GB2450994A

GB2450994A - A structural insulated panel

Info

Publication number: GB2450994A
Application number: GB0812638A
Authority: GB
Inventors: William Patrick Smee; John Richard Smee
Original assignee: ORMUS Ltd
Current assignee: ORMUS Ltd
Priority date: 2007-07-11
Filing date: 2008-07-10
Publication date: 2009-01-14
Anticipated expiration: 2028-07-10
Also published as: GB2450994B; GB0812638D0; IES20080570A2; GB2450994A8; IE20080571A1; GB0713444D0

Abstract

The present invention relates to an improved structural insulated panel for use in domestic and/or commercial buildings and a process for its manufacture. Ideally, the process for the manufacture of the structural insulated panel comprises the following general steps obtaining a first planar face layer 5a and a second planar face layer 5b; affixing elongate cross-members 6 with spaced apart recesses 8; forming a hollow panel with hollow channels 7 linked by the spaced apart recesses 8; placing the hollow panel in an injection press; injecting pre-cured polyurethane in-situ into the hollow panel to form a single layer of pre-cured polyurethane; allowing the pre-cured polyurethane to expand to form a structural insulated panel, such that the inner side of the first and second face layers surround a single layer of polyurethane linking the channels; curing and storing the structural insulated panel.

Description

"AN INSULATED PANEL" The present invention relates to an improved

structural insulated panel for use in domestic and/or commercial buildings and a process for its manufacture.

The use of stress skinned panels for construction began in the 1930s. In the 1940's, early forms of Structural Insulated Panels were developed using corrugated paperboard cores with various skin materials of plywood, tempered hardboard and treated paperboard. In the 1960's, panels consisting of a polystyrene core and paper overlaid with plywood skins were commonly used in building. These panels have performed well to the present day.

Structural insulated panels (SIPs) in their present form are a composite building matenal.

A SIP essentially consists of one or two face layers of structural board surrounding a core of insulating material. A strong, structural bond between the layers is essential to enhance the load bearing capacity of the SIP. SIPs are a modem method of construction and are becoming increasingly popular with consumers. SIPs have many advantages, such as, they are light and versatile, they are thermally efficient and have low air leakage and they can be erected quickly using relatively easy construction practices. They are currently used in domestic and light engineering construction.

Generally, the structural board used in the SIP is Oriented Strand Board (OSB) and the insulating core material may be either polystyrene foam or polyurethane foam. However, many other materials can be used. For example, some SIPs use fibre-cement or plywood for the panels, and agricultural fibre, such as wheat straw, for the insulating core. Other SIPs use natural material, such as wool or other natural fibre, as the insulating core. Optionally, some SIP manufacturers include load bearing rafters, joists and studs in the SIPs to allow the panel to bear the weight, stress and deflections of the roof. In others, the load is either borne by the skin of the panel or by underlying, separately constructed, rafters which are independent of the panel.

The use of SIPs brings many benefits when compared to a conventional building. A well built home using SIPs will have a tighter building envelope and the walls will have a higher insulation value, which leads to fewer air leakages and a decrease in operating costs for maintaining a comfortable interior environment for the occupants. Also, due to the standardised and all-in-one nature of SIPs, construction time can be reduced and fewer tradespersons are required.

Furthermore, an OSB SIP outperforms conventional timber framed construction structurally and maintains the versatility of the timber framed house when incorporating custom designs. Also, since SIPs work as framing, insulation, and exterior sheathing, and can come pre-cut from the factory for the specific job, the exterior building envelope can be built quickly.

Dimensionally SIPs tend to come in sizes from about Im to 6m in width. Much of the time manufacturers produce the 1 m sections for ease of transportation and handling, however, the use of the longest panel possible will create the most efficient SIPS building. Thus, these types of insulated panels can be made specifically according to the dimensions of the building or can be trimmed to specific orders Some illustrative patents covering various constructions of SIPs include, for example, UK Patent Nos. 2,436, 989, 2,280,916,2, 194, 262 and 2, 146, 681. The majority of these patents relate to conventional SIPs with inner and outer layers, cross members located between the layers and a foam core located in the channels between the cross members.

There are many different types of SIPs and some patents covering various different constructions for different uses are outlined below.

For example, GB 1,589,715 discloses a panel comprising a corrugated metallic inter structure between a pair of spaced layers for use in used in greenhouse glazing. In addition, DE 2611893 discloses a panel comprising a flat covered panel and a corrugated bitumen felt panel filled with a foam layer which is rigidly bonded to both panels and contains reinforcing strips. Such a panel has limited use and would not be suitable for use as a roof panel as there are no anchor parts on the corrugated side for nailing on batons to fix roof tiles on the outside or plasterboard on the inside. Thus, this type of panel is not very practical for multiple end uses. Finally, SU 1161676 relates to a cellular structural panel made of fibreglass with pyramid shaped cell rows and reinforcing stringers. Support members are placed next to the pyramid shapes and these appear to have slots. These patents are mentioned as general background teachings only, highlighting the diverse types of SIPs disclosed to date.

However, despite these advances and the provision of many alternative SIP constructions there remains a need for a single integrated insulated panel with high load beanng capacity which can be used in multiple applications, such as for use as an intermediate floor, wall and/or roof panel.

Furthermore, it would be desirable to provide panels which have good thermal properties and insulation qualities to meet with the various new national and international building regulations, including The Irish Building Regulations 2005 Technical Guidance Document L Conservation of Fuel and Energy (May 2006 Edition) Department of the Environment, Heritage and Local Government and the EU Directive 2002/91/EC on the Energy Perfomiance of Buildings.

Thus, there is a need to develop an improved SIP suitable for use as a wall, roof or floor panel which deals with many of these problems.

According to a first aspect of the invention, there is provided a process for the manufacture of a structural insulated panel suitable for use as floor, wall or roof panels, wherein the structural insulated panel comprises a first and second planar face layer, each face layer with an outer and an inner side, such that the inner face layers are parallel and surround a polyurethane core, wherein the process comprises the following steps: obtaining a first planar face layer and a second planar face layer; affixing at least two elongate cross-members to the inner side of the first face layer, wherein each cross-member has at least one, preferably two or more, spaced apart recesses on one side; affixing the second face layer to the first face layer by the cross members to form a hollow panel such that first and second inner face layers are parallel and the cross-members define a number of hollow channels within the hollow panel which are linked by the spaced apart recesses; placing the hollow panel in an injection press which has been heated to approximately 30 C to 60 C such that the spaced apart recesses are located adjacent to the base of the injection press; injecting pre-cured polyurethane in-situ, under high-pressure, into the hollow panel; aftowing the pre-cured polyurethane to form an even layer of pre-cured polyurethane within hollow panel such that a single layer of pre-cured polyurethane is formed which links each of the hollow channels through the spaced apart recesses; allowing the pre-cured polyurethane to expand to form a structural insulated panel, such that the inner side of the first and second face layers surround a single layer of polyurethane linking the channels; leaving the structural insulated panel to cure; storing the structural insulated panel at room temperature.

It will be understood that the hollow panel may be assembled within the injection press, such as a compression table press or a sandwich press. Thus, the entire process may take place within a compression table press. Alternatively, the hollow panel many be manufactured elsewhere and placed in the injection press prior to the injection steps. It will also be understood that any suitable injection press may be used such as a compression or sandwich press may be used. Ideally a compression table press is used.

According to a second aspect of the invention, there is provided a structural insulated panel comprising first and second planar of flat face layers, each face layer with an outer and an inner side, such that the inner sides of the face layers are parallel and surround a polyurethane core characterised in that two or more elongate cross- members are fixed to the inner side of both planar face layers to define a number of channels in the panel wherein each cross-member incorporates at least one, preferably two or more, spaced apart recesses on one side adjacent to the first face layer, such that the inner side of the first and second face layers surround a single layer of high density cellular rigid polyurethane foam linking the channels between the two face layers.

Ideally, the structural insulated panel is manufactured in accordance with the method of the invention.

Advantageously, the insulated panels manufactured in accordance with the present invention have multiple uses and may be used as roof, wall or floor SIPs. The use of SIPs as floor panels is of particular benefit when used above an uninsulated floor. -7.-

Ideally, the polyurethane used is high-density cellular rigid polyurethane (PUR).

Alternatively, poly isocyanurate (PIR) may be used. Other polyurethanes may be used.

The polyurethane is injected into the hollow panel as pre-cured polyurethane. Heat within the hollow panel/injection press causes the pre-cured polyurethane to foam and cure to form a rigid polyurethane with good thermal properties.

It will be understood that the "cross-members" of the invention essentially comprise a longitudinal/elongate element which is affixed along one edge to the inner side of the face layer. The cross-members connect opposite sides of the face layers and are placed parallel to each other to define a number of hollow channels within the panel. The cross-member may be a rafter or stud. Ideally, the cross-member is of timber construction e.g. oriented strand board or a solid timber rafter. Any number of cross-members may be present. The number of cross-members used depends on the size of the face layers being used and the number of desired hollow channels to be formed. Ideally, at least two, three, four, five or six cross-members may be present. Advantageously, we have found that the use of three cross-members provide the desired physical properties in the resultant SIP.

It will also be understood that the "spaced apart recesses" of the invention can be formed by simply cutting out recesses along one edge of the cross-member. Alternatively, the "spaced apart recesses" can be formed by the addition of spacer elements along one edge of the cross-member. Such spacer elements will ideally be of timber construction and permanently fixed or adhered to the cross-member. Ideally, two or more spaced apart recesses are present, although any number can be contemplated. The spaced apart recesses are present along one edge of the cross-member adjacent to the first face layer.

Placing the recesses adjacent to the first face layer provides a significant advantage when adding the pre-cured polyurethane to the hollow panel. It ensures that the pre-cured polyurethane forms an even and continuous single layer covering the entire first face layer.

The pre-cured polyurethane forms a level or even surface across the entire first face layer, so that when the hollow panel with pre-cured polyurethane is subjected to curing conditions, the polyurethane cures as a single continuous layer of foam evenly across the whole panel. In addition, the formation of air pockets as the foam cures can be minimized.

Controlling the way in which the pre-cured polyurethane cures within the panel ensures that the resultant SIPs had the desired physical properties in terms of thermal insulation and load bearing capacity, According to an alternative embodiment of the invention, spaced apart recesses may be present along both sides of the cross-members which are adjacent to the first and second layers.

The process of the present in invention provides several advantages.

Firstly, the presence of the cross-members which are affixed to the panels provides great structural rigidity in the SIP and increases the load bearing capacity of the SIP. Essentially, the cross-member acts as a T-beam, with the composite section having greater flexural rigidity than the cross-member or panel. This adds to the stiffness, bending and shear resistance of the SIPs enabling the production and use of longer SIPs than previously attainable.

Secondly, the use of the sandwich or compression press in the process of the present invention provides the advantage that the polyurethane foam is moulded or compressed in the press. This makes the resultant foam core stronger and more uniform when compared to foam that is sprayed into an open mould (free rise foam).

Thirdly, the polyurethane foam is injected under high pressure. This facilitates the better mixing of the initial chemicals and therefore results in a better quality and more uniform.

Essentially, the high pressure machine produces a finer cell structure in the resultant foam.

Another major advantage in the process of the present application is that the injected core forms a single layer within and linking the channels of the panel. This is possible due to the spacer elements or spaced apart recessed in the cross-members which allow free movement of the injected core throughout the previously hollow channels within the panel and this significant advantage is expanded on above. This single layer of foam core combined with the structural integrity provided by the cross-members themselves, provides significant advantages over and above known SIPs. Thus, the SIPs of the invention are strong in load bearing capacity For these reasons and due to the specific construction of the hollow panel and the combination with the high pressure injection process, the process of the present invention ensures that no air-pockets develop in the cellular core. This is a significant improvement over known processes, in that reduction/elimination of air pockets enables the insulated panel to achieve higher thermal ratings which are desirable for today's consumer.

Thus, the SIPs of the present invention contribute to a better building energy rating based on the lower U-values of the resultant panels. This is important commercially and to meet the standards set by the various national and international building regulations. The SIPs of the present invention have significantly improved thermal properties in comparison with standard roof constructions.

Another advantage of the process of the present invention is that it allows for the off-site fabrication of SIPs.

Furthermore, there is no handling of the injected core as the insulation is injected in a closed apparatus (the press) and cured therein.

Finally, the high pressure machine does not require solvent flushing so that the need for a blowing agent, such as methaline chloride is eliminated. This is particularly relevant if an Eco Friendly' GWP (Global Warming Potential) rating is sought.

According to a preferred embodiment of this aspect of the present invention, the polyurethane is injected at a speed of approximately 1 140g/sec. Although, it will be understood that the speed of injection will depend on the volume of the panel to be filled and the type injection machine used. Thus, speeds higher or lower may be used in practice.

According to a still preferred embodiment of the present invention, the compression table press is heated to approximately 45 degrees Celsius prior to the injection step.

Advantageously, this ensures a fast even spread of polyurethane throughout the hollow core. Ideally, the compression table press is heated using a closed water heating system.

According to a further embodiment of the present invention, a releasing agent is applied to the compression press prior placing the first panel in the compression press. This ensures that the polyurethane does not adhere to the compression press when the panels are removed. Ideally the releasing agent is a wax.

Ideally, the polyurethane is injected into the hollow core, using a nozzle or lance, at regular intervals along one side of the hollow panel. Ideally, injection is commenced at a central location along one side of the hollow panel.

Preferably, the face panels are wood-based face layers of timber construction, such as onented strand board, solid timber rafters or other high density material. The cross-members and spacer elements may also be made of the same material.

According to another embodiment of the present invention, the structural insulated panel after formation is left in the press for at least 60 minutes after injection. This allows the expanded foam core to cure.

According to another embodiment of the present invention, the panel is removed from the press and subsequently stored at a temperature of approximately 22 degrees Celsius for at least 24 hours. This ensures that no shrinkage of the polyurethane core takes place after injection and curing.

According to another embodiment of the present invention the structural insulated panel is subject to further processing steps including cuthng the structural insulted panel to a desired size.

Additionally, a tongue and groove structure may be formed within the polyurethane foam core wherein one side of SIP has a tongue and the opposite side has a groove.

Advantageously, this facilitates the on-site fabrication of the building. Such a tongue and groove structure may be formed by choosing appropriately moulded injection press side profiles. The injected polyurethane will then take the form of the injection press side profiles.

According to a more specific embodiment of this aspect of the invention, the process of the invention comprises the following steps: obtaining two planar face layers, each face layer with an outer and an inner side; placing the first face layer in a compression table press; affixing at least two elongate cross-members to the inner side of the second face layer wherein each cross-member has at least one, preferably two or more, spaced apart recesses on the side not attached to the second face layer; placing the second face layer on the compression table press such that first and second inner face layers are parallel and the first and second face layers form a hollow panel with a number of hollow channels defined by the elonagLecross-members; injecting polyurethane under high-pressure in-situ into the hollow channels to form a structural insulated panel, such that the inner side of the first and second face layers surround a single layer of polyurethane linking the channels between the two face layers; leaving the insulated panel to cure.

According to a still more specific embodiment of this aspect of the invention, the panels are manufactured by the following steps: cross-members with spaced apart recesses are fixed to a first panel using steel screws, preferably shemdised steel screws; a second panel (also called the soffit) is placed on a compression table press; the first panel with cross-members with spaced apart recesses is placed on the compression table press over the second panel to form a hollow panel; the hollow panel is secured in the compression press; rigid polyurethane insulation foam core is formed in-situ within the hollow panel by chemical reaction after injection under pressure at a discharge rate of approximately 11 40g/sec to form the structural insulated panel; the structural insualted panel is left in the press for approximately 45 minutes to cure, depending on the depth of the panel.

Conveniently, quality control checks are camed out on resultant structural insualted panel.

Ideally, appropriate controls are applied throughout the production process. These include but are not limited to checks on rafter dimensions, quality and moisture content, screw fixings, and thickness and properties of insulation.

The panel material, preferably OSB board, undergoes random quality checking to ensure it conforms to the specified length, breath and thickness. Ideally, the cross-members are timber rafters with a stress grade of approximately C18. This is verified by ensuring that each rafter has been stamped with the stress grade. The rafters are also checked for straightness, wane and notches. Once inspected, raw materials are stored indoors so that their quality does not deteriorate.

After manufacture of the SIP, the SIPs are ideally subjected to further quality control. The polyurethane core is checked for colour, consistency and texture. Panel dimensions, screw size and spacing are also checked. Conveniently, product markings are sprayed on the panel skins. These generally indicate the panel weight and the position of the rafters (to ensure counter batons are nailed in the correct side of the panel on site). A batch code which denotes the date of manufacture, and the press where the panel was produced, is then stamped on every panel. Furthermore, random destructive testing is carried out to ensure that the core remains consistent and free of air pockets.

According to a second aspect of the invention, there is provided a structural insulated panel comprising first and second face layers, each face layer with an outer and an inner side, ) such that the inner sides of the face layers are parallel and surround a polyurethane core characterised in that two or more elongate cross-members are fixed to the inner side of both face layers to define a number of channels in the panel wherein each cross-member incorporates at least one, preferably two or more, spaced apart recesses on one side adjacent to the first face layer, such that the inner side of the first and second face layers surround a single layer of high density cellular rigid polyurethane foam linking the channels between the two face layers.

Ideally, the insulated panel comprises two or more cross-members. Conveniently, the cross-members are fixed to the top panel using steel screws, preferably shemdised steel screws.

Preferably, the polyurethane foam core forms a tongue structure on one edge of the panel.

and the polyurethane foam core forms a groove structure on the opposite edge of the panel. This tongue and groove structure facilitates an improved seal and fitting thereby reducing the incidence of air leakage and contributing to the overall improved thermal properties.

Ideally, the insulated panel has a U-value of less than 0.2. This U value is determined by adding the U value for the planar face panels and the foamed core, ideally a foam core of approximately 120 to 260mm, preferably 175 to 250mm, more preferably 130 to 180mm is desirable.

It will be understood that the insulated panel may be used as a wall, roof or floor panel.

According to a more specific embodiment of this aspect of the invention, the insulated panels comprise at least three cross-members fixed to a soffit or bottom board/face layer and a top board/face layer, with rigid polyurethane foam injected under pressure in the voids or channels, between the cross-members. An essential feature is the presence of spaced apart recesses on one edge of the cross-members adjacent to the face layer. The spaced apart member may be cut-outs or recesses in the cross-member or may comprise additional spacer elements which are fixed to one side of the cross-member. These spaced apart recesses enable the polyurethane foam to form a single layer covering all the hollow channels and provide significant advantages over and above known SIPs.

ideally, the panel is from approximately 190 to 270mm in thickness. Generally each outer skin (i.e the planar face layer) is approximately 6 to 12mm in thickness. Ideally, the polyurethane core is form 175 to 250mm in thickness. These dimensions can be varied depending on the end use of the SIP.

According to another embodiment of the invention, the insulated panel may be used as a roof panel. The roof panels can be used to replace rafters and insulation. Ideally, the panels are used to provide insulation and structural support to slate and tiled roofs with pitches of between approximately 17.50 and approximately 60 and also in flat roofs, in either domestic and commercial buildings. For this type of usage, the panels are fixed at ridge and eaves level, to a structurally designed ridge beam and wail plate respectively and if required, with a structural purlin at intermediate level.

Some advantages in using the panel according to the invention as a roof panel are listed as follows. Some of these advantages are also applicable to use as floor or wall panels.

a) Immediate use of the roof void area which is much less intrusive than conventional roof construction. This provides a home owner with an additional functional space requiring little or no modification.

b) Insulation values: The panel according to the invention far exceeds the Building Regulations Part L Building Regulations 2005, Technical Guidance Document L, Conservation of Fuel and Energy ( May 2006 edition. Published by the Department of the Environment, Heritage and Local Government) requirement for thermal insulation in a domestic construction. This will contribute to a greater Building Energy Rating, thereby cutting down on the Carbon Dioxide emissions from space heating of the building. Use of fossil fuels in heating produce carbon dioxide on combustion, leading to increased green house gases released to the atmosphere.

Improved insulation reduces the burning of fuel, reducing emissions and lowering cost.

c) Speed of Construction: Use of the panel according to the invention replaces the need for cutting rafters and placing of insulation. It seals the building as it is being laid thereby reducing the number of operatives and amount of time needed to complete the work.

d) Seals the roof space of building: improved sealing of roof space reduces leakage of warm air to atmosphere due to reduced joints and interfaces when compared with conventional roof construction.

e) Minimum Training: The panels according to the invention can be placed with minimum of training thereby reducing need for highly qualified operatives.

The invention will now be described by reference to the following non-limiting examples and figures.

Figure 1 shows a cross section of a conventional SIP; Figures 2 to 4 shows the process in a step-wise fashion; and Figure 5 shows a structural insulated panel made in accordance with the invention.

Figure 1 shows the structure of a conventional SIP (1) comprising two face layers (2) and a rigid cellular insulation core (3). Conventionally, the face layer (2) is made of wood based boards such as Oriented Strand Board (OSB) and mineral based board such as cement bonded particle board (CBPB). Ideally, the face layers are approximately 6 to 18mm thick.

The core (3) is ideally polyurethane (PUR) or polyisocyanurate (PIR). If phenolic foam (PF) forms the core then an additional step of gluing the core to the face layers must be incorporated. Alternatively, natural materials such as wool or other natural fibre may be used as the core (3).

Figure 2 shows the first step in the process for the manufacture of a SIP according to the invention. In this figure, a first planar face layer (5a) is shown. Cross-members (6) are fitted to the inner side of the face layer (5). Recesses (8) are formed along one edge of the cross- member by fitting a number of spacer blocks or elements (9) to the edge of the cross-member as shown. Alternatively, recesses (8) may be formed by providing cut-outs in the cross-member itself (this is not shown).

It will be understood that the hollow panel may be manufactured within the compression press. Alternatively, after manufacture the hollow panel may be placed in the compression press for the subsequent injection steps.

Figure 3 shows the second step in the process where the second planar face layer (5b) is fitted to the first face layer (5a) to form a hollow panel. Ideally, steel screws are used to fix the planar face sheetstogether via the cross-members. In this step, the second face layer (Sb) is fixed to the cross-member (6) spacer blocks (9), thereby, defining a set of recesses (8) and hollow channels (7) with the resultant hollow panel.

Figure 4 shows the resultant hollow panel with hollow channels (7). This hollow panel is either formed within the compression table press (not shown) or after formation simply placed into the compression table press (not shown).

One very important aspect of the invention, is that the hollow panel is placed or formed within the compression press such that the recesses (8) within the cross-members are located adjacent to the base face panel/compression press. This is crucial as it enables the injected polyurethane to form an even layer over the complete base panel linking each hollow channel within the hollow panel. Thus, these figures are for illustrative purposes only and as such when the hollow panel is formed or placed within the compression press, it will be understood that the recesses (8) within the cross-members will be located adjacent to the injection press.

Once this is done the injection of the polyurethane into the hollow channels (7) takes place.

Figure 5 shows the resultant SIP (4) of the invention after injection of the polyurethane core and after removal from the injection press. The panel (4) comprises two face layers (5a, Sb) and cross-members (6) affixed to at least one side of the face layers and defining channels (7) in the panel The cross-members (6) have recesses (not shown) cut-out or spacer blocks (not shown) at spaced apart intervals along the length of one side adjacent to one of the face layers (5) which link both face layers (5a, 5b). The polyurethane core thus forms a single composite layer joining all the channels (7) within the SIP (4). The SIP (4) remains in the compression press for at least 40 minutes until curing and cooling has taken place.

The invention is further defined by reference to the examples described below. The examples are representative and should not be construed to limit the scope of the invention in any way.

Example I -Manufacture of Structural Insulated Panel A hollow panel comprising two planar face layers with three elongate cross-members defining hollow channels within the hollow panel was assembled using the protocol outlined below. Each cross-member had a number of recesses cut-out at spaced apart intervals on one elongate side.

The hollow panel according to this Example was made of solid timber rafters, although, it will be appreciated that other materials such as oriented strand board may be used. In addition the number of cross-members in the hollow panel may be increased or decreased depending on the size of the panel to be manufactured. Finally and alternatively, spacer members may be affixed to the elongate cross-member to provide for recesses in the cross-members.

The first general step in the manufacture of the SIP is preparation of the compression press and the assembly of the hollow panel.

Preparation of the Compression Press Before commencing the injection process, the compression press was prepared by drilling a series of approximately 7mm diameter "breathing" holes at approximately 300mm intervals along the length of the aluminum profile of the compression press. These breathing holes are needed to allow air to escape from the hollow panel as it is being filled with polyurethane and so to prevent the build up of air bubbles.

In addition and in order to provide direct access to the hollow core of the hollow panel, the aluminum profiles of the compression press are provided with a series of approximately 25mm filling holes situated at regular intervals along the aluminum profile. These filling holes are set to the diameter of the high pressure injection nozzle. The filling holes are generally located centrally along the side of the panel.

A releasing agent or wax was then applied to the aluminum profiles in order to prevent the polyurethane adhering to the profiles when the SIPs are removed from the press.

Assembly of the Hollow Panel The first general step in the manufacture of the SIPs is the construction of the hollow panel.

Ideally, construction of the hollow panel takes place within a compression or table press.

However, it will also be understood that the hollow panel may be constructed outside the compression or table press, and placed in the compression or table press after initial construction.

Dunng the manufacturing process of the hollow panel according to the present example, one planar face panel (the first panel) was placed in a compression table press. The three elongate cross-members with recesses were affixed to inner side of a second face panel (the second panel) such that, when assembled as a hollow panel, the recesses would be located directly adjacent to the fit-st panel and the base of the compression press.

Subsequently, the second panel with cross-members was then placed in the compression press with inner sides of both face panels parallel, thus, ensuring the cross-members define a number of hollow channels within the panel.

The hollow panel was then secured in the compression press by a series of pins fixed approximately 12mm from the top of the aluminum profile of the compression press.

Masking tape was placed around the perimeter of the panels to prevent any leakage of polyurethane, which could stain the panel. The compression bed ceiling or top was placed over the hollow panel.

Heating the Hollow Panel within the Compression Press The fully prepared hollow panel within the compression press was heated to approximately 45 C. This heating step facilitates the fast even spread of polyurethane throughout the hollow panel after injected. The compression press bed, ceiling and aluminum side profiles were brought to the desired 45 C temperature by means of a closed water heated system.

The second general step in the manufacture of the SIP is the injection under high pressure of a polyurethane core into the hollow channels to form a cellular ngid core. Once the cellular ngid core has cured then the SIP is ready for use.

Calibrating and Setting the High-Pressure Injection Machine To determine the quantity of pre-cured polyurethane foam to be injected into the hollow core, the volume of the panel was calculated and multiplied by the density of the polyurethane, which in this Example was 45kg/cubic metre. The output of the high pressure injection machine output was factory calibrated and set by the manufacturer as 11 40glsec. The volume of the hollow was then divided by the output of the high-pressure injection machine answer to give a shot time for the panel. The shot-time is the number of seconds the high-pressure injection machine will need to run in order to achieve the required output of polyurethane at 1140 glsec. The shot time was then programmed into the high pressure injection machine.

High Pressure Injection of Polyurethane into Hollow Panel To inject the foam, the nozzle of the high pressure injection machine was placed into the filling holes which were previously drilled into the aluminum profile. The high pressure injection machine was then activated and the injection machine automatically dispensed the pie-cured polyurethane into the hollow core via the nozzle for the pre-set shot time.

The pre-cured polyurethane was allowed to spread evenly across the base of the entire hollow first panel through the recesses in the cross-members to form a unified layer of polyurethane throughout the hollow panel. The formation of an even layer of pre-cured polyurethane across the base of the entire hollow panel is an essential aspect of the invention. This ensures that the polyurethane expands evenly throughout the panel and ensures that air bubbles or other discrepancies are minimized to result in an even foam with good thermal insulation properties.

Once the pie-cured polyurethane has been injected into the heated compression press/hollow panel, the polyurethane cures and forms an even layer of foamed polyurethane. The compression press has already been heated to approximately 45 C and the heat starts the polyurethane to commencing foaming and curing and the polyurethane spreads and rises throughout the hollow core. Dunng expansion, the polyurethane pushes the air in the hollow core out through the series of breathing holes drilled in the aluminum profile, thus, eliminating any residual air pockets. When the polyurethane began to appear through the breathing holes, this provided a visual indication that all the residual the air had been expelled.

After use and when the resultant SIP was removed from the compression press, the breathing holes were drilled out before the next hollow core was placed in the press. This ensured that the air holes did not become blocked.

The hollow panel with injected polyurethane remained in the heated compression press for approximately 60 minutes to allow the foamed polyurethane to cure fully to form the SIP.

The SIP was removed from the compression press and brought to an inspection area where it was inspected before storage.

The SIP remained at an ambient temperature of approximately 22 degrees Celsius for at least 24 hours after removal from the press. This was to prevent shnnkage of the polyurethane core within the SIP.

Example 2 -Strength Testing SIPs made according to Example 1 were subjected to load testing with weights ranging from 256kg, 464kg tol200kg. All SIPs were able to take these loads and no negative effects to the SIPs were observed.

Example 3-Thermal Property Testing The U-value (thermal property) of the SIPs made according to Example 1 was established by calculation based on the thermal resistivity of each of the materials within the SIP, including the face panels, cross-members and the insulation core.

The SIPs had a foam core from approximately 130 to 180mm. In addition each face panel was approximately 6 to 12mm in depth. The U- value of SIPs manufactured according to the process of the present invention was found to be less than 0.2 and has excellent thermal properties.

In the specification, the terms "comprise, comprises, comprised and comprising" and any variation thereof and the terms "include, includes, included and including" and any variation thereof are considered to be totally interchangeable and they should all be afforded the widest interpretation.

The invention is not limited to the embodiments described above but may be varied within the scope of the claims.

Claims

1. A process for the manufacture of a structural insulated panel suitable for use as floor, wall or roof panels, wherein the structural insulated panel comprises first and second planar face layers, each face layer with an outer and an inner side, such that the inner face layers are parallel and surround a polyurethane core, wherein the process comprises the following steps: obtaining a first planar face layer and a second planar face layer; affixing at least two elongate cross-members to the inner side of the first face layer, wherein each cross-member has at least one, preferably two or more, spaced apart recesses on one side; affixing the second face layer to the first face layer by the cross members to form a hollow panel such that first and second inner face layers are parallel and the cross-members define a number of hollow channels within the hollow panel which are linked by the spaced apart recesses; placing the hollow panel in an injection press which has been heated to approximately 30 C to 60 C such that the spaced apart recesses are located adjacent to the base of the injection press; injecting pre-cured polyurethane in-situ, under high-pressure, into the hollow panel; allowing the pre-cured polyurethane to form an even layer of pre-cured polyurethane within hollow panel such that a single layer of pre-cured polyurethane is formed which links each of the hollow channels through the spaced apart recesses; allowing the pre-cured polyurethane to expand to form a structural insulated panel, such that the inner side of the first and second face layers surround a single layer of polyurethane linking the channels; leaving the structural insulated panel to cure; storing the structural insulated panel at room temperature.

2. The process according to claim I wherein the hollow panel is formed within the injection press.

3. The process according to claim I wherein the injection press is a compression press.

4. The process according to any of claims 1 to 3 wherein the polyurethane is high-density cellular rigid polyurethane foam or polyisocyanurate.

5. The process according to any of the preceding claims wherein the polyurethane is injected at a speed of approximately 1140 g/sec.

6. The process according to any of claims 2 to 5 wherein the injection press is heated to degrees Celsius.

7. The process according to claim 6 wherein the injection press is heated using a closed water heating system.

8. The process according to any of claims 2 to 7 wherein a releasing agent, preferably wax, is applied to the injection press before injection.

9. The process according to any of the preceding claims wherein the polyurethane is injected through the injection press, using a nozzle, at regular intervals along one side of the hollow panel.

10. The process according to any of the preceding claims wherein the face layers comprise oriented strand board (OSB) or timber rafters.

11. The process according to any of the preceding claims wherein the structural insulated panel remains in the injection press for at least 60 minutes after injection.

12. The process according to claim 11 wherein the structural insulated panel is removed from the injection press and subsequently stored at a temperature of approximately 22 degrees Celsius for at least 24 hours.

13. The process according to any of the preceding claims wherein the structural insulated panel is subject to further processing steps, including cutting the structural insulated panel to a set size.

14. The process according to any of the preceding claims wherein the structural insulated panel is formed with a tongue and groove structure along opposite edges of the polyurethane core.

15. A structural insulated panel made in accordance with any of claim 1 to 15 comprising first and second planar face layers, each face layer with an outer and an inner side, such that the inner sides of the face layers are parallel and surround a polyurethane core charactensed in that two or more elongate cross-members are fixed to the inner side of both face layers to define a number of channels in the panel wherein each cross-member incorporates at least one, preferably two or more, spaced apart recesses on one side adjacent to the first face layer, such that the inner side of the first and second face layers surround a single layer of high density cellular rigid polyurethane foam linking the channels between the two face layers.

16. An insulated panel according to claim 15 comprising two or more cross-members.

17. An insulated panel according to claim 15 or claim 16 wherein the polyurethane is high-density cellular rigid polyurethane foam or polyisocyanurate.

18. An insulated panel according to any of claims 15 to 17 wherein the polyurethane forms a tongue structure along at least one edge of the structural insulated panel.

19. An insulated panel according to any of claims 15 to 18 wherein the polyurethane forms a groove structure along at least one edge of the structural insulated panel.

20. An insulated panel according to any of claims 15 to 19 with a U-value of less than 0.2.

21. An insulated panel according to any of claims 15 to 20 for use as a wall, roof or floor panel.