The comment “Window film is simply a sticky backed plastic” might have been true thirty years ago, but contradicts and misunderstands the complex technology, high quality, high performance materials that are used in modern window film.
In their simplest forms, window film is composed of a polyester substrate to which a scratch resistant coating is applied on one side; a mounting adhesive layer and a protective release liner is applied to the other side. When the release liner is removed, the side of the film with the adhesive is applied to the surface of the glass. All components must have high optical quality to allow undistorted vision through the glass and film. A standard window film might have eight layers and undergo up to seven manufacturing processes.
The performance and durability of window film is determined by the type and quality of the component used in the film and the construction used. The essential components include:
- Protective Release Liner: A film, usually polyester, which is used to cover the adhesive and protect it from contamination before installation.
- Adhesive: High quality, low or zero distortion adhesives that adheres the polyester film to glass; types used for automotive installations retain high adhesion even on double curved glass.
- Polyester Film: A strong, high clarity, high quality plastic film – more than one layer may be used with a laminating adhesive to produce a multi-layered structure.
- Scratch Resistant Coating: A hard acrylic coating that provides protection for the polyester against scratching and abrasion.
- Dyes, metals, alloys and UV inhibitors are added to produce the specific properties desired.
All components must have high optical quality to allow undistorted vision through the glass and film.
Figure 1 shows a multi-layer window film sample that has gone through several manufacturing processes; quality control of raw materials, manufacture and end product adds further to these processes.
Very precise processes are required to ensure high quality. They include:
Coating (Figure 1): Adhesives and scratch resistant coatings are transferred from a container to a roller and then rolled onto the surface of the polyester.
Laminating: A film coated with adhesive is adhered to a second uncoated film, using a roller system to press the two films together.
Metallizing (Figure 2): Polyester film is wound around a water-cooled roller in a large metal vacuum chamber. Metal – usually aluminium – is evaporated onto the cold surface of the film.
Sputtering (Figure 3): Using similar equipment, a metal or alloy target is bombarded with positive ions to knock (sputter) atoms of metal out of the target and onto the cold film surface. A larger number of different metals and alloys can be sputtered and some, such as nickel, may also have extra resistance to corrosion. This process is slower but more precise than metallizing.
Colouring (Figure 4): The colouring of window film may be achieved in several different ways. The adhesive may be coloured before coating it on the film or a laminating layer may be coloured. The use of dyes or pigments may be used to colour the actual polyester base film after it is manufactured or during the extrusion process itself. The manufacturer of any specific film would be able to explain the process used in its construction and the reasons, uses and benefits that may result.
Figure 2: Metallizing of polyester (PET) film
Figure 3: Sputtering of polyester (PET) film
Figure 4: Deep dyeing of polyester film – the finished film must be a high clarity, low distortion product