WO2023127876A1 - Ultra-high molecular weight polyethylene fiber - Google Patents

Abstract

The present invention addresses the problem of providing: an ultra-high molecular weight polyethylene fiber having both moldability during processing and dimensional stability during use; and a method for manufacturing the same. This ultra-high molecular weight polyethylene fiber comprises ethylene having an intrinsic viscosity [η] of 5.0-40.0 dL/g and a repeat unit of 90 mol% or more, and includes at least one alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group, wherein the number of alkyl branches representing the number of the alkyl side chains per 1000 carbon atoms is 0.6-1.4/1000 carbon atoms.

Description

ultra high molecular weight polyethylene fiber

The present invention relates to ultra-high molecular weight polyethylene fibers, and more particularly to ultra-high molecular weight polyethylene fibers having excellent creep resistance properties.

So-called ultra-high molecular weight polyethylene is used in various applications because of its good properties such as impact resistance.
However, ultra-high molecular weight polyethylene fibers have the drawback that they easily slip between molecular chains and tend to creep. For this reason, techniques have been proposed to improve creep resistance by, for example, introducing branches into ultra-high molecular weight polyethylene fibers (Patent Documents 1 and 2).

In addition, techniques have been proposed to further improve properties such as tensile strength and elastic modulus by reducing defects existing inside ultra-high molecular weight polyethylene fibers (Patent Documents 3 to 5).

JP-A-64-38439 JP-A-6-280111 WO 01/012885 JP 2006-089898 A JP 2006-045753 A

With the expansion of the use of ultra-high molecular weight polyethylene fibers, improvements in various properties such as creep resistance are required for ultra-high molecular weight polyethylene fibers. It was difficult to improve the characteristics while maintaining workability.

The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide an ultra-high molecular weight polyethylene fiber having both moldability during processing and dimensional stability during use, and a method for producing the same. is to provide

The present invention, which has solved the above problems, has the following configuration.
[1] Made of ethylene having a limiting viscosity [η] of 5.0 dL/g or more and 40.0 dL/g or less and a repeating unit of 90 mol% or more,
containing at least one alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group;
the number of alkyl branches, which means the number of alkyl side chains per 1000 carbon atoms, is 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less;
Ultra high molecular weight polyethylene fiber.

A preferred embodiment of the polyethylene fiber of the present invention has the following configuration.
[2] the ratio of the number of alkyl branches to the elongation stress of the polyethylene fiber is 2 to 30/1000 carbon atoms/MPa;
In creep measurement at a measurement load of 6.6 g/dtex, the creep rate at a measurement temperature of 140°C is 2.0 × 10 ^-3 sec ^-1 or more, and the creep speed at a measurement temperature of 60°C is 4.0 × 10 ^-7 sec ^-1 or less,
The ultra-high molecular weight polyethylene fiber according to [1] above.

[3] In creep measurement at a measurement load of 6.6 g/dtex,
The time to rupture at a measurement temperature of 140 ° C. is less than 1.2 minutes, and
The time to fracture at a measurement temperature of 60 ° C. is 216 hours or more,
The ultra-high molecular weight polyethylene fiber according to the above [1] or [2].
[4] In thermal stress measurement,
The ultra-high molecular weight polyethylene fiber according to any one of [1] to [3] above, wherein the ratio of the storage modulus at 70°C to the storage modulus at 120°C is 1.5 or more.
[5] The polyethylene fiber is composed of one or more single yarns, and the single yarn has a tensile strength of 18 cN/dtex or more, an initial elastic modulus of 500 cN/dtex or more, and a breaking elongation of 3.0% or more. The ultra-high molecular weight polyethylene fiber according to any one of [1] to [4] above.
[6] The ultra-high molecular weight polyethylene fiber according to any one of [1] to [5], wherein the ratio of weight average molecular weight to number average molecular weight is 3.0 or more.

[7] Twisted yarn containing the ultra-high molecular weight polyethylene fiber according to any one of [1] to [6] above.
[8] A braid containing the ultra-high molecular weight polyethylene fiber according to any one of [1] to [6] above.
[9] A rope comprising the ultra-high molecular weight polyethylene fiber according to any one of [1] to [6] above.
[10] The rope according to [9] above, which is used for mooring a floating structure on the ocean.

Moreover, the method for producing an ultra-high molecular weight polyethylene fiber according to the present invention, which has solved the above problems, has the following configuration.
[11] A method for producing an ultra-high molecular weight polyethylene fiber obtained through a dissolving step, a spinning step, and a drawing step, comprising:
The dissolving step includes
Made of ethylene having a limiting viscosity [η] of 5.0 dL/g or more and 40.0 dL/g or less and a repeating unit of 90 mol% or more,
containing at least one alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group;
A step of dissolving polyethylene having an alkyl branch number of 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less, which means the number of alkyl side chains per 1000 carbon atoms, in a solvent. can be,
The spinning process is
A step of discharging the obtained polyethylene solution from a spinning nozzle at a temperature 15° C. or more higher than the melting point of the polyethylene, and then cooling it to 60° C. or less,
The stretching step is
While drawing the obtained polyethylene yarn one or more times,
In the step of setting the drawing temperature at the final drawing to 140° C. or more and less than 155° C., the drawing time at 2 minutes or more and 8 minutes or less, and the tension of the yarn at the time of drawing at 1.5 cN/dtex or more and 8 cN/dtex or less. be.

The ultra-high molecular weight polyethylene fiber of the present invention has both moldability during processing and dimensional stability during use. Moreover, the production method of the present invention is suitable for producing ultra-high molecular weight polyethylene fibers having the above properties.

The inventors of the present invention have extensively studied ultra-high molecular weight polyethylene fibers that have both moldability during processing and dimensional stability during use. It has been found that the creep properties suitable for processing and the creep properties suitable for use are obtained depending on the difference in temperature. Ultra-high molecular weight polyethylene fibers having such characteristics are not only excellent in heat moldability (hereinafter referred to as heat moldability), but also can be used even when a load is applied to the ultra-high molecular weight polyethylene fibers in an outdoor environment. The change in the amount of strain can be small, and the change in dimension after the load is removed can also be small (these are called dimensional stability).
The ultra-high molecular weight polyethylene fiber (hereinafter referred to as polyethylene fiber) of the present invention will be described below.
In the present invention, the creep property at 140°C (140°C creep property), which is an index for heat moldability, and the creep property at 60°C (60°C creep property), which is an index for dimensional stability during use, are defined. ing.
The relationship between the heat moldability and the 140° C. creep property is that the heat moldability is improved when the 140° C. creep property is low, that is, when creep at 140° C. is easy.
The relationship between the dimensional stability and the 60° C. creep property is that the 60° C. creep property is high, that is, the 60° C. creep resistance is low (good creep resistance) and the dimensional stability is good.
Therefore, the polyethylene fiber of the present invention has low 140° C. creep property and high 60° C. creep property by satisfying the following requirements, so that it has excellent heat moldability and excellent dimensional stability in outdoor use environments. have. The outdoor use environment means outdoor use within the range of temperature changes due to seasons and the like.
The evaluation of 140°C creep property is preferably based on creep rate at 140°C (140°C creep rate) or rupture life at 140°C (140°C rupture life), more preferably 140°C creep. Rating based on both speed and 140° C. judged life.
Evaluation of 60°C creep property is preferably based on creep rate at 60°C (60°C creep rate) or rupture life at 60°C (60°C rupture life), more preferably 60°C creep rate. and 60° C. rupture life.
In the present invention, in ultra-high molecular weight polyethylene fibers having a predetermined intrinsic viscosity [η], if the number of alkyl branches is within a predetermined range, the balance between 140 ° C. creep property and 60 ° C. creep property can be appropriately controlled. Both moldability and dimensional stability can be achieved.
Any range can be selected for each of the evaluation items of the 140° C. creep property evaluation and the 60° C. creep property evaluation, and the combination of the items can also be made by combining the selected ranges. .

In the present invention, the polyethylene fiber includes a single yarn (monofilament) and a multifilament consisting of a plurality of single yarns, preferably a multifilament. The number of single yarns constituting the multifilament can be appropriately selected according to the application, and is preferably 5 or more, more preferably 10 or more, still more preferably 15 or more.

The polyethylene fiber of the present invention is made of ethylene having a limiting viscosity [η] of 5.0 dL/g or more and 40.0 dL/g or less and a repeating unit of 90 mol% or more.

Intrinsic viscosity [η]
The polyethylene used in the present invention has an ultrahigh molecular weight, and the intrinsic viscosity of the polyethylene is 5.0 dL/g or more, preferably 8.0 dL/g or more, and 40.0 dL/g or less, preferably 30.0 dL/g. /g or less, more preferably 25.0 dL/g or less. Alternatively, it is 5.0 to 40.0 dL/g, preferably 8.0 to 30.0 dL/g, more preferably 8.0 to 25.0 dL/g.
When the intrinsic viscosity is less than 5.0 dL/g, the tensile strength of the final polyethylene fiber becomes low, and it may not be possible to obtain a polyethylene fiber having a desired high strength, for example, a tensile strength of 18 cN/dtex or more. Also, the desired heat moldability and dimensional stability of the polyethylene fibers cannot be obtained.
If the intrinsic viscosity exceeds 40.0 dL/g, the processability will deteriorate, making it difficult to produce polyethylene fibers.
The numerical ranges of the lower and upper limits of the intrinsic viscosity can be determined by arbitrarily combining the above values (the following numerical ranges can also be similarly determined by combining arbitrary upper and lower limits).

Repeating Unit In the polyethylene constituting the polyethylene fiber of the present invention, 90 mol % or more of the repeating unit is ethylene. The repeating unit of ethylene is preferably 92 mol % or more, more preferably 94 mol % or more, still more preferably 98 mol % or more.
It is also a preferred embodiment to use copolymers of ethylene and minor amounts of other monomers of the present invention as long as they do not adversely affect the thermoformability and dimensional stability of the polyethylene fibers. Examples of other monomers include α-olefins, acrylic acid and its derivatives, methacrylic acid and its derivatives, vinylsilane and its derivatives, and the like. In addition, these are copolymers of copolymers (ethylene and other monomers), blends of homopolyethylene and ethylene-based copolymers, and homopolyethylene and other homopolymers (α-olefins, etc.). It may be a blend and may have partial cross-linking.

The polyethylene fiber of the present invention contains at least one alkyl side chain selected from the group consisting of methyl groups, ethyl groups, and butyl groups,
The number of alkyl branches, which means the number of alkyl side chains per 1000 carbon atoms, is 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less.
The alkyl side chains can be arbitrarily combined, and when two or more types are used, they may be a combination of different functional groups, a combination of the same functional groups, or a combination of the same functional group and a different functional group. may For example, if it is one type, it is preferably any one of a methyl group, an ethyl group, and a butyl group. For example, two groups are preferably methyl group and ethyl group, methyl group and butyl group, ethyl group and butyl group, methyl group and methyl group, ethyl group and ethyl group, or butyl group and butyl group. Further, for example, if there are three types, they may be all different functional groups, all the same functional groups, or a combination of the same functional groups and different functional groups. When the number of alkyl branches is less than 0.6/1000 carbon atoms, the creep rate is high both at 140°C and 60°C, and the heat moldability (molding processability) at 140°C is good, while the temperature at 60°C is high. Creep resistance (dimensional stability) tends to be poor.
As the number of alkyl branches increases, the creep rate decreases at both 140°C and 60°C, so the heat moldability decreases, while the creep resistance at 60°C improves.
When the number of alkyl branches becomes extremely large (for example, about 6.0/1000 carbon atoms), drawing becomes difficult, and the tensile strength of the final polyethylene fiber becomes low. The creep rate tends to increase remarkably, and the heat moldability recovers, but the creep resistance at 60°C deteriorates.
As a result of the phenomenon described above, both heat moldability and creep resistance can be improved by adjusting the number of alkyl branches to the range of 0.6 to 1.4/1000 carbon atoms.
Among the above alkyl side chains, the ethyl side chain is preferable because it is excellent in thermoformability.

The number of alkyl branches (hereinafter referred to as the number of alkyl branches), which means the number of alkyl side chains per 1,000 carbon atoms contained in the polyethylene fiber of the present invention, is 0.6/1,000 carbon atoms or more, preferably 0.7. per 1,000 or more carbon atoms, more preferably 0.8 per 1,000 or more carbon atoms, still more preferably 0.9 per 1,000 or more carbon atoms, and 1.4 per 1,000 or less carbon atoms, More preferably, it is 1.3/1000 or less carbon atoms. The number of alkyl branches is, for example, 0.6/1000 to 1.4 carbon atoms/1000 carbon atoms, preferably 0.7/1000 to 1.3 carbon atoms/1000 carbon atoms, more preferably may be 0.8/1000 to 1.3 carbon atoms/1000 carbon atoms, more preferably 0.9/1000 to 1.3 carbon atoms/1000 carbon atoms.
In the ultra-high molecular weight polyethylene fiber of the present invention, the intrinsic viscosity [η], the repeating unit of ethylene, the alkyl side chain, and the number of alkyl branches can be combined with arbitrary values. Furthermore, the ultra-high molecular weight polyethylene fiber of the present invention can be combined with any of the following preferred embodiments of the present invention in addition to the above arbitrary combinations, and each preferred embodiment can be combined with any value. . Preferred embodiments include, for example, the number of alkyl branches/elongation stress, requirements (i) to (iv) for creep measurement at a measurement load of 6.6 g/dtex, ratio of storage elastic moduli, tensile strength, initial elastic modulus, elongation at break degree, weight average molecular weight ratio, weight average molecular weight, and the like.

Another preferred embodiment of the polyethylene fiber of the present invention is that the ratio of the number of alkyl branches to the elongation stress of the polyethylene fiber is 2 to 30/1000 carbon atoms/MPa.
The polyethylene fiber having the number of alkyl branches of 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less has a ratio of the number of alkyl branches to the elongation stress of the polyethylene fiber (number of alkyl branches/elongation stress) is preferably 2/1000 carbon atoms/MPa or more, more preferably 2.1/1000 carbon atoms/MPa or more, preferably 30/1000 carbon atoms/MPa or less, more preferably is 25/1000 carbon atoms/MPa or less, more preferably 20/1000 carbon atoms/MPa or less.
The number of alkyl branches/elongation stress is, for example, preferably 2/1000 carbon atoms/MPa to 30/1000 carbon atoms/MPa, more preferably 2.1/1000 carbon atoms/MPa to 25/carbon 1000 atoms/MPa, more preferably 2.1 atoms/1000 carbon atoms/MPa or more to 20 atoms/1000 carbon atoms/MPa.
If the intrinsic viscosity and the number of alkyl branches are satisfied, and the ratio of the number of alkyl branches to the elongation stress is within the above specific range, it contributes to the improvement of heat moldability and dimensional stability.
The ratio of the number of alkyl branches to the elongation stress can be controlled, for example, by the intrinsic viscosity of raw material polyethylene. When raw material polyethylene with a very low intrinsic viscosity is used, the intrinsic viscosity of the fiber becomes small, so the elongation stress also becomes small, and as a result, the ratio of the number of alkyl branches to the elongation stress increases.

The 140° C. creep property and 60° C. creep property of the polyethylene fiber of the present invention are preferably the following (i) and (ii), more preferably the following (i) to (iv), in creep measurement at a measurement load of 6.6 g/dtex. ) are preferably satisfied. Alternatively, the following (i) (ii) and (iii), or the following (i) (ii) and (iv) may be satisfied, or the following (iii) and (iv), or the following (iii) It may be a combination of (iv) and (i) and/or (ii) below.
In the above combinations, arbitrary values may be combined to determine the range.
(i) A creep rate of 2.0×10 ⁻³ sec ⁻¹ or more at a measurement temperature of 140° C. (ii) A creep rate of 4.0×10 ⁻⁷ sec ⁻¹ or less at a measurement temperature of 60° C. (iii) A measurement temperature of 140° C. Less than 1.2 minutes to rupture at ° C. (iv) 216 hours or more to rupture at a measurement temperature of 60 ° C.

(i) In creep measurement at a measurement temperature of 140°C and a measurement load of 6.6 g/dtex, the creep rate is preferably 2.0 × 10 ^-3 sec ^-1 or more, more preferably 2.1 × 10 ^-3 sec ^-1 above, more preferably 2.3×10 ⁻³ sec ⁻¹ or more, still more preferably 2.5×10 ⁻³ sec ⁻¹ or more, and preferably 6.0×10 ⁻³ sec ⁻¹ or less, It is more preferably 5.5×10 ⁻³ sec ⁻¹ or less, still more preferably 5.0×10 ⁻³ sec ⁻¹ or less. The above (i) creep rate is preferably 2.0×10 ⁻³ sec ⁻¹ to 6.0×10 ⁻³ sec ⁻¹ , more preferably 2.1×10 ⁻³ sec ⁻¹ to 5.5× 10 ^-3 sec ^-1 , more preferably 2.3×10 ^-3 sec ^-1 to 5.0×10 ^-3 sec ^-1 , still more preferably 2.5×10 ^-3 sec ^-1 to 5.0 ×10 ^-3 sec ^-1 or less.
The measurement temperature of 140° C. is a temperature considering the temperature conditions during processing of polyethylene fibers, and the 140° C. creep rate is a value set as a standard that contributes to the improvement of thermoformability.
If the 140° C. creep rate is too slow, heat molding of polyethylene fibers may become difficult.
Although the upper limit is not particularly limited, the above range is preferable in consideration of the balance with the 60° C. creep resistance.

(ii) In creep measurement at a measurement temperature of 60°C and a measurement load of 6.6 g/dtex, the creep rate is preferably 4.0 × 10 ^-7 sec ^-1 or less, more preferably 3.95 × 10 ^-7 sec ^{-1 .} below, more preferably 3.93×10 ⁻⁷ sec ⁻¹ or less, preferably 3.0×10 ⁻⁸ sec ⁻¹ or more, more preferably 6.0×10 ⁻⁸ sec ⁻¹ or more, and further It is preferably 8.0×10 ⁻⁸ sec ⁻¹ or more. The above (ii) creep rate is preferably 3.0×10 ⁻⁸ sec ⁻¹ to 4.0×10 ⁻⁷ sec ⁻¹ , more preferably 6.0×10 ⁻⁸ sec ⁻¹ to 3.95× 10 ^-7 sec ^-1 , more preferably 8.0×10 ^-8 sec ^-1 to 3.93×10 ^-7 sec ^-1 .
The measurement temperature of 60°C is a temperature considering the use environment of the product using the polyethylene fiber of the present invention, and the 60°C creep rate is a value set as a standard that contributes to the improvement of dimensional stability at normal use temperature.
If the 60° C. creep rate is too fast, the dimensional change of polyethylene fibers may increase even when used at around room temperature.
Although the lower limit is not particularly limited, the above range is preferable in consideration of the balance with the 140° C. creep resistance.

(iii) In creep measurement at a measurement temperature of 140°C and a measurement load of 6.6 g/dtex, the time required to break (140°C breaking life) is preferably less than 1.2 minutes, more preferably 1.1 minutes or less. is.
The 140° C. rupture life is a value set as a standard that contributes to the improvement of heat moldability.
If the time to rupture is too short, the polyethylene fibers may break frequently during molding, making processing difficult.
Although the lower limit is not particularly limited, it is preferably 0.1 minute or more in consideration of the balance with other requirements. The (iii) 140° C. rupture life is preferably 0.1 minutes to less than 1.2 minutes, more preferably 0.1 minutes to 1.1 minutes.

(iv) In creep measurement at a measurement temperature of 60°C and a measurement load of 6.6 g/dtex, the time required to break (60°C breaking life) is preferably 216 hours or more, more preferably 225 hours or more.
The 60° C. rupture life is a value set as a standard contributing to improvement in dimensional stability at normal operating temperature (for example, room temperature).
If the time to rupture is too short, the product life may be shortened.

In the thermal stress measurement, the polyethylene fiber of the present invention has a ratio of the storage modulus at 70 ° C. to the storage modulus at 120 ° C. (70 ° C. storage modulus / 120 ° C. storage modulus: hereinafter referred to as the storage modulus ratio However, if it is in a specific range, it contributes to improving the creep balance at low and high temperatures, and is a preferred embodiment for ensuring heat workability and dimensional stability.
The storage modulus ratio is preferably 1.5 or more, more preferably 1.6 or more.
When the ratio of storage elastic modulus is increased, polyethylene fibers are less affected by environmental changes even at room temperature and can retain good physical properties. In addition, while the elasticity at high temperatures is relatively lowered to improve the workability, the elasticity at low temperatures is relatively increased to contribute to the creep resistance.

It is also a preferred embodiment that the polyethylene fiber of the present invention is composed of one or more single yarns, and the tensile strength, breaking elongation, and initial elastic modulus of this single yarn are within specific ranges.
Tensile strength The tensile strength of the single yarn constituting the polyethylene fiber of the present invention is preferably 18 cN/dtex or more, more preferably 20 cN/dtex or more, still more preferably 25 cN/dtex or more, and even more preferably 30 cN/dtex or more. , preferably 85 cN/dtex or less, more preferably 60 cN/dtex or less. The tensile strength is, for example, preferably 18 cN/dtex to 85 cN/dtex, more preferably 20 cN/dtex to 60 cN/dtex, still more preferably 25 cN/dtex to 60 cN/dtex, still more preferably 30 cN/dtex to 60 cN/dtex. be.
By increasing the tensile strength of the single yarn, the amount of distortion of the polyethylene fiber when a load is applied can be reduced. Therefore, it is suitable for applications requiring high dimensional stability, for example.
The higher the tensile strength of the single yarn, the more preferable it is, so the upper limit is not limited.

Initial elastic modulus The initial elastic modulus of the single yarn constituting the polyethylene fiber of the present invention is preferably 500 cN/dtex or more, more preferably 600 cN/dtex or more, still more preferably 700 cN/dtex or more, and preferably 1500 cN/dtex. Below, it is more preferably 1400 cN/dtex or less, still more preferably 1300 cN/dtex or less, and even more preferably 1200 cN/dtex or less. The initial elastic modulus is, for example, preferably 500 cN/dtex to 1500 cN/dtex, more preferably 600 cN/dtex to 1400 cN/dtex, still more preferably 700 cN/dtex to 1300 cN/dtex, still more preferably 700 cN/dtex to 1200 cN/dtex. is.
If the initial elastic modulus of the single yarn is too low, the physical properties and shape of the polyethylene fiber may change due to external force.
If the initial elastic modulus of the single yarn is too high, the elasticity of the yarn becomes too high, which impairs the suppleness of the yarn.

Breaking elongation The breaking elongation of the single yarn constituting the polyethylene fiber of the present invention is preferably 3.0% or more, more preferably 3.4% or more, still more preferably 3.7% or more, and preferably It is 7.0% or less, more preferably 6.0% or less, still more preferably 5.0% or less. The elongation at break is, for example, preferably 3.0% to 7.0%, more preferably 3.4% to 6.0%, still more preferably 3.7% to 5.0%.
If the breaking elongation of the single yarn is too low, the single yarn breakage and fluffing may easily occur when the polyethylene fiber is slightly distorted.
If the elongation at break of the single yarn is too high, the heat processing of the polyethylene fiber may become difficult and the dimensional stability may be impaired.

It is also a preferred embodiment that the polyethylene fiber of the present invention contains polyethylene having a ratio of weight average molecular weight to number average molecular weight of 4.0 or more.
The weight-average molecular weight to number-average molecular weight ratio (Mw/Mn) of the polyethylene constituting the polyethylene fiber is more preferably 4.2 or more, and still more preferably 4.5 or more. Although the upper limit of Mw/Mn is not particularly limited, it is preferably 9.0 or less, more preferably 8.0 or less, and still more preferably 7.5 or less. The weight average molecular weight ratio (Mw/Mn) is, for example, preferably 4.0 to 9.0, more preferably 4.2 to 8.0, still more preferably 4.5 to 7.5.
If the ratio of the weight average molecular weight to the number average molecular weight of polyethylene is too small, the creep phenomenon will hardly occur. While this works well to improve creep resistance at 60°C, it works badly to improve moldability at 140°C. When the creep resistance at 60°C is sufficiently high but the moldability at 140°C is poor, it is preferable to improve the moldability by increasing Mw/Mn.
If the ratio of the weight average molecular weight to the number average molecular weight of polyethylene is too high, the tensile strength of the final polyethylene fiber may be low and the creep resistance may be poor.

The polyethylene fiber of the present invention is ultra-high molecular weight polyethylene, and the weight average molecular weight of the polyethylene is preferably 490,000 or more, more preferably 550,000 or more, still more preferably 800,000 or more, and preferably It is 8,000,000 or less, more preferably 6,000,000 or less, and still more preferably 5,000,000 or less. The weight average molecular weight is, for example, preferably 490,000 to 8,000,000, more preferably 550,000 to 6,000,000, still more preferably 800,000 to 5,000,000.
If the weight-average molecular weight is too low, the number of molecular ends per cross-sectional area of the polyethylene fiber increases, which may cause structural defects, and the tensile strength and initial elastic modulus of the polyethylene fiber cannot be sufficiently increased even if drawing or the like is performed. Moreover, the desired heat workability and dimensional stability may not be obtained.
If the weight-average molecular weight is too high, the tension of the polyethylene fiber during drawing becomes too high, causing breakage, and the like, making it difficult to produce the polyethylene fiber.

The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polyethylene of the present invention are values determined by gel permeation chromatography (GPC measurement method). The measurement conditions are the conditions described in Examples.

Since the polyethylene fiber of the present invention has both thermoformability during processing and dimensional stability during use, the polyethylene fiber of the present invention can be processed to suit various uses. In addition, the product containing the polyethylene fiber of the present invention can be used for a long period of time because the dimensional change over time is small even when a load is applied. Therefore, since the frequency of product replacement can be reduced, the environmental load can be reduced.
The polyethylene fiber of the present invention may be either a single yarn (monofilament) or a multifilament obtained by twisting a plurality of single yarns, and can be used as appropriate depending on the application.
Examples of the multifilament include a twisted yarn obtained by twisting a plurality of single yarns, a braid obtained by combining a plurality of single yarns, a rope obtained by twisting a plurality of twisted yarns, and the like. Twisted yarns, braids, and ropes may contain the ultra-high molecular weight polyethylene fibers of the present invention. It may be a high-molecular-weight polyethylene fiber, or may be composed only of the ultra-high-molecular-weight polyethylene fiber of the present invention.

In particular, the rope using the polyethylene fiber of the present invention is lightweight, has high strength, and has excellent creep resistance. useful for mooring ropes. Since floating structures are built offshore, conventional heavy mooring ropes such as chains and wires can solve the problem of prolonging the transportation period on a carrier ship and the mooring rope installation period. The mooring rope (mooring rope) for a floating structure using the polyethylene fibers of the present invention is lighter than conventional chains, wires, and the like, so it is easy to transport and install, and contributes to shortening the construction period.
Moreover, the floating structure is moored for several years, and a tensile load is constantly applied to maintain the position of the floating structure. Therefore, with conventional polyethylene fibers, there is a concern that the fibers will gradually expand under tension and the floating structure will move. However, since the rope for floating structure using the polyethylene fiber of the present invention has a lower creep than the conventional rope, it is effective in holding the position of the floating structure. Since the polyethylene fiber of the present invention has low creep and excellent seawater resistance (resistance to deterioration of physical properties against seawater), it exhibits particularly excellent effects in marine applications as described above.
In addition, the method of applying the polyethylene fiber of the present invention to a rope for a floating structure is, for example, a plurality of raw yarns are plied, and 12 strands are twisted once or multiple times. A sub-rope is prepared using a plurality of sub-ropes, and a torque-neutral construction or a torque-matched construction is used to make a full rope, and if necessary, a cover is attached to prevent sand from entering.

The above multifilaments and monofilaments can be applied to various uses, such as nets, fishing lines, material protective covers, woven fabrics, knitted fabrics, reinforcing fabrics, kite strings, bow strings, sail cloths, curtain materials, protective materials, bulletproof materials, and medical applications. sutures, artificial tendons, artificial muscles, fiber-reinforced resin reinforcing materials, cement reinforcing materials, fiber-reinforced rubber reinforcing materials, machine tool parts, battery separators, chemical filters, etc., industrial materials and products with excellent performance and design and can be widely applied.

The above-described method for producing the polyethylene fiber of the present invention will be described below, but the method for producing the polyethylene fiber of the present invention is not limited to the following explanation, and can be produced by appropriately changing it. In addition, each condition in the production process can be selected from any range, and the combination of each condition can be combined with each other. can produce fibers.

The polyethylene fiber of the present invention can be produced through, for example, a melting process, a spinning process, and a drawing process.
In the dissolution step of the present invention, a raw material polyethylene having a high molecular weight, specifically, an intrinsic viscosity [η] of 5.0 dL / g or more and 40.0 dL / g or less and a repeating unit of 90% or more is made of ethylene, and methyl at least one alkyl side chain selected from the group consisting of groups, ethyl groups, and butyl groups, and the number of alkyl branches, which means the number of said alkyl side chains per 1000 carbon atoms, is 0.6/carbon atom This is a step of dissolving polyethylene having 1000 or more and 1.4 carbon atoms/1000 or less carbon atoms in a solvent.

The raw material polyethylene consists of ethylene having an intrinsic viscosity [η] of 5.0 dL/g or more and 40.0 dL/g or less and a repeating unit of 90% or more.
The intrinsic viscosity of polyethylene is preferably 5.0 dL/g or more, more preferably 8.0 dL/g or more, preferably 40.0 dL/g or less, more preferably 30.0 dL/g or less, and still more preferably 25.0 dL/g or less. Intrinsic viscosity is preferably 5.0 to 40.0 dL/g, more preferably 8.0 to 30.0 dL/g, still more preferably 8.0 to 25.0 dL/g.
If the intrinsic viscosity is too low, the desired heat processability and dimensional stability of polyethylene fibers may not be obtained.
If the intrinsic viscosity is too high, it may become difficult to produce polyethylene fibers.

In raw material polyethylene, 90 mol % or more of repeating units are ethylene. The repeating unit of ethylene is preferably 92 mol % or more, more preferably 94 mol % or more, still more preferably 98 mol % or more.
As already mentioned, it is also a preferred embodiment to use copolymers of ethylene with minor amounts of other monomers according to the invention. Other monomers include the compounds already described.

Further, the raw material polyethylene contains at least one alkyl side chain selected from the group consisting of methyl groups, ethyl groups, and butyl groups, and the number of alkyl branches, which means the number of alkyl side chains per 1000 carbon atoms, is preferred. has 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less.
As already explained, the above-mentioned alkyl side chains and the number of alkyl branches within a predetermined range are requirements specified for obtaining heat processability and dimensional stability of polyethylene fibers. The preferred range and the like are the same as those of the polyethylene fiber already explained. The alkyl side chain is at least one selected from the group consisting of methyl group, ethyl group and butyl group, and these can be arbitrarily combined. When two or more types are used, a combination of different functional groups, a combination of the same functional groups, or a combination of the same functional group and a different functional group may be used. Examples of combinations are the same as those described for the above repeating units, and the above description is incorporated.

A polyethylene solution is prepared by dissolving the preferred raw material polyethylene. The solvent is preferably a volatile organic solvent such as decalin or tetralin, a solid at room temperature, or a non-volatile solvent.

The concentration of polyethylene in the polyethylene solution is preferably 0.5% by mass or more and 40% by mass or less, more preferably 2.0% by mass or more and 30% by mass or less, and still more preferably 3.0% by mass or more and 20% by mass or less. is. The concentration of polyethylene is, for example, preferably 0.5 to 40% by mass, more preferably 2.0 to 30% by mass, still more preferably 3.0 to 20% by mass.
If the polyethylene concentration is too low, production efficiency can be very poor.
If the polyethylene concentration is too high, it may become difficult to discharge from a nozzle described later in the gel spinning method due to the extremely high molecular weight.
As for the polyethylene concentration, it is desirable to select an optimum concentration according to the intrinsic viscosity [η] of the raw material polyethylene.

Various known methods can be employed for the polyethylene solution. For example, a polyethylene solution can be prepared by known methods such as using a twin-screw extruder; suspending solid polyethylene in a solvent and stirring at a high temperature.
The mixing conditions for the raw material polyethylene and the solvent are preferably within a temperature range of 150° C. or higher and 200° C. or lower for 1 minute or longer and 80 minutes or shorter.
If the temperature is maintained within the above temperature range for too short a time, incomplete mixing may occur and a uniform polyethylene solution may not be obtained.
If the temperature is maintained in the above temperature range for too long, a large number of breakages and crosslinks of the polyethylene molecules occur, which may make it difficult to achieve both heat processability and dimensional stability.
Depending on the molecular weight and concentration of the polymer, mixing at a temperature exceeding 200°C may be required. In this case, the mixing time in the temperature range exceeding 200°C is preferably 30 minutes or less. If it exceeds 30 minutes, too many breaks and cross-links of the polyethylene molecules may occur beyond the spinnable range. The above-mentioned spinnable range means that spinning is possible at preferably 10 m/min or more, and the spinning tension at that time is 0.01 cN or more and 300 cN or less per single yarn.

In the spinning step of the present invention, the polyethylene solution obtained above is discharged at a temperature 15 ° C. or more higher than the melting point of the polyethylene using a nozzle having holes through which the solution flows, and then cooled to 60 ° C. or less. It is a process to do.
The polyethylene solution is heated to a temperature that is preferably 15° C. or higher, more preferably 20° C. or higher, and still more preferably 30° C. or higher than the melting point of polyethylene.
When the polyethylene solution is heated, the raw material polyethylene dispersed in the solvent is dissolved to obtain a uniform polyethylene solution.

The polyethylene solution heated to the above temperature is extruded using, for example, an extruder, and then supplied to a spinning nozzle (spinneret) using a constant supply device or the like. After that, a thread (gel thread) is formed by discharging the polyethylene solution through the fine holes provided in the spinning nozzle.
It is desirable that the temperature of the polyethylene passing through the spinning nozzle is the melting point of polyethylene or higher, preferably 140° C. or higher, more preferably 150° C. or higher, and lower than the thermal decomposition temperature of polyethylene.
If the temperature of the polyethylene is too low, the viscosity of the polyethylene may decrease, making it difficult to take up the polyethylene fibrous material.
If the temperature of polyethylene is too high, the polyethylene solvent boils immediately after it is discharged from the spinning nozzle, which may easily cause yarn breakage.

The time required for the polyethylene solution to pass through an orifice provided inside the spinning nozzle and be discharged from the pores of the spinning nozzle (hereinafter referred to as the orifice passage time) is preferably 1 second or longer and 8 minutes or shorter.
If the orifice passage time is too short, the flow of the polyethylene solution in the orifice may be disturbed and the polyethylene solution may not be discharged stably. In addition, the structure of the entire single yarn may become non-uniform due to the influence of turbulence in the flow of the polyethylene solution.
If the orifice passage time is too long, the polyethylene molecules are extruded with little orientation, and the spinning tension per single yarn may be outside the above range. In addition, the crystal structure of the obtained single yarn becomes non-uniform, and the desired characteristics may not be obtained.

The polyethylene solution is preferably discharged from a spinning nozzle having a diameter of 0.2 to 3.5 mm, more preferably 0.5 to 2.5 mm, at a discharge rate of preferably 0.1 g/min or more.
Also, the number of ejection pores provided in the spinning nozzle may be appropriately adjusted according to the number of threads constituting the polyethylene fiber, and the number of pores may be singular or plural. For example, the number of pores is preferably 1 or more, more preferably 5 or more.
The diameter of the pore may be appropriately set according to the application, but considering the physical properties of the single yarn such as tensile strength, initial elastic modulus, and elongation at break, the diameter of the pore is preferably 0.2 mm or more, It is more preferably 0.3 mm or more, still more preferably 0.5 mm or more, preferably 3.5 mm or less, more preferably 3.0 mm or less, still more preferably 2.0 mm or less. Also, the diameter of the pores is preferably 0.2 to 3.5 mm, more preferably 0.3 to 3.0 mm, still more preferably 0.5 to 2.0 mm.

It is preferable that the temperature difference between the pores of the spinning nozzle is small so that the amount of polyethylene solution discharged from each of the pores of the spinning nozzle is as uniform as possible. Specifically, the variation coefficient CV of the discharge amount in each pore ((standard deviation of the discharge amount in all the pores provided in the spinning nozzle) / (average value of the discharge amount in all the pores provided in the spinning nozzle )×100) is preferably 20% or less, more preferably 18% or less.
In order to achieve the above coefficient of variation CV, the difference between the maximum temperature and the minimum temperature of all pores is preferably 10°C or less, more preferably 8°C or less.
Among all the pores, the method of reducing the temperature difference between the pores with the highest temperature and the pores with the lowest temperature is to shield the spinning nozzle from direct contact with the outside air; shielding from the outside air with a shielding plate;

The atmosphere in which the filaments (gel filaments) discharged from the pores are cooled by the refrigerant after being discharged from the pores is not particularly limited. Alternatively, a dry-wet quench method using a miscible liquid or an immiscible liquid such as water may be used.

The discharged yarn (gel yarn) is taken up at a speed of preferably 800 m/min or less, more preferably 200 m/min or less while being cooled with a cooling medium.
The temperature of the cooling medium is adjusted to cool the yarn (gel yarn) to preferably 60° C. or lower, more preferably 35° C. or lower, preferably 10° C. or higher, more preferably 12° C. or higher. Cooling is, for example, preferably 60°C to 10°C, more preferably 35°C to 12°C.
If the temperature of the yarn (gel yarn) is too high or too low, the crystal structure of the polyethylene yarn becomes uneven and the physical properties such as tensile strength are greatly reduced, resulting in a loss of polyethylene fiber obtained by drawing. Heat workability and dimensional stability may be significantly reduced.
The cooling medium may be either a miscible liquid that is miscible with the solvent of the polyethylene solution or an immiscible liquid such as water that is immiscible with the solvent of the polyethylene solution.

After cooling, the solvent present in the polyethylene yarn may be removed before the drawing process, or the drawing process may be performed while the solvent is removed during the drawing process.
The solvent extraction method may be appropriately selected according to the type of solvent. For example, if the solvent is a volatile solvent, the solvent may be removed in a heat medium such as inert gas or steam, or a heat medium such as a heating roller may be used. Moreover, in the case of a non-volatile solvent, extraction may be performed using a known extractant.
The shorter the time from the end of cooling to the removal of the solvent (hereinafter referred to as solvent removal time), the better. The solvent removal time is the time until the amount of residual solvent in the polyethylene yarn becomes 10% or less, preferably within 10 hours, more preferably within 2 hours, and even more preferably within 30 minutes.
If the solvent removal time is too long, the crystalline structure of the polyethylene yarn may become non-uniform.

The polyethylene fiber of the present invention may be a monofilament consisting of one single yarn, or may be a multifilament consisting of a plurality of single yarns twisted together. The method of forming the multifilament is not particularly limited, and various known methods can be employed. For example, a large number of filaments ejected from the pores may be squeezed into a multifilament bundle.

In the drawing process of the present invention, the obtained polyethylene yarn (undrawn yarn) is drawn once or more, and the drawing temperature at the last drawing is 140 ° C. or more and less than 155 ° C., and the drawing time is 2 minutes or more and 8 minutes. Within this step, the tension applied to the yarn during drawing is set to 1.5 cN/dtex or more and 8 cN/dtex or less.
The drawing step is performed continuously or after winding the undrawn yarn taken in the spinning step. In the drawing step, the undrawn yarn is drawn several times in a heated state. The drawing may be performed once or in multiple steps so as to achieve a desired draw ratio, but the number of times of drawing is preferably 6 or less.
The stretching step may be performed in a heat medium atmosphere or may be performed using a heating roller. Examples of the heat medium include air, inert gas such as nitrogen, water vapor, liquid medium, and the like.

The total draw ratio of the undrawn yarn is preferably 7.0 times or more and 60 times or less, more preferably 8.0 times or more and 55 times or less, regardless of whether the drawing process is a single stage or a multi-stage drawing process. times or less, more preferably 9.0 times or more and 50 times or less. The total draw ratio is, for example, preferably 7.0 to 60 times, more preferably 8.0 to 55 times, still more preferably 9.0 to 50 times.
Stretching is preferably carried out at a temperature below the melting point of polyethylene. When stretching is performed multiple times, it is preferable to increase the temperature during the stretching as the process progresses to a later stage. The drawing temperature in the final stage of drawing is preferably 140° C. or higher, more preferably 145° C. or higher, and preferably 155° C. or lower, more preferably 150° C. or lower. The stretching temperature in the final stage of stretching is, for example, preferably 140°C to 155°C, more preferably 145°C to 150°C.

The drawing time of the final drawing is preferably 2 minutes or more, preferably 8 minutes or less, more preferably 6 minutes or less, and even more preferably 4 minutes or less. The stretching time is, for example, preferably 2 to 8 minutes, more preferably 2 to 6 minutes, still more preferably 2 to 4 minutes.
If the final stretching time is too long, the molecular chains relax during the stretching even if the production conditions other than the stretching time are set within a suitable range, which may deteriorate the heat processability and dimensional stability.

The deformation speed during stretching is preferably 0.0001 s ^-1 or more, more preferably 0.008 s ^-1 or more, and preferably 0.8 s ^-1 or less, more preferably 0.1 s ^-1 or less. The deformation speed is, for example, preferably 0.0001 s ^-1 to 0.8 s ^-1 , more preferably 0.008 s ^-1 to 0.1 s ^-1 .
The deformation speed can be calculated from the draw ratio of the polyethylene fiber, the drawing speed, and the length of the drawing section.
Deformation speed (s ⁻¹ )=[(stretching speed−stretching speed/stretching ratio)/stretching section length]
If the deformation speed is too high, the polyethylene fibers are broken before reaching a sufficient draw ratio, which is not preferable.
If the deformation speed is too slow, the molecular chains are relaxed during drawing, so that polyethylene fibers having sufficient strength and elastic modulus cannot be obtained, and the tensile strength and initial elastic modulus of the polyethylene fibers are also lowered, which is not preferable.

The tension applied to the yarn at the final drawing is preferably 1.5 cN/dtex or more, more preferably 2.0 cN/dtex or more, still more preferably 2.5 cN/dtex or more, and preferably 8 cN/dtex or less, It is more preferably 5 cN/dtex or less, still more preferably 4 cN/dtex or less, still more preferably 3 cN/dtex or less. The tension is, for example, preferably 1.5 to 8 cN/dtex, more preferably 2.0 to 5 cN/dtex, still more preferably 2.5 to 4 cN/dtex, still more preferably 2.5 to 3 cN/dtex. .
If the tension during stretching is too low, heat processability and dimensional stability may not be improved.
If the tension during drawing is too high, yarn breakage or the like may occur, making production difficult.

The stretched polyethylene fiber is preferably wound by various known methods and under known winding conditions.

Others In order to impart other functions to the polyethylene fiber of the present invention, additives such as antioxidants and anti-reduction agents, pH adjusters, surface tension reducing agents, thickeners, humectants, and thickening agents are added. Various known additives such as staining agents, preservatives, antifungal agents, antistatic agents, pigments, mineral fibers, other organic fibers, metal fibers, and sequestering agents may be added.

This application claims the benefit of priority based on Japanese Patent Application No. 2021-212367 filed on December 27, 2021. The entire contents of the specification of Japanese Patent Application No. 2021-212367 filed on December 27, 2021 are incorporated herein by reference.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and can be modified appropriately within the scope that can conform to the gist of the above and later descriptions. It is of course possible to implement them, and all of them are included in the technical scope of the present invention.

The measurement conditions and evaluation criteria for the characteristics of each sample are as follows.

(1) Intrinsic Viscosity Decalin at a temperature of 135° C. was used as the solvent, and the specific viscosity of various dilute solutions was measured using an Ubbelohde capillary viscosity tube. The intrinsic viscosity was determined from the point of extrapolation to the origin of a straight line obtained by least-squares approximation from the plot of dilute solution viscosity versus concentration. For measurement, the sample was divided or cut into lengths of about 3 mm, 1% by mass of an antioxidant ("Yoshinox (registered trademark) BHT" manufactured by API Corporation) was added to the sample, and 135 C. for 4 hours with stirring to prepare a measurement solution.

(2) weight average molecular weight (Mw), number average molecular weight (Mn)
The weight average molecular weight (Mw) and number average molecular weight (Mn) of each sample were determined using gel permeation chromatography (GPC). Measurement was performed by washing a fiber sample cut to a length of about 2 mm with acetone twice for 15 minutes, followed by solvent (1,2,4-trichlorobenzene with 0.1% antioxidant BHT added). was added, dissolved by shaking at 140° C. for 2.5 hours, and heated and filtered through a 0.5 μm sintered filter to obtain a measurement solution.
・Column: TSKgel GMH _HR -H(20)HT×3
(7.8mm ID x 300mm x 3)
- Eluent: 1,2,4-trichlorobenzene (0.05% BHT added)
・Flow rate: 1.0 mL/min
・Detector: RI detector (polarity)
・Column temperature: 140°C
・Injection volume: 300 μL
・Sample concentration: 0.1 mg/mL
・Molecular weight standard: standard polystyrene

(3) Number of alkyl branches 250 mg of each sample was dissolved in o-dichlorobenzene + p-dichlorobenzene-d4 (7 + 3 vol) at 145 ° C., ¹³ C-NMR was measured at 120 ° C., and the resulting ¹³ C-NMR spectrum Estimated according to the following criteria.
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 integrated value of the ethylene chain peak is 1000, the peak integrated value at 37.5 ppm is A, the peak integrated value at 34 ppm is B, and the peak integrated value at 23.5 ppm is C, the number of methyl side chains is A/ 2 (pieces/1000C), the number of ethyl side chains is B/2 (pieces/1000C), and the number of butyl side chains is C/2 (pieces/1000C).

(4) Elongation stress In the present invention, as follows, the same as the above ISO standard "JIS K 6936-2: 2007, Plastics-Ultrahigh molecular weight polyethylene (PE-UHMW) molding and extrusion materials-Part 2: Test piece The elongation stress of the polyethylene fiber was measured by press molding and elongation stress test in almost accordance with the test method for elongation stress of ultra-high molecular weight polyethylene molding materials in Annex A (normative). As described above, the main difference between the JIS K 6936-2:2007 method and the present invention is that the carrier is changed from a clamp to a chuck, and the measurement environment is changed from a liquid phase (such as in silicon oil) to a gas phase. The point is that it was changed to
Specifically, the sample was first washed with acetone and then press-molded under the following conditions to prepare a sheet-like test piece.
Molding temperature: 210°C, preheating conditions: 5 MPa for 15 minutes, total molding conditions: 10 MPa for 30 minutes, average cooling rate: 15°C/minute, molded article removal temperature: 40°C or less, testing machine used: Ohtake Machine Industry Co., Ltd. ) was used. Using the obtained test piece, the elongation stress was measured under the following conditions.
The test piece is cut from a press molded product (see JIS K 6936-2: 2007 Annex A Fig. 3 test piece for the shape of the test piece), the number of test pieces is 6, the distance between grips is 20 mm, the test temperature is 150 ° C ± 2°C (in the gas phase), the tester used is a precision universal testing machine Autograph AG-I 100kN manufactured by Shimadzu Corporation, the capacity of the tester is a load cell type of 1kN, and the test load is 600% of the parallel narrow part of the test piece. A load (unit: MPa) was applied with six different weights so that the time required for elongation was in the range of 1 to 20 minutes. From the results of 6 test pieces, the horizontal axis is each measurement time (unit: minutes), the vertical axis is each stress (unit: MPa), and the estimated tensile stress that reaches 600% elongation in 10 minutes was calculated. The estimated tensile stress was taken as elongation stress (unit: MPa).

(5) Fineness A sample was cut into 10 m lengths at five different locations, the weights were measured, and the fineness (dtex) was determined using the average value of the five locations.

(6) Tensile strength, initial elastic modulus, and elongation at break These were measured according to JIS L1013 8.5.1.
Specifically, using Orientec's "Tensilon", the strain-stress curve was obtained under the 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%. , the tensile strength (cN/dtex) was calculated from the stress at the breaking point of the obtained curve, and the elongation at break was calculated from the elongation.
Also, the elastic modulus (cN/dtex) was calculated from the tangent line giving the maximum gradient near the origin of the obtained curve.
These were measured 10 times and expressed as the average value. The initial load applied to the sample during measurement was 1/10 of the mass (g) per 10,000 m of the sample.
The tensile strength, initial elastic modulus, and elongation at break of the polyethylene fiber (stretched multifilament) were evaluated according to the following criteria.
Tensile strength 35 cN / dtex or more: ○ Less than 35 cN / dtex: ×
Initial elastic modulus 950 cN/dtex or more: ○ Less than 950 cN/dtex: ×
Breaking elongation 4% or more: ○ Less than 4%: ×

(7) Thermal stress A thermal stress strain measuring device (manufactured by Seiko Instruments Inc., "TMA/SS120C") was used for the measurement. Prepare a sample to have a length of 20 mm, set the initial load to 0.01764 cN / dtex, heat up from room temperature (20 ° C.) to the melting point at a heating rate of 20 ° C./min, and thermal stress at which thermal shrinkage becomes maximum. and its temperature was measured.

(8) Creep resistance Creep measurement was performed using a dynamic viscoelasticity measuring device (TA Instruments "DMA-Q800") with a sample length of 10 mm (length between chucks) and a preload of 0.10 N. measurement temperature (60 ° C. or 140 ° C.), a load of 6.6 g / dtex for the fineness of the sample, a soak time of 1.00 min, and a date sampling interval of 0.50 s / pt. Measurements were taken until the sample broke.
After the measurement, the sample elongation ε _i (t) [% unit], creep rate τ [1/sec unit], and the time until fracture were obtained from the measurement data by the following methods.
Let t ₀ =0 sec be the time when the load starts to be applied to the sample, and L0 be the sample length at that time. When the sample length at a certain time t is L _(t) , the sample elongation ε _i (t) [in %] is expressed as follows.
ε _i (t) [% unit] = (L _(t) - L ₀ ) x 100/L ₀
The creep rate τ [in 1/sec] is defined as the change in length of the sample in 1 second steps of time and is given by:
τ _i =(ε _i −ε _i−1 )/(t _i −t _i−1 )×1/100
The time obtained by subtracting the time of the measurement data when the load started to be applied to the sample from the time of the final measurement data when the sample was broken and the measurement was completed was defined as the creep life.
The creep rate was calculated by the above formula for all measurement data from the time when the load started to be applied to the sample (t ₀ =0 sec) until the sample fractured, and the minimum value was taken as the creep rate of the measured sample.

(Example 1)
A polyethylene fiber was produced using raw material polyethylene containing two or more types of ultrahigh molecular weight polyethylene having different average molecular weights, which was subjected to ethylene polymerization in the presence of a Ziegler catalyst.
Specifically, ultra high molecular weight polyethylene (A), ultra high molecular weight polyethylene (B), and decahydronaphthalene (decalin) shown in Table 1 are combined into ultra high molecular weight polyethylene (A): ultra high molecular weight polyethylene (B). : decalin = 2.9:6.1:91.0 (weight ratio) to obtain a slurry-like liquid.
The obtained slurry-like liquid was dissolved in a twin-screw extruder equipped with a mixing and conveying section, and the obtained polyethylene solution was extruded from a spinneret at a spinneret surface temperature of 175°C and a single hole discharge rate of 3.0 g/min. Dispensed. The number of orifices formed in the spinneret was 16 and the orifice diameter was 0.8 mm.
Next, while taking up the extruded filament, the filament was cooled at a speed of 80.0 m / min using a water cooling bath at 20 ° C. with a distance between the nozzle and the water surface of 1.5 cm, and 16 single yarns were obtained. An unstretched multifilament (gel yarn) consisting of Continuously, the undrawn multifilament was stretched 1.5 times while being dried with hot air at 110°C, and further stretched continuously by 2.7 times with hot air at 140°C, so that the total draw ratio was 4.0. A double first drawn yarn was obtained.
The obtained first drawn yarn was further drawn by 2.8 times with hot air at 150° C., and the drawn multifilament was immediately wound up in the drawn state.
Table 1 shows the number of ethyl branches of the thus obtained drawn multifilament, the elongation stress, and the number of ethyl branches with respect to the elongation stress.
Table 1 shows the results of measuring the fineness, tensile strength, initial elastic modulus, breaking elongation, and creep resistance of the drawn multifilament.

(Example 2)
Ultra high molecular weight polyethylene (A): ultra high molecular weight polyethylene (B): decalin = 3.4: 5.6: 91.0 (weight ratio) to form a slurry liquid, and the obtained first drawn yarn A drawn multifilament was obtained in the same manner as in Example 1, except that the was further drawn with hot air at 149°C. Table 1 shows the measurement results.

(Example 3)
While changing the ultra high molecular weight polyethylene (A), ultra high molecular weight polyethylene (A): ultra high molecular weight polyethylene (B): decalin = 4.0: 5.0: 91.0 (weight ratio) mixed to slurry A drawn multifilament was obtained in the same manner as in Example 1, except that a liquid was obtained. Table 1 shows the measurement results.

(Comparative example 1)
Without using ultra high molecular weight polyethylene (A), ultra high molecular weight polyethylene (B): decalin = 9.0: 91.0 (weight ratio) mixed to form a slurry liquid, and the obtained first drawn yarn A drawn multifilament was obtained in the same manner as in Example 1, except that the was further drawn with hot air at 151°C. Table 1 shows the measurement results.

(Comparative example 2)
Without using ultra high molecular weight polyethylene (B), ultra high molecular weight polyethylene (A): decalin = 9.0: 91.0 (weight ratio) mixed to form a slurry liquid, and the obtained first drawn yarn A drawn multifilament was obtained in the same manner as in Example 1, except that the was further drawn with hot air at 148°C. Table 1 shows the measurement results.

(Comparative Example 3)
Ultra high molecular weight polyethylene (A) and ultra high molecular weight polyethylene (B) are changed, and ultra high molecular weight polyethylene (A): ultra high molecular weight polyethylene (B): decalin = 7.7: 1.3: 91.0 ( weight ratio) to form a slurry liquid. In Comparative Example 3, since the first drawn yarn obtained in the same manner as in Example 1 could not be further drawn, Table 1 shows the measurement results for the first drawn yarn.

(Comparative Example 4)
Ultra high molecular weight polyethylene (A) and ultra high molecular weight polyethylene (B) are changed, and ultra high molecular weight polyethylene (A): ultra high molecular weight polyethylene (B): decalin = 5.3: 3.7: 91.0 ( A drawn multifilament was obtained in the same manner as in Example 1, except that the resulting first drawn yarn was further drawn with hot air at 145°C. Table 1 shows the measurement results.

As shown in Table 1, Examples 1 to 3 satisfied 140°C creep resistance and 60°C creep resistance.
Comparative Example 1 is an example in which the number of alkyl branches is 0/1000 carbon atoms. Comparative Example 1 has a high creep rate at both 140°C and 60°C, and good moldability at 140°C, but poor dimensional stability at 60°C.
Comparative Example 2 is an example in which the number of alkyl branches is more than 0/1000 carbon atoms and less than 0.6/1000 carbon atoms. In Comparative Example 2, the creep rate was slow at both 140°C and 60°C, and the dimensional stability at 60°C was good, but the moldability at 140°C was poor.
Comparative Examples 3 and 4 are examples in which the number of alkyl branches is increased to over 1.4/1000 carbon atoms.
Comparative Example 3 has a short creep rupture life at both 140° C. and 60° C., and is inferior in heat moldability and dimensional stability.
In Comparative Example 4, the creep rate is remarkably high at both 140° C. and 60° C., and both heat moldability and dimensional stability are inferior.

Claims (11)

1. Made of ethylene having a limiting viscosity [η] of 5.0 dL/g or more and 40.0 dL/g or less and a repeating unit of 90 mol% or more,
   containing at least one alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group;
   the number of alkyl branches, which means the number of alkyl side chains per 1000 carbon atoms, is 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less;
   Ultra high molecular weight polyethylene fiber.
2. The ratio of the number of alkyl branches to the elongation stress of the polyethylene fiber is 2 to 30/1000 carbon atoms/MPa,
   In the creep measurement at a measurement load of 6.6 g / dtex,
   a creep rate of 2.0×10 ⁻³ sec ⁻¹ or more at a measurement temperature of 140° C. and a creep rate of 4.0×10 ⁻⁷ sec ⁻¹ or less at a measurement temperature of 60° C.,
   The ultra-high molecular weight polyethylene fiber according to claim 1.
3. In the creep measurement at a measurement load of 6.6 g / dtex,
   The time to rupture at a measurement temperature of 140 ° C. is less than 1.2 minutes, and
   The time to fracture at a measurement temperature of 60 ° C. is 216 hours or more,
   The ultra-high molecular weight polyethylene fiber according to claim 1 or 2.
4. In thermal stress measurement,
   The polyethylene fiber according to claim 1, wherein the ratio of the storage modulus at 70°C to the storage modulus at 120°C is 1.5 or more.
5. The polyethylene fiber is composed of one or more single yarns, and the single yarn has a tensile strength of 18 cN/dtex or more, an initial elastic modulus of 500 cN/dtex or more, and a breaking elongation of 3.0% or more. 2. The ultra-high molecular weight polyethylene fiber according to 1.
6. The ultra-high molecular weight polyethylene fiber according to claim 1, wherein the ratio of weight average molecular weight to number average molecular weight is 4.0 or more.
7. A twisted yarn containing the ultra-high molecular weight polyethylene fiber according to claim 1.
8. A braid containing the ultra-high molecular weight polyethylene fiber according to claim 1.
9. A rope containing the ultra-high molecular weight polyethylene fiber according to claim 1.
10. The rope according to claim 9, which is used for mooring a floating structure on the ocean.
11. A method for producing ultra-high molecular weight polyethylene fibers obtained through a dissolution process, a spinning process, and a drawing process,
    The dissolving step includes
    Made of ethylene having a limiting viscosity [η] of 5.0 dL/g or more and 40.0 dL/g or less and a repeating unit of 90 mol% or more,
    containing at least one alkyl side chain selected from the group consisting of a methyl group, an ethyl group, and a butyl group;
    A step of dissolving polyethylene having an alkyl branch number of 0.6/1000 carbon atoms or more and 1.4/1000 carbon atoms or less, which means the number of alkyl side chains per 1000 carbon atoms, in a solvent. can be,
    The spinning process is
    A step of discharging the obtained polyethylene solution from a spinning nozzle at a temperature 15° C. or more higher than the melting point of the polyethylene, and then cooling it to 60° C. or less,
    The stretching step is
    While drawing the obtained polyethylene yarn one or more times,
    In the step of setting the drawing temperature at the final drawing to 140° C. or more and less than 155° C., the drawing time at 2 minutes or more and 8 minutes or less, and the tension of the yarn at the time of drawing at 1.5 cN/dtex or more and 8 cN/dtex or less. be.