EP0131215A2 - Recording materials with improved photosensitivity - Google Patents

Abstract

The invention relates to electrophotographic recording materials with electrically conductive supports, charge-generating compounds or sensitizers, charge-transporting compounds and an addition of metal acetylacetonates with a high photoconductivity and a low dark conductivity, as well as their use for reprographic purposes and the production of electrophotographic printing forms, in particular offset printing forms.

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. Materials made of polymeric binders, which can be adapted to the special requirements of the respective field of application, low molecular weight organic compounds, which are soluble in the binders even in higher concentrations and are capable of transporting charge carriers of the electric current, and compounds are advantageous for use in the reproduction sector , 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 multilayer electrophotographic recording material described in DE-OS 22 20 408 consists of an electrically conductive carrier material, a first, containing dye, about 0.005 to 2 pm thick, by exposure to _! actinic light charge carrier of the electric current generating layer of dark insulating 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 on 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.

It has now been found that improved electrophotographic recording materials with electrically conductive supports, charge-generating compounds or sensitizers, charge-transporting compounds, binders and special additives can be obtained if they are 0.5 to 30% by weight, but preferably 3 up to 15% by weight, based on the proportion of binder in the layer containing charge transport compounds containing metal acetylacetonates [(pentanedionates - (2,4 »).

It has been shown that 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 been shown that all metal acetylacetonates improve photosensitivity, colored metal acetylacetonates - such as copper (II) acetylacetonate (blue), chromium (III) acetylacetonate (bordorot), iron (III) acetylacetonate (red), nickel (II ) acetylacetonate (turquoise green), palladium (II) acetylacetonate - but negatively affect the effect of the sensitizer, so that overall only slight improvements in photosensitivity result.

• - Cadmiumacotylacetonat (Bis[pentandionato-(2,4)]-cadmium(II))
• - Natriumacetylacetonat (Pentandionato-(2,4)-natrium)
• Magnesiumacetylacetonat (8is[pentandionato-(2,4)]-magnesium),
• - Zinkacetylacetonat (Bis[pentandionato-(2,4)]-zink(II))
• Zirkonacetylacetonat (Tetrakis[pentandionato-(2,4)]-zirkonium(V)) und
• Titanylacetylacetonat (Bis[pentandionato-(2,4)]-titanyl(IV), aber auch Aluminiumacetylacetonat (Tris[pentandionato-(2,4)]-aluminium(III) (rosa) ist sehr geeignet.

The metal acetylacetonates colorless in solution and in the mixture, such as

• - Cadmium acotylacetonate (bis [pentandionato- (2,4)] - cadmium (II))
• - sodium acetylacetonate (pentanedionato (2,4) sodium)
• Magnesium acetylacetonate (8is [pentandionato- (2,4)] - magnesium),
• - zinc acetylacetonate (bis [pentandionato- (2,4)] - zinc (II))
• Zirconium acetylacetonate (tetrakis [pentandionato (2,4)] zirconium (V)) and
• Titanium acetylacetonate (bis [pentandionato- (2,4)] - titanyl (IV), but also aluminum acetylacetonate (tris [pentandionato- (2,4)] - aluminum (III) (pink) is very suitable.

These acetylacetonates are also soluble in sufficient organic solvents.

It is particularly surprising that the addition of the 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 an improved differentiation between exposed and unexposed areas of the loaded surface also improves the photosensitivity 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 (for example US Pat. No. 3,037,861, US Pat. No. 3,553,009, US 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 acetylacetonates achieved according to the invention cannot be derived from the known additives for the person skilled in the art.

The photosensitivity-improving metal acetylacetonates 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 proportion of binder, one or more of the metal acetylacetonates according to the invention. The layers are advantageously applied from an approximately 5% strength by weight solution in a suitable organic solvent to the cleaned conductive carrier material in such a way that a dry layer thickness of approximately 0 , 8 to 40 µm (depending on the intended use, in particular 0.8 to 6 pm for electrophotographic printing forms) resu lted.

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 (bl), 45 to 75 parts by weight of (b2) and, if appropriate, 5 to 25 parts by weight of the additives (b3).

The first layer is advantageously applied to the support material in a thickness of 0.005 to 5, in particular 0.1 to 0.9, pm 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 is preferred minium, zinc, magnesium, copper or multi-metal plates, eg raw or pre-treated, z.8. roughened and / or anodized aluminum sheets, aluminum foils, polymer films with a metallized surface such as aluminum-coated polyethylene terephthalate films or also electrically conductive special papers. Carriers for printing forms advantageously have a thickness of 0.08 to approximately 0.3 mm.

The type of suitable organic binders for the layers depends on the intended use of the recording material. For the copy sector, e.g. 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 substrate 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, in particular 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. Suitable are e.g. Copolymers of methacrylic acid and methacrylic acid esters, especially copolymers of styrene and maleic anhydride and of styrene, methacrylic acid and methacrylic acid esters, provided that 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 water typical for cleaning.

Suitable charge carrier-producing compounds or sensitizers are e.g. for systems applied in one layer, 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.I. 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 31 10 960.

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. Poly (N-vinyl carbazole).

For the respective use, the electrophotographic recording material according to the invention can contain conventional additives, e.g. Leveling agent and plasticizer 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 in terms of resolution and 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 very high-resolution image reproduction results in a good resolution. Thanks to a high charge contrast, even fine halftone dots can be reproduced well in the light tone ranges will. 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 with red light without image loss.

The production of electrophotographic offset printing forms takes place, as usual, 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 downstream 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. through hydrophilization and rubber coating of 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 evenly charged to a surface potential of - 600 volts with a DC corona of - 8.5 kV at a distance of 1 cm and then exposed to the white light of a high-pressure xenon 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 _I 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 [pantandionato- (2,4)] - -Zinc (II) (zinc acetylacetonate) are dissolved in a mixture of tetrahydrofuran and ethyl acetate, the solution is applied to an electrically conductive support made of an electrolytically roughened and then anodically oxidized aluminum sheet 0.15 mm thick so that after the solvent has evaporated off and drying for 30 minutes at 85 ° C results in a dry layer thickness of 4 µm. 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 1, 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-value photosensitivities are 22.4 µJ.cm ^-2 and 23.5 µJ.cm ^-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 pm 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-l, 2.3, 0.2 parts of crystal violet (CI 42555) and 4 parts of bis [pentandionato- (2,4)] - zirconium ₈ - (IV) are made from a 5% solution in tetrahydrofuran onto an electrolytically roughened and anodized aluminum foil 0.15 mm thick in one Dry layer thickness of about 4 microns applied.

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.

Following 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-l, 2.3, 0.6 parts of methyl violet (CI 42535) and 6 parts of bis [pentandionato- (2,4)] - zinc dissolved in a mixture of tetrahydrofuran and methyl glycol acetate and applied as a layer with a dry layer thickness of 3.5 microns on 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: 9,10-tetracarboxylic acid diimide bis-benzimidazole with a chlorine content of about 38% and 50 parts of a commercially available copolymer is placed on a polyethylene terephthalate film with a vapor-deposited, conductive aluminum layer in a thickness of about 300 R. from vinyl chloride, acrylic acid and a maleic acid diester in a thickness of about 0.55 μm applied as a charge carrier-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 (12)

1. Electrophotographic recording materials with electrically conductive supports, binders, charge-generating compounds or sensitizers, charge-transporting compounds and additives, characterized in that they contain 0.5 to 30% by weight, based on the proportion of binder in the charge-transporting compounds containing layer of a metal acetylacetonate. 2. Electrophotographic recording materials according to claim 1, characterized in that they contain the metal acetylacetonate in an amount of 3 to 15 wt .-%. 3. Electrophotographic recording materials according to claim 1, characterized in that they contain a colorless metal acetylacetonate in solution and in the mixture. 4. Electrophotographic recording materials according to one of claims 1 to 3, characterized in that they contain zinc acetylacetonate (bis [pentandionato- (2,4)] - zinc) as metal acetylacetonate. 5. Electrophotographic recording materials according to one of claims 1 to 3, characterized in that they contain magnesium acetylacetonate (bis [pentandionato- (2,4)] - magnesium) as metal acetylacetonate. 6. Electrophotographic recording materials according to one of claims 1 to 3, characterized in that they contain zirconium acetylacetonate (tetrakis [pentandionato- (2,4)] - zirconium (IV)) as metal acetylacetonate. 7. Electrophotographic recording materials according to one of claims 1 to 6, characterized in that they have an electrically conductive carrier, a layer with charge carrier-producing compounds and a further layer with charge carrier transporting compounds, the 0.5 to 30 wt .-%, based on the binder of this layer contain metal acetylacetonates. 8. Recording materials for the production of electrophotographic printing plates according to one of claims 1 to 7, characterized in that they have a photo-semiconducting layer on a carrier material suitable for printing plates with a thickness of 0.08 to 0.6 mm a) at least one binder, b) at least one connection transporting charge carriers, c) at least one dye as a sensitizer, d) at least one metal acetylacetonate and e) possibly contains further additives. 9. Recording materials according to claim 8, characterized in that the binder is soluble in basic aqueous or aqueous-alcoholic solvents. 10 recording materials according to claims 8 and 9, characterized ^g ekenn- characterized in that the binder polymerized, a copolymer of styrene, maleic anhydride and acrylic and / or methacrylic acid with a content of maleic anhydride groups of from 5 to 50 wt .-%, fraction on polymerized acrylic and / or methacrylic acid groups from 5 to 35% by weight. 11. Use of the electrophotographic recording materials according to claims 1 to 7 for reprographic purposes. 12. Use of the electrophotographic recording materials according to one of claims 1 to 6 or 8 to 10 for the production of electrophotographic printing forms, in particular offset printing forms.