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How to control the ;’fish eye' phenomenon of PVC resin
- Aug 27, 2018 -

1. Characteristics of [fish eye]

Fisheye is essentially a small amount of PVC particles with special high molecular weight generated during polymerization.

Because of its very low ability to absorb plasticizers, it can only be swelled by plasticizers under normal processing conditions and can not be plasticized. However, a considerable part of the fisheye encountered in the processing process belongs to the plastic pseudo-fisheye, which is a linear structural resin with high molecular weight. Due to the difference of molecular weight of the resin, the plasticization of low molecular weight PVC resin is faster than that of high molecular weight PVC resin under the same processing conditions, resulting in false fish eye.

Two. Effect of fisheye on the properties of processed products

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

Too much fish eye will roughen the surface of the product and reduce the physical properties of the whole product, mainly in the mechanical strength of the processed products. At the same time, [fish eye] may also become the center of degradation, resulting in product fading.

Too much fish-eye in PVC resin will make the processing technology difficult to control. It is easy to break and break bubbles in the process of blowing film. The uniformity of the film is also difficult to control. The film produced has many surface spots and is easy to break in use. In the finished film or transparent sheet, "fish-eye" is opaque. The existence of crystal dots seriously affects the appearance and overall physical properties of products.

Three, preventive measures

1. In the actual production, the flushing situation of each kettle is observed regularly, and the flushing time is adjusted according to the specific situation. If necessary, the kettle should be cleaned up manually in time.

2. Ensure that the polymerization temperature is stable, so that the molecular weight distribution can be concentrated and the pseudo-fish eye can be reduced.

3. Determine the pH value of the polymerization system, and adjust it according to the actual situation, which can effectively reduce the production of fish eye.

4. Strictly control the monomer quality, especially its high boiling content, to prevent solubilized particles from producing fish eyes.

5. It is an effective way to shorten the reaction time and reduce the polymerization conversion rate according to the actual production situation.