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screen printing => General Screen Printing => Topic started by: DCSP John on October 29, 2013, 10:56:15 AM
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This issue creeps up sometimes.. mostly with blue inks...
Changing squeegee pressure, squeegee angle, speed, blade never seems to be the right fix.
There are uniform wavy lines that sometimes appear when the highlight blue is printed over an underbase...
For the life of me I cannot isolate what causes this uniform wavy pattern...
Screens nice and tight... maybe its a viscosity issue with our blue ink? Sounds like a newb issue.. but plagues
us form time to time. Any thoughts?
John
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If it done on every print, I'd say it's more your underbase. That's a new one to me.
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Looks to me like a heat (as in too much) problem. Could be something else. i do not have enough info. If you want to call me I'll figure it out. 678-412-1395
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I get the same problem usually with blues and forest greens , usually worst on double hit white bases. We use newmans and have resorted to sometimes flashing and printing a second hit.
I would like to figure out as well.
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Strange huh? The mystery continues..
It almost as if the underbase is too smooth...
We use as minimal amount of underbase flash as possible, so I have eliminated heat as a cause..
Yep.. If we let it run, the waves would be on every print..
A quick fix is to swap ink for a thicker ink. Usually eliminates the issue. But, I see this as a band aid, and
not a real solution to the problem.
John
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Just taking a wild guess here it could be in the weave of the shirt, and the ink is following that pattern. To test I would look at a shirt and see if you can see any waves and then print to see if if has that pattern or you could have a bad pallet?
Darryl
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I hear you. but when this occurs we test across a variety of shirts/weaves to see if the fabric is the culprit..
Same crazy lines across all fabrics. Has to be under base related, or top coat related...
John
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I had this a long time ago with panelframes, 200 mesh count on top of base (which I think was 110) using S mesh on roller frames eliminated the issue, some sort of mesh interference or dragging issue with the lower tension. Very open squeegee angle helped it too.
Are you using a pneumatic print head? that probably makes the issue worse as well.
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Blue pigments are notorious for this problem. Increased mesh open area is the usual band-aid for this one.
Has to do with shape of blue pigments when ground and there relative transparency.
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Thats correct Greg
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Yes, the blue pigments are long and skinny while the white is round, or spherical. The blue ink exacerbates any ink deposit inconsistencies that are probably there with other prints but not as noticeable. Blue on top of an underbase is always touchy.
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We print for Goodwill HQ a lot and one repeat job requires a large blue block on the back I had the same issue the first time we ran it and I pulled my hair out of my head. switched screens several times base and the blue to no avail. I was using high mesh for the blue since it was on top of white and everytime I tried a new screen I stuck with a high mesh. Finally i got fed up with it and went with a 160 and bam waves were gone.
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BTW........WB/DC will fix this. Pigments are ground finer.
But you know I was going to say that!
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So that's why I really prefer the WFX "super opaque" royals and blues. Really appreciate learning stuff like this. I would have looked at that off our air head press and figured the blade was chattering or printing inconsistently.
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Yeah, never knew why it happened, just know that thickener and/or lower mesh is the fix.
I hate how runny most royals are anyways, but I guess that goes with the color.
Awesome to finally learn the science behind it.
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Royals or Marine pigments are short bodied and weak. The opposite can be said of yellows. Weight a gal of each.
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I usually see the coolest patterns from an underbase and overprint mesh that are the same count but stretched just a bit different--the neat one to me was the guy on TSF with two 110's that did this. :o
Always seemed to me this was usually an interaction between the mesh marks in an underbase, and where the knuckles of your overprint screen fall--but I base this on absolutely nothing but the WTF prints I've seen.
If you need the detail of a high mesh screen, try tossing Union Maxo's in your blue screens and try to reproduce this problem... ;D
Of course, the transparent blues usually look the best... but only if anyone's paying that much attention.
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We have always been able to compensate for this issue by swapping out for a high opacity blue...
However, when its a custom PMS color, its not as easy as a quick color swap...
We will try and forward think the color builds, using thin threads for blues that require underbasing...
I learned something new today. Thanks, fellas...
John
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Foo, I'm with ya on the mesh weave/knuckle patterning. Sometimes using the same mesh for UB and top color is no bueno and I always suspected it was because of this. A 225/40 sometimes covers/looks much better over a white 150/48 base than another 150/48, for example.
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Ok, I learn something today too, so whats with union columbia blue being so tacky, just when you think you got screen printing down...comes another curve LOL
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I CAN get this problem on both manual and auto. Sometimes it's the weave but
I can usually eliminate it by changing squegee pressure/angle. Especially with
manual that is the culprit. On the auto it can be pressure, angle OR speed or a
combination of any or all of the above.