GB1602198A - Electrically conductive non-woven fabric - Google Patents

Description

(54) ELECTRICALLY CONDUCTIVE NON-WOVEN FABRIC (71) We, WEBRON PRODUCTS LIM1TED, a British Company of Bacup Road, Rawtenstall, Rossendale, Lancashire BB4 7JL do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to electrically conductive material and more particularly electrically conductive non-woven fabric.

The production of so called antistatic fabrics is already well known. Antistatic in this context is intended to mean that the fabric will not allow the build-up of an electrostatic charge to cause electrical discharge when the potential is sufficient to bridge an air gap between the fabric and earth. An antistatic material continuously leaks any charge to an earthing point and thus prevents any excessive build-up. Such antistatic materials may be woven or nonwoven for example needlefelts.

A woven antistatic fabric includes yarns which are electrically conductive. The conductive yarns may consist of 100% conductive fibres such as stainless steels or a proportion of such fibres. Moreover conductive yarns may be employed as warp and/or weft yarns.

In electrically conductive non-woven fabric the conventional practice is to mix conductive fibres into the fibres or fibre blend from which a felt is to be made so tha the conductive fibres being distributed substantially uniformly through the resultant fabric in all directions.

Although such a known fabric can dissipate a static charge of several thousand volts its surface resistivity which is generally of the order of 104 ohms/sq to 107 ohms/sq but is insufficient to conduct a low voltage current through the material. It has been found that a needlefelt capable of conducting a low voltage current through its thickness and along its surface must have conductive fibres present in an amount such as to produce a surface resistivity of less than 104 ohms/sq and preferably less than 103 ohms/sq. By low voltage current is meant the current that will flow when a low voltage, say 10 volts, is applied across the surface or thickness of the material for example if a potential of 5 volts is applied across the surface of material having a surface resistivity of 103 ohms/sq then the current will be 5 mili amps.

If, however, the proportion of conductive fibres in the needlefelt is increased to give the desired resistivity then the fabric becomes uncommercial to produce because the minimum proportion of such fibres is about 25% by weight.

The present invention has been made from a consideration of this problem.

According to the present invention there is provided an electrically conductive non-woven fabric comprising a felt having a layer of electrically conductive fibres on one side thereof and needled to the felt so that at least some of said electrically conductive fibres are present at the surface on the other side of said felt.

In accordance with the present invention therefore no attempt is made to produce a fabric with conductive fibres distributed uniformly throughout. Instead the electrical conductivity of the fabric is assured by virtue of the layer of conductive fibres. Contact with the layer is achieved by the needling as aforesaid which also has the effect of linking the felt to the layer of conductive fibres.

In one embodiment of the invention the layer of conductive fibres is applied to one side of a felt and needling effected using barbed needles to push the conductive fibres through the felt to the exposed surface thereof. If desired, however, the conductive layer may be disposed between two felt layers in which case needling is carried out from both sides of the composite structure to push conductive fibres to both surfaces thereof.

If the needling as aforesaid is not sufficient to hold the fabric together it is possible to employ a binder fibre.

The fabric construction depends on the end use to which it is to be put; if both surfaces of the conductive fabric have to have some abrasion resistance the conductive fibre layer must normally be in the thickness of the fabric; if only one surface or neither surface requires to have any abrasion resistance, the conductive fibre layer can be on one surface of the felt.

Other parameters affecting the conductivity of the finished fabric are the number of conductive fibres present per unit area as well as the overall weight of conductive fibres: the needle density imparted to the fabric which determines the number of fibre tufts pushed to the surface the the needle penetration depth when pushing the fibre tufts to the surface of the felt.

Other factors influencing the surface conductivity are the staple length of the conductive fibres and the type of fibre admixed to the conductive fibre to act as either a carrier or binder fibre.

To assist in appreciating how the foregoing parameters affect the fabric, a brief description of the method of manufacture will be given. It is assumed that the basic felt which does not contain conductive fibres has been made and is either in two layers (for combining to either side of the conductive layer) or one layer. The conductive fibre can then either be blended with a carrier fibre or a binder fibre and fed into the carding machine or can be fed independently into the carding machine. The conductive fibres or blend is carded preferably on a small worker and clearer roll card to prevent fibre damage and staple length reduction and fed onto one of the felt surfaces.The fabric with the conductive fibre layer added then either has the second layer of felt added before passing to the needleloom or passes direct to the needleloom where the composite material receives its needling to produce the fibre tufts.

The needleloom and carding machine used are of the conventional types well known in the art of producing needlefelts.

The combining of the two layers is sometimes satisfactorily achieved by the needling from both sides of the fabric but more usually requires the assistance of the binder fibre. This binder fibre is usually one which has a lower melting point than the fibres of the main body of fabric, for example Grilon K115 (Trademark of Grilon S.A.) copolyamide fibre. The carrier fibre is used when a low area weight of conductive fibre is satisfactory and the number of fibres is insufficient to produce a carded web of sufficient regularity for laying onto the fabric. The carrier fibre used will generally be a fibre of the type used in the main body of the fabric or will be a binder fibre to improve adhesion of the conductive fibre layer to one surface of the fabric.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which; Figure 1 is a section through one form of conductive fabric; Figure 2 is a section through another embodiment of a conductive fabric; and Figures 3 to 5 are graphs.

Referring to Figure 1 the fabric comprises a felt layer 10 which does not contain conductive fibres. A layer 12 of conductive fibres is laid on the felt layer 10 and needled so that conductive fibres are pushed through the felt layer 10 to the surface thereof as referenced 14.

In the embodiment of Figure 2 the layer 12 of conductive fibres is covered by a further felt layer 16. The structure is needled from both sides so that conductive fibres extend to the surface of layer 16 as referenced 18.

The following Examples further illustrate the invention: In the Examples the basic felt used was a 15 oz/sq.yd tennis ball felt consisting of wool and nylon fibres and the conductive fibre layer consisted of Bekinox* stainless steel fibre.

(* Registered trademark of N.V. Bekaert SA).

EXAMPLE I Using 12 micron diameter stainless steel fibre (Bekinox), various area weight of fibre were needled onto the surface of the felt using a needle density of 1,000 needles per sq. inch and a needle penetration of 12 mm (approx. 6 barb).

The surface resistivity was measured on the opposite side of the felt to the conductive fibre layer: five felts were tested at 25 gum2~, 50 glum2,75 g/m2, 100 g/m2 and 125 g/m conductive fibre addition.

Figure 3 shows the increase in conductivity (reciprocal of resistivity) with increase in area weight of conductive fibre layer.

EXAMPLE 2 Using an area weight of 50 gIns2 stainless steel fibre, 8, 12 and 22 micron fibre webs were needled onto the surface of the felt using a needle density of 500 needles per sq. inch and a penetration of 12 mm. The 8 micron fibre web has approximately twice the number of fibres per unit area as the 12 micron fibre web and approximately eight times the number of fibres as the 22 micron fibre web. As would be expected the greater the number of fibres, the lower the surface resistivity.

Figure 4 illustrates the increase in resistivity with decrease in number of fibres per unit area.

EXAMPLE 3 Using an area weight of 50 gIns2 stainless steel Bekinox fibre web of 12 microns diameter added to the basic felt the surface resistivity ws measured as the needle density was increased i.e. as the number of fibre tufts increased.

Figure 5 illustrates the decrease in surface resistivity as the needle density increases. The surface resistivity increases beyond a certain level of needle density because the needling action tends to shorten the staple length of the conductive fibres and thereby reduces the con ductive path length and points of contact between conductive fibres.

The electrically conductive fabric of the invention can be used in many different circum stances. One use for the invention is as a cover for tennis balls. For that particular application a non-woven fabric having the conductive fibre layer on one surface of the felt is used. The tennis ball surface is the opposite face to that of the conductive fibre layer and the conductive fibre tufts pushed through enable the ball to conduct electricity. In this particular application the fabric is coated with pressure sensitive neoprane rubber to enable it to adhere permanently to the core of the tennis ball. To aid this adhesion it has been found an improvement to blend wool or nylon fibre with the stainless steel conductive fibre prior to carding.

WHAT WE CLAIM IS: 1. An electrically conductive non-woven fabric comprising a felt having a layer of electrically conductive fibres on one side thereof and needled to the felt so that at least some of said electrically conductive fibres are present at the surface on the other side of said felt.

2. An electrically conductive non-woven fabric as claimed in Claim 1, wherein the layer of conductive fibres is sandwiched between said felt and a further layer of felt.

3. An electrically conductive non-woven fabric as claimed in Claim 2, wherein the layer of conductive fibres is needled to said other layer of felt so that at least some of said conductive fibres are present at the surface of said other felt layer.

4. An electrically conductive non-woven fabric as claimed in any preceding claim, wherein the conductive fibres are blended with a carrier fibre.

5. An electrically conductive non-woven fabric substantially as described herein with reference to Figure 2 of the accompanying drawing.

6. A tennis ball covered with non-woven fabric as claimed in any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. a non-woven fabric having the conductive fibre layer on one surface of the felt is used. The tennis ball surface is the opposite face to that of the conductive fibre layer and the conductive fibre tufts pushed through enable the ball to conduct electricity. In this particular application the fabric is coated with pressure sensitive neoprane rubber to enable it to adhere permanently to the core of the tennis ball. To aid this adhesion it has been found an improvement to blend wool or nylon fibre with the stainless steel conductive fibre prior to carding. WHAT WE CLAIM IS:

1. An electrically conductive non-woven fabric comprising a felt having a layer of electrically conductive fibres on one side thereof and needled to the felt so that at least some of said electrically conductive fibres are present at the surface on the other side of said felt.

2. An electrically conductive non-woven fabric as claimed in Claim 1, wherein the layer of conductive fibres is sandwiched between said felt and a further layer of felt.

3. An electrically conductive non-woven fabric as claimed in Claim 2, wherein the layer of conductive fibres is needled to said other layer of felt so that at least some of said conductive fibres are present at the surface of said other felt layer.

4. An electrically conductive non-woven fabric as claimed in any preceding claim, wherein the conductive fibres are blended with a carrier fibre.

5. An electrically conductive non-woven fabric substantially as described herein with reference to Figure 2 of the accompanying drawing.

6. A tennis ball covered with non-woven fabric as claimed in any preceding claim.