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The invention relates to a reinforced structure and in particular to a reinforced board useful as the wall of a container, building or the like. The structure may also be used as a vehicle body, partition, screen, or the like. The wall may be a sidewall, floor roof or tray. One particular use of the board is as a wall of a refrigerated container which may be a fixed part of a vehicle or a separate container.

It is known to make a board of two panels joined together with an infill in between. It is known to use a honeycomb structure as the infill, the walls of the honeycomb cells being made of say coated paper, or plastic or metal. The cells of the honeycomb may be empty so that only air is present, although it is known to coat the walls of the cells with various materials see e.g. US-A-3170827. It has also been proposed to fill the cells of the honeycomb with a reinforcing filling material see e.g. ΞP-A-0008960.

It is one object of the invention to provide a wall structure which is lightweight, thermally insulating and of high mechanical strength.

In one aspect the invention provides a board comprising two spaced apart panels and an infill between the panels , the infill comprising a grid formed of walls defining cells,- the walls extending from one panel towards the other, the cells being filled with set material, a discontinuity being present to prevent the transfer of heat and/or moisture from one panel to the other panel along a cell wall.

The discontinuity may take a variety of forms. In one option, the discontinuity comprises a layer or sheet of set material such as plastics, e.g. polyurethane foam or neoprene disposed along the inner surface of one or both panels. In another option, the honeycomb cells are present adjacent the inner surface of each panel, and a middle layer of set resin foam is present in between. In a much preferred feature, the discontinuity comprises an airtight sealed chamber present near the midline of the board.

The honeycomb may be formed of paper, coated paper (preferably resin coated), metal strip or foil; or the like. The section may be of rectangular parallel piped shape having cells of hexagonal, octagonal, ellipsoidal, circular or like cross sectional shape. The density of the cells may be varied.

One or both panels may be of cardboard, hardboard, mineral board, plywood, laminates, reinforced plastics and metals e.g. aluminium, steel, stainless steel; and the like.

The settable material may be hydraulic (as in the case of cement or the like) or a hardenable resin, e.g. polystyrene, isocyanate, polyurethane, polyester, phenolic or the like. It is preferred that the set material take the form of a foam for lightness in weight. Additives may be present, especially fillers, the proportion of which may be varied according to the desired compressive strength, heat insulation or the like.

The set material may be a single or multi component polyurethane system adapted to provide a foam. Such a single component system comprises a prepolymer with a blocked or bonded NCO group and a latent hardener which in the presence of moisture are converted into reactive compounds so that curing can take place. The component may include fillers, catalysts, auxiliary curing agents and like additives. The prepolymer may be formed by reacting a polyisocyanate, typically an aromatic diisocyanate, with polyols and chain extending and/or cross linking agents.

In order that the invention may be well understood it will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 to 5 are each transverse sections through different embodiments of the invention.

The same reference numerals are used to describe the- same parts in the different embodiments .

The board of Figure 1 comprises a single layer of a honeycomb structure, defining a plurality of cells C. The honeycomb is made of resin coated paper. A sheet of metal, plastics, wood or like is present on the top PI and bottom P2 of the honeycomb; preferably the sheet is of stainless steel. Each cell C of the honeycomb is filled with a hardened or cured low density plastics foam, typically a polyurethane foam S. Sidewalls W are secured to the top and PI and the bottom panel P2 to close the edges of the board.

A sheet 20 of polyurethane foam or neoprene is laid between the top edge of the cell grid and the upper stainless steel panel Pi. This prevents moisture and/or heat flowing up or down the cell wall to bridge the board. In Figure 2 , there are two such sheets 20 one located on the inner face of each of the panels PI, P2, and which may be of the same or different material. In the embodiment of Figure 3, the honeycomb is in the middle of the board with a relatively thick layer 25,26 of set polyurethane foam on each side so that the honeycomb is not in contact with the outer panels . In the embodiment of Figure 4 , there are two honeycombs, each bonded to a respective panel, a layer 27 of honeycomb-free set polyurethane being present in between. In Figure 5, the board has two elongate board parts Bl, B2, separated by a vacuum chamber 21. As shown the upper part has empty or full cells. The vacuum chamber includes sealed end walls 22. One of the boards incorporates a vacuum port 23 by which the chamber is evacuated. Dessicant may be placed in the vacuum chamber to reduce condensation. The board of Figure 5 is made by locating one board part on the other, with the end walls 22 in between. The walls 22 are sealed in gas tight manner to both board parts. A vacuum is created in the chamber 21, through the port 23. The chamber may be connected to a vacuum pump to withdraw any air which penetrates the seal; a pressure gauge may be provided and arranged to switch on the vacuum pump in the event that air penetrates the chamber.

The invention is not limited to the embodiments shown. For example, the resin need not be a polyurethane, and not all the cells need be filled. The walls of the cells may be apertured, to allow set polyurethane or other resin foam to bridge from one cell to the next.