TECHNOLOGY | COMPOSITES Property Density, g/cm3 (ISO 1183)


Tensile strength,MPa (ISO 527) Tensile breaking stress, % (ISO 527) Bending strength, MPa (ISO 178) Flexural modulus, MPa (ISO 178) Charpy impact strength, kJ/m2


Durafide PPS 1135MF1 1150MF1


Standard Low warpage 1.56 162 1.9


1.68 130 1.7


227 (ISO 179)


Deflection temperature under 1.8MPa load, ˚C (ISO 75-1) Properties of metal adhesion grades offered by Polyplastics


10,500 11


226


of insert metals to produce direct metal-resin bonding with metal insert moulding alone, without the need for any special surface treatments of the metal. It also highlights metal surface treatments that work without heating/cooling systems. These include technologies like NMT (Nano


Molding Technology, developed around 15 years ago by Taisei Plas in Japan), which uses chemical products to etch the metal surface, and which has been used mostly for production of mobile electron- ics; NMT has attracted the attention of several major materials companies, including DSM and SABIC. More recently developed treatment technolo- gies include Laseridge from Japanese company Yamase, and DLAMP from Daicel Polymer (Polyplas- tics’ majority shareholder), which use laser irradia- tion treatment to perform the surface treatment. Surface treatments using chemicals treat the entire insert metal uniformly, but laser irradiation surface treatment can be more selective, Polyplastics notes. At the Fakuma 2018 fair last October, Fraun- hofer Institute for Chemical Technology (ICT) in Pfinztal, Germany, presented a process based on plasma-enhanced chemical vapour deposition (PECVD) to improve adhesion of metal compo- nents to over-moulded plastics by creating a “nano- porous” surface on the metal that provides a mechanical key for the plastics melt. Tests using metal-PPS hybrids have shown that PECVD can


Right: Photo shows cohesive failure of the polymer in a metal-polymer composite with a nano-porous metal layer


190


12,800 6.5


260 Duranex PBT 940MA 930MA


Standard Low permittivity 1.57 150 3.3


1.51 130 3.1


220


10,400 15


210 195


8,800 11


210


increase bond strength by 270%. Also at Fakuma 2019, compounder Akro-Plastic demonstrated samples of metal-plastic test pieces that show exceptional interfacial bond strength. Moulded over steel, Akromid B3GF30 7 PST, a modified PA6 with 30% glass, showed a tensile shear strength at the bond of over 50MPa – far higher than can be achieved with rival bonding technologies, claims Thilo Stier, Head of Innovation and Sales – while more recent development work has led to very good adhesion to aluminium as well. Tensile shear strength of over 30 MPa with an overlap area of 12.5 by 25 mm have been obtained, and in some tests, the metal broke before the bond. PST stands for Plasma SealTight, which refers to a plasma treatment process that enables the creation of a bond between metal and plastic that is not only very strong, but is also resistant after thermal cycling to ingress of liquids – something that cannot be guaranteed with standard over-moulding. The metal insert is first treated using a two-stage


atmospheric plasma treatment process developed with another German company, Plasmatreat. The process involves cleaning the surface with one plasma, then applying a silicone-based bonding agent onto the surface using plasma polymerisa- tion. This results in a very thin glass-like layer that can bond with the polyamide when the metal is over-moulded; the whole procedure can be carried out next to the injection moulding machine, as Plasmatreat demonstrated at K2016, in collabora- tion with Akro-Plastic and other partners. Stier says the strength of the bond does not fall with rising temperature, unlike with other treatments. The process works with various polyamides and also thermoplastic polyesters, he says. Plasmatreat and Akro-Plastic say the process


“precisely matches the composition of an anti- corrosive plasma-polymerised layer to the recipe for the plastic compound and the process param- eters, to ensure a long-time stable, media-tight bond of the injection-moulded part.”


42 INJECTION WORLD | January/February 2019


� www.injectionworld.com


PHOTO: FRAUNHOFER ICT


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