Multilayer pipe

Abstract

This invention provides a multilayer pipe with a polypropylene resin innermost layer, which can be used as piping for transporting ultrapure water. The multilayer pipe system of this invention is used for transporting ultrapure water and includes a first layer and a gas barrier layer. The first layer constitutes the innermost layer and is mainly composed of polypropylene resin. The gas barrier layer is disposed at least further outward than the first layer and has gas barrier properties.

Description

[Technical Field]

[0001] This invention relates to a multilayer tube. [Previous Technology]

[0002] In the manufacture of precision devices such as semiconductor devices or liquid crystal display devices, ultrapure water purified to extremely high purity is used in wet processes such as cleaning. If metal ions or the like are present in the water at concentrations above a specified level, they may adsorb onto the wafer surface and adversely affect the quality of the precision device. Therefore, it is essential to thoroughly limit the impurities in the ultrapure water.

[0003] Impurities can also be introduced into ultrapure water in the piping of the ultrapure water transport pipeline. As for the piping material, metals such as stainless steel with excellent gas barrier properties are sometimes used, but considering the effect of metal leaching from the piping, it is considered better to use resin.

[0004] For example, Patent Document 1 discloses a multilayer pipe characterized in that it is used for piping ultrapure water and comprises: a first resin layer containing fluororesin and in contact with ultrapure water; and a second resin layer containing a non-permeable resin and disposed on the outer peripheral surface of the first resin layer. Furthermore, it discloses a third resin layer disposed on the outer peripheral surface of the second resin layer to protect the second resin layer, and polyethylene is used as the third resin layer.

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

[0006] Pipes made of fluoropolymers such as PVDF have disadvantages in terms of workability and cost compared to other ordinary pipes. Furthermore, since ultra-high purity cleaning solutions mostly contain dialumina hydrocarbons such as 3-dialuminapropane and are used at 60°C, they also have the problem of faster degradation.

[0007] Therefore, for example, a pipe is proposed that uses an HDPE layer comprising high-density polyethylene and a fluorinated lubricant in the innermost layer, as shown in Patent Document 2. [Prior Art Documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2010-234576 [Patent Document 2] Japanese Patent Application Publication No. 2022-159129 [Summary of the Invention]

[0009] [Problem to be solved by the invention] As described in the above-mentioned Patent Document 2, research has been conducted on the use of polyethylene resin in the innermost layer of the piping for ultrapure water, but sufficient research has not been conducted on the use of polypropylene resin in the innermost layer.

[0010] The object of this invention is to provide a multilayer pipe that uses polypropylene resin in the innermost layer and can be used as piping for transporting ultrapure water. [Technical Means for Solving the Problem]

[0011] To achieve the above objective, the multilayer piping system of the first invention is used for transporting ultrapure water and includes a first layer, a second layer, and a third layer. The first layer constitutes the innermost layer and is mainly composed of polypropylene resin. The second layer is disposed outside the first layer and is mainly composed of adhesive polyolefin resin. The third layer has gas barrier properties and is disposed outside the second layer.

[0012] Thus, even when the innermost layer of the multilayer tube of the present invention is made of a polypropylene resin as the main component, the oxygen barrier properties that can be used in the transportation of semiconductor cleaning fluid can be ensured by the outer layer with gas barrier properties, and it can be used as a pipe for ultrapure water.

[0013] The multilayer pipe system of the second invention The multilayer pipe of the first invention, and the amount of calcium leaching measured according to SEMI F-57 does not reach 30 μg / m2.

[0014] This provides a multilayer pipe that can be used as piping for ultrapure water.

[0015] The third invention is a multilayer pipe system. The first invention is a multilayer pipe, and the thickness of the third layer is more than 80 μm and less than 500 μm.

[0016] By setting the thickness of the gas-barrier third layer to 80 μm or more, the oxygen permeability can be reduced so that it can be used for the transportation of ultrapure water. Furthermore, by increasing the thickness of the third layer, the oxygen permeability can be reduced, but as the upper limit for use in actual products, it is set to 500 μm.

[0017] The fourth invention is a multilayer pipe system. The first invention is a multilayer pipe, and further includes a core material layer. The core material layer is disposed between the first layer and the second layer, and is mainly composed of polypropylene resin.

[0018] For example, by using a material with a lower cost than the first layer for the core layer, the strength of the multilayer tube can be ensured and the cost reduced.

[0019] The fifth invention is a multilayer pipe system. The first invention is a multilayer pipe, and the third layer contains an ethylene-vinyl alcohol copolymer as the main component.

[0020] This improves the formability of multilayer tubes. [Effects of the Invention]

[0021] According to the present invention, a multilayer pipe is provided in which polypropylene resin is used in the innermost layer and can be used as piping for transporting ultrapure water.

Implementation Method

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0024] (Multilayer tube 1) Figure 1(a) is a cross-sectional view of multilayer tube 1. Figure 2(b) is a cross-sectional view of multilayer tube 1', which is another example of multilayer tube 1.

[0025] The multilayer tube 1 shown in Figure 1(a) includes a first layer 11, a second layer 12, and a third layer 13. The first layer 11 constitutes the innermost layer of the multilayer tube 1. The first layer 11 constitutes the inner surface 1b of the multilayer tube 1. The first layer 11 contains polypropylene resin as the main component. The second layer 12 is disposed outside the first layer 11. The second layer 12 contains adhesive polyolefin resin as the main component. The third layer 13 is a gas barrier layer with gas barrier properties. The third layer 13 constitutes the outer surface 1c of the multilayer tube 1.

[0026] The multilayer tube 1' shown in Figure 1(b) includes a first layer 11, a core layer 14, a second layer 12, and a third layer 13. In the multilayer tube 1', the core layer 14 is disposed between the first layer 11 and the second layer 12. The first layer 11 constitutes the innermost layer of the multilayer tube 1'. The first layer 11 constitutes the inner surface 1b' of the multilayer tube 1'. The third layer 13 constitutes the outer surface 1c' of the multilayer tube 1'.

[0027] (Layer 11) Layer 11 contains polypropylene resin as the main component. The main component refers to the component with the highest content based on mass. The main component is the component with a content of at least 50%. The lower limit of the content of polypropylene resin in Layer 11 is preferably 50% by mass, more preferably 70% by mass, further preferably 80% by mass, sometimes further preferably 90% by mass, and sometimes further preferably 95% by mass.

[0028] There are no particular limitations on the polypropylene resin included as a main component in the first layer 11. Examples include homopolymer polypropylene, block polypropylene, and atactic polypropylene. Ethylene is commonly used as a copolymer component in block polypropylene and atactic polypropylene.

[0029] The calcium concentration in layer 11 is adjusted so that the calcium dissolution amount measured according to SEMI F-57 does not reach 30 μg / m2. The calcium concentration of layer 11 is 360 ppm or less, preferably 55 ppm or less, and even more preferably 50 ppm or less. If the calcium concentration exceeds 60 ppm, the calcium dissolution in the ultrapure water becomes excessive, which may fail to meet the required quality of ultrapure water.

[0030] From the viewpoint of further suppressing the amount of calcium leaching in ultrapure water, the calcium concentration of the first layer 11 is preferably as small as possible. However, from the viewpoint of obtaining good thermal stability or long-term strength of the polypropylene resin composition, the inclusion of trace amounts of calcium is unavoidable.

[0031] That is, if the amount of neutralizing agent added to the polypropylene resin polymerized using Ziegler catalyst is insufficient, catalyst residue will exist in the resin in an active state, which may reduce the thermal stability or long-term strength of the polypropylene resin composition.

[0032] Therefore, in this embodiment, a minimum amount of neutralizing agent must be added to neutralize the catalyst residue. Taking the above into consideration, the calcium concentration of the first layer 11 is 10 ppm or more, preferably 13 ppm or more, more preferably 15 ppm or more, and even more preferably 20 ppm or more.

[0033] From the viewpoint of ensuring thermal stability, the oxidation induction time (OIT) of the first layer 11 at 210°C is preferably 20 minutes or more. If the oxidation induction time at 210°C is less than 20 minutes, there is a risk of resin deterioration during heat processing of the polypropylene resin, resulting in a decrease in long-term strength or an increase in particles originating from deterioration, which is undesirable in this embodiment.

[0034] From the viewpoint of fully ensuring the long-term strength of the piping material for ultrapure water, as for the thermal internal pressure creep performance when the first layer 11 is formed into piping material, it is preferable that when a circumferential stress of 5.0 MPa is applied to the piping material at 80°C, the piping material will not be damaged for more than 3,000 hours.

[0035] The first layer 11 may or may not contain antioxidants. Furthermore, examples of antioxidants include: phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, aromatic amine antioxidants, and lactone antioxidants.

[0036] Examples of phenolic antioxidants include: pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethyl bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and N,N'-hexane-1,6-diylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. [-tert-butyl-4-hydroxyphenyl)propionamide], phenylpropionic 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"-(1,3,5-trimethylbenzene-2,4,6-triyl)tri-p-cresol, 4,6-bis(dodecylthiomethyl)-o-cresol, 4,6-bis(octylthio) (3,5-di-tert-butyl-4-hydroxy-m-tolyl)propionate, hexamethylene bis[3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-tris(2,4,6(1H,3H,5H)-trione, 1,3,5- Tris[(4-tert-butyl-3-hydroxy-2,6-dimethyl)methyl]-1,3,5-tris(2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-tris(2,4,5)-2-ylamino]phenol, and [{3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl}methyl]diethyl isophosphite, etc.

[0037] When using phenolic antioxidants, only one type may be used, or two or more types may be used in combination. From the point of view of preventing calcium dissolution, it is preferable that they do not have oxygen originating from sources other than phenolic groups. Examples include: 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(trimethylbenzene-2,4,6-triyl)tri-p-cresol, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-tris(2-ylamino)phenol, 4,4',4"-(1-methylpropylene-3-yl)tri(6-tert-butyl-m-cresol), and 6,6'-di-tert-butyl-4,4'-butylidene bis-m-cresol, etc. Furthermore, when using phenolic antioxidants with oxygen derived from sources other than phenolic groups as antioxidants, it is preferable that the calcium concentration in the polyethylene resin is 50 ppm or less. Moreover, examples of functional groups with oxygen derived from sources other than phenolic groups include: ester groups, carbonyl groups, carboxyl groups, ether groups, nitro groups, nitroso groups, amide groups, oxoazo groups, sulfonyl groups, etc.

[0038] 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]dioxaphosphazene-6-yl]oxy]ethyl]amine, pentaerythritol diphosphite (2,4-di-tert-butylphenyl) bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl) ethyl phosphite, and tetra(2,4-di-tert-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphite, etc.

[0039] Examples of sulfur-based antioxidants include: dilauryl thiodipropionate, dimyristyl thiodipropionate, distearate thiodipropionate, pentaerythritol tetra(3-lauryl thiopropionate), etc.

[0040] As aromatic amine antioxidants, examples include monoamine compounds such as diphenylamine compounds, quinoline compounds, and naphthylamine compounds, or diamine compounds such as phenylenediamine compounds and benzimidazole compounds.

[0041] Examples of diphenylamine compounds include: p-(p-toluene-sulfonylamino)-diphenylamine, 4,4'-(α,α-dimethylbenzyl)-diphenylamine, and 4,4'-dioctyl-diphenylamine derivatives. Examples of quinoline compounds include 2,2,4-trimethyl-1,2-dihydroquinoline polymers.

[0042] Examples of naphthylamine compounds include: phenyl-α-naphthylamine, N,N'-di-2-naphthyl-p-phenylenediamine, etc.

[0043] Examples of phenylenediamine compounds include: N-N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-phenyl-N'-(3-methacryloxy-2-hydroxypropyl)-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, mixtures of N-N'-diphenyl-p-phenylenediamine, diaryl-p-phenylenediamine derivatives or mixtures thereof.

[0044] Examples of benzimidazole compounds include: 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, zinc salt of 2-mercaptobenzimidazole, zinc salt of 2-mercaptomethylbenzimidazole, etc.

[0045] Examples of lactone-based antioxidants include the reaction product of 3-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene. Regarding the content of the antioxidant in the first layer 11, from the viewpoint of suppressing the effects of oxygen and ensuring better strength, examples include 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 antioxidant content is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0046] The first layer 11 may contain a light stabilizer or may not contain one; from the viewpoint of preventing the dissolution of total organic carbon (TOC), it is preferable to contain no light stabilizer. Furthermore, hindered amine light stabilizers (HALS) can be cited as examples of light stabilizers. Also, the first layer 11 of this embodiment is preferably substantially free of light stabilizers. Here, "substantially free" means not actively adding light stabilizers, meaning allowing unavoidable contamination as an impurity. The lower the concentration of the light stabilizer that is unavoidably contaminated as an impurity, the better.

[0047] As hindered amine light stabilizers, examples include: NH-type hindered amine compounds, NR-type hindered amine compounds and N-OR-type hindered amine compounds.

[0048] Examples of NH-type hindered amine compounds include: TINUVIN 770DF, CHIMASSORB 2020FDL, CHIMASSORB 944FDL (all trade names, manufactured by BASF), Adekastab LA-68, Adekastab LA-57 (both trade names, manufactured by ADEKA), Cyasorb UV-3346, Cyasorb UV-3853 (both trade names, manufactured by SUN CHEMICAL), etc.

[0049] Examples of hindered amine compounds of the NR type include: TINUVIN 622SF, TINUVIN 765, TINUVIN PA144, CHIMASSORB 119, TINUVIN 111 (all trade names, manufactured by BASF), SABOSTAB UV119 (trade name, manufactured by SABO), Adekastab LA-63P, Adekastab LA-52 (all trade names, manufactured by ADEKA), etc.

[0050] As N-OR type hindered amine compounds, examples include: TINUVIN 123, TINUVIN 5100, TINUVIN NOR371FF, FLAMESTAB NOR116FF (all trade names, manufactured by BASF), etc.

[0051] Layer 11 may or may not contain an ultraviolet absorber (UVA). Furthermore, examples of UV absorbers include: benzophenone-based UV absorbers, salicylate-based UV absorbers, benzoic acid ester-based UV absorbers, benzotriazole-based UV absorbers, cyanoacrylate-based UV absorbers, quenchers, etc. For polyethylene or polypropylene, benzophenone-based UV absorbers and benzotriazole-based UV absorbers are particularly preferred.

[0052] Examples of benzophenone-based ultraviolet absorbers include 2-hydroxy-4-methoxy-benzophenone.

[0053] Examples of benzotriazole-based ultraviolet absorbers include: 2-(2-hydroxy-5-methylphenyl)benzotriazole (Sumisorb 200, manufactured by Sumika Chemtex), 2-(2-hydroxy-5-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole (Tinuvin 326, manufactured by BASF), 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole (Tinuvin 327, manufactured by BASF), and 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole (Tinuvin 328, manufactured by BASF).

[0054] From the viewpoint of obtaining good rigidity of the polypropylene resin composition, the density of the polypropylene resin composition of the first layer 11 is preferably 0.900 g / cm3 or more, more preferably 0.901 g / cm3 or more, and even more preferably 0.902 g / cm3 or more. Furthermore, from the viewpoint of obtaining good long-term durability and flexibility of the polypropylene resin composition, the density is preferably 0.910 g / cm3 or less, more preferably 0.909 g / cm3 or less, and even more preferably 0.908 g / cm3. The density is a value established according to JISK6922-2:1997.

[0055] The smoothness (arithmetic mean roughness Ra) of the inner surface of the first layer 11 is not particularly limited, for example, it can be 0.50 μm or less. From the viewpoint of obtaining low leaching properties of the piping, the smoothness of the inner surface of the first layer 11 can be preferably 0.40 μm or less, and more preferably 0.35 μm or less.

[0056] The thickness t1 of the first layer 11 is preferably 0.5 mm to 16 mm. More specifically, in the case of a multilayer tube 1 with a diameter of 25A, the thickness t1 is preferably 2 mm to 3.5 mm. In the case of a multilayer tube 1' with a diameter of 25A, the thickness t1 is preferably 0.5 mm to 1.5 mm. In the case of a multilayer tube 1 with a diameter of 75A, the thickness t1 is preferably 4 mm to 7 mm. In the case of a multilayer tube 1' with a diameter of 75A, the thickness t1 is preferably 0.5 mm to 3 mm. In the case of a multilayer tube 1 with a diameter of 200A, the thickness t1 is preferably 12 mm to 16 mm. In the case of a multilayer tube 1' with a diameter of 200A, the thickness t1 is preferably 0.5 mm to 3 mm.

[0057] (Core Material Layer 14) As shown in Figure 1(b), the core material layer 14 is disposed outside the first layer 11. The core material layer 14 is mainly composed of polypropylene resin. The main component refers to the component with the highest content based on mass. The main component is the component with a content of at least 50%. The lower limit of the content of polypropylene resin in the core material layer 14 is preferably 50% by mass, more preferably 70% by mass, and even more preferably 80% by mass, sometimes even more preferably 90% by mass, and sometimes even more preferably 95% by mass.

[0058] The polypropylene resin used in the core layer 14 may be the same as or different from the polypropylene resin used in the first layer 11. From the viewpoint of improving the adhesion between the two layers and exhibiting better strength when the two layers are in contact and laminated, it is preferable to use the same polypropylene resin.

[0059] The amount of calcium leaching measured according to EMIF-57 for the material (polypropylene resin composition) of the core layer 14, from the viewpoint of ensuring the strength of the semiconductor cleaning solution piping in an operating environment of 60°C, can be preferably 30 μg / m2 or more, more preferably 50 μg / m2 or more, further preferably 70 μg / m2 or more, even more preferably 80 μg / m2 or more, particularly preferably 90 μg / m2 or more, and even more preferably 95 μg / m2 or more.

[0060] Because the multilayer tube 1' of the present invention has excellent calcium and organic component leaching inhibition effect, even if the core material layer 14 contains a large amount of calcium, calcium leaching can be effectively inhibited. From this perspective, as a preferred example of the above-mentioned calcium leaching amount, the range can be 80 μg / m² or more, 90 μg / m² or more, or 95 μg / m² or more. Furthermore, as an upper limit of the above-mentioned calcium leaching amount, there is no particular limitation; from the perspective of inhibiting calcium leaching, examples can be 120 μg / m² or less, 110 μg / m² or less, or 100 μg / m² or less. Furthermore, the calcium concentration in the material (polyolefin resin composition) of the core layer 14 is not particularly limited as long as the above-mentioned calcium dissolution amount is met. From the viewpoint of ensuring the strength of the semiconductor cleaning solution piping in an operating environment of 60°C, examples include 20 ppm or more, preferably 30 ppm or more, more preferably 40 ppm or more, even more preferably 50 ppm or more, and even more preferably 60 ppm or more. Furthermore, as the upper limit of the above-mentioned calcium concentration range, from the viewpoint of suppressing insufficient strength caused by the calcium itself becoming the starting point of damage, and from the viewpoint of suppressing the dissolution of calcium and organic components, examples include 200 ppm or less, preferably 150 ppm or less, even more preferably 130 ppm or less, and even more preferably 100 ppm or less.

[0061] The amount of organic components (TOC) leached from the material (polyolefin resin composition) of the core layer 14, as measured by EMIF-57, can, for example, exceed 30,000 μg / m². Since the multilayer tube 1' of the present invention has excellent effect in suppressing the leaching of calcium and organic components, even if the material of the core layer 14 contains a large amount of organic components, the leaching of organic components can be effectively suppressed. From this perspective, a preferred example of the above-mentioned amount of organic component leaching is 31,000 μg / m² or more, preferably 31,500 μg / m² or more. Furthermore, there is no particular limitation on the upper limit of the above-mentioned amount of organic component leaching; from the perspective of suppressing the leaching of organic components, examples include 35,000 μg / m² or less, preferably 34,000 μg / m² or less, more preferably 33,000 μg / m² or less, and even more preferably 32,000 μg / m² or less.

[0062] The core material layer 14 may contain pigment. This allows for color changes with the first layer 11, and enables confirmation that the inner side of the core material layer 14 is covered by the first layer 11. Furthermore, when the multilayer tube 1' is welded together, by observing that the colored core material layer 14 does not overflow from the inner surface of the joint, it can be confirmed that the inner surface of the joint is covered by the low-leaching material of the first layer 11, facilitating quality control. As pigment, previously known organic pigments, inorganic pigments, extender pigments, etc., can all be used, without particular limitation. Examples of organic pigments include phthalocyanine, azo, condensed azo, anthraquinone, pyrene-perylene, indigo-thioindigo, isoindolinone, azomethine azo, diazonium, quinacridone, aniline black, and triphenylmethane. Examples of inorganic pigments include carbon black, titanium dioxide, iron oxide, iron hydroxide, chromium oxide, spinel-type calcined pigments, lead chromate, molybdenum chromium red, iron blue, aluminum powder, and bronze powder. Examples of extender pigments include calcium carbonate, barium sulfate, silicon oxide, and aluminum hydroxide. Pigments are used individually or in combination with the specified color in the core layer 14.

[0063] The content of pigment in the core material layer 14 is not particularly limited as long as the above-mentioned color difference can be set, but it is preferably 0.05 wt% or more and 1.00 wt% or less.

[0064] The core layer 14 preferably contains an antioxidant. Examples of antioxidants, similar to those in the first layer 11, include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, aromatic amine antioxidants, and lactone antioxidants. Regarding the content of the antioxidant in the core layer 14, from the viewpoint of suppressing the effects of oxygen and ensuring better strength, an amount of 0.01% by weight or more, preferably 0.1% by weight or more, can be used. The upper limit of the antioxidant content can be 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0065] Furthermore, the thickness of the core material layer 14 is preferably 0.5 mm to 15.5 mm. Specifically, in the case of a multilayer tube 1' with a diameter of 25A, the thickness t4 of the core material layer 14 is preferably 0.5 mm to 3 mm. In the case of a multilayer tube 1' with a diameter of 75A, the thickness t4 of the core material layer 14 is preferably 1 mm to 6.5 mm. In the case of a multilayer tube 1' with a diameter of 200A, the thickness t4 of the core material layer 14 is preferably 9 mm to 15.5 mm.

[0066] (Second Layer 12) As shown in Figure 1(a), the second layer 12 is disposed outside the first layer 11. The second layer 12 bonds the third layer 13 to the outside of the first layer 11. As shown in Figure 1(b), the second layer 12 is disposed outside the core layer 14. The second layer 12 bonds the third layer 13 to the outside of the core layer 14. Regarding the material of the second layer 12, which functions as an adhesive layer, it is preferably an adhesive polyolefin resin. The second layer 12 contains an adhesive polyolefin resin as a main component. The main component refers to the component with the highest content based on mass. The main component is a component with a content of at least 50%. The lower limit of the content of the adhesive polyolefin resin in the second layer 12 is preferably 50% by mass, more preferably 70% by mass, and even more preferably 80% by mass, sometimes even more preferably 90% by mass, and sometimes even more preferably 95% by mass. For example, maleic anhydride-modified adhesive polyethylene can be used as an adhesive polyolefin resin.

[0067] The thickness t2 of the second layer 12 is not particularly limited as long as it is sufficient to bond the third layer 13 to the first layer 11 or the core material layer 14, but is preferably 50 μm or more and 500 μm or less. Furthermore, even if the types and diameters of the multilayer tubes 1 and 1' are different, the preferred range of thickness t2 is the same.

[0068] (Third layer 13) By providing a third layer 13 as a gas barrier layer, gas dissolution in ultrapure water can be effectively suppressed. Furthermore, since the third layer 13 prevents oxygen from the outer surfaces 1c, 1c' of the multilayer tubes 1, 1' from penetrating into the innermost first layer 11 or the core material layer 14, the long-term strength of the multilayer tubes 1, 1' can also be improved. Moreover, the provision of a gas barrier layer is also superior in terms of effectively suppressing gas dissolution in ultrapure water.

[0069] Examples of materials for the third layer 13 include ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride resin (PVDC), and nylon-based resins. The third layer 13 contains ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride resin (PVDC), or nylon-based resin as a main component. The main component is a component with a content of at least 50%. The lower limit of the content of ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride resin (PVDC), or nylon-based resin in the third layer 13 is preferably 50% by mass, more preferably 70% by mass, and even more preferably 80% by mass, sometimes even more preferably 90% by mass, and sometimes even more preferably 95% by mass. From the viewpoint of moldability, it is preferable to use ethylene-vinyl alcohol copolymer (EVOH) as an adhesive polyolefin resin as the material of the third layer 13.

[0070] The thickness t3 of the gas barrier layer is not particularly limited as long as it is sufficient to ensure the gas barrier properties of the polypropylene resin. It is preferably 80 μm to 500 μm, and more preferably 100 μm to 270 μm. In order to obtain the same oxygen permeability as when PVDF is used in the innermost layer of the tube, the thickness t3 of the third layer 13 is preferably 100 μm or more. Furthermore, even if the types and diameters of the multilayer tubes 1 and 1' are different, the preferred range of thickness t3 is the same.

[0071] (Applications of piping materials for ultrapure water) The multilayer pipes 1 and 1' of the embodiments of the present invention can be used for transporting ultrapure water. Specifically, the multilayer pipes 1 and 1' of the embodiments of the present invention can be used as piping within an ultrapure water manufacturing apparatus, piping for transporting ultrapure water from the ultrapure water manufacturing apparatus to the point of use, and piping for returning ultrapure water from the point of use, etc. Furthermore, as defined in the present invention, ultrapure water is defined as having a resistivity of 10 MΩ·cm or more at 25°C, more precisely, a resistivity of 15 MΩ·cm or more at 25°C, and even more precisely, a resistivity of 18 MΩ·cm or more at 25°C.

[0072] The multilayer pipes 1 and 1' of the embodiments of the present invention are preferably used for piping in nuclear power generation where the water quality requirements for ultrapure water are particularly strict, or in the manufacturing process of pharmaceuticals, semiconductor devices, or liquid crystals. More preferably, they are used for transporting ultrapure water in wet processing steps such as cleaning in the manufacturing process of semiconductor devices. As for the semiconductor device, it is preferable to have a higher density; specifically, it is more preferable to use it in the manufacturing process of semiconductor devices with a minimum linewidth of 65 nm or less. As for specifications related to the quality of ultrapure water used in semiconductor manufacturing, SEMI F75 can be cited as an example.

[0073] Furthermore, since the multilayer pipes 1 and 1' of the embodiments of the present invention have a layer containing polypropylene resin as the main component, they have excellent workability. For example, butt welding or EF (electrofusion) welding can be easily performed at relatively low temperatures.

[0074] (Manufacturing of Multilayer Pipes) The multilayer pipes 1 and 1' of the embodiments of the present invention can be manufactured by the following method: preparing a first layer 11, whose main component is polypropylene resin, forming the inner surface 1b of the pipe material, and a core layer 14, whose main component is polypropylene resin, as needed; preparing a second layer 12, whose material is adhesive polyolefin resin; and preparing a third layer 13, which forms the outer surface, as a coating resin; and co-extruding the layers in such a way that the thickness of each layer is a predetermined thickness. Since the multilayer pipes of the embodiments of the present invention are made of polypropylene resin, they can be manufactured at a low cost.

[0075] (Other embodiments) One embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment and various modifications can be made without departing from the spirit of the invention.

[0076] (A) In the multilayer tube 1' of the above embodiment, a first layer 11, a core material layer 14, a second layer 12 and a third layer are arranged in sequence, but it is not limited to this, and other layers may be arranged between the core material layer 14 and the second layer 12.

[0077] (B) In the multilayer tubes 1 and 1' of the above embodiment, the third layer 13, which serves as the air barrier layer, constitutes the outer surface 1c and 1c', but other layers may also be provided on the outer side of the third layer 13.

[0078] (C) The layer structure of the multilayer tubes 1 and 1' in the above embodiment can be applied to joints (elbow joints, straight joints, T-joints, cross joints, flange joints, etc.) used when connecting resin tubes, and can also be applied to electrofusion joints.

[0079] (Example) Next, the multilayer tube of this embodiment will be described in detail using the example.

[0080] In Examples 1 to 6, the oxygen barrier properties of the multilayer tube 1 described in the above embodiments were measured by changing the diameter and the thickness of the third layer. NOVATEC PP and EA9FTD manufactured by Japan Polypropylene Co., Ltd. were used as the material for the first layer 11, i.e., a polypropylene resin (referred to as PP in the table). The material for the second layer 12 was maleic anhydride-modified adhesive polyethylene (referred to as adhesive PE in the table). The material for the third layer 13 was ethylene-vinyl alcohol copolymer (referred to as EVOH in the table). The thickness of the third layer is shown below (Table 1).

[0081] For the oxygen barrier performance test, the oxygen permeability was determined using the isobaric method according to JIS K7126-2. The oxygen barrier values ​​in Table 1 below represent the oxygen permeability per unit area of ​​the piping.

[0082] (Table 1) Example 1 Example 2 Example 3 Example 4 Example 5 Example 5 Example 6 caliber 25A 75A 200A 25A 25A 25A 25A Level 1 PP PP PP PP PP PP PP 2nd floor Adhesive PE Adhesive PE Adhesive PE Adhesive PE Adhesive PE Adhesive PE Adhesive PE 3rd floor EVOH EVOH EVOH EVOH EVOH EVOH EVOH Thickness of the 3rd layer (mm) 0.1 0.1 0.1 0.08 0.25 0.5 0.05 Oxygen barrier properties (*) 0.29 0.28 0.27 0.31 0.15 0.04 0.48 result ◎ ◎ ◎ ◎ ◎ ◎ ○ *Oxygen permeability per unit area of ​​piping (cc / m2･24 hr･atm)

[0083] In Comparative Example 1, the oxygen barrier properties of a single-layer tube consisting only of a layer formed of polyvinylidene fluoride (PVDF) (KUREHA KF POLYMER manufactured by KUREHA Co., Ltd.) were measured.

[0084] In Comparative Example 2, the oxygen barrier properties of a single-layer pipe consisting only of a layer formed from a polyethylene resin were measured. NOVATEC PP and EA9FTD manufactured by Japan Polypropylene Co., Ltd. were used as the polyethylene resin.

[0085] (Table 2) Comparative Example 1 Comparative Example 2 caliber 25A 25A Level 1 PVDF PP 2nd floor - - 3rd floor - - Thickness of the 3rd layer (mm) - - Oxygen barrier properties (*) 0.29 0.79 result ◎ × *Oxygen permeability per unit area of ​​piping (cc / m2･24 hr･atm)

[0086] An oxygen permeability of 0.5 or less is defined as acceptable (○), and 0.35 or less is defined as good (◎). As shown in Examples 1 to 6, it can be seen that the oxygen permeability decreases as the thickness of the third layer increases. In Examples 1 to 5, since the oxygen permeability is 0.35 or less, it is good. In Example 6, since the thickness of the third layer is 50 μm, the oxygen permeability becomes 0.48, so although it is outside the good range, it is within the acceptable range. Furthermore, as shown in Comparative Example 2, when the third layer is not provided, the oxygen permeability exceeds 0.5, resulting in a defect. Furthermore, it can be seen that in order to ensure the same oxygen barrier properties (oxygen permeability 0.29) as the single-layer PVDF tube shown in Comparative Example 1, the thickness of the third layer is preferably 100 μm or more.

[0087] Based on the above, it can be seen that for multilayer pipes using polypropylene resin in the innermost layer, by configuring a third layer with gas barrier properties, it can be used as piping for transporting ultrapure water. [Simplified Explanation of the Diagram]

[0022] Figure 1(a) is a cross-sectional view of a multilayer tube in an embodiment of the present invention, and (b) is a cross-sectional view of a multilayer tube in another embodiment of the present invention.

Claims

1. A multilayer tube for transporting ultrapure water, comprising: a first layer constituting the innermost layer and mainly composed of a polypropylene resin; a gas barrier layer disposed at least on the outer side of the first layer and having gas barrier properties; a second layer disposed outside the first layer and inside the gas barrier layer, and mainly composed of an adhesive polyolefin resin; and a core layer disposed between the first layer and the second layer, and mainly composed of a polypropylene resin.

2. For the multilayer tube of claim 1, wherein the calcium leaching amount of the first layer, as measured according to SEMI F-57, does not reach 30 μg / m2.

3. The multilayer tube as requested in item 1, wherein the thickness of the aforementioned gas barrier layer is 80 μm or more and 500 μm or less.

4. The multilayer tube of claim 1, wherein the gas barrier layer comprises an ethylene-vinyl alcohol copolymer as the main component.

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