Flexible fibrous endothermic sheet material for fire protection

DETAILED DESCRIPTION The inorganic fibers used in the protective material of this invention are refractory materials which combine high strength, good thermal resistance and the ability to retain relatively high levels of high density endothermic filler.
Examples of useful inorganic fibers include graphite, silica, alumina-silica, calcium oxide-silica, asbestos, and glass fibers.
Alumino-silicate fibers are preferred and are available commercially under the trademarks Fiberfrax SK-2600 from the Carborundum Company, Cerafiber from Manville Corporation and Kaowool from Babcock and Wilcox.
The fiber diameter is usually less than about 6 micrometers, preferably less than one micrometer.
Grades of fiberglass having relatively small fiber diameters (0.
4-0.
9 micrometers) offer a lower fiber bulk density and allow ATH filler level to be increased significantly.
Larger fiber diameters result in a material with a lower number of fibers for a given mass, yielding sheets of lower tensile strength, and are usually more difficult to handle on paper making machinery.
The physical properties of a typical alumino-silicate (Fiberfrax) are: continuous use limit 1260.
degree.
C.
; melting point 1790.
degree.
C.
; normal packing density 96-192 kg/m.
sup.
3 ; fiber lengths up to 102 mm; specific gravity 2.
73 and fiber strength of 2.
76.
times.
10.
sup.
9 N/m.
sup.
2.
Blends of fiberglass and ceramic fibers (e.
g.
5% ceramic and 3% fiberglass in the total composition) have been particularly useful, since they help prevent the shrinkage which may occur if fiberglass is the only fiber used in the sheet.
The amount of organic binder is preferably 1-6 weight percent of the total, more preferably about 2%.
Suitable binders can include various polymers and elastomers in latex form, for example, natural rubber latex, styrene-butadiene latices, butadiene acrylonitrile latices, and latices of acrylate and methacrylate polymers and copolymers (e.
g.
, polymethyl acrylate, polyethyl acrylate, and polymethyl methacrylate).
It is preferred to use halogen-free polymers to avoid decomposition and release of noxious and corrosive halogen gases during a fire