Tube and manufacturing method thereof

Abstract

To provide a tube in which residual stress is eliminated while maintaining flexibility. [Solution] 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, the thermoplastic resin composition containing 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, in a 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 phases in a cross section within a range of 5 μm from the center in the thickness direction of the tube is referred to as the circularity (center), the circularity (inner surface) and the circularity (center) being expressed by formula (1) and formula (2): 0.35≦Circularity (inner surface)≦1.0 (1) 60≦Circularity(inner surface) / Circularity(center)×100≦120 (2) Meet the tube.

Description

[Technical field]

[0001] The present invention relates to a tube and a method for manufacturing the same. More particularly, the present invention relates to a tube having low residual stress and a method for manufacturing the same. [Background technology]

[0002] JP 2020-105284 A (Patent Document 1) discloses a refrigerant transport hose in which the inner layer of the hose for transporting refrigerant in an automobile air conditioner is extruded into a tube using a thermoplastic resin composition consisting of a matrix containing a thermoplastic resin and a domain containing rubber dispersed in the matrix. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-105284 A Summary of the Invention [Problem 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 in that it has residual stress, which is not preferable in the hot environment in which the hose is used. The present invention provides a tube that eliminates residual stress while maintaining flexibility. [Means for solving the problem]

[0005] The present invention (I) is a tube containing a thermoplastic resin composition having a sea-island structure consisting of an island phase containing a 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 along a plane including the central axis, the circularity of the island phase in a cross section ranging from the inner surface of the tube to 5 μm in the thickness direction is called the circularity (inner surface), and the circularity of the island phase in a cross section ranging from the center 5 μm in the thickness direction of the tube is called the circularity (center). The circularity (inner surface) and the circularity (center) are expressed by 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 is characterized in that: 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 extrusion molding.

[0006] The present invention includes the following embodiments. [1] A tube comprising a thermoplastic resin composition having a sea-island structure consisting of an island phase containing a 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 along a plane including the central axis, the circularity of the island phase in a cross section ranging from the inner surface of the tube to 5 μm in the thickness direction is called the circularity (inner surface), and the circularity of the island phase in a cross section ranging from the center 5 μm in the thickness direction of the tube is called the circularity (center). The circularity (inner surface) and the circularity (center) are expressed by the following formulas (1) and (2): 0.35≦Circularity (inner surface)≦1.0 (1) 60≦Circularity(inner surface) / Circularity(center)×100≦120 (2) Meet the tube. [2] When the tube is cut along a plane including the central axis, the aspect ratio of the island phase in the cross section from the inner surface of the tube to 5 μm in the thickness direction is called the aspect ratio (inner surface), and the aspect ratio of the island phase in the cross section within the central 5 μm in the thickness direction of the tube is called the aspect ratio (center). The aspect ratio (inner surface) and the aspect ratio (center) are expressed by Equation (3) and Equation (4): 1≦aspect ratio (inner surface)≦3 (3) 90≦aspect ratio(inner surface) / aspect ratio(center)×100≦150 (4) The tube described in [1] satisfies the above. [3] The tube described in [1], 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 [1], wherein the thermoplastic resin comprises 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 described in [1], wherein the rubber is crosslinked. [8] A method for producing the tube described in [1], the method comprising the step of extruding a thermoplastic resin composition into a tubular shape by draw extrusion. Effect of the Invention

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

[0008] [Figure 1] FIG. 1 is a scanning probe micrograph of a cross section of the tube of Example 1. [Diagram 2] FIG. 2 is a scanning probe micrograph of a cross section of the tube of Example 2. [Diagram 3] FIG. 3 is a scanning probe micrograph of a cross section of the tube of Example 3. [Figure 4] FIG. 4 is a scanning probe micrograph of a cross section of the tube of Example 5. [Diagram 5] FIG. 5 is a scanning probe micrograph of a cross section of the tube of Example 6. [Figure 6] FIG. 6 is a scanning probe micrograph of a cross section of the tube of Example 7. [Figure 7] FIG. 7 is a scanning probe microscope photograph of a cross section of the tube of Comparative Example 1. [Figure 8] FIG. 8 shows a cross section of the tube from which the micrograph was taken. [Figure 9] FIG. 9 is a diagram for explaining the method of the curl test. [Figure 10] FIG. 10 is a schematic cross-sectional view of a die for draw extrusion molding. [Figure 11] FIG. 11 is a schematic cross-sectional view of a die for solid extrusion molding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention relates to a tube comprising a thermoplastic resin composition having a sea-island structure composed of an island phase containing a 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 along a plane including the central axis, the circularity of the island phase in a cross section ranging from the inner surface of the tube to 5 μm in the thickness direction is called the circularity (inner surface), and the circularity of the island phase in a cross section ranging from the center 5 μm in the thickness direction of the tube is called the circularity (center). The circularity (inner surface) and the circularity (center) are expressed by 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 is characterized in that:

[0010] FIG. 8 is a diagram showing a cross section of a tube 1 for taking a microphotograph. FIG. 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 FIG. 8(b) is an enlarged view of the circled portion of 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 center line in the thickness direction of the tube, 6 is a range from the inner surface of the tube to 5 μm in the thickness direction, and 7 is a range of 5 μm in the thickness direction of the tube. The range 7 of 5 μm in the thickness direction of the tube is, in other words, a range sandwiched between a line 8 2.5 μm away from the center line 5 in the thickness direction of the tube and a line 9 2.5 μm away 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 phase in a cross section of the tube 1 in a range 6 from the inner surface 3 to 5 μm in the thickness direction is referred to as the circularity (inner surface), and the circularity of the island phase in a cross section of the tube in a range 7 of 5 μm from the center in the thickness direction is referred to as the circularity (center), and the circularity (inner surface) and the circularity (center) are expressed by the following formulas (1) and (2): 0.35≦Circularity (inner surface)≦1.0 (1) 60≦Circularity(inner surface) / Circularity(center)×100≦120 (2) Meet the following. The tube of the present invention preferably has the formula (1'): 0.36≦Circularity (inner surface)≦1.0 (1′) More preferably, the formula (1″): 0.38≦Circularity (inner surface)≦1.0 (1″) Meet the following. The tube of the present invention preferably has the formula (2'): 65≦Circularity(inner surface) / Circularity(center)×100≦120 (2′) More preferably, the formula (2" is satisfied): 70≦Circularity(inner surface) / Circularity(center)×100≦115 (2″) Meet the following. 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 occurrence of cracks is small.

[0012] Here, the circularity is defined by 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 cross section of the tube 1 is cut along a plane including the central axis 2 of the tube 1, the aspect ratio of the island phase in a cross section of the tube 1 in a range 6 from the inner surface 3 to 5 μm in the thickness direction is referred to as the aspect ratio (inner surface), and the aspect ratio of the island phase in a cross section of the tube 1 in a central 5 μm range 7 in the thickness direction is referred to as the aspect ratio (center). The aspect ratio (inner surface) and the aspect ratio (center) preferably 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) Meet the following. The tube of the present invention is more preferably a tube of the formula (3'): 1≦Aspect ratio (inner surface)≦2.9 (3′) and more preferably satisfies formula (3″): 1≦Aspect ratio (inner surface)≦2.85 … (3″) Meet the following. The tube of the present invention is more preferably a tube of the formula (4'): 90≦aspect ratio(inner surface) / aspect ratio(center)×100≦148 (4′) and more preferably satisfies formula (4″): 100≦aspect ratio(inner surface) / aspect ratio(center)×100≦145 ··· (4″) Meet the following. By satisfying formulas (3) and (4), the tube has even less residual stress, and when the tube is used as the inner layer of a hose for transporting a refrigerant, 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 approximating one island phase to an ellipse. The ellipse approximation can be performed by measurement using the Fit Ellipse function of 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 with an atomic force microscope (AFM) which is a scanning probe microscope (SPM). There is no particular limit to the measurement mode, but tapping mode is preferably used. Also, observation may be performed using an electron microscope (scanning electron microscope (SEM), transmission electron microscope (TEM)), etc. A cross section of 5 μm long and 5 μm wide was photographed using a microscope. The cross-sectional image was binarized using the image processing software ImageJ, with the histogram peaks and the middle of the peaks as the boundaries. 2 For all islands having an area of ​​10,000 nm or more, the circularity is calculated and the average value is calculated. 2 For all islands having an area equal to or greater than this, an ellipse approximation is performed to determine the major and minor axes, the aspect ratio (major axis / minor axis) is calculated, and the average value is calculated.

[0016] Figure 1 shows scanning probe micrographs of a cross section of the tube of Example 1. Figure 1(a) shows a scanning probe micrograph of a cross section ranging from the inner surface of the tube of Example 1 to 5 µm in the thickness direction, and Figure 1(b) shows a scanning probe micrograph of a cross section ranging from the central 5 µm in the thickness direction of the tube of Example 1. Similarly, Figure 2 shows scanning probe micrographs of the cross sections of the tubes of Example 2, Figure 3 shows Example 3, Figure 4 shows Example 5, Figure 5 shows Example 6, Figure 6 shows Example 7, and Figure 7 shows Comparative Example 1, where (a) shows a scanning probe micrograph of the cross section in the range from the inner surface of the tube to 5 μm in the thickness direction, and (b) shows a scanning probe micrograph of the cross section in the range of 5 μm in the center of the thickness direction of the tube.

[0017] In conventional tubes, the island phase on the inner surface side is stretched, and 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 Figure 7). It is believed that the difference in morphology between the inner surface and the center in the thickness direction causes residual stress. Hoses using tubes with residual stress are subject to shape changes 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 an island phase containing a rubber and a sea phase containing a thermoplastic resin. The thermoplastic resin composition constituting the tube of the present invention has an island-in-a-sea structure consisting of an island phase and a sea phase. The island-in-a-sea structure allows the compounding of a large amount of rubber while maintaining gas barrier properties, and makes it possible to achieve both flexibility and gas barrier properties.

[0019] The island facies contains rubber. The rubber preferably includes, but is not limited to, an elastomer having a polyisobutylene backbone. A polyisobutylene backbone is a chemical structure formed by polymerizing a plurality of isobutylene units, i.e., -[-CH2-C(CH3)2-] n- (where n is an integer of 2 or more). When the rubber contains an elastomer with a polyisobutylene skeleton, it is 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 impaired.

[0020] The marine phase comprises a thermoplastic resin. The thermoplastic resin is not limited, but preferably contains polyamide. When the thermoplastic resin contains polyamide, it is possible to achieve both flexibility and gas barrier properties. The polyamide is preferably, but not limited to, 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 the thermoplastic resin are within this range, a dispersed form of a sea-island structure in which the rubber forms an island phase 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, a processing aid, etc.

[0023] The thermoplastic resin composition preferably contains an antioxidant. When the thermoplastic resin composition contains an antioxidant, 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 in its molecular structure an aromatic ring having two secondary amines as substituents, and 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 the rubber and the 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 containing the viscosity stabilizer, the 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 good processability. Viscosity stabilizers include divalent metal oxides, ammonium salts, and carboxylates. Examples of the divalent metal oxide include zinc oxide, magnesium oxide, copper oxide, calcium oxide, and iron oxide, with zinc oxide or magnesium oxide being preferred, and zinc oxide being more preferred. Examples of the ammonium salt include ammonium carbonate, ammonium hydrogen carbonate, ammonium chloride, ammonium bromide, ammonium sulfate, ammonium nitrate, ammonium acetate, and alkyl ammonium. Examples of the carboxylate include sodium acetate, potassium acetate, zinc acetate, copper acetate, sodium oxalate, ammonium oxalate, calcium oxalate, and iron oxalate. The viscosity stabilizer is most preferably 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, the 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 good processability.

[0025] The thermoplastic resin composition preferably contains a processing aid, which contributes to improving the extrusion processability of the thermoplastic resin composition. Examples of the processing aid 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 the fatty acid amide 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 the rubber and the thermoplastic resin.

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

[0027] The method for producing the tube of the present invention is not particularly limited, and a known general production method can be used. Specifically, it is possible to adopt solid extrusion molding or draw-down extrusion molding, which are known as extrusion molding methods for electric wires, etc. By controlling the extrusion conditions, such as the extrusion set temperature (die temperature), extrusion rotation speed (extruder screw rotation speed), tube thickness, tube inner diameter, etc., 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 more and 260° C. or less. If the temperature is less than 230° C., the extrusion torque increases, resulting in poor processability. If the temperature is more than 260° C., scorching may occur during retention in the extruder, resulting in poor appearance. The screw rotation speed during extrusion of the thermoplastic resin composition varies depending on the size of the extruder and the type of the screw, but for example, in a 40 mmΦ single screw extruder, it can be 8 rpm to 50 rpm. If it is 8 rpm or less, the residence time will be long, and material deterioration will be accelerated. If it is 50 rpm or more, excessive shear heat will be generated, and material deterioration will be accelerated.

[0028] The present invention (II) relates to a method for producing the tube of the present invention (I), wherein 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 molding. 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. Draw-down extrusion molding is a molding method in which a core material 12 and a molten thermoplastic resin composition 13 come into contact with each other outside a mold 10 after leaving a die 14, as shown in FIG. On the other hand, solid extrusion molding is a molding method characterized in that a core material 12 and a molten thermoplastic resin composition 13 come into contact with each other under pressure within a die 14 . The outer diameter of the core material 12 is, for example, not less than 8 mm and not more than 25 mm. In the draw-down extrusion molding, internally pressurized air may be used instead of using a core material, and the die shown in FIG. 10 does not necessarily have to be used. The cross-sectional area draw-down ratio in the draw-down extrusion molding is preferably from 1 to 100. If it is within the preferred range, a molding speed sufficient for productivity can be obtained, and mechanical properties become good. The drawdown balance in the drawdown extrusion molding is preferably 1.00 or more and 1.20 or less. If it is in the preferred range, the dimensional stability during molding is good. The cross-sectional area drawdown rate and the drawdown balance are defined by equations (6) and (7). Cross-sectional area drawdown rate = (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 an inner layer of a hose, including, but not limited to, a hose for transporting refrigerants. Specific examples of hoses using the tube of the present invention include hoses containing the tube of the present invention as an inner layer, or hoses containing an inner layer, a reinforcing layer, and an outer layer, characterized in that the inner layer is the tube of the present invention. EXAMPLES

[0030] [raw materials] The raw materials used in the following examples and comparative examples are as follows. Butyl rubber: ExxonMobil Chemical's brominated isobutylene-p-methylstyrene copolymer rubber "EXXPRO" (registered trademark) 3745 Acid-modified polyolefin: Maleic acid-modified α-olefin copolymer "Tafmer" (registered trademark) MH7010 manufactured by Mitsui Chemicals, Inc. Polyamide 6: Ube Industries, Ltd. Polyamide 6 "UBE Nylon" (registered trademark) 1011FB Polyamide 6 / 12: Polyamide 6 / 12 copolymer "UBE Nylon" (registered trademark) 7024B manufactured by Ube Industries, Ltd. Polyamide 12: UBE STA (registered trademark) 3012U, polyamide 12 manufactured by Ube Industries, Ltd. Antioxidant: Solutia's phenylenediamine-based antioxidant "SANTOFLEX" (registered trademark) 6PPD (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 master batch, 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 fed 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 a pellet-shaped thermoplastic resin composition for the inner layer.

[0032] [Tube creation] The thermoplastic resin composition was extruded onto the core material in a tubular shape using a 40 mmφ extruder under the conditions shown in Tables 1 and 2, and the core material was removed to prepare a tube. In the table, "drawdown" means that the product was produced by drawdown extrusion molding, and indicates that a manufacturing method was used in which the thermoplastic resin composition was brought into contact with the core material outside the mold, as shown in Figure 10. In the table, "solid" means that it was produced by solid extrusion molding, and indicates that a manufacturing method was used in which the thermoplastic resin composition core material was in contact inside the mold, as shown in Figure 11. The thermoplastic resin composition of Comparative Example 2 was not suitable for making a tube, so no tube was produced.

[0033] The circularity and aspect ratio of the island phases of the produced tubes were evaluated, and a curl test was performed. 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 islands] The cross section of the tube cut on a plane passing through the central axis of the tube was photographed with an atomic force microscope (AFM) (scanning probe microscope (SPM)) in tapping mode over an area of ​​5 μm vertical and 5 μm horizontal. The cross section image was binarized using the image processing software ImageJ with the histogram peaks and the middle of the peaks as boundaries. 2 For all islands having an area of ​​10,000 nm or more, the circularity (Circ. term) was calculated and the average value was calculated. 2 For all islands with an area equal to or greater than this, an 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 calculated.

[0035] [Curl test] A test piece with the shape shown in Figure 9(a) is cut out from the tube, and placed in an oven with the thin part facing up and held vertically. It is heated at 150°C for 30 minutes, and the curl after heating is observed. The test piece bends toward the inner surface when heated, which indicates that the shrinkage force is greater on the inner surface than on the outer surface, and 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 length direction of the thick part (vertical line) is defined as the curl angle. The larger the curl angle, the greater the residual stress on the inner surface side is judged to be. A curl angle of less than 10° is displayed as ◯, and a curl angle of 10° or more is displayed as ×.

[0036] [Flexibility] The thermoplastic resin composition was molded into a sheet with 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 sheets thus produced, with an average thickness of 1.0 mm, were punched out into JIS No. 6 dumbbell shapes, and tensile tests were carried out 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. A 10% modulus of 20 MPa or less was evaluated as having good flexibility (◯), and a 10% modulus of more than 20 MPa was evaluated as having poor flexibility (×).

[0037] [Table 1]

[0038] [Table 2]

[0039] The present disclosure includes the following inventions. Invention [1] A tube comprising a thermoplastic resin composition having a sea-island structure consisting 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 along a plane including the central axis, the circularity of the island phase in a cross section ranging from the inner surface of the tube to 5 μm in the thickness direction is called the circularity (inner surface), and the circularity of the island phase in a cross section ranging from the center 5 μm in the thickness direction of the tube is called the circularity (center). The circularity (inner surface) and the circularity (center) are expressed by the following formulas (1) and (2): 0.35≦Circularity (inner surface)≦1.0 (1) 60≦Circularity(inner surface) / Circularity(center)×100≦120 (2) Meet the tube. Invention [2] When the aspect ratio of the island phase in a cross section of the tube cut along a plane including the central axis thereof is defined as the aspect ratio (inner surface) in the range from the inner surface of the tube to 5 μm in the thickness direction, and the aspect ratio of the island phase in a cross section of the tube within the central 5 μm in the thickness direction is defined as the aspect ratio (center), the aspect ratio (inner surface) and the aspect ratio (center) are expressed by the following formulas (3) and (4): 1≦aspect ratio (inner surface)≦3 (3) 90≦aspect ratio(inner surface) / aspect ratio(center)×100≦150 (4) The tube according to the invention [1] satisfies the above requirements. Invention [3] The tube according to invention [1] or [2], wherein the rubber comprises 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 comprises 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 producing a tube according to any one of Inventions [1] to [7], the method comprising a step of extruding a thermoplastic resin composition into a tubular shape by draw extrusion molding. [Industrial Applicability]

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

[0041] 1 tube 2 center axis 3. Inside surface of tube 4. Outer surface of tube 5 Center line of tube thickness 6 Within 5μm from the inner surface of the tube in the thickness direction 7. Within the central 5 μm area of ​​the tube thickness 8. A line 2.5 μm away from the center line 5 in the thickness direction of the tube 9 A line 2.5 μm inward from the center line 5 in the thickness direction of the tube 10. Die for drawing extrusion 11 Extrusion molding die 12 Core material 13 Thermoplastic resin composition 14 Dice

Claims

1. A method for producing a tube containing a thermoplastic resin composition having an island-in-sea structure composed of an island phase containing a rubber and a sea phase containing a thermoplastic resin, comprising the steps of: The thermoplastic resin composition comprises 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, In a cross section of the tube cut along a plane including the central axis of the tube, the circularity of the island phase 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 phase in a cross section extending 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) are expressed by the following formulas (1) and (2): 0.35≦Circularity (inner surface)≦1.0 (1) 60≦Circularity (inner surface) / Circularity (center)×100≦120 (2) Fulfilling When the aspect ratio of the island phase in a cross section ranging from the inner surface to 5 μm 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 ranging from the center 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) are expressed by the following formulas (3) and (4): 1≦aspect ratio (inner surface)≦3 ... (3) 90≦aspect ratio (inner surface) / aspect ratio (center)×100≦150 … (4) Fulfilling The method includes the steps of extruding a thermoplastic resin composition into a tubular shape by draw extrusion; The cross-sectional area draw-down ratio in the draw-down extrusion molding is 1 or more and 100 or less, The method of claim 1, wherein the drawdown balance in the drawdown extrusion is 1.00 or more and 1.20 or less.

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

3. The method according to claim 2, 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.

4. The method of claim 1 , wherein the thermoplastic resin comprises a polyamide.

5. The method according to claim 4, 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.

6. The method of claim 1 wherein the rubber is crosslinked.

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