Radiation imagery chemistry: process – composition – or product th – Transfer procedure between image and image layer – image... – Diffusion transfer process – element – or identified image...
Reexamination Certificate
1996-04-22
2001-09-04
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Transfer procedure between image and image layer, image...
Diffusion transfer process, element, or identified image...
C430S249000, C430S251000, C430S403000, C430S451000, C430S452000, C430S453000, C430S456000
Reexamination Certificate
active
06284426
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an alkaline processing solution for the silver complex diffusion transfer reversal process. More particularly the present invention relates to an alkaline processing solution, said solution reducing the sticking tendency of the emulsion layer to the transporting system. Furthermore the present invention relates to a method for producing an improved lithographic printing plate.
BACKGROUND OF THE INVENTION
The principles of the silver complex diffusion transfer reversal process, hereinafter called DTR-process, have been described e.g. in U.S. Pat. No. 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 non-developed silver halide of an information-wise exposed photographic silver halide emulsion layer material is transformed with a so-called silver halide solvent into soluble silver complex compounds which are allowed to diffuse into an image-receiving element and are reduced therein with a developing agent, generally in the presence of physical development nuclei, to form a silver image having reversed image density values (“DTR-image”) with respect to the black silver image obtained in the exposed areas of the photographic material.
A DTR-image bearing material can be used as a planographic printing plate wherein the DTR-silver image areas form the water-repellant ink-receptive areas on a water-receptive ink-repellant background.
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 material (a so-called two-sheet DTR element) or in the image-receiving layer of a so-called single-support-element, also called mono-sheet element, which contains at least one photographic silver halide emulsion layer integral with an image-receiving layer in waterpermeable relationship therewith. It is the latter mono-sheet version which is preferred for the preparation of offset printing plates by the DTR method.
Two types of the mono-sheet DTR offset printing plate exist. According to a first type disclosed in e.g. U.S. Pat. No. 4,722,535 and GB-1,241,661 a support is provided in the order given with a silver halide emulsion layer and a layer containing physical development nuclei serving as the image-receiving layer. After information-wise exposure and development the imaged element is used as a printing plate without the removal of the useless emulsion layers.
According to a second type of mono-sheet DTR offset printing plate a support, commonly anodized aluminium, is provided in the order given with a layer of physical development nuclei and a silver halide emulsion layer. After information-wise exposure and development the imaged element is washed with water to remove the emulsion layers so that a support carrying a silver image is left which is used as a printing plate. Such type of lithographic printing plates are disclosed in e.g. EP-A-278,766 and EP-A-410,500.
When using such type of mono-sheet DTR offset printing plate it has been found that when the emulsion is swollen with developing liquid sticking of the emulsion layer to the transporting rollers often occurs. This may cause image failures. In particular a bad ink acceptance, scumming, and low printing endurance of the plate may be noted.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved alkaline processing solution for preparing a high quality lithographic printing plate according to the DTR-process using an imaging element having a hydrophilic base.
It is a further object of the present invention to provide a method for preparing a high quality lithographic printing plate according to the DTR-process using an imaging element having a hydrophilic base.
Further objects of the present invention will become clear from the description hereinafter.
According to the present invention there is provided an alkaline processing solution containing at least one silver halide solvent other than sulfite, characterized in that said alkaline processing solution further contains aluminium ions in an amount of at least 0.3 g/l.
According to the present invention there is also provided a method for making a lithographic printing plate according to the DTR-process comprising the steps of:
information-wise exposing an imaging element comprising in the order given (i) a hydrophilic base, (ii) an image receiving layer containing physical development nuclei and (iii) a silver halide emulsion layer,
developing said information-wise exposed imaging element using an aqueous alkaline processing solution in the presence of at least one developing agent and at least one silver halide solvent to obtain a silver image on said hydrophilic support and
removing said silver halide emulsion layer and any optional layer on top of said silver image to expose said silver image by means of washing with rinsing water,
characterized in that said alkaline processing solution contains aluminium ions in an amount of at least 0.3 g/l.
DETAILED DESCRIPTION OF THE INVENTION
Lithographic printing plates are obtained according to the DTR-process with a uniform good quality with respect to maximum density, gradient, good ink acceptance in the printing areas, no ink acceptance in the non-printing areas (no staining) and no sticking of the emulsion layer to the guiding rollers when an alkaline processing solution containing aluminium ions in an amount of at least 0.3 g/l is used. More preferably the alkaline processing solution contains aluminium ions in an amount of at least 0.6 g/l. The alkaline processing solution preferably does not contain more than 10 g/l of aluminium ions.
The use of an alkaline processing solution containing aluminium ions in a colour diffusion transfer photographic film unit has been disclosed e.g. in Research Disclosure No. 16,156 (September 1977) as a buffering agent and in U.S. Pat. No. 4,649,095 in the presence of minute amounts of sulfite for avoiding post-transfer. However, from these disclosures it could not be expected that the addition of aluminium ions to the alkaline processing solution would prevent sticking of the emulsion layer to the guiding rollers during the development.
The imaging element is preferably prepared by coating the different layers on a hydrophilic base. Alternatively the different layers may be laminated to said image receiving layer from a temporary base holding the layers in reverse order as disclosed in U.S. Ser. No. 07/783,244.
The hydrophilic base can be a hardened hydrophilic layer, containing a hydrophilic synthetic homopolymer or copolymer and being hardened with a hydrolyzed tetraalkyl orthosilicate crosslinking agent coated on a flexible hydrophobic support. More preferably the hydrophilic base is an aluminium support.
The aluminium support of the imaging element for use in accordance with the present invention can be made of pure aluminium or of an aluminium alloy, the aluminium content of which is at least 95%. The thickness of the support usually ranges from about 0.13 to about 0.50 mm.
The preparation of aluminium or aluminium alloy foils for lithographic offset printing comprises the following steps graining, anodizing, and optionally sealing of the foil.
Graining and anodization of the foil are necessary to obtain a lithographic printing plate that allows to produce high-quality prints in accordance with the present invention. Sealing is not necessary but may still improve the printing results. Preferably the aluminium foil has a roughness with a CLA value between 0.2 and 1.5 &mgr;m, an anodization layer with a thickness between 0.4 and 2.0 &mgr;M and is sealed with an aqueous bicarbonate solution.
The graining, anodizing, and sealing of the aluminium foil can be performed as described in e.g. in EP-A 567.178, U.S. Pat. No. 3,861,917 and in the documents referred to therein.
The image receiving layer for use in accordance with the present invention is preferably free of hydrophilic binder bu
Coppens Paul
Vervloet Ludo
AGFA-GEVAERT
Breiner & Breiner L.L.C.
Schilling Richard L.
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