JP7358775B2 - polyethylene fiber - Google Patents

Description

The present invention is applicable to various sports clothing, high-performance textiles such as bulletproof/protective clothing, and protective gloves, various rope products such as tag ropes, mooring ropes, yacht ropes, and construction ropes, various braided cord products such as fishing lines, blind cables, and more. This paper relates to a new high-strength polyethylene fiber that can be used in a wide range of industrial applications, such as chemical filters, battery separators, curtain materials for tents, etc., reinforcing fibers for sports equipment such as helmets and ski boards, and composites such as speaker cones.

Regarding high-strength polyethylene fibers, it is known that ultra-stretched, unprecedented high-strength, high-modulus fibers can be obtained by using ultra-high molecular weight polyethylene as a raw material and using the so-called "gel spinning method" (for example, Patent Document 1) has already been widely used in industry. Although these high-strength polyethylene fibers have extremely high strength and high elastic modulus, there is a demand from the market for improvement regarding shortcomings originating from their raw materials. For example, ultra-high molecular weight polyethylene, which is the raw material for high-strength polyethylene fibers, has an extremely simple primary structure and does not have hydrogen bonds between molecular chains, so slippage between molecular chains easily occurs and the load is reduced. If the condition continues for a long time, the fibers will elongate, so-called creep elongation is large, and in applications where loads are applied for a long time, such as braids, twisted yarn, fishing lines, ropes, nets, etc., the range of use is It was restricted.

In order to solve this problem, for example, Patent Document 2 and Patent Document 3 propose polyethylene fibers having ethyl side chains and the like. However, since ethyl side chains and the like significantly inhibit stretchability, the number of side chains is limited in order to maintain high strength and productivity, and the high level of creep properties required by the recent market has not been achieved.

Special Publication No. 60-47922 Japanese Patent Application Publication No. 6-280111 WO2017/102618 publication

The object of the present invention was made against the background of the problems of the prior art described above, and it is an object of the present invention to provide a polyethylene fiber that has high strength and extremely excellent creep resistance.

As a result of intensive research to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention is as follows.

1. In creep measurement at a measurement temperature of 70°C and a measurement load of 20% breaking load, the creep rate is 9.0 x 10-8 sec-1 or less, the elongation 24 hours after the start of the measurement is 2.7% or less, and It takes more than 30 hours to reach an elongation of 3.0%, the elongation after 96 hours from the start of measurement is less than 5.0%, and the URN in the longitudinal direction is less than 16%. polyethylene fiber.
2. By differential scanning calorimetry (DSC measurement), the temperature was raised from 30 to 200°C at a rate of 10°C/min (1st temperature rise), held at 200°C for 5 minutes, and then lowered from 200 to 30°C at a rate of 10°C/min. , after holding at 30℃ for 5 minutes, the temperature is raised from 30 to 200℃ at a rate of 10 minutes/min (2nd temperature increase), the peak temperature of the melting point at the 1st temperature increase is 140℃ or less, and the peak temperature of the melting point is 140℃ or less. The amount of heat in the range of 100 to 170°C is 255 J/g or less, the amount of heat in the range of 70 to 150°C in the second temperature increase is 130 J/g or less, and the URN in the longitudinal direction is 16% or less. A polyethylene fiber characterized by:
3. 3. The polyethylene fiber as described in 1 or 2 above, which contains an alkyl side chain of any one of methyl, ethyl, and butyl groups, and has a number of alkyl side chains of 1.0 or more per 1000 carbon atoms.
4. 4. The polyethylene fiber according to any one of 1 to 3 above, characterized in that it contains two or more types of ultra-high molecular weight polyethylenes having different molecular weights that have been subjected to ethylene polymerization in the presence of a Ziegler catalyst.
5. 5. The polyethylene fiber according to any one of 1 to 4 above, which has a strength of 20 cN/dtex or more and an initial elastic modulus of 500 cN/dtex or more.
6. Braids, twisted yarns, fishing lines, ropes, and nets containing the polyethylene fibers described in 1 to 5 above.

Since the polyethylene fiber according to the present invention has excellent creep resistance, it can be widely used in braids, twisted yarns, fishing lines, ropes, nets, etc.

Conditions during sample setting and creep amount measurement in creep measurement Normal state of measurement in creep measurement

The present invention will be explained in detail below.
The polyethylene of the present invention has a creep rate of 9.0×10 ⁻⁸ sec ⁻¹ or less in creep measurement at a measurement temperature of 70° C. and a measurement load of 20% breaking load, and an elongation of 2.0×10 −8 sec −1 or less after 24 hours from the start of the measurement. 7% or less, the time to reach elongation of 3.0% is 30 hours or more, the elongation after 96 hours from the start of measurement is 5.0% or less, and the URN in the longitudinal direction is 16% or less. It is preferable that
Further, it is more preferable that the creep life described below is 120 hours or more.

More preferably, the URN of thick and thin spots in the longitudinal direction is 15.7% or less, and even more preferably 15.5 or less.

Polyethylene fibers that satisfy these characteristics have extremely little deformation even in applications such as ropes and nets that are exposed to tension for long periods of time in harsh environments such as outdoors, and the lifespan of the product is greatly improved. This is because it contributes to economic efficiency and environmental conservation.

The polyethylene fiber of the present invention has a melting point peak temperature measured by differential scanning calorimetry (DSC measurement) from 30 to 200°C at a heating rate of 10°C/min (1st temperature rise) and a sample amount of 2.0 mg. The temperature is preferably 140°C or lower.
The inventors of the present invention have discovered that such polyethylene fibers have excellent stretchability and can obtain sufficiently high strength and elastic modulus even when they contain alkyl side chains.
Moreover, it is preferable that the melting point peak temperature of the polyethylene fiber of the present invention at the 1st temperature increase is not lower than 125°C. When the melting point peak temperature is lower than 125° C., stretchability is improved, but sufficient strength and elastic modulus may not be obtained due to low molecular weight or insufficient crystallization.
The temperature is more preferably 130° C. or higher, and even more preferably 132° C. or higher.

The polyethylene fiber of the present invention preferably has a calorific value of 255 J/g or less in the range of 100 to 170° C. of the melting point peak at the 1st temperature increase. Moreover, it is preferable that the polyethylene fiber of the present invention has a calorific value of 130 J/g or less in the range of 70 to 150° C. of the melting point peak at the second temperature increase. This is because such polyethylene fibers exhibit excellent creep properties.
The calorific value of the melting point peak at the 1st temperature increase is considered to indicate the contribution of the alkyl side chain in the polyethylene fiber as steric hindrance. That is, it is thought that the alkyl side chain acts as a steric hindrance, disturbs the crystal structure of the relevant part, lowers the amount of heat for crystal melting, and at the same time prevents polyethylene molecules from slipping and exhibits excellent creep properties.
In addition, it is considered that the amount of heat at the melting point peak at the second temperature increase reflects the number of alkyl side chains in the raw material polyethylene.

The polyethylene fiber of the present invention preferably contains an alkyl side chain of any one of methyl, ethyl, and butyl groups, and the number of alkyl side chains is preferably 1.0 or more per 1000 carbon atoms. This is because such polyethylene fibers can effectively prevent polyethylene molecules from slipping and exhibit excellent creep properties. The alkyl side chain may be present in one or both of the ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst and the ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a metallocene catalyst, which will be described later. , the total number may be 1.0 or more. The number of alkyl side chains is more preferably 1.3 or more, more preferably 1.5 or more per 1000 carbon atoms.

The polyethylene fiber of the present invention preferably contains two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights.
By including components with different molecular weights, the amount of heat in the 1st temperature increase and the 2nd temperature increase is 255 J/g or less and 130 J/g or less, respectively.Even if the DSC measurement has a large number of alkyl side chains, The present inventors have discovered that the melting point peak temperature at the first temperature increase is lower than 140° C., that is, it is possible to obtain a polyethylene fiber with excellent drawability, high strength, and high elastic modulus.

The two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights are preferably those obtained by ethylene polymerization mainly in the presence of a Ziegler catalyst. The inventors of the present invention have discovered that fibers made of such ultra-high molecular weight polyethylene can have small thick and thin spots in the longitudinal direction.
This is presumably because the polyethylene obtained in the presence of Ziegler's catalyst has a large molecular weight distribution, and the range in which the molecular weights overlap is large between polyethylenes with different average molecular weights, ensuring continuity of the molecular weight distribution.
Of course, polyethylene obtained in the presence of a metallocene catalyst, for example, may be included as long as it satisfies the above-mentioned fiber properties.

The polyethylene fiber of the present invention preferably has a strength of 20 cN/dtex or more and an initial elastic modulus of 500 cN/dtex or more. This is because such polyethylene fibers can be widely used in industry. More preferably, the strength is 25 cN/dtex or more, the initial elastic modulus is 600 cN/dtex or more, and even more preferably the strength is 30 cN/dtex or more, and the initial elastic modulus is 850 cN/dtex or more.

The polyethylene fibers of the present invention can be used for braids, twisted yarns, fishing lines, ropes, and nets. This is because these uses are often exposed to tension for long periods of time under harsh environments, and the polyethylene fibers of the present invention exhibit the effects.

Hereinafter, a preferred method for producing the polyethylene fiber of the present invention will be explained.

[Raw material polyethylene]
The polyethylene fiber of the present invention preferably uses ultra-high molecular weight polyethylene as its raw material polyethylene.

The intrinsic viscosity [η] of such raw material polyethylene is 5.0 dL/g or more and 40.0 dL/g or less. More preferably, it is 8.0 dL/g or more and 35.0 dL/g or less, and even more preferably 10.0 dL/g or more and 30.0 dL/g or less. If the intrinsic viscosity is less than 5.0 dL/g, the final tensile strength of the polyethylene fiber will be low, and it may not be possible to obtain a high-strength polyethylene fiber that exceeds the desired strength (for example, a strength of 20 cN/dtex or more). . In addition, if the intrinsic viscosity is higher than 40.0 dL/g, the drawability may decrease and a desired high-strength fiber may not be obtained.

In addition, the raw material polyethylene contains an alkyl side chain of methyl, ethyl, or butyl group per 1000 carbon atoms, and the number of alkyl side chains is 1.0 or more and 20.0 or less per 1000 carbon atoms. have More preferably, the number is 1.3 or more and 15.0 or less, and still more preferably 1.5 or more and 10.0 or less. If the number of alkyl side chains is less than 1.0, excellent creep properties may not be obtained. Furthermore, if the number of alkyl side chains is more than 20.0, the drawability may decrease and a desired high-strength fiber may not be obtained.

When using two or more raw material polyethylenes having different molecular weights, which will be described later, an alkyl side chain may be added to one or both of them. The present inventors have discovered that the creep performance of polyethylene fibers can be organized by the number of alkyl side chains in the polyethylene fibers as a whole.

As the raw material polyethylene for the polyethylene fiber of the present invention, it is preferable to use a blend of two or more types with different molecular weights, and among these raw material polyethylenes, polyethylene with a large molecular weight (hereinafter referred to as "H polyethylene") and polyethylene with a low molecular weight are used. It is preferable that the difference in intrinsic viscosity between polyethylene (hereinafter referred to as "L polyethylene") is about 2.0 dL/g or more. The inventors of the present application have discovered that due to the action of L-polyethylene, sufficient stretchability can be obtained even if it has many alkyl side chains, and that the high strength potential of H-polyethylene can be fully brought out. be.
The upper limit of the difference in intrinsic viscosity between H polyethylene and L polyethylene is preferably 15.0 dL/g or less in order to obtain the polyethylene fiber of the present invention. This is because if the molecular weight of L-polyethylene is small, the stretchability will be improved, but if the blending amount is increased, it will be difficult to obtain fibers with high strength.

The blending ratio of H polyethylene and L polyethylene may be adjusted in consideration of the number of alkyl side chains and the difference in intrinsic viscosity of each polyethylene so as to obtain polyethylene within the range of the present invention.

The method for producing the polyethylene fiber of the present invention is preferably a gel spinning method. Specifically, the method for producing polyethylene fibers of the present invention includes a dissolution step of dissolving raw material polyethylene in a solvent to obtain a polyethylene solution, and discharging the polyethylene solution from a nozzle at a temperature equal to or higher than the melting point of the polyethylene. It is preferable to include a spinning process in which the yarn is cooled with a refrigerant, a drying process in which the solvent is removed from the discharged undrawn yarn, a stretching process in which the yarn is stretched, and a process in which the stretched drawn yarn is wound up. Each process will be explained below.

[Dissolution process]
In producing the polyethylene fiber of the present invention, it is recommended to dissolve high molecular weight polyethylene to prepare a polyethylene solution. As the solvent for polyethylene, for example, volatile organic solvents such as decalin and tetralin, and non-volatile solvents such as paraffin can be used. The concentration of polyethylene in the polyethylene solution is preferably 0.5% by mass or more and 40.0% by mass or less, more preferably 2.0% by mass or more and 30% by mass or less, even more preferably 3.0% by mass or more and 20% by mass. % or less. If the polyethylene concentration is less than 0.5% by mass, production efficiency will be extremely poor. Further, if the polyethylene concentration is higher than 40.0% by mass, the molecular weight is very large, and it may become difficult to discharge from a nozzle described below in the gel spinning method.

[Spinning process]
The above-mentioned polyethylene solution is extruded using an extruder or the like at a temperature 10° C. or more higher than the melting point of polyethylene, and then fed to a spinning nozzle using a quantitative feeding device. Thereafter, a thread (gel thread-like) is formed by discharging the polyethylene solution through a spinning nozzle in which a plurality of orifices are arranged. The temperature up to the spinneret is below the thermal decomposition temperature of polyethylene.
Next, the discharged gel threads are taken out while being cooled with a cooling medium. 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.

[Drying/stretching process]
The filament (undrawn filament) taken in the above-mentioned spinning process is wound up continuously or once, and then subjected to a drying/stretching process. The purpose of the drying step is to remove the solvent, and in the case of a volatile solvent, it may be carried out in a heat medium atmosphere or by using a heating roller. Examples of the medium include air, inert gas such as nitrogen, water vapor, and liquid medium. When a nonvolatile solvent is used, a method of extraction using an extractant or the like can be mentioned. As the extractant, chloroform, benzene, heptane, nonane, decane, ethanol, higher alcohol, etc. can be used.
In the subsequent drawing step, the undrawn yarn is heated and drawn so that the yarn speed at the exit is several times that of the yarn speed at the entrance of the drawing step. Stretching may be done once or divided into multiple times, but preferably once or more and three times or less. The stretching step may be performed in a heat medium atmosphere or may use a heated roller. Examples of the medium include air, an inert gas such as nitrogen, water vapor, and a liquid medium.
The inventors have found that by stretching the stretching temperature at a temperature 1.0 to 10.0 degrees Celsius lower than when the raw polyethylene does not contain alkyl side chains, the stretchability is improved and the final fiber is It was found that this leads to an improvement in strength. This is thought to be due to the fact that the melting point becomes lower when the raw material polyethylene contains an alkyl side chain.

EXAMPLES The present invention will be specifically explained below by way of examples, but the present invention is not limited thereto. In addition, the measurement and evaluation of characteristic values in the examples were performed as follows.

(1) Intrinsic viscosity Measure the specific viscosity of various dilute solutions in decalin at 135°C using an Ubbelohde capillary viscosity tube, plot the viscosity against the concentration, and trace it to the origin of the straight line obtained by least squares approximation. The intrinsic viscosity was determined from the extrapolation point. To the sample, 1% by mass of an antioxidant (manufactured by API Corporation, "Yoshinox (registered trademark) BHT") was added and dissolved with stirring at 135° C. for 4 hours to prepare a measurement solution.

(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, C-NMR was measured at 120°C, and the following 13C-NMR spectrum was obtained. The estimate was made according to the following.
When the ethylene chain peak of polyethylene is 30 ppm, the peak derived from the methyl side chain is detected around 37.5 ppm, the peak derived from the ethyl side chain is detected around 34 ppm, and the peak derived from the butyl side chain is detected around 23.5 ppm. . When the integral value of the ethylene chain peak is 1000, if the peak integral value of 37.5 ppm is A, the peak integral value of 34 ppm is B, and the peak integral value of 23.5 ppm is C, the number of methyl side chains is A/ 2 (pieces/1000C), the number of ethyl side chains can be calculated as B/2 (pieces/1000C), and the number of butyl side chains can be calculated as C/2 (pieces/1000C).

(3) Fineness Samples were cut into 10 m pieces at five different locations, their weights were measured, and the average value was used to determine the fineness (dtex).

(4) Tensile strength, elongation at break, and initial elastic modulus Measured in accordance with JIS L1013 8.5.1. Using "Tensilon" manufactured by Orientech Co., Ltd., a strain-stress curve was determined under the conditions of a sample length of 200 mm (length between chucks), an elongation speed of 100 mm/min, an ambient temperature of 20°C, and a relative humidity of 65%.The obtained curve The tensile strength (cN/dtex) was calculated from the stress at the breaking point, the elongation at break was calculated from the elongation, and the elastic modulus (cN/dtex) was calculated from the tangent giving the maximum slope near the origin of the curve. In addition, the number of measurements was 10 times, and the average value was expressed. The initial load applied to the sample during measurement was 1/10 of the mass (g) per 10,000 m of the sample.

(5) Differential scanning calorimetry (DSC measurement)
This was carried out using "DSCQ100" manufactured by TA Instruments. Cut the sample into pieces of 3 to 5 mm or less, fill and seal approximately 2 mg into an aluminum pan, and use a similar empty aluminum pan as a reference to heat the sample from 30 to 200 °C at a heating rate of 10 °C/min under nitrogen gas. (1st temperature increase), held at 200℃ for 5 minutes, lowered the temperature from 200 to 30℃, held at 30℃ for 5 minutes, and increased the temperature from 30 to 200℃ (2nd temperature increase) A temperature-rising DSC curve was obtained. The endothermic peak top temperature obtained from the temperature rising DSC curve was defined as the melting point peak temperature. Further, the heat of fusion [unit: J/g] in the range of 100 to 170°C was taken as the amount of heat in the 1st temperature increase, and the heat of fusion [unit: J/g] in the range of 70 to 150°C was taken as the amount of heat in the 1st temperature increase.

(6) Creep As shown in Figures 1 and 2, one free end of the sample is fixed, a predetermined load is applied to the other end, and the portion between both ends of the sample is heated to a predetermined temperature, and the measurement time is Creep measurements were performed by reading the amount of change in the sample each time. More specific examples of measurement methods are described below.

Prepare a metal plate (length: 70.0 cm, surface polished to a mirror finish) that can be heated to a predetermined temperature (70.0°C) and maintain that temperature, and place the sample on the metal plate without twisting. Place them so that they are touching. One of the free ends of the sample is fixed at the part protruding from the metal plate, and an initial load (load is 0.2 g/dtex) is applied to the other end at the part protruding from the metal end. After making marks on the sample on the metal plate in two places so that the sample length is 50.0 cm, remove the initial load and attach a predetermined load (a load equivalent to 20% of the breaking load of the sample) to the metal plate. Start the measurement by closing the lid from the top to prevent contact with the sample above (the lid and sample are not in contact). The lid is opened every hour for 5 hours from the start of measurement, then every 12 hours, and at 24 hours and 96 hours, and the distance of the mark made initially is read. Continue measuring until the sample breaks.
The elongation ε _i [in mm] of the sample at a certain time t is the difference between the distance L _(t) between the marks made on the sample at that time t and the distance L ₀ (50.0 cm) between the marks made on the initial sample. Yes, and is shown as follows.
ε _i (t) [% unit] = (L _(t) - L ₀ ) × 100/L ₀
The creep rate τ [in units of 1/sec] is defined as the change in length of the sample in 1 second increments, and is expressed as follows.
τ _i =(ε _i -ε _i-1 )/(t _i -t _i-1 )×1/100
Measure from the start of measurement until the sample breaks, plot the creep rate for each measurement time on a logarithmic scale, and take the minimum value as the creep rate of the measured sample. The reading time immediately before the reading time when the sample fracture was observed is defined as the creep life (the time when the final sample length was read is defined as the creep life).

(7) Thick spots URN%
Absolute values of mMax 0.017 m and mmin 0.017 m measured using USTER TESTER 5-C800 manufactured by USTER under the conditions of measurement mode Normal, yarn feeding speed 25 m/min, measurement time 5 minutes, twister 3200 m-1. The sum of the values was defined as the thick and thin spot URN% of the sample.

(Example 1)
Using a Ziegler catalyst for polymerization, ultra-high molecular weight polyethylene (A) containing no long chain branching has an intrinsic viscosity of 20.0 dL/g, and a Ziegler catalyst for polymerization has an intrinsic viscosity of 15.9 dL/g and carbon atoms. Ultra-high molecular weight polyethylene (B) having 3.5 ethyl branches per 1000 pieces and decahydronaphthalene (decalin) are mixed at a weight ratio of (A):(B):decalin=3:6:91 to form a slurry liquid. was formed. The intrinsic viscosity difference was 4.1 dL/g. The material was dissolved in a twin screw extruder equipped with a mixing and conveying section, and the resulting polyethylene solution was discharged from a spinneret at a single hole discharge rate of 3.0 g/min at a spinneret surface temperature of 175°C. The number of orifices formed in the spinneret was 16, and the orifice diameter was 0.8 mm. While taking up the discharged filament, the filament was cooled down using a 20°C water-cooled bath with a distance of 1.5 cm between the nozzle and the water surface at a speed of 60.0 m/min, and a filament made of 16 single filaments was cooled. A drawn multifilament (gel yarn) is obtained, and the undrawn multifilament is continuously stretched to 1.5 times while drying with hot air at 110°C, and further continuously stretched to 3.3 times with hot air at 140°C. A first drawn yarn with a total draw ratio of 5.0 times was obtained. The obtained first drawn yarn was further drawn 2.3 times with hot air at 145° C., and the drawn multifilament was immediately wound up in the drawn state. The obtained drawn multifilament had an intrinsic viscosity of 14.1 dL/g, physical properties of fineness of 62 dtex, strength of 33 cN/dtex, initial elastic modulus of 1016 cN/dtex, and elongation at break of 4.1%. The number of side chains was 2.0 per 1000 carbon atoms. The creep measurement results show that the creep rate is 5.6×10 ^-8 sec ^-1 , the elongation 24 hours after the start of measurement is 2.6%, and the time it takes to reach 3.0% elongation is 41 hours. The elongation 96 hours after the start of measurement was 4.7%, and the creep life was 281 hours. URN was 13.0%. As a result of DSC measurement of this fiber sample, the melting point peak temperature was 139° C. and the amount of heat was 236 J/g at the 1st temperature increase, and the amount of heat at the 2nd temperature increase was 123 J/g.

(Example 2)
From Example 1, the ultra-high molecular weight polyethylene (B) was changed to ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 18.0 dL/g and 2.9 ethyl branches per 1000 carbon atoms, and the intrinsic viscosity difference was 2. .0 dL/g, and a drawn multifilament was obtained in the same manner as in Example 1 except for that. The obtained drawn multifilament had an intrinsic viscosity of 14.6 dL/g, physical properties of a fineness of 63 dtex, a strength of 35 cN/dtex, an initial elastic modulus of 1048 cN/dtex, and a breaking elongation of 4.0%. The number of side chains was 2.0 per 1000 carbon atoms. The creep measurement results show that the creep rate is 4.8・10 ^-8 sec ^-1 , the elongation 24 hours after the start of the measurement is 2.5%, and it takes 53 hours to reach the elongation 3.0%. The elongation at 96 hours from the start of measurement was 4.6%, and the creep life was 245 hours. URN was 15.5%. As a result of DSC measurement of this fiber sample, the melting point peak temperature was 139° C. and the amount of heat was 242 J/g at the first temperature increase, and the amount of heat at the second temperature increase was 122 J/g.

(Comparative example 1)
The ultra-high molecular weight polyethylene fiber "Izanasu Grade SK777" manufactured by Toyobo Co., Ltd. has an intrinsic viscosity of 16.5 dL/g, physical properties of fineness of 1775 dtex, strength of 35 cN/dtex, initial elastic modulus of 1190 cN/dtex, and elongation at break of 3. 6%, and the number of alkyl side chains contained in the fiber was 0 per 1000 carbon atoms. The creep measurement results showed that the creep rate was 3.6×10 ^-6 sec ^-1 , and the elongation could not be read 24 hours after the start of the measurement because rupture was confirmed 24 hours after the start of the measurement, and the elongation was 3.0. It took 2 hours to reach %, and the elongation could not be read 96 hours after the start of measurement. Creep life was 17 hours. URN was 15.8%. The results of DSC measurement of this fiber sample showed that the melting point peak temperature was 146° C. and the amount of heat was 253 J/g at the 1st temperature increase, and the amount of heat at the 2nd temperature increase was 146 J/g.

(Comparative example 2)
A Ziegler catalyst was used for polymerization, ultra-high molecular weight polyethylene (C) having an intrinsic viscosity of 20.0 dL/g and 0.5 ethyl side chains per 1000 carbon atoms was used, and the weight ratio (C): decalin was used. = 9:91, the take-up speed from the water cooling bath was changed to 40.0 m/min, and the obtained first drawn yarn was stretched 4.0 times. I got the filament. The resulting drawn multifilament had an intrinsic viscosity of 15.6 dL/g, physical properties of a fineness of 76 dtex, a strength of 31 cN/dtex, an initial elastic modulus of 1050 cN/dtex, and a breaking elongation of 4.1%. The number of side chains was 0.5 per 1000 carbon atoms. The creep measurement results show that the creep rate is 2.8×10 ^-7 sec-1, the elongation 24 hours after the start of the measurement is 4.7%, and it takes 15 hours to reach the elongation 3.0%. The elongation after 96 hours from the start of the measurement was 13.5%, the creep life was 101 hours, and the creep performance was inferior to the examples. Moreover, URN was 19.4%. As a result of DSC measurement of this fiber sample, the melting point peak temperature at the 1st temperature increase was 142° C., the amount of heat was 258 J/g, and the amount of heat at the 2nd temperature increase was 135 J/g.

(Comparative example 3)
From Example 1, ultra-high molecular weight polyethylene (B) was changed to ultra-high molecular weight polyethylene having an intrinsic viscosity of 16.9 dL/g and 2.9 ethyl branches per 1000 carbon atoms by using a metallocene catalyst for polymerization. , the take-up speed of the water-cooled bath was changed to 100.0 m/min, and the undrawn multifilament was stretched 1.5 times while drying with hot air at 110 °C, and then stretched 2.7 times with hot air at 140 °C. A drawn multifilament was obtained in the same manner as in Example 1 except for the following. The obtained drawn multifilament had an intrinsic viscosity of 13.9 dL/g, a physical property of fineness of 46 dtex, strength of 33 cN/dtex, initial elastic modulus of 842 cN/dtex, and elongation at break of 4.5%, and the alkyl contained in the fiber. The number of side chains was 2.0 per 1000 carbon atoms. The creep measurement results show that the creep rate is 1.2×10 ^-8 sec ^-1 , the elongation 24 hours after the start of measurement is 1.5%, and the time it takes to reach 3.0% elongation is 353 hours. The elongation at 96 hours from the start of measurement was 1.8%, and the creep life was 389 hours. URN was 22.2%, which was a poor result for thick and thin spots. The results of DSC measurement of this fiber sample showed that the melting point peak temperature was 139° C. and the amount of heat was 241 J/g at the 1st temperature increase, and the amount of heat at the 2nd temperature increase was 118 J/g.

Since the polyethylene fiber of the present invention has excellent creep resistance, it can be widely used, especially in applications where tension is extended for a long time in harsh environments, such as braided cords, twisted yarns, fishing lines, ropes, and nets. It is possible and will greatly contribute to the development of industry.

1. Sample 2. Metal plate 3. Load 4. Fixed end of sample5. lid

Claims (2)

Contains an alkyl side chain of any of methyl, ethyl, and butyl groups, the number of alkyl side chains is 1.0 or more per 1000 carbon atoms, and the molecular weight is different when ethylene polymerization is performed in the presence of a Ziegler catalyst A polyethylene fiber containing two or more types of ultra-high molecular weight polyethylene,
In creep measurement at a measurement temperature of 70°C and a measurement load of 20% breaking load, the creep rate is 9.0 × 10 ^-8 sec ^-1 or less, and the elongation 24 hours after the start of the measurement is 2.7% or less, and the time taken to reach elongation of 3.0% is 30 hours or more, the elongation after 96 hours from the start of measurement is 5.0% or less, and the thick and thin spots URN in the longitudinal direction are 16% or less,
By differential scanning calorimetry (DSC measurement), the temperature was raised from 30 to 200°C at a rate of 10°C/min (1st temperature rise), held at 200°C for 5 minutes, and then lowered from 200 to 30°C at a rate of 10°C/min. , after holding at 30℃ for 5 minutes, the temperature is raised from 30 to 200℃ at a rate of 10 minutes/min (2nd temperature increase), the peak temperature of the melting point at the 1st temperature increase is 140℃ or less, and the peak temperature of the melting point is 140℃ or less. The amount of heat in the range of 100 to 170°C is 255 J/g or less, the amount of heat in the range of 70 to 150°C in the second temperature increase is 130 J/g or less, and the URN in the longitudinal direction is 16% or less. can be,
A polyethylene fiber characterized by having a strength of 20 cN/dtex or more and an initial elastic modulus of 500 cN/dtex or more . Braids, twisted yarns, fishing lines, ropes and nets comprising the polyethylene fibers according to claim 1.