Selecting the best float glass coating technology

Date: 21 February 2017

Magnetron sputtering is the most common PVD process. Sputtered coatings are generally referred to as "soft-coat" because they are "painted on" by ionized metals directed at the glass.

CVD coatings are referred to as "hard-coat" because they are burned onto the glass and become part of the structure. These coatings can be harder than the glass itself and boost chemical resistance.

Both types of coating offer advantages and disadvantages. When evaluating the best option for a glass manufacturing facility, coating performance and ease of fabrication are important factors.

Sputtered coatings are applied independently of the float glass manufacturing process ("off-line"). Thin films are formed by accelerating high energy ions from targets toward the glass surface at low temperatures.

The ions bombard the glass surface forming uniform thin layers. The bond is weak, causing a "soft coating" that is more easily scratched or damaged and chemically fragile.

Commercial sputtered coatings are applied in a vacuum chamber and typically consist of 6-12 layers of thin metallic and oxide coatings. Silver is the active layer for "Low E" (low emissivity) sputtered coatings.

Remaining layers include barriers, color modification oxide layers, and sacrificial metal layers. Sputter manufactures use these additional layers to offer more products than pyrolytic producers offer.

Offline sputtered soft-coating offers a few benefits:

Many companies embrace sputter coating for the advantages listed above. Glass distributors only coating choice is to install sputter systems, which accounts for their popularity. However, glass manufacturers have other options and should consider the disadvantages of sputter coating listed below:

Chemical Vapor Deposition (CVD) can produce a variety of aesthetic and functional coatings. Chemical vapors are brought to the hot glass surface with specialized coaters during glass manufacturing.

The vapors react with the hot glass (600°C to 700°C) and form a covalent bond. This results in a hard and robust coating that enhances the strength and stain resistance of the glass.

Fragile sputtered soft-coatings can be accidently wiped off during normal handling. Manufacturers and fabricators handle CVD coatings with the same procedures and equipment as standard float glass resulting in higher yields, higher profit, excellent lead times, and improved customer service.

Typical Single Flow CVD Coater

Pyrolytic CVD coatings offer several benefits:

While possessing several benefits from a production standpoint, CVD is not as widely used as sputtering for the following reasons:

For a glass manufacturer, which type of coated glass is best depends on a number of factors, including where customers are located, the size and type of operation, inventory turns, desired durability, etc.

However, for most glass manufacturers, pyrolytic CVD technology is superior due to lower capital cost, lower operating cost, and higher throughput.

For downstream customers, both sputter coated and pyrolytic glass are viewed as high-performance glass products.

Architects and building owners are generally open to using both products and are primarily concerned with aesthetics which slightly favors CVD.