Silicone rubber is a material widely used in various fields, including electrical and household appliances. Can I use silicone rubber to make electrical insulation coatings or touchscreens for electronic products? Is silicone rubber an insulator or a conductor? These questions will be answered in this article.
Is Silicone Conductive?
Silicone is a non-metallic material, so ordinary silicone, like glass, is not electrically conductive. Silicone is generally used as an electrical insulating material in the sealing enclosures of electronic components.
When specific fillers are added to silicone, it can become electrically conductive and transmit current in specific locations. You can choose silicone with different conductivity levels for your product, depending on your needs.
Why Is Silicone an Electrical Insulator?
Silicone rubber is a type of synthetic rubber, also known as silicone elastomer, due to its flexibility and elasticity. Its molecules contain a backbone composed of silicon and oxygen atoms. Many organic groups, such as methyl groups, are attached to this backbone. These backbones are interconnected, forming a three-dimensional network structure.
Because there are very few free electrons in the molecules, and electrons find it difficult to flow and conduct electricity, silicone itself is an electrical insulator.
In addition, the fillers, additives, and vulcanization methods used in the manufacturing process of silicone also affect the conductivity of the silicone rubber.
What Is Silicone Made Of? How Compositions Affect Safety and Performance contains more information about the components of silicone.
Electrical Insulation Properties of Ordinary Silicone Rubber
Silicone rubber is an excellent electrical insulating material. It has stable electrical insulation properties in most cases and is flexible and durable.
- High electrical resistivity:Ordinary silicone isn’t a good conductor of electricity. Its resistivity is typically between 10¹³ Ω·cm and 10¹⁵ Ω·cm, effectively preventing current from passing through. Its dielectric constant is also only 2.5–3.5. This insulating property remains unchanged even when the silicone rubber is in water.
- Thermal stability:Silicone is a material that can be used in baking and has excellent resistance to high temperatures. It also performs well at low temperatures. Silicone maintains good insulation properties between –60°C and 230°C.
- Weather resistance:Silicone rubber can withstand ozone and UV radiation, which makes it suitable for use in outdoor cable insulation.
- Chemical inertness:The molecular backbone composed of silicon and oxygen gives it strong chemical compatibility. Except for a few substances like fuel and strong acids, silicone is not easily corroded when in contact with most materials.
- Flexibility:In addition to being non-conductive, silicone also has flexible and elastic properties. It can withstand a certain amount of external force and only undergoes slight permanent deformation.
- Biocompatibility:Silicone rubber can be manufactured into medical-grade materials. Medical silicone is non-toxic and odorless, and can safely come into contact with human tissues, skin, or mucous membranes.
Can Silicone Become Conductive?
The electrical insulation properties of silicone materials are not absolute. In some cases, silicone can also conduct electricity, making it suitable for applications requiring electrically conductive seals.
Besides aging and damage that can lead to electrical insulation failure, the main method to make silicone conductive is to add conductive fillers during the manufacturing process. Carbon-based fillers such as carbon black, graphite, and carbon nanotubes, as well as metal-based fillers such as silver and copper, are the most commonly used conductive fillers.
Carbon Black
Carbon black is a low-cost conductive filler. While enabling electrical conductivity in silicone rubber, it can also improve the tear resistance, hardness, and other physical properties of the silicone to some extent. Silicone rubber with added carbon black can achieve a resistivity of 10⁻²–10⁴ Ω•cm. Carbon black also makes the silicone rubber less flammable.
While mechanical properties are improved, the flexibility of conductive silicone rubber with carbon black filler decreases. Carbon black also limits the color options for conductive silicone rubber, restricting it to black. If you want to create products with an attractive appearance using conductive silicone rubber, conductive silicone containing carbon black might prevent you from realizing some of your design ideas.
Producing high-quality conductive silicone rubber using carbon black is relatively difficult. When you choose to use conductive silicone rubber with carbon black filler to manufacture medical devices, the carbon on the surface can easily flake off during use, which can also become a problem. Dusting is another major drawback of carbon black.
Metal-based Fillers such as Silver
Conductive rubber made with silver, copper, and other particulate fillers has superior conductivity compared to other fillers. Metal-based fillers can reduce the resistivity of silicone rubber to 10⁻⁴–10⁻¹ Ω•cm. This makes them suitable for use in high-efficiency electromagnetic interference shielding gaskets.
They also make the silicone rubber more similar to the metal itself, resulting in a harder and more wear-resistant material.
However, these metal-based fillers are often expensive and prone to “rusting” like iron, a drawback not found in other materials. Over time, the conductivity of the conductive silicone rubber gradually decreases. Like carbon black, metal-based fillers also cause the silicone rubber to lose some flexibility and become heavier.
Achieving good bonding between metal-based fillers and silicone rubber also requires advanced technology. They are not materials that easily combine with silicone rubber.
Graphite
The graphite filler added to silicone is generally nickel-plated graphite. Although it is essentially carbon, like carbon black, it has superior conductivity and is often used as an electrode material. It allows the resistivity range of the silicone rubber to be maintained within the range of 10⁻¹ to 10⁵ Ω·cm. Unlike conductive silicone rubber with carbon black filler, silicone rubber using graphite as a filler can be made gray.
Conductive silicone rubber requires a large amount of graphite filler, which makes the conductive silicone rubber very heavy, which is not ideal for certain everyday consumer products that focus on lightness.
Graphite fillers are not easily dispersed uniformly in silicone rubber, which affects the electrical conductivity stability of the silicone rubber. Silicone rubber with a large amount of graphite filler becomes very viscous, increasing processing difficulties. Graphite fillers can also alter the physical properties of silicone rubber, making it less flexible.
Carbon Nanotubes(CNTs)
Carbon nanotubes are another type of carbon-based filler material. A significant advantage of carbon nanotubes compared to other fillers is that only a small amount needs to be added to silicone rubber to achieve the desired resistivity. They are quite stable, as corrosion-resistant as silicone rubber itself, and provide much more stable electrical conductivity than materials like carbon black.
Under the influence of carbon nanotube fillers, the resistivity of silicone rubber can be reduced to a range of 10⁻² to 10⁴ Ω·cm. Improved wear resistance, hardness, and thermal conductivity are also among the changes brought about by carbon nanotube fillers. Conductive silicone rubber using graphene nanotubes (SWCNTs) can come in a wider range of colors, giving you more design choices.
On the other hand, carbon nanotubes are actually a rather troublesome filler for both manufacturers and buyers. If you purchase conductive silicone rubber containing carbon nanotube fillers from a manufacturer with substandard technology, the aggregation of fillers within the silicone will significantly affect its conductivity stability and lifespan.
It is also quite expensive and is generally used as a high-end sensor material or in combination with other carbon fillers.
Mixed Fillers
Single types of fillers present various problems in terms of cost and electrical conductivity stability, so mixed fillers composed of these materials have become the choice for many conductive silicone rubbers. By adjusting the type and proportion of fillers, conductive silicone rubber can achieve different levels of electrical conductivity.
How is Conductive Silicone Rubber Made?
The manufacturing process of conductive silicone rubber is similar to that of ordinary silicone rubber, but the fillers and additives used are different, and an additional post-curing step is included.
Step 1: Select appropriate base materials based on requirements and formulation. This will determine the properties and applications of the conductive silicone rubber. Polydimethylsiloxane (PDMS) is typically the starting point for the manufacture of conductive silicone rubber.
Step 2: The conductive fillers and additives are uniformly mixed into the raw materials. This step determines the conductive stability of the conductive silicone and also reflects whether the manufacturer possesses sophisticated technology. Generally speaking, the machine used for mixing is a two-roll mill.
Step 3: A vulcanizing agent is used to cure silicone rubber into a usable form. Compared to peroxides, which produce byproducts, high-quality conductive silicone rubber utilizes platinum catalysts to achieve more stable conductivity.
Step 4: The silicone rubber is heated and pressurized using equipment to mold it into the desired shape. For long, strip-shaped silicone products, extrusion molding is used instead of compression molding to form them into the appropriate shape. For the production of more precise parts, manufacturers use injection molding to process liquid silicone rubber (LSR).
Step 5: To make conductive silicone rubber purer and its conductivity more stable, secondary vulcanization is often performed.
Step 6: Shape and test the conductive silicone rubber’s various properties to ensure quality.
Conductive Silicone Rubber Properties
- Conductivity:Depending on the type and content of the added fillers, the electrical conductivity of conductive silicone rubber varies. The resistivity of conductive silicone rubber can be adjusted over a wide range, from 10⁻⁴ to 10⁰ Ω·cm for use in electromagnetic shielding, to 10⁶–10⁸ Ω·cm for use in antistatic applications.
- Stability:Conductive silicone rubber has a long service life.
- Wide temperature tolerance range: Similar to ordinary silicone rubber, the conductive properties of conductive silicone rubber don’t change significantly within the temperature range of -60°C to 200°C.
- Weather resistance:It has good resistance to ozone and UV in outdoor environments.
- Chemical compatibility: It rarely reacts with other chemicals.
- Biocompatibility:Conductive silicone rubber that has passed safety certification and toxicity tests can be used in medical devices and is unlikely to cause allergies.
- Flexibility:Although its physical and mechanical properties are somewhat different from those of ordinary silicone rubber, it is still a generally flexible material.
Applications of Silicone Rubber in Electrical Insulation
Power Systems
Ordinary silicone rubber can provide long-term stable electrical insulation in outdoor environments, so it can be used to manufacture insulation layers or insulating components for wires and cables, and can also be used in high-voltage electrical facilities.
Electronic and Appliance Sealing
Due to its excellent flexibility, thermal stability, and cushioning properties, silicone rubber can be used as sealing rings and potting materials for electronic components. Appliance seals made with silicone rubber not only provide electrical insulation, but their corrosion and moisture resistance allow for longer service life, enhancing the reputation of your appliances.
Automotive Manufacturing
Silicone can be used in automotive wire harness seals and battery seals. For new energy vehicles that use electricity, the electrical insulation properties of silicone are even more important.
Medical Field
Electrically insulating silicone can also be used in the medical field, but before that, it must pass ISO 10993 safety certification and a series of tests. Certified silicone rubber is safe and can be used as electrical insulation seals for medical devices and surgical equipment.
Applications of Conductive Silicone Rubber
Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) Shielding Components
Highly conductive silicone rubber can provide effective support for 5G equipment, shielding gaskets, and other products requiring both high conductivity and sealing performance, preventing interference from other devices and components.
Electrostatic Discharge (ESD) Protection Components
Conductive silicone rubber with relatively weak conductivity can be used in the form of grounding mats and conveyor belts to help industrial or electronic equipment slowly release static charges. It prevents static electricity from affecting your equipment or causing fire hazards.
Industrial Applications
Seals and adhesives made from conductive silicone rubber perform very well in both conducting electrical current and resisting chemical corrosion, ensuring long-term usability. Some conductive silicone rubbers that can also conduct heat can serve the dual purpose of conducting electricity and dissipating heat.
Medical Field
Due to its conductivity and biocompatibility, safety-certified conductive silicone rubber is frequently used as the material for the small pads that are placed on patients’ skin for electrocardiogram (ECG) devices. Conductive gels applied to the body to enhance conductivity also contain this component. It can also be a suitable choice for the electrode pads of your defibrillator.
Consumer Goods
You may have seen conductive silicone rubber in everyday consumer products. Silicone buttons, keyboards, and touchscreens offer a pleasant feel and are popular with consumers. It can also be used as a flexible electrode material.
FAQ
What Are the Different Types of Conductive Silicone Rubber?
- Conductive High-Temperature Vulcanized Silicone Rubber (HCR):This type of conductive silicone rubber is more resistant to high temperatures and has higher mechanical strength, so it is generally used in the manufacture of industrial seals and gaskets.
- Conductive Room Temperature Vulcanized Silicone Rubber (RTV):A type of conductive silicone rubber that can cure at room temperature. It is the main material for conductive adhesives.
- Conductive Liquid Silicone Rubber (LSR): Due to its good fluidity, this type of conductive silicone rubber is best suited for making fine conductive components.
Recommended reading: A Simple Guide to Silicone Rubber Types and Applications.
Conductive Silicone Rubber vs. Metals vs. Conductive Rubber
Metals have the best electrical conductivity and electromagnetic shielding properties among these three materials, but they are hard and easily corroded.
Conductive rubber has the advantage of being resistant to oil and fuel-based chemicals, but it isn’t as resistant to high and low temperatures as silicone rubber and metal. It is also prone to aging and deformation.
Silicone rubber is the most adaptable to outdoor environments and is safe and non-toxic, but it is not wear-resistant and cannot be in prolonged contact with fuels and other substances.
Silicone vs. PVC vs. PTFE(Teflon)
Silicone rubber is a versatile electrical insulation material. It is soft and corrosion-resistant, can operate over a wide temperature range, but it is relatively prone to wear, making it more suitable for applications in electric vehicles and the medical field.
PVC is cheap and moderately flexible, but it is not resistant to low or high temperatures or chemical corrosion, making it more suitable for conventional consumer products.
PTFE is the most expensive of the three electrical insulation materials. It is highly corrosion-resistant and difficult to burn, but it is relatively rigid, making it more suitable for extreme environments.
Can I Order Custom Conductive Silicone Rubber?
You can customize the color, size, conductivity, and shape, such as sheets and tubes, of conductive silicone rubber from the manufacturer, but there is usually a minimum order quantity requirement. After you send your specific requirements, a professional team will configure the appropriate conductive silicone rubber for you and will typically send a sample for your reference.
Is Conductive Silicone More Expensive than Regular Conductive Materials?
Yes, due to technical requirements and differences in fillers and manufacturing processes, conductive silicone rubber is more expensive than ordinary conductive materials. In fact, conductive silicone rubber is very durable and can save you a lot of maintenance and replacement costs, making it a very cost-effective choice.
Final Thoughts
Whether used as an electrical insulator or a conductive material, the quality of silicone rubber is important to product performance. As a professional silicone product supplier, Legensilico offers a range of products from industrial-grade silicone to FDA-compliant medical-grade silicone and provides customized services. If you would like to learn more about the conductivity of silicone, contact us today!
