Copolymerized Polyester Resin for Can Coatings
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Solution Overview
Problem
Conventional high molecular weight saturated polyester resins used in coating compositions for cans and pre-coated metals suffer from cloudiness and reduced processability due to hydrolysis under high-temperature conditions, compromising hot water resistance and chemical resistance.
Innovation Solution
A copolymerized saturated polyester resin is developed with a specific molecular weight range and composition, incorporating aromatic dicarboxylic acids, trifunctional carboxylic acids, alicyclic polyhydric alcohols, and aliphatic polyhydric alcohols, which suppress moisture penetration and diffusion, enhancing hot water and chemical resistance while maintaining processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high molecular weight saturated polyester resin is used, then processability is improved, but hot water resistance deteriorates due to cloudiness and hydrolysis at high temperature
Solution Approach 1:
The patent changes the molecular weight parameters of the polyester resin to a specific range (number average molecular weight: 12,000 to 20,000 g/mol, weight average molecular weight: 30,000 to 80,000 g/mol, PDI: 2.5 to 4.0) and adjusts the glass transition temperature (40°C to 70°C) to achieve both good processability and hot water resistance by optimizing the balance between molecular weight and thermal properties
Solution Approach 2:
The patent uses a composite approach by combining polyester resin with specific additives including phenolic resins (0.1 to 5 parts by weight per 100 parts polyester resin) and other functional additives to enhance hot water resistance and chemical resistance while maintaining processability
2Reliability
If glass transition temperature of polyester resin is increased to suppress fluidity at high temperature, then hot water resistance is improved, but processability greatly deteriorates and solubility in organic solvent is reduced
Solution Approach 1:
The patent optimizes the glass transition temperature to a specific range (40°C to 70°C) rather than maximizing it, and carefully controls molecular weight parameters (PDI: 2.5 to 4.0) to achieve the right balance between high-temperature stability and processability, avoiding the trade-off by finding an optimal parameter window
3Ease of manufacture
If glass transition temperature of polyester resin is not significantly increased, then processability is maintained, but hot water resistance and chemical resistance are insufficient
Solution Approach 1:
The patent adds phenolic resins and other functional additives to the polyester resin system to enhance hot water resistance and chemical resistance without needing to significantly increase the glass transition temperature, allowing processability to be maintained while achieving the required reliability
4Reliability
If polyester resin is used for can coating requiring sterilization, then chemical resistance to food is needed, but cloudiness occurs under high-temperature sterilization conditions
Solution Approach 1:
The patent adjusts molecular weight parameters and glass transition temperature to prevent cloudiness during high-temperature sterilization while maintaining chemical resistance to food, by optimizing the resin structure to be stable under sterilization conditions
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 copolymerized resin achieves excellent hot water resistance, chemical resistance, and adhesion to metal substrates, making it suitable for high-temperature sterilization and food contact applications without compromising processability.
Implementation Method 1
The phenomenon in which a coating film formed from a polyester resin becomes cloudy by water or a compound under a high-temperature condition is known to be mainly caused by hydrolysis of the polyester resin by moisture penetrated and diffused to the coating film
Implementation Method 2
the proper branch structure of a polyester resin can maintain the excellent processability thereof and remarkably improve the hot water resistance and chemical resistance by suppressing the fluidity of a coating film
Data Source
AI summary
The present invention relates to a copolymerized saturated polyester resin and a coating composition containing same. Provided are a copolymerized saturated polyester resin and a coating composition having excellent hot water resistance, chemical resistance and processability when formed into a coating film, and showing excellent adhesiveness to a metal base, and thus particularly useful for coating a can and pre-coated metal (PCM).