Plastic inner liner for pressurised gas tank

Abstract

The invention relates to a plastic inner liner (1) for a pressurised gas tank (3), the inner liner (1) defining an inner volume for storing a pressurised gas and being manufactured by extrusion blow moulding of a tubular parison, the inner liner (1) comprising a gas barrier layer (10) therein. According to the invention, the barrier layer (10) of the inner liner (1) is located between a first parting line of the inner liner and a second parting line of the inner liner, the first parting line and the second parting line of the inner liner being located opposite one another.

Description

Inner plastic casing for pressurized gas tank

[0001] The invention relates to tanks for containing pressurized gases, particularly tanks installed in motor vehicles. More specifically, the invention relates to an inner plastic casing for a pressurized gas tank and a method for manufacturing such an inner plastic casing. The invention also relates to a pressurized gas tank for a vehicle, as well as a vehicle comprising such a pressurized gas tank. The gases in question include, but are not limited to, natural gas, biogas, liquefied petroleum gas, and hydrogen.

[0002] The various functions of these tanks are:

[0003] • to contain the gas under pressure, that is to say, to mechanically resist the pressure,

[0004] • ensure a watertight seal against the outside,

[0005] • Ensure pressurized gas filling using a solenoid valve mounted on a nozzle,

[0006] • deliver the pressurized gas using the same solenoid valve mounted on the nozzle,

[0007] • to attach to a load-bearing structure,

[0008] • withstand the conditions of transport and use,

[0009] • to withstand external environmental aggressions, both mechanical and thermal,

[0010] • to withstand the manufacturing conditions of the tanks.

[0011] These tanks can be mounted on all types of fixed or mobile equipment (road vehicles, rail, sea, air, space). Pressurized gas tanks are manufactured from metallic materials or, more recently, from composite materials, for reasons of weight reduction and safety.

[0012] Regarding composite material tanks, also called composite tanks, their watertightness is generally achieved by installing an internal liner, which seals the container against its contents. Depending on the tank manufacturer, internal liners are available in metallic or plastic materials.

[0013] The inner plastic casing includes at least one opening for filling and emptying the tank. It is manufactured by injection molding, rotational molding, or blow molding of a thermoplastic or thermosetting polymer material (abbreviated as "thermoset") such as polyethylene, polyamide, polyphthalamide, polyurethane, silicone, or polyoxymethylene. Advantageously, the thermoplastic polymer material is reinforced with fibers to form a composite material. Examples of reinforcing fibers include glass fibers, carbon fibers, basalt fibers, aramid fibers, polymer fibers, silica fibers, polyethylene fibers, natural fibers, metallic fibers, metal alloy fibers, or ceramic fibers. These fibers increase the deformation resistance of the composite material.In a polymer material reinforced with fibers, the fibers and the polymer are intertwined to form a single-piece material. Such a composite material is described by the Applicant in its French patent application No. 18 72197 filed on November 30, 2018 and published under No. 3 089 160.

[0014] This inner shell, or liner, is then covered with a liner reinforcement layer made of composite material, which forms the tank body—that is, the tank's structural integrity. This structure must be able to withstand the pressures exerted by the gas inside the tank (hereinafter referred to as "internal pressure"). The reinforcement layer is not generally required to ensure the tank's watertightness.

[0015] This reinforcement package consists of:

[0016] • a reinforcement generally made of fibers, for example continuous fibers of glass, carbon, basalt, or others such as silica fibers or even plant fibers,

[0017] • A resin that is either deposited simultaneously with the fiber (filament winding process) or after the casing has been created to form a dry "preform". This dry preform is then consolidated to give it the necessary rigidity. This consolidation is achieved by injecting resin, by infiltrating the resin through the preform (infusion process), or by impregnating the resin under vacuum.

[0018] The inner shell or liner, made of plastic, whose main function is to define a gas storage volume, must also exhibit low gas permeability, particularly to gases composed of small molecules such as hydrogen. Thus, document WO2020 / 223666 A1 discloses a composite tank whose inner shell or liner has a gas barrier layer on its outer surface. This barrier layer is applied using slow and / or complex processes such as dip coating, vapor deposition, or wrapping a sheet around the central part of a cylindrical inner shell. Furthermore, the inner shell is obtained by welding injection-molded domes to the ends of a central extruded section, which creates a weldability problem when the central section includes a barrier layer.In addition, a barrier layer positioned on the surface of the liner (interior or exterior) requires strong adhesion otherwise it will be exposed to delamination phenomena over time by hydrogen diffusion.

[0019] US patent application 2024 / 263740A1 discloses an inner shell for a pressurized gas tank made of welded sections. This shell exhibits weld-related weaknesses and variations in the thickness of the inner shell, particularly in the areas corresponding to the ends of the gas barrier layer. Furthermore, this type of shell requires a complex manufacturing process involving numerous steps.

[0020] The invention aims in particular to overcome these drawbacks of the prior art.

[0021] More specifically, an objective of the invention, in at least one of its embodiments, is to provide an inner envelope or liner made of plastic material comprising a barrier layer exhibiting good resistance to delamination.

[0022] Another objective of the invention, in at least one of its embodiments, is to implement a method for manufacturing an internal casing or liner made of plastic material for a pressurized gas tank.

[0023] The invention, in at least one of its embodiments, also aims to provide a pressurized gas tank for a vehicle, as well as a vehicle comprising such a pressurized gas tank.

[0024] According to a particular embodiment, the invention relates to an internal plastic casing for a pressurized gas tank, the internal casing defining an internal storage volume for a pressurized gas and having come from blow-extrusion of a tubular parison, the internal casing extending along a longitudinal axis and comprising a gas barrier layer within it.

[0025] According to the invention, the inner envelope is such that the barrier layer of the inner envelope is strictly localized between a first joint plane of the inner envelope and a second joint plane of the inner envelope, said first joint plane and second joint plane of the inner envelope being located opposite each other, the first joint plane and the second joint plane of the inner envelope each corresponding to a bead of the inner envelope, said inner envelope being of a single piece and having a thickness variation of less than 0.5 mm in the areas corresponding to the ends of the barrier layer, this thickness variation being taken along the longitudinal axis.

[0026] The general principle of the invention is based on the presence of a gas barrier layer within the inner envelope located between a first parting plane of the inner envelope and a second parting plane of the inner envelope, said first and second parting planes of the inner envelope being located opposite each other, said inner envelope having come from blow-molded extrusion of a tubular parison, the first and second parting planes of the inner envelope each corresponding to a bead of the inner envelope, said inner envelope being of a single piece and having a thickness variation of less than 0.5 mm in the areas corresponding to the ends of the barrier layer, this thickness variation being taken along the longitudinal axis.

[0027] Thus, the invention is based on a completely new and inventive approach to an inner shell for a pressurized gas tank, obtained by blow-extrusion of a tubular parison comprising a gas barrier layer within the inner shell. The barrier layer is located between a first and a second parting plane of the inner shell situated opposite each other. The first and second parting planes of the inner shell each correspond to a bead of the inner shell. The inner shell is a single piece and has a thickness variation of less than 0.5 mm in the areas corresponding to the ends of the barrier layer, this thickness variation being measured along the longitudinal axis. Such an inner shell produced by blow-extrusion of a tubular parison is easily obtained in a single piece and does not require lengthy manufacturing times.Furthermore, a barrier layer located within the inner shell reduces the risk of delamination due to gas diffusion, particularly hydrogen, within the shell. Finally, a barrier layer located between the first and second parting lines of the inner shell prevents pinching of the barrier layer during mold closure. Due to the use of a blow molding process of a tubular parison for manufacturing the inner shell, a pinch zone is present in the regions of the inner shell corresponding to the parting lines, resulting in ridges on the inner shell. This pinch zone is susceptible to blistering due to its greater local thickness and to delamination.A first and second flat joint plane, both lacking the barrier layer, avoids these problems and also improves the weld between the two parts of the tubular parison. Furthermore, the presence of a barrier layer within the inner polyamide sheath, for example, allows for a reduction in the sheath's thickness, thus increasing its usable volume by approximately 2 to 5%, depending on its shape.

[0028] The terms "first parting line and second parting line of the inner shell" refer to the areas where the tubular parison is pinched during mold closure. These parting lines are characterized by the presence of bulges, in other words, a variation in the thickness of the inner shell or a bulge in it.

[0029] The term "barrier layer" refers to a layer in which the permeation of the gas intended to be contained in the reservoir comprising the inner shell, preferably hydrogen, is slower compared with a part of the inner shell of the same thickness not comprising it.

[0030] The expression "one-piece inner casing" means that the inner casing is a single piece and is not the result of assembling parts joined by welding, for example.

[0031] Advantageously, the inner plastic casing for a pressurized gas tank according to the invention is such that the barrier layer extends over the entire cross-section of the inner casing.

[0032] Thus, an inner plastic envelope including a barrier layer extending over the entire cross-section of the inner envelope reduces the preferential leakage path of the gas contained in the inner envelope.

[0033] The expression "the barrier layer extends over the entire cross-section of the inner envelope" refers to the fact that the barrier layer is present over the entire slice of the inner envelope cut along a transverse plane. The cross-section of the inner envelope is generally oblong, oval, elliptical, circular, or polygonal; preferably, in the case of a polygonal cross-section, it is a polygon with 4 to 8 equal sides. Most preferably, the cross-section of the inner envelope is oblong, oval, elliptical, or circular.

[0034] According to a preferred embodiment, the internal plastic casing for a pressurized gas tank according to the invention is such that it is based on a material selected from a polyamide and a polyethylene, preferably a high-density polyethylene (PHED), more preferably a polyamide selected from the group consisting of Nylon PA-6, PA6,6 copolymer, Nylon PA-11, Nylon PA-12 and n-mXD6 polyarylamide, preferably Nylon PA-6.

[0035] Thus, an inner layer of high-density polyethylene (HDPE) provides a liner with lower hydrogen permeability and improved mechanical properties; moreover, HDPE is less expensive and lighter compared to nylon, for example. An inner layer of polyamide, chosen from the group consisting of Nylon PA-6, PA6,6 copolymer, Nylon PA-11, Nylon PA-12, and n-mXD6 polyarylamide, preferably Nylon PA-6, provides an inner layer with lower hydrogen permeability and also better mechanical properties.

[0036] According to a preferred embodiment, the internal plastic casing for a pressurized gas tank according to the invention is such that the barrier layer is based on a material selected from polyvinylidene fluoride, ethylene vinyl alcohol (EVOH), propylene polyvinyl alcohol (PVOH) and butylene polyvinyl alcohol (BVOH).

[0037] Thus, the presence of a barrier layer within the inner polyamide envelope, for example, makes it possible to reduce the thickness of the inner envelope and thus increase the usable volume of the envelope by about 2 to 5% depending on the shape of the latter.

[0038] According to a preferred embodiment of at least one of the two preceding embodiments, the inner plastic casing for a pressurized gas tank comprises at least one additive selected from a compatibilizing agent, a grafting agent, and an anchoring agent. A compatibilizing agent is a chemical compound designed to stabilize a mixture of naturally immiscible chemical compounds, preventing phase separations, for example. The compatibilizing agent is generally incorporated into one or both of the naturally immiscible chemical compounds. Upon mixing the immiscible compounds, the compatibilizing agent reacts with each compound to form:

[0039] • Covalent chemical bonds (reduction, oxidation, condensation,…)

[0040] • Polar or nonpolar physical bonds such as hydrogen bonds, sulfide bonds, Van der Waals type bonds, dipole moment interactions.

[0041] This type of mixing generally takes place in the liquid phase to ensure intimate contact at the molecular level of the compounds (mixing in solution or in the molten state), it can also occur during the co-extrusion of PA6 and EVOH, PA6 and PVOH or PA6 and BVOH from the molten state.

[0042] Examples of compatibilizing agents include:

[0043] - Ionomers, such as methacrylic or acrylic ionomers,

[0044] - Silanes and siloxanes,

[0045] - Maleic anhydrides.

[0046] A grafting agent is a chemical grafting agent that enables a chemical reaction creating covalent bonds, or a physical grafting agent that enables strong polar interactions or hydrogen bonds. An anchoring agent is an agent that enables co-crystallization at the interface during the cooling of materials from their molten state.

[0047] According to a preferred embodiment, the inner plastic casing for a pressurized gas tank according to the invention is such that it comprises barrier layer adhesion promoters, said adhesion promoters being carboxylic groups grafted onto polyethylene or polyamide or anhydride groups grafted onto polyethylene or polyamide or amine groups grafted onto polyethylene or polyamide for a barrier layer of ethylene vinyl alcohol, propylene polyvinyl alcohol or butylene polyvinyl alcohol.

[0048] Thus, an inner envelope made of polyethylene or polyamide including adhesion promoters of a barrier layer made of ethylene vinyl alcohol, propylene polyvinyl alcohol or butylene polyvinyl alcohol improves the adhesion of the barrier layer within the inner envelope.

[0049] According to a preferred embodiment of the preceding one, the inner plastic casing for a pressurized gas tank according to the invention is such that the adhesion promoters are maleic anhydride groups grafted onto polyethylene or polyamide. The grafted maleic anhydride groups, being more reactive, allow for good adhesion.

[0050] According to a preferred embodiment, the internal plastic casing for a pressurized gas tank according to the invention is such that the thickness of the barrier layer is between 10 and 250µm, preferably between 10 and 150µm.

[0051] Thus, the presence of a barrier layer with a thickness between 10 and 250µm, preferably between 10 and 150µm within the inner envelope allows for low gas permeation, particularly of hydrogen in the case of an inner envelope based on polyamide for example.

[0052] According to a preferred embodiment, the internal plastic casing for a pressurized gas tank according to the invention is such that it has a central part with a cross-section of polygonal shape or oblong shape or oval shape or elliptical shape or circular shape, preferably a central part with a cross-section of circular shape or oval shape or elliptical shape or oblong shape, between the two joint planes.

[0053] Thus, a central section part of polygonal, circular, oval, elliptical or oblong shape allows for easier application of a reinforcement envelope made of composite material including reinforcing fibers and / or particles, as well as easier demolding of the inner envelope.

[0054] According to a preferred embodiment of the preceding embodiment, the internal plastic casing for a pressurized gas tank according to the invention is such that it has a curved transition zone between the central part and a joint plane.

[0055] Thus, the presence of this curved transition zone between the central part and a joint plane allows for an easier and more uniform application of a reinforcement envelope made of composite material including fibers and / or reinforcing particles.

[0056] According to a preferred embodiment of one of the two preceding embodiments, the internal plastic casing for a pressurized gas tank according to the invention is such that the barrier layer extends over more than 80% of the length of the central part.

[0057] Thus, a barrier layer extending over more than 80% of the length of the central part makes it possible to reduce gas permeation through the envelope while maintaining a good barrier effect.

[0058] According to a preferred embodiment, the inner plastic casing for the gas tank according to the invention is such that the barrier layer is located in the center of the thickness of the inner casing.

[0059] Thus, a barrier layer located in the center of the thickness of the inner envelope reduces the risk of alteration of the barrier layer and improves its protection.

[0060] The invention also relates to a pressurized gas tank comprising an inner casing as described above, said tank also comprising a reinforcing casing made of composite material comprising reinforcing fibers and / or particles.

[0061] The invention also relates to a vehicle comprising a pressurized gas tank as described above

[0062] The invention also aims to provide a method for manufacturing an inner plastic casing, the inner casing defining an internal volume for storing a gas under pressure.

[0063] The method according to the invention is such that it comprises the following steps:

[0064] • extrusion of a first part of a tubular parison comprising a layer of a first plastic material

[0065] • extrusion of a second part of the tubular parison comprising a barrier layer of a second material sandwiched between a first layer of the first plastic material and a third layer of the first plastic material

[0066] • extrusion of a third part of the tubular parison comprising the third layer or the first layer in the first plastic material

[0067] • insertion of the parison into a mold

[0068] • Closing of the mold and pinching of the first part of the tubular parison and the second part of the tubular parison

[0069] • Blowing the parison

[0070] • Opening the mold

[0071] • Obtaining an internal casing for a pressurized gas tank.

[0072] The general principle of the process according to the invention is based on a sequential multilayer extrusion process, in which a barrier layer of a second material is present only during the formation of the central part of the inner shell and is discontinued during the formation of the shell ends. This barrier layer has a lower permeability compared to the base material of the inner shell, or first material. The central part of the shell is preferably cylindrical, while the ends of the inner shell, formed from the first and third parts of the tubular parison, are generally dome-shaped.

[0073] Thus the process according to the invention allows the rapid and simple manufacture of an inner envelope, said manufacture not requiring a welding step between the central part and the ends of the inner envelope.

[0074] According to a preferred embodiment, the manufacturing process for an internal plastic casing for a pressurized gas tank according to the invention is such that the first plastic material is based on polyamide or polyethylene, preferably a high-density polyethylene (PHED), more preferably a polyamide selected from the group consisting of Nylon PA-6, PA6,6 copolymer, Nylon PA-11, Nylon PA-12 and n-mXD6 polyarylamide, preferably Nylon PA-6.

[0075] According to a preferred embodiment, the manufacturing process for an internal plastic casing for a pressurized gas tank according to the invention is such that the second material is based on polyvinylidene fluoride, ethylene vinyl alcohol, propylene polyvinyl alcohol or butylene polyvinyl alcohol.

[0076] According to a preferred embodiment, the manufacturing process for an internal plastic casing for a pressurized gas tank according to the invention is such that the length of the second part of the tubular parison corresponds to at least 60% of the length of the tubular parison enclosed in the mold. Brief description of the figures

[0077] Other features and advantages of the invention will become clearer upon reading the following description of a preferred embodiment, given by way of simple illustrative and non-limiting example, and the accompanying drawings, among which:

[0078] presents a longitudinal section of an internal plastic casing for a pressurized gas tank, the internal casing defining an internal storage volume for a pressurized gas and being manufactured by blow molding of a tubular parison.

[0079] illustrates the pinching zones of the internal envelope presented at the.

[0080] describes a pressurized gas reservoir comprising an inner shell as shown in Figures 1 and 2.

[0081] illustrates an extrusion device enabling the production of a tubular parison used for the manufacture of an inner casing as shown in figures 1 and 2. Detailed description

[0082] In connection with this, we present an embodiment of an internal plastic casing 1 for a pressurized gas reservoir. The internal casing 1 defines an internal storage volume for a pressurized gas, comprising a gas barrier layer 10 within it, and is formed by blow molding of a tubular parison. The internal casing 1 extends along a longitudinal axis (X). The barrier layer 10 of the internal casing 1 is located between a first parting plane of the internal casing and a second parting plane of the internal casing, said first and second parting planes of the internal casing being located opposite each other. The first and second parting planes correspond to a pinching zone of the tubular parison during the formation of the internal casing 1 by the mold.The first and second parting lines of the inner shell each correspond to a bead of the inner shell, said inner shell being a single piece and exhibiting a thickness variation of less than 0.5 mm in the areas corresponding to the ends of the barrier layer, this thickness variation being measured along the longitudinal axis (X). The inner shell 1 comprises a central portion 11, preferably cylindrical in shape, the ends of the inner shell generally being domed 12a, 12b. The first and second parting lines are preferably present only on a portion of the ends of the inner shell, which are generally domed 12a, 12b. The inner shell 1 is made of a material selected from a polyamide and a polyethylene, preferably a high-density polyethylene (HDPE), more preferably a polyamide, preferably Nylon PA-6.The barrier layer 10 is based on a material selected from polyvinylidene fluoride, ethylene vinyl alcohol, propylene polyvinyl alcohol and butylene polyvinyl alcohol and said barrier layer 10 not extending over more than 80% of the length of the central part 11.

[0083] Figure 1 illustrates the location of different zones constituting the inner shell 1, defining an internal storage volume for a pressurized gas. This inner shell includes a gas barrier layer 10 within it, manufactured by blow molding a tubular parison. The first and second parting lines correspond to a pinching zone of the tubular parison during the formation of the inner shell 1 by the mold. The first and second parting lines of the inner shell each correspond to a bead of the inner shell. This inner shell is a single piece and exhibits a thickness variation of less than 0.5 mm in the areas corresponding to the ends of the barrier layer, this thickness variation being measured along the longitudinal axis (X). The inner shell 1 comprises a central portion 11, preferably cylindrical in shape, with the ends of the inner shell generally being domed 12a, 12b.The domes comprising a pinch zone A without a barrier layer 10, a curved transition zone B between the central part and a joint plane and a zone C corresponding to the central part 11 of the inner envelope 1 comprising a barrier layer over at least 80% of its length.

[0084] A gas pressure tank 3 is described, comprising an inner shell 1 defining an internal storage volume for a gas under pressure, including a gas barrier layer 10 within it, manufactured by blow molding from a tubular parison. The inner shell 1 is surrounded by a reinforcing shell 2 made of a composite material comprising reinforcing fibers and / or particles. The gas pressure tank is equipped with an end fitting 4 serving as a means for attaching an outlet or inlet valve.

[0085] Figure 20 illustrates an extrusion device for obtaining a tubular parison used in the manufacture of an inner casing. This extrusion device allows for a sequenced extrusion process comprising the following steps:

[0086] • extrusion of a first part of a tubular parison comprising a layer of a first plastic material

[0087] • extrusion of a second part of the tubular parison comprising a barrier layer of a second material sandwiched between the first layer of the first plastic material and a third layer of the first plastic material

[0088] • extrusion of a third part of the tubular parison comprising the third layer in the first plastic material.

[0089] The extrusion device 20 comprises an extrusion head equipped with a first accumulator 21 containing a first plastic material selected from polyamide and polyethylene, preferably high-density polyethylene (HDPE), more preferably a polyamide, preferably Nylon PA-6, and a first extrusion unit 24 for the first material, and a second accumulator 22 containing a second material selected from polyvinylidene fluoride, ethylene vinyl alcohol, polyvinyl propylene alcohol, and polyvinyl butylene alcohol, and a second extrusion unit 25 for the second material. The extrusion principle is based on continuous extrusion of the first material and discontinuous or sequential extrusion of the second material.This process allows for the creation of a tubular parison with successive sections along the extrusion direction: sections with a barrier layer (second part of the tubular parison) and sections without a barrier layer (first and third parts of the tubular parison). After extrusion, the tubular parison is inserted into a mold consisting of at least two half-shells that close around the tubular parison, securing it at the first and third parts of the tubular parison. The parison is then blown into the mold to create the inner shell for a pressurized gas tank; the mold is then opened, and the inner shell for the pressurized gas tank is retrieved. List of references

[0090] 1: Inner casing 2: Reinforcing casing 3: Pressurized gas reservoir 4: Nozzle 10: Gas barrier layer 11: Central section 12a, 12b: Dome 20: Extrusion device 21: First accumulator 22: Second accumulator 24: First extrusion unit 25: Second extrusion unit

Claims

Plastic inner casing (1) for pressurized gas tank (3), the inner casing (1) defining an internal volume for storing a pressurized gas and having been blow-molded from a tubular parison, the inner casing (1) extending along a longitudinal axis (X) and comprising a gas barrier layer (10) within it, the inner casing (1) being characterized in that the barrier layer of the inner casing is strictly located between a first parting plane of the inner casing and a second parting plane of the inner casing, said first and second parting planes of the inner casing being located opposite each other, the first and second parting planes of the inner casing each corresponding to a bead of the inner casing, said inner casing being of a single piece and having a thickness variation of less than 0.5 mm in the areas corresponding to the ends of the barrier layer, this variation in thickness being taken along the longitudinal axis (X). Inner plastic casing (1) for pressurized gas tank (3) according to claim 1, wherein the barrier layer (10) extends over the entire cross-section of the inner casing. Inner plastic casing (1) for pressurized gas tank (3) according to any one of the preceding claims, wherein the inner casing (1) is based on a material selected from polyamide and polyethylene. Inner plastic casing (1) for pressurized gas tank (3) according to any one of the preceding claims, such that the barrier layer (10) is based on a material selected from polyvinylidene fluoride, ethylene vinyl alcohol, propylene polyvinyl alcohol and butylene polyvinyl alcohol. Inner plastic casing (1) for pressurized gas tank (3) according to claims 3 and 4, wherein it comprises at least one additive selected from a compensating agent, a grafting agent and an inking agent. Inner plastic casing for pressurized gas tank according to any one of the preceding claims, such that the thickness of the barrier layer is between 10 and 250µm. Inner plastic casing (1) for pressurized gas tank (3) according to any one of the preceding claims, such that it has a central part (11) of polygonal cross-section or of circular cross-section or of oval cross-section or of elliptical cross-section or of oblong cross-section between the two joint planes. Inner plastic casing (1) for pressurized gas tank (3) according to the preceding claim, such that it has a curved transition zone between the central part (11) and a joint plane. Inner plastic casing (1) for pressurized gas tank (3) according to any one of claims 7 to 8, wherein the barrier layer (10) extends over more than 80% of the length of the central part (11). Inner plastic casing (1) for pressurized gas tank (3) according to any one of the preceding claims, such that the barrier layer (10) is located at the center of the thickness of the inner casing (1). Pressurized gas reservoir (3) comprising an inner casing (1) according to any one of the preceding claims and a reinforcing casing (2) made of composite material comprising reinforcing fibers and / or particles. Method for manufacturing an inner casing (1) made of plastic material for a pressurized gas tank (3), the inner casing (1) defining an internal volume for storing a pressurized gas,The process is characterized in that it comprises the following steps: • extrusion of a first part of a tubular parison comprising a layer of a first plastic material • extrusion of a second part of the tubular parison comprising a barrier layer (10) of a second material sandwiched between a first layer of the first plastic material and a third layer of the first plastic material • extrusion of a third part of the tubular parison comprising the third layer or the first layer of the first plastic material • insertion of the parison into a mold • closing of the mold and pinching of the first part of the tubular parison and the third part of the tubular parison • blowing of the parison • opening of the mold • obtaining an internal casing (1) for a pressurized gas tank (3). Method of manufacturing an inner plastic casing (1) for a pressurized gas tank (3) according to the preceding claim, wherein the first plastic material is based on polyamide or polyethylene. Method of manufacturing an inner plastic casing (1) for a pressurized gas tank (3) according to any one of claims 12 to 13, wherein the second material is based on polyvinylidene fluoride, ethylene vinyl alcohol, propylene polyvinyl alcohol or butylene polyvinyl alcohol. Method of manufacturing an inner plastic casing (1) for a pressurized gas tank (3) according to any one of claims 12 to 14, wherein the length of the second part of the tubular parison corresponds to at least 60% of the length of the tubular parison enclosed in the mold.

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