Crystalline Polyester Resin Coating for Retort-Resistant Metal Cans
Find Innovative SolutionsGenerate Solutions
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, making them unsuitable for food and beverage cans.
Innovation Solution
A crystalline polyester resin with specific compositions of polycarboxylic acid and polyalcohol components, including orthophthalic acid and 1,4-butanediol, is developed to form a coating film without a curing agent, ensuring excellent solvent solubility, retort resistance, and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epoxy-based coatings or vinyl chloride-based coatings are used to achieve corrosion resistance and flavor properties, then the coating provides adequate protection, but harmful substances such as bisphenol A, formaldehyde, and dioxin are present
Solution Approach 1:
The invention extracts and eliminates harmful substances (bisphenol A, formaldehyde, dioxin) from the coating system by replacing epoxy-based, vinyl chloride-based, and phenolic-based coatings with crystalline polyester-based coatings that do not contain these harmful components, while maintaining the essential corrosion resistance function
Solution Approach 2:
The invention changes the chemical composition parameters of the coating by specifying precise compositional ranges for the crystalline polyester (including copolymerization proportions of dicarboxylic acid and diol components) and limiting content of harmful substances to below detection limits, thereby transforming the coating from harmful to safe
2Object-affected harmful factors
If crystalline polyester resin is used to eliminate harmful substances and improve safety, then the coating becomes free from harmful substances, but solvent solubility and processability are insufficient
Solution Approach 1:
The invention creates a composite coating system combining crystalline polyester resin with specific additives (polyester resin, extender pigment, lubricant, and solvent) where each component complements the others to achieve both safety (no harmful substances) and manufacturability (adequate solvent solubility and processability)
Solution Approach 2:
The invention optimizes the compositional parameters of the crystalline polyester resin, specifically controlling the copolymerization proportions of dicarboxylic acid (30-70 mol%) and diol (70-30 mol%), along with adding specific additives, to achieve the desired balance between safety and solvent solubility
3Reliability
If crystalline polyester resin with high crystallinity is used to improve retort resistance, then the coating maintains stability under high-temperature conditions, but molecular planarity and symmetry reduce solvent solubility
Solution Approach 1:
The invention precisely controls the compositional parameters of the crystalline polyester resin, including the copolymerization proportions of dicarboxylic acid and diol components, to achieve an optimal balance where the resin maintains sufficient crystallinity for retort resistance while preserving adequate solvent solubility for manufacturability
Data Source
AI summary
An object of the present invention is to provide a crystalline polyester resin that contains no curing agent and thus excludes a harmful substance such as bisphenol A and formaldehyde, that has excellent solvent solubility, and that is capable of forming a coating film having excellent properties such as processability and retort resistance; a coating material composition containing the crystalline polyester resin; a coating film; and a metal can. A crystalline polyester resin containing a polycarboxylic acid component and a polyalcohol component as copolymerization components, wherein the crystalline polyester resin contains 4 to 48 mol% of orthophthalic acid as the polycarboxylic acid component, and 48 mol% or more of 1,4-butanediol and less than 40 mol% of ethylene glycol as the polyalcohol component, and wherein the crystalline polyester resin has a melting point of 120 to 160°C.