Random Copolymer Polypropylene (RCPP) is a polypropylene copolymer containing a small (2-6% w) amount of ethylene. RCPP is used for applications that require improved clarity over homopolymer polypropylene. For example, the properties of RCPPs make them attractive for use in the manufacture of food containers for refrigerator and freezer use. However, RCPP, like homopolymer polypropylene, has a low impact strength, which leads to whitening under minor impact events, a phenomenon commonly known as blushing or hazing. The tendency towards blushing makes RCPPs unattractive for certain uses, such as food containers.
In U.S. Pat. No. 4,904,731, which disclosure is incorporated herein by reference, it was found that a hydrogenated block copolymer comprising at least two polymeric blocks containing predominately monoalkenyl aromatic hydrocarbon monomer units and at least one block containing a predominately hydrogenated, conjugated diene unit, or a blend of the hydrogenated block copolymer and linear low density polyethylene (LLDPE) can be combined with the RCPP to improve impact resistance and clarity. However, impact related hazing problems are still seen in this polymer when it is are used at low temperature. Therefore, even greater impact resistance and clarity, particularly at low temperatures, would be very desirable.
USPTO Backgrounds
USPTO Backgrounds