Causes and prevention of crystal points in stretch film

1. The influence of the raw materials of the product, the influence of raw materials refers to the residual catalyst influence of the raw materials.
During the molding process, the polymer melt containing the catalyst sticks to the surface of the production equipment, and at high temperatures, the residual catalyst continues to catalyze the polymerization of the polymer, so excessive polymerization will be formed. Different membrane manufacturers have different polymerization equipment and processes, and the purity of residual catalyst treatment is different, which has different effects on the crystal point of the polymer in the membrane film, such as the residual catalyst content in the polymer is low, the equipment structure is good, and the raw material itself contains less crystal points.
2. The influence of oxygen in the polymer This is mainly when the processing temperature is high, oxygen will oxidize the polymer to produce free radicals adsorbed in the mouth die wall, free radicals as the active center to trigger other polymer molecular chain reactions, here to form a high concentration of unstable polymer, at high temperature into variegated spots. Adding a certain amount of antioxidant has the effect of preventing the formation of film crystal points.
3. The influence of stretch film processing technology, processing equipment, processing technology is mainly affected by temperature control, and the membrane raw materials will be heated for a long time, excessive polymerization and degradation will lead to crystal points. In fact, many times it is caused by the device, such as:
(1) The design of the die part of the film blowing machine is not good and there are dead angles, resulting in a small amount of raw materials being heated, excessive polymerization and degradation for a long time;
(2) The length-diameter ratio configuration of the film blowing molding machinery and the poor die head design;
(3) Due to the long-term accumulation of the screw or the inner wall of the screw, some carbonized things are produced, and these carbonized things can be used as gel points, constantly adsorbing more impurities to it, and also constantly staining the membrane to cause the so-called crystal points.
4. Pigment filler, masterbatch and other effects
Masterbatches are usually added to the production of stretch film, and poor dispersion of masterbatches will lead to undesirable defects such as crystal points, such as unstable surface treatment of pigments selected in masterbatches, and "agglomeration" during masterbatch processing to form "pink spots"; The carrier resin of the masterbatch is not compatible with the film-forming raw material.