New Henkel adhesive meets high-temperature, long-life demands
Doug Smock, contributing editor -- Design News, January 13, 2010

The expected surge of the solar cell industry in the next four years is triggering a wave of new materials technology, particularly for the protective backsheet, which is usually a multi-film laminate anchored by DuPont's Tedlar fluroropolymer film.

"The demands on this composite sheet are particularly high," says Stefan Tomke, who heads product development at Henkel for laminating adhesives. "During the 20 to 25 years of its service lifetime, the backsheet is expected to continuously withstand all the tough weathering conditions to which it is exposed in its roof-top position."

Extreme hydrolysis is a particular problem, and the adhesives especially need to exhibit enormous resilience. UV resistance is also paramount as the backsheet must not be allowed to yellow.

Two-Component Adhesive
"Added to this is the fact that, during the laminate manufacturing process, the adhesives have to readily withstand temperatures of up to 150C for periods of 25 to 35 minutes," Tomke says. Henkel developed a new two-component adhesive under the Liofil brand that provides thermal resistance at temperatures of 200C, and provide 2,000 hours of weathering at 85C and 85 percent relative humidity without deterioration.

A start-up company in California is launching new backsheet materials made from plant-based plastics. One film material is made from castor oil-based nylon 11, while a new cellulosic sheet is made from a cotton feedstock. DuPont, meanwhile, is investing $120 million to boost capacity 50 percent for the resins used to make Tedlar films.

Mitsubishi Plastics has developed an ultra-higher barrier film for back sheets used in crystalline silicon solar modules that require a humidity barrier of 0.2g/m2/day, and one for thin PV cells that need humidity barrier of 0.02g/m2/day. The Back-Barrier is also being developed for use in dye-sensitized and organic thin-film solar cells, which require an even higher humidity barrier. Developed in Japan, Mitsubishi's new barrier films rely on a variety of polymer substrates that are treated with ionized solutions.

Other interesting advances are also taking place in adhesive. Henkel's Emerson & Cuming brand developed ECCOBONDTM CA 3556 HF for high throughput solar cell production processes. The new adhesive creates a flexible electrically conductive bond with high peel strength and long term.

New film and adhesives technologies will boost longevity of solar cells and boost their performance. Photo: Henkel