Yarns, high wear resistance fabrics and objects made therefrom

This invention relates to yarns and fabrics containing nylon staple fibre and high-tenacity man-made cellulosic staple fibre, and objects like garments, beddings or upholstery made therefrom, and has particular reference to fabrics having a high resistance to wear whilst retaining a high comfort level.

Certain forms of workwear, including that for use in conditions of high abrasion, have been found to wear very quickly. This is particularly true for workwear intended for use in sandy conditions. It is known that cellulosic fibres such as cotton, viscose rayon or Lyocell can be made into garments which have a high level of comfort. This is because the garments absorb moisture and have a cool comfortable touch. However cellulosic pure garments do not have a very high level of abrasion resistance.

Abrasion resistance in fabrics and garments is measured by the Martindale test and in this patent application always the number of rubs until 2 threads break is given. This is a standard fabric test details of which are set out in ASTM D4966-98 and in ISO 12947.

50%/50% cotton/polyester fabrics have a good comfort level, but have a abrasion resistance of 20,000 to 50,000 rubs, depending for example on the fabric construction, weight, etc.. But even this is insufficient to extremely demanding conditions such as desert. It is also known that the abrasion resistance of cotton containing fabrics can be increased by producing a cotton/nylon fabric. The fabric used by the US Army for desert camouflage uniforms is a 50%/50% cotton/nylon fabric, known as NyCo, with a Martindale resistance of greater than 80,000 rubs.

In addition fabrics need to have adequate tear strength. Tear strength is the force required to start or continue a tear in a fabric under specified conditions. The details of the tear strength test are set out in ASTM D-2261, ASTM D-2262 and BS EN ISO 13937.

The specification is set by the required performance. For example for a 2x1 twill polyester/cotton battledress according to U.K. specifications a tear strength of 28 N in the warp and 20 N in the weft is required. The so called ripstop fabrics can have different requirements, e. g. 25 N warp and 60 N weft.

Lyocell is the generic name for a man-made cellulosic fibre produced without the formation of a derivative from a solution of cellulose in an aqueous organic compound, normally N-methylmorpholine-N-oxide (NMMO). Lyocell has a much higher tenacity than regular viscose. While Lyocell in the conditioned state normally shows a tenacity at break of about 37 cN/tex, regular viscose under the same conditions shows a tenacity at break lower than 25, but strongly depending on the individual production process.

Nylon-6.6, for comparison, has a break tenacity of about 56 cN/tex and cotton of about 25cN/tex.

In addition to the cotton and nylon fabrics used by the US Army, certain nylon/Lyocell fabrics have been produced on an experimental basis. These nylon/Lyocell fabrics have been produced by weaving a Lyocell weft into a continuous filament nylon warp. Although Lyocell is produced as a staple fibre, and spun into yarns to enable it to be woven or knitted to form garments, this is not the case for nylon. Much nylon is made as continuous filament material which is made up into warps. A warp is effectively a set of threads which are wound

round a cylinder and placed on a loom before weaving begins. The weft thread is passed backwards and forwards though the warp often using a shuttle. Warps require to be made up before weaving can begin and warps of continuous nylon filaments were available. The experimental fabrics were made by weaving a Lyocell tread as a weft through the continuous filament nylon warps. Such fabrics have not been commercially used on any scale and were made purely as an experiment. Nylon staple fibres, i. e. fibres cut to a definite length after extrusion and spun to yarns, were never used for this application.

Another man-made cellulosic fibre besides Lyocell is Modal, which is produced by a modified viscose process. Modal is a high-tenacity man-made cellulosic fibre, too, as it shows a tenacity at break of about 35 cN/tex in the conditioned state. According to the definition of the BISFA Modal fibres are cellulose fibres having a high breaking force and a high wet modulus. The breaking force (B _c ) of a Modal fibre in the conditioned state is B _c (cN) > 1 ,3λ/T+2T. The force (B _m ) required to produce an elongation of 5 % in the wet state of a Modal fibre is B _m (cN) ≥ 0,5*VT. T is the mean linear density in decitex

Mixtures of Lyocell and Modal are also known in the market, but up to now they are not sold in bigger amounts.

It is an object of the present invention to provide a fabric which has a good balance between comfort for the wearer of garments made from the fabric and a good abrasion and tear resistance. Obtaining a good level of either comfort or wear and tear resistance is something which is easily done. It is however much more difficult to obtain both in a fabric, as the fabric properties required for good comfort and the fabric properties required for good wear and tear resistance are often mutually exclusive.

It is a further preferred object to produce a fabric which can be uniformly dyed, particularly with the dyes commonly used in dyeing military uniforms where such dyes have infra red (IR) reflectance characteristics which can be tailored to the nature of the camouflage applied to the uniform.

Known FR finishes usually significantly reduce the mechanical properties of fabrics containing cellulosic fibres. It is therefore still a further preferred object to produce a fabric which can be treated with a flame retarding (TR") finish, e. g. Proban®, without losing too much strength and abrasion resistance.

A further object of the invention is to provide a yarn which can be used to produce a fabric with the above mentioned properties.

By the present invention there is provided a yarn formed of an intimate blend of nylon staple fibre and high-tenacity man-made cellulosic staple fibre and a fabric containing said yarn. Preferably the high-tenacity man-made cellulosic staple fibre shows a tenacity at break in conditioned state of more than 32 cN/tex.

The yarn may contain 10 to 75% nylon and the fabric may contain from 10% to 50% nylon. Preferably the balance in each case is high-tenacity man- made cellulosic fibre but in any event the fabric made from the yarn must contain at least 50% high-tenacity man-made cellulosic fibre.

The term nylon as used herein refers to the group of plastics known as polyamides. Nylons are typified by amide groups (CONH) and encompass a range of material types e.g. Nylon 4,6; Nylon 6; Nylon 6,6; Nylon 12 ;Nylon 6,12. All are suitable but nylon 6 and nylon 6,6 are preferred.

Further preferably the nylon and high-tenacity man-made cellulosic fibres are both of the same or closely similar mean linear density ("titre") in decitex (dtex). For example a 1.7 dtex or 1.4 dtex Lyocell fibre can be blended with a 1.7 or 2.0 dtex nylon fibre. In general similar mean linear densities mean a difference of not more than 50% between the two fibres.

The staple fibre length of the nylon and the high-tenacity man-made cellulosic fibres is also the same or very similar. For example a 38 mm staple Lyocell fibres can be blended with 35 to 40 mm nylon staple fibres, more preferably with 38mm nylon staple fibres. In general similar fibre lengths mean a difference of not more than 15% in length between the two fibres.

The high-tenacity man-made cellulosic fibre preferably is a Lyocell staple fibre, a Modal staple fibre or a mixture thereof.

Lyocell as well as Modal have a higher break tenacity than other cellulosics including cotton. They also have a high wet strength. Therefore a significant effect on the tear resistance of the fabric can be expected. But as nylon has a still higher break tenacity the artisan would expect that the tear resistance of a fibric containing both nylon and a high-tenacity man-made cellulosic fibre will decrease if the amount of nylon decreases. Therefore the artisan would incorporate only as much cellulosic fibre as is needed to create enough comfort to the wearer.

But surprisingly it has been found that by the incorporation of increasing amounts of high-tenacity man-made cellulosic fibres the tear resistance of the resulting fabric increases. Thus a fabric formed of yarns blended from high- tenacity man-made cellulosic staple fibre and nylon staple fibre have a high

tensile strength and gain strength form both the nylon fibres and the high-tenacity man-made cellulosic fibres.

Additionally it has been found that to get the benefit of this both staple nylon and staple high-tenacity man-made cellulosic fibre must be used to make up the yarn.

When high-tenacity man-made cellulosic fibre is blended with nylon there is no advantage to go over 20% nylon. Abrasion resistance, tensile strength and tear strength have all very nearly reached a level suitable for high-performance applications.

The high-tenacity man-made cellulosic fibre can be a dull fibre, that is to say man-made cellulosic containing a matting agent, for example TiO ₂ . This may give certain advantages like enhanced sun protection for the use in desert areas.

The high-tenacity man-made cellulosic fibre may be a bright fibre, that is to say a high-tenacity man-made cellulosic fibre not containing a matting agent.

By the present invention there is also provided a fabric which contains a yarn as described above.

Furthermore by the present invention there is also provided a fabric which contains a yarn formed of an intimate blend of nylon staple fibre and high-tenacity man-made cellulosic staple fibre. The fabric according to the invention may contain from 10% to 50% nylon. Preferably said fabric is a woven fabric and contains said yarn in both the warp and the weft.

The fabric may have a basis weight in the region of 100 to 500 g/m ² preferably 120 to 300 g/m ² , further preferably 180 to 250 g/m ² .

The fabric may be a twill fabric and may be a 2x1 twill. It could also be of another construction, e. g. plain.

Preferably the fabric has a Martindale abrasion resistance of at least 60,000 rubs, preferably at least 100,000 rubs, and a tear resistance of at least 20 newtons, preferably at least 30 newtons.

As the fabrics according to the invention are mainly used for military applications and workwear, they may be treated by several finishes, like print dyes, FR finishes or IR reflectance finishes. According to general experience those finishes may affect the original properties of the fibres or yarns. But for example if a Proban® FR finish is applied on top of the fabric according to the invention, the strengths are pretty much maintained. Both tensile and tear strength drop by about 10-15% but abrasion remains above 100,000.

The Proban® process is based on the application of THPC (Tetra- kishydroxymethylphosphonium chloride) with urea to generate a pre-condensate. This pre-condensate is padded onto the fabric and the fabric dried to ~15% moisture content. The fabric is then exposed to ammonia vapours in a special reaction chamber, followed by oxidation with hydrogen peroxide. This process is well known to the expert. Chemicals and instructions are available from Rhodia.

A similar suitable FR finish is the Pyrovatex® finish, which is also known to be applicable to cellulosic fibres such as Modal or Lyocell. Pyrovatex® is a durable phosphorus containing finish created by the use of N-methylol dimethylphosphonopropionamide in combination with trimethylolmelamine and

phosphoric acid as catalyst in a pad-dry-cure process. Chemicals and instructions are available from Huntsman.

Due to the intended use the yarns according to the invention may also be used in knits. The resulting knitted fabrics show a very high burst strength combined with superior wear comfort. The abrasion resistance of knitted fabrics shows the same dependence from the mixture ratio cellulosic/nylon than in woven fabrics. Because the construction of a knitted fabric is more open, the abrasion resistance as can be measured by the Martindale test in general is lower compared to woven fabrics. Nevertheless for many applications a knitted construction is needed, especially when the demand for wear comfort and elasticity is high but has to be combined with certain durability requirements, for example for corporate wear. For those applications an abrasion resistance of at least 25.000 rubs would be sufficient

The fabrics according to the invention can be used for the manufacture of workwear, corporate wear or uniforms. Due to their good abrasion resistance they can also be used for the manufacture of upholstery fabric for furniture, office chairs or seats in transportation vehicles like cars, coaches, trains or planes. On upholstery fabrics according to the invention also FR finishes are applicable. For such purposes also non-durable FR chemicals, which are well-known by the expert, such as a mixture of boric acid and borax or ammonium salts of strong acids, especially phosporic acid, such as diammonium phosphate or ammonium sulfamate or ammonium bromide are applicable. A further field of use for the fabrics according to the invention is the manufacture of beddings for hospital and hotels, especially where industrial laundries are used for the laundering.

One possibility to even increase the positive properties of the products according to the invention is the use of Lyocell fibres with incorporated Chitosan, which is

already known from WO 2004/007818 and Austrian utility model AT 008 388 U2. This will give to the fabrics an anti-bacterial function as well as enhanced skin friendliness.

Also possible is the combination of Chitosan-incorporated Lyocell fibres with finishes as described above, especially with FR finishes like Proban® or Pyrovatex®. It will perform especially in applications where a fabric should have both advantageous properties.

Yet another object of the present invention is a garment, containing a fabric as described above. Such a garment preferably is a workwear, corporate wear or a uniform, but can also be any other type of garment, for which the typical properties of said fabric are advantageous.

Another object of the present invention is upholstery or bedding, containing this fabric as well as a furniture containing said upholstery.

The invention will now be illustrated by examples. These examples are not limiting the scope of the invention in any way.

Examples 1 to 6

Commercially available PA-6.6 staple fibres with a titer of 2.0 dtex and 38 mm cut length were mixed in the ratios described in table 1 with commercially available TENCEL® staple fibres with a titer of 1.4 dtex and 38 mm cut length and spun to a yarn of Nm 1/26 (Ne 1/15).

The yarns were further processed by weaving a 2x1 twill with a weight of 249 g/m ² and 32 ends and 24 picks. The woven fabrics were then singed, desized, scoured, dried, heat set at 205 ⁰ C, printed to meet the IR reflectance

specifications from military and finished with an FC water repellent. These methods are well known to anyone skilled in the art.

The tear strength in the warp as well as in the weft direction was measured and the Martindale test was applied to each so-finished fabric.

Table 1

It can be clearly derived from table 1 that the highest improvement of the mechanical properties of the fabric appears when increasing the Nylon content from zero to 20 %. Then the practically important values are obtained and further increased amounts of Nylon will only result in slight improvements. Martindale tests were stopped for economic reasons when a level of 100.000 rubs was reached.

On the fabrics from examples 1 , 3, 4 and 5 the GATS-test was applied, which gives an impression about the rate at which sweat will move away from the body of the wearer. The graphs are shown in Fig. 1. The trend to point out is that generally the higher the TENCEL content, the faster the uptake of water (slope of

the graph, and the higher the volume that can be held (height of the graph). The speed is the key point.

Example 7 to 9:

2x1 twills were made out of a Ne 1/15 yarn containing a mixture Tencel/PA-6.6

70%/30% (w/w) of fibres according to example 1. Weight and finish varied according to Table 2, but the process steps were the same as in Examples 1 to

6.

In example 8 a conventional Proban® treatment was applied afterwards. In example 9 a different fabric construction was made, but by using the same yarns as in example 7.

Table 2

It can be seen that all three fabrics according to the invention fulfill the U.K. Military specification of 28 cN (warp), 20 cN (weft) and 45.000 Martindale rubs. The fabric of example 8 also passed the flame retardant test of EN 532.

Example 10:

A 2x1 ripstop twill with 30 ends/22 picks and 180 g/ m ² was made from the 70/30 yarn of example 4 but with a 350f/136 nylon filament ripstop thread as every ninth pick. Table 3 shows the comparison with the U.K. military specification for ripstop fabric.

Table 3

Examples 11 to 13: A single jersey was knitted using a ring yarn Nm50/1 containing the same fibres as used in examples 2 to 6 with the various compositions listed in Table 4. The knitted fabrics were dyed with a common reactive dyestuff.

Table 4

Like in the woven fabrics a strong increase in abrasion resistance by adding small amounts of nylon was observed.

Example 14:

A yarn was made as in example 3, but using a 1 ,4 dtex chitosan-containing Lyocell fibre (Tencel C" by Lenzing AG ₁ containing 0,5 % (w/w) Chitosan in the fibre) instead of the regular Tencel fibre. The ratio Tencel C : PA 6.6 was 80%/20% (w/w). This yarn was processed into a 2x1 twill with a weight of 203 g/m ² . The measured properties are listed in table 5.

Example 15:

A yarn was made as in example 3, but using a 1 ,4 dtex Modal fibre produced by Lenzing AG instead of the Tencel fibre. The ratio Modal : PA 6.6 was 80%/20% (w/w). This yarn was processed into a 2x1 twill with a weight of 212 g/m ² . The measured properties are listed in table 5.

Table 5