Photopolymer Platemaking Quandry…
Hello all, I am a long time lurker of these boards- and the experience gained has been invaluable.
I’ve ventured into the world of platemaking, and have tinkered with both steel backed and poly backed Toyobo 152’s (using both with a milled base locked into the chase.
My question is this….I have a small exposure/washout unit that I was able to obtain second hand (it’s very unique so as far as I can tell. It is a small standalone unit that does both). My plates are just not receiving close to the necessary detail for the work that I am doing (I’m looking to hold about 10 pt. fonts or so). Any kind of script lettering tends to fuse together to look like something of a roughly formed polymer word shaped mess.
The unit that I am using has 6 of the UV cylinder bulbs (excuse my lack of terminology here), and following the Toyobo data sheet I’m exposing for around 3 - 4 minutes (of course the unit also has a vacuum unit wherein a piece of kreen seals the negative onto the plate in an airtight manner.
I think I’m either exposing for too short of a time or too long of a time, because before I even attempt the washout I can see the exposed photopolymer doesn’t have enough fine detail. I’ve tinkered with it but I’m hoping to get some advice from the experts here.
A secondary issue, and this may be related to the primary one, is that on some script fonts the ligatures of letters start to peel off during washout and they get either washed away or become loose from the photopolymer.
Any ideas? This is driving me nuts. I can post photos if what I’m describing isn’t clear.
Thanks!
ProfPres
before you go experimenting with exposure time, you should make sure that the negative you are using is dense enough. i was told that they should be as close to 5 as possible if not more.
i also purchased my exposure unit used and had to replace all of the bulbs before i could get a decent plate out of it. they were original to the machine and at least 15 years old.
Should have mentioned. The negatives I’m using are silver backed professionally processed by a film output service. The black is very dense.
It sounds like:
1. the exposure is insufficient to make the image you desire. It could be the bulbs as cleanwash mentions.
2. You might not be getting sufficiently good contact between the negative and the plate. Check that the negative’s emulsion is on the side which contacts the plate material and that the vacuum is sufficient to keep the negative in close contact as well. The negative should not be allowed to droop over the edges of the plate. It should either be cut to fit the plate size with no overlap or pieces of old plates or paperboard the same thickness as the plate be added to allow the film to stay on the same plane as the plate surface.
I can hold down to 4pt. type with my equipement and plate materials.
Even proferssional service providers sometimes give film of insufficent desnity for photopolymer use, which is far more critical than for offset platemaking, the normal demaand. Hold the film up to the fluorescent lights and look through the black areas. If you can see any transparency, it it not dense enough. The weak areas can be just patches that aren’t read at the edge by a desitometer. 3.5 is the minumum density, and my densitometer only goes up to 4.0.
When the material peels up from the bottom that can be from excessive washout time. But if it is breaking away from the top during washout, that may be insufficient exposure. You need to do test exposures with a 16-step platemakers grayscale to find the normal exposure for your specific material. Then adjust exxposures for specific image conditions (more for fine detail, less for coarse and reverse).
As jhenry says, complete contact between neg and plate is essential. With a krene-type exposure unit, I generally put golderod masking material around the edges of the neg so I don’t have to trim off that dead matter and can make plate at working size.
Thanks for the replies.
The negative looks good- no possible light filtering through the “black” of the negative.
Ok so here is the situation- taking the advice from here and from others. I reduced the washout water temp and that helps with the letters separating a little- it still happens a bit but I do think it’s eventually an exposure issue.
I ordered new bulbs today so I’ll give that a go tommorow.
It could simply be that the image that I am attempting to process into a plate is too fine. I’m attaching an image with the trouble areas circled in red. The plate size is about 3” x 5” if that helps.
Any other thoughts?
Many Many Many thanks to all that responded.
Film.jpg
The areas with fine whiteline detail (in finished print) need a shorter exposure than the areas of fine blackline detail when using a 152 thickness plate; I often mask such images to dodge and burn as needed. The thinnest plates have considerably more latitude. In all things start from manufacturer’s specifications for grayscale, exposure, washout temperature, post exposure, etc.
i use kf95 plates- i’m not sure if it is the case with all, but it is recommended that the line weight stays at .25 point or larger. with anything smaller, there is no guarantee.