DE69510297T2 - Process for the production of an aluminum foil for use as a support in lithographic printing plates - Google Patents

Description

1. Technical field of the invention.

The present invention relates to a process for producing an aluminum foil which is suitable as a support for an imaging element for producing a printing plate according to the silver salt diffusion transfer process.

2. General state of the art.

The principles of the silver complex diffusion transfer reversal process, hereinafter referred to as the DTR process, are described, for example, in US-P 2 352 014 and in the book "Photographic Silver Halide Diffusion Processes" by André Rott and Edith Weyde - The Focal Press - London and New York, (1972).

In the DTR process, the undeveloped silver halide of an information-exposed photographic silver halide emulsion layer material is converted by means of a so-called silver halide solvent into soluble silver complex compounds, which are then allowed to diffuse into an image-receiving element, where they are reduced with a developer substance, usually in the presence of physical development nuclei, whereby a silver image with image density values that are inverted compared to the black silver image obtained in the exposed areas of the photographic material ("DTR image") is produced.

A material bearing a DTR image can be used as a planographic printing plate in which the DTR silver image areas form the water-repellent ink-receptive areas on a water-receptive ink-repellent substrate.

The DTR image can be formed in the image-receiving layer of a sheet or web material which is a separate element with respect to the photographic silver halide emulsion layer material (a so-called DTR double-sheet element) or in the image-receiving layer of a so-called single-support element which is also a single-sheet element and which contains at least one photographic silver halide emulsion layer which forms a unit with an image-receiving layer which is in a water-permeable relationship thereto. This latter monosheet variant is preferred for the production of offset printing plates according to the DTR process.

There are two types of DTR monosheet offset printing plates. The first type, as described in US-P 4 722 535 and GB-P 1 241 661, contains on a support in the order indicated a silver halide emulsion layer and a layer containing physical development nuclei serving as the image-receiving layer. After information-based exposure and development, the imaged element is used as a printing plate without separating the emulsion layer.

A second type of DTR monosheet offset printing plate contains on a hydrophilic support a layer containing physical development nuclei and a silver halide emulsion layer in the order indicated. After information-wise exposure and development, the emulsion layer is separated from the imaged element, leaving a support bearing a silver image used as a printing plate. Such a type of lithographic printing plate is described, for example, in US-P 3,511,656.

As a support for this latter type of printing plate, a roughened and anodized aluminum foil is preferred. After roughening, chemical etching is preferably carried out using an aqueous acid-containing solution, as described in EP-A 567 178. Alternatively, chemical etching can be carried out using an aqueous alkali-containing solution, as described in EP-A 567 178.

In order to obtain such printing plates using the DTR process with good printing properties, ie good ink absorption in the image areas and no ink absorption in the non-image areas, referred to as spotting or foaming, and a high print run stability, the image receiving layer containing the physical development nuclei should have strong adhesion to the aluminum foil. If the adhesion of the image-receiving layer to the aluminum foil is weak, a certain amount of the silver image precipitated in the image-receiving layer will be removed together with the silver halide emulsion layer during rinsing of the imaging element, whereby the effective yield or amount of silver precipitated in the image-receiving layer and, consequently, the printing life will be low. If the adhesion of the image-receiving layer to the aluminum foil is low, the silver image will also wear off more quickly during the printing process.

3. Summary of the invention.

The present invention relates to a process for producing an aluminum foil which has a strong adhesion for an image-receiving layer containing physical development nuclei.

Another object of the present invention is a DTR monosheet material with an aluminum support for producing a lithographic printing plate with good printing properties.

Further objects of the present invention will become apparent from the following description.

The present invention provides a method for producing an aluminum foil, wherein an aluminum foil is first roughened and then anodized, characterized in that the aluminum foil is etched after roughening and before anodizing with an alkaline solution containing a strong alkali in a total amount of between 3 g/l and 75 g/l and thereafter with an acidic solution containing a strong acid in a total amount of at least 150 g/l.

The present invention further provides a DTR monosheet material which contains, on the aluminum support obtained by the process described above, an image-receiving layer containing physical development nuclei and a silver halide emulsion layer in water-permeable contact with the image-receiving layer in the order indicated.

4. Detailed description of the invention.

We have found according to the invention that by etching an already roughened but not yet anodized aluminum foil with an alkaline solution containing a strong alkali in a total amount of between 3 g/l and 75 g/l and then with an acidic solution containing a strong acid in a total amount of at least 150 g/l, the adhesion of an image-receiving layer containing physical development nuclei to the aluminum foil is improved, which is demonstrated by the higher amount of silver precipitated in the image-receiving layer when the aluminum foil provided with an image-receiving layer is used in a DTR process.

DE-A-22 51 382 describes a method for etching an aluminum foil, in which an alkaline etching is first carried out with a 10% aqueous sodium hydroxide solution and then an acidic etching with a 20% nitric acid solution. This etching prevents blackening of the grained aluminum foil during anodizing, but the DE-A document mentioned does not deal with the problem that the present invention attempts to solve. Moreover, the concentration of strong base is considerably higher than is suitable for the present patent application and the alkaline etching is too aggressive.

US-A 3,756,826 relates to the preparatory processing of the aluminum surface for the purpose of coating it with photosensitive coatings. A slightly alkaline etching followed by a cleaning nitric acid treatment can be used. No silver halide layers are proposed as photosensitive layers.

DE-A 22 51 382 describes a process for producing aluminum supports, characterized in that a grained aluminum surface is etched with an alkaline or acidic etching solution in a range between 0.5 and 30 g/m² and then the etched surface is subjected to anodic anodizing. In the examples, the aluminum plate is etched in an alkaline solution and then in an acidic medium. No silver halide layers are proposed as light-sensitive layers.

As mentioned above, a DTR image produced on a hydrophilic background, i.e. a hydrophilic aluminum foil, can be used in lithographic printing. Due to the improved adhesion of the nuclei to the aluminum foil produced according to the invention, more silver precipitates in the image-receiving layer and a silver image with improved wear resistance and consequently a high print run stability can be obtained.

In the present invention, roughening is followed by a chemical etching treatment of the aluminum foil with a solution containing a strong alkali in a total amount of between 3 g/l and 75 g/l. This chemical etching is preferably carried out at a temperature of between 15°C and 50°C, particularly preferably between 20°C and 40°C. Temperatures that are too low during chemical etching can lead to weak adhesion of the image-receiving layer to the aluminum foil.

Suitable alkalis for use in this aqueous etching solution are preferably inorganic strong alkalis, whereby strong alkalis are alkalis with a pKa of at least 13. Examples of particularly suitable alkalis are, for example, NaOH, KOH, etc. or mixtures thereof. Salts of a strong alkali and a weak acid can also be used in admixture with strong alkalis, e.g. sodium gluconate. The total amount of alkali in this aqueous etching solution is preferably between 4 g/l and 50 g/l, particularly preferably between 5 g/l and 25 g/l. The duration of this chemical etching is preferably between 3 s and 5 min. and particularly preferably between 5 s and 4 min.

According to the invention, chemical etching with an aqueous solution containing a strong alkali is followed by chemical etching treatment with an aqueous solution containing a strong acid. This acidic chemical etching is preferably carried out at a temperature of at least 30°C, particularly preferably at least 40°C and very particularly preferably at least 50°C. Temperatures that are too low during acidic chemical etching can lead to weak adhesion of the image-receiving layer to the Aluminium foil. Although there is no specific maximum temperature for this acidic chemical etching, for ease of etching the temperature is generally kept below the boiling point of the solution, preferably below 90ºC.

Suitable acids for use in the aqueous acidic etching solution are preferably strong inorganic acids, whereby strong acids are acids with a pKa of at most 1. Examples of particularly suitable acids are, for example, H₂SO₄, HCl, HNO₃, HF, H₃PO₄, etc. or mixtures thereof. Weak acids can also be used in admixture with strong acids. The total amount of acid in the aqueous acidic etching solution is preferably at least 200 g/l and particularly preferably at least 250 g/l. The duration of this chemical etching is preferably between 3 s and 5 min and particularly preferably between 4 s and 4 min.

Between etching with an alkaline solution and etching with an acid solution, the aluminium foil may be rinsed with demineralised water at a temperature between 15ºC and 30ºC.

The aluminum support of the imaging element used in the invention can be made of pure aluminum or of an aluminum alloy with a minimum aluminum content of 95%. The thickness of the support is usually between about 0.13 and about 0.50 mm.

The production of aluminium foil or foil made of an aluminium alloy for use in lithographic offset printing includes the following steps: graining, anodising and, if necessary, post-processing of the foil.

The graining and anodizing of the foil are essential to obtain a lithographic printing plate with which high quality copies can be obtained according to the invention. Post-processing is not necessary but can result in further improvement of the printing results. The aluminium foil preferably has a roughness with a CLA value between 0.2 and 1.5 µm, contains an anodizing layer with a thickness between 0.4 and 2.0 um and is post-processed with an aqueous bicarbonate solution.

According to the invention, the roughening of the aluminum foil can be carried out using methods that are well known in the current state of the art.

The surface of the aluminum substrate may be roughened either by mechanical, chemical or electrochemical graining or by a combination thereof in order to obtain a satisfactory adhesion of a silver halide emulsion layer to the aluminum support and a good water retention capacity in the areas which will form the non-image areas on the plate surface.

Mechanical graining can be done by, for example, sandblasting, ball graining, rod graining, brush graining, mud graining or a combination of these, etc.

Chemical graining can be carried out as described in Japanese Patent Application No. 61304/76, for example, by alkali etching with a saturated aqueous solution of an aluminum salt of a mineral acid, etc.

The electrochemical graining process is preferred because it can provide a uniform surface roughness with a high average specific surface area and a very fine and uniform grain structure, which is usually desired for use in lithographic printing plates.

In order to obtain a fine-grained surface topography, the concentration and temperature of the electrolyte solution and the current form and current density should be optimally measured.

Electrochemical graining in the present invention can be carried out by feeding an alternating current or a direct current into an electrolytic solution containing hydrogen chloride and/or nitric acid. Other aqueous solutions that can be used in electrochemical graining include acids such as HNO3, H2SO4 and H3PO4, which if required additionally contain one or more corrosion inhibitors such as Al(NO3)3, AlCl3, boric acid, chromic acid, sulfates, chlorides, nitrates, monoamines, diamines, aldehydes, phosphates, H2O2, etc.

The electrochemical graining according to the invention can be carried out with single-phase and three-phase alternating current. AC waves can be a sine wave, a square wave, a trapezoidal wave, etc. The anodic charge can be higher or lower than the cathodic charge. The voltage applied to the aluminum plate is 1-60 V and preferably 10-35 V. A current density of 3-150 Amp/dm2 is applied for 5-240 s. The temperature of the electrolytic graining solution is between 5 and 50°C. Electrochemical graining is preferably carried out with an alternating current between 10 Hz and 300 Hz.

Mechanical and electrochemical processes can be combined as described in US-P 4,476,006 and 4,477,317.

According to the invention, the roughening is adjusted so that an arithmetic mean roughness value (Ra) of the surface between 0.3 and 1.3 µm is obtained.

Roughening is preferably preceded by a degreasing treatment, which mainly serves to remove fatty substances from the surface of the aluminium foil.

For this purpose, the aluminum foil may be subjected to a degreasing treatment with a surfactant and/or an aqueous alkaline solution to remove rolling oil, dust, rust and other impurities from the foil surface. Degreasing may be carried out by a two-step treatment in which the aluminum foil is treated with an alkaline solution and then cleaned in an acid solution or degreased in an acid solution and then cleaned with an alkaline solution. Acid solutions preferably contain chromic acid, phosphoric acid or sulfuric acid and usable alkaline solutions may contain NaOH, KOH, etc.

After the second chemical etching with an aqueous solution containing a strong acid in a total amount of at least 150 g/l, the aluminum foil is anodized according to the invention, for example by the following method.

The granulated aluminum foil used as an anode in a solution containing sulfuric acid, phosphoric acid, oxalic acid, chromic acid or organic acids such as sulphamic acid, benzosulphonic acid, etc. or mixtures thereof, is supplied with an electric current. An electrolyte concentration of 1 to 70% by weight can be used in a temperature range of 0 to 70ºC, preferably 35ºC to 60ºC and most preferably 40ºC to 50ºC. The anode current density can vary between 1 and 50 A/dm² and the voltage between 1 and 100 V to obtain an anodised film with a weight of between 1 and 8 g/m² Al₂O₃.H₂O. The anodised aluminium foil can then be rinsed with demineralised water at a temperature of between 10 and 80ºC.

After the anodizing phase, the anodized surface can be further processed, such as sealed. Sealing the pores of the aluminum oxide layer created by anodizing is a technique known to experts in the field of aluminum anodizing. This technique is described, for example, under the title "Sealingkwaliteit en sealing-controle von geanodiseerd Aluminium" in the "Belgisch-Nederlands Tijdschrift voor Oppervlaktetechnieken van materialen", 24th year/January 1980. The porous anodized aluminum surface can be sealed using various methods.

Preferably, the post-processing is carried out by treating a grained and anodized aluminum support with an aqueous bicarbonate solution as described in EP-A 567 178, which is incorporated by reference into this document.

Preferably, a rinsing step is carried out between each of the above-described steps in order to avoid the liquid used in a particular step mixing with the liquid of the previous step and becoming unclean.

To improve the image sharpness and thus the sharpness of the final printed copy, the anodized layer can be colored in the mass with an antihalation dye or antihalation pigment, as described in JA-Pu 58-14797, for example.

After the production of the aluminum foil as described above, the aluminum foil can be coated immediately or at a later stage with a solution containing the physical development nuclei.

The image-receiving layer containing physical development nuclei can be free of hydrophilic binder, but preferably contains small amounts of, for example, up to 80% by weight, based on the total weight of this layer, of a hydrophilic colloid such as, for example, polyvinyl alcohol, to improve the hydrophilicity of the surface.

Sulfides of heavy metals, such as antimony, bismuth, cadmium, cobalt, lead, nickel, palladium, platinum, silver and zinc sulfides, are preferred as development nuclei for use in accordance with the present invention. Particularly suitable development nuclei according to the invention are palladium sulfide nuclei. Other suitable development nuclei include salts such as selenides, polyselenides, polysulfides, mercaptans and tin(II) halides. Heavy metals, preferably silver, gold, platinum, palladium and mercury, can be used in colloidal form.

The aluminum support according to the invention is particularly suitable for the production of a DTR monosheet material. According to the process according to the invention for obtaining a DTR monosheet material, an aluminum foil produced as described above and coated with an image-receiving layer is coated with a light-sensitive layer which is in water-permeable contact with the image-receiving layer.

Layers in water-permeable contact with one another are layers that are adjacent to one another or are only separated from one another by one or more water-permeable layers. When choosing the water-permeable layer, consideration is given to ensuring that it does not largely inhibit or limit the diffusion of water or of compounds contained in an aqueous solution, e.g. developers or complexed silver.

The light-sensitive layer used in the invention can be any layer containing a hydrophilic colloidal binder and at least one silver halide emulsion, at least one of the silver halide emulsions being light-sensitive.

The photographic silver halide emulsion(s) used in the invention can be prepared from soluble silver salts and soluble halides by various methods, such as those described, for example, by P. Glafkidès in "Chimie et Physique Photographiques", Paul Montel, Paris (1967), by G. F. Duffin in "Photographic Emulsion Chemistry", The Focal Press, London (1966), and by V. L. Zelikman et al in "Making and Coating Photographic Emulsion", The Focal Press, London (1966).

According to the invention, the silver halide emulsion or silver halide emulsions preferably consist mainly of silver chloride with a fraction of silver bromide that is in the range from 1 mol% to 40 mol%. A silver halide emulsion containing at least 70 mol% silver chloride is particularly preferred.

The average particle size of the silver halide grains can vary between 0.10 and 0.70 µm, preferably between 0.25 and 0.45 µm.

Preferably during the precipitation step, iridium and/or rhodium containing compounds or a mixture of both compounds are added. The ratio of these added compounds varies between 10-8 and 10-3 moles per mole of AgNO3, preferably between 10-7 and 10-5 moles per mole of AgNO3.

The emulsions can be chemically sensitized, for example, by adding sulfur-containing compounds such as allyl isothiocyanate, allyl thiourea and sodium thiosulfate during the chemical ripening stage. Reducing agents, such as the tin compounds described in BE-P 493 464 and 568 687, and polyamines such as diethylenetriamine or derivatives of aminomethanesulfonic acid can also be used as chemical sensitizers. Other suitable chemical sensitizers are noble metals and noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium. This chemical sensitization process is described in the article by R. KOSLOWSKY, Z. Wiss. Photogr. Photophys. Photochem. 46, 65-72 (1951).

In addition to negative-acting silver halide emulsions, which are preferred due to their high light sensitivity, direct positive silver halide emulsions producing a positive silver image in the emulsion layer(s) and a negative image on the image-receiving layer can also be used.

Suitable direct positive silver halide emulsions for use in the present invention are prefogged silver halide emulsions or primarily internal latent image forming silver halide emulsions.

Internal latent image silver halide emulsions that can be used according to the invention are described, for example, in US-A 2 592 250, 3 206 313, 3 271 157, 3 447 927, 3 511 662, 3 737 313, 3 761 276, GB-A 1 027 146 and in JA-P 34 213/77. However, the silver halide emulsions used according to the invention are not limited to the silver halide emulsions described in these documents.

The other type of prefogged direct positive silver halide emulsions usable in accordance with the invention can be prepared by total exposure of a silver halide emulsion to light and/or by chemical fogging of a silver halide emulsion. The preparation of chemical fog nuclei can be carried out by various chemical sensitization processes.

Chemical fogging can be carried out by reduction or by means of a compound which is more electropositive than silver, e.g. gold salts, platinum salts, iridium salts, etc., or a combination of both. Reduction fogging of the silver halide grains can be carried out under silver halide precipitation or silver halide ripening conditions with a high pH and/or a low pAg, as described, for example, by Wood in J. Phot. Sci. 1 (1953), 163, or by processing with reducing agents, e.g. tin(II) salts such as tin(II) chloride, tin complexes and tin chelates of the (poly)amino(poly)carboxylic acid type described in GB-P 1 209 050, formaldehyde, hydrazine, hydroxylamine, sulphur compounds, e.g. thiourea dioxide, phosphonium salts, e.g. tetra(hydroxymethyl) phosphonium chloride, polyamines, e.g. diethylenetriamine, bis(p-aminoethyl) sulfide and its water-soluble salts, hydrazine derivatives, alkali arsenite, amine borane, etc. or mixtures thereof.

If the silver halide grains are fogged using a reducing agent, e.g. thiourea dioxide, and a compound of a metal that is more electropositive than silver, in particular a gold compound, the reducing agent is preferably used first and then the gold compound. However, both compounds can also be used in reverse order or simultaneously.

In addition to the chemical fogging processes described above, chemical fogging can also be carried out using the fogging agents mentioned above in combination with a sulfur-containing sensitizer, e.g. sodium thiosulfate, or a thiocyanic acid compound, e.g. potassium thiocyanate.

The silver halide emulsions of the DTR element can be spectrally sensitized depending on the spectral emission of the exposure source for which the DTR element is designed.

Sensitizing dyes for the visible spectral range include methine dyes such as those described by F. M. Hamer in "The Cyanine Dyes and Related Compounds", 1964, John Wiley & Sons. Dyes that can be used for this purpose include cyanine dyes, merocyanine dyes, cyanine complex dyes, merocyanine complex dyes, homeopolar cyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. Dyes belonging to the cyanine dyes, merocyanine dyes and merocyanine complex dyes are particularly valuable.

In the case of a conventional light source such as tungsten light, a sensitizing dye for the green range is required. When exposed to an argon ion laser, a sensitizing dye for the blue range is incorporated. When exposed to a red light source such as an LED diode or a He-Ne laser, a sensitizing dye for the red range is used. When exposed to a semiconductor laser, special spectral sensitizing dyes suitable for the near infrared are used. required. Suitable sensitizing dyes for the infrared range are known from, among others, US Pat. Nos. 2,095,854, 2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921, 3,582,344, 3,623,881 and 3,695,888.

Sensitizing dyes preferred according to the invention for the blue, green, red and infrared range are described in EP-A 554 585.

To improve the sensitivity in the red or near infrared range, so-called supersensitizers can be used in combination with red or infrared sensitizing dyes. Suitable supersensitizers can be found in article 28952 in Research Disclosure, Volume 289, May 1988. The spectral sensitizers can be added to the photographic emulsions in the form of an aqueous solution, a solution in an organic solvent or in the form of a dispersion.

The silver halide emulsions can contain the usual emulsion stabilizers. Suitable emulsion stabilizers are azaindenes, preferably tetra- or pentaazaindenes, especially those substituted with hydroxyl or amino groups. Such compounds are described by BIRR in Z. Wiss. Photogr. Photophys. Photochem. 47, 2-27 (1952). Other suitable emulsion stabilizers include heterocyclic mercapto compounds.

The silver halide emulsion layers usually contain gelatin as a hydrophilic colloid binder. Mixtures of different gelatins with different viscosity values can be used to adjust the rheological properties of the layer. Instead of or together with gelatin, one or more other natural and/or synthetic hydrophilic colloids can be used, e.g. albumin, casein, zein, polyvinyl alcohol, alginic acids or salts thereof, cellulose derivatives such as carboxymethyl cellulose, modified gelatin, e.g. phthaloyl gelatin, etc.

The gelatin layer(s) is (are) preferably substantially unhardened. Substantially unhardened means that when such a gelatin layer is applied in a dry thickness of 1.2 g/m² on a coated on a subbed polyethylene terephthalate film support, dried for 3 days at 57ºC and 35% RH (relative humidity) and then immersed in water at 30ºC, the gelatin layer is dissolved by more than 95% by weight within 5 minutes.

The silver halide emulsions can contain pH-controlling ingredients. Preferably, at least one gelatin layer is applied at a pH not below the isoelectric point of the gelatin in order to avoid interactions between the gelatin layer and the intermediate layer mentioned below. Particularly preferably, the gelatin layer adjacent to the intermediate layer is applied at a pH not below the isoelectric point of the gelatin. Most particularly preferably, all gelatin layers are applied at a pH not below the isoelectric point of their gelatin. Other ingredients such as antifoggants, development accelerators, wetting agents and hardeners for gelatin can also be included. The silver halide emulsion layer can contain screen dyes which absorb the scattered light and thereby increase the image sharpness. Suitable light-absorbing dyes are, among others: in US-P 4 092 168, US-P 4 311 787 and DE-P 2453 217.

More detailed information on the composition, preparation and application of silver halide emulsions suitable for use in the present invention can be found, for example, in the Product Licensing Index, Volume 92, December 1971, Item 9232, pp. 107-109.

The imaging element preferably also contains an interlayer between the image-receiving layer on the hydrophilic surface of a support and the photosensitive layer(s) to facilitate removal of the photosensitive layer(s) to reveal the silver image formed in the image-receiving layer upon processing of the imaging element.

In a particular embodiment, the intermediate layer is a water-swellable intermediate layer applied at a rate of 0.01 to 2.0 g/m2 containing at least one non-proteinaceous hydrophilic film-forming polymer, e.g. polyvinyl alcohol, and optionally an antihalation dye or an antihalation pigment, as described in EP-A-410500.

In a further embodiment, the intermediate layer is a layer containing hydrophobic polymer beads produced by polymerizing at least one ethylenically unsaturated monomer and having an average diameter of not less than 0.2 µm. Preferably, this intermediate layer contains the hydrophobic polymer beads in a quantity of up to 80% of its total weight in the dry state. More detailed information can be found in EP-A 483 415.

An additional intermediate layer, optionally located between the silver halide emulsion layer and the water-swellable intermediate layer or the intermediate layer containing hydrophobic polymeric beads, may incorporate one or more ingredients such as, among others, antihalation dyes or pigments, developers, silver halide solvents, carrier precursors and anticorrosive substances.

The silver halide emulsion layer and any other layers can be coated onto the aluminum support according to the invention coated with an image-receiving layer using conventional coating techniques such as cascade coating or curtain coating. Alternatively, these layers can be first coated onto a temporary support such as a polyester support and then laminated onto the aluminum support as described in EP-A 410 500.

If the imaging element is produced by laminating a layer assembly containing a photosensitive layer on the image-receiving layer, the intermediate layer(s) is/are coated onto the photosensitive layer(s), the water-swellable intermediate layer or the intermediate layer containing hydrophobic polymers obtained by polymerization of at least one ethylenically unsaturated monomer manufactured polymer beads with a mean diameter of not less than 0.2 µm, which constitutes the top layer.

Although the aluminum support according to the invention is primarily used as a support for a DTR single sheet material, it is equally suitable for use as a receiving material in a DTR double sheet process.

The imaging element in the present invention can be informationally exposed in an apparatus selected according to its specific application.

A wide variety of cameras are commercially available for exposing the light-sensitive silver halide emulsion. Horizontal, vertical and darkroom type cameras and contact exposure devices are available for each particular class of reprographic work. The imaging element in the present invention can also be exposed using, among others, a laser exposure unit and a cathode ray tube.

In the present invention, the development and diffusion transfer of the information-wise exposed imaging element, whereby a silver image is formed in the photosensitive layer and the unreduced silver halide or its complexes formed therefrom can diffuse imagewise from the photosensitive layer to the image-receiving layer to form a silver image therein, are carried out using an aqueous alkaline solution in the presence of at least one developing agent and at least one silver halide solvent. The developing agent(s) and/or the silver halide solvent(s) can be incorporated into the aqueous alkaline solution and/or the imaging element.

A silver halide solvent is used in the aqueous alkaline solution preferably in an amount between 0.05 wt.% and 5 wt.%, particularly preferably between 0.5 wt.% and 2 wt.%. The silver halide solvent acting as a complexing agent for silver halide is preferably a water-soluble thiosulfate or thiocyanate, e.g. Sodium, potassium or ammonium thiosulfate and sodium, potassium or ammonium thiocyanate.

Other silver halide solvents for use in the present invention include sulfite, amines, 2-mercaptobenzoic acid, cyclic imide compounds such as uracil, 5,5-dialkylhydantoins, alkylsulfones and oxazolidones.

Other silver halide solvents for use in the present invention are alkanolamines. Examples of alkanolamines suitable for use in the present invention correspond to the following formula.

in which X and X' each independently represent a hydrogen atom, a hydroxyl group or an amino group, 1 and m represent 0 or integers of 1 or more and n represents an integer of 1 or more. The alkanolamines can be used in a concentration preferably set between 0.1% by weight and 5% by weight in the alkaline processing liquid. The alkanolamine can, however, be partially or completely present in one or more layers of the imaging element.

Thioethers are preferred as further silver halide solvents that can be used according to the invention. Thioethers corresponding to the following general formula are preferably used:

Z-(R¹-S)t-R²-S-R³-Y

in which Z and Y each independently represent a hydrogen atom, an alkyl group, an amino group, an ammonium group, a hydroxyl group, a sulpho group, a carboxyl group, an aminocarbonyl group or an aminosulphonyl group, R¹, R² and R³ each independently represent an alkylene group which may be substituted and optionally contain an oxygen bridge, and t is an integer from 0 to 10. Examples of thioether compounds corresponding to the above formula are known, for example, from US-P-4 960 683 and from EP-A-554 585.

Still further suitable silver halide solvents are 1,2,4-triazolium-3-thiolates, preferably 1,2, 4-triazolium-3-thiolates substituted by at least one substituent from the group consisting of a C₁-C₈ alkyl group having at least 3 fluorine atoms, a C₄-C₁₀ hydrocarbon group and a 4-amino group which is substituted by a C₁-C₈ alkyl group having at least 3 fluorine atoms and/or a C₄-C₁₀ hydrocarbon group.

Combinations of different silver halide solvents may also be used and it is also possible to incorporate at least one silver halide solvent into a suitable layer of the imaging element and at least one other silver halide solvent into the developer solution.

The alkaline processing liquid may also contain a developing agent or agents. In this case, the alkaline processing liquid is referred to as a developer. On the other hand, certain developing agents or all of the developing agents may be contained in one or more layers of the photographic material or imaging element. If all of the developing agents are contained in the imaging element, the alkaline processing liquid is referred to as an activating agent or activator liquid.

Silver halide developers which can be used according to the invention are preferably of the p-dihydroxybenzene type, e.g. hydroquinone, methylhydroquinone or chlorohydroquinone, preferably in combination with an auxiliary developer of the 1-phenyl-3-pyrazolidinone type and/or p-monomethylaminophenol. Particularly useful auxiliary developers are the 1-phenyl-3-pyrazolidinones. Even more preferred, especially if they are incorporated in the photographic material, are 1-phenyl-3-pyrazolidinones whose water solubility is enhanced by a hydrophilic substituent such as a hydroxyl group, amino group, carboxylic acid group, sulfonic acid group, etc. Examples of 1-phenyl-3-pyrazolidinones substituted with one or more hydrophilic groups are e.g. 1-phenyl-4,4-dimethyl-2-hydroxy-3-pyrazolidone, 1-(4-carboxyphenyl)-4,4-dimethyl-3-pyrazolidone, etc. However, other developers are also possible.

The hydroquinone-type developers are preferably used in an amount of between 0.05 mol and 0.40 mol per litre and the auxiliary developer(s) are preferably used in an amount of between 1.8 x 10⁻³ and 2.0 x 10⁻¹ mol per litre.

The aqueous alkaline solution according to the invention may further contain sulfite, e.g. sodium sulfite, in an amount between 40 g and 180 g per liter, preferably between 60 g and 160 g per liter, in combination with another silver halide solvent.

The following ranges of amounts given for the developers, silver halide solvents and sulfite refer to the amount of these compounds contained as dissolved substances in the aqueous alkaline solution during DTR processing, regardless of whether these compounds are part of the aqueous alkaline solution or are dissolved from the layers in which they are present after the aqueous alkaline solution is applied thereto.

The aqueous alkaline solution suitable for use in the present invention preferably contains aluminum ions in a minimum amount of 0.3 g/l, and more preferably 0.6 g/l, in order to avoid that the emulsion layer will stick to the conveyor rollers due to swelling of the emulsion in contact with the aqueous alkaline solution.

The pH value of the alkaline processing liquid is preferably between 9 and 14, particularly preferably between 10 and 13, but depends on the type of silver halide emulsion material to be developed, the development time used and the processing temperature.

The processing conditions such as temperature and time can vary within wide limits, provided that the mechanical strength of the materials to be processed is not adversely affected and no decomposition of the materials is caused.

The pH value of the alkaline processing liquid can be adjusted using an organic or inorganic alkaline substance or a combination of these. Examples of inorganic alkaline substances include sodium and potassium hydroxides, alkali metal salts of phosphoric acid and/or silicic acid, e.g. trisodium phosphate, orthosilicates, metasilicates, sodium or potassium hydrosilicates and sodium carbonate, etc. Examples of organic alkaline substances include alkanolamines. In the latter case, the alkanolamines provide the pH value or help to maintain it and serve as silver halide complexing agents.

To improve the hydrophobicity of the silver image produced in the image-receiving layer, the aqueous alkaline solution can also contain hydrophobic agents. As a rule, these compounds contain a mercapto group or thiolate group and one or more hydrophobic substituents. Particularly preferred hydrophobic agents are mercapto-1,3,4-thiadiazoles as described in DE-A 12 28 927 and US-P 4 563 410, 2-mercapto-5-heptyl-oxa-3,4-diazole and long-chain (containing at least 5 carbon atoms) alkyl-substituted mercaptotetrazoles. The hydrophobic agents can be used alone or in combination with one another.

These hydrophobic compounds can preferably be added to the aqueous alkaline solution in an amount of between 0.1 and 3 g per liter and preferably in admixture with 1-phenyl-5-mercaptotetrazole, the 1-phenyl-5-mercaptotetrazole being used in an amount of, for example, 50 mg to 1.2 g per liter of solution and the solution can contain a small amount of ethanol to improve the dissolution of these compounds.

The aqueous alkaline solution may contain other ingredients such as antioxidants, calcium complexing agents, silver sludge inhibitors and hardeners including latent hardeners.

The aqueous alkaline solution can of course be regenerated by known methods, independent of whether or not the solution contains developing agent(s) and/or silver halide solvent(s).

Although often not necessary, development can be stopped with a so-called stabilizer liquid, which is actually an acid stop bath with a pH value preferably between 5 and 7.

Preferred are buffered stop bath compositions containing a mixture of sodium dihydrogen orthophosphate and disodium hydrogen orthophosphate and having a pH in the above range.

The development and diffusion transfer can be initiated in various ways, for example by rubbing with a roller, by coating with an absorbent agent, such as a cotton ball or sponge, or by immersing the material to be treated in the liquid composition. Both processes are preferably carried out in an automatic machine and, as a rule, at a temperature of between 18ºC and 30ºC and for a period of between 5 s and 5 min.

After the silver image has been formed on the hydrophilic surface of a support, the excess of aqueous alkaline solution remaining on the support can be removed, preferably by passing the film through a pair of squeezing rollers.

The silver image thus obtained in the layer containing physical development nuclei is then revealed by removing all layers on the layer containing physical development nuclei from the imaging element, thereby revealing the imaged surface of the hydrophilic support.

According to a particularly preferred embodiment of the present invention, the silver image in the layer containing physical development nuclei is revealed by washing off all layers on the layer containing physical development nuclei with rinsing water.

The temperature of the rinsing water can vary within wide limits, but is preferably between 30ºC and 50ºC, particularly preferably between 35ºC and 45ºC.

The imaged surface of the hydrophilic surface of a support may be subjected to chemical processing to improve the hydrophilicity of the non-silver image parts and the oleophilicity of the silver image.

This chemical post-treatment is preferably carried out with a lithographic composition, often called a finishing agent, which contains at least one compound which improves the ink attraction and/or the varnish attraction of the silver image and also at least one compound which improves the ink repellency properties of the hydrophilic surface.

Suitable ingredients for the finishing agent are, for example, organic compounds containing a mercapto group, such as the above-mentioned hydrophobic compounds for the alkaline solution. Preferred compounds correspond to one of the following formulas:

in which R⁵ is a hydrogen atom or an acyl group and R⁴ is an alkyl group, aryl group or aralkyl group. Particularly preferred are compounds according to one of the above formulas, where R⁵ is an alkyl group containing between 3 and 16 carbon atoms. The hydrophobizing agent(s) is (are) preferably present in a total concentration of between 0.1 g/l and 10 g/l, particularly preferably in a total concentration between 0.3 g/l and 3 g/l, in the finishing agent.

Additives that improve the oleophobic paint repellency of the hydrophilic surface areas include carbohydrates such as acid polysaccharides such as gum arabic, carboxymethylcellulose, sodium alginate, propylene glycol esters of alginic acid, hydroxyethyl starch, dextrin, hydroxyethylcellulose, polyvinylpyrrolidone, polystyrene sulfonic acid, polyglycols that are the reaction products of ethylene oxide and/or propylene oxide with water or an alcohol, and polyvinyl alcohol. Optionally, hygroscopic substances such as sorbitol, glycerin, tri(hydroxyethyl)esters of glycerin, and Turkey red oil can also be added.

Furthermore, one or more surfactants are preferably added to the finishing agent, the concentration of which can vary within wide limits, provided that the finishing agent does not produce excessive foam when finishing the plates. Preferred surfactants are anionic or non-ionic surface-active compounds.

A suitable finish, as described in US-A-4,563,410, is a composition containing a solution of a mercaptotriazole in a solution of polyethylene oxide having a molecular weight of 4,000. Other suitable finishes are described in US-A-4,062,682, among others.

During the initial stage of the finishing treatment, the surface bearing the silver image may be in a dry or wet state. In general, the finishing treatment does not take long, usually not more than about 30 seconds, and can be carried out immediately after the processing and uncovering stages, preferably at a finishing temperature of between 30ºC and 60ºC.

The finishing agent can be applied in various ways, e.g. by rubbing with a roller, by coating with an absorbent agent, e.g. with a cotton ball or sponge, or by dipping the material to be treated in the finishing agent. Hydrophobizing the printing plate image can also be carried out automatically by guiding the printing plate through an apparatus which comprises a narrow channel containing the finishing agent and which conveys the printing plate at the end of the channel between two squeezing rollers which remove the excess liquid.

After the hydrophilic surface of a support bearing the silver image has been treated with the finishing agent, it can be used as a printing plate.

The present invention will now be illustrated by the following example, but is not limited thereto. All parts, percentages and ratios are by weight unless otherwise indicated.

EXAMPLE 1

A 0.30 mm thick aluminium foil (AA 1050) is degreased by immersing the foil in an aqueous solution containing 5 g/l sodium hydroxide at 50ºC and rinsing it with demineralised water. The foil is then electrochemically grained at a temperature of 35ºC and a current density of 1,200 A/m² using an alternating current in an aqueous solution containing 4 g/l hydrochloric acid, 4 g/l hydroboric acid and 0.5 g/l aluminium ions to obtain a surface topography with an arithmetic mean roughness Ra of 0.5 µm. After rinsing with demineralized water, the aluminum plate is then etched with an aqueous solution containing 300 g/l sulfuric acid at 60ºC for 180 s and rinsed with demineralized water at 25ºC for 30 s. The foil is then anodized in an aqueous solution containing 200 g/l sulfuric acid to obtain an anodic oxidation foil containing 2.60 gm² Al₂O₃·H₂O, then washed with demineralized water, subsequently post-processed with a solution containing 20 g/l sodium bicarbonate at 40ºC for 30 s and finally dried. The aluminum foil thus obtained is called support A.

A carrier B is produced analogously to the process described above, but with the difference that the aluminium foil etched for 20 s at 25ºC with an aqueous solution containing 5 g/l sodium hydroxide and then rinsed for 30 s with demineralized water at 25ºC.

A support C is prepared analogously to the process described above for support A, but with the difference that after the aluminum foil has been etched for 180 s with an aqueous solution containing 300 g/l of sulfuric acid at 60ºC and rinsed for 30 s with demineralized water at 25ºC, it is etched for 20 s with an aqueous solution containing 5 g/l of sodium hydroxide and rinsed for 30 s with demineralized water at 25ºC.

A support D is prepared analogously to the procedure described above for support B, but with the difference that, after the aluminum foil has been etched for 20 s at 25ºC with an aqueous solution containing 5 g/l of sodium hydroxide and rinsed for 30 s with demineralized water at 25ºC, it is etched for 180 s at 60ºC with an aqueous solution containing 300 g/l of sulfuric acid and rinsed for 30 s with demineralized water at 25ºC.

The 4 resulting aluminum supports are each coated with a silver receiving layer containing 1.1 mg/m² PdS as physical development nuclei.

An intermediate layer of an aqueous composition is then cast onto the dry silver receiving layer, the resulting layer containing 0.5 g of polymethyl methacrylate beads/m² after drying and the aqueous composition containing the following ingredients:

a 20% dispersion of polymethylmethacrylate beads with an average diameter of 1.0 µm in a mixture with equal volumes of water and ethanol 50 ml

Helioechtpapierrot BL (registered trademark for a dye distributed by BAYER AG, D-5090 Leverkusen, Germany) 2.5 g

Saponins 2.5 g

Sodium oleylmethyl tauride 1.25 g

demineralized water 300 ml

(pH value: 5.6)

Finally, a substantially unhardened, light-sensitive, negative-acting, cadmium-free, 1 mmol 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene per mole AgX silver chloride-bromoiodide gelatin emulsion layer (97.98/2/0.02 mol-%) is applied to the intermediate layer, the silver halide being applied in an amount corresponding to 2.40 g silver nitrate/m² and the gelatin content of the emulsion layer being 1.58 g/m², the gelatin content consisting of 0.7 g/m² gelatin with a viscosity of 21 mPa·s and the remainder being gelatin with a viscosity of 14 mPa·s.

The 4 resulting non-exposed DTR monosheet materials are immersed for 8 s at 25ºC in a freshly prepared developer solution with the following composition.

Carboxymethylcellulose 4 g

Sodium hydroxide 22.5 g

anhydrous sodium sulphite 120 g

Hydroquinone 20 g

1-Phenyl-4-methyl-3-pyrazolidinone 6 g

Potassium bromide 0.75 g

anhydrous sodium thiosulfate 8 g

Ethylenediaminetetraacetic acid tetrasodium salt 2 g

demineralized water until filled to 1,000 ml

pH (24ºC) = 13

The initiated diffusion transfer is allowed to continue for 30 s to create a silver layer on the 4 supports.

To remove the developed silver halide emulsion layer and the swollen interlayer from the aluminum foils, the developed DTR monosheet materials are rinsed with a water jet for 30 s at 30ºC.

The amount of silver deposit (silver yield) in the image receiving layer is then measured with a (from Philips X-ray fluorescence analysis spectrophotometer PHILIPS 1400 (sold separately). The results obtained for each of the 4 DTR materials are listed in Table 1 below. Table 1

Remarks

a) Silver yield in the image-receiving layer after processing with the finishing agent.

b) Silver yield in the image-receiving layer after rubbing the finished plate with a cotton ball moistened with water.

From the foregoing it can be seen that by etching the roughened aluminium foil with an alkaline solution containing 5 g/l of sodium hydroxide and then with an acidic solution containing 300 g/l of sulphuric acid (inventive support D), the silver yield is better than when the aluminium foil is etched only with an acidic solution containing 300 g/l of sulphuric acid (comparative support A), and much better than when the aluminium foil is etched only with an alkaline solution containing 5 g/l of sodium hydroxide (comparative support B) or with an acidic solution containing 300 g/l of sulphuric acid and then with an alkaline solution containing 5 g/l of sodium hydroxide (comparative support C). Since the silver yield is an important parameter influencing the printing strength of the printing plate, the print strength can be increased by alkaline etching of the aluminium foil with an alkaline solution containing a strong alkali in a total amount of between 3 g/l and 75 g/l and then by acid etching of the aluminium foil with an acidic solution containing a strong acid in a total amount of at least 150 g/l.

Claims (8)

1. A process for producing an aluminum foil, wherein an aluminum foil is first roughened and then anodized, the aluminum foil being etched after roughening and before anodizing with an alkaline solution containing a strong alkali in a total amount of between 3 g/l and 75 g/l and then with an acidic solution containing a strong acid in a total amount of at least 150 g/l, and an image-receiving layer containing physical development nuclei is applied to the aluminum foil, characterized in that a silver halide emulsion layer is further coated on the image-receiving layer. 2. Process according to claim 1, characterized in that the alkaline solution contains a strong alkali in a total amount between 4 g/l and 50 g/l. 3. Process according to claim 1 or 2, characterized in that the alkaline solution has a temperature between 15ºC and 50ºC. 4. Process according to any one of claims 1 to 3, characterized in that the acidic solution contains a strong acid in a total amount of at least 200 g/l. 5. Process according to any one of claims 1 to 4, characterized in that the acidic solution has a temperature between 30ºC and 90ºC. 6. Process according to any one of claims 1 to 5, characterized in that the anodizing is carried out at a temperature between 35ºC and 60ºC. 7. A method according to any one of claims 1 to 6, characterized in that the aluminium foil is Anodizing is followed by an aqueous bicarbonate solution. 8. Use of a roughened and anodized aluminum foil as a support in the manufacture of a single-sheet material usable by the silver salt diffusion transfer process, wherein a layer containing physical development nuclei and a silver halide emulsion layer are applied to the aluminum foil in the specified order, characterized in that the aluminum foil is etched after roughening and before anodizing with an alkaline solution containing a strong alkali in a total amount of between 3 g/l and 75 g/l and then with an acidic solution containing a strong acid in a total amount of at least 150 g/l.