Film Insert Moulding (FIM) is rapidly becoming an established method of producing high quality profiled or three dimensional parts for a wide range of applications, writes Richard Townsend.

The FIM process offers considerable benefits over conventional methods of component manufacture and in-mould decoration; in particular, it enables the number of process operations and component parts to be significantly reduced, while improving productivity, quality and the functionality and aesthetics of the finished product. These benefits have recently been further enhanced with the introduction of anti-reflective, anti-glare films and by a new generation of metallic and pearlescent inks. The FIM process depends on effective collaboration between screen printers, thermoformers and injection moulders, involving four basic steps: printing, forming, trimming and moulding.

An image is firstly screen printed onto the underside of a special hardcoated film, such as Autotype HiForm; images can be produced either singly or in multiples, for example, up to 80 mobile phone covers can be incorporated in a 1.0m2 sheet of film.

Printed sheets are then transferred to a vacuum, pressure or thermoforming press, where they are formed to the exact shape of the components; the outer side of film thus becomes the outer side of the finished component.

The sheet is then trimmed and individual components die-cut to size.

Each is inserted in a female injection mould cavity, where molten polymer is injected behind the film, bonding the two materials together to create a solid and finished part ready for subsequent product assembly.

The film therefore forms a tough protective skin over the complete surface of the part, which can be shaped extremely accurately, while print definition is normally within +/-0.2mm.

In addition, for products such as mobile phones it is possible to integrate the printed and base-colour case and the clear display window into a single component.

The process depends on the performance of the film and inks, plus exact control of the production systems, to ensure consistent process conditions.

In particular, the films used must offer high levels of surface hardness, to resist surface abrasion, scratching and possible exposure to solvents and cleaning fluids.

They should also be able to withstand yellowing, caused by prolonged exposure to sunlight, have high levels of transparency, so that backlighting can easily be incorporated, and be able to accommodate embossed or textured surface finishes.

The characteristics described above are common to many film materials.

The latest films, however, extend this functionality by combing both anti-glare and anti-reflective properties.

These are essential in all applications, such as automotive instrument panels or PDAs, where screens or displays are used to present information, and have been developed jointly by MacDermid Autotype and the Fraunhofer Institute for Solar Energy in Germany, following research into the nano-structures found in the eyes of moths.

These compound eye structures have evolved to collect as much light as possible without reflection, in order to prevent moths being detected by night time predators.

Manufactured using nano replication techniques, the new film is the first of its kind to combine anti-reflective and anti-glare properties on a hardcoated substrate that is both dimensionally stable and easily formable.

This makes it ideal for use in film insert moulding and offers new opportunities for product designers and processors alike, as it reflects less than 1% of visible light, regardless of viewing angle, and eliminates the problems of iridescence and light glare that are often associated with conventional materials.

A further area of development is in the field of specialised inks for the FIM process.

Conventional screen print inks are not generally formulated to withstand the higher temperatures and mechanical stresses generally imposed during thermoforming and injection moulding.

To address this, manufacturers such as Proell are introducing a new generation of solvent based inks that offer superior performance characteristics for printing onto the PMMA and polycarbonate substrates normally used for FIM based components.

In addition, the growing availability of metallic and pearlescent inks is further extending the options for designers, while simultaneously enhancing the ease with which thermoformers and moulders can process materials.

Although these new films and inks do not generally require special handling or processing it is worth noting that the film insert moulding does require careful attention to factors such as tool design, pressure and vacuum settings, the type of resins used, the temperature and pressure of injection, injection gate design and the distance from gate to ink surface, if high quality parts are to be produced.

Film Insert Moulding is an extremely effective process, offering low unit costs, for both low and high volume production, with the ability easily to customise short run components through changes during the screen print stage.

Perhaps as importantly, with the latest generation of inks and resins it gives plastics processors a new range of opportunities in an ever more competitive marketplace.