Silk Screen printing
You may be familiar with other applications for screen
printing (also referred to as silk-screen), such as
balloons, pens and textiles.
If we were to send a CD down an offset web press,
the rollers would soon turn our fragile CD into a nice
collection of plastic bits. A nicer, gentler approach
is needed. Enter the silk-screen machine. The CD slides
effortlessly along a conveyer system and stops under
a yellow sheet of synthetic material (fabric mesh)
for each color needed. A squeegee then drags ink across
the disc's surface.
In the past real silk was used as the mesh but advances
in synthetic materials have increased reliability and
reduced cost. The old name stuck around and we still
call it silk-screening.
The positive films are laid directly on top of the
mesh. Ultraviolet light is shone onto the assembly.
Where there is an image on the positive film, no light
gets through to the emulsion on the screening assembly
beneath, leaving it unexposed. Where the film is clear,
the light passes through and hits the emulsion, causing
it to harden. When the development process is complete,
the unexposed, soft areas of emulsion are washed away,
leaving only the porous fabric mesh.
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Idiosyncrasies of screen printing
The idiosyncrasies of screen printing and the surface
of the CD that can affect your designs include:
The standard line screen for images on disc is 100lpi
resulting in a possible loss of image detail (compared
with 150 lpi booklets).
It is almost impossible to match the colors on your
booklet with the CD silk-screen. Use complimentary
colors and designs.
Spot color rather than CMYK printing will give you
crisper results. Registering a CMYK CD label is more
challenging because it is round.
The thick applications of ink required for screen
printing can make fine lines and detail disappear (including
very small type and serifs under 6 points).
Because the disc surface is metallic silver, not
paper white, you may need to add an additional white
flood under the color to allow more accurate tone and
detail.
Designs with gradual fades from one color to another
may reproduce poorly due to dot gain and tonal jump
that make colors darker and produce pronounced dots
in the image. Anything below 15% of a color tone usually
disappears and anything 85% or greater just closes
up and becomes 100% tone.
Because the disc's innards switch from aluminum,
to a mirror band, to clear plastic, ink color appears
differently on the clear inner hub, the mirror band,
and the main silver surface of the disc. To eliminate
this problem, a white flood is added which equalizes
the surface beneath the silk screened inks.
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