Screen printing has proven itself as an effective method of decorating three-dimensional items and unusually shaped products at high production speeds. This article introduces the printing systems used for such jobs and the innovations they feature to accommodate challenging products.
By Harald Gavin
Once the machine designers mastered synchronizing the movements for printing onto round items, they looked at the drive problems and synchronization issues of printing onto containers with oval and square shapes (Figure 1). Two servo axes—one for the fixture rotation and one for the screen movement—were found insufficient for printing onto oval containers. Printing a wrap-around image onto an oval or square container requires additional servo axes: one for the squeegee and one for each printhead (where the printhead is the combination of squeegee and screen). The simultaneous movements of container, screen, squeegee, and printhead during printing onto an oval container are illustrated in the sidebar on page 36.
Synchronizing the movements of four servo axes during printing—three servo axes in a printing station and the servo axis of the fixture—enables print-ing onto items with a wide variety of shapes. The press keeps the squeegee’s edge accurately in contact with the printing area, thereby making it possible to follow a complex contour of the cross-section of a printing area. The contour can have linear, round, and oval elements. For example, it becomes possible to print a wrap-around onto a square bottle that has round corners (assuming the corner radii are great enough).
Independence of the printing movements
Independence of the printing movements in the printing stations enables screen printers to set different printing movements for each station. For example, in one printing station an image can be printed onto the flat front of a D-shaped container, while in the next printing station, an image can be printed onto the container’s round back. Independent printing movements also make it possible to control a squeegee’s movement along the axis of a slim, square container rather than perpendicular to the axis (Figure 2). This requires a different mechanical design in the printing station: The squeegee head has to rotate by 90° and must have a guide for moving the squeegee along the axis of the container.
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