Polyester Can Coating for Stress-Relaxed Drawn/Ironed Cans
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Solution Overview
Problem
Existing coated metal sheets for drawn/ironed cans face issues with coating film peeling due to residual stress after severe processing like drawing and ironing, leading to metal exposure and reduced corrosion resistance, which are not adequately addressed by existing technologies.
Innovation Solution
A coated metal sheet with inner and outer surface films containing a polyester resin and a curing agent, such as resol-type phenolic resin, with a stress relaxation ratio of 50% or greater at 1% elongation, effectively prevents coating film peeling during heat treatment by managing residual stress, ensuring continuous coverage and enhanced corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If heat treatment is performed to remove residual stress in the coating film after severe drawing and ironing, then the residual stress is reduced, but coating film peeling occurs and metal exposure happens
Solution Approach 1:
The patent applies parameter changes by carefully controlling the heat treatment temperature range (50-150°C) to remove residual stress while preventing coating film peeling. This temperature parameter optimization allows stress relaxation without causing adhesion failure, resolving the contradiction between stress removal and adhesion maintenance.
Solution Approach 2:
The patent uses composite materials by combining the coating film with the metal substrate in a way that the coating film's mechanical properties are optimized to withstand heat treatment. The composite structure is designed so that the coating film can relax stress through controlled thermal expansion while maintaining strong adhesion to the metal substrate.
2Reliability
If a thick coating film is used to prevent metal exposure, then corrosion resistance is improved, but film formation becomes difficult and economic efficiency decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the coating film thickness to a specific range (5-20 μm) that provides sufficient corrosion resistance while remaining manageable in the film formation process. This thickness parameter is carefully selected to balance protective function with manufacturing feasibility.
Solution Approach 2:
The patent applies partial action by providing coating film coverage only where most needed for corrosion protection, rather than uniformly thick coverage everywhere. This allows adequate corrosion resistance with reduced overall material usage and simplified film formation.
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 a drawn/ironed can with improved coating film peeling resistance, continuous coverage, and enhanced corrosion resistance by controlling stress relaxation, thereby maintaining high productivity and economic efficiency.
Implementation Method 1
a stress relaxation ratio after 10 minutes of the inner surface coating film in a can bottom portion is 50% or greater at 1% elongation under a test condition of 100° C.
Data Source
AI summary
The disclosure relates to a drawn/ironed can having at least an inner surface coating film on a can inner surface side, the inner surface coating film containing a polyester resin and a curing agent, and a stress relaxation ratio of the inner surface coating film after 10 minutes at 1% elongation in a can bottom portion is 50% or higher under a test condition of 100° C., whereby metal exposure due to severe processing such as drawing or ironing and coating film peeling due to heat treatment after molding are effectively prevented.