Polyester-Coated Seamless Can Necking for Retort Whitening Resistance
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Solution Overview
Problem
Existing polyester-resin-coated seamless cans face issues with retort brushing (white spots) and white streaks under high-temperature high-humidity conditions, such as retort sterilization, due to insufficient adhesion and crystallization of the resin coating, leading to appearance defects and peeling.
Innovation Solution
A seamless can design with controlled crystallinity and adhesion properties, achieved by specific ratios and orientations of PET and PBT in the resin coating, along with controlled heating processes, to suppress whitening and peeling, ensuring excellent adhesion and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PBT content in the polyester film is increased to suppress retort brushing and white streaks, then the retort resistance and appearance quality are improved, but the adhesion to the metal sheet deteriorates and the resin coating may be scraped off during drawing and ironing
Solution Approach 1:
The patent applies parameter changes by precisely controlling the PBT content within 5-40 wt% and the PET content within 60-95 wt%, rather than using extreme values. This optimized composition range resolves the contradiction by finding the balance point where sufficient PBT provides retort resistance while adequate PET maintains adhesion strength.
Solution Approach 2:
The patent uses a composite polyester resin system combining PBT and PET in specific proportions. This composite material approach allows the resin coating to simultaneously exhibit the retort resistance properties of PBT and the adhesion properties of PET, resolving the contradiction between these two opposing requirements.
2Object-affected harmful factors
If the PBT content is increased to improve retort resistance, then whitening suppression is enhanced, but the resin coating is scraped off during forming processes resulting in metal exposure and appearance deterioration
Solution Approach 1:
The patent controls the PBT content within 5-40 wt% to optimize the balance between whitening suppression and appearance quality. This parameter optimization ensures that the resin coating has sufficient elasticity and adhesion to withstand forming processes without scraping off, while still providing adequate resistance against retort brushing and white streaks.
3Strength
If the resin coating adhesion is improved to prevent peeling during retort sterilization, then the coating integrity is maintained, but the suppression of retort brushing and white streaks is insufficient
Solution Approach 1:
The patent employs a composite polyester resin system with PBT (5-40 wt%) providing retort resistance and PET (60-95 wt%) providing adhesion. This composite formulation allows the coating to simultaneously achieve strong adhesion preventing peeling during retort sterilization and sufficient resistance against retort brushing and white streaks.
Solution Approach 2:
The patent optimizes the resin composition parameters by controlling PBT content at 5-40 wt% and PET content at 60-95 wt%, creating a balanced formulation that achieves both strong adhesion and adequate retort resistance without the trade-offs of extreme compositions.
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 effectively prevents retort brushing and white streaks, maintains adhesion, and enhances corrosion resistance, even under high-temperature conditions, by controlling the crystallinity and orientation of the resin coating.
Implementation Method 1
parts such as a can bottom portion to which water droplets have adhered crystallize and cause whitening
Implementation Method 2
a value (cps/μm) calculated by dividing a maximum value of peak intensity in a range satisfying 15°≤2θ≤19° of an outer-surface polyester resin coating based on an X-ray diffraction method
Data Source
AI summary
A polyester-resin-coated seamless can including a reduced diameter portion obtained by neck processing within a distance of 0% to 15% from a can body uppermost portion with respect to a total height of the can from the can body uppermost portion to a can bottom of the can. A ratio Im/Iu is 1.0 or more, where Iu (cps/μm) is calculated by dividing a maximum peak intensity in a range satisfying 15°≤2θ≤19° of an outer-surface coating in a maximum reduced diameter portion of the reduced diameter portion by a thickness of the coating at the measurement site, and Im (cps/μm) is calculated by dividing a maximum peak intensity in a range satisfying 15°≤2θ≤19° of outer-surface coating at a measurement site within a distance of 45% to 60% from the can body uppermost portion by a thickness of the outer-surface coating at the measurement site.