This article examines the flat-glass manufacturing process and explores several decorating methods that you can use to crack into this large market.
By Wim Zoomer
For instance, a screen with a print area of 6.5 x 16 ft is quite common and requires a frame with a sloped profile to control the tension of the polyester mesh. Dyed polyester mesh is only used for printing halftones and relatively fine details, as a dyed fabric minimizes light scatter during exposure.
Today, screenmaking for flat-glass decoration typically involves using an automatic coating machine to apply a direct emulsion to the mesh. The stencilmaking process is increasingly becoming filmless. For the large-sized screens, the image is transferred to the emulsion using a computer-to-screen (CTS) system, which is considerably beneficial when the printer wants to accepts one-off work. The CTS prints a positive image of a high-density black wax or ink directly onto the emulsion's surface, preventing these parts from being exposed to UV light. Newer systems directly expose the screen using lasers or digital micro-mirror devices.
Manually operated or automatic screen-printing presses can be used to decorate glass, depending on the number and/or the size of the panes to be printed. Glass panes of different sizes require continuous adjustment of the imaging area. Many printers use masking tape to prevent the screen from depositing paste on unwanted areas of the substrate.
Rotary screen printing
Flatbed screen printing is a popular method for decorating glass. However, rotary screen-printing equipment (Figure 2) is another powerful tool that, when the job involves flat glass, can be even more versatile than a flatbed screen press. Rotary presses use a cylindrical screen, allowing for a continuous print (Figure 3). The screen always rotates in the same direction, whereas the squeegee, which is inside the screen cylinder, remains stationary. The enamel ink is fed into the wedge between the inside of the screen and the squeegee. The squeegee fills the mesh with enamel ink, shears off the excess, and transfers the enamel to the substrate. For an all-over surface coating, no image is on the screen—the screen area used for coating is fully open. Rotary screen printing requires no floodbar, which results in a substantially higher print speed. Glass is fed into the rotary screen-printing machine as continuous sheet, thereby eliminating the necessity to print individual panels.
A very innovative machine, based on the principle of sheet-fed rotary screen printing, enables glass substrates of any size to be coated or printed without the need to clean the substrate's edges. This patented invention uses a special paste stripping roller connected to a rotary screen-printing system to prevent edge spoiling. In this system, the rotary screen has a second squeegee that removes excess paste within the screen and transfers it onto the stripping roller. A paste scraper, shaped like a trough, removes the paste from the stripping roller and collects the paste. The printing area on the rotary screen is entirely free of paste before starting the next print operation. This invention enables printing onto glass panes of different dimensions and shapes in any random order and ensures cleanly printed patterns each time.
Rotary screen printing enables manufacturers to apply water-based, or more volatile, pastes to glass. The screen cylinder is effectively closed, which minimizes unwanted evaporation and opens up options in demanding applications such as printing high volumes of solar cells, imaging ultra-thin coatings, printing pastes with electrically conductive and luminescent characteristics, and more.
Seeing the possibilities
Glass is a unique substrate worth investigating for the production of decorative elements, graphics, signage, and industrial components. It also can be an ideal vehicle for showing off your capabilities and most compelling work, whether you concentrate on screen printing or digital imaging. When you consider the numerous opportunities and applications that await, and the fact that you may already have a lot of the equipment needed for glass decoration, the potential for profit should become crystal clear.
Editor's note: The concepts expressed in this article are detailed in the 180-page book "Printing Flat Glass," by Wim Zoomer, and were presented during the international Glasstec show in October 2006. For more information, visit http://www.technical language.eu.
About the author
Wim Zoomer is the owner of Netherlands-based Technical Language, a consulting and communication business that focuses on screen printing and other printing processes. He has written nu-merous editorials for screen-printing journals and is frequently called on to translate technical documents, manuals, books, advertisements, and other materials between English, French, German, Spanish, and Dutch. He can be reached at firstname.lastname@example.org.
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