5. ConclusionThree different wavele

5. ConclusionThree different wavelengths, 1064, 532 and 355 nm wereapplied to construct micro-hole arrays on the surface of the PUsynthetic leather for improvement of WVP, and the optimizedpulse energy for the 1064, 532, and 355 nm laser are 0.8, 1.1,and 0.26 mJ, respectively. The diameter of the laser-drilled micro-holes increases with an increase in pulse energy. The influencesof laser beam wavelength and pulse energy on the diameter ofthe micro-holes are concluded as follows: for the 1064 nm laser-drilled samples, the diameter changes from 15 ?m to 20 ?m atthe pulse energy ranging from 0.3 mJ to 0.8 mJ; for the 532 nmlaser-drilled samples, the diameter changes from 12 ?m to 15 ?mat the pulse energy ranging from 0.5 mJ to 1.1 mJ; for the 355 nmlaser-drilled samples, the diameter changes from 8 ?m to 10 ?mat the pulse energy ranging from 0.18 mJ to 0.26 mJ. In addition,increase in pulse energy makes the depths of the micro-holesincrease as well. The maximum depths of the micro-holes areabout 21, 60 and 69 ?m achieved by the 1064 nm laser, the 532 nmlaser and the 355 nm laser, respectively. Analysis of the interactionmechanism between laser beams at three kinds of laser wave-lengthsand the PU synthetic leather shows that laser micro-drillingat 355 nm wavelength displays both photochemical ablation andphotothermal ablation, while laser micro-drilling at 1064 and532 nm wavelengths leads to photothermal ablation only. The WVPincreases significantly after laser micro-drilling. Compared with theuntreated samples, the highest WVP growth ratio is 38.4%, 46.8%and 53.5% achieved by the 1064 nm laser, the 532 nm laser and the355 nm laser, respectively. Laser micro-hole drilling also leads todecrease of slit tear resistance. Compared with the untreated sam-ples, the highest decreasing ratio of slit tear resistance is 11.1%,14.8%, and 22.5% treated by the 1064 nm laser, the 532 nm laserand the 355 nm laser, respectively. The decrease in slit tear resis-tance does not influence performance of PU synthetic leather, sincethe slit tear resistance of the laser-drilled samples is still higherthan that of natural leather. Samples drilled by the 355 nm laserdisplay the maximum WVP value as well as satisfactory slit tearresistance. Consequently, the best laser system for patterning PUsynthetic leather is the 355 nm laser.