High‐frequency proximity heating was used to rapidly heat injection molds. The principle is based on the proximity effect between a pair of mold inserts facing each other with a small gap and forming a high‐frequency electric loop. Because of the proximity effect, the high‐frequency current will flow at the inner surfaces of the facing pair, thus selectively heating the mold surface. With this method, the electrical insulation layer beneath the mold surface can be eliminated, resulting in a mold insert made of a single metal. A mold with a cavity of 25 × 50 mm2 was constructed with careful design on its electrical, structural, and thermal performance. Air pockets with reinforcing ribs were embedded right beneath the mold surface for enhancing the heating performance. The resulting mold cavity can be rapidly heated from room temperature to about 240°C in 5 s with an apparent heating power of 93 W/cm2. The new mold heating method was applied to thin‐wall molding and micromolding, and in all testing cases, short cycle times less than a minute were achieved. POLYM. ENG. SCI. 46:938–945, 2006. © 2006 Society of Plastics Engineers

Although the hot embossing process is gaining popularity in molding polymer micro/nano structures, it needs a breakthrough improvement in reducing cycle time before it can become a mass-production process. In this study, an embossing tool with a rapid heating and cooling capability was investigated to reduce the cycle time. During the process, the embossing tool was rapidly heated to above the polymer softening temperature (in less than a couple of seconds), pressed against a roomtemperature polymer substrate, and subsequently rapidly cooled for mold separation. Different miniaturized features including microsquare and hexagonal wells, microcircular holes, and submicron surface features were successfully produced using the new process with a total embossing cycle time around 20 s. The fatigue test result indicated that the new embossing technology is durable and reliable for microscale feature replication.

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