Patent Publication Number: US-10765572-B2

Title: Method of assembling at least two units, and a corresponding assembled structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase entry under 35 U.S.C. § 371 of International Application No. PCT/FR2015/050867, filed on Apr. 2, 2015, which claims priority to French Patent Application No. 1452957, filed on Apr. 3, 2014. 
     TECHNICAL FIELD 
     The present disclosure relates to a method of assembling a plurality of units. 
     BACKGROUND OF THE PRESENT DISCLOSURE 
     Numerous products are obtained by assembling a plurality of units, in particular a plurality of layers or sheets. This applies in particular to belts, which are generally formed by using heat to assemble together two solid and continuous bands that are separated by a layer of reinforcing cords. 
     Whatever the application, the various units are positioned relative to one another prior to being secured together. Several problems can then arise. The prepositioned units may be shifted unintentionally, either before or during assembly, thereby slowing down the fabrication process or fabricating a product that is defective and will need to be rejected. Worse, such an unintended shift of one or more of the units can be difficult to detect during fabrication, and might lead to danger for the user of the final product. 
     In order to mitigate those problems and make the positioning of the various units before and during assembly reliable, proposals have been made to use pre-assembly means such as clamps or staples. Nevertheless, such means can be difficult to remove, thereby making repositioning very difficult in the event of an error. They can also lead to localized stress zones in the product. They can also be impossible to extract, thereby leaving foreign bodies in the final product. 
     In certain applications, attempts have been made to use adhesive means for pre-assembly since they are less intrusive. For example, in the field of belts, it is known to apply an adhesive composition to the reinforcing cords in order to hold the two bands placed on either side of them in position. 
     With such means, it still remains difficult after the event to correct poor positioning of the units. Such adhesive means can be difficult to fabricate given the environmental standards and regulations that need to be complied with. They also present the drawback of easily losing their adhesive properties over time or as a consequence of poor storage conditions. 
     OBJECT AND SUMMARY OF THE PRESENT DISCLOSURE 
     One of the objects of the present disclosure is thus to provide a method enabling the above-specified drawbacks of the prior art to be remedied. 
     This object is achieved by a method comprising providing a first unit having a field of grip elements, in particular hooks, and a second unit provided with retention means suitable for co-operating with the grip elements of the first unit in order to provide a self-gripping fastening; putting the first and second units into contact in such a manner that the grip elements of the first unit and the retention means of the second unit provide a self-gripping fastening; and treating a treatment zone of the self-gripping fastening in order to deform the grip elements of the first unit and/or the retention means of the second unit, whereby the first and second units are permanently secured to each other, thereby forming an assembled structure. 
     In the method of the present disclosure, the first and second units are prepositioned prior to them being secured to each other permanently in a manner that is made reliable by means of a self-gripping fastening of the kind also referred to as a “contact closure” or a “touch fastener”. The term “self-gripping fastening” should be understood herein as designating a connection that enables the first and second units to be held stationary relative to each other in at least one direction, in particular a tangential direction and/or a direction orthogonal to the junction surface between said units, which junction surface may be plane, or curved, or may present any other appropriate profile. 
     Under such circumstances, in particular when the self-gripping fastening holds the first and second units together stationary in a direction orthogonal to the junction surface between the two units, it can be undone only by applying a force that is considerably greater than the force applied to the two units while they are being fastened together. 
     A self-gripping fastening thus makes it possible, without effort, to hold at least two units together temporarily in a manner that is effective. 
     Where necessary, it also allows them to be separated and repositioned easily and repeatedly, while continuing to ensure that they end up being held in position at the time they are secured together permanently. 
     The prepositioning may also be performed without risk of damaging the units, with no external tool or attachment means being necessary. 
     In the present disclosure, a grip element may present any shape suitable for co-operating with complementary retention means in order to form a self-gripping closure of the above-defined type, which may be male-male, male-female, or hybrid. 
     A grip element may be a hook. The term “hook” should be understood herein as being an element that is suitable for hooking (in particular to a loop or a fiber), and in particular an element formed by a stem and a hook portion overlying said stem and extending laterally therefrom. Thus, an element in the form of a mushroom, a barb, a hook with one or two grip tabs, or the like, should be understood as being a hook in the meaning of the invention. 
     A grip element may also be in the form merely of a stem. 
     In conventional manner, these elements are grouped together so as to form a field. In the present application, a “field” of elements should be understood as constituting a plurality of elements, in particular at least 50 elements, and more particularly at least 200 elements, that may be distributed regularly or otherwise. 
     The size of the grip elements and the number of elements per unit area (density of the field of grip embodiments) may vary considerably. For example, the grip elements may present a total height measured orthogonally to the surface of the base from which they project that lies in the range 0.1 millimeters (mm) to 5 mm, and preferably in the range 0.5 mm to 1.5 mm. Preferably, the density of the field lies in the range 1 element per square centimeter (cm 2 ) to 2000 elements/cm 2 , and preferably in the range 10 elements/cm 2  to 1200 elements/cm 2 . 
     The retention means of the second unit may also have a wide variety of forms. 
     In the present application, the retention means may comprise a field of grip elements. 
     In another example, the retention means comprise fibers. In the present application, the term “fiber” should be understood as being an element that is fine and elongate, whether continuous or discontinuous, and in particular a fiber or a filament. The fibers may be assembled together to form a non-woven material. They may also be woven together. They may also be assembled in a bundle, thus forming a tow. The fibers may be synthetic fibers (carbon, aramid, or glass fibers) or they may be natural fibers (flax). 
     In an example, the second unit may thus comprise a non-woven layer of fibers that form retention means. In a variant, the second unit may also comprise a woven fabric provided with a field of loops forming retention means. 
     In order to secure the first and second units together permanently, the self-gripping fastening is treated in a treatment zone so as to deform those grip elements of the first unit and/or those retention means of the second unit that are situated in the treatment zone. 
     The self-gripping fastening may be treated in various ways, that may be considered as alternatives or that may possibly be used in combination. In non-exhaustive manner, the treatment may thus comprise applying pressure, vibration, friction, or radiation to the self-gripping fastening and/or using chemical treatment with at least one solvent and/or heat treatment, e.g. ultrasound heating (in particular generating ultrasound vibration using a sonotrode). 
     In an implementation, the treatment is such that after being deformed, the grip elements or the retention means form reinforcing means of the assembled structure. 
     In the present application, reinforcing means of a structure are means that confer on said structure a substantial portion (e.g. at least 20%, preferably at least 30%, more preferably at least 50%) of its ability to withstand at least one type of stress, in particular mechanical stress (e.g. traction strength, compression strength, or shear strength), or thermal stress, or chemical stress. 
     In a particular example, the treatment is such that after being deformed, the grip elements or the retention means retain a shape that is generally unchanged. 
     The term “generally unchanged” should be understood as being a shape that although possibly modified compared with the original shape, whether in terms of dimensions or structure, nevertheless conserves the mechanical retention properties of the element. 
     In this context, a fiber may possibly change diameter, length, or shape, while generally continuing to constitute retention means, in particular a fiber. A hook or a barb may have its shape and/or its dimensions modified (preferably the characteristic dimensions of the element, in particular its height, its width, and/or its thickness, vary by no more than 20%, preferably no more than 10%, still more preferably by no more than 5% relative to their initial values), while generally remaining a grip element. By way of example, on being deformed, a hook or a barb may become a stem. 
     In an example, when the treatment is heat treatment, the self-gripping fastening is subjected to a working temperature higher than a first melting temperature for one only of the grip elements and of the retention means. 
     In an example, the difference between the melting temperatures of the grip elements and of the retention means may be at least 5° C., preferably at least 10° C., or more preferably at least 20° C., for example. 
     It is common practice for a portion of a product to need to be reinforced, in order to improve its ability to withstand mechanical, thermal, or chemical stress. By way of example, such reinforcement may be the result of including reinforcing means in the product. The above-specified provisions of the method of the present disclosure enable a product to be reinforced by incorporating reinforcing means therein that may be in the form of fibers or of grip elements. 
     Because of the self-gripping fastening initially provided between the first and second units, the reinforcing means are held in position both before and during the treatment. Their proper positioning within the assembled final structure is thus ensured, thereby guaranteeing good reinforcement. When the reinforcing means are constituted by grip elements, care should be taken for example to avoid those elements being tilted or folded over during treatment, since that would be detrimental to the reinforcing effect. When the reinforcing means are constituted by fibers, care should be taken in particular to avoid the fibers moving too far away from the unit that is to be reinforced or failing to be uniformly distributed over that unit. 
     The method of the present disclosure may also be used for fabricating a composite element in which the retention means of one of the first and second units form reinforcing means and the retention means of the other unit form a matrix in which said reinforcing means are embedded. 
     In an example, the treatment zone forms a continuous line. 
     By way of example, it extends over a length of at least 1 centimeter (cm), and preferably at least 3 cm. 
     In another example, it is also possible for the treatment zone to be discontinuous, and in particular it may be formed by a set of spots. 
     The treatment zone preferably represents at least 50%, preferably at least 80%, in particular at least 95% of the total extent of the self-gripping fastening. 
     In a particularly preferred implementation, the treatment zone covers the entire self-gripping fastening. Still more preferably, it covers the entire surface area of the field of grip elements and/or of retention means. 
     In an example, the self-gripping fastening covers at least 50%, preferably at least 80%, and in particular at least 95% of the extent of the zone of contact between the first and second units. 
     In an example, the first and second units may be treated beyond the self-gripping fastening. In particular, the units may be treated in full. 
     The grip elements and/or the retention means may be made of a composite or polymer material that is suitable for melting at least once, in particular they may be made out of a thermoplastic material, a polymer that can be cured or post-cured. 
     In non-limiting manner, the grip elements and/or the retention means may thus be made out of any of the following materials: polyethylene, polypropylene or some other olefin homopolymer or copolymer such as ethylenes or alpha olefins sold under the names Affinity®, Engage®, or Exact®, or semi-crystalline polyolefins sold under the names Vistamaxx® or Versify®, or the elastomer thermoplastics sold under the names Santoprène®, Sofprene®, or Thermolast®; polyurethane of polyester, polyether, or polycarbonate type, in particular polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), PET copolymer (PETG), poly(epsilon-caprolactone) (PCL), polylactic acid (PLA), polyester-based copolymers such as Hytrel® and Arnitel®; polyamides (PA), e.g. such as PA6, PA6.6, PA11, and PAl2, polyamide-based copolymers such as Pebax® and Vestamid®, homopolymer or copolymer polyoximethylene (POM), and alloys containing at least one of the above-specified polymers. 
     In an example, the grip elements and/or the retention means include metal particles, generally embedded in the thermoplastic material constituting them. These metal particles make it possible, in particular during heat treatment, for the self-gripping fastening to be heated more rapidly and in more uniform manner locally, thereby improving its treatment, e.g. by induction heating. 
     The method of the present disclosure may also be used to assemble together more than two units. In an implementation, the method comprises providing a third unit comprising a field of grip elements suitable for co-operating with the retention means of the second unit in order to provide a self-gripping fastening; putting the second and third units into contact so that the second unit is arranged between the first and third units, and the grip elements of the third unit and the retention means of the second unit provide a second self-gripping fastening; and treating a treatment zone of the second self-gripping fastening to deform the grip elements of the third unit and/or the retention means of the second unit, whereby the second and third units are permanently secured to each other. 
     Preferably, the self-gripping fastenings provided between the second unit and the first and third units respectively are treated simultaneously in a single treatment step. 
     In a particular implementation, prior to the treatment, the grip elements of the first unit and the grip elements of the third unit are put into co-operation, the retention means of the second unit lying between said grip elements. 
     In an example, the units are assembled together continuously, on a production line. 
     Under such circumstances, and by way of example, the first and second units form respective longitudinally-extending strips, the first and second units being superposed continuously (in line) in a longitudinal direction over at least one contact zone where the grip element of the first unit and the retention means of the second unit provide a self-gripping fastening, and said self-gripping fastening is treated continuously (in line) in the longitudinal direction over at least one treatment zone. The treatment zone may be continuous or discontinuous. By way of example, the treatment may be performed by means of a wheel making continuous contact (when the treatment zone comprises at least one continuous strip), or point contact (when the treatment zone comprises a plurality of distinct zones that are spaced apart in the longitudinal direction). 
     The method of the present disclosure may have various applications, in particular in the field of hygiene. 
     In one example utilization, the method may be used for fabricating hook-carriers for diapers. 
     Under such circumstances, in particular, the first unit has a field of hooks and the second unit is a non-woven material, the first and second units being superposed over at least one zone of contact where the hooks of the first unit and the fibers of the second unit provide a self-gripping fastening, while preserving on opposite sides of the zone of contact both a free portion of the first unit having hooks, and also a free portion of the second unit, with the self-gripping fastening being processed so as to secure the first and second units together. 
     It should be observed that the term “free portion of a unit” is used to mean a portion that is not in contact with the other of the first and second portions, and that has retention means that are generally (but not necessarily) operational, i.e. suitable for co-operating with other means in order to form a self-gripping fastening. 
     In a second example utilization, the method of the present disclosure may be used for reinforcing a base, in particular a sheet or a composite element, by means of at least one reinforcing element of the eyelet type, at a location for a hole in said base. Under such circumstances, the reinforcing insert generally constitutes the first unit and the base generally constitutes the second unit. 
     The term “location for a hole” is used herein to mean a location where the base is pierced or where it is going to be pierced. 
     The present disclosure also provides a structure comprising at least a first layer including retention means for a self-gripping fastening and at least one second layer co-operating with the first layer over at least one assembly zone holding captive the retention means, whereby the first and second layers are permanently secured to each other. 
     The retention means may comprise fibers. More particularly, said layer may be constituted by a sheet of woven or non-woven fibers. 
     In another example, the retention means are grip elements, in particular hooks. For example, the first layer comprises a base having at least one face that has a field of grip elements projecting therefrom. 
     In an example, a structure of the present disclosure may be a hook-carrier for diapers. Such a hook-carrier comprises a base layer provided with a plurality of hooks and a fiber layer, generally a non-woven fiber layer, that are connected together in an assembly zone. 
     In yet another example, the structure of the present disclosure comprises a base and a reinforcing insert having a through bore that is fastened to a location in said base for a hole. 
     Generally, the bore in the insert is arranged facing the location for a hole in the base. 
     By way of example, the base may be a sheet, in particular a tarpaulin, e.g. constituted by a layer of non-woven material, or indeed a composite element, e.g. an internal trim panel for a vehicle. 
     Several implementations are described in the present disclosure. Nevertheless, unless specified to the contrary, the characteristics described with reference to any one implementation may be applied to any other implementation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure can be well understood and its advantages appear better on reading the following detailed description of various implementations shown as non-limiting examples. The description refers to the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing two units that are to be assembled together by a first implementation of the method of the present disclosure; 
         FIG. 2A  is a side view of two  FIG. 1  units, prior to being put into contact; 
         FIG. 2B  is a side view of the two  FIG. 1  units connected together by a self-gripping fastening; 
         FIG. 2C  is a side view of the structure that results from final assembly of the first and second units of  FIG. 1 ; 
         FIG. 3  is a diagram showing the treatment zone of the  FIG. 2B  self-gripping fastening; 
         FIGS. 4A to 4C  show variant distributions for the treatment of the self-gripping fastening of  FIG. 2B ; 
         FIG. 5A  is a section showing three units that are to be assembled together by a second implementation of the method of the present disclosure, the unit being shown prior to being put into contact; 
         FIG. 5B  is a section showing the three units of  FIG. 5A  connected together by a self-gripping fastening; 
         FIG. 5C  is a section of the structure that results from final assembly of the three units of  FIG. 5A ; 
         FIG. 6  shows a variant of the second implementation of the method of the present disclosure; 
         FIGS. 7A to 7C  show successive steps in a third implementation of the method of the present disclosure; 
         FIG. 8  shows a first variant of the third implementation of the method of the present disclosure; 
         FIG. 9  shows a second variant of the third implementation of the method of the present disclosure; 
         FIG. 10  is an overall view of a commonly-used diaper; 
         FIG. 11  shows a line for fabricating hook-carriers for diapers by implementing the method of the present disclosure; 
         FIGS. 12A and 12B  are sections respectively on XIIA-XIIA and XIIB-XIIB of  FIG. 11 ; 
         FIG. 13  shows a base that is to be reinforced locally by a reinforcing insert; 
         FIGS. 14A to 14D  are sections on XIV of  FIG. 13  showing the various steps of assembling the reinforcing insert; 
         FIGS. 15A and 15B  show a variant implementation of the assembly method of  FIGS. 13 and 14A to 14D ; and 
         FIG. 16  shows a variant of the reinforcing method of  FIGS. 13 and 14A to 14D . 
     
    
    
     DETAILED DESCRIPTION OF IMPLEMENTATIONS 
       FIGS. 1 to 3  show how a structure  100 A (see  FIG. 2C ) is made by assembling together a first unit  10  and a second unit  20  in a first implementation of the method of the present disclosure. 
     The first unit  10  is made out of a first thermoplastic material M 1  that melts at a temperature T 1 , in particular a curable polymer such as polyethylene for which T 1  is equal to 120° C. In the particular example of  FIGS. 1 to 3 , the first material M 1  also contains a plurality of metal particles  40  that perform a function that is described in detail below in the present disclosure. 
     As shown in  FIG. 1 , the first unit  10  comprises a base  11  defined by two main surfaces  11   a  and  11   b , which surfaces in this example are rectangular, substantially plane, and parallel, being of length L 1  and of width  11 . 
     A plurality of grip elements  12  project from one of these main surfaces  11   a  (referred to below as the “junction” surface), forming a field  13  of grip elements. By way of example, the grip elements  12  may be injection molded together with the base  11 . They are thus integral with the base  11 , in other words forming a single piece therewith, without any interface or discontinuity, in particular at microscopic level, where they join the base  11 . 
     In this example, the grip elements  12  are hooks, each comprising a stem  14  projecting from the junction surface in a direction that is substantially orthogonal to said surface, and a grip portion  15  that overlies said stem  14  and has two grip tabs extending laterally from the stem, on either side thereof. 
     In the example, the field  13  of hooks extends over the entire width  11  and the entire length L 1  of the base  11 . Naturally, this distribution could be very different depending on the intended application. The grip elements may cover only a portion of the surface of the first unit from which they project, e.g. at least 95%, or indeed less than 5%. 
     The grip elements  12  advantageously present a total height measured orthogonally to the surface  11   a  of the base  11  that lies in the range 0.1 mm to 5 mm, and the density of the field lies in the range 1 element/cm 2  to 2000 elements/cm 2 . 
     The second unit  20  is made of a second thermoplastic material M 2  that melts at a temperature T 2  higher than T 1 , in particular a polymer such as a polyamide for which T 2  is equal to 260° C. 
     The second unit  20  presents a structure that is very similar to the structure of the first unit  10 , and it is therefore not described in detail below. It likewise comprises a base  21  defined by two surfaces  21   a  and  21   b  that in this example are substantially plane and rectangular, of length L 2  (identical to L 1  in this example) and of width l 2  (identical to L 1  in this example). 
     As shown in  FIG. 1 , the second unit  20  has retention means  22  adapted to co-operate with the grip elements  12  of the first unit  10 . 
     In the example, the retention means  22  are grip elements complementary to the hooks  12 , and in particular they are hooks of the same shape, forming a field  23  of hooks. 
     The field  23  of hooks of the second unit  20  in this example occupies only a fraction of the junction surface  21   a  from which it projects. 
     During assembly, and as shown in  FIG. 2A , the first and second units  10  and  20  are positioned in such a manner that their respective junction surfaces  11   a  and  21   a  face each other. 
     As shown in  FIG. 2B , the first and second units  10  and  20  are then brought into contact in a desired relative position. 
     In  FIGS. 2B and 3 , in particular, reference C designates the zone of contact between the first and second units  10  and  20 . In this zone of contact C, the fields  13  and  23  of hooks of the first and second units  10  and  20  face each other in at least a determined zone, where they provide a self-gripping fastening referenced F resulting from co-operation between their grip elements  12  and  22 . 
     In this state, said self-gripping fastening F holds the first and second units  10  and  20  stationary relative to each other in a direction orthogonal to their junction surfaces  11   a ,  21   a , and also in directions tangential to those surfaces. Nevertheless, they are not held permanently, and it is easy for the two units  10  and  20  to be separated in order to be repositioned, should that be necessary. 
     Finally, and as shown in  FIG. 2C , the self-gripping fastening F is treated in a treatment zone (referenced Z and represented by stippling in  FIG. 3 ) corresponding in this example to the entire zone of the self-gripping fastening F, so as to secure the first and second units  10  and  20  together in permanent manner. 
     Nevertheless, this example is not limiting. In certain circumstances, the treatment zone Z may extend over a fraction only of the self-gripping fastening F. In the example of  FIG. 4A , the treatment zone Z is thus in the form of a strip extending over only a fraction of the length of the self-gripping fastening F, but extending all the way across the first and second units  10  and  20  along a continuous line, extending in the width direction in this example. In the examples of  FIGS. 4B and 4C , the treatment zone Z comprises a plurality of strips, extending parallel to one another or forming a grid. In other variants, the treatment zone may also be in the form of a plurality of spots or the equivalent. 
     In the example of  FIGS. 1 to 3 , the treatment zone Z is subjected to a temperature T that is higher than T 1  but lower than T 2 , thereby causing the first unit to be deformed in said zone. 
     The metal particles  40 , which should be understood to be optional, serve in this example to ensure that temperature increases rapidly and uniformly within the first material. 
     As shown in  FIG. 2C , the base  11  and the hooks  12  of the first element  10  melt so as to coat the hooks  22  of the second unit  20  that have remained intact (since they do not deform). 
     In order to ensure that treatment is effective, avoiding deformation of the hooks  22  of the second unit, the difference between the respective melting temperatures T 1  and T 2  of the first and second materials M 1  and M 2  should be not less than 5° C., preferably not less than 10° C., and more particularly not less than 20° C. 
     The resulting assembled structure  100 A is a one-piece block comprising a first layer  51  including the retention means for a self-gripping fastening, specifically the hooks  22 , and a second layer  52  co-operating with the first layer  51  over at least one assembly zone  55  and holding captive the retention means  22 , whereby the first and second layers  51  and  52  are permanently secured to each other. 
     The structure  100 A thus forms a composite element having a matrix formed by the material of the second layer (resulting from the deformation of the first unit) and the reinforcing means are formed by the grip elements of the first layer  51 , serving in particular to improve the shear and/or traction strength of the structure. 
     In a variant, it should be observed that the melting temperature of the first unit could equally well be higher than the melting temperature of the second unit. 
       FIGS. 5A to 5C  show a structure  100 B (see the figure) that is made by assembling together a first unit  10 , a second unit  20 , and a third unit  30  in a second implementation of the present disclosure. 
     As shown in  FIG. 5A , the first unit  10  is similar to that described with reference to  FIG. 1  in particular. It is therefore not described again. 
     In this example, the second unit  20  is constituted by a layer of non-woven material, made out of a thermoplastic material that melts at a temperature T 2 , higher than T 1 . The retention means  22  of the second unit  20 , which are adapted to co-operate with the hooks  12  of the first unit  10 , are formed by the tangled fibers constituting the non-woven material. 
     A non-woven material is made up of a plurality of fibers that are bonded together and that generally form a sheet. The fibers may be bonded together mechanically, chemically, or thermally. Three major types of non-woven material are presently known: dry-laid nonwovens (carded thermobonded—airlaid thermobonded—spunlace—airthrough—carded needle punched, etc.); wet-laid nonwovens; and spunmelt nonwovens (spunbond, meltblown, or a combination of both (SM, SMS, SMMS, SSMMS, . . . ), electrospun, melt-film fibrillated, solvent-spun, . . . ). 
     The third unit  30  is made of a meltable polymer material that, in this example, is identical to the material M 1  constituting the first unit  10 . 
     In the same manner, its structure is similar to that of the first unit  10 . It thus comprises a base  31  defined by two substantially plane and parallel surfaces  31   a  and  31   b  together with a plurality of grip elements  32  adapted to co-operate with the retention means  22  of the second unit  20 . In the example, these grip elements  32  form a field  33  of hooks projecting from one of the surfaces  31   a  of the base  31  (referred to below as the “junction” surface). 
     During assembly, and as shown in  FIG. 5B , the first and second units  10  and  20  are put into contact in a desired position. The fibers  22  of the second unit co-operate with the hooks  12  of the first unit  10  to provide a first self-gripping fastening F 1 . 
     In the same manner, the second unit  20  and the third unit  30  are put into contact in a desired position. The fibers  22  of the second unit  20  co-operate with the hooks  12  of the third unit  30  to provide a second self-gripping fastening F 2 . 
     By means of these self-gripping fastenings F 1  and F 2 , all three units  10 ,  20 , and  30  are held in position relative to one another. If they are poorly positioned, they can easily be detached and then repositioned, and this can be done a large number of times without damaging them. 
     In the example, the three above-mentioned units  10 ,  20 , and  30  are assembled together permanently by heat treatment, which consists in subjecting the stack to a temperature T that is lower than T 2  but higher than T 1 . 
     Under the effect of heat, the first and third units  10  and  30  deform and bond together, holding captive the fibers  22  of the non-woven material, which fibers themselves remain substantially intact, with the first, second, and third units thus being permanently secured to one another. 
     As shown in  FIG. 5C , the resulting assembled structure  100 B is a composite unit comprising a first layer  51  including retention means that have been used in a self-gripping fastening, specifically the fibers  22 , and a second layer  52  resulting from the deformation of the first and third units, co-operating with the first layer  51  over at least one assembly zone and holding the retention means  22  captive, whereby the first and second layers  51  and  52  are permanently secured to each other. 
     The fibers  22  form reinforcing means for the assembled structure  100 B, serving in particular to increase its stiffness and its traction strength, and preventing the first and third units  10  and  30  from separating. In a variant implementation shown in  FIG. 6 , the positioning of the three units  10 ,  20 , and  30  may be secured further in additional manner by bringing the hooks  12  of the first unit  10  and the hooks  32  of the third unit  30  into mutual co-operation prior to applying the heat treatment. 
     As can be seen from the above, the method of the present disclosure can advantageously be used in order to form a reinforced structure. A third implementation of the method of the present disclosure illustrates such a use and is shown diagrammatically in  FIGS. 7A to 7C . 
     In this example, a first unit  10  that is to be reinforced is made of a polymer material that melts at a temperature T 1 , and is substantially identical to the first unit described above with reference in particular to  FIG. 1 . 
     A second unit  20  that is formed by a layer of non-woven material constituted by tangled fibers  22  (see  FIG. 7A ) is put into contact with the junction surface  11   a  of the first unit  10  from which its grip elements  12  project, so that said fibers  22  co-operate with the hooks  12  of the first unit  10  in order to provide a self-gripping fastening F. 
     In this position, as shown in  FIG. 7B , the layer of non-woven material is held stationary relative to the first unit in directions that are tangential to the junction surface  11   a  and in a direction orthogonal thereto. 
     Thereafter, the self-gripping fastening F is subjected to a temperature T that is higher than T 1  but lower than T 2 , e.g. obtained by using a sonotrode to generate ultrasound vibration. In this position, the base  11  and the hooks  12  of the first unit melt, and they coat the fibers  22  of the non-woven material, which fibers remain substantially intact. 
     The first and second units  10  and  20  then constitute a single-piece assembled structure  100 C of composite form, as shown in  FIG. 7C , comprising a layer forming a matrix  52  that results from deformation of the first unit, holding captive the retention means for a self-gripping fastening, specifically the fibers  22 . 
     In a first variant of this third implementation, shown in  FIG. 8 , the first unit  10  is made of a material that melts at a temperature T 2  higher than the melting temperature T 1  of the second unit  20 . 
     When the self-gripping fastening F made between the two units is treated by being subjected to an intermediate temperature, higher than T 1  but lower than T 2 , the fibers  22  melt and coat the hooks  12 , that have themselves remained intact. 
     The first and second units  10  and  20  then constitute a single-piece structure  100 D of composite form comprising a matrix (resulting from deformation of the second unit  20 ) reinforced by the hooks  12  of the first unit  10 . 
     In a second variant implementation shown in  FIG. 9 , the self-gripping fastening F is treated by being subjected to a temperature that is higher than the melting temperatures of the first and second units  10  and  20 . 
     Under such circumstances, under the effect of high temperature, the hooks  12  melt while nevertheless retaining a generally substantially cylindrical shape. 
     The fibers  22  melt and serve to coat the deformed hooks  12 ′. 
     The method of the present disclosure has a wide variety of applications in numerous fields. Non-exhaustive examples are given below. 
     By way of example, the method of the present disclosure may advantageously be used in the field of hygiene, in particular for fabricating hook-carriers for closing diapers. 
     The method of the present disclosure may also be used in the automotive or aviation fields, in particular for fastening trim on doors, roof panels, or covers. 
       FIGS. 10, 11, 12A, and 12B  show a particular application of the method of the present disclosure for fabricating hook-carriers for diapers. 
     A diaper  60  of the kind shown in  FIG. 10  usually comprises:
         a main or pant portion  62  having an inside face for coming into contact with the baby&#39;s skin and generally presenting an internal portion that is absorbent and an external portion that is waterproof;   a front strip  64  centered on a plane of symmetry P of the diaper, fastened to the front of the pant portion  62  and presenting on its outside surface fibers  65 , in particular loops, that are to co-operate with self-gripping hooks;   two tabs  66 , that are generally elastic, being fastened to the back of the pant portion  62  (on either side of the plane of symmetry P of the diaper  60 ); and   two hook-carriers  100 F′ provided with self-gripping hooks that are to co-operate with the loops of the front strip in order to close the diaper  60  (as shown in  FIG. 10 ), each hook-carrier  100 F′ being fastened to a respective one of the tabs  66 .       

     As shown in  FIG. 10 , a hook-carrier  100 F′ generally comprises a support portion  72  comprising fibers (generally in a non-woven material) and that is fastened to the tabs  66  (generally by heat sealing) and a fastener portion  74  that is provided on a front face with self-gripping hooks  12  that are to co-operate with the loop-forming fibers of the front strip  64  of the diaper  60 , in order to close said diaper. 
     In conventional manner, these two portions  10  and  20  can be assembled by attaching the rear face of a tape without hooks on a non-woven tape by means of heat sealing or adhesive. These methods present the drawback of requiring guide means for the tape that are accurate and reliable in order to ensure they are properly prepositioned prior to heat sealing or using adhesive. Furthermore, the traction strength of hook-carriers obtained in this way is sometimes insufficient, leading to the support and fastener portions unsticking or separating. 
     The assembly method of the present disclosure enables the above-specified problems to be solved. 
       FIG. 11  shows the method being applied on a hook-carrier fabrication line. 
     A first unit  10  in this example is in the form of a fastener tape of width  11  extending in a longitudinal direction X 1  and having a junction face  11   a  covered in a field  13  of hooks, and a second unit  20  that is constituted by a support tape made of non-woven material, of width  12  and extending in a longitudinal direction X 2 . 
     In a first step represented by the segment referenced T 1  in  FIG. 11 , the first and second tapes  10  and  20  are arranged parallel to each other and continuously superposed in a longitudinal or machine direction X over a contact zone C of width lc, the support tape  20  thus covering part of the junction face  11   a  of the fastener tape  10 . 
     In the contact zone C, the hooks  12  of the fastener tape  10  and the fibers  22  of the support tape  20  provide a self-gripping fastening F. In this example the fastening F extends over all of said contact zone C. 
     The two tapes  10  and  20  are superposed in such a manner that a free portion  18  of the fastener tape  10  carrying the hooks  12 , and a free portion  28  of the support tape  20 , are preserved on either side of the contact zone C. 
       FIG. 12A  shows the first and second units  10  and  20  at the end of this first step. The two tapes  10  and  20  are held in position relative to each other by the self-gripping fastening F, and there is no need for additional guide and holder means. 
     In the second step illustrated by the segment T 2 , the self-gripping fastening F is treated continuously in the machine direction X. 
     In this example, the treatment zone Z extends over the entire zone of contact C, and the treatment is performed by means of a wheel M, in particular a heater wheel, applying pressure against the two tapes  10  and  20  in order to deform the hooks  12  of the fastener tape  10  and/or the fibers  22  of the support tape  20  in order to secure them to each other. 
     The treatment could also be performed without applying heat, applying only pressure, or indeed by applying only heat, in particular remotely, or indeed by any other appropriate treatment. 
     Depending on the materials selected to form the fastener tape  10  and the support tape  20 , and depending on treatment conditions (temperature, applied pressure, etc.), the treatment may correspond to any of the examples shown and described above, in particular with reference to  FIGS. 7A to 7C, 8, and 9 . The characteristics described with reference to those examples are therefore not repeated here. 
     In order to avoid damaging hooks  12  present on the free portion  18  of the fastener tape  10 , the method is nevertheless preferably performed in the manner described with reference to  FIG. 8 . In other words: the fastener tape  10  is made of a material that melts at a temperature T 2  higher than the melting temperature T 1  of the support tape  20 . The self-gripping fastening F made between the two tapes  10  and  20  is treated by being subjected to an intermediate temperature that is higher than T 1  but lower than T 2 , such that the fibers  22  melt, and coat the hooks  12  that have themselves remained intact. 
     The resulting assembled structure  100 F is shown in  FIG. 12B . It has a first layer  51  constituted by the fastener tape  10  and comprising retention means for a self-gripping fastening (specifically the intact hooks  12  of the fastener tape  10 ), and a second layer  52  resulting from local deformation of the support tape  20 , coating the retention means  12  over an assembly zone  55  corresponding to the treatment zone in order to hold them captive and secure said layers to each other. 
     In a third step illustrated by the segment T 3 , the assembled structure  100 F is cut along a direction Y that extends substantially transversely relative to the machine direction X, thereby forming a plurality of hook-carriers  100 F′ for diapers. 
     The hook-carrier  100 F′ as obtained in this way is equivalent to the above-defined assembled structure  100 F, of which it forms a fragment. It comprises:
         a fastener portion  74  (formed by the free portion  18  of the fastener tape  10 ) comprising a substantially plane base defined by two main faces, a front face and a rear face, and hooks  12  projecting from the front face of said base;   a support portion  72  made of non-woven material (formed by the free portion  28  of the support tape) situated on the front side of the base and extending in a plane that intersects the hooks  12 ; and   between the fastener portion and the support portion (in a plane intersecting both the non-woven material and the hooks), an assembly zone.       

       FIGS. 13 to 16  show another particular application of the method of the present disclosure for fabricating an assembled structure comprising a base, in particular a sheet or a composite material, that is reinforced in the vicinity of the location of a hole. 
     A sheet or tarpaulin often presents holes are to receive fastener means such as elastic straps, bungees, or the like. 
     Such a sheet is generally reinforced in the neighborhood of such holes by generally annular hollow reinforcing inserts of the eyelet type. Such eyelets are conventionally fastened by clip-fastening, which results in local deformation of the sheet and thus in a loss of strength. 
     In other applications, it is also necessary to make holes in composite elements in order to fasten them to a support, thereby running the risk of locally damaging or weakening said elements. 
     The assembly method of the present disclosure constitutes an advantageous solution for solving this problem. 
       FIG. 13  shows a first unit  10  in the form of a reinforcing insert and a second unit  20  formed by a sheet of fibers, a non-woven material in this example. 
     The reinforcing insert  10  is for fastening to the sheet  20  at a location  26  for a hole, as shown diagrammatically in  FIG. 13 , in other words at a location  26  of the sheet  20  that already has a hole, or that is to have a hole made therein (which is more usual, and as described in the present example). 
     In the example shown, the reinforcing insert  10  is generally cylindrical in shape about a main axis A, and it defines a central through bore  16 . 
     The reinforcing insert  10  has at least one junction surface  11   a  extending substantially orthogonally to the main axis A and having a field of grip elements  12  projecting therefrom and suitable for co-operating with fibers  22  of the sheet  20  in order to provide a self-gripping fastening F. 
     In the example of  FIG. 12 , the junction surface  11   a  is an axial end face of the insert  10 . 
     More particular, the grip elements  12  are distributed over all of said end face  11   a.    
     The way the reinforcing insert  10  is assembled on the sheet  20  is shown in greater detail in  FIGS. 14A to 14D . 
     In a first step shown in  FIGS. 14A and 14B , the reinforcing insert  10  is brought into contact with the sheet  20  so that the grip elements  12  that project from its junction surface  11   a  come to co-operate with the fibers  22  of the sheet  20  in order to make a self-gripping fastening F. The bore  16  is placed substantially in register with the location  26  for the hole. 
     In a second step shown in  FIG. 14C , the self-gripping fastening F is treated. Depending on the materials selected for forming the sheet  20  and the grip elements  12  of the reinforcing insert  10 , and depending on treatment conditions (temperature, applied pressure, etc.), the treatment may correspond to any of the examples shown and described above, in particular with reference to  FIGS. 7A to 7C, 8, and 9 . The characteristics described with reference to those examples are therefore not repeated here. 
     In this example, the hooks  12  of the insert  10  melt under the effect of the treatment and coat the fibers  22  of the sheet  20  that remain substantially intact. The assembled structure  100 G comprising the sheet  20  reinforced by the reinforcing insert  10  is shown in  FIG. 14C . It comprises a first layer  51  constituted by the sheet  20  with retention means for a self-gripping fastening (specifically the fibers  22 ), and a second layer resulting from deformation of the hooks  12  of the insert  10 , which coat the retention means  22  in an assembly zone  55 . 
     Generally, in a third step shown in  FIG. 14D , the sheet  20  is then pierced at the location  26  for the hole, substantially along the main axis of the reinforcing insert  10 . 
     The sheet  20  is thus reinforced in the neighborhood of its hole location  26  but without being damaged or deformed around the reinforcing insert  10 . Furthermore, the insert  10  is fastened in reliable and permanent manner ensuring a long life for the assembly. 
     Nevertheless, the example shown is not limiting. 
     In  FIG. 16 , the insert  10  presents an external collar  17  at one of its axial ends that is referred to as its bottom end  10   a , and its junction surface carrying the gripper elements  12  is the face  17   a  of said collar  17  that faces towards its top end  10   b.    
     As shown in the figure, the insert is then inserted through an orifice that has already been made in the sheet  20  so that said junction surface  17   a  is brought into contact with the sheet  20  in order to provide the self-gripping fastening F for securing the two units together. 
     The method of the present disclosure may also be used for fabricating a composite material that is reinforced by at least one reinforcing insert. 
     Under such circumstances, the initial steps of the method are substantially identical to those described with reference to  FIGS. 13 and 14A to 14C . 
     In order to form the composite element, in a step shown in  FIG. 15A , the sheet  20  is associated with a third unit  30 , specifically a resin. By way of example, the sheet is placed in a mold (not shown) presenting the shape that is desired or the composite element, and it is impregnated with the resin  30  inside the mold. The resin then forms the matrix of the composite, with the fibers  22  of the sheet  20  constituting its reinforcing means. The assembled structure  100 H comprising the composite  90  reinforced by the reinforcing insert  10  is shown in  FIG. 15A . 
     The composite  90  as obtained in this way can then be pierced through the insert without risk of damage, as shown in  FIG. 15B . 
     In a variant, the second and third units  20  and  30  may also be assembled by performing the method of the present disclosure, in particular using the implementations described with reference to  FIGS. 1 to 9 . 
     By way of example, a composite element reinforced by at least one insert at a location for a hole may be fabricated in a manner similar to the example of  FIGS. 5A to 5C , the first unit being constituted by the insert  10 , the second unit being constituted by the sheet  20 , and the third unit  30  comprising a base with a field of grip elements adapted to co-operate with the fibers of the sheet  20 . 
     The first and second units form a first self-gripping fastening at the junction surface of the insert. 
     The second and third units form a second self-gripping fastening that preferably extends over their entire area of contact. 
     The first self-gripping fastening may be treated first, followed by the second, or vice versa. It is also possible for both self-gripping fastenings to be treated simultaneously. 
     Finally, the second and third units form a composite element in which the reinforcing means are formed by the fibers of the sheet, which have remained intact. The first unit is secured to the composite element in order to reinforce it at the location of its hole.