A cooling tube material having a double-layer structure

Abstract

The application provides a cooling pipe material with a double-layer structure. The cooling pipe comprises a two-layer structure of an A layer and a B layer, wherein the A layer is an outer layer and the B layer is an inner layer; the A layer is a flexible modified nylon 12, and the B layer is a grafted modified polyolefin alloy. The cooling pipe and the material have the advantages of hydrolysis resistance, alcoholysis resistance, water vapor transmission resistance, low-temperature impact resistance, stress cracking resistance, simple forming process, small equipment investment and the like.

Description

Technical Field

[0001] This invention belongs to the field of modified plastics technology, and specifically relates to a cooling pipe material with a double-layer structure. Background Technology

[0002] With the introduction and implementation of a series of policies and measures such as carbon peaking and carbon neutrality, electric vehicles powered by electricity have developed rapidly, and their market share has increased year by year. Compared with traditional fuel vehicles, electric vehicles require a significantly longer total length of cooling pipes for their battery packs and electric motors, leading to a corresponding increase in the demand for lightweighting, although the operating temperature requirements are somewhat lower. Traditional fuel vehicles use vulcanized EPDM rubber with a braided layer for their cooling pipes, which is a thermosetting material, non-recyclable, and typically 3-4mm thick, making them quite heavy. In contrast, the thermoplastic nylon 12 cooling pipes without a braided layer, which are now widely used in electric vehicles, effectively solve the problems of lightweighting and recyclability.

[0003] Nylon 12 is an excellent lightweight material for automobiles, widely used in automotive fluid delivery pipelines. It is highly irreplaceable, with applications including fuel lines, lubricating oil lines, vacuum brake booster lines, pneumatic brake lines, electric vehicle coolant lines, and quick-connect fittings for these lines – all critical components in the automotive industry. Its key properties, such as fuel resistance, water vapor permeability, hydrolysis resistance, burst pressure, and interlayer adhesion, are significantly superior to other nylon materials. Its safety and reliability improve the overall quality and lifespan of automobiles. Compared to metal tubing, nylon 12 tubing has significant advantages: it is lightweight, with a density of only 1.00–1.03 g / cm³. 3 Nylon 12 tubing offers several advantages over rubber hoses. It reduces overall vehicle weight and fuel consumption; its flexibility allows for easy arrangement and design freedom, minimizing the need for joints; it boasts high safety and toughness, resisting deformation from external impacts and exhibiting excellent vibration, fatigue, and corrosion resistance; it provides good joint sealing and convenient installation; and it is easy to extrude and has a simple manufacturing process. Compared to rubber hoses, Nylon 12 tubing offers the following advantages: minimal volume deformation, effectively reducing vehicle braking distance when used in air brake systems; thin walls, small size, and light weight, without affecting spatial layout; excellent aging resistance; short molding cycle, saving energy; no vulcanization or braiding layer required, simplifying processing; thermoplasticity, recyclability, and compliance with low-carbon and environmentally friendly requirements. With the development of new energy vehicles, hybrid vehicles require Nylon 12 as a cooling pipe material for their fuel systems, battery cooling systems, and motor cooling systems.

[0004] However, nylon 12 contains amide bonds in its molecular chain. Coolants often contain large amounts of ethylene glycol, and these amide bonds are prone to hydrolysis and chain scission under the influence of hydroxyl groups. This leads to a decrease in the mechanical properties of nylon 12, increased water vapor permeability, and affects the service life of the cooling pipes, as well as the overall vehicle safety and environmental performance. Currently, commercially available plastic cooling system pipes are mainly single-layer nylon or three-layer pipes with a polypropylene inner layer, a nylon 12 outer layer, and an adhesive layer in between. Both of these solutions can achieve the current cooling system's transport function.

[0005] Chinese patent CN102582134A discloses a coolant conduit comprising the following layers: I. an outer layer made of a polyamide molding composition, and II. an inner layer containing polypropylene and at least 0.02% by weight of a heat stabilizer. The coolant conduit exhibits high heat aging resistance and high brittle fracture strength.

[0006] Chinese patent CN111601995A discloses a laminated tube with excellent low-temperature impact resistance, high-temperature compressive strength, flexibility, dimensional stability, and resistance to leaching of low molecular weight substances and ionic components.

[0007] Chinese patent CN207145786U discloses a coolant delivery pipe for an automotive battery pack, characterized in that the coolant delivery pipe for the automotive battery pack comprises, from the inside out, an inner layer, an adhesive layer, and an outer layer; wherein, the inner layer is a PPA, PPS, or Nylon 12 material layer; and the outer layer is a TPV material layer.

[0008] Chinese Patent CN101067467A discloses a tube comprising the following layers: an outer layer made of a molding material containing at least 40% by weight of polyamide and whose monomer units contain an average of at least 8 carbon atoms, and a layer made of polypropylene molding material, wherein a) the outer diameter of the tube is 6-20 mm, b) the wall thickness is 1.0-2.0 mm, and c) the thickness of the polypropylene layer is 25-75% of the wall thickness. The tube is used as a compressed air braking line, which can be manufactured inexpensively and has high burst strength and excellent low-temperature impact toughness.

[0009] The aforementioned patented cooling pipes are essentially three-layer structures: the inner layer is modified polypropylene (PP), the middle layer is a bonding resin whose main component is polypropylene grafted with maleic anhydride (PP-g-MAH), and the outer layer is modified polyamide 12 (nylon 12). However, polypropylene has poor low-temperature toughness, resulting in poor low-temperature performance. The cooling pipe is prone to low-temperature stress cracking, leading to a high risk of failure. Furthermore, an intermediate bonding layer is essential, but bonding layer technology is controlled by only a few foreign suppliers, making it a critical bottleneck material. The three-layer extrusion equipment also currently relies on imports, significantly limiting the large-scale application of this type of material in my country and greatly hindering the development of electric vehicles in the country. Summary of the Invention

[0010] To overcome the shortcomings of the prior art, the present invention provides a cooling pipe material with a double-layer structure and its preparation method. This type of cooling pipe and material has outstanding advantages such as resistance to hydrolysis, alcoholysis, water vapor permeation, low temperature impact, stress cracking, simple molding process, and low equipment investment.

[0011] To achieve the above technical effects, the present invention adopts the following technical solution:

[0012] A cooling pipe with a double-layer structure, the cooling pipe comprising a two-layer structure of layer A and layer B, wherein layer A is the outer layer, which is flexible modified nylon 12, and layer B is the inner layer, which is grafted modified polyolefin alloy.

[0013] Layer A comprises the following components, based on the total mass of Layer A:

[0014] Nylon 12 65-98wt%, preferably 78-95wt%;

[0015] Plasticizer 0-14wt%, preferably 0-12wt%;

[0016] Toughening agent 2-25wt%, preferably 3-20wt%;

[0017] Antioxidant 0-3wt%, preferably 0.1-2wt%;

[0018] Light stabilizer 0-3wt%, preferably 0-2wt%;

[0019] Lubricant 0-3wt%, preferably 0-2wt%;

[0020] Colorant 0-3wt%, preferably 0-2wt%;

[0021] Layer B comprises the following components, based on the total mass of Layer B:

[0022] Co-LLDPE-g-MAH 15-35wt%, preferably 20-30wt%;

[0023] PB-1 10-40wt%, preferably 20-30wt%;

[0024] VHMWPE 10-25wt%, preferably 15-20wt%;

[0025] UHMWPE 15-30wt%, preferably 20-25wt%;

[0026] Antioxidant 0-3wt%, preferably 0.1-2wt%;

[0027] Lubricant 0-3wt%, preferably 0-2wt%;

[0028] Colorant 0-3wt%, preferably 0-2wt%.

[0029] In this invention, the grafted modified polyolefin material exhibits excellent compatibility with nylon 12. By introducing polar groups, the adhesion between the polyolefin material and nylon 12 material is improved. The two materials are bonded through chemical bonds, eliminating the need for adhesive layer materials. Furthermore, a domestically produced, mature double-layer pipeline extruder is used instead of an imported triple-layer or higher extruder, which greatly reduces investment in production equipment and lowers the entry barrier to this field.

[0030] The double-layer cooling pipe produced by this invention has excellent low-temperature resistance. The PB-1 component in the inner layer has excellent low-temperature impact resistance, which is far superior to the low-temperature impact resistance of the PP material in the inner layer of common multi-layer pipes. The outer layer is made of plasticized and toughened nylon 12 material, which has high low-temperature impact resistance. Therefore, both the inner and outer layers have high low-temperature impact strength, and the risk of low-temperature stress cracking is low under low ambient temperature conditions.

[0031] The inner layer material contains ultra-high molecular weight polyethylene (UHMWPE). UHMWPE, with its extremely high molecular weight, possesses excellent resistance to solvent corrosion and alcoholysis. However, existing polypropylene inner layers are prone to microcracks under long-term contact with coolant media, leading to coolant reaching the polyamide outer layer through these microcracks and causing pipeline failure. This is because polypropylene contains a large number of tertiary carbon atoms, which are highly unstable and easily degrade under free radical attack, resulting in a significant decrease in molecular weight and the formation of microcracks. In contrast, polyethylene contains very few tertiary carbon atoms. When two polyethylene molecular free radicals collide, molecular free radical coupling terminates, forming a network cross-linked structure. This further increases the already high molecular weight of UHMWPE, thus suppressing the formation of microcracks.

[0032] This invention optimizes the content of polar functional groups, combining the properties of both inner and outer layer materials while avoiding hydrolysis caused by excessive polar functional group content, thus enabling the material to maintain high performance under long-term coolant resistance.

[0033] After Co-LLDPE-g-MAH is melt-extruded with PB-1, VHMWPE, and UHMWPE, localized chain free radical cross-linking reactions occur, forming a micro-crosslinked structure. This structure effectively inhibits molecular chain degradation and avoids the formation of microcracks, thereby further reducing the risk of coolant corrosion to the entire pipeline. The high-molecular-weight grafted modified polyolefin alloy material with a micro-crosslinked structure as the inner layer effectively prevents coolant from contacting and corroding the outer flexible modified nylon 12 material, effectively avoiding hydrolysis and alcoholysis reactions of the nylon material, thus extending the service life of the cooling pipe.

[0034] In this invention, the relative viscosity of the nylon 12 is 1.4-2.8, preferably 1.5-2.3.

[0035] In this invention, the plasticizer in layer A is p-hydroxybenzoic acid ester and / or aryl sulfonamide, preferably one or more of p-benzenesulfonamide, N-butylbenzenesulfonamide, methyl p-hydroxybenzoate, N-methylbenzenesulfonamide, ethyl p-hydroxybenzoate, octyl p-hydroxybenzoate, p-isohexadecyl p-hydroxybenzoate, toluenesulfonic acid-n-octylamide, benzenesulfonic acid-n-butylamide, and benzenesulfonic acid-2-ethylhexylamide, more preferably one or more of N-butylbenzenesulfonamide, methyl p-hydroxybenzoate, and octyl p-hydroxybenzoate.

[0036] In this invention, the toughening agent in layer A is a copolymer of polyamide elastomer and / or polar monomer and polymer elastomer; wherein, the polyamide elastomer is an elastomer prepared by transesterification and polycondensation reaction of lactam, dicarboxylic acid and polyether polyol as raw materials, and its Shore hardness is preferably 25D-72D; the polar monomer is at least one of maleic anhydride and its derivatives, acrylate and its derivatives and glycidyl methacrylate; the polymer elastomer is one or more of ethylene-α-olefin copolymer (POE), ethylene-propylene copolymer (EPR), ethylene-propylene-nonconjugated diene copolymer (EPDM), styrene-butadiene copolymer (SBS), polyethylene-polystyrene-polypropylene terpolymer, polyethylene-polypropylene-polybutene terpolymer, styrene-acrylonitrile copolymer, ethylene-acrylate copolymer, ethylene-acrylate copolymer-maleic anhydride, ethylene-acrylate copolymer-glycidyl methacrylate, such as Pebax 2533, GR216, N416, N493, A560, 4170, and Royaltuf. Models include 527, AX8900, PTW, SOG-03, CMG-5805L, VA1801, and MH-5020C.

[0037] In this invention, the antioxidant comprises one or more of the following: copper salt antioxidants, phosphate antioxidants, hindered phenolic antioxidants, hindered amine antioxidants, phosphite antioxidants, thioester antioxidants, and polymeric antioxidants, preferably copper salt antioxidants, such as H320, H324, H1607, H3336, H3376, H3386, AO-K, KL-36, S5050, etc.

[0038] In this invention, the light stabilizer in layer A includes one or more of ultraviolet absorbers, free radical scavengers, and light shielding agents, preferably one or more of UV312, UV329, UV234, UV360, 770, 944, 622, and S-EED.

[0039] In this invention, the lubricant in layer A comprises one or more of the following: polyethylene wax, low molecular weight ester, metal soap, stearic acid complex ester, amide wax, montan wax, and low viscosity bisphenol A epoxy resin.

[0040] In this invention, the colorant in layer A includes one or more of pigments, dyes, carbon black, and masterbatches.

[0041] In this invention, the Co-LLDPE-g-MAH in layer B is a graft copolymer formed by the free radical reaction of copolymerized linear low-density polyethylene (Co-LLDPE) and maleic anhydride (MAH) under the action of an initiator; preferably, the MAH grafting rate is 0.1-5 wt%, more preferably 0.2-4.5 wt%, and more preferably 0.5-4 wt%, based on the total mass of the graft copolymer.

[0042] In this invention, PB-1 in layer B is polybutene-1 with a number average molecular weight of 100,000 to 800,000, preferably 200,000 to 500,000.

[0043] In this invention, the VHMWPE in the B layer is polyethylene with a number average molecular weight of 300,000 to 1,000,000, preferably 400,000 to 600,000.

[0044] In this invention, the UHMWPE in the B layer is polyethylene with a number average molecular weight of 1 million to 15 million, preferably 2 million to 5 million.

[0045] In this invention, the antioxidant in layer B includes one or more of hindered phenolic antioxidants, hindered amine antioxidants, phosphite antioxidants, thioester antioxidants, and polymeric antioxidants, preferably hindered phenolic antioxidants and / or phosphite antioxidants, such as 1010, 1076, 168, 686, etc.

[0046] In this invention, the lubricant in layer B comprises one or more of the following: polyethylene wax, low molecular weight ester, metal soap, stearic acid complex ester, amide wax, montan wax, and low viscosity bisphenol A epoxy resin.

[0047] Another object of the present invention is to provide an application of a cooling pipe material having a double-layer structure.

[0048] One application of the above-mentioned cooling pipe material with a double-layer structure, wherein the material is used in the thermal management system of an electric vehicle.

[0049] The materials of the cooling pipe A layer and B layer are obtained by co-extrusion using a multi-layer pipe extruder. All molding processes and parameters known to those skilled in the art can be used as the molding method of this invention.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] (1) Graft-modified polyolefin materials have excellent compatibility with nylon 12. By introducing polar groups, the adhesion between polyolefin materials and nylon 12 materials is improved. The two materials are bonded through chemical bonds, eliminating the need for adhesive layer materials. Furthermore, a domestically produced double-layer pipeline extruder with mature technology is used instead of an imported triple-layer or higher extruder, which greatly reduces the investment in production equipment and the entry threshold in this field.

[0052] (2) The double-layer cooling pipe produced by this invention has good low-temperature resistance and high resistance to low-temperature impact. Therefore, both the inner and outer layers have high low-temperature impact strength, and the risk of low-temperature stress cracking is low when the ambient temperature is low.

[0053] (3) The inner layer material contains ultra-high molecular weight polyethylene (UHMWPE). UHMWPE has excellent resistance to solvent corrosion and alcoholysis due to its extremely high molecular weight. However, the polypropylene inner layer of the existing technology is prone to microcracks under long-term contact with coolant medium. As a result, the coolant reaches the polyamide outer layer through the microcracks, which leads to pipeline failure.

[0054] (4) By optimizing the content of polar functional groups, the material can have both the properties of inner and outer layers, while avoiding hydrolysis caused by excessive polar functional group content, thus achieving high performance of the material under long-term coolant resistance.

[0055] (5) After Co-LLDPE-g-MAH is melt-extruded with PB-1, VHMWPE and UHMWPE, a local chain free radical cross-linking reaction occurs, forming a micro-cross-linked structure, which effectively avoids the hydrolysis and alcoholysis reaction of nylon materials, thereby extending the service life of the cooling pipe. Detailed Implementation

[0056] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the content of the present invention includes, but is not limited to, these embodiments.

[0057] Weigh the raw materials of the flexible modified nylon 12 according to the components and proportions (parts by weight) in Tables 1 and 2, mix them in a high-speed mixer for 5 minutes, mix the raw materials evenly, and extrude the blended material through a twin-screw extruder to obtain the modified polyolefin material. The twin-screw extruder has a screw diameter of 28 mm, an extrusion screw length-to-diameter ratio of 40, and an extrusion speed of 600 rpm / min.

[0058] 41E762, MAH, and DCP were added to a reactive twin-screw extruder in a mass ratio of 100:4:0.3. The barrel temperature was set to 80℃, 120℃, 180℃, 180℃, 170℃, 160℃, 160℃, 150℃, 150℃, and 160℃. The mixture was melt-blended, extruded, and granulated to obtain Co-LLDPE-g-MAH(A).

[0059] 528, MAH, and DCP were added to a reactive twin-screw extruder at a mass ratio of 100:4:0.3. The barrel temperatures were 80℃, 120℃, 180℃, 180℃, 170℃, 160℃, 160℃, 150℃, 150℃, and 160℃. The mixture was then melt-blended, extruded, and granulated to obtain Co-LLDPE-g-MAH(B).

[0060] 41E762, MAH, and DCP were added to a reactive twin-screw extruder at a mass ratio of 100:7:0.3. The barrel temperatures were 80℃, 120℃, 180℃, 180℃, 170℃, 160℃, 160℃, 150℃, 150℃, and 160℃. The mixture was then melt-blended, extruded, and granulated to obtain Co-LLDPE-g-MAH(C).

[0061] Weigh the raw materials according to the components and proportions (parts by weight) in Tables 1 and 2 for the grafted modified polyolefin alloy, mix them in a high-speed mixer for 5 minutes to ensure uniform mixing, and then extrude and granulate the mixture through a twin-screw extruder to obtain the grafted modified polyolefin alloy material. The twin-screw extruder has a screw diameter of 35 mm, a length-to-diameter ratio of 58, and an extrusion speed of 800 rpm / min.

[0062] Table 1

[0063]

[0064]

[0065] Table 2

[0066]

[0067] A double-layer pipeline was formed by using flexible modified nylon 12 as the outer layer and grafted modified polyolefin alloy as the inner layer through a multi-layer co-extrusion extruder (a single-screw extruder from Mailefer AG, Switzerland, was selected here; the outer layer extruder parameters were set as follows: temperature 235℃-240℃-240℃-240℃-240℃-240℃-240℃, screw speed 20-55 rpm; the inner layer extruder parameters were set as follows: temperature 165℃-180℃-190℃-190℃-180℃-180℃-180℃-180℃, screw speed 20-55 rpm). The parameters of each layer are shown in Table 3.

[0068] Table 3

[0069]

[0070] *Ten sample tubes were randomly selected for the low-temperature impact test. 1 / 10 represents 10 tubes, with 1 tube failing. The test passed if ≤1 tube failed.

[0071] **Comparative Example 1 is a commercially available 8×1mm size.** The MLT8000 series features a three-layer cooling tube with Nylon 12 as the outer layer, PP-g-MAH as the middle layer, and modified PP as the inner layer.

[0072] Comparative Examples 1 and 2 use B4 and B5 as inner layers, respectively. B4 and B5 are not the solutions of this invention. B4 uses 5000S HDPE, and B5 uses 3003 PP. The comparison shows that the performance of the inner layer is that of an alloy material. Comparative Example 3 is a comparison of commercially available 3-layer solutions. Comparative Example 4 is a comparison illustrating the control of the content of grafted components.

[0073] As can be seen from the test results in Table 3, a cooling pipe material with a double-layer structure can be obtained through the above formulation and preparation method. The resin components, plasticizers, toughening agents, antioxidants, etc. will all have different degrees of influence on the product performance.

[0074] Comparisons of Examples 1, 2, 3, and 4 show that the larger the thickness ratio of layer A to layer B, the higher the burst pressure strength, tensile strength, elongation at break, interlayer adhesion, and low-temperature impact strength of the double-layer structure cooling pipe. However, the tensile strength retention rate is lower after 100℃ / 1000h of resistance to coolant (ethylene glycol: water = 50:50).

[0075] The comparison of Examples 1 and 6 shows that by adjusting the material formulations of layer A and layer B, higher burst pressure strength, tensile strength, elongation at break, interlaminar adhesion, low-temperature impact strength, and tensile strength retention rate after 100℃ / 1000h in coolant (ethylene glycol: water = 50:50) can be obtained.

[0076] The comparison of Examples 2, 5, and 7 with Comparative Examples 1 and 2 shows that the cooling pipe material with a double-layer structure, using flexible modified nylon 12 as the outer layer and grafted modified polyolefin alloy as the inner layer, exhibits higher burst pressure strength, tensile strength, elongation at break, interlayer adhesion, low-temperature impact strength, and tensile strength retention rate after 100℃ / 1000h under cooling liquid (ethylene glycol:water = 50:50). The interlayer adhesion data strongly demonstrates that the grafted modified polyolefin alloy provides effective adhesion to the flexible modified nylon 12, sufficient to eliminate the need for an adhesive layer.

[0077] The comparison of Examples 2, 5, 7 and Comparative Example 3 shows that the cooling pipe material with a double-layer structure, using flexible modified nylon 12 as the outer layer and grafted modified polyolefin alloy as the inner layer, has higher burst pressure strength, tensile strength, elongation at break, interlayer adhesion, low-temperature impact strength, and tensile strength retention rate after 100℃ / 1000h under the condition of coolant (ethylene glycol: water = 50:50).

[0078] A comparison of Example 7 and Comparative Example 4 shows that an excessively high grafting rate of polar functional groups in the inner polyolefin material is detrimental to the material's long-term coolant resistance performance, and the tensile strength retention rate after 100℃ / 1000h of coolant (ethylene glycol: water = 50:50) resistance is significantly lower.

[0079] It should be noted that the above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cooling tube having a double-layer structure, characterized by comprising: The cooling tube comprises a two-layer structure of A and B layers, wherein the A layer is an outer layer and is a flexible modified nylon 12, and the B layer is an inner layer and is a graft modified polyolefin alloy; The A layer comprises the following components, based on the total mass of the A layer: Nylon 12 65-98 wt%; Plasticizer 0-14 wt%; Toughening agent 2-25 wt%; Antioxidant 0-3 wt%; Light stabilizer 0-3 wt%; Lubricant 0-3 wt%; Colorant 0-3 wt%; The B layer comprises the following components, based on the total mass of the B layer: Co-LLDPE-g-MAH 15-40 wt%; PB-1 10-40 wt%; VHMWPE 10-25 wt%; UHMWPE 15-30 wt%; Antioxidant 0-3 wt%; Lubricant 0-3 wt%; Colorant 0-3 wt%.

2. The cooling tube of claim 1, wherein The A layer comprises the following components, based on the total mass of the A layer: Nylon 12 78-95 wt%; Plasticizer 0-12 wt%; Toughening agent 3-20 wt%; Antioxidant 0.1-2 wt%; Light stabilizer 0-2 wt%; Lubricant 0-2 wt%; Colorant 0-2 wt%; The B layer comprises the following components, based on the total mass of the B layer: Co-LLDPE-g-MAH 20-38 wt%; PB-1 20-30 wt%; VHMWPE 15-20 wt%; UHMWPE 20-25 wt%; Antioxidant 0.1-2 wt%; Lubricant 0-2 wt%; Colorant 0-2 wt%.

3. The cooling tube of claim 1, wherein The relative viscosity of the nylon 12 is 1.4-2.

8.

4. The cooling tube of claim 3, wherein The relative viscosity of the nylon 12 is 1.5-2.

3.

5. The cooling tube according to claim 1 or 2, characterized in that The plasticizer in the A layer is p-hydroxybenzoic acid ester and / or aryl sulfonic acid amide.

6. The cooling tube of claim 5, wherein The plasticizer in the A layer is one or more of P-benzenesulfonamide, N-butylbenzenesulfonamide, methyl p-hydroxybenzoate, N-methylbenzenesulfonamide, ethyl hydroxybenzoate, octyl p-hydroxybenzoate, p-hydroxybenzoic acid-iso-hexadecyl ester, toluenesulfonic acid-n-octylamide, benzene sulfonic acid-2-ethylhexylamide.

7. The cooling tube of claim 6, wherein The plasticizer in the A layer is one or more of N-butylbenzenesulfonamide, methyl p-hydroxybenzoate, octyl p-hydroxybenzoate.

8. The cooling tube of claim 1, wherein The toughening agent in the A layer is a polyamide elastomer and / or a copolymer of a polar monomer and a polymer elastomer; wherein the polyamide elastomer is an elastomer made by ester exchange and polycondensation reaction with a lactam, a dicarboxylic acid and a polyether polyol as raw materials; the polar monomer is at least one of maleic anhydride and its derivatives, acrylate and its derivatives, and glycidyl methacrylate; and the polymer elastomer is one or more of ethylene-alpha olefin copolymer (POE), ethylene-propylene copolymer (EPR), ethylene-propylene-non-conjugated diene copolymer (EPDM), styrene-butadiene copolymer (SBS), polyethylene-polyphenylethylene-polypropylene terpolymer, polyethylene-polypropylene-polybutene terpolymer, styrene-acrylonitrile copolymer, ethylene-acrylate copolymer, ethylene-acrylate copolymer-maleic anhydride, and ethylene-acrylate copolymer-glycidyl methacrylate.

9. The cooling tube of claim 8, wherein, The polyamide elastomer in the A layer has a Shore hardness of 25D-72D.

10. The cooling tube of claim 1, wherein The antioxidant comprises one or more of copper salt antioxidant, phosphate antioxidant, hindered phenol antioxidant, hindered amine antioxidant, phosphite antioxidant, thioester antioxidant, and macromolecular antioxidant.

11. The cooling tube of claim 10, wherein The antioxidant is a copper salt antioxidant.

12. The cooling tube of claim 1, wherein The light stabilizer in the A layer comprises one or more of ultraviolet absorber, free radical scavenger, and light shielding agent.

13. The cooling tube of claim 12, wherein, The light stabilizer in the A layer comprises one or more of UV312, UV329, UV234, UV360, 770, 944, 622, and S-EED.

14. The cooling tube of claim 1, wherein The lubricant in the A layer comprises one or more of polyethylene wax, low molecular ester, metal soap, amide wax, montan wax, and low viscosity bisphenol A epoxy resin.

15. The cooling tube of claim 1, wherein, The colorant in the A layer comprises one or more of pigment, dye, and color master batch.

16. The cooling tube of claim 1, wherein The Co-LLDPE-g-MAH in the B layer is a graft copolymer of copolymerized linear low density polyethylene (Co-LLDPE) and maleic anhydride (MAH) generated by free radical reaction under the action of an initiator.

17. The cooling tube of claim 16, wherein, The MAH grafting rate is 0.1-5wt%, based on the total mass of the graft copolymer.

18. The cooling tube of claim 17, wherein, The MAH grafting rate is 0.2-4.5wt%, based on the total mass of the graft copolymer.

19. The cooling tube of claim 18, wherein, The MAH grafting rate is 0.5-4wt%, based on the total mass of the graft copolymer.

20. The cooling tube of claim 1, wherein, The PB-1 in the B layer is polybutene-1 with a number average molecular weight of 100-800 thousand.

21. The cooling tube of claim 20, wherein, The PB-1 in the B layer is polybutene-1 with a number average molecular weight of 200-500 thousand.

22. The cooling tube of claim 1, wherein, The VHMWPE in the B layer is polyethylene with a number average molecular weight of 30-100 million.

23. The cooling tube of claim 22, wherein, The VHMWPE in the B layer is polyethylene with a number average molecular weight of 40-60 million.

24. The cooling tube of claim 1, wherein, The UHMWPE in the B layer is polyethylene with a number average molecular weight of 100-1500 million.

25. The cooling tube of claim 24, wherein, The UHMWPE in the B layer is polyethylene with a number average molecular weight of 200-500 million.

26. The cooling tube of claim 1, wherein The antioxidant in the B layer comprises one or more of hindered phenol antioxidant, hindered amine antioxidant, phosphite antioxidant, thioester antioxidant, and macromolecular antioxidant.

27. The cooling tube of claim 26, wherein, The antioxidant in the B layer is a hindered phenolic antioxidant and / or a phosphite antioxidant.

28. The cooling tube of claim 1, wherein, The lubricant in the B layer includes one or more of polyethylene waxes, low molecular esters, metal soaps, stearic acid complex esters, amide waxes, montan waxes, and low viscosity bisphenol A epoxy resins.

29. Use of a cooling tube having a double-layer structure according to any one of claims 1 to 28, characterized in that The cooling pipe is used for thermal management systems of electric vehicles and energy storage power stations.

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