The present invention relates to a building element which comprises at least a first cover layer and a second cover layer, which are connected to opposite sides of an intermediate core consisting of at least a first core material and a second core material. The building element can be used in load-bearing floor structures or walls in house construction, preferably in construction of smaller houses.

Different types of building elements with so-called sandwich structure, for use in wall and roof structures, are previously known. One example is sandwich elements consisting of a core of polystyrene or polyurethane foam which has been provided with cover layers of metal sheeting on one or both sides by means of gluing. A disadvantage of this type of building elements is that they may rapidly lose their load-bearing ability if they are exposed to high temperatures in the event of fire, since the metal sheets start to buckle and the core material softens or even turns into gaseous state so that the sandwich structure collapses.

A building element intended to solve the above-mentioned problem of poor fire resistance is described in SE 450 020. This building element comprises a board-shaped insulating core of polystyrene or similar material, and two thin steel sheets covering the side surfaces of the insulation board. An additional board, in the form of a wood fibre or gypsum board, or the like, is disposed between at least one of the metal sheets and the insulation board. The additional board is intended to maintain the load-bearing ability of the element for a certain period of time when the element is subjected to external heat, and to prevent the formation of gaseous phase of the core material by insulating the board from the external heat supply and absorbing latent heat therefrom. This effect is achieved in that the board is partially carbonized when a wood fibre board is used, and by means of vaporization of crystal water when a gypsum board is used.

EP 1 253 257 describes a method for manufacturing a surface element, for a wall or a floor or a roof, having another type of sandwich structure. The described method is claimed to make production of surface elements of different sizes easier and cheaper and comprises that a plurality of sandwich plates are produced and wherein to produce a sandwich plate at least one insulating plate is placed on a lower cover plate and wherein an upper cover plate is placed on the insulating plate, wherein the individual sandwich plates are joined to one another by their lateral edges to a sandwich web, after which the sandwich web is cut up or sawn up into the individual surface elements. The cover plates in the surface elements manufactured according to EP 1 253 257 can be selected from the group gypsum panels, wood chip panels, vermiculite panels, whereas panels of expanded plastic, preferably expanded polystyrene, are used as insulating panels. According to EP 1 253 257, the cover plates can be joined to the insulating plates by means of an adhesive, which can be a polyurethane adhesive, and the insulating plates can be separated from each other by means of reinforcing ribs, preferably consisting of wood.

In addition to the above-mentioned problem of poor fire resistance, many of the previously known building elements with sandwich structure have the disadvantage that they do not have sufficient strength and load-bearing ability to be usable in load-bearing floor structures or walls, without using reinforcing ribs or intermediate girders of wood, supporting frameworks of metal, or other additional supporting structures. The use of such supporting structures of wood or metal increases the risk of structure-borne sound propagation in the finished building.

A first object of the present invention is therefore to provide a building element having an improved sandwich structure, which is bearing and not only self-supporting and which gives the building element sufficient strength and load-bearing ability to be usable in both load-bearing floor structures and bearing walls without any additional support structure, at the same time as the building element minimizes the risk of structure-borne sound propagation and meets the high demands for sound insulating ability and also heat insulating ability placed on the construction of modern houses.

This first object is achieved by means of a building element according to claim 1, comprising at least a first cover layer and a second cover layer, which are connected to opposite sides of an intermediate core consisting of at least a first core material and a second core material, wherein the first and/or the second cover layer comprises one or several stiffening layers having a thickness of at least 5 mm and a modulus of elasticity which is higher than 3000 MPa and higher than the moduli of elasticity of said core materials, wherein the first core material has a higher modulus of elasticity than the modulus of elasticity of the second core material, which has a modulus of elasticity lower than 10 MPa, wherein the intermediate core is constituted by one or several edge pieces of the first core material surrounding one or several intermediate pieces of the second core material, wherein said one or several intermediate pieces of the second core material covers/cover at least 60 % of the area delimited by said one or several edge pieces of the first core material, wherein the first and the second cover layer, respectively, exhibit outer edge regions which are connected in a shear-resistant manner to opposite sides of said one or several edge pieces of the first core material by means of a fire-resistant adhesive, and wherein said fire-resistant adhesive covers at least 5 % of the area of the inwardly facing surface of the respective cover layer in order to provide a shear-resistant connection where the first and second cover layer are fixed at a distance from each other of at least 70 mm via the intermediate first core material which serves as a spacing element.

A second object of the present invention is to provide a building element which reduces the risk of a possible fire getting hold of the building element and spreading between different spaces in a building.

This second object is achieved by means of a building element according to claim 3, where at least the outwardly facing side of one of or both the cover layers in the building element exhibits a fire-resistant layer which has better fire resistance than the other material layers in said cover layer and/or better fire resistance than at least one of said core materials.

A third object of the present invention is to provide a building element which reduces the risk of the sandwich structure of the element collapsing due to the load-bearing material in the core softening, turning into gaseous state, or igniting during a fire.

This third object is achieved by means of a building element according to claim 8, where the first core material is a foam material with high fire resistance.

A fourth object of the present invention is to provide a building element which reduces the risk of sound and heat insulating material in the core igniting during a fire.

This fourth object is achieved by means of a building element according to claim 11, where the second core material consists of one or several fire-resistant or fire-inhibiting materials selected from the group consisting of glass wool, rock wool, or cellulose wool treated with flame-inhibiting agents.

A fifth object of the present invention is to provide a building element whose sandwich structure is capable of maintaining its load-bearing ability for a sufficiently long period of time during a fire.

This fifth object is achieved by means of a building element according to claim 12, where the fire-resistant adhesive providing the shear-resistant connection between the cover layers and the core material and/or between boards comprised in the cover layers is a fire-resistant adhesive with a shear strength of at least 5 MPa at 110 °C.

A sixth object of the present invention is to provide a building element having a sandwich structure which can be manufactured by a simple manufacturing process from easily available materials and at a relatively low total cost, but which still has sufficient strength and load-bearing ability to be used in load-bearing floor structures and walls and where it can provide very good sound insulating ability and small risk of structure-borne sound propagation, high heat insulating ability and good fire resistance.

This sixth object is achieved by means of a building element according to claim 19, where both the first and the second cover layer consist of double fibre-reinforced gypsum boards, where the first core material is provided in the form of ribs of a PET foam, where the second core material is provided in the form of mineral wool boards, and where the fibre-reinforced gypsum boards and the ribs of PET foam are glued together by a fire-resistant polyurethane adhesive containing at least 30 % by weight of chalk.

Further objects of the invention and the features enabling these objects to be achieved will become evident from the following description.

In the following, the invention will be described in a number of different embodiments with reference to the accompanying drawings, in which:

• Figure 1 is a schematic perspective view of a building element according to a preferred embodiment of the invention, in which different pieces of core material have been indicated with dashed lines;
• Figure 2 is a schematic perspective view of the first and second cover layers, respectively, and the pieces of first and second core material, respectively, which are to be glued together in order to produce the building element according to the embodiment shown in Figure 1;
• Figure 3 is a schematic plan view illustrating the positioning of the first and second core materials, respectively, inside the core of the building element according to the embodiment shown in Figure 1; and
• Figure 4 is a cut sectional view of the building element according to the embodiment shown in Figure 1, as seen in the longitudinal direction of the building element, in which it can be seen that the cover layers outside the intermediate core consist of two stiffening layers of board material glued together.

In the following, a number of embodiments of a building element according to the invention will be described in greater detail with reference to the accompanying Figures 1-4.

Figure 1 is a schematic perspective view of a building element according to a preferred embodiment of the invention, Figure 2 is a schematic perspective view of cover layers and pieces of first and second core material, respectively, which are to be glued together in order to form the building element, Figure 3 is a schematic plan view illustrating the positioning of the core materials inside the core, and Figure 4 is a cut sectional view, as seen in the longitudinal direction of the building element, in which it can be seen that the cover layers outside the core consist of two stiffening layers of board material glued together in the shown embodiment.

As is evident from the figures, the building element 10 according to the invention comprises at least a first cover layer 11 and a second cover layer 19, which are connected to opposite sides of an intermediate core consisting of at least a first core material 12, 13, 14, 15, 16 and a second core material 17, 18.

As is illustrated in Figure 4, the first 11 and/or the second cover layer 19 comprises one or several stiffening layers 11', 11"; 19'; 19" having a thickness of at least 5 mm and a modulus of elasticity which is higher than 3000 MPa and higher than the moduli of elasticity of the core materials 12, 13, 14, 15, 16; 17, 18.
The first core material 12, 13, 14, 15, 16 has a higher modulus of elasticity than the modulus of elasticity of the second core material 17, 18, which has a modulus of elasticity lower than 10 MPa. Accordingly, the first core material has a modulus of elasticity between the moduli of elasticity of the second core material and of the stiffening layers, respectively, and is intended to interact with the stiffening layers in order to give the building element high shear strength and load-bearing ability, whereas the second core material has a very low modulus of elasticity and is intended to give the building element good sound insulating and heat insulating ability.
As is evident from Figure 2, the intermediate core is constituted by one or several edge pieces 12, 13, 15, 16 of the first core material surrounding one or several intermediate pieces 17, 18 of the second core material, wherein said one or several intermediate pieces 17, 18 of the second core material cover at least 60 % of the area delimited by said one or several edge pieces 12, 13, 15, 16 of the first core material. It has been found that such a design of the core gives the building element good sound insulating ability and minimal propagation of structure-borne sound.
As is also evident from Figure 2, the first 11 and the second cover layer 19, respectively, exhibit outer edge regions 20, 21, 22, 23; 24, 25, 26, 27 which are connected in a shear-resistant manner to opposite sides of said one or several edge pieces 12, 13, 15, 16 of the first core material by means of a fire-resistant adhesive (not shown in the figures). The fire-resistant adhesive covers at least 5 % of the area of the inwardly facing surface of the outer edge regions 20, 21, 22, 23; 24, 25, 26, 27 of the respective cover layer 11, 19 in order to provide a shear-resistant connection where the first 11 and second cover layer 19 are fixed at a distance from each other of at least 70 mm via the intermediate first core material 12, 13, 15, 16 which serves as a spacing element. The first core material has, of course, to cover more than said 5 %. It has been found to be necessary that the fire-resistant adhesive covers at least 5 % of said area to enable the sandwich structure of the building element to maintain its load-bearing ability for a sufficiently long period time during a fire, and that a distance between the cover layers of at least 70 mm is required in order to give the sandwich structure of the building element sufficiently high shear strength and load-bearing ability for the intended use.

To give the building element 10 an even better load-bearing ability, it preferably comprises at least one, relative to said edge piece(s) 12, 13, 15, 16 and said cover layers 11, 19, inner piece 14 of the first core material which is disposed between at least two of said intermediate pieces 17, 18 of the second core material, as is evident from Figure 2, wherein said first 11 and said second cover layers 19, respectively, further exhibit, relative to said outer edge regions 20, 21, 22, 23; 24, 25, 26, 27, inner regions 28; 29 which are connected in a shear-resistant manner to opposite sides of said at least one intermediate piece 14 of the first core material by means of said fire-resistant adhesive. Accordingly, pieces or ribs of the first core material are preferably provided along the edges of the entire building element and inside the core, e.g. with a c-c distance of 600 mm, but also around any recesses in the building element for windows, doors or other purposes.

In a preferred embodiment, illustrated in Figure 4, at least the outwardly facing side of one of or both the cover layers 11, 19 in the building element 10 exhibits a fire-resistant layer 11', 19' which has better fire resistance than the other material layers in said cover layer and/or better fire resistance than at least one of said core materials 12, 13, 14, 15, 16. Such a design reduces the risk of a possible fire getting a hold of the building element.

The first 11 and/or second cover layer 19 advantageously consist(s) of several boards 11', 11"; 19', 19" of identical or different board materials glued to each other in a shear-resistant manner. Such a design provides an opportunity to optimize the characteristics of the building element for different applications, and to use cheaper board materials in one of or both the cover layers when the building element is intended for less demanding applications.

In a preferred embodiment, the outwardly facing side 11'; 19' of the first 11 and/or second cover layer 19 in the building element 10 consists of a board material selected from the group consisting of gypsum boards, fibre-reinforced gypsum boards and fibre cement boards. Such a choice of material gives the building element good fire resistance.

In one advantageous embodiment, the outwardly facing side 11'; 19' of the first 11 and/or second cover layer 19 in the building element 10 consists of a board material containing only inorganic matter. Such a choice of material reduces the risk of mould growth if the building element is to be used in humid spaces.

In another embodiment, the inwardly facing side 11"; 19" of the first 11 and/or second cover layer 19 in the building element 10 consists of a board material selected from the group consisting of gypsum boards, fibre-reinforced gypsum boards, fibre cement boards, wood fibre boards or plywood. This embodiment makes it possible to manufacture building elements with different characteristics and material costs using easily available board materials.

In a preferred embodiment of the building element 10 according to the invention, the first core material 12, 13, 14, 15, 16 is a foam material with high fire resistance. Such a choice of material reduces the risk of the sandwich structure of the element collapsing due to the load-bearing material in the core softening, turning into gaseous state, or igniting during a fire. The first core material 12, 13, 14, 15, 16 preferably consists of one or several materials selected from the group consisting of PET foams, PVC foams and glass foams. Such materials are commercially available.

In the building element 10 according to the invention, the second core material 17, 18 preferably consists of one or several porous materials of loose or loosely bonded organic and/or inorganic fibres. In a preferred embodiment, the second core material 17, 18 consists of one or several fire-resistant or fire-inhibiting materials selected from the group consisting of glass wool, rock wool, or cellulose wool treated with flame-inhibiting agents. Such a choice of material reduces the risk of the sound and heat insulating material in the core igniting during a fire.

In a preferred embodiment of the building element 10 according to the invention, the fire-resistant adhesive providing the shear-resistant connection between the cover layers 11; 19 and the core material 12, 13, 14, 15, 16 and/or between boards 11', 11"; 19', 19" comprised in the cover layers is a fire-resistant adhesive with a shear strength of at least 5 MPa at 110 °C. Such a choice of adhesive provides a building element whose sandwich structure is capable of maintaining its load-bearing ability for a sufficiently long period of time during a fire. In an even more advantageous embodiment, the fire-resistant adhesive is a fire-resistant adhesive which retains a shear strength of at least 2 MPa up to at least 130 °C.

The fire-resistant adhesive providing the shear-resistant connection between the cover layers 11; 19 and the core material 12, 13, 14, 15, 16 and/or between boards 11', 11"; 19', 19" comprised in the cover layers is preferably a fire-resistant adhesive selected from the group consisting of polyurethane adhesives with flame-retarding filler and cement-based adhesives. In a preferred embodiment, the fire-resistant adhesive is a fire-resistant polyurethane adhesive containing at least 30 % by weight of flame-retarding filler, ever more advantageously at least 50 % by weight of flame-retarding filler. The flame-retarding filler is preferably calcium carbonate, particularly advantageously in the form of chalk, or calcium sulphate in the form of gypsum which has a fire-retarding ability owing to crystal water, but also other fire-retarding fillers are conceivable, such as talc, sand, etc.

In a first particularly advantageous embodiment of the invention, the first 11 cover layer, the intermediate core material 12, 13, 14, 15, 16, the second cover layer 19, and the intermediate shear-resistant, fire-resistant adhesive layers give the building element 10 a total thickness of at least 100 mm, for use as a wall element.

In a second particularly advantageous embodiment of the invention, the first 11 cover layer, the intermediate core material 12, 13, 14, 15, 16, the second cover layer 19, and the intermediate shear-resistant, fire-resistant adhesive layers give the building element 10 a total thickness of at least 150 mm, for use as a floor structure element.

In particularly preferred embodiment of the building element according to the invention, both the first 11 and the second cover layer 19 consist of double fibre-reinforced gypsum boards 11', 11"; 19', 19". The first core material is provided in the form of ribs 12, 13, 14, 15, 16 of a PET foam, whereas the second core material is provided in the form of mineral wool boards 17, 18. The fibre-reinforced gypsum boards 11', 11"; 19', 19" and the ribs 12, 13, 14, 15, 16 of PET foam are glued together by a fire-resistant polyurethane adhesive containing at least 30 % by weight of chalk. Such a building element has a sandwich structure which can be manufactured by a simple manufacturing process with only a few process steps. For example, in its most simple design, the process can comprise cutting-up of cover layers and pieces of core material starting from commercially available board materials and foam materials, respectively, laying-out of first cover layer, application of fire-resistant adhesive, laying-out of pieces of first and second core materials, respectively, in a desired pattern, adhesive application, application of second cover layer, drying/curing of the fire-resistant adhesive, and possibly trimming or other finishing of the building element. The process steps may be substantially manual or automated to desired degree. The sandwich structure according to the invention consists of easily available materials, which together result in a relatively low total cost, but still give the building element a sufficient strength and load-bearing ability to be used in load-bearing floor structures or walls, and where it can provide very good sound insulating ability and small risk of structure-borne sound propagation, high heat insulating ability, and good fire resistance.

In the foregoing, the present invention has been described with the aid of a number of different embodiments and with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the described embodiments and to what is shown in drawings, but that also other embodiments are conceivable within the scope of the invention as it is defined by the following claims.