POLYETHYLENE YARN, METHOD OF MANUFACTURING THE SAME, AND SKIN COOLING FABRIC COMPRISING THE SAME

Abstract

A polyethylene yarn is disclosed that provides the user with a soft tactile feel, as well as a cooling sensation, and also has improved weaving capabilities, enabling the manufacture of skin-cooling fabrics with excellent pilling resistance, abrasion resistance, cut resistance, and sewability. A method for manufacturing the yarn and a skin-cooling fabric incorporating the yarn are also disclosed. In a force-elongation curve of the polyethylene yarn obtained by measuring at room temperature, (i) the elongation at a force of 1 g / d is 0.5 to 3%, (ii) the elongation at a force of 3 g / d is 5.5 to 10%, and (iii) the difference between the elongation at a force of 4 g / d and the elongation at maximum force is 5.5 to 25%. The polyethylene yarn has a tenacity of 55 to 120 J / m³ at room temperature.

Description

POLYETHYLENE YARN, METHOD OF MANUFACTURING THE SAME, AND SKIN COOLING FABRIC COMPRISING THE SAME Technical field of the invention The present invention relates to a polyethylene yarn, a method for manufacturing the same, and a skin-cooling fabric incorporating the same. More particularly, the present invention relates to a polyethylene yarn capable of providing the user with a soft tactile feel, as well as a cooling sensation, and also having improved weaving capabilities that allow for the manufacture of a skin-cooling fabric with excellent pilling resistance, abrasion resistance, cut resistance, and sewability, a method for manufacturing the same, and a skin-cooling fabric incorporating the same. Background of the invention As global warming progresses, there is a growing need for fabrics that can be used to withstand intense heat. Factors that can be considered in the development of fabrics that can be used to withstand intense heat include (i) eliminating the factors that cause intense heat and (ii) removing heat from the wearer's skin. Methods have been proposed that focus on eliminating intense heat sources, reflect light by applying an inorganic compound to the fiber surface (e.g., see JP 4227837B), scatter light by dispersing fine inorganic particles within and on the fiber surface (e.g., see JP 2004-292982A), and similar approaches. However, blocking these external factors can only prevent additional intense heat, and for users who already experience heat, there is a limit to how far it can go. Not only is this not a significant solution, but it also degrades the fabric's tactile feel. On the other hand, as a method capable of removing heat from a user's skin, a method for improving the moisture absorption of the fabric in order to utilize the evaporative heat of sweat (for example, see document JP 2002-266206A), a method for increasing a contact area between the skin and the fabric in order to increase heat transfer from the skin to the fabric (for example, see document JP 2009-24272A), and similar measures have been proposed. However, when using the evaporative heat of sweat, since the fabric's function depends heavily on external factors such as humidity or the user's body type, consistency cannot be guaranteed. Similarly, when increasing the contact area between the skin and the fabric, the fabric's air permeability decreases as the contact area increases, thus limiting the desired cooling effect. Therefore, it may be desirable to increase heat transfer from the skin to the fabric by improving the thermal conductivity of the fabric itself. To achieve this purpose, JP 2010-236130A proposes manufacturing fabrics using ultra-high-strength polyethylene fibers (Dyneema® SK60) that have high thermal conductivity. zncfrnn / zznz / E / YiAi However, the Dyneema® SK60 fiber used in JP 2010-236130A is an ultra-high-molecular-weight polyethylene (UHMWPE) fiber with a weight-average molecular weight of 600,000 g / mol or higher. While it exhibits high thermal conductivity, its high melt viscosity means it can only be produced using a gel spinning method. This poses a significant environmental risk and requires considerable costs for organic solvent recovery. Furthermore, Dyneema® SK60 fiber has a high tensile strength of 28 g / d or higher, a high tensile modulus of 759 g / d or higher, and a low elongation at break of 3 to 4%, with an elongation at a force of 1 g / d on the strength-elongation curve of less than 0.At 5%, the weaving capacity is poor and the stiffness is too high, making it unsuitable for use in the manufacture of skin-cooling fabrics intended to come into contact with the user's skin. Furthermore, since Dyneema® SK60 fiber has a high tenacity of over 120 J / m³, its use may reduce the cutting and sewing capabilities of the resulting fabric. Detailed description of this disclosure Technical problem Therefore, the present invention is directed to providing a polyethylene yarn that can prevent one or more of the problems due to the limitations and disadvantages of related techniques, a method for manufacturing the same, and a skin-cooling fabric incorporating the same. One aspect of the present invention is to provide a polyethylene yarn capable of providing the user with a soft tactile feel, as well as a cooling perception or sensation, and having improved weaving ability that allows the manufacture of skin-cooling fabrics with excellent pilling resistance, abrasion resistance, cutting ability, and sewing ability. Another aspect of the present invention is to provide a method for manufacturing a polyethylene yarn capable of providing the user with a soft tactile feel, as well as a cooling perception or sensation, and also having improved weaving capabilities that allow the manufacture of skin-cooling fabrics that have excellent pilling resistance, abrasion resistance, cutting ability, and sewing ability. Another aspect of the present invention is to provide a fabric capable of giving the user a soft tactile feel, as well as a cooling sensation or feeling, and also having excellent pilling resistance, abrasion resistance, cutting ability, and sewing ability. Additional advantages, objects, and features of the ambition will be partly set forth in the following description and partly become apparent to those skilled in the art after examining the following, or may be learned by the practice of the invention. Technical solution According to one aspect of the present invention as described above, a polyethylene yarn is provided, wherein in a force-elongation curve of the polyethylene yarn zncfrnn / zznz / E / YiAi obtained by measurements at room temperature, (i) the elongation at a force of 1 g / d is from 0.5 to 3%, (ii) the elongation at a force of 3 g / d is from 5.5 to 10%, and (iii) the difference between the elongation at a force of 4 g / d and the elongation at a maximum force is from 5.5 to 25%, and wherein the polyethylene yarn has a tenacity of 55 to 120 J / m3 at room temperature. Polyethylene yarn can have a tensile strength of more than 4 g / d and less than 6 g / d, a tensile modulus of 15 to 80 g / d, an elongation at break of 14 to 55%, and a crystallinity of 60 to 85%. Polyethylene yarn can have an average molecular weight (Mw) of 50,000 to 99,000 g / mol and a polydispersity index (PDI) of 5 to 9. Polyethylene yarn can have an overall fineness of 75 to 450 denier (8.3 x 10-6 to 5 x 105kg / m), and polyethylene yarn can include a plurality of filaments each having a fineness of 1 to 5 denier (1.11 x 10'7 to 5.56 x 10-7kg / m). Polyethylene yarn can have a crossed circular section. According to another aspect of the present invention, a skin-cooling fabric formed from polyethylene yarn is provided, wherein the skin-cooling fabric at 20°C has a thermal conductivity in the thickness direction of 0.0001 W / cm°C or more, a heat transfer coefficient in the thickness direction of 0.001 W / cm2°C or more, and a cooling sensation on contact (Qmax) of 0.1 W / cm2 or more. The pilling resistance of the skin-cooling fabric measured in accordance with ASTM D 4970-07 may be grade 4 or higher, and the abrasion resistance of the skin-cooling fabric measured in accordance with the Martindale method as specified in KS K ISO 12947-2: 2014 may be 5000 cycles or more. The area density of the skin cooling fabric can be from 75 to 800 g / m2. According to another aspect of the present invention, a method for manufacturing a polyethylene yarn is provided, which includes the steps of: melting a polyethylene having a density of 0.941 to 0.965 g / cm3, a weight average molecular weight (Mw) of 50,000 to 99,000 g / mol, a polydispersity index (PDI) of 5.5 to 9 and a melt index (MI) (at 190 °C) of 6 to 21 g / 10 min, extruding the molten polyethylene through a spinneret having a plurality of spin holes; cooling a plurality of filaments formed when the molten polyethylene is discharged from the spinneret holes; and drawing a multifilament composed of the cooled filaments. The stretching step can be performed at a stretching ratio of 2.5 to 8.5. The general description relating to the present invention provided above is intended solely to illustrate or disclose the present invention and should not be construed as limiting the scope of the present invention. Advantageous effects The polyethylene yarn for a skin-cooling fabric of the present invention has high thermal conductivity, tenacity adjusted to an appropriate range, and excellent weaving ability, and can be easily manufactured at a relatively low cost without causing environmental problems. Furthermore, the skin-cooling fabric woven from the polyethylene yarn of the present invention (i) can consistently provide a user with a cooling sensation regardless of external factors such as humidity, (ii) can continuously provide a user with a sufficient cooling sensation without sacrificing air permeability, (iii) can provide a soft tactile sensation to a user, (iv) can improve the durability of the final product by having high pilling resistance and abrasion resistance, and (v) can improve the productivity of the final product by having excellent cutting and sewing capabilities. Brief description of the drawings The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated into and form a part of this application, illustrate embodiments of the invention, and together with the description serve to explain the principle of the invention. Figure 1 schematically shows an apparatus for manufacturing a polyethylene thread according to an embodiment of the present invention. Figure 2 schematically shows an apparatus for measuring the sensation of cold on contact (Qmax) of a skin-cooling fabric. Figure 3 schematically shows an apparatus for measuring thermal conductivity and heat transfer coefficient in the thickness direction of the skin-cooling fabric. Detailed description of the modalities The embodiments of the present invention are described in detail below with reference to the accompanying figures. However, the embodiments described below are provided for illustrative purposes only to aid in a clear understanding of the present invention and should not be interpreted as limiting its scope. In order for the user to feel a sufficient cooling sensation, the threads used in the manufacture of the skin-cooling fabric are preferably polymer threads with high thermal conductivity. In a solid, heat is generally transferred through the movement of free electrons and lattice vibrations called phonons. In a metal, heat is transferred primarily through the movement of free electrons. Conversely, in non-metallic materials such as polymers, heat is mainly transferred through phonons within the solid (especially along molecular chains connected by covalent bonds). To improve the thermal conductivity of the fabric so that the user can perceive a cooling sensation, it is necessary to improve the heat transfer capacity through the phonon of the polymer yarn by increasing the crystallinity of the polymer yarn to 60% or more. According to the present invention, high-density polyethylene (HDPE) is used to produce a polymer yarn of such high crystallinity. This is because yarns made from high-density polyethylene (HDPE) with a density of 0.941 to 0.965 g / cm³ have relatively high crystallinity compared to yarns made from low-density polyethylene (LDPE) with a density of 0.910 to 0.925 g / cm³ and yarns made from linear low-density polyethylene (LLDPE) with a density of 0.915 to 0.930 g / cm³. Meanwhile, high-density polyethylene (HDPE) yarn can be classified into ultra-high-molecular-weight polyethylene (UHMWPE) yarn and high-molecular-weight polyethylene (HMWPE) yarn according to its weight-average molecular weight (Mw). UHMWPE generally refers to a linear polyethylene with a weight-average molecular weight (Mw) of 600,000 g / mol or higher, while HMWPE generally refers to a linear polyethylene with a weight-average molecular weight (Mw) of 20,000 to 250,000 g / mol. As mentioned earlier, since UHMWPE yarns such as Dyneema® can only be produced by gel spinning due to the high melt viscosity of UHMWPE, there is the problem of causing environmental issues and requiring considerable costs to recover the organic solvent. Since HMWPE has a relatively low melt viscosity compared to UHMWPE, melt spinning is possible, and as a result, the environmental and high-cost problems associated with UHMWPE yarns can be overcome. Therefore, the polyethylene yarn for a skin-cooling fabric of the present invention is a yarn formed from HMWPE. In the force-elongation curve of the polyethylene yarn of the present invention obtained by measurement at room temperature, (i) elongation at a force of 1 g / d is 0.5 to 3%, (ii) elongation at a force of 3 g / d is 5.5 to 10%, and (iii) the difference between the elongation at a force of 4 g / d and the elongation at the maximum force (i.e., tensile strength) is 5.5 to 25%. Furthermore, the polyethylene yarn of the present invention has a tenacity of 55 to 120 J / m3 at room temperature. If the elongation at a force of 1 g / d of the polyethylene yarn is too low, the fabric woven from the yarn becomes too stiff (i.e., the fabric stiffness is too high), resulting in an unpleasant tactile sensation for the user. Therefore, it is preferable for the elongation at a force of 1 g / d of the polyethylene yarn to be 0.5% or more. However, if the elongation at a force of 1 g / d of the polyethylene yarn is too high, a phenomenon occurs in which the yarn stretches during weaving, making it difficult to adjust the fabric density to the required level. Therefore, the elongation at a force of 1 g / d of the polyethylene yarn is preferably 3% or less. Specifically, the “elongation at a force of 1 g / d of the polyethylene yarn can be 0.5 to 3%, 1.0 to 3.0%, 1.0 to 2.0% or 1.4 to 2.0%.” zncfrnn / zznz / E / YiAi If the elongation at a force of 3 g / d of the polyethylene yarn is too low, there is a high risk of yarn breakage during the fabric weaving process to which a predetermined amount of tension is applied. Therefore, the elongation at a force of 3 g / d of the polyethylene yarn is preferably 5.5% or higher. However, if the elongation at a force of 3 g / d of the polyethylene yarn is too high, the ripple effect is not sufficiently expressed during fabric weaving, resulting in a fabric with low tear resistance and low durability. Therefore, the elongation at a force of 3 g / d of the polyethylene yarn is preferably 10% or less. Specifically, the “elongation at a force of 3 g / d of the polyethylene yarn can be 5.5 to 10%, 6.0 to 9.0% or 6.0 to 8.5%. Tenacity is an area between the force-elongation curve (x-axis: elongation, y-axis: force) and the x-axis (integral value), which tends to increase as the difference between the elongation at a force of 4 g / dy and the elongation at the maximum force increases. If the difference between elongation at 4 g / d and elongation at maximum strength of the polyethylene yarn is too small, or if the tenacity of the polyethylene yarn is too low, the pilling resistance and abrasion resistance of the fabric woven from the yarn will not be satisfactory. Specifically, since the polyethylene yarn has a difference between elongation at 4 g / d and elongation at maximum strength of 5.5% or more, and a tenacity of 55 J / m³ or more, the skin-cooling fabric produced with this material has pilling resistance of grade 4 or higher (measured according to ASTM D 4970-07) and abrasion resistance of 5000 cycles or more (measured according to the Martindale method as specified in KS K ISO 12947-2: 2014). However, if the difference between the elongation at a force of 4 g / d and the elongation at the maximum force of the polyethylene yarn is too large, or if the tenacity of the polyethylene yarn is too high, the cutting and sewing capabilities of the fabric woven from the yarn will be poor, thus reducing the productivity of the final product. Furthermore, the use of expensive specialized cutting and sewing machines to overcome these problems leads to increased production costs. Therefore, the difference between the elongation at a force of 4 g / d and the elongation at the maximum force of the polyethylene yarn should preferably be 25% or less. Additionally, the tenacity of the polyethylene yarn should preferably be 120 J / m³ or less. Specifically, the difference between the elongation at a force of 4 g / dy and the elongation at the maximum force of the polyethylene yarn can be 5.5 at 25%, 9.0 at 20%, or 9.5 at 15%. Polyethylene yarn can have a tenacity of 55 to 120 J / m3, or 60 to 100 J / m3, or 65 to 95 J / m3 at room temperature. Furthermore, the polyethylene yarn according to one embodiment of the present invention has a tensile strength of 4 g / d ± 6 g / d, a tensile modulus of 15 to 80 g / d, an elongation at break of 14 to 55%, and a crystallinity of 60 to 85%. Preferably, the polyethylene yarn has a tensile strength of 4.5 g / d to 5.5 g / d, a tensile modulus of 40 to 60 g / d, an elongation at break of 20 to 35%, and a crystallinity of 70 to 80%. zncfrnn / zznz / E / YiAi If the tensile strength is greater than 6 g / d, the tensile modulus is greater than 80 g / d, or the elongation at break is less than 14%, the polyethylene yarn not only has poor weaving capabilities, but the fabric produced with this yarn is also excessively stiff, which can cause discomfort to the wearer. Conversely, if the tensile strength is 4 g / d or less, the tensile modulus is less than 15 g / d, or the elongation at break exceeds 55%, pilling may occur in the fabric, and even fabric tearing may occur with continuous use of fabrics made from these polyethylene yarns. If the crystallinity of the polyethylene yarn is less than 60%, its thermal conductivity is low, and therefore, the fabric made from it cannot provide the user with a sufficient cooling sensation. That is, given that polyethylene yarn has a crystallinity of 60 to 85%, the skin-cooling fabric produced with it can have a thermal conductivity in the thickness direction of 0.0001 W / cm-°C or more, a heat transfer coefficient in the thickness direction of 0.001 W / cm²-°C or more at 20°C, and a cooling sensation on contact (Qmax) of 0.1 W / cm² or more. The polyethylene yarn according to one embodiment of the present invention has a weight average molecular weight (Mw) of 50,000 to 99,000 g / mol and a polydispersity index (PDI) of 5 to 9, or 5.5 to 7.0. The polydispersity index (PDI) is the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), also known as the molecular weight distribution index (MWD). The weight average molecular weight (Mw) and the polydispersity index (PDI) of polyethylene yarn are closely related to the physical properties of the polyethylene used as raw material. The polyethylene yarn of the present invention may have a DPF (denier per filament) of 1 to 5. That is, the polyethylene yarn may include a plurality of filaments each with a fineness of 1 to 5 deniers (1.11 x 10⁻⁷ to 5.56 x 10⁻⁷ kg / m). In addition, the polyethylene yarn of the present invention may have an overall fineness of 75 to 450 deniers (8.3 x 10⁻⁶ to 5 x 10⁻⁵ kg / m). In a polyethylene yarn with a predetermined overall fineness, if the fineness of each filament exceeds 5 denier (5.56 x 10'7 kg / m), the softness of the fabric made from the polyethylene yarn becomes insufficient, and the contact area with the body becomes small, making it impossible to provide the wearer with a sufficient cooling sensation. Generally, the DPF (Discharge Per Hole) can be adjusted by the amount of discharge per hole of a spinneret (hereafter referred to as the single-hole discharge amount) and the draw ratio. The polyethylene yarn of the present invention may have a cross-circular cross-section or a non-cross-circular cross-section, but it is desirable to have a cross-circular cross-section from the point of view that it can provide a uniform cooling sensation to the user. The skin-cooling fabric of the present invention, manufactured from the polyethylene yarn described above, can be a woven or knitted fabric having a weight per unit area (i.e., area density) of 75 to 800 g / m². If the area density of the fabric is less than 75 g / m², the fabric density will be insufficient, and there will be many gaps in the fabric. These gaps reduce the cooling sensation. The polyethylene used as raw material for the manufacture of the polyethylene yarn of the present invention has a density of 0.941 to 0.965 g / cm3, a weight average molecular weight (Mw) of 50,000 to 99,000 g / mol, and a melt index (MI) (at 190 °C) of 6 to 21 g / 10 min. Furthermore, considering that the polydispersity index may decrease during the spinning process, the polyethylene of the present invention used as raw material has a polydispersity index (PDI) of 5.5 to 9, which is slightly higher than the target polydispersity index (i.e., the polydispersity index of the yarn). To manufacture a fabric that provides a high cooling sensation, the polyethylene yarn must have a high crystallinity of 60 to 85%, and to manufacture a polyethylene yarn with such high crystallinity, it is desirable to use a high-density polyethylene (HDPE) that has a density of 0.941 to 0.965 g / cm3. When the weight-average molecular weight (Mw) of the polyethylene used as raw material is less than 50,000 g / mol, the resulting polyethylene yarn is unlikely to exhibit a tensile strength of 4 g / dµm or a tensile modulus of 15 g / dµm, and as a result, pilling may occur in the fabrics. Conversely, when the weight-average molecular weight (Mw) of the polyethylene exceeds 99,000 g / mol, the weaving properties of the polyethylene yarn are poor due to excessively high tensile strength and modulus; the stiffness is too high, making it unsuitable for use in the manufacture of skin-cooling fabrics intended to come into contact with the user's skin. When the polydispersity index (PDI) of the polyethylene used as raw material is less than 5.5, melt flow is poor due to the relatively narrow molecular weight distribution, and processability during melt extrusion deteriorates, leading to yarn breakage due to uneven discharge during the spinning process. Conversely, when the PDI of HDPE exceeds 9, melt flow and processability during melt extrusion are improved due to the broad molecular weight distribution. However, the low molecular weight polyethylene content is excessive, making it difficult for the final polyethylene yarn to achieve a tensile strength of 4 g / dL and a tensile modulus of 15 g / dL. As a result, pilling can form relatively easily in fabrics. When the melt index (MI) of the polyethylene used as raw material is less than 6 g / 10 min, it is difficult to guarantee uniform flow in a 100 extruder due to the high viscosity and low flowability of the molten polyethylene. This reduces the uniformity and processability of the extruded mixture, increasing the risk of yarn breakage during the spinning process. On the other hand, when the melt index (MI) of the polyethylene exceeds 21 g / 10 min, flow in the 100 extruder becomes relatively good, but it may be difficult to achieve a final polyethylene yarn with a tensile strength greater than 4 g / d and a tensile modulus greater than 15 g / d. Optionally, a fluorine-based polymer can be added to the polyethylene. As a method for adding the fluorine-based polymer, mention can be made of (i) a method for injecting a master mix containing polyethylene and a fluorine-based polymer together with a polyethylene chip into the extruder 100 and then melting them together, or (ii) a method for injecting the fluorine-based polymer into an extruder 100 through a side feeder while injecting the polyethylene chip into the extruder 100, and then melting them together. By adding a fluorine-based polymer to polyethylene, yarn breakage during the spinning and multi-stage drawing processes can be further reduced, thereby improving productivity. As a non-limiting example, the fluorine-based polymer added to the polyethylene could be a tetrafluoroethylene copolymer. The fluorine-based polymer can be added to the polyethylene in such a quantity that the fluorine content in the final yarn increases from 50 to 2500 ppm. After the polyethylene having the physical properties described above is injected into the extruder 100 and melted, the molten polyethylene is transferred to a spindle 200 by means of a screw (not shown) in the extruder 100, and is extruded through a plurality of spin holes formed in the spindle 200. The number of holes in spindle 200 can be determined according to the DPF and the overall fineness of the yarn produced. For example, when manufacturing yarn with an overall fineness of 75 denier (8.3 × 10⁻⁶ kg / m), spindle 200 can have from 20 to 75 holes. Furthermore, when manufacturing yarn with an overall fineness of 450 denier (5 × 10⁻⁵ kg / m), spindle 200 can have from 90 to 450 holes, preferably from 100 to 400 holes. The melting step in extruder 100 and the extrusion step through die 200 are preferably performed at 150 to 315 °C, preferably 250 to 315 °C, more preferably 265 to 310 °C. That is, extruder 100 and die 200 are preferably maintained at 150 to 315 °C, preferably 250 to 315 °C, more preferably 265 to 310 °C. When the spinning temperature is below 150°C, the low temperature can cause the HDPE to melt unevenly, making spinning difficult. Conversely, when the spinning temperature exceeds 315°C, the polyethylene can thermally decompose, making it difficult to achieve the desired strength. The L / D ratio, which is the ratio between the hole length L and the hole diameter D of die 200, can range from 3 to 40. When L / D is less than 3, a swelling phenomenon occurs during melt extrusion, making it difficult to control the elastic behavior of the polyethylene, resulting in poor spinning properties. Furthermore, when L / D exceeds 40, a non-uniform discharge phenomenon can occur due to a decrease in pressure, along with yarn breakage caused by necking of the molten polyethylene passing through die 200. As the molten polyethylene is discharged from the holes of spinneret 200, solidification of the polyethylene is initiated by the difference between the spinning temperature and the ambient temperature, and a semi-solidified filament is formed simultaneously. In this specification, both the semi-solidified filament and the fully solidified filament are collectively referred to as filament. The plurality of filaments 11 solidifies completely upon cooling in a cooling zone 300. The cooling of the filaments 11 can be carried out by an air cooling method. In cooling zone 300, the cooling of the filaments 11 is preferably carried out to 15 to 40 °C using cooling air with a wind speed of 0.2 to 1 m / s. When the cooling temperature is below 15 °C, the elongation may be insufficient due to overcooling, which can lead to yarn breakage during the drawing process. When the cooling temperature exceeds 40 °C, the fineness deviation between the filaments 11 increases due to uneven solidification, which can also lead to yarn breakage during the drawing process. Subsequently, the filaments 11 that cool and solidify completely are converged by a converging part 400 to form a multifilament 10. As illustrated in Figure 1, the method of the present invention may further include a step of applying an oil to the cooled filaments 11 using an oil roller (OR) or oil jet, before forming the multifilament 10. The oil application step may be carried out by means of a metered lubrication (MO) method. Optionally, the multifilament formation step 10 through a converging part 400 and the oil application step can be performed at the same time. As illustrated in Figure 1, the polyethylene yarn of the present invention can be produced by a direct draw spinning (DSD) process. The multifilament 10 is transferred directly to a multi-stage drawing part 500 comprising a plurality of traction roller parts GR1...GRn and multi-stage drawing at a total draw ratio of 2.5 to 8.5, preferably 3.5 to 7.5, and then wound onto a winder 600. Alternatively, after the multifilament 10 is first wound as an unstretched yarn, the unstretched yarn can be stretched, thereby manufacturing the polyethylene yarn of the present invention. The polyethylene yarn of the present invention can be manufactured by a two-step process of first melting the spun polyethylene to produce an unstretched yarn and then stretching the unstretched yarn. If the total draw ratio applied in the drawing process is less than 3.5, in particular less than 2.5, (i) the polyethylene yarn finally obtained cannot have a crystallinity equal to or greater than 60% and, therefore, the fabric manufactured from the yarn cannot provide the user with a sufficient cooling sensation, and (ii) the polyethylene yarn cannot have a strength greater than 4 g / d, a tensile modulus equal to or greater than 15 g / d, and an elongation at break equal to or less than 55%, and as a result, pilling may occur in the fabric produced from the yarn. Furthermore, when the total draw ratio exceeds 7.5, and specifically 8.5, the resulting polyethylene yarn must not have a tensile strength of 6 g / d or less, a tensile modulus of 80 g / d or less, or an elongation at break of 14% or more. Therefore, not only is the weaving capacity of the polyethylene yarn poor, but the fabric produced with it also becomes excessively stiff, causing discomfort to the wearer. If the linear speed of the first traction roller part (GR1) is determined, which determines the spinning speed of the melt yarn of the present invention, the linear speed of the remaining traction roller parts is appropriately determined so that in the multi-stage drawing part 500, a total drawing ratio of 2.5 to 8.5, preferably 3.5 to 7.5, can be applied to the multifilament 10. zncfrnn / zznz / E / YiAi According to one embodiment of the present invention, by properly setting the temperature of the traction roller parts (GR1... GRn) of the multi-stage drawing part 500 in the range of 40 to 140 °C, the thermal adjustment of the polyethylene yarn can be carried out through the multi-stage drawing part 500. For example, the temperature of the first part of the traction roller (GR1) can be from 40 to 80 °C, and the temperature of the last part of the traction roller (GRn) can be from 110 to 140 °C. The temperature of each of the traction roller parts, excluding the first and last parts (GR1, GRn), can be set to be equal to or higher than the temperature of the immediately preceding part of the traction roller. The temperature of the last part of the traction roller (GRn) can be set to be equal to or higher than the temperature of the immediately preceding part of the traction roller, but it can be set slightly lower than that temperature. The multi-stage drawing and thermal adjustment of the multifilament 10 are carried out simultaneously by the multi-stage drawing part 500, and the multi-stage drawn multifilament 10 is wound around the winder 600, thus completing the manufacture of the polyethylene yarn for a skin-cooling fabric of the present invention. From this point forward, the present invention will be described in more detail by way of examples. However, these examples are only to aid in understanding the present invention, and its scope is not limited to them. Example 1 A polyethylene yarn containing 200 filaments and a total fineness of 400 deniers (4.44 x 10⁵ kg / m) was produced using the apparatus illustrated in Figure 1. In detail, a polyethylene chip with a density of 0.961 g / cm³, a weight average molecular weight (Mw) of 87.660 g / mol, a polydispersity index (PDI) of 6.4, and a melt index (MI at 190 °C) of 11.9 g / 10 min was injected into an extruder 100. The molten polyethylene was extruded through a die 200 having 200 holes. The L / D ratio, which is the ratio of hole length L to hole diameter D of the die 200, was 6. The die temperature was 265 °C. The filaments 11 formed while being discharged from spinneret 200 were finally cooled to 30 °C by cooling air having a wind speed of 0.45 m / s in a cooling zone 300, and converged into a multifilament 10 by the converging unit 400 and moved to the multi-stage drawing part 500. The 500 multi-stage drawing part consisted of a total of five stage traction rollers, the temperature of the traction roller parts was set to 70 to 115 °C, and the temperature of the rear stage roller part was set to be equal to or higher than the temperature of the immediately preceding roller part. After the multifilament 10 was stretched to a total draw ratio of 7.5 by the multi-stage draw part 500, it was wound onto a winder 600, thus obtaining a polyethylene yarn. Example 2 A polyethylene yarn was obtained in the same way as in Example 1, except that a polyethylene chip with a density of 0.958 g / cm3, a weight average molecular weight (Mw) of 98,290 g / mol, a polydispersity index (PDI) of 8.4, and a melt index (MI at 190 °C) of 6.1 g / 10 min was used, and the spinneret temperature was 275 °C. Example 3 A polyethylene yarn was obtained in the same way as in Example 1, except that a polyethylene chip with a density of 0.948 g / cm3, a weight average molecular weight (Mw) of 78,620 g / mol, a polydispersity index (PDI) of 8.2, and a melt index (MI at 190 °C) of 15.5 g / 10 min was used, the spinneret temperature was 255 °C, and the total draw ratio was 6.8. Comparative Example 1 A polyethylene yarn was obtained in the same way as in Example 1, except that a polyethylene chip with a density of 0.962 g / cm3, a weight average molecular weight (Mw) of 98,550 g / mol, a polydispersity index (PDI) of 4.9, and a melt index (MI at 190 °C) of 6.1 g / 10 min was used, and the spinneret temperature was 285 °C. Comparative Example 2 A polyethylene yarn was obtained in the same way as in Example 1, except that a polyethylene chip with a density of 0.961 g / cm3, a weight average molecular weight (Mw) of 98,230 g / mol, a polydispersity index (PDI) of 7.0, and a melt index (MI at 190 °C) of 2.9 g / 10 min was used. The spinneret temperature was 290 °C, and the total draw ratio was 8.6. Comparative Example 3 A polyethylene yarn was obtained in the same way as in Example 1, except that a polyethylene chip with a density of 0.961 g / cm3, a weight average molecular weight (Mw) of 180,550 g / mol, a polydispersity index (PDI) of 6.4, and a melt index (MI at 190 °C) of 0.6 g / 10 min was used, the spinneret temperature was 300 °C, it was drawn to a total draw ratio of 14 through the multi-stage drawing part 500 consisting of a total of eight stage traction roll parts, and the temperature of the traction roll parts was set at 75 to 125 °C. Test Example 1 The properties of strength-elongation, toughness, tensile strength, tensile modulus, elongation at break, crystallinity, and polydispersity index (PDI) of the polyethylene yarn prepared by each of examples 1 to 3 and comparative examples 1 to 3 were measured as follows, and the results are shown in Tables 1 and 2 below. (1) Strength-elongation properties, tensile strength, tensile modulus, elongation at break and tenacity of polyethylene yarn The force-elongation curves (x-axis: elongation, y-axis: force) of the polyethylene yarns at room temperature were determined using an Instron universal tensile tester (Instron Engineering Corp., Canton, Mass.) in accordance with ASTM D885 (sample length: 250 mm, tensile speed: 300 mm / min, and initial load: 0.05 g / d). Elongation at a force of 1 g / d, elongation at a force of 3 g / d, the difference between the elongation at a force of 4 g / d and the elongation at maximum force, the tensile strength, the tensile modulus (zncfrnn / zznz / E / YiAi), and the elongation at break of the polyethylene yarn were determined respectively from the force-elongation curve. Furthermore, the toughness of the polyethylene yarn was determined by calculating the area between the force-elongation curve (x-axis: elongation, y-axis: force) and the x-axis through integration. (2) Crystallization of polyethylene thread The crystallinity of the polyethylene thread was measured using an XRD (X-ray diffractometer) instrument (manufacturer: PANalytical, model name: EMPYREAN). Specifically, the polyethylene thread was cut to prepare a sample 2.5 cm long. The sample was attached to a sample holder, and the measurement was then performed under the following conditions. - Light source (X-ray source): Cu-Ka radiation Power: 45 KV x 25 mA - Mode: continuous scan mode - Scanning angle range: 10° to 40° - Scanning speed: 0.17s (3) Polydispersity index (PDI) of polyethylene yarn After completely dissolving the polyethylene yarn in the following solvent, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polyethylene were determined respectively using the following gel permeation chromatography (GPC), and then the ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) was calculated, thus obtaining the polydispersity index (PDI) of the polyethylene yarn. - Analytical equipment: PL-GPC 220 System - Column: 2 x PLGEL MIXED-B (7.5 x 300 mm) - Column temperature: 160 °C - Solvent: trichlorobenzene (TCB) + 0.04% by weight of dibutylhydroxytoluene (BHT) (after drying with 0.1% CaCl) - Dissolution conditions: Measure the solution that passed through the glass filter (0.7 pm) after dissolution at 160 °C for 1 to 4 hours. - Injector, Detector temperature: 160 °C - Detector: IR Detector - Flow rate: 1.0 mL / min - Injection volume: 200 pL - Sample of the standard: polystyrene zncfrnn / zznz / E / YiAi Table 1 Example 1 Example 2 Example 3 PE Density (g / cm3) 0.961 0.958 0.948 Mw (g / mol) 87,660 98,290 78,620 PDI 6.4 8.4 8.2 MI (g / 10 min) 11.9 6.1 15.5 Row temperature (°C) 265 275 255 Proportion of total stretch 7.5 7.5 6.8 PE Yarn Elongation (%) at 1 g / d 1.75 1.92 1.45 Elongation (%) at 3 g / d 7.1 8.3 6.2 | Elongation (%) at 4 g / d Elongation (%) at maximum strength | (%) 15 12 9.5 Hardness (J / m3) 86 92 65 Tensile Strength (g / d) 4.6 5.3 4.3 Tensile Modulus (g / d) 49.6 56.3 42.6 Elongation at break (%) 25 22 28 Crystallinity (%) 72 74 71 PDI 5.6 6.8 6.3 zncfrnn / zznz / E / YiAi Table 2 Comparative example 1 Comparative example 2 Comparative example 3 PE Density (g / cm3) 0.962 0.961 0.961 Mw (g / mol) 98,550 98,230 180,550 PDI 4.9 7.0 6.4 MI (g / 10 min) 6.1 2.9 0.6 Row temperature (°C) 285 290 300 Total Draw Ratio 7.5 8.6 14 PE Yarn Elongation (%) at 1 g / d 0.95 0.82 0.45 Elongation (%) at 3 g / d 4.4 4.8 1.52 | Elongation (%) at 4 g / d Elongation (%) at maximum resistance | (%) 7.0 5.2 4.7 Tenacity (J / m3) 52 50 72 Tensile strength (g / d) 6.5 7.2 17.3 Tensile modulus (g / d) 63.4 68.4 485 Elongation at break (%) 13.5 11.8 6.6 Crystallinity (%) 73 74 80 PDI 3.3 4.9 4.4 Example 4 The plain weave was made using the polyethylene yarn from example 1 as both warp and weft yarn, thus producing a fabric that has a warp density of 11.8 ea / cm (30 ea / in) and a weft density of 11.8 ea / cm (30 ea / in). Example 5 A fabric was manufactured in the same way as in example 4, except that the polyethylene yarn from example 2 was used instead of the polyethylene yarn from example 1. Example 6 A fabric was manufactured in the same way as in example 4, except that the polyethylene yarn from example 3 was used instead of the polyethylene yarn from example 1. Comparative Example 4 A fabric was manufactured in the same way as in example 4, except that polyethylene from comparative example 1 was used instead of the polyethylene yarn from example 1. Comparative Example 5 A fabric was manufactured in the same way as in example 4, except that polyethylene from comparative example 2 was used instead of the polyethylene yarn from example 1. Comparative example 6 A fabric was manufactured in the same way as in example 4, except that polyethylene from comparative example 3 was used instead of the polyethylene yarn from example 1. The thread of zncfrnn / zznz / E / YiAi was used. Test Example 2 The sensation of cold to the touch (Qmax), thermal conductivity (thickness direction), heat transfer coefficient (thickness direction), pilling resistance, abrasion resistance, and stiffness of the fabrics manufactured respectively by examples 4 to 6 and comparative examples 4 to 6 were measured as follows, and the results are shown in Tables 3 and 4 below. (1) Cold sensation upon contact (Qmax) of the fabrics A 20 x 20 cm fabric sample was prepared and then left to stand for 24 hours under conditions of a temperature of 20 ± 2 °C and a relative humidity of 65 ± 2%. The cold sensation on contact (Qmax) of the fabric was then measured using a KES-F7 THERMO LABO II apparatus (Kato Tech Co., LTD.) in the test environment of a temperature of 20 ± 2 °C and 65 ± 2 % RH. In detail, as illustrated in Figure 2, fabric sample 23 was placed on a base plate (also called a water tank) 21 maintained at 20 °C, and a T-Box 22a (contact area: 3 x 3 cm) heated to 30 °C was placed on fabric sample 23 for only 1 second. That is, the other surface of fabric sample 23, the one in contact with the base plate 21, was instantaneously brought into contact with the T-Box 22a. The contact pressure applied to fabric sample 23 by the T-Box 22a was 6 gf / cm². The Qmax value displayed on a monitor (not shown) connected to the apparatus was then recorded. The test was repeated 10 times, and the arithmetic mean of the Qmax values ​​obtained was calculated. (2) Thermal conductivity and heat transfer coefficient of fabrics A 20 x 20 cm fabric sample was prepared and then left to stand for 24 hours under conditions of a temperature of 20 ± 2 °C and a relative humidity of 65 ± 2%. Afterwards, the thermal conductivity and heat transfer coefficient of the fabric were measured using a KES-F7 THERMO LABO II apparatus (Kato Tech Co., LTD.) under the test environment of a temperature of 20 ± 2 °C and 65 ± 2 % RH. In detail, as illustrated in Figure 3, fabric sample 23 was placed on a base plate 21 maintained at 20 °C, and T-Box 22b (contact area: 5 x 5 cm) heated to 30 °C was placed on fabric sample 23 for 1 minute. Even while T-Box 22b was in contact with fabric sample 23, heat was continuously supplied to T-Box 22b to maintain the temperature at 30 °C. The amount of heat (i.e., heat flow loss) supplied to maintain the temperature of T-Box 22b was displayed on a monitor (not shown) connected to the apparatus. The test was repeated 5 times, and the arithmetic mean of the heat flow loss was calculated. The thermal conductivity and heat transfer coefficient of the fabric were then calculated using Equations 2 and 3. [Equation 2] K = (W*D) / (A*AT) [Equation 3] K = K / D where K is a thermal conductivity (W / cm°C), D is a thickness (cm) of the fabric sample 23, A is a contact area (= 25 cm2) of the BT-Box 22b, ΔT is a temperature difference (= 10 °C) on both sides of the fabric sample 23, W is a heat flow loss (watt) and k is a heat transfer coefficient (W / cm2°C). (3) Fabric stiffness The stiffness of the fabric was measured by the circular bending method using a stiffness measuring device in accordance with ASTM D 4032. As the stiffness (kgf) is lower, the fabric has softer properties. (4) Resistance to fraying of fabrics The fabric's pilling resistance was measured using a Martindale tester in accordance with ASTM D 4970-07 (friction movement frequency: 200 total cycles). The pilling resistance grade criteria are as follows. - Grade 1: Very severe freezing - Grade 2: Severe freezing - Grade 3: Moderate freezing - Grade 4: Light frizz - Grade 5: Non-pilling (5) Abrasion resistance of fabrics The abrasion resistance of the fabric was measured using a Martindale tester in accordance with the Martindale method as specified in KS K ISO 12947-2: 2014. In detail, the number of cycles until two threads in the fabric broke was measured. zncfrnn / zznz / E / YiAi Table 3 Example 4 Example 5 Example 6 Qmax (W / cm2) 0.159 0.167 0.149 Thermal conductivity (W / cm-°C) 0.00043 0.00048 0.00039 Heat transfer coefficient (W / cm2 °C) 0.0126 0.0142 0.0123 Stiffness (kgf) 0.45 0.52 0.43 Rutting resistance (grade) 4 4 4 Abrasion resistance (cycles) 6530 7560 5280 Table 4 Comparative Example 4 Comparative Example 5 Comparative Example 6 Qmax (W / cm2) 0.166 0.167 0.168 Thermal Conductivity (W / cm°C) 0.00053 0.00058 0.00062 Heat Transfer Coefficient (W / cm2 °C) 0.00147 0.00149 0.00153 Stiffness (kgf) 0.65 0.72 0.95 Rutting Resistance (grade) 3 3 4 Abrasion Resistance (cycles) 4510 4730 18540 Explanation of the symbols 100: extruder 200: spinneret 300: Cooling zone 11: Filaments O: oil roller 400: converging part 10: Multifilament 500: Multi-stage drawing part GR1: first part of traction roller GRn: last part of traction roller 600: winder 22a: T-Box 23: fabric sample 21: motherboard 22b: BT-Box

Claims

1. A polyethylene yarn, wherein in a force-elongation curve of the polyethylene yarn obtained by measurements at room temperature, (i) the elongation at a force of 1 g / d is 0.5 to 3%, (ii) the elongation at a force of 3 g / d is 5.5 to 10% and (iii) the difference between the elongation at a force of 4 g / d and the elongation at a maximum force is 5.5 to 25%, and the polyethylene yarn has a tenacity of 55 to 120 J / m3 at room temperature.

2. The polyethylene yarn according to claim 1 wherein the polyethylene yarn has a tensile strength of more than 4 g / d but less than 6 g / d, a tensile modulus of 15 to 80 g / d, an elongation at break of 14 to 55%, and a crystallinity of 60 to 85%.

3. The polyethylene yarn according to claim 1 wherein the polyethylene yarn has an average molecular weight (Mw) of 50,000 to 99,000 g / mol and a polydispersity index (PDI) of 5 to 9.

4. The polyethylene yarn according to claim 1 wherein the polyethylene yarn has an overall fineness of 75 to 450 denier, and the polyethylene yarn includes a plurality of filaments each having a fineness of 1 to 5 denier.

5. The polyethylene yarn according to claim 1 wherein the polyethylene yarn has a crossed circular section.

6. A skin-cooling fabric formed from polyethylene yarn according to any of claims 1 to 5, wherein the skin-cooling fabric at 20°C has a thermal conductivity in the thickness direction of 0.0001 W / cm-°C or more, a heat transfer coefficient in the thickness direction of 0.001 W / cm2-°C or more, and a contact cooling sensation (Qmax) of 0.1 W / cm2 or more.

7. The skin-cooling fabric according to claim 6, wherein the pilling resistance of the skin-cooling fabric measured in accordance with ASTM D 4970-07 is grade 4 or higher, and the abrasion resistance of the skin-cooling fabric measured in accordance with the Martindale method as specified in KS K ISO 12947-2: 2014 is 5000 cycles or more.

8. The skin-cooling fabric according to claim 6, wherein an area density of the skin-cooling fabric is 75 to 800 g / m2.

9. A method for manufacturing a polyethylene yarn comprising the steps of: melting a polyethylene with a density of 0.941 to 0.965 g / cm3, a weight average molecular weight (Mw) of 50,000 to 99,000 g / mol, a polydispersity index (PDI) of 5.5 to 9, and a melt index (MI) (at 190 °C) of 6 to 21 g / 10min; extruding the molten polyethylene through a spinneret having a plurality of spin holes; cooling a plurality of filaments formed when the molten polyethylene is discharged from the spinneret holes; and drawing a multifilament composed of the cooled filaments.

10. The method of manufacturing a polyethylene yarn according to claim 9, wherein the drawing step is performed at a draw ratio of 2.5 to 8.5.

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