GB2274459A - Intumescent fire protection coatings - Google Patents

Abstract

A non-halogen-containing, water based, intumescent fire protection coating composition comprising an ethylene vinyl acetate binary copolymer latex binder and zinc oxide.

Description

INTUMESCENT FIRE PROTECTION COATINGS This invention relates to coating compositions which impart fire-resistance to surfaces and in particular to water-based, non-halogen-containing intumescent, fire protection coating compositions.

The use of intumescent coatings for fire protection is well known, and is reviewed for example by J.H.

Troitzsch in Prog. Org. Coat. volume 11 No. 1 pp. 41 to 69 (1983) and also by H.L. Vandersall in J. Fire & BR< Flammability, volume 2 pp. 97 to 140 (1971).

Such formulations normally contain some form of binder, a blowing agent or spumific, an acid forming catalyst, and a char forming or carbonific material. The material is applied, like a paint, to the surface to be protected and allowed to dry. When subsequently heated in a fire, the catalyst, spumific, carbonific and binder react together to form a thick layer of foamed char.

Halogen containing materials (e.g. chlorinated wax) may be added to improve fire resistance properties.

Other materials which may be present include additional water, pigments, coalescing agents, thickeners, reinforcing/anti-crack agents, fungicide, dispersing agents, and a variety of other materials commonly used as additives to paints.

Fire resistance performance of coating compositions has generally been achieved or enhanced by the incorporation of halogenated materials. These types of materials have considerable drawbacks in terms of smoke production and toxicity concerns, relating both to combustion products and also to disposal of the compounds themselves. There is a desire towards the replacement of these flame retardants by zero halogen alternatives.

A further limitation of the use of halogenated flame retardant coatings is that during combustion they emit large amounts of corrosive smoke. Combustion products of halogen containing materials, in particular HCl and HBr, contribute significantly to these effects. The corrosivity of smoke is of particular importance in electrical/electronic applications, since a small fire involving halogenated insulation materials may generate sufficient corrosive combustion products to cause widespread damage to other equipment not directly involved in the fire.

A limitation of intumescent coatings is that the expanded char produced during fire exposure is of limited strength and durability. Eventually, the char is converted to ash and falls away. This factor limits the degree of protection that may be provided to a substrate.

It has now been found that non-halogen intumescent coatings having good char strength and burn through resistance may be obtained by employing the combination of zinc oxide and a particular binder.

According to the present invention there is provided a non-halogen-containing, water based, intumescent'fire protection coating composition characterised in that it comprises an ethylene vinyl acetate binary copolymer latex binder and zinc oxide.

The compositions of the invention may be used as a surface covering for penetration seals to improve thermal insulation of mineral wool based systems, and as a cable coating to provide a barrier against flame spread. The compositions may be applied in a similar manner to paint, e.g. brushing or spraying, and dry to a white flexible film. When heated in a fire, the coating expands by up to twenty times in volume to form a thick insulating layer of fire resistant char.

Compositions of the invention display excellent fire resistance properties and exhibit low smoke and toxic gas production upon combustion. In particular, a surprisingly high char strength and high burn through resistance is exhibited which is attributable to the presence of the combination of the ethylene vinyl acetate binary copolymer (EVA) latex binder and zinc oxide.

The use of ethylene vinyl acetate copolymers as water based latex binders is known, although grades additionally incorporating vinyl chloride monomer are normally preferred as the halogen content confers additional fire resistance.

The present invention employs as a binder binary copolymers of ethylene and vinyl acetate, i.e. copolymers that do not contain significant numbers of repeat units that are derived from monomers other than ethylene and vinyl acetate. As is well known in the art of polymer chemistry, copolymers seldom exist as well-defined "pure" compounds, but rather-as statistical mixtures of chains of different lengths in which the monomer repeat units may be distributed in a random or non-random fashion.

Impurities in the starting monomers and side reactions during (or after) polymerisation can introduce minor amounts of additional functionalities on the chains.

Such "impurities" are usually impossible to separate or eliminate from the intended product. For the purposes of the present invention, it is assumed that up to 5% of the repeat units of the binder polymer may bear functionalities other than those derived directly from ethylene or vinyl acetate, but preferably no more than 38 of the repeat units bear such functionalities, most preferably no more than 1%.

The use of zinc oxide as a filler in polymeric formulations is known, for example, Handbook of Fillers for Plastics, eds. Katz and Milewski, Van Nostrand Reinhold (1987), p235, discloses that zinc oxide may be used to improve resistance to weathering, and promote hardness, heat stability, and electrical conductivity of polymers. Zinc oxide has also been used as a synergist with halogen containing flame retardant materials, e.g.

as disclosed by Cull is and Hirschler in pp291 to 293 of The Combustion of Organic Polymers, Oxford University Press (1981). There has been no disclosure of the use of zinc oxide in a non-halogen EVA latex based intumescent compositions.

The EVA latex binder is generally present in an amount such that the EVA provides at least 7.5%, usually from 7.5 to 35%, preferably about 16.5% of the total weight of solids of the composition. A suitable binder is commercially available under the trade name VINNAPAS EZ36 from Wacker. Terpolymers comprising vinyl acetate, ethylene and a further monomer e.g. vinyl chloride, acrylate etc. are not suitable for use in the invention.

The zinc oxide is generally present in an amount of at least 0.15%, usually in the range 0.75 to 7.5% by weight based on the total weight of solids in the composition. If the zinc oxide is absent or replaced by another material, such as titanium oxide, the char strength and burn through resistance of the composition is deleteriously affected.

The compositions additionally comprise an intumescent system e.g. a spumific, such as melamine, in combination with an acid forming catalyst, such as ammonium polyphosphate, and a carbonific material, such as pentaerythritol.

Additional intumescent materials may be added, such as glass frits, sodium silicate or alkali metal silicate/borate mixtures as described in U.S. Patent No.

4,521,333. The use of silicate granules in intumescent materials is described in European Patent Application No.

0346001.

The compositions may further comprise one or more of the following additives: pigments, e.g. titanium dioxide, iron oxides coalescing agents, e.g. white spirit, 2,2,4 trimethyl-1,3-pentanediol, thickeners, e.g. cellulose ether, fumed silica, aqueous acrylic dispersions, reinforcing agents, e.g. talc, a mixture of mica, qartz and chlorite, fungicides, e.g. 2-n-octyl-4-isothiazolin-3-one, dispersing agents, e.g. ammonium salt of polyacrylate, sodium polyphosphate, defoaming agents, e.g. Byk 035, pH adjusters, e.g. sodium hydroxide.

Other materials which are used as additives in water based paints may also be employed.

A typical formulation would be as follows: Parts by Weight Water 5 to 30 Thickeners up to 5 NaOH up to 2 (of aqueous solution e.g. 10% solids) Dispersants up to 5 (of aqueous solution e.g. 10% solids) EVA latex 10 to 40 (of aqueous dispersion e.g. 55% solids) Fungicide up to 0.5 Titanium dioxide up to 10 Zinc oxide 0.5 to 5 Pentaerythritol 5 to 25 Ammonium polyphosphate 5 to 25 Melamine 5 to 30 Coalescing agents up to 5 Reinforcing agent up to 25 The components of the compositions may be mixed in equipment commonly used for the preparation of water based paints, including planetary mixers and high dispersion mixers.

The compositions of the invention are applied in the same way as a water based emulsion paint, e.g. by brushing, roller coating, dipping and spraying to a variety of surfaces. The normal applied thickness is in the range of 0.2 to 5mm. The fire protection effectiveness of the coating increases with film thickness. The compositions may be used to provide a fire resistant seal to mineral wool based electrical and mechanical through penetrations e.g. cables, cable trays, steel pipes, when used as a coating on the mineral wool board and penetrating items.

The compositions may also be applied to cables to suppress flame spread. By protecting the cable insulation from combustion, the coating will thereby reduce the generation of toxic and corrosive HCl gas from PVC insulated cables. The intumescent coating expands many times in a fire to produce a high volume of protecting char and therefore only a thin coating layer needs to be applied to the cables which does not significantly affect the radiation of heat from cables during normal current carrying operation.

The invention will now be illustrated by the following Examples.

In the Examples the following materials were used: Natrosol 250GR, Hydroxyethylcellulose commercially available from Aqualon; Calgon "P/T", a sodium polyphosphate glass commercially available from Calgon and formulated as a 10% by weight solution in water; Pigment Distributor A, an ammonium salt of polyacrylate commercially available from BASF; Vinnapas EZ-36, an aqueous dispersion of copolymer of vinyl acetate and ethylene commercially available from Wacker; Vinnapas CEZl6, an aqueous dispersion of terpolymer of vinyl acetate and ethylene and vinyl chloride commercially available from Wacker; Vinnapas EAF60, an aqueous dispersion of terpolymer of vinyl acetate and ethylene and acrylate commercially available from Wacker; Pentaerythritol "D/S", fine ground pentaerythritol commercially available from Degussa;; Texanol, 2,2, 4-trimethyl-l, 3-pentanediol monoisobutyrate commercially available from Honeywill & BR< Stein; Exolit 422, ammonium polyphosphate commercially available from Hoechst; Melamine 003, melamine commercially available from DSM Chemicals; Byk-035, a mixture of hydrophobic components in paraffin based mineral oil commercially available from Byk-Chemie; Titanium dioxide, Bayertitan R-KB-4 commercially available from Bayer; Plastorit Naintsch 0.25, a mixture of mica, quartz and chlorite commercially available from Naintsch Mineralwerke; Zinc oxide-l0, ZnO commercially available from Durham Chemicals; White spirit, a petroleum distillate commercially available from Alcohols Limited; Skane M-8, 45% 2-n-octyl-4-isothiazolin-3-one in propylene glycol commercially available from Rohm & Haas;; Rohagit SD 15, an aqueous dispersion of acrylic resin based on acrylester and methacrylic acid commercially available from Rohn & Haas; CabOSil M5, fumed silica commercially available from Cabot Corporation; Pyrosafe Flammoplast KS-1, an intumescent coating commercially available from SVT; Fomox WMP, an intumescent mastic-coating commercially available from Bayer; Intumescent coating 38104 commercially available from Hilti; Orgol FS, an intumescent coating commercially available from Minnesota Mining and Manufacturing Company; and FireDam 150, a caulk commercially available from Minnesota Mining and Manufacturing Company.

Examples 1 to 5 disclose the preparation of intumescent compositions of this invention.

Examples 6 to 13 are comparative examples. The fire test performance of the formulations are shown in Examples 14 and 15 and the smoke and toxic gas emission is demonstrated in Example 16.

Examples 1 to 5 The formulations of Examples 1 to 5 are detailed in Tables 1 and 2.

The coating formulations of Examples 1 to 4 were mixed in a planetary mixer with two litre capacity with batch sizes of 1 to 2kg. A "Kenwood Chef" planetary mixer, with a "K" blade mixing head was used. Mixing speeds were varied throughout the blending process to achieve optimum dispersion.

The ingredients were added to the mixing bowl in the order given in Tables 1 and 2 with continuous mixing.

Each material was mixed until thoroughly dispersed before adding the next ingredient. When completely blended, the mixture was stored in an airtight non-metallic container.

The coating formulation of Example 5 was mixed in a pilot scale 30kg batch using a mixing vessel with a high speed dispersion blade and a slow orbital scraper blade.

Table 1

Addition Material I Parts by weight order Example 1 2 3 4 5 1 Demineralised 17.6 17.0 12.0 12.0 17.0 water 16 Rohagit SD15 0.2 - - 1.0 1.0 16 CabOSil M5 - 1.0 0.5 17 Byk 035 0.7 - - All formulations additionally contain the ingredients of Table 2.

Table 2

Addition Material Parts by order weight 2 Natrosol 250GR 0.4 3 NaOH (10%) 0.1 4 Calgon "P/T" (10%) 2.8 5 Pigment Dist. A 0.3 6 Vinnapas EZ-36 20.5 7 Skane M8 0.1 8 Titanium dioxide 3.1 9 Zinc oxide10 2.0 10 Pentaerythritol 13.3 11 Exolit 422 13.3 12 Melamine 003 15.6 13 Texanol 0.9 14 White spirit 0.9 15 Plastorit 9.2 Examples 1 to 5 of this invention, all contain both an EVA latex binder (Vinnapas EZ36) and zinc oxide, and are non-halogen formulations. They contain varying amounts of thickening agents, either Rohagit SD15 or CabOSil M5. Example 1 also contains a defoamer (Byk 035). These variations in thickener and defoamer content give rise to slightly different viscosities and coating characteristics of the paints produced.

Examples 6 to 9 Four further formulations detailed in Tables 3 and 4 were prepared using the general procedure of Examples 1 to 4.

Table 3

Addition Material Parts by weight order Example 6 7 8 9 1 Demineralised 17.0 15.0 18.7 18.7 water 6 Vinnapas EZ-36 20.5 - - - 6 Vinnapas CEZ-16 - 22.5 - - 6 Vinnapas EAF-60 - - 18.8 18.8 8 Titanium dioxide 5.0 3.1 3.1 3.1 9 Zinc oxide-l0 - 2.0 2.0 2.0 16 Rohagit SD15 1.0 0.4 1.0 16 16 CabOSil M5 - - - 0.5 All formulations additionally contain the ingredients of Table 4. Table 4

Addition Material Parts by order ~ weight 2 Natrosol 250GR 0.4 3 NaOH (10%) 0.1 4 Calgon "P/T" (10%) 2.8 5 Pigment Dist. A 0.3 7 Skane M8 0.1 10 Pentaerythritol 13.3 11 Exolit 422 13.3 12 Melamine 003 15.6 13 Texanol 0.9 14 White spirit 0.9 15 Plastorit 9.2 In Example 6, an EVA binder was used but zinc oxide was replaced by additional titanium dioxide. Examples 7 to 9 contain zinc oxide, but with the EVA binder replaced by a terpolymer latex, which is a polymer of ethylene, vinyl acetate and a third monomer. The third monomer is either vinyl chloride (Vinnapas CEZl6, Example 7) or an acrylate (Vinnapas EAF60, Examples 8 and 9).

Examples 10 to 13 The following commercially available intumescent fire protection coatings were also evaluated as comparative Examples:

Example sample Source Material No.

10 Hilti Intumescent coating 38104 11 Bayer Fomox WMP 12 SVT Pyrosafe Flammoplast KS-1 13 3M Orgol FS Coating Example 14 The utility of the compositions described above was evaluated by coating out samples on aluminium foil, to an approximate wet coating thickness of 3mm, allowing these to dry for at least one week, and then exposing the coated foil to fire using a cone calorimeter. The use of the cone calorimeter to measure rates of heat and visible smoke release is described in ASTM test method E1354 (1990). In the Example, it was used to provide reproducible combustion conditions for the coating samples.

For each material, an approximate 1.5mm thick sample of dried coating on aluminium foil was exposed for 60 minutes on the cone calorimeter (50kW/m2 irradiation) in a horizontal orientation, and the initial expansion (after 10 minutes) and final char height (after 60 minutes) were compared. The results are reported in Table 5.

Table 5

Example Char height (mum) (initially 1.5mm thick) Initial After 60 expansion minutes 1 30 20 2 15 to 20 20 3 30 25 to 30 4 30 25 5 30 25 6 30 to 35 < 10 7 10 to 15 < 5 8 < 10 not measured 9 5 to 10 < 5 10 50 < 5 11 20 < 5 12 50 < 5 13 30 < 10 All of the materials (with the exception of some of the comparative examples) intumesced greatly initially, but the level of char from the Examples of this invention remaining intact after 1 hour was much greater than for any of the comparative examples. This comparison demonstrates the improvement in burn through resistance or durability of the intumescent char produced by the compositions of the invention.

Example 15 In order to demonstrate the effectiveness of the intumescent coating in a mineral wool board based concrete wall penetration seal, a sample of the formulation in Example 1 was used to coat a penetration seal for large scale fire testing in the wall of a 1 m3 furnace, following in general the ISO 834 standard.

Furnace pressure was set to 13 + 2 pascal.

Penetrating items (all lm length) were: 1. a steel cable tray (200 x 60mm), with power and telephone cables, all coated on a total length of 460mm symmetrically to wall centre, and 2. a steel pipe of 63mm diameter, 3mm wall (not coated).

The rest of the opening (300 x 300mm) in 10cm thick light weight concrete wall (density approximately 600kg/m3) was closed off with mineral wool boards (150kg/m3) 60mm thick, cut to fit tight between penetrating items and concrete, and installed on both faces of the concrete wall.

The dried thickness of coating used for this test was approximately lmm on the faces and cut edges of mineral wool, 0.4mm on cables, and 0.2mm on cable tray.

Around the perimeter of each penetrating item, a bead of 3M FireDam 150 Caulk was applied to work as a cold smoke seal. Coating on mineral wool board was also extended 50mm onto concrete to form a cold smoke seal.

Thermocouples were located on the mineral wool boards and on the penetrating items at 25mm from wall surface and 25mm beyond end of coating.

Good fire resistance was obtained, with temperature ratings (time to reach 200 C) of at least 120 minutes for cable tray and mineral wool board, at least 90 minutes for cable, and at least 60 minutes for steel pipe.

Example 16 In this Example, the levels of emission of smoke and carbon monoxide produced during combustion of a composition of this invention (non-halogen formulation) are compared with a commercially available intumescent coating which contains chlorine.

Samples of coatings on aluminium foil were prepared as described in Example 14, using formulations of Example 5 and Example 12 (Pyrosafe Flammoplast KS-l, comparative). Both materials were examined by energy dispersive X-ray elemental analysis (EDAX). The coating from Example 12 was found to contain chlorine. No chlorine was seen in the coating from Example 5.

Both of these materials were subjected to cone calorimeter fire tests as described in Example 14 except that the tests were terminated after 10 minutes. The emissions of smoke (SEA in table) and CO were measured during the test.

Cona calorimeter Material peak SEA mean CO (m2/kg) (kg/kg) Example 1 (non-halogen) 151.7 0.0052 Example 12 (contains C1) 523.0 0.0160 This comparison demonstrates the reduced smoke and CO emission from the non-halogen example of this invention. Also, since the Examples of this invention do not contain chlorine, there is no possibility of the emission of toxic and corrosive HCl gas.

Claims (17)

1. A non-halogen-containing, water based, intumescent fire protection coating composition characterised in that it comprises an ethylene vinyl acetate binary copolymer latex binder and zinc oxide.

2. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 1 in which the ethylene vinyl acetate binary copolymer contains less than 3% of repeat units of functionalities other than those derived directly from ethylene or vinyl acetate.

3. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 2 in which the ethylene vinyl acetate binary copolymer contains less than 1% of repeat units of functionalities other than those derived directly from ethylene or vinyl acetate.

4. A non-halogen-containing, water based, intumescent fire protection coating as claimed in any preceding Claim in which zinc oxide is present in an amount of at least 0.15% by weight based on the total weight of solids.

5. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 4 in which zinc oxide is present in an amount in the range 0.75 to 7.5% by weight based on the total weight of solids.

6. A non-halogen-containing, water based, intumescent fire protection coating as claimed in any preceding Claim in which the ethylene vinyl acetate binder is present in an amount of at least 7.5% by weight based on the total weight of solids.

7. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 6 in which the ethylene vinyl acetate binder is present in an amount in the range 7.5 to 35% by weight based on the total weight of solids.

8. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 6 or Claim 7 in which the ethylene vinyl acetate binder is present in an amount of about 16.5% by weight based on the total weight of solids.

9. A non-halogen-containing, water based, intumescent fire protection coating as claimed in any preceding Claim comprising an intumescent system including a spumific, catalyst and carbonific material.

10. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 9 in which the spumific is melamine.

11. A non-halogen-containing, water based, intumescent fire protection coating as claimed in Claim 10 in which the intumescent system comprises melamine, ammonium polyphosphate and penataerythritol.

12. A non-halogen-containing, water based, intumescent fire protection coating as claimed in any preceding Claim which additionally comprises one or more components selected from pigments, coalescing agents, thickeners, reinforcing agents, fungicides, dispersing agents, pH adjusters, and defoaming agents.

13. A non-halogen-containing, water based, intumescent coating composition substantially as herein described with reference to any one of Examples 1 to 5.

14. A method of imparting fire resistance to a surface which comprises applying to the surface a composition as claimed in any preceding Claim.

15. A method as claimed in Claim 14 in which the surface comprises mineral wool board, cable, cable tray, concrete, steel, wood or other building material.

16. A method as claimed in Claim 14 substantially as herein described with reference to any one of Examples 14 to 16.

17. An article having a surface coated with a composition as claimed in any one of Claims 1 to 13.