Polyester-Resin-Coated Seamless Can for Retort Brushing 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 inadequate adhesion and crystallization of the resin coating, leading to appearance defects and peeling.
Innovation Solution
A seamless can design with specific ratios and orientations of polyester resin coatings on the inner and outer surfaces, controlled by X-ray diffraction and Raman spectroscopy, to suppress crystallization and enhance adhesion, along with controlled heating processes to maintain resin integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PBT content in the polyester film is increased to suppress retort brushing, then the retort resistance is improved, but the resin coating may be scraped off during drawing and ironing, resulting in exposure of the metal and deterioration in appearance properties
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%, along with controlling the molecular weight and intrinsic viscosity of the polyester resin. These parameter optimizations allow the resin to have sufficient flexibility during forming processes while maintaining adequate retort resistance, resolving the contradiction between suppressing retort brushing and preventing resin scraping.
2Reliability
If the PBT content is increased to suppress whitening, then the retort brushing resistance is improved, but the adhesion to the metal sheet deteriorates, and the resin coating is peeled off during retort sterilization treatment
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: PBT content (5-40 wt%), PET content (60-95 wt%), intrinsic viscosity (0.4-1.2 dL/g), and molecular weight (15,000-50,000). This multi-parameter optimization ensures the resin achieves both sufficient adhesion to the metal sheet and adequate resistance to retort brushing, preventing both peeling and whitening.
3Strength
If the polyester film has low PBT content to maintain adhesion, then the resin coating adhesion is improved, but the film cannot sufficiently suppress whitening such as retort brushing under high-temperature high-humidity conditions
Solution Approach 1:
The patent determines that a PBT content of 5-40 wt% provides the optimal balance: sufficient adhesion while effectively suppressing retort brushing. Additionally, controlling the intrinsic viscosity (0.4-1.2 dL/g) and molecular weight (15,000-50,000) ensures the resin maintains proper adhesion properties while achieving adequate retort resistance.
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 resin adhesion, and ensures excellent corrosion resistance and appearance properties under high-temperature conditions.
Implementation Method 1
a problem called retort brushing (white spots) has arisen, in which 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
Implementation Method 3
a full width at half maximum (FWHM) and an orientation index MOu based on microscopic Raman spectroscopy of an inner-surface polyester-resin-coated surface
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.