The mechanism of action of external lubricants

2022-03-10   Pageview:276

The properties of thermoplastic polymers and other substances at the contact interface are determined by external lubrication. For example, in the adhesion of plastic melt to the hot metal surface, the external lubricant has a demoulding effect; it plays a wetting and dispersing role when the plastic is mixed and dispersed with pigments and fillers.

1. Mold release

In many engineering thermoplastics, montan wax, oxidized PE wax, pentaerythritol tetrastearic acid and long chain alkane sulfonate are commonly used as lubricants. Plastic PVC needs stearic acid; hard PVC needs montanic acid derivatives, that is, oligomeric fatty acid esters are not sensitive to exudation. In the processing, oxidized PE wax with strong release effect is used, and PVC is used with medium oxidation degree PE wax.

2. Reduce friction

Reduce dynamic friction between melt and processing equipment

Paraffin wax and mineral hydrocarbon wax will form a lubricating layer between the PVC solution and metal processing equipment, resulting in good lubricity; high-melting synthetic paraffin wax can slow down plasticization very well, but it is difficult to accurately content; Oxidized low-molecular-weight PE wax can finely adjust the formula; polar plastics have poor compatibility with lubricants, which can easily lead to turbidity, and are limited to opaque formulations.

3. Prevent melt fracture

High viscosity at high shear rates causes a common surface phenomenon of “melt fracture”; produced by vibrational changes between sticking and sliding, especially in the processing of LLDPE; lubricants can address this. question. Such as thermoplastic fluoroelastomers, it will significantly reduce the relative viscosity/relative shear between LDPE and LLDPE, avoiding the “shark skin” phenomenon of surface irregularities in blown film.

4. Influence on the surface of the finished product

Lubricants change the surface properties of plastic products, such as flatness and gloss, due to their surface effects. At the same time lubricant accumulation on the surface also has a detrimental effect. Release action, slip action, anti-blocking action and anti-slip action.

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