The “crystal points” are actually some “overpolymers”, and the molecular weight of the polymer at the “point” site is higher than that of the surrounding PE of the same kind. Due to its high molecular weight, it has a higher melting point and higher viscosity.
In the process of film blowing, the polymer at the product point cannot be uniformly fused with the surrounding polymer of the same kind. After the melt is formed into a film, it is formed before the surrounding polymer of the same kind. Thus, a “clump-like” solidified body is formed. It is called “crystal point”.
The reason for the formation of crystal points
(1): There is residual catalyst in the polymer: the polymer melt sticking to the surface of the production equipment, at high temperature, the residual catalyst continues to catalyze the polymerization of the polymer, thus forming an excessive polymer.
The polymerization equipment and process of different resin manufacturers are different, and the purity of the residual catalyst is different, which has different effects on the quality of the polymer in the blown film. For example, the residual catalyst content in the polymer is low, the equipment structure is good, and the raw materials There are few points in itself
(2) Film blowing process and equipment: some film blowing machine die parts are poorly designed and have dead ends, resulting in a small amount of raw materials being heated, excessively polymerized and degraded for a long time; the aspect ratio configuration of the blow molding machine and the design of the die head are not good .
(3) Dispersion of the masterbatch: the surface treatment of the pigment selected in the masterbatch is unstable, and “agglomeration” forms “powder spots” during the processing of the masterbatch
(4) The bulk resin of the color masterbatch is not compatible with the film blowing raw material.
It has been scientifically confirmed that the discoloration of the film is related to the presence of BHT-type antioxidants in the raw materials.
Too much dispersant in the masterbatch will precipitate on the surface of the film, affecting sealing and printing
The surface treatment of titanium dioxide in the masterbatch is not good or the low molecular weight in the masterbatch is thermally decomposed