TMCD-DMPOA Polyester Waterborne Coatings for Metal Packaging
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Solution Overview
Problem
Waterborne polyester coatings for metal packaging face challenges in achieving a balance of desirable properties such as corrosion resistance, flexibility, and microcracking resistance, particularly due to limitations in molecular weight and crosslinking, which affect their performance in processing and sterilization conditions.
Innovation Solution
A waterborne coating composition comprising 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) and dimethylolpropionic acid (DMPOA) as key components, allowing for high molecular weights and suitable dispersity, thereby enhancing hydroxyl and carboxyl functionality for improved crosslinking and water dispersibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher crosslinking is used to improve corrosion resistance, acid resistance, stain resistance, and retort resistance, then these protective properties are improved, but flexibility deteriorates, leading to reduced microcracking resistance and bending ability during processing
Solution Approach 1:
The patent changes the chemical parameters of the polyester resin by incorporating DMPOA, which introduces additional acid functionality. This allows for high molecular weights without gelation while maintaining desirable dispersity. The resin achieves hydroxyl numbers lower than 30 KOH/mg and acid numbers lower than 5 mgKOH/g, creating sufficient carboxyl end groups for water dispersibility without requiring acrylic modifications that would compromise coating performance.
Solution Approach 2:
The patent creates a composite resin system combining TMCD polyester moieties with DMPOA functional groups. This composite structure simultaneously provides high molecular weights, effective hydroxyl functionality for crosslinking, and sufficient carboxyl groups for water dispersibility, achieving a balance between crosslinking density and flexibility that neither component could achieve alone.
2Reliability
If high molecular weight polyesters are used to withstand processing conditions during can fabrication, then processing resistance is improved, but water dispersibility deteriorates due to insufficient carboxyl end groups
Solution Approach 1:
The patent changes the functional group composition by incorporating DMPOA, which provides carboxyl end groups that enable water dispersibility even at high molecular weights. The resin achieves the necessary balance between molecular weight for processing resistance and acid number for water dispersibility without requiring acrylic modifications.
3Ease of operation
If traditional acrylic modifications are used to impart water dispersibility, then water dispersibility is improved, but overall coating performance deteriorates
Solution Approach 1:
The patent extracts and eliminates the need for traditional acrylic modifications by incorporating DMPOA directly into the polyester backbone. This removes the harmful element (acrylic modifications that compromise performance) while maintaining the beneficial function (water dispersibility through carboxyl groups from DMPOA).
Solution Approach 2:
The patent uses DMPOA as an intermediary functional monomer that provides both structural integrity and water dispersibility. Instead of using acrylic modifiers as a separate component, DMPOA acts as an integrated mediator within the polyester chain that simultaneously contributes to molecular weight, crosslinking functionality, and water dispersibility.
Data Source
AI summary
Disclosed are novel curable polyesters comprising the reaction product of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) and dimethylolpropionic acid. The curable polyesters have particular utility in waterborne coating compositions. Such waterborne coating compositions provide a good balance of desirable coating properties for metal packaging applications.