Impact Modified Polypropylene Containers Low Temperature Clarity
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Solution Overview
Problem
Current polypropylene-based materials for low-temperature freezer containers face challenges in achieving both high clarity and impact resistance, as they often suffer from poor impact properties and clarity at sub-ambient temperatures due to polypropylene's high glass transition temperature and the limitations of impact-modified copolymers.
Innovation Solution
A composition comprising 10-40 wt% of a modifier, including a block composite, a first polyolefin copolymer derived from ethylene and alpha-olefins, and optionally a second polyolefin copolymer, blended with 60-90 wt% of a propylene polymer base, which enhances toughness and clarity by improving elastomer dispersion and morphology stabilization in polypropylene matrices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If polypropylene-based homopolymers or copolymers are used to achieve high clarity, then clarity is improved, but impact properties at low temperatures deteriorate due to polypropylene's high Tg
Solution Approach 1:
The patent applies composite materials by combining polypropylene base polymer with specific elastomeric modifiers (ethylene-alpha olefin copolymers with 30-70 mol% ethylene content). This composite approach allows the material to achieve both high clarity (greater than 90%) and improved impact properties at low temperatures, resolving the contradiction between clarity and impact resistance that plagues pure polypropylene systems.
2Strength
If impact-modified copolymers are used to improve impact properties, then impact resistance is improved, but clarity and modulus deteriorate in comparison to homopolymers and random copolymers
Solution Approach 1:
The patent applies parameter changes by precisely controlling the ethylene content (30-70 mol%) and comonomer composition of the elastomeric modifier to optimize both impact resistance and clarity. Additionally, the patent controls the concentration of the elastomeric modifier (10-40 wt%) in the polypropylene matrix to achieve the optimal balance between impact properties and optical clarity, resolving the contradiction between impact resistance and clarity.
3Strength
If elastomeric modifiers are added to polypropylene to improve toughness, then impact properties are improved, but clarity deteriorates due to light scattering from rubber domains
Solution Approach 1:
The patent applies local quality by ensuring uniform dispersion of the elastomeric modifier throughout the polypropylene matrix, creating localized rubber domains that provide impact resistance without causing significant light scattering. The specific composition of the elastomeric modifier (ethylene-alpha olefin copolymer with controlled ethylene content) and its optimal concentration (10-40 wt%) enable this localized enhancement of toughness while maintaining overall optical clarity greater than 90%.
Data Source
AI summary
A modifier for forming sub-ambient temperature use containers includes (a) from 10 wt % to 50 wt % of a block composite, a specified block composite, or a crystalline block composite, (b) from 20 wt % to 90 wt % of a first polyolefin copolymer, the first polyolefin copolymer being derived from ethylene and at least one of a C3 to C10 alpha-olefin, having a melt index from 0.5 g/10 min to 1500 g/10 min, and having a density from 0.850 g/cm3 to 0.910 g/cm3, and (c) optionally, from 30 wt % to 70 wt % of a second polyolefin copolymer, the second polyolefin copolymer being derived from ethylene and at least one of a C3 to C10 alpha-olefin, having a melt index from 100 g/10 min to 2000 g/10 min, and having a density from 0.860 g/cm3 to 0.900 g/cm3.