IMPROVEMENTS IN SEWING METHODS AND MACHINES

Abstract: Sewing method, comprising bonding sewing threads (52) to themselves or to one another, or bonding fabric layers (50, 51) together, by using an adhesive (57) having an elasticity which is measured by an elongation at break of at least 10-20 %, and preferably between 50 and 150 %. A chain-stitch is formed and locked, at the points of interlocking of successive loops of its single or double threads, with a bonding adhesive, whereby to form a pseudo lock-stitch. The bonding adhesive is chosen from among polymeric adhesives that can be formed by curing a precursor by means of U.V. light, e.g. acrylate-based photo-polymers. The bonding adhesive is applied by injecting a polymerizable precursor at the point where the adhesive bond is to be produced and then polymerizing the same.

Description: IMPROVEMENTS IN SEWING METHODS AND MACHINES Field of the Invention This invention relates to sewing methods and machines, and more specifically to novel sewing method and machines in which threads are bonded to fabrics or to other threads, or the engagement of interlocking threads is strengthened, by means of adhesives, whereby to substitute or improve conventional sewing method and machines. Background of the Invention Conventional lock-stitch type sewing machines which have been known in the art for a very long time, use several procedures to create a stitch. In the procedure called "Chain- Stitch", which is widely used, a single or double thread is carried downwards and back upwards through the fabric, forming interlocking loops. The Chain-Stitch technique provides increased elasticity and does not require a lower bobbin thread, but forms an unstable connection which may unravel. In EP-A-0219177 a sewing machine is described which comprises adhesive means, constituted by thermoplastic or thermosetting synthetic bonding material, for bonding a thread into fixed positioned relationship with the fabric stock to be sewn. In a preferred form of the invention of said application, the sewing machine comprises, in combination with an upper thread bobbin and means for forming loops of said thread, as in conventional lock-stitch sewing machines, means for bringing a lower thread into contact with said loops, and means for bonding it in fixed positioned relationship to the fabric stock by bonding it to the underside of the fabric stock or to the -2- upper thread, or for sequentially bonding to one another segments of said lower thread. This bonding technique too has disadvantages, because it results in loss of elasticity and does not provide the desired combination of strength and durability. It is therefore a purpose of this invention to eliminate the said drawbacks and to provide sewing methods and machines that form sewing connections between fabrics in garments having an optimal combination of strength, elasticity and durability. It is another purpose to provide such an optimal combination by means of mechanical devices and materials that are neither complex nor expensive or difficult to use. It is a further purpose to achieve sewing methods and machines that retain the positive features of known techniques and eliminate their negative features. Other purposes and advantages of the invention will appear as the description proceeds. Summary of the Invention The invention, generally, provides a sewing method which comprises bonding sewing threads to themselves or to one another, or bonding fabric layers together, by the use of an adhesive having a high elasticity. The elasticity of the bonding adhesive is preferably measured by its elongation at break, which must be at least 10-20% or higher, for instance, from 50 to 150%.A test for measuring the elongation at break of the adhesive will be described hereinafter, and the values of said elongation, as set forth in this specification and claims, are understood to be determined by said test. According to a first aspect of the invention, a Chain-Stitch is locked, at the points of interlocking of successive loops of its single or double thread, with a bonding adhesive. The resulting stitch becomes stabilized and cannot unravel as the ordinary Chain-Stitch, and in fact behaves like a Lock-Stitch, so that it could be called "pseudo Lock-Stitch". According to another aspect of the invention, stitching is carried out by means of a single thread that is passed through the fabric from one side and bonded on the other side of the fabric by means of a bonding adhesive, having the elasticity hereinbefore defined. E.g., an upper or lower thread may be used and be bonded to the fabric at its other side. According to a further aspect of the invention, stitching is carried out by means of two threads, one of which that is passed through the fabric from one side and bonded, without interlocking, on the other side of the fabric to the other thread, by means of a bonding adhesive, having the elasticity hereinbefore defined. According to a still further aspect of the invention, fabrics are bonded without the use of threads, by means of a bonding adhesive, having the elasticity hereinbefore defined. The elongation at break of the bonding adhesive, according to the invention, is measured by the following test. A thread having a diameter of 1 mm. is -4- formed by spinning the polymer precursor, by any convenient spinning means, such as by an extruder, to form a filament, and polymerizing it by UV light irradiation at the exit from the spinning nozzle, the extrusion being at such a speed that the precursor may fully polymerize before it is collected in any convenient manner , such as on a bobbin. The resulting filament is subjected to determination of the elongation at break on a dynamometer, by the usual technique of the textile art. Examples of polymeric adhesives useful for carrying the invention into practice are any adhesives that can be formed by curing a precursor by means of UV light. Acrylate based adhesives are an example, but chemically different polymeric adhesives are known to persons skilled in the art. According to another aspect of the invention, the bonding adhesive is applied by injecting a precursor, which is monomeric or oligomeric, polymerizable substance, in a fluid state, at the point where the adhesive bond is to be produced, each injection lasting for a very short time, in the order of thousands of a second, and then polymerizing the same, preferably by irradiation with UV light. The UV light may be produced by laser or by another source. The appropriate wavelength of the UV light can be determined by skilled persons depending on the type of polymer precursor and polymer to be obtained therefrom. In any case, the suppliers of the polymer precursor will furnish the necessary information to whoever carries this invention into practice. The injection and polymerization must be carried out under such conditions that the polymerizing radiation will not impinge on the monomeric or oligomeric adhesive precursor before or at the time of its injection. This can -5- be achieved, in one embodiment of the invention, by using repetitive injections followed by UV pulses with a time difference so that they do not overlap. This way, the precursor cannot be subjected to polymerizing radiation at the moment it issues from the injection nozzle. According to another embodiment of the invention, the injection nozzle, on the one hand, and the source of polymerizing radiation, on the other, are spatially separated to such an extent that any mutual influence is prevented, and the precursor, injected at one point, is then shifted to the point on which the polymerizing radiation impinges. According to a further, preferred embodiment, the direction of the injection (injection axis) and the direction of the radiation (radiation axis) form an angle, so that the radiation impinges on the polymer adhesive precursor only at the intersection of the two axes, which is the point at which the adhesive bond must be formed. Brief Description of the Drawings In the drawings: Fig. 1 schematically illustrates a prior art Lock -Stitch; Fig. 2 schematically illustrates a prior art Chain-Stitch; Fig. 3 schematically illustrates a Chain-Stitch strengthened according to an embodiment of the invention; Fig. 4 schematically illustrates the use of an upper thread bonded to the lower side of the fabric, according to another embodiment; Figs. 5a an 5b schematically illustrates the bonding of fabrics by adhesives without the use of a thread; Figs. 6 and 7 schematically illustrate the bonding without interlocking of a thread, passing through the fabric from one side thereof, to another thread located on the other side of the fabric; and -6- Fig. 8 schematically illustrates an embodiment of the injection and polymerization phases of the method of the invention. Brief Description of Preferred Embodiments Fig. 1 schematically illustrates in cross-section a conventional Lock-Stitch. For simplicity of illustration, in this figure the fabric stock to be sewn is shown as consisting of a single layer and being interrupted to leave open spaces where the two threads interlock. A similar style of illustration will be used in most figures, but it will be understood that in practice two or more layers of fabric are superimposed and stitched together and that threads pass though them without creating open spaces. The fabric stock is indicated by numeral 10, the upper thread by numeral 11, and the lower thread by numeral 12. It will be seen that loops of the two threads interlock at the points 13. Fig. 1 is merely illustrative of the prior art and does not relate to an embodiment of the invention. Fig. 2 illustrates, similarly to Fig. 1, a conventional Chain-Stitch. Two juxtaposed fabrics are indicated at 50-51, the thread at 52, and it is seen that the various loops of the threads interlock at points 54-. Fig. 3 shows the same Chain-Stitch as Fig. 2, but with the interlocking points 54 strengthened by an adhesive bond 53. The bond being made of a sufficiently elastic material, does not detract significantly from the flexibility and the elasticity of the textile structure, but secures the Chain-Stitch against unraveling. -7- Fig. 4 shows a (single or double) thread 26 that passes from the upper side of fabric 27 to the lower side thereof and is adhesively bonded thereto as indicated at 28. Fig. 5a shows two fabrics 50 and 51 connected by adhesive seals 49 at spaced points. Fig. 5b shows how the adhesive bond is obtained. The two fabrics are advanced in the direction of the arrow and are spread apart as shown at 58 to permit injection therebetween of adhesive drops 55 by means of an injector 56. The fabrics are advanced by increments equal to the distance between successive seals 52 and are juxtaposed. Sources of UV light, such as optical bundles 57 connected to a UV light generator, not shown, are placed at a predetermined position on the two sides of the fabrics. When each adhesive drop 55 reaches a position between said sources, UV radiation, is applied for a time and with a fluence sufficient to effect polymerization of the adhesive and transform the drops 55 into the seals 52. Alternatively, the fabrics could be advanced continuously and the UV light sources could be moved synchronically with it, so as to remain in the same relative position with respect to the fabrics for the time required to produce polymerization. If the polymerization occurs rapidly enough, depending on the type of the adhesives and on the fluence of the irradiation, no motion of the UV light sources will be required. In the embodiment shown in Figs. 5b, the UV light passes through the fabrics. Most fabrics are sufficiently permeable to the light to permit a sufficiently strong irradiation to permeate therethrough and produce the polymerization. Otherwise, it would be possible to move the UV light sources alternatively towards and away from the fabrics, to cause them to penetrate into the fabrics better to irradiate the adhesive. Synchronizing -8- such a motion with the advancement of the fabrics would be an easy task for an expert person. Fig. 6 shows the stitching of a fabric 30 by means of an upper thread 31 which is passed through the fabric as shown at 32, and a lower thread 33, which is not passed through the fabric. The lowermost points of thread 31, closest to thread 33, are bonded to said thread 33 by adhesive 34. However, in this particular embodiment, said lowermost portions of thread 31 are broadened to form loops 35, which afford a better area for the bonding to the thread 33 through the adhesive 34. Fig. 7 shows a similar embodiment in which a fabric 40 is stitched by means of a lower thread 41, which passes through the fabric as shown at 42, and a thread 43 which does not pass through the fabric. The two threads are bonded to one another by adhesive 44, which bond is permitted by bending thread 41 in hook-like shape, as indicated at 45. It will be evident that in both these embodiments, as in general in all the embodiments of the invention in which a thread is passed through the fabric, it is irrelevant whether the thread is an upper or lower one, and whether bonding correspondingly occurs on the lower or upper side of the fabric. It will also be evident that whenever a single thread is illustrated, a double thread could be used. Fig. 8 illustrates the injection and polymerization of the adhesive in one embodiment of the invention. In this particular embodiment, two fabric layers 50 and 51 are shown as stitched together by means of a Chain-Stitch generally indicated at 53. The adhesive is applied to the interlocking portions 54 of the Chain-Stitch. For this purpose, an injector 55 is shown having a nozzle 56, and a single drop 57 of polymer precursor is schematically shown as directed towards one of the points of interlock 54 in direction indicated by broken line 60, which will be called "the injection axis". A source of UV light 58, of any suitable kind, generates UV light radiation, which is directed by means of a fiber optic channel 59 or other suitable means to the same point of interlock 54, in a direction schematically indicated by broken line 61, which will be called "the radiation axis". The injector 55 may be of any suitable type, e.g., a piston injector, but works in a pulsed manner, viz. produces a drop of polymer precursor at a time. The UV generator may work in a pulsed or CW mode, as preferred, but at any rate, the radiation does not impinge on the polymer precursor's drops 57 until they have reached a place 54 where thread loops interlock. In this manner, premature polymerization is avoided. It will be understood that the distance between the injector and the generator and the angle between the ejection and the radiation axes may depend on the type of UV generator and of injector used, and, particularly, on whether the UV generator works in pulsed or CW mode. The apparatus of the invention shifts the fabrics, with the thread, synchronically with the ejection of a drop 57, at such a rate that the fabrics and the thread advance by a distance equal to the distance between two successive points of thread loop interlock in a time equal to the interval between the ejection of successive drops, and remains standing in a position in which one of such points will receive a polymer precursor drop during a period of time sufficient for the drop to reach its destination point and for the -10- UV radiation to accomplish the polymerization. As long as the fabric is advanced in such a manner, the embodiment of Fig. 8 can be modified, if desired,, by causing the injection axis and the radiation axis not to intersect one another, but to intersect the thread to be bonded at points having a distance from one another that is equal to or a multiple of the distance between two successive points of thread loop interlock, or, in general, the distance between two successive bonding points. Thus a drop of adhesive precursor will the deposited at a bonding point, and then polymerized at a position successively assumed by said bonding point. Once again, the parameters that must be respected for the polymerization to occur depend on the polymer used and will be known to the skilled person, and anyway can be communicated by the polymer supplier. While Fig. 8 shows the adhesive injection and polymerization in the case of the strengthening of Chain-Stitch, it will be evident that the adhesive can be so injected and polymerized in any embodiment of the invention. While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention may be carried into practice by persons skilled in the art with many variations, adaptations and modifications, without departing from its spirit or exceeding the scope of the claims.

Claims: -11- CLAIMS 1. Sewing method, comprising bonding sewing threads to themselves or to one another, or bonding fabric layers -together, by the use of an adhesive having an elasticity measured by an elongation at break of at least 10-20%, and preferably between 50 and 150 %. 2. Sewing method according to claim 1, comprising forming a Chain-Stitch and locking the same, at the points of interlocking of successive loops of its single or double threads, with a bonding adhesive, whereby to form a pseudo Lock-Stitch. 3. Sewing method, according to claim 1, wherein the bonding adhesive is chosen from among polymeric adhesives that can be formed by curing a precursor by means of U.V. light, e.g. acrylate-based photo-polymers. 4. Sewing method according to claim 1, wherein the bonding adhesive is applied by injecting a polymerizable precursor at the point where the adhesive bond is to be produced and then polymerizing the same. 5. Sewing method according to claim 3, wherein the precursor is polymerized by irradiation with UV light. 6. Sewing method according to claim 3, wherein the injection and polymerization are carried out under such conditions that the polymerizing radiation will not impinge on the precursor at the time of its injection. -12- 7. Sewing method according to claim 6, comprising carrying out the injection by pulses, producing a drop of polymer precursor at each pulse and directing it to the point where adhesive bonding is to be effected. 8. Sewing method according to claim 6, wherein the injection axis and the radiation axis are at an angle and intersect only at the point where adhesive bonding is to be effected. 9. Sewing method according to claim 7, comprising using a pulsed UV beam, alternating the radiation and injection pulses so that they never overlap. 10. Sewing method according to claim 6, comprising carrying out the injection and the irradiation at points spatially separated to such an extent that any mutual influence is prevented. 11. Sewing method according to claim 1, wherein stitching is carried out by means of a single thread that is passed through the fabric from one side and bonded on the other side of the fabric by means of a bonding adhesive 12. Sewing method according to claim 7, wherein each injection is carried out for a very short time, in the order of 1 to 20 thousands of a second. 13. Sewing method according to claim 1, comprising bonding fabrics without the use of threads, by means of a bonding adhesive. 14. Use of a bonding adhesive having an elasticity measured by an elongation at break of at least 10-20%, and preferably between 50 and 150%, -13- for strengthening sewing stitches, substantially as described in the specification.. 15. Use a bonding adhesive having an-elasticity measured by an elongation at break of at least 10-20%, and preferably between 50 and 150 %, for bonding sewing threads to themselves or to one another or to a fabric,, substantially as described in the specification.

Inventors: EILAM YAIR, EILAM, YAIR
Applicants: EILAM YAIR, NEO STITCH LTD, EILAM, YAIR, NEO-STITCH LTD.
Application year: 1999
Main classification: B32B31
IPC codes: B05C11, B32B38, D05B1, D05B17, D05B23