The class of hollow glass microspheres selected for a masterbatch depends on the end use of the TPO component. For example, the pressures involved in TPO molding require hollow glass microspheres with elevated crush strength. Hollow glass microspheres strength is generally proportional to density, and thus lower-strength bubbles are less dense, and offer greater potential for TPO weight reduction than thicker-walled, higher-strength bubbles.
Hollow glass microspheres size impacts TPO surface finish as well as stress transmission through the composite, with smaller bubbles contributing to more favorable impact and tensile properties. In general, higher-strength bubbles are required for injected molded interior and exterior automotive components, and other industrial components.
The modulus (stiffness) of a part also increases in proportion to the ratio of hollow glass microspheres to resin. The positive attributes of increased stiffness and heat distortion temperature (HDT) as well as decreasing coefficient of linear thermal expansion (CLTE), shrink, warp, and sink marks continue to improve as the percentage of hollow glass microspheres in the resin mix rises. Tensile strength, elongation, and impact strength tend to decrease as well. Complementary additives in the masterbatch can modify these values to some degree.
In general, plastics are flexible and experience ductile failure under stress, while glass adds stiffness but is more prone to brittle breakage, It is possible to improve TPO impact strength by adding an impact modifier to the masterbatch that reduces potential for brittle failure while maintaining the stiffness advantage.
The concentration of hollow glass microspheres in a masterbatch additive mix varies, but can be as much as 50% by weight, depending on customer requirements. Finished parts made using this masterbatch hollow glass microsphere concentration will be 20% or more lighter than resin-only parts.
Process tests show that a Noble masterbatch formulation with hollow glass microspheres can cut TPO injection molding production time as much as 20%. This benefit is apparently related to changes in thermal properties that result from displacing resin with hollow glass (reduced mass), and the resulting time savings are concentrated primarily during the cooling period.”
This article comes from plasticstoday edit released
