Hollow braid and hollow structure including hollow braid

Abstract

The problem addressed by the present invention is to provide a hollow braid that retains a hollow shape even in a high-temperature environment and that has excellent permeability.　A hollow braid comprises synthetic fibers having a melting point or a thermal decomposition temperature of 280°C or higher, and the hollow braid has a void coefficient of 1,000 or less as calculated according to formula (1) and a K value of 140‒215 as calculated according to formula (2). (1) void coefficient = [total fineness (dtex)]1 / 2 × [braid pitch (braids / 2.54 cm)] × [1 – (twist coefficient1 / 2 / 100)] (2) K value = [total fineness (dtex) × number of ends (ends)] / [braid pitch (braids / 2.54 cm)]

Description

Hollow braid and hollow structure including hollow braid

[0001] SUMMARY The present disclosure relates to hollow braids and hollow structures including hollow braids.

[0002] Porous hollow fiber membranes, which are hollow structures formed by integrating a hollow braid with a resin, are used as filtration membranes in water treatment devices, humidifying or dehumidifying membranes in fuel cell devices, etc. Patent Document 1 (JP-A-2003-102666) discloses a technique for this type of technology, in which a polyvinylidene fluoride (PVDF) resin membrane is formed on the outer surface of a cylindrical hollow braid made of synthetic fibers, using a specific method. Patent Document 1 describes that the hollow structure has high mechanical strength and excellent dimensional stability because the resin membrane is firmly bonded to the braid.

[0003] Patent Document 2 discloses that in a porous hollow fiber membrane, which is a hollow structure having a PVDF resin film on the outer peripheral surface of a hollow braid, the braid has a braiding density of 70 / inch (25.4 mm) or more, or a yarn fineness of 360 to 500 dtex and a filament count of 48 to 76. Patent Document 2 also discloses that by using a braid with a specific configuration in the production of a hollow fiber membrane, it becomes possible to control the amount of resin permeating into the braid structure, and to form a uniform, crack-free resin film on the surface of the braid.

[0004] Furthermore, Patent Document 3 discloses a cylindrical braid used as a hollow braid for a protective sleeve for a motor component, the braid being made of synthetic filament yarns, the single fibers of which have a fineness of 30 to 100 dtex, and each yarn or cord constituting one braid unit of the braid having 4 to 50 single fibers. The braid of Patent Document 3 is a braid knitted using yarns or cords in which the single fibers have a specific fineness and the number of filaments is within a specific range. Patent Document 3 also describes that the braid has an appropriate compressive elastic modulus and is resistant to flattening, making it easy to work with, lightweight, and cost-effective.

[0005] JP 2016-10792 A JP 2018-75522 A JP 2007-63730 A

[0006] Hollow braids have a wide range of applications, and there is a demand for braids that can be used stably in harsher environments, particularly high-temperature environments and environments where chemicals are used. In view of this situation, an object of the present invention is to provide a hollow braid that maintains its hollow shape even in high-temperature environments and has excellent permeability.

[0007] As a result of extensive research, the present inventors have found that when a hollow braid is made using synthetic fibers having a melting point or thermal decomposition temperature of 280°C or higher as a material for the braid, and the braid has a void coefficient and a K value within a specific range, the braid maintains its hollow shape even in a high-temperature environment and has excellent permeability.

[0008] The hollow braid according to the present disclosure is made of synthetic fibers having a melting point or thermal decomposition temperature of 280°C or higher, and has a void coefficient calculated according to the following formula (1) of 1,000 or less, and a K value calculated according to the following formula (2) of 140 to 215. Void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient １／２ / 100)} Formula (1) K value={(total fineness (dtex) × number of hits (hits)} / {braid pitch (braids / 2.54 cm)} Formula (2)

[0009] When a hollow braid is constructed using fibers with a high melting point or that are resistant to thermal decomposition, the resulting hollow braid has high heat resistance. However, when such fibers are used to construct a hollow braid, although heat resistance is achieved, it has been found that it is difficult to achieve both shape stability and permeability at high temperatures. As a result of further investigation, the inventors have found that when a hollow braid is constructed with a void coefficient and a K value each falling within a specific range, a braid made of heat-resistant fibers can be obtained that retains its shape even in a high-temperature environment and has excellent permeability, and have arrived at the present invention.

[0010] The synthetic fibers may be any one of polyphenylene sulfide fibers, polyarylate fibers, and aramid fibers, or a combination thereof.

[0011] The hollow braid according to the present disclosure is made of any one or combination of polyphenylene sulfide fibers, polyarylate fibers, aramid fibers, polyether ether ketone fibers, polyethersulfone fibers, and polyimide fibers, and has a void coefficient calculated according to the following formula (1) of 1,000 or less and a K value calculated according to the following formula (2) of 140 to 215: void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient １／２ / 100)} Formula (1) K value={(total fineness (dtex) × number of hits (hits)} / {braid pitch (braids / 2.54 cm)} Formula (2)

[0012] In the hollow braid, the total fineness may be 10 dtex or more and 2000 dtex or less.

[0013] In the hollow braid, the number of strands may be 8 strands or more and 64 strands or less.

[0014] The hollow braid may have a hollow ratio of 50% to 90% as calculated according to the following formula (3): Hollow ratio (%) = {(inner diameter of cross section of hollow braid / outer diameter of cross section of hollow braid)} × 100 (3)

[0015] The hollow structure according to the present disclosure is a hollow structure including the hollow braid described above.

[0016] According to the hollow braid according to the present disclosure, a hollow braid is provided that maintains its hollow shape even in a high-temperature environment and has excellent permeability.

[0017] Hereinafter, embodiments of the hollow braid and hollow structure according to the present disclosure will be specifically described. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more, and B or less."

[0018] The hollow braid according to the present disclosure is made of synthetic fibers having a melting point or thermal decomposition temperature of 280°C or higher, and has a void coefficient calculated according to the following formula (1) of 1,000 or less, and a K value calculated according to the following formula (2) of 140 to 215. Void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient１／２ / 100)} Formula (1) K value={(total fineness (dtex) × number of hits (hits)} / {braid pitch (braids / 2.54 cm)} Formula (2)

[0019] (Hollow braid) The hollow braid according to the present disclosure is cylindrical and has holes penetrating along the length. The outer diameter of the hollow braid is not particularly limited, but may be, for example, 1 mm or more and 10 mm or less, and preferably 1 mm or more and 5 mm or less. The outer diameter of the hollow braid is the outer diameter of the hollow braid when it is cut perpendicularly to the length direction. The method for measuring the outer diameter is described in detail in the Examples. If the outer diameter of the hollow braid is less than 1 mm, fibers with a small total fineness will be used, which will make fuzzing and thread breakage more likely to occur during braiding, and appropriate performance will not be achieved. If the outer diameter of the hollow braid exceeds 10 mm, fewer hollow cords will be able to fit within a unit area, resulting in a small surface area, making the hollow braid unsuitable for use as a hollow fiber membrane substrate, etc.

[0020] The inner diameter of the hollow braid is not particularly limited, but may be, for example, 0.5 mm to 10 mm, and preferably 1 mm to 5 mm. The inner diameter of the hollow braid is the inner diameter of the circumferential surface formed by the fibers when the hollow braid is crossed perpendicularly to the longitudinal direction, in other words, the diameter of the hollow portion. The method for measuring the inner diameter will be described in detail in the Examples.

[0021] The thickness of the hollow braid is half the difference between the outer diameter and the inner diameter. The thickness is not particularly limited, but may be, for example, 0.05 mm or more and 1 mm or less, and preferably 0.1 mm or more and 0.5 mm or less.

[0022] The hollow ratio of a hollow braid is calculated according to the following formula (3): Hollow ratio (%) = (inner diameter of cross section of braid / outer diameter of cross section of braid) × 100 (3) The hollow ratio of a hollow braid according to the present disclosure is appropriately selected depending on the application of the hollow braid, but may be 50% or more and 90% or less, and preferably 80% or more and 90% or less.

[0023] The hollow braid is cylindrical, and its cross-sectional shape is preferably close to a perfect circle. The circularity (flatness) of a hollow braid is expressed by the flattening ratio, which is the ratio of the major axis to the minor axis, and is calculated by the following formula (4): Flattening ratio (%) = (minor axis / major axis) × 100 (4) Here, the major axis refers to the largest outer diameter of the cross section of the hollow braid, and the minor axis refers to the smallest outer diameter of the cross section of the hollow braid. The method for measuring the flattening ratio is described in detail in the Examples. The flattening ratio of the hollow braid may be 80% or more, and is preferably 90% or more. Furthermore, it is preferable that the flattening ratio does not change much even in a high-temperature environment.

[0024] The hollow braid according to the present disclosure is usually knitted from round cords braided on a braiding machine, and has a void coefficient calculated according to the following formula (1) of 1,000 or less, preferably 800 or less. If the void coefficient exceeds 1,000, permeability tends to be impaired. Void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient １／２ / 100)}...Formula (1)

[0025] The hollow braid according to the present disclosure preferably has a K value calculated according to the following formula (2) of 140 or more and 215 or less. When the K value is 140 or more, the braid is likely to maintain its hollow shape even when placed in a high-temperature environment. When the K value is 215 or less, it is believed that the braid does not become too hard and is likely to return to its original shape even when deformed at high temperatures. Furthermore, when the K value is within this range, even when used as a hollow structure, the film thickness of the hollow braid is likely to be in an appropriate range, the hollow shape is maintained, and the hollow braid is likely to function as an appropriate support. K value = {(total fineness (dtex) × number of stitches (stitches)} / {braid pitch (stitches / 2.54 cm)} ... formula (2)

[0026] The number of strikes of the hollow braid according to the present disclosure is not particularly limited as long as the K value of the braid falls within the above range, but may be 8 strikes or more and 64 strikes or less, and specifically may be 8, 12 strikes, 16 strikes, 24 strikes, 32 strikes, etc. From the viewpoint of setting the K value within an appropriate range, it is preferable that the number of strikes is 16 strikes or more and 32 strikes or less. The number of strikes is the number of bobbins used in a braiding machine for braiding.

[0027] (Fibers Constituting the Hollow Braid) The synthetic fibers constituting the hollow braid according to the present disclosure and having a melting point or thermal decomposition temperature of 280°C or higher may be monofilaments or multifilaments, but are preferably multifilaments. The total fineness of the synthetic fibers is preferably in the range of 10 to 2,000 dtex, more preferably 50 to 500 dtex. The single filament fineness of the synthetic fibers is preferably 5 dtex or less, more preferably 2.5 dtex or less. The number of filaments is preferably in the range of 3 to 1,000, more preferably 10 to 800.

[0028] The fibers constituting the hollow braid according to the present disclosure may be untwisted yarn or twisted yarn, as long as the void coefficient of the braid falls within the above range. In the case of twisted yarn, the number of twists is not particularly limited, but for example, when the total fineness is 220 dtex, the number of twists may be 80 T / m or more and 1000 T / m or less. The twist coefficient represented by the following formula (5) may be 5 or more and 500 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 100 or less. Twist coefficient (K) = (T × D １／２ ) ÷ 100 (5) (T: number of twists (T / m), D: total fineness (dtex))

[0029] The hollow braid according to the present disclosure is composed of synthetic fibers having a melting point or thermal decomposition temperature of 280° C. or higher. Examples of synthetic fibers having a melting point or thermal decomposition temperature of 280° C. or higher include polyphenylene sulfide (PPS) fibers, polyarylate fibers such as liquid crystal polyester (LCP), polyether ether ketone (PEEK) fibers, polyimide (PI) fibers, polyether sulfone (PES) fibers, polytetrafluoroethylene (PTFE) fibers, aramid fibers such as polyparaphenylene terephthalamide (PPTA), polyparaphenylene benzobisoxazole (PBO) fibers, etc. Among these, the hollow braid according to the present disclosure is preferably composed of any one of polyphenylene sulfide fibers, polyarylate fibers, and aramid fibers, or a combination thereof.

[0030] The melting point of synthetic fibers can be measured using differential scanning calorimetry (DSC). Specific examples of melting point measurement methods are described in detail in the Examples. The thermal decomposition temperature of synthetic fibers refers to the temperature at which the weight of the fiber decreases by 5% when thermogravimetric analysis (TGA) is performed under a nitrogen atmosphere, and can be measured using thermogravimetric analysis. A specific method for measuring the thermal decomposition temperature is as follows: A fiber sample (5-8 mg) is placed on an aluminum pan with a diameter of 5 mm, and heated in the temperature range of 40-580°C under air (heating rate: 10, 5, or 3°C / min) or in a 100 mL / min nitrogen gas flow (heating rate: 10°C / min). The weight change of each fiber sample is measured using a thermogravimetric analyzer. The temperature at which the weight of the fiber sample decreases by 5% is defined as the thermal decomposition temperature. There are no limitations on the thermogravimetric analyzer (TGA), but an EXSTAR 7200 manufactured by Seiko Instruments, Inc., for example, can be used.

[0031] It is also preferable to use synthetic fibers having a melting point or thermal decomposition temperature of 280° C. or higher and high chemical resistance. Examples of such fibers include PPS fibers, LCP fibers, PEEK fibers, PI fibers, PES fibers, and PTFE fibers.

[0032] It is particularly preferable to use polyphenylene sulfide (PPS) fiber as the fiber constituting the hollow braid. PPS fiber is a fiber obtained by melt spinning a polyphenylene sulfide resin made of a polymer having p-phenylene sulfide units as the main repeating unit (structural unit). Polyphenylene sulfide polymer types include crosslinked types, semi-crosslinked types, and linear types, with the linear type being preferred in terms of spinnability and stretchability.

[0033] In addition to polyphenylene resin, the PPS fiber may contain small amounts of various additives such as inorganic substances such as various metal oxides, kaolin, and silica, colorants, delustering agents, flame retardants, antioxidants, ultraviolet absorbers, infrared absorbers, crystal nucleating agents, fluorescent brighteners, end-group capping agents, and compatibilizers.

[0034] The cross-sectional shape of a single PPS fiber is not particularly limited, and the outer shape of the single fiber may be circular, triangular, square, hollow, or the like.

[0035] There are no particular restrictions on the strength of the PPS fiber, but it is preferable that it be 3 cN / dtex or more and that the elongation be 20% or more.

[0036] It is particularly preferable to use polyarylate fibers as the fibers constituting the hollow braid. Polyarylate fibers are also called wholly aromatic polyester fibers. Wholly aromatic polyester fibers have high tensile strength and can withstand the tensile load when used as a cord. In addition, their melting temperature is high, at 300 to 360°C, and there is little deterioration in physical properties due to thermal decomposition, etc., even in high-temperature environments.

[0037] Wholly aromatic polyester fibers are formed from wholly aromatic polyester polymers. Wholly aromatic polyester polymers consist of aromatic dicarboxylic acids, aromatic diols, and / or aromatic hydroxycarboxylic acids, or derivatives thereof, and may also include copolymers of these with alicyclic dicarboxylic acids, alicyclic diols, aliphatic diols, or derivatives thereof. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, 4,4'-dicarboxydiphenyl, 2,6-dicarboxynaphthalene, 1,2-bis(4-carboxyphenoxy)ethane, etc., and their nucleus-substituted derivatives with alkyl, aryl, alkoxy, and halogen groups. Examples of aromatic diols include hydroquinone, resorcinol, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxybenzophenone, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylethane, 2,2-bis(4-hydroxyphenyl)propane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfide, 2,6-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, etc., and their respective nucleus-substituted derivatives with alkyl, aryl, alkoxy, and halogen groups. Examples of aromatic hydroxycarboxylic acids include p-hydroxybenzoic acid, m-hydroxybenzoic acid, 2-hydroxynaphthalene-6-carboxylic acid, 1-hydroxynaphthalene-5-carboxylic acid, etc., and their respective nucleus-substituted derivatives with alkyl, aryl, alkoxy, and halogen groups. Alicyclic dicarboxylic acids include trans-1,4-dicarboxycyclohexane, cis-1,4-dicarboxycyclohexane, etc., and their alkyl, aryl, and halogen nucleus-substituted derivatives. Alicyclic and aliphatic diols include trans-1,4-dihydroxycyclohexane, cis-1,4-dihydroxycyclohexane, ethylene glycol, 1,4-butanediol, and xylylenediol.

[0038] Among these combinations, preferred wholly aromatic polyester polymers include, for example, (a) copolyesters consisting of 40 to 70 mol% of p-hydroxybenzoic acid residues, 15 to 30 mol% of the above-mentioned aromatic dicarboxylic acid residues, and 15 to 30 mol% of aromatic diol residues; (b) copolyesters consisting of terephthalic acid and / or isophthalic acid and chlorohydroquinone, phenylhydroquinone, and / or hydroquinone; and (c) copolyesters consisting of 20 to 80 mol% of p-hydroxybenzoic acid residues and 20 to 80 mol% of 2-hydroxynaphthalene-6-carboxylic acid residues.

[0039] The wholly aromatic polyester fiber may contain other polymers or additives (pigments, carbon, heat stabilizers, ultraviolet absorbers, lubricants, fluorescent whitening agents, etc.) to the extent that the tenacity of the fiber is not substantially reduced.

[0040] (Physical Properties of Hollow Braid) The hollow braid according to the present disclosure maintains its hollow shape well even in a high-temperature environment. Shape retention is expressed as an index of the change in the flattening of the hollow braid before and after high-temperature treatment. As described above, the flattening of the hollow braid according to the present disclosure may be 80% or more, preferably 90% or more, and more preferably 95% or more. The flattening after high-temperature treatment in which the braid is kept in a hot-air dryer at 170°C for 20 minutes may also be 80% or more, preferably 90% or more, and more preferably 95% or more. The change (decrease) in the flattening due to the high-temperature treatment may be 20% or less, preferably 10% or less, more preferably 5% or less, and more preferably 0%. In other words, it is more preferable that there is no decrease in the flattening before and after the high-temperature treatment.

[0041] The hollow braid according to the present disclosure exhibits little decrease in strength even in a high-temperature environment and has high heat resistance. Heat resistance is expressed as an index of the change in strength of the hollow braid before and after high-temperature treatment. After high-temperature treatment in which the braid is kept in a hot air dryer at 200°C for 24 hours, the tensile strength is preferably maintained at 80% or more, and more preferably at 90% or more, of the tensile strength before the high-temperature treatment.

[0042] The hollow braid according to the present disclosure has a high compressive modulus, and maintains its hollow shape well even when deformation occurs due to changes in pressure, etc. The compressive modulus is a value measured in accordance with JIS L 1096, and the measurement method is described in detail in the Examples. The compressive modulus of the hollow braid according to the present disclosure may be 80% or more, and preferably 90% or more. The hollow braid according to the present disclosure is made of synthetic fibers having a melting point or thermal decomposition temperature of 280°C or higher, and a hollow braid with a high compressive modulus is realized by setting the void coefficient and K value within specific ranges.

[0043] The hollow braid according to the present disclosure has high permeability and is suitable for use as a hollow structure constituting a hollow fiber membrane or the like. The permeability is a value measured in accordance with JIS L1907 7.1.2 Byreck method, and the measurement method is described in detail in the Examples. The permeability (Byreck method) of the hollow braid according to the present disclosure is 10 mm or more, preferably 15 mm or more, and more preferably 20 mm or more. The hollow braid according to the present disclosure is composed of synthetic fibers having a melting point or thermal decomposition temperature of 280°C or higher, and by setting the void coefficient and K value within specific ranges, a hollow braid with high heat resistance and high permeability is realized. Permeability indicates the ease with which liquids permeate into a hollow structure. A hollow braid with high permeability has appropriate voids that allow liquids to quickly permeate, and it is believed that this configuration allows liquids and gases to quickly pass from the inside of the hollow braid (the hollow portion on the inner diameter side) to the outside (the outer surface side). For this reason, the hollow braid according to the present disclosure can be suitably used in hollow fiber membranes and the like that are used in a manner in which a fluid passes through the mesh structure of the hollow braid.

[0044] (Method for manufacturing hollow braid) The method for manufacturing a hollow braid according to the present disclosure is not particularly limited, and the braid can be manufactured by a known braiding method. The fibers constituting the braid may be manufactured by a known method, or commercially available products may be obtained and used. As a braiding method, for example, a fiber bobbin as the material is prepared and subjected to the braiding process either as is or after twisting using a device such as a ring twister. Multiple fibers may be twisted together during twisting. One or an appropriate number of fibers as the material are wound onto a carrier bobbin for a braiding machine. The carrier bobbin is set in the braiding machine and braided. The braided hollow braid is preferably subjected to a heat shrinkage treatment such as dry heat shrinkage or hot water treatment.

[0045] (Hollow Structure) The hollow structure according to the present disclosure includes the hollow braid described above. The hollow structure may be a hollow structure having a resin layer (resin film) on the outer periphery of the hollow braid described above. The resin layer may partially or entirely permeate the hollow braid, integrating the resin layer and the hollow braid. The method for forming the resin film is not particularly limited, and examples include a method of applying a film-forming solution to the outer periphery of the hollow braid, a method of immersing the hollow braid in the film-forming solution, and a method of spraying the film-forming solution on the outer periphery of the hollow braid. The hollow braid to which the film-forming solution has been applied may be further subjected to processes such as coagulation of the film-forming solution, washing, and drying to form a hollow structure having a resin film on its surface.

[0046] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the examples described below.

[0047] Example 1 1. Production of PPS Fiber: p-Polyphenylene sulfide (PPS) resin (moisture content: 20 ppm) with a melt flow rate of 160 g / 10 min was prepared and melted at a spinning temperature of 328°C. The molten PPS resin was extruded using a spinneret with 48 holes at a throughput rate resulting in an undrawn fineness of 68.75 dtex. The extruded PPS yarn was cooled with cold air at 25°C in a uniflow cooling device, and then an oil was applied to the yarn using an oiling nozzle. The yarn was then passed through two unheated godet rolls at a speed of 1,570 m / min and wound onto a bobbin using a winder to obtain a polyphenylene sulfide undrawn yarn bobbin. The yarn was then drawn using a drawing machine. The stretching machine used was equipped with a creel, an unheated feed roll (1st R), a preheating heater roll (2nd R), a plate heater for heat setting installed between the draw rolls, and a winding section. An unstretched yarn bobbin was placed on the creel, preheated at 100°C, stretched 3.2 times, heat-set at 172°C, and wound at a stretching speed of 800 m / min. This procedure yielded a PPS fiber (total fineness 220 dtex, 48 filaments, single yarn fineness 4.6 dtex, melting point 280°C). The melting point of the PPS fiber was measured in a nitrogen atmosphere at a heating rate of 10°C / min using a differential scanning calorimeter (DSC) (PerkinElmer "Differential Scanning Calorimeter (DSC) Input Compensation Type Double Furnace DSC8500"), and the same applies to the other fibers used in the examples and comparative examples.

[0048] The obtained PPS fibers were twisted at 200 T / m (twist factor 30) using a ring twisting machine, and braided at 32 strands using a braiding machine to form a hollow braid with a braid pitch of 50 braids / inch (2.54 cm). The obtained hollow braid was wound into a skein and subjected to a hot water treatment (98°C x 60 minutes) using an Obermeyer dyeing machine to obtain the hollow braid of Example 1.

[0049] 3. Construction and Evaluation of Hollow Braids For the obtained hollow braids, the void coefficient was calculated according to the following formula (1) and the K value was calculated according to the formula (2): Void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient １／２ / 100)} Equation (1) K value={(total fineness (dtex)×number of stitches (stitches)} / {braid pitch (stitches / 2.54 cm)} Equation (2) Furthermore, the outer diameter, inner diameter, hollowness, flattening retention coefficient, compressive modulus, permeability, heat resistance, and chemical resistance of the obtained hollow braid were evaluated. Each measurement and evaluation was performed by the following methods.

[0050] <Outer diameter, inner diameter, hollow ratio> The outer diameter and inner diameter of the obtained hollow braid were measured by the following method. The hollow ratio was calculated according to the following formula (3). Measurement of outer diameter: A cross section perpendicular to the length direction of the braid was measured with a digital caliper. Measurements were taken at 10 different points along the length of the braid and the average value was taken as the outer diameter (mm) of the hollow braid. Measurement of inner diameter: The film thickness of the cross section perpendicular to the length direction of the hollow braid was measured with a digital caliper, and the value of outer diameter - (film thickness x 2) was taken as the inner diameter (mm). As with the outer diameter, the average value of measurements taken at 10 points was taken as the inner diameter (mm) of the hollow braid. Hollow ratio (%) = (inner diameter of cross section of braid / outer diameter of cross section of braid) x 100 (3)

[0051] <Flatness and Flatness Retention Coefficient> The cross section of the hollow braid was observed under a microscope, and the outer diameter at the longest point was measured as the major axis (mm), and the outer diameter at the shortest point was measured as the minor axis (mm). The major and minor axes were measured at 10 points on the braid, and the average values ​​were taken as the major and minor axes of the hollow braid. The flatness (%) of the hollow braid was calculated from the major and minor axes according to the following formula (4): Flatness (%) = (minor axis / major axis) x 100 (4) Furthermore, the hollow braid was treated in a hot air dryer at 170°C for 20 minutes, and the major and minor axes of the braid after the heat treatment were similarly measured to calculate the flatness. The flatness retention coefficient was calculated from the flatness before and after the heat treatment. Flatness retention coefficient = flatness of hollow braid after heat treatment (%) / flatness of hollow braid before heat treatment (%)

[0052] <Compressive modulus> With reference to JIS L1096:2010 8.20, a hollow braid having a sample length of 50 mm was placed at rest, and the outer diameter of the hollow braid: T ０ Then, the braid was left for 1 minute under a constant compressive load of 1.47 N, and the outer diameter of the hollow braid under the load: T １Next, the applied pressure was removed, and after leaving it for 1 minute, the outer diameter: T' (mm) was measured again under an initial load of 0.245 N. ０ The obtained T ０ , T １ , T' ０ The value of was introduced into the following formula to calculate the compressive modulus: Compressive modulus (%) = [(T' ０ -T １ ) / (T ０ -T １ ) × 100 The evaluation criteria for compressive modulus were as follows: Compressive modulus 90% or more: A+ (very good) Compressive modulus less than 90% and 80% or more: A (good) Compressive modulus less than 80% and 50% or more: B (slightly poor) Compressive modulus less than 50%: C (poor)

[0053] <Permeability> According to the Byreck method of JIS L1907:2010 7.1.2, the lower end 20 mm of a hollow cord cut to 200 mm was immersed in water, and after leaving it for 10 minutes, the height to which the water rose was measured. The evaluation criteria for permeability were as follows: Height of water rises 20 mm or more: A+ (very good); Height of water rises 15 mm or more but less than 20 mm: A (good); Height of water rises 10 mm or more but less than 15 mm: B (slightly poor); Height of water rises less than 10 mm: C (poor).

[0054] <Heat Resistance> The tensile strength of the hollow braid was measured using a tension and compression tester (Technograph TGI manufactured by Minebea Mitsumi). The hollow braid was treated in a hot air dryer at 200°C for 24 hours, and the tensile strength after treatment was measured in the same manner. The strength retention was calculated from the tensile strengths before and after treatment. Strength retention (%) = (strength after heat treatment (N) / strength before heat treatment (N)) x 100. The heat resistance was evaluated based on the following criteria: Strength retention of 90% or more: A+ (very good) Strength retention of 80% or more but less than 90%: A (good) Strength retention of 50% or more but less than 80%: B (slightly poor) Strength retention of less than 50%: C (poor)

[0055] <Chemical Resistance> The tensile strength of the hollow braid was measured using a tension and compression tester (Technograph TGI manufactured by Minebea Mitsumi). The hollow braid was immersed in a 1N sodium hydroxide solution at 80°C for 100 hours, and the strength after immersion was measured in the same manner. The strength retention was calculated from the tensile strength before and after treatment. Strength retention (%) = Strength after immersion treatment (N) / Strength before immersion treatment (N) x 100. The chemical resistance was evaluated based on the following criteria: Strength retention of 90% or more: A+ (very good) Strength retention of 80% or more but less than 90%: A (good) Strength retention of 50% or more but less than 80%: B (slightly poor) Strength retention of less than 50%: C (poor)

[0056] Example 2 A hollow braid was produced in the same manner as in Example 1, except that untwisted PPS fibers were used as the PPS fibers constituting the braid, and evaluation was carried out in the same manner as in Example 1.

[0057] Example 3 A hollow braid was produced in the same manner as in Example 1, except that PPS fibers having a twist of 540 T / m (twist coefficient 80) were used as the PPS fibers constituting the braid, and evaluation was carried out in the same manner as in Example 1.

[0058] [Example 4] A hollow braid was produced in the same manner as in Example 1, except that PPS fibers having a total fineness of 330 dtex and a twist of 150 T / m (twist coefficient 27) were used as the PPS fibers constituting the braid, and evaluation was carried out in the same manner as in Example 1.

[0059] Example 5 A hollow braid was produced in the same manner as in Example 1, except that untwisted PPS fibers having a total fineness of 330 dtex were used as the PPS fibers constituting the braid, and evaluation was carried out in the same manner as in Example 1.

[0060] [Example 6] A hollow braid was produced in the same manner as in Example 1, except that the PPS fibers constituting the braid had a total fineness of 440 dtex and a twist of 120 T / m (twist coefficient 25) and the braid had 24 ends, and evaluation was carried out in the same manner as in Example 1.

[0061] [Example 7] A hollow braid was produced in the same manner as in Example 1, except that untwisted LCP fibers (Zexion (registered trademark), manufactured by KB Seiren Co., Ltd., melting point 326°C) having a total fineness of 220 dtex were used as the fibers constituting the braid, and evaluation was carried out in the same manner as in Example 1.

[0062] [Example 8] A hollow braid was produced in the same manner as in Example 1, except that untwisted PPTA fibers having a total fineness of 220 dtex were used as the fibers constituting the braid, and evaluation was carried out in the same manner as in Example 1. The thermal decomposition temperature of the PPTA fibers was 400°C or higher.

[0063] Comparative Example 1 A hollow braid was produced in the same manner as in Example 1 except that the number of braids was 24 and the braid pitch was 55 braids / inch (2.54 cm), and evaluation was carried out in the same manner as in Example 1.

[0064] Comparative Example 2 A hollow braid was produced in the same manner as in Example 1, except that untwisted PPS fibers were used as the PPS fibers constituting the braid, the number of braids was 24, and the braid pitch was 55 braids / inch (2.54 cm), and evaluation was carried out in the same manner as in Example 1.

[0065] Comparative Example 3 A hollow braid was produced in the same manner as in Example 1, except that untwisted PPS fibers having a total fineness of 440 dtex were used as the PPS fibers constituting the braid, the number of braids was 24, and the braid pitch was 45 braids / inch (2.54 cm), and evaluation was carried out in the same manner as in Example 1.

[0066] Comparative Example 4 A hollow braid was produced in the same manner as in Example 1, except that untwisted PPS fibers having a total fineness of 440 dtex were used as the PPS fibers constituting the braid, the number of braids was 32, and the braid pitch was 70 braids / inch (2.54 cm), and evaluation was carried out in the same manner as in Example 1.

[0067] Comparative Example 5 A hollow braid was produced in the same manner as in Example 1, except that PET fibers (manufactured by KB Seiren Co., Ltd., melting point 255°C) having a total fineness of 220 dtex and a twist of 200 T / m (twist coefficient 30) were used as the fibers constituting the braid, and evaluation was performed in the same manner as in Example 1.

[0068] The structures and evaluation results of the hollow braids of Examples 1 to 8 and Comparative Examples 1 to 5 are summarized in Table 1.

[0069]

[0070] As shown in Table 1, the hollow braids of Examples 1 to 8 all had a flatness retention coefficient of 0.96 or more, and retained their shape even after heat treatment. In addition, the compressive modulus, permeability, heat resistance, and chemical resistance were all evaluated as A+ or A.

[0071] On the other hand, Comparative Example 1, in which the K value was less than 100, had a flatness retention coefficient of 0.77, and deformation of the hollow braid due to heat treatment was confirmed. Furthermore, the compressive modulus was evaluated as B, and shape recovery after pressure application was insufficient. Furthermore, Comparative Example 2, in which the K value was less than 100, also had a flatness retention coefficient of 0.79, and deformation of the hollow braid due to heat treatment was confirmed. Furthermore, the compressive modulus was evaluated as B, and shape recovery after pressure application was insufficient. Furthermore, Comparative Example 3, in which the K value exceeded 215, had a flatness retention coefficient of 0.79, and deformation of the hollow braid due to heat treatment was confirmed. Furthermore, Comparative Example 4, in which the void coefficient exceeded 1,000, had insufficient permeability. Furthermore, Comparative Example 5, in which PET fibers were used as the synthetic fibers, had insufficient heat resistance and chemical resistance.

[0072] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0073] The hollow braid according to the present disclosure has shape retention, compressive elasticity, heat resistance, and permeability in high-temperature environments, and can be suitably used as a substrate for a porous hollow fiber membrane or a sleeve material for a motor, etc., even in high-temperature and high-humidity environments.

Claims

1. A hollow braid made of synthetic fibers with a melting point or thermal decomposition temperature of 280°C or higher, having a void coefficient of 1,000 or less as calculated according to the following formula (1), and a K value of 140 to 215 as calculated according to the following formula (2): void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient １／２ / 100)} (1) K value = {(total fineness (dtex) × number of hits (hits)} / {braid pitch (braids / 2.54 cm)} (2) 2. The hollow braid according to claim 1, wherein the synthetic fibers are any one of polyphenylene sulfide fibers, polyarylate fibers, and aramid fibers, or a combination thereof.

3. A hollow braid made of one or a combination of polyphenylene sulfide fiber, polyarylate fiber, aramid fiber, polyether ether ketone fiber, polyether sulfone fiber, and polyimide fiber, having a void coefficient of 1,000 or less as calculated according to the following formula (1), and a K value of 140 to 215 as calculated according to the following formula (2): void coefficient = {total fineness (dtex)} １／２ × {braid pitch (braid / 2.54 cm)} × {1 - (twist coefficient １／２ / 100)} (1) K value = {(total fineness (dtex) × number of hits (hits)} / {braid pitch (braids / 2.54 cm)} (2) 4. The hollow braid according to any one of claims 1 to 3, wherein the total fineness is 10 dtex or more and 2,000 dtex or less.

5. The hollow braid according to any one of claims 1 to 4, wherein the number of strands is 8 strands or more and 64 strands or less.

6. The hollow braid according to any one of claims 1 to 5, wherein the hollow ratio calculated according to the following formula (3) is 50% or more and 90% or less: Hollow ratio (%) = (inner diameter of cross section of hollow braid / outer diameter of cross section of hollow braid) x 100 (3) 7. A hollow structure comprising the hollow braid according to any one of claims 1 to 6.

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