TSB
screen printing => General Screen Printing => Topic started by: Prosperi-Tees on January 01, 2014, 09:27:08 PM
-
Don't know if you can see it in the pics but in long runs my screens are developing lines, not pinholes but horizontal lines popping up across the whole screen. Only thing I can think of would be maybe some contamination on the squeegee blade? But I cant find anything. Any other ideas?
-
Looks to me like the emulsion on the squeegee side of the screen is breaking down. If you look through a loupe at the screen you will probably see exposed mesh thread where those lines are developing. Thus making a small amount of ink deposit to run through the screen mesh. Possible other reasons but to me looks like that is the case. The screen could be underexposed causing the emulsion on the squeegee side not to be fully hardened or there's simply not enough emulsion bridging from the top to bottom side of screen. Lots of pressure/hard durometer squeegees will break the emulsion down pretty quick but I'd look at your coating, exposure times, pressure and squeegee blade to fix this. Like I said possible other reasons/fixes but that's what I'm seeing.
Danny
-
Thanks Danny,
I coated this screen (160) with the glisten method.
I am using a diazo emulsion.
Exposed for 10 minutes, 240 watt blacklight.
Probably printing with too much pressure.
Blade is a 75 duro almost brand new.
I can try to lighten up on pressure but then I don't get the screen cleared unless I stroke it twice. This is a fairly new static screen and probably has the highest tension of all my screens although I don't know what that is. I need to do something with the screen inventory for sure.
-
Static electricity whipping if erratic or screen breakdown if in same spots.
Is it different every time?
-
Interesting on the static electricity, I am getting shocked everytime I load a shirt and smooth it out. and the pattern is different every time.
-
Yeah if you can't see breakdown under magnification,
ink stringing from static is probably it. Sounds like you are shearing
well, maybe too fast of a stroke or too much off contact may let screen "snap" off and with it ink.
Some water in a spray bottle on the end stack of tees or there are more ways
of dealing with static.
-
Oops I see what you mean now, I am getting different lines from screen to screen but not from print to print. Maybe I need a fast exposing emulsion for my weak light source.
-
I really think its emulsion breaking down on the actual mesh thread. Clean the screen with press wash on both sides and examine the emulsion. Through a loupe its probably missing and might be able to see it without a loupe. I would lay the squeegee blade over more and go with a lower durometer 65 or less and look at coating/exposure as well.
-
If the marks are in the screen/emulsion, then you might want to look at pre-coat screen contamination too. Are you wiping the screens with anything or using a squeegee prior to coating?
-
Its definitely breaking down, I can see the lines thru the screen. Im not doing anything prior to coating, should I?
-
I'd say just make sure prior to coating the screen has been rinsed very well and completely dry prior to coating. When I've seen this problem in my shop it was a result of underexposure on the squeegee side of the screen. While rinsing the screen after exposure a lot of the underexposed emulsion was rinsed off which in turn exposes threads on the squeegee side. Like I've said, might not be the fix or the problem but this has been my experience with similar problems. If your using glisten method, screens are clean and dry my bet is on under exposure.
Danny
-
I think I will try a faster exposing emulsion, and maybe set out in the sun to dry after washout.
-
I think I will try a faster exposing emulsion, and maybe set out in the sun to dry after washout.
If you don't need the diazo, (for water resistance, etc) definitely go for a fast photo-polymer. You really need a lamp that exposes in the correct UV range, and it should be bigger than 240W.
-
If the issue follows the screen, (same screen same place every time you use the screen then I would inspect the clean screen for scratched filaments in the mesh. We have seen this on a couple of our screens where the mesh has been scratched or abraded by our scrub pad or something and a thin coating of emulsion will bust out after time in use.
Under magnification we actually see fiber fingers breaking away from the weave that looks a lot like fibers on a shirts although not as dense or concentrated.
The static electricity is interesting and may also be playing a factor as static charges will collect and exit a charged item from a concentration point such as a stray fiber finger in the mesh. If static electricity is involver the ink mark I think would not be consistent every time but actually grow larger over time.
Let us know what you discover please.
mooseman
-
Oops I see what you mean now, I am getting different lines from screen to screen but not from print to print. Maybe I need a fast exposing emulsion for my weak light source.
look at the glass on your light unit. there may be something on it...
underexposure/emulsion breakdown would be my guess as well.
-
All of the above, and definitely look at getting a better light source...
Steve
-
i think its in the design, meaning the multiple, wider horizontal lines in your stencil are causing the squeegee to 'stutter or hiccup' after the squeegie makes a pass on the open areas..
Open areas are in parallel with the squeegee, causing the blade to 'jump', leading to the pre mature screen break down immediately after the open areas.
At least thats my 2 cents. We have seen it happen here. Back off pressure, softer squeegee or more angle is a fix.
John
-
i think its in the design, meaning the multiple, wider horizontal lines in your stencil are causing the squeegee to 'stutter or hiccup' after the squeegie makes a pass on the open areas..
Open areas are in parallel with the squeegee, causing the blade to 'jump', leading to the pre mature screen break down immediately after the open areas.
At least thats my 2 cents. We have seen it happen here. Back off pressure, softer squeegee or more angle is a fix.
John
I think this is exactly it. I can hear the squeegee stutter when going over those lines, although it is not only in those horizontal lines but in other areas of the design with larger open areas.
-
John pretty much nailed it but you still have an issue with the emulsion as well. What mesh count is that for the black? The lower the count the more its going to skip.
-
John pretty much nailed it but you still have an issue with the emulsion as well. What mesh count is that for the black? The lower the count the more its going to skip.
I went with a 160 on this one. My 180's are way too loose. And I was worried my 230's that I would have to double stroke which I really didn't want to do with 1500 pieces.