BACKGROUND OF THE INVENTION

EielcLoiihe n vention

This invention relates to intumescent compositions for use in the construction of wall systems. More particularly this invention relates to intumescent compositions and basecoats formed therefrom that significantly reduce the rate of heat conduction through wall system components, e.g., cement board, during the early stages of exposure to fire.

Description of Related Art

Cement board, a thin, reinforced cementitious panel, has become increasingly popular as a durable substrate for interior and exterior building applications. In interior applications, cement board is used as a substrate for ceramic tile in bathrooms, shower rooms, and other areas where the walls are subject to frequent splashing of water and high humidity. As an exterior substrate, cement board is finding use as a base for masonry systems, painted exteriors, and, in particular, finish coatings, both cement based and synthetic stucco finishes.

Usually, cement board of Va inch (12.7 millimeters) to 5/8 inch (16 millimeters) is used in building applications. When cement board is used as a substrate for a finish coating, e.g., a stucco or textured finish, a basecoat is usually used with the cement board. When cement board is used to cover one surface of a wall system the joints between the cement board form a depression that may be difficult to fill by use of the finish coating alone. A basecoat, when applied to one surface of a cement board, provides a uniform, level surface to which the finish coating may be applied. A basecoat, in conjunction with a joint tape or mesh embedded therein, levels out depressions at the joints between cement boards. The basecoat also levels out any slight variations on the surface of the cement board itself.

Normally, in most construction applications, the finish coating is applied to a substrate by troweling the finish coating onto the substrate. A certain amount of liquid must be retained in the finish coating to permit proper application. If too much liquid is drawn from the finish coating by the substrate, the finish coating may tear or form an irregular surface during troweling. If an insufficient amount of liquid is drawn from the finish coating by the substrate, an adequate mechanical bond will not be formed between the finish coating and the substrate. The basecoat provides a substrate with a uniform rate of water absorption across its surface to permit the formation of a good mechanical bond between the finish coating and basecoat while not drawing an excessive amount of water from the finish coating.

Whether cement board is used alone or, as is more typically the case, as a component of a wall system, the fire-retardant property of the cement board and the wall system is of great importance. Test standards, such as

ASTM E 119 and Japanese Test Standard JIS (Japanese Industrial Standard)

A 1301 , measure the fire resistance or the heat conductivity of the wall system.

ASTM E 119 describes fire test standards that are applicable to assemblies of masonry units and to composite assemblies of structural materials for buildings, including wall systems. ASTM E 119 specifies that one side of a wall system comprising, e.g., interior wallboard, studs, insulation, and exterior panel, be exposed to a fire. The temperature of the fire has a specific time-temperature profile for the duration of the test. The temperature of the unexposed side of the wall system is measured. To pass this test the unexposed side must not exceed a certain temperature during the duration of the test.

JIS A 1301 specifies the method of fire test for wooden structural parts of buildings such as, walls, columns, beams, and flooring. The component of the wall system that is weakest with respect to fire-retardance is the component that is tested. In the case of wall system (interior wallboard,

studs, insulation, and exterior panel), a single construction panel is tested. A single construction board or panel or a board with a basecoat must be exposed to a flame source having a specified time-temperature profile. The temperature on the unexposed side of the panel must not exceed 500°F (260°C) over the duration of the test.

To pass JIS A 1301 a cement board may have to be as much as 1 inch (25 millimeters) thick. When cement board of this thickness is used with a typical basecoat in a wall system, a significant increase in the structural support for the wall system may be necessary. It is desirable to provide a basecoat that will provide increased fire-retardation and reduce the heat conductivity of a cement board/basecoat system without a significant increase in weight of the cement board /basecoat system. Further, it is desirable to have a basecoat for use with existing cement board that will decrease the thermal conductivity of the basecoat and cement board without requiring modification to the cement board.

Intumescent paints and fire-retardant coating compositions containing carbonifics, film-forming binders and phosphorous materials are well known in the art. Ward, UK Patent Application 2 280 130, discloses a paint coating, for gypsum board walls and ceilings, that contains a liquid carrier, an intumescent solid, an organic binder, and a filler. The binder is preferably a polyvinyl acetate or a polyacrylate. The intumescent solid is preferably exfoliating graphite or sodium silicate. Levine, U.S. Patent No. 5,356,568, discloses a paint coating containing an organic binder, an inorganic binder, a heat- activated blowing agent, a carbonific, a phosphorous-containing material, a halogen-containing material, an inorganic filler, and an organic solvent. Ward and Levine disclose paints for coating substrates, but which do not provide the surface leveling and liquid absorption characteristics necessary to serve as a basecoat for a finish coating such as stucco or textured finishes. Redfarn, U.S. Patent No. 4,645,782, discloses an intumescent putty or mastic for filling the spaces between doors and windows and adjacent structures, e.g., door frames and window frames. The putty of Redfarn,

although capable of spanning a significant distance is not suitable for use as a basecoat as it does not provide a level surface over large areas as is needed for use with textured finishes. Further, Redfarn does not provide the absorption characteristics needed of a basecoat.

SUMMARY OF THE INVENTION It is an object of this invention to provide an intumescent composition, for use as a basecoat on a substrate that, when exposed to elevated temperatures, will reduce the heat conductivity of the basecoat/substrate system.

Another object of this invention is to provide an intumescent composition, for use as a basecoat on cement board, that when dry will provide a uniform, level surface as a substrate for interior and exterior finishes.

Another object of this invention is to provide an intumescent composition for use as a basecoat on cement board that, when dry will have a sufficient rate of water absorption to draw the liquid binder from the finish coating into the surface of the basecoat in order to form a strong mechanical bond between the basecoat and finish coating. The rate of water absorption is such that a sufficient amount of water will remain in the finish coating to permit normal application by use of a trowel.

Another object of this invention is to provide an intumescent composition for use as a basecoat on a substrate that, when exposed to the high temperature conditions present during a fire, will intumesce to reduce the rate of heat conduction through the substrate/basecoat system. Another object of this invention is to provide an intumescent composition for use as a basecoat on cement board that will provide a sufficient reduction in the heat transfer rate through the cement board/basecoat subsystem so as to meet fire code standards without the need to modify the cement board itself. These and other objectives of the invention, which will become apparent from the following description, have been achieved by a novel composition, for use as a basecoat on a substrate, comprising, by weight: from

about 5% to about 20% of an organic binder; from about 5% to about 30 % of an intumescent material comprising a carbonific and a spumific; from about 40% to about 70% of a nonfibrous filler, and from about 5% to about 20% water. Preferably, the intumescent composition comprises, by weight: from about 10% to about 15% of an organic binder; from about 15 to about 20 % of an intumescent material comprising a carbonific and a spumific; from about 50% to about 60 % of a nonfibrous filler; and from about 8% to about 14% water. The intumescent composition is capable of being troweled onto a surface of a substrate to cover a surface area of less than about 0.75 m ² /l of the composition, preferably less than about 0.60 m ² /l the composition and, more preferably, less than about 0.36 m ² /l of the composition.

The organic binder in the intumescent composition of the invention is preferably an acrylic copolymer or an acrylic-styrene copolymer or, more preferably, a blend thereof. The preferred carbonific in the intumescent composition of this invention is a blend of ammonium polyphosphate and pentaerythritol. Melamine is the preferred spumific or blowing agent. The filler comprises a blend of particles , of which, at least 18% by weight are larger than 75 microns and preferably at least 10% by weight are larger than 297 microns. The filler can be a blend of organic or inorganic particles, or both. Preferably, the filler is a blend of inorganic materials such as quartz, calcium carbonate, and aluminum silicate. In addition, flyash, pumice, expanded perlite, expanded clay, or expanded vermiculite can be used as inorganic fillers. Fibrous fillers should not be used, because the fibers tend to agglomerate during troweling of the basecoat onto the substrate, resulting in an irregular surface. When dry, the composition of this invention provides a uniform, level basecoat surface as a substrate for interior and exterior finishes. Also, the intumescent basecoat, when dry, has a sufficient rate of water absorption to draw the liquid binder from a finish coating into the surface of the basecoat in order to form a strong mechanical bond between the basecoat and finish coating. The rate of water absorption is such that a sufficient amount of water will remain in the finish coating to permit normal application by use of a trowel.

The intumescent composition described above is to be used with cement board to provide a basecoat substrate for finish coatings. The liquid basecoat composition described herein is applied by trowel to a depth of from 1/16 inch (1.6mm) to about 1/8th inch (3.1 mm) on one surface of the cement board.

DETAILED DESCRIPTION OF THE INVENTION The present invention is specifically directed to an intumescent composition particularly suitable for use as a basecoat on cement board. The intumescent basecoat reduces the rate at which heat is conducted through the cement board/basecoat system when the system is exposed to fire. The basecoat is an aqueous solvent-based, thermally activated, intumescent coating. The basecoat is a durable coating which provides a monolithic surface for textured finishes. The basecoat is tough, yet flexible, over a wide range of operational temperatures. When exposed to high temperatures, the dried basecoat volatilizes, exhibiting a volume increase through the formation of an open, multicellular matrix, reducing the rate at which heat is transferred through the basecoat and the underlying substrate. Throughout this specification all percentages and proportions are by weight, unless otherwise specifically indicated.

In a preferred embodiment, the formulation of the basecoat composition is as follows: organic binder 5 to 20% thickening agent 0.05 to 1.5% filler 40 to 70% carbonific 4 to 20% spumific 1 to 10% preservatives 0.01 to 0.5% other additives 1 to 5% aqueous solvent 5 to 20%

The organic binder functions to impart structural integrity to the applied basecoat after application and drying. The organic binder can be any suitable binder for use with a water-based system, such as, but not limited to, acrylic polymers, styrenic polymers, vinyl acetate polymers, and copolymers and blends thereof. In some preferred embodiments the binder comprises a blend of an acrylic copolymer and an acrylic/styrene copolymer, the blend comprising a major (more than 50%) proportion of acrylic repeating units and a minor (less than 50%) proportion of styrene repeating units. In a particularly preferred embodiment the organic binder comprises a blend of about 65% of an acrylic copolymer identified by the trademark, RHOPLEX EI-8764, commercially available from Rohm and Haas Co. and about 35% of an acrylic/styrene copolymer identified by the trademark, ACRONAL 567D, commercially available from BASF Corporation. The thickening agent can be any suitable thickening agent for use with a water based system, such as, but not limited to, cellulosic thickening agents, the class of thickening agents known as alkali-swellable thickening agents, or attapulgite clay. The filler can be any suitable filler for use in the construction of building products. The filler can be an organic filler such as expanded polystyrene or polypropylene. Inorganic fillers such as sand (quartz), limestone, flyash, and an aluminum silicate can be used. To reduce the weight of the basecoat composition, lightweight aggregates such as pumice and the expanded forms of perlite, clay, and vermiculite can also be added to the basecoat composition of this invention. The filler can be a blend of organic or inorganic particles, or both. The filler should comprise particles, of which at least 18% by weight are larger than 75 microns (ASTM 200 mesh); preferably at least 10% by weight of the particles are larger than 297 microns (ASTM 50 mesh). The use of fibrous fillers should be avoided, as they tend to agglomerate, forming larger lumps which result in unevenness of the basecoat surface. However, fiberglass mesh or the like can be embedded in the basecoat to improve the structural integrity of the basecoat. In such case a layer of the inventive composition is applied to the surface of the cement board.

A mesh material is placed on the resulting basecoat while it is still wet and is pressed into the basecoat with a trowel. A second layer of the composition is then applied on top of the mesh material with a trowel to complete the reinforced basecoat.

Upon heating, the carbonific reacts to form a carbonaceous char or film. For this invention, the use of a carbonific combination of pentaerythritol and ammonium phosphate is the preferred carbonific. However, other polyphosphates may be used with this invention. Further, other polyols such as dipentaerythritol can be used. Any spumific that is compatible with the carbonific can be used. Some examples of such spumifics are urea, dicyandiamide, and melamine. The preferred spumific for this invention is melamine. It is thought that when the basecoat containing the carbonfic agents is heated the phosphate decomposes, forming phosphoric acid. This esterifies the hydroxyl groups of the pentaerythritol, which subsequently decomposes, forming water and a carbonaceous char, regenerating the phosphoric acid. As the char forms, the basecoat softens and the spumific decomposes, liberating nonflammable gases. These gases expand the softened carbonaceous char into a foam. Processing aids can be added to the product to improve the workability of the basecoat composition during application. Such additives can include clays, medium or fine particle solids, organic solvents, alcohols, or waxes. Such additives are not critical to the invention, however, they may improve the working properties of the composition. Preservatives can be added to the composition to improve its storage life and life while in use. Preferably, small amounts of common well-known fungicides and bactericides are added to the inventive composition. Some examples of common fungicides useful in the invention are: amine/organotins; zinc dimethyldithio carbamate; 2-n-octyl-4-iso-thioazoline-3-one (e.g., commercially available from Rohm and Haas under the trademark, SKANE M-

8); 3-iodo-2-propynyl butyl carbamate; diiodomethyl p-tolyl sulfone; and tetrachloroisophthalonitrile. Some examples of common bactericides useful in

the invention are: 2-(hydroxymethyl amino) ethanol; 1-(3-chloroallyl)-3,5,7- triaza-1-azoniaadamantane chloride; a blend of 5-chloro-2-methyl-4- isothiazolin-3-one and 2-methyl-4-isothiazoline-3-one (e.g., commercially available from Rohm and Haas under the trademark, KATHON LX); and oxazoladine-heterocyclic amine.

An antifreeze, such as, ethylene glycol or propylene glycol can be added to improve storage life by protecting the composition against damage that could otherwise be caused by freezing.

EXAMPLE!

A basecoat composition containing the following components was prepared:

Compound Weight percent kg

Water 1 9.8 4.43 methyl hydroxypropyl cellulose 0.2 0.082

RHOPLEX EI-8764 6.6 3.0

ACRONAL 567D 3.5 1.6

2,2,4-trimethyl-1 -3-pentanediol monoisobutyrate 0.3 0.132 mineral spirits 0.3 0.132 sand ^** 38 17.28 limestone ^** 14.5 6.60 silica aluminum alloy ^** 4.5 2.06 ammonium polyphosphate 11.9 5.39 melamine 3.7 1.66 pentaerythritol 3.5 1.60

2-aminoisobutalol 0.02 0.009

KATHON LX 0.05 0.023

SKANE M-8 0.05 0.023

DREWPLUS L-475 ^* 0.1 0.041 attapulgite clay 0.5 0.223 nepheline syenite ^* * 0.95 0.427 paraffin 0.2 0.082 ethylene glycol 0.2 0.105 Water 2 1.3 0.600

^* Trademark designation for a combination of silica and aliphatic petroleum distillates commercially available from Drew Chemical Corporation.

^** fillers

The sand used in Example 1 has the following typical sieve analysis:

ASTM Standard cumulative weight % of particles not

Sieva≤ize passing through that sieve size

30 0

40 12

50 64 70 87

100 96

140 99

200 100

< 200 Trace

Water 1 and the methyl hydroxypropyl cellulose were placed in a Hobart mixer and blended at low speed to disperse the cellulose. The acrylic copolymer and the acrylic-styrene copolymer were then added and allowed to disperse. The remaining ingredients, except water 2, were added and allowed to mix. Water 2 was then added to bring the basecoat composition to a suitable viscosity for storage and later use.

The basecoat composition was applied using a trowel to one side of a 5/8 inch DUROCK Cement panel to create an overall basecoat thickness of 0.10 inch (2.5 mm). In order to accomplish this, a layer of the intumescent composition was applied to the outer surface of the cement board first. A sheet of alkali-resistant fiberglass mesh was placed on this first layer and pressed into its surface with a trowel. A top layer of the basecoat composition was applied to bring the overall basecoat thickness to 0.10 inch. The panel was tested in accordance with Japanese Test Standard JIS A 1301. The average temperature on the unexposed side of the cement board reached 388°F during the test, thereby passing the test.

The intumescent material (ammonium polyphosphate, melamine, and pentaerythritol), comprises 19.1% of the composition of Example 1. In a comparative test a similar composition was prepared, but with the intumescent material comprising about 50% of the composition. This comparative composition could not be properly spread by a trowel to form a basecoat on a substrate.

Thus, in accordance with the invention, there has been provided an intumescent composition, that when used to form a basecoat on a substrate and exposed to elevated temperatures will reduce the heat conductivity of the basecoat/substrate system. There has also been provided an intumescent composition, for use with cement board, that when dried produces a uniform, level basecoat surface as a substrate for interior and exterior finishes. There has also been provided an intumescent composition, for use to form a basecoat on cement board, that when dried will have a sufficient rate of water absorption to draw the liquid binder from the finish coating into the surface of the basecoat in order to form a strong mechanical bond between the basecoat and finish coating. The rate of water absorption is such that a sufficient amount of water will remain in the finish coating to permit normal application by use of a trowel. There has also been provided an intumescent composition for use to form a basecoat on a substrate, that when exposed to the high temperature conditions present during a fire, will intumesce to reduce the rate of heat conduction

through the substrate/basecoat system. Additionally, there has been provided an intumescent composition for use to form a basecoat on cement board that will provide a sufficient reduction in the heat transfer rate through the cement board/basecoat system so as to meet fire code standards without the need to modify the cement board itself.

With this description of the invention in detail, those skilled in the art will appreciate that modification may be made to the invention without departing from the spirit thereof. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments that have been illustrated and described. Rather, it is intended that the scope of the invention be determined by the scope of the appended claims.