Static structures (e.g. – buildings) – With exposed configuration having acoustical function – Absorbing material behind foraminous facing sheet
Reexamination Certificate
1999-09-23
2003-07-29
Nakarani, D. S. (Department: 1773)
Static structures (e.g., buildings)
With exposed configuration having acoustical function
Absorbing material behind foraminous facing sheet
C181S284000, C181S290000, C181S294000, C181S295000
Reexamination Certificate
active
06598358
ABSTRACT:
RELATED APPLICATIONS
This application is filed pursuant to 35 USC §371 of international application No. PCT/EP98/00328, filed Jan. 22, 1998, which in turn claims priority to German application No. 197 02 238.3, filed Jan. 24, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of aerogels for deadening structure-borne and/or impact sounds.
2. Description of the Related Art
Understood by structure-borne sound within the context of the present document is sound propagating in solid substances; understood by impact sound is sound which arises e.g. during the inspection of covers or moving of chairs and which is emitted as structure-borne sound and partly also as airborne sound (company brochure of Rhinolith Damstoffe GmbH; Technical data: in 150 Bauphysik 6/96; W. Reichardt: “Grundlagen der technischen Akustik” [Fundamentals of technical acoustics], Akademische Verlagsgesellschaft, Leipzig, 1968).
Conventional materials which attenuate structure-borne and impact sound based on polystyrene, polyolefins and polyurethanes are produced with the use of propellants, such as FCKW's, CO
2
or pentane. The cell structure of the foam produced by propellants is responsible for the high impact and structure-borne sound-attenuating capacity. However, such propellants are harmful to the environment, since they slowly escape into the atmosphere.
Other attenuating substances for structure-borne and impact sounds based on mineral or glass-fiber wool can emit fibers and/or fiber fragments during their production, installation and dissembling, as well as during their use. This leads to a harmful effect on the environment and humans who handle these substances or are exposed thereto.
Aerogels, particularly those having porosities over 60% and densities below 0.6 g/cm
3
have an extremely low thermal conductivity. For this reason they are used as heat-insulating materials, such as described e.g. in EP-A-0 171 722. In addition, the velocity of sound in aerogels has a very low value for solids, which can be utilized for the production of airborne sound-deadening materials.
Aerogels, considered in the broad sense, i.e. in the sense of “gel with air as dispersing agent”, are produced by drying a suitable gel. Falling under the designation “aerogel” within this meaning are aerogels in the narrower sense, xerogels and kryogels. Here, a dried gel is designated as aerogels in the narrow sense when the liquid of the gel has been extensively eliminated at temperatures above the critical temperature and starting from pressures above the critical pressure. On the other hand, if the liquid of the gel is eliminated under subcritical conditions, e.g. during the formation of a liquid-vapor boundary phase, then the resulting gel is often referred to also as a xerogel.
In using the term aerogel in the present application, aerogels are considered in the broad sense, i.e. in the sense of “gel with air as dispersing agent.”
Different processes for the preparation of aerogels by supercritical or subcritical drying are disclosed e.g. in EP-A-0 396 076, WO 92/03378, WO 94/25149. WO 92/20623 and EP-A-0 658 513.
The aerogels obtained by supercritical drying are generally hydrophilic or have only a brief hydrophobicity, whereas aerogels dried under subcritical conditions, are permanently hydrophobic, due to their mode of production (in general, by silylation before drying).
Beyond this, aerogels may basically be classified into inorganic and organic aerogels, with inorganic aerogels known already since 1931 (S. S. Kistler, Nature 1931, 127, 741), whereas organic aerogels prepared from the most varied starting materials, e.g. from melamine formaldehyde, are known only since a few years (R. W. Pekala, J. Mater. Sci. 1989, 24, 3221).
Known in the art are aerogel-containing composite materials which, because of their low thermal conductivity, are used as thermal insulation materials. Such composite materials are disclosed, e.g., in EP-A-0 340 707, EP-A-0 667 370, WO 96/12683, WO 96/15997, WO 96/15998, DE-A-44 30 642 and DE-A-44 30 669.
Furthermore, DE-A 44 30 642, DE-A 44 30 669, WO 96/19607 and German patent application 195 33 564.3 disclose the airborne sound-deadening behavior of aerogel-containing composite materials.
It would be of great advantage to have a material available which, apart from good heat insulation properties, at the same time possesses good structure-borne and/or impact sound-deadening properties.
This applies particularly to insulation jobs in building construction. As an example, mention may be made of impact sound deadening in the floor region. Here, the use of such an insulating material would lead to a reduced insulation thickness and thus to a gain in room height. At constant room height this would reduce the building material requirement and the overall height of a multi-storied building. If, in addition, such an insulating material has a lower density than insulating constructions hitherto used, this fact would have positive effects on overall statics, since the building can, on the whole, be constructed to be lighter. If a system containing such an insulation material can be installed and processed independently of outside weathering and requires little or no drying or curing times, this leads to large savings of time and cost in the construction of the whole building.
Another sphere of application of such insulating materials is insulation between footings, such as e.g. machine bases or bases of buildings or building parts having separate foundations.
OBJECTS OF THE INVENTION
Hence, the object of the present invention was, on the one hand, to provide new materials suitable for the deadening of structure-borne and/or impact sound, which can be prepared in a simple manner and in any desired shape and whose size can be changed at the site where they are used, and, on the other hand to look for new aerogel applications.
SUMMARY OF THE INVENTION
This object is accomplished by the use of aerogel particles for deadening structure-borne or impact sound.
DETAILED DESCRIPTION OF THE INVENTION
In general, the aerogels used are those based on metal oxides which are suitable for the sol-gel technique (C. J. Brinker and G. W. Scherer: Sol-Gel Science 1990, Chapters 2 and 3), such as e.g. Si or Al compounds or those on the basis of organic substances suitable for the sol-gel techniques, such as melamine-formaldehyde condensates (U.S. Pat. No. 5,086,085) or resorcinol-formaldehyde condensates (U.S. Pat. No. 4,873,218). Mixtures of the above-mentioned materials may also be used. Used with preference are aerogels containing Si compounds, and SiO
2
aerogels in particular.
In a particularly preferred embodiment the aerogel particles have permanently hydrophobic surface groups. Suitable groups for permanent hydrophobization are e.g. silyl groups of general formula —Si [R]
n
, where n=1, 2 or 3, and preferably trisubstituted silyl groups where the R radicals, generally independently of one another, are the same or different and are a hydrogen atom or a nonreactive organic linear, branched, cyclic, aromatic or heteroaromatic radical, preferably C
1
-C
18
-alkyl or C
6
-C
14
-aryl, especially preferably C
1
-C
6
-alkyl, cyclohexyl or phenyl, and particularly methyl or ethyl. Especially advantageous for permanent hydrophobization of the aerogel is the use of trimethylsilyl groups. The incorporation of these groups can take place as described e.g. in WO 94/25149 or German patent application 196 48 798.6, or be carried out by gas-phase reaction between the aerogel and e.g. an activated trialkylsilane derivative, such as a chlorotrialkylsilane or a hexaalkyldisilazane (cf. R. Iler, The Chemistry of Silica, Wiley & Sons, 1979). Compared with OH groups the hydrophobic surface groups prepared in this manner extensively reduce the dielectric loss factor and dielectric constant.
Depending on the air humidity, aerogel particles having hydrophilic surface groups can adsorb water, as a result of which the dielectric constant and dielectric loss factor c
Frank Dierk
Schmidt Marc
Schwertfeger Fritz
Cabot Corporation
Frommer & Lawrence & Haug LLP
Nakarani D. S.
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