The first step in the process of screen printing is the creation of the film positive. A film positive is artwork (text and/or images) on a transparent or translucent material. For best results the artwork must be opaque enough to block light from exposing the emulsion during the screen exposure process.
There are many ways to create the film positive but the easiest way is to load transparency film into your laser or ink-jet printer (be sure to select the correct type for your printer type) and then print your design (in black) onto the transparency film.
For best results, the printed artwork should not allow any light to pass through. If you notice that you can still see light through the transparency, one trick is to use an opaque black pen to fill any remaining areas. The other trick is to double up the transparency film (i.e. print 2 or even three copies of the design and stack them together). Make sure you tape them together (with clear tape) to ensure that they don’t move around during the exposure process.
Also, for complicated designs where registration needs to be perfect, make sure to print registration marks on each color separation as well. Typically, 3 marks are placed outside of the artwork area. The marks consists of a circle with a cross in the middle. I usually just tape over these during the printing process to block ink from coming through.
Vellum can also be used to print your design. Vellum is not completely transparent but will allow enough light to pass through to expose the screen properly. A good rule of thumb is to increase exposure time by 20% when using vellum.
Another technique is to draw your artwork directly onto the transparency film using india ink. You can also draw onto a white piece of paper and go to Kinko’s or Staples and have them print onto transparency film for you.
Step 1 - Either scan or create your artwork on your computer. Make sure that you set all your artwork to print as black as possible! If you printing multiple colors for your print, each color needs to be printed separately in black.
Step 2 - Transparency film can be purchased at Staples or Office Depot. Make sure that it is the correct type for your printer. I use 3M Transparency film with great results.
Step 3 - Warm up your printer and be sure to print your transparencies during the same time frame. There may be some shrinkage on transparencies due to the heat so it’s best to print them at the same time for consistency. There is also specialty transparency that does not shrink but I have never needed to use it so far.
Step 4 - After printing has occurred, hold the transparency against a light to see if the artwork is completely opaque. This is very important. If light can pass through the art work, it can lead to poor results during the exposure process.
Step 5 - In this example I have doubled up the transparencies in order to get the artwork completely opaque. The above example shows blue painter’s tape for illustration purposes but the ideal tape to use is doublesided sticky tape to align the transparencies.
Step 6 - Here’s the final artwork, ready to be burned onto a screen!
{ 2 comments… read them below or add one }
Can the film effect the printing ink deposit on printed surface?
For instance if the film not opaque enough, the ink deposit will be less ?
Is that true ?
If the film is not opaque that means your screen will not washout properly, therefore resulting in less ink passing through the mesh. For best results make sure the film is opaque or double up on the film.