EP0198488B1 - Electrophotographic recording material - Google Patents

Description

• A) einem für den Offsetdruck geeigneten elektrisch leitfähigen Aluminiumträgerblech in einer Dicke von 0,1 bis 0,6 mm mit z. B. einer elektrolytisch aufgerauhten oder anodisierten Oberfläche, und
• B) der elektrophotograpischen Schicht aus
  • B1) mindestens einem mit allen in der Rezeptur vorhandenen Komponenten verträglichen Bindemittel, das in offsettypischen Auswaschmedien löslich ist,
  • B2) einer niedermolekularen Ladungstransportverbindung,
  • B3) mindestens einem Sensibilisator für den gewünschten aktinischen Bereich und
  • B4) weiteren Zusätzen, die die allgemeinen Schichteigenschaften verbessern.

The use of homogeneously sensitized photoconductor layers for the production of electrophotographic printing forms, in particular electrophotographic offset printing forms, is known. Such layers and the associated processes are e.g. B. in DE-PS-1 117 391 and in DE-OS-2 322 047 and 2 526 720 described. In a conventional embodiment of these photoconductor layers and printing forms, the photoconductor layer applied to the electrically conductive substrate is charged, exposed imagewise, developed with liquid or dry toner for the image, the toner image is fixed by heating, and the printing plate is developed by removing the unstressed photoconductor layer. The offset printing form obtained takes on ink at the toner image areas and water at the exposed areas of the carrier surface. Such electrophotographic offset printing forms essentially consist of

• A) an electrically conductive aluminum carrier sheet suitable for offset printing in a thickness of 0.1 to 0.6 mm with z. B. an electrolytically roughened or anodized surface, and
• B) the electrophotographic layer
  • B1) at least one binder which is compatible with all of the components present in the formulation and which is soluble in offset-typical washout media,
  • B2) a low-molecular charge transport compound,
  • B3) at least one sensitizer for the desired actinic range and
  • B4) further additives which improve the general layer properties.

A high proportion of charge transport compounds B2) is required for the correct functioning of these electrophotographic layers. Good results are only achieved if the concentration of B2) exceeds 35% by weight; often up to 50% by weight is necessary in order to be able to maintain sufficiently short exposure times, as are required today by the offset printer.

Problems often arise in practice. Such high concentrations of B2) lead to poor electrokinetic properties of the layers. The exposure times are shortened, but the dark conductivity - which should be as low as possible to prevent the surface charge from running off - becomes impermissibly large. It may even be that at a high concentration, e.g. B. of over 40 wt .-%, the loadability of the layer in the dark becomes difficult because when loaded by means of a corona, the surface potential flows off faster than it can be sprayed on. If the corona is then switched off, a potential loss occurs very quickly, which can go so far that toner can no longer be bound electrostatically; d. H. the latent charge image can no longer be converted into a toner image.

It was an object of the present invention to develop electrophotographic layers for copying layers, in particular offset printing forms, which at the same time have high loadability, extremely low dark conductivity and good printing properties with high photosensitivity.

und mindestens einer Verbindung der Formel

It has been found that the object is achieved if a mixture of two charge transport compounds is used, the structure of which is different. Accordingly, the present invention relates to an electrophotographic recording material which is composed of A) a conductive support and B) an electrophotographic layer of organic materials and which is characterized in that the electrophotographic layer (B) as charge transport compounds is a mixture of at least one compound of the formula

and at least one compound of the formula

• R³ und R⁴ unabhängig voneinander für Wasserstoff, C,- bis C₄-Alkyl, C,- bis C₄-Alkoxy oder Halogen und
• R6, R⁷, R8 und R⁹ unabhängig voneinander für C₁- bis C₄-Alkyl, Phenyl-, -C₁- oder C₂-alkyl oder Cyclohexyl stehen.
• Bevorzugt sind Ladungstransportverbindungen (1) und (11), in denen
• R^l für Methyl, Ethyl oder Benzyl,
• R2 für Methyl, Ethyl oder Phenyl,
• R3 für Wasserstoff, 5-Methoxy oder 5-Ethoxy,
• R4 für Wasserstoff und
• R6, R⁷, R8 und R⁹ für Methyl, Ethyl, Propyl oder Butyl stehen.

in a ratio of 9: 1 to 0.6: 1 parts by weight, wherein in the formulas R ¹ and R ² independently of one another for C ₁ -C ₆ -alkyl, allyl, phenyl-C ₁ -C ₄ -alkyl or for optionally phenyl substituted by C ₁ to C ₄ alkyl, C ₁ to C ₄ alkoxy and / or halogen,

• R ³ and R ⁴ independently of one another for hydrogen, C, - to C ₄ alkyl, C, - to C ₄ alkoxy or halogen and
• R6, R ⁷ , R8 and R ⁹ independently of one another are C ₁ to C ₄ alkyl, phenyl, C ₁ or C ₂ alkyl or cyclohexyl.
• Charge transport compounds (1) and (11) in which
• R ^{l is} methyl, ethyl or benzyl,
• R2 for methyl, ethyl or phenyl,
• R3 for hydrogen, 5-methoxy or 5-ethoxy,
• R4 for hydrogen and
• R6, R ⁷ , R8 and R ^{9 represent} methyl, ethyl, propyl or butyl.

Particularly noteworthy as charge transport compounds are a mixture of (I) and (II), in which R ¹ for ethyl, R ² for phenyl, R ³ for 5-methoxy, R ⁴ for hydrogen and R ⁶ , R ⁷ , R ⁸ and R ^{9 represents} ethyl.

The ratio of (1) to (11) is 9: 1 to 0.6: 1 parts by weight, preferably 3.5: 1 to 0.7: 1.

Particularly good results are obtained with a mixture of (1) and (11) when the weight ratio of (I): (11) is in the range from 2.3: 1 to 0.8: 1.

Compounds (1) and (11) are known as charge transport compounds and, when used alone, also give good exposure properties. However, the compounds (I) and (11) at the concentrations required for high light sensitive systems pose the problems described above. It was surprising and not to be expected for the person skilled in the art that when using a combination of the charge carrier transport compounds (I) with (11) which are chemically very different from one another, the problems and difficulties described above do not occur.

From the prior art, e.g. B. EP-A-11 980, mixtures of charge transport compounds are known, but only mixtures of chemically very closely related charge transport compounds are used. The use of the mixtures is intended to prevent the charge transport compounds from crystallizing at the required high concentration. An improvement in the electrophotographic properties - the object of the present invention - cannot be seen from the information and cannot be derived from the results.

• 1) eine gleich gute bis höhere Photoempfindlichkeit als die bessere Komponente allein;
• 2) eine deutlich geringere Dunkelentladung als bei Anwendung der beiden Komponenten allein;
• 3) eine raschere Potentialabnahme bei Belichtung und ein höheres Oberflächenpotential als bei Anwendung der beiden Komponenten allein;
• 4) keine Beeinflussung (Änderung) der Auswascheigenschaften der Schicht und
• 5) keine Beeinflussung (Änderung) der Druckeigenschaften gegenüber Schichten, die nur (I) oder (11) enthalten und
• 6) die beiden Ladungstansportverbindungen sind miteinander verträglich.

The recording material according to the invention has the following properties:

• 1) equally good to higher photosensitivity than the better component alone;
• 2) a significantly lower dark discharge than when using the two components alone;
• 3) a faster decrease in potential upon exposure and a higher surface potential than when using the two components alone;
• 4) no influence (change) on the washout properties of the layer and
• 5) no influence (change) in the printing properties compared to layers which only contain (I) or (11) and
• 6) the two charge transport connections are compatible with each other.

The compatibility of (1) and (11) with each other was not to be expected, since from Phys. Rev. Lett. 37 (1976), p. 1360 it is known that two charge carrier transport connections mutually interfere with each other. It is all the more surprising to find that the mixture works at least as well or even better than the single component with the best effect.

The mixture of the charge carrier transporting compounds (I) and (11) to be used according to the invention can advantageously be used both in single-layer and in multi-layered recording systems applied to aluminum sheet suitable for offset printing.

Suitable single-layer systems preferably have a layer (B) of (a) 65 to 35% by weight of a binder, (b) 30 to 60, in particular 38 to 46% by weight of the mixture according to the invention on a conductive carrier material (A) the charge carrier transporting compounds (I) and (11), (c) optionally up to 15% by weight of a further, essentially inactive binder and (d) 0.02 to 2.5% by weight of a charge carrier when actinically exposed producing compound, in particular a suitable dye. The layers are advantageously applied to the cleaned conductive carrier material from an approximately 6% by weight solution in a suitable organic solvent in such a way that, after the solvent has been flashed off, a dry layer thickness of approximately 0.8 to 40 μm, depending on the intended use , in particular 0.8 to 6 µm in electrophotographic printing forms.

Suitable multilayer systems have on an electroconductive support material (A) z. B. (a) a charge carrier generating layer and (ß) a charge transport layer from 30 to 60 wt .-% of the mixture of the charge transport compounds of the formulas (1) and (11), 65 to 35 wt .-% of an organic binder and optionally up to 15% by weight of further additives which improve the mechanical properties of the layer. The first layer is advantageously applied to the support material in a thickness of 0.005 to 5 μm, in particular 0.1 to 0.9 μm, as a solution in a suitable solvent. After the application, the second layer is applied in a thickness that results in a layer thickness of 5 to 25, in particular 7 to 15 μm, after drying the composite structure.

As an electrically conductive carrier such. B. raw or pretreated, e.g. B. roughened and / or anodized aluminum sheets or aluminum foils with thicknesses of 0.08 to 0.6 mm into consideration.

The type of suitable organic binders for the layers depends on the intended use of the recording materials. For the copy sector, z. B. cellulose ethers, polyester resins, polyvinyl chlorides, polycarbonates, copolymers such as styrene-maleic anhydride copolymers or vinyl chloride-maleic anhydride copolymers or mixtures of such binders. In their selection, their film-forming and electrical properties, their adhesive strength on the carrier material and their solubility properties play a special role. Particularly suitable for recording materials for the production of electrophotographic printing plates and especially for those for offset printing are those which are soluble in basic, aqueous or alcoholic solvents. These are primarily substances with alkali-solubilizing groups such as anhydride, carboxyl, sulfonic acid, phenol or sulfonimide groups. Preference is given to binders, especially those with high acid numbers, which are readily soluble in basic aqueous-alcoholic solvent systems and have an average molecular weight (weight average) of 800 to 80,000 and in particular 1,500 to 50,000. Are suitable for. B. copolymers of methacrylic acid and methacrylic acid esters, especially copolymers of styrene and Maleic anhydride and from styrene, methacrylic acid and methacrylic acid ester, insofar as they have the above solubility condition. Although binders with free carboxyl groups are known to undesirably increase the dark conductivity of the electrophotographic layers and thereby lead to poor stressing results, such binders can easily be adapted to the charge transport compounds used according to the invention. It has been shown that copolymers of styrene, maleic anhydride and acrylic or methacrylic acid, the proportion of copolymerized maleic anhydride from 5 to 50 wt .-% and a proportion of polymerized acrylic or methacrylic acid from 5 to 35, in particular 10 to 30 wt .-% have satisfactory electrophotographic layers with sufficient dark conductivity. They have excellent solubility in washing-out agents consisting of 75% by weight of water, 23% by weight of isobutanol and 2% by weight of soda, but are insoluble in offset-typical wiping water.

Suitable charge carrier-producing compounds or sensitizers are e.g. B. for single-layer systems, such as those used for the production of electrophotographic printing forms, dyes from the triarylmethane series, xanthene dyes and cyanine dyes. Very good results were obtained with the compounds of the formula I according to the invention and rhodamine B (CI 45170), rhodamine 6 G (CI 45160), malachite green (CI Basic Green 4; CI 42 000), methyl violet (CI 42535) or crystal violet (CI 42555) receive. In systems applied in multiple layers, the dye or pigment is present in a separate layer which generates charge carriers. Azo dyes, phthalocyanines, isoindoline dyes and perylene tetracarboxylic acid derivatives are effective here. Particularly good results are achieved with perylene-3,4,9,10-tetracarboxylic acid diimide derivatives, as described in DE-OS-3 110 954 and 3 110 960.

For the respective use, the electrophotographic recording material according to the invention may contain conventional additives, e.g. B. leveling agents and plasticizers in the photoconductive layer or adhesion promoter between carrier and layer.

The materials according to the invention have clear advantages when used for the production of electrophotographic printing forms and meet high demands with regard to the resolution capacity and the print run. The high sensitivity to light allows the exposure time during processing in the repro camera to be reduced by about half compared to commercially available materials. A good resolution results from a very sharp image reproduction. Thanks to a high charge contrast, fine halftone dots can also be reproduced well in the clear tone word areas. Furthermore, the exposure of the layers leads to very low residual stresses and the images obtained during the concreting are characterized by good basic freedom in the non-image areas. Since the spectral sensitivity of the layers drops sharply at 600 nm, the layers can be handled with red light without loss of image.

The production of electrophotographic offset printing forms takes place, as usual, by electrostatically charging the electrophotographic recording material using a high-voltage corona, directly following image-wise exposure, developing the electrostatic latent charge image present using a dry or liquid toner, fixing the toner by means of a downstream melting process and the like Removal of the unstressed, photo-semiconducting layer using a suitable wash-out solvent. The printing form thus obtained can be prepared in a known manner for offset printing, for. B. by hydrophilizing and gumming the water-bearing surface.

The following exemplary embodiments are intended to explain the recording materials according to the invention in addition.

The parts and percentages given relate to the weight.

example 1

• a) 54.6 g of a copolymer of 70% by weight of styrene, 24% by weight of acrylic acid and 6% by weight of maleic anhydride, 28 parts by weight of 2- (diethylaminophenyl) benzotriazole-1, are dissolved in 900 g of tetrahydrofuran, 2.3 (la), 17 parts by weight of 2,5-bis (4'-diethylaminophenyl) oxadiazole-1,3,4 (Ila) and 0.4 parts by weight of CI Basic Red 1; C.I. No. 45160 solved. This solution is applied in such a wet layer thickness to an offset aluminum carrier sheet that after drying for 30 minutes at 80 ° C. a dry layer thickness of 4 μm remains.
• b) This plate is loaded with a corona at a distance of 10 mm and an associated high voltage source of 6.75 kV to a surface potential of -850 volts. The speed of the potential acceptance is determined. After the corona has been switched off, the loaded plate remains in the dark for 20 seconds, the percentage potential drop in relation to the originally existing potential being recorded. Then the white light from a high-pressure xenon lamp with a light intensity of 60 uW.cm- ^{2 is} exposed at the plate level and the measurement is carried out:
  • - the potential acceptance at the start of the loading in V / s,
  • - time to load with 850 V in s,
  • - percentage drop in potential in the dark,
  • - the light-induced potential drop in%, based on the potential immediately before exposure,
  • -the residual potential at the end of the measuring process. The results are summarized in Table 1.

Comparative Example 1

The procedure was as in Example 1a), but the oxdiazole (IIa) was replaced by the same amount of benzotriazole (la).

Comparative Example 2

The procedure was as in Example 1a), but the benzotriazole (Ia) was replaced by the same amount of oxdiazole (Ila).

Comparative Example 3

The procedure was as in Example 1a), but the oxdiazole (Ila) was replaced by the same amount of triphenylamine, a low-molecular charge transport compound which is very well known from the prior art.

Example 2

The procedure was as in Example 1a), but 22.5 parts (la) and 22.5 parts (IIa) were used.

Example 3

The procedure was as in Example 1a), but 33.75 parts (la) and 11.25 parts (Ila) were used.

Example 4

The procedure was as in Example 1a), but a mixture of 30.2 parts (la) and 14.8 parts (IIa) was used.

Example 5

The procedure was as in Example 1, but a mixture of 28 parts of 2- (N-ethyl-N-phenylaminophenyl) -5-methoxybenzotriazole-1,2,3 (Ib) and 17 parts of 2,5-bis- (4th '-di-n-butylaminophenyl) oxadiazole-1,3,4 (Ilb) used.

The testing of the layers obtained according to Examples 2, 3, 4 and 5 and of the layers obtained according to Comparative Examples 1, 2 and 3 was carried out in accordance with Example 1b). The results are summarized in the table.

Claims (10)

1. An electrophotographic recording material composed of A) a conductive base and B) an electrophotographic layer of organic materials, wherein the electrophotographic layer (B) contains, as charge-transporting compounds, a mixture of one or more compounds of the formula

and one or more compounds of the formula

in a weight ratio of from 9 : 1 to 0.6 : 1, and, in the formulae, R^l and R² independently of one another are each C₁-C₆-alkyl, allyl or phenyl-C₁-C₄-alkyl or are each phenyl which is unsubstituted or substituted by C₁-C₄-alkyl, C_l-C₄-alkoxy and/or halogen, R³ and R⁴ independently of one another are each hydrogen, C₁-C₄-alkyl, C_l-C₄- alkoxy or halogen and R⁶, R⁷, R⁸ and R⁹ independently of one another are each C₁-C₄-alkyl, phenyl-C₁- or -C₂- alkyl or cyclohexyl.

2. A recording material as claimed in claim 1, wherein the layer (B) contains charge-transporting compounds of the formulae (I) and (II) in which R^l is methyl, ethyl or benzyl, R² is methyl, ethyl or phenyl, R³ is hydrogen, 5-methoxy or 5-ethoxy, R⁴ is hydrogen and R⁶, R⁷, R⁸ and R⁹ are each methyl, ethyl, propyl or butyl.

3. A recording material as claimed in claim 2, wherein R^l is ethyl, R² is phenyl, R³ is 5-methoxy, R⁴ is hydrogen and R⁶, R⁷, R⁸ and R⁹ are each ethyl.

4. A recording material as claimed in claim 1, or 2 or 3, wherein the weight ratio of the compound (I) to compound (II) is in the range from 2.3 : 1 to 0.8 : 1.

5. A recording material as claimed in claim 1 or 2 or 3 or 4, wherein the electrophotographic layer (B) contains from 30 to 60, preferably from 38 to 46, % by weight, based on (B), of (I) and (II).

6. A recording material as claimed in claim 1 or 2 or 3 or 4 or 5, wherein the electrophotographic layer (B) contains from 0 to 5 % by weight, based on (b), of one or more activators.

7. A process for the preparation of an electrophotographic recording material consisting of (A) a conductive base and (B) an electrophotographic layer of organic materials as claimed in claim 1 or 2 or 3 or 4 or 5 or 6, wherein the layer (B) is applied in the form of a solution onto the base (A) by means of a knife coater or a roller coater.

8. A process as claimed in claim 7, wherein the layer (B) is applied in a thickness of from 0.8 to 40, preferably from 0.8 to 6 µm.

9. A process as claimed in claim 7 or 8, wherein a base suitable for offset printing, preferably an electrically roughened, anodically oxidized and sealed aluminum base, is used as (A).

10. Use of the recording materials as claimed in claim 1 or 2 or 3 or 4 or 5 or 6 in electrophotographic offset printing.