In many applications, additives or additional layers beyond simple paints are used to extend the lifetime or quality of the paint coatings. These additives or additional layers are oftentimes invisible, both those that are on and those that are in the product, without careful inspection and, even then, may only be obvious when chemical analysis is conducted. Some additives even require knowledge of the application method and type to be known prior to removal of the paint coating.
When approaching a new application, it’s important to understand how these coating and additives may impact the removal rate, whether positively or negatively. Of course, knowing the chemical composition is critical when assessing health and safety risks as well, as particulate generation should always be treated carefully, but we will focus on the removal effects here.
UV Barriers
Specialized paints with either additives or additional coatings which reflect ultraviolet light have become common in a broad variety of applications. Where previously UV reflective coatings were only used in specialty areas where ultra-long lifetimes and quality preservation were tantamount, such are preserving art, the relatively low cost of modern UV reflective systems allow them to be easily adopted. Most commonly these are used in automotive paint applications, and not just in high-end applications.
The high photon energy of UV light causes discoloration and degradation of paint much faster than the visible and infrared portions of the spectrum. Rejecting the UV before it reaches the paint not only preserves the color and enhances paint lifetime, but there is also a measurable effect in reducing the solar heating during warm summer months. In a more explicitly thermal application so-called “radiant barrier,” house paints and roofing tiles can significantly reduce cooling costs during the summer.
Detachment based paint removal is compatible with UV protection coating systems. Additionally, Latex and two-part linear polyurethane coatings are also semi-transparent to near infrared (NIR) radiation. With our laser wavelength of 1064nm being squarely in the NIR band, the additional transparency/transmission helps to accelerate the detachment effect we target for rapid laser paint removal. If the UV barriers also absorbed or reflected the NIR laser radiation, the removal rates would be reduced significantly.
Hardeners
Hardened paints such as urethanes, enamels, and ceramics have specialty applications where preventing chips is critical. Hardened paints are also used in applications where additional topcoats are impractical to use to protect the paint layers. In aerospace applications where corrosion is one of the primary risks to the aircraft durability and safety, specialty hardened paints are used to increase the paint lifetime. Oftentimes these hardened paints are also useful in high-temperature applications, such as on engines or exhaust manifolds, especially in industrial settings.
Hardeners can be used to maintain or improve NIR translucency. The increased transmission through the paint to the interface between the paint and substrate help efficiently absorb the laser energy, generating lift-off.
Hardened coatings feature a slightly higher detachment threshold but maintain a steeper detachment rate. This effect is due to the higher pressure which must be achieved to crack the hard and oftentimes thick paint layer. Higher pulse energies are recommended.
In the graph below, you can see the extra 25-50% energy that is necessary to move into the fast removal regime when switching from a simple white to a hardened white paint.
