Fabrication Of Micro-Structure On Thermoplastic Polymer Thin Films By Roll-to-Roll Hot Embossing

Optical polymer thin films have wide application prospects in photovoltaic products such as flexible displays,organic light-emitting diode illuminations and thin-film solar cells.Some specific micro-structures fabricated on the thin films playing a role in light-guiding can effectively improve the performance of thin-film photovoltaic products.The improvement depends on accuracy of the micro-structures.Therefore,how to fulfill accurate and successive fabrication of the micro-structures on the thin films is a significant problem.In this thesis,micro-structure was fabricated on poly(ethylene terephthalate-co-1,4-cylclohexylenedimethylene terephthalate)(PETG)thin films by roll-to-roll hot embossing method.Effects of roller temperature,roller speed and applied pressure on forming quality of micro-structure on PETG films were investigated.Reflection properties of micro-structure on PETG films were observed by optical microscope.Then,thermal properties and rheological behaviors of ethylene-vinyl acetate copolymer(EVA)with various vinyl acetate(VA)contents were studied.Forming quality of micro-structure on EVA films embossed at different roller temperature was evaluated.The properties of EVA and the height of micro-structure were correlated.Furthermore,we prepared polyvinyl chloride(PVC)/methyl methacrylate-butadiene-styrene copolymer(MBS)/EVA blends films and conducted UV-irradiation experiments.Effects of UV-irradiation on PVC blends with different dosages of MBS and EVA were investigated.Our main work is as follows:PETG films with a thickness of 0.15 mm were prepared by tape casting method.Roll-to-roll hot embossing experiments were conducted on the PETG films at different roller temperatures,roller speeds and applied pressures.Forming quality of micro-structure was observed by scanning electronic microscope(SEM)and confocal scanning microscope(CSM).The average height and defect density of micro-structure were measured.The results showed that high roller temperature was in favor of improving forming quality of micro-structure,but caused difficulty in demolding.High roller speed led to low height and high defect density.With increasing applied pressure,the height of micro-structure first increased and then stable in a saturated value.The forming quality of micro-structure embossed at 150-160 °C,0.1 m/min,350 N was the best.Reflection light spots were observed by microscope and optical properties of the embossed films were characterized by transmittance test.The results showed that transmittance of the embossed side was over 90% and that of the smooth side was less than 40%,which demonstrated that PETG films maintained high optical transparency after embossing and the micro-structure had excellent reflection performance.Micro-structure was also fabricated on EVA films with various VA contents by roll-to-roll hot embossing.Effects of roller temperature on forming quality of micro-structure on EVA films were investigated.Differential scanning calorimetry(DSC),rubber processing analysis(RPA)showed that with increasing VA content,the melting point,crystallinity and complex viscosity of EVA decreased.Three dimensional features and heights of micro-structure were characterized by CSM,and correlated to the properties of EVA.The results showed that both complex viscosity and relaxation rate of EVA had effects on the heights of micro-structure.Low viscosity and high relaxation rate were in favor of improving heights of micro-structure.PVC/MBS/EVA blends films were prepared by melt blending method.The relative amounts of carbonyl group and conjugated carbon-carbon double bond were characterized by Fourier transform infrared spectrometer(FTIR)and ultraviolet-visible spectrometer(UV-vis).After substituting EVA partly for MBS,the amounts of carbonyl group and conjugated carbon-carbon double bond generated during UV-irradiation decreased.The results of tensile test and transmittance measurement showed that substituting EVA partly for MBS had few effects on the mechanical properties and optical transparency of the blends.Tensile impact test showed that the tensile impact strength of the blends after substituting EVA partly for MBS decreased slightly.