JP7592980B2 - Polyethylene Fiber - Google Patents

Description

The present invention relates to a new high-strength polyethylene fiber that can be used in a wide range of industrial applications, including high-performance textiles such as various sportswear, bulletproof and protective clothing, and protective gloves; various rope products such as tug ropes, mooring ropes, yacht ropes, and construction ropes; various braided products such as fishing lines and blind cables; and curtain materials such as chemical filters, battery separators, and tents; and reinforcing fibers for sports products such as helmets and skis, and composites such as speaker cones.

For example, it is known that high-strength polyethylene fibers are made from ultra-high molecular weight polyethylene, and ultra-drawn fibers with high strength and high elasticity that have never been seen before can be obtained by the so-called "gel spinning method" (for example, Patent Document 1), and are already widely used in industry. These high-strength polyethylene fibers have extremely excellent high strength and high elasticity, but there is a demand from the market for improvements regarding the shortcomings that originate from the raw material. 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. Therefore, if a load is applied for a long time, the fiber will elongate, and so-called creep elongation will increase. As a result, the range of use has been limited in applications where a load is applied for a long time, such as braids, twisted threads, fishing lines, ropes, nets, etc.

To solve this problem, for example, Patent Documents 2 and 3 propose polyethylene fibers with ethyl side chains. However, since ethyl side chains and the like significantly impair extensibility, the number of side chains is limited in order to maintain high strength and productivity, and the high creep property level required by the market in recent years is not achieved.

For example, Patent Document 4 discloses ultra-high molecular weight polyethylene fibers that have improved creep life and strength properties, but further improvements in properties are required.

Special Publication No. 60-47922 Japanese Patent Application Publication No. 6-280111 International Publication No. 2017/102618 Patent No. 6069676

The present invention was made in response to the problems of the conventional technology described above, and its purpose is to provide a polyethylene fiber that is both high strength and has excellent creep resistance.

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

[1] An ultra-high molecular weight polyethylene fiber containing an ethyl branch in a side chain,
The ultra-high molecular weight polyethylene fiber is characterized in that the ratio of the number of ethyl branches per 1000 carbon atoms in the polyethylene fiber (C ₂ H ₅ /1000C) to the tensile stress of the polyethylene fiber (MPa) {(C ₂ H ₅ /1000C)/(tensile stress)} is 2 to 30 branches/1000 carbon atoms/MPa.

[2] In creep measurements at a measurement temperature of 70° C. and a measurement load of 6.6 g/dtex,
A creep rate of 9.0×10 ⁻⁸ sec ⁻¹ or less,
The elongation after 24 hours from the start of the measurement is 2.7% or less.
The ultra-high molecular weight polyethylene fiber according to the above-mentioned [1], wherein the elongation after 96 hours from the start of measurement is 5.0% or less, and the time required to reach an elongation of 3.0% is 30 hours or more.

[3] The ultra-high molecular weight polyethylene fiber according to the above [1] or [2], wherein the number of ethyl branches per 1000 carbon atoms (C ₂ H ₅ /1000C) is more than 1.1.

[4] When a polyethylene fiber is heated from 30° C. to 200° C. at a rate of 10° C./min (1st heating), held at 200° C. for 5 minutes, cooled from 200° C. to 30° C. at a rate of 10° C./min, held at 30° C. for 5 minutes, and then heated from 30° C. to 200° C. at a rate of 10° C./min (2nd heating),
The peak temperature of the melting point of the polyethylene fiber in the first heating step is 141° C. or less;
The ultra-high molecular weight polyethylene fiber according to any one of [1] to [3] above, wherein the heat quantity in the range of 70°C to 150°C until the peak temperature of the polyethylene fiber is reached in the 2nd heating step is 134 J/g or less.

[5] Ultra-high molecular weight polyethylene fiber according to any one of [1] to [4] above, having a tensile strength of 20 cN/dtex or more.

[6] A braid, twisted thread, fishing line, rope, or net containing the ultra-high molecular weight polyethylene fiber described in any one of [1] to [5] above.

The polyethylene fiber of the present invention has high strength and excellent creep resistance, making it suitable for a wide range of applications, including braids, twisted yarns, fishing lines, ropes, and nets.

FIG. 1 is a diagram showing the state when a sample is set in a creep measurement and when the amount of creep is measured. FIG. 2 is a diagram showing the measurement conditions in the creep measurement.

The inventors conducted research based on the structure of Patent Document 4 in order to provide ultra-high molecular weight polyethylene fibers that have high strength and excellent creep resistance.

Specifically, Patent Document 4 discloses that an ultra-high molecular weight polyethylene fiber containing ethyl branches, in which the ratio of the number of ethyl branches per 1000 carbon atoms (C ₂ H ₅ /1000C) to the tensile stress ES of the ultra-high molecular weight polyethylene polymer is 1.00 to 3.00 mm ² /N, has a creep life of at least 125 hours when a load of 600 MPa is applied at a temperature of 70° C. Here, the "tensile stress of the polymer" means the stress required to elongate by 600% in 10 minutes when a measurement sample obtained by compression molding a polymer and molding it into a specific shape is pulled under various loads at a predetermined temperature (150° C.) and the time until it elongates by 600% is measured, and Patent Document 4 measures the tensile stress of the polymer based on ISO 11542-2A.

In addition, in the above-mentioned Patent Document 4, the number of ethyl branches per 1,000 carbon atoms is preferably 0.40 to 1.10, and in the examples, polyethylene with an ethyl branch number of 0.69 or 1.05 is used.

However, according to the results of the inventors' investigations, it was found that when the ratio of the number of ethyl branches per 1000 carbon atoms to the tensile stress of the polyethylene fiber is controlled to 2 to 30/1000 carbon atoms/MPa as in the present invention, exceeding the upper limit of Patent Document 4, the strength and creep resistance (especially strength) are surprisingly improved compared to Patent Document 4. To achieve this, the inventors discovered that it is necessary to increase the number of ethyl branches per 1000 carbon atoms, preferably by controlling it to more than 1.1, which is more than that of Patent Document 4, and thus completed the present invention.

In examining the elongation stress, the following modifications were made in the present invention.
First, in the present invention, since it was not possible to measure the tensile stress according to the ISO standard as in Patent Document 4, the tensile stress was measured using a method similar to the ISO standard (the support was changed from a clamp to a chuck, and the measurement environment was changed from a liquid phase (e.g., in silicone oil) to a gas phase. Details are described in the Examples section below).
Furthermore, in the present invention, in order to more reliably grasp the characteristics of the fiber, the tensile stress of the polyethylene fiber itself was measured, instead of the tensile stress of the polymer as in Patent Document 4. According to the results of the inventors' investigations, since the tensile stress of the polymer has a good correlation with the intrinsic viscosity of the fiber, it was possible to relate the configuration of Patent Document ₄ , which is directed to a _polymer {ratio ( _C2H5 /1000C)/(tensile stress of the polymer)} to the configuration of the present invention, which is directed to a fiber {ratio ( _C2H5 /1000C)/(tensile stress of the fiber)}.

Polyethylene fibers that satisfy the above characteristics undergo very little deformation even in applications such as ropes and nets that are exposed to long periods of tension in harsh outdoor environments, dramatically improving the product's lifespan and contributing to both economic efficiency and environmental conservation.

The configuration of the present invention is explained in detail below.

[Polyethylene fiber]
As described above, the polyethylene fiber of the present invention is an ultra-high molecular weight polyethylene fiber containing ethyl branches in the side chains, and is characterized in that the ratio of the number of ethyl branches per 1000 carbon atoms in the polyethylene fiber (C ₂ H ₅ /1000C) to the tensile stress of the polyethylene fiber {(number of ethyl branches)/(tensile stress); unit: ethyl branches/1000 carbon atoms/MPa. Hereinafter, this may be abbreviated simply as "the ratio of the number of ethyl branches to the tensile stress"} is 2 to 30/1000 carbon atoms/MPa. The above ratio is set to ensure the desired high strength and creep resistance. If the ratio is less than 2/1000 carbon atoms/MPa, the creep resistance decreases. On the other hand, if the ratio is more than 30/1000 carbon atoms/MPa, the tensile strength decreases.
The above ratio is preferably 2.5 to 25 atoms/1000 carbon atoms/MPa, and more preferably 3.0 to 20 atoms/1000 carbon atoms/MPa.
The above ratio can be controlled by, for example, the intrinsic viscosity of the raw polyethylene. For example, when a raw polyethylene with a very low intrinsic viscosity is used, the intrinsic viscosity of the fiber is low, and therefore the elongation stress is also low, resulting in a high ratio (see Comparative Example 3 in Table 1 below).

Here, the "number of ethyl branches per 1000 carbon atoms ( _C2H5 / _1000C ); hereinafter, sometimes simply referred to as the number of ethyl branches" constituting the above ratio is preferably more than 1.1, because such a polyethylene fiber can effectively prevent polyethylene molecules from slipping, thereby exhibiting excellent creep resistance.

In addition, the aforementioned Patent Document 4 specifies the number of butyl branches in addition to the number of ethyl branches. However, according to the results of the inventors' investigations, polyethylene fibers with butyl branches are difficult to process, so in the present invention, we have decided to specify only the number of ethyl branches.

The number of ethyl branches (unit:/1000 carbon atoms) is preferably more than 1.1, more preferably more than 1.10, even more preferably 1.3 or more, and even more preferably 1.5 or more. There is no particular upper limit from the viewpoint of creep resistance, but if the upper limit is too high, the extensibility decreases and the desired high strength fiber cannot be obtained, so it is preferably 20 or less. More preferably, it is 15 or less, and even more preferably 10 or less.

Here, the number of ethyl branches refers to the number of ethyl branches contained in the polyethylene fiber.

The polyethylene fiber of the present invention has excellent creep resistance. Here, "excellent creep resistance" means that the fiber satisfies all of the following requirements (i) to (iv) in a creep measurement performed at a measurement temperature of 70° C. and a measurement load of 6.6 g/dtex:
(i) a creep rate of 9.0×10 ⁻⁸ sec ⁻¹ or less;
(ii) elongation 24 hours after the start of measurement is 2.7% or less;
(iii) the elongation after 96 hours from the start of the measurement is 5.0% or less, and (iv) the time required to reach an elongation of 3.0% is 30 hours or more.

The polyethylene fiber of the present invention preferably has a tensile strength of 20 cN/dtex or more. This is because such polyethylene fibers have high strength and high elastic modulus and can be widely used in industry. More preferably, the tensile strength is 25 cN/dtex or more, and even more preferably, the tensile strength is 30 cN/dtex or more. There is no particular upper limit to the tensile strength, but it is technically and industrially difficult to obtain polyethylene fibers with a tensile strength of more than 60 cN/dtex. Hereinafter, tensile strength may be abbreviated to strength. The initial elastic modulus is preferably 500 cN/dtex or more. More preferably, the initial elastic modulus is 600 cN/dtex or more, and even more preferably, the initial elastic modulus is 700 cN/dtex or more. There is no particular upper limit to the initial elastic modulus, but if it exceeds 2000 cN/dtex, it is not preferable because it becomes difficult to align the fibers during the molding process of the braid or rope, and single yarn breakage occurs. The breaking elongation is preferably 3.0% or more. More preferably, the breaking elongation is 3.2% or more, and even more preferably, the breaking elongation is 3.4% or more. There is no particular upper limit to the breaking elongation, but it is preferable that the breaking elongation is 7.0% or less. If the breaking elongation is lower than 3.0%, it is difficult to align the fibers during the molding process of the braided cord or rope, and single yarn breakage occurs, which is not preferable. If the breaking elongation is higher than 7.0%, it is technically and industrially difficult to obtain polyethylene fibers with a tensile strength within the above range.

The polyethylene fiber of the present invention has excellent strength and creep resistance, and is therefore suitable for use in applications where it is exposed to tension for long periods of time in harsh environments, such as braids, twisted yarns, fishing lines, ropes, and nets.

The above polyethylene fiber has a peak melting temperature of 141°C or less when measured by differential scanning calorimetry (DSC measurement) at a heating rate of 10°C/min (1st heating) from 30°C to 200°C with a sample amount of 2.0 mg. Such polyethylene fiber has excellent stretchability, and can obtain sufficiently high strength and elastic modulus even when it contains alkyl side chains. The melting peak temperature in the 1st heating is considered to indicate the contribution of the alkyl side chains in the polyethylene fiber as a steric hindrance. That is, the alkyl side chains become steric hindrances, disturbing the crystal structure of the part, lowering the crystal melting temperature, and at the same time preventing the polyethylene molecules from slipping, and exhibiting excellent creep properties. In addition, it is preferable that the melting peak temperature in the 1st heating is not lower than 125°C. If the melting peak temperature is lower than 125°C, the stretchability is improved, but sufficient strength and elastic modulus may not be obtained due to a low molecular weight or insufficient crystallization. More preferably, it is 130°C or higher, and even more preferably 132°C or higher.

The polyethylene fiber has a heat quantity of 134 J/g or less in the range of 70°C to 150°C until the melting point peak temperature is reached in the second heating step. The heat quantity in the second heating step is thought to reflect the number of alkyl side chains in the raw polyethylene.

The peak temperature of the first heating rise and the heat quantity in the second heating rise measured by differential scanning calorimetry (DSC measurement) are specifically values measured when polyethylene fiber is heated from 30°C to 200°C at a rate of 10°C/min (first heating rise), held at 200°C for 5 minutes, cooled from 200°C to 30°C at a rate of 10°C/min, held at 30°C for 5 minutes, and then heated from 30°C to 200°C at a rate of 10°C/min (second heating rise).

[Raw material polyethylene]
As described above, the number of ethyl branches in the polyethylene fiber of the present invention is preferably as high as more than 1.1 (unit: branches/1000 carbon atoms). By increasing the number of ethyl branches in this manner, the ratio of the number of ethyl branches to the elongation stress of the polyethylene fiber is controlled in the range of 2 to 30 branches/MPa, and as a result, a polyethylene fiber having excellent tensile strength and creep resistance is obtained. The above-mentioned Patent Document 4 does not disclose anything about improving strength and creep resistance by increasing the number of ethyl branches as in the present invention.

The raw polyethylene used in the present invention may be configured so that the number of ethyl branches of the polyethylene fiber is controlled within the above range, but it is recommended to use, for example, the following raw polyethylene: As shown in the examples described later, it has been found that, regardless of the form of raw polyethylene used, the desired properties can be obtained as long as the number of ethyl branches satisfies, preferably, more than 1.1 (unit: branch/1000 carbon atoms).
(i) A raw polyethylene (blend) containing ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a Ziegler catalyst and ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a metallocene catalyst.
(ii) A raw polyethylene blend containing two or more types of ultra-high molecular weight polyethylene having different average molecular weights or different numbers of ethyl branches.
(iii) A raw polyethylene (not a blend) consisting of an ultra-high molecular weight polyethylene obtained by polymerizing ethylene in the presence of a Ziegler catalyst or an ultra-high molecular weight polyethylene obtained by polymerizing ethylene in the presence of a metallocene catalyst.

In the above (i) and (iii), the ethyl branch may be present in either 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.

The above (ii) is an embodiment in which two or more types of raw polyethylenes differing in average molecular weight, molecular weight distribution, or number of ethyl branches are blended together to ensure polyethylene fibers with excellent stretchability, high strength, and high elasticity (see Examples 2 to 7 in Table 1 below).

Here, "polyethylenes with different average molecular weights" refers to polyethylenes in which the difference in intrinsic viscosity between a polyethylene with a high average molecular weight (hereinafter referred to as "H polyethylene") and a polyethylene with a low average molecular weight (hereinafter referred to as "L polyethylene") is preferably about 2.0 dL/g or more. More preferably, it is 3.0 dL/g or more. According to the results of the inventors' studies, it was found that L polyethylene contributes to stretchability and H polyethylene contributes to strength, and that the action of L polyethylene provides sufficient stretchability even if the polyethylene has many alkyl side chains (ethyl branches in this invention), and that the strength-enhancing potential of H polyethylene can be fully demonstrated.

The difference in intrinsic viscosity between the H-polyethylene and L-polyethylene is preferably 15.0 dL/g or less. More preferably, it is 10.0 dL/g or less. As mentioned above, a smaller average molecular weight improves extensibility, but a larger amount of L-polyethylene tends to make it difficult to obtain high-strength fibers.

In the above (i) or (ii), the number of blends is not particularly limited and may be, for example, two, three or four types. However, in order to ensure the desired creep resistance and high mechanical strength while also taking into consideration improvements in moldability, it is preferable to blend two or more (preferably two) types of raw polyethylenes that differ in the average molecular weight, molecular weight distribution or number of ethyl branches.

In contrast, the above (iii) is not an embodiment in which multiple raw polyethylenes are blended as in the above (i) or (ii), but an embodiment in which a single ultra-high molecular weight polyethylene obtained in the presence of a Ziegler catalyst or a metallocene catalyst is used (see Example 1 in Table 1 below). According to the results of experiments by the present inventors, even in the non-blended embodiment (iii) above, a polyethylene fiber with the desired creep resistance and high strength was obtained. However, it was found that the blended embodiment (i) or (ii) above allows for a higher draw ratio from the first drawn yarn described below, and the tensile strength of the obtained polyethylene fiber is even higher. The above-mentioned Patent Document 4 does not disclose at all the use of these raw polyethylenes (i) to (iii).

Each aspect is described in detail below.

Regarding (i): The raw polyethylene used in the present invention may be a blend of ultra-high molecular weight polyethylene (hereinafter referred to as "Ziegler polyethylene") obtained by ethylene polymerization in the presence of a Ziegler catalyst as in (i) above, and ultra-high molecular weight polyethylene (hereinafter referred to as "metallocene polyethylene") obtained by ethylene polymerization in the presence of a metallocene catalyst. In this case, it is recommended to use Ziegler polyethylene as polyethylene with a large average molecular weight (H polyethylene) and metallocene polyethylene as polyethylene with a small average molecular weight (L polyethylene). This is because Ziegler polyethylene has a wide molecular weight distribution, and the high molecular weight component contributes to the function of H polyethylene, i.e., to high strength. On the other hand, metallocene polyethylene has a narrower molecular weight distribution than Ziegler polyethylene, and the low molecular weight component contributes to the function of L polyethylene, i.e., to improved stretchability. As a result, it was found that a polyethylene fiber with excellent stretchability, high strength, and high elastic modulus was obtained.

In order to achieve mainly stretchability and high strength, it is preferable that the Ziegler polyethylene does not have ethyl branches, and it is preferable that only the metallocene polyethylene has ethyl branches. It is known that the presence of branches inhibits stretchability and makes it difficult to achieve high strength, and as mentioned above, due to the influence of the average molecular weight and molecular weight distribution, it is preferable to have ethyl branches on the metallocene polyethylene side, as this provides excellent stretchability.

The blend ratio of H-polyethylene and L-polyethylene may be adjusted appropriately to obtain the polyethylene fiber of the present invention, taking into consideration the difference in the number of ethyl side chains and the intrinsic viscosity of each of them. For example, the blend ratio of H-polyethylene and L-polyethylene is preferably H-polyethylene:L-polyethylene (weight ratio) = 10-90:90-10. From the viewpoint of a uniform blend of both polymers, it is even more preferable to blend at 30-70:70-30.

Regarding (ii), the raw polyethylene used in the present invention may be one obtained by polymerizing two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights in the presence of a Ziegler catalyst or a metallocene catalyst as described above in (ii). Fibers made of such ultra-high molecular weight polyethylene also have excellent stretchability and tensile strength.
The above (ii) is preferably obtained by ethylene polymerization mainly in the presence of a Ziegler catalyst. As described above, the polyethylene obtained in the presence of a Ziegler catalyst has a wide molecular weight distribution, and the molecular weight overlap range is large between polyethylenes having different average molecular weights, and the continuity of the molecular weight distribution is ensured, so that it is presumed that the processing conditions for processing the raw material into fibers are wide.

Regarding (iii), the raw polyethylene used in the present invention may be a single ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst or a metallocene catalyst as in (iii) above [not a blend as opposed to (i) and (ii) above]. Fibers made of such ultra-high molecular weight polyethylene also have excellent stretchability and strength.
However, for the same reason as in (ii) above, it is preferred that ethylene is polymerized mainly in the presence of a Ziegler catalyst.

[Method of producing polyethylene fibers]
Next, a preferred method for producing the polyethylene fiber of the present invention will be described.

[Raw material polyethylene]
For the polyethylene fiber of the present invention, it is preferable to use ultra-high molecular weight polyethylene as the raw polyethylene.

In the present invention, the index of "ultra-high molecular weight" is expressed by the intrinsic viscosity [η].
Specifically, the intrinsic viscosity [η] of such raw 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, even more preferably, it is 10.0 dL/g or more and 30.0 dL/g or less, and even more preferably, it is 12.0 dL/g or more and 30.0 dL/g or less. If the intrinsic viscosity is less than 5.0 dL/g, the tensile strength of the final polyethylene fiber is low, and a polyethylene fiber having a desired high strength (for example, a tensile strength of 20 cN/dtex or more) may not be obtained. On the other hand, if the intrinsic viscosity is more than 40.0 dL/g, the stretchability is reduced, and a desired high strength fiber may not be obtained.

In addition, the raw polyethylene contains ethyl groups (ethyl branches) in its side chains, and the preferred range of the number of ethyl branches is as described above.

When using two or more types of raw polyethylene, it is sufficient that one or both of them have an ethyl group in the side chain.

The polyethylene fiber of the present invention is preferably produced by a gel spinning method. Specifically, the production method preferably includes a dissolving step in which raw polyethylene is dissolved in a solvent to obtain a polyethylene solution; a spinning step in which the polyethylene solution is discharged from a nozzle at a temperature equal to or higher than the melting point of the raw polyethylene and the discharged yarn is cooled with a refrigerant; a drying step in which the solvent is removed from the discharged undrawn yarn, a drawing step in which drawing is performed; and a winding step in which the drawn drawn yarn is wound. Each step is described below.

[Dissolving process]
First, it is recommended to prepare a polyethylene solution by dissolving a high molecular weight raw polyethylene. As the solvent for the raw polyethylene, for example, a volatile organic solvent such as decalin or tetralin; or a non-volatile solvent such as paraffin can be used. 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 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, the production efficiency is very poor. On the other hand, if the polyethylene concentration is more than 40% by mass, the molecular weight is very large, and it may be difficult to extrude from a nozzle described later in the gel spinning method.

[Spinning process]
The above-mentioned polyethylene solution is extruded using an extruder or the like at a temperature equal to or higher than the melting point of the raw polyethylene (preferably at least 10°C higher than the melting point), and is supplied to a spinning nozzle using a constant-volume supply device. The polyethylene solution is then discharged through a spinning nozzle having a plurality of orifices arranged therein to form threads (gel threads). The temperature up to the spinneret is set to be lower than the thermal decomposition temperature of the raw polyethylene. Note that extrusion is performed at a temperature equal to or higher than the melting point of the raw polyethylene.

Next, the extruded gel filaments are collected 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 and stretching process]
The filament (undrawn filament) taken up in the spinning process is continuously or once wound up, and then dried and drawn. The drying process is aimed at removing the solvent, and the solvent may be removed in a heat medium atmosphere or by using a heated roller in the case of a volatile solvent. Examples of the heat medium include air, inert gas such as nitrogen, water vapor, and liquid medium. Alternatively, a non-volatile solvent may be used, and in that case, a method of extraction using an extractant or the like may be used. Examples of the extractant include chloroform, benzene, heptane, nonane, decane, ethanol, and higher alcohols.

In the subsequent drawing step, the undrawn yarn is preferably heated and drawn so that the yarn speed at the exit of the drawing step is several times the yarn speed at the entrance. Drawing may be performed once or in multiple steps, but it is preferable to draw at least once and not more than three times. The drawing step may be performed in a heat medium atmosphere or using a heated roller. Examples of heat medium include air, inert gases such as nitrogen, water vapor, and liquid media.

Here, it was found that stretching at a temperature 1.0 to 10.0°C lower than when the raw polyethylene does not contain ethyl branches improves stretchability and ultimately fiber strength. This is thought to be mainly due to the fact that the melting point is lower when the raw polyethylene side chains contain ethyl branches. Specifically, although this varies depending on the number of ethyl branches in the polyethylene fiber, it is preferable to stretch at a temperature of, for example, 130 to 150°C. It is even more preferable to stretch at a temperature of 132 to 148°C.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the following examples, and can be modified within the scope of the purpose described above and below, and all such modifications are included in the technical scope of the present invention. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

The various properties of the polyethylene fibers in the following examples were measured as follows and evaluated according to the following criteria.

(1) Intrinsic Viscosity Using an Ubbelohde capillary viscosity tube, the specific viscosity of various dilute solutions was measured in decalin at 135°C, the viscosity was plotted against the concentration, and the intrinsic viscosity was determined from the extrapolation point to the origin of the straight line obtained by least squares approximation. The measurement solution was prepared by adding 1% by mass of an antioxidant (manufactured by API Corporation, "Yoshinox (registered trademark) BHT") to the sample and dissolving it by stirring at 135°C for 4 hours.

(2) Number of ethyl branches 250 mg of each sample was taken and dissolved in o-dichlorobenzene + p-dichlorobenzene- _d4 (7 vol% + 3 vol%) at 145° C. C-NMR was measured at 120° C., and the number of ethyl branches was estimated from the obtained ¹³ C-NMR spectrum as follows.

When the ethylene chain peak of polyethylene is 30 ppm, the peak due to the ethyl side chain is detected at around 34 ppm. When the integral value of the ethylene chain peak is 1000 and the peak integral value at 34 ppm is A, the number of ethyl side chains can be calculated as A/2 (units/1000C).

(3) Elongation Stress In the present invention, press molding and an elongation stress test were performed in substantial accordance with the test method for elongation stress of ultra-high molecular weight polyethylene molding materials in "JIS K 6936-2:2007, Plastics - Ultra-high molecular weight polyethylene (PE-UHMW) molding and extrusion materials - Part 2: Preparation of test pieces and determination of properties," Annex A (Regulations), which is the same as the above ISO standard, to measure the elongation stress of the polyethylene fiber. As described above, the main difference between the measurement method of the present invention and the JIS K 6936-2:2007 method is that the support is changed from a clamp to a chuck, and the measurement environment is changed from a liquid phase (e.g., in silicone oil) to a gas phase.

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: 15 minutes at 5 MPa, total molding conditions: 30 minutes at 10 MPa, average cooling rate: 15°C/min, molded product removal temperature: 40°C or less, test machine used: electric heat press machine manufactured by Otake Machinery Co., Ltd.

The elongation stress of the obtained test piece was measured under the following conditions.
The test pieces were cut from press molded products (see JIS K 6936-2:2007 Appendix A Figure 3 Test Piece for the test piece shape), the number of test pieces was 6, the grip distance was 20 mm, the test temperature was 150 ° C ± 2 ° C (in gas phase), the test machine used was Shimadzu Corporation's precision universal testing machine Autograph AG-I 100 kN, the test machine capacity was load cell type 1 kN, and the test load was 6 different weights so that the time required for 600% elongation of the parallel narrow part of the test piece was within the range of 1 to 20 minutes. From the results of the six test pieces, the horizontal axis was the measurement time (unit: minutes) and the vertical axis was the stress (unit: MPa), and the estimated tensile stress that reached 600% elongation in 10 minutes was calculated, and the calculated estimated tensile stress was the elongation stress (unit: MPa).

(4) Fineness A sample was cut into 10 m pieces at five different positions, the weights of the pieces were measured, and the fineness (dtex) was calculated using the average value of the five pieces.

(5) Tensile strength, elongation at break, and initial elastic modulus These were measured in accordance with JIS L1013 8.5.1.
Specifically, using a "Tensilon" manufactured by Orientec Co., Ltd., a strain-stress curve was obtained under conditions of a sample length of 200 mm (length between chucks), an elongation rate of 100 mm/min, an atmospheric temperature of 20° C., and a relative humidity of 65%, and the tensile strength (cN/dtex) was calculated from the stress at the breaking point of the obtained curve, and the breaking elongation was calculated from the elongation.
The elastic modulus (cN/dtex) was calculated from the tangent line giving the maximum gradient near the origin of the obtained curve.
The measurements were performed 10 times, and the average values were expressed. The initial load applied to the sample during the measurements was 1/10 of the mass (g) per 10,000 m of the sample.

(6) Differential scanning calorimetry (DSC measurement)
The measurement was performed using a TA Instruments "DSCQ100". The sample was cut to 3-5 mm or less, and about 2 mg was filled and sealed in an aluminum pan. Using a similar empty aluminum pan as a reference, the temperature was raised from 30°C to 200°C at a heating rate of 10°C/min under nitrogen gas (1st heating), held at 200°C for 5 minutes, the temperature was lowered from 200 to 30°C at a rate of 10°C/min, held at 30°C for 5 minutes, and the temperature was raised from 30°C to 200°C at a rate of 10°C/min (2nd heating) to obtain a heating DSC curve. From the heating DSC curve, the endothermic peak top temperature at the 1st heating was taken as the melting point peak temperature at the 1st heating. In addition, the heat of fusion [unit: J/g] in the range of 70°C to 150°C at the 2nd heating was taken as the heat at the 2nd heating.

(7) Creep resistance As shown in Figures 1 and 2, one free end of the sample was fixed, a specified load was applied to the other free end, and the portion between the two ends of the sample was heated to a specified temperature, and the amount of change in the sample was read at each measurement time to measure creep. The specific measurement method is as follows.

A metal plate (length 70.0 cm, mirror-finished surface) capable of being heated to a predetermined temperature (70° C. in this embodiment) and maintaining that temperature was prepared.
The sample was placed on the metal plate in contact with the metal plate without being twisted.
As shown in FIG. 1, one of the free ends of the sample was fixed at the portion protruding from the metal plate, and an initial load (load of 0.2 g/dtex) was applied to the other free end at the portion protruding from the metal end.
After marking two points on the sample on the metal plate at a distance of 50.0 cm along the sample length, the initial load was removed and a specified load (6.6 g/dtex) was applied. Next, as shown in Figure 2, a lid was closed from above to keep the sample warm without touching it on the metal plate (the lid and the sample were not in contact), and creep measurement was started. The lid was opened every hour for the first 5 hours from the start of measurement, and every 12 hours thereafter, and at each time point of 24 hours and 96 hours, and the distance between the marks initially made was read. Specific measurement times were 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 17 hours (5 hours + 12 hours), 24 hours, 29 hours (17 hours + 12 hours), 41 hours (29 hours + 12 hours), 53 hours (41 hours + 12 hours), 65 hours (53 hours + 12 hours), 77 hours (65 hours + 12 hours), 89 hours (77 hours + 12 hours), 96 hours, 101 hours (89 hours + 12 hours), 113 hours (101 hours + 12 hours), 125 hours (113 hours + 12 hours), and measurements were taken every +12 hours thereafter.
The creep measurements were continued until the specimen broke.

Here, the elongation ε _i (mm) of a 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 initially made on the sample, and the amount of elongation (strain) ε _i (t) (%) is expressed as follows:
ε _i (t) (%) = (L _(t) - L ₀ ) × 100/L ₀

The creep rate τ (1/sec) is defined as the change in length of the sample per second, and the creep rate τ _i for each measurement time is expressed as follows:
τ _i (1/sec) = (ε _i −ε _i-1 )/(t _i − _{t i-1} )×1/100

As described above, the distance between the marks was measured from the start of the measurement until the sample broke, and the creep rate τ _i for each measurement time was plotted on a logarithmic scale, with the minimum value being taken as the creep rate of the measured sample.
The creep life of the measured sample was determined as the reading time immediately before the reading time at which the sample was broken. In other words, the time at which the final sample length was read was determined as the creep life. In this embodiment, when the creep life measured in this manner reached 509 hours or more, it was determined that the creep life was far longer than that of the conventional technology, and no further measurements were made. In this case, the creep life was recorded as "509 hours or more."

Example 1
In this example, polyethylene fibers were produced using the raw material polyethylene (iii) consisting of a single ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst.
Specifically, a Ziegler catalyst was used for polymerization, and ultra-high molecular weight polyethylene (A) having an intrinsic viscosity of 15.6 dL/g and 3.4 ethyl side chains per 1,000 carbon atoms was mixed with decahydronaphthalene (decalin) as a solvent in a weight ratio of ultra-high molecular weight polyethylene (A):decalin = 9:91 to form a slurry liquid.
The slurry liquid thus obtained was dissolved in a twin-screw extruder equipped with a mixing and conveying section, and the resulting polyethylene solution was extruded from the spinneret at a single-hole output 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.
Next, the discharged filament was collected and cooled at a speed of 80.0 m/min using a 20°C water-cooled bath with a nozzle-to-water surface distance of 1.5 cm to obtain an undrawn multifilament (gel yarn) consisting of 16 single yarns. The undrawn multifilament was then stretched 1.5 times while drying with hot air at 110°C, and further continuously stretched 2.7 times with hot air at 140°C to obtain a first stretched yarn with a total stretch ratio of 4.0 times.
The obtained first drawn yarn was further drawn 2.3 times with hot air at 141° C., and the drawn multifilament was immediately wound up in the drawn state.
The number of ethyl branches of the drawn multifilament thus obtained was 3.4/1000C, the elongation stress was 0.24 MPa, and the ratio of the number of ethyl branches to the elongation stress was 14.2/MPa.
The physical properties of the drawn multifilament were a fineness of 62 dtex, a tensile strength of 33 cN/dtex, an initial modulus of elasticity of 796 cN/dtex, and a breaking elongation of 4.7%. The creep measurement results were a creep rate of 7.5×10 ⁻¹⁰ sec ⁻¹ , an elongation of 1.5% 24 hours after the start of measurement, an elongation of 1.5% 96 hours after the start of measurement, a time to reach an elongation of 3.0% of 509 hours or more (elongation of 1.7% at 509 hours), and a creep life of 509 hours or more. The results of DSC measurement of this fiber sample showed that the melting point peak temperature in the first heating was 136° C., and the heat quantity in the second heating was 124 J/g.

Example 2
In this example, polyethylene fibers were produced using the raw polyethylene material containing two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights, which were subjected to ethylene polymerization in the presence of a Ziegler catalyst as described above in (ii).
Specifically, in Example 1 above, an ultra-high molecular weight polyethylene (A) having an intrinsic viscosity of 15.6 dL/g and 3.4 ethyl side chains per 1000 carbon atoms, an ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 20.0 dL/g and no ethyl side chains, and decahydronaphthalene (decalin) were mixed in a ratio of ultra-high molecular weight polyethylene (A):ultra-high molecular weight polyethylene (B):decalin = 5.3:3.7:91.0 (weight ratio) to obtain a slurry liquid, and a drawn multifilament was obtained in the same manner as in Example 1 above, except that the first drawn yarn was drawn 2.8 times with hot air at 145°C.
The number of ethyl branches of the drawn multifilament thus obtained was 2.0/1000C, the elongation stress was 0.26 MPa, and the ratio of the number of ethyl branches to the elongation stress was 7.7/MPa.
The physical properties of the drawn multifilament were a fineness of 47 dtex, a tensile strength of 36 cN/dtex, an initial modulus of elasticity of 1094 cN/dtex, and a breaking elongation of 4.1%. The creep measurement results were a creep rate of 8.7×10 ⁻⁹ sec ⁻¹ , an elongation of 1.5% 24 hours after the start of measurement, an elongation of 2.2% 96 hours after the start of measurement, a time to reach an elongation of 3.0% of 173 hours, and a creep life of 509 hours or more. The results of DSC measurement of this fiber sample were a melting point peak temperature of 139° C. in the first heating, and a heat quantity of 123 J/g in the second heating.

Example 3
In this example, polyethylene fibers were produced using the raw polyethylene material containing two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights, which were subjected to ethylene polymerization in the presence of a Ziegler catalyst as described above in (ii).
Specifically, in Example 1, ultra-high molecular weight polyethylene (C) having an intrinsic viscosity of 17.0 dL/g and 2.0 ethyl side chains per 1000 carbon atoms, which was polymerized using a Ziegler catalyst, ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 20.0 dL/g and no ethyl side chains, which was polymerized using a Ziegler catalyst, and decahydronaphthalene (decalin) were mixed in a ratio of ultra-high molecular weight polyethylene (C):ultra-high molecular weight polyethylene (B):decalin = 6.8:2.2:91.0 (weight ratio) to obtain a slurry liquid, and a drawn multifilament was obtained in the same manner as in Example 1, except that the first drawn yarn was drawn 3.0 times with hot air at 145 ° C.
The number of ethyl branches of the drawn multifilament thus obtained was 1.5/1000C, the elongation stress was 0.34 MPa, and the ratio of the number of ethyl branches to the elongation stress was 4.4/MPa.
The physical properties of the drawn multifilament were a fineness of 45 dtex, a tensile strength of 39 cN/dtex, an initial modulus of elasticity of 1214 cN/dtex, and a breaking elongation of 3.9%. The creep measurement results were a creep rate of 4.9×10 ⁻⁹ sec ⁻¹ , an elongation of 1.0% 24 hours after the start of measurement, an elongation of 1.3% 96 hours after the start of measurement, a time to reach an elongation of 3.0% of 437 hours, and a creep life of 509 hours or more. The results of DSC measurement of this fiber sample were a melting point peak temperature of 140° C. in the first heating, and a heat quantity of 130 J/g in the second heating.

Example 4
In this example, polyethylene fibers were produced using the raw polyethylene material containing two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights, which were subjected to ethylene polymerization in the presence of a Ziegler catalyst as described above in (ii).
Specifically, in Example 1 above, ultra-high molecular weight polyethylene (D) having an intrinsic viscosity of 18.0 dL/g and 2.9 ethyl side chains per 1000 carbon atoms, which was polymerized using a Ziegler catalyst, and ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 20.0 dL/g and no ethyl side chains, which was polymerized using a Ziegler catalyst, and decahydronaphthalene (decalin) were polymerized to obtain the following: ultra-high molecular weight polyethylene (D): ultra-high molecular weight polyethylene (B): decalin = 6.2 A drawn multifilament was obtained in the same manner as in Example 1 above, except that the undrawn multifilament was 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 to obtain a first drawn yarn with a total draw ratio of 5.0 times, and that the first drawn yarn was drawn with hot air at 145°C.
The number of ethyl branches of the drawn multifilament thus obtained was 2.0/1000C, the elongation stress was 0.41 MPa, and the ratio of the number of ethyl branches to the elongation stress was 4.8/MPa.
The physical properties of the drawn multifilament were a fineness of 63 dtex, a tensile strength of 35 cN/dtex, an initial modulus of elasticity of 1048 cN/dtex, and a breaking elongation of 4.0%. The creep measurement results were a creep rate of 4.8×10 ⁻⁸ sec ⁻¹ , an elongation of 2.5% 24 hours after the start of measurement, an elongation of 4.6% 96 hours after the start of measurement, a time to reach an elongation of 3.0% of 53 hours, and a creep life of 245 hours or more. The results of DSC measurement of this fiber sample were a melting point peak temperature of 139° C. in the first heating, and a heat quantity of 123 J/g in the second heating.

(Example 5)
In this example, polyethylene fibers were produced using raw polyethylene materials containing ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a Ziegler catalyst and ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a metallocene catalyst, as described above in (i).
Specifically, in Example 1 above, ultra-high molecular weight polyethylene (E) having an intrinsic viscosity of 16.3 dL/g and 7.0 ethyl side chains per 1000 carbon atoms, which was polymerized using a metallocene catalyst, and ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 20.0 dL/g and no ethyl side chains, which was polymerized using a Ziegler catalyst, and decahydronaphthalene (decalin) were mixed in a slurry-like liquid ratio of ultra-high molecular weight polyethylene (E):ultra-high molecular weight polyethylene (B):decalin = 2.6:6.4:91.0 (weight ratio), and a drawn multifilament was obtained in the same manner as in Example 1 above, except that the first drawn yarn was drawn 3.5 times with hot air at 145 ° C.
The number of ethyl branches of the drawn multifilament thus obtained was 2.0/1000C, the elongation stress was 0.48 MPa, and the ratio of the number of ethyl branches to the elongation stress was 4.2/MPa.
The physical properties of the drawn multifilament were a fineness of 40 dtex, a tensile strength of 38 cN/dtex, an initial modulus of elasticity of 1255 cN/dtex, and a breaking elongation of 3.7%. The creep measurement results showed a creep rate of 1.1×10 ⁻⁹ sec ⁻¹ , an elongation of 1.4% 24 hours after the start of the measurement, an elongation of 2.0% 96 hours after the start of the measurement, a time to reach an elongation of 3.0% of 233 hours, and a creep life of 509 hours or more. The DSC measurement results of this fiber sample showed a melting point peak temperature of 140° C. in the first heating and a heat quantity of 128 J/g in the second heating.

Example 6
In this example, polyethylene fibers were produced using raw polyethylene materials containing ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a Ziegler catalyst and ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a metallocene catalyst, as described above in (i).
Specifically, in Example 1 above, ultra-high molecular weight polyethylene (F) having an intrinsic viscosity of 16.8 dL/g and 2.9 ethyl side chains per 1000 carbon atoms, which was polymerized using a metallocene catalyst, ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 20.0 dL/g and no alkyl side chains, which was polymerized using a Ziegler catalyst, and decahydronaphthalene (decalin) were mixed in a slurry-like liquid ratio of ultra-high molecular weight polyethylene (F):ultra-high molecular weight polyethylene (B):decalin = 4.7:4.3:91.0 (weight ratio), and a drawn multifilament was obtained in the same manner as in Example 1 above, except that the first drawn yarn was drawn 2.5 times with hot air at 145°C.
The number of ethyl branches of the drawn multifilament thus obtained was 1.5/1000C, the elongation stress was 0.36 MPa, and the ratio of the number of ethyl branches to the elongation stress was 4.2/MPa.
The physical properties of the drawn multifilament were a fineness of 50 dtex, a tensile strength of 35 cN/dtex, an initial modulus of elasticity of 989 cN/dtex, and a breaking elongation of 4.4%. The creep measurement results showed a creep rate of 3.1×10 ⁻⁸ sec ⁻¹ , an elongation of 2.4% 24 hours after the start of measurement, an elongation of 3.6% 96 hours after the start of measurement, a time to reach an elongation of 3.0% of 53 hours, and a creep life of 353 hours. The results of DSC measurement of this fiber sample showed a melting point peak temperature of 139° C. in the first heating and a heat quantity of 121 J/g in the second heating.

(Example 7)
In this example, polyethylene fibers were produced using raw polyethylene materials containing ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a Ziegler catalyst and ultra-high molecular weight polyethylene subjected to ethylene polymerization in the presence of a metallocene catalyst, as described above in (i).
Specifically, in the above Example 1, a metallocene catalyst was used for polymerization, and ultra-high molecular weight polyethylene (F) having an intrinsic viscosity of 16.8 dL/g and 2.9 ethyl side chains per 1000 carbon atoms, and a Ziegler catalyst was used for polymerization, and ultra-high molecular weight polyethylene (B) having an intrinsic viscosity of 20.0 dL/g and no alkyl side chains and decahydronaphthalene (decalin) were mixed in a slurry-like liquid with ultra-high molecular weight polyethylene (F): ultra-high molecular weight polyethylene (B): decalin = 6.2: 2.8: 91.0 (weight ratio), the take-up speed from the spinneret was changed to 100.0 m/min, and the first drawn yarn was drawn with hot air at 145 ° C., except that a drawn multifilament was obtained in the same manner as in the above Example 1. The number of ethyl branches of the drawn multifilament thus obtained was 2.0/1000C, the elongation stress was 0.32 MPa, and the ratio of the number of ethyl branches to the elongation stress was 6.3/MPa. The physical properties of the drawn multifilament were a fineness of 46 dtex, a strength of 33 cN/dtex, an initial modulus of elasticity of 842 cN/dtex, and a breaking elongation of 4.5%. The creep measurement results showed a creep rate of 1.2×10 ⁻⁸ sec ⁻¹ , an elongation of 1.5% 24 hours after the start of the measurement, an elongation of 1.8% 96 hours after the start of the measurement, a time to reach an elongation of 3.0% of 353 hours or more, and a creep life of 389 hours. The results of DSC measurement of this fiber sample showed a melting point peak temperature of 139° C. in the first heating and a heat quantity of 118 J/g in the second heating.

(Comparative Example 1)
The ultra-high molecular weight polyethylene fiber "IZANAS Grade SK777" manufactured by Toyobo Co., Ltd. had an ethyl branch number of 0.0/1000C, an elongation stress of 0.58 MPa, and a ratio of the ethyl branch number to the elongation stress of 0.0/MPa. The physical properties were a fineness of 1775 dtex, a tensile strength of 35 cN/dtex, an initial elastic modulus of 1190 cN/dtex, and a breaking elongation of 3.6%.
The creep resistance was 3.6×10 ⁻⁶ sec ⁻¹ , the time to reach 3.0% elongation was 2 hours, and the creep life was 17 hours. Since breakage was confirmed 24 hours after the start of the measurement, the elongation could not be measured 24 hours after the start of the measurement. Similarly, the elongation could not be measured 96 hours after the start of the measurement. Thus, the creep resistance of Comparative Example 1 was inferior to any of the above Examples. The results of the DSC measurement of this fiber sample showed that the melting point peak temperature in the first heating was 146° C., and the heat quantity in the second heating was 146 J/g.

(Comparative Example 2)
A drawn multifilament was obtained in the same manner as in Example 1, except that the ultra-high molecular weight polyethylene (A) was changed to an ultra-high molecular weight polyethylene (G) having an intrinsic viscosity of 20.0 dL/g and 0.5 ethyl side chains per 1,000 carbon atoms, which was polymerized using a Ziegler catalyst, and the first drawn yarn was drawn 2.8 times with hot air at 148°C.
The number of ethyl branches of the drawn multifilament thus obtained was 0.5/1000C, the elongation stress was 0.41 MPa, and the ratio of the number of ethyl branches to the elongation stress was 1.2/MPa. The physical properties were a fineness of 48 dtex, a tensile strength of 36 cN/dtex, an initial elastic modulus of 1125 cN/dtex, and a breaking elongation of 3.8%.
The creep resistance was as follows: creep rate: 2.8 x ^10-7 sec ^-1 , elongation: 4.7% 24 hours after the start of measurement, elongation: 13.5% 96 hours after the start of measurement, time to reach elongation of 3.0%: 17 hours, creep life: 101 hours. Thus, the creep resistance of Comparative Example 2 was inferior to any of the above Examples. The results of DSC measurement of this fiber sample showed that the melting point peak temperature in the first heating was 142°C, and the heat quantity in the second heating was 135 J/g.

(Comparative Example 3)
In the above Example 1, ultra-high molecular weight polyethylene (A) was polymerized using a metallocene catalyst, and an ultra-high molecular weight polyethylene (E) having an intrinsic viscosity of 16.3 dL / g and 7.0 ethyl side chains per 1000 carbon atoms; an ultra-high molecular weight polyethylene (H) having an intrinsic viscosity of 11.4 dL / g and no ethyl side chains using a Ziegler catalyst; and decahydronaphthalene (decalin) was changed to ultra-high molecular weight polyethylene (E): ultra-high molecular weight polyethylene (H): decalin = 7.7: 1.3: 91.0 (weight ratio), and the first drawn yarn was drawn 1.5 times with hot air at 140 ° C., and a drawn multifilament was obtained in the same manner as in the above Example 1. The number of ethyl branches of the drawn multifilament thus obtained was 6.0 pieces / 1000 C, the elongation stress was 0.14 MPa, and the ratio of the number of ethyl branches to the elongation stress was 42.9 pieces / MPa. The physical properties were a fineness of 89 dtex, a tensile strength of 19 cN/dtex, an initial elastic modulus of 323 cN/dtex, and a breaking elongation of 4.6%. The draw ratio of 1.5 times from the first drawn yarn to the drawn multifilament was the maximum draw ratio, and it was not possible to increase the draw ratio any higher.
Since the fiber properties of Comparative Example 3 were inferior to those of any of the Examples, creep resistance was not evaluated, and DSC measurement was not performed.

1. Sample 2. Metal plate 3. Load 4. Fixed end of sample 5. Lid

Claims (10)

An ultra-high molecular weight polyethylene fiber containing ethyl branches in its side chains,
the ratio of the number of ethyl branches per 1000 carbon atoms in the polyethylene fiber (C ₂ H ₅ /1000C) to the tensile stress (MPa) of the polyethylene fiber determined by the following measurement method {(C ₂ H ₅ /1000C)/(tensile stress)} is 2 to 30 branches/1000 carbon atoms/MPa;
The polyethylene fiber is characterized in that it contains any one of the following ultra-high molecular weight polyethylenes (i) to (ii) :
(i) Ultra-high molecular weight polyethylene including both ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst and ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a metallocene catalyst.
(ii) Two or more kinds of ultra-high molecular weight polyethylenes having different average molecular weights and/or different numbers of ethyl branches, at least one of which is an ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst.
The elongation stress (MPa) of the polyethylene fiber was measured by washing the polyethylene fiber with acetone, and then subjecting the polyethylene fiber to press molding at a molding temperature of 210°C, preheating conditions of 5 MPa for 15 minutes, total molding conditions of 10 MPa for 30 minutes, average cooling rate of 15°C/min, molded product removal temperature of 40°C or less, and using a test machine: an electric heat press machine manufactured by Ohtake Machinery Co., Ltd. to produce a sheet-like test piece (JIS K 6936-2:2007 Appendix A Figure 3 test piece), with a gripping distance of 20 mm, a test temperature of 150°C ± 2°C (in a gas phase), and using a precision universal testing machine Autograph AG-I manufactured by Shimadzu Corporation. A test was performed on six test pieces, with a load of 100 kN, a test machine capacity of 1 kN by load cell type, and six different weights (units: MPa) applied so that the time required for 600% elongation of the parallel narrow portion of the test piece was within the range of 1 to 20 minutes. From the results, the horizontal axis represents each measurement time (units: minutes) and the vertical axis represents each stress (units: MPa), and an estimated tensile stress that reaches 600% elongation in 10 minutes is calculated, and the calculated estimated tensile stress is the elongation stress (units: MPa). In a creep measurement at a measurement temperature of 70° C. and a measurement load of 6.6 g/dtex,
A creep rate of 9.0×10 ⁻⁸ sec ⁻¹ or less,
The elongation after 24 hours from the start of the measurement is 2.7% or less.
2. The ultra-high molecular weight polyethylene fiber according to claim 1, wherein the elongation after 96 hours from the start of measurement is 5.0% or less, and the time required to reach an elongation of 3.0% is 30 hours or more. _3. The ultra-high molecular weight polyethylene fiber according to claim 1 or 2, wherein the number of ethyl branches per 1000 carbon atoms ( _C2H5 /1000C) is more than 1.1. In differential scanning calorimetry (DSC) of a polyethylene fiber, the fiber was heated from 30° C. to 200° C. at a rate of 10° C./min (first heating), held at 200° C. for 5 minutes, cooled from 200° C. to 30° C. at a rate of 10° C./min, held at 30° C. for 5 minutes, and then heated from 30° C. to 200° C. at a rate of 10° C./min (second heating).
The peak temperature of the melting point of the polyethylene fiber in the first heating step is 141° C. or less;
The ultra-high molecular weight polyethylene fiber according to any one of claims 1 to 3, wherein the heat amount in the range of 70°C to 150°C until the peak temperature of the polyethylene fiber is reached in the 2nd heating step is 134 J/g or less. An ultra-high molecular weight polyethylene fiber according to any one of claims 1 to 4, having a tensile strength of 20 cN/dtex or more. A braid, twisted thread, fishing line, rope, or net containing the ultra-high molecular weight polyethylene fiber according to any one of claims 1 to 5. 2. The ultra-high molecular weight polyethylene fiber according to claim 1, wherein in (i), the ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst has a larger average molecular weight than the ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a metallocene catalyst. 8. The ultra-high molecular weight polyethylene fiber according to claim 7, wherein in (i), the ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a Ziegler catalyst has no ethyl branches, and the ultra-high molecular weight polyethylene obtained by ethylene polymerization in the presence of a metallocene catalyst has ethyl branches. 2. The ultra-high molecular weight polyethylene fiber according to claim 1, wherein in (ii), the two or more kinds of ultra-high molecular weight polyethylenes differing in average molecular weight and/or number of ethyl branches are such that one is an ultra-high molecular weight polyethylene having ethyl branches, and the other is an ultra-high molecular weight polyethylene having no ethyl branches. 2. The ultra-high molecular weight polyethylene fiber according to claim 1, wherein in (ii), a difference in intrinsic viscosity between the two or more kinds of ultra-high molecular weight polyethylenes differing in average molecular weight and/or number of ethyl branches is 2.0 dL/g or more and 15.0 dL/g or less.

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