Project: Nanoscopic control of production tools for the polymer industry

The demand from the European plastics industry for new surface functionalities and surface finishes of mass-produced polymer parts is increasing in order to be able to differentiate its production from low-cost countries. Today, industrial polymer shaping tools are made by precision processes such as milling or grinding of steel, and the surface topography is typically obtained by other less well-controlled processes such as polishing or etching. This project will develop a revolutionary, highly innovative process for controlling the surface topography of production tools. A thin layer (<1µm) of a liquid reactive silicon oxide precursor is deposited on the surface of the tool, and may be easily structured or polished with advanced methods originally developed for the semiconductor industry. Finally the tool may be heat treated to allow the reactive silicon oxide precursor to cross-link, forming a hard, durable coating of fused silica with the intended surface topography. The method has been demonstrated to be durable for more than 66.000 replications in high-temperature (400°C), high-pressure (2000 bar) injection molding processes without loss of surface fidelity, it has been demonstrated to allow superior polishing abilities compared to steel (Ra<2 nm), and has been successfully demonstrated to allow easy transfer of large-area functional nanostructures on complex 3D surfaces. The project includes two research Ps (InMold and Halmstad University) and two commercialization Ps (Polerteknik and Svensk Industrigravyr)._x000D__x000D_The process consists of a number of steps: First a tool or a mold for polymer shaping is manufactured by conventional means, i.e. mechanical milling, electric discharge milling, cutting or other mchanical methods. These methods will normally result in a surface roughness between 200 nm and 1000 nm. For a surface to be reflective, the surface roughness has to be lowered to about 20-30 nm, which is conventionally done by abrasive diamond polishing. Instead of making a diamond polishing, and thereby removing material and changing the mold geometry, the tool is cleaned and surface activated to ensure good adhesion to the proposed coating. The coating is applied by either spin coating, spray coating or dip coating. The coating process results in a coating of reactive silicon oxide precursor (Hydrogen Silsesquioxane, HSQ) with a controllable thickness between a few hundreds of nanometers and one micrometer. The coating is somewhat conformal in the sense that underlying structures will be visible on the surface topography of the HSQ coating, but not as pronounced as on the underlying surface. After the coating step, a reflow polishing may be performed, where the tool and the coating is heated to 200C in protected atmosphere, allowing the coating to melt and spontaneously minimize its surface area, driven by surface energy forces. This process has been demonstrated to give sub-nm surface roughness on the final tool. After the reflow process there are several options, depending on the desired surface topography; if a shiny, highly polished topography is the target, the tool is simply heated to 300C in a normal atmosphere, resulting in a cross-linking of the HSQ to form a coating of fused silice. This coating is very hard, and is very durable in various polymer shaping processes, such as injection molding or roll-to-roll extrusion. If a controlled glossiness is the target, the crosslinked fused silica may be etched in a weak solution of fluoric acid (HF). If a functional nanostructured surface is the target, a master nanostructure (the stamp) made in nickel by conventional means (e.g. the LIGA process) is embossed into the surface of the HSQ coating prior to crosslinking. After the removal of the stamp, a replica of the stamps nanopattern is left in the HSQ coating. This coating may then be crosslinked in a normal atmosphere (not in protected atmosphere, as the HSQ would then reflow) at 300C. After the final step in the surface topography definition, the mold may be used directly in a polymer shaping process, or it may optinally be coated with an anti-stiction layer (most relevant for nanostructured and etched surfaces) based on a monolayer of a fluor-carbon silane (e.g. FDTS) to improve slip properties during the molding process._x000D__x000D_Proof of concept have been made on both the durability as described above (66.000 replications of a nanostructured surface), the functionality (very low surface roughness shiny or highly transparent surfaces, optically diffractive nanostructures, see annex), and the ability to functionalize complex 3D surfaces.

Acronym NanoCon (Reference Number: 7096)
Duration 02/01/2012 - 31/12/2014
Project Topic An innovative method for controlling surface topography is developed and brought to the market. The method will allow for new functionalities such as optical effects and physical effects to be realized in mass-produced products, as well as simplifying existing processes such as polishing and etcing.
Project Results
(after finalisation)
Processes:_x000D__x000D_- pre-processing: most types of metal working for manufacture of molds was investigated. this was not originally intended, but was necessary to ensure marketability. Etched surfaces, EDM, milled, sanded, grinded, polished, sandblasted, microblasted surfaces were all coated by the processes developed in Nanocon._x000D__x000D_- cleaning: the cleaning procedures could be established. It was found that ultra-sound bath using solvents, followed by manual wiping was required for most surfaces. This cleaning was followed by plasma treatment, however, towards the end of the project we found plasma heating could be dismissed for some types of metal._x000D__x000D_- spray-coating: the procedure met many difficulties. The chosen ultra-sonic nozzle caused issues of generating particles in the HSQ, which led to defects in the polishing glass layer. The particles could not be removed over a long period of time. It was found very recently that different formulations of the resist could minimize the problem, however, confirmation of these results were not possible within the project and until now._x000D__x000D_- spin-coating: was abandoned early on is it was found to apply to a very limited subset of molds._x000D__x000D_-dip-coating: the dip-coating process was found to solve problems of particles on the polished areas, however, it also met with complications regarding geometry. A sharp edge draws a liquid droplet, which will leave a thick HSQ layer behind, which will eventually flake off after curing. Hence, a subset of simpler molds can be treated using this procedure._x000D__x000D_- curing: The curing of the HSQ on top of steel was varied over several investigations. Eventually, the process time and temperature was found, which allowed consistent reproduction of results._x000D__x000D_- post-polishing: only mild post-polishing was found to lead to improvements. In general, it was found that post-polishing would increase roughness rather than decrease it._x000D__x000D_Polishing using HSQ:_x000D_It was found that the polishing method could be verified. It was possible to reduce the surface roughness of a machined metal sample by more than 5 times in one process. Processes included both spray and dip.coating. _x000D__x000D_It was also found that the hardness and durability of the polished samples were improved due to the HSQ coating. This was a major discovery and strongly supports the marketability._x000D__x000D_It was found that the HSQ could also nanopolish and protect a highly structured surface, such as an etched surface._x000D__x000D_Finally, it was found that HSQ could support nanostructures made by imprint, which after curing would be hard enough to withstand many cycles of injection moulding (> 100.000 times)._x000D_
Network Eurostars
Call Eurostars Cut-Off 7

Project partner

Number Name Role Country
4 Polerteknik ApS Partner Denmark
4 Halmstad University Partner Sweden
4 Svensk Industrigravyr AB Partner Sweden
4 InMold Biosystems A/S Coordinator Denmark