Weldable Polymer-Coated Tinplate for 3-Piece Cans
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Solution Overview
Problem
The existing methods for producing polymer-coated steel sheets for 3-piece cans require additional coating removal before welding, leading to inefficiencies and potential shrinkage issues during the lamination process, which affects the weldability and dimensional stability of the cans.
Innovation Solution
A process involving extrusion of polymer films, slitting them into wide and narrow strips, and applying the wide strips onto preheated tinplate using a nip-roll assembly, followed by post-heating and quenching to ensure a stable, weldable surface without the need for coating removal, thereby preventing shrinkage and ensuring dimensional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional coating is applied to protect thin tin layer, then corrosion resistance is improved, but weldability deteriorates because coating must be removed before welding
Solution Approach 1:
The coating is segmented into distinct functional layers: a thin tin layer (5-20 µm) for corrosion protection and a polymer coating layer for protection and aesthetics. This segmentation allows each layer to perform its specific function while the polymer layer is designed to be weldable, eliminating the need to remove coating before welding.
Solution Approach 2:
The tin layer thickness is reduced from conventional 50 µm to 5-20 µm, and a polymer coating is applied to compensate for the reduced corrosion protection. This parameter change allows weight reduction while maintaining corrosion resistance, and the polymer coating is specifically formulated to be weldable.
2Manufacturing precision
If biaxially oriented PET film is used and slitted to create bare strips, then dimensionally controlled uncoated areas are achieved, but accuracy depends on film shrinkage requiring stretched material
Solution Approach 1:
The polymer coating is applied to the tinplate before the welding and forming operations. The coating is designed to be weldable and dimensionally stable during subsequent processing, eliminating the need for pre-stretching or pre-shrinking operations to control dimensions.
Solution Approach 2:
The patent uses a polymer coating composition with specific glass transition temperature and melting point parameters that ensure dimensional stability during welding and forming operations, eliminating the shrinkage issues associated with biaxially oriented films.
3Loss of substance
If polymer coating is applied to protect thin tin layer, then lacquer use is reduced, but coating shrinkage during lacquer curing affects dimensional stability
Solution Approach 1:
The coating system is a composite structure with a thin tin layer (5-20 µm) providing corrosion protection and a polymer coating layer providing additional protection and weldability. This composite structure eliminates the need for thick lacquer applications while maintaining dimensional stability through proper polymer selection.
Solution Approach 2:
The polymer coating is selected with specific thermal properties (glass transition temperature, melting point) that ensure it remains dimensionally stable during the lacquer curing process, preventing shrinkage and maintaining can body dimensional accuracy.
4Quantity of substance
If tin layer thickness is reduced to lower cost, then material cost is reduced, but corrosion resistance deteriorates
Solution Approach 1:
The coating system combines a thin tin layer (5-20 µm) with a polymer coating layer. The tin layer provides base corrosion protection while the polymer coating enhances corrosion resistance and provides weldability, allowing significant tin reduction while maintaining or improving overall corrosion protection.
Solution Approach 2:
The tin layer thickness is reduced from 50 µm to 5-20 µm, representing a 60-90% reduction in tin usage. The polymer coating is specifically formulated to compensate for this reduction and maintain corrosion resistance while enabling weldability.
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
This method allows for the production of weldable polymer-coated tinplate with reduced lacquer use and improved dimensional control, preventing coating shrinkage during and after lamination, thus enhancing the manufacturing efficiency and stability of 3-piece cans.
Implementation Method 1
post-heating the polymer coated tinplate in a post-heat device to a temperature above the melting point of the polymer film or films
Implementation Method 2
quenching the post-heated polymer coated tinplate
Implementation Method 3
preheating the tinplate and subsequently coating the wide polymer film strips onto the preheated tinplate
Data Source
AI summary
A method for producing polymer coated steel sheet for 3-piece cans and 3-piece cans produced thereof.