More than "simply a sticky plastic"
The comment "window film is simply a sticky plastic" may have been true thirty years ago. Today however, the complex and demanding technologies used by the industry is producing high quality and high performance window films.
The world of window films
People often have misconceptions about of window films as they associate them with dark or mirrored-tint on vehicles and buildings. However by reading this, you will realise this is not the case. Window films are now manufactured using incresingly high-tech processes and their use with existing and, in some cases, new glazing systems, can enhance your every day working and living environment.
Architects and designers today are using glazing systems in buildings and vehicles as a major part of the construction and window films can enhance these systems to provide cost-effective solutions for energy savings all year-round(solar gain, UV protection), provide more safety/security (protection in the event of accident, vandalism, explosion or glass failure) and enhance privacy.
Insight into Manufacturing
In their simplest forms, window films are 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.
Window Film Technology / Components
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
Are added to produce the specific properties desired.
All components must have high optical quality to allow undistorted vision through the glass + film.
Window Film Technology / Manufacturing Process
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.
Figure 1
Structure of a typical window film
a. release liner with sillicone coating
b. adhesive layer with UV inhibitor
c. clear or tinted polyester film
d. adhesive layer
e. metallised layer for heat rejection on clear polyester film
f. scratch-resistant coating
Layer c. may have added UV inhibitors for extended durability
Laminating
A film coated with adhesive is adhered to a second uncoated film, using a roller system to press the two films together.
Metallising (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.
Figure 2
Metallizing of polyester (PET) 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.
Figure 3
Sputtering of polyester (PET) film
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 4
Deep dyeing of polyester film – the finished film must be a high clarity, low distortion product
Quality and Durability
Technology transforms our lives; even if most of the time it is difficult to appreciate the technology used to produce apparently simple materials. For example, up to 230 layers are used in some window film to create its advanced properties. Advanced technology makes window film highly durable, quality products.
Quality window film complements and enhances the benefits of glazing. Window film during the coating and laminating process undergoes quality control inspections as shown in this equipment that utilises laser inspection technology
Quality and durability from film construction
It is important to ensure that the product selected comes from a high quality, world-class manufacturer because film construction, the materials and process controls used by the manufacturer strongly affect quality and durability. For example, good quality manufacturers will be concerned about constituents such as:
UV Protection
Adding UV protection to the adhesive and to the polyester film enhances durability.
Location of colours
The colour in a film may be provided by different constituent parts and in different locations within the construction. Such variations can provide a variety of effects both in performance and in durability and it is worth checking with the manufacturer of any particular film on how the film is made, how it will perform and how long it may be expected to last.
Coating uniformity
Metallized coatings must be uniform; high quality manufacturers carefully control coating processes – for example,
many sputtered coatings can be controlled to within 1% of the performance specification. Non-uniform coatings not only look bad but often do not have the properties claimed.
Quality from clean technology
Window film manufacturers take advantage of modern technologies to make high quality products by carrying out certain important production processes in ultra-clean environments. A clean room controls and limits the number and size of airborne particles.
Particles of ≥ 0.010 mm (i.e. 10 microns – 100 times smaller than the full stop at the end of this sentence) are filtered out. A Class 10 000 clean room has no more than 10 000 of these size particles per cubic metre of air compared with the millions of larger-sized particles per cubic metre of air in our normal environment. Adhesives used in window film are also filtered to eliminate foreign particles of more than a few microns. Machine operators also wear cleaned overalls and hair nets.
Quality from quality control testing
Window film manufacturers test their products for a wide variety of properties to monitor and control the properties and quality of the finished product, for example:
• Adhesion to glass
• Tear strength
• Colour
• Tensile strength
• Metallization variation
• Lamination strength
• Scratch resistance
• Solar-optical properties such as solar energy rejection, glare reduction, visible light transmission and UV resistance. In addition, good quality, high performance window film is manufactured with three essential attributes:
• The film layer(s) used are of high strength and are made from optically clear polyester.
• Laminating adhesives to strongly bond individual film layers together and provide good optical properties.
• The adhesive bonding the film to the glass with the correct coat weight on safety / security film in order to keep broken glass pieces together in event of glass breakage.
Durability - warranty
Window films have progressed rapidly over the last decade and have long since gained their reputation for extended lifetime, good scratch resistance and high performance.
Warranties may vary in their criteria of coverage depending on the film type and its function, the geographical location and the film’s construction. Furthermore the periods of the warranties may vary from two years to fifteen years. The most important thing to look for is that it is a warranty from the manufacturer themselves.
Durability from resistance to weathering testing
Window film manufacturers routinely test window film products for resistance to weathering. Over the years, window film manufacturers have developed a very good understanding of weathering testing as their products are constantly exposed to the rays from the sun through the glass.
Weathering resistance is essential for window film because they are continuously exposed to the sun. Sunlight contains damaging Ultra-Violet radiation; less well known is the fact that visible light and Infra-Red energy from the sun can also damage materials – so window film must resist both the degradation and the daily cycles of heating and cooling caused by solar energy.
Accelerated weathering simulates high levels of solar energy (including UV), humidity, etc. found in hot and humid locations where degradation of the film is expected to be the worst. Testing is also done in 'real world' conditions in hot-humid and hot-dry locations. Only when the manufacturer is satisfied that the window film has the required durability is the product launched onto the market.