Flexible tube

Abstract

To provide a flexible pipe with excellent water resistance and oil resistance, in which even when water, oil, or water-oil mixtures such as water-soluble oil are distributed, hardening or clouding does not occur for a long period of time.SOLUTION: A flexible pipe comprises a resin layer made of a polyvinyl chloride resin composition that comes into direct contact with fluid flowing inside. The polyvinyl chloride resin composition contains 55 to 85 pts.wt. with respect to a plasticizer per 100 pts.wt. of polyvinyl chloride, and the plasticizer contains 30 to 70 pts.wt. of a polyester-based plasticizer with a number average molecular weight of 1000 to 4000, based on 100 pts.wt. of the total plasticizer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flexible pipe made of polyvinyl chloride that is highly water-resistant and oil-resistant. [Background technology]

[0002] Piping such as tubes and hoses used in fields such as resin molding, printing, automobiles, machine tools, and industrial parts require water resistance, oil resistance, and chemical resistance to transport water and oil for various purposes, as well as flexibility to allow placement in a variety of devices and facilities. Polyvinyl chloride resin offers an excellent balance between various properties and cost, and flexible tubes and hoses are used, formed by extrusion molding of soft vinyl chloride resin compositions plasticized by the addition of plasticizers. Furthermore, water-soluble cutting oils and grinding oils diluted with water are often used as coolants for industrial processing machines, requiring flexible tubes that are both water-resistant and oil-resistant.

[0003] Phthalate ester plasticizers, such as dioctyl phthalate (DOP) and diisononyl phthalate (DINP), are commonly used in polyvinyl chloride resins. However, these plasticizers are prone to migration when oil-based fluids are used. The resulting migration of the plasticizer from the polyvinyl chloride resin causes the flexible pipe to harden, making pipe replacement difficult and placing strain on the equipment when used in moving parts. Furthermore, these flexible pipes are typically connected to equipment using fittings. The flexible pipe is inserted into a nipple with an irregular outer surface and then tightly tightened from the outside with a fastener to reduce its diameter, sealing the flexible pipe and fitting. However, as the flexible pipe hardens and loses its elasticity, it loses its adhesion to the nipple, resulting in leaks. Furthermore, migration of the plasticizer causes the flexible pipe itself to become cloudy and lose its transparency, making it difficult to see the flow path from the outside.

[0004] As a method for preventing such migration of plasticizers, for example, Patent Document 1 discloses a highly flexible vinyl chloride resin composition comprising a vinyl chloride resin having a degree of polymerization in the range of 1700 to 4000, and a plasticizer added to the vinyl chloride resin by combining 30 to 50% of a phthalate ester plasticizer, 30 to 50% of a trimellitate ester plasticizer, and 10 to 40% of a polyester-based plasticizer, wherein the normal ratio of the plasticizer is 30 to 80%, and the composition contains 80 to 150 parts by weight of the plasticizer and 0.05 to 1 part by weight of a coupling agent per 100 parts by weight of the vinyl chloride resin.

[0005] Furthermore, for example, Patent Document 2 discloses a flexible tube that can be used for food applications, which is manufactured by extruding a resin composition made of a chlorine-containing resin to which at least a plasticizer has been added into a tubular shape using an extrusion molding machine, and which is characterized in that the resin composition contains 100 parts by weight of polyvinyl chloride as the chlorine-containing resin, 60 to 80 parts by weight of an adipic acid-based polyester having an average molecular weight of 2,000 to 4,000 as the plasticizer, and 0.1 to 3.0 parts by weight of a lubricant made of an acrylic polymer resin having a molecular weight of 10,000 to 400,000.

[0006] Furthermore, for example, Patent Document 3 exemplifies a flexible hose for transporting food liquids, comprising at least one outer protective layer made of a first flexible polymer material and at least one inner layer made of a second polymer material that is in direct contact with the fluid being transported, wherein the at least second flexible polymer material comprises polyvinyl chloride, and the at least second polymer material comprises a plasticizer that has a migration level low enough to maintain the flexibility of the second polymer material substantially unchanged over time, and the plasticizer is selected from the group consisting of non-phthalate additives so that it can be non-toxic and non-contaminating to the food being transported. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5990019 [Patent Document 2] Patent No. 5692686 [Patent Document 3] U.S. Patent No. 8,057,877 Summary of the Invention [Problem to be solved by the invention]

[0008] However, although the technology disclosed in Patent Document 1 mentions the migration of plasticizers when they come into contact with ABS resin, the content of polyester-based plasticizers, which are polymer plasticizers, is small, so when oil-based fluids are passed through them, the migration of plasticizers cannot be prevented, and the flexible tube hardens.

[0009] The technology disclosed in Patent Document 2 exemplifies a flexible tube containing a large amount of adipic acid-based polyester as a polymer plasticizer, which has excellent low elution in oily fluids, but because polyester-based plasticizers are hydrolyzed to low molecular weight, when water or a mixture of water and oil is passed through the tube, the plasticizer is hydrolyzed and migrates, causing the flexible tube to harden. Furthermore, it discloses that resin compositions containing a large amount of polyester plasticizer with a high molecular weight have a significantly high melt viscosity and poor moldability, so the introduction of an external lubricant is used, but the inclusion of these external lubricants weakens the bonds between molecules, leading to a partial decrease in the strength of the flexible tube.

[0010] Furthermore, the technology disclosed in Patent Document 3 uses a non-phthalate plasticizer in the inner layer, which reduces the level of plasticizer leaching measured according to ASTM D 3291, and mentions low contamination of drinking water and irrigation water, but makes no mention of the molecular weight of the plasticizer or the associated oil resistance and water resistance, and even if the molecular weight of a non-phthalate plasticizer is small, plasticizer migration cannot be prevented when an oily fluid is passed through it, resulting in hardening of the flexible tube. Furthermore, if the resin compositions constituting the inner layer and the outer protective layer are different, the above-mentioned plasticizer migration in the inner layer will result in a significant difference in hardness between the inner layer and the outer protective layer, causing the problem of delamination between the layers when the flexible tube is bent, etc.

[0011] The present invention addresses these problems and aims to provide a flexible tube that has excellent water and oil resistance and does not harden or become cloudy over a long period of time even when water, oil, or a mixture of water and oil such as water-soluble oil is passed through it. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the flexible tube of the present invention. The flexible tube of the present invention is a flexible tube having a resin layer made of a polyvinyl chloride resin composition that comes into direct contact with a fluid flowing therethrough, characterized in that the polyvinyl chloride resin composition contains 55 to 85 parts by weight of a plasticizer per 100 parts by weight of polyvinyl chloride, and the plasticizer contains 30 to 70 parts by weight of a polyester-based plasticizer having a number average molecular weight of 1000 to 4000, relative to 100 parts by weight of the total amount of the plasticizer. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a flexible tube that has excellent water resistance and oil resistance and does not harden or peel over a long period of time even when water, oil, or a mixture of water and oil such as water-soluble oil is passed through it. DETAILED DESCRIPTION OF THE INVENTION

[0014] A preferred embodiment of the flexible tube of the present invention will be described in detail below. In this embodiment, a flexible tube having a resin layer is exemplified. The resin layer of this embodiment is provided so as to be in direct contact with the fluid flowing inside the flexible tube, and is made of a resin composition formed from polyvinyl chloride (polyvinyl chloride resin composition).

[0015] (Polyvinyl chloride) The polyvinyl chloride constituting the resin composition preferably has an average degree of polymerization of 1100 to 2700, more preferably 1300 to 2500. By adjusting the average degree of polymerization of the polyvinyl chloride to fall within the above range, it is possible to obtain a flexible tube with little migration of plasticizer and excellent mechanical strength such as tensile strength.

[0016] (plasticizer) The resin composition constituting the flexible tube of this embodiment preferably contains 55 to 85 parts by weight, more preferably 60 to 80 parts by weight, of plasticizer per 100 parts by weight of polyvinyl chloride. If the plasticizer content is less than 55 parts by weight, the resin composition becomes hard, making it impossible to obtain a flexible flexible tube. On the other hand, if the plasticizer content is more than 85 parts by weight, the hardness is likely to change due to elution or hydrolysis of the plasticizer, resulting in a flexible tube that is uncomfortable to use. In addition, in the case of a multi-layer tube having multiple layers stacked together, problems such as peeling between layers can occur when the flexible tube is bent.

[0017] The plasticizer of this embodiment contains at least one polyester-based plasticizer. The content of the polyester-based plasticizer is preferably 30 to 70 parts by weight, more preferably 40 to 60 parts by weight, based on 100 parts by weight of the total plasticizer. If the content of the polyester-based plasticizer is less than 30 parts by weight, the plasticizer will elute when an oil-based fluid is passed through it, causing the flexible tube to harden, making it impossible to obtain a flexible flexible tube. On the other hand, if the content of the polyester-based plasticizer is more than 70 parts by weight, the polyester-based plasticizer will hydrolyze when an aqueous fluid such as water or water-soluble cutting oil is passed through it, causing the flexible tube to harden, making it impossible to obtain a flexible flexible tube. Furthermore, the melt viscosity of the resin composition will increase, making it necessary to add an external lubricant to improve moldability, which will reduce the strength of the flexible tube.

[0018] The number-average molecular weight of the polyester-based plasticizer is preferably 1000 to 4000, and more preferably 1500 to 3000. If the number-average molecular weight of the polyester-based plasticizer is less than 1000, the amount of low-molecular-weight components in the polyester-based plasticizer increases, resulting in increased migration of the plasticizer into the oil-based fluid, while if the number-average molecular weight is greater than 4000, the amount of high-molecular-weight components in the polyester-based plasticizer increases, resulting in reduced compatibility with polyvinyl chloride and a large change in hardness due to hydrolysis, making it impossible to obtain a flexible tube that does not harden even when water or oil is passed through it.

[0019] The dispersity, which is the value obtained by dividing the weight-average molecular weight of the polyester-based plasticizer by the number-average molecular weight, is preferably 1.5 to 1.9, and more preferably 1.65 to 1.75. If the dispersity is lower than 1.5, the polyester-based plasticizer contains more high-molecular-weight components, which reduces compatibility with polyvinyl chloride and increases the change in hardness due to hydrolysis. On the other hand, if the dispersity is higher than 1.9, the polyester-based plasticizer contains more low-molecular-weight components, which increases the migration of the plasticizer into the oil-based fluid, making it impossible to obtain a flexible tube that does not harden even when water or oil is passed through it.

[0020] The viscosity of the polyester-based plasticizer is preferably 100 to 5000 mPa·s, and more preferably 2000 to 4000 mPa·s. Viscosity correlates with molecular weight, and by setting the viscosity of the polyester-based plasticizer within this range, the plasticizer will have little volatilization or migration to oil and little hydrolysis, making it possible to obtain a flexible tube that will not harden even when water or oil is passed through it. In addition, the acid value is preferably 1 or less, and the hydroxyl value is preferably 30 or less.

[0021] The polyester plasticizer is preferably a dicarboxylic acid polyester produced by reacting a diol component, an organic dicarboxylic acid component, and a terminal capping agent.

[0022] Examples of diol components include 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5-heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol. 2-methyl-1,3-propanediol and 3-methyl-1,5-pentanediol are preferred as essential components due to their excellent low-temperature flexibility and oil resistance.

[0023] Examples of organic dicarboxylic acid components include adipic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, and hydrogenated dimer acids. Examples of organic dicarboxylic acid components include adipic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, and aliphatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, orthophthalic acid, and naphthalenedicarboxylic acid. Examples of organic dicarboxylic acid components include alicyclic dicarboxylic acids such as 1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 1,4-dicarboxylmethylenecyclohexane. Adipic acid is preferably used as an essential component because of its excellent plasticization efficiency and oil resistance.

[0024] The end terminator is a monohydric aliphatic alcohol or a monohydric aliphatic organic acid. Examples of the monohydric aliphatic alcohol include methanol, ethanol, 1-propanol, 2-propanol, butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, amyl alcohol, hexanol, isohexanol, heptanol, 2-heptanol, octanol, isooctanol, 2-ethylhexanol, nonanol, isononanol, decanol, isodecanol, undecanol, isoundecanol, dodecanol, benzyl alcohol, 2-butyloctanol, 2-butyldecanol, 2-hexyloctanol, 2-hexyldecanol, stearyl alcohol, 2-octyldecanol, 2-hexyldodecanol, 2-octyldodecanol, 2-decyltetradecanol, tridecyl alcohol, and isotridecyl alcohol. These may be used alone or in combination. Examples of monovalent aliphatic organic acids include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, caprylic acid, 2-ethylhexanoic acid, pelargonic acid, capric acid, neodecanoic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, coconut oil fatty acid, and the like, which may be used alone or in combination of two or more.

[0025] Examples of plasticizers other than polyester-based plasticizers include phthalic acid-based plasticizers such as dibutyl phthalate, butylhexyl phthalate, diheptyl phthalate, dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, and dioctyl terephthalate; adipic acid-based plasticizers such as dioctyl adipate, diisononyl adipate, diisodecyl adipate, and di(butyldiglycol) adipate; tetrahydrophthalic acid-based plasticizers, azelaic acid-based plasticizers, sebacic acid-based plasticizers, stearic acid-based plasticizers, citric acid-based plasticizers, trimellitic acid-based plasticizers, pyromellitic acid-based plasticizers, biphenylene polycarboxylic acid-based plasticizers, epoxidized linseed oil, epoxidized soybean oil, and mixtures thereof. Diisononyl phthalate is preferred because it has an excellent balance of compatibility with polyvinyl chloride, cost, plasticizing efficiency, and the like.

[0026] (additives) The resin composition constituting the flexible tube of this embodiment may contain various additives depending on the application and method of use, such as a heat stabilizer, a light stabilizer, an ultraviolet absorber, an antioxidant, an antifogging agent, an antistatic agent, a flame retardant, a filler, an internal lubricant, a fluorescent agent, a disinfectant, a metal deactivator, a mold release agent, and a pigment.

[0027] (Resin composition) The resin composition constituting the flexible tube of this embodiment preferably has an IRHD hardness of 55 to 85, more preferably 65 to 75, measured in accordance with ISO 48, in order to impart appropriate flexibility to the flexible tube.

[0028] In order to impart appropriate flexibility to the flexible tube, the resin composition constituting the flexible tube of this embodiment preferably has an elongation measured in accordance with JIS K 6723 of 380 to 460%, more preferably 410 to 430%.

[0029] The resin composition constituting the flexible tube of this embodiment preferably has a tensile strength measured in accordance with JIS K 6723 of 10 to 25 MPa, more preferably 15 to 20 MPa, in order to impart appropriate flexibility to the flexible tube.

[0030] (flexible tube) Examples of the structure of the flexible tube of this embodiment include a single-layer tube made of a single material, a multi-layer tube made by laminating multiple layers with different physical properties, and a hose with reinforcing material between layers.

[0031] Examples of the reinforcing material include a single or multiple braid made of polyester, PET, nylon (registered trademark), or aramid fiber, etc.; a monofilament made of olefin resin, polyester resin, etc.; a multifilament made by weaving thin monofilaments (single fibers); a flat yarn (or tape yarn) made of tape-shaped thread; a metal wire made of stainless steel, steel, etc., or a coil made of a hard material similar to stainless steel; piano wire; and combinations thereof.

[0032] 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, etc. in the fields of resin molding, printing, automobiles, machine tools, industrial parts, etc. Even when water, oil, or a mixture of water and oil such as water-soluble oil is passed through it, it maintains its flexibility without hardening or peeling over a long period of time, and is therefore particularly suitable as a hose for passing water such as industrial water or cooling water, lubricating oil, insulating oil, cleaning oil, rust-preventive oil, cooling oil, cutting oil, grinding oil, mineral oil, synthetic oil, or other machine oil, water-soluble oils obtained by adding a surfactant to any of these oils and diluting them with water, or mixed wastewater of water and oil.

[0033] The flexible tube of the present embodiment described above can provide the following effects: Compared to conventional flexible tubes, the flexible tube of the present invention can maintain its flexibility for a long period of time without hardening or peeling, even when a mixture of water and oil, such as water, oil, or water-soluble oil, is passed through it, and can be used as a tube with a much longer life than conventional products.

[0034] 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. [Example]

[0035] The present invention will be described in more detail below with reference to examples and comparative examples, but the scope of the present invention is not limited thereto. In these examples, flexible tubes of Examples 1 to 14 and Comparative Examples 1 to 6 were fabricated, and hardness evaluation tests and peel evaluation tests were conducted on each of the fabricated flexible tubes. Examples 1 to 14 and Comparative Examples 1 to 6 will be described below.

[0036] Table 1 below shows the compounding ratios of Examples 1 to 14. Table 2 below shows the compounding ratios of Comparative Examples 1 to 6. The values ​​in Tables 1 and 2 indicate parts by weight. A total of 20 flexible tubes of Examples 1 to 14 and Comparative Examples 1 to 6 were produced by extruding resin compositions mixed at the compounding ratios shown in Tables 1 and 2 using an extrusion molding machine to form inner and outer layers, and then disposing a reinforcing layer made of a braided polyester thread between the inner and outer layers. Each of the produced flexible tubes had an inner diameter of 19 mm and a wall thickness of 3.5 mm (inner layer 1.9 mm, outer layer 1.6 mm).

[0037] As shown in Table 1, for example, in Example 1, 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700 was mixed with 34 parts by weight of an adipic acid polyester having a number average molecular weight of 2000 to 2500 as a polyester-based plasticizer, and 34 parts by weight of diisononyl phthalate (DINP) as a non-polyester-based plasticizer. In Example 11, polyvinyl chloride having a degree of polymerization of 1100 was mixed, and in Example 12, polyvinyl chloride having a degree of polymerization of 2700 was mixed.

[0038] In Example 8, 34 parts by weight of an adipic acid polyester having a number average molecular weight of 1000 to 1500 was mixed as a polyester-based plasticizer with 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700, and in Example 9, 34 parts by weight of an adipic acid polyester having a number average molecular weight of 3500 to 4000 was mixed with 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700. In Example 10, 34 parts by weight of trioctyl trimellitate (TOTM) was mixed as a plasticizer other than polyester-based plasticizers.

[0039] As shown in Table 2, for example, in Comparative Example 1, 25 parts by weight of an adipic acid polyester having a number average molecular weight of 2000 to 2500 as a polyester-based plasticizer and 25 parts by weight of DINP as a non-polyester plasticizer were mixed with 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700. In Comparative Example 6, 34 parts by weight of an adipic acid polyester having a number average molecular weight of 4000 to 4500 as a polyester-based plasticizer were mixed with 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700.

[0040] [Table 1]

[0041] [Table 2]

[0042] The hardness and peeling evaluation tests were carried out using the following methods to measure and evaluate the following three conditions: (1) the initial state; (2) after extrusion molding of a flexible tube, filling it with No. 2 insulating oil, and leaving it at a temperature of 60±3°C for 7 days; and (3) after extrusion molding of a flexible tube, filling it with pure water (manufactured by Seiki Pharmaceutical Co., Ltd.), and leaving it at a temperature of 60±3°C for 6 months. Table 3 below shows the results of the evaluation tests for Examples 1 to 14. Table 4 below shows the results of the evaluation tests for Comparative Examples 1 to 6.

[0043] <Hardness evaluation test> The hardness evaluation test was conducted based on ISO 48 "Vulcanized or plastic rubber - Determination of hardness" by measuring the IRHD hardness using an Excel Micro-Normal Rubber Hardness Tester MICRO-IRHD-1. In this test, the flexible tube was cut open and the average of the hardness measured in four mutually perpendicular directions in the radial direction of the inner surface of the flow channel was taken as the hardness of the flexible tube being evaluated. The hardness was evaluated as follows for (1) the initial state, (2) after filling with oil, and (3) after filling with water.

[0044] The evaluation method for (1) was such that, since the hardness corresponds to the flexibility of the flexible tube, a hardness of less than 75 degrees was rated as ◎ (very flexible), 75 degrees or more but less than 80 degrees as 〇 (flexible), 80 degrees or more but less than 85 degrees as △ (slightly hard), and 85 degrees or more as × (hard). For (2) and (3), a change in hardness compared to the hardness in (1) of less than 20% was rated as ◎, 20% or more but less than 25% as 〇, 25% or more but less than 30% as △, and 30% or more as ×.

[0045] <Peeling evaluation test> The peeling evaluation test was performed by cutting each flexible tube to a length of 360 mm, sealing one end with a stopper nipple, supplying air from the other end, and repeatedly bending the flexible tube to a bending radius of 100 mm and returning it to its original position while maintaining a pressurized state of 0.5 MPa. The evaluation method was to check the condition of the flexible tube after 20,000 bends at a bending speed of 30 times per minute, and marking it as ◎ if there was no peeling between the layers, and × if there was peeling.

[0046] [Table 3]

[0047] [Table 4]

[0048] As shown in Tables 3 and 4, the flexible tubes of each Example were found to be more flexible than Comparative Examples 1 to 6, and showed little change in hardness and no peeling even when water or oil was passed through them. These evaluation results showed that the flexible tubes of each Example were flexible tubes with excellent water resistance and oil resistance that did not harden or peel over long periods of time even when water, oil, or a mixture of water and oil such as water-soluble oil was passed through them.

[0049] In Comparative Example 1, the content of plasticizer was low, so the hardness in the initial state was higher than 80 degrees, and the flexibility was significantly poor. Furthermore, the flexible tube was not flexible enough to be bent 20,000 times when evaluating peeling.

[0050] Comparative Example 2 contained a large amount of plasticizer and was initially low in hardness and flexible, but the hardness changed significantly due to plasticizer migration and hydrolysis, and when water or oil was passed through it, the hardness increased and flexibility was significantly impaired.

[0051] In Comparative Examples 3 to 6, the content of the polyester plasticizer was uneven, which resulted in migration of the plasticizer into the oil or hydrolysis by water, resulting in increased hardness and a significant loss of flexibility when water or oil was passed through. Furthermore, the significantly increased hardness of the inner layer increased the difference in hardness between the inner and outer layers, resulting in delamination between the layers during repeated bending.

[0052] These results confirmed that the flexible tubes of each example are flexible tubes with excellent water and oil resistance that do not harden or peel over long periods of time even when water, oil, or a mixture of water and oil such as water-soluble oil is passed through them, and therefore can be suitably used in fields such as resin molding, printing, automobiles, machine tools, and industrial parts for passing water such as industrial water and cooling water, lubricating oil, insulating oil, cleaning oil, rust-preventive oil, cooling oil, cutting oil, grinding oil, mineral oil, and machine oil such as synthetic oil, water-soluble oils obtained by adding a surfactant to these oils and diluting them with water, and mixed wastewater of water and oil.

Claims

1. A flexible pipe having a resin layer made of a polyvinyl chloride resin composition that comes into direct contact with a fluid flowing therethrough, the polyvinyl chloride resin composition contains 56 to 68 parts by weight of a plasticizer per 100 parts by weight of polyvinyl chloride, and has an IRHD hardness of 55 to 85 as measured in accordance with ISO 48; The polyvinyl chloride has an average degree of polymerization of 1700, The plasticizer contains 50 parts by weight of a polyester-based plasticizer having a number average molecular weight of 2000 to 2500, based on 100 parts by weight of the total amount of the plasticizer. A flexible tube characterized by:

2. the polyester plasticizer has a dispersity of 1.5 to 1.9, which is the value obtained by dividing the weight average molecular weight by the number average molecular weight; 2. The flexible tube according to claim 1.

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