In the past a problem with liguid photopolymer was that chemicals were involved to process the plates and they required back-exposure, which is a bit of a hassle. Sheet photopolymer is already back-exposed.
Things may have changed, don't know. A BASF rep was in the shop a few years back when they first developed a water-washout back-exposed sheet photopolymer for flexography. Basically all that was required was a higher temperature adjustment for the bath and the use of soft water.
The market for flexography is huge but without adequate resources it is very difficult to compete in it as the established processors have kept the cost really really low, basically by providing film-making capabilities in house.
I thought about it for a second or two, but photopolymer plate processing isn't all that engaging an activity. I'd rather be printing.
Most of the established processors also provide plates for letterpress, and by using lessor quality stock and running the stuff out on a 9-5 basis, can keep the cost very low as well. If quality concerns aren't a significant factor its almost better to seek out a processor whose rates are bargain basement. There is a place in Southern California that sells processed plates at near what it costs me to buy the raw material.
> There has been some discussion about metal-backed and plastic-backed
> Has any one tried plastic-backed plates made from liquid
> 15-20 years ago liquid photopolymers from W.R. Grace (later
> now MacDermid) were widely used for letterpress printing of
> books (Cameron Book Press). Though most of liquid photopolymer is
> to make flexible plates for corrugated and rubber stamps, grades
> A hardness of 65 and 90 are still available. Small plates can be
made in a
> home-made exposure unit and developed with water.