Technical Field

The present invention relates to a building board which can be used for lining-out framing (similar to plasterboard), or in combination with a layer of insulating material as an insulating wall, floor, roof, or ceiling panel, or as a component of a structural insulated sandwich panel.

Background Art

A wide variety of different types of building boards are available and their uses range from lining out framing, providing exterior cladding, or as a stand-alone structural panel. Some panels may also be used as roofing panels and/or for flooring.

Known building board types include sheet-metal based panels, wood composites of various types and plasterboard. Plasterboard essentially is a layer of paper with a thicker layer of gypsum (calcium sulphate dihydrate) deposited over the paper backing.

For any building board, it is advantageous for the panel to be high-strength, dimensionally stable, waterproof or at least water resistant, capable of providing a high level of heat and sound insulation, and easy to cut to size and to handle.

Disclosure of Invention

An object of the present invention is the provision of a building board which provides the above properties to a higher level than a majority of the existing building board products, and which also is comparatively fire resistant.

The present invention provides a building board which includes the following ingredients:

• a magnesium based composition which forms at least 50% of the board by volume, and which consists of magnesium sulphate or a mixture of a major portion of magnesium sulphate and a minor portion of magnesium oxide;

• glassfibre reinforcement;

• perlite;

• ash filler;

• wood flour. Preferably, the magnesium based composition forms approximately 76% by volume of the board and consists of 40-61% by volume magnesium sulphate and 36-15% by volume of magnesium oxide.

Preferably also, the perlite is present at 5-10% by volume and each of the ash filler and the wood flour is present at 3-8% by volume; most preferably, the wood flour is bamboo. Preferably also, the glass fibre reinforcement includes 4 sheets of woven glass fibre and one sheet of non-woven glass fibre.

The present invention further provides a composite panel which consists of 2 parallel building boards as described above secured one to each side of a sheet of phenolic closed cell insulation.

Brief Description of Drawings

By way of example only, a preferred embodiment of the present invention is described in detail, with reference to the accompanying drawing, in which:

Figure 1 is a flowchart showing the steps of manufacturing a building panel in accordance with the present invention.

Best Mode for Carrying Out the Invention

Referring to Figure 1 , a casting tray of known type is provided:- the casting tray provides a flat horizontal surface of the same size as the desired size of the board being cast, with peripheral edges having a height greater than the final height of the panel. The casting tray is made of a material which is capable of being heated to the curing temperature of 650°C without damage or distortion.

The cast board may be flat, or may be formed with rebates or rims or other features, as required.

The finished size of each board may of course be varied as required, but typical boards would be 1200 mm wide, 3000 mm long and approximately 10 mm thick.

In a preferred formulation of the present invention, the constituents of the board are as follows:

• magnesium sulphate 54% by volume • magnesium oxide 17% by volume

• perlite 8% by volume

• ash filler 3% by volume

• additives 10% by volume

• wood flour (preferably bamboo) 5% by volume

• water 3% by volume in the finished, cured board

The additives may include one or more of magnesite, dolomite, brucite and phosphoric acid; these additives assist in the mixing and the binding of the other ingredients.

The dry ingredients are thoroughly mixed in an industrial mixer of known type, and water is added to produce a pourable slurry; typically, about 27% by volume of water is required.

Four sheets of woven glassfibre mesh and one sheet of nonwoven glassfibre mesh, (all 820 GSM) are cut to the size of the casting tray.

A first layer of slurry, approximately 2 mm thick, is poured onto the casting tray, and a first glassfibre sheet is placed over the surface of the slurry. Then a second layer of slurry, approximately 2 mm thick, is poured on top of the first glassfibre sheet, and a second glassfibre sheet is placed over the surface of the second layer of slurry. This process is repeated, with a sheet of glassfibre approximately every 2 mm through the thickness of the board, until the desired thickness of the board is completed. The outer surfaces of the board (top and bottom) are formed from the slurry.

The mould with the layers of slurry and glassfibre is then fed under one or more rollers to spread the slurry evenly and size the resulting board to the correct thickness.

The casting tray may then be moved into an oven and raised to a temperature of up to 650°C to cure the slurry. The tray remains in the oven for approximately 3 to 4 days, and then the cure is completed at ambient temperature for about 2 weeks. However, curing the board in an oven is necessary only during winter or periods of exceptionally high humidity. If the ambient humidity is relatively low, the cast board can be left to air dry and cure for 3 to 4 weeks, omitting the oven drying stage entirely. The fully cured board has a water content of approximately 3% by volume. Another method is to dry the board in a low-humidity room maintained at about 35-40°C for 3-4 weeks.

Once the board is fully cured, the board can be used as a single board, or can be formed into an insulated panel by gluing a layer of foam insulation onto one surface of the panel. In a preferred form of the invention, two parallel boards are formed into an insulated sandwich panel by securing a sheet of insulation between the two parallel boards.

A range of suitable closed cell foam fire resistant insulating materials is available, but preferably the insulation used is a closed cell foam phenolic insulation. The preferred phenolic insulation has a density of approximately 70 - 75 KG per square metre; this density is significantly greater than standard phenolic foam and results in a lowered thermal conductivity: - typically 0.019 - 0.02 W per metre Kelvin, compared to 0.025 - 0.027 W per metre Kelvin for a standard phenolic foam.

Preferably, the thickness of the phenolic insulation is 60 - 80 mm.

Typical physical properties of the preferred phenolic insulation are shown in the table below:-

The exterior surfaces of the boards can be finished by sanding and/or by the application of finishes such as paint, tiles or wallpaper. The board does not give off any toxic gases while it is being made or cured, nor once it is cured. The board is robust and dimensionally stable, and is easily cut to size.

Further, the boards can be nailed or screwed without damage: - typically, the screw strength pull-out for a screw screwed into a board is 800 -1000 N.

The sandwich panel made with the boards and a layer of phenolic insulation has a fire rating of 3 to 4 hours at 800°C.

The sandwich panel has a heat insulation (R) rating of 4.0 - 5.0, and a sound transmission class (STC) of 80 - 100.

Single boards and insulated single panels can be used for partitions, internal wall linings and tile backboards. The sandwich panels may be used for forming exterior walls and are approved for use up to 14 m without structural support, and may also be used for roofing, flooring or forming interior walls.

The single boards and the insulated sandwich panels are highly resistant to mould, fungi and insects including termites. Further, the board is recyclable.

It will be appreciated that the board and the sandwich panels can be made in a wide variety of shapes and sizes, as required. The amount of glassfibre reinforcing can be reduced for some end uses (e.g. partition walls) or can be increased to increase the strength of the board.