Flexible tube

Abstract

[Problem] To provide a flexible tube that is pliable, has excellent shape retention, is not damaged during negative pressure due to fluid transfer, and has excellent restorability after flat compression. [Solution] This flexible tube comprises: an inner layer that is composed of a flexible material; a monofilament that is helically wound along the outer surface of the inner layer; a multifilament that is helically wound around the outer side of the monofilament in a direction intersecting the monofilament; and an outer layer that is composed of a flexible material coated on the outer side of the multifilament. The resin material constituting the monofilament has a flexural strength of 65-95 MPa as measured according to ASTM D790 and a flexural modulus of 1.5-3.0 GPa.

Description

flexible tube

[0001] The present invention relates to a flexible tube, and more particularly to a flexible tube that is flexible, has excellent shape retention, is not damaged when subjected to negative pressure due to fluid transport, and has excellent restoring properties after being flattened and compressed.

[0002] Hoses used in fields such as resin molding, printing, automobiles, machine tools, industrial parts, and agriculture require flexibility that allows them to be placed in a variety of devices and facilities. To improve pressure resistance while maintaining flexibility, hoses with a reinforcing layer formed by braiding multifilaments, which are bundles of multiple fibers, are known. Shape retention is also required so that the flow path does not become blocked due to deformation even when bent more slightly. Flexible tubes with excellent shape retention are known, in which a reinforcing layer is formed by spirally winding monofilaments made of resin formed by extrusion molding, which are more rigid than multifilaments. Furthermore, flexible tubes with reinforcing layers formed using both multifilaments and monofilaments are known from the perspective of achieving both flexibility and shape retention. These flexible tubes are used as piping for various chemical raw materials, chemicals, air, various gases, powders, fluids, water, oil, water-soluble oils, coolants, etc., in applications where moving parts or space saving are required, such as incorporation into various devices in fields such as resin molding, printing, automobiles, machine tools, industrial parts, agriculture, pharmaceutical manufacturing, medical care, physics and chemistry, food manufacturing, and semiconductor manufacturing, or in equipment connecting devices to chillers.

[0003] Patent Document 1 discloses a pressure-resistant hose comprising an inner tube made of a plastic harder than rubber, at least one fibrous reinforcement layer made of monofilaments with a diameter of 0.3 millimeters or more and provided unbonded to the outside of the inner tube, and an outer tube provided outside the fibrous reinforcement layer. Patent Document 2 discloses a multilayer pressure-resistant hose characterized in that a reinforcing thread is interposed between the inner resin layer and the outer resin layer, the reinforcing thread being a monofilament, and the contacting portions of the inner resin layer and the outer resin layer being fixed to each other. Patent Document 3 discloses a multilayer pressure-resistant hose in which multiple reinforcing threads are wound helically between the inner and outer layers, crossing each other. In this multilayer pressure-resistant hose, the reinforcing thread is a multifilament wound helically around the outer surface of the inner layer, and a monofilament wound helically around the outer surface, crossing each other in a mesh pattern. At these intersections, the tension of the monofilaments forms recesses in the multifilaments, and the monofilaments are engaged with the recesses to form reinforcing layers made of the multifilaments and monofilaments between the inner layer and the outer layer, thereby improving the shape retention and flexibility of the hose.

[0004] Japanese Utility Model Publication No. 2-29348 Japanese Patent Application Laid-Open No. 2006-194347 Japanese Patent No. 5070526

[0005] However, Patent Document 1 discloses a technology for improving the shape retention of a hose and suppressing kinking by using highly rigid monofilaments in the fibrous reinforcing layer. However, there is a problem that the hose can be compressed flat due to external forces that exceed the shape retention of the hose, such as when hoses overlap each other or when the hose is stepped on by a person or a cart after installation. If the hose has low resilience, the hose will remain plastically deformed and block the flow path, preventing satisfactory fluid flow.

[0006] Furthermore, Patent Document 2 discloses a technology that improves pressure resistance by using only monofilaments as reinforcing threads. However, because the rigidity of the hose itself is very high and deformation such as bending or twisting is unlikely to occur, when the hose is used in a moving part, a large repulsive force is generated when the hose is bent, which places a load on the connection with the fitting, resulting in problems such as disconnection, leakage, or breakage.

[0007] Furthermore, for example, in semiconductor manufacturing plants, there is an equipment configuration in which utility equipment such as a chiller and water treatment equipment is located on the first floor, and liquid is delivered to the manufacturing area on the second floor using a pump, etc. In such a configuration, a hose that is placed across floors may be subjected to negative pressure when the delivery of liquid is stopped, as the remaining fluid moves downward due to gravity. Therefore, in a hose such as that disclosed in Patent Document 3, repeated application of negative pressure causes separation between the outer layer supported by monofilaments that are highly rigid and have excellent shape retention, and the multifilaments and inner layer that are flexible and have poor shape retention, resulting in the problem of clogging of the flow path.

[0008] The present invention addresses these problems and aims to provide a flexible tube that is flexible, has excellent shape retention, does not break when subjected to negative pressure due to fluid transport, and has excellent recovery properties after being flattened and compressed.

[0009] After extensive research, the inventors have found that the above-mentioned problems can be solved by a flexible tube of the present invention. The flexible tube of the present invention comprises an inner layer made of a flexible material, a monofilament wound spirally along the outer surface of the inner layer, a multifilament wound spirally around the monofilament in a direction intersecting the monofilament, and an outer layer made of a flexible material covering the outside of the multifilament, wherein the resin material constituting the monofilament has a flexural strength of 65 to 95 MPa and a flexural modulus of 1.5 to 3.0 GPa, as measured in accordance with ASTM D790.

[0010] According to the present invention, it is possible to provide a flexible tube that is flexible, has excellent shape retention, is not damaged when subjected to negative pressure due to fluid transfer, and has excellent restoring ability after being flattened and compressed.

[0011] A preferred embodiment of the flexible tube of the present invention will be described in detail below. The flexible tube illustrated in this embodiment includes a first layer (inner layer) made of a flexible material, a monofilament wound spirally along the outer surface of the first layer, a multifilament wound spirally around the monofilament in a direction intersecting the monofilament, and a second layer (outer layer) made of a flexible material that covers the outside of the multifilament.

[0012] <Flexible Material> The flexible material is not particularly limited, and suitable flexible materials include resins, rubbers, elastomers, etc. Specific examples of flexible materials include polyvinyl chloride resins, polyamide resins, polyurethane resins, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymers, ethylene-acrylate copolymers such as ethylene-methyl acrylate copolymers and ethylene-ethyl acrylate copolymers, ethylene-methacrylate copolymers such as ethylene-methyl methacrylate copolymers and ethylene-ethyl methacrylate copolymers, olefin resins such as polypropylene and propylene-α-olefin copolymers, ethylene / tetrafluoroethylene copolymer (ETFE), polyvinyl chloride resins, polyvinyl acetate copolymers, polyvinyl acrylate copolymers, polyvinyl meth ... Examples of the fluororesin include fluororesins such as tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene / chlorotrifluoroethylene copolymer (ECTFE), and tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride terpolymer (THV), polyamide-based elastomers, urethane-based elastomers, styrene-based elastomers, olefin-based elastomers, fluorine-based elastomers, silicone rubber, urethane rubber, nitrile rubber, styrene-butadiene rubber, chloroprene rubber, ethylene propylene diene rubber, and combinations thereof.

[0013] If necessary, additives may be added to the flexible material to impart functions such as flexibility, thermal stability, light stability, and weather resistance. Additives include plasticizers and stabilizers that impart flexibility. Examples of plasticizers include alkyl hydroxybenzoate plasticizers with a molecular weight of 200 to 400 and adipic acid polyesters with a molecular weight of 2000 to 2500. These plasticizers have low elution in oil-based fluids and foods, and can maintain physical properties such as flexibility over long periods of time, but are not limited to these. In addition to the above-mentioned components, various additives (heat stabilizers, light stabilizers, UV absorbers, antioxidants, antifogging agents, antistatic agents, etc.) may also be added to the flexible material.

[0014] <Monofilament> The monofilament is made of a resin material. The resin material constituting the monofilament preferably has a bending strength of 65 to 95 MPa, more preferably 75 to 85 MPa, measured in accordance with ASTM D790. If the bending strength is less than 65 MPa, the rigidity of the monofilament is low and the shape retention of the flexible tube is poor, resulting in the hose being easily deformed by external forces and being compressed flat to an irreversible state, causing problems such as blocking the flow path. On the other hand, if the bending strength is greater than 95 MPa, the rigidity of the monofilament is high and the hose is difficult to deform in the bending or twisting directions, resulting in a flexible tube that is uncomfortable to use. In addition, when used in a moving part, a large repulsive force is generated when bent, putting a load on the connection with the fitting, causing problems such as disconnection, leakage, or breakage.

[0015] Furthermore, the resin material constituting the monofilament preferably has a flexural modulus of 1.5 to 3.0 GPa, more preferably 2.0 to 2.5 GPa, as measured in accordance with ASTM D790. If the flexural modulus of the resin material is less than 1.5 GPa, the hose's recovery is poor. When the hose is compressed flat by an external force exceeding its shape retention, the hose remains plastically deformed, blocking the flow path, resulting in an insufficient fluid flow. On the other hand, if the flexural modulus of the resin material is greater than 3.0 GPa, the repulsive force when the hose is bent or twisted increases, resulting in a flexible tube that is uncomfortable to use. Furthermore, when used in a moving part, a large repulsive force is generated when bent, which places a load on the connection with the fitting, causing problems such as disconnection, leakage, or breakage. By setting the flexural modulus of the resin material to 1.5 to 3.0 GPa, a flexible tube can be obtained that has excellent recovery when compressed flat and is less likely to break even when a load is applied to the connection with the fitting.

[0016] Furthermore, the resin material constituting the monofilament preferably has a tensile yield strength of 45 to 60 MPa, more preferably 50 to 55 MPa, as measured in accordance with ASTM D 638. By ensuring that the tensile yield strength of the resin material falls within this range, a flexible tube with excellent pressure resistance and shape retention can be obtained without the monofilament breaking.

[0017] Examples of resin materials constituting the monofilament include synthetic fibers formed by extrusion molding of polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT), as well as thermoplastic resins such as polyamide resin, polypropylene resin, fluororesin, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyetherimide (PEI), and polyacetal (POM). In particular, it is preferable to use polyethylene terephthalate (PET), which has an excellent balance of bending elasticity and mechanical strength such as rigidity and toughness, and can be easily molded uniformly to a predetermined outer diameter.

[0018] The outer diameter, number of strands, etc. of the monofilament can be selected appropriately depending on the operating pressure, the diameter and wall thickness of the flexible tube, the material, etc. In view of the relationship between the pressure resistance and wall thickness of a typical flexible tube, the outer diameter of the monofilament is preferably about 0.5 to 2 mm, and by setting the outer diameter of the monofilament within this range, the flexible material is not excessively reduced even in areas where the monofilament is present, and a flexible tube with excellent pressure resistance can be obtained.

[0019] The monofilament preferably has a breaking strength per unit fineness of 0.2 N / tex or more, which makes the monofilament less likely to break and allows the production of a flexible tube with excellent pressure resistance.

[0020] Furthermore, the breaking elongation of the monofilament is preferably 30 to 40%. By keeping the breaking elongation within this range, the monofilament can be stretched appropriately to follow the deformation of the flexible tube, and a flexible tube with excellent flexibility and pressure resistance can be obtained.

[0021] <Multifilament> Examples of the multifilament include a single thread made by twisting together polyester such as PET or PBT, nylon (registered trademark), or aramid fiber.

[0022] The thickness, number of strands, number of twists, etc. of the multifilament can be selected as appropriate depending on the operating pressure, the diameter and thickness of the flexible tube, the material, etc. In view of the relationship between the pressure resistance and thickness of a typical flexible tube, the thickness of the multifilament is preferably about 1000 to 1500 decitex; by keeping the thickness within this range, the amount of flexible material is not excessively reduced even in areas where the multifilament is present, and a flexible tube with excellent pressure resistance can be obtained.

[0023] Furthermore, the multifilament preferably has a breaking strength per unit fineness of 0.5 N / tex or more, which makes the multifilament less likely to break and allows a flexible tube with excellent pressure resistance to be obtained.

[0024] Furthermore, it is preferable that the multifilament has a breaking elongation of 10 to 30%. By setting the breaking elongation within this range, the multifilament can be stretched appropriately in response to deformation of the flexible tube, and a flexible tube with excellent flexibility and pressure resistance can be obtained.

[0025] <Flexible tube> If, unlike the laminated structure of the flexible tube of this embodiment, the multifilaments are arranged on the inner layer side of the monofilaments in the flexible tube, repeated application of negative pressure to the flexible tube will cause peeling between the outer layer supported by the monofilaments, which are highly rigid and have excellent shape retention, and the multifilaments and inner layer, which are flexible and have poor shape retention, resulting in the problem of blocking the flow path.

[0026] In contrast, in the flexible tube of this embodiment, the monofilaments and multifilaments are laminated as described above. This not only prevents the multifilaments from being supported by the monofilaments and peeling off under negative pressure, but also provides a lattice-like reinforcement between the multifilaments and monofilaments, resulting in high resistance to negative pressure and a flexible tube with superior shape retention compared to conventional flexible tubes. Furthermore, when the internal pressure increases, the monofilaments expand as the inner layer expands, reducing breaks in the inner layer due to partial penetration of the multifilaments. This prevents fluid from entering through such breaks, thereby enabling the flexible tube to be used for a long period of time. Furthermore, the flexible material of the outer layer fills the space formed by the intersections of the monofilaments and multifilaments, and its inner circumferential surface adheres closely to the outer circumferential surface of the inner layer. This reduces the likelihood of air being trapped at the intersections of the monofilaments and multifilaments, preventing air bubbles from remaining at the intersections.

[0027] The monofilaments and multifilaments in the flexible tube of this embodiment are preferably wound at equal intervals in the circumferential and axial directions at approximately equal angles, thereby making it possible to obtain a flexible tube with excellent pressure resistance.

[0028] Furthermore, it is known from experience that in this type of flexible tube, when the flexible tube expands under pressure, the monofilament and multifilament braids remain stationary at a certain angle. If the braid angle is defined as the sum of the acute angle between the tube axis and the monofilament and the acute angle between the tube axis and the multifilament, a flexible tube with even better pressure resistance can be obtained by pre-braiding the tube at a braid angle close to 100 to 110°, which is the braid angle in a stationary state. A more preferable braid angle is 102 to 106°. It is undesirable, however, if the monofilament and the multifilament are wound in the same direction, the flexible tube will stretch while twisting under pressure, causing unexpected contact with surrounding devices or moving parts and resulting in damage.

[0029] As long as the flexible tube of this embodiment has the above-described configuration, it may be a flexible tube in which a layer made of another flexible material is further laminated on the outside of the second layer, or may have an innermost layer or an outermost layer. The total number of layers of the flexible tube is not particularly limited, and it may have at least two layers.

[0030] The flexible tube of this embodiment can be used as piping for various chemical raw materials, chemicals, air, various gases, powders, fluids, water, oil, water-soluble oil, coolants, etc. in applications where moving parts and space saving are required, such as incorporation into various devices in the fields of resin molding, printing, automobiles, machine tools, industrial parts, agriculture, pharmaceutical manufacturing, medical care, physics and chemistry, food manufacturing, and semiconductor manufacturing, or in equipment connecting devices to chillers.

[0031] The flexible tube of this embodiment described above has the following advantages: The flexible tube of this embodiment is flexible and has excellent shape retention, is not damaged when subjected to negative pressure due to fluid transport, and has excellent recovery ability after being flattened and compressed, and can be used as a tube with a much longer life than conventional products.

[0032] As described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0033] The present invention will be described in more detail below with reference to examples and comparative examples, but the technical scope of the present invention is not limited thereto. In these examples, flexible tubes of Examples 1 to 9 and Comparative Examples 1 to 5 were fabricated and evaluated for breakage, peeling, and crushing. The flexible tubes were fabricated by braiding monofilaments and multifilaments between the inner and outer layers. Examples 1 to 9 and Comparative Examples 1 to 5 will be described below.

[0034] The monofilaments used in the flexible tubes of Examples 1 to 9 and Comparative Examples 1 to 5 were varied in bending strength, bending modulus, breaking strength per unit fineness, and breaking elongation by appropriately manipulating various parameters. Furthermore, for the flexible tubes of Examples 1 to 9 and Comparative Examples 1 to 5, the following reinforcement method A or B was used to form a reinforcing layer made of monofilaments and multifilaments. A: The monofilament was spirally wound along the outer surface of the inner layer, and the multifilament was spirally wound in a direction intersecting the outer side of the monofilament to form a reinforcing layer. The braiding angle between the monofilament and the multifilament was 104°, and the braiding pitch, represented by the axial distance between the intersection of the monofilament and the multifilament (in the axial direction of the flexible tube), was 5 mm. B: The multifilament was spirally wound along the outer surface of the inner layer, and the monofilament was spirally wound in a direction intersecting the outer side of the multifilament to form a reinforcing layer. The braiding angle and braiding pitch were the same as those of reinforcement method A.

[0035] Table 1 below shows various parameters of the monofilaments and the reinforcement methods used for the flexible tubes of Examples 1 to 9 and Comparative Examples 1 to 5. The flexible tube of Example 1 was produced by mixing 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700, 36 parts by weight of an adipic acid-based polyester having a number-average molecular weight of 2000 to 2500 as a polyester-based plasticizer, and 39 parts by weight of diisononyl phthalate (DINP) as a non-polyester plasticizer, and extruding the mixture using an extruder to form inner and outer layers, and then disposing a reinforcing layer between the inner and outer layers using reinforcement method A. The monofilament used was made by extruding PET resin having a flexural strength of 81 MPa and a flexural modulus of 2.3 GPa into a single fiber having a diameter of 1.0 mm using an extruder, and having a breaking strength per unit fineness of 0.23 N / tex and a breaking elongation of 32%. The multifilament was made by braiding polyester yarns and had a breaking strength per unit fineness of 1.43 N / tex and a breaking elongation of 14%. The flexible tube of Example 1 had an inner diameter of 25 mm and a wall thickness of 4 mm (inner layer: 1.7 mm, outer layer: 2.3 mm).

[0036] The flexible tubes of Examples 2 to 9 and Comparative Examples 1 to 6 were made using monofilaments with various parameters shown in Table 1 below, with the compositions and blending amounts of the inner and outer layers and the multifilaments used being the same as those of the flexible tube of Example 1, and were produced by the same method as the flexible tube of Example 1. The flexible tubes of Examples 2 to 9 and Comparative Examples 1 to 6, like the flexible tube of Example 1, had an inner diameter of 25 mm and a wall thickness of 4 mm (inner layer: 1.7 mm, outer layer: 2.3 mm).

[0037]

[0038] The flexible tubes of Examples 1 to 9 and Comparative Examples 1 to 5 were evaluated for breakage, peeling, and crushing using the following methods. The evaluation tests were carried out in an environment of 23°C, and the flexible tubes were left to stand in the environment of 23°C for 24 hours before the various evaluation tests were carried out. The evaluation results are shown in Table 2 below.

[0039]

[0040] <Failure> Damage was evaluated by a twisting and bending test. Each flexible tube was subjected to a twisting and bending test, and visual inspection was performed. A mark of ◎ was given if no change was observed, a mark of ◯ was given if damage such as cracks remained in the inner layer, a mark of △ was given if damage such as cracks reached the reinforcement layer, and a mark of × was given if leakage occurred due to damage. The twisting and bending test was conducted to compare the resistance of each flexible tube to bending when twisted. Specifically, the test involved repeatedly subjecting the flexible tube to a lengthening motion using a bending tester. In this test, the moving direction of the device was the X direction, the direction perpendicular to the X direction and horizontal to the ground was the Y direction, and the direction perpendicular to the X and Y directions was the Z direction. The ends of a flexible tube cut to a length of 600 mm in the axial direction were inserted into two male-threaded hose fittings, each positioned 310 mm apart in the X direction and 220 mm apart in the Y direction, and fixed with a band to prevent the flexible tube and the fittings from rotating relative to each other. Then, one cycle consisted of moving one joint 220 mm in the X direction to approach the other joint and then returning it to its original position. After 400,000 cycles of twisting and bending were performed at a rate of 30 cycles per minute, the flexible tube was checked for any damage or leaks.

[0041] <Peeling> Peeling was evaluated by a negative pressure test. Each flexible tube was subjected to a negative pressure test. A rating of ⊚ was given if no peeling occurred between the inner and outer layers, and a rating of × if peeling occurred. The negative pressure test was conducted to compare the resistance to peeling between layers when negative pressure was applied intermittently to each flexible tube. In this test, a metal fitting was inserted into one end of the flexible tube to block it, and the pressure was intermittently reduced from the other end. One cycle consisted of intermittent pressure reductions at 0 mmHg, -200 mmHg, -400 mmHg, -600 mmHg, and -760 mmHg while maintaining each pressure for 3 minutes, and then returning the pressure to 0 mmHg. After 1,000 cycles of pressure reduction, the state of peeling of the flexible tube was checked.

[0042] <Collapse> Collapse was evaluated by a compression test. Each flexible tube was subjected to a compression test, and the ratio of the minor axis of the flexible tube after the compression test to the outer diameter of the flexible tube before the compression test was used as the recovery rate. A recovery rate of 90% or more was evaluated as ⊚, a recovery rate of 70% or more but less than 90% was evaluated as ◯, a recovery rate of 50% or more but less than 70% was evaluated as △, and a recovery rate of less than 50% was evaluated as ×. The compression test was conducted to confirm the recovery state of each flexible tube after it was compressed flat by an external force. In this test, a load was applied to the center of a 600 mm-long cut flexible tube (outer diameter 33 mm) over a length of 75 mm, compressing it until it became an approximately oval shape with a minor axis of 9.9 mm. The load was then removed after 5 seconds. The flexible tube was then left as it was after the load was removed, and the minor axis of the flexible tube was measured after 1 hour.

[0043] As shown in Table 2, the flexible tubes of each Example were found to be free from damage due to twisting and bending and peeling due to negative pressure, to have excellent recovery properties after compression, and to be free from leakage and blockage, compared to the flexible tubes of each Comparative Example.

[0044] On the other hand, the flexible tube of Comparative Example 1 had low flexural strength of the resin used for the monofilament, resulting in low monofilament rigidity and significantly poorer recovery. The flexible tube of Comparative Example 2 had low flexural modulus of elasticity of the resin used for the monofilament, resulting in low monofilament elasticity and significantly poorer recovery. The flexible tube of Comparative Example 3 had high flexural modulus of elasticity of the resin used for the monofilament, resulting in high repulsion force of the monofilament, and the load applied to the connection when bent was large, resulting in breakage leading to leakage. The flexible tube of Comparative Example 4 had high flexural strength of the resin used for the monofilament, resulting in high monofilament rigidity, and the load applied to the connection when bent was large, resulting in breakage leading to leakage. The flexible tube of Comparative Example 5 had multifilaments located closer to the inner layer than the monofilament, resulting in peeling of the inner layer and multifilaments from the monofilament and outer layer due to repeated negative pressure.

[0045] The above results demonstrate that the flexible tubes of each example are flexible and have excellent shape retention, are free from damage and peeling when subjected to negative pressure during fluid transport even when used in moving parts or narrow spaces, have excellent recovery after flattening and compression, and have a much longer lifespan than conventional products. Therefore, the flexible tubes of each example embodying the present invention can be suitably used as piping for various chemical raw materials, chemicals, air, various gases, powders, fluids, water, oil, water-soluble oils, coolants, etc., in applications requiring moving parts and space-saving features, such as installation within various devices in fields such as resin molding, printing, automobiles, machine tools, industrial parts, agriculture, pharmaceutical manufacturing, medical care, physics and chemistry, food manufacturing, and semiconductor manufacturing, or in equipment connecting devices to chillers.

Claims

1. A flexible pipe comprising: an inner layer made of a flexible material; a monofilament wound spirally along the outer surface of said inner layer; a multifilament wound spirally around the outside of said monofilament in a direction intersecting said monofilament; and an outer layer made of a flexible material covering the outside of said multifilament, wherein the resin material constituting said monofilament has a flexural strength of 65 to 95 MPa and a flexural modulus of 1.5 to 3.0 GPa, measured in accordance with ASTM D790.

2. The flexible tube according to claim 1, wherein the resin material constituting the monofilament is polyethylene terephthalate.

3. A flexible tube according to claim 1 or 2, characterized in that the breaking strength of the monofilament is 0.2 N / tex or more and the breaking elongation is 30 to 40%.