EP0131215B1 - Recording materials with improved photosensitivity - Google Patents

Description

The invention relates to electrophotographic recording materials with electrically conductive supports, charge carrier-producing compounds or sensitizers, charge carrier transporting compounds and special additives.

Electrophotographic processes, materials required therefor and various variants for the construction of recording materials are known. Advantages for use in the reproduction sector are materials made of polymeric binders that can be adapted to the special requirements of the respective field of application, low molecular weight organic compounds that are soluble in the binders even in higher concentrations and are capable of transporting charge carriers of the electrical current, and compounds , in particular dyes or pigments, which generate charge carriers of the electrical current by absorption of the actinic light radiated imagewise and which can transfer them to the charge-transporting compounds with the aid of the electrical field impressed from the outside by the electrostatic surface charge. Depending on the field of application of the recording material, these charge carrier-producing compounds can be introduced as a separate layer within a composite structure (cf. DE-OS 22 20 408) or in the form of monodisperse dissolved dye molecules in the mixture of binder and charge carrier-carrying compounds (cf. PS 1 058 836). The multi-layer electrophotographic recording material described in DE-OS 22 20 408 consists of an electrically conductive carrier material, a first, dye-containing, about 0.005 to 2 ₁ in the thick layer which generates charge carriers of the electric current by exposure to actinic light and consists of insulating in the dark, organic materials with at least one charge-transporting compound.

It is also known to use photoconductive organic compounds for the production of electrophotographic printing forms and in particular electrophotographic offset printing forms (cf. DE-PS 1 117 391 and 1 120 875, DE-AS 15 22 497 and 27 26 116).

The increased demands on reproduction systems require a variety of recording materials and systems in order to be able to find optimal solutions for special problems. Good resolution and good emphasis are desired. The often criticized inadequate emphasis, which indicates an unfavorable field strength differentiation between exposed and unexposed areas, is often due to an excessive dark conductivity of the recording material in the loaded state, so that there is an insufficient surface charge density before the actinic imagewise exposure.

High photosensitivity is particularly desirable in order to reduce the required process times. In the production of electrophotographic offset printing plates in particular, the necessary exposure time plays an important role. Here, however, the existing systems are frequently criticized.

The object of the present invention was to develop electrophotographic recording materials, in particular for the production of electrophotographic printing forms, such as offset printing forms, which have improved photosensitivity, at the same time a low dark conductivity and good resolution.

• Mischung farblosem enthalten.
  • Cadmiumacetylacetonat
  • (Bis[pentandionato-(2,4)]-cadmium(11)),
  • Natriumacetylacetonat
  • (Pentandionato-(2,4)-natrium),
  • Magnesiumacetylacetonat
  • (Bis[pentandionato-(2,4)]-magnesium),
  • Zinkacetylacetonat
  • (Bis[pentandionato-(2,4)]-zink(ll)),
  • Zirkonacetylacetonat
  • (Tetrakis[pentandionato-(2,4)]-zirkonium(V))
• oder
  • Titanylacetylacetonat
  • (Bis[pentandionato-(2,4)]-titanyl(IV)

It has now been found that so improved electrophotographic recording materials consisting of an electrically conductive support and one or more layer (s) of, charge-generating compounds or sensitizers, charge-transporting compounds, binders and additives are obtained when they as additives 0.5 up to 30% by weight, but preferably 3 to 15% by weight, based on the proportion of binder in the layer containing compounds carrying charge carriers, in solution and in the layer

• Mix colorless included.
  • Cadmium acetylacetonate
  • (Bis [pentandionato- (2,4)] - cadmium (11)),
  • Sodium acetylacetonate
  • (Pentandionato (2,4) sodium),
  • Magnesium acetylacetonate
  • (Bis [pentandionato- (2,4)] - magnesium),
  • Zinc acetylacetonate
  • (Bis [pentandionato- (2,4)] - zinc (ll)),
  • Zirconium acetylacetonate
  • (Tetrakis [pentandionato- (2,4)] - zirconium (V))
• or
  • Titanyl acetylacetonate
  • (Bis [pentandionato- (2,4)] - titanyl (IV)

It has been shown that very particularly improved photosensitivities of the recording materials are obtained if metal acetylacetonates are used as special additives which are colorless in solution and in the mixture, ie do not absorb in the visible spectral range and in the absorption range of the sensitizer. It has shown that all metal acetylacetonates improve photosensitivity, colored metal acetylacetonates - such as copper (11) acetylacetonate (blue), chromium (III) acetylacetonate (bordorot), iron (III) acetylacetonate (red), nickel (II ) acetylacetonate (turquoise green), palladium (11) acetylacetonate - however negatively influence the effect of the sensitizer, so that overall only slight improvements in photosensitivity result.

These acetylacetonates are also soluble in sufficient organic solvents.

It is very particularly surprising that the addition of the colorless metal acetylacetonates according to the invention greatly improves the photosensitivity and at the same time also significantly increases the maximum potential acceptance of the electrophotographic recording materials without changing the dark properties, so that, at the same time, an improved differentiation between exposed and unexposed areas of the loaded areas is added to the photosensitivity Surface occurs.

It is known to the person skilled in the art that metal halides - such as zinc chloride, magnesium bromide, aluminum chloride - and ketones - such as acetophenone, benzophenone, benzil - can also improve the photosensitivity of certain organic photo semiconductor layers in small amounts (e.g. US 3,037,861, US 3,553 009, U.S. 3,620,723). However, metal acetylacetonates are not included. It has also been confirmed that additions of metal halides and ketones do not produce the effects according to the invention. The effect of the colorless acetylacetonates achieved according to the invention cannot be derived from the known additives for the person skilled in the art. Even the electrophotographic recording material known from Chemical Abstracts, volume 80, number 18, page 446, section 102 292 r could not give the person skilled in the art the suggestion to select colorless metal acetylacetonates for the solution of the task according to the invention, because the intensely colored, bordorote in the relevant recording material Crom (III) acetylacetonate is used, which adversely affects the action of the sensitizer.

The colorless metal acetylacetonates which improve the photosensitivity and are used according to the invention can advantageously be used both in single-layer and in multi-layer recording systems applied to electroconductive supports.

Suitable single-layer systems preferably have a layer of (a) 45 to 75 parts by weight of a binder, (b) 30 to 60, in particular 35 to 50 parts by weight of a charge carrier transporting compound, (c) optionally 5 to 25 parts by weight of another on a conductive carrier material , essentially inactive binder, (d) 0.05 to 0.8 parts by weight of a compound which generates charge carriers upon actinic exposure, in particular a suitable dye, and (e) 0.5 to 30, in particular 3 to 15% by weight, based on the binder portion, one or more of the metal acetylacetonates according to the invention on the layers are advantageously applied from an approximately 5% by weight solution in a suitable organic solvent to the cleaned conductive carrier material in such a way that a dry layer thickness of approx 0.8 to 40 ₁ im (depending on the intended use, in particular 0.8 to 6 µm for electrophotographic printing forms) results.

Suitable multilayer systems advantageously have on an electroconductive carrier material (a) a layer with compounds generating charge carriers and (b) a further layer with (b1) at least one charge carrier transporting compound, (b2) at least one organic binder and (b3) optionally further, in particular additives which improve the mechanical properties of the layer, layer (b) containing 0.5 to 30 and preferably 3 to 15% by weight, based on the proportion of binder, of one or more of the metal acetylacetonates according to the invention. The layer (b) advantageously contains 30 to 60 parts by weight of (b1), 45 to 75 parts by weight of (b2) and, if appropriate, 5 to parts by weight of the additives (b3).

The first layer is advantageously applied to the carrier material in a thickness of 0.005 to 5, in particular 0.1 to 0.9) from solution in a suitable solvent. After the application, the second layer is advantageously 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.

In principle, all conductive carrier materials can be used as electrically conductive carriers, insofar as they are suitable for the area of application. Depending on the field of application of the recording materials, aluminum, zinc, magnesium, copper or multi-metal plates, for. B. raw or pretreated, e.g. B. roughened and / or anodized aluminum sheets, aluminum foils, polymer films with a metallized surface such as aluminum-coated polyethylene terephthalate films or electrically conductive special papers. Carriers for printing forms advantageously have a thickness of 0.08 to approximately 0.6 mm.

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 above all substances with alkali-solubilizing groups such as anhydride, carboxyl, sulfonic acid, phenol or sulfonimide groups. Preferred are 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 150,000 and in particular 1,200 and 80,000. Are suitable for. B. copolymers of methacrylic acid and methacrylic acid esters, especially copolymers of styrene and maleic anhydride and of styrene, methacrylic acid and methacrylic acid esters, 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. 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 copolymerized acrylic or methacrylic acid from 5 to 35 and 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 rhodamine B (C.I. 45170), rhodamine 6 G (C.I. 45160), malachite green (C.I. 42000), methyl violet (C.I. 42535) and crystal violet (C.1.42555). 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 particularly effective here. Good results are achieved with perylene-3,4: 9,10-tetracarboxylic acid diimide derivatives, as described in DE-OS 31 10 954 and 3110 960.

Suitable compounds carrying electrical charge carriers are known to the person skilled in the art. Mention may be made of oxazole derivatives (DBP 11 20 875), oxdiazole derivatives (DBP 10 58 836), triazole derivatives (DBP 10 60 260), azomethines (US 3 041 165), pyrazoline derivatives (DBP 10 60 714) and imidazole derivatives (DBP 11 06 599). Benztriazole derivatives (German patent application P 32 15 968.4) and hydrazone derivatives (German patent application P 32 01 202.0) are preferred. These are usually low molecular weight compounds which are well compatible with the organic binders in the required amount. However, polymeric charge transport compounds can also be used, e.g. B. Poly (N-vinyl carbazole).

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 electrophotographic recording materials according to the invention are distinguished by a combination of very good properties, in particular a high photoconductivity with a very low dark conductivity, so that the layers are very suitable for copying technology.

They have clear advantages when used for the production of electrophotographic printing forms and meet high demands with regard to the resolution and the print run. The high sensitivity to light allows the exposure time during processing in the repro camera to be reduced by up to half compared to conventional materials. A good resolution results from a very sharp image reproduction. Thanks to a high charge contrast, even fine halftone dots in the light tonal ranges can be reproduced well. 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. The spectral sensitivity drops sharply at 600 nm, so that the layers can be handled under red light without image loss.

As usual, the production of electrophotographic offset printing forms is carried out by electrostatically charging the electrophotographic recording material using a high-voltage corona, immediately following image-wise exposure, developing the electrostatic latent charge image present using a dry or liquid toner, fixing the toner by means of a subsequent melting process and removing it the unstressed, photo-semiconducting layer by means of a suitable washout solvent. The printing form thus obtained can still be prepared in a known manner for offset printing, e.g. B. by hydrophilizing and gumming the water-bearing surface.

The following examples are intended to further illustrate the invention. The parts and percentages given relate to the weight.

The layers are covered with a DC corona of - 8.5 kV at a distance of 1 cm evenly charged to a surface potential of - 600 volts and then exposed with the white light of a xenon high-pressure lamp with an illuminance of 10µW.cm ^-2 in the layer plane. The photo-induced potential drop during the exposure is tracked over time until the surface potential has fallen below 5% of the originally present value. Then the time is determined which elapses before the surface potential drops by half, corrected by the amount of the dark drop. The half-value photosensitivity as the product of half-life and illuminance in the plate plane is given in µJ.cm ^-2 . Furthermore, according to the xerographic method, the maximum potential acceptance in volts, the time until the recording materials are charged to -500 volts at a corona voltage of -8.5 kV at a distance of 10 mm, the potential drop in the dark in 20 seconds and the total photo-induced potential drop determined in% with an irradiated energy of 1 mJ.cm ^-2 .

example 1

55 parts of a copolymer of 70% styrene, 6% maleic anhydride and 24% acrylic acid with an average molecular weight M _w of about 2000.45 parts of 2- (N, N-diethylphenyl) -6-methoxybenztriazole-1,2,3,0 6 parts of methyl violet (CI 42535) and 5 parts of bis [pentandionato- (2,4)] - zinc (II) (zinc acetylacetonate) are dissolved in a mixture of tetrahydrofuran and ethyl acetate, the solution is electrolytically roughened on an electrically conductive support and then anodized aluminum sheet 0.15 mm thick applied so that after evaporation of the solvent and drying for 30 minutes at 85 ° C, a dry layer thickness of 4 microns results. The xerographic test reveals a half-value photosensitivity of 19.6 µJ.cm ^-2 .

Comparative Example 1

The procedure is as in Example 1, but the addition of zinc acetylacetonate is omitted. A half-value photosensitivity of 35.4 µJ.cm ^{-2 is} measured.

Comparative Example 2

The procedure is as in Example 1, but the same amount of pure acetylacetone (1,3-diketone) is used instead of the zinc acetylacetonate. The half-value photosensitivity is 33.6 µJ.cm ^-2 .

Comparative Example 3

The procedure is as in Example, but the zinc acetylacetonate is replaced by the same amount of zinc chloride (pre-dissolved in a little water). A half-value photosensitivity of 31.4 µJ.cm ^{-2 is} determined.

Examples 2 and 3

The procedure is as in Example 1, but the zinc acetylacetonate is replaced by bis [pentandionato (2,4)] magnesium (magnesium acetylacetonate, Example 2) or tetrakis [pentandionato (2,4)] zirconium (IV) (Zirconium acetylacetonate, Example 3) replaced. The half photosensitivities amount to 22.4 and 23.5 μJ.cm ^-2 J.cm- ^{p. 2}

Example 4

60 parts of a copolymer of 80% styrene and 20% acrylic acid with an average molecular weight of 1600, 36 parts of p-diethylaminobenzaldehyde diphenylhydrazone, 1 part of rhodamine 6 G (CI 45160) and 8 parts of bis [pentandionato- (2,4)] - zinc dissolved in tetrahydrofuran / methylglycol 1: 1 and applied in a dry layer thickness of 5.5 µm on a finely brushed aluminum sheet. A half-value photosensitivity of 9.6 µJ.cm ^{-2 is} determined on this electrophotographic recording material.

Comparative Example 4

The procedure is as in Example 4, but the zinc acetylacetonate is omitted. The half-value photosensitivity is now 16.2 µJ.cm ^-2 .

Example 5

50 parts of a copolymer of 60% styrene and 40% of a maleic acid semi-esterified with methanol with an average molecular weight M _w of 10,000, 50 parts of 2- (4'-diethylaminophenyl) benzotriazole-1,2,3, 0.2 parts of crystal violet (CI 42555) and 4 parts of bis [pentandionato- (2,4)) - zirconium- (IV) applied from a 5% solution in tetrahydrofuran to an electrolytically roughened and anodized aluminum foil of 0.15 mm thickness in a dry layer thickness of approximately 4 μm. After a charge, this printing plate is exposed in a camera for 12 seconds using a high-voltage corona. It is then developed with a powder toner that is burned-in at 160 ° C and resistant to abrasion. The unconcrete layer is washed off with a mixture of 0.5% soda, 25% isopropanol and 74.5% water, which exposes the aluminum surface. The solutions are spread over the layer with a cotton ball. The differentiation into hydrophilic and oleophilic areas desired in offset printing is obtained, the carrier surface providing the hydrophilic areas.

After the treatment with the alkaline liquid, the printing plate is rinsed with water and the hydrophilicity of the support surface is further increased by wiping with dilute phosphoric acid solution. After inking with bold ink, it is used to print in a known manner in offset printing machines.

Example 6 and Comparative Example 5

55 parts of a copolymer of 55% styrene, 30% acrylic acid and 15% maleic anhydride with an average molecular weight M _w of 35,000, 45 parts of 2- (N, N-diethylaminophenyl) benzotriazole-1,2,3, 0.6 parts Methyl violet (CI 42535) and 6 parts of bis [pentandionato- (2,4)] - zinc are dissolved in a mixture of tetrahydrofuran and methylglycol acetate and applied as a layer with a dry layer thickness of 3.5 µm to a fine-brushed aluminum sheet. The comparison layer 5 is produced as in Example 6 but without the zinc acetylacetonate.

• a) Zeit bis zur Aufladung auf -500 V (-8,5 kV, 10 mm): 1,8 s (2,2 s);
• b) maximale Potentialakzeptanz: 1700 V (1380 V);
• c) Dunkelabfall (20 s, -600 V): 17 % (16 %);
• d) photoinduzierter Potentialabfall (1 mJ.cm^-2): 96,5 % (87,0 %).

The following characteristics are measured on the two layers (comparative example in brackets) using the xerographic method:

• a) Time to charge to -500 V (-8.5 kV, 10 mm): 1.8 s (2.2 s);
• b) maximum potential acceptance: 1700 V (1380 V);
• c) dark drop (20 s, -600 V): 17% (16%);
• d) photo-induced potential drop (1 mJ.cm ^-2 ): 96.5% (87.0%).

Example 7 and Comparative Example 6

A layer of 60 parts of a chlorinated perylene-3,4: 9,1-tetracarboxylic acid diimide bisbenzimidazole with a chlorine content of about 38% and 50 parts of a commercially available copolymer is formed on a polyethylene terephthalate film with a vapor-deposited, conductive aluminum layer in a thickness of approximately 300 Å Vinyl chloride, acrylic acid and a maleic acid diester applied in a thickness of about 0.55 microns as a charge-generating layer.

A charge transport layer consisting of 45 parts of a commercially available polycarbonate binder with a melting range of 220 to 230 ° C, 10 parts of a polyester with an acid number of about 40 and a molecular weight of about 4,500, 40 is made from a solution in ethyl acetate onto this layer which generates charge carriers Parts of p-diethylaminobenzaldehyde diphenylhydrazone and 4 parts of bis [pentandionato- (2,4)] - zinc applied in such a way that after drying off the solvent and drying for 30 minutes at 80 ° C., a dry layer thickness of 12 μm results.

A half-value photosensitivity of 2.8 µJ.cm ^{-2 is} determined on this layer. The same layer without zinc acetylacetonate has a half-value photosensitivity of about 4.8 µJ.cm ^-2 . If the layer of Example 7 is used as a copy film in a commercially available copier with dry toner, copies of good quality and in large numbers can be produced with it.

Claims (8)

1. An electrophotographic recording material which comprises an electrically conductive base and one or more layers consisting of binders, charge carrier-producing compounds or sensitizers, charge carrier-transporting compounds and additives, characterized in that it contains, as additive, from 0.5 to 30 % by weight, based on the amount of binder in the layer containing the charge carrier-transporting compounds, of cadmium acetylacetonate, sodium acetylacetonate, magnesium acetylacetonate, zinc acetylacetonate, zirconium acetylacetonate or titanyl acetylacetonate which is colorless in solution and in the mixture.

2. An electrophotographic recording material as claimed in claim 1, characterized in that it contains the metal acetylacetonate in an amount of from 3 to 15 % by weight.

3. An electrophotographic recording material as claimed in claim 1 or 2, characterized in that it has a layer containing charge carrier-producing compounds, and a further layer containing charge carrier-transporting compounds.

4. An electrophotographic recording material as claimed in any of claims 1 to 3 for the production of printing plates, characterized in that it comprises a 0.08 - 0.6 mm thick base suitable for printing plates and a photosemiconductive layer containing

a) one or more binders,

b) one or more charge carrier-transporting compounds,

c) one or more dyes as sensitizers, and

d) one or more metal acetylacetonates as defined in claim 1, with or without

e) further additives.

5. A recording material as claimed in claim 4, characterized in that the binder is soluble in basic aqueous or aqueous-alcoholic solvents.

6. A recording material as claimed in claim 4 or 5, characterized in that the binder is a copolymer of styrene, maleic anhydride and acrylic and/or methacrylic acid, the copolymer containing from 5 to 50 % by weight of maleic anhydride groups as copolymerized units, and from 5 to 35 % by weight of acrylic and/or methacrylic acid groups as copolymerized units.

7. The use of an electrophotographic recording material as claimed in claims 1 to 3 for reprographic purposes.

8. The use of an electrophotographic recording material as claimed in claim 1 or 2 or any of claims 4 to 6 for the production of electrophotograhic printing plates, particularly offset printing plates.