Shirty/HOWTO

Notes from screen print test session 23.06.09

• Material bought from Wöco:
  • Screen with frame
  • Emulsion
  • Sensitizer
  • Paint
  • "Squeegee"
  • Cleaning agent to clean away hardened emulsion
• Sensitize emulsion:
  • Fill up the small sensitizer bottle with water
  • Add to the box with emulsion
  • Stir well
• Coat screen with emulsion
  • Do this away from bright light or sunlight
  • Use the "squeegee" to coat the screen with emulsion
  • Do this from both sides repeatedly to get an even coverage and an even surface as a result
• Dry the coated screen (this will taka 30-60 minutes)
  • Place horizontally in a _dark_ room
  • To speed up, use a fan (occationally using a hairdryer might also help)
• Prepare the design
  • Design a positive 1-color bitmap image (i.e. what you see is where the ink goes)
  • Print on a transparent foil using as dense ink as possible
  • Our printout was not very dense due to a broken/out-of-ink printer
• Expose the screen
  • Place the screen with the flat side down on a horizontal surface
  • Place the printed transparent foil onto the screen
  • Mount a UV lamp lighting downwards with ca. 1 meter distance
  • We used the IR+UV lamp from the Chemielabor. Note! The UV lamp won't work lighting downwards, for some reason. Alternative setup: tape the transparent foil to the screen with _transparent_ tape. Cover the backside with something non-reflective.
  • Exposure time: 15-20 minutes. This depends on the thickness of the emulsion, too short and the opaque areas have not hardened, too long and thin lines in your design bleed together.
• Clean away the non-hardened emulsion
  • Use warm/hot water with as much pressure as you can get from a shower head
  • Since our print wasn't very dense, this had an effect on the exposure: Less well-covered areas had clear half-hardened emulsion. These areas, in addition to areas with small details were a lot harder to wash away. Using a dishwashing brush helped a lot.
  • If some emulsion doesn't come off, use a small _plastic_ tool (e.g. a reprapped palm stylus) to _carefully_ scrape away the remaining emulsion.
  • Now, let the screen dry. Shouldn't take long.
• Apply paint
  • Line up a bit of paint just outside the motive
  • Using the squeegee, carefully drag the paint over the motive so the whole motive is covered with paint
  • If it's not fully covered, drag it back again
  • Using a bit more pressure, drag the squeegee once over the entire motive
  • Carefully lift the screen from the motive
  • Every once in a while, clean away dried paint from the screen with water
• Drying
  • Using a hair dryer, lightly dry the fabric
  • At this point, to make the print permanent, an iron should be used on the fabric. We didn't have one available, so who knows what will happen now..

Neue Erkenntnisse aus einer Session im August '09

• Eine Belichtungszeit von fünf Minuten ist ausreichend
• Farben kann man mischen, aber Vorsicht, die dunkelere Farbe (zb. bei gelb und rot ist rot dominat) sollte nur ganz langsam und vorsichtig beigemischt werden
• Testdrucke auf t-shirts macht man am besten linksrum, auf der innenseite