Polyester Resin Can Coating Retort Resistance
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Solution Overview
Problem
Current polyester resins used for can coatings, such as polyvinyl chloride-based and epoxy-phenol-based resins, face issues with health hazards, environmental concerns, and inadequate performance in terms of processability, curability, retort resistance, and dent resistance, while existing polyester resin solutions do not adequately address these challenges.
Innovation Solution
A polyester resin is developed with a specific composition of terephthalic acid, 2,6-naphthalenedicarboxylic acid, ethylene glycol, and 1,2-propylene glycol, combined with a blocked isocyanate curing agent, to achieve high curability and resistance to retort, content, and dent impacts, ensuring excellent processability and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyvinyl chloride-based resins are used as base resin for can coating, then retort resistance and content resistance are improved, but health safety deteriorates due to carcinogenic vinyl chloride monomer and toxic gas generation during incineration
Solution Approach 1:
The invention extracts and eliminates the harmful vinyl chloride monomer component from the resin system by replacing polyvinyl chloride-based resins with polyester-based resins that do not contain or generate carcinogenic substances, while maintaining the required retort resistance through alternative chemical composition
Solution Approach 2:
The invention changes the chemical composition parameters by specifying precise copolymerization ratios of terephthalic acid (80-97.5 mol%), isophthalic acid (0-20 mol%), and sebacic acid (0-10 mol%), along with glycol component ratios, to achieve a resin system that provides both retort resistance and health safety without toxic gas generation
2Strength
If epoxy-phenol-based resins are used as base resin for can coating, then adhesion to metal is improved, but processability deteriorates due to high baking temperature requirements causing foaming
Solution Approach 1:
The invention changes the chemical composition parameters by using polyester-based resins with specific acid value ranges (15-80 mg KOH/g) and molecular weight characteristics that enable curing at lower temperatures (100-200°C) compared to epoxy-phenol resins, thereby improving processability and preventing foaming while maintaining adhesion through optimized resin structure
Solution Approach 2:
The invention creates a composite resin system combining polyester base resin with specific curing agents and additives to achieve both good adhesion to metal surfaces and improved processability at lower baking temperatures, avoiding the foaming issues associated with high-temperature curing of epoxy-phenol resins
3Object-affected harmful factors
If polyester-based resins are used to replace harmful resins, then health safety and environmental compatibility are improved, but curability and processability deteriorate
Solution Approach 1:
The invention introduces specific curing agents as intermediaries that react with the polyester-based resin to achieve proper curability. The curing agents facilitate crosslinking and film formation at appropriate temperatures, enabling the environmentally friendly polyester system to achieve the necessary curability that pure polyester resins alone cannot provide
Solution Approach 2:
The invention optimizes the molecular weight, acid value, and copolymerization ratio parameters of the polyester-based resin to balance environmental compatibility with curability. By controlling the resin's chemical structure parameters, the system achieves both health safety and adequate curability through proper formulation
4Object-generated harmful factors
If polyester-based resins are used for can coating, then toxic gas generation during incineration is reduced, but dent resistance deteriorates
Solution Approach 1:
The invention creates a composite coating system using polyester-based resin combined with specific curing agents and functional additives that enhance dent resistance. This composite formulation maintains the environmental advantage of reduced toxic gas generation during incineration while compensating for the inherently lower dent resistance of polyester resins compared to traditional options
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 resulting coating film exhibits superior processability, curability, retort resistance, content resistance, and dent resistance, making it suitable for use in food and beverage cans without generating toxic gases during incineration and avoiding environmental hormone concerns.
Implementation Method 1
curability
Implementation Method 2
retort resistance
Implementation Method 3
dent resistance
Data Source
AI summary
This invention provides a polyester resin that is capable of forming a coating film having extremely excellent curability, processability, retort resistance, content resistance, and dent resistance, and also provides a resin composition for a coating composition containing the polyester resin. The polyester resin obtained from a polycarboxylic acid component and a polyol component, wherein the polyester resin meets the conditions (i) to iii) described below:(i) among the polycarboxylic acid components constituting the polyester resin, the total copolymerization ratio of terephthalic acid component and 2,6-naphthalenedicarboxylic acid component is 80 mol % or more;(ii) among the polycarboxylic acid components constituting the polyester resin, the copolymerization ratio of 2,6-naphthalenedicarboxylic acid component is 2 to 80 mol %; and(iii) among the polyol components constituting the polyester resin, the total copolymerization ratio of ethylene glycol component and 1,2-propylene-glycol component is 50 mol % or more, wherein the copolymerization ratio of 1,2-propylene-glycol component is excessive relative to the copolymerization ratio of the ethylene glycol component.