WO2009013532A2

WO2009013532A2 - Coating compositions

Info

Publication number: WO2009013532A2
Application number: PCT/GB2008/050599
Authority: WO
Inventors: Samuel John Bradford; Simon Jamie Hallam; Andrew Philip Taylor
Original assignee: Leighs Paints
Priority date: 2007-07-21
Filing date: 2008-07-18
Publication date: 2009-01-29
Also published as: WO2009013532A3; GB0714298D0; GB2451233A

Abstract

A coating composition comprises at least one intumescent ingredient incorporated into a resin binder which forms a protective polymeric coating, in use. The resin binder contains at least one covalently bonded phosphorus containing component.

Description

COATING COMPOSITIONS

The present invention relates to intumescent coating compositions that have particular, but not exclusive, application in protecting steel structures in a fire situation .

Intumescent coating compositions are commonly used to protect steel components against the effects of fire conditions known to the art including cellulosic (the burning of paper, wood, etc.), hydrocarbon (petrochemical liquids and gases) and/or jetfire (a hydrocarbon fuel ejected under high pressure) .

During a fire situation, a steel structure will absorb heat. The rate of heat absorption depends on the specific dimensions of the steel columns and beams used in the structure. A relevant measure is known as the Hp/A value of the section, where Hp is the ^Λheated' perimeter of the steel when viewed in cross-section, and A is the cross- sectional area.

A steel section with a large perimeter (Hp) will receive more heat than one with a smaller perimeter. Also the greater the cross-sectional area (A) , the more heat the steel section can absorb. Thus, a large, thin, lightweight steel section having a high Hp/A value will heat up more quickly than a small, thick, heavy section having a lower Hp/A value.

The thickness of the applied coating depends on the Hp/A value of the steel section, its configuration, the type of fire scenario, and the level of fire protection required. The latter is typically specified from 30 to 180 minutes, this being the time taken for the steel to reach its critical failure temperature under standard test conditions. It should be noted that variations do occur in failure temperature criteria. For example, if a cellulosic fire is being considered, the failure temperature is regarded as being between 500⁰C and 750⁰C. If a hydrocarbon fire situation is being evaluated, commonly an extra safety margin is applied and a failure temperature of 400⁰C is used. These values apply mostly in Europe, whereas in the USA, the most common failure temperature is regarded as 1100⁰F (593°C) .

Intumescent coating compositions contain a resin system containing intumescent ingredients that under the influence of heat, react together to produce an insulating foam or ^Λchar' , which has a low thermal conductivity and a volume many times that of the original coating. This char greatly reduces the rate of heating experienced by the steel, thus extending the time before the steel reaches its critical failure temperature and loses its integrity, causing the structure to collapse, thereby allowing additional time for safe evacuation. In some instances intumescent coatings can provide a ^Λlife barrier' . This is where a compartment has the outer faces of walls (bulkheads) or floor/ceilings (deckheads) coated, thus causing a reduction in the passage of heat into the compartment, contributing to the possibility of personnel surviving the effects of the fire scenario.

The dry film thickness of intumescent coating applied varies from 250μm to many millimetres, depending on the level of fire protection required. With prior art intumescent coatings for cellulosic fires the typical thickness is between 250μm and 5mm. These tend to be based on thermoplastic resin systems such as acrylate, or vinyl resins. Hydrocarbon fire protection however is largely based on thermosetting epoxy resin technology and requires thicknesses from 3mm to 18mm.

These coatings are suitable for both on-site and in-shop application .

The present invention seeks to achieve a substantial reduction in the film thickness of intumescent coating required to protect a given substrate from the effects of fire .

According to a first aspect of the present invention there is provided a coating composition comprising at least one intumescent ingredient incorporated into a resin binder which forms a protective polymeric coating in use, wherein the resin binder contains at least one covalently bonded phosphorus containing component.

The coating composition of the invention generally requires significantly lower film thicknesses (compared to existing products) to provide the same duration of hydrocarbon fire protection.

Furthermore the invention can be used to significantly reduce the loading of epoxy fireproofing required for a cellulosic (or other) fire protection project.

Preferably the polymeric coating is formed in use by curing of the resin binder. Preferably the resulting cured matrix includes the covalently bonded phosphorus containing component as a bonded-in component.

The coating composition is such that it can be coated onto a surface, and remain in place, as the polymeric coating forms. When applied it may suitably be a liquid, or a formable material, for example a gel, mastic, paste or the like. It may comprise one or more solid components, and thus could be a suspension or dispersion.

The coating composition of the invention, in one preferred embodiment, has a viscosity, prior to the commencement of the formation into the polymeric coating (i.e. pre-cure, in a preferred embodiment) in the range from 100 to 1000 poise, preferably 400 to 600 poise, measured on a Bohlin Rheometer CVO 50 at a shear rate of 10 reciprocal seconds at 40⁰C.

Preferably the protective polymeric coating is a rigid material.

The coating composition of the invention in one preferred embodiment, when formed into the protective polymeric coating, has a room temperature (e.g. 20⁰C) glass transition temperature, in the range 50⁰C to 70⁰C as measured by differential scanning calorimetery .

The coating composition of the invention, in one preferred embodiment, when formed into the protective polymeric coating, has a room temperature (e.g. 20⁰C) compressive modulus in the range IGPa to 2GPa as measured in accordance with ASTM D695. The coating composition of the invention, in one preferred embodiment, when formed into the protective polymeric coating, when tested on a Thermogravimetric analyser, from 20⁰C to 1000⁰C at 20°C/min shows weight retention of 50% - 65 % at 500 ⁰C, preferably 55% - 60%.

The coating composition of the invention, in one preferred embodiment, when formed into the protective polymeric coating, has a smoke index of below 75 when tested at 25kW/sqm according to IMO resolution MSC 61 (67) 1996; Annex 1, Part 2 - either with or without a pilot flame.

Suitably the present invention utilises an approach where the coating composition is supplied in more than one component - for example a base component and a curing or initiator component. Preferably the components are mixed immediately prior to use. The individual components may contain different parts of the coating composition that will, when mixed, undergo chemical reactions to cause the molecular weight to rise.

These reactions can be condensation reactions, chemical reactions between two species such as epoxy and amine / amide, or free radical polymerisation. In one embodiment of this invention they are between epoxy and polyamide resins .

The coating composition includes a phosphorus containing moiety that may react with other components of the coating composition. Suitable phosphorus containing moieties include diglycidyl methyl phosphonate, triglicidyl phosphate, bis [2- (methacryloyloxy) ethyl] phosphate, and dihydroxaphosphaphenanthrene oxide (DOPO) , or various adducts thereof. In a first embodiment, the phosphorus containing moiety is an adduct of DOPO and a novolac resin. The novolac resin used can have an epoxy functionality of between 2 and 8. In the first embodiment this functionality is preferably between 2 and 4. Preferably the phosphorus-containing moiety (most preferably a DOPO novolac adduct) contributes between 0.1 and 3.75% by weight of phosphorus to the resin binder.

Proprietary adducts of DOPO are available. These are solids at ambient temperature, and can be obtained either in the raw form, or pre-dissolved in liquid epoxy resins.

The use of phosphorus species incorporated into a resin backbone has been previously claimed to enhance the flame retardancy of products including textiles and plastics.

The total resin components ideally constitute from 20% to 80% by weight of the coating composition. More preferably the total resin components constitute from 30% to 70% by weight of the coating composition. In a preferred embodiment the total resin components constitute from 40% to 60% by weight of the coating composition.

The intumescent ingredients suitably comprise one or more components which supply the following functions: an acid source; a carbon source; and a spumific or gas source. Preferably an inorganic "nucleating agent" is present. Optionally additives, which may be solid or liquid in nature, may be added to aid char formation on burning, and/or strengthen the char layer. The coating compositions of the present invention ideally contain at least one acid source, examples of which include ammonium polyphosphate, melamine phosphate, magnesium sulphate and boric acid. The preferred acid source for the present invention is a blend of ammonium polyphosphate and boric acid.

The acid source preferably constitutes from 10% to 70% by weight of the coating composition. More preferably the acid source constitutes from 20% to 60% by weight of the coating composition. In this embodiment it is most preferred that the acid source constitutes from 30% to 50% by weight of the coating composition.

The coating compositions of the present invention ideally contain at least one carbon source, examples of which include polyhydric alcohols such as pentaerythritol, and dipentaerythritol . Starch and expandable graphite are other possible carbon sources, and the carbon source can be the binder system, for example a polyamide cured epoxy binder system. The preferred carbon source in one embodiment is the resin binder.

The resin binder preferably constitutes from 20% to 70% by weight of the coating composition. More preferably the resin binder constitutes from 30% to 60% by weight of the coating composition. In one embodiment it is most preferred that the resin binder constitutes from 40% to 50% by weight of the coating composition.

The coating compositions of the present invention ideally contain at least one gas source, examples of which include any of:- melamine, melamine phosphate, melamine borate, melamine formaldehyde, melamine cyanurate, tris-

(hydroxyethyl) isocyanurate (THEIC), ammonium polyphosphate or chlorinated paraffin. The resin binder itself may be a gas source as it undergoes decomposition. The preferred gas source is melamine.

The gas source preferably constitutes from 5% to 40% by weight of the coating composition.

More preferably the gas source constitutes from 5% to 30% by weight of the coating composition. In this embodiment it is most preferred that the gas source constitutes from 5% to 20% by weight of the coating composition.

It will be understood that one component may supply more than one function of the intumescent ingredients. Thus, melamine phosphate could be the acid source and the gas source; or the resin binder could be the carbon source and the gas source, as well as being a major component of the polymer coating. When one component supplies more than one function, the component may be present in an amount selected from any definition herein, applying to the relevant functions. For example melamine phosphate present as an acid source and as a gas source may be present in an amount of from 5 to 60% by weight of the coating composition. More preferably, in such a situation where one component supplies more than one function, the component is present in an amount satisfying each definition herein, applying to the relevant functions; for example melamine phosphate is most preferably present in an amount of from 20 to 40% by weight of the coating composition . Under the influence of heat (between 100°C and 200°C) the resin components melt and begin to flow. As the temperature increases (>200°C) the acid source, usually by decomposition, produces copious amounts of acid which can react with other constituents in the coating. If the acid source is ammonium polyphosphate, polyphosphoric acids are released which can react with the carbon source to form polyphosphoric acid esters. The decomposition of these esters leads to the formation of carbon compounds, which together with a blowing agent such as melamine, give rise to a carbon foam or char. Although not an essential ingredient in intumescent reactions, inorganic "nucleating" agents are a preferred ingredient since they promote sites for the intumescent char to form, improve the thermal resistance properties and stability of the intumescent char during a fire. The coating compositions of the present invention ideally contain at least one nucleating agent, examples of which include titanium dioxide, zinc oxide, aluminium oxide, silica, metal oxides such as cerium oxide, lanthanum oxide and zirconium oxide, mica and bentonite clay. A preferred nucleating agent is titanium dioxide which also provides opacity to the coating.

The nucleating agent preferably constitutes from 1% to 25% by weight of the coating composition. More preferably the nucleating agent constitutes from 1% to 10% of the coating composition. In this embodiment it is most preferred that the nucleating agent constitutes from 1% to 5% by weight of the coating composition. Further optional additives may be optionally included as part of the intumescent ingredients to aid char formation and to strengthen the char and prevent char degradation especially in jetfire scenarios. Such additives include solids such as zinc borate, zinc stannate, zinc hydroxystannate, glass flake, glass spheres, polymeric spheres, fibres (ceramic, mineral, glass/silica based) , aluminium hydroxide, antimony oxide, boron phosphate, fumed silica.

The total intumescent ingredients ideally constitute from 40% to 85% by weight of the coating composition. More preferably the total intumescent ingredients constitute from 50% to 75% by weight of the coating composition.

In order that the intumescent coating compositions of the present invention can be applied at a desired thickness in a single coat application it is preferred to modify the rheology of the coating composition as applied, by the incorporation of a thixotrope. Suitable thixotropic additives include organically modified inorganic clays such as bentonite clays, hectorite clays or attapulgite clays, organic wax thixotropes based on castor oil and fumed silica. The most preferred thixotropic additives are wax thixotropes.

The thixotropic additive preferably constitutes from 0% to 2% by weight of the coating composition. A more preferred level is from 0.05% to 1%.

To improve or facilitate dispersion of the intumescent ingredients and also to reduce the overall viscosity of the intumescent coating, it may be necessary to incorporate wetting/dispersion additives. Such additives are usually liquid in form and can be supplied solvent free. Where required preferably a solvent free wetting agent is used. Preferably a wetting agent with acid functionality is recommended. Preferably a wetting/dispersion additive is present at a level in the range 0% to 2% by weight of the coating composition.

The components of the coating compositions are preferably blended together by the coating manufacturer using high speed dispersion equipment, whereby the solid intumescent ingredients are wetted out and dispersed in the resin components. Optional dispersion aids may be incorporated to facilitate this process.

In accordance with a second aspect of the invention there is provided a method of coating a steel body for protection during a fire situation, the method comprising applying a liquid or formable composition of the first aspect around the steel body, and allowing it to form a protective polymeric coating around the steel body.

Preferably the mean thickness of the polymeric coating is at least 3mm, preferably at least 6mm. Preferably the mean thickness of the polymeric coating is not greater than 14mm, preferably not greater than 10mm.

Suitable preferred methods of application of the aforesaid compositions are by means of a plural component spray system. The two components are prewarmed and pumped separately in the correct ratio through fluid lines to a mixing device. This device mixes the two components automatically and then dispenses the mixed homogenous coating down a fluid line to the application head.

The coating compositions of the present invention can be applied to steel sections up to several metres in length with a gauge thickness typically ranging from 5mm to 30mm or greater. Depending on the Hp/A of the steel section coating can be applied at the required thickness to achieve up to 180 minutes fire protection.

Preferably a steel body coated with a coating composition of the present invention and tested in accordance with BS476 Part 20, 1987, using the hydrocarbon heating curve, takes at least 50 minutes to reach a Critical Failure Temperature (CFT) of 400⁰C.

Preferably the steel body coated with a coating composition of the present invention and tested as described above takes at least 20% longer to reach the CFT of 400⁰C than a corresponding coated and tested steel body when the coating composition is identical except that it does not contain a covalently bonded phosphorus containing component, preferably at least 30% longer, most preferably at least 40% longer.

Steel sections requiring fire protection are normally blast cleaned prior to the application of an intumescent coating to remove millscale and other deposits that may lead to premature failure of the intumescent coating, either on prolonged atmospheric exposure or during a fire situation. In order to prevent deterioration of the blast cleaned surface, particularly where there is a delay in applying the intumescent coating, it is normal practice to apply a primer coating. This is often the case when the intumescent coating is applied on site.

Examples of suitable primers are coatings based on epoxy, modified epoxy (such as modified with polyvinyl butyral) , polyurethane, acrylic, vinyl and chlorinated rubber. Primers based on epoxy are preferred.

The thickness of the primer is ideally in the range from 15 microns to 250 microns. Preferably the thickness should be in the range from 25 microns to 100 microns.

A decorative topcoat may be applied to the cured intumescent coatings of the present invention, particularly to provide colour to exposed steelwork. A topcoat if correctly formulated will also enhance the durability of the intumescent coating compositions. A clear sealer may also be suitable.

Examples of suitable decorative topcoats are coatings based on epoxy, polyurethane, alkyd, acrylic, vinyl and chlorinated rubber. Decorative topcoats based on urethane or epoxy are preferred.

The thickness of the decorative topcoat can vary from 15 microns to 250 microns. Preferably the thickness should be in the range from 25 microns to 75 microns, as too high a thickness of topcoat may inhibit the intumescent reactions .

In order that the present invention may be more readily understood, some specific examples thereof are set out below.

Four test formulations were produced, having the following components :

The components were prepared on a high shear mixer by pre- blending the liquid components, adding the wetting agent, and then dispersing the solid ingredients until a homogenous mixture was obtained. The last two ingredients to be incorporated were the wax thixotrope and then the ceramic fibre. The base and additive components were then mixed immediately prior to use, forming a mastic-like material which could be applied either by trowel, or using a plural component spray machine.

The above exemplary formulations were applied to a one metre steel I-section having a web length of 203mm, a flange length of 203mm and a weight of 52kg per metre

(Theoretical Hp/A =180). The sections were allowed to cure for a minimum of seven days before being fire-tested in a Im³ furnace according to BS476 Part 20, 1987 using the hydrocarbon heating curve. The dry film thickness (DFT) and the time taken for the steel section to reach the Critical Failure Temperature (CFT) of 400°C was recorded, and is summarised in the table below.

DFT Corrected Time is an arithmetical correction back to the target thickness of 8mm, enabling comparison to be made between samples of different thicknesses.

The effect of increasing phosphorus content in the resin binder can clearly be seen.

Examples of the invention as defined above, formed into protective polymeric coatings, were tested for weight retention on a Thermogravimetric analyser, from 20⁰C to 1000⁰C at 20°C/min and showed a weight retention of 50% - 65 % at 500 ⁰C. Examples of the invention as defined above, formed into protective polymeric coatings, were tested for smoke formation and gave smoke index of below 75 when tested at 25kW/sqm according to IMO resolution MSC 61 (67) 1996; Annex 1, Part 2; both with and without a pilot flame.

It is to be understood that the above-described embodiment is by way of example only. Many modifications and variations are possible.

Claims

1. A coating composition comprising at least one intumescent ingredient incorporated into a resin binder which forms a protective polymeric coating in use, wherein the resin binder contains at least one covalently bonded phosphorus containing component.

2. A coating composition as claimed in claim 1, comprising a first component and a second, curing component, the components when mixed forming the coating composition, that composition initially being a liquid or formable material.

3. A coating composition as claimed in claim 1 or 2, wherein the phosphorus containing component reacts with other components of the coating composition.

4. A coating composition as claimed in any preceding claim wherein the phosphorus containing component is selected from diglycidyl methyl phosphonate, triglicidyl phosphate, bis [2- (methacryloyloxy) ethyl] phosphate, and dihydroxaphosphaphenanthrene oxide (DOPO) , or adducts thereof .

5. A coating composition as claimed in claim 4 wherein the phosphorus containing component is an adduct of dihydroxaphosphaphenanthrene oxide and a novolac resin.

6. A coating composition as claimed in claim 5 wherein the novolac resin has an epoxy functionality of between 2 and 8.

7. A coating composition as claimed in any preceding claim wherein the covalently bonded phosphorus containing component contributes between 0.1 and 3.75% by weight of phosphorus to the resin binder.

8. A method of coating a steel body for protection during a fire situation, the method comprising applying a liquid or formable composition as claimed in any preceding claim around the steel body, and allowing it to form the protective polymeric material around the steel body.

9. A coating composition or method of achieving fire protection using a coating composition, the composition or method being substantially as hereinbefore described with particular reference to the accompanying examples.