The Screen Printing Process
The screen printing process originated with the Chinese hundreds of years ago. In its simplest terms it involves applying a stencil to a mesh screen and forcing ink through the screen onto a piece of paper, fabric or in our case - a t-shirt. Although the technology involved to accomplish this has changed significantly over the years the basic process remains the same.
Everything begins with artwork…
Today all artwork becomes digital. The t-shirt art is either created on the computer, scanned into the computer or photographed and loaded into the computer. The image can then be edited in a graphics program such as Illustrator, Corel or Photoshop to prepare it for colour separation. Screen printing involves printing layers of individual colours to create the final composite image. So by using a graphics program the image is separated into its constituent colours. A separate “film positive” or transparency is then output for each colour. The art is now ready for transferring to a screen…
Screens
The screens involved in silk screening are just as the name suggests - a fine mesh screen stretched tight on a frame. The screen mesh is completely coated with a thin layer of light sensitive photo-emulsion. The screen is then allowed to dry in a dark cabinet. After it is completely dry, a film positive can be laid over the mesh and it is exposed to light.
The light “fixes” or hardens the emulsion that it strikes. Where the light is blocked by the image area of the film positive the emulsion remains “unfixed”. Subsequently the screen is washed with water. The fixed area of emulsion remain and the unfixed areas of emulsion wash away. This leaves open areas on the screen in the shape of the image. This step is repeated for each colour of ink to be printed.
The screens are then taken to the press - Living Planet has an eight colour manual press - and set up for printing. This involves aligning or “registering” all of the screens so that each colour printed fits together like a puzzle with the other colours and creates the complete image exactly as it was originally created. The screens are clamped into place so that each print will be created exactly the same.
Inks
Inks have been specially designed for printing on fabrics for maximum washability and colourfastness. An ink colour can be created to match any shade or pantone that is required. The inks are then applied to their respective screens and a squeegee is placed in each screen.
Printing
A shirt is placed on the shirtboard part of the press. It’s carefully aligned so that the print is applied in the proper area on the shirt. The first screen is lowered onto the shirt and the squeegee is used to push the ink across the screen. A small amount of ink is forced through the mesh opening onto the shirt.
This is then repeated for each colour to be applied. The screen printing press is constructed with guides for the screens to be lowered into them so that the print will fall in exactly the same place each time.
Curing
During the print process it may be necessary to dry certain layers of ink before subsequent layers are printed. This is known as “flash” curing or “spot” curing. It allows multi colored prints to be created without the colours bleeding together to prevent blurry or mis-coloured prints. This is especially necessary when printing on dark shirts where an extra underprint of white is usually required in order to create a final print with vibrant colours.
When all of the colours have been printed, the shirt is carefully removed from the press and run through another dryer for a final cure. All inks have to be cured to completely dry them and bond them permanently to the fabric. A conveyor dryer is used for this. The shirts are carefully laid on the belt of the dryer where they are carried through the heat tunnel to reach a temperature of 320 degrees F. ( 160 degrees C) Upon exiting the dryer the shirts are complete and ready to wear or be boxed for shipping.
Cleaning
The job is not over though until the clean-up is completed. All excess inks are returned to their containers. Squeegees and tools are wiped down, cleaned with soy-based cleaners and prepared for re-use. The screens are also wiped down and rinsed with soy cleaners to remove the last traces of ink. An eco-friendly chemical is applied to the screens to dissolve the emulsion and the screens are pressure washed to get them back to their original state - ready to start the process again.
