Extrusion of highly filled flexible polymer sheet

Abstract

Highly-filled polymer systems include color masterbatches, feedstocks for powder injection molding, and rigid sheets with high levels of flame retardants, but they have not been explored for flexible sheet. This work investigated the (a) selecting a polymer matrix with enough melt strength and flexibility to form a stable sheet with high filler loading, (b) the maximum achievable filler loading for the sheet, and (c) optimizing the process of extruding a highly-filled flexible polymer system. Extrusion grade low-density polyethylene (LDPE) provided sufficient flexibility and permitted a maximum filler loading of 36 vol% (~78 wt%). Good dispersion of the nanoparticle filler, however, required two passes through multiple screw extruders and a small reduction in the viscosity of the LDPE. Sheet with thickness of 415 μm, surface roughness of <1 μm, and sufficient flexibility was extruded continuously at a rate of 10 m/min., but it required a more traditional coat hanger manifold to prevent filler hang up in the sheet die. The filler particles were distributed uniformly through the core and skin of the sheet, giving the sheet good mechanical properties.

Printed planar tunable composite right/left‐handed leaky‐wave antenna based on a tunable polymer‐BST substrate

“…SEM imaging showed good dispersion of the BST within the LDPE. 32,33 3 | RF MEASUREMENT AND CHARACTERIZATION RF measurement methodologies need to be utilized to characterize the dielectric properties as a function of frequency and measuring tunability after the BST-LDPE composites thin sheet substrates were prepared. To characterize the dielectric properties of the LDPE-BST composites, two techniques are exploited: conventional waveguide technique 51 and the free space measurement technique.…”

“…The substrate included 15 wt% of a processing aid (light mineral oil), for ease of processing. The LDPE with 34 vol% BST was extruded into 600‐μm‐thick sheet using a sheet extrusion line with 38‐mm‐diameter single screw extruder (Welex Co.), 150‐mm‐wide sheet die, and a chill roll stack as described previously 32,33 . The extruded sheet (Figure 1) had BST loading level of 34.4 ± 0.4 (measured using thermogravimetric analysis), and surface roughness of less than 1 μm (which is required for printed electronics applications).…”

“…23,26,31 More recently, polymer-BST composites were investigated that could be used in flexible electronics and the sheets were fabricated by high production plastics film processing techniques. 32,33 These polymer-BST composites combine the advantages of the mechanical flexibility of the polymer and the ferroelectric properties of the BST to produce tunable substrates conducive to printed electronics. The polymers were selected based on their low loss tangent at the frequencies of interest as well as their ease of fabrication.…”

“…The BST particles were incorporated into the polymer melts using twin screw extrusion and formed into film using a sheet extrusion process as previously reported. 32,33 Using these processes, the BST filler was distributed uniformly into the polymer matrix, permitting uniform electromagnetic and mechanical properties in the polymer-BST sheet. These polymer-BST substrates exhibited high dielectric constants, low dielectric losses, and tunabilities in the RF region.…”

“…The stoichiometry of BST particles, the particle size, and particle loading were selected to obtain the highest tunability and dielectric constant. The BST particles were incorporated into the polymer melts using twin screw extrusion and formed into film using a sheet extrusion process as previously reported 32,33 . Using these processes, the BST filler was distributed uniformly into the polymer matrix, permitting uniform electromagnetic and mechanical properties in the polymer‐BST sheet.…”