1.Crystal point
The “crystal point” is actually some “excessive polymer”, the molecular weight of the polymer at the “point” is higher than the molecular weight of the same PE around. Because of its high molecular weight, it has a higher melting point and higher viscosity.
In the process of film blowing, the point polymer cannot be evenly integrated with the surrounding homopolymers, and after the melt is formed into a film, it is knotted before the surrounding homopolymers. As a result, it forms a “clumpy” solidified body. This is called “crystal point”.
Causes of crystalline spots
(1)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 polymer polymerization, thus forming excessive polymer.
Different resin manufacturers have different polymerization equipment and processes, and there are differences in the purity of the residual catalysts, which have different effects on the polymer in the blown film, for example, low residual catalyst content in the polymer, good equipment structure, the raw material itself contains fewer product points
(2) film-blowing process, equipment: some film-blowing machine die head part design is poor, there are dead ends, resulting in a small amount of raw materials for a long time by heat, excessive polymerization, degradation; blowing mold mechanical aspect ratio configuration, die head design is poor.
(3) Dispersion of masterbatches: the surface treatment of pigments selected in masterbatches is unstable, and “agglomerates” form “powder points” during the masterbatch processing.
(4) Poor compatibility between masterbatch resin and blown film material.
2.Film discoloration
It has been scientifically proven that the discoloration of the film is related to the BHT type of antioxidants contained in the raw material.
3.Sealing
Too much dispersant in the masterbatch will precipitate on the surface of the film and affect the sealing and printing.
4.Mold mouth precipitation
Poor surface treatment of titanium dioxide in masterbatch or thermal decomposition of low molecules in masterbatch
