Abstract:
A microporous insulation material contains an ingredient which exhibits a phase transition and functions to maintain temperatures attained by an object shielded by the microporous insulation material, during exposure of the microporous insulation material to a high temperature environment, at an acceptable level over a given period of time. The insulation material is especially suitable for insulating flight data and voice recorder systems. The microporous insulation material contains inorganic particulate material; endothermic compounds, (optionally) an opacifier, inorganic fiber and preferably, a dry resin or other binder. The inorganic particulate material can comprise only hydrophilic material or both hydrophilic and hydrophobic material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of (allowed) U.S. patent application Ser. No. 08/510,348, filed Aug. 2, 1995, now U.S. Pat. No. 5,804,294. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a microporous insulation containing one or more ingredients which undergo phase transitions as the temperature of the microporous insulation is raised and, in particular, to such an insulation material that is suited for use in shielding flight data and voice recorders from fires and high temperature environments. 
     There are numerous insulating applications, such as, fire safes, cable trays and fire walls where it is desirable or necessary to insulate and protect items, devices, assemblies and/or areas from high temperature environments or fire. One very important insulating application is the insulation and shielding of flight data and voice recorders from the high temperature environment and fire frequently present after an aircraft has crashed. U.S. Pat. No. 4,694,119; issued Sep. 15, 1987; and entitled &#34;Heat Shielded Memory Unit for an Aircraft Flight Data Recorder&#34;, discloses an insulating system in which a layer of wax encapsulates the recorder and, in turn, is enclosed within a thermal liner of MIN-K 2000 insulation or a similar insulation liner. At a certain temperature the wax undergoes a phase transition and functions as a heat sink to keep the temperature of the recorder below a certain critical temperature. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a microporous insulation which includes endothermic compounds within the insulation structure and further enhances the already excellent insulating properties of the microporous insulation. Unlike the insulation system of the &#39;119 patent, a separate layer of wax or other phase transition material is not required. The endothermic compounds within the microporous insulation of the present invention undergo phase changes when exposed to certain elevated temperatures, redirect thermal energy, maintain the temperature of the microporous insulation at a certain level for a period of time, and release chemically bound water and/or mechanically bound water and/or other gases which carry away additional heat from the component(s) or assembly(s) being insulated and shielded from a high temperature environment. 
     The microporous insulation of the present invention is especially suitable for insulating applications involving fire and other high temperature environments. When compared with certain traditional microporous insulation systems of the same thickness used for flight data recorder applications, the microporous insulation of the present invention has shown a 40-130% increase in the survival time of protected components. It is expected that the microporous insulation of the present invention would exhibit similar results in other high temperature applications. 
     The microporous insulation material of the invention contains inorganic particulate material; an endothermic compound; (optionally) an opacifier; inorganic fiber; water and preferably, where structural integrity is required, a dry resin binder. When the microporous insulation material is to be used for applications where moisture may negatively impact the item or assembly being protected, the inorganic particulate material is hydrophilic and is processed as a dry powder. When the microporous insulation material is to be used for applications where moisture can be tolerated, the inorganic particulate material is partially hydrophilic and partially hydrophobic and is processed to allow the absorption of water. The amount of water that the microporous insulation will hold is controlled by the amount of hydrophilic particulate material used in the insulation and the structural integrity of the insulation is maintained by the hydrophobic particulate material in the microporous insulation. The addition of water to the microporous insulation material results in an insulation that maintains the temperature of the insulation material at about 250° F. or below for an extended period of time during environmental exposures of up to 2000° Fahrenheit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of the process for making the microporous insulation material of the present invention. 
     FIG. 2 graphically depicts the temperature versus time characteristics of two embodiments of the present invention and three insulations currently used to shield and insulate flight data recorders. 
     FIG. 3 graphically depicts the temperature versus time characteristics of three embodiments (including an embodiment without water added) of the present invention and two insulations currently used to shield and insulate flight data recorders. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The microporous insulation of the present invention contains the following ingredients at the indicated weight percentage levels or ranges which are based upon the dry weight of the microporous insulation material prior to adding any water to the water saturated embodiments. 
     
                       TABLE 1______________________________________INGREDIENTS          WT %______________________________________Inorganic Particulate Material(s)                20-60Endothermic Compound(s)                10-60Opacifier(s)         05-20Inorganic Reinforcing Fiber                03-15Dry Resin Binder      0-06______________________________________ 
    
     Alternatively, the microporous insulation material may comprise: 
     
                       TABLE 2______________________________________INGREDIENTS          WT %______________________________________Inorganic Particulate Material(s)                20-80Endothermic Compound(s)                05-75Opacifier(s)          0-30Inorganic Reinforcing Fiber                01-15Binder                0-06______________________________________ 
    
     Again, these ranges are based upon the dry weight of the microporous insulation material prior to adding any water to the water saturated embodiments. Any individual ingredient range from Table 2, furthermore, may be substituted for the corresponding range shown in Table 1 in appropriate circumstances. 
     The inorganic particulate material(s) and the endothermic compound(s) make up 50--approximately 89 wt % of the microporous insulation material. The microporous insulation material to be used in dry systems where moisture can be detrimental to the item or assembly being insulated and shielded, uses a hydrophilic inorganic particulate material. The microporous insulation material to be used in water soaked systems where the item or assembly being insulated and shielded can tolerate moisture, uses a blend of the inorganic particulate materials with about 50-95 wt % of the inorganic particulate material being hydrophilic and about 5-50 wt % of the inorganic particulate material being hydrophobic and preferably about 70-95 wt % of the inorganic particulate material being hydrophilic and about 5-30 wt % of the inorganic particulate material being hydrophobic. 
     In one preferred embodiment of the present invention, the microporous insulation material comprises about: (a) 34-38 wt % inorganic particulate material; 47-51 wt % endothermic compound(s); 7-8 wt % opacifier(s); 4-6 wt % inorganic fiber; and 0-3 wt % dry resin binder. Two examples of this embodiment are a microporous insulation material which contains about: (a) 36.5 wt % fumed silica with a surface area of about 200 m 2  /g; 49 wt % aluminum trihydrate; 7.5 wt % silicone powder; 4 wt % quartz fiber; 1 wt % glass fiber; and 2 wt % phenol formaldehyde wherein the fumed silica is hydrophilic and a microporous insulation material, identical to the first microporous insulation material, except that the fumed silica is about 85 wt % hydrophilic and 15 wt % hydrophobic plus the addition of water. 
     In a second preferred binderless embodiment of the present invention, the microporous insulation material comprises about: 28-32 wt % inorganic particulate material(s); 48-52 wt % endothermic compound(s); 13-17 wt % opacifier(s); and 4-5 wt % inorganic fiber. Two examples of this second preferred embodiment are a microporous insulation material containing about: 30.5 wt % fumed silica with a surface area of about 200 m 2  /g; 50 wt % alumina trihydrate; 15 wt % silicone powder; and 4.5 wt % glass and amorphous wool fiber wherein the fumed silica is hydrophilic and a second microporous insulation material, identical to the first, except that about 85 wt % of the fumed silica is hydrophilic and 15 wt % of the fumed silica is hydrophobic plus water. This binderless embodiment of the microporous insulation material of the present invention is used where the microporous insulation material is encapsulated within a covering and in other applications where the integrity of the microporous insulation material is not important for the application. 
     Yet another preferred embodiment of the present invention is a microporous insulation material comprising approximately 40 wt % inorganic particulate materials, approximately 49 wt % endothermic compound(s), approximately 6 wt % inorganic fibers, and approximately 5 wt % binder. In this embodiment, 30 wt % of the material is fumed alumina, with the remaining 10 wt % of the inorganic particulate materials being fumed silica. Various other embodiments may include fumed alumina instead of any or all of any fumed silica otherwise present as an inorganic particulate material. 
     The hydrophilic inorganic particulate material employed in the present invention acts as a filler and a bulking agent in both the dry insulation system and the wet insulation system of the present invention. In the wet insulation system, the hydrophilic inorganic particulate material also functions to absorb and retain water which undergoes a phase change at about 212° F. to maintain the microporous insulation at about this temperature for an extended period of time. Examples of hydrophilic particulate material which can be utilized in the present invention include, but are not limited to, fumed silica, silica fume, precipitated silica, micron size synthetic amorphous silica and other fumed oxides. The surface area of the hydrophilic inorganic particulate material will generally be greater than 100 m 2  /g, and preferably, greater than about 150 m 2  /g. 
     The hydrophobic inorganic particulate material functions to make the microporous insulation microporous and thermally efficient and to maintain the structural integrity of the microporous insulation after water has been introduced into the microporous insulation material and absorbed by the hydrophilic inorganic particulate material. Examples of hydrophobic inorganic particulate materials which can be utilized in the present invention include, but are not limited to, fumed silica, silica fume, precipitated silica, micron size synthetic amorphous silica and other fumed oxides which have been surface treated to make the materials hydrophobic. A preferred hydrophobic inorganic particulate material is fumed silica which has been surface treated with silane to make the fumed silica water resistant. The surface area of the hydrophobic inorganic particulate material will generally be greater than about 50 m 2  /g and preferably, greater than about 90 m2/g. 
     At least one endothermic compound is employed in the microporous insulation material of the present invention. Examples of the forgoing endothermic compounds which can be utilized in the present invention include, but are not limited to, alumina trihydrate, magnesium carbonate-hydrate, melamine and water. As used herein, the term &#34;endothermic compound&#34; with respect to alumina trihydrate and magnesium carbonate-hydrate means that these materials are endothermic upon dehydration. 
     At least one opacifier is employed in some embodiments of the microporous insulation material of the present invention. Examples of suitable opacifying agents which can be utilized in the present invention are silicone, titania, calcined clay, magnesium oxide, silicone carbide, carbon and other metal oxides. 
     At least one type of inorganic fiber is employed in the microporous insulation material of the present invention. Examples of suitable inorganic fibers which can be used in the present invention are quartz fibers, glass fibers, refractory fibers, amorphous fibers, and mineral wool fibers. 
     When a binder is employed in the microporous insulation material of the present invention, preferably the binder is a dry resin binder such as, phenol formaldehyde or other thermosetting resins. Those skilled in the art will recognize that other suitable binders exist or may be used as well. 
     Preferably, as schematically illustrated in FIG. 1, the microporous insulation material of the present invention is made by preparing a dry mixture of the inorganic particulate material (hydrophilic or a blend of hydrophilic and hydrophobic) and endothermic compound(s) and introducing the inorganic particulate material and endothermic compound(s) into a dry mixer. The opacifier(s), the inorganic reinforcing fibers, and the dry resin binder (if used) are also added to the dry mixer and the ingredients are blended. The blended ingredients forming the microporous insulation material are then pressed to a desired shaped in a conventional press. If desired heat may be applied to set the binder. The shaped microporous insulation can then be further processed, including machining to desired tolerances, or otherwise fabricated for the intended application. In the wet insulation system of the present invention, water can now be introduced into the microporous insulation material to be absorbed by the hydrophilic inorganic particulate material. The amount of water allowed to soak into the wet insulation system is controlled by the amount of hydrophilic-inorganic particulate material contained in the microporous insulation material. 
     FIGS. 2 and 3 graphically illustrate test results for the microporous insulation of the present invention in its dry form and wet form when compared to examples of insulations currently used to insulate flight data recorders. In the graphs, the insulations currently used to insulate flight data recorders and used for comparison are MIN-K 2000 insulation; MIN-K 1302 insulation (both manufactured by Schuller International Inc.) and E5A-water soaked insulation (manufactured by Minnesota Mining and Manufacturing). The microporous insulation of the present invention in its dry form is referred to as MIN-K 1302 WITH ATH (DRY) in FIG. 3. The microporous insulation of the present invention in its wet form (water soaked) is referred to as MIX 138-MIN-K 1302 W/ATH &amp; WATER and MIN-K 1302 W/WATER in both FIGS. 2 and 3. The amount of hydrophobic fumed silica used in the wet forms was from 5-30 wt % of the fumed silica. The insulation samples were of the same thickness, enclosed an aluminum heat sink where the temperature was measured and were placed in a furnace having a temperature of about 2000° F. 
     The test results show that the microporous insulation of the present invention (wet form) maintained the temperature of the aluminum heat sink below 300° F. for an extended period of time much greater than that of the currently used insulation materials. The test results show that the microporous insulation of the present invention (dry form) maintained the temperature of the aluminum heat sink below 300° F. for a longer period of time than the currently used MIN-R 1302 insulation and MIN-K 2000 insulation. 
     In describing the invention, certain embodiments have been used to illustrate the invention and the practices thereof. However, the invention is not limited to these specific embodiments as other embodiments and modifications within the spirit of the invention will readily occur to those skilled in the art on reading this specification. Thus, the invention is not intended to be limited to the specific embodiments disclosed, but is to be limited only by the claims appended hereto.