Classified by Purpose
Curing agents are typically categorized into room-temperature curing agents and heat-curing agents depending on their application. Epoxy resins usually exhibit excellent performance when cured at high temperatures. However, coatings and adhesives used in civil engineering often cannot be heated, so they rely on room-temperature curing. As a result, most of them use fatty amines, alicyclic amines, and polyamides, especially during winter. These materials are often used in combination with polyisocyanates or have the disadvantage of emitting odors from polyester resins.
Medium-temperature and high-temperature curing agents are selected based on the heat resistance of the object and the properties of the cured product, such as heat resistance, adhesion, and chemical resistance. Polyamines and anhydrides are commonly chosen for this purpose. Anhydride-cured products have excellent electrical properties, making them widely used in electronics and electrical appliances.
Polyamine-cured products offer good adhesion, alkali resistance, and water resistance. Aromatic polyamines also show strong chemical resistance. The amino group’s nitrogen can form hydrogen bonds with metal surfaces, providing effective rust prevention. The higher the amine concentration, the better the rust protection. Acid anhydride curing agents react with epoxy resin to form ester bonds, offering strong resistance to both organic and inorganic acids. These products generally outperform polyamines in electrical properties.
Classified by Usage
Curing agents are divided into room-temperature and high-temperature types based on their usage. Room-temperature curing agents are suitable for applications without a heating process, while high-temperature curing agents, also known as blocked curing agents, remain stable at normal temperatures and can coexist with water-based resins like aqueous polyurethane, water-based acrylate, fluorine emulsion, and silicone emulsion for extended periods. When subjected to heat treatment (above 95°C), the isocyanate (-NCO) groups in the curing agent react with functional groups such as hydroxyl, carboxyl, or amino groups in the aqueous resin, forming a crosslinked structure that significantly enhances the performance of the aqueous resin.
Blocked curing agents improve upon traditional ones by requiring two components, which can lead to issues like inaccurate dosing and waste. Despite this, their application range is extensive. For example, Moore Chemical’s blocked water-based isocyanate curing agent has multiple uses: 1) as an internal crosslinking agent in one-component thermosetting water-based coatings, it improves water resistance, chemical resistance, wear resistance, adhesion, and mechanical properties; 2) as a bridging agent for organic fluorine or silicone emulsions, it helps fix these materials onto cotton or polyester fibers, enhancing washing resistance; 3) as an internal crosslinking agent for textile coatings and printing adhesives, it boosts adhesion and washability; 4) as a one-component curing agent for metal and glass baking paints, it replaces amino resins, avoids formaldehyde emissions, and offers excellent yellowing resistance; 5) as a treatment agent for polyester or polyester cord fabrics, it improves bonding between polyester and rubber; 6) as a curing agent for cathodic electrophoretic coatings, it enhances overall coating performance.
In China, there are various room-temperature curing agents available, such as XR-100 from Xirun Chemical, which offers a wide selection and good cost-performance. Imported products like those from Bayer are more expensive but provide stable quality. However, the market currently has fewer types of blocked curing agents available domestically.
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