There are several techniques for disc printing, but only two are used by high volume commercial replication plants. Other techniques such as thermal printing and printed label adhesion involve less setup, but are generally considered too slow and of an inferior colour quality to be used for high volume commercial runs.
The original high volume technique, still used for many solid colour Pantone print runs today, is known as screen-printing.
This technique involves creating film positives of each colour separation, then developing this film onto a fine silk sheet stretched between metal plates. The silk is woven to an exact density (usually 150 to 180 threads per inch) and the reverse image appears as black on the silk sheet. Up to five or six silk screens can be assembled onto the rotating screen print machine, with different colour inks mixed for each print screen. As the discs pass at high speed through each colour station, a rubber block is pressed over the screen – drawing new ink onto the screen in one movement, then pressing this ink through the non-reversed areas of the silk directly onto the disc as it is shunted into place under the screen. The disc then passes under a UV light, which dries the ink, before it is shunted under the next colour station.
Fine tuning controls allow screen print operators to accurately ‘register’ each colour – ensuring that the final multiple colour image is a crisp clear picture. Poorly registered print runs will result in out of focus images. Depending on the complexity of the image, several discs will be scrapped while the operator fine tunes the screens to a properly focussed registration. This is the historical and still valid reason that inexact quantities of discs may be produced and charged by the plant.
The more popular current technique is known as offset printer. Generally used for high resolution (300 dpi) cmyk full colour discs, the offset print setup is quite different to screen printing.
Starting with film negatives (rather than positives for screen print), the colour separations are developed onto a photo sensitive metal print plate, identical to any commercial offset print plate such as that used for booklets, inlay, slicks and digipak or wallet printing.
These plates are then inserted into a high speed specialised offset printing, which sends the discs around underneath each colour plate in rotation. The plates are aligned via fine tuning controls to ‘register’ or focus the image, in the same manner as a screen printer.
Offset printers are generally five or six colour station printers, allowing for the standard cyan, magenta, yellow and black (cmyk) process inks that create a full colour photograph image, plus one or two specially mixed Pantone or spot colour inks if required.
The surface of a disc is silver (or very occasionally gold or other colours) after replication. Unless an ink is printed at 100% density on the silver disc surface, the colour will be affected by the metallic colour underneath. For 99% of projects, accurate bright colours are more important.
For full colour cmyk designs, we will always recommend printing a white base underneath the design. It is free of charge and will ensure that the cmyk image colour is more accurately produced. If you want to incorporate sections of silver into your artwork, then we recommend reversing only these areas out of a solid black 18mm to 118mm diameter separation in your artwork and bringing it to our attention via email when placing the order.