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How to control the 'fish eye'phenomenon of PVC resin
- Nov 05, 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 low ability to absorb plasticizers, it can only be swelled by plasticizers under normal processing conditions, but can not be plasticized. However, a considerable portion of the fish eyes encountered during processing belong to plasticized pseudo-fish eyes, which are linear structural resins with high molecular weight. Due to the difference of molecular weight of 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 eye.

Two. Effect of fisheye on the properties of processed products

Fisheye is a gel particle, which affects the strength of the film, the insulation property of the cable material, and the sound quality of the disc.

[Fisheye] Too much will make the surface of the product rough 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 also make the processing process difficult to control, bubble breakage and uniformity of the film are difficult to control in the process of blowing film. The film produced has many defects such as surface spots and easy to be damaged in use; the fish eye in the finished film or transparent sheet is opaque. The existence of crystal dots seriously affects the appearance and overall physical properties of products.

Three, preventive measures

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

2. Ensure that the temperature of the polymerization is stable, so that the distribution of molecular weight can be concentrated and the false fisheye can be reduced.

3. Measuring the pH value of the polymerization system and adjusting it according to the actual situation can effectively reduce the production of fish eye.

4. Strictly control the mass of monomers, especially the content of high boiling substances, in order to prevent the formation of fish eyes by solubilizing particles.

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