JP7745782B2 - Melt-anisotropic aromatic polyester fiber and its manufacturing method - Google Patents

Description

Related Applications

This application claims priority to Patent Application No. 2022-199790, filed in Japan on December 14, 2022, the entire contents of which are incorporated herein by reference.

The present invention relates to melt-anisotropic aromatic polyester fibers and a method for producing the same.

General-purpose fibers such as general-purpose polyester fibers are often used for tension members, but because thinner diameters are required for cables and cords to make electrical appliances more compact, attention is being paid to super fibers that are strong enough even with a thin diameter. Furthermore, for applications such as optical cables, even a slight stretch of optical fiber causes an accelerated decrease in communication speed, so liquid crystal polymer fibers (melt-anisotropic aromatic polyester fibers, aramid fibers, etc.) with high dimensional stability are used. Melt-anisotropic aromatic polyester fibers are known to have excellent dimensional stability because, through spinning, raw spun yarns with high orientation in the fiber axis are obtained, and the degree of crystallinity can then be increased by heat-treating the raw spun yarns and solid-state polymerization.

For example, regarding the crystallinity of melt-anisotropic aromatic polyester fibers, Patent Document 1 (JP 2010-150694 A) discloses liquid crystalline polyester fibers characterized in that, in wide-angle X-ray diffraction measurements using CuKα radiation as a radiation source, the half-width of a peak with a maximum at 18 to 22 degrees from the equatorial direction is 3.5 degrees or more.

Furthermore, with regard to a method for producing a melt-anisotropic aromatic polyester fiber, Patent Document 2 (JP-A-3-227407) discloses a method for spinning a melt-anisotropic aromatic polyester, which comprises, when extruding and spinning a melt-anisotropic aromatic polyester using a vented extruder, reducing the pressure at the vent to 100 to 760 mmHg, adjusting the tip pressure of the extruder to 5 to 30 kg/ ^cm2 , and then increasing the pressure to 40 to 200 kg/ ^cm2 using a gear pump with a volumetric efficiency of 50 to 90%, and passing the polyester through a filter for spinning.

JP 2010-150694 A Japanese Patent Application Publication No. 3-227407

However, to extend the lifespan of various applications such as electrical appliances, even greater dimensional stability than conventional melt-anisotropic aromatic polyester fibers is required, and creep properties need to be improved. However, Patent Documents 1 and 2 do not mention any improvement in creep properties.

Therefore, the present invention aims to solve the above problems and provide a melt-anisotropic aromatic polyester fiber with excellent creep properties.

As a result of extensive research to achieve the above object, the inventors of the present invention have found that when the kneading conditions in melt spinning are changed, there is a difference in the creep properties of the melt-anisotropic aromatic polyester fiber obtained by subsequently heat-treating the spun raw yarn.
Then, taking into consideration the relationship with creep properties, the inventors focused on the crystalline structure of melt-anisotropic aromatic polyester fibers and found that melt-anisotropic aromatic polyester fibers with superior creep properties have a high degree of orthorhombic crystallization.
As a result of further research, the inventors discovered that in melt spinning, by kneading molten anisotropic aromatic polyester at low temperature in a twin-screw extruder, it is possible to apply shear at a high viscosity, thereby enabling the production of a spun raw yarn having a more uniform microcrystalline structure. Perhaps this is because by heat-treating such a spun raw yarn, the molecular chains are densely packed during solid-state polymerization, thereby increasing the proportion of orthorhombic crystals, which have a denser crystal structure, which led to the completion of the present invention.

That is, the present invention can be configured in the following manner.
[Aspect 1]
A melt-anisotropic aromatic polyester fiber having a degree of orthorhombic crystallinity in the crystalline component of 15.0% or more (preferably 16.0% or more, more preferably 17.0% or more, even more preferably 18.0% or more, and 25.0% or less, preferably 24.0% or less, more preferably 23.0% or less).
[Aspect 2]
A melt-anisotropic aromatic polyester fiber according to aspect 1, wherein the melt-anisotropic aromatic polyester fiber has a density of 1.4080 g/cm ³ or more as determined by a density gradient tube.
[Aspect 3]
A melt-anisotropic aromatic polyester fiber according to Aspect 1 or 2, comprising a melt-anisotropic aromatic polyester having 50 mol % or more (preferably 53 mol % or more, more preferably 60 mol % or more, even more preferably 65 mol % or more, and still more preferably 70 mol % or more) of structural units derived from 4-hydroxybenzoic acid.
Aspect 4
A melt-anisotropic aromatic polyester fiber according to any one of Aspects 1 to 3, wherein the melt-anisotropic aromatic polyester fiber has a melting point of 260 to 380°C (preferably 270 to 360°C, more preferably 275 to 340°C, and even more preferably 275 to 330°C) as measured with a differential scanning calorimeter in a nitrogen atmosphere at a temperature rise rate of 10°C/min.
Aspect 5
A fiber structure comprising at least a portion of the melt-anisotropic aromatic polyester fiber according to any one of Aspects 1 to 4.
Aspect 6
a step of melt-kneading the melt-anisotropic aromatic polyester using a twin-screw extruder at a barrel temperature from a resin feed section to an outlet of a kneading section that is lower _than the melting point Mp of the melt-anisotropic aromatic polyester, Mp being ₀ (preferably Mp _-5 °C or lower, more preferably Mp _-10 °C or lower, and even more preferably Mp _-15 °C or lower), where Mp is the melting point of the melt-anisotropic aromatic polyester as measured by a differential scanning calorimeter in a nitrogen atmosphere at a temperature increase rate of 10°C/min;
a step of spinning the molten mixture to obtain a raw spun yarn;
a step of heat treating the obtained raw spinning yarn;
A method for producing a melt-anisotropic aromatic polyester fiber, comprising at least
Aspect 7
A method for producing a melt-anisotropic aromatic polyester fiber according to Aspect 6, wherein the melt-kneading is performed under conditions where the residence time in the kneading section of the twin-screw extruder is 10 seconds or more (preferably 15 seconds or more, more preferably 20 seconds or more).

As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms "at least one," unless the content clearly dictates otherwise. As used herein, the terms "and/or," "at least one," and "one or more" include any and all combinations of the associated listed items.

Note that any combination of at least two elements disclosed in the claims and/or the specification and/or the drawings is included in the present invention. In particular, any combination of two or more of the claims described in the claims is included in the present invention.

The melt-anisotropic aromatic polyester fiber of the present invention has excellent creep properties. Furthermore, the manufacturing method of the present invention can produce melt-anisotropic aromatic polyester fiber with a high degree of orthorhombic crystallization.

The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and description purposes and should not be used to define the scope of the present invention, which is defined by the appended claims. The drawings are not necessarily drawn to scale and may be exaggerated to illustrate the principles of the present invention.
FIG. 1 is a schematic diagram illustrating a method for producing a melt-anisotropic aromatic polyester fiber according to one embodiment of the present invention.

[Melt-form anisotropic aromatic polyester fiber]
The melt-anisotropic aromatic polyester fiber of the present invention contains a melt-anisotropic aromatic polyester. The melt-anisotropic aromatic polyester is composed of structural units derived from, for example, an aromatic diol, an aromatic dicarboxylic acid, an aromatic hydroxycarboxylic acid, etc., and the structural units derived from the aromatic diol, aromatic dicarboxylic acid, and aromatic hydroxycarboxylic acid are not particularly limited in chemical composition as long as the effects of the present invention are not impaired. Furthermore, the melt-anisotropic aromatic polyester may contain structural units derived from an aromatic diamine, an aromatic hydroxyamine, or an aromatic aminocarboxylic acid, as long as the effects of the present invention are not impaired. For example, preferred structural units include those shown in Table 1.

In the structural units in Table 1, m is an integer between 0 and 2, and each Y in the formula, ranging from 1 to the maximum number of possible substitutions, is independently a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), etc.

More preferred structural units include the structural units described in examples (1) to (18) in Tables 2, 3, and 4 below. Note that when a structural unit in a formula is a structural unit that can exhibit multiple structures, two or more such structural units may be combined and used as structural units that constitute the polymer.

In the structural units of Tables 2, 3, and 4, n is an integer of 1 or 2, and each of the structural units n=1 and n=2 may exist alone or in combination, and Y1 and Y2 may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having ₁ to ₄ carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), etc. Of these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

Z can also be exemplified by substituents represented by the following formula:

The melt-anisotropic aromatic polyester may preferably be a combination having a naphthalene skeleton as a structural unit. It is particularly preferred to include both a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, structural unit (A) may be represented by the following formula (A), and structural unit (B) may be represented by the following formula (B). From the perspective of improving melt moldability, the ratio of structural unit (A) to structural unit (B) may preferably be in the range of 9/1 to 1/1, more preferably 7/1 to 1/1, and even more preferably 5/1 to 1/1.

The total of the structural units (A) and (B) may be, for example, 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, based on the total structural units. A melt-type anisotropic aromatic polyester in which the structural unit (B) accounts for 4 to 45 mol% of the polymer is particularly preferred.

The melt-anisotropic aromatic polyester may contain structural units derived from 4-hydroxybenzoic acid, preferably at a content of 50 mol% or more, more preferably at a content of 53 mol% or more, even more preferably at a content of 60 mol% or more, even more preferably at a content of 65 mol% or more, and particularly preferably at a content of 70 mol% or more. The upper limit of the content of structural units derived from 4-hydroxybenzoic acid in the melt-anisotropic aromatic polyester is not particularly limited, but may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

The melting point (hereinafter sometimes referred to as _Mp0 ) of the melt-anisotropic aromatic polyester used in the present invention is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, even more preferably 260 to 360°C, and even more preferably 260 to 330°C. In this specification, the melting point is the main absorption peak temperature observed when measured using a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of a sample is placed in an aluminum pan and sealed in a DSC apparatus. Nitrogen is flowed as a carrier gas at a flow rate of 200 mL/min, and the endothermic peak is measured when the temperature is increased from room temperature (e.g., 25°C) at a rate of 10°C/min. If a clear peak does not appear in the first run of DSC measurement due to the type of polymer, the polymer should be heated at a rate of 50°C/min to a temperature 50°C higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then cooled to 50°C at a rate of 80°C/min, and then the endothermic peak should be measured at a heating rate of 10°C/min.

The melt-melt anisotropic aromatic polyester fiber may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin, as long as the effects of the present invention are not impaired. It may also contain various additives such as inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, colorants such as carbon black, dyes, and pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

The melt-anisotropic aromatic polyester fiber of the present invention may contain 50% by weight or more of melt-anisotropic aromatic polyester, preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 99.9% by weight or more.

The melt-anisotropic aromatic polyester fiber of the present invention has a degree of orthorhombic crystallinity in the crystalline component of 15.0% or more. Melt-anisotropic aromatic polyesters have crystalline components such as orthorhombic and hexagonal crystallinity. Orthorhombic crystallinity has a crystalline structure in which molecular chains are more densely packed. Therefore, melt-anisotropic aromatic polyester fibers with a high proportion of orthorhombic crystallinity in the crystalline component not only have high crystallinity and orientation, but also have excellent creep properties due to their dense crystalline structure. The degree of orthorhombic crystallinity may be preferably 16.0% or more, more preferably 17.0% or more, and even more preferably 18.0% or more. Furthermore, the degree of orthorhombic crystallinity may be, for example, 25.0% or less, preferably 24.0% or less, and more preferably 23.0% or less. In this specification, the degree of orthorhombic crystallinity of the melt-anisotropic aromatic polyester fiber is calculated from diffraction peaks derived from orthorhombic crystals and hexagonal crystals in an X-ray diffraction profile obtained by wide-angle X-ray diffraction measurement (for example, diffraction peaks appearing near a diffraction angle 2θ of 19 to 21°, etc.), and is a value measured by the method described in the Examples below.

The melt-anisotropic aromatic polyester fiber of the present invention has a high density due to a high proportion of orthorhombic crystals in which molecular chains are densely packed, and may have a density of 1.4080 g/ ^cm3 or more, for example, as determined by a density gradient tube. The upper limit of the density is not particularly limited, and may be, for example, 1.4200 g/ ^cm3 or less, although this depends on the composition of the melt-anisotropic aromatic polyester, etc. In this specification, the density of the melt-anisotropic aromatic polyester fiber is a value measured by the method described in the examples below.

The melt-anisotropic aromatic polyester fiber of the present invention may have a melting point of 260 to 380°C, preferably 270 to 360°C, more preferably 275 to 340°C, and even more preferably 275 to 330°C. The melting point of the melt-anisotropic aromatic polyester fiber is elevated from the melting point (Mp) of the raw spinning yarn by solid-state polymerization. The melting point of the melt-anisotropic aromatic polyester fiber is a value measured by the method described in the Examples below.

The melt-anisotropic aromatic polyester fiber of the present invention may have a tensile strength of 20 cN/dtex or more, preferably 24 cN/dtex or more, and more preferably 25 cN/dtex or more. The upper limit of the tensile strength is not particularly limited, but may be, for example, approximately 40 cN/dtex. The tensile strength of the melt-anisotropic aromatic polyester fiber is a value measured by the method described in the Examples below.

The melt-anisotropic aromatic polyester fiber of the present invention may have a time until the fiber breaks in a creep test using the method described in the Examples below of 30 hours or more, preferably 60 hours or more, and more preferably 68 hours or more.

The single fiber fineness of the melt-anisotropic aromatic polyester fiber of the present invention can be appropriately selected depending on the application, etc. For example, the single fiber fineness may be 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. However, from the perspective of responding to the miniaturization of electrical appliances, etc., a finer fineness is preferred, for example, 7 dtex or less. Furthermore, the lower limit of the single fiber fineness is not particularly limited, but may be, for example, approximately 0.01 dtex. The single fiber fineness is a value measured by the method described in the Examples below.

The melt-anisotropic aromatic polyester fiber of the present invention may be a monofilament or a multifilament. In the case of a multifilament, the number of filaments can be selected appropriately depending on the application, etc. For example, the number of filaments may be 2 to 5,000, preferably 3 to 4,000, and more preferably 5 to 3,000.

The total fineness of the melt-anisotropic aromatic polyester fiber of the present invention can be appropriately selected depending on the application, etc. For example, the total fineness may be 50,000 dtex or less, preferably 10,000 dtex or less, more preferably 2,000 dtex or less, and even more preferably 1,000 dtex or less. There is no particular lower limit to the total fineness, but it may be, for example, about 1 dtex.

[Method for producing melt anisotropic aromatic polyester fiber]
The method for producing the melt-anisotropic aromatic polyester fiber of the present invention comprises the steps of:
a step of melt-kneading a molten anisotropic aromatic polyester using a twin-screw extruder at a barrel temperature from a resin feed section to an outlet of a kneading section of the extruder at a melting point Mp of ₀ , the melting point being measured at a temperature rise rate of 10°C _/ min in a nitrogen atmosphere using a differential scanning calorimeter;
a step of spinning the molten mixture to obtain a raw spun yarn;
and a step of heat-treating the obtained raw spinning yarn.

In the present invention, the kneading property of the molten anisotropic aromatic polyester is improved by using a twin-screw extruder, and the molten anisotropic aromatic polyester is kneaded in a high-viscosity state by setting the temperature in the kneading section of the twin-screw extruder to a low temperature below the melting point, thereby making it possible to efficiently impart shear to the molten anisotropic aromatic polyester. It should be noted that, while it is common to promote melting by heating the resin to a temperature above the melting point of the resin to be added, this is the opposite temperature condition to the melting point of the resin.
Moreover, by spinning the molten kneaded material that has been subjected to shearing by kneading at such a low temperature, it is possible to obtain a spun raw yarn having a more uniform microcrystalline structure, and in this spun raw yarn, the molecular chains are densely packed during solid-state polymerization by heat treatment, thereby increasing the proportion of orthorhombic crystals, which have a denser crystal structure.
Furthermore, by applying shear during kneading at low temperatures, compared to conventional heating above the melting point of the resin, more mechanical energy can be applied than the thermal energy, and melting can be promoted more than under conventional melt-kneading conditions. As a result, in addition to the formation of a crystalline structure, it is also possible to reduce the amount of unmelted material remaining, which makes it less likely for filters installed to remove foreign matter to become clogged and suppresses the occurrence of yarn breakage during spinning.
It is also commonly known to use a single-screw extruder in the melt spinning method, but if the extruder temperature is set below the melting point as described above, poor resin biting, pressure fluctuations, and increased torque occur, making stable spinning impossible. This is thought to be due to the fact that, while the twin-screw extruder is designed to melt the resin by generating heat due to high shear, in the case of a single-screw extruder, the contribution of heat transfer from the extruder barrel during melting is significant. Therefore, the same effect cannot be obtained using a single-screw extruder in the present invention.

The method for producing melt-anisotropic aromatic polyester fibers is described below with reference to FIG. 1. FIG. 1 is a schematic diagram showing the internal configuration of a twin-screw extruder 100 used in the production of melt-anisotropic aromatic polyester fibers according to one embodiment of the present invention, viewed from the side. As shown in FIG. 1, the twin-screw extruder 100 includes a hopper 11 for feeding the molten anisotropic aromatic polyester, a barrel 12, a screw 13 that rotates within the barrel 12, and a vent 14. The barrel 12 includes a resin feed section 21, a kneading section 22, and a transport section 23, arranged from upstream to downstream. The resin feed section 21, the kneading section 22, and the transport section 23 each include screw elements 13a, 13b, and 13c of the screw 13. Note that the screw 13 (screw elements 13a, 13b, and 13c) represents one of the screws in the twin-screw extruder 100. FIG. 1 shows a simplified structure for explaining the method for producing a melt-anisotropic aromatic polyester fiber of the present invention, but a plurality of various types of equipment may be provided as needed, and in addition to the equipment shown in the figure, equipment generally used in twin-screw extruders may also be provided.

In FIG. 1, the solid molten anisotropic aromatic polyester introduced from the hopper 11 is transported in the X direction, which is the direction of travel, within the barrel 12 by the rotation of the screw 13, and is heated by a known heating means, such as a heater, installed in the barrel 12. In addition to heat transfer from the heating means, the solid molten anisotropic aromatic polyester melts as it travels in the X direction by applying shear between the inner wall of the barrel 12 and the screw 13 and between the screws 13. The molten anisotropic aromatic polyester may also be introduced into the twin-screw extruder 100 as a resin composition containing the molten anisotropic aromatic polyester, the thermoplastic polymer described above, and various additives.

In the resin feed section 21, the solid molten anisotropic aromatic polyester supplied from the hopper 11 moves in the X direction while being compressed in its solid state by the rotation of the screw 13, and is gradually melted by heat transfer from the heating means of the barrel 12 and the shear applied by the rotation of the screw 13. The screw element 13a used in the resin feed section 21 may be, for example, a full-flight screw.

In the kneading section 22, kneading is performed using shear-imparting screw elements, such as kneading disks, as the screw elements 13b, thereby promoting the melting of the molten anisotropic aromatic polyester containing solids transported from the resin feed section 21. While Figure 1 shows one kneading section 22, multiple kneading sections may be provided.

In the transport section 23, the viscosity of the molten mixture obtained in the kneading section 22 can be adjusted when transporting it to the spinning head. The screw element 13c used in the transport section 23 is, for example, a full-flight screw.

In the present invention, by setting the temperatures of the resin feed section 21 and the kneading section 22 in the barrel 12 to a low temperature below the melting point Mp ₀ of the molten anisotropic aromatic polyester to be fed into the twin-screw extruder 100, it is possible to efficiently impart shear to the molten anisotropic aromatic polyester in a highly viscous state. The temperature of the barrel 12 from the resin feed section 21 to the outlet of the kneading section 22 may preferably be Mp ₀ -5°C or less, more preferably Mp ₀ -10°C or less, and even more preferably Mp ₀ -15°C or less. Furthermore, from the viewpoint of promoting melting by heating, it may be Mp ₀ -100°C or higher, preferably Mp ₀ -90°C or higher, and more preferably Mp ₀ -80°C or higher. In the production method of the present invention, when there are multiple kneading sections, the barrel temperature from the resin feed section to the outlet of the kneading section refers to the barrel temperature up to the outlet of the kneading section that is most downstream and adjacent to the transport section.

The heating means installed in the barrel 12 may be temperature controlled differently for each region in the direction of travel from the upstream side to the downstream side, and it is preferable that the temperature of the barrel 12 from the resin feed section 21 to the outlet of the kneading section 22 be adjusted so that it gradually increases within the above temperature range.

In the present invention, the temperatures of the resin feed section 21 and the kneading section 22 in the barrel 12 may be adjusted within the above-mentioned temperature range, and the temperature of the barrel 12 in the subsequent transport section 23 may be Mp ₀ or higher, preferably Mp ₀ + 10°C or higher, and more preferably Mp ₀ + 20°C or higher, from the viewpoint of adjusting the viscosity during spinning. Furthermore, from the viewpoint of suppressing decomposition of the molten anisotropic aromatic polyester, the temperature may be 400°C or lower, preferably 370°C or lower, and more preferably 350°C or lower.

The residence time in the kneading section 22 may be 10 seconds or more, preferably 15 seconds or more, and more preferably 20 seconds or more, from the viewpoint of efficiently applying shear to the molten anisotropic aromatic polyester and improving spinnability. Furthermore, from the viewpoint of suppressing deterioration of the molten anisotropic aromatic polyester, it may be 300 seconds or less, preferably 180 seconds or less, and more preferably 130 seconds or less. The residence time in the kneading section can be calculated using the following formula based on the volume of the kneading section and the discharge rate.
(Vacuum in barrel [cm ³ ])=(Volume in kneading section barrel [cm ³ ])−(Volume of kneading section screw [cm ³ ])
(Residence time in kneading section [s])=(space in barrel [cm ³ ])/(volumetric discharge rate [cm ³ /s])

Depending on the type of melt-anisotropic aromatic polyester and spinning conditions, the capacity, distribution, and arrangement of the resin feed section, kneading section, and transport section, as well as the screw shape and gaps between the screws, may be designed as appropriate. In addition to screw elements such as full-flight screws and kneading discs, screw elements that return the material in the opposite direction to the direction of travel from upstream to downstream, such as back-kneading discs, may also be used. A seal ring may also be used on the element at the outlet of the kneading section to efficiently retain the resin in the kneading section and to improve sealing performance upstream of the vent.

Because air bubbles may be trapped in the twin-screw extruder 100 during melt-kneading due to air entrapment or other reasons, it is preferable to degas the twin-screw extruder 100 by, for example, installing a vent 14 in the twin-screw extruder 100 and connecting a vacuum pump or the like to reduce the pressure inside the twin-screw extruder 100. For example, the degree of vacuum may be an absolute pressure of 100 kPa or less, preferably 80 kPa or less, and more preferably 60 kPa or less.

The molten mixture obtained by melt-kneading in the twin-screw extruder 100 is then metered by a gear pump (not shown) from the transport section 23 and transported to the spinning head. To prevent the molten mixture from being contaminated with foreign matter such as unmelted material, a filter may be provided before or after the gear pump after it is transported from the twin-screw extruder 100. In the present invention, melt-kneading in the twin-screw extruder can reduce the amount of unmelted material remaining, making the filter less likely to clog and enabling stable spinning.

After being transported to the spinning head, the molten mixture is extruded through a nozzle at a predetermined spinning temperature, and the resulting yarn is wound around a godet roller or the like to produce a spun raw yarn of melt-anisotropic aromatic polyester fiber. The spinning temperature (spinneret temperature) may be, for example, Mp 0 -30 to Mp ₀ +60°C, preferably Mp ₀ -25°C to Mp ₀ +50°C, and more preferably Mp ₀ -20°C to Mp ₀ +45°C, relative to the melting point Mp 0 of the melt-anisotropic aromatic polyester. The spinning temperature may be from the barrel temperature of the kneading section + ₁₀ °C to the barrel temperature of the kneading section +120° _C , preferably the barrel temperature of the kneading section +15°C to the barrel temperature of the kneading section +100°C, more preferably the barrel temperature of the kneading section +20°C to the barrel temperature of the kneading section +90°C, and even more preferably the barrel temperature of the kneading section +30°C to the barrel temperature of the kneading section +80°C. When the spinning temperature (spinneret temperature) is equal to or lower than the upper limit, deterioration of the resin near the spinneret can be suppressed, and poor processability due to thread breakage and yellowing of the product are less likely to occur.

Perhaps because the spun yarn forms a more uniform microcrystalline structure, heat treatment of the spun yarn promotes solid-state polymerization of the molten anisotropic aromatic polyester, raising the melting point from the melting point (Mp) of the spun yarn and increasing the degree of orthorhombic crystallinity in the heat-treated fiber. The heat treatment method used in the heat treatment process is not particularly limited; for example, it may be a batch-type heat treatment or a continuous heat treatment via conveying. The melting point (Mp) of the spun yarn can be measured using the same method as the melting point of the molten anisotropic aromatic polyester fiber.

For example, in a batch-type heat treatment, the material may be wound around a bobbin in a packaged state, or in a skein or tow state. A packaged state is preferred because it simplifies the equipment and improves productivity. The bobbin must be able to withstand the temperatures of solid-state polymerization, and is preferably made of a metal such as aluminum, brass, iron, or stainless steel.

When continuous heat treatment is performed by conveyance, the conveyance method may be either contact conveyance (e.g., conveyor system, support roll system, or heat treatment system using heated rollers) or non-contact conveyance (roll-to-roll system). Furthermore, the treatment path does not have to be straight; folding rollers or guides may be placed within the device to appropriately change the length, angle, curvature, etc. of the treatment path during heat treatment.

The heat treatment process can be carried out using known methods, such as atmospheric heating and contact heating. Suitable atmospheres include air, inert gases (e.g., nitrogen, argon), or a combination thereof. Heat treatment can also be carried out under reduced pressure.

In the heat treatment step, the heat treatment temperature may be 250 to 350°C, preferably 255 to 320°C, more preferably 260 to 315°C, and more preferably 280 to 310°C. Furthermore, the heat treatment temperature may be lower than the melting point (Mp) of the raw spun yarn subjected to the heat treatment step to prevent melting. For example, within the range of 250 to 350°C, the heat treatment temperature may be Mp-50°C or higher but lower than Mp°C, preferably Mp-40°C or higher but lower than Mp°C, and more preferably Mp-30°C or higher but lower than Mp°C. In the heat treatment step, the melting point of the molten anisotropic aromatic polyester fiber increases as the solid-state polymerization progresses. Therefore, the initial heat treatment temperature in the heat treatment step may be set lower than the melting point (Mp) of the raw spun yarn. From the perspective of efficient strength improvement, the heat treatment temperature may be gradually increased according to the progress of the solid-state polymerization, and the heat treatment may be performed at a temperature higher than the melting point (melting point of the raw spun yarn) at the time of the heat treatment step.

The heat treatment time for the heat treatment step can be set appropriately depending on the heat treatment method and heat treatment temperature. For example, it can be set within a range of 15 minutes to 30 hours, preferably 2 to 24 hours, and more preferably 3 to 20 hours. Here, the heat treatment time refers to the holding time at a specified heat treatment temperature (e.g., the maximum temperature).

In the manufacturing method of the melt-anisotropic aromatic polyester fiber of the present invention, for example, a known oil agent or anti-fusing agent may be applied before the heat treatment step to improve the fiber bundling ability or prevent fusing during heat treatment.

[Fiber structure]
The melt-anisotropic aromatic polyester fiber of the present invention can be used in various applications as a fiber structure containing at least a portion thereof. The fiber structure containing the melt-anisotropic aromatic polyester fiber of the present invention can be used in any fiber form, such as staple fiber, short-cut fiber, filament yarn, spun yarn, string-like material, or rope. The melt-anisotropic aromatic polyester fiber can also be used as various fabrics, such as nonwoven fabrics, woven fabrics, and knitted fabrics. Such fibers and fabrics can be produced using the melt-anisotropic aromatic polyester fiber by known methods.

The fiber structure of the present invention may be formed by combining melt-anisotropic aromatic polyester fibers with other fibers, as long as the effects of the present invention are not impaired. For example, composite fibers using melt-anisotropic aromatic polyester fibers with other fibers (e.g., blended yarns in which melt-anisotropic aromatic polyester fibers are blended with other fibers) can be used. Also, composite fabrics using melt-anisotropic aromatic polyester fibers with other fibers (e.g., blended fabrics in which melt-anisotropic aromatic polyester fibers are blended with other fibers, and laminates of fabrics made of melt-anisotropic aromatic polyester fibers with fabrics made of other fibers) can be used.

The melt-melt anisotropic aromatic polyester fiber of the present invention can be used in the form of various fiber structures for a variety of applications, including general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various textile products. For example, it can be used in advanced processed products such as tension members (electric wires, optical fibers, umbilical cables, heater wire cores, earphone cords, and other electrical cords), sailcloth, ropes (marine, mountain climbing, crane, yacht, tug, etc.), ropes, land nets, slings, lifelines, fishing lines, sewing threads, screen cords, fishing nets, longlines, geogrids, protective gloves, ripstop protective clothing and outdoor apparel, rider suits, sports rackets, guts, reinforcing materials for medical catheters, sutures, screen gauze, filters, base fabrics for printed circuit boards, mesh conveyor belts, papermaking belts, dryer canvas, airships, balloons, airbags, speaker cones, reinforcing materials for various hoses and pipes, and reinforcing materials for rubber and plastic materials such as tires and conveyor belts. In particular, the melt-dispersed anisotropic aromatic polyester fiber of the present invention has excellent creep properties and can therefore be suitably used as a tension member.

The present invention will be described in more detail below based on examples, but the present invention is not limited by these examples. In the following examples and comparative examples, various physical properties were measured using the following methods.

(Melting point of resin chips (granular moldings) and fibers)
The melting point was determined using a differential scanning calorimeter (DSC; "DSC60A Plus" manufactured by Shimadzu Corporation) in accordance with JIS K 7121. Specifically, 4 to 6 mg of a sample was placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen was then introduced as a carrier gas at a flow rate of 200 mL/min, and the endothermic peak derived from the molten anisotropic aromatic polyester was measured when the temperature was raised from 25°C at a rate of 10°C/min.

(Boost amount)
50 kg of molten anisotropic aromatic polyester melt-kneaded under various conditions in a twin-screw extruder was transported to a container equipped with a metal nonwoven fabric filter having a diameter of 76 mm and a mesh size of 30 μm, and the filter was allowed to pass through. The pressure was monitored using a resin pressure meter GC75 manufactured by Nagano Keiki Co., Ltd. installed in the container, and the amount of pressure increase before and after the filter was recorded.

(Spinnability)
The molten anisotropic aromatic polyester was discharged, and a spinning test was carried out for 3 days after winding was started. The number of times that yarn breakage occurred during this time was counted and evaluated according to the following criteria.
◎: Number of thread breaks 0 times/day 〇: Number of thread breaks more than 0 times/day but less than 0.7 times/day △: Number of thread breaks 0.7 times/day or more but less than 2.0 times/day ×: Number of thread breaks 2.0 times/day or more

(Orthorhombic crystallinity)
The melt anisotropic aromatic polyester fiber was mounted on a fiber holder, and wide-angle X-ray diffraction (WAXD) measurement was performed by a transmission method under the following measurement conditions, with X-rays incident perpendicular to the fiber axis.
Measurement device: Bruker "D8 Discover IμS"
Detector: 2D PSPC/VANTEC-500
X-ray source: Cu
Current: 1mA
Voltage: 50 kV
Exposure time: 10 minutes Collimator diameter: 0.5 mm
Camera length: 17cm
Detector position (2θ): 20°
Sample position (ω): 10°
Inclination angle (Ψ): 90°
Measurement temperature: room temperature (about 25℃)

An X-ray diffraction profile was obtained under the following conditions, with the horizontal axis representing the diffraction angle (2θ) and the vertical axis representing the intensity.
Integration range: 2θ = 5 to 35°, γ (azimuth angle) = 250 to 290°
Step width: 0.05° (diffraction angle)

In the obtained X-ray diffraction profile, a straight line was drawn connecting the values at 2θ = 5° and 35° to set a baseline. Based on this newly set baseline, the difference in intensity on the vertical axis from the measured data to the baseline was converted into profile data with the new intensity.

After baseline correction, the amorphous peak was fitted to the profile data using a pseudo-Voigt function (Lorentzian function ratio: α = 0) with the peak height, peak top position, σ, and asymmetry parameter as variables. The initial peak top position of the fitting function was set to approximately 20.6°. The peak area of this fitting function was calculated as the amorphous amount (D).

For Peak A (peak top position near 19°), Peak B (peak top position near 20.5°), and Peak C (peak top position near 27°) of the baseline-corrected profile data, the following function was used to fit the crystalline peaks, with the peak height, peak top position, and σ as variables. All crystalline peaks were assumed to be symmetric.
Peak A: Pseudo-Voigt function (α=1)
Peak B: Pseudo-Voigt function (α=0)
Peak C: pseudo-Voigt function (α=0.5)

Then, fitting was performed using the least squares method to minimize the difference between the sum of all fitting functions, including the fitting function for the amorphous peak obtained above, and the baseline-corrected profile data. The peak areas of these fitting functions were calculated as the amounts of crystallinity (A), (B), and (C), respectively.

The degree of orthorhombic crystallinity was calculated from the following formula using the crystal amount (A) of peak A derived from hexagonal crystals and the crystal amount (B) of peak B derived from orthorhombic crystals.
Orthorhombicity (%) = (B) / {(A) + (B)} × 100

(fiber density)
Density measurements were carried out with reference to the density gradient tube method (JIS L 1013:2010 8.17.2). In order to compare slight density differences due to differences in fiber packing caused by orthorhombic crystallization, each sample was measured five times, and the average value was rounded to four decimal places.

(Total fineness, single fiber fineness)
Based on JIS L 1013:2010 8.3.1 A method, a 10 m reel of melt-anisotropic aromatic polyester fiber was taken using a measuring instrument "Wrap Reel by Motor Driven" manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd., and its weight (g) was multiplied by 1000 to perform measurements three times per level. The average value of the three measurements was taken as the total fineness (dtex) of the obtained melt-anisotropic aromatic polyester fiber. The quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

(Tensile strength)
With reference to JIS L 1013:2010 8.5.1, a strength and elongation tester "TENSORAPID5" manufactured by USTER Technologies was used to conduct five tensile tests for each sample under conditions of a test length of 30 cm, a tensile speed of 15 cm/min, and an initial load of 0.33 g/dtex, and the average tensile strength (cN) of the five tests was divided by the total fineness (dtex) measured by the above-mentioned method to calculate the tensile strength (cN/dtex).

(Creep characteristics)
Using a creep tester "525-R CREEP TESTER" manufactured by Mize Testing Instruments Co., Ltd., measurement was started at a measurement temperature of 20°C when a load of 0.18 N/dtex was applied to a fiber with a test length of 300 mm, and the time until the fiber broke was measured. Measurements were carried out three times per sample, and the average value was calculated.

[Example 1]
Chips (granular molded bodies) of a melt anisotropic aromatic polyester (Mp ₀ : 278 ° C.) having a 73/27 (mol%) ratio of structural units (A) derived from 4-hydroxybenzoic acid and structural units (B) derived from 6-hydroxy-2-naphthoic acid were dried with hot air at 120 ° C. for 4 hours or more. Thereafter, the mixture was placed in a twin-screw extruder with a barrel void volume of 14.7 cm ³ in the kneading section, and melt-kneaded at a barrel temperature of 260 ° C. from the resin feed section to the kneading section outlet and a barrel temperature of 325 ° C. in the transport section downstream from the kneading section outlet. The residence time in the kneading section was adjusted to 21 seconds. At this time, a vacuum pump was connected to the vent section midway through the twin-screw extruder via a metal pipe, and the polymer-unfilled space in the twin-screw extruder was decompressed to 30 kPa. The molten mixture was then supplied to the spinning head from the twin-screw extruder while being metered using a gear pump. The spinning head was equipped with a spinneret with a hole diameter of 0.10 mmφ and 100 holes. The spinneret temperature was set to 320°C, and the molten mixture was discharged at a volumetric throughput of 42.0 ^cm3 /min to obtain a spun raw yarn of 560 dtex/100 f. The obtained spun raw yarn was then heat-treated at 275°C for 16 hours in a nitrogen atmosphere to obtain a heat-treated yarn of melt-anisotropic aromatic polyester fiber. The analytical results of the obtained melt-anisotropic aromatic polyester fiber are shown in Table 5.

[Example 2]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the void volume in the barrel of the kneading section was 44.1 cm ³ , the barrel temperature from the resin feed section to the kneading section outlet was 240°C, the volumetric throughput rate was 126.1 cm ³ /min, and the number of holes in the spinneret was 300.

[Example 3]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 220°C.

[Example 4]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 200°C.

[Example 5]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the void volume in the barrel of the kneading section was 29.4 cm ³ , the barrel temperature from the resin feed section to the kneading section outlet was 230°C, the volumetric throughput rate was 30.2 cm ³ /min, and the residence time in the kneading section was 58.5 seconds.

[Example 6]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was 250°C, the volumetric throughput was 7.0 ^cm3 /min, the residence time in the kneading section was 126 seconds, and the number of holes in the spinneret was 10.

[Example 7]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was 230°C, the volumetric throughput rate was 58.8 cm ³ /min, and the residence time in the kneading section was 15 seconds.

[Example 8]
Melt-anisotropic aromatic polyester fibers were obtained in the same manner as in Example 1, except that the volumetric throughput rate was 96.9 cm ³ /min and the residence time in the kneading zone was 9.1 seconds.

[Example 9]
Chips (granular molded bodies) of a melt anisotropic aromatic polyester (Mp ₀ : 311 ° C.) having a 78/22 (mol%) ratio of structural units (A) derived from 4-hydroxybenzoic acid and structural units (B) derived from 6-hydroxy-2-naphthoic acid were dried with hot air at 120 ° C. for 4 hours or more. Thereafter, the mixture was placed in a twin-screw extruder with a barrel void volume of 14.7 cm ³ in the kneading section, and melt-kneaded at a barrel temperature of 270 ° C. from the resin feed section to the kneading section outlet and a barrel temperature of 340 ° C. in the transport section downstream from the kneading section outlet. The residence time in the kneading section was adjusted to 21 seconds. At this time, a vacuum pump was connected to the vent section midway through the twin-screw extruder via a metal pipe, and the polymer-unfilled space in the twin-screw extruder was decompressed to 30 kPa. The molten mixture was then supplied to the spinning head from the twin-screw extruder while being metered using a gear pump. The spinning head was equipped with a spinneret with a hole diameter of 0.10 mmφ and 100 holes, and the spinneret temperature was set to 340°C. The molten mixture was discharged at a volumetric throughput of 42.0 ^cm3 /min to obtain a spun raw yarn of 560 dtex/100 f. The spun raw yarn was then heat-treated at 280°C for 16 hours in a nitrogen atmosphere to obtain a heat-treated yarn of melt-anisotropic aromatic polyester fiber.

[Comparative Example 1]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that a φ50 mm single-screw extruder without a vent was used and the barrel temperature excluding the resin feed section was set to 320°C.

[Comparative Example 2]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 300°C.

[Comparative Example 3]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 1, except that the barrel temperature from the resin feed section to the kneading section outlet was set to 285°C.

[Comparative Example 4]
A melt-anisotropic aromatic polyester fiber was obtained in the same manner as in Example 9, except that a φ50 mm single-screw extruder without a vent was used and the barrel temperature excluding the resin feed section was set to 350°C.

As shown in Table 5, in Examples 1 to 9, the barrel temperature from the resin feed section to the kneading section outlet of the twin-screw extruder was set to specific low-temperature conditions during melt kneading, thereby enabling the production of melt-anisotropic aromatic polyester fibers with a high degree of orthorhombic crystallization. Therefore, the melt-anisotropic aromatic polyester fibers of Examples 1 to 9 have excellent creep properties.

On the other hand, in Comparative Examples 1 and 4, a single-screw extruder was used, and the barrel temperature from the resin feed section to the kneading section outlet was high, so the degree of orthorhombic crystallinity could not be increased. Furthermore, in Comparative Examples 2 and 3, a twin-screw extruder was used, but the barrel temperature from the resin feed section to the kneading section outlet was high, so the degree of orthorhombic crystallinity could not be increased. Therefore, the melt-anisotropic aromatic polyester fibers of Comparative Examples 1 to 4 have inferior creep properties compared to Examples 1 to 9.

The melt-dispersed anisotropic aromatic polyester fiber of the present invention can be used for a variety of purposes, including general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various textile products, and can be used, for example, as a tension member.

As described above, a preferred embodiment of the present invention has been described with reference to the drawings, but various additions, modifications, or deletions are possible without departing from the spirit of the present invention, and such additions, modifications, or deletions are also included within the scope of the present invention.

100: Twin-screw extruder 11: Hopper 12: Barrel 13: Screw 13a, 13b, 13c: Screw element 14: Vent 21: Resin feed section 22: Kneading section 23: Transport section X: Flow direction

Claims (7)

Melt-anisotropic aromatic polyester fiber having an orthorhombic crystallinity of 15.0% or more in the crystalline component. 2. The melt-anisotropic aromatic polyester fiber according to claim 1, wherein the density determined by a density gradient tube is 1.4080 g/cm ³ or more. The melt-anisotropic aromatic polyester fiber according to claim 1 or 2, comprising a melt-anisotropic aromatic polyester having 50 mol % or more of structural units derived from 4-hydroxybenzoic acid. The melt-anisotropic aromatic polyester fiber according to claim 1 or 2, having a melting point of 260 to 380°C as measured by a differential scanning calorimeter in a nitrogen atmosphere at a heating rate of 10°C/min. A fiber structure comprising at least a portion of the melt-dispersed anisotropic aromatic polyester fiber described in claim 1 or 2. a step of melt-kneading a molten anisotropic aromatic polyester using a twin-screw extruder at a barrel temperature from a resin feed section to an outlet of a kneading section of the extruder at a melting point Mp of ₀ , the melting point being measured at a temperature rise rate of 10°C _/ min in a nitrogen atmosphere using a differential scanning calorimeter;
a step of spinning the molten mixture to obtain a raw spun yarn;
a step of heat treating the obtained raw spinning yarn;
A method for producing a melt-anisotropic aromatic polyester fiber, comprising at least The method for producing melt-anisotropic aromatic polyester fibers according to claim 6, wherein the melt-kneading is carried out under conditions where the residence time in the kneading section of the twin-screw extruder is 10 seconds or more.