What is Epoxy Resin?
Epoxy is a family of thermosetting resins used as adhesives, laminating resins, coatings for grinding wheels, fire-retardant coatings and insulating materials. It is supplied in both liquid and solid forms. Solids are often preferred because they do not evaporate or degrade as much as liquids over time, though both serve similar purposes. Before it cures, epoxy can be blended with fillers, modifiers and reinforcements to make the cured material stronger, tougher or more flexible. As an adhesive it can be formulated for anything from a light bond to a joint that resists heat, water and chemicals.
What Makes Up Epoxy Resin?
Chemically, epoxy resins (polyepoxides) are organic compounds containing epoxide groups: carbon chains covalently bonded to oxygen, hydrogen and, in some types, nitrogen. On their own they are reactive intermediates. Mixed with a curing agent (a hardener) and, usually, heat, the epoxide groups react and cross-link into a rigid three-dimensional network. That is what makes epoxy a thermoset: once cured it will not melt again, and it becomes hard, tough and chemically resistant.
What are the Types of Epoxy Resin?
Epoxies fall into two principal categories: glycidyl and non-glycidyl. Non-glycidyl resins are aliphatic or cycloaliphatic. Glycidyl resins divide into glycidyl-amine, glycidyl-ether and glycidyl-ester types. Glycidyl ethers are the most common, especially the bisphenol and novolac grades. Brief descriptions of each:
Bisphenol Epoxy Resins:
Bisphenol-A diglycidyl ether (BADGE, or DGEBA) is the most widely used commercial epoxy. It is produced by reacting bisphenol-A with epichlorohydrin, and by varying the ratio manufacturers make grades from low-viscosity liquids to solids.
Aliphatic Epoxy Resins:
Aliphatic epoxies are made either by epoxidizing double bonds (cycloaliphatic epoxides and epoxidized vegetable oils) or by reaction with epichlorohydrin (glycidyl ethers and esters). Cycloaliphatic types carry one or more aliphatic rings with an oxirane ring in the molecule. They are chlorine-free, with low viscosity, good weather resistance and low dielectric constants.
Novolac Epoxy Resins:
Novolacs start as phenol or cresol reacted with formaldehyde; reacting that novolac with epichlorohydrin gives epoxy phenol novolac (EPN) or epoxy cresol novolac (ECN). Their high functionality gives a dense cross-link, so they offer good adhesion, heat resistance and chemical resistance.
Halogenated Epoxy Resins:
Halogenated epoxies include ingredients chosen for specific properties. Brominated bisphenol-A is added for flame resistance, which is how most FR-4 laminate earns its rating, and fluorinated compounds are used in some electrical applications. The drawback is cost, and some applications now call for halogen-free alternatives.
Glycidyl Amine Epoxy Resins:
Glycidyl-amine epoxies are made by reacting aromatic amines with epichlorohydrin. They have high functionality, cure to a high cross-link density and are used where strength at elevated temperature matters. Many have low to medium viscosity at room temperature.
What is Epoxy Resin Used For?
Epoxy is familiar at home, in craft pours, countertop and floor refinishing, but its bigger role is industrial.
The paints and coatings industry uses it for insulating and protective coatings on vessels, satellite systems, spacecraft and aircraft. In renewable energy it coats and protects steel structures at hydroelectric plants.
Wind energy depends on it: epoxy composites are essential to large wind turbine blades, where their strength-to-weight ratio makes longer blades possible.
Hospitals and food processing plants use epoxy floors because hygiene comes first. Epoxy flooring stands up to strong cleaning chemicals, and it can be finished with an anti-slip texture to help prevent accidents.
Epoxy Resin in Industrial Laminates
At Current, epoxy is a laminating resin. Woven glass cloth is impregnated with epoxy, partially cured into prepreg, stacked and pressed under heat and pressure into sheet, or convolutely wound into tube. The resin system decides the grade:
- G-10 and FR-4: glass-epoxy with the best all-round strength and electrical properties at room temperature. FR-4 uses a flame-retardant, typically brominated, epoxy.
- G-11 and FR-5: a higher-temperature epoxy that keeps at least half its flexural strength at 150 °C.
- Non-brominated G-10: glass-epoxy made without halogenated flame retardants, also used for cryogenic service.
- Copper clad laminate: FR-4 with copper bonded to one or both faces, the starting material for printed circuit boards.
Epoxy is also one of the resins we use for carbon fiber plate and tube. The properties comparison shows how the epoxy grades compare with phenolic and melamine laminates.
What are the Benefits of Epoxy Resin?
Its advantages include:
Resistance:
Once cured, epoxy resists moisture and oil and withstands many chemicals, including acids and solvents. It also tolerates heat, shock and vibration well.
High Versatility:
Epoxy adheres to a wide range of materials, including wood, stone, concrete, plastic, glass and metal, which makes it useful in industries from HVAC and construction to marine.
Low Shrinkage:
Epoxies shrink very little as they cure, which keeps internal stress low and improves adhesion and dimensional accuracy.
Strong Mechanical Properties:
Compressive, flexural and tensile strength are all high, and cured epoxy resists degradation over time, which is why it is the resin of choice for structural and electrical laminates.
Attractive Appearance:
Epoxy cures to a clear, glossy, abrasion-resistant finish and can be colored with pigments, which is also why FR-4 is available in so many colors.
A Final Recap on Industrial Epoxy Resin
Industrial epoxy resin is an extremely versatile material, with many types and uses from coatings and adhesives to the glass-epoxy laminates in circuit boards and electrical equipment. If your application needs an epoxy laminate as sheet, tube, rod or a machined part, send us the details and we will recommend a grade.