GB2287722A - Shaped composite insulating material - Google Patents

Abstract

A heat insulating material is made by forming ceramic fibres into a blanket, and applying an aqueous dispersion of exfoliated vermiculite to the blanket so as to wet the surface and a portion of the interior. The wet blanket is shaped and then dried, when the vermiculate forms an outer coating.

Description

SHAPED COMPOSITE tNSULs G MATERIAL Background of the Invention This invention relates to a light weight, preformed heat insulating materials having excellent physical properties and very high temperature resistance.

Blankets of inorganic fibers are widely employed as heat insulators, and a variety of organic binders, typically phenolic materials, have been applied to maintain fiber integrity. Organic binders, however, disadvantageously give off harinful gasses when heated. Also, when heated organic binders loose their structural integrity.

It is also known to apply a aqueous dispersion of vermiculite to a flat blanket or textile of yarns which are not fire resistant, as disclosed in U.S. Patent No. 4,543,287 which is hereby incorporated by reference.

Upon removal of the water, the vermiculite lamellae reside as a coating on the fibers, rendering them more resistant to fire.

A silica dispersion is available from DuPont identified by the (R.T.M.) tradename Ludo7 This product is heat resistant but contains organic material that ofE-gases in heat Also, insulating materials made with ceramic blankets are rigid like board and resist movement Ludox tends to powder when abraded or handled.

Other heat resistant silicates such as sodium or potassium silicate give very rigid products. The silicates are alkaline and may destroy the ceramic fiber over a period of time reducing them to dust Summary of the Invention A shaped composite insulating material is prepared by first preparing a water dispersion of vermiculite which is free of organic materials. The dispersion is then applied to a woven or nonwoven blanket or substrate of ceramic, glass or other fibers in an amount sufficient to render the blanket pitiable and fordable. The substrate or sections thereof are formed into the desired final shape. The water is removed by dying, and the remaining vermiculite provides a solid binder, serving to retain the substrate or blanket in the desired shape.

The resulting shaped insulating material can withstand temperatures up to XX00 F, without release of any volatiles. Organic binders typically loose structural integrity at temperatures between 250 F and 500 F. The material of the invention will maintain structural integrity at elevated temperatures. i.e., temperatures of 500 F or greater. The formed material is a good sound attenuator, and is somewhat flexible to facilitate installation. The vermicrrlite binder also serves to encapsulate any loose fibers thus improving handling, and reducing safety risks from inhaling or possibility of swallowing loose fibers and the#skin irritation. The benefits of the composite insulating material of the invention are: Flexible; rigidity determined by process Easily handled Heat resistant Improved acoustical properties oNon gassing at all temperatures Vermiculite gives a film that will lock in fibers Description of the Preferred Embodiment The vermiaiiite dispersions employed herein are prepared by a variety of known methods. The dispersions are produced by chemical exfoliation of vermiculite, a naturally occurring magneslum-alii=imun silicate material, into platelets or lamellae having a high aspect ratio and a particle size in the order of 50 microns. While both organic and inorganic compounds have been employed to exfoliate the vermiculite, the preferred material of the present invention is one that is free of organic materials.

Ready-made inorganic exfoliated vermiculite is commercially available and may be dispersed directly in water. One commercially available vermiculite is marketed by WR Grace & Co. - Cony, 72 Whittemore (R.T.M.) Ave., Cambridge, MA 02140 under the tradename MicroLite#.

As used herein, the term "ceramic fibers" means polycrystalline metal oxide fibers having a high melt temperature typically in excess of 3,000" F. Ceramic fibers generally contain aluminum oxide or calcium oxide and silica, as well as smaller amounts of other oxides, such as ferric, titanium and magnesium A typical ceramic fiber will comprise, for example, in excess of 30% aluminum or calcium oxide, in excess of 45% silica, with any remainder as other metallic oxides. The above definition, therefore, excludes other inorganic fibers such as grass and asbestos. As a non-equivalent alternative, glass fibers may be employed at substantially lower temperature applications.

The ceramic fibers are formed into a substantially fat substrate or blanket by any of several well known methods. For example, the fibers may be placed on a flat surface and needled with barbed needles to entangle the fibers and form a cohesive blanket. The substrate or blanket may also be made by paper making process.

I, The ceramic substrates or blankets are manufactured in various densities, typically 3-12 pounds per cubic foot Lower density blankets typically have superior insulating properties but are more fragile than the higher densities The most desired thickness and density is based on the performance required of the finished part Thick sections of low density blankets give the best insulating properties.

An aqueous inorganic dispersion of vermiculite is prepared by mixing exfoliated vermiculite with water. The mixture will typically comprise from about 2 to about 30 percent solids.

The aqueous dispersion is then applied to the ceramic fiber blanket by any suitable coating technique, such as spraying, roller coating, dipping, o'r the l i ks Sufficient dispersion is applied to at least partially penetrate the surface of the blanket and wet a portion of the interior. Upon application of the aqueous dispersion, the blanket becomes pliable or moldable.

The amount of vermiculite solids in the dispersion and the rate of application to the ceramic blanket will vary, depending on the processing conditions, the thickness of the blanket, and the desired staidness of the final producL The blanket may have a thickness in the order of 0.062 to 6 inches. For most applications the blanket will have a thickness in the range of 0.25 to 1.0 inches. The amount of dispersion applied will be in the order of from about 2 to about 50% vermiculite solids per square foot based on the weight of the ceramic blanket Following application of the dispersion, the blanket is formed or molded into any desired shape. The wet blanket may be formed by hand, or with the aid of a mandrel or forming surface, or may be slightly compressed between the opposed surfaces of a mold. Preferably, the overall thickness of the original blanket is not substantially changed in order to maintain maximum thermal performance characteristics. Of course, the blanket may be cut into any desired shape prior to or after application of the binder dispersion.

Following application of dispersion and forming, the shaped blanket is dried, either by air drying or application of heat. Upon drying, the vermiculite is converted into a solid body, maintaining the formed ceramic fiber blanket in its formed shape.

In addition to the molding methods described above, the wet blanket may be molded around the actual part of the structure to be protected and allowed to dry, thus providing the part or sttticture with a protective thermal barrier.

Upon application of the vermiculite, followed by forming and drying, the composite retains the molded shape in a permanent manner, with the outer vermiculite coating serving to surround, encapsulate and immobilize the fibers of the ceramic blanket This, the molded form can be used and handled without any substantial shedding of fibers, and the composite is typically somewhat resilient.

An example of shaped composite insulating material is made as follows. A 40 inch width of 8 pounds per cubic foot density, one half inch thickness ceramic blanket is passed through a press with clicker dies.

These dies cut to size the desired shape for the preform. These preforms can also be obtained from a calendar equipped with cutting dies.

The preforms are impregnated by dipping into a 15% aqueous dispersion of vermiculite. The ceramic blanket is highly absorbent and the dip time is approximately 5 seconds. In some cases the dispersion is pigmented to give a more attractive product The ceramic blanket with the impregnant is placed into the bottom of a multiple cavity mold. The mold is placed in a hot press where the top of the mold compresses the preform lightly to form the desired shape. The pressure is low and the mold design determines the thickness and shape of the finished part. The temperature of the press is adequate to evaporate the water from the blanket, leaving only the solid venniculite patticles.

The dwell time in the press is based on the weight of the wet ceramic preform, typically from OS to 10 minutes. The shaped parts are removed from the mold and excess flash is removed with a cutter. The parts are inspected and packed for shipment.

While the preferred embodiment of the present imrention has been shown and described, it is to be understood that various modifications and changes could be made thereto without departing from the scope of the appended claims.

Claims (11)

1. A method of making a shaped composite insulating material, said method comprising the steps of applying an aqueous dispersion of vermiculite lamellae to a ceramic fiber substrate in a sufficient amount to make the substrate pliable, shaping the substrate into a three dimensional form, and then drying said substrate to retain said substrate in said form at elevated temperatures.

2. The method of Claim 1 wherein the shaping and drying of the substrate is conducted in a heated mold.

3. The method of Claim 1 wherein the aqueous dispersion of vermiculite lamellae is substantially free of organic materials.

4. The method of Claim 1 wherein said substrate comprises woven and nonwoven blankets.

5. The method of Claim 4 wherein said blanket has a thickener of from about 0.062 to about 6.0 inches.

6. The method of Claim 5 wherein said blanket has a density of from about 3 to about 12 pounds per foot.

7. A composite insulating material, said material comprising a blanket of ceramic fibers in a three dimensional form and held in such form by a binder, said binder encapsulating the outer layers of said blanket and consisting essentially of vermiculite lamellae free of organic materials.

8. The composite insulating material of Claim 7 wherein said material is capable of maintaining structural integrity at temperatures in excess of 5000F.

9. Method of making an insulating material, said method comprising the steps of providing a blanket of inorganic fibers, coating and at least partially impregnating said blanket with an aqueous dispersion of a binder consisting essentially of vermiculite lamellae free of organic materials, forming the web blanket into a three dimensional shape, and then drying the blanket to leave the vermiculite as a permanent binder.

10. The method of Claim 9 wherein said inorganic fibers are ceramic fibers having a melt temperature in excess of 30000F.

11. The method of Claim 10 wherein said blanket has a density of from about 3 to about 12 pounds per cubic foot.