Re: [PPLetterpress] exposure times: plastic vs metal
There is an antihalation (pre-exposed) layer on the floor of sheet photopolymer. (This is why you can't washout out completely to the floor.) In the earlier years of photopolymer, back-exposure was required to create this effect.
So, type of backing (polyester film, steel, or other metal) is not in any way a significant factor in exposure. Much more important is the thickness of the photopolymer itself and, specifically (within this), its hardness rating. In plates configured for letterpress, however, hardness ratings are limited to a somewhat narrow range.
Variations in washout and drying times are also primarily dependent upon sheet thickness.
chuck sumner wrote:
>I'm wondering if anyone has words reguarding boxcar vs metal backed
>ie: three minutes for a metal plate is roughly X minutes with a boxcar...
>I would think the boxcars are lower, but I dont really want to waste a
>bunch finding out.