If Zinc stearate is too much, it will decomposen PVC or shown some black points. It will become to whiten zinc sulphide after absorbing sulfide in air  at  poor primary stainablity. It is not used independently for PVC products, but with any others.They are widely used as lubricants, slipping agents, heat-stabilizers, mould releasing agents and accelerants in plastic, machinery engineering, rubber, paints and inks industry etc.