Fluid transport tube and method of manufacturing same

Abstract

In a fluid transport tube (1) having a plurality of layers (2, 3) layered therein, an outer layer (3) of the plurality of layers (2, 3) is made of a thermoplastic elastomer foam body. An inner layer (2) of the plurality of layers (2, 3) is made of a thermoplastic elastomer or a thermoplastic resin. The outer layer (3) and the inner layer (2) are tightly attached to each other. The expansion ratio of the thermoplastic elastomer foam body is 2-5.5 fold. This allows an improvement in heat insulation and production stability of the fluid transport tube (1).

Description

Fluid transport tube CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2022-194106 filed on December 5, 2022, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a fluid transport tube for transporting a fluid.

[0003] Patent Document 1 describes a thermally insulated hose for transporting a fluid, which has improved thermal insulation. The thermally insulated hose in Patent Document 1 includes an outer layer (hereinafter referred to as a foam layer) having a foam material, a reinforcing layer, and an inner layer. The foam layer, the reinforcing layer, and the inner layer are integrated by vulcanization.

[0004] Japanese Patent Application Laid-Open No. 2005-188577

[0005] The heat-insulating hose of Patent Document 1 is formed by covering the inner layer with a reinforcing layer and a foam layer, and then molding the hose into a desired shape. The foam layer, reinforcing layer, and inner layer are then integrated by vulcanization.

[0006] However, it is difficult to simultaneously perform rubber vulcanization molding and foam molding under the same manufacturing conditions. For example, if rubber foam molding is prioritized, the vulcanization molding will be insufficient, resulting in insufficient strength. Conversely, if vulcanization molding is prioritized, the foaming agent may not foam sufficiently, or as foaming progresses, the foaming gas may escape from the foam layer, resulting in low foaming. This makes it difficult to stably manufacture thermally insulated hoses.

[0007] In view of the above, an object of the present disclosure is to provide a tube for transporting fluid that is excellent in heat insulation and manufacturing stability.

[0008] In order to achieve the above object, a fluid transport tube according to one embodiment of the present disclosure is a fluid transport tube having a plurality of laminated layers, wherein an outer layer of the plurality of layers is made of a thermoplastic elastomer foam, and an inner layer of the plurality of layers is made of a thermoplastic elastomer or a thermoplastic resin, the outer layer and the inner layer are in close contact with each other, and the expansion ratio of the thermoplastic elastomer foam is 2 times or more and 5.5 times or less.

[0009] This reduces the thermal conductivity of the outer layer and reduces the variation in thermal conductivity between individual fluid transport tubes during manufacturing, thereby improving the heat insulation and manufacturing stability of the fluid transport tube.

[0010] Furthermore, a fluid transport tube according to one aspect of the present disclosure is a fluid transport tube having a plurality of laminated layers, wherein an outer layer of the plurality of layers is made of a thermoplastic elastomer foam, an inner layer of the plurality of layers is made of a thermoplastic elastomer or a thermoplastic resin, a reinforcing layer is provided between the outer layer and the inner layer in close contact with each of the outer layer and the inner layer, and the expansion ratio of the thermoplastic elastomer foam is 2 times or more and 5.5 times or less.

[0011] This reduces the thermal conductivity of the outer layer and reduces the variation in thermal conductivity between individual fluid transport tubes during manufacturing, thereby improving the heat insulation and manufacturing stability of the fluid transport tube.

[0012] FIG. 1 is a cross-sectional view of a fluid transportation tube according to a first embodiment; FIG. 2 is an explanatory diagram for explaining a manufacturing method of a fluid transportation tube; FIG. 3 is a characteristic diagram showing the relationship between the expansion ratio and thermal conductivity of an olefin-based foamed tube; FIG. 4 is a characteristic diagram showing the relationship between the expansion ratio and variation in thermal conductivity of an olefin-based foamed tube; FIG. 5 is a characteristic diagram showing the relationship between the expansion ratio and thermal conductivity of a styrene-based foamed tube; FIG. 6 is a characteristic diagram showing the relationship between the expansion ratio and variation in thermal conductivity of a styrene-based foamed tube; FIG. 7 is a microscope photograph showing a cross-section of an outer layer in the first embodiment; FIG. 8 is a cross-sectional view of a fluid transportation tube according to a second embodiment; FIG. 9 is a cross-sectional view of a fluid transportation tube according to a third embodiment.

[0013] Hereinafter, several embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to matters described in the preceding embodiment will be assigned the same reference numerals, and duplicated explanations may be omitted. In each embodiment, when only a part of the configuration is described, other previously described embodiments may be applied to the other parts of the configuration. In addition to combinations of parts that are specifically specified as being combinable in each embodiment, it is also possible to partially combine embodiments even if not specified, as long as there is no particular problem with the combination.

[0014] First Embodiment A first embodiment will be described below with reference to the drawings. In this first embodiment, a fluid transport tube is used as a hot water transport tube for transporting hot water used as a heating heat source in an air conditioning system of an electric vehicle. Antifreeze liquid (LLC) or water can be used as the hot water. As the antifreeze liquid, for example, a glycol-based antifreeze liquid can be used.

[0015] As shown in Fig. 1, the fluid transport tube 1 of this embodiment is composed of multiple layers. The multiple layers are laminated in this order from the inside out: an inner layer 2 and an outer layer 3. An internal space is formed inside the inner layer 2, through which hot water flows.

[0016] The inner layer 2 is made of a thermoplastic elastomer or a thermoplastic resin, such as an olefin-based thermoplastic elastomer, an olefin-based resin, a polyamide-based resin, a polyphenylene sulfide (PPS) resin, or a mixture thereof.

[0017] The outer layer 3 is made of a thermoplastic elastomer foam. For example, an olefin-based thermoplastic elastomer foam, a styrene-based thermoplastic elastomer foam, or a urethane-based thermoplastic elastomer foam can be used as the outer layer 3. More specifically, a foam obtained by foaming an olefin-based thermoplastic elastomer, a styrene-based thermoplastic elastomer, or a urethane-based thermoplastic elastomer with thermally expandable microcapsules can be used as the outer layer 3. A skin layer (not shown) may be provided on the outside of the outer layer 3.

[0018] The inner layer 2 and the outer layer 3 are in close contact with each other. In this specification, "close contact" refers not only to a state in which the resin or elastomer portion of the outer layer 3 is in contact with the inner layer 2, but also includes the following state: that is, it also includes a state in which cells are uniformly formed in the foam of the outer layer 3 and the cells of the outer layer 3 are partially in contact with the inner layer 2.

[0019] Here, a thermoplastic elastomer is a polymeric material consisting of a mixture of hard segments made of a resin component and soft segments made of a resin component or rubber component. The hardness of the thermoplastic elastomer can be adjusted by changing the mixing ratio of the hard and soft segments.

[0020] For example, when the fluid transport tube 1 is applied to piping in the engine room of a vehicle, the mixing ratio of the soft segment of the thermoplastic elastomer is increased, thereby increasing the flexibility of the fluid transport tube 1 and improving the handleability.

[0021] Furthermore, when the fluid transport tube 1 is used as a pipe disposed under the floor of a vehicle, the mixing ratio of the hard segment of the thermoplastic elastomer is increased, thereby increasing the rigidity of the fluid transport tube 1 and reducing the number of fixing portions to the vehicle body.

[0022] The olefin-based thermoplastic elastomer is a mixture of PP (polypropylene) or PE (polyethylene) as a hard segment and EPDM (ethylene propylene diene rubber) or EPM (ethylene propylene rubber) as a soft segment.

[0023] The styrene-based thermoplastic elastomer uses PS (polystyrene) as the hard segment and PE (polyethylene), PB (polybutadiene), polyethylene-polybutylene, etc. as the soft segment. For example, SEBS (styrene-ethylene-butylene-styrene block copolymer) can be used as the styrene-based thermoplastic elastomer.

[0024] The fluid transport tube 1 of this embodiment is formed by coextrusion molding, in which a material for the inner layer 2 (hereinafter referred to as the inner layer material) and a material for the outer layer 3 (hereinafter referred to as the outer layer material) are simultaneously extruded. Specifically, the inner layer material and the outer layer material are coextruded through a die provided at the tip of a coextruder, thereby forming the fluid transport tube 1, which is a laminate of the inner layer 2 and the outer layer 3.

[0025] According to this manufacturing method, the inner layer 2 and the outer layer 3 can be molded simultaneously, which improves the adhesive strength between the inner layer 2 and the outer layer 3. Furthermore, the manufacturing time of the fluid transport tube 1 can be shortened.

[0026] The fluid transportation tube 1 of this embodiment may be formed by a method other than co-extrusion, for example, by single-layer extrusion molding in a batch process or a continuous process as described below.

[0027] In the single-layer extrusion molding in the batch process, first, the inner layer material is charged into the hopper of the extruder, and the inner layer 2 is extruded singly into a tubular shape to form the inner layer tube. Subsequently, the outer layer material is charged into the hopper, and the inner layer tube is covered with the outer layer 3 while being drawn off. In this way, the fluid transport tube 1, which is a laminate of the inner layer 2 and the outer layer 3, is formed.

[0028] According to this production method, the inner layer 2 and the outer layer 3 can be produced under optional temperature and flow rate conditions, making it easy to adjust the optimum production conditions for the dimensions and degree of expansion of the fluid transport tube 1. Furthermore, because the inner layer 2 and the outer layer 3 are produced sequentially using a single extruder, there is no need to increase the number of extruders, and production can be carried out on a minimum scale.

[0029] Furthermore, in single-layer extrusion molding using a continuous process, two extruders are prepared, and the fluid transport tube 1 is produced using a continuous process. Specifically, as shown in Fig. 2, the inner layer material is first charged into a hopper (not shown) of a first extruder 51 and extruded through a first cylinder 52 to form the inner layer 2, and the inner layer 2 is passed through a first water tank to stabilize its dimensions. Subsequently, the inner layer 2 is coated with the outer layer material using a second cylinder 55 of a second extruder 54, and the inner layer 2 and outer layer 3 are then cooled again in a second water tank 56. This forms the fluid transport tube 1, which is a laminate of the inner layer 2 and the outer layer 3.

[0030] In this manufacturing method, two extruders are used, which eliminates the need to change extrusion materials during manufacturing, and enables manufacturing in a short time compared to a batch process. Furthermore, compared to co-extrusion molding, which cools the inner layer 2 via the outer layer 3, the inner layer 2 and the outer layer 3 can be cooled in a short time.

[0031] Here, the present inventors have investigated the expansion ratio of the outer layer 3 of the fluid transportation tube 1. First, the inventors have investigated the expansion ratio of the outer layer 3 when an olefin-based thermoplastic elastomer foam is used as the outer layer 3.

[0032] First, the inventors extruded several types of olefin-based foamed tubes with different expansion ratios and measured the thermal conductivity of each of the obtained olefin-based foamed tubes. Specifically, six types of mixtures were prepared by mixing LE-3170N (manufactured by Riken Technos Corporation) as an olefin-based thermoplastic elastomer with P501E1 (manufactured by Sekisui Chemical Co., Ltd.) as thermally expandable microcapsules in amounts of 3, 5, 8, 10, 15, and 25 parts by weight.

[0033] These six types of mixtures were extruded using a general-purpose resin extruder manufactured by IKG Corporation to produce olefin-based foamed tubes with an inner diameter of φ16 and an outer diameter of φ20. The extrusion molding conditions were as follows: cylinder and die temperatures of the general-purpose resin extruder: 170 to 220°C, and an extrusion flow rate: 0.01 to 0.04 kg / s. The produced olefin-based foamed tubes were measured with a hydrometer to find that their expansion ratios were 1.4 to 5.7 times.

[0034] Next, the thermal conductivity of the olefin foam tube was measured. First, the olefin foam tube was covered on a φ17 aluminum pipe, and a heat flow sensor (model D0001TC) manufactured by Denso Corporation and polyimide tape were attached to the olefin foam tube. Then, 80°C hot water was circulated through the aluminum pipe at a flow rate of 5 L / min using a chiller manufactured by Apiste Corporation, and the heat flow (unit: W) of the olefin foam tube was measured to calculate the thermal conductivity. The results are shown in Figure 3.

[0035] The horizontal axis of the graph in Fig. 3 represents the expansion ratio of the olefin-based foamed tube. The vertical axis of the graph in Fig. 3 represents the thermal conductivity index. The thermal conductivity index is expressed as an index, with 1 representing the state in which the tube does not contain a foaming agent, i.e., the expansion ratio is 1.

[0036] When the calculated values ​​of the thermal conductivity of the olefin foamed tube are organized for each expansion ratio, data showing multiple thermal conductivities are present for each expansion ratio. That is, the thermal conductivity varies with the expansion ratio. The thermal conductivity on the vertical axis of the graph in Fig. 3 represents the average value of multiple calculated values.

[0037] As is clear from Fig. 3, when the expansion ratio of the olefin foamed tube is between 1 and 2, the thermal conductivity decreases rapidly as the expansion ratio increases. When the expansion ratio of the olefin foamed tube is 2 or more, the degree of decrease in thermal conductivity with increasing expansion ratio decreases. Therefore, when the expansion ratio of the olefin foamed tube is 2 or more, low thermal conductivity, i.e., high thermal insulation, can be ensured.

[0038] Next, the variation in thermal conductivity with respect to the expansion ratio of the olefin-based foamed tube was calculated, and the results are shown in FIG.

[0039] The horizontal axis of the graph in Fig. 4 represents the expansion ratio of the olefin-based foamed tube. The vertical axis of the graph in Fig. 4 represents the coefficient of variation in thermal conductivity. The coefficient of variation in thermal conductivity is expressed as an index, with the coefficient of variation in thermal conductivity when the tube does not contain a foaming agent, i.e., when the expansion ratio is 1 (hereinafter also referred to as the initial state), being set to 1. The coefficient of variation in thermal conductivity refers to the difference between the maximum and minimum values ​​of thermal conductivity. For example, if the coefficient of variation in thermal conductivity at a certain expansion ratio is half the coefficient of variation in thermal conductivity in the initial state, the coefficient of variation in thermal conductivity is 0.5.

[0040] 4, as the expansion ratio of the olefin-based foamed tube increases, the variation in thermal conductivity decreases. This is believed to be due to the following reasons.

[0041] In other words, thermoplastic elastomers composed of multiple components with different thermal conductivities have a large variation in thermal conductivity due to the heterogeneity of the material. As the expansion ratio increases, the components of the thermoplastic elastomer are replaced by hydrocarbon gas encapsulated in the thermally expandable microcapsules, hydrocarbon gas released when the thermally expandable microcapsules rupture during production, air resulting from defects during production, or a mixture of hydrocarbon gas and air. Because hydrocarbon gas and the mixed gas have a small variation in thermal conductivity, it is thought that the variation in the thermal conductivity of the foamed tube decreases as the expansion ratio increases.

[0042] Furthermore, when the expansion ratio is small, not only does the thermal conductivity vary due to the inhomogeneity of the thermoplastic elastomer material, but the thermally expandable microcapsules tend to be mixed unevenly. If the thermally expandable microcapsules are expanded in this state, the distribution of bubbles in the expansion tube tends to become uneven, making it difficult to reduce the range of variation in thermal conductivity.

[0043] Furthermore, as is clear from Fig. 4, when the expansion ratio of the olefin foamed tube is between 1 and 3 times, the variation in thermal conductivity decreases rapidly as the expansion ratio increases. When the expansion ratio of the olefin foamed tube is greater than 3 times, the variation in thermal conductivity remains almost unchanged even when the expansion ratio is increased. Therefore, if the expansion ratio of the olefin foamed tube is greater than 3 times, a state in which the variation in thermal conductivity is small can be ensured, thereby ensuring the manufacturing stability of the foamed tube.

[0044] Next, the crack resistance of the olefin foamed tube when bent was evaluated. Specifically, the olefin foamed tube was manually placed around an R120 jig at a 90° angle, and the occurrence of cracks and fissures in the foamed tube was visually confirmed. As a result, no cracks occurred when the expansion ratio was 5.5 times or less, but cracks occurred when the expansion ratio was 5.7 times. Therefore, by setting the expansion ratio of the olefin foamed tube to 5.5 times or less, the occurrence of cracks can be suppressed.

[0045] Next, the inventors of the present invention investigated the expansion ratio of the outer layer 3 when a styrene-based thermoplastic elastomer foam was used as the outer layer 3 .

[0046] First, the present inventors extruded several types of styrene foam tubes with different expansion ratios and measured the thermal conductivity of each of the obtained styrene foam tubes. Specifically, styrene foam tubes were produced under the same conditions as those for the above-mentioned olefin foam tube, except that T-A80NT manufactured by Aron Kasei Co., Ltd. was used as the styrene thermoplastic elastomer instead of LE-3170N. When the produced styrene foam tubes were measured with a hydrometer, the expansion ratios were found to be 1.2 to 4.8 times.

[0047] Next, the thermal conductivity of the styrene foamed tube was measured under the same conditions as those for the olefin foamed tube. The results are shown in FIG.

[0048] As is clear from Fig. 5, when the expansion ratio of the styrene foam tube is between 1 and 2, the thermal conductivity decreases rapidly as the expansion ratio increases. When the expansion ratio of the styrene foam tube is 2 or more, the degree of decrease in thermal conductivity with increasing expansion ratio decreases. Therefore, when the expansion ratio of the styrene foam tube is 2 or more, low thermal conductivity, i.e., high thermal insulation, can be ensured.

[0049] Next, the variation in thermal conductivity with respect to the expansion ratio of the styrene foam tube was calculated, and the results are shown in FIG.

[0050] As is clear from Fig. 6, the styrene foamed tube also showed the same tendency as the olefin foamed tube with respect to the variation in thermal conductivity with respect to the expansion ratio. Therefore, if the expansion ratio of the styrene foamed tube is set to be greater than 3 times, the variation in thermal conductivity can be kept small, thereby ensuring the production stability of the foamed tube.

[0051] Next, the crack resistance of the styrene foamed tube when bent was evaluated. The evaluation conditions were the same as those for evaluating the crack resistance of the olefin foamed tube when bent. As a result, no cracks occurred when the expansion ratio was 4.8 times or less. Therefore, by setting the expansion ratio of the styrene foamed tube to 4.8 times or less, the occurrence of cracks can be suppressed.

[0052] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0053] Example 1 An olefin-based thermoplastic elastomer, GA-1190N, manufactured by Riken Technos Corporation, was prepared as the inner layer material. An outer layer material was prepared by mixing 5 parts by weight of thermally expandable microcapsules, P501E1, manufactured by Sekisui Chemical Co., Ltd., with LE-3170N, an olefin-based thermoplastic elastomer, manufactured by Riken Technos Corporation.

[0054] Next, the inner layer material and the outer layer material were co-extruded using a co-extruder manufactured by IKG Corporation to produce a fluid transport tube 1 having an inner diameter of φ16 and an outer diameter of φ24. The extrusion conditions were set so that the inner layer 2 had an inner diameter of φ16 and an outer diameter of φ20, and the outer layer 3 had an inner diameter of φ20 and an outer diameter of φ24. The cylinder and die temperatures of the co-extruder were set to 170 to 220°C, and the extrusion flow rate was set to 0.01 to 0.04 kg / sec. When the outer layer 3 of the produced fluid transport tube 1 was measured with a hydrometer, the expansion ratio was found to be 2.1 times.

[0055] Example 2 The same material as in Example 1 was prepared as the inner layer material. The outer layer material was prepared by mixing 10 parts by weight of P501E1, a thermally expandable microcapsule manufactured by Sekisui Chemical Co., Ltd., with LE-3170N, an olefin-based thermoplastic elastomer manufactured by Riken Technos Corporation.

[0056] Next, the inner layer material and the outer layer material were co-extruded under the same conditions as in Example 1 to produce a fluid transport tube 1. When the outer layer 3 of the produced fluid transport tube 1 was measured with a hydrometer, the expansion ratio was found to be 3.2 times.

[0057] (Example 3) The same material as in Example 1 was prepared as the inner layer material. The outer layer material was prepared by mixing 8 parts by weight of P501E1, a thermally expandable microcapsule manufactured by Sekisui Chemical Co., Ltd. with T-A80NT, a styrene-based thermoplastic elastomer manufactured by Aron Kasei Co., Ltd.

[0058] Next, the inner layer material and the outer layer material were co-extruded under the same conditions as in Example 1 to produce a fluid transport tube 1. When the outer layer 3 of the produced fluid transport tube 1 was measured with a hydrometer, the expansion ratio was found to be 2 times.

[0059] Example 4 The same material as in Example 1 was prepared as the inner layer material. The outer layer material was prepared by mixing 15 parts by weight of P501E1, a thermally expandable microcapsule manufactured by Sekisui Chemical Co., Ltd. with T-A80NT, a styrene-based thermoplastic elastomer manufactured by Aron Kasei Co., Ltd.

[0060] Next, the inner layer material and the outer layer material were co-extruded under the same conditions as in Example 1 to produce a fluid transport tube 1. When the outer layer 3 of the produced fluid transport tube 1 was measured with a hydrometer, the expansion ratio was found to be 3 times.

[0061] (Comparative Example) As a comparative example, a heater hose was prepared in which both the inner and outer layers were made of ethylene propylene diene (EPDM) rubber. The heater hose had an inner diameter of φ16 and an outer diameter of φ24. In the heater hose, the inner layer had an inner diameter of φ16 and an outer diameter of φ20, and the outer layer had an inner diameter of φ20 and an outer diameter of φ24, and a reinforcing layer made of braided polyamide-based reinforcing yarn was present between the inner and outer layers.

[0062] (Flexibility Test) The fluid transport tubes of Examples 1 to 4 (hereinafter also simply referred to as "Tube 1") and the heater hose of the Comparative Example were each cut to a length of 300 mm. Both ends of the cut tube or hose were held and manually aligned at a 90° angle against an R120 jig. In this state, the tubes or hoses were visually inspected for any abnormalities such as kinks (i.e., bends), cracks, or breaks.

[0063] (Heat Dissipation Measurement) Tube 1 of Examples 1 to 4 and the heater hose of the Comparative Example were each covered on an aluminum pipe having an outer diameter of φ17, and a heat flow sensor (model D0001TC) manufactured by Denso Corporation and polyimide tape were attached to the aluminum pipe. Hot water at 80°C was then circulated through the aluminum pipe at a flow rate of 5 L / min using a chiller manufactured by Apiste Corporation, and the heat flow (unit: W) was measured to calculate the heat dissipation (unit: W / m).

[0064] (Pressure Test) The tubes 1 of Examples 1 to 4 and the heater hose of the Comparative Example were each inserted into an aluminum pipe having an outer diameter of 17 mm and fastened with a worm drive hose clip (model OX-SS) manufactured by Orbit Corporation. A pressure of 108 kPa was then applied using a testing machine. In this state, the tubes were visually inspected for cracks, breaks, or other abnormalities.

[0065] (High-Temperature Storage Test) Aluminum piping with sealed ends was inserted into each of the tubes 1 of Examples 1 to 4 and the heater hose of the comparative example, and then fastened with a worm drive hose clip (model OX-SS) manufactured by Orbit Corporation. Next, a mixture of Toyota Motor Corporation's Super Long Life Coolant (model 08889-01005) and purified water diluted 1:1 was sealed into the tube 1 and heater hose, and they were placed in a high-temperature testing machine at 100°C and left for 168 hours. After that, the tube 1 and heater hose were removed, and the tube 1 and heater hose were visually inspected for cracks, breaks, or other abnormalities. (Evaluation) The results of the above tests and measurements are shown in Table 1.

[0066] As shown in Table 1, no cracks, breaks, or other abnormalities were found in the flexibility test, pressure test, or high-temperature storage test for either the tube 1 of Examples 1 to 4 or the heater hose of the comparative example. The results of the heat dissipation measurement showed that the heat dissipation of the tube 1 of Examples 1 to 4 was lower than that of the heater hose of the comparative example. This revealed that the heat insulating properties of the tube 1 of Examples 1 to 4 were higher than that of the heater hose of the comparative example.

[0067] (Cross-Section Observation) Next, a cross-section of the outer layer 3 of the fluid transport tube 1 was observed. As in Example 1 above, an outer layer material was prepared by mixing LE-3170N, an olefin-based thermoplastic elastomer manufactured by Riken Technos Corporation, with P501E1, a thermally expandable microcapsule manufactured by Sekisui Chemical Co., Ltd. When the outer layer material was extrusion-molded, the expansion ratio of the outer layer 3 was 3.8 times. The particle diameter of the thermally expandable microcapsules before expansion was 22 to 42 μm (average 28 μm), and the particle diameter after expansion was 65 to 132 μm (average 92 μm).

[0068] The outer layer 3 thus produced was cut, and the cut surface was observed under a microscope. The resulting microscopic photograph is shown in Figure 7. As shown in Figure 7, it was confirmed that bubbles 30 resulting from the thermally expandable microcapsules were uniformly arranged in the outer layer 3.

[0069] As described above, in the fluid transport tube 1 of this embodiment, the expansion ratio of the thermoplastic elastomer foam in the outer layer 3 is set to 2 times or more and 5.5 times or less. This reduces the thermal conductivity of the outer layer 3 and reduces the variation in thermal conductivity between individual fluid transport tubes 1 during production. This makes it possible to improve the thermal insulation and manufacturing stability of the fluid transport tube 1.

[0070] Furthermore, by setting the expansion ratio of the thermoplastic elastomer foam of the outer layer 3 to be greater than 3 times and equal to or less than 5.5 times, it is possible to reduce the thermal conductivity of the outer layer 3 and more reliably reduce the variation in thermal conductivity between individual fluid transport tubes 1 during production. Therefore, it is possible to more reliably improve the heat insulation and manufacturing stability of the fluid transport tube 1.

[0071] In this embodiment, an olefin-based thermoplastic elastomer foam or a styrene-based thermoplastic elastomer is used for the outer layer 3. An olefin-based thermoplastic elastomer or an olefin-based thermoplastic resin is used for the inner layer 2.

[0072] Olefin-based thermoplastic elastomers, olefin-based resins, and styrene-based thermoplastic elastomers have excellent heat resistance, low-temperature stability, and weather resistance. Therefore, by using an olefin-based thermoplastic elastomer, olefin-based resin, or styrene-based thermoplastic elastomer for the inner layer 2 and the outer layer 3, the fluid transportation tube 1 can be suitably mounted on a vehicle. Furthermore, because olefin-based thermoplastic elastomers, olefin-based resins, and styrene-based thermoplastic elastomers are inexpensive materials, it is possible to reduce manufacturing costs.

[0073] In this embodiment, the inner layer 2 is made of a resin different from the thermoplastic elastomer contained in the outer layer 3. In this way, because the resin is harder than the thermoplastic elastomer, even if the inner layer 2 is made thin, it is possible to ensure heat resistance and pressure resistance against the fluid flowing inside. Furthermore, the outer layer 3 can be made thicker by the amount that the inner layer 2 is made thin. For this reason, it is possible to improve the thermal insulation properties even for a fluid transportation tube 1 with the same inner and outer diameters.

[0074] Furthermore, in the fluid transport tube 1 of this embodiment, thermally expandable microcapsules are contained in the outer layer 3. Thermally expandable microcapsules have a high expansion ratio and stable expandability, so that the outer layer 3 can be reliably expanded at a desired expansion ratio.

[0075] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to the drawings. This embodiment is different from the first embodiment in the configuration between the inner layer 2 and the outer layer 3.

[0076] 8, the fluid transport tube 1 of this embodiment is made of a hard resin or elastomer. In the fluid transport tube 1 of this embodiment, a reinforcing layer 4 is provided between the outer layer 3 and the inner layer 2. The reinforcing layer 4 is in close contact with both the outer layer 3 and the inner layer 2.

[0077] The same materials as those in the first embodiment can be used for the outer layer 3 and the inner layer 2. For the reinforcing layer 4, for example, an adhesive such as a polyamide resin, a polyphenylene sulfide resin, or a mixture thereof, or maleic acid-modified polypropylene can be used.

[0078] An adhesive such as maleic acid-modified polypropylene may be provided between the inner layer 2 and the reinforcing layer 4 and / or between the outer layer 3 and the reinforcing layer 4 (hereinafter referred to as interlayer), thereby improving the adhesive strength between the layers.

[0079] Other configurations of the fluid transport tube 1 are the same as those of the first embodiment. Therefore, the fluid transport tube 1 of this embodiment can also achieve the same effects as those of the first embodiment. That is, the fluid transport tube 1 of this embodiment can improve heat insulation and manufacturing stability.

[0080] Furthermore, in the fluid transport tube 1 of this embodiment, a reinforcing layer 4 is provided between the outer layer 3 and the inner layer 2. By providing the reinforcing layer 4, it is possible to improve the heat resistance and pressure resistance strength of the fluid transport tube 1, and also to suppress thermal deformation.

[0081] Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to the drawings. This embodiment is different from the second embodiment in the configurations of the inner layer 2 and the reinforcing layer 4.

[0082] As shown in Fig. 9, the fluid transport tube 1 of this embodiment is made of a highly flexible resin or elastomer. Specifically, the inner layer 2 is made of a highly flexible thermoplastic elastomer. For example, an olefin-based thermoplastic elastomer can be used as the inner layer 2. The outer layer 3 can be made of the same material as in the first embodiment.

[0083] The reinforcing layer 4 may be a known reinforcing layer in which reinforcing yarns are braided in a spiral or braid shape. Examples of reinforcing yarns that may be used include polyester, polyamide (nylon), polyvinyl alcohol (vinylon), rayon, aramid, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). These yarns may also be subjected to an adhesive treatment. Examples of adhesive treatments that may be used include resorcinol-formalin-rubber latex (RFL) treatment.

[0084] Other configurations of the fluid transport tube 1 are the same as those of the first embodiment. Therefore, the fluid transport tube 1 of this embodiment can also achieve the same effects as those of the first embodiment. That is, the fluid transport tube 1 of this embodiment can improve heat insulation and manufacturing stability.

[0085] Furthermore, in the fluid transport tube 1 of this embodiment, a highly flexible thermoplastic elastomer is used as the inner layer 2, and a reinforcing layer 4 is provided between the outer layer 3 and the inner layer 2. This makes it possible to improve flexibility with the inner layer 2, while ensuring heat resistance and pressure resistance by providing the reinforcing layer 4. Therefore, the fluid transport tube 1 can achieve both high flexibility and high heat resistance and pressure resistance.

[0086] The present disclosure is not limited to the above-described embodiments, and various modifications can be made as follows within the scope of the present disclosure.

[0087] (1) In the above-described embodiment, examples have been described in which the fluid transport tube according to the present disclosure is applied to a fluid transport tube 1 having two layers, that is, an inner layer 2 and an outer layer 3, or a fluid transport tube 1 having three layers, that is, an inner layer 2, an outer layer 3, and a reinforcing layer 4, but the present disclosure is not limited to this. The fluid transport tube according to the present disclosure may also be applied to a fluid transport tube having four or more layers.

[0088] (2) In the above-described embodiment, the fluid transport tube 1 is formed by extrusion molding, but the present invention is not limited to this. For example, the fluid transport tube 1 may be formed by injection molding.

[0089] In this case, the inner layer material is first filled into an inner layer mold in an injection molding machine and allowed to cool and solidify within the inner layer mold, after which the mold is opened and the inner layer 2 is removed. The inner layer 2 is then inserted into the core of the outer layer mold. An outer layer material containing a foaming agent (i.e., thermally expandable microcapsules) is then poured into a hopper and filled into the outer layer mold, and the inserted inner layer 2 is coated with the outer layer 3. When molding the outer layer 3, a short-shot method may be used in which the outer layer mold is filled with an amount of outer layer material that is less than the cavity volume, and the outer layer material is filled into the entire outer layer mold by foaming force (i.e., the force of expanding bubbles).

[0090] (3) In the above-described embodiment, an example was described in which the fluid transport tube according to the present disclosure was applied to a tube for transporting hot water in an electric vehicle. However, the application of the fluid transport tube is not limited to this.

[0091] For example, the fluid transport tube may be used as a coolant and hot water transport tube in a hybrid vehicle that obtains driving power from an electric motor and an internal combustion engine (i.e., an engine), or in a plug-in hybrid vehicle that can charge the battery with power supplied from an external power source when the vehicle is stopped.Furthermore, the fluid transport tube may be used as a coolant and hot water transport tube installed in the cooling circuit of the motor or battery of an electric vehicle.

[0092] (Other) The features of the fluid transportation tube disclosed in this specification are as follows. (Item 1) A fluid transportation tube having multiple layers (2, 3) laminated together, wherein an outer layer (3) of the multiple layers is made of a thermoplastic elastomer foam, and an inner layer (2) of the multiple layers is made of a thermoplastic elastomer or a thermoplastic resin, the outer layer and the inner layer are in close contact with each other, and the expansion ratio of the thermoplastic elastomer foam is 2 to 5.5 times. (Item 2) A fluid transportation tube having multiple layers (2 to 4) laminated together, wherein the outer layer (3) of the multiple layers is made of a thermoplastic elastomer foam, and the inner layer (2) of the multiple layers is made of a thermoplastic elastomer or a thermoplastic resin, and a reinforcing layer (4) is provided between the outer layer and the inner layer and is in close contact with each of the outer layer and the inner layer, and the expansion ratio of the thermoplastic elastomer foam is 2 to 5.5 times. (Item 3) The fluid transport tube according to item 1 or 2, wherein the expansion ratio of the thermoplastic elastomer foam is greater than 3 and less than or equal to 5.5. (Item 4) The fluid transport tube according to any one of items 1 to 3, wherein the outer layer is made of an olefin-based thermoplastic elastomer foam, and the inner layer is made of an olefin-based thermoplastic elastomer or an olefin-based thermoplastic resin. (Item 5) The fluid transport tube according to item 1 or 2, wherein the outer layer is made of a styrene-based thermoplastic elastomer foam, and the inner layer is made of an olefin-based thermoplastic elastomer or an olefin-based thermoplastic resin, and the expansion ratio of the styrene-based thermoplastic elastomer foam is greater than or equal to 2 and less than or equal to 4.8. (Item 6) The fluid transport tube according to any one of items 1 to 5, wherein the inner layer is made of a resin different from the thermoplastic elastomer contained in the outer layer. (Item 7) The fluid transport tube according to any one of items 1 to 6, wherein the outer layer contains thermally expandable microcapsules.

[0093] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A fluid transport tube that is mounted on an electric vehicle that obtains all or part of its driving force from an electric motor and that has multiple layers (2, 3) laminated thereon, Among the multiple layers, the outer layer (3) is made of a thermoplastic elastomer foam, Among the multiple layers, the inner layer (2) is made of a thermoplastic elastomer or a thermoplastic resin, the outer layer and the inner layer are in close contact with each other over the entire periphery, The tube for transporting a fluid, wherein the expansion ratio of the thermoplastic elastomer foam is 2 times or more and 5.5 times or less.

2. A fluid transport tube that is mounted on an electric vehicle that obtains all or part of its driving force from an electric motor and that is composed of multiple layers (2 to 4) stacked together, Among the multiple layers, the outer layer (3) is made of a thermoplastic elastomer foam, Among the multiple layers, the inner layer (2) is made of a thermoplastic elastomer or a thermoplastic resin, A reinforcing layer (4) is provided between the outer layer and the inner layer, and is in close contact with each of the outer layer and the inner layer over the entire periphery, The tube for transporting a fluid, wherein the expansion ratio of the thermoplastic elastomer foam is 2 times or more and 5.5 times or less.

3. A fluid transport tube as described in claim 2, wherein the reinforcing layer is a polyamide resin, a polyphenylene sulfide resin, or a mixture thereof, or an adhesive.

4. A fluid transport tube as described in claim 2, wherein the reinforcing layer is formed by braiding reinforcing yarns.

5. 3. The tube for transporting a fluid according to claim 1, wherein the expansion ratio of the thermoplastic elastomer foam is more than 3 times and not more than 5.5 times.

6. A tube for transporting fluid as described in claim 1 or 2, wherein the foaming ratio of the thermoplastic elastomer foam is greater than 3 times and not more than 5.5 times (excluding the range where the foaming ratio is 3.6 times or less).

7. The outer layer is made of an olefin-based thermoplastic elastomer foam, 3. The fluid transport tube according to claim 1, wherein the inner layer is made of an olefin-based thermoplastic elastomer or an olefin-based thermoplastic resin.

8. The outer layer is made of a styrene-based thermoplastic elastomer foam, The inner layer is made of an olefin-based thermoplastic elastomer or an olefin-based thermoplastic resin, 3. The tube for transporting a fluid according to claim 1, wherein the expansion ratio of the styrene-based thermoplastic elastomer foam is 2 times or more and 4.8 times or less.

9. 3. The fluid transport tube according to claim 1, wherein the inner layer is made of a resin different from the thermoplastic elastomer contained in the outer layer.

10. 3. The fluid transport tube according to claim 1, wherein the outer layer contains thermally expandable microcapsules.

11. A method for producing a fluid transport tube according to claim 1 or 2, comprising the steps of: A method for producing a tube for transporting a fluid, comprising a co-extrusion molding step of simultaneously extruding the material for the inner layer and the material for the outer layer.

12. A method for producing a fluid transport tube according to claim 1 or 2, comprising the steps of: extruding the inner layer into a tubular shape to form an inner layer tube; and covering the outer layer while taking up the inner layer tube.

13. A method for manufacturing a fluid transport tube according to claim 1 or 2, comprising the steps of: a step of extruding the inner layer in a first extruder (51) and then cooling the inner layer in a first water tank; a step of coating the inner layer with a material for the outer layer in a second extruder (54) and then cooling the inner layer and the outer layer in a second water tank (56).