Laminated Metal Sheet Retort Whitening Resistance
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Solution Overview
Problem
Laminated metal sheets used in food can containers face issues with retort whitening and shock resistance, requiring a solution that enhances mechanical characteristics and prevents retort whitening while maintaining design integrity.
Innovation Solution
A laminated metal sheet design featuring a metal sheet with an exterior polyester resin layer containing 30-60% copolymerized polyethylene terephthalate and 40-70% polybutylene terephthalate, and an interior polyester resin layer with a copolymerization component of less than 14 mol%, both with a degree of residual orientation between 2-50%, to improve thermal crystallization and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyester resin film is used on the exterior of a food can container, then food sanitation performance is improved, but retort whitening occurs during high-temperature sterilization
Solution Approach 1:
The patent changes the chemical composition parameters of the polyester resin film by incorporating specific copolymerized polyethylene terephthalate (30-60 mass%) and polybutylene terephthalate (40-70 mass%) with controlled copolymerization component content (<6 mol% and <14 mol% respectively). This parameter modification allows the film to maintain food sanitation performance while preventing retort whitening through enhanced thermal stability and controlled crystallization behavior during high-temperature sterilization
Solution Approach 2:
The patent creates a composite polyester resin system by combining multiple polyester components with specific ratios. The exterior layer uses a composite of copolymerized polyethylene terephthalate and polybutylene terephthalate, while the interior layer uses copolymerized polyethylene terephthalate. This composite structure provides both food sanitation performance and resistance to retort whitening by distributing functional properties across different material components
2Object-affected harmful factors
If the polyester resin film is made more resistant to retort whitening by increasing crystallization rate, then retort whitening is suppressed, but shock resistance and mechanical characteristics deteriorate
Solution Approach 1:
The patent applies local quality by creating two polyester resin layers with different compositions and properties: the exterior layer (30-60 mass% copolymerized PET, 40-70 mass% PBT) optimized for retort whitening resistance, and the interior layer (<14 mol% copolymerized PET) optimized for shock resistance and mechanical characteristics. Each layer performs its specific function locally without compromising the other, allowing simultaneous achievement of retort resistance and mechanical strength
Solution Approach 2:
The patent modifies physical parameters including the degree of residual orientation (2-50%) and thickness (6 μm or more) of the polyester resin layers. These parameter changes enable the exterior layer to achieve retort whitening resistance through controlled crystallization while the interior layer maintains shock resistance through appropriate mechanical properties, resolving the contradiction between thermal stability and mechanical strength
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 solution provides retort whitening resistance and shock resistance, maintaining excellent mechanical characteristics for food can containers, enabling effective forming and durability during processing and storage.
Implementation Method 1
both having a degree of residual orientation in a range of not less than 2% and not more than 50%
Data Source
AI summary
A first polyester resin layer formed on a surface of a metal sheet to serve as the exterior of a container after being formed into the container contains not less than 30% by mass and not more than 60% by mass of polyethylene terephthalate or copolymerized polyethylene terephthalate having a copolymerization component content of less than 6 mol%, and not less than 40% by mass and not more than 70% by mass of polybutylene terephthalate. A second polyester resin layer formed on a surface of the metal sheet to serve as the interior of a container after being formed into the container is copolymerized polyethylene terephthalate having a copolymerization component content of less than 14 mol%. The degree of residual orientation of the first and the second polyester resin layers is in a range of not less than 2% and not more than 50%. The thicknesses of the first and the second polyester resin layers after lamination are not less than 6 µm.