Causes and solutions for plastic crystals

The cause of the crystal point

The crystal point is usually caused by machinery, processing technology, materials, and the like. However, the mechanism by which the polymer produces a crystal point is due to the generation of a polymer, so that it is possible to cause a crystal point as long as a polymer is likely to be generated.

Influence of raw materials

1. The influence of raw materials actually refers to the residual catalyst influence of raw materials.

There are some catalyst residues in the production of the polymer. During the molding process, the polymer melt containing the catalyst sticks to the surface of the production equipment. At high temperature, the residual catalyst continues to undergo catalytic polymerization on the polymer, thus forming an excessive polymerization. Object.

Different resin manufacturers have different polymerization equipments and processes, and the purity of residual catalysts is different. It has different effects on the crystal lattice generation 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 materials are good. It has fewer crystal points.

2. The effect of oxygen in the polymer is mainly because when the processing temperature is high, oxygen will oxidize the polymer to generate free radicals to adsorb on the wall of the die, and the free radical acts as an active center to initiate the reaction of other polymer molecular chains, forming a high here. The unstable polymer at a concentration becomes a motley point at high temperatures.

Adding a certain amount of antioxidants prevents oxygen from forming on the crystal point.

3. The influence of processing technology and equipment

The processing technology is mainly the influence of temperature control. The raw materials are heated, over-polymerized and degraded for a long time, which leads to the generation of crystal points.

In fact, many times it is caused by equipment. For example, the die-cutting part of the blown film machine is poorly designed and has a dead angle, which causes a small amount of raw materials to be heated, over-polymerized and degraded for a long time. The length-to-diameter ratio of the blow molding machine and the poor die design are poor. Etc.; above the screw or on the inner wall of the barrel, due to long-term accumulation, some carbonized things are produced, and these charred things can be used as gel points to continuously adsorb more impurities onto it, and also continuously adhere to the film. Causes a so-called crystal point. All in all, the regular cleaning of the molding equipment is beneficial to reduce the production of crystal points.

4. Effects of pigments, masterbatches, etc.

Nowadays, the film production habits add color masterbatch. The poor dispersion of the masterbatch will lead to poor defects such as crystal points. For example, the surface treatment of the pigment used in the color masterbatch is unstable, and “agglomerate” during the processing of the masterbatch to form a “powder point”. The carrier resin of the masterbatch is poorly compatible with the film-forming raw material.

Method of reducing or eliminating crystal points

Knowing the reasons for the formation of the above crystal dots, it is easy to control them, and the following four methods are listed for you:

1. The raw material is selected from the purified resin to reduce the influence of the catalyst;

2. Increase the fineness of the filter in the film forming process, and change the filter screen (especially the old equipment) to facilitate the reduction of the crystal point;

3. Add an appropriate amount of antioxidants;

4. Add steel surface lubricants during the production process to reduce the viscosity of the polymer melt on the surface of the equipment.