Polyamide fiber for tire cord and its manufacturing method

Abstract

Provided are: polyamide fibers for a tire cord, with which cutting of a cord during steps for producing a tire cord and tire cord fabric is suppressed; a method for producing same; a twisted yarn cord using the fibers; and cord fabric using the cord. The present invention relates to polyamide fibers for a tire cord and a method for producing same, wherein the air-knot strength of the polyamide fibers in an environment at a temperature of 180°C is 3.5-6.0 cN / dtex.

Description

[Technical Field]

[0001] The present invention relates to a polyamide fiber for tire cords and a method for producing the same, as well as a twisted cord using the fiber and a cord fabric using the cord. [Background technology]

[0002] Polyamide fibers have excellent toughness, adhesive properties, and fatigue resistance, and are therefore widely used as rubber reinforcing fibers for tire cords and other applications in trucks, buses, construction, and aircraft.

[0003] As described in Patent Document 1 below, radial tires for aircraft are generally used under high internal pressure and high load conditions, so there are strong demands for load-bearing capacity and suppression of tire radial growth. In addition, with increasing demands for cost reduction and weight reduction, it is important for the reinforcing fibers used in radial tires for aircraft to reduce the amount of fiber without impairing its functionality. To satisfy these demands, there is a need to develop fibers with higher strength and rigidity.

[0004] As described in Patent Document 2, a known method for producing a tire reinforcement cord involves forming a twisted cord from polyamide fibers, then applying an adhesive treatment (hereinafter also referred to as "dipping") to the twisted cord, and then subjecting the twisted cord to a tension heat treatment under tension. To obtain a reinforcement cord with higher strength and rigidity, twisted cords have come to be subjected to tension heat treatment under higher tension. This increases the strength after the dipping treatment, contributing to further weight reduction of the tire and enabling the cord to be used in tires for higher load applications.

[0005] On the other hand, when polyamide fibers are used as rubber reinforcing fibers, twisted cords (hereinafter also referred to as "raw cords") are generally used, which are made by twisting a multifilament, which is an assembly of multiple monofilaments, and twisting these together in pairs or triplicates. However, when manufacturing raw cords, variations in length may occur, and depending on the application, extremely long raw cords may be required. In such cases, it may be necessary to connect the raw cords together at their ends.

[0006] A commonly known method for joining raw cords is the air splicing method, which involves entangling the fibers. This method offers the advantages of easy joining and excellent workability, as well as minimizing the swelling of the joining portion (hereinafter also referred to as "air knot").

[0007] However, tire cords or tire cord cord fabrics having air knots connected by the air splicing method have a problem that, during the above-mentioned dipping, the twisted cords cannot withstand the tension during the tension heat treatment under high temperature and high tension, and the cords are prone to breakage, resulting in broken portions. Such broken portions in dipped cords or dipped fabrics are treated as defective products and distinguished from normal products, so the current situation is that the production of tire cords and tire cord cord fabrics is plagued by the problem of cord breakage. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2019-508595 [Patent Document 2] Japanese Patent Application Publication No. 1-174628 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above-mentioned problems of the conventional art, an object of the present invention is to provide a polyamide fiber for tire cords that is suppressed from cord breakage during the manufacturing process of tire cords and tire cord fabrics. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the inventors conducted extensive research and experiments and unexpectedly discovered that air knot strength is important for preventing cord breakage under high temperature tension in the manufacturing process of tire cords and tire cord woven fabrics, which led to the completion of the invention.

[0011] That is, the present invention is as follows. [1] A polyamide fiber for tire cords having an air knot strength of 3.5 cN / dtex or more and 6.0 cN / dtex or less in an environment at a temperature of 180°C. [2] The polyamide fiber for tire cord according to [1] above, wherein the number of inter-trip entanglements is 13 or more / m and 30 or less / m. [3] The polyamide fiber for tire cords according to [1] or [2] above, having an air knot strength at 25°C of 6.4 cN / dtex or more and 9.0 cN / dtex or less. [4] The polyamide fiber for tire cord according to any one of [1] to [3] above, which has a knot strength at 25°C of 4.5 cN / dtex or more and 6.5 cN / dtex or less. [5] The polyamide fiber for tire cord according to any one of [1] to [4] above, which has a tensile strength of 8.7 cN / dtex or more and 11.0 cN / dtex or less. [6] The polyamide fiber for tire cord according to any one of [1] to [5] above, which has dimensional stability of 12% or more and 20% or less. [7] A polyamide fiber for tire cord according to any one of [1] to [6] above, wherein an ionic surfactant is applied to the surface in an amount of 0.01% by weight or more and 0.1% by weight or less per weight of the fiber. [8] The following physical properties (1) to (5): (1) The total fineness is 900 dtex or more and 2500 dtex or less; (2) The elongation is 15% or more and 25% or less; (3) The boiling water shrinkage rate is 4% or more and 8% or less; (4) The finish adhesion rate is 0.5% by weight or more and 1.5% by weight or less; and (5) The number of single yarns is 100 or more and 400 or less; The polyamide fiber for tire cord according to any one of the above [1] to [7], which is a multifilament yarn having the following structure: [9] The polyamide fiber for tire cord according to any one of the above [1] to [8], which has an air knot.

[10] A twisted cord using the polyamide fiber for tire cords described in [9] above.

[11] A bamboo blind fabric using the twisted yarn cord described in

[10] above.

[12] A method for producing a polyamide fiber for a tire cord, comprising the steps of: spinning a polyamide fiber by melt spinning; passing the polyamide fiber through one or more finishing agent application devices and a multi-stage drawing roller; and winding the multi-stage drawing roller at a fixed drawing temperature of 205°C or higher and 240°C or lower, according to any one of [1] to [9]. [Effects of the Invention]

[0012] The polyamide fiber for tire cords of the present invention is inhibited from cord breakage under high temperature and tension during the manufacturing process of tire cords and tire cord fabrics. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of an apparatus for producing polyamide fibers for tire cords according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail. One embodiment of the present invention is a polyamide fiber for tire cord, which has an air knot strength of 3.5 cN / dtex or more and 6.0 cN / dtex or less in an environment at a temperature of 180°C. The air knot strength of the polyamide fiber for tire cords of this embodiment in an environment at a temperature of 180°C is 3.5 cN / dtex or more and 6.0 cN / dtex or less, preferably 4.0 cN / dtex or more and 5.0 cN / dtex or less, and more preferably 4.2 cN / dtex or more and 4.5 cN / dtex or less. The air knot strength can be measured by the method described in the Examples below. An air knot strength of 3.5 cN / dtex or more in an environment at a temperature of 180°C can suppress twisted cord breakage during tension heat treatment. On the other hand, an air knot strength of 6.0 cN / dtex or less in an environment at a temperature of 180°C can prevent the single yarns in the air knot portion from becoming too tightly entangled, and less likely to cause unevenness in the thickness of the cord fabric due to an increase in the gauge at the seam. The air knot strength is measured by performing a specific air knot operation on the fiber and measures its yarn joining properties, and is a characteristic of the fiber.

[0015] The air knot strength at 25°C (room temperature) of the polyamide fiber for tire cords of this embodiment is preferably 6.4 cN / dtex or more and 9.0 cN / dtex or less, more preferably 6.8 cN / dtex or more and 8.0 cN / dtex or less, and even more preferably 7.0 cN / dtex or more and 7.5 cN / dtex or less. If the room temperature air knot strength is 6.4 cN / dtex or more, cord breakage can be suppressed even under tension heat treatment. On the other hand, if the room temperature air knot strength is 9.0 cN / dtex or less, excessively dense entanglement of the single yarns in the air knot portion can be avoided, and unevenness in the thickness of the cord fabric due to a thicker gauge at the seam is less likely to occur.

[0016] The knot strength at room temperature (25°C) of the polyamide fiber for tire cord of this embodiment is preferably 4.5 cN / dtex or more and 6.5 cN / dtex or less, more preferably 5.0 cN / dtex or more and 6.0 cN / dtex or less, and even more preferably 5.2 cN / dtex or more and 5.8 cN / dtex or less. When the knot strength at 25°C is 4.5 cN / dtex or more, cord breakage during tension heat treatment can be suppressed. On the other hand, when the knot strength at 25°C is 6.5 cN / dtex or less, production can be performed without a significant decrease in process stability due to an increase in fluff or yarn breakage.

[0017] The tensile strength of the polyamide fiber for tire cords of this embodiment is preferably 8.7 cN / dtex or more and 11.0 cN / dtex or less, more preferably 9.0 cN / dtex or more and 10.5 cN / dtex or less, and even more preferably 9.4 cN / dtex or more and 10.2 cN / dtex or less. A tensile strength of 8.7 cN / dtex or more provides excellent tensile strength, which contributes to the development of the air knot strength and knot strength. On the other hand, a tensile strength of 11.0 cN / dtex or less allows production without a significant decrease in process stability due to increased fuzz or yarn breakage.

[0018] The dimensional stability of the polyamide fiber for tire cords of this embodiment is preferably 12% or more and 20% or less, more preferably 15% or more and 19% or less, and even more preferably 16% or more and 18% or less. Dimensional stability can be determined by the sum of the boiling water shrinkage of the fiber and the intermediate elongation (elongation at a load of 1 / 2 the breaking strength). Dimensional stability of 12% or more improves toughness in rubber reinforcement applications such as tire cords. On the other hand, dimensional stability of 20% or less contributes to strength retention at high temperatures, excellent tensile strength at high temperatures, and contributes to the expression of the air knot strength in an environment at 180°C and knot strength at 25°C.

[0019] The intertrip entanglement number of the polyamide fiber for tire cord of this embodiment is preferably 13 or more and 30 or less, more preferably 13 or more and 25 or less, and even more preferably 17 or more and 23 or less. The intertrip entanglement number refers to the degree of entanglement measured by an automatic entanglement tester, which satisfies 60% strength relative to the trip level. If the intertrip entanglement number is 13 or more, entanglement of single yarns during air knot formation is promoted, resulting in a fiber with excellent air knot strength even in an environment at a temperature of 180°C. On the other hand, if the intertrip entanglement number is 30 or less, single yarn unraveling during the twisting process and the resulting single yarn fuzzing are suppressed, preventing a decrease in twisting efficiency and a loss of woven quality. In addition, from the viewpoint of making the shape of the air knots uniform and suppressing hanging slack during the production of the cord fabric, it is also preferable that the number of inter-trip entanglements is 25 or more and 30 or less per meter.

[0020] The polyamide fiber for tire cord of this embodiment preferably has an ionic surfactant attached in an amount of 0.01 wt% to 0.1 wt% per fiber weight, more preferably 0.012 wt% to 0.08 wt%, and even more preferably 0.02 wt% to 0.06 wt%. The inclusion of an ionic surfactant at this level enhances the effects of other finishing agent components, improving the extreme pressure properties of the yarn, facilitating dispersion of stress applied to air knots during tension, and improving knot strength. The high strength of the polyamide fiber, combined with the presence of the ionic surfactant on the fiber surface, improves knot strength. An ionic surfactant content of 0.01 wt% or more improves knot strength and contributes to improved air knot strength. On the other hand, an ionic surfactant content of 0.1 wt% or less reduces roll surface contamination during the drawing process, leading to increased roll cleaning frequency. The ionic surfactant can be applied to the polyamide fiber by applying a finishing agent during the spinning process.

[0021] The polyamide fiber for tire cord of the present embodiment has the following physical properties (1) to (5): (1) The total fineness is 900 dtex or more and 2500 dtex or less; (2) The elongation is 15% or more and 25% or less; (3) The boiling water shrinkage rate is 4% or more and 8% or less; (4) The finish adhesion rate is 0.5% by weight or more and 1.5% by weight or less; and (5) The number of single yarns is 100 or more and 400 or less; Multifilament yarns having a total fineness of 900 dtex or more have sufficient mechanical properties when used to make tire cords and tire cord woven fabrics. On the other hand, from the viewpoint of weight reduction, those having a total fineness of 2500 dtex or less are preferred.

[0022] The elongation is preferably 15 to 25%. If the elongation is 15% or more, sufficient toughness can be obtained for rubber reinforcement applications such as tire cords. Furthermore, there is a trade-off between elongation and strength, and in order to achieve a balance with strength, the elongation is preferably 25% or less.

[0023] The boiling water shrinkage is preferably in the range of 4 to 8%. If the boiling water shrinkage is 4.0% or more, the heat shrinkage stress is high, which suppresses stretching during dipping, making it possible to obtain a high-strength dipped cord. On the other hand, if the boiling water shrinkage is 8.0% or less, the dimensional stability is excellent and contributes to the development of air knot strength at high temperatures.

[0024] In addition, the deposition rate of the finishing agent applied to the yarn during the spinning process is preferably in the range of 0.5% by weight to 1.5% by weight. Polyamide fibers for rubber reinforcement applications, such as tire cords, are drawn at high tension against a drawing roll. Therefore, the finishing agent, which reduces the frictional resistance between the individual fibers that make up the fiber, must be uniformly deposited on the fiber surface in order to provide excellent extreme-pressure properties and reduced frictional resistance with metal surfaces (smoothness). This prevents a decrease in strength of the vulcanized cord and improves fatigue resistance. If the deposition amount of the finishing agent is less than 0.5% by weight, the effect of reducing extreme-pressure properties and frictional resistance with metal surfaces (smoothness) is insufficient, making it difficult to consistently produce high-strength polyamide fibers. Furthermore, if the deposition amount of the finishing agent exceeds 1.5% by weight, the penetration of the dipping solution into the polyamide fiber during dipping is hindered, significantly reducing adhesion to rubber.

[0025] The number of single filaments is preferably 100 or more and 400 or less. A multifilament having 100 or more single filaments increases the specific surface area and can flexibly respond to external stress, improving rubber adhesion and fatigue resistance. On the other hand, a single filament number of 400 or less can prevent the single filaments from fusing together during melt spinning.

[0026] The polyamide fiber for tire cords in this embodiment may be at least one fiber selected from the group consisting of polyamide 6, polyamide 6·6, polyamide 11, polyamide 12, polyamide 6·10, polyamide 6·12, polyamide 4·6, their copolymers, and mixtures thereof. Among these, polyamide 6·6 fiber primarily made of polyhexamethylene adipamide fiber is preferred. Polyhexamethylene adipamide refers to a polyamide fiber composed of 100% hexamethylenediamine and adipic acid and having a melting point of 250°C or higher. Polyamide 6·6 fiber may also be a fiber made of a polymer obtained by copolymerizing or blending polyhexamethylene adipamide with polyamide 8, polyamide 6·I, polyamide 10, polyamide 6·T, etc., as long as the melting point is not less than 250°C.

[0027] Another embodiment of the present invention is a method for producing a polyamide fiber for a tire cord, in which a polyamide fiber spun by melt spinning is passed through one or more finishing agent application devices and a multi-stage drawing roller and wound up, and the drawing fixation temperature of the multi-stage drawing roller is 205°C or higher and 240°C or lower. An example of the method for producing polyamide fibers for tire cords according to the present embodiment of the present invention will now be described. FIG. 1 is an explanatory diagram showing an example of equipment for producing the tire cord polyamide fiber of this embodiment. First, a molten polymer is uniformly heated in a part of a spinning machine called a spin head 1 and spun out from a spinneret 2. The spun polymer passes through a heating cylinder 3 located directly below the spinneret and is solidified by cold air from a cooling chamber 4 to form a yarn. The yarn gathered at each end is then treated with a finishing agent in a finishing agent application device 5 and then proceeds to a drawing process using a group of rollers consisting of a take-up roller 6, a first roller 7, a second roller 8, a third roller 9, and a fourth roller 10. Specifically, the yarn is taken up at a predetermined speed by roller 6, then guided under slight tension to a first-stage roller 7, from which it is drawn by multiple heated and drawn rollers 8, 9, and 10. The yarn is then fed to an entanglement device 11 and wound up on a winder 12.

[0028] The finishing agent applicator 5 is not particularly limited, but typically a roll or nozzle type is used. The amount of finishing agent applied by the finishing agent applicator 5 is preferably 0.5% by weight or more and 1.5% by weight or less per fiber weight. A finishing agent content of 0.5% by weight or more allows for stable processing from twisting to dip processing, eliminating single yarn breakage and improving quality. A finishing agent content of 1.5% by weight or less prevents problems such as pulling out at knots.

[0029] When applying a finishing agent to fibers, an ionic surfactant can be applied to the fibers. The ionic surfactant includes at least one selected from the group consisting of anionic surfactants containing a P atom and anionic surfactants containing an S atom. The anionic surfactant containing a P atom is not particularly limited, but examples thereof include metal salts or amine salts of alkyl phosphate esters (hereinafter abbreviated as phosphate), and metal salts or amine salts of polyoxyethylene alkyl phosphate. More specific examples thereof include potassium lauryl phosphate, sodium lauryl phosphate, potassium octyl phosphate, and sodium octyl phosphate. The anionic surfactant containing an S atom is not particularly limited, but examples thereof include alkanesulfonates.

[0030] In addition to the ionic surfactants described above, it is preferable to use a component of the finishing agent to be oiled that has excellent smoothness and heat resistance so that the yarn can be smoothly drawn during the spinning process, from the viewpoint of yarn quality and industrial material applications. The component serving as the smoothing agent is preferably an ester compound. It is preferable to use at least one ester compound selected from the group consisting of ester compounds having three or more ester bonds in the molecule and ester compounds having a sulfur element in the molecule.

[0031] Examples of ester compounds having a sulfur element in the molecule include (1) ester compounds of a dicarboxylic acid and a monohydric alcohol, such as dialkylthiodipropionate, and (2) ester compounds of a monocarboxylic acid and a monohydric alcohol, such as alkylmercaptopropionate.

[0032] Examples of ester compounds having three or more ester bonds in the molecule include (3) ester compounds of polyhydric alcohols and monocarboxylic acids, such as trimethylolpropane trialchelate, glycerin trifatty acid ester, pentaerythritol tetrafatty acid ester, and trimethylolpropane fatty acid ester, (4) ester compounds of polyhydric carboxylic acids and monohydric alcohols, such as trialkyl trimellitate and triethyl citrate, and (5) natural fats and oils, such as castor oil, palm oil, and refined rapeseed oil. These components may be used alone or in combination of two or more.

[0033] Nonionic surfactants can be used as agents for adjusting emulsifying and frictional effects. Examples include: (1) polyoxyalkylene polyhydric alcohol fatty acid ester-type nonionic surfactants such as ether ester compounds obtained by condensing at least one compound selected from the group consisting of polyethylene glycol dialkylates, polyoxyethylene sorbitan monoalkylates, polyoxybutylene sorbitan trialchelates, polyoxypropylene castor oils, polyoxyethylene hydrogenated castor oils, polyoxyethylene propylene hydrogenated castor oil trialchelates, polyoxyethylene hydrogenated castor oil trialchelates, ethylene oxide (hereinafter also referred to as EO) adducts of castor oils, and EO adducts of hydrogenated castor oils with monocarboxylic acids and dicarboxylic acids; and (2) at least one compound selected from the group consisting of organic acids, organic alcohols, organic amines, and organic amides. Compounds having an alkylene oxide having 2 to 4 carbon atoms added to a species, more specifically, for example, ether-type nonionic surfactants such as polyoxyethylene fatty acid esters, polyoxyethylene fatty acid ester methyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene polyoxypropylene nonylphenyl ethers, polyoxyethylene alkylamino ethers, and polyoxyethylene fatty acid amide ethers; (3) polyhydric alcohol partial ester-type nonionic surfactants such as sorbitan mono-fatty acid esters, sorbitan tri-fatty acid esters, and glycerin mono-fatty acid esters; and (4) alkylamide-type nonionic surfactants such as diethanolamine mono-fatty acid amides. These components may be used alone or in combination of two or more.

[0034] The application of the finishing agent is not limited to a diluted one with mineral oil or a water-based emulsion, but it is preferable to apply it as an emulsion when considering compatibility with water in subsequent processes.

[0035] The multi-stage heated stretching rollers 10 apply a stretch-fixing temperature of 205°C or higher and 240°C or lower. The stretch-fixing temperature is preferably 210°C or higher and 230°C or lower, and more preferably 215°C or higher and 220°C or lower. A stretch-fixing temperature of 205°C or higher provides excellent dimensional stability at high temperatures during cord processing. On the other hand, if the stretch-fixing temperature is 240°C or higher, it is difficult to stably produce polyamide fibers with a boiling water shrinkage of 4% or higher.

[0036] The entanglement imparting device 11 can be a known device that sprays compressed fluid onto the yarn using an entanglement nozzle. Preferably, the compressed fluid is supplied to the yarn with an energy of 1.0 to 1.5 kW. The compressed fluid supply energy (air supply energy) can be calculated by multiplying the supply pressure (MPa) by the flow rate (Nm3 / hr). By appropriately selecting the supply pressure and the fluid inlet diameter of the entanglement nozzle, the above-mentioned supply energy range can be satisfied. More preferably, the supply energy is 1.3 kW or more and 1.5 kW or less. By satisfying the above-mentioned supply energy range, a suitable inter-trip entanglement number can be obtained without impairing process stability during twisting, which promotes entanglement of single yarns during air knot formation and results in a fiber with excellent air knot strength.

[0037] The polyamide fiber of this embodiment can be suitably used for twisted cords (tire cords) connected by air knots and for cord fabrics using the same. By using the polyamide fiber of this embodiment, cord breakage during the manufacturing process of twisted cords and cord fabrics can be suppressed. [Example]

[0038] EXAMPLES Next, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. First, the definitions and measurement methods of the physical properties used in the examples and comparative examples will be explained.

[0039] (1) Strong air knot, strength The connecting yarn was a Joint Air 116 manufactured by Machinetex Co., Ltd., and the chamber and chamber cover of the air splicer were appropriately selected and attached depending on the fineness, and the polyamide fibers were spliced ​​using the air splicer's specified procedure under the following conditions. Supply air pressure: 0.5MPa Air injection time: 1 second Thread length: 20mm For a 150 mm fiber sample (binder thread) having one air knot, the tensile breaking strength was measured in accordance with JIS L 1013 8.5 at test temperatures of 25°C (room temperature) and 180°C, and a pulling speed of 300 mm / min, and the air knot strength at each temperature was recorded. Measurements were made twice per level, and the average value was recorded as the air knot strength.

[0040] (2) Knot strength and strength According to JIS L 1013 8.6, a 150 mm fiber sample was measured at a pulling speed of 300 mm / min at 25° C. Measurements were carried out twice for each level, and the average value was taken as the knot strength.

[0041] (3) Number of inter-trips The number of entanglements at 60% strength of the trip level (intertrip number) was measured using a RAPID 600V manufactured by Lenzing Instruments under the conditions shown in Table 1 in accordance with ASTM D 4724. The measurement was carried out 10 times per level, and the average value was taken as the intertrip number. [Table 1]

[0042] (4) Fineness The measurement was carried out in accordance with JIS L 1013 8.3.1 Method A, except that the rewinding speed was set to 60 times / min.

[0043] (5) Tensile strength, tensile strength, elongation, intermediate elongation According to JIS L 1013 8.5, a 150 mm fiber sample was measured at a pulling speed of 300 mm / min. Measurements were performed three times per level, and the average value was used as the tensile strength. However, the intermediate elongation was the elongation (%) at a load of 1 / 2 the breaking strength.

[0044] (6) Finishing agent adhesion rate Measurements were made in accordance with JIS L 1013 8.27 using cyclohexane as the solvent.

[0045] (7) Boiling water shrinkage Measurement was carried out in accordance with JIS L 1013 8.18.

[0046] (8) Dimensional stability The shrinkage was calculated by adding the obtained boiling water shrinkage and intermediate elongation (elongation at a load of 1 / 2 the breaking strength).

[0047] (9) Twisted filament disorder The raw yarn was twisted twice with a first twist of 26.5 turns per 100 mm and a second twist of 26.5 turns per 100 mm. The raw yarn package was then spliced ​​using an air knotter, similar to the air knot strength measurement described above, to create a continuous twist. This twisted yarn cord was used to weave a blind, and the supplied twisted yarn cord was counted for filament disorder, which required removal for weaving, using a Daikosha KH-700 infrared sensor and a Kasuga Electric SF2-A photocell sensor. Filament disorder includes loose or frayed single yarns in the twisted yarn cord, which may cause thickness unevenness when the blind is made. Filament disorder in the twisted yarn cord was evaluated per 1,000 strands and 1,000 meters of twisted yarn cord according to the following criteria. (Evaluation criteria) ◎: The number of filament disturbances is less than 1.0; ○: The number of filament disturbances is 1.0 or more and less than 5.0; △: The number of filament disturbances is 5.0 or more and less than 10.0; ×: The number of disordered filaments is 10.0 or more.

[0048] (10) Flatness In the blind weaving process obtained in (9) above, the blinds were visually inspected after weaving, and the hanging slack of the twisted cords was counted. Hanging slack includes cases where the twisted cords are taut or loose, causing the blind to be out of alignment with other cords, resulting in uneven streaks. If the twisted cords are taut, they will appear glossy, and if they are loose, they will appear blackish. Hanging slack was evaluated per 2,000 twisted cords and 1,000 m, according to the following evaluation criteria. (Evaluation criteria) ◎: The number of hanging slacks is less than 1.0; ○: The hanging slack is 1.0 or more, but it can be corrected by adjusting the tension of the roll of fabric; ×: The number of loose ends is 1.0 or more, and the cord needs to be replaced.

[0049] (11) Cord break Using the twisted cord obtained in (9) above, a 3200m long cord fabric was produced with a width of 1580mm, a pick count of 2.0 / 50mm, a warp count of 1091, and a warp density of 34.5 / inch. The fabric was then dipped in RFL liquid (resorcinol-formalin-latex liquid) at a processing speed of 86m / min, a processing temperature of 140-240°C, and a processing tension of 300-5500kgf. This weaving and processing process was repeated 10 times. The processing passability was evaluated. Cord breakage was evaluated according to the following criteria. (Evaluation criteria) ○: The cord breakage occurred less than 0.1 times, and there was no problem with process passability; △: Cord breakage occurred 0.1 times or more but less than 2 times; ×: Cord breakage occurred two or more times, and there was a problem with process passability.

[0050] [Examples 1 to 4, Comparative Example 1] A polyhexamethylene adipamide polymer with a relative formic acid viscosity of 82 was obtained by a known melt polymerization method using a vacuum at the final stage of the melt polymerization. This polymer, in its molten state, was introduced into a melt spinning machine and drawing machine, as shown in FIG. 1 , to obtain a high-tenacity polyhexamethylene adipamide fiber with a fiber density of 1440 dtex / 210 f. Specifically, the polymer was melted at 300°C, uniformly heated at 305°C in a spin head 1, and extruded through a spinneret 2 with 210 holes. The extruded fiber was passed through a 70 mm-long heating cylinder 3 set at 300°C under a heated atmosphere, and then cooled and solidified in a cold air chamber 4 to form a filament. The filament then passed through a finishing agent applicator 5, a take-up roller 6, a first roller 7 to a third roller 9, and a fourth roller 10 set at 220°C, entangled in an entanglement applicator 11, and wound on a winder 12. Between the first roller 7 and the fourth roller 10, the draw ratio was changed and the yarn was wound so that the resulting raw yarn tensile strength would be the value (8.46 cN to 9.99 cN) shown in Table 2 below. The wound fibers were twisted to prepare raw cord and woven fabrics, which were then dipped in an RFL liquid.

[0051] The finishing agent applicator 5 applied a finishing agent (containing 1.5% by weight of an ionic surfactant) with the following composition to a deposition rate of 1.1% by weight. Compressed air was applied to the entanglement applicator 11 at 0.45 MPa, with an air supply energy of 1.3 kW. The resulting polyamide 66 fibers were evaluated for tensile strength, air knot strength, knot strength, entanglement strength, dimensional stability, and other characteristics. Additionally, the process stability, twisting filament disorder, and cord breakage in the twisting and dipping processes were evaluated. The results are shown in Table 2 below. (Finishing agent composition) (a1) Trimethylolpropane trilaurate: 10 parts by weight (a2) Dioleylthiodipropionate: 40 parts by weight (b) POEO stearyl polyether: 20 parts by weight (c1) Hydrogenated castor oil EO25 triisostearate: 15 parts by weight (c2) Hydrogenated castor oil EO25 maleic acid stearate: 15 parts by weight (d) Ionic surfactants (d1) Sodium alkyl (C10-16) sulfate: 0.5 parts by weight (d2) Alkyl (C12-18) acid phosphate, alkyl (C12-14) amine salt: 1 part by weight

[0052] [Example 5] The same procedure as in Example 1 was carried out except that the air supply energy in the entanglement step was set to 1.0 kW. The results are shown in Table 2 below.

[0053] [Example 6] The same procedure as in Example 1 was carried out except that in the stretching step, the stretching and fixing temperature was set to 210° C. The results are shown in Table 2 below.

[0054] [Example 7] The same procedure as in Example 1 was carried out, except that a finishing agent containing 4.5% by weight of an ionic surfactant of the following composition was applied in the oiling step. The results are shown in Table 2 below. (ionic surfactants) (d1) Sodium alkyl (C10-16) sulfate: 1.5 parts by weight (d2) Alkyl (C12-18) acid phosphate, alkyl (C12-14) amine salt: 3 parts by weight

[0055] Comparative Example 2 The same procedure as in Example 1 was carried out except that the air supply energy in the entanglement step was set to 1.6 kW. The results are shown in Table 2 below.

[0056] Comparative Example 3 The same procedure as in Example 1 was carried out except that the air supply energy in the entanglement step was set to 1.8 kW. The results are shown in Table 2 below.

[0057] Comparative Example 4 The same procedure as in Example 1 was carried out except that in the stretching step, the stretching and fixing temperature was set to 200° C. The results are shown in Table 2 below.

[0058] Comparative Example 5 The same procedure as in Example 1 was carried out, except that in the oiling step, a finishing agent not containing an ionic surfactant was applied so that the adhesion rate was 1.1% by weight. The results are shown in Table 2 below.

[0059] Comparative Example 6 The same procedure as in Example 1 was carried out, except that a finishing agent containing 0.7% by weight of an ionic surfactant of the following composition was applied in the oiling step. The results are shown in Table 2 below. (ionic surfactants) (d1) Sodium alkyl (C10-16) sulfate: 0.2 parts by weight (d2) Alkyl (C12-18) acid phosphate, alkyl (C12-14) amine salt: 0.5 parts by weight

[0060] Comparative Example 7 The same procedure as in Example 1 was repeated except that a finishing agent containing no ionic surfactant was applied in the oiling step to a deposition rate of 1.1 wt % and the fiber tensile strength was 8.49 cN / stex. The results are shown in Table 2 below.

[0061] [Comparative Example 8] The same procedure as in Example 1 was carried out except that the air supply energy in the entanglement step was set to 0.8 kW. The results are shown in Table 2 below.

[0062] [Table 2] [Industrial Applicability]

[0063] The polyamide fiber for tire cords of the present invention is inhibited from cord breakage under high temperature and tension during the manufacturing process of tire cords and tire cord fabrics. [Explanation of symbols]

[0064] 1 Spin Head 2 spinneret 3 Heating cylinder 4. Cold air chamber 5. Finishing agent application device 6 Take-up roller 7 First Roller 8 Second Roller 9 Third Roller 10 Fourth Roller 11 Interlacing device 12 Winding machine

Claims

1. A polyamide fiber yarn for a tire cord having an air knot portion, wherein the air knot strength of the air knot portion in an environment at a temperature of 180°C is 3.5 cN / dtex or more and 6.0 cN / dtex or less.

2. 2. The polyamide fiber yarn for tire cord according to claim 1, wherein the number of intertrip entanglements is 13 or more / m and 30 or less / m.

3. 3. The polyamide fiber yarn for a tire cord according to claim 1 or 2, wherein the air knot strength at 25°C of the air knot portion is 6.4 cN / dtex or more and 9.0 cN / dtex or less.

4. 3. The polyamide fiber yarn for tire cord according to claim 1 or 2, having a knot strength at 25°C of 4.5 cN / dtex or more and 6.5 cN / dtex or less.

5. 3. The polyamide fiber yarn for tire cord according to claim 1 or 2, having a tensile strength of 8.7 cN / dtex or more and 11.0 cN / dtex or less.

6. 3. The polyamide fiber yarn for tire cord according to claim 1 or 2, which has a dimensional stability of 12% or more and 20% or less.

7. 3. The polyamide fiber yarn for tire cord according to claim 1, wherein an ionic surfactant is applied to the surface in an amount of 0.01% by weight or more and 0.1% by weight or less per weight of the fiber.

8. The following physical properties (1) to (5): (1) The total fineness is 900 dtex or more and 2500 dtex or less; (2) The elongation is 15% or more and 25% or less; (3) The boiling water shrinkage rate is 4% or more and 8% or less; (4) The finish deposition rate is 0.5% by weight or more and 1.5% by weight or less; and (5) The number of single yarns is 100 or more and 400 or less; The polyamide fiber yarn for tire cord according to claim 1 or 2, which is a multifilament yarn having the following structure:

9. A twisted cord using the polyamide fiber yarn for tire cords according to claim 1 or 2.

10. A woven blind fabric using the twisted yarn cord according to claim 9.

11. 3. A method for producing a polyamide fiber yarn for a tire cord, comprising the steps of: spinning a polyamide fiber by melt spinning; passing the polyamide fiber through one or more finishing agent application devices and a multistage drawing roller; and winding the yarn; wherein the drawing fixing temperature of the multistage drawing roller is 205°C or higher and 240°C or lower.

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