High performance insulations

Details High performance insulations High performance insulations

1999-08-06

2002-05-07

Morris, Terrel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Noninterengaged fiber-containing paper-free web or sheet...

C428S220000, C428S297400, C442S079000, C442S082000, C442S136000, C442S361000, C442S409000, C442S415000

Reexamination Certificate

active

06383623

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
This invention pertains to high performance materials having superior thermal and/or acoustic insulative properties. More particularly, this invention relates to low-density thermal and acoustic insulation which can withstand elevated temperatures while retaining its insulative properties. In addition, this invention concerns insulation material suitable for use in aviation. Other aspects of the invention involve methods for manufacturing such insulation.
A modern airplane has a layer of insulation located just inside the plane's exterior skin for the purpose of limiting the flow of heat into and out of the plane's cabin. Since the temperature at the cruising altitude of commercial jets may be −30°, while the temperature in the cabin is approximately 70°, the resulting 100° temperature gradient would, unless thermal insulation is used, lead to a significant loss of heat from the cabin.
Insulation also serves to reduce the noise level in the cabin, such noise being produced both by the plane's engine(s) and the plane's motion through the air.
Typically, the insulation used in planes is composed of singular or multiple layers of finely spun fiberglass blankets of various densities designed for thermal and acoustic protection, the latter against both high frequency sounds from jet engine noise as well as structural-borne lower frequency sounds. This material is very fine in fiber diameter and tends to fracture easily.
Conventional aircraft insulation has a number of shortcomings. As highlighted by several recent incidents involving the suspected failure of aircraft insulation, the most problematic of these shortcomings is the material's performance in fires. At elevated temperatures, which may typically approach 2000° F., conventional aircraft interior materials, including insulation, because of the materials from which it is made, begins emitting substantial quantities of thick, toxic smoke. Carbon monoxide and hydrogen cyanide are the two principal toxic combustion gases. Most cabin furnishings contain carbon and will generate both carbon monoxide and carbon dioxide when burned. Burning wool, silk and many nitrogen-containing synthetics will produce the more toxic hydrogen cyanide gas. Irritant gases such as hydrogen chloride and acrolein, are generated from burning wire insulation and some other cabin materials. Generally, carbon dioxide levels increase and oxygen concentrations decrease during fires. Although fire is a great danger, it has been determined that the toxic smoke produced by the smoldering insulation and interior materials is a grave threat in its own right. The blinding smoke will interfere with the evacuating passengers, finding the plane's emergency exits, and because it is toxic, it may asphyxiate passengers who do not escape quickly. More people could be killed through asphyxiation by toxic smoke than might die in the fire itself.
Recent incidents involving the suspected failure of aircraft insulation confirm the need for safer, more thermally-stable insulation. In October of 1998, the Federal Aviation Administration (FAA), responding to the crash of a Swissair flight near Halifax, Nova Scotia, a month earlier, recommended the replacement of the insulation in nearly all of the world's 12,000 passenger jet planes. The FAA has also warned that the Mylar insulation used in passenger planes can catch fire when exposed to electrical shorts, and so the FAA has established new flammability standards for airplane insulation that require materials to with stand higher temperatures for extended periods of time.
One approach to improving aircraft insulation's performance is to provide the insulation with a protective outer layer. The FAA has investigated “hardening” aircraft fuselages to increase the time it takes flames outside an aircraft to burn through the plane's fuselage. One “hardening” technique under investigation involves using heat-stabilized, oxidized polyacrylonitrile fiber (PAN), which may double the time it takes flames to penetrate into the plane's cabin. Barrier materials, such as those utilizing PAN, are composed of a random fiber mat or felt used in conjunction with existing fiberglass systems for improved fuselage burnthrough times.
Incidentally, this “hardening” approach is similar to that described in U.S. Pat. No. 5,578,368. The '368 patent describes a material for use in sleeping bags having a protective outer layer made from aramid fiber, and the patent says this aramid layer imparts fire-resistance.
Accordingly, there is a real need for aircraft insulation which is able to sustain high temperatures without burning, smoking, degrading or outgassing. It is also desirable that when such insulation finally burns, it does so in a self-extinguishing manner.
“Low-performance” insulation commonly used in building construction for wall and ceiling barriers, as well as pipe wrappings, and even in aerospace applications such as aircraft thermal blankets, is typically made from a lightweight batting of glass fibers held together by a thermoset phenolic resin binder. This insulation material, commonly referred to as “fiberglass insulation”, is inexpensive and may be suitable as a low temperature thermal insulator and sound absorbing material. Such insulation has a number of serious shortcomings.
For example, fiberglass insulation is brittle in nature, meaning that when it is handled, airborne glass particles are produced. Those working with the fiberglass insulation may inhale the airborne glass particles, irritating their lungs. Glass particles may lodge in the workers' skin, also causing irritation. Although those handling the fiberglass insulation can protect themselves by using respiratory masks and wearing protective gear, that results in added expense and inconvenience.
Another shortcoming of fiberglass insulation is that the material is hydrophilic, meaning water can permeate into and be absorbed by the insulation. The absorbed water decreases the insulation's thermal and acoustic properties, and also increases the insulation's weight, which is a serious problem if the insulation is used in aviation. Since airplane insulation is mounted against the plane's skin, the insulation becomes quite cold when the plane is in flight. When warm, moist air, such as the air in the cabin, passes over the insulation, the water in that air condenses on and collects in the cold insulation. Over time, the insulation may become soggy, reducing its insulating abilities, and heavy, increasing the plane's operating costs. While it may be possible to reduce water absorption by treating the fiberglass insulation or providing a barrier layer, this complicates the manufacturing process and makes the insulation more expensive.
Accordingly, there is a need for alternative insulative materials which have superior thermal and acoustic properties, without the inherent disadvantages of conventional insulation.
DESCRIPTION OF THE RELATED ART
It is generally known to provide composite materials, typically, textiles or filtration members, in which non-thermoplastic materials, for example, aramid fibers, are combined with thermoplastic materials, for example, polyphenylene fibers. A variety of such composite materials are discussed in U.S. Pat. No. 4,502,364, U.S. Pat. No. 4,840,838, U.S. Pat. No. 5,649,435, U.S. Pat. No. 5,160,485, U.S. Pat. No. 5,194,322, U.S. Pat. No. 5,316,834, U.S. Pat. No. 5,433,998, U.S. Pat. No. 5,529,826, and U.S. Pat. No. 5,753,001.
Blending of non-thermoplastic fibers with thermoplastic fibers to form consolidated composite materials is discussed in U.S. Pat. No. 4,195,112 and U.S. Pat. No. 4,780,59. The structures described in these patents are meant to serve as high density composite materials, and are intended to be used as load bearing and structural panels or as shape retaining moldable forms. It is important in considering these compositions to note that the disclosed structures are quite dense and fully consolidate

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