It’s an experience every driver has had: pull into the parking lot, shut off the engine, open the door, get out, reach for the door, and ouch! get zapped. The reason for this unpleasant phenomenon is an electrostatic discharge. When one nonconducting material (such as the wool of a driver’s trousers) comes into tight contact with another nonconducting material (such as the polyester of a car seat), both contact surfaces become electrically charged. For a while, this friction goes unnoticed, but when the two materials are separated again (for example, as the driver gets out), the charges are discharged by way of a conductor (such as the metal of a car’s roof or door). Voltages are high enough that sparks arc over as the driver’s hand approaches the door. There is a simple preventive measure: touching any metal part before getting out of the car lets the charges drain off right away, avoiding that pesky zap.
Another problem caused by static electricity in a car is far less easily solved. Plastic parts in the passenger compartment collect electric charges, both due to people getting in or out and due to the air flow circulated by the ventilating / air conditioning system. Charged plastics attract minuscule dust particles, creating an unattractive smudgy film made more conspicuous by the light color scheme of modern passenger compartments. Even new cars must be painstakingly cleaned for buyers to pick up spotless vehicles. After a new car has been parked in the customer’s driveway for a few weeks, the owner will be unpleasantly surprised to find that fine dust has made its way into every little corner. So a big German car manufacturer decided to tackle the problem and joined forces with Clariant to develop a solution based on the permanent antistatics of its Masterbatches Division. |  |
The reason that plastics become electrically charged is their poor conductivity. Once generated on a plastic surface, electric charges remain stationary and unable to drain off. Antistatics reverse this development by increasing a material’s conductivity until electric charges become mobile, able to dissipate to an earth connection within a relatively short period of time.
Traditional antistatics, such as those used in plastic packaging, are water-attracting surfactants added to and dispersed in the plastic material. Antistatics of this kind are not integrated into the material they are added to, but migrate to the plastic’s surface where they form a molecular hygroscopic film that absorbs air humidity. This humidity will lower the electric surface resistivity, enabling electric charges to drain off. However, migrating antistatics have inherent shortcomings: they are water-soluble, washable and volatile upon air contact, which causes them eventually to lose their effect. Moreover, their effectiveness depends on air humidity. If air is too dry, such as on a cold winter’s day, dissipation of electric charges by migrating antistatics does not work very well. Still, they are well suited for packaging, where long service life is not particularly important.
When it comes to the use in vehicles, however, long service life is crucial. After all, a car is supposed to keep on looking good even after it has been on the road for a few years. For this reason, there is only one solution for enhancing molded parts such as sunglass storage compartments or overhead consoles, and that solution is permanent antistatics. Permanent antistatics are inherently dissipative polymers or IDPs for short. IDPs are conductive along their molecular chains and, creating a three-dimensional network, form a solid compound with the basic plastic. Plastics compounded this way feature not only reduced surface resistivity, but reduced overall volume resistivity.
While a similar effect may be achieved by adding carbon black or carbon fibers, plastics treated this way turn gray or black, making it impossible to color them. In contrast, permanent antistatics are transparent in many polymers such as polyolefins, polyesters or thermoplastic polyurethanes (TPUs), so coloring remains an easy option. |