Curing is the process by which a powder coating is transformed from soft powder into a hard, durable coating. The curing process occurs when the powder is heated to a specific temperature for a certain amount of time. During this process, a number of chemical reactions take place that cause the powder coating to cure and form a crosslinked network.
The curing temperature and time are critical factors that determine the performance and appearance of the powder coating. If the temperature is too low or the time is too short, the coating will not cure properly and the coating will be weaker, lower gloss, and otherwise incorrect.
Conversely, if the temperature is too high or the time is too long, the coating will become discolored and brittle, again affecting its performance.
Key to the equation is crosslinking, crosslinking is the process by which the polymer molecules in a powder coating bond together and form a strong and durable "network." Crosslinking occurs during the curing process when the powder coating is heated. The heat causes the polymer molecules to become excited and react with each other, forming covalent bonds.
The degree of crosslinking is the most significant factor in determining the performance of the powder coating. A higher degree of crosslinking results in a more durable and resistant coating. The crosslink density can be controlled by adjusting the curing temperature and time, the makeup of the powder itself, and the treatment of the substrate. Higher temperatures and longer curing times generally lead to a higher degree of crosslinking.
The steps to the curing process are as follows:
Melting
When the powder coating is heated, it melts and flows, forming a continuous film over the metal substrate. The melting stage is critical for the coating to adhere properly to the metal surface and form a uniform thickness.
Gelling
As the powder coating continues to heat up, it reaches a point where it begins to solidify and form a gel-like structure.
Chemical Bonding
As the now-gelled powder coating continues to become hotter, a series of chemical reactions occur between the polymer molecules. These reactions cause the polymer chains to bond together, forming a crosslinked network.
Baking / Curing
The final stage of the process is curing. During this stage, the crosslinked network becomes more extensive and hardens into the final coating, which is durable and resistant to damage.
Proper curing is an essential part of the powder coating process. Work with the experts, and have your valuable parts coated at Ultra Metal Finishing.