Yarns and fibers for anti-static protection from Swicofil

Kindly note that this product is no longer in our program. Swicofil will try to find a suitable alternative.

Electrical conductivity in textiles

Electrical conductivity and resistivity

R = U/I

One can distinguish three types of resistivity according to whether the material is presented in a linear, surface or volume format.

• The linear resistivity p_l of a filiform element is characterized by the measure of the resistance compared to its length and is expressed in ohm/centimeter (O/cm):

p_l = R/L

with R = resistance in ohms,
L = the length of the sample.

• The surface resistivity p_s characterizes flat materials of little thickness such as fabrics, and it is expressed in ohm (O) or in ohm/squared (O/¨)

p_{s =} R x 2 Pi /ln/r₂/r₁)

with R = the resistance in ohms, r₂ = the radius of the internal electrode, 
r₁ = the radius of the external electrode.

• The volumic resistivity p_V characterizes the three dimensional materials by the measure oft the resistance R compared to the surface S, and to the length L. It is expressed in ohm.centimetre (O.cm):

p_{v =} R x S/L

with R = resistance in ohms, 
S = the surface of the electrodes, 
L = the length of the sample.

The standardized measures

A textile electro-conductor is characterized mainly by the measure of its electrical resistivity. The principle of this measure involves disposing on the sample some conductive electrodes, to the terminals of which is applied a tension in order to determine the resulting current. The resistivity derives from a calculation taking account of the current, the tension and the dimensions of the fitting. Numerous standards in different countries are based on this measurement principle. Here are two most used.

• NF EN 1149 standard “Electrostatic properties of protective clothing”. This is the reference in Europe for characterizing textiles. In the future it will be composed of five parts, of which the first two have been approved:
  
  - NF EN 1149-1 “Surface resistivity“. It states that the superficial electrical resistivity of an antistatic textile should be less than 5 x 1010 ohms.
  
  - NF EN 1149-2 “Transverse electrical resistance”. It allows one to determine the electrical resistance through any material.
  
  Part 3 of this standard is now being drawn up, and it will allow one to characterize through friction or induction method those textiles using yarns with a conductor core. Part 4 will define the measuring principles on clothing and Part 5 the product requirements.
  

• NF EN 1815 standard “Resilient and textile floor coverings – Measuring the propensity to accumulate electrostatic charges”. It allows one to determine the static electricity produced when a person walks on a textile floor covering.

Conduction of textile surfaces

The scale of electrical conduction covers a broad range, from surface resistivity of more than 1014 ohms down to resistivity of less than one ohm. The applications for conductor textiles are linked to this scale of resistivity.

Applications involving the transport of electrical data, EMI shielding and heating textiles call for relatively low resistivity levels (less than 103 ohms), while the anti-statics are happy with performances of around 1010 ohms.

The products

One can distinguish on the one hand conductive fibers and yarns, and on the other, those textiles which receive a conductive treatment on the finished product.

Among the conductor fibers there are the intrinsically conductive fibers, along with polymer fibers on which is grafted a conductive function. 

In the first category one finds the fibers of metal or metallic alloys, as well as those of pure carbon. 

The fibers group, which is made conductive, is much broader, notably with all those fibers charged with carbon for antistatic applications. These fibers have a polymer base (polyester or polyamide for example), which is co-extruded with a polymer charged with carbon black. These products are generally used as grids during weaving to ensure a meshing, which ensures elimination of electrostatic charges.

The applications for antistatic textiles are the most numerous, to include:

• clothing for “white rooms”;

• work wear for explosive or inflammable environments;

• work wear and floor coverings for computer rooms;

• air filtration;

• conveyor belts; and

• ready-to-wear clothing (antistatic for comfort).

For applications calling for a lower resistivity (conduction, shielding or heating fabrics), one uses metallic fibers or directly metallized textiles. The family of conductor polymers, which are the naturally conductive plastics, is in full development by the major chemical industry groups (Bayer, Ormecon, DSM, etc.), and more new textile applications should thus be launched in the years to come.

R-stat