FR2567067A1 - Process for manufacturing furniture covers having an irregular surface, with a ultrasonic welding machine, and cover obtained thereby - Google Patents

Abstract

The invention relates to a method for manufacturing furniture covers. According to the invention, ultrasonic welding horns 4A and opposing protuberances are arranged in order to conform to a final shape to which the cover is to correspond; a surface layer 1, upholstery padding 2 and a support layer 3 are sandwiched between the arrangement of horns and the arrangement of protuberances; the three-layer body is compressed between these arrangements and the body is subjected to an ultrasonic wave in order to heat and weld the body in its selected zones. The invention applies especially to the covering of car interiors or of furniture.

Description

 The invention relates to a method of manufacturing trim pads for various uses, such as, for example, seat cushions or decorative trim applied to the interior of an automobile or to a piece of furniture.

 Figures 1 to 5 show lining covers according to the prior art. More particularly, Figure 1 shows, in section, a seat cushion as comprising a surface layer 1, a polyurethane foam padding 2 and a support layer 3 in the order named. As can be seen, the surface layer 1 is heat welded to the underlying padding 2 along weld lines A, while the backing layer 3 is heat welded to the padding 2 which covers it along weld lines 2a.

 As can be seen in Figure 2, the surface layer has parallel and oblique grooves or grooves formed therein in relief. These parallel and oblique grooves a and b intersect the weld lines 8 as indicated, for example, in Aa and Ab. FIG. 3 shows a part of the surface layer where two parallel and oblique grooves "a" and "b "cross a single weld line A. on an enlarged scale FIG. 4 is an enlarged sectional view of the surface layer made along line IV-iV of FIG. 3.

Sometimes these grooves can be curved. The problem of a lining cover according to the prior art resides in the fact that the weld is ~ incomplete in the crossing zones Aa, Ab where the parallel and oblique grooves cross the weld lines, for the following reasons
(a) When a dielectric heating or other heating and welding device is applied to a crossing zone, the empty space prevents the production of heat as much as elsewhere in the surface layer 1. More particularly, in the case of dielectric heating, the production of heat due to intermolecular friction in the thickness of the dielectric material is insufficient to ensure complete welding in a crossing zone. Even if the empty space in the crossing zone is compressed to reduce its volume, the bulk density of the dielectric material still remains at a low value compared to the solid part of the surface layer and therefore the amount of heat produced in the crossing zone is inadequate to produce such a good weld in the crossing than elsewhere in the surface layer. A heating and welding method other than dielectric heating also does not allow the formation of a complete weld in a crossing zone. More particularly, one cannot obtain a weld in the crossing zone or else one cannot obtain a weld as strong and reliable as elsewhere in the surface layer.

 (b) In the case where the parallel and oblique lines cross the weld lines at a relatively small angle, this results in elongated crossing zones, and as a result the above-mentioned defect is increased.

 (c) An ordinary polyurethane, such as that used in a sewn fabric cushion, is less lumpy and has better elasticity and better physical properties than a low melting polyurethane foam or a foam polyurethane impregnated with a welding agent. However, ordinary polyurethane has a relatively high welding temperature and therefore perfect welding at the crossing areas is almost impossible. Therefore, ordinary polyurethane, although desirable to use, cannot in reality be used.

 It's the same with the article (e) below.

 (d) Polypropylene and other materials which have a relatively low dielectric loss, or which can produce sparks when subjected to a high frequency electric field, cannot be used as the material of the surface layer; incomplete welds may result in the crossing areas Aa, Ab in a striped surface layer, or in the hollow areas in a raised surface layer E see article (e) belowj, and the pleasant appearance of the surface layer can be damaged by sparks. Sometimes sparks appear on a surface layer coated with a flame retardant coating and the like although the appearance of the sparks depends on the kind of coating material used.

 (e) FIG. 5 shows a surface layer I in relief which carries hollow zones C. Welding is almost impossible in any crossing zone where a weld line crosses a hollow. Even if each hollow area in a surface layer is very small as in the case of spaces between stitches in knitted fabric or coarse yarn, welding to the underlying padding is almost impossible. We encounter the same difficulty in welding a surface layer having an embossed pattern on its back.

 Ordinary fabric, knitted fabric or non-woven fabric has an irregular surface and therefore this fabric cannot be firmly welded to the underlying upholstery. Likewise, no perfect weld can be obtained at a crossing point where a weld line crosses overlapping layers.

 (f) In the case where a dyed fabric is used as surface layer 1 and in the case where the dye used contains a metal, the dyed part of the fabric when it is subjected to dielectric heating, may have its appearance gEté.

 (g) In the event that dielectric heating or any other conventional heating and welding technique cannot produce a firm weld of a surface layer to the underlying padding, the surface layer and the underlying padding must be sewn together.

It is tedious work.

 The present invention relates to a method of welding a surface layer, a padding and a support layer, without having the drawbacks described above.

 To achieve this objective, in a method of manufacturing lining covers according to the invention, ultrasonic welding is used to thereby weld a surface layer, a padding and a support layer whatever the material used to form these three layers or whatever the surface condition of these layers.

The invention will be better understood, and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, made with reference to the appended schematic drawings given solely by way of example illustrating several embodiments of the invention and in which
- Figure 1 is a schematic sectional view of a trim cover;
- Figure 2 shows, in plan, a fragment of the trim cover;
- Figure 3 shows crossing areas Aa and Ab where a weld line "A" cuts two grooves "a" and "b" on an enlarged scale;
- Figure 4 is a schematic sectional view of a portion of the trim cover made along the line IV-IV of Figure 3; ;
- Figure 5 shows, in plan, a fragment of a trim cover in relief;
- Figure 6 is a schematic sectional view of a three-layer body sandwiched between opposite support plates of horns to be welded by ultrasound;
- Figure 7 is a sectional view of the three-layer body sandwiched between opposite supports; and
FIG. 8 is a schematic sectional view of one of the horns to be welded by ultrasound, taken along line VIII-VIII of FIG. 7.

 In FIG. 6, a surface layer 1, a padding 2 and a support layer 3 are arranged in the named order, and the three-layer body thus formed is sandwiched between two opposite support plates 4 and 5 More particularly, the lower support 5 is pushed against the surface layer 7 with associated protuberances Sa (width "t") applied along the weld lines n, which extend through grooves "a", "b tl as shown in Figure 3. The upper support 4 is pushed against the support layer 3 with the associated horns 4A (width 11T '!) applied to the support layer in relation to the protrusions Sa. As is aforementioned, there is an empty space at each crossing area where the weld line crosses grooves.

 A force is applied to the upper support plate 4 to compress the body in three layers, and then an ultrasonic vibration is transmitted by each horn of the upper plate 4 to the protuberance of the lower plate 5 through the support layer 3 , the upholstery 2 and the surface layer I.

The surface layer 1 is compressed so that the empty spaces at the crossing zones ka, Ab are reduced in volume and the ultrasonic wave passes through these reduced empty spaces. Then, heat is produced in particular around the areas of the support layer 3 just below the horns to be welded by ultrasound 4A (width 'Te') and around the areas of the surface layer 1 just above the protrusions (width 't3 and therefore the surface layer I is welded to the padding 2 which covers it along the weld lines as shown in 2a in Figure 1. As can be seen, the horn to be welded by ultrasound has a relatively large PPT width compared to the width 19t of the opposite protuberance and therefore the ultrasonic wave of the horn converges towards the counter-projection, thereby effectively heating and welding the surface layer 1 to the padding covering it 2 along each weld line Similarly, the support layer 3 is heated and welded to the underlying padding in the selected areas of the support layer just below the horns to be welded by ultrasound.

 The dielectric heating method requires an insulation sheet. Usually, the ultrasonic heating method does not require an insulation sheet. there are, however, some occasions when the use of an insulation sheet is effective in improving heat production, although this depends on the kind of material that is used. Then, an insulation sheet is placed between the upper plate 4 and the support layer 3 to improve the weld effect. A sheet of high frequency fabric was placed on the backing layer 3 and then a sheet of Empire fabric was placed on the sheet of high frequency fabric. These fabrics have been subjected to the heat produced by the ultrasonic wave, thereby accelerating the heating of the underlying three-layer body. Empire fabric, when heated, may soften, but high frequency fabric or a silicone coated fabric cannot soften at a high temperature, and is easy to separate from a mold. A sheet of glass fiber coated with ethylene tetrafluoride resin, which is superior in heat resistance and easy to separate from a mold, can be used for the same purpose.

In one example of ultrasonic welding using a sheet of glass fiber coated with ethylene tetrafluoride resin, the ultrasonic welding machine operated at 22 kHz.

 Figure 8 shows a schematic sectional view taken along the line Vili-Vili of Figure 7 and looking as indicated by the arrows. As can be seen, the horn 4 is made up of sections 4A, 4B, 4C ... and these sections can operate independently.

However, in the case of a relatively short weld line, the horn should not be cut. When 1ton actually undertakes ultrasonic welding, the positional relationship of the horn, the three-layer body and the protrusions shown in Figures 6 and 7 can be returned.

 As already mentioned above in articles (b), (c), (d) and (e), the voids in the crossing zones Aa, Ab prevent complete welds of the surface layer and of the intermediate upholstery support layer in the crossing zones when dielectric heating or any other conventional heating is applied. Likewise, as already described above in articles (c), (d), ( f) and (g), a complete weld does not occur in a material whose dielectric loss remains at a low value and lion cannot obtain a satisfactory weld in an ordinary polyurethane upholstery or a material which can cause sparks when is subjected to a high frequency electric field However, ultrasonic welding ensures the complete welding of such materials as well as materials with irregular or raised surface.

 The ultrasonic welding technique does not require an insulation sheet. Even if this insulation sheet is used in ultrasonic welding, it is not consumed as it would be with dielectric heating. Only a few defective products were obtained compared to other heating and welding methods, and the production price was relatively low.

 The resistance of the weld is increased, and a pleasant appearance is guaranteed.

 The method according to the invention should not be limited to lining covers each comprising a surface layer, a padding and a support layer.

The method according to the invention can also be applied to lining covers each comprising a surface layer, padding and a hard panel in place of the support layer. Then, such a trim cover can be used as an ornamental trim to be applied inside an automobile door or to a piece of furniture for ornamental or decorative purposes.

Claims (3)

R E X E N D I C A T I O N S  1.- Method of manufacturing a lining cover, characterized in that it consists of  arranging horns to be welded by ultrasound (4A) and opposite protuberances (5a) so as to be in conformity with a given final shape to which said cover must correspond;  sandwiching a surface layer (1), a padding (2) and a backing layer (3) or a hard panel between the arrangement of the horns to be welded by ultrasound and the arrangement of the opposite protuberances;  compress the body in three layers between these arrangements; and  subject the body in three layers to an ultrasonic wave to heat and weld the body in three layers in its selected areas.  2. Method according to claim 1, characterized in that the aforementioned step of preparing an arrangement of horns to be welded by ultrasound consists in arranging a certain number of horn sections so that they are in conformity with a given final shape to which said cover must match.  3. Upholstery cover, characterized in that it comprises a three-layer structure composed of a surface layer (î) with undulations, of a padding (2) made of ordinary polyurethane foam and of a material d 'support (3), which are welded together in parts given by the heat produced by an ultrasonic vibration, the undulations of said surface layer being flattened and welded to said given parts by application of the pressure of a horn means ultrasound (4A)