Read on to find out more about the latest technologies available for this screen-printing specialty.
By Harald Gavin
Servo-based screen-printing machines provide new options for screen printing intricate images onto bottles and containers with sophisticated shapes in one machine pass. During printing, the movements of screens, squeegees, and fixtures in the printing stations depend on the shapes of the items. For cylindrical items, the fixtures rotate and screens move horizontally. For oval-shaped items, the fixtures rotate, screens move horizontally, and, at the same time, the printheads with screen carriages and squeegees move vertically (Figures 4A and 4B). For square items, the fixtures and screens are stationary, and the squeegees move horizontally.
When individual servomotors drive the printing mechanisms, then the print movements in each printing station are independent of the movements in the other stations. This means it's possible to print onto differently shaped surfaces at different printing stations. For example, during a single pass through the machine, a D-shaped bottle can be printed on its round front in one printing station and then on its flat back in the next printing station.
Container and bottle shapes are becoming more complex. In addition to simple shapes such as round, square, and oval, there are combinations of shapes and subtle transitions from one shape to another. Printing onto these types of products is a challenge because the horizontal speed of the screen has to be synchronized with the surface speed of the rotating bottle during printing. Presses for decorating such products feature motion controllers that use geometric data about the product's cross-section to control and synchronize press movements during the print cycle.
If the bottle is slightly conical, the press operator has to select a cross-section within the printing area. The shape of this cross-section will be used to calculate the surface speed, and this speed will be synchronized with the horizontal speed of the screen. The choice is a compromise because only the surface speed of a printing area with the selected cross-section will be equal to the speed of the horizontally moving screen. The surface speed of a printing area with a larger cross-section than the one selected will be faster than the speed of the screen, while the surface speed of a printing area with a smaller cross-section will be slower than the speed of the screen.
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