Anti-static compound additive

Until fairly recently most plastics were purchased fully compounded in the colour required for moulding or extrusion, but with a view to offering ranges of colours more cheaply and conveniently it is quite usual now for machines to be fed with blends of natural thermoplastic and masterbatch—a convenient wax-like base containing appropriate concentrations of colorant and other additives (such as anti-static agent). The supply of masterbatches has become an important specialized business. 

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. 

In addition to the straightforward application of conductors and semi-conductors, there are some interesting examples of other uses. Polymers derived from 3,4-ethylenedioxythiophene are produced commercially as anti-static agents and substituted compounds have found particular application in electrochromic devices - substances that change colour on application of an electric current. 

Anti-static agents Rubber compounds Additives in grease Others... 

Compounds dissipate a surface charge and can be processed by normal thermoplastic methods. Typical applications are boxes and in-plant handling containers for electronic components or chemicals where there is a risk of explosion from a spark. Medical products also increasingly have ESD specification, especially for use in an operating theatre. Packaging products such as flexible films also require some form of anti-static treatment, either by means of an additive, or by using external field generators. 

This will be mainly to offer a range of colours, while only needing to hold stocks of natural material, or to add or boost specific properties, such as UV stability, anti-static properties or flame retardancy. To facilitate in-plant compounding, most suppliers have developed systems that efficiently and reproducibly deliver a controlled package of additives to a compound, using either a specialized concentrate or a masterbatch formulation. 

To maintain the performance of plastics, various additives such as plasticizers, antioxidants, anti-static agents and flame retardants are compounded into plastic products. Some of these plastic additives are leached from plastic product waste, and may threaten humans and wildlife. An example is the release of nonylphenols, or endocrine-disrupting chemicals, from plastic tubes that are employed for scientific research. This is described in a chapter entitled Here, There, and Everywhere in a well-known book on endocrine disruption, Our Stolen Future, by Colbom, Dumanoski and Meyers (1996). 

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