In injection molding, the ejection forces decrease when the surface roughne
ss of mold decreases. However, the election forces increase contrary in the
area of surface roughness is less than 0.2 mu mRa. Several kinds of PVD fi
lms are coated on the mold cores to prevent the increasing of ejection farc
es. Some of these PVD films showed effective prevention of increasing of ej
ection forces.