4.1 In general, with materials of these types, softening point does not take place at a definite temperature. As the temperature rises, these materials gradually change from brittle or exceedingly thick and slow-flowing materials to softer and less viscous liquids. For this reason, the determination of the softening point must be made by a fixed, arbitrary, and closely defined method if the results obtained are to be comparable.
1.1 This test method covers the determination of softening point of resins using a Mettler cup and ball apparatus, and may, under user-defined conditions, give results comparable to those obtained by Test Methods E28.