Published: Jan 2002
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THERE ARE TIMES when radiation curing alone may be limited in its ability to effect cure. The technique depends on “line-of-sight” contact of radiation with molecules that can be activated to initiate polymerization. If an object has shadowed areas, as for example, under the chips or other components on a printed circuit assembly, no cure will take place in the shadowed area unless a means of directing radiation under the component is devised. Similar difficulties can be encountered on other three-dimensional objects. The main reason for seeking a system that can be cured with radiation, followed by another means of curing or vice-versa, is to overcome or alleviate such difficulties, as well as to improve properties. The use of two or more mechanisms to effect cure is known as dual cure or hybrid cure. The usual goal of such cure systems is to take advantage of the extremely rapid cure rate of radiation induced curing and obtain a tack-free system, and ultimate properties are obtained in the second step, typically, a thermally induced cure.