Polycarbonates (PC) are synthetic thermoplastic resins derived from bisphenols and phosgenes, or their derivatives. They are linear polyesters of carbonic acid and can be formed from dihydroxy compounds and carbonate diesters, or by ester interchange. Polymerization may be in aqueous, interfacial, or in nonaqueous solution. Polycarbonates are a useful class of polymers having many desired properties. They are highly regarded for optical clarity and enhanced impact resistance and ductility at room temperature or below.
Impact modifiers are incorporated into polymeric resins to improve the impact strength of finished articles made from such resins. Exemplary impact modifiers include acrylonitrile-butadiene-styrene (ABS) and methacrylate-butadiene-styrene (MBS) polymers. ABS and MBS polymers are synthetic thermoplastic resins made by polymerizing acrylonitrile or methacrylate, respectively, with styrene in the presence of polybutadiene. The properties of ABS and MBS can be modified by varying the relative proportions of the basic components, the degree of grafting, the molecular weight, etc. Overall, ABS and MBS are generally strong, and lightweight thermoplastics.
Flame retardant (FR) polycarbonate/acrylonitrile-butadiene-styrene blends are used in a variety of applications such as computer and business equipment, battery chargers, industrial housings, etc. These amorphous thermoplastic blends have many desired properties and/or characteristics, including high impact strength, heat resistance, good processability, weather and ozone resistance, good ductility, electrical resistance, aesthetic characteristics, etc. However, when making thin-walled parts, it is generally beneficial to provide a flow promoter to lower the melt viscosity and better enable the composition to be formed into a thin-walled part using a molding process. For non-flame retardant compositions, the use of a flow promoter is not problematic. However, as many flow promoters can themselves be flammable, their use in flame retardant compositions has been limited.
Accordingly, it would be beneficial to provide a flame retardant polycarbonate resin composition that includes flow promoters to help produce thin-walled parts but that does not have the issues associated with flame retardance and/or impact properties. It would also be beneficial to provide a flame retardant polycarbonate resin composition that has improved physical properties, such as heat deflection temperature, modulus and/or impact strength, despite the inclusion of a flow promoter.