Heat-Resistant Multilayer Container with Propylene Copolymer Barrier
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Solution Overview
Problem
Conventional multilayer containers with propylene-based polymers excel in glossiness but lack heat resistance, making them unsuitable for retort sterilization due to poor compatibility between polyethylene and propylene-based polymers, which also affects transparency.
Innovation Solution
A heat-resistant multilayer container design featuring an outermost layer of high-MFR homopolypropylene, an inner layer of low-MFR homopolypropylene with ethylene-α-olefin copolymer, and a barrier layer, optimized for thermoforming with a deep-drawn shape and enhanced crystallinity, including a crystal nucleating agent to improve formability and impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyethylene resin layer is applied for inner layer to improve impact resistance, then impact resistance is improved, but heat resistance deteriorates making retort sterilization impossible
Solution Approach 1:
The patent changes the material parameters by replacing polyethylene with a propylene-based random copolymer having specific compositional parameters (5-30 mass% ethylene content, MFR of 0.4-6.0 g/10min, melting point of 150-170°C). This parameter optimization allows the material to achieve both improved impact resistance and sufficient heat resistance for retort sterilization, resolving the contradiction between these two properties.
Solution Approach 2:
The patent creates a composite material system by formulating a propylene-based random copolymer with specific ethylene content (5-30 mass%) and blending it with other propylene-based polymers. This composite approach combines the toughness benefits of ethylene incorporation with the heat resistance of propylene, achieving both impact resistance and heat resistance simultaneously.
2Strength
If polyethylene is blended with propylene-based polymer to improve impact resistance, then impact resistance is improved, but transparency deteriorates due to poor compatibility
Solution Approach 1:
The patent achieves homogeneity by using a propylene-based random copolymer where ethylene units are randomly distributed within the propylene matrix, creating a homogeneous single-phase structure. This eliminates the phase separation and poor compatibility issues that occur with polyethylene blending, maintaining transparency while providing impact resistance through compositional homogeneity rather than mechanical mixing of incompatible polymers.
3Illumination intensity
If propylene-based polymer with high glossiness is used for outer layer, then glossiness is improved, but impact resistance becomes inferior
Solution Approach 1:
The patent applies local quality by creating a multilayer structure where the outer layer uses a propylene-based random copolymer optimized for glossiness (higher crystallinity, specific MFR range) while the inner layer uses the same or similar material optimized for impact resistance (5-30 mass% ethylene content). This allows each layer to be locally optimized for its specific function while maintaining overall container performance.
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 container achieves excellent impact resistance, heat resistance, and glossiness, allowing for successful retort sterilization with minimal volume shrinkage and maintaining transparency, while the additional layers provide improved gas barrier and oxygen absorption properties.
Implementation Method 1
containing a crystal nucleating agent in an amount of 0.001 to 5 parts by weight per 100 parts by weight of the propylene-based polymer
Implementation Method 2
a volume shrinkage of not more than 5% based on a volume before and after heat sterilization at 121°C for 30 minutes
Data Source
Figure 1~5
AI summary
The present invention provides a multilayer container including: an outermost layer 1 containing a propylene-based polymer A containing homopolypropylene as a main component having a melt flow rate in a range of 2.0 to 10.0 g/10min; an inner layer 2 containing 50 to 99% by weight of a propylene-based polymer B containing homopolypropylene as a main component having a melt flow rate of not more than 5.0 g/10min and an isotactic index of not less than 93%, and 1 to 50% by weight of an ethylene-α-olefin copolymer C; and a barrier layer 4 occupying 5 to 20% by weight of the whole container. The ratio (L/D) of container height (L) to diameter (D) is not less than 0.5, and a volume shrinkage based on volume measured before and after heat sterilization at 121°C for 30 minutes is not more than 5%. The container has excellent glossiness and impact resistance, and can be used for retort sterilization.