Glass Coating Technology Comparison

A variety of techniques are available to deposit thin films onto flat glass. The most widely used of these for producing high-quality functional coatings can be subdivided into two classes: Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD). PVD processes include many approaches of which sputtering is one, and is also the one most widely used for glass. Sputter coatings are generally referred to as "soft coat glass" and are applied using PVD processes. Pyrolytic coatings are applied using CVD methods and are referred to as "hard coating".

Both coating methods have advantages and disadvantages. It is essential to consider the performance and handling factors that best meet product and manufacturing needs when evaluating which system is right for a glass manufacturing facility.

A Stewart Engineers AcuraCoat® CVD Under-Coater for on-line pyrolytic CVD glass coating.

Disadvantages and Advantages of Magnetron Sputtering Technology

Sputtered coatings are applied off-line, independently of the float glass manufacturing process. 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, which is why the process is called "soft coating".

Commercial sputtered coatings are produced by depositing between six and twelve layers of thin metallic and oxide coatings onto the surface of the glass in a vacuum chamber. Silver is the active layer for low-emissivity sputtered coatings. Additional layers include barriers, color modification, oxide layers, and sacrificial metal layers.

Glass distributors have little choice but to install sputter systems to grow their businesses, which accounts for the popularity of these types of systems; however, glass manufacturers have other options and must consider the disadvantages of sputter coating glass:

Advantages and Disadvantages of CVD process

Chemical Vapor Deposition (CVD) is used to produce aesthetic and functional coatings as an alternative to PVD. Specialized coaters produce CVD hard coatings by passing metal oxides over semi-molten glass (600 - 700C) in the tin bath or annealing lehr. A chemical reaction occurs, joining the vapor with the glass surface permanently, through a strong covalent bond. The result is a hard and robust coating that enhances the strength and stain resistance of the glass.

These hard coatings, which cannot be accidentally wiped off during normal handling, are more durable than soft and fragile sputtered coatings. Manufacturers and fabricators handle CVD hard coatings with the same procedures and equipment as standard float glass, resulting in higher yields, higher profit, excellent lead times, and improved customer service.

Pyrolytic CVD hard coatings offer other benefits as well:
Which is best?
The type of coated glass that is best depends on several factors for a glass manufacturer, including where customers are located, the size and type of operation, inventory turns, and required durability.

For most glass manufacturers, pyrolytic CVD technology is superior due to lower capital and operating costs and higher throughput.

Downstream customers view both sputter coated glass and pyrolytic glass as high-performance glass products. Architects and building owners are generally open to using both products and are primarily concerned with aesthetics that favor CVD.

If your company is interested in determining the feasibility of a pyrolytic CVD hard coater, check out the Stewart Engineers AcuraCoat® CVD coater today.