Using Dihydrazides as Thermal Latent Curing Agents in Epoxy-Based Sealing Materials for Liquid Crystal Displays

Abstract

In this study, highly adhesive epoxy-based sealing materials for liquid crystal (LC) displays were fabricated using different types of dihydrazides as thermal latent curing agents. Their curing characteristics, mechanical properties, LC contamination levels, and electro-optical characteristics were investigated depending on the chemical structure of dihydrazides. The epoxy-based sealing material containing a dihydrazide derivative with a bulky heterocyclic ring afforded a high heat curing conversion of 90.4%, high adhesion strength of 54.3 kgf cm−2, and a high elongation of 57.3% due to the relatively low melting characteristic under heat treatment compared to those involving dihydrazides with short aliphatic or aromatic spacers. In addition, the proposed sealing material exhibited an extremely low LC contamination level of 9 µm, which is essential to the successful operation of LC displays. With respect to electro-optical properties of the LC device, it was found that a dihydrazide derivative with a bulky heterocyclic ring afforded a normal voltage-dependent transmittance curve and fast response time due to the prevention of abnormal homogeneous LC alignment. This study developed highly adhesive and robust epoxy-based sealing materials based on the use of dihydrazides as thermal latent curing agents for advanced LC displays.

Synthesis of Acid Hydrazides from Carboxylic Acids in Continuous Flow

“…The title compound was prepared according to the general flow procedure A. Pump 1 delivered a 1.5 M solution of adipic acid (5.0 g, 34.2 mmol, 1 equiv) in methanol ( Malonic Dihydrazide (6). The title compound was prepared according to the general flow procedure A.…”

“…As a subset of this family, acid dihydrazides find significant applications in a variety of industrial and academic settings owing to their benchtop stability and unique reactivity profile . Accordingly, they are commonly used as curing agents for epoxy resins, corrosion inhibitors, biomimetic hydrogels, or as precursors for the synthesis of acyl azides and diisocyanates. , In this context, we recently reported a scalable methodology for the synthesis of renewable isocyanates in continuous flow via in situ acyl azide generation from corresponding hydrazides ( 3 ) followed by a thermally induced Curtius rearrangement (Scheme B) . Using this methodology, a variety of mono- and diisocyanates can be synthesized, with the latter used to manufacture polyurethanes with a wide range of material properties …”