Multilayer tubular member and manufacturing method thereof

Abstract

To provide a tubular member that has excellent bending resistance and also takes into consideration reducing an environmental load.SOLUTION: A multilayer tubular member is formed by laminating an inner layer and an outer layer formed of a resin material, and the yield strain of the resin material forming the outer layer is larger than the yield strain of the resin material forming the inner layer. The resin material forming the inner layer and the resin material forming the outer layer are substantially the same resin material. The resin material forming the outer layer uses a recycled resin material that is obtained by recycling another article formed of the resin material forming the inner layer as a resin material, thereby increasing the yield strain.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multilayer tubular member having a plurality of layers laminated thereon, for use in factory facilities, semiconductor manufacturing equipment, and the like.

[0002] Synthetic resin tubular members (tubes) are used for piping in factory facilities, semiconductor manufacturing equipment, and various other industrial devices.

[0003] Such tubular members are often made of chemically stable synthetic resins, and fluororesins are often used, to prevent impurities from eluting into the liquid flowing through the piping. In particular, in the piping of semiconductor manufacturing equipment, where high-purity special chemicals are passed, the elution of impurities is strictly restricted, and so piping is often made of special synthetic resins.

[0004] Piping for industrial equipment and the like is often installed in narrow spaces in a bent state, so a certain level of flexibility and bending resistance is required. However, fluororesin is generally hard, and there are cases in which its flexibility and bending resistance are insufficient.

[0005] Although fluororesins with improved flex resistance, such as the fluororesin described in Patent Document 1, have been proposed, they require specific materials and blends, which poses the problem of being expensive.

[0006] Furthermore, fluororesins made from such specific materials and blends may contain impurities and may not be suitable for use as piping.

[0007] Another issue related to fluororesin is that emissions from the chemical industry sector involved in the production of fluororesin are the second largest in terms of energy-related carbon dioxide emissions from the industrial sector in Japan in fiscal year 2020 (Non-Patent Document 1). Considering the environmental impact, it is preferable to reduce the amount of fluororesin used. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2014-55290 A [Non-patent literature]

[0009] [Non-Patent Document 1] Ministry of the Environment: Greenhouse gas emissions (final figures) for fiscal year 2020 (Reiwa 2) Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a tubular member that can be suitably used for piping, particularly for liquid piping, and that has excellent bending resistance while also taking into consideration reduction of the environmental load. [Means for solving the problem]

[0011] As a result of thorough investigation into the structure of tubular members, the inventors discovered that by stacking layers made of resin materials with different yield strains, it is possible to improve bending resistance and also contribute to reducing the environmental load. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a multi-layer tubular member of the present invention. [Diagram 2] FIG. 4 is a schematic diagram showing stress generated in a bent portion of a multilayer tubular member. [Diagram 3] 4 is a flow chart of a method for obtaining a multi-layer tubular member of the present invention. [Figure 4] These are the results of metal elution tests. [Diagram 5] This is a method for checking the minimum bending radius. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The multilayer tubular member of the present invention will now be described with reference to the drawings.

[0014] As shown in FIG. 1, the multilayer tubular member 1 of the present invention is composed of an inner layer 10 and an outer layer 20 provided on the outer periphery of the inner layer 10, and is characterized in that the inner layer 10 is formed from a first fluororesin, and the outer layer 20 is formed from a second fluororesin that is substantially the same as the first fluororesin.

[0015] "Substantially the same" means that although specific physical properties are different, the essential parts of the resin, such as the type, ingredients, brand, etc. of the resin itself, are the same. An example of a specific physical property is the yield strain, which will be described later.

[0016] By forming the inner layer 10 and the outer layer 20 from substantially the same material, the inner layer 10 and the outer layer 20 can be easily integrated together, which contributes to improving the strength of the multilayer tubular member 1.

[0017] An example of the second fluororesin that is substantially the same as the first fluororesin is a recycled fluororesin obtained by recycling an article formed from the first fluororesin into a fluororesin that is in a state where it can be used to form a new article.

[0018] Examples of items made from the first fluororesin include tubes, wire coating materials, films, tapes, and sample containers. These items that are discarded after use can be collected, crushed, washed, and molded into pellets, allowing for the production of recycled fluororesin using the discarded items as raw materials.

[0019] In the process of converting an article made from the first fluororesin into recycled fluororesin, changes in physical properties occur due to the influence of thermal history, etc., and it is possible to obtain a second fluororesin that is substantially identical to the first fluororesin.

[0020] One of the physical properties that changes in the process of converting an article made from the first fluororesin into recycled fluororesin is the yield strain, and the yield strain of the second fluororesin tends to increase compared to the yield strain of the first fluororesin.

[0021] Yield strain refers to the tensile yield strain measured according to JIS K-7161-1:2014, and is the tensile strain corresponding to the yield point in a tensile test.

[0022] When bending a tubular member such as a tube, if the bending radius becomes smaller than a predetermined value, kinks will occur in the tubular member.

[0023] When a tubular member is bent, a force that pulls the tubular member (tensile stress) occurs in the portion located on the outside of the bend, while a force that compresses the tubular member (compressive stress) occurs in the portion located on the inside of the bend, as shown in Figure 2. One of the causes of kinking in a tubular member is the progressive deformation of the material that constitutes the tubular member due to these stresses when it is bent.

[0024] The multilayer tubular member 1 of the present invention has a multilayer structure consisting of an inner layer 10 and an outer layer 20. By making the yield strain of the outer layer 20 greater than the yield strain of the inner layer 10, the occurrence of kinking is suppressed and the minimum bending radius can be reduced, contributing to improved bending resistance.

[0025] Although it is not clear why the structure of the present invention suppresses the occurrence of kinks, as shown in FIG. 2, outer layer 20 is located at the outermost and innermost parts of the bend, and therefore the tensile stress on the outer side of the bend and the compressive stress on the inner side of the bend act mainly on outer layer 20.

[0026] Since a material with a large yield strain has room to undergo a certain amount of elastic deformation in response to stress, it is presumed that by using a material with a large yield strain for the outer layer 20 of the multilayer tubular member 1, the deformation of the outer layer 20 due to tensile stress and compressive stress generated at the bend can be kept within the range of elastic deformation, and as a result, deformation of the inner layer 10 which is integrated with the outer layer 20 is also suppressed, thereby suppressing the occurrence of kinking.

[0027] The yield strain of the outer layer 20 is preferably 1.2 times or more the yield strain of the inner layer 10. By providing a difference of 20% or more between the yield strains of the inner layer 10 and the outer layer 20, a difference in behavior with respect to bending between the inner layer 10 and the outer layer 20 is reliably manifested, which contributes to improving bending resistance.

[0028] Moreover, the yield strain of the outer layer 20 is preferably equal to or less than twice the yield strain of the inner layer 10. By setting the yield strain of the outer layer 20 at a certain value or less, a difference in behavior with respect to bending is imparted between the inner layer 10 and the outer layer 20, while preventing an excessive difference in behavior from occurring, which contributes to stabilizing bending resistance.

[0029] If the purpose is to suppress kinking, the tubular member may be formed only from the second fluororesin which has a large yield strain. However, when considering use as a pipe for carrying liquid, it is preferable to avoid contact of the second fluororesin with the liquid, and therefore the inner layer 10 which comes into contact with the liquid is formed from the first fluororesin.

[0030] In the present invention, the first fluororesin forming the inner layer 10 may be appropriately selected from various fluororesins, and PFA, FEP, ETFE, etc. may be used.

[0031] From the viewpoint of suppressing the elution of impurities and the like into the liquid flowing inside the multilayer tubular member 1, a fluororesin whose end group has been fluorinated can be preferably used as the first fluororesin.

[0032] Since fluororesin whose end groups have been fluorinated is particularly chemically stable among various fluororesins, by forming the inner layer 10 from this, it is possible to minimize the elution of impurities and the like into the liquid flowing inside the multilayer tubular member 1.

[0033] Among fluororesins whose end groups have been fluorinated, fluorinated PFA can be particularly preferably used.

[0034] In the present invention, the ratio of the thickness of the inner layer 10 to the thickness of the outer layer 20 is not particularly limited, but in consideration of obtaining the effects due to the presence of the inner layer 10 and the effects due to the presence of the outer layer 20, it is desirable to set the ratio of the thickness of the inner layer 10 to the thickness of the outer layer 20 within the range of 1:9 to 9:1.

[0035] It is more preferable that the ratio of the thickness of the inner layer 10 to the thickness of the outer layer 20 is within the range of 2:8 to 5:5. When the thickness of the outer layer 20 accounts for 50% or more of the thickness of the multilayer tubular member 1, this contributes to stabilizing the effect of the presence of the outer layer 20, and when the thickness of the inner layer 10 accounts for 20% or more of the thickness of the multilayer tubular member 1, the effect of the presence of the inner layer 10 can also be stably obtained.

[0036] In addition, it is desirable for the specific thickness of the inner layer 10 to be 0.2 mm or more. In particular, when recycled fluororesin is used as the second fluororesin, it is preferable to use an embodiment in which the thickness of the inner layer 10 is 0.2 mm or more.

[0037] The surface condition of an article formed from the recycled fluororesin may change from the surface condition of an article formed from the original first fluororesin, and as one example, the arithmetic mean roughness Ra tends to increase.

[0038] If the thickness of the inner layer 10 is excessively thin, the effects of the surface condition of the outer layer 20 at the interface between the inner layer 10 and the outer layer 20 (such as an increase in the arithmetic mean roughness Ra) will appear on the inner surface of the inner layer 10, and the surface condition of the inner surface of the inner layer 10 may change from the state expected when the first fluororesin is used.

[0039] By setting the thickness of the inner layer 10 to 0.2 mm or more, the influence of the surface condition of the outer layer 20 on the inner surface of the inner layer 10 can be suppressed, and the surface condition of the inner surface of the inner layer 10 can be maintained in a desired state.

[0040] There is no particular upper limit to the thickness of the inner layer 10, which may be set appropriately depending on the desired functions of the multilayer tubular member 1, but is usually set to about 0.2 to 0.5 mm.

[0041] Even if the thickness of the inner layer 10 is less than 0.2 mm, it can be used as one form of the multilayer tubular member 1 of the present invention so long as the surface condition of the inner peripheral surface is not an issue.

[0042] Furthermore, in cases where the surface condition of the article formed from the original first fluororesin is very good, or where the surface condition can be controlled in the process of forming the article from the recycled fluororesin, the thickness of the inner layer 10 may be 0.2 mm or less if the desired surface condition can be achieved even when the article is formed from the recycled fluororesin.

[0043] Although the present invention assumes that the inner layer 10 and the outer layer 20 are formed from substantially the same resin, there is a difference in yield strain between the inner layer 10 and the outer layer 20. To indicate that there is a difference in some of the physical properties, it is desirable to provide an identification element that allows the inner layer 10 and the outer layer 20 to be visually distinguished from each other.

[0044] As a distinguishing factor, a color difference (a difference in color between the inner layer 10 and the outer layer 20) is preferably used, which is simple and allows easy visual distinction.

[0045] When forming the multilayer tubular member 1 using a fluororesin, which is normally colorless or transparent, an identification element can be provided by making one of the inner layer 10 or the outer layer 20 colorless or transparent and coloring the other with a pigment, colorant, or the like.

[0046] In consideration of preventing the leaching of impurities and the like into the liquid flowing through the multilayer tubular member 1, it is desirable to avoid adding pigments, colorants, and the like that could become impurities to the inner layer 10, and an embodiment in which an identification element is provided by coloring the outer layer 20 can be preferably used in the present invention.

[0047] When coloring the outer layer 20, in addition to a mode in which the entire outer layer 20 is colored, a mode in which a strip-shaped colored portion is provided in the outer layer 20 along the longitudinal direction of the multilayer tubular member 1, or a mode in which ink or the like is applied or printed on the entire surface or part of the surface of the outer layer 20 can also be used.

[0048] As with the inner layer 10, if it is desired to avoid adding pigments, colorants, etc. to the outer layer 20, it is preferable to process or modify the surface of the outer layer 20 and use the processing or modification marks as an identification element.

[0049] When processing marks or modification marks are used as the identification element, laser marking marks by laser marking are preferably used. Laser marking can easily form processing marks or modification marks, and since melting marks or thermal discoloration occurs due to the energy of the laser, it is possible to form an identification element that is easily visually recognizable.

[0050] Laser marking may be performed using a commercially available laser marking device, and a carbon dioxide gas laser marking device having a high absorption rate for fluororesin is preferably used.

[0051] An example of a method for obtaining the multi-layer tubular member 1 of the present invention includes the following steps.

[0052] (1) Article forming step: An article is formed using the first fluororesin and used as the article.

[0053] (2) Recycling process: Items that have finished being used and would otherwise be discarded are collected, crushed, washed, and molded into pellets to obtain recycled fluororesin made from discarded items.

[0054] (3) Multilayer tubular member molding step: The first fluororesin is extruded as the inner layer 10 and the recycled fluororesin is extruded as the outer layer 20 to obtain the multilayer tubular member 1.

[0055] A specific example of the article forming step is extrusion molding the first fluororesin to produce a single-layer tubular member (single-layer tube), which can be used as a tube.

[0056] As described above, the yield strain tends to decrease in the process of converting an article formed from the first fluororesin into a recycled fluororesin. Therefore, by using recycled fluororesin obtained by reusing an article formed from the first fluororesin that forms the inner layer 10 for the outer layer 20, it is possible to change the yield strain while using substantially the same fluororesin as the inner layer 10.

[0057] In addition, by using recycled fluororesin for the outer layer 20, waste can be reduced while the amount of new first fluororesin used can be suppressed, thereby contributing to reducing the environmental impact.

[0058] When coloring the outer layer 20, a pigment, colorant, etc. may be added to color the recycled resin material in the above-mentioned recycling process, or a pigment, colorant, etc. may be mixed with the recycled resin material in the multilayer tubular member molding process and extrusion molding may be performed. By coloring the outer layer 20, it functions as an identification element for indicating differences in physical properties, as well as an identification element for indicating that it is made of recycled fluororesin.

[0059] In addition, by relating the color density of the recycled fluororesin colored in the recycling process to the recycling history of the recycled fluororesin, it is also possible to manage the number of times the recycled fluororesin has been recycled.

[0060] Specifically, one management method involves increasing the color density in proportion to the number of times the recycled fluororesin has been recycled, and when the color density reaches a threshold, it is determined that the limit of the number of times it has been recycled has been reached, and the material is then discarded without being recycled.

[0061] FIG. 3 is a flowchart showing the method for obtaining the multilayer tubular member 1 described above and the method for managing the number of times the recycled fluororesin is recycled.

[0062] When a laser marking mark is used as the identification element, the laser marking may be applied to the outer layer 20 during or after the multi-layer tubular member molding process.

[0063] (Example) Below, we will describe an example of the multilayer tubular member 1 of the present invention and its manufacturing method, but the embodiment of the multilayer tubular member 1 of the present invention and its manufacturing method are not limited to the following, and the yield strain and dimensions can be changed as appropriate within the technical concept of the present invention.

[0064] (1. Article forming process) A single-layer tube with an inner diameter of 4 mm and an outer diameter of 6 mm was extruded from fluorinated PFA exhibiting a yield strain of 2.4%. The minimum bending radius was confirmed to be 20 mm using the measurement method described below.

[0065] The result of the metal elution test, which will be described later, conducted on the produced fluorinated PFA single-wall tube is shown in Figure 4. No elution of metal impurities was confirmed, and the tube is at a level suitable for use as chemical piping in semiconductor manufacturing equipment.

[0066] (2.Regeneration process) The single-walled tubes were crushed, washed, and molded into pellets to produce recycled fluororesin, which had a yield strain of 3.5%.

[0067] To confirm this, a single-layer tube with an inner diameter of 4 mm and an outer diameter of 6 mm was extruded using only recycled fluororesin, and the minimum bending radius was confirmed to be 12 mm.

[0068] The results of a metal elution test conducted on a single-walled tube made from recycled fluororesin are shown in Figure 4. It was confirmed that the concentrations of copper, iron, nickel, and zinc were high, and that the elution of metal impurities was at a level that would make it difficult to use the tube for chemical piping in semiconductor manufacturing equipment.

[0069] (3. Multi-layer tubular component molding process) A two-layer multilayer tubular member 1 was extrusion molded using the fluororesin used in the above article formation process as the inner layer 10 and the recycled fluororesin as the outer layer 20. During extrusion molding, a pigment was mixed into the recycled fluororesin to color the outer layer 20 green. The multilayer tubular member 1 had an inner diameter of 4 mm, an outer diameter of 6 mm, a wall thickness of the inner layer 10 of 0.2 mm, and a wall thickness of the outer layer 20 of 0.8 mm.

[0070] The minimum bending radius of the manufactured multilayer tubular member 1 was 15 mm, and the effect of improving bending resistance by reducing the yield strain of the outer layer 20 was confirmed.

[0071] By obtaining recycled fluororesin from a single-layer tube extruded from fluororesin, it was possible to obtain a material with a small yield strain, while being substantially the same material as the inner layer 10. In the examples, a single-layer tube was extruded to obtain recycled fluororesin, but in practical use, obtaining recycled resin material from resin tubes scheduled for disposal is economical and contributes to reducing the environmental load.

[0072] (Metal elution test) After the inner circumferential surface of the tubular member 100 to be measured is washed with ultrapure water, the inside is filled with a 1% nitric acid aqueous solution, both ends are sealed, and it is left at room temperature for 24 hours. For sealing, a PTFE plug that has been confirmed in advance to be non-reactive with the 1% nitric acid aqueous solution is used.

[0073] After 24 hours have passed, the 1% nitric acid aqueous solution sealed in the tubular member 100 is analyzed by an inductively coupled plasma mass spectrometer (ICP-MS) to measure the amount of metal impurities contained in the 1% nitric acid aqueous solution.

[0074] (Minimum bending radius measurement) A method for measuring the minimum bend radius will be described with reference to FIG.

[0075] As shown in the schematic diagram of FIG. 4, the minimum bending radius is measured by bending a tubular member 100 to be measured, which has been cut to a length of 150 mm, into a U-shape and fixing an end portion 102.

[0076] While keeping the ends 102 straight, the ends 102 are brought closer to each other at a predetermined speed to reduce the bending radius of the U-shaped bent portion 101. Half the value of the distance 2r between the ends 102 when a kink occurs in the bent portion is defined as the minimum bending radius r.

[0077] (Evaluation of the surface condition of the inner surface according to changes in the thickness of the inner layer) Multilayer tubular members 1 were produced with different thicknesses of the inner layer 10 and the outer layer 20, and the change in the surface condition of the inner peripheral surface of the multilayer tubular member 1 associated with the change in thickness of the inner layer 10 was observed.

[0078] The total thickness of the inner layer 10 and the outer layer 20 was fixed at 1.0 mm, and four types of samples were prepared by varying the thicknesses of the inner layer 10 and the outer layer 20 as shown in Table 1. Sample 2 corresponds to the multilayer tubular member 1 of the above-mentioned example, and the other samples were prepared in accordance with the example except that the thicknesses of the inner layer 10 and the outer layer 20 were varied.

[0079] As comparative samples, a single-layer tube made only from the above-mentioned fluorinated PFA (Comparative Example 1; for convenience, the thickness of the inner layer is described as 1.0 mm) and a single-layer tube made only from recycled fluororesin (Comparative Example 2; for convenience, the thickness of the outer layer is described as 1.0 mm) were also evaluated.

[0080] The surface condition of the inner peripheral surface was evaluated by measuring the arithmetic mean roughness Ra and maximum height Rz using a confocal laser microscope VK-X1000 manufactured by Keyence Corporation at a lens magnification of 1000. The measurement results are shown in Table 1.

[0081] [Table 1]

[0082] Sample 1 exhibits a surface condition similar to that of the single-layer tube of Comparative Example 1, which was made only from recycled fluororesin. When the thickness of the inner layer 10 is less than 0.2 mm, it can be evaluated that the surface condition of the inner surface of the inner layer 10 is not significantly different from the surface condition of an article made from recycled fluororesin.

[0083] Samples 2 to 4 show a surface condition similar to that of the single-layer tube of Comparative Example 2 made only of fluorinated PFA, and have a smoother surface than Sample 1. When the thickness of the inner layer 10 is 0.2 mm or more, the surface condition of the inner peripheral surface of the inner layer 10 is not affected by the recycled fluororesin used in the outer layer 20, and it can be evaluated that the original surface condition of an article made of fluorinated PFA is maintained.

[0084] Incidentally, sample 1 can also be used as one embodiment of the multilayer tubular member 1 of the present invention, so long as the surface condition of the inner peripheral surface is not a factor.

[0085] (Summary of the embodiment) The technical ideas grasped from the above-described embodiment will be described by using the reference numerals and the like in the embodiment. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiment.

[0086] [1] A multilayer tubular member (1) comprising at least an inner layer (10) and an outer layer (20) laminated together, the inner layer (10) being formed from a first fluororesin, and the outer layer (20) being formed from a second fluororesin that is substantially the same as the first fluororesin.

[0087] [2] The multilayer tubular member (1) according to the above [1], characterized in that the second fluororesin is a recycled fluororesin recycled from an article formed from the first fluororesin.

[0088] [3] The multilayer tubular member according to [1] or [2] above, characterized in that the thickness of the inner layer (10) is 0.2 mm or more.

[0089] [4] The multilayer tubular member (1) according to any one of the above [1] to [3], wherein the yield strain of the second fluororesin is greater than the yield strain of the first fluororesin.

[0090] [5] The multilayer tubular member (1) according to any one of the above [1] to [4], wherein the yield strain of the second fluororesin is 1.2 times or more the yield strain of the first fluororesin.

[0091] [6] The multilayer tubular member (1) according to any one of the above [1] to [5], wherein the yield strain of the second fluororesin is not more than twice the yield strain of the first fluororesin.

[0092] [7] The multilayer tubular member (1) according to any one of the above [1] to [6], characterized in having an identification element for visually distinguishing between the inner layer (10) and the outer layer (20).

[0093] [8] The multilayer tubular member (1) according to [7] above, wherein the identification element is a color difference between the inner layer (10) and the outer layer (20).

[0094] [9] The multilayer tubular member (1) according to the above item [8], characterized in that the inner layer (10) is formed to be colorless or transparent, and the outer layer (20) is colored, thereby forming a color difference.

[0095]

[10] The multilayer tubular member (1) according to [7] above, characterized in that the identification element is a processing mark or modification mark formed on the outer layer (20).

[0096]

[11] The multilayer tubular member (1) according to the above

[10] , wherein the processing marks or modification marks are laser marking marks.

[0097]

[12] A method for producing a multi-layer tubular member (1) having at least an inner layer (10) and an outer layer (20) laminated thereto, the method comprising: an article formation step of forming an article using a first fluororesin; a recycling step of obtaining recycled fluororesin using discarded articles as a raw material; and a multi-layer tubular member extrusion step of obtaining the multi-layer tubular member (1) by extruding the first fluororesin as the inner layer (10) and the recycled fluororesin as the outer layer (20).

[0098]

[13] A method for producing the multi-layer tubular member (1) described in

[12] above, characterized in that the recycled fluororesin material is colored in the recycling step or the multi-layer tubular member extrusion step.

[0099]

[14] A method for producing the multilayer tubular member (1) described in

[13] above, characterized in that the number of times the recycled fluoromaterial is recycled is managed by correlating the color concentration of the recycled fluororesin colored in the recycling process with the recycling history of the recycled fluororesin.

[0100]

[15] A method for producing a multi-layer tubular member according to the above

[12] , characterized in that the outer layer (20) is laser marked during or after the multi-layer tubular member extrusion process.

[0101]

[16] A method for producing a multi-layer tubular member (1) according to any one of the above

[12] to

[15] , characterized in that the article forming step comprises extrusion molding a first fluororesin to produce a single-layer tubular member, and utilizing the single-layer tubular member. [Industrial Applicability]

[0102] The multilayer tubular member of the present invention is suitably used for piping in factory equipment, semiconductor manufacturing equipment, and various other industrial equipment, but the uses are not limited thereto and it can be used in a variety of applications. [Explanation of symbols]

[0103] 1 Multilayer tubular member 10 Inner layer 20 outer layer 100 Tubular member 101 U-shaped bending section 102 End

Claims

1. A multi-layer tubular member having at least an inner layer and an outer layer laminated thereon, The inner layer is formed of a first fluororesin, The multi-layer tubular member, wherein said outer layer is formed of a second fluororesin substantially the same as said first fluororesin.

2. 2. The multi-layer tubular member according to claim 1, wherein the second fluororesin is a recycled fluororesin recycled from an article formed from the first fluororesin.

3. 3. The multi-layer tubular member according to claim 2, wherein the wall thickness of the inner layer is 0.2 mm or more.

4. 4. The multi-layer tubular member according to claim 1, wherein the second fluororesin has a yield strain greater than the yield strain of the first fluororesin.

5. 5. The multi-layer tubular member according to claim 4, wherein the yield strain of the second fluororesin is at least 1.2 times the yield strain of the first fluororesin.

6. 6. The multi-layer tubular member according to claim 5, wherein the yield strain of the second fluororesin is not more than twice the yield strain of the first fluororesin.

7. The multi-layer tubular member according to any one of claims 1 to 3, characterized in that it has an identification element for visually distinguishing the inner layer from the outer layer.

8. 8. The multi-layer tubular member of claim 7, wherein the distinguishing feature is a color difference between the inner layer and the outer layer.

9. 9. The multi-layer tubular member according to claim 8, wherein the color difference is formed by forming the inner layer to be colorless or transparent and the outer layer to be colored.

10. 8. The multi-layer tubular member of claim 7, wherein the identification element is a processing mark or modification mark formed on the outer layer.

11. The multi-layer tubular member according to claim 10, wherein the processing marks or modification marks are laser marking marks.

12. 5. The multi-layer tubular member of claim 4, further comprising an identifying element for visually distinguishing said inner layer from said outer layer.

13. 13. The multi-layer tubular member of claim 12, wherein the distinguishing feature is a color difference between the inner layer and the outer layer.

14. 14. The multi-layer tubular member according to claim 13, wherein the color difference is formed by forming the inner layer to be colorless or transparent and the outer layer to be colored.

15. 13. The multi-layer tubular member of claim 12, wherein the identification element is a processing mark or modification mark formed in the outer layer.

16. The multi-layer tubular member according to claim 15, wherein the processing marks or modification marks are laser marking marks.

17. A method for producing a multi-layer tubular member having at least an inner layer and an outer layer laminated thereon, comprising the steps of: an article forming step of forming an article using the first fluororesin; A regeneration process for obtaining recycled fluororesin using the discarded articles as raw materials; a multi-layer tubular member extrusion step of extruding the first fluororesin as the inner layer and the recycled fluororesin as the outer layer to obtain a multi-layer tubular member.

18. The method for producing a multi-layer tubular member according to claim 17, wherein the recycled fluororesin is colored in the recycling step or in the multi-layer tubular member extrusion step.

19. The method for producing a multilayer tubular member according to claim 18, wherein in the recycling step, the color density of the recycled fluororesin is associated with the recycling history of the recycled fluororesin, thereby managing the number of times the recycled fluororesin has been recycled.

20. 18. The method for producing a multi-layer tubular member according to claim 17, further comprising the step of laser marking the outer layer during or after the step of extruding the multi-layer tubular member.

21. The method for producing a multi-layer tubular member according to any one of claims 17 to 20, wherein the article forming step comprises extruding the first fluororesin to produce a single-layer tubular member, and utilizing the single-layer tubular member.

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