A propylene copolymer composition comprising A) a propylene butylene copolymer which is—free of phthalicacid esters as well as decomposition products thereof; —obtained by a Ziegler-Natta catalyst and B) at least one α-nucleating agent, the propylene copolymer composition having—a MFR (2.16 kg/210° C.) in the range of 2 to 100 g/10 min—a melting point Tm(1) of less than 140° C.—a melting point Tm(2) of at least 150° C., said Tm(2) being associated with more than 75% of the total melting enthalpy and whereby the propylene copolymer—has monomer units derived from a) propylene in an amount of 90.0-98.0 mol.-% b) butylene in an amount of 2.0-10.0 mol.-% with respect to the total weight of the propylene butylene copolymer—an isotacticity mm % as determined by 13C NMR spectroscopy of below 99.0%; and—a Koenig-B parameter with respect to butylene as determined by 13C NMR spectroscopy of more than 0.98.