EVOH Laminate Shear Viscosity Control for Streak-Free Forming
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Solution Overview
Problem
EVOH resin compositions used in packaging materials face challenges in stretchability and gas barrier properties, particularly during vacuum/air-pressure forming, where streaks and appearance failures occur due to differences in ethylene content and melt viscosity of the resins, leading to boundary disturbances and uneven tension during the molding process.
Innovation Solution
A laminate structure comprising a layer of saponified ethylene/vinyl ester copolymer (EVOH resin) and a thermoplastic resin, with a specific shear viscosity ratio between the EVOH resin and adhesive resin, and a difference in ethylene content between two EVOH resins, is used to inhibit boundary disorders and maintain gas barrier properties, preventing streaks during vacuum/air-pressure forming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If EVOH resin with high ethylene content is used to improve stretchability, then stretchability is improved, but gas barrier properties decrease
Solution Approach 1:
The patent uses a laminate structure combining EVOH resin layer with another thermoplastic resin layer (such as polypropylene or polystyrene) to achieve both stretchability and gas barrier properties. The EVOH layer provides gas barrier functionality while the other thermoplastic resin layer provides stretchability and structural support, allowing the container to be formed through vacuum/air-pressure forming without compromising either property.
2Reliability
If EVOH resin is used alone to maintain gas barrier properties, then gas barrier properties are maintained, but appearance failures occur during molding due to poor stretchability
Solution Approach 1:
The patent employs a laminate structure where EVOH resin layer is combined with another thermoplastic resin layer that has better stretchability and formability. This composite structure allows the EVOH layer to maintain gas barrier properties while the other resin layer accommodates the stretching and forming processes, preventing appearance failures such as streaks and cracks during vacuum/air-pressure forming.
3Ease of operation
If laminate structure with EVOH resin and other thermoplastic resin is used to improve stretchability, then stretchability is improved, but streaks occur during vacuum/air-pressure forming due to boundary disturbances
Solution Approach 1:
The patent optimizes specific parameters including the thickness ratio between EVOH layer and other thermoplastic resin layer, the shear viscosity ratio of the resins, and the ethylene content difference between EVOH resins. By controlling these parameters within specific ranges, the patent achieves uniform resin flow during vacuum/air-pressure forming, preventing boundary disturbances and streak formation while maintaining improved stretchability.
4Reliability
If EVOH resins with different ethylene content are combined to achieve both gas barrier and stretchability, then both properties are attained, but boundary disturbances occur leading to streaks
Solution Approach 1:
The patent carefully controls the ethylene content difference between EVOH resins to be within a specific range (3-20% by mole). This parameter control ensures that the EVOH resins have compatible flow characteristics and viscosity, preventing boundary disturbances and streak formation during vacuum/air-pressure forming while still achieving both gas barrier properties and stretchability.
Data Source
AI summary
The laminate of the present invention a laminate comprising a layer comprising a saponified ethylene/vinyl ester copolymer and a layer which comprises a thermoplastic resin that is not an EVOH resin and which has been laminated to at least one surface of the layer comprising a saponified ethylene/vinyl ester copolymer via a layer comprising an adhesive resin, wherein shear viscosity ratio of the saponified ethylene/vinyl ester copolymer and the adhesive resin (saponified ethylene/vinyl ester copolymer to adhesive resin) is 0.70-1.50 at a shear rate of 0.1 [1/s] and 0.90-1.10 at a shear rate of 1.0 [1/s].