Application of surface treatments on releasing adhesion force during thermoplastic polyurethane injection molding process

With injection molding process, thermoplastic polyurethane is generally used to fabricate shoes, boots, rollers and golf balls, etc. However, serious adhesion causes molded part difficult to be released from tool surface. To alleviate adhesion force during ejection stage, chromium-nitride (CrN) based and diamond like carbon (DLC) coatings prepared by physical vapor deposition were coated on mold cavity surface. Single layer CrN and modifying CrN coatings were found to be beneficial to alleviate adhesion force whereas multilayer CrN and DLC surface treatments were ineffective during continuous experiments. Further investigation found that single layer CrN and modifying CrN both had excellent water-repellency properties with low surface energy and exhibited the distinctive conical structure with uniform grain size. Although multilayer CrN coating exhibited similar morphology as that of single layer CrN coating, it showed significant variations in grain size and height. In contrary, although DLC coating adequately showed uniform topography, its larger grain size and wider valley between grains both lead to larger adhesion force due to mechanical anchoring. POLYM. ENG. SCI., 57:299–305, 2017.