Anyone know what might be causing this issue: straight line distortion?
I've been having an issue on projects whenever I am printing a fine, straight line - let's say between .75pt and 1pt. I get this subtle wobbly distortion (see image), which is actually pretty noticeable when viewed at arms length. I looked at the film and it's perfect, so the distortion must be occurring during exposure or washout. Upon further inspection of the burnt screen, it appears that the distortion is visible in the stencil. So the question is, how did it become distorted during the exposure or washout. I have a vacuum exposure unit. I am using a 255 screen. Could it just be a characteristic of the mesh that I just haven't noticed before, that "just happens" with screenprinting. Anyone have this issue before? Anyone know what is causing it? Any ideas for fixing the problem.
Thoughts would be greatly welcomed!
Last edited by FairweatherPress; 10-08-2012 at 10:12 PM.
I had this effect happen to me once, it turned out (in my case) to have been the mesh angle of the screen i used. (the screen came from a shop that did a lot of 4 color process stuff) I got over it by rotating the film on the unexposed screen slightly and then printing izt on a funny angle on the table.... a pain until i got new screens and then all was hunky-dory. I think they are at 43 degrees now or something ... 90 maybe....
anyway, your problem might be TOTALLY different al all my typing here to no avail...
your stencil is being distorted by the fabric weave.
some solutions include rotating the lines of the film so they don't run parallel or just slightly off parallel to the threads. (like Steph is describing)
Also, if you have a 'regular' (read cheap) emulsion and you are coating real thin, you might not be forming the best edge on your stencil below the mesh - the last bit of stencil your ink knows before it meets the paper. High performance stencils form crispy straight walled stencils. Cheap ones, and thin coated, follow the threads and imprint the ink lay with a wave.
Does that make any sense?
For the straightest printed lines, people use cappillex or indirect emulsion - it sits below the mesh. You can imitate this (its called emulsion over mesh, or Rz) by coating your screen with direct. let dry horizontal, then coat again on the bottom to build up the thickness a bit.
then wash the fuck out of it, both sides, and make sure you have developed it completely.
.....and don't tell me you are using white mesh...
Thanks for the feedback everyone. I am going to first try rotating the film slightly and then go from there. I will post back with results. how much of an angle should I rotate the film do you think? Just a smidge? Lets say I measured the right side of the film to be 5" from the edge of the screen and then I measured the left side of the film to be 5-1/4" from the edge of the screen. Would that be enough?
How much movement in angle you'll need is difficult to say, not knowing the angles you've got on your screens now... just give it a good noticable shift, no minor pussyfooty details...
BUT... While you're at it.... TAKE ANDYS TIP and coat your screens properly. It's a thing that slipped my mind, and it's kind of an important one. I normally do a 2/2 emulsion coating (first emulsion-flood table side ('front') of screen, then 1 on the ink side or 'back', one front again and the last one i ALWAYS apply from the 'back' (always with good pressure... you'll scoop some emulsion back with your second pass-overs so it shouldn't be a trippy mess.) Then as Andy points out, dry em horizontally with the 'front' side facing down.
So I did some experimenting and this is what ended up happening:
Tactic 1: I rotated the film about 10 degrees on the screen and that actually made the issue worse.
Tactic 2: I tried Andy's advice of coating the bottom of an already coated and dried screen. This seemed to make things slightly better, EXCEPT: I think I should have exposed the screen even longer then the additional minute I added to the exposure. AND: When coating the screen a second time, I found it difficult to get the emulsion to coat smoothly onto the already dried emulsion. The burn didn't go that well, because of the mentioned issues, but I did get to see the stencil and it still had a bit of visible distortion in those straight lines. Ug.
Tactic 3: I used a lower mesh screen (175 mesh) and this fixed my problem. I imagine that either the screen is stretched differently then the ones I had been using, or the thicker emulsion (because of the coarser mesh) fixed the issue.
In the end, I am glad that I was able to fix the issue and complete the project by using the 175 mesh screen, but I am bummed that Any and Steph's suggestions didn't seem to help. So I don't feel like I've really solved the problem aside from using that lower mesh screen.
Additional thoughts would be awesome. Thanks guys!
Phew! well there you go. practice beats theory.
rotating the film in the right direction, to the right amount did just come down to luck in my case it seems. and the new screens worked fine for me so I never went there again.
your thoughts on the coarser mesh holding more emulsion is right, but like you say, it doesn't tell us what went wrong with the fine mesh screen as the problem you had shouldn't really be an issue
.... oh the mysterious ways of the screen...
...glad to have been of absolutely no help to you at all