Multilayer tube

Abstract

Provided is a multilayer pipe having a small bending point radius and improved buckling durability. The multilayer pipe (10) is a hollow pipe in which a plurality of layers are laminated in the thickness direction, the plurality of layers comprise: a first layer (11) on the inner peripheral side, which is formed from a modified adhesive fluororesin; a second layer (12) that is formed from an ethylene-vinyl alcohol copolymer resin modified by an acetoacetyl group on the outer periphery of the first layer (11) and has gas barrier properties; and a third layer (13) that is formed from a modified polyolefin resin modified by an acidic functional group on the outer periphery of the second layer (12). Wherein the ratio of the thickness of the second layer (12) to the total thickness of the pipe comprising the first layer (11), the second layer (12), and the third layer (13) is 6 / 10 or more.

Description

Technical Field

[0001] The present invention relates to a multi-layer tube. Background Art

[0002] The multilayer tube is used as an ink supply tube, for example. It is well known that when the atmosphere outside the multilayer tube penetrates through the wall thickness of the multilayer tube and reaches the ink inside the multilayer tube, it affects the properties of the ink and the coating accuracy. Therefore, in the multilayer tube used as an ink supply tube, gas barrier properties are an important factor. In order to ensure gas barrier properties, ethylene-vinyl alcohol copolymer (hereinafter also referred to as EVOH) is used as a material constituting the multilayer tube.

[0003] Patent Document 1 discloses a multilayer tube composed of a plurality of layers including an antistatic layer composed of a thermoplastic resin and an antistatic agent and a gas barrier layer composed of a gas barrier resin which is a saponified product of an ethylene-vinyl acetate copolymer.

[0004] Patent document 2 discloses an ink supply tube comprising: an inner layer composed of ethylene-tetrafluoroethylene copolymer resin, a first intermediate layer composed of polyamide resin, a second intermediate layer composed of ethylene-vinyl alcohol copolymer resin, a third intermediate layer composed of polyolefin resin and an outer layer composed of thermoplastic resin or elastomer.

[0005] Patent document 3 discloses an ink supply tube comprising: a first layer formed of an ethylene-tetrafluoroethylene copolymer resin, a second layer formed of a modified ethylene-tetrafluoroethylene copolymer resin, a third layer formed of a polyamide resin, etc., a fourth layer formed of an ethylene-vinyl alcohol copolymer resin, and a fifth layer formed of a modified polypropylene resin. Prior art literature Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-160899 Patent Document 2: International Publication No. 2016 / 186111 Patent Document 3: Japanese Patent Application Publication No. 2021-94857 Summary of the invention Problems to be solved by the invention

[0007] Since EVOH is very hard compared to other resin materials for tubes, the tubes using EVOH to improve the gas barrier properties are also hard, so the radius of the bending (kink) point is large and the bending durability is reduced. If the bending durability of the tube is low, there is a problem that cracks are easily generated due to bending when the tube is used in a part that is repeatedly bent such as a movable piping. When cracks appear in the tube, the gas barrier properties of the tube are reduced. In particular, in inkjet printers, the printing speed is increasing, and the ink supply tubes used in inkjet printers are required to have high bending durability.

[0008] An object of the present invention is to provide a multilayer tube having a small bending point radius and improved buckling durability. Means for solving problems

[0009] The multilayer tube of the present invention is a hollow tube having a plurality of layers stacked in a thickness direction, wherein the plurality of layers include: a first layer on the inner circumference formed of a modified adhesive fluororesin; a second layer formed on the outer circumference of the first layer by an ethylene-vinyl alcohol copolymer resin modified by an acetoacetyl group and having gas barrier properties; and a third layer formed on the outer circumference of the second layer by a modified polyolefin resin modified by an acidic functional group, wherein the ratio of the wall thickness of the second layer to the total wall thickness of the tube including the first layer, the second layer and the third layer is 6 / 10 or more. Effects of the Invention

[0010] According to the present invention, it is possible to provide a multilayer tube having a small bending point radius and improved buckling durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a partially removed perspective view of the ink supply tube according to the present embodiment. Figure 2 It is a schematic diagram showing the structure of a bending stiffness test apparatus. Figure 3 It is a graph showing the bending stiffness test results. DETAILED DESCRIPTION

[0012] (Implementation Method) Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0013] (Structure of the multilayer tube 10) Figure 1 1 shows a multilayer tube 10 having a three-layer structure in this embodiment. The multilayer tube 10 is a hollow structure. The multilayer tube 10 includes a first layer 11, a second layer 12, and a third layer 13 in order from the inner circumference. The first layer 11 is arranged on the innermost circumference, the second layer 12 is formed on the outer circumference of the first layer 11, and the third layer 13 is formed on the outer circumference of the second layer 12.

[0014] The first layer 11 is a modified adhesive fluororesin. The modified adhesive fluororesin forming the first layer 11 can be a known substance, which is a substance obtained by introducing one or more adhesive functional groups into at least the terminal or side chain of a homopolymer or copolymer such as a copolymer having an ethylene (hereinafter also referred to as "E") unit and a tetrafluoroethylene (hereinafter also referred to as "TFE") unit (hereinafter also referred to as an ethylene-tetrafluoroethylene copolymer, also referred to as "ETFE"), a copolymer having a TFE unit and a perfluoro(alkyl vinyl ether) unit, a copolymer having a TFE unit and a hexafluoropropylene unit, or a polymer having a vinylidene fluoride unit. Examples of the adhesive functional group include a carboxyl group, a carboxylic anhydride residue, an epoxy group, a hydroxyl group, an isocyanate group, an ester group, an amide group, an aldehyde group, an amine group, a hydrolyzable silyl group, a cyano group, a carbon-carbon double bond, a sulfonic acid group, and an ether group.

[0015] The modified adhesive fluororesin has excellent chemical resistance and low water absorption, and is therefore most suitable as a protective material for the gas barrier layer and can prevent the gas barrier performance of the gas barrier layer from decreasing. Among them, modified ETFE is preferably used due to its chemical resistance and the flexibility required for the tube.

[0016] The second layer 12 is formed of an ethylene-vinyl alcohol copolymer resin modified by an acetoacetyl group (hereinafter referred to as a "modified EVOH resin").

[0017] The modified EVOH resin contains a vinyl alcohol unit represented by the following formula (1), a vinyl acetoacetate unit represented by the following formula (2), and an ethylene unit represented by the following formula (3).

[0018] [Chemical formula 1]

[0019] [Chemical formula 2]

[0020] [Chemical formula 3]

[0021] The flexural modulus of the modified EVOH resin is, for example, 200 [MPa] (ISO17823°C, 50% RH, 2 mm / min). In addition, the oxygen permeability is, for example, 120 [cc. 20 μm / m 2 .day.atm] (20℃, 65%RH), although it is 0.27[cc.20μm / m 2.day.atm], but shows that it has gas barrier properties against oxygen.

[0022] The second layer 12 is formed of a modified EVOH resin and therefore has gas barrier properties. The higher the ratio of acetoethylene units, the higher the flexibility of the EVOH resin and the lower the gas barrier properties. The higher the ratio of acetoacetate units, the lower the flexibility of the EVOH resin and the higher the gas barrier properties. Considering the balance between flexibility and gas barrier properties, the preferred ethylene composition ratio is greater than 20 mol% and less than 60 mol%. Furthermore, from the viewpoint of flexibility and gas barrier properties, the ethylene composition ratio in the present embodiment is preferably greater than 29 mol% and less than 45 mol%.

[0023] The third layer 13 is a modified polyolefin resin. The modified polyolefin resin is obtained by modifying a polyethylene resin such as a high-density polyethylene resin (HDPE), a low-density polyethylene resin (LDPE), a linear low-density polyethylene resin (LLDPE), an ultra-low-density polyethylene resin (VLDPE), and a polyolefin resin such as a polypropylene resin with an acidic functional group. Preferably, the modified polyolefin resin is modified with a carboxylic acid or a derivative thereof, for example, by introducing acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, anhydrides of these acids, or esters of these acids into the polyolefin resin.

[0024] The modified polyolefin resin forming the third layer 13 can be strongly bonded to the modified EVOH resin by modification with an acidic functional group. The modified polyolefin resin is used by coextrusion with a modified adhesive fluororesin, but since the molding temperature is high in this case, a modified polypropylene resin is preferably used.

[0025] In the multilayer tube 10, the ratio of the wall thickness of the second layer 12 to the total wall thickness of the tube including the first layer 11, the second layer 12 and the third layer 13 is 6 / 10 or more. For example, when the total wall thickness of the tube is 1.0 mm, the wall thickness of the second layer 12 is 0.6 mm or more. The wall thickness of the first layer 11 and the third layer 13 can be appropriately selected within a range of 0.4 mm or less in total. For example, when the wall thickness of the second layer 12 is 0.6 mm, the wall thickness of the first layer 11 can be set to 0.1 mm, and the wall thickness of the third layer can be set to 0.3 mm.

[0026] Preferably, in the multilayer tube 10, the ratio of the wall thickness of the second layer 12 to the total wall thickness of the tube including the first layer 11, the second layer 12 and the third layer 13 is 7 / 10 or more, and more preferably 8 / 10 or more. For example, when the total wall thickness of the tube is 1.0 mm, the wall thickness of the second layer 12 is preferably 0.7 mm or more, and more preferably 0.8 mm or more. The wall thickness of the first layer 11 and the third layer 13 is preferably 0.3 mm or less in total, and more preferably 0.2 mm or less, and can be appropriately selected within this range. For example, when the wall thickness of the second layer 12 is 0.7 mm, the wall thickness of the first layer 11 can be set to 0.1 mm, and the wall thickness of the third layer can be set to 0.2 mm. For example, when the wall thickness of the second layer 12 is 0.8 mm, the wall thickness of the first layer 11 can be set to 0.1 mm, and the wall thickness of the third layer can be set to 0.1 mm.

[0027] Since the second layer 12 is composed of the modified EVOH resin, the gas barrier properties of the multilayer tube 10 can be ensured.

[0028] Since the first layer 11 is formed of the modified ETFE resin, the multilayer tube 10 has chemical resistance and low moisture permeability. For example, when the multilayer tube 10 is applied to a tube for ink supply, it is possible to suppress the color of the ink from remaining.

[0029] Since the third layer 13 is formed of a modified polyolefin resin into which an acidic functional group is introduced, the bonding strength with the second layer 12 can be improved. In addition, the third layer 13 is formed of a modified polyolefin resin into which an acidic functional group is introduced, thereby suppressing the reduction of transparency. For example, when the multilayer tube 10 is applied to an ink supply tube, the ink flowing inside can be better identified from the outside. By forming the third layer 13 from a modified polyolefin resin, the moldability can be improved.

[0030] (Function and Effect of Multilayer Tube 10) The multilayer tube 10 of the present embodiment has the second layer 12 made of modified EVOH resin, and the ratio of the wall thickness of the second layer 12 to the total wall thickness of the tube including the first layer 11 , the second layer 12 , and the third layer 13 is 6 / 10 or more.

[0031] The modified EVOH resin constituting the second layer 12 is softer than EVOH resin and has gas barrier properties. Since the modified EVOH resin is used instead of EVOH resin in the second layer 12 for obtaining gas barrier properties, the multilayer tube 10 does not become too hard. In addition, by setting the wall thickness of the second layer 12 using the modified EVOH resin within the above range, the gas barrier properties of the multilayer tube 10 can be ensured. The multilayer tube 10 of this embodiment is softer than a multilayer tube using EVOH resin as a gas barrier layer. Therefore, the multilayer tube 10 of this embodiment is a multilayer tube with a small bending point radius and improved buckling durability.

[0032] The multilayer tube 10 of the present embodiment can be used for conveying fluids such as water or liquids or gases containing organic solvents, or powders. The multilayer tube 10 of the present embodiment can ensure gas barrier properties through the second layer 12, so that oxidation of the fluid and the like retained inside the multilayer tube 10 and volatilization of the solvent can be suppressed. The multilayer tube 10 of the present embodiment is particularly suitable for ink supply tubes that require gas barrier properties. The supplied ink can use either aqueous ink or oily ink. The multilayer tube 10 of the present embodiment is particularly preferably suitable for ink supply tubes for inkjet printers because it has a small bending point radius and improved bending durability. Compared with inkjet printers with high printing speeds, it can achieve a long replacement cycle and piping in narrow locations.

[0033] (Method for Manufacturing Multilayer Tube 10) The following is a method for manufacturing the multilayer tube 10 configured as described above. For example, in the multilayer tube 10, three resins constituting the first layer 11, the second layer 12, and the third layer 13 may be extruded simultaneously, stacked in a cylindrical shape, and molded in one process. Alternatively, after forming the first layer 11 as the inner layer by an inner layer extruder, the second layer 12 may be formed on the outer peripheral surface of the first layer 11 by an outer layer extruder, and the third layer 13 may be formed on the outer peripheral surface of the second layer 12 by an outer layer extruder.

[0034] (Example) Next, examples of the multilayered tube 10 according to the above-described embodiment and comparative examples thereof will be described.

[0035] Here, the first layer 11 is used as the innermost layer, and the second layer 12 and the third layer 13 are formed from the outside of the first layer by co-extrusion molding, and a sample of the multilayer tube of Example 1 having the structure shown in Table 1 is produced. As the material of the first layer 11, a modified ETFE resin is used. As the material of the second layer 12, a modified EVOH resin is used. As the material of the third layer 13, a modified polyolefin resin modified with an acidic functional group is used. The molding of the multilayer tube with a three-layer structure is carried out by extruding three resins simultaneously by co-extrusion molding. The dimensions of the multilayer tube are all 6 mm in outer diameter and 4 mm in inner diameter, and the total wall thickness from the first layer 11 to the third layer 13 is 1 mm (i.e. (6 mm-4 mm) / 2=1 mm), and the wall thickness of the first layer 11, the second layer 12 and the third layer 13 is the structure shown in Table 1.

[0036] In the same manner as in Example 1, the wall thickness of each layer was changed as shown in Table 1, and samples of multilayer tubes of Example 2, Example 3, Comparative Example 4, and Comparative Example 5 were produced.

[0037] A sample of a multilayer tube of Comparative Example 1 having the structure shown in Table 1 was prepared using modified ETFE resin as the material for the first layer, PA612 as the material for the second layer, EVOH resin as the material for the third layer, PA612 as the material for the fourth layer, and modified polyolefin as the material for the fifth layer.

[0038] As the multilayer tube of Comparative Example 2, a commercially available multilayer tube having the structure shown in Table 1 was used.

[0039] A sample of a multilayer tube of Comparative Example 3 having the structure shown in Table 1 was produced using a modified ETFE resin as the material of the first layer and a mixture of PA11 and PA12 as the material of the second layer.

[0040] As shown in Table 1, in the multilayer tube of Example 1, the second layer is formed of a modified EVOH resin, and the ratio of the wall thickness of the second layer (0.6 mm) to the total wall thickness (1.0 mm) of the tube including the first layer, the second layer and the third layer is 6 / 10. In the multilayer tube of Example 2, the ratio of the wall thickness of the second layer (0.7 mm) to the total wall thickness (1.0 mm) of the tube is 7 / 10. In the multilayer tube of Example 3, the ratio of the wall thickness of the second layer (0.8 mm) to the total wall thickness (1.0 mm) of the tube is 8 / 10. The multilayer tubes of Comparative Examples 1 to 3 do not have a layer formed of a modified EVOH resin. In the multilayer tubes of Comparative Examples 4 to 5, although the second layer is formed of a modified EVOH resin, the ratio of the wall thickness of the second layer to the total wall thickness (1.0 mm) of the tube is less than 6 / 10.

[0041] Table 1

[0042] Bending rigidity, gas barrier properties, flexural durability and transparency were evaluated for a total of eight types of multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5 having the structures shown in Table 1. The results of these evaluations are shown in Table 2 and described below.

[0043] (Bending stiffness test) The samples of the multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5 were subjected to a bending rigidity test. Figure 2The bending stiffness test device 31 shown was used to conduct the bending stiffness test. First, each multilayer tube sample was placed in a constant temperature and humidity chamber (23°C, 50% RH) for more than 24 hours and then installed on the bending stiffness test device 31. In addition, the multilayer tube was cut into a length obtained by the formula: length (mm) = π(R+OD / 2) + (2×OD). In the formula, R is the tube bending radius (mm) at the beginning of the test, and OD is the tube outer diameter (mm), which is 336 mm in this test. By moving the movable part 33 set on the track toward the fixed part 32 at a speed of 100 mm / min, the multilayer tube 10 was gradually bent, and the bending radius (mm) relative to the bending load (N) was studied.

[0044] Figure 3 : is a graph showing the results of the bending stiffness test. The vertical axis represents the bending load (N), and the horizontal axis represents the bending radius (mm). Example 1 is represented by point X, Example 2 is represented by curve a, Example 3 is represented by curve b, Comparative Example 1 is represented by curve c, Comparative Example 2 is represented by curve d, Comparative Example 3 is represented by curve e, Comparative Example 4 is represented by curve f, and Comparative Example 5 is represented by curve g.

[0045] The bending point radius of the multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5 was studied. The bending point radius is the bending radius of the multilayer tube 10 when the multilayer tube 10 is bent. The number of tests was set to 5, and the average value of the bending point radius of each Example and Comparative Example was calculated. The bending point radius was smaller than the multilayer tube of Comparative Example 1 (11.0 mm or less) and was marked as "◎", the bending point radius was the same as the multilayer tube of Comparative Example 1 (greater than 11.0 mm and less than 13.6 mm) and was marked as "○", and the bending point radius was larger than the multilayer tube of Comparative Example 1 (greater than 13.6 mm) and was marked as "×". The results are recorded in the "Bending Rigidity" column of Table 2.

[0046] exist Figure 3 In FIG. 1 , point X represents the bending point radius of the multilayer tube of Example 1. Figure 3 The dotted line of "13.6 mm (Comparative Example 1)" in FIG. 1 represents the bending point radius of Comparative Example 1. Figure 3 As shown in Table 2, it was confirmed that the bending radius of the peak of the curve in the multilayer tubes of Examples 2 to 3 was smaller than that of the multilayer tube of Comparative Example 1. As shown in Table 2, it was confirmed that the bending point radius of the multilayer tubes of Examples 1 to 3 was smaller than that of the multilayer tube of Comparative Example 2. It was confirmed that the multilayer tubes of Examples 1 to 3 were more difficult to bend than the multilayer tubes of Comparative Examples 1 and 2.

[0047] (Gas barrier test) The multilayer tubes of Examples 1 to 3, Comparative Examples 1 and 3 were subjected to a gas barrier test. The dissolved oxygen saturation rate in the gas barrier test was measured using a dissolved oxygen meter (Toko Chemical Research Institute Co., Ltd., TD-51 [polarography]). In the gas barrier test, degassed toluene solvent was added to the sample of each multilayer tube, both ends were sealed, and the tube was left to stand in an environment with a temperature of 23°C and a humidity of 50%. The dissolved oxygen saturation rate of the degassed toluene solvent in the multilayer tube was measured to evaluate the gas barrier properties. The determination of the dissolved oxygen saturation rate was carried out 7 days after the start of the test. The dissolved oxygen saturation rate is the dissolved oxygen content of the degassed toluene until the dissolved oxygen content stabilizes as 0. min , the dissolved oxygen content of oxygen-saturated toluene is set to O max , the dissolved oxygen content in the gas barrier test is set to O test , calculated by the following formula. Dissolved oxygen saturation rate (%) = (O test -O min ) / (O max -O min )×100 Toluene is degassed by reducing the pressure of toluene under ultrasonic irradiation. Toluene saturated with oxygen is prepared by aerating toluene until the increase in the amount of dissolved oxygen converges and stabilizes. The lower the dissolved oxygen saturation rate, the higher the gas barrier properties of the multilayer tube.

[0048] For the multilayer tubes of Examples 1 to 3, Comparative Examples 1 and 3, the dissolved oxygen saturation rates after 7 days from the start of the gas barrier test are shown in Table 2. Here, the reference values ​​of the dissolved oxygen saturation rate after 7 days were set to 50% and 10%, and "◎" was indicated when it was 10% or less, "○" was indicated when it was greater than 10% and less than 50%, and "×" was indicated when it was greater than 50%, and the results were recorded in the "Gas Barrier Property" column of Table 2.

[0049] As shown in Table 2, it was confirmed that the gas barrier properties of the multilayer tubes of Examples 1 to 3 were as good as that of the multilayer tube of Comparative Example 1.

[0050] (Buckling durability test) The multilayer tubes of Examples 1 to 3, Comparative Examples 1, 2, 4, and 5 were subjected to a buckling durability test. In the buckling durability test, samples of each multilayer tube of Examples 1 to 3, Comparative Examples 1, 2, 4, and 5 were mounted on a buckling durability tester, and buckled under the conditions of a test temperature of 23°C, a sample length of 300 mm, no sealing liquid, a curvature of R40 during buckling, a buckling speed of 300 times / min, and a stroke length of 140 mm, and the number of bucklings until cracks occurred was measured. Here, one buckling was measured as one reciprocation.

[0051] The number of buckling times at which cracks occurred for the multilayer tubes of Examples 1 to 3, Comparative Examples 1, 2, 4, and 5 is shown in Table 2. Here, the reference value of the number of buckling times at which cracks occurred was set to 470,000 times, and a value exceeding the reference value was marked as "○", and a value below the reference value was marked as "×", and the results were recorded in the "Buckling Durability" column of Table 2.

[0052] As shown in Table 2, it was confirmed that the multilayer tubes of Examples 1 to 3 had better buckling durability than the multilayer tubes of Comparative Examples 1, 2, 4, and 5.

[0053] (Transparency test) The transparency test was conducted on the samples of the multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5. The transparency test was conducted by sealing toluene in each multilayer tube sample and judging whether the liquid level gauge could detect the liquid level of the sealed toluene (whether there was a reaction). The evaluation was conducted using a liquid level gauge (manufactured by Omron Corporation, Japan, EE-SPX613) with the sensitivity set to Low.

[0054] The presence or absence of the liquid level gauge response for the multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5 is shown in Table 2. Here, "○" indicates a response to the liquid level gauge, and "×" indicates a non-response to the liquid level gauge. The results are recorded in the "Transparency" column of Table 2.

[0055] As shown in Table 2, it was confirmed that the multilayer tubes of Examples 1 to 3 had the same good transparency as Comparative Examples 2 to 5.

[0056] Table 2

[0057] As described above, the multilayer tubes of Examples 1 to 3 show good results in terms of bending rigidity, gas barrier properties, flexural durability, and transparency. The multilayer tube of Comparative Example 1 has good bending rigidity and gas barrier properties, but poor flexural durability and transparency. The multilayer tube of Comparative Example 2 has good transparency, but poor bending rigidity and flexural durability. The multilayer tube of Comparative Example 3 has good bending rigidity and transparency, but poor gas barrier properties. The multilayer tube of Comparative Example 4 has good transparency, but poor bending rigidity and flexural durability. The multilayer tube of Comparative Example 5 has good transparency, but poor bending rigidity and flexural durability. It can be considered that the multilayer tubes of Examples 1 to 3 have a high comprehensive evaluation compared to the multilayer tubes of Comparative Examples 1 to 5.

[0058] The present invention is not limited to the above-mentioned embodiment, and can be appropriately changed within the scope of the gist of the present invention. It is also possible to further have an innermost layer formed of unmodified ethylene-tetrafluoroethylene copolymer resin on the inner peripheral side of the first layer 11. It is also possible to further have an intermediate layer formed of polyamide or the like between the first layer 11 and the second layer 12. Explanation of symbols

[0059] 10: Multilayer tube; 11: First layer; 12: Second layer; 13: The third floor; 31: Bending stiffness test device; 32: fixed part; 33: Movable part.

Claims

1. A multilayer tube, which is a hollow tube having a plurality of layers stacked in a thickness direction, wherein: The multiple layers include: The first layer on the inner peripheral side is formed of a modified adhesive fluororesin; a second layer having a gas barrier property, formed on the periphery of the first layer from an ethylene-vinyl alcohol copolymer resin modified with an acetoacetyl group; and A third layer is formed on the periphery of the second layer from a modified polyolefin resin modified with an acidic functional group, The ratio of the wall thickness of the second layer to the total wall thickness of the tube including the first layer, the second layer and the third layer is 6 / 10 or more.

2. The multilayer tube according to claim 1, wherein A ratio of a wall thickness of the second layer to a total wall thickness of the tube including the first layer, the second layer, and the third layer is 7 / 10 or more.

3. The multilayer tube according to claim 1, wherein A ratio of a wall thickness of the second layer to a total wall thickness of the tube including the first layer, the second layer, and the third layer is 8 / 10 or more.

4. The multilayer tube according to claim 1, wherein The ethylene-vinyl alcohol copolymer resin modified with an acetoacetyl group contains a vinyl alcohol unit represented by the following formula (1), a vinyl acetoacetate unit represented by the following formula (2), and an ethylene unit represented by the following formula (3). [Chemical formula 4] 5. The multilayer tube according to any one of claims 1 to 4, wherein: The modified adhesive fluororesin is a modified ethylene-tetrafluoroethylene copolymer resin.

6. The multilayer tube according to any one of claims 1 to 4, wherein: The modified polyolefin resin is a modified polypropylene resin.

7. The multilayer tube according to any one of claims 1 to 4, wherein: The modified adhesive fluororesin is a modified ethylene-tetrafluoroethylene copolymer resin, and the modified polyolefin resin is a modified polypropylene resin.

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