Surface roughness reduction using spray-coated hydrogen silsesquioxane reflow

Abstract

a b s t r a c tSurface roughness or texture is the most visible property of any object, including injection molded plastic parts. Roughness of the injection molding (IM) tool cavity directly affects not only appearance and perception of quality, but often also the function of all manufactured plastic parts. So called "optically smooth" plastic surfaces is one example, where low roughness of a tool cavity is desirable. Such tool surfaces can be very expensive to fabricate using conventional means, such as abrasive diamond polishing or diamond turning. We present a novel process to coat machined metal parts with hydrogen silsesquioxane (HSQ) to reduce their surface roughness. Results from the testing of surfaces made from two starting roughnesses are presented; one polished with grit 2500 sandpaper, another with grit 11.000 diamond polishing paste. We characterize the two surfaces with AFM, SEM and optical profilometry before and after coating. We show that the HSQ coating is able to reduce peak-to-valley roughness more than 20 times on the sandpaper polished sample, from 2.44(±0.99) m to 104(±22) nm and more than 10 times for the paste polished sample from 1.85(±0.63) m to 162(±28) nm while roughness averages are reduced 10 and 3 times respectively. We completed more than 10,000 injection molding cycles without detectable degradation of the HSQ coating. This result opens new possibilities for molding of affordable plastic parts with perfect surface finish.

Reduction of microbial biofilm formation using hydrophobic nano-silica coating on cooling tower fill material

“…Studies have shown that the surface roughness of materials strongly influences the degree of bacterial adhesion to surfaces (Mitik-Dineva et al, 2009;Truong et al, 2010). Cech et al (2013) also observed a reduction of surface roughness for different materials after the coating process.…”

Hydrogen silsesquioxane mold coatings for improved replication of nanopatterns by injection molding

“…However, for large scale production they lack the wear resistance offered by those materials typically used in industry, such as tool steel. Thermally cured planar HSQ films have previously been used for injection molding [45] and for hot embossing [42], and we have recently observed minimum wear after injection molding >100 000 replicas on planar HSQ films (unpublished results). Above 400 °C, the Si-H bonds in the monomer dissociates and a cross-linked silica network forms, as previously reported and also verified by infrared spectroscopy in the current work (supplementary figure S1).…”

“…Heat treated HSQ forms a silica-like material that easily reacts with silane-based chemistry employed for applying anti-stiction coatings to the stamp for improved release of polymer replicas [7,19,20,44]. In addition, planar HSQ films have been used as a surface coating on steel molds to lower the surface roughness [45] and we have recently observed an injection molding lifetime of at least 100 000 cycles without measurable wear or defect formation in planar HSQ films of micrometer scale thickness on steel molds (unpublished data). Here, we show an improved filling of nanoscale holes using heat treated nanopatterned HSQ films under isothermal mold conditions compared to an all-metal electroplated nickel shim with an outer chromium/gold coating.…”

Multiphysics modelling of manufacturing processes: A review

“…A manufacturing process resembling some of the same methods as presented here, though with a nickel foil used for transferring the nanostructures, has been shown in the literature. [134][135][136] Furthermore, other manufacturing processes associated with additive manufacturing (AM) such as direct laser writing (DLW) allow for creating sub-100 nm structures with similar functionalities as mentioned above. 137 However, the method presented in this work allows for resolutions as achieved in the semiconductor industry and the waferbased platform makes the process competitive to the AM methods in a mass production environment.…”