Hard coated or pyrolytic coated reflective glasses are those in which the coating is applied when the glass is manufactured,i.e. it is an online coating process. In this process of coating, the glass is fused into the glass at 650-700 degree celcius, and on cooling, the coating becomes a part of the glass.
Primary advantage of hard coated glass is the durability, it could also be handled like normal/annealed glass, could be easily heat strengthened, toughened, laminated or curved. These glasses could also be used in single glazing without any fear of losing the coating. Soft coat glasses (to be discussed in the next post) are susceptible to scratch and degradation over time, and requires special handling, hard coated glasses were invented just to counter this problem. Only disadvantage is the variety of colors available when compared to off line coating.
Hard coated glasses could be made either by atmospheric pressure vapor deposition (APCVD) or by spray technology. In APCVD process, the coating additives are vaporized and loaded on to a gas stream, the resulting gas feed is directed towards the glass at above 600 degree Celsius. This results in the formation of a ceramic coating which becomes a part of the glass as the glass is in a semi-molten state. APCVD process could be easily tuned to give a high deposition rate and the desired constant result.
Spray hard coated glass is manufactured by spraying liquid composition of coating additives on to the semi-molten glass. This process could not produce a uniform desired result like APCVD, as the process is not easily controllable or tunable, the deposition rate would also vary from APCVD.
Some of the companies manufacturing APCVD hard coated glasses : Glaverbel (AGC Europe), AIS (Asahi India) and Pilkington.