Method of making a liquid crystal alignment layer

Abstract

A method of making a liquid crystal alignment layer comprising the steps of: (i) providing a layer on a substrate, the layer comprising a polythiophene according to formula (I): wherein R1 and R2 each independently represent hydrogen or a C1-C4 alkyl group or together represent a C1-C4 alkylene group or a cycloalkylene group; and (ii) mechanically rendering the layer liquid crystal aligning; a liquid crystal alignment layer obtainable by the above-mentioned method; a liquid crystal device incorporating the above-mentioned liquid crystal alignment layer; a liquid crystal display comprising the above-mentioned liquid crystal alignment layer or the above-mentioned liquid crystal device; and the use of the polythiophene according to formula (I) for aligning liquid crystals.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of making a liquid crystal alignment layer; and a liquid crystal alignment layer obtainable therewith. BACKGROUND OF THE INVENTION [0002] Liquid crystal displays (LCDs) typically contain a display cell consisting of two sandwiched substrates which each carry at their inner surface a patterned electroconductive layer and a liquid crystal alignment layer. These substrates are kept apart by so-called spacers and the volume thus obtained is filled with a liquid crystal composition. The orientation of the liquid crystal molecules therein is determined by an interaction with the liquid crystal alignment layer which may contain anisotropically oriented polymer molecules. Upon application of an electric field, the orientation of the liquid crystal molecules can be switched from one orientation to another, and a modulation of the light output through crossed polarisers is thereby obtained. [0003] Generally, the substrate...

AI Technical Summary

Benefits of technology

This approach enables the production of flexible, all-organic LCDs with reduced manufacturing costs, as the polythiophene layer can function as both an electrode and alignment layer, eliminating the need for indium-tin oxide and allowing for the use of cheaper, easier-to-manufacture flexible displays.

Problems solved by technology

A truly flexible display should not contain inorganic layers on the plastic substrate, since the brittleness of inorganic compositions causes the formation of defects upon bending the display.

The method of making PI alignment layers is complex and requires careful control of many parameters which may affect the final quality of the display.

The baking step is generally performed in vacuum, otherwise the PI alignment layer does not adhere well to the substrate and may be disrupted during rubbing, especially at the areas of the patterned electroconductive layer at which the ITO layer has been etched out.

The high temperature required during the baking step as well as the use of various organic solvents renders these prior art methods incompatible with many plastic substrates.

Other problems are associated with the low stability of the PI precursor (must be stored at low temperature) and the disposal of organic solvents and other chemicals which are necessary in these conventional methods.

The build-up of electrostatic charges in the PI layer, e.g. during rubbing, is a particularly serious problem as dust particles are attracted thereby, which, once trapped in the display cell, may cause poor alignment, severe wedging of the substrates or electrical breakdown by short circuiting across the dust particle.

Such methods are also suitable for aligning polythiophene layers, but are not a suitable alternative for conventional PI layers because of their thermal instability.

However, experimental evidence is only provided for polymer produced with p-xylylene and various polyparaphenylene precursors.

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