CHLORIDE

Technical Field

[0001] This invention relates to a board for use as a building material as a cladding or internal wall sheet material. The invention provides in one embodiment, a sheet materia! of composite construction, having some advantageous properties.

Background Art

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.

[0003] Plasterboard such as that sold as Gyprock TM, also composite cement fibreboard which formerly was an asbestos cement product, have been used as building materiais as daddtng and sheeting for internal wails. Cement fibreboard has been used for external wail and under-eve cladding, due to its superior weathering characteristics, whereas plasterboard is used as an internal wal! cladding. Neither of these building materiais are particularly fire retardant, and cement fibreboard is known to spall when heated.

[0004] Throughout the specification unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Summary of Invention

[0005] It is an object of this invention to provide a composite board having fire retardant properties.

[0006] In accordance with one aspect of the present invention there i provided a method of forming a composite board, comprising the following steps: providing a mould into which the composite board is to be formed! preparing a facing composition comprising a pourabie and spreadaUle slurry of a solid component including at least 59% by weight magnesium oxide powder, optional components, and inert impurities, and a first aqueous solution of MgCI ₂ at S.G. of from 1,05 to 1.20; preparing a main body composition comprising a pourabie and spreadab!e slurry of a solid component including 7% to 40% by votume magnesium oxide, 10% to 85% by volume of a particulate ceiiufosie material, and from 5% to 40% by volume of a non-celtulosic lightening filler, and. a second aqueous solution of gCfe at S.G. of from 1.05 to 1.20; pouring the facing composition into said mould and spreading the facing composition substantially evenly in said mould with at least one woven cloth reinforcing sheet layer contained therein or thereon, in a first layer to a thickness of from about 1 mm to 6 mm; pouring the main body composition into said mould and spreading the main body composition on top of said first layer, in a second layer to a thickness of from about 3 mm; placing and containing said mould in a controlled atmosphere to cure and dry.

[0007] Inert impurities included in the solid component would typically include impurities included in the magnesium oxide component. These vary depending on the source of the MgO, and may include other magnesium components, calcium compounds, and iron containing impurities.

[0008] Preferably the facing composition is poured in a first layer to a thickness of from about 1 mm to 5mm,

[0009] Preferably the facing composition is poured in a first layer to a thickness of from about 1 mm to 4mm.

[0010] Preferably the facing composition is poured in a first layer to a thickness of from about 1 mm to 3mm.

[0011] Preferably the facing composition is poured in a first layer to a thickness of from about 1,5 mm to 3mm, [0012] Preferably the facing composition is poured in a first layer to a thickness of in the order of anywhere between 1.5 mm, 2 mm, 2,5 mm and 3mm.

[0013] Preferably said facing composition solid component comprises at least 85% by weight of magnesium oxide of at least 70% purity. However, it is most preferred that the magnesium oxide has a purity in the range of 97% to 99%.

[0014] Preferably said facing composition solid component includes up to 15% by weight of one or more dry hydrated silicates. These may be selected from days including kaolin. The inclusion of this component imparts improved flexibility to the composite board.

[0015] Preferably said facing composition solid component includes u to 15% by weight of kaolin.

[0016] Preferably said facing composition solid component includes up to 5% by weight of aluminium oxide powder.

[0017] Preferably said facing composition solid component includes up to 4% by weight of aluminium oxide powder.

[0018] Preferably said facing composition solid component includes up to 3% by weight of aluminium oxide powder.

[0019] Other optional components may include carbon, colourants and dyes.

[0020] Preferably said first aqueous solution has an S.G. of from about 1.11 to 1.19.

[0021] Preferably said first aqueous solution has an S.G. of from about 1.12 to 1.18.

[0022] Preferably said first aqueous solution has an S,G, of from about 1.13 to 1.17.

[0023] Preferably said first aqueous solution has an S.G. of from about .1,14 to 1.16.

[0024] Preferably said first aqueous solution has an S.G. of about 1.15 to 1.17.

[0025] Preferably said first aqueous solution includes up to 15% by volume of sodium silicate. The addition of sodium silicate reduces porosity of the cured composite board, improves water resistance of the composite board, and aids in the curing process,

[0026] Preferably said first aqueous solution includes up to 10% by volume of sodium silicate,

[0027] The proportion of solid component to first aqueous solution is about 1.8: 1 to 1.5: 1 by weight, and most preferably about 1.6: 1,

[0028] Preferably said second aqueous solution has an S.G. of from about 1.11 to 1.19.

[0029] Preferably said second aqueous solution has aft S.G, of from about 1.12 to 1.18.

[0030] Preferabl said second aqueous solution has an S.G. of from about 1.13 to 1.17.

[0031] Preferably said second aqueous solution has an S.G. of from about 1,14 to 1.16.

[0032] Preferably said second aqueous solution has an S.G. of about 1.15 to 1.17.

[0033] Preferably said second aqueous solution includes up to 15% by volume of sodium silicate,

[0034] Preferably said second aqueous solution includes up to 10% by volume of sodium silicate,

[0035] Preferabl the woven cloth reinforcing sheet layer is a woven fibreglass mesh.

[0036] Preferably there is one woven cloth reinforcing sheet layer contained within the facing composition layer.

[0037] Preferably there are two woven cloth reinforcing sheet layers contained within the facing composition layer.

[0038] Alternatively o additionally, preferably there may be one woven cloth reinforcing sheet layer at the boundary of the facing composition layer and the main body composition layer. £0039] Preferably there is one woven cloth reinforcing sheet layer contained within the facing composition iayer, and one woven cloth reinforcing sheet layer at the boundary of the facing composition iayer and the main body composition layer.

[0040] Preferably there is provided at least one woven cloth reinforcing sheet iayer contained within said main body composition.

[0041] Preferably said main body composition includes from 8% to 35% by volume of magnesium oxide.

[0042] Preferably said main body composition includes from 9 to 30% by volume of magnesium oxide.

[0043] Preferably said main body composition includes from 10% to 20% by voiume of magnesium oxide,

[0044] Preferably said main body composition includes from 12% to 18% by volume of magnesium oxide.

[0045] Preferably said main body composition includes from 40% to 80% by volume of said particulate cellulosic material.

[0046] Preferably said main body composition includes from 50% to 75% by volume of said particulate cellulosic material.

[0047] Preferably said main body composition includes from 60% to 75% b voiume of said particulate cellulosic material.

[0048] Preferably said particulate cellulosic material is selected from sawdust, wood chips, bark chips, by-products of cropping including husks and hulls.

[0049] Preferably said main body composition includes by voiume from 5% to 10% of rice husk as part of said particulate ceiluiosic material,

[0050] Preferably said main body composition includes from 8% to 30% by volume of said non-cellulosic lightening fiifer,

[0051] Preferably said main body composition includes from 10% to 20% by volume Of said ήοη-c ^' eilulosic lightening filler. [0052] Preferably said main body composition includes about 15% by volume of said non-cel!uiosic lightening filler.

[0053] Preferabiy said non-ceilulosic lightening filler is selected from one or more of expanded perfite, expanded foam polymer beads such as polystyrene foam beads. The non-celluiosic lightening ftiler acts to reduce the weight of the finished product.

[0054] Preferably said main body composition solid component includes up to 10% by volume of one of more dry hydrated silicate compositions. These may be selected from clays including kaolin.

[0055] Preferably said main body composition solid component includes up to 8% by volume of kaolin.

[0056] Preferably said main body composition solid component includes up to 5% by volume of kaolin.

[0057] Preferabiy said main body composition solid component includes up to 5% by volume of aluminium oxide powder.

[0058] Preferably said main body composition solid component includes up to 4% by volume of aluminium oxide powder.

[0059] Preferably said main body composition solid component includes up to 3% toy volume of aluminium oxide powder.

[0060] Preferably said main body composition solid component includes up to i% b volume of boric acid,

[0061] Preferably said main body composition solid component includes about 0.5% by volume of boric acid,

[0062] The proportion of solid component to second aqueous solution is about 1.8: 1 to 1.5: 1, and most preferably about 1.6: 1; however, the exact amount depends on the moisture component of the dry ingredients.

[0063] Preferably, prior to placing the mould in a ki!n for the wet composition board to cure and dry, an additional step is included comprising placing a single layer of fabric on the exposed surface of the slurry forming the main body composition, to bond therewith. This may comprise hessian or another similar soft woven fabric, and provides a soft surface so that cured composite board can be stacked once extracted from the mould, without scratching the surface of the facing composition.

[0064] Preferably also before placing the mould in a kiin for the wet composition board to cure and dry, a further additional ste is included comprising

compressing the uncured board with at least one roller to extrude excess thickness and provide a uniform thickness in the product prior to curing.

[0055] Preferably the step of placing and containing said mould in a controlled atmosphere to cure and dry comprises placing the mould in an atmosphere having a temperature of from 30 degrees Celsius to SO degrees Celsius for a nominal 12 hour period. Following this, preferably the cured product is separated from the moulds, and the cured product is subject to a further low temperature (at 25 degrees Celsius low humidity curing process for a nominal period of one week.

[0Q66] The kiln drying is a low temperature operation, at 30 degrees Celsius fo about 12 hours. This time would be increased if a lower temperature is used. The important point is not to drive off the excess moisture before full curing has taken place.

[0067] On curing and drying of the composite board It is removed from the moulds and has its edges trimmed to the required board size.

[0068] Also in accordance with the invention there is provided a composite panel product made in accordance with the above described method,

[0069] Further, in accordance with the invention there is provided a composite building product having a facing layer formed from a facing composition comprising a pourable and spreadable slurry of a solid component including at least 59% by weight magnesium oxide powder, optional components, and inert impurities, and a first aqueous solution of MgCI ₂ at S.G. of from 1.05 to 1.20, spread to a thickness of from 1 mm to 6 mm and having at least one woven cloth reinforcing sheet layer contained therein.

Description of Embodiments

[0070] Two preferred embodiments will now be described i the following description of a process for producing a fire resistant composite board for use in external and internal cladding for walls and ceilings in buildings. The finished cladding product comprises sheets of 3.9 metres x 1.2 metres, and 8 mm thick,

[0071] To make the cladding product, a mould of 4.0 metres x 1,3 metres is provided, with sides to contain the slurry used in the method. The mould is laid on a horizontal surface so that the slurry does not flow which would result in an uneven thickness in the completed composite board. The mould surface is iubricated with a vegetable oil mould release agent, prior to commencing the first pour.

[0072] A solution of magnesium chloride is prepared having a specific gravity of 1.17.

[0073] A facing surface slurry is then made using some of the solution. The facing surface slurry comprises 98% by weight of reactive magnesium oxide powder and 2% by weight aluminium oxide, mixed in a mixing vessel with an auger prior to adding the solution, with mixing, to form a slurry. The total weight of solids required for the facing surface slurry for a single 4 metre x 1.3 metre mould will depend on the actual thickness required in the facing surface layer. Nine litres of solution is added for every 16 kg of solid. The magnesium oxide powder is calcined dolomite, and may contain impurities comprising magnesium carbonate, calcium compounds (oxide, carbonate, and chloride, and ferric impurities.

[0074] A main body slurry is made comprising by volume, 14% reactiv magnesium oxide, 64.5% dry sawdust, 15% expanded perlite, 6% rice hull, and 0.5% boric acid also mixed in a mixing vessel with an auger, before solution is added to form a slurry. The weight of solids required for the main body slurry for a single 4 metre x 1.3 metre mould will depend on the actual thickness required in the main body layer. The slurry of the main body is of thicker paste like consistency than the facing surface slurry, In practice the amount of solution required to form the main body slurry is determined by the moisture content in the solids.

[0075] The slurries are both prepared on a just-in-time basis, since the hydraulic setting process will commence, and for obvious reasons it is necessary that the curing process take place in the mould as opposed to in the mixing vessel. [0076] After the application of mould release into the mould, a layer of finishing slurry is spread to a nomina! 3mm thickness, This is followed by the placement of a layer of reinforcing in the form of fibreglass woven cloth, with application of lightl weighted wiper which is wiped across the surface to smooth the cloth level, contacting the doth with the slurry and excluding air. A further layer of finishing slurry is spread to a nominal 3mm thickness. This is followed by the placement of a layer of reinforcing in the form of fibreglass woven cloth, with application of a lightly weighted wiper which is wiped across the surface to smooth the clot level, contacting the cloth with the slurry to excluding air,

[0077] This is immediately followed by the application of a layer of main body slurry of nominal 3mm thickness, followed by lying a layer of soft cloth onto the top. To provide a uniform thickness in the completed composite board, while contained in the mould the boards are pushed through a roller, with excess slurry being pushed out at the sides.

[0078] The boards are taken to a heat curing room where they are held at a constant temperature of from 30°C to 50°C, nominally 40°C for 12 hours before being separated from the mould, stacked standing on their ends, and subjected to heat curing for a further week at a constant temperature of 25°C at low humidity. The composite boards are them trimmed to the required size.

[0079] It will be understood that while a composite board having two reinforcing weave layers is disclosed with a first weave layer within the finishing layer and another at the boundary of the finishing layer and the main body layer, other arrangements including the addition of a further weave layer within the main body layer are possible. The particular embodiment described is intended for a wall cladding. The thickness described is intended for internal use, and a thicker cladding (by making the main body thickness greater, optionally with a layer of fibreglass cfoth reinforcing contained within), might be considered more secure for external use. The composite panel according to the invention is fire resistant, and also will not evolve dangerous fumes when heated. In contrast, competing products promoted as being fire resistant tend to evolve toxic fumes that overcome occupants of a building in which they are used.

[0080] A second embodiment comprises a 3 mm nominal thickness layer of facing slurry poured and spread into the mould. This is followed by the placement of a layer of reinforcing in the form of fibreglass woven cloth, with application of lightly weighted wiper which is wiped across the surface to smooth the cloth level contacting the cloth with the slurry and excluding air. A layer of main body slurry is spread to a nominal 3mm thickness. This is followed by the placement of a layer of reinforcing in the form of fibreglass woven cloth, with application of a lightly weighted wiper which is wiped across the surface to smooth the cloth level, contacting the cloth with the slurry to excluding air.

[0081] This is immediately followed by the application of a further layer of main body slurry of nominal 3mm thickness, followed by lying a layer of soft doth onto the top. Again, to provide a uniform thickness in the completed composite board, while contained in the mould the boards are pushed through a roller, with excess slurry being pushed out at the sides.

[0082] Heat curing is then undertaken as described for the first embodiment. The board of the second embodiment has a lighter weight than that of the first, while retaining the heat resistance and fire retardant properties,

[0083] In a fire, the boards of both embodiments produce a much lower level of toxic fumes than known building panels, improving the prospects for occupants surviving a fire, providing that the fire does not take hold within th room clad by board according to the embodiments. The facing layer side of the board is that which is on the outside of an wall construction, whether external or internal. The cloth layer will be internal and will abut face any internal studs in a wall or joists in a ceiling, forming building frame work.

[0084] It will be understood that various changes may be made to some of the components within the mix. Increasing the cellulose content results in a product that is more machinable. Colorants and dyes may be added to the slurries for cosmetic purposes. Expanded perlite and polystyrene foam spheres may be added in the main body layer, particularly where a thicker layer in the main body is employed, to reduce the weight of the completed panel,

[0085] Othe moulded products are possible utilising the method disclosed for the composite panel, such as corrugated panels and roofing tiles.