State of the art Common sewing threads are generally made of staple fibres or in the form of sheath/core threads, called corespun threads.

1. Staplefibres 7. l Cotton vs synthetic yarns In the production of the sewing threads spun from staple fibres, cotton was first used, but in the two last decades polyester (PES) and polyamide (PAD) staple fibres have also been frequently applied, mainly due to their essentially higher tenacity, when compared with the relatively low tenacity of cotton sewing threads. The disadvantage of synthetic yams and filaments is that they cannot be dyed in a simple (one stage) process together with the cotton garments after sewing, as in the case of cotton threads.

1. 2 Cotton and lyocell blends Therefore, in recent years, sewing threads composed of a blend of cotton and lyocell staple yams have appeared on the market. Lyocell fibres present a new kind of cellulosic fibres, in their chemical composition similar to viscose fibres, but their production cycle is based on a special organic solvent (NMMO amin oxid) which is recovered within the actual cycle. Lyocell textile linear products can be also manufactured in the form of continuous filaments.

The technology of lyocell filament production is described, for example, in US patent No. 6013367 Cellulose multifilament yarn and woven fabrics produced therefrom. Thus, lyocell filaments and fibres, the latter known also as Tencel fibres (brand name for their textile version), present an ecological advantage, due to big water savings during their manufacturing and due to their production from renewable natural material (wood pulp).

The aforementioned sewing threads spun from this blend of cotton and lyocell fibres exhibit the advantage of the possibility of their simultaneous and single phase dyeing with the sewn garment, but their tenacity, dimensional stability and abrasion resistance are still low and therefore such sewing thread is still not suitable enough for sewing heavy garments such as denims. The US patent No. 6136432 Sewing thread, articles sewn therewith, and dyeing of such articles claims a sewing thread consisting of lyocell (staple) fibres and a small proportion (between 5% and 30% in weight) of synthetic fibres (to increase the tenacity and abrasion resistance of this complex thread) which can be dyed together in a simple process, provided that the portion of synthetic fibres is low.

2. Corespun sewing threads The sewing of heavy cotton fabric requires the use of corespun sewing threads, which, like any other sewing threads, are composed of at least 2 individual yarns, twisted together in opposite directions, in order to balance the resulting torque.

These individual yams in turn consist of continuous filaments, mainly PES filaments located in the central part (core) of the yarn, which is wrapped with short fibre (staple) yarns. These wrap fibres are prepared by drawing them out of the"rowings"on the drawing frame. The corespun filaments thus ensure the tenacity and dimensional stability of the sewing thread, whereas the wrap fibres protect the synthetic core filaments from overheating caused by friction which is generated in the needle eye when the sewing process runs at high speed.

2. 1 PES vs cotton wrap When the wrap consisting of PES staple fibres is applied, the process for dyeing the PES/PES corespun sewing thread comprises a single phase (not at the same time as the garment, since 100% PES garments are rare).

However, corespun PES/PES threads should be available in many colours and shades, which is costly and which takes time, so that the"just in time"delivery principle cannot be easily applied. Moreover, 100% PES corespun sewing threads are unpopular in many countries (such as the USA) due to their shiny (synthetic) appearance.

In case of dyeing of the corespun sewing threads containing the cotton wrap the even more costly double-stage dyeing process is necessary. In spite of their price, these cotton-like corespun sewing threads containing the PES core filaments (which should be dyed on the same colour as the wrap, since the degree of wrapping is never 100%), are very demanded at the market, due to their natural appearance.

2.2 PES vs Viscose core To avoid the necessity of double-stage dyeing, the natural solution could depend on the application of continuous viscose filaments instead of continuous PES filaments. Unfortunately, the tenacity, mechanical stability and resistance of viscose filaments are quite poor, hence the use of these corespun yams would not bring any advantage.

3. Simple continuous filaments (PES, Viscose or Lyocell) Sometimes simple continuous filaments (textured, interlaced or thermally treated) are also used as sewing threads. Nevertheless, the use of single PES filaments is limited by their overheating in the sewing needles. A special solution for this problem is covered by the US patent NO. 4523426 High temperature resistant sewing thread composed of the blend of smooth textured synthetic filaments. The reduction of the friction heat, according to this patent, is achieved by the special combination of thin and bulky areas along the thread.

The viscose filaments, as already mentioned, exhibit very low abrasion resistance, and the application of simple lyocell filaments, which are still not commonly available on the market, is avoided due to the"surface fibrillation" effect. Under pressure and friction, the lyocell fibres or filaments separate into ultrafine fibres, which causes extreme friction of these fibres or filaments during their passage through small openings. That is why, in spite of their excellent mechanical properties, lyocell fibres have not been as widely applied in textile technologies as expected.

Summary of the advantages of this new sewing thread The disadvantages of common corespun sewing threads (namely, the need to keep a large amount of different coloured threads in stock, the danger of their overheating in the needle during high speed sewing, the impossibility of maintaining their natural appearance over their whole surface, the impossibility of their natural decomposition when dumped) are missing or reduced with the new corespun sewing thread, composed of at least two individual sheath/core yarns, comprising a continuous filament core and a cotton wrap, consisting of at least 50% in weight of the lyocell core and of at least 15% in weight of the cotton or viscose fibre wrap, in terms of the total sewing thread weight. The patent claims allow also the use of small proportion of synthetic filaments in the yarn cores, in order to increase the abrasion resistance of the resulting sewing thread.

This small content of synthetic filaments still should allow the single dyeing of the sewing thread.

The field of applications is similar to the applications of common PES/PES corespun sewing threads or cotton/PES sewing threads: sewing of medium and heavy 100% raw cotton garments, mainly based on denim (jeans) fabrics, velvet fabrics, fustian fabrics, flannel fabrics, cotton jackets, cotton protective clothing, etc. , mainly garments which will be sewn with a new thread in raw colour, and the whole garment will then be dyed in a single process.

The new sewing thread exhibits the following advantages: 1. The new corespun sewing thread is suitable to satisfy current market demands, i. e. "just in time"delivery of products. Because lyocell, cotton and viscose fibres are of cellulosic origin, they can be dyed either as a thread only, or together with the sewn product, within a single dyeing procedure (preferably by direct dyestuffs), which results in big economic savings. This will reduce the stock of threads, originally dyed in up to 300 colours and shades, thus bringing about big economic effects. The possible use of small proportions of synthetic continuous filaments in the yarn core of different dyeability should not cause problems in respect of the colour and shade of the final sewing thread.

2. Tenacity, elasticity and dimensional stability are equal to or better than the parameters characterising PES/cotton corespun sewing threads.

3. An ecological sewing thread made mainly of renewable natural resources, which will automatically decompose when dumped. The waste thread can be also burned without (or with reduced) generation of toxic gases.

4. A sewing thread, highly resistant against increased temperatures caused by friction generated during the sewing process, capable of keeping up with technological developments in modern sewing machines, unlike common cotton/PES corespun sewing threads.

5. A sewing thread characterized by stable cotton or viscose wrap coating due the high surface friction typical for lyocell filaments and fibres. Thanks to this friction, the cellulosic wrap should exhibit excellent adhesion to the lyocell surface.

The sewing thread of the invention is a sewing thread composed of at least two corespun yams comprising a continuous filament core and a cellulosic fibre wrap, consisting of at least 50% in weight of lyocell filaments, located in the individual yarn cores, and at least 15% in weight of the cellulosic fibre wrap, all the proportions being considered in terms of the total thread weight.

The cellulosic fibre wrap is made of cotton or viscose using a small proportion of filaments of viscose or other filaments (even synthetic ones) located together with the lyocell filaments in the individual yams cores.

Example An example of the cross-section of this new corespun thread is shown in Fig. 1, where the whole sewing thread (1) consists of 3 individual yams (2), each of which consists of continuous core filaments (3) and a wrap (4). It can be mentioned, as an example of the production technology of this sewing thread, that the core filament has a fineness of 132 dtex, the fibres of the cotton wrap exhibit a fineness of 65 dtex, the twist of the individual yams being 790 v/m and the twist of the total sewing thread being 810 v/m.

To make the whole sewing thread more compact, a special kind of thermal and/or chemical treatment can be applied. This treatment is the result of special know-how.