Crystalline Polyester Can Coating With Low-Solvent Retort Resistance
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Solution Overview
Problem
Existing coatings for metal cans, such as epoxy-based and vinyl chloride-based coatings, contain harmful substances like bisphenol A and formaldehyde, and lack adequate retort resistance and solvent solubility, while aqueous coatings require organic solvents and have insufficient processability.
Innovation Solution
A crystalline polyester resin with a melting point of 120° C. to 160° C., crystallinity of 60% to 90%, and acid value of 180 eq/ton or more, formulated through specific aging treatment, is used to create an aqueous dispersion that forms a coating film with excellent retort resistance and solvent solubility, eliminating the need for curing agents and reducing harmful substance content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional epoxy-based coatings are used to achieve corrosion resistance and flavor properties, then the coating provides adequate protection, but harmful substances like bisphenol A are present and retort resistance is poor
Solution Approach 1:
The patent changes the chemical composition parameters by using crystalline polyester resin with specific melting point (120-160°C) and crystallinity (60-90%), replacing epoxy-based coatings to eliminate harmful substances like bisphenol A while maintaining corrosion resistance and improving retort resistance
Solution Approach 2:
The patent uses composite material strategy by formulating an aqueous dispersion containing crystalline polyester resin combined with specific curing agents, creating a multi-component coating system that achieves both safety (no harmful substances) and performance (corrosion resistance, retort resistance)
2Reliability
If the melting point of crystalline polyester resin is increased to improve retort resistance, then retort resistance is improved, but solvent solubility is deteriorated and aqueous dispersion cannot be formed
Solution Approach 1:
The patent optimizes the melting point parameter to a specific range (120-160°C) that balances retort resistance and solvent solubility, and controls crystallinity (60-90%) to maintain both heat resistance and processability, enabling formation of aqueous dispersion
3Ease of operation
If high-acid-value acrylic modified polyester resin is used to improve processability, then processability is improved, but sufficient processability cannot be achieved and retort resistance decreases due to unreacted crosslinking agent
Solution Approach 1:
The patent controls the acid value of crystalline polyester resin within a specific range (150-250 mg KOH/g) to achieve adequate processability while ensuring complete reaction with curing agents, eliminating unreacted portions that would compromise retort resistance
Solution Approach 2:
The patent uses a different chemical approach by selecting specific curing agents that react completely with the crystalline polyester resin, avoiding the use of β-hydroxyalkylamide crosslinking agents that leave unreacted portions and cause retort resistance problems
4Object-affected harmful factors
If aqueous coating is used to reduce harmful substances and environmental contamination, then harmful substance content is reduced, but organic solvent is still needed and processability is insufficient
Solution Approach 1:
The patent optimizes the acid value parameter (150-250 mg KOH/g) to provide adequate reactivity for processability while maintaining aqueous formulation, enabling the coating to be applied and cured effectively with minimal organic solvent
Solution Approach 2:
The patent introduces crystalline polyester resin with specific crystallinity as an intermediary that enables adequate processability in aqueous systems, acting as a bridge between the requirement for low harmful substances and the need for sufficient processability
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 crystalline polyester resin aqueous dispersion enables the formation of a coating film with enhanced processability, retort resistance, and minimal use of organic solvents, suitable for metal cans, excluding harmful substances like bisphenol A and formaldehyde.
Implementation Method 1
The crystalline polyester resin (A) has a crystallinity of 60% to 90%, wherein the crystallinity is determined from a heat quantity of fusion (J/g) of an endothermic peak obtained when the crystalline polyester resin (A) is heated from −50° C. to 200° C. at 20° C./min by differential scanning calorimetry (DSC) after subjected to an aging treatment at 100° C. for 10 minutes.
Implementation Method 2
The crystalline polyester resin (A) has a melting point of 120° C. to 160° C.
Data Source
AI summary
A crystalline polyester resin aqueous dispersion containing a crystalline polyester resin has excellent solvent solubility and therefore needs only a small amount of an organic solvent to form an aqueous dispersion, and is capable of forming a coating film that has excellent processability and retort resistance. The crystalline polyester resin aqueous dispersion contains a crystalline polyester resin satisfying requirements (1) to (3) described below. (1) The crystalline polyester resin has a melting point of 120° C. to 160° C. (2) The crystalline polyester resin has a crystallinity of 60% to 90%, the crystallinity being determined from a heat quantity of fusion (J/g) of an endothermic peak obtained when the crystalline polyester resin is heated from −50° C. to 200° C. at 20° C./min by differential scanning calorimetry (DSC) after subjected to an aging treatment at 100° C. for 10 minutes. (3) The crystalline polyester resin has an acid value of 180 eq/ton or more.