Method for producing fluororesin structure and fluororesin structure

Abstract

To provide a method for manufacturing a fluororesin structure, in which separation between an inner portion and an outer portion is suppressed, and a flexibility is high, and the fluororesin structure.SOLUTION: There is provided a fluororesin structure that comprises: a non-porous inner portion; and a porous outer portion positioned outside the non-porous inner portion, and the inner portion and the outer portion comprise polytetrafluoroethylene resin. There is also provided a manufacturing method that comprises: obtaining a tubular or string-shaped first extruded product; obtaining an internal precursor 22 by subjecting the first extruded product to a first uniaxial stretching of 3.0 times or less in a longitudinal direction; obtaining a second extruded product 31 having a tubular shape; obtaining a composite precursor by subjecting the second extruded product to a second uniaxial stretching in the longitudinal direction in a state where the inner precursor is placed in a tube-shaped hollow portion of the second extruded product; and calcining the composite precursor. The first extruded product and the second extruded product are obtained by performing extrusion molding a first mixture and a second mixture containing polytetrafluoroethylene fine powder, respectively.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a fluororesin structure and a fluororesin structure.

Background Art

[0002] Tubes formed of tetrafluoroethylene resin, that is, polytetrafluoroethylene (PTFE) resin, are excellent in lubricity, chemical resistance, heat resistance, etc., and are thus applied in a wide range of fields. Since PTFE resin is a material lacking in flexibility and flexibility, a tube having a multi-layer structure including an outer layer having a porous structure is used as a means for preventing kinks (folds) when the PTFE resin tube is bent at a small radius. Such a multi-layer structure tube includes an inner layer having a non-porous solid structure in order to maintain its function as a flow path for chemicals and the like.

[0003] For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 7-1630) describes a flexible multi-layer tube including a first layer made of polytetrafluoroethylene having a solid structure and a second layer made of polytetrafluoroethylene having a porous structure laminated on the outer peripheral surface thereof, and the first layer and the second layer are integrated by heat fusion. The first layer is formed by firing a wound body obtained by winding and fixing a film of solid structure PTFE on a core material, and the second layer is formed by firing a wound body obtained by winding and fixing a porous PTFE film on a wound body of the first layer material. However, it is presumed that only a thin layer can be formed for the second layer. There is a concern about breakage in a tube including a thin layer. In addition, in forming each layer, since the PTFE film is wound and fixed, a step is generated, which is considered to affect the flexibility and the design of the device in which the tube is incorporated. In addition, the document suggests that the adhesion between the first layer and the second layer is weak and there is a possibility of delamination between the layers during bending. Although an adhesive layer made of a thermoplastic fluororesin can be interposed between the layers for the purpose of avoiding delamination, since a foreign substance different from PTFE is introduced, the characteristics of PTFE may be impaired.

[0004] Patent Document 2 (Japanese Patent Application Laid-Open No. 10-337405) describes a method for manufacturing a fluororesin tube in which a porous structure layer and a non-porous structure layer are integrated in the thickness direction. The method includes stretching and orienting the fluororesin tube at least in one axial direction, applying an aqueous suspension of the fluororesin to the outer surface or inner surface of the tube, and firing the tube in a state where it is fixed in the stretching axis direction. A tube obtained by extruding a mixture of a material powder of the fluororesin and a liquid lubricant in a tube shape and then heating and removing the liquid lubricant is made porous by stretching at least in one axial direction. By firing the suspension applied to one surface, a non-porous layer is formed. Since the porous structure layer and the non-porous structure layer are integrated in the thickness direction, when used as a membrane material in a device for vacuum degassing a drug or the like, excellent degassing treatment efficiency can be exhibited and tube permeation of the treatment liquid can be prevented. As the non-porous layer, it is presumed that a thin one can be obtained from its formation method. Also, since deterioration due to heat accumulates when heating is repeated, it is difficult to form a thick layer when the method of firing the coating film of the suspension is adopted. In addition, when functioning as a membrane material for degassing treatment, the wall thickness of the entire tube is expected to remain as thin as about 0.1 mm, for example.

[0005] Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-46314) describes an endoscope in which a pipeline formed of a tube having an inner layer and an outer layer is extended inside. The inner layer is formed of polytetrafluoroethylene having a solid structure, and the outer layer is formed of polytetrafluoroethylene having a porous structure. However, both the inner layer and the outer layer disposed in a part of a predetermined length range of the tube are formed of polytetrafluoroethylene having a solid structure. The porous structure of the outer layer is formed by simultaneously extruding the inner layer and the outer layer and stretching and foaming only the outer layer to make it porous. In this method, it is presumed that it is difficult to make the porous structure of the outer layer have a high porosity. A tube with a low porosity of the outer layer may lack flexibility and may not allow free routing.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-1630 [Patent Document 2] Japanese Patent Application Publication No. 10-337405 [Patent Document 3] JP 2001-46314 A Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a method for producing a fluororesin structure in which peeling between an inner portion and an outer portion is suppressed and which has high flexibility, and to provide said fluororesin structure. [Means for solving the problem]

[0008] The method for producing a fluororesin structure includes a non-porous inner portion and a porous outer portion located outside the inner portion. The inner portion contains polytetrafluoroethylene resin. The outer portion contains polytetrafluoroethylene resin. The production method includes obtaining a tubular or string-shaped first extrusion molded product, and extruding a porous material from the first extrusion molded product in the longitudinal direction. More than 1.1 times The method includes: performing a first uniaxial stretching of 3.0 times or less to obtain an internal precursor; obtaining a second extrusion molded product having a tube shape; performing a second uniaxial stretching in the longitudinal direction of the second extrusion molded product with the internal precursor placed in a hollow portion of the tube shape of the second extrusion molded product to obtain a composite precursor; and calcining the composite precursor. The manufacturing method further includes firing the internal precursor after performing the first uniaxial stretching and before installing the internal precursor inside the tubular hollow portion of the second extruded product. The first extrusion molded product is obtained by extruding a first mixture containing polytetrafluoroethylene fine powder, and the second extrusion molded product is obtained by extruding a second mixture containing polytetrafluoroethylene fine powder. Effect of the Invention

[0009] By the above-mentioned manufacturing method, it is possible to manufacture a fluororesin structure in which peeling between the inner region and the outer region when bent is suppressed. [Brief description of the drawings]

[0010] [Figure 1] Cross-sectional view schematically showing an example of extrusion molding. [Figure 2] Cross-sectional view schematically showing an example of second uniaxial stretching for a second extruded product. [Figure 3] Cross-sectional view schematically showing an example of second extrusion molding. [Figure 4] Schematic cross-sectional view showing an example of an extrusion molding machine. [Figure 5] Schematic cross-sectional view showing an example of another extrusion molding machine. [Figure 6] Perspective view schematically showing an example of a fluororesin structure. [Figure 7] Cross-sectional view taken along the virtual plane VII-VII' shown in FIG. 6. [Figure 8] Perspective view schematically showing an example of another fluororesin structure. [Figure 9] Cross-sectional view taken along the virtual plane IX-IX' shown in FIG. 8.

Mode for Carrying Out the Invention

[0011] The method for manufacturing a fluororesin structure according to an embodiment of the invention includes obtaining a first extruded product in a tube shape or a string shape, performing first uniaxial stretching of 3.0 times or less in the longitudinal direction on the first extruded product to obtain an internal precursor, obtaining a second extruded product having a tube shape, performing second uniaxial stretching in the longitudinal direction on the second extruded product with the internal precursor installed in the hollow portion of the tube shape of the second extruded product to obtain a composite precursor, and performing firing on the composite precursor. The first extruded product is obtained by extruding a first mixture containing polytetrafluoroethylene fine powder. The second extruded product is obtained by extruding a second mixture containing polytetrafluoroethylene fine powder.

[0012] According to the above manufacturing method, a fluororesin structure including a non-porous inner part and an outer part located outside the inner part and being porous can be obtained. Both the inner part and the outer part contain polytetrafluoroethylene resin. The fluororesin structure can be a multilayer tube including an inner layer in the shape of a tube as the inner part and an outer layer in the shape of a tube as the outer part. Alternatively, the fluororesin structure can be a composite structure cord including a core having a string or rod shape as the inner part and an outer layer in the shape of a tube as the outer part. In any form, the outer part (outer layer) can be said to be a sleeve for the inner part (inner layer or core).

[0013] In a multilayer tube including a non-porous solid structure inner layer for airtightness and prevention of liquid leakage and a porous outer layer for imparting flexibility and bendability, a plurality of different layers are arranged adjacent to each other in the radial direction. If the adhesion between the layers is insufficient, peeling may occur between the layers and the performance may be impaired. Similarly, for a structure including a solid structure core instead of a tube-shaped inner layer, if the adhesion between the core and the outer layer is insufficient, the performance may be impaired due to peeling.

[0014] Also, if the thickness (radial thickness) of one or both of the inner layer and the outer layer is small, the thin layer may break when the structure is bent.

[0015] The fluororesin structure obtained by the above manufacturing method is excellent in flexibility and peeling between the inner part and the outer part during bending is suppressed. Also, since both the inner part and the outer part are formed by extrusion molding, they can be set to arbitrary dimensions (for example, the thickness of the layer), and a thin layer that is easily broken can be avoided. That is, due to excellent flexibility, free layout is possible, the dimension design can be arbitrarily selected, and since the durability is high, it can be suitably applied to various uses.

[0016] As an aspect of the multilayer tube of the fluororesin structure, it has excellent flexibility compared to the solid single-layer tube of fluororesin, and the air permeability of the side wall is suppressed compared to the porous single-layer tube. Its uses include, for example, members of medical instruments such as endoscopes and catheters, and pipelines as flow paths for various fluids.

[0017] In the aspect of the composite structure cord of the fluororesin structure, no wrinkles occur and no peeling occurs between the core and the outer layer (inner part and outer part) during bending. Its uses include, for example, a dielectric waveguide. The core and the outer layer of the composite structure cord can be the core and the cladding of a flexible waveguide, respectively.

[0018] As the PTFE fine powder, a material widely used for the extrusion molding of PTFE molded products can be used. The fine powder is obtained by coagulating and drying an aqueous dispersion obtained by emulsion polymerization. The fine powder may mainly consist of, for example, primary particles generated by polymerization aggregated into secondary particles having a particle size of about 400 μm to 500 μm. The above range is a typical example of the secondary particle diameter, and fine powders with a secondary particle diameter of 200 μm or less or 800 μm or more can also be used.

[0019] The PTFE fine powder can be a powder containing only PTFE without fillers, additives, etc. That is, the PTFE fine powder can be virgin PTFE powder composed of PTFE. Or, the PTFE fine powder may contain additives. For example, a contrast agent such as barium sulfate or bismuth can be added to the PTFE fine powder as a material for a medical multilayer tube.

[0020] As the PTFE fine powder used in the first mixture for extruding the intermediate molded product of the inner part, PTFE powder which is a homopolymer composed of a single monomer may be used, or PTFE powder which is a copolymer obtained by copolymerizing different monomers may be used. Examples of the copolymer include materials which expand by heating by containing a modifying property. For example, a modified type PTFE containing a side chain of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) system can be used.

[0021] As the PTFE fine powder used in the second mixture for extruding the intermediate molded product of the outer part, high molecular weight PTFE can be preferably used from the viewpoint of being easily made porous. This is because a polymer with a high molecular weight has high strength and is difficult to break when stretched (second uniaxial stretching) for making porous. The suitability of the PTFE fine powder as a material for the second mixture is as follows, and a high molecular weight homopolymer is most suitable: modified polymer < low molecular weight homopolymer < medium molecular weight homopolymer < high molecular weight homopolymer. Although materials with a lower molecular weight are more easily made porous, their strength also decreases, so they are easily broken, and attention should be paid during stretching.

[0022] For example, by mixing an extrusion aid such as a lubricant with the PTFE fine powder, a paste-like mixture (the first mixture or the second mixture) can be obtained. By extruding the mixture containing the PTFE fine powder into a tube shape, an extruded product in the shape of a tube can be obtained. By extruding the mixture into a string shape or a rod shape, an extruded product having the shape of a string or a rod can be obtained.

[0023] The first extruded product obtained by extrusion molding using the first mixture takes the form of a tube, a string, or a rod depending on the shape and application of the fluororesin structure to be manufactured. Since the fluororesin structure and the members contained therein are flexible, the shapes of "string" and "rod" mentioned here are synonymous. For example, when manufacturing a multilayer tube, a first extruded product having the shape of a single-layer tube is formed. Or, for example, when manufacturing a composite structure cord, a first extruded product having a rod shape is formed.

[0024] The second extruded product obtained by extrusion molding using the second mixture takes the form of a tube. For example, a second extruded product having the shape of a single-layer tube is formed.

[0025] Examples of the extrusion aid include commonly used solvent naphtha (e.g., registered trademark: ISOPAR E, manufactured by Exxon Chemical Co., Ltd.), white oil, liquid paraffin having 6 to 12 carbon atoms (e.g., registered trademark: Cactus Normal Paraffin N-10, manufactured by Japan Energy Corporation), and fluorine-based solvents containing amorphous fluoropolymers.

[0026] The compositions of the first mixture and the second mixture may be the same as or different from each other.

[0027] The mixture (the first mixture or the second mixture) obtained by mixing PTFE fine powder and an extrusion aid may be aged before being subjected to extrusion molding. Also, the aged mixture may be compressed to produce a preform (billet). By compression, air in the PTFE fine powder can be removed, and the uniformity of the extruded product can be improved. The shape of the preform is not particularly limited, but it can be, for example, a cylindrical shape or a columnar shape. The preform made of the mixture is put into an extruder and extrusion molding is performed.

[0028] By the first extrusion using the first mixture, for example, a first extruded product having a tube shape with a wall thickness of 0.32 mm or more and 3 mm or less is obtained. Alternatively, by the first extrusion, for example, a first extruded product having a string shape with a diameter of 0.32 mm or more and 9 mm or less is obtained. The first extruded product in the tube shape may have an inner diameter of, for example, 1 mm or more and 20 mm or less. The first extruded product in the tube shape preferably has an inner diameter of 2 mm or more and 5 mm or less, and more preferably has an inner diameter of 2.5 mm or more and 4.5 mm or less. The first extruded product in the tube shape may have an outer diameter of, for example, 3 mm or more and 9 mm or less. Also, the first extruded product may have a multi-lumen shape having a plurality of inner diameters.

[0029] By the second extrusion using the second mixture, for example, a second extruded product having a tube shape with a wall thickness of 0.5 mm or more and 15 mm or less is obtained. The second extruded product may have an inner diameter of, for example, 2 mm or more and less than 9 mm.

[0030] During extrusion, heating may be performed. For example, by setting the temperature of the die (e.g., die or die head) of the extruder to 30°C or more and 120°C or less, extrusion may be performed while heating. It is preferable to heat the die to 40°C or more and 80°C or less.

[0031] Prior to uniaxial stretching (the first uniaxial stretching or the second uniaxial stretching), it is preferable to dry and bake the extruded product (the first extruded product or the second extruded product). Also, uniaxial stretching may be performed while drying and baking. Typical extrusion aids volatilize at about 100°C to 300°C. Alternatively, during stretching, the extruded product may not be dried, and drying may be performed before baking. Drying and baking may be continuously performed by raising the temperature from the drying temperature to the baking temperature.

[0032] Regarding the second extruded product, the internal precursor obtained by performing the first uniaxial stretching described later on the first extruded product can also be used as a core wire. By performing extrusion using the internal precursor as a core wire, the internal precursor can be directly coated with the second extruded product.

[0033] When stretching is carried out after drying and firing, an internal precursor can be obtained by performing first uniaxial stretching on the first extruded product in the longitudinal direction by 3.0 times or less. By limiting the stretching to a weak stretch up to a length of 3.0 times or less, the formation of pores in the PTFE resin can be avoided and a dense structure can be maintained. When stretching, drying, and firing are carried out in the same process, care should be taken to limit the first uniaxial stretching to 1.5 times or less in the longitudinal direction. The first uniaxial stretching is preferably carried out such that the length of the internal precursor obtained by stretching is 1.1 times or more the length of the first extruded product before stretching. When stretching is carried out by 1.1 times or more, when the internal precursor changes to the inner part by firing in the subsequent stage, its outer diameter expands in the radial direction. The inner part formed by the expansion of the internal precursor is in a state where the adhesion force with the outer part on its outer diameter surface is increased. That is, the expansion of the internal precursor leads to a reduction in the peeling between the inner part and the outer part.

[0034] With the internal precursor installed in the tubular hollow part of the second extruded product, a composite precursor is obtained by performing second uniaxial stretching on the second extruded product in the longitudinal direction. The internal precursor can be installed in the hollow part of the second extruded product, for example, by inserting it into the tube of the second extruded product obtained by separate extrusion molding. Alternatively, as described above, the second extruded product may be directly formed on the outer diameter surface of the internal precursor by the second extrusion molding using the internal precursor as the core wire, so as to obtain a state where the internal precursor is installed in the tubular shape of the second extruded product.

[0035] Although the second uniaxial stretching is carried out with the internal precursor inside the tube of the second extruded product, in the second uniaxial stretching, only the second extruded product is stretched and the internal precursor is not stretched. For example, by grasping both ends of the second extruded product in the longitudinal direction and pulling in the opposite direction, only the second extruded product is stretched. The second extruded product is made porous by the second uniaxial stretching to obtain an external precursor. In this way, a composite precursor including the internal precursor and the external precursor adjacent to and overlapping its outer diameter is obtained.

[0036] The second uniaxial stretching is performed under the condition that the second extruded product becomes porous and the inner diameter of the obtained outer precursor is less than the outer diameter of the inner precursor. The "condition of becoming an inner diameter less than the outer diameter of the inner precursor" as used herein refers to the stretching condition equivalent to the condition that when the second extruded product is stretched alone assuming a state where the inner precursor is not included in the tube, the inner diameter after stretching is less than the outer diameter of the inner precursor. For example, a porous layer with a high porosity can be obtained as the outer part by stretching 1.9 times or more and 10 times or less. Regarding the inner diameter after stretching, it can be controlled by adjusting the inner diameter of the second extruded product before stretching in addition to the stretching ratio.

[0037] During the second uniaxial stretching, the inner precursor is not stretched and does not follow the stretching of the second extruded product. Therefore, the composite precursor may include a portion where the outer precursor and the inner precursor do not overlap and only the outer precursor remains. Such an excess outer precursor may be cut off before firing. Alternatively, the excess outer part that may remain after firing may be cut off.

[0038] Both the first uniaxial stretching and the second uniaxial stretching may be performed in a heating environment. For example, the first uniaxial stretching is performed at a temperature of 50°C or higher and 450°C or lower. Also, for example, the second uniaxial stretching is performed at a temperature of 50°C or higher and 340°C or lower.

[0039] After performing the first uniaxial stretching on the first extruded product, before installing the obtained inner precursor into the tubular hollow part of the second extruded product, the inner precursor may be fired. By pre-firing the inner precursor in this way, the handleability is improved. The firing can be performed, for example, at a temperature of 340°C or higher, which is the melting point of PTFE. Alternatively, semi-firing may be performed at a temperature lower than the melting point. As a specific example, firing at 340°C or higher and 450°C or lower can be mentioned.

[0040] By performing thermal analysis using a differential scanning calorimeter (DSC), the firing degree of the PTFE molded product can be confirmed. In the DSC curve obtained by measuring the fired PTFE, a peak attributed to the melting point can be observed near 327°C. In the DSC curve for the unfired PTFE, the peak of the melting point appears near 340°C. In the DSC curve for the semi-fired PTFE, peaks of the melting point can appear both near 327°C and near 340°C. Alternatively, the DSC curve of the semi-fired PTFE can show a large and broad waveform over the range of 327°C to 340°C.

[0041] After the second uniaxial stretching, by firing the composite precursor, a fluororesin structure including a non-porous inner part and a porous outer part provided outside thereof is obtained. By this main firing, both the outer precursor and the inner precursor are fired and integrated together.

[0042] During firing, the inner diameter surface of the outer precursor is pressed against the inner precursor, and the inner precursor expands as described above. That is, firing proceeds in a state where stress is applied from both sides toward the interface at the interface where the outer precursor and the inner precursor are in contact. By firing in this state, the inner precursor and the outer precursor melt, so that a fluororesin structure including a highly adhered and integrated inner part and outer part is obtained. The bonding strength between the inner part and the outer part is high, and peeling hardly occurs.

[0043] This main firing is performed at a temperature equal to or higher than the melting point of PTFE. By firing at a temperature equal to or higher than the melting point of PTFE, the inner precursor gels and expands. For example, this main firing is performed at a temperature of 340°C or higher and 450°C or lower. Also, it is desirable that this main firing be performed for 3 minutes or more.

[0044] A specific example of the method for manufacturing the fluororesin structure will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an example of extrusion molding. Specifically, FIG. 1 shows an example of the production of the first extruded product which is an intermediate molded product of the inner part and / or the inner precursor. FIG. 2 is a cross-sectional view schematically showing an example of the second uniaxial stretching of the second extruded product.

[0045] The extrusion die 51 of the extruder 50 is filled with a first mixture 20 containing PTFE fine powder. The first mixture 20 is a mixture of PTFE fine powder and other materials such as extrusion aids. The first mixture 20 can be, for example, a paste containing PTFE fine powder. Alternatively, the first mixture 20 can be a compression molded body (billet) containing PTFE fine powder.

[0046] A mandrel 55 is inserted inside the extrusion die 51.

[0047] By moving the extrusion ram 53 towards the discharge port 52, the first mixture 20 is extruded from the discharge port 52 while being compressed. Thus, a tubular first extruded product 21 is obtained.

[0048] For example, a core pin is installed at the tip of the mandrel 55 inside the extrusion die 51, and the inner diameter of the tube can be controlled by the diameter of the core pin. By adjusting the diameter of the discharge port 52 of the extrusion die 51, the outer diameter of the first extruded product 21 can be controlled. Also, in order to control the outer diameter, for example, a sizing die with appropriate dimensions may be used. By adjusting the core pin diameter and the diameter of the discharge port 52 (or die dimensions), the wall thickness of the first extruded product 21 can be controlled.

[0049] The first extruded product 21 is supplied to a drying furnace 61 and dried there. In the illustrated example, the extrusion and drying are set to be performed continuously, but this is not the case. For example, drying and firing may be performed in the same step in the drying furnace 61, or the obtained first extruded product 21 may be batch-fed for drying. Also, drying and firing may be omitted.

[0050] It is desirable to apply tension to the first extruded product 21 by means of a tension pulley 91 and a guide roller 92 arranged on the downstream side of the extruder 50 to prevent sagging. Further, by appropriately controlling the tension applied to the first extruded product 21 by the tension pulley 91 and the guide roller 92 on the downstream side of the extruder 50 and the drying furnace 61, the first uniaxial stretching can be continuously performed after extrusion and drying on the same production line. For example, the internal precursor 22 obtained by the first uniaxial stretching of the first extruded product 21 can be wound around a winding roll 93. Alternatively, the first uniaxial stretching of the first extruded product 21 may be performed batchwise.

[0051] The second extruded product, which is an intermediate formed product of the outer part, can be obtained, for example, by performing a second extrusion similar to the first extrusion for the first extruded product. A second mixture is used instead of the first mixture 20, and it is appropriately adjusted according to the core pin diameter and the dimensions of the outer part for manufacturing the discharge port 52 (or die dimensions). However, for the second extruded product, no stretching treatment is performed at this point. Since the details of the second extrusion are the same as those of the first extrusion except for this, the illustration is omitted.

[0052] FIG. 2 schematically shows an example of the second uniaxial stretching. The second uniaxial stretching is performed in a state where the internal precursor 22 is contained in the tubular second extruded product 31. For example, the internal precursor 22 obtained by performing the first uniaxial stretching is inserted into the hollow portion of the second extruded product 31 obtained by the second extrusion. Alternatively, the second extruded product 31 may be directly coated on the outer diameter of the internal precursor 22 as in the example described later with reference to FIG. 3. Further, in the illustrated example, a tubular internal precursor 22 is used, but an internal precursor having a string or rod shape may be used instead.

[0053] Along the longitudinal direction of the inner precursor 22 and the second extruded product 31, uniaxial stretching is performed only on the second extruded product 31. For example, both end portions of the second extruded product 31 along the first direction 100 along the longitudinal direction are gripped by the chuck 70 and pulled along the first direction 100. Note that the first direction 100 may correspond to the cylindrical axis when the tube shape of the second extruded product 31 is regarded as a cylindrical shape. That is, the first direction 100 may correspond to a direction orthogonal to the circular cross section of the second extruded product 31.

[0054] The illustrated chuck 70 includes a chuck frame 71, a screw shaft 73, a jaw 72 connected to the chuck frame 71 via the screw shaft 73, and a knob 74 for manually operating the screw shaft 73. Further, the chuck 70 includes a connecting portion 75 for connection with a tensile device such as a tensile testing machine, for example. The chuck 70 grips the end portion of the second extruded product 31 with the jaw 72. By the operation of the device connected to the chuck 70 via the connecting portion 75, the chuck 70 that grips each end portion of the second extruded product 31 along the first direction 100 is moved in the opposite direction along the first direction 100, and the second uniaxial stretching of the second extruded product 31 is performed. As long as the end portion of the second extruded product 31 can be gripped by the chuck 70, the design of the chuck 70 is not limited to that shown in the figure.

[0055] FIG. 3 is a cross-sectional view schematically showing an example of the second extrusion molding. Specifically, FIG. 3 shows an example of performing the second extrusion molding using the inner precursor as a core wire. Here, a tubular inner precursor that functions as a core wire is illustrated, but a string-shaped extruded product may be used as the core wire instead.

[0056] The extrusion die 51 provided in the extruder 50 is filled with a second mixture 30 containing PTFE fine powder. The second mixture 30 is a mixture of PTFE fine powder and other materials such as an extrusion aid. The second mixture 30 may be, for example, a paste containing PTFE fine powder. Alternatively, the second mixture 30 may be a compression molded body (billet) containing PTFE fine powder.

[0057] Inside the extrusion die 51, the internal precursor 22 sent out from the supply roll 90 is supplied as a core wire. The internal precursor 22 passes through the inside of the extrusion die 51 and is drawn out from the discharge port 52 of the extrusion die 51 to the outside.

[0058] When the extrusion ram 53 is moved toward the discharge port 52, the second mixture 30 is extruded from the discharge port 52 together with the internal precursor 22 while being compressed. In this way, a tubular second extruded product 31 that covers the outer periphery of the internal precursor 22 is obtained.

[0059] The inner diameter of the tube of the second extruded product 31 can be controlled by selecting an internal precursor 22 having an appropriate outer diameter. By adjusting the diameter of the discharge port 52 of the extrusion die 51, the outer diameter of the second extruded product 31 can be controlled. Also, in order to control the outer diameter, for example, a sizing die of an appropriate size may be used. By adjusting the outer diameter of the internal precursor 22 and the diameter of the discharge port 52 (or die size), the wall thickness of the second extruded product 31 can be controlled.

[0060] The second extruded product 31 on the internal precursor 22 is supplied to a drying furnace 61 and dried there. In the illustrated example, the extrusion and drying are set to be performed continuously, but this is not the only case. For example, the drying furnace 61 may be omitted, or the obtained second extruded product 31 may be dried in batches. Also, drying may be omitted.

[0061] It is desirable to apply tension to the internal precursor 22 and the second extruded product 31 by tension pulleys 91 and guide rollers 92 arranged before and after the extruder 50 to prevent sagging. The second extruded product 31 can be wound around a winding roll 93 with the internal precursor 22 included in the tube.

[0062] Perform a second uniaxial stretching on the second extruded product 31 formed on the inner precursor 22. The details of the second uniaxial stretching for the second extruded product 31 when performing the second extrusion using the inner precursor 22 as the core wire are the same as those when inserting the separately extruded inner precursor 22 into the second extruded product 31, so the description thereof is omitted.

[0063] For the extrusion of the tubular extruded product, for example, an extruder having the structure shown in FIG. 4 can be used. FIG. 4 is a schematic cross-sectional view showing an example of the extruder. FIG. 4 may correspond to a more detailed view of the extruder 50 shown in FIG. 1.

[0064] The extruder in the illustrated example has a cylinder 51a and a die 51c disposed via a seal ring 51b below the cylinder 51a. Further, below this die 51c, a die 51d with a band heater 54 wound around the outer peripheral portion is disposed. Inside the cylinder 51a, a mandrel 55 is disposed via a ram 53a and a ram head 53b. A core pin 51e is connected to the lower portion of the mandrel 55. Generally, a center ring bush 56 is inserted into the tip (lower end) of the die 51d.

[0065] Note that the inclined angle (θ) of the central portion of the die 51c can be, for example, 30° or more and 60° or less. When forming at a high reduction ratio (RR: Reduction Ratio), the inclined angle (θ) is preferably 10° or more and 20° or less. Further, the die portion can be heated to, for example, 50°C or more and 60°C or less by the band heater 54 or the like.

[0066] In an extruder having such a configuration, as shown in FIG. 4, when the cross-sectional area of the cylinder-mandrel portion is S1 and the cross-sectional area of the die-core pin is S2, the above RR becomes S1 / S2, and the higher the RR, the larger the reduction ratio.

[0067] FIG. 5 is a schematic cross-sectional view of an extruder of another example. FIG. 5 may correspond to a more detailed view of the extruder 50 shown in FIG. 3. For FIG. 5, the same members as those in FIG. 4 are denoted by the same reference numerals and will be described. The extruder does not have a core pin and has a guide tube 57. An internal precursor as a core wire is inserted into this guide tube 57. A clearance is provided between the straight portion of the die 51d and the guide tube 57. Note that the extruder may further include split cylindrical frame bodies 58a and 58b and an annular clamp 59 for fixing these frame bodies 58a and 58b on the outer circumferences of the cylinder 51a and the die 51c.

[0068] After performing the second uniaxial stretching, firing is performed with the internal precursor remaining installed in the external precursor, whereby a fluororesin structure including a non-porous solid inner portion and a porous outer portion adjacent to the inner portion is obtained. The outer portion may have, for example, a porosity of 10% or more and 90% or less. When a first extruded product having a tubular structure and thus an internal precursor is formed, a multilayer tube including a tubular inner layer as the inner portion and a tubular outer layer as the outer portion can be obtained. When a first extruded product having a string-shaped structure and thus an internal precursor is formed, a composite structure cord including a string-shaped core as the inner portion and a tubular outer layer as the outer portion can be obtained.

[0069] Examples of the fluororesin structure are shown in FIGS. 6-9.

[0070] FIG. 6 is a perspective view schematically showing an example of the fluororesin structure, and FIG. 7 is a cross-sectional view taken along the virtual plane VII-VII' shown in FIG. 6. Specifically, FIGS. 6 and 7 show an aspect of the fluororesin structure as a multilayer tube. FIG. 7 shows a cross-section orthogonal to the tube axis direction of the multilayer tube.

[0071] The multilayer tube 1 shown in FIGS. 6 and 7 has a circular tube shape. The multilayer tube 1 has a two-layer structure in which an inner layer tube 2 and an outer layer tube 3 are laminated in the radial direction of the circular tube. It is desirable that both the inner layer tube 2 and the outer layer tube 3 have a circular cross-section.

[0072] The inner tube 2 may have a wall thickness of, for example, 0.02 mm or more and 2.5 mm or less. The outer tube 3 may have a wall thickness of, for example, 0.3 mm or more and 8 mm or less.

[0073] The multi-layer tube 1 may have an outermost diameter D of, for example, 3 mm or more and 25 mm or less. EX The "outermost diameter" referred to here may correspond to the outer diameter of the outer tube 3. The multi-layer tube 1 may have an interface diameter D of, for example, 3 mm or more and 9 mm or less. IF The "interface diameter" referred to here means the diameter when the interface between the inner tube 2 and the outer tube 3 is regarded as the outer diameter, that is, it can also be said to be the outer diameter of the inner tube 2. The multi-layer tube 1 may have an innermost diameter D of, for example, 2 mm or more and 5 mm or less. IN The "innermost diameter" referred to here may correspond to the inner diameter of the inner tube 2.

[0074] The outer tube 3 may have a porosity of, for example, 10% or more and 90% or less.

[0075] FIG. 8 is a perspective view schematically showing a fluororesin structure of another example, and FIG. 9 is a cross-sectional view taken along the virtual plane IX-IX' shown in FIG. 8. Specifically, FIGS. 8 and 9 show an aspect as a composite structure cord of the fluororesin structure. FIG. 9 shows a cross-section orthogonal to the main axis of the composite structure cord.

[0076] The composite structure cord 10 shown in FIGS. 8 and 9 has a cylindrical string shape. The composite structure cord 10 includes a cord core 12 and an outer layer 13 provided adjacent to the outer periphery of the cord core 12. It is desirable that both the cord core 12 and the outer layer 13 have a circular cross-section.

[0077] The cord core 12 may have a diameter of, for example, 0.3 mm or more and 10 mm or less. The diameter of the cord core 12 corresponds to the interface diameter D of the composite structure cord 10. IF The outer layer 13 may have a wall thickness of 0.3 mm or more and 8 mm or less. Also, the composite structure cord 10 may have an outermost diameter D of, for example, 3 mm or more and 25 mm or less.EX may have. The "outermost diameter" as used herein may correspond to the outer diameter of the outer layer 13.

[0078] The outer layer 13 may have, for example, a porosity of 10% or more and 90% or less.

[0079] As follows, it can be confirmed that a fluororesin structure of a composite structure including two parts is obtained. By cutting the structure at a cross-section intersecting the main axis of the fluororesin structure, the cross-section is exposed. The obtained cross-section is observed with an optical microscope. A visual difference can be observed between the inner part which is the solid part and the outer part which is the porous part. In that case, the inner part and the outer part can be distinguished by cross-section observation. Also, the dimensions of each of the inner part and the outer part can be measured at the cross-section.

[0080] The resin material forming each part of the fluororesin structure can be confirmed as follows. By using a differential scanning calorimeter (DSC) and measuring the melting point, it is possible to confirm that the resin material is PTFE.

[0081] [Examples] (Example 1) A two-layer PTFE resin multi-layer tube having an inner layer and an outer layer as illustrated in FIGS. 6 and 7 was manufactured by the same method as the manufacturing method described with reference to FIGS. 1 and 2 and FIGS. 4 and 5. Specifically, it is as follows.

[0082] For the formation of the inner layer (inner part), Teflon (registered trademark) PTFE fine powder 640-J manufactured by Mitsui Chemicals Fluoro Products Co., Ltd. was used. For the formation of the outer layer (outer part), Teflon (registered trademark) PTFE fine powder 650-J manufactured by Mitsui Chemicals Fluoro Products Co., Ltd. was used.

[0083] The inner tube precursor (tubular internal precursor) was obtained by the following procedure. After adding 18 parts by mass of naphtha (extrusion aid) to 100 parts by mass of PTFE fine powder (640-J), the mixture was mixed at room temperature using a turbular mixer to prepare a first mixture. Subsequently, the first mixture was formed into a cylindrical shape using a preforming machine. The obtained preform was put into an extruder equipped with a die of φ5.9 (mm) and a core pin (chip) of φ4.1 (mm). The extrusion molding was carried out while pulling the tube in synchronization with the extrusion, and the obtained first extruded product was dried in a heating furnace set at 180°C to 200°C to remove the extrusion aid.

[0084] Uniaxial stretching in the longitudinal direction (first uniaxial stretching) was performed on the first extruded product in a temperature environment of 100°C. At this time, weak stretching was performed so that the length in the longitudinal direction became about 1.5 times. Subsequently, pre-sintering was carried out in a heating furnace set at 380°C to 400°C to obtain an inner tube precursor.

[0085] The second extruded product, which is an intermediate formed product of the part constituting the outer layer, 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 (650-J), the mixture was mixed at room temperature using a turbular mixer to prepare a second mixture. Subsequently, the second mixture was formed into a cylindrical shape using a preforming machine. The obtained preform was put into an extruder equipped with a die of φ7.05 (mm) and a core pin of φ5.70 (mm). The extrusion molding was carried out while pulling the tube in synchronization with the extrusion, and the obtained first extruded product was dried in a heating furnace set at 180°C to 200°C to remove the extrusion aid.

[0086] An inner layer tube precursor was installed in the tubular hollow part of the obtained second extruded product. One end and the other end along the longitudinal direction of the second extruded product were respectively fixed to the chucks for holding test samples of the stretching machine so that only the second extruded product provided on the outside was stretched, and uniaxial stretching (second uniaxial stretching) in the length direction was performed in a temperature environment of 100 °C. At this time, stretching was performed so that the length in the longitudinal direction became 2.8 times. By this stretching process, only the outer layer tubular molded product was made porous, and a multi-layer precursor (tubular composite precursor) of a solid-structured inner layer tube precursor and a porous outer layer tube precursor was obtained.

[0087] The obtained multi-layer precursor was fired in a heating furnace set at 380 °C for 10 minutes or more. Portions of the fired product that did not include the inner layer tube and only had the outer layer tube at both ends in the longitudinal direction were cut off to obtain a multi-layer tube (tubular fluororesin structure).

[0088] (Example 2) A PTFE resin multi-layer tube was manufactured by the same procedure as in Example 1, except that the dimensional design during extrusion molding was changed as follows. The die used for extruding the first extruded product was changed to one with a diameter of φ6.3 (mm), and the core pin was changed to one with an outer diameter of 5.5 (mm). The die used for extruding the second extruded product was changed to one with a diameter of φ7.65 (mm), and the core pin was changed to one with an outer diameter of 6.15 (mm).

[0089] (Example 3) A PTFE resin multi-layer tube having a two-layer structure with an inner layer and an outer layer was manufactured by the same manufacturing method as the example described with reference to FIG. 3. Specifically, it is as follows.

[0090] For the formation of the inner layer (inner part), POLYFLON (registered trademark) F-302, a PTFE fine powder manufactured by Daikin Industries, Ltd., was used. For the formation of the outer layer (outer part), TEFLON (registered trademark) PTFE fine powder 650-J manufactured by Mitsui Chemicals Fluoro Products Co., Ltd. was used.

[0091] First, an inner layer tube precursor was obtained in the same procedure as in Example 1, except that the above F-302 was used as the PTFE fine powder and the dimensional design during extrusion molding was changed as follows. When extruding the first extruded product, the die used was changed to one with a diameter of φ4.15 (mm), and a guide tube with an outer diameter of 3.75 (mm) was used instead of the core pin.

[0092] Next, using the above inner layer tube precursor as the core wire, and using the above 650-J as the PTFE fine powder, extrusion molding was performed in the same procedure as in Example 1 except that the die used during extrusion molding was changed to one with a diameter of φ5.0 (mm) to obtain a second extruded product. For the obtained second extruded product, uniaxial stretching (second uniaxial stretching) to make only the outer layer porous, firing, and cutting off the excess outer layer tube were carried out in the same procedure as in Example 1 to obtain a multilayer tube (tubular fluororesin structure).

[0093] (Example 4) A PTFE resin multilayer tube was manufactured in the same procedure as in Example 3, except that the dimensional design during extrusion molding was changed as follows. The same first extruded product as in Example 3 was used, and the die used when extruding the second extruded product was changed to one with a diameter of φ4.9 (mm).

[0094] (Example 5) A PTFE resin composite structure cord having a core (inner part) and an outer layer (outer part) as shown in FIGS. 8 and 9 was manufactured. Specifically, it is as follows.

[0095] For the formation of both the core (inner part) and the outer layer (outer part), Polyflon (registered trademark) F-104, a PTFE fine powder manufactured by Daikin Industries, Ltd., was used.

[0096] The core precursor (string-like internal precursor) was obtained by the following procedure. 18 parts by mass of naphtha (extrusion aid) was added to 100 parts by mass of PTFE fine powder, and then mixed at room temperature using a turbular mixer to prepare a first mixture. Subsequently, the first mixture was formed into a cylindrical shape using a preforming machine. The obtained preform was put into an extruder equipped with a die of φ7.9 (mm) and extrusion molded. The obtained first extruded product was dried in a heating furnace set at 180°C to 200°C to remove the extrusion aid.

[0097] Uniaxial stretching in the longitudinal direction (first uniaxial stretching) was performed on the first extruded product under a temperature environment of 200°C. At this time, weak stretching was performed so that the length in the longitudinal direction became about 1.5 times. Next, pre-sintering was performed in a heating furnace set at 380°C to 400°C to obtain a core precursor.

[0098] A second extruded product was obtained in the same procedure as in Example 1, except that the above F-104 was used as the PTFE fine powder and the dimensional design during extrusion molding was changed as follows. The die used for extruding the first extruded product was changed to one with a diameter of φ22.5 (mm), and the core pin was changed to one with an outer diameter of 8.5 (mm).

[0099] The core precursor was instead installed in the hollow part of the obtained second extruded product. Uniaxial stretching (second uniaxial stretching) for making only the outer layer porous was performed on the second extruded product with the core precursor held inside under the same procedure as in Example 1, except that the temperature setting was changed to 270°C. Subsequently, firing was performed under the same conditions as in Example 1, and the surplus outer layer tube was cut off in the same manner as in Example 1 to obtain a composite structure cord (string-like fluororesin structure).

[0100] (Comparative Example) A two-layer PTFE resin multi-layer tube having an inner layer and an outer layer was manufactured by the following method.

[0101] An inner tube precursor (internal precursor) was manufactured in the same procedure as in Example 1, except that the weak stretching (first-axis stretching) was omitted. Extrusion molding was performed in the same procedure as in Example 1, except that the core pin used when extruding the second extruded product was changed to a core pin with a diameter of φ5.9, to obtain a second extruded product. The second extruded product was uniaxially stretched to 2.8 times its length in the longitudinal direction in a temperature environment of 100 °C to make it porous. Next, the inner tube precursor was inserted into the hollow part of the stretched second extruded product. The second extruded product with the inner tube precursor inserted was fired in a heating furnace set at 350 °C to 370 °C to obtain a PTFE resin multi-layer tube.

[0102] For the various fluororesin structures manufactured in Examples 1-5 and the comparative example, dimensional measurements were performed by the method described above. The measurement results are shown in Table 1. Specifically, Table 1 shows the outer diameter, interface diameter, inner diameter, thickness of the outer part, and thickness of the inner part of each structure. The "interface diameter" referred to here means the diameter when the interface between the inner part and the outer part is regarded as the outer diameter, that is, it can also be said to be the outer diameter of the inner part. For the structure (composite structure cord) of Example 5 that is not hollow, the inner diameter is denoted as "zero". Table 1 also shows the shape of each structure.

[0103]

Table 1

[0104] For each fluororesin structure, the adhesion between the inner part and the outer part was evaluated by the following method. For the molded products (multi-layer tubes) obtained in Examples 1-4 and the comparative example, evaluation was performed using a universal testing machine. For the molded product (composite structure cord) of Example 5 with a large diameter, since another method was used, it will be described separately.

[0105] Each of the tube sections of a certain length cut out from each of the multi-layer tubes obtained in Examples 1-4 and the comparative example was longitudinally split in half so that the cut surface was along the length direction. After one of the cut tubes was opened into a strip shape, the dimensions were adjusted by cutting to obtain a strip-shaped test piece with a width of about 5 mm.

[0106] At the cross-sections of both end faces in the longitudinal direction of each test piece, a cut was made with a razor blade between the solid layer (non-porous layer) and the porous layer visible there. The solid layer on one end side and the porous layer on the other end side were fixed with the chucks of a universal testing machine, respectively, and a tearing test was carried out. The tearing test was carried out under the following conditions: chuck pressure: 0.3 MPa; tearing speed: 200 mm / min; tearing length: about 50 mm.

[0107] Regarding the multi-layer tubes of Examples 1-4, no delamination occurred between the solid layer and the porous layer. Instead, cohesive delamination was observed within the porous layer. In the multi-layer tubes of the comparative examples, delamination between the solid layer and the porous layer was confirmed.

[0108] Regarding Examples 1-4 in which no interfacial delamination was confirmed in the above tearing test, it was evaluated by the following tensile test whether the inner layer tube and the outer layer tube broke separately or simultaneously.

[0109] Each of the tube segments of a certain length cut out from each multi-layer tube was pulled using a universal testing machine under the following conditions until breakage was confirmed at least in the outer layer: chuck pressure: 0.3 MPa; initial distance between chucks: 40 mm; tensile speed: 50 mm / min.

[0110] For any of Examples 1-4, simultaneous breakage of the outer layer and the inner layer was confirmed. Also, for any of Examples 1-4, no interfacial delamination was observed in the samples after the test.

[0111] From the results of the above two tests, it can be seen that in Examples 1-4, a multi-layer tube with high bondability between the inner layer tube and the outer layer tube and difficult to cause interfacial delamination was obtained.

[0112] Regarding the composite structure cord obtained in Example 5, the adhesion between the inner part and the outer part was evaluated by the following method. In a sample of a certain length cut out from the obtained composite structure cord, cuts were made along the longitudinal direction at two opposite positions on the side surface in the porous tube part (outer part) of the outer layer. The solid rod part (cord-like inner part) corresponding to the cord core and the porous tube part were each clamped with a radio pincer and manually pulled in the opposite direction along the longitudinal direction. Although the porous tube part could be partially peeled off from the solid rod part, the porous tube part broke in the radial direction halfway. From the test results, it can be seen that in the composite structure cord manufactured in Example 5, a composite structure cord with high bondability between the solid rod part and the porous tube part and difficult to peel was obtained.

[0113] The results of each test are summarized in Table 2.

[0114]

Table 2

[0115] According to the embodiments described above, a method for manufacturing a fluororesin structure and a fluororesin structure obtained by the manufacturing method are provided. The fluororesin structure includes an inner part that contains polytetrafluoroethylene resin and is non-porous, and an outer part that is located like a sleeve outside the inner part and contains polytetrafluoroethylene resin and is porous. The manufacturing method includes obtaining a first extruded product in a tube shape or a string shape, performing a first uniaxial stretching on the first extruded product in the longitudinal direction by 3.0 times or less to obtain an internal precursor, obtaining a second extruded product having a tube shape, performing a second uniaxial stretching on the second extruded product with the internal precursor installed in the hollow part of the tube shape of the second extruded product to obtain a composite precursor, and performing firing on the composite precursor. The first extruded product is obtained by extruding a first mixture containing polytetrafluoroethylene fine powder. The second extruded product is obtained by extruding a second mixture containing polytetrafluoroethylene fine powder. The provided fluororesin structure is excellent in peel resistance between the inner part and the outer part.

[0116] Note that the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist thereof at the implementation stage. Also, the respective embodiments may be implemented in appropriate combination, and in that case, the combined effects can be obtained. Furthermore, the above embodiments include various inventions, and various inventions can be extracted by combinations selected from a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiments, if the problem can be solved and the effects can be obtained, the configuration from which these constituent elements are deleted can be extracted as an invention. The invention described in the original claims of the present application is appended below. [1] An inner part that contains polytetrafluoroethylene resin and is non-porous, An outer part that is located outside the inner part and contains polytetrafluoroethylene resin and is porous A method for manufacturing a fluororesin structure, comprising: Extruding a first mixture containing polytetrafluoroethylene fine powder to obtain a first extruded product in the shape of a tube or a string; Performing a first uniaxial stretching on the first extruded product in the longitudinal direction by 3.0 times or less to obtain an internal precursor; Extruding a second mixture containing polytetrafluoroethylene fine powder to obtain a second extruded product having a tubular shape; Performing a second uniaxial stretching on the second extruded product in the longitudinal direction with the internal precursor installed inside the tubular hollow portion of the second extruded product to obtain a composite precursor; Firing the composite precursor. [2] The manufacturing method according to [1], further comprising firing the internal precursor after performing the first uniaxial stretching and before installing the internal precursor inside the tubular hollow portion of the second extruded product. [3] A fluororesin structure obtained by the manufacturing method according to [1] or [2].[[]END]] [4] The fluororesin structure according to [3], wherein the outer part has a porosity of 10% or more and 90% or less. [5] The fluororesin structure according to [3] or [4], wherein the outer part has a tubular shape with a wall thickness of 0.3 mm or more and 8 mm or less, and the inner part has a tubular shape with a wall thickness of 0.02 mm or more and 2.5 mm or less. [6] The fluororesin structure according to [3] or [4], wherein the outer part has a tubular shape with a wall thickness of 0.3 mm or more and 8 mm or less, and the inner part has a string shape with a diameter of 0.3 mm or more and 10 mm or less.

Explanation of Symbols

[0117] 1... multi-layer tube, 2... inner layer tube, 3... outer layer tube, 10... composite structure cord, 12... cord core, 13... outer layer, 20... first mixture, 21... first extruded product, 22... internal precursor, 30... second mixture, 31... second extruded product, 50... extruder, 51... extrusion die, 51a... cylinder, 51b... seal ring, 51c... die, 51d... die head, 51e... core pin, 52... discharge port, 53... extrusion ram, 53a... ram, 53b... ram head, 54... band heater, 55... mandrel, 56... center ring bush, 57... guide tube, 58a... frame, 58b... frame, 59... clamp, 61... drying furnace, 70... chuck, 71... chuck frame, 72... jaw, 73... screw shaft, 74... knob, 75... connecting part, 90... supply roll, 91... tension pulley, 92... guide roller, 93... take-up roll.

Claims

1. An inner part that contains polytetrafluoroethylene resin and is non-porous, An outer part that is located outside the inner part and contains polytetrafluoroethylene resin and is porous, A method for manufacturing a fluororesin structure, comprising: Extruding a first mixture containing polytetrafluoroethylene fine powder to obtain a first extruded product in the shape of a tube or a string; Performing a first uniaxial stretching on the first extruded product in the longitudinal direction by 1.1 times or more and 3.0 times or less to obtain an internal precursor; Extruding a second mixture containing polytetrafluoroethylene fine powder to obtain a second extruded product having a tube shape; Performing a second uniaxial stretching on the second extruded product in the longitudinal direction in a state where the internal precursor is installed in the hollow part of the tube shape of the second extruded product to obtain a composite precursor; Firing the composite precursor, The manufacturing method further includes firing the internal precursor after performing the first uniaxial stretching and before installing the internal precursor in the hollow part of the tube shape of the second extruded product.

2. The manufacturing method according to Claim 1, wherein in the obtained fluororesin structure, the outer part has a porosity of 10% or more and 90% or less.

3. The manufacturing method according to Claim 1 or 2, wherein in the obtained fluororesin structure, the outer part has a tube shape with a wall thickness of 0.3 mm or more and 8 mm or less, and the inner part has a tube shape with a wall thickness of 0.02 mm or more and 2.5 mm or less.

4. The manufacturing method according to Claim 1 or 2, wherein in the obtained fluororesin structure, the outer part has a tube shape with a wall thickness of 0.3 mm or more and 8 mm or less, and the inner part has a string shape with a diameter of 0.3 mm or more and 10 mm or less.

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