Polyamide for making polyamide yarn having improved mechanical and thermo-mechanical properties

Abstract

A polyamide suitable for making drawn polyamide yarn which exhibits (i) an RV of about 90 to about 200; and (ii) a polyamide molecular weight distribution characterized by Mz / Mw in the range of ≥ 1.40 and ≤ 1.50 ±0.03.

Description

POLYAMIDE FOR MAKING POLYAMIDE YARN HAVING IMPROVED MECHANICAL AND THERMO-MECHANICAL PROPERTIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present disclosure claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 63 / 529,154, filed July 27, 2023, U.S. Provisional Patent Application Serial No. 63 / 529,161 filed July 27, 2023, U.S. Provisional Patent Application Serial No. 63 / 661,603 filed June 19, 2024, U.S. Provisional Patent Application Serial No. 63 / 661,600 filed June 19, 2024 and U.S. Provisional Patent Application Serial No. 63 / 661,599 filed June 19, 2024; the contents of which are hereby incorporated by reference herein in their entireties.FIELD

[0002] The present application relates to polyamides, particularly polyamide 6,6 (PA66), having a high relative viscosity suitable for making yarn with improved mechanical and / or thermomechanical properties. In particular, the application relates to polyamides suitable for making yarn for use in tire cord which exhibits improved fatigue resistance and cured-in-rubber strength. In addition, the polyamides are suitable for making yarn for use in industrial articles such as cords, threads, and ropes.BACKGROUND

[0003] Tire cord is a fabric element that is used to provide dimensional stability to the tire, and to help support the weight of a vehicle. Tire cord acts as a reinforcing material and can enhance durability of the tires. Tire cord can be made from a variety of materials including steel, rayon and polyester. Another common group of fibers that are being used for tire cord production are made of polyamide (or nylon polymer) which are considered as a high strength option when enhanced performance is required. Tire cord can be obtained by twisting or plying polyamide fibers. An adhesion treatment agent may be applied to the surface. The twisted yarns may also go through a process of heat setting before being embedded in rubber and eventually becoming one of the many parts of a tire.

[0004] During use, tires go through many cycles of loading and unloading during their lifetime which causes the yarns used therein, as reinforcing components, to lose their mechanical strength. As the number of loading cycles increases this can contribute to lowering the strength of tires and ultimately to tire deformation and failure. The loss of mechanical strength is referred to as “fatigue” and retention of mechanical strength is referred to as fatigue resistance.

[0005] One of the most important properties of fibers used in tire cords is fatigue resistance. Different methods have been previously used to enable improved fatigue resistance of tire cords made from polyamide. Examples of such methods are as follows:• A hybrid tire cord as described in patent publication CN113260747 B can be made of multifilament aromatic polyamide, aramid spun yarn, nylon, or polyester multifilament.• A sea-island composite industrial filaments (Sea-island fiber, also known as superconjugate fiber is formed by a core component dispersed in another polymer in a longitudinally continuous way. Patent publication W02007112665 describes a process for producing a sea-island composite industrial filaments including polyester as an island component and making polyamide the sea component. The sea-island composites produced by this method provide improved fatigue resistance amongst other features.)• Using specific treatment liquids comprised of emulsion-based and oil-based liquids are described in patent publications JP2566993 B2 and JP2782510 B2. These treatments are applied in the spinning process of the yarns to reduce the fiber-to-fiber friction.• A spinning process condition that is described in patent publication JP3281115 B2 through which certain dynamic mechanical properties are met.

[0006] In reference JP2015034361 A, it is reported that for making high strength polyamide fibers it is preferred to obtain a sulfuric acid relative viscosity (SARV) in the range of 3.5 - 3.8 by the solid-phase polymerization to run the liquid-phase and solid-phase polymerization equipment efficiently. Additionally, benzenesulfonate compound (5 - 300 ppm) is added as an oxidation stabilizer to the water used for cooling the cast polymer (exiting polymerization autoclaves) to reduce thermal oxidation and degradation of polymer during the solid-phase polymerization and melt spinning. The reference EP3674458 reports that the use of a PA66 fiber with SARV of more than 3.5 causes poor cost efficiency and challenges in fiber drawing, leading to problems achieving the requisite fiber strength. (A SARV of 3.5 translates to a formic acid RV of 95.) According to these references, the use of a fiber of more than 3.5 SARV, without using thebenzenesulfonate compound, would result in frequent filament breakage and thus would be technically and economically unsuitable for producing continuous polyamide multifilament yarns.

[0007] Continuous demand for better performance of tires, for example for higher mileages, or for electric vehicles (EVs) with higher torque and vehicle weight applied to the tires, etc., shows that there is still a need for new material for tire cord fabrics and particularly for polyamides and polyamide yarns which are suitable for improving the fatigue resistance and curedin-rubber strength of tire cords.

[0008] Other industrial applications for high strength polyamide yarn include sewing thread, belt cord such as conveyor belt cord, ropes, parachute cord and filtering fabrics. A vast majority of industrial yarn applications either during the manufacturing process or at the end-use condition involve the yarns tolerating an applied stress while being exposed to elevated temperatures. For example, a sewing thread (a type of thread that is used specifically for sewing fabric together) is kept under stress during the sewing process, and it must maintain its integrity when it contacts and passes through the needle. The sewing needle usually gets heated as a result of friction forces when it goes through many cycles of stitching at a high rate. Another example is the yarns used in belt cords such as conveyor belt cords, the internal temperature of which is increased upon going through many cycles of loading / unloading. Therefore, improvement of thermo-mechanical properties of yarns can address the shortcomings of current state of the art PA66 yarns and allow for their application in even harsher conditions.

[0009] Various methods have been previously used to enable improved thermomechanical properties of PA66 yarns and articles made thereof. See, for example, Kim, J., Kim, K., & Lee, J. (2014), Controlling birefringence ratio of drawn nylon-6, 6 yarn by altering drawing temperature and draw ratio (Fibers and Polymers, 15(11), 2299-2306). In another example patent publication CN115536838 describes the copolymerization of 1,5-pentamethylene diamine, hexamethylene diamine, and adipic acid and producing PA56-66 is claimed to improve the performance of co-polyamide resin and spinning product.

[0010] The current invention is also in contrast with other work that in general tries to strengthen the mechanical properties of polyamide yarn by increasing the linear density of the yarns. For example, a higher decitex yarn used for sewing thread can potentially withstand larger stresses, but this inevitably means that the amount of material used, and the thickness of the thread, and therefore the stich holes in the fabric will be larger.

[0011] In reference JP2015034361 A, it is reported that for making high strength polyamide fibers it is preferred to obtain a sulfuric acid relative viscosity (SARV) in the range of 3.5 - 3.8 by the solid-phase polymerization to run the liquid-phase and solid-phase polymerization equipment efficiently. Additionally, benzenesulfonate compound (5 - 300 ppm) is added as an oxidation stabilizer to the water used for cooling the cast polymer (exiting polymerization autoclaves) to reduce thermal oxidation and degradation of polymer during the solid-phase polymerization and melt spinning. The reference EP3674458 reports that the use of a PA66 fiber with SARV (relative viscosity measured by the sulfuric acid method, ASTM D789-19) of more than 3.5 causes poor cost efficiency and challenges in fiber drawing, leading to problems achieving the requisite fiber strength. (A SARV of 3.5 translates to a formic acid RV of 95.) According to these references, the use of a fiber of more than 3.5 SARV, without using the benzenesulfonate compound, would result in frequent filament breakage and thus would be technically and economically unsuitable for producing continuous polyamide multifilament yarns.

[0012] Accordingly, there is still a need for new material for industrial yarns having improved mechanical and / or thermo-mechanical properties.

[0013] It is an object of this invention to address the aforementioned problems. It is a particular object of this invention to provide polyamides suitable for making yarn for use in tire cord which exhibits improved fatigue resistance and cured-in-rubber strength. It is a further particular object of this invention to provide polyamides suitable for making drawn yarn for use in cords, threads, and ropes, which have improved mechanical and / or thermo-mechanical properties.SUMMARY

[0014] In accordance with a first aspect of the invention, there is provided a polyamide suitable for making drawn polyamide yarn which exhibits (i) a formic acid relative viscosity (RV) of about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03, and preferably (iii) a tenacity of >8.5 cN / dtex. It will be appreciated that these formic acid relative viscosity values are those of the polyamide constituting the drawn yarn. The polyamide is suitable for making drawn polyamide yarn for tire cord which has improved fatigue resistance and / or cured-in-rubber strength, relative to a tire cord made from drawn polyamide yarn not having the characteristics recited herein, and in particular drawn polyamide yarn not having the combination of formic acid relative viscosity (RV) and molecularweight distribution (Mz / Mw) characteristics, and particularly not having the combination of RV, Mz / Mw and tenacity characteristics. In particular, the inventors have found that the fatigue resistance and / or cured- in-rubber strength is higher than that provided by a drawn polyamide yarn having a lower relative viscosity and an Mz / Mwvalue outside of the stated range, and higher than that provided by a drawn polyamide yarn having a lower relative viscosity and lower tenacity and an Mz / Mw value outside of the stated range.

[0015] Tire cord made from said drawn polyamide yarn preferably exhibits a cured-in- rubber strength of > 50 N, preferably > 70 N, preferably > 100 N, preferably > 130 N, preferably > 150 N, preferably > 180 N, preferably > 210 N, preferably > 220 N.

[0016] In a particularly preferred embodiment, the tire cord has a cured-in-rubber strength of > 150 N, preferably > 180 N, preferably > 210 N, preferably > 220 N. It will be appreciated that the higher cured-in rubber strength ranges of this particularly preferred embodiment are achievable using drawn yarns of higher linear density.

[0017] Tire cord made from said polyamide yarn preferably exhibits a fatigue resistance (as measured herein as the breaking strength retention relative to the strength before being fatigued) of >35%, preferably >50%, preferably >65%, preferably >70%. In a preferred embodiment the fatigue resistance is from about 70 % to about 90%.

[0018] In accordance with a second aspect of the invention there is provided a polyamide suitable for making drawn polyamide yarn which exhibits: (i) formic acid relative viscosity (RV) of about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03; and (iii) an elongation at maximum force that is greater than 15.0% of its original dimension. Again, it will be appreciated that these formic acid relative viscosity values are those of the polyamide constituting the drawn yarn. The polyamide is suitable for making drawn polyamide yarn which exhibits improved melt-through resistance in respect of a fabric made from said yarn, compared to a drawn polyamide yarn not having the combination of formic acid relative viscosity (RV) and molecular weight distribution (Mz / Mw) characteristics, and in particular compared to a drawn polyamide yarn having a lower formic acid relative viscosity and an Mz / Mwvalue outside of the stated range.

[0019] The melt-through resistance at 350°C of fabrics made from said yarn and measured as described herein is preferably > 3.00 seconds, preferably > 3.20 seconds, preferably > 3.40 seconds.

[0020] The melt-through resistance at 650°C of fabrics made from said yarn and measured as described herein is preferably > 0.70 seconds, preferably > 0.80 seconds.

[0021] The preferred polyamide for both the first and second aspects of the invention is polyhexamethylene adipamide (also known as polyamide 66, PA66 or nylon 66).

[0022] It will be appreciated that the molecular weight distribution (Mz / Mw) parameter described herein is that of the polyamide constituting the drawn yarn. For both the first and second aspects of the invention, said polyamide molecular weight distribution characterized by Mz / Mwis preferably in the range of 1.42 to 1.49 ±0.03, preferably 1.45 to 1.48 ±0.03.

[0023] A drawn polyamide yarn may be prepared from the polyamide of the first or second aspects by a method comprising the steps of: a) shear heating flakes of said polyamide until the polymer reaches a molten state; b) extruding the molten polyamide through spinnerets; c) cooling the molten polymer that exits the spinnerets to solidify the filaments; d) applying a lubricant to the filaments; e) drawing the filaments by passing the filaments through one or more heated rollers to stretch and align the molecules; f) relaxing the drawn yarns by passing through another set of one or more rollers to achieve the required shrinkage on the final yarn; and g) winding the finished filaments onto bobbins.

[0024] In a third aspect of the invention, there is provided the use of the polyamide of the first aspect in a tire cord for the purpose of improving the fatigue resistance and / or cured-in-rubber strength thereof tire cord wherein said polyamide is present in said tire cord in the form of drawn polyamide yarn which exhibits (i) an RV of about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03.

[0025] In a fourth aspect of the invention, there is provided the use of the polyamide of the first aspect in a tire cord for the purpose of improving the fatigue resistance and / or cured-in- rubber strength of a tire cord made from drawn polyamide yarn made from said polyamide.

[0026] In a fifth aspect of the invention, there is provided the use of the polyamide of the first aspect in a tire for the purpose of enhancing the durability thereof wherein said polyamide is present in said tire in the form of a tire cord made from drawn polyamide yarn which exhibits (i)an RV of about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mw in the range of > 1.40 and < 1.50 ±0.03.

[0027] In a sixth aspect of the invention, there is provided the use of the polyamide of the first aspect for the purpose of enhancing the durability of a tire comprising a tire cord made from drawn polyamide yarn made from said polyamide.

[0028] The use of the polyamide according to the third to sixth aspects is of particular utility in respect of polyamide yarns which exhibit a tenacity of >8.0 cN / dtex (preferably >8.5 cN / dtex), and preferably also an energy to break of at least 2.5 J and / or an elongation at maximum force of about 10 to about 30 percent (particularly at least 15.0 percent), and / or an elongation at 45N of about 7 to about 12 % (particularly about 8.5 to about 12%), preferably with the preferred thresholds and ranges for these parameters as defined herein.

[0029] A tire cord may be prepared from said drawn polyamide yarn by any method conventional in the art for preparing tire cord. In general, the method comprises the steps of: a) twisting single yarns in Z or S direction wherein said single yarns are the drawn polyamide yarns defined in the first aspect of the invention; and b) plying two or more single yarns together and twisting them in a direction which is opposite to the direction of twist in the single yarns, preferably with a similar number of twists per unit length as each single yarn.

[0030] For the intended application of tire manufacture, the tire cord produced in this way is normally then further processed by weaving the cords into fabric, which is then used in tire fabrication. The tire cord of the present invention is suitable as at least the warp component of the fabric. Typically 1000-1500 of such tire cords are woven into the fabric as the warp component. The drawn polyamide yarn of the present invention may be used, alternatively or additionally, as the weft component (also referred to as “fill” or “pick” yarn) of the fabric. Where drawn polyamide yarn of the present invention is present only as the warp component, any conventional weft component may be used. The weft component of tire cord fabric is normally present in the fabric at a relatively lower density than the warp component. The primary function of the weft component is to maintain a uniform warp spacing during subsequent processing, such as transportation, dipping, heat-treatment, calendering and tire fabrication etc. The fabric is then dipped in a cord adhesive solution, as is well-known in the art. Adhesives suitable for bonding the fabric to rubber compounds include resorcinol formaldehyde latex (RFL) mixtures. The fabric is then dried undercontrolled temperature and tension and for a controlled amount of time. The drying temperature should be below the melting point of the polyamide. For instance, tire cord made from drawn PA66 yarn is typically heat-treated under tension at a temperature of from about 150 to about 250°C preferably for a period in the range of from 10 seconds to 2 minutes, preferably under a 5 to 20% stretch.

[0031] It will be appreciated that the disclosures and preferences disclosed herein for the first aspect of the invention also apply to the third to sixth aspects of the invention.

[0032] In a seventh aspect of the invention, there is provided the use of the polyamide of the second aspect in an industrial article selected from a cord, thread, rope and filtering fabric for the purpose of improving the mechanical strength and / or thermo-mechanical properties of said industrial article, wherein said polyamide is present in said industrial article in the form of drawn polyamide yarn which exhibits: (i) an RV of from about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03; and (iii) an elongation at maximum force of greater than 15.0% of its original dimension.

[0033] In an eighth aspect of the invention, there is provided the use of the polyamide of the second aspect in an industrial article selected from a cord, thread, rope and filtering fabric, for the purpose of improving the mechanical strength and / or thermo-mechanical properties of said industrial article made from or comprising drawn polyamide yarn made from said polyamide.

[0034] In a ninth aspect of the invention, there is provided the use of the polyamide of the second aspect in a sewing thread made from or comprising drawn polyamide yarn made from said polyamide, particularly for the purpose of improving the mechanical and / or thermo-mechanical properties of said sewing thread.

[0035] Preferably said industrial article is a cord, thread or rope, more preferably a thread. Preferably said thread is a sewing thread. Preferably said cord is a belt cord such as conveyor belt cord or a parachute cord.

[0036] Mechanical strength is suitably measured via conventional tensile testing as is known in the art.

[0037] A sewing thread may be prepared from said drawn polyamide yarn by a process comprising the steps of: a) twisting; b) plying two or more single yarns together;c) optionally dyeing; d) bonding; and e) coating.

[0038] Said method for preparing a sewing thread preferably comprises the steps of: a) twisting single yarns; b) plying two or more single yarns together to form a thread; c) optionally dyeing the thread and; d) bonding the thread by addition of a resin to the core of thread to hold the single yarns together during manufacturing and use. e) coating / lubricating the outside of the plied thread to reduce the abrasion of final thread against contact surfaces and help with the structural integrity of the thread.

[0039] The sewing threads made from or comprising a drawn polyamide yarn made from a polyamide according to the second aspect of the invention are suitable for preparing a stitched fabric comprising one or more pieces of fabric and one or more sewing threads wherein the sewing threads form stitches in said one or more pieces of fabric. Said fabric may be any suitable fabric conventional in the art, including a woven or non-woven fabric. The fabric may be made from synthetic or natural fibers, for instance synthetic polymer fibers. Said stitched fabric may further comprise a non-fabric layer, such that said stitched fabric comprises one or more pieces of fabric, one or more sewing threads, and one or more non-fabric layers (such as leather or polymer sheet etc.), wherein the sewing threads form stitches in said one or more pieces of fabric and said one or more non-fabric layers.

[0040] It will be appreciated that the disclosures and preferences disclosed herein for the second aspect of the invention also apply to the seventh to ninth aspects of the invention.

[0041] Unless stated to the contrary, the following disclosure is applicable equally to the polyamides of the first and second aspects of the invention.DETAILED DESCRIPTION OF THE INVENTION

[0042] As a rule of thumb, an increase in the molecular weight of polymer would be expected to improve the mechanical properties of products made with said polymer. The longer chains enable higher number of physical entanglements, and in some cases chemical crosslinkingwill also contribute to the changes in the behavior of material against mechanical forces. However, such changes can have contrasting impacts and so it is difficult to predict the exact balance of properties influenced by macromolecular structure changes. For example, increasing the molecular weight theoretically makes the material stronger due to higher entanglement, but can also result in a more brittle and degraded polymer, which means the polymer will break at smaller deformations. Therefore, making a higher molecular weight polymer is not always advantageous for the requirements of the end-use application.

[0043] PA66 is one of the commonly used engineered thermoplastics. PA66 is synthesized by polycondensation of hexamethylenediamine and adipic acid. PA66 is also referred to as nylon 66 and these terms are used interchangeably herein. Polyamides and particularly PA66 are often used as the base polymer for tire cord fabric and industrial yarn due to their high mechanical strength, thermal resistance, and energy absorption characteristics relative to fabrics made with other polymers.

[0044] The yarns of the present disclosure are composed of fibers which are in the form of continuous multi-filaments. In one embodiment, such filaments are formed by extrusion of molten polymer through spinnerets at high temperatures and pressures and subsequent quenched in air, coated with spin finish lubricant, drawn between pairs of godets, entangled along the length of the fiber to make a coherent yarn and then wound up on cardboard tubes as bobbins.

[0045] 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 (SSP) step, typically conducted under dry nitrogen at elevated temperature (for instance about 180°C).

[0046] An increase in molecular weight of aliphatic polyamides (such as PA66) is expected to increase the strength. However, the melt viscosity also increases with higher molecular weight, which makes the polymer processing more difficult. A common solution to this problem is to increase the processing temperature to reduce the polymer melt viscosity. This, however, comes at the cost of polyamide degradation which negatively affects the quality of polymer. As a result,when the molten polymer is spun, it cannot be drawn enough and therefore the achievable mechanical properties such as tenacity, elongation at maximum force and energy to break will be limited. Overall, therefore, simply increasing molecular weight is a difficult way to improve properties of polymeric materials because striking the correct balance in properties is a significant challenge. However, the present inventors have found that making polyamide (preferably PA66) yarns with higher RV and modulating the molecular weight distribution of the polymers provides yarns with improved mechanical and / or thermo-mechanical properties.

[0047] It is known in the art that more severe conditions during polymerization (including temperature and residence time) can promote the formation of undesired side products. Certain of these undesired side products are referred to in the industry as “gel.” Gel formation in polyamide (and particularly PA66) refers to the process by which the polymer chains in the material crosslink and form a three-dimensional network, resulting in a gel-like structure. As gel formation increases, the fraction of linear polymer chains in the polymer decreases and therefore the molecular weight distribution diverges from the most probable Flory molecular weight distribution of linear condensation polymers (Flory, P. J., Molecular size distribution in linear condensation polymers, Journal of the American Chemical Society, 1936, 58(10), 1877-1885). Thus, the measured molecular weight distribution (measured as Mz / Mw) of step-growth polymers like polyamide 66 is considered an indicator of the polymer’s linearity or lack thereof. Gelling is typically initiated by exposure to excessive heat, radiation, or other chemical agents that cause the polymer chains to become crosslinked. The degree of crosslinking can affect the mechanical and physical properties of the polyamide, such as its strength, stiffness, and water absorption. Gel formation can also alter the processing behavior of polyamide, requiring adjustments to be made in the manufacturing process to ensure consistent quality and performance. It is known in the art that micro- or nanoparticles of gelled polymer in the yarn create stress concentration points that hinder the drawing process of the yarns and limit the achievable tenacity and elongation at break.

[0048] The present inventors have found that controlling the value of the Mz / Mwparameter results in unexpected improvements in fiber properties. In particular, the present inventors observed that, at a drawn yarn RV range of 90-200 (and particularly in the range of 90-150, more particularly 90-130, and more particularly 90-120), if the polymer constituting the yarn has amolecular weight distribution (Mz / Mw) higher than 1.50, it fails in the spinning process due to frequent filament and process breakages which makes the process uneconomical.

[0049] The Mz / Mw parameter is measured by Size Exclusion Chromatography (SEC), as described hereinbelow. It will be appreciated that the values of the Mz / Mwparameter referred to herein are qualified with an error bar of ±0.03 in order to capture the uncertainty of the measurement method.

[0050] The inventors have observed that the Mz / Mwparameter provides a precise measure of the molecular weight distribution (particularly its breadth) which allows accurate comparison between different samples.

[0051] It will be appreciated that the Mz / Mwparameter can be modulated using techniques which are conventional in the art and known to the skilled person. In particular, by controlling the process conditions during polymerization, the molecular weight distribution and gel formation, and hence the Mz / Mwparameter, can be controlled. For example, pre-heating the polyamide flakes before an SSP step is known to allow a shorter residence time in SSP which results in narrower molecular weight distribution of the resulting polymer (TWI651341-B). Another method is to limit the content of bishexamethylenetriamine within the polymer through directly subjecting an equimolar salt of adipic acid and hexamethylenediamine (HMD) to an SSP step while replenishing the escaped amount of HMD followed by melt polymerization and another SSP step (JP-3005692- B). Other known strategies to control the molecular weight distribution and the Mz / Mwparameter of polyamides include addition of polymerization catalysts, such as phosphoric acid or sodium hypophosphite, and modulation of the heating and decompression of the polymerization medium (EP-2871201-A). Other conventional methods for adjusting the molecular weight distribution and the parameter Mz / Mwinclude blending resins which have different molecular weights (EP- 3127945-A).

[0052] The polyamide of particular utility in the present invention is or comprises PA66, and preferably the polyamide is PA66. However, in alternative embodiments the polyamide may be or may comprise at least one polyamide selected from 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). The preferred PA66 polyamide may be presentin the yarns disclosed herein in combination with one or more of any of said polyamides of said alternative embodiments.

[0053] In general, the drawn polyamide yarns made from the polyamides of the present invention preferably have a linear density in the range of from about 50 to about 3000 decitex.

[0054] In respect of the first aspect of the invention, said drawn polyamide yarn preferably has a linear density in the range from about 200 to about 3000 decitex, preferably from about 300 to about 2500 decitex, preferably from about 400 to about 2500 decitex, preferably from about 600 to about 2300 decitex.

[0055] In respect of the second aspect of the invention, said drawn polyamide yarn preferably has a linear density in the range from about 50 to about 2500 decitex, preferably from about 100 to about 2000 decitex, preferably from about 150 to about 1500 decitex.

[0056] In general, the polyamide yarns made from the polyamides of the present invention preferably have 10 to about 450 filaments.

[0057] In respect of the first aspect of the invention, the number of filaments in the yarn is preferably about 30 to about 450, preferably about 60 to about 300, preferably about 100 to about 250.

[0058] In respect of the second aspect of the invention, the number of filaments in the yarn is preferably about 10 to about 300, preferably about 20 to about 200, preferably about 30 to about 150.

[0059] In general, the tenacity of the drawn polyamide yarn is preferably > 6.5 cN / dtex, preferably > 7.0 cN / dtex, preferably > 7.5 cN / dtex, preferably > 8.0 cN / dtex, preferably > 8.5 cN / dtex, preferably > 9.0 cN / dtex.

[0060] In the first aspect of the invention, the tenacity of the drawn polyamide yarn is preferably > 8.0 cN / dtex, preferably > 8.5 cN / dtex, preferably > 9.0 cN / dtex. Of particular utility in the first aspect of the invention are drawn polyamide yarns which exhibit: (i) a formic acid relative viscosity (RV) of about 90 to about 200; (ii) a polyamide molecular weight distribution (Mz / Mw) in the range of > 1.40 and < 1.50 ±0.03; and (iii) a tenacity of >8.5 cN / dtex (preferably >9.0 cN / dtex).

[0061] In the second aspect of the invention, the tenacity of the drawn polyamide yarn is preferably > 6.5 cN / dtex, preferably > 7.0 cN / dtex, preferably > 7.5 cN / dtex, preferably > 8.0 cN / dtex, preferably > 8.5 cN / dtex, preferably > 9.0 cN / dtex. Of particular utility in the secondaspect of the invention, particularly within the context of the end-uses of the seventh, eighth and ninth aspects of the invention, are drawn polyamide yarns which exhibit: (i) a formic acid relative viscosity (RV) of about 90 to about 200; (ii) a polyamide molecular weight distribution (Mz / Mw) in the range of 1.40 to 1.50 ±0.03; (iii) an elongation at maximum force that is greater than 15.0% of its original dimension; and (iv) a tenacity of >8.5 cN / dtex (preferably >9.0 cN / dtex).

[0062] In the first aspect of the invention, the drawn polyamide yarn preferably exhibits an elongation at maximum force of about 10.0 to about 30.0 percent, preferably about 15.0 to about 30.0 percent, preferably about 15.0 to about 27.0 percent, preferably about 15.0 to about 25.0 percent, preferably about 16.0 to about 25.0 percent, preferably about 17.0 to about 25.0 percent, preferably about 18.0 to about 25.0 percent of the original dimensions.

[0063] In the second aspect of the invention, the drawn polyamide yarn preferably exhibits an elongation at maximum force of about 15.0 to about 30.0 percent, preferably about 15.0 to about 27.0 percent, preferably about 15.0 to about 25.0 percent, preferably about 16.0 to about 25.0 percent, preferably about 17.0 to about 25.0 percent, preferably about 18.0 to about 25.0 percent, of the yarn’s original dimensions.

[0064] In the first aspect of the invention, said drawn polyamide yarn preferably exhibits elongation at 45 N of about 7% to about 12%, preferably about 8% to about 12%, preferably 8.5% to about 12%, preferably about 9% to about 12% relative to the initial length of the yarn before testing.

[0065] In general, the drawn polyamide yarn preferably exhibits an energy to break of more than 0.6 J, preferably more than 0.8 J and preferably more than 1.0 J. It will be appreciated that yarns with a higher linear density exhibit a higher energy to break.

[0066] In the first aspect of the invention, the drawn polyamide yarn preferably exhibits an energy to break of at least 0.6 J, preferably at least 1.0 J, preferably at least 1.5 J, preferably at least 2.0 J, preferably at least 2.5 J, preferably at least 2.8 J. In a most preferred embodiment, the energy to break of the drawn polyamide yarn is preferably at least 2.5 J, preferably at least 2.8 J.

[0067] In the second aspect of the invention, the drawn polyamide yarn preferably exhibits an energy to break of more than 0.6 J, preferably more than 0.8 J and preferably more than 1.0 J. The energy to break of the drawn polyamide yarn is preferably more than 0.6 J and less than 1.5 J, preferably more than 0.8 J and less than 1.5 J and preferably more than 1.0 J and less than 1.5 J.

[0068] The formic acid relative viscosity (RV) of the polyamide is about 90 to about 200, preferably about 90 to about 150, preferably about 90 to about 130, preferably about 90 to about 120. Preferably, the RV is at least 95. Thus, preferably the RV is about 95 to about 200, preferably about 95 to about 150, preferably about 95 to about 130, preferably about 95 to about 120.

[0069] The formic acid relative viscosity (RV) of the drawn polyamide yarn is about 90 to about 200, preferably about 90 to about 150, preferably about 90 to about 130, preferably about 90 to about 120. Preferably, the RV is at least 95. Thus, preferably the RV is about 95 to about 200, preferably about 95 to about 150, preferably about 95 to about 130, preferably about 95 to about 120. It was observed that the RV of the polyamide decreases during processing of the yarn, which the inventors speculate is a result of polymer degradation during yarn manufacture and processing, and particularly as a result of the high temperatures and mechanical stress experienced during the spinning process. The RV reduction during processing of the yarn was observed to be more significant at higher molecular weights (i.e. at higher starting RVs of the polyamide starting material). Thus, the RV of the drawn polyamide yarn is typically lower than the RV of the starting polyamide.

[0070] The formic acid relative viscosity (RV) is measured according to ASTM D789-19 (2019) using a 90% formic acid solution, as reported hereinbelow.

[0071] There is a correlation between viscosity and molecular weight. Higher molecular weight polymers generally result in higher RV values. The molecular weight and RV affects the mechanical and physical properties of the polyamide (preferably PA66) in different applications, as well as consistency and quality in the manufacturing process.

[0072] The process of producing high RV polyamide fiber involves carefully controlling the polymerization reaction to achieve a high degree of polymerization, or chain length, in the resulting polymer. As is known in the art, this can be accomplished by adjusting reaction conditions such as temperature, pressure, and catalyst concentration, to optimize the polymerization kinetics and control the molecular weight distribution.

[0073] It will be appreciated that the yarns described herein are drawn yarns.

[0074] The percent of dry heat shrinkage of the drawn polyamide yarn is preferably about 5 to about 10 percent, preferably about 6 to about 8 percent, about 6 to about 7 percent of the length of drawn fibers before the test.

[0075] The polyamides of the present invention and the yarns made therefrom preferably do not include benzene sulfonate compounds, as the inclusion of such compounds may not be suitable for all applications. Additionally or alternatively, the present methods and products do not comprise phosphorous-containing compounds. Phosphorus-containing acid compounds may or may not be included in the polymer as catalyzer or an agent to further improve polymer stability against oxidation at higher temperatures. According to reference EP2188421 Bl and US4966949 A, examples of suitable compounds include X— (CH2)n PO3 R2, wherein X is selected from 2- pyridyl, -NH2, NHR', and N(R')2, n=2 to 5, R and R' independently are H or alkyl; 2- aminoethylphosphonic acid, potassium tolylphosphinate, or phenylphosphinic acid. Preferred compounds include 2-(2'-pyridyl) ethyl phosphonic acid, and metal hypophosphite salts including sodium and manganous hypophosphite. A base such as an alkali metal bicarbonate can be added to the catalyst to minimize thermal degradation, as described in US 5,116,919.

[0076] Preferably, the polyamides do not contain a phenolic antioxidant stabilizer, in particular a hindered phenolic stabilizer. Such compounds include alkyl-substituted and / or arylsubstituted phenols, particularly such hindered phenols compounds.

[0077] The drawn polyamide yarns (particularly a PA66 yarn) can be a made by a method which includes shear heating flakes of said polyamide until the polymer reaches a molten state. The heating is followed by extrusion of the molten polyamide through spinnerets with multiple holes and rapidly cooling the molten polymer that exits the spinnerets to solidify the filaments. Cooling can be done by a stream of air. A lubricant is then applied to filaments. The filaments are then passed through a series of one or more heated rollers to stretch and align the molecules. This process is called drawing. Drawing can occur in multiple stages with rollers rotating at different speeds and at different temperatures. The drawn yarns are then relaxed by passing through another set of one or more rollers to achieve the required shrinkage on the final yarn. The finished filaments are wound onto bobbins and optionally further processed.

[0078] In the second aspect of the invention relating to polyamides for use in industrial articles comprising or prepared from a drawn polyamide yarn as described herein, wherein said industrial article is a cord, thread (preferably a sewing thread, preferably a sewing thread suitable for sewing fabric together), rope or filtering fabric, the yarn preferably exhibits a tenacity of >8.5 cN / dtex (preferably > 9.0 cN / dtex). In this preferred aspect of the invention, the industrial article is not a woven fabric and is particularly not an airbag.

[0079] In the second aspect of the invention relating to polyamides for use in threads, the thread is preferably prepared by twisting single yarns, also known as “singling twist” (which is usually in the S direction), with a defined number of twists per unit length which gives the single yarns flexibility and mechanical strength. The next step is plying two or more single yarns together and twisting them in a direction which is opposite to that in the single yarns in order to balance the effect of twisting, which is also known as “finishing twist” (usually in the Z direction), with a defined number of twists per unit length to make the sewing thread. While plied yarns having an S singling twist and a Z finishing twist are more common, it is also known in the art to make plied yarns having a Z singling twist with an S finishing twist. Moreover, the plied yarns may be further twisted. Thus, in one embodiment, a thread may have an SZS form, with S-twisted singles made into Z-twisted plies which are then combined with an S-twist. In another embodiment, a thread may have a ZSZ form. Other embodiments for thread include threads having an SSZ or a ZZS pattern. The finished thread can then be dyed, and the (optional) dyeing may vary based on the final application. If chosen, dyeing can be done by wet processing. Bonding, also known as “inbonding”, which includes addition of a resin to the core of thread can help in holding the single yarns together during the sewing process. The twisted tread can be coated, also known as out- bonding or lubricating, which includes lubricating the outside of the plied thread and usually reduces the abrasion of final thread against contact surfaces and helps with the structural integrity of the sewing thread.

[0080] In a tenth aspect of the invention, there is provided the use of the polyamide of the second aspect in an airbag, wherein the polyamide is present in said airbag in the form of drawn polyamide yarn which exhibits: (i) an RV of from about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03; (iii) an elongation at maximum force of greater than 15.0% of its original dimension; and preferably (iv) a tenacity of <8.5 cN / dtex, preferably a tenacity of >6.5 cN / dtex and <8.5 cN / dtex, wherein the airbag is made from a woven fabric comprising or prepared from said polyamide yarn. Typically, the tenacity is within the preferred ranges described above in respect of the second aspect. Advantageously, such use is for the purpose of providing improved mechanical and / or thermomechanical properties to the airbag, and particularly improved melt-through resistance as defined herein. It will be appreciated that the disclosures and preferences disclosed herein for the secondaspect of the invention in respect of the polyamide yarn also apply to the tenth aspect of the invention.

[0081] In an eleventh aspect of the invention, there is provided a polyamide which exhibits (i) a formic acid relative viscosity (RV) in the range of from about 90 to about 200; and (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03. The polyamide may be used to manufacture drawn polyamide yarn as defined in the first and second aspects of the invention. It will be appreciated from the foregoing disclosure that the RV exhibited by said drawn polyamide yarn is typically lower than the RV exhibited by said polyamide starting material.

[0082] It will be appreciated that the disclosures and preferences disclosed herein for the first and second aspects of the invention also apply to the eleventh aspect of the invention.Test Methods:

[0083] The features of the polyamide yarn are evaluated using the following test methods.Linear Density of Yarn

[0084] Linear density of yarns is measured according to ASTM DI 907 - Option 6 with zero twist added.Dry Heat Shrinkage

[0085] Dry heat shrinkage of yarns is measured in hot air according to the method described in ASTM D4974 at a temperature of 177 °C and under 0.045 gf / dtex tension for a duration of 2 minutes.Formic Acid Relative Viscosity (Drawn Fiber RV)

[0086] The relative viscosity (RV) is measured on the fiber according to ASTM D789-19 (2019) using a 90% formic acid solution. One 20 g fiber sample is required for each replicate of this analysis. The drawn fiber RV specifically applies to measurement of RV on fibers samples collected after the spinning and drawing processes. 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 fiber 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. Thisprocedure is then repeated. Once the second methylene chloride rinse is complete, the fiber 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 fiber sample with clean pressurized air. The fiber is then allowed to air dry completely in an exhaust hood. Once dry, ASTM D789-19 is followed to measure the formic acid relative viscosity of the drawn fiber sample.

[0087] The RV of the polyamide starting material is measured using the same ASTM method.Fiber tensile testing

[0088] Maximum force (N) and elongation at maximum force (%) is assessed according to standard ASTM D3822 / D3822M-14 (2020) but with the amendments as listed below.

[0089] The initial gauge (clamp) length set on the Instron tensile tester is 254 mm. The Instron crosshead speed is set at 300mm / min. Fiber specimens are cut initially to size 350 mm and while one end is fixed within the upper (moving) grip, the fiber is twisted 3 tpi (twist per inch). The other end is then fixed within the lower grip of the Instron. Tensile testing is done on 10 specimens cut from the same bobbin. The reported result for maximum force (also known as breaking force or breaking load) is the average of the maximum force results of the 10 specimens which are tested in Newtons (N). The reported result for elongation at maximum force (also known as elongation at break, percentage elongation or percentage extension) is the mean average of the elongation at maximum force results of the 10 specimens which are tested (%). Tenacity is measured by the following equation.Tenacity (cN / dtex) = Maximum Force (cN) / Linear Density (dTex)

[0090] Energy to break (J) is a measure of work required to break a fiber sample and is calculated based on the fiber tensile results (obtained as detailed above) as the area under the stressstrain curve.

[0091] The elongation at 45N is also assessed using the methodology described above.Mz / Mwvalue by Size Exclusion Chromatography (SEC)

[0092] The absolute molar mass distributions of the yarn samples are measured using size exclusion chromatography (SEC) with refractive index (RI) and multi-angle light scattering (MALS) detection. Two 300 x 7.5 mm PL hexafluoroisopropanol (HFIP) gel columns are used with guards together with Wyatt Technology HELEOS multi-angle light scattering and Wyatt Technology Optilab T-rEX refractive index detectors. The temperature of columns and the RI detectors is kept at 40 and 30°C, respectively. The samples are prepared at a nominal concentration of 2 mg / mL in mobile phase consisting of 0.01 M tetraethylammonium nitrate (TEAN) in hexafluoroisopropanol (HFIP). After dissolving for 4 hours, the sample solutions are filtered through 0.45-pm polytetrafluoroethylene (PTFE) syringe filters and a volume of 200 pL is injected in the mobile phase flow for each measurement. Flow rate of solvent is 0.8 ml / min, and the run time is 40 minutes for each measurement. The molar mass averages for each sample are calculated by averaging the results from two injections of the sample and the molecular weight distribution is calculated as follows: z — average molecular weight Molecular weight distribution (Mz / Mw= - - - - - - - - — weight average molecular weight

[0093] As is conventional in the art, Mz and Mw are defined as follows:where n = 1 gives M = Mw, and n = 2 gives M = MzFatigue Resistance, as measured by Disk Fatigue testing

[0094] Tire cords are made by twisting two separate yarns at Z direction at a specified number of twists per unit length (8.5 tpi was used in this study) and then twisting them together at S direction at a specified number of twists per unit length (8.5 tpi was used in this study). The cords are then passed through the adhesive bath containing resorcinol formaldehyde latex (RFL) mixture and then dried at 150 °C for ca. 1 min under tension.

[0095] The cords are then embedded in rubber and the rubber is cured to make the test specimens. The breaking strength loss of cords made of yarns are measured according to ASTM D6588 / D6588M-11(2016). The test is done under 15% compression and 10% tension for 11.5hours. Cured-in-rubber cords are removed from the embedding rubber after the specimens are fatigued and the breaking strength loss is measured using the following equation:Breaking Strength Loss (%)Breaking Strength before fatigue cycles (IV) — Breaking strength after fatigue cycles (IV) Breaking Strength before fatigue cycles (IV)Cured-in-rubber strength

[0096] Tire cords are made using the method described in the previous section. Cured-in- rubber strength is measured by wrapping adhesive (RFL) treated cord around a 7.3 cm by 27.6 cm clean, flat steel plate with approximately 0.6 mm spacing between adjacent wraps of cord. When the desired number of wraps (generally 5) have been made, the two ends of the cord are tied together at the back of the plate using a double square knot to firmly secure the sample to the plate. A 7.3 cm by 27.6 cm piece of rubber of appropriate composition (in this case a typical passenger tire carcass stock formulation), 0.76 mm thick, is placed on top of the cords wrapped around the plate. The sample is then cured in a hydraulic press for 20 minutes at 177±2 °C under 3.3 (3000 kgm) tons pressure. At the end of the curing cycle the sample is removed from the press and the exposed cords on the back side of the plate are immediately cut. After cooling to room temperature, the cords are pulled from the rubber and then allowed to condition at 24°C / 55% RH for at least 48 hours. Cured-in-rubber breaking strength is then determined using a 15.2 cm gauge length and a strain rate of 120% / min.Characterizing the Yarn using Fabric Testing

[0097] In the second aspect of the invention, the yarn is evaluated for thermo-mechanical properties by weaving the yarn into fabric. The woven fabrics are tested for resistance to melt at temperatures which are chosen to be representative of end use conditions. Fabric is woven through a conventional method using a symmetrical construction, with 20.5 ends / cm for both warp and weft directions and a fabric weight of 219±4 g / cm2. A minimum of 3 fabric samples are tested and measured as followed for reproducibility. Fabric samples are conditioned at 20°C ± 2 °C at a relative humidity of 65% ± 4% for 24 hours prior to testing, according to IS0139:2005(E).Melt-through resistance

[0098] To measure the melt-through resistance of the woven fabric, a “hot rod” test is used. Each fabric piece is 75 mm wide (warp direction) and 100 cm long (weft direction). This test uses an AISI Type A2 tool steel cylindrical rod, which is 50 mm 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 37.0 g, with a specific heat capacity of 461 J / (kgK). 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 350°C and 650°C. The first test site must be at least 20 cm from the fabric selvedge. Light sensors osi honed in the deli very tube and 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 upper light beam and the lower light beam, wherein the total time equals the residence time of the rod on the fabric plus 0.2 seconds (which is the free-fall time it takes for the rod to pass between the light beams 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 improved properties including increased thermo-mechanical resistance. Each test is repeated 10 times, and a mean average calculated, to characterize the time required to melt through the fabric sample in seconds.Processability

[0099] During the spinning trials, the condition of multifilament is monitored between spinneret and winders and the processability is rated with a number between 1 and 4, where 1 is the best condition and the lowest number of breaks is seen and 4 the worst condition (comparatively) and it means the process goes through many breaks and has to be started over every few minutes.Examples

[0100] A series of example yarns are selected to evaluate the features of polyamides having varying relative viscosity and Mz / Mwvalues and according to the first aspect of the invention. The polymerization conditions of the PA66 of Examples 1 and 2 are adjusted using the techniques described hereinabove to provide a combination of high RV and Mz / Mw1values which fall within claim 1. Comparative Examples 1 to 4 exhibit either RV or Mz / Mwvalues which fall outside claim 1. Comparative Examples 3 and 4 correspond to Comparative Examples 1 and 2 but produced using lower draw ratios. The yarns are evaluated according to the measurement methods disclosed herein, and the results are presented in Table 1. For fatigue resistance and cured-in-rubber strength, tire cords are made by twisting two separate yarns per example (1400 dtex each) at Z direction (8.5 tpi) then twisting them together at S direction (8.5 tpi).Table 1

[0101] The RV of a yarn generally increases with increasing molecular weight and as such can be used as a representative measurement for the molecular weight of a sample. Examples 1 and 2 are provided to exemplify yarns having an RV in the preferred range of 90- 130. Comparative Examples 1 and 3 are selected to have a lower molecular weight and consequently a lower RV, below the preferred range. Comparative Examples 2 and 4 were intended to provide examples with a higher molecular weight and consequently a higher RV of about 140, but were instead foundto have an RV value of 102. While not wishing to be bound by theory, it is speculated that the lower-than-expected RV for Comparative Examples 2 and 4 is the result of polymer degradation which occurs more frequently in processing of higher molecular weight polyamides.

[0102] As can be seen from the results in table 1, Comparative Example 2 exhibits an elongation at maximum force of only 14.6% and an energy to break of only 2.3 J, which is lower than the other samples. Thus, while the fatigue resistance (strength retention) of Comparative Example 2 is comparable with that of Example 2, the strength was already at a low level. Additionally, the processability is worse for Comparative Example 2 than for the other samples. These results suggest that increased degradation is occurring in this sample.

[0103] Table 1 shows fatigue resistance improves as RV increases for Example 1,Example 2 and Comparative Example 1. Comparative Example 2, which is expected to have the highest molecular weight, does not have a higher RV but rather, has comparable fatigue resistance to Example 2. As noted above, it is thought that the RV for the Comparative Example 2 is lower than expected due to degradation occurring during the processing. Taking the elevated degradation of Comparative Example 2 into account, the data shows a correlation between increasing RV (as a representation of increased molecular weight) and improved fatigue resistance.

[0104] The samples of Table 1 are analyzed for molecular weight distribution in the fully drawn fiber. It is observed that when the polymerization process is controlled well enough to avoid degradation and branching, and to achieve the desired molecular weight distribution (Mz / Mw) of the present invention, an increase in RV results in both higher fatigue resistance (strength retention) and cured-in-rubber strength. In other words, the improvement of both fatigue resistance and cured-in-rubber strength associated with higher molecular weight (RV) is only observed when the Mz / Mwof the polymer constituting the drawn yarn is within the ranges of the present invention. Comparative example 2 does not follow the same trend as other examples and it can be seen that it has a Mz / Mwoutside of the claimed range and accordingly, processability is the worst amongst other examples and both the fatigue and cured-in- rubber strength is not improved.

[0105] A further series of yarns are selected to evaluate the features of polyamides having varying relative viscosity and Mz / Mwvalues and according to the second aspect of the invention. The polymerization conditions of the PA66 of Examples 1 and 2 are adjusted as described for the previous series of yarns. The yarns are evaluated according to the measurementmethods disclosed herein, and the results are presented in Table 2. For the analysis of the fabric properties (melt-through resistance), the woven fabric has a construction of 20.5 x 20.9 ends / cm and a fabric weight of 222.6 g / m2.Table 2

[0106] Examples 1 and 2 exemplify yarns having an RV in the preferred range of90-130. Comparative Example 1 has a lower molecular weight and consequently a lower RV, below the preferred range. Comparative Example 2 was intended to provide an example with ahigher molecular weight and consequently a higher RV of about 140 but was instead found to have an RV value of 102 which, as described hereinabove is likely the result of polymer degradation.

[0107] Comparative Example 2 exhibits an elongation at maximum force of only 14.6% and an energy to break of only 0.7 J, which is lower than the other samples. Additionally, the processability is worse for Comparative Example 2 than for the other samples. These results suggest that increased degradation is occurring in this sample.

[0108] Table 2 shows that as the relative viscosity increases for ComparativeExample 1, Example 1 and Example 2, the melt-through resistance for a fabric composed of the yarn increases at both 350 °C and 650 °C. However, for Comparative Example 2 the melt-through resistance drops. It is speculated that this may be the result of degradation occurring in the production of the Comparative Example 2. Taking the elevated degradation of Comparative Example 2 into account, the data show that the melt-through resistance is improved as the RV increases.

[0109] The samples of Table 2 are analyzed for molecular weight distribution of the fully drawn fiber. It is observed that when the polymerization process is controlled wellenough to avoid degradation and branching, and to achieve a molecular weight distribution (Mz / Mw) that is more than 1.40 and less than 1.50, an increase in RV results in higher melt-through resistance. In other words, the improvement of melt-through resistance which is associated with higher RV and molecular weight is only observed when the Mz / Mwof the polymer constituting the drawn yarn is more than 1.40 and less than 1.50. Comparative example 2 does not follow the same trend as other examples and it can be seen that it has Mz / Mwoutside the desired range and accordingly, processability is the worst amongst other examples and melt-through resistance is not improved.

[0110] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the purpose and scope of the invention as outlined in the claims appended hereto. Any examples provided herein are included solely for the purpose of illustrating the invention and are not intended to limit the invention in any way. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.

Claims

Claims1. A polyamide suitable for making drawn polyamide yarn which exhibits (i) an RV of about 90 to about 200; and (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03.

2. The polyamide of claim 1 wherein said polyamide molecular weight distribution Mz / Mwis in the range of from 1.42 to 1.49 ±0.03, preferably from 1.45 to 1.48 ±0.03.

3. A polyamide according to any preceding claim wherein said RV is about 90 to about 150, preferably 90-130, preferably 90-120, and preferably greater than 95.

4. A polyamide according to any claim 3 wherein said RV exhibited by said drawn polyamide yarn is less than the RV exhibited by said polyamide suitable for making said drawn polyamide yarn.

5. A polyamide according to any preceding claim wherein said polyamide yarn has a linear density in the range of from about 50 to about 3000 decitex.

6. A polyamide according to any preceding claim wherein said polyamide yarn has 10 to about 450 filaments.

7. A polyamide according to any preceding claim wherein said polyamide yarn exhibits a tenacity of > 6.5 cN / dtex, preferably > 7.0 cN / dtex, preferably > 7.5 cN / dtex, preferably > 8.0 cN / dtex, preferably > 8.5 cN / dtex, preferably > 9.0 cN / dtex.

8. A polyamide according to any preceding claim wherein said polyamide yarn exhibits an energy to break of more than 0.6 J, preferably more than 0.8 J and preferably more than 1.0 J.

9. The polyamide according to any preceding claim wherein the polyamide yarn exhibits a dry heat shrinkage is 5-10%.

10. The polyamide of any preceding claim which does not contain benzenesulfonate compound or contains benzenesulfonate in amounts of less than 5 ppm.

11. The polyamide according to any preceding claim further comprising a phosphorous- containing compound, preferably selected from: compounds defined by the formula X- (CH2)nPO3R2, wherein X is selected from 2-pyridyl, -NH2, NHR', and N(R')2, n=2 to 5, R and R' independently are H or alkyl; 2-aminoethylphosphonic acid, potassium tolylphosphinate, orphenylphosphinic acid; 2-(2'-pyridyl) ethyl phosphonic acid; and metal hypophosphite salts including sodium and manganous hypophosphite.

12. The polyamide according to any of claims 1 to 10 which does not comprise a phosphorous- containing compound.

13. The polyamide according to any preceding claim which does not contain a phenolic antioxidant stabilizer, in particular a hindered phenolic stabilizer, in particular alkyl-substituted and / or aryl-substituted phenols.

14. The polyamide according to any preceding claim wherein the polyamide is or comprises at least one polyamide selected from polyamide 6,6 (PA66), 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), and preferably wherein the polyamide is or comprises PA66.

15. The polyamide according to any preceding claim wherein the polyamide is PA66.

16. A polyamide according to any of claims 1 to 15 which is suitable for making drawn yarn which exhibits (i) an RV of about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03, and preferably (iii) a tenacity of >8.5 cN / dtex.

17. A polyamide according to claim 16 wherein said polyamide yarn has a linear density in the range from about 200 to about 3000 decitex, preferably from about 300 to about 2500 decitex, preferably from about 400 to about 2500 decitex, preferably from about 600 to about 2300 decitex.

18. A polyamide according to claim 16 or 17 wherein said polyamide yarn has a number of filaments of about 30 to about 450, preferably about 60 to about 300, preferably about 100 to about 250.

19. A polyamide according to any of claims 16 to 18 wherein said drawn polyamide yarn exhibits an elongation at maximum force of about 10.0 to about 30.0 percent, preferably about 15.0 to about 30.0 percent, preferably about 15.0 to about 27.0 percent, preferably about 15.0 to about 25.0 percent, preferably about 16.0 to about 25.0 percent, preferably about 17.0 to about 25.0 percent, preferably about 18.0 to about 25.0 percent of the original dimensions.

20. A polyamide according to any of claims 16 to 19, wherein said drawn polyamide yarn exhibits elongation at 45 N of about 7% to about 12%, preferably about 8% to about 12%, preferably 8.5% to about 12%, preferably about 9% to about 12% relative to the initial length of the yarn before testing.

21. A polyamide according to any of claims 16 to 20, wherein said drawn polyamide yarn exhibits an energy to break of at least 0.6 J, preferably at least 1.0 J, preferably at least 1.5 J, preferably at least 2.0 J, preferably at least 2.5 J, preferably at least 2.8 J.

22. A polyamide according to any of claims 16 to 21 wherein said drawn polyamide yarn is suitable for making tire cord, preferably wherein said tire cord exhibits improved fatigue resistance and / or cured-in-rubber strength, relative to a tire cord made from drawn polyamide yarn not having said combination of RV and Mz / Mwcharacteristics.

23. A polyamide according to any of claims 16 to 22 wherein tire cord made from said drawn polyamide yarn exhibits a cured-in-rubber strength of > 50 N, preferably > 70 N, preferably > 100 N, preferably > 130 N, preferably > 150 N, preferably > 180 N, preferably > 210 N, preferably > 220 N.

24. A polyamide according to any of claims 16 to 23 wherein tire cord made from said drawn polyamide yarn exhibits a fatigue resistance of >35%, preferably >50%, preferably >65%, preferably >70%, preferably from about 70 % to about 90%.

25. A polyamide according to any of claims 1 to 15 which is suitable for making drawn polyamide yarn which exhibits: (i) an RV of from about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03; and (iii) an elongation at maximum force of greater than 15.0% of its original dimension.

26. The polyamide according to claim 25 wherein said polyamide yarn has a linear density of from about 50 to about 2500 decitex.

27. The polyamide according to claim 25 or 26 wherein said polyamide yarn has from about 10 to about 300 filaments.

28. A polyamide according to any of claims 25 to 27 wherein said polyamide yarn exhibits an elongation at maximum force of about 15.0 to about 30.0 percent, preferably about 15.0 to about 27.0 percent, preferably about 15.0 to about 25.0 percent, preferably about 16.0 to about 25.0percent, preferably about 17.0 to about 25.0 percent, preferably about 18.0 to about 25.0 percent of the original dimensions.

29. The polyamide according to any of claims 25 to 28 wherein said polyamide yarn exhibits an energy to break of more than 0.6 J, preferably more than 0.8 J and preferably more than 1.0 J; and preferably more than 0.6 J and less than 1.5 J, preferably more than 0.8 J and less than 1.5 J and preferably more than 1.0 J and less than 1.5 J.

30. The polyamide according to any of claims 25 to 29 wherein said drawn polyamide yarn exhibits improved results in the melt-through resistance test in respect of a fabric made from said yarn compared to a drawn polyamide yarn not having the combination of RV and Mz / Mwcharacteristics.

31. The polyamide according to any of claims 25 to 30 which exhibits one or more of i) a melt- through resistance at 350°C of > 3.20 seconds; and / or ii) a melt-through resistance at 650°C of > 0.70 seconds, measured as described herein.

32. The use of the polyamide according to any of claims 16 to 24 in a tire cord for the purpose of improving the fatigue resistance and / or cured-in-rubber strength thereof wherein said polyamide is present in said tire cord in the form of drawn polyamide yarn which exhibits (i) an RV of about 90 to about 200; and (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03.

33. The use of the polyamide according to any of claims 16 to 24 in a tire for the purpose of enhancing the durability thereof wherein said polyamide is present in said tire in the form of a tire cord made from drawn polyamide yarn which exhibits (i) an RV of about 90 to about 200; and (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03.

34. The use of the polyamide according to any of claims 25 to 31 in an industrial article selected from a cord, thread, rope and filtering fabric for the purpose of improving the mechanical strength and / or thermo-mechanical properties of said industrial article, wherein said polyamide is present in said industrial article in the form of drawn polyamide yarn which exhibits: (i) an RV of from about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwinthe range of 1.40 to 1.50 ±0.03; and (iii) an elongation at maximum force of greater than 15.0% of its original dimension.

35. The use according to claim 34 wherein said industrial article is a cord, thread or rope, more preferably a thread, preferably wherein said thread is a sewing thread, preferably wherein said cord is a belt cord such as conveyor belt cord or a parachute cord.

36. The use of the polyamide according to claims 25 to 31 in an airbag, wherein said polyamide is present in said airbag in the form of drawn polyamide yarn which exhibits: (i) an RV of from about 90 to about 200; (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03; (iii) an elongation at maximum force of greater than 15.0% of its original dimension; and preferably (iv) a tenacity of <8.5 cN / dtex, preferably a tenacity of >6.5 cN / dtex and <8.5 cN / dtex, preferably a tenacity of >8.0 cN / dtex and <8.5 cN / dtex, wherein the airbag is made from a woven fabric comprising or prepared from said drawn polyamide yarn, preferably wherein such use is for the purpose of providing improved mechanical and / or thermomechanical properties to the airbag, and particularly improved melt-through resistance.

37. A polyamide which exhibits (i) a formic acid relative viscosity (RV) in the range of from about 90 to about 200; and (ii) a polyamide molecular weight distribution characterized by Mz / Mwin the range of > 1.40 and < 1.50 ±0.03.

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