Difference between revisions of "Screen printing"

Revision as of 06:09, 31 October 2008

Overview

Screen printing requires more chemistry than wood block, and to be honest I have a lot less experience with it because it requires more preparation and prohibitively expensive materials, light a Light Exposure Table. But it certainly has it's strengths. Color registration is pretty easy, you can easily reproduce an image almost infinitely. It also recreates a drawing on transparency almost perfectly.

Materials

• Drawing - You have options here. It needs to be some sort of ink or wax, something permanent
  • Acrylic pens - Fine or Medium tip. Whatever.
  • India Ink
  • Rapidograph - pricey, but totally worth it
  • Transparency
  • Transparent, double-sided tape
  • Mylar - it's a kind of high quality transparency, comes in bulk rolls you can cut down later
  • Acetate - pricier transparency. Comes in pads, have to be mail ordered. Really great stuff, doesn't smudge and doesn't crease.
    • Durolar is a versatile new kind of acetate that holds digital work, hand drawing, ink brush, anything that would work on anything else.

• Screen - It's like a sieve, or a fine filter.
  • There are different kinds, but I like a screen made of ultra-fine silk threads drawn tight around an aluminum frame.
  • $20 - $40 from iMcClain's or Dick Blick, depends on size.
  • ~20X20", more if you want multiple colors - a margin of two or three inches around the edge of the screen is considered unprintable, do to the amount of pressure exerted so close the edge on a screen

• Screen chemicals
  • Light sensitive photo-emulsion. Thick green goop, hardens with exposure to light.
    • Emulsion is a time sensitive chemical. From the moment it is blended, it is gradually exposing in its container. A number of factors can be used to accelerate or decelerate this process. This may merit its own wiki page, but in summary: Bright light, heat, and moisture cause it to dry and harden and accelerate its exposure rate.
  • Scoop, for applying emulsion to screen
  • Spoon/Ladel for handling emulsion

• Light Exposure Table - for burning your image into the screen. Should be several inches larger than your screen so that the screen sits flat on the top.
• Some kind of opaque sheet to lay over the screen as it exposes.
  • You will need to generate pressure to hold your image up against the screen during exposure. Plan to have several pounds worth of weight to sit flat on top of the screen.

• Printing
  • Sheet of clean, unmarred, plexi-glass, bigger than your screen (tabletop is fine, but harder to clean)
  • Water based ink, whatever color(s) you want your image in
  • Squeegee - varnished wood handle, flat rubber tip
    • Should be as close to the width of your screen as possible, so you only have to pull it across the screen once.
  • Print medium
    • Paper
    • Canvas
    • Shirt - Must not have buttons, pockets or zippers near or opposite the area you wish to print on. Any of these could pop the screen when pulling the print
      • Multiple colors are harder to achieve, so shirt designs basically need to be one color (probably black for now) for an operation this size.
      • Black shirts, everybody wants 'em, but white ink is never thick enough to print well with just one run. It's always harder to print on black, and white is the only color that stands out on black. Black material is hard to print on, white ink is very, very thin and hard to work with without extra registration and extreme care. So, I prefer not to bother.
  • Unicorn Tears (EOptional)- a special blend of bleach and water for black shirts with black imagery.

• Cleaning
  • Shop Towels OR
  • Rags from torn up old clothing
  • Simple Green - Engine cleaner
  • Baby Wipes - good enough for your ass, will certainly clean up oil based ink.
  • Hose, powerful shower head OR
    • Power Washer is a major expense, but might be worth it in the long run.

Drawing

• You have options here.
  • Nice ink pens
    • NOT sharpies, they're not thick enough.
    • Rapidographs are slightly more expensive, ($2 each) but they're awesome
    • Acrylic ink pens - cheaper but totally work.
    • Indigo ink, brushes - more painterly than I like to work with, but whatever floats your boat.
    • Photoshop, etc can also be used, to create (or modify) an image, which can then be printed via laser printer onto a tranparency.
• Draw your pretty picture on a sheet of transparancy, mylar or acetate. Can be any size, but it's better if it fits in one screen. Multiple screen images can be done for large scale work though. For a tshirt, your image probably ought to fit in a 8.5 x 11 sheet of transparancy
  • Do not allow your transparency to be bent, folded, spindled or mutilated. It will show up in the final product.
• Try to avoid smudging or excess oils on your transparency, like finger prints.

Coat the Screen

• Get all your stuff out and ready, this gets complicated and it is time sensitive.
• Take your emulsion, pour it into your scoop, moving the ladel across the round edge so it always drips into the scoop and not over the edge.
• Have your screen standing upright
  • In whichever orientation is closest to the length of your scoop.
• With the hard edge of the scoop, press the scoop up against the screen and tilt it so the emulsion starts to run into the screen.
• Push the scoop up the screen, applying a thin coat of emulsion to the screen all the way to the edge.
• Repeat in multiple columns until the front of the screen is entirely, evenly coated.
• Flip the screen over and repeat so now you're applying emulsion to the backside.
• Repeat for both sides until there are no streaks.
• Scoop up your excess with your scoop, and get it back in the bucket. The stuff is expensive, don't let it go to waste.

Exposure

• Immediately after coating the screen, get it in a dark cabinet to dry. It absolutely must not be left in the light, emulsion is light sensitive. It will harden (expose) with light and if that happens, the screen is ruined, you have to wash it out and start all over again.
• Let it sit to dry in a dark cabinet (or whatever container is) for about several hours,
  • Maybe just an hour or two if you can sit a rotary fan on it inside the cabinet.
• When the screen is bone dry, you can expose it.
• Take your image, and tape it to the screen. When looking at the screen through the back, it should be face up just like you want it to look on the final product.
• Take your screen with image attached to your light table,
  • Set the screen face down in the middle of the table.
  • Lay a sheet of rubber, or a towel, something that won't let light through over the screen. Weigh it down with what ever's handy, just try not to let light through. I like free weights and old paint cans.

• Exposure Time
  • Sadly, this part is trial and error and depends on your light table. Could take longer, could take less time. You just have to play and see. You can be off by 30 seconds and it'll make your image weird. Sucks but it's true.
  • Fresh Emulsion takes significantly longer to expose than older, stale emulsion. Fresh emulsion at my table (within one month of mixing) seems to take about 5:30 to harden. With older emulsion (after 90 days) about 2:00 will suffice
    • Try not to look directly at the bulb, it's bad for your eyes.
• Now the image is burned into your screen. Peel your transparency off, you might be able to see a faint outline of your image already.
  • Take the screen to a dumping sink, your backyard, wherever you're gonna dump the stuff.
  • With a powerful shower head, or power washer, rinse out the screen. Use as much pressure as it takes that after a few minutes the parts of the screen that were shielded from the light by your ink image will was out, revealing the transparent screen beneath the emulsion. You'll see a transparent version of your drawing in the green emulsion.
• Let the screen dry.
  • Now that it's wet, you can let it sit in the light, it's exposed as much as it's going to be.
  • It has to be bone dry before you can move on, so either let it sit overnight or put a fan on it.

Printing

• Set your medium on a flat surface, tabletop, sheet of plexi, whatever.
  • Preferably a vacuum base, but that comes later. Maybe someday...
• Set your screen face down on top of your medium.
• Take your ladle, take some ink and distribute it in a strip across one end of your screen.
• Flood the screen
• Get a partner to help you hold down the screen so it doesn't move. They should hold it from the opposite end of where you're standing.
  • Pick up the end of your screen closest to you, and with your squeegee gently push some ink across the screen, pushing the ink into the screen. There should be ink in every part of the screen that contains your image.
• Set your squeegee down at the top of the screen, at about a 60 degree angle. Pushing down kinda hard, pull the squeegee towards you, pushing ink through the screen onto your medium.
• Pick the screen up, and behold your image.
• Take your next medium (another sheet of paper, another shirt) and set it under the screen
• You don't have to flood the screen every time, but you can see if there's still enough ink in there.
  • If not, the image will be spotty or faint.
  • It can be tricky, but you can realign the paper with your screen, flood the screen and try to line it up perfectly to give it a second chance.
  • Good luck with that, it's not easy.

Clean up

• You can't let the ink dry in the screen, so with your ladle scoop and palletteout as much of it as you can
• Sponge up the rest for rapid drying, or wash out with a hose.
• Clean the table top or glass you were working on. A little bit of ink can come through, you don't want that to dry and set.