'Polycarbonate (PC) auto glazing is being used mostly in Europe for front and rear quarter widows, fixed side windows, rear-door fixed window sections, small transparent body panels and larger panoramic sunroof systems. This substitution from conventional material like glass is resulting in greater styling freedom as well as weight savings of up to 50%.
Global demand for sunroofs for automotive applications is expected to rise from 15 mln units in 2006 to 22.4 mln units in 2010. Demand for total panoramic roof is expected to jump from 2% in 2003 to 40% in 2010- and a sizeable chunk of this market is expected to be captured by moulded PC, albeit with the essential feature of improved surface protection.

Conventionally, the standard has been a hard coating applied after moulding the PC substrate to provide scratch resistance and UV protection. However, in-mould films might replace hard coatings. A major benefit of in-mould film laminating is the ability to produce completely finished glazing right out of the mould. This could eliminate downstream coating operations while reducing the chance for scrap generation during parts handling. In-mould film laminating could result in offering moulders a wider processing window. It could become possible to operate machines at injection pressures and speeds similar to those used for back moulding. This will eliminate the need to operate machines under special conditions�such as an injection-compression process required to mould the substrate under low-stress conditions to ensure both optical quality and retention of a hard coat. In-mould film laminating may allow use of more conventional PC grades.

Special PC grades have been developed for glazing, providing good flow and higher optical clarity than conventional materials, as well as adhesion to a hard coat. PC delivers excellent impact resistance but poor weatherability, while acrylic causes excellent weatherability but lower impact strength. A combination of both is desirable, without unduly compromising the impact behaviour of PC critical for glazing. It may be undesirable to make plastic glazing too strong, as this could block the escape of the occupants of vehicles in case of an accident. One solution could be to using a blown rather than cast acrylic film, because blown film contains fine flaws created at the frost line in the bubble, which can serve as crack-initiation points on impact from inside the vehicle. PC/acrylic �hybrids� in the mould can be created by use of a coinjection process instead of film-insert lamination.
Film laminates offer more than physical protection to PC glazing. They can also add functionality. Light-absorbing particles in the film instantly control visible light transmission from optically clear to very dark and also provide over 99% UV blockage and reduces solar heating of the car interior. This can save energy by reducing the size of the air-conditioning unit required in the vehicle. The film can also provide added strength, durability and acoustic insulation.
SPD-Smart film with Research Frontiers' patented Suspended Particle Device (SPD) technology incorporates an emulsion of microscopic, encapsulated poly-iodide liquid crystals. In an idle state, these light-blocking particles are randomly oriented in the film and block over 99% of visible light. When an electrical voltage is applied, the particles align so that light can pass through. SPD-Smart film is used only in laminate structures where it is sandwiched between two pieces of plastic or glass. SPD-Smart film can be bonded to PC with polyurethane adhesive.

Glass-reinforced film for clear, structural parts is also being explored, though glass reinforcements have not been used in transparent thermoplastics. One concept was to pre-wet woven glass with a clear, low-viscosity, transparent wetting agent. This prepreg can be placed on the outer surface of a part to deliver a maximum mechanical benefit and provide a hard surface. In one process glass fabric covered with acrylic or polyester powder was placed in a press between an acrylic film and a PTFE release film. Heat and pressure melted the powder to wet out the glass and squeezed out the air, resulting in an acrylic film with glass on one side. This product could then be laid in a mould and back-moulded with PC. However, the results are not satisfactory as it results in some degree of haze.
Nanocomposite technology is also being used for glazing. Small amounts of nanoclay or metal oxide ceramic particles can be added to PC or acrylic, resulting in increased abrasion, solvent, and moisture resistance without loss of clarity.

Heat-cured wet coatings or lacquers based on acrylic or siloxane resins remain the most common approach for PC glazing and headlamp lenses. These are being replaced by viable options like gas-phase deposition technologies such as chemical vapour deposition (CVD), physical vapour deposition (PVD), or plasma-enhanced chemical vapor deposition (PECVD), especially for large glazing parts. Though with wet coating, it is easy to embed UV protection, very good surface hardness can sometimes be difficult to achieve. For higher hardness, a switch from the low-cost organic polymers like siloxanes to more expensive liquid siloxanes containing nano-particles could be made. Because wet coatings entail the use of solvents, they add to costs for environmental protection. The various vacuum-deposition coating processes have limited use with plastics, focused mainly on smaller applications such as eyeglass lenses and non-transparent decorative parts like automotive down-light reflectors.
The need of the hour is a plasma coating process that keeps production costs low, has short process times, a high deposition rate and large-area deposition capability. Two promising new technologies that may fill that void are a Plasma-Array system developed at the University of Eindhoven in the Netherlands and the Duo-Plasmaline deposition system developed at the University of Stuttgart's Institute for Plasma Research. The new Duo-Plasmaline PECVD coating system delivers high deposition rates of organic or inorganic materials (such as siloxane, quartz, or diamond) using a low-pressure, low-energy plasma generated by a linear source of high-frequency microwave energy. The low-energy system reportedly means low damage and low thermal impact to the substrate. Different gases can be used by the system, including hydrogen, oxygen, argon or nitrogen. Ongoing research is looking at ways to reduce or eliminate micro-cracking during thermal cycling and to achieve UV protection without pre-lacquering the PC.
The new Plasma-Array PECVD system carries out vacuum deposition of a hard, transparent, quartz-like film on PC in a solvent-free process. It has a deposition area of 80 x 60 cm and deposition rate of 1-3 microns/minute while holding thickness distribution to ±15% of target or tighter. A multi-layer coating system, Exatec 900 system, in development since 2004, includes a proprietary siloxane wet coat followed by PECVD. The full Exatec 900 system provides both scratch and UV protection and allows for intermediate printing steps in which inks and dyes can be applied for additional functionality such as light control, decorative effects, defrosting systems and radio antennas.