1、The characteristics of "fisheye"
Fish eye "is essentially a small amount of PVC particles with ultra-high molecular weight generated during the polymerization process.
Due to its extremely low ability to absorb plasticizers, it can only be expanded by plasticizers under normal processing conditions and cannot be plasticized. However, a considerable portion of the "fish eyes" encountered during the processing belong to plasticized pseudo "fish eyes", which are linear structural resins with high molecular weight. Due to differences in resin molecular weight, low molecular weight PVC resin plasticizes faster while high molecular weight PVC resin plasticizes slower under the same processing conditions, resulting in false "fish eyes".
2、The influence of "fisheye" on the performance of processed products
The "fish eye" is a gel particle, which will affect the strength of the film, the insulation performance of the cable material, the sound quality of the record, etc.
Excessive "fish eyes" can make the surface of the product rough, reducing the physical properties of the entire product, mainly manifested in a decrease in the mechanical strength of the processed product. Meanwhile, "fish eyes" may also become the center of degradation, leading to product fading.
Excessive "fish eyes" in PVC resin can also make the processing technology difficult to control. Bubble breakage and breakage are prone to occur during the blown film process, and the uniformity of the film is also difficult to control. The produced film has the disadvantages of many surface spots and easy damage during use; Fish eyes exist in the form of opaque crystal dots in finished films or transparent sheets, which seriously affects the appearance and overall physical properties of the product.
3、Preventive measures
1. In actual production, the flushing situation of each kettle should be observed regularly, and the flushing time should be adjusted according to the specific situation. If necessary, manual cleaning should be carried out in a timely manner.
2. Ensure stable polymerization reaction temperature, which can concentrate the molecular weight distribution and reduce false "fish eyes".
3. Measure the pH value of the polymerization system and adjust it according to the actual situation, which can effectively reduce the occurrence of "fish eyes".
4. Strictly control the quality of monomers, especially their high boiling point content, to prevent the formation of "fish eyes" due to solubilizing particles.
5. Shortening reaction time and reducing polymerization conversion rate based on actual production conditions are effective ways to reduce "fish eyes".