As technology has improved, so has our ability to venture further than we have before. However, with new possibilities, we face new challenges. Electrical applications are met with varied conditions, all of which need to be meticulously prepared for. These can include a deep sea environment which would require resistance to salt water at high pressure, and instruments sent into outer space which are expected to be resistant to vacuum and solar radiation. Terrstiral applications include monitoring equipment, which may need to be resistant to cleaning materials used to maintain hygiene and appearance of the equipment.
Why Use Polymers
A typical electrical system will consist of a support structure that enables the construction of circuitry whilst providing insulation between components of the circuit. An example could be a printed circuit board, which contains materials such as epoxy resin, phenol-formaldehyde, or polyester resin. Switches may be constructed from thermosetting polymers as the main switch body, moulded with a specific structure to enable certain mechanical operations to take place. Other components such as push buttons may be manufactured by injection moulding of thermoplastics materials. This circuitry may then be placed in a moulded housing that enables protection from the environment.
Plastics have a long history of use in electrical devices due to their insulative properties. Some thermosetting resins were developed during the 19th century and enabled the development of light switches and telephones. Thermoplastics, such as PVC, are used as cable or wire insulation and have the added benefit of low flammability.
Some electrical systems are manufactured as “box-out, box-in” components, in which case the component is either disposable or returned to the manufacturer for repair. Other systems may be designed to be maintained in the field, in which case the housing needs to be designed in such a way that the electrical components are accessible. This type of design may require the use of elastomeric materials to provide an environmental seal, to prevent ingress of substances that could affect electrical function.
Therefore, a wide range of elastomers, thermoplastics and thermosets may be used in the construction of an electrical device. Some of these materials may contain volatile substances that could lead to corrosion of the contacts and circuits within the device. For example, residual sulphur or amine compounds are known to react with copper leading to a breakdown in conductivity. If sulphur vulcanised elastomer is found to give appropriate physical properties, it may be necessary, to ensure that levels of vulcanisation chemicals are kept to a minimum. Selection of appropriate polymer compounds is necessary to ensure compatibility with the electrical components within the device.
Another factor to consider is the permeability of the polymer. Unlike materials such as glass and metals, polymers are permeable to varying degrees according to the type of chemical substance that is brought into contact with the electrical device. In general, elastomers are more permeable than plastics. Therefore, their inclusion in the design of a device needs to be considered in terms of the degree of exposure and location of the seal within the device.
The challenge, therefore, is to identify materials with the appropriate physical properties that also provide chemical compatibility and chemical protection. The consultancy team at Smithers Rapra has an extensive knowledge of polymeric materials and are able to assist with material specification for electrical devices to ensure that the correct polymers are identified for a given application.
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