Common processing problems and solutions of PVC heat stabilizers

Common processing problems and solutions of PVC heat stabilizers

【Introduction】

PVC heat stabilizers are key additives to ensure the processing performance and service life of polyvinyl chloride (PVC), but in the actual production process, problems such as insufficient thermal stability, precipitation, and poor compatibility are often encountered, which affect product quality and production efficiency. This article sorts out the common processing problems of PVC heat stabilizers and their countermeasures.

1. Insufficient thermal stability leads to decomposition and discoloration of PVC

Problem manifestation:

Yellowing and black spots appear on PVC during processing

Stripes or fog defects appear on the surface of the product

Decrease in mechanical strength, affecting service life

Main reasons:

Insufficient amount of heat stabilizer added or low efficiency

Processing temperature is too high, exceeding the tolerance range of the stabilizer

Lubricants or other additives in the formula affect the effect of the stabilizer

Solution:

✔ Optimize the amount of stabilizer and select high-efficiency composite stabilizers (such as calcium zinc, organic tin, etc.)

✔ Strictly control the processing temperature (such as the extruder temperature does not exceed 200℃)

✔ Adjust the formula to avoid reaction with acidic or oxidizing additives

2. Stabilizer precipitation (frosting, scaling)

Problem manifestation:

White powder appears on the surface of the product (frosting)

Scaling is deposited on the mold or screw, affecting production efficiency

Main reasons:

Poor compatibility between stabilizer and PVC

Excessive use of low molecular weight stabilizers (such as stearates)

Large temperature fluctuations during processing

Solution:

✔ Select high molecular weight or surface treated stabilizers (such as modified calcium zinc stabilizers)

✔ Optimize the formula and reduce the amount of stearic acid lubricants

✔ Keep the processing temperature stable to avoid local overheating

3. Lubricity imbalance affects processing fluidity

Problem manifestation:

Unstable melt viscosity, difficult extrusion or injection molding

Uneven gloss on the surface of the product, flow marks

Main reasons:

The lubricity of the stabilizer itself is insufficient or too strong

Poor synergy with internal and external lubricants

Solution:

✔ Select stabilizers with appropriate lubrication properties (such as some organic tin stabilizers with inherent lubricity)

✔ Adjust the ratio of internal and external lubricants to ensure balanced melt flow

4. Environmentally friendly stabilizers have a narrow processing window

Problem manifestation:

Environmentally friendly stabilizers such as calcium zinc are sensitive to temperature and are prone to decomposition

The processing technology has a low tolerance rate and a decrease in the yield rate

Main reasons:

The thermal stability efficiency of environmentally friendly stabilizers (such as calcium zinc) is usually lower than that of lead salts

Weak adaptability to shear force and temperature changes

Solution:

✔ Use compounding technology (such as calcium zinc + β-diketone auxiliary stabilizer)

✔ Optimize screw combination and processing parameters to reduce shear heat

✔ Introduce processing aids (such as acrylates) to broaden the processing window

V. Interaction with pigments or fillers causes color difference

Problem manifestation:

Product color deviation, especially light-colored or transparent products

Color changes after long-term use

Main reasons:

Metal ions (such as zinc) in stabilizers react with sulfide pigments

Fillers (such as calcium carbonate) adsorb stabilizer components

Solutions:

✔ Choose non-reactive stabilizers (such as organotin or rare earth stabilizers)

✔ Surface treat fillers to reduce adsorption

✔ Add chelating agents (such as phosphites) to inhibit metal ion activity