JP4524644B2 - Method for producing high-strength polyethylene fiber - Google Patents

Description

The present invention relates to various sports clothing, high-performance textiles such as bulletproof / protective clothing / protective gloves and various safety goods, various rope products such as tag ropes, mooring ropes, yacht ropes, construction ropes, various braids such as fishing lines and blind cables. Products, net products such as fishing nets and ball-proof nets, reinforcement materials such as chemical filters and battery separators, various non-woven fabrics, curtain materials such as tents, sports such as helmets and skis, speaker cones, prepregs, concrete The present invention relates to a method for producing a novel high-strength polyethylene fiber applicable to a wide range of industries such as a reinforcing fiber for composites such as reinforcement . More specifically, the present invention relates to a method for producing a high-strength polyethylene fiber having a small variation in single yarn strength.

With regard to high-strength polyethylene fibers, it is known that ultra-high molecular weight polyethylene is used as a raw material, and so-called “gel spinning” can produce unprecedented high-strength and high-modulus fibers, which are already widely used in industry. (For example, Patent Document 1 and Patent Document 2).
Japanese Patent Publication No. 60-47922 Japanese Patent Publication No. 64-8732

  In recent years, the use of high-strength polyethylene fibers is expanding not only in the above-mentioned applications but also in a wide range of fields, and there is a strong demand not only for higher strength and higher elastic modulus, but also for homogenization of the yarn properties.

An effective means to satisfy these broad requirements is to minimize the number of defects present in the interior of the fiber. In addition, the filaments constituting the fibers are uniform. In the conventional gel spinning method, the internal defect structure has not been suppressed to a sufficiently low level. Further, the variation in the strength of each filament constituting the fiber was also large. The present inventors consider these causes as follows.

  When using the conventional method called gel spinning, super-stretching operation is possible and high strength and high elastic modulus are achieved, and the resulting fiber structure is observed with a long-period structure in small-angle X-ray scattering measurement. Although it crystallizes and orders so highly that it does not occur, as will be described in detail later, a defect structure that cannot be erased by any means is generated, so when this agglomeration gives stress to the fiber, a large stress is generated inside the fiber. There was a problem that the distribution was attracted. The fiber skin core structure is considered to be one of the defect structures.

  The inventors have found that it is most important to keep the monoclinic-derived crystal size low in order to bring the knot strength to a good state. The reason is not clear, but when the X-ray diffraction of the resulting polyethylene fiber is taken, the diffraction point derived from the orthorhombic crystal system is the main, but some peaks derived from monoclinic diffraction can be confirmed. As a result of this study, it was found that it is important to keep the crystal size derived from monoclinic diffraction below a certain level. The reason for this is not exactly clear, but I understand that it is roughly as follows. That is, when stretched from the state of the xerogel without the solvent, it was found that the size of the monoclinic-derived crystal grows relatively large, probably because there are few solvent molecules that inhibit the growth of the monoclinic crystal. When the monoclinic crystal grows to a size larger than a certain limit, stress concentration occurs between the monoclinic-derived crystal and the orthorhombic-derived crystal when the fiber is deformed, which can be a starting point for fracture. . As a result, it is disadvantageous from the viewpoint of nodule strength, which is not preferable.

  Next, the inventors have found that there is a correlation between the knot strength and the fine crystal size constituting the fiber, the orientation, and the variation of these structural parameters at each part of the fiber. In order to improve the knot strength, the ideal state is that the fiber can be bent flexibly and arbitrarily regardless of whether it is viewed microscopically or macroscopically. At this time, it is necessary to suppress the possibility of destruction of the fiber microstructure due to the bending as low as possible. At this time, the crystal orientation and crystal size of the fiber must be as high and large as possible. At the same time, if the fiber is too large and too high, the contrast (contrast) with the remaining amorphous region is too high, resulting in poor knot strength. Furthermore, the inventors have found that it is important to make the crystal size and orientation at each part of the fiber approximately the same. This is because if there is structural non-uniformity in the crystal size and orientation between each part of the microstructure, especially between adjacent parts, stress concentration occurs starting from the non-uniform part when deformation is applied. As a result, the nodule strength is reduced.

  The stress distribution generated in the structure can be measured, for example, using the Raman scattering method as shown by Young et al. (Journal of Materials Science, 29, 510 (1994)). The Raman band, that is, the reference vibration position, is determined by solving an equation composed of the force constant of the molecular chain constituting the fiber and the shape of the molecule (internal coordinates) (E. B. Wilson, J. C. Decius). , PC Cross, Molecular Vibrations, Dover Publications (1980), as a theoretical explanation of this phenomenon, for example, as given by Wool et al. (Macromolecules, 16, 1907 (1983)).

  When structural non-uniformity such as defect aggregation exists, the stress generated by the site in the fiber differs when external strain is applied. This change can be detected as a change in the band profile. Conversely, when stress is applied to the fiber, the stress distribution induced in the fiber can be quantified by examining the relationship between the strength and the change in the Raman band profile. Become. That is, the fiber having a small structure non-uniformity takes a value in a region having a Raman shift factor, as will be described later.

  In addition to the above, the high-strength polyethylene fiber by the “gel spinning method” disclosed so far, because of its highly oriented structure, the tensile strength is very strong, but when the fiber is bent like the knot strength, There was a drawback that it was easily broken at low stress. Furthermore, if a non-uniform structure exists in the fiber in the cross-sectional direction of the fiber, such as a skin core structure, the fiber is more easily broken in a bent state. The inventors have intensively studied and found that a small fiber having a non-uniform structure is strong in a pulled state in a bent state. That is, it has been found that fibers having a small structural non-uniformity have a higher ratio of knot strength to tensile strength.

  The disadvantages of the high-strength polyethylene fibers by the “gel spinning method” disclosed so far are that the strength between single yarn fibers depends on the state after spinning through the nozzle holes, compared to the fibers obtained by the ordinary melt spinning method. This will cause unevenness. For this reason, there is a problem that a single yarn having a significantly lower strength than the average fineness of the yarn exists. When a single fiber having a strength lower than the average strength is present in the fiber, for example, when the fiber is subjected to friction. In particular, when this fiber is used for fishing lines, ropes, bulletproofs, protective clothing, etc., if thick unevenness exists, stress concentrates in the thin part and breaks. In addition, in the manufacturing process, it causes a process trouble due to single yarn breakage, and adversely affects productivity.

It is an object of the present invention to provide a method for producing a high-strength polyethylene fiber that is excellent in uniformity with less variation in strength between single yarns, in which these problems are improved.

1. Spinning process in which high-molecular-weight polyethylene having an intrinsic viscosity of 5 or more is dissolved using a volatile organic solvent, the solution discharged from the spinneret is cooled, and the resulting undrawn yarn is heated to remove the solvent. A method for producing a high-strength polyethylene fiber comprising a stretching step of stretching while
In the spinning step, a high-strength polyethylene fiber having a monoclinic-derived crystal size of 8 nm or less is produced using the cooling means (1) below.
(1) Discharge using a cooling medium at a cooling rate of 1000 ° C./s or more and so that the difference in speed between the cooling medium and the gel yarn is 30 m / min or less as a cumulative speed difference defined by the following formula. Cooling the gel yarn uniformly Cumulative speed difference = ∫ (Thread speed-Cooling medium speed in the thread take-up direction)
2. The high-strength polyethylene fiber according to the above 1, wherein the cooling medium of (1) is used to cover the gas medium space that travels until the discharged gel yarn discharged from the spinneret contacts the cooling medium. Production method.
3. Using the cooling means of (1) , (a) a method in which a funnel is attached to the center of a cylindrical bath and the liquid and the gel yarn are drawn simultaneously, or (b) the gel yarn is placed along the falling liquid like a waterfall. The method for producing a high-strength polyethylene fiber as described in 1 above, wherein any one of the methods for simultaneously drawing is used.
4). 3. The method for producing high-strength polyethylene fiber as described in 2 above, wherein the member is made of a material having a heat insulating structure.
5). 5. The method for producing high-strength polyethylene fibers according to any one of 1 to 4, wherein the cooling medium is a liquid and the liquid level fluctuation is 1 mm or less.
6). 2. The method for producing a high-strength polyethylene fiber as described in 1 above, wherein the following (2) is further used as a cooling means .
(2) In the spinning process, within the range of plus or minus 10 ℃ relative to the nozzle temperature.
Controlled inert gas within 1 m / s independently for each of the discharge solutions
Supply at a speed to cool the yarn uniformly.
7). 7. The method for producing high-strength polyethylene fiber according to any one of 1 to 6, wherein the high-strength polyethylene fiber is a multifilament.
8). 8. The method for producing high-strength polyethylene fibers according to any one of 1 to 7, wherein the high-strength polyethylene fibers have an average strength of 20 cN / dTex or more.
9. 9. The high-strength polyethylene fiber as described in 7 or 8 above, wherein the monofilament constituting the high-strength polyethylene fiber has a breaking elongation of 2.5% to 6.0%.
10. 10. The method for producing high-strength polyethylene fiber according to any one of 7 to 9, wherein the knot strength retention of the monofilament constituting the high-strength polyethylene fiber is 40% or more. "

  To provide a uniform high-strength polyethylene fiber with a minimum of defects existing inside the fiber that has not been suppressed to a sufficiently low level in the conventional gel spinning method and a small variation in the strength of the filaments constituting the multifilament. Made possible.

Hereinafter, the present invention will be described in detail.
Regarding the method for obtaining the fiber according to the present invention, a new method is required. For example, the following method is recommended, but the method is not limited thereto. That is, in the production of this fiber, the intrinsic viscosity [η] of the high molecular weight polyethylene used as the raw material needs to be 5 or more, preferably 8 or more, more preferably 10 or more. . When the intrinsic viscosity is less than 5, a high-strength fiber having a desired strength exceeding 20 cN / dtex may not be obtained. On the other hand, the intrinsic viscosity [η] of polyethylene is desirably 35 or less, more preferably 30 or less, and further preferably 25 or less. If the intrinsic viscosity is too high, processability is lowered and fiberization becomes difficult.

  The ultra high molecular weight polyethylene in the present invention is characterized in that the repeating unit is substantially ethylene, and a small amount of other monomers such as α-olefin, acrylic acid and its derivatives, methacrylic acid and its derivatives, vinylsilane and its It may be a copolymer with a derivative or the like, or may be a copolymer with these copolymers, a copolymer with an ethylene homopolymer, or a homopolymer such as another α-olefin. . In particular, the use of α-olefins such as propylene and butene-1 and a copolymer to add some short-chain or long-chain branching provides stability in spinning, especially in spinning and drawing, in producing this fiber. This is more preferable. However, if the content other than ethylene is excessively increased, it becomes an obstructive factor for stretching. Therefore, from the viewpoint of obtaining a high-strength and high-modulus fiber, other monomers such as α-olefin are 0.2 mol% or less in monomer units. Preferably, the content is 0.1 mol% or less. Of course, it may be a homopolymer of ethylene alone.

  In the production method recommended by the present invention, it is preferable to dissolve such a high molecular weight polyethylene using a volatile organic solvent such as decalin or tetralin. With a room-temperature solid or non-volatile solvent, the spinning productivity is very poor. The reason for this is that by using a volatile solvent, the solvent present on the surface of the gel yarn after being discharged from the spinneret slightly evaporates in the initial stage of spinning. It is estimated that the spinning state is stabilized by the cooling effect due to the latent heat of evaporation accompanying the evaporation of the solvent at this time. The concentration at the time of dissolution is preferably 30 wt% or less, more preferably 20 wt% or less. There is a need to select an optimum concentration according to the intrinsic viscosity [η] of the raw ultrahigh molecular weight polyethylene. Further, in the spinning stage, the spinneret temperature is preferably 30 ° C. or more from the melting point of polyethylene and below the boiling point of the solvent used. In the temperature range near the melting point of polyethylene, the viscosity of the polymer is too high and cannot be taken up at a rapid rate. Further, a temperature higher than the boiling point of the solvent to be used is not preferable because the solvent boils immediately after leaving the spinneret, and yarn breakage frequently occurs immediately below the spinneret.

  The mixed dope used can be prepared by various methods, for example, by suspending solid polyethylene in a solvent and then stirring at a high temperature, or by using a twin screw extruder equipped with a mixing and conveying unit. It can be manufactured by using.

  In the method of the present invention, the mixed dope is formed into a dope filament through a spinneret in which a plurality of orifices are arranged. The temperature during conversion to the dope filament must be selected above the melting point. This melting point will of course depend on the solvent chosen, the concentration and the wt% of the polyethylene, and is preferably at least 140 ° C. or higher, preferably at least 150 ° C. or higher. Of course, this temperature is selected below the decomposition temperature of the polyethylene.

Factors important in the method for producing uniform fibers of the present invention will be described. The first factor is to supply a pre-rectified high-temperature inert gas independently to each of the discharge solutions discharged from the orifices under the nozzle. At this time, the speed of the inert gas supplied is preferably within 1 m / s. When it is 1 m / s or more, the solvent evaporation rate is increased, and a non-uniform structure can be formed in the yarn cross-sectional direction. Furthermore, the fiber may break.
Further, it is desirable that the maximum value of the velocity difference of the gas for cooling each single filament of the dope filament is at least 0.5 m / second or less, preferably at least 0.3 m / second. If it is 0.5 m / second or more, the solvent evaporation rate unevenness between the single yarns becomes large, so that the structure non-uniformity between the dope filaments may become remarkable.

In the method of the present invention, the temperature of the inert gas is within a range of plus or minus 15 degrees, preferably within plus or minus 10 degrees, more preferably within plus or minus 5 degrees with respect to the nozzle temperature. When the temperature difference is large, the temperature gradient in the single yarn cross-sectional direction becomes large, and there is a possibility that a non-uniform structure can be formed in the single yarn cross-sectional direction.
Further, by supplying an inert gas independently to each discharge yarn shape, the cooling state of each yarn shape becomes uniform, and an undrawn yarn having a uniform structure is obtained. By uniformly stretching the unstretched yarn having this uniform structure, it is possible to obtain a desired uniform high-strength polyethylene fiber.

The second factor is the rapid and uniform cooling of the discharged gel yarn discharged from the spinneret and the speed difference between the cooling medium and the gel yarn. The cooling rate is preferably 1000 degrees / s or more, more preferably 3000 degrees / s or more. Regarding the speed difference, it is preferable that the integrated value of the speed difference (integrated with the time after discharge from the die), that is, the cumulative speed difference is 30 m / min or less. More preferably, it is 15 m / min or less. As described above, an undrawn yarn having excellent uniformity can be obtained. Here, the accumulated speed difference can be calculated as follows.
Cumulative speed difference = ∫ (thread speed-speed of cooling medium in the thread take-up direction)

Thus, it becomes possible to manufacture an undrawn yarn with a uniform fiber cross-sectional direction by rapidly and uniformly cooling. When the cooling rate of the discharge thread is slow, a non-uniform state occurs in the internal structure of the fiber. In the case of multifilaments, non-uniformity among the filaments increases when the cooling state of each filament is different. Further, if the speed difference between the take-off yarn shape and the cooling medium is large, it becomes difficult to take up at a sufficient spinning speed due to the frictional force acting between the take-up yarn shape and the cooling medium.
In order to obtain such a cooling rate, it is recommended to use a liquid having a large heat transfer coefficient as a cooling medium. Among these, a liquid that is incompatible with the solvent to be used is preferable. For example, water is recommended for simplicity.

  In order to reduce the accumulated speed difference, the following method can be considered, but the present invention is not limited thereto. For example, a method in which a funnel is attached to the center of a cylindrical bath and the liquid and the gel yarn are drawn simultaneously, or the gel yarn is taken along the falling liquid like a waterfall at the same time is recommended. By using such a method, it is possible to reduce the cumulative speed difference as compared with the case where the gel yarn is cooled using a stationary liquid.

  The third factor is that the gas medium space that travels until the discharged gel yarn discharged from the spinneret comes into contact with the cooling medium is covered with a member. When the gas medium space is not shielded from the external space, the discharge gel filament cooling rate and the solvent evaporation rate from the discharge gel filament fluctuate for each monofilament in the gas medium space due to fluctuations in the temperature and wind speed of the external space. However, the structure between the monofilaments becomes non-uniform. Furthermore, the monofilament may break. It is recommended that the member has a heat insulating structure. For example, heat-resistant glass is recommended so that the state of the discharged gel yarn can be visually recognized. When it is not necessary to visually recognize the state of the discharged gel yarn, a metal member having a double structure through a substantially vacuum part may be used.

  When a liquid is used as the cooling medium, the liquid level fluctuation must be 1 mm or less. When the liquid level fluctuation exceeds 1 mm, the fluctuation of the passage time of the gas medium space between the longitudinal direction of the monofilaments and between the monofilaments becomes remarkable, and the nonuniform structure of the monofilament becomes remarkable in the longitudinal direction and between the filaments. In particular, when the liquid level fluctuation is severe, the monofilament breaks in the gas medium space.

  When a liquid that is incompatible with the solvent and has a higher specific gravity than the solvent is used as the cooling medium, the solvent volatilized from the discharged gel filaments liquefies while passing through the gas medium, and the upper layer of the cooling medium over time To accumulate. It is necessary to continuously remove the accumulated solvent from the portion where the gel filament enters the cooling medium. When the accumulated solvent is not removed, the thickness of the solvent layer accumulated at the gel thread entry increases with time, and the gel threads are fused. When the gel yarns are severely fused, the yarn physical properties are remarkably lowered.

The obtained unstretched yarn is further heated and stretched several times while removing the solvent, and in some cases, it is possible to produce a high-strength polyethylene fiber excellent in the uniformity of the internal structure described above. Become. At this time, the deformation speed of the fiber at the time of drawing is raised as an important parameter. If the deformation rate of the fiber is too high, the fiber breaks before reaching a sufficient draw ratio, which is not preferable. On the other hand, if the deformation rate of the fiber is too slow, the molecular chain is relaxed during stretching, and the fiber becomes thin by stretching, but a fiber having high physical properties cannot be obtained. Preferably, preferably 0.005 s ^-1 or 0.5 s ^-1 or less at a deformation rate. More preferably, at 0.01s ^-1 or 0.1s ^-1 or less. The deformation rate can be calculated from the draw ratio of the fiber, the draw rate, and the heating section length of the oven. That is, deformation rate (s ⁻¹ ) = (1-1 / stretching ratio) stretching speed / length of heating section. In order to obtain a fiber having a desired strength, it is recommended that the draw ratio of the fiber is 10 times or more, preferably 12 times or more, and more preferably 15 times or more.

  The crystal size derived from the monoclinic is desirably 8 nm or less, and more desirably 7 nm or less. When the crystal size is larger than 8 nm, when the fiber is deformed, stress concentration occurs between the monoclinic-derived microcrystals and the orthorhombic-derived microcrystals, which may be a starting point of fracture.

In the present invention, the ratio of the crystal size derived from the ortholonevic crystal (200) and the (020) diffraction plane of the high-strength polyethylene fiber is preferably 0.85 or more and 1.15 or less, more preferably 0.9 or more and 1. 1 or less. Here, the ratio of the crystal size derived from the orthorhombic crystal (200) and the (020) diffraction plane is the crystal size corresponding to the length in the direction perpendicular to the (200) plane and the length in the direction perpendicular to the (020) plane. This means that the crystal size is equivalent.
When the crystal size ratio is less than 0.85 or greater than 1.15, when considering the shape of the crystal, it becomes a form selectively grown in one axial direction, so when the fiber is deformed, It is considered that collisions occur between the microcrystals existing around, leading to stress concentration and structural destruction.

The stress Raman shift factor of the high-strength polyethylene fiber in the present invention is preferably −4.5 cm ⁻¹ / (cN / dTex) or more, more preferably −4.0 cm ⁻¹ / (cN / dTex) or more. . When the stress Raman shift factor is less than −4.5 cm ⁻¹ / (cN / dTex), the existence of a stress distribution due to stress concentration is suggested.

  The average strength of the high-strength polyethylene fiber in the present invention is preferably 20 cN / dTex or more, more preferably 22 cN / dTex or more, and particularly preferably 24 cN / dTex or more. When the average strength is less than 20 cN / dTex, when an application product is created, the strength as the product may be insufficient.

  In the present invention, the knot strength retention of the monofilament constituting the high-strength polyethylene fiber is desirably 40% or more, more desirably 43%, and particularly desirably 45% or more. When the retention rate of knot strength is less than 40%, the yarn may be damaged during the process when an application product is produced.

  The CV showing the variation in the single yarn strength of the monofilaments constituting the high-strength polyethylene fiber in the present invention is preferably 25% or less, more preferably 23% or less, and particularly preferably 21% or less. When the CV indicating the variation in the single yarn strength is greater than 25%, when the application product is produced, the variation in strength as the product may occur, which is not desirable.

  The breaking elongation of the monofilament constituting the high-strength polyethylene fiber in the present invention is preferably 2.5% or more and 6.0% or less, more preferably 3.0% or more and 5.5% or less, and particularly preferably. Is 3.5% or more and 5.0% or less. When the elongation at break is less than 2.5%, it is not desirable because it leads to a decrease in operability due to breakage of the single yarn of the fiber during the manufacturing process. When the elongation at break exceeds 6.0%, the effect of permanent deformation cannot be ignored when used as a product, which is not desirable.

  The monofilament fineness of the monofilament constituting the high-strength polyethylene fiber in the present invention is desirably 10 dTex or less, more desirably 8 dTex or less, and particularly desirably 6 dTex or less. If the single yarn fineness is 10 dTex or more, it may be difficult to improve the product performance to the desired mechanical properties in the fiber production process. The single yarn fineness is desirably small, but if it is too thin, fluff is liable to stand, and it is desirably 0.1 dTex or more.

  The melting point of the high-strength polyethylene fiber in the present invention is preferably 145 ° C. or higher, more preferably 148 ° C. or higher. When the melting point of the fiber is 145 ° C. or higher, the fiber can withstand higher temperatures in a process that requires heating, which is desirable from the viewpoint of labor saving in processing.

  Hereinafter, measurement methods and measurement conditions relating to characteristic values in the present invention will be described.

(Strength / elongation / elastic modulus of multifilament)
For the strength and elastic modulus in the present invention, “Tensilon” manufactured by Orientic Co., Ltd. was used, and the strain-stress curve was set at an ambient temperature of 20 ° C. and relative humidity under the conditions of a sample length of 200 mm (length between chucks) and an elongation rate of 100% / min Measured under 65% condition, and calculate the elastic modulus (cN / dTex) from the tangent that gives the maximum gradient near the origin of the curve, strength (cN / dTex), elongation (%) from the stress and elongation at the breaking point. Asked. In addition, each value used the average value of 10 times of measured values.

(Strength of single fiber)
As for the strength and elastic modulus of the filament (single fiber), ten single yarns (filaments) were randomly extracted from one multifilament to be measured. When the number of filaments was less than 10, all single yarns (filaments) were measured.
In the measurement, about 2 m of each single fiber was taken out, 1 m of the fiber was used, the weight was measured, and the fineness (dTex) was converted into 10,000 m. When measuring the length of this single yarn fiber 1 m, a constant length sample was prepared by applying a load of about 1/10 of the single yarn fineness. The remaining part was used to measure the strength in the same way as the strength of the fiber. CV is calculated by the following formula.
CV = standard deviation of single yarn strength / average value of single yarn strength × 100

(Nodule strength retention rate of single fiber)
As for the strength and elastic modulus of the filament (single fiber), ten single yarns (filaments) were randomly extracted from one multifilament to be measured. When the number of filaments was less than 10, all single yarns (filaments) were measured.
In the measurement, about 2 m of each single fiber was taken out, 1 m of the fiber was used, the weight was measured, and the fineness (dTex) was converted into 10,000 m. When measuring the length of this single yarn fiber 1 m, a constant length sample was prepared by applying a load of about 1/10 of the single yarn fineness. Further, the remaining part of the fiber was used to make a knot in the middle of a single fiber, and then a tensile test was performed in the same manner as the strength of the fiber. At this time, how to make a knot was performed according to FIG. 3 described in JIS L1013. The direction of the knot is always the same, and is b in FIG.
Knot strength retention = average value of single yarn knot strength / average value of single yarn strength × 100

(Intrinsic viscosity)
The specific viscosity of various dilute solutions is measured with an Ubbelohde capillary viscosity tube at 135 degrees decalin, and the intrinsic viscosity is calculated from the extrapolation point to the origin of the straight line obtained by the least square approximation of the plot for the viscosity concentration. Were determined. When measuring, divide or cut the sample into approximately 5 mm lengths, add 1 wt% antioxidant (trade name “Yoshinox BHT” manufactured by Yoshitomi Pharmaceutical) to the polymer, and stir at 135 ° C. for 4 hours. The measurement solution was prepared by dissolution.

(Differential scanning calorimeter measurement)
Differential scanning calorimetry was measured using a DSC7 model manufactured by PerkinElmer, Inc. and filled with about 5 mg of a sample cut in advance to 5 mm or less in an aluminum pan, and the same empty aluminum pan was used as a reference at 10 ° / min. The temperature was increased from room temperature to 200 degrees at a rate of temperature increase, and the endothermic peak was determined. The temperature at the peak top of the melting peak appearing on the lowest temperature side of the obtained curve was taken as the melting point.

(Raman scattering measurement)
The Raman scattering spectrum was measured by the following method. The Raman measuring device (spectrometer) was measured using a Renishaw system 1000. The light source was a helium-neon laser (wavelength 633 nm), and the measurement was performed with the fibers placed so that the fiber axis was parallel to the polarization direction. Single fiber (monofilament) is split from yarn and pasted on the center line of a hole in a cardboard with a rectangular hole (50 mm in length and 10 mm in width) so that the long axis coincides with the fiber axis, and both ends are bonded with epoxy Stopped with an agent (Araldite) and left for more than 2 days. The fiber is then attached to a jig whose length can be adjusted with a micrometer, the cardboard holding the single fiber is carefully cut out, a predetermined load is applied to the fiber, and it is placed on the microscope stage of the Raman scattering device. Was measured. At this time, the stress and strain acting on the fiber were measured simultaneously. Measurement of Raman data was collected by the resolution per one pixel for the 1350 cm ^-1 from the measurement range 850 cm ^-1 in Static Mode to 1 cm ^-1 or less. As the peak used for the analysis, a band of 1128 cm ⁻¹ belonging to the symmetrical stretching mode of the C—C skeleton bond was adopted. In order to accurately determine the band centroid position and line width (standard deviation of the profile around the band centroid, square root of the second moment), the curve can be fit well by approximating the profile as a composite of two Gaussian functions. I understood. It was found that when the distortion was applied, the peak positions of the two Gaussian functions did not match and the distance between them increased. In such a case, in the present invention, the band position is not considered as the apex of the peak profile, but is defined as the band peak position by the centroid position of the two Gaussian peaks. The definition is shown in Equation 1 (center of gravity, <x>). A graph is created by plotting the band centroid position <x> and the stress applied to the fiber. The slope of the approximate curve passing through the origin using the least square method of the obtained plot was defined as the stress Raman shift factor.

<X> = ∫x f (x) dx / ∫f (x) dx
f (x) = f1 (x−a) + f2 (x−b)
Here, fi represents a Gaussian function.

[Evaluation method of crystal size and orientation]
Crystal size and orientation evaluation were measured using an X-ray diffraction method. As an X-ray source, a large synchrotron radiation facility SPring8 was used as an X-ray source, and a BL24XU hatch was used. The energy of the X-ray used is 10 keV (λ = 1.398Å). The X-rays taken out through the undulator were monochromatized through a monochromator (silicon crystal (111) plane) and then set to converge at the sample position using a phase zone plate. The size of the focal point is adjusted so that the diameter is 3 μm or less both vertically and horizontally. The sample fiber is placed on the XYZ stage so that the fiber axis is horizontal. The Thomson scattering intensity was measured by finely moving the stage while detecting using a separately installed Thomson scattering detector, and the point where the intensity reached the maximum was determined as the center of the fiber. Since the X-ray intensity is very high, the sample is damaged if the exposure time of the sample is too long. Therefore, the exposure time during X-ray diffraction measurement was set to be within 2 minutes. Under these measurement conditions, a beam was applied to five or more sites at substantially equal intervals from the skin portion to the center portion of the fiber, and X-ray diffraction patterns were measured for each location. X-ray diffraction patterns were recorded using a Fuji imaging plate. Data reading was performed using Fuji microluminography. The recorded image data was transferred to a personal computer, and the line width was evaluated after cutting out data in the equator direction and the azimuth direction. The crystal size (ACS) was calculated from the half-value width β of the diffraction profile in the equator direction using the Scherrer equation [Equation 1] shown below. The identification of diffraction peaks was in accordance with Bunn et al. (Trans Faraday Soc., 35, 482 (1939)). As the crystal size, an average value obtained by measuring and evaluating 5 points or more was adopted. CV was calculated using the following formula.
CV = standard deviation of crystal size / average value of crystal size × 100

  [Formula 1] ACS = 0.9λ / βcos θ

  Here, λ is the wavelength of the X-ray used, and 2θ is the diffraction angle.

The orientation angle OA was the half width of the profile obtained by scanning in the azimuth direction for each of the obtained two-dimensional diffraction patterns. An average value obtained by measuring and evaluating five or more points was adopted as the orientation angle. CV was calculated using the following formula.
CV = standard deviation of orientation angle / average value of orientation angle × 100

[Evaluation method of monoclinic crystal size]
The crystal size was measured using an X-ray diffraction method. The apparatus used for the measurement is Rigaku Lint 2500. A copper counter cathode was selected as the X-ray source. The operation output was 40 kV 200 mA. The collimator was 0.5 mm, the fiber was attached to a fiber sample stage, and the counter was scanned in the equator direction and meridian direction to measure the X-ray diffraction intensity distribution. At this time, the light receiving slit was selected to be 1/2 ° for both the vertical limit and the horizontal limit. The crystal size (ACS) was calculated from the half-value width β of the diffraction profile using the Scherrer equation [Equation 2] shown below.

  [Formula 2] ACS = 0.9λ / β0 cos θ

However, β0 = (β2 −βs) 0.5
Here, λ is the wavelength of the X-ray used, 2θ is the diffraction angle, and βs is the half width of the X-ray beam itself measured using a standard sample.

The crystal size of the monoclinic was determined by calculating the ACS using the Scherrer equation from the line width of the diffraction point derived from the monoclinic (010). The diffraction peaks were identified according to Seto et al. (Jap. J. Appl. Phys., 7, 31 (1968)). The ratio of orthorhombic crystal size is (20
0) The crystal size derived from the diffraction plane was divided by the crystal size derived from the (020) diffraction plane.

(Examples 1-3)
Ultra high molecular weight polyethylene having an intrinsic viscosity of 21.2 dl / g and decahydronaphthalene were mixed at a weight ratio of 8:92 to form a slurry liquid. This material is melted by a twin screw extruder equipped with a mixing and conveying section, and the resulting transparent uniform material is extruded through an orifice having 30 holes and a diameter of 0.8 mm, which is 1.8 g / min. did. By passing the extruded dissolved substance through a 10 mm long air gap through a cylindrical flow tube (covered with heat resistant glass of 5 mm thickness and shielded from the external space) filled with water in a steady flow, liquid The surface fluctuation is suppressed to 0.5 mm or less, and the decahydronaphthalene accumulated on the liquid surface is uniformly cooled while continuously removing from the portion where the extruded dissolved material enters the water surface, and the solvent in the extruded dissolved material The gel yarn was taken up at a spinning speed of 60 m / min without removing from the extruded dissolved material. At this time, the cooling rate of the fiber was 9667 degrees / s, and the cumulative speed difference was 5 m / min. Then, the gel fiber was drawn up at a draw ratio of 3 times in a nitrogen heating oven without taking up the gel fiber, and the drawn yarn was taken up. Next, the fiber was drawn at a draw ratio of up to 6.5 times at 149 degrees to obtain drawn yarns having various draw ratios. Various physical properties of the obtained polyethylene fiber are shown in Table 1.

(Examples 4 and 5)
An ultra-high molecular weight polyethylene polymer having an intrinsic viscosity of 19.8 dl / g was dissolved in a slurry mixture of 10 wt% and decahydronaphthalene 90 wt% with a screw type kneader set at a temperature of 230 ° C. A single-hole discharge amount of 1.2 g / min was supplied to a die having a diameter of 0.6 mm set to 400 degrees by a lightweight pump. In the collar-type quenching equipment installed directly under each nozzle, pay attention to the rectification of 0.1 m / s of nitrogen gas, and evenly strike each thread to be discharged as much as possible. A polyethylene fiber was produced in the same manner as in Example 1 except that a very small amount of decalin was evaporated and further passed through an air gap in a nitrogen atmosphere. In addition, the draw ratio of the second stage was 4.5 and 6.0 times. At this time,
The nitrogen temperature used for quenching was controlled at 178 degrees. Moreover, temperature control was not performed regarding the air gap. Table 1 shows the physical property values of the obtained fibers. It was found to be very uniform and have high strength.

(Comparative Example 1)
Dissolve an ultrahigh molecular weight polyethylene having an intrinsic viscosity of 19.6 with a screw-type kneader set at a temperature of 230 ° C. while dispersing a slurry mixture of 10 wt% and decahydronaphthalene 90 wt%, and set the temperature to 175 ° C. A single-hole discharge rate of 1.6 g / min was supplied to a die having 400 holes with a diameter of 0.6 mm by a lightweight pump. Care is taken to rectify nitrogen gas adjusted to 100 degrees at a high speed of 1.2 m / s at a slit-like gas supply orifice installed directly under the nozzle, and decalin on the surface of the fiber so that it strikes the yarn as evenly as possible. The decalin remaining in the fiber was evaporated with a nitrogen flow set at 115 ° C., and was taken up at a speed of 80 m / min with a Nelson-shaped roller installed downstream of the nozzle. At this time, the length of the quench section was 1.0 m, the cooling rate of the fiber was 100 degrees / s, and the cumulative speed difference was 80 m / min. Subsequently, the obtained fiber was stretched 4.0 times in a heating oven at 125 degrees, and this fiber was subsequently stretched 4.1 times in a heating oven set at 149 degrees. Uniform fibers could be obtained without breaking during the process. Table 1 shows the physical property values of the obtained fibers.

(Comparative Example 2)
Dissolve in a screw-type kneader set at a temperature of 230 ° C. while dispersing a slurry mixture of 15 wt% of the ultrahigh molecular weight polymer (C) having an intrinsic viscosity of 10.6 and 85 wt% of paraffin wax. Then, a single hole discharge rate of 2.0 g / min was supplied to a die having a diameter of 1.0 mm set to 190 degrees and 400 holes by a lightweight pump. It was immersed in a spinning bath filled with 15-degree n-hexane with an air gap of 30 mm. The soaked fiber was taken up at a speed of 50 m / min with a Nelson-shaped roller. At this time, the cooling rate of the fiber was 4861 degrees / s, and the cumulative speed difference was 50 m / min. Subsequently, the obtained fiber was stretched 3.0 times in a heating oven at 125 degrees, and the fiber was further stretched by 3 in a heating oven set at 149 degrees and then stretched by 1.5 times again. . Uniform fibers could be obtained without breaking during the process. Table 1 shows the physical property values of the obtained fibers.

(Comparative Example 3)
The undrawn fiber prepared and wound under the same conditions as in Comparative Example 1 was immersed in ethanol for 3 days to remove decalin remaining in the yarn, and then air-dried for 2 days to produce a xerogel fiber. Further, the xerogel fiber was stretched 4.0 times in a heating oven at 125 ° C. Subsequently, this fiber was stretched 4.3 times in a heating oven set at 155 ° C. Uniform fibers could be obtained without breaking on the way.

Since the high-strength polyethylene fiber obtained by the production method of the present invention is a polyethylene fiber having high strength, high elastic modulus and uniform fiber internal structure, various sports clothing, bulletproof / protective clothing, protective gloves, various safety products, etc. High-performance textiles, tag rope, mooring rope, yacht rope, various rope products such as construction rope, various braided products such as fishing line, blind cable, net products such as fishing nets and ball-proof nets, chemical filters, battery separators, etc. It can be applied to a wide range of industries such as reinforcing materials or various non-woven fabrics, curtain materials such as tents, and reinforcing fibers for sports such as helmets and skis, composites such as speaker cones, prepregs, and concrete reinforcements.

Claims (10)

Spinning process in which high-molecular-weight polyethylene having an intrinsic viscosity of 5 or more is dissolved using a volatile organic solvent, the solution discharged from the spinneret is cooled, and the resulting undrawn yarn is heated to remove the solvent. A method for producing a high-strength polyethylene fiber comprising a stretching step of stretching while
In the spinning step, a high-strength polyethylene fiber having a monoclinic-derived crystal size of 8 nm or less is produced using the cooling means (1) below.
(1) Discharge using a cooling medium at a cooling rate of 1000 ° C./s or more and so that the difference in speed between the cooling medium and the gel yarn is 30 m / min or less as a cumulative speed difference defined by the following formula. Cooling the gel yarn uniformly Cumulative speed difference = ∫ (Thread speed-Cooling medium speed in the thread take-up direction) 2. The high-strength polyethylene fiber according to claim 1, wherein the cooling medium of (1) is used to cover the gas medium space that travels until the discharged gel yarn discharged from the spinneret comes into contact with the cooling medium. Manufacturing method. Using the cooling means of (1) , (a) a method in which a funnel is attached to the center of a cylindrical bath and the liquid and the gel yarn are drawn simultaneously, or (b) the gel yarn is placed along the falling liquid like a waterfall. The method for producing a high-strength polyethylene fiber according to claim 1, wherein any one of the methods for simultaneously drawing is used.   The method for producing a high-strength polyethylene fiber according to claim 2, wherein the member is made of a material having a heat insulating structure.   The method for producing a high-strength polyethylene fiber according to any one of claims 1 to 4, wherein the cooling medium is a liquid and the liquid level fluctuation is 1 mm or less. The method for producing a high-strength polyethylene fiber according to claim 1 , wherein the following (2) is further used as a cooling means .
(2) in the spinning process, the range of ± 10 ° C. relative to the temperature of the nozzle
Controlled inert gas within 1 m / s independently for each of the discharge solutions
Supply at a speed to cool the yarn uniformly.   The method for producing a high-strength polyethylene fiber according to any one of claims 1 to 6, wherein the high-strength polyethylene fiber is a multifilament.   The average strength of the high-strength polyethylene fiber is 20 cN / dTex or more, The method for producing a high-strength polyethylene fiber according to any one of claims 1 to 7.   The high-strength polyethylene fiber according to claim 7 or 8, wherein the breaking elongation of the monofilament constituting the high-strength polyethylene fiber is 2.5% or more and 6.0% or less.   The method for producing high-strength polyethylene fibers according to any one of claims 7 to 9, wherein the knot strength retention of the monofilaments constituting the high-strength polyethylene fibers is 40% or more. "