Composite Fabricating Basics Step 4: Proper Curing

The affinity of an amine compound (curing agent) to moisture and carbon dioxide creates a carbonate compound and forms what is called amine blush. Amine blush is a wax-like layer that forms as most epoxies cure. If the epoxy system is cured in extreme humidity (>70%). It will be seen as a white and waxy layer that must be removed by physical sanding of the surface followed by an acetone wipe.
Although we have formulated the MAX CLR, MAX BOND and MAX GPE product line to be resistant to amine-blush, it is recommended not to mix any resin systems in high humidity conditions (greater than 60%). Always make sure that the substrate or material the epoxy resin system is being applied to is as dry as possible to insure the best cured performance.

Latent epoxy resins are systems that are mixed together at room temperature and will begin polymerization but it will not achieve full cure unless it is exposed to a heat cure cycle. In general, these are high performance systems that demonstrate exceptional performance under extreme conditions such as high mechanical performance under heat and cryogenics temperatures, chemical resistance or any environment that epoxy room temperature system perform marginally or poorly.  Upon the mixing of the resin and curing agent polymerization will begin and will only achieve partial cure. Some resins may appear cured or dry to the touch,  this state is called ‘B-Stage Cure’ ,but upon application of force will either be gummy or brittle almost glass-like and  will dissolve in most solvents. The semi-cured resin must be exposed to an elevated temperature for it to continue polymerization and achieve full cure.

Similar to “addition cure” or catalytic polymerization, Ultraviolet Curing is another method that has gained popular use in the polymer adhesives and coatings application. It offers a unique curing mechanism that converts a liquid polymer into a solid plastic upon exposure to UV radiation. The two common commercially significant method are “FREE RADICAL INITIATION” and CATIONIC REACTION. In both reaction polymerization occurs via decomposition of a Photoiniator blended within the resin system; upon exposure to adequate wavelength of Ultraviolet energy the photoinitator degrades and cause a ring opening or cleavage of the photoinitiator molecule and induces rapid polymerization or cross linking.

The polymerization reaction can be either free radical or cationic and occurs almost instantaneous creation of a polymer network.

This type of epoxy system will not polymerized unless it is exposed to the activation temperature of the curing agent which can be as low as 200F and as high as 400F. In most instances our MAX EPOXY SYSTEMS epoxy system can be stored at room temperature and remain liquid for up to six months and longer.

If a process oven is not available, an infared heat lamp can be used for larger parts. 

POSSIBLE HEAT CURING TECHNIQUES

If an oven is not available to provide the needed thermal post cure, exposing the assemble part to direct solar heat(sun exposure) for a period will provide enough heat cure for the part to be handled. Other heat curing such as infrared heat lamps can be used if a heat chamber or oven is not available.