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Borohydrides M a k e Better Foams
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N e w process for gett ing vinyl f o a m is versatile, inexpensive, and uses simple equipment
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STEPS TO VINYL FOAMS. Foam compound is first p o u r e d into mold cavity (up p e r left ) ; then plastisol exrjands a n d fills mold. Mold is closed ( u p p e r right ) a n d is placed in press for fusion (lower l e f t ) . Result: finished vinyl form (lower r i g h t ) . Process forms foam a t either room t e m p e r a t u r e o r h i g h e r
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chemically activated borohydrides as blowing agents—that's working wonders with vinyl foam. T h e new scheme gives greater manufacturing versatility, requires simpler process equipment a n d techniques, a n d turns out a better prod uct in the bargain, says B. F. Good rich's sponge products division, which fathered the process. Goodrich's n e w route brackets t h e t w o present commercial nieiliocls for making vinyl foams—it forms foams at either room temperature or higher; temperature h a s to b e raised to 350° F . in order to set the foam. T h e other processes require heat t o form a n d / o r s e t the foam. This foam control can slice production time a n d equipment costs, says Goodrich, a n d can make it possible to tailor a com p o u n d for a production scheme. T h e "elastomer process," t h e first used for vinyl foams, is strictly mechan ical. Carbon dioxide is dissolved in a olastiso! at higher than atmospheric pressure a n d reduced temperature. W h e n released, the plastisol conies out
as a foam. But if h e a t isn't applied im mediately, to set u p trie foam, it reverts to a liquid. T h e n , D u Pont introduced its BL-353 process, which adds a heat sensitive compound to t h e plastisol; this com pound releases nitrogen on heating. Here, the plastisol flows into t h e mold as a liquid, is h e a t e d ίυ 190 = F . a n d held (heating time depends on m a t e rial thickness) to produce a foam, then raised to a b o u t 350° K. to set i t . L a t e r , Du Pont a d d e d a refinement—a pat ented heat exchange nozzle to raise t h e plastisol to foaming temperature before it goes into t h e m o l d . r Goodrich FuHs
