Friday, 1 October 2010

Design For Print : Screen Printing

The use of stencils to apply an image goes back many centuries, but it was only at the beginning of the 20th century that this was allied to the use of a screen, giving the process its name. A stencil, cut out by hand or made digitally or photographically, is supported on a screen of synthetic fibre (such as nylon or polyester), or metal. Originally, this screen was made of silk - hence the earlier name 'silkscreen printing'. The screen is stretched tightly over a frame of wood or metal, and ink is spread across the screen my means of a rubber squeegee that squeezes ink through the screen in the image areas. The stencil prevents ink going through in non-image areas.
Many screen printing presses are manually operated and consist of a simple frame hinged to a flat surface. The equipment can be very cheap and, as such, it is often used by people printing at home. There are also semi-automatic presses in which, while the screen is raised and lowered and the squeegee is pulled across the screen automatically, the material to be printed has to be inserted and removed by hand. Fully automatic presses also feed and deliver the paper or material automatically and some have an impression cylinder that holds the paper while the screen moves in unison and squeegee remains stationary. These presses can attain speeds of up to 6,000 copies per hour.
The fact that the process can apply a very thick film of ink onto a large sheet makes it ideal for posters. Also, virtually any type of material can be printed on including; wood, fabric, glass, plastic and metal. Screen printing is therefore used for plastic and metal signs, t-shirts, CDs and DVDs, bottles and transfers.

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