Polyester Can Coating Composition for Crack-Resistant DRD Forming
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Solution Overview
Problem
Current methods for coating aluminum or steel sheets before forming metal cans result in high failure rates due to cracking and peeling of the finish during the forming process, leading to increased production costs.
Innovation Solution
A coating composition comprising 60-90% active hydrogen-containing polyester, 0.1-10% polyanhydride, and 5-30% curing agent is applied to a metal substrate, cured, and then formed into cans, providing a flexible and ductile finish that prevents cracking and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyvinyl chloride coatings are used as formable finish on aluminum sheets, then the coating can be applied before can forming, but the coating cracks and peels during can forming and bead formation
Solution Approach 1:
The patent changes the chemical composition parameters of the coating system by using reactive polyester resins with specific molecular weights (15,000-50,000) and functionality (2-4), combined with polyanhydride curing agents in controlled ratios (0.1-10% polyanhydride, 5-30% curing agent). These parameter changes enable the coating to maintain flexibility and adhesion during severe forming operations while achieving proper cure.
Solution Approach 2:
The patent creates a composite coating system combining multiple components: active hydrogen-containing polyester resins, polyanhydrides with specific structural formulas, and curing agents reactive with active hydrogens. This composite material approach provides both the flexibility needed for forming and the durability required for bead formation without cracking or peeling.
2Productivity
If coating is applied before can forming, then production cost is reduced by eliminating post-forming coating step, but coating failure increases due to cracking and peeling
Solution Approach 1:
The patent implements preliminary coating application on the flat aluminum sheet before can forming operations. The specially formulated coating system is applied to the substrate and then cured to form a durable finish that withstands subsequent drawing and bead formation processes, eliminating the need for a separate post-forming coating step.
Solution Approach 2:
The patent modifies the coating composition parameters including polyester molecular weight (15,000-50,000), acid value (<5), hydroxyl value (<10), and the ratios of coating components to achieve optimal balance between formability and durability, allowing pre-forming coating to succeed where conventional coatings fail.
3Reliability
If conventional coatings are used on formed cans, then coating protection is achieved, but separate post-forming coating step increases production cost and time
Solution Approach 1:
The patent merges the coating application step with the pre-forming operations by applying the coating to the flat sheet before forming. This consolidation eliminates the separate post-forming coating step, reducing production complexity while maintaining coating protection through the use of the specially formulated flexible and durable coating system.
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 significantly reduces the failure rate of the coating finish during can formation, enhancing the durability and flexibility of the coating, thus lowering production costs by eliminating the need for a separate coating step after can formation.
Implementation Method 1
a curing agent reactive with the active hydrogens associated with (a) and (b)
Data Source
AI summary
A coating composition includes: (a) 60 to 90 percent by weight of an active hydrogen-containing polyester having a number average molecular weight of at least 23,000, an acid value below 5 and a hydroxyl value below 10, (b) 0.1 to 10 percent by weight of a polyanhydride, and (c) 5 to 30 percent by weight of a curing agent reactive with the active hydrogens associated with (a) and (b), the percentages being based on weight of resin solids of the coating composition, where the reaction product of the coating composition forms a single coating without including a thermoplastic polymer. The coating composition is useful in coating food and beverage containers, particularly 2-piece cans formed by drawing and redrawing (DRD).