Constant Temperature Microfeature Embossing with Slowly Crystallizing Polymers

Abstract

A new microfeature embossing method utilizing a slowly crystallizing mechanism was investigated to eliminate thermal cycling, as needed in standard hot embossing. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by melt casting onto a chilled roll. The resulting amorphous film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than the polymer's half-time of crystallization. During constant-temperature embossing, the film is softened first, caused by rubber softening of the amorphous phase, and is then hardened, resulting from the crystallization of the amorphous phase at the same embossing temperature. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio microribs, were consistently patterned using a total cycle time about 40s. The embossed films were characterized using DSC and rotational rheometry to elucidate the physical mechanism for softening and hardening the polymer during constant-temperature embossing.

Micromolding of polymers

“…In theory, any materials (not necessarily a thermoplastic) that can be softened and solidified during processing can be used in embossing. Rather than using solvents or a chemical curing process, Yao et al (2007a) have investigated the feasibility of utilizing the unique property of slowly crystallizing polymers for achieving constant-temperature embossing. The recently developed solvent-assisted embossing method (Khang and Lee, 2000;Wang et al, 2005) may be considered as a specific method falling into this category.…”

“…In addition, other softening and/or solidification processes, including solvent-assisted plastication (Khang and Lee, 2000;Wang et al, 2005) and isothermal softening and solidification of a slowly crystallizing polymer (Yao et al, 2007a), have also been reported in micromolding applications. In some cases, radiation-based curing methods are more useful.…”

Constant-temperature embossing of supercooled polymer films

“…Recently, the authors in a technical communication have conceptualized a new method for constant‐temperature embossing using supercooled amorphous polymers as embossing polymers. Slowly crystallizing polymers such as PET and PEEK can be quenched during melt processing to produce amorphous films with reasonable mechanical properties.…”