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Thursday November 11th, 2021

Electrical properties of rubber raw materials

Due to the development of manufacturing technologies, components of certain equipment are becoming smaller and faster. However, rapid modernization leads to the production of equipment vulnerable and sensitive to electric charge.

This issue proves to be a major challenge for many industries, since a sudden electric discharge may cause severe material damage and lead to failure of machines with ESD sensitive components. Protection against electrostatic discharge is essential in industrial environments since volatile substances can bring about additional hazards.

This article introduces rubber materials that are applied for their insulating properties as well as rubbers and elastomers that are known for their capability of electrical conductivity.

Electrically conductive rubbers

Electrically conductive rubbers have relatively low resistance and therefore are effective electrical conductors.

Electromagnetic interference is a common problem to occur in high-voltage environments, namely because the equipment causes interference to other electrical devices during operation. The disturbance generated by electromagnetic interference can be prevented by applying electrically conductive rubbers that comply with EMC (Electromagnetic compatibility) standards.

Because of galvanic corrosion – the corrosive effect created when different metallic materials come into contact with each other – the electrode potential of each metallic material must be taken into account when choosing the appropriate mixture.

PropertiesElectrically conductive rubbers
Resistance103 – 106 Ohm/m2
Hardness40-80 Shore A
TypeNR, EPDM, Silicone, NBR, CR, VITON

 

What makes conductive elastomers conductive?

Rubber becomes electrically conductive due to metal particles mixed into the raw material. The degree of conductivity always depends on the conductivity of the particles added to the raw mixture.

Increase in electrical resistance of metals is directly proportional to the increase in temperature. The most conductive raw materials are elastomers with added silver because silver has the best thermal conductivity. However, wires are most often made of copper or gold, because silver might become discolored by high voltages. Copper is favored because of its affordable price, while gold is preferred because of its extreme corrosion resistance.

As a cost-effective solution, additives of lower price and worse conductivity are coated with materials of good conductivity, like:

  • silver-coated glass,
  • silver-coated aluminum,
  • nickel-coated graphite.

 

Even a customized, special-purpose rubber component can be made conductive. The mixture used to create a rubber component should always be chosen according to the purpose for which the component is intended.

What is electrically conductive rubber used for?

Electrically conductive rubbers are used by various industries, mostly because they are suitable for:

  • dust separation, filtering,
  • antistatic purposes,
  • rubber to metal bonding,
  • electrical connections,
  • muscle stimulation,
  • electromagnetic shielding of offices.

 

Static rubbers

As for their conductivity, static or dissipative rubbers are in between antistatic and conductive rubbers in terms of electrical properties. These rubbers are conductors, but less so than compounds made with specifically conductive raw materials.

PropertiesSemiconductor rubbers
Resistance106 – 109 Ohm/m2
Hardness40-80 Shore A
TypeNR, EPDM, Silicone, NBR, CR, VITON

 

What makes static or dissipative rubbers resemble semiconductors?

Similar to electrically conductive rubbers, the conductivity of static rubbers is mainly determined by the properties of the additives used. They are most often made by adding copper and can be found as rubber belts in printers and copiers.

ESD and antistatic rubbers

Definitions of ESD and antistatic properties

ESD protection prevents high-energy sparking by allowing electricity to divert quickly and in a controlled manner.

Antistatic rubbers prevent charge buildup because their properties balance electrons with positively charged ions. Electrical charges are conducted by grounding.

 

ESD risk reduction with rubber

Electrostatic (triboelectric) charging is oftentimes the result of two identical or different materials joining, separating or frictionally interacting.

Due to the electrostatic discharge caused by friction, the surface of sliding objects or the object itself becomes electrically charged, which can be dangerous. An electrostatic discharge has the ability to change – either to deteriorate or to annihilate – the electric properties of semiconductor objects. In cleanrooms, surfaces charged with static electricity attract and retain dirt, making them difficult to clean.

For ESD protection, the best strategy is to prevent and neutralize the development of static electricity at the same time.

The risk of electrostatic discharge can be minimized and prevented by appropriate protection.

If the charge has already been created, the most effective way to neutralize it is by grounding.

One major advantage of ESD rubber is its ability to dissipate the electric charge, meaning that it transfers only a small fraction of the electrical charge compared to conductive or semi-conductive rubber.

PropertiesESD antistatic rubbers
Resistance109 – 1012 Ohm/m2
Hardness40-80 Shore A
TypeNR, EPDM, NBR, CR, VITON

 

What makes ESD rubbers antistatic?

Its antistatic properties are caused by either solid or liquid special additives. Among antistatic additives we distinguish:

  • antistatic agents,
  • antistatic inorganic compounds,
  • and conductive polymers.

 

Within antistatic agents, a distinction is made between organic small molecule antistatic agents, within which there are:

  • cationic,
  • anionic,
  • non-ionic,
  • and zwitterionic antistatic agents.

 

Permanent antistatic agents also belong to this category of special additives.

As for antistatic inorganic compounds, the most widely used are:

  • soot,
  • carbon fibers,
  • metallic fibers,
  • and polymer.

 

Soot is particularly suitable for ESD applications given that it is the most cost-effective material for this purpose. However, its applicability is limited due to its suboptimal mechanical properties and its availability only in black.

Unlike soot, carbon fiber with an atactic (PAN) structure is easy to use for a variety of applications thanks to its good mechanical properties, even though it is more costly.

 

What are antistatic ESD rubbers used for?

Technologies that reduce static damage are becoming increasingly popular in industrial applications. Most commonly, ESD materials are used in electronic component and equipment manufacturing to dissipate or ground unwanted discharges.

Protective equipment and garments of personnel working in high-voltage areas are made of ESD materials in order to prevent life-threatening accidents. They are also used in agriculture, shopping malls, and the food industry.

Electrically insulating rubber

Let us take a look at rubbers that are most suitable for electrical insulation. Insulating materials prevent or restrict the flow of electrons within or across their surface.

Insulating rubbers are electrically resistive and hard to ground, so they are not ESD materials. They retain their static charge on their surface for a long time.

PropertiesElectrical insulating rubber
Resistanceover 1013 Ohm/m2
Hardness40-80 Shore A
TypeNR, EPDM, Silicone, NBR, CR, VITON

 

What causes its insulating property?

Rubber is a natural dielectric constant, so it blocks the flow of electric charge since its molecular structure prevents the free flow of electrons. It is an ideal insulating material given its electrical resistance.

Given its flexibility and cushioning, it is a perfect choice for mats and insulation. As additives might affect its conductivity, strict attention must be paid to the composition of electrical insulating rubbers.

Where are electrically insulating rubbers used?

They are most often used as insulating rubber mats, fillers, rubber tubes and cable gaskets in electrical rooms, where there is a high risk of electric shock and their use is subject to strict regulations.

Electrically conductive and insulating rubbers from SIC Hungary

For 80 years, SIC Ltd. has been manufacturing raw materials for the rubber industry for both special and customized purposes. If you are looking for electrically conductive or insulating rubber materials of good quality, please do not hesitate to contact us and we will help you choose the most suitable materials; whether they be shading rubber mats, conductive rubber profiles, ESD or insulating rubber mats.

 

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