Polyester Can Coating Composition for Thin-Film Dry Drawing
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Solution Overview
Problem
Existing methods for manufacturing drawn and ironed cans using coated metal sheets face issues with can making processability, substrate adhesion properties, and flavor sorption resistance, including coating film defects and peeling, as well as flavor component sorption on the coating film.
Innovation Solution
A coating composition comprising a polyester resin blend with specific acid values and glass transition temperatures, combined with a resol-type phenol resin as a curing agent and a solvent-based formulation, is applied to the metal sheet to form a coating film with enhanced adhesion and resistance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thermoplastic resin film is applied to the metal sheet beforehand, then drawing and ironing processing can be performed under dry conditions without liquid coolant, but the film thickness must be certain or greater which increases cost
Solution Approach 1:
The patent changes the chemical composition parameters of the coating film by using a polyester resin blend with specific acid values (combining low acid value resin <10 mg KOH/g and medium acid value resin 10-50 mg KOH/g) and controlling glass transition temperature (>40°C), enabling thin film formulation that maintains dry processing capability
Solution Approach 2:
The patent creates a composite coating system by blending polyester resins with different acid values and adding curing agents (phenolic resin, amino resin, or carboxylic acid anhydride) to form a crosslinked coating film that achieves both thin film thickness and adequate lubrication performance
2Quantity of substance
If drawing and ironing processing is applied to a coated metal sheet, then economy is improved with thin coating film, but coating film defects occur during can making processing
Solution Approach 1:
The patent optimizes the glass transition temperature parameter of the polyester resin blend to be greater than 40°C, which provides adequate lubrication during drawing and ironing processing while maintaining film integrity, preventing coating film defects during can making
Solution Approach 2:
The patent creates local quality differentiation by using a resin blend where low acid value polyester resin (<10 mg KOH/g) provides lubrication at the metal-coating interface during forming, while medium acid value polyester resin (10-50 mg KOH/g) ensures adequate adhesion to the substrate
3Quantity of substance
If drawing and ironing processing is applied to a coated metal sheet, then economy is improved with thin coating film, but coating film peels off from substrate
Solution Approach 1:
The patent controls the acid value parameter of the polyester resin blend between 2.0-16.0 mg KOH/g (combining low acid value <10 and medium acid value 10-50 resins), which balances adhesion strength and lubrication performance, preventing peeling while enabling thin film formulation
Solution Approach 2:
The patent applies preliminary chemical treatment to the substrate surface before coating application, including phosphating, chromating, or silane treatment, which creates a chemically active surface that enhances the adhesion of the polyester resin coating to the metal substrate
4Strength
If a coating film is applied to can interior surface, then substrate adhesion is improved, but flavor components are sorbed on the coating film
Solution Approach 1:
The patent adjusts the glass transition temperature parameter of the polyester resin blend to be greater than 40°C, which reduces the resin's molecular mobility and sorption capacity for flavor components like limonene, while maintaining adequate substrate adhesion through optimized acid value
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 solution provides coated metal sheets with improved can making processability, substrate adhesion, and flavor sorption resistance, preventing coating film defects and peeling, and reducing flavor component sorption, thus ensuring high-quality drawn and ironed cans.
Implementation Method 1
a curing agent, and a curing catalyst, the above-described problems can be solved together at high levels by (1) using polyester resins of different acid values in combination and also setting the glass transition temperatures of the individual resins at a predetermined temperature or higher, or (2) using a polyester resin having a glass transition temperature of a predetermined temperature or higher and also setting the amount of the curing catalyst, which is to be blended to promote the crosslinking reaction between the polyester resin and the curing agent
Implementation Method 2
the coating film has lubricating function. In addition, these processes are also superior in economy when the coating film is formed as a thin film
Implementation Method 3
the flavor of contents changes if flavor components (aroma components) such as limonene contained in the contents undergo sorption on the coating film when the contents are filled in a container manufactured by such drawing and ironing processing
Data Source
AI summary
A coating composition including a polyester resin blend as a principal resin, the polyester resin blend containing a polyester resin having a glass transition temperature of higher than 40° C. and an acid value of less than 10 mg KOH/g and (B) a polyester resin having a glass transition. temperature of higher than 40° C. and an acid value of 10 mg KOH/g or more and less than 50 mg KOH/g, and (C) a curing agent. Alternatively, a coating composition containing a polyester resin, as a principal resin, having a glass transition temperature of 60° C. or higher, a resol-type phenol resin. and/or an amino resin as a curing agent, and an organic sulfonic acid-based catalyst and/or a phosphoric acid-based catalyst as a curing catalyst, in which a content of the curing catalyst is less than. 0.2 part by mass per 100 parts by mass of the principal resin. Provided is a coating composition that can manufacture a coated metal sheet and a drawn and ironed can, which have can making processability, substrate adhesion properties, and flavor sorption resistance all together.