Polyethylene composition for injection molded caps and closure articles
AssigneeBorealis Technology Oy
InventorsKatrin Nord-Varhaug, Svein Staal Eggen, Hans Joerg Fell
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Abstract
The present invention relates to a multimodal polyethylene composition wherein (i) the composition has an MFR2 of 0.1 to 100 g/10 min, (ii) the shear thinning index SHI(1,100) and the log MFR2 of the composition satisfy the following relation: SHI(1,100)≧−10.58 log MFR2 [g/10 min]/(g/10 min)+12.94, and (iii) the composition has an environmental stress crack resistance ESCR of 10 h or more. Furthermore, the present invention relates to a process for the production of said composition, an injection moulded article, in particular a cap or closure, comprising said composition and to the use of said composition for the production of an injection moulded article.
Claims20
A polyethylene composition, wherein the composition has:
- (i) an MFR2, determined according to ISO 1133 at 190° C. and at a loading of 2.16 kg, of 0.1 to 100 g/10 min, and a spiral flow,
- (ii) the spiral flow and the MFR2 of the composition satisfy the following relation:
- Spiral flow(1000 bar) (cm)>2MFR2 (g/10 min)cm/(g/10 min)+41,
- (iii) an environmental stress crack resistance ESCR of 10 h or more, and
- (iv) a density of 930 kg/m3 or higher.
A process comprising the steps of:
- i) polymerizing ethylene monomers, and optionally one or more alpha-olefin comonomers, in the presence of a Ziegler-Natta catalyst to obtain a first ethylene homo- or copolymer fraction (A),
- ii) polymerizing ethylene monomers, and optionally one or more alpha-olefin comonomers, in the presence of a Ziegler-Natta catalyst to obtain a second ethylene homo- or copolymer fraction (B) having a higher average molecular weight than fraction (A),
- wherein the second polymerization step is carried out in the presence of the polymerization product of the first step, so as to form a polyethylene composition having:
- (i) an MFR2 of 0.1 to 100 g/10 min, determined according to ISO 1133 at 190° C. and at a loading of 2.16 kg, of 0.1 to 100 g/10 min, and a spiral flow,
- (ii) the spiral flow and the MFR2 of the composition satisfy the following relation:
- Spiral flow(1000 bar) (cm)≧2MFR2 (g/10 min)cm/(g/10 min)+41,
- (iii) an environmental stress crack resistance ESCR of 10 h or more, and
- (iv) a density of 930 kg/m3 or higher.
Dependencies are inferred from the claim text.