Physical properties of silicones

Silicones are the polymers that consist mostly of silicon (sometimes mistakenly spelled cilicone), oxygen, hydrogen and carbon. These polymers are used in production of silicone rubber, silicone resign, silicone grease and silicone oil. Silicones possess several extremely useful properties that give them clear advantage over the other materials used for the same purposes. Silicone Rubber Keypads are:
• Chemically inert
• Nontoxic
• Thermally stable, meaning that their physical properties do not change over a large range of temperatures (-100°C to 250 °C)
• Resistant to microbiological growth
• Waterproof (this quality allows to use silicones as watertight seals)
• Non-sticky, which comes in handy when silicon rubber buttons are used in the electronic products that require manual operations (oscilloscopes, ammeters, programmable logic controllers, etc)
• Electrical insulators
• Resistant to ultraviolet light (UV light), ozone and oxygen
• Non-corrosive
• Eco-friendly

Silicone Rubber Buttons

Silicones as chemical compounds
Silicones rubber is a mixture of organic and inorganic components whose general chemical formula is [R2SiO], where R stands for either methyl or ethyl or phenyl organic groups of molecules, depending on the application. (Si-O-Si-O-Si-O …) are the chains of inorganic silicone-oxygen molecules.
Silicone rubber’s properties depend on spatial positions of the Si-O chains and the chain lengths. It is possible to change physical properties of a silicone rubber compound by changing positions of its molecules.
Advantages of using silicone rubber buttons in electronic products
Electronic products such as remote controls, industrial keypads, medical devices, calculators and many other small electronics have incorporated the use of silicone rubber buttons. Silicone rubber buttons are resilient to many external forces, provide tactile feedback, can be printed on and numerous other features. One of the most common features of silicone rubber keypads is molding a carbon contact pill on the backside. The carbon contact pill will complete a circuit on a PCB when the silicone rubber is pressed. This method of completing a circuit is cost effective and very reliable because it removes the need for a mechanical tactile switch.
When electronic devices are operated in low temperature situations the buttons must still function properly when pressed. These buttons are made mostly out of silicone rubber because of its ability to withstand very low temperatures.
Ultraviolet light is used in many medical devices. Silicone rubber buttons are an ideal choice of relays for these devices because of silicone’s ability to resist the UV light.
Being nontoxic, silicone rubber buttons do not release harmful toxins into the atmosphere. Electronic toys for children are equipped with such buttons so that the children are not exposed to harmful toxins.
One of the main advantages of silicone rubber buttons is their low price. It makes sense for the companies producing electronic equipment to use these buttons to help keep their production prices low.
Customization of silicone rubber buttons
The processes that are used to manufacture silicone rubber products are compression molding and injection molding.
Compression molding or vulcanization occurs when silicone rubber enters chemical reaction with ether one of the following chemical compounds: sulfur, peroxides, urethane crosslinkers, metallic oxides, duece, and acetoxysilane. During the vulcanization process silicone rubber takes the shape of a mould.
During injection molding silicone material is forced into a heated barrel where it melts. Then the liquid silicone is forced under pressure, into a cold cavity (mould) of a certain shape. The material takes the shape of a mold and slowly hardens as its temperature drops.
The mould can be designed in such way that the end product of an injection molding process is a set of the buttons of any sizes and shapes (the silicone rubber buttons coming out of the same mould do not have to be of the same size and shape).
Compression molding and silicone injection molding both take advantage of multiples cavities in a mold. A single cavity produces a full silicone rubber button or silicone keypad, a cavity can be duplicated so that there are multiple cavities in a single mold. For example a 32 cavity mold will produce 32 silicone rubber keypads each time the mold is cycled. Using multiple cavities in a mold lowers the machine time which in turn lowers the cost per piece to manufacture a custom silicone rubber keypad.