Coating compositions and textile fabrics coated therewith

Details Coating compositions and textile fabrics coated therewith Coating compositions and textile fabrics coated therewith

2002-02-13

2004-03-23

Robertson, Jeffrey B. (Department: 1712)

Stock material or miscellaneous articles

Composite

Of silicon containing

C427S387000, C524S588000

Reexamination Certificate

active

06709752

ABSTRACT:

The present invention relates to a coating composition for textile fabrics and to textile fabrics coated with such compositions, and in particular to a fabric coated with a silicone-based coating composition capable of maintaining a pressure barrier between two areas with a pressure differential. The invention also relates to a process of preparing such textile fabrics and to airbags made with coated fabrics.
Coating compositions for textile substrates, which provide a flexible coat on the fabric, e.g. to decrease permeability of the fabric or to improve thermal protection of the fabric are well known in the art, and are described in many patent specifications, such as those referred to below. The present invention is particularly concerned with coating compositions which give a silicone-based elastomeric finish. It is traditionally required to use an adhesion promoter in such compositions to ensure good adhesion to the fabric and to maintain a good shelf life of the coated textile fabric.
EP 553840 describes a liquid silicone rubber coating composition for application to airbags in automobiles, which comprises a polydiorganosiloxane having alkenyl groups, an polyorganosiloxane resin, an inorganic filler, a certain polyorganohydrosiloxane, a platinum group metal catalyst and an epoxy group-containing organosilicon compound. EP 646672 describes a fabric for airbags impregnated with a silicone composition comprising a linear polyorganosiloxane having aliphatic unsaturation, a certain polyorganohydrosiloxane, a catalyst promoting addition reaction, a hydrophobic silica, a flame retardant and optionally an adhesion promoting agent.
While fabrics coated with such compositions may be satisfactory for airbag applications, they do not satisfy requirements where pressurised fluids are to be retained in a fabric envelope for a relatively long period. This requirement exists for example in the application of such coatings to side curtain airbags for the automotive industry. These side curtain airbags are intended to inflate at the time of impact, as do conventional airbags. The side curtains unfold to form a cushioned curtain between passengers and some of the side of the car body, e.g., the windows. As the intention is not merely to cushion the blow on impact itself, as is the case for conventional driver and passenger airbags, but e.g. to protect passengers when a car is rolling, it is important that the side curtain air bag is sufficiently pressurised during such rolling process. Where conventional driver and passenger airbags only need to retain pressure for a fraction of a second, it is desirable that side curtain airbags maintain a suitable pressure for a few seconds. Similar applications exist where a pressurised fabric structure is desired to maintain a certain fluid pressure for a relatively extended period of time, e.g. in emergency chutes for aeroplanes, inflatable rafts etc.
EP 886164 describes a coated fabric comprising a textile fabric coated with at least two layers of an polyorganosiloxane-based elastomeric material, characterised in that the first layer is coated onto the fabric and has an elongation-at-break of at least 400% and in that the second layer has a tear-strength of at least 30 kN/m. However the application of 2 coats onto a fabric substrate causes additional work and cost to the manufacturing process and may provide a final coating of fairly high coat weight. There is a need to provide coatings which will perform well in the side curtain applications, but which require only a single coat and still provide good performance, preferably at lower coat weight.
According to a first aspect of the invention, there is provided a coating composition for textile fabrics, which is curable to an elastomeric finish, which comprises a first, second and third organopolysiloxane having aliphatically unsaturated hydrocarbon or hydrocarbonoxy substituents, an organosilicon crosslinker having at least 3 silicon-bonded hydrogen atoms, a catalyst able to promote the reaction of the aliphacally unsaturated hydrocarbon or hydrocarbonoxy substituents with Si—H groups and a reinforcing filler, wherein the first and second a organopolysiloxanes have aliphatically unsaturated hydrocarbon or hydrocarbonoxy substituents only at the terminal siloxane units, the first organopolysiloxane having a viscosity at 25° C. of from 50 to 650 mm
2
/s, the second organopolysiloxane having a viscosity at 25° C. of at least 10,000 mm
2
/s and wherein the third organopolysiloxane has aliphatically unsaturated hydrocarbon or hydrocarbonoxy substituents at terminal siloxane units and on siloxane units in the siloxane polymer chain.
We have found surprisingly that such coating compositions do not need any adhesion promoters to ensure good adhesion to textile fabrics. We have also found that fabrics coated according to the present invention are beneficial in standard airbags and other inflatable safety restraint devices.
The coating composition comprises organopolysiloxanes which are able to cure to an elastomeric finish via an addition reaction. Useful organopolysiloxanes comprise units of the general formula R
a
R′
b
SiO
4-a-b/2
(I), wherein R is a monovalent hydrocarbon group having up to 18 carbon atoms, R′ is a monovalent hydrocarbon or hydrocarbonoxy group having aliphatic unsaturation,
a
and
b
have a value of from 0 to 3, the sum of
a+b
being no more than 3, provided the conditions outlined above for the organopolysiloxane materials are complied with.
Preferably the first and second organosiloxane polymers are of a generally linear nature having the general structure (II)
wherein R and R′ have the same meaning as above, and wherein x is an integer to allow the organopolysiloxane to fulfill the requirements for the viscosity range, mentioned above, for example a value of up to 300, preferably from 75 to 250, more preferably 100 to 200 for the first organopolysiloxane and having a value of at least 300, preferably from 400 to 1000, more preferably 450 to 1000 for the second organopolysiloxane. It is particularly preferred that R denotes an alkyl or aryl group having from 1 to 8 carbon atoms, e.g. methyl, ethyl, propyl, isobutyl, hexyl, phenyl or octyl. More preferably at least 50% of all R groups are methyl groups, most preferably substantially all R groups are methyl groups. R′ is an aliphatically unsaturated hydrocarbon or hydrocarbonoxy group, preferably a hydrocarbon group having from 2 to 22 carbon atoms, more preferably 2 to 8 carbon atoms, most preferably 2 or 6 carbon atoms. It is particularly preferred that the aliphatically unsaturated group is an alkenyl group, although alkynyl groups may also be used. Particularly useful are vinyl, allyl and hexenyl groups, most preferably having terminal unsaturation. It is most preferred that first organopolysiloxane is an &agr;,&ohgr;-vinyldimethylsiloxy polydimethylsiloxane polymer having a viscosity of from 50 to 650 mm
2
/s at 25° C., more preferably 100 to 600 mm
2
/s, most preferably 300 to 600 mm
2
/s. It is also most preferred that second organopolysiloxane is an &agr;,&ohgr;-vinyldimethylsiloxy polydimethylsiloxane polymer having a viscosity of from 10,000 to 90,000 mm
2
/s at 25° C., more preferably 20,000 to 80,000 mm
2
/s, most preferably 40,000 to 70,000 mm
2
/s.
Preferably the third organosiloxane polymer is also of a generally linear nature having the general structure (III)
wherein R and R′ have the same meaning as above, and wherein y is zero or an integer and z has a value of at least 1. The value of y+z is no more than 300, preferably from 100 to 200, more preferably from 120 to 180. The value of z is preferably at least 2, more preferably from 2 to 20, most preferably 2 to 5. It is most preferred that third organopolysiloxane is an &agr;,&ohgr;-vinyldimethylsiloxy polydimethylsiloxane polymethylvinylsiloxy co-polymer having a viscosity of from 50 to 650 mm
2
/s at 25° C., more preferably 100 to 600 mm
2
/s, most preferably 300 to 600 mm
2
/s.
The relative amounts of first second and thir

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