Tube and manufacturing method of the same

Abstract

To provide a tube that dissolves residual stress while retaining flexibility.SOLUTION: A tube contains a thermoplastic resin composition having a sea-island structure comprising a rubber-containing island phase and a thermoplastic resin-containing sea phase, wherein the thermoplastic resin composition contains 100 pts.mass of rubber, and 30 to 120 pts.mass of a thermoplastic resin, the tube has a thickness of 0.1 mm or more, and when a circularity of the island phase in a cross section in a range from an inner surface of the tube to 5 μm in a thickness direction in cross sections made when cutting the tube on a flat surface including a central axis of the tube is called as a circularity (inner surface), and a circularity of the island phase in a cross section in a range of 5 μm of the center in the thickness direction of the tube is called as a circularity (center), the circularity (inner surface) and the circularity (center) satisfy the formula (1) and the formula (2): 0.35≤circularity (inner surface)≤1.0 ... (1); and 60≤circularity (inner surface) / circularity (center)×100≤120 ... (2).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tube and a method for manufacturing the same. More specifically, the present invention relates to a tube having less residual stress and a method for manufacturing the same.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the inner layer tube of the refrigerant transport hose disclosed in Patent Document 1 has a problem that residual stress exists. This is not preferable in a hot environment during hose use. The present invention provides a tube in which residual stress is eliminated while maintaining flexibility.

Means for Solving the Problems

[0005] The present invention (I) is a tube containing a thermoplastic resin composition having a sea-island structure composed of an island phase containing rubber and a sea phase containing a thermoplastic resin, The thermoplastic resin composition contains 100 parts by mass of rubber and 30 to 120 parts by mass of a thermoplastic resin, The tube has a thickness of 0.1 mm or more, When the tube is cut by a plane including the central axis of the tube, among the cross-sections, the roundness of the island phase in the cross-section in the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as roundness (inner surface), and when the roundness of the island phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as roundness (central), roundness (inner surface) and roundness (central) satisfy the following formulas (1) and (2): 0.35 ≤ roundness (inner surface) ≤ 1.0 ··· (1) 60 ≤ roundness (inner surface) / roundness (central) × 100 ≤ 120 ··· (2) characterized by satisfying the above conditions. The present invention (II) is a method for manufacturing the tube of the present invention (I), the method comprising the step of extruding a thermoplastic resin composition into a tube shape by draw-down extrusion.

[0006] The present invention includes the following embodiments. [1] A tube comprising a thermoplastic resin composition having a sea-island structure composed of an island phase containing rubber and a sea phase containing a thermoplastic resin, the thermoplastic resin composition contains 100 parts by mass of rubber and 30 to 120 parts by mass of a thermoplastic resin, the tube has a thickness of 0.1 mm or more, When the tube is cut by a plane including the central axis of the tube, among the cross-sections, the roundness of the island phase in the cross-section in the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as roundness (inner surface), and when the roundness of the island phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as roundness (central), roundness (inner surface) and roundness (central) satisfy the following formulas (1) and (2): 0.35 ≤ roundness (inner surface) ≤ 1.0 ··· (1) 60 ≤ roundness (inner surface) / roundness (central) × 100 ≤ 120 ··· (2) the tube satisfying the above conditions. [2] When the tube is cut in a plane including the central axis of the tube, among the cross-sections, the aspect ratio of the island phase in the cross-section in the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as the aspect ratio (inner surface), and when the aspect ratio of the island phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as the aspect ratio (central), when the aspect ratio (inner surface) and the aspect ratio (central) satisfy the formulas (3) and (4): 1 ≤ aspect ratio (inner surface) ≤ 3 ··· (3) 90 ≤ aspect ratio (inner surface) / aspect ratio (central) × 100 ≤ 150 ··· (4) The tube according to [1], which satisfies the above conditions. [3] The tube according to [1], wherein the rubber contains an elastomer having a polyisobutylene backbone. [4] The tube according to [3], wherein the elastomer having a polyisobutylene backbone 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 [1], wherein the thermoplastic resin contains 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 [1], wherein the rubber is crosslinked. [8] A method for manufacturing the tube according to [1], the method including a step of extruding a thermoplastic resin composition into a tube shape by draw-down extrusion molding.

Advantages of the Invention

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

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0009] The present invention relates to a tube containing a thermoplastic resin composition having a sea-island structure composed of an island phase containing rubber and a sea phase containing a thermoplastic resin, The thermoplastic resin composition contains 100 parts by mass of rubber and 30 to 120 parts by mass of a thermoplastic resin, The tube has a thickness of 0.1 mm or more, When the tube is cut by a plane including the central axis of the tube, among the cross-sections, the roundness of the island phase in the cross-section within the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as roundness (inner surface), and when the roundness of the island phase in the cross-section within the range of the central 5 μm in the thickness direction of the tube is referred to as roundness (central), roundness (inner surface) and roundness (central) satisfy the following formulas (1) and (2): 0.35 ≤ roundness (inner surface) ≤ 1.0 ··· (1) 60 ≤ roundness (inner surface) / roundness (central) × 100 ≤ 120 ··· (2) It is characterized by satisfying the above conditions.

[0010] FIG. 8 is a diagram showing a cross-section of the tube 1 for taking a micrograph. FIG. 8(a) shows a cross-section when the tube 1 is cut by a plane passing through the central axis 2 of the tube 1, and FIG. 8(b) is an enlarged view of the portion surrounded by the circle in FIG. 8(a). In FIG. 8, 3 is the inner surface of the tube, 4 is the outer surface of the tube, 5 is the central line in the thickness direction of the tube, 6 indicates the range within 5 μm in the thickness direction from the inner surface of the tube, and 7 indicates the range of the central 5 μm in the thickness direction of the tube. In other words, the range of the central 5 μm in the thickness direction of the tube 7 refers to the range sandwiched between a line 8 that is 2.5 μm away from the central line 5 of the tube in the thickness direction to the outside and a line 9 that is 2.5 μm away from the central line 5 of the tube in the thickness direction to the inside.

[0011] For the tube 1 of the present invention, when the roundness of the island phase in the cross-section within the range of 5 μm in the thickness direction from the inner surface 3 of the tube in the cross-section when the tube 1 is cut by a plane including the central axis 2 of the tube 1 is referred to as roundness (inner surface), and the roundness of the island phase in the cross-section within the range of the central 5 μm in the thickness direction of the tube is referred to as roundness (central), roundness (inner surface) and roundness (central) satisfy the following formulas (1) and (2): 0.35 ≤ roundness (inner surface) ≤ 1.0 ··· (1) 60 ≤ roundness (inner surface) / roundness (central) × 100 ≤ 120 ··· (2) satisfy the above conditions. The tube of the present invention preferably satisfies the formula (1'): 0.36 ≤ Circularity (inner surface) ≤ 1.0 ··· (1′) is satisfied, and more preferably, the formula (1″): 0.38 ≤ Circularity (inner surface) ≤ 1.0 ··· (1″) is satisfied. The tube of the present invention preferably satisfies the formula (2′): 65 ≤ Circularity (inner surface) / Circularity (center) × 100 ≤ 120 ··· (2′) and more preferably, the formula (2″): 70 ≤ Circularity (inner surface) / Circularity (center) × 100 ≤ 115 ··· (2″) is satisfied. By satisfying the formula (1) and the formula (2), the tube has less residual stress, and when the tube is used as the inner layer of a refrigerant transport hose, the occurrence of cracks is less.

[0012] Here, the circularity is defined by the formula (5) when the area of one island phase is represented by S and the perimeter of the island phase is represented by L. 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] When the tube 1 of the present invention is cut in a plane including the central axis 2 of the tube 1, among the cross-sections, the aspect ratio of the island phase in the cross-section of the range 6 from the inner surface 3 of the tube 1 in the thickness direction up to 5 μm is referred to as the aspect ratio (inner surface), and when the aspect ratio of the island phase in the cross-section of the range 7 of the central 5 μm 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 formula (3) and the formula (4): 1 ≤ Aspect ratio (inner surface) ≤ 3 ··· (3) 90 ≤ Aspect ratio (inner surface) / Aspect ratio (center) × 100 ≤ 150 ··· (4) is satisfied. The tube of the present invention more preferably satisfies the formula (3′): 1 ≤ Aspect ratio (inner surface) ≤ 2.9 ··· (3′) satisfies, and more preferably, the formula (3″): 1 ≦ aspect ratio (inner surface) ≦ 2.85 ··· (3″) satisfies it. The tube of the present invention more preferably satisfies the formula (4′): 90 ≦ aspect ratio (inner surface) / aspect ratio (center) × 100 ≦ 148 ··· (4′) satisfies, and more preferably, the formula (4″): 100 ≦ aspect ratio (inner surface) / aspect ratio (center) × 100 ≦ 145 ··· (4″) satisfies it. By satisfying the formula (3) and the formula (4), the tube has even less residual stress, and when the tube is used as the inner layer of a refrigerant transport hose, the occurrence of cracks is even less.

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

[0015] When the tube 1 is cut by a plane passing through the central axis 2 of the tube 1, the cross-section can be observed with an atomic force microscope (AFM) which is a scanning probe microscope (SPM). The measurement mode is not particularly limited, but the tapping mode is preferably used. Also, it may be observed using an electron microscope (scanning electron microscope (SEM), transmission electron microscope (TEM), etc.). Take a cross-section of 5 μm in length and 5 μm in width with a microscope, and the obtained cross-sectional image is binarized using the image processing software ImageJ with the midpoint between the peaks of the histogram as the boundary. In the binarized image, for all island phases having an area of 10000 nm 2 or more, calculate the circularity and obtain the average value. Also, for all island phases having an area of 10000 nm 2 or more, perform elliptical approximation, obtain the major axis and minor axis, calculate the aspect ratio (major axis / minor axis), and obtain the average value.

[0016] FIG. 1 shows a scanning probe microscope photograph of a cross-section of the tube of Example 1. FIG. 1(a) shows a scanning probe microscope photograph of a cross-section in the range from the inner surface of the tube of Example 1 to a thickness of 5 μm in the thickness direction, and FIG. 1(b) shows a scanning probe microscope photograph of a cross-section in the range of the central 5 μm in the thickness direction of the tube of Example 1. Similarly, FIG. 2 shows a scanning probe microscope photograph of a cross-section of the tube of Example 2, FIG. 3 shows a scanning probe microscope photograph of a cross-section of the tube of Example 3, FIG. 4 shows a scanning probe microscope photograph of a cross-section of the tube of Example 5, FIG. 5 shows a scanning probe microscope photograph of a cross-section of the tube of Example 6, FIG. 6 shows a scanning probe microscope photograph of a cross-section of the tube of Example 7, and FIG. 7 shows a scanning probe microscope photograph of a cross-section of the tube of Comparative Example 1. (a) shows a scanning probe microscope photograph of a cross-section in the range from the inner surface of the tube to a thickness of 5 μm in the thickness direction, and (b) shows a scanning probe microscope photograph of a cross-section in the range of the central 5 μm in the thickness direction of the tube.

[0017] In the conventional tube, the island phase on the inner surface side is extended. As a result, the circularity of the island phase near the inner surface is smaller than that of the island phase at the center in the thickness direction, and the aspect ratio of the island phase near the inner surface is higher than that of the island phase at the center in the thickness direction (see FIG. 7). The difference in morphology between the vicinity of the inner surface and the center in the thickness direction is considered to cause residual stress. A hose using a tube having residual stress has a concern about shape change during high-temperature use.

[0018] The tube of the present invention contains a thermoplastic resin composition having a sea-island structure composed of an island phase containing rubber and a sea phase containing a thermoplastic resin. The thermoplastic resin composition constituting the tube of the present invention has a sea-island structure composed of an island phase and a sea phase. By having a sea-island structure, a large amount of rubber can be blended while maintaining gas barrier properties, and both flexibility and gas barrier properties can be achieved.

[0019] The island phase contains rubber. The rubber preferably includes, but is not limited to, an elastomer having a polyisobutylene skeleton. The polyisobutylene skeleton is a chemical structure formed by polymerization of a plurality of isobutylenes, that is, -[-CH 2 -C(CH 3 ) 2 -] n-(However, n is an integer of 2 or more.) It refers to a chemical structure represented by this. By including an elastomer having a polyisobutylene skeleton in the rubber, it becomes possible to achieve both flexibility and gas barrier properties. 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 the effects of the present invention are not inhibited.

[0020] The sea phase contains a thermoplastic resin. The thermoplastic resin is not limited, but preferably includes a polyamide. By including a polyamide in the thermoplastic resin, it becomes possible to achieve both flexibility and gas barrier properties. The polyamide is not limited, but is preferably 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 inhibited.

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

[0022] The thermoplastic resin composition may contain components other than rubber and thermoplastic resin. Examples of components other than rubber and thermoplastic resin include resins other than thermoplastic resin, crosslinking agents, antioxidants, viscosity stabilizers, processing aids, and the like.

[0023] The thermoplastic resin composition preferably contains an antioxidant. By including an antioxidant in the thermoplastic resin composition, the heat aging resistance is improved. Examples of the antioxidant include phenylenediamine-based antioxidants and quinoline-based antioxidants. The phenylenediamine-based antioxidant refers to an antioxidant having an aromatic ring with two secondary amines as substituents in its molecular structure. Preferably, it is 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. Preferably, it is 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, 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 crosslinking agents for rubber.

[0024] The thermoplastic resin composition preferably contains a viscosity stabilizer. By including a viscosity stabilizer, an increase in viscosity during extrusion molding of the thermoplastic resin composition can be suppressed, and the generation of stagnant materials can be effectively reduced, resulting in good processability. Examples of the viscosity stabilizer include divalent metal oxides, ammonium salts, carboxylates, and the like. Examples of the divalent metal oxides include zinc oxide, magnesium oxide, copper oxide, calcium oxide, iron oxide, etc., with zinc oxide or magnesium oxide being preferred, and zinc oxide being more preferred. Examples of the ammonium salts include ammonium carbonate, ammonium hydrogen carbonate, ammonium chloride, ammonium bromide, ammonium sulfate, ammonium nitrate, ammonium acetate, alkylammonium, etc. Examples of the carboxylates include sodium acetate, potassium acetate, zinc acetate, copper acetate, sodium oxalate, ammonium oxalate, calcium oxalate, iron oxalate, etc. The viscosity stabilizer is most preferably zinc oxide. Based on 100 parts by mass of the total amount of the rubber and the thermoplastic resin, 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 still more preferably 0.5 to 5 parts by mass. Preferably, 50% by mass or more of the viscosity stabilizer is contained in the matrix. When the thermoplastic resin composition is extrusion-molded, the increase in viscosity can be suppressed and the generation of residues can be effectively reduced by containing 50% by mass or more of the viscosity stabilizer in the matrix, so that the processability is improved.

[0025] The thermoplastic resin composition preferably contains a processing aid. The processing aid contributes to the improvement of the extrusion processability of the thermoplastic resin composition. Examples of the processing aids include fatty acids, fatty acid metal salts, fatty acid esters, fatty acid amides, etc. Examples of the fatty acids include stearic acid, palmitic acid, lauric acid, oleic acid, linoleic acid, etc., with stearic acid being preferred. Examples of the fatty acid metal salts include calcium stearate, potassium stearate, zinc stearate, magnesium stearate, sodium stearate, etc., with calcium stearate being preferred. Examples of the fatty acid ester include glycerin monostearate, sorbitan stearate, stearyl stearate, ethylene glycol distearate, and the like. Examples of the fatty acid amide include stearic acid monoamide, oleic acid monoamide, ethylene bisstearic acid amide, and the like. 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 still 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.

[0026] The rubber is preferably crosslinked. By crosslinking the rubber, the fatigue resistance can be improved. To crosslink the rubber, a crosslinking agent may be blended into the thermoplastic resin composition. Examples of the crosslinking agent include phenylenediamine-based antioxidants, quinoline-based antioxidants, etc. Among them, phenylenediamine-based antioxidants are 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 the 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, it is possible to adopt full extrusion molding or draw-down extrusion molding, which are known as extrusion molding methods for electric wires and the like. By controlling extrusion conditions, such as the extrusion set temperature (die temperature), extrusion rotation speed (rotation speed of the screw of the extruder), tube wall thickness, tube inner diameter, etc., the desired roundness (inner surface), roundness (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. If it is 230°C or lower, the extrusion torque increases, resulting in deteriorated processability. If it is 260°C or higher, burning may occur during residence in the extruder, and the appearance may deteriorate. The screw rotation speed during the extrusion of the thermoplastic resin composition varies depending on the size of the extruder and the type of screw. For example, with a 40 mmΦ single-screw extruder, it can be set between 8 rpm and 50 rpm. If it is below 8 rpm, the residence time becomes long, promoting material degradation. If it is above 50 rpm, material degradation is promoted due to excessive shear heating.

[0028] The present invention (II) relates to a method for manufacturing the tube of the present invention (I). The method of the present invention (II) is characterized by including a step of extruding the thermoplastic resin composition into a tube shape by draw-down extrusion molding. FIG. 10 shows a schematic cross-sectional view of the die 10 for draw-down extrusion molding. FIG. 11 shows a schematic cross-sectional view of the die 11 for full extrusion molding. As shown in FIG. 10, draw-down extrusion molding is a molding method in which the core material 12 and the molten thermoplastic resin composition 13 come into contact outside the die 10 after exiting the die 14. On the other hand, full extrusion molding is a molding method characterized in that the core material 12 and the molten thermoplastic resin composition 13 come into contact under pressure inside the die 14. The outer diameter of the core material 12 is, for example, 8 mm or more and 25 mm or less. In draw-down extrusion molding, internal pressure air may be used instead of the core material, and it is not necessarily required to use the die shown in FIG. 10. The cross-sectional area draw-down ratio in draw-down extrusion molding is preferably 1 or more and 100 or less. Within a preferable range, a molding speed sufficient for productivity can be obtained, and the mechanical properties also become good. The draw-down balance in draw-down extrusion molding is preferably 1.00 or more and 1.20 or less. Within a preferable range, the dimensional stability during molding becomes good. The cross-sectional area draw-down ratio and the draw-down balance are defined by formula (6) and formula (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 : Opening diameter of the die D t : Outer diameter of the pin D o : Outer diameter of the tube D i : Inner diameter of the tube (outer diameter of the core material)

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

Example

[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 Company 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. Anti-aging agent: Phenylene diamine-based anti-aging agent "SANTOFLEX" (registered trademark) 6PPD (substance name: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) manufactured by Solutia Viscosity stabilizer: Three types of zinc oxide manufactured by Shoindo Chemical Industry Co., Ltd. (zinc oxide content shown in the table is added as a masterbatch of zinc oxide mixed with polyamide 6) Processing aid - 1: Calcium stearate SC-PG manufactured by Sakai Chemical Industry Co., Ltd. Processing aid - 2: Industrial stearic acid manufactured by Chiba Fatty Acids Co., Ltd.

[0031] [Preparation of thermoplastic resin composition] Each raw material was put into a twin-screw kneading extruder (manufactured by Nippon Steel Works, Ltd.) at the compounding ratios shown in Tables 1 and 2 and kneaded at 235°C for 3 minutes. The kneaded product was continuously extruded from the extruder in a strand shape, cooled with water, and cut with a cutter to obtain a pellet-shaped thermoplastic resin composition for the inner layer.

[0032] [Production of tube] On the core material, the thermoplastic resin composition was extruded into a tube shape by a 40 mmφ extruder under the conditions shown in Tables 1 and 2, and the core material was removed to produce a tube. In the table, "pull-down" means that it was produced by pull-down extrusion molding, and as shown in Figure 10, it indicates that a manufacturing method was adopted in which the thermoplastic resin composition and the core material were brought into contact outside the mold. In the table, "filling" means that it was produced by filling extrusion molding, and as shown in Figure 11, it indicates that a manufacturing method was adopted in which the thermoplastic resin composition core material was brought into contact inside the mold. Note that since the thermoplastic resin composition of Comparative Example 2 was not suitable for tubes, no tube was produced.

[0033] For the produced tubes, the roundness and aspect ratio of the island phase were evaluated, 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. Note that the measurement methods for each evaluation item are as follows.

[0034] [Circularity and aspect ratio of island phase] When the tube was cut by a plane passing through the central axis of the tube, the cross-section was measured with an atomic force microscope (AFM), which is a scanning probe microscope (SPM), in tapping mode, and an area of 5 μm in length and 5 μm in width was photographed. The obtained cross-sectional image was binarized using image processing software ImageJ with the midpoint between the peaks of the histogram as the boundary. In the binarized image, for all island phases having an area of 10000 nm 2 or more, the circularity (Circ. term) was calculated and the average value was obtained. Also, for all island phases having an area of 10000 nm 2 or more, an ellipse approximation was performed to obtain the major axis (Major term) and the minor axis (Minor term), the aspect ratio (major axis / minor axis) was calculated, and the average value was obtained.

[0035] [Curl test] A test piece having the shape shown in Fig. 9(a) was cut out from the tube, placed in an oven while being held vertically with the narrow part facing up, heated at 150 °C for 30 minutes, and the curl after heating was observed. The test piece bends toward the inner surface side due to heating, which indicates that the shrinking force is greater on the inner surface side than on the outer surface side, and is considered to be caused by the residual stress on the inner surface side. Fig. 9(b) shows an example of the test piece before heating, and Fig. 9(c) shows the state of the test piece after heating. The angle formed by the straight line connecting the tip and the base of the narrow part of the test piece after heating with the straight line (vertical line) in the length direction of the thick part is defined as the curl angle. The larger the curl angle, the greater the residual stress on the inner surface side is determined to be. When the curl angle is less than 10°, it is indicated as 〇, and when the curl angle is 10° or more, it is indicated as ×.

[0036] [Flexibility] The thermoplastic resin composition was molded into a sheet with an average thickness of 1.0 mm under the conditions of a cylinder and die temperature 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 using a 40 mmφ single-screw extruder with a 200 mm wide T-die (manufactured by Plastech Co., Ltd.). The sheet with an average thickness of 1.0 mm produced was punched into a JIS No. 6 dumbbell shape, and a tensile test was conducted 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 determined from the obtained stress-strain curve and taken as the 10% modulus. When the 10% modulus was 20 MPa or less, it was evaluated as having good flexibility (〇), and when the 10% modulus was greater than 20 MPa, it was evaluated as having poor flexibility (×).

[0037]

Table 1

[0038]

Table 2

[0039] The present disclosure includes the following inventions. Invention [1] A tube containing a thermoplastic resin composition having a sea-island structure composed of an island phase 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 a thermoplastic resin, the tube has a thickness of 0.1 mm or more, when the tube is cut in a plane including the central axis of the tube, among the cross-sections, the circularity of the island phase in the cross-section in the range 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 phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as the circularity (central), when the circularity (inner surface) and the circularity (central) satisfy the formulas (1) and (2): 0.35 ≦ circularity (inner surface) ≦ 1.0 ··· (1) 60 ≦ circularity (inner surface) / circularity (central) × 100 ≦ 120 ··· (2) the tube satisfying the above. Invention [2] When the tube is cut in a plane including the central axis of the tube, among the cross-sections, the aspect ratio of the island phase in the cross-section in the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as the aspect ratio (inner surface), and the aspect ratio of the island phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as the aspect ratio (central). When the aspect ratio (inner surface) and the aspect ratio (central) satisfy the formulas (3) and (4): 1 ≤ aspect ratio (inner surface) ≤ 3 ··· (3) 90 ≤ aspect ratio (inner surface) / aspect ratio (central) × 100 ≤ 150 ··· (4) The tube according to Invention [1], which satisfies the above conditions. Invention [3] The tube according to Invention [1] or [2], wherein the rubber contains an elastomer having a polyisobutylene skeleton. Invention [4] The tube according to Invention [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. Invention [5] The tube according to any one of Inventions [1] to [4], wherein the thermoplastic resin contains polyamide. Invention [6] The tube according to Invention [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. Invention [7] The tube according to any one of Inventions [1] to [6], wherein the rubber is crosslinked. Invention [8] A method for manufacturing the tube according to any one of Inventions [1] to [7], the method including a step of extruding a thermoplastic resin composition into a tube shape by draw-down extrusion molding.

Industrial Applicability

[0040] The tube of the present invention can be suitably used as the inner layer of a refrigerant transport hose.

Explanation of Signs

[0041] 1 Tube 2 Central axis 3 Inner surface of the tube 4 Outer surface of the tube 5 Central line in the thickness direction of the tube 6 Range from the inner surface of the tube to 5 μm in the thickness direction 7 Range of 5 μm at the center in the thickness direction of the tube 8 Line 2.5 μm away from the central line 5 of the tube in the thickness direction to the outside 9 Line 2.5 μm away from the central line 5 of the tube in the thickness direction to the inside 10 Die for draw extrusion molding 11 Die for solid extrusion molding 12 Core material 13 Thermoplastic resin composition 14 Die

Claims

1. A tube comprising a thermoplastic resin composition having a sea-island structure composed of an island phase 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 a thermoplastic resin, the tube has a thickness of 0.1 mm or more, when the tube is cut in a plane including the central axis of the tube, among the cross-sections, the circularity of the island phase in the cross-section in the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as circularity (inner surface), and the circularity of the island phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as circularity (central), when circularity (inner surface) and circularity (central) satisfy the formulas (1) and (2): 0.35 ≦ circularity (inner surface) ≦ 1.0... (1) 60 ≦ circularity (inner surface) / circularity (central) × 100 ≦ 120... (2) A tube satisfying the above.

2. When the tube is cut in a plane including the central axis of the tube, among the cross-sections, the aspect ratio of the island phase in the cross-section in the range of 5 μm in the thickness direction from the inner surface of the tube is referred to as aspect ratio (inner surface), and the aspect ratio of the island phase in the cross-section in the range of the central 5 μm in the thickness direction of the tube is referred to as aspect ratio (central), when aspect ratio (inner surface) and aspect ratio (central) satisfy the formulas (3) and (4): 1 ≦ aspect ratio (inner surface) ≦ 3... (3) 90 ≦ aspect ratio (inner surface) / aspect ratio (central) × 100 ≦ 150... (4) The tube according to Claim 1, satisfying the above.

3. The tube according to Claim 1, wherein the rubber contains an elastomer having a polyisobutylene backbone.

4. The tube according to Claim 3, wherein the elastomer having a polyisobutylene backbone 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 Claim 1, wherein the thermoplastic resin contains 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 claim 1, wherein the rubber is crosslinked.

8. A method for manufacturing the tube according to claim 1, the method comprising the step of extruding a thermoplastic resin composition into a tube shape by draw-down extrusion.

Images