Due to their chemical compositions, most elastomers, including rubbers, polyurethanes and silicones, are natural insulators. Electrical conductivity can be improved in these materials by including conductive additives in the material’s manufacturing process. In the case of polyurethanes, using conductive additives will result in semi-conductive materials. The specifics of the chemistry being employed will determine the conductivity level, as well as the physical properties the material will possess. In this post we will discuss some of the technologies used to make polyurethanes electrically conductive, the benefits of including conductive polyurethanes in product design, and end use applications for these engineered materials.
Not All Conductivity is Created Equal
One of the traditional methods used to create semi-conductive polyurethanes included the use of carbon black. Carbon black is the result of incomplete combustion of some fuels, particularly oil-based fuels. Chemically speaking, carbon black is a lattice of crystal-like carbon molecules that are electrically conductive. Carbon black is inert when introduced to polyurethane chemistry, making it easy to include in traditional molding processes. In this method, the solid carbon black particles are surrounded and held in place by the polyurethane matrix. While carbon black accomplishes the goal of making polyurethanes conductive, it can also create some unwanted problems:
- Uniformity of Conductivity - As the carbon black solids settle in the liquid polyurethane mixture, they will tend to concentrate in the direction of gravity. This means that the resulting material will not have uniform conductivity. In other words, as the product wears it will experience charges in conductivity.
- Leaves a Mark - During operation, when the carbon black in the polyurethane comes in contact with other materials, it will leave marks on the surface it is contacting, much like a pencil lead. This is problematic in media handling applications, where these markings can cause unwanted results.
- Overstays its Invite - As polyurethane products made with carbon black wear, the material matrix keeping the carbon black in place will give way, letting the carbon molecules out into the environment. This unwanted debris can cause major issues in electrical or mechanical devices.
MPC’s Durethane® C employs our patented metal salts technology to create semi-conductive polyurethanes without the problems created by carbon black. We do this by dissolving the conductive elements in the liquid polymer in a controlled environment, prior to curing the material. This process assures that the conductive elements are homogeneously dissipated throughout the polyurethane mixture.
Within the mixture, the polyurethane molecules engage in an electro-chemical interaction with the conductive elements, which is maintained through the casting process. This process creates conductive materials that maintain the robust physical properties of polyurethanes.
When to use Conductive Polyurethanes
Semi-conductive polyurethanes are ideal for dissipating static build-up or transferring an electrical charge. In the first case, electrostatic build-up. This powerful combination of electrical conductivity and durable material properties make conductive polyurethanes ideal in a variety of industries, including: may occur in a mechanical operation as friction is generated. If not controlled, static build-up may generate a discharge that can damage sensitive electronics or disrupt the user experience. Conductive polyurethanes can be included in a design to safely and effectively bring static build-up to ground. Conductive polyurethanes can also play a key role in electro-mechanical mechanisms that require superior material properties and the transfer of electrical charges.
- Medical Devices
- Cleanroom Systems
- Food Processing
- Conveyance Systems
- Digital Printing & Imaging
- Currency Handling
- Electronics and Electronics Manufacturing
Semi-conductive polyurethanes can play a key role in assemblies or mechanisms that generate static or require a charge to be transferred. When making material decisions in product design it is important to consider the physical properties required for successful operation, as well as the material’s wear life.
To learn more about conductive polyurethane, download our Durethane® C Conductive Technology Overview: