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
1999-09-29
2001-10-09
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...
C430S403000, C396S573000, C396S582000, C396S587000, C396S626000, C396S627000, C396S628000
Reexamination Certificate
active
06300034
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for processing imaged elements; in particular, it is concerned with the processing of presensitised plate precursors in order to produce lithographic printing plates. More specifically, the invention is associated with a method for the processing of a presensitised plate precursor comprising a substrate having coated thereon a light sensitive layer including a silver halide emulsion, whereby improved image quality and press performance may be achieved by the elimination of localised developer exhaustion which can occur during processing. The invention also provides an apparatus for the performance of said method.
Silver halides are used for imaging applications in a number of ways. Particularly suitable coatings include those based on the silver complex diffusion transfer- or DTR-process, the principles of which have been fully described in U.S Pat. No. 2,352,014 and in the publication “Photographic Silver Halide Diffusion Processes” by Andre Rott and Edith Weyde, The Focal Press, London and New York, 1972.
In the DTR process, the unexposed silver halide in an information-wise exposed silver halide emulsion layer is transformed, by treatment 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 by means of a developing agent, generally in the presence of physical development nuclei, to form a metallic 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 produced in this way may be used as a planographic printing plate wherein the DTR silver image areas form water-repellent, ink-receptive image areas on a water-receptive, ink-repellent background.
Two different types of DTR system are available. A two-sheet DTR system includes a first element comprising a photographic silver halide emulsion material and a separate image-receiving second element, generally containing a physical development nuclei layer; after forming an image in the image-receiving element, the two elements are placed in contact in the presence of one or more developing agents and one or more silver halide solvents in the presence of an alkaline processing liquid, and subsequently peeled apart, to provide a metallic silver layer in the second element. A single sheet DTR system comprises a single element including a silver halide emulsion layer which is integral, and in water permeable relationship, with an image-receiving layer, which again generally includes a physical development nuclei layer. Following exposure, the element is treated with one or more developing agents and one or more silver halide solvents in the presence of an alkaline processing liquid in order to provide a metallic silver layer in the image-receiving layer. The present invention is concerned with the latter type of DTR system.
Single sheet DTR systems are themselves provided in two alternative versions. U.S Pat. No. 4,722,535 and British Patent No. 1241661 describe a system wherein a support is provided on its surface with a silver halide emulsion layer, over which is provided an image-receiving layer including physical development nuclei; following information-wise exposure, and subsequent development, the imaged element may be used as a printing plate without removal of the spent emulsion layer. Alternatively, a DTR system may comprise a support provided on its surface with an image-receiving layer including physical development nuclei, over which is provided a silver halide emulsion layer; after information-wise exposure, and subsequent development, the imaged element is washed with water to remove the spent emulsion layer, to leave a support carrying a silver image which may then be utilised as a printing plate. Lithographic printing plates produced from the latter type of system are disclosed in European Patents Nos. 131462, 278766 and 410500.
The present invention is concerned with the means of processing imaged elements—in particular, printing plate precursors—based on the latter type of single sheet DTR system, in which the image-receiving layer, containing physical development nuclei, is in direct contact with the support. For printing applications, the support in such a system typically comprises aluminium which has preferably been grained and anodised on one surface in order to improve its lithographic characteristics. Whilst systems of this type are particularly suitable for printing applications, however, the method of processing of the systems is found to be critical to the subsequent performance of the printing plates obtained.
During the processing stages, the areas of an imaged element exposed to actinic radiation undergo a process known as chemical development. Said process involves the conversion of exposed silver halide grains into filamentary metallic silver by the action of a reducing agent dissolved in the developer solution. Typically, the reducing agent—otherwise referred to as a developing agent—comprises hydroquinone which is provided in aqueous alkaline solution. The reduction process may be represented schematically by the following equation:
2AgX+H
2
Q+2OH
−
=2Ag+Q+2X
−
+2H
2
O [1]
where H
2
Q is hydroquinone and X is chloride, bromide or iodide, or any combination thereof.
By contrast, in the unexposed areas the silver halide crystals are complexed by a silver halide solvent, which is typically a simple inorganic salt such as sodium thiosulphate. The resulting complex then diffuses to the nucleation surface which, in the case of a single sheet DTR system in which the image-receiving layer is in direct contact with the support, comprises a substrate surface onto which has been coated a nucleating layer; said nucleating layer typically comprises a colloidal metal or metal sulphide. Reduction then takes place by the action of a reducing agent which, again, is typically supplied in the form of an alkaline solution of hydroquinone. This process is generally referred to as physical development and results in the production of a form of silver which can successfully accept lithographic ink for subsequent printing applications. The physical development process can be schematically represented by the following equations:
AgX+2S
2
O
3
2−
=[Ag(S
2
O
3
)
2
]
3−
+X
−
[2]
2[Ag(S
2
O
3
)
2
]
3−
+H
2
Q+2OH
−
=2Ag+Q+4S
2
O
3
2−
+2H
2
O [3]
where the symbols have the meanings previously ascribed.
The conditions of processing, including pH, temperature and concentration of reducing agent, are chosen such that the chemical development process is essentially complete within 2 or 3 seconds of the moment at which the exposed parts of the plate come into contact with the developer, whilst the time taken for completion of the physical development process can be in the region of 30-45 seconds. Thus, during the course of the development process, it is possible for a small, isolated image area, or an unexposed area which is surrounded by a large exposed or background area, of the imaged element to experience a localised rapid depletion of reducing (developing) agent, and a fall in the alkalinity of the developing solution in the area surrounding the small, isolated image. Such local exhaustion of developer would occur within a time period of only 2-3 seconds and, therefore, before the physical development process had effectively commenced.
In addition to the rapid depletion of active ingredients in the developing solution, the situation would be exacerbated by the fact that a build-up of halide would occur in the exhausted developer, this having a potentially deleterious effect on the mode of formation of silver during the physical development process. Hence, the rapid local increase in the concentration
Blanchard Simon John
Gwilt Malcolm Bryan
AGFA-GEVAERT
Breiner & Breiner L.L.C.
Schilling Richard L.
LandOfFree
Processing method and apparatus for imaged elements does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Processing method and apparatus for imaged elements, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Processing method and apparatus for imaged elements will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2598264