Tuesday, 8 June 2010
Screen Printing Notes
I teach printing workshops at Megalo Print Studio in Canberra. The following are course notes for my students.
SCREEN PRINTING STEPS
1. Degrease your screen
Degreasing your screen helps the emulsion to stick properly to the mesh. If you dont do this you may get small spots or fingerprints which resist the emulsion.
Wet screen and clean with sugar soap or commercial degreaser applied with sponge and wash both sides.
* Use AJAX when using mesh for the first time.
Dry screen. Approximately 30 mins in the drying cupboard
2. Create stencil for photo emulsion
The cheapest and easiest way to do this is to create a photocopy of the image you want to print. Clear black and white images convert best to screenprint. If you use an image with greyscale remember that this will print less clearly.\
Oil the photocopy using vegetable oil which will make the paper transparent. Absorb any excess oil with newsprint.
3. Emulse your screen
Make sure you wear gloves for this - otherwise your fingers will be stained yellow!!
Dont forget emulsion is light sensitive - so do this step in a darkened room.
Choose an applicator that is slightly smaller than the inside measurement of the screen.
Fill applicator 2/3 full with emulsion. Using the sharp side apply one coat of emulsion to both sides of the mesh. Repeat process to remove excess emulsion.
Clean any drips on the frame & return excess emulsion in the applicator to the container. Wash applicator thoroughly with water.
Place screen in drying cupboard (on the higher shelves so that wet screens dont drip on your freshly emulsed screen). Drying time is approximately 30 mins.
4. Expose Image on Light Table
Make sure the glass on the exposure table is clean.
Place your image right side up (this is particularly important if your design has text. It should be up the same way as we read it).
Place the flat side of the screen on top of your stencil. Make sure the image is in the centre of the screen.
Drape the cords over the edges of the frame to allow for the vaccum to work properly.
Carefully lower the lid and secure using the clips.
Set the timer for the appropriate time. Exposure time will vary depending on the mesh and image used. For fabric screens (43T mesh) recommended time is 2.5 minutes.
After setting the timer, turn on the vaccum and wait for the rubber to cling firmly to the screen - then turn on the UV lights by flicking the righthand switch. The exposure table will turn itself off after the preset time has expired.
Flick both timer and light switches up to the ‘off’ position.
5. Wash out exposed screen
Lightly wet both sides of the screen using the low pressure hose. This will ‘set’ the image and prevent it from further reacting to light. Carefully wash your image out (it will appear slowly) increasing the pressure slowly. Remember that the emulsion on the flat side of the screen is stronger because it has had more contact with the light. A light spray of water should remove most emulsion and you can use the high pressure hose to remove stuborn bits - but be careful not to wash your image off!
Always wear earmuffs when washing out screens as this noise can cause permanent hearing damamge.
Dry screen in drying cupboard - approximately 30 mins - time for a cup of tea and a biscuit.
Finally - we’re up to the fun bit!!
Switch on the ventilation
Choose a squeegee that is slightly larger than the image and small enough to fit within the frame, making sure it has a smooth edge so that it doesnt leave ridges in the print paste when printing.
Tape the edges of the screen to prevent print paste bleeding through the edges of the emulsed areas. Packing or masking tape works best for this. Now is also a good time to fix any little spots which may have appeared whilst washing out the image - you can do this by spotting a little emulsion on these areas and allowing to dry. Re expose the image to bake the emulsion - which gives the image a longer print life.
Dollop a generous amount of print paste at the top of the screen, above the image, spreading it evenly along the top of the frame.
Hold the squeegee at a 45 degree angle to the fabric table firmly drag it across the screen, from top to bottom, pulling towards you.
Repeat this process 2-3 times depending on the image and the fabric you are printing on. Fine fabrics such as silk require less pressure and less pulls than a heavy cotton canvas - this is where you need to experiment to find out what works best for you.
Allow image to dry before printing on top of it, as the wet paste on the fabric can transfer to the back of the screen.
Wash screen out between colours and make sure you dont let the ink dry on the screen as this will ruin the mesh.
7. Removing the Emulsion
Always wear gloves, eye protection, earmuffs and make sure the ventilation switch is turned on.
Remove any tape that is on the screen.
Squirt stripper onto both sides of screen and work in thoroughly with a sponge. Allow to soak for a couple of minutes.
Turn on high pressure hose (following instructions on the wall) pointing the hose at the trough and then across and onto the screen. Make sure the gun is kept about 30cm away from the mesh as the pressure can distort and even tear holes in the mesh! Keep the gun moving constantly over the mesh pausing briefly over stubborn areas.
Always check to make sure all the emulsion has been removed by holding it up to the light. The mesh should be transparent to look through.
Return the cleaned screen back to the rack of screens for hire.