No.114: Polyester Powder Coatings

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1. Product Overview

Polyester powder coatings are innovative coatings known for their flexibility and durability, suitable for a broad range of products. These coatings are recognized for their benefits across diverse fields, including home appliances, building materials, external fences, heavy electrical machinery, construction equipment, agricultural machinery, automotive parts, and general metal products. As thermosetting polyester-based coatings, they offer superior primary physical properties, hardness, chemical resistance, and corrosion resistance, making them applicable for both outdoor and indoor use. 

2. Technical Details

The technology of thermosetting polyester powder coatings is divided into two main categories: urethane-modified and triglycidyl isocyanurate (TGIC) cured types. The urethane-modified type is based on polyester resins with hydroxyl groups on their end chains or side chains, crosslinked with blocked isocyanates, and undergoes a curing process at 165-190°C for 20-30 minutes, where the isocyanate compounds react with the hydroxyl groups of the polyester resin to form the coating film. On the other hand, TGIC cured polyester types use polyester resins with terminal carboxyl groups and glycidyl compounds, utilizing TGIC as the curing agent. Recently, types using HAA (β-hydroxyalkylamide) as a curing agent have gained attention for their environmental and health benefits, where the carboxyl groups of the polyester resin and HAA form ester bonds, utilizing a reaction that volatilizes only water (H2O). 

3. Advantages

The greatest advantage of polyester powder coatings lies in their appearance and physical properties. They provide excellent chemical resistance, corrosion resistance, and weatherability, enduring diverse environmental conditions. Moreover, the use of urethane or HAA curing agents allows for environmentally and health-conscious coating options, particularly with HAA curing agents, which significantly reduce environmental impact during the curing process as only water is volatilized. Additionally, application by electrostatic spraying is possible, with typical coating thicknesses ranging from 50 to 80μm, allowing for uniform coating films on fine parts and objects with complex shapes. 

4. Disadvantages

The main disadvantage of urethane-modified polyester powder coatings is the volatilization of blocking agents during the curing process, which can lead to smoke and tar generation in the oven, and issues like foaming of the coating film during thick-coat applications. TGIC cured polyester powder coatings require special attention due to the sensitizing and toxic nature of the curing agent, limiting their use. While coatings using HAA curing agents initially raised concerns about water resistance, improvements have since brought their performance to a practical level. 


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