GB2269548A - Fire resistant insulation materials and manufacture thereof - Google Patents

Abstract

A fire resistant insulation material comprising a substrate of insulation material having on a surface thereof a coating of a fire resistant coating which forms, on exposure to a fire, a layer of carbon char and an inorganic glassy phase which adheres to the substrate and protects the carbon char from high temperature oxidation.

Description

2269548 FIRE RESISTANT INSULATION MATERIALS AND MANUFACTURE THEREOF The

present invention relates to a fire resistant insulation material and to a method of producing a fire resistant insulation material.

It is known to use insulation materials for heat insulation in a wide variety of building structures. Such insulation materials include mineral wools, ceramic wools and insulation products made of foamed or expanded plastics materials. Mineral fibre insulation products, particularly those based on rock wool, are used commonly in applications where good resistance against fire damage is required, for example in the protection of structural steel work which is used in modern building construction techniques. A function of the insulation is generally to retard possible distortion of the steel, and consequential partial or complete collapse of the building, when the structure is subjected to a fire for a period sufficient for the building to be fully evacuated. In a less serious fire, the insulation can also be effective in reducing damage costs through minimization of structural deterioration. In further applications, suitable insulation materials can also be used to stop or retard the spread of the fire f rom one area of a building to another. Typical examples of such applications would be the use of insulation materials in wall penetrations which are used to pass services around the building or under suspended floors.

Commonly used insulation materials such as slabs of rock wool are fairly effective in achieving the desired levels of fire protection. However, the rock wool needs to be used in substantial thicknesses, from say about 30 to 100 mm and at a relatively high density, generally in excess of 3 kg/m Accordingly, for some applications where fire 2 - resistance is required, the insulation material can occupy a significant space in the building which otherwise could be used for other purposes. Furthermore, the mass of a large volume of insulation can also be a disadvantage where floor loadings are critical.

It is also known to use such insulation materials for marine applications in which it would be disadvantageous to have excess mass constituted by a large volume of insulation material.

The present invention aims to improve the fire resistance of such insulation materials in order at least partially to alleviate those problems with known insulation materials.

Accordingly, the present invention provides a fire resistant insulation material comprising a substrate of insulation material having on a surface thereof a fire resistant coating which forms, on exposure to a fire, a layer of carbon char and an inorganic glassy phase which adheres to the substrate and protects the carbon char from high temperature oxidation.

The present invention also provides a method for producing a fire resistant insulation material, the method comprising providing an insulation substrate and applying to a surface of the substrate a fire resistant coating which forms on exposure to a fire a layer of carbon char and an inorganic glassy phase which adheres to the substrate and protects the carbon char from high temperature oxidation.

Preferably, the fire resistant coating comprises an epoxy resin and at least one fire resistant additive which can form the inorganic glassy phase an exposure to a fire.

The f ire resistant insulating material of the present invention: may be used to provide fire protection of structural steel work in a building or to provide fire protection between adjacent stories or adjacent rooms in a building.

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawing, in which:- FIG. 1 is a section through a fire resistant insulation material in accordance with an embodiment of the present invention.

Referring to Figure 1, there is shown a mineral wool insulation slab 2 which in particular is composed of rock wool. Slab 2 carries a coating layer 4 of fire resistant composition. The coating layer 4 comprises an epoxide resin composition including at least one fire resistant additive and the composition of the coating layer will be described in detail hereinbelow. The coating layer 4 is thin relative to the thickness of the slab 2. The addition of a relatively thin layer of fire resistant composition to the surface of the insulation slab 2 has been found to be very effective in either increasing the fire resistance of a given thickness of the insulation or in maintaining the fire resistant properties of the insulation even at reduced thickness. When the insulation material is rock wool, which is moderately porous, the fire resistant composition, which is applied to the insulating slab 2 as a liquid to form the coating layer 4, can controllably penetrate into the rock wool so that the thermally stable rock wool f ibres act as a reinforcement and support for the fire resistant composition. Typically, the liquid epoxy resin-based f ire resistant composition is sprayed onto the surf ace of the mineral fibre slab in order to form a coating layer 4 on the slab which penetrates into the surface thereof to a depth of approximately f rom 5 to 8 mm. Alternatively, the liquid fire resistant composition can be applied to the base insulation material by a roller coater, blade or curtain coater, the choice of application technique being dependent upon the properties of the liquid fire resistant composition and the required fire resistance of the ultimate insulation product.

When the insulation material is composed of a material other than mineral wool, for example one with a lower softening temperature such as glass wool, it may be preferable that the coating layer should penetrate the surface of the insulation material to a lesser depth or substantially not at all. For example, with a glass wool substrate the coating may be as little as 1/2 mm thick on the surface of the glass fibre substrate, the fire resistant composition having been applied by a blade.

The fire resistant composition includes a plastics resin which acts as a base polymer, which, when it is subjected to a fire, produces a carbon char which provides enhanced fire protection. The base polymer also acts as a binder for other fire resistant constituents of the coating. The plastics resin may be an epoxy resin, an unsaturated polyester resin or a polyurethane resin. An epoxy resin is preferred. The epoxy resin is selected from Bis-phenol A or Bis-phenol F resin or it may be an epoxidised resin of the novalac type.. A suitable Bis-phenol F epoxy resin is sold by Shell Chemicals, U.K. under the trade name Epikote 862. Blends or mixtures of these epoxy resins may be used in accordance with the invention. The viscosity of the epoxy resin is modified to enable it to be applied as a liquid to the insulation material substrate. The epoxy resin is preferably diluted with aliphatic epoxide resins in order to reduce the viscosity of the epoxy resin mixture. Typical aliphatic epoxy resins for controlling viscosity are diepoxides such as diglycidyl ethers and non-glycidyl ether diepoxides, in particular the aliphatic - 5 epoxy resins may be selected from butadiene diepoxide; diglycidyl ether; butanediol digylcidyl ether; and diethylene gylcol diglycidyl ether. A most preferred aliphatic epoxy resin additive is a polyoxyalkylene diglycidyl ether which is sold under the trade mark DER 736 and is available from Dow Chemicals, UK. DER 736 has an epoxide equivalent weight of 175 to 205 mmol/kg and a viscosity of 30 to 36 centipoise at 25 0 C. However, alkanediol diglycidyl ethers, for example butanediol diglycidyl ethers, have been found to be more effective than polyoxyalkylene diglycidyl ethers at reducing viscosity of the epoxy resin without adversely affecting the fire resistance properties of the composition.

The aliphatic diepoxides are epoxy resins which react with epoxy resin curing agents and become an integral part of the molecular structure of the cured epoxy resin system. Any suitable curing agent which is known for curing epoxy resins may be employed in accordance with the present invention, although preferred curing agents are trialkoxyboroxines such as trimethoxyboroxine (TMB) or tributoxyboroxine. TMB is available in commerce from Strem Chemicals, Inc, of Newburyport, Mass. U.S.A. Alternatively, the curing agentmay comprise tri-m,p-cresol borate or an amine. -It is preferred to use a curing agent other than an amine because the use of an amine curing agent generates relatively more smoke when it is subjected to a fire. A boron-containing curing agent such as trimethoxyboroxine or tributoxyboroxine, which is less expensive than trimethoxyboroxine, has the advantage that the presence of the boron in the composition results in the formation of a glassy borate phase when the fire resistant composition is subjected to a fire. This phase promotes the increased stability of the carbon char which is formed on decomposition of the organic components, particularly the epoxy resin components, and acts both to adhere the carbon char to the insulation material substrate and to retain the carbon char in a coherent, non-f riable layer. The glassy borate phase thus forms a hard coating including the carbon char on the insulating material which is strongly fire resistant. The glassy phase adheres strongly to the substrate and the mechanical impregnation of the carbon char with the glass ensures that the carbon char is thereby firmly held on the substrate surface. In addition, the coating of the carbon char by the inorganic glassy phase provides the carbon char with a slow ablation rate at high temperatures so that the carbon char is not oxidized by air at such temperatures. The coatings made in accordance with the present invention have been tested in fire tests at temperatures up to about 820 0 C and the carbon char has remained protected by the glassy phase on the substrate surface after been subjected to those temperatures. The carbon char was not removed from the substrate surface as a result of high temperature oxidation in air. - The composition of the epoxy resin/curing agent system is controlled so as to have a viscosity in the uncured resin which permits the composition to be sprayed or otherwise coated as desired onto the insulation substrate. A typical viscosity range of the liquid coating is from 2500 tP 6000 centipoise at 25 0 C. Typically, the epoxy components comprise around 30% by weight of the total composition, with about 70% by weight of the total composition being additives, more particularly fire resistant and fire retardant additives. The liquid fire resistant composition may in particular comprise up to about 70% of the long chain epoxy resin, such as bisphenol F epoxy resin. The liquid fire resistant composition may comprise up to about -70% aliphatic epoxy resin, such as DER 736 or an alkanediol diglycidyl ether, such as butanediol diglycidyl ether. These two ranges are obviously controlled in the final composition to ensure that the composition has the desired -viscosity and also the appropriate ultimate epoxy structure to enable the fire resistant additives to be supported and retained in the coating layer. The liquid fire resistant compositi6n also comprises from 5 to 20% by weight of the curing agent, in particular when the curing agent is a trialkoxyboroxine. - The liquid fire resistant composition of the preferred embodiments of the present invention also includes, in addition to a boron-containing curing agent for the epoxy resin system, such as trimethoxyboroxine, a boron compound which is not a curing agent for the epoxy resin but which enhances char stability through increased borate glass formation. The use of such a boron-containing compound in an epoxy resin composition is disclosed in our EP-A-0500317 published 26th August 1992. The boron compound which is not a curing agent for the epoxy resin may be a sterically hindered boroester or a sterically hindered boric anhydride, the steric hindrance preventing it from functioning as a curing agent for the epoxy resin. Such a boron compound is generally a compound which is not effective as a Lewis acid and does not react with the epoxy groups of the resin. However, boron compounds may be used which react only slowly with the epoxy resins so that, when the curing agent is present, it reacts preferentially with the epoxy resin so that there is little or no reaction between the boron compound which is not a curing agent and the epoxy resin. The preferred boroesters used in accordance with the invention have a relatively high proportion of boron, and thus a relatively high proportion of BO bonds, which mean that when the boroester is subjected to a fire, borate glass is formed on decomposition of the added boron compounds. Typically, the boroesters are polyborates, e.g. biborates, and the boric anhydride is bifunctional with respect to borates. This not only reduces the volatility of the boron content in the boron compound thereby enhancing the glass forming effect, and thus the fire resistance, when the composition is subjected to a fire but also tends to enhance the degree of glass forming due to the increased BO bonding in the composition. We have found that the preferred boroestert in accordance with the invention, which are biborates, have broad decomposition profiles when heated, i.e. they tend to decompose over a broad temperature range and also at high temperatures. This enhances the glass forming effect and gives greater fire resistance. Preferably, the added boron compound is an organoboron compound which comprises at least 5 wt % boron usually from 5 to 20% boron, more preferably from 5 to 8 wt % boron.

Examples of suitable boroesters are the trialkyl boroesters of general formula B(OR) 3 where R is a radical containing 1 to 18 preferably 1 to 8 carbon atoms. Preferred boroesters of this formula are those in which.R is a secondary or tertiary alkyl group or a aryl group containing 6 to 18 carbon atoms. A preferred boroester is BORESTER 5 (tri-n-octyl borate, a colourless liquid containing 2.7% by weight boron).

Other preferred boroesters, are those derived from a diol and boric acid which tend to have a high boron content combined with a high degree of steric hindrance. Especially preferred boroesters are trialkylene biborates wherein the alkylene group contains 2 to 8 carbon atoms, for example, BORESTER 35 tri-(1,3-butanediol) biborate, a colourless to pale yellow liquid containing 7.1% by weight of boron, BORESTER 7, tri(2methyl-2,4-pentanediol) biborate, a colourless liquid containing 5.9% by weight of boron, and BORESTER 15, tri octylene glycol diborate, a liquid containing 4.76 wt % of boron.

An example of a suitable sterically hindered boric anhydride is BORESTER 33, hexylene glycol boric anhydride, a colourless to pale yellow liquid containing 7.5% by weight of boron. BORESTER is a trade mark and the BORESTER compounds referred to herein are available in commerce from US Borax Inc of Anaheim, California, U.S.A.

Other boresters which could be employed in the present invention "-are unsaturated borates, such as BORESTER 22, triallyl borate (C 9 H 15 0 3 B, boron content 5.94 wt %); amino boresters, such as BORESTER 20, triethanolamine borate (C 5 H 12 0 3 NB, boron content 6.89 wt %), BORESTER 21, tri-iso-propanolamine borate (C 9 H 12 0 3 NB)l boron content 5.44 wt%) and BORESTER 110,2-(B-dimethylamino ethoxy)-4-methyl1,3,2 dioxaboriname, (C 8 H 18 BNO 3 boron content 5.8 wt and polyborate esters, such as methyl polyborate E(CH 3 0) 3 B] 2 (B 2 0 3)x where X 2 -3, boron content not less than 20 wt The amino boresters would be used particularly with amine curing agents for the epoxy resin.

Preferably, the fire resistant composition contains f rom about 1 to 20% by weight of the added boron compound, when the boron compound is in the form of a boroester.

Other components which may be incorporated in the f ire resistant composition include phosphates and phosphites, such as those proposed in GB-B-2092594 and GB-B-2058076, and also halogenated, usually chlorinated, organic compounds used f or their f lame retardant properties. Examples of such suitable phosphates' include tris-2-chlorethyl phosphate (TCEP) tri's(dichloroisopropyl) phosphate (TDCP), tris(monochloroisopropyl) phosphate, tributoxyethyl phosphate, trioctyl phosphate, diphenyl chlorophosphate, (available in commerce, from Aldrich Chemical Company of Gillingham, Dorset, England), chlorinated diphosphate esters (available in commerce from Albright and Wilson Ltd of Warley, West Midlands, England as AMGARD V6 and AMGARD V7), and high molecular weight polyphosphates -such as those available from Albright and Wilson as AMGARD V19 and ANTIBLAZE 19. Phosphonates e.g. Albright and Wilson's AMGARD DMMP, dimethyl methyl phosphonate, may also be used.

Examples of suitable phosphites include tris-2-chloro ethyl phosphite (TCEPi), diphenyl phosphite and dibutyl phosphite.

The added phosphate or phosphite compound may be present in an amount f rom about 5 to 20% by weight in the fire resistant composition.

The fire resistant composition also preferably includes calcium carbonate in an amount up to about 15% by weight. The calcium carbonate particles are preferably coated with a stearate to enable the calcium carbonate to be dispersed throughout the liquid fire resistant composition. The calcium carbonate acts as a flame suppressant since on being subjected to a fire it decomposes to provide a refractory oxide of calcium oxide and carbon dioxide gas which acts to suppress flames and reduce thermal oxidation. The ref ractory oxide penetrates the carbon char and assists in stabilising the char layer. Such coated and uncoated calcium carbonate particles suitable for use in the present invention are available from ICI Chemicals, UK under the trade name Winnofil.

The fire resistant composition may include magnesium carbonate and/or magnesium hydroxide as flame suppressants as an alternative to, or in addition to, calcium carbonate.

The fire resistant composition also preferably includes an endothermic cooling agent and a preferred such additive is aluminium trihydrate (Al(OH) 3) which is available in commerce from Croxton and Garry Ltd, Surrey, England under the trade names of Trihyde OL104, OL107 and OL111 nad the Trihyde range in general. When aluminium trihydrate is heated it decomposes to aluminium oxide and water with an endothermic reaction. This provides cooling of the fire resistant coating to a temperature below that required to sustain the combustion process. The decomposition reaction also leads to the evolution of water vapour which dilutes the combustible fuel in the solid and gaseous phases such that the lower ignition limit of the gas mixture is not exceeded. This can reduce smoke generation when the coating is subjected to a fire. The decomposition oxide formed enhances the mechanical properties of the carbon char formed from the pyrolysis of the polymeric and organic components. Thus the use of aluminium trihydrate greatly increases the fire resistance of the coating. An endothermic decomposition additive such as aluminium trihydrate may be present in up to about 40% by weight in the composition.. An alternative endotli ermic fire retardant is hydrated zinc borate which is available in commerce from US Borax Inc, of Anaheim, California, U.S.A. under the trade name Firebrake.

In accordance with a preferred aspect of the invention, the fire resistant composition can be made intumescent to a desired degree so that when the fire resistant coating is subjected to a fire a slightly porous char results from the action of gaseous decomposition products which are released from the coating. For some fire resistant insulation products and for some applications in which such products are employed, the presence of an intumescent material in the fire resistant coating can be beneficial for increasing the fire performance. This can be achieved by incorporating intumescent materials, for example phosphate compounds such as TCEP referred to hereinabove, into the composition. The added boron compounds such as borate esters act as secondary intumescent materials and enhance the intumescent effect. The addition of aluminium trihydrate causes a suppression of the intumescent effect because the compound tends to shrink on decomposition. It is also possible to incorporate chemical blowing agents already known for use in intumescent materials into the composition to enhance the intumescence. The calcium carbonate additive can act as such a blowing agent. In the fire resistant composition, the amounts of these various components are controlled so as to provide the desired degree of intumescence in the ultimate coating.

In the manufacture of the flame resistant insulation material 'in accordance with the present invention, the viscosity of the liquid fire resistant composition is first reduced by blending the epoxy resin or resins with the lower viscosity liquids such as the phosphate or borate esters. The inorganic solid materials such as aluminium hydroxide, zinc borate or treated calcium carbonate are then incorporated in to the mixture gradually under the action of a high shear mixer. In the case of particularly viscous compositions, gentle heating may be used to reduce the viscosity and so as to enable more intimate mixing. In the case of a batch production process, the curing agent for the epoxy resins is the last constituent to be stirred into the flame resistant mixture, giving a usable pot life of the order of one hour. In the case of a continuous application process, the catalyst may be metered and mixed directly into the fire resistant composition immediately prior to application thereof to the insulating material substrate.

As indicated above, the liquid fire resistant composition is applied to the insulation material as a surface coating by spraying or otherwise. After application, the curing of the liquid fire resistant composition may be accelerated by gentle, heat, although optimum fire resistant properties may generally be achieved if the material is left to cure at an ambient temperature for a number of days.

The potential level of additional fire protection afforded by the application of the epoxy resin fire resistant composition was tested by subjecting fire resistant insulation materials made in accordance with the present invention to impingement by a high temperature gas flame. The thickness and particularly the integrity and stability of the char so formed gave a good indication as to the additional fire protection afforded by the fire resistant layer. The test also provides an assessment of the comparative level of smoke emission and surface flaming between -the various compositions and it is obviously desirable that both smoke emission and flaming be minimised.

The present invention will be further illustrated with reference to the following non-limiting Example.

In the following Comparative Example and Example, a glass wool substrate is tested for fire resistance. However. it should be comprehended that glass wool inslation slabs are generally not used for fire protection purposes because of the relevatively low softening point of the glass. Nevertheless, use of glass wool in the following Comparative Example and Example provides a good indication as to the extra level of fire protection provided by the fire resistant coating of the present invention.

Comparative Example 1 A glass wool insulation slab around 18 mm thick was subjected to a gas flame at a temperature of around 700 0 C. The gas flame burnt a hole completely through the the glass wool insulating slab after a period of about 20 seconds.

Example 1

The glass wool insluation material of Comparative Example 1 was coated with an epoxy resin fire resistant composition to form a fire resistant coating layer on the glass wool of the insulating material, the composition being in accordance with the present invention.- A typical fire resistant composition used in this Example comprises 25 parts Bisphenol-F epoxy resin, 25 parts DER 736 aliphatic epoxy resin, 30 parts aluminium trihydrate, 10 parts TCEP, 2 parts Borester 33 and 8 parts trimethoxyboroxine, all parts being by weight.The coating was achieved by blading the liquid onto the surface of the glass wool slab and the thickness'- of the coating layer was around 1/2 mm. The coated surface was subjected to the same gas flame as that of Comparative Example 1. After a period of around 5 to 10 minutes, a charred and glassy surface was present on the glass wool substrate but no hole had been burnt through the substrate. The surface of the- substrate had retained its integrity.

The successful performance of the fire resistant coating on glass wool in accordance with this Example broadens the potential applications of glass wool products, in which the products are required to be fire resistant, such applications not having been normally considered for glass wool products. Glass wool does have some advantageous properties over rock wool, such as lower density for the same insulation value, and so the present invention may permit glass wool insulation products coated with a fire resistant coating in accordance with the present invention to be employed where heretofore it was not possible to use glass wool products.

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Claims (30)

CLAIMS:

1. A fire resistant insulation material comprising a substrate of insulation material having on a surf ace thereof a fire resistant coating which forms, on exposure to a fire, a layer of carbon char and an inorganic glassy phase which adheres to the substrate and protects the carbon char from high temperature oxidation.

2. A fire resistant insulation material according to claim 1 wherein the coating comprises an epoxy resin and at least one fire resistant additive which can form the inorganic glassy phase on exposure to a fire.

3. A fire resistant insulation material according to claim 2 wherein the epoxy resin comprises a mixture of a first epoxy resin selected from at least one of a Bisphenol-F, Bisphenol-A or novolac epoxy resin and a second aliphatic epoxy resin.

4. A fire resistant insulation material according to claim 3 wherein the second aliphatic epoxy resin is a polyoxyalkylene diglycidyl ether or an alkanediol digylcidyl ether.

5. A fire resistant insulation material according to any one of claims 2 to 4 wherein the epoxy resin-containing coating has been coated onto the insulation material as a liquid having a viscosity of from 2500 to 6000 centipoise at 25 0 C.

6. A fire resistant insulation material according to any one of claims 2 to 5 wherein the epoxy resin has been cured with a boron-containing curing agent.

7. A fire resistant insulation material according to claim 6 wherein the curing agent is a trialkoxy boroxine.

8. A f ire resistant insulation material according to any one of claims 2 to 7 wherein the at least one fire resistant additive includes an organoboron compound which is not a curing agent for the epoxy resin.

9. A fire resistant insulation material according to claim 8 wherein the organoboron compound is a borate ester or boric anhydride.

10. A fire resistant insulation material according to any foregoing claims wherein the coating includes an intumescent material.

11. A fire resistant insulation material according to any foregoing claim wherein the substrate comprises mineral wool.

12. A fire resistant insulation material according to any foregoing claim wherein the coating has been applied to the substrate as a liquid and then cured.

13. A fire resistant laminate substantially as hereinbefore described with reference to the accompanying drawing.

14. A fire resistant laminate substantially as hereinbefore described with reference to Example 1.

15. A method for producing a fire resistant insulation material, the method comprising providing an insulation substrate and applying to a surface of the substrate a fire resistant coating which forms, on exposure to a fire, a layer of carbon char and an inorganic glassy phase which adheres to the substrate and protects the carbon char from high temperature oxidation.

16. A method according to claim 15 wherein the coating comprises epoxy resin including at least one fire resistant additive which can form the inorganic glassy phase on exposure to a fire.

17. A method according to claim 16 wherein the epoxy resin comprises a mixture of a f irst epoxy resin selected f rom at least one of a BisphenolF, Bisphenol-A or novolac epoxy resin and a second aliphatic epoxy resin.

18. A method according to claim 16 or claim 17 wherein the second aliphatic epoxy resin is a polyoxyalkylene diglycidyl ether.

19. A method according to any one of claims 16 to 18 wherein the epoxy resin-containing coating is coated onto the insulation substrate as a liquid having a viscosity of from 2500 to 6000 centipoise at 25 0 C.

20. A method according to any one of claims 16 to 19 wherein the epoxy resin is cured with a boron-containing curing agent.

21. A method according to claim 20 wherein the curing agent is a trialkoxy boroxine.

22. A method according to any one of claims 16 to 21 wherein the at least one fire resistant additive includes an organoboron compound which is not a curing agent for the epoxy resin.

23. A method according to claim 22 wherein the organoboron compound is a borate, ester or boric anhydride.

24. A method according to any one of claims 15 to 23 wherein the coating inciudes an intumescent material.

25. A method according to any one of claims 15 to 24 wherein the substrate comprises mineral wool.

26. A method according to any one. of claims 15 to 25 wherein the coating layer has been applied to the substrate as a liquid and then cured.

27. A method for producing a fire resistant insulation material substantially as hereinbefore described with reference to the accompanying drawing.

28. A method for producing a fire resistant insulation material substantially as hereinbefore described with reference to Example 1.

29. Use of a fire resistant insulating material according to any one of claims 1 to 14 to provide fire protection of structural steel work in a building.

30. Use of a fire resistant insluation material according to any one of claims 1 to 14 to provide fire protection between adjacent stories or adjacent rooms in a building.