Free Meniscus Coating Using Compressed Carbon Dioxide

Abstract

This thesis investigates the use of compressed carbon dioxide as a replacement solvent for web based coating processes including the free meniscus based devices.

We use theory, such as Tallmadge's Four Force Inertial Theory, to show why carbon dioxide based free meniscus coaters are advantageous over normal coating processes.

We show theoretically that thinner films can be formed at faster rates, that important deposition forces can be controlled, that there is better penetration into porous materials, that there are less capillary forces, that films may have increased uniformity, and that there is better process control.

This research also details how coatings can be applied by using a novel high pressure free meniscus coater (hFMC) to deposit thin films of important perfluorpolyether lubricants for microelectronics.

The coater was designed as part of this thesis. We have investigated what substrates can be coated by showing that compressed gaseous carbon dioxide induces the wetting of low enery surfaces by low Mw coating precursors. We have shown that the hFMC device can be used to take advantage of the induced wetting. Biocompatible precursors have been coated onto porous PTFE and polymerized at high pressure. The coating process results in porous PTFE with significantly different properties than uncoated samples. We have also investigated what materials can be coated from carbon dioxide by studying the rheological effects of carbon dioxide on coating precursors.

We find that changing the backbone structure, end groups, or side groups on the precursor affect the mixture viscosity. The results of this investigation open up new potential applications of this environmentally benign coating process.