PVC foamed products - unbalanced characterization of various auxiliaries (Ⅱ)
3. Internal lubricant
The commonly used inner lubricants include stearic acid, 60, monoglyceride, 316, etc.
Insufficient internal lubrication, poor dispersion of materials, uneven plasticization, difficult to control the thickness of products, foam board in the middle of the thick on both sides of the thin, may also appear white belt, and cavity adhesion and local overheating and other phenomena;
Too much internal lubrication, foam products brittle, heat resistance decline, and under a certain temperature and pressure melting effect into external lubrication, resulting in lubrication imbalance;
Lack of internal and external lubrication, melt viscosity is large, plasticizing torque is large, melt wall adhesion phenomenon is serious, the material surface has yellow decomposition line, the surface smoothness is poor, mechanical properties of products reduced;
Internal and external lubrication are excessive, plasticizing torque is small, melt plasticization is obviously insufficient, although the smoothness of products but pressure point adhesion is poor, serious impact on the mechanical properties of products;
Less internal lubrication, more external lubrication, significantly extend the plasticizing time, reduce the plasticizing torque, product molding difficulties, brittle;
More internal lubrication, less external lubrication, plasticizing time significantly shortened, there are more serious wall adhesion phenomenon, thermal stability time shortened, the surface of products have yellow line decomposition;
4, calcium powder
Foaming products generally choose about 1200 mesh of light calcium is appropriate, calcium powder is easy to absorb moisture and form bubbles on the surface of products, such as silver grain, affect the appearance and physical properties, so pay attention to the rainy season storage.
When the particle size of calcium carbonate is too large, it is easy to mix unevenly, the plasticizing time of the mixture is delayed, and the screw torque is low.
When the particle size of calcium carbonate is too small, agglomeration is likely to occur, which changes from small particles to large ones, similar to the consequence of too large particles.
When the dosage of calcium carbonate is too low, the number of foam holes decreases and the foaming rate decreases.
When the dosage of calcium carbonate is too much, the relative content of resin in the component decreases, the melt strength decreases, and the fracture of the plate is easy to appear.