The main causes of fisheye are as follows:
(1) the molecular weight distribution of the resin is relatively broad, because the group with high molecular weight is not particularly easy to plasticize, so it is easy to produce "fish eyes";
(2) impurities that cannot be plasticized are mixed into PVC resin polymerization post-treatment or resin processing, which will also lead to the occurrence of "fish eyes";
To solve this problem, we can take the following three measures:
(1) raw material processing, mainly in the beginning of * to increase the screening strength of PVC resin, increase the number of screening, and pay attention to the environmental health of ingredients, keep raw materials clean to avoid other impurities mixed;
(2) further improve kneading process, implement batch and batch addition of materials in the same kettle, and strictly follow related procedures of kneading feeding.In addition, the good control of PVC resin stabilizer, filler and other solid powder mixing time, to ensure that in the plasticizer after the full absorption and uniform expected swelling.The whole kneading process should be carried out at a low temperature for a long time, which will reduce the appearance of "fish eyes".
(3) further strict control of the extrusion process, in the extrusion processing equipment fixed conditions, control the extrusion temperature, screw speed and other processing technology is to promote the full plasticization of materials * means.In general, good control of the cooling screw at high temperature and high speed can enhance the shear effect in plasticization, so as to reduce the PVC resin "fisheye" situation.