Multilayer pipe and piping structure

Abstract

To provide a multilayer pipe capable of facilitating determination of defective construction.SOLUTION: A multilayer pipe 2, 2' comprises a first layer 61 and a second layer 62. The first layer 61 constitutes the innermost layer and is mainly composed of a polyolefin resin or a vinyl chloride resin. The second layer 62 is disposed outside the first layer 61 and is mainly composed of a polyolefin resin or a vinyl chloride resin. The calcium elution level of the first layer 61, measured in accordance with SEMI F-57, is less than 30 μg / m2. The color difference ΔE between the first layer 61 and the second layer 62 is 0.5 or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a multi-layer pipe and a piping structure. [Background technology]

[0002] In the manufacture of precision devices such as semiconductor devices and liquid crystal display devices, ultrapure water that has been refined to an extremely high degree of purity is used in wet processes such as cleaning. If metal ions or the like are present in the water at a concentration above a certain level, the metals will be adsorbed onto the wafer surface or the like, adversely affecting the quality of the precision device, so the amount of impurities in the ultrapure water is strictly limited.

[0003] Impurities can also get mixed into ultrapure water in the piping that makes up the ultrapure water transport line. Metals such as stainless steel, which have excellent gas barrier properties, have been used as piping materials, but considering the impact of metal elution from the piping, it is considered preferable to use resin.

[0004] For example, Patent Document 1 discloses a multi-layer pipe for piping ultrapure water, characterized in that it comprises a first resin layer made of fluororesin that comes into contact with the ultrapure water, and a second resin layer made of gas-impermeable resin that is provided on the outer circumferential surface of the first resin layer. It further discloses that a third resin layer that protects the second resin layer is provided on the outer circumferential surface of the second resin layer, and that polyethylene is used for the third resin layer.

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

[0006] Fluororesin piping such as PVDF has disadvantages in terms of ease of installation and cost compared to other common piping. Furthermore, ultra-high purity cleaning solutions often contain dialumoalkanes such as 3-dialuminopropane, and they are used at 60°C, which causes rapid deterioration.

[0007] For this reason, for example, a multi-layer pipe has been proposed in which a polyolefin resin is used for the innermost layer, as shown in Patent Document 2. The multi-layer pipe shown in Patent Document 2 has a first polyolefin resin layer constituting the innermost layer, and a second polyolefin resin layer disposed on the outer side of the first polyolefin resin layer. The first polyolefin resin layer has a calcium elution amount of 30 μg / m 2 This limits the amount of impurities that can be mixed into the ultrapure water.

[0008] On the other hand, when connecting pipes, methods such as butt welding and fusion via an electrofusion joint are used. An electrofusion joint comprises a joint body made of thermoplastic resin with pipe receptacles formed at both ends into which the pipes to be connected are inserted, and a positioning protrusion protruding inward from the inner peripheral surface of the joint body (see, for example, Patent Document 3). The positioning protrusion positions the pipe inserted into the pipe receptacle. An electric heating wire is provided in the pipe receptacle, and by generating heat, the resin around the heating wire fuses with the resin of the pipe, connecting the electric fusion joint and the pipe. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2010-234576 A [Patent Document 2] Patent Publication No. 2021-55764 [Patent Document 3] Japanese Patent Application Publication No. 2023-46656 Summary of the Invention [Problem to be solved by the invention]

[0010] When welding pipes as described above, it is desirable to be able to instantly detect any construction defects, since poor construction can lead to water leakage. Furthermore, when welding multi-layer pipes as shown in Patent Document 3, if not only the first polyolefin resin layer but also the second polyolefin resin layer is exposed on the flow path side surface of the raised portion (bead) of the joint, this can lead to a decrease in water quality.

[0011] The present disclosure aims to provide a multi-layer pipe and a piping structure that allow for easy detection of construction defects. [Means for solving the problem]

[0012] To achieve the above object, the multi-layer pipe according to the first disclosure comprises a first layer and a second layer. The first layer constitutes the innermost layer and is primarily composed of a polyolefin resin or a vinyl chloride resin. The second layer is disposed outside the first layer and is primarily composed of a polyolefin resin or a vinyl chloride resin. The amount of calcium elution from the first layer measured in accordance with SEMI F-57 is 30 μg / m 2 The color difference ΔE between the first and second layers is 0.5 or more.

[0013] For example, if the first and second layers are the same color, it is impossible to determine whether the material that forms the second layer is exposed to the bead surface during fusion. However, by creating a color difference between the first and second layers, it is possible to visually check whether the material that forms the second layer is exposed to the bead surface, making it possible to determine whether the fusion is poor.

[0014] The multi-layer pipe according to the second disclosure is the multi-layer pipe according to the first disclosure, wherein the ratio of the thickness of the first layer to the total thickness of the first layer and the second layer is 0.011 or more and 0.500 or less.

[0015] This makes it possible to limit the elution of impurities into the liquid flowing through the multi-layer pipe. For example, when used to transport ultrapure water, if the ratio is less than 0.011, the thickness of the first layer will be thin and impurities may elute, but by setting the ratio to 0.011 or more, the thickness of the first layer can be secured and the elution of impurities can be limited.

[0016] The multi-layer pipe according to the third disclosure is the multi-layer pipe according to the first disclosure, wherein the thickness of the first layer is 0.06 mm or more and 5.0 mm or less.

[0017] This makes it possible to limit the elution of impurities into the liquid flowing through the multi-layer pipe. For example, when used to transport ultrapure water, if the thickness of the first layer is less than 0.06 mm, the thickness of the first layer will be too thin and impurities may elute, but by setting the thickness to 0.06 mm or more, the thickness of the first layer can be ensured and the elution of impurities can be limited.

[0018] The multi-layer pipe according to the fourth disclosure is the multi-layer pipe according to the first disclosure, wherein the calcium elution amount of the second layer measured in accordance with SEMI F-57 is 30 μg / m 2 That's all.

[0019] Thus, the calcium elution rate of the second layer was 30 μg / m 2 Since the above can be tolerated, calcium can be contained in the second layer, thereby ensuring strength.

[0020] The multi-layer pipe according to the fifth disclosure is the multi-layer pipe according to the first disclosure, in which the color difference ΔE between the first layer and the second layer is 1.0 or more.

[0021] This increases the color difference between the first and second layers, making it easier to determine whether the second layer is exposed to the bead surface.

[0022] The multi-layer pipe according to the sixth disclosure is the multi-layer pipe according to the first disclosure, further comprising a gas barrier layer disposed outside the second layer.

[0023] This effectively prevents gas from dissolving in the liquid flowing through the multi-layer pipe.

[0024] The multi-layer pipe according to the seventh disclosure is the multi-layer pipe according to the first disclosure, and is used for transporting a semiconductor cleaning liquid.

[0025] This allows the pipe to be used as a pipe for transporting ultrapure water used as a semiconductor cleaning liquid.

[0026] The multi-layer pipe according to the eighth disclosure comprises a first layer and a second layer. The first layer constitutes the innermost layer and is primarily composed of a polyolefin resin or vinyl chloride resin. The second layer is disposed outside the first layer and primarily contains a polyolefin resin or vinyl chloride resin and also contains a pigment.

[0027] This allows the second layer to be colored, providing a color difference between the first and second layers.

[0028] A piping structure according to a ninth disclosure is a piping structure in which a pair of multi-layer pipes according to any one of the first to seventh disclosures are fused together with an electrofusion joint. The electrofusion joint has a cylindrical main body having joint sockets at both ends into which the multi-layer pipes are inserted, a stopper portion that restricts the end of one inserted multi-layer pipe and the end of the other inserted multi-layer pipe and protrudes inward from the main body, and a heating portion including an electric heating wire disposed in the stopper portion. The piping structure is formed by the end of one multi-layer pipe and the end of the other multi-layer pipe and has a bead that protrudes inward, the inner surface of the bead being formed by a first layer, and the second layer being covered by the first layer.

[0029] In this way, when the second layer is covered by the first layer in the bead, the material forming the second layer cannot be seen on the surface of the bead, so it can be determined that the application is good.

[0030] The piping structure according to the tenth disclosure is a piping structure in which the ends of a pair of multi-layer pipes according to any one of the first to eighth disclosures are fused together, and is formed by the end of one multi-layer pipe and the end of the other multi-layer pipe, and has a bead protruding inward, the inner surface of the bead being formed by a first layer, and the second layer being covered by the first layer.

[0031] In this way, when the second layer is covered by the first layer in the bead, the material forming the second layer cannot be seen on the surface of the bead, so it can be determined that the application is good. [Effects of the Invention]

[0032] According to the present disclosure, it is possible to provide a multi-layer pipe, a piping structure, and a fusion method that allow construction defects to be easily determined. [Brief explanation of the drawings]

[0033] [Figure 1] 1A and 1B are diagrams showing a multi-layer pipe, an electric fusion joint, and a multi-layer pipe according to a first embodiment of the present disclosure. [Figure 2] (a) is a cross-sectional view of a multi-layer pipe according to the first embodiment of the present disclosure; (b) is a cross-sectional view of a multi-layer pipe according to another example of the first embodiment of the present disclosure; [Figure 3] 1 is a diagram showing a cross-sectional configuration of an electrofusion joint according to a first embodiment of the present disclosure. [Figure 4] 4 is a cross-sectional view showing the state in which a multilayer pipe is inserted into the electric fusion joint of FIG. 3. FIG. [Figure 5] 1 is a cross-sectional view showing a multi-layer pipe, an electric fusion joint, and a state in which the multi-layer pipe is well fused. FIG. [Figure 6] 1 is a cross-sectional view showing a multi-layer pipe, an electric fusion joint, and a state in which the multi-layer pipe is poorly fused. [Figure 7] (a) A view along the multi-layer pipe showing a state in which the multi-layer pipe, the electric fusion joint, and the multi-layer pipe are well fused, and (b) a view along the multi-layer pipe showing a state in which the multi-layer pipe, the electric fusion joint, and the multi-layer pipe are poorly fused. [Figure 8]FIG. 10 is a diagram showing a pair of multi-layer pipes according to a second embodiment of the present disclosure. [Figure 9] FIG. 1 is a cross-sectional view showing a pair of multi-layer pipes in a well-fused state. [Figure 10] FIG. 1 is a cross-sectional view showing a state in which a pair of multi-layer pipes are poorly fused together. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0035] (Embodiment 1) <Configuration> (Outline of piping structure 100) Fig. 1 is a diagram showing an electrofusion joint 1 according to an embodiment of the present disclosure, a multi-layer pipe 2 (an example of a multi-layer pipe) connected by the electrofusion joint, and a multi-layer pipe 3 (an example of a multi-layer pipe). Fig. 1 can also be considered an exploded view of a piping structure 100. The piping structure 100 includes, for example, the electrofusion joint 1, the multi-layer pipe 2, and the multi-layer pipe 3. As shown in Fig. 1, the electrofusion joint 1 is fused to the multi-layer pipe 2 and the multi-layer pipe 3, connecting the multi-layer pipe 2 and the multi-layer pipe 3.

[0036] Multi-layer pipe 2 and multi-layer pipe 3 have circular cross-sectional flow paths 2f and 3f extending therethrough. Electro-fusion joint 1 has a circular cross-sectional flow path 1f extending therethrough. When multi-layer pipe 2 and multi-layer pipe 3 are connected by electro-fusion joint 1, the axes of the flow paths of multi-layer pipe 2, multi-layer pipe 3, and electro-fusion joint 1 are aligned on the same line.

[0037] The direction in which the axis of each of the flow paths of the electric fusion joint 1, the multi-layer pipe 2, and the multi-layer pipe 3 extends is referred to as the axial direction A. In addition, in the electric fusion joint 1, the multi-layer pipe 2, and the multi-layer pipe 3, the direction perpendicular to and moving away from each axis is referred to as the radial direction B, and the direction rotating around each axis is referred to as the circumferential direction C.

[0038] The multi-layer pipe 2 moves relative to the electric fusion joint 1 in the direction of arrow A1 in the axial direction A and is connected to the electric fusion joint 1. Furthermore, the multi-layer pipe 3 moves relative to the electric fusion joint 1 in the direction of arrow A2 in the axial direction A and is connected to the electric fusion joint 1. The state in which the multi-layer pipe 2 and the multi-layer pipe 3 are fused and connected to the electric fusion joint 1 constitutes the piping structure 100.

[0039] (Double-layer pipes 2 and 3) Since the multi-layer pipe 2 and the multi-layer pipe 3 have the same configuration, the multi-layer pipe 2 will be described as an example. Fig. 2(a) is a cross-sectional view of the multi-layer pipe 2. Fig. 2(b) is a cross-sectional view showing a multi-layer pipe 2', which is another example of the multi-layer pipe 2.

[0040] The multi-layer pipe 2 shown in FIG. 2(a) includes a first layer 61 and a second layer 62. The first layer 61 constitutes the innermost layer of the multi-layer pipe 2. The first layer 61 forms the inner surface 2b of the multi-layer pipe 2. The first layer 61 contains a polyolefin resin as a main component. The second layer 62 is disposed on the outside of the first layer 61. The second layer 62 contains a polyolefin resin as a main component and also contains a pigment. As will be described in more detail below, the second layer 62 is colored with a pigment, giving it a different color from the first layer 61. The outer surface 2c of the multi-layer pipe 2 is formed by the second layer 62.

[0041] The multi-layer pipe 2' shown in Figure 2(b) includes a first layer 61, a second layer 62, an adhesive layer 63, and a gas barrier layer 64. In the multi-layer pipe 2', the gas barrier layer 64 is disposed outside the second layer 62 of the multi-layer pipe 2 with the adhesive layer 63 interposed therebetween. The first layer 61 constitutes the innermost layer of the multi-layer pipe 2'. The first layer 61 forms the inner surface 2b' of the multi-layer pipe 2'. The gas barrier layer 64 forms the outer surface 2c' of the multi-layer pipe 2'.

[0042] The multi-layer pipe 3 may also have the same configuration as the multi-layer pipe 2' shown in FIG. 2(b).

[0043] (1st layer 61) The first layer 61 constitutes the innermost layer of the multi-layer pipe 2. The first layer 61 forms the inner surface 2b of the multi-layer pipe 2. The first layer 61 contains a polyolefin resin as a main component. The main component refers to the component with the highest content by mass. The main component refers to a component with a content of at least 50%. The lower limit of the polyolefin resin content in the first layer 61 is preferably 50% by mass, more preferably 70% by mass, even more preferably 80% by mass, sometimes even more preferably 90% by mass, and sometimes even more preferably 95% by mass.

[0044] The polyolefin-based resin contained as a main component in the first layer 61 is not particularly limited, and may be a polymer containing a monomer unit derived from an olefin. Examples include polyethylene-based resins, ethylene-alkenyl carboxylic acid ester copolymer resins, ethylene-α-olefin copolymer resins, polypropylene-based resins, polybutene-based resins, and poly(4-methyl-1-pentene)-based resins. These polyolefin-based resins may be used alone or in combination of two or more. Among these polyolefin-based resins, polyethylene-based resins and polypropylene-based resins are preferred from the viewpoint of improving the strength of the semiconductor cleaning liquid pipe. Furthermore, among polyethylene-based resins and polypropylene-based resins, polyethylene-based 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.

[0045] Examples of polypropylene resins include homopolypropylene, block polypropylene, and random polypropylene. Ethylene is usually used as a copolymerization component in block polypropylene and random polypropylene. Examples of polybutene resins include polybutene-1.

[0046] The polyethylene resin may be copolymerized with an α-olefin, if necessary. Examples of the α-olefin to be copolymerized with the polyethylene resin 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.

[0047] The polyethylene resin is polymerized using a catalyst containing one or more transition metal derivatives. From the viewpoint of ensuring long-term durability, in this embodiment, polymerization is carried out using a Ziegler catalyst. When polymerizing the polyethylene resin using a Ziegler catalyst, a chlorine-based catalyst is used in an amount appropriately determined by a person skilled in the art to perform multi-stage polymerization, and then a neutralizing agent for neutralizing the chlorine-based catalyst, and preferably an antioxidant, are added as well. The Ziegler catalyst used in the present invention is well known, and examples of the catalyst systems used include those described in JP-A-53-78287, JP-A-54-21483, JP-A-55-71707, and JP-A-58-225105.

[0048] Specifically, a catalyst system can be mentioned which comprises a solid catalyst component obtained by contacting a tetravalent titanium compound with a co-ground product obtained by co-grounding aluminum trihalide, an organosilicon compound having an Si-O bond, and a magnesium alcoholate, and an organoaluminum compound.

[0049] The solid catalyst component preferably contains 1 to 15% by weight of titanium atoms. Preferred organosilicon compounds include those having a phenyl group or an aralkyl group, such as diphenyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, triphenylethoxysilane, and triphenylmethoxysilane.

[0050] In producing the co-ground product, the proportions of aluminum trihalide and organosilicon compound used per mole of magnesium alcoholate are generally 0.02 to 1.0 moles, preferably 0.05 to 0.20 moles, and the molar ratio of aluminum atoms in the aluminum trihalide to silicon atoms in the organosilicon compound is preferably 0.5 to 2.0.

[0051] To produce the co-ground product, a conventional method may be applied using a mill such as a rotary ball mill, a vibrating ball mill, or a colloid mill, which are commonly used in producing this type of solid catalyst component. The average particle size of the obtained co-ground product is usually 50 to 200 μm, and the specific surface area is usually 20 to 200 m. 2 / g.

[0052] The co-ground product thus obtained is contacted with a tetravalent titanium compound in the liquid phase to obtain a solid catalyst component. 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, or tri-i-butylaluminum.

[0053] Examples of the neutralizing agent include fatty acid metal salts such as calcium stearate, zinc stearate, and magnesium stearate, and hydrotalcites.

[0054] However, if polyethylene resin is polymerized using magnesium stearate or hydrotalcite as a neutralizing agent, when the resulting resin is molded into a piping material, a large amount of aluminum and magnesium will dissolve into water, which is not preferred for this embodiment.

[0055] In contrast, when polyethylene resin is polymerized using calcium stearate as a neutralizing agent, the metal elution of aluminum and magnesium as described above does not occur, and favorable low elution properties can be obtained, so calcium stearate is a preferred neutralizing agent in this embodiment.

[0056] High-density polyethylene (HDPE) is preferred as a polyethylene-based resin composition, as it provides sufficient pressure resistance against water pressure during water transport and allows for thin pipe walls. Among high-density polyethylenes (HDPEs), HDPEs classified as PE100 or higher in the pressure-resistant class according to ISO 9080, ISO 1167, and ISO 12162 are more preferred in order to ensure the long-term durability of piping materials for ultrapure water. Even among HDPEs classified as PE100 or higher, HDPEs with high resistance to slow crack growth (slow crack growth resistance) are preferred to further enhance the safety of the pipe system and to have high fluidity to improve the smoothness of the inner surface of the pipe. Note that slow crack growth refers to a type of damage caused by stress concentration, such as scratches on the piping material or at the joint between the pipe and the fitting.

[0057] As an index of a polyethylene resin composition that satisfies the pressure resistance class of PE100 or more and has good fluidity, specifically, the melt flow rate (MFR) of the polyethylene resin composition at a temperature of 190°C and a load of 21.6 kg is used. 21.6 ) is 6g / 10min or more and 25g / 10min or less, and the FR (MFR) is the ratio of the melt flow rate (MFR5) to the MFR21.6 at a temperature of 190°C and a load of 5kg. 21.6 / MFR5) is 25 or more and 60 or less, and the density is 0.946 g / cm 3 More than 0.960g / cm 3 It is preferable that:

[0058] MFR of polyethylene resin composition 21.6 If the MFR is less than 6g / 10min, the fluidity of the resin material will be low, the mold transferability will be poor, and the smoothness of the inner surface of the pipe will be insufficient. 21.6 If the FR exceeds 25g / 10min, it becomes difficult to design a resin that satisfies PE100. Also, if the FR is less than 25, the molecular weight distribution of the polyethylene resin composition becomes narrow, so it is difficult to achieve the target MFR 21.6On the other hand, if the FR exceeds 60, the impact resistance of the polyethylene resin composition decreases, and the safety of the piping material may be impaired. 3 If the density is less than 0.960 g / cm, the pressure resistance performance will decrease and it will be difficult to reach PE100. 3 If the temperature exceeds this value, the resistance to slow cracking of the piping material will decrease, and the safety of the piping system will decrease over the long term.

[0059] Furthermore, the resin composition for achieving the above polyethylene-based resin composition is preferably composed of multiple components, specifically, a high molecular weight component (A) and a low molecular weight component (B).

[0060] High molecular weight component (A) is MFR 21.6 The resin composition has a melt flow rate (MFR2.16) of 20 g / 10 min to 500 g / 10 min, preferably 50 g / 10 min to 300 g / 10 min, a melt flow rate (MFR2.16) 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.

[0061] MFR of the high molecular weight component (A) constituting the polyethylene resin composition 21.6 If the MFR is less than 0.05g / 10min, 21.6 To achieve this, it is necessary to increase the MFR of the low molecular weight component, but in that case, the difference in viscosity between the high molecular weight component and the low molecular weight component when melted increases, reducing compatibility, resulting in a decrease in various mechanical properties including slow crack resistance and roughening of the inner surface of the pipe due to flow instability. 21.6If the elongation coefficient exceeds 1.0 g / 10 min, various mechanical properties are reduced, and in particular, slow crack growth resistance is significantly reduced. If the α-olefin content is less than 0.8 mol%, slow crack growth resistance is reduced, and if it exceeds 2.0 mol%, the rigidity of the polyethylene resin composition is reduced, making it difficult to design a resin that reaches PE100. If the content of high molecular weight component (A) is less than 35 wt%, the durability of the piping is reduced, and if it exceeds 50 wt%, the rigidity of the polyethylene resin composition is reduced, making it difficult to design a resin that reaches PE100.

[0062] If the MFR2.16 of the low-molecular-weight component (B) constituting the polyethylene resin composition is less than 20 g / 10 min, the flowability of the polyethylene resin composition will be reduced, resulting in poor 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, particularly impact resistance, will be significantly reduced.

[0063] The α-olefin content here includes not only the α-olefins fed to the reactor and copolymerized during polymerization, but also by-produced short-chain branches (e.g., ethyl branches, methyl branches). The α-olefin content is measured by C-NMR. The α-olefin content can be increased or decreased by increasing or decreasing the amount of α-olefin fed to be copolymerized with ethylene.

[0064] The calcium elution amount measured in accordance with SEMI F-57 for the first layer 61 is 30 μg / m 2 The calcium concentration in the first layer 61 is adjusted to be less than 360 ppm. The calcium concentration in the first 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 eluted into the ultrapure water becomes excessive, making it impossible to satisfy the required quality of ultrapure water.

[0065] From the viewpoint of further suppressing the amount of calcium eluted into ultrapure water, it is preferable that the calcium concentration of the first layer 61 is as low as possible; however, from the viewpoint of obtaining good thermal stability and long-term strength of the polyethylene resin composition, the inclusion of a small amount of calcium is unavoidable.

[0066] That is, when the amount of neutralizing agent added to a polyethylene resin polymerized using a Ziegler catalyst is insufficient, catalyst residue remains active in the resin, which may result in a decrease in the thermal stability and long-term strength of the polyethylene resin composition.

[0067] Therefore, in this embodiment, it is essential to add the minimum amount of neutralizing agent necessary to neutralize the catalyst residue. In consideration of the above, the calcium concentration in the first 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.

[0068] From the viewpoint of ensuring thermal stability, the oxidation induction time (OIT) of the first layer 61 at 210°C is preferably 20 minutes or more. If the oxidation induction time at 210°C is less than 20 minutes, the polyethylene resin may deteriorate when thermally processed, resulting in a decrease in long-term strength and an increase in particles derived from the deterioration, which is not preferable for this embodiment.

[0069] A 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 of piping materials for ultrapure water, the hot internal pressure creep performance when the first layer 61 is molded as a piping material is preferably such 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.

[0070] The material properties of the polyethylene resin composition more preferably have a pressure resistance of "PE100" or higher as specified in the ISO 9080, ISO 1167, and ISO 12162 standards. "PE100" refers to polyethylene in which the LPL value, which is the minimum guaranteed stress after 50 years at 20°C estimated by extrapolation using a multiple correlation average after measuring stress-rupture time curves for at least 9,000 hours at three different temperatures, with the maximum and minimum temperatures being at least 50°C apart, is 10 MPa or higher and 11.19 MPa or lower, according to the classification table specified in ISO 12162.

[0071] The first layer 61 may or may not contain an antioxidant. Examples of the antioxidant include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, aromatic amine-based antioxidants, and lactone-based antioxidants.

[0072] 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, 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 methylthiomethyl)-o-cresol, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene bis[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 ,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-triazin-2-ylamino]phenol, and diethyl[{3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl}methyl]phosphonate.

[0073] When a phenolic antioxidant is used, a single 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 groups other than the phenol group. Examples of the antioxidant 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-triazin-2-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 a phenolic antioxidant containing oxygen derived from groups other than the phenol group is used as the antioxidant, the calcium concentration in the polyethylene resin is preferably 50 ppm or less. Examples of functional groups having oxygen derived from groups other than phenol groups include ester groups, carbonyl groups, carboxy groups, ether groups, nitro groups, nitroso groups, amide groups, azoxy groups, and sulfo groups.

[0074] 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]dioxaphosphen-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′-diylbisphosphonite.

[0075] Examples of sulfur-based antioxidants include dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, and pentaerythrityl tetrakis(3-laurylthiopropionate).

[0076] Examples of aromatic amine antioxidants include monoamine compounds such as diphenylamine compounds, quinoline compounds, and naphthylamine compounds, and diamine compounds such as phenylenediamine compounds and benzimidazole compounds.

[0077] Diphenylamine compounds include p-(p-toluenesulfonylamido)-diphenylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, and 4,4'-dioctyldiphenylamine derivatives. Quinoline compounds include 2,2,4-trimethyl-1,2-dihydroquinoline polymers.

[0078] Examples of naphthylamine compounds include phenyl-α-naphthylamine and N,N'-di-2-naphthyl-p-phenylenediamine.

[0079] 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, a mixture of N-N'-diphenyl-p-phenylenediamines, diaryl-p-phenylenediamine derivatives or mixtures thereof.

[0080] Examples of the benzimidazole compound include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, the zinc salt of 2-mercaptobenzimidazole, and the zinc salt of 2-mercaptomethylbenzimidazole.

[0081] Examples of lactone antioxidants include a reaction product of 3-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene. From the viewpoint of suppressing the effects of oxygen and ensuring desirable strength, the content of the antioxidant in the first 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. The upper limit of the content of the antioxidant is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0082] The first layer 61 may or may not contain a light stabilizer, but preferably does not contain a light stabilizer in order to prevent the elution of total organic carbon (TOC). Examples of light stabilizers include hindered amine light stabilizers (HALS). Furthermore, the first layer 61 of this embodiment preferably does not substantially contain a light stabilizer. Here, "substantially does not contain" means that light stabilizers are not actively added, but that unavoidable inclusion as impurities is permitted. The lower the concentration of light stabilizers that are inevitably mixed in as impurities, the better.

[0083] Examples of the hindered amine light stabilizer include NH-type hindered amine compounds, NR-type hindered amine compounds, and N-OR-type hindered amine compounds.

[0084] Examples of NH-type hindered amine compounds include Tinuvin 770DF, Kimassorb 2020FDL, Kimassorb 944FDL (all trade names, manufactured by BASF), Adeka STAB LA-68, Adeka STAB LA-57 (all trade names, manufactured by Adeka Corporation), Cyasorb UV-3346, Cyasorb UV-3853 (all trade names, manufactured by Sun Chemical Company), and the like.

[0085] Examples of the NR-type hindered amine compound include Tinuvin 622SF, Tinuvin 765, Tinuvin PA144, Chimassorb 119, and Tinuvin 111 (all trade names, manufactured by BASF), Savostab UV119 (trade name, manufactured by Sabo Corporation), Adekastab LA-63P, and Adekastab LA-52 (all trade names, manufactured by Adeka Corporation).

[0086] Examples of the N-OR type hindered amine compound include Tinuvin 123, Tinuvin 5100, Tinuvin NOR371FF, and Flame Stab NOR116FF (all trade names, manufactured by BASF).

[0087] The first layer 61 may or may not contain an ultraviolet absorber (UVA). Examples of ultraviolet absorbers include benzophenone-based ultraviolet absorbers, salumarate-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.

[0088] Benzophenone-based ultraviolet absorbers include 2-hydroxy-4-methoxy-benzophenone.

[0089] Examples of benzotriazole-based ultraviolet 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).

[0090] The density of the polyethylene resin composition of the first layer 61 is preferably 0.946 g / cm 3 from the viewpoint of obtaining good rigidity of the polyethylene resin composition. 3 More preferably, 0.947 g / cm 3 More preferably, 0.948 g / cm 3 The density is preferably 0.960 g / cm from the viewpoint of obtaining good long-term durability and flexibility of the polyethylene resin composition. 3 or less, more preferably 0.957 g / cm 3 or less, more preferably 0.953 g / cm 3 The density is a value established in accordance with JIS K6922-2:1997.

[0091] The melt flow rate (MFR) of the polyethylene resin composition of the first layer 61 at a temperature of 190°C and a load of 21.6 kg 21.6 In order to obtain good processability of the polyethylene resin composition, the MFR 21.6 The MFR is preferably 8 g / 10 min or more, more preferably 12 g / 10 min or more, and even more preferably 15 g / min or more. 21.6 The MFR is preferably 22 g / 10 min or less, and more preferably 20 g / 10 min or less. 21.6 is a value established in accordance with JISK6922-2:1997.

[0092] The inner surface smoothness (arithmetic mean roughness Ra) of the first layer 61 is not particularly limited, and may be, for example, 0.50 μm or less. From the viewpoint of obtaining favorable low elution properties of the pipe, the inner surface smoothness of the first layer 61 is preferably 0.40 μm or less, and more preferably 0.35 μm or less.

[0093] The ratio of the thickness of the first layer 61 to the total thickness of the first layer 61 and the second layer 62 is preferably 0.011 or more and 0.500 or less.

[0094] The thickness of the first layer 61 is preferably 0.06 mm or more and 5.0 mm or less.

[0095] (2nd layer 62) The second layer 62 is disposed on the outside of the first layer 61. The second layer 62 contains a polyolefin resin as a main component. The polyolefin resin used for the second layer 62 is not particularly limited and can be appropriately selected from the polyolefin resins listed above as being used for the first layer 61. Among the polyolefin resins listed above, high-density polyethylene (HDPE) is preferred from the viewpoint of suppressing the elution of low-molecular-weight components and / or durability when the pipe is cleaned with chemicals. The polyolefin resin used for the second layer 62 may be the same or different from the polyolefin resin used for the first layer 61. However, when the two layers are laminated in contact with each other, it is more preferred that the two layers be the same type of polyolefin resin in order to improve adhesion between the two layers and achieve a desired strength.

[0096] The second layer 62 contains a pigment. Any of conventionally known organic pigments, inorganic pigments, and extender pigments can be used as the pigment, without any particular limitation. 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 oxide-based, iron oxide-based, iron hydroxide-based, chromium oxide-based, spinnel-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 oxide-based, and aluminum hydroxide-based pigments. Pigments can be used alone or in combination to achieve the desired color for the second layer 62.

[0097] The color of the second layer 62 is set so that the color difference ΔE between the first layer 61 and the second layer 62 is 0.5 or more. The color difference ΔE is preferably 1.0, and more preferably 2.0 or more. For example, the first layer 61 can be set to white, and the second layer 62 can be set to blue. Alternatively, the second layer 62 can be set to a yellowish color.

[0098] The content of the pigment in the second layer 62 is not particularly limited as long as the above color difference can be achieved, but it is preferably 0.05 wt % or more and 1.00 wt % or less.

[0099] The amount of calcium elution measured in accordance with EMIF-57 from the material (polyolefin resin composition) of the second layer 62 is preferably 30 μg / m from the viewpoint of ensuring the strength of the semiconductor cleaning liquid piping in a 60° C. environment. 2 More preferably, 50 μg / m 2 More preferably, 70 μg / m 2 More preferably, 80 μg / m 2 More than 90 μg / m 2 More particularly preferably 95 μg / m 2 The above can be mentioned.

[0100] The multi-layer pipes 2 and 3 of the present invention have an excellent effect of suppressing the elution of calcium and organic components, and can effectively suppress the elution of calcium even if the material of the second layer 62 contains a large amount of calcium. From this perspective, a suitable example of the amount of calcium elution is 80 μg / m within the above range. 2 More than 90μg / m 2 or more, or 95 μg / m 2 The upper limit of the amount of calcium elution is not particularly limited, but from the viewpoint of suppressing calcium elution, it is 120 μg / m 2 Below, 110μg / m 2 or less, or 100 μg / m 2Examples include the following. The calcium concentration in the material (polyolefin resin composition) of the second 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 liquid piping in an operating environment of 60°C, it can be, 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. The upper limit of the calcium concentration range can be, 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, from the viewpoint of preventing a lack of strength caused by the contained calcium itself becoming the starting point of fracture and from the viewpoint of preventing the elution of calcium and organic components.

[0101] The amount of organic components (TOC) eluted from the material (polyolefin resin composition) of the second layer 62, as measured in accordance with EMIF-57, is, for example, 30,000 μg / m 2 The multi-layer pipes 2 and 3 of the present invention are excellent in the effect of suppressing the elution of calcium and organic components, and therefore can effectively suppress the elution of organic components even if the material of the second layer 62 contains a large amount of organic components. From this perspective, a suitable example of the amount of eluted organic components is 31,000 μg / m 2 or more, preferably 31,500 μg / m 2 The upper limit of the amount of eluted organic components is not particularly limited, but from the viewpoint of suppressing elution of organic components, it is, for example, 35,000 μg / m 2 or less, preferably 34000 μg / m 2 or less, more preferably 33,000 μg / m 2 or less, more preferably 32000 μg / m 2 The following are included:

[0102] The second layer 62 preferably contains an antioxidant. Examples of antioxidants include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, aromatic amine-based antioxidants, and lactone-based antioxidants. From the viewpoint of suppressing the effects of oxygen and ensuring desirable strength, the content of the antioxidant in the second layer 62 is, for example, 0.01% by weight or more, and preferably 0.1% by weight or more. The upper limit of the content of the antioxidant is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0103] The thickness of the second layer 62 is preferably 1.5 mm or more and 15 mm or less.

[0104] (Adhesive layer 63, gas barrier layer 64) As shown in FIG. 2(b), the adhesive layer 63 is disposed on the outside of the second layer 62. The adhesive layer 63 adheres the gas barrier layer 64 to the outside of the second layer 62. From the viewpoint of achieving a desired strength, the adhesive layer 63 is preferably made of the same type of polyolefin resin. For example, maleic anhydride-modified adhesive polyethylene can be used.

[0105] The provision of the gas barrier layer 64 effectively prevents gas from dissolving in ultrapure water. The gas barrier layer 64 also prevents oxygen from penetrating from the outer surfaces 2c, 3c of the multi-layer pipes 2, 3 (for example, the multi-layer pipe 2) into the first layer 61 or the second layer 62, which are the innermost layers, and therefore improves the long-term strength of the multi-layer pipes 2, 3. The provision of a gas barrier layer is also preferable in that it effectively prevents gas from dissolving in ultrapure water.

[0106] Examples of materials for the gas barrier layer include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride resin (PVDC), and polyacrylonitrile (PAN), and preferably polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH).

[0107] The thickness t3 of the gas barrier layer is not particularly limited as long as it is a thickness that can at least ensure the gas barrier properties of the polyethylene resin, but is, for example, 30 to 300 μm, preferably 50 to 250 μm, and more preferably 70 to 250 μm.

[0108] (Electrical fusion joint 1) 3 is a diagram showing the cross-sectional structure of the electrofusion joint 1. The electrofusion joint 1 contains a thermoplastic resin. As shown in FIG. 3, 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 attachment portion 16.

[0109] (Main body 11) The main body 11 is made of a thermoplastic resin. The main body 11 is cylindrical and has a fitting socket portion 21, a fitting socket portion 22, and a connecting portion 23. There are no particular limitations on the thermoplastic resin that forms the main body 11, and the same thermoplastic resin as that used for the first layer 61 may be used. The thermoplastic resin may also be a polyolefin such as polyethylene having a melting point of less than 230°C, or PE (polyethylene) with a low elution amount. The thermoplastic resin may also be HDPE (high density polyethylene resin) with a melting point of about 130°C with a low elution amount.

[0110] The fitting receptacle 21 is arranged on one end 11b side of the main body 11. The multi-layer pipe 2 is inserted inside the fitting receptacle 21. The fitting receptacle 22 is cylindrical. The fitting receptacle 22 is arranged on the other end 11c side of the main body 11. The fitting receptacle 22 is cylindrical. The multi-layer pipe 3 is inserted inside the fitting receptacle 22.

[0111] 2, the connecting portion 23 is connected to the fitting socket portion 21 and the fitting socket portion 22, and connects the fitting socket portion 21 and the fitting socket portion 22. The connecting portion 23 is a portion that connects the fitting socket portion 21 and the fitting socket portion 22, and the stopper portion 12 is provided on the inside in the radial direction B.

[0112] The fitting socket portion 21 has a protrusion 24 that protrudes inward in the radial direction B from the inner surface 11a. The protrusion 24 is annular. The protrusion 24 is formed around the entire circumference along the circumferential direction C. The protrusion 24 is arranged side by side with the stopper portion 12 in the axial direction A. The protrusion 24 protrudes radially inward less than the stopper portion 12. The protrusion 24 forms a stepped shape on the inner peripheral surface of the fitting socket portion 21. The protrusion 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 toward the inside in the radial direction B. The circumferential surface 24b is a radially inner end of the protrusion 24. The circumferential surface 24b is formed from the radially inner end of the side surface 24a toward the stopper portion 12 (toward the end 11c) and is connected to the stopper portion 12. The peripheral surface 24b is formed parallel to the axial direction A. In this specification, "perpendicular" may include a design tolerance and includes a range that is generally accepted as perpendicular. In this specification, "parallel" may include a design tolerance and includes a range that is generally accepted as parallel.

[0113] The fitting socket portion 22 has a protrusion 25 that protrudes inward in the radial direction B from the inner surface 11a. The protrusion 25 is annular. The protrusion 25 is formed around the entire circumference along the circumferential direction C. The protrusion 25 is arranged side by side with the stopper portion 12 in the axial direction A. The protrusion 25 protrudes radially inward less than the stopper portion 12. The protrusion 25 forms a stepped shape on the inner peripheral surface of the fitting socket portion 21. The protrusion 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 toward the inside in the radial direction B. The circumferential surface 25b is a radially inner end of the protrusion 25. The circumferential surface 25b is formed from the radially inner end of the side surface 25a toward the stopper portion 12 (toward the end 11b) and is connected to the stopper portion 12. The peripheral surface 25b is formed parallel to the axial direction A.

[0114] 4 is a cross-sectional view showing the state in which the multi-layer pipe 2 is inserted into the inside of the joint socket 21 of the electric fusion joint 1, and the multi-layer pipe 3 is inserted into the inside of the joint socket 22. As shown in FIG. 4, the multi-layer pipe 2 is inserted into the inside of the protruding portion 24 of the joint socket 21. The multi-layer pipe 3 is inserted into the inside of the protruding portion 25 of the joint socket 22.

[0115] (Stopper part 12) The stopper portion 12 is formed in an annular shape. The stopper portion 12 is formed as a ridge around the entire periphery on the inner surface 11a of the main body portion 11 along the circumferential direction C. The stopper portion 12 contains a thermoplastic resin. The stopper portion 12 is preferably made of the same thermoplastic resin as that used in the main body portion 11. Therefore, the thermoplastic resin used to form the stopper portion 12 may be the same as that used in the first layer 61, or a polyolefin such as polyethylene having a melting point of less than 230°C. PE (polyethylene), which has a low elution amount, may also be used as the thermoplastic resin. HDPE (high-density polyethylene resin), which has a melting point of about 130°C and has a low elution amount, may also be used as the thermoplastic resin.

[0116] 3, the stopper portion 12 is formed so as to protrude radially inward from the inner surface 11a of the main body portion 11. The stopper portion 12 is disposed on the inner side of the connecting portion 23 of the main body portion 11 in the radial direction B. The stopper portion 12 may be formed as a single member together with the main body portion 11, or may be formed as a separate member from the main body portion 11.

[0117] 3, the stopper portion 12 is disposed between the protrusions 24 and 25. The stopper portion 12 has a first side surface 12a, a second side surface 12b, and a peripheral surface 12c. The peripheral surface 12c is the radially inner end of the stopper portion 12.

[0118] The first side surface 12a is formed from the end of the peripheral surface 24b of the protrusion 24 opposite to the side surface 24a toward the inside in the radial direction B. The first side surface 12a is formed perpendicular to the axial direction A.

[0119] The second side surface 12b is formed from the end of the circumferential surface 25b of the protrusion 25 opposite to the side surface 25a toward the inside in the radial direction B. The second side surface 12b is formed perpendicular to the axial direction A.

[0120] The peripheral surface 12c connects the radially inner end of the first side surface 12a to the radially inner end of the second side surface 12b. The peripheral surface 12c is formed parallel to the inner surface 11a of the main body portion 11.

[0121] When the multi-layer pipe 2 is inserted into the fitting socket 21, the end 2a of the multi-layer pipe 2 comes into contact with the first side surface 12a of the stopper 12, restricting the insertion position of the end 2a, as shown in Fig. 4. The end 2a of the multi-layer pipe 2 coming into contact with the first side surface 12a includes cases where the end 2a comes into direct contact with the first side surface 12a and cases where the end 2a comes into indirect contact with the first side surface 12a via a heating wire 33 (described later) of the stopper heating part 15.

[0122] When the multi-layer pipe 3 is inserted into the fitting receptacle 22, the end 3a of the multi-layer pipe 3 comes into contact with the second side surface 12b of the stopper portion 12, restricting the insertion position of the end 3a, as shown in Fig. 4. The end 3a coming into contact with the second side surface 12b includes cases where the end 3a comes into direct contact with the second side surface 12b, and cases where the end 3a comes into indirect contact with the second side surface 12b via a heating wire 33 (described later) of the stopper heating portion 15. When the multi-layer pipes 2, 3 are inserted into the fitting receptacles 21, 22, the protruding height of the stopper portion 12 is formed to be lower than the inner surfaces 2b, 3b of the multi-layer pipes 2, 3.

[0123] (Heat generating parts 13 and 14) As shown in Figure 3, the socket heating parts 13, 14 are provided in the joint socket parts 21, 22. As shown in Figure 3, the socket heating part 13 has a heating wire 31 embedded in the protruding part 24 of the joint socket part 21. The heating wire 31 is arranged so as to be wound around the peripheral surface 24b in two circumferential directions. The heating wire 31 is arranged near the peripheral surface 24b. The heating wire 31 may be embedded in the protruding part 24 so that a portion of it is exposed from the peripheral surface 24b or the side surface 24a to the flow path 1f side, or it may be completely embedded. The protruding part 24 is formed to a length that allows the heating wire 31 to be wound around it two times in the axial direction A.

[0124] As shown in Figure 3, the socket heating portion 14 has a heating wire 32 embedded in the protruding portion 25 of the fitting socket portion 22. The heating wire 32 is arranged so as to be wound around the peripheral surface 25b in two circumferential directions. The heating wire 32 is arranged near the peripheral surface 25b. The heating wire 32 may be embedded in the protruding portion 25 so that a portion of the heating wire 32 is exposed from the peripheral surface 25b or the side surface 25a to the flow path 1f side, or may be completely embedded. The protruding portion 25 is formed to a length that allows the heating wire 32 to be wound around it two times in the axial direction A.

[0125] The heating wire 31 has, for example, a conductor 31a, an insulating coating 31b, and a resin coating 31c. The heating wire 32 has, for example, a conductor 32a, an insulating coating 31b, and a resin coating 32c. The conductor wires 31a and 32a can be made of, for example, nichrome wire, iron-chrome type 2 wire, iron-chrome type 1 wire, or nickel-chrome wire.

[0126] The insulating coatings 31b and 32b are provided to cover the periphery of the conductive wires 31a and 32a. The melting point of the insulating coatings 31b and 32b is 230°C or higher. In this embodiment, it is preferable that the insulating coatings 31b and 32b are set to a temperature that 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°C). The insulating coatings 31b and 32b can be formed, for example, from a fluorine-based resin or an imide-based resin, but are more preferably formed from a polyimide-based resin. Note that the heating wires 31 and 32 do not necessarily have the insulating coatings 31b and 32b. The coating resins 31c and 32c are provided to cover the periphery of the insulating coatings 31b and 32b. The coating resins 31c and 32c are formed from a thermoplastic resin. The coating resins 31c and 32c may be the same resin as the thermoplastic resin used in the main body 11. Examples of the thermoplastic resin include polyolefins such as polyethylene having a melting point of less than 230°C. As the thermoplastic resin, PE (polyethylene) which has a low elution amount may be used. As the thermoplastic resin, HDPE (high density polyethylene resin) which has a melting point of about 130°C and has a low elution amount may be used.

[0127] The receiving port heating portion 13 is provided symmetrically with respect to the receiving port heating portion 14 and the stopper portion 12. In this embodiment, the heating wires 31 and 32 are wound so as to be in contact with each other in the axial direction A, but they may also be wound so as not to be in contact with each other and a gap may be provided.

[0128] As shown in Fig. 3, socket heating portion 13 is disposed adjacent to stopper portion 12 in the axial direction A. Also, socket heating portion 14 is disposed adjacent to stopper portion 12 in the axial direction A. For example, as shown in Fig. 3, heating wire 31 is disposed so as to be in contact with imaginary surface M1 formed by extending first side surface 12a outward in the radial direction B. Also, as shown in Fig. 3, heating wire 32 is disposed so as to be in contact with imaginary surface M2 formed by extending second side surface 12b outward in the radial direction B.

[0129] In this way, the receiving port heating portions 13, 14 are arranged next to the stopper portion 12 in the axial direction A so as to be in contact with the imaginary surfaces M1, M2, but a predetermined gap may be provided between the receiving port heating portions 13, 14 and the stopper portion 12.

[0130] Furthermore, in each of the receiving port heating parts 13, 14, the heating wires 31, 32 are wound in contact with each other for two turns along the axial direction A, but this is not limited to two turns, and they may be wound multiple times along the axial direction A. Furthermore, they may not be in contact with each other in whole or in part. Furthermore, there may be multiple portions where a predetermined number of adjacent portions are provided.

[0131] Furthermore, although the socket heating portion 13 and the socket heating portion 14 are provided symmetrically on either side of the stopper portion 12, this is not the only possible configuration. For example, the heating wire 31 may be wound two times around the joint socket portion 21 on one side of the stopper portion 12, and the heating wire 32 may be wound three times around the joint socket portion 22 on the other side.

[0132] (Stopper heating part 15) The stopper heating portion 15 is provided in the stopper portion 12. The stopper heating portion 15 has a heating wire 33. The heating wire 33 is provided in the stopper portion 12 so as to be wound in the circumferential direction C along the axial direction A. In this embodiment, the heating wire 33 is wound around the stopper portion 12, for example, four times along the axial direction A, but this is not limited to four times, as long as it is wound multiple times along the axial direction A. In the stopper heating portion 15 of this embodiment, adjacent heating wires 33 are all in contact with each other, but gaps may be provided.

[0133] The heating wire 33 is embedded in the stopper portion 12 so as to be in contact with the peripheral surface 12c of the stopper portion 12, but may also be embedded in the stopper portion 12 so that a portion of the heating wire 33 is exposed on the flow path 1f side from the first side surface 12a, the second side surface 12b, or the peripheral surface 12c, or may be embedded at a predetermined distance from the peripheral surface 12c of the stopper portion 12. The stopper portion 12 is formed to a length that allows the heating wire 33 to be wound four times in the axial direction A.

[0134] 3, the heating wire 33 includes a conductor 33a, an insulating coating 33b, and a coating resin 33c. The conductor 33a may be made of, for example, a nichrome wire, an iron-chrome type 2 wire, an iron-chrome type 1 wire, or a nickel-chrome wire.

[0135] The insulating coating 33b is provided to cover the periphery of the conductive wire 33a. The melting point of the insulating coating 33b is 230°C or higher. In this embodiment, it is preferable that the insulating coating 33b is set to a temperature that 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°C). The insulating coating 33b can be formed of, for example, a fluorine-based resin or an imide-based resin, but is more preferably formed of a polyimide-based resin. Note that the heating wire 33 does not necessarily have the insulating coating 33b. The coating resin 33c is provided to cover the periphery of the insulating coating 33b. The coating resin 33c is formed of a thermoplastic resin. The coating resin 33c may be the same resin as the thermoplastic resin used in the main body 11. Examples of the thermoplastic resin include polyolefins such as polyethylene having a melting point of less than 230°C. PE (polyethylene), which has a low elution amount, may also be used as the thermoplastic resin. As the thermoplastic resin, HDPE (high density polyethylene resin) having a melting point of about 130° C. and a small amount of elution may be used.

[0136] In this embodiment, in the stopper heating portion 15, one heating wire 33 is wound four times so as to contact the adjacent wires, but this is not limited to this and may be three or fewer turns or five or more turns. Furthermore, the stopper heating portion 15 may be formed by winding two or more heating wires 33 instead of one. The heating wires 33 may be wound so that all or part of them do not contact the adjacent wires.

[0137] (Connector mounting part 16) As shown in FIG. 3, the connector mounting portion 16 has two pins 41b and 41c. The two pins 41b and 41c are provided to protrude radially outward from the outer surface 11d of the main body 11. As shown in FIG. 3, one of the two pins 41b and 41c, pin 41b, is located near end 11b of the main body 11, and the other pin 41c is located near end 11c. Although not shown, the two pins 41b and 41c are connected to the heating wires 31 and 32 of the socket heating portions 13 and 14 and the heating wire 33 of the stopper heating portion 15. The pin 41b, heating wire 31, heating wire 32, heating wire 33, and pin 41c are connected in this order. In this embodiment, the heating wires 31, 32, and 33 are a single heating wire. This single heating wire extends from pin 41b to receptacle heating portion 13, forms receptacle heating portion 13, stopper heating portion 15, and receptacle heating portion 14 in that order, and extends to pin 41c. When connectors of fusion device 4 are attached to pins 41b and 41c and electricity is applied, heating wires 31, 32, and 33 generate heat.

[0138] (fusion method) A fusion method according to an embodiment of the present disclosure will be described.

[0139] First, the multi-layer pipe 2 is inserted into the fitting socket 21 of the electrofusion joint 1 until the relative movement of the end 2a of the multi-layer pipe 2 is restricted by the stopper 12. Then, the multi-layer pipe 3 is inserted into the fitting socket 22 of the electrofusion joint 1 until the relative movement of the end 3a of the multi-layer pipe 3 is restricted by the stopper 12. Figure 4 shows the state in which the multi-layer pipe 2 and the multi-layer pipe 3 are inserted into the electrofusion joint 1. When inserting the multi-layer pipes into the electrofusion joint 1, the outer surface of the end 2a and the vicinity of the end 2a of the multi-layer pipe 2 and the outer surface of the end 3a and the vicinity of the end 3a of the multi-layer pipe 3 may be scraped.

[0140] Next, a connector of a fusion device (not shown) is attached to the two pins 41b, 41c of the connector attachment portion 16. Then, electricity is passed through the heating wires 31 to 33 while the multi-layer pipes 2, 3 are pressed against the stopper portion 12 of the electric fusion joint 1.

[0141] Next, the molten multi-layer pipe 2, the electric fusion joint 1, and the multi-layer pipe 3 are cooled for a predetermined time. The multi-layer pipes 2 and 3 may be pressed against the stopper portion 12 until the cooling is completed, or may be stopped when the heating is stopped.

[0142] 5 is a cross-sectional view showing the state in which the multi-layer pipe 2, the electric fusion joint 1, and the multi-layer pipe 3 are fused. The stopper portion 12, the end portion 2a of the multi-layer pipe 2, and the end portion 3a of the multi-layer pipe 3 melt, and the molten portions are pressed and narrowed by the multi-layer pipes 2 and 3, filling the gap between the multi-layer pipes 2 and 3 to form a bead R. The bead R is formed by melting the coating resin 33c of the heating wire 33, the stopper portion 12, the end portion 2a of the multi-layer pipe 2, and the thermoplastic resin in the end portion 3a of the multi-layer pipe 3. When the multi-layer pipes 2 and 3 are pressed against the stopper portion 12 in a molten resin state, the multi-layer pipes 2 and 3 move toward the inside of the electric fusion joint 1 while crushing the stopper portion 12, and a bead R is formed according to the amount of movement. In addition, the outer surface 2c of the multi-layer pipe 2 and the resin around the heating wire 31 of the inlet heating part 13 are fused together, and the outer surface 3c of the multi-layer pipe 3 and the resin around the heating wire 32 of the inlet heating part 14 are fused together.

[0143] When fusion is good, as shown in FIG. 5, in the bead R, the second layer 62 is covered by the first layer 61, and the material forming the second 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 by the material forming the first layer 61. FIG. 6 is a diagram showing a case where fusion is not good and the material forming the second layer 62 is exposed on the flow path side surface Rs of the bead R. In the bead R, the portion of the material forming the second layer 62 exposed on the flow path side surface Rs is shown as exposed portion 62P. In this case, there is a risk that impurities (such as calcium in an amount greater than a specified amount) will elute into the liquid from exposed portion 62P exposed on the flow path side.

[0144] In this embodiment, a color difference is provided between the second layer 62 and the first layer 61, so that the worker can easily determine the exposure of the material forming the second layer 62, as shown in Figures 7(a) and 7(b).

[0145] 7(a) is a view of the piping structure 100 shown in FIG. 5 viewed from the multi-layer pipe 2 side, and FIG. 7(b) is a view of the piping structure 100 shown in FIG. 6 viewed from the multi-layer pipe 2 side.

[0146] In Figure 7(a), the fusion is performed well, so the surface RS of the bead R is formed by the material that forms the first layer 61, and the material that forms the second layer 62 is not visible, but in Figure 7(b), the fusion is not performed well, so an exposed portion 62P where the material that forms the second layer 62 is exposed on the flow path side surface RS of the bead R can be seen.

[0147] Therefore, by recognizing the exposed portion 62P where the material forming the second layer 62 is exposed, it is possible to easily determine whether the construction is defective.

[0148] (Embodiment 2) In the piping structure 100 of embodiment 1, the multi-layer pipe 2 and the multi-layer pipe 3 are connected using an electric fusion joint 1, while in the piping structure 200 of embodiment 2, the multi-layer pipe 2 and the multi-layer pipe 3 are connected by butt welding.

[0149] In butt welding, the end 2a of the multi-layer pipe 2 and the end 3a of the multi-layer pipe 3 are each heated, causing the end 2a and the end 3a to melt. After heating, the end 2a of the multi-layer pipe 2 and the end 3a of the multi-layer pipe 3 are pressed against each other, as shown in Figure 8. The molten end 2a and the end 3a are pressed against each other, forming a bead R, as shown in Figure 9. The bead R is a portion that protrudes inward from the inner surfaces 2b and 3b.

[0150] In the piping structure 200 of this embodiment 2, when the fusion is good, as shown in Figure 9, the flow path side surface Rs of the bead R is formed only by the material forming the first layer 61, and the second layer 62 in the bead R is covered by the first layer 61, and the material forming the second layer 62 is not exposed on the flow path side surface RS.

[0151] 10, if the fusion is not performed satisfactorily, the material forming the second layer 62 is exposed on the flow path side surface Rs of the bead R, as in the first embodiment, and the exposed portion 62P can be seen when viewed along the axial direction A. This allows the worker to easily determine whether the fusion is not performed satisfactorily.

[0152] (Ultrapure water piping applications) The multi-layer pipe of the embodiment of the present invention can be used for transporting ultrapure water. Specifically, the multi-layer pipe of the embodiment of the present invention can be used as piping within an ultrapure water production system, piping for transporting ultrapure water from an ultrapure water production system to a use point, piping for returning ultrapure water from a use point, etc. Note that ultrapure water in this invention is defined as water having a resistivity of 10 MΩ·cm or more at 25°C, more strictly, a resistivity of 15 MΩ·cm or more at 25°C, and even more strictly, a resistivity of 18 MΩ·cm or more at 25°C.

[0153] The multi-layer pipe according to an embodiment of the present invention is preferably used as water piping for nuclear power generation, which requires particularly strict water quality for ultrapure water, or as ultrapure water transport piping used in wet processing steps such as cleaning in the manufacturing process of pharmaceuticals, semiconductor devices, or liquid crystals, more preferably semiconductor devices. The semiconductor devices in question are preferably those with a higher integration density, and more specifically, are more preferably used in manufacturing processes for semiconductor devices with a minimum line width of 65 nm or less. Standards for the quality of ultrapure water used in semiconductor manufacturing include, for example, SEMI F75.

[0154] Furthermore, the multi-layer pipe according to the embodiment of the present invention has a polyolefin resin layer, which makes it easy to work with, for example, butt fusion welding or electrofusion welding (EF) welding at a relatively low temperature.

[0155] (Manufacturing of multi-layer pipes) The multi-layer pipe of the embodiment according to the present invention can be manufactured by preparing a polyethylene-based resin that is the main component of the first layer 61 that forms the inner surface 2b of the piping material, a polyethylene-based resin that is the main component of the second layer 62, and optionally preparing a coating resin that forms the outer gas barrier layer 64, and co-extrusion molding the layers so that each layer has a predetermined thickness. Because the multi-layer pipe of the embodiment according to the present invention is made of a polyolefin-based resin, it can be manufactured inexpensively.

[0156] (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.

[0157] (A) In the above embodiment, the first layer 61 contains a polyolefin resin as a main component, but it is not limited to polyolefin resin, and the first layer 61 may contain a vinyl chloride resin as a main component. Furthermore, the second layer 62 contains a polyolefin resin as a main component, but it is not limited to polyolefin resin, and the second layer 62 may contain a vinyl chloride resin as a main component.

[0158] (B) In the above embodiment, the second layer 62 contains a pigment. In the above embodiment, the second layer 62 is colored with a pigment to provide a color difference between the first layer 61, but the second layer 62 is not limited to a pigment and may be colored with any material that can provide a color difference between the first layer 61 and the second layer 62. For example, the second layer 62 may contain a dye or a colorant and be colored with the dye or colorant. Furthermore, in the above embodiment, the second layer 62 is colored, but the first layer 61 may be colored with a pigment, dye, colorant, or the like. (C) The materials forming the multi-layer pipe 2 and the multi-layer pipe 3 in the above embodiment may be the same or different. Also, the multi-layer pipe 2 as shown in Fig. 2(a) may be connected to a four-layer multi-layer pipe as shown in Fig. 2(b).

[0159] (D) 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.

[0160] (E) In the above embodiment, the socket heat generating portion 13 and the socket heat generating portion 14 are provided symmetrically on both sides of the stopper portion 12, but this is not limiting.

[0161] (F) In the above embodiment, the flow paths of the electrofusion joint 1 are all formed straight, but they may also be elbow joints in which the flow paths are curved.

[0162] (G) In the first embodiment, the same heating wires 31, 32, and 33 are used for the inlet heating parts 13 and 14 and the stopper heating part 15, and therefore all of the heating wires 31, 32, and 33 are provided with an insulating coating, but this is not limited to this. However, it is preferable that at least the heating wire 33 is provided with an insulating coating. This is because the heating wires 33 are pressurized by the multi-layer pipes 2 and 3, and are likely to come into contact with each other.

[0163] (H) 2(b), the multi-layer pipe 2' is a four-layer pipe including a first layer 61, a second layer 62, an adhesive layer 63, and a gas barrier layer 64, but it is not limited to four layers and may have five or more layers. In short, it is sufficient that the multi-layer pipe 2' includes at least the first layer 61 and the second layer 62.

[0164] (Example) Next, the multi-layer pipe of this embodiment will be described in detail using examples.

[0165] In this example, it was confirmed whether or not poor construction could be determined visually, and the results are shown in Table 1 below.

[0166] Example 1 In Example 1, the pair of multi-layer pipes to be connected were the same. As the multi-layer pipe, the two-layer multi-layer pipe 2 shown in Fig. 2(a) of the embodiment was used. The nominal diameter of the multi-layer pipe in Example 1 was 25A.

[0167] HDPE1 was used for the first layer 61 of the multi-layer pipe. Novatec HB534N (manufactured by Japan Polyethylene Co., Ltd.) was used as HDPE1. Novatec HB534N is a completely additive-free high-density polyethylene that does not contain any antioxidants. The thickness t1 of the first layer 61 was set to 0.5 mm. HDPE2 was used for the second layer 62 of the multi-layer pipe. Novatec HE222W (manufactured by Japan Polyethylene Co., Ltd.) was used as HDPE2. Novatec HE222W is a PE100-grade high-density polyethylene that contains antioxidants. The thickness t2 of the second layer 62 was set to 2.7 mm. The second layer 62 contains 0.30 wt% pigment. A light blue pigment, which is a cyan pigment, was used as the pigment.

[0168] The color difference between the pressed plate of material forming the first layer 61 and the pressed plate of material forming the second layer 62 was measured, and the color difference ΔE between the first layer 61 and the second layer 62 was measured. A colorimetric color difference meter (ZE-2000, Nippon Denshoku Co., Ltd.) was used to measure ΔE. As shown in Table 1, ΔE was 1.6.

[0169] The pair of multi-layer pipes was connected by fusion splicing using an electric fusion joint 1 (denoted as EF in the table) according to the embodiment to create a piping structure.

[0170] In this Example 1, as shown in the "Presence or Absence of Installation Defects" row in Table 1, a piping structure with "no" installation defects and a piping structure with "present" installation defects were created. The piping structure with "no" installation defects was created as described in the above embodiment, with the axes of the pipes aligned to prevent installation defects from occurring during installation. The piping structure with "present" installation defects was created by connecting the pipes at an angle of 5° to each other, causing installation defects to occur during installation.

[0171] The workers visually inspected the constructed piping structures for defects. When the exposed material of the second layer 62 could not be visually confirmed by the visual inspection and the calcium elution amount and TOC elution amount, which will be described later, were within the specified range, a "-" was entered in Table 1.

[0172] On the other hand, when viewed along the multi-layer pipe, the exposed material forming the second layer 62 can be seen and the construction can be judged to be poor, which is marked as "Good." When this cannot be judged visually and the amount of calcium leaching and TOC leaching is greater than the specified range, which indicates poor construction, the mark is marked as "Poor."

[0173] The amount of calcium elution and TOC elution were measured for the created piping structure. The amount of calcium elution was 30 μg / m 2 Less than 30,000 μg / m 2 If the amount of calcium elution is less than 30 μg / m, the elution performance is judged as "Good" (Good). 2 or more, or TOC elution amount is 30,000 μg / m 2 In the above cases, the dissolution performance was judged as poor "X".

[0174] As a result of visually inspecting the piping structure of Example 1 with "no" construction defects by an operator, there was no exposed material forming the second layer 62 on the bead R.

[0175] In Example 1, the calcium elution amount was 7 μg / m 2 The TOC elution amount was 5000 μg / m 2 And it was good.

[0176] On the other hand, visual inspection of the piping structure with poor construction revealed that the material forming the second layer 62 was exposed to the bead R, making the construction poorly visible. Measurements of the amounts of calcium elution and TOC elution for this piping structure revealed that the amounts of elution were high and poor. Thus, in Example 1, poor construction could be determined by visual inspection.

[0177] Example 2 In Example 2, a pair of multi-layer pipes was used in which the mass % of the pigment contained in the second layer 62 was changed to 0.05% compared to Example 1. Except for this, the same experiment as in Example 1 was conducted, piping structures were created, and evaluations were performed in the same manner as in Example 1. In Example 2, only piping structures with "no" construction defects were created.

[0178] In Example 2, no exposure of the material forming the second layer 62 was visually confirmed. The piping structure of Example 2 was subjected to measurements of the amount of calcium elution and the amount of TOC elution, and both were found to be good.

[0179] Example 3 In Example 3, a pair of multi-layer pipes was used in which the mass % of the pigment contained in the second layer 62 was changed to 0.50% compared to Example 1. Except for this, the same experiment as in Example 1 was conducted, piping structures were created, and evaluations were performed in the same manner as in Example 1. In Example 3, as in Example 1, piping structures with and without construction defects were created.

[0180] In the piping structure with "no" construction defects, no exposed material of the second layer 62 could be visually confirmed. Measurements of the amounts of calcium elution and TOC elution were carried out on this piping structure, and both were found to be good.

[0181] In the piping structure with "Poor Construction", the poor construction was visible. Furthermore, when the amount of calcium elution and TOC elution were measured for this piping structure, the amount of elution was high and both were poor.

[0182] As described above, in Example 3, poor construction could be determined by visual inspection.

[0183] Example 4 In Example 4, a pair of multi-layer pipes was used in which the mass % of the pigment contained in the second layer 62 was changed to 0.03% compared to Example 1. Except for this, the same experiment as in Example 1 was conducted, piping structures were created, and evaluations were performed in the same manner as in Example 1. In Example 4, as in Example 1, piping structures with and without construction defects were created.

[0184] In the piping structure with "no" construction defects, no exposed material of the second layer 62 could be visually confirmed. Measurements of the amounts of calcium elution and TOC elution were carried out on this piping structure, and both were found to be good.

[0185] In the piping structure with "Poor Construction", the poor construction was visible. Furthermore, when the amount of calcium elution and TOC elution were measured for this piping structure, the amount of elution was high and both were poor.

[0186] As described above, in Example 4, poor construction could be determined by visual inspection.

[0187] Example 5 In Example 5, a pair of multi-layer pipes similar to those in Example 1 were connected by butt welding, and the same evaluation was carried out as in Example 1. In Example 5, similar to Example 1, piping structures with and without construction defects were created.

[0188] In the piping structure with "no" construction defects, no exposed material of the second layer 62 could be visually confirmed. Measurements of the amounts of calcium elution and TOC elution were carried out on this piping structure, and both were found to be good.

[0189] On the other hand, visual inspection of the piping structure with poor construction revealed that the material forming the second layer 62 was exposed to the bead R, making the construction poorly visible. Furthermore, measurements of the amounts of calcium elution and TOC elution for this piping structure revealed that the amounts of elution were high and poor.

[0190] In this way, in this Example 5, it was possible to determine poor construction by visual inspection.

[0191] Example 6 In Example 6, a multi-layer pipe and an electric fusion joint with a different nominal diameter than those in Example 1 were used. In Example 6, a multi-layer pipe with a nominal diameter of 75A was used. An electric fusion joint corresponding to the nominal diameter of the multi-layer pipe was used. In Example 6, a piping structure with "no" construction defects and a piping structure with "present" construction defects were created.

[0192] In the multi-layer pipe of Example 6, the thickness t1 of the first layer 61 was set to 0.5 mm, and the thickness t2 of the second layer 62 was set to 5.2 mm.

[0193] In the piping structure with "no" construction defects, no exposed material of the second layer 62 could be visually confirmed. Measurements of the amounts of calcium elution and TOC elution were carried out on this piping structure, and both were found to be good.

[0194] On the other hand, in the piping structure with "defective construction", the material forming the second layer 62 was visible and it was determined to be defective construction. When the amount of calcium elution and the amount of TOC elution were measured for this piping structure, both amounts were found to be large and defective.

[0195] From the above, in this Example 6, poor construction could be determined by visual inspection.

[0196] Example 7 In Example 7, a multi-layer pipe and an electric fusion joint with a different nominal diameter than those in Example 1 were used. In Example 6, a multi-layer pipe with a nominal diameter of 200A was used. An electric fusion joint corresponding to the nominal diameter of the multi-layer pipe was used. In Example 6, a piping structure with "no" construction defects and a piping structure with "present" construction defects were created.

[0197] In the multi-layer pipe of Example 7, the thickness t1 of the first layer 61 was set to 3.0 mm, and the thickness t2 of the second layer 62 was set to 10.5 mm.

[0198] In the piping structure with "no" construction defects, no exposed material of the second layer 62 could be visually confirmed. Measurements of the amounts of calcium elution and TOC elution were carried out on this piping structure, and both were found to be good.

[0199] On the other hand, in the piping structure with "defective construction", the material forming the second layer 62 was visible and it was determined to be defective construction. When the amount of calcium elution and the amount of TOC elution were measured for this piping structure, both amounts were found to be large and defective.

[0200] From the above, in this Example 7, it was possible to determine poor construction by visual inspection.

[0201] Example 8 In Example 8, unlike Example 1, polypropylene (PP) was used as the main component of the first layer 61 of the multi-layer pipe, and polypropylene was used as the main component of the second layer 62. In Example 8, piping structures with and without construction defects were created.

[0202] In the piping structures with "no" construction defects, no exposed material forming the second layer 62 was visible in the visual inspection.

[0203] Measurements of calcium elution and TOC elution were carried out for this piping structure, and the results were good.

[0204] On the other hand, in the piping structure with "defective construction", the material forming the second layer 62 was visible and it was determined to be defective construction. When the amount of calcium elution and the amount of TOC elution were measured for this piping structure, both amounts were found to be large and defective.

[0205] From the above, in this Example 8, it was possible to determine poor construction by visual inspection.

[0206] (Examples 9 and 10) In Examples 9 and 10, a pair of multi-layer pipes was used in which the amount of pigment contained in the second layer 62 was changed compared to Example 1. Except for this, the same experiment as in Example 1 was conducted to create piping structures. In Examples 9 and 10, only piping structures with construction defects were created.

[0207] In the piping structures of Examples 9 and 10, poor construction was visible.

[0208] Furthermore, the amounts of calcium elution and TOC elution were measured for the piping structures of Examples 9 and 10, and the amounts of elution were both large and poor.

[0209] In Examples 9 and 10, poor construction could be determined by visual inspection.

[0210] Example 11 In Example 11, unlike Example 2, a four-layer multi-layer pipe as shown in Figure 2(b) was used. The thickness t3 of the gas barrier layer was set to 0.1 mm. In Example 11, piping structures with and without construction defects were created.

[0211] In the piping structures with "no" construction defects, no exposed material forming the second layer 62 was visible in the visual inspection.

[0212] Measurements of calcium elution and TOC elution were carried out for this piping structure, and the results were good.

[0213] When the piping structure with a construction defect was visually inspected for construction defects, the material forming the second layer 62 in the bead was visible, and it was determined to be construction defects. When the amount of calcium elution and the amount of TOC elution were measured for this piping structure, the amount of elution was high and both were defective.

[0214] In this Example 11, poor construction could be determined by visual inspection.

[0215] (Comparative Example 1) In Comparative Example 1, a pair of multi-layer pipes was used in which the amount of pigment contained in the second layer 62 was changed compared to Example 1. Except for this, the same experiment as in Example 1 was conducted to create a piping structure. In Comparative Example 1, ΔE was 0.4. Furthermore, in Comparative Example 1, piping structures with and without poor construction were created.

[0216] In the piping structure with "no" construction defects, no exposed material of the second layer 62 could be visually confirmed. Measurements of the amounts of calcium elution and TOC elution were carried out on this piping structure, and both were found to be good.

[0217] When the piping structure with a "presence" of construction defects was visually inspected, it was found that the material forming the second layer 62 in the bead was not visible, and it could not be determined that the construction was defective. When the amounts of calcium elution and TOC elution were measured for this piping structure, the amounts of elution were both high and poor.

[0218] As described above, when the color difference ΔE between the first layer 61 and the second layer 62 is 0.4, it is understood that even if the second layer 62 is exposed to the bead, the color difference is too small to be discernible.

[0219] (Table 1) TIFF2025132576000002.tif230125

[0220] As described above, exposure of the material of the second layer 62 at the bead R due to poor construction results in poor calcium and TOC elution amounts. However, by setting the color difference ΔE between the first layer 61 and the second layer 62 to 0.5 or more, the exposed material of the second layer 62 can be visually confirmed, and poor construction can be recognized. [Explanation of symbols]

[0221] 2: Multi-layer pipe 3: Multi-layer pipe 61: 1st layer 62: 2nd layer

Claims

1. a first layer constituting the innermost layer and containing a polyolefin resin or a vinyl chloride resin as a main component; a second layer disposed outside the first layer and containing a polyolefin resin or a vinyl chloride resin as a main component; The amount of calcium elution from the first layer measured in accordance with SEMI F-57 is 30 μg / m ２ is less than a color difference ΔE between the first layer and the second layer being 0.5 or more; Multi-layer pipe.

2. a ratio of the thickness of the first layer to the total thickness of the first layer and the second layer is 0.011 or more and 0.500 or less; The multi-layer pipe according to claim 1.

3. The thickness of the first layer is 0.06 mm or more and 5.0 mm or less. The multi-layer pipe according to claim 1.

4. The amount of calcium elution from the second layer measured in accordance with SEMI F-57 is 30 μg / m ２ That's all. The multi-layer pipe according to claim 1.

5. a color difference ΔE between the first layer and the second layer being 1.0 or more; The multi-layer pipe according to claim 1.

6. Further comprising a gas barrier layer disposed on the outside of the second layer. The multi-layer pipe according to claim 1.

7. Used for transporting semiconductor cleaning fluids, The multi-layer pipe according to claim 1.

8. a first layer constituting the innermost layer and containing a polyolefin resin or a vinyl chloride resin as a main component; a second layer disposed outside the first layer, containing a polyolefin resin or a vinyl chloride resin as a main component, and containing a pigment; Multi-layer pipe.

9. A pair of multi-layer pipes according to any one of claims 1 to 8; a cylindrical main body portion having joint socket portions at both ends into which each of the multi-layer pipes is inserted; A stopper portion protruding inward from the main body portion, which restricts the end of one of the multi-layer pipes to be inserted and restricts the end of the other multi-layer pipe to be inserted; a heating portion including a heating wire disposed in the stopper portion, A piping structure in which an electric fusion joint is fused, a bead formed by an end of the one multi-layer pipe and an end of the other multi-layer pipe and protruding inward; an inner surface of the bead is formed by the first layer, and the second layer is covered by the first layer; Piping structure.

10. A piping structure in which the ends of a pair of multi-layer pipes according to any one of claims 1 to 8 are fused together, a bead formed by an end of the one multi-layer pipe and an end of the other multi-layer pipe and protruding inward; an inner surface of the bead is formed by the first layer, and the second layer is covered by the first layer; Piping structure.

Images