Ethylene-Vinyl Alcohol Multilayer Structure for Oxygen Barrier Stability
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Solution Overview
Problem
Existing multilayer structures for packaging materials face issues with oxygen-gas barrier performance under high humidity, adhesion to substrates, and generation of harmful gases during incineration, particularly when using ethylene-vinyl alcohol copolymers with high ethylene unit content or polyvinylidene chloride coatings.
Innovation Solution
A multilayer structure comprising a layer of ethylene-vinyl alcohol copolymer with a specific ethylene unit content, viscosity-average polymerization degree, and saponification degree, along with a block character of ethylene units between 0.90 to 0.99, and a layer of polyolefin, polyester, or polyamide resin, ensuring excellent viscosity stability and uniform application over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum foil is used as an intermediate layer to achieve perfect oxygen-gas barrier performance, then oxygen barrier performance is improved, but residue is left during incineration and metal detectors cannot detect the content when used as packaging material
Solution Approach 1:
The patent removes aluminum foil from the multilayer structure and replaces it with organic polymer layers (PVDC, PVA, and ethylene-vinyl alcohol copolymer). This extraction of the metal component eliminates residue during incineration while maintaining oxygen barrier performance through the carefully designed polymer layer composition and thickness.
Solution Approach 2:
The patent changes the material composition parameters by specifying precise ethylene unit content (1-19 mol%), viscosity-average polymerization degree (200-5000), and saponification degree (80-99.7 mol%) of the ethylene-vinyl alcohol copolymer. These parameter changes enable the organic layers to achieve oxygen barrier performance comparable to aluminum foil without the harmful effects of metal incineration.
2Reliability
If polyvinylidene chloride is used to achieve good oxygen-gas barrier performance under high humidity, then oxygen barrier performance is improved, but hydrogen chloride gas is generated during incineration
Solution Approach 1:
The patent removes PVDC from the multilayer structure and replaces it with ethylene-vinyl alcohol copolymer and other organic polymers. This extraction eliminates the generation of hydrogen chloride gas during incineration while maintaining moisture resistance and oxygen barrier performance through the alternative polymer composition.
Solution Approach 2:
The patent uses biodegradable or easily decomposable organic polymer materials that do not generate harmful gases when incinerated. These materials are designed to be environmentally friendly and safe for disposal, replacing the persistent and harmful PVDC coating.
3Stability of the object's composition
If ethylene-vinyl alcohol copolymer containing 20 mol% or more of ethylene units is used to restrict moisture absorption, then moisture absorption is reduced, but uniformity of the resulting coating film is insufficient
Solution Approach 1:
The patent optimizes the ethylene unit content to a specific range (1-19 mol%, preferably 3-15 mol%) rather than using 20 mol% or more. This parameter change maintains moisture absorption resistance while ensuring proper coating film uniformity. The patent also controls viscosity-average polymerization degree (200-5000) and saponification degree (80-99.7 mol%) to achieve both moisture resistance and coating uniformity.
4Reliability
If fully saponified unmodified polyvinyl alcohol is used to achieve excellent oxygen-gas barrier performance, then oxygen barrier performance is improved, but the material is hygroscopic and adhesive to substrate is poor
Solution Approach 1:
The patent creates a composite multilayer structure where ethylene-vinyl alcohol copolymer is combined with PVDC or other polymer layers. The ethylene-vinyl alcohol copolymer provides oxygen barrier performance, while the complementary layers provide moisture resistance and improved adhesion to substrates like OPP and OPET, overcoming the limitations of unmodified PVA.
Solution Approach 2:
The patent assigns different functional properties to different layers: the ethylene-vinyl alcohol copolymer layer primarily provides oxygen barrier performance, while other layers provide moisture resistance and adhesion enhancement. This local differentiation of material properties allows each layer to optimize its specific function without compromising overall performance.
Data Source
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AI summary
There is provided a multilayer structure comprising a layer (A) containing an ethylene-vinyl alcohol copolymer having an ethylene unit content of 1 mol% or more and less than 20 mol%, a viscosity-average polymerization degree of 200 to 5000, and a saponification degree of 80 to 99.7 mol%, wherein a block character of ethylene units is 0.90 to 0.99; and a layer (B) containing at least one resin selected from the group consisting of a polyolefin resin, a polyester resin and a polyamide resin. Such a multilayer structure has excellent oxygen-gas barrier performance. In addition, an aqueous solution containing the ethylene-vinyl alcohol copolymer exhibits excellent viscosity stability even after long-term storage. Therefore, even after a long period of time from preparation of the aqueous solution, it can be uniformly applied to a substrate and thus, a multilayer structure having excellent oxygen-gas barrier performance can be provided.