Patent Publication Number: US-2021186218-A1

Title: Chair with flexible lumbar support

Description:
The invention relates to a chair with flexible lumbar support. The invention more particularly relates to a chair with a seat back, a fixed structure, non-folding, lightweight, but providing efficient lumbar support adaptive to the user. 
     According to prior art, a chair with a fixed structure may for example be composed of wood and comprise a seat back. According to one example embodiment, the seat back comprises two uprights generally prolonging the back legs, these uprights being connected by cross pieces. Said cross pieces thus perform 3 main functions:
         a mechanical function to keep the seat back and the chair as a whole rigid;   a function to support the user&#39;s back when the user is seated on the chair;   a gripping function, such that the seat base can be gripped by the seat back, particularly to move it.       

     These rigid cross-pieces make it impossible to obtain efficient dorsolumbar support adaptive to the user&#39;s morphology. However, efficient dorsolumbar support is an essential element in determining whether or not a chair is comfortable. To achieve this, in prior art, the seat back is lined with a lumbar support cushion installed between the uprights. Other seat back constructions, particularly in the field of office chairs, can also provide adaptive and efficient lumbar support. All these solutions according to prior art have the disadvantage that they increase the weight of the chair and detract from its aesthetics. 
     The invention aims to overcome the disadvantages of prior art and to achieve this, relates to a chair comprising: 
     a. a tubular frame; 
     b. a seat base fixed to said frame, said seat base and said frame forming the seat; 
     c. a tubular arch forming the seat back and connected to two of the legs of the frame; 
     d. an elastic dorsolumbar support comprising two ends, one of which is free and the other is connected to the seat; 
     and in which the frame and the tubular arch are composed of a composite material with fibre reinforcement, comprising a natural fibre, particular a plant fibre 
     Thus, the tubular arch of the seat back provides stiffness and gripping functions, while the dorsolumbar support that is not connected to this arch provides sufficient elasticity and a “spring effect” such that it can adapt to the user&#39;s morphology while providing efficient support. The composition consisting of a composite material confers sufficient stiffness and strength on the chair to prevent the need to use cross-pieces like those used on a wooden chair according to prior art, and thus enable sufficient elastic movement to provide the dorsolumbar support to obtain this support. The use of a natural origin reinforcing fibre means that the chair can be manufactured while respecting the principle of sustainable development, particularly in terms of carbon balance and exploitation of natural resources, at least as advantageous as a wooden chair, while assuring the chair is light weight, comparable with or even lighter than wooden chairs or chairs with a steel structure. 
     The invention is advantageously used for the embodiments presented below, that can be considered in isolation or in any technically feasible combination. 
     Advantageously, the connection between the dorsolumbar support and the seat is a removable connection. Thus, the chair is adaptable in terms of firmness and its aesthetics, through the use of different lumbar supports. 
     Advantageously, the tubular section of the arch can vary between its connections to the two legs. Thus, the arch is optimised in terms of strength, weight and stiffness depending on the composite material used. Similarly, the tubular section of the frame legs varies between their ends that will be in contact with the floor and their connection to the seat base. 
     Advantageously, the seat base is composed of a plastic material. This embodiment can reduce the weight of the chair and also adapt it to outdoor use and make economic assembly and fabrication methods possible. 
     According to another embodiment, the seat base is composed of a metallic material. The embodiment makes it possible to give the chair a “bistro” style. 
     Advantageously, the seat base comprises a connecting ring with the frame and a part called the seat cushion, assembled with said ring. This embodiment makes it possible to customise the seat cushion, and particularly to make the seat cushion and the ring from different materials, with different colours or different finishes. 
     In alternative embodiments, the dorsolumbar support is also composed of a plastic material that may or may not be reinforced by fibres. Thus, depending on the nature of the constituent material, said dorsolumbar support is more or less flexible, to adapt to the support required by the user and corresponds to different aesthetics of the chair according to the invention. 
     The invention also relates to a preconstituted assembly, or kit, comprising a chair for which the connection of the dorsolumbar support to the seat can be disassembled, and several dorsolumbar supports. Thus, said chair can be adapted to modify its firmness and aesthetics. 
     The invention also relates to a preconstituted assembly or kit comprising a chair and several seat cushions. This embodiment alone or in combination with the previous embodiment makes it possible for the user to customise the chair. 
    
    
     
       The invention is described below in its different preferred embodiments, that are in no way limitative, with reference to  FIGS. 1 and 2 , in which: 
         FIG. 1  shows a front view of an example embodiment of the chair according to the invention; 
         FIG. 2  shows an exploded partial left side view of the chair in  FIG. 1 ; and 
         FIG. 3  is a partial front view of an example embodiment of the chair according to the invention comprising an arch in two parts, a detailed view shows an example of how the two parts of the arch are assembled. 
     
    
    
       FIG. 1 , according to one example embodiment, the chair according to the invention comprises a seat base ( 110 ) preferably composed of a single plastic piece. For example, the plastic material forming said seat base is a biosourced polymer such as a polyethylene, a polyamide, cellulose acetate or a methyl polymethacrylate, for example such biosourced products are distributed by the Arkema® group, 420 rue d&#39;Estienne d&#39;Orves, 92705 Colombes France, while other suppliers offer similar products. According to one particular embodiment, the material forming said seat base is composed of a matrix of a first biosourced polymer reinforced by fibres of a second biosourced polymer with a higher melting temperature than the first polymer. Said seat base is advantageously composed of a single moulded part and thus contributes to the stiffness of the chair. According to one particular embodiment, the seat base ( 110 ) is substantially in the shape of a bowl and comprises a stiff ring frame ( 111 ) and a more flexible slightly curved part ( 112 ) acting as a seat cushion. According to one alternative embodiment, the seat base of the chair according to the invention is composed of a lightweight metallic material that can be injection moulded, for example a magnesium alloy. 
     According to one particular embodiment, the ring ( 111 ) and the seat cushion ( 112 ) are two separate parts assembled by clipping, bolting or gluing. This embodiment makes it possible to customise the chair while rationalising production by keeping a maximum number of parts common to the different models. As non-limitative examples, the ring is composed of a plastic material and the seat cushion is composed of a metallic material, or the ring is composed of a metallic material and the seat cushion is made of cane formed from plastic or natural fibres. 
     According to one example embodiment, the chair according to the invention comprises a frame comprising 4 legs ( 121 ,  122 ,  123 ,  124 ). Alternatively, the frame comprises 3 legs. Said legs are tubes preferably composed of a composite material with a fibrous stiffener. Thus, the legs are stiff and lightweight. Preferably, the composite material forming said legs ( 121 ,  122 ,  123 ,  124 ) comprises a biosourced polymer matrix, for example a polyamide, particularly PA11, or a polyethylene, reinforced by continuous fibres, entirely or partially of plant origin. As a non-limitative example, said plant fibres may be linen fibres, jute fibres, hemp fibres, sisal fibres or bamboo fibres. The legs are assembled to the seat base thus forming the seat of the chair according to the invention. Advantageously, the material forming the legs and the material forming the seat base are chosen such that they can easily be assembled by welding, for example by selecting thermoplastic polymer matrices, or by thermal fusion bonding. This embodiment enables a very slender style and is used in preference when the seat base is made of a transparent material. 
     Alternatively or additionally, the legs can be assembled to the seat base by a mechanical assembly, for example by insertion of the legs into sheaths made when the seat base is moulded. In this case, the seat base comprises a smooth outside appearance in the form of a bowl, and a functional face on the inside of the bowl shape, comprising arrangements adapted to the assembly or ribs. According to this embodiment, the seat base is made by using an injection moulding process using dynamic induction heating of the mould as described in document EP 2 861 399. 
     The chair according to the invention comprises a tubular arch ( 130 ) forming the back of said chair, and connected to the two legs ( 123 ,  124 ) of the frame. Depending on the variant embodiments, the connection of the arch to the legs ( 123 ,  124 ) is made by integrating the arch and legs assembly into a single piece, in this case the seat comprises appropriate means of making the connection with this part. According to another variant, the connection of the arch ( 130 ) with the legs ( 123 ,  124 ) is made by sheaths moulded with the seat base, such that the seat base, the frame and the arch, after assembly, form a rigid assembly without the need for a cross piece. 
     According to one embodiment, said assembly by insertion is complemented by gluing or welding, depending on the nature of the materials used. Thus, the structure of the chair according to the invention can easily be assembled without tools, which also facilitates its storage and delivery, particularly for mail order sales. The tubular arch ( 130 ) is made from a composite material similar to that used to make the frame. Advantageously, the fibre content and the nature of the reinforcing fibres or the mixture of reinforcing fibres used in the legs and in the arch are different, to achieve appropriate mechanical properties of these components or for aesthetic reasons. The use of reinforcing fibres from plant origin makes the frame and the arch particularly aesthetic without it being necessary to paint them. 
     According to this example embodiment, the dorsolumbar support ( 140 ) extends substantially inside the space delimited by the tubular arch ( 130 ), such that said arch forms a means of gripping the chair so that it can easily be moved, particularly because the materials from which the chair is made enable light weight construction. 
     According to another example embodiment, the seat base ( 110 ) is also made of a composite material reinforced by fibres comprising plant fibres. According to this particular embodiment, the seat base is made by a process for compaction and consolidation of a stack of fibrous plies, making use of dynamic induction heating of the mould, as described in document EP 2 694 277. This application method also enables the integration of a printed décor into the stratification of the composite forming the seat base, particularly on the part ( 112 ) acting as a cushion, on which the décor cannot then be degraded. 
     The use of a method involving induction heating of the mould to obtain uniform heating over the entire surface of the mould, and thus to obtain a very attractive appearance, without any defect in the appearance or discolouration of the visible face of the seat base, regardless of whether or not it comprises a technical face, and regardless of whether or not it is made of plastic, composite or a light metal alloy. When the seat base comprises a technical face, this technical face is advantageously insert moulded, particularly by injection, on the preform. 
     Obtaining a uniform temperature in the mould and subsequently control of the viscosity of the moulded material, also makes it possible to mould décor in upstanding or indented relief on the different elements forming the chair according to the invention. 
     Advantageously, the tubes forming the legs and the arch are also made using a dynamic induction heating method as described, for example, in document FR 2 915 053, using a woven preform comprising polymer fibres mixed with reinforcing fibres. These methods make it possible to fabricate the structure of the chair quickly in a production line. The section of the tubes forming the legs and the arch is an ovoid or polygonal cross-section that is advantageously variable between the two ends of each of these components. In order to obtain this variation of the cross-section, the braid forming the preform is made on a solid core or in the form of an inflatable bladder reproducing the change in cross-section. 
     The use of plastic materials and composite materials shaped in moulds for fabrication of the structure of the chair according to the invention makes it possible to make dimensionally precise parts that are easy to assemble without any play, that are not sensitive to humidity and that have stable dimensions. Thus, although lightweight, the chair according to the invention is long lasting. 
     The rigid structure of the seat back and the seat make it possible to integrate a dorsolumbar support ( 140 ), that according to one example embodiment is contained in the space delimited by the arch. Said lumbar support ( 140 ) is composed of a polymer material that may or may not be reinforced by fibres containing natural fibres. According to one example embodiment, said support is fabricated by a compaction and consolidation method as described in document EP 2 694 277 and comprises a décor integrated in the stratification. Said support ( 140 ) is connected to the seat, for example by nesting one of its ends in a well or a sheath in the seat base or by clipping and/or bolting on the frame ( 111 ) of said seat base. 
       FIG. 2 , according to one example embodiment of the dorsolumbar support ( 140 ) and the arch ( 130 ) are curved towards the back of the chair. According to this embodiment, the arch is made by moulding in a slide mould to enable assured removal from the mould. 
       FIG. 3 , according to one alternative embodiment, the tubular arch ( 330 ) is made in two parts ( 331 ,  332 ), the two parts being connected by an assembly part ( 335 ), advantageously obtained by injection moulding of a biosourced polymer, that may or may not be reinforced by short fibres, themselves biosourced. This embodiment can avoid the use of a slide mould to make the tubular arch and thus reduce the investment necessary for production of the chair according to the invention. 
     With reference once again to  FIG. 2 , the free end of the dorsolumbar support and the nature of its constituent material are such that said support has a flexibility that enables it to adapt to the morphology of the user of the chair according to the invention. Said dorsolumbar support ( 140 ) being assembled with the seat, advantageously without tools by clipping or insertion, the chair according to the invention is advantageously marketed as a kit with different shapes of dorsolumbar supports made of different materials, with different stiffnesses or different decors. Advantageously, said kit is marketed as an on line sales model in which the customer selects a seat base and dorsolumbar support assembly with a frame and an arch so as to form a customised chair, that can easily be disassembled by a message service and assembled by the customer. 
     The above description and example embodiments show that the invention achieves the stated purpose, namely a comfortable, lightweight chair comprising an easily customised dorsolumbar support that can be made on a production line.