Polyacrylate graft rubber copolymer B and an impact modified thermoplastic molding composition thereof, where the graft copolymer B is composed of: B1: 50 to 70 wt.-% crosslinked acrylate polymer graft base B1 B2: 30 to 50 wt.-% graft shell B2 comprising a first layer B21 of vinylaromatic monomers, and a second layer B22 of vinylaromatic monomers B21-1 and nitrile monomers B22-2: wherein the particle diameter dw of the graft base BI is 255 to 290 nm; the fraction of B21 is 10 to 26 wt.-%; and the amount of B22-2, is 20 to 30 wt.-%.