Polyolefin Composition Tiger Stripe Reduction
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Solution Overview
Problem
Polypropylene-based materials used in automotive applications often suffer from 'tiger stripes,' which are color and gloss variations due to talc fillers, compromising optical surface properties, and existing solutions fail to balance mechanical properties, melt flow rate, and cost effectively.
Innovation Solution
A polyolefin composition comprising a first and second heterophasic propylene copolymer with specific melt flow indices and ethylene content, combined with an inorganic filler, to enhance mechanical properties and reduce tiger stripes while maintaining cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If talc filler is added to polypropylene-based materials to achieve low CLTE and desired mechanical properties, then mechanical strength and thermal stability are improved, but optical surface properties deteriorate and tiger stripes increase
Solution Approach 1:
The patent changes the chemical composition parameters of the rubber phase by incorporating specific aromatic compounds (ethylbenzene, propylbenzene, butylbenzene) in controlled amounts (0.1-5.0 wt% each) within the heterophasic polypropylene copolymer structure. This compositional modification alters the rheological behavior of the molten polymer, reducing its sensitivity to filler additions and thereby suppressing tiger stripe formation while maintaining mechanical strength and low CLTE properties.
2Strength
If heterophasic polypropylene copolymer with rubber phase is used to improve impact strength, then impact resistance is enhanced, but tiger stripe formation increases due to unstable mold filling properties
Solution Approach 1:
The patent creates a heterogeneous structure within the rubber phase by locally incorporating aromatic compounds (ethylbenzene, propylbenzene, butylbenzene) at specific concentrations (0.1-5.0 wt% each) within the heterophasic polypropylene copolymer. This local compositional variation modifies the rheological properties in the rubber phase regions, stabilizing mold filling behavior and reducing tiger stripe formation while preserving the impact strength enhancement provided by the rubber phase.
3Object-affected harmful factors
If masterbatch diluted with additional polyolefins is used to reduce tiger stripes, then optical surface properties are improved, but mechanical properties and cost-effectiveness deteriorate
Solution Approach 1:
The patent incorporates the aromatic compounds (ethylbenzene, propylbenzene, butylbenzene) directly into the heterophasic polypropylene copolymer structure during the polymerization process, before the material is processed into final products. This preliminary incorporation ensures that the rubber phase already possesses the modified rheological properties needed to suppress tiger stripes, eliminating the need for subsequent masterbatch dilution and preserving both mechanical properties and cost-effectiveness.
Data Source
Figure 1~3
AI summary
The present invention relates to a polyolefin composition comprising a first heterophasic propylene copolymer and a second heterophasic propylene copolymer, wherein the first heterophasic propylene copolymer comprises: from 70 - 90 wt% of a first polypropylene having a melt flow index of from 55 - 85 g/10 min as measured according to ISO 1133 (2.16 kg and 230°C), from 10 - 30 wt% of a first ethylene α-olefin copolymer having a melt flow index of from 2.5 - 5.0 g/10min in accordance with ISO 1133 (2,16kg and 230°C), the respective amounts of first polypropylene and first ethylene α-olefin copolymer being based on the weight of the first heterophasic propylene copolymer and wherein the second heterophasic propylene copolymer comprises: from 60 - 85 wt% of a second polypropylene having a melt flow index of from 50 - 100 g/10 min as measured according to ISO 1133 (2,16 kg, 230°C), from 15 - 40 wt% of a second ethylene α-olefin copolymer having a melt flow index of from 0.050 - 0.30 g/1 Omin in accordance with ISO 1133 (2,16kg and 230°C), the respective amounts of second polypropylene and second ethylene α-olefin copolymer being based on the weight of the second heterophasic propylene copolymer, and wherein a weight ratio of said first and second heterophasic propylene copolymer is from 1 to 10. The invention further relates to automotive parts comprising said composition and having good tiger stripe performance.