Japan Steelworks (JSW) has developed a low pressure compression process to form molded parts with nanoscale details, high aspect ratios, and sharp edges. Cycle times are typically a minute or less. Microfluidics could be a major application for the new technology.
JSW has conducted research on the process at its Hiroshima Research Laboratory and demonstrated the process at IPF Japan two weeks ago. It’s called the Micro-Nano Melt Transcription Molding Process (MTM) and it may be in high demand for medical and electronics applications looking for extremely fine detail in a mass production process.
The MTM machine consists of a plasticization and injection unit, a compression unit, a coating unit, a mold base and heating and cooling equipment. A machine used in a test described in the Journal of Photopolymer Science and Technology has a maximum compression force of 130 kN (13.3 tonnes). Maximum stamp size for the press is 148.5mm (5.8 inches) by 24mm 0.9 inches).
The nano hole arrays in one example have walls with a width of 60nm and a height of 270nm, creating an aspect ratio of 4.5. The walls have partition holes with diameters of 250nm. Parts can be molded with polymethylmethacrylate (PMMA), polystyrene and polycarbonate, among other resins. The well patterns for cells with an aspect ratio of 8.1 were molded uniformly over the surface area of 100mm by 125mm with the cycle time of slightly over one minute, according to JSW.
The process is possible due to the fluidity, wettability and low modulus of molten thermoplastics. In the process, molten plastic is deposited on a heated surface that has a fine pattern. The mold is closed, force is applied, the part cools, and is then ejected. JSW describes the injection phase as a “coating” process—without any temperature drop. The surface used in a test was described as a silicone stamp. A nickel stamp was also used for tests.
Important molding parameters include melt temperature, stamp temperature, compression pressure, and compression time. The JSW researchers say they prefer to use a plastic melt as opposed to a plastic film because of the importance of wettability on the stamp. The fluidity is necessary to fill the tiny spaces in the pattern under very low pressure in a short time.
In an example provided with polycarbonate, the melt temperature is 270C (518F), stamp temperature is 165C (329F), the compression pressure is 0.5 MPa (72.5psi) and the compression time is one second.
According to Stephen Moore of PlasticsToday.com, the process could be used to make precision products such as lenticular lenses and biochips.
The technical contact at JSW is Kazutoshi Yakemoto (Kazutoshi_Yakemoto@hiro.jsw.co.jp)