EP0004944A2 - Material for electrophotographic recording - Google Patents

Abstract

Electrophotographic recording material consisting 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, in which a mixture of at least one polymethine and at least one triarylmethane dye with a respective absorption between about 400 and 550 nm or 550 and 720 nm is used, wherein the sensitizing dye mixture can contain about 25 to 90 percent by weight, based on the mixture, of polymethine dye.

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 thereby expand their radiation sensitivity in the visible part of the spectrum is 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 14 47 907) to sensitize photoconductor layers panchromatically by a combination of several dyes, ie over the entire visible spectral range. Mixtures of acridine yellow (CI 46 025), acridine orange (CI 46 CO5), rhodamine B (CI 45 170) and brilliant green (CI 42 040) are used to achieve a relatively uniform sensitization between about 400 and 700 nm, whereby the selective sensitizing effect of the individual dyes added to a panchromatic sensitivity.

It is also known (DE-OS 23 53 639) to sensitize electrophotographic recording material with a photoconductive multilayer system by panchromatically 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 specially applied layers which, depending on 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 25 26 720) to use an electrophotographic material for the 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 comprising an electrically conductive layer support and a panchromatically sensitized photoconductive layer composed of organic photoconductor, binder, sensitizing dye and conventional additives, which is characterized in that the photoconductive layer as a sensitizing dye is a mixture of polymethine and triarylmethane dye with a respective absorption of the dye contains between about 400 and 550 nm or 550 and 720 nm. 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, which is necessary in the production of printing forms and printed circuits.

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 you combine one component from each of the above two groups and examine the spectral course of the sensitivity, you will find that in the range 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 surprising relationship can be seen in the attached figure, where 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 ( 2) Brilliant green and for whose dye mixture (3) is plotted against the wavelength. An observation can be found when a third sensitizing dye is added 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 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 the dyes to be used also decreases, depending on the 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 is exploited. 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.

Possible sensitizing dyes to be used according to the invention from the group of the polymethine dyes with an absorption between approximately 400 and 550 nm are: astrazone yellow 3G (CI 48 055), astrazone yellow 5G (CI 48 065), basic yellow 52 115 (CI 48 060), Astrazon Yellow GRL (CI Basic Yellow 29), Astrazon Yellow 7GLL (CI Basic Yellow 21), Astra Yellow R (CI Basic Yellow 44), Astrazon Orange G (CI 48 035), Astrazon Orange R (CI 48 040) and Astrazon Orange 3R (CI Basic Orange 27 ).

As sensitizing dyes to be used from the series of triarylmethane dyes which sensitize in the spectral range from 550 to 720 nm, u. a. suitable; 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 (CI 42 600), pure chromoxane blue B (CI 43 830), Naphthalene green V (CI 44 025), Victorian blue B (CI 42 595) and wool real blue FGL (CI 44 505).

Sensitizing dye mixtures are preferably used which contain astrazone orange R as the polymethine dye and brilliant green, crystal violet or victoria blue B as the triarylmethane dye.

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. By means of a certain mixture, the spectral range of the photoconductive layer can be adapted to the lamp type used in the copying machine. For the use of 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 one in the short-wave spectral range or increasing sensitivity.

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 0.5 and about 0.001% based on the photoconductor.

Monomers such as polymeric aromatic and heterocyclic compounds are suitable as organic photoconductors. Particularly monomers are heterocyclic compounds such as oxdiazole derivatives, which are described in German Patent 10 58 836 are used. These include, in particular, 2,5-bis (p-diethylaminophenyl) oxdiazole-1,3,4. Other suitable monomeric photoconductive compounds are, for example, triphenylamine derivatives, more highly condensed aromatic compounds such as anthracene, benzo-condensed heterocycles, pyrazoline or imidazole derivatives, including triazole and oxazole derivatives as disclosed in German patents 10 60 260 and 11 20 875.

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 foils or plates, plastic foils that have been made conductive on the surface or to prevent the penetration of solvents are used 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 method according to the invention is used in the production of printing forms, metallic substrates, 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, as conventional additives, flow control agents and plasticizers in the photoconductive layer and / or between the support and the layer _; Adhesion promoter included.

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 14 47 907 under Example 2. For this purpose, 2 g of 2,5-bis (p-diethylaminophenyl) -1,3,4-oxdiazole and 2 g of a copolymer of styrene and maleic anhydride are dissolved in 40 g of methyl glycol. A solution of 3 mg acridine yellow G (CI 46 025), 2 mg acridine orange (CI 46 005), 1 mg rhodamine B extra (CI 45 170) and 1 mg brilliant green (C, I, 42 040) is added to the solution in 3 ml of methanol too. 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 (CI 48 040) and 1 mg 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 2 2 energy required to discharge the layer charged to -400 V in the dark to -50 V is 45 µJ / cm ² at 487 nm and 41 µJ / cm ² at 505 nm. at 532 nm 62 µJ / cm ² , at 552 nm 168 µJ / cm ² and at 2 650 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 % and 70 g of tetrahydrofuran are added as sensitizers to 200 mg of astrazone orange R (CI 48 040) 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 16 21 478 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 latent charge image 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 non-toner-covered bodies with a solution that is obtained by the fact that man'50 g Na ₂ SiO ₃ · 9 H ₂ 0 dissolved in 250 g of glycerol (ig 86%) and g with 390 ethylene glycol and Diluted with 310 g of methanol, a planographic printing plate is obtained with which very large print 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 -400 V 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 latent charge image formed is developed with a liquid developer as described in British Patent No. 1,465,926. For this purpose, 1.5 g of a high vacuum bitumen with a softening point of 130-140 ° is dispersed in a solution of 6.5 g of a pentaerythritol resin ester in 1000 ml of an isoparaffin with a boiling range between 185 and 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 print run stability of 60,000 to 80,000 copies is obtained.

Example 3

To produce a panchromatically sensitive layer for an electrophotographic film material, 21 g of polyvinyl carbazole are dissolved in a mixture of 15 g of toluene, 75 g of tetrahydrofuran and 75 g of dimethylformamide. 21 mg of crystal violet (C.I. 42 555) and 7 mg of astrazon orange R (C.I. 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 (5)

1. Electrophotographic recording material made from 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, binding agent, sensitizing dye and conventional additives, characterized in that the photoconductive layer as a sensitizing dye is a mixture from polymethine and triarylmethane dye with a respective absorption of the dye between about 400 and 550 nm or 550 and 720 nm. 2. Recording material according to claim 1, characterized in that the photoconductive layer as a polymethine dye Astrazonorange R (CI 48 040), Astrazonorange G (CI 48 035), Astrazon Yellow 3G (CI 48 055), Astrazon Yellow 5G (CI 48 065), Basic Yellow 52 115 (CI 48 060), Astrazon yellow GRL (CI Basic Yellow 29), Astrazon yellow 7 GLL (CI Basic Yellow 21), Astra yellow R (CI Basic Yellow 44) and / or Astrazon orange 3R (C. I, Basic Orange 27) , 3. Recording material according to claim 1, characterized in that the photoconductive layer 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 (CI 42 600), chromoxane pure blue B (CI 43 830), naphthalene green V (CI 44 025), Victorian pure blue B (C, I. 42 595) and / or wool real blue FGL (CI 44 505). 4. Recording material according to claims 1 to 3, characterized in that the photoconductive layer contains as a sensitizing dye astrazone orange round brilliant green or crystal violet or victoria pure blue B. 5. Recording material according to claims 1 to 4, characterized in that the sensitizing dye mixture contains about 25 to 90 percent by weight, based on the mixture, of polymethine dye.

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