Abstract: A catalyst composition comprising a bis-amide compound represented by the formula ##STR1## wherein M is zirconium, hafnium or titanium; each N is a three coordinate nitrogen atom; each e is Si, Ge or Sn; each Z is, independently, a hydride or R; each R is, independently, a hydrocarbyl one or more carbon atoms of which may be substituted by an element selected from Si, O, P, N and S; L is a neutral Lewis base and m is a number from 0 to 2; or a dimer thereof and a second component. Preferably the second component is a compound which is capable of providing a bulky and labile anion ?A!.sup.-, which anion is substantially non-coordinating under the reaction conditions and contains at least one boron atom. Also provided is a process for oligomerizing or co-oligomerizing alpha olefins in the presence of this catalyst composition.

Abstract: The invention relates to screen printing apparatus which comprises a printing station, means for feeding a web of material to be printed to the printing station and away therefrom, a squeegee mounted at the printing station for cooperation with a screen printing mesh, means for attaching a screen printing mesh tensioned on a frame so that part of the mesh is at the printing station, means for reciprocating such a screen printing mesh in a frame through the printing station, means for feeding ink to one side of the squeegee, a profiled support at the printing station for supporting the material to be printed, and means for advancing the screen mesh in a frame and the material to be printed at the same speed past the printing station while biasing the screen mesh by means of the squeegee towards the support. According to the invention the profiled support is movable in order to compensate for changes in the shape of the screen mesh during the printing stroke.