Building Panel BACKGROUND OF THE INVENTION Polyurethane and polystyrene foam-filled sandwich insulation panels are used as building elements within the construction industry. Foam-filled insulation panels of this type have steel facings and are often used, for example, to construct large food storage or preparation areas within existing buildings. These panel constructions have proven to be a major fire hazard in that in the event of a fire, the steel facings conceal degradation of the foam core as the fire spreads undetected. Thermal bowing caused by differential expansion between the steel facings eventually causes structural failure where the steel facings delaminate from the foam core, usually without any warning. Poor fire stability has caused loss of life on more than one occasion and has led some companies and insurers to refuse to use polyurethane or polystyrene filled insulation panels.

One suggested alternative are insulation panels made from high density mineral wool. However, mineral wool panels offer significantly poor resistance to moisture (a particular problem for chilled and refrigerated areas) and provide the added complication of introducing a source of fibres which needs to be strictly managed in a food processing environment.

It has also been proposed to use phenolic foams in this market because of their excellent fire resistant properties. However panels including such materials have not entered the market to date apparently as a result of the phenolic foams being high modulus materials and hence demonstrating a rigidity which does not accommodate the thermal movement of the steel facing sheets. Thus such panels have delaminated under normal usage conditions which has lead to their failure in the market place.

SUMMARY OF THE INVENTION According to the present invention, a laminated building panel comprises a foamed phenolic-resin based core

sandwiched between sheets of polyester or polycarbonate based flame resistant thermoplastics material.

In the present invention a phenolic-resin based foam-filled building panel is faced with a fire resistant polyester or polycarbonate-based thermoplastics material.

The use of a fire resistant thermoplastics material to provide fire protection to the foam core overcomes the existing problem of differential expansion and resultant delamination associated with steel facings and phenolic foam and prevents the undetected spread of fire via the core of such panels. Accordingly, the building panel of the present invention provides a very much improved fire stability. The building panel is also much lighter than steel-faced panels.

Preferably the building panel is faced with a thermoplastic polyester. Preferably the thermoplastic polyester is derived from terephthalic acid. It may be a crystalline or an amorphous polyethylene terephthalate (PET) such as that sold under the trade mark"Hostaglas"by Hoechst AG, or PETG. This material has a British Standards Class 1 and B1 DIN flame spread rating in the United Kingdom and meets a number of international food contact requirements. Alternatively the thermoplastic polyester may be another type of polyalkylene terephthalate such as PTT (polytrimethylene terephthalate) or PEN (polyethylenepaphthalate).

The thermoplastic sheets may have glass fibre reinforcement embedded within them. This increases the stability of the sheet, particularly at high temperatures.

The thermoplastic sheets may be bonded directly to the foamed phenolic core. Alternatively, a layer of glass tissue or glass mat may be interposed between the foamed polymer core and at least one of the thermoplastic sheets to improve facing adhesion and also to provide an additional barrier to flame penetration, thereby making the fire resistance of the panel comparable with that of steel faced insulation panels. The glass tissue or glass mat may

be applied onto a pre-formed thermoplastics sheet by heating the thermoplastics sheet to soften its surface.

The thermoplastics sheets may be flat or may be thermoformed to apply a pattern to their surface. This pattern may be functional but is more likely to be provided solely as decoration.

As mentioned above, the foamed polymer core is a phenolic foam. Phenolic foam provides an improved alternative to existing polyurethane and polystyrene cores because of its inherent fire and smoke performance.

Preferably, the foamed phenolic core is a rigid foam.

However a resilient phenolic foam particularly one based on Blagden Chemicals Celobond phenolic resins may be used.

This provides a less rigid foam at the foam/facing interface and this can be an advantage.

The building panel may be manufactured over a number of stages. For example, the foamed phenolic core may be extruded, expanded or fabricated into panels of the required size with the thermoplastics sheets made separately and applied later. Heat may be used to bond the thermoplastics sheets to the foamed phenolic core or a commercial adhesive may be used. As an alternative, the thermoplastics sheets may be made first and the foamed phenolic core formed in situ by injecting material between the sheets as part of a continuous or discontinuous production process.

BRIEF DESCRIPTION OF THE DRAWINGS An example of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a laminated building panel in accordance with the present invention; Figure 2 shows a cross-section of the building panel of Figure 1 taken along the line A-A; Figure 3 shows a building constructed from a number of the panels of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Figure 1 shows a laminated building panel 1 which comprises a phenolic foam core 2 and sheets 3 of a Class 1 flame spread (United Kingdom BS476 Part 7: 1997) fire resistant thermoplastics material sold under the trade name Hostaglas by Hoechst AG. A cross-section of the panel 1 is shown in Figure 2. A layer of glass tissue 4 is interposed between the foam core 2 and the thermoplastic sheets 3 to provide an additional barrier to flame penetration i. e. to improve flame resistance. Typically, the thermoplastics sheets 3 have a thickness of up to 3mm, and more usually less than lmm. The overall thickness of the panel 1 is between 50mm and 200mm.

The panel 1 is formed by injecting the plastics foam material using a withdrawing lance between preformed thermoplastics sheets to which the glass tissue has already been applied. The thermoplastics sheets 3 are held facing each other and are separated by a predetermined distance corresponding to the required depth of the phenolic foam core 2. As the phenolic foam cures it bonds to the glass tissue layers 4 and to the inner surface of the thermoplastics sheets 3.

Figure 3 shows an example of a building 5 constructed from the panels 1. Typically, this structure would be erected in an existing building to provide a large and well insulated cold storage area for a food processing plant.

The present invention is further illustrated by way of the following Example.

Example Phenolic foam composite panels were manufactured to a size of 600 mm x 600 mm x 70 mm using traditional injection foaming techniques. The facings utilised on the panels were thermoplastic in nature, being made of polyethylene terephthalate (PET). As polyethylene terephthalate can exist in both amorphous and crystalline states, panels were made with both types of material. In addition, glass reinforcement was impressed behind the facing materials in

selected panels to improve primary adhesion and assist in providing better fire resistance.

Three sets of panels were made from each combination (four combinations in all): one for physical testing; one for fire testing; and the third as a reference. Physical tests revealed that the foams produced were satisfactory in terms of compressive strength and density. Adhesion was also found to be adequate with failure generally occurring in the body of the foam rather than at the interface of the foam and facing. Fire tests were particularly encouraging with all samples submitted passing the one hour insulation criterion of BS476 Pt. 20: 1987.

The results of physical testing are summarised as follows: Property Amorphous Amorphous Crystalline Crystalline (Mean Values) (No Glass) (Glass) (No Glass) (Glass) Compr. Strength 155 231 212 200 Density (kg/cm) 59 56 56 59 Strength/Density Ratio 2.63 4.13 3.79 3.39 Tensile Adhesion 126 160 113 95 Adhesion/Strength 0.81 0.69* 0.53 0.48 * Failure observed in foam core, not at surface The test methods used were as follows: Compressive Strength-BS 4370 Method 3 Direct Tensile Adhesion-BS EN 1607 Core Density-BS EN 845