Pattern replication in polypropylene films by hot embossing

The hot embossing of electron beam generated structures with linewidths of 0.35–3.25 μm has been examined in biaxially-oriented polypropylene (BOPP). The individual test elements consisted of pixels of 30 × 30 μm containing a specific configuration of symbols and lettering. The embossing of these features has been performed as a function of temperature (80–140 °C) and applied pressure (2–20 kPa). Significant increases in both embossed depth and sidewall angle were evident over the temperature range 100–130 °C with a leveling off at higher temperatures attributed to the onset of a regime of viscous liquid flow. At temperatures within this regime, a critical level of pressure was required to fill the mold features. Accurate embossing of medium and coarse lettering (0.50–0.65 μm linewidth) and geometric symbols (1.25–3.25 μm linewidth) has been demonstrated at a temperature of 130 °C and an applied pressure ⩾13 kPa. The depth of the finest lettering (0.35 μm linewidth) was incompletely embossed under these conditions.