Bimodal polypropylene random copolymer with improved gamma-irradiation resistance
The present invention relates to bimodal polypropylene random copolymers comprising ethylene as comonomer and articles made thereof, having an improved resistance against γ-irradiation and are especially suitable for application in the medical, pharmaceutical or diagnostic field.
1. A bimodal polypropylene random copolymer, comprising:
a) 24.95-55.0 wt. % of a first polypropylene fraction being a propylene homopolymer,
b) 44.95-75.0 wt. % of a second polypropylene fraction being a random copolymer of propylene and ethylene as comonomer, comprising 4.0-10.0 wt. % of comonomer, and
c) 0.05-0.5 wt. % of a soluble nucleating agent, the soluble nucleating agent being selected from the group consisting of sorbitol based nucleating agents, nonitol based nucleating agents, and benzene-trisamides,
wherein the bimodal polypropylene random copolymer comprises a total comonomer content of 3.0-7.0 wt. % and 5.0-15.0 wt. % of a fraction soluble in cold xylene (XCS),
wherein the bimodal polypropylene random copolymer is polymerized in the presence of a metallocene catalyst,
wherein the bimodal polypropylene random copolymer has a molecular weight distribution MWD of 2.4 to 3.6,
wherein the bimodal polypropylene random copolymer has a König B parameter of 0.50 to 1.20, and
wherein the bimodal polypropylene random copolymer has a first melting temperature (Tm1) in the range of 145 to 155° C. and a second melting temperature (Tm2) in the range of 110 to 137° C.
2. The bimodal polypropylene random copolymer according to claim 1 , wherein the bimodal polypropylene random copolymer has a Melt Flow Rate determined according to ISO1133 at 230° C. and 2.16 kg (MFR230/2.16) of 1.0-70.0 g/10 min.
3. The bimodal polypropylene random copolymer according to claim 1 , wherein the bimodal polypropylene random copolymer has a Haze of at most 20.0% when measured according to ASTM D1003 on 1 mm injection moulded plaques.
4. The bimodal polypropylene random copolymer according to claim 1 , wherein the bimodal polypropylene random copolymer has a retained notched Impact Strength rNIS after irradiation with 50 kGy (rNIS (50; days) ) according a formula
rNIS
(
5
0
;
days
)
[
%
]
=
γ
NIS
(
5
0
;
days
)
*
1
0
0
NIS
(
0
;
days
)
of at least 90.0%, wherein “days” is heat exposure at 80° C. for 60 days.
5. The bimodal polypropylene random copolymer according to claim 1 , wherein the soluble nucleating agent is selected from the group consisting of sorbitol based nucleating agents and nonitol based nucleating agents.
6. A moulded article comprising the bimodal polypropylene random copolymer according to claim 1 .
7. The moulded article according to claim 6 , wherein the moulded article is a medical, pharmaceutical or diagnostic article.