The application of Low Shrinkage Additive (LSA) and Low Profile Additive (LPA) is the key element supporting the fast development of SMC industry, reducing the previous shrink percentage form 5-8% to 0.
Presently the main LSA/LPA agents are: PS, PE (0.1-0.3% shrinkage) and PMMA (0.05%). The new product PVAC can reduce the shrinkage to 0 and even minus shrinkage.
The anti-shrinkage theory: When UP and PS are under polymerization, the LPA make up the position to be shrinked during caring.
Comparison of Bending&pulling strength with LSA/LPA influece in SMC.
LSA/LPA None PS PMMA PVAC
P.strength/mpa 96.5 74.8 72.9 62.5
B.Strength/mpa 180.2 167.3 166.0 159.2
Best Rate of PVAC in UP as LSA/LPA:
P. Strength 20-39%，（The less The better）
B. Strength 20-38%，（The less the better）
The best rate of PVAC's anti-shrinkage is 12-16%. I.E. 40% PVAC dissolves in 60% PS. The even liquid will take 30-40% in the final mixture (UP, FRP, Fillings, liquids etc).
