Field of the invention

[0001] The present invention relates to finished woven fabrics comprising spun synthetic polyamide yarn which are suitable as improved airbag fabrics, and a method of making said fabrics.

Background to the invention

[0002] Inflatable airbags are a key component of vehicle safety systems and are installed in virtually every vehicle produced globally. Typically, inflatable airbags are made from woven fabric of nylon or polyester yarns. To meet the requirements for effective inflation, airbag fabric must meet certain tensile strength requirements and have the ability to resist the passage of air, and it is therefore desirable for airbags to have a very low air permeability. As used herein, “airbag” means inflatable passive safety restraints for automobiles and many other forms of transportation, including aviation applications.

[0003] Fabrics comprising layers or coatings to reduce air permeability are commonly employed in airbags. Such prior art woven fabrics containing additional layers or coatings are referred to herein as “coated woven fabrics”, and take the form of any coating, web, net, laminate or film, used to impart a reduction in air permeability. US-5,897,929 describes a polyester or polyamide fabric coated with a porosity-blocking layer of polyamide material. US-5,110,666 describes a fabric substrate that may be coated with a polycarbonate-polyether polyurethane which provides certain permeability, flexibility, toughness, and thermal resistance benefits. US-5,076,975 describes a molding operation for forming an elastomer-coated fabric having a defined shape. US- 5,763,330 describes a method for extrusion coating a polyethylene resin onto a nylon fabric. The woven fabrics from which airbags are traditionally manufactured may also be coated with elastic materials, notably silicone-based coatings such as polydimethylsiloxane (PDMS), rubber coatings such as polychloroprene, or polyurethanes, to manage the air permeability of the fabric. Examples of webs, nets and films include polyurethane, polyacrylate, polyamide, polyester, polyolefins, polyolefin elastomers and blends and copolymers thereof. However, the coatings are expensive, thereby increasing the cost of the airbag. Moreover, coatings at the levels conventionally required to impart a significant reduction of air permeability increase the fabric thickness and/or hinder the foldability of these fabrics, which is a necessary characteristic for airbags. As a result, the airbag modules in which such fabrics are contained are relatively large.

[0004] In recent years, the number of airbags, and the area of coverage for these airbags within various types of vehicular cabins has increased. Multiple air bag configurations in use include airbags for the front seating area, for side impact protection, for rear seat use, for use in headliner area inflatable curtains, and for use in inflatable seat belts or pedestrian airbags. There is a continuing automotive trend towards smaller and lighter vehicles, meaning that less space is available for mandatory safety items such as airbags. It is an object of automobile manufacturers to improve crash impact safety systems in general, and particularly airbag modules, in terms of safety, environmental footprint and cost.

[0005] Reduction of airbag module weight per unit area of deployable airbag generally enables total weight reduction without safety compromise. This has become even more important as the number of airbags per vehicle has risen sharply to provide passenger protection at multiple angles. Airbag modules are therefore required to be more efficient in both size and weight.

[0006] Reduction of airbag inflator size also enables total weight reduction and increased cost savings. To ensure equal efficacy, the smaller inflators are hotter than historical counterparts. [0007] The trend in the airbag module industry is towards thinner, lighter fabrics used with smaller, hotter inflators. However, this more aggressive design has resulted in experienced events where hot particles and/or hot gases from airbag deployment discharges have penetrated airbag fabrics, injuring vehicle passengers and resulting in the recall of millions of modules. Protection from hot particle penetration and release of hot gases, collectively referred to herein as fabric pinhole failures, becomes increasingly important as the number of airbags per vehicle and their relative proximity to the passenger increases in the effort to improve vehicle safety. Potential solutions to pinhole failures include selecting fabric materials with higher latent heat of melting, increasing fabric weights and applying coating chemistries.

[0008] There remains a need for improved fabrics which are suitable for use in modern airbag modules.

[0009] It is an object of this invention to provide airbag fabrics which have a greater resistance to pinhole failure, in order to maintain gains in airbag module weight reduction and improved cost efficiency. Thus, it is a particular object of this invention to provide airbag fabrics which have a greater resistance to pinhole failure and which are also relatively thinner and lighter than conventional airbag fabrics, but without significant detriment to the air permeability performance.

Summary of the invention

[00010] According to a first aspect of the present invention, there is provided the use of a woven fabric to improve the resistance to pinhole failure of an airbag made therefrom, wherein said woven fabric comprises spun synthetic polyamide yarn, wherein on one or both sides of the woven fabric there is disposed a coating layer having a coat-weight of no more than 12 g/m ² , and wherein the bulk density of the coated fabric is greater than 850 kg/m ³ .

[00011] According to a second aspect of the present invention, there is provided a method of improving the resistance to pinhole failure of an airbag, said method comprising the steps of (i) providing a woven fabric comprising spun synthetic polyamide yarn wherein said fabric is made from polyamide yarn woven in the warp direction and weft direction, (ii) subjecting said woven fabric to a High Temperature-High Pressure (HTHP) treatment, preferably wherein said HTHP treatment is calendering, (iii) disposing on one or both sides of the woven fabric a coating to provide a coating layer having a dry coat-weight of no more than 12 g/m ² ; and (iv) constructing the airbag from said HTHP-treated woven fabric, wherein the coated HTHP-treated woven fabric exhibits a bulk density of greater than 850 kg/m ³ .

[00012] According to a third aspect of the present invention, there is provided a woven fabric comprising spun synthetic polyamide yarn, wherein on one or both sides of the woven fabric there is disposed a coating layer having a coat-weight of no more than 12 g/m ² wherein no intervening layer or material is disposed between the surface of the woven fabric and said coating, wherein the bulk density of the coated woven fabric is greater than 850 kg/m ³ .

[00013] According to a fourth aspect of the present invention, there is provided a method of making a woven fabric comprising the steps of (i) weaving a spun synthetic polyamide yarn and (ii) subjecting the resulting woven fabric to a High Temperature-High Pressure (HTHP) treatment, (iii) disposing on one or both sides of the HTHP-treated woven fabric a coating to provide a coating layer having a dry coat-weight of no more than 12 g/m ² , wherein no intervening layer or material is disposed between said HTHP-treated woven fabric and said coating, wherein the coated HTHP- treated woven fabric exhibits a bulk density of greater than 850 kg/m ³ .

[00014] Advantageously, the total thickness of the coated woven fabric is no more than 0.28 mm, the coated woven fabric exhibits a thermal resistance constant (Y) at 450°C in the range of from 0.55 to 3.00, and the coated woven fabric exhibits a static air permeability (SAP) of no more than 0.2 l/dm ² /min. Advantageously, the surface of the woven fabric on which the coating is disposed exhibits a surface roughness S _a which is no more than 30.00, preferably no more than 27.00, preferably no more than 25.00, preferably no more than 23.00 pm. As described hereinbelow, the coating is advantageously a continuous coating.

[00015] Preferably, said woven fabric is made from polyamide yarns of a single polymer type and titer woven in both the warp direction and weft direction. [00016] The woven fabric exhibits an improved melt-through resistance, measured as defined herein. The woven fabric preferably exhibits a melt-through resistance at 450°C of least 2.00 seconds, preferably at least 2.10 seconds, preferably at least 2.20 seconds, preferably at least 2.30 seconds, preferably at least 2.40 seconds, preferably at least 2.50 seconds, preferably at least 2.60 seconds, preferably at least 2.70 seconds. The inventors have found that the melt-through resistance of a fabric is predictive of the likelihood of pinhole failures in a full airbag module deployment test. Melt-through resistance improves with fabric weight, where heavier weight fabrics provide higher melt-through resistance, and also varies as a function of fabric thickness.

[00017] The inventors have also found that the thermal resistance constant (X) of the fabric, measured as defined herein, is particularly predictive of the likelihood of pinhole failures in a full airbag module deployment test. The woven fabric of the invention should exhibit a thermal resistance constant (X) at 450°C of at least 7.5, preferably at least 8.0, preferably at least 8.5, preferably no more than 12.0, preferably no more than 11.0, typically no more than 10.5 and typically no more than 10.0, and preferably in the range of from 7.5 to 12.0, preferably from 8.0 to 11 .0, preferably from 8.5 to 11 .0, preferably 8.5 to 11 .0, preferably 8.5 to 10.5 “C.s.mnr ¹ . The woven fabric of the present invention should exhibit a thermal resistance constant (X) at 650°C of at least 4.0, preferably at least 4.5, preferably at least 5.0, preferably no more than 8.0, preferably no more than 7.5, typically no more than 7.0, and preferably in the range of from 4.0 to 8.0, preferably from 4.5 to 8.0, preferably from 5.0 to 8.0°C.s.mnr ¹ .

[00018] The inventors have also found that the coating-weighted thermal resistance constant (Y) of the fabric, measured as defined herein, is predictive of the likelihood of pinhole failures. The woven fabric of the invention should exhibit a coating-weighted thermal resistance constant (Y) at 450°C in the range of from 0.55 to 3.00, preferably at least 0.80, preferably at least 0.90, preferably at least 1 .00, preferably no more than 2.50, typically no more than 2.00, and preferably from 0.80 to 3.00, preferably from 0.90 to 2.50 °C.s/mm fabric thickness/gm ² coat-weight. The woven fabric of the present invention should exhibit a coating-weighted thermal resistance constant (Y) at 650°C in the range of from 0.35 to 3.00, preferably at least 0.50, preferably at least 0.80, preferably at least 0.90, preferably no more than 2.50, and typically no more than 2.00, and preferably from 0.50 to 3.00, preferably from 0.90 to 2.50 °C.s/mm fabric thickness/gm ² coat-weight.

[00019] Such fabrics show improved resistance to hot particulate penetration through the airbag during deployment in the new, more effective airbag module designs.

Detailed description of the invention [00020] The woven fabrics of the present invention are composed of high tenacity spun synthetic polyamide yarns. The yarns are made from fibers which are in the form of continuous filaments. Such filaments are formed by extrusion of molten polymer through spinnerets at high temperatures and pressures, and subsequently quenched in air, coated with spin finish lubricant, drawn between pairs of godets, lightly textured to provide enough entanglement to make a coherent yarn, and then wound up on cardboard tubes, as bobbins.

[00021] The spin finish on the filaments facilitates the processing of yarn during its production and may be subsequently removed to provide the finished woven fabric, depending on the requirements of subsequent processing. Removal of the spin finish may be effected prior to, during or after weaving (preferably during or after weaving), according to conventional techniques well- known in the art.

[00022] In the woven fabrics of the present invention, at least a majority (and preferably all) of the yarn used in the warp direction of fabric is preferably formed from synthetic fibre made from a single polyamide composition. Similarly, at least a majority (and preferably all) of the yarn used in the weft direction of fabric is preferably formed from synthetic fibre made from a single polyamide composition. In a preferred but non-limiting embodiment, at least a majority (and preferably all) of the yarn used in the warp direction and weft direction of fabric is formed from synthetic fibre formed from a single polyamide composition. Preferably a single polyamide is used in each of the warp and weft directions and preferably the same polyamide is used in both the warp and weft directions. [00023] Suitable polyamide fibers are preferably selected from those formed from nylon 6,6, nylon 6, nylon 6,12, nylon 7, nylon 12, nylon 4,6 or copolymers or blends thereof. In a preferred but non-limiting embodiment, the polyamide is nylon 6,6.

[00024] In this invention, the viscosity of the polyamide is measured as relative viscosity (RV), and defined as the formic acid relative viscosity, which is measured at two stages during manufacture of the woven fabric. The first RV measurement is taken immediately after extrusion of a polyamide fiber from the spinneret, and before any application of spin finish and before drawing, and this measurement is referred to as the “fiber RV”. The second RV measurement is taken from polyamide yarn in the finished fabric, and this measurement is referred to herein as the “fabric RV”. The inventors have observed that the RV of the polyamide reduces significantly during manufacture of the fabric, primarily as a result of drawing the extruded fiber during the subsequent spinning process. The fabric RV is therefore significantly lower than the fiber RV.

[00025] The fiber RV in this invention is at least 66, preferably at least 68, preferably at least 70, preferably at least 75, preferably at least 78, preferably at least 80, preferably at least 85, preferably at least 90, and typically no more than 150, typically no more than 110, typically no more than 100, typically no more than 95. Preferably, the fiber RV is in the range of from 68 to 150, preferably from 70 to 110, preferably from 75 to 110, preferably from 78 to 110, preferably from 85 to 100.

[00026] The inventors observed no evident relationship between melt-through resistance and the melting point of the polyamide in either the base yarn or the fabric. Thus, the positive correlation observed by the inventors between melt-though resistance and relative viscosity is surprising given that the melting point of the higher-RV polyamide yarn is effectively indistinguishable from the melting point of a corresponding lower-RV polyamide yarn over the relevant relative viscosity range.

[00027] Polyamide yarns which exhibit such values for the fiber RV may be prepared by means conventional in the art. For instance, relative viscosity may be increased by increasing the degree of polymerization, i.e. the molecular weight, of the polyamide as is known in the art. For instance, the molecular weight and relative viscosity may be increased by a solid state polymerization step, typically conducted under dry nitrogen at elevated temperature (for instance about 180°C).

[00028] In the woven fabrics of the present invention, at least a majority (and preferably all) of the yarn in the warp direction is yarn having a tenacity from 6.0 to 9.0 cN/dtex. Similarly, at least a majority (and preferably all) of the yarn in the weft direction is yarn having a tenacity from 6.0 to 9.0 cN/dtex. In a preferred but non-limiting embodiment, at least a majority (and preferably all) of the yarn in the warp and weft directions is yarn having a tenacity from 6.0 to 9.0 cN/dtex.

[00029] The yarn used in the present invention preferably has a linear mass density in the range from about 100 to about 2000 decitex, preferably from about 150 to about 1000 decitex, preferably from about 150 to about 940 decitex, preferably from about 150 to about 750 decitex, preferably in the range of greater than 250 to about 750 decitex, preferably from about 300 to about 750 decitex, preferably from about 350 to about 750 decitex.

[00030] The linear mass density of fiber which constitutes the yarn is preferably in the range from about 1 to about 25 decitex per filament (DPF), or from about 2 to about 12 decitex per filament (DPF).

[00031] The woven fabric of the present invention is preferably made from yarn having from 90 to 300 ends/dm, preferably from 160 to 240 ends/dm, preferably at least 180 ends/dm, preferably at least 190 ends/dm, and preferably from 180 to 220 ends/dm. Preferably, the woven fabric exhibits a symmetrical construction. Thus, the ends/dm of the warp yarn is preferably the same as the ends/dm of the weft yarn.

[00032] The woven fabric of the present invention may be formed from warp and weft yarns using weaving techniques known in the art. Suitable weaving techniques include, but are not limited to a plain weave, twill weave, satin weave, modified weaves of these types, or a multi-axial weave. Suitable looms that can be used for weaving include a waterjet loom, airjet loom or rapier loom, and preferably the loom is a waterjet loom. The fabrics may be finished according to any methods known in the art, including drying on loom, scouring, can drying and heat setting. Preferably, the woven fabric of the present invention is a waterjet woven fabric which is dried on loom, or dried by a separate process. In waterjet weaving, the dissolution of spin finish in water, and the rubbing of yarns against one another and the heddles and reed of the loom, causes removal of the spin finish lubricant from the yarn.

[00033] The woven fabric of the present invention is manufactured by subjecting a woven fabric to elevated temperature and pressure (referred to herein as High Temperature-High Pressure (HTHP) treatment).

[00034] The HTHP treatment step has been disclosed in WO-2017/079499-A and WO- 2018/204154-A, the disclosure of which HTHP treatment step is incorporated herein by reference.

In these methods, a woven fabric having a top surface and a bottom surface is treated in order to permanently modify the cross-section and fuse at least a portion of the fibers in the yarn on the top surface or at least a portion of the fibers in the yarn on the bottom surface, and preferably at least a portion of the fibers in the yarn on each of the top and bottom surfaces. In a preferred embodiment, the woven fabric is treated in order to permanently modify the cross-section and fuse at least a majority of the fibers in the yarn on the top surface or at least a majority of the fibers in the yarn on the bottom surface, and preferably a majority of the fibers in the yarn on each of the top and bottom surfaces.

[00035] The HTHP treatment of the woven fabric is effected at a temperature sufficient to permanently modify the cross-section and fuse at least a portion of the fibers in the yarn. In one embodiment, the temperature used is above the softening temperature of the yarn. Preferably, HTHP treatment is conducted at temperatures in the range of from about 130°C to about 240°C, preferably in the range of from about 220°C to about 240°C. In particular, fabrics formed from nylon 6,6 yarn are suitably HTHP-treated at temperatures in the range of from about 220°C to about 240°C. Preferably, the fabrics are HTHP-treated at high pressures in the range of from about 28Mpa to about 115MPa, preferably in the range of from about 35 to about 70 MPa, preferably in the range of from about 50 to about 65 MPa, typically at about 57 MPa. The pressure is calculated from the total applied force on the area of fabric at the calender nip point. Preferably, the fabrics are HTHP-treated at a line speed in the range of from about 5 to about 80 m/min, preferably from about 5 to about 70 m/min, preferably from about 5 to about 50 m/min, and preferably at least 10 m/min. HTHP treatment may be effected by any method known in the art to apply temperatures and pressures to a woven fabric, and suitable to permanently modify the cross-section and fuse at least a portion of the fibers in the yarn. In a preferred embodiment, the HTHP treatment is or comprises a calendering step, preferably hot-roll calendering.

[00036] In a preferred embodiment, the HTHP treatment is conducted in the presence of a heat transfer fluid, for instance as taught in WO-2018/204154-A, the disclosure of which process is incorporated herein by reference. The heat transfer fluid may be a liquid or a vapour, which may be added during the HTHP treatment step or in added in a prior step of the fabric production process and retained by the yarn. In one non-limiting embodiment, the presence of a heat transfer fluid results from the carry-over of residual moisture introduced by weaving with a water jet loom, or from a washing or scouring process, or from a dyeing process. Preferably, the heat transfer fluid is or comprises water, or is predominantly water. Where the heat transfer fluid is a vapour, it may be or predominantly be or comprise steam. The heat transfer fluid may be applied by a bath, or by a foulard liquid application system or by a liquid spray system or by a vapor phase application system. The heat transfer fluid should be inert or benign so as not to damage the fabric, and may be any liquid or vapor fitting that description. Preferably, the heat transfer fluid is present in an amount of from 5 to 30, preferably from 10 to 20, preferably from 12 to 18 wt%, based on the weight of the dry fabric. The use of a heat transfer fluid allows a reduction in the temperature and/or pressure (particularly temperature) used in the HTHP process, relative to a process in which a heat-transfer fluid is not used. Thus, in this embodiment the HTHP treatment may be conducted at a temperature in the range of 100 to 240°C, preferably in the range of 150 to 210°C, preferably in the range of 150 to 190°C, and a pressure in the range of from 28 to 115 MPa, preferably in the range of from 35 to 70 MPa, preferably in the range of from about 40 to about 65 MPa, or in the range of from 40 to 55 MPa. In one embodiment the temperature is below the dry softening temperature of the yarn. Alternatively, the use of a heat transfer fluid allows an increase in the production speed of the HTHP treatment, relative to a process in which a heat-transfer fluid is not used, without detriment to the reduction in the permeability of the resultant fabric.

[00037] The term “permanently modified cross-section”, as used herein and as illustrated in WO-2017/079499-A (the disclosures of which illustrations are incorporated herein by reference), refers to a fiber cross-section that is a modified or compressed version of the cross-section of the majority of the fiber present in the fabric. The fiber may have any cross-section known in the art, including but not limited to circular, multi-lobal, tri-lobal, hexa-lobal or rectangular. In a preferred but non-limiting embodiment, the fiber has a circular cross-section (i.e. prior to HTHP-treatment). In a preferred but non-limiting embodiment, the permanently modified cross-section results in at least a portion of the fiber being substantially flat. [00038] Thus, a portion of the fibers in the treated fabric suitably exhibit an aspect ratio of from about 1.2:1 to about 10:1. As used herein, an aspect ratio of 1 :1 describes a fiber cross section with a common radius from its centre to its outer surface; i.e. a fiber with a circular cross section has an aspect ratio of 1 :1. In the HTHP-treated woven fabrics of the present invention, fibers on the surface of the woven fabric exhibit have a flattened cross section in at least 1 dimension and so have an aspect ratio of at least 1.2:1.

[00039] The term “permanent” or “permanently”, as used herein, means that the modified cross- section does not revert to its original shape, as exemplified by the age testing in WO-2017/079499- A (the disclosures of which age-testing are incorporated herein by reference).

[00040] The woven fabric resulting from the HTHP treatment exhibits fibers which have a permanently modified cross-section and which are fused together so that air permeability and porosity of the fabric is reduced when compared to woven fabrics formed from the same synthetic fibers without such HTHP treatment, while maintaining good packing performance, high tensile strength of the fabric, low fabric weight and low cost.

[00041] The HTHP treatment (preferably) calendering increases the fabric density but does not measurably increase RV. Nor does it change the observed melt point of the woven fabric. Surprisingly, however, calendering is observed to improve the melt-through resistance of the fabric. Thus, the present invention provides a woven fabric which exhibits desirably low air permeability and high resistance to pinhole failures for a desirably low fabric weight by the application of a calendering process to a woven fabric comprising high RV yarn.

[00042] The calendered woven fabrics disclosed herein exhibit both improved melt-through resistance and very low air permeability and are characterized by a combination of features. [00043] In particular, the woven fabric exhibits a bulk density of at least 850 kg/m ³ , preferably at least 875 kg/m ³ , preferably at least 900 kg/m ³ , preferably at least 925 kg/m ³ , preferably at least 950 kg/m ³ , preferably at least 975 kg/m ³ . Preferably, the density is no more than 1200 kg/m ³ , preferably no more than 1100 kg/m ³ , typically no more than 1000 kg/m ³ . References to the bulk density of the fabric in this invention are to the bulk density of the coated, HTHP-treated woven fabric.

[00044] The RV of the polyamide in the woven fabric (referred to herein as the “fabric RV”) of the present invention, i.e. the HTHP-treated woven fabric, is preferably at least 60, preferably at least 65, preferably at least 70, preferably at least 75, preferably at least 78, preferably at least 80, preferably at least 85, preferably at least 90, and typically no more than 150, typically no more than 110, typically no more than 100. Preferably, the fabric RV is in the range of from 75 to 110, preferably from 78 to 110, preferably from 85 to 100. [00045] The inventors have observed that increased polymer viscosity and bulk density together provide improved melt-through resistance and a higher thermal resistance constant. The inventors have found that the RV density factor, measured as defined herein, is predictive of the likelihood of pinhole failures in a full airbag module deployment test. An RV density factor is defined herein using each of the two measurements for relative viscosity, to provide a “fiber RV density factor” and a “fabric RV density factor”.

[00046] Preferably, the fiber relative viscosity (RV) density factor is at least 62,500, preferably at least 63,000, more preferably at least 65,000, preferably at least 67,000, preferably at least 70,000, preferably at least 75,000, preferably at least 80,000, preferably at least 85,000, and preferably not more than 100,000, preferably not more than 95,000, preferably not more than 92,000, and preferably in the range of 63,000 to 100,000, more preferably 65,000 to 95,000 and more preferably 67,000 to 92,000.

[00047] Preferably, the fabric relative viscosity (RV) density factor is at least 55,000, preferably at least 58,000, preferably at least 60,000, preferably at least 65,000, preferably at least 70,000, preferably at least 75,000, preferably at least 80,000, preferably no more than 95,000, preferably no more than 90,000, and preferably no more than 88,000, and preferably in the range of 55,000 to 95,000, preferably from 58,000 to 90,000, preferably from 60,000 to 88,000.

[00048] The HTHP-treated woven fabrics described herein exhibit an advantageous combination of high density and a flat surface, which enables the subsequent application of a coherent and continuous coating layer at a very low coat-weight to the HTHP-treated woven fabric. The term “flat surface” means that the HTHP-woven fabric should preferably exhibit a surface roughness S _a which is no more than 30.00, preferably no more than 27.00, preferably no more than 25.00, preferably no more than 23.00 pm as measured by ISO 25178-2:2012. The S _a parameter is defined as the mean of the absolute values of the surface departure above and below the mean plane of the surface, as is well-known in the art. A surface defined by the afore-mentioned S _a values is surprisingly effective in combination with the high density of the woven fabric to provide very low air permeability and excellent melt-through resistance in a relatively thin and lightweight fabric as described herein.

[00049] The woven fabric exhibits said coating layer on one or both sides of the fabric, preferably only one side of the fabric. Where the coating is present on only one side of the woven fabric, the coating is preferably present on the side which forms an internal surface of the airbag made from said fabric. [00050] Any suitable technique may be used to apply the coating layer, including gravure coating, immersion, knife-over-roll coating, curtain coating, knife over air coating, reverse roll, rotary screen, transfer, extrusion, hot melt, lamination, impregnation and metering rod.

[00051] The coating layer may be any coating layer suitable for reducing air permeability on polyamide woven fabrics in airbags, and several such materials are known in the art. Suitably the coating layer is an elastic material. Of particular utility are elastomeric polymers. Thus, the coating layer may be selected from, for instance, silicone coatings (i.e. polysiloxanes, including PDMS or PDMS-based materials), rubber coatings such as polychloroprene, and polyurethanes.

[00052] Silicones are particularly preferred, and in particular elastomeric polysiloxanes. The silicone is preferably water-dispersible. The silicone is preferably thermally curable. Silicones suitable for coating woven fabrics in the manufacture of airbags are well known in the art.

[00053] The woven fabric of the present invention is characterized by a coating layer which is present in an amount of from 1 .0 to 12.0, preferably from 1 .0 to 10.0, preferably from 4.0 to 10.0, preferably from 4.0 to less than 10.0, preferably from 4.5 to 9.5 g/m ² . As used herein, the amounts of coating refer to the dry weight of the coating layer in the finished fabric. Thus, the woven fabrics of the present invention contain a lightweight coating, which advantageously reduces the overall weight and bulk of the fabric, reduces the material cost, and minimizes the environmental impact via polymer recycling. The inventors have surprisingly found that the coated HTHP-treated woven fabrics described herein exhibit excellent resistance to pinhole failures, even with such a lightweight coating, while maintaining very low air permeability.

[00054] Advantageously, the coating of the coated woven fabrics disclosed herein is a continuous coating. The coating is suitably disposed over the whole surface area of a side of the woven fabric. As used herein, a continuous coating means that the coating is in the form of a coherent film across the surface of the woven fabric. The coating suitably fills the interstices of the woven fabric.

[00055] The coating is disposed directly on the HTHP-treated woven fabric, i.e. the coating is in direct contact with the woven fabric. Thus, the coating is in direct contact with the woven fabric across the whole surface area of the side of the woven fabric to which the coating is applied. In particular, the coated woven fabrics disclosed herein do not comprise an intervening layer disposed on the whole or part of the HTHP-treated woven fabric between the surface of the woven fabric and said coating. As used herein, the term “intervening layer” means a material that is present across all or part of the surface of the woven fabric between the woven fabric and the overlying coating layer. The term “intervening layer” encompasses, for instance, a sealant material (such as a hot melt sealant material)) disposed on the whole or part of the surface of the woven fabric. [00056] The coated woven fabrics disclosed herein preferably exhibit a total fabric weight of from 50 to 500 g/m ² , preferably no more than 300 g/m ² , preferably no more than 260 g/m ² , preferably no more than 225 g/m ² , and preferably at least about 80 g/m ² , preferably at least about 100 g/m ² , preferably at least about 125 g/m ² , preferably at least about 150 g/m ² , and typically at least 170 g/m ² . In a preferred embodiment, the woven fabrics of the present invention exhibit a total fabric weight of from 125 to 260 g/m ² , preferably from 150 to 260 g/m ² , preferably from 170 to 235 g/m ² , preferably from 170 to 220 g/m ² .

[00057] The total thickness of the coated woven fabrics disclosed herein is preferably no more than 0.28, preferably no more than 0.27 mm, preferably no more than 0.26 mm, preferably no more than 0.25 mm, preferably no more than 0.24mm, preferably no more than 0.23 mm, preferably no more than 0.22 mm, and typically at least 0.18 mm.

[00058] The coated woven fabric disclosed herein preferably exhibits a static air permeability (SAP) of no more than 0.5, preferably no more than 0.3, preferably no more than 0.2, preferably no more than 0.1 l/dm ² /min. The SAP referred to herein is the SAP of the fabric in its unaged state. [00059] The coated woven fabric disclosed herein preferably exhibits a dynamic air permeability (DAP) of no more than 200, preferably no more than 150, preferably no more than 100 mm/s. The DAP referred to herein is the DAP of the fabric in its unaged state.

[00060] Preferably, the tear strength of the coated woven fabric in both the warp and weft directions is at least 120 N, preferably at least 150 N, preferably at least 170 N when the fabric is unaged.

[00061] The coated woven fabric exhibits elevated tensile strength in each and preferably both of the warp and weft directions, preferably at least 1000N, preferably at least 1500N, preferably at least 2000N, preferably at least 2500N, preferably at least 3000N.

[00062] In a particularly preferred embodiment, the woven fabric described herein is a woven fabric comprising spun synthetic polyamide yarn, wherein on one or both sides of the woven fabric there is disposed a continuous coating layer having a coat-weight of no more than 12 g/m ² wherein no intervening layer or material is disposed between the surface of the woven fabric and said coating, wherein the bulk density of the coated woven fabric is greater than 850 kg/m ³ , wherein the total thickness of the coated woven fabric is no more than 0.28 mm, and the coated woven fabric exhibits a static air permeability (SAP) of no more than 0.2 l/dm ² /min. The coated woven fabric should exhibit a thermal resistance constant (Y) at 450°C in the range of from 0.55 to 3.00. The surface of the woven fabric on which the coating is disposed should exhibit a surface roughness S _a which is no more than 30.00, preferably no more than 27.00, preferably no more than 25.00, preferably no more than 23.00 pm.

[00063] In a fifth aspect, the present invention further provides an article made from the woven fabric described herein, or made from the woven fabric produced by the process described herein, wherein the article is selected from an airbag, sailcloth, inflatable slides, temporary shelters, tents, ducts, coverings and printed media, and particularly wherein the article is an airbag. The term “airbags”, as used herein, includes airbag cushions. Airbag cushions are typically formed from multiple panels of fabrics and can be rapidly inflated. The woven fabrics described herein are preferably used in airbags sewn from multiple pieces of fabric. Thus, an airbag according to the fifth aspect of the invention is particularly an airbag other than a one piece woven (OPW) airbag. [00064] It will be appreciated that the preferences and elements and steps described hereinabove are equally applicable to the first, second, third, fourth and fifth aspects of the invention.

[00065] The following test methods were used to characterize the woven fabrics disclosed herein.

[00066] fi) Formic Acid Relative Viscosity

The relative viscosity (RV) was measured on the fiber sample (collected immediately after fiber extrusion from the spinneret) according to ASTM D789-19 using a 90% formic acid solution. Relative viscosity was also measured on a 20 gram sample of the finished woven fabric, i.e. after removal of any residual spin finish. Preferably, the fabric sample is treated prior to RV measurement in order to remove any remaining fiber lubricant oil, also known as spin finish. To remove the lubricant, each piece of fabric is soaked in enough methylene chloride to fully cover the sample. The sample is allowed to soak in a covered extraction funnel for twenty minutes with stirring. This procedure is then repeated. Once the second methylene chloride rinse is complete, the fabric is soaked in enough 1 :1 methanol:methylene chloride to fully cover the sample. The sample is allowed to soak in a covered extraction funnel for twenty minutes with stirring. This procedure is repeated twice more. Once all five soak steps are complete, remaining solvent is blown out of the fabric sample with clean pressurized air. The fabric is then allowed to air dry completely in an exhaust hood. Once dry, ASTM D789-19 is followed to measure the relative viscosity of the fabric sample.

[00067] fii) Melt-through resistance

To measure the melt-through resistance of the woven fabric, a “hot rod” test was used. Each fabric piece is 75 mm wide (warp direction) and 100 cm long (weft direction). Three fabric pieces are required per fabric sample (one per test temperature). Prior to testing, the fabric pieces are conditioned in a controlled atmosphere (20 ± 2°C and 65 ± 4% RH) for at least 24 hours before testing. This test uses a 12L14 carbon steel cylindrical rod, which is 50 m in length, 11 mm in diameter and each end being rounded at its edges with a 2mm radius giving a flat end which is 7mm in diameter, and weighing 36.5 g, with a specific heat capacity of 502.4J/(kg°K). The rod is heated to a controlled temperature in a muffle furnace for at least one hour to ensure temperature stabilization before testing. The hot rod is transferred to a delivery tube and brought into contact with a fabric piece which is mounted horizontally below the delivery tube. The fabric pieces are tested at 450°C, 550°C and 650°C. The first test site must be at least 20 cm from the fabric selvedge. A light-sensor in the delivery tube and a piezo-electric sensor attached to the catch tray positioned underneath the fabric allow a precise measurement of the time required for the rod to penetrate through the fabric once contact is made. The recorded time in the test is the total time (seconds) between the rod breaking the light beam and hitting the catch tray, wherein the total time equals the residence time of the rod on the fabric plus 0.19 seconds (which is the free-fall time it takes for the rod to pass between the light beam and the catch tray with no fabric present). The time required for the rod to melt through the fabric (i.e. the residence time of the rod on the fabric) is then calculated and this time period is defined as the melt-through resistance. Longer melt-through times indicate increased thermal resistance. Each test is repeated 10 times at each temperature to characterize the time required to melt through the fabric sample in seconds.

[00068] (///) Thermal Resistance Constant (X) and Coating-Weighted Thermal Resistance

Constant (Y)

The thermal resistance constant (X) is calculated from the melt-through resistance according to the formula: thermal resistance constant (X) = (T x t) / (600 x D) where T is the temperature (°C) of the MTR test; t is the MTR (seconds) measured as described herein; and D is the thickness (mm) of the fabric.

The coating-weighted thermal resistance constant (Y) is calculated from the thermal resistance constant (X) according to the formula: thermal resistance constant (Y) = X/C _w where C _w is the dry coat-weight of the coating in g/m ² .

[00069] (iv) Fabric Count

Fabric count was assessed using ISO-7211-2.

[00070] (v) Fabric Thickness

Thickness testing is conducted on fabric specimens which have been conditioned to standard laboratory conditions of 20±2°C & 65±4% RH for at least 24hrs. The specimens are cut from the fabric in such a way that no two specimens possess any common warp or weft yarns. Specimens are not cut within 20cm of either selvedge or at any creased, obviously damaged or dirty fabric regions. Specimens are suitably cut using a cutter die with a hydraulic press. The thickness of five specimens is measured with an electronic micrometer of testing range 0-25mm by 0.001mm (with 6.5mm diameter jaw faces) and the result recorded. The reported result (in units of mm) is the mean average of five individual specimen results.

[00071] (vi) Fabric Weight

Fabric weight was measured according to ISO 3801 (1977) with EASC amendments, and in accordance with EASC instruction 99040180 covering fabric testing (sections 3.05 & 4.01). Weight testing is conducted on samples of fabric which have been conditioned to standard laboratory conditions of 20±2°C & 65±4% RH for at least 24hrs. Five square specimens of size 10x10cm are cut (each orientated on the bias at 45° to the warp direction) from the sample in a diagonal line pattern across the fabric in such a way that no two specimens possess any common warp or weft yarns. Specimens are not cut within 10cm of either selvedge or at any creased, obviously damaged or dirty fabric regions. Specimens are cut using a 10x10cm cutter die with a hydraulic press. Once cut, the five specimens are weighed in a 3 decimal place balance in units of grams & the result recorded. Each result is multiplied by 100 to give the fabric weight in g/m ² . The reported fabric weight result is the mean average of five results.

[00072] Mi) Bulk density

The bulk density of the fabric is calculated by dividing the fabric weight per unit area (g/m ² ) by the fabric thickness measurement (mm) with a conversion to units of kg/m ³ .

[00073] Mii) Static Air Permeability (SAP)

Static Air Permeability SAP was measured according to ISO 9237 but with the following amendments:

(a) The test area is 100cm ² .

(b) The test pressure (partial vacuum) is 500 Pa.

(c) Each individual test value is corrected for edge leakage.

(d) Static Air Permeability testing is conducted at six sites on a test fabric in a sampling pattern across and along the fabric in order to test 6 separate areas of warp and weft threadlines within the fabric.

(e) The reported Static Air Permeability (in units of l/dm ² /min) is the mean average of the six measurements

[00074] fix) Dynamic Air Permeability (DAP)

Dynamic Air Permeability is defined as the average velocity (mm/s) of air or gas in the selected test pressure range of 30-70kPa, converted to a pressure of 100kPa (14.2 psi) and a temperature of 20°C. Dynamic Air Permeability is measured according to test standard ASTM D6476 but with the following amendments:

(a) The limits of the measured pressure range (as set on the test instrument) are 30-70kPa

(b) The start pressure (as set on the test instrument) is adjusted to achieve a peak pressure of 100±5kPa.

(c) The test head volume is 400cm ³ unless the specified start pressure cannot be achieved with this head, in which case an interchangeable test head of volume 100, 200, 800 or 1600cm ³ is used, as appropriate for the fabric under test.

(d) Dynamic Air Permeability testing is conducted at six sites on a test fabric in a sampling pattern across and along the fabric in order to test 6 separate areas of warp and weft threadlines within the fabric.

(e) The reported Dynamic Air Permeability (in units of mm/second) is the mean average of the six measurements.

[00075] (x) Fabric tensile testing

The tensile properties of the woven fabric, to determine maximum force (N) and elongation at maximum force (%), is measured according to standard ISO 13934-1 but with the amendments as listed below:

(a) The initial gauge (clamp) length set on the Instron tensile tester is 200mm

(b) The Instron crosshead speed is set at 200mm/min

(c) Fabric specimens are cut initially to size 350x60mm but are then frayed down by unravelling the long edge threadlines to a testing width of 50mm.

(d) Tensile testing is conducted on 5 warp direction and 5 weft direction specimens cut from each test fabric in a diagonal cross pattern and avoiding any areas within 200mm of the fabric selvedges.

(e) The maximum force (also known as breaking force or breaking load) is reported as the mean average of the maximum force results of the five warp direction specimens and the five weft direction specimens, in Newtons (N).

(f) The elongation at maximum force (also known as percentage elongation or percentage extension) is reported as the mean average of the elongation at maximum force results of the five warp direction specimens and (separately) of the five weft direction specimens, as a percentage

[00076] (xi) Tear force

The tear force (also known as tear strength) of the fabric, expressed in Newtons (N), is determined according to standard ISO 13937-2 with the amendments as listed below: (a) The fabric specimen size is 150mm x 200mm (with a 100mm slit extending from the midpoint of the narrow end to the center.

(b) Tear testing is conducted on 5 warp direction & 5 weft direction specimens cut from each test fabric in a diagonal cross pattern and avoiding any areas within 200mm of the fabric selvedges.

(c) Warp direction tear results are obtained from tested specimens where the tear is made across the warp (i.e. warp threadlines are torn) whilst weft direction results are obtained from tested specimens where the tear is made across the weft (i.e. weft threadlines are torn).

(d) Each leg of the specimens is folded in half to be secured in the Instron clamp grips according to ISO 13937-2 annex D/D.2

(e) Evaluation of test results is according to ISO 13937-2 section 10.2 “Calculation using electronic devices”.

(f) The warp tear force is reported as the mean average of the tear force results of the five warp direction specimens, whilst the weft tear force is reported as the mean average of the tear force results of the five weft direction specimens, in Newtons (N).

[00077] (xii) RV Density Factor

An RV density factor is calculated by multiplying the relevant measurement of the formic acid relative viscosity (RV) with the bulk density (kg/m ³ ), to provide a “fiber RV density factor” and a “fabric RV density factor”.

[00078] (xiii) Surface Roughness

Fabric samples were placed onto the stage of a Keyance VR 5000 optical Profilometer. A 40* magnification was used to analyze the samples, and the average of a minimum of 5 evenly distributed measurement points were calculated from the fabric sample. Each "point" defines a square measurement zone of 25 mm ² area and the values of Sa were measured by setting the L- Filter to be 1 mm. This was in accordance to ISO 25178-2:2012.

[00079] The present invention is further illustrated by the following examples. It will be appreciated that the examples are for illustrative purposes only and are not intended to limit the invention as described above. Modification of detail may be made thereto without departing from the scope of the invention.

Examples

Example 1 [00080] A series of woven fabrics (21.5x21.5 construction; fabric RV of 67) was manufactured with Nylon 6,6 yarn (fiber RV of 72; linear mass density of 350 dtex (except for fabrics 7 and 8 in which the linear mass density was 470 dtex)), subjected to varying calendering conditions and coating levels. Fabrics 1 , 2, 5, 7 and 8 were not subject to the calendering process. Fabrics 3 and 6 were subjected to calendering under a temperature of 168°C, force of 300N/mm, 43MPa pressure, speed of 15m/min, 15% water by weight, and calendered on both sides. Fabrics 4 and 9 were subjected to calendering under a temperature of 205°C, force of 300N/mm, 43MPa pressure, speed of 15m/min, 15% water by weight, and calendered on both sides. Fabrics 1 , 2, 3, 4 and 7 were then coated with a liquid silicone elastomer at levels of 14.3, 18.8, 9.1 , 4.9 and 25 g/m ² respectively. Fabric 7 represents a conventional non-calendered silicone-coated woven fabric. Fabrics 5, 6, 8 and 9 were not coated. The melt-through resistance of each fabric was measured, and the thermal resistance constant (X) and coating-weighted thermal resistance constant (Y) calculated. The results are shown in Table 1 , in which: the column “Cal.” reports whether or not calendering was used to make the fabrics; “T (mm)” refers to the fabric thickness; “MTR” refers to melt-through resistance (s); X refers to the Thermal Resistance Constant; and Y refers to the Coating-Weighted Thermal Resistance Constant.

[00081] Fabrics 3 and 4 are fabrics according to the present invention. The results in Table

1 demonstrate the effect of calendering with the combination of various coating levels. A higher level of coating correlates with improved (higher) melt through resistance and improved (lower) air permeability, which is clear from comparing the non-calendered fabrics 2, 1 and 5. Thus, as the level of coating decreases from 18.8 g/m ² to 14.3 g/m ² to zero, the melt through resistance decreases and the air permeability increases.

[00082] Surprisingly, however, calendering the fabric prior to coating (Fabric 3) allows the coating level to be reduced to 9.1 g/m ² while achieving melt-through resistance which approaches that of the heavily coated Fabric 2 (18.8 g/m ² ), and which is superior to the medium-level coated Fabric 1 (14.3 g/m ² ), and which simultaneously achieves improved (lower) air permeability. Moreover, the higher-temperature calendering of Fabric 4 allows the coating level to be reduced to only 4.9 g/m ² while exhibiting comparable or superior melt-through resistance relative to Fabric 3, and still out performing the medium-level coated Fabric 1 (14.3 g/m ² ), and while simultaneously retaining excellent air permeability. These examples illustrate that improved melt-through resistance can be achieved with significantly lower coating levels without significant detriment to air permeability performance by calendering the fabric. [00083] The surface roughness was measured on the woven fabric prior to coating, and the results shown in Table 2. Fabrics 3 and 4, exhibited a coherent and continuous silicone coating across the surface of the woven fabric.

Table 1

Table 2