Multilayer tube

Abstract

To provide a multilayer tube having a small kink point radius and enhanced bending durability.SOLUTION: A multilayer tube 10 is a hollow tube in which a plurality of layers is laminated in a thickness direction. The plurality of layers includes: a first layer 11 that is formed of a modified adhesive fluoro resin; a second layer 12 that has a gas barrier property, is formed on an outer periphery of the first layer 11, and is formed using an ethylene vinyl alcohol copolymer resin modified with an aceto-acetyl group; and a third layer 13 that is formed on an outer periphery of the second layer 12 and is formed with a modified polyolefin resin modified with an acidic functional group. A ratio of a wall thickness of the second layer 12 to an overall wall thickness of the tube including the first layer 11, the second layer 12, and the third layer 13 is 6 / 10 or greater.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Multilayer tubes are used, for example, as ink supply tubes. It is known that if the air outside the multilayer tube penetrates the thickness of the multilayer tube and reaches the ink inside the multilayer tube, it will affect the properties of the ink and the coating accuracy. For this reason, gas barrier properties are an important factor for multilayer tubes used as ink supply tubes. To ensure gas barrier properties, for example, ethylene-vinyl alcohol copolymer (hereinafter also referred to as EVOH) is used as a material that constitutes the multilayer tube.

[0003] Patent Document 1 discloses a multi-layer tube that is composed of multiple 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, the gas barrier resin being a saponified product of an ethylene-vinyl acetate copolymer.

[0004] Patent Document 2 discloses an ink supply tube having an inner layer made of an ethylene-tetrafluoroethylene copolymer resin or the like, a first intermediate layer made of a polyamide resin, a second intermediate layer made of an ethylene-vinyl alcohol copolymer resin, a third intermediate layer made of a polyolefin resin, and an outer layer made of a thermoplastic resin or an elastomer.

[0005] Patent Document 3 discloses an ink supply tube having 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 or the like, a fourth layer formed of an ethylene-vinyl alcohol copolymer resin, and a fifth layer formed of a modified polypropylene resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-160899 A [Patent Document 2] International Publication No. 2016 / 186111 [Patent Document 3] Patent Publication No. 2021-94857 Summary of the Invention [Problem to be solved by the invention]

[0007] EVOH has extremely hard properties compared to other resin materials for tubes, and therefore tubes using EVOH to enhance the above-mentioned gas barrier properties are also hard, resulting in a large kink radius and low bending durability. If the bending durability of a tube is low, there is a problem that the tube is prone to cracking when used in a part that is repeatedly and continuously bent, such as a movable pipe. If a tube cracks, the gas barrier properties of the tube will decrease. In particular, with the printing speed of inkjet printers increasing, high bending durability is required for the ink supply tubes used in inkjet printers.

[0008] An object of the present invention is to provide a multi-layer tube having a small kink point radius and improved bending durability. [Means for solving the problem]

[0009] The multi-layer tube of the present invention is a hollow tube having a plurality of layers laminated in the thickness direction, the plurality of layers comprising a first layer on the inner periphery formed of a modified adhesive fluororesin, a second layer having gas barrier properties formed on the outer periphery of the first layer of an ethylene-vinyl alcohol copolymer resin modified with an acetoacetyl group, and a third layer formed on the outer periphery of the second layer of a modified polyolefin resin modified with an acidic functional group, the ratio of the wall thickness of the second layer to the overall wall thickness of the tube including the first layer, the second layer, and the third layer being 6 / 10 or more. Effect of the Invention

[0010] According to the present invention, it is possible to provide a multi-layer tube having a small kink point radius and improved bending durability. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a perspective view of the ink supply tube according to the embodiment with a portion thereof removed. [Diagram 2] FIG. 2 is a diagram showing a schematic configuration of a bending stiffness testing device. [Diagram 3] FIG. 13 is a diagram showing bending stiffness test results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0013] (Configuration of multi-layer tube 10) 1 shows a multi-layer tube 10 having a three-layer structure according to this embodiment. The multi-layer tube 10 has a hollow structure. The multi-layer tube 10 includes, in order from the inner periphery, a first layer 11, a second layer 12, and a third layer 13. The first layer 11 is disposed on the innermost periphery, the second layer 12 is formed on the outer periphery of the first layer 11, and the third layer 13 is formed on the outer periphery of the second layer 12.

[0014] The first layer 11 is a modified adhesive fluororesin. The modified adhesive fluororesin forming the first layer 11 may be a known one, and may be a copolymer having ethylene (hereinafter also referred to as "E") units and tetrafluoroethylene (hereinafter also referred to as "TFE") units (hereinafter also referred to as ethylene-tetrafluoroethylene copolymer, also referred to as "ETFE"), a copolymer having TFE units and perfluoro(alkyl vinyl ether) units, a copolymer having TFE units and hexafluoropropylene units, a polymer having vinylidene fluoride units, or the like, in which one or more adhesive functional groups are introduced at least at the end or side chain of a homopolymer or copolymer. 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 amino group, a hydrolyzable silyl group, a cyano group, a carbon-carbon double bond, a sulfonic acid group, and an ether group.

[0015] The above-mentioned modified adhesive fluororesin has excellent chemical resistance and low water absorption, making it ideal as a protective material for the gas barrier layer and preventing a decrease in the gas barrier performance of the gas barrier layer. Among them, modified ETFE is preferred because of its chemical resistance and the flexibility required for tubes.

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

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

[0018] [ka]

[0019] [ka]

[0020] [ka]

[0021] The modified EVOH resin has a flexural modulus of, for example, 200 [MPa] (ISO178 23°C, 50% RH, 2 mm / min). The oxygen permeability coefficient is, for example, 120 [cc.20 μm / m 2 .day.atm] (20℃, 65%RH), and the viscosity of 32mol% EVOH resin is 0.27[cc.20μm / m 2 Although this value is larger than the [.day.atm] value, it indicates that the material has gas barrier properties against oxygen.

[0022] The second layer 12 has gas barrier properties because it is formed of a modified EVOH resin. 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 vinyl acetoacetate units, the lower the flexibility of the EVOH resin and the higher the gas barrier properties. In consideration of the balance between flexibility and gas barrier properties, the preferred ethylene composition ratio is 20 mol% or more and 60 mol% or less. Furthermore, from the viewpoint of flexibility and gas barrier properties, the ethylene composition ratio in this embodiment is desirably 29 mol% or more and 45 mol% or less.

[0023] The third layer 13 is a modified polyolefin resin. The modified polyolefin resin is a polyethylene resin such as high density polyethylene resin (HDPE), low density polyethylene resin (LDPE), linear low density polyethylene resin (LLDPE), very low density polyethylene resin (VLDPE), and polyolefin resin such as polypropylene resin, which is modified with an acidic functional group, preferably with a carboxylic acid or a derivative thereof, and is obtained, 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 is modified with an acidic functional group, and thus can strongly adhere to the modified EVOH resin. The modified polyolefin resin is used by co-extrusion with, for example, a modified adhesive fluororesin, and in this case, it is preferable to use a modified polypropylene resin since the molding temperature is high.

[0025] In the multi-layer 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 thicknesses 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 0.1 mm and the wall thickness of the third layer can be 0.3 mm.

[0026] Preferably, 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 of the multi-layer tube 10 is 7 / 10 or more, 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, more preferably 0.8 mm or more. The total wall thickness of the first layer 11 and the third layer 13 is preferably 0.3 mm or less, 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 0.1 mm, and the wall thickness of the third layer can be 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 0.1 mm, and the wall thickness of the third layer can be 0.1 mm.

[0027] Since the second layer 12 is made of a modified EVOH resin, the gas barrier properties of the multi-layer tube 10 can be ensured.

[0028] Since the first layer 11 is formed of the modified ETFE resin, the multi-layer tube 10 has chemical resistance and low moisture permeability. For example, when the multi-layer tube 10 is used as an ink supply tube, ink color residue can be suppressed.

[0029] The third layer 13 is formed of a modified polyolefin resin having an acidic functional group introduced therein, and therefore the bonding strength with the second layer 12 can be improved. Furthermore, the third layer 13 is formed of a modified polyolefin resin having an acidic functional group introduced therein, thereby suppressing a decrease in transparency. For example, when the multi-layer tube 10 is applied to an ink supply tube, the ink flowing inside can be more easily seen from the outside. Forming the third layer 13 of a modified polyolefin resin can improve moldability.

[0030] (Actions and Effects of Multilayer Tube 10) The multi-layer tube 10 of this embodiment has a second layer 12 made of a modified EVOH resin, the thickness of which is 6 / 10 or more relative to the overall thickness of the tube including the first layer 11, the second layer 12, and the third layer 13.

[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, not the EVOH resin, is used for the second layer 12 for obtaining gas barrier properties, the multi-layer tube 10 does not become too hard. Furthermore, by setting the thickness of the second layer 12 using the modified EVOH resin within the above range, the gas barrier properties of the multi-layer tube 10 can be ensured. The multi-layer tube 10 of this embodiment is softer than a multi-layer tube using an EVOH resin as a gas barrier layer. Therefore, the multi-layer tube 10 of this embodiment is a multi-layer tube with a small kink point radius and improved bending durability.

[0032] The multilayer tube 10 of this embodiment can be used for transporting fluids such as liquids or gases containing water or organic solvents, or powdery materials. The multilayer tube 10 of this embodiment can ensure gas barrier properties by the second layer 12, so that oxidation of fluids and the like remaining inside the multilayer tube 10 and evaporation of the solvent can be suppressed. The multilayer tube 10 of this embodiment can be particularly used as an ink supply tube that requires gas barrier properties. Either water-based ink or oil-based ink can be supplied. The multilayer tube 10 of this embodiment has a small kink point radius and high bending durability, so it can be particularly preferably used as an ink supply tube for inkjet printers, and can extend the replacement cycle and be installed in narrow spaces for inkjet printers that are becoming faster in printing speed.

[0033] (Method of manufacturing the multi-layer tube 10) Next, a method for manufacturing the multi-layer tube 10 configured as described above will be described. For example, the multi-layer tube 10 can be formed in one step by simultaneously extruding the three types of resins constituting the first layer 11, the second layer 12, and the third layer 13 and laminating them into a cylindrical shape. Also, after the first layer 11, which will be the inner layer, is formed by an inner layer extruder, the second layer 12 can be formed on the outer peripheral surface of this first layer 11 by an outer layer extruder, and the third layer 13 can be further formed on the outer peripheral surface of the second layer 12 by the outer layer extruder.

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

[0035] Here, the first layer 11 was the innermost layer, and the second layer 12 and the third layer 13 were formed from the outside of the first layer by co-extrusion molding to produce a sample of a multi-layer tube according to Example 1 having the configuration shown in Table 1. The material of the first layer 11 was a modified ETFE resin. The material of the second layer 12 was a modified EVOH resin. The material of the third layer 13 was a modified polyolefin resin modified with an acidic functional group. The multi-layer tube with a three-layer structure was formed by simultaneously extruding three types of resins by co-extrusion molding. The size of the multi-layer tube was an outer diameter of 6 mm and an inner diameter of 4 mm, and the total thickness of the first layer 11 to the third layer 13 was 1 mm (i.e., (6 mm-4 mm) / 2=1 mm), and the thicknesses of the first layer 11, the second layer 12, and the third layer 13 were configured as shown in Table 1.

[0036] In the same manner as in Example 1, the thickness of each layer was changed as shown in Table 1 to prepare samples of multi-layer tubes according to Examples 2, 3, Comparative Example 4, and Comparative Example 5.

[0037] A sample of a multi-layer tube according to Comparative Example 1 having the configuration shown in Table 1 was created using modified ETFE resin as the first layer material, PA612 as the second layer material, EVOH resin as the third layer material, PA612 as the fourth layer material, and modified polyolefin as the fifth layer material.

[0038] As the multi-layer tube according to Comparative Example 2, a commercially available multi-layer tube having the structure shown in Table 1 was used.

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

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

[0041] [Table 1]

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

[0043] (Bending stiffness test) The bending stiffness test was carried out on the multilayer tube samples of Examples 1 to 3 and Comparative Examples 1 to 5. The bending stiffness test was carried out using a bending stiffness tester 31 shown in FIG. 2. First, each multilayer tube sample was left to stand in a constant temperature and humidity room (23°C, 50% RH) for 24 hours or more, and then attached to the bending stiffness tester 31. The multilayer tube was cut to a length calculated by length (mm) = π(R + OD / 2) + (2 x OD). Here, R: tube bending radius (mm) at the start of the test, OD: tube outer diameter (mm), which was set to 336 mm in this test. The movable part 33 provided on the rail was moved toward the fixed part 32 at a speed of 100 mm / min to gradually bend the multilayer tube 10, and the bending radius (mm) relative to the bending load (N) was examined.

[0044] 3 is a diagram showing the bending stiffness test results. The vertical axis indicates bending load (N) and the horizontal axis indicates bending radius (mm). Example 1 is indicated by point x, Example 2 by graph a, Example 3 by graph b, Comparative Example 1 by graph c, Comparative Example 2 by graph d, Comparative Example 3 by graph e, Comparative Example 4 by graph f, and Comparative Example 5 by graph g.

[0045] The kink point radius of the multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5 was examined. The kink point radius is the bending radius of the multilayer tube 10 when a kink occurs in the multilayer tube 10. Five tests were conducted, and the average of the kink point radii of each Example and Comparative Example was calculated. If the kink point radius was smaller than that of the multilayer tube of Comparative Example 1 (11.0 mm or less), it was marked with "◎", if it was equivalent to that of the multilayer tube of Comparative Example 1 (more than 11.0 mm and less than 13.6 mm), it was marked with "◯", and if it was larger than that of the multilayer tube of Comparative Example 1 (more than 13.6 mm), it was marked with "X". The results are shown in the "Bending stiffness" column in Table 2.

[0046] In FIG. 3, point x indicates the kink point radius of the multilayer tube of Example 1. The dashed line labeled "13.6 mm (Comparative Example 1)" in FIG. 3 indicates the kink point radius of Comparative Example 1. As shown in FIG. 3, it was confirmed that the multilayer tubes of Examples 2 to 3 have smaller bending radii at the peaks of the graph than, for example, the multilayer tube of Comparative Example 1. As shown in Table 2, it was confirmed that the kink point radii of the multilayer tubes of Examples 1 to 3 are smaller than that of the multilayer tube of Comparative Example 2. From this, it was confirmed that the multilayer tubes of Examples 1 to 3 are less likely to break than the multilayer tubes of Comparative Examples 1 and 2.

[0047] (Gas barrier test) A gas barrier property test was carried out for the multilayer tubes of Examples 1 to 3, Comparative Example 1, and Comparative Example 3. The dissolved oxygen saturation rate in the gas barrier property test was measured using a dissolved oxygen meter (Toko Chemical Laboratory Co., Ltd., TD-51 [polarographic method]). In the gas barrier property test, degassed toluene solvent was poured into each multilayer tube sample, both ends were sealed, and the sample was left to stand in an environment of a temperature of 23°C and a humidity of 50%, and then the dissolved oxygen saturation rate of the degassed toluene solvent in the multilayer tube was measured to evaluate the gas barrier property. The dissolved oxygen saturation rate was measured 7 days after the start of the test. The dissolved oxygen saturation rate was calculated from the following formula, where Omin is the amount of dissolved oxygen in toluene degassed until the amount of dissolved oxygen stabilized, Omax is the amount of dissolved oxygen in toluene saturated with oxygen, and Otest is the amount of dissolved oxygen in the gas barrier test. Dissolved oxygen saturation rate (%) = (Otest-Omin) / (Omax-Omin) x 100 Toluene was degassed by reducing the pressure under ultrasonic irradiation. Toluene saturated with oxygen was prepared by aerating toluene until the increase in the amount of dissolved oxygen ceased and became stable. The lower the dissolved oxygen saturation rate, the higher the gas barrier property of the multilayer tube.

[0048] For the multilayer tubes of Examples 1 to 3, Comparative Example 1, and Comparative Example 3, the dissolved oxygen saturation rate 7 days after the start of the gas barrier test is shown in Table 2. Here, the standard values ​​for the dissolved oxygen saturation rate after 7 days were set to 50% and 10%, with 10% or less being marked as "◎", greater than 10% and less than 50% being marked as "◯", and greater than 50% being marked as "X". The results are shown in the "Gas barrier property" column in Table 2.

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

[0050] (Flexibility test) A bending durability test was conducted on the multilayer tubes of Examples 1 to 3, Comparative Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 5. In the bending durability test, a sample of each of the multilayer tubes of Examples 1 to 3, Comparative Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 5 was attached to a bending durability tester, and the sample was bent under the conditions of a test temperature of 23° C., a sample length of 300 mm, no enclosed liquid, a curvature when bent of R40, a bending speed of 300 times / min, and a stroke length of 140 mm, and the number of times the sample was bent until a crack occurred was measured. Here, one bending was counted as one round trip.

[0051] Table 2 shows the number of flexing cycles at which cracks occur for the multilayer tubes of Examples 1 to 3, Comparative Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 5. Here, the standard number of flexing cycles at which cracks occur was set at 470,000, and a result exceeding the standard value was marked as "◯", and a result equal to or less than the standard value was marked as "X". The results are shown in the "Flexing durability" column in Table 2.

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

[0053] (Transparency test) A transparency test was conducted on the multilayer tube samples 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 checking whether a level gauge could detect (react to) the liquid level of the sealed toluene. A level gauge (EE-SPX613, manufactured by Omron Corporation) was used for the evaluation, and the evaluation was conducted with the sensitivity set to Low.

[0054] For the multilayer tubes of Examples 1 to 3 and Comparative Examples 1 to 5, the presence or absence of a reaction of the level gauge is shown in Table 2. Here, the presence or absence of a reaction of the level gauge is indicated as "◯", and the absence or absence of a reaction of the level gauge is indicated as "×". The results are shown in the "Transparency" column in Table 2.

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

[0056] [Table 2]

[0057] As described above, the multilayer tubes of Examples 1 to 3 showed good results in terms of bending rigidity, gas barrier properties, bending durability, and transparency. The multilayer tube of Comparative Example 1 had good bending rigidity and gas barrier properties, but not good bending durability and transparency. The multilayer tube of Comparative Example 2 had good transparency, but not good bending rigidity and bending durability. The multilayer tube of Comparative Example 3 had good bending rigidity and transparency, but not good gas barrier properties. The multilayer tube of Comparative Example 4 had good transparency, but not good bending rigidity and bending durability. The multilayer tube of Comparative Example 5 had good transparency, but not good bending rigidity and bending durability. From this, it can be said that the multilayer tubes of Examples 1 to 3 are evaluated more highly overall than the multilayer tubes of Comparative Examples 1 to 5.

[0058] The present invention is not limited to the above embodiment, and can be modified as appropriate within the scope of the present invention. An innermost layer made of unmodified ethylene-tetrafluoroethylene copolymer resin may be further provided on the inner periphery side of the first layer 11. An intermediate layer made of polyamide or the like may be further provided between the first layer 11 and the second layer 12. [Explanation of symbols]

[0059] 10 Multilayer tube 11 1st layer 12 2nd layer 13 3rd layer 31 Bending stiffness testing device 32 Fixed part 33 Moving parts

Claims

1. A hollow tube having a plurality of layers laminated in the thickness direction, The plurality of layers include a first layer on an inner periphery side formed of a modified adhesive fluororesin; a second layer having gas barrier properties and formed on the outer periphery of the first layer using an ethylene-vinyl alcohol copolymer resin modified with an acetoacetyl group; a third layer formed on the outer periphery of the second layer and made of a modified polyolefin resin modified with an acidic functional group; Equipped with 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. Multi-layer tube.

2. 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 7 / 10 or more. The multi-layer tube according to claim 1 .

3. 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 8 / 10 or more. The multi-layer tube according to claim 1 .

4. The acetoacetyl-modified ethylene-vinyl alcohol copolymer 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): The multi-layer tube according to claim 1 . 【Chemistry 4】

5. The modified adhesive fluororesin is a modified ethylene-tetrafluoroethylene copolymer resin. The multilayer tube according to any one of claims 1 to 4.

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

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

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