GB2246136A - Intumescent coating compositions - Google Patents

Abstract

Conventional phosphate catalyzed intumescent coatings designed as either fire protection coatings or fire retardant coatings are improved in appearance and rendered more durable by the partial or complete substitution of the normal pigmentation, commonly rutile titanium oxide, with precipitated hydrated aluminium silicates.

Description

THE IMPROVEMENT OF THE APPEARANCE AND PERFORMANCE OF INTUMESCENT COATINGS BY THE INCORPORATION OF PRECIPITATED HYDRATED ALUMINIUM SILICATES (0) We Prometheus Developments Ltd., a body corporate organised according to the laws of the United Kingdom and Northern Ireland, of 24 Mount Pleasant Drive, Belper, Derbyshire, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (5) The present invention concerns a method for the manufacture of intumescent coatings. The use and utility of intumescent coatings is described in the following, together with a synopsis of the shortcomings of current commercial formulations.This invention relates to the replacement of one of the common components of intumescent coatings with proprietary precipitated hydrated aluminium silicates in order to improve the durability and appearance of conventional intumescent coatings, to allow the control of the colouration of these coatings and to reduce the cost of the raw materials used in their manufacture.

(10) Intumescent coatings are commonly applied to the surface of elements of construction in order to prevent or delay the onset of structural collapse in the event of fire. Such coatings are also applied to barriers or bulkheads separating compartments or penetration between compartments. The function of the coating, in this case, is to prevent or assist in preventing the passage of fire from one compartment to the other via the separating barrier or bulkhead. Such coatings are also applied to the surface of substrates either to reduce the tendency of a flammable substance to ignite, or to provide a decorative or sealer coat to substances that are non-infiammable in themselves but require some form of protection other than from fire.

(15) Within the prior art, formulations for intumescent coatings commonly contain rutile titanium dioxide as an essential component of the formulation. What we have found is that precipitated hydrated aluminium silicates may be substituted, in part or in whole, for that component of the intumescent coating formulation with benefits in performance under fire conditions, with reduction in cost of the raw materials of the formulation and to provide the ability to control the colour of the dried film of the intumescent coating. The modification also improves the durability of the applied film.

(20) With respect to the prior art, intumescent coatings consist of a source of acid phosphates, a poly hydroxy organic material and a source of inert gas. These materials are bound in a conventional polymeric binder that may be a styrene or vinyl toluene acrylic a styrene or vinyl toluene butadiene copolymer or a styrene or vinyl toluene acrylonitrile. The binder may alternatively be polyvinyl alcohol, polyvinyl acetate, polyvinyl buty ral, urea or melamine formaldehyde or a polyvinylivinylidene chloride. Epoxy resins cured with a variety of amine functional curing agents are also conventionally used. In all cases a plasticiser consisting of a chlorinated paraffin or a phosphate ester, possibly halogenated are also incorporated.

(25) Intumescent fire retarding compositions act by providing, under the influence of heat, an expanded layer of relatively incombustible material which serves to insulate the substrate and prevent ready access of oxygen thereto, thus reducing or delaying the overheating andJor combustion of the substrate. A balance of properties has to be maintained. The greater the degree of sxpansion the thicker the insulating layer, but if the expansion is too great the intumesced material may become detached from the substrate and fail to protect it.

C Intumescent materials have been known for many years, and may be based on various components. For example GB 2151237 (British Petroleum) discloses compositions comprising chlorinated polymer, phenol/formaldehyde novolak and a chlorinated or phosphorous containing plasticiser, G B 2012296 (Chemie Ling) compositions of expandable graphite, hydrated alumina and a binder of halogenated elastomer and alkylphenollformaldehyde resin, and GB 1604908 (Minnesota Mining) compositions of unexpanded vermiculite, inorganic fibrous filler, elastomer and clay.The most usual formulation comprises a binder, a char forming material ( carbonific") and an expanding material ("spumific"), optionally with other materials such as anti-drip materials (eg. inorganic fibrous materials, PTFE), catalysts for the decomposition of the carbonific (eg. latent acids such as ammonium phosphates) and smoke suppressants (eg. metal oxides).Typical examples of such basic formulations are US 4442157 (Mars) of phenolic resin binder, ammonium polyphosphate, pentaerythritol (carbonific) and dicyandiamide (spumific) to which is added polyvinyl alcohol, GB 755551 (Dow) of binder, latent acid catalyst, polyol carbonific (starch or pentaerythritol) and spumific (nitrogenous compound such as urea, dicyandiamide or guanidine), US 3562197 (Sears) of binder, ammonium polyphosphate, carbonific (urea or melamine compound) and a polyol (starch, protein, pentaerythritol) and EP 0138546 (Dixon International) of elastomeric binder, amino-resin binder, ammonium phosphate, carbonific (pentaerythritol sugar, starch) and spumific (polyamido compound such as dicyandiamide or guanidine).

As can be seen the components are not necessarily confined to a single function. This may further be seen in GB 2007689 (Montedison) where a reaction product of an amido compound and an aldehyde functions as carbonific and spumific, EP 0142074 (PPG Industries) where an epoxy resin binder functions as carbonific, EP 0139401 (Dixon International) where an amino resin functions as binder and spumific and US 3969291 (Fukuba) where a water-soluble amidopolyphosphate functions both as catalyst and as spumific.

Low molecular weight components may be subject to loss by leaching, volatilization or other mechanism, and in such cases the long term efficacy of the intumescent composition may be a matter of doubt which could only be fully confirmed by destructive testing. Attempts have been made to reduce this problem by using high molecular weight polymeric materials, such as starches, proteins polypentaerythritols and epoxy resins as carbonifiers and aminoplasts and like condensates as spumifiers: Hence, in the prior art little or no importance is given to the role of the inorganic pigmentation as of importance in influencing or strengthening the foamlchar.

(35) Therefore, from the prior art, phosphate catalyzed intumescent coatings may be considered to consist of (1) A source of non volatile acid usually ammonium polyphosphates. These are referred to as the "Catalyst" and consist of about 25% of the total formulation.

Materials that are in current use are ammonium polyphosphates, ammonium orthophosphates and melamine phosphates.

(2) An organic substance (usually a polyol) that can be decomposed by the liberated acid from the catalyst to reduce to a source of carbon. Conventionally referred to a8 the carbonific".

Materials that are in current use are pentaerythritol, dipentaerythritol, tripentaerythritol. Starch in various forms has been used in the past.

(3) A source of inert volatile gases that assist the formation of the foamichar.

Conventionally referred to as the "spumescent". Normally melamine is used, various melamine salts such as (melamine phosphate) and dicyandiamide is used. Melamine or urea derivatives have been utilised in some patents and formulations.

(40) The mode of action of an intumescent product, under the influence of heat, as the temperature increases can be simplified into the following sequen :- (1) The Binder system softens to a highly viscous melt. Generally this occurs from 70 C onwards.

(2) Some of the plasticiser and spumescent decompose emitting inert gas that blankets the surface of the coating preventing ignition of the organic components by the f,re sours.

This will be observed from 90 C up to and beyond the point of intumescence.

(3) The catalyst loses ammonia, releasing liquid acid and lowering the viscosity of the melt.

This occurs progressively from 1500 C upwards.

(4) The carbonific melts and reacts with the liquid acid reducing to carbon and releasing water vapour.

(5) The spumescent decomposes releasing inert gas that expands the melt into a soft foam.

Reactions 2,3, & will occur simultaneously at about 2100 C.

(6) The foam partially decomposes and sets into a relatively rigid char.

(7) The residual acid reacts with the pigmentary materials, if present, to form refractory phosphates.

(8) The carbonaceous char is gradually ablated by the fire source, reducing the strength of the char.

Phosphorous is lost from the system, if not trapped by reaction with refractory oxides.

(9) The residual refractory may melt or undergo phase transitions, depending on its composition.

(45) Therefore, the majority of the prior art addresses itself to the role of the reaction products.

However, in addition to the basic intumescent components described above, an inorganic pigment, conventionally pigmentary rutile titanium dioxide is incorporated in these formulations. This rutile titania serves two functions.

Apart from its conventional pigmentary effect, the titania also serves to trap the liberated phosphoric acids in the foam char. These refractory residues formed from reaction between the titania and the liberated phosphoric acids occur at 550 C and prevent the loss of mass from the volatile phosphorous pentoxide, as in stages 7,8 and 9 in the summary above.

(50) What we have found is that precipitated hydrated alumina silicates typified by Ketjensil SM 405 (a proprietary product sold under that trademark ) will functionally perform as a replacement in total or part for titania oxide as a pigmentation for conventional phosphate catalyzed intumescents of the form described. Precipitated hydrated aluminium silicates also have the ability to entrap the liberated phosphoric acid as is illustrated by the TGA curves diagram 1. The precipitated hydrated aluminium silicate may be substituted in such formulations as shown in table 1. These formulations perform almost identically under fire test conditions when evaluated as fire protection products for the fire protection of steel as is illustrated in diagram 2.

Alternatively, the material may be substituted for titania dioxide as shown in a water based formulation as shown in table 4. This material performs identically in the surface spread of flame test conditions.

52 Precipitated aluminium silicates are produced by adding water glass to a mixed metal salt solution under controlled conditions with subsequent filtration, drying and milling. The product will typically contain magnesium and sodium as well as aluminium.

(65) Table 1 Conventional Phosphate Catalyzed Intumescent formulations COMPONENT EXAMPLE Titania aluminium pigmented silicate pigmented Aliphatic Essosolve 50 270 270 Solvent Co-Solvent 2-butoxyethanol40 40 Newtonian Resin Pliolite AC8070 70 Thixotropic Resin Pliolite AC5 30 30 Chlorinated Paraffin 70 % Solid Cereclor 70 100 100 Ammonium Poly Phosphate Amgard MC 250 250 Melamine 75 75 Dipentaerythritol 75 75 Rutile Titania Tiona 535 90 Precipitated Hydrated - 35 Aluminium Silicate Ketjensil SM40 Flow Additive Tegoglide 1 1 PVC 60.5 59.7 Typically, the resins are dissolved in the solvent mixture at low shear. When dissolution is complete the pigmentary materials are dispersed in the resin solution using a conventional high shear technique disperser.

(80) it has been shown (Monsanto Technical Bulletin iclscs 270 pg 11) that durability of an intumescent coating is inversely related to its Pigment Volume Concentration and its efficiency as a fire retardant is directly related to its PVC.

As intumescent formulations are conventionally formulated at Critical PVC, then the apparent small advantage in PVC gives a useful advantage in performance.

Further, as intumescent coatings degrade under environmental conditions by reaction of the marginally soluble ammonium polyphosphate with the melamine present in the formulation, this reaction being mediated by absorbed water, a buffering effect produced by the strong cations present on the precipitated hydrated aluminium silicates serves to prevent this degradation reaction.

(35) Additionally, we have found that precipitated hydrated aluminium silicates may also be incorporated in intumescent coatings to produce through coloured intumescent coatings. If attempts are made, as in the prior art, to produce through coloured intumescent coatings a pigment that will replace titania dioxide must be used. If conventional inert pigmentary material, consisting of a metallic oxide is incorporated in the formulation, invariably the metallic oxide reacts with the liberated phosphoric oxide at temperatures below that at which the phosphoric acid is required to catalyze the process of the intumescence.

(90) Likewise, if attempts are made to reduce the very high covering power of pigmentary rutile titanium dioxide by replacing it with conventional extenders such as calcium carbonate, the liberated condensed phosphoric acids will react with such materials to form precipitated phosphates before the phosphoric acid can be used in the intumescent process. Additionally, attempts to produce black or grey intumescent coatings by the addition of conventional carbon blacks fail because the very high specific surface are of the pigment increases the melt viscosity to the point that the spumescent is unable to produce an adequate foam.

(96) What we have found is that if the rutile titanium dioxide is wholly or partially substituted by precipitated hydrated aluminium silicates, oil and solvent soluble dies and some organic pigments may be added to the intumescent formulation to provide through coloured intumescent coatings in a wide range of colours.

The dies selected are typically azo metal complexes, azo methine metal complexes and phthalocyaninelmetal azo complexes, typified by the products marketed by Sandoz Products Ltd. under the trade mark Savinyl. No more than 1.5 % by weight of these products are required to produce intense, strong colours.

Table 2 lists the oil soluble dies considered suitable.

(100) Table 2 Oil soluble dyes suitable for incorporation in through coloured intumescent coatings listed by Ci name.

Solvent yellow 79, 83:1, 83, 62.

Solvent Orange 41, 62.

Solvent Red 92, 124, 89, 8, 91, 127.

Acid Violet. 66.

Solvent Blue 45, 44.

Solvent Brown 28.

Solvent Black 45.

Additionally, up to 5% by weight of any oil insoluble organic pigment that has negligible ash on firing, such as is listed in table 4, below may be incorporated to produce strongly coloured intumescent coatings, with performance under fire conditions little different from an equivalent formulation based on rutile titanium.

Typical formulations are shown in table 4, 5 & .

(106) Table 3. Organic pigments euitable for use with intumescent coatings incorporating precipitated hydrated aluminium silicate. Listed by Cl name.

Pigments yellow 1 ,3,12,13,13,and 17.

Pigments Orange 5,12, and 16 Pigments Red 1,2,3,4,5,17,18,22,23, 38, 48,49,52,53, 54,57,60, 63, 81,83, and 90.

Acid red 26 Pigments violet 1,3, and 5.

Pigments Blue 1,2,9,14,15,19,and 24.

Pigments Green 1,4,7, and 8.

(110) Table 4 Example Formulations for through coloured intumescents based on a PVA resin Green Blue Black Red Water 30.9 30.9 30.9 30.9 Methoxy Propanol 3.0 3.0 3.0 3.0 Savinyl green 2GLS 0.9 - - Savinyl Blue GLS - 0.9 Savinyl Red 3BLS - - 0.9 Savinyl Black RLS - - - 0.05 Cerecior 63L 3.4 3.4 3.4 3.4 Potassium Tripolyphosphate 0.1 0.1 0.1 0.1 Ammonium Polyphosphate 23.0 23.0 23.0 23.0 Dipentaerythritol 11.5 11.5 11.5 11.5 Melamine 11.5 11.5 11.5 11.5 Ketjensil SM405 4.0 4.0 4.0 4.0 Rutile Titanium Dioxide 0.4 0.4 0.4 Mowilith DW460F 17.2 17.2 17.2 17.2 Savinyl is a trade name of Sandoz Ltd.

Ketjensil SM405 is a proprietary hydrated precipitated aluminium silicate produced under that trade mark by AKZO Chemicals Ltd.

Cereclor is a trade mark of ICI for chlorinated paraffins for which Cereclor 63L is a generic representative in this and the succeeding formulations.

The Savinyl dies are pre-dissolved in the methoxy propanol, to which is added the Cerachlor 63L.

This is added to the water containing the potassium tripolyphosphonate.

The remaining solids are dispersed into this mixture using a conventional high shear disperser.

The PVA resin is then mixed into the millbase when adequate dispersion is obtained.

(115) Table 5 Formulations for through coloured Intumescents based on Urea Formaldehydes Green Blue Red Black Water 22.1 22.1 22.1 22.1 Methoxy Propanol .67 0.67 0.67 0.67 Savinyl green 2GLS 0.2 - Savinyl Blue GLS - 0.2 Savinyl Red 3BLS - - 0.2 Savinyl Black RLS - - - 0.01 Dimethyl methyl Phosphonate 3.3 3.3 3.3 3.3 Ammonium Polyphosphate 41.6 41.6 41.6 41.6 Ketjensil SM405 9.9 9.9 9.9 9.9 Rutile Titanium Dioxide 0.4 0.4 0.4 Ammonia solution 35 % Adjust pH to above 9.0 Urea Formaldehyde 22.1 22.1 22.1 22.1 80 % solution The dies are pre-dissolved in the methoxy propanol. This is added to the water containing the dimethyl methyl phosphonate.

The remaining solids are dispersed into this mixture using a conventional high shear disperser.

The pH is adjusted to above 9.0 with ammonia solution.

The urea formaldehyde resin solution is then mixed into the millbase when adequate dispersion is obtained.

(120) Table 6 Formulations for through coloured intumescent coatings based on Epoxy Resins, illustrating the use of ash free organic pigments Yellow Blue Red Black Bisphenol A LV Resin 20.5 20.5 20.5 20.5 Pentaerythritol Diglycidyl Ether 5.3 5.3 5.3 5.3 Methoxy Propanol 0.8 0.8 0.8 0.8 Savinyl Black RLS - - - 0.01 Pigment Yellow 17 0.28 - Pigment Blue 2 - 0.28 Acid Red - 0.28 Dimethyl methyl Phosphonate 0.92 0.92 0.92 0.92 Diacetone Alcohol 0.54 0.54 0.54 0.54 Ammonium polyphosphate 33.5 33.5 33.5 33.5 Ketjensil SM405 12.1 12.1 12.1 12.1 Rutile Titanium Dioxide 1.3 1.3 1.3 1.3 Dipentaerythritol 9.3 9.3 9.3 9.3 Melamine 9.3 9.3 9.3 9.3 The black die is pre-dissolved in the methoxy propanol.This is added to the bisphenol, a low viscosity epoxy resin, and the reactive dilutant dissolved in the diacetone alcohol and the dimethyl methyl phosphonate.

The pigments are pre-dispersed in either phosphate plasticiser or the reactive dilutant. The remaining solids are dispersed into this mixture using a conventional high shear disperser.

This comprises part A of the formulation. The product can then be cured by addition of an amine functional hardener for which an example is Araldite HY943 which is a used to cure the above formulations as part b, at a ratio of 10 parts of the epoxy formulation to one part of the hardener.

(125) Thus, irrespective of the resin type selected as a base for the intumescent coating precipitated hydrated aluminium silicates may incorporated in the product. One novel use is in water dispersed alkyds resins. It is commonly asserted that alkyd resins may not be used as the basis for intumescent coatings (e.g. R.W.Reeves Advances in Fire Retardants ,1975 ). This, however, is not true. Providing an adequate level of plasticiser is incorporated in the formulation, the only limitation on the behaviour of am intumescent coating formulated on alkyd resins is the thickness of the coating that will adequately oxidatively through dry. We have found that intumescent coatings usable as fire retardants can be formed from water dispersed alkyds containing 90-110 % of the weight of the alkyd resin and formulated at the same ratios of catalyst, spumific and carbonific given in the preceding formulations and as is known from the prior art.

We have found that using this system, together with precipitated hydrated aluminium silicates and the associated colouring matter of the types given above thin fire retardant coatings can be formed in a complete range of colours.

Claims (2)

1. (11 30) Claims

   (1) A phosphate catalyzed intumescent coating differentiated from other preceding formulations by containing a proportion of a hydrated precipitated aluminium silicate of not less than 5% of the insoluble material.

   The conventional intumescent components consisting of a source of phosphoric acids such as ammonium orthophosphate and/or ammonium polyphosphate and or melamine phosphate, an organic substance capable of being reduced to a carbon char by the acids liberated by heating the phosphate salts, such as pentaerythritol or its dimer and trimer, and a source of inert gas such as melamine and/or its salts and/or dicyandiamide.

   These components to be in the ratio of between
2. 2.5:1:1 and 1:1:0 in the order given above. Added to this mixture is between 5 and 50% of the weight of the above components of a precipitated hydrated aluminium silicate.

   These components to be dispersed in a resinous material consisting of either vinyltoluene and/or styrene acrylic copolymers, vinyl toluene and/ styrene butadiene copolymers and vinyl toluene and/or styrene acrylonitrile copolymers or admixtures of any of the foregoing resins together with suitable volatile solvents and plasticisers of the chlorinated paraffins or phosphate or phthalate ester type, together with conventional paint additives to improve the film formation properties.

   (2) An intumescent coating as described in claim 1 in which the insoluble components are dispersed in a water dispersed or soluble resin that may be either a polyvinyl acetate and/or butyral, a polyvinyl acetate ethylene oxide copolymer or a vinyl chloride/vinylidene chloride, an acrylic, styrene acrylic, styrene maleic or half ester thereof, or any admixture of the above, together with plasticisers as described in claim one and coalescing solvents appropriate to the resin dispersion.

   (3) An intumescent coating as described in claim 1 in which the insoluble intumescent components are dispersed in a water dispersed alkyd resin together with plasticisers as described in claim 1, drying agents and suitable coalescing solvents.

   (4) An intumescent coating consisting of the insoluble components as described in claim 1 but held in an aqueous dispersion to which is to be added, at or prior to the time of application, a urea or melamine formaldehyde dispersed in an aqueous solution. The ratio of ammonium salts to carbonific to sources of inert gas to be between the ratios of 2.5 :1:1 and 2.5:0:0 in this claim.

   (5) An intumescent coating as described iri claims 1 ,2,3,and 4 to which a proportion of white pigmentation that may be titanium dioxide or zinc oxide or barium sulphate, the addition of such white pigment not to exceed 50 % of the proportion of hydrated precipitated aluminium silicate.

   g A intumescent coating as described in claims 1,2,3,4, and 5 which is colured by the addition solvent of an oil soluble die that may be a azo metal complex, azo methine metal complex or pthalocyanine metal complex.

   (7) An intumescent coating as described in claims 1,2,3,4,5 and 6 to which is added any organic or organometallic pigment with an ash of less than 11%, when fired to 10000 C, not exceeding 5% of the total non volatile content of the wet coating.