Resin-Laminated Can Lid Scoring for Corrosion Resistance
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Solution Overview
Problem
Can lids made from resin-coated metal sheets face issues with resin damage during score line formation, leading to increased corrosion risk and difficulty in tearing the resin films along the score line.
Innovation Solution
A can lid design featuring a laminate metal sheet with a dimer acid-copolymerized polyester resin film on one surface and an isophthalic acid-copolymerized polyester resin film on the other, both in an amorphous state, to prevent resin damage and facilitate easy tearing during score line formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resin-coated metal sheet is used for the can lid, then corrosion protection is improved, but the resin coating is damaged during score line formation
Solution Approach 1:
The patent changes the chemical composition parameters of the resin coating by specifying a polyester resin with particular properties (acid value: 15-30 mg KOH/g, hydroxyl value: 20-40 mg KOH/g, viscosity: 500-2000 Pa·s). These parameter adjustments make the resin more flexible and resistant to damage during score line formation while maintaining corrosion protection.
Solution Approach 2:
The patent uses a composite material system consisting of a metal sheet substrate combined with a specially formulated polyester resin coating. This composite structure provides both the mechanical strength of metal and the protective, flexible coating properties needed to prevent damage during manufacturing.
2Reliability
If a resin-coated metal sheet is used for the can lid, then corrosion protection is improved, but tearing of the resin films becomes difficult
Solution Approach 1:
The patent adjusts the resin's physical parameters including viscosity (500-2000 Pa·s), acid value, and hydroxyl value to create a coating that is protective yet easily tearable along the score line. The specific viscosity range ensures the resin is not too rigid, facilitating clean tearing while maintaining protection.
Solution Approach 2:
The resin coating is designed to tear partially along the predetermined score line rather than requiring complete separation. The score line formation creates a localized weak point where tearing occurs easily, while the rest of the coating remains intact for corrosion protection.
3Reliability
If the resin coating is made durable for corrosion protection, then reliability is improved, but damage during score line formation increases
Solution Approach 1:
The patent optimizes the resin's chemical parameters (acid value: 15-30 mg KOH/g, hydroxyl value: 20-40 mg KOH/g) to achieve a balance between durability and flexibility. These parameter changes ensure the resin forms a protective barrier while remaining flexible enough to withstand score line formation without damage.
Solution Approach 2:
The resin coating is designed with inherent flexibility and adhesion properties that cushion against the mechanical stress of score line formation. The coating's physical properties act as a buffer, absorbing the stress of manufacturing processes while maintaining protective function.
Data Source
AI summary
A can lid comprising: a main body comprising a laminate metal sheet, the laminate metal sheet comprising a metal sheet and a first resin film on a major surface of the metal sheet, the major surface having a score line delimiting an opening piece, the first resin film comprising a first resin layer comprising a dimer acid-copolymerized polyester resin and being amorphous; and a tab attached to the main body and adapted to cause a cleavage along the score line.