JP2001316939A - High strength polyethylene fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high strength polyethylene fiber having an epoch-making strength and a high melting point and suitable for various uses via a melt- spinning process, and to provide a method for producing the same. SOLUTION: This high strength polyethylene fiber is obtained by mixing (A) a high mol.wt. polymer having an intrinsic viscosity [η] (g/dl) of >=3 and a mol.wt. distribution Mw/Mn of <=4 with a small amount of (B) an ultrahigh mol.wt. polymer having an intrinsic viscosity of at least two times that of the polymer (A), melt-kneading the mixture, melt-spinning the kneaded product and then drawing the spun fiber. The obtained high strength polyethylene fiber has a tensile strength of at least 15 cN/dtex and has a peak temperature of >=140 deg.C in the highest temperature region among heat peaks of fusion determined by the measurement of differential scanning calories.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to protective clothing and sports clothing, such as various ropes, fishing lines, nets and sheet materials for civil engineering and construction, fabrics and nonwoven fabrics for chemical filters and separators, bulletproof vests, helmets and the like. The present invention relates to a high-strength polyethylene fiber which can be widely used for industrial materials and textile applications, such as an impact-resistant composite and a reinforcing material for a sports composite, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, attempts have been made to obtain high-strength and high-modulus fibers from ultrahigh-molecular-weight polyethylene as a raw material, and fibers having very high strength and elastic modulus have been reported. For example, JP-A-56-15408 discloses that
There is disclosed a so-called "gel spinning method" in which a gel fiber obtained by dissolving ultrahigh molecular weight polyethylene in a solvent is drawn at a high magnification.

[0003] High-strength polyethylene fibers obtained by the "gel spinning method" are known to have very high strength and elastic modulus as organic fibers, and are also extremely excellent in impact resistance. Its application is expanding in use. However, in the gel spinning method, it is necessary to use a large amount of a solvent in the production process, so that not only is it costly and expensive to collect and purify the solvent, but also environmental issues are regarded as important in recent years. There is a need for a method for producing high-strength polyethylene fibers that does not use solvents.

Conventionally, there has been an attempt to obtain a high-strength polyethylene fiber by a melt spinning method as a method not using a solvent.
For example, Japanese Patent Publication No. 63-23203 discloses that a special high molecular weight polymer having a weight average molecular weight of 300,000 or more and a ratio of number average molecular weight to weight average molecular weight, that is, a so-called molecular weight distribution index (Mw / Mn) of 5 or more is melted. There is a technical disclosure that high-strength fibers having excellent creep characteristics are obtained by spinning. In addition, Japanese Patent Application Laid-Open Publication No. Hei 8-504891 discloses the use of high-density polyethylene having a weight-average molecular weight of 125,000 to 175,000 and a molecular weight distribution index (Mw / Mn) of less than 5 in an extremely limited range. There is a technical disclosure that high-strength polyethylene fibers were obtained by performing melt spinning.

[0005] In these techniques, it is obvious that the higher the molecular weight, the higher the fiber strength, but the higher the molecular weight, the more entanglement between the molecules becomes, and there is a problem that melt spinning becomes difficult. . From this viewpoint, it is presumed that JP-B-63-23203 employs a formulation that broadens the molecular weight distribution. That is, in the publication, as a result, by using a polymer having a wide molecular weight distribution, a low-viscosity component acts as a plasticizer to reduce the viscosity at the time of melting, so that the molecular weight exceeds 300,000. It is presumed that melt spinning was possible even with a high molecular weight.
On the other hand, as the molecular weight distribution becomes wider, the mechanical properties of the fiber,
In particular, the strength is expected to decrease, and narrowing the molecular weight distribution is preferable in terms of physical properties.
As disclosed in Japanese Patent No. 04891, if a polymer having a molecular weight distribution of less than 5 is used, the weight-average molecular weight is 17.5 from the viewpoint of melt viscosity and spinning stability in a fiber production process.
The limit was around 10,000. Such a low average molecular weight means that even if melt spinning is enabled, the physical properties of relatively obtainable fibers are at a much lower level than, for example, the gel spinning method using a solvent. .

[0006]

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a high-strength polyethylene fiber having physical properties comparable to those of a conventional gel spinning method even in a melt spinning method.

[0007]

According to the present invention, an intrinsic viscosity [η] (g / dl) in a fiber state is 2 or more and 8 or less, and / or has a tensile strength of at least 15 cN / dtex, Further, the present invention provides a high-strength polyethylene fiber characterized in that the peak temperature in the highest temperature range of the heat of fusion determined by differential scanning calorimetry (DSC) is 140 ° C or higher.

In the present invention, the intrinsic viscosity [η] (g / dl) is 3 or more, and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is increased. A high molecular weight polymer (A) 9 having an ethylene component as the main component, which is 4 or less
9.9 parts by weight to 90 parts by weight, and an ultrahigh molecular weight polymer (B) mainly composed of an ethylene component, having an intrinsic viscosity at least twice the intrinsic viscosity of the high molecular weight polymer (A). It is intended to provide a method for producing a high-strength polyethylene fiber, which comprises spinning and stretching a mixture consisting of 1 part by weight to 10 parts by weight after melt-kneading.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polyethylene constituting the high-strength polyethylene fiber of the present invention is characterized in that its repeating unit is substantially ethylene, and is a copolymer of ethylene and a specific α-olefin. You may. In addition, other monomers such as acrylic acid and its derivatives,
Third components such as methacrylic acid and its derivatives, vinylsilane and its derivatives may be contained in trace amounts. α
It is more preferable to use a copolymer with an olefin, particularly propylene, butene-1 or the like, so that short-chain branching is contained to a certain extent in spinning and drawing when producing the present fiber. However, if the content other than ethylene is too large, it will be a hindrance to basic performance such as tensile strength. Therefore, from the viewpoint of obtaining high-strength and high-modulus fibers, the content is preferably 3 mol% or less in monomer units.

[0010] The high molecular weight polymer (A) and the ultra high molecular weight polymer (B) used in the production method of the present invention are also characterized in that the repeating unit is substantially ethylene, as described above. And a specific α-olefin, and may further contain a small amount of other monomers.

In the production method of the present invention, the average molecular weight and the molecular weight distribution of the high molecular weight polymer (A) as the main polymer are very important. First, regarding the average molecular weight,
From the viewpoint of performing melt spinning, the intrinsic viscosity [η] (g / dl) is 3
It is preferably at least 10 and at most 10. Here, the intrinsic viscosity [η] (g / dl) of the present invention can be converted into a viscosity average molecular weight (Mv) by the following equation. Mv = (2.64 × 10 ³ [η]) ^{1.388 When} converted using this equation, the optimum polymer used for the high molecular weight polymer (A) is about 250,000 in terms of viscosity average molecular weight. It is in the range of about 1.3 million. In the technical data in this technical field, there are many cases where the weight average molecular weight is used as an index of the molecular weight, but it is common sense that the viscosity average molecular weight and the weight average molecular weight have close values although there are some differences (however, The viscosity average molecular weight does not exceed the weight average molecular weight). In the present invention, the intrinsic viscosity and the converted viscosity average molecular weight are used as indicators of the polymer molecular weight. Intrinsic viscosity [η] (g) of the high molecular weight polymer (A)
If (/ dl) is less than 3, it will be difficult to achieve high strength such as 15 cN / dtex or more in the obtained polyethylene fiber. The intrinsic viscosity of the polymer (A) is preferably 4 or more, more preferably 4.5 or more. On the other hand, when the intrinsic viscosity of the polymer (A) exceeds 10, the melt viscosity becomes extremely high, and melt extrusion becomes practically impossible. As a result, some solvent or plasticizer is required, which does not fit the purpose of the present invention.

The essence of the present invention is that a very small amount of the ultrahigh molecular weight polymer (B) is added to the polymer (A) as the main polymer.
In addition, the spinnability (spinning speed) is remarkably improved, and the strength, elastic modulus and melting point of the obtained fiber far surpass those of the fiber obtained by conventional melt spinning.
The point is that high-performance fibers can be obtained as they approach the level of fibers obtained by the gel spinning method, and further, new fibers can be obtained which, for example, surpass those from the viewpoint of fatigue resistance and the like.

JP-A-11-269717 discloses a technique in which a high-strength fiber is obtained by similarly adding a high-molecular-weight polypropylene to a range of melt-spinnable polypropylene. It is not clear whether this technology can be applied to systems that have high crystallinity like polyethylene and the crystals are considered to inhibit stretching, but even if two types of polymers having different average molecular weights have a wide molecular weight distribution and are mixed together. However, it is difficult to obtain good fibers only by unnecessarily widening the molecular weight distribution, and it is presumed that this is particularly remarkable in the case of polyethylene. Therefore, in the present invention, the molecular weight distribution (Mw / M
n) is set to 4 or less. The molecular weight distribution is preferably 3 or less, more preferably 2.7 or less. Such a polymer having a narrow molecular weight distribution can be easily obtained by using a so-called metallocene-based catalyst, but is not limited thereto.

In the present invention, such a high molecular weight polymer (A) having a narrow molecular weight distribution has a limiting viscosity of at least twice, preferably at least three times, more preferably at least four times that of the polymer (A). It is to add a very small amount of an ultrahigh molecular weight polymer (B) having an extremely large molecular weight which is twice or more. It goes without saying that the addition amount is optimally adjusted according to the molecular weight of the ultrahigh molecular weight polymer (B) as long as it is within the range of the blending ratio of the two polymers (A) and (B). For example, when an ultrahigh molecular weight polymer (B) having an intrinsic viscosity exceeding 20 which cannot be melt-spun usually is used, its addition amount of about 1% by weight of the whole mixture is sufficient. The molecular weight distribution (Mw / Mn) of the ultrahigh molecular weight polymer (B) added at this time is not particularly limited. Rather polymer (B)
It is preferable to select a relatively wide molecular weight distribution of 4 or more. The blending ratio of both polymers (A) and (B) is more preferably 99.5 for high molecular weight polymer (A).
Ultra high molecular weight polymer (B) 0.5 to 90 parts by weight
10 parts by weight.

As described above, the conventional purpose of adding the ultrahigh molecular weight polymer (B) in a range where melt spinning cannot be performed is as follows.
It is common knowledge that the melt viscosity is significantly improved, and in some cases spinning becomes difficult without complete melting. In general, it is anticipated by those skilled in the art that the spinning speed and the like will be rather reduced by the ultrahigh molecular weight polymer component, even if they are uniformly melted. It was found that the maximum spinning speed in the stable region was significantly improved, although the tension at increased.
Although the reason is not clear, first, the main polymer (A) having a low molecular weight with respect to the ultrahigh molecular weight polymer (B) functions as a kind of solvent and plasticizer, and enables a uniform molten state even at a relatively low temperature. Probably because of. It is preferable to narrow the molecular weight distribution of the polymer from the viewpoint of efficiently utilizing the ultimate performance of the molecular chain to the strength and average physical properties of the fiber. On the other hand, when a polymer having a molecular weight distribution of 5 or less, particularly 3 or less, is used, it is estimated that the rheological flow behavior in the spinning approaches a Newtonian fluid. In such a case, it is presumed that the molten strand extruded from the nozzle cannot easily follow the deformation at a high deformation speed and easily breaks, that is, a so-called capillary breaking phenomenon is likely to occur. The addition of a few ultra-high molecular weight polymers here dramatically eliminates these capillary breaks in melt spinning, as well as a slight increase in molecular weight distribution without significantly affecting average physical properties. It is presumed to act as follows.

In the production method of the present invention, the above mixture comprising the high molecular weight polymer (A) and the ultra high molecular weight polymer (B) is melt-kneaded without using a solvent, and then spun and drawn. As such a melt spinning method, a known method can be applied. For example, the melting temperature is 200
It is preferable that the stretching temperature is 135 to 150 ° C. and the stretching ratio is 5 times or more. Also,
Stretching is preferably performed in two or more steps.

By the above-mentioned production method, a high-strength polyethylene fiber having an intrinsic viscosity [η] (g / dl) in a fiber state of 2 or more and 8 or less can be obtained. By having such an intrinsic viscosity, especially when the intrinsic viscosity is 2 or more, a high-strength polyethylene fiber having a tensile strength of 15 cN / dtex or more can be obtained. Here, when the intrinsic viscosity [η] (g / dl) in the fiber state is less than 2, not only high strength is not obtained, but also the creep characteristics of the obtained yarn are remarkably deteriorated, and the yarn cannot be used. If it exceeds, stretching becomes extremely difficult, and it is difficult to obtain a high-strength yarn.

In addition, a special high-strength polyethylene fiber having a peak temperature of the highest heat of fusion of 140 ° C. or higher in differential scanning calorimetry (DSC) can be obtained by the above-mentioned production method. When the heat of fusion of such a high-strength polyethylene fiber is determined by differential scanning calorimetry, the peak usually considered to be a folded crystal at a low temperature side of around 100 ° C. to 120 ° C. and the peak of 130 ° C.
Normally, peaks which appear to be derived from the crystal stretched in the high temperature part appear. It is known that the peak of the high-temperature portion changes its peak temperature depending on the orientation state of the molecular chain. In particular, when the molecular chain is completely extended, the equilibrium melting point (141%) of the polyethylene crystal is obtained.
° C) is known to be near or above. The high-strength polyethylene fiber of the present invention is characterized in that the peak temperature of the highest temperature among the peaks in the high-temperature portion, which is considered to be derived from the elongated crystal, is 140 ° C. or higher. This is a surprising value considering that the polyethylene fiber obtained by ordinary melt spinning has a temperature of at most 135 ° C. This is suggestive by estimating the microstructure of the fiber and estimating the role of the ultrahigh molecular weight polymer (B). That is, since the peak of the highest temperature is considered to be derived from the elongated crystal as described above, in the high-strength polyethylene fiber of the present invention, the ultrahigh molecular weight polymer (B) is oriented and crystallized first by spinning, Thereafter, it is presumed that the high molecular weight polymer (A), which is the main part, forms a so-called shish kebab structure that crystallizes around it. In this case, it is considered that a very small amount of the ultra-high molecular weight polymer (B) is important to reduce the tension in spinning, and to obtain a unique fiber microstructure and extremely high strength properties and a high melting point in melt spinning. Can be Although there is no evidence that a shish kebab-like structure was obtained in the melt-spun state, it is based on the above presumption that it can be distinguished by DSC from polyethylene fiber via melt-spinning obtained from a normal lamella structure,
Both can be distinguished by intensity and DSC.

The manufacturing method of the high-strength polyethylene fiber of the present invention is not particularly limited as long as it has the above-mentioned properties. For example, the high-strength polyethylene fiber is manufactured by a gel spinning method instead of a melt spinning method. Is also good. However, in view of the object of the present invention to provide a high-strength polyethylene fiber having physical properties comparable to the gel spinning method while being a low-cost melt spinning method without using a solvent, it is manufactured by the melt spinning method. Is preferred.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The measuring method and measuring conditions relating to characteristic values in the present invention will be described below. (Differential scanning calorimetry) The differential scanning calorimetry was performed using a differential scanning calorimeter “DSC7” manufactured by PerkinElmer. Approximately 5 mg of a sample (fiber) cut in advance to 5 mm or less is filled and sealed in an aluminum pan, and the temperature is raised from room temperature to 200 ° C. under an inert gas at a rate of 5 ° C./min. And the endothermic peak was determined.
The temperature of the highest peak was determined from the obtained curve.

(Measurement of molecular weight distribution) Molecular weight distribution Mw / Mn
Was measured by gel permeation chromatography. The equipment used was “150C” manufactured by Waters.
ALC / GPC ", and the measurement was performed at a temperature of 145 ° C. using a“ GMHXL series ”manufactured by Toso Corporation as a column. The calibration curve of the molecular weight was created using "Polystyrene-High Molecular Weight Calibration Kit" manufactured by Polymer Laboratories. The sample solution was added with an antioxidant (“Irgafos168” manufactured by Ciba-Geigy) equivalent to 0.2% by weight of the polymer so as to be 0.02% by weight in trichlorobenzene, and dissolved at 140 ° C. for about 8 hours. Was used.

(Strength and elastic modulus) The strength and elastic modulus were measured using Orientic "Tensilon" sample length 200
mm, the strain-stress curve was measured under the conditions of an ambient temperature of 25 ° C. and a relative humidity of 65% under the condition of an elongation rate of 100% / min. The modulus of elasticity (cN / dtex) was calculated from the tangent line giving the maximum gradient of. In addition, each value used the average value of 10 measured values.

(Intrinsic viscosity) The specific viscosities of various dilute solutions were measured using an Ubbelohde capillary viscometer with decalin at 135 ° C., and the straight line obtained by the least-square approximation of the plot of the concentration of the viscosity with respect to the concentration was measured. The intrinsic viscosity was determined from the extrapolated point. At the time of measurement, if the raw material polymer is in the form of a powder, the sample is kept in that shape, and if the powder is a lump or a fibrous sample, the sample is divided or cut into lengths of about 5 mm, and 1% by weight of the polymer is oxidized. An inhibitor (trade name "Yoshinox BHT" manufactured by Yoshitomi Pharmaceutical) was added, and 135
The solution was stirred at 4 ° C. for 4 hours to prepare a measurement solution.

Hereinafter, the present invention will be described with reference to examples.

(Example 1) Linear high-density polyethylene polymer (A) 99 polymerized with a metallocene catalyst having an intrinsic viscosity of 3.2 and a molecular weight distribution Mw / Mn of 2.5.
Parts by weight and a linear ultra-high molecular weight polyethylene polymer (B) polymerized with a conventional Ziegler-Natta catalyst and having an intrinsic viscosity of 30.5 and a molecular weight distribution Mw / Mn of about 5.6.
The powdery mixture consisting of 1 part by weight was melted and extruded with a single-screw mixing extruder. Specifically, after the above mixture is melted at a temperature of 270 ° C., a die having orifices having a diameter of 0.9 mm and 24 holes is set at 275 ° C. so that the discharge rate of each hole is 2.4 g / min. Immediately after extruding and passing through a heating zone of about 50 cm, winding was performed at a speed of 500 m / min while cooling with an air stream at room temperature. The drawn yarn was immediately stretched three times in an oven at 120 ° C., and then 4.5 in an oven adjusted to 146 ° C.
It was drawn twice to obtain a high-strength polyethylene fiber. Table 1 shows various physical properties (intrinsic viscosity, fineness, strength, elastic modulus, and maximum peak temperature by differential scanning calorimetry) of the obtained fiber.

In Example 1, excellent spinnability was exhibited without yarn breakage in spinning or the like, and the obtained fibers also had extremely high strength and elastic modulus as polyethylene obtained by melt spinning. I was

(Example 2) As the main component polymer (A), a linear high-density polyethylene polymer having an intrinsic viscosity of 8.5 and a molecular weight distribution Mw / Mn of 2.5 polymerized with a metallocene catalyst was used. As the ultra-high molecular weight polymer (B), the intrinsic viscosity polymerized with a usual Ziegler-Natta catalyst is 18.0 and its molecular weight distribution Mw / Mn
Is about 8.0, and the mixing ratio of both is 95 parts by weight of the polymer (A) and 5 parts by weight of the polymer (B).
A drawn yarn was obtained in the same manner as described above. Table 1 shows various physical properties (intrinsic viscosity, fineness, strength, elastic modulus, maximum peak temperature) of the obtained fiber. In Example 2, although the stretchability was slightly lower than that in Example 1, generally satisfactory physical properties were obtained.

Example 3 A drawn yarn was obtained in the same manner as in Example 1 except that the linear high-density polyethylene polymer of Example 2 was used as the main component polymer (A). Various properties of the obtained fiber (intrinsic viscosity, fineness, strength, elastic modulus,
The maximum peak temperature is shown in Table 1. In Example 3, although the stretchability was further reduced, a high-strength polyethylene fiber having practically high strength and heat resistance could be obtained.

(Comparative Example 1) Using the main component polymer (A) of Example 1, spinning was attempted in the same manner as in Example 1 except that the ultrahigh molecular weight polymer (B) was not added. At that time, various changes were made from the conditions of Example 1 such that the melting temperature and the spinning temperature were optimized, but in each case, significant pulsation (draw resonance) occurred in the spinning,
Let alone winding, it was also difficult to collect a sufficient thread-like sample directly below the nozzle.

(Comparative Example 2) Spinning was attempted using the main component polymer (A) of Example 2 without adding the ultrahigh molecular weight polymer (B) in the same manner as in Example 2 except for the addition. The melt viscosity of the polymer (A) was extremely high, the extrusion was very unstable, and it was difficult to obtain continuous fibers. However, although it was possible to obtain fibers for a short period of time for measuring the physical properties of the fiber as compared with Comparative Example 1, the properties were unsatisfactory as shown in Table 1 of the physical properties.

Comparative Example 3 A powder comprising the linear high-density polyethylene polymer (A) of Example 1 (80 parts by weight) and the linear ultrahigh molecular weight polyethylene polymer (B) of Example 1 (20 parts by weight) Using the above mixture, spinning and stretching were carried out in the same manner as in Example 1 except for the above. The viscosity increased significantly during spinning, and the spinning speed had to be reduced to 100 m / min. In the stretching, the film could be stretched three times in an oven at 120 ° C., but in the subsequent stretching in an oven adjusted to 146 ° C., the maximum was 2.1 times. Therefore, as shown in Table 1, the properties of the obtained fiber were not satisfactory at a low level.

(Comparative Example 4) Instead of the linear high-density polyethylene polymer (A) of Example 1, the intrinsic viscosity obtained by polymerization using an ordinary Ziegler-Natta catalyst was 3.5, and its molecular weight distribution Mw / Except for using a linear high-density polyethylene having Mn of 7.2, spinning and
Stretching was performed. The maximum spinning speed was 300 m / min, and the maximum draw ratio of the second stage was 2.5 times as in Comparative Example 3. The physical properties of the obtained fibers were also low as shown in Table 1.

[0033]

[Table 1]

[0034]

As described above, according to the present invention, high-strength polyethylene fibers having excellent strength and a high melting point can be obtained even in the melt spinning method. Therefore, the fiber can be manufactured stably without any problem, and therefore, both the performance of the fiber and the productivity (spinning speed) can be compatible. Therefore, it is possible to provide a high-strength polyethylene fiber that is suitable for various industrial uses and has excellent cost performance.

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Claims (5)

[Claims] (1) An intrinsic viscosity [η] (g / dl) in a fiber state is 2 or more and 8 or less, and a peak temperature in the highest temperature range in a heat of fusion peak obtained by differential scanning calorimetry is 140 ° C. or more. A high-strength polyethylene fiber, which is characterized in that: 2. The high-strength polyethylene fiber according to claim 1, having a tensile strength of at least 15 cN / dtex. 3. A high-strength polyethylene fiber having a tensile strength of at least 15 cN / dtex and having a peak temperature in the highest temperature range of 140 ° C. or higher in a heat of fusion peak determined by differential scanning calorimetry. 4. An intrinsic viscosity [η] (g / dl) of 3 or more, and a weight average molecular weight (Mw) and a number average molecular weight (M
n): 99.9 parts by weight to 90 parts by weight of a high molecular weight polymer (A) mainly composed of an ethylene component having a ratio (Mw / Mn) of 4 or less to the limit of the high molecular weight polymer (A) A mixture comprising 0.1 to 10 parts by weight of an ultrahigh molecular weight polymer (B) having an intrinsic viscosity of at least twice the viscosity and mainly composed of an ethylene component, which is obtained by spinning and drawing. Characterized by high strength polyethylene fiber. 5. An intrinsic viscosity [η] (g / dl) of 3 or more, and its weight average molecular weight (Mw) and number average molecular weight (M
n): 99.9 parts by weight to 90 parts by weight of a high molecular weight polymer (A) mainly composed of an ethylene component having a ratio (Mw / Mn) of 4 or less to the limit of the high molecular weight polymer (A) A mixture of 0.1 to 10 parts by weight of an ultrahigh molecular weight polymer (B) having an intrinsic viscosity of at least twice the viscosity and mainly composed of an ethylene component is melt-kneaded, and then subjected to spinning and kneading. A method for producing a high-strength polyethylene fiber, comprising drawing.