Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Two or more non-extruded coatings or impregnations
Patent
1997-06-19
1998-07-28
Bell, James J.
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Two or more non-extruded coatings or impregnations
428 75, 428367, 428373, 442364, 442365, 442375, B32B 104
Patent
active
057860599
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a composite material having at least one layer of fiber web and aerogel particles, to a process for its production and to its use.
Aerogels, especially those having porosities above 60% and densities below 0.4 g/cm.sup.3, have a very low density, a high porosity and a low pore diameter and so an extremely low thermal conductivity and hence find application as thermal insulation materials, for example as described in EP-A-0 171 722.
However, the high porosity also leads to low mechanical stability not only of the gel from which the aerogel is dried but also of the dried aerogel itself.
Aerogels in the wider sense, i.e. in the sense of "gel having air as dispersion medium", are produced by drying a suitable gel. The term "aerogel" in this sense embraces aerogels in the narrower sense, xerogels and cryogels. A dried gel is an aerogel in the narrower sense when the liquid of the gel has been removed at temperatures above the critical temperature and starting from pressures above the critical pressure. If, by contrast, the liquid of the gel is removed subcritically, for example through formation of a liquid-vapor boundary phase, the resulting gel is termed a xerogel. It is to be noted that the gels of the invention are aerogels, in the sense of gel having air as dispersion medium.
The shaping of the aerogel is completed during the sol-gel transition. Once the solid gel structure has formed, the external shape can only be altered through comminution, for example grinding, the material being too brittle for any other form of processing.
However, there are many applications for which it is necessary to use the aerogels in the form of certain shaped structures. In principle, shaping is possible during gelling. However, the diffusion-governed exchange of solvents which is typically necessary during production (see, for example, U.S. Pat. No. 4,610,863, EP-A 0 396 076 re aerogels; see, for example, WO 93/06044 re aerogel composite materials) and the similarly diffusion-governed drying would lead to uneconomically long production times. It is therefore sensible to carry out any shaping after the formation of the aerogel, i.e. after drying, without any significant applications-dictated change taking place to the internal structure of the aerogel.
There are many applications, for example the insulation of curved or irregularly shaped surfaces, requiring flexible panels or mats composed of an insulant.
DE-A 33 46 180 describes bending-resistant panels composed of pressed structures based on pyrogenic silica aerogel in conjunction with a reinforcement in the form of long mineral fibers. However, the pyrogenic silica aerogel is not an aerogel within the above meaning, since it is not produced by drying a gel and hence has a completely different pore structure; it is therefore mechanically more stable and can therefore be pressed without destroying the microstructure, but it has a higher thermal conductivity than typical aerogels within the above meaning. The surface of such pressed structures is very sensitive and therefore has to be hardened, for example through the use of a binder at the surface or has to be protected by lamination with a film. Furthermore, the resulting pressed structure is not compressible.
Furthermore, German patent application P 44 18 843.9 describes a mat composed of a fiber-reinforced xerogel. These mats have very low thermal conductivity because of the very high aerogel content, but their production takes a relatively long time because of the above-described diffusion problems. More particularly, the production of thicker mats is only sensibly possible by combining a plurality of thin mats and hence necessitates additional expense.
It is an object of the present invention to provide a granular aerogel composite material which has low thermal conductivity, is mechanically stable and makes it simple to produce mats or panels.
This object is achieved by a composite material having at least one layer of fiber web and aerogel particles, wherein the fiber we
REFERENCES:
patent: 4808202 (1989-02-01), Nishikawa et al.
patent: 5221573 (1993-06-01), Baigas, Jr.
patent: 5256476 (1993-10-01), Tanaka et al.
patent: 5271780 (1993-12-01), Baigas, Jr.
Frank Dierk
Thonnessen Franz
Zimmermann Andreas
Bell James J.
Hoechst Aktiengesellschaft
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