Ein Wärmeabsorptionsglas KG 3 der Firma Schott & Gen., Mainz, und ein Neutralfilter mit 15 % Transparenz sind der Lampe vorgeschaltet. Die Lichtintensität in der Meßbene liegt im Bereich von 70 - 170 _/uW/cm ; sie wird unmittelbar nach Ermistlung der Hellabfallkurve mit einem Opto-Meter Model -80 X United Detector Technology, Inc.) gemessen. Die Aufadungshche (U_o) und die phetoinduzierte Hellabfallkurve werden über ein Elektrometer 610 CR der Fa. Keithley Instruments, USA, durch eine transparente Sonde oszillographisch aufgezeichnet. Die Photoleiterschicht wird durch die Aufladungshöhe in Volt (U_o) und diejenige Zeit .T 1/2) charakterisiert, nach der die Hälfte der Aufladung (U_o /2) erreicht ist. Das Produkt aus T_1/2 und der gemessenen Lichtintensität I [_/uW/cm²] ist die Halbwertsenergie E_1/2 [_/uJ/cm²].
  
  

mit 2,5-Bis-(4'-diäthylaminophenyl) -oxdiazol-1,3,4 aufgebracht.The photosensitivity of the photoconductive double layers produced is carried out as follows:

• To determine the heat discharge curves, the test sample moves on a rotating plate through a charging device to the exposure station, where it is continuously exposed to an XBO 150 xenon lamp from Osram. A heat absorption glass KG 3 from Schott & Gen., Mainz, and a neutral filter with 15% transparency are connected upstream of the lamp. The light intensity in the Meßbene is in the range 70-170 _/ uW / cm; it becomes effective immediately after being tortured the light decay curve measured with an Opto-Meter Model -80 X United Detector Technology, Inc.). The charge level (U _o ) and the pheto-induced light decay curve are recorded oscillographically using a 610 CR electrometer from Keithley Instruments, USA, using a transparent probe. The photoconductor layer is characterized by the charge level in volts (U _o ) and the time .T 1/2) after which half the charge (U _o / 2) has been reached. The product of T _1/2 and the measured light intensity I [ _/ uW / cm ² ] is the half-value energy E _1/2 [ _/ uJ / cm ² ].
  
  

applied with 2,5-bis (4'-diethylaminophenyl) oxdiazole-1,3,4.

• 

The manufacturing and measuring conditions are analogous to Example 1; the layer thickness of the spun-on Decik layer is approximately ⁷ _/ um:

• 

Example 3

The flexibility of photoconductor layers with cellulose acyl esters such as cellulose acetobutyrates of different viscosities is examined. A polyester layer producing a Laduna carrier is applied to polyester films of different thicknesses which have been made conductive by aluminum vapor deposition, as listed in Example 1.

A charge transport layer is applied over it, which consists of equal parts by weight of 2,5-bis (4'-diethyl-. Aminophenyl) oxydiazole-1,3,4 and the respective cellulose acetobutyrate. The layers applied from tetrahydrofuran solutions have layer weights in the range of 7-9 g / m ² .

For the novel recording materials that both 18 and 12 mm roll diameter at the stipulated substrate thicknesses only few or no crazing under these substantial Bie ^g e-stresses occur appears.

In contrast, a clear differentiation with regard to the layer thickness and the roller diameter is observed in photoconductor layers with polyester resins or with vinyl chloride / vinyl acetate copolymers.

Analogous to the preparation described in these examples, a charge transport layer composition comprising 50 parts by weight of photoconductor, 25 parts by weight of polyester resin and 25 parts by weight of vinyl chloride / vinyl acetate copolymer is applied in a layer thickness of 9-10 g / m ² to a dye layer in accordance with Example 1 and subjected to the bending stress test. After that, no, on the 125 m thick isolated short hair cracks and on the 190 um thick polyester film very strong and long hair cracks _{/ /} contact at 25 mm roller diameter and 5000 rounds in the photoconductive layer on polyester film of 75 _/ um thickness at all on. In addition, occasional hairline cracks occur with a roller diameter of 18 mm and a carrier thickness of 75 μm.

Example 4

In an 8% tetrahydrofuran solution from equal parts by weight of 2,5-bis (4'-diethylaminophcnyl) oxdiazole-1,3,4 and a cellulose acctobutyrate with an acetyl content of 13.5% is suspended in a 5% amount (based on solids content) of the pigment according to Example 1.

For dispersion in a Perl Mill PM 1 (Draiswerke, Mannheim), the batch was first adjusted to a 25% concentration and the pigment dye in the highly viscous solution was ground intensively for 2 hours. This solution was then diluted to the coating batch given above. The pigment-dispersion layer is then according to arrangement _/ homogeneously in Figure 1 on an aluminum foil of 100 m in thickness with a layer thickness of approximately 5 _/ um applied. The measurement is carried out analogously to the conditions specified in Example 1 (light intensity approx. 100 _/ uW / cm ² , xenon light XBO 150): negative charging = 390 V, E _1/2 = 16.5 _/ uJ / cm ²

Example 5

(4'-diethylaminophenyl) oxdiazole-1,3,4 and cellulose acetobutyrate with an acetyl content of 5% (layer thickness approx. 7 µm; arrangement according to FIG. 4).

• E_1/2 = 8,7 _/uJ/cm².

The photosensitivity is determined analogously to example 1 (light intensity 90 _/ uW / cm ² ; xenon XBO 150) and gives a negative charge of 330 V:

• E _1/2 = 8.7 _/ uJ / cm ² .

Example 6

A condensation product of 3-bromopyrene and formaldehyde in accordance with DT-OS 21 37 288 is used as a polymer charge-transport compound.

As described in Example 1, a perinone dye layer, CI 71105, according to DT-OS'22 39923, 75 _/ evaporated to thick polyester film vapor-coated aluminum in an amount of 90 mg / m ² on one and a tetrahydrofuran solution of 70 parts by weight, of the condensation product is applied together with 30 parts by weight of a cellulose acetobutyrate with 5% acetyl groups, having a viscosity of 20 poises in about 5 _/ um thick layer after drying.

The photosensitivity measurement, with a light intensity of 90 _/ uW / cm ² and xenon lamp XBO 150, gives a value of E _1/2 = 7.3 _/ uJ / cm ² when the layer is negatively charged to 410 volts.

Using the dye according to Example 1 gives a negative charge of 630 volts E _1/2 to 4.9 _/ uJ / cm ² . Using a polynuclear chincn as a dye (Hostapermscharlach GO, CI 59 300) and using a cellulose acetobutyrate with a viscosity of about 75 poises and an acetyl group content of 13.5%, a photosensitivity with negative charging to 430 volts becomes E _1/2 4.7 _/ uJ / cm ² measured.

Example 7

On a dye layer, as described in Example 1, a solution of 50 parts by weight of 2,5-bis- (4'-diethylaminophenyl) oxdiazole-1,3,4 together with 40 parts by weight of a cellulose acetobutyrate with 13.5% acetyl groups and one Viscosity of about 75 poises and 10 parts by weight of a cellulose acetate with an acetyl group content of about 40% and a viscosity of 40 poises applied and dried to a layer thickness of 8-9 _/ um.

The photosensitivity is determined at 85 _/ uW / cm ² light intensity and when charged to -800 volts to E _1/2 = 2.9 _/ uJ / cm ² .

Claims (9)

1. Electrophotographic recording material composed of an electrically conductive support, optionally an insulating intermediate layer and a photoconductive layer comprising at least one charge-generating and charge-transporting compound, binder and conventional additive containing layer, characterized in that the recording material with a 75 to 250 _/ um thick support worked as a photoconductor tape is so flexible that it repeatedly runs over rolls of at least 18 mm in diameter, does not tend to hairline cracks and that it contains cellulose acyl ester as a binder with an acetyl content of at most 30% and a viscosity of over 15 poises, measured according to ASTM D 817- 65, Formula A and D 1343-56. 2. Recording material according to claim 1, characterized in that the cellulose acyl ester has an acetyl content of at most 15% and a viscosity of over ^- 15 poises. 3. Recording material according to claim 1, characterized in that the cellulose acyl ester has an acetyl content vop of at most 15% and a viscosity of over 50 poises. 4. Recording material according to claims 1 to 3, characterized in that the cellulose acyl ester has acyl groups with 2 to 4 carbon atoms. 5. Recording material according to claims 1 to 4, characterized in that the cellulose acyl ester is a cellulose acetate butyrate with a butyryl content ven at least 15%. 6. Recording material according to claim 5, characterized in that the cellulose acyl ester is cellulose acetobutyrate with at most 15% acetyl content and has a viscosity in the range of 60-110 poises. 7. Recording material according to claims 1 to 6, characterized in that the ratio of cellulose acyl ester to charge-transporting compound is in the range between 20 to 60 parts by weight to 80 to 40 parts by weight. 8. Recording material according to claims l'to 7, comprising a according to the order of the layers 100 to 250, um thick electrically conductive support _/ vapor-deposited aluminum of up to 250 um thick electrically conductive support of polyester film, a charge carrier generating layer from 0.005 to 2 _/ um thickness and a 2 to 20 _/ um thick charge transport kit consisting of 40 to 60 parts by weight of a monomeric organic charge transporting compound and 60 to 40 parts by weight of cellulose acyl ester. 9. Recording material according to claims 2 to 8, characterized in that the charge carrier generating layer contains cellulose acyl ester.

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