As a model of polymer-sustained-alignment liquid crystal display (PSA-LCD), the LC cells having the polymer layers produced from the homopolymers and copolymers of 4,4ʹ-dimethacryloyl-oxy-biphenyl (4,4ʹ-DMABiph) and 2,6-dimethacryloyl-oxy-naphthalene (2,6-DMANaph) were prepared and investigated image sticking phenomenon with evaluations of residual direct current voltage (V_rDC) and difference in pre-tilt angle before and after application of alternate current (AC) voltage (Δtilt). The V_rDC was effectively improved by adding a small amount of 2,6-DMANaph to 4,4ʹ-DMABiph because the concentrations of radicals and ions in the LC layer were decreased due to increase in the rate constant of the polymerisation with the addition of 2,6-DMANaph under UV light exposure. The Δtilt was proportionally increased with increasing the weight ratio of 2,6-DMANaph in the mixed monomers of 4,4ʹ-DMABiph and 2,6-DMANaph. We confirmed that the range of the weight ratio for 2,6-DMANaph in the mixed monomers of 4,4ʹ-DMABiph and 2,6-DMANaph from 10 to 25 wt% was useful for obtaining the small level of image sticking in the PSA-LCD.

We propose a novel method to fabricate a uniaxially homogeneous alignment of liquid crystal (LC) molecules without using a conventional alignment layer such as polyimide film. The method produces the polymer alignment layer (PAL) by polymerisation of the monomer including in the LC layer above the T_NI of the LC material. The fringe-field switching (FFS) mode LC cell with the PAL (FFS-PAL-LC cell) produced from the monomer 4,4ʹ-di-mehacryloyl-oxy chalcone (4,4ʹ-DMOCh) exhibited enough level of alignment state and electro-optical property compared with the FFS-LC cell having the conventional polyimide-type alignment layer. We can expect that the FFS-PAL-LC cell is useful for next-generation displays such as flexible liquid crystal displays (LCDs) because the method does not need high-temperature process of over 200°C.

Polymer-sustained-alignment liquid crystal display has high potential for low power consumption, fast response, and low level of image sticking. In this study, we clarified the mechanism for a formation of a polymer layer with polymerization of the monomer 2,6-dimethacryloyl-oxy-naphthalene (2,6-DMANaph) without initiators under UV light exposure. Experimental results revealed that the polymerization of 2,6-DMANaph occurred with the generation of radicals from the monomer as reactive intermediates of a photo-Fries rearrangement. It took about 20 min for 0.5 wt. % of the monomer in the LC to convert to the polymer, indicating that the generation of the radicals derived from the reactive intermediates of the photo-Fries rearrangement is effective for the formation of the polymer layer. Voltage holding ratio of the LC cell having the polymer layer formed from the monomer 2,6-DMANaph was over 99%, which was comparably high value.