Flexible Can Coating Composition for Crack-Free DRD Forming
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Solution Overview
Problem
Current methods for coating aluminum or steel sheets before forming cans result in high failure rates due to cracking and peeling of the finish during the forming process, leading to increased production costs and reduced can durability.
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 a formable finish on aluminum sheets, then the coating can be applied before can forming, but the finish cracks and peels during bead forming
Solution Approach 1:
The patent modifies the chemical composition parameters of the coating by using polyester resins with specific molecular weight ranges (15,000-50,000) and controlled functionality (2-4), along with specific polyanhydride hardeners and catalysts, to achieve both formability and crack resistance
Solution Approach 2:
The patent creates a composite coating system combining polyester resin, polyanhydride hardener, and catalyst in specific ratios (60-90% polyester, 0.1-10% polyanhydride, 5-30% curing agent) to achieve synergistic properties of flexibility, adhesion, and crack resistance during forming
2Reliability
If a coating is sprayed on after can formation, then the coating can be applied to the formed can, but this increases production cost and time
Solution Approach 1:
The patent applies the coating to the aluminum sheet before can forming operations, allowing the coating to be cured and providing protection during subsequent forming, bead crimping, and sterilization processes without requiring post-forming coating steps
3Productivity
If the coating is applied before can forming, then production cost is reduced, but the coating must withstand severe deformation without cracking
Solution Approach 1:
The patent adjusts the molecular weight of polyester resin to 15,000-50,000 and controls the acid value (2-5) and hydroxyl value (5-10) to optimize the balance between coating flexibility for forming and strength to resist cracking during deformation
Solution Approach 2:
The patent creates a flexible coating film that can accommodate the severe deformation during can forming and bead crimping through the use of low-functionality polyester resins and appropriate plasticizers, preventing crack formation while maintaining coating integrity
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 coating failures during can formation, enhancing the durability and flexibility of the finish while eliminating the need for a separate coating step after can formation, thereby lowering production costs and improving can integrity.
Implementation Method 1
a curing agent reactive with the active hydrogens associated with (a) and (b)
Data Source
AI summary
A coating composition comprising a high molecular weight polyester, a trimellitic anhydride-polyol adduct and a curing agent is disclosed. The compositions are useful in coating food and beverage containers, particularly 2-piece cans formed by drawing and redrawing (DRD).