Hansen, Hans Nørgaard

Islam, Aminul

Two component injection moulding has widespread industrial applications. Still the technology is yet to gain its full potential in highly demanding and technically challenging applications areas. The smart use of this technology can open the doors for cost effective and convergent manufacturing techniques for both macro and micro applications

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Two component injection moulding: Present and future perspectivesIslam, Aminul; Hansen, Hans NørgaardLink to article, DOI:10.1002/spepro.000049Publication date:2009Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Islam, A., & Hansen, H. N. (2009). Two component injection moulding: Present and future perspectives Societyof Plastic Engineers: Plastic Research Online. Accessed Jan 01, 2009, fromhttp://www.4spepro.org/view.php?source=000049-2009-06-18DOI: 10.1002/spepro.00004910.1002/spepro.000049Two-component injectionmolding: present and futureperspectivesAminul Islam and Hans Nørgaard HansenA technology that promises cost-effective and convergent manufactur-ing approaches for both macro and micro applications still has a wayto go.Injection-molding techniques that combine two different plasticmaterials—and in particular their associated properties—in the sameproduct are known as two-component (2C) molding. The screwdriverhandle, toothbrush, and computer mouse are all familiar examples of2C products. These molding techniques are used to combine hard andsoft plastic materials, to make movable flexible joints, as well as to in-crease the aesthetic value of a product. More advanced applications ofthe technology include molded interconnect devices (MIDs), acousticabsorbers, and parts for sealing. 2C molding has also recently attractedinterest as a promising solution to ejection problems and for makinghigh-aspect-ratio (i.e., of length to diameter greater than 10:1) mi-crostructures.Two of the most important technical considerations in 2C moldingare polymer-polymer bond strength and the interface between poly-mers. In most applications, good bonding is critical to the mechanicalperformance of the final product and also to prevent plastic parts frombreaking during ejection after molding. Likewise, uses such as selectivemetallization of polymers and micro-2C molding, as well as aesthetics,depend on a sharp and well-defined interface between materials.Our own experimental investigations show that polymer-polymerbond strength is affected by injection-molding process parameters,surface roughness of parts, and material solubility, and also by envi-ronmental factors such as humidity, corrosion, and thermal cycle. Con-ditions that favor the melting and mixing of plastics during 2C moldingincrease the possibility of good bonding. But some materials—for ex-ample, liquid crystal polymer and polyoxymethelene—have poor nat-ural adhesion. Consequently, we are often left with a tradeoff betweenpolymer-polymer bond strength and interface quality. Parameters andconditions that increase bonding negatively affect the interface of theFigure 1. Design of an on-off switch for a hearing aid. Left: Conven-tional design. Right: New design based on two-component (2C) moldedinterconnect device technology.2C molded part. We have also observed that high affinity of two poly-mers hinders the selectivity of any subsequent metallization process.The problems associated with bond strength and interface qualityin 2C molding can be overcome with the right choice of materials,process parameters, material shot sequence, and also by smart design of2C products. Detailed technical discussion of these issues is availableContinued on next page10.1002/spepro.000049 Page 2/2Figure 2. Selectively metallized 2C-molded plastic part for a hearingaid on-off switch. Ultem PEI 1000 and Noryl GTX810 are polymer ma-terials for injection molding.elsewhere.1 For example, we have experimented with MID productionusing micro-based 2C molding. We optimized the choice of materials,process parameters, and molding shot sequence to obtain a well-definedinterface and sufficient adhesion. We were also able to selectively met-allize the plastic part. The result is a new design for an on-off switch fora hearing aid that has potential for low-cost, high-volume production.Figure 1 shows the comparative design of the switch. Figure 2 showsthe selectively metallized 2C core part for the device.Micro-MID fabrication by 2C molding requires modification ofmaterials, processes, and parts design beyond polymer-polymer bondstrength and the plastic interface.1 The high surface-area-to-volume ra-tio of microproducts changes the wettability, friction, adhesion, andthermal interaction between the second-shot polymer melt and the first-shot substrate. Especially for micro-MIDs, the quality of the interfacebetween plastics is more important than the adhesion between them. Apolymer material with poor natural adhesion may be ill suited to macroproducts, but it may still work very well in 2C micromolding becauseof the size effect of the surface. More importantly, selective metalliza-tion benefits from the absence of an interfacial mixing zone in the caseof a poorly adhering material pair.22C molding is growing rapidly and advancing from the macro tothe micro area. Intelligent use of the technology offers cost-effectiveand industrially adaptive solutions to many technical problems. It canpotentially replace polymer welding and manual assembly for a widerange of plastic product categories. The quality of 2C-molded partscan often be optimized by tuning the factors described here. Thesuccess of current work is paving the way to microapplications, in-cluding MID fabrication. Our next research objective is to test thefeasibility of integrated micro-insert and 2C-molding techniques formultimaterial applications. We also plan to further investigate the ejec-tion problems associated with microinjection molding and to producehigh-aspect-ratio microstructures using reverse-2C molding.The authors gratefully acknowledge support from the Danish Ministryof Science, Technology, and Innovation for the project Selective MicroMetallization of Polymers (Polymetal, contract 61568), and from PulseApS, Denmark.Author InformationAminul Islam and Hans Nørgaard HansenDepartment of Mechanical EngineeringTechnical University of DenmarkCopenhagen, DenmarkHans Nørgaard Hansen is full professor of micromanufacturing. Hisresearch activities comprise design and manufacture of micromechani-cal systems in polymers and metals. He heads the department’s Sectionon Manufacturing Engineering.Aminul Islam received his PhD from the Technical University ofDenmark in 2008. His research is mainly focused on two-componentinjection moulding, micro injection moulding, and the developing con-vergent micro-manufacturing process for high-volume industrial appli-cations.References1. A. Islam, Two Component Micro Injection Moulding for Moulded InterconnectDevices, PhD thesis, Technical University of Denmark, 2008.2. A. Islam, H. N. Hansen, P. T. Tang, and J. Sun, Process chains for the manufac-turing of moulded interconnect devices, Int’l J. Adv. Manufact. Technol., 2008.doi:10.1007/s00170-008-1660-9c© 2009 Society of Plastics Engineers (SPE)

Two component injection moulding: Present and future perspectives

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Two component injection moulding: Present and future perspectives

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