In the family of elastometers, silicone rubber stands out as a transformational force that shaped the modern world. From cars to phones to medical devices, silicone has penetrated the very fabric of multiple industries. The product continues to facilitate the advancement of innovation. Product developers and engineers consistently choose this material over any other to visualize their concepts and improve on the current devices. One such product that has been continually created from keypads is silicone rubber. To make this leap, the rubber industry, along with its silicone agent, had to weather through the waves of the industrial experimentation and accidental discoveries.
Elastomers – Industrial Age Rubbers
The name “silicone” was introduced by Professor F. S. Kipping and his assistants at Nottingham University of England in the early 1900’s. Mistakenly taking silicone for the organic ketones, the material was given the name “silicoketones” or “silicones” for short (Lewis, 1962). As the research intensified, silicone rubber was eventually placed in the proper family of elastomers.
Elastomers (rubbers) are amorphous polymers that include polyisoprene or (natural rubber) polybutadiene, polyisobutylene, and polyurethanes. Known to have tensile, versatile, and resilient properties, elastomers are used for a variety of uses. Such items include seals, adhesives, and molded flexible parts. Ranging in attributes and applications, elastomers are not made the same. Variables including chemical compatibility, temperature, pressure, and mechanical wear define the usage of a particular elastomer.
The end-user industries, including automotive, electronics, healthcare and consumer goods, that focus on delivering to customer expectations favor silicone over any other elastomer. According to the MarketsandMarkets.com research report:
R&D is a key part of the global silicone elastomers market. The manufacturing companies, associations, and end-product manufacturers infuse high investments for future advancements and technology modifications of silicone elastomers applications to replace natural rubber and other rubber substitutes and match the new demands coming from various types of applications.
So why do end-product developers choose silicone over any other material? What makes it the rubber of choice?
Destiny by Structure
Silicone rubber is a synthesized elastomer made from a cross-linked silicon-based polymer strengthened by a filler. It is silicone’s structure that makes it so unique. Unlike most rubbers that contain polymer chains of carbon, silicone rubbers have silicon in polymer chains instead of carbon. The inorganic foundation of silicone is responsible for silicone’s high resistance to fungus and chemicals. With the backbone made of silicon and oxygen found in other high temperature materials such as quartz, glass, and sand, the material has the capacity to withstand extreme exposures. The carbon-to-carbon linkages of most other rubbers leave them susceptible to heat, ozone, and, UV, and other aging factors.
Silicone’s structure has a longer bond length and larger bond angles. Given the longer bond length, the molecules make it so the compound can stretch further. In turn, this improves the overall flexibility of the compound. The strong bond between oxygen and silicon results in the compound’s inertness.
Silicone Rubber and Its Benefits
Compared to other elastomers (See Table 1), silicone rubber demonstrates outstanding properties, making it the best and only choice in many instances (Crowther, 2001):
• Temperature resistance
Silicone delivers where other elastomers fail. Silicone rubber has “an extraordinary property that sets it apart from other elastomers – its elastic behavior changes only slightly with change in temperature” (Visakh, 2013). Able to withstand the broadest spectrum of temperatures (from -100 °F to +550 °F) of all other elastomers, it is built for demanding settings.
• Heat Resistance
Silicone is hard to inflame; it burns without releasing toxins down to a non-conductive ash; the combustion products are not toxic (Franta, 2012).
• Weather Resistance
According to Anil K. Bhowmick and Howard Stephens (2000), “the performance of silicone rubber is far superior to that of other elastomers in most rigorous environments. Silicone rubber is able to resist aging influence of sunlight, ozone, and gases that damage other rubbers. It is naturally water, acid, fungus, and mineral-resistant. In addition, silicone possesses superior corona and radiation resistance (Franta, 2012).
Silicone rubber is inherently stable and will not react with chemicals. Because silicone rubber is a highly inert material, it is widely used in medical applications and medical implants (Visakh, 2013).
• Compression Set
Silicone rubber has a compression set analogous to that of natural rubbers at temperatures of -40°F to +212°F. Silicone rubber offers superior performance at temperatures below -40°F and greater than +212°F.
• Hardness Flexibility
Silicone is available in a wide range of hardness rates from 20 to 80 shore “A”. This range enables developers to choose the hardness and material construction specific to the intended function.
These and other benefits of silicone rubber define its wide application in the industries such as automobile, healthcare, textile, household products, architecture, and electronics. Without silicone rubber, clothing would drench from rain and snow. Without silicone rubber buildings and cars would suffer from environmental stress, while patients would receive limited care and diagnostic help. However, the “closest” we get to silicone rubber is while operating electronics with the help of keypads.
Table 1: Comparison Chart of Most Common Elastomers
|Hardness Range (IRHD)||40-100||30-90||40-80||50-95||30-85|
|Colors||Limited range||Full range||Full range||Limited range||Limited range|
|Weather Resistance||Fair to Good||Good||Excellent||Excellent||Excellent|
|HeatResistance||Good||Fair to Good||Excellent||Excellent||Good to Excellent|
|Ozone Resistance||Poor to Fair||Excellent||Excellent||Excellent||Excellent|
|Elongation||Good||Good||Excellent||Fair to Good||Good|
|Resilience or Rebound||Fair to Good||Very Good||Good||Fair||Good|
|Water Resistance||Good to Excellent||Good||Good to Excellent||Good||Excellent|
|Animal & Vegetable Oil Resistance||Very Good||Good||Good||Excellent||Good|
|Alcohols Resistance||Fair to Good||Very Good||Good||Good||Fair to Good|
|Compression Set||Good||Fair to Good||Good to Excellent||Good to Excellent||Good|
|Temperature Range(Fahrenheit)||(-50)-300 °F||(-50)-250 °F||(-100)-550 °F||0-450 °F||(-50)-300 °F|
Why Keypads are Made of Silicone Rubber
Given its unique properties, silicone rubber is optimal for the environment of keypads. It enables such products to have the following attributes:
• Weather Resistance
Keypads made of silicone rubber are well-suited for applications in industrial equipment. This is especially true for those that are exposed to extreme temperatures, or those which may experience weather changes during the manufacturing and delivery process.
• Liquid Resistance
Unlike plastic keyboards that are susceptible to liquid damage, silicone keypads stay responsive despite the contact with liquids. Silicone rubber keypads are water-resistant. Such ability to withstand water makes them a priority choice for healthcare institutions where equipment has to be sterilized and cleaned after use.
• Noise Cancellation
Since silicone keypads have an elastic structure. They produce zero noise when keys are touched. This feature is excellent for noise-sensitive environments, but it also benefits consumer sector (TV and home theaters), eliminating the potential cause of distraction.
• Maximum Lifecycle
Since rubber keypads are highly resistant to corrosion and oxidation. The keypads can last longer than the keypads made of other rubbers. According to M. Goosey (1999), “The silicone elastomer used for the keypad retains its elastic properties over a long life without the adverse changes due to ageing characteristics of other elastomers.” Even with the prolonged and active usage, silicone keypads stay resistant to damage.
• Light Penetration and Coloration
The silicone compound can be made nearly translucent and still perform as expected. Other elastomers need additional processing to enhance their physical appearance, and are cause for potential opacity.
• Flexibility and Gentle Touch
Silicone is a flexible material, which allows product developers to have a full control over appearance and shape of the devices. Silicone-made keypads are able to withstand over a million button operations without deformation. The hardness of the material can be modified allowing for improved comfort of operation.
Developed out of the necessity to substitute natural rubber, silicone has become an essential material of the modern-day manufacturing. The rubber finds application in an array of end-user industries such as healthcare, automotive, architecture, consumer goods, and electronics, and continues to assist with bringing innovation to life.
The unique properties of silicone rubber, stemming from its structural difference, make it the “rubber of choice” for many product developers and engineers. Its flexibility, weather resistance, and compatibility with other elements enable product designers to craft equipment that is user-oriented and fully-customized. Silicone-made keypads inherit these properties and offer ease-of-use and longer life cycles. They are able to withstand extensive usage in both normal and extreme environments, and perform without fault. They allow for modifications and tailoring to fully reflect creativity of their designers. With silicone-based keypads, operation of work and home devices is comfortable, safe, and easy.
Bhowmick, A.K. & Stephens, H. (2000, Nov. 2). Handbook of Elastomers, Second Edition, CRC Press.
Crowther, Bryan G. (2001, Jan. 1). Handbook of Rubber Bonding. iSmithers Rapra Publishing.
Franta, I. (2012, Dec. 2). Elastomers and Rubber Compounding Materials, Elsevier.
Goosey, M. (1999, Apr. 30). Plastics for Electronics, Second Edition, Springer Science & Business Media.
Lewis, F.M. (1962). “The Science and Technology of Silicone Rubber”. Rubber Chemistry and Technology: November 1962, Vol. 35, No. 5, pp. 1222-1275.
MarketsandMarkets. (2014, December). “Silicone Elastomers Market by Type (HTV, RTV, & LSR), & by Application (Automotive, E&E, Industrial Machinery, Consumer Goods & Others) – Global Forecast to 2019.” MarketsandMarkets.com.
Visakh, P. M. (2013, Mar. 29). Advances in Elastomers I: Blends and Interpenetrating Networks, Springer Science & Business Media.