Usually we encounter this name when reviewing the tarps available in the market. But what does it really mean that a material is antistatic, how is it obtained and, most importantly, when do we need it? Here you will find an overview of the most useful information.
What is an antistatic material?
Electrical resistance of materials is important wherever we may encounter static electricity, usually provoked by friction. Most plastic materials are natural electrical insulators, and the resistance of normal PVC materials lies within the limits of 10E10 Ω – 10E11 Ω (according to DIN54345 T1). However, in certain circumstances there arises a need to use materials with reduced electrical resistance – these are the materials that we call ‘antistatic’.
When an electrically charged material comes into contact with a conductor, the transfer of energy takes place very quickly and abruptly. The spark resulting from this contact is able to ignite gas, for example in tunnels or mines, destroy electrical equipment by producing very high voltage (above 20 kV) or start a fire. Fortunately, the current is very low, and if not, the combination of the high voltage and current would be dangerous for people.
Production of antistatic materials involves transforming insulating materials into electrical energy conductors. Materials transformed into conductors have the ability to disperse electrical loads continuously and impede their build-up to dangerous levels.
What to consider when buying antistatic materials
Check fabric specification; for antistatics the most important parameter is the ‘surface resistance’ (measured in ohms).
An example parameter looks like this: 10E9, 10E08, 10E10 and here is where you have to be careful. In this notation, the number that appears after the letter ”E” is the number of zeros, for example:
10E08 Ω = 100 0000 0000
10E10 Ω = 10 0000 0000 0000
Therefore 10E10 is a value about 100 times higher than 10E08, which means that it has 100 times more resistance, and thus 100 times lower antistatic properties. It is recommended, therefore, to look for the lowest parameter value to get the highest antistatic properties.
How are antistatic properties obtained?
There are two methods of obtaining antistatic properties:
1. PVC formula
(so-called “typically antistatic”) – antistatic agents are added to the PVC paste at the stage of its manufacture. Maximum resistance achieved by the material in this process is >5x10E9 Ω. These materials come in a variety of colours and can be processed by means of hot air and high frequency welding.
(so-called ”highly antistatic”) – finished material is coated with black varnish with graphite of very high antistatic properties (< 5x10E9 Ohm). It is not possible to weld such materials with high frequency welding machines. An example of such a material is B7675 (<10E6 Ω).
In theory, materials from the highly antistatic group maintain these properties virtually ”forever”. In typically antistatic materials the antistatic agents migrate towards the surface, which therefore changes the antistatic properties:
While storing materials
– change of properties during storage is quite slow, but can result, after a longer time on the materials’ surface, in antistatic agents making the materials become less high-frequency weldable.
After final installation
– antistatic agents are exposed to moisture during indoor use and/or rain in the case of outdoor use. However, there is a great difference in both cases. It may be that in the case of outdoor use, the loss of properties can occur even after two years; yet the same material used indoors can still adequately retain its properties after five years.
Contrary to some theories, the results of customer tests are the most reliable. They seem to indicate that the antistatic properties diminish over time in case of both technologies.
Welding of antistatic materials
As a rule, the more antistatic a material is, the worse its welding properties are, while highly antistatic materials (2nd technology) are completely HF unweldable. Interestingly, even typically antistatic materials (1st technology), which can be HP welded immediately after production, can become a lot less weldable (as a result of antistatic agents’ migration).
- welding curtains,
- air tunnels,
- ventilation tunnels,
- containers for the transport of electrical equipment.