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How to control the fisheye phenomenon of PVC resin

Jun 01, 2020

1. Features of "Fisheye"

"Fisheye" is essentially a small amount of PVC particles with high molecular weight produced during the polymerization process.

Due to its extremely low ability to absorb plasticizers, it can only be swelled by plasticizers under normal processing conditions and cannot be plasticized. However, a considerable part of the "fisheyes" encountered during processing are plasticized pseudo- "fisheyes". Such pseudo- "fisheyes" are linear structural resins with high molecular weight. Due to the difference in resin molecular mass, under the same processing technology conditions, the low molecular weight PVC resin plasticizes quickly, while the high molecular weight PVC resin plasticizes slowly, resulting in a false "fish eye".

2. the effect of "fisheye" on the performance of processed products

"Fisheye" is a gel particle, which affects the strength of the film, the insulation performance of the cable material, and the sound quality of the record.

Excessive "fish eyes" will make the surface of the product rough, reducing the physical properties of the entire product, mainly due to the decrease in the mechanical strength of the processed product. At the same time, "fish eyes" may also become the center of degradation, causing the product to fade.

Too much "fisheye" in PVC resin also makes the processing process more difficult to control, and it is easy to break or break bubbles during the blown film process. The uniformity of the film is also difficult to control. There are many shortcomings that are easy to break in use; "fish eyes" in the finished film or transparent sheet exist in the form of opaque crystal dots, which seriously affects the appearance and overall physical properties of the product.

3. Preventive measures

(1). In actual production, regularly observe the flushing situation of each kettle, and adjust the flushing time according to the specific situation. If necessary, it should be cleaned up manually in time.

(2). Make sure the temperature of the polymerization reaction is stable, so that the molecular mass distribution can be concentrated, and false "fish eyes" can be reduced.

(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 the monomer, especially its high boiler content, in order to prevent the solubilized particles from producing "fish eyes".

(5).Shortening the reaction time according to the actual production situation and reducing the polymerization conversion rate is an effective way to reduce "fish eyes".