The present invention relates to a procedure for keeping together threads by means of which buttons are attached by being sewn in place on garments or other textile products, in conjunction with which a piece of material consisting of plastic is caused to be positioned between the aforementioned garment and a heatable welding horn or similar heating tool, and in which the keeping together is achieved by the application of heat in the area of the intended attachment part for the button or the garment, so that a part of the aforementioned piece of plastic material is fused together with the collection of threads on the opposite side of the garment on which the button is sewn in place. The invention is intended to be applied in the first instance to garments or other textiles which exhibit a number of buttons sewn on by means of threads. In this case, the principal object of the invention is to cause the same loose threads that are used for sewing-on of the buttons to be locked in such a way that these threads do not separate allowing the buttons subsequently to fall off. One problem associated with this, however, is that the button will come away if you pull on a loose thread. Previously disclosed through WO 9851174 Al are a procedure and an arrangement for fusing together threads which sew buttons in place on textiles. The previous procedure was to cause either a layer of Teflon® to be arranged on the welding tool, or a strip of Teflon to be positioned between the welding tool and the threads that is was wished to fuse together with the plastic material in the covering piece of plastic material. The first-mentioned procedure resulted in the layer of Teflon® wearing away rapidly when the aforementioned piece of plastic material was heated. The other alternative was to cause a tape consisting of Teflon® to be positioned between the welding tool and the garment, onto which a collection of threads in the sewn-on button would be compressed against a retainer arrangement, which resulted in this strip also being subjected to wear after a short time, and in the function of the strip being inferior with the associated risk of the heating tool adhering to whatever it came into contact with during the heating process and pressing against the retainer arrangement. The principal object of the present invention is thus, by- simple and effective means, to enable a solution to be found to the aforementioned problems and without the heating tool concerned becoming attached to the means that are utilized for the purpose of fusing together with the sewing thread that is so arranged as to secure the buttons in question, and to enable this to be done in a rational and effective manner. The aforementioned object is achieved by. means of a procedure in accordance with the present invention, which is characterized essentially in that the aforementioned piece of plastic material exhibits a surface coating consisting of silicon, paraffin or some other similar, heat-resistant material on its side facing towards the heatable welding horn or similar heating tool, in that the welding horn and the garment with the sewn-on button with an interjacent surface-coated piece of plastic material are caused to be compressed relative to one another, in conjunction with which the aforementioned surface coating on the piece of plastic material prevents the welding horn and the piece of plastic material from becoming fused together. Further objects of the invention are to make available an arrangement that lends itself to use for the implementation of the aforementioned procedure for making available a garment of this kind with its buttons in accordance with the invention and the actual article in question. The aforementioned further objects are achieved by means of an arrangement and garments in accordance with the Patent Claims. The underlying idea of the invention involves the use of a thin strip of plastic film with welding tools for fusion in textiles in large or small areas that will lock together sewing threads and textile threads to prevent them from becoming detached from one another. The invention is intended to be used first and foremost for garments and in these to fuse together and lock the threads that are used for sewing buttons so that these threads do not separate and allow the buttons to become detached, and the strip of plastic film does not become attached to the welding tool in this case, but a part of the plastic strip fuses with threads in the cloth and the sewing threads which hold the buttons. The nature of the material used for the plastic film is such that it melts easily and can be combined with the textile threads, and the side of the strip of plastic film that faces towards the welding horn of the welding tool exhibits a surface that does not become attached to the welding horn when the latter becomes hot. The strip of plastic film is preferably made of polyethylene with a surface coating on one side consisting of silicon or a material with the same characteristics. The strips are rolled up into suitable lengths for use in welding equipment with a feeding facility for each welding operation. The invention thus solves the problem as before, whereby the welding horns were surface-treated with Teflon® or with Teflon® film as a parting agent. The Teflon® wears relatively rapidly, however, which means that the strip of plastic film adheres securely to the welding horns, and this in turn is associated with expensive production stoppages and the costly scrapping of defective garments. The invention is described below as a number of preferred illustrative embodiments, in conjunction with which reference is made to the accompanying drawings, in which: Fig. 1 illustrates schematically as a perspective view the function of the invention with a strip of plastic that is located on one side and is capable of being actuated by a heating tool for the fusing together of the threads in buttons that have been sewn in place, Fig. 2 shows a cross section through a part of a garment with sewn-on and secured buttons, Fig. 3 shows a part of a garment viewed from the front with buttons sewn on, Fig. 4 shows an arrangement that is suitable for use for the fusion of sewn-on buttons, Fig. 5 shows the arrangement in greater detail in the effective position, Fig. 6 shows the front side of a shirt with buttons sewn on, and Fig. 7 shows the rear side of the aforementioned shirt with threads for the sewn-on buttons that have been fused and secured in this way. A procedure for keeping together threads 4 by means of which buttons 8 are attached by being sewn in place on garments 5 or other textile products, where the keeping together is achieved by the application of heat in the area of the intended attachment part 27 of the button or the garment, is shown as an example in Fig. 1. For this purpose, a piece of material 1 consisting of a fusible plastic, which exhibits a surface coating 14 consisting of silicon, paraffin or some other similar heat-resistant material on its side 13 facing towards a heatable welding horn or similar heating tool 2, is caused to be positioned between the aforementioned garment 5 and the welding horn 2. Thus, when the welding horn 2 and the garment 5 are compressed relative to one another with the button 8 sewn in place and with the interjacent, surface-coated 14 piece 1 of plastic material, so that a part of the aforementioned piece 1 of plastic material fuses with the collection 12 of threads on the opposite side 3 of the garment 5, to which the button 8 is sewn, the aforementioned surface coating 14 on the piece 1 of plastic material prevents the welding horn 2 and the piece 1 of plastic material from fusing together. A strip that is simpler and cheaper than previously can now also be applied, and the material used in the threads no longer needs to consist of plastic. A further advantage of arranging a coating 14 of silicon, etc., is that the silicon is securely attached to the strip 1. When a part of the aforementioned strip is attached to the button 8, by the plastic in the strip fusing into and around the collection of threads in the sewn-on button, the remaining silicon coating functions in such a way as to prevent the sole of the iron, when ironing the shirt, from catching on and becoming stuck to the plastic. For the purposes of the rational production of garments 5, etc., a piece 1 of plastic material in the form of a strip that is driven manually or automatically is fed in the intended direction 16 through the intended fusing station 15. In this case, the welding horn 2 is caused to be pressed down in the direction 17 of the aforementioned collection of threads on the side of the button 8 and the garment 5 that faces away, that is to say normally the rear side 3, so that the front tip part 2A of the welding horn 2 produces a circular hole 18 in the strip 1 of plastic material and a corresponding circular form on the resulting fused area 7 over the textile 6 or other material of which the garment consists. The strip 1 of plastic material is preferably caused to pass over two deflector rollers 19, 20 situated at a mutual distance from one another and between which a thermal shield 21 with a centrally located transcurrent hole 22 extends above a hollow retainer arrangement 23 executed from a soft material, in which the button 8 is accommodated during the fusion stage. The strip 1 is thus fed from one strip roller 24 to the other 25, and the garment 5, for example shirts, is positioned with the intended buttons facing towards an intended support 26 and accommodated in the intended retainer arrangement 23 therein. In conjunction with pressing the welding horn 2 down through the hole 22, the tip 2A of the welding horn 2 removes a ring-shaped part from the plastic strip by the application of heat and causes it to fuse together with the collection 12 of threads and the surrounding attachment part 27 of the material of the garment. The welding horn 2 is prevented from sticking to the strip 1 thanks to the aforementioned heat-resistant coating 14 of silicon, etc. An arrangement 28 in accordance with the present invention, which is so arranged as to be applied for the accomplishment of a procedure of the kind indicated above, and which is illustrated in the drawings in Fig. 4, comprises a strip 1 of plastic film, preferably consisting of polyethylene, which has a surface coating 14 consisting of silicon, paraffin or some other similar heat-resistant material, which is so arranged as to prevent adhesion to a heating tool 2 for exerting pressure on the aforementioned strip of plastic film along one surface 13 of the strip. The aforementioned strip 1 is so arranged as to be capable of moving past a fusing station 15 and is so arranged as to be capable of being stopped in the intended fusing position I. Also provided is a heatable welding horn 2 or other similar heating tool that is so arranged as to be capable of displacement relative to a retainer arrangement 23, and the aforementioned welding horn 2 is capable of actuation by means of, for example, a jack in order to press it against the surface-coated strip 1 of plastic film and the collection 12 of threads situated beneath/behind it in order to bring about fusion of a part of the aforementioned strip 1 of plastic film with the aforementioned collection 12 of threads and the surrounding attachment part 27 of the textile material in the intended garment 5 without the strip 1 of plastic film sticking to the aforementioned intended welding horn 2 that is capable of being compressed in conjunction with fusion. The aforementioned welding horn 2 preferably exhibits a concave and circular form at the heating tip, as a consequence of which the resulting fused part 7 also exhibits circular peripheral form. In order to protect the garments 5 from heat from the machine 29, a thermal shield 21 is provided with a central hole 22 and extends beneath the welding horn 2 and is attached to each of two deflector rollers 19, 20 for the strip 1. This thermal shield 21 may consist of thick plastic or textile material. A subjacent, hollow, soft retainer arrangement 23 to accommodate a button 8 is provided below and directly in line with the aforementioned welding horn 2 and the hole 22 in the thermal shield 21, on the top side of a cloth support 26 extending across the direction of feed 16 of the strip. The function of the arrangement should have emerged clearly from the foregoing and with the aid of the drawings. Garments 5 or other products consisting of a textile or other material, which exhibit a number of buttons 8 sewn into the aforementioned garments 5 by means of threads 4, where the resulting collection 12 of threads situated on the surface 3 of the garment facing away from the button 8 is so arranged as to be fused together, have the collection 12 of threads and the adjacent attachment part 27 of the garment 5 surrounded by a part 7 of the strip of plastic film covered with silicon or a similar surface coating 14 that is fused together with the same, in conjunction with which the aforementioned fused part 7 of the strip 1 of plastic film preferably exhibits circular peripheral form. The material of which the sewing threads 4 consist is of not significance for the attachment of the buttons 8 in this case. The threads 4 extend through holes 11 in the button 8 and through the textile to form transverse top threads 10 and a thread neck 9 in the sewn-on button 8. It is thus as easy to secure cotton threads by the application of heat as it is to secure threads made from a synthetic material. The invention is naturally not restricted to the embodiments described above and illustrated in the accompanying drawings. Modifications are possible, in particular with regard to the nature of the various parts, or by the use of equivalent technology, but without departing from the area of protection afforded to the invention, as defined in the Patent Claims.