Polyester-Coated Steel Can Forming With Heat-Tuned Adhesion
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Solution Overview
Problem
Polyester resin-coated metal sheets used in can production face issues with impact resistance and brittleness, especially after heat treatment, leading to potential cracking and peeling, particularly when filled with high-salt or steam-treated contents, and existing solutions are either expensive or inadequate in corrosion resistance.
Innovation Solution
A resin-coated steel can with a biaxially-stretched polyester film on the inner surface and a coated or printed outer surface, subjected to specific drawing and post-heating processes to achieve enhanced adhesion and corrosion resistance, using a general-purpose polyester resin for economic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyester resin is coated in a non-oriented state to prevent peeling and cracks during working, then workability is improved, but impact resistance deteriorates after forming
Solution Approach 1:
The polyester resin is pre-coated in a non-oriented state to ensure good workability during can forming, preventing peeling and cracks during the drawing process. After the can is formed, a post-heating treatment is applied to orient the resin molecules and improve impact resistance, thus resolving the contradiction between workability and final strength
Solution Approach 2:
The patent changes the physical state parameters of the polyester resin through temperature control. Initially, the resin is applied in a non-oriented state at lower temperatures for good workability. After can forming, post-heating at 80-150°C for 1-30 minutes transforms the resin to an oriented state with improved crystallinity and impact resistance
2Strength
If the resin coating is subjected to post-heating to improve adhesion, then adhesion is improved, but brittleness increases leading to cracks
Solution Approach 1:
The patent precisely controls the post-heating parameters (temperature range of 80-150°C and time of 1-30 minutes) to achieve the desired balance. This controlled heating increases adhesion by promoting resin-metal bonding while limiting excessive crystallization that would cause brittleness and cracking
Solution Approach 2:
The patent uses a biaxially stretched polyester resin film as a composite material with specific properties. The film's pre-stretched structure and controlled crystallinity (30-60%) provide a foundation that responds predictably to post-heating, achieving adhesion improvement without excessive brittleness
3Reliability
If a general-purpose polyester resin is used for economic efficiency, then cost is reduced, but corrosion resistance deteriorates
Solution Approach 1:
The patent changes the physical and structural parameters of the general-purpose polyester resin through controlled post-heating. This treatment increases the resin's crystallinity to 30-60% and improves its molecular orientation, thereby enhancing corrosion resistance and barrier properties without requiring expensive specialized resins
Solution Approach 2:
The patent converts the initially poor corrosion resistance of general-purpose polyester resin into a benefit through post-heating treatment. The controlled heating process transforms the resin structure to provide excellent corrosion and sulfide stain resistance, turning an economically efficient but performance-deficient material into a high-performance coating
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 process improves the adhesion and corrosion resistance of the resin coating, preventing peeling and cracking, even under high-salt and steam conditions, while maintaining economic efficiency by using a general-purpose polyester resin.
Implementation Method 1
the biaxially-stretched polyester film on the side wall of the can inner surface has a crystallinity of 42 to 52%, and the shrinkage in the can height direction is less than 10% the can height upon raising the temperature of the biaxially-stretched polyester film on the can inner surface side wall from 23°C to 130°C
Implementation Method 2
the adhesion is remarkably improved even though the coating is a polyester resin film of a general-purpose composition
Data Source
Figure 1(a)~3(c)
AI summary
The present invention relates to a resin-coated steel can provided with a remarkably improved adhesion of a resin coating and excellent corrosion resistance (impact resistance and barrier property), and a method for producing the same by using a resin-coated steel sheet having a resin coating formed from a polyester resin film of an economically efficient general-purpose composition. More specifically, the present invention relates to a resin-coated steel can produced by drawing or draw-redrawing a resin-coated steel sheet at least having a surface serving as a can inner surface coated with a biaxially-stretched polyester film and a surface serving as a can outer surface that is coated and/or printed. The biaxially-stretched polyester film on the can inner surface side wall has a crystallinity in a range of 42 to 52%, and a shrinkage (shrinkage in the can height direction upon raising the temperature from 23°C to 130°C at a rate of 5°C/min.) of the biaxially-stretched polyester film on the can inner surface side wall is less than 10% of the can height.