Description of Invention

This invention is concerned with improvements relating to bonded panel structures.

A conventional bonded panel comprises a corrugated or fluted layer, conventionally of heavy-duty paper such as Kraft, and inner and outer layers, conventionally also of heavy-duty paper such as Kraft, bonded to the core by a heat-softenable adhesive such as polyethylene. Such a conventionally bonded panel may be moulded by the application of heat and pressure, the inner and/or outer layers slipping over the core whilst the moulding takes place, and the adhesive setting on cooling with the panel in its moulded configuration. Such a bonded panel is conventionally used on the interior of motor vehicles, the inner layer being attached, such as by the use of adhesive, by ties, by clips or simple press-fitting, to the vehicle body surface, the outer layer being covered by a decorative layer.

Increasing attention is paid to the rigidity of such panels, and to ensuring that such panels provide a high degree of sound absorbtion. Typically the layer of Kraft will have a weight of between 100 and 200 grams per square metre, particularly lying in the range 135 to 165 grams per square metre.

Thus a more effective bonded panel structure comprises inner and outer layers afforded by a laminate of a lower weight paper and a heavy-duty paper bonded together by polyethylene, with the corrugated core similarly being afforded by a lower weight paper laminated with the heavy-duty paper such as Kraft.

Attempts to increase further the robustness of such bonded panel structures by the addition of further layers have met with the difficulty of deformation, particularly where the deformation involved the production of corners or bending around curved and small radii.

According to this invention there is provided a bonded panel structure comprising a first laminate comprising a first layer, a second layer, and a corrugated layer between the first and second layers, and a second laminate comprising at least one layer, and a corrugated layer adjacent to said one layer, wherein for the first laminate one of said first and second layers is securely fixed to the corrugated layer and the other layer is fixed to the corrugated layer along one edge margin only, and for the second laminate said one layer is fixed to the corrugated layer thereof, to permit on deformation of the bonded panel structure relative movement between some at least of the layers, the two laminates being bonded together by a heat-softenable adhesive.

Preferably the two laminates are secured to each other along an edge margin only.

Preferably interposed between the first and second laminates is a layer of heat-softenable adhesive, which may be secured to and between the two laminates along said one edge margin only, or may be provided on an outermost layer of one of the laminates.

By providing the capability of some of the various layers to move relative to one another during deformation, the bonded panel structure may be formed relatively easily into a desired shape by the use of heat and pressure, and moulded into a desired shape with the avoidance of wrinkles. Preferably the layer which is fixed to the corrugated layer along one edge margin only provides an outer surface of the bonded panel structure, i.e. that layer which moves relative to the remainder of the bonded panel structure to the greatest extent.

Preferably the said edge margin along which the layer or layers are secured together extends along a line which lies at right angles to the direction of relative movement between the various components of the bonded panel structure, or at least at right angles to the direction in which most such movement takes place.

If desired the corrugated layer of the second laminate may be brought into contact directly with the first laminate, through the intermediary of a layer

of adhesive as hereinbefore described, but if desired, and in particular if desired to provide a stronger bonded panel structure, the second laminate may comprise in addition to said one layer a further layer between which and said one layer the corrugated layer is sandwiched, said one layer and said further layers corresponding to the second layer and the first layer of the first laminate respectively.

Thus when the second layer of the first laminate is bonded to the first layer of the second laminate, upon deformation the first layer of the first laminate moves relative to the corrugated layer of the first laminate, whilst the first layer of the second laminate moves relative to the corrugated layer of the second laminate.

Preferably the first and second layers comprise heavy duty paper such as Kraft, provided on at least the side thereof facing another component of the bonded panel structure a layer of heat-softenable adhesive. If desired however, at least one of the first and second layers may itself be in the form of a laminate of first and second layers, conveniently comprising a layer of heavy duty paper such as Kraft, and a layer of lower weight paper, conveniently being bonded together by a layer of heat-softenable adhesive.

The corrugations of the first corrugated layer may extend in a direction parallel to the corrugations of the second corrugated layer, conveniently said corrugations both extending in directions generally parallel to the edge margin at which the two laminates are secured together. In this way relative movement between the corrugated layers and their adjacent, non-corrugated layers may be effected relatively easily, permitting uniform deformation of the bonded panel structure.

Alternatively one of the corrugated layers may extend at right angles to the other, so as to extend transversely to the edge margin at which the two laminates are secured together, providing the laminate with a higher resistance to deformation in a direction parallel to said edge margin.

There will now be given a detailed descriptions, to be read with reference to the accompanying drawings, of three bonded panel structures which are preferred embodiments of this invention, having been selected for the purposes of illustrating the invention by way of example.

In the accompanying drawings:

Figure 1 is a schematic sectional view of the bonded panel structure which is the first embodiment of this invention;

Figure 2 is a schematic sectional view of the bonded panel structure which is the second embodiment of this invention; and

Figure 3 is a schematic sectional view of the bonded panel structure which is the third embodiment of this invention.

The bonded panel structure which is the first embodiment of this invention, comprises first and second laminates A and B, bonded together along a line 19 extending along one edge only of the bonded panel structure.

The first laminate comprises a first layer E, a second layer F, and a corrugated layer 16 sandwiched between the first and second layers. The first layer E comprises an outer layer 8 of relatively light weight paper such as 40gms to 60gms Kraft paper, an inner layer 10 of heavy duty Kraft, conveniently within the range 135gms to 165gms, said inner and outer layers being bonded together by a layer 9 of adhesive. The second layer F comprises a layer 10 of heavy duty Kraft, similarly conveniently within the range 135gms to 165gms, each of the layers 10 being provided on their inner side with a layer 11 of polyethylene.

Sandwiched between the first and second layers E and F is a corrugated layer 16, conveniently also of Kraft lying within the range 135gms to 165gms, said corrugated layer 16 being bonded to the first layer E along an edge margin 18 and being bonded to the second layer F along a plurality of lines X by said layer 11 of adhesive, said lines X extending parallel to the line 18. Particularly, the corrugated layer 16 is not bonded to the layer 10 of the first layer E by the layer 11 at other locations, specifically the locations Y.

The second laminate B comprises a layer G similar to the layer E, comprising a layer of paper 8 and a layer of heavy duty Kraft 10 secured thereto by a layer of adhesive 9, a layer of adhesive 11 being provided on the inner side, and a corrugated layer 16 also of heavy duty Kraft secured to the layer G by the adhesive layer 11 along lines X.

The second laminate B is secured to the first laminate A along the side edge margin 19, parallel to the lines X, and the line 18, by the adhesive of the layer 9 of the first laminate.

In the use of the bonded panel structure which is the first embodiment of this invention, on placing one of the outer layers (either the first layer E of the first laminate, or the layer G of the second laminate) on a mould surface, and by applying heat and pressure to the opposite side, the layer E of the first laminate will be free to move across the corrugated layer 16 of the first laminate, whilst for the second laminate the corrugated layer will be free to move across the second layer F of the first laminate. On arrival at the desired shape, the panel structure is held in position allowing the layers of adhesive to soften and to ensure the provision of a good bond with the adjacent layer, whereupon the panel structure is allowed to cool to ensure the retention of the panel structure in the shape to which it has been formed.

Whilst in the first embodiment the layer of adhesive which is effected to secure the two laminates together is provided by a layer of polyethylene on the second layer F of the first laminate, if desired this may be effected by a loose layer secured between the two laminates along said edge margin 18 only.

The bonded panel structure which is the second embodiment of this invention is similar to the first, and will be described hereinafter primarily in as much as it differs from the first embodiment, similar numerals being used to identify similar parts.

In the second embodiment, the first and second laminates are similar, each comprising first and second layers E and F, G and H respectively afforded by a layer of light-weight paper 8 bonded to a layer of heavy duty Kraft 10 by an

intermediate layer 9 of adhesive, the first layer being bonded to the intervening corrugated layer 16 along a side edge margin 18 only, whilst the second layer F, G respectively is bonded to the corrugated layer 16 along a plurality of lines X parallel to said lines 18. Specifically, in the second embodiment, the corrugated layer is not bonded to the other layers along the corresponding lines Y.

A layer 20 of heat-softenable adhesive is freely positioned between the two laminates, being secured thereto along the edge margin 19, permitting relative flexing movement between the two laminates to take place about a longitudinal axis afforded by said edge margin 19, permitting relative movement between the components of the two laminates as the bonded panel structure is moulded into a desired shape, prior to securing together of the component parts thereof into an integral, rigid assembly.

By the use of the invention a bonded panel structure of high strength may be obtained relatively inexpensively, and may be moulded into a desired form with a significant reduction in the tendency for the outer layer specifically to "wrinkle", allowing decorative trim to be applied thereto more efficaciously.

If desired the layers of the bonded panel structure may be provided with holes to assist in the absorbtion of sound, in a conventional manner.

The bonded panel structure which is the third embodiment of this invention comprises first and second laminates J and K bonded together at an edge margin, specifically along a line 59 (figure 3), each of said laminates J and K comprising an outer layer 61 of Kraft, and, on the inner side thereof a corrugated layer 63 also of Kraft, said corrugated layer being bonded to said layer 61 along lines 65 at which the two layers are in contact.

Bonded to and located between the two laminates J and K is a layer 67 of Kraft, provided on one surface (as is shown, the surface adjacent to the laminate J) with a layer 69 of a heat-soft nuggle adhesive such as polyethylene. Located between the layer 67 and the laminate K is a sheet 71 of polyethylene film, said layer 67 and said file 71 being secured to the two laminates along the line 59.

When the bonded panel structure which is the third embodiment of this invention is located in a heated press, relative movement may take place between the various layers thereof, particularly to layer 61 and the layer 63 through the softening of the adhesive at 65, and between the laminates J and K relative to each other and relative to the layer 67 by virtue of the adhesive on opposite sides of the layer 67, as shown at 69 and 71.

In all three embodiments the corrugated layers of the laminates are shown with the corrugations extending along lines generally parallel to the line along which the two laminates are secured together. If desired however at least one of the corrugated layers may be attached to the layer of Kraft with the corrugations extending at right angles, to provide additional strength to the bonded panel structure along lines extending parallel to the line along which the laminates are secured together. Indeed, it is feasible to have both corrugated layers extending at right angles to the directions shown in the drawings, such that the corrugations extend along lines extending at right angles to the line along which the laminates are secured together.