Stock material or miscellaneous articles – All metal or with adjacent metals – Surface feature
Patent
1996-05-20
1999-12-07
Zimmerman, John J.
Stock material or miscellaneous articles
All metal or with adjacent metals
Surface feature
428650, 428332, 428457, 101453, 430302, B32B 1504, B32B 1520, B23P 900, B41N 104
Patent
active
059980443
DESCRIPTION:
BRIEF SUMMARY
This invention is directed to rolled aluminium sheet having a surface that is rough, and to a method of making the sheet. Although other uses are envisaged, the main application of this rough-surface aluminium sheet is expected to be as lithographic plate supports.
Most lithographic printing is from aluminium plates. These are typically 0.15 to 0.51 mm thick, depending on the size and type of press, although thinner sheets laminated to supports are also used. Aluminium sheet for lithographic plates is generally produced by rolling. This results in a metallurgical structure which is elongated in the rolling direction. The surface of the rolled sheet has marks (roll lines) extending longitudinally, which are not desired in the final grained product, and careful preparation of the rolls is necessary to minimise this effect.
To make an aluminium sheet suitable for use as a lithographic plate support, the surface needs to be roughened or grained. Standard techniques for this include: mechanical graining by the use of balls or abrasives or wire brushing; electrochemical graining, by the application of an AC current in an acidic electrolyte; and chemical graining, by simple immersion in an etch. Roughening is carried out in order to enhance the adhesion of an organic coating on the support, and to improve the water retention properties of the uncoated support surface. Application to the support of a photosensitive layer, followed by irradiation and development, generally result in a lithographic plate having ink-receptive image areas which carry an organic coating, and water-retaining non-image areas, the latter generally being the uncovered support surface. For this purpose the aluminium sheet needs to be roughened on a scale of approximately 1 to 15 .mu.m.
The cost of the graining or roughening step is an important part of the economics of lithographic plate support manufacture. One advantage of the method of the present invention is that it makes possible a reduction in the time and energy used for graining.
In a different field, aluminium foil e.g. for domestic purposes is generally made by pack rolling. By this technique, a pack of two or more ribbons of aluminium is passed between the rolls, and the rolled sheets thereafter separated. The aluminium ribbons need to carry sufficient lubricant to prevent welding of adjacent sheets in the nip of the rolls, but this is often present without the need for deliberate additions. When two ribbons are pack rolled, each of the resulting sheets has a bright surface, which was in contact with the roll; and a matt surface which was in contact with the other sheet. When a pack of more than two aluminium ribbons is pack rolled, all sheets except the two outermost ones have two matt surfaces.
Pack rolling has, as noted, been widely used for many years in the production of aluminium foil for the retail market. We are aware of two published proposals to use pack rolled aluminium sheet as a lithographic plate support. The first is in British patent specification 2,001,559 published in February 1979. The second is in Japanese patent application 57203593 published in December 1982. But in our hands, pack rolled aluminium sheet is not satisfactory as a lithographic plate support, because the organic material which is applied to form a lipophilic image area does not bond well and rapidly flakes off. To the best of applicants' knowledge, pack rolled aluminium sheet has never achieved commercial success as lithographic plate support; and certainly not for long print runs.
EP-A-115 678 describes a technique for preparing Al sheet for use as a lithographic plate support by repeated pack rolling.
This invention is based on an initial discovery that subjecting the matt surface of pack rolled aluminium sheet to a roughening or graining process dramatically improves the properties of the sheet as lithographic plate support. Only a minor roughening or graining treatment is necessary to achieve this effect. The inventors have analysed the topography of their roughened surfaces, and have defi
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Amor Martin Philip
Ball Jonathan
Limbach Peter Karl Ferdinand
Alcan International Limited
LaVilla Michael
Zimmerman John J.
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