Abstract:
A seat cushion, in particular for folding automobile vehicle seat, and its method of manufacture, the cushion having a lower face adapted to be in contact with a supporting frame and covered with a protective film of expanded synthetic plastic material that is resistant to wear and adheres to the expanded synthetic plastic material of the cushion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a seat cushion, in particular for automobile vehicles, essentially made of an expanded synthetic plastic material, such a polyurethane foam or the like. 
     2. Description of the Prior Art 
     A cushion of this type is generally associated with a supporting frame formed by a metal grid which is pressed onto the lower face of the cushion or embedded in the expanded material thereof. 
     A cover of woven fabric or the like covers the upper face and the sides of the cushion and is fixed, usually stapled, to the frame, whether the latter is applied to the lower face of the cushion or embedded in the expanded material thereof (in which case parts of the frame are flush with the surface of the cushion and provide stapling points). 
     The lower face of the cushion is generally covered with a protective film (because the foam is mechanically weak) which is simply held between the frame and the cushion when the frame is external to the cushion or which is fixed with the cover to the parts of the frame provided for this purpose when the latter is embedded in the material of the cushion. 
     In all cases the protective film is not fixed directly to the cushion and can therefore move relative to it, becoming locally deformed and taking on a less than perfect esthetic appearance, giving the impression of defective manufacture. This is particularly important when the cushion forms the seat cushion of a folding automobile vehicle seat because the lower face of the cushion is substantially vertical and clearly visible when the seat is in the folded position, which is prejudicial to the brand image of the vehicle and its manufacturer. 
     OBJECT OF THE INVENTION 
     The object of the invention is to provide a simple, effective and inexpensive solution to the above problem. 
     SUMMARY OF THE INVENTION 
     For this purpose, the present invention provides a seat cushion, made of an expanded synthetic plastic material and having a lower face associated with a supporting frame, wherein at least part of the lower face of the cushion is covered with a protective film of synthetic plastic material that is resistant to wear and adheres to the expanded synthetic plastic material of the cushion. 
     The adherence of the film to the expanded plastics material of the cushion and its resistance to abrasion guarantee a long service life of the cushion, the lower face of which retains a clean and defect-free appearance. When the supporting frame is applied to the lower face of the cushion, the film is interposed between the supporting frame and the expanded material of the cushion, it mechanically protects the expanded material from damage that could be caused by the frame and reduces or eliminates the noise that could otherwise be caused by the material of the cushion rubbing on the frame or on the floor of the vehicle. 
     When the supporting frame is embedded in the plastics material of the cushion near the lower face thereof, the film covers the lower face of the cushion and protects it from any damage. 
     In a preferred embodiment of the invention, this film is made of an expanded plastics material and is heat-formed. 
     The expanded material is preferably a chemically reticulated polyethylene having a density in the range from approximately 70 kg/m 3  to approximately 120 kg/m 3 . 
     This constitutes an excellent compromise between the weight, thickness and mechanical strength of the film. 
     The invention also proposes a method of manufacturing a seat cushion as claimed above, this method consisting in supplying a plastics material that can be expanded into a mold in the shape of the cushion to be made, placing in said mold, on a wall corresponding to the lower face of said cushion, a protective film of a material resistant to wear before supplying said plastics material that can be expanded into said mold, and causing said film to adhere to the supplied plastics material by virtue of chemical compatibility or by adhesive bonding by means of an appropriate adhesive. 
     It is of course advantageous for the material of the film to adhere naturally to the plastics material of the cushion. Failing this, it is sufficient to deposit a film of an appropriate adhesive material onto the face of the film that is to be in contact with the supplied plastics material that can be expanded before placing the film in the mold. 
     The invention enables economic manufacture of an expanded plastics material seat cushion with a lower face which has a covering of durable appearance and which is resistant to abrasion and which can be applied to a supporting frame without being damaged thereby. 
     The invention therefore applies to all seat cushions made of an expanded plastics material and more particularly to cushions which form part of a folding automobile vehicle seat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Further features and advantages of the invention will be apparent from the following particular description of a preferred embodiment of the invention as illustrated in the corresponding accompanying drawing in which: 
     FIG. 1 is a diagrammatic perspective view of the lower face of a seat cushion in accordance with the invention. 
     FIG. 2 is a longitudinal sectional view taken along line II—II of FIG. 1; and 
     FIG. 3 is a transverse cross section of a second embodiment of the invention corresponding to a view taken along line III—III of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This embodiment of a cushion in accordance with the invention, which is shown inverted so that its lower face is visible, forms part of a folding automobile vehicle seat and essentially comprises a part  10  molded from an expanded plastics material, for example polyurethane foam, comprising a seat part  12  of substantially rectangular or square shape joined on three sides to a peripheral rim  14 . 
     The lower face  16  of the cushion is designed to be supported by a supporting frame  18  (shown diagrammatically in FIG. 1, but omitted in FIGS. 2 and 3) which is generally a grid made of metal wires having a diameter in the order of 6 mm and which is sufficiently strong to support the weight of a person sitting on the cushion. The grid is also used to staple on a cover of woven fabric or the like which covers the cushion. 
     In accordance with the invention, a strong and light protective film  20  covers the lower face  16  of the part  12  of the cushion and adheres to or is glued to all of the surface thereof, to protect it against mechanical damage (impact, rubbing on a rigid surface, etc) and to form a durable coating of clean appearance. 
     In the example shown, the film  20  is disposed between the frame  18  and the cushion part  12 , protects the latter from rubbing on the frame  18  and prevents squeaks caused by the polyurethane foam rubbing on the frame. 
     The film is advantageously made of a thermoplastics material so that it can be heat-formed to the exact shape of the lower face  16  of the cushion part  12 . To reduce the weight whilst retaining adequate thickness, the thermoplastics material is expanded. To improve its mechanical characteristics, the material can be reticulated, preferably by chemical agents or possibly by physical agents. In a prefered embodiment, reticulated expanded polyethylene is used having a density in the range from approximately 70 kg/m 3  to approximately 120 kg/n 3 , preferably in the order of 90 kg/m 3 , the thickness of the film  20  then being in the range from approximately 2 mm to approximately 3 mm. The density of the polyurethane foam forming the cushion is in this embodiment in the order of 40 kg/m 3  to 50 kg/m 3 . 
     The method of manufacturing the cushion in accordance with the invention is as follows: 
     The protective film, which is available off the shelf in long lengths and with the required thickness, is passed through an oven in which it is quickly heated to its softening temperature, from where it is transferred to a heat-forming mold and then to a cutting press. Each heat-formed sheet is cut and then placed in a mold for manufacturing the cushion by pouring or injecting a plastics material that can be expanded, for example polyurethane. The softening of the surface of the material of the film  20  resulting from its heating in the mold and its contact with the poured or injected material encourages its adhesion to the material. When the film  20  is of reticulated expanded polyethylene and the cushion is of expanded polyurethane, they adhere totally at an interface temperature in the order of 100° C. to 120° C. in the mold without it being necessary to use an adhesive material. 
     If the materials of the film and the cushion are incompatible or their adhesion is defective, a film of an appropriate adhesive material is deposited onto the face of the film  20  that is to come into contact with the material of the cushion, the film is then placed in the mold and the plastics material which can be expanded is poured or injected into the mold, as mentioned above. 
     In a different embodiment of the invention and as shown in FIG. 3, the supporting frame  18  is embedded within the cushion material instead of being applied to its lower face  16  or to the film  20 . In this case, to manufacture the cushion, the first step is to place the heat-formed film  20  in the mold, after which the frame is placed in the mold in the required manner relative to the film and the plastics material that can be expanded is poured or injected into the mold. 
     In all cases, after reticulating the material that can be expanded, the mold is opened and the unit assembly comprising the film  20  and the cushion  10  is removed. 
     The film  20  can cover the lower face  16  of the seat part  12  of the cushion and at least part of the flanks of the part  12 , as shown in the drawing. 
     Alternatively, it can also cover all or part of the lower face of the peripheral rim  14 , as shown in chain-dotted line in FIGS. 2 and 3.