EP0004944B1 - Material for electrophotographic recording - Google Patents

Description

The present invention relates to an electrophotographic recording material composed of an electrically conductive layer support, in particular suitable for the production of printing forms or printed circuits, and a panchromatically sensitized photoconductive layer composed of organic photoconductor, binder, sensitizing dye and conventional additives.

It is known (German patent application R 16 768 IVa / 57 b dated September 20, 1956) to use photoconductors for electrophotographic reproduction which are radiation-sensitive in the range from 375 to 390 nm and whose radiation sensitivity is thereby extended into the visible part of the spectrum that a dye or dye mixtures are added which are capable of absorbing the radiation energy and transferring this energy to the photoconductor. These include dyes of the most diverse classes of compounds such as phthalein dyes, triphenylmethane dyes, cyanine dyes, heterocyclic dyes and unclassified dyes.

It is also known (DE-OS 1447 907) to sensitize photoconductor layers panchromatically by means of a combination of several dyes, ie over the entire visible spectral range. Mixtures of acridine yellow (CI 46 025), acridine orange (CI 46005), rhodamine B (CI 45 170) and brilliant green (C. 1. 42 040) are used to achieve a relatively uniform sensitization between about 400 and 700 nm, whereby the selective sensitizing, ₃ effect of the individual dyes adds up to a panchromatic sensitivity.

It is also known (DE-OS 2 353 639) to panchromatically sensitize electrophotographic recording material with a photoconductive multilayer system by building up a dye layer from at least two pigment dyes which absorb longer and shorter waves in different spectral ranges.

Disadvantages in the one case are the high number of dyes to be used, their compatibility with one another is not always given, and in the other case the use of pigment dyes in layers to be applied which, according to their required properties, cannot be removed or can only be removed incompletely and mostly by means of High vacuum evaporation must be applied to the substrate.

It is also known (DE-AS 2 526 720) to use an electrophotographic material for electrophotographic reproduction which contains a cyanine dye having an absorption maximum between 400 and 550 nm in the photoconductive layer. However, such a material is only in the near absorption region of the photoconductor itself, i. H. in the blue spectral range, sensitive.

It was an object of the present invention to provide an electrophotographic recording material which is panchromatically sensitized, easy to produce and easy to handle and, with uniformly good sensitivity over the entire visible spectral range, enables the production of excellent reproductions.

This object is achieved by an electrophotographic recording material composed of an electrically conductive layer support which is particularly suitable for the production of printing forms or printed circuits and a panchromatically sensitized photoconductive layer composed of organic photoconductor, binder, sensitizing dye from a mixture of water-soluble polymethine and triaryl methane dye and customary additives, which characterized in that the photoconductive layer as polymethine dye astrazone orange R (CI 48 040), astrazone orange G (CI 48 035), astrazone yellow 3G (CI 48055), astrazone yellow 5G (CI 48065), basic yellow 52115 (CI 48 060), astrazone yellow GRL (CI Basic Yellow 29), Astrazongelb 7GLL (CI Basic Yellow 21), Astragelb R (CI Basic Yellow 44) or Astrazonorange 3R (CI Basic Orange 27) and as triarylmethane dye malachite green (CI 42 000), brilliant green (CI 42 040) , Acid violet 6BN (CI 42 552), crystal violet (C. I. 42 555), fanal blue RM (C.I. 42 600), pure chromoxane blue B (C.I. 43830), naphthalene green V (C.I. 44 025), victoria pure blue B (C.I. 42 595) or wool blue FGL (C.I. 44 505). The recording material according to the invention is particularly useful when the photoconductive layer has to be further treated after decoating by decoating the non-image parts.

Achieving a uniform panchromatic sensitivity with a photoconductor layer even when using only two sensitizing dyes, if one selects them from the series of polymethine dyes with an absorption between approximately 400 and 550 nm and from the series of triarylmethane dyes with an absorption between approximately 550 and 720 nm , was unexpected.

When examining the sensitizing effect of the individual components, it is found that the sensitivity drops sharply in the spectral range around 550 nm. However, if one combines each component from the two groups mentioned above and examines the spectral course of the sensitivity, it is found that in the region around 550 nm the sensitivity is higher than expected and approaches the maxima of the two individual components. The pronounced sensitivity minimum to be expected in the overlap area of the two dye components does not occur. This surprises The accompanying figure can be seen from the attached figure, so the spectral sensitivity (E) of the photoconductive layer for the discharge from -400 volts (U _o ) to -50 volts (U) for the dye (1) astrazone orange R, the dye (2nd ) Brilliant green and for the dye mixture (3) is plotted against the wavelength. This observation is confirmed by adding a third sensitizing dye to the mixture described above, which sensitizes in the spectral range around 550 nm. It is then found that in this area the third dye can practically no longer increase the sensitivity.

The use of only two water-soluble sensitizer dyes simplifies the production of panchromatically sensitive photoconductor layers considerably.

In many cases, the amount of dyes to be used also decreases depending on the type of photoconductor used. Since the sensitizer dyes are generally salts whose addition to the photoconductor layer causes a certain dark conductivity, the use of a smaller amount very often brings about improved electrophotographic properties of the layer. Panchromatic sensitization in itself has advantages in that the light provided by the light sources used in reproduction technology is better utilized. In practice, this means shorter exposure times and thus time and energy savings. It is also possible, because of the improved properties, to reduce the proportion of photoconductor in the photoconductive layer.

The recording material in the photoconductive layer preferably contains astrazone orange R as the sensitizing dye and brilliant green or crystal violet or victoria blue B.

The mixing ratio of the sensitizing dyes to one another is variable and depends, for example, on the light source present in the copier, on the absorption region of the photoconductor used and on the type of the respective sensitizer. The ratio can therefore fluctuate within wide limits. The spectral range of the photoconductive layer can be adapted to the lamp type used in the copying machine by a certain mixture. When using the conventional halogen tungsten lamps, taking into account the increasing emission of these lamps in the red spectral range, it is advantageous to have a photoconductor layer which has a higher or increasing sensitivity in the short-wave spectral range.

Although the mixing ratio of the dyes is not critical, sensitizing mixtures containing about 25 to 90 percent by weight, based on the mixture, of polymethine dye are generally preferred.

The proportion by weight of sensitizing dye mixture in the photoconductive layer can also be different and depends essentially on the desired or required sensitivity. The amount by weight of dye mixture will generally vary between about 5 and about 0.001% based on the photoconductor.

Monomers such as polymeric aromatic and heterocyclic compounds are suitable as organic photoconductors. Particularly heterocyclic compounds such as oxdiazole derivatives, which are mentioned in German patent 1,058,836, are used as monomers. These include, in particular, 2,5-bis (p-diethylaminaphenyl) axdiazal-1,3,4. Other suitable monomeric photoconductive compounds are, for example, triphenylamine derivatives, more highly condensed aromatic compounds such as anthracene, benzo-fused heterocycles, pyrazoline or imidazole derivatives, including triazole and oxazole derivatives as disclosed in German Patents 1,060,260 and 1,120,875 .

Examples of suitable polymers are vinylaromatic polymers such as polyvinylanthracene, polyacenaphthylene or their copolymers. Poly-N-vinylcarbazole or copolymers of N-vinylcarbazole with an N-vinylcarbazole content of at least about 40% have proven particularly useful. Also suitable are formaldehyde condensation products with various aromatics such as. B. condensates of formaldehyde and 3-bromopyrene.

Natural or synthetic resins are suitable as binders with regard to flexibility, film properties and adhesive strength. These include in particular polyester resins such. B. Mixed polyester of iso- and terephthalic acid with glycol. Silicone resins such as three-dimensionally cross-linked phenylmethyl siloxanes or so-called reactive resins, as are known under the name DD lacquers, have also proven to be suitable. Copolymers of styrene and maleic anhydride, but also polycarbonate resins, can also be used well.

The proportion by weight of binder to photoconductor in the photoconductive layer is different and will generally be greater in the presence of monomeric photoconductors, sometimes over 50%, preferably in a ratio of about 1: 1, than in the presence of polymeric photoconductors, where the binder can also be entirely absent .

Depending on the field of application, metal foil or plates, plastic foils made superficially conductive or specially made conductive foils against the penetration of solvents are suitable as layer support materials for the panchromatically sensitized photoconductor layers. Plastic films made superficially conductive are used when an electrophotographic film material is to be produced using the panchromatically sensitized layer. If the material sensitized according to the invention is used in the field of office copying, paper is used as the carrier material.

If the material according to the invention is used in the production of printing forms, metallic layer supports, in particular aluminum, are used. The aluminum foils used are expediently roughened mechanically or electrochemically on the surface and, in special cases, anodized.

The electrophotographic recording material can contain leveling agents and plasticizers as conventional additives in the photoconductive layer and / or adhesion promoters between the layer support and the layer.

The invention will be explained in more detail with reference to the comparative example and the following examples.

A panchromatic layer is first produced, as described in DE-OS 1 447 907 under Example 2. To do this, dissolve 2 g

2,5-bis (p-diethylaminophenyl) -1,3,4-oxdiazole and 2 g of a copolymer of styrene and maleic anhydride in 40 g of methyl glycol. A solution of 2 mg of acridine yellow G (CI 46 025), 2 mg of acridine orange (CI 46 005), 1 mg of rhodamine B extra (CI 45170) and 1 mg of brilliant green (CI 42 040) in 3 ml of methanol is added to the solution. The total solution is applied to an aluminum foil and then the solvent is evaporated. A panchromatic layer is obtained in this way. If one now determines the energy required to discharge the layer charged to -400 V in the dark to -50 V, the following values are obtained: at 487 nm 139 µJ / cm ² , at 505 nm 177 µJ / cm ² , at 532 nm 172 µJ / cm ² , at 552 nm 165 µJ / cm ² and at 650 nm 195 µJ / cm ² .

The comparison layer is obtained if 5 mg of astrazone orange R (C. 1. 48 040) and 1 mg of brilliant green (CI 42 040) are added to the solution of photoconductor and binder described above instead of the four dyes mentioned, a composition which corresponds to the material for curve 3 in the attached figure. The energy required to discharge the layer charged to -400 V in the dark to -50 V is 45 µJ / cm ² at 487 nm, 41 µJ / cm ² at 505 nm, 62 µJ / cm ² at 532 nm, and 168 at 552 nm µJ / cm ² and at 650 nm 156 µJ / cm ² .

example 1

A solution of 4 g of 2-vinyl-4- (2'-chlorophenyl) -5- (4'-diethylaminophenyl) oxazole and 9 g of a copolymer of styrene and maleic anhydride in a mixture of 45 g of methyl glycol, 20 g of butyl acetate 85% ig and 70 g of tetrahydrofuran are added as sensitizers to 200 mg of astrazon orange R (CI 48040) and 40 mg of brilliant green (CI 42 040). The solution is applied to an electrochemically roughened and anodized aluminum foil which was aftertreated in accordance with DE-OS 1621 478 with polyvinylphosphonic acid. After the solvent has evaporated, a photoconductor layer which is sensitive in the spectral range from 400 to 700 nm is obtained, with the aid of which a printing form for offset printing is produced in the following way.

The layer is charged in the dark with a corona to -430 volts and exposed in a repro camera at aperture 14 for ten seconds, using 10 MH lamps of 600 W each as the light source. The resulting latent charge pattern is developed with a dry toner using a magnetic roller. The toner image is fixed by the action of heat. After removal of the photoconductor layer at the points not covered with toner with a solution which is obtained by dissolving 50 g of Na ₂ SiO ₃ .9H ₂ O in 250 g of glycerol (86%) and with 390 g of ethylene glycol and 310 If you dilute g of methanol, you get a planographic printing plate with which very long runs can be printed.

Example 2

A panchromatic photoconductor layer for the production of a printing form for small offset printing is obtained if a solution of 5 g of 2,5-bis (p-diethylaminophenyl) -1,3,4-oxdiazole and 5 g of a copolymer of styrene and maleic anhydride are combined in one Mixture of 62 g of methylglycol, 15 g of butyl acetate (85%) and 13 g of butanone, 250 mg of astra yellow (CI Basic Yellow 44) and 50 mg of victoria pure blue (CI 42 595) are added, and this solution onto a mechanically roughened 100 μ thick aluminum foil so that after evaporation of the solvent an approximately 5 micron thick layer is formed.

The layer is charged to -400V in the dark and exposed in a repro camera for 20 seconds at aperture 11, 8 light bulbs of 500 watts each being used as the light source. The resulting latent charge image is developed with a liquid developer as described in British Patent No. 1465 926. By dispersing 1.5 g of a high-vacuum bitumen with a softening point of 130-140 ⁰ in a solution of 6.5 g of a Pentaerythritharzesters in 1000 ml of a lsoparaffins having a boiling range 185-210 °. After development, the photoconductor layer is removed at the non-image areas, using a solution whose preparation is described in Example 1. A printing plate for small offset printing with a circulation stability of 60,000 to 80,000 copies is obtained.

Example 3

For the production of a panchromatically sensitive layer for an electrophotograph The film material is dissolved in 21 g of polyvinyl carbazole in a mixture of 150 g of toluene, 75 g of tetrahydrofuran and 75 g of dimethylformamide. 21 mg of crystal violet (CI 42 555) and 7 mg of astrazone orange R (CI 48 040) are added to the solution and applied to a polyester film made superficially conductive by vaporization with indium tin oxide. After the solvents have evaporated, a panchromatic film material is obtained which can be used as an electrophotographic duplicating film.

To do this, the film is charged in the dark to a surface potential of -400 V and exposed in contact under a film negative, the exposure time for a 100 watt lamp at a distance of 65 cm being 10 seconds. The charge image is developed with a commercially available developer, the developer particles of which are negatively charged. The result is a high-contrast film positive with good resolution.

Claims (3)

1. An electrophotographic recording material comprising an electrically conductive support, in particular a support adapted for the preparation of printing forms or printed circuits, and a panchromatically sensitized photoconductive layer which comprises an organic photoconductor, a binder, a mixture of watersoluble sensitizing dyes comprising a polymethine dye and a triarylmethane dye, and conventional additives characterized in that the photoconductive layer contains as the polymethine dye, Astrazon Orange R (C. I. 48040), Astrazon Orange G (C. I. 48 035), Astrazon Yellow 3G (C. I. 48 055), Astrazon Yellow 5G (C. I. 48 065), Basic Yellow 52 115 (C. I. 48 060), Astrazon Yellow GRL (C. I. Basic Yellow 29), Astrazon Yellow 7GLL (C. I. Basic Yellow 21), Astra Yellow R (C. I. Basic Yellow 44), or Astrazon Orange 3R (C. I. Basic Orange 27) and as the triarylmethane dye, Malachite Green (C. I. 42 000), Brilliant Green (C. I. 42040), Acid Violet 6BN (C. I. 42552), Crystal Violet (C. 1. 42 555), Fanal Blue RM (C. I. 42 600), Chromoxane Pure Blue B (C. I. 43 830), Naphthalene Green V (C. I. 44 025), Victoria Pure Blue B (C. I. 42 595) or Wool Fast Blue FGL (C. I. 44 505).

2. A recording material according to claim 1, in which the photoconductive layer contains Astrazon Orange R and Brilliant Green or Crystal Violet or Victoria Pure Blue B as the sensitizing dyes.

3. A recording material according to claim 1 or claim 2, in which the mixture of sensitizing dyes contains between about 25 and 90 percent by weight of a polymethine dye, calculated on the weight of the mixture.

Images