Flexible pipe

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 excellent in water resistance and oil resistance and is flexible.

Background Art

[0002] Pipes such as tubes and hoses used in the resin molding field, printing field, automotive field, machine tool field, industrial parts field, etc. are required to have water resistance, oil resistance, chemical resistance to transport water and oil for various purposes, and flexibility to be arranged in various devices and equipment. Vinyl chloride resin is excellent in the balance of various properties and cost, and flexible pipes such as tubes and hoses formed by extrusion molding a soft vinyl chloride resin composition plasticized by adding a plasticizer are used. In addition, as the coolant liquid used in industrial processing machines, many are diluted water-soluble cutting oils and grinding oils with water, and flexible pipes having both water resistance and oil resistance are required.

[0003] Phthalate plasticizers such as dioctyl phthalate (DOP) and diisononyl phthalate (DINP) are generally used as plasticizers for vinyl chloride resins. However, these are likely to migrate when an oily fluid flows through, and the plasticizer escapes from the vinyl chloride resin, causing the flexible pipe to harden, deteriorating the workability during pipe replacement, or imposing a load on the device when used in the movable part of the device. In addition, these flexible pipes are usually connected to the device using a joint, inserted into a nipple having irregularities on the outer peripheral surface, and the water stop between the flexible pipe and the joint is performed by strongly tightening with a clamp from the outside to reduce the diameter. However, there is also a problem that the adhesion to the nipple deteriorates due to the hardening of the flexible pipe and the decrease in elasticity, resulting in leakage. Furthermore, there is also a problem that the flexible pipe itself becomes cloudy and loses transparency due to the migration of the plasticizer, making it impossible to visually recognize the condition of the flow path from the outside.

[0004] As a method for preventing the migration of such plasticizers, for example, Patent Document 1 discloses a vinyl chloride resin having a degree of polymerization in the range of 1700 to 4000, 30 to 50% of a phthalic acid ester plasticizer, 30 to 50% of a trimellitic acid ester plasticizer, and 10 to 40% of a polyester plasticizer, and a plasticizer added to the vinyl chloride resin by combining them, wherein the normal rate of the plasticizer is 30 to 80%, and 80 to 150 parts by weight of the plasticizer and 0.05 to 1 part by weight of a coupling agent are contained per 100 parts by weight of the vinyl chloride resin. A highly flexible vinyl chloride resin composition is disclosed.

[0005] Further, for example, Patent Document 2 discloses a flexible tube that can be used for food applications and is manufactured by extruding a resin composition composed of a chlorine-containing resin added with at least a plasticizer into a tubular shape by an extrusion molding machine. The resin composition contains 60 to 80 parts by weight of an adipic acid-based polyester having an average molecular weight of 2000 to 4000 as the plasticizer and 0.1 to 3.0 parts by weight of a lubricant composed of an acrylic polymer resin having a molecular weight of 10,000 to 400,000 with respect to 100 parts by weight of polyvinyl chloride as the chlorine-containing resin. A flexible tube is disclosed.

[0006] Further, for example, Patent Document 3 discloses a flexible hose for transporting food liquids, which includes at least one outer protective layer 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 to be transported. The at least second flexible polymer material contains polyvinyl chloride, and the at least second polymer material contains a plasticizer having a low migration level such that the flexibility of the second polymer material is substantially maintained over time. The plasticizer is selected from the group consisting of non-phthalate additives so as to be non-toxic and non-polluting to the food being transported. A flexible hose is exemplified.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] However, in the technology disclosed in Patent Document 1 above, although there is mention of the migration of plasticizers when in contact with ABS resin, since the content of polyester-based plasticizers, which are polymer plasticizers, is small, it is not possible to prevent the migration of plasticizers when an oily fluid flows through, and the flexible tube hardens.

[0009] Also, in the technology disclosed in Patent Document 2 above, a flexible tube containing a large amount of adipic acid-based polyester as a polymer plasticizer is exemplified and it is excellent in low elution properties into oily fluids. However, since polyester-based plasticizers are reduced in molecular weight by hydrolysis, when water or a mixture of water and oil flows through, the plasticizer is hydrolyzed and migrates, and the flexible tube hardens. Furthermore, although it is disclosed that an external lubricant is introduced because a resin composition containing a large amount of polyester plasticizer with a high molecular weight has a significantly increased melt viscosity and a decreased moldability, containing these external lubricants weakens the bonding between molecules, leading to a decrease in the partial strength of the flexible tube.

[0010] In addition, in the technology disclosed in Patent Document 3 mentioned above, by using a non-phthalic plasticizer in the inner layer, the exudation level of the plasticizer measured according to ASTM D 3291 is low, and although there is mention of low contamination to drinking water and irrigation water, there is no mention of the molecular weight of the plasticizer and the accompanying oil resistance and water resistance. Even in the case of non-phthalic plasticizers, when the molecular weight is small, it is impossible to prevent the migration of the plasticizer when an oily fluid flows through, and the flexible pipe will harden. Further, when the resin compositions constituting the inner layer and the outer protective layer are different, as a result of the above-mentioned migration of the plasticizer occurring in the inner layer, the hardness of the inner layer and the outer protective layer is significantly different, and problems such as delamination between the layers occur during operations such as bending the flexible pipe.

[0011] An object of the present invention is to address such problems, and an object of the present invention is to provide a flexible pipe that is excellent in water resistance and oil resistance and does not harden or become cloudy over a long period of time even when a mixture of water and oil such as water, oil, and water-soluble oil flows through.

Means for Solving the Problems

[0012] As a result of intensive studies, the inventor of the present invention has found that the above problems can be solved by the flexible pipe of the present invention. The flexible pipe of the present invention is a flexible pipe provided with a resin layer made of a polyvinyl chloride resin composition that is in direct contact with the fluid flowing inside, and the polyvinyl chloride resin composition contains 55 to 85 parts by weight of a plasticizer with respect to 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 when the total amount of the plasticizer is 100 parts by weight.

Effects of the Invention

[0013] According to the present invention, it is possible to provide a flexible pipe that is excellent in water resistance and oil resistance and does not harden or delaminate over a long period of time even when a mixture of water and oil such as water, oil, and water-soluble oil flows through.

Modes for Carrying Out the Invention

[0014] Hereinafter, a preferred embodiment of the flexible pipe of the present invention will be described in detail. In this embodiment, a flexible pipe provided with 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 pipe, and is made of a resin composition (polyvinyl chloride resin composition) formed from polyvinyl chloride.

[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 setting the average degree of polymerization of polyvinyl chloride within the above range, there is less migration of the plasticizer, and a flexible flexible pipe excellent in mechanical strength such as tensile strength can be obtained.

[0016] (Plasticizer) The resin composition constituting the flexible pipe of this embodiment preferably contains 55 to 85 parts by weight of a plasticizer with respect to 100 parts by weight of polyvinyl chloride, more preferably 60 to 80 parts by weight. When the content of the plasticizer is less than 55 parts by weight, the resin composition becomes hard and a flexible flexible pipe cannot be obtained. On the other hand, when the content of the plasticizer 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 pipe with poor usability. In addition, in a multilayer pipe in which a plurality of layers are laminated, a problem of delamination between layers occurs during operations such as bending the flexible pipe.

[0017] The plasticizer of this embodiment contains at least one polyester-based plasticizer. The content of the polyester-based plasticizer preferably contains 30 to 70 parts by weight when the total amount of the plasticizer is 100 parts by weight, more preferably 40 to 60 parts by weight. When the content rate of the polyester-based plasticizer is less than 30 parts by weight, the plasticizer elutes when an oily fluid flows through, and the flexible pipe hardens, and a flexible flexible pipe cannot be obtained. On the other hand, when the content rate of the polyester-based plasticizer is more than 70 parts by weight, the polyester-based plasticizer hydrolyzes when an aqueous fluid such as water or a water-soluble cutting oil flows through, and the flexible pipe hardens. In addition to not being able to obtain a flexible flexible pipe, since the melt viscosity of the resin composition increases, the inclusion of an external lubricant is essential for improving the moldability, and the strength of the flexible pipe decreases.

[0018] The number average molecular weight of the polyester plasticizer is preferably from 1,000 to 4,000, more preferably from 1,500 to 3,000. When the number average molecular weight of the polyester plasticizer is less than 1,000, the amount of low molecular components in the polyester plasticizer increases, and the migration of the plasticizer to the oily fluid increases. On the other hand, when the number average molecular weight is greater than 4,000, the amount of high molecular components in the polyester plasticizer increases, the compatibility with polyvinyl chloride decreases, and the change in hardness due to hydrolysis becomes large, and a flexible flexible tube that does not harden even when water or oil flows through cannot be obtained.

[0019] The dispersity, which is the value obtained by dividing the weight average molecular weight of the polyester plasticizer by the number average molecular weight, is preferably from 1.5 to 1.9, more preferably from 1.65 to 1.75. When the dispersity is less than 1.5, the amount of high molecular components in the polyester plasticizer increases, the compatibility with polyvinyl chloride decreases, and the change in hardness due to hydrolysis becomes large. On the other hand, when the dispersity is greater than 1.9, the amount of low molecular components in the polyester plasticizer increases, the migration of the plasticizer to the oily fluid increases, and a flexible flexible tube that does not harden even when water or oil flows through cannot be obtained.

[0020] The viscosity of the polyester plasticizer is preferably from 100 to 5,000 mPa·s, more preferably from 2,000 to 4,000 mPa·s. The viscosity is correlated with the molecular weight. By setting the viscosity of the polyester plasticizer within this range, a plasticizer with less volatilization and migration to oil and less hydrolysis can be obtained, and a flexible flexible tube that does not harden even when water or oil flows through can be obtained. Further, the acid value is preferably 1 or less, and the hydroxyl value is preferably 30 or less.

[0021] As the polyester plasticizer, a dicarboxylic acid polyester produced by reacting a diol component, an organic dicarboxylic acid component and a terminal terminator is preferred.

[0022] As the diol component, 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, 1,10-decanediol, etc. can be mentioned. Since they are excellent in low-temperature flexibility and oil resistance, it is preferable to use 2-methyl-1,3-propanediol and 3-methyl-1,5-pentanediol as essential components.

[0023] As the organic dicarboxylic acid component, aliphatic dicarboxylic acids such as 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, hydrogenated dimer acid, etc., aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, etc., 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, 1,4-dicarboxymethylenecyclohexane, etc. can be mentioned. Since they are excellent in plasticizing efficiency and oil resistance, it is preferable to use adipic acid as an essential component.

[0024] The terminal stopper consists of 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, isotridecyl alcohol, etc. These can be used alone or as a mixture of two or more. Examples of the monohydric aliphatic organic acid 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, etc. These can be used alone or as a mixture of two or more.

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

[0026] (Additive) The resin composition constituting the flexible pipe of the present embodiment can contain various additives according to the use and usage method. Examples of the additives include heat stabilizers, light stabilizers, ultraviolet absorbers, antioxidants, anti-fogging agents, antistatic agents, flame retardants, fillers, internal lubricants, fluorescent agents, bactericides, metal deactivators, mold release agents, pigments, and the like.

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

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

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

[0030] (Flexible tube) Examples of the structure of the flexible tube of the present embodiment include a single-layer tube made of a single material, a multilayer tube in which a plurality of layers having different physical properties are laminated, a hose provided with a reinforcing material between the layers, and the like.

[0031] Examples of the above-mentioned reinforcing material include a plurality of or a single blade made of polyester, PET, nylon (registered trademark) or aramid fiber, a monofilament made of an olefin resin, a polyester resin, etc., a multifilament knitted from thin monofilaments (monofilament: single fiber), a flat yarn (or tape yarn) made of tape-like yarn, a metal wire made of stainless steel, steel, etc. or a coil made of a hard material similar to stainless steel, a piano wire, and a combination thereof.

[0032] The flexible tube of the present embodiment can be used as a pipe for various chemical raw materials, chemicals, air, various gases, powders, fluids, water, oil, water-soluble oil, etc. in the resin molding field, printing field, automotive field, machine tool field, industrial parts field, etc. Since it maintains flexibility without hardening or peeling over a long period even when a mixture of water and oil such as water, oil, and water-soluble oil flows through it, it is particularly suitable as a hose for industrial water, cooling water, etc., lubricating oil, insulating oil, cleaning oil, rust preventive oil, cooling oil, cutting oil, grinding oil, mineral oil, synthetic oil, etc. machine oil, and water-soluble oil diluted with water by adding a surfactant to these oils and mixed drainage of water and oil.

[0033] According to the flexible tube of the present embodiment described above, the following effects can be obtained. That is, compared with the conventional flexible tube, the flexible tube of the present invention can maintain flexibility without hardening or peeling over a long period even when a mixture of water and oil such as water, oil, and water-soluble oil flows through it, and can be used as a product with a much longer lifespan than conventional products.

[0034] As described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

Examples

[0035] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the description scope of the present invention is not limited thereto. In this example, flexible tubes of Examples 1 to 14 and Comparative Examples 1 to 6 were produced, and a hardness evaluation test and a peeling evaluation test were performed on each of the produced flexible tubes. Examples 1 to 14 and Comparative Examples 1 to 6 will be described below.

[0036] The mixing ratios of Examples 1 to 14 are shown in Table 1 below. Also, the mixing ratios of Comparative Examples 1 to 6 are shown in Table 2 below. Note that the numerical 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 a resin composition mixed at the mixing ratios shown in Tables 1 and 2 using an extrusion molding machine to form an inner layer and an outer layer, and disposing a reinforcing layer composed of a blade in which polyester yarns were braided between the inner layer and the outer layer. Each of the produced flexible tubes has 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, 34 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 34 parts by weight of diisononyl phthalate (DINP) as a plasticizer other than the polyester-based were mixed with 100 parts by weight of polyvinyl chloride having a degree of polymerization of 1700. Also, as the polyvinyl chloride, one having a degree of polymerization of 1100 was mixed in Example 11, and one having a degree of polymerization of 2700 was mixed in Example 12.

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

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

[0040]

Table 1

[0041]

Table 2

[0042] Also, for the hardness evaluation test and peel evaluation test, which are the measurement items, the following three states were measured and evaluated respectively by the following method: (1) the initial state, (2) after the flexible tube was extrusion molded, filled with No. 2 insulating oil, and left standing for 7 days while maintaining a temperature of 60 ± 3°C, and (3) after the flexible tube was extrusion molded, filled with pure water (manufactured by Shoei Chemical Industry Co., Ltd.), and left standing for 6 months while maintaining a temperature of 60 ± 3°C. The results of each evaluation test for Examples 1 to 14 are shown in Table 3 below. The results of each evaluation test for Comparative Examples 1 to 6 are shown in Table 4 below.

[0043] <Hardness Evaluation Test> The hardness evaluation test was conducted by measuring the IRHD hardness using a Micro-Normal Rubber Hardness Tester MICRO-IRHD-1 manufactured by Excel based on ISO 48 "Vulcanized or Plasticized Rubber - Determination of Hardness". In this test, the flexible pipe was cut open, and the hardness of the flexible pipe, which was the average of the hardnesses in four directions orthogonal to each other in the radial direction of the inner surface of the flow path, was used as the evaluation target. The hardness was evaluated as follows for (1) the initial state, (2) after filling with oil, and (3) after filling with water.

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

[0045] <Peeling Evaluation Test> The peeling evaluation test was conducted by cutting each flexible pipe to a length of 360 mm, supplying air from one end while sealing the other end with a plug nipple, and repeating the operation of bending the flexible pipe to a bending radius of 100 mm and then returning it to its original state while maintaining a pressurized state of 0.5 MPa. The evaluation method was to check the state of the flexible pipe after 20,000 bending cycles at a bending speed of 30 cycles per minute. If there was no delamination between the layers, it was rated as ◎, and if there was delamination, it was rated as ×.

[0046]

Table 3

[0047]

Table 4

[0048] As shown in Table 3 and Table 4, the flexible tubes of each example were found to be flexible compared to Comparative Examples 1 to 6, with little change in hardness and no peeling even when water or oil flowed through them. From these evaluation results, it was found that the flexible tubes of each example are flexible tubes with excellent water resistance and oil resistance, which do not harden or peel over a long period even when a mixture of water and oil such as water, oil, and water-soluble oil flows through them.

[0049] In Comparative Example 1, since the content of the plasticizer was low, the hardness in the initial state was higher than 80 degrees, and the flexibility was significantly inferior. Also, when evaluating peeling, since the flexible tube was not flexible, it was not possible to perform 20,000 flexures.

[0050] In Comparative Example 2, the content of the plasticizer was high, and the hardness in the initial state was low and flexible. However, the change in hardness due to the migration and hydrolysis of the plasticizer was large, and when water or oil flowed through it, the hardness increased and the flexibility was significantly impaired.

[0051] In Comparative Examples 3 to 6, since there was a bias in the content of the polyester plasticizer, the migration of the plasticizer into the oil or hydrolysis by water occurred, and when water or oil flowed through it, the hardness increased and the flexibility was significantly impaired. Also, since the hardness of the inner layer became significantly high, the hardness difference between the inner layer and the outer layer increased, and peeling occurred between the layers during repeated flexure.

[0052] As a result, since the flexible tubes of each example are flexible tubes with excellent water resistance and oil resistance, which do not harden or peel over a long period even when a mixture of water and oil such as water, oil, and water-soluble oil flows through them, in the resin molding field, printing field, automotive field, machine tool field, industrial parts field, etc., water such as industrial water and cooling water, mechanical oils such as lubricating oil, insulating oil, cleaning oil, rust preventive oil, cooling oil, cutting oil, grinding oil, mineral oil, synthetic oil, and water-soluble oils obtained by adding a surfactant to these oils and diluting with water or mixed drainage of water and oil can be suitably used for applications where they flow through.

Claims

1. A flexible pipe comprising a resin layer made of a polyvinyl chloride resin composition that is in direct contact with a fluid flowing inside, wherein the polyvinyl chloride resin composition contains 55 to 85 parts by weight of a plasticizer with respect to 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 1,000 to 4,000 when the total amount of the plasticizer is 100 parts by weight, characterized in that it is a flexible pipe.

2. The degree of polymerization of the polyvinyl chloride is 1,100 to 2,700, characterized in that it is the flexible pipe according to Claim 1.

3. The dispersity, which is a value obtained by dividing the weight average molecular weight of the polyester-based plasticizer by the number average molecular weight, is 1.5 to 1.9, characterized in that it is the flexible pipe according to Claim 1 or 2.

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