Pipes, piping structures, and methods for manufacturing pipes

Abstract

To provide a pipe that can be used for transporting ultrapure water, a piping structure equipped with the pipe, and a method for manufacturing the pipe. [Solution] A pipe 2 used for transporting ultrapure water, comprising a first resin layer 61 constituting the innermost layer and mainly composed of polyolefin resin, polyvinyl chloride, or polyvinylidene fluoride. The inner surface 2s of the first resin layer 61 is free of foreign matter with the longest straight length of 500 μm or more.

Description

[Technical Field]

[0001] This disclosure relates to pipes, piping structures, and methods for manufacturing pipes. [Background technology]

[0002] In the manufacturing of precision devices such as semiconductor devices or liquid crystal displays, ultrapure water purified to extremely high purity is used in wet processes such as cleaning. If metal ions or other impurities are present in the water above a certain concentration, the metal will adsorb onto the wafer surface, adversely affecting the quality of the precision device. Therefore, strict control over impurities in ultrapure water is carried out.

[0003] The contamination of ultrapure water with impurities can also occur in the piping that makes up the ultrapure water transport line. While metals such as stainless steel, which have excellent gas barrier properties, have been used as the material for the piping, it is considered preferable to use resin considering the effects of metal leaching from the piping.

[0004] For example, Patent Document 1 discloses a multilayer pipe for piping ultrapure water, characterized by comprising a first resin layer made of fluororesin that comes into contact with ultrapure water, and a second resin layer made of a gas-impermeable resin that is provided on the outer surface of the first resin layer. Furthermore, it is disclosed that a third resin layer is provided on the outer surface of the second resin layer to protect the second resin layer, and that polyethylene is used as the third resin layer.

[0005] Among the resins used as materials for piping for ultrapure water, polyvinylidene fluoride (PVDF) is used in all applications in the semiconductor field, including piping within ultrapure water production equipment and piping for transporting ultrapure water from ultrapure water production equipment to the point of use, and has become the technical standard for ultrapure water piping materials.

[0006] Piping made of fluororesin such as PVDF has disadvantages in terms of workability and cost compared to other common piping. Furthermore, there is also a problem that the ultra-high purity cleaning liquid often contains dialuminoalkanes such as 3-dialuminopropane and deteriorates quickly because it is used under the condition of 60°C.

[0007] Therefore, for example, a multilayer pipe in which a polyolefin resin is used for the innermost layer, as shown in Patent Document 2, has been proposed. The multilayer pipe shown in Patent Document 2 has a first polyolefin resin layer constituting the innermost layer and a second polyolefin resin layer disposed outside the first polyolefin resin layer. The first polyolefin resin layer is set so that the calcium elution amount is less than 30 μg / m 2 and the mixing of impurities into ultrapure water is restricted.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, on the inner surface of the olefin resin pipe, there were scattered tea-colored or black foreign substances due to resin burns caused by residence in the extruder and the mold, or foreign substances due to contamination during raw material input. FIG. 10(a) is a photograph showing a state where foreign substances are present on the inner surface of the olefin resin pipe. FIG. 10(b) is an enlarged view of part V in FIG. 10(a). FIG. 10(a) shows a cross-sectional view of the olefin resin pipe 1001. In FIG. 10(a), a plurality of foreign substances F are present on the inner surface 1001s of the olefin resin pipe 1001. In FIG. 10(a), the foreign substances F are surrounded by a black magic marker.

[0010] If such foreign matter is present on the inner surface of the pipe, there is a risk of particles or metals leaching out, making it unsuitable for transporting ultrapure water.

[0011] This disclosure aims to provide a pipe that can be used for transporting ultrapure water, a piping structure equipped with the pipe, and a method for manufacturing the pipe. [Means for solving the problem]

[0012] To achieve the above objective, the pipe according to the first disclosure is a pipe used for transporting ultrapure water, and comprises a first layer constituting the innermost layer, mainly composed of a polyolefin resin, polyvinyl chloride, or polyvinylidene fluoride. The inner surface of the first layer is free of foreign matter with the longest straight length of 500 μm or more.

[0013] Thus, even in pipes where the innermost layer is made of polyolefin resin, polyvinyl chloride, or polyvinylidene fluoride as the main component, there are no foreign objects with a longest straight length of 500 μm or more on the inner surface of the innermost layer that comes into contact with the transported fluid. Therefore, particle generation and metal leaching can be reduced, and the pipes can be used for transporting ultrapure water.

[0014] The pipe according to the second disclosure is the pipe according to the first disclosure, further comprising a second layer located outside the first layer. This makes it possible to provide a multi-layered pipe that can be used for transporting ultrapure water.

[0015] The pipe according to the third disclosure is the pipe according to the second disclosure, wherein the second layer is mainly composed of an adhesive polyolefin resin. This allows other layers, such as a gas barrier layer, to be laminated on the outside of the second layer.

[0016] The pipe relating to the fourth disclosure is the pipe relating to the second disclosure, and the thickness of the second layer is 50 μm or more and 100 μm or less. A thickness of 50 μm is sufficient to exhibit adequate adhesive strength. Furthermore, by setting the thickness to 100 μm or less, the total thickness of the adhesive layer and the gas barrier layer can be reduced to 320 μm or less. 320 μm is set so that the adhesive layer and the gas barrier can be peeled off using an application tool.

[0017] The tube relating to the fifth disclosure is the tube relating to the first disclosure, with a calcium elution amount of 30 μg / m³ measured in accordance with SEMI F-57. 2 It is less than [a certain value]. This makes it possible to provide a pipe that can be used as a piping for ultrapure water.

[0018] The pipe according to the sixth disclosure is the pipe according to the second disclosure, further comprising a gas barrier layer disposed on the outside of the second layer and having gas barrier properties. In this way, even when the innermost layer of the pipe according to the present disclosure is made of a polyolefin resin as the main component, by arranging a gas barrier layer on the outside, oxygen barrier properties suitable for transporting ultrapure water can be ensured.

[0019] The pipe according to the seventh disclosure is the pipe according to the second disclosure, further comprising a core material layer disposed between the first layer and the second layer, the core material layer being mainly composed of a polyolefin resin. For example, by using a material that is less expensive than the first layer for the core material layer, the strength of the pipe can be ensured while reducing costs.

[0020] The pipe according to the eighth disclosure is the pipe according to the first disclosure, wherein the first layer mainly contains a polyolefin resin, and the polyolefin resin of the first layer is polyethylene or polypropylene. This makes it possible to provide a pipe that can be used for transporting ultrapure water by providing an innermost layer mainly composed of polyethylene or polypropylene.

[0021] The piping structure relating to the ninth disclosure is a piping structure in which a pair of pipes from any of the first to eighth disclosures are fused with an electrofusion joint. The electrofusion joint has a cylindrical body, a stopper, and a heating element. The body has joint sockets at both ends into which each pipe is inserted. The stopper restricts the end of one pipe to be inserted and the end of the other pipe to be inserted, and protrudes inward from the body. The heating element includes an electric heating wire positioned in the stopper. The piping structure is formed by the end of one pipe and the end of the other pipe and has a bead that protrudes inward. The inner surface of the bead is formed by a first layer and is free of foreign matter with a longest straight length of 500 μm or more.

[0022] Thus, the inner surface of the bead is formed by the first layer, and there are no foreign objects with a longest straight length of 500 μm or more. Therefore, even when pipes are connected using electrofusion joints, particle generation and metal leaching can be reduced, making it suitable for transporting ultrapure water.

[0023] A method for manufacturing a pipe according to the tenth disclosure comprises an extrusion molding step. The extrusion molding step involves extruding a material mainly composed of a polyolefin resin, polyvinyl chloride, or polyvinylidene fluoride from an extruder to form a first layer constituting the innermost layer. In the extrusion molding step, the temperature of the material in the extruder is 170 degrees Celsius or higher and 230 degrees Celsius or lower, and the material extruded from the extruder is supplied to the mold via at least one of a mesh, a screen changer, and a polymer filter for removing foreign matter.

[0024] Thus, by setting a low temperature for the material inside the extruder during the extrusion molding step, the generation of brown or black foreign matter due to resin burning can be suppressed. Furthermore, by supplying the material to the mold through at least one of a mesh, a screen changer, and a polymer filter, foreign matter contaminants can be removed. As a result, it is possible to manufacture pipes that can be used as piping for ultrapure water.

[0025] The method for manufacturing a tube according to the eleventh disclosure is the method for manufacturing a tube according to the tenth disclosure, wherein the extruder is nitrogen-purged in the extrusion molding step. This removes oxygen from inside the extruder and suppresses the generation of brown or black foreign matter due to resin burning. [Effects of the Invention]

[0026] According to this disclosure, it is possible to provide a pipe that can be used for transporting ultrapure water, a piping structure equipped with the pipe, and a method for manufacturing the pipe. [Brief explanation of the drawing]

[0027] [Figure 1] This figure shows a pipe, an electrofusion joint, and a pipe in Embodiment 1 according to the present disclosure. [Figure 2A] This is a cross-sectional view of the pipe according to Embodiment 1 of this disclosure. [Figure 2B] This is a cross-sectional view of another example of the pipe of Embodiment 1 according to the present disclosure. [Figure 2C] This is a cross-sectional view of another example of the pipe of Embodiment 1 according to the present disclosure. [Figure 2D] This is a cross-sectional view of another example of the pipe of Embodiment 1 according to the present disclosure. [Figure 3] (a) and (b) are diagrams showing examples of foreign objects. [Figure 4A] This figure shows the pipe manufacturing apparatus according to Embodiment 1 of the present disclosure. [Figure 4B] This figure shows another example of the pipe manufacturing apparatus of Embodiment 1 according to the present disclosure. [Figure 5] This is a cross-sectional view showing an electrofusion joint used when connecting pipes according to the embodiments of this disclosure. [Figure 6] Figure 5 is a cross-sectional view showing the state in which a pipe is inserted into the electrofusion joint. [Figure 7] This is a cross-sectional diagram showing pipes, electrofusion joints, and the state in which the pipes are fused together. [Figure 8] This figure shows a pair of pipes in Embodiment 2 of the present disclosure. [Figure 9]This is a cross-sectional diagram showing a state in which a pair of pipes are fused together. [Figure 10] (a) This figure shows the state in which foreign matter is present on the inner surface of a conventional polyolefin resin pipe. (b) This is an enlarged view of section V in Figure 10(a). [Modes for carrying out the invention]

[0028] Embodiments relating to this disclosure will be described below with reference to the drawings.

[0029] (Embodiment 1) <Structure> (Overview of piping structure 100) Figure 1 shows an electrofusion joint 1, a pipe 2, and a pipe 3 connected by the electrofusion joint in an embodiment of the present disclosure. Figure 1 can also be considered an exploded view of the piping structure 100. The piping structure 100 includes, for example, an electrofusion joint 1, a pipe 2, and a pipe 3. As shown in Figure 1, the electrofusion joint 1 is fused to the pipes 2 and 3, connecting the pipes 2 and 3.

[0030] Pipes 2 and 3 have circular cross-sectional flow channels 2f and 3f extending inside them. The electrofusion joint 1 has a circular cross-sectional flow channel 1f extending inside it. When pipes 2 and 3 are connected by the electrofusion joint 1, the axes of the flow channels in pipes 2 and 3 and the electrofusion joint 1 are aligned on the same straight line.

[0031] Furthermore, the direction in which the axes of each of the electrofusion joint 1, pipe 2, and pipe 3 extend with respect to the flow path is defined as the axial direction A. In addition, the direction in which the electrofusion joint 1, pipe 2, and pipe 3 move toward or away from each other perpendicular to their respective axes is defined as the radial direction B, and the direction in which they rotate around their respective axes is defined as the circumferential direction C.

[0032] Pipe 2 moves relative to the electrofusion joint 1 in the direction of arrow A1 within the axial direction A and connects to the electrofusion joint 1. Similarly, pipe 3 moves relative to the electrofusion joint 1 in the direction of arrow A2 within the axial direction A and connects to the electrofusion joint 1. The state in which pipes 2 and 3 are fused and connected to the electrofusion joint 1 constitutes the piping structure 100.

[0033] (tube 2, 3) Since pipes 2 and 3 have similar configurations, pipe 2 will be used as an example for explanation. Figures 2A to 2C are cross-sectional views showing pipes 2A to 2D, which are examples of the configuration of pipe 2 in this embodiment. Figure 2A is a cross-sectional view of pipe 2A, which is an example of pipe 2. Figure 2B is a cross-sectional view showing pipe 2B, which is an example of pipe 2. Figure 2C is a cross-sectional view showing pipe 2C, which is an example of pipe 2. Figure 2D is a cross-sectional view showing pipe 2D, which is an example of pipe 2.

[0034] The pipe 2A shown in Figure 2A includes a first resin layer 61 (an example of the first layer) and a second resin layer 62 (an example of the core material layer). The first resin layer 61 constitutes the innermost layer of the pipe 2. The first resin layer 61 forms the inner surface 2s of the pipe 2. The second resin layer 62 is located outside the first resin layer 61. The outer surface 2t of the pipe 2 is formed by the second resin layer 62.

[0035] The pipe 2B shown in Figure 2B includes a first resin layer 61, a second resin layer 62, an adhesive layer 63 (an example of the second layer), and a gas barrier layer 64. In pipe 2B, the gas barrier layer 64 is positioned outside the second resin layer 62 of pipe 2A via the adhesive layer 63. The first resin layer 61 constitutes the innermost layer of pipe 2B. The first resin layer 61 forms the inner surface 2s of pipe 2B. The gas barrier layer 64 forms the outer surface 2t of pipe 2B.

[0036] The pipe 2C shown in Figure 2C includes a first resin layer 61, an adhesive layer 63, and a gas barrier layer 64. In pipe 2C, a second resin layer 62 is not provided, compared to pipe 2B. In pipe 2C, the gas barrier layer 64 is arranged on the outside of the first resin layer 61 via the adhesive layer 63. The first resin layer 61 constitutes the innermost layer of pipe 2C. The first resin layer 61 forms the inner surface 2s of pipe 2C. The gas barrier layer 64 forms the outer surface 2t of pipe 2C.

[0037] The pipe D shown in Figure 2D is a single-layer pipe. The pipe 2D includes a first resin layer 61. The first resin layer 61 forms the inner surface 2s of the pipe 2D and the outer surface 2t of the pipe 2D.

[0038] In the pipes 2 (pipes 2A to 2D) of this embodiment, there are no foreign objects on the inner surface 2s with a longest straight length of 500 μm or more. Figures 3(a) and 3(b) show examples of foreign objects F. As shown in Figure 3(a), the longest straight line is the longest straight line L contained in the foreign object F in a plan view looking at the inner surface 2s from the central axis of pipe 2. Also, as shown in Figure 3(b), even if the foreign object F has an elongated shape in one direction, the longest straight line is the longest straight line L contained in the foreign object F.

[0039] In this embodiment, the inner surface 2s of the pipe 2 is free of foreign matter with a longest straight length of 500 μm or more. The inner surface 2s of the pipe 2 contains 1 foreign matter per meter with a longest straight length L of 400 μm or more and less than 500 μm. 2 The following is preferable: On the inner surface 2s of the pipe 2, there is one foreign object per meter whose longest straight length L is 300 μm or more and less than 400 μm. 2 The following is preferable: The inner surface 2s of the pipe 2 contains 2 foreign objects per meter, with the longest straight length L being 200 μm or more and less than 300 μm. 2 The following is preferable: The inner surface 2s of the pipe 2 contains 2 foreign objects per meter, with the longest straight length L being 100 μm or more and less than 200 μm. 2 The following is preferable. Foreign matter F can be detected by visual inspection using a limit sample. Alternatively, it can be inspected using a camera that photographs the inner surface 2s of the pipe 2.

[0040] Pipe 2 can use any of the configurations of pipes 2A to 2D described above. Similarly, pipe 3 may also use any of the configurations of pipes 2A to 2D shown in Figure 2A. In the following figures, the inner surface of pipe 3 is indicated by 3s and the outer surface by 3t.

[0041] (1st resin layer 61) The first resin layer 61 constitutes the innermost layer of pipes 2A to 2D. The first resin layer 61 forms the inner surface 2s of pipe 2. The first resin layer 61 may be any resin with low elemental elution properties as described in SEMI F57, and may mainly contain polyolefin resins (polyethylene (PE), polypropylene (PP)), polyvinyl chloride (PVC), or polyvinylidene fluoride (PVDF). The main component refers to the component with the highest mass content. The main component is a component with a content of at least 50%. The lower limit of the resin content included as the main component in the first resin layer 61 is preferably 50% by mass, more preferably 70% by mass, even more preferably 80% by mass, and may also be 90% by mass, and may also be 95% by mass.

[0042] The polyolefin resin included as the main component in the first resin layer 61 is not particularly limited and may be any polymer containing monomer units derived from olefins. Examples include polyethylene resins, ethylene-carboxylic acid alkenyl ester copolymer resins, ethylene-α-olefin copolymer resins, polypropylene resins, polybutene resins, and poly(4-methyl-1-pentene) resins. These polyolefin resins may be used individually or in combination of two or more. Among these polyolefin resins, polyethylene resins and polypropylene resins are preferred from the viewpoint of improving the strength of the semiconductor cleaning fluid piping. Furthermore, among polyethylene resins and polypropylene resins, polyethylene resins are more preferred from the viewpoint of suppressing the content of low molecular weight components and thereby suppressing the elution of organic components into ultrapure water.

[0043] Examples of polypropylene resins include homopolypropylene, block polypropylene, and random polypropylene. The copolymer component in block polypropylene and random polypropylene is typically ethylene. Examples of polybutene resins include polybutene-1.

[0044] Polyethylene resins may be copolymerized with α-olefins as needed. Examples of α-olefins copolymerized with polyethylene resins include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-butene-1-hexene, 1-butene-4-methyl-1-pentene, and 1-butene-1-octene.

[0045] Polyethylene resins are polymerized using a catalyst containing one or more transition metal derivatives. In this embodiment, polymerization is carried out using a Ziegler catalyst to ensure long-term durability. When polymerizing polyethylene resins using a Ziegler catalyst, a chlorine-based catalyst is used in an amount appropriately determined by those skilled in the art for multi-stage polymerization, and then a neutralizing agent to neutralize the chlorine-based catalyst and preferably an antioxidant are also added. The Ziegler catalyst used in this invention is a well-known one, and for example, catalyst systems described in Japanese Patent Publication Nos. 53-78287, 54-21483, 55-71707, and 58-225105 are used.

[0046] Specifically, examples include catalyst systems consisting of a solid catalyst component obtained by contacting a tetravalent titanium compound with a co-pulverized product obtained by co-pulverizing aluminum trihalide, an organosilicon compound having a Si-O bond, and magnesium alkoxide, and an organoaluminum compound.

[0047] The solid catalyst component preferably contains 1 to 15% by weight of titanium atoms. The organosilicon compound preferably has a phenyl group and an aralkyl group, such as diphenyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, triphenylethoxysilane, and triphenylmethoxysilane.

[0048] In producing the co-ground product, the ratio of aluminum trihalide and organosilicon compound used per mole of magnesium alkoxide is generally 0.02 to 1.0 mole each, with 0.05 to 0.20 moles being particularly preferred. Furthermore, the ratio of aluminum atoms of aluminum trihalide to silicon atoms of the organosilicon compound is preferably 0.5 to 2.0 moles.

[0049] To produce the co-pulverized product, the usual methods can be applied using grinders such as rotary ball mills, vibrating ball mills, and colloidal mills, which are commonly used when producing this type of solid catalyst component. The average particle size of the resulting co-pulverized product is typically 50-200 μm, and the specific surface area is 20-200 m². 2 It is / g.

[0050] A solid catalyst component is obtained by contacting the co-pulverized product obtained as described above with a tetravalent titanium compound in the liquid phase. The organoaluminum compound used in combination with the solid catalyst component is preferably a trialkylaluminum compound, such as triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, and tri-i-butylaluminum.

[0051] Examples of neutralizing agents include fatty acid metal salts such as calcium stearate, zinc stearate, and magnesium stearate, as well as hydrotalcites.

[0052] However, when polyethylene resins are polymerized using magnesium stearate or hydrotalcite as a neutralizing agent, a large amount of aluminum and magnesium leach into the water when the resulting resin is molded into piping material, which is undesirable in this embodiment.

[0053] In contrast, when polyethylene resin polymerization is carried out using calcium stearate as a neutralizing agent, the metal elution of aluminum and magnesium described above does not occur, and good low elution properties can be obtained, making it a preferred neutralizing agent in this embodiment.

[0054] As the polyethylene resin composition, high-density polyethylene (HDPE) is preferred from the viewpoint of obtaining sufficient pressure resistance performance against the water pressure during water supply and being able to reduce the pipe wall thickness. Among high-density polyethylenes (HDPEs), from the viewpoint of ensuring the long-term durability of the pipe material for ultrapure water, HDPE classified into a pressure resistance class of PE100 or higher in ISO9080, ISO1167, and ISO12162 is more preferred. Furthermore, even among HDPEs classified into a pressure resistance class of PE100 or higher, HDPE with high resistance to slow crack growth (slow crack growth resistance) and better pipe inner surface smoothness to further enhance the safety of the pipe system and having high fluidity is preferred. Note that slow crack growth refers to a failure mode that occurs due to stress concentration such as scratches on the pipe material or the joint between the pipe and the fitting.

[0055] As an index of the polyethylene resin composition that satisfies a pressure resistance class of PE100 or higher and has good fluidity, specifically, the melt flow rate (MFR 21.6 ) at a temperature of 190°C and a load of 21.6 kg of the polyethylene resin composition is 6 g / 10 min or more and 25 g / 10 min or less, and the flow ratio (FR(MFR 21.6 / MFR5)), which is the ratio of the melt flow rate (MFR5) at a temperature of 190°C and a load of 5 kg to MFR21.6, is 25 or more and 60 or less, and the density is 0.946 g / cm 3 or more and 0.960 g / cm 3 or less.

[0056] When the MFR 21.6 of the polyethylene resin composition is less than 6 g / 10 min, the fluidity of the resin material is low, the mold transferability is poor, and the smoothness of the pipe inner surface becomes insufficient. On the other hand, when the MFR 21.6 exceeds 25 g / 10 min, it becomes difficult to design a resin that satisfies PE100. Also, when the FR is less than 25, the molecular weight distribution of the polyethylene resin composition becomes narrow, so the target MFR 21.6This makes it difficult to achieve both low-speed crack resistance and low-speed crack resistance. On the other hand, if FR exceeds 60, the impact resistance of the polyethylene resin composition decreases, which may compromise the safety of the piping material. Regarding density, it is 0.946 g / cm³. 3 If the density is less than 0.960 g / cm³, the pressure resistance performance decreases, making it difficult to reach PE100. 3 If the value exceeds this limit, the low-speed crack formation resistance of the piping material decreases, thus reducing the safety of the pipe system in long-term use.

[0057] Furthermore, to achieve the above polyethylene-based resin composition, it is preferable that the resin composition consists of multiple components, specifically a high molecular weight component (A) and a low molecular weight component (B).

[0058] High molecular weight component (A) is MFR 21.6 The high molecular weight component (A) has a melt flow rate (MFR 2.16) of 0.05 g / 10 min to 1.0 g / 10 min, preferably 0.1 g / 10 min to 0.5 g / 10 min, the α-olefin content other than ethylene is 0.8 mol% to 2.0 mol%, preferably 0.9 mol% to 1.6 mol%, and the content ratio of the high molecular weight component (A) to the total resin composition is 35% to 50% by weight, preferably 37% to 43% by weight. On the other hand, the low molecular weight component (B) has a melt flow rate (MFR 2.16) of 20 g / 10 min to 500 g / 10 min, preferably 50 g / 10 min to 300 g / 10 min, at a temperature of 190°C and a load of 2.16 kg.

[0059] MFR of high molecular weight component (A) constituting polyethylene resin composition 21.6 If the value is less than 0.05g / 10min, the target MFR 21.6 To achieve this, it is necessary to increase the MFR of the low molecular weight component, but in that case, the viscosity difference between the high-molecular-weight component and the low-molecular-weight component during melting becomes large, reducing mismatch, and as a result, various mechanical properties, including resistance to slow-speed cracks, decrease, and roughening of the inner surface of the pipe occurs due to flow instability. On the other hand, MFR 21.6If the content exceeds 1.0 g / 10 min, various mechanical properties will decrease, and in particular, resistance to slow crack growth will decrease significantly. Regarding the α-olefin content, if it is less than 0.8 mol%, resistance to slow crack growth will decrease, and if it exceeds 2.0 mol%, the rigidity of the polyethylene resin composition will decrease, making it difficult to design a resin that can reach PE100. Regarding the content ratio of high molecular weight component (A), if it is less than 35 wt%, the durability of the piping will decrease, and if it exceeds 50 wt%, the rigidity of the polyethylene resin composition will decrease, making it difficult to design a resin that can reach PE100.

[0060] If the MFR2.16 of the low molecular weight component (B) constituting the polyethylene resin composition is less than 20 g / 10 min, the fluidity of the polyethylene resin composition decreases, resulting in reduced mold transferability and insufficient smoothness of the inner surface of the pipe. On the other hand, if the MFR2.16 exceeds 500 g / 10 min, various mechanical properties deteriorate, particularly impact resistance.

[0061] The α-olefin content referred to here includes not only the α-olefins that are fed into the reactor and copolymerized during polymerization, but also short-chain branching (e.g., ethyl branching, methyl branching) produced as by-products. The α-olefin content is measured by 13C-NMR. The α-olefin content can be increased or decreased by increasing or decreasing the amount of α-olefin supplied for copolymerization with ethylene.

[0062] The calcium elution amount of the first resin layer 61, measured according to SEMI F-57, was 30 μg / m². 2 The calcium concentration in the first resin layer 61 is adjusted so that it is less than 60 ppm. The calcium concentration in the first resin layer 61 is 360 ppm or less, preferably 55 ppm or less, and more preferably 50 ppm or less. If the calcium concentration exceeds 60 ppm, the amount of calcium leached into the ultrapure water becomes excessive, and the required quality of the ultrapure water cannot be met.

[0063] From the viewpoint of further suppressing the amount of calcium leached into ultrapure water, it is preferable to keep the calcium concentration of the first resin layer 61 as low as possible. However, from the viewpoint of obtaining good thermal stability and long-term strength of the polyethylene-based resin composition or polypropylene-based resin composition, the inclusion of trace amounts of calcium is unavoidable.

[0064] In other words, if the amount of neutralizing agent added to the polyethylene or polypropylene resin composition polymerized using the Ziegler catalyst is insufficient, the catalyst residue may remain active in the resin, potentially reducing the thermal stability and long-term strength of the polyethylene or polypropylene resin composition.

[0065] Therefore, in this embodiment, it is essential to add the minimum necessary amount of neutralizing agent to neutralize the catalyst residue. Considering the above, the calcium concentration of the first resin layer 61 is 10 ppm or more, preferably 13 ppm or more, more preferably 15 ppm or more, and even more preferably 20 ppm or more.

[0066] The oxidation induction time (OIT) of the first resin layer 61 at 210°C is preferably 20 minutes or more from the viewpoint of ensuring thermal stability. If the oxidation induction time at 210°C is less than 20 minutes, the polyethylene resin or polypropylene may deteriorate when heat-processed, which may lead to a decrease in long-term strength or an increase in particles derived from the deteriorated material, and this is undesirable in this embodiment.

[0067] The hot internal pressure creep test is widely used as a method for evaluating the long-term strength of polyethylene resins used as piping materials. From the viewpoint of ensuring sufficient long-term strength for piping materials for ultrapure water, when the first resin layer 61 is molded as piping material, it is preferable that the piping material does not break for 3,000 hours or more when a circumferential stress of 5.0 MPa is applied to the piping material at 80°C.

[0068] The material properties of polyethylene resin compositions are more preferably such that they have a pressure resistance performance of "PE100" or higher, as described in ISO9080, ISO1167, and ISO12162 standards. "PE100" refers to polyethylene in which, in a hot internal pressure creep test, the stress-rupture time curves are measured for at least 9,000 hours at three different temperature levels where the maximum and minimum temperatures are separated by 50°C or more, and the LPL value, which is estimated by extrapolation of the minimum guaranteed stress after 50 years at 20°C using the multiple correlation mean, is between 10 MPa and 11.19 MPa in the classification table specified in ISO12162.

[0069] The first resin layer 61 may or may not contain an antioxidant. Examples of antioxidants include phenolic antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, aromatic amine-based antioxidants, and lactone-based antioxidants.

[0070] Examples of phenolic antioxidants include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and N,N'-hexane-1,6-diylbis[3-(3,5- [Di-tert-butyl-4-hydroxyphenyl)propionamide], benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy, C7-C9 side-chain alkyl ester, 3,3',3'',5,5',5''-hexa-tert-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(dodecylthiomethyl)-o-cresol, 4,6-bis(octyl Luthiomethyl)-o-cresol, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1 Examples include 3,5-tris[(4-tert-butyl-3-hydroxy-2,6-xylyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-triazine2-ylamino]phenol, and diethyl[{3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl}methyl]phosphonate.

[0071] When using phenolic antioxidants, one type may be used alone, or two or more types may be used in combination. However, from the viewpoint of preventing calcium elution, it is preferable that the antioxidant does not contain oxygen derived from a group other than the phenol group. Examples include 3,3',3'',5,5',5''-hexa-tert-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-triazine2-ylamino]phenol, 4,4',4''-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), and 6,6'-di-tert-butyl-4,4'-butylidenebis-m-cresol. Furthermore, when using a phenolic antioxidant that contains oxygen derived from a group other than the phenol group, it is preferable that the calcium concentration in the polyethylene resin be 50 ppm or less. Examples of functional groups containing oxygen derived from groups other than phenol groups include ester groups, carbonyl groups, carboxyl groups, ether groups, nitro groups, nitroso groups, amide groups, azixy groups, and sulfo groups.

[0072] Examples of phosphorus-based antioxidants include tris(2,4-di-tert-butylphenyl) phosphite, tris[2-[[2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphefin-6-yl]oxy]ethyl]amine, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphorous acid, and tetrakis(2,4-di-tert-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonate.

[0073] Examples of sulfur-based antioxidants include dilaurylthiodipropionate, dimyristylthiodipropionate, distearylthiodipropionate, and pentaerythrityltetrakis(3-laurylthiopropionate).

[0074] Examples of aromatic amine antioxidants include monoamine compounds such as diphenylamine compounds, quinoline compounds, and naphthylamine compounds, as well as diamine compounds such as phenylenediamine compounds and benzimidazole compounds.

[0075] Examples of diphenylamine compounds include p-(p-toluenesulfonylamide)-diphenylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, and 4,4'-dioctyl diphenylamine derivatives. Examples of quinoline compounds include 2,2,4-trimethyl-1,2-dihydroquinoline polymers.

[0076] Examples of naphthylamine compounds include phenyl-α-naphthylamine and N,N'-di-2-naphthyl-p-phenylenediamine.

[0077] Examples of phenylenediamine compounds include N-N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, mixtures of N-N'-diphenyl-p-phenylenediamine, diaryl-p-phenylenediamine derivatives or mixtures thereof.

[0078] Examples of benzimidazole compounds include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, zinc salt of 2-mercaptobenzimidazole, and zinc salt of 2-mercaptomethylbenzimidazole.

[0079] Examples of lactone-based antioxidants include reaction products of 3-hydroxy-5,7-di-tert-butylfuran-2-one and o-xylene. The antioxidant content in the first resin layer 61 is, for example, 0.01% by weight or more, preferably 0.03% by weight or more, and more preferably 0.05% by weight or more, from the viewpoint of suppressing the effect of oxygen and ensuring desirable strength. The upper limit of the antioxidant content is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0080] The first resin layer 61 may or may not contain a light stabilizer, but it is preferable that it does not contain a light stabilizer from the viewpoint of preventing total organic carbon (TOC) elution. Examples of light stabilizers include hindered amine light stabilizers (HALS). Furthermore, it is preferable that the first resin layer 61 in this embodiment is substantially free of light stabilizers. Here, substantially free means that light stabilizers are not actively added, and that unavoidable inclusion as impurities is acceptable. The lower the concentration of light stabilizers that are inevitably included as impurities, the better.

[0081] Examples of hindered amine-based light stabilizers include NH-type hindered amine compounds, NR-type hindered amine compounds, and N-OR-type hindered amine compounds.

[0082] Examples of NH-type hindered amine compounds include Tinuvin 770DF, Kimasove 2020FDL, Kimasove 944FDL (all trade names, manufactured by BASF), Adeka Stab LA-68, Adeka Stab LA-57 (both trade names, manufactured by Adeka), Siasorb UV-3346, Siasorb UV-3853 (both trade names, manufactured by Sun Chemical Co., Ltd.).

[0083] Examples of NR-type hindered amine compounds include tinubine 622SF, tinubine 765, tinubine PA144, kimasoub 119, tinubine 111 (all trade names, manufactured by BASF), savostab UV119 (trade name, manufactured by Savo), adekastab LA-63P, and adekastab LA-52 (all trade names, manufactured by adeka).

[0084] Examples of N-OR type hindered amine compounds include tinuvin 123, tinuvin 5100, tinuvin NOR371FF, and flame stub NOR116FF (all trade names, manufactured by BASF).

[0085] The first resin layer 61 may or may not contain an ultraviolet absorber (UVA). Examples of ultraviolet absorbers include benzophenone-based ultraviolet absorbers, salmalate-based ultraviolet absorbers, benzocoat-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and quenchers. For polyethylene or polypropylene, benzophenone-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are particularly preferred as ultraviolet absorbers.

[0086] Examples of benzophenone-based UV absorbers include 2-hydroxy-4-methoxy-benzophenone.

[0087] Examples of benzotriazole-based UV absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole (Sumisorb 200, manufactured by Sumika Chemtex Co., Ltd.), 2-(2-hydroxy-5-t-butyl-5-methylphenyl)-5-chlorobenzotriazole (Tinuvin 326, manufactured by BASF), 2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole (Tinuvin 327, manufactured by BASF), and 2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole (Tinuvin 328, manufactured by BASF).

[0088] When a polyethylene-based resin is used as the main component of the first resin layer 61, the density of the polyethylene-based resin composition is preferably 0.946 g / cm³ from the viewpoint of obtaining good rigidity of the polyethylene-based resin composition. 3 More preferably 0.947 g / cm³ 3 More preferably 0.948 g / cm³ 3 The above points are listed above. Furthermore, from the viewpoint of obtaining good long-term durability and flexibility of the polyethylene resin composition, the density is preferably 0.960 g / cm³. 3 More preferably, 0.957 g / cm³ 3 More preferably, 0.953 g / cm³ 3 These are some examples. The density is a value determined in accordance with JIS K6922-2:1997.

[0089] The melt flow rate (MFR) of the polyethylene resin composition of the first resin layer 61 at a temperature of 190°C and a load of 21.6 kg. 21.6 ) includes 6 g / 10 min to 25 g / 10 min. From the viewpoint of obtaining good processability of polyethylene resin composition, the MFR 21.6 Preferably, the MFR is 8 g / 10 min or more, more preferably 12 g / 10 min or more, and even more preferably 15 g / min or more. Furthermore, from the viewpoint of obtaining good long-term durability of the resin, the MFR 21.6 Preferably, the MFR is 22 g / 10 min or less, more preferably 20 g / 10 min or less. 21.6 This value is established in accordance with JIS K6922-2:1997.

[0090] When a polypropylene resin is used as the main component of the first resin layer 61, the density of the polypropylene resin composition is preferably 0.900 g / cm³ from the viewpoint of obtaining good rigidity of the polypropylene resin composition. 3 More preferably 0.901 g / cm³ 3 More preferably 0.902 g / cm³ 3 The above points are listed above. Furthermore, from the viewpoint of obtaining good long-term durability and flexibility of the polypropylene resin composition, the density is preferably 0.910 g / cm³. 3More preferably, 0.909 g / cm³ 3 More preferably, 0.908 g / cm³ 3 These are some examples. The density is a value determined in accordance with JIS K6922-2:1997.

[0091] The inner surface smoothness (arithmetic mean roughness Ra) of the first resin layer 61 is not particularly limited, and for example, it can be 0.50 μm or less. From the viewpoint of obtaining good low elution properties of the piping, the inner surface smoothness of the first resin layer 61 is preferably 0.40 μm or less, and more preferably 0.35 μm or less.

[0092] The thickness t1 of the first resin layer 61 is preferably 0.06 mm or more and 16.0 mm or less. For example, 0.5 mm or more and 16 mm or less is preferred. More specifically, for pipe 2C with a diameter of 25A, the thickness t1 is preferably 2 mm or more and 3.5 mm or less. For pipe 2B with a diameter of 25A, the thickness t1 is preferably 0.5 mm or more and 1.5 mm or less. For pipe 2C with a diameter of 75A, the thickness t1 is preferably 4 mm or more and 7 mm or less. For pipe 2B with a diameter of 75A, the thickness t1 is preferably 0.5 mm or more and 3 mm or less. For pipe 2C with a diameter of 200A, the thickness t1 is preferably 12 mm or more and 16 mm or less. For pipe 2B with a diameter of 200A, the thickness t1 is preferably 0.5 mm or more and 3 mm or less. For pipes 2A and 2D, t1 is preferably 5.0 mm or more.

[0093] (Second resin layer 62) Since the second resin layer 62 does not constitute the innermost layer, unlike the first resin layer 61, it may have a large amount of calcium elution. The second resin layer 62 (an example of a core material layer) is located outside the first resin layer 61. The second resin layer 62 mainly contains, for example, polyolefin resin (polyethylene (PE), polypropylene (PP)), polyvinyl chloride (PVC), or polyvinylidene fluoride (PVDF). The main component refers to the component with the highest mass content. The main component is a component with a content of at least 50%. The lower limit of the resin content included as the main component in the second resin layer 62 is preferably 50% by mass, more preferably 70% by mass, even more preferably 80% by mass, and may also be 90% by mass, and may also be 95% by mass.

[0094] The polyolefin resin used in the second resin layer 62 is not particularly limited and can be appropriately selected from among the polyolefin resins listed above as being used in the first resin layer 61. Among the polyolefin resins mentioned above, high-density polyethylene (HDPE) is preferred from the viewpoint of suppressing the elution of low molecular weight components and / or durability when pipes are cleaned with chemicals. The polyolefin resin used in the second resin layer 62 may be the same type as the polyolefin resin used in the first resin layer 61 or a different type, but when the two layers are laminated in contact with each other, it is more preferable to use the same type of polyolefin resin from the viewpoint of improving the adhesion between the two layers and achieving desirable strength.

[0095] The calcium elution amount of the material (polyolefin resin composition) of the second resin layer 62, as measured in accordance with EMIF-57, is preferably 30 μg / m², from the viewpoint of ensuring the strength of the semiconductor cleaning solution piping in a 60°C operating environment. 2 Above all, a comfortable 50 μg / m² 2 More preferably 70 μg / m² 2 More preferably, 80 μg / m² 2 The above is particularly preferably 90 μg / m² 2 More preferably 95 μg / m² 2 The above points can be raised.

[0096] The first resin layer 61 of the tubes 2A to 2C of the present invention has excellent effect in suppressing the elution of calcium and organic components. Therefore, even if the material of the second resin layer 62 contains a large amount of calcium, the elution of calcium can be effectively suppressed. From this viewpoint, a suitable example of the above calcium elution amount is 80 μg / m² within the above range. 2 More than 90μg / m 2 Above or above, or 95 μg / m² 2 The above points are listed. Furthermore, there is no particular limit to the upper limit of the calcium elution amount, but from the viewpoint of suppressing calcium elution, 120 μg / m² is recommended. 2 Below, 110μg / m 2 The following, or 100 μg / m² 2 The following are examples. Furthermore, the calcium concentration in the material (polyolefin resin composition) of the second resin layer 62 is not particularly limited as long as it satisfies the above-mentioned calcium elution amount, but from the viewpoint of ensuring the strength of the semiconductor cleaning solution piping in a 60°C operating environment, for example, 20 ppm or more, preferably 30 ppm or more, more preferably 40 ppm or more, even more preferably 50 ppm or more, and even more preferably 60 ppm or more. Furthermore, as an upper limit of the above calcium concentration range, from the viewpoint of suppressing insufficient strength due to the calcium itself acting as the starting point for fracture, and from the viewpoint of suppressing the elution of calcium and organic components, for example, 200 ppm or less, preferably 150 ppm or less, more preferably 130 ppm or less, and even more preferably 100 ppm or less.

[0097] The amount of organic components (TOC) eluted from the material (polyolefin resin composition) of the second resin layer 62, as measured in accordance with EMIF-57, is, for example, 30,000 μg / m². 2 One example is the extremely high efficiency of the tubes 2 and 3 of the present invention. Because the tubes 2 and 3 of the present invention have excellent effects in suppressing the elution of calcium and organic components, even if the material of the second resin layer 62 contains a large amount of organic components, the elution of organic components can be effectively suppressed. From this viewpoint, a suitable example of the amount of organic component eluted is 31,000 μg / m². 2 Preferably, the above is 31500 μg / m².2 The above points are listed. Furthermore, there is no particular limit to the upper limit of the amount of organic components eluted, but from the viewpoint of suppressing the elution of organic components, for example, 35,000 μg / m³ is used. 2 Preferably, 34,000 μg / m² 2 More preferably, 33,000 μg / m² 2 More preferably, 32,000 μg / m² 2 The following are listed:

[0098] The second resin layer 62 may contain a pigment. This allows for a different color from the first resin layer 61, and makes it possible to confirm whether the inside of the second resin layer 62 is covered by the first resin layer 61. Furthermore, when the pipe 2 is fusion-bonded, by visually confirming that the colored second resin layer 62 material does not protrude from the inner surface of the joint, it is possible to confirm whether the inner surface of the joint is covered by the low-eluting first resin layer 61 material, thereby facilitating quality control. Any conventionally known organic pigments, inorganic pigments, or extender pigments can be used as the pigment, and are not particularly limited. Examples of organic pigments include phthalocyanine-based, azo-based, condensed azo-based, anthraquinone-based, perinone / perylene-based, indigo / thioindigo-based, isoindolinone-based, azomethine azo-based, dioxazine-based, quinacridone-based, aniline black-based, and triphenylmethane-based pigments. Examples of inorganic pigments include carbon black-based, titanium dioxide-based, iron oxide-based, iron hydroxide-based, chromium oxide-based, spinel-type calcined pigments, lead chromate-based, vermilion chromate-based, Prussian blue-based, aluminum powder, and bronze powder. Examples of extender pigments include calcium carbonate-based, barium sulfate-based, silicon dioxide-based, and aluminum hydroxide-based pigments. The pigments are used individually or in combination so that the second resin layer 62 becomes a predetermined color.

[0099] The second resin layer 62 preferably contains an antioxidant. Examples of antioxidants include phenolic antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, aromatic amine-based antioxidants, and lactone-based antioxidants. From the viewpoint of suppressing the effect of oxygen and ensuring desirable strength, the antioxidant content in the second resin layer 62 is, for example, 0.01% by weight or more, preferably 0.1% by weight or more, and the upper limit of the antioxidant content is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0100] Furthermore, the thickness t2 of the second resin layer 62 is preferably 1.5 mm or more and 15 mm or less.

[0101] (adhesive layer 63) In pipe 2B shown in Figure 2B, the adhesive layer 63 is positioned outside the second resin layer 62. The adhesive layer 63 adheres the gas barrier layer 64 to the outside of the second resin layer 62. In pipe 2C shown in Figure 2C, the adhesive layer 63 is positioned outside the first resin layer 61. The adhesive layer 63 adheres the gas barrier layer 64 to the outside of the first resin layer 61. Adhesive polyolefin resin is preferred as the material for the adhesive layer 63. The adhesive layer 63 contains adhesive polyolefin resin as its main component. The main component refers to the component with the highest mass content. The main component is a component with a content of at least 50%. The lower limit of the content of adhesive polyolefin resin in the adhesive layer 63 is preferably 50% by mass, more preferably 70% by mass, even more preferably 80% by mass, and may also be 90% by mass and may also be 95% by mass. From the viewpoint of achieving desirable strength, it is more preferable that the adhesive polyolefin resin be of the same type. For example, maleic anhydride-modified adhesive polyethylene can be used.

[0102] The thickness t3 of the adhesive layer 63 is not particularly limited as long as it is thick enough to bond the gas barrier layer 64 to the first resin layer 61 or the second resin layer 62, but it is preferably 50 μm or more and 500 μm or less, and more preferably 50 μm or more and 100 μm or less. Note that the preferred range of thickness t3 is the same even if the type of pipe 2A to 2D and the diameter are different. (Gas barrier layer 64) By providing the gas barrier layer 64, the dissolution of gas into ultrapure water can be effectively suppressed. Furthermore, the gas barrier layer 64 prevents oxygen from the outer surfaces 2t and 3t of the pipes 2 and 3 from penetrating into the innermost first resin layer 61 or the second resin layer 62, thereby improving the long-term strength of the pipes 2 and 3. Providing the gas barrier layer is also preferable because it effectively suppresses the dissolution of gas into ultrapure water.

[0103] Examples of materials for the gas barrier layer include polyvinyl alcohol (PVA), ethylene vinyl alcohol copolymer (EVOH), polyvinylidene chloride resin (PVDC), and polyacrylonitrile (PAN), with polyvinyl alcohol (PVA) and ethylene vinyl alcohol copolymer (EVOH) being preferred.

[0104] The thickness t4 of the gas barrier layer is not particularly limited as long as it is thick enough to ensure the gas barrier properties of the polyolefin resin placed on the inside, but it is preferably 80 μm or more and 500 μm or less, and more preferably 100 μm or more and 270 μm or less. Note that the preferred range of thickness t4 is the same even if the type of pipe 2A to 2D and the diameter are different.

[0105] (Manufacturing of pipes 2 and 3) Figure 4A is a schematic diagram showing a manufacturing apparatus 200 for manufacturing pipe 2A. The manufacturing apparatus 200 is a device for manufacturing a pipe having two layers by co-extrusion. The manufacturing apparatus 200 comprises a first extruder 210, a nitrogen purging device 220, a mesh 230, a second extruder 240, a two-layer pipe mold 250, a forming tube 260, and a vacuum water bath 270.

[0106] The first extruder 210 extrudes the material that will form the first resin layer 61 toward the two-layer pipe mold 250. The first extruder 210 has a screw 211 and a heater 212. The screw 211 rotates to extrude the material that will form the first resin layer 61 toward the two-layer pipe mold 250. The heater 212 heats the material inside the first extruder 210 to a temperature of, for example, 170 degrees Celsius or more and 240 degrees Celsius or less. For example, in the case of a material mainly composed of polyethylene, the heater 212 heats the material to a temperature of 170 degrees Celsius or more and 210 degrees Celsius or less. In the case of a material mainly composed of polypropylene, the heater 212 heats the material to a temperature of 210 degrees Celsius or more and 240 degrees Celsius or less.

[0107] The nitrogen purging device 220 supplies nitrogen into the first extruder 210 to purge the inside of the first extruder 210 with nitrogen.

[0108] The mesh 230 is located at the material outlet of the first extruder 210. The mesh 230 removes foreign matter mixed into the material. A screen changer or polymer filter may be provided instead of, or in conjunction with, the mesh. The mesh 230 may be a combination of multiple meshes.

[0109] The second extruder 240 extrudes the material that will form the second resin layer 62 toward the two-layer pipe mold 250. The second extruder 240 has a screw 241 and a heater 242. The screw 241 rotates to extrude the material that will form the second resin layer 62 toward the two-layer pipe mold 250. The heater 242 heats the material inside the second extruder 240 to a temperature of, for example, 170 degrees Celsius or more and 240 degrees Celsius or less. For example, in the case of a material mainly composed of polyethylene, the heater 212 heats the material to a temperature of 170 degrees Celsius or more and 210 degrees Celsius or less. In the case of a material mainly composed of polypropylene, the heater 212 heats the material to a temperature of 210 degrees Celsius or more and 240 degrees Celsius or less.

[0110] The two-layer pipe mold 250 is a mold for forming a two-layer pipe. A two-layer pipe is formed by extruding material from the first extruder 210 and the second extruder 240 into the two-layer pipe mold 250.

[0111] The forming tube 260 shapes the pipe extruded from the two-layer pipe mold 250 to a predetermined outer diameter. The forming tube 260 is positioned at the inlet of the vacuum water bath 270.

[0112] The vacuum water bath 270 cools the pipe extruded from the two-layer pipe mold 250. Figure 4A shows the pipe 2A being extruded in the vacuum water bath 270. The molding direction is indicated by arrow E.

[0113] As described above, pipes 2A and 2B can be manufactured using the manufacturing apparatus 200. Furthermore, by lowering the temperature of the material inside the first extruder 210, which extrudes the material forming the first resin layer 61 that constitutes the innermost layer, carbonization of the material inside the extruder can be suppressed, and the generation of foreign matter can be reduced. In addition, by purging the inside of the first extruder 210 with nitrogen, carbonization of the material inside the extruder can be suppressed, and the generation of foreign matter can be reduced. By arranging the mesh 230, foreign matter can be removed from the material supplied to the two-layer pipe mold 250, thereby suppressing foreign matter on the inner surface 2s. Note that pipe 2B shown in Figure 2B can be manufactured by forming an adhesive layer 63 and a gas barrier layer 64 on pipe 2A manufactured in the manufacturing apparatus 200 in a subsequent process.

[0114] Tubes 2C and 2D, which do not have a second resin layer 62, can be manufactured using a manufacturing apparatus 201 as shown in Figure 4B. The manufacturing apparatus 201 comprises a first extruder 210, a nitrogen purging device 220, a mesh 230, a single-layer pipe mold 251, a forming tube 260, and a vacuum water tank 270. Compared to the manufacturing apparatus 200, the manufacturing apparatus 201 does not have a second extruder 240, and a single-layer pipe mold 251 is provided instead of a two-layer pipe mold 250. The material for forming the first resin layer 61, which is fed into the first extruder 210, is supplied to the single-layer pipe mold 251 to extrude a single-layer pipe, and the pipe extruded from the single-layer pipe mold 251 is formed to a predetermined outer diameter by the forming tube 250.

[0115] In the case of pipe 2C, an adhesive layer 63 and a gas barrier layer 64 can be formed in a subsequent process on the single-layer pipe mainly composed of polyolefin resin.

[0116] (Electric fusion joint 1) Figure 5 shows the cross-sectional configuration of the electrofusion joint 1. The electrofusion joint 1 contains a thermoplastic resin. As shown in Figure 5, the electrofusion joint 1 has a main body portion 11, a stopper portion 12, socket heating portions 13 and 14, a stopper heating portion 15, and a connector mounting portion 16.

[0117] (Main body 11) The main body 11 is made of a thermoplastic resin. The main body 11 is cylindrical and has a joint socket 21, a joint socket 22, and a connecting portion 23. The thermoplastic resin forming the main body 11 is not particularly limited, but the same as the first resin layer 61 or the second resin layer 62 may be used. Alternatively, a polyolefin such as polyethylene with a melting point of less than 230°C may be used as the thermoplastic resin, or PE (polyethylene) with low elution may be used. Alternatively, HDPE (high-density polyethylene resin) with a melting point of about 130°C and low elution may be used as the thermoplastic resin.

[0118] The joint socket portion 21 is located on one end 11b of the main body portion 11. The pipe 2 is inserted inside the joint socket portion 21. The joint socket portion 22 is cylindrical. The joint socket portion 22 is located on the other end 11c of the main body portion 11. The joint socket portion 22 is cylindrical. The pipe 3 is inserted inside the joint socket portion 22.

[0119] As shown in Figure 2, the connecting section 23 is connected to the joint socket section 21 and the joint socket section 22, and connects the joint socket section 21 and the joint socket section 22. The connecting section 23 is the part that connects the joint socket section 21 and the joint socket section 22, and the stopper section 12 is provided on the inside in the radial direction B.

[0120] The joint socket portion 21 has a projection 24 that protrudes inward in the radial direction B from the inner surface 11a. The projection 24 is annular in shape. The projection 24 is formed along the entire circumference in the circumferential direction C. The projection 24 is positioned parallel to the stopper portion 12 in the axial direction A. The projection 24 protrudes less radially inward than the stopper portion 12. The projection 24 forms a stepped shape on the inner circumferential surface of the joint socket portion 21. The projection 24 has a side surface 24a and a circumferential surface 24b. The side surface 24a is formed perpendicular to the axial direction A from the inner surface 11a of the main body portion 11 inward in the radial direction B. The circumferential surface 24b is the radially inward end of the projection 24. The circumferential surface 24b is formed from the radially inward end of the side surface 24a toward the stopper portion 12 (end 11c direction) and is connected to the stopper portion 12. The circumferential surface 24b is formed parallel to the axial direction A. In this specification, "perpendicular" includes a range that is considered perpendicular according to common sense, even if it includes design tolerances. Also, in this specification, "parallel" includes a range that is considered parallel according to common sense, even if it includes design tolerances.

[0121] The joint socket portion 22 has a projection 25 that protrudes inward from the inner surface 11a in the radial direction B. The projection 25 is annular in shape. The projection 25 is formed along the entire circumference in the circumferential direction C. The projection 25 is positioned parallel to the stopper portion 12 in the axial direction A. The projection 25 protrudes less radially inward than the stopper portion 12. The projection 25 forms a stepped shape on the inner circumferential surface of the joint socket portion 21. The projection 25 has a side surface 25a and a circumferential surface 25b. The side surface 25a is formed perpendicular to the axial direction A from the inner surface 11a of the main body portion 11 inward in the radial direction B. The circumferential surface 25b is the radially inward end of the projection 25. The circumferential surface 25b is formed from the radially inward end of the side surface 25a toward the direction of the stopper portion 12 (end 11b direction) and is connected to the stopper portion 12. The circumferential surface 25b is formed parallel to the axial direction A.

[0122] Figure 6 is a cross-sectional view showing the state in which pipe 2 is inserted inside the joint socket portion 21 of the electrofusion joint 1, and pipe 3 is inserted inside the joint socket portion 22. As shown in Figure 6, pipe 2 is inserted inside the protruding portion 24 of the joint socket portion 21. Pipe 3 is inserted inside the protruding portion 25 of the joint socket portion 22.

[0123] (Stopper part 12) The stopper portion 12 is formed in an annular shape. The stopper portion 12 is formed as a ridge along the circumferential direction C on the inner surface 11a of the main body portion 11, extending around its entire circumference. The stopper portion 12 contains a thermoplastic resin. Preferably, the same thermoplastic resin used in the main body portion 11 is used for the stopper portion 12. Therefore, as the thermoplastic resin forming the stopper portion 12, the same as that used in the first resin layer 61, or a polyolefin such as polyethylene with a melting point of less than 230°C can be used. As the thermoplastic resin, PE (polyethylene) with a low elution rate may be used. As the thermoplastic resin, HDPE (high-density polyethylene resin) with a melting point of about 130°C and a low elution rate may be used.

[0124] As shown in Figure 5, the stopper portion 12 is formed to protrude radially inward from the inner surface 11a of the main body portion 11. The stopper portion 12 is also positioned radially inward B of the connecting portion 23 of the main body portion 11. The stopper portion 12 may be formed as a single component with the main body portion 11, or as a separate component from the main body portion 11.

[0125] As shown in Figure 5, the stopper portion 12 is positioned between the protrusions 24 and 25. The stopper portion 12 has a first side surface 12a, a second side surface 12b, and a circumferential surface 12c. The circumferential surface 12c is the radially inward end of the stopper portion 12.

[0126] The first side surface 12a is formed extending radially inward in the direction B from the end of the circumferential surface 24b of the protruding portion 24 that is opposite to the side surface 24a. The first side surface 12a is formed perpendicular to the axial direction A.

[0127] The second side surface 12b is formed extending radially inward in the direction B from the end of the circumferential surface 25b of the protrusion 25 that is opposite to the side surface 25a. The second side surface 12b is formed perpendicular to the axial direction A.

[0128] The circumferential surface 12c connects the radially inner end of the first side surface 12a and the radially inner end of the second side surface 12b. The circumferential surface 12c is formed parallel to the inner surface 11a of the main body portion 11.

[0129] When the pipe 2 is inserted into the joint socket portion 21, as shown in Figure 6, the end portion 2a of the pipe 2 comes into contact with the first side surface 12a of the stopper portion 12, thereby restricting the insertion position of the end portion 2a. Note that contact between the end portion 2a of the pipe 2 and the first side surface 12a includes cases where the end portion 2a directly contacts the first side surface 12a and cases where the end portion 2a indirectly contacts the first side surface 12a via the heating element 33 (described later) of the stopper heating element 15.

[0130] When the pipe 3 is inserted into the joint socket portion 22, as shown in Figure 6, the end 3a of the pipe 3 comes into contact with the second side surface 12b of the stopper portion 12, restricting the insertion position of the end 3a. Contact of the end 3a with the second side surface 12b includes cases where the end 3a directly contacts the second side surface 12b, and cases where the end 3a indirectly contacts the second side surface 12b via the heating element 33 (described later) of the stopper heating element 15. When the pipes 2 and 3 are inserted into the joint socket portions 21 and 22, the protruding height of the stopper portion 12 (position of the circumferential surface 12c) is formed to be lower than the inner surfaces 2s and 3s of the pipes 2 and 3.

[0131] (Receptacle heating elements 13, 14) As shown in Figure 6, the socket heating elements 13 and 14 are provided in the joint sockets 21 and 22. As shown in Figure 6, the socket heating element 13 has a heating element 31 embedded in a projection 24 of the joint socket 21. The heating element 31 is arranged to be wound around the circumferential surface 24b twice. The heating element 31 is located near the circumferential surface 24b. The heating element 31 may be partially embedded in the projection 24 so as to be exposed on the flow path 1f side from the circumferential surface 24b or side surface 24a, or it may be completely embedded. The projection 24 is formed to a length that allows the heating element 31 to be wound around twice in the axial direction A, but it is not limited to two turns and can be changed according to the length around which the heating element 31 is wound.

[0132] As shown in Figure 5, the socket heating element 14 has a heating element 32 embedded in the projection 25 of the joint socket 22. The heating element 32 is arranged to be wound around the circumferential surface 25b twice. The heating element 32 is located near the circumferential surface 25b. The heating element 32 may be partially embedded in the projection 25 so that it is exposed on the flow path 1f side from the circumferential surface 25b or side surface 25a, or it may be completely embedded. The projection 25 is formed to a length that allows the heating element 32 to be wound around twice in the axial direction A, but it is not limited to two turns and can be changed according to the length around which the heating element 32 is wound.

[0133] The heating element 31 includes, for example, a conductor 31a, an insulating coating 31b, and a covering resin 31c. The heating element 32 includes, for example, a conductor 32a, an insulating coating 31b, and a covering resin 32c. The conductors 31a and 32a can be, for example, nichrome wire, iron-chromium type 2 wire, iron-chromium type 1 wire, nickel-chromium wire, etc.

[0134] The insulating coatings 31b and 32b are provided to cover the periphery of the conductors 31a and 32a. The insulating coatings 31b and 32b have a melting point of 230 degrees Celsius or higher. In this embodiment, it is preferable that the melting point is set to a temperature at which the thermoplastic resin does not melt even at the temperature at which the thermoplastic resin melts (for example, in the case of polyethylene, the heating element is heated to 220 degrees Celsius). The insulating coatings 31b and 32b can be formed from, for example, a fluororesin or an imide resin, but it is more preferable to form them from a polyimide resin. Note that the heating elements 31 and 32 do not necessarily have insulating coatings 31b and 32b. The covering resins 31c and 32c are provided to cover the periphery of the insulating coatings 31b and 32b. The covering resins 31c and 32c are made of thermoplastic resin. The covering resins 31c and 32c may be the same resin as the thermoplastic resin used in the main body 11. Examples of thermoplastic resins include polyolefins such as polyethylene, which have a melting point of less than 230°C. As the thermoplastic resin, PE (polyethylene) with low elution rates may be used. Alternatively, HDPE (high-density polyethylene resin) with a melting point of approximately 130°C and low elution rates may be used as the thermoplastic resin.

[0135] The receiving port heating section 13 is provided symmetrically with respect to the receiving port heating section 14 and the stopper section 12. In this embodiment, the heating wires 31 and 32 are wound so as to be in contact in the axial direction A, but a gap may be provided between them without contact.

[0136] As shown in Figure 5, in the axial direction A, the receiving port heating element 13 is positioned adjacent to the stopper element 12. Also, in the axial direction A, the receiving port heating element 14 is positioned adjacent to the stopper element 12. For example, as shown in Figure 5, the heating element 31 is positioned so as to be in contact with a virtual surface M1 that extends radially outward in the direction B, with the first side surface 12a. Also, for example, as shown in Figure 5, the heating element 32 is positioned so as to be in contact with a virtual surface M2 that extends radially outward in the direction B, with the second side surface 12b.

[0137] Thus, the socket heating elements 13 and 14 are arranged in the axial direction A so as to be adjacent to the stopper element 12 and in contact with virtual surfaces M1 and M2, but a predetermined gap may be provided between the socket heating elements 13 and 14 and the stopper element 12.

[0138] Furthermore, in each of the receiving port heating sections 13 and 14, the heating wires 31 and 32 are wound around the axial direction A in contact with each other for two turns, but this is not limited to two turns; they may be wound only once, or multiple times along the axial direction A. Also, they do not need to be in contact with each other in whole or in part. In addition, there may be multiple sections where a predetermined number of heating elements are adjacent to each other.

[0139] Furthermore, although the socket heating section 13 and the socket heating section 14 are provided symmetrically on either side of the stopper section 12, this is not the only arrangement. For example, the heating wire 31 may be wound around the stopper section 12 twice in one joint socket section 21, and the heating wire 32 may be wound around the stopper section 22 three times.

[0140] (Stopper heating element 15) The stopper heating element 15 is provided on the stopper section 12. The stopper heating element 15 has a heating element 33. The heating element 33 is provided on the stopper section 12 so as to be wound around the circumferential direction C along the axial direction A. In this embodiment, the heating element 33 is wound around the stopper section 12 for example four times along the axial direction A, but it is not limited to four times; it is sufficient to be wound multiple times along the axial direction A. The heating element 33 can also be said to be wound around the stopper section 12 in a single helix. In the stopper heating element 15 of this embodiment, all adjacent heating elements 33 are in contact, but gaps may be provided.

[0141] The heating element 33 is embedded in the stopper portion 12 so as to be in contact with the circumferential surface 12c of the stopper portion 12. However, a portion of the heating element 33 may be embedded in the stopper portion 12 so as to be exposed to the flow path 1f side from the first side surface 12a, the second side surface 12b, or the circumferential surface 12c, or it may be embedded at a predetermined distance from the circumferential surface 12c of the stopper portion 12. The stopper portion 12 is formed to a length that allows the heating element 33 to be wound around it four times in the axial direction A.

[0142] The heating element 33 has, for example, a conductor 33a, an insulating coating 33b, and a covering resin 33c, as shown in Figure 5. The conductor 33a can be, for example, a nichrome wire, an iron-chromium type 2 wire, an iron-chromium type 1 wire, a nickel-chromium wire, or the like.

[0143] The insulating film 33b is provided so as to cover the periphery of the conductor 33a. The insulating film 33b has a melting point of 230 degrees Celsius or higher. In this embodiment, it is preferable that the temperature is set so that it does not melt even at the temperature at which the thermoplastic resin melts (for example, in the case of polyethylene, the heating wire is heated to 220 degrees Celsius). The insulating film 33b can be formed from, for example, a fluororesin or an imide resin, but it is more preferable to form it from a polyimide resin. Note that the heating wire 33 does not have to have an insulating film 33b. The covering resin 33c is provided so as to cover the periphery of the insulating film 33b. The covering resin 33c is formed from a thermoplastic resin. The covering resin 33c may be the same resin as the thermoplastic resin used in the main body 11. Examples of thermoplastic resins include polyolefins such as polyethylene with a melting point of less than 230°C. PE (polyethylene), which has a low elution rate, may be used as the thermoplastic resin. As the thermoplastic resin, HDPE (high-density polyethylene resin) with a melting point of about 130°C and low elution rate may be used.

[0144] In this embodiment, one heating element 33 is wound around the stopper heating element 15 four times so as to be in contact with the adjacent element, but this is not limited to this, and it may be wound three times or less or five times or more. Furthermore, the stopper heating element 15 may be formed by winding two or more heating elements 33 instead of just one. The heating elements 33 may be wound so that all or part of them are not in contact with the adjacent element.

[0145] (Connector mounting section 16) As shown in Figure 5, the connector mounting portion 16 has two pins 41b and 41c. The two pins 41b and 41c are provided so as to protrude radially outward from the outer surface 11d of the main body portion 11. One of the two pins 41b, 41c, is located near the end 11b of the main body portion 11, as shown in Figure 5, and the other pin 41c is located near the end 11c. The two pins 41b and 41c are connected to the heating wires 31 and 32 of the receiving port heating portions 13 and 14 and the heating wire 33 of the stopper heating portion 15, although these are not shown. The connections are in the order of pin 41b, heating wire 31, heating wire 32, heating wire 33 and pin 41c. In this embodiment, heating wires 31, 32, and 33 are a single heating wire. This single heating element extends from pin 41b to the socket heating element 13, sequentially forming the socket heating element 13, the stopper heating element 15, and the socket heating element 14, and then extends to pin 41c. When the connector of the fusion splicer 4 is attached to pins 41b and 41c and power is supplied, the heating elements 31, 32, and 33 generate heat.

[0146] (fusion method) This document describes the fusion method of the embodiment described herein, as well as the manufacturing method of the piping structure 100. In the diagrams describing the fusion method, pipes with the configuration of pipe 2A are used as pipes 2 and 3, but the same applies when pipes 2B, 2C, or 2D are used.

[0147] First, pipe 2 is inserted into the joint socket 21 of the electrofusion joint 1 until the relative movement of pipe 2's end 2a is restricted by the stopper portion 12. Then, pipe 3 is inserted into the joint socket 22 of the electrofusion joint 1 until the relative movement of pipe 3's end 3a is restricted by the stopper portion 12. Figure 6 shows the state in which pipes 2 and 3 are inserted into the electrofusion joint 1. Note that when inserting them into the electrofusion joint 1, the outer surfaces of pipe 2a and the vicinity of end 2a, and the outer surfaces of pipe 3a and the vicinity of end 3a may be scraped.

[0148] Next, a connector from a fusion splicing device (not shown) is attached to the two pins 41b and 41c of the connector mounting portion 16. Then, while the pipes 2 and 3 are pressed against the stopper portion 12 of the electric fusion joint 1, current is supplied to the heating wires 31-33.

[0149] Next, the molten pipe 2, the electrofusion joint 1, and the pipe 3 are cooled for a predetermined time. The pressure of pipes 2 and 3 against the stopper portion 12 may be continued until the cooling is complete, or it may be stopped when the heating stops.

[0150] Figure 7 is a cross-sectional view showing the state in which pipe 2, electrofusion joint 1, and pipe 3 are fused together. The stopper portion 12, the end 2a of pipe 2, and the end 3a of pipe 3 are melted, and the molten portion is pushed and narrowed by pipes 2 and 3, filling the space between pipes 2 and 3 and forming a bead R. The bead R is formed by the melting of the thermoplastic resin of the coating resin 33c of the heating element 33, the stopper portion 12, the end 2a of pipe 2, and the end 3a of pipe 3. Due to the pressure of pipes 2 and 3 against the stopper portion 12 while the resin is molten, pipes 2 and 3 move inward into the electrofusion joint 1 while crushing the stopper portion 12, and the bead R is formed according to the amount of movement. In addition, the outer surface 2t of pipe 2 and the resin around the heating element 31 of the socket heating element 13 are fused together, and the outer surface 3t of pipe 3 and the resin around the heating element 32 of the socket heating element 14 are fused together.

[0151] As shown in Figure 7, in the bead R, the second resin layer 62 is covered by the first resin layer 61, and the material forming the second resin layer 62 is not exposed on the flow path side surface RS of the bead R. The flow path side surface Rs of the bead R is formed only of the material forming the first resin layer 61. Thus, in the piping structure 100 of this embodiment, the inner surface through which the fluid flows is formed by the first resin layer 61 in which foreign matter is suppressed, and therefore the elution of impurities can be suppressed.

[0152] (Embodiment 2) In Embodiment 1, the piping structure 100 connects pipe 2 and pipe 3 using an electrofusion joint 1, while in Embodiment 2, the piping structure 300 is created by connecting pipe 2 and pipe 3 by butt fusion.

[0153] In butt fusion, the ends 2a of pipe 2 and 3a of pipe 3 are heated, causing them to melt. After heating, as shown in Figure 8, the ends 2a of pipe 2 and 3a of pipe 3 are pressed against each other. The pressing of the molten ends 2a and 3a together forms a bead R, as shown in Figure 9. The bead R is the portion that protrudes inward from the inner surfaces 2s and 3s.

[0154] In the piping structure 300 of this second embodiment, as shown in Figure 9, the flow path side surface Rs of the bead R is formed only by the material that forms the first resin layer 61, and the second resin layer 62 in the bead R is covered by the first resin layer 61, and the material that forms the second resin layer 62 is not exposed on the flow path side surface RS. In this way, in the piping structure 300 of this embodiment, the inner surface through which the fluid flows is formed by the first resin layer 61 in which foreign matter is suppressed, thus suppressing the elution of impurities.

[0155] (Applications of piping materials for ultrapure water) The pipes of the embodiments of the present invention can be used for transporting ultrapure water. Specifically, the pipes of the embodiments of the present invention can be used as piping within an ultrapure water production apparatus, piping for transporting ultrapure water from the ultrapure water production apparatus to a point of use, and piping for returning ultrapure water from a point of use. In this invention, ultrapure water is defined as having a resistivity of 10 MΩ·cm or more at 25°C, more precisely, a resistivity of 15 MΩ·cm or more at 25°C, and even more precisely, a resistivity of 18 MΩ·cm or more at 25°C.

[0156] The pipes of the embodiments of the present invention are preferably transport pipes for ultrapure water used in water piping for nuclear power plants, or in wet processing processes such as cleaning in the manufacturing of pharmaceuticals, semiconductor devices, or liquid crystals, and more preferably in the manufacturing of semiconductor devices, where the required water quality for ultrapure water is particularly stringent. Semiconductor devices with a higher degree of integration are preferred, and more specifically, those used in the manufacturing process of semiconductor devices with a minimum line width of 65 nm or less are preferred. Examples of standards related to the quality of ultrapure water used in semiconductor manufacturing include SEMI F75.

[0157] Furthermore, since the pipes of the embodiments of the present invention have a polyolefin resin layer, they offer excellent workability. For example, fusion bonding methods such as butt fusion bonding and EF (electrofusion) bonding can be easily performed at relatively low temperatures.

[0158] (Other embodiments) Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention.

[0159] (A) In the pipe 2B of the above embodiment, the first resin layer 61, the second resin layer 62, the adhesive layer 63, and the gas barrier layer 64 are arranged in that order, but the arrangement is not limited to this, and another layer may be placed between the second resin layer 62 and the adhesive layer 63. In the pipe 2C of the above embodiment, the first resin layer 61, the adhesive layer 63, and the gas barrier layer 64 are arranged in that order, but another layer may be placed between the first resin layer 61 and the adhesive layer 63.

[0160] (B) In the pipes 2B and 2C of the above embodiment, the gas barrier layer 64 constitutes the outer surface 2t, but another layer may be provided outside the gas barrier layer 64.

[0161] (C) The structure of pipe 2 in the above embodiment may be applied to fittings used when connecting resin pipes (elbow fittings, straight fittings, tee fittings, cross fittings, flange fittings, etc.), or it may be applied to the electrofusion fitting 1 in this embodiment. (D) In the above embodiment, the second resin layer 62 is colored with a pigment to create a color difference between it and the first resin layer 61. However, it is not limited to pigments; any method that can create a color difference between the first resin layer 61 and the second resin layer 62 is acceptable. For example, the second resin layer 62 may contain a dye or coloring agent and be colored by the dye or coloring agent. Also, in the above embodiment, the second resin layer 62 is colored, but the first resin layer 61 may be colored with a pigment, dye, or coloring agent, etc.

[0162] (E) The materials forming pipes 2 and 3 in the above embodiment may be the same or different. Alternatively, one of the pipes shown in Figures 2A to 2D may be used as pipe 2, and one of the other pipes shown in Figures 2A to 2D may be used as pipe 3, and these pipes may be connected.

[0163] (F) In the above embodiment, the outer diameter of the stopper portion 12 is circular when viewed along the axial direction A, but it is not limited to a circle and may be polygonal in shape.

[0164] (G) In the above embodiment 1, the same heating elements 31, 32, and 33 are used for the receiving port heating elements 13 and 14 and the stopper heating element 15, so an insulating coating is provided on all heating elements 31, 32, and 33, but this is not the only option. However, it is preferable that at least heating element 33 is provided with an insulating coating. This is because the heating elements 33 are pressurized by pipes 2 and 3 and are more likely to come into contact with each other.

[0165] (Examples) Next, the pipe of this embodiment will be described in detail using an example.

[0166] Using Examples 1-6 and Comparative Examples 1-4, the amount of calcium eluted was evaluated for tubes with different lengths of the longest straightest foreign matter present on the inner surface.

[0167] In Examples 1 to 6, single-layer pipes having only the first resin layer were used. The manufacturing apparatus 201 shown in Figure 4B was used to create the single-layer pipes. For the mesh 230, a combination of 40 mesh per inch (wire diameter Φ0.21 mm, open area 75%) and 150 mesh per inch (wire diameter Φ0.065 mm, open area 71%) was used.

[0168] In Example 1, polypropylene (Novatec PP, EA9FTD, manufactured by Nippon Polypropylene Co., Ltd.) was used as the material for the first resin layer 61. Extrusion molding was performed while heating the resin material in the first extruder 210 with a heater 212 to a temperature of 225°C, and a pipe with a diameter of 25A was formed. The inner surface of the formed pipe was photographed using a fiberscope (Keyence: VH-F61A), and the length L of the longest straight piece of foreign matter was measured. In addition, the amount of calcium leached from the pipe in Example 1 was measured in accordance with SEMI F-57. The results are shown in (Table 1) below. The length L and amount of calcium leached were measured in the same manner for the following examples and comparative examples.

[0169] In Example 2, polyethylene (Novatec HB534N, manufactured by Nippon Polyethylene Co., Ltd.) was used as the material for the first resin layer 61. Extrusion molding was performed while heating the resin in the first extruder 210 with a heater 212 to 190°C, thereby forming a pipe with a diameter of 25A.

[0170] In Example 3, a pipe with a diameter of 75A was formed under the same conditions as in Example 1.

[0171] In Example 4, a pipe with a diameter of 75A was formed under the same conditions as in Example 2.

[0172] In Example 5, a pipe with a diameter of 200A was formed under the same conditions as in Example 1.

[0173] In Example 4, a pipe with a diameter of 200A was formed under the same conditions as in Example 2. (Table 1) TIFF2026061660000002.tif53170 In Comparative Examples 1 to 4, single-layer tubes having only the first resin layer were used. For the production of the single-layer tubes, a device was used that lacked the mesh 230 and nitrogen purging device 220 compared to the manufacturing device 201 shown in Figure 4B.

[0174] In Comparative Example 1, polypropylene (Novatec PP, EA9FTD, manufactured by Nippon Polypropylene Co., Ltd.) was used as the material for the first resin layer. Extrusion molding was performed while heating the resin material in the first extruder 210 with a heater 212 to a temperature of 240°C, thereby forming a pipe with a diameter of 25A.

[0175] In Comparative Example 2, polyethylene (Novatec HB534N, manufactured by Nippon Polyethylene Co., Ltd.) was used as the material for the first resin layer. Extrusion molding was performed while heating the resin in the first extruder 210 with a heater 212 to 200°C, and a pipe with a diameter of 25A was formed.

[0176] In Comparative Example 3, a pipe with a diameter of 200A was formed under the same conditions as in Example 1.

[0177] In Comparative Example 4, a pipe with a diameter of 200A was formed under the same conditions as in Example 2.

[0178] The results for Comparative Examples 1-4 are shown in Table 2. (Table 2) TIFF2026061660000003.tif52170

[0179] Based on the above, in tubes where foreign matter with a length L of 500 μm or more is present on the inner surface, the calcium elution rate is 30 μg / m³. 2 Therefore, it is not suitable for transporting ultrapure water, and in tubes without foreign matter larger than L (500 μm), the calcium elution rate is 30 μg / m³. 2 Since the result is less than this, it can be used for transporting ultrapure water. [Explanation of Symbols]

[0180] 2: tube 61: 1st resin layer 62: 2nd resin layer

Claims

1. A pipe used for transporting ultrapure water, The innermost layer comprises a first layer mainly composed of polyolefin resin, polyvinyl chloride, or polyvinylidene fluoride. A tube in which the inner surface of the first layer is free of foreign matter with a longest straight length of 500 μm or more.

2. The invention further comprises a second layer located outside the first layer, The pipe according to claim 1.

3. The second layer mainly consists of an adhesive polyolefin resin. The pipe according to claim 2.

4. The thickness of the second layer is 50 μm or more and 100 μm or less. The pipe according to claim 2.

5. The calcium elution amount measured according to SEMI F-57 is 30 μg / m³. ２ Less than, The pipe according to claim 1.

6. The second layer is further provided with a gas barrier layer located on the outside of the second layer and having gas barrier properties. The pipe according to claim 2.

7. The first layer and the second layer are further provided with a core material layer mainly composed of a polyolefin resin, The pipe according to claim 2.

8. The first layer mainly contains the polyolefin resin, The polyolefin resin of the first layer is polyethylene or polypropylene. The pipe according to claim 1.

9. A pair of pipes according to any one of claims 1 to 8, A cylindrical main body having fitting sockets at both ends into which each of the aforementioned pipes is inserted, A stopper portion that restricts one end of the inserted pipe and restricts the other end of the inserted pipe, and which protrudes inward from the main body, The heating element includes a heating wire arranged in the stopper portion, An electrofusion joint and a piping structure in which they are fused together, It is formed by the end of one pipe and the end of the other pipe, and has a bead that protrudes inward, The inner surface of the bead is formed by the first layer and is free from foreign matter with a longest straight length of 500 μm or more. Piping structure.

10. The process includes an extrusion molding step in which a material mainly composed of polyolefin resin, polyvinyl chloride, or polyvinylidene fluoride is supplied from an extruder to a mold to form the first layer that constitutes the innermost layer. In the extrusion molding step, the temperature of the material inside the extruder is 170 degrees Celsius or higher and 230 degrees Celsius or lower. The material extruded from the extruder is supplied to the mold via at least one of a mesh, a screen changer, and a polymer filter for removing foreign matter. A method for manufacturing pipes.

11. In the extrusion molding step, the extruder is purged with nitrogen. The method for manufacturing a pipe according to claim 10.

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