Heat-resistant high-strength polyethylene terephthalate yarn and tire cord

Abstract

The present invention relates to a high-strength polyethylene terephthalate yarn and tire cord having improved heat resistance. The polyethylene terephthalate tire cord according to the present invention has excellent physical properties even under high-temperature conditions, and maintains a high strength retention rate at high temperatures relative to room temperature, thereby achieving high heat resistance. Accordingly, a decrease in cord strength at high temperatures during molding is alleviated, thus making it possible to reduce tire weight. In addition, degradation of physical properties caused by an increase in tire temperature during high-speed driving of a vehicle is minimized, thereby reducing tire rolling resistance, improving handling performance, and enhancing vehicle fuel efficiency.

Description

Heat-resistant high-strength polyethylene terephthalate yarn and tire cord

[0001] The present invention relates to a high-strength polyethylene terephthalate yarn with improved heat resistance and a tire cord, and more specifically, to a heat-resistant high-strength polyethylene terephthalate yarn and a tire cord that, when used as a tire cord, exhibit excellent heat resistance, dimensional stability at high temperatures, and shape stability, thereby improving the handling performance and fuel efficiency of a vehicle.

[0002] High-strength polyethylene terephthalate yarn is widely used in various industrial applications, including tires, seat belts, conveyor belts, V-belts, and hoses.

[0003] Tire cords manufactured using high-strength polyethylene terephthalate yarns suffer from a degradation in physical properties during tire molding (vulcanization process). This is due to insufficient heat resistance resulting from an excessive increase in fiber molecular orientation, leading to a decrease in cord strength and elastic modulus. Consequently, this leads to a decline in tire performance (e.g., handling performance) as physical properties deteriorate due to the rise in tire temperature during high-speed driving. Furthermore, even if dimensional stability is partially improved through increased fiber crystallinity, a decrease in high-temperature heat resistance occurs, as the elastic modulus does not improve in the high-temperature environment (~80°C) encountered during driving.

[0004] [Prior Art Literature]

[0005] [Patent Literature]

[0006] (Patent Document 1) US 4101525 B

[0007] (Patent Document 2) US 5067538 B

[0008] (Patent Document 3) US 5472781 B

[0009] (Patent Document 4) EP 0423213 B

[0010] The present invention aims to solve the problems of the prior art as described above. One objective of the present invention is to provide an industrial polyester yarn that possesses excellent shape stability and high strength characteristics while preventing a decrease in cord strength at high temperatures.

[0011] Another objective of the present invention is to provide a polyester tire cord that has an elastic modulus equivalent to that of rayon even in high-temperature environments of 120°C or higher, and has excellent dimensional stability and heat resistance.

[0012] Another objective of the present invention is to provide a high-performance tire that includes a tire cord with excellent dimensional stability, enabling weight reduction and improved fuel efficiency performance through reduced rolling resistance.

[0013] One aspect of the present invention for solving the above-mentioned problem relates to a polyethylene terephthalate yarn having a strength of 9.0 g / d or more, a dry heat shrinkage rate within the range of 6.0 to 10.0%, and a dimensional stability (ES) within the range of 11.0 to 16.0%.

[0014] The above polyethylene terephthalate yarn has a fineness of 500 to 3000 denier. The above polyethylene terephthalate yarn has a viscosity of 0.90 to 0.95 and an intermediate elongation of 4.0 to 6.0 (@4.5 g / d).

[0015] In the present invention, the polyethylene terephthalate yarn may include recycled polyethylene terephthalate or biomass-based polyethylene terephthalate.

[0016] Another aspect of the present invention for solving the above-mentioned problem relates to a tire cord comprising the high-strength polyethylene terephthalate yarn.

[0017] The above tire cord has a strength retention rate at 80°C (strength at room temperature before vulcanization / strength at 80°C after vulcanization) of 70% or more, a strength of 5.0 g / d or more, and an intermediate elongation (@2.25 g / d) of 4~6%.

[0018] The above tire cord has a strength retention rate of 65% or more at 80°C after curing at 170°C for 15 minutes under a load of 0.01 g / d, a cord strength of 4.8 g / d or more, and an intermediate elongation (@ 2.25 g / d) of 9~11%.

[0019] The above tire cord has a cord strength of 7.0 g / d or more at room temperature, an intermediate elongation (@ 2.25 g / d) of 3~5%, and a dry heat shrinkage rate of 3% or less.

[0020] Another aspect of the present invention for solving the above-mentioned problem is,

[0021] A step of manufacturing extruded yarn by melt-extruding polyethylene terephthalate chips at a spinning speed of 2,300 to 3,100 m / min;

[0022] A step of manufacturing an unoriented yarn by spinning the above-mentioned extruded yarn using a spindraft of 400 to 700;

[0023] A step of producing a yarn by stretching the above unoriented yarn using a 5-stage godet roller to have a drawing ratio of 2.0 to 2.6 and an intrinsic elongation coefficient of 160 to 300, at a final spinning speed of 6000 to 7000 m / min; and

[0024] The present invention relates to a method for manufacturing a tire cord, characterized by including the step of manufacturing a dip cord by twisting and dipping the above yarn.

[0025] Another aspect of the present invention for solving the above-mentioned problem relates to a tire comprising a tire cord of the present invention.

[0026] The tire cord using the PET yarn of the present invention improves the reduction in cord strength at high temperatures, and the polyester tire cord of the present invention can minimize deformation of the tire shape due to its excellent heat resistance, dimensional stability, and shape stability.

[0027] In addition, when using the heat-resistant high-strength PET tire cord of the present invention, tire weight reduction can be achieved with minimal reduction in cord strength due to temperature during tire molding, and the degradation of physical properties caused by the rise in tire temperature during high-speed driving can be minimized, thereby reducing tire rolling resistance, improving handling performance, and enhancing fuel efficiency.

[0028] The present invention will be described in more detail below.

[0029] In describing the present invention, if it is determined that a detailed description of related prior art may obscure the essence of the invention, such detailed description will be omitted.

[0030] When a part in this specification is described as "comprising" a certain component (component), this means that, unless specifically stated otherwise, it does not exclude other components (components) but may include additional components.

[0031] As used in this specification, "cord" refers to a reinforcing strand constituting the reinforcing structure of a tire, and means a product formed by twisting and combining several strands of yarn.

[0032] In this specification, "polyethylene terephthalate yarn" means a yarn made of any one of unregenerated virgin polyethylene terephthalate, regenerated polyethylene terephthalate, or biomass-based polyethylene terephthalate.

[0033] In the present invention, "dimensional stability (ES)" is represented as the sum of intermediate elongation (E) and dry heat shrinkage rate (S). Since tires with a low dimensional stability (ES) value have a small amount of deformation due to heat, tires using cords with a low ES value have higher uniformity and can improve tire performance compared to tires using cords with a high ES value.

[0034] In this specification, "spin draft" refers to the ratio of the linear velocity (m / min) of the first stretching roller to the polymer extrusion velocity per unit area at the spinning nozzle. If the spin draft is greater than 1, a predetermined stretching has already occurred.

[0035] In this specification, "specific draw ratio" refers to the ratio of spin draft to total draw ratio.

[0036] In this specification, "tenacity" is stress expressed as force per unit line density (gm / tex or gm / denier) of an undeformed specimen.

[0037] As used in this specification, the term "tire cord" refers to a plied yarn coated with an adhesive so that it can be directly applied to rubber products, and is also referred to as "dip cord."

[0038] One aspect of the present invention for solving the above-mentioned problem relates to a polyethylene terephthalate yarn having a strength of 9.0 g / d or more, a dry heat shrinkage rate within the range of 6.0 to 10.0%, and a dimensional stability (ES) within the range of 11.0 to 16.0%.

[0039] In the present invention, the strength of the polyester yarn may be 9.0 g / d or higher, or 9.0 g / d to 9.6 g / d, preferably 9.3 g / d to 9.5 g / d. The strength of the polyester yarn must be 9.0 g / d or higher in terms of yarn characteristics that can impart sufficient mechanical properties and durability when manufacturing tire cords.

[0040] The above polyester yarn has a dry heat shrinkage rate of 6.0% to 10.0% or less, measured under conditions of 0.05 g / d after oven heat treatment at 150°C for 30 minutes, preferably 6.2% to 9.9%, more preferably 6.5% to 9.0% or 7% to 9%.

[0041] If the above dry heat shrinkage rate is less than 6.0% or exceeds 10.0%, it is undesirable because the strength and shape stability of the tire cord are reduced. The above dry heat shrinkage rate is based on a value measured under conditions where a fixed load is applied at 177°C for 30 minutes.

[0042] Generally, vulcanizing a tire changes the dry heat shrinkage rate and intermediate elongation of the cord. The sum of the dry heat shrinkage rate and intermediate elongation can be viewed as similar to the concept of modulus of the cord after the tire is fully manufactured. In other words, a correlation is formed where a lower ES value leads to a higher modulus. A higher modulus results in a greater amount of force generated due to tire deformation, making steering easier; conversely, since it is possible to generate the same amount of tension with less deformation, steering performance is improved, and dimensional stability against deformation can be judged to be excellent. Therefore, the ES value is utilized as a physical property to assess the excellence of cord performance during tire manufacturing. In the present invention, by setting the dimensional stability value of the polyester yarn to 11.0% to 16.0%, steering stability is secured, and stable tire manufacturing is also possible.

[0043] In addition, when manufacturing tires, tires with a low ES value have a smaller amount of deformation due to heat, which improves the uniformity of the tire and, consequently, improves the overall uniformity of the tire. Therefore, in the case of tires using cords with a low ES value, the uniformity of the tire is higher than that of tires using cords with a high ES value, so it is possible to improve tire performance.

[0044] The fineness of the above polyethylene terephthalate yarn may be 500 to 3000 denier, more preferably 1300 to 1800 denier, and more preferably 1400 to 1600 denier. The above polyethylene terephthalate yarn has a viscosity of 0.90 to 0.95 and an intermediate elongation of 4.0 to 6.0 (@4.5 g / d). The fineness of the yarn may be 500 denier or higher in terms of yarn characteristics that can impart sufficient mechanical properties and durability when manufacturing tire cords, and may be 3000 denier or lower in terms of minimizing weaving density to secure excellent thickness and thereby improve the softness of the fabric. If the intermediate elongation does not meet the above requirements, when used for tire cords, shape deformation due to differences in cord elasticity modulus increases during tire manufacturing, which may result in tire defects and performance degradation.

[0045] The above polyethylene terephthalate yarn has a crystallinity of 45% to 50% and an orientation degree (△n) of 0.20 to 0.23. If the crystallinity of the yarn is less than 45%, the crystallinity is insufficient and thermal stability is poor, which may lead to a decrease in the strength utilization rate, which is undesirable. If the orientation degree is less than 0.20, the orientation is reduced, the crystalline portion cannot develop, and the uniformity of the length distribution of molecular chains in the amorphous portion is reduced, so a dense structure of molecular chains cannot be formed, resulting in a decrease in the strength of the yarn and the strength and strength utilization rate in the tire cord. If the orientation degree exceeds 0.23, the drawability is reduced, which is undesirable.

[0046] The polyethylene terephthalate polymer used in the present invention contains at least 85 mol% of ethylene terephthalate units and preferably consists only of ethylene terephthalate units. Optionally, the polyethylene terephthalate may incorporate a small amount of units derived from one or more ester-forming components other than ethylene glycol and aromatic dicarboxylic acids or derivatives thereof as copolymer units.

[0047] Examples of other ester-forming components copolymerizable with ethylene terephthalate units include glycols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, etc., and dicarboxylic acids such as terephthalic acid, isophthalic acid, hexahydroterephthalic acid, stilbene dicarboxylic acid, nonbenzoic acid, adipic acid, sebacic acid, and azelaic acid.

[0048] In one embodiment, the polyethylene terephthalate yarn may include recycled polyethylene terephthalate. In one embodiment, the polyethylene terephthalate yarn may include recycled polyethylene terephthalate in an amount of 10 wt% or more, 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0049] In this specification, "recycled polyethylene terephthalate" may refer to polyethylene terephthalate that has been recycled for the purpose of reuse after being discarded following its initial use for specific purposes, such as containers, fibers, tire cords, etc. In this specification, recycled polyethylene terephthalate may be mechanically recycled polyethylene terephthalate and / or chemically recycled polyethylene terephthalate.

[0050] Isophthalic acid is an isomer of terephthalic acid, and generally, recycled polyethylene terephthalate contains isophthalic acid. In particular, polyethylene terephthalate used for containers in PET bottles contains isophthalic acid to make processing easier, and recycled polyethylene terephthalate made by recycling this contains 0 mol% to 5 mol% of isophthalic acid.

[0051] In one embodiment, the polyethylene terephthalate yarn may include biomass-based polyethylene terephthalate. In one embodiment, the polyethylene terephthalate yarn may include biomass-based polyethylene terephthalate in an amount of 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more. In one embodiment, the polyethylene terephthalate yarn may include 100 wt% of biomass-based polyethylene terephthalate.

[0052] The "biomass-based polyethylene terephthalate" of the present invention refers to a case where any one of ethylene glycol and / or terephthalic dicarboxylic acid or derivatives thereof is a biomass-based renewable resource. For example, in the case of ethylene glycol, biomass-based ethylene glycol is produced from sugarcane.

[0053] The polyethylene terephthalate chip for manufacturing a polyester yarn according to the present invention is preferably a molten mixture of terephthalic acid (TPA) and ethylene glycol raw material in a ratio of 1 to 1.1 to 2.0, and the molten mixture is subjected to an ester exchange reaction and a condensation polypolymerization reaction to produce a raw chip with an intrinsic viscosity of 0.60 to 0.70 dl / g, and then solid-state polymerized at a temperature of 230 to 245 ℃ and under vacuum to have an intrinsic viscosity of 1.00 to 1.14 dl / g.

[0054] If the intrinsic viscosity of the chip is less than 1.00 dl / g, the intrinsic viscosity of the final yarn is lowered, making it impossible to achieve high strength as a tire cord after heat treatment, and if the intrinsic viscosity of the chip exceeds 1.14 dl / g, excessive heat generation and increased screw load during polymer melting make melt spinning impossible.

[0055] Another aspect of the present invention for solving the above-mentioned problem relates to a tire cord comprising the high-strength polyethylene terephthalate yarn.

[0056] The tire cord using the PET yarn of the present invention has a cord strength of 5.0 g / d or more when measured at a high temperature of 80°C, a strength retention rate at 80°C (strength at room temperature before vulcanization / strength at 80°C after vulcanization) of 70% or more, preferably 70% to 80%, and an intermediate elongation of 4~6% at 2.25 g / d after vulcanization of the cord, and has excellent heat resistance with a high modulus and a high strength retention rate at high temperatures. The tire cord has a strength retention rate of 65% or more at 80°C after curing at 170°C for 15 minutes under a load of 0.01 g / d, preferably 65% ​​to 70%, a cord strength of 4.8 g / d or more, and an intermediate elongation of 9~11% at 2.25 g / d.

[0057] The above tire cord has a cord strength of 7.0 g / d or more at room temperature, an intermediate elongation (@2.25 g / d) of 3 to 5%, a dry heat shrinkage rate of 3% or less, and preferably 2.5 to 3.0.

[0058] Another aspect of the present invention for solving the above-mentioned problem relates to a method for manufacturing a tire cord, characterized by comprising the steps of: melt-extruding polyethylene terephthalate chips to produce an extruded yarn at a speed of 2300 to 3100 m / min; spinning the extruded yarn into a spindraft of 400 to 700 to produce an unoriented yarn; stretching the unoriented yarn using a 5-stage godet roller to produce a yarn with a stretching ratio of 2.0 to 2.6 and an intrinsic stretching coefficient of 160 to 300; and twisting and dipping the yarn to produce a dip cord.

[0059] The following describes in detail the steps for manufacturing polyethylene terephthalate yarn. In the present invention, the manufacturing of polyethylene terephthalate yarn for tire cords involves increasing the spin-draft to a range of 400 to 700 through ultra-high-speed spinning at a spinning speed of 6,000 to 7,000, setting the intrinsic elongation coefficient to a range of 160 to 300, and adjusting the total elongation ratio of the yarn to a range of 2.0 to 2.6 to change the microstructure of the final yarn, thereby enabling the production of a tire cord having improved heat resistance and dimensional stability compared to conventional polyethylene terephthalate yarns and dip cords.

[0060] First, a method for manufacturing polyethylene terephthalate yarn may include a step of manufacturing an extruded yarn by melting polyethylene terephthalate (PET) chips having an intrinsic viscosity of 1.0 or higher and extruding them while passing them through a nozzle. Here, the polyethylene terephthalate polymer may contain at least 90 mol% of ethylene terephthalate units, but may optionally contain only ethylene terephthalate units.

[0061] Optionally, the polyethylene terephthalate may comprise a small amount of copolymer units derived from ethylene glycol and terephthalic dicarboxylic acid or derivatives thereof and one or more ester-forming components.

[0062] Examples of other ester-forming components copolymerizable with polyethylene terephthalate units include glycols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, etc., and dicarboxylic acids such as terephthalic acid, isophthalic acid, hexahydroterephthalic acid, stilbendicarboxylic acid, nonbenzoic acid, adipic acid, sebacic acid, and azelaic acid.

[0063] Terephthalic acid (TPA) and ethylene glycol raw materials are melt-mixed with manufactured polyethylene terephthalate chips in a ratio of 2.0 to 2.3, and the melt mixture undergoes ester exchange and condensation polymerization reactions to form raw chips. Subsequently, the raw chips undergo solid-state polymerization at a temperature of 230 to 245°C and under vacuum to have an intrinsic viscosity of 1.0 to 1.14. At this time, if the intrinsic viscosity of the raw chips is less than 1.0, the intrinsic viscosity of the final drawn yarn is low, making it impossible to exhibit high strength as a processed cord after heat treatment; if the intrinsic viscosity of the chips exceeds 1.14, the spinning tension increases excessively, and the cross-section of the extruded yarn becomes uneven, causing many filament cuts to occur during drawing, resulting in poor drawing workability.

[0064] Polyethylene terephthalate chips as described above are melted and extruded while passing through a nozzle to produce an extruded yarn. Subsequently, the extruded yarn is passed through a cooling zone to rapidly cool and solidify. Depending on the method of blowing cooling air into the cooling zone, open quenching, circular closed quenching, radial outflow quenching, and radial inflow quenching methods may be applied, but are not limited thereto. At this time, the temperature of the cooling air injected into the cooling zone for rapid cooling is controlled to 10 to 30°C. This rapid cooling, utilizing the rapid temperature difference between the hood and the cooling zone, is intended to increase the solidification point and spinning tension of the extruded polymer, thereby increasing the orientation of the unoriented yarn and the formation of connecting chains between crystals.

[0065] Afterward, the extruded yarn, which has solidified while passing through a cooling zone, can be oiled to a weight of 0.3 to 1.0% by means of an oil application device that applies an oil with excellent elongation and thermal efficiency while reducing the friction coefficient between individual yarns.

[0066] The above-mentioned oiled extruded yarn is spun to form an unoriented yarn. At this time, the spin draft may be 400 to 700. In the present invention, if the spin draft value of the wound yarn is less than 400, a problem may arise in which high heat resistance cannot be secured as the crystalline structure is less expressed in the microstructure. If the spin draft value exceeds 700, a problem may arise in which the strength is reduced.

[0067] In addition, the spinning speed is preferably 6,000 to 7,000 m / min, and when spinning at the spin draft and spinning speed within the above range, the strength and high modulus of the yarn can be secured even at a low draw ratio. If the spinning speed exceeds 7,000 m / min, the drawability of the undrawn yarn decreases, and the strength and drawability of the yarn may be reduced.

[0068] Subsequently, the above-mentioned unoriented yarn is passed through a multi-stage stretching roller to multi-stage stretch and produce a yarn. The stretching roller of the present invention consists of a 5-stage Godet roller. A yarn is formed by stretching the yarn that has passed through the first stretching roller by passing it through a series of stretching rollers using a spin draw method.

[0069] In addition, it is preferable that the total draw ratio (DRt) of the yarn formed as described above is 2.0 to 2.6. If the draw ratio is less than 2.0, the strength is insufficient, and if it exceeds 2.6, workability is reduced.

[0070] In the present invention, the specific draw ratio (Spin draft / draw ratio) is set within the range of 160 to 300. If the specific draw ratio is less than 160, the dimensional stability and heat resistance of the tire cord may be reduced due to an excessive increase in dry heat shrinkage. Conversely, if the specific draw ratio exceeds 300, the strength and heat resistance of the tire cord may be reduced due to an excessive increase in crystallization.

[0071] The polyethylene terephthalate yarn produced in this way has a strength of 9.0 g / d or more, a dry heat shrinkage rate of 6.0% to 10.0% under the condition of 0.05 g / d after oven heat treatment at 150°C for 30 minutes, and a dimensional stability index (medium elongation + dry heat shrinkage rate) of 11.0 to 16.0, and has excellent dry heat shrinkage rate and dimensional stability.

[0072] Subsequently, a dip cord is manufactured by twisting, weaving, and dipping the manufactured polyethylene terephthalate yarn. First, the manufactured polyethylene terephthalate yarn is woven by twisting the top and bottom at 300 to 500 TPM (Twist Per Meter), but is not limited thereto. The twist is manufactured by applying a ply twist to the polyethylene terephthalate yarn and then applying a cable twist to combine them; generally, the top and bottom twists are applied with the same number of twists (level of twist) or, if necessary, different number of twists.

[0073] In the present invention, the upper and lower twists of the polyethylene terephthalate dip cord are set to the same value, ranging from 300 / 300 TPM to 500 TPM. When the upper and lower twists are set to the same value, the manufactured dip cord is made to maintain a straight line without exhibiting rotation or twisting, thereby maximizing the expression of physical properties. At this time, if the upper and lower twists are less than 300 / 300 TPM, the cutting elongation of the raw cord decreases, making it prone to a decrease in fatigue resistance, and if they exceed 500 / 500 TPM, the decrease in strength is significant, making it unsuitable for tire cords.

[0074] The manufactured 'Raw Cord' is woven using a weaving machine, and the resulting fabric is immersed in a dipping solution and then cured to produce a 'Dip Cord' for tire cords with a resin layer attached to the surface of the 'Raw Cord'. Dipping is performed to improve the disadvantage of tire cord fibers, which originally have poor adhesion to rubber.

[0075] The manufactured raw cord can be immersed in a primary treatment solution, followed by primary drying and primary heat treatment. The primary treatment solution may use a blocked isocyanate, an epoxy compound, and a vinylpyridine latex for adhesion between the polyethylene terephthalate cord and the rubber.

[0076] The above first drying should avoid rapid processing at high temperatures, and it is preferable to perform it at 100 to 200°C for 130 to 170 seconds. If the above first drying temperature is below 100°C, drying may not be sufficiently achieved, and gel may form due to the treatment solution when heat-treated after drying; if it exceeds 200°C, gel may form due to the treatment solution due to rapid drying, and uneven adhesion between the cord and the treatment solution may occur.

[0077] The above first heat treatment is performed so that the cord impregnated in the treatment solution has appropriate adhesion to the tire rubber, and it is preferable that the heat treatment be carried out at a temperature of 230 to 260°C for 110 to 180 seconds. If the heat treatment is performed for less than 110 seconds, the reaction time of the adhesive solution is insufficient, resulting in lower adhesion, and if the heat treatment is performed for more than 180 seconds, the hardness of the treatment solution decreases, which may reduce the fatigue resistance of the cord.

[0078] Subsequently, a dip cord can be manufactured by immersing the raw cord in a secondary treatment solution, followed by secondary drying and secondary heat treatment. For example, resorcinol formalin latex (RFL) may be used as the secondary treatment solution, but it is not necessarily limited to this. The raw cord impregnated in the secondary treatment solution is dried and heat-treated to manufacture the dip cord. The secondary drying is preferably carried out at 130 to 210°C for 70 to 120 seconds. The secondary heat treatment is performed to ensure that the cord impregnated in the treatment solution has appropriate adhesion to tire rubber, and the heat treatment is preferably carried out at a temperature of 220 to 260°C for 30 to 80 seconds.

[0079] Another aspect of the present invention relates to a tire comprising the tire cord of the present invention. The polyethylene terephthalate dip cord of the present invention can be used for manufacturing a carcass layer. Particularly preferably, it can be advantageously applied as a carcass of an electric vehicle tire.

[0080] According to the present invention, by using a high-strength PET tire cord with excellent heat resistance as the carcass, tire weight reduction is possible, and rolling resistance can be reduced while improving high-speed driving stability, fuel efficiency, handling performance, and durability. The tire cord of the present invention can minimize tire deformation during high-speed driving. Furthermore, according to the present invention, the reduction in strength and modulus that may occur during the manufacturing process of the tire cord, particularly during the heat treatment process, can be minimized.

[0081] The structure and effects of the present invention will be explained in more detail below with specific examples and comparative examples, but these examples are merely intended to provide a clearer understanding of the present invention and are not intended to limit the scope of the present invention.

[0082]

[0083] [Examples 1-4 and Comparative Examples 1-2: Preparation of Polyethylene Terephthalate Yarn]

[0084] Examples 1-4

[0085] A solid-state polymerized polyethylene terephthalate chip containing 200 ppm of antimony metal was prepared with an intrinsic viscosity (IV) of 1.08 and a moisture content of 10 ppm. The prepared chip was melt-spun using an extruder at a temperature of 290°C with a spinning draft as shown in Table 1 below. Subsequently, the extruded yarn was solidified by passing it through a heating zone (atmosphere temperature 350°C) with a length of 220 mm directly below the nozzle and a cooling zone (cooling air blowing with a wind speed of 20°C and 0.5 m / sec) with a length of 530 mm, and then oiled with a solvent-applied spinning lubricant (containing 70% paraffin oil components). This unoriented yarn was wound at the spinning speed of the yarn as shown in Table 1 below, and after multi-stage stretching, the unoriented yarn was stretched using a 5-stage godet roller to have the spinning speed (speed of G1), stretching ratio, and intrinsic stretching coefficient listed in Table 1 below, and the final spinning speed (speed of G4) was wound at a speed of 6000 m / min or more to produce a final polyethylene terephthalate yarn.

[0086]

[0087] Comparative Examples 1~2

[0088] Polyethylene terephthalate drawn yarns of Comparative Examples 1 and 2 were prepared by varying spinning conditions such as spinning speed, spin draft, draw ratio, and intrinsic elongation coefficient as shown in Table 1 below, in the same manner as Example 1.

[0089]

[0090] Examples 5-8 and Comparative Examples 3-4: Manufacture of tire cord

[0091] Tire cords of Examples 5 to 8 and Comparative Examples 3 to 4 were manufactured using the polyethylene terephthalate yarns prepared in Examples 1 to 4 and Comparative Examples 1-2, respectively, in the same way and under the same conditions.

[0092] Specifically, two strands of untwisted yarn (Z-direction) with a twist count of 390 TPM were prepared using polyethylene terephthalate yarn, and these two strands of untwisted yarn were twisted together in the upper direction (S-direction) with a twist count of 390 TPM to produce a plied yarn. The plied yarn thus produced was passed through a resorcinol-formaldehyde-latex (RFL) adhesive solution, followed by drying and heat treatment to complete the tire cord yarn.

[0093] A tire cord was manufactured by immersing the manufactured cord in an adhesive solution of (epoxy resin + Pexul) in a dipping tank, drying it in a drying zone at 170°C under 2.0% elongation for 150 seconds, heat-setting it in a high-temperature elongation zone at 240°C under 1.0% elongation for 150 seconds, then immersing it again in resorcinol formalin latex (RFL), drying it at 170°C for 100 seconds, and heat-setting it at 240°C under -1.5% elongation for 40 seconds.

[0094]

[0095] Test example

[0096] The physical properties of the polyethylene terephthalate yarns and tire cords prepared in the examples and comparative examples were evaluated and are shown in Tables 1 and 2 below. In the examples and comparative examples, the characteristics of the yarns and tire cords, etc., were evaluated in the following manner.

[0097] (1) Intrinsic viscosity (IV):

[0098] 0.1 g of the sample was dissolved for 90 minutes in a reagent (90°C) mixed with phenol and 1,1,2,3-tetrachloroethanol in a weight ratio of 6:4 to a concentration of 0.4 g / 100 ml, then transferred to a Ubbelohde viscometer and maintained in a 30°C constant temperature bath for 10 minutes, and the drop time of the solution was determined using the viscometer and an aspirator. The drop time of the solvent was also determined in the same way, and then the relative viscosity (RV) and intrinsic viscosity (IV) values ​​were calculated using the following Equations 1 and 2.

[0099] [Formula 1]

[0100] Relative Viscosity (RV) = Dropping seconds of sample / Dropping seconds of solvent

[0101] [Equation 2]

[0102] Intrinsic Viscosity (IV) = 1 / 4 × (RV - 1) / concentration + 3 / 4 × (ln RV / concentration)

[0103] (2) Strength, strength and elongation:

[0104] According to the JIS-L1017 ASTM D885 method, after being left at 25°C and 65%RH for 24 hours, the specimen was measured using an Instron low-speed elongation tensile testing machine with a specimen length of 250 mm and a tensile speed of 300 m / min. The measured strength was calculated by dividing the value by the denier, and the elongation at break was measured as the elongation at break.

[0105] (3) Intermediate believer(E):

[0106] In accordance with the JIS-L1017 ASTM D885 method, the elongation at a load of 4.5 g / d for the yarn and the elongation at a load of 2.25 g / d for the cord were measured from the elongation load curve obtained using an Instron low-speed elongation type tensile testing machine.

[0107] (4) Dry heat shrinkage rate (S):

[0108] After being left at 25℃ and 65% RH for 24 hours, the dry heat shrinkage rate of the yarn was calculated using the ratio of the length (L0) measured under a static load of 0.05 g / d and the length (L1) measured under a static load of 0.05 g / d after heat treatment at 150℃ for 30 minutes using an oven. In contrast, the dry heat shrinkage rate of the cord was calculated using Testrite by the ratio of the length (L0) measured under a static load of 0.05 g / d and the length (L1) after treatment at 177℃ for 2 minutes under a static load of 0.05 g / d.

[0109] [Equation 3]

[0110] S(%) = (L0 - L1) / L0 × 100

[0111] (5) Dimensional stability (ES):

[0112] In the present invention, the elongation under a constant load is called the intermediate elongation (E), and (S) represents the dry heat shrinkage rate of claim (4) above. In the present invention, the sum of the intermediate elongation (E) and the dry heat shrinkage rate (S) is called ES.

[0113] [Equation 4]

[0114] ES = Elongation at specific load + Shrinkage

[0115] (6) Strength retention rate:

[0116] 1) Strength retention rate (%, 25℃-80℃)

[0117] The ratio of the cord strength measured after leaving the tire cord at 25℃ and 65% RH for 24 hours to the cord strength measured at 80℃ was calculated.

[0118] 2) Strength retention rate (%, before and after vulcanization)

[0119] It was calculated as the ratio of the cord strength measured after vulcanizing the tire cord at 170°C for 15 minutes (0.01 g / d) and leaving it at 25°C and 65% RH for 24 hours to the cord strength before vulcanization.

[0120] 3) Strength retention rate (%, after vulcanization at 25℃-80℃)

[0121] It was calculated as the ratio of the cord strength measured after vulcanizing the tire cord at 170°C for 15 minutes under a load of 0.01 g / d and leaving it at 25°C and 65% RH for 24 hours to the cord strength at 80°C. (Strength measured at room temperature before vulcanization / Strength measured at 80°C after vulcanization)

[0122] (7) Spin Draft:

[0123] The spin draft was calculated by the ratio of the polymer velocity at the nozzle to the linear velocity of the first godet roller using the following Equation 5.

[0124] [Formula 5]

[0125] Spin Draft = V1 / V0

[0126] In the above formula,

[0127] V1 : GR1 linear velocity (m / min),

[0128] V0 : Discharge rate / Cross-sectional area = Q / (πD2 / 4×ρ),

[0129] Q: Discharge rate (g / min),

[0130] D : Nozzle diameter (mm),

[0131] ρ : Melt density (1.18 g / cm³)

[0132] (8) Specific Draw Ratio:

[0133] The intrinsic elongation coefficient was calculated using the following Equation 6. A lower intrinsic elongation coefficient increases dimensional stability.

[0134] [Equation 6]

[0135] Intrinsic elongation coefficient = Spin draft / Elongation ratio

[0136] (9) Degree of crystallization (%):

[0137] The degree of crystalinity is measured by the density method using a density gradient tube. If the density of the crystalline region is ρc, the density of the amorphous region is ρa, and the density of the sample is ρ, the degree of crystalinity (X) is calculated according to the following Equation 7.

[0138] [Equation 7]

[0139] Degree of crystallinity (X)(%) = (ρc - ρ) / (ρc - ρa) × 100

[0140] For polyester, ρc=1.455 g / cm³ and ρa=1.355 g / cm³.

[0141] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Spinning Conditions Extruded Yarn Spinning Speed ​​(m / min) 1870 2770 2350 2520 2850 3100 Spinning Speed ​​(m / min) 5600 6500 6000 6300 6500 6700 Spin Draft 440 730 410 570 630 632 Draw Ratio 3.00 2.35 2.55 2.50 2.28 2.16 Specific Draw Ratio 147 311 16 122 827 629 Yarn Viscosity (IV, dl / g)0.93 0.93 0.93 0.93 0.93 0.93 Degree of Crystallization (%) 40% 52% 46% 48% 49% 50% Degree of Orientation (△n) 0.22 0.23 0.23 0.22 0.22 0.23 Fineness (Denier) 1560 1560 1560 1560 1560 1560 Strength (kg) 14.5 14.0 14.5 14.5 14.5 Strength (g / d) 9.3 9.0 9.3 9.3 9.3 9.3 Medium Elongation (%, @4.5g / d) 4.8 6.0 5.8 5.4 5.6 5.0 Fracture Elongation (%) 11.0 13.9 13.5 13.6 13.5 13.0 Dry Heat Shrinkage (%, @150×30')12.5 4.9 9.9 0 7.8 6.2 Dimensional Stability (ES) (%) 17.3 10.9 15.7 14.4 13.4 11.2

[0142] As shown in Table 1 above, the polyethylene terephthalate yarns prepared in Examples 1 to 4 have a strength of 9.0 g / d or more, a dry heat shrinkage rate of 6.0 to 10.0%, and a dimensional stability (ES) of 11.0 to 16.0%. In particular, it was confirmed that the degree of crystallization of the polyethylene terephthalate yarns of the above examples is within the range of 45 to 50%, and the degree of orientation (△n) is within the range of 0.20 to 0.23.

[0143] Comparative Example 3 Comparative Example 4 Example 5 Example 6 Example 7 Example 8 Deep Code 25℃ Structure (denier / ply) 1500d / 2ply 1500d / 2ply 1500d / 2ply 1500d / 2ply 1500d / 2ply 1500d / 2ply Softness (TPM) 390 390 390 390 390 390 Denier 34 30 34 30 34 30 34 30 34 30 Strength (kg) 25.0 23.8 24.5 25.2 25.5 25.3 Strength (g / d) 7.3 6.9 7.1 7.3 7.4 7.4 Medium Elongation (%, @2.25g / d)3.5 4.0 4.2 4.2 4.0 3.9 Cutting Length (%) 13.5 13.8 14.8 14.5 14.0 14.0 Dry Heat Shrinkage (%) (177℃×2'×0.05g / d) 4.0 2.8 2.7 2.7 2.9 2.9 E-S (%) 7.5 6.8 6.9 6.9 6.9 6.8 Strength (kg) 15.5 16.2 17.2 18.0 18.5 18.0 Strength Retention (%, 25℃-80℃) 62% 68% 70% 71% 73% 71% Strength (g / d) 4.5 4.7 5.0 5.2 5.4 5.2 Medium Length (%, @2.25g / d)6.24.85.35.35.25.0 Cutting Elongation (%) 13.5 11.5 12.0 12.2 12.0 12.0 Deep Code After Vulcanization 25℃ Strength (kg) 22.0 23.2 24.4 25.2 25.4 25.0 Strength Retention Rate (%, Before & After Vulcanization) 88% 97% 100% 100% 100% 99% Strength (g / d) 6.4 6.8 7.17.3 7.4 7.3 Medium Elongation (%, @2.25g / d)10.09.09.49.49.09.0 Cutting Elongation(%)18.519.022.823.022.020.080℃ Strength(kg)13.815.116.517.017.116.8 Strength Retention Rate(%, after vulcanization 25℃-80℃)55%63%67%67%67%66% Strength(g / d)4.04.04.85.05.04.9 Medium Elongation(%, @2.25g / d)11.59.510.510.510.310.0 Cutting Elongation(%)14.514.018.018.117.517.0

[0144] As confirmed by the results of Table 2 above, the dip cords manufactured using the PET yarn according to the present invention (Examples 5 to 8) not only have superior strength at high temperatures compared to the dip cords using conventional PET cord yarn (Comparative Examples 3 and 4), but also show improved strength retention rate at high temperatures (80°C).

[0145] Therefore, the tire cord of the present invention can achieve tire weight reduction by minimizing the decrease in cord strength due to temperature during actual tire molding, and the degradation of physical properties caused by the rise in tire temperature during high-speed driving can be minimized, thereby enabling a reduction in tire rolling resistance, improvement in handling performance, and improvement in vehicle fuel efficiency.

[0146] [Aspects]

[0147] Side 1. Polyethylene terephthalate yarn having a strength of 9.0 g / d or more, a dry heat shrinkage rate in the range of 6.0 to 10.0%, and a dimensional stability (ES) in the range of 11.0 to 16.0%.

[0148] Aspect 2. The polyethylene terephthalate yarn according to claim 1, characterized in that the polyethylene terephthalate yarn has a fineness of 500 to 3000 denier.

[0149] A polyethylene terephthalate yarn characterized in that, in any one of the above aspects, the polyethylene terephthalate yarn has a viscosity of 0.90 to 0.95 and an intermediate elongation of 4.0 to 6.0 (@4.5 g / d).

[0150] Aspect 4. In any one of the above aspects, the polyethylene terephthalate yarn is characterized by having a degree of crystallization of 45% to 50% and a degree of orientation (△n) of 0.20 to 0.23.

[0151] Aspect 5. A polyethylene terephthalate yarn characterized in that, in any one of the above aspects, the polyethylene terephthalate yarn comprises recycled polyethylene terephthalate.

[0152] Aspect 6. A polyethylene terephthalate yarn characterized in that, in any one of the above aspects, the polyethylene terephthalate yarn comprises biomass-based polyethylene terephthalate.

[0153] Side 7. A tire cord comprising a high-strength polyethylene terephthalate yarn of any one of sides 1 to 6.

[0154] Side 8. The tire cord according to Side 7, characterized in that the tire cord has a strength retention rate (cord strength at 25°C / cord strength at 80°C) of 70% or more at 80°C, a strength of 5.0 g / d or more, and an intermediate elongation (@2.25 g / d) of 4~6%.

[0155] Side 9. The tire cord according to side 7 or 8, characterized in that the tire cord has a strength retention rate of 65% or more at 80°C after curing (170°C × 15 min × 0.01 g / d), a cord strength of 4.8 g / d or more, and an intermediate elongation (@2.25 g / d) of 9~11%.

[0156] Side 10. In any one of the above sides 7 to 9, the tire cord is characterized by having a cord strength of 7.0 g / d or more at room temperature, an intermediate elongation (@2.25 g / d) of 3 to 5%, and a dry heat shrinkage rate of 3% or less.

[0157] Side 11. A step of manufacturing extruded yarn by melt-extruding polyethylene terephthalate chips at a spinning speed of 2300 to 3100 m / min;

[0158] A step of manufacturing an unoriented yarn by spinning the above-mentioned extruded yarn using a spindraft of 400 to 700;

[0159] A step of manufacturing yarn by stretching the above unoriented yarn using a 5-stage godet roller to have a drawing ratio of 2.0 to 2.6 and an intrinsic elongation coefficient of 160 to 300, and winding it at a speed of 6000 to 7000 m / min; and

[0160] A method for manufacturing a tire cord characterized by including the step of manufacturing a dip cord by twisting and dipping the above yarn.

[0161] Side 12. A tire comprising a tire code according to any one of sides 7 to 10.

[0162] All optional and preferred features and variations of the embodiments and dependent claims described herein may be used in all aspects taught herein. Furthermore, all optional and preferred features and variations of the embodiments described herein, as well as individual features of the dependent claims, are combined and interchangeable with one another. In other embodiments, some features may be omitted. Features may be used in any compatible arrangement.

[0163] Although the present invention has been described in detail above, such description is for the purpose of illustrating the invention, and it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention. Accordingly, such changes should be understood as being included within the scope of protection of the present invention as defined by the appended claims.

Claims

1. Polyethylene terephthalate yarn having a strength of 9.0 g / d or more, a dry heat shrinkage rate in the range of 6.0 to 10.0%, and a dimensional stability (ES) in the range of 11.0 to 16.0%.

2. The polyethylene terephthalate yarn according to claim 1, characterized in that the polyethylene terephthalate yarn has a fineness of 500 to 3000 denier.

3. The polyethylene terephthalate yarn according to claim 1, characterized in that the polyethylene terephthalate yarn has a viscosity of 0.90 to 0.95 and an intermediate elongation of 4.0 to 6.0 (@4.5 g / d).

4. The polyethylene terephthalate yarn according to claim 1, characterized in that the polyethylene terephthalate yarn has a degree of crystallization of 45% to 50% and a degree of orientation (△n) of 0.20 to 0.

23.

5. The polyethylene terephthalate yarn according to claim 1, characterized in that the polyethylene terephthalate yarn comprises recycled polyethylene terephthalate.

6. The polyethylene terephthalate yarn according to claim 1, characterized in that the polyethylene terephthalate yarn comprises biomass-based polyethylene terephthalate.

7. Tire cord comprising the high-strength polyethylene terephthalate yarn of claim 1.

8. The tire cord according to claim 7, characterized in that the tire cord has a strength retention rate at 80°C (cord strength at room temperature before vulcanization / cord strength at 80°C after vulcanization) of 70% or more, a strength of 5.0 g / d or more, and an intermediate elongation (@2.25 g / d) of 4~6%.

9. The tire cord according to claim 7, characterized in that the tire cord has a strength retention rate of 65% or more at 80°C after curing at 170°C for 15 minutes under a load of 0.01 g / d, a cord strength of 4.8 g / d or more, and an intermediate elongation (@2.25 g / d) of 9~11%.

10. The tire cord according to claim 7, characterized in that the tire cord has a cord strength of 7.0 g / d or more at room temperature, an intermediate elongation (@2.25 g / d) of 3 to 5%, and a dry heat shrinkage rate of 3% or less.

11. A step of manufacturing extruded yarn by melt-extruding polyethylene terephthalate chips at a spinning speed of 2300 to 3100 m / min; A step of manufacturing an unoriented yarn by spinning the above-mentioned extruded yarn using a spindraft of 400 to 700; A step of manufacturing yarn by stretching the above unoriented yarn using a 5-stage godet roller to have a stretching ratio of 2.0 to 2.6 and an intrinsic elongation coefficient of 160 to 300, and winding at a final spinning speed of 6000 to 7000 m / min; and A method for manufacturing a tire cord characterized by including the step of manufacturing a dip cord by twisting and dipping the above yarn.

12. A tire containing the tire code of paragraph 10.

13. In claim 12, the tire comprises a tread portion, a pair of sidewalls disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewalls, wherein a carcass is disposed between the pair of bead portions, and wherein the carcass is composed of the polyester tire cord.