To provide a polyethylene fiber, a product using the polyethylene fiber, and a method for producing the polyethylene fiber.

Abstract

To provide a polyethylene fiber suppressed in fiber unevenness and fusion and excellent in resistance.SOLUTION: A polyethylene fiber having a minimum rate of 1 * 10 - 8 sec - 1 or less in a measurement in which a diameter (μm) of a single yarn fineness is a horizontal axis, a frequency (%) is a vertical axis, and a half width of a peak including a diameter of a mode value with respect to a diameter indicating the mode value of a distribution curve is 0.1 to 0.7, the measurement temperature is 20 °C, and the measurement load is 800 MPa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to polyethylene fibers, products using the polyethylene fibers, and a method for producing the polyethylene fibers. [Background technology]

[0002] Ultra-high molecular weight polyethylene fibers (hereinafter sometimes referred to as polyethylene fibers), which are made from ultra-high molecular weight polyethylene, have excellent weather resistance and chemical resistance due to the fact that they are made from polyethylene, and are also lightweight and have extremely high strength, making them widely used in various industrial fields. In recent years, ropes made of polyethylene fibers have been attracting attention as an alternative to steel chains used in mooring ships, offshore markers, marine energy equipment, and marine structures. However, polyethylene fibers have the drawback of having no hydrogen bonds between molecular chains and little steric hindrance, which means that slippage between molecular chains occurs easily, resulting in large creep elongation. Therefore, there has been a demand for polyethylene fibers with improved creep resistance.

[0003] As a technique for improving the creep resistance of polyethylene fibers, for example, Patent Documents 1 and 2 propose polyethylene fibers having alkyl side chains such as ethyl. However, raw material polyethylene with alkyl side chains was prone to fiber irregularities (hereinafter simply referred to as fiber irregularities) in which fibers fused together during the spinning process or the flowability at the discharge port deteriorated, resulting in thick and thin portions in the longitudinal direction of the fiber and uneven diameters. Furthermore, in order to improve the strength of polyethylene fibers, it is necessary to increase the drawing temperature, but undrawn polyethylene yarns having alkyl side chains have the problem that they tend to fuse together when the drawing temperature is increased. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-280111 [Patent Document 2] WO2017 / 102618 publication Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyethylene fiber which is suppressed from causing fiber unevenness and fusion and which has excellent creep resistance. [Means for solving the problem]

[0006] The present invention, which has solved the above problems, has the following configuration. [1] In a distribution of single fiber fineness with the diameter (μm) on the horizontal axis and the frequency (%) on the vertical axis, the half-value width of the peak containing the diameter of the mode (half-value width / mode) relative to the diameter showing the mode of the distribution curve is 0.1 to 0.7, In creep measurements at a temperature of 20°C and a load of 800 MPa, the minimum creep rate was 1×10 -8 sec -1 A polyethylene fiber characterized by: [2] The polyethylene fiber according to [1], wherein, in differential scanning calorimetry (DSC) measurement, the fiber is heated from 30°C to 200°C at a rate of 10°C / min (first heating), held at 200°C for 5 minutes, cooled from 200°C to 30°C at a rate of 10°C / min, held at 30°C for 5 minutes, and then heated from 30°C to 200°C at a rate of 10°C / min (second heating), and the peak melting point in the second heating is 125°C to 131°C. [3] The polyethylene fiber according to [1] or [2], wherein the area of ​​the region sandwiched between the distribution curve and the horizontal axis, the area of ​​the region having a diameter that is at least twice the mode of the diameter, is 40% or less of the total area. [4] The polyethylene fiber according to any one of [1] to [3], which has a calcium content of 1 to 300 ppm. [5] The polyethylene fiber according to any one of [1] to [4], wherein the creep rate (800MPa / 1200MPa) after 800 hours from the start of measurement at a measurement temperature of 20°C and a measurement load of 1200MPa is 15 to 45 relative to the creep rate after 800 hours from the start of measurement at a measurement temperature of 20°C and a measurement load of 800MPa. [6] The polyethylene fiber according to any one of [1] to [5], wherein the polyethylene fiber has an intrinsic viscosity of 5.0 to 40 dl / g. [7] A polyethylene fiber according to any one of [1] to [6], which contains an alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group, and the number of said alkyl side chains per 1,000 carbon atoms is 0.5 to 3.0. [8] The polyethylene fiber according to any one of [1] to [7], which has a tensile strength of 15 cN / dtex or more. [9] A braid, twisted yarn, fishing line, rope, or net containing the polyethylene fiber according to any one of [1] to [8] above.

[0007] The method for producing polyethylene fibers according to the present invention, which has solved the above problems, has the following features.

[10] A spinning step of gel-spinning a mixture containing calcium stearate and a polyethylene solution to obtain fibers; a drawing step of multistage drawing the fibers obtained in the spinning step, A method for producing polyethylene fibers, wherein the final draw ratio (total draw ratio / final draw ratio) is 0.3 to 2.0 relative to the total draw ratio obtained by subtracting the final draw ratio from the total draw ratio in the multistage drawing step. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide polyethylene fibers that are suppressed in fiber unevenness and fusion and have excellent creep resistance. Therefore, products such as polyethylene fiber ropes using the polyethylene fibers of the present invention are suitable for applications such as mooring of marine structures. The production method of the present invention is also suitable for producing the polyethylene fiber of the present invention. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic explanatory diagram of a distribution curve in which the horizontal axis represents the diameter (μm) of single yarn fineness and the vertical axis represents the frequency (%). DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors have investigated the production process of ultra-high molecular weight polyethylene fibers with alkylene side chains. In the gel spinning method using ultra-high molecular weight polyethylene as a raw material, it was found that ultra-high molecular weight polyethylene with alkyl side chains is prone to flow unevenness during extrusion in the spinning process, resulting in fiber unevenness in the spun yarn (gel-like yarn) and fiber fusion. The present inventors have conducted extensive research into means for suppressing fiber unevenness and fusion during the spinning process, and as a result have found that adding calcium stearate to the spinning raw material improves the fluidity during spinning, suppresses flow unevenness, and effectively suppresses fiber unevenness and fusion. Furthermore, in the drawing process, conventional undrawn yarns were prone to yarn breakage and fiber fusion when drawn at high temperatures, but it was found that the undrawn yarns obtained by adding calcium stearate to the spinning raw material were less prone to yarn breakage and fiber fusion even when drawn at high temperatures.

[0011] The polyethylene fiber of the present invention has the following configuration. In a distribution where the horizontal axis represents the diameter (μm) of the single yarn fineness and the vertical axis represents the frequency (%), the half-value width of the peak containing the diameter of the mode (half-value width / mode) relative to the diameter showing the mode of the distribution curve is 0.1 to 0.7, In creep measurements at a temperature of 20°C and a load of 800 MPa, the minimum creep rate was 1×10 -8 sec -1 The following is the result.

[0012] The relationship between the half-value width and the mode of the fiber based on the above distribution curve (half-value width / mode) is an index showing fusion and fiber unevenness of polyethylene fibers. A schematic diagram is shown in Figure 1. If there is a lot of fusion or fiber unevenness in the polyethylene fibers, the half-width of the peak will broaden, and the half-width of the peak containing the mode diameter relative to the fiber diameter showing the mode (hereinafter sometimes referred to as half-width / mode) will increase. If the half-width / mode value exceeds 0.7, there will be a lot of fusion fibers and fiber unevenness, and the strength of the polyethylene fiber will decrease. When the half width / mode is 0.1 to 0.7, fiber unevenness and fusion are suppressed, and the fiber diameter is highly uniform, which contributes to increasing the strength of the polyethylene fiber. The half width / mode is preferably 0.1 to 0.6, and more preferably 0.2 to 0.5. The lower limit of 0.1 was set in consideration of measurement error, but it may be a lower value, for example, a value close to 0. The upper and lower limits of the ranges of values ​​in this specification mean "greater than or equal to" and "less than or equal to," respectively. The upper and lower limits of the ranges of values ​​may be changed independently, and in such cases, the values ​​may be replaced with values ​​indicating a preferred range in the specification or values ​​shown in the examples.

[0013] The diameter (μm) of the polyethylene fiber can be adjusted depending on the application, but if the diameter is too small, the polyethylene fiber will be easily broken, and if the diameter is too large, the flexibility will decrease, which may result in poor bending fatigue resistance. The diameter of the polyethylene fiber of the present invention is preferably 2 to 50 μm, more preferably 5 to 30 μm.

[0014] In the present invention, in the area of ​​the region sandwiched between the distribution curve and the horizontal axis, the area of ​​the region having a diameter twice or more the most frequent fiber diameter (hereinafter sometimes referred to as 2D) is preferably 40% or less, more preferably 30% or less, and even more preferably 25% or less of the total area (2D area / total area). When fibers fuse or become uneven, the diameter increases. If the area of ​​the region with a diameter more than twice the mode of the fiber diameter increases, it can cause a decrease in strength and elongation properties. In the polyethylene fiber of the present invention, fusion of fibers and fiber unevenness are suppressed, and therefore the area of ​​the D2 region shows a low value. The smaller the area of ​​the D2 region, the less fused fibers and fiber unevenness there will be, which is preferable, and the lower limit is not particularly limited and may be, for example, 0%.

[0015] In the present invention, the various values ​​of the polyethylene fiber such as diameter, half-width, 2D region area, creep rate, differential scanning calorimetry, calcium content, strength properties, etc. are values ​​based on the measurement methods in the Examples.

[0016] The polyethylene fiber of the present invention has a minimum creep rate of 1×10 in a creep measurement at a measurement temperature of 20° C. and a measurement load of 800 MPa. -8 sec -1 The following is the result. The polyethylene fiber of the present invention has a minimum creep rate of 1×10 -8 sec -1 Since the fiber has a hardness of 0.01 to 0.1 mm, the change in strain is small even under high load, and the fiber has excellent creep resistance. Therefore, products using the polyethylene fiber of the present invention have excellent dimensional stability and a significantly longer product life. The smaller the minimum creep rate, the more stable the fiber is and the less deformation it will undergo, which is preferable. The minimum creep rate is preferably 1×10 -9 sec -1 Less than 1×10, more preferably -10 sec -1 The following is the result.

[0017] It is also preferable that the polyethylene fiber of the present invention has a minimum creep rate (800MPa / 1200MPa) measured at a temperature of 20°C, a load of 1200MPa and after 800 hours from the start of measurement relative to the minimum creep rate measured at a temperature of 20°C, a load of 800MPa and after 800 hours from the start of measurement, such that the ratio is 15 to 45. When the ratio of the minimum creep rates at different loads (800 MPa / 1200 MPa) is within a specified range, the change in strain is small even under high loads, resulting in superior creep resistance. Furthermore, polyethylene fibers with a minimum creep rate ratio within the specified range have sufficient strength properties and good creep properties (evaluated at an 800 MPa creep rate). The ratio of the minimum creep rates under different loads (800 MPa / 1200 MPa) is preferably 15-45, more preferably 20-40, and even more preferably 25-35.

[0018] It is also preferable that the polyethylene fiber of the present invention contains at least any one of alkyl side chains, such as a methyl group, an ethyl group, and a butyl group, and that the number of the alkyl side chains is 0.5 to 3.0 per 1000 carbon atoms. Introducing a certain number of alkyl side chains into polyethylene fibers can prevent slippage of polyethylene molecules and improve creep resistance, contributing to an improvement in the minimum creep rate and the ratio of the minimum creep rates. The number of alkyl side chains in the polyethylene fiber is preferably 0.5 to 3.0, more preferably 1.0 to 2.5, and even more preferably 1.5 to 2.0 per 1000 carbon atoms.

[0019] Furthermore, in differential scanning calorimetry (DSC) of the polyethylene fiber of the present invention, when the temperature is increased from 30°C to 200°C at a rate of 10°C / min (1st heating), held at 200°C for 5 minutes, cooled from 200°C to 30°C at a rate of 10°C / min, held at 30°C for 5 minutes, and then increased from 30°C to 200°C at a rate of 10°C / min (2nd heating), the peak melting point temperature in the 2nd heating (DSC2nd) is preferably 125°C to 131°C. In a preferred embodiment of the present invention, alkyl side chains are introduced into the polyethylene fiber. However, since it is difficult to determine the introduction state of the alkyl side chains from the polyethylene fiber, this is determined by DSC measurement. That is, the polyethylene fiber is heated (first heating) to dissolve it and return it to the polymer, and then a second heating (second heating) is performed to determine the properties of the polymer itself. That is, the introduction state of the alkyl side chains can be determined based on the second heating. In the present invention, if the peak temperature of the melting point in the second heating (DSC2nd) is within the following range, it can be determined that the desired alkyl side chains have been introduced. If the peak temperature of the melting point in the second heating (DSC2nd) is within the specified range, the elongation properties are excellent and also contribute to improvements in strength properties and minimum creep rate. The peak temperature of the melting point in the second temperature rise (DSC2nd) is preferably 125 to 131°C, more preferably 126 to 130°C, and even more preferably 127 to 129°C.

[0020] The amount of calcium contained in the polyethylene fiber of the present invention is preferably 1 to 300 ppm. The polyethylene fibers of the present invention contain calcium derived from the calcium stearate added to the spinning raw material. The amount of calcium contained in the polyethylene fibers is not particularly limited, but when calcium stearate is added to the extent that the desired effect is achieved, the polyethylene fibers may contain, for example, about 1 to 300 ppm of calcium.

[0021] The polyethylene fiber of the present invention is an ultra-high molecular weight polyethylene fiber (UHMW-PE) having a molecular weight of several hundred thousand to several million, and in the present invention, the index of ultra-high molecular weight is expressed by the intrinsic viscosity (η). The intrinsic viscosity of the polyethylene fiber is preferably 5.0 dl / g to 40 dl / g, more preferably 8.0 dl / g to 35.0 dl / g, and even more preferably 10.0 dl / g to 30.0 dl / g. In a preferred embodiment, the upper limit is 25 dl / g or less, or 20 dl / g or less. If the intrinsic viscosity is high, the tensile strength of the polyethylene fiber increases, and the fiber can be made stronger. Furthermore, if the intrinsic viscosity is too high, single yarn breakage may occur frequently in the post-processing into products such as ropes.

[0022] As long as the intrinsic viscosity is within the above range, two or more raw material polyethylenes with different molecular weights or raw material polyethylenes with different numbers of alkyl side chains may be used, and the preferred configurations are as described below.

[0023] The polyethylene fiber of the present invention preferably has a tensile strength (sometimes referred to as strength) of 15 cN / dtex or more, since sufficient strength properties can be imparted to the fiber. The tensile strength of the polyethylene fiber of the present invention is preferably 20 cN / dtex or more, more preferably 25 cN / dtex or more, and even more preferably 30 cN / dtex or more. The higher the tensile strength, the better, so there is no upper limit, but it may be determined appropriately depending on the application, and may be, for example, 60 cN / dtex or less.

[0024] The present invention includes a multifilament made of the above polyethylene fiber. The multifilament may be made of preferably 5 or more polyethylene fibers, more preferably 10 or more polyethylene fibers, and even more preferably 15 or more polyethylene fibers.

[0025] The polyethylene fiber of the present invention is suitable for products such as braids, twisted yarns, fishing lines, ropes, and nets. In particular, ropes using the polyethylene fiber of the present invention have high strength and excellent creep resistance, and are therefore suitable for applications in which they are exposed to severe environments, such as outdoors, under tension for long periods of time. They are particularly suitable for use as tendons used outdoors under high tension, such as mooring ropes for floating structures such as floating power generation facilities, marine ropes, and ship ropes.

[0026] Hereinafter, the polyethylene fiber of the present invention will be described based on the gel spinning method, which is a preferred production method, but the production method of the polyethylene fiber of the present invention is not limited to the following and can be appropriately changed so as to obtain the above-mentioned properties.

[0027] [Raw material polyethylene] For the ultra-high molecular weight polyethylene fiber of the present invention, it is preferable to use ultra-high molecular weight polyethylene having alkyl side chains as a raw material (hereinafter, sometimes referred to as raw polyethylene).

[0028] The intrinsic viscosity [η] of the raw material polyethylene is preferably 5.0 dl / g to 40.0 dl / g, more preferably 8.0 dl / g to 35.0 dl / g, and even more preferably 10.0 dl / g to 30.0 dl / g. In a preferred embodiment, the upper limit of the intrinsic viscosity is 25 dl / g or less, or 20 dl / g or less. If the intrinsic viscosity is too low, the tensile strength of the polyethylene fiber will be low, and high-strength polyethylene fiber may not be obtained, whereas if the intrinsic viscosity is too high, the stretchability may be reduced.

[0029] The raw polyethylene contains at least one alkyl side chain selected from methyl, ethyl, and butyl groups, and the number of alkyl side chains is preferably 0.5 to 3.0, more preferably 1.0 to 2.5, and even more preferably 1.5 to 2.0 per 1,000 carbon atoms. A small number of alkyl side chains may result in poor creep properties. A large number of alkyl side chains may result in poor yield of the desired high-strength polyethylene fiber. By appropriately controlling the number of alkyl side chains as described above, breakage during drawing can be suppressed, and the polyethylene fiber of the present invention can be obtained. When two or more raw polyethylenes with different molecular weights are used, it is sufficient that the raw polyethylene after blending satisfies the above-mentioned predetermined number of alkyl side chains; polyethylene containing no alkyl side chains may also be used as the blended raw material.

[0030] In the present invention, one or more types of raw polyethylene may be used. When two or more types of raw polyethylene are used, either two or more types of raw polyethylene having different molecular weights or raw polyethylene having different numbers of alkyl side chains are preferred, and a suitable combination of these raw polyethylenes may also be used.

[0031] When raw material polyethylenes with different numbers of alkyl side chains are used, the number of alkyl side chains in each raw material polyethylene is not particularly limited as long as the total number of alkyl side chains in the raw material polyethylenes after mixing falls within the above-mentioned predetermined range. Therefore, raw material polyethylenes with no alkyl side chains and raw material polyethylenes with alkyl side chains may be mixed. When raw material polyethylenes having different numbers of alkyl side chains are used, the molecular weights of the raw material polyethylenes may be different or the same.

[0032] When two or more raw polyethylenes having different molecular weights are used, the difference in intrinsic viscosity between the polyethylene with a higher molecular weight (hereinafter referred to as "H polyethylene") and the polyethylene with a lower molecular weight (hereinafter referred to as "L polyethylene") is preferably 2.0 to 15.0 dl / g. When two or more types of raw polyethylene are used, the L-polyethylene allows for sufficient stretchability even when the number of alkyl side chains is increased, while the H-polyethylene allows for high strength.

[0033] The blend ratio of H-polyethylene to L-polyethylene may be adjusted taking into consideration the difference in the number of alkyl side chains and the intrinsic viscosity of each polyethylene. The blend ratio of H-polyethylene to L-polyethylene (H-polyethylene:L-polyethylene (weight ratio)) is preferably 10-90:90-10, more preferably 30-70:70-30.

[0034] The raw material polyethylene is preferably a blend of ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst (hereinafter referred to as "Ziegler polyethylene") and ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a metallocene catalyst (hereinafter referred to as "metallocene polyethylene"). It is also more preferable to use Ziegler polyethylene as H polyethylene and metallocene polyethylene as L polyethylene. Ziegler polyethylene has a wide molecular weight distribution, and when used as H polyethylene, it contributes to higher strength. Metallocene polyethylene has a narrower molecular weight distribution than Ziegler polyethylene, and when used as L polyethylene, it contributes to improved stretchability. As a result, the raw polyethylene of the above combination has excellent stretchability and high strength, and the resulting polyethylene fiber is.

[0035] Furthermore, in order to achieve both enhanced stretchability and high strength, it is preferable that the Ziegler polyethylene does not have alkyl side chains, and that only the metallocene polyethylene has alkyl side chains. If alkyl side chains are introduced into the Ziegler polyethylene, stretchability may be impaired, making it impossible to achieve sufficient high strength. On the other hand, even if alkyl side chains are introduced into the metallocene polyethylene, sufficient stretchability can be ensured due to its low molecular weight and narrow molecular weight distribution.

[0036] [Dissolution process] The dissolving step is a step of dissolving raw polyethylene to prepare a raw polyethylene solution. Examples of the solvent include volatile organic solvents such as decalin and tetralin; and non-volatile solvents such as paraffin. The concentration of raw material polyethylene in the raw material polyethylene solution is preferably 0.5 to 40.0% by mass, more preferably 2.0 to 30.0% by mass, and even more preferably 3.0 to 20.0% by mass. If the raw polyethylene concentration is low, production efficiency may be significantly reduced. If the raw polyethylene concentration is high and the molecular weight is too high, nozzle discharge problems may occur, such as clogging.

[0037] The raw polyethylene solution of the present invention is a mixture containing calcium stearate. When the raw polyethylene solution contains calcium stearate, the calcium stearate improves the fluidity during extrusion in the spinning process, thereby preventing fusion and unevenness of the fibers, and also preventing fusion during the drawing process. The calcium stearate concentration in the raw polyethylene solution is preferably 1 to 300 ppm, more preferably 1 to 200 ppm, and even more preferably 10 to 100 ppm. By appropriately controlling the calcium concentration as described above, breakage during stretching can be suppressed and strength properties can be improved. Calcium stearate may be added before or after the raw polyethylene is dissolved.

[0038] [Spinning process] The spinning process is a process in which a polyethylene solution is discharged from a nozzle at a temperature equal to or higher than the melting point of the polyethylene, and the discharged threads (gel threads) are cooled with a refrigerant. The polyethylene solution is extruded using an extruder or the like at a temperature preferably 10°C or more higher than the melting point of the raw polyethylene, and then supplied to a spinning nozzle using a constant-volume feeder. The polyethylene solution is then extruded through a spinning nozzle equipped with an array of multiple orifices to form fibers in a gel-swollen state (gel yarns). The temperature up to the spinneret is kept below the thermal decomposition temperature of polyethylene. The number of orifices can be adjusted appropriately depending on the number of fibers constituting the multifilament. The extruded gel yarn is then taken up while being cooled with a cooling medium to obtain an undrawn yarn. The cooling method may be, for example, a dry quenching method using an inert gas such as air or nitrogen, or a dry / wet quenching method using a miscible liquid or an immiscible liquid such as water.

[0039] [Drying / stretching process] The drying and drawing process includes a drying process for removing the solvent from the discharged undrawn yarn, and a drawing process for drawing the undrawn yarn after the drying process. The drying step is intended to remove the solvent, and in the case of a volatile solvent, the solvent may be removed in a heat medium atmosphere or by using a heated roller. Examples of the medium include air, inert gases such as nitrogen, water vapor, liquid media, etc. When a non-volatile solvent is used, an extraction method using an extractant or the like can be used. As the extractant, chloroform, benzene, heptane, nonane, decane, ethanol, higher alcohols, etc. can be used.

[0040] In the drawing step, the undrawn yarn is drawn in a heated state so that the yarn speed at the outlet of the drawing step is several times the yarn speed at the inlet. The undrawn yarn is desirably drawn in multiple stages to achieve a high draw ratio while preventing yarn breakage, etc., and preferably in three or more stages, more preferably in three stages. The stretching step may be carried out in a heat medium atmosphere or using a heated roller, and examples of the medium include air, an inert gas such as nitrogen, water vapor, and a liquid medium.

[0041] The stretching temperature during stretching is preferably 1.0° C. to 10.0° C. lower than when the raw polyethylene does not contain alkyl side chains. Stretching at the above temperature improves stretchability, which contributes to improving strength. The drawing temperature in the latter drawing stage is set higher than that in the former drawing stage. The drawing temperature in the latter drawing stage is set higher because the orientation and crystallinity of the film increase and the melting point also increases by drawing. Therefore, the manufacturing method of the present invention can improve strength properties. If the raw polyethylene contains alkyl side chains, the melting point will be low, so the drawing temperature in the first drawing stage is preferably equal to or higher than the crystal dispersion temperature of the polyethylene and less than 120°C, more preferably 80 to 115°C, and even more preferably 90 to 110°C. The stretching temperature in the latter stretching stage is higher than the stretching temperature in the former stretching stage, and is preferably 120 to 145°C, more preferably 125 to 140°C. In the case of the more preferred three-stage drawing of the present invention, the third-stage drawing temperature is preferably DSC2nd+15° C. or higher.

[0042] The total stretching ratio, which is the sum of all stretching ratios in the stretching steps, is preferably 6 to 30, more preferably 8 to 25, and even more preferably 10 to 20. The total stretching ratio is a value obtained by multiplying the stretching ratios in all stages, and for example, in the case of three-stage stretching, the total stretching ratio is the first-stage stretching ratio × the second-stage stretching ratio × the third-stage stretching ratio. In the present invention, the stretching ratio in the final stage of stretching is preferably adjusted, and more preferably the stretching ratio in the third stage in the case of three-stage stretching. The stretching ratio ratio of the final stretching stage is the final stretching ratio relative to the total stretching ratio obtained by dividing the stretching ratio of the final stage (hereinafter referred to as the final stretching ratio) from the total stretching ratio obtained by adding up all stretching ratios, i.e., [total stretching ratio / final stretching ratio]. The final stretching ratio (total stretching ratio / final stretching ratio) is 0.3 to 2.0, preferably 0.3 to 1.6, more preferably 0.4 to 1.4, and even more preferably 0.4 to 1.0. For example, when the number of stretching stages is three, the final stretching ratio is calculated by [(first-stage stretching ratio × second-stage stretching ratio) / third-stage stretching ratio], and it is preferable to adjust the third-stage stretching ratio so that it falls within the above range. By appropriately controlling the draw ratio as described above, breakage during drawing can be suppressed and strength properties can be improved. [Example]

[0043] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the invention by making appropriate modifications within the scope of the above and below-described aims, and all such modifications are included in the technical scope of the present invention.

[0044] (1) Intrinsic viscosity Using an Ubbelohde capillary viscometer, the specific viscosity of various dilute solutions in decalin at 135°C was measured, and the viscosity was plotted against the concentration. The intrinsic viscosity was determined from the extrapolated point to the origin of the straight line obtained by least squares approximation. 1% by mass of an antioxidant (Yoshinox (registered trademark) BHT, manufactured by API Corporation) was added to the sample, and the solution was stirred and dissolved at 135°C for 4 hours to prepare a measurement solution.

[0045] (2) Number of alkyl side chains 250 mg of each sample was dissolved in o-dichlorobenzene + p-dichlorobenzene-d4 (7 + 3 vol) at 145 °C, and C-NMR was measured at 120 °C. From the obtained C-NMR spectrum, estimation was performed as follows. When the ethylene chain peak of polyethylene is taken as 30 ppm, the peak derived from the methyl side chain is detected at around 37.5 ppm, the peak derived from the ethyl side chain is detected at around 34 ppm, and the peak derived from the butyl side chain is detected at around 23.5 ppm. When the integral value of the ethylene chain peak is taken as 1000, the peak integral value at 37.5 ppm is taken as A, the peak integral value at 34 ppm as B, and the peak integral value at 23.5 ppm as C, the number of methyl side chains can be calculated as A / 2 (number / 1000C), the number of ethyl side chains as B / 2 (number / 1000C), and the number of butyl side chains as C / 2 (number / 1000C).

[0046] (3) Calcium content (i) Pretreatment: Approximately 0.5 g of sample was collected and kept at 550°C for 8 hours in an air atmosphere to carbonize and incinerate it. The residue was then dissolved in 1.2 N hydrochloric acid to prepare a measurement sample. (ii) Measurement: The metal concentration of the measurement sample was measured by ICP emission spectrometry to obtain the calcium content. Measurement device: SPECTROBLUE TI (manufactured by SPECTRO) Measurement conditions Plasma output: 1400W Plasma gas flow rate: 12 L / min Nebulizer gas flow rate: 1.0 L / min Auxiliary gas flow rate: 1.0 L / min

[0047] (4) Creep rate (4-1) Creep rate under a test load of 800 MPa The fineness (dtex) of the sample (multifilament) is measured in accordance with ISO2060, and the specific gravity is measured using the density gradient tube method JIS K 7112, and the load equivalent to 800 MPa is calculated from the cross-sectional area of ​​the fiber. The ambient temperature was set to 20°C, and air clamp chucks were attached to the top and bottom of a universal tensile testing machine (Instron: 5965). Both ends of the sample were clamped so that the length was 300 mm. The calculated load was applied at a chuck speed of 10 mm / min. Measurements were then conducted while maintaining the load constant (constant load test) even as the sample stretched, and the sample elongation and time were recorded. Recording timing was done in increments of at least 1 second. The average rate of change over time was continuously plotted as the creep rate (1 / s), and the creep rate was calculated for the region 1 / s. The average value was calculated for the entire series, from 200 hours after the start of measurements to 800 hours, or 400 hours before the time of failure. ε i (t)[% unit]=(L(t)-L0)×100 / L0 The creep rate τ [unit: 1 / sec] is the change in length of the sample per second and is expressed as follows: τ i =(ε i -ε i-1 ) / (t i -t i-1 ) x 1 / 100 Measurement is continued from the start of measurement until the sample breaks, and the creep rate for each measurement time is plotted on a logarithmic scale, with the minimum value being the minimum creep rate of the measured sample.

[0048] (4-2) Creep rate after 800 hours under test loads of 800 MPa and 1200 MPa The average creep rate was measured from 800 hours to 810 hours under a measurement load of 800 MPa in the same manner as in (4-1) above, except that the final measurement time for the creep rate was set to 800 hours. In addition, the creep rate was measured after 800 to 810 hours at a measurement load of 1200 MPa in the same manner as in (4-1) above, except that the measurement load was 1200 MPa and the final measurement time for the creep rate was 800 hours. Based on the obtained measured values, the creep ratio (800 MPa / 1200 MPa) was calculated.

[0049] (5) DSC2nd melting point peak temperature (differential scanning calorimetry) The measurement was performed using a TA Instruments "DSC25." The sample was cut into 3-5 mm pieces and packed and sealed in an aluminum pan (approximately 2 mg). Using a similar empty aluminum pan as a reference, the temperature was increased from 30 to 200°C at a heating rate of 10°C / min under nitrogen gas at 50 mL / min (first heating), held at 200°C for 5 minutes, then decreased from 200 to 30°C, held at 30°C for 5 minutes, and increased from 30 to 200°C (second heating) to obtain a heating DSC curve. The endothermic peak top temperature obtained in the heating DSC curve was taken as the melting point peak temperature.

[0050] (6) Half-width / mode The sample was cut with a blade to a length of 0.5 mm, and the number of filaments was adjusted to approximately 60,000. The prepared sample was stirred in deionized water for 3 minutes to thoroughly disperse the sample in the water. After that, the fiber diameter distribution was measured while stirring to ensure the sample remained uniformly dispersed. A Diamlength carbon / glass fiber diameter length measuring instrument manufactured by Fibremetrics Pty Ltd was used for the measurement. The fiber diameter was calculated by rounding the value to the nearest 1 μm. A histogram of the fiber diameter distribution, as shown in Figure 1, was obtained, and the most frequently occurring diameter in this histogram was designated the "modal diameter" (mode) (unit: μm). The half value of the peak value of this mode diameter was determined as the half width. Further, the half width / mode was calculated based on the above half width and mode.

[0051] (7) Cumulative percentage of areas more than twice the modal diameter (area of ​​2D regions and total area) The fiber diameter (2D) twice the modal diameter (mode) (Figure 1) was calculated, and the percentage of all fibers with a diameter twice or more was defined as the "cumulative percentage twice or more the modal diameter," and the area of ​​the region 2D or more was calculated (unit: %). The area within the diameter range of 0 to 150 μm in the histogram of the above fiber diameter distribution was calculated as the "total area."

[0052] (8) Strength characteristics (tensile strength) Measurements were performed in accordance with JIS L1013 8.5.1. Using an Orientec "Tensilon Universal Testing Machine," strain-stress curves were measured under conditions of a sample length of 200 mm (length between chucks), an elongation rate of 100 mm / min, an ambient temperature of 20°C, and a relative humidity of 65%, and the tensile strength (cN / dtex) was calculated from the stress and elongation at the break point. The initial load applied to the sample during measurement was 1 / 10 of the fineness (cN / dtex). The average value of 10 measurements was used. The initial load applied to the sample during measurement was 1 / 10 of the mass (g) per 10,000 m of sample. In this invention, the tensile strength (32 cN / dtex) of Example 3 was defined as 100, and the tensile strengths of other Examples were reported based on this. A value of less than 100 was evaluated as insufficient, 100 as good, and over 100 as excellent.

[0053] (9) Stretching properties The yarn breakage rate is an index of operational stability during mass production, and the yarn breakage rate during drawing in Example 3, which showed a good yarn breakage rate, was set to 100. Using this as the reference value, the yarn breakage rates during drawing in other Examples were recorded. A value less than 100 was evaluated as insufficient, 100 as good, and more than 100 as excellent.

[0054] Example 1 Ultra-high molecular weight polyethylene (A), which was polymerized using a Ziegler catalyst and had an intrinsic viscosity of 20.0 dL / g and no long-chain branches, and ultra-high molecular weight polyethylene (B), which was polymerized using a Ziegler catalyst and had an intrinsic viscosity of 15 dL / g and 3.5 ethyl branches per 1000 carbon atoms, were mixed in a weight ratio of (A):(B) = 71:29 to obtain a mixed polyethylene. Calcium stearate was added and mixed so that the calcium content was 10 ppm relative to the amount of mixed polyethylene, and the resulting mixture was mixed with decahydronaphthalene (decalin) in a weight ratio (mixture:decalin) of 9:91 to obtain a slurry-like liquid (gel-like substance). The slurry liquid was dissolved in a twin-screw extruder equipped with a mixing and conveying section, and the resulting polyethylene solution was extruded from a spinneret at a single-hole output rate of 2.0 g / min at a spinneret surface temperature of 175° C. The spinneret had 16 orifices, each with a diameter of 0.8 mm. The discharged yarn was collected and cooled at a speed of 60.0 m / min using a 20°C water-cooled bath with a nozzle-to-water surface distance of 1.5 cm, to produce an unstretched multifilament (gel yarn) consisting of 16 single yarns. The unstretched multifilament was then stretched 2.0 times while drying under hot air at 110°C (first-stage drawing), and further continuously stretched 2.4 times under hot air at 140°C (second-stage drawing) to obtain a first stretched yarn. The obtained first drawn yarn was further drawn (third-stage drawing) under hot air at 145°C, with the third-stage draw ratio adjusted to 1.0 (= (first-stage draw ratio × second-stage draw ratio) / (third-stage draw ratio)) relative to the total draw ratio, and the drawn multifilament was immediately wound up in the drawn state. The physical properties of the drawn multifilament thus obtained were measured and are shown in Table 1.

[0055] Examples 2 and 3, Comparative Examples 6 to 8 A drawn multifilament was produced in the same manner as in Example 1, except that the number of alkyl side chains in the ultra-high molecular weight polyethylene was changed as shown in Table 1.

[0056] Examples 4 and 5, Comparative Examples 1 and 2 A drawn multifilament was produced in the same manner as in Example 1, except that the draw ratio in the third stage was changed as shown in Table 1.

[0057] Examples 6 and 7, Comparative Examples 3 to 5 Drawn multifilaments were produced in the same manner as in Example 2 (Examples 6 and 7, Comparative Examples 3 and 4) or Example 3 (Comparative Example 5), except that the amount of calcium stearate added was changed and the calcium content in the drawn multifilaments (polyethylene fibers) was set as shown in Table 1.

[0058] [Table 1]

[0059] Examples 1 to 7 are examples of the present invention, and were excellent in strength properties and stretchability. In Example 8, the final stretching ratio (total stretching ratio / final stretching ratio) was not adjusted sufficiently in the production process, and the film broke during stretching. Example 9 did not contain calcium, and the half-width of the peak containing the mode diameter relative to the diameter showing the mode of the distribution curve (half-width / mode) was outside the range of the invention, so the strength properties and elongation properties were poor. Example 10 had an excess of calcium and broke when stretched. Example 11 did not contain calcium, and the half-width / mode (value of half-width) exceeded the range of the invention. The area of ​​the region with a diameter more than twice the mode diameter (2D area / total area) exceeded the preferred range of the invention, and the strength and elongation properties were poor. Example 12 is an example in which the minimum creep rate at 800 MPa does not satisfy the range of the present invention. Note that Example 12 is a reference example in which the number of alkyl side chains, creep ratio (800 MPa / 1200 MPa), and melting point peak temperature in the second heating step (DSC2nd) do not satisfy the preferred embodiments of the present invention. Example 13 did not satisfy the number of alkyl side chains that is a preferred embodiment of the present invention, and broke during stretching. [Industrial Applicability]

[0060] Applications of the polyethylene fiber of the present invention include, for example, high-performance textiles such as various sportswear, bulletproof / protective clothing, and protective gloves; various rope products such as tug ropes, mooring ropes, yacht ropes, and construction ropes; various twisted yarn and braided cord products such as fishing lines, fishing / agricultural nets, and blind cables; chemical filters, battery separators, and sheathing materials for tents; and reinforcing fibers for sports products such as helmets and skis, and composites such as speaker cones.

Claims

1. In a distribution in which the horizontal axis represents the diameter (μm) of the single yarn fineness and the vertical axis represents the frequency (%), the half width of the peak containing the diameter of the mode (half width / mode) relative to the diameter showing the mode of the distribution curve is 0.1 to 0.7, In creep measurements at a measurement temperature of 20°C and a measurement load of 800 MPa, the minimum creep rate was 1 x 10 －８ sec －１ A polyethylene fiber characterized by:

2. 2. The polyethylene fiber according to claim 1, wherein, in differential scanning calorimetry (DSC) measurement, the fiber is heated from 30°C to 200°C at a rate of 10°C / min (first heating), held at 200°C for 5 minutes, cooled from 200°C to 30°C at a rate of 10°C / min, held at 30°C for 5 minutes, and then heated from 30°C to 200°C at a rate of 10°C / min (second heating), and the peak melting point during the second heating is 125°C to 131°C.

3. 2. The polyethylene fiber according to claim 1, wherein, in the area of ​​the region sandwiched between the distribution curve and the horizontal axis, the area of ​​the region having a diameter equal to or greater than twice the mode of the diameter is 40% or less of the total area.

4. 2. The polyethylene fiber according to claim 1, having a calcium content of 1 to 300 ppm.

5. 2. The polyethylene fiber according to claim 1, wherein the creep rate (800 MPa / 1200 MPa) measured at a temperature of 20°C, a load of 1200 MPa, and after 800 hours from the start of measurement relative to the creep rate measured at a temperature of 20°C, a load of 800 MPa, and after 800 hours from the start of measurement is 15 to 45.

6. 2. The polyethylene fiber according to claim 1, wherein the polyethylene fiber has an intrinsic viscosity of 5.0 to 40 dl / g.

7. 2. The polyethylene fiber according to claim 1, which contains an alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group, and the number of said alkyl side chains is 0.5 to 3.0 per 1,000 carbon atoms.

8. 2. The polyethylene fiber according to claim 1, having a tensile strength of 15 cN / dtex or more.

9. A braid, twisted yarn, fishing line, rope, or net comprising the polyethylene fiber according to any one of claims 1 to 8.

10. a spinning step of gel-spinning a mixture containing calcium stearate and a polyethylene solution to obtain fibers; a drawing step of multistage drawing the fibers obtained in the spinning step, a ratio of a final draw ratio to a total draw ratio obtained by subtracting a final draw ratio from a total draw ratio in the multistage drawing step (total draw ratio / final draw ratio) of 0.3 to 2.0.

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