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1. Amine curing agents (fatty amines, cyclic amines, modified fatty amines, IPD, TETA, etc.)

✅  Reaction mechanism: Amine active hydrogen directly undergoes ring opening addition with epoxy, and can react at room temperature with significant heat release ✅  characteristics

· Curing speed: fast, short gel at room temperature; Modified cyclic amines can achieve low-temperature curing at around 5 ℃

Applicable period: Short (especially short for small molecule fatty amines)

Paint film: high hardness, high cross-linking density, and good chemical resistance; Slightly brittle

Disadvantages: Small molecule fatty amines are prone to moisture absorption, whitening, and salt staining, and have a strong odor irritation; The aromatic amine version has higher heat resistance, but it needs to be cured by heating and has a carcinogenic risk. Coatings are rarely used

Color: Alicyclic amine light color, better resistance to yellowing than ordinary fatty amines, suitable for transparent topcoats ✅  Formula application: fast drying flooring, repair materials, high gloss epoxy topcoat, high solid content flooring; Not suitable for long-term anti-corrosion of damp substrates

2. Polyamide curing agent (low molecular weight polyamide, dimer fatty acid+polyamine condensation)

✅  Reaction mechanism: Similarly, amine hydrogenation epoxides have long fatty acid flexible chains and amide groups on their molecules ✅  characteristics

Curing speed: curing at room temperature is slow, and curing at low temperatures (<10 ℃) is very slow, making it easy to dry on the surface but not on the inside

Applicable period: very long, high tolerance for mixing ratio (no need to get stuck)

Paint film: Strong toughness, adhesion, water resistance, salt spray resistance, low internal stress, and not easy to crack; Moderate hardness

Disadvantages: Poor heat resistance (low HDT), less resistant to strong solvents than pure amines and anhydrides; Color tends to be yellowish ✅  Formula application: Epoxy anti-corrosion primer, steel structure, ship, concrete wet base primer, is the most mainstream curing agent for anti-corrosion epoxy

3. Anhydride curing agent (methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, etc.)

✅  Reaction mechanism: Anhydride and epoxy must be heated and promoted to form ester bonds for cross-linking; Almost no reaction at room temperature ✅  characteristics

· Curing conditions: medium high temperature curing (100 – 160 ℃), almost no gel at room temperature

Applicable period: extremely long, can be stored at room temperature for a long time after mixing

Paint film: Tg, high thermal deformation temperature, top-notch electrical insulation performance, and resistance to strong chemical media; The paint film is hard and brittle

Disadvantages: It is prone to hydrolysis when in contact with water, and the storage and construction environment must be dry; We need an oven, which cannot be used for on-site engineering ✅  Formula application: electronic sealing, transformers, composite materials, high temperature resistant epoxy, almost not used for on-site construction coatings

Supplement the key points that are prone to pitfalls

1. Phenolic amine (Cadley type) does not belong to these three categories: it is a separate category, mainly used for low-temperature and humid surface curing, heavy-duty anti-corrosion primer, and has stronger water resistance than ordinary polyamide;

2. Aliphatic amine ≠ Fatty amine: Aliphatic amine is an amine based saturated ring with low color and yellowing, and amine cream is much lighter than straight chain fatty amine. It is currently the mainstream for floor coatings;

3. Polyamide is not Amidamine: Amidamine has a faster curing speed and better low temperature, which is intermediate between polyamide and modified fatty amine;

4. The anhydride system paint film is ester bond, which will hydrolyze and degrade under long-term hot water and strong alkali, and the anti-corrosion coating is basically not touched.