EVOH Resin Composition for Flexible Bag-in-Box Oxygen Barrier
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Solution Overview
Problem
Conventional EVOH-based multilayer structures for bag-in-box containers face challenges with pinhole creation due to rigidity and lack of flexibility during transport, requiring improved mechanical strength and bending resistance without special extrusion conditions.
Innovation Solution
A resin composition comprising ethylene-vinyl alcohol copolymer (EVOH), unmodified ethylene-α-olefin copolymer, acid modified ethylene-α-olefin copolymer, and alkali metal salt, blended in specific ratios to achieve enhanced stability, oxygen barrier properties, and flexibility, with a melt flow rate that supports microdispersion and reduced die build-up during extrusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional EVOH layer is used in a multilayer structure, then oxygen barrier properties are improved, but flexibility and bending resistance deteriorate, leading to pinhole creation during transport
Solution Approach 1:
The patent changes the molecular weight parameters of the EVOH resin, specifically using EVOH with a number-average molecular weight of 50,000 to 200,000 and a weight-average molecular weight of 200,000 to 800,000. This parameter optimization maintains the oxygen barrier properties while improving flexibility and bending resistance to prevent pinhole formation during transport
Solution Approach 2:
The patent creates a composite multilayer structure combining EVOH resin with specific polyolefin resins. The multilayer structure includes an EVOH layer and a polyolefin layer, where the polyolefin provides flexibility and bending resistance while the EVOH maintains oxygen barrier properties, preventing pinhole creation during transport
2Reliability
If EVOH resin with high crystallinity is used, then oxygen barrier properties are improved, but melt moldability deteriorates, making the film rigid and prone to pinholes
Solution Approach 1:
The patent optimizes the molecular weight parameters of the EVOH resin, using a number-average molecular weight of 50,000 to 200,000 and a weight-average molecular weight of 200,000 to 800,000. This parameter adjustment improves melt moldability while maintaining oxygen barrier properties, allowing the film to be processed without creating pinholes
3Strength
If the inner container is made flexible for transport, then bending resistance is improved, but pinhole creation increases due to repeated bending
Solution Approach 1:
The patent uses EVOH resin with optimized molecular weight parameters (number-average molecular weight of 50,000 to 200,000 and weight-average molecular weight of 200,000 to 800,000) which provides both flexibility for transport and resistance to pinhole formation during repeated bending
Solution Approach 2:
The patent creates a composite multilayer structure where the EVOH layer provides pinhole resistance during bending while the polyolefin layer provides flexibility, allowing the inner container to withstand repeated bending during transport without creating pinholes
Data Source
AI summary
A resin composition is provided that contains: an EVOH (A); an unmodified ethylene-α-olefin copolymer (B); an acid modified ethylene-α-olefin copolymer (C); and alkali metal salt (D), wherein a mass ratio [(A)/((B)+(C))] is from 80/20 to 65/35, a mass ratio [(B)/(C)] is from 92/8 to 70/30, (A) has an MFR of not less than 8.0 g/10 min. and not more than 15 g/10 min., a content of (D) is not less than 25 ppm and not more than 300 ppm in terms of metal, and the resin composition has an MFR of not less than 2.0 g/10 min. and not more than 4.0 g/10 min. The use of this resin composition enables production of a multilayer structure and an inner container for a bag-in-box having excellent oxygen barrier properties and high flexibility and bending resistance.