Crystalline Polyester Can Coating Without Curing Agents
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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 sufficient processability and retort resistance, while aqueous coatings require organic solvents and have poor solvent solubility.
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 processability and retort resistance without a curing agent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional epoxy-based coatings are used, then corrosion resistance and flavor properties are improved, but harmful substances like bisphenol A are generated
Solution Approach 1:
The invention changes the chemical composition parameters of the coating by using polyester resin with specific characteristics (melting point 120-160°C, crystallinity 60-90%, acid value 180 eq/ton or more) instead of epoxy resin, thereby eliminating harmful substances while maintaining protective functions
Solution Approach 2:
The invention replaces expensive and harmful epoxy-based coatings with a more environmentally friendly polyester-based aqueous dispersion that achieves the same protective function without generating harmful substances like bisphenol A
2Ease of operation
If high-acid-value acrylic modified polyester resin is used, then aqueous dispersion is achieved, but processability is insufficient
Solution Approach 1:
The invention optimizes the acid value parameter to 180 eq/ton or more, which provides sufficient reactivity for aqueous dispersion formation while maintaining adequate processability during can forming operations
Solution Approach 2:
The invention uses a composite resin system combining polyester resin with specific crystalline structure and controlled acid value, achieving both aqueous dispersibility and manufacturing processability that single-component systems cannot provide
3Reliability
If crystalline polyester resin with high melting point is used, then retort resistance is improved, but solvent solubility is deteriorated
Solution Approach 1:
The invention precisely controls the melting point parameter within 120-160°C range, which is high enough to provide retort resistance but low enough to maintain solvent solubility for aqueous dispersion formation
Solution Approach 2:
The invention creates a composite resin system with specific crystalline structure that balances thermal stability for retort resistance with molecular characteristics that maintain solvent interaction for dispersion formation
4Reliability
If curing agent is added to improve crosslinking, then coating performance is improved, but harmful substances and complexity increase
Solution Approach 1:
The polyester resin itself provides the necessary reactivity and crosslinking capability through its functional groups, eliminating the need for separate curing agents and simplifying the coating composition
Solution Approach 2:
The invention extracts and removes the curing agent component from the coating system, relying solely on the polyester resin's inherent properties to achieve the required coating performance
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 provides a coating film with improved solvent solubility, reduced harmful substance content, and enhanced retort resistance, suitable for metal cans.
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
Data Source
AI summary
An object of the present invention is to provide a crystalline polyester resin aqueous dispersion containing a crystalline polyester resin that has excellent solvent solubility and therefore needs only a small amount of an organic solvent used to form an aqueous dispersion, and being capable of forming a coating film that has excellent properties such as processability and retort resistance; a coating composition containing the crystalline polyester resin aqueous dispersion; a coating film; and a metal can. Another object of the present invention is to obtain a coating that contains no curing agent and therefore excludes a harmful substance such as bisphenol A and formaldehyde. A crystalline polyester resin aqueous dispersion containing a crystalline polyester resin (A) satisfying requirements (1) to (3) described below. (1) The crystalline polyester resin (A) has a melting point of 120°C to 160°C. (2) 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. (3) The crystalline polyester resin (A) has an acid value of 180 eq/ton or more.