Anti-static/conductive additives

Table 11.1 At a glance anti-static/conductive additives...

Anti-static additives are capable of modifying the properties of plastics in such a way that they become anti-static, conductive, and/or improve electromagnetic interference shielding (EMI). Carbon fibers, conductive carbon powders, and other electricaUy-conductive materials are used for this purpose. 

It is believed that to avoid any risk of explosion, the electrical conductivity of jet fuel should fall between 50 and 450 pS/m. This level is attained using anti-static additives which are metallic salts (chromium, calcium) added at very low levels on the order of 1 ppm. 

Rubbers are usually electrically insulating and this property is widely exploited in cables and various components in electrical appliances. They can also be made anti-static and even conducting by the addition of suitable carbon blacks. In all cases, it is the combination of the electrical properties and the inherent flexibility of rubbers which makes them attractive for particular applications. 

In the early stages of the development, the electrical properties of impression roll coverings were rather erratic. In this country, conductivity was imparted by means of conductive, structured carbon black fillers. It turned out that the exact steps in manufacture, such as milling temperature were as important as formulations. The conductivity of compounds made with Buna N was very strain sensitive. In Europe, conductivity was imparted by Anti-static additives. The electrical properties were more predictable, but resistance to wear left much to be desired. The manufacture of suitable roll coverings has been a real challenge to roll manufacturers, and suitable coverings have been available in the last five years on a very consistent basis. New Material which contain conductive polymers (Hercules Inc.) require some warm up before the desired conductivity level is reached, but have very uniform predictable electrical properties and stand up well to the wear and tear of press operations. 

Additives with specific functions (such as flame retardants, anti-statics, and conductives) are now also expected to make a contribution to facilitating processability. Traditional fillers, such as calcium carbonates, are surface modified to give them additional value and, at the other end of the spectrum, highly sophisticated polymers such as fluoroplastics are being modified to play key roles as processing aids. 

Figure 11.1. Carbon black additives can also conduct electricity, offering a simple and effective means of providing anti-static properties or EMI shielding.

Since the dissipation of the static charge is a function of the liquids conductivity, anti-static additives may be used. These additives do not reduce static generation, but will permit the charge to dissipate more quickly. They should be introduced at the distribution beginning point, and their effectiveness may be reduced by passage through clay filters. 

---