How Epoxy Resin Works: The Chemistry
Epoxy resins contain epoxide groups (oxirane rings) that react with hardener molecules — typically amines, anhydrides, or polyamides. This exothermic reaction creates a three-dimensional cross-linked polymer network. The curing process is irreversible: once cured, epoxy cannot be re-melted.
The most common industrial epoxy resins are based on Bisphenol A diglycidyl ether (BADGE), produced by reacting bisphenol A with epichlorohydrin. The result is a clear to pale-yellow viscous liquid with an epoxy equivalent weight (EEW) of approximately 182–196 g/eq.
Epoxy Resin Types: Technical Comparison
Global Optimals supplies five standard liquid epoxy resins suitable for industrial coatings, self-leveling floors, and composite manufacturing:
| Grade | EEW (g/eq) | Viscosity at 25°C (mPa·s) | Color (Gardner) | Best Application |
|---|---|---|---|---|
| KER 828 | 185–192 | 11,000–14,000 | ≤ 1 | Universal: floors, coatings, adhesives |
| DY-128 | 182–192 | 8,000–12,000 | ≤ 1 | Thin coatings, lower-viscosity formulations |
| Gelr-128 | 184–190 | 10,000–13,000 | ≤ 1 | Composites, structural adhesives |
| CYD-128 | 184–190 | 10,000–14,000 | ≤ 1 | Industrial floors, anti-corrosion coatings |
| KER 3001x75 | 480–540 | 800–1,200 (in solution) | ≤ 3 | Flexible coatings, primers, elastic systems |
Note: KER 3001x75 is a high-molecular-weight resin supplied as a 75% solution in benzyl alcohol. Its EEW refers to the solid resin, not the solution.
Hardener Selection: KH-816 vs Cardolite NC-562
Selecting the correct hardener is as important as the resin choice. The wrong hardener causes incomplete curing, surface defects, or premature failure.
| Property | KH-816 | Cardolite NC-562 |
|---|---|---|
| Chemistry | Modified cycloaliphatic amine | Cardanol-based phenalkamine |
| Mix ratio (pbw) | 100 : 25–30 | 100 : 30–40 |
| Pot life at 25°C | 30–40 min | 45–60 min |
| Touch-dry | 6–8 h | 8–12 h |
| Full cure | 7 days | 7 days |
| Moisture tolerance | Low — dry substrate required | High — cures in humid conditions |
| Min. application temp. | +10°C | +5°C |
| Flexibility | Rigid | Semi-flexible |
| Typical use | Dry interiors, standard floors | Outdoor, damp substrates, primers |
Key Additives and Their Functions
Fillers — Blanc fixe (BaSO4)
Blanc fixe L and N grades are synthetic barium sulfate fillers with d50 particle size of 2–5 µm. In epoxy floor formulations they provide:
- Reduced shrinkage during curing (typical loading: 20–40% w/w)
- Increased surface hardness and abrasion resistance (Shore D increase: ~5–8 points)
- Enhanced gloss — smoother particle size distribution improves optical leveling
- Chemical inertness — stable against acids pH > 1 and alkalis pH < 13
Defoamer — TEGO AIREX 900
Silicone-free polymeric defoamer. Addition rate: 0.1–0.5% w/w. Eliminates micro-bubbles during mixing and application, preventing pinholes in the cured film. Compatible with all standard amine-cured epoxy systems.
Surface Leveling — GLIDE B 1484
Polyether-modified polysiloxane flow and leveling agent. Addition rate: 0.1–0.3% w/w. Reduces surface tension to achieve a mirror-like finish and eliminates cratering.
Dispersant — TEGO Dispers 670
High-molecular-weight block copolymer dispersant. Used at 1–3% on pigment weight. Ensures uniform pigment distribution and prevents flocculation in pigmented floor coatings.
Reactive Diluents
Benzyl alcohol — reduces system viscosity and improves substrate wetting. Addition rate: up to 5% w/w. Participates in the curing reaction. C12-C14 AGE (Alkyl Glycidyl Ether) — mono-functional reactive diluent. Lowers viscosity without reducing crosslink density as significantly as non-reactive diluents.
Industrial Applications
- Self-leveling industrial floors (2–6 mm) — warehouses, food processing plants, hospitals, clean rooms
- Anti-corrosion coatings — pipelines, storage tanks, marine structures, bridges
- Composite materials — wind turbine blades, aerospace panels, sporting goods
- Structural adhesives — bonding metals, concrete, ceramics
- Electrical insulation — potting compounds, encapsulants for electronics
- Road markings — high-durability traffic paint systems
Safety and Handling Guidelines
Follow these practices when working with uncured epoxy systems:
- Wear nitrile gloves (not latex — epoxy permeates latex within 10 minutes)
- Use safety glasses with side shields; amine hardeners cause severe eye irritation
- Ensure adequate ventilation — amine vapors from KH-816 have a TLV-TWA of 2 ppm
- Cured epoxy is chemically inert and safe for food-adjacent surfaces (check specific certification)
- Store resin and hardener separately at 15–25°C, away from moisture; shelf life: 12 months
