Tube for liquid refrigerant piping

Abstract

Provided is a tube for liquid refrigerant piping, the tube being capable of satisfactorily suppressing elution of ions and being capable of functioning well even in a low-temperature environment. A tube 1 for liquid refrigerant piping comprises a first layer 11 that is molded from polypropylene and partitions a flow path 10 for a refrigerant, and a second layer 12 that is molded from a dynamic crosslinking thermoplastic elastomer and is laminated on the outer-peripheral side of the first layer 11. The second layer 12 is of such wall thickness as to maintain the flexibility of the first layer 11 at a low temperature. The wall thickness of the first layer 11 is set to 10-40% of the total wall thickness of the first layer 11 and the second layer 12.

Description

Liquid refrigerant piping tube

[0001] The present invention relates to a tube for piping a liquid refrigerant.

[0002] Patent Document 1 discloses a multi-layer pipe having a tubular inner layer and a tubular outer layer covering the inner layer. The inner layer is molded, for example, from a cross-linkable silane-modified thermoplastic resin. Examples of cross-linkable silane-modified thermoplastic resins include silane-modified polypropylene. The outer layer is molded, for example, from a cross-linked thermoplastic rubber (TPV). The multi-layer pipe is used in a shoe sole as an assembly that is welded together. The outer layer enables good welding.

[0003] JP 2021-55844 A JP 2013-37972 A

[0004] Patent Document 2 discloses a hose used in the cooling system of a fuel cell. The hose defines a flow path for ion-exchanged water. The hose is molded from a dynamically crosslinked olefin-based thermoplastic elastomer (TPV). TPV maintains its flexibility in low-temperature environments, allowing the hose to function well even in cold climates. However, TPV contains rubber in its composition, which contains additives such as fillers and vulcanization accelerators, making it unable to sufficiently suppress the elution of ions.

[0005] If ion elution is not sufficiently suppressed in liquid refrigerant piping tubes, when coolant liquid is used as the liquid refrigerant, the coolant liquid contains additives that stabilize the water quality, and the additives are consumed by ion elution, resulting in increased coolant replacement cycles.In addition, when liquid refrigerant piping tubes are used in electric vehicles, which use high-voltage electricity, if the electrical resistance of the coolant is low, it will be connected to the body through the coolant or radiator, which can cause the problem of not being able to ensure insulation.

[0006] An object of the present invention is to provide a tube for piping a liquid refrigerant that can effectively suppress the elution of ions and that can function well even in a low-temperature environment.

[0007] A liquid refrigerant piping tube according to one embodiment of the present invention comprises a first layer molded from polypropylene and defining a flow path for the refrigerant, and a second layer molded from a dynamically crosslinked thermoplastic elastomer and laminated on the outer periphery of the first layer, wherein the second layer has a thickness that maintains the flexibility of the first layer at low temperatures, and the thickness of the first layer is set to be 10% or more and 40% or less of the total thickness of the first layer and the second layer.

[0008] According to the disclosed embodiments as described above, it is possible to provide a liquid refrigerant piping tube that can effectively suppress ion elution and function well even in low-temperature environments.

[0009] 1 is a schematic cross-sectional view of a liquid refrigerant piping tube according to an embodiment of the present invention.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] (Configuration of Tube 1 for Piping Liquid Refrigerant) Fig. 1 is a schematic cross-sectional view of a tube 1 for piping a liquid refrigerant according to this embodiment. As shown in Fig. 1, the tube 1 for piping a liquid refrigerant is a hollow tube formed by laminating multiple layers in the thickness direction from the inner periphery to the outer periphery, and includes a first layer 11 which is an inner layer and a second layer 12 which is an outer layer. The first layer 11 defines a flow path 10 for the liquid refrigerant.

[0012] The first layer 11 is formed from polypropylene. Unmodified polypropylene is used, but modified polypropylene may also be used. The modified polypropylene is not particularly limited, but may be, for example, modified with an acidic functional group, such as carboxylic acid or a derivative thereof, by introducing, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, anhydrides of these acids, or esters of these acids into polypropylene.

[0013] The second layer 12 is molded from a dynamically crosslinked thermoplastic elastomer (TPV). Dynamically crosslinked thermoplastic elastomers (TPV) are elastomers obtained by dynamically crosslinking a thermoplastic resin and rubber, and have a structure in which rubber particles are finely dispersed in a thermoplastic resin matrix. Dynamically crosslinked thermoplastic elastomers (TPV) are produced by dynamically crosslinking a mixture of a thermoplastic resin and rubber with the addition of a crosslinking agent. Examples of thermoplastic resins used to form dynamically crosslinked thermoplastic elastomers (TPV) include polypropylene (PP), polyamide (PA), polybutylene terephthalate (PBT), polylactic acid (PLA), and ethylene-vinyl alcohol copolymer resin (EVOH). Examples of rubbers used to form dynamically crosslinked thermoplastic elastomers (TPV) include ethylene propylene diene rubber (EPDM), butyl rubber (IIR), acrylic rubber (ACM), hydrogenated nitrile rubber (H-NBR), natural rubber (NR), epoxidized natural rubber (ENR), and silicone rubber (SR).

[0014] In the liquid refrigerant piping tube 1 of this embodiment, the second layer 12 has a thickness that maintains the flexibility of the first layer 11 at low temperatures. The thickness of the first layer 11 is set to be 10% to 40% of the total thickness of the first layer 11 and the second layer 12. By setting the thicknesses of the first layer 11 and the second layer 12 in this manner, the impact resistance of the liquid refrigerant piping tube 1 can be ensured satisfactorily.

[0015] The thickness of the second layer 12 is preferably set to 60% or more and 90% or less of the total thickness of the first layer 11 and the second layer 12. If the thickness of the second layer 12 is less than 60% of the total thickness of the first layer 11 and the second layer 12, the flexibility required for a tube for piping a liquid refrigerant cannot be ensured, and if it exceeds 90%, the pressure resistance required for a tube for piping a liquid refrigerant cannot be ensured, which is not preferable.

[0016] In the liquid refrigerant piping tube 1 of this embodiment, the thickness of the first layer 11 is set to, for example, 0.1 mm or more. The provision of the first layer 11 effectively prevents ions from eluting into the refrigerant flowing through the flow path 10, even at high temperatures. The thickness of the second layer 12 is set to, for example, 0.6 mm or more. Setting the thickness of the second layer 12 in this manner ensures good impact resistance of the first layer 11 even in low-temperature environments.

[0017] In the liquid refrigerant piping tube 1 of this embodiment, the hardness of the second layer 12 is set to, for example, a range of 84A to 55D in durometer hardness as defined in ISO 868. The liquid refrigerant piping tube 1 can ensure good flexibility in both low-temperature and high-temperature environments.

[0018] The liquid refrigerant piping tube 1 of this embodiment is preferably configured so that when pure water is sealed in the flow path 10 and maintained at 70°C for 500 hours, the change in the conductivity of the pure water is kept to 26.0 μS / cm or less. This effectively prevents ions from eluting into the refrigerant flowing through the flow path 10.

[0019] In the liquid refrigerant piping tube 1 of this embodiment, the first layer 11 and the second layer 12 can be simultaneously formed by, for example, extrusion molding. The interface between the first layer 11 and the second layer 12 may be heat-sealed. Alternatively, the first layer 11 may be formed by extrusion molding, and then the second layer 12 may be formed around the outer periphery of the first layer 11 by extrusion molding.

[0020] In the liquid refrigerant piping tube 1 of this embodiment, an adhesive layer or other layer may be sandwiched between the first layer 11 and the second layer 12.

[0021] In the liquid refrigerant piping tube 1 of this embodiment, the tensile modulus (JIS K 7162) of the polypropylene constituting the first layer 11 is 50 MPa or more and 2000 MPa or less, preferably 650 MPa or more and 1500 MPa or less, and the tensile modulus of the dynamically crosslinked thermoplastic elastomer constituting the second layer 12 is 200 MPa or more and 2300 MPa or less, preferably 300 MPa or more and 1300 MPa or less, thereby achieving both flexibility during installation and pressure resistance at high temperatures.

[0022] The shape of the liquid refrigerant piping tube 1 of this embodiment is not particularly limited, and may be, for example, a straight shape or a corrugated (bellows) shape.

[0023] (Operations and Effects) According to the liquid refrigerant piping tube 1 of this embodiment, it is possible to effectively suppress the elution of ions, and further, it is possible to function well even in a low-temperature environment.

[0024] (Examples) The ion elution and low-temperature impact resistance of the liquid refrigerant piping tube 1 according to this embodiment were examined. For the examination, a sample tube with an overall wall thickness of 1 mm was prepared. The sample tube consisted of a first layer molded from polypropylene (PP) and a second layer molded from a dynamically crosslinked thermoplastic elastomer (TPV) laminated on the outer periphery of the first layer. The dynamically crosslinked thermoplastic elastomer (TPV) was an elastomer obtained by dynamically crosslinking polypropylene (PP) and ethylene propylene diene rubber (EPDM). In the sample tube of Example 1, the thickness of the first layer was set to 0.1 mm, and the thickness of the second layer was set to 0.9 mm. In the sample tube of Example 2, the thickness of the first layer was set to 0.2 mm, and the thickness of the second layer was set to 0.8 mm. In the sample tube of Example 3, the thickness of the first layer was set to 0.3 mm, and the thickness of the second layer was set to 0.7 mm. In the sample tube of Example 4, the thickness of the first layer was set to 0.4 mm, and the thickness of the second layer was set to 0.6 mm.

[0025] Four comparative examples were prepared for the verification. The sample tube of Comparative Example 1 was molded from polyamide 11 (PA11). The sample tube of Comparative Example 2 was composed of a first layer molded from ethylene-tetrafluoroethylene copolymer resin (ETFE) and a second layer molded from polyamide 12 (PA12) laminated on the outer periphery of the first layer. The sample tube of Comparative Example 3 was molded from ethylene propylene diene rubber (EPDM). The sample tube of Comparative Example 4 was composed of a first layer molded from polypropylene (PP) and a second layer molded from dynamically crosslinked thermoplastic elastomer (TPV) laminated on the outer periphery of the first layer, with the thickness of the first layer set to 0.8 mm and the thickness of the second layer set to 0.2 mm.

[0026] (Ion Elution Test) The ion elution was examined for the sample tubes of Examples 1 to 4 and Comparative Examples 1 to 4. Pure water was sealed in each sample tube. Before sealing, the conductivity of the pure water was 0.8 μS / cm. The sample tubes were left in an environment at 70°C for 500 hours. After leaving the tubes at 70°C for 500 hours, the temperature was adjusted to 40°C, and the conductivity of the pure water was measured. In the sample tube of Example 1, the conductivity of the pure water increased to 16.5 μS / cm after 500 hours of leaving. The change in conductivity was 15.7 μS / cm. The sample tubes of Examples 2, 3, and 4 also had similar conductivities. It was confirmed that the increase in conductivity was suppressed in the sample tubes of Examples 1 to 4. In the sample tube of Comparative Example 1, the conductivity of the pure water increased to 66.3 μS / cm after leaving the tubes for 500 hours. The change in conductivity was 65.5 μS / cm. In the sample tube of Comparative Example 2, after being left standing for 500 hours, the conductivity of pure water increased to 26.2 μS / cm. The change in conductivity was 25.4 μS / cm. In the sample tube of Comparative Example 3, the conductivity of pure water after being left standing for 500 hours was 80.4 μS / cm. The change in conductivity was 79.6 μS / cm. The sample tube of Comparative Example 4 had the same conductivity as Examples 1 to 4. In the sample tubes of Comparative Example 1 and Comparative Example 3, the change in conductivity exceeded 26.0 μS / cm, confirming an increase in conductivity. In the sample tubes of Comparative Example 2 and Comparative Example 4, the change in conductivity was 26.0 μS / cm or less, confirming that the increase in conductivity was suppressed.

[0027] The test results for ion elution in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1. The construction of each sample tube is shown in Table 1 as follows: the sample tube in Example 1 is PP(0.1) / TPV, the sample tube in Example 2 is PP(0.2) / TPV, the sample tube in Example 3 is PP(0.3) / TPV, the sample tube in Example 4 is PP(0.4) / TPV, the sample tube in Comparative Example 1 is PA11, the sample tube in Comparative Example 2 is ETFE / PA12, the sample tube in Comparative Example 3 is EPDM, and the sample tube in Comparative Example 4 is PP(0.8) / TPV. In Table 1, sample tubes whose pure water conductivity change after standing at 70°C for 500 hours was 26.0 μS / cm or less were indicated with a "◯", and sample tubes whose conductivity change exceeded 26.0 μS / cm were indicated with a "X".

[0028] (Low-Temperature Impact Resistance Test) The impact resistance in a low-temperature environment (low-temperature impact resistance) of the sample tubes according to Examples 1 to 4 and Comparative Examples 1 to 4 was examined. Each sample tube was placed in a cryostat and placed in an environment of minus 30 degrees Celsius for at least four hours. Then, in accordance with JASO F409, a weight of 0.45 kg was dropped onto the sample tube from a height of 305 mm in the direction of gravity, and the sample tube was observed for cracks. Five individual tubes were tested for each sample tube.

[0029] In the sample tubes of Examples 1 to 4, no cracks were observed in any of the samples in a temperature environment of minus 30 degrees Celsius. In the sample tubes of Examples 1 to 4, good impact resistance was confirmed under conditions of minus 30 degrees Celsius.

[0030] In the sample tubes of Comparative Examples 1 to 3, no cracks were observed in any of the samples in a temperature environment of minus 30 degrees Celsius.

[0031] In the sample tube of Comparative Example 4, cracks were observed in at least some of the sample tubes at minus 30 degrees Celsius.

[0032] In Table 1, sample tubes in which no cracks were observed under each temperature environment in the above-mentioned low-temperature impact resistance test are indicated with an "O" and sample tubes in which cracks were observed are indicated with an "X".

[0033] (Weight) The weights per meter of the sample tubes according to Examples 1 to 4 and Comparative Examples 1 to 4 were compared. The weight per meter of the sample tube of Comparative Example 1 was used as the reference and was indicated as "◯" in Table 1. The weights per meter of the sample tubes of Examples 1 to 4 and Comparative Example 4 were smaller than that of the sample tube of Comparative Example 1, and were indicated as "◎" in Table 1. The weights per meter of the sample tubes of Comparative Examples 2 and 3 were larger than that of the sample tube of Comparative Example 1, and were indicated as "×" in Table 1.

[0034]

[0035] (Example of Application) The liquid refrigerant piping tube 1 of this embodiment can be applied to a refrigerant path connected to a cooling device that supplies refrigerant to a cell stack in a fuel cell installed in a fuel cell vehicle, for example. An insulating liquid, such as an insulating antifreeze, can be used as the refrigerant. Current leakage from the cell stack to the refrigerant can be prevented.

[0036] Now, imagine a situation where a fuel cell vehicle is running in a high-temperature environment (for example, an ambient temperature of 50°C). The fuel cell stack generates heat in response to its action. The cooling device cools the fuel cell in response to the circulation of the refrigerant. The cooling device works to maintain the fuel cell at approximately 80°C. Because polypropylene and dynamically crosslinked thermoplastic elastomer are heat-resistant, the liquid refrigerant piping tube 1 can function well even when the refrigerant reaches high temperatures. The presence of the first layer 11 effectively prevents ions from leaching out of the refrigerant flowing through the flow path 10, even at high temperatures. An increase in the conductivity of the refrigerant can be effectively suppressed.

[0037] Next, consider a scenario in which a fuel cell vehicle is running in a low-temperature environment (e.g., a temperature of minus 30 degrees Celsius). The fuel cell stack generates heat in response to its operation. The cooling device cools the fuel cell by circulating the refrigerant. The cooling device's operation allows the fuel cell to be maintained at approximately 80 degrees Celsius. Since the second layer 12 is laminated on the outer periphery of the first layer 11, the impact resistance of the first layer 11 can be ensured even in a low-temperature environment. If the second layer 12 is thinner than the specified thickness, the first layer 11 loses flexibility in a low-temperature environment. As a result, the impact resistance of the first layer 11 decreases. If the second layer 12 is thicker than the specified thickness, the weight of the liquid refrigerant piping tube 1 increases unnecessarily because the specific gravity of the dynamically crosslinked thermoplastic elastomer is greater than that of polypropylene.

[0038] The liquid refrigerant piping tube 1 of this embodiment can be applied to a refrigerant path connected to a cooling device of a server computer installed in a data center. An insulating liquid, such as an insulating antifreeze, can be used as the liquid refrigerant. Cooling by the cooling device can prevent short circuits in the wiring of the server computer.

[0039] Now, imagine a scenario in which a server computer is being transported or operated in a high-temperature environment (e.g., room temperature of 50°C). A cooling device cools the server computer by circulating a liquid refrigerant. The cooling device's function allows the GPU and CPU to be maintained at a predetermined temperature. Because polypropylene resin and dynamically crosslinked thermoplastic elastomer have heat resistance, they can function well even when the liquid refrigerant reaches high temperatures. Even at high temperatures, elution of ions into the liquid refrigerant flowing through the flow path 10 can be effectively suppressed, and an increase in the electrical conductivity of the liquid refrigerant can be effectively suppressed.

[0040] Next, consider a scenario in which a server computer is transported or operated in a low-temperature environment (e.g., room temperature of minus 30 degrees Celsius). A cooling device cools the server computer by circulating a liquid refrigerant. The cooling device maintains the GPU and CPU at a predetermined temperature. Since the second layer 12 is laminated on the outer periphery of the first layer 11, the impact resistance of the first layer 11 is maintained even in a low-temperature environment. If the second layer 12 is thinner than the predetermined thickness, the flexibility of the first layer 11 will be lost in a low-temperature environment. As a result, the impact resistance of the first layer 11 will be reduced. If the second layer 12 is thicker than the predetermined thickness, the weight of the liquid refrigerant piping tube 1 will be unnecessarily increased because the specific gravity of the dynamically crosslinked thermoplastic elastomer is greater than that of polypropylene. This allows server computers to be transported and data centers to be built even in cold regions.

[0041] The liquid refrigerant piping tube 1 of this embodiment can be applied to a refrigerant path connecting to an immersion tank provided for each chip, such as a GPU or CPU, in a server computer, or for each board, such as a graphics board including a GPU or a motherboard including a CPU. The liquid refrigerant piping tube 1 can function well even when the server computer is placed in a low-temperature environment, such as at an altitude of 10,000 m or outside the atmosphere.

[0042] REFERENCE SIGNS LIST 1 Liquid refrigerant piping tube 10 Flow path 11 First layer 12 Second layer

Claims

1. A tube for piping a liquid refrigerant, comprising: a first layer molded from polypropylene and defining a refrigerant flow path; and a second layer molded from a dynamically crosslinked thermoplastic elastomer and laminated on the outer periphery of the first layer, wherein the second layer has a thickness that maintains the flexibility of the first layer at low temperatures, and the thickness of the first layer is set to be 10% to 40% of the total thickness of the first and second layers.

2. The liquid refrigerant piping tube according to claim 1, wherein the thickness of the first layer is set to 0.1 mm or more.

3. The liquid refrigerant piping tube according to claim 1, wherein the thickness of the second layer is set to 0.6 mm or more.

4. The liquid refrigerant piping tube according to claim 1, wherein the hardness of the second layer is in the range of 84A to 55D in terms of durometer hardness as specified in ISO 868.

5. A liquid refrigerant piping tube according to any one of claims 1 to 4, characterized in that when pure water is sealed in the flow path and maintained at 70°C for 500 hours, the change in conductivity of the pure water is kept to 26.0 μS / cm or less.

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