Covestro develops PU window frames for China's housing market

BEIJING—Covestro has joined forces with China's Academy of Building Research to develop energy-efficient, flame-retardant polyurethane window frames.

The program, titled "Experimental Platform for Energy and Environment of Future Residential Buildings," also involves Germany's window and door technology supplier Gretsch-Unitas Group. Chinese composite materials maker Zhejiang Deyilong Technology also is in the group, Covestro said.

"(Innovative energy efficient windows) are in high demand in China. Energy efficiency standards for buildings are becoming increasingly stringent," said Irene Li, head of Covestro's polyurethane research and development in the Asia Pacific.

Covestro said that its Badur PU grades are the basis for the three products made so far by the project.

Two of these are for standard casement windows. These have a whole-window thermal conductivity coefficient below 1.5w/m²k. A separate design with much greater insulation also has been developed. This has a conductivity coefficient below 0.8w/m²k.

The standard casement design comes in two styles. The first is an all-polyurethane design with coefficient of linear thermal expansion close to that of cement. This makes it possible to build without a wall void to allow for thermal expansion and contraction.

The second standard product uses fiberglass-reinforced polyurethane as the thermal insulation bridge. This is enclosed in aluminium.

Finally, the program has developed a window to passive house standards. The thermal conductivity of the windows can be as low as 0.77w/m²k and features an argon-filled unit supported in a reinforced PU. This design has a subframe built for energy efficiency, corrosion resistance and waterproofing.

Covestro added that it has also developed PU waterborne coatings with strong adhesion to glass fiber. This can make reinforced PU substrates with weathering and UV aging resistance, according to Covestro.