EP0194624B1 - Electrophotographic recording material - Google Patents

Description

The present invention relates to an electrophotographic recording material consisting of an electrically conductive support and at least one photoconductive layer containing photoconductors, sensitizing dyes, binders and conventional additives.

It is known to use photoconductors for electrophotographic reproduction which are sensitive to radiation down to the short-wave visible part of the spectrum and whose radiation sensitivity in the visible part of the spectrum can be expanded by adding one or more sensitizing dyes which transmit longer-wave energy to transmit the energy Are capable of light on the photoconductor. This includes dyes from a wide variety of compound classes.

It is known (DE-AS 25 26 720, corresponding to US Pat. No. 4,063,948) to use an electrophotographic recording material for electrophotographic reproduction which contains a cyanine dye sensitizing in the blue spectral range in the photoconductive layer. However, such sensitization does not make it possible to register radiation in the green and red areas of the spectrum, for example.

It is also known (DE-OS 14 47 907, corresponding to US-PS 3,458,310) to sensitize photoconductor layers to visible red. Mixtures of acridine yellow, acridine orange, rhodamine dye and brilliant green are used for this purpose, which are added in one or else separately in different layers (DE-OS 23 53 639, corresponding to US Pat. No. 3,992,205), the effect of the individual dyes adding up or else a different sensitization occurs (DE-OS 28 17 428, corresponding to US Pat. No. 4,252,880).

Such panchromatic sensitizations have advantages in that the light sources used in reproduction technology with a high proportion of red are better used. In practice, this means shorter exposure times and thus time and energy savings. Because of the improved sensitivity, it is also possible to reduce the proportion of photoconductor in the photoconductive layer.

Since a sensitizer usually does not cover the entire visible area of the spectrum, it is necessary to mix several sensitizers. However, it is very difficult to obtain sensitizations that meet the diverse needs of reproductive technology.

DE-A 21 37 325 discloses an electrophotographic recording material which contains at least one cyanine dye. It is also specified which one Cyanine dye must be selected if sensitization is required for blue, green or red light. However, this does not result in panchromatic sensitization of electrophotographic recording material with organic or inorganic photoconductor.

The present invention was based on the object of sensitizing electrophotographic recording material with organic or inorganic photoconductor in such a way that sensitization from the area of intrinsic sensitivity of the photoconductor to over approximately 700 nm is obtained, the individual sensitizations overlapping as much as possible so that the resulting sensitization of the emission corresponds to a light source emitting in the entire visible region, such as an Hg-Ga burner. On the other hand, the sensitization should be such that sensitization maxima are present which are in the area of the emission of conventional lasers, such as argon ion lasers, krypton lasers or LED diodes. It was also an object of the invention to use a mixture of dyes which are derived from the same heterocycle for reasons of compatibility.

The solution to the problem is based on an electrophotographic recording material consisting of an electrically conductive support and at least one photoconductive layer containing photoconductor, sensitizing dye of the 3,3'-dimethylindolenine type, Binder and usual additives. It is characterized in that at least three sensitizing dyes are present, two of which are bis (3,3'-dimethylindolenyl) tri and pentamethine cyanines, which sensitize in different wavelengths, and in addition that a cyanine dye from the group Astrazonorange R (CI 48040), Astrazon Orange G (CI 48035), Astrazon Yellow 3G (CI 48055), Astrazon Yellow 5G (CI 48065) and Basic Yellow 52115 (CI 48060) or a bis-benzoxazole trimethine cyanine is present.

According to the invention, bis- (3,3'-dimethylindolenyl) tri- and pentamethine cyanines, as represented by the attached formulas Nos. 1 and 2, are present as sensitizing dyes of the 3,3'-dimethylindolenine type.

As already mentioned, cyanine dyes from the group Astrazonorange R (CI 48040) - represented as Formula 3 -, Astrazonorange G (CI 48035), Astrazon Yellow 3G (CI 48055), Astrazon Yellow 5G (CI 48065) and Basic Yellow 52115 (Sensitizing Dyes) CI 48060) used according to the invention.

It has been shown that the sensitizing dyes have different effects for different types of photoconductors. Therefore, when using inorganic photoconductor such as zinc oxide, bis-benzoxazole trimethine cyanine is alternatively used in the photoconductive layer (formula 4). Compounds of this type are in the unpublished DE-A 34 05 487 proposed as a sensitizing dye.

The selection and mixing ratio of the dyes according to the invention ensure that various organic or inorganic photoconductors can be sensitized well in a range from about 400 to 700 nm.

The spectral sensitizing dye according to formula No. 1 used according to the invention is characterized by intensive sensitization in red with a sensitization maximum at 670 nm and a shoulder at 640 nm. For example, it is more intense and sensitizes longer-wave than the commonly used brilliant green, as can be seen from the attached FIG. 2.

The sensitizing dye according to formula No. 2 used in admixture with sensitizing dye No. 1 sensitizes in the green with a sensitizing maximum at 560 nm and a shoulder at approx. 500 nm.

Figure 3 shows the spectral sensitization by dye according to formula 2. The sensitizing dye according to formula No. 3 sensitizes in blue with a maximum around 500 nm, as can be seen from the attached FIG. 1.

The sensitization characteristics can generally be found in the spectrograms attached in FIGS. 1 to 3. 1 shows the sensitization characteristic in the range from 400 to about 700 nm by mixing three different dyes for organic photoconductors (mixture of the dyes according to formula 1 + 2 + 3) or ZnO photoconductors (mixture of the dyes according to formula 1 + 2 + 4) at.

The sensitizing dyes 1, 2 and 4 according to the invention are prepared by the procedures customary in the chemistry of cyanine dyes and known to the person skilled in the art. (W. Koenig, B. 57, 685 (1924), DE-PS 410.487, A. Claisen, B. 36, 3667 (1903)).

The concentration of the sensitizing dyes according to the invention depends on the photoconductor used in the individual case, the desired effect and on the sensitizing dyes used themselves. Usually 0.05 to 1.0 percent by weight of individual dyes, based on the weight of the photoconductor, are added. The effect of the sensitizing dye according to formula No. 1 can be increased by changing the mixing ratio from, for example, 1: 1: 1 to 0.5: 1: 1 for the sensitizing dyes 1, 2 and 4.

The photoconductive layer can be in either a single or a multiple layer arrangement, with charge carrier generation and charge transport taking place together or separately.

Both organic and inorganic compounds can be used as photoconductors. Monomers such as polymeric aromatic carbocyclic or heterocyclic compounds may be mentioned as organic photoconductors.

Oxdiazole derivatives, such as 2,5-bis (4'-diethylaminophenyl) -1,3,4-oxdiazole, described in DE-PS 10 58 836 (corresponding to US Pat. No. 3,189,447), or oxazole derivatives, such as 2-vinyl, are preferably used. 4- (2'-chlorophenyl) -5- (4'-diethylaminophenyl) oxazole or 2-phenyl-4- (2'-chlorophenyl) -5- (4'-diethylaminophenyl) oxazole, described in DE-PS 10 60 260 (corresponding to US Pat. No. 3,112,197) or 11 20 875 (corresponding to US Pat. No. 3,257,203).

Pyrazoline derivatives, such as are known from German Patent Application 10 60 714, corresponding to US Pat. No. 3,180,729, or hydrazone compounds, known, for example, from DE-OS 29 19 791, corresponding to US Pat. No. 4,278,747, can also be used.

Examples of suitable polymeric compounds are vinylaromatic polymers, such as polyvinylanthracene, polyacenaphthylene or copolymers. Poly-N-vinylcarbazole or copolymers of N-vinylcarbazole with an N-vinylcarbazole content of at least about 40 percent by weight have proven particularly useful.

Known natural or synthetic resins are suitable as binders with regard to the flexibility of the film-forming properties and the adhesive strength. In addition to the film-forming and electrical properties and because of the adhesive strength on the substrate, solubility properties also play a role in their selection. For example, polyester resins, such as mixed polyesters of iso- and terephthalic acid with glycol, or silicone resins, such as three-dimensionally crosslinked phenylmethylsiloxanes, or so-called reaction resins, as are known under the name DD lacquers, are suitable. Polycarbonate resins can also be used well. Binders which are soluble in aqueous or alcoholic solvent systems, optionally with the addition of acid or alkali, are particularly suitable for the preferred use of the recording material according to the invention for the production of printing forms. Suitable According to this, binders are high-molecular substances which carry alkali-solubilizing groups, such as acid anhydride, carboxyl, phenol, sulfonic acid, sulfonamide or sulfonimide groups. Copolymers with anhydride groups can be used with particularly good success, since the lack of free acid groups means that the dark conductivity of the photoconductive layer is low despite good alkali solubility.

Zinc oxide is preferably mentioned as the inorganic photoconductor. The grain size of the photoconductive zinc oxide used is approximately 0.1 to 15 μm. Suitable binders with a specific resistance of 10⁷ to 10¹⁴ Ω.cm in this case are polymeric or resinous binders or mixtures thereof. Suitable for this are polyurethane, polyester, polycarbonates, polystyrenes, chlorinated rubber, acrylic resins, alkyd resins, silica resins or vinyl acetate copolymers, such as vinyl chloride acetate resin.

The photoconductive layer with zinc oxide as the photoconductor can contain between 50 and about 95 percent by weight of the photoconductive particles. A preferred weight ratio of the binder to the particles is between 1: 4 and 1:10.

The supports of the recording material can be flat or cylindrical and can be made in a known manner from a metal plate, a metal foil, from metallized paper or papers or foils, which are coated with an electrically conductive plastic.

In the known manner, toner images can be produced on the recording material according to the invention, but it is also possible to transfer either the charge image or the toner image to an image receiving material.

In a known manner, a printing form or a printed circuit can also be obtained after imaging, development and stripping of the photoconductor layer at the non-image locations and, if appropriate, etching away the metal layer at the non-image locations.

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

The following examples are intended to explain the invention in more detail, but not to limit it thereto:

example 1

To a solution of 8 g of 2-vinyl-4- (2'-chlorophenyl-5- (4'-diethylaminophenyl) oxazole and 18 g of a copolymer of styrene and maleic acid hydride, in a mixture of 90 g of methyl glycol, 140 g of tetrahydrofuran and 40 g of 85% butyl acetate, 0.04 g each of Sensitizing Dyes Nos. 1, 2 and 3 were added. The solution was applied to an electrochemically roughened and anodized aluminum foil, the surface of which was pretreated with polyvinylphosphonic acid as described in DE-OS 16 21 478 (corresponding to US Pat. No. 4,153,461). After the solvent had evaporated, a photosensitive layer in the range from about 420 to 730 nm was obtained. The sensitization spectrogram can be found in the attached FIG. 1.

A printing plate for offset printing was produced from this recording material in the following manner. The photoconductive layer was charged to -430 V in the dark with the aid of a corona, then exposed in a repro camera at aperture 14 for eight seconds using an Hg-Ga burner (5000 W M023-Sylvania). The resulting latent charge image was developed with a commercially available dry toner using a magnetic roller and the toner image was fixed by heat. After removing the photoconductive layer at the points not covered with toner with a solution which is obtained by dissolving 50 g Na₂SiO₃ x 9 H₂O in 250 g glycerol (86%) and diluting with 390 g ethylene glycol and 310 g methanol, a planographic printing form was obtained, with which it was possible to print in large numbers.

Example 2

A solution of 10 g of 2-phenyl-4- (2'-chlorophenyl) -5- (4'diethylaminophenyl) oxazole, 15 g of a copolymer of styrene and maleic anhydride with a softening point of 210 ° C., 116 g of tetrahydrofuran, 33 g of butyl acetate, 76 g of methylglycol and 1.5 g of the sensitizing dyes of the formulas 1, 2 and 3, in a ratio of 1: 1: 0.5, were applied to an aluminum-coated, 100 μm thick polyester film. After the solvent had evaporated, an approximately 5 μm thick photoconductive layer with a spectral sensitivity of approximately 400 nm to approximately 730 nm resulted.

After exposure of the original with MH radiators, development with an electrophotographic developer and removal of the photoconductor layer at the non-image locations by the process described in DE-PS 23 22 047 (corresponding to US Pat. No. 4,066,453), the exposed, evaporated aluminum layer was treated with 2 n sodium hydroxide solution removed. A printed circuit was obtained in this way.

Similar results were obtained if 2,5-bis- (4'-diethylaminophenyl) -1,3,4-oxdiazole was used as the photoconductor instead of the specified oxazole.

Example 3

A 100 µm thick aluminum foil was provided with a photoconductive layer. The photoconductive layer was prepared as follows: 100 parts by weight of photoconductive zinc oxide were mixed together with 40 parts by weight of a 50% solution of a modified multipolymer of the vinyl acetate in toluene. The mixture was ball-milled for about 3 hours and then applied to the paper support to a dry coat weight of about 30 g / m² using a wire doctor. The solution had been added in a ratio of 1: 1: 1 each 0.5% individual dye, based on the weight of the photoconductor, of sensitizing dye according to formulas 1, 2 and 4.

The layer was charged with a corona (voltage 5 kV negative, distance 25 mm) and with an argon ion laser in the power range 0.2 to 0.5 mW (nominal power 50 mW, output power 15 mW) at a feed rate of 400 lines / cm illustrated in a conventional machine which is used for the production of printing forms and further processed in the manner customary for ZnO printing plates.

Claims (9)

1. Electrophotographic recording material comprising an electrically conductive layer support and at least one photoconductive layer containing photoconductor, sensitizing dye of the 3,3'-dimethylindolenine type, binder and customary additives, wherein at least three sensitizing dyes are present of which two represent bis-(3,3'-dimethylindolenyl)-tri- and penta-methine-cyanines, which have a sensitizing action in different wavelength regions and wherein a cyanine dye from the group consisting of Astrazone Orange R (C.I. 48040), Astrazone Orange G (C.I. 48035), Astrazone Yellow 3G (C.I. 48055), Astrazone Yellow 5G (C.I. 48065) and Basic Yellow 52115 (C.I. 48060) or a bis-benzoxazoletrimethinecyanine is additionally present.
2. A recording material as claimed in claim 1, wherein the photoconductor represents an organic compound from the group of the oxazole, oxadiazole, hydrazone or pyrazoline derivatives.
3. A recording material as claimed in claim 2, wherein the photoconductor is 2,5-bis-(4'-diethylaminophenyl)-1,3,4-oxadiazole.
4. A recording material as claimed in claim 2, wherein the photoconductor is 2-vinyl-4-(2'-chlorophenyl)-5-(4'-diethylaminophenyl)-oxazole.
5. A recording material as claimed in claim 2, wherein the photoconductor is 2-phenyl-4-(2'-chlorophenyl)-5-(4'-diethylaminophenyl)-oxazole.
6. A recording material as claimed in claim 1, wherein the photoconductor represents an inorganic compound.
7. A recording material as claimed in claim 6, wherein the photoconductor is zinc oxide.
8. A recording material as claimed in claim 1 for preparing printing plates having a metal base or metallized film as a layer support.
9. A recording material as claimed in claim 1, wherein the photoconductive layer contains as binder a styrene/maleic anhydride copolymer or a phenolic resin.

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