DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to photoimageable elements that include a substrate on which is coated a photosensitive composition for imaging and a protective overcoating.
The protective overcoating is coated over the photosensitive composition and can be one or more layers of material.
The protective overcoating, i.
e.
, overcoat, protects the photosensitive composition from the detrimental effects of oxygen and water.
In the practice of the invention, the substrate can be made from materials such as plastics, e.
g.
polyester, polyolefin, nylon, and the like; ceramics, e.
g.
, glass, porcelain, and the like; or metals, e.
g.
, aluminum, stainless steel, and the like.
Preferably, the substrate is a sheet material made from a dimensionally and chemically stable base material.
Suitable such sheet materials include polyester films, such as poly(ethylene terephthalate) and poly(butylene terephthalate), preferably having a thickness of about 1-15 mils (0.
025-0.
38 mm), and more preferably about 1.
5-5 mils (0.
038-0.
13 mm), and metal foils and sheeting such as aluminum sheeting, preferably having a thickness of about 2-20 mils (0.
05-0.
5 mm), and more preferably about 4-15 mils (0.
1-0.
38 mm).
For proofing films and certain label applications, for example, it is particularly desirable if the substrate is a transparent, generally colorless, sheet material.
The substrate can be optionally treated to enhance adhesion of the photosensitive material to the substrate, if desired.
Useful priming processes for polymeric materials, such as polyester films, include flame treatment, corona treatment, and chemical priming with, for example, melamine-acrylate or methacryate resins or low molecular weight polyester resins such as those available under the tradename VITEL 2700 from Goodyear Tire and Rubber Co.
, Apple Grove, W.
Va.
Many polymeric substrates can be purchased pretreated, i.
e.
, wherein one or more of these surface treatment processes has been performed by the vendor
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Adhesives and Rubbers 
