company news about Causes of calcium zinc stabilizer precipitation in PVC rigid products

Calcium Zinc stabilizer is widely used in the production and processing of PVC rigid products. Different precipitation

phenomena have been troubling the production personnel. The general precipitates are mouth mold precipitates, shape

mold precipitates, mandrel mold confluent core sticky mold precipitates, vacuum precipitates and so on.

There are two main aspects to analyze from the situation of precipitation:

1. Precipitation site:

Precipitate from the hot working parts: screw surface, die lip in the mouth die area, die core support or core die surface. Precipitation from the cold processing parts: mold mouth, mold inner surface vacuum seam, cooling water pollution.

2. Mechanism of precipitation:

When the organic solid components with low compatibility with PVC resin appear thermal degradation, the temperature and melting pressure will be transferred to the melt surface. Then adhere to the equipment, mold metal surface deposition. It can be divided into "hot compaction" and "cold condensation".

It can be seen from the above two points that the main factors affecting the material precipitation are the production pressure has changed, the temperature in the mold has changed, the composition of the production raw material and the degree has changed, the special material melt strength has changed.

Problem points of calcium and zinc stabilizer precipitation in the processing of PVC hard products:

1, the material is easier to hydrophilic and metalphilic substances.

2. The plasticizing time is faster.

3, the volatile content of the material is higher.

4, low melt strength, better mobility.

How can we reduce the occurrence of PVC hard product precipitation?

Choice of extruder:

1. The extruder models should match the products produced:

2, the use of high filling formula, should be equipped with high shear performance screw:

3, vacuum to improve the vacuum degree, reduce the volatile components of the material:

4. Effective heating and cooling system to prevent over-molding of materials in later stage:

Matching of extrusion mold:

1. Select the extrusion amount matching with the extruder:

2. Appropriate compression ratio of the split cone of the extrusion die head to reduce the expansion of the die:

3. The temperature setting of the mouth mold molding plate is appropriate:

4. Design of inlet grooving and temperature gradient of vacuum shaping section:

5. Design of auxiliary module for a section of vacuum shaping mold:

Processing technology control:

1. Reasonable mixing process temperature setting to adapt to seasonal temperature changes:

2. Grasp the curing time of dry mixture;

3, mixing pot exhaust unobstructed:

4. Set reasonable extrusion process temperature to avoid high process temperature:

5, avoid setting the mold melting pressure gradient changes greatly:

Compatibility of calcium Zinc stabilizer components with resin:

1, ordinary calcium stearate with more easy to spray frost at the same time with zinc stearate, PVC resin between the phase melting is not too good. The organic stabilizer added to the components of calcium and zinc stabilizer is more likely to precipitate to form calcium and zinc salts.

2. Tetrascitriol can inhibit zinc burning, but it is easy to migrate due to its small molecular weight. The whiskers were modified and used after esterification.

3. The compatibility between wax and PVC with various external lubricants is poor, and the possibility of precipitation is greater.