HI. I am new to the forum and a newbie at screenprinting. I am having issues with the emulsion not holding up during washout. Here is what I am doing, I hope someone can help! I am using Holden's 206 , dual cure emulsion with a mix in sensitizer.It is purple. I degreased the screens, let them dry completely, and then we have coated them, have tried one coat per side, and also 2 coats per side. Dried them in the drying cabinet,some for 3 hours with the cabinet on, some have also sat for an additional 3-4 days without the cabinet running. Exposed them for 5 min using a 1000 watt burn unit. and then rinsed them out with cold water from a spray nozzle on the garden hose. We have also tried pouring warm water over both sides prior to hosing off. It seems like sometimes the emulsion holds up and doesn't wash out, other times, it starts to break down around the image edges and starts to peel away. We have tried a couple different methods and seem to not get the same results every time. My question is could the warm water break down the emulsion, could we be spraying out the image too long and breaking down the emulsion(sometimes we have to spray out the image for up to 15 min to get all the image clear). Being a newbie not sure what is going on, and just wanting to get this figured out. Also, the shop is only heated when we are in it. Usually gets down to low 40's in temp. It's cold and snowy outside right now, could the humidity be the problem? Any suggestions would be awesome!! Thank you so much!!
Last edited by TwinCityTees; January 29th, 2009 at 03:53 PM.
Reason: misspelled word
You may need a stronger light source, or longer exposure time. It sounds to me like you are under exposing. Have you tried the sun (if you can see it)? If you do, do some reading on it as you will only need to step outside for a couple seconds to expose. Another thing to try would be to wet the screen, rub the image area (the part you want to wash out) kind of vigorously with the butt of your hand to kind of agitate and loosen the emulsion. Then set the screen down and walk away from it for anywhere from 5-10 minutes, then go back to it and gently try to rinse the image area clear... If the emulsion is breaking down around the image area, the screen has either been wet too long, or it is under exposed. We have always used cold water, I am not sure what the affects warm water would have on the screen.
Dan,
Thanks. We are in Ohio where the temps are brrrrrrrr right now, we are washing the screens outside, where it is below freezing at times, could the cold temps be causing any issues. It is strange because some screens hold and others don't,sometimes it is screens out of the same batches. Unfortunately, no sunlight this time of year. The image shows up well in the emulsion once burnt. We weren't sure if we were keeping them too wet and spraying too long. Will try the hand on them and letting them set for a little while.
Hmmm.... We are in California where it is balmy and warm right now, around 69 degrees (sorry for that)... I really have no idea how the cold might affect it. When you say some hold and some don't and they're all out of the same batches, are they all the same mesh? Different meshes expose differently and need to be washed differently. Where is your exposure unit, is that outside too? Another question to ask yourself is what kind of film and ink on your film are you using? If the image on your film is not super opaque, the light could be exposing some of your image area causing washout problems. Not sure exactly how little sunlight you have right now, but you can still expose a screen even when it is overcast.
If the stencil washes out - it wasn't exposed with enough UV-A energy to harden, so it dissolves with water and rinses down the drain; just like it is supposed to.
All your other variables are a distraction. Temperature has no effect on the UV reaction required for hardening stencils.
Measuring UV Exposure
It is the primary job of the screen maker to learn how to judge exposure. Invisible UV energy reacts with emulsion sensitizer and hardens the stencil so it won't dissolve with water and rinse down the drain. You block UV energy with a positive during exposure so the image area dissolves when you develop the stencil with water.
Screen makers can only expose one side of the stencil, so it is important for the UV energy to move through the stencil, all the way to the back, where the squeegee blade will rub the stencil where it is weakest.
When the stencil doesn't hold in the mesh, it didn't get enough exposure. Start by checking the suggested exposure time on the product Technical Data Sheet. These estimated time charts are based on known commercial screen printing UV light sources (which you mynot have) on 305 mesh. You can measure your lamp with two exposures using a US$10 Stouffer 21 Step Scale to measure the stencil hardness, then refine your exposure with an exposure calculator.
Emulsion not holding up 
