Retort Packaging Multilayer Structure for Stable Gas Barrier
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Solution Overview
Problem
Conventional packaging materials for retort foods face issues with gas barrier properties deteriorating due to stretching or bending processes, and recyclability is hindered by non-uniform mixing during recovery, particularly with aluminum foils or polyester films.
Innovation Solution
A multilayer structure comprising a resin layer made of a specific ethylene-vinyl alcohol copolymer (EVOH) and polyamide (PA) with an inorganic layer, optimized in terms of composition and thickness, providing excellent gas barrier properties and appearance after stretching or retorting, and enabling effective recyclability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum foil or vapor-deposited gas barrier film is used, then gas barrier properties and retort resistance are improved, but recyclability deteriorates due to difficulty in uniform mixing during melt-mixing
Solution Approach 1:
The patent uses a composite resin composition consisting of EVOH and PA blended together. This composite material provides both excellent gas barrier properties (through EVOH's hydrogen bonding network) and retort resistance (through PA's thermal stability), while remaining compatible with melt-mixing recycling processes unlike aluminum foil or vapor-deposited films
Solution Approach 2:
The patent optimizes the blending ratio of EVOH to PA within 70:30 to 95:5 by mass. This parameter adjustment ensures sufficient gas barrier properties while maintaining good processability and recyclability, resolving the contradiction between performance and ease of manufacturing
2Reliability
If EVOH is used as gas barrier resin, then gas barrier properties in dry state are improved, but gas barrier properties deteriorate after retorting process due to moisture absorption and hydrogen bonding relaxation
Solution Approach 1:
The patent introduces PA as an intermediary material that bridges the gap between EVOH molecules. The PA components fill spaces between EVOH chains and form a continuous network that maintains the hydrogen bonding structure even after retorting, preventing moisture-induced degradation and maintaining stable gas barrier properties
Solution Approach 2:
By creating a composite system where PA and EVOH work synergistically, the patent achieves both high gas barrier properties and stability after retorting. The PA matrix supports the EVOH hydrogen bonding network, ensuring compositional stability under humid hot conditions
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 multilayer structure maintains superior gas barrier and appearance post-processing, facilitating recycling with improved uniformity and reduced defects, making it suitable for retort packaging.
Implementation Method 1
an inorganic barrier layer which is laminated in adjacent to the barrier resin layer
Implementation Method 2
is crystallized and densified by hydrogen bonding between hydroxy groups in the molecule, exhibiting gas barrier properties
Data Source
AI summary
There is provided a multilayer structure comprising at least a barrier resin layer (X) and an inorganic barrier layer (Y) with a thickness of 500 nm or less which is adjacent to the barrier resin layer (X), wherein the layer (X) is made of a resin composition (x) comprising an ethylene-vinyl alcohol copolymer (A) and a polyamide (B) in a mass ratio (A/B) of 55/45 to 98/2, and the ethylene-vinyl alcohol copolymer (A) has an ethylene content of 20 to 46 mol % and a saponification degree of 90 mol % or more. Thus, there can be provided a multilayer structure having excellent gas barrier properties and appearance even after being subjected to stretching process or retorting process followed by bending process, and a packaging material for retort therewith.