DESCRIPTION

FIELD OF APPLICATION

The present invention relates to an electrically conductive yarn for producing protective garments.

Description of the prior art

Electrically conductive garments are commonly used as electrical protections during potential working at medium, high or very high voltage. The conductivity of the garment makes it functionally comparable to a Faraday cage that protects the operator wearing it.

It is known that technical difficulties are encountered when producing conductive garments intended to preserve their conductive properties even after washing, during which the yarn may be submitted to such mechanical, chemical and thermal stresses as to oxidise the metal materials which provide the conductive properties.

WO 2008114296 discloses an electrically conductive knitting yarn used in garments for working under electric potential. The yarn disclosed is composed of conductive strands, e.g. made of silver-coated nylon, and fire-resistant strands, such as meta polyaramide. Nylon in turn requires fireproof treatment.

The yarn of WO 2008114296 already offers good electrical properties, ensuring the conductivity required by the reference standards (e.g. IEC 60895), even after washing.

US 2020032430 discloses an electrically conductive yarn that includes, at least, a core strand, a first wrapped strand that wraps around the core strand, and a second strand that wraps with, or around, the assembly of the core strand and first wrapped strand. The first wrapped strand in some embodiments is a silver-coated copper strand. Such a yarn may be woven in a loom to produce fabrics which have, in the embodiments mentioned, a grammage ranging from 250 to 315 g/m ² . Such a fabric may have a resistance of less than 0.7 /m after ten washes.

Problem of the prior art

The yarn of WO 2008114296, when knitted, results in the production of heavy garments, due to both the high silver content, around 30% by weight in the final product, and the thickness of the yarn.

The Applicant found that in particularly hot climatic zones, operators hardly bear the weight of garments made according to WO 2008114296. They sometimes prefer to use lighter conductive garments, although they are aware that they have lower electrical performance, and that in some cases they do not provide the level of protection required by the standards, especially after washing. Thus, they expose their health to considerable risk.

The Applicant has tried to make the yarn of WO 2008114296 thinner in order to obtain lighter garments. However, in the conductive strands of WO 2008114296 it is not possible to remove nylon or another similar material as a core to support the silver. Therefore, making the yarn thinner means having to reduce the silver content and the final garment loses its advantageous electrical properties (either upon manufacturing or only after washing).

SUMMARY OF THE INVENTION

In this context, the technical task underlying the present invention is to provide an electrically conductive yarn which overcomes the drawbacks of the prior art described above.

In particular, it is the object of the present invention to make available an electrically conductive yarn that makes it possible to produce effective, yet lightweight, protective garments.

The defined technical task and the specified objects are substantially achieved by an electrically conductive yarn, and furthermore by fabrics, sewing threads, garments, and in particular a suit, made from such a yarn, according to the technical characteristics set forth in one or more of the accompanying claims.

A conductive strand of the yarn is made with a core made of a first metal and a coating made of a second different, preferably noble, metal. The combination of two metals makes it possible to preserve the inner metal from oxidation. Furthermore, as the core of the strand is conductive, unlike WO 2008114296 the electrical properties are maintained even when the strand becomes thin enough to manufacture light garments.

The first conductive strand is twisted with a second strand that is fireproof, which is preferably provided with conductive properties too, as it is made, for example, of aramid and steel.

The yarn of the invention has been found to have electrical properties even higher than WO 2008114296. In addition, the thinness of the first strand allows the yarn to be woven in a loom, and thus makes it possible to produce suits that are bearable even in the hottest countries.

Surprisingly, the electrical properties are also far greater than the fabric of US 2020032430. In fact, the Applicant was able to produce fabrics according to the invention with a resistance of less than 30 m /m.

DETAILED DESCRIPTION

One aspect of the invention relates to an electrically conductive yarn. Such a yarn is suitable for the production of fabrics, e.g. loom-woven or knitted fabrics, as well as sewing threads intended to be used in protective garments for potential working at medium, high or very high voltage.

The yarn comprises a first strand and a different second strand, coupled and twisted together. Preferably, the yarn consists in the assembly of the first and second strands twinned and twisted together. In particular, no further strand is wrapped or twisted with the assembly of the first and second yarn. Thus, an external side surface of the yarn is identified exclusively by exposed portions of the first and second strand.

In the preferred embodiment, the coupling of the two strands together is carried out with a number of turns equal to 280 per metre, with a tolerance of less than 10.

The first strand is electrically conductive. According to one aspect of the invention, the first strand comprises a core made of a first metal and a coating made of a different second metal.

The first and second metals are preferably selected from metals with a high electrical conductivity. In addition, the second metal preferably has a higher standard electrode potential than the first metal, and more preferably the second metal is selected from among the noble metals. In the preferred embodiment, the second metal is silver, while the first metal may be, for example, copper or aluminium.

The coating of the second metal thereby protects the first metal from oxidation and preserves the conductive properties thereof even after washing. Furthermore, the core of the first metal acts as a mechanical support for the second metal, as is generally required when a second metal such as silver is used in strands for textile use. The first metal may then cost less than the second metal.

In the preferred embodiment, a weight ratio between the second metal and the first metal of the first strand is between 2: 100 and 10:100, e.g. equal to 5:100.

An embodiment of a first strand has a thickness of between 20 and 60 pm, in particular 40 pm.

The second strand comprises fire-resistant synthetic fibres. The preferred synthetic fibres are aramid, in particular meta-aramid, fibres. In addition to fire resistance, the second strand performs structural functions to provide mechanical strength to the yarn, having a higher mechanical strength than the first strand.

Preferably, the second strand also has electrical conduction properties. More in detail, the second strand comprises metal, electrically conductive fibres in an intimate blend with the synthetic fibres. Among the metal fibres of the second strand, fibres made of a steel alloy are preferred.

In the preferred embodiment, the second strand comprises aramid ranging from 30 to 80% by weight, preferably from 50 to 70%, more preferably 60%. Steel, on the other hand, is expected to be 20-70% by weight, preferably 30-50%, more preferably 40%.

As known, a strand of aramid and steel in intimate blend may be obtained by dispersing steel particles in aramid fluffs, and then processing the aramid fluffs into strand form.

The count of the second strand may be between 40 and 60 Nm, preferably equal to 50 Nm. The thinness of the second strand, as well as the first strand, helps making the garments obtained from the yarn lighter.

Following the coupling by twisting of the first and second strands, the yarn has a count between 20000 and 40000 Nk, preferably equal to 28000 Nk.

Advantageously, the yarn hitherto described is suitable for producing loom-woven fabrics, knitted fabrics and sewing strands, which are also object of the present invention, as well as garments incorporating said fabrics.

As known, loom-woven fabrics are lighter than knitted fabrics, and are therefore particularly suitable for the purposes of the invention for producing garments such as lightweight protective suits that are effective in electrical protection.

Knitted fabrics are more suitable for other types of garments, as they are known to stay very flexible and elastic even within the fabric working plane. Vice versa, loom-woven fabrics have a relatively rigid weave that maintains the orientation of the various yarn portions. Knitted fabrics are therefore preferable for gloves, socks or protective facial garments.

As known, every fabric has a fabric structure consisting of one or more structure yarns, wherein each structure yarn identifies a respective laying path. For example, in a loom- woven fabric, there may be two structure yarns, i.e. one warp and one weft yarn, which are laid along distinct paths and intertwined with each other. In a knitted fabric, there may be a single structure yarn, which is laid along a path that intertwines with itself to form elementary knitted portions.

Fabrics wherein at least one of the structure yarns, preferably each one of them, consists exclusively of one of the conductive yarns hitherto described, or of several specimens of the conductive yarns described, preferably identical, twisted together, are of particular interest for the invention. Here it is understood that each structure yarn identifies alone the respective laying path. This is meant to exclude that several structure yarns are arranged together along the same laying path, for example by being twisted together, or wrapped one on the other. In such a case, the structure yarn should be considered as the assembly of all the yarns thus twisted or wrapped.

EXAMPLE 1: YARN

As a first strand, a strand with a copper core and silver coating is selected, at a ratio of 50 g of silver per kilogram of copper. The diameter of the first strand is 0.04 mm.

As a second strand, a strand made of meta-aramid (60%) and steel (40%) in intimate blend, with a count of 50 Nm, is selected.

The two yarns are twinned and twisted together to obtain a yarn with a count of 28000 Nk.

EXAMPLE 2: LOOM WOVEN FABRIC

A plurality of yarns according to Example 1 are used as weft and warp in a loom weaving, resulting in a fabric with a predetermined weave. The preferred weave is a plain weave, i.e. alternating a (single) weft strand with a (single) warp strand. However, other weaves, such as a twill weave, alternating two weft strands and two warp strands, are permissible.

Subsequent analysis of the fabric has led to reveal as a composition, in terms of fibre number, 79.6% aramid and 20.4% metal fibres (thus including steel, copper and silver). The measuring method is microscope counting of the types of fibres in a sample of 1000 fibres.

The fabric has a mass per unit area of between 100 and 300 g/m ² , in particular 210 g/m ² .

The fabric is treated so as to have a stain-resistant coating.

Resistance measurements complying with the standards, carried out by applying electrodes spaced apart from each other along weft, warp directions and directions oblique thereto, gave results between 23 and 27 mQ/m.

EXAMPLE 3: KNITTED FABRIC

A plurality of yarns according to Example 1, in particular four yarns, are coupled and twisted to obtain a thicker yarn, also referred to as a superior yarn, suitable for knitting. The superior yarn is thus knitted to obtain a knitted fabric.

Subsequent analysis of the fabric has led to reveal as a composition, in terms of fibre number, 69.1% aramid and 30.9% metal fibres (thus including steel, copper and silver). The measuring method is microscope counting of the types of fibres in a sample of 1000 fibres.

The percentages obtained with these measurements differ from Example 2, because each type of yarn weaving may alter the size and thus the number of individual fibres.

The fabric has a mass per unit area of between 600 and 1000 g/m ² , in particular 781 g/m ² .

The fabric is treated so as to have a stain-resistant coating.

EXAMPLE 4: SEWING THREAD

A plurality of yarns according to Example 1 , in particular three yarns, are coupled and twisted to obtain a sewing thread.

The sewing thread has a count between 20 and 40 Nm, preferably equal to 30 Nm.

The sewing thread is treated so as to have a paraffin coating.