Presensitized
Printing plate 8 By Mr. Bob Gumbinner
While
the slurry brush plates which used the zirconium fluoride interlayer
performed well in the print shops, under humid conditions the
chemically etched plates sometimes failed to hold the image. We
called this walk off. 3M offered us a license to use the silicate
interlayer for a 12% royalty. For a few months we made some of these
which we called Lithocoat to distinguish them from the zirconium
fluoride interlayer plates and send them to customers who had
complained of walk off. Ray Lauzon kept track of the production of
these. At that time, Simon Chu discovered that if, after the diazo
sensitizer had been coated on the zirconium interlayer plates, they
were overcoated with Uvinul MS-40, 2 hydroxy-4 methoxy benzophenone
5 sulfonic acid, the diazo was no longer water soluble and walk off
no longer occurred. To give further insurance against humid
conditions, a less water soluble Uvinul D-50, tetrahydroxy
benzophenione, was coated on top. We quickly added two more squeeze
roll costing stations to the diazo coaters to make the plates with
these protective coatings. I do not believe we paid 3M royalties for
the few plates we made between accepting the license and the
production of the MS-40 coated plates.