US Patent 7133209 Transparent molding composition for optical applications

A molding composition which is composed of at least 60% by weight of transparent polyamide, where the molding composition comprises an effective amount of one or more optical brighteners, and where the amount of the optical brightener has been judged in such a way thata) the b value, which is a measure of yellowness, is at most 7, and moreoverb) between 370 and 430 nm, at least in a lower part of the range, the transmittance is smaller than 1%, measured at a layer thickness of 4 mm,can be processed to give products which are substantially impermeable to UV light.