Stress relaxation in blocks of poly-methacryl-imide¨ foam - by heating block surfaces to 75-180 deg. C at rate so inside temp. does not exceed 70 deg. C. then cooling to room temp.

摘要

Process for reducing stress in blocks of polymethacrylimide foam (I) with two parallel plane surfaces involves heating the surfaces of the block (internal temp. below 50 deg. C) to a temp. of 75-180 deg. C at such a rate that the internal temp., does not exceed 70 deg. C, and then cooling to room temp. After cooling, the block is divided into two or more slabs by one or more cuts parallel to the surfaces; the surfaces are heated by radiant heat, pref. applied for less than 5 mins. USE/ADVANTAGE - The invention provides a stress relaxation process for blocks of (I) obtd. by heating methacrylic acid/methacrylonitrile copolymer at 200 deg. C, as described e.g. in DE-A 3519005; stresses induced by cooling can result in a curvature of up to 100 mm in a slab 2500 mm long cut from such a block which had not been annealed. (0/1)