Multilayer structure with improved hydrogen barrier

Abstract

This invention relates to a multilayer structure for storing or transporting hydrogen-containing gases, wherein the multilayer structure comprises at least three layers, including an inner layer comprising at least one first polymer, an intermediate layer comprising an ethylene-vinyl alcohol copolymer, and an outer layer comprising at least one second polymer, wherein the water vapor permeability of the inner layer is lower than that of the outer layer. The multilayer structure exhibits excellent hydrogen barrier properties. Therefore, the multilayer structure is suitable for use in hydrogen storage containers and hydrogen transport pipelines.

Description

Technical Field

[0001] The present invention relates to a multilayer structure having improved hydrogen barrier properties and means for hydrogen storage and transportation including the structure. Background Technology

[0002] Currently used composite hydrogen tanks typically contain a single-layer liner made of impact-modified polyamide (PA) or polyolefin. However, a problem with polyolefin liners, and even PA liners, is that they may exhibit insufficient barrier properties for hydrogen.

[0003] Ethylene-vinyl alcohol copolymer (EVOH) is known to be an excellent barrier material for various gases, including hydrogen. JP2016-135833A (PTL 1) describes a single-layer liner for pressure vessels, made of a resin composition containing EVOH, an acid-modified ethylene-α-olefin copolymer, and glycerol. It describes this single-layer liner as being formed by injection molding and exhibiting excellent hydrogen barrier properties. Before filling with high-pressure hydrogen, carbon fibers are wound around the surface of the liner and fixed with an epoxy resin adhesive to form a reinforcing layer. However, because EVOH resin is rigid, the impact resistance of the single-layer liner remains insufficient even when it contains rubber and / or plasticizers.

[0004] Therefore, multilayer structures including layers containing EVOH have already been described. For this purpose, US 2014 / 0008373 A1 (PTL 2) describes a multilayer structure comprising an inner PA layer, an intermediate EVOH layer, and an outer high-density polyethylene (HDPE) layer. The HDPE outer layer is described as a moisture barrier from the outside in because the external environment typically has a much higher moisture level than hydrogen, which typically has a moisture level close to or as low as 0% RH.

[0005] This type of moisture barrier layer facing the external environment is frequently used because the gas barrier performance of EVOH is known to depend on the humidity level. For example, Polymer Testing, Volume 93, January 2021, 106979 (NPL 1) describes the nitrogen barrier performance of EVOH as a function of relative humidity (RH) as reaching a maximum at approximately 30-35% RH, and then rapidly decreasing with increasing RH.

[0006] US 6,033,749 A (PTL 3) describes a fuel canister for gasoline comprising a multi-layer structure including an EVOH layer having inner and outer HDPE layers bonded by adhesive resin layers, wherein the ratio (I / O) is less than about 40 / 60, where I is the total thickness of the layer located inside the EVOH layer, and O is the total thickness of the layer located outside the EVOH layer. It describes how shifting the EVOH layer inward improves gasoline barrier properties and impact resistance compared to a case where the EVOH layer is located in the center.

[0007] Reference List

[0008] Patent documents

[0009] PTL 1: JP 2016-135833 A

[0010] PTL 2: US 2014 / 0008373 A1

[0011] PTL 3: US 6,033,749 A

[0012] Non-patent literature

[0013] NPL 1: Polymer Testing, Volume 93, January 2021, 106979 Summary of the Invention

[0014] Technical issues

[0015] To address the aforementioned problems, one object of the present invention is to provide a multilayer structure with excellent hydrogen barrier properties. Another object is to provide a hydrogen storage container and a hydrogen transport pipeline comprising the multilayer structure described above.

[0016] Problem Solution

[0017] The above problem can be solved by providing a multilayer structure for storing or transporting hydrogen-containing gases, wherein the multilayer structure comprises at least three layers, and the at least three layers include:

[0018] a. An inner layer comprising at least one first polymer,

[0019] b. An intermediate layer comprising an ethylene-vinyl alcohol copolymer, and

[0020] c. Outer layer, comprising at least one second polymer.

[0021] Furthermore, the water-vapour transmission rate of the inner layer, measured according to ISO 15106-2:2003 at 38°C and 90% RH, is lower than that of the outer layer, measured according to ISO 15106-2:2003 at 38°C and 90% RH.

[0022] Beneficial effects of the invention

[0023] The multilayer structure of this invention exhibits excellent hydrogen barrier performance. The hydrogen barrier performance can be improved by adjusting the water vapor permeability of the inner and outer layers. Therefore, hydrogen storage containers and hydrogen transport pipelines with the multilayer structure described above also possess excellent hydrogen barrier performance. Detailed Implementation

[0024] As described in Polymer Testing (NPL 1), the excellent gas barrier properties of EVOH are well-known. Furthermore, as shown in Figure 10 of NPL 1, the nitrogen barrier properties of EVOH as a function of relative humidity (RH) reach a maximum at approximately 30-35% RH, and then decrease rapidly with increasing RH. At these higher RH levels, water molecules are considered to act as plasticizers and weaken intermolecular and intramolecular hydrogen bonds, which in turn leads to increased chain mobility, making nitrogen molecules more permeable and thus reducing the barrier effect of EVOH. Additionally, Figure 10 shows that moisture absorption significantly impairs nitrogen barrier properties as ethylene content decreases.

[0025] Surprisingly, the inventors have now discovered that EVOH exhibits different behavior in terms of hydrogen barrier properties. Unexpectedly, the hydrogen barrier properties of EVOH reach their maximum at a much higher level of approximately 75% RH, while significantly decreasing towards lower moisture levels. In other words, we have found that hydrogen barrier properties are improved in EVOH with higher water content due to increased relative humidity.

[0026] Therefore, it is preferred that the water content of the intermediate layer in the multilayer structure of the present invention is 1.1% by mass or higher and 4% by mass or lower. This improves the hydrogen barrier performance of the intermediate layer. It is believed that as the water content of EVOH increases, the hydrogen bonds between polymer chains in EVOH are weakened, increasing the mobility of the polymer chains and leading to a deterioration in barrier performance against nonpolar molecules such as gases including oxygen, nitrogen, and carbon dioxide, as well as gasoline. However, contrary to common sense, it has been found that hydrogen barrier performance is maximized when a certain level or higher of water is present. The water content of the intermediate layer is more preferably 1.2% by mass or higher, and even more preferably 1.3% by mass or higher. Meanwhile, if the water content is too high, the barrier performance can be deteriorated, and therefore the water content is more preferably 3% by mass or lower, and even more preferably 2.5% by mass or lower.

[0027] Based on these surprising findings, the object of this invention is to provide a multilayer structure with improved hydrogen barrier properties. A further object of this invention is to provide a multilayer structure exhibiting further improved mechanical strength and recyclability. This invention has solved these and other problems.

[0028] In a first aspect, the present invention relates to a multilayer structure for storing or transporting a gas containing hydrogen, wherein the multilayer structure comprises at least three layers, the at least three layers comprising:

[0029] a. An inner layer comprising at least one first polymer,

[0030] b. An intermediate layer comprising an ethylene-vinyl alcohol copolymer (EVOH), and

[0031] c. Outer layer, comprising at least one second polymer.

[0032] Furthermore, the water vapor transmission rate of the inner layer, measured according to ISO 15106-2:2003 at 38°C and 90% RH, is lower than that of the outer layer, measured according to ISO 15106-2:2003 at 38°C and 90% RH.

[0033] Therefore, unlike the multilayer structure described in US 2014 / 0008373 A1 (PTL 2), the multilayer structure of this invention has a higher water barrier on the side facing the hydrogen-containing gas space than on the side facing the external environment. This allows the EVOH layer contained within the multilayer structure to withstand higher levels of RH, and thus allows for improved hydrogen barrier.

[0034] The water vapor transmission rate (WVTR) of the inner and outer layers was measured as an independent monolayer using AMETEK MOCON's "MOCONPERMATRAN W3 / 33" according to ISO 15106-2:2003 at 38°C and 90% RH.

[0035] The WVTR ratio, defined as the WVTR of the outer layer divided by the WVTR of the inner layer, is greater than 1.0. Preferably, the WVTR ratio is greater than 1.5, more preferably greater than 2.0, even more preferably greater than 2.5, and most preferably greater than 5.0.

[0036] The EVOH in the intermediate layer contains ethylene and vinyl alcohol units as the main structural units. In addition to ethylene and vinyl alcohol units, it may contain one or more other types of structural units. However, the content of the other structural units described above is preferably 10 mol% or less, more preferably 5 mol% or less, further preferably 2 mol% or less, and most preferably, the other structural units are substantially absent.

[0037] EVOH is typically obtained by copolymerizing ethylene and vinyl acetate, followed by saponification of the resulting ethylene-vinyl acetate copolymer.

[0038] The lower limit of the ethylene unit content (i.e., the ratio of the number of ethylene units to the total number of monomer units in EVOH) is preferably 20 mol%, more preferably 22 mol%. On the other hand, the upper limit of the ethylene unit content is preferably 70 mol%, more preferably 60 mol%, even more preferably 55 mol%, and particularly preferably 50 mol%. Furthermore, it is preferable that the ethylene content is between 20 and 60 mol%, more preferably between 20 and 50 mol%, and most preferably between 20 and 35 mol%.

[0039] To achieve exceptionally good hydrogen barrier performance, the ethylene content of EVOH is preferably 20 mol% or higher and 30 mol% or lower. More preferably, it is 28 mol% or lower, and even more preferably, it is 26 mol% or lower. It is generally believed that when using EVOH with a low ethylene content under high humidity, the increased water content weakens the hydrogen bonds between polymer chains, increasing polymer chain mobility and leading to deterioration of barrier performance. However, it has been found that the hydrogen barrier performance is maximized in a state containing a certain level or higher of water. Therefore, from the perspective of hydrogen barrier performance, using EVOH with a low ethylene content in an aqueous state is optimal.

[0040] Preferably, the lower limit of the degree of saponification of EVOH (i.e., the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl acetate units in EVOH) is 80 mol%, more preferably 95 mol%, particularly preferably 99 mol%, and most preferably 99.9 mol%.

[0041] From the perspective of thermal stability and viscosity adjustment, the EVOH layer preferably contains compounds such as acids and metal ions. Examples of such compounds include alkali metal salts, carboxylic acids, phosphoric acid compounds, and boron compounds, and specific examples are described below. Here, these compounds can be used as a premix with EVOH.

[0042] From the perspective of thermal stability and viscosity adjustment, the intermediate layer of the present invention preferably contains a phosphate compound, an alkali metal ion, a divalent metal ion, a boron compound, or a carboxylic acid. When a metal salt is contained, the metal salt forms a hydrate, which can appropriately maintain the water content of the intermediate layer. Furthermore, when a boron compound is contained, impact resistance can be improved.

[0043] The intermediate layer preferably contains a phosphate compound. The phosphate compound prevents defects such as streaks and fisheyes, while improving long-term operating performance. Examples of phosphate compounds include salts of phosphoric acid, such as phosphates and phosphites. The phosphate can be any form of first-generation, second-generation, or third-generation phosphate. There is no limitation on the type of cation in the phosphate, but salts of alkali metals and alkaline earth metals are preferred. Among these, compounds containing phosphate ions, such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate, are more preferred, and sodium dihydrogen phosphate and dipotassium hydrogen phosphate are further preferred. When the intermediate layer contains a compound containing phosphate ions as the phosphate compound, the lower limit of the phosphate ion content is preferably 5 ppm, more preferably 10 ppm, further preferably 20 ppm, and particularly preferably 30 ppm. The upper limit of the phosphate compound content in the intermediate layer is preferably 200 ppm, more preferably 150 ppm, and further preferably 100 ppm. When the phosphate compound reaches the lower limit or higher, or the upper limit or lower, the thermal stability is improved and the generation of gel-like particles, coloring, etc., can be minimized during long-term melt molding.

[0044] The intermediate layer preferably contains alkali metal ions. Alkali metal ions can be one type or a combination of two or more types. Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions, with sodium or potassium ions being preferred from an industrial availability perspective. Examples of alkali metal salts providing alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes. Among these, aliphatic carboxylates and phosphates are preferred from an availability perspective; specifically, sodium acetate, potassium acetate, sodium phosphate, potassium phosphate, sodium stearate, and potassium stearate are preferred. When the intermediate layer contains alkali metal ions, the lower limit of the alkali metal ion content is preferably 10 ppm, more preferably 100 ppm, and even more preferably 150 ppm. Meanwhile, the upper limit of the alkali metal ion content is preferably 400 ppm, more preferably 350 ppm. When the alkali metal ion content is at or above the above lower limit, the interlayer adhesion of the obtained multilayer structure tends to be improved. Meanwhile, when the metal ion content is at or below the aforementioned upper limit, the resistance to discoloration tends to be improved.

[0045] The intermediate layer preferably contains 5 ppm or higher and 200 ppm or lower phosphate ions, and 10 ppm or higher and 400 ppm or lower alkali metal ions.

[0046] In some cases, the intermediate layer preferably contains divalent metal ions. For example, with the presence of divalent metal ions, the thermal degradation of EVOH in recycled trim is suppressed, and the formation of gels and particles in the resulting molded articles can be inhibited. Examples of divalent metal ions include beryllium, magnesium, calcium, strontium, barium, and zinc ions, with magnesium, calcium, and zinc ions being preferred from an industrial usability perspective. Preferred examples of divalent metal salts providing divalent metal ions include carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes, with carboxylates being preferred. The carboxylic acid constituting the carboxylate is preferably a carboxylic acid having 1 to 30 carbon atoms, specifically acetic acid, propionic acid, butyric acid, stearic acid, lauric acid, montanic acid, behenic acid, octanoic acid, sebacic acid, recinoleic acid, myristic acid, and palmitic acid. Among these, acetic acid and stearic acid are preferred.

[0047] The intermediate layer preferably contains a carboxylic acid. The carboxylic acid prevents coloring of the resin composition and the molded article and inhibits gelation during melt molding. Examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, and lactic acid. The carboxylic acid is preferably a carboxylic acid having four or fewer carbon atoms, more preferably acetic acid. When the intermediate layer contains a carboxylic acid, the lower limit of the carboxylic acid content is preferably 50 ppm, more preferably 80 ppm, and even more preferably 120 ppm. The upper limit of the carboxylic acid content is preferably 1,000 ppm, more preferably 500 ppm, and even more preferably 400 ppm. When the carboxylic acid content is at or above the above lower limit, sufficient color inhibition effect can be achieved, and yellowing can be adequately suppressed. Meanwhile, when the carboxylic acid content is at or below the above upper limit, gelation during melt molding, especially during long-term melt molding, is suppressed, giving the molded article, etc., a good appearance. Here, a combination of acetic acid and acetate is more preferred, and a combination of acetic acid and sodium acetate is even more preferred.

[0048] The intermediate layer preferably contains a boron compound, which can prevent torque variations during heating and melting. Examples of boron compounds include, but are not limited to, boric acid, borate esters, borates, and borohydrides. Specifically, boric acid includes orthoboric acid, metaboric acid, and tetraboric acid; borate esters include triethyl borate and trimethyl borate; and borates include alkali metal salts and alkaline earth metal salts of the various boric acids mentioned above, and borax. Among these compounds, orthoboric acid (hereinafter sometimes simply referred to as "boric acid") is preferred. The boron compound content, based on elemental boron, is preferably 50 ppm or higher and 400 ppm or lower. When the boron compound content is 50 ppm or higher, melt moldability tends to be stable; more preferably, the content is 70 ppm or higher, and even more preferably 100 ppm or higher. Meanwhile, when the boron compound content is 400 ppm or lower, deterioration of moldability tends to be prevented; more preferably, the content is 350 ppm or lower, and optionally 300 ppm or lower.

[0049] In addition to the EVOH described above, the intermediate layer may also contain additives such as heat stabilizers, ultraviolet absorbers, antioxidants, plasticizers, antistatic agents, lubricants, colorants, and fillers, within the range that does not impair the purpose of the invention. When the intermediate layer contains such additives other than those described above, the amount of such additives relative to the total mass of the intermediate layer is preferably no more than 10% by mass, more preferably no more than 5% by mass, and particularly preferably no more than 3% by mass.

[0050] Suitable antioxidants used in this article are materials that inhibit the oxidative degradation or cross-linking of EVOH, and include 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 4,4′-thiobis-(6-tert-butylphenol), 2,2′-methylenebis-(4-methyl-6-tert-butylphenol), octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate, 4,4′-thiobis-(6-tert-butylphenol), tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and 3,3′-bis(3,5-di-tert-butyl-4-hydroxyphenyl)-N,N′-hexamethylenedipropionamide.

[0051] Suitable plasticizers include diethyl phthalate, dibutyl phthalate, dioctyl phthalate, waxes, liquid paraffin, phosphate esters, etc.

[0052] Suitable ultraviolet absorbers include ethyl 2-cyano-3,3′-diphenylacrylate, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)5-chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, etc.

[0053] Suitable antistatic agents include pentaerythritol monostearate, sorbitol monopalmitate, sulfated polyolefins, and polyethylene oxide.

[0054] Suitable lubricants include ethylene bis(stearamide) and butyl stearate.

[0055] Preferably, the intermediate layer does not contain any additional polymers other than EVOH. However, the intermediate layer may also preferably contain at least one additional polymer selected from elastomers, polyolefins, polyesters, polyurethanes, and polyamides.

[0056] The elastomers used in this invention can be selected from thermoplastic styrene elastomers or α-olefin copolymers, ethylene-propylene rubber (EPR), acrylic rubber (ACM), acrylonitrile-butadiene rubber (NBR), butadiene rubber (PBD, BR), isoprene rubber (IR), natural rubber (NR), styrene-butadiene rubber (SBR), and styrene copolymers (SBS, SIS). Preferably, thermoplastic styrene elastomers or α-olefin copolymers are selected, and more preferably, acid-modified thermoplastic styrene elastomers or α-olefin copolymers are selected.

[0057] There are no particular limitations on the thermoplastic styrene elastomer, and those known in the art can be used. Thermoplastic styrene elastomers typically have a styrene monomer polymer block (Hb) as a hard segment and a conjugated diene compound polymer block or its hydrogenated block (Sb) as a soft segment. The structure of such thermoplastic styrene elastomers can be a diblock structure represented by Hb-Sb, a triblock structure represented by Hb-Sb-Hb or Sb-Hb-Sb, a tetrablock structure represented by Hb-Sb-Hb-Sb, or a multiblock structure in which a total of five or more Hb and Sb are linearly bonded.

[0058] Examples of α-olefin copolymers include, but are not limited to, ethylene-propylene copolymers (EP), ethylene-butene copolymers (EB), propylene-butene copolymers (PB), and butene-ethylene copolymers (BE).

[0059] Such elastomers in EVOH are preferably acid-modified thermoplastic styrene elastomers or α-olefin copolymers, as well as mixtures of acid-modified elastomers and unmodified elastomers.

[0060] In this paper, acid modification is carried out by copolymerization, partially replacing the monomers constituting α-olefin copolymers or thermoplastic styrene elastomers with α,β-unsaturated carboxylic acids or their anhydrides, or alternatively by introducing α,β-unsaturated carboxylic acids or their anhydrides into some side chains through, for example, grafting reactions (e.g., free radical addition). Examples of α,β-unsaturated carboxylic acids or their anhydrides used in the above-described acid modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride. Among these, maleic anhydride may be suitably used.

[0061] In these, the intermediate layer preferably contains 70% by mass or higher and 99% by mass or lower EVOH, and 1% by mass or higher and 30% by mass or lower acid-modified ethylene-α-olefin copolymer. The intermediate layer containing the acid-modified ethylene-α-olefin copolymer allows for a multilayer structure with excellent impact resistance. The content of the acid-modified ethylene-α-olefin copolymer is more preferably 2% by mass or higher, and even more preferably 5% by mass or higher. Here, the content of EVOH is more preferably 98% by mass or lower, and even more preferably 95% by mass or lower. Meanwhile, from the perspective of gas barrier performance, the content of EVOH is preferably 70% by mass or higher, more preferably 80% by mass or higher, and even more preferably 85% by mass or higher. Here, the content of the acid-modified ethylene-α-olefin copolymer is preferably 30% by mass or lower, more preferably 20% by mass or lower, and even more preferably 15% by mass or lower.

[0062] The first polymer of the inner layer and the second polymer of the outer layer can have the same or different chemical compositions. In other words, the inner and outer layers can be made of the same or different materials, including optional additives. The multilayer structure sandwiched between resins other than EVOH allows for the provision of hydrogen storage containers or hydrogen transport pipelines, or linings thereof, that are resistant to damage caused by deformation due to pressure changes in the contents and impacts from the outside.

[0063] In a first preferred embodiment, the first polymer and the second polymer have the same chemical composition. To make the water barrier of the outer layer less than that of the inner layer, the thickness of the inner layer is preferably greater than the thickness of the outer layer.

[0064] In the multilayer structure of the present invention, a ratio (I / O) of 60 / 40 or higher and 99 / 1 or lower is preferred, where I is the total thickness of the layers located inside the intermediate layer and O is the total thickness of the layers located outside the intermediate layer. In other words, in the multilayer structure, the intermediate layer is preferably disposed outside the center of all layers. As described above, it has been found that EVOH in a water-containing state improves hydrogen barrier performance. Generally, in hydrogen storage containers, high-pressure hydrogen with a relative humidity of about 0% is often filled in the container, and therefore, the container absorbs moisture from the outside due to the relative humidity of the surrounding environment. In hydrogen transport pipelines, the internal relative humidity is often also low. In this case, in order to maintain a high water content in the intermediate layer of the multilayer structure, it is preferable to disposed the intermediate layer outward. A ratio (I / O) of 70 / 30 or higher is more preferred, further preferred is 75 / 25 or higher, and particularly preferred is 80 / 20 or higher. Meanwhile, since an excessively high I / O ratio is unsuitable from an impact resistance perspective in some cases, an I / O ratio of 98 / 2 or lower is more preferred, further preferred to be 95 / 5 or lower, and particularly preferred to be 90 / 10 or lower. It is known that for containers filled with hydrophobic contents such as gasoline, moving the EVOH layer inward is preferable from a barrier performance perspective (see, for example, PTL 3), but conversely, for hydrogen, moving the layer outward is preferable.

[0065] There are no particular limitations on the thickness ratio of the layers constituting the multilayer structure of the present invention, but a ratio (A / B) of 3 / 97 or higher and 30 / 70 or lower is preferred, where A is the thickness of the intermediate layer and B is the total thickness of the multilayer structure. Sandwiched between inner and outer layers of a certain thickness, the multilayer structure can possess excellent mechanical strength. Furthermore, since the intermediate layer of the present invention has excellent hydrogen barrier properties, even multilayer structures with small thicknesses can have sufficient barrier properties. A ratio (A / B) of 5 / 95 or higher is more preferred, and 20 / 80 or lower is even more preferred.

[0066] Preferably, the thickness of the outer layer is equal to or less than 25 mm, more preferably equal to or less than 5 mm, and most preferably equal to or less than 1 mm. When the multilayer structure is used for a thin inner liner, the thickness of the outer layer is preferably equal to or less than 0.5 mm, more preferably equal to or less than 0.4 mm, and most preferably equal to or less than 0.2 mm. On the other hand, the thickness is preferably equal to or greater than 0.05 mm, equal to or greater than 0.1 mm, and most preferably equal to or greater than 0.15 mm. Furthermore, preferably, the thickness of the outer layer is between 0.05 mm and 0.15 mm.

[0067] Preferably, the thickness of the inner layer is equal to or less than 20 mm, more preferably equal to or less than 5 mm, and most preferably equal to or less than 2 mm. When the multilayer structure is used for a thin liner, the thickness of the inner layer is preferably equal to or less than 1.0 mm, more preferably equal to or less than 0.9 mm, and most preferably equal to or less than 0.8 mm. On the other hand, the thickness is preferably equal to or greater than 0.2 mm, more preferably equal to or greater than 0.5 mm. Furthermore, preferably, the thickness of the inner layer is between 0.3 mm and 0.7 mm.

[0068] Preferably, the thickness of the intermediate layer is equal to or less than 10 mm, more preferably equal to or less than 5 mm, and most preferably equal to or less than 1 mm. However, the multilayer structure of the present invention provides significantly improved hydrogen barrier performance. It is possible to select a primary hydrogen barrier layer containing EVOH with a considerably low thickness. Preferably, the thickness of the intermediate layer is less than 0.5 mm, more preferably equal to or less than 0.4 mm, and most preferably equal to or less than 0.2 mm. On the other hand, the thickness is preferably equal to or greater than 0.05 mm, equal to or greater than 0.1 mm, and most preferably equal to or greater than 0.2 mm. Furthermore, preferably, the thickness of the intermediate layer is between 0.05 mm and 0.15 mm. When the thickness of the intermediate layer is within the above range, excellent hydrogen barrier performance and impact resistance can be achieved.

[0069] Preferably, the total thickness of all layers in the multilayer structure is equal to or less than 50 mm, more preferably equal to or less than 30 mm, and most preferably equal to or less than 20 mm. When the multilayer structure is used for a thin inner liner, the thickness of the outer layer is preferably equal to or less than 10 mm, more preferably equal to or less than 7.5 mm, and most preferably equal to or less than 5 mm. On the other hand, the thickness is preferably equal to or greater than 0.3 mm, equal to or greater than 0.5 mm, and most preferably equal to or greater than 0.7 mm. When superior hydrogen barrier properties and impact resistance are required, the lower limit can be 0.8 mm or higher, or 1.0 mm or higher.

[0070] To provide good adhesion between the EVOH layer and the inner and / or outer layers, and to prevent the EVOH layer from separating from the inner and / or outer layers during production or use, the multilayer structure according to the invention preferably includes at least one adhesive layer between the inner and intermediate layers and / or between the outer and intermediate layers. Such adhesive layers are known in the art and may incorporate polar functional groups to promote compatibility with polar materials and non-polar functional groups to maintain compatibility with non-polar layers. Examples of materials available for such adhesive layers include anhydride-modified polyolefins, such as maleic anhydride-grafted polypropylene and polyethylene, such as "Bynel 40E529" available from DuPont and "Admer HB030" available from Mitsui Chemicals, Inc., and ethylene polar terpolymers, such as "LOTADER" available from Arkema.

[0071] Preferably, the thickness of the adhesive layer is equal to or less than 5 mm, more preferably equal to or less than 3 mm, and most preferably equal to or less than 1 mm. When the multilayer structure is used for a thin liner, the thickness of the adhesive layer is preferably equal to or less than 0.2 mm, more preferably equal to or less than 0.1 mm, and most preferably equal to or less than 0.075 mm. On the other hand, the thickness is preferably equal to or greater than 0.01 mm, equal to or greater than 0.02 mm, and most preferably equal to or greater than 0.04 mm. Furthermore, preferably, the thickness of the adhesive layer is between 0.03 mm and 0.07 mm.

[0072] As used in this article, “thickness” should refer to the average thickness of individual layers after the fabrication of a multilayer structure.

[0073] Furthermore, preferably, the multilayer structure does not contain any other layers, but is composed of the following:

[0074] a. Inner layer, comprising at least one first polymer

[0075] b. An intermediate layer comprising an ethylene-vinyl alcohol copolymer, and

[0076] c. Outer layer, which contains at least one second polymer.

[0077] The first and second polymers are independently selected from polyamide (PA), polyethylene (PE), especially high-density polyethylene (HDPE) or low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), "Teflon" (polytetrafluoroethylene), thermoplastic polyurethane (TPU), polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVOH), and ethylene tetrafluoroethylene (ETFE).

[0078] Polyamide resins are polymers containing amide bonds and can be obtained through ring-opening polymerization of lactams, condensation polymerization of aminocarboxylic acids or diamines with dicarboxylic acids, etc.

[0079] Examples of lactams include ε-caprolactam and ω-laurolactam.

[0080] Examples of aminocarboxylic acids include 6-aminohexanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and p-aminomethylbenzoic acid.

[0081] Examples of diamines include tetramethylenediamine, hexamethylenediamine, undecylmethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 5-methylnonamethylenediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, m-phenylenediamine, p-phenylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminopropyl)piperazine, and aminoethylpiperazine.

[0082] Examples of dicarboxylic acids include succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, decahydronaphthalenedicarboxylic acid, norbornanedicarboxylic acid, tricyclodecanedicarboxylic acid, pentacyclododecanedicarboxylic acid, isophoronedicarboxylic acid, 3,9-bis(2-carboxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, trimellitic acid, pyromellitic acid, pyromellitic tetracarboxylic acid, tricarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 2-methylterephthalic acid, naphthalenedicarboxylic acid, biphenyl dicarboxylic acid, and tetraphosphorusdicarboxylic acid.

[0083] Specific examples of polyamide resins include aliphatic polyamide resins such as polycaprolactam (Nylon 6), polylaurolactam (Nylon 12), polyhexamethylene adipamide (Nylon 66), polyhexamethylene azelaate (Nylon 69), polyhexamethylene sebacate (Nylon 610), nylon 46, nylon 6 / 66, nylon 6 / 12, and the condensation product of 11-aminoundecanoic acid (Nylon 11), and aromatic polyamide resins such as polyhexamethylene isophthalamide (Nylon 6IP), isophthalamide / adipic acid copolymer (Nylon MXD6), isophthalamide / adipic acid / isophthalic acid copolymer, and 1,9-nonanediamine / 2-methyl-1,8-octyldiamine / terephthalic acid copolymer (Nylon 9T). These can be used alone or as a mixture of two or more of them.

[0084] Among these polyamide resins, nylon MXD6, which exhibits superior gas barrier properties, is particularly preferred. Regarding the diamine component of nylon MXD6, it is preferable to contain at least 70 mol% m-phenylenediamine. Regarding the dicarboxylic acid component, it is preferable to contain at least 70 mol% adipic acid. When nylon MXD6 is obtained from monomers blended as described above, even superior gas barrier properties and mechanical properties can be achieved.

[0085] To improve mechanical properties, polyamides can optionally be compounded with elastomers, such as thermoplastic styrene elastomers or α-olefin copolymers, acrylic rubber (ACM), acrylonitrile-butadiene rubber (NBR), butadiene rubber (PBD, BR), isoprene rubber (IR), and natural rubber (NR). Thermoplastic styrene elastomers or α-olefin copolymers are preferred. In addition to improved mechanical properties, the addition of nonpolar elastomers will also reduce the WVTR of this composite material.

[0086] To enhance compatibility with polyamides, the elastomer in the polyamide is preferably an acid-modified thermoplastic styrene elastomer or an α-olefin copolymer, as well as a mixture of acid-modified elastomers and unmodified elastomers.

[0087] TPU can be obtained from polymeric polyols, organic polyisocyanates, and optional chain extenders and other components. Polymeric polyols are substances having multiple hydroxyl groups. Examples of polymeric polyols include polyester polyols, polyether polyols, polycarbonate polyols, and their cocondensates (e.g., polyester-ether-polyols). These polymeric polyols can be used alone of one type or as a mixture of two types.

[0088] Because fluorinated polymers are relatively more expensive than non-fluorinated polymers, the first polymer is preferably a non-fluorinated polymer. More preferably, the first polymer is a polyamide or a polyolefin. More preferably, the first polymer is HDPE. Furthermore, preferably, the second polymer is a non-fluorinated polymer. Specifically, the second polymer is a polyamide (PA).

[0089] The gas used in this invention contains hydrogen as a major component. The hydrogen content in the entire gas is preferably 80% by volume or higher, more preferably 90% by volume or higher, further preferably 95% by volume or higher, particularly preferably 99% by volume or higher, and the gas can be substantially composed of hydrogen. The gas may contain a small amount of moisture, but the relative humidity is preferably 20% or lower, more preferably 10% or lower, further preferably 5% or lower, and particularly preferably substantially free of moisture (relative humidity of 0%). However, other components may also be present in the gas. These components may include, but are not limited to, methane, ethane, ethylene, acetylene, propane, propylene, butane, nitrogen, oxygen, argon, carbon dioxide, carbon monoxide, ammonia, and hydrogen sulfide. The gas is processed in the hydrogen storage container or hydrogen transport pipeline of this invention. For hydrogen transport pipelines, depending on the location of use, hydrogen containing a large amount of moisture may be transported. For example, there may be situations where hydrogen used as a fuel cell material is transported while water is mixed into the gas as a reaction product. When transporting such hydrogen containing a large amount of moisture, the pipeline of this invention is not very efficient.

[0090] Preferably, the H2TR of the multilayer structure is less than 15, more preferably less than 12.5, even more preferably less than 11, and particularly less than 10 cm. 3 / (m 2 .tian.atm).

[0091] In the multilayer structure of the present invention, the first polymer is preferably high-density polyethylene (HDPE). Therefore, a resin with lower water vapor permeability can be disposed on the inner layer side. Similarly, the second polymer is preferably polyamide (PA). Therefore, a resin with higher water vapor permeability can be disposed on the outer layer side, and impact resistance is improved.

[0092] A preferred embodiment of the multilayer structure of the present invention is a multilayer structure in which both the first polymer and the second polymer are high-density polyethylene (HDPE), and the ratio (I / O) is 60 / 40 or higher and 99 / 1 or lower, where I is the total thickness of the layer located inside the interlayer, and O is the total thickness of the layer located outside the interlayer. Placing the interlayer on the outside allows for an increase in the water content of the interlayer. Furthermore, HDPE has a low water vapor permeability, thus suppressing variations in the water content of the interlayer. In addition, both the first polymer and the second polymer are made from the same heat-stable resin, thereby improving recyclability. Here, recyclability is further improved when the interlayer contains a certain amount of phosphate ions, alkali metal ions, divalent metal ions, or carboxylic acids in addition to EVOH.

[0093] Another embodiment of the multilayer structure of the present invention is a multilayer structure in which the first polymer is high-density polyethylene (HDPE) and the second polymer is polyamide (PA), and the ratio (I / O) is 60 / 40 or higher and 99 / 1 or lower, where I is the total thickness of the layers located inside the intermediate layer, and O is the total thickness of the layers located outside the intermediate layer. Placing the intermediate layer on the outside allows for an increase in its water content. When the second polymer is made of polyamide, the water content of the intermediate layer can increase rapidly in response to ambient humidity, and impact resistance is improved.

[0094] There are no particular limitations on the method of producing the multilayer structure of the present invention, as long as the method can advantageously laminate and bond the individual layers, and any known method such as co-extrusion, pasting, coating, bonding and attaching can be used.

[0095] Preferably, after producing the multilayer structure of the present invention, and before storing or transporting hydrogen, the multilayer structure is aged in a high relative humidity environment to adjust the water content of the intermediate layer to 1.1% by mass or higher and 4% by mass or lower. Therefore, excellent hydrogen barrier properties can be exhibited at the same time as the storage or transport of hydrogen begins. There are no particular limitations on the aging method; for example, the multilayer structure can be placed in a high temperature and high humidity environment for a certain period of time.

[0096] Another aspect of the present invention relates to a hydrogen storage container or hydrogen transport pipeline comprising a multi-layer structure as described above, or a hydrogen storage container or hydrogen transport pipeline composed of a multi-layer structure as described above.

[0097] Another aspect of the invention relates to the use of the multilayer structure as described above in hydrogen storage tanks, as a liner of hydrogen storage tanks, in hydrogen transport pipelines, or as a liner of hydrogen transport pipelines.

[0098] The multilayer structure of the present invention can itself be used as a hydrogen storage container or a hydrogen transport pipeline. However, since hydrogen pressure is often elevated in these applications, the multilayer structure of the present invention is used as a liner, the exterior of which can be covered with a reinforcing material. There are no particular limitations on the configuration of the reinforcing material, and typically, the reinforcing material, made of high-strength fibers such as carbon fiber and glass fiber, is fixed with a curable resin. For example, an example in JP 2016-135833 A (PTL 1) describes carbon fiber wrapped around the periphery of the liner and fixed with epoxy resin. Because the fiber reinforcing material tends to have gaps and the highly polar curable resin, such as epoxy resin, typically has a high water vapor permeability, the inner side of the fiber reinforcing material layer typically has a humidity comparable to that of the outer air. Therefore, even when such a reinforcing material layer is further fixed to the outer side of the multilayer structure of the present invention, it is not included in the total thickness of the multilayer structure.

[0099] A suitable embodiment of the hydrogen storage container of the present invention is a hydrogen storage container wherein the first polymer is HDPE and the second polymer is HDPE or PA, and the ratio (I / O) is 60 / 40 or higher and 99 / 1 or lower, where I is the total thickness of the layer located inside the interlayer and O is the total thickness of the layer located outside the interlayer. Positioning the interlayer on the outside allows for an increase in its water content. When the second polymer is HDPE, it has a low water vapor permeability and therefore can suppress changes in the water content of the interlayer. Furthermore, both the first and second polymers are made of the same heat-stabilized resin, allowing for improved recyclability. When the second polymer is PA, the water content of the interlayer can increase rapidly in response to ambient humidity, and shock resistance is improved.

[0100] Another suitable embodiment of the hydrogen storage container of the present invention is a hydrogen storage container in which the first polymer is HDPE and the second polymer is PA, and the ratio (A / B) is 3 / 97 or higher and 30 / 70 or lower, where A is the thickness of the interlayer and B is the total thickness of the multilayer structure. When the water vapor permeability of the outer layer is greater than that of the inner layer, the water content of the interlayer can be increased. Furthermore, a good balance between mechanical strength and gas barrier properties is achieved when the ratio (A / B) is within a certain range. When the second polymer is polyamide, the water content of the interlayer can increase rapidly in response to ambient humidity, and impact resistance is improved.

[0101] A suitable embodiment of the hydrogen transport pipeline of the present invention is a hydrogen transport pipeline wherein the first polymer is HDPE and the second polymer is HDPE or PA, and the ratio (I / O) is 60 / 40 or higher and 99 / 1 or lower, where I is the total thickness of the layer located inside the interlayer and O is the total thickness of the layer located outside the interlayer, and the relative humidity of the transported gas is 20% RH or lower. With the interlayer positioned on the outside, the water content of the interlayer can be increased, and this is more effective when the relative humidity of the transported gas is 20% or lower. When the second polymer is HDPE, it has a low water vapor permeability, thus suppressing changes in the water content of the interlayer. Furthermore, both the first and second polymers are made of the same heat-stabilized resin, allowing for improved recyclability. When the second polymer is polyamide, the water content of the interlayer can increase rapidly in response to ambient humidity, and impact resistance is improved.

[0102] Another suitable embodiment of the hydrogen transport pipeline of the present invention is a hydrogen transport pipeline wherein the first polymer is HDPE and the second polymer is PA, and the relative humidity of the transported gas is 20% or lower. When the water vapor transmission rate of the outer layer is greater than that of the inner layer, the water content of the intermediate layer can be increased, and this is more effective when the relative humidity of the transported gas is 20% or lower.

[0103] The multilayer structure of this invention can be used, but is not limited to, various hydrogen storage containers and hydrogen transport pipelines. Preferably, the multilayer structure is used in motor vehicles, more preferably in fuel cell electric vehicles (FCEVs). Fuel cell electric vehicles are clean vehicles where exhaust gases are only water, but one issue is how to handle high-pressure hydrogen. Although the multilayer structure of this invention is made of resin, it not only has excellent hydrogen barrier properties but also excellent impact resistance. Therefore, considering the balance between environmental performance and safety, the multilayer structure of this invention is suitable as a hydrogen storage container or hydrogen transport pipeline installed in fuel cell electric vehicles.

[0104] Example

[0105] Example 1

[0106] Five-layer flat sheets with the following thicknesses were prepared on the Collin co-extrusion line by co-extruding high-density polyethylene (HDPE) for the inner and outer layers, adhesive resin (Adh) as the adhesive layer, and pure EVOH for the intermediate layer.

[0107] (Outer side = purge gas side) HDPE / Adh / EVOH / Adh / HDPE (Inner side = H2 gas side): 100 / 50 / 100 / 50 / 700μm

[0108] HDPE: High-density polyethylene HB111R, commercially available from Ineos, with a melt index of 6.0 g / 10 min (190℃, 21.6 kg load) and a density of 0.945 g / cm³. 3 .

[0109] Adh: Maleic anhydride-modified polyethylene "Admer GT6E", commercially available from Mitsui Chemicals Europe GmbH, with a melt index of 1.1 g / 10 min (190 °C, 2.16 kg load) and a density of 0.92 g / cm³. 3 .

[0110] EVOH-32: An ethylene-vinyl alcohol copolymer with an ethylene content of 32 mol%, a saponification degree of 99.9 mol%, a melt index of 1.6 g / 10 min (190℃, 2.16 kg load), and a density of 1.18 g / cm³. 3 This EVOH contains 100 ppm acetic acid, 40 ppm phosphate ions, 150 ppm sodium ions, and 180 ppm (in boron atoms) boric acid.

[0111] The water vapor transmission rate (WVTR) of the inner layer (700 μm HDPE) and outer layer (100 μm HDPE) was measured as an independent monolayer at 38°C and 90% RH, according to ISO 15106-2:2003 using AMETEK MOCON's "MOCONPERMATRAN W3 / 33". Specifically, for the inner and outer layers used in the examples and reference examples, the water vapor transmission rate was measured at 38°C under the conditions of 90% relative humidity on the water vapor supply side, 0% relative humidity on the carrier gas side, and a carrier gas flow rate of 50 mL / min.

[0112] After molding, the multilayer structure undergoes humidity conditioning treatment. During this treatment, the inner side of the multilayer structure is kept in contact with air at 20°C and 0% RH, while the outer side is kept in contact with air at 20°C and 50% RH for one month to regulate humidity. The water content of the intermediate layer after this humidity conditioning is measured using a Karl Fischer moisture meter. Specifically, the humidity-conditioned multilayer sheet is cut into sheets of appropriate size, and the outer and inner layers are scraped off using a slicer, leaving only the intermediate layer. The water content of the obtained intermediate layer is measured. As a result, the water content of the intermediate layer is 1.4% by mass.

[0113] The hydrogen permeability (H2TR) of this moisture-controlled multilayer sheet was measured according to ISO 15106-2:2003 using a custom-designed temperature-controlled permeation chamber equipped with a "MOCON" test chamber. All measurements were performed at 20°C. A custom-designed EasyCal unit (Umwelttechnik MCZ GmbH) was used to regulate and humidify the test gas and purge gas flows in the chamber via two independent channels, each equipped with an "EL-FLOW" gas mass flow controller (MFC) and a "μ-FLOW" liquid MFC (Bronkhorst High-Tech BV). Hydrogen (the test gas) was maintained at 0% relative humidity, while nitrogen (used as the purge gas) was maintained at 50% relative humidity. High-purity hydrogen and nitrogen were purchased from Messer Belgium NV. The high-purity analyzer (HPA) detection system consisted of a TRACE 1300GC (Thermo Fisher Scientific Inc.) with an extended heated valve box. The H2TR of the multilayer structure is 10.2 cm. 3 / m 2 .day.atm.

[0114] Cyclic testing was performed on the molded multilayer structure. The multilayer structure was pulverized by a pulverizer and then loaded into... In a single-screw extruder, extrusion tests were conducted under the conditions described below. For Examples 2 to 5, 10 below and Reference Examples 1 to 3, the extrusion tests were conducted under the same conditions.

[0115] Screw speed: 95 rpm

[0116] Temperature settings for barrel and die head: C1 / C2 / C3 / C4 / C5 / D = 190℃ / 215℃ / 215℃ / 215℃ / 215℃

[0117] Number of holes in the die head: 6 holes

[0118] The die-lip deposition rate 30 minutes after extrusion began was evaluated according to the following criteria. Die-lip deposition is an indicator of recyclability. As a result, the evaluation grade was A.

[0119] A: There is basically no die lip deposition.

[0120] B: Minor die lip deposition

[0121] C: Significant amount of die lip deposition

[0122] As described above, the inner side of the multilayer structure was kept in contact with air at 20°C and 0% RH, while the outer side was kept in contact with air at 20°C and 50% RH for one month to regulate humidity. The multilayer structure was cut into specimens with dimensions of 25cm wide and 25cm long. The specimens were mounted on clamps with a height of 30mm, with the outer side facing upwards, and under test conditions of 23±2°C, a 500g iron ball was dropped from a height of 100cm to impact the specimens. No dents or cracks were observed in the specimens.

[0123] Simultaneously, the molded multilayer structure underwent separate humidity conditioning. During this conditioning process, the inner side of the multilayer structure was kept in contact with air at 40°C and 0% RH, while the outer side was kept in contact with air at 40°C and 90% RH for four months to regulate humidity. The water content of the intermediate layer after this humidity conditioning was measured using a Karl Fischer moisture meter, and the water content of the intermediate layer was 6.1% by mass. An impact test was performed using a specimen of the humidity-conditioned multilayer structure as described above, and indentation was observed in the specimen.

[0124] Refer to Examples 1 and 2

[0125] The same procedure described in Example 1 was repeated, except that a different HDPE layer thickness was used to change the position and relative humidity of the EVOH layer in the multilayer sheet structure. The results and layer thicknesses are summarized in Table 1. For practical purposes, the transmittance results reported with reference to Example 2 were measured using the multilayer sheet from Example 1 with opposite orientations.

[0126] Example 2

[0127] Repeat the same procedure described in Example 1, except that the EVOH is replaced with an EVOH variety with a lower ethylene content:

[0128] EVOH-27: An ethylene-vinyl alcohol copolymer with an ethylene content of 27 mol%, a saponification degree of 99.9 mol%, a melt index of 4.0 g / 10 min (210℃, 2.16 kg load), and a density of 1.21 g / cm³. 3 This EVOH contains 100 ppm acetic acid, 40 ppm phosphate ions, 150 ppm sodium ions, and 180 ppm (in boron atoms) boric acid.

[0129] The multi-layer structure was humidified by keeping the inner side of the multi-layer structure in contact with air at 20°C and 0% RH, while keeping the outer side in contact with air at 20°C and 50% RH for one month. The multi-layer structure was cut into specimens with dimensions of 25cm wide and 25cm long. The specimens were mounted on clamps with a height of 30mm, with the outer side facing upwards, and under test conditions of 23±2°C, a 1000g iron ball was dropped from a height of 100cm to impact the specimens, and an indentation was observed in the specimens.

[0130] Example 3

[0131] Repeat the same procedure described in Example 1, except that the EVOH is replaced with an impact-modified 27 mol% ethylene EVOH variety.

[0132] EVOH-27: Same as the EVOH used in Example 2.

[0133] Elastomer: Maleic anhydride-modified α-olefin copolymer "TAFMER MH7010" from Mitsui Chemicals Europe GmbH; melt index: 0.9 g / 10 min (190℃, 2.16 kg load), density: 0.870 g / cm³ 3 .

[0134] EVOH-27-Elastomer: A melt blend of 90% by weight EVOH-27 and 10% by weight elastomer.

[0135] The multilayer structure was humidified by keeping the inner side in contact with air at 20°C and 0% RH while keeping the outer side in contact with air at 20°C and 50% RH for one month. The multilayer structure was cut into test specimens and subjected to impact as described in Example 2. No dents or cracks were observed in the test specimens. This indicates that the multilayer structure of Example 3 exhibits higher impact resistance than the multilayer structure of Example 2.

[0136] Example 4

[0137] Repeat the same procedure described in Example 1, except that the EVOH is replaced with an EVOH variety with a lower ethylene content.

[0138] EVOH-24: An ethylene-vinyl alcohol copolymer with an ethylene content of 24 mol%, a saponification degree of 99.9 mol%, a melt index of 2.2 g / 10 min (210℃, 2.16 kg load), and a density of 1.22 g / cm³. 3 This EVOH contains 100 ppm acetic acid, 40 ppm phosphate ions, 150 ppm sodium ions, and 180 ppm (in boron atoms) boric acid.

[0139] Example 5 and Reference Example 3

[0140] Repeat the same procedure described in Example 1, except that the HDPE is replaced with a thermoplastic polyurethane (TPU) resin layer. Since direct bonding can be achieved between the EVOH and the selected TPU resin, an intermediate adhesive resin layer is not required.

[0141] TPU: Lubrizol "ESTANE" TS 92AP7 NAT 055 from The Lubrizol Corporation, with a density of 1.20 g / cm³. 3 .

[0142] The test results and layer thicknesses are summarized in Table 1.

[0143] Example 6 and Reference Example 4

[0144] Repeat the same procedure described in Example 1, except that the HDPE and adhesive resin layer are replaced with polyamide 6 (Nylon-6, PA6) and polyamide 6 / 12 (Nylon 6 / 12, PA6.12). Since direct adhesion can be achieved between the EVOH and the selected polyamide, no additional adhesive resin layer is required.

[0145] PA6: UBE Nylon 1018SE from UBE Industries Ltd., melt index: 9 g / 10 min (235℃, 2.16 kg load), density: 1.14 g / cm³ 3 .

[0146] PA6.12: Teknor Apex's "Chemlon 890H"

[0147] The test results and layer thicknesses are summarized in Table 1.

[0148] Cyclic testing was performed on the molded multilayer structure. The multilayer structure was pulverized by a pulverizer and then loaded into... In a single-screw extruder, extrusion tests were conducted under the conditions described below. For Examples 7 to 10 below and Reference Examples 5 to 7, the extrusion tests were conducted under the same conditions.

[0149] Screw speed: 95 rpm

[0150] Temperature settings for barrel and die head: C1 / C2 / C3 / C4 / C5 / D = 190℃ / 230℃ / 230℃ / 230℃ / 230℃

[0151] Number of holes in the die head: 6 holes

[0152] The multilayer structure obtained in Example 6 was humidified by keeping the inner side of the multilayer structure in contact with air at 20°C and 0% RH, while keeping the outer side in contact with air at 20°C and 50% RH for one month. The multilayer structure was cut into specimens with dimensions of 25cm wide and 25cm long. The specimens were mounted on clamps with a height of 30mm, with the outer side facing upwards, and under test conditions of 23±2°C, a 1000g iron ball was dropped from a height of 100cm three times to impact the specimens, and indentations were observed in the specimens.

[0153] Example 7 and Reference Example 5

[0154] Repeat the same procedure described in Example 1, except that the HDPE and adhesive resin layers are replaced with polyamide 6 (Nylon-6, PA6) and polyamide 12 (Nylon-12, PA12) layers. Due to insufficient direct adhesion between EVOH and PA12, an additional PA6-12 and PA6-based layer (PA-Adh) is placed between the EVOH and PA12 layers.

[0155] PA-Adh: Vestamid SX8002, a plasticized and impact-modified extrusion molding composition based on PA6.12 and PA6 from EVONIK Resource Efficiency GmbH.

[0156] PA12: Polyamide 12″UBESTA 3030XA″ from UBE Industries Ltd., melt index: 2.0 g / 10 min (235℃, 2.16 kg load), density: 1.02 g / cm³ 3 .

[0157] The test results and layer thicknesses are summarized in Table 1.

[0158] Example 8 and Reference Example 6

[0159] Repeat the same procedure described in Example 1, except that the HDPE and adhesive resin layers are replaced with polyamide 6 (nylon-6, PA6) on one side of the EVOH layer and a composite blend of polyamide 6 and elastomer (PA6-elastomer) on the other side.

[0160] PA6: UBE Nylon 1018SE from UBE Industries Ltd., melt index: 9 g / 10 min (235℃, 2.16 kg load), density: 1.14 g / cm³ 3 .

[0161] Elastomer: Maleic anhydride-modified α-olefin copolymer "TAFMER MH7010", commercially available from Mitsui Chemicals Europe GmbH, with a melt index of 0.9 g / 10 min (190 °C, 2.16 kg load) and a density of 0.870 g / cm³. 3 .

[0162] PA6-Elastomer: A melt blend of 80% by weight PA6 and 20% by weight elastomer.

[0163] The test results and layer thicknesses are summarized in Table 1.

[0164] The multilayer structure obtained in Example 8 was humidified by keeping the inner side in contact with air at 20°C and 0% RH while keeping the outer side in contact with air at 20°C and 50% RH for one month. The multilayer structure was cut into specimens and subjected to impact as described in Example 6. No dents or cracks were observed in the specimens. This indicates that the multilayer structure of Example 8 exhibits higher impact resistance than the multilayer structure of Example 6.

[0165] Example 9 and Comparative Example 7

[0166] Repeat the same procedure described in Example 1, except that the HDPE and adhesive resin layers are replaced with polyamide 6 (PA6) on the inside or outside of the EVOH.

[0167] Example 10

[0168] The production and evaluation of multilayer sheets were carried out as described in Example 1, except that, in Example 9, the thicknesses of the outer and inner layers were changed as described in Table 1.

[0169] Example 11

[0170] The multilayer sheet was produced and evaluated as described in Example 1, with EVOH-32′ replaced by EVOH-32. EVOH-32′ is identical to EVOH-32 except for the absence of boric acid. The multilayer structure obtained in Example 11 was humidified by keeping the inner side in contact with air at 20°C and 0% RH while keeping the outer side in contact with air at 20°C and 50% RH, and its impact resistance was evaluated as described in Example 1, with dents observed in the samples. In contrast, no dents or cracks were observed in the samples in Example 1. Therefore, the excellent impact resistance exhibited in Example 1 containing boric acid was confirmed.

[0171] [Table 1]

[0172]

Claims

1. A multilayer structure for storing or transporting a gas containing hydrogen, wherein the multilayer structure comprises at least three layers, the at least three layers comprising: a. An inner layer comprising at least one first polymer, b. An intermediate layer comprising an ethylene-vinyl alcohol copolymer, and c. An outer layer comprising at least one second polymer. The first polymer and the second polymer are independently selected from polyamide, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, thermoplastic polyurethane, polyvinylidene fluoride, polyvinyl alcohol, and ethylene tetrafluoroethylene. Furthermore, the water vapor transmission rate of the inner layer, measured according to ISO 15106-2:2003 at 38°C and 90% RH, is lower than that of the outer layer, measured according to ISO 15106-2:2003 at 38°C and 90% RH. The intermediate layer contains 5 ppm or higher and 200 ppm or lower phosphate ions, and 10 ppm or higher and 400 ppm or lower alkali metal ions.

2. The multilayer structure according to claim 1, wherein the ratio I / O is 60 / 40 or higher and 99 / 1 or lower, wherein I is the total thickness of the layers located inside the intermediate layer and O is the total thickness of the layers located outside the intermediate layer.

3. The multilayer structure according to claim 1 or 2, wherein the ratio A / B is 3 / 97 or higher and 30 / 70 or lower, wherein A is the thickness of the intermediate layer and B is the thickness of the multilayer structure.

4. The multilayer structure according to claim 1 or 2, wherein the first polymer and the second polymer have the same chemical composition, and wherein the thickness of the inner layer is greater than the thickness of the outer layer.

5. The multilayer structure according to claim 1 or 2, wherein the first polymer is high-density polyethylene.

6. The multilayer structure according to claim 1, wherein the first polymer and the second polymer are both high-density polyethylene, and the ratio I / O is 60 / 40 or higher and 99 / 1 or lower, wherein I is the total thickness of the layer located inside the intermediate layer, and O is the total thickness of the layer located outside the intermediate layer.

7. The multilayer structure according to claim 1 or 2, wherein the second polymer is a polyamide.

8. The multilayer structure according to claim 7, wherein the first polymer is high-density polyethylene and the second polymer is polyamide, and the ratio I / O is 60 / 40 or higher and 99 / 1 or lower, wherein I is the total thickness of the layer located inside the intermediate layer and O is the total thickness of the layer located outside the intermediate layer.

9. The multilayer structure according to claim 1 or 2, wherein the ethylene content of the ethylene-vinyl alcohol copolymer is between 20 and 60 mol%.

10. The multilayer structure according to claim 9, wherein the ethylene-vinyl alcohol copolymer has an ethylene content of 20 mol% or higher and 30 mol% or lower.

11. The multilayer structure according to claim 1 or 2, wherein the intermediate layer comprises a boron compound at 50 ppm or higher and 400 ppm or lower, based on boron element.

12. The multilayer structure according to claim 1 or 2, wherein the intermediate layer further comprises at least one additional polymer selected from polyolefins, polyesters, polyurethanes and polyamides.

13. The multilayer structure according to claim 1 or 2, wherein the intermediate layer further comprises an elastomer selected from thermoplastic styrene elastomers, α-olefin copolymers, ethylene-propylene rubber, acrylic rubber, acrylonitrile-butadiene rubber, butadiene rubber, isoprene rubber, natural rubber, styrene-butadiene rubber, and styrene copolymers.

14. The multilayer structure of claim 12, wherein the intermediate layer comprises 70% or more and 99% or less by mass of an ethylene-vinyl alcohol copolymer and 1% or more and 30% or less by mass of an acid-modified ethylene-α-olefin copolymer.

15. The multilayer structure according to claim 1 or 2, wherein the water content of the intermediate layer is 1.1% by mass or higher and 4% by mass or lower.

16. The multilayer structure according to claim 1 or 2, wherein the gas comprises 99% or more hydrogen by volume.

17. The multilayer structure according to claim 1 or 2, wherein the relative humidity of the gas is 20% or lower.

18. A hydrogen storage container comprising a multilayer structure according to any one of claims 1 to 17.

19. A hydrogen storage container comprising a multilayer structure according to any one of claims 1 to 17.

20. A hydrogen transport pipeline comprising a multi-layer structure according to any one of claims 1 to 17.

21. A hydrogen transport pipeline comprising a multi-layer structure according to any one of claims 1 to 17.

22. The hydrogen storage container according to claim 18 or 19, wherein the first polymer is high-density polyethylene and the second polymer is high-density polyethylene or polyamide, and the ratio I / O is 60 / 40 or higher and 99 / 1 or lower, wherein I is the total thickness of the layer located inside the intermediate layer and O is the total thickness of the layer located outside the intermediate layer.

23. The hydrogen storage container according to claim 18 or 19, wherein the first polymer is high-density polyethylene and the second polymer is polyamide, and the ratio A / B is 3 / 97 or higher and 30 / 70 or lower, wherein A is the thickness of the intermediate layer and B is the thickness of the multilayer structure.

24. The hydrogen transport pipeline according to claim 20 or 21, wherein the first polymer is high-density polyethylene and the second polymer is high-density polyethylene or polyamide, and the ratio I / O is 60 / 40 or higher and 99 / 1 or lower, wherein I is the total thickness of the layer located inside the intermediate layer and O is the total thickness of the layer located outside the intermediate layer, and the relative humidity of the gas is 20% or lower.

25. The hydrogen transport pipeline according to claim 20 or 21, wherein the first polymer is high-density polyethylene and the second polymer is polyamide, and the relative humidity of the gas is 20% or lower.

26. Use of the multilayer structure according to any one of claims 1 to 17 in a hydrogen storage tank, a liner of a hydrogen storage tank, a hydrogen transport pipeline, or a liner of a hydrogen transport pipeline.

27. The use according to claim 26, wherein the multilayer structure is aged in a high relative humidity environment prior to storage or transportation of hydrogen to adjust the water content of the intermediate layer to 1.1% by mass or higher and 4% by mass or lower.

28. The use according to claim 26 or 27, wherein the multilayer structure is used in a motor vehicle.

29. A fuel cell electric vehicle comprising a multi-layer structure according to any one of claims 1 to 17.

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