DYED FILM
Single-Ply Dyed Window Film with Standard Scratch Resistant Hard
coat
From there, three separate technologies are applied to achieve
different performance characteristics. The first is simply a dye, which
absorbs heat. Because most films are applied to the inside surfaces
of windows, it's easy to imagine that the absorbed heat would
disperse indoors. In fact, the heat rejected by the film is stored largely
in the glass, and is drawn away by external air movement. A tiny
percentage does bleed inward, but because the average speed of
external air movement is so much greater-the daily average is 15 mph,
versus 1/2 mph indoors-the ratio is 30:1 or better in favor of outdoor
heat dissipation. Because double-glazed windows don't allow air
movement between panes, interior-dyed films should not be used on
thermal glass.
The other two processes, called deposition technology (vacuum
coating/metallizing) and sputtering technology (advanced metallizing),
deposit a layer of metallic particles on the film, giving it a reflective
coating. In each case, a second layer of film protects the coating.
Metallized films reject heat by reflecting it before it can be transferred
through the glass.
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DEPOSITED FILM
In deposition technology, the film is drawn through a tank containing
metal ingots-usually aluminum or nickel-chrome, and occasionally
copper. A vacuum is created by reducing the pressure in the tank,
which is then flooded with argon gas and the ingots are heated. The
heat causes the metal to give up particles that migrate to the film's
surface. The density of the metal deposition is controlled by the speed
of the film through the chamber.
While deposition technology works well and is relatively inexpensive, it
has its limits. To be effective, the metallized coating must be fairly
thick, as the particles are comparatively large. What this means at a
practical level is that it produces a darker, more highly mirrored
surface. And second, the list of metals that can be deposited evenly is
fairly short, which means fewer product options.
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SPUTTERED FILM
Two-Ply Metallized Window Film with Metallized and UV Treated Film
Layers
Sputtering technology is more complicated. Sputtering is also done in
a vacuum chamber, but the metallizing is achieved at the atomic level.
In brief, electromagnetic fields direct streams of ions from a
chemically inert gas (usually argon) toward the metal. This ion
bombardment, which is often described as "atomic billiards," causes
groups of atoms to dislodge in small bursts and scatter uniformly
across the film.
The practical benefits of sputtering are that 25 to 30 different metals
can be used and the metallized coating is much lighter. It's possible to
sputter metal in a layer one-hundredth the thickness of a human hair.
Different metals are chosen to subtract specific bands of radiation
from the solar spectrum. The result is a highly reflective layer with very
little mirror effect, heat absorption or color shift. Because sputtering is
more expensive, these films occupy the high end of the price range.
Metallic films control radiation through reflectivity. Simplified film
consists of polyester layers, metallic coating, adhesive and scratch-
resistant coatings.
While the performance characteristics of dyed and metallic films are
generally distinct, there is some overlap. Heat-absorbing dyed films
are somewhat reflective, and metallic films do absorb some heat
because of the mass and color of the metals involved.
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HYBRID FILM
To further complicate the issue, many films contain both dyes and
reflective metals. By combining dyes and metals, the negative effects
of each can be reduced without sacrificing performance. A good
example is gray dye and titanium coating. If used alone, dye would
darken the film significantly, while the titanium would produce a highly
mirrored surface. When paired, less of each can be used, resulting in
a film that is relatively bright and non reflective.
This point is significant, if only because it quells the notion that the
darkest films reject the most heat. In most cases, dark films are
chosen because they offer greater privacy.
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