Use of the same for the manufacture of polyamide yarn and tire cord with improved fatigue resistance

Abstract

It has a relative viscosity (RV) of approximately 90 to approximately 200 and a molecular weight distribution (M) of ≥1.40 and ≤1.50±0.03. z / M w A stretched polyamide (preferably PA66) high-tenacity yarn containing PA66 characterized by ). The yarn finds useful in a variety of end applications, including tire cords. The yarn provides improved fatigue resistance and / or cured rubber strength.

Description

[Technical Field]

[0001] (Cross-reference of related applications) This disclosure claims priority and benefits of U.S. Provisional Patent Application No. 63 / 529,154, filed July 27, 2023, U.S. Provisional Patent Application No. 63 / 529,161, filed July 27, 2023, U.S. Provisional Patent Application No. 63 / 661,603, filed June 19, 2024, U.S. Provisional Patent Application No. 63 / 661,600, and U.S. Provisional Patent Application No. 63 / 661,599, filed June 19, 2024, the contents of which are incorporated herein by reference in their entirety.

[0002] (Field of invention) This invention relates to a polyamide yarn suitable for tire cord fabrics. In particular, this application relates to a polyamide yarn having improved properties such as fatigue resistance and rubber hardening strength suitable for tire cord fabrics, and to a method for producing a polyamide yarn. [Background technology]

[0003] Tire cord is a fabric element used to provide dimensional stability to tires and help support the weight of the vehicle. Tire cord acts as a reinforcing material and can improve the durability of the tire. Tire cord can be made from a variety of materials, including steel, rayon, and polyester. Another common group of fibers used in tire cord manufacturing is made from polyamide (or nylon polymer), which is considered a high-strength option when improved performance is required. Tire cord can be obtained by twisting or layering polyamide fibers. The surface may be coated with an adhesive treatment. The twisted yarn may also undergo a thermosetting process before being embedded in rubber and ultimately becoming one of the many components of the tire.

[0004] During use, tires undergo numerous loading and unloading cycles throughout their lifespan, causing the yarn used as a reinforcing component in the tire to lose its mechanical strength. As the number of loading cycles increases, this reduces the tire's strength and can eventually contribute to tire deformation and failure. The loss of mechanical strength is called "fatigue," while the retention of mechanical strength is called fatigue resistance.

[0005] One of the most important properties of the fibers used in tire cords is fatigue resistance. Various methods have been used to improve the fatigue resistance of tire cords made from polyamide. Examples of such methods are as follows: ●Hybrid tire cords, such as those described in Chinese Patent Application Publication No. 113260747(B), may be made from multifilament aromatic polyamide, aramid spun yarn, nylon, or polyester multifilament. ●(Sea-island composite industrial filaments, also known as super-composite fibers, are formed by a core component continuously dispersed longitudinally within another polymer. International Publication No. 2007112665 ​​describes a process for producing sea-island composite industrial filaments containing polyester as the island component and polyamide as the sea component. Sea-island composite materials produced by this method offer improved fatigue resistance, among other characteristics.) ●The use of specific treatment solutions consisting of emulsion-based and oil-based liquids is described in Japanese Patent Publication No. 2566993(B2) and Japanese Patent Publication No. 2782510(B2). These treatments are applied in the yarn spinning process to reduce interfiber friction. ● Spinning process conditions described in Japanese Patent Publication No. 3281115(B2), wherein specific dynamic mechanical properties are satisfied.

[0006] Japanese Patent Publication No. 2015034361(A), cited in the references, reports that in order to efficiently operate liquid-phase and solid-phase polymerization apparatuses for producing high-strength polyamide fibers, it is preferable to obtain a sulfuric acid relative viscosity (SARV) in the range of 3.5 to 3.8 by solid-phase polymerization. Furthermore, a benzenesulfonate compound (5 to 300 ppm) is added as an oxidation stabilizer to the water (coming out of the polymerization autoclave) used to cool the cast polymer to reduce thermal oxidation and decomposition of the polymer during solid-phase polymerization and melt spinning. European Patent No. 3674458, cited in the references, reports that the use of PA66 fibers with an SARV greater than 3.5 results in low cost-efficiency and challenges in fiber drawing, leading to problems in achieving the required fiber strength. (SARV of 3.5 is converted to formate RV of 95.) According to these references, using fibers with an SARV greater than 3.5 without using a benzenesulfonate compound results in frequent filament breakage and is therefore technically and economically unsuitable for producing continuous polyamide multifilament yarn.

[0007] For example, the ongoing demand for better tire performance, such as for electric vehicles (EVs) with higher torque and vehicle weight applied to the tires, indicates that there is still a need for new materials for tire cord fabrics, particularly for polyamides with improved fatigue resistance and rubber-interhardening strength.

[0008] The object of the present invention is to address the above-mentioned problems, and in particular to provide a polyamide yarn for use in tire cord fabrics. [Overview of the project]

[0009] According to one aspect of the present invention, a polyamide material having improved fatigue resistance and / or cured strength in rubber is provided. Preferably, the polyamide is polyhexamethylene adipamide (also known as polyamide 66, PA66 or nylon 66). The improvement of one or both of these properties is compared with polyamide materials that do not have the features described herein, particularly those that do not have a combination of formic acid relative viscosity (RV) and molecular weight distribution (M z / M w ), and particularly those that do not have a combination of RV, M z / M w and tenacity characteristics.

[0010] Particularly, a drawn polyamide (preferably PA66) yarn is provided, which has a formic acid relative viscosity (RV) of about 90 to about 200 and a molecular weight distribution (M z / M w ) in the range of ≧1.40 and ≦1.50 ± 0.03, preferably ≧1.42 and ≦1.49 ± 0.03, preferably ≧1.45 and ≦1.48 ± 0.03. Preferably, the yarn exhibits a tenacity of >8.5 cN / dtex.

[0011] Particularly, the inventors have found that such yarns provide higher fatigue resistance and / or cured strength in rubber than those provided by drawn polyamide (preferably PA66) yarns having a lower formic acid relative viscosity and an M z / M w value outside the specified range, and also higher than those provided by drawn polyamide (preferably PA66) yarns having a lower formic acid relative viscosity, a lower tenacity and an M z / M w value outside the specified range.

[0012] In another aspect, a tire cord made from or including a drawn polyamide (preferably PA66) yarn according to the present application is provided.

[0013] The tire cord has a rubber curing strength of preferably ≥50N, preferably ≥70N, preferably ≥100N, preferably ≥130N, preferably ≥150N, preferably ≥180N, preferably ≥210N, and preferably ≥220N.

[0014] In a particularly preferred embodiment, the tire cord has a curing strength in rubber of ≥150N, preferably ≥180N, preferably ≥210N, and preferably ≥220N. It will be understood that the higher curing strength range in this particularly preferred embodiment can be achieved by using a stretched yarn with a higher linear density.

[0015] In a further embodiment, the use of a stretched polyamide (preferably PA66) yarn as defined herein in a tire cord is provided for the purpose of improving the fatigue resistance and / or hardening strength in rubber of the tire cord including the aforementioned yarn. The use of a yarn for such purposes is particularly useful with respect to a yarn exhibiting a tenacity of >8.0 cN / dtex (preferably >8.5 cN / dtex), preferably a breaking energy of at least 2.5 J, and / or elongation at maximum force of about 10 to about 30 percent (particularly at least 15.0 percent), and / or elongation at 45 N of about 7 to about 12% (particularly about 8.5 to about 12%), preferably having preferred thresholds and ranges of these parameters as defined herein.

[0016] In a further embodiment, the use of tire cords comprising a stretched polyamide (preferably PA66) yarn as defined herein is provided for the purpose of improving the durability of the tire.

[0017] In a further aspect of the present invention, a tire is provided that includes tire cords as defined herein.

[0018] In a further embodiment, a method for preparing a stretched polyamide (preferably PA66) yarn according to the present application, a) A step of shearing and heating polyamide (preferably PA66) flakes until the polymer reaches a molten state, b) A step of extruding the molten polymer through a spinneret, c) A step of cooling the molten polymer coming out of the spinneret to solidify the filament, d) The process of applying lubricant to the filament, e) A step of stretching the filament by passing it through one or more heated rollers to stretch and align the molecules, f) A step of loosening the stretched yarn by passing it through another set of one or more rollers to achieve the shrinkage required for the final yarn, A method is provided which includes the step of winding the completed filament onto a bobbin.

[0019] A further aspect of the present invention relates to a method for preparing tire cord from stretched polyamide yarn as described herein, a) A step of twisting a single yarn in the Z or S direction, wherein the single yarn is a stretched polyamide yarn as described herein, b) A method is provided which includes the step of stacking two or more single yarns together and twisting them in the opposite direction to the twist direction of the single yarns, preferably with the same number of twists per unit length as each single yarn.

[0020] For the intended use in tire manufacturing, the tire cords thus produced are typically further processed by weaving the cords into a fabric ("tire cord fabric") and then used in tire manufacturing. The tire cords of the present invention are preferred as at least the warp component of the fabric. Typically, 1000 to 1500 such tire cords are woven into the fabric as the warp component. The stretched polyamide yarn of the present invention may be used alternatively or additionally as the weft component (also called "fill" or "pick" yarn) of the fabric. If the stretched polyamide yarn of the present invention is present only as a warp yarn component, any conventional weft component may be used. The weft component of tire cord fabric is typically present in the fabric at a relatively lower density than the warp component. The main function of the weft component is to maintain uniform warp spacing during subsequent processing such as transport, dipping, heat treatment, calendering, and tire manufacturing. The fabric is then dipped in a cord adhesive solution, as is well known in the art. Suitable adhesives for bonding fabrics to rubber compounds include resorcinol formaldehyde tex (RFL) mixtures. The fabric is then dried for a controlled amount of time under controlled temperature and tension. The drying temperature should be lower than the melting point of the polyamide. For example, tire cords made from drawn PA66 yarn are typically heat-treated under tension at a temperature of about 150 to about 250°C for a time preferably in the range of 10 seconds to 2 minutes, preferably under 5 to 20% elongation.

[0021] In a further aspect of the present invention, a tire cord fabric is provided which includes a tire cord made from or containing a stretched polyamide (preferably PA66) yarn according to the present invention. [Modes for carrying out the invention]

[0022] The object of the present invention is to provide an industrial yarn having improved fatigue resistance and rubber curing strength characteristics.

[0023] As a rule of thumb, increasing the molecular weight of a polymer (particularly PA66) is expected to improve the mechanical properties of products made from the aforementioned polymers. Longer chains allow for a greater number of physical entanglements, and in some cases, chemical crosslinking also contributes to changes in the material's behavior under mechanical forces. However, since such changes can have contrasting effects, it is difficult to predict the exact balance of properties affected by changes in polymer structure. For example, increasing the molecular weight theoretically makes the material stronger due to higher entanglements, but it may also result in a more brittle or degraded polymer, meaning the polymer breaks with less deformation. Therefore, producing polymers with higher molecular weights is not always advantageous to meet the requirements of the end application.

[0024] PA66 is one of the commonly used processed thermoplastics. PA66 is synthesized by polycondensation of hexamethylenediamine and adipic acid. PA66 is also known as nylon 66, and these terms are used interchangeably herein. Polyamides, particularly PA66, are often used as base polymers for tire cord fabrics due to their high mechanical strength, heat resistance, and energy absorption characteristics.

[0025] The tire cord yarn of the present disclosure is composed of fibers in the form of continuous multifilaments. In one embodiment, such filaments are formed by extruding a molten polymer at high temperature and pressure through a spinneret, subsequently quenched in air, coated with a spinning finish lubricant, stretched between a pair of rolls, and intertwined along the length of the fibers to produce a coherent yarn, which is then wound onto a cardboard tube as a bobbin.

[0026] Polyamides can be produced by conventional means known in the art. They can be produced via biosynthetic pathways or from intermediates produced via conventional petrochemical pathways. The relative viscosity of polyamides can be increased by increasing the degree of polymerization, i.e., the molecular weight, as is known in the art. For example, molecular weight and relative viscosity can typically be increased by solid-state polymerization (SSP) steps carried out under dry nitrogen at high temperatures (e.g., about 180°C).

[0027] Increasing the molecular weight of aliphatic polyamides (such as PA66) is expected to increase their strength. However, melt viscosity also increases with higher molecular weight, making polymer processing more difficult. A common solution to this problem is to increase the processing temperature to reduce the polymer's melt viscosity. However, this comes at the cost of polyamide decomposition, which negatively impacts the quality of the polymer. As a result, when the molten polymer is spun, it cannot be sufficiently stretched, and therefore the achievable mechanical properties such as tenacity, elongation at maximum force, and fracture energy are limited. Thus, simply increasing the molecular weight is a difficult way to improve the properties of polymer materials, as achieving the right balance of properties is a critical challenge overall. However, the inventors have found that by producing polyamide (preferably PA66) yarns with higher RV and adjusting the molecular weight distribution of the polymer, yarns with improved fatigue resistance can be provided.

[0028] It is known in the art that harsher conditions during polymerization (including temperature and residence time) can promote the formation of undesirable byproducts. Some of these undesirable byproducts are referred to in the industry as "gels." Gel formation in polyamides (particularly PA66) refers to the process by which polymer chains in the material crosslink, forming a three-dimensional network and resulting in a gel-like structure. As gel formation increases, the proportion of linear polymer chains in the polymer decreases, and therefore the molecular weight distribution deviates from the Flory molecular weight distribution, which is most likely for linear condensation polymers (Flory, PJ, Molecular size distribution in linear condensation polymers, Journal of the American Chemical Society, 1936, 58(10), 1877-1885). Thus, the measured molecular weight distribution of sequentially grown polymers such as polyamide 66 (M z / M w The degree of crosslinking (measured as) is considered an indicator of the linearity or lack thereof of the polymer. Gelation is typically initiated by exposure to excessive heat, radiation, or other chemical agents that crosslink polymer chains. The degree of crosslinking can affect the mechanical and physical properties of polyamides, such as their strength, stiffness, and water absorption. Gel formation can also alter the processing behavior of polyamides, requiring adjustments in the manufacturing process to ensure consistent quality and performance. It is known in the art that microparticles or nanoparticles of gelled polymers in a yarn can interfere with the yarn's stretching process, creating stress concentration points that limit the achievable tenacity and elongation at break.

[0029] The inventors of the present invention, M z / M w We found that controlling the parameter values ​​resulted in unexpected improvements in fiber properties. In particular, we found that in the stretched yarn RV range of 90-200 (especially 90-150, more specifically 90-130, and more specifically 90-120), the polymer constituting the yarn had a molecular weight distribution (M) higher than 1.50. z / M wWhen this condition is present, it has been observed that the spinning process fails due to frequent filament and process breakage, making the process uneconomical.

[0030] M z / M w The parameters are measured by size exclusion chromatography (SEC) as described below. M referred to herein z / M w It will be understood that the parameter values ​​are limited by an error bar of ±0.03 to account for the uncertainty of the measurement method. The molecular weight distribution (M) described herein z / M w The parameters will be understood to be those of the polyamide that makes up the drawn yarn.

[0031] The inventors of the present invention, M z / M w We observed that the parameters provide an accurate measure (especially its width) of the molecular weight distribution, enabling precise comparisons between different samples.

[0032] M z / M w It will be understood that the parameters can be modulated using techniques that are conventional in the art and known to those skilled in the art. In particular, by controlling the process conditions during polymerization, the molecular weight distribution and gel formation, and thus M z / M w Parameters can be controlled. For example, preheating the polyamide flakes before the SSP process can shorten the residence time in SSP, and as a result, it is known that the molecular weight distribution of the resulting polymer (TWI651341-B) becomes narrower. Another method involves directly subjecting an equimolar salt of adipic acid and hexamethylenediamine (HMD) to the SSP process, melt polymerization while replenishing the lost HMD, and then subjecting it to the SSP process again to limit the bishexamethylenediamine content in the polymer (Japanese Patent No. 3005692(B)). z / M wOther known strategies for controlling parameters include the addition of polymerization catalysts such as phosphoric acid or sodium hypophosphite, and the adjustment of heating and vacuum of the polymerization medium (European Patent No. 2871201(A)). Molecular weight distribution and parameter M z / M w Other conventional methods for adjusting include blending resins having different molecular weights (European Patent No. 3127945(A)).

[0033] In the present invention, the polyamide particularly useful is PA66, or includes it, and preferably the polyamide is PA66. However, in alternative embodiments, the polyamide may be or include 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 yarn disclosed herein in combination with one or more of the aforementioned polyamides of the alternative embodiments described above.

[0034] The yarn of this disclosure preferably has a linear density in the range of about 200 to about 3000 decitex, preferably about 300 to about 2500 decitex, preferably about 400 to about 2500 decitex, and preferably about 600 to about 2300 decitex.

[0035] The number of filaments in the yarn is preferably about 30 to about 450, preferably about 60 to about 300, and preferably about 100 to about 250.

[0036] The yarn tenacity is preferably >8.0 cN / dtex, preferably >8.5 cN / dtex, and preferably >9.0 cN / dtex. Particularly useful in the present invention is a yarn having a formic acid relative viscosity (RV) of about 90 to about 200 and a tenacity of >8.5 cN / dtex (preferably >9.0 cN / dtex), and a molecular weight distribution (M) 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. z / M w This yarn contains a polyamide (preferably PA66) characterized by the following:

[0037] The yarn preferably exhibits elongation at maximum force of about 10.0 to about 30.0 percent of its original dimensions, 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, and preferably about 18.0 to about 25.0 percent.

[0038] The elongation of the yarn at 45N is preferably about 7% to about 12%, preferably about 8% to about 12%, preferably 8.5% to about 12%, and preferably about 9% to about 12%, relative to the initial length of the yarn before testing.

[0039] The fracture energy of the yarn is preferably 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, and preferably at least 2.8 J. It will be understood that yarns with higher linear densities will exhibit higher fracture energies. In a preferred embodiment, the fracture energy of the yarn is preferably at least 2.5 J, and preferably at least 2.8 J.

[0040] The formic acid relative viscosity (RV) of the drawn yarn is about 90 to about 200, preferably about 90 to about 150, preferably about 90 to about 130, and preferably about 90 to about 120. Preferably, the yarn has an RV of at least 95. Therefore, preferably, the RV is about 95 to about 200, preferably about 95 to about 150, preferably about 95 to about 130, and preferably about 95 to about 120.

[0041] The formic acid relative viscosity (RV) is measured according to ASTM D789-19 (2019) using a 90% formic acid solution, as reported below. It will be understood that the formic acid relative viscosity values ​​defined herein are those of the polyamide constituting the stretched yarn.

[0042] There is a correlation between viscosity and molecular weight. Polymers with higher molecular weights generally result in higher RV values. Molecular weight and RV affect the mechanical and physical properties of polyamides in different applications, as well as their consistency and quality in the manufacturing process.

[0043] The process for producing high-RV polyamide fibers 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 achieved by adjusting reaction conditions such as temperature, pressure, and catalyst concentration to optimize the polymerization reaction rate and control the molecular weight distribution.

[0044] It will be understood that the yarn described herein is a drawn yarn.

[0045] The dry heat shrinkage rate of the yarn is preferably about 5 to 10 percent, preferably about 6 to 8 percent, or about 6 to 7 percent, relative to the stretched fibers before testing.

[0046] Fatigue resistance is measured herein as the percentage of fracture strength retained relative to the pre-fatigue strength, and is preferably >35%, preferably >50%, preferably >65%, and preferably >70%. In preferred embodiments, fatigue resistance is approximately 70% to approximately 90%.

[0047] Fatigue resistance and hardening strength in rubber are measured in tire cords manufactured from or containing the polyamide (preferably PA66) yarn of the present invention.

[0048] Further embodiments of the methods and products of the present invention preferably do not include the use of benzenesulfonate compounds, as including benzenesulfonate compounds is not suitable for all applications. Additionally or alternatively, the methods and products disclosed herein do not include phosphorus-containing compounds. Phosphorus-containing compounds may or may not be included in the polymer as catalysts or as agents to further improve polymer stability against decomposition at higher temperatures. References: According to European Patent No. 2188421(B1) and U.S. Patent No. 4966949(A), examples of suitable compounds include X(CH2) n The formula contains PO3R2, where X is selected from 2-pyridyl, -NH2, NHR', and N(R')2, n=2 to 5, and R and R' are independently H or alkyl, 2-aminoethylphosphonic acid, potassium tolylphosphinate, or phenylphosphinic acid. Preferred compounds include 2-(2'-pyridyl)ethylphosphonic acid and metal hypophosphites, including sodium hypophosphite and manganese hypophosphite. As described in U.S. Patent No. 5,116,919, a base such as an alkali metal bicarbonate can be added to the catalyst to minimize thermal decomposition.

[0049] Preferably, the polyamide used in the present invention does not contain phenolic antioxidant stabilizers, particularly hindered phenolic stabilizers. Examples of such compounds include alkyl-substituted and / or aryl-substituted phenols, particularly such hindered phenol compounds.

[0050] Another aspect of the present invention provides a method for producing the polyamide PA66 yarn described herein. In one embodiment, the method comprises shear heating polyamide 66 flakes until the polymer reaches a molten state. After heating, the molten polyamide is extruded through a spinneret having multiple holes, and the molten polymer exiting the spinneret is rapidly cooled to solidify the filament. Cooling may be carried out by an airflow. A lubricant is then applied to the filament. The filament is then passed through a series of one or more heated rollers to stretch and align the molecules. This process is called drawing. Drawing may be carried out in multiple stages using rollers rotating at different speeds and different temperatures. The drawn yarn is then relaxed by passing it through another set of one or more rollers to achieve the shrinkage required for the final yarn. The finished filament is wound onto a bobbin and optionally further processed.

[0051] In a further aspect of the present invention, a method for preparing tire cords from a stretched polyamide (preferably PA66) yarn described herein is provided. The tire cords can be prepared using any conventional method known in the art. Preferably, the method comprises a) twisting a single yarn in the Z or S direction, wherein the single yarn is a stretched polyamide yarn described herein, b) A step of stacking two or more single yarns together and twisting them in the opposite direction to the twist direction of the single yarns, preferably with the same number of twists per unit length as each single yarn.

[0052] The resulting tire cord can then be further processed as described above. Test method:

[0053] The characteristics of polyamide yarn are evaluated using the following test methods. Linear density of yarn

[0054] The linear density of the yarn is measured with zero twist added, according to ASTM DI 907-Option 6. Dry heat shrinkage rate

[0055] The dry heat shrinkage rate of the yarn is measured in hot air for 2 minutes at a temperature of 177°C under a tension of 0.045 gf / dtex, according to the method described in ASTM D4974. Formic acid relative viscosity (RV) (stretched fiber RV)

[0056] Relative viscosity (RV) is measured for fibers using a 90% formic acid solution according to ASTM D789-19 (2019). One 20 g fiber sample is required for each iteration of this analysis. Stretched fiber RV is specifically applied to the measurement of RV on fiber samples collected after the spinning process. Prior to RV measurement, each sample is treated to remove residual fiber lubricants, also known as spinning finishing agents. To remove the lubricants, each fiber sample is immersed in a sufficient amount of methylene chloride to completely cover the sample. This allows the sample to be immersed for 20 minutes with stirring in a lidded extraction funnel. This procedure is then repeated. Once the second methylene chloride wash is complete, the fiber is immersed in a sufficient amount of 1:1 methanol:methylene chloride to completely cover the sample. This allows the sample to be immersed for 20 minutes with stirring in a lidded extraction funnel. This procedure is repeated two more times. Once all five immersion steps are complete, any remaining solvent is blown off the fiber samples with clean, pressurized air. Next, the fibers are completely air-dried in an exhaust hood. Once dry, the formic acid relative viscosity of the stretched fiber sample is measured according to ASTM D789-19. Fiber tensile test

[0057] The maximum force (N) and elongation at maximum force (%) are evaluated according to the standard ASTM D3822 / D3822M-14 (2020), but are tested using the modifications listed below.

[0058] The initial gauge (clamp) length set on the Instron tensile testing machine is 254 mm. The Instron crosshead speed is set to 300 mm / min. The fiber specimen is first cut to a size of 350 mm, and the fibers are twisted at 3 tpi (twists per inch) while one end is fixed in the upper (moving) grip. The other end is then fixed in the lower grip of the Instron. Tensile testing is performed 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 tested in Newtons (N). The reported result for elongation at maximum force (also known as elongation at break, elongation rate, or stretch rate) is the average (%) of the elongation results at maximum force of the 10 specimens tested. Tenacity is measured by the following formula.

[0059] Tenacity (cN / dtex) = Maximum force (cN) / Linear density (dTex)

[0060] The fracture energy (J) is a measure of the work required to break a fiber sample and is calculated as the area under the stress-strain curve based on the fiber tensile results (which are obtained as detailed above).

[0061] The elongation at 45N is also evaluated using the methodology described above. Size exclusion chromatography (SEC) z / M w value

[0062] The absolute molar mass distribution of the yarn sample is measured using size exclusion chromatography (SEC) with refractive index (RI) and multi-angle light scattering (MALS) detection. Two 300 × 7.5 mm PL hexafluoroisopropanol (HFIP) gel columns are used with guards, along with Wyatt Technology HELEOS multi-angle light scattering and Wyatt Technology Optilab T-rEX refractive index detectors. The column and RI detector temperatures are maintained at 40 and 30°C, respectively. The sample is prepared at a nominal concentration of 2 mg / mL in a mobile phase consisting of 0.01 M tetraethylammonium nitrate (TEAN) in hexafluoroisopropanol (HFIP). After dissolution for 4 hours, the sample solution is filtered through a 0.45 μm polytetrafluoroethylene (PTFE) syringe filter, and a volume of 200 μL is injected into the mobile phase stream for each measurement. The solvent flow rate is 0.8 mL / min, and the run time is 40 minutes for each measurement. The molar mass average of each sample is calculated by averaging the results from two injections of the sample, and the molecular weight distribution is calculated as follows:

number

[0063] As is common in the field, Mz and Mw are defined as follows:

number

[0064] The tire cord is manufactured by twisting two separate yarns in the Z direction at a specific number of twists per unit length (8.5 tpi was used in this study), and then twisting them together in the S direction at a specific number of twists per unit length (8.5 tpi was used in this study). The cord is then passed through an adhesive bath containing a resorcinol formaldehyde tex (RFL) mixture, and then dried under tension at 150°C for about 1 minute.

[0065] Next, the cord is embedded in rubber, and the rubber is cured to prepare a test specimen. The tensile strength loss of the cord prepared from the yarn is measured according to ASTM D6588 / D6588M-11(2016). The test is performed for 11.5 hours under 15% compression and 10% tension. After the test specimen has fatigued, the cured cord in the rubber is removed from the embedded rubber, and the tensile strength loss is measured using the following formula:

number

[0066] The tire cord is prepared using the method described in the previous section. The curing strength in rubber is measured by wrapping the adhesive (RFL) treated cord around a clean, flat steel plate measuring 7.3 cm × 27.6 cm, leaving a gap of approximately 0.6 mm between adjacent wraps of cord. After wrapping the desired number of times (generally 5 times), the two ends of the cord are tied together at the rear of the plate using a double square knot to firmly secure the sample to the plate. A 7.3 cm × 27.6 cm piece of rubber with a thickness of 0.76 mm and a suitable composition (in this case, a typical passenger car tire carcass stock compound) is placed on top of the cord wrapped around the plate. The sample is then cured in a hydraulic press at 177 ± 2°C for 20 minutes under a pressure of 3.3 tons (3000 kgm). At the end of the curing cycle, the sample is removed from the press and the exposed cord on the back of the plate is immediately cut. After cooling to room temperature, the cord is pulled from the rubber and then conditioned at 24°C / 55% RH for at least 48 hours. The cured rupture strength in the rubber is then determined using a gauge length of 15.2 cm and a strain rate of 120% / min. Processability

[0067] During the spinning test, the condition of the multifilament was monitored between the spinneret and the winding machine, and the processability was evaluated on a number between 1 and 4, where 1 is the best condition with the fewest breaks, and 4 is the (relatively) worst condition, meaning that the process had to be restarted every few minutes after many breaks. [Examples]

[0068] Select yarns from a series of embodiments to determine various relative viscosities and M z / M w The characteristics of the yarn having the value are evaluated. The polymerization conditions of PA66 in Examples 1 and 2 have high RV and M values ​​that fall within the range of Claim 1. z / M w To provide a combination of values, the above techniques described herein are used to make adjustments. Comparative Examples 1-4 are RV or M outside the scope of Claim 1. z / M wThe values ​​are shown. Comparative Examples 3 and 4 correspond to Comparative Examples 1 and 2, but were manufactured using lower elongation ratios. The yarns were evaluated according to the measurement methods disclosed herein, and the results are shown in Table 1. For fatigue resistance and rubber curing strength, the tire cords were manufactured by twisting two separate yarns (1400 dtex each) in the Z direction (8.5 tpi) and then twisting them together in the S direction (8.5 tpi) for each example. [Table 1]

[0069] The RV of a yarn generally increases with increasing molecular weight and can therefore be used as a representative measure of the molecular weight of a sample. Examples 1 and 2 are provided to illustrate yarns having an RV in the preferred range of 90–130. Comparative Examples 1 and 3 are selected to have lower molecular weights, and therefore lower RVs, below the preferred range. Comparative Examples 2 and 4 were intended to provide examples with higher molecular weights, and therefore higher RVs of about 140, but were instead found to have an RV value of 102. While we do not wish to be bound by theory, it is presumed that the lower-than-expected RVs for Comparative Examples 2 and 4 are a result of polymer degradation, which occurs more frequently in the processing of higher molecular weight polyamides.

[0070] As can be seen from the results in Table 1, Comparative Example 2 showed only 14.6% elongation at maximum force and a fracture energy of only 2.3 J, which is lower than the other samples. Thus, although the fatigue resistance (strength retention rate) of Comparative Example 2 was similar to that of Example 2, its strength was already at a low level. Furthermore, Comparative Example 2 had worse processability compared to the other samples. These results suggest that increased decomposition occurred in this sample.

[0071] Table 1 shows that fatigue resistance improves as RV increases for Examples 1, 2, and Comparative Example 1. Comparative Example 2, which is expected to have the highest molecular weight, does not have a higher RV and rather exhibits fatigue resistance comparable to Example 2. As mentioned above, the RV of Comparative Example 2 is considered to be lower than expected due to decomposition that occurs during processing. Taking this into account, the data shows a correlation between the increase in RV (as an indicator of the increase in molecular weight) and the improvement in fatigue resistance.

[0072] The samples in Table 1 are analyzed for molecular weight distribution in fully stretched fibers. The polymerization process avoids decomposition and branching, resulting in the desired molecular weight distribution (M) of the present invention. z / M w When controlled well enough to achieve RV, an increase in RV is observed to result in both higher fatigue resistance (strength retention rate) and curing strength in the rubber. In other words, the improvement in both fatigue resistance and curing strength in the rubber associated with higher molecular weight (RV) is due to the M of the polymer constituting the stretched yarn. z / M w This is observed only when it is within the scope of the present invention. Comparative Example 2 does not follow the same trend as the other examples, and it is outside the scope of the claims. z / M w It has the following characteristics, and therefore, processability is the worst among the other embodiments, and both fatigue and cured rubber strength are not improved.

[0073] Although the present invention has been described with reference to certain 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 herein. Any embodiments provided herein are included solely for illustrative purposes and are not intended to limit the invention. All prior art disclosures listed herein are incorporated herein by reference in their entirety.

Claims

1. It has a formic acid relative viscosity (RV) of approximately 90 to approximately 200, contains PA66, and has a molecular weight distribution (M) in the range of ≥1.40 and ≤1.50±0.

03. ｚ / M ｗ A stretched polyamide yarn characterized by the following:

2. The polyamide yarn according to claim 1, wherein the molecular weight distribution (Mz / Mw) is in the range of ≥1.42 and ≤1.49±0.03, preferably ≥1.45 and ≤1.48±0.

03.

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

4. The yarn is a polyamide yarn according to any one of claims 1 to 3, having RV > 90.

5. The polyamide yarn according to any one of claims 1 to 4, wherein the linear density of the yarn is 200 to 3000 decitex.

6. The polyamide yarn according to any one of claims 1 to 5, wherein the number of filaments in the yarn is 30 to 450.

7. The polyamide yarn according to any one of claims 1 to 6, wherein the tenacity of the yarn is >8.0 cN / dtex, preferably >8.5 cN / dtex, preferably >9.0 cN / dtex.

8. The polyamide yarn according to any one of claims 1 to 7, wherein the breaking energy of the yarn is 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, and preferably at least 2.8 J.

9. The polyamide yarn according to any one of claims 1 to 8, wherein the 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, and preferably about 18.0 to about 25.0 percent of the original dimensions.

10. The polyamide yarn according to any one of claims 1 to 9, wherein the dry heat shrinkage rate is 5 to 10%.

11. The polyamide yarn according to any one of claims 1 to 10, wherein the elongation at 45N is approximately 7 to approximately 12%.

12. A polyamide yarn according to any one of claims 1 to 11, which does not contain a benzenesulfonate compound or contains benzenesulfonate in an amount of less than 5 ppm.

13. The polyamide yarn further contains a phosphorus-containing compound as a heat stabilizer, preferably the phosphorus-containing compound is of the formula X-(CH ２ ) ｎ PO ３ R ２ Selected from compounds defined by, where X is 2-pyridyl, -NH ２ , NHR', and N(R') ２ A polyamide yarn according to any one of claims 1 to 12, wherein n = 2 to 5, and R and R' are independently H or alkyl, 2-aminoethylphosphonic acid, potassium tolylphosphinate, or phenylphosphinic acid, 2-(2'-pyridyl)ethylphosphonic acid, and a metal hypophosphate containing sodium hypophosphite and manganese hypophosphite.

14. A polyamide yarn according to any one of claims 1 to 12, which does not contain phosphorus-containing compounds.

15. A polyamide yarn according to any one of claims 1 to 14, which does not contain a phenolic antioxidant stabilizer, particularly a hindered phenolic stabilizer, and particularly an alkyl-substituted and / or aryl-substituted phenol.

16. The polyamide yarn according to any one of claims 1 to 15, wherein the yarn exhibits a tenacity of >8.5 cN / dtex (preferably >9.0 cN / dtex), and elongation at a maximum force of at least 15.0 percent, and preferably also exhibits a breaking energy of at least 2.5 J and / or elongation at 45 N of about 8.5 to about 12 percent.

17. Lower relative viscosity and Mz / M outside the above range ｗ The polyamide yarn according to any one of claims 1 to 16, which provides higher fatigue resistance and / or cured rubber strength than that provided by a polyamide yarn having a value.

18. The polyamide yarn according to any one of claims 1 to 17, wherein the polyamide is 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), preferably the polyamide is PA66, or comprises PA66, preferably the polyamide is PA66.

19. A tire cord made from or comprising the yarn described in any one of claims 1 to 18.

20. The tire cord according to claim 19, wherein the fatigue resistance is greater than 35%, preferably greater than 50%, preferably greater than 65%, and preferably about 70% to about 90%.

21. The tire cord according to claim 19 or 20, wherein the rubber hardening strength of the tire cord is ≥50N, preferably ≥70N, preferably ≥100N, preferably ≥130N, preferably ≥150N, preferably >≥180N, preferably ≥210N, preferably ≥220N.

22. A method for preparing a stretched yarn according to any one of claims 1 to 18, a) A step of shearing and heating polyamide flakes until the polymer reaches a molten state, b) A step of extruding the molten polymer through a spinneret, c) A step of cooling the molten polymer coming out of the spinneret to solidify the filament, d) A step of applying lubricant to the filament, e) A step of stretching the filament by passing it through one or more heated rollers to stretch and align the molecules, f) A step of loosening the stretched yarn by passing it through another set of one or more rollers to achieve the required shrinkage for the final yarn, g) A method comprising the step of winding the completed filament onto a bobbin.

23. The method according to claim 22, wherein the stretching in step e) is carried out in multiple stages using rolls rotating at different speeds and different temperatures.

24. A method for preparing a tire cord according to any one of claims 19 to 21, a) Twisting a single yarn in the Z or S direction, wherein the single yarn is a stretched polyamide yarn as described herein, b) A method comprising stacking two or more single yarns together and twisting them in the opposite direction to the twist direction of the single yarns, preferably with the same number of twists per unit length as each single yarn.

25. A tire comprising a tire code as described in any one of claims 19 to 21.

26. Use of a stretched polyamide yarn in a tire cord according to any one of claims 1 to 18, for the purpose of improving the fatigue resistance and / or hardening strength in rubber of a tire cord containing the yarn, wherein the yarn has a formic acid relative viscosity (RV) of about 90 to about 200 and a molecular weight distribution (M) in the range of ≥1.40 and ≤1.50±0.

03. ｚ / M ｗ Uses include polyamides characterized by ).

27. The use of a tire cord according to any one of claims 19 to 21 in a tire, for the purpose of improving the durability of the tire, wherein the stretched polyamide yarn has a formic acid relative viscosity (RV) of about 90 to about 200 and a molecular weight distribution (M) in the range of ≥1.40 and ≤1.50±0.

03. ｚ / M ｗ Uses include polyamides characterized by ).

28. A tire cord fabric made from or comprising a tire cord as described in any one of claims 19 to 21.

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