DE2059540C3 - Electrophotographic recording material with a photoconductive layer - Google Patents

Description

The invention relates to electrophotographic recording material with a photo-conductive layer, the at least one polymeric, aromatic photoconductor as an electron donor, an electron acceptor and optionally additives of binders, and / or the adhesion and / or the surface structure Contains substances.

The polymeric photoconductors are poly-N-vinylcarbazole, Poly-C-vinylcarbazole, copolymers of N-vinylcarbazole or polycondensed aromas, for example in the Belgian patents 88 050 and 5 92 557 or the German Auslegeschrift 09 032.

It is known to increase the sensitivity of organic photoconductors by adding electron acceptors to improve in the area of visible light. This is described in DE-AS 1111 935. 11 27 218 and 12 33 265 described. However, only those concentrations of electron acceptor are used in these processes, which correspond to those of conventional optical sensitizers (DE-AS 10 68 115). in the DE-AS 12 19 795, however, proposes the addition of considerably larger amounts of electron acceptor. Here is a system consisting of an electron acceptor as the actual photoconductor and Electron donor as a sensitizer. In this process, too, optical Sensitizers used.

It is known from DE-AS 15 22 718, a PhötöIeiteF mixture from equal parts by weight of polyvinyl carbazole and 2,4,7-trinitrofluorenone, corresponding to one Molar ratio of 1: 0.63, combined with a thin coating of a non-conductive polymeric material to use. There are also from BE-PS 6 99 851 photoconductor layers known to have a charge transfer complex of a polymerized heterocyclic vinyl vex bond and trinitrofluoreaon as electron acceptor in molar ratios of 1: (0.49 to 1.23). It is finally known from DE-AS 18 10 757, in a method for the transmission of electrostatic Charge images from a photoconductor layer

to use a dielectric layer, photoconductor layers based on charge transfer complexes, in which as photoconductors, polymers of one or more vinyl heterocyclic compounds and as activators Compounds that have strongly polar groups such as halogens. Have cyano, nitro, etc. groups, to be used in wide proportions. Here it is in In some cases it is advisable to use molar ratios of 1: 1 of the two components, the proportion of the activator can often be about 0.7 to 13 moles based on 1 mole of the photoconductor. This knowledge In spite of the multitude of possibilities, only lead to a useful combination of polyvinyl carbazole and trinitrofluorenone in a mixture of 1 mol of acceptor to 1 mol of photoconductor, based on its monomer unit. This means that there is no greater choice of suitable compounds.

There are also calculations and measurements of electron affinities of acceptors of various constitution and in various mixing ratios sen known with polyvinyl carbazole and other donors (W. Wagner et al, Photographic Science and Engineering, 14, (1970), pp. 205 and 207, R. Foster Organic Charge Transfer Complexes, 1969, Academic Press London, New York) from which it appears that none Relationship exists that includes all acceptors that however the size of the donor and acceptor can be important and that there is a linear relationship between Photo conductivity and elevtron affinity of such There are acceptors, which have a similar electronic structure own. Useful donor / acceptor combinations are not known from this.

It is a disadvantage of the photoconductive layers known from the prior art. that they contain a photoconductor system that is comparatively insufficiently highly sensitive and / or that the electron acceptors present in them have to be added in too large a quantity or are only accessible with difficulty.
It is the object of the present invention to provide a selection principle for suitable electron acceptors for photoconductor layers of electrophoresis recording materials which, in a relatively high concentration, together with polymeric, aromatic photoconductors, result in highly sensitive layers.

The invention relates to an electrophotographic recording material comprising a photoconductive layer which :: eptor with at least one crossed konjugier · ten, preferably symmetrical π-electron system as a activator, and optionally further additives corresponds V ₁ holds at least one polymeric aromatic photoconductor as an electron donor a Elektronenak . The material according to the invention is characterized in that the photoconductive layer has the photoconductor with an ionization potential between 5 and 8 eV in a mixture with 03-13 mol of an electron acceptor from the group of 3,6-dinitronaphthalic acid imides or anhydrides, the 3, 6-Dinitroacenaphthenchinons, des Se-Dinitro ^ -dihydrophenalendions- ^, des

3,6,8-TriniirochinoIons, des 3,6,8-Trinitrocurnarins _0C Jer of 5,8-Dinitro-9b-borano-phenalene with an electron affinity between 0.5 and 1.5 eV, preferably between 0.7 and 1 , 3 eV per mole of monomeric unit of the photoconductor

It has been found that deeply colored layers are then formed, thanks to the broad charge transfer absorption band are sensitized in the entire region of the visible spectrum when the photoconductor is on Ionization potential - d. H. the energy that is necessary to form an electron from the molecule to remove a radical cation - below 8 eV and that is not significantly lower than 5 eV.

If the ionization potential of the photoconductor is too low it was further found that not only, as intended, under the action of the absorbed light Electron and a defect electron are formed, but this already in a disturbing way in the dark under the action of the charge applied to the photoconductor layer with the hooves of a corona and the The resulting field strength takes place kmn. If the ionization potential of the photoconductor is greater than that of 8 eV results in a sensitivity in the UV range or in the short-wave range of the visible spectrum.

In all areas of application of the recording material according to the invention, the photoconductor layer is charged to high voltages in the dark. This treatment is possible with the methods mentioned in the prior art without restricting the photoconductor electron donor and electron acceptor material, since the concentrations of added electron acceptor or electron donor are too low to be able to significantly influence the charging process. In order to achieve the far greater sensitivities that are necessary for electrophotographic copying machines, however, higher concentrations of acceptor have to be added. In these cases it is advantageous then to make the abovementioned restriction to certain monomeric units of the photoconductor. Soft monomer units can be used as partners for the electron acceptors, taking into account the results of Pysh and Yang (J. Amer. Soc. 85 2124 [1963]) from the tables of the oxidation potentials of organic windings (Chem. Rev. 68 452 [ 1968]). According to this, only donor monomer units are possible whose oxidation potential E '/ 2 is in the range from 1.5 to 0.2 V when the test conditions specified there are observed.

The process of photoconductivity in a sensitized or activated polymeric photoconductor can be such as can be characterized as follows.

The polymer photoconductor

-D-D-D-D-D-

is sensitized by the known methods with any electron acceptor A or activated.

- D — D — D — D — D— A.

By light absorption, especially of the wavelength known as the charge transfer absorption band or by a hermetic reaction there is an electron transfer from the donor to the acceptor instead

—D — D s — D — D — D—

This completes the decisive step of the photoconductive process: the positive charge of the radical cation D ⁹ is delocalized under the influence of the sufficiently strong electric field, that is to say it can move freely.

—D — D — D — D — D-- -

The known processes of sensitization or activation thus ensure an improvement in the Conductivity through holes: the number and mobility of holes is increased.

However, if the electron acceptor is added in a much higher concentration, the result is a charge transfer complex of the following kind:

—D — D — D — D — D—
AAAAA

This is where it is in the absorption process or

thermally transferred electron is not isolated in an acceptor molecule, but that The resulting radical anion is surrounded by molecules of the same type as is the donor radical cation

- D - D - D-- D - D -

AAAAA

Under the influence of the electric field, the excess electron of the radical anion can now be more or less free be mobile and migrate by the same mechanism as the positive charge of the radical cation

AAAAA

This migration of electrical charge within a chain of donor and acceptor molecules is due to the fact that, due to the formation of radical anions within this chain, homeopolar Charge transfer complexes arise:

Α ^Θ - * Α with the radical anion as donor and the

original molecule as an acceptor
D® «-D with the radical cation as acceptor and the original molecule as donor.

The advantage of the present invention is based on the fact that through a suitable choice of the acceptor molecule what is achieved is that the homeopolar charge-transfer interaction is particularly intense. this causes an increase in the mobility not only of the defect electrons but also of the electrons. In order to it is achieved that the absorption of the photon creates two mobile charge carriers while according to the known processes, only one mobile charge carrier could arise per photon.

The compounds suitable according to the invention have a relatively high electron affinity and a particularly large dislocation of the negative charge des during the exposure of the charge transfer complex

resulting radical anion. However, the electron affinity is allowed also not be too large, otherwise undesirable electron transfer in the ground state or too little donor effect of the radical anion formed on exposure occurs.

The photosensitivity increasing used in the material according to the invention are symbolized as follows Electron acceptors

i A ₂

enable the following reactions

+ Ie-

d. H. the takeover of an electron from the donor photoconductor by the electron acceptor and mesomerism of the resulting radical anion. The greater the number of low-energy, mesomeric Structures ir. A molecule, the greater the likelihood of further delocalization across several molecules. It was recognized that the electron acceptor, in order to meet these requirements, has the following characteristics: at least two electron-withdrawing substituents, a so-called cross-conjugated; r-electron system. that both allows continuous conjugation in the excited state as well as after the uptake of an electron, the formation of radical anions must have a particularly high degree of delocalization of the negative charge or the radical site and there should be special residues on this system for better processing be present, which provide improved solubility properties.

The advantage of these electron acceptors over the well-known 2,4,7-trinitrofluorenone exists on the one hand in the greater choice of suitable connections and the considerably safer and easier ones Depiction. The extinction of the layers that can be produced with these compounds is also lower than that the trinitrofluorenone layers, making it easier to use highly sensitive material for a reflex copier system can be produced.

The compounds listed in the table are, for example, electron acceptors according to the invention suitable these are

3,6-dinitronaphthalic anhydride
5,8-Dinitro-Z3-dihydro-phenaIendione-1,3
3,5-dinitroacenaphthenquinone
3,6,8-trinitroquinoline
3,6,8-trinitrocoumarin
3,6-dinitronaphthalimide
N-methyl-3,6-dinitronaphthalimide
N- (3-methoxypropyl) -3,6-dinitronaphthalimide
N-phenyl-3,6-dinitronaphthalimide
N- (n-Octadecyl) -3,6-dinitro-naphthaIimide
N- (n-hexadecyl) -3,6-dinitro-naphthalimide
N- {p-nitrophenyl) -3,6-dinitro-naphthalimide
N- (n-butyl) -3,6-dinitro-naphthalimide
N- {tert -butyl) -3,6-dinitro-naphthalimide
N- {2,2-dimethoxy-ethyl) -3,6-dinitronaphthalimide

N- (n-Buiyloxy-propyl) -3,6-dinitro-

naphthalimide
5,8-dinitro-9b-borano-phenals

The substances from the group of the 3,6-dinitronaphthalic acid imides or anhydrides, in particular

N-isobutyl-3,6'dinitronaphthalic acid imide,

N- (tert-butyl) -3,6-dinitronaphthalic acid imide,

N- (3-methoxypropyl) -3,6-dinitronaphthal-

acidimide or
N- (2,2-dimethoxyethyl) -3.6-dinitronaphthal-

acid imide,

prove to be particularly suitable.

The electrophotographic recording material according to the invention with a photoconductive layer finds ¹ . Use in eiek'ropho '^ grnnhUrhen copier machines or as an electrophotographic printing plate. It can also be used as a material for printed circuit boards.

With the electron acceptors used according to the invention, those mentioned at the outset can be used process polymeric photoconductors into particularly highly sensitive electrophotographic layers. Particularly These electron acceptors are well suited for solubilizing poly-N-vinylcarbazoI. To do this, the electron acceptor in a molar concentration of more than 0.3 mol. based on 1 mol of monomeric unit of the photoconductor, dissolved or suspended in suitable solvents.

Suitable solvents are, for example, methylene chloride, tetrahydrofuran, dioxane, cyclohexanone, chlorobenzene or toluene. If necessary, further polymeric substances are added which lead to an improvement in the adhesive strength and the smoothness of the layer. Suitable as such are perchlorinated, aromatic or aliphatic plasticizers or wetting agents, polyester resins or polyvinyl ethers and one or more of the commercially available leveling and plasticizing agents. The solution or suspension is applied to a carrier material by a known method. Suitable carrier materials are in particular extremely smooth films made of polyesters, polyolefins, cellulose derivatives or the like, which have been given a conductive layer by coating with conductive polymers, carbon black or metals; metal-vapor-deposited films, in particular aluminum-vapor-deposited films, are preferably used. With such a recording material, for example, a drum is covered, around which in a known manner a charging corona, exposure device for imagewise exposure, development station for developing the latent electrostatic image with toner powder, transfer device for transferring the toner image from the photoconductive layer to paper and arrangement for cleaning the photoconductor layer are arranged.
The electrophotographic recording materials can also be used in copier machines in which not toner particles but rather the latent electrostatic images are transferred to a dielectric layer and developed there both dry and liquid.

The copies produced are razor-sharp and free of ground. The copying speed corresponds roughly to that of a machine with a selenium layer.
In the presence of alkali-reactive

Anhydride and / or phenolic hydroxyl groups in the electron acceptor of the material according to the invention have the particular advantage of being able to produce printing plates whose layers can be hydrophilized with a mixture of aqueous alkalis and a solvent such as tetrahydrofuran or dioxane; In this way, an image-wise hydrophilization can be carried out in a simple manner after an electrophotographic toner image has been produced on the layer in a conventional manner. D ^: (> hydrophilization takes place only on the non-image parts.

The invention is described in more detail by means of the following examples. The photoconductive used for this purpose Layers were applied on a conventional coating machine using the so-called »kiss-coat process« or by pouring the solution onto a rotating plate with an aluminiman to be coated Using a field mill or other field strength measuring instrument, the following voltage drop values or determine residual stresses:

Voltage drop

20th

example 1

5.27 grams of poly-N-vinyl carbazole

3.42 g of 3,6-dinitronaphthalic anhydride

(Formula I) (0.41 moles per mole of poly-N-vinylcarbazole)

0.41 g polyester glue
90.9 grams of tetrahydrofuran

The solids are dissolved in tetrahydrofuran with stirring. On a coating machine, at a coating speed of approx. 3 m / min, a layer thickness of approx. 10.5 g / m ^{2 is obtained} .

Such a layer can be charged to approx. -700 V with the aid of a conventional corona will. With a step wedge (21 steps, factor 0.15) from Kodak it was possible to use an illuminance of 1150 Lux (tungsten wire lamp) 5 (1 see) levels be exposed. It is also important here that the gradation, i.e. H. the charge depending on the Exposure is pretty steep. This means that a given charge can be carried out in extremely short times a given amount of light can be reduced considerably.

Example 2

538 grams of poly-N-vinyl carbazole

4.40 g of 3,6-dinitronaphthalic anhydride

(Formula I)

(0.56 moles per mole of poly-N-vinylcarbazole)
0.41 g polyester glue
89.8 grams of tetrahydrofuran

The solution and then the layer is produced as described in Example 1.

At a coating speed of approx. 3 m / min, a layer thickness of 133 g / m ^{2 is obtained} . The charge is then -1000 V. With an illumination with 1150 Lux one observes 5 (1 see) exposed steps. Taking into account the higher charge, this means an increase in sensitivity compared to example 1. _

If the layers described in Examples 1 and 2 are used in a copier as indicated above, by stretching the coated foils on a drum and charging them with the aid of a corona switched to -6.5 KV, then (difference between
Dark and light voltage)

Residual stress

10 Example 1
Example 2

410 V
380 V

310 V
200 V

15 These measurements were carried out at a speed of rotation of the drum of 6 rpm with an aperture of 5.6; an amount of light of 11.9 lux / sec was measured.

The measured voltage drop and the residual voltage are sufficient for an image development with With the help of a commercially available toner, which is produced by a cascade device together with a carrier material - such as z. B. Glass balls - is thrown onto the drum surface with the electrostatic image. To this Copies of any template can be made using the layers of Examples 1 and 2. Due to the sensitivity reaching far into the visible (see Fig. 1), the color reproduction is perfect possible, which has particular advantages compared to selenium layers. The copies are rich in contrast and without reason.

For layers according to Examples 1 and 2, the compounds whose formulas have been given below are suitable. In order to be able to show a number of examples that the electrophotographic sensitivity caused by these classes of substances z. B. of the polymeric photoconductor poly-N-vinylcarbazole is so large that a copier of the types described above can be operated with its help, the following method is chosen: Increasing amounts of the electron acceptors listed in Table 1 were solutions with constant amounts of poly N-vinylcarbazole added as a photoconductor. A binding agent was also added. The solutions obtained in this way were cast onto rotating aluminum plates to form layers which had an average thickness of 4-7 g / m ² .

The electrophotographic sensitivity of these layers was determined with a step wedge by the charged layers through a step wedge (density factor 0.15.21 steps) with a tungsten wire lamp were exposed. The tungsten wire lamp generated 1150 lux in the sample plane. One Another method to describe the photosensitivity was used: According to Arneth and Lorenz (Reprographie 3, 199 [1963]) is an exact physical measure for the light sensitivity, the half-life the decrease in charge when light is irradiated on the charged photoconductor layer It indicates in which Half of the original charge is reached after the start of irradiation. In the following This half-life is also given in examples. A xenon high pressure lamp served as the light source, which generated 300 lux in the sample plane. Most of the time the photoconductive layers were negatively charged; but some examples showed a sufficiently high sensitivity with positive charging.

The dependence of the photosensitivity on the concentration was shown in FIG. 2 shown.

In the following examples the photoconductor layer had the following composition:

30 g of poly-N-vinyl carbazole and 24 g of a hard resin based on chlorinated rubber were dissolved in 750 g of dioxane and 570 g of Buf.non-2. To 100 ml of this solution the specified electron acceptors were added, so that the specified concentrations of moles Electron acceptor per mole of N-vinylcarbazole (NVCa) resulted.

To demonstrate the technical progress of the present invention over the known Processes for sensitizing photoconductors are given from example 15, comparative examples with the Results of sensitivity.

Half-life:

32.5 msec at -430 V charge.

Example 7

N-methyl-3,6-dinitronaphthalimide (formula VlI) maximum sensitivity for: " 0.39 mol per mol NVCa (limited by the poor solubility) with 3 exposed levels

with 1 second exposure time OK exposed steps with 10 sec exposure time (Charge: -310V) Half-life: 40 msec at - 395 V charge.

example

3,6-Dinitronaphthalic anhydride (Formula I) maximum sensitivity for:

0.68-1.02 moles per mole of NVCa with 6 levels exposed

at 1 sec exposure time 12 exposed steps at 10 sec exposure time (Charge: -340V) Half-life: 50 msec at - 420 V charge.

Example 4

3,6-DinitronaphthaHmid (Formula VI) maximum sensitivity at: 0.6 moles per mole of NVCa with 4 stages completed

at 1 sec exposure time 10 exposed steps at 10 sec exposure time (Charge: -300V) Half-life: 50 msec at a -325 V charge.

Example 5

N-phenyl-3,6-dinitronaphthalimide (Formula IX) maximum sensitivity for: "' 03 moles per mole of NVCa (limited by the poor solubility of the imide) 2 exposed levels

at 1 second exposure time 8 exposed steps at 10 seconds exposure time (Charging here at -300V) Half-life: 45 msec at -360V charging.

Example 6

N-methoxypropyl-3,6-dinitronaphthalimide (formula VIII)

maximum sensitivity at:

0.77-1.10 moles per mole of NVCa with 2 finished steps at ϊ see exposure time 8 finished steps at 10 see exposure time (charge: -350V)

Example 8

N- (n-octadecyl) -3,6-dinitro-naphthalimide

(Formula X)

maximum sensitivity at:

0.15 moles per mole of NVCa (limited by solubility)

Half-life: 72 msec with a -410 V charge.

Example 9

N- (n-Hexadecyl) -3,6-dinitronaphthalimide (Formula XI)

maximum sensitivity at:

0.25 moles per month! NVCa (limited by solubility)

Half-life: 74 msec with - 380 V charge.

Example 10

N- (p-nitrophenyl) -3,6-dinitronaphthaliii.id (Formula XII)

maximum sensitivity at:

03 MoI per mole of NVCa (limited by solubility)

Half-life: 57 msec at -480 V charge.

the

Example 11

N- (n-butyl) -3,6-dinitronaphthalinud (formula XIII) maximum sensitivity at:

0.45 moles per mole of NVCa half-life: 80 msec at +285 V charge.

Example 12

N- (tert-butyl) -3,6-dinitronaphthalimide (Formula XIV)

maximum sensitivity at: 0.45 mol per mol NVCa half-life: 34 msec at -590 V charge.

Example 13

N- {2 £ -dimethoxy-ethyl) -3,6-dinitronaphthalimide (Formula XV)

It

maximum sensitivity at:
0.85MdPrOMoINVCa
Half-life: 37 msec at -590 V charge.

Example 20

Example 14

N- (n-Butyloxy-prop, yl) -3,6-dinitro-naphthalimide

(Formula XVl)

maximum sensitivity at:

0.7 moles per mole of NVCa

Half-life: 48 msec at -400 V charge.

The following examples are comparative examples to demonstrate the particular effect of the above Compounds described in comparison with those given in the literature (Table 2).

Example 15

From the above poly-N-vinylcarbazole solution was added with the addition of 50 mg Rhodamine B extra per 50 ml (1:20 weight ratio) to the poly-N-vinylcarb- “Zol produced a layer in the same way as above.

Half-life: 400 msec (-335 V).

Example 16

A layer was produced in the same way as in Example 15, but with a further addition of Tetrachlorophthalic anhydride (Formula I, Table 2) (100 mg per 50 ml of solution or 0.13 mol per mol NVCa).

Half-life: 170 msec (-320 V).

As described in Example 1, photoconductor layers were used made of the following composition:

36 g of a pyrene formaldehyde condensate prepared

according to DE-AS 12 18 286 and
18 g of a copolymer of vinyl chloride and vinyl acetate

and were dissolved in 300 g of tetrahydrofuran and, for each 58 g of this solution, the electron acceptors indicated below added, the specified molar ratios acceptor to monomer component pyrene result:

A. 3,6-Dinitronaphthalic anhydride (Table I ₁ Formula I) 0.5 moles per mole of pyrene.

When charged to -830 V, the layer produced had a half-life of 76 ms.

B. 3,6-Dinitronaphthalimide (Table 1, Formula VI) O ^ MoI per mole of pyrene.

A charge of -1300 volts results in a half-life of 62 ms.

C Tetrachlorophthalic anhydride (Table 2, Formula 1) 03 moles per mole of pyrene.

A charge of -990 volts resulted in a half-life of only 150 ms.

35

Example 1/

13,6,8-tetranitrocarbazole (formula II, table 2)
maximum sensitivity at:

1.0 Mo! per mole of NVCa

Half-life: 290 msec (-140 V).

In tetranitrocarbazole, the nitrogen atom acts like an electron donor, which is what the above formulation means of the claimed compounds is inconsistent

Example! 18th

23-dichloronaphthoquinone-1,4 (formula III,
Tab. 2) maximum sensitivity at:

0.62 moles per mole of NVCa

4 exposed levels at 10 see exposure time (tungsten lamp as described above)

Half-life: 135 msec (-350 V).

Example 19

23-Dicyanonaphthoquinone-1,4 (Formula IV,
Tab. 2) maximum sensitivity at:

0.4 moles per mole of NVCa

Half-life: 400 msec (-30 V).

In this case the electron affinity is too great (see Sect. Page 3 ff.): You can no longer charge such a photoconductor layer sufficiently.

Tabel !

O O O

CC

50

60 O ₁ N

NO ₂

O ₂ N

NO ₂

O O

Il Il c-c

O ₂ N

O ₂ N

NO ₂ j

C ₁₁₅ H,

30th

O = C C = O

40

O ₂ N

NO ₂

(XIi) {

CH ₂ -CH ₂ -CH ₂ -OCH ₃

(VIII)

45 50 55 60 65

UC ₁ H ₉

/ \ O = C C = O

O ₂ N

NO ₁

o = c): = o

IO ₂ N NO ₂ Y.

(XIII) I.

(XIV)

Continuation tower

Cl 0

(XV)

ίο

15th

20th

(XVI)

25th

30th

(XVIl)

35

(D

Cl 0

45

(H)

(1111

50

55

60

(IV)

65

1 sheet of drawings

Claims (3)

Patent claims: 1. Electrophotographic recording material with a photoconductive layer which contains at least one polymeric aromatic photoconductor as electron donor, an electron acceptor with at least one cross-conjugated, preferably symmetrical jr electron system as activator and optionally other additives, characterized by the combination that the photoconductive layer is the photoconductor with an ionization potential between 5 and 8 eV in a mixture with 03-13 mol of an electron acceptor from the group of 3,6-dinitronaphthalic acid imides or anhydrides, 3,6-dinitroacenaphthenquinone, Se-dinitro ^ -dihydrophenaJendions-13, the 3 , 6,8-trinitroquinoline, of 3,6,8-tri.nitrocoumarins .rxter of 5,8-dinitro-9b-borano-phenalene with an electron affinity between 05 and 1.5 eV, preferably between 0.7 and 13 eV, per mole of monomeric unit of the photoconductor. 2. Recording material according to claim 1, characterized in that the photoconductive Layer contains a 3,6-dinitronaphthalic acid imide as electron acceptor 3. Recording material according to claim 1 or 2, characterized in that the photoconductive Layer an electron acceptor with an anhydride or phenolic hydroxyl group contains.