What is crystal point? I believe that friends who make films must be familiar with the term "crystal point", which is simply a product defect.

The academic explanation is that the molecular weight of the polymer is higher than the molecular weight of the same polymer around, and the excessive polymer is produced.

Causes of crystal points

Crystal points are usually caused by machinery and equipment, processing technology, materials, etc. However, the mechanism of polymer crystal points is due to the production of excessive polymer, so as long as it is possible to generate excessive polymer, it may cause crystal points.

1. The influence of raw materials

It is said that the influence of raw materials actually refers to the influence of residual catalysts of raw materials.

There will be some catalyst residues during polymer production. During the molding process, the polymer melt containing the catalyst sticks to the surface of the production equipment. At high temperatures, the remaining catalyst continues to catalyze the polymerization of the polymer, thus forming excessive polymerization. Things.

The polymerization equipment and processes of different resin manufacturers are different, and the purity of the residual catalyst is different, which has different effects on the crystal points of the polymer in the film formation. For example, the residual catalyst content in the polymer is low, the equipment structure is good, and the raw material It contains fewer crystal points.

2. The influence of oxygen in polymer

This is mainly because when the processing temperature is high, oxygen will oxidize the polymer to produce free radicals that are adsorbed on the die wall, and the free radicals act as the active center to trigger other polymers.

The molecular chain reaction of the compound, where a high concentration of unstable polymer is formed, becomes variegated

Adding a certain amount of antioxidants can prevent the effect of oxygen on the crystal points.

3. The influence of processing technology and equipment

The processing technology is mainly affected by temperature control, and the raw materials will be heated for a long time, excessive polymerization, and degradation will cause crystal points.

In fact, many times are caused by equipment, such as the poor design of the die head of the film blowing machine and the existence of dead corners, which cause a small amount of raw materials to be heated for a long time, excessive polymerization, and degradation; the aspect ratio configuration of the blow molding machine, the poor die design, etc. ; Due to the long-term accumulation on the screw or the inner wall of the screw barrel, some carbonized things are produced, and these carbonized things can be used as gel points, constantly adsorbing more impurities to it, and also constantly sticking to the film. The so-called crystal point. All in all, regular cleaning of the molding equipment helps to reduce the generation of crystal points.

4. The influence of pigments, fillers, masterbatch, etc.

Nowadays, film production is accustomed to adding color masterbatch. Poor dispersion of the color masterbatch can lead to undesirable defects such as crystal points. For example, the surface treatment of the selected pigments in the color masterbatch is unstable and "agglomerates" during the processing of the color masterbatch to form "powder spots". "; The carrier resin of the color masterbatch has poor compatibility with the film-forming raw materials.

Methods to reduce or eliminate crystal points

Understanding the reasons for the formation of the above crystal points can be easily controlled. Here are four methods for you:

1. Choose purified resin as raw material to reduce the influence of catalyst;

2. Increasing the fineness of the filter screen during the film forming process, and changing the filter screen frequently (especially for obsolete equipment) is conducive to the reduction of crystal points;

3. Add appropriate amount of antioxidants, etc.;

4. Add steel surface lubricant during the production process to reduce polymer melt sticking on the equipment surface;