Traditional post-mould decoration can be relatively expensive to
achieve and the results sometimes lack long term durability. In this
article, Tim Wright describes the benefits of an alternative process -
film insert moulding
Post-mould techniques are traditionally used for decorating moulded
products, ranging from the outer shells or cases of mobile phones, to key
panels on white and brown goods, heater and ventilation controls in cars
and fascia components on medical devices. Although many of these
techniques have been used for some years and offer known benefits,
inherent limitations of the processes involved mean that there are almost
always disadvantages or compromises to be addressed, in terms of
production costs or finished part quality. Now, however, a new generation
of in-mould decoration (IMD) techniques, and in particular film insert
moulding look set to change the way companies design and manufacture
products, with reduced cost and improved quality.
Traditionally, there have been five main methods of post-mould
decorating, of which spray painting is perhaps one of the most widely
used. This process is relatively straightforward, can be used for any
shape or size of part and gives good colour and lustre effects. It does,
however, make it difficult to achieve a durable hard coat or patterned
finishes, cannot be backlit, requires a high level of capital investment,
generates considerable waste and the process can generate environmental
concerns.
Similarly, laser etching uses at least one paint, or sometimes ink layer
that is then cut back by a high powered laser to reveal the underlying
surface, creating graphics, text or patterns as required. This method
produces good results, often with complex graphics, but is normally
restricted only to two colours and has long cycle times of up to 20
seconds per part produced. This can be reduced by using more powerful,
and therefore more expensive, lasers but the process is still slower than
spray painting.
A third technique is appliqué, where a pre-printed label is simply
applied to the part. Although this is an inexpensive process and high
quality labels are easy to produce, they are prone to peeling and do not
generally appear to be an integrated part of the moulding. A more
effective process is Aquagraphics. This is a water transfer process where
a pre-printed water soluble film is applied to a moulding, enabling
extremely high definition effects, such as wood grain on car panels, to
be produced. The downside is that the transfer must be protected by a
spray coat, while waste and part production costs are high. Finally, pad
printing offers a simple method of applying graphics and text to moulded
parts, especially in small areas, but again suffers from problems of
durability, cannot be backlit and is only suitable for low volumes, as
output is slow at about 250 units per hour.
By comparison, the latest film insert moulding (FIM) technique offers a
number of important benefits in a wide range of applications. In
particular, it provides far greater design flexibility than competing
processes, enabling complex multi-colour, metallic or photographic
quality images to be created, with the option of backlighting.
Additionally, FIM offers the potential of production cost savings through
process optimisation and a reduction in the number of components and
stages normally required, plus the ability to minimise waste. The
technique can be used for small and large volume production runs and can
also produce deep drawn profiles.
The FIM technique
An image is first screen printed on the underside of a special
hard-coated film.
Images can be produced either singly or in multiples; for example, up to
80 mobile 'phone covers can be produced from a 1.0m² sheet of film.
Printed sheets are then transferred to a vacuum, pressure or
thermoforming press where they are formed to