PE/EVOH Multilayer Structure for Crack-Resistant Orientation
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Solution Overview
Problem
Existing multilayer structures with oxygen barrier properties, such as PE/EVOH films, face issues during orientation due to cracking of the EVOH layer, leading to loss of barrier properties, and adhesive lamination processes using non-PE based adhesives complicate recycling.
Innovation Solution
A recyclable multilayer structure comprising a polyethylene film layer oriented in the machine direction, a copolymer of ethylene and vinyl alcohol (EVOH) layer, and tie layers on both sides of the EVOH layer, produced through coextrusion or extrusion coating processes, ensuring stability and recyclability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If EVOH layer is used in multilayer structure for oxygen barrier, then oxygen barrier properties are improved, but the structure becomes problematic during orientation operations due to cracking of EVOH layer
Solution Approach 1:
The patent divides the multilayer structure into distinct functional layers: an outer polyethylene layer (layer A) that undergoes orientation, an intermediate EVOH barrier layer (layer B), and an inner polyethylene layer (layer C). This segmentation allows each layer to perform its specific function without compromising the others, solving the cracking issue by isolating the EVOH layer from orientation stresses.
Solution Approach 2:
The patent introduces a tie layer (layer D) made of polyethylene or polyethylene copolymer as an intermediary between the EVOH layer and the outer polyethylene layer. This tie layer acts as a buffer that absorbs orientation stresses and prevents stress transfer to the brittle EVOH layer, thereby preventing cracking while maintaining the oxygen barrier function.
2Ease of manufacture
If adhesive lamination process is used to produce barrier films, then production flexibility is improved, but recycling becomes problematic due to non-PE based adhesives and metal or ceramic layers
Solution Approach 1:
The patent uses polyethylene-based materials consistently throughout all layers (layer A, layer C, and layer D), creating a homogeneous polymer composition. This homogeneity enables the entire structure to be processed together in recycling facilities designed for polyethylene, eliminating the recycling problems associated with mixed materials like metal, ceramic, or non-PE adhesives.
Solution Approach 2:
The tie layer made of polyethylene or polyethylene copolymer serves multiple functions: it provides adhesion between layers, acts as a stress buffer during orientation, and ensures recyclability by maintaining PE-based composition throughout the structure. This multi-functionality resolves the contradiction between manufacturing flexibility and recyclability.
Data Source
AI summary
The present invention deals with a multilayer structure comprising a first polyethylene layer as a first external layer. The first polyethylene layer is oriented in at least machine direction. The structure also comprises a second polyethylene layer as a second external layer. It further comprises a layer made of a copolymer of ethylene and vinyl alcohol (EVOH) between the first external layer and the second external layer and a tie layer on each side of the EVOH layer. Furthermore, the tie layers comprise one or more copolymers of ethylene.