PP Crop marks curling
Hello,
I have been processing my own photopolymer plates without a problem until recently. I was hoping for some tips and guidance to help troubleshoot.
During the drying process, our crop marks are curling upwards. It is as though they no longer want to be part of the bottom of the polymer.
Here is a photo of the problem:
http://www.ewebs.com/cropprob.jpg
The circumstances:
- Crop marks are 0.5pt.
- We have had no problems with 0.5pt crop marks in the past
- While artwork is finely detailed, the rest of the plate will expose and dry fine.
- Usually we: Expose for 2 mins. Wash-out for 3-4mins. Dry for 8-10mins. Re-expose for 4 mins.
- We have tried first exposing for 3 mins, but it makes little difference
- I have tried exposing using a different polymer sheet, but it makes no difference
- We notice the crops start curling up after 4 mins drying
- Polymer is “Mavelon DF3-94B”
- It has been raining recently, and room temperate dropped to approx 20 degrees celcius
Any tips to help troubleshoot would be appreciated.
Thankyou
cropprob.jpg
Although I have never seen something like this happen to my plates, I owuld go back to the basics, are the negatives OK, do you have sufficient vacuum? The exposure is bound to be the problem, are all the lights working? Try a piece of plate material at 5 minutes exposure just to totally rule out exposure.
Is the material old? The plate material requires greater exposure as it ages.
Sounds like a drying problem. Are your letting them air dry? Are they drying in a machine or in front of a fan?
What do you use to get the water off once you wash out the plate?
Another possibility to check is that the shoulder of the image is sloped properly rather than straight or even undercut. If you are exposing with a diffuse light source you could be getting undercut, and while it would not be critical for larger areas it would cause a thin line like that to have too little support. Are you using a point light source like an arc light in a platemaker?
Bob
Bob:
It is the diffuse light source which is required to for a good shoulders in platemaking. That is why the commercial production units use flourescent tubes very close to the film/plate sandwich. The diffuse light spreads out and forms the properly angled shoulders during exposure. A point source light will produce a line without sufficient support.
It does appear to me that too little exposure is most likely the culprit in this case.
JHenry
Although I have only worked with steel-backed plates, I thought some plastic backed plates used a back exposure to strengthen the base of the image.
With steel-backed plates I sometimes mask and give very fine lines a supplementary exposure.
Two things. Make sure your water is clean, and that the plates do not sit in the water longer than they should.
My .25 crops will peel, or fall off if they are in water too long.
As long as the water is clean, and I take them out at the correct time, they are fine.