Screen Printing Forum

Yo.
I've recently started using screens with a lower mesh count than I'm used to (now 90T) and am having problems developing; when I wash out my screens, the image is degrading massively, the emulsion just won't stay on the screen. This extends to clean ink off the screen- the emulsion comes off even when I wipe it gently with a sponge...

is the solution a longer/shorter exposure time? or is it more complicated than that?

Help!
Cheers

Lower mesh counts, if you're using
direct emulsion, will have a thicker
coat of emulsion.

This will require more time to expose.

ace.
I was exposing for 190 seconds under a 5kw UV lamp, so if i up it to around 240?

thanks for your help!

on coarse mesh screens, first do a double coat each side, see if that gives you a better coverage. If it is still too thin after washout and increasing your time, or with lots of pinholes, either get a better emulsion, or do a second coating on the bottom of the screen once the first coating patteren is dry. this will build the thickness and give you a stronger stencil - it will also inrease the exposure time.

Instead of just randomly upping time, get an exposure calc from Autotype(expensive) Chromaline (cheaper) or do a step wedge exposure test with a piece of black paper or ruby (cheapest)

white meshes are going to expose in 1/2 -2/3 the time of yellow.

but it sure sounds like you are underexposed.

A perfect exposure will leave you with a hard solid stencil after washout - run your hand across - does it give off slime?, then keep washing - a properly exposed screen is not affected by too much washout. If it is slimey, then up your exposure time. You want to find the balance point between a hard stencil, and keeping your detail.

A good high solids stencil material helps a lot.