Abstract:
A method of manufacturing textured thread textured thread comprises the steps of: processing textured yarn having a zero or near-zero twist by applying a singles twist thereto; plying at least two textured yarns together by twisting them in a direction opposing the singles twist; wherein the singles twists lie in the range 4 to 20 turns per inch and the plying twist lies in the range 2 to 18 turns per inch.

Description:
BACKGROUND TO THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to sewing thread and its manufacture and, more particularly, to the manufacture of what is known as “textured thread”. 
         [0003]    2. Description of Related Art 
         [0004]    One of the basic elements of manufacture of sewing thread is what is referred to in the art as “yarn”. A simple yarn is produced by combining single fibres or filaments. One way of combining fibres is by applying a twist to them, known as a singling twist (since there is but a single group of fibres that are being twisted together). The application of a twist to filaments to produce a yarn is not essential, however, and fibres may also be combined without doing so. The characteristics of the fibres which are combined to form the yarn play a significant role in the eventual characteristic of a sewing thread for whose manufacture, ultimately, such yarns are used; as do the characteristics of the yarns themselves. 
         [0005]    Yarns can be manufactured from a variety of fibres, such as staple fibres which are lengths of fibre; and continuous filaments which are typically made of artificial material by processes such as melt-spinning. Threads are created by ‘plying’ together two or more yarns by twisting the yarns around each other. 
         [0006]    One particular kind of thread is known as “textured thread”. This is produced from yarn which has had a ‘texture’ applied to it subsequent to the individual filaments being combined with each other. Texturing can be achieved by, for example, directing an air jet at the yarn shortly after the filaments produced by melt-spinning exit the melt-spinning apparatus (i.e. when it is still soft and susceptible to disruption) or by what is known as “false twisting”. False twisting is a process in which the combined filaments are first twisted and set in that condition by heat (typically steam heat), following which they are then once again untwisted. False twisted yarn has no twist, but a ‘memory’ in the filaments which make up the yarn, introduced by the heating process, nonetheless causes them to behave as if they were twisted. Textured yarn and thread manufactured from textured yarn therefore both have, as a result of this characteristic, a relatively soft ‘handle’ (i.e. feeling to touch) relatively high bulk (i.e. low density) and high elongation (i.e. longitudinal elasticity under tension). Textured thread therefore tends to be of use in certain areas of garments where soft seams are required. It has the advantage of being inexpensive to manufacture primarily because relatively inexpensive raw materials are used. However, its characteristics make it a difficult thread to work with because of its susceptibility to cause sewing faults such as snagging, looping and breaking during sewing operations. Further, it has relatively low strength. Accordingly, textured thread is unsuitable for wider applications, such as apparel stitching (i.e. stitching of panels of fabric to construct garments). 
       SUMMARY OF THE INVENTION 
       [0007]    A first aspect of the present invention lies in an appreciation of the ability to employ textured thread more widely in circumstances where the above-mentioned problems can be overcome. According to a first embodiment of the present invention, textured thread is manufactured by plying yarns having a zero or near-zero twist, the twist imparted to the plied yarns being substantively greater than that previously thought to be acceptable in a textured thread. 
         [0008]    A further aspect of the present invention provides a method of producing a textured thread. Yet a further independent aspect of the present invention provides a method of apparel stitching using textured thread having the characteristics of an embodiment of textured thread according to the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of the present invention will now be described, by of example, and with reference to the accompanying drawings in which: 
           [0010]      FIG. 1  is a schematic illustration of a melt-spinning apparatus for producing continuous filaments and continuous filament yarn; 
           [0011]      FIG. 2  is a detail of  FIG. 1 ; 
           [0012]      FIG. 3  is  FIG. 2  is a schematic illustration of a further step in the manufacturing process of textured filament yarn; 
           [0013]      FIGS. 4A and 4B  are illustrations of thread manufacture from multi-ply yarn; 
           [0014]      FIG. 5  is a flow chart of the steps involved in the manufacture; 
           [0015]      FIG. 6  is a schematic section through a twisting apparatus employed in an embodiment of the present invention; 
           [0016]      FIG. 7  is a table showing characteristic parameters of thread produced according to embodiments of the present invention; and 
           [0017]      FIG. 8  is a table showing parameters of preferred embodiments of method according to the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    Referring now to  FIG. 1 , continuous polyester filaments for the production of yarn are manufactured by means of a melt spinning apparatus  10 . Polymer chips are placed into a hopper  12  from which they descend into a heated cavity  14  where they are melted. Subsequently, a pump  16  forces the molten polymer  18 , under pressure. into a chamber  19  having, in the present example, four spinneret drums  20   a  to  20   d . Referring now additionally to  FIG. 2 , each spinneret drum comprises a plurality of fine apertures  24 , through which the molten polymer is extruded to create filaments  30  from which yarn can be constructed. Where it is desired to manufacture continuous filament yarn, the filaments are  30  combined to create a yarn  32  which is then wound on to a bobbin  40 . The combining can be performed in one of a number of ways. In one example, interfilament adhesion is achieved by bringing the filaments into proximity with each other and then applying an air jet to the filaments to cause intermittent points of the filaments into contact with each other. An alternative is to draw the filaments via a heated godet (a special kind of guiding roller) and, simultaneously, applying a low-level of twist to the filaments using, for example, conventional ring spinning techniques. The combining operation is shown schematically as occurring ‘downstream’ of the extrusion from the spinneret  20 A. Whereas spinneret  20   a  produces continuous filaments, spinnerets  20   b  to  20   d,  in the illustrated example, are adapted for generating staple fibres and so deposit their filaments into cans  42   a  to  42   c  from which the filaments are subsequently processed. 
         [0019]    Referring now to  FIG. 3 , the continuous filament yarn is then unwound from the bobbin  40  and passed through suitably configured guide and pinch rollers  44 ,  46  in order to stretch the yarn, whereupon it is wound, relatively loosely, onto filament bobbin ready for use by a thread manufacturer. 
         [0020]    The continuous filament yarn whose manufacture has thus far been described is also known as a flat filament yarn, mimicking to some degree the characteristics of silk filaments and is entirely conventional. 
         [0021]    Referring now to  FIGS. 4A and 4B , yarn supplied on the cheese can then be spun into a thread suitable for use in sewing in a number of ways. For example, 3 individual yarns may be ‘plied’ together in the manner illustrated in  FIG. 4A  in order to create, in the present example, a 3-ply sewing thread. It will be noted, from  FIG. 4A , that the filaments of the yarn are twisted in an anticlockwise direction (known as Z twist) where as the yarns are twisted together in a clockwise direction (known as S wist) with the level of twist in each component stage being carefully calculated to produce a stable sewing thread in the final composite product. Alternatively, referring now to  FIG. 4B , two yarns may be plied together and then two or more such plied yarns are plied into a corded thread. These are merely two examples offered to provide the reader with an opportunity to assimilate the terminology used at various stages in the manufacturing process, and other combinations and permutation of these manufacturing techniques may be applied to produce different configurations of thread. Thus far, the processes described are entirely conventional processes. 
         [0022]    As mentioned previously, it is known to produce “textured” yarn which, in turn, may then be used to manufacture ‘textured’ sewing thread. One way in which textured yarn is manufactured is by imparting high pressure air to the yarn formed of continuous filaments. The air serves to disrupt the regularity of the yarn before it has entirely cooled, thereby to impart the requisite “texture” to it. Another manner of providing a texture is to impart what is known as a false twist. The continuous filament yarn is first twisted and then is set into that condition by steam heat; thereafter, it is once again untwisted. The result is that the final twist in the yarn is zero but the filaments of the yarn have a memory of their original, twisted configuration (hence the term ‘false’ twist). This false twist causes the individual filaments within the yarn to tend to twist, loop and snarl within its body thereby resulting in a relatively soft and bulky yarn having the requisite textured properties. Referring once again to  FIG. 1 , where textured yarn is produced by the ‘false twisting’ process the filaments  30  will typically (though not necessarily) be initially combined by means of the ring spinning operation. Where textured yarn is produced by applying an air jet then the combining of the filaments  30  may advantageously be achieved by this technique also. 
         [0023]    Traditionally, thread manufactured of textured yarn, although having desirable properties of high bulk and high levels of elongation (that is to say elastic longitudinal expansion under tension) and a soft handle, has proved to be unsuitable for the majority of uses such as apparel sewing (that is to say the joining of fabric panels as part of a manufacture of a garment). Typically, reasons for this include low relative strength of such thread, together with a tendency to cause sewing defects such as breaking during sewing, snagging within the machine, skipping a stitch or the bobbin chase failing to catch the thread properly. 
         [0024]    The inventors of the present invention have observed that the limitations on the use of textured threads arise, inter alia, from the characteristic of limited cohesion between individual filaments of the textured yarn from which the thread is made. Such limited cohesion allows the fibres of the yarn to open up and/or separate from each other during sewing. This, in turn, can result in broken filaments and may even result in total failure of the thread as a whole. The inventors have realised that it is possible to apply twist levels to textured yarn which are greater than those in the prior art and therefore serve to avoid the problems which arise from low fibre cohesion; yet, at the same time, maintain a sufficiently low degree of twist within the yarn to enable yarns to be plied together at a sufficiently low counter-torque (i.e. acting antagonistically to the torque applied by the twist in the individual yarns) that the resultant thread retains the desirable characteristics of textured thread. Further, the inventors have appreciated that, in processing the yarns to make this new textured thread, the tensions which are applied are preferably sufficiently low to avoid elongating the yarns to such an extent that the resultant, plied thread takes on more of the characteristics of traditional, flat filament yarn which lacks the bulk and soft handle of textured thread. This ‘squaring of the circle’, previously considered to be impossible, results in textured thread which is suitable for needle sewing and therefore can be used for apparel stitching, where previously this was not thought to be possible. 
         [0025]    Referring now to  FIG. 5 , an outline of the process by which thread according to embodiments of the present invention is manufactured will now be described. At step  510  the cheese of false-twist textured singles yarn is unwound. At step  512  the singles yarn is then stretched and has a twist imparted to it whereupon. For finer thread sizes, this step is followed immediately by the plying step  514 , typically with both the twisting step  512  and the plying step  514  being performed on a single, “2 for 1” twisting machine. 
         [0026]    Alternatively, for heavier thread sizes, two separate steps are typically performed. Thus, the stretch and twist step  512  is then followed at step  516  by winding of the twisted singles yarn onto a spool (usually known as a ‘pirn’). Thereafter, the two or more singles yarns are then plied together at step  518  on a separate machine. In either case, both plying steps  514  or  518  are followed by a further winding step  520  of the resultant griege thread. The griege thread is then dyed at step  522  in the conventional manner used for other polyester yarns, that is to say autoclaving for natural white thread, and conventional package dyeing for other colours. The dyed thread has lubricant applied to it in the conventional manner and is lubricated and finish wound onto a user package at step  524 . 
         [0027]    Referring now to  FIG. 6 , one manner of achieving step  512  in the method of  FIG. 5  is shown. A textured yarn  610  is wound onto a bobbin  612  which is, in turn, adapted to rotate about an axis A. The yarn  610  is drawn off the bobbin  612  and routed through the bobbin spindle  614  about which the bobbin  612  can rotate. The yarn  610  thus passes around the outside of the bobbin and, via a guide hook  616 . Rotation of the bobbin as the yarn  610  is drawn off it causes the fibres of the yarn to acquire a twist, with the degree of twist being determined by the relative speed of linear travel of the yarn as it is drawn off the bobbin to the speed of rotation of the bobbin. Where the size of the twisted singles yarn is such as to require twisting and plying on separate machines, the twisted yarn is then wound onto a pirn  618  ready for plying. 
         [0028]    The twist imparted to the yarn at step  512  is lower than that which is typically applied to continuous, flat filament yarn. It has been found that applying such levels of twist causes the resultant thread to exhibit very few, if any textured characteristics, or to a very small degree. Accordingly, the levels of twist applied are greater, than those applied in conventional textured thread manufacture but lower than those applied when creating thread from continuous, flat filament yarn. 
         [0029]    Conventionally, textured thread is manufactured by plying several textured filament yarns together. Typically, the yarns are given very low amounts of twist; typically in the region of ½ to 1 turn per inch; the degree of twist imparted upon plying multiple yarns together to create thread is necessarily related to that twist level (in order for the plied thread to have a neutral overall torque, or at least a stable construction) and so is correspondingly low. Conventional wisdom has consistently held that it is not possible to impart any greater levels of twist to create textured thread for a variety of reasons, amongst which is the belief that doing so causes the thread manufactured from textured filament yarn to lose the very characteristics for which it is used in the first place. 
         [0030]    According to an embodiment of the present invention, textured continuous filament yarn is spun into a sewing thread which is then capable of being used for apparel stitching and other, similar uses previously thought improper in textured thread. An embodiment of the present invention produces a textured thread suitable for sewing is manufactured by a method which comprises the steps of: creating a continuous filament yarn having a false twist thereby imparting texture to the yarn; imparting a further twist in the range of between 5.5 and 18.7 turns per inch to the false twisted continuous filament yarn, the twist being in a first rotational direction; generating a thread by plying two or more textured continuous filament yarns with each other in a second rotational direction, and having a twist within the range 3.9 to 17 turns per inch. 
         [0031]    Details of specific values and ranges of twisting and plying combinations for different thread weights (expressed both in terms of denier, tex and decitex parameters) are illustrated in this table both in turns per inch (TPI) and turns per metre (TPM) in  FIG. 7 . 
         [0032]    Referring now additionally to  FIG. 8 , a further table is shown in which examples of the linear and processing speeds and tensioning employed for manufacture of threads having the characteristics set out in  FIG. 7  above are set out. The first set of rows provides details of the parameters for the process step  512 . The second set of rows provides details of the process of step  514  and  520 . Thus the first two rows combined provide parameters for the process route set out in  FIG. 5  as including steps  512 ,  514  and  520 ; the first, third and fourth sets of rows in combination provide details of the process route in  FIG. 5  provided by steps  512 ,  516 ,  518  and  520 . 
         [0033]      FIG. 8  effectively provides a comparison table, in which the processing of textured polyester thread or yarn as the case may be (TXP) in accordance with embodiments of the present invention is compared to the standard processing parameters used for continuous filament (CF). It can be seen that, in the majority of cases, the speeds at which the TXP is processed is slower than that used in standard processes; and, in addition, that the tensioning of the TXP during processing is also lower. This is counter-intuitive, in that, classically, speeds are desired to be as high as possible in order to produce as much thread in as short a time as possible. Embodiments of the method according to the present invention, however, provide for lower speeds at lower tensions. This ensures that the thread is not ‘debulked’ by the processing which would cause it to lose some of its texture. The tension differences between the processing of standard CF thread and that of TXP in accordance with embodiments of the present invention are expressed in percentages. Thus, for example, a percentage difference of 36% indicates that the TXP thread is processed at 64% of the tension for standard CF thread. The speeds differ from relatively small comparative reductions, such as the case of 5300 reduced from 5600 in the case of plying 18 Tex yarn, the latter being around 94% slower; to 10,500 RPM reduced to 8700, with the latter being around 83% of the standard speed in the case of 45 Tex. 
         [0034]    Textured thread created in this way has a number of advantages. Textured filament yarn is relatively inexpensive as a raw material and its manufactured into textured thread requires relatively fewer manufacturing steps than would be the case for a thread which would be required to perform equivalent functions, such as a corespun thread. Further because lower levels of twist are imparted than for thread made of conventional, flat filament continuous yarn, the thread has a lower profile when used for apparel stitching (which, of course, textured yarn was never previously suitable for). The relatively higher levels of elongation of the resultant thread when compared with conventional continuous flat filament thread is also an advantage when used for the seams of active wear garments, which frequently require a higher stretch due to the character of the fabric employed.