Crystalline Polyester Aqueous Dispersion for Retort-Resistant Can Coatings
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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 specific melting points, endothermic peaks, and acid values is used to form an aqueous dispersion, eliminating the need for curing agents and ensuring excellent processability and retort resistance.
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 patent changes the chemical composition parameters by using crystalline polyester resin instead of epoxy resin, maintaining protective functions while eliminating harmful substances like bisphenol A and formaldehyde
Solution Approach 2:
The patent uses a water-based coating system that can be applied and cured without requiring complex curing agents, simplifying the coating system and reducing harmful byproducts
2Object-generated harmful factors
If aqueous coating is used to eliminate harmful substances, then harmful substance content is reduced, but solvent solubility and coating performance are deteriorated
Solution Approach 1:
The patent uses composite crystalline polyester resin with specific molecular structure characteristics (melting point 120-160°C, specific endothermic peaks) that combines water solubility with excellent coating performance including adhesion, flexibility, and retort resistance
Solution Approach 2:
The patent optimizes the molecular parameters of the polyester resin including melting point, endothermic peak temperatures, and acid value to achieve both water solubility and superior coating performance without requiring organic solvents
3Reliability
If crystalline polyester resin with high melting point is used to improve retort resistance, then retort resistance is improved, but solvent solubility is deteriorated
Solution Approach 1:
The patent precisely controls the melting point parameter within 120-160°C and optimizes endothermic peak characteristics to achieve the optimal balance between retort resistance and water solubility, eliminating the need for organic solvents
4Ease of operation
If acrylic modified polyester resin with high acid value is used to improve processability, then processability is improved, but sufficient processability and retort resistance cannot be achieved
Solution Approach 1:
The patent uses crystalline polyester resin with specific crystalline structure and controlled acid value (50-200 mg KOH/g) that provides both excellent processability during can forming operations and superior retort resistance, overcoming the limitations of acrylic modified polyester resins
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 achieves a coating film with improved solvent solubility, reduced harmful substance content, and enhanced retort resistance, suitable for beverage and food cans.
Implementation Method 1
The crystalline polyester resin has a melting point of 120°C to 160°C
Implementation Method 2
the crystalline polyester resin has at least one endothermic peak between 70°C and 120°C and at least one endothermic peak between 121°C and 160°C when heated from -50°C to 200°C at 20°C/min by differential scanning calorimetry (DSC)
Data Source
Figure 1
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 at least one endothermic peak between 70°C and 120°C and at least one endothermic peak between 121°C and 160°C when heated from -50°C to 200°C at 20°C/min by differential scanning calorimetry (DSC) after subjected to an aging treatment at 80°C for 10 minutes. (3) The crystalline polyester resin (A) has an acid value of 180 eq/ton or more.