You may have shied away from choosing epoxy resin as a molding material due to concerns about its high cost and reputation as a more niche, less well-rounded polymer when compared to polyurethane, polyester or vinyl ester. However, in truth, epoxy resin possesses a number of benefits, including but not limited to high strength, excellent adhesion and minimal shrinkage during removal from the mold. Epoxy is also an excellent choice as a component of fiber-reinforced plastic (FRP). While it may not possess polyurethane’s versatility, epoxy is still an excellent resin which today sees wide use in a number of industries.
What is Epoxy Resin?
Like polyurethane, polyester and vinyl ester, epoxy is a thermoset polymer which begins its life in liquid form but ultimately achieves solid form via a process called curing, which is usually carried out in a mold. It is characterized by a recognizable brown or amber color in its natural, unpainted state.
The term “epoxy “comes from a chemical structure consisting of a bond between one oxygen atoms and two pre-bonded compounds containing carbon atoms. Epoxies are complex, 3-dimensional molecules with a long chain structure, which is the cause of their excellent strength and other beneficial mechanical properties.
Epoxy was first developed by Dr. Paul Schlack in Germany in the year 1934. Schlack initially derived epoxy from petroleum. This process was refined by Dr. Pierre Castan in Switzerland in 1938; Castan studied epoxy on behalf of the petroleum company which today exists as Shell Chemicals. While petroleum derivation is still a process used to create epoxy resins today, further research has led to the development of plant-derived epoxies, which are considered more environmentally friendly and simpler to dispose of or recycle.
Molding with Epoxy Resin
Epoxy resin can be successfully used in a number of molding processes. Because of its ability to cure at low temperatures compared to other materials, epoxy resin has seen frequent use in combination with an open mold. Open-mold processes which often utilize epoxy include resin transfer molding and filament winding, though it is also possible to use epoxy in closed-mold injection molding.
Unlike polyurethane or polyester, epoxy cures via the addition of a hardener to a liquid epoxide. The two components are stored separately before being mixed and cured during the molding process. While there are a variety of epoxides and hardeners which can be used to create epoxy resin, commonly used components include the epoxide epichlorohydrin and the hardening amine triethylenetetramine.
Because the reaction which produces the epoxy resin is an addition reaction, in which both components play an active role, it is important to carefully control the ratio of epoxide to hardener used. An incorrect ratio can result in bits of un-cured hardener remaining in the finished product, which weakens the resulting part as well as decreasing its aesthetic appeal. At Romeo RIM, our engineers can help you find the perfect balance to create a strong, tough, blemish-free epoxy!
Epoxy can also be combined with a reinforcing fiber to produce fiber reinforced plastic, a sturdy material with a wide variety of uses. When molding with epoxy, either the hand lay-up process (placing the fibers in the mold by hand) or the spray-up (spraying the fibers into the mold via pneumatic gun) can be used.
While any of the common fiber reinforcements (glass, carbon, aramid, and basalt) can be used in conjunction with epoxy resin, glass is most frequently chosen due to its high stiffness complimenting the natural stiffness and strength of epoxy. A glass and epoxy FRP composite is uniquely tough and durable even when compared with similar reinforced plastics.
Benefits of Epoxy Resin
The primary advantage of epoxy, which sets it apart from other thermoset polymers, is its excellent adhesion. The unparalleled adhesion of epoxy resin has led to its wide use in the manufacture of paints, sealants, varnishes, casting compounds, caulking compounds and glues. Epoxy-based adhesives are widely utilized in high-performance industries including aerospace and consumer watercraft.
In addition, epoxy resin is strong, tough, stiff and highly resistant to extreme heat, extreme cold, electricity and a number of chemicals – particularly solutions which are basic in nature. It experiences good dimensional stability and fatigue, even over time and after exposure to the elements. It is more viscous than other similar materials, featuring an average viscosity of 900 centipoise. These excellent mechanical properties can be further enhanced via the addition of reinforcing fibers, particularly glass.
Finishes produced via epoxy molding are often considered to be less aesthetically pleasing than those of other materials. However, epoxy’s excellent adhesion does mean that it can easily be colored and painted. Epoxy resin products also experience next to zero shrinkage when being removed from the mold, creating an unparalleled consistency across even the largest of production runs.
While epoxy is slightly more expensive and experiences slightly longer cure times than materials such as polyester, it can in fact be surprisingly cost effective. The low cure temperatures (no higher than 300 degrees Fahrenheit / 150 degrees Celsius, and quite often lower) mean that no expensive heating setup is required. In addition, low cure temperatures also make epoxy resin viable with open-mold process, which saves money on the materials needed for the manufacture of the molds themselves.
In addition to its niche as a paint, adhesive or sealant, epoxy has also seen a number of uses across a wide range of industries. Its electrical resistance has led to its use in the manufacture of electronics, electrical components and insulators. Its strength and stability has recommended epoxy for use in airplane parts, waterproofing varnishes and the hulls of watercraft.
If you need a strong, stiff, adhesive material which will hold up even after exposed to heat, cold, wind, salt water, or chemicals, consider epoxy resin. Contact us at Romeo RIM today to learn more about how you can use epoxy in your next manufacturing project!