펨토초 레이저 유도 주기 구조물 (LIPSS) 기반 나노 마스터몰드의 PET 핫스탬핑 전사 특성 및 블로우 성형용 구조색 필름 적용 연구
Femtosecond Laser-Induced Period Surface Structure (LIPSS) Nano Master Molds: PET Hot Stamping Replication and Application to Blow-Molded STructural Color Films
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In this study, an amplified Ti:sapphire femtosecond (fs) laser system was employed to fabricate laser-induced periodic surface structures (LIPSS) on the surface of a mold steel (STAVAX). The laser system was operated at a repetition rate of 5 kHz with a central wavelength of 800 nm. To fabricate LIPSS, fs laser pulses were weakly focused onto the surface at normal incidence with a fluence ranging from 0.18 to 0.22 J/cm². Under these conditions, the fabricated LIPSS exhibited a period of 0.733 μm, a height of 0.367 μm, and a groove thickness of 0.657 μm, resulting in the emergence of structural coloration. Using the LIPSS, the hot stamping transfer characteristics and structural coloration of the nanoscale patterns were evaluated on polyethylene terephthalate (PET) films. The hot stamping process window was derived through a Taguchi L18 experimental design with various PET film thicknesses (36, 50, and 250 μm), pressures (2.0, 3.5, and 5.0 MPa), temperatures (220 and 230 ℃), and processing time conditions (180 and 240 s) as control factors. Optimal transfer performance, including transfer rate and releasability, was achieved under conditions of 250 μm film thickness, 5.0 MPa pressure, 230 ℃ temperature, and 240 s processing time. Under these optimized conditions, the nano-patterns transferred onto the PET films exhibited deviations in width, height, and period of less than 0.1 μm. Furthermore, the CIE L*a*b* color coordinates revealed angle-dependent structural color behavior, with slight variations in the a* and b* values depending on the observation angle. Finally, considering the expected elongation ratio during stretch blow molding, potential changes in the pattern period and corresponding structural coloration were examined. The results confirmed that a “nanofilm + micromold” configuration, where a nano-structured structural color film fabricated via pre-hot stamping is applied through IML (in-mold labeling), is advantageous in terms of structural color stability and overall process feasibility.
Abstract
In this study, an amplified Ti:sapphire femtosecond (fs) laser system was employed to fabricate laser-induced periodic surface structures (LIPSS) on the surface of a mold steel (STAVAX). The laser system was operated at a repetition rate of 5 kHz with a central wavelength of 800 nm. To fabricate LIPSS, fs laser pulses were weakly focused onto the surface at normal incidence with a fluence ranging from 0.18 to 0.22 J/cm². Under these conditions, the fabricated LIPSS exhibited a period of 0.733 μm, a height of 0.367 μm, and a groove thickness of 0.657 μm, resulting in the emergence of structural coloration. Using the LIPSS, the hot stamping transfer characteristics and structural coloration of the nanoscale patterns were evaluated on polyethylene terephthalate (PET) films. The hot stamping process window was derived through a Taguchi L18 experimental design with various PET film thicknesses (36, 50, and 250 μm), pressures (2.0, 3.5, and 5.0 MPa), temperatures (220 and 230 ℃), and processing time conditions (180 and 240 s) as control factors. Optimal transfer performance, including transfer rate and releasability, was achieved under conditions of 250 μm film thickness, 5.0 MPa pressure, 230 ℃ temperature, and 240 s processing time. Under these optimized conditions, the nano-patterns transferred onto the PET films exhibited deviations in width, height, and period of less than 0.1 μm. Furthermore, the CIE L*a*b* color coordinates revealed angle-dependent structural color behavior, with slight variations in the a* and b* values depending on the observation angle. Finally, considering the expected elongation ratio during stretch blow molding, potential changes in the pattern period and corresponding structural coloration were examined. The results confirmed that a “nanofilm + micromold” configuration, where a nano-structured structural color film fabricated via pre-hot stamping is applied through IML (in-mold labeling), is advantageous in terms of structural color stability and overall process feasibility.