Evaporation is not how modern urethanes, polyurethanes, and epoxies cure. In fact, only 25% of the curing process is truly drying or evaporating. Paints cure by a process called cross-linking. Cross-linking is a process that forms chemical bonds between two separate molecular chains, generally polymers. This cross-linking is added, and a much harder more durable bond is formed if some of the solvent remains in the paint as the cross-linking takes place. As this three-dimensional molecular structure is formed, the resulting coating is more shear-resistant, has a higher temperature resistance, and is oil and solvent resistant. This process takes an extended period, and is aided when small amounts of solvent remain in the coating.
Though the cross-linking takes some time, the paint does not remain wet. Cross-linking can be sped up by applying heat or radiation, and most manufacturers recommend “baking” of polymer paints after spraying to speed up the curing process. By applying heat of 100° to 140° F for a specific amount of time (generally 40 minutes, or with some hyper-curing clears only 8 minutes), the cross-linking can be sped up. Still, after the coating has been baked and the surface of the paint reaches ambient (room) temperature, it is not fully cured. The surface is mar-resistant; it can be sanded and polished, and can then be delivered back to the customer. But most paint manufacturers recommend that the vehicle not be waxed for up to 90 days. Waxing applies a sealant to the surface of the coating and does not allow the final gas-out of the remaining solvents, which needs to occur for the coating to completely cure.
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