EP4469631A1

EP4469631A1 - Airbag fabrics with improved seam performance

Info

Publication number: EP4469631A1
Application number: EP23700354.6A
Authority: EP
Inventors: Neil Hunt; Jenna OTT; Anand VISWANATH
Original assignee: Invista Textiles UK Ltd
Current assignee: Invista Textiles UK Ltd
Priority date: 2022-01-28
Filing date: 2023-01-10
Publication date: 2024-12-04
Also published as: KR20240110059A; MX2024005014A; WO2023144638A1; US20250003119A1; CA3236682A1; CN118302567A; GB202202878D0; JP2025502372A; TW202336303A

Abstract

A woven fabric formed from polyamide fibers, wherein: a. the woven fabric exhibits a Fabric Relative Viscosity of ≥90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s; wherein the fabric exhibits improved seam performance in deployment in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction.

Description

AIRBAG FABRICS WITH IMPROVED SEAM PERFORMANCE

The present invention relates to woven fabrics suitable for airbags, the use of such woven fabrics for improving airbag properties, methods for making airbag fabrics and the airbags themselves. The invention further relates to sewing threads.

Background

There is a continuing trend within frontal airbag cushions (driver and passenger) towards hotter and smaller inflators in airbag modules. Such higher output inflators mean that the airbag cushions need to be more robust in maintaining performance under the higher temperatures and higher pressures experienced during deployment. Additionally, there is a trend towards minimizing the size and weight of the internal components of automobiles to optimize efficiency. Coincidentally, changing crash test requirements are causing cushions to become larger, which leads to more difficulty in achieving good packability, and further increases stress on the cushion. Thus, there is a requirement for airbag cushion modules to maintain robustness under high temperature and pressures, at favorable cost, and without compromising the packability or compactness of the airbag. Correspondingly, it would be desirable to improve the mechanical integrity and thermal resistance of the airbag cushions within the airbag module, without the need for additional material, such as the use of heavier fabrics, or reinforcement materials. For frontal airbags the need for improved mechanical robustness and thermally resistant fabrics is particularly acute.

A significant issue for the airbag designer is the performance of the airbag cushion at the seam, where heated pressurized gas created during the deployment can create high stress areas on small sections of the fabric along the seam. This is primarily due to the presence of the sewing thread along the seam. This results in movement of warp and weft threads relative to each other, and localized stretching of threads within the fabric. This leads to enlargement of the sewing holes and results in a phenomenon known as "seam combing". Since frontal airbags are usually filled with hot gas, the presence of small holes in an otherwise very low porosity structure leads to preferential flow of hot gas through the holes, which can cause softening of the yarn, reduction in tensile modulus and increased stretch for equivalent load. Thus, seam combing becomes an increasingly critical failure mode of the airbag cushion with the move towards higher output inflators in airbag modules. This has the potential to lead to unacceptable performance of the cushion through uncontrolled gas leakage, as it creates a preferred path for the hot gas from the inflation to leak, with particularly severe events leading to melting and tearing of the structure. There is significant value in overcoming this problem in a manner that does not compromise the "compactness" of the airbag cushion.

Conventionally, the seam combing effect for airbag cushions can be improved by the use of fabrics with increased weight or density or higher construction, use of silicone coatings, and by alternative reinforcements such as seam tapes, seam sealants or heat shields. However, all these approaches negatively impact the complexity, cost and packability of the airbag cushion. Hence, there remains a need to further improve the fabric's mechanical robustness and thermal resistance without compromising the optimized balance of cost, complexity and packability of the airbag cushion.

WO2021193966 Al and EP 2264235 Bl describe how improvements may be made to seam slippage behavior in airbags, by weaving high tenacity polyamide fibers into dense fabrics, having high edgecomb resistance. A relationship of fabric RV with improved seam robustness of the fabric is not disclosed. In reference EP3674458, which discloses a lightweight airbag fabric with improved robustness, it is reported that use of a fiber with sulfuric acid relative viscosity (RV) of more than 3.5 causes poor cost efficiency, challenges in fiber drawing, leading to problems achieving the requisite fiber strength. For context, a sulfuric acid RV of 3.5 translates to a formic acid RV of 95. According to this reference, a fiber of more than 3.5 sulfuric acid RV would thus be unsuitable for yarn manufacture for airbag fiber.

It is an object of this invention to address the afore-mentioned problems, and in particular to provide improved woven fabrics and airbags made therefrom which exhibit greater mechanical robustness and thermal resistance during deployment, particularly without compromising the optimized balance of cost, complexity and packability of the airbag.

Summary of the invention

The problem of poor seam performance, and in particular seam combing, where the seam has a higher tendency to open under high heat (thermal load) and high pressure (mechanical stress), is solved by the use of a polyamide fabric having a high fabric RV, which provides resistance to the flow of hot gas. The problem of poor seam performance had previously been addressed by using fabrics of high construction. However, the inventors have found that increasing the RV of the polyamide can achieve improved seam performance, which is of particular utility in fabrics of lighter construction. This benefit is particularly pronounced when the dynamic air permeability is less than 500 mm/s and when the fabric Edgecomb Resistance exceeds 500N. The concept of using higher RV fibers to improve the resistance of the fabric to melting due to contact with hot metal particulates has been explored in the past, but the effect of RV on seam performance has not been described.

The term 'Fabric RV' as used herein specifically applies to measurement of RV on fibers extracted from fabric, rather than fiber samples collected in the spinning process. Conventionally, fiber RV refers to the RV of fiber collected from beneath the spinneret, that is prior to being drawn over the godets on the spinning machine. It is known that fiber RV reduces significantly going from freefall yarn to the drawn yarn in the final fabric, the extent of which depends on the processes involved in the manufacture of the fiber and fabric. In this invention, the 'Fabric RV' is defined as the formic acid relative viscosity, measured as described herein below.

According to a first aspect of the present invention, there is provided a woven fabric formed from polyamide fibers, wherein: a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s; wherein the fabric exhibits improved seam performance in deployment in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction, as measured by the Hot Air Seam Combing Test as defined herein.

Thus, the inventors have discovered that the mechanical robustness and thermal resistance of the airbag fabric at the seam may be improved by use of a polyamide fabric having a high Fabric RV, which is facilitated by the use of higher molecular weight or higher relative viscosity (RV) polyamide fiber in the fabric. In particular, the aspect of improved resistance to deformation or reduced stretching of the fabric and fiber at the seam location is observed with the use of a fabric with relative viscosities (RV) of at least 90. Preferentially, the seam combing effect is significantly reduced through the use of fabrics having a Fabric RV of>100, and preferably Fabric RV is greater than 100. Preferably, the Fabric RV is in the range of 90 to 200, more preferably 90 to 150, more preferably 90 to 130. Preferably, the Fabric RV is in the range of 100 to 200, more preferably 100 to 150, more preferably 100 to 130. Preferably in each of the afore-mentioned ranges, the Fabric RV is greater than 100.

Detailed description of the invention

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.

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. In the woven fabrics of the present invention, it is preferred that the polyamide is or comprises at least one polyamide selected from nylon 6,6 (PA-6,6), nylon 6 (PA-6), nylon 7 (PA-7), nylon 4,6 (PA-4,6), nylon 4,10 (PA-4,10), nylon 5,6 (PA-5,6), nylon 5,10 (PA-5,10), nylon 6,10 (PA-6,10), nylon 12 (PA-12) and nylon 6,12 (PA-6,12). Where multiple polyamides are present, the polyamide may be copolymers or blends of said polyamides. In a preferred but non-limiting embodiment, the polyamide is nylon 6,6.

At least a majority (and preferably all) of the yarn used in the warp direction of fabric is preferably formed from synthetic fiber 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 fiber 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 fiber 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.

The polyamide may be manufactured by conventional means known in the art. The polyamides may be manufactured from intermediates produced via a biosynthetic pathway or via conventional petrochemical route. The relative viscosity of the polyamide 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).

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 10.0 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 10.0 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 10.0 cN/dtex.

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.

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).

The woven fabric of the present invention is preferably made from yarn having at least 14.0 ends/cm, preferably from 14.0 to 30.0 ends/cm, preferably from 14.0 to 24.0 ends/cm, preferably from 16.0 to 24.0 ends/cm, preferably no more than 22.5 ends/cm, preferably no more than 21.0 ends/cm, preferably from 16.0 to 22.5 ends/cm, preferably from 16.0 to 21.0 ends/cm. Preferably, the woven fabric exhibits a symmetrical construction. Thus, the ends/cm of the warp yarn is preferably the same as the ends/cm of the weft yarn.

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. Preferably the weave is a plain 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 fabrics are heat-set woven fabrics. Thus, preferably the methods of the present invention comprise a heat-setting step after weaving and scouring to provide the final finished fabric.

After finishing, the woven fabrics are preferably used to manufacture articles therefrom without further processing. In particular, the woven fabrics are preferably not subjected to elevated temperature and pressure, for instance by calendering and/or in a way which permanently modifies the cross-section and fuses some, or all of the fibers in the yarn on the top and/or bottom surfaces.

The woven fabrics preferably exhibit a total fabric weight of from 130 to 500 g/m², preferably no more than 300 g/m², preferably no more than 260 g/m², preferably no more than 250 g/m², preferably no more than 225 g/m², preferably no more than 220 g/m², and preferably at least about 140 g/m², preferably at least about 150 g/m², preferably at least about 160 g/m², and typically at least 180 g/m². In a preferred embodiment, the woven fabrics of the present invention exhibit a total fabric weight of from 160 to 260 g/m², preferably from 170 to 225 g/m², preferably from 170 to 220 g/m².

The total thickness of the woven fabrics is preferably no more than 0.40 mm, preferably no more than 0.35mm, and preferably at least 0.16 mm, typically at least 0.22 mm, typically at least 0.26 mm, typically at least 0.29mm, and typically at least 0.30 mm. Preferably, the total fabric thickness is from 0.28 to 0.40 mm, preferably from 0.29 to 0.40 mm, preferably from 0.30 to 0.35 mm.

The woven fabric of the present invention preferably exhibits a bulk density of no more than 750 kg/m³, preferably no more than 725 kg/m³, typically no more than 700 kg/m³.

The woven fabrics exhibit a dynamic air permeability (DAP) of no more than 500, preferably no more than 450, preferably no more than 400, preferably no more than 300, preferably no more than 200 mm/s when the fabric is unaged.

The woven fabrics preferably exhibit a static air permeability (SAP) of no more than 4.0, preferably no more than 3.0, preferably no more than 2.5, preferably no more than 2.0 l/dm²/min when the fabric is unaged. Edgecomb resistance is a measure of the relative tendency of a fabric to pull apart under seam stress. Maintaining good edgecomb resistance is important to ensure that the fabric remains stable to relative movement between warp and weft threadlines and seams before or during hot gas deployment. The woven fabrics of the present invention exhibit and edgecomb resistance of at least 500 N, preferably at least 600N, preferably at least 700N, and preferably at least 800N, in each of the warp and weft directions.

The stiffness of the fabric is an important measure of the ability of the fabric to fit into and deploy from airbag modules. The fabric preferably exhibits a relatively low stiffness in order to improve packing efficiency and facilitate smooth deployment, but should do so while at least maintaining high edgecomb resistance. Various properties of the yarn influence fabric stiffness, including decitex, decitex per filament, fabric weight, construction and thickness. The stiffness of the woven fabrics also varies with the heat-setting conventionally effected during fabric manufacture to provide the final finished woven fabric which forms the airbag or other article. In particular, heat-setting normally increases the stiffness of the fabric. The stiffness of the woven fabrics of the present invention should be no more than 38.0 N, preferably no more than 35.0 N, preferably no more than 30.0 N, preferably no more than 28.0 N, preferably no more than 25.0 N in each of the warp and weft directions.

The cloth cover factor of a fabric is a numerical value indicating the extent to which the area of a fabric is covered by component yarns. The cloth cover factor of the fabric of the present invention is preferably at least 78, preferably at least 85, preferably at least 90. Typically, the cloth cover factor is no more than 100. For the provision of lightweight fabrics having surprisingly good seam performance and advantageously low stiffness, the cloth cover factor is preferably no more than 97, preferably no more than 95, and an advantageous balance of low stiffness and good seam performance may even be achieved at cloth cover factors of no more than 92, while retaining acceptably low permeability. Preferably the cloth cover factor is in the range of from 78 to 97, preferably 85 to 97, preferably 85 to 95, or 85 to 92.

Preferably, the tear strength of the fabric in each of the warp and weft directions is at least 120 N, preferably at least 140 N, preferably at least 150 N, preferably at least 170 N when the fabric is unaged.

The tensile breaking force (also referred to herein as maximum force) of the woven fabric in each of the warp and weft directions is preferably at least 3000 N, preferably at least 3200 N, preferably at least 3500 N, when the fabric is unaged.

The tensile elongation at maximum force of the woven fabric in each of the warp and weft directions is preferably at least 20%, preferably at least 25%, preferably at least 28%, preferably at least 30%, when the fabric is unaged.

The woven fabrics of the present invention preferably exhibit a seam open area (or seam combing index) of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch, preferably < 0.15 mm²/stitch, preferably < 0.10 mm²/stitch as measured by the Hot Air Seam Combing Test described herein.

To advance the objectives of weight reduction and improving packability, and also to minimize the material cost and environmental impact via polymer recycling, woven fabrics of the present invention are preferably uncoated. Fabrics comprising layers or coatings to reduce air permeability are commonly employed in airbags. However, a further non-limiting embodiment is for the fabrics of the present invention to be "coated" such that further improvements may be made to the permeability or the resistance of the fabric to hot particulates and gases from the inflator. Woven fabrics containing additional layers or coatings are referred to herein as "coated woven fabrics", wherein said "coating" takes the form of any coating, web, net, laminate or film, which may have been used, for instance, to impart a reduction in air permeability or improvement in thermal resistance. Examples of such coatings include polychloroprene, silicone based coatings, polydimethylenesiloxane, polyurethane and rubber compositions. Examples of such webs, nets and films include polyurethane, polyacrylate, polyamide, polyester, polyolefins, polyolefin elastomers and blends and copolymers thereof. It will be appreciated that the preferred uncoated woven fabrics of the present invention are not "coated woven fabrics" as defined herein.

The woven fabrics of the present invention find particular utility as airbag fabrics. The woven fabric may also be used to make an article selected from sailcloth, inflatable slides, temporary shelters, tents, ducts, coverings and printed media. 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, the airbags of particular interest in the present invention are airbags other than a one piece woven (OPW) airbag. The present invention is applicable to frontal, knee, far side, side/thorax and side curtain airbags, but is of particular utility in frontal airbags, such as driver and passenger airbags where thermal and mechanical loading is very high, and the airbags tend to be uncoated.

According to a second aspect of the invention, there is provided a woven fabric formed from polyamide fibers, wherein: a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s; wherein the fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch, preferably < 0.15 mm²/stitch, preferably < 0.10 mm²/stitch, as measured by the Hot Air Seam Combing Test described herein.

According to a third aspect of the invention, there is provided an article, and preferably an airbag, made from the fabric of the first or second aspects.

According to a fourth aspect of the invention, there is provided the use of a fabric according to the first or second aspects as an airbag fabric for the purpose of improving seam performance of the airbag in deployment. For a fabric according to the second aspect, the improvement is such that the fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch etc. as defined above. For a fabric according to the first aspect, the improvement is evaluated in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction. Seam Open Area and the improvement in seam performance are measured by the Hot Air Seam Combing Test defined herein.

According to a fifth aspect of the invention, there is provided a method of improving seam performance of an airbag in deployment, said method comprising making an airbag from a woven fabric according to the first aspect or second aspects. For a fabric according to the second aspect, the improvement is such that the fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch etc. as defined above. For a fabric according to the first aspect, the improvement is evaluated in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction. Seam Open Area and the improvement in seam performance are measured by the Hot Air Seam Combing Test defined herein.

According to a sixth aspect of the invention, there is provided a sewing thread formed by twisting polyamide fibers, wherein fibers extracted from the thread exhibit an RV > 90. The sewing thread may be used to impart improved robustness to the seam, particularly the seam of an airbag. It will be appreciated that the RV of said fibers extracted from said thread according to the sixth aspect of the invention is measured according to the test for Fabric RV described herein.

It will be appreciated that the disclosures and preferences described herein for the first aspect of the invention apply equally to all other aspects of the invention.

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

Test Methods

Fabric Relative Vi:

The Fabric RV specifically applies to measurement of RV on fibers extracted from fabric, rather than fiber samples collected in the spinning process. The term "Fabric RV" as used herein refers to the RV measured by the following test. The relative viscosity (RV) is measured on the fabric according to ASTM D789-19 (2019) using a 90% formic acid solution. One 20 g fabric sample is required for each replicate of this analysis. Prior to RV measurement, each sample is treated to remove any remaining fiber lubricant oil, also known as spin finish. To remove the lubricant, each sample 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 methanokmethylene 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.

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 lOOkPa (14.2 psi) and a temperature of 20° C. Another parameter, the curve exponent E (of the air permeability curve), is also measured automatically during Dynamic Air Permeability testing but this has no units. Dynamic Air Permeability is tested according to test standard ASTM D6476-12 (2021) but with the following amendments:

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

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

The test head volume is 400cm³ unless the specified start pressure cannot be achieved with this head, in which case one of the other interchangeable test heads (volumes 100, 200, 800 & 1600cm³) should be used as is found to be appropriate for the fabric under test. Dynamic Air Permeability testing is done 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.

The reported Dynamic Air Permeability result is the mean value of the six DAP measurements in units of mm/second.

Static Air Permeability (SAP)

Static air permeability (in units of l/dm²/min) is tested according to test standard ISO 9237 (1995) but with the amendments as listed below:

The test area is 100cm²

The test pressure (partial vacuum) is 500 Pa.

Each individual test value is corrected for edge leakage.

Static Air Permeability testing is done 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.

The reported Static Air Permeability result is the mean value of the six corrected measurements in units of l/dm²/min

Fabric tensile testing

Maximum force (N) and elongation at maximum force (%) is tested according to standard ISO 13934- 1 (2013) but with the amendments as listed below:

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

The Instron crosshead speed is set at 200mm/min

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.

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

The reported result for maximum force (also known as breaking force or breaking load) is the mean average of the maximum force results of the five warp direction specimens & (separately) the five weft direction specimens which were tested in Newtons (N).

The reported result for elongation at maximum force (also known as percentage elongation or percentage extension) is the mean average of the elongation at maximum force results of the five warp direction specimens & (separately) the five weft direction specimens which were tested (%).

Tear force

Tear force (also known as tear strength) is measured in Newtons (N) and is tested according to standard ISO 13937-2 (2000) but with the amendments as listed below:

The fabric specimen size is 150mm x 200mm (with a 100mm slit extending from the midpoint of the narrow end to the center. Tear testing is done on 5 warp direction & 5 weft direction specimens cut from each test fabric in a diagonal cross pattern & avoiding any areas within 200mm of the fabric selvedges.

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).

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

Evaluation of test results is according to ISO 13937-2 section 10.2 "Calculation using electronic devices".

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

Edgecomb resistance

Edgecomb resistance (also known as edge pullout testing) is measured in Newtons (N) and is tested according to standard ASTM D6479-15 (2020) but with the amendments as listed below:

The edge distance shall be 5mm - this is the distance between the end of the test specimen (which during testing is positioned on a narrow ledge machined in the test specimen holder) & the line of pins which perform the "pullout", i.e. this is the length of the section of threadlines pulled out during the test.

Edgecomb resistance testing is done on 5 warp direction & 5 weft direction specimens cut from each test fabric in a diagonal cross pattern & avoiding any areas within 200mm of the fabric selvedges.

The warp direction edgecomb resistance results are obtained from testing specimens with the long dimension parallel to the warp yarns, whilst weft direction results are obtained from testing specimens where the long dimension is parallel to the weft yarns.

The reported result for warp edgecomb resistance is the mean average of the edgecomb resistance results of the five warp direction specimens in Newtons (N), whilst for weft edgecomb resistance it is the mean average of the results of the five weft direction specimens.

Stiffness

The stiffness in Newtons (N) of the fabric (also referred to herein as "King stiffness") is measured by the circular bend procedure and is tested using a J. A. King pneumatic stiffness tester according to standard ASTM D4032-08 (2016) but with the amendments as listed below:

The plunger stroke speed is 2000mm/min

Stiffness testing is done on 5 warp direction & 5 weft direction specimens cut from each test fabric in a diagonal cross pattern & avoiding any areas within 200mm of the fabric selvedges.

Each 200x100mm specimen is single folded across the narrow dimension before being placed on the instrument testing platform for testing The reported result (in Newtons) for warp stiffness is the mean average of the stiffness results of the five warp direction specimens whilst the result for weft stiffness is the mean average of the five weft direction specimens.

The warp direction stiffness results are obtained from tested specimens where the longest dimension (200mm) is parallel to the fabric warp direction, whilst weft direction results are obtained from tested specimens where the longest dimension (200mm) is parallel to the fabric weft direction.

Fabric Count or Construction

Fabric count was assessed using ISO-7211-2 (1984). Fabric construction is determined as warp ends/cm and weft ends or picks/cm.

Fabric Thickness

Thickness testing is conducted on fabric specimens according to ISO 5084 (1996) 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.

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/m². The reported fabric weight result is the mean average of five results.

Cover Factor Calculation

The fabric cover factor is calculated by the following equation:

(warp ends/cm * V(decitex/100)) + (weft picks/cm * V(decitex/100))

Fabric Bulk Density

The bulk density of the fabric is calculated by dividing the fabric weight per unit area (g/m²) by the fabric thickness measurement (mm) with a conversion to units of kg/m³.

Seam Open Area The seam performance of the fabrics was evaluated by measuring the Seam Open Area by the Hot Air Seam Combing test method, which simulates the conditions during deployment of a woven airbag. The test is designed to study the seam of the woven fabric as it is heated under load.

Two pieces of woven fabric with warp and weft yarns aligned are overlaid and a single seam is stitched in a lockstitch pattern (5 stitches/cm) 19 mm from the cut edge. A PTFE-coated glass sewing thread of 2800 dtex (e.g. Fil-tec BC24 Glass Lube 2 lb, part #11031) is used so that only the hot fabric deformation could be observed.

While the sewn fabrics are on top of each other, a template is laid against the cut edge of the sewn fabrics and a test strip is marked and cut according to the following dimensions: beginning at the cut edge, a 59 mm length (in the warp yarn direction) and a width of 75 mm; the width of the strip then tapered from 75 mm to 50 mm over the next 10 mm length, and, finally, the width of the strip is 50 mm for the last 150 mm length (see Figure 1). The cut fabric is then unfolded.

The upper end of the sewn strip is clamped to a fixed beam, and a 46 kg load is applied to the lower end corresponding to an approximate filament yarn stress of 10 cN/tex, (which corresponds to the stress on the yarns in a typical woven air bag at the maximum airbag inflation pressure). A Milwaukee Tool Variable Temperature Corded Heat Gun Model # 8988-20, with a spreader nozzle at operating temperature of 532°C, is rotated so the tip of the nozzle is aligned 32 mm away from the seam, with the air flow being 90° to the plane of the fabric, with the other side of the fabric not being exposed to the hot air. The seam is heated in this manner for 20 seconds with a volumetric air flow rate of 29.3 m³/hr, at which time the hot air gun is rotated away from the seam and the fabric allowed to cool to room temperature.

Five fabric samples are tested and measured as followed for reproducibility. The final result is the average of the results of the five samples. Fabric samples were conditioned at 20°C ± 2 °C at a relative humidity of 65% ± 4% for 24 hours prior to testing, according to ISO139:2005(E). The cooled samples are then backlit with an LED light source placed approximately 2 cm behind the sample. While the cooled sample is still under the tension created by the pull weight, a Dino-lite digital microscope is used to photograph the seam area to provide photographic images of sufficient resolution to enable a measurement precision of ±lmm (preferably the photographic images are enlarged to a size of 21cm x 28cm). The images are then examined for visible openings at the seam (combing). The visible openings are defined as the opening seen between the stitches and the next threadline of extended fibers at the seam. The image area (Magnification = 23x ± 0.5x) covers a minimum of 9 consecutive stitches (centered at the middle of the stitched sample at 37.5 mm, with the total width of the stitched sample being 75 mm) to provide sufficient reproducibility between samples. Measurements are taken of these visible openings by marking the open areas with trapezoidal elements using image analysis software. The summation of the area of these trapezoids becomes the total seam area for the sample, and this is then divided by the number of stitches evaluated to provide the seam combing area/stitch for the sample. The microscope reference scale is used to calculate the true dimensions of the seam open areas in units of mm² (since these dimensions are preferably obtained from an enlarged image). This metric is defined as the "Seam Open Area" (also referred to as the "Seam Combing Index"). Optionally, image analysis software can calculate the Seam Open Area in an automated manner.

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

A series of woven fabrics were prepared using conventional methods and in accordance with the description hereinabove. The woven fabrics had the properties shown in Table 1, measured as defined herein. Table 1 - Properties of Fabrics

It was surprisingly observed that the Seam Open Area following exposure to thermal and mechanical load in the Hot Air Seam Combing test was significantly lower for the high fabric RV samples of inventive Examples 1 and 2 compared to the conventional fabrics with the relatively lower fabric RVs of Comparative Examples 1-3, without detriment to the mechanical properties of the fabric.

Moreover, the Seam Open Area of the inventive examples is comparable with the Seam Open Area of Comparative Example 4, which has a much higher fabric construction and weight. Thus, the present invention surprisingly enables excellent seam robustness without needing to increase fabric construction and weight. In addition, the woven fabrics of the present invention allow a reduction in the stiffness of the fabric, which in combination with the reduced fabric weight and thickness lead to improved packability, relative to fabrics with higher construction and weight, while retaining acceptably low air permeability.

Thus, the inventive woven fabrics having a high fabric RV surprisingly provide a combination of excellent seam performance, low stiffness and thickness (and hence improved packability), excellent mechanical properties and low air permeability which is not shown by any of the conventional fabrics. Moreover, the inventive fabrics are able to achieve this at low material cost and relatively lower manufacturing complexity, compared to conventional fabrics.

The Edgecomb Resistance was high in all samples tested. The inventors did not observe any correlation of Fabric RV with Edgecomb Resistance, despite the strong correlation of Fabric RV with Seam Open Area, indicating that the improvement in seam performance described herein is independent to Edgecomb Resistance. The present invention therefore provides a novel and unexpected technical contribution to airbag manufacture.

Claims

I. A woven fabric formed from polyamide fibers, wherein: a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s; wherein the fabric exhibits improved seam performance in deployment in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction, as measured by the Hot Air Seam Combing Test as defined herein.

2. The fabric of claim 1 wherein the fabric exhibits a Seam Open Area of <0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch, preferably < 0.15 mm²/stitch, preferably < 0.10 mm²/stitch, as measured by the Hot Air Seam Combing Test described herein.

3. A woven fabric formed from polyamide fibers, wherein: a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s; wherein the fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch, preferably < 0.15 mm²/stitch, preferably < 0.10 mm²/stitch, as measured by the Hot Air Seam Combing Test described herein.

4. The fabric of any preceding claim where the Fabric RV is in the range of 90 to 200, more preferably 90 to 150, more preferably 90 to 130, preferably wherein the Fabric RV is at least 100.

5. The fabric of any preceding claim which exhibits a stiffness of no more than 38.0 N, preferably no more than 35.0 N, preferably no more than 30.0 N, preferably no more than 28.0 N, preferably no more than 25.0 N in each of the warp and weft directions.

6. The fabric of any preceding claim which exhibits a cloth cover factor of at least 78, preferably at least 85, preferably at least 90, and typically no more than 100.

7. The fabric of any preceding claim which exhibits a cloth cover factor of no more than 97, preferably no more than 95, preferably no more than 92, and preferably from 78 to 97, preferably from 85 to 97, preferably from 85 to 95, preferably from 85 to 92.

8. The fabric of any preceding claim wherein the Edgecomb Resistance is at least 600N, preferably at least 700N.

9. The fabric of any preceding claim wherein the Dynamic Air Permeability is no more than 450 mm/s.

10. The fabric of any preceding claim wherein the static air permeability (SAP) is no more than 4.0, preferably no more than 2.5 l/dm²/min.

II. The fabric of any preceding claim wherein the polyamide is or comprises at least one selected from nylon 6,6 (PA-6,6), nylon 6 (PA-6), nylon 7 (PA-7), nylon 4,6 (PA-4,6), nylon 4,10 (PA-4,10), nylon 5,6 (PA-5,6), nylon 5,10 (PA-5,10), nylon 6,10 (PA-6,10), nylon 12 (PA- 12) and nylon 6,12 (PA-6,12).

12. The fabric of any preceding claim wherein the polyamide is or comprises PA-6,6.

13. The fabric of any preceding claim wherein the fabric exhibits a construction of from 16.0 to 22.5 ends/cm, preferably from 16.0 to 21.0 ends/cm.

14. The fabric of any preceding claim which exhibits a total fabric weight of from 130 to 260 g/m², preferably from 170 to 225 g/m² or from 170 to 220 g/m².

15. The fabric of any preceding claim which exhibits a total thickness of no more than 0.40 mm, preferably no more than 0.35 mm, preferably from 0.28 to 0.40 mm, preferably from 0.30 to 0.35 mm.

16. The fabric of any preceding claim which exhibits a bulk density of no more than 750 kg/m³, preferably no more than 725 kg/m³, typically no more than 700 kg/m³, and/or wherein the woven fabrics have not been calendered or otherwise subjected to elevated temperature and pressure.

17. The fabric of any preceding claim wherein: a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s, preferably no more than 450 mm/s; d. the fabric has a stiffness of no more than 38.0 N, preferably no more than 35.0 N, preferably no more than 30.0 N; e. the fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch; f. the fabric preferably exhibits a cloth cover factor of from 85 to 97, preferably from 85 to 95, preferably from 85 to 92, and/or a total fabric weight of from 170 to 240 g/m², preferably from 170 to 225 g/m² preferably from 170 to 220 g/m² and g. the fabric preferably exhibits a bulk density of no more than 750 kg/m³.

18. The fabric of any preceding claim where the polyamide is manufactured from intermediates produced via a biosynthetic pathway or a petrochemical pathway.

19. The fabric of any preceding claim which is a plain weave fabric.

20. The fabric of any preceding claim which is uncoated.

21. The fabric of any of claims 1 to 19 which is coated.

22. The fabric of any preceding claim which is an airbag fabric.

23. An airbag made from the fabric of any claims 1 to 22.

24. The airbag of claim 23 which is a frontal, knee, far side or side/thorax airbag, and/or is an airbag which is not a one-piece-woven (OPW) airbag.

25. A sewing thread formed by twisting polyamide fibers, wherein fibers extracted from the thread exhibit an RV > 90.

26. Use of a woven fabric formed from polyamide fibers, wherein: a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; and c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s, as an airbag fabric for the purpose of improving seam performance of the airbag in deployment, preferably such that said fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch, and/or wherein said improvement is evaluated in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction, wherein Seam Open Area and the improvement in seam performance is measured by the Hot Air Seam Combing Test as defined herein.

27. A method of improving seam performance of an airbag in deployment, said method comprising making an airbag from a woven fabric formed from polyamide fibers, wherein; a. the woven fabric exhibits a Fabric Relative Viscosity (Fabric RV) of >90; b. the Edgecomb Resistance of the fabric is at least 500N in each of the warp and the weft directions; and c. the fabric has a Dynamic Air Permeability of no more than 500 mm/s, preferably wherein said fabric exhibits a Seam Open Area of < 0.20 mm²/stitch, preferably < 0.18 mm²/stitch, preferably < 0.16 mm²/stitch, and/or wherein said fabric exhibits improved seam performance in comparison to a control fabric characterized by <90 Fabric RV with the same fabric construction, wherein Seam Open Area and the improvement in seam performance is measured by the Hot Air Seam Combing Test as defined herein. A use according to claim 26 or a method according to claim 27 wherein said woven fabric is as defined in any of claims 1 to 22.