Multilayer tube

1. A multilayer tube comprising at least four layers, having a layer (a), a layer (b), a layer (c), and a layer (d); wherein,

the layer (a) contains an aliphatic polyamide (A),

the layer (b) contains a polyamide 6/66/12 composition (B2), the layer (c) contains a saponified ethylene-vinyl acetate copolymer (C), and the layer (d) contains a semi-aromatic polyamide composition (D1) or a semi-aromatic polyamide composition (D2); and,

the aliphatic polyamide (A) does not contain polycaproamide or poly(caproamide/hexamethylene adipamide/dodecanamide)

the Polyamide 6/66/12 composition (B2) contains at least 50% by mass to 98% by mass of a mixtures containing Polyamide 6/66/12 and at least one type of polyamide selected from the group consisting of polyhexamethylene sebacamide (Polyamide 610), polyhexamethylene dodecanamide (Polyamide 612), polynonamethylene decamide (Polyamide 910), polynonamethylene dodecamide (polyamide 912), polydecamethylene decamide (Polyamide 1010), polydecamethylene dodecamide (Polyamide 1012) and polydodecamethylene dodecamide (Polyamide 1212), 1% by mass to 20% by mass of a plasticizer (B3), and 1% by mass to 30% by mass of an olefin polymer (B4) having a bending elastic modulus of 500 MPa or less as measured in compliance with ISO 178,

wherein the Polyamide 6/66/12 of the Polyamide 6/66/12 composition (B2) the mass ratio of the total number of caproamide units and hexamethylene units to the number of dodecaneamide units is 81:19 percent by mass to 95:5 percent by mass based on 100 percent by mass of the total number of caproamide units, hexamethylene adipamide units and dodecaneamide units,

the semi-aromatic polyamide composition (D1) contains a semi-aromatic polyamide (d1) and the semi-aromatic polyamide (d1) has a diamine units containing 50 mol % or more of an aliphatic diamine unit having 9 to 13 carbon atoms based on the total number of diamine units, and a carboxylic acid unit containing 50 mol % or more of a terephthalic acid unit and/or naphthalene dicarboxylic acid unit based on the total number of carboxylic acid units, and

the semi-aromatic polyamide composition (D2) contains a semi-aromatic polyamide (d2) and the semi-aromatic polyamide (d2) has a diamine unit containing 50 mol % or more of a xylylenediamine unit and/or bis(aminomethyl)naphthalene unit based on the total number of diamine units and a carboxylic acid unit containing 50 mol % or more of an aliphatic dicarboxylic acid unit having 8 to 13 carbon atoms based on the total number of dicarboxylic acid units.

2. The multilayer tube according to claim 1 , wherein the aliphatic polyamide (A) is at least one type of homopolymer selected from the group consisting of polyundecanamide (Polyamide 11), polydodecanamide (Polyamide 12), polyhexamethylene adipamide (Polyamide 66), polyhexamethylene decamide (Polyamide 610), polyhexamethylene dodecamide (Polyamide 612), polydecamethylene decamide (Polyamide 1010), polydecamethylene dodecamide (Polyamide 1012) and polydodecamethylene dodecamide (Polyamide 1212), and/or a copolymer using a plurality of types of raw material monomers that form these.

3. The multilayer tube according to claim 1 , wherein the ethylene content of the saponified ethylene-vinyl acetate copolymer (C) is 15 mol % to 60 mol % and the degree of saponification is 90 mol % or more.

4. The multilayer tube according to claim 1 , wherein the layer (a) is arranged in the outermost layer and the layer (c) is arranged between the layer (a) and the layer (d).

5. The multilayer tube according to claim 1 , wherein the layer (b) is arranged on at least one side that contacts the layer (c).

6. The multilayer tube according to claim 1 , wherein an electrically conductive layer comprising the semi-aromatic polyamide composition (D) containing an electrically conductive filler is arranged in the innermost layer of the multilayer tube.

7. The multilayer tube according to claim 1 , which is produced by a co-extrusion processing method.

8. The multilayer tube according to claim 1 , which is used as a fuel tube.

9. A multilayer tube comprising at least five layers, having a layer (a), a layer (b), a layer (c), a layer (d) and a layer (e), wherein,

the layer (a) contains an aliphatic polyamide (A),

the layer (b) contains a Polyamide 6 composition (B1) and/or a Polyamide 6/66/12 composition (B2),

the layer (c) contains a saponified ethylene-vinyl acetate copolymer (C),

the layer (d) contains a semi-aromatic polyamide composition (D1) or a semi-aromatic polyamide composition (D2), and

the layer (e) contains a fluorine-containing polymer (E) in which a functional group having reactivity with an amino group is introduced into the molecular chain thereof and,

the aliphatic polyamide (A) does not contain polycaproamide (Polyamide 6) or poly(caproamide/hexamethylene adipamide/dodecanamide),

the Polyamide 6 composition (B1) contains 50% by mass to 98% by mass of polycaproamide (Polyamide 6), 1% by mass to 20% by mass of a plasticizer (B3), and 1% by mass to 30% by mass of an olefin polymer (B4) having a bending elastic modulus of 500 MPa or less as measured in compliance with ISO 178,

the Polyamide 6/66/12 composition (B2) contains 50% by mass to 98% by mass of a polyamide mixture containing Polyamide 6/66/12 and at least one type of polyamide selected from the group consisting of polyhexamethylene sebacamide (Polyamide 610), polyhexamethylene dodecanamide (Polyamide 612), polynonamethylene decamide (Polyamide 910), polynonamethylene dodecamide (Polyamide 912), polydecamethylene decamide (Polyamide 1010), polydecamethylene dodecamide (Polyamide 1012) and polydodecamethylene dodecamide (polyamide 1212), 1% by mass to 20% by mass of a plasticizer (B3), and 1% by mass to 30% by mass of an olefin polymer (B4) having a bending elastic modulus of 500 MPa or less as measured in compliance with ISO 178,

the semi-aromatic polyamide composition (D1) contains a semi-aromatic polyamide (d1), and the semi-aromatic polyamide (d1) has a diamine unit containing 50 mol % or more of an aliphatic diamine unit having 9 to 13 carbon atoms based on the total number of diamine units, and a carboxylic acid unit containing 50 mol % or more of a terephthalic acid unit and/or naphthalene dicarboxylic acid unit based on the total number of carboxylic acid units, and

the semi-aromatic polyamide composition (D2) contains a semi-aromatic polyamide (d2), and the semi-aromatic polyamide (d2) has a diamine unit containing 50 mol % or more of a xylylenediamine unit and/or bis(aminomethyl)naphthalene unit based on the total number of diamine units and a carboxylic acid unit containing 50 mol % or more of an aliphatic dicarboxylic acid unit having 8 to 13 carbon atoms based on the total number of dicarboxylic acid units.

10. The multilayer tube according to claim 9 , wherein the layer (a) is arranged in the outermost layer, and the layer (c) and the layer (d) are arranged between the layer (a) and the layer (e).

11. The multilayer tube according to claim 9 , wherein the layer (b) is arranged on at least one side in contact with the layer (c).

12. The multilayer tube according to claim 9 , wherein an electrically conductive layer comprising a fluorine-containing polymer composition containing an electrically conductive filler is arranged in the innermost layer of the multilayer tube.

13. The multilayer tube according to claim 9 , which is produced by a co-extrusion processing method.

14. The multilayer tube according to claim 9 , which is used as a fuel tube.

15. A method for producing the multilayer tube according to claim 1 , which comprises co-extrusion processing.

16. A method for producing the multilayer tube according to claim 9 , which comprises co-extrusion processing.