Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which...
Reexamination Certificate
2000-05-23
2003-05-13
Dawson, Robert (Department: 1712)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
C428S368000, C428S391000, C428S036100, C428S036600, C528S015000, C528S031000, C524S783000, C524S785000, C524S862000, C525S478000, C280S728100
Reexamination Certificate
active
06562737
ABSTRACT:
The general field of the invention is that of cold-curing silicone compositions, in particular those of the two-component type (RTV II), which crosslink by hydrosilylation or polyaddition in order to produce a thin-film elastomer. These crosslinked compositions are, among others, suitable as a coating, for example for protection or for mechanical reinforcement, on various substrates made of flexible, in particular textile, material, such as woven, knitted or non-woven fibrous substrates, for example.
Such silicone coatings are generally obtained by coating the substrate, followed by curing, which proceeds by the polyaddition of unsaturated (alkenyl, e.g. Vi—Si) groups of one polyorganosiloxane onto hydrogens of the same or of another polyorganosiloxane.
These silicone compositions have found a major outlet in the coating of flexible—woven, knitted or non-woven—materials used for the manufacture of bags for the individual protection of the occupants of vehicles, also called airbags.
For more details about airbags, reference may be made, in particular, to French Patent FR-A-2,668,106.
The present invention also relates to the application of the silicones, e.g. (RTV II), in the manufacture of such airbags.
Conventionally, the latter are formed from a fabric made of synthetic fibre, for example made of polyamide (Nylon)®, covered on at least one of these sides with a layer of an elastomer of the chloroprene type. The presence of such a protective layer or coating is necessary because of the fact that the gases released by the gas generator (for example: carbon monoxide, NO
x
) in the event of an impact are extremely hot and contain incandescent particles capable of damaging the Nylon® bag. The inner protective layer of elastomer must therefore be particularly resistant to high temperatures and to mechanical stresses. It is also important that this elastomer coating be in the form of a uniform thin film adhering strongly to the substrate made of synthetic fabric which forms the walls of the airbag.
Silicone compositions have easily supplanted chloroprenes in this application since it has turned out that the former better meet the impermeability requirements, even with small amounts deposited, the ageing withstand requirements (preservation of the thermal, mechanical and adhesion properties over time) and compatability with manufacturing the airbag by stitching. Compositions that can be used for a car airbag application are described especially in EP-A-0,533,840 and U.S. Pat. No. 5,296,298, as well as in EP-A-0,681,014 which proposes a formulation having improved adhesion properties.
These formulations also have two types of drawback.
The first is that the elastomer obtained may have quite a tacky feel, which, apart from the disagreeable nature of the feel, may be prejudicial to the mechanical properties and behaviour of the coated substrate. In the field of vehicle airbags, given that the value of the friction coefficient depends in particular on the ability of the bag to be deployed, an improvement would be particularly welcome.
The second is related to the constant search for as low as possible a weight of the coated fabric and for formulations allowing this, while still retaining the properties required by these applications.
The use of hollow microspheres has become widespread in the field of bulk silicone elastomers, such as the elastomers used in the fields of mammary prostheses, seals and gaskets, shock, vibration and sound absorbers, etc.
Thus, EP-A-0,722,989 proposes to increase the erosion resistance of crosslinked organosiloxane compositions used as abrasion seals between moving and stationary elements in motors and compressors, by incorporating a polyaddition composition, a reinforcing system which comprises an organosiloxane resin, finely divided quartz, heat-resistant microspheres, in particular rigid microspheres of the glass-microsphere type, or else microspheres formed from an epoxy or phenolic resin.
EP-A-0,733,672 relates to the field of silicone elastomers obtained from a room-temperature curable polyaddition two-component system generally available to the public in a single delivery device.
The objective is thus to increase the thermal resistance and reduce the cost of the two-component system, this being achieved by incorporating, into the conventional reactive-oil/catalyst composition, a filling filler formed from an elastic microsphere having an inorganic coating, for example of calcium carbonate. The choice of flexible microspheres, which are therefore not liable to be broken during their passage through the mixer of the delivery device, has made it possible to incorporate microspheres in this type of product.
Rigid or elastic microspheres have also been proposed in the field of the coating of textiles or similar substrates. However, they have been so in very special applications not related to the invention, in which the technical problems to be solved were not comparable.
Glass microspheres have thus been proposed for coating, as a thick layer (>3 mm), fabrics in the field of fire resistance. Thus, RU-A-2,039,070 proposes to coat a fabric with a silicone rubber filled with glass microspheres, by applying successive layers of a composition containing from 20 to 79.5% by weight of siloxane elastomer, from 20 to 60% by weight of glass microspheres and from 0.5 to 20% of nitride.
Moreover, patent U.S. Pat. No. 4,495,227 describes silicone compositions intended for coating fabric so as to make them water-impermeable and water-repellent while allowing them to have good air permeability and moisture permeability. These are polycondensation or polyaddition compositions which consists [sic] of reactive oils and of a corresponding catalyst. Added to these compositions are from 1 to 200 parts by weight of a foaming or blowing agent per 100 parts of crosslinkable silicone composition. Various agents have been proposed: heat-decomposable organic blowing agents such as azobisisobutyronitrile, dinitriso [sic] pentamethylene tetramine, azobisformamide; blowing agents of the microcapsule type, such as microcapsules containing a solvent based on a halogenated or non-halogenated hydrocarbon, on ether or on alcohol, for example isobutane, n-hexane, diethyl ether, methyl alcohol, methylene chloride, trichloroethane, in a polyvinylidene chloride resin sphere; or else water or alcohol microcapsules in a silicone resin. The fabric is coated with such a composition, this operation being followed by a preliminary drying step and thee a heating step, so as to crosslink the composition and, at the same time, to generate the foaming.
The objective of the present invention is to make improvements in the field of the coating of textile substrates or the like, in particular for the manufacture of vehicle airbags and most especially for reducing the friction coefficient of the crosslinked silicone elastomer with respect to the support and to allow the coating thickness on the substrate to be increased, without increasing the weight of the coated substrate, all this without prejudicing the other expected properties, or even by improving them, especially:
the fire and temperature resistance,
the creasing and abrasion resistance (scrub test),
the tear strength,
the thermal insulation.
Another objective of the invention is to allow the cost of the coating to be reduced so as to widen the field of use of the silicone coating and thus profit from the advantageous properties of this type of coating in applications hitherto excluded from the field of application for cost reasons.
More specifically, a first subject of the present invention is a coating composition of the type of those which are cold-curing (RTV elastomers, the vulcanization or curing of which can be accelerated when they are heated), characterized in that it comprises, as a mixture:
(1) at least one polyorganosiloxane having, per molecule, at least two C
2
-C
6
alkenyl groups linked to the silicon,
(2) at least one polyorganosiloxane having, per molecule, at least two hydrogen atoms linked to the silicon,
Bohin Fabrice
Dalbe Bernard
Dumont Laurent
Heilmann Jens
Kaiser Uwe
Burns Doane Swecker & Mathis L.L.P.
Dawson Robert
Keehan Christopher M
Rhodia Chimie
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