COMPOSITE ELEMENT

FIELD OF THE INVENTION

This invention relates to a composite element and a method of manufacturing composite elements, more particularly, but not exclusively, to composite panels that can be used in the furnishing, shop-fitting, building and construction, signage, packing, pallet and numerous other industries.

BACKGROUND TO THE INVENTION

Typical materials used for panels include timber, chipboard, medium density fibreboard and plywood. Chipboard is the cheaper alternative to solid wood. However, it is also weaker with a generally poor finish, unless laminated. Medium density fibreboard, while far stronger than chipboard, is more harmful to work with as it is made with urea-formaldehyde resin and releases formaldehyde in low concentrations over time, which may be harmful to some individuals. Plywood, also a better alternative to chipboard, like all the above materials needs to be finished, for example with paint or a trim to neaten the appearance of the edges.

Composite materials, formed by the combining of two or more materials, often have unique properties based on the combination of the different properties of the individual components. Some of the greatest advantages of composite materials are their strength and stiffness generally, although not necessarily, combined with lightness that is characteristic of many of such composite materials. This type of material has found use in a number of applications, for example in boat hulls, surfboards, building and ceiling panels including doors and sporting goods. The structure of a traditional composite panel includes a core layer sandwiched between two surface layers. The cost of composite sheet material can become high when using specially manufactured synthetic materials or natural resources, the sources of which are on the decrease. It is particularly desirable to use recycled or recyclable material for the core. A material of choice in this respect is corrugated cardboard in a variety of different configurations, typically with the corrugations or flutes of the corrugated cardboard extending in the direction of the thickness of the composite panel.

However, corrugated cardboard has not been used very successfully as a core in composite panels due to the difficulty in laminating such a core between surface layers or forming a continuous layer over its surfaces with a suitable material. One of the difficulties faced is that of an excess of air becoming trapped in the core and later expansion thereof possibly causing bubbling or de-lamination when the panel is subjected to heat.

Also, existing panels using corrugated cardboard cores are frequently not seamlessly encapsulated, but rather have visible joints between the surface material along each edge. This is not only unsightly but permits the ingress of moisture into the core, frequently with deleterious consequences.

There is thus a need for composite elements that address the issues mentioned above and for a method of manufacturing such composite elements. There is also a need for high quality finish and a strong structure. SUMMARY OF THE INVENTION

In accordance with this invention there is provided a method of manufacturing a composite element having a core with a plurality of sides and a surface layer on at least one side thereof, the method including applying a settable plastics material to a flexible, generally sheet-like mould which corresponds to one of the sides of the core; adhering the side of the core directly to the plastics material; allowing the plastics material to at least partially set; and

peeling the mould from the at least partially set plastics material.

The composite element is typically a panel having a core extending between two opposite surface layers formed by the set plastics material and the method is applied to both of the two sides of the core. Whilst not being limiting on the scope of the invention, such a panel could have a thickness of from 1 0 to 1 00 mm ; commonly from 15 to 50 mm and frequently about 25 to 40 mm. The surface layers could have a thickness of from about 1 mm up to about 1 0 mm and most commonly of from 1 .5 mm to about 5 mm.

Further features of the method provide for the settable plastics material to be selected from the group comprising materials selected from epoxy resins, polyester resins and, polyurethanes; for the settable plastics material to include a foaming agent in a quantity aimed at causing an expansion of the plastics material from about 20% to about 200%, preferably from about 50% to 1 50%, and most preferably in the region of 1 00%; for the settable plastics material to include a filler material such as sand or natural vermiculite; for reinforcing fibres such as glass or other reinforcing fibres to be applied to the settable plastics material with any reinforcing fibres optionally being chopped and applied to the surface of the liquid plastics material immediately after its application to the flexible sheet-like mould; and for the settable plastics material to include a suitable pigment to provide a required colour to a final exposed surface of a panel..

The method may, in instances in which a coating is required on the surface of the set plastics material, include the preparatory steps of first applying a coating material to the generally sheet-like mould; allowing the coating material to at least partially dry or set as may be dictated by its compatibility with the properties of the liquid plastics material, but typically allowing the coating material to fully dry or set; and thereafter applying the settable plastics material thereto and carrying out the balance of the method as defined above.

Further features of the method provide for the coating material to be selected from the group comprising materials of the general nature of a gel coat, acrylics, enamels, oil and resin based coatings and most importantly, water based coatings. Clearly, the coating material may include any required pigment to provide a desired colour to an exposed surface of the coating material. Even further features of the method provide for the flexible sheet-like mould to be made from a plastics material of a type to which the settable plastics material does not readily adhere. Such materials may be suitable grades of polypropylene and polyethylene. A suitable sheet of plastics material for use as a mould may have a thickness anywhere in the range of from about 1 mm to about 10 mm with a commonly suitable thickness being from about 2 to about 5 mm and conveniently about 3 mm. The most important factor is that the sheet must flex sufficiently to enable peeling of the mould sheet away from the formed plastics material to be initiated. Of course, if required, a suitable release agent could be applied to the surface of the flexible sheet-like mould preparatory to carrying out the method of the invention.

Whilst the flexible sheet-like mould would typically be flat, it is within the scope of this invention that it could be curved in a single direction or in multiple reverse directions in order to provide a wave-like shape.

Also, the surface of the flexible sheet-like mould that contacts the plastics material or coating could be provided with a required texture or relief image formations including corporate logos and any other required visual effects or designs. A texture could alternatively, or in addition, be provided by applying to the surface of the flexible sheet-like mould, a powder that may be employed for the purpose of providing a matt finish to the surface of the coating layer or set plastics material, as the case may be, or a particulate substance aimed at providing a different aesthetic effect of the coating layer or set plastics material

Further features of the method provide for the core to be made from corrugated cardboard, honeycomb cardboard, or corrugated or so-called fluted polymer material wherein the corrugations, honeycomb formations or flutes typically, although not necessarily, extend in a direction corresponding to the thickness of the composite element.

Alternatively, the core could be a suitably thick sheet of foamed polystyrene, foamed polyurethane or other lightweight and preferably inexpensive material in which instance the settable plastics material is selected to be compatible with the foamed sheet or other material that defines the core.

As a further alternative, the core could be of a more robust nature and could even be a chipboard or other particle board, solid wood, plywood, expanded vermiculite or mineral fibre board. In such an instance the method of the invention may be used to provide a substantially permanent finish to a generally rigid panel. Yet further features of the method provide for the settable plastics material and any coating material to be applied to a pair of flexible moulds corresponding to each of a pair of opposite sides of the core in which instance the core is then sandwiched between the two moulds such that the core is in contact with the plastics material ; and for the plastics material to be allowed to at least partially set before peeling the moulds from the plastics material. In accordance with a second aspect of this invention there is provided a composite element having a core and at least one generally planar surface layer, the composite element being characterised in that the material of the surface layer is a set plastics material that at least partially conforms to the shape of the surface of the core in a manner that is consistent with the core having been applied directly to unset or partially set plastics material followed by final setting of the plastics material.

Further features of the second aspect of the invention provide for the core material to be selected from the group consisting of corrugated cardboard and corrugated or fluted plastics material; and for the set plastics material to be selected from the group consisting of epoxy resins, polyester resins and polyurethanes with the set plastics material preferably being somewhat foamed; and for the plastics material to include a filler and / or a fibre reinforcing material.

Still further features of the invention provide for a coating material to be carried on the external surface of the set plastics material and for the core to be encapsulated by set plastics material on both major sides of the core as well as the edges thereof.

In order that the invention may be more fully understood one example thereof follows with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a partly broken away perspective view of a composite panel;

Figure 2 is an elevation of one form of flexible mould with an unset or partially set surface layer thereon; is a sectional elevation of the core material sandwiched between the flexible moulds carrying the surface layer and showing also a pre-applied coating material ;

Figure 4 is a perspective view of a set of flexible moulds;

Figure 5 is a sectional elevation of the core material sandwiched between the flexible moulds carrying the surface layer and showing also a pre-applied coating material

Figure 6 is a perspective view of a second embodiment of a flexible mould;

Figure 7 is a perspective view of a flexible mould especially configured for applying a surface layer to the edges of a panel; and, Figure 8 is a sectional elevation of the mould illustrated in Figure 7 in use on a composite panel.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS A composite panel (1 ) is shown in Figure 1 and includes a core (3) having a surface layer (5) on each of the two main sides thereof. The core (3) is, in this embodiment of the invention, made up of multiple strips of corrugated cardboard attached to each other with the corrugations extending in the direction of the thickness of the panel in order to provide the most effective strength to the panel.

It will, however, be appreciated that the core (3) could also be made from any other materials, as indicated above.

Referring still to Figure 1 , the surface layer (5) is a settable plastics material that in this embodiment is a polyurethane material that is applied to the core (3) according to the following method of the invention. The use of polyurethane material is important from the point of view that it can be expanded somewhat and, in this embodiment of the invention, a foaming agent is added to the polyurethane in an amount that is aimed at creating an expansion of the polyurethane material of about 1 00% during curing. The use of such a material has been found to have significant advantages in that any unevenness of the core surface to which it is applied can be effectively accommodated and also, the use of such a settable plastics material avoids the transfer of any visible patterns of the core surface that may otherwise be transferred upon curing of the settable plastics material.

Referring more particularly to Figures 2 and 3, a pair of flexible mould sheets (15) is used wherein each mould sheet corresponds to one of the major opposed sides of the core (3). The mould sheets may conveniently be a suitable grade of polypropylene having a thickness of about 3 mm and are, in this particular instance, flat.

A thin layer of the polyurethane plastics material is applied in a liquid state to one surface of each flexible sheet in order to form, once the polyurethane has set, a surface layer (5). The thin layer can be applied in any suitable manner such as by means of a roller, spraying, or, in the instance of manual application, by laying spaced strings a monofilaments onto the mould sheets and using their diameter as a guide for a an applicator blade or the like.

As shown in Figure 3, before the surface layer (5) has had time to cure to any appreciable extent, the core (3) is sandwiched between the flexible sheets (15) to contact the uncured polyurethane that is to form the surface layers (5). A number of similarly sandwiched cores may be stacked on top of each other, without the need for spacers in between, and pressure applied to the stack, or example in a suitable press. Alternatively, a weight could be placed upon the stack to exert the required pressure. Depending on the settable plastics material used for the surface layer, curing time can be a few hours.

Once the settable plastics (5) has cured sufficiently, the moulds (15) are removed by simply peeling each mould sheet off the settable plastics material (5). The flexibility of the mould sheets as well has the inability of the surface layer to adhere strongly to the plastics material of the moulds (15) enables this important step to be achieved. The flexibility of the mould sheet (15) plays a vital role in achieving this. The thickness of the flexible sheet (15) also plays an important role and should ideally be between 1 mm and 5mm. In a preferred embodiment the thickness of the flexible sheet is 3mm. The result is a composite panel having the major opposed surfaces (7, 9) of the core coated with the suitable plastics material and the composite panel may be trimmed and squared. In many instances that will be the end of the production process if finishing of the side edges is not required. Reverting to the method of the invention, and as shown in Figure 5, a coating material (6) may first be applied to the flexible mould sheets (15) before application of the liquid plastics material that forms the surface layer. The coating material (6) is, in such an instance, allowed to at least partially set before applying the liquid plastics material to form the surface layer (5). It is preferred that a water based coating material be used and come in such an instance, it is important that it dry completely before application of the suitable plastics material to it.

In such an instance, when the flexible mould sheets have been removed in the surface layer (5) will have a coating on its external surface. The coating may be of any suitable type and it has been found that a water-based acrylic paint, optionally thickened as may be required, is particularly suitable for the purpose. It is to be noted that the coating material becomes permanently bonded to the surface layer and cannot be scratched or peeled off, provided that suitable compatibility is present. In certain instances the coating material (6) may also act as a release agent. A powder or coarse particulate material can also be applied to the surface of the mould sheet to create a matt or embossed appearance to the panel.

In the instances in which it is decided to cover the side edges (1 1 , 13), of the panel they are then coated in a similar fashion. Sufficiently flexible strips of polypropylene (19, 21 ) acting as mould sheets and corresponding to the respective side edges (1 1 , 13) similarly have a layer of settable plastics material applied to them and optionally an preceding layer of coating material and in this instance the settable plastics material may be the same polyurethane material or, may be an epoxy resin that is applied to the edges and allowed to cure with the core in contact therewith. The relevant mould sheets are shown in Figure 4. It will be understood that the polyurethane or epoxy resin also acts as an adhesive. Although more expensive than a polyurethane, epoxy has the advantage of providing a seamless joint with the coating material along the adjoining edges.

It is to be mentioned that in order to achieve an effective seal, it is sometimes advantageous to apply a sealant tape such as a masking tape to the edges of the set plastics material to ensure that liquid polyurethane or epoxy does not leak onto the edges of the already formed surface.

For convenience, opposite pairs of side edges (1 1 , 13) may be sequentially coated by sandwiching the core between the moulds. However, both pairs of side edges can be coated simultaneously.

Alternatively, as shown in Figure 6 a boxlike mould (30) can be used in similar fashion but with all the sides of the core (3) being coated simultaneously.

A further embodiment of a mould (35) for applying a surface layer to the side edges of a panel is shown in Figures 7 and 8. The mould (35) is channel shaped with a web (37) and sides (39) which are shaped to provide a snug fit over the edge regions of the major opposed surface layers of the element. Once more a sealing tape such as masking tape may be employed along the edges of the already formed surface layers. The channel shaped mould (35) may be made from a flat sheet of mould material that is scored in one way or another along lines where the web joins the sides so that the sides can hinge around these lines. This arrangement has the added advantage that the sides can be folded backwards in order to apply the coating, where same is used, and the liquid settable plastics material to the web without it contacting the surface of the sides. Once the web is in place, the sides can be hinged around the scored lines and clamped against the surface layer on each side of the panel simply using a plurality of suitable clamps. The length of the mould (35) corresponds to that of the side edge over which it fits. In use, the polyurethane or epoxy resin, optionally preceded by a coating layer, is applied to the web (37) of the mould (35) and the resin is then sandwiched between the side edge of the panel and the web (37) by securing the sides (39) of the mould (35) over the major opposed surface layers (7, 9) of the panel. Once the resin has set, the mould is removed.

All the side edges can be coated simultaneously with appropriately mitred moulds, or sequentially, and there is no need to apply external pressure to maintain the moulds against the core. The inner sides of the mould may be slightly tapered to promote a snug fit over the panel.

By radiusing the channel section between the web and its sides, a rounded edge can be obtained which obviates further machining.

The composite element has the great advantage of enabling the use of so- called "green" components such as corrugated cardboard or a corrugated polymer material.

The method of the invention can thus be used to provide encapsulated core material with seamless edges and a clean finish. The edges and the surfaces may be further worked if desired. It will be appreciated that the composite element can have any suitable shape; could be flat or curved and could be used in a wide variety of applications.