WO1999037724A1

WO1999037724A1 - Fire retardant paint

Info

Publication number: WO1999037724A1
Application number: PCT/GB1999/000198
Authority: WO
Inventors: Branton Screeton
Original assignee: Branton Screeton
Priority date: 1998-01-21
Filing date: 1999-01-21
Publication date: 1999-07-29
Also published as: AU2068999A; GB9801274D0

Abstract

The invention relates to a coating composition suitable for application to a surface for the purpose of slowing the spread of fire in the event that the surface to which the composition is applied catches fire.

Description

Fire retardant paint

The present invention relates to a coating composition, particularly suitable for application to a surface for the purpose of slowing the spread of fire in the event that the surface to which the composition is applied catches fire.

The composition is especially useful to coat the roofs of buildings, where the unprotected roof cover is at risk of catching fire. Such roof cover may, for instance, comprise an exterior layer of a bituminous nature. Substrates on which the composition may be used with advantage include asphalt, mineral felts, butyl rubber sheeting, wooden materials and metals such as copper vent pipes and aluminium flashings.

Prior attempts to provide surface coating compositions for such a purpose have been less than satisfactory. For example, fire-proof and fire retardant paints have previously been made, by mixing resin emulsions with fire retardants. Japanese patent application J- 05/086310 describes foamable paints for use in iron frames. J-63/221176 discloses fire- proofing and heat-insulating paints formed from shale, silicon carbide and powdery frit aggregates in conjunction with an alkali silicate binder. GB2203157 discloses a similar composition that melts progressively under conditions of fire to provide a fused protective layer that prevents the access of oxygen to the environs of the fire. Finely powdered dry zeolite has also been added to paint compositions in order to reduce their thermal conductivity and to reduce flame spread in the event of fire.

These compositions are expensive and require skilled mixing at the site of application. Furthermore, many are only suitable for certain surfaces or materials and have limitations in slowing the spread of flame during a real fire event when medium, high or very high temperatures exist.

There thus exists a need for an inexpensive air-drying coating composition in a form that does not require skilled mixing at the site of use, but which forms a durable fire retardant coating when applied to the surface of a material. The composition thus protects the coated surface from the effects of excessive heat absorption. According to the present invention there is provided a coating composition comprising a pigment component dispersed in a binder component, wherein the pigment component contains in particulate form both a white mineral pigment and a laminar solid and the binder component substantially consists of a plasticised polymeric binder dissolved in an alcohol, wherein said binder component additionally comprises a fire retardant.

The fire retardancy of the composition of the present invention is provided by a combination or confluence of two effects. These are first that when heated, the composition forms a crust that acts to retain flammable vapours that are emitted by the burning material. The speed with which the composition vitrifies increases with temperature, such that the coating actually becomes more effective at raised temperatures. Second, the highly reflective nature of the composition reflects the heat away from the coated material in the event of fire.

The tendency of the compound to vitrify is caused by the inclusion of fire retardants such as natural low melting point glass and ceramic soda ash materials as part of the resin binder component of the composition. When heated beyond their activation temperatures of around 350°C, the soda ash composite material begins to melt and flow around the hot or burning material. The resultant encapsulation inhibits the access of oxygen to the burning material and thus restricts burning. Accordingly, the amount of by-products is also reduced. The overall effect produced is to create a highly stable char structure with a concomitant reduced smoke and gas yield from the burning material.

At higher temperatures of between 900° and 1000°C, further components in the mixture devitrefy, passing from a glassy to a crystalline state, resulting in a great rise in the viscosity of the burning or hot material. This restricts the access of oxygen to the material and thus reduces the rapidity with which the flames spread. Preferably, these components comprise low melting point glass and ceramic materials that are based on silicates and borosilicates.

These materials are present in the mixture at proportions of between 10 and 30%, preferably between 12 and 20%. At proportions above 20%, the reflective property of the composition becomes impaired. The high reflectivity of the composition is caused by the presence of particulate white mineral pigment in the composition. This pigment is preferably rutile titanium dioxide (about 97 per cent TiO₂) but others may be used, such as anatase titanium dioxide, zinc oxide, antimony oxide or mixtures of these. Aluminium can be used if the solvent is anhydrous. The white mineral pigment should preferably be such as to yield in a finished coating a relative reflectivity of at least 92 per cent.

It is particularly preferred that the pigment comprises a minor portion of an anatase titanium dioxide. For example, the pigment may comprise from 2 to 20%, preferably 5 to 10% anatase titanium dioxide and from 80-98%, preferably 90 -95% rutile titanium dioxide. The presence of anatase titanium dioxide causes the surface of the dried coating composition to generate continuously a fine dust. The dust, which constitutes only a minute quantity of the coating material, is continuously eroded by the elements. This process, which is known as chalking, helps to keep the coated surface clean (and hence more reflective) because a new surface is continually being exposed.

The pigment may be of the normal quality supplied to the paint industry, preferably has a particle size below lμ and should preferably be present in the composition in a proportion of between 15 and 30 per cent by weight. Additional coloured pigment compatible with the rest of the composition may be included if desired.

The particulate laminar solid also serves to diffuse heat away from the coated material by virtue of its characteristic platelet form. The most favoured laminar solid is mica in flake form. The platelet particles tend to overlap and form a barrier. Other materials that may be used include combinations of mica with chlorite and quartz (Plastorit®), exfoliated vermiculite, magnesium silicate, talc and glass flake (Flakeglas®) or mixtures of these. The laminar solid is preferably employed in amounts from 4 to 7 per cent by weight based on the composition.

The preferred composition may thus contain 20 to 35 per cent by wet weight of the pigment component, comprising both pigment and laminar solid. The polymeric binder is preferably an alcohol-soluble vinyl or acrylic resin and preferably constitutes 10 to 25 per cent by weight of the composition. The function of the resin is to bind the pigment. The viscosity and eventual film thickness is also governed by the properties of the solvent. Accordingly, the proportions of polymeric binder are chosen to produce a dry film thickness sufficient to exhibit a solid finish on a black substrate in two applications. Vinyl resins that are particularly suitable are vinyl ester polymers, and especially copolymers of vinyl esters.

Other polymeric binders that may be used include, for example, cyclohexanone/formaldehyde resins, cyclic ketone condensation resins, and liquid polybutadiene. The resin selected should be water resistant, and should be soluble in solvents, e.g. alcohols, which do not dissolve the intended substrate.

The most preferred resin is a copolymer of vinyl acetate with vinyl caprate composed for instance of 17 parts acetate to 3 parts of caprate. This resin is internally plasticised by the caprate component but a further plasticiser for the binder resin is preferably included in the composition. Another preferred binder resin is polyvinyl acetate/maleate.

Suitable plasticisers for compositions of the present invention include any organic liquid plasticiser. Presently, dibutyl phthalate is preferred, although dibutyl maleate, diamyl phthalate and dicapryl phthalate may also be used. In the future it is envisaged that organic liquid plasticisers will be discovered that are more environmentally friendly than phthalates and in this instance such substitutes will be preferred. In general, the plasticiser is selected for compatibility with the binder resin and with the resin solvent, its lack of toxicity and its duration of effectiveness. The proportion of plasticiser is chosen according to the desired increase in film flexibility.

In relation to the use of the composition on bituminous substrates, ester plasticisers are most reliable because they do not tend to migrate into the bitumen. In this context the plasticiser must be soluble in solvents (e.g. alcohols) which do not dissolve bitumen, which would exclude drying and non-drying vegetable oils, fats and stearates. 5

The solvent selected must be a solvent for the polymeric binder and should be non-toxic. Industrial alcohol (containing 90 to 95 parts of alcohol, the remainder being substantially all water) is favoured but isopropanol, butanol, diacetone alcohol and mixtures of these may be used. One advantage of using such alcohol-based solvents is that they evaporate soon after the composition has been applied to a surface. Furthermore, alcohols do not adsorb to bituminous surfaces. The amount of solvent employed in the composition may for example be from 50 to 60 per cent by weight of the composition.

The polymeric binder may be supplied in the form of a solution in the solvent containing for instance approximately 50 per cent solids. In relation to use of the composition on a bituminous substrate, the solvent should preferably not contain any aliphatic or aromatic hydrocarbon, nor a halogenated solvent or ketone.

The composition as a whole usefully has a viscosity measured with the No. 4 Ford cup at 25°C, of 51 to 65. It can have a measure of thixotropic behaviour as long as this does not interfere with flow on the substrate and wetting of the substrate. The most preferred ratio of pigment to binder on a solids basis lies between 1 part and 2 parts pigment to 1 part binder, giving high opacity and high reflectivity. The composition may be prepared, for example, by mixing the polymeric binder, plasticiser and solvent, then adding the pigment component and laminar solid so that the pigments are rapidly wetted. Thorough dispersion and wetting of the pigments with the solvent medium is important. The pigment may advantageously be dispersed initially in only part of the prepared binder solution, to form a concentrate as a paste to be diluted on site.

The compositions dry by solvent evaporation in air. They are most advantageously applied on any material that may be at risk from fire. For example, roofs and roofing material is very susceptible to damage from fire, particularly in dry climates or even in temperate climates during dry spells, when the incidence of forest or bush fires brings risk of fire caused by flaming sparks. In areas where modern fire-resistant construction materials are not available, the simple application of fire-retardant paint will protect a roof from fire in most instances. Even if a roof is not totally fire-proof, application of the fire retardant paint may slow the course of the fire, so facilitating its extinction and allowing evacuation of any persons from the vicinity of the fire. For application, the compositions of the present invention can be used on any dry and frost free horizontal, vertical or sloping surface, applied in dry weather. They are readily applied by roller or by airless spray, or in small areas by brush, preferably in two coats, to yield a fast drying, uniform layer.

One embodiment of the present invention is illustrated in the following example. Further aspects and embodiments of the present invention will be apparent to those skilled in the art. For example, the proportions of the components may be varied to suit particular or local conditions or substrates. All parts refer to weight.

EXAMPLE

A composition is made by dispersing 80 parts of titanium white pigment and 17 parts of mica flake, by grinding them in a dispersion mill, in a resin solution that has been previously prepared by dissolving 50 parts of coacryl 2207, 35 parts resin solids in aqueous ethanol, in 53 further parts of aqueous ethanol and incorporating 3.5 parts of dibutyl phthalate as plasticiser. Coacryl 2207 is an 85:15 copolymer of vinyl acetate and vinyl caprate, supplied as a solution of approximately 52 per cent solids content. The aqueous alcohol contains 90-95 per cent industrial ethanol.

The composition is storable in sealed containers and dries in air to a water-resistant film with excellent weathering and sunshine reflecting properties. An antifungal compound such as Diuron biocide and/or an algaecide may be included in a minor proportion in the composition. Suitable algaecides will be well known to those of skill in the art.

To this composition is added low melting point glass compounds at 75 Og per 5 litres of the composition.

This composition provides protection particularly against oxidation effects on the substrate as well as against thermal effects. When asphalt, which is thermoplastic, has been covered by treatment with the composition, it remains cooler than it otherwise would, and is therefore not so liable to be damaged or punctured by movement over the surface. Additionally, the composition is slightly flexible so that it will not crack or flake when the surface matrix expands or contracts caused by fluctuations of temperature. The composition is also stable in damp conditions or under circumstances when the composition is submerged for long periods of time, such as may occur on a roof surface after heavy rainfall.

Claims

1. A coating composition comprising a pigment component dispersed in a binder component, wherein the pigment component contains in particulate form both a white mineral pigment and a laminar solid and the binder component substantially consists of a plasticised polymeric binder dissolved in an alcohol, wherein said binder additionally comprises a fire retardant.

2. A composition according to claim 1, wherein said fire retardant comprises low melting point glass and/or ceramic soda ash compounds.

3. A composition according to claim 2, wherein said fire retardant comprises silicates and/or borosilicates.

4. A composition according to any of claims 1 to 3 wherein said fire retardant is present in said composition at between 12 and 20% by wet weight.

5. A composition according to any preceding claim, wherein the particulate white mineral pigment is rutile titanium dioxide, anatase titanium dioxide, zinc oxide or antimony oxide.

6. A composition according to claim 5, containing additional coloured pigment.

7. A composition according to any preceding claim, wherein the laminar solid is present in the composition in proportions of between 4 and 7 per cent by wet weight.

8. A composition according to any preceding claim, wherein the particular laminar solid is selected from mica flakes, exfoliated vermiculite, talc, glass flake, combinations of mica with other minerals, and mixtures thereof.

9. A composition according to any preceding claim, wherein the pigment component is present in the composition in proportions of between 20 and 35 per cent by wet weight.

10. A composition according to any one of claims 1 to 9, wherein the white mineral pigment component is present in the composition in proportions of between 15 and 30 per cent by wet weight.

11. A composition according to any preceding claim wherein said polymeric binder is selected from alcohol soluble vinyl and acrylic resins.

12. A composition according to claim 11, wherein the vinyl resin comprises a polymer of at least one vinyl ester.

13. A composition according to claim 12, wherein the vinyl resin is a copolymer of vinyl acetate and vinyl caprate.

14. A composition according to claim 13, wherein the vinyl resin is a copolymer of about 85 per cent vinyl acetate with about 15 per cent vinyl caprate.

15. A composition according to claim 14, wherein the vinyl resin is a copolymer of vinyl acetate and vinyl maleate.

16. A composition according to any preceding claim wherein said binder resin is present in the composition in proportions of between 10 and 25 per cent by weight calculated on a solids basis.

17. A composition according to any preceding claim, comprising 50 to 60 per cent of alcohol solvent for the resin based on the composition.

18. A composition according to claim 17, wherein said alcohol is selected from ethanol, aqueous ethanol, butanol, isopropanol and mixtures thereof.

19. A composition according to any preceding claim, which further comprises an added plasticiser for the binder resin. 10

20. A composition according to claim 19, wherein the plasticiser is any organic liquid plasticiser.

21. A composition according to claim 19 or 20, wherein the plasticiser is selected from dibutyl phthalate, dibutyl maleate, diamyl phthalate and dicapryl phthalate.

22. A coating composition comprising about 22 per cent of titanium dioxide, about 4 per cent of mica flake, about 18 per cent of a copolymer of about 17 parts vinyl acetate with about 3 parts vinyl caprate, about 1 per cent of dibutyl phthalate, and about 55 per cent of an aqueous alcohol solvent which contains 90 to 95 parts per 100 of industrial ethanol, the said percentages being based on the total composition.

23. A coating composition comprising a pigment component dispersed in a binder component substantially as described in the foregoing example.

24. A substrate coated with a composition as claimed in any preceding claim.

25. A substrate according to claim 24 wherein said substrate is bituminous.

26. Use of a composition according to any one of claims 1-23 as a fire retardant paint.