Printing – Planographic – Lithographic plate making – and processes of making or using...
Patent
1991-05-22
1992-12-08
Crowder, Clifford D.
Printing
Planographic
Lithographic plate making, and processes of making or using...
430302, B41N 303, B41C 110
Patent
active
051688131
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a baking treatment of a lithographic printing plate.
It is well known that the inclusion of a baking stage in a lithographic printing plate treatment process increases the "run length" of the plate on a press very considerably. It is therefore usual for lithographic plate processing equipment suppliers to include a plate baking oven in their range of equipment, and which bakes the plate to produce a durable ink-receptive image area on the processed lithographic plate.
In the treatment of a lithographic printing plate, it is first exposed and then developed by hand or by the use of a processor to reveal the underlying substrate in the non-image area, prior to coating of the plate with a pre-baking solution. The plate then passes through the baking oven where it is subjected to a sufficient level of heat to convert the image area into a more durable form.
A number of baking solutions are commercially available, including Ultratherm and Thermotect, (available from Horsell Graphic Industries and Howson-Algraphy respectively) and these give generally satisfactory results, and which are of generally similar character in that they both form a water soluble layer on the processed plate.
The purpose of the baking solution is to provide temporary shielding of the non-image areas from contact with contaminants, during the baking stage, while enabling the image areas to be baked and thereby improve their durability in use on the press. Therefore, the baking solution, which forms a water soluble layer prior to baking, is believed to form a physical barrier to any contaminating material present e.g. in the oven or emanating from the image areas, but it must also be such that it does not adversely effect the image by dissolving it, or rendering image areas non ink receptive, or non-image areas ink receptive. Also, the water soluble layer is readily removable after the baking process, without the image and non-image areas being adversely affected. The use of water soluble pre-baking solutions forms the subject of, and is disclosed in more detail in UK patent 1513368.
When water soluble pre-baking solutions are employed, including particularly Ultratherm, there are serious problems if there is likely to be a long delay between issuing from the baking oven and use of the treated plate on the press. When only a short delay is anticipated, the baked plates can be taken to the press without any further treatment being required. However, if a long delay is likely, then it is usually necessary to apply three further steps in the processing of the plates after the baking step, including a rinsing step, application of a post-baking (storage gum) and a final drying step. After the rinsing step. Ultrafin or Unifin (the trade marks of Horsell Graphic Industries and Howson Algraphy respectively) is usually employed in the post-baking stage, but this may give rise to certain problems as set out later.
If these further steps are not included, and there is a lengthy delay between issue from the baking oven and use on the press, then the following technical problems can arise: together, image areas without some form of image cleaning.
However, even with the further steps included, while this does solve the problems of (a) clear background, (b) blinding, and (c) storage life, the use of these specifically available storage gums render the plates "tacky" so that they are awkward to handle and liable to pick up dirt, and can be difficult to transport through automatic conveyors contained within plate bending equipment.
The invention therefore seeks to enable an improved treatment of pre-sensitised printing plates in which a baking stage is required, by using a pre-baking solution which does not require a post-baking water rinsing stage.
The invention is therefore based on the use of a different material to form the pre-baking solution, and which does not result in the formation of a water soluble layer which, at least with preferred examples, can be subsequently removed after the baking stage, and which can result i
REFERENCES:
patent: 3909267 (1975-09-01), Iwano et al.
patent: 4063507 (1977-12-01), Toyama et al.
patent: 4191570 (1980-03-01), Herting et al.
patent: 4355096 (1982-10-01), Walls
patent: 4572889 (1986-02-01), Imai et al.
Abstract of Japan vol. 10, No. 88 (JP-A-60.225798)
Abstract of Japan vol. 10, No. 100 (JP-A-60.236796)
International Search Report (PCT/GB89/02267).
Riley David
Turner Gregory
Crowder Clifford D.
Horsell PLC
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