Tube and method for manufacturing same

Abstract

The present invention provides a tube in which residual stress is eliminated while maintaining flexibility. The tube includes a thermoplastic resin composition having a sea-island structure comprising a rubber-containing island phase and a thermoplastic resin-containing sea phase. The thermoplastic resin composition contains 100 parts by mass of rubber and 30 to 120 parts by mass of thermoplastic resin. The tube is at least 0.1 mm thick. Let circularity (inner surface) denote the circularity of the island phase in a cross section of the tube when cut by a plane containing the center axis of the tube, said cross section having a range of 5 μm in the thickness direction from the inner surface of the tube, and let circularity (central) denote the circularity of the island phase in the cross section of the central 5 μm range of the tube in the thickness direction; in this case, the circularity (inner surface) and the circularity (central) satisfy the following expressions (1) and (2): (1) 0.35 ≤ circularity (inner surface) ≤ 1.0; (2) 60 ≤ circularity (inner surface) / circularity (central) × 100 ≤ 120.

Description

Tube and manufacturing method thereof

[0001] The present invention relates to a tube and a method for manufacturing the same, and more particularly to a tube with low residual stress and a method for manufacturing the same.

[0002] Japanese Patent Laid-Open Publication No. 2020-105284 (Patent Document 1) discloses a refrigerant transport hose for an automobile air conditioner, in which the inner layer of the hose is extruded into a tube using a thermoplastic resin composition comprising a matrix containing a thermoplastic resin and domains containing rubber dispersed in the matrix.

[0003] Japanese Patent Application Laid-Open No. 2020-105284

[0004] However, the inner layer tube of the refrigerant transport hose disclosed in Patent Document 1 has a problem of residual stress, which is undesirable in the hot environment in which the hose is used. The present invention provides a tube that eliminates residual stress while maintaining flexibility.

[0005] The present invention (I) is a tube comprising a thermoplastic resin composition having an islands-in-sea structure consisting of island phases containing rubber and a sea phase containing a thermoplastic resin, wherein the thermoplastic resin composition comprises 100 parts by mass of rubber and 30 to 120 parts by mass of thermoplastic resin, the tube having a thickness of 0.1 mm or more, and wherein, in a cross section of the tube cut along a plane including the central axis of the tube, the circularity of the island phases in a cross section ranging from the inner surface of the tube to 5 μm in the thickness direction is referred to as the circularity (inner surface), and the circularity of the island phases in a cross section ranging from the central 5 μm in the thickness direction of the tube is referred to as the circularity (center), the circularity (inner surface) and the circularity (center) satisfy the following formulas (1) and (2): 0.35≦circularity (inner surface)≦1.0 (1) 60≦circularity (inner surface) / circularity (center)×100≦120 (2) The present invention (II) is a method for producing the tube of the present invention (I), characterized in that the method includes a step of extruding a thermoplastic resin composition into a tubular shape by draw-down extrusion molding.

[0006] The present invention includes the following embodiments: [1] A tube containing a thermoplastic resin composition having an islands-in-sea structure consisting of island phases containing rubber and a sea phase containing a thermoplastic resin, wherein the thermoplastic resin composition contains 100 parts by mass of rubber and 30 to 120 parts by mass of thermoplastic resin, the tube has a thickness of 0.1 mm or more, and when the circularity of the island phases in a cross section obtained by cutting the tube along a plane including the central axis of the tube and extending from the inner surface of the tube to 5 μm in the thickness direction is referred to as the circularity (inner surface), and the circularity of the island phases in a cross section extending within the central 5 μm in the thickness direction of the tube is referred to as the circularity (center), the circularity (inner surface) and the circularity (center) satisfy the following formulas (1) and (2): 0.35≦circularity (inner surface)≦1.0 (1) 60≦circularity (inner surface) / circularity (center)×100≦120 (2). [2] The tube according to [1], wherein, among cross sections obtained by cutting the tube along a plane including the central axis of the tube, the aspect ratio of the island phases in a cross section extending from the inner surface of the tube to 5 μm in the thickness direction is referred to as the aspect ratio (inner surface), and the aspect ratio of the island phases in a cross section extending within the central 5 μm in the thickness direction of the tube is referred to as the aspect ratio (center), the aspect ratio (inner surface) and the aspect ratio (center) satisfy the following formulas (3) and (4): 1≦aspect ratio (inner surface)≦3 (3) 90≦aspect ratio (inner surface) / aspect ratio (center)×100≦150 (4) [3] The tube according to [1] or [2], wherein the rubber comprises an elastomer having a polyisobutylene skeleton. [4] The tube according to [3], wherein the elastomer having a polyisobutylene skeleton is at least one selected from the group consisting of butyl rubber, halogenated butyl rubber, isobutylene-p-methylstyrene copolymer rubber, halogenated isobutylene-p-methylstyrene copolymer rubber, and styrene-isobutylene-styrene block copolymer. [5] The tube according to any one of [1] to [4], wherein the thermoplastic resin comprises a polyamide.[6] The tube according to [5], wherein the polyamide is at least one selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 6 / 66 copolymer, polyamide 6 / 12 copolymer, polyamide 46, polyamide 6T, polyamide 9T, and polyamide MXD6. [7] The tube according to any one of [1] to [6], wherein the rubber is crosslinked. [8] A method for producing the tube according to any one of [1] to [7], comprising a step of extruding a thermoplastic resin composition into a tubular shape by draw extrusion molding.

[0007] The tube of the present invention has low residual stress.

[0008] FIG. 1 is a scanning probe micrograph of the cross section of the tube of Example 1. FIG. 2 is a scanning probe micrograph of the cross section of the tube of Example 2. FIG. 3 is a scanning probe micrograph of the cross section of the tube of Example 3. FIG. 4 is a scanning probe micrograph of the cross section of the tube of Example 5. FIG. 5 is a scanning probe micrograph of the cross section of the tube of Example 6. FIG. 6 is a scanning probe micrograph of the cross section of the tube of Example 7. FIG. 7 is a scanning probe micrograph of the cross section of the tube of Comparative Example 1. FIG. 8 is a diagram showing the cross section of the tube from which the micrograph was taken. FIG. 9 is a diagram for explaining the method of the curl test. FIG. 10 is a schematic cross section of a die for draw extrusion molding. FIG. 11 is a schematic cross section of a die for solid extrusion molding.

[0009] The present invention provides a tube comprising a thermoplastic resin composition having an islands-in-sea structure consisting of island phases containing rubber and a sea phase containing a thermoplastic resin, wherein the thermoplastic resin composition comprises 100 parts by mass of rubber and 30 to 120 parts by mass of a thermoplastic resin, the tube having a thickness of 0.1 mm or more, and wherein, in a cross section obtained by cutting the tube along a plane including the central axis of the tube, the circularity of the island phases in a cross section extending from the inner surface of the tube to 5 μm in the thickness direction is referred to as the circularity (inner surface), and the circularity of the island phases in a cross section extending within a central 5 μm in the thickness direction of the tube is referred to as the circularity (center), and the circularity (inner surface) and the circularity (center) satisfy the following formulas (1) and (2): 0.35≦circularity (inner surface)≦1.0 (1), 60≦circularity (inner surface) / circularity (center)×100≦120 (2).

[0010] Figure 8 shows a cross section of a tube 1 for which a micrograph is taken. Figure 8(a) shows a cross section of the tube 1 cut along a plane passing through the central axis 2 of the tube 1, and Figure 8(b) is an enlarged view of the circled portion of Figure 8(a). In Figure 8, 3 denotes the inner surface of the tube, 4 denotes the outer surface of the tube, 5 denotes the center line of the tube in the thickness direction, 6 denotes the range extending 5 μm from the inner surface of the tube in the thickness direction, and 7 denotes the central 5 μm range in the thickness direction of the tube. In other words, the central 5 μm range 7 in the thickness direction of the tube refers to the range sandwiched between a line 8 located 2.5 μm outward from the center line 5 in the thickness direction of the tube and a line 9 located 2.5 μm inward from the center line 5 in the thickness direction of the tube.

[0011] In the tube 1 of the present invention, when the tube 1 is cut along a plane including the central axis 2 of the tube 1, the circularity of the island phases in a cross section extending from the inner surface 3 of the tube to 5 μm in the thickness direction of the tube is referred to as the circularity (inner surface), and the circularity of the island phases in a cross section extending from the inner surface 3 of the tube to 5 μm in the thickness direction of the tube is referred to as the circularity (center). The circularity (inner surface) and the circularity (center) satisfy the following formulas (1) and (2): 0.35≦circularity (inner surface)≦1.0 (1) 60≦circularity (inner surface) / circularity (center)×100≦120 (2) The tube of the present invention preferably satisfies the formula (1′): 0.36≦circularity (inner surface)≦1.0 (1′), and more preferably satisfies the formula (1″): 0.38≦circularity (inner surface)≦1.0 (1″). The tube of the present invention preferably satisfies the formula (2'): 65≦circularity (inner surface) / circularity (center)×100≦120 (2'), and more preferably satisfies the formula (2"): 70≦circularity (inner surface) / circularity (center)×100≦115 (2"). By satisfying formulas (1) and (2), the tube has little residual stress, and when the tube is used as the inner layer of a hose for transporting a refrigerant, the tube is less likely to develop cracks.

[0012] Here, the circularity is defined by the formula (5) where S is the area of ​​one island phase and L is the perimeter of the island phase: Circularity=4πS / L ２ ... (5) The circularity of a perfect circle is 1, and the closer the circularity is to 1, the closer the shape of the island phase is to a perfect circle.

[0013] In the tube 1 of the present invention, when the tube 1 is cut along a plane including the central axis 2 of the tube 1, the aspect ratio of the island phases in a cross section of the tube 1 within a range 6 from the inner surface 3 of the tube 1 in the thickness direction of 5 μm is referred to as the aspect ratio (inner surface), and the aspect ratio of the island phases in a cross section of the tube 1 within a central 5 μm range 7 in the thickness direction of the tube 1 is referred to as the aspect ratio (center). The aspect ratio (inner surface) and the aspect ratio (center) preferably satisfy the following equations (3) and (4): 1≦aspect ratio (inner surface)≦3 (3), and 90≦aspect ratio (inner surface) / aspect ratio (center)×100≦150 (4). The tube of the present invention more preferably satisfies formula (3'): 1≦aspect ratio (inner surface)≦2.9 (3'), and even more preferably satisfies formula (3"): 1≦aspect ratio (inner surface)≦2.85 (3"). The tube of the present invention more preferably satisfies formula (4'): 90≦aspect ratio (inner surface) / aspect ratio (center)×100≦148 (4'), and even more preferably satisfies formula (4"): 100≦aspect ratio (inner surface) / aspect ratio (center)×100≦145 (4"). By satisfying formulas (3) and (4), the tube has even less residual stress and is even less likely to develop cracks when used as the inner layer of a hose for transporting a refrigerant.

[0014] Here, the aspect ratio refers to the ratio of the major axis to the minor axis, calculated from the major axis and the minor axis of an ellipse obtained by approximating one island phase to an ellipse. The ellipse approximation can be performed by measurement using Fit Ellipse in the image processing software ImageJ.

[0015] The cross section of the tube 1 cut along a plane passing through the central axis 2 of the tube 1 can be observed using an atomic force microscope (AFM), which is a scanning probe microscope (SPM). While the measurement mode is not particularly limited, tapping mode is preferably used. Observation may also be performed using an electron microscope (scanning electron microscope (SEM), transmission electron microscope (TEM)), etc. A cross section measuring 5 μm vertically and 5 μm horizontally is photographed using the microscope, and the resulting cross-sectional image is binarized using the image processing software ImageJ, with the histogram peaks and the middle of the peaks as boundaries. In the binarized image, a 10,000 nm ２ The circularity is calculated for all island phases having an area of ​​10,000 nm or more, and the average value is calculated. ２ For all island phases having the above area, ellipse approximation is performed to determine the major axis and minor axis, and the aspect ratio (major axis / minor axis) is calculated, and the average value is determined.

[0016] Fig. 1 shows scanning probe micrographs of the cross section of the tube of Example 1. Fig. 1(a) shows a scanning probe micrograph of the cross section of the tube of Example 1, extending from the inner surface to 5 µm in the thickness direction, and Fig. 1(b) shows a scanning probe micrograph of the cross section of the tube of Example 1, extending from the inner surface to 5 µm in the thickness direction. Similarly, Fig. 2 shows scanning probe micrographs of the cross section of the tube of Example 2, Fig. 3 shows scanning probe micrographs of the cross section of the tube of Example 3, Fig. 4 shows scanning probe micrographs of the cross section of the tube of Example 5, Fig. 5 shows scanning probe micrographs of the cross section of the tube of Example 6, Fig. 6 shows scanning probe micrographs of the cross section of the tube of Example 7, and Fig. 7 shows scanning probe micrographs of the cross section of the tube of Comparative Example 1, with (a) showing a scanning probe micrograph of the cross section of the tube, extending from the inner surface to 5 µm in the thickness direction, and (b) showing a scanning probe micrograph of the cross section of the tube, extending from the inner surface to 5 µm in the thickness direction.

[0017] In conventional tubes, the island phases on the inner surface side are stretched. As a result, the circularity of the island phases near the inner surface is smaller than that of the island phases in the thickness direction center, and the aspect ratio of the island phases near the inner surface is higher than that of the island phases in the thickness direction center (see Figure 7). It is believed that the difference in morphology between the inner surface and the thickness direction center causes residual stress. Hoses using tubes with residual stress may lose their shape when used at high temperatures.

[0018] The tube of the present invention contains a thermoplastic resin composition having an islands-in-a-sea structure consisting of island phases containing rubber and a sea phase containing a thermoplastic resin. The thermoplastic resin composition constituting the tube of the present invention has an islands-in-a-sea structure consisting of island phases and a sea phase. The islands-in-a-sea structure makes it possible to compound a large amount of rubber while maintaining gas barrier properties, thereby achieving both flexibility and gas barrier properties.

[0019] The island phase contains rubber. The rubber preferably contains, but is not limited to, an elastomer having a polyisobutylene backbone. The polyisobutylene backbone is a chemical structure formed by polymerizing a plurality of isobutylene units, i.e., —[—CH ２ -C(CH ３ ) ２ -] ｎ - (where n is an integer of 2 or greater). By including an elastomer having a polyisobutylene skeleton in the rubber, both flexibility and gas barrier properties can be achieved. The elastomer having a polyisobutylene skeleton is not limited as long as it has a polyisobutylene skeleton, but is preferably at least one selected from the group consisting of butyl rubber (IIR), halogenated butyl rubber, isobutylene-p-methylstyrene copolymer rubber (IPMS), halogenated isobutylene-p-methylstyrene copolymer rubber, and styrene-isobutylene-styrene block copolymer (SIBS), and more preferably brominated isobutylene-p-methylstyrene copolymer rubber (BIMS). The island phase may contain components other than rubber as long as they do not impair the effects of the present invention.

[0020] The sea phase contains a thermoplastic resin. The thermoplastic resin is not limited, but preferably contains a polyamide. When the thermoplastic resin contains a polyamide, both flexibility and gas barrier properties can be achieved. The polyamide is not limited, but preferably is at least one selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 6 / 66 copolymer, polyamide 6 / 12 copolymer, polyamide 46, polyamide 6T, polyamide 9T, and polyamide MXD6. The sea phase may contain components other than the thermoplastic resin, as long as the effects of the present invention are not impaired.

[0021] The thermoplastic resin composition contains 100 parts by mass of rubber and 30 to 120 parts by mass of thermoplastic resin. The content of the thermoplastic resin in the thermoplastic resin composition is 30 to 120 parts by mass, and preferably 30 to 115 parts by mass, based on 100 parts by mass of rubber. When the contents of the rubber and thermoplastic resin are within these numerical ranges, a dispersed form of a sea-island structure in which the rubber forms island phases is ensured, and flexibility and gas barrier properties can be ensured.

[0022] The thermoplastic resin composition may contain components other than the rubber and the thermoplastic resin, such as a resin other than the thermoplastic resin, a crosslinking agent, an antioxidant, a viscosity stabilizer, and a processing aid.

[0023] The thermoplastic resin composition preferably contains an antioxidant. By including an antioxidant in the thermoplastic resin composition, heat aging resistance is improved. Examples of antioxidants include phenylenediamine-based antioxidants and quinoline-based antioxidants. The phenylenediamine-based antioxidant refers to an antioxidant having an aromatic ring with two secondary amine substituents in its molecular structure. It is preferably at least one selected from the group consisting of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N,N'-diphenyl-p-phenylenediamine, and more preferably N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine. The quinoline-based antioxidant refers to an antioxidant having a quinoline skeleton in its molecular structure, and is preferably a 2,2,4-trimethyl-1,2-dihydroquinoline polymer. The content of the antioxidant in the thermoplastic resin composition is preferably 0.1 to 10 parts by mass, and more preferably 0.1 to 5.0 parts by mass, based on 100 parts by mass of the total amount of rubber and thermoplastic resin. The phenylenediamine-based antioxidant and the quinoline-based antioxidant also function as a crosslinking agent for rubber.

[0024] The thermoplastic resin composition preferably contains a viscosity stabilizer. By including a viscosity stabilizer, the increase in viscosity during extrusion molding of the thermoplastic resin composition can be suppressed, effectively reducing the occurrence of retention, thereby improving processability. Examples of viscosity stabilizers include divalent metal oxides, ammonium salts, and carboxylates. Examples of divalent metal oxides include zinc oxide, magnesium oxide, copper oxide, calcium oxide, and iron oxide. Zinc oxide or magnesium oxide is preferred, and zinc oxide is more preferred. Examples of ammonium salts include ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium bromide, ammonium sulfate, ammonium nitrate, ammonium acetate, and alkylammonium salts. Examples of carboxylates include sodium acetate, potassium acetate, zinc acetate, copper acetate, sodium oxalate, ammonium oxalate, calcium oxalate, and iron oxalate. The most preferred viscosity stabilizer is zinc oxide. The content of the viscosity stabilizer in the thermoplastic resin composition is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the total amount of the rubber and the thermoplastic resin. It is preferable that 50% by mass or more of the viscosity stabilizer is contained in the matrix. By containing 50% by mass or more of the viscosity stabilizer in the matrix, an increase in viscosity during extrusion molding of the thermoplastic resin composition can be suppressed, and the occurrence of retained matter can be effectively reduced, resulting in improved processability.

[0025] The thermoplastic resin composition preferably contains a processing aid. The processing aid contributes to improving the extrusion processability of the thermoplastic resin composition. Examples of processing aids include fatty acids, fatty acid metal salts, fatty acid esters, and fatty acid amides. Examples of fatty acids include stearic acid, palmitic acid, lauric acid, oleic acid, and linoleic acid, with stearic acid being preferred. Examples of fatty acid metal salts include calcium stearate, potassium stearate, zinc stearate, magnesium stearate, and sodium stearate, with calcium stearate being preferred. Examples of fatty acid esters include glycerin monostearate, sorbitan stearate, stearyl stearate, and ethylene glycol distearate. Examples of fatty acid amides include stearic acid monoamide, oleic acid monoamide, and ethylene bisstearic acid amide. The content of the processing aid in the thermoplastic resin composition is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and even more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the total amount of rubber and thermoplastic resin.

[0026] The rubber is preferably crosslinked. Crosslinking the rubber can improve fatigue resistance. To crosslink the rubber, a crosslinking agent may be blended into the thermoplastic resin composition. Examples of crosslinking agents include phenylenediamine-based antioxidants and quinoline-based antioxidants, with phenylenediamine-based antioxidants being preferred. The content of the crosslinking agent is preferably 1.0 to 10 parts by mass, more preferably 1.0 to 6.0 parts by mass, based on 100 parts by mass of rubber.

[0027] The manufacturing method of the tube of the present invention is not particularly limited, and known general manufacturing methods can be used. Specifically, solid extrusion molding and draw-down extrusion molding, which are known extrusion molding methods for electric wires, etc., can be used. By controlling the extrusion conditions, such as the extrusion set temperature (die temperature), extrusion rotation speed (extruder screw rotation speed), tube wall thickness, and tube inner diameter, the desired circularity (inner surface), circularity (center), aspect ratio (inner surface), and aspect ratio (center) can be obtained. The extrusion temperature of the thermoplastic resin composition can be, for example, 230°C or higher and 260°C or lower. At temperatures below 230°C, the extrusion torque increases, resulting in poor processability. At temperatures above 260°C, discoloration may occur during residence in the extruder, potentially resulting in poor appearance. The screw rotation speed during extrusion of the thermoplastic resin composition varies depending on the size and type of extruder, but can be, for example, 8 rpm or higher and 50 rpm or lower in a 40 mmφ single-screw extruder. At temperatures below 8 rpm, the residence time increases, accelerating material degradation. If the rotational speed is 50 rpm or more, excessive shear heat is generated, which accelerates material deterioration.

[0028] The present invention (II) relates to a method for producing the tube of the present invention (I). The method of the present invention (II) is characterized by including a step of extruding a thermoplastic resin composition into a tubular shape by draw extrusion. FIG. 10 shows a schematic cross-sectional view of a die 10 for draw extrusion molding. FIG. 11 shows a schematic cross-sectional view of a die 11 for solid extrusion molding. As shown in FIG. 10, draw extrusion molding is a molding method in which a core material 12 and a molten thermoplastic resin composition 13 come into contact outside the die 10 after exiting a die 14. On the other hand, solid extrusion molding is a molding method characterized by the core material 12 and the molten thermoplastic resin composition 13 coming into contact under pressure within the die 14. The outer diameter of the core material 12 is, for example, 8 mm to 25 mm. In draw extrusion molding, internally pressurized air may be used instead of a core material, and the die shown in FIG. 10 does not necessarily need to be used. The cross-sectional area draw-down ratio in draw extrusion molding is preferably 1 to 100. Within the preferred range, a molding speed sufficient for productivity can be obtained, and mechanical properties are also good. The draw-down balance in draw-down extrusion molding is preferably 1.00 or more and 1.20 or less. Within the preferred range, dimensional stability during molding is good. The cross-sectional area draw-down ratio and the draw-down balance are defined by equations (6) and (7). Cross-sectional area draw-down ratio = (D ｄ ２ -D ｔ ２ ) / (D ｏ ２ -D ｉ ２ ) ... (6) Withdrawal balance = (D ｄ / D ｔ ) / (D ｏ / D ｉ ) ... (7) However, D ｄ : Die opening diameter D ｔ : Outer diameter of pin D ｏ : Tube outer diameter D ｉ : Tube inner diameter (core outer diameter)

[0029] The tube of the present invention can be used as the inner layer of a hose, although its application is not limited thereto. Examples of the hose include, but are not limited to, a hose for transporting a refrigerant. Specific examples of hoses using the tube of the present invention include a hose containing the tube of the present invention as the inner layer, or a hose containing an inner layer, a reinforcing layer, and an outer layer, wherein the inner layer is the tube of the present invention.

[0030] [Raw Materials] The raw materials used in the following examples and comparative examples are as follows. Butyl rubber: Brominated isobutylene-p-methylstyrene copolymer rubber "EXXPRO" (registered trademark) 3745 manufactured by ExxonMobil Chemical Corporation Acid-modified polyolefin: Maleic acid-modified α-olefin copolymer "TAFMER" (registered trademark) MH7010 manufactured by Mitsui Chemicals, Inc. Polyamide 6: Polyamide 6 "UBE NYLON" (registered trademark) 1011FB manufactured by Ube Industries, Ltd. Polyamide 6 / 12: Polyamide 6 / 12 copolymer "UBE NYLON" (registered trademark) 7024B manufactured by Ube Industries, Ltd. Polyamide 12: Polyamide 12 "UBESTA" (registered trademark) 3012U manufactured by Ube Industries, Ltd. Antioxidant: Phenylenediamine-based antioxidant "SANTOFLEX" (registered trademark) 6PPD manufactured by Solutia (substance name: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) Viscosity stabilizer: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. (zinc oxide is mixed with polyamide 6 as a masterbatch, and the amount of zinc oxide listed in the table is added) Processing aid-1: Calcium stearate SC-PG manufactured by Sakai Chemical Industry Co., Ltd. Processing aid-2: Industrial stearic acid manufactured by Chiba Fatty Acid Co., Ltd.

[0031] [Preparation of Thermoplastic Resin Composition] The raw materials were charged into a twin-screw kneading extruder (manufactured by The Japan Steel Works, Ltd.) in the blending ratios shown in Tables 1 and 2, and kneaded for 3 minutes at 235° C. The kneaded product was continuously extruded from the extruder in the form of a strand, cooled with water, and then cut with a cutter to obtain pellets of a thermoplastic resin composition for an inner layer.

[0032] [Tube Production] Tubes were produced by extruding the thermoplastic resin composition onto a core material using a 40 mmφ extruder under the conditions shown in Tables 1 and 2, and then removing the core material. In the tables, "drawdown" means that the composition was produced by drawdown extrusion molding, and indicates that a manufacturing method was used in which the thermoplastic resin composition and the core material were brought into contact with each other outside the mold, as shown in Figure 10. In the tables, "solid" means that the composition was produced by solid extrusion molding, and indicates that a manufacturing method was used in which the thermoplastic resin composition and the core material were brought into contact with each other inside the mold, as shown in Figure 11. The thermoplastic resin composition of Comparative Example 2 was not suitable for tube production, so no tube was produced.

[0033] The produced tubes were evaluated for circularity and aspect ratio of the island phases, and a curl test was conducted. The flexibility of the thermoplastic resin composition was evaluated. The evaluation results are shown in Tables 1 and 2. The measurement methods for each evaluation item are as follows.

[0034] [Circularity and aspect ratio of island phases] A cross section of a tube cut along a plane passing through the central axis of the tube was photographed using an atomic force microscope (AFM) (scanning probe microscope (SPM)) in tapping mode over a range of 5 μm in length and 5 μm in width. The obtained cross-sectional image was binarized using image processing software ImageJ, with the histogram peaks and the middle of the peaks as boundaries. In the binarized image, the circularity and aspect ratio of the island phases were measured at 10,000 nm. ２ The circularity (Circ. term) was calculated for all island phases having an area of ​​10,000 nm or more, and the average value was determined. ２ For all island phases having the above areas, ellipse approximation was performed to determine the major axis (major term) and minor axis (minor term), and the aspect ratio (major axis / minor axis) was calculated, and the average value was determined.

[0035] [Curl Test] A test piece having the shape shown in Figure 9(a) was cut from the tube, placed in an oven with the thin part facing up and held vertically, and heated at 150°C for 30 minutes. The curl after heating was observed. The test piece bent toward the inner surface upon heating, indicating that the shrinkage force was greater on the inner surface than on the outer surface, which is thought to be due to residual stress on the inner surface. Figure 9(b) shows an example of a test piece before heating, and Figure 9(c) shows the state of the test piece after heating. The angle between the line connecting the tip of the thin part of the test piece after heating and the line (vertical line) in the longitudinal direction of the thick part (vertical line) was defined as the curl angle. The larger the curl angle, the greater the residual stress on the inner surface. A curl angle of less than 10° was marked with a circle, and a curl angle of 10° or more was marked with an x.

[0036] [Flexibility] The thermoplastic resin composition was molded into a sheet having an average thickness of 1.0 mm using a 40 mmφ single-screw extruder with a 200 mm wide T-type die (manufactured by Plagiken Co., Ltd.), with the cylinder and die temperatures set to the melting point of the polymer component with the highest melting point in the thermoplastic resin composition + 10 ° C., a cooling roll temperature of 50 ° C., and a take-up speed of 3 m / min. The sheet having an average thickness of 1.0 mm was punched into a JIS No. 6 dumbbell shape and subjected to a tensile test in accordance with JIS K7161 at a temperature of 25 ° C., a relative humidity of 50%, and a speed of 500 mm / min. The stress at 10% elongation was calculated from the obtained stress-strain curve, and this was taken as the 10% modulus. When the 10% modulus was 20 MPa or less, the flexibility was evaluated as good (◯), and when the 10% modulus was greater than 20 MPa, the flexibility was evaluated as poor (×).

[0037]

[0038]

[0039] The tube of the present invention can be suitably used as the inner layer of a hose for transporting a refrigerant.

[0040] DESCRIPTION OF SYMBOLS 1 Tube 2 Central axis 3 Inner surface of tube 4 Outer surface of tube 5 Center line in thickness direction of tube 6 Range from inner surface of tube to 5 μm in thickness direction 7 Center 5 μm range in thickness direction of tube 8 Line 2.5 μm outward from center line 5 in thickness direction of tube 9 Line 2.5 μm inward from center line 5 in thickness direction of tube 10 Die for draw-down extrusion 11 Die for solid extrusion 12 Core material 13 Thermoplastic resin composition 14 Die

Claims

1. A tube comprising a thermoplastic resin composition having an islands-in-sea structure consisting of islands phases containing rubber and a sea phase containing a thermoplastic resin, the thermoplastic resin composition comprising 100 parts by mass of rubber and 30 to 120 parts by mass of thermoplastic resin, the tube having a thickness of 0.1 mm or more, the circularity of the island phases in a cross section obtained by cutting the tube along a plane including the central axis of the tube from the inner surface of the tube to 5 μm in the thickness direction is referred to as the circularity (inner surface), and the circularity of the island phases in a cross section within a central 5 μm in the thickness direction of the tube is referred to as the circularity (center), the circularity (inner surface) and the circularity (center) satisfy the following formulas (1) and (2): 0.35≦circularity (inner surface)≦1.0 ... (1) 60≦circularity (inner surface) / circularity (center)×100≦120 ... (2) 2. The tube according to claim 1, wherein the aspect ratio of the island phase in a cross section obtained by cutting the tube along a plane including the central axis of the tube in a range from the inner surface of the tube in the thickness direction of the tube is referred to as the aspect ratio (inner surface), and the aspect ratio of the island phase in a cross section within a central 5 μm in the thickness direction of the tube is referred to as the aspect ratio (center), wherein the aspect ratio (inner surface) and the aspect ratio (center) satisfy formulas (3) and (4): 1≦aspect ratio (inner surface)≦3 ... (3) 90≦aspect ratio (inner surface) / aspect ratio (center) × 100≦150 ... (4).

3. The tube of claim 1 or 2, wherein the rubber comprises an elastomer having a polyisobutylene backbone.

4. The tube according to claim 3, wherein the elastomer having a polyisobutylene skeleton is at least one member selected from the group consisting of butyl rubber, halogenated butyl rubber, isobutylene-p-methylstyrene copolymer rubber, halogenated isobutylene-p-methylstyrene copolymer rubber, and styrene-isobutylene-styrene block copolymer.

5. The tube of any one of claims 1 to 4, wherein the thermoplastic resin comprises a polyamide.

6. The tube according to claim 5, wherein the polyamide is at least one selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 6 / 66 copolymer, polyamide 6 / 12 copolymer, polyamide 46, polyamide 6T, polyamide 9T and polyamide MXD6.

7. The tube according to any one of claims 1 to 6, wherein the rubber is crosslinked.

8. A method for producing the tube according to any one of claims 1 to 7, said method comprising the step of extruding the thermoplastic resin composition into a tubular shape by draw extrusion.

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