Atmospheric Pressure Thermal CVD

Thermal CVD (APTCVD) has many potential advantages over other forms of coating technology, which can give valuable commercial advantage in certain areas of glass coating technology. APCVD can be relatively simple, and cost competitive. It is capable of producing high growth rates over large-areas, and is particularly suited to high volume continuous growth processes, such as those employed in the glass industry. APCVD technology is capable of producing some of the most durable, and process-able, optical quality, coatings available

CVD films, in general, are very hard, can have very rapid deposition rates, characteristic film properties (e.g. crystallinity) and have the potential for low cost and high volumes. These last two advantages are most strikingly achievable when CVD is employed at atmospheric pressure, when low capital costs and continuous operation is achievable. APCVD has already demonstrated the ability to grow films rapidly, 10–20 nm s–1 is typical, and up to 100 nm s–1 has been reported5. Such rapid rates allow the potential for short residence times in the coating region and “in-line” coating applications are a significant exploitation advantage. TCO films fabricated by CVD have been available for some time. The films are easily handle-able and can be manufactured in quantity and at reasonable cost

Float line application

The integration of CVD Coating into the glass production line incurs significant challenges, which have to be overcome. The Glass line speed can be up to 1000mhr-1 , the glass ribbon is standardly over 3 meters wide, and typical required film thicknesses can be several hundreds of nms. Such film thicknesses (at line speeds) require growth rates of tens of nms s-1, and can reach 100 nm s-1. In certain cases more than one coater head is essential to achieve final target film thickness, even for one layer. Selection of the integration position on the float line is a critical decision. As a general rule, the further upstream (and therefore the hotter the glass), the harder and more durable the film produced, and the faster the growth rate achieved. However the higher temperatures result in significant challenges for engineering and precursor chemistry. Most CVD coating is undertaken in the cooler part of the bath, or in the hotter part of the Lehr (and especially in the Lehr gap)

A number of variants of CVD coating have been exploited on glass, over the years. The primary differences related to the whether the coating is undertaken on-line (i.e. actually on the glass production line) or off-line. In addition, the mechanism for precursor delivery is a second major variant, liquid spray and powder spray systems have been used commercially for many year. CVD Technologies concentrates on “true vapour CVD” where the precursors are vapourised fully prior to delivery to the Coater head, and also to on-line technology. This CVD technology is the most widely employed in current Glass manufacturing