Polyethylene fibers, product using said polyethylene fibers, and method for producing said polyethylene fibers

Abstract

Provided are polyethylene fibers in which fiber unevenness and fusion are suppressed and which are excellent in creep resistance.　The polyethylene fibers are characterized in that, in a single yarn fineness distribution where the diameter (μm) is represented by the horizontal axis and the frequency (%) is represented by the vertical axis, the ratio of the half-value width of a peak that includes the diameter corresponding to the mode of the distribution curve to the diameter corresponding to the mode (half-value width / mode) is 0.1- 0.7, and the lowest creep speed found in creep measurement performed at a measurement temperature of 20°C with a measurement load of 800 MPa is 1×10-8 sec-1 or less.

Description

Polyethylene fiber, product using said polyethylene fiber, and method for producing said polyethylene fiber

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

[0002] Ultra-high molecular weight polyethylene fibers (hereinafter sometimes referred to as polyethylene fibers), made from ultra-high molecular weight polyethylene, are widely used in various industrial fields due to their excellent weather resistance and chemical resistance, as well as their light weight and extremely high strength. In recent years, ropes made from polyethylene fibers have attracted attention as an alternative to steel chains used in mooring ships, offshore markers, marine energy equipment, and marine structures. However, polyethylene fibers lack hydrogen bonds between molecular chains and have little steric hindrance, which means that molecular chain slippage easily occurs, resulting in high creep elongation. Therefore, there has been a demand for improved creep resistance in polyethylene fibers.

[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 groups. However, raw polyethylene having alkyl side chains is prone to fusing together during the spinning process, reducing the fluidity at the discharge port, and resulting in fiber irregularities (hereinafter simply referred to as fiber irregularities) in which thick and thin portions are formed in the fiber longitudinal direction and the diameter is nonuniform. Furthermore, while the drawing temperature must be increased to improve the strength of polyethylene fibers, undrawn polyethylene yarns having alkyl side chains have the problem of being prone to fusing when the drawing temperature is increased.

[0004] JP 6-280111 Publication WO2017 / 102618 Publication

[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.

[0006] The present invention, which has solved the above problems, has the following features: [1] In a distribution of single filament fineness, with the horizontal axis representing the diameter (μm) and the vertical axis representing 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, and in creep measurements at a measurement temperature of 20°C and a measurement load of 800 MPa, the minimum creep rate is 1×10 －８ sec －１ [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, in the area of ​​the region sandwiched between the distribution curve and the horizontal axis, the area of ​​a region having a diameter equal to or greater than twice the mode of the diameter is 40% or less of the total area. [4] The polyethylene fiber according to any of [1] to [3], wherein the calcium content is 1 to 300 ppm. [5] The polyethylene fiber according to any one of [1] to [4], wherein the creep rate (800 MPa / 1200 MPa) measured at a temperature of 20°C, under a load of 1200 MPa, and after 800 hours from the start of measurement is 15 to 45 relative to the creep rate measured at a temperature of 20°C, under a load of 800 MPa, and after 800 hours from the start of measurement. [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] The polyethylene fiber according to any one of [1] to [6], wherein the polyethylene fiber contains an alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group, and wherein the number of the alkyl side chains per 1000 carbon atoms is 0.5 to 3.0. [8] The polyethylene fiber according to any one of [1] to [7], wherein the polyethylene fiber has 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 [1] to [8].

[10] A bulletproof / protective clothing or protective glove impact-resistant member comprising the polyethylene fiber according to any one of [1] to [8] above.

[0007] The present invention also provides a method for producing a polyethylene fiber that has solved the above-mentioned problems, comprising the following steps:

[11] A method for producing a polyethylene fiber, comprising: a spinning step of gel-spinning a mixture containing calcium stearate and a polyethylene solution to obtain a fiber; and a drawing step of multistage drawing the fiber obtained in the spinning step, 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 dividing the final draw ratio by the total draw ratio in the multistage drawing step (total draw ratio / final draw ratio).

[12] A method for producing a polyethylene fiber according to

[11] , wherein the polyethylene solution contains 0.5 to 40.0 mass% of polyethylene having an alkyl side chain of any one of methyl, ethyl, and butyl groups, and having 0.5 to 3.0 alkyl side chains per 1,000 carbon atoms.

[13] A method for producing a polyethylene fiber according to

[11] or

[12] , wherein the polyethylene solution contains two or more polyethylenes having different molecular weights, and wherein the difference in intrinsic viscosity between the polyethylene with a higher molecular weight and the polyethylene with a lower molecular weight is 2.0 to 15.0 dl / g.

[14] The method for producing a polyethylene fiber according to any one of

[11] to

[13] , wherein the concentration of calcium stearate contained in the polyethylene solution is 1 to 300 ppm.

[15] The method for producing a polyethylene fiber according to any one of

[11] to

[14] , wherein the multistage drawing is three or more stages and the total draw ratio is 6 to 30.

[16] The method for producing a polyethylene fiber according to

[11] to

[15] , wherein the multistage drawing has a drawing temperature in a first stage that is equal to or higher than the crystal dispersion temperature of polyethylene and lower than 120°C, and a drawing temperature in a second stage that is higher than the drawing temperature in the first stage.

[0008] According to the present invention, it is possible to provide a polyethylene fiber in which fiber unevenness and fusion are suppressed and which has excellent creep resistance. Therefore, products such as polyethylene fiber ropes using the polyethylene fiber of the present invention are suitable for applications such as mooring of marine structures. Furthermore, the production method of the present invention is suitable for producing the polyethylene fiber of the present invention.

[0009] FIG. 1 is a schematic explanatory diagram of a distribution curve with the diameter (μm) of single yarn fineness on the horizontal axis and the frequency (%) on the vertical axis.

[0010] The present inventors have investigated the production process of ultra-high molecular weight polyethylene fibers having alkyl side chains introduced therein. In gel spinning using ultra-high molecular weight polyethylene as a raw material, it was found that the ultra-high molecular weight polyethylene having alkyl side chains is prone to flow unevenness during extrusion in the spinning process, resulting in fiber unevenness and fiber fusion in the spun yarn (gel-like yarn). The present inventors have extensively investigated means for suppressing fiber unevenness and fusion during the spinning process, and have found that adding calcium stearate to the spinning raw material improves the flow during spinning, suppresses flow unevenness, and effectively suppresses fiber unevenness and fiber fusion. Furthermore, in the drawing process, while conventional undrawn yarns are prone to yarn breakage and fiber fusion when drawn at high temperatures, it was found that undrawn yarns obtained by adding calcium stearate to the spinning raw material are 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 of single fiber fineness, with the horizontal axis representing the diameter (μm) and the vertical axis representing 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, and in creep measurements conducted at a measurement temperature of 20°C and a measurement load of 800 MPa, the minimum creep rate is 1×10 －８ sec －１ The following is the result.

[0012] The relationship between the half-width and mode of the fiber based on the distribution curve (half-width / mode) is an index of fusion and fiber unevenness of the polyethylene fiber. A schematic diagram is shown in FIG. 1 . When there is a large amount of fusion and fiber unevenness in the polyethylene fiber, the half-width of the peak broadens, 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) becomes large. When the half-width / mode exceeds 0.7, there are many fused fibers and fiber unevenness, and the strength of the polyethylene fiber decreases. When the half-width / mode is 0.1 to 0.7, fiber unevenness and fusion are suppressed, and the fiber diameter is highly uniform, contributing to high strength of the polyethylene fiber. The half-width / mode is preferably 0.1 to 0.6, more preferably 0.2 to 0.5. The lower limit of 0.1 was set to 0.1 in consideration of measurement error, but it may be lower, for example, 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 may be adjusted appropriately depending on the application, but if the diameter of the polyethylene fiber is too small, it will be easily broken. If the diameter of the polyethylene fiber is too large, its flexibility will decrease, and its bending fatigue resistance may decrease. 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 at least twice the mode of the 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). Fiber fusion and fiber unevenness increase the diameter. If the area of ​​the region having a diameter at least twice the mode of the fiber diameter increases, this may cause a decrease in strength properties and elongation properties. Since fiber fusion and fiber unevenness are suppressed in the polyethylene fiber of the present invention, the area of ​​the 2D region exhibits a low value. A smaller area of ​​the 2D region is preferable because it reduces fiber fusion and fiber unevenness, 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 polyethylene fiber of the present invention has a minimum creep rate of 1×10 －８ sec －１ Since the minimum creep rate is less than 1×10, the change in strain is small even under high load, and the product has excellent creep resistance. Therefore, products using the polyethylene fiber of the present invention have excellent dimensional stability, and the product life is significantly improved. The smaller the minimum creep rate, the more stable the fiber is and the less deformation it will have, so it is preferable. The minimum creep rate is preferably 1×10 －９ sec －１ or less, more preferably 1 × 10 －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 (800 MPa / 1200 MPa) of 15 to 45 when measured at a temperature of 20°C, a load of 1200 MPa, and 800 hours after the start of measurement relative to the minimum creep rate when measured at a temperature of 20°C, a load of 800 MPa, and 800 hours after the start of measurement. When the ratio of the minimum creep rates under different loads (800 MPa / 1200 MPa) is within a predetermined range, the change in strain is small even under high loads, and the fiber has better creep resistance. Furthermore, polyethylene fibers having a minimum creep rate ratio within the predetermined 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 to 45, more preferably 20 to 40, and even more preferably 25 to 35.

[0018] The polyethylene fiber of the present invention preferably contains at least one alkyl side chain selected from the group consisting of methyl, ethyl, and butyl groups, with the number of alkyl side chains being 0.5 to 3.0 per 1,000 carbon atoms. Introducing a predetermined number of alkyl side chains into the polyethylene fiber can prevent slippage of the polyethylene molecules, improving creep resistance and contributing to improvements in the minimum creep rate and the minimum creep rate ratio. 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 1,000 carbon atoms.

[0019] Furthermore, in differential scanning calorimetry (DSC) of the polyethylene fiber of the present invention, 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). The peak melting point temperature (DSC 2nd) during the second heating 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 state of introduction of the alkyl side chains from the polyethylene fiber, this is determined by DSC measurement. That is, the polyethylene fiber is heated (first heating), melted, and returned to the polymer, and then a second heating (second heating) is performed to determine the properties of the polymer itself. The state of introduction of the alkyl side chains can be determined based on this second heating. In the present invention, if the peak temperature of the melting point during the second heating (DSC 2nd) 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 during the second heating (DSC 2nd) is within the specified range, the elongation characteristics are excellent and it also contributes to improving the strength characteristics and minimum creep rate. The peak temperature of the melting point during the second heating (DSC 2nd) 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 calcium contained in the polyethylene fiber of the present invention is derived from calcium stearate added to the spinning raw material. The amount of calcium contained in the polyethylene fiber is not particularly limited, but when calcium stearate is added to an amount that produces the desired effect, the polyethylene fiber may contain calcium in an amount of, for example, about 1 to 300 ppm.

[0021] The polyethylene fibers of the present invention are ultra-high molecular weight polyethylene fibers (UHMW-PE) having a molecular weight of several hundred thousand to several million. In the present invention, the index of ultra-high molecular weight is expressed by the intrinsic viscosity (η). The intrinsic viscosity of the polyethylene fibers 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. A high intrinsic viscosity increases the tensile strength of the polyethylene fibers, allowing for increased strength. Furthermore, if the intrinsic viscosity is too high, frequent single-fiber breakage may occur during subsequent processing into products such as ropes.

[0022] As long as the intrinsic viscosity is within the above range, two or more raw material polyethylenes having different molecular weights or raw material polyethylenes having 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. There is no upper limit, but this can be determined appropriately depending on the application, and it may be, for example, 60 cN / dtex or less.

[0024] The present invention includes a multifilament composed of the above polyethylene fiber. The multifilament may be composed 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 (hereinafter sometimes referred to as raw material polyethylene) as a raw material.

[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 may be low, making it impossible to obtain a high-strength polyethylene fiber. Furthermore, if the intrinsic viscosity is too high, the elongation properties may be reduced.

[0029] The raw material polyethylene contains at least one alkyl side chain selected from the group consisting of 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 a failure to obtain 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 material polyethylenes with different molecular weights are used, it is sufficient that the raw material polyethylene after blending satisfies the above-mentioned predetermined number of alkyl side chains; polyethylenes containing no alkyl side chains may also be used in 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, two or more types of raw polyethylene having different molecular weights or different numbers of alkyl side chains are preferred, and a suitable combination of these raw polyethylenes may also be used.

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

[0032] When two or more types of raw polyethylene 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 action of the L polyethylene ensures sufficient stretchability even when the number of alkyl side chains is increased, and the H polyethylene contributes to 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, and is preferably 10-90:90-10, more preferably 30-70:70-30, by weight.

[0034] The raw 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 more preferable to use Ziegler polyethylene as H polyethylene and metallocene polyethylene as L polyethylene. Ziegler polyethylene has a broad molecular weight distribution, and when used as H polyethylene, it contributes to high strength. Metallocene polyethylene has a narrower molecular weight distribution than Ziegler polyethylene, and when used as L polyethylene, it contributes to improved stretchability. In one embodiment, the raw polyethylenes of the above combination are suitable for polyethylene fibers that are excellent in stretchability and high in strength.

[0035] In one embodiment, in order to achieve both enhanced stretchability and high strength, it is preferable that the Ziegler polyethylene has no alkyl side chains, and 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] [Dissolving Step] The dissolving step is a step in which raw polyethylene is dissolved to prepare a raw polyethylene solution. Examples of solvents include volatile organic solvents such as decalin and tetralin; and non-volatile solvents such as paraffin. The raw polyethylene concentration in the raw 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. Furthermore, if the raw polyethylene concentration is high and the molecular weight is very high, problems with ejection from the nozzle 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 suppressing fiber fusion and fiber unevenness, and also suppressing 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 drawing can be suppressed and strength properties can be improved. Calcium stearate may be added before or after dissolving the raw polyethylene.

[0038] [Spinning Process] The spinning process involves extruding a polyethylene solution from a nozzle at a temperature equal to or higher than the melting point of the polyethylene and cooling the extruded yarn (gel yarn) 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 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 a gel-swollen fiber (gel yarn). The temperature up to the spinneret is set below the thermal decomposition temperature of polyethylene. The number of orifices may be adjusted appropriately depending on the number of fibers constituting the multifilament. The extruded gel yarn is then withdrawn while being cooled with a refrigerant, yielding 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 and Stretching Process] The drying and stretching process consists of a drying process for removing the solvent from the discharged unstretched yarn, and a stretching process for stretching the unstretched yarn after the drying process. The purpose of the drying process is 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, an inert gas such as nitrogen, water vapor, and a liquid medium. When a non-volatile solvent is used, an extraction method using an extractant or the like can be used. Examples of the extractant that can be used include chloroform, benzene, heptane, nonane, decane, ethanol, and higher alcohols.

[0040] In the drawing step, the undrawn yarn is heated and drawn 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, preferably three or more stages, more preferably three stages, to achieve a high draw ratio while preventing yarn breakage and the like. The drawing step may be carried out in a heat medium atmosphere, or a heated roller may be used. 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 this temperature improves stretchability, contributing to improved strength. The stretching temperature in the latter stretching stage is higher than that in the former stretching stage. Because stretching increases orientation and crystallinity and also increases the melting point, the stretching temperature in the latter stretching stage is higher. Therefore, the production method of the present invention can improve strength properties. Because the melting point decreases when the raw polyethylene contains alkyl side chains, the stretching temperature in the former stretching stage is preferably equal to or higher than the crystal dispersion temperature of polyethylene but 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, preferably 120 to 145°C, more preferably 125 to 140°C. In the case of the more preferred three-stage stretching of the present invention, the third-stage stretching temperature is preferably DSC2nd+15° C. or higher.

[0042] The total draw ratio, which is the sum of all draw ratios in the drawing steps, is preferably 6 to 30 times, more preferably 8 to 25 times, and even more preferably 10 to 20 times. The total draw ratio is the value obtained by multiplying the draw ratios of all stages; for example, in the case of three-stage drawing, the total draw ratio is the first-stage draw ratio × the second-stage draw ratio × the third-stage draw ratio. In the present invention, the draw ratio ratio of the final stage of drawing is preferably adjusted, and more preferably the third-stage draw ratio in the case of three-stage drawing. The draw ratio ratio of the final stage of drawing is the final draw ratio relative to the total draw ratio obtained by dividing the draw ratio of the final stage (hereinafter referred to as the final draw ratio) from the total draw ratio obtained by summing all draw ratios, i.e., [total draw ratio / final draw ratio]. The final draw ratio (total draw ratio / final draw 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 draw stages is three, the final draw ratio is calculated by [(first-stage draw ratio x second-stage draw ratio) / third-stage draw ratio], and it is preferable to adjust the third-stage draw 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.

[0043] This application claims the benefit of priority based on Japanese Patent Application No. 2024-108831, filed on July 5, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-108831, filed on July 5, 2024, are incorporated herein by reference.

[0044] The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is of course 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.

[0045] (1) Intrinsic Viscosity Using an Ubbelohde capillary viscosity tube, 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 sample was stirred and dissolved at 135°C for 4 hours to prepare a measurement solution.

[0046] (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. The number of alkyl side chains was estimated from the obtained C-NMR spectrum as follows. When the ethylene chain peak of polyethylene is set to 30 ppm, the peak derived from methyl side chains is detected around 37.5 ppm, the peak derived from ethyl side chains is detected around 34 ppm, and the peak derived from butyl side chains is detected around 23.5 ppm. When the integral value of the ethylene chain peak is set to 1000, the peak integral value at 37.5 ppm is set to A, the peak integral value at 34 ppm is set to B, and the peak integral value at 23.5 ppm is set to C, the number of methyl side chains can be calculated as A / 2 (numbers / 1000 C), the number of ethyl side chains is set to B / 2 (numbers / 1000 C), and the number of butyl side chains is set to C / 2 (numbers / 1000 C).

[0047] (3) Calcium content (i) Pretreatment: Approximately 0.5 g of sample was collected and heated in an air atmosphere from 100°C by increasing the temperature by 50°C every hour until it reached 400°C. After pre-drying on a hot plate, the sample was kept at 550°C in an electric furnace for 8 hours to carbonize and incinerate it. The residue was then dissolved in 1.2N 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 power: 1400 W Plasma gas flow rate: 12 L / min Nebulizer gas flow rate: 1.0 L / min Auxiliary gas flow rate: 1.0 L / min

[0048] (4) Creep Rate (4-1) Creep Rate at a Measurement Load of 800 MPa The fineness (dtex) of the sample (multifilament) was measured according to ISO 2060, and the specific gravity was measured using the density gradient tube method JIS K 7112. The load equivalent to 800 MPa was 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 tester (Instron: 5965). Both ends of the sample were gripped so that the length was 300 mm, and the calculated load was applied at a chuck speed of 10 mm / min. Then, the sample was measured while maintaining the load constant even when stretched (constant load test), and the sample elongation and time were recorded. The recording timing was recorded in increments of at least 1 second. The average rate of change in 1-hour units is continuously plotted as the creep rate (1 / s), and the region is determined as the creep rate. The average value is calculated from 200 hours to 800 hours from the start of measurement or 400 hours before the break time. ε ｉ (t) [% unit] = (L(t) - L ０ ) x 100 / L ０ The creep rate τ (units: 1 / sec) is the change in length of the sample per second of time and is given by: 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.

[0049] (4-2) Creep Rates after 800 Hours at a Measurement Load of 800 MPa and 1200 MPa The average creep rate from 800 hours to 810 hours at a measurement load of 800 MPa was measured in the same manner as in (4-1) above, except that the final measurement time for the creep rate was changed to 800 hours. Also, the creep rate from 800 hours to 810 hours at a measurement load of 1200 MPa was measured in the same manner as in (4-1) above, except that the measurement load was changed to 1200 MPa and the final measurement time for the creep rate was changed to 800 hours. The creep ratio (800 MPa / 1200 MPa) was calculated based on the obtained measurements.

[0050] (5) DSC 2nd melting point peak temperature (differential scanning calorimetry) was performed using a TA Instruments "DSC25". The sample was cut into lengths of 3 to 5 mm, filled and sealed in an aluminum pan with approximately 2 mg. Using a similar empty aluminum pan as a reference, the temperature was increased from 30°C to 200°C at a heating rate of 10°C / min under nitrogen gas at 50 ml / min (1st heating), held at 200°C for 5 minutes, decreased from 200°C to 30°C at a heating rate of 10°C / min, held at 30°C for 5 minutes, and increased from 30°C to 200°C at a heating rate of 10°C / min (2nd 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.

[0051] (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, thoroughly dispersed in water, and then the fiber diameter distribution was measured while stirring so that the sample remained uniformly dispersed during measurement. A carbon / glass fiber diameter length measuring instrument, Diameter Length, manufactured by Fibremetrics Pty Ltd., was used for the measurement. The fiber diameter was calculated by rounding the fiber diameter to the nearest 1 μm. A histogram of the fiber diameter distribution, as illustrated in FIG. 1, was obtained, and the most frequent diameter in this histogram was designated the "mode diameter" (mode) (unit: μm). Half the peak value of this mode diameter value was designated the half-width. The half-width / mode was also calculated based on the half-width and mode.

[0052] (7) Cumulative proportion of fiber diameters twice or more the modal diameter (area of ​​2D region and total area) The fiber diameter (2D) twice the modal diameter (mode) (Fig. 1) was calculated, and the proportion of all fiber diameters twice or more was defined as the "cumulative proportion of fiber diameters twice or more the modal diameter," and the area of ​​the 2D or larger region was calculated (unit: %). In addition, the region within the diameter range of 0 to 150 µm in the histogram of the fiber diameter distribution was calculated as the "total area."

[0053] (8) Strength Properties (Tensile Strength) Measurements were made in accordance with JIS L1013 8.5.1. Using a "Tensilon Universal Testing Machine" manufactured by Orientec Co., Ltd., 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 (cN / dtex) of the fineness. The average value of 10 measured values ​​was used. In the present invention, the tensile strength (32 cN / dtex) of Example 3 was defined as 100, and the tensile strengths of other Examples were described based on this. A value of less than 100 was evaluated as insufficient, 100 as good, and more than 100 as excellent.

[0054] (9) Drawing characteristics The yarn breakage rate is an index of operational stability during mass production, and the yarn breakage rate during drawing of Example 3, which showed a good yarn breakage rate, was set to 100. Using this as a reference value, the yarn breakage rates during drawing of other Examples were recorded. A value less than 100 was evaluated as insufficient, 100 as good, and more than 100 as excellent.

[0055] Example 1: Ultra-high molecular weight polyethylene (A), polymerized using a Ziegler catalyst and having an intrinsic viscosity of 20.0 dl / g and no long-chain branches, and ultra-high molecular weight polyethylene (B), polymerized using a Ziegler catalyst and having an intrinsic viscosity of 15 dl / g and 3.5 ethyl branches per 1,000 carbon atoms, were mixed in a weight ratio of (A):(B) = 71:29 to obtain a polyethylene blend. Calcium stearate was added and mixed to obtain a calcium content of 10 ppm relative to the amount of polyethylene blend. The resulting mixture was mixed with decahydronaphthalene (decalin) in a weight ratio (mixture:decalin) of 9:91 to obtain a slurry 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 spinneret surface temperature of 175°C and a single-hole throughput rate of 2.0 g / min. The spinneret had 16 orifices, each with a diameter of 0.8 mm. The discharged yarn was taken up 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, while being cooled to produce an undrawn multifilament (gel yarn) consisting of 16 single yarns. The undrawn multifilament was then continuously drawn 2.0 times while drying in hot air at 110°C (first-stage drawing), and further continuously drawn 2.4 times in hot air at 140°C (second-stage drawing) to obtain a first drawn yarn. The obtained first drawn yarn was further drawn (third-stage drawing) in hot air at 145°C, with the third-stage draw ratio adjusted to 1.0 with respect to the total draw ratio (= (first-stage draw ratio × second-stage draw ratio) / (third-stage draw ratio), and the drawn multifilament was immediately wound up in the drawn state. The physical properties of the obtained drawn multifilament were measured and are shown in Table 1.

[0056] Examples 2, 3, 12 and 13 Drawn multifilaments were 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.

[0057] Examples 4, 5 and 8 Drawn multifilaments were produced in the same manner as in Example 2, except that the draw ratio in the third stage was changed as shown in Table 1.

[0058] Examples 6, 7, 9, 10, 11 Drawn multifilaments were produced in the same manner as in Example 2 (Examples 6, 7, 9, 10) or Example 3 (Example 11), except that the amount of calcium stearate added was changed and the calcium content in the drawn multifilament (polyethylene fiber) was set as shown in Table 1.

[0059]

[0060] Examples 1 to 7 are examples of the present invention and exhibited excellent strength and stretchability. Example 8 broke during stretching due to insufficient adjustment of the final stretch ratio (total stretch ratio / final stretch ratio) during the manufacturing process. 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) exceeded the range of the present invention, resulting in poor strength and stretchability. Example 10 contained excessive calcium, resulting in fracture during stretching. Example 11 did not contain calcium, and the half-width / mode value exceeded the range of the present invention, and the area of ​​the region with a diameter more than twice the mode diameter (2D area / total area) exceeded the preferred range of the present invention, resulting in poor strength and stretchability. Example 12 is an example in which the 800 MPa minimum creep rate did not satisfy the range of the present invention. Example 12 is a reference example that does not satisfy the preferred embodiments of the present invention in terms of the number of alkyl side chains, creep ratio (800 MPa / 1200 MPa), and peak melting point temperature in the second heating step (DSC 2nd). Example 13 does not satisfy the preferred embodiments of the present invention in terms of the number of alkyl side chains, and breakage occurred during stretching.

[0061] Examples of uses of the polyethylene fiber of the present invention include 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 and agricultural nets, and blind cables; chemical filters, battery separators, and sheathing materials for tents and the like; and reinforcing fibers for sports products such as helmets and skis, and composites such as speaker cones.

Claims

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

2. The polyethylene fiber according to claim 1, wherein, in differential scanning calorimetry (DSC), 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. The polyethylene fiber according to claim 1, wherein the area of ​​the region sandwiched between the distribution curve and the horizontal axis, where 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. The polyethylene fiber according to claim 1, having a calcium content of 1 to 300 ppm.

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

7. The polyethylene fiber according to claim 1, which contains alkyl side chains selected from the group consisting of methyl, ethyl, and butyl groups, 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 claim 1, having a tensile strength of 15 cN / dtex or more.

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

10. A bulletproof / protective clothing or protective glove impact-resistant member comprising the polyethylene fiber according to any one of claims 1 to 8.

11. A method for producing polyethylene fibers, comprising: a spinning step of gel-spinning a mixture containing calcium stearate and a polyethylene solution to obtain fibers; and a drawing step of multi-stage drawing the fibers obtained in the spinning step, wherein the ratio of the final draw ratio to the total draw ratio obtained by dividing the final draw ratio by the total draw ratio in the multi-stage drawing step (total draw ratio / final draw ratio) is 0.3 to 2.

0.

12. A method for producing polyethylene fibers according to claim 11, wherein the polyethylene solution contains 0.5 to 40.0 mass% of polyethylene containing alkyl side chains of any one of methyl, ethyl, and butyl groups, and the number of alkyl side chains is 0.5 to 3.0 per 1,000 carbon atoms.

13. The method for producing polyethylene fibers according to claim 11, wherein the polyethylene solution contains two or more polyethylenes with different molecular weights, and the difference in intrinsic viscosity between the polyethylene with a higher molecular weight and the polyethylene with a lower molecular weight is 2.0 to 15.0 dl / g.

14. The method for producing polyethylene fibers according to claim 11, wherein the concentration of calcium stearate contained in the polyethylene solution is 1 to 300 ppm.

15. The method for producing polyethylene fibers according to claim 11, wherein the multistage drawing is three or more stages of drawing, and the total draw ratio is 6 to 30 times.

16. A method for producing polyethylene fibers as described in claim 11, wherein the multi-stage drawing is performed such that the drawing temperature in the first stage is equal to or higher than the crystal dispersion temperature of polyethylene but less than 120°C, and the drawing temperature in the second stage is higher than the drawing temperature in the first stage.

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