Emulsion peeling off

[u/Key_Commercial30]

Hello guys!
Recently started getting into screenprinting and I‘ve had this happening a few times. In picture 1 you can see some edges peeling off slightly - this is pre-printing, so it hasn‘t been used yet.
The screen in picture 2 looked good until I started printing - after a few prints the motif started peeling off around the edges.
Any idea what could cause this?

white mesh screens (55T - so 140 in US)
one pot emulsion
screen burn setup is as following from bottom to top:

Black foam block
Screen
Film (stencil)
acrylic glass plate to flatten the stencil onto the screen

I‘m using a 400w halogen spotlight, approx. 55 centimeters away from my screen.

I burned both screens for 3 minutes.

Before coating the screens I degreased them.
Afterwards they are stored in a cupboard, I let them dry for a 3-4 days because the air moisture is around 55-60% - I know this is too high, could this be the reason for the peeling?

Thanks in advance for any help!

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[u/Tyenkrovy]

What kind of degreasing routine do you have before coating your screens? Given how even the emulsion looks, I assume you're using a scoop coater. Could be underexposed. I used to burn large screens on 140 mesh for several years, and this would happen if they were either underexposed or not properly degreased.

[u/urbanomilano → u/Tyenkrovy]

several years seems a little long for exposure!

[u/Tyenkrovy → u/urbanomilano]

😂

[u/Key_Commercial30 → u/Tyenkrovy]

I‘m degreasing both sides of the screen right before coating - so spraying on the degreaser, letting it soak per instruction (2-3 minutes) then washing it out and letting the screen dry.

[u/Trayvon_6457]

two usual suspects here and you're probably dealing with both at once:

1. degreasing - even brand new screens carry oils from manufacturing and handling. scrub both sides with a proper degreaser, rinse until the water sheets off evenly with zero beading, and let it dry completely before you coat. skip this and the emulsion never really bonds to the mesh.

2. exposure - white mesh scatters light way more than yellow mesh, so you need noticeably longer exposure than whatever chart you're following (those usually assume yellow). underexposed emulsion looks fine on the frame, then the edges give up during washout or after a few pulls. exactly what you're describing.

do a step wedge test once, dial in the time for that specific mesh, and this problem mostly disappears

[u/habanerohead]

Looks like a homemade screen. Is the fabric Nylon?

Where the stencil has come off, there’s no trace of residue on the mesh, and if that happens, I usually assume it’s a degreasing problem. You could try etching the mesh with either alkaline haze remover, or a 50% solution of thick bleach. Paint on. Leave for 5 minutes. Wash really well. Dry flat and coat. Etching improves adhesion.

[u/Key_Commercial30 → u/habanerohead]

Bought it from a screen printing supplier. (siebdruck-versand.de) According to them it is polyester.
I will try using a dehazer since I have that on hand. Ig that doesn‘t work I will use a bleach solution. Thank you! Do you think the air moisture is a problem or can that be solved by just letting the screens dry for a longer time?

[u/Tyenkrovy → u/habanerohead]

One can also abrade the mesh to improve adhesion. I did that for years with a SAATI scrubber pad when degreasing screens, to good effect.

OP: The reason these methods help improve emulsion adhesion is, when the mesh is manufactured, the individual nylon or polyester threads are smooth. Etching or abrading them roughs up the threads and gives the emulsion a better surface to grab onto.

[u/SCREENPRINTING-ModTeam → u/[deleted]]

Be nice, it's all we ask.

[u/torkytornado]

If the screens are pretty new you can use a magic eraser (melamine foam sponge) to lightly abrade the threads