CA2659378A1 - Compositions and methods for the protection of substrates from heat flux and fire - Google Patents

Abstract

A flame or heat flux protective coating composition, which includes a fiberglass dispersion in silicone. A flame or heat flux protective sheet, which includes fiberglass and silicone in a sheet form, wherein the fiberglass is dispersed in the silicone or the fiberglass is a woven cloth coated with the silicone is also presented. Articles incorporating the flame or heat flux protective coating or sheet form and methods for coating an article with the flame or heat flux protective coating composition are also presented.

Description

COMPOSITIONS AND METHODS FOR THE PROTECTION OF SUBSTRATES
FROM HEAT FLUX AND FIRE

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Serial No.
60/834,696, which was filed on August 1, 2006, the disclosure of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of grant W15QKN-06-P-0262 awarded by the United States Army.

BACKGROUND OF THE INVENTION

Thermal barrier coatings (TBC) insulate and protect a substrate from prolonged or excessive heat flux and enable the substrate material to retain its mechanical property integrity during service. Selection of the type of system and its components depends upon the application. Heat may be dissipated away from a substrate by several methods, including heat sinks, active cooling, transpiration cooling, radiation cooling, and intumescence.

A need exists for a coating that is able to protect a substrate from exposure to high temperatures and possesses a high strain to failure (i.e. toughness) and adhesion capabilities under harsh, cold temperatures while subject to high mechanical stresses.

SUMMARY OF THE INVENTION

The present invention is directed to a flame or heat flux protective coating composition, which includes a fiberglass dispersion in silicone. Also presented is a flame or heat flux protective sheet, which includes fiberglass and silicone in a sheet form, wherein the fiberglass is dispersed in the silicone or the fiberglass is a woven cloth coated with the silicone. A method for coating an article with a flame or heat flux protective coating and articles incorporating the flame or heat flux protective coating or sheet form are also presented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table setting forth descriptions of the tested coatings;
FIG. 2 is a graph of temperature versus time for the flame test; and FIG. 3 is a graph depicting average flame test results.

DETAILED DESCRIPTION OF THE INVENTION

The fiberglass component imparts high emissivity to the composition of the present invention. Emissivity is a material's ability to absorb and radiate energy as a function of its temperature and is defined herein as the ratio of the total energy radiated by a material to a black body at the same temperature. A black body absorbs all electromagnetic radiation and is an ideal radiator with an emissivity of 1. The emissivities of all non-black body objects are less than one and are determined by the object's temperature, surface characteristics, geometric shape and size, and chemical composition. In order to dissipate heat, high emissivity values close to one are desirable. The emissivity of fiberglass ranges from 0.87-0.95.

Fiberglass also provides the coating composition with relatively low heat conductivity and, thus, a high thermal insulation value. For example, one end of a strand of fiberglass is able to radiate heat away from a coated substrate when subjected to high temperatures, while the other end of the same strand insulates the substrate from the radiated heat.

The fiberglass component is present in an amount suitable to promote effective radiation cooling when exposed to heat. In one embodiment, the fiberglass component is present in an amount from about 4% to about 14% by weight of the composition. Preferably, the amount of fiberglass is from about 8% to about 14% by weight of the composition, more preferably from about 8% to about 12% by weight of the composition.

The fiberglass component can have any suitable fiber length and diameter.
The fiberglass component can also include fibers having a mixture of suitable lengths and diameters. Preferably, the fiber length ranges from about 1mm to about 20mm.
A preferred fiber diameter ranges from about 6 m to about 19 m. Optionally, at least a portion of sizing material is removed from the fiberglass component prior to combining with the silicone component.

The silicone component provides the coating with mechanical flexibility and thermal stability over a broad temperature range (e.g. -110 - 400 F).
Additionally, the decomposition of the silicone component at high temperatures (e.g. greater than 400 F) into silicon dioxide and silicon oxide absorbs a large amount of energy from the heat source. Furthermore, as a result of silicone degradation, large surface areas of fiberglass are exposed. The matted network of exposed fiberglass increases the coating's degree of radiative cooling and serves as insulation by remaining grounded in the cooler under layers of silicone near the protected substrate surface.
Preferably, the silicone component includes dimethylsiloxane and polydimethylsiloxane.

Another aspect of the current invention includes a method for applying a flame or heat flux protective coating composition to at least a portion of an article, wherein the composition includes a fiberglass dispersion in silicone. In a preferred embodiment, the coating is applied by brushing onto a substrate. In another embodiment, the coating is applied by dipping a substrate into the coating composition. When applying the coating, an even layer is not critical but the coating should be thick enough to obstruct vision of the underlying surface.

Another aspect of the current invention includes an article, wherein at least a portion is coated with a composition, which includes a fiberglass dispersion in silicone.

Suitable substrates for the coated article include, for example, thermoplastics, thermoplastic composites, polyethylene, wood, stone, metal (e.g. steel), ceramics, glass, masonry materials (e.g. brick, marble, granite, travertine, limestone, concrete block, glass block, tile, etc.), and the like. For example, U.S. Patent Nos.
6,191,228, 5,951,940, 5,916,932, 5,789,477, and 5,298,214 disclose structural recycled plastic lumber composites made from post-consumer and post-industrial plastics, in which polyolefins are blended with polystyrene or a thermoplastic coated fiber material such as fiberglass. The disclosures of all five patents are incorporated herein by reference.

The coated article can have any shape or form, for example, a round cross-section, a rectangular cross-section, an hourglass cross-section, a sheet form, or a combination thereof. Exemplary forms for plastic composites are disclosed in U.S.
Application No. 60/486,205 filed July 8, 2003, U.S. Application No. 60/683,115 filed May19, 2005, U.S. Application No. 10/563,883 filed January 9, 2006, and International Application No. PCT/US06/19311 filed May 19, 2006. The disclosures of all of which are incorporated herein by reference. In one embodiment, the article is an L-Beam, I-Beam, a C-Beam, a T-Beam, or a combination thereof.

Exemplary articles suitable for coating with the composition of the present invention include, but are not limited to, steel ammunition boxes, railroad ties, plastic piping, lumber, sheet piling, boat hulls, pick-up truck beds, gasoline canisters, fuel tanks in automobiles, airplanes, ships, and submarines, areas near high temperature operating components, such as ignition champers, infrastructure, for example, building support structures and cables in suspension bridges, high-pressure storage tanks, and the like.

The composition of the present invention can also be incorporated into a sheet form. For example, the silicone and fiberglass components can be combined in an extruder and extruded into a sheet die. In another embodiment, a woven fiberglass cloth is coated with the silicone component.

Exemplary applications for the sheet forms of the present invention include, but are not limited to, fabrics, for example, fire protective clothing and blankets, and sheets applied to any of the articles mentioned above as being suitable for coating with the composition of the present invention.

The following non-limiting examples set forth herein below illustrate certain aspects of the invention.

EXAMPLES
Example 1 - Sample preparation 5 Blends of 4, 6, 8, 10, 12, and 14 % by weight fiberglass in silicone, with trace amounts of silicone oil, were prepared. The components were blended in a mixer and applied to a steel coupon with a putty knife targeting a thickness of 1.6 mm or less.
The fiberglass/silicone coatings were compared against seven commercial products (FIG. 1) in a low temperature flexural test and a direct high temperature flame test.
The coatings were applied to standard 76 by 152 by 0.735 mm steel coupons.
Three specimens per sample, or coating type, were tested for both experiments.

Example 2 - Low temperature flexural test Coated steel plates were annealed in dry ice, approximately -79 C, for at least minutes followed by bending around a 0.64 cm mandrel to an angle of 180 .
15 During the test, photographs were taken of each specimen at 30 , 90 , and 180 of bending. Visual observation provided information about a coating's response to thermal shock when bonded to a steel substrate and indicated the type and severity of surface damage incurred due to bending at low temperatures. A successful coating did not have surface damage after testing.

During bending, the coating stretches to accommodate the substrate's new, larger surface area. The surface of the coating is in tension and receives the highest percent strain during bending. Thus, crack formation is initiated at the coating surface. Failure of the coating is indicated by crack development and propagation in the coating and delamination. Common modes of failure included tiny crack formation parallel to the bending axis in the deformation region, large cracks that caused pieces of the coating to detach and expose the substrate, and some brittle failure. In some cases, the coating delaminated as well. These types of surface failure indicate a coating with low strain to failure at low temperatures that will detach or delaminate, expose the substrate, and create a point source of radiative heat.

As indicated in FIG. 1, Products A, B, C, D, E, and G failed the low temperature flexural test due to crack formation. At more severe bending angles, the initial cracks simply propagated, caused pieces of the coating to detach from the substrate, and/or the coating delaminated. In the Product C sample, 2 of 3 specimens passed, and in the Product G sample, 1 of 3 specimens passed. However, all specimens per sample must pass the test in order to be considered successful.
Product H, a silicone-based coating, is the only commercial coating tested that did not suffer any surface damage and passed the low temperature flexural test. The fiberglass/silicone composite coating did not suffer any surface damage, remained adhered to the substrate during bending, and passed the low temperature bend test.
The coating thickness does not appear to significantly affect low temperature performance. For Product E and the fiberglass/silicone composite, specimens were prepared at various thicknesses. All Product E specimens failed while all fiberglass/silicone composite specimens passed.

Example 3 - Flame test A flame produced by a propane torch was applied normal to the coated side of a specimen. An IR sensor (Omega OS550 Series Infrared Industrial Pyrometer) was aligned on the same axis as the flame and measured temperature as a function of time on the back side of the vertical steel coupon. The inner cone length of the flame was adjusted to 3.175 cm, and the tip of the inner cone, the hottest part of the flame, was positioned directly on the sample's surface 2.54 cm above the bottom edge and at the center across the sample width. This configuration delivered worst case scenario results for high temperature direct point heating. The adiabatic flame temperature of propane in air is approximately 1,927 C +/- 38 C. The flame was applied for a total duration of ten minutes. A coating is considered to fail the flame test if the maximum temperature detected by the IR sensor exceeds 316 C. The maximum temperature reached for each coating was compared against the control specimen, an uncoated steel plate, as a point of reference.

The flame test results are presented graphically in FIGS. 2 and 3. The average temperature versus time data collected during the flame test for each sample is presented in FIG. 2, and the average maximum temperature and standard deviation per sample in FIG. 3. The 12 % fiberglass/silicone coating maintained the lowest maximum temperature of all of the coatings. In FIG. 3, the black horizontal line signifies the pass/fail temperature limit of 316 C and delineates the coatings that passed the flame test from those that did not (e.g. coatings with a maximum temperature below the line pass, while those above the line fail).

Coatings with a maximum temperature below the limit were Products D and E
and the fiberglass/silicone composite coatings (excluding the 6 Io fiberglass composition) (FIG. 1). The average maximum temperatures of Products A, B, C, F, G, and H exceeded the limit, thus failing the test.

The foregoing examples and description of the preferred embodiments should be taken as illustrating, rather than as limiting the present invention as defined by the claims. As will be readily appreciated, numerous variations and combinations of the features set forth above can be utilized without departing from the present invention as set forth in the claims. Such variations are not regarded as a departure from the spirit and script of the invention, and all such variations are intended to be included within the scope of the following claims.

Claims (13)

1. A flame or heat flux protective coating composition comprising a fiberglass dispersion in silicone.

2. The composition of claim 1, wherein said fiberglass is present in an amount from about 8% to about 14% by weight of the composition.

3. The composition of claim 2, wherein said fiberglass is present in an amount from about 8% to about 12% by weight of the composition.

4. The composition of claim 1, wherein said fiberglass comprises fibers having a length from about 1mm to about 20mm.

5. The composition of claim 1, wherein said fiberglass comprises fibers having a diameter from about 6µm to about 19µm.

6. The composition of claim 1, wherein at least a portion of sizing material has been removed from said fiberglass.

7. An article comprising at least a portion of a surface coated with the composition of claim 1.

8. The article of claim 7, wherein the surface comprises a material selected from the group consisting of metal, thermoplastics, thermoplastic composites, polyethylene, wood, stone, ceramics, glass, masonry materials, and combinations thereof.

9. The article of claim 7, wherein said article is selected from the group consisting of steel ammunition boxes, railroad ties, plastic piping, lumber, sheet piling, boat hulls, pick-up truck beds, gasoline canisters, fuel tanks in automobiles, airplanes, ships, and submarines, areas near high temperature operating components, infrastructure, building support structures, cables in suspension bridges, and high-pressure storage tanks.

10. A flame or heat flux protective sheet comprising fiberglass and silicone in a sheet form, wherein the fiberglass is dispersed in the silicone or the fiberglass is a woven cloth coated with the silicone.

11. An article comprising the sheet of claim 10, wherein the article is selected from the group consisting of fabrics, steel ammunition boxes, railroad ties, plastic piping, lumber, sheet piling, boat hulls, pick-up truck beds, gasoline canisters, fuel tanks in automobiles, airplanes, ships, and submarines, areas near high temperature operating components, infrastructure, building support structures, cables in suspension bridges, and high-pressure storage tanks.

12. The article of claim 11, wherein said fabric is incorporated in fire protective clothing or a fire protective blanket.

13. A method for coating an article with a flame or heat flux protective coating layer comprising applying the composition of claim 1 to at least a portion of said article.