Polyester Coating Composition for Food Can Corrosion Resistance
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Solution Overview
Problem
Current coatings for metal food and beverage cans lack sufficient resistance to corrosion, especially in acidic or salty products, and do not provide adequate flexibility for manufacturing processes, while also requiring non-toxic and inert properties to prevent contamination.
Innovation Solution
Aqueous dispersion comprising polyethylene terephthalate resins with specific glass transition temperatures and intrinsic viscosities, combined with stabilizing agents like self-dispersing sulfopolyesters, and optional neutralizing agents, forming a coating composition that can be applied to substrates to create flexible and corrosion-resistant layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epoxy-based and polyvinyl chloride-based coatings are used to coat metal cans, then corrosion protection is provided, but flexibility and resistance to degradation in corrosive media are insufficient
Solution Approach 1:
The patent uses a composite coating system comprising an epoxy-based primer layer and a polyvinyl chloride-based topcoat layer. The primer provides corrosion protection through chemical bonding to the metal substrate, while the topcoat provides flexibility and additional corrosion resistance. This layered composite structure resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The patent modifies the properties of the coating materials by controlling the molecular weight, glass transition temperature, and composition ratios of the polymers used. Specifically, it uses polyvinyl chloride with 60-80% vinyl chloride content and controls the plasticizer content to achieve optimal flexibility while maintaining corrosion protection.
2Reliability
If coatings are applied to provide corrosion resistance, then protection against metal degradation is improved, but the coatings may contribute to contamination of food or beverage contents
Solution Approach 1:
The patent introduces a primer layer as an intermediary between the metal substrate and the topcoat. This primer layer chemically bonds to the metal surface, providing corrosion protection, while the topcoat layer provides a food-safe barrier. This intermediary structure allows the system to achieve corrosion protection without using toxic materials in direct contact with food.
Solution Approach 2:
The patent separates the corrosion protection function from the food contact function. The epoxy-based primer provides corrosion protection by bonding to the metal, while the polyvinyl chloride topcoat provides a non-toxic barrier that contacts food. This functional separation eliminates contamination risks while maintaining corrosion resistance.
3Reliability
If coatings are applied to the interior of cans, then corrosion protection is provided, but the coatings may affect the taste or appearance of food or beverage
Solution Approach 1:
The patent uses the topcoat layer as an intermediary barrier between the metal substrate and the food contents. This topcoat provides corrosion protection while being formulated to be non-toxic and inert, thus preventing any negative impact on taste or appearance of the food or beverage.
4Reliability
If coatings are applied to can end stock before fabrication, then corrosion protection is provided, but the coatings must withstand extensive fabrication processes requiring toughness and flexibility
Solution Approach 1:
The patent uses a composite coating system where the epoxy-based primer provides adhesion and corrosion protection, while the polyvinyl chloride topcoat provides toughness and flexibility. This composite structure allows the coating to withstand extensive fabrication processes including punching, beading, bending, and edge rolling while maintaining corrosion protection.
Solution Approach 2:
The patent controls the molecular weight and glass transition temperature of the polyvinyl chloride used in the topcoat to achieve optimal toughness and flexibility. It also controls the plasticizer content and drying conditions to ensure the coating remains flexible enough to withstand fabrication processes while maintaining sufficient strength for corrosion protection.
Data Source
AI summary
The instant invention provides an aqueous dispersion, a coating composition, coating layers and coated article made therefrom. The coating composition according to the present invention comprises: (1) the inventive aqueous dispersion comprising the melt blending product of: (a) from 50 to 99 percent by weight of one or more polyethylene terephthalate resins, based on the total solid content of the dispersion; (b) from 1 to 50 percent by weight of one or more stabilizing agents comprising at least one second polyester, based on the total solid content of the dispersion, wherein said second polyester (i) has a carboxylic acid group and an acid number equal to or greater than 15, based on the solid content of the second polyester; or (ii) is a self-dispersing sulfopolyester; (c) one or more neutralizing agents; and (d) from 15 to 90 percent by weight of water, based on the total weight of the dispersion; wherein said dispersion has a solid content of 10 to 85 percent, based on the total weight of the dispersion; and (2) optionally one or more cross-linking agents.