Lamination

This step is carried out in a laminator, a table that can be heated and furnished with a cover that tightly closes the edges. The cover has an internal chamber and a diaphragm that separates this from the chamber containing the module. Both chambers can be independently evacuated: this configuration allows the module to be kept in a vacuum while mechanical pressure is exerted on it.

During the lamination process, both chambers are evacuated while the temperature is raised above the EVA melting point (around 120 °C). Vacuum is important to extract air (to prevent voids from forming), moisture and other gases. The EVA flows and soaks the cells. After a few minutes, with the module chamber still in vacuum, the upper chamber is filled with air so that the diaphragm presses the laminate. When temperature reaches 150 °C, the curing stage begins: the curing agents induce cross-linking of the EVA chains, i. e. chemical bonds are formed transversally among the long molecules that before curing are only weakly linked to one another. The plastic then acquires elastomeric, rubber-like properties, and indeed the curing step is a close analogy to the vulcanization of rubber. The total process takes around 12-15 min for standard EVA [184, 185].

Lamination used to be a bottleneck in the module fabrication process. To improve throughput several solutions have been followed by the industry: (i) commercial ultra-fast-curing EVA formulations that have allowed the reductions of curing time to less than 10 min nowadays; (ii) alternative materials based on silicones, polyurethanes, ionomers or polyolefins with process time in the range of 2-4 min are under evaluation; and (iii) a large lamination area – up to 10m2 – or in a multilevel layout enabling simultaneous process of several modules or very large ones.

Updated: August 23, 2015 — 6:57 am