Patent Publication Number: US-RE46104-E

Title: Method of making a sandwich-type composite panel having a living hinge and panel obtained by performing the method

Description:
TECHNICAL FIELD 
     This invention relates, in general, to the field of panels having a sandwich-type composite structure with a cellular core and, in particular, to such panels and methods of making such panels so that the panels have a living hinge. 
     Overview 
     Sandwich-type panels having cellular cores have very important characteristics because of their light weight and high strength. Conventionally, such panels are constructed by sandwiching a cellular core having low strength characteristics between two skins, each of which is much thinner than the cellular core but has excellent mechanical characteristics. 
     The prior art discloses a method of making a panel of sandwich-type composite structure having a cellular core in a single processing step. In that method, the panel is made by subjecting a stack of layers of material to cold-pressing in a mold. As shown in  FIG. 1 , the stack is made up of: at least a first skin made of a stampable reinforced thermoplastics material, a cellular core made of a thermoplastics material, and a second skin also made of a stampable reinforced thermoplastics material. The stack may also include one or more external covering layers made of a woven or non-woven thermoplastic material. The skins are typically pre-heated outside the mold to a softening temperature. 
     Such a method is particularly advantageous because of the fact that it makes it possible, in a single operation, to generate cohesion and bonding between the various layers of the composite structure as shown in  FIG. 2 , and to shape the resulting panel while preserving all of the mechanical properties imparted by the cellular-core sandwich structure. 
     Panels of sandwich-type composition structure having a cellular core have rigidity characteristics sufficient to enable mechanical structures subjected to large stresses to be reinforced structurally without making them too heavy. Such panels are in common use in shipbuilding, aircraft construction, and rail vehicle construction. 
     To maximize the functionality of such panels, it is known, in particular, that hinges can be added so that the panels can be hinged to other panels. Such hinges are separate parts that are fixed to the panels by gluing, welding, riveting, or some other fastening technique. 
     Such hinges are fixed to the sandwich-structure composite panels in a separate and subsequent operation, after said panels have been formed. That subsequent operation requires an additional workstation, be it automated or otherwise, which increases, in particular, the manufacturing time and the manufacturing cost of the finished parts. 
     In addition, the fact that separate external parts are mounted on a composite panel of the sandwich-type is a source of quality defects, and thus adds to the cost of making such panels. 
     Published U.S. Patent Application 2005/0189674 discloses a method of making a composite panel of sandwich structure provided with a hinge. The panel includes a stack made up of a first skin of a reinforced thermoplastics material, a cellular core made of a thermoplastics material, and a second skin made of a reinforced thermoplastics material. The panel is formed by pressing the stack in a mold. The first and second skins are preheated to a softening temperature. As shown in  FIGS. 3 and 4 , after the panel has formed, an incision is made at a determined place in the panel so as to cut through one of the first and second skins, and substantially through the entire thickness of the cellular core, while leaving the other skin intact so that it forms a living hinge between two portions of the incised panel. 
     Other U.S. patent documents related to the present invention include: U.S. Pat. Nos. 5,502,930; 5,915,445; 6,050,630; 6,102,464; 6,435,577; 6,537,413; 6,655,299; 6,682,675; 6,748,876; 6,790,026; 6,682,676; 6,825,803; 6,843,525; 6,890,023; 6,981,863; 7,090,274; 7,909,379; 7,919,031; 8,117,972; 2006/0255611; and 2008/0185866. 
     One problem associated with living hinges of the prior art panels is that the panels are quite strong but the living hinges may not be strong enough during extended use. Also, the cost of making such living hinges may be significant on a mass production basis as additional process steps may be required to make the living hinges outside of the mold which makes the panels. 
     SUMMARY OF EXAMPLE EMBODIMENTS 
     An object of at least one embodiment of the present invention is to provide a low-cost, high volume method of making light-weight and strong sandwich-type composite panels having living hinges and panels obtained by performing the method wherein the resulting living hinges are strong enough so they function properly during extended use without the need for additional materials or additional post processing steps. 
     In carrying out the above object and other objects of at least one method embodiment of the invention, a method of making a sandwich-type composite panel having a living hinge is provided. The method includes providing a stack including first and second reinforced thermoplastic skins and a thermoplastic cellular core disposed between the skins. The method also includes heating the skins to a softening temperature wherein the first skin is stretchable when heated to the softening temperature. The method further includes applying a pressure to the stack after the step of heating to form the composite panel. The method still further includes crushing a portion of the composite panel at a predetermined location simultaneously with the step of applying to locally compact and separate the cellular core at the predetermined location to form two side portions of the panel and a crushed portion of the panel between the two side portions. The first skin stretches during the step of crushing while remaining intact between the two side portions. The first and second skins are bonded together at the predetermined location to form the living hinge between the two side portions. 
     Further in carrying out the above object and other objects of at least one method embodiment of the present invention, a method of making a carpeted sandwich-type composite panel having a living hinge is provided. The method includes providing a stack including first and second reinforced thermoplastic skins, a thermoplastic cellular core disposed between the skins and a thermoplastic covering layer for covering the second skin. The method also includes heating the skins to a softening temperature wherein the first skin is stretchable when heated to the softening temperature. The method further includes applying a pressure to the stack after the step of heating to form the carpeted composite panel. Finally, the method includes crushing a portion of the composite panel at a predetermined location simultaneously with the step of applying to locally compact and separate the cellular core at the predetermined location to form two side portions of the panel and a crushed portion of the panel between the two side portions. The first skin stretches during the step of crushing while remaining intact between the two side portions, The covering layer and the first and second skins at the predetermined location are bonded together to form the living hinge between the two side portions. 
     The first and second skins may be chemically bonded to each other at the predetermined location to form the living hinge. 
     The covering layer may be a resin carpet for covering the second skin. The resin may be polypropylene. 
     The cellular core may be a honeycomb core. 
     Each or one of the skins may be fiber reinforced. 
     The thermoplastic of the skins, the carpet and the core may be polypropylene. 
     The panel may have a thickness in the range of 5 to 25 mm. 
     The living hinge may have a thickness less than 3 mm, such as 2 mm or less. 
     At least one of the skins may be a woven skin such as a woven polypropylene skin. 
     At least one of the skins may be a woven polypropylene skin. 
     The pressure may lie in a range including 10×10 5  Pa to 30×10 5  Pa. 
     Further in carrying out the above object and other objects of at least one carpeted panel embodiment of the present invention, a carpeted panel of a composite-type composite structure is made by performing one of the above-noted methods. The panel includes a stack having a first skin of a reinforced thermoplastic material, a cellular core of a thermoplastic material, a second skin of a reinforced thermoplastic material and a covering layer of a thermoplastics material. The panel also includes a living hinge defined by the crushed portion. 
     Still further in carrying out the above object and other objects of at least one panel embodiment of the present invention, a panel of sandwich-type composite structure is made by performing another one of the above-noted methods. The panel includes a stack having a first skin of a reinforced thermoplastics material, a cellular core of a thermoplastics material, and a second skin of a reinforced thermoplastics material. The panel also includes a living hinge defined by the crushed portion. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated, various embodiments may include all, some or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view showing various separate layers of a prior art stack of thermoplastic-based layers of material; 
         FIG. 2  is a top perspective sectional view, of the stack of  FIG. 1  after low-pressure, cold compression molding; 
         FIGS. 3 and 4  are side views, partially broken away and in cross section, of a prior art sandwich-type composite panel having a living hinge and method of making the living hinge; 
         FIG. 5  is an environmental view, partially broken away, showing a pair of carpeted sandwich-type composite panels having living hinges constructed in accordance with at least one method embodiment of the present invention; 
         FIG. 6  is a side view, partially broken away and in cross section, of a stack of material positioned between two halves of a mold in its open position wherein one of the mold halves has a protrusion or relief for forming the living hinge of the panel; 
         FIG. 7  is a view similar to the view of  FIG. 6  but with the mold in its closed position to form the panel and its living hinge in accordance with at least one method embodiment of the invention; 
         FIG. 8  is an enlarged view of a portion of the view of  FIG. 7  to show the living hinge of  FIG. 7  in detail; 
         FIG. 9  is an enlarged view, similar to the view of  FIG. 8 , but showing a second embodiment of a living hinge wherein one of the skins has been pushed into and merged with the other skin to form a living hinge of reduced thickness as compared to the living hinge of  FIG. 8 ; and 
         FIGS. 10a-10f  are side views, partially broken away and in cross section, of various alternative sizes and shapes for the crushing protrusion of the mold of  FIGS. 6-9 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring now to the  FIGS. 5-9 , in general, one embodiment of a method of making a sandwich-type composite panel, two of which are generally indicated at  10  in  FIG. 5 , having a living hinge  12  is provided. The hinged panels  10  are shown in  FIG. 5  as forming separate parts of an automotive vehicle load floor, generally indicated at  13 . However, it is to be understood that one or more panels  10  constructed in accordance with at least one embodiment of the present invention may be used in a wide variety of environments. The panels  10  in  FIG. 5  are shown carpeted but at least one embodiment of the invention does not require such carpeting. 
     The method may include providing a stack of material, generally indicated at  14  in  FIG. 6 , located or positioned within a mold, generally indicated at  22 . The stack  14  includes first and second reinforced thermoplastic skins  16  and  18 , respectively, a thermoplastic cellular core  20  disposed between the skins  16  and  18  and a covering layer of  21  thermoplastics material which covers the second skin  18 . The skins  16  and  18  are heated typically outside of the mold  22  to a softening temperature. The mold  22  is preferably a low pressure compression mold which performs a thermo compression process on the stack  14 . The mold  22  has an upper mold half or part  24  and a lower mold half or part  26 . The upper mold part  24  has a protrusion  28  extending towards the lower mold half  26  for crushing purposes as described in detail below. 
     The first skin  16  is stretchable when heated to the softening temperature and stretches when a pressure is applied to the stack  14  by the inner mold surfaces of the mold halves  24  and  26  including the outer surface of the protrusion  28  within the mold  22  to form the composite panel  10  with the living hinge  12 . A portion  32  of the composite panel  10  ( FIG. 6 ) is crushed at a predetermined location simultaneously with the step of applying the pressure to locally compact and separate the cellular core  20  at the predetermined location to form two side portions  34  and  36  ( FIG. 7 ) of the panel  10  and the crushed portion  32  therebetween. The first skin  16  stretches during the step of crushing while remaining intact between the two side portions  34  and  36 . The first and second skins  16  and  18 , respectively, of the crushed portion  32  are chemically bonded together to form the living hinge  12  at the predetermined location between the two side portions  34  and  36 . 
     As previously mentioned, the stack  14  of  FIG. 6  may also preferably include the thermoplastic covering layer  21  for covering the second skin  18  when making a carpeted panel such as the carpeted panels  10  of  FIG. 5 . While not shown, the stack  14  may also include a second thermoplastic covering layer for at least partially covering the first skin  16  so that a cover portion of the resulting panel  10  is carpeted on its top and bottom surfaces 
     The covering layer  21  may be a resin carpet and the resin may be polypropylene. One side or both sides of the cover portion of the panel  10  may be covered with an outer covering layer made of a woven or non-woven material (typically of the carpet type). 
     The cellular core  20  may be a honeycomb core. In this example, the cellular core  20  is an open-celled structure of the type made up of tubes or of a honeycomb, and it is made mainly of polyolefin and preferably of polypropylene. It is also possible to use a cellular structure having closed cells of the foam type. 
     Each of the skins  16  and  18  may be fiber reinforced. The thermoplastic of the skins  16  and  18 , one or more covering layers  21  and the core  20  may be polypropylene. At least one of the skins  16  and  18  may be a woven skin, such as polypropylene skin. The first and second skins  16  and  18  may be reinforced with fibers, e.g., glass fibers, carbon fibers or natural fibers. The first and second skins  16  and  18  may advantageously be made up of woven glass fiber fabric and of a thermoplastics material. 
     The resulting panel  10  may have a thickness in the range of 5 to 25 mm and the crushed portion of the panel  10  may have a thickness less than 3 mm such as 2 mm or less. 
     In one example method of making such a panel, the panel  10  is formed by pressing the stack  14  in the low-pressure, cold-forming mold  22 , the stack  14  being made up of the first skin  16 , the cellular core  20 , and the second skin  18 . The stack may be pressed at a pressure lying in the range 10×10 5  Pa. to 30×10 5  Pa. The first and second skins  16  and  18  are preferably pre-heated in the method to make them malleable and stretchable. Advantageously, in order to soften the first and second skins, heat is applied to a pre-assembly constituted by the stack made up of at least the first skin  16 , of the cellular core  20 , and of the second skin  18  so that, while the panel  10  is being formed in the mold  22 , the first and second skins  16  and  18  have a forming temperature lying approximately in the range 160° C. to 200° C., and, in this example, about 180° C. 
     The protrusion  28  may have other shapes in cross section as shown in  FIGS. 10a-10f  in order for the mold  22  to perform the crushing step during the pressure application step. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.