What is a photopolymer plate ?
A photopolymer plate is a photo reactive film attached to a substrate to support it during processing and printing. Typically the substrate is a mylar or steel sheet.
Simply put the photo reactive material is exposed to Ultraviolet light through a piece of artwork on a clear acetate sheet, developed in warm water, hardened and then printed on an etching process precisely like a standard zinc or copper etched plate.
Since I have never had much success with photopolymer with a mylar backing I exclusively use Toyobo branded steel backed plates.
Toyobo plates are widely available and come in two types, but each is backed by thin steel plate 300 microns (0.30mm) thick.KM95 have an active coating that is 0.93mm making plus the steel makes 1.23mm thickness overallKM73 plates are 0.73mm of coating plus the 0.3mm steel makes 1.03mm overall plate thickness I prefer to use Toyobo KM95 plates as they allow for a deeper etch .
The photoactive film
The most important part of the plate is the photoactive film that covers the front surface of the plate will take the image for printing.
When the light proof packing is removed you will see that the active face of the plate that is khaki green in colour is protected by a thin transparent plastic sheet. This needs to be removed and discarded before processing.
When fresh, the photoactive surface of the plate is covered with a film of short-chain molecules. The molecules are likely single molecules, maybe some are double or triple linked molecules, but these are soft and soluble in water. If the plate was put into warm water without any exposure to ultraviolet light, the layer would dissolve and wash away leaving nothing to print or carry an image.
Where the parts the photoactive layer are exposed to ultraviolet light a polymerisation process slowly beginnings. Over time more and more of the small molecules link together to make longer and longer chains of polymer. The longest of these chains will become hard and insoluble in water. See the diagram below.
The photopolymer plates I have been using are manufactured by Toyobo MC in Japan.
In the UK Toyobo photopolymer plates are available from several sources including:
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Intaglio Printmaker (London) mail order available
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Jackson's Art Supplies London (2), Hove & Gloucester) mail order available
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Iron Bridge Fine Art (IronBridge, Telford, Shropshire) mail order available
