What is the cause of the fisheye of PVC resin?

There are many ways to form fisheyes. For example, the molecular weight distribution of PVC is too wide, which results in low molecular weight plasticization under the same processing conditions, while molecules with high molecular weight are slow to plasticize. If the processing conditions are certain, the plasticized slow polymer will appear in the case of fake fish eyes in the product.

Improper distribution of the initiator will cause the concentration of the initiator in the polymerization system to be too high, causing the local reaction of the polymerization system to be too fast, and the heat is difficult to be transmitted in time, resulting in local overheating to form fish eyes. Inappropriate choice of initiator, easy to lead to PVC cross-linking, the formation of permanent "fish eye", the initiator is not properly matched, due to the difference in reaction temperature before and after, easy to form a temporary fish eye.

If the stirring speed is too slow, the particles are unevenly dispersed and easily opened. However, the stirring speed is too fast, and the oil droplets formed by the stirring shearing slightly rupture the film to cause the particles to be granulated. In both cases, large particles are prone to occur, forming a temporary fisheye.Ethylene-Vinyl Acetate, The pH of the polymerization system is generally controlled between 7.0 and 8.5. The poor quality of the desalted water forms the water in the fish eye containing salt. The ions will destroy the dispersant and form the fisheye.

The presence of impurities in vcm, such as the presence of high-boiling chlorinated hydrocarbons in vcm, not only affects the pvc molecular link structure, but also has a strong dissolution effect on pvc, and reduces the porosity of the particles to form a tighter spherical shape. Particles. Such granules are difficult to plasticize during processing and plasticization to form fish eyes. Sodium Hexametaphosphate ,Under normal circumstances, the conversion rate of vcm is greater than 15%, and the condenser is used later. If it is used in advance, the formation of pvc particles is unstable and the adhesion is strong, which will cause impact on the formation of the polymerization system and easily generate large particles. Fisheye.

In the production of ultra-low molecular weight pvc resin, in order to reduce the reaction temperature, it is necessary to add a chain transfer agent, but some chain transfer agents can reduce the protection of the dispersant and may lead to the formation of fish eyes.