Polyamide industrial yarn with improved thermo-mechanical properties

Abstract

A high tenacity drawn polyamide (preferably PA66) yarn finding utility as an industrial thread and having a formic acid relative viscosity (RV) of about 90 to about 200, a molecular weight distribution characterized by Mz / Mw in the range of 1.40 to 1.50 ±0.03 and an elongation at maximum force is greater than 15.0% of its original dimension.

Description

POLYAMIDE INDUSTRIAL YARN WITH IMPROVED 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 polyamide yarn having a high relative viscosity with improved thermo-mechanical properties. In particular, the present application relates to higher molecular weight polyamide 6,6 (PA66), used for making yarns having improved thermomechanical properties and the industrial articles made thereof including cords, threads, and ropes.BACKGROUND

[0003] High strength polyamide fiber is a well-known yarn that is used in industrial applications such as 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.

[0004] 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.

[0005] 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.

[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 (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.

[0007] Accordingly, there is still a need for new material for industrial yarns having improved thermo-mechanical properties.

[0008] It is an object of this invention to address the aforementioned problems and in particular to provide a polyamide yarn having improved thermo-mechanical properties and the industrial articles made thereof including cords, threads, and ropes.SUMMARY

[0009] In accordance with one aspect of the invention there is provided a polyamide yarn having improved thermo-mechanical properties. The polyamide is preferably polyhexamethylene adipamide (also known as polyamide 66, PA66 or nylon 66). The improvement in thermomechanical properties is exhibited relative to a polyamide yarn not having the characteristics recited herein, and in particular polyamide yarn not having the combination of formic acid relative viscosity (RV) and molecular weight distribution (Mz / Mw) characteristics.

[0010] In a further aspect there is provided a drawn polyamide (preferably PA66) yarn having formic acid relative viscosity (RV) of about 90 to about 200, wherein said polyamide has a molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03 and wherein the yarn exhibits an elongation at maximum force that is greater than 15.0% of its original dimension. The yarn exhibits improved results in the melt-through resistance test in respect of a fabric made from said yarn, compared to a polyamide (preferably PA66) yarn not having the formic acid relative viscosity (RV) and molecular weight distribution (Mz / Mw) characteristics, and in particular compared to a polyamide (preferably PA66) yarn having a lower formic acid relative viscosity and an Mz / Mwvalue outside of the stated range.

[0011] Preferably, the polyamide (preferably PA66) yarn exhibits a molecular weight distribution characterized by Mz / Mwin the range of 1.42 to 1.49 ±0.03, preferably 1.45 to 1.48 ±0.03. It will be appreciated that the molecular weight distribution (Mz / Mw) parameter described herein is that of the polyamide constituting the drawn yarn.

[0012] In a further aspect said polyamide yarn is suitable for use in a sewing thread.

[0013] In a further aspect there is provided a method of preparing the drawn polyamide yarn as defined herein 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 andg) winding the finished filaments onto bobbins.

[0014] In a further aspect there is provided a method of preparing a sewing thread from the drawn polyamide yarn as defined herein comprising the steps of: a) twisting; b) plying two or more single yarns together; c) optionally dyeing; d) bonding; and e) coating, all as further described below. Thus, said method 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.

[0015] In a further aspect of the invention there is provided 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, and wherein at least one of said sewing threads comprises or is prepared from a drawn polyamide (preferably PA66) yarn as defined herein. 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. In this further aspect of the invention, 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 nonfabric 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.

[0016] In a further aspect of the invention, there is provided the use of the drawn polyamide yarn as defined herein as or in the manufacture of an industrial article selected from a cord, thread, rope and filtering fabric, particularly from a cord, thread or rope, particularly a thread andparticularly a sewing thread. Polyamide yarns used in this way provide improvements in the mechanical strength of the article made therefrom and particularly the thermo-mechanical properties of the article made therefrom. Mechanical strength is suitably measured via conventional tensile testing as is known in the art.DETAILED DESCRIPTION OF THE INVENTION

[0017] It is an object of this invention to provide industrial yarn made of polyamide (preferably PA66) yarns with drawn yarn RV higher than 90 (measured as described in the test methods) which have improved thermo-mechanical properties.

[0018] As a rule of thumb, an increase in the molecular weight of polymer (PA66 in particular) 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 crosslinking will 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.

[0019] 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. PA66 is often used as the base polymer for industrial yarn due to its high mechanical strength, thermal resistance, and energy absorption characteristics relative to fabrics made with other polymers.

[0020] The industrial fibers 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.

[0021] 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 viaconventional 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).

[0022] 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 thermo-mechanical properties.

[0023] 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 propertiesof 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.

[0024] 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 90-120), if the polymer constituting the yarn has a molecular 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.

[0025] 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.

[0026] 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.

[0027] 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).

[0028] 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 present in the yarns disclosed herein in combination with one or more of any of said polyamides of said alternative embodiments.

[0029] The yarn of the present disclosure 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.

[0030] 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.

[0031] The tenacity of the 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 present invention is a yarn having a formic acid relative viscosity (RV) of about 90 to about 200 and an elongation at maximum force that is greater than 15.0% of its original dimension and a tenacity of >8.5 cN / dtex (preferably > 9.0 cN / dtex), and comprising polyamide (preferably PA66) characterized by a molecular weight distribution (Mz / Mw) in the range of> 1.40 and < 1.50 ±0.03, preferably > 1.42 and < 1.49 ±0.03 and preferably > 1.45 and <1.48 ±0.03.

[0032] The 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.

[0033] The energy to break of the yarn is preferably more than 0.6 J, preferably more than 0.8 J and preferably more than 1.0 J. The energy to break of the 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.

[0034] The formic acid relative viscosity (RV) of the drawn yarn in the present invention 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 yarn has an RV of 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.

[0035] The formic acid relative viscosity (RV) is measured according to ASTM D789-19 (2019) using a 90% formic acid solution, as reported hereinbelow. It will be appreciated that the formic acid relative viscosity values defined herein are those of the polyamide constituting the drawn yarn.

[0036] 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.

[0037] 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.

[0038] It will be appreciated that the yarns described herein are drawn yarns.

[0039] The percent of dry heat shrinkage of the 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.

[0040] 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.

[0041] 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.

[0042] It is a further aspect of the present methods and products that they preferably do not include using 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 ormay 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.

[0043] Preferably, the polyamide used in the present invention does not contain a phenolic antioxidant stabilizer, in particular a hindered phenolic stabilizer. Such compounds include alkylsubstituted and / or aryl-substituted phenols, particularly such hindered phenols compounds.

[0044] In another aspect of the invention there is provided a method of making a polyamide yarn, and particularly a PA66 yarn. In an embodiment the method 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.

[0045] In a most preferred aspect, the invention provides an industrial article comprising or prepared from a polyamide (preferably PA66) yarn as defined herein, preferably wherein said industrial article is a cord, thread, rope or filtering fabric, particularly a cord, thread or rope, preferably wherein said thread is a sewing thread (preferably a sewing thread suitable for sewing fabric together), preferably wherein said cord is a belt cord such as conveyor belt cord, or parachute cord. Preferably, said industrial article is prepared from a polyamide (preferably PA66) yarn as defined herein. In this preferred aspect of the invention, the yarn 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.

[0046] In a particularly preferred aspect of the invention there is provided a thread, preferably a sewing thread, preferably a sewing thread suitable for sewing fabric together, wherein the thread comprises or is prepared from the yarn as described herein, and preferably is prepared from said yarn. In this particularly preferred aspect of the invention, the yarn exhibits a tenacity of >8.5 cN / dtex (preferably > 9.0 cN / dtex).

[0047] In still a further aspect there is provided a method of preparing said thread. 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.

[0048] In an alternative aspect of the invention, there is provided an airbag made from a woven fabric wherein said woven fabric comprises or is prepared from a polyamide (preferably PA66) yarn as defined herein, preferably wherein the yarn exhibits a tenacity of <8.5 cN / dtex, preferably a tenacity of >6.5 cN / dtex and <8.5 cN / dtex, and typically wherein the tenacity is within the preferred ranges described hereinabove.Test Methods:

[0049] The features of the polyamide yarn are evaluated using the following test methods.Linear Density of Yarn

[0050] Linear density of yarns is measured according to ASTM DI 907 - Option 6 with zero twist added.Dry Heat Shrinkage

[0051] 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 (RV) (Drawn Fiber RV)

[0052] 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. This procedure 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.Fiber tensile testing

[0053] 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.

[0054] 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 andwhile 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)

[0055] 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.Mz / Mwvalue by Size Exclusion Chromatography (SEC)

[0056] 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

[0057] As is conventional in the art, Mz and Mw are defined as follows:where n = 1 gives M = Mw, and n = 2 gives M = MzCharacterizing the Fiber using Fabric Testing

[0058] To evaluate (or quantify) the improved thermo-mechanical properties of the yarn, the article is woven into fabric, and the woven fabrics then tested for resistance to melt. The tests utilize 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 follows 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

[0059] 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 posi honed in the delivery 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 I ln beain, 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

[0060] 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

[0061] A series of example yarns are selected to evaluate the features of the yarns having varying relative viscosity and Mz / Mwvalues. 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 / Mwvalues which fall within claim 1. Comparative Examples 1 and 2 exhibit either RV or Mz / Mw values which fall outside claim 1. The yarns are evaluated according to the measurement methods disclosed herein, and the results are presented in Table 1. 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 1

[0062] 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 Example 1 is selected to have a lower molecular weight and consequently a lower RV, below the preferred range. Comparative Example 2 was intended to provide an example with a highermolecular weight and consequently a higher RV of about 140, but was instead found to 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 Example 2 is the result of polymer degradation which occurs more frequently in processing of higher molecular weight polyamides.

[0063] 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 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.

[0064] Table 1 shows that as the relative viscosity increases for Comparative Example 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.

[0065] The samples of Table 1 are analyzed for molecular weight distribution of the fully drawn fiber. It is observed that when the polymerization process is controlled well-enough 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.

[0066] 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 drawn polyamide yarn having a formic acid relative viscosity (RV) of from about 90 to about 200, wherein said polyamide has a molecular weight distribution characterized by Mz / Mwin the range of 1.40 to 1.50 ±0.03, wherein the yarn exhibits an elongation at maximum force of greater than 15.0% of its original dimension.

2. The polyamide yarn according to claim 1 wherein the RV is from about 90 to about 150, preferably 90-130, preferably 90-120.

3. The polyamide yarn according to any preceding claim wherein the yarn has RV greater than 95.

4. The polyamide yarn of any preceding claim wherein the molecular weight distribution Mz / Mw is in the range of from 1.42 to 1.49 ±0.03, preferably from 1.45 to 1.48 ±0.03.

5. The polyamide yarn according to any preceding claim having a linear density of from about 50 to about 2500 decitex.

6. The polyamide yarn according to any preceding claim having from about 10 to about 300 filaments.

7. The polyamide yarn according to any preceding claim having 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, and more preferably >9.0 cN / dtex.

8. The polyamide yarn according to any preceding claim wherein the yarn exhibits an elongation at maximum force of about 15.0 to about 30.0 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.

9. The polyamide yarn according to any preceding claim wherein the energy to break of the yarn is more than 0.6, preferably more than 0.8 and preferably more than 1.0, or wherein the energy to break of the yarn is more than 0.6 and less than 1.5 J, preferably more than 0.8 and less than 1.5 J and preferably more than 1.0 and less than 1.5 J.

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

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

12. The polyamide yarn 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, -NHz, NHR', and N(R')z, n=2 to 5, R and R' independently are H or alkyl; 2-aminoethylphosphonic acid, potassium tolylphosphinate, or phenylphosphinic acid; 2-(2'-pyridyl) ethyl phosphonic acid; and metal hypophosphite salts including sodium and manganous hypophosphite.

13. The polyamide yarn according to any of claims 1 to 11 which does not comprise a phosphorous-containing compound.

14. The polyamide yarn 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.

15. The polyamide yarn according to any preceding claim wherein the yarn exhibits improved results in the melt-through resistance test in respect of a fabric made from said yarn.

16. The polyamide yarn according to claim 15 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.

17. The polyamide yarn 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, and preferably wherein the polyamide is PA66.

18. A method of making a drawn polyamide yarn according to any one of claims 1-17, comprising the steps of: a. shear heating polyamide flakes until the polymer reaches a molten state; b. extruding the molten polyamide through spinnerets with one or more holes;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 them through one or more heated rollers to stretch and align the molecules; f. relaxing the drawn filaments by passing through another set of one or more rollers to achieve the required shrinkage on a final yarn; and g. winding up the finished yarn onto bobbins.

19. A method according to claim 18 wherein the drawing step e) occurs in multiple stages with rollers rotating at different speeds and at different temperatures.

20. A method according to claim 18 or 19 wherein a benzenesulfonate is not added to, or used in, any step of the method, or is added or used in amounts of less than 5 ppm.

21. An industrial article comprising or prepared from a drawn polyamide yarn according to any of claims 1 to 17, preferably wherein said industrial article is a cord, thread, rope or filtering fabric, particularly a cord, thread or rope, 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.

22. An industrial article according to claim 21 which is a thread, preferably a sewing thread, preferably a sewing thread suitable for sewing fabric together.

23. An industrial article according to claim 21 or 22 wherein the yarn exhibits a tenacity of >8.5 cN / dtex, preferably > 9.0 cN / dtex.

24. An industrial article according to any of claims 21-23 which is not a woven fabric and is particularly not an airbag.

25. An airbag made from a woven fabric wherein said woven fabric comprises or is prepared from a drawn polyamide yarn according to any of claims 1 to 17, preferably wherein the yarn exhibits a tenacity of >6.5 cN / dtex and <8.5 cN / dtex, typically >8.0 cN / dtex and <8.5 cN / dtex.

26. A method of preparing the thread of claim 22 comprising 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.

27. 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, and wherein at least one of said sewing threads comprises or is prepared from a drawn polyamide yarn according to any of claims 1 to 17.

28. The use of the drawn polyamide yarn as defined in any of claims 1-17 as or in the manufacture of an industrial article selected from a cord, thread, rope and filtering fabric, particularly from a cord, thread or rope, preferably wherein said thread is a sewing thread, preferably wherein said cord is a belt cord such as conveyor belt cord or parachute cord, and particularly wherein said industrial article is a thread and particularly a sewing thread, and preferably wherein said use is for the purpose of improving the mechanical strength of the article made therefrom and particularly the thermo-mechanical properties of the article made therefrom.

Images