Plate making with Jet LSL94 FL - advice needed.

I make my own plates using a fairly basic set-up and have had good results with Toyobo KF95.

I recently started using Jet LSL94 FL plates for letterpress printing.

When I did initial tests with small 2”X1” plates the results were excellent. The detail was superior to Toyobo KF95. However, when I started making larger plates 4” x 6” the results were not as good.

The main problem has been, after the initial exposure, when washing plates out I am unable to wash out all of the unexposed parts of the plate. Those areas remain tacky and slippery. Usually I would use a roller-sponge to dry off the excess water (before drying), but if I do, the sticky areas stick to the sponge making a mess. The plate would then need rinsing, taking me back to square one. I worry about the plates deteriorating with repeated use.

The other problem is cleaning the plates after printing. Usually I’d use water miscible press wash (clean spirit) and a soft cloth. Because of the stickiness inherent in the plates, any loose fibres stick and gunk up. Do the plates remain water soluble after they have been cured?

I’ve followed the instructions on Jet’s website as closely as possible.

Does anyone use Jet LSL94 FL and get good results?

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Following the info on Jet’ s website as close
As possible, doesn’t cut it.
The plates are now so developed that exacting
Measures have to be met to make a perfect plate.
A degree off in the bath can create havoc.

And before it becomes a side stepped discussion,
I make film and plates on a commercial unit and
Have used polymer plates since mid 80’s

I have used Jet plates in the past, and do not remember encountering the problems you have mentioned. Are the plates fresh stock? I have had problems with any type of plate if the age of the plate is such that it doesn’t respond properly to washout.

If you can’t dry the plates after washout with the sponge roller, you might just rinse well with cold water (to set up the remaining polymer) and allow them to dry fully prior to the post exposure. Use a long post exposure will give the background areas of the plate enough exposure to fully cure, eliminating most moisture-based problems in cleaning ink from the plates after printing. I might be good to use a solvent rather than a water miscible cleaner for the plates after printing.

John H.

Thanks very much for the advice from Typenut and jhenry on this topic.

I have contacted the manufacturer, USA the UK supplier for more info and a data sheet, which I hope will give me what I need to iron out the problems.

The Jet USA website said that the plate had quite a “wide exposure latitude” and quoted an ideal washout temperature of <27 degrees centigrade, but suggested that washout time could be increased or decreased depending on a lower or higher temperature. So this made me think that the process was not an exact one.

Is there a way of knowing if the plates you buy are fresh stock? The packaging doesn’t have a date ( or processing instructions for that matter). It’s food for thought though.

Jet USA website info also says use half the post exposure time of first exposure. Would a long post exposure damage the plate? Make the plate more brittle maybe?

Also when cleaning the plate after printing I’d generally avoided using a solvent because the ink would be repelled when re-using plates.

Knowing manufacturer’s specs is critical in photopolymer. The plates I use specify double the main exposure for post-exposure, not half. But that might over-harden other brands of material making them brittle. I’ve seen hard-range plates left out in room-light shatter from additional incident exposure.
Not all solvents are the same in effect on photopolymer. Some are fine, others cause swelling or delamination. Residue is always a bad thing, and something like kerosene, though mild, will leave a lot of ink-repellant residue. Alcohol will draw moisture out of the plate. Plates take moisture out of the environment despite drying and post-exposure, affecting durometer.