Structural Regulation of Microcellular Thermotropic Liquid Crystalline Polymer with Low‐Dielectric Properties During Supercritical Fluid Foaming Process

Abstract

The rapid development of wireless communication technology is increasing the requirements for 5G electronic devices, especially the lining materials for RF (radio frequency) components. Thermotropic liquid crystal polyester (TLCP) with microcellular structure attracts attention due to its excellent performance. However, in 5G applications, the uniformity and controllability of the cellular morphology is very important, as it directly affects the quality and performance stability of TLCP foams. Accordingly, in this paper, the melting behavior and rheological behavior of TLCP were investigated, and the supercritical fluid foaming behavior of TLCP in the isotropic state was studied. The TLCP foams were prepared by a one‐step rapid depressurization foaming method at different temperature and pressure, with cell diameter in the range of 67.5‐283.9 μm and the material density in the range of 0.37‐0.25 g/cm3. In order to broaden the distribution of cell diameter and the density of TLCP foams, the mixture foaming agent of N2 and CO2 was used in foaming process. The TLCP foaming material with a cell diameter of 40.5 μm was obtained with pure N2 at 330 °C and 10 MPa. When the N2 to CO2 partial pressure ratio was 3:7, the maximum cell diameter was 139.2 μm at the same temperature and pressure. When mixture foaming agents were used, the cell diameter was widened to the range of 40.5‐283.9 μm, and the material density was widened to the range of 0.70‐0.25 g/cm3, which realized the controllable preparation of cell diameter and material density of TLCP. The dielectric constant and dielectric loss of TLCP foams can be as low as 1.35 and 0.85‰ at 10 GHz, respectively. The structural regulation of low‐dielectric TLCP microcellular materials was achieved for the first time by way of varying the temperature, pressure, and co‐blowing agent ratio.This article is protected by copyright. All rights reserved.