Study on the effect of laser-induced oxidation on color change and hydrophilicity of 2D codes

Abstract

The effect of laser-induced oxidation on color change and surface wettability of anti-oil and super-hydrophobic two-dimensional code (2D Code) is demonstrated, where the color change and wettability are very important to the reading quality and durability of 2D Code. The poor oleophobicity and hydrophobicity, which render laser direct part marking of 2D Code inadequate for application in oil pollution, corrosion environment, are greatly improved with combination method of accurate laser-induced oxidation and surface modification. To obtain the control mechanism for the color change and wettability of 2D Code, the influence of laser processing parameters on the oxidation and microstructure change of the modules laser-marked on titanium alloy were studied, and then the influence of oxidation, microstructure and surface modification processing parameters on the hydrophilicity of 2D Code were analyzed. From the experimental results, with the laser energy density increasing, the oxidation degree increases and the modules show platinum grey, violet blue, graphite black, light ivory, jet black and other color states, with its hydrophilicity of the modules laser processed becoming stronger first and weaker later. The modules also present various microstructures with different laser processing parameters, such as pits, cracks, wormlike protrusions, which also have an important effect on the color change and wettability of modules. By laser parameters optimizing, it is found that when laser power is 10 W, Q frequency 45 KHZ, scanning speed 200 mm/s and hatching spacing 0.03 mm, the 2D code with high contrast and hydrophilic oleophylic property was obtained, where the static water contact angle could be a minimum to about 6.0° and the static oil contact angle could be a minimum to 8.1°. After the surface modification processing, where a coating consisting of heptadecafluorotrichlorosilane and n-heptanea with specific ratio is sprayed by special process on the surface, the 2D code show anti-oil and super-hydrophobic property, within the static water contact angle being a maximum to about 178.7° and the static oil contact angle being a maximum to 132.8°. In addition, it is found that the stronger hydrophilicity of modules laser processed before coating spraying, the stronger hydrophobicity of 2D code after coating spraying shall show.