Tube and method for manufacturing a tube

Abstract

The present invention provides a tube having relatively high tear resistance in the longitudinal direction, and a method for manufacturing the tube. [Solution] The tube is made of one or more types of thermoplastic resin. In this tube, multiple regularly arranged air bubbles are formed inside, and the multiple air bubbles provide tearability in the longitudinal direction.

Description

Technical Field

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[0001] The present invention relates to a tube and a method for manufacturing the tube.

Background Art

[0002] Japanese Patent No. 6791858 (Patent Document 1) discloses a fluororesin tube having tearability in the longitudinal direction. In this fluororesin tube, for example, excellent tearability is realized by forming a weld line in the longitudinal direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tube having relatively high tearability in the longitudinal direction and a method for manufacturing the tube.

Means for Solving the Problems

[0005] A tube according to an aspect of the present invention is composed of one or more types of thermoplastic resins. In this tube, a plurality of regularly arranged bubbles are formed inside, and the plurality of bubbles impart tearability in the longitudinal direction.

[0006] In this tube, tearability in the longitudinal direction is imparted by a plurality of regularly arranged bubbles. Therefore, according to this tube, higher tearability in the longitudinal direction can be realized as compared with the case where a plurality of regularly arranged bubbles are not formed inside.

[0007] In this tube, when the tube is cut perpendicular to its length, multiple air bubbles may be arranged radially in the cross-section.

[0008] In this tube, multiple air bubbles are arranged radially. Therefore, this tube can provide tear resistance along the length at various locations.

[0009] This tube may be heat-shrinkable.

[0010] In this tube, one or more types of thermoplastic resin may include at least one of a tetrafluoroethylene-hexafluoropropylene copolymer and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0011] A method for manufacturing a tube according to another aspect of the present invention is the tube manufacturing method described above. This tube manufacturing method includes the step of manufacturing a tube by performing extrusion molding while a thermoplastic resin is supplied in a starved state.

[0012] In this tube manufacturing method, extrusion molding is performed with a starved supply of thermoplastic resin. In this case, multiple air bubbles are incorporated into the thermoplastic resin during extrusion molding. These multiple air bubbles incorporated into the thermoplastic resin concentrate in areas with relatively low pressure. As a result, the multiple air bubbles are arranged regularly in the manufactured tube. Consequently, this tube manufacturing method makes it possible to produce a tube with relatively high tear resistance in the longitudinal direction. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a tube having relatively high tear resistance in the longitudinal direction, and a method for manufacturing the tube. [Brief explanation of the drawing]

[0014] [Figure 1]It is a plan view schematically showing a tube. [Figure 2] It is a view schematically showing a cross section taken along line II-II in FIG. 1. [Figure 3] It is a side cross-sectional view schematically showing a manufacturing apparatus for a tube. [Figure 4] It is a cross-sectional view taken along line IV-IV of the spider in FIG. 3. [Figure 5] It is a view for explaining a first other example of a formation pattern of a group including a plurality of bubbles. [Figure 6] It is a view for explaining a second other example of a formation pattern of a group including a plurality of bubbles. [Figure 7] It is a view for explaining a first other example of an arrangement of a plurality of bubbles. [Figure 8] It is a view for explaining a second other example of an arrangement of a plurality of bubbles. [Figure 9] It is a view showing a cross-sectional photograph of a tube of an example. [Figure 10] It is a view showing the transition of a test force when a tube of an example is torn. [Figure 11] It is a view showing the transition of a test force when a tube of Comparative Example 1 is torn. [Figure 12] It is a view showing the transition of a test force when a tube of Comparative Example 2 is torn.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments according to one aspect of the present invention (hereinafter, also referred to as "the present embodiments") will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated. Also, for ease of understanding, each drawing is schematically drawn with appropriate omissions or exaggerations of the subject.

[0016] [1. Configuration of Tube] FIG. 1 is a plan view schematically showing a tube 10 according to the present embodiment. Referring to FIG. 1, the tube 10 is made of, for example, a thermoplastic resin and has heat shrinkability. This heat shrinkability can be suitably imparted, for example, by expanding the inner diameter of a thermoplastic resin tube in a heated state by applying pressure from the inside. The tube 10 has a cylindrical shape, and a space 12 is formed by the inner peripheral surface of the tube 10. For example, when covering (temporarily covering) products such as electric wires, lead wires, catheters, guide wires, etc. with the tube 10, these products are inserted into the tube 10 having heat shrinkability, and the tube 10 is heat-shrunk, whereby the tube 10 can be suitably adhered to and covered these products.

[0017] The tube 10 is made of, for example, a thermoplastic fluororesin. The thermoplastic fluororesin is preferably a thermoplastic resin that can be formed into a tube shape by heat-melting extrusion molding at a temperature of about 260°C - 450°C, preferably about 280°C - 420°C.

[0018] Examples of the thermoplastic fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0019] From the viewpoint of imparting particularly excellent tear resistance to the tube 10, the thermoplastic fluororesin is preferably a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

[0020] Figure 2 is a schematic diagram showing the II-II cross-section of Figure 1. As shown in Figure 2, this cross-section (the cross-section obtained when the tube 10 is cut perpendicular to the length direction of the tube 10) shows that multiple weld lines L1 are formed at certain intervals in the circumferential direction. For example, the multiple weld lines L1 are formed at approximately 45-degree intervals in the circumferential direction.

[0021] Furthermore, this cross-section reveals that multiple bubbles B1 are arranged regularly. "Multiple bubbles B1 are arranged regularly" means that the bubbles B1 are not evenly distributed throughout, but rather concentrated in specific areas. In this example, the bubbles B1 are not evenly distributed throughout, but rather arranged radially. More specifically, multiple groups G1, each composed of multiple bubbles B1, are formed at certain intervals in the circumferential direction. For example, groups G1 are formed approximately every 45 degrees in the circumferential direction. Each group G1 is located between two adjacent weld lines L1. In each group G1, at least two bubbles intersect a hypothetical straight line passing through the center of the tube 10. Because the parts other than groups G1 are transparent, the inside of the tube 10 is easily visible.

[0022] Each of the multiple air bubbles B1 extends in the longitudinal direction of the tube 10. When the tube 10 is torn, each group G1 acts as the trigger for the tear. In other words, in the tube 10, tearability in the longitudinal direction is provided by the multiple air bubbles B1 arranged regularly. Therefore, the tube 10 can achieve higher tearability in the longitudinal direction compared to a tube in which multiple air bubbles B1 are not formed inside. In addition, in the tube 10, the multiple air bubbles B1 are arranged radially. Therefore, the tube 10 can provide tearability in the longitudinal direction at various positions. On the other hand, because the strength of the parts other than group G1 is sufficiently high, the tube 10 achieves sufficiently high tensile strength and bending strength.

[0023] [2. Method for manufacturing tubes] Figure 3 is a schematic side cross-sectional view showing the manufacturing apparatus 20 for the tube 10. As shown in Figure 3, the manufacturing apparatus 20 is an extrusion machine, for example, a single-screw extruder. The manufacturing apparatus 20 includes, for example, a cylinder 22 with a circular cross-section and a spider 24 positioned inside the cylinder 22.

[0024] When the manufacturing apparatus 20 is in operation, the inside of the cylinder 22 is heated, and the molten state of the material flowing inside is maintained. The spider 24 is a mold and is movable both upstream and downstream within the cylinder 22. The thermoplastic resin, which is the material for the tube 10, is extruded in a molten state from the upstream to the downstream direction of the cylinder 22.

[0025] Figure 4 is a cross-sectional view of the spider 24 along line IV-IV in Figure 3. As shown in Figure 4, the spider 24 includes an inner circumferential base 25, an outer circumferential base 26, and a number of legs 27 (eight in this example) provided between the inner circumferential base 25 and the outer circumferential base 26. The number of legs 27 extends radially from the inner circumferential base 25 to the outer circumferential base 26. The thermoplastic resin flowing through the cylinder 22 is temporarily branched by the legs 27, passes through the flow path 28, and then rejoins. This forms a weld line L1 in the tube 10.

[0026] In the manufacture of the tube 10, extrusion molding is performed with the thermoplastic resin supplied to the cylinder 22 in a starved state. For example, the starved state in the cylinder 22 is preferably 5% or more and 45% or less, preferably 10% or more and 40% or less, and more preferably 15% or more and 30% or less. By performing extrusion molding with the thermoplastic resin supplied to the cylinder 22 in a starved state, multiple air bubbles B1 are incorporated into the thermoplastic resin during extrusion molding. The multiple air bubbles B1 incorporated into the thermoplastic resin concentrate in areas with relatively low pressure. In this example, multiple air bubbles B1 concentrate in the region between two adjacent weld lines L1. That is, in the tube 10, the multiple air bubbles B1 are arranged regularly. As a result, relatively high tear resistance in the longitudinal direction is achieved in the tube 10.

[0027] [3. Features] As described above, in the tube 10 according to this embodiment, tear resistance in the longitudinal direction is provided by a plurality of regularly arranged air bubbles B1. Therefore, the tube 10 can achieve higher tear resistance in the longitudinal direction compared to a case where a plurality of regularly arranged air bubbles B1 are not formed inside.

[0028] [4. Other Embodiments] The concept of the above embodiment is not limited to the embodiment described above. Below, an example of another embodiment to which the concept of the above embodiment can be applied will be described.

[0029] <4-1> In the above embodiment, multiple weld lines L1 were formed in the tube 10. However, in the tube 10, multiple weld lines L1 are not necessarily formed, as long as multiple regularly arranged air bubbles B1 are formed inside.

[0030] <4-2> Furthermore, in the above embodiment, groups G1 were formed at approximately 45-degree intervals in the circumferential direction. However, the formation pattern of groups G1 is not limited to this.

[0031] Figure 5 is a diagram illustrating a first other example of a group G1 formation pattern containing multiple bubbles B1. Referring to Figure 5, in tube 10A, when tube 10A is cut in a direction perpendicular to the longitudinal direction, groups G1 are formed at intervals of approximately 180 degrees in the cross-section. The formation pattern of group G1 may be as shown. The interval at which groups G1 are formed may be any degree.

[0032] Figure 6 is a diagram illustrating a second example of a group G1 formation pattern containing multiple bubbles B1. Referring to Figure 6, in tube 10B, only one group G1 may be formed in the cross-section when tube 10B is cut in a direction perpendicular to the longitudinal direction. The formation pattern of group G1 may be as follows.

[0033] <4-3> Furthermore, the arrangement of the multiple bubbles B1 is not limited to that shown in the above embodiment. Compared to the above embodiment, the multiple bubbles B1 may be spread out in the circumferential direction, or they may be concentrated in one part of the inner circumference and the outer circumference.

[0034] Figure 7 is a diagram illustrating another first example of the arrangement of multiple bubbles B1. Referring to Figure 7, in tube 10C, the multiple bubbles B1 are spread circumferentially compared to those shown in the above embodiment. The arrangement of multiple bubbles B1 may be as follows.

[0035] Figure 8 is a diagram illustrating a second alternative example of the arrangement of multiple bubbles B1. Referring to Figure 8, in tube 10D, the multiple bubbles B1 are concentrated closer to the inner circumference compared to the embodiment shown above. The arrangement of multiple bubbles B1 may be as shown.

[0036] <4-4> Furthermore, in the above embodiment, the tube 10 was made of one type of thermoplastic resin. However, the tube 10 does not necessarily have to be made of one type of thermoplastic resin. The tube 10 may be made of multiple thermoplastic resins. In this case, it is preferable that the multiple thermoplastic resins include at least one of a tetrafluoroethylene-hexafluoropropylene copolymer and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0037] <4-5> Furthermore, in the above embodiment, bubbles B1 were formed inside the tube 10 due to air incorporated into the thermoplastic resin by extrusion molding in a starved state. However, the bubbles B1 formed inside the tube 10 do not necessarily have to be formed due to air incorporated into the thermoplastic resin by extrusion molding in a starved state. The bubbles B1 formed inside the tube 10 may be formed, for example, due to water vapor or foaming components incorporated into the thermoplastic resin.

[0038] Embodiments of the present invention have been described illustratively above. That is, a detailed description and accompanying drawings have been disclosed for illustrative purposes. Therefore, some of the components described in the detailed description and accompanying drawings may not be essential for solving the problem. Consequently, the mere fact that these non-essential components are described in the detailed description and accompanying drawings does not mean that they should be immediately assumed to be essential.

[0039] Furthermore, the above embodiments are merely illustrative in every respect of the present invention. The above embodiments can be improved or modified in various ways within the scope of the present invention. For example, at least a part of the configuration of one embodiment may be combined with at least a part of the configuration of any other embodiment. In other words, in carrying out the present invention, specific configurations can be appropriately adopted depending on the embodiment. [Examples]

[0040] The following describes embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

[0041] [1. Examples and Comparative Examples] Tubes for Example and Comparative Examples 1 and 2 were manufactured by extruding FEP resin (MFR: 6-7 g / min) using a 20 mm extruder. When manufacturing the tube for Example, the screw rotation speed was 9 rotations / min, the resin discharge rate was 360 g / h, and the starvation rate was 26%. When manufacturing the tube for Comparative Example 1, the screw rotation speed was 6 rotations / min, the resin discharge rate was 324.2 g / h, and the starvation rate was 0%. When manufacturing the tube for Comparative Example 2, the screw rotation speed was 6 rotations / min, the resin discharge rate was 348.8 g / h, and the starvation rate was 0%.

[0042] Figure 9 is a cross-sectional photograph of the tube in the example. As shown in Figure 9, in the tube in the example, multiple air bubbles were arranged radially inside. On the other hand, in the tubes of Comparative Examples 1 and 2, no air bubbles were arranged inside.

[0043] [2. Various Tests] <2-1. Tear resistance evaluation> The ability to tear each tube by hand was evaluated by having the worker tear each tube by hand. Specifically, eight tubes of each type (Example and Comparative Examples 1 and 2) were prepared, and the number of tubes out of the eight that could be torn by hand was evaluated for each type of tube.

[0044] <2-2. Measurement of tear strength> For each tube (100 mm in length) in the Examples and Comparative Examples 1 and 2, a 40 mm cut was made at one end, and the test force (N) was measured by tearing it at a speed of 200 mm / min using a tensile testing machine. The test force was the average value of the test force in the stable section of the tube after it began to tear (hereinafter also referred to as the "steady-state tear section"). The tear strength was calculated by dividing the average value of the test force in the steady-state tear section by twice the wall thickness.

[0045] [3. Test Results] <3-1. Results of tear resistance evaluation> Regarding the tubes in the example, all eight tubes could be torn by hand. Regarding the tubes in Comparative Example 1, five out of eight tubes could be torn by hand (three tubes could not be torn by hand). Regarding the tubes in Comparative Example 2, all eight tubes could be torn by hand.

[0046] <3-2. Results of tear strength measurement> Figure 10 shows the change in test force during tearing of the tube in the example. Referring to Figure 10, the tear strength of the tube in the example was calculated by dividing the average value of the test force in the steady-state tearing section by twice the wall thickness, and the result was 1.5 N / mm. In the tube in the example, the difference between the test force at the start of tearing and the test force in the steady-state tearing section was small. For example, the difference between the test force at the start of tearing and the maximum value of the test force in the steady-state tearing section was less than 30%.

[0047] Figure 11 shows the change in test force during tearing of the tube of Comparative Example 1. Referring to Figure 11, the tear strength of the tube of Comparative Example 1 was calculated by dividing the average value of the test force in the steady-state tearing section by twice the wall thickness, and the result was 5.3 N / mm. In the tube of Comparative Example 1, the difference between the test force at the start of tearing and the test force in the steady-state tearing section was larger compared to the tube of the example.

[0048] Figure 12 shows the change in test force during tearing of the tube of Comparative Example 2. Referring to Figure 12, the tear strength of the tube of Comparative Example 2 was calculated by dividing the average value of the test force in the steady-state tearing section by twice the wall thickness, and the result was 6.1 N / mm. In the tube of Comparative Example 2, the difference between the test force at the start of tearing and the test force in the steady-state tearing section was larger compared to the tube of the example. [Explanation of Symbols]

[0049] 10, 10A, 10B, 10C, 10D Tubes, 12 Space, 20 Manufacturing equipment, 22 Cylinder, 24 Spider, 25 Inner base, 26 Outer base, 27 Legs, 28 Flow path, B1 Bubble, G1 Group, L1 Weld line.

Claims

1. A tube made of one or more types of thermoplastic resin, Multiple bubbles are formed inside, arranged in a regular pattern. A tube in which tearability in the longitudinal direction is provided by the aforementioned plurality of air bubbles.

2. The tube according to claim 1, wherein when the tube is cut in a direction perpendicular to the longitudinal direction, the plurality of air bubbles are arranged radially when the cross-section is viewed.

3. A tube according to claim 1 or claim 2, which is heat-shrinkable.

4. The tube according to claim 1 or claim 2, wherein the one or more types of thermoplastic resins include at least one of a tetrafluoroethylene-hexafluoropropylene copolymer and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

5. A method for manufacturing a tube according to claim 1 or claim 2, A method for manufacturing a tube, comprising the step of manufacturing the tube by performing extrusion molding while the thermoplastic resin is supplied in a starvation state.

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