Types of Low-e Coatings and

Processes for Applying Them

Gateway Corporate Center

Architect: O’Brien + Associates

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.

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

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.