Nowadays some processes such as welding or cutting metals, or surface treatment of plastics have been industrialized using laser systems. Therefore, thermal and chemical treatment can be strongly localized leaving the rest of material unaffected. Consequently, the laser technique allows thermally transforming heat-sensitive substrates or to process materials. In particular, aesthetic laser marking is a technological process of industrial interest. This work focus on studying the laser marking process of carbon black (CB) filled ABS plastic materials using two different laser wavelengths, 355 nm (UV) and 1064 nm (IR). The goal is to obtain white marks on dark ABS polymer surfaces, which are usually associated to a foaming effect in the polymer. The total energy deposited by both lasers has been maintained very similar to study the role of the material absorption considering the differences in the laser wavelengths. The IR laser mainly interacts with the CB, as the ABS absorption at the IR laser wavelength is very low. The energy is directly transformed in thermal energy increasing the temperature of the pigment resulting in a foam formation and a polymer pyrolisis. Moreover, the interaction of the laser can produce the degradation and elimination of the CB from the marked area improving the contrast of the mark but if the material is overexposed to the laser energy, a degradation of the structure is produced becoming a carbonization, which tends to black color, and material removing. By contrast, the mechanism in the case of the UV laser source is characterized mainly by a photochemical effect resulting in color change with negligible thermal side effects. A superficial analysis has been performed in order to study how the surface is affected by the laser irradiation. The results of the final color, topography and chemical structure of marked polymers are analyzed and compared in terms of the wavelength used. It has been demonstrated that both the amount of black additive and laser wavelength used strongly affect the aesthetical laser marking process. It can be also conclude that the laser marking process on black ABS has the potential for on line plastic processing.

Resumen del trabajo presentado al XIV Congreso Nacional de Materiales celebrado en Gijón del 8 al 10 de junio de 2016.

Peer reviewed