Compressed foamable PVC film prodn. for making relief - using inhibitor or initiator, by calendering premix contg. lubricant below foaming temp.

摘要

Prodn. of slightly compressed foamable PVC films, which can be inhibited and activated and contain an undecomposed blowing agent, is carried out by calendering. A PVC of the suspension and/or emulsion type is used and the shear force during premixing is reduced by adding a lubricant. Mixing is carried out only until the mixt. gels and the gel is rolled out on a 2- and multi-calender below the decomposition temp. of the blowing agent. Suspension PVC with a K value below 75 or a mixt. of suspension and emulsion PVC, both with a K value below 75, is used. An internal and external lubricant, esp. hydroxystearic acid, is added. The pH of the PVC is shifted towards neutral by adding a buffer. Premixing is carried out at 110-150 -eg.C and calendering at a lower temp. The film is useful for making prods. with a structurised surface by after-treatment with inhibitor or initiator as required. This makes the prodn. of relief surfaces cheaper and allows a high degree of recycling of scrap.