Curing-Agent-Free Polyester Resin Coatings for Retort Resistance
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Solution Overview
Problem
Existing polyester resin compositions for metal cans and lids face issues with processability, curability, retort resistance, and the generation of harmful outgases due to the use of curing agents, while also posing health and environmental concerns.
Innovation Solution
A polyester resin composition with a high acid value and specific tetrahydrofuran-insoluble content, cured without a curing agent, achieving balanced curability and processability, and enhanced retort resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a polyester resin composition with high acid value is used to achieve curability without curing agents, then harmful outgas generation is reduced, but processability deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the acid value within 150-400 eq/ton and the tetrahydrofuran-insoluble matter content within 5-30 mass% after heating treatment. These parameter optimizations enable the polyester resin to achieve curability without curing agents while maintaining adequate processability during can forming operations.
2Reliability
If the acid value is increased to improve curability, then retort resistance improves, but processability worsens
Solution Approach 1:
The patent resolves this contradiction by optimizing the acid value parameter to a specific range (150-400 eq/ton) rather than simply increasing it. This controlled parameter change ensures sufficient retort resistance while preventing excessive crosslinking that would harm processability.
Solution Approach 2:
The patent applies partial action by using a moderate acid value within an optimized range rather than maximum possible values. This partial optimization achieves the necessary retort resistance without over-crosslinking, thereby maintaining processability.
3Strength
If a curing agent is used to achieve curability, then adhesion improves, but harmful outgas generation increases
Solution Approach 1:
The patent extracts and eliminates the curing agent component from the coating system. Instead of using external curing agents that generate harmful outgases, the invention enables the polyester resin itself to provide curability through its controlled acid value and tetrahydrofuran-insoluble matter content, thereby removing the source of harmful emissions while maintaining adhesion.
Solution Approach 2:
The polyester resin performs the curing function itself without requiring separate curing agents. The resin's inherent properties (acid value and insoluble matter content) enable it to crosslink and adhere to the substrate autonomously, eliminating the need for additional chemical components that would generate harmful outgases.
Data Source
AI summary
It is provided that a polyester resin and a polyester resin composition that allow reduction of harmful outgas and can form a coating film having excellent characteristics such as curability, retort resistance, and processability. A polyester resin composition comprising polyester resin (A), wherein the polyester resin composition satisfies the following requirements (i) to (iii), (i) the polyester resin (A) has an acid value of 100 eq/ton or more, (ii) the polyester resin composition substantially contains no curing agent, and (iii) a content of tetrahydrofuran-insoluble matter is 10 mass% or more when the polyester resin composition has been heated at 240°C for one hour.