Best of plastics: Electrical and electronics
Monday, September 12, 2016
Note: This is the first of a five-part "best of" series covering trends, material/process advances and applications in electrical and electronics, barrier packaging, medical, bioplastics and 3-D printing.
Manufacturers in the various electrical/electronic (E/E) sectors can choose from an enormous and versatile range of plastics to meet every requirement. Depending on the electronic component or device, designers choose plastics for their rigidity or flexibility, toughness/durability, resistance to low or high voltage and their electrical insulation or conductive qualities.
Ease of fabrication into complex shapes can also be a requirement for E/E applications. Depending on their targeted application or operating environment, the plastic material's mechanical properties, temperature/chemical resistance and flame retardant properties must also be considered.
The ongoing miniaturization of circuit boards and components such as computer chips increasingly relies on high-performance plastics to provide tough, dimensionally stable parts, often with thin walls that can withstand both the stress of assembly and the strain of use.
As a result of these many property requirements, the E/E sector is a significant consumer of engineering and high-performance specialty polymers.
Plastics Institute of America
Electrical/electronic plastics market usage by material type.
The E/E market is the world's third-largest plastics market after packaging and building and construction. Plastics have been a basic material for housing electronics, insulating components from all types of interference and protecting both parts and users.
Let's start by looking at a recently commercialized transparent conductive polycarbonate (PC) film. SABIC IP and Cima NanoTech, a smart nanomaterials company, have jointly developed the plastics industry's first transparent conductive polycarbonate film. The new PC film has a new series of transparent conductive materials that are lightweight with excellent transparency, outstanding conductivity and high flexibility.
The development uses Cima Nanotech's patented Sante technology to apply a coating of self-assembling nanoparticles to Lexan PC film. Sante nanoparticle technology is an innovative conductive coating that self-assembles into a random mesh-like network when coated onto a substrate.
The film could translate into faster response touchscreens for consumer electronics, transparent "no-line" anti-fogging for car windows, better electromagnetic interference (EMI) shielding for electronics, and transparent WiFi/Bluetooth antennas for mobile devices like smartphones, tablets, laptops and all-in-one computers.
SANTE nanoparticle conductive network (top); PET/PC film layering process (bottom).
The transparent conductive films are manufactured by wet coating the Sante conductive coating on polyethylene terephthalate (PET) via a roll-to-roll manufacturing process. The coating cures to form a random conductive mesh-like pattern that possesses high transparency at low surface resistance and is mechanically flexible. The Sante coating:
- Has high conductivity — it has low surface resistance that is more than 10 times better than Indium Tin Oxide (ITO).
- Has excellent optics — high transparency, non-moiré (no parallel line effect).
- Is flexible — withstands flexing, stretching, tension and torsion, and is thermoformable and moldable into 3-D curved surfaces.
Sante light transmittance to surface resistivity technology comparison.
Next, a recent breakthrough in pultruded/overwrapped, thermoplastic composite transmission line is a notable plastics technical marketing advance. Wire and cable producers are making greater use of new and upgraded materials from resin suppliers and compounders to meet evolving market needs. These can be in areas such as stiffness and shielding, weight reduction, safety and environmental resistance.
The recently introduced C7 Overhead Conductor developed by Southwire Co. LLC and Celanese Corporation offers a new option for utility transmission lines. The C7 Overhead Conductor features a multistranded composite core of Celstran continuous fiber-reinforced thermoplastic rods (CFR-TPR) from Celanese.
The new transmission conductor delivers nearly double the capacity and exhibits less sag than the same diameter aluminum conductor steel-reinforced (ACSR) product. The design allows for minimum sag at higher power transfer, and the stranded Celstran CFR-TPR core means there is no single point of failure for the overhead conductor.
The C7 Overhead Conductor is comprised of seven 3.2-mm (millimeter) diameter strands of carbon fiber — or more, depending on cable diameter — pultruded with polyphenylene sulfide (PPS) and then overwrapped with a polyether ether ketone (PEEK) material to provide protection from galvanic corrosion and to provide abrasion resistance from other strands.
The bundled strands, overwrapped by Southwire with an aluminum conductor, provide a redundancy of structural support in high-load conditions, which means that the failure of one or two or three strands will not result in failure of the entire line. In addition, the carbon fiber core operates at a generally lower temperature, which maximizes energy throughput and minimizes capacity loss. The carbon fiber can also operate hotter without damaging the line.
This combination of materials provides distinct advantages compared to alternative "high temperature low sag" technology and conventional conductors:
- The only all-thermoplastic composite core with high-temperature performance (180 to 225 degrees C)
- Minimal thermal expansion — lowest level available in a composite core for minimal sag increase at high power transfer
- Light weight — high strength-to-weight ratio
- Multielement core — no single point of failure, unlike monolithic constructs
- Flexible and robust — installs like traditional conductor without the need for special training and equipment
- Use of conventional connectors — traditional, crew-friendly, two-piece compression fittings
C7 overhead transmission conductor.
Continuing, 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 mold-maker Georg Kaufmann together with 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.
Georg Kaufmann Formenbau AG
Electronic surface functionality molding technology.
Finally, in the field of miniaturized electronics, work continues rapidly in creating a functional 3-D-printed ear. Researchers at Princeton University are integrating silver nanoparticles and biopolymer laced tissue to create a functional ear using off-the-shelf 3-D printing equipment, followed by cell culture.
The primary purpose of the work was to explore an efficient and versatile method of merging electronics with tissue. The technique allowed the researchers to combine the antenna electronics with tissue within the highly complex topology of a human ear. The researchers used an ordinary 3-D printer to combine a matrix of hydrogel and calf cells with silver nanoparticles that form an antenna. The calf cells later developed into cartilage.
In general, there are mechanical and thermal challenges with interfacing electronic materials with biological materials. Using the approach to build and grow the biology up with the electronics synergistically and in a 3-D interwoven format overcomes these difficulties. The finished ear consists of a coiled antenna inside a cartilage structure. Two wires lead from the base of the ear and wind around a helical "cochlea."
In the Princeton synthetic ear, electrical signals could be connected to a patient's nerve endings, similar to a hearing aid. The current system receives radio waves, but there are plans to integrate other materials, such as pressure sensitive electronic sensors to enable the ear to register acoustic sounds.
Bionic ear (left) and 3-D-printed ear process (right).
This is the first time that researchers have demonstrated that 3-D printing is an effective strategy for interweaving tissue with electronics. Funding has been provided by the Defense Advanced Research Projects Agency (DARPA), the Air Force Office of Scientific Research, National Institute of Health (NIH), and the Grand Challenges Program at Princeton University.
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