Mineral wool, that is wool formed from fibres of inorganic materials, usually glass or rock, has long been used to form the insulating core to steel faced composite panels, manufactured predominantly for the construction industry. The theory of the mechanical properties of sandwich elements indicates that the resistance to any load supplied to a composite panel is primarily a function of the stiffness and strength of the steel, or other, facings. The structural purpose of the core material is primarily to keep the surface layers apart so that the laminate can function as a composite, i.e. a light-weight stiff structure.

Mineral wool, especially rockwool, is produced in slabs, in which the fibres lie mainly parallel to the plane of the slab. The earliest composite panel designs simply incorporated these rigid slabs of standard insulation material between the two facing panels, adhesive being applied at the interfaces between the slab and the facing materials. In this configuration the primary orientation of the fibres is parallel to that of the surface layer and with this orientation the composite sandwich element exhibits limited resistance to loading applied perpendicular to the element. Improvements to composite panel design were afforded by rearranging the mineral wool so that the fibres lie primarily _at right angles to the plane of the sandwich element. This was achieved by cutting the slab of material produced in the normal manner into slices at regular intervals, usually perpendicular to the machine direction, so as to form substantially rectangular slices of wool, known as lamellae. To form a sandwich element of the

lamellae, several lamellae were laid side by side, each lamella being positioned such that the fibres of the wool lie in a substantially perpendicular direction with respect to the plane of the element. The facing layers were adhered in the usual fashion, by the application of a layer of adhesive between the facing layer and the underlying mineral wool. With this arrangement of lamellae, the adhesion of the facing layers to the mineral wool was improved, there was an increased compressive strength at right angles to the plane of the panel and the load bearing capacity perpendicular to the panel was improved.

The first panels of the type mentioned in the previous paragraph had the lamellae arranged parallel to the shorter sides of the panel element and extending from one long side to the other. A problem with such a lay-up is that each joint between adjacent lamellae represents a plane of weakness. Thus it was found that with the application of a load to the panel, they tended to fail by means of wrinkling (local buckling) at the joints between lamellae. The joints represent areas of high stress concentration. Once the wrinkling has started, the panel loses its load bearing capacity (that is it exhibits very low bending stiffness) and continues to fail very quickly.

An improved lay-up used the lamellae with their longitudinal axis parallel to the long side of the panel element. Since the lamellae have a limited length, depending on the width of product produced by the line, generally two or more rows of these longitudinal arranged lamellae needed to be incorporated for the desired size panel. The joints between rows of lamellae still represent weaknesses, and the panels tend to fail at inadequate loads.

WO-A-90/07038 and WO-A-90/07039 describe sandwich elements in which the weakening effect of joints is eliminated by distributing the lamellae in a staggered arrangement. The arrangement avoids the presence of a

_{Mιt ΛΛ} _ PCT/GB92/01 21404

single joint extending from one long side of the panel to another.

All of the above described panel elements formed from lamellae are so called loose-lay arrangements. There is no 5 adhesive between adjacent lamellae, which are simply laid side by side and held in position by the adhesive between the facing layers and the wall. It is generally considered disadvantageous to adhere adjacent lamellae to one another by providing adhesion between their facing surfaces, since 0 such a layer may act as a bridge for transmission of heat or sound or other vibration. The positioning of lamellae in such loose-lay arrangements, especially with the complex staggered arrangements illustrated in the two international patent publications mentioned above, is time consuming. 5 Some of the above mentioned problems have been solved by the development described in EP-A-449414. That specification describes a product which comprises a board formed from several mineral wool lamellae arranged side by side, having the fibres arranged substantially 0 perpendicular to the panel, and which are held together by the application of a net adhered to the lamellae across the panel surface. The net may be formed of synthetic fibres or filaments or be a fabric or scrim of inorganic or organic fibres. The lamellae are preferably held in 5 compression across the plane of the panel. The panels thereby produced are used to make sandwich elements by placing them between the usual facing layers. However it is generally necessary to use more than one of the boards to form a single panel element. Although the "twin-scrim 0 lamellae" boards provide elements in which the weakness at joints between the boards are reduced, but which still have joints between boards which result in lines of weakness in the finished product. Furthermore it is difficult or impossible to produce a board which 5 incorporates a staggered edge profile which could make use of the minimisation of lines of weaknesses achieved by th staggered arrangement described in the PCT Internationa

patent publications mentioned above. Even if it were possible the edges of such panels would be somewhat fragile.

In GB-A-1400692 a method for producing parallel faced mats of mineral fibre is described in which a plurality of mineral wool slabs are assembled to form a packet (i.e. a cuboidal block) in which the slabs are held together by adhesive applied across adjoining faces, and the packet is then sliced by a band saw to form the mats. The slabs are arranged and the packet is sliced so that the fibres lie primarily perpendicular to the major faces of the mat. In one arrangement the slabs are arranged in the packet in a "fish-bone pattern" in which two groups of slabs are arranged with the planes of the slabs of the two groups perpendicular to one another and at an angle of about 45°

• to the horizontal and perpendicular to the vertical face cut by the saw blade. GB-A-1401131 describes a similar arrangement which includes the attachment by adhesive of a stiff backing sheet (for instance plasterboard) to at least one of the major faces of mat.

One problem with the mats described in these two specifications is that the method of manufacturing requires the use of adhesive in large quantities to adhere the slabs together in the packet and this is expensive and reduces the sound and heat insulation properties of the resultant mat.

An improved structural panel according to the present invention is substantially rectangular having side edges and end edges and is formed from a plurality of mineral wool lamellae arranged side by side such that the fibres of the mineral wool lie substantially perpendicular to the plane of the panel and such that there is no rectilinear joint between lamellae which extends from one side edge to the other side edge of the panel in a perpendicular direction, and is characterised in that the lamellae are arranged with their longitudinal direction at an angle in the range 25-65° to the side edges of the panel.

The structural panel is usually a sandwich element of the type generally described above, that is it comprises a facing layer on at lease one, and usually both, sides of the panel and adhered thereto. The facing layers may be any of those commonly used for such products, including sheet metal especially steel or aluminium, glass, wood, laminates, glass reinforced plastics, or combinations of any of these. The facing layers may have decorative and/or protective coatings on their outer surfaces. Furthermore the sandwich element may include a frame found in the mineral wool and/or facing layers at the panel edge.

There is generally no adhesive applied between facing surfaces of adjacent lamellae. Although the sandwich element may be made from loose-lay lamellae, this invention is of particular benefit where the element is formed from boards, each board comprising several mineral wool lamellae held together in side by side relationship by a net arranged across at least one, and preferably both, of the planar surfaces of the board and bonded to the mineral wool, the board having at least one side which is parallel to the long edges of the lamellae from which it is formed and another side edge which is parallel to the side edges of the structural panel/element. A convenient shape for at least one of the boards is a parallelogram which has an acute angle in the range 25-65°. In a parallelogram, the lamellae lie with their longitudinal direction parallel to one pair of sides and the board is arranged in the structural panel with the other pair of sides parallel to the panel side edges, so that the longitudinal direction of the lamellae then lie at the desired angle in the range 25-

65° to the side edges of the panel.

Preferably the boards from which a structural panel is formed include triangular shaped boards. Preferably these include substantially right angle triangular shaped panels, which form one or more corners of the structural panel. Such right angle triangular shaped boards generally have the lamellae arranged with their longitudinal directio

parallel to the longest side of the triangle. Right angle triangular elements, for instance whose longest side is the same length as one pair of parallelogram sides are convenient for use to form a panel with a parallelogram shaped board.

Alternatively triangular shaped boards may be combined side by side to form parallelogram shapes which may then be combined with other triangular shaped boards (including right angle triangle shaped boards) to form the rectangular structural panel.

By a judicious selection of board shapes, a minimum number of different boards may be used to make a structural element, or even a number of structural elements of different size, with minimal wastage. Another shape of board which it may be convenient to incorporate into the structural panel is trapezoidal, generally with one of the sides joining the pair of parallel sides being substantially perpendicular thereto and the other side being at an angle to the perpendicular, the acute angle being in the range 25-65°. A panel may for instance consist of at least two pairs of such trapezoidal boards, each said pair being arranged so as to form a parallelogram having the perpendicular edges in abutment, and the pairs being arranged side by side such that the abutting edge joints are staggered with respect to one another and preferably so that the edges of the two parallelograms joined to the edge forming the interface between the two pairs of boards are co-extensive and form part of the side edge of the structural panel. The lamellae in a board used to make a structural panel are preferably held together by a net adhered to the lamellae ^s described in EP-A-449,414. Preferably therefore the lamellae are held in compression, for optimal strength. The adhesive is generally a heat-activatable adhesive such as a fusible material or a hot-melt adhesive, or is curable by means other than heat.

The angle at which the lamellae are arranged with respect to the side edges of the panel lies between 25° and 65°. The angle is chosen so as to provide optimal strength characteristics in the final product, as well as the desired width of panel of the product, for ease of cutting, for minimising the number of different shaped pieces which require to be used in the final product. It is found most convenient for the angle to be about 30° or about 60° or, most preferably, 45°. According to a further aspect of the invention a new board, suitable for forming sandwich structural elements, is formed from several lamellae arranged side by side with the fibres of the mineral wool lying substantially perpendicular to the plane of the board, is triangular or quadrilateral shaped, in which the longitudinal direction of the lamellae lies parallel to one of the sides and which includes an acute angle in the range 25-65°.

Preferably the board is right angle triangular or is a parallelogram. The above mentioned boards of this second aspect of the invention may be made by producing a board comprising several lamellae arranged side by side, adhering the lamellae together using a net, and then cutting the panel to the desired shape of board. For instance the intermediate board may be of the same approximate shape as the desired final panel, so that the final cutting operation is primarily a trimming operation. Alternatively the lamellae may be arranged to form a parallel sided elongate web, which is subsequently cut to the desired shape, each elongate web thereby being used to form several boards, preferably with no waste between boards. The lamellae may be arranged transverse to the longitudinal length of such a web, so that the web width is generally the length of the lamellae. Alternatively the lamellae may be arranged longitudinally with respect to the elongate web. In this instance the web is generally longer than a single lamella, so that lamellae are laid with ends

abutting one another. Preferably the abutting ends of lamellae in adjacent rows are staggered with respect to each other in the manner described in the two above mentioned International patent publications. It is particularly convenient for such an elongate web to be cut to form parallelogram shaped boards, having an acute angle in the range 25-65° as desired. In order to form the final structural panel, such a parallelogram is simply rotated in its plane about the acute angle and placed side by side with appropriately size triangular boards and optionally another parallelogram shaped board to form the rectangular structural panel of the first aspect of the invention.

According to a further aspect of the invention, there is provided a process for forming the novel structural panel in which a plurality of mineral wool lamellae are laid side by side such that the mineral fibres lie substantially perpendicular to the plane of the panel and such that there is no rectilinear joint between lamellae which extends from one side edge of the panel to the other side edge of the panel in a direction parallel to the end edges, characterised in that each of the lamellae are arranged with their longitudinal direction at an angle in the range 25-65° to the side edges of the panel. Preferably the process comprises a first step in which several lamellae are formed into a board by arranging them side by side and adhering a net across at least one surface of the board, the board having at least one side parallel with the longitudinal direction of the lamellae, and a second step, in which several boards are arranged in side by side relationship such that all of the lamellae of at least one of the boards, and preferably all of the boards, are arranged at an angle in the range 25-65° with respect to the side edges of the rectangular structural element.

The element formed in this aspect of the invention preferably has the preferred features of the element described above.

According to a further aspect of the invention there is provided a process in which the novel board of the second aspect of the invention is formed, and in the process several mineral wool lamellae are arranged side by side such that the fibres of the mineral wool lie in a substantially perpendicular direction to the plain of the board, and are joined together by the adhesion across at least one, and preferably across both faces of the board of a scrim, and then cutting the board to the desired shape, being a triangle or quadrilateral, to one side of which the longitudinal direction of the lamellae is parallel, and which includes an acute angle in the range 25-65 ^β C between at least two of the sides.

The process for forming the novel boards may be followed by a process of arranging the boards to form a structural element, which is in accordance with the second step of the first aspect of the process.

The mineral wool used in the present invention may comprise glass wool, but is preferably rockwool. The mineral wool preferably comprises a binder, of known type, usually a hydrophobic binder to impart moisture resistance. The mineral wool used generally has a density of at least 50 kg/m and up to 200 kg/m . Preferably the density is in the range 80-180 kg/m . Where the lamellae are first joined to form boards, the method of board formation is generally as described in EP-A-449414. Thus net may comprise a fabric, a scrim or a non-woven bath of an inorganic mineral fibre, for instance glass fibre, or of synthetic organic fibre or filaments. The use of a scrim is essential in order that adhesive applied to the facing layers in a structural sandwich element may penetrate through the net to the underlying mineral wool, so as to achieve adequate adhesion. Suitable adhesives for adhering the net to the lamellae are generally curable adhesives or hot melt adhesives.

When the structural panel is a sandwich element, the facing layers are adhered by conventional adhesives to the

mineral wool. One particular convenient form of adhesive is a water-activated foaming polyurethane adhesive. The adhesive is applied, generally by spraying, to one or both of the mineral wool or facing layer surface, is subsequently sprayed with water to foam and activate the adhesive, and the components are then joined in a press and allowed to cure.

A finished structural panel is conveniently provided in a width in the range 200-1500 mm, preferably in the range 300-1200 mm. A standard width of structural panel is 600 mm. The height (or length of the panel) may be any convenient length, for instance at least l m, for instance at least 1.5 m, for instance around 2 m or more. The panel is preferably less than 3 m in length, more preferably less than 2.5 in length. For some uses panels with dimensions outside these ranges may be convenient.

The panel is useful for many applications in the construction industry, for instance as internal wall panels, cladding for buildings, roofing or ceiling panels or even floor or walk-on ceiling panels. The panels have improved load bearing capacity, since joints forming lines of weakness running perpendicularly across the panel are avoided, and it is in these load bearing applications that the present invention is of most benefit. The use of lamellae angled to the edges of a panel is believed to improve the transmission of forces across the panel so that there is a minimisation of stress concentration at joints between lamellae or boards.

The invention is further illustrated in the accompanying drawings, in which:

Figure 1 is a perspective view of a slab of rockwool with lamella that has been sliced from it;

Figures 2a and 2b are plan views of two lay-up arrangements of lamellae used for structural panels in the prior art;

Figure 3 is a plan view of an elongate web formed from several lamellae arranged transverse to the longitudinal

direction of the web, indicating the position of the cut for making suitable boards of the invention;

Figure 4 shows the arrangement of boards cut according to figure 3 to form a structural element; and Figure 5 is a perspective view of a board having the layout of figure 4 and with the facing layer and scrim partially cut away.

Referring first to figure 1 a slab of binder fixed mineral wool as produced by the normal machinery is illustrated. The slab l is produced continuously having the width illustrated, being the distance between points A and B. The slab has cut ends, 2 and 3. The fibres, which are visible at end 2 and along side 4 can be seen to lie substantially parallel with the plane of the slab. To form lamellae the slab is cut intermittently across its width, along the surface A B C D to form a lamella 5.

Several such lamellae may be arranged to form a sandwich element or board to be used therein by lying them side by side such that the fibres lie substantially perpendicular to the plane of the board or element.

In figure 2 two lay-ups of lamellae which have been used in the prior art are illustrated. In figure 2a a longitudinal arrangement is shown in which two rows 6, 7, each comprising five lamellae are used. From a comparison of the arrangement of lamellae 5 in figure 1 and figure 2a it can be seen that what was previously the thickness of the slab used as the starting material becomes the width of the lamella in the plane of the panel, that is the distance B c and A D. The thickness of the panel is determined by the thickness of the slices cut from the slab of mineral wool. With the arrangement of figure 2a there is a joint between lamellae 8 which extends from one side 9 of the panel to the other side 10 running substantially perpendicular to those side edges. This joint acts to concentrate stresses and when the panel is subjected to forces applied perpendicular to the plane of the panel.

when it is supported at both ends, leads to wrinkling along the joint 8 and subsequent failure.

Figure 2b shows another arrangement of lamellae to form a panel as used in the prior art. In this arrangement the lamellae are arranged transverse to the long edges 11, 12 of the panel. In this embodiment there are joints between each pair of adjacent lamellae each of which acts as a line of weakness leading to failure under applied loads. In figure 3 a longitudinal web 13 is formed from several lamellae 14, 15, arranged transverse to the longitudinal direction of the web and extending across the whole width thereof. As in figures 2a and b, the lamellae are arranged so that the fibres of the wool lie substantially perpendicular to the plane of the web. Not shown in the diagram are scrims adhered across both surfaces of the web by means of which the lamellae are held together, usually under compression as described in EP-A- 449,414. At intervals along the length of the web it is cut along lines 16 and 17, each at the same angle, in this instance of 45°. The angle may alternatively be at any value between 25 and 65°.

The board formed by cutting along lines 16 and 17 is a parallelogram having an acute angle of 45° and having corners E, F, G and H. Also shown in figure 3 is a cut along another line 18, which is also at an angle of 45° to the sides of the web, but in the opposite direction to line 17. This cut forms a right angle triangle with corners J, K and L.

The boards cut from the web illustrated in figure 3 are laid up to form a structural element as indicated schematically in figure 4. The rectangular element has side edges 20, 21 and end edges 22, 23 and is formed from the parallelogram 19 having corners E, F, G, H and two similar triangles 24, 25. Triangle 24 has corners J, K, L, which correspond to those shown in igure 3. As can be

seen from figure 4 the lamellae 14, 15 of the parallelogram shaped board, as well as the lamellae 26, 27 of each of the triangular boards, each have their longitudinal lengths at an angle of around 45° to the side edges 20, 21 of the element.

Figure 5 shows further details of the board of figure 4. It can be seen that the fibres 28 of the lamellae are arranged substantially perpendicular to the plane of the element 29. Each board, 19, 26 and 27 is formed from several lamellae 14, 15 held together by a scrim 36, 30. The scrim is formed from glass fabric, although organic fibres, usually synthetic fibres, can be used instead. Since the scrim is part of the board, there is a joint 31 between adjacent boards 19, 27, throughout the scrim and lamellae. There is on the opposite side of each board a further scrim 32, 33. Each of the scrims is adhered to the underlying lamellae by means of a hot-melt adhesive such as fusible polyethylene by subjecting the laminate of lamellae, polyethylene and scrims to a heat teatment. Across the entire arrangement of boards on each side there is provided a facing layer 34, 35. In this instance the facing layer is formed from sheet steel. The facing layer is attached to the lamellae/scrim boards by means of further adhesive, usually a water-activated foaming polyurethane adhesive which is applied to one surface before the components are assembled and placed in a press for curing of the adhesive.