MULTIMODAL POLYETHYLENE COMPOSITION, MIXED CATALYST AND PROCESS FOR PREPARING THE COMPOSITION

摘要

A multimodal polyethylene composition, in particular suitable for the preparation of films, but also textile articles, blow molded articles and injection molded articles is described. The polyethylene composition of the invention comprises at least three ethylene polymer fractions having distinct molecular weights or comonomer contents, said at least three ethylene polymer fractions comprising at least one first ethylene polymer fraction having a first molecular weight, a first comonomer content lower than a predetermined value and a first density; at least one second ethylene polymer fraction having a second molecular weight higher than said first molecular weight, a second comonomer content higher than said first comonomer content, and a second density; and at least one third ethylene polymer fraction having a third molecular weight higher than said first molecular weight, a third comonomer content lower than a predetermined value, and a third density; wherein said at least one first ethylene polymer fraction and said at least third ethylene polymer fraction are prepared by the use of a first and, respectively, third catalyst and said at least one second ethylene polymer fraction is prepared by the use of a second catalyst of the single site type. The films prepared from the composition of the invention have improved water vapor barrier properties. Furthermore, a mixed catalyst system comprising at least three catalyst components and a process particularly suitable to prepare the composition of the invention are described.