Window film is a self-adhesive material that can be applied to new or existing glazing to solve a number of problems. Solar control, privacy, decorative and anti shatter films have been around for many years, specialist films such as anti graffiti and anti fog films are also being widely used in today’s’ market.
In its simplest form window film is a thin sheet of polyester, adhesive and then a thin polyester backing liner. Additional sheets of polyester can be found on many films, two sheets of polyester is called two-ply, some safety and security films are also available in three ply. A metalized or dyed layer can sometimes be added between these sheets of polyester to add colour or tint and a scratch resistant coating can be found on the majority of films to protect from every day wear and tear bokeh.
Window film can be fitted to most type of glazing, they can all be fitted to flat glass but some films can also be fitted to raised or patterned glass depending on the flexibility of the film and the type of pattern, if the pattern is too raised the film may not be successfully installed, however there is usually a flat side to all patterned glass. Another problem type of glazing can be compound curves found on the windscreens of cars. This is because the glass is curved in two directions, the film can be easily applied to glass curved in one direction but if it’s a compound curve you will probably need to heat shrink the film, specialist car window tints are available for this, these are usually a thinner material and are specially made to be heat shrinkable more so than a standard window film.
There are three technologies that give different performance characteristics, these are; dyed, deposited and sputtered.
Dyed window film
Dyed films are usually on the cheaper end of the market but these films shouldn’t be disregarded, as there are some very good dyed films on the market. The bottom end of the market is glue tinted, glue tinted films have the dye mixed with the adhesive (scratch resistant coating (not always present), polyester sheet(s), adhesive mixed with dye, backing liner). These are usually sold on the Asian and South American market but are still sold in Europe. These films are not usually particularly colour stable, as there’s very little protection for the dye, as such they can fade very quickly. Because the dye is mixed with the adhesive the colour is not always uniform and the colour can be moved during installation.
A better type of dyed film is one that has the dye sandwiched inside two sheets of polyester, this film is much more colour stable as it is protected by the polyester sheets, this also provides no problems when installing as the adhesive is clear and there can be no colour shift. These films can very often be supplied with as much as ten years warranty.
One of the common misconceptions with dyed film is that it can disperse heat into the property. As dyed films can absorb heat and it’s fitted inside it’s easy to see why people think this. However most of the heat is held in the glass and because the wind speed outside is so much greater than inside (wind speed averages over 15mph outdoors but only ½ mph indoors) the external air draws the heat outside. Some heat is leaked into the property but most heat is dissipated outdoors.
As double glazed units allow no air movement in between the glass, interior dyed films aren’t always suitable for this type of glazing and you should make sure that you check on it’s suitability before installing as installation on the wrong type of glazing can cause thermal cracking.
Deposited window film
Deposited window film is created by drawing film through a tank of metal ingots (usually aluminum or nickel chrome, but sometimes copper). Pressure is then reduced in the tank creating a vacuum and the tank is filled with argon gas. When the tank is filled with gas the metal ingots are the heated, the heat causes the metal to give up particles, which in turn migrate to the films surface in an even layer. The density of the metal deposits can be controlled easily by altering the speed of the film through the chamber.
Sputtered window film
Sputtering is the most complicated procedure for creating window film. This process is also carried out in a vacuum but the metallization in this process is achieved at atomic level. Electromagnetic fields direct streams of ions from a chemically inert gas (usually Argon) towards the metal. This ion bombardment (often referred to as “atomic billiards”) causes groups of atoms to dislodge in small bursts and scatter uniformly across the film.
The benefits of sputtering are that around 30 different types of metals can be used; various metals can be chosen to subtract specific radiation from the solar spectrum. The metalized coating is much lighter; a sputtered metal can be created in a layer one-hundredth of the thickness of a human hair.