Reaction Measurement of Unsaturated Polyester Solutions Used in Sheet Molding Compounds with Magnesium Oxide: Viscometry vs. Chemorheometry

摘要

It is understood by most Sheet Molding Compound (SMC) producers that not all grades of magnesium oxide thicken a polyester resin equally. Of the grades that can thicken, many will rarely thicken an SMC paste at the same rate on a lot-to-lot basis. This variation directly impacts a suppliers' production control plan, and more importantly, it delays the time of delivery to customers. Of significant importance, this variation can adversely affect the quality and reliability of molded SMC parts. To avoid this problem, the industry typically uses a two-day room temperature thickening test to approximate production performance. The two-day delay requires the thickener dispersion producer to hold the work in progress in queue for up to a week. This quality approval step provides a critical value-add to consumers, but from the producers perspective, it represents special handling and a potential "missed ship date". To address the delay between the manufacturing and shipment of magnesium oxide/hydroxide dispersions, Plasticolors employs the use of a novel, scientifically developed test method called chemorheometry. Chemorheometry shortens the previous two-day predictive test into a twenty-five minute quality control method. Key to this innovation is a laboratory instrument known as a rheometer. A more advanced analytical instrument than the currently used viscometer. Rheometers measure fluid flow across a series of stress and strain restraints, not a single point measurement as common with viscometers. The instrument's output is a quantifiable evaluation of fluid flow for the thickened resin mixture. The paper explains the benefits of the method.