What Does Overcure Mean?
An overcure is a condition in which the parameters of a curing process were exceeded. Generally, the term implies the occurrence of defects in the polymeric material that was overcured. As curing is a hardening process, overcurring may result in a material that is over hardened. However, depending on the material and curing conditions, reversion of hardness, cracking, delamination of coatings, loss of flexibility, changes in aesthetic qualities, loss of adhesion and brittleness can occur.
While the typical cause for overcuring is a prolonged exposure in the curing conditions, excessive temperature, light radiation or the amount of curing agent may cause performance deficiencies in the resultant material.
Corrosionpedia Explains Overcure
Although the chemical details of the curing process depend on the specific chemical ingredients, the central concept is a chemical polymerization that produces the desired properties of the polymer. Overcuring is essentially an excessive amount of reacting, which may cause more polymerization reactions, cross-linking reactions or adverse side reactions than wanted. The overcured material will then have different properties than the ideally cured material. Being chemically different, the color and gloss of the resultant material might differ from expectation.
Synthetic rubbers typically stiffen from overcuring, along with a drop in tensile strength and elongation and a rise in the modulus. Natural rubbers, on the other hand, undergo reversion, or a softening of the rubber, along with a decrease of modulus and tensile strength. Many of these undesired effects are associated with prolonged heating or overheating during the curing process, but may also arise during overexposure to UV light during a light curing process.
Changes in adhesive properties are also associated with overcuring, which particularly affects paints and coatings and may cause undesired failures such as delamination.