Polypropylene Battery Case Composition for Stress Whitening Resistance
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Solution Overview
Problem
Current polypropylene compositions used in battery cases lack sufficient stiffness and stress whitening resistance, necessitating an improvement in these properties for enhanced performance.
Innovation Solution
A polymer composition comprising polypropylene, a first copolymer of ethylene and α-olefin with a density of 0.891 to 0.912 g/cm3, and a second copolymer of ethylene and α-olefin with a density of 0.859 to 0.881 g/cm3, with a polypropylene content of 71 to 87 wt% and a ratio of the second copolymer to the first copolymer between 3.8 to 1.0, which is produced using a Ziegler-Natta catalyst and processed through sequential polymerization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polypropylene composition is used for battery case, then it provides basic structural properties, but stiffness and stress whitening resistance are insufficient
Solution Approach 1:
The patent applies composite materials by combining polypropylene with a specific ratio of ethylene-α-olefin copolymers (first and second copolymers with different densities). This multi-component polymer composition creates a composite material system where each component contributes different properties: polypropylene provides stiffness while the copolymers improve stress whitening resistance, achieving both desired properties simultaneously
Solution Approach 2:
The patent employs parameter changes by precisely controlling the density parameters of the copolymers (first copolymer: 0.891-0.912 g/cm³, second copolymer: 0.859-0.881 g/cm³) and their ratio (3.8 to 1.0). By adjusting these physical parameters within specific ranges, the composition achieves optimal balance between stiffness and stress whitening resistance
2Strength
If polypropylene content is increased to improve stiffness, then flexural strength increases, but stress whitening resistance deteriorates
Solution Approach 1:
The patent applies local quality by introducing copolymers with specific local characteristics (different densities and compositions) into the polypropylene matrix. The first copolymer (higher density) and second copolymer (lower density) provide localized modifications to the polymer structure, enabling different regions of the material to contribute differently to overall performance - maintaining stiffness while resisting stress whitening
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition achieves superior stiffness with a flexural strength of at least 30.0 MPa and improved stress whitening resistance, making it suitable for battery case applications.
Implementation Method 1
produced using a Ziegler-Natta catalyst and processed through sequential polymerization
Data Source
AI summary
A polypropylene composition includes (A) a polypropylene, (B1) a first copolymer of ethylene and α-olefin having a density of 0.891 to 0.912 g/cm3, and (B2) a second copolymer of ethylene and α-olefin having a density in the range of 0.859 to 0.881 g/cm3, wherein the amount of (A) the polypropylene is in the range from 71 to 87 wt % based on the total amount of the polymer composition, and wherein the ratio between the amount of the (B2) second copolymer of ethylene and α-olefin and the amount of the (B1) first copolymer of ethylene and α-olefin is in the range from 3.8 to 1.0. The polypropylene composition has improved stress whitening resistance. A battery case including the polypropylene composition is also disclosed.