Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-12-05
2003-07-01
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S031000, C528S032000, C528S039000
Reexamination Certificate
active
06586551
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 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.
In order to prevent the gases released by the gas generator from getting into the passenger compartment, it is important to ensure that the airbag exhibits good and constant impermeability. The elastomer coating must also allow this objective to be achieved, even when deposited in small amounts.
Another constraint which is imposed on the elastomer coating is that of the ageing behaviour, i.e. the retention of the thermal, mechanical and adhesion properties over time. This constraint is all the more acute since the airbags are stored in folded form in motor vehicles, before their eventually life-saving expansion in the event of an accident.
As another criterion, one which is not negligible, it should be noted that the protective coating must not cause problems with regard to the manufacture of the airbag, which is by stitching.
Silicone compositions have easily supplanted chloroprenes in this application since it has turned out that the latter do not satisfactorily meet all the specifications referred to above. Compositions which can be used for airbag applications in motor vehicles are described, in particular, in EP-A-0,533,840 and U.S. Pat. No. 5,296,298.
According to EP-A-0,553,840, these known silicone compositions contain:
(A) a polydiorganosiloxane having at least two alkenyl groups per molecule,
(B) a polyorganohydrogenosiloxane having at least two hydrogen atoms linked to the silicon in each molecule,
(C) a metal catalyst, the metal being of the platinum group,
(D) an adhesion promoter consisting of an epoxy-functional organosilicon compound,
(E) an inorganic filler,
(F) a polyorganosiloxane resin, and
(G) optionally a compound used as a crosslinking inhibitor.
In U.S. Pat. No. 5,296,298, the aforementioned constituents (A) to (E) are again found but it should be noted that the adhesion promoter (D) consists here of the combination of an epoxy-functional organosilicon compound with an alkoxylated silane containing, per molecule, a (meth)acryl or (meth)acryloxy group and, optionally, with an aluminium chelate, while the inorganic filler (E) is given as being optional, although it is used in all the examples, 1 to 20, illustrating the invention.
However, the aforementioned known silicone compositions suffer from the drawback of not adhering sufficiently well to the polyamide fabric of the bag in order to guarantee optimum reliability, so very important with regard to road safety.
It is to the credit of the Applicant Company to have proposed in Document EP-A-0,681,014 a solution which aims to remedy the drawbacks of the prior art. The problematic at the basis of the invention claimed in this other document of the prior art is to obtain a silicone composition which can be applied in particular as an airbag inner coating and which, for this purpose, has the most favourable properties in terms of, in particular, fire and temperature resistance, mechanical properties, ageing behaviour, adhesion and surface uniformity, the adhesion to substrates made of textile material being most particularly desirable. The solution proposed by this invention consists in using:
a silicone coating composition of the type of those which are cold-curing (RTV) consisting of the mixture formed by:
(I) at least one polyorganosiloxane having, per molecule, at least two C
2
-C
6
alkenyl groups linked to the silicon,
(II) at least one polyorganosiloxane having, per molecule, at least two hydrogen atoms linked to the silicon,
(III) a catalytically effective amount of at least one catalyst, composed of at least one metal belonging to the platinum group,
(IV) an adhesion promoter,
(V) optionally a mineral filler,
(VI) optionally at least one crosslinking inhibitor, and
(VII) optionally at least one polyorganosiloxane resin,
in which the adhesion promoter consists exclusively of the at least ternary combination of the following ingredients:
(IV.1) at least one alkoxylated organosilane containing, per molecule, at least one C
2
-C
6
alkenyl group,
(IV.2) at least one organosilicon compound which includes at least one epoxy radical,
(IV.3) at least one metal M chelate and/or one metal alkoxide of general formula: M(OJ)
n
, with n=the valency of M and J=a linear or branched C
1
-C
8
alkyl, M being selected from the group formed by:
Ti, Zr, Ge, Li, Mn, Fe, Al and Mg.
A reinforcing filler such as a pyrogenic silica is always present in the experimental part of Document EP-A-0,681,014.
In some applications, in particular for manufacturing airbags, for reasons of economic competitiveness it is desired to apply very thin layers of silicone. The Applicant Company has found that coating compositions containing a reinforcing filler do not make it possible easily to obtain, using the conventional technique of the doctor-blade type, very low add-on weights of the coating layer such as, for example, those less than the value of about 30 g/m
2
.
One object of the present invention is to propose a novel silicone coating composition which makes it possible to reduce the add-on weight of the coating layer without correspondingly changing the coating technique or the operation of the corresponding machine.
Another object of the present invention is to provide a novel silicone coating composition which makes it possible to obtain coatings whose add-on weight may easily be reduced, as required, down to a value as low as one less than approximately 30 g/m
2
.
Yet another object of the present invention is to provide a novel silicone coating composition which makes it possible to obtain, compared with what happens with filled compositions, according to Document EP-A-0,681,014, having the same add-on weight, properties of the coated substrate, in particular with regard to:
fire and temperature resistance, which are at the very least equivalent,
creasing and abrasion resistance (scrub test), which are improved,
tear strength, which are also improved,
thermal insulation, which are also improved.
These objects, among others, are achieved by the present invention which consists in selecting from all the possibilities offered in Document EP-A-0,681,01
Bohin Fabrice
Pouchelon Alain
Moore Margaret G.
Rhodia Chimie
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