JP2000226721A - High-strength polyethylene yarn - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an extrafine high-strength polyethylene yarn having high strength/high modulus of elasticity and excellent heat resistance in spite of being extrafine yarn having <=0.6 denier. SOLUTION: This high-strength polyethylene yarn is a molecule orientated yarn consisting essentially of a high-molecular weight polyethylene which has >=5 intrinsic viscosity [η] and has a repeating unit composed of ethylene, has <=0.6 denier average fineness of its single yarn, at least two endothermic peaks at >=140 deg.C in melting obtained by differential scanning calorimeter(DSC) and >150 deg.C temperature of endothermic peaks existing at the highest temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is widely used in industrial applications such as high performance textiles such as various sports garments and bulletproof / protective garments, and various nonwoven fabrics which can be used for various filters, battery separators or reinforcing materials thereof. A possible new high strength polyethylene fiber.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Publication No. 60-47922, for example, a high-strength polyethylene fiber is made from ultra-high molecular weight polyethylene as a raw material, and a so-called "gel spinning method" is used to obtain an unprecedented high-strength and high-elasticity. It is known that high modulus fibers can be obtained, and is already widely used in industry. These high strength polyethylene fibers have high strength
Contrary to the advantage of a high elastic modulus, there are cases in which the high elastic modulus of the fiber causes troubles in various applications due to disaster. For example, when a high-strength polyethylene fiber is used as an ordinary fabric, the texture is very hard, and it is extremely unsuitable from the viewpoint of comfortable wearing. Also, when high-strength polyethylene fibers are used for bulletproof vests, it is necessary to increase the number of layers of the woven fabric in order to improve a very high target threat in recent years, and as a result, the thickness of the fabric increases and the mobility decreases. Therefore, a very strong fiber having a low basis weight has been desired. Further, in recent years, various olefin-based fibers and films have been used for various battery separators, but in the case where high-strength polyethylene fibers are used as the nonwoven fabric or the reinforcing material, in response to a demand for a more compact battery, There has been a demand for a high-strength polyethylene fiber capable of producing a thin nonwoven fabric while maintaining high strength.

[0003]

The most effective means for responding to these wide-ranging demands is to reduce the fineness of a single fiber while maintaining the strength of the fiber. However, the yarn obtained by the above-described gel spinning method usually has an average single fiber fineness of 1 denier to 10 denier, and for example, low density of 0.8 denier as well as 0.6 denier or less as in the present invention. Even if yarns of fineness can be obtained very instantaneously, it is practically impossible to obtain them with sufficient productivity that can be carried out industrially. Physical properties were remarkably deteriorated and were not practically usable.

[0004] The inventors presume the cause as follows. In other words, in the gel spinning method for producing fibers using a raw material having an extremely high intrinsic viscosity, it is necessary to stretch the molecular chains to the limit in order to obtain high-strength fibers. Requires a very high tensile stress in the spinning and drawing steps, and the solution discharged by spinning and the intermediate drawn yarn in the middle must withstand the stress without breaking. Decreasing the denier means that the cross-sectional area of the solution or the fiber is reduced, and it is not possible to withstand a high tension sufficient for drawing, and as a result, the solution / filament breaks.
The present inventors have studied diligently and succeeded in obtaining a very low-denier and high-strength polyethylene fiber, which was difficult to obtain by such a method as the conventional gel spinning method, and reached the present invention. .

[0005]

That is, the present invention provides a high-molecular-weight polyethylene having an intrinsic viscosity [η] of 5 or more, preferably 8 or more, more preferably 10 or more, and whose repeating unit is mainly composed of ethylene. The average fiber size of the single fiber is 0.6 denier or less, and the endothermic peak at the time of melting determined by a differential scanning calorimeter (DSC) is 140 ° C. or more,
And the peak temperature at the highest temperature is 15
A high-strength polyethylene fiber characterized by exceeding 0 ° C. is provided. The present invention also provides a high-strength polyethylene fiber characterized in that the fiber is a substantially homopolymer containing 0.2 mol% or less of a copolymer component other than ethylene contained in the fiber. The present invention will be described below.

In the present invention, it is important that the average denier of the single fiber of the high-strength polyethylene fiber is 0.6 denier or less, and it is preferably 0.05 to 0.3 denier. If it exceeds 0.6 denier, the effect of reducing the fiber denier becomes smaller than that of the existing single fiber denier of 1 denier. For example, it has been experimentally found that there is a critical point in the sensory evaluation of the degree of flexibility of the fabric with respect to the rigidity of the fabric at around 0.6 denier. On the other hand, if it exceeds 0.6 denier, the effect of reducing the thickness of the nonwoven fabric is not sufficient.

As described above, the fiber of the present invention has an extremely low average denier, but according to the conventional knowledge, the fiber properties are extremely low. However, for example, by adopting a manufacturing method described later, it is possible to obtain a fiber having a strength and an elastic modulus equivalent to those of a conventional fiber, despite being a fine denier. The fiber of the present invention has a strength of 20 g / d or more and an elastic modulus of 800 g / d or more.

[0008] The fibers having an extremely small average denier of the single fibers according to the present invention show not only fineness but also structurally very unique characteristics as compared with conventional high-strength polyethylene fibers. The first characteristic of the fiber of the present invention is that the fiber has at least two endothermic peaks upon melting determined by a differential scanning calorimeter (DSC), and the temperature of the peak at the highest temperature exceeds 150 ° C. For example, JP-A-63-2
Japanese Patent No. 75708 discloses that a high strength polyethylene fiber is obtained by using a special raw material such as copolymerization of α-olefin other than ethylene, and the fiber is wrapped around an aluminum pan or the like. There is a technical disclosure that a peak appears at a high temperature when measured, and a plurality of endothermic peaks are observed, but when such a fiber is subjected to DSC measurement under tension restraint, an increase in melting point or, in some cases, crystal transition or the like is caused. The occurrence of a plurality of peaks is well known and is a known finding. The present invention is a high-strength polyethylene fiber composed of a homopolymer having substantially only ethylene units. In the DSC measurement method of the present invention described later, the fiber is once cut to about 5 mm and measured in an unrestricted state. Even in such a case, a high-strength polyethylene fiber having a plurality of melting peaks at such a high temperature,
Not previously known. Such a high melting point peak suggests that there is a so-called extended chain crystal structure, which is different from ordinary polyethylene crystals, as a reason why there are multiple melting peaks in the high temperature region even in the unconstrained state. It is estimated that you are. Such a structure in which many extended chain crystals are present will support the tension in the spinning process, which will be described later, and will not break the fiber even with a very fine fineness, and will be sufficient to stretch the molecule sufficiently. It is estimated that this corresponds to the ability to transmit the stress.

As described above, the method for producing the present fiber requires a careful and novel production method. For example, the following method is recommended, but is not limited thereto. That is, in producing the present fiber, the intrinsic viscosity [η] of the high-molecular-weight polyethylene used as the raw material must be 5 or more, preferably 8 or more, and more preferably 10 or more. Not only is it not possible to obtain a high-strength fiber having an intrinsic viscosity of less than 5 but more than 20 g / d, which is originally desired, and it is difficult to obtain a fiber having a denier of 0.6 or less.

If the intrinsic viscosity is less than 5, the molecular chains slip through each other at the spinning stage, and the tension cannot be transmitted between the molecular chains by spinning, so that a high-strength fiber cannot be obtained. In the present invention, the main component of the polymer is an ethylene component of 99.5 mol% or more, preferably 99.8 mol%.
It is important that the polyethylene is a homopolymer of substantially 1% or more. It is recommended that ethylene be used as a 100 mol% raw material except for the branches or terminals formed by adding a small amount or for forming a side reaction for the purpose of improving the polymerization rate or the like. As the copolymerization component such as α-olefin increases, although the cause is not clear, the strength of the solution during spinning (spinning stress leading to breakage) decreases, and even at the same intrinsic viscosity, breakage occurs by spinning at a low stress.

In the production method recommended by the present invention, such high molecular weight polyethylene is uniformly dissolved using a volatile solvent such as decalin / tetralin or a non-volatile solvent such as paraffin or solid paraffin. Dope can be obtained. At this time, the concentration is preferably 50% or less, more preferably 30% or less. It is important to mention that the solution is a volatile solvent. A room temperature solid or a non-volatile solvent has a limit of substantially around 3 denier, and a single fiber having a low fineness of 0.6 denier or less cannot be obtained. The reason is that by using a volatile solvent, the solvent on the surface evaporates more positively in the spinning stage. This is presumed to form a so-called skin layer having a high concentration and a more oriented molecular chain on the fiber surface. In the common sense of the conventional spinning technology, such a skin-core structure causes a decrease in fiber strength,
It is a common knowledge of those skilled in the art of dry spinning or wet spinning of not only gel spinning but also polyvinyl alcohol and polyacrylonitrile, as well as gel spinning, to avoid uneven structures in the cross-sectional direction such as skin core structure as much as possible. Met.

Contrary to this common knowledge, the present inventors have rather positively formed a skin core structure at the spinning stage, and used the generated skin layer to propagate the spinning stress, thereby making the fiber yarn very thin. Nevertheless, they have found that they can withstand sufficient drawing tension in spinning and drawing necessary to obtain high-strength fibers, and have reached the present invention.

That is, although the plurality of endothermic peaks and their values at high temperatures in the DSC measurement of the fiber of the present invention are thought to correspond to these extended chains mainly present in the skin layer, it is uncertain. However, the unique structure such as the fiber of the present invention or the obtained thermal property is not only that the fineness of the single fiber of the fiber of the present invention is low, but also that it has excellent heat resistance and special rigidity of the surface. It is expected that the impact propagation speed will be improved by this, and by laminating it, it is possible to realize a bulletproof vest with light weight and improved shock absorption as a fiber with new characteristics such as application in various industrial fields Can be expected. In particular, in the field of battery separators and their reinforcing materials where chemical resistance is required, the better the crystallinity of the fiber surface, the better their chemical durability will give better results,
It goes without saying that the very thin fibers have the advantage of making the whole product compact.

Therefore, when producing the present fiber, first,
It is important to design a nozzle that extrudes the fibers uniformly. The diameter of the nozzle port is 0.5 mm or less, more preferably 0.3 mm or less.
mm or less is recommended. In this patent, the most important factor is to forcibly supply a high-temperature inert gas to the discharged solution coming out under the nozzle and to actively evaporate the solvent on the surface of the yarn. This allows a thin skin layer to be formed on the surface, withstands the tensile strength of spinning, and provides smooth molecular orientation by stretching. It is recommended that the temperature at this time be 60 ° C. or higher, preferably 80 ° C. or higher, and more preferably 100 ° C. or higher. On this occasion,
It is recommended to use an inert gas such as nitrogen as the gas.

The fiber thus obtained may be stretched several times while evaporating the remaining solvent after being heated again, and may be stretched in multiple stages in some cases. The heat resistance derived from the skin-core structure once formed by spinning does not disappear in the subsequent drawing, and a novel fiber having the above-mentioned extremely excellent properties can be obtained.

The measurement method and measurement conditions relating to characteristic values in the present invention will be described below.

(Strength and Elastic Modulus) The strength and elastic modulus in the present invention were measured using "Tensilon" manufactured by Orientic.
Sample length 200 mm (length between chucks), extension speed 100
The strain-stress curve is measured under the conditions of an ambient temperature of 20 ° C. and a relative humidity of 65% under the conditions of% / min, and the stress at the break point of the curve is given by the strength (g / d) and the maximum gradient near the origin of the curve The elastic modulus (g / d) was calculated from the tangent line. In addition, each value used the average value of 10 measured values.

(Intrinsic Viscosity) The specific viscosities of various diluted solutions were measured with decalin at 135 ° C. using an Ubbelohde type capillary viscometer, and the straight line obtained by the least-square approximation of a plot of the concentration of the viscosity was determined. The intrinsic viscosity was determined from the extrapolated point. When measuring, the sample is divided or cut into a length of about 5 mm, and 1 wt% based on the polymer.
(Trade name "Yoshinox BHT" manufactured by Yoshitomi Pharmaceutical Co., Ltd.) was added and dissolved by stirring at 135 ° C. for 4 hours to prepare a measurement solution.

(Differential Scanning Calorimeter Measurement) For differential scanning calorimeter measurement, "DSC7" manufactured by PerkinElmer Co. was used. 5 in advance
The sample (fiber) cut to less than 5 mm
mg and sealed, and the same empty aluminum pan was used as a reference at a rate of 5 ° C./min.
The temperature was raised to 00 ° C., and the endothermic peak was determined. From the obtained curve, the number of melting peaks and the temperature of the highest peak were determined.

[0020]

The present invention will be described below with reference to examples. (Example 1) A screw type set to a temperature of 230 ° C while dispersing a slurry-like mixture of 10 wt% of a main component polymer (C) of an ultrahigh molecular weight polymer having an intrinsic viscosity of 20.1 and 90 wt% of decahydronaphthalene. Melted with a kneading machine, and 0.2 mm in diameter set at 170 ° C.
A single hole discharge rate of 0.0 with a lightweight pump in a base with 0 holes
8 g / min was fed. 100m at a high speed of 1.2m / min with a slit-shaped gas supply orifice installed just below the nozzle.
Careful to the rectification of the nitrogen gas adjusted to ℃, the decalin on the fiber surface was positively evaporated by hitting the yarn as evenly as possible, and then immediately cooled by the air flow set at 30 ℃ The solvent was taken up at a speed of 50 m / min by a Nelson-shaped roller provided downstream of the nozzle. At this time, the amount of the solvent contained in the thread was reduced to about half of the original weight. Subsequently, the obtained fiber was drawn three times in a heating oven at 100 ° C.
The film was stretched 4.6 times in a heating oven set at a temperature of ° C.
Uniform fibers could be obtained without breakage in the middle. The average fineness of the single fibers was 0.11, and thus the total fineness of the fibers was 220 denier. Table 1 shows the physical property values of the obtained fibers. It was found to have very high strength and high melting temperature by DSC.

(Example 2) Spinning was carried out in the same manner as in Example 1, except that a polymer having an intrinsic viscosity of 10 was used as the main component polymer and the viscosity of the solution was 30%.
In the first-stage stretching, three-fold stretching was possible, and in the second-stage stretching, the limit was 2.5 times. Table 2 shows the results.
The drawn yarn had a single fiber degree of 0.57 denier and an overall fiber degree of 1150 denier. The fiber degree was high and the strength was slightly reduced. In addition, the measurement result of DSC is shown in FIG.

(Comparative Example 1) In the experiment of Example 1, the application of hot air at the gas slit immediately below the nozzle was stopped, and cooling was immediately performed with nitrogen gas at 30 ° C. Spinning is 20m /
Min is the maximum, and the subsequent stretching is also 2.0 times in one-step stretching,
The maximum of the two-stage stretching was 2.2 times. The physical properties thus obtained are shown in Table 1, and the degree of single fiber is 0.82 denier, which is the desired 0.1%.
Ultrafine fibers of 6 denier or less could not be obtained.

(Comparative Example 2) The same operation was carried out using an ultrahigh molecular weight polyethylene obtained by copolymerizing the polymer of Example 1 with an intrinsic viscosity of 20.1 and copolymerizing 1 mol% of a propylene monomer. Under the same conditions, yarn breakage during spinning frequently occurred, and satisfactory spun yarn could not be obtained.

[0024]

[Table 1]

[0025]

According to the present invention, it is possible to provide a novel ultra-fine high-strength polyethylene fiber which has a high strength and a high elastic modulus while being ultra-fine at 0.6 denier or less and has excellent heat resistance.

Claims (5)

[Claims] 1. A molecular oriented fiber having a limiting viscosity [η] of 5 or more whose main repeating unit is a high molecular weight polyethylene composed of ethylene, wherein the average fineness of a single fiber is 0.6 denier or less. An endothermic peak upon melting determined by a differential scanning calorimeter (DSC) is at least 2 at 140 ° C or higher.
A high-strength polyethylene fiber which is present and has a temperature of an endothermic peak at the highest temperature exceeding 150 ° C. 2. The high-strength polyethylene fiber according to claim 1, wherein the molecular oriented fiber has a strength of 20 g / d or more and an elastic modulus of 800 g / d or more. 3. The molecularly oriented fiber has an ethylene component of 99.5 m.
2. The high-strength polyethylene fiber according to claim 1, wherein the high-strength polyethylene fiber is made of a substantially homopolymer that is at least ol% of high molecular weight polyethylene. 4. The high-strength polyethylene fiber according to claim 1, wherein the intrinsic viscosity [η] of the molecularly oriented fiber is 10 or more. 5. An average fineness of a single fiber of the molecular orientation fiber is 0.3.
The high-strength polyethylene fiber according to claim 1, wherein the fiber is denier or less.