Method of manufacturing a seat element by moulding a frame on upholstery, and seat element made thereby.

The present invention relates to a method for producing a seat element or the like using a laceration-resistant lining, of the type described in French patent application No. 79 02 063 filed on January 26, 1979 in the name of Applicant. It also relates to the seat element obtained by said process.

It will be recalled that the trim element described in the French patent application already cited involves at least three very distinct elements, namely:<ul id="ul0001" list-style="none"><li>¹) A relatively thick, compact plastic cover layer which, due to its thickness and compactness, constitutes a first obstacle to laceration. This covering layer, which is not subjected to any stress whatsoever in tension, has a low elasticity in its plane but good flexibility.</li><li>2) A network, formed of a continuous sheet of metal springs, in a spiral (helical) shape, the axes of which are parallel to the cover layer of compact plastic material, and whose turns are intertwined with each other, so as to obtain, in plan view, a structure in the form of a checkerboard, with very slightly extensible meshes, making it possible to stop the penetration and the progression of a sharp object (the springs cannot be separated to allow the passage of said object), the turns of said springs coming, from one side, substantially flush against the underside of the cover layer.</li><li>3) An intermediate bonding layer between the covering layer and the sheet of springs, this layer being made of a plastic foam of thickness less than the diameter of the turns of the springs of said sheet and adhered, on one side to the underside of the cover layer of compact plastic material and partially coating the turns of the spring ply (over a fraction of the thickness of the spring ply).</li></ul>

To make a seat element using such a trim, it is necessary to cut the trim to dimensions and then fix it, by at least part of its periphery, to the rigid structure of the seat or on a rigid element such as a frame intended to be attached to the seat structure.

It can be seen that, in the case of the lining element described above, this fixing turns out to be a delicate operation due to the part of the sheet of springs emerging, projecting, from the intermediate layer of plastic foam. .

The use of the usual methods to ensure this fixing such as pinching, nailing, screwing or even welding of the sheet of springs on a peripheral frame has many drawbacks, namely:<ul id="ul0002" list-style="none"><li>- the employment of a relatively large workforce,</li><li>- relatively high manufacturing costs,</li><li>- the difficulty in achieving a seat with a light structure and having a pleasant aesthetic appearance.</li></ul>

The invention therefore aims to eliminate these drawbacks. To this end, it proposes a method consisting in molding, on the periphery of the lining, a rigid frame of a suitably chosen plastic material. It is clear that such a molding involves solving the problem posed by the part of the sheet of springs protruding outside the intermediate layer. Indeed, because of the springs, it is hardly possible to design a mold coming to assemble, in a sealed manner, on the lining. The molding material will therefore flow into the free space located at the level of the spring ply.

To overcome this obstacle, the method according to the invention therefore comprises the following operations:<ul id="ul0003" list-style="none"><li>- Cutting the filling,</li><li>- The deposition, at a slight distance from the peripheral edge, on the side where the sheet of springs emerges, of a plastic cord having elasticity properties, this cord adhering to the intermediate layer of plastic foam, and coming to coat, by exceeding it, the part of the sheet of springs leaving said intermediate layer. This cord is in particular intended to serve as a sealing element during the molding of the rigid frame.</li><li>- The establishment of the peripheral edge of the lining in the cavity of a peripheral mold, the seal between the lining and the mold being ensured, on one side by the contact of the mold wall with the external face of the lining, and, on the other side, by the contact of the mold wall on the sealing bead, and</li><li>- Pouring or injecting a suitably chosen plastic material inside the mold.</li></ul>

According to another characteristic of the invention, a stress is exerted on the lining, during the positioning and molding phase, with a view to giving it, by varying its flexibility, a curved shape. This curved shape will then remain after the setting of the plastic constituting the frame.

In order to obtain a good compromise, resistance to laceration, resistance to wear, flexibility and comfort, the invention proposes to use for the realization of the network, springs having a wire diameter of the order of 0, 5 to 1.5 mm and a diameter of turns from 10 to 20 mm.

Furthermore, the turns of the springs will preferably be coated in the intermediate layer of plastic foam over 3 to 1 of their diameter. Below 50%, the sheet will tend to peel off (tearing of the plastic foam). Above 80%, the spring wires may damage the foam.

An advantage of the previously described packing resides in that it combines, in a very particular way, the flexibility of the compact plastic covering layer and the flexibility of the spring ply.

Indeed, if one causes a bending of the lining, this will oppose a restoring force which will tend to return it to its initial position, this restoring force consisting of the result of the flexibility of the covering layer of material. plastic and the elasticity of the part of the coils of the springs which is not coated in the intermediate layer of plastic foam. This property has an important advantage, namely: if a slit is made in the cover layer, for example using a knife, this slit will tend to close thanks to the flexibility of the whole of the trim and will therefore remain practically invisible.

In its version proposed in the French patent application already cited, the sheet of springs is constituted by a plurality of helical springs with parallel axes arranged side by side, and the turns of each of the springs of which are intermingled with the turns of the two springs adjacent to it. The intermingling of these turns is obtained by rotating each of the springs around its axis so that it comes to engage in the turns of the springs which are adjacent to it.

However, according to an advantageous embodiment of the invention, the spring ply can be formed by an intermingling of two spring plies, such as that previously described, the springs of the first ply being oriented perpendicular to the springs of the second tablecloth. This solution has the following advantages in particular<ul id="ul0004" list-style="none"><li>- It makes it possible to obtain a greater density of coil turns near the underside of the cover layer, these coils extending in two perpendicular directions and constituting a sort of checkerboard in relief. This gives better resistance to laceration and the penetration of a sharp object.</li><li>- It makes it possible to obtain a ply in which the springs are self-held in position without requiring the use of external elements, which is not the case in the previous solution, in which the springs can move slightly towards each other (variations in axial deviations).</li><li>- It makes it possible to obtain a better homogeneity of the flexibility of the whole of the spring ply (same flexibility in the direction of the axes of the two intertwined spring plies).</li></ul>

According to another embodiment of the invention, the lining element further comprises, between the covering layer and the connecting layer of plastic foam, an interlayer of a few tenths of a mm, for example of 6/10, in fiberglass fabric. This intermediate layer on which the tops of the spring coils come to carry out several functions:<ul id="ul0005" list-style="none"><li>- It facilitates the production of the cover element, in particular in the case where the plastic material of the cover layer and of the bonding layer is made of silicone elastomer or of polyethylene.</li><li>- It makes it possible to homogenize the mechanical stresses between the sheet of springs and the cover layer.</li><li>-It avoids a mosaic effect due to the sheet of springs and visible on the outer surface of the cover layer.</li><li>- It increases the fire resistance of the entire roofing element.</li></ul>

The lining element according to the invention may further comprise a fabric covering, for example wool, covering the upper face of the covering layer.

In the case where this fabric is of the velvet type, it has, in addition to comfort, the advantage of making a slit made on the covering layer completely invisible (the fibers of the velvet then completely masking the slit).

It should be noted that the cover layer and the tie layer are preferably. made of plastic of the same kind, for example based on polyvinyl chloride (PVC), silicone elastomer or polyethylene.

By way of example, in the case where the plastic material is based on PVC, this plastic material can comprise:<ul id="ul0006" list-style="none"><li>- PVC,</li><li>- a usual plasticizer,</li><li>- mineral fillers,</li><li>- a usual fire resistance agent,</li><li>- a thermal stabilizer making it possible to avoid the decomposition of PVC at the casting temperature,</li><li>- And as regards the bonding layer of plastic foam, a blowing agent which can consist of azodicarbonamide in an amount of 2 parts of blowing agent per 100 parts of PVC resin.</li></ul>

In the case where the plastic material is a silicone elastomer:<ul id="ul0007" list-style="none"><li>- the cover layer may consist of Silastic Q 39 591 from the company US DOW CORNING, and</li><li>- the plastic foam bonding layer may consist of Silastic GP 590 DOW CORNING with, as blowing agent, azodicarbonamide. It should be noted in this regard that, in this case, the percentage of blowing agent should not exceed 2% because, beyond this percentage, it becomes a vulcanization inhibitor of the silicone elastomer (Il preferably be 1.25%).</li></ul>

According to another characteristic of the invention, the production of the above lining comprises the following steps:<ul id="ul0008" list-style="none"><li>1) The compact covering layer, for example PVC, is poured at room temperature onto a mold, the molding face possibly having in relief a negative of a design to be obtained (graining of the mold).</li><li>2) The cover layer is prepolymerized in an oven, at a temperature of the order of 180 ° C. for a period of the order of 3 to 5 minutes, then allowed to cool so as to obtain a lowering of the temperature of the material of about 50 ° C, for example from 120 ° to 70 ° C.</li><li>3) The bonding layer is then poured at room temperature, for example with a mixture of PVC and blowing agent.</li><li>4) The continuous layer of springs is placed on the liquid bonding layer. The sheet of springs then sinks into the bonding layer until it reaches the covering layer which has been prepolymerized and which is therefore more cured.</li><li>5) The two layers of plastic are then polymerized in an oven at a temperature of 180 ° and for a period of approximately 25 min.</li><li>6) Deheat and allow to cool to room temperature before handling the filling.</li><li>7) The trim elements are then cut to the shapes and dimensions required.</li></ul>

It should be noted that in the first step of the embodiment described above, the molding face of the mold may be initially covered with a fabric, produced using a natural or synthetic material which cannot be altered by the temperature of polymerization. In this case, we obtain trim elements covered with fabric.

According to a second embodiment, the manufacture of the lining comprises the following steps:<ul id="ul0009" list-style="none"><li>1) The covering layer, for example PVC or silicone elastomer, is poured at ambient temperature, the molding face of the mold possibly having in relief the negative of a design to be obtained, or being covered with a fabric.</li><li>2) A fiberglass interlayer fabric is placed on this cover layer.</li><li>3) The plastic bonding layer is poured cold (resin mixed with blowing agent).</li><li>4) The continuous sheet of springs is placed on this liquid bonding layer. The spring ply then sinks into the bonding layer until it reaches the glass fiber interlayer.</li><li>5) The two layers of plastic are then polymerized in an oven at a temperature of 180 ° and for a period of approximately 25 min.</li><li>6) Deheat and allow to cool to room temperature before handling the filling.</li><li>7) The trim elements are then cut to the shapes and dimensions required.</li></ul>

Regarding the choice of plastic used, it should be noted that:<ul id="ul0010" list-style="none"><li>- The PVC solution has the advantage of being relatively low cost. In addition, one can obtain a Shore hardness of the order of 30. On the other hand, the drawback of this solution lies in the fact that one cannot solve the problem of harmful gassing during a fire;</li><li>- the elastomeric silicone solution has the advantage of much better fire resistance (classification, smoke emission, toxicity). However, its cost is higher and its maximum hardness, of the order of 50 Shore, is less than that of PVC.</li></ul>

Advantageously, the curved shape can be obtained by keeping the covering covered, for example by suction on a matrix having the desired shape.

Of course, the invention also relates to the seat element or the like, obtained by the method described above.

Embodiments of the invention will be described below, by way of nonlimiting examples, with reference to the appended drawings in which:<ul id="ul0011" list-style="none"><li>- Figure 1 is a schematic cross section of a packing element which may be suitable in the method according to the invention, in which the sheet of springs is constituted by a plurality of helical springs with parallel axes;</li><li>- Figure 2 is a schematic view, in exploded perspective, of the element shown in Figure 1;</li><li>- Figure 3 shows, in top view, a sheet of springs constituted by an intermingling of two sheets of springs with perpendicular axis;</li><li>- Figure 4 is a top view to illustrate the embodiment (intermingling) of the ply shown in Figure 3.</li><li>- Figures 5 to 8 schematically represent the different steps of the method for producing a seat element according to the invention;</li><li>- Figure 9 shows, in perspective, a seat element obtained by said method;</li><li>- Figures 10 and 11 show a cut part of the seat element shown in Figure 9, this part being viewed from above (Figure 10), and viewed from below (Figure 11).</li></ul>

The packing element shown in FIGS. 1 and 2 comprises a covering layer 1 of compact plastic material such as silicone elastomers, polyethylene, and compact polyvinyl chloride (PVC), for example of density of the order from 1.18 to 1.30, Shore hardness from 40 to 98, this covering layer 1 being relatively thick, for example of the order of 5 mm.

The underside 2 of this covering layer 1 is secured, by means of an intermediate layer of foam of the same plastic material 3, to a network 4 formed by a continuous sheet of metal springs 5 ​​in a spiral, with parallel axes between them and to the cover layer 1.

The turns of these springs 5 ​​are intertwined with each other, as previously described, and are flush, on one side, against the underside of the covering layer 1.

These springs 5 ​​can be produced for example using steel wires with a diameter of the order of 5 to 15 / 10ths of a mm. The diameter of the turns can then be between 10 to 20 mm.

The intermediate layer 3 can be made of plastic foam (PVC, silicones, polyethylene), with a density that can for example vary from 1 to 1.25 mm.

As previously indicated, the thickness of this intermediate layer ₃ Equals <maths id="math0001" num=""><img file="EP0100276A2_D0001.tif" /></maths>at <maths id="math0002" num=""><img file="EP0100276A2_D0002.tif" /></maths> of the diameter of the turns of the springs 5, so that the turns are only partially coated in the plastic foam.

The previously described trim element has many advantages, both in terms of comfort and in terms of laceration resistance:<ul id="ul0012" list-style="none"><li>- first of all, due to the relatively large thickness of the cover layer 1 and the multiplicity of the tops of the turns of the springs 5 ​​coming into contact with this cover layer 1, the user, while sitting does not not feel the presence of the springs 5;</li><li>- in addition, during a laceration attempt, the cutting object which will first of all have great difficulty in penetrating into the covering layer 1 because of its hardness and its thickness, will then be stopped by the continuous network springs 5 ​​which are flush against the underside 2 of the cover layer 1.</li></ul>

Consequently, it will only very slightly reach the plastic foam 3. In no case will the slit practiced be able to propagate by itself. On the contrary, this slot will close naturally thanks to the flexibility of the spring ply and the cover so that the laceration attempt will have no serious consequences, requiring repair or replacement of the lining.

It will be noted that the layer of PVC constituting the covering 1 can advantageously be fireproofed, which gives, due to its thickness, very good fire resistance of the entire lining (of course, the intermediate layer 3 , also, be flame retardant).

In the event of a rupture of one of the metal turns constituting the network 4, the end of this broken turn can only very easily cross the surface layer, which eliminates the risk of injuring a user.

It will be recalled that in the examples shown in FIGS. 1 and 2, the spring ply 4 is constituted by a plurality of helical springs 5 ​​with parallel axes and substantially in the same plane. The turns of each of the springs 5 ​​are intertwined with the turns of the two springs 5 ​​which are adjacent to it. Lⁱentrem^g- Lement of these turns is obtained by rotating each of these springs 5 ​​around its axis so that it comes to engage in the turns of the springs which are adjacent to it (action similar to that of a screwing).

The ply shown in Figure 3 is obtained by intertwining two plies of springs of the type described above, the axes of the springs of the first ply being perpendicular_fto the axes of the springs of the second ply. We see that this double intermingling allows to accentuate, seen from above, the checkerboard configuration.

Figure 4 illustrates the principle of this double entanglement. In this figure, for greater clarity, the first ply consists only of three intertwined springs A1, A2, A3 while the second ply oriented perpendicular to the first, only consists of the springs B1, B2, B3 . At the intersection of these two layers, we find the accented checkerboard configuration shown in Figure 3.

It should be recalled that FIGS. 3 and 4 are views from above (in a plane) and do not allow the relief of the coil springs to be brought out, which should not be confused with flat springs.

As previously mentioned, the lining element according to the invention may further comprise, adhering to the upper face of the covering layer, a fabric covering, preferably wool and, between the covering layer and the intermediate layer of connection, an intermediate sheet of fabric 6 of glass fibers 7 of thickness preferably equal to approximately 6 / 10ths of a mm. The covering and the interlayer ply have been shown in broken lines in FIGS. 1 and 2.

As previously mentioned, the first phase of the process for producing a seat element according to the invention consists in cutting (FIG. 5) a trim element such as those shown for example in FIGS. 1 and 3.

The second phase of the process consists in pouring, (FIG. 6) near the peripheral edge 15 of the lining element, on the side of the spring ply 5, a plastic bead 16 having elasticity properties. This cord 16 coats the outer part of the turns of the spring ply 5 in the corresponding zone and adheres to the intermediate layer 3 made of plastic foam.

The third phase consists in engaging the peripheral border 15 inside the cavity 17 of a mold 18 of corresponding shape, the cavity of which has a section corresponding to that of the frame 19 which it is desired to produce. At the same time, the lining is shaped by keeping it applied, by its cover 1, to a matrix 20 having the desired shape 21. To this end, the matrix comprises a plurality of holes 22 connected to a vacuum generator (not shown). The packing element is therefore sucked on the matrix 20 and, thanks to its flexibility, follows the shape 21 of this matrix 20 (FIG. 7).

In this position, the plastic intended to make the frame 19 is poured or injected into the mold 18. This plastic material coats the peripheral edge 15 of the trim element, including the end of the sheet of springs 5 This gives an excellent anchorage.

The last phase of the process consists of demolding the seat element, once the plastic forming the frame 19 has solidified. Due to the rigidity of this frame 19, the packing element retains the prestressed shape provided by the die 20.

The method according to the invention therefore makes it possible to obtain _kseat elements such as, for example, that shown in FIGS. 9 to 11.

In this seat element, the trim element has, naturally, at the rear 23 a slightly convex shape and, at the front 24, a flat or slightly concave shape. Thanks to the mechanical properties of this filling, this shape will be preserved even after use.