AU2007100101A4 - Thermal Wallboard and its Manufacture - Google Patents

Description

AUSTRALIA

Patents Act 1990 INNOVATION PATENT SPECIFICATION

APPLICANT:

ADDRESS:

INVENTOR:

ADDRESS:

ADDRESS FOR

SERVICE:

ASSOCIATED

PROVISIONAL:

Kingham Pty Ltd [ABN 79 105 652 891] 4 Short Street, Collector, NSW, 2581 JOHNSTONE, Wayne Thomas 4 Short Street, Collector, NSW, 2581 Paul A Grant and Associates PO Box 7460, Fisher, ACT, 2611 Application No. 2006900709 Application Date: 14 February 2006 INVENTION TITLE: Thermal Wallboard and its Manufacture The invention is described in the following statement:- TITLE: THERMAL WALLBOARD AND ITS MANUFACTURE TECHNICAL FIELD This invention relates to lightweight, high thermal-resistance wallboards suitable for use as in place of plasterboard for the lining of buildings. It also relates to methods for the manufacture of such wallboard.

BACKGROUND TO THE INVENTION Plasterboard of between 10 and 13 mm thick is widely used in Australia and many io other countries for the internal lining of houses and commercial buildings. More flexible plasterboard of about 6 mm thick is used for lining curved ceilings and walls, while plasterboard of up to 25 mm thick is used to line lift shafts and the like where a higher fire rating is required. In the USA, plasterboard is commonly called 'drywall', to contrast it with waterproof external cladding for buildings.

Plasterboard is manufactured by casting gypsum slurry (incorporating a number of flow-enhancement and setting agents) in a mould that is lined with cardboard to produce a board that has a solid gypsum core and a cardboard exterior providing necessary tensile reinforcement. Its poor moisture resistance leads to degradation in humid climates and to total disintegration of wall linings in flooded homes. Its poor thermal insulation causes most of the undesirable heat gain or heat loss in domestic buildings of brick veneer construction with carpets and ceiling insulation.

Expanded (foamed) rigid polystyrene and similar plastic material is known to have excellent thermal insulation and moisture-resistant properties and is commonly used to line cool rooms. Indeed polystyrene boards of 50 mm (and greater) thickness that have layers of aluminium sheeting bonded to their outer surfaces are sold as modular boards for use in the construction of cool-rooms, refrigerated spaces and the like.

With increasing concern with the thermal efficiency of domestic housing great advantage would arise from the use of a substitute drywall product of high thermal resistance that can substitute directly for the 10 12 mm plasterboard most commonly used in the lining of the ceilings and external walls of domestic and light industrial buildings.

OUTLINE OF THE INVENTION From one aspect, this invention comprises a wallboard adapted for use as a substitute or direct replacement for conventional plasterboard as the internal lining for rooms in houses and other buildings, the wallboard comprising a core of rigid plastic foam having first and second planar sides, and a layer of paper adhered to and covering each side of the core. The wallboard has an appearance and a finish lo that approximate those of the plasterboard thereby allowing the wallboard to be cut, hung, stopped, jointed and/or painted in the substantially the same manner as plasterboard. However, the wallboard offers greatly superior thermal resistance with respect to plasterboard and is much lighter so that it is much easier to handle and hang.

The preferred plastic core material is polystyrene foam because of its economy, but polyurethane, polyisocyanurate and other polymer foams may also be used.

For small production runs, a large block of the polymer foam can be cast in a mould and then cut by hot-wire or other means into sheets approximating the dimension of the desired wallboard. For larger production runs, the polymer foam can be extruded continuously through a mould to precisely the desired thickness and width. Alternatively, the plastic core material can be extruded as a catalyzed monomer paste into the cavity of a mould that is lined with paper/cardboard, the paste is then aerated or allowed to foam in situ to fill the cavity and bond securely with the fibrous paper or cardboard lining as it cures. The expansion or foaming can be stimulated by heating the polymer and mould.

The paper (or light cardboard) employed is preferably a Kraft paper with a finish and appearance that approximates that used on conventional plasterboard. I have found that paper having a weight of between 250 and 500 gm/m 2 but preferably between 350 and 450 gm/m 2 with a roughness of 3000 4000 ml/min to be suitable. Papers of different weights and finishes may be used on the front and back faces of the wallboard, either for economy or strength. If desired, one face of one or both paper layers can be pre-coated with a thin reflective foil layer to further enhance both thermal resistance and fire-rating. Preferably, the foil or reflective layer is applied to the external (back) face of the back layer of paper, but it can also be applied to the back of the face or front layer of paper. Instead of precoated paper, a separate foil layer can be separately glued onto the back face of either or both paper layers back layer of paper or onto either or both faces of the core sheet before the paper layers are applied with additional glue.

The paper is preferably treated, before or after application to the core, with a io flame retardant and strengthening or toughening solution so as to improve the fire-resistance and mechanical properties of the wallboard. The solution is preferably aqueous, the flame retardants can be inorganic polyphosphates and/or borax and the toughing components can be butyl glycol acetate and/or phenolic resin. Suitable solutions of this type can be obtained from CHT Australia Pty Ltd of Victoria. It is also envisaged that additional strength can be provided by bonding an open fiberglass or other mesh between the paper and the core. Alternatively, the mesh may be incorporated in the a reflective layer mentioned above.

The paper is preferably adhered to the core using a hot-melt EVA [ethylene-vinylacetate] glue which is not solvent-based and does not eat into the surface of the core material. Such glues are obtainable from Bostik and are commonly formulated with resins, wax, stabilizers and plasticizers to facilitate sprayapplication, which is preferred.

The paper is preferably glued to the core by spraying the core with the hot liquid glue to evenly cover the surface and immediately applying the paper under pressure onto the freshly sprayed surface. Preferably, the paper is rolled onto one or both sides of the core to dispense the layer or layers of paper from the roll while applying pressure on the layer against the core. Suitable calendar rollers may be used to apply paper drawn from the paper roll, rather than pressing the paper roll itself onto the core.

As EVA glues of the type favoured here 'go off' in approximately five seconds after spraying under normal ambient conditions, care needs to be taken to apply the paper to the sprayed core within two or three second of the glue being sprayed. This can be achieved with slab-cut cores by employing a fixed spray manifold and calendar roller above and transverse to the core, the calendar roller being located close to the manifold. The cut core sheet is then pushed past the spray head and under the roller so that the paper layer is pressed to the top surface of the core immediately after spraying. Another core sheet can be pushed against the end of the first, and so on, so that the glued and paper layer can be lo continuously applied, the paper then being cut to separate the coated boards. To coat the other side of the core sheets, they are turned over and pushed through the applicator one after another again, the paper being cut between the boards as before.

While the paper can be applied to pre-cut extruded core sheets in exactly the same way as for slab-cut cast sheets, it will be more efficient to extrude the core continuously into and through a mould in which it expands and to then continuously spray glue on one or both surface and to apply paper to one or both sides from a calendaring roll or rolls. The continuous coated strip can then be cut into lengths for shipment. This technique, known in the art for other products, requires significant capital investment and is contingent on large volume production.

Whether slab-cut or extruded core sheets are used, their long edges may be rebated for jointing (like plasterboard). This can be simply done by sanding the edges of the board prior to coating with paper or, less preferably, by pressing the edges of the board to compress the core material.

DESCRIPTION OF EXAMPLES Having portrayed the nature of the present invention, particular examples will now be described with reference to the accompanying drawings. However, those skilled in the art will appreciate that many variations and modifications can be made to the examples without departing from the scope of the invention as outlined above. In the accompanying drawings: Figure 1, is a perspective view of a wallboard that comprises the first example of the invention, showing the various components of the board.

Figure 2 is a side elevation of the wallboard of Figure 1.

Figure 3 is a perspective view of a wallboard that comprises the second 1o example of the invention, showing the various components of the board.

Figure 4 is a side elevation of the wallboard of Figure 3.

Figure 5 is a diagrammatic illustration of one method of manufacturing the wallboard of the first example.

The wallboard 10 of the first example, shown in Figures 1 and 2, comprises an extruded or cast core sheet 12 of rigid polystyrene foam, that has edge rebates or tapers 14 formed therein on its front face (shown uppermost), a layer of glue indicated at 16, a backing paper layer 18a applied to the back of sheet 12, a front or face paper layer 18b applied to the front or face of core sheet 12, paper layers 18a and 18b being applied onto glue layers 16 while they are still sticky. The face paper layer 18b is pressed onto core 12 so that it will conform to the shape of edge rebates 14 in core sheet 12 so that similar edge rebates 14a are formed in the face of the finished wallboard. Such rebates are commonly used in conventional plasterboard and allow the use of jointing tapes and over-plastering of joints between hung sheets.

In this example, paper layers 18a and 18b are Kraft paper of about 400 gm/m 2 and a surface roughness of about 3500 ml/min, which has been found to (i) approximate the finish of the cardboard used on conventional plasterboard and (ii) take an aqueous toughening/fire-retardant solution with good effect. As already noted, one or both of a paper layers may have a thin reflective backing foil applied thereto during manufacture, though this will add to the weight of the paper.

Alternatively, a separate reflective foil layer or layers can be applied before or after the paper is applied. In this example, a foil layer 20 is applied to the back of back layer 18a only. This is most effective where, as in many parts of Australia, it is more important for comfort and energy efficiency to reduce the flow of heat into a house during summer than out of it during winter. Paper of the type indicated above is available from Amcor.

In this example, glue 16 is a non-solvent hot-melt glue that is preferably sprayed onto core 12 as a heated liquid. As indicated above, a hot-melt ethylene-vinylacetate glue is preferred and is obtainable from Bostik. Such glues are commonly formulated with resins, wax, stabilizers and plasticizers to facilitate sprayapplication, which is preferred.

The fire-retardant and toughening solution (not shown in the drawings) that is applied to treat the Kraft paper can be applied to order by the paper manufacturer or separately as a coating after the wallboard has been formed. The former is preferred for batch production from slab-cut foamed plastic core sheets, as in this example. The treatment contributes significantly to the strength, durability and fire resistance of the product. In this example, a water-based solution is used in which the flame retardants are inorganic polyphosphates and/or borax and the toughing components are butyl glycol acetate and/or phenolic resin. Suitable solutions of this type can be obtained from CHT Australia Pty Ltd of Victoria.

The wallboard 50 of the second example, shown in Figures 3 and 4, comprises a phenolic foam core 52 that has edge rebates or tapers 54 on its front face, glue layers 56 on the front and back faces of core 52, a paper face layer 58a and a paper back layer 58b, as in the first example. However, in this case, a fiberglass reinforcing mesh 60 is interposed between the core 52 and paper sheeting 58 on each side to confer additional strength to the resultant product. In one variant, mesh 60 maybe incorporated into a paper-core foil sheet (or replaced by such a sheet) but, if so, an additional layer of glue (not shown) will be needed to secure the respective paper layer (58a or 58b) to the foil sheet. The front face 58a of the finished board is the inner face when the board is hung in a room of a building and has edge rebates 54a.

Thus wallboard 50 is a lightweight thermally insulating product that can be manufactured and supplied in large sizes and yet will be self-supporting and easy to handle for installation. Even when supplied in conventional sheet sizes, the use of reinforcing mesh 60 has the significant advantage of greatly improving the puncture resistance of the product, both with respect to the un-reinforced wallboard 10 of the first example and conventional plasterboard. Of course, significant further thermal benefit is obtained by incorporating reflective foil layers as well.

One system 100 of manufacturing a wallboard of the invention like that of the second example as described above is illustrated in Figure 5. However, it will be assumed that an open reinforcing mesh is needed only on the face of the wallboard behind the front paper layer.

Referring to Figure 5, a polystyrene foam core extruder 101 generates a continuous core sheet 102 that is sized between roll sets 104 before advancing to a gluing station 106 in which glue 108 is applied via nozzles to the top and bottom surfaces of core. Open fiberglass mesh 110 is fed onto top glued surface of core 102 from a roll 112 and is quickly followed by a top paper sheet covering 114 from a roll 116. A similar roll 118 of paper feeds sheet 120 onto bottom glued surface of core 102. The assembly is then compressed between heated pressure belts or chain of a press assembly 122 that ensures intimate contact between the glued components while the glue is curing and effect finish sizing of the completed wallboard. Core sizing roll sets 104 and finishing press 122 are shaped so as to form the side rebates along the edges of the wallboard (not shown), if desired.

Wallboards of the examples can be made to various thicknesses according to the thermal properties desired. Standard thicknesses used in Australia for plasterboard tend to be 9.6mm and 12mm and these sizes can be duplicated so that the fitting of window and door architraves and skirtings can be identical to those used for plasterboard. However, in order to achieve good thermal insulation properties, I prefer a 20 mm thick board. With a polystyrene core this can provide a thermal conductivity of less than 0.3W/mK and with a phenolic core less than .03 W/mK, which are many times better than plasterboard. Further, as already indicated, the boards of the present invention are much lighter than plasterboard less than one half their weight in fact.

While a number of examples have been described, those skilled in the art will appreciate that many variations and additions to the examples can be made without departing from the scope of the invention as set out in the following claims.