Understanding the different types of low e glass coatings and the processes for applying them.

1. Types of Low-e Coatings and
Processes for Applying Them
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Architect: O’Brien + Associates

2. Processes for Applying Low-e Coatings
Low-e Coatings: Outstanding Thermal Performance
Low-emissivity or “low-e” glass coatings are metallic layers
applied to float glass to reflect long-wavelength energy back
toward its source. Heat stays outside during the summer and
inside during the winter. “Emissivity” is a measure of a surface’s
ability to admit and emit long-wave infrared radiation.
There are two common types of low-e coated glass:
• Solar control low-e coatings are designed to reflect high
levels of infrared, or heat, energy while allowing high levels
of visible light transmittance. The highest-performing solar
control low-e coatings are produced using the MSVD or “soft
coat” process.
• Passive low-e coatings are designed to transmit high levels
of both infrared and visible light and can be produced using
both pyrolytic (hard coat) or MSVD (soft coat) manufacturing
processes.

3. Processes for Applying Low-e Coatings
Pyrolytic Coating Process (Chemical Vapor Deposition)
Because the chemical coatings are applied to the glass
while it is still hot, the pyrolytic process forms a strong
thermal bond between the coating and the glass
substrate, thus the term “hard coat.”
Melting—The raw
materials become
molten at temperatures
reaching 2,900°F.
Refinement—The molten glass is
homogenized and bubbles are
removed. Then the molten glass
is cooled to approximately 2,000°F.
The glass ribbon goes through the
cooling tunnel or “lehr,” which lowers
the glass temperature to almost room
temperature.
Deposition—A chemical vapor is sprayed onto the glass
ribbon during the float process, either inside the bath or
between the bath and the annealing lehr, while the glass
is still at temperatures of approximately 1,100° to 1,300° F.
Melter
Refiner
Tin Bath
Lehr

4. Processes for Applying Low-e Coatings
MSVD Coating Process
High-voltage
Electric Circuit
Vacuum
Chamber
Magnetron sputtered vacuum deposition (MSVD)
or “sputtered” glass coatings are applied off-line
at room temperature after the actual glass
manufacturing process. Although softer and less
durable than pyrolytic coatings, MSVD coatings
offer superior solar control performance.
The glass to be sputtered is loaded
into a high-voltage electric circuit.
It then is fed into a vacuum chamber of
process gas, where plasma is formed.
An ion discharge takes
place inside the chamber.
The positive-charged ions
are attracted to and collide
with the glass at very high
speed. Atoms are released
and deposited on the glass,
forming a microscopically
thin coating.