Screen Printing Forum

Hello evryone, I am attempting to print shirts with gradients in them in which i must burn dots into my screen. It is a black and white design getting printed on a black shirt. I figured I would burn the dots in the screen so that all I have to do is print the white and the black will come from the shirt. Ive burnt 3 screens so far and everytime I rinse the image out, emulsion that is supposed to stay gets washed out. I thought I was over expopsing so I went from 3 minutes to 2 minutes to 1 minute and the same thing happens every time. IS THERE A TRICK TO SUCCESSFULLY BURNING HALFTONE DOTS INTO A SCREEN?

You are not overexposing you are underexposing. If the parts of the stencil (screen+emulsion) that are supposed to be hard emulsion are washing away, then those parts aren't getting enough light. Or if you have made a really bone-head move, then you didn't inverse your film to take into account that you're printing a negative image.

If you are doing halftones for the first time you really should use a vacuum bed, otherwise you'll get undercutting.
...and increase your exposure time!

The reason I thought I was overexposing is because when I rinse out the image, some of the dots that are supposed to stay get washed out, but the rest of the image looks fine. I thought I was exposing too long and as a result, light was making its way through the black of my film positive and exposing those dots not supposed to get light. Is this a possibility? Also, when I exposed it for 3 minutes, it took longer than normal to wash out the image. I also have fast drying, fast exposing emulsion that is being used.

If the dots were getting overexposed then they wouldn't wash out.

It's probably undercutting, if you don't have good contact with the emulsion then light gets under the black and exposes your dots!

One thing that I have found that helps undercutting when shooting dot is to place a piece of black substrate on the squeegee side of the screen and then expose as usual.

Yeah that sounds like a good idea with the black substrate. I was also thinking of compensating the dot loss by printing bigger dots on my film positive. That way when undercutting occurs, it will cut the dots down where they are supposed to be.

What are you using to expose your screens. I expose screens all day long and never have issues with undercutting (granted I have a vacuum exposer)

Im using a raynar exposure unit. I just set up shop and Im still trying to get my exposure times right. I decided to do test strips at different times to find out what time is the best for halftone dots. Its easy burning everything else, its just these halftone dots that I need to figure out.

What lpi are your dots?

I take it you are using direct emulsion how are you coating your screens? What emulsion are you using? Also there is always film myself I like Autotypes CX film if you are using a solvent based ink it's a tad on the expensive side but it works wonders.

Im printing at 40 lpi with a 45 degree angle. The emulsion im using is croma blue. Ive been coating the print side first then the squeegee side second and washing it out of the print side.

I take it that you are scoop coating your emulsion by hand. What mesh count are you using? How many passes of emulsion are you putting on your screen? I have had to coat my courser mesh screens using a 1-1 technique and then maybe face coat the print side to get the dots to expose properly. Also try washing both sides of the screen when you do your wash out wet down both sides of the screen let set for a couple of minutes then do your wash out. I hope some of this will help

SUCCESS!!! I finally got it. The dots came out perfectly, no flaws, no hotspots. Turned out I was under exposing it. More like grossly under exposing it. I did a test strip and found out that a 10 minute exposure time was the right time for me. I made a custom exposure unit using my Ranar exposure unit and a work bench. Blueprints aside, the light was about 3 feet away from the screen. It may sound crazy but it worked and thats all that matters. Thanks to everyone for all the advice. Greatly appreciated.

It's not crazy. That's what I told you was happening.
Congrats

Good Job Like I always say if you don't succeed at first try try again and thats screen printing.