GB2409812A

GB2409812A - Fire barrier

Info

Publication number: GB2409812A
Application number: GB0400124A
Authority: GB
Inventors: David Charles Aslin
Original assignee: Prometheus Developments Ltd
Current assignee: Prometheus Developments Ltd
Priority date: 2004-01-06
Filing date: 2004-01-06
Publication date: 2005-07-13
Anticipated expiration: 2024-01-06
Also published as: GB0400124D0; GB2409812B

Abstract

A fire barrier 10 comprises a first layer 12 which is flexible under fire conditions and a second layer 14 which comprises a support material incorporating a material expandable under fire conditions. The first layer may comprise a textile skin of glass fibre or basalt cloth, or a mild steel skin. The second layer may comprise a polymer matrix containing an exfoliable graphite. An inner core 16 comprising alternating layers of aluminium foil 22 and an absorbent paper 24 may be present.

Description

240981 2

COMPOSITE STRUCTURE

This invention relates to composite structures. More particularly, but not exclusively, the invention relates to composite structures in the form of fire barriers.

Conventional flexible fire barriers are of two types, namely those simply providing integrity against fire penetrations and those providing insulation.

This latter condition is indicated by the ability of such structures to maintain the cold face of the fire barrier below an average temperature of 140 C above ambient when the hot face of such a barrier is exposed to a standard fire, as represented by that defined in En 1361 for defined periods usually in excess of fifteen minutes.

Examples of such flexible barriers are disclosed in EP 0715670 and GB 2351021. The barriers disclosed by these prior specifications consist of outer textile skins of woven glass fibres backed by substantial layers of aluminium foil separated by a fire resistant fibrous insulating pad. The barriers rely on the effect of the aluminium foils as radiation barriers and the minor insulative effect of the fibrous pad. The outer textile skins add very little to the insulation value but serve to maintain the integrity of the structure. The separate layers of these products are mechanically assembled by stitching or stapling. However, the maximum insulation performance to a back-face temperature of 140 C above ambient is thirty minutes against the BS 476 parts 20 and 22 Fire Test Regimes.

Another prior specification namely, EP 5258216 discloses a flexible fire barrier formed by stitching textile skins into cells containing efoliable graphite as a means of preventing avalanching of the expanded exfoliable graphite.

According to one aspect of this invention, there is provided a composite structure comprising first and second layers, the first layer being flexible under \ fire conditions, and the second layer comprising a support material incorporating an expandable material, wherein the expandable material is expandable under fire conditions.

Preferably, the fire barrier includes a third layer. The third layer may provide insulation against the transfer of heat through the composite structure.

Preferably, the third layer comprises a plurality of metal sheets to restrict heat transfer by acting as a radiation barrier. Preferably, one or more respective separating layers are provided to separate adjacent metal sheets from one another. The, or each, separating layer may comprise an insulating material capable of restricting heat transfer by conduction. The metal sheets may be of a metal foil, for example an aluminium foil. The insulating material may comprise paper, which may be in the form of sheets of paper.

The separating layer may be affixed to the metal sheets, conveniently by a water based adhesive material. The third separating layer may be endothermic. In the preferred embodiment, the water based adhesive is absorbed onto the paper layers, whereby under fire conditions the adhesive or the papers layers acts as an endothermic absorber preventing heating transmission by the latent heat of evaporation of water. Thus, in the preferred embodiment, the third layer acts as a radiation barrier and can absorb heat as an endothermic layer.

The adhesive material may be a water based glue. Alternatively, the adhesive material may comprise a thickened composition, said composition comprising water and a thickener. The thickener may be selected from methyl cellulose, ethyl cellulose, polyvinyl alcohols, polysaccharide gums, polyethylene oxides, polyethylene glycols, organic flours such as corn flour, polyacrylic acids, and sodium salts of cross linked polyacrylates. \

In a first embodiment, the first layer may comprise a rigidifying material to render the first layer rigid during non-fire conditions. The rigidifying material may be such as to be rendered flexible under fire conditions.

The rigidifying material may be capable of softening or under fire conditions.

The first layer may include a flexible material, such as a textile material.

The rigidifying material may be provided on the flexible material.

In a first embodiment, the rigidifying material may comprise a thermo plastics material which may be coated onto the flexible material. In a second embodiment, the first layer may comprise a flexible material which may be a textile material. In this second embodiment, the first layer may be devoid of said rigidifying material.

The textile material may comprise a glass fibre or basalt cloth. The textile material may be woven, or formed of continuous fibre mat.

Alternatively, the first layer may comprise a skin formed of a suitable metallic material, for example, mild steel, which may be less than 1 mm thick.

The support material in the second layer may comprise a polymeric or plastics material capable of supporting the expandable material. Preferably, the polymeric material comprises a reaction product of a polyol with an isocyanate, desirably a multi-functional isocyanate. The polyol may be a low hydroxyl linear polyester, a polyether, a hydroxyl functional dimethyl siloxane, or a mixture, or a copolymer, of two or more of the aforementioned polymeric materials. The reaction product may be formed in the presence of curing accelerators. Suitable accelerators would be readily known by persons skilled in the art. A blowing agent may be added to the reaction mixture, the blowing agent may be water.

The support material is preferably polyurethane, and may be a cold curing two part polyurethane.

The support material is preferably a material that can be applied at a temperature below the activation temperature of the expandable material, and below the boiling point of water. Preferably, the support material comprises a foamed material. Preferably, the support material is formed by a foaming or blowing agent. The blowing agent may comprise water.

The support material may comprise a polyurethane matrix, which may incorporate the expandable material in cells therein. The expandable material may be present in an amount of between 300 and 7000 gms per square metro.

The expandable material may comprise exfoliable graphite.

The support material may comprise a matrix and the second layer may be formed by introducing the expandable material into said matrix. Where the support material includes an isocyanate, for example in the case of polyurethane, any water in the expandable material may react with the isocyanate to produce carbon dioxide, thereby causing the support material to foam.

The second layer may be provided on the first layer by allowing the support material to foam onto the first layer, thereby adhering strongly to the first layer.

The fire barrier may comprise a fourth layer which may be provided on the opposite side of the third layer to the second layer. The fourth layer may be the same as the second layer.

The fire barrier may comprise a fifth layer which may be provided on the opposite side of the fourth layer to the third layer. The fifth layer may be the same as the first layer.

According to another aspect of this invention, there is provided a fire protective composite barrier comprising skins that are both fire resistant and are or become flexible under fire conditions, where the core consists of a flame retarded flexible polyurethane that may be foamed by the addition of water, and is loaded with exfoliable graphite between 300 and 7000 gms per square metro, optionally containing a further endothermic inner core composed of 3 or more layers of aluminium foil each separated with paper onto which has been absorbed water containing a thickening agent.

The outer skins may comprise fire resistant textiles woven from glass or basalt.

The textile of the outer skin may have a thermoplastic matrix embedding the textile.

The outer skin may comprise thin mild steel sheet 1 mm or less in thickness.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawing which is a schematic sectional side view of part of a composite structure.

Referring to the drawing, there is shown a composite structure in the form of a fire barrier 10 comprising a plurality of layers.

The fire barrier 10 comprises two first or outer layers 12 arranged opposite each other. Inwardly adjacent of each of the outer layers 12 there is provided a respective second or intermediate layer 14. Between each of the second layers 14 there is provided a third or core layer 16.

Each of the outer layers 12 comprises an outer textile skin 18 which 5may comprise glass fibre or basalt cloth. The textile skin 18 may be woven, or formed of continuous fibre mat.

If desired, the textile skins 18 can be bound in a thermo-plastic resin 20, or other suitable material which is rigid at room temperature, but which 10soKens and becomes fully or partially flexible under fire conditions. The material in which the textile skin 18 is bound may be a polymer matrix.

One function of the outer textile skin, 18 is to provide durable outer support layer to the structure, particularly during transport and installation. A 15further function is to contain the intermediate and core layers 14, 16 during fire conditions.

As an alternative to outer textile skins 18 comprising glass fibre or a basalt cloth, the textile skins 18 may be replaced by a mild steel skin having a 20thickness of less than 1 mm.

Where the outer layers 12 are formed of a mild steel skin, they have a thickness of less than 1 mm. The use of mild steel has the advantage that it softens and loses most of its tensile strength at about 550 C since a standard 25fire is likely to raise a temperature of an exposed hot face to 550 C within 4.5 minutes, the thin hot steel skin acts as a flexible skin.

The second or intermediate layer 14 comprises a polymer matrix, in which the pores of the matrix contain an exfoliable graphite.

The intermediate layer 14 preferably comprises a polyurethane material, but it will be appreciated that any suitable polymeric material can be used, providing it can contain and support the exfoliable graphite. The most suitable polymeric materials are those which may be applied at temperatures below the activation temperatures of the exfoliable graphite and below the boiling point of water, in the event that water is included in the structure of the core layer 16.

In the preferred embodiment, the polymeric material is a cold curing two part polyurethane system comprising a polyol, in which the polyol is either a low hydroxile linear polyester, a polyether a hydroxile functional dimethyl siloxane or mixtures thereof, reacted with a multi functional isocyanates, in the presence of curing accelerators, which would be known by persons skilled in the art. The polyurethane material so produced forms a binder, and should preferably contain flame retardants, for example liquid phosphanate or ortho phosphate flame retardants. Also included in the reaction mixture may be blowing agents appropiate to flexible polyurethane foams, for example water.

Exfoliable graphite consists of native graphite treated with various acids, such as sulphuric, nitric or hydrofluoric acid. These added acids (known as "intercalate") become entrapped with water between the planes of the graphite crystals at up to 10% of the weight of the exfoliable graphite.

When exfoliable graphite is exposed to heat, the entrapped acids and water are released as gas causing the graphite to expand to up to 250 times its original volume.

The introduction of exfoliable graphite into a polyurethane matrix causes water present in the exfoliable graphite to react with the isocyanate groups of the polyurethane molecules to produce carbon dioxide. This causes the polyurethane to foam. Advantage may be taken of this by introducing conventional polyurethane foam control agents to refine the structure of the cells in the foam so produced. It is possible to add further water to the mixture, with suitable adjustment of the amount of isocyanate in order to provide further expansion of the foamed layers.

An advantage of the presence of the foam polyurethane is that it serves to protect the core layer 16. In addition, the flexibility of the layers allows easy transport and handling of the fire barrier 10. The foamed intermediate layers 14 provide passive insulation by virtue of their low conductivity which can be advantageous not only during fire conditions but also in continuous use. A further advantage is that the exfoliable graphite in the polyurethane foam of the intermediate layer 14 expands during exposure to a fire to form an insulating layer.

During the manufacture of the fire barrier 10, each of the polyurethane intermediate layer 14 is formed by wet reaction onto the outer layers 12. As a result, the intermediate layers 14 adhere to the outer layers 12. During fire conditions, the intermediate layer 14 expands into itself thereby restraining a tendency of exfoliable graphite to expand uncontrollably to form a loose incoherent mass of the exfoliable graphite incapable of supporting its own weight. In the preferred embodiment therefore, the expanded exfoliable graphite is restrained by its mode of formation and by the restraint imposed thereon by the outer layer 12 and the inner core 16.

The inner core layer 16 acts as a radiation barrier and comprises a plurality of alternating layers of thin aluminium foil 22 separated by layers of an absorbent paper 24. The aluminium foil 22 is adhered to the paper 24 by the use of a water based adhesive. An advantage of the core layer 16 in the preferred embodiment is that a very light gauge aluminium foil may be used, because it is installed in the centre of the fire barrier 10 and is protected by the outer layers 12 and the intermediate layers 14. A further advantage of the preferred embodiment is that a plurality of alternating layers of aluminium foil and paper are provided. Radiation barriers rely on the successive reduction of radiation which is proportional to the emmisivity of material. Thus, for example, where the emmisivity is 0.2 then only 20% of the incident radiation can be transmitted through the first barrier. Likewise, the same proportion of radiation incident on a second foil sheet 22 is transmitted therethrough. This reduction continues by the same proportion for each sheet of foil used.

However, in known radiation barriers, only two heavy foils are used. Such radiation barriers need not only to be robust enough to support themselves during insulation and under fire conditions, but the also have limited efficacy due to the limited number of the sheets of foil used.

l O The natural choice for the material of the foil is aluminium which has a melting point of 550 C. As a result, it follows that in prior art radiation barriers, where the first barrier is almost directly exposed to the fire, there is a risk that the first foil layer will be destroyed by the fire.

A further advantage of the core layer 16 in the preferred embodiment is that paper is used to separate the foil layers 22. This prevents contact between adjacent foil layers 22, thereby preventing the transmission of heat by conduction. Moreover, the temperatures attained by the core layer 16 will be significantly less than the temperatures experienced by the outer layers 12, due to the insulation provided by the expanded exfoliable graphite in the intermediate layers 14. The result of this is that the paper layers 24 merely pyrolise into carbon and maintain separation of the foil layers 22.

The aluminium foil 22, which may be 30 to 35 microns in thickness, and may be no more than 30 microns in thickness, can be annealed, un-annealed, or an alloy of aluminium. The separating layer arranged between adjacent foil sheets 22 may be an absorbent paper, for example a single ply, having a film weight in excess of 45 grams per square metre and a thickness of 100 microns. The thickness of the separating layer may be achieved by quilting or crimping the layer. Alternatively, the separating layer 24 may be formed of viscose having a film weight in excess of 45 grams per square metro and a thickness of 100 microns.

The absorption of water into the separation layer may enhance the performance of the fire barrier 10. Thickeners are added to the water to prevent it from draining out under fire conditions. The thickeners also provide additional adhesive strength to the structure. The thickener may comprise methyl cellulose, ethyl cellulose, poly vinyl alcohols, polysaccharide gum, polyethylene oxides, polyethylene glycols, organic flours such as conrflour, polyacrylic acids, and sodium salts of crosslinked polyacrylates, or a combination of the above.

The use of the water based adhesive is also advantageous in the preferred embodiment, in that the adhesive is absorbed onto the paper layers 24 and sealed within the polyurethane intermediate layers 14. As a result, the adhesive cannot be lost by evaporation. Hence, under fire conditions, the adhesive on the paper layer 24 acts as an endothermic absorber preventing heat transmission by latent heat of evaporation of water. It is known to provide fire prevention systems using a similar mechanism, in the case of hydrolised water in plaster based products. However, in the preferred embodiment, the water is present as trapped free water and is therefore available as an endothermic absorber at a lower temperature than prior art systems relying on water of hydrolisation. Moreover, in view of the fact that the water contributes nothing to the durability of the system, its evaporation results in no loss of the physical properties of the structure under fire conditions. The presence of water assists in the controlled pyrolisis of the paper separators.

The procedure for making the fire barrier 10 is as follows: The formation of the inner core 16 comprises the following steps: (a) A water soluble glue or thickener is dissolved or disbursed in water to obtain a thick paste capable of application by roller.

(b) A sheet of aluminium foil is laid flat on a lay-up table and coated with the paste with conventional paint rollers.

(c) A sheet of paper as described above is laid over the pasted aluminium foil.

(d) A second sheet of aluminium foil is laid out on the lay-up table and pasted as described above. The second sheet is laid with its wet surface l O downwards onto the upper surface of the sheet of paper. Paste is applied to the upper surface of the second sheet of foil with the roller. This step has the advantage of compacting and consolidating the first sheet of aluminium foil and the first sheet of paper.

(f) A second sheet of paper is laid onto the wet upper surface of the second sheet of aluminium foil and the steps of (b) to (e) are repeated until the required number of sheets of aluminium foil and interleaving paper sheets are used.

(g) The edges of the foils are folded over to form a crease, and this crease is consolidated with hard rollers. The consolidation of the crease seals the wet paste into the inner core 16.

Assembly of the barrier 10 is as follows: (h) The mixture of the polyols and isocyanate compound are blended with liquid flame retardants, curing accelerators and, if desired, water and foam control agents. The exfoliable graphite is then dispersed in the mixture. The mixture is then divided into two equal parts.

(i) A textile outer skin 18 as described above is laid upon the lay up

table.

(j) An isocyanate, in an appropriate amount that would be appreciated by a person skilled in the art, is added to one of the parts of the polyol mixture described in step (h) and mixed thoroughly.

(k) The mixture formed in (j) is applied to the upper face of the outer textile skin 18 which will form one of the outer layer 12 and smoothed out.

This will provide one of the intermediate layers 14. The step of smoothing out the mixture can be carried out by rubber scraper blades.

(I) The inner core 16 formed as described above is laid onto the mixture on the textile outer skin 12.

(m) The appropriate amount of the isocyanate material is added to the second part of the mixture formed in (h) and then mixed thoroughly.

(n) The mixture formed in (m) is applied to the upper face of the inner core and roughly smoothed out as described in (k) above. This will provide the other intermediate layer 14.

(h) The second outer layer 12 is laid onto the mixture described in (n) and the structure consolidated with hard rollers applied to the upper surface of the outer layer 12. A weighted board is applied onto the skin and left to cure.

During curing, the urethane mixture will foam, which will compensate for any unevenness during the safe of applying the mixture to the outer textile skins 18 and any voids between the outer textile skins 18 will be filled.

Reference is now made to Table 1, which shows examples of polyurethane composite fire barriers according to the preferred embodiment of the invention constructed as described above which were tested as fire barriers on an indicative furnace capable of reproducing the specified standard fire conditions.

When the structures shown in Table 1 are placed under fire conditions, the backface thermal response curves of temperature against timeshow two plateaux. The first plateau is between 60 C and 90 C. The height of the plateau is determined by the amount of exfoliable graphite in the fire barrier and by the degree of expansion of the intermediate layer 14 which is depended upon the amount of water in the structure. The length of time that this plateau in the curve is maintained is determined by the water loading of the adhesive or other mixture applied between the foil sheet in the core 16 and the paper layers. When the water in the core layer 16 has evaporated, the thermal response curve rises from the first plateau to a second plateau which is determined by the number of layers of oil in the barrier 10. In an extreme example shown in sample 11 in Table 1, the time to a backface temperature of 140 C above ambient temperature is shown as 15 minutes.

With six foil layers, in the case of sample 11, the second plateau temperature of the backface was maintained for a significant period beyond the failure point at 140 C above ambient.

The example shown in Table 1 show that the textile outer layer 12 may be either glass or basalt cloth and that the weight of this layer is largely irrelevant for fire protection periods of up to one hour. The polyols in the mixture were reacted with a stochiometrically correct amount of methyl phenyl di iscoyanate mixed isomers. The level of the liquid flame retardants added was sufficient to render the reactive polyurethane nonflammable and to maintain the flexibility of the internal core layer.

In all cases shown in Table 1, the aluminium foil in the core 16 was 30 35 microns and, as indicated by Table 1, the separating layers between the foils was cellulose, or a cellulose derived woven layer, including cotton.

The examples in Table 1 show that the preferred embodiment is not necessarily limited to outer layers 12 but are flexible when not under fire condition. Twintex() L used in example 13 is a composite consisting of polypropylene reinforced by glass woven rovings. When under fire conditions, the polypropylene is lost by combustion and pyrolysis thereby leaving the flexible woven rovings to support the expanded exfoliable graphite in the same manner as other woven textiles as described above. For example 14 shows how the invention may be extended to other materials used in the outer layers 12 have become flexible when heated.

Various modifications can be made without departure from the scope of the invention Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.