Roll-To-Roll nanoimprinted backlight devices

Roll-to-roll nanoimprinting (RRNIL) or roll-to-roll hot embossing is relatively simple high volume manufacturing process which leads to low-cost devices. Thermal RRNIL process requires a bendable stamp, flexible substrate and roll-to-roll printing machine. The potential of RRNIL on flexible polymer films has been studied actively in the last few years. In this work we demonstrate the fabrication of backlight device on 50 mm wide and 95 micron thick cellulose acetate (CA) web (from Clarifoil). Optical binary grating design and Ni-mold were produced by Modines Ltd.. The size of backlight structure is 30 mm x 60 mm consisting a blocks of 5 micron wide cavities as shown. More than 500 devices as printed on CA-film in continuous roll-to-roll process. Printing speed was varied from 0.1 to 1.0 m/min when pressure were maximized at 118 oC, which is close to the glass transition temperature(125 oC) of CA film. The pressure of ca. 20 MPa was applied in the process. These parameters were optimized for continuous printing process. Higher temperatures or pressures can lead to a break of the web, which prevents continuous processing. In this process we have used a custom made nanoimprinter device. The quality of the roll-to-roll imprinted binary gratings was analyzed by a number of printed devices. The structure depth in the Ni-mold is 1.5 micron, while the structure depth is 1.2 micron in the CA-web respectively. No major changes can be seen among first 100 printed structures. The shape and dept of the printed structures proves also, that Ni-stamp can be used at least 100 times without damages. In the experiments no anti-adhesion treatment was used. The structures have been analyzed using optical microscopy, confocal microscopy and AFM.