Specialty processing techniques advancing electronic end-use development
By Don Rosato

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Note: This is the third article of a four-part series covering electrical and electronic (E/E) device (1) trends, (2) material advances, (3) process technologies and (4) applications.


What is an emerging specialty plastic processing trend in electronics?
  • 1. Molded surface functionality
  • 2. Microextruded CNT
  • 3. Nonsticking graphene film laminates
  • 4. Laser-scribed graphene micro-supercapacitors

End-use electronic application plastic process development is responding to the ongoing need for smaller electronic devices that in turn call for smaller, thinner electrical components. Convergence among computer, consumer electronics and telecom industries continue to blur the lines between information, entertainment and communication.

To start off with, plastics processors can use new surface-functionality injection molding technologies to integrate production of functional surfaces, substrate and sensor technology in a single process cycle. Complex plastic components can now light up or heat up at a touch, opening new applications for plastic components with integrated electronics and functional surfaces. The process can be used, for example, to produce special lighting effects or provide heatable armrests or seat surfaces in cars, ski lifts or sports stadiums.

The innovative technology developed by Swiss moldmaker Georg Kaufmann and project partners uses injection and reaction molding in high-precision molds, combined with application-specific automation to add heating circuits, lights or more to molded parts while in the mold. Major partners in the international project included materials specialist Evonik RÖhm GmbH, electroluminescence specialist Lumitec AG and the Technical University of Chemnitz. Parts leave the mold as fully functional systems.

Rear injection molding is used at pressures low enough so the integrated sensors and surface materials are not damaged. Sensors are encapsulated between the surface material and the thermoplastics backing or substrate. A proprietary coating carries a current across the parts surface.

Electronic surface functionality molding technology.

Potential application areas include the automobile industry, entertainment electronics, domestic appliances and even functional furniture.

Continuing, Lati Thermoplastic Industries SpA and extrusion machinery supplier Gimac di Maccagnan Giorgio have jointly developed an innovative electrically conductive yarn with unique properties and capabilities. The yarn, 0.20 millimeters in diameter, is formed by drawing a microextruded carbon nanotube (CNT) reinforced PA12 (polyamide or nylon 12) compound.

Electroconductive CNT reinforced PA12 yarn.

The CNT, evenly dispersed in the resin matrix, ensures uniform electrical properties in the resultant yarn. The electrically conductive yarn has a resistance of approximately 8 kilo-Ohms per centimeter of yarn, but can be tuned by adjusting resin CNT content and conversion parameters.

The yarn, which is not fragile, remains perfectly flexible, even when tightly bent. The absence of CNT agglomerates that otherwise may give rise to discontinuity in the polymer matrix accounts for this flexibility. This excellent yarn deformation is combined with good tensile strength and mechanical properties. The electrical properties of the yarn are expected to allow a number of unique applications in the electronics, automotive, medical and mechatronics industry segments.

Graphene structure.

Finally, researchers at the University of California at Los Angeles (UCLA) have found a way to fabricate graphene films and graphene high-energy storage capacitors, without any sticking together. Graphene, a sheet of graphite just one atom thick, has an extremely high surface area and electrical conductivity that suggests it would offer high energy and power densities. Unfortunately, graphene has proved difficult to fabricate, and samples that are produced often stick together, reducing their surface area.

The UCLA researchers take a PET (polyethylene terephthalate) DVD disc and apply a layer of plastic, followed by a film of graphite oxide, which they then insert into a standard DVD drive. The in-built laser chemically reduces the graphite oxide to graphene. Having removed the disc, the researchers peel off the plastic — now coated in graphene — and cut it into whatever shapes they desire.

The "consumer-grade" LightScribe DVD burner used was able to build more than 100 supercapacitors on one DVD in less than 30 minutes. The graphene films are made into capacitors by filling space between two parallel sheets of laser-scribed graphene with an electrolyte, phosphoric acid.

These capacitors are highly flexible and have an electrical performance that surpasses other commercial energy-storage devices. Compared with a carbon electrochemical capacitor, for instance, these graphene capacitors have energy densities that are twice as high and power densities 20 times higher. Bendable and twistable, applications foreseen include flexible power supplies for roll-up computer displays, wearable electronics, and energy-storage systems in combination with flexible PV (photovoltaic) cells.

The UCLA process seen above starts with graphite oxide because it can be suspended in water. This allows a lab technician to evenly distribute the substance on a plastic surface. Note the use of optical discs. The second part of the process involves hitting the dried layer of graphite oxide with a laser. This can be done with a consumer DVD drive. The result is graphene that can be used in circuits and may have potential as a unique supercapacitor. A more in depth look at the UCLA process now follows.

Fabrication process for laser-scribed graphene micro-supercapacitors: (a) a graphene-based film supported on a sheet is placed on a DVD media disc. The disc is inserted into a LightScribe DVD drive, and a computer-designed microcircuit is etched onto the film at precise locations to produce graphene circuits. (b) Copper tape is applied along the edges to improve the electrical contacts, and the interdigitated area is defined by polyimide (Kapton) tape. An electrolyte overcoat (c) is then added. Results in (d, e) a planar micro-supercapacitor.

Traditional methods for the fabrication of micro-supercapacitors involve labor-intensive lithographic techniques that have proven difficult for building cost-effective devices, thus limiting their commercial application. The next step is to demonstrate that the fabrication volume can be improved, while minimizing cost.

Dr. Donald V. "Don" Rosato serves as president of PlastiSource, Inc. a prototype manufacturing, technology development and marketing advisory firm located in Concord, Mass., and is the author of the Vol 1 & 2 "Plastics Technology Handbook".