Fluororesin multi-layer tube

Abstract

To provide a fluorine resin multilayer tube that achieves both of resistance to elongation in a longitudinal direction and flexibility for bending and has excellent permeation resistance and airtightness.SOLUTION: A fluorine resin multilayer tube has an inner layer that contains a polytetrafluoroethylene resin and has a solid structure, and an outer layer that is in contact with the inner layer, wherein the outer layer contains a polytetrafluoroethylene resin and has a porous structure. The inner layer has the inner thickness that is smaller than the outer thickness of the outer layer. The inner thickness is 2 μm or more and 30 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-layer fluororesin tube. [Background technology]

[0002] Polytetrafluoroethylene (PTFE) resin tubes are used in a wide range of fields due to their excellent lubricity, chemical resistance, and heat resistance. PTFE also has a low coefficient of friction, and is often used for sliding purposes. For example, in catheter treatment, PTFE resin tubes are used as the interior material of catheters to allow treatment tools to pass smoothly through the catheter.

[0003] For catheters that pass through blood vessels, soft tubes are preferred so as not to damage the blood vessels. In particular, the tip of the catheter is required to be very flexible. However, when using a soft tube, there is a drawback in that the tube stretches in the longitudinal direction of the product when passing a treatment tool through the tube, making it difficult to pass the treatment tool through. The elongation stress of the PTFE tube in the longitudinal direction of the product is largely due to the stress of PTFE. It is possible to increase the thickness of the PTFE to increase the stress in order to suppress deformation, but there is a problem that the thicker the PTFE, the harder it becomes. To solve these problems, a porous PTFE made of fibers called fibrils that are soft even when the PTFE thickness is increased can be used, but since it has an open-cell tube wall, there is a concern that it cannot withstand the pressure of transporting the drug solution and may penetrate into the pores or air bubbles may be drawn in from the pores.

[0004] A method of using expanded PTFE to increase the deformation stress has been reported. For example, Patent Document 1 (JP Patent Publication No. 2016-528966) discloses that a microcatheter is strengthened by including an expanded PTFE liner. However, since the strength is improved by expanding PTFE, the molecular orientation in the longitudinal direction is strong, making it prone to tearing. A contrast medium may be introduced into the body via a catheter, but since high pressure is applied when the contrast medium is injected, there is a risk that the expanded PTFE tube will tear.

[0005] Also, a multi-layer PTFE tube containing a solid layer and a porous layer has been reported.

[0006] For example, Patent Document 2 (JP Patent Publication 7-1630A) describes a flexible multi-layer tube that is made of a first layer made of solid polytetrafluoroethylene and a second layer made of porous polytetrafluoroethylene laminated on the outer circumferential surface of the first layer, and that is integrated with the second layer by thermal fusion. Since both the first layer and the second layer, i.e., the solid layer and the porous layer, are tube-shaped bodies made by winding and fixing PTFE films, steps are generated. Therefore, although it is applicable to applications in which relatively large tubes such as endoscopes are used, it is not suitable for catheter applications that require precision in diameter size.

[0007] Patent Document 3 (JP Patent Publication 2001-46314 A) describes an endoscope in which a duct formed of a PTFE tube having a porous structure with an inner layer and an outer layer is extended inside. Patent Document 3 describes that the inner layer and the outer layer are extruded simultaneously, and then only the outer layer is stretched and foamed to make it porous, thereby forming a porous structure. However, no specific means are described, and it is unclear how only the outer layer can be stretched and foamed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2016-528966 [Patent Document 2] Japanese Patent Application Publication No. 7-1630 [Patent Document 3] JP 2001-46314 A Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a multi-layer fluororesin tube which has both resistance to longitudinal elongation and flexibility in bending, and which is excellent in permeation resistance and airtightness. [Means for solving the problem]

[0010] The fluororesin multi-layer tube has a two-layer structure including an inner layer containing polytetrafluoroethylene resin and having a solid structure, and an outer layer that is in contact with the inner layer and contains polytetrafluoroethylene resin and has a porous structure. The fluororesin multi-layer tube is 0.69mm The inner layer has an outer diameter. The inner layer has a thickness smaller than the outer layer. The inner layer thickness is 20 The thickness is in the range of 30 μm to 30 μm. Effect of the Invention

[0011] The above-mentioned multi-layer fluororesin tube has both resistance to longitudinal elongation and flexibility to bending, and is excellent in permeation resistance and airtightness. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view illustrating an example of a multi-layer fluororesin tube. [Diagram 2] 3 is a cross-sectional view taken along imaginary plane II-II' shown in FIG. 2. [Diagram 3] FIG. 2 is a cross-sectional view showing an example of forming an inner layer of a multi-layer fluororesin tube by extrusion molding. [Figure 4] FIG. 2 is a cross-sectional view showing an example of forming an inner layer of a multi-layer fluororesin tube by a dip coating method. [Diagram 5] FIG. 2 is a cross-sectional view illustrating an example of extrusion molding for forming an outer layer of a multi-layer fluororesin tube. [Figure 6] FIG. 2 is a conceptual diagram for explaining a method for evaluating the flexibility of a multi-layer fluororesin tube according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The fluororesin multi-layer tube according to an embodiment of the present invention includes an inner layer having a solid structure and an outer layer in contact with the inner layer and having a porous structure. The inner layer and the outer layer each include a polytetrafluoroethylene resin. The inner layer has a thickness smaller than that of the outer layer and is within a range of 2 μm to 30 μm.

[0014] The above-mentioned fluororesin multi-layer tube has a multi-layer structure including an inner layer and an outer layer, and is therefore thicker than each of the individual single layers, so deformation in the longitudinal direction is suppressed. Furthermore, because the outer layer has a porous structure, the multi-layer tube as a whole is thicker, but has excellent flexibility in lateral bending. In other words, because the multi-layer tube is soft, it has a small bending radius and is less likely to kink (break). In addition, because the fluororesin multi-layer tube has a solid structure, i.e., an inner layer with a non-porous structure, there is no concern about the generation of air bubbles or the penetration of chemical solutions.

[0015] An example of a multi-layer fluororesin tube is shown in FIG. 1 and FIG.

[0016] Fig. 1 is a perspective view that shows a schematic diagram of an example of a multi-layered fluororesin tube, and Fig. 2 is a cross-sectional view taken along imaginary plane II-II' shown in Fig. 1. Fig. 2 shows a cross section perpendicular to the longitudinal direction of the multi-layered fluororesin tube, i.e., the tube axis direction.

[0017] The multi-layer tube 1 shown in Figures 1 and 2 has a circular tubular shape. The multi-layer tube 1 has a two-layer structure in which an inner layer 2 and an outer layer 3 are laminated in the radial direction of the circular tube. It is preferable that both the inner layer 2 and the outer layer 3 have a circular cross section.

[0018] The inner layer 2 is made of a PTFE tube having a solid structure. In other words, the inner layer 2 is an inner layer tube containing PTFE. The inner layer thickness T IN is the thickness T of the outer layer 3 EX Thinner. Inner layer thickness T IN is in the range of 2 μm to 30 μm.

[0019] The outer layer 3 is made of a PTFE tube having a porous structure made of fibrils. In other words, the outer layer 3 is an outer layer tube containing PTFE. The outer layer thickness T of the outer layer 3 EX The outer layer thickness T may be, for example, in the range of 10 μm to 100 μm. EX is the thickness T of the inner layer 2 IN Also, the outer layer thickness T EX is the inner layer thickness T IN It is desirable that the value be more than 2 times and less than 9 times.

[0020] The multi-layer tube 1 has an outer diameter D of, for example, 0.5 mm or more and 3 mm or less. EX The outer diameter D of the multi-layer tube 1 may be EX may correspond to the outer diameter of the outer layer 3. The multi-layer tube 1 has an inner diameter D IN The inner diameter D of the multi-layer tube 1 may be IN may correspond to the inner diameter of the inner layer 2.

[0021] Such a multi-layer tube can be obtained, for example, by the following manufacturing method. Specifically, the manufacturing method of the multi-layer tube includes the steps of obtaining a first tubular extrusion product by a first extrusion molding using a first mixture containing polytetrafluoroethylene fine powder, performing a first firing on the first extrusion product to obtain a first tubular precursor having a solid structure, forming a second extrusion product on the outer surface of the first tubular precursor by a second extrusion molding using a second mixture containing polytetrafluoroethylene fine powder to obtain a second tubular precursor, and performing a second firing on the second tubular precursor to obtain a fluororesin multi-layer tube including an inner layer having a solid structure and an outer layer having a porous structure. Another method for manufacturing a multi-layer tube includes applying a polytetrafluoroethylene dispersion to the outer surface of a core wire to obtain a first coating, performing a first firing on the polytetrafluoroethylene coating to obtain a first tubular precursor having a solid structure, forming a second coating on the outer surface of the first tubular precursor by extrusion molding of a mixture containing polytetrafluoroethylene fine powder to obtain a second tubular precursor, and performing a second firing on the second tubular precursor to obtain a multi-layer fluororesin tube including an inner layer having a solid structure and an outer layer having a porous structure.

[0022] That is, the method for producing a multi-layer tube includes forming a thin-walled solid PTFE tube by extruding and baking a tubular extrusion product or by applying and baking a PTFE dispersion liquid by a dip coating method or the like, and then coating the outer surface of the obtained thin-walled tube by extrusion molding and baking it to form a porous PTFE layer.

[0023] First, a method for obtaining a solid PTFE tube that is to be the inner layer by extrusion molding (first extrusion molding) will be described.

[0024] As the PTFE fine powder, materials commonly used for extrusion molding of PTFE molded products can be used. Fine powder is obtained by coagulating and drying an aqueous dispersion obtained by emulsion polymerization. For example, the fine powder may be mainly composed of primary particles generated by polymerization that have aggregated to a particle size of 500 μm.

[0025] As the PTFE fine powder, a powder of only PTFE without any fillers or additives, for example, virgin PTFE powder, can be used. Such PTFE fine powder is made of PTFE. It is preferable to use virgin PTFE powder for forming the inner layer.

[0026] Alternatively, a filled PTFE fine powder containing a composite material containing PTFE powder and a filler may be used. For example, an imide resin powder can be mixed with the PTFE powder as the filler. By forming an outer layer using a mixed powder of PTFE powder and imide resin powder, the wear resistance of the outer surface of the tube can be improved. In addition, by including a conductive material such as a carbon material as the filler, electrical properties can be imparted to the tube.

[0027] For example, a paste-like mixture (first mixture) can be obtained by mixing an extrusion aid such as a lubricant with PTFE fine powder. A tubular first extrusion molded product can be obtained by extruding the mixture containing PTFE fine powder into a tube shape (first extrusion molding). For example, a first coating can be formed by extruding the PTFE mixture onto the outer surface of a core wire. A solid PTFE tube can be obtained as a first tubular precursor by baking the obtained first extrusion molded product (first baking).

[0028] Examples of extrusion aids include the commonly used solvent naphtha (e.g., registered trademark: Isoper E, manufactured by Exxon Chemical Co.), white oil, and liquid paraffin having 6 to 12 carbon atoms (e.g., registered trademark: Cactus Normal Paraffin N-10, manufactured by Japan Energy Corporation).

[0029] The mixture obtained by mixing the PTFE fine powder and the extrusion aid may be aged before being subjected to extrusion molding. The aged mixture may be compressed to produce a compression molded body (billet). By compressing, air in the PTFE fine powder can be removed, and the uniformity of the extrusion molded product can be improved. The shape of the compression molded body is not particularly limited, but may be, for example, a cylindrical shape. The compression molded body is placed in an extruder and extrusion molding is performed.

[0030] During extrusion molding of the first extrusion molded product (first extrusion molding), it is desirable to make the extrusion speed of the mixture or compression molded body containing PTFE fine powder and the take-up speed of the core wire approximately equal. By making the speeds equal, it becomes easier to keep the thickness of the first extrusion molded product (first coating) that covers the core wire uniform along the longitudinal direction.

[0031] During extrusion molding, heating may be performed. For example, extrusion molding may be performed while heating by setting the temperature of the mold (e.g., die or die) of the extruder to 40° C. or more and 120° C. or less. It is preferable to heat the mold to 50° C. or more and 60° C. or less.

[0032] A core wire may be used in the first extrusion molding. By performing extrusion molding so as to cover the outer periphery of the core wire with a mixture containing PTFE fine powder, a tubular first extrusion molding product, i.e., a first coating, can be formed on the core wire. In addition, by subjecting the first extrusion molding product (first coating) on ​​the core wire to firing (first firing) as it is, a first tubular precursor in which the core wire is covered can be obtained. By using a core wire, handling properties during and after production are improved.

[0033] The core wire may be made of, for example, a metal wire made of a metal such as copper or aluminum, or a core material made of resin. The diameter of the core wire may be appropriately changed depending on the desired inner diameter of the tube.

[0034] The first extrusion molding, for example the first coating formed on the core wire, is baked (first baking) to obtain a first tubular precursor that will become the inner layer of the multi-layer fluororesin tube.

[0035] The baking temperature in baking (first baking) of the first extrusion molding (for example, the first coating on the core wire) is not particularly limited. It is desirable to bake at a temperature exceeding the melting point of PTFE, 345°C, for example, at a temperature of 400°C or higher.

[0036] Prior to firing, the extrusion molded product may be dried, for example, to remove the extrusion aid. However, since typical extrusion aids volatilize at about 200° C., they will volatilize during firing even if they are not removed in advance. Therefore, drying may be omitted.

[0037] It is preferable not to stretch the first extrusion molding. In order to improve the permeation resistance and airtightness of the inner layer of the multi-layer tube as a solid structure, it is preferable not to stretch the first extrusion molding, which is a precursor of the inner layer.

[0038] Next, a method for forming a solid PTFE tube that serves as the inner layer by coating a PTFE dispersion will be described.

[0039] The PTFE dispersion contains a dispersion medium and PTFE powder in the dispersion medium. As the PTFE dispersion, a material that is generally used in a method for forming a resin tube by coating, such as a dip coating method, can be used. For example, the PTFE dispersion is an aqueous dispersion liquid in which PTFE powder is dispersed in an aqueous dispersion medium by emulsion polymerization. The PTFE dispersion can be a suspension containing PTFE powder.

[0040] The dispersion medium may be, for example, water, etc. The composition of the PTFE dispersion is not particularly limited, and for example, a dispersion liquid or suspension having a composition commonly used in techniques such as dip coating can be used.

[0041] The PTFE powder contained in the PTFE dispersion is preferably a powder of PTFE only, without any fillers or additives. That is, the PTFE dispersion is preferably one in which a powder made of PTFE is dispersed in a dispersion medium. The PTFE dispersion is preferably a dispersion of virgin PTFE.

[0042] The first coating, i.e., the dispersed PTFE coating, is obtained by applying the PTFE dispersion to the outer surface of the core wire. To apply the PTFE dispersion, for example, the core wire can be immersed in the PTFE dispersion. Specifically, it is preferable to adopt a dip coating method. In the dip coating method, a uniform coating thickness can be formed by passing the core wire through the PTFE dispersion and pulling it up at a constant speed.

[0043] The core wire may be the same as the core wire that can be used in the first extrusion molding described above.

[0044] The first coating obtained by applying the PTFE dispersion onto the core wire is baked (first baking), thus obtaining a first tubular precursor that will become the inner layer of the fluororesin multi-layer tube.

[0045] After applying the PTFE dispersion once and then baking, the outer surface of the obtained tube may be further coated with the PTFE dispersion and then baked. By alternately repeating the application of the dispersion and the baking, the wall thickness of the tube can be adjusted to a desired thickness.

[0046] Alternatively, after applying the PTFE dispersion and baking, a filler-containing dispersion containing a composite material containing PTFE powder and a filler may be applied and baked. For example, by adding a conductive material such as a carbon material as the filler, electrical properties can be imparted to the tube. However, it is preferable that the dispersion directly applied to the outer surface of the core wire is a PTFE dispersion that does not contain a filler.

[0047] The baking temperature in baking the first coating on the core wire (first baking) is not particularly limited, but it is preferable to bake at a temperature exceeding the melting point of PTFE, 345°C, for example, at a temperature of 400°C or higher.

[0048] Next, a method for forming a porous outer layer on a solid PTFE tube by extrusion molding to obtain a multi-layer tube will be described.

[0049] The PTFE fine powder may be the same as the PTFE fine powder that can be used in the first extrusion molding described above. The PTFE fine powder may be either virgin PTFE powder or filled PTFE fine powder.

[0050] In the same manner as in the preparation of the mixture (first mixture) used in the first extrusion molding, for example, an extrusion aid such as a lubricant may be mixed with PTFE fine powder to obtain a paste-like mixture (second mixture). The mixture containing PTFE fine powder may be extruded onto the outer surface of the first tubular precursor to form a second coating. The second tubular precursor thus obtained, which contains the first tubular precursor and the second coating, may be fired (second firing) to obtain a multi-layered PTFE tube, i.e., a multi-layered fluororesin tube.

[0051] That is, a first tubular precursor, which is a precursor of the inner layer of the multi-layer tube, is used as a core wire and extrusion molding is performed to cover the first tubular precursor with a second coating of PTFE resin to obtain a second tubular precursor. The second tubular precursor is baked to convert the second coating into a tubular PTFE layer, thereby obtaining a multi-layer fluororesin tube in which a tubular inner layer and a tubular outer layer are overlapped.

[0052] The first tubular precursor as a core wire used in the extrusion molding (second extrusion molding) of the second coating may be a solid PTFE tube obtained by the first extrusion molding described above, or may be a solid PTFE tube obtained by the method of applying the PTFE dispersion described above.

[0053] As with the mixture (first mixture) used in the first extrusion molding, the mixture (second mixture) used in the extrusion molding of the second coating (second extrusion molding) may be aged or a compression molded body (billet) may be made before being subjected to extrusion molding.

[0054] During extrusion molding of the second coating (second extrusion molding), the first tubular precursor as the core wire is taken up at a speed faster than the extrusion speed of the mixture or compression molded body containing the PTFE fine powder. By making the take-up speed faster than the extrusion speed, the second coating having a porous structure, and thus the outer layer having a porous structure, can be obtained. Since the take-up speed of the first tubular precursor is faster, the PTFE resin attached to the surface is stretched in the longitudinal direction, so that the second coating does not become dense and a porous layer is formed.

[0055] During extrusion molding, heating may be performed. For example, extrusion molding may be performed while heating by setting the temperature of the mold (e.g., die or die) of the extruder to 40° C. or more and 120° C. or less. It is preferable to heat the mold to 50° C. or more and 60° C. or less.

[0056] The firing temperature in firing the second tubular precursor (second firing) is not particularly limited. It is preferable to fire the second tubular precursor at a temperature higher than the melting point of PTFE, 345° C., for example, at a temperature of 400° C. or higher.

[0057] Prior to firing, the extrusion aid may be removed by drying. As described above, typical extrusion aids volatilize at about 200°C, so they will volatilize during firing even if they are not removed in advance. Therefore, drying may be omitted.

[0058] A specific example of a method for producing a fluororesin tube will be described with reference to the drawings. FIG. 3 is a cross-sectional view that shows a schematic example of a method for forming a first tubular precursor that will be the inner layer of a fluororesin multilayer tube by extrusion molding. That is, FIG. 3 shows an example of the first extrusion molding. FIG. 4 is a cross-sectional view that shows a schematic example of a method for forming a first tubular precursor that will be the inner layer of a fluororesin multilayer tube by dip coating. FIG. 5 is a cross-sectional view that shows a schematic example of a method for producing a fluororesin tube by forming a second tubular precursor that will be the outer layer of a fluororesin multilayer tube by extrusion molding. The example shown in FIG. 5 can be an example of the second extrusion molding.

[0059] First, with reference to FIG. 3, an example of a method for forming a precursor of the inner layer by extrusion molding, that is, a first extrusion molding, will be described.

[0060] An extrusion die 51 provided in an extrusion molding machine 50 is filled with an admixture 20 containing PTFE fine powder. The admixture 20 is a mixture of PTFE fine powder and other materials such as an extrusion aid. The admixture 20 may be, for example, a paste containing PTFE fine powder. Alternatively, the admixture 20 may be a compression molded body (billet) containing PTFE fine powder.

[0061] The core wire 40, which is unwound from a supply roll 90, is supplied into the inside of the extrusion die 51. The core wire 40 passes through the inside of the extrusion die 51 and is pulled out from the discharge port 52 of the extrusion die 51 to the outside.

[0062] As the extrusion ram 53 is moved toward the discharge port 52, the mixture 20 is compressed and adheres to the outer surface of the core wire 40, and is extruded from the discharge port 52 together with the core wire 40 as the first coating 21. Here, it is desirable to synchronize the movement of the extrusion ram 53 with the take-up of the core wire 40 so that the speed at which the first coating 21 is extruded from the discharge port 52 is approximately the same as the take-up speed of the core wire 40. In this way, the outer periphery of the core wire 40 is covered with the tubular first coating 21 (first extrusion product).

[0063] The first coating 21 on the core wire 40 is fed to a drying furnace 61, where it is dried (first drying). Then, the first coating 21 is fed to a heating furnace 62, where it is subjected to a first firing. By the first firing, a first tubular precursor 22 having a solid structure and in a form in which the core wire 40 is coated is obtained.

[0064] The first tubular precursor 22 on the core wire 40 is supplied to the winding roll 93 via the cooling device 63. The cooling means by the cooling device 63 is not particularly limited and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of guide rollers 92 may be set so that the distance from the heating furnace 62 to the winding roll 93 is long, thereby increasing the heat dissipation time. The arrangement and number of guide rollers 92 are not limited to those shown in the figure. The first tubular precursor 22 is wound up on the winding roll 93 while still including the core wire 40.

[0065] It is desirable to apply tension to the core wire 40 and its covering by means of tension pulleys 91 and guide rollers 92 disposed before and after the extrusion molding machine 50 to prevent sagging. The number and positions of the tension pulleys 91 are not limited to the example shown in the figure, and may be increased or decreased. Moreover, the tension pulleys 91 may be omitted.

[0066] Next, an example of a method for forming a precursor of the inner layer by a dip coating method will be described with reference to FIG.

[0067] The core wire 40 is unwound from a supply roll 90 and supplied to the dispersion liquid 23 in the bath 70. The dispersion liquid 23 is a PTFE dispersion. The core wire 40 is immersed in the dispersion liquid 23 and then pulled up. The dispersion liquid 23 is applied to the outer surface of the core wire 40 via the dip coating, and the first coating 21 is obtained.

[0068] The core wire 40 and the first coating 21 coating the outer periphery thereof are supplied to a drying furnace 61, where they are dried (first drying). Then, the core wire 40 and the first coating 21 are supplied to a heating furnace 62, where they are subjected to a first firing. By the first firing, a first tubular precursor 22 having a solid structure and coating the core wire 40 is obtained.

[0069] The first tubular precursor 22 on the core wire 40 is supplied to a take-up roll 93 via a cooling device 63. The cooling means used by the cooling device 63 is not particularly limited and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of guide rollers 92 may be set so that the distance from the heating furnace 62 to the take-up roll 93 is long, thereby increasing the heat dissipation time. In addition, the arrangement and number of guide rollers 92 are not limited to those shown in the figure.

[0070] Furthermore, the first tubular precursor 22 may be resupplied in sequence to the bath 70, the drying oven 61, the heating oven 62, and optionally the cooling device 63 before being supplied to the take-up roll 93. The resupply of the first tubular precursor 22 to the bath 70, the drying oven 61, the heating oven 62, and optionally the cooling device 63 may be repeated multiple times depending on the desired thickness of the inner layer 2.

[0071] It is desirable to apply tension to the core wire 40 and its coating by tension pulleys 91 and guide rollers 92 disposed at the front and rear of the bath 70 to prevent sagging. The number and positions of the tension pulleys 91 are not limited to the example shown in the figure, and may be increased or decreased. Furthermore, the tension pulleys 91 may be omitted. The first tubular precursor 22, including the core wire 40, is wound up around a winding roll 93.

[0072] Next, an example of a method for forming an outer layer by extrusion molding will be described with reference to Fig. 5. The example shown in Fig. 5 may be a second extrusion molding.

[0073] An extrusion die 51 provided in an extrusion molding machine 50 is filled with an admixture 30 containing PTFE fine powder. The admixture 30 is a mixture of PTFE fine powder and other materials such as an extrusion aid. The admixture 30 may be, for example, a paste containing PTFE fine powder. Alternatively, the admixture 30 may be a compression molded body (billet) containing PTFE fine powder.

[0074] A first tubular precursor 22 delivered from a supply roll 90 is supplied into the inside of the extrusion die 51. The first tubular precursor 22 covers the outer periphery of the core wire 40, and the first tubular precursor 22 is supplied together with the core wire 40. The first tubular precursor 22 on the core wire 40 passes through the inside of the extrusion die 51 and is drawn out from a discharge port 52 of the extrusion die 51 to the outside.

[0075] The first tubular precursor 22 may be obtained by the first extrusion molding exemplified in Fig. 3. Alternatively, the first tubular precursor 22 may be obtained by the dip coating method exemplified in Fig. 4.

[0076] As the extrusion ram 53 is moved toward the discharge port 52, the mixture 30 is compressed and adheres to the outer surface of the first tubular precursor, and is extruded from the discharge port 52 together with the first tubular precursor 22 and the core wire 40 as the second coating 31. The first tubular precursor 22 and the core wire 40 are pulled off at a speed faster than the speed at which the second coating 31 is extruded from the discharge port 52. In this way, the outer periphery of the first tubular precursor 22 is covered with the tubular second coating 31, and the second tubular precursor 10 is obtained.

[0077] The second tubular precursor 10 is supplied to a drying furnace 61 and is subjected to drying (second drying) there. Then, the second coating 31 is supplied to a heating furnace 62 and is subjected to a second firing there. Through the second firing, a multi-layer tube 1 having a two-layer structure including an inner layer 2 which is a solid layer and an outer layer 3 which is a porous layer is obtained. The inner layer 2 corresponds to the first tubular precursor 22 which is reheated by the second firing.

[0078] The multilayer tube 1 on the core wire 40 is supplied to the take-up roll 93 via the cooling device 63. The cooling means used by the cooling device 63 is not particularly limited and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of guide rollers 92 may be set so that the distance from the heating furnace 62 to the take-up roll 93 is long, thereby increasing the heat dissipation time. The arrangement and number of guide rollers 92 are not limited to those shown in the figure. The multilayer tube 1 is taken up by the take-up roll 93 while still including the core wire 40.

[0079] It is desirable to apply tension to the core wire 40 and its covering by means of tension pulleys 91 and guide rollers 92 disposed before and after the extrusion molding machine 50 to prevent sagging. The number and positions of the tension pulleys 91 are not limited to the example shown in the figure, and may be increased or decreased. Moreover, the tension pulleys 91 may be omitted.

[0080] When in use, the hollow structure of the multi-layer tube 1 can be used by removing the core wire 40. For example, when manufacturing a catheter, the core wire 40 is removed and the multi-layer tube 1 is used as a member of the catheter.

[0081] The above example is one example of the production of such a fluororesin multilayer tube, but the production method is not limited to the above example. For example, after the first baking, the core wire 40 and the first tubular precursor 22 may be directly supplied to the extrusion molding machine 50 without being wound up on the winding roll 93, and the process from supplying the core wire 40 to completing the multilayer tube 1 and winding it up may be performed continuously.

[0082] It can be confirmed that a fluororesin multilayer tube including an inner layer and an outer layer has been obtained as follows. The fluororesin multilayer tube is cut at a cut surface intersecting the main axis of the tube to expose a cross section. The cross section obtained is observed under an optical microscope. A difference in appearance between the solid inner layer and the porous outer layer can be visually recognized. In this case, the inner layer and the outer layer can be distinguished by observing the cross section. Furthermore, the dimensions of the inner layer and the outer layer can be measured on the cross section.

[0083] The resin material forming each part of the fluororesin multi-layer tube can be identified as follows: It is possible to confirm that the resin material is PTFE by measuring the melting point using a differential scanning calorimeter (DSC).

[0084] [Example] Example 1 A PTFE resin tube was manufactured by the same manufacturing method as that described with reference to Fig. 3 and Fig. 5. That is, an inner layer was formed by the first extrusion molding, and an outer layer was formed by the second extrusion molding, to manufacture a PTFE multi-layer tube. The details are as follows.

[0085] The PTFE fine powder used for extrusion molding of the inner layer was Teflon (registered trademark) PTFE fine powder 641-J manufactured by Mitsui-Chemours Fluoro Products, Inc. The PTFE fine powder used for extrusion molding of the outer layer was PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd.

[0086] An inner layer tube (first tubular precursor) was obtained by the following procedure. After adding 21 parts by mass of naphtha (extrusion aid) to 100 parts by mass of PTFE fine powder (641-J) for the inner layer, the mixture was mixed at room temperature using a turbular mixer to prepare a mixture. The mixture was then molded into a cylindrical shape using a preformer. The obtained preform was placed in an extruder equipped with a die and guide tube with a size that results in a wall thickness of 20 μm. Next, a silver-plated copper wire with an outer diameter of φ0.49 (mm) as a core wire was placed in the paste extruder so as to pass through the cylindrical hollow part and guide tube of the preform. Extrusion molding (first extrusion molding) was performed while pulling the core wire in synchronization with the extrusion, and the obtained first extrusion molded product was subjected to a first drying at 180°C to 200°C and a first firing at 380°C to 400°C. The resulting polytetrafluoroethylene resin tube having a solid structure (first tubular precursor) was cooled and then wound up on a roll.

[0087] A porous outer layer was formed on the outer surface of the inner tube by the following procedure, to obtain a two-layer PTFE tube.

[0088] After adding 21 parts by mass of naphtha (extrusion aid) to 100 parts by mass of PTFE fine powder (F201) for the outer layer, the mixture was mixed at room temperature using a turbular mixer to prepare a mixture. The mixture was then molded into a cylindrical shape using a preformer. The obtained preform was placed in an extruder equipped with a die and a guide tube of a size that would result in a thickness of 100 μm for two layers of PTFE. Next, the inner layer tube on the copper wire obtained as described above as the core wire was placed in the paste extruder so as to pass through the cylindrical hollow part and guide tube of the preform. Extrusion molding (second extrusion molding) was performed while pulling the core wire at a speed faster than the extrusion speed, and the obtained extrusion molded product (second tubular precursor) was subjected to a second drying at 180°C to 200°C and a second baking at 380°C to 400°C. The obtained two-layered polytetrafluoroethylene resin tube was cooled and then wound on a roll.

[0089] Example 2 A two-layered polytetrafluoroethylene resin tube was produced in the same manner as in Example 1, except for the following changes: The PTFE fine powder for the inner layer was changed to PTFE fine powder Polyflon (registered trademark) F208 manufactured by Daikin Industries, Ltd. The die used in the first extrusion molding was changed to a size that resulted in a wall thickness of 30 μm.

[0090] Comparative Example 1 A two-layered polytetrafluoroethylene resin tube was produced in the same manner as in Example 1, except for the following changes: The PTFE fine powder for the inner layer was changed to PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. The die used in the first extrusion molding was changed to a size that gave a wall thickness of 50 μm.

[0091] Comparative Example 2 A single extrusion run was performed to form a solid monolayer tube, as described below.

[0092] A solid PTFE tube was produced by the same procedure as the first extrusion molding in Example 1, except for the following changes: The PTFE fine powder was changed to PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. The die used in the extrusion molding (corresponding to the first extrusion molding) was changed to a size that gave a wall thickness of 100 μm.

[0093] No outer layer was formed on the obtained PTFE tube, thus obtaining a single-layer tube having a solid structure.

[0094] Comparative Example 3 As described below, a single extrusion molding method was used to form a single-layer tube with a porous structure.

[0095] A PTFE tube having a porous structure was manufactured by the same procedure as the second extrusion molding in Example 1, except for the following changes: The PTFE fine powder was changed to PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd. As the core wire, a single silver-plated copper wire having an outer diameter of φ0.49 (mm) was used instead of an inner layer tube.

[0096] Thus, a single-wall tube having a porous structure and a wall thickness of 100 μm was obtained.

[0097] <Evaluation> (Check the tube thickness) The dimensions of each of the tubes produced in Examples 1-2 and Comparative Examples 1-3 were measured by the method described above to determine the wall thickness of each of the inner layer and the outer layer. The measurement results are shown in Table 1 below.

[0098] (Measurement of 10% strain stress) The elongation strength of each tube was evaluated as follows.

[0099] A certain length of each tube section cut out from each tube obtained in Examples 1-2 and Comparative Examples 1-3 was fixed at both longitudinal ends with the chucks of a universal testing machine and subjected to a tensile test. The tensile strength was gradually increased, and the stress at the point where the length of the tube increased by 10% due to strain was recorded as the 10% strain stress.

[0100] (Tube flexibility evaluation) The flexibility of each tube was evaluated as follows.

[0101] One end and the other end of each tube were held vertically so that the longitudinal direction of the tube was parallel to the direction of gravity. The upper held part was gradually lowered, and the tube was bent under its own weight, and the length of the bent part was measured when the angle formed by the line connecting the upper end that drooped down and the upper holding position with the remaining part of the tube from the upper holding position to the lower holding position, which was still held vertically, reached 90 degrees.

[0102] The state in which the tube is bent under its own weight to the above angle of 90 degrees will be described with reference to Fig. 6. Note that Fig. 6 illustrates a multi-layer tube 1 as an example, but single-layer tubes such as the tubes obtained in Comparative Examples 2 and 3 can also be evaluated in the same manner.

[0103] The multi-layer tube 1 shown in FIG. 6 is held vertically at two points, one end and the middle of the tube, and the part that is not held and extends beyond the middle of the tube is bent by its own weight, and the other end of the tube hangs down. The part of the tube that is held vertically is not bent because the end located at the lower side is the lower holding position 11 and the part held in the middle of the tube is the upper holding position 12, and is supported vertically. The imaginary line connecting the upper end 13, which corresponds to the end of the hanging part (the other end) and the upper holding position 12, is shown by the dashed line 14. The part held above and below between the upper holding position 12 and the lower holding position 11 and the dashed line 14 intersect at the upper holding position 12, and the angle θ between them is 90 degrees. In this state, the length along the multi-layer tube 1 from the upper end 13 to the upper holding position 12 was measured. The larger the value of this length, the stronger the force supporting its own weight and the more rigid it is. In other words, the smaller the value of this length, the softer it is.

[0104] The measurement results for each tube are summarized in Table 1 below. Specifically, Table 1 shows the thickness of the inner layer having a solid structure (inner layer thickness), the thickness of the outer layer having a porous structure (outer layer thickness), and the outermost diameter of the tube (outer diameter D EX ), 10% strain stress, and the length at which it yields to its own weight and bends to a 90 degree position. In Comparative Examples 2 and 3, single-layer tubes were produced, but for convenience, the single layer is designated as the "inner layer" or "outer layer" depending on whether it had a solid structure or a porous structure.

[0105] [Table 1]

[0106] As shown in Table 1, for both the tubes of Example 1-2 and Comparative Example 1-3, in which the total thickness of the inner and outer layers combined is 100 μm, the strain stress with respect to elongation in the longitudinal direction was similar, regardless of the ratio of solid structure and porous structure or the presence or absence of the structure. On the other hand, in Example 1-2 and Comparative Example 3, a more flexible tube was obtained compared to Comparative Example 1-2. As such, in Example 1-2 and Comparative Example 3, a soft tube was obtained while maintaining its resistance to elongation. However, since the tube of Comparative Example 3 had a single-layer porous structure, it was not suitable for applications that required permeation prevention or airtightness.

[0107] According to the embodiment described above, a fluororesin multilayer tube is provided that includes an inner layer containing a polytetrafluoroethylene resin and an outer layer containing a polytetrafluoroethylene resin. The inner layer has a solid structure. The outer layer is in contact with the inner layer and has a porous structure. The inner layer has a thickness thinner than the outer layer. The inner layer thickness is within a range of 2 μm to 30 μm. The fluororesin multilayer tube has both resistance to longitudinal elongation and flexibility to bending, and is excellent in permeation resistance and airtightness.

[0108] The present invention is not limited to the above-mentioned embodiment, and can be modified in various ways without departing from the gist of the present invention. The embodiments may be combined as appropriate, and in that case, the combined effect can be obtained. Furthermore, the above-mentioned embodiment includes various inventions, and various inventions can be extracted by combinations selected from the multiple components disclosed. For example, if the problem can be solved and the effect can be obtained even if some components are deleted from all the components shown in the embodiment, the configuration from which the components are deleted can be extracted as an invention. The invention as originally claimed in the present application is set forth below. [1] An inner layer containing polytetrafluoroethylene resin and having a solid structure; a fluororesin multilayer tube comprising: an outer layer in contact with the inner layer, which contains polytetrafluoroethylene resin and has a porous structure, wherein the inner layer has a thickness smaller than that of the outer layer, and the inner layer thickness is within a range of 2 μm or more and 30 μm or less. [2] The fluororesin multi-layer tube according to [1], wherein the thickness of the outer layer is within the range of 10 μm or more and 100 μm or less. [3] The multi-layer fluororesin tube according to [1] or [2], wherein the thickness of the outer layer is more than twice but not more than nine times the thickness of the inner layer. [4] The multi-layer fluororesin tube according to any one of [1] to [3], having an outer diameter of 0.5 mm or more and 3 mm or less. [Explanation of symbols]

[0109] 1...multilayer tube, 2...inner layer, 3...outer layer, 10...second tubular precursor, 11...lower holding position, 12...upper holding position, 13...upper end, 20...mixture, 21...first coating, 22...first tubular precursor, 23...dispersion, 30...mixture, 31...second coating, 40...core wire, 50...extrusion molding machine, 51...extrusion die, 52...discharge port, 53...extrusion ram, 61...drying furnace, 62...heating furnace, 63...cooling device, 70...bath, 90...supply roll, 91...tension pulley, 92...guide roller, 93...take-up roll.

Claims

1. An inner layer containing polytetrafluoroethylene resin and having a solid structure; A fluororesin multilayer tube having a two-layer structure including an outer layer in contact with the inner layer and containing polytetrafluoroethylene resin and having a porous structure, the tube having an outer diameter of 0.69 mm, the inner layer thickness of the inner layer being thinner than the outer layer thickness of the outer layer, and the inner layer thickness being within the range of 20 μm or more and 30 μm or less.

2. 2. The fluororesin multi-layer tube according to claim 1, wherein the thickness of the outer layer is within a range of 70 μm or more and 80 μm or less.

Images