High pressure tank

Abstract

This invention relates to a high-pressure vessel, comprising: a resin liner for the high-pressure vessel having at least one opening; an aluminum connector installed in the opening; and a reinforcing layer formed on the outer surface of the liner. An alumina film is formed on the surface of the aluminum connector. The alumina film has a porous surface layer composed of columnar particles with an average height of 10 to 100 nm dispersedly. The average area ratio of the protrusions of the columnar particles in a randomly sampled 400 nm viewing angle of the porous surface layer is 5.0 to 26.0%, and the average number of columnar particles in a randomly sampled 400 nm viewing angle of the porous surface layer is 500 to 2000.

Description

Technical Field

[0001] This invention relates to high-pressure tanks. Background Technology

[0002] In the past, high-pressure vessels have been used as containers for containing fluids such as gases. Known high-pressure vessels include those with a resin liner, a reinforcing layer formed on the outer periphery of the liner, and a joint. Furthermore, in such high-pressure vessels, for example, as described in Japanese Patent Application Publication No. 2015-031307 (Patent Document 1) and Japanese Patent Application Publication No. 2015-169323 (Patent Document 2), an O-ring is used at the joint between the joint and the resin liner to ensure airtightness.

[0003] Thus, in the field of high-pressure vessels, O-rings have traditionally been used to ensure the airtightness of the interface between adjacent joints and the resin liner. This is because the metal forming the joint and the resin forming the liner are materials with vastly different properties, such as their coefficients of linear expansion, making it difficult to ensure the desired high level of airtightness when they are directly joined. On the other hand, from the perspective of design freedom, there is a desire for a technology that can ensure high airtightness even for gases with small molecular structures, such as hydrogen and helium, without using O-rings at the joint between the joint and the resin liner.

[0004] Furthermore, as a technique for bonding metal and resin, for example, International Patent Publication No. 2015 / 083845 (Patent Document 3) discloses a method comprising: a surface treatment step of anodizing an aluminum substrate to form an aluminum oxide film having a porous surface layer on the surface of the aluminum substrate, wherein the porous surface layer is composed of columnar structures with an average height of 10 to 100 nm dispersedly, and the average value of the total cross-sectional area of ​​the columnar structures within a randomly sampled 400 nm viewing angle is 8000 nm. 2 ~128000nm 2 The average number of columnar bodies within a randomly sampled 400nm viewing angle is 10 to 430; and the bonding process, wherein an aluminum substrate is bonded to a resin via an alumina film having the porous surface layer formed by the surface treatment process. Summary of the Invention

[0005] The technology described in Patent Document 3 is a technology that can make the bonding strength between metal and resin very strong. However, even if the technology of bonding metal and resin as described in Patent Document 3 is applied to the bonding between the metal forming the joint and the resin forming the liner, it may not be sufficient from the viewpoint of sufficiently suppressing the leakage of gases with small molecular structures such as hydrogen and helium from the interface (bonding part) between the metal (joint) and the resin (liner).

[0006] The present invention was made in view of the problems of the prior art described above, and its object is to provide a high-pressure tank that does not necessarily require the use of O-rings at the joint between the connector and the resin liner, and can prevent gas leakage from the interface between the connector and the resin liner to a high degree even if the sealed gas is a gas with a small molecular structure such as hydrogen or helium, thus having excellent airtightness.

[0007] The inventors of this invention conducted repeated and in-depth research to achieve the above-mentioned objectives, and as a result, discovered that by comprising a resin liner for a high-pressure vessel having at least one opening, an aluminum connector installed at the opening, and a reinforcing layer formed on the outer surface of the liner, and forming an alumina film on the surface of the aluminum connector, the alumina film having a porous surface layer composed of columnar bodies with an average height of 10 to 100 nm dispersedly, the average convex area ratio of the columnar bodies in a randomly sampled 400 nm viewing angle of the porous surface layer being 5.0 to 26.0%, and the average number of columnar bodies in a randomly sampled 400 nm viewing angle of the porous surface layer being 500 to 2000, the high-pressure vessel obtained thereby does not necessarily require the use of an O-ring at the joint between the connector and the resin liner, and even if the sealed gas is a gas with a small molecular structure such as hydrogen or helium, it can prevent gas leakage from the interface between the connector and the resin liner to a high level, and can have very excellent airtightness, thus completing the present invention.

[0008] That is, the present invention provides the following methods.

[0009] [1] A high-pressure tank, comprising:

[0010] The high-pressure tank has a resin liner and at least one opening.

[0011] An aluminum connector is installed at the opening; and

[0012] A reinforcing layer is formed on the outer surface of the liner.

[0013] An aluminum oxide film is formed on the surface of the aluminum connector.

[0014] The alumina film has a porous surface layer composed of columnar structures with an average height of 10–100 nm.

[0015] The average area ratio of the protrusions of the columnar structures within a 400 nm viewing angle of the porous surface layer was 5.0%–26.0%, and

[0016] The average number of columnar structures within a 400nm viewing angle of the porous surface layer is 500 to 2000.

[0017] [2] According to the high-pressure tank described in [1], the average value of the total perimeter of the columnar cross-section within a 400 nm viewing angle of the randomly sampled porous surface layer is 15000 to 50000 nm.

[0018] [3] The high-pressure vessel according to [1] or [2], wherein the high-pressure vessel is a vessel for hydrogen.

[0019] [4] The high-pressure tank according to any one of [1] to [3], wherein the aluminum connector is joined to the liner via a porous surface layer on the surface of the aluminum connector.

[0020] [5] The high-pressure tank according to any one of [1] to [4], wherein the junction of the aluminum joint and the liner has a He leakage rate of less than 10 liters after 10 seconds from the start of the He leakage test. -7 Pa·m 3 / s airtightness.

[0021] [6] The high-pressure vessel according to any one of [1] to [5], wherein the layer other than the porous surface layer in the alumina film is a layer with an average film thickness of 300 nm to 20 μm.

[0022] Furthermore, the reasons why the high-pressure vessel of the present invention can achieve the above-mentioned objectives may not be clear, but the inventors of the present invention speculate as follows. Firstly, conventionally, in the field of high-pressure vessels (high-pressure containers), when the molecular structure of the sealed gas, such as in a hydrogen tank, is small, airtightness is ensured by physical airtight structures such as sealing via O-rings. Secondly, regarding the airtightness of high-pressure vessels (high-pressure containers), there has been almost no quantitative evaluation of the metal-resin interface in the past; generally, the airtightness of these interfaces has only been simply determined. Thus, for the metal-resin interface, there has been no distinction made between levels of gas sealing, such as liquid sealing or gas sealing. Furthermore, a technique that allows the leakage of small-molecule gases (helium, hydrogen) from their interface to be close to (or approximately equivalent to) the gas permeability of the resin material by directly bonding the metal and resin has not been reported to date. In this invention, an alumina film is formed on the surface of the aluminum connector, creating a porous surface layer with columnar structures of average height 10-100 nm. Furthermore, the average area ratio of the protrusions of these columnar structures within a randomly sampled 400 nm viewing angle of the porous surface layer is 5.0-26.0%, and the average number of columnar structures within a randomly sampled 400 nm viewing angle of the porous surface layer is 500-2000. Because the alumina film has this specific porous structure (uneven structure) with finely dispersed columnar structures, at the interface between the connector and the resin liner, during their bonding, the resin of the liner enters from the surface side of the alumina film towards the inside of the porous surface of the alumina film, and the resin and connector... The seamless bonding at the nanometer (nm) level ensures sufficient reliability of the bonding state. Furthermore, based on the porous surface layer with the specific porous structure described above, a so-called labyrinth effect is achieved, significantly extending the interface length between the interface and the resin (liner). (Preferably, based on its structure, the interface length can be extended such that the average total perimeter of the columnar cross-sections within a randomly sampled 400nm viewing angle of the porous surface layer is 15000–50000nm). Therefore, even gases with small molecular structures such as hydrogen and helium can be effectively suppressed from the interface between the interface and the resin liner. Thus, the inventors of this invention conjecture that the high-pressure vessel of this invention, based on its structure, effectively suppresses gas leakage from the metal-resin bonding interface to a high degree, regardless of the use of O-rings, resulting in very high airtightness. Additionally, according to this invention, very high airtightness can be ensured even without the use of O-rings between the connector and the liner, thus enabling a simple structure without O-rings at the joint of the high-pressure vessel. Furthermore, the inventors of this invention speculate that by not using an O-ring at the joint between the connector and the liner, costs such as the material cost of the O-ring can be reduced, thereby improving economy or increasing design freedom.

[0023] According to the present invention, a high-pressure vessel can be provided that does not necessarily require the use of an O-ring at the joint between the connector and the resin liner, and can prevent gas leakage from the interface between the connector and the resin liner to a high degree, even if the sealed gas is a gas with a small molecular structure such as hydrogen or helium, thus exhibiting excellent airtightness. Attached Figure Description

[0024] Figure 1 This is a schematic longitudinal sectional view illustrating a preferred embodiment of the high-pressure tank of the present invention. Detailed Implementation

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in the following description and drawings, the same or equivalent elements will be labeled with the same reference numerals, and repeated descriptions will be omitted.

[0026] Figure 1 This is a schematic longitudinal sectional view illustrating a preferred embodiment of the high-pressure tank of the present invention. Figure 1 The high-pressure tank 1 shown includes: a resin liner 10 for the high-pressure tank, having an opening; an aluminum connector 11 installed in the opening; and a reinforcing layer 12 formed on the outer surface of the liner 10.

[0027] (Resin lining 10)

[0028] The inner liner 10 has an opening and an internal storage space for storing high-pressure gas. Furthermore, the inner liner 10 is made of resin. There are no particular limitations on the resin used; it can be appropriately selected based on the type of fluid, ensuring that the fluid (gas, etc.) filled inside does not leak to the outside. For example, thermoplastic resins such as general-purpose plastics, general-purpose engineering plastics, and super engineering plastics, as well as thermosetting resins suitable for general resin molding such as injection molding and hot pressing, are preferred. Such thermoplastic or thermosetting resins can be used alone or in combination of two or more.

[0029] As general-purpose plastics, general-purpose engineering plastics, super engineering plastics, and thermosetting resins, known materials can be used appropriately without particular restrictions. However, from the viewpoint that even repeated filling and releasing of high-pressure gas (especially high-pressure hydrogen) can further suppress the generation of defects and enable the production of molded articles with excellent weld characteristics more efficiently, resin compositions of polyamide resins such as polyamide 6 (nylon 6), polyamide 66 (nylon 66), polyamide 11 (nylon 11), polyamide 12 (nylon 12), and polyamide 610 are preferred; polyethylene synthetic resins or ethylene synthetic resins such as high-density polyethylene (HDPE), polyethylene, and ethylene copolymers; and gas barrier materials such as polyoxymethylene (POM) and ethylene-vinyl alcohol copolymer (EVOH). Among these, resin compositions of polyamide 6, polyamide 66, and polyamide 11 are particularly preferred.

[0030] Furthermore, without impairing the effects of the present invention, various additives may be incorporated into the resin used to form the liner 10. By incorporating additives, effects such as increased elastic modulus of the resin (due to the effect of inorganic fillers such as carbon fiber and glass fiber), polarity changes (due to the effect of rubber, elastomers, and other resins), degradation inhibition, and delayed decomposition reaction (due to the effect of antioxidants, etc.) can be expected to further improve the bonding strength with the joint, improve the wettability of the resin-metal interface, further improve the interfacial adhesion, and improve long-term stability (heat resistance, resistance to damp heat, water resistance, etc.). There are no particular limitations on such additives. Examples include flame retardants, antioxidants, UV absorbers, hydrolysis inhibitors, light stabilizers, UV absorbers, antistatic agents, lubricants, release agents, nucleating agents, viscosity modifiers, colorants, dyes, antibacterial agents, silane coupling agents, and other surface treatment agents; fibrous materials such as graphite, carbon nanofibers, and other carbon nanofillers; synthetic fibers such as glass fiber, carbon fiber, and aramid; and natural fibers such as cellulose, chitin, and chitosan; as well as inorganic fillers such as layered silicates like mica and kaolinite, calcium carbonate, calcium phosphate, titanium dioxide, silicon dioxide, whiskers, alumina, boron nitride, aluminum nitride, silicon nitride, silicon carbide, diamond, and zinc oxide. Such additives can be used alone or in combination with two or more. Furthermore, there are no particular limitations on the formulation method of such additives. For example, conventional methods can be used, such as mixing the resin and additives in a solvent, or melting and mixing the resin and additives using an extruder with a single or multi-screw screw, a rubber roller mill, or a Banbury mixer. Additionally, when using a low-viscosity thermosetting resin as the resin, compounding can also be performed using a rotary mixer.

[0031] (Aluminum connector 11)

[0032] An aluminum connector 11 is installed at the opening of the liner 10. Thus, the aluminum connector 11 installed at the opening of the liner 10 functions as an opening for the high-pressure tank 1 and as a mounting part for installing piping and valves to the tank body.

[0033] Furthermore, the aluminum connector 11 is a connector formed by forming an aluminum oxide film on its surface. Such an aluminum connector 11 formed by forming an aluminum oxide film on its surface can be formed, for example, by performing an anodizing process on an aluminum substrate (the substrate for the connector).

[0034] There are no particular restrictions on the aluminum substrate used for such aluminum connectors 11. Any aluminum material capable of forming an alumina coating can be used, such as known pure aluminum or aluminum alloys. Furthermore, there are no particular restrictions on the composition of the aluminum alloy; various alloys, represented by those specified in the Japanese Industrial Standards (JIS), can be used. For example, alloys from the 1000 to 8000 series specified by JIS can be used, as well as various die-casting grade alloys. The 1000 series refers to high-purity aluminum alloys; the others are alloys containing copper (Al-Cu alloys, 2000 series), manganese (Al-Mn alloys, 3000 series), silicon (Al-Si alloys, 4000 series), magnesium (Al-Mg alloys, 5000 series), magnesium-silicon (Al-Mg-Si alloys, 6000 series), zinc-magnesium (Al-Zn-Mg alloys, 7000 series), or other metals suitable for various purposes (Al-other metal alloys, 8000 series). Not only high-purity aluminum alloys can be used, but also various currently used aluminum alloys. There are no particular limitations on the shape of the aluminum substrate used for connector 11; for example, an aluminum substrate can be processed into the desired shape according to the application of the high-pressure vessel using known metalworking methods such as cutting, stamping, machining, and grinding. Alternatively, the desired aluminum substrate can also be manufactured by forging or casting.

[0035] Furthermore, the alumina film formed on the surface of the aluminum connector 11 is an alumina film that is a porous surface layer having columnar structures with an average height of 10 to 100 nm dispersedly arranged. The average area ratio of the protrusions of the columnar structures within a randomly sampled 400 nm viewing angle of the porous surface layer is 5.0 to 26.0%, and the average number of columnar structures within a randomly sampled 400 nm viewing angle of the porous surface layer is 500 to 2000. In addition, the term "porous surface layer" as used in this invention refers to a layer made of alumina having an uneven structure (an uneven structure with columnar structures as protrusions) formed by the dispersed arrangement of the columnar structures.

[0036] The alumina film has a porous surface layer composed of columnar structures with an average height of 10 to 100 nm. If the average height of such columnar structures is less than the lower limit, it is difficult to control the height during manufacturing, and it is difficult to adequately embed (engage) the resin of the liner 10 during bonding. On the other hand, if the average height of the columnar structures exceeds the upper limit, the processing for forming such columnar structures is time-consuming and costly. From the viewpoint of performance and productivity, the average height of such columnar structures is more preferably 10 to 80 nm, and particularly preferably 20 to 70 nm. Furthermore, the method for measuring the average height of the columnar structures will be described later.

[0037] Furthermore, for the porous surface layer of the alumina film, the average area ratio of the protrusions of the columnar structures within a randomly sampled 400 nm viewing angle needs to be 5.0% to 26.0%. When such an average area ratio of protrusions is less than the lower limit, the labyrinth effect cannot be fully utilized by the porous surface layer, and gas leakage from the interface between the liner and the connector cannot be prevented to a sufficiently high level. On the other hand, if the average area ratio of the protrusions exceeds the upper limit, there are too many columnar structures (protrusions), and therefore the formation of the uneven structure is insufficient, the labyrinth effect of the porous surface layer cannot be fully utilized, and gas leakage from the interface between the liner and the connector still cannot be prevented to a sufficiently high level. Furthermore, the average area ratio of the protrusions of the columnar structures within a randomly sampled 400 nm viewing angle is more preferably 10.0% to 20.0%, particularly preferably 10.0% to 18.0%, and most preferably 11.0% to 17.5%. The method for measuring the average area ratio of the protrusions of the columnar structures will be described later.

[0038] Furthermore, the porous surface layer of the alumina film requires an average number of columnar structures within a randomly sampled 400 nm viewing angle of 500 to 2000. If the average number of such columnar structures is less than the lower limit, the surface area of ​​the portion of the resin embedded (biting into) the liner 10 becomes smaller, making it difficult to achieve a sufficient labyrinth effect based on the uneven structure of the columnar structures at the joint interface, thus failing to prevent gas leakage from the joint interface between the liner and the connector to a sufficiently high level. On the other hand, if the average number of columnar structures exceeds the upper limit, it is not possible to sufficiently ensure the space for resin or the like to penetrate, making it difficult for resin or the like to penetrate the porous surface and fully exhibit the labyrinth effect, thus failing to prevent gas leakage from the joint interface between the liner and the connector to a sufficiently high level. Furthermore, from the viewpoint of the amount of resin embedded (biting into) the liner 10 and ensuring the space for resin penetration into the liner 10, the average number of columnar particles within a 400nm viewing angle of such random sampling is more preferably 500 to 1200, more preferably 650 to 1000, and particularly preferably 670 to 900. The method for determining the average number of columnar particles will be described later.

[0039] Furthermore, for the porous surface layer of the alumina film, the average total perimeter of the columnar cross-sections within a randomly sampled 400 nm viewing angle is preferably 15,000–50,000 nm (more preferably 19,000–45,000 nm, particularly preferably 20,000–40,000 nm). If the average total perimeter of the columnar cross-sections is less than the lower limit, there is a tendency for the columnar structure to become thinner and the strength of the columnar structure to become insufficient, and there is also a tendency for the so-called labyrinth effect to be insufficiently obtained, and for gas leakage from the interface between the liner and the joint to be prevented to a sufficiently high level. On the other hand, if the average total perimeter of the columnar cross-sections exceeds the upper limit, the size of the space formed by the columns of the porous surface layer becomes smaller, and therefore there is still a tendency for the labyrinth effect based on the uneven structure of the columns to be insufficiently obtained, and for gas leakage from the interface between the liner and the joint to be prevented to a sufficiently high level. The method for measuring the average total perimeter of the columnar cross-sections will be described later.

[0040] The following describes the methods for measuring various characteristics (such as the average height of columnar structures) of the porous surface layer of the alumina film.

[0041] <Method for determining the average height of columnar structures in porous surface layers>

[0042] The average height of the columnar structures in the porous surface layer of the alumina film can be determined as follows: First, a cross-section of the porous surface layer of the alumina film is photographed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to obtain an image of the cross-section (e.g., an SEM image or a TEM image). Furthermore, such cross-sectional images are taken from at least five randomly sampled areas (five fields of view) within the porous surface layer. Next, the average height of the columnar structures in the porous surface layer is determined by observing the obtained SEM or TEM images. The following method is used to determine the average height of the columnar structures in the porous surface layer.

[0043] Specifically, firstly, for each image of a porous surface layer containing 30 to 100 columnar protrusions (images of at least 5 randomly sampled locations (5 fields of view) of the porous surface layer, measuring 365 nm vertically and 630 nm horizontally), the columnar protrusion with the largest (maximum value) distance (height) between its upper end and the boundary of the surrounding layer is selected, along with the columnar protrusion with the smallest (minimum value). The midpoint between this maximum and minimum value is taken as the average value. The difference between this average value and the maximum (or minimum) value is used as three times the standard deviation (σ) to obtain a normal distribution. The average height of the porous surface layer in that image is then calculated based on the obtained normal distribution. Next, the average height of the columnar protrusions in the porous surface layer is calculated by averaging the average heights of all images (images of the aforementioned randomly sampled locations).

[0044] Furthermore, the porous surface layer of the alumina film is mainly composed of alumina (or aluminum hydroxide), which is non-conductive. Therefore, there is a concern that electrons may remain on the sample surface during SEM observation, leading to charging. Thus, it is preferable to coat the surface with a conductive material (Au, Pt, Os, C, etc.) to prevent charging during SEM observation. There are no particular restrictions on the coating conditions; any known conditions suitable for the measurement can be used. Additionally, a magnification of 20,000 to 200,000x is preferable for SEM observation. Furthermore, the magnification is preferably set appropriately according to the film's structure, such that the diameter of the pores in the porous surface layer of the alumina film can be measured, and at least 100 pores can be identified in the measurement area (for example, the measurement area can be set to approximately 500 nm). 2 (Situations such as left and right).

[0045] <Methods for determining the average convexity area ratio of columnar structures in porous surface layers, the average number of columnar structures in porous surface layers, and the average total perimeter of columnar cross-sections>

[0046] The average value of the convex area ratio of the columnar bodies in the porous surface layer of the alumina film, the average value of the number of columnar bodies in the porous surface layer, and the average value of the total perimeter of the columnar body cross-section can be calculated as follows.

[0047] First, images (e.g., SEM images) of the surface and cross-section of 3-5 randomly sampled regions of the porous surface layer of the alumina film are obtained. Next, each image is imported into image analysis software, and after noise removal and other necessary processing, it is converted to an 8-bit image (grayscale). Within this grayscale image, a region for processing is randomly selected (a randomly sampled region with a 400nm viewing angle). This selection of processing regions is achieved by randomly sampling at least 5 regions with a 400nm viewing angle from the images of the 3-5 randomly sampled regions of the porous surface layer (all grayscale images) (ensuring a total of at least 5 processing regions are selected for the following processing). Then, a brightness threshold is set for each processing region. For example, a brightness level above a specified threshold is selected in the 8-bit image. Next, particle separation processing is performed on particles selected based on brightness levels above the set threshold. This particle separation processing is performed using any known method. For example, representative methods include image segmentation methods, such as automatic thresholding, edge-based methods, and morphological methods used in the segmentation of objects in contact, such as Watershed transformation. Specifically, for example, particles can be separated using Watershed refinement. This separation method automatically cuts off or separates the contact portions of individual particles. Specifically, it involves first creating an Euclidean distance map (EDM), then creating the final erosion points (UEPs) of the EDM, and extending each UEP (maximum or vertex of the EDM) as far as possible to the edge of the particle or the edge of other UEPs (growing regions). Then, based on the obtained images of all treated areas (images of at least five randomly sampled treated areas), the average convexity area ratio of the columnar structures in the porous surface layer, the average number of columnar structures in the porous surface layer, and the average total perimeter of the columnar cross-sections can be calculated. Furthermore, the above series of analyses can be performed using one image analysis software, or a combination of multiple image analysis software, or various analysis and processing software. Specifically, ImageJ (an image processing software developed by the National Institutes of Health) and commercially available image analysis software can be used.

[0048] More specifically, for example, SEM images of the surface and cross-section of 3-5 randomly sampled regions of the porous surface layer of the alumina film are captured, and each image is analyzed using ImageJ image analysis software. Then, the SEM images of the surface and cross-section of the randomly sampled 3-5 regions of the porous surface layer are imported into ImageJ, converted to 8-bit (256 levels, grayscale), and the processing area (randomly sampled regions at a 400nm viewing angle) is randomly selected. Furthermore, the processing area is selected by randomly sampling at least 5 regions at a 400nm viewing angle from the images of the 3-5 randomly sampled regions of the porous surface layer. Then, using the images of each processing area, the images are binarized, and watershed thinning processes are performed to separate the particles. Based on the results of all processed areas, the average value of the convex area ratio of the columnar structures in the porous surface layer, the average value of the number of columnar structures in the porous surface layer, and the average value of the total perimeter of the columnar cross-sections are obtained. As a preferred example of this method, the following method can be cited.

[0049] First, SEM images of the surface and cross-section of 3-5 randomly sampled regions of the porous surface layer of the alumina coating are captured. Next, for each captured image, noise-removed images are analyzed using ImageJ 1.47 (developed by the National Institutes of Health, available at http: / / rsbweb.nih.gov / ij / ). Then, each image is converted to 8 bits (256 levels, grayscale), and a processing region (a randomly sampled region at a 400nm viewing angle) is randomly selected (this processing region is determined by randomly sampling at least 5 regions at a 400nm viewing angle from the images of 3-5 randomly sampled regions of the porous surface layer (all grayscale images)). When analyzing these processed regions, binarization is performed first. Furthermore, in the brightness threshold setting process, a predetermined threshold is selected as the boundary that can be visually identified as the first layer, and brightness levels above this threshold are selected from the images. Regarding the threshold setting, specifically, in the image obtained by 8-biting the SEM image that can distinguish the first layer (surface layer) from other layers, the brightness (e.g., 150) of the end of the other layer (e.g., the end of the intermediate layer connected to the porous surface layer, or the end of the aluminum substrate in the absence of an intermediate layer) is used as the threshold. Next, in the image of the processed area, particles selected based on brightness above the set threshold are separated. This particle separation process is based on Watershed thinning. First, an EDM (Euclidean Distance Map) is created, and then the final erosion points (UEPs) of the EDM are created. Adjacent faces (boundary faces) are determined by extending each UEP (extreme erosion point, maximum or vertex of the EDM) as far as possible to the end (edge) of the particle, or to the boundary (edge) of another (adjacent) growing (expanding) UEP region. Then, a minimum value is determined, and blocks of dimensions above that value are counted. The area, perimeter, and coordinates of each block are further obtained using ImageJ. Then, based on the results of all the obtained images (images of more than 5 randomly sampled processing areas), the average value of the convex area ratio of the columnar bodies in the porous surface layer, the average value of the number of columnar bodies in the porous surface layer, and the average value of the total perimeter of the columnar body cross section are calculated.

[0050] (1) Determination of the average convex area ratio of columnar bodies within a 400 nm viewing angle of randomly sampled porous surface layers:

[0051] First, as mentioned earlier, images (e.g., SEM images) of 3 to 5 randomly sampled regions of the porous surface layer are used. For each image, the image is imported into software (ImageJ, etc.) and converted to 8 bits (256 levels, grayscale). In the resulting grayscale image, a processing region is randomly selected (a region at a 400nm viewing angle randomly sampled from the surface image). (Furthermore, the processing region is selected by randomly sampling at least 5 regions at a 400nm viewing angle from the grayscale image of 3 to 5 randomly sampled regions of the porous surface layer.) After binarizing the randomly sampled image within a 400nm viewing angle (with a threshold value that allows selection of convex parts based on SEM image contrast), watershed thinning is performed to segment the image (thus modulating the overlap of convex parts). The area of ​​each block is calculated, and the sum of the areas of each block is used to calculate the sum of the areas of the columnar parts forming convex parts in the image of a processed region. The proportion of the columnar parts' area within the image of the processed region (convexity area ratio) is then calculated. Thus, for each image of a randomly sampled region (processed region) at 5 or more locations with a 400nm viewing angle, the convexity area ratio is calculated. Then, the average convexity area ratio of all images (images of randomly sampled regions at 5 or more locations with a 400nm viewing angle) is calculated, and this average is used as the average convexity area ratio of the columnar parts within the randomly sampled 400nm viewing angle.

[0052] (2) Determination of the average number of columnar structures within a 400 nm viewing angle from a random sample of the porous surface layer:

[0053] First, as mentioned earlier, images (e.g., SEM images) of 3 to 5 randomly sampled regions of the porous surface layer are used. For each image, the image is imported into software (ImageJ, etc.) and converted to 8 bits (256 levels, grayscale). In the resulting grayscale image, a processing region (a region randomly sampled from the surface image at a 400nm viewing angle) is randomly selected. (Furthermore, the processing region is selected by randomly sampling at least 5 regions at a 400nm viewing angle from the grayscale image of 3 to 5 randomly sampled regions of the porous surface layer.) After binarizing the image within the randomly sampled 400nm viewing angle (the image of the processing region), it is segmented using Watershed thinning to obtain the total number of blocks in the image of the processing region. Thus, for each image of a region with at least 5 randomly sampled 400nm viewing angles, the total number of blocks is obtained. Then, the average number of blocks in all images (images of 5 or more randomly sampled regions at a 400nm viewing angle (processing area)) is calculated, and the obtained average is used as the average number of columns in the randomly sampled 400nm viewing angle.

[0054] (3) Determination of the average total perimeter of columnar cross-sections within a 400 nm viewing angle of randomly sampled porous surface layers:

[0055] First, as mentioned earlier, images (e.g., SEM images) of 3 to 5 randomly sampled regions of the cross-section of the porous surface layer are used. For each image, the image is imported into software (ImageJ, etc.) and converted to 8 bits (256 levels, grayscale). In the resulting grayscale image, a processing region (a region randomly sampled from the cross-sectional image at a 400nm viewing angle) is randomly selected. (Furthermore, the processing region is selected by randomly sampling at least 5 regions at a 400nm viewing angle from the grayscale image of 3 to 5 randomly sampled regions of the porous surface layer.) After binarizing the image within the randomly sampled 400nm viewing angle (the image of the processing region), the perimeters of each counted block in the image of the processing region are added together to obtain the total perimeter of the columnar cross-section in the image of the processing region. Thus, for each image of the randomly sampled 5 or more regions at a 400nm viewing angle (the processing region), the total perimeter of the columnar cross-section is obtained. Then, the average of the total perimeter of the columnar cross-sections of all images (images of more than 5 randomly sampled regions with a 400nm viewing angle) is calculated, and the obtained average value is used as the average of the total perimeter of the columnar cross-sections within the randomly sampled 400nm viewing angle.

[0056] By employing the method described above, the average value of the convex area ratio of the columnar bodies in the porous surface layer of the alumina film, the average value of the number of columnar bodies in the porous surface layer, and the average value of the total perimeter of the columnar body cross-section can be obtained respectively.

[0057] Furthermore, the alumina film formed on the aluminum connector 11 only requires the formation of the aforementioned specific porous surface layer on its outer surface (the surface opposite to the substrate side). For example, multiple anodizing processes can be performed to form a layer (intermediate layer) composed of the alumina film other than the aforementioned porous surface layer, and then the aforementioned specific porous surface layer is formed on top of this layer, resulting in a film having both an intermediate layer (the layer between the aluminum substrate and the porous surface layer) and a porous surface layer. As such an intermediate layer, a porous intermediate layer with an average film thickness of 300 nm to 20 μm is preferred, more preferably a porous intermediate layer with an average film thickness of 300 nm to 15 μm, and particularly preferably a porous intermediate layer with an average film thickness of 300 nm to 10 μm. Furthermore, as such an intermediate layer, a porous intermediate layer with micro-recesses having an average pore size of 5 to 50 nm (more preferably 5 to 30 nm, and particularly preferably 10 to 20 nm) is preferred. Furthermore, as such a porous interlayer with micro-recesses, it is more preferable that the average interpore spacing of the micro-recesses is 5–90 nm (more preferably 10–70 nm, particularly preferably 20–50 nm). In addition, the shape of the micro-recesses in the porous interlayer with micro-recesses is not particularly limited. For example, it can be any shape, such as a oriented shape growing in a direction perpendicular to the surface of the aluminum substrate, a shape growing in a random direction relative to the surface of the aluminum substrate without orientation (e.g., an ant-nest structure, a three-dimensional mesh structure where the recesses are wrapped in a three-dimensional mesh, a random shape, etc.), or a straight shape without orientation. Furthermore, such a porous interlayer in an alumina film can also be formed from multiple layers.

[0058] There are no particular limitations on the method used to manufacture the aluminum connector 11 having such an alumina coating. Except for appropriately selecting conditions to manufacture a porous surface layer that satisfies the aforementioned conditions, the method described in International Publication No. 2015 / 083845 can be applied. Furthermore, when using the method described in International Publication No. 2015 / 083845, anyone skilled in the art can appropriately change conditions such as voltage and processing time according to a design aimed at creating the aforementioned porous surface layer, thus forming the desired porous surface layer.

[0059] As a method for manufacturing an aluminum connector 11 having such an alumina film, it is preferable to use, for example, anodizing an aluminum substrate (multiple anodizing processes are performed if an intermediate layer is also formed) to form an alumina film having the porous surface layer on the surface of the aluminum substrate.

[0060] There are no particular limitations to this anodizing process (which may involve multiple treatments depending on the situation), and well-known anodizing methods can be appropriately employed. For example, an aluminum substrate can be used as the anode, an insoluble electrode as the cathode, and electrolysis can be performed in an acidic solution to anodize the surface of the aluminum substrate (multiple anodizing treatments may be performed depending on the situation) to form an aluminum oxide film (anodic oxide film) having the porous surface layer described above.

[0061] There are no particular restrictions on the electrolysis method, cathode, electrolyte, concentration and temperature of the electrolyte, current density, voltage, and electrolysis time used in such anodizing process. The anodizing process method and conditions that can form the shape and structure of the target alumina film, i.e. the shape and structure of the target porous surface layer (and the shape and structure of the target porous intermediate layer in the case of forming an intermediate layer) can be appropriately selected.

[0062] There are no particular restrictions on the electrolytic method used in this anodizing process; for example, cyclic electrolysis, constant current electrolysis, constant potential electrolysis, pulsed constant potential electrolysis, and pulsed constant current electrolysis can be used. Furthermore, there are no particular restrictions on the cathode used in this anodizing process; for example, any cathode can be used as long as it does not react with acidic solutions or has significantly low conductivity. Insoluble conductive materials such as platinum, lead, stainless steel, and carbon are commonly used. Additionally, there are no particular restrictions on the electrolyte solution used in this anodizing process; for example, acidic solutions such as phosphoric acid, chromic acid, oxalic acid, and sulfuric acid solutions can be used, and one or a mixture of two or more of them can be used.

[0063] Furthermore, the concentration of the acidic solution used in such anodizing processing can be appropriately selected based on the type of electrolyte solution used, the shape and structure of the porous surface layer and / or the intermediate layer to be formed, etc. For example, when using an aqueous sulfuric acid solution as the acidic solution, a concentration of 0.01 to 10 mol / L is preferred, and when using an aqueous oxalic acid solution as the acidic solution, a concentration of 0.01 to 10 mol / L is also preferred. Additionally, the temperature of the acidic solution is preferably -10 to 80°C, more preferably -10 to 60°C. By performing anodizing processing at this temperature, an alumina film (a film composed of the porous surface layer, or a film composed of an intermediate layer and a porous surface layer, etc.) can be easily formed on the surface of the aluminum substrate. When the temperature of such an acidic solution is below the lower limit, there is a tendency for the columnar structure of the porous surface layer and / or the porous intermediate layer to be difficult to form; on the other hand, if the upper limit is exceeded, the dissolution of the anodized film becomes severe, thus there is a tendency for the columnar structure to be difficult to form. Furthermore, the electrolytic processing time in the anodizing process is preferably 30 seconds to 100 minutes.

[0064] As a preferred method for such anodizing treatment, we will take the case of forming an alumina film (anodic oxide film) having an intermediate layer and a porous surface layer by performing multiple anodizing treatments as an example. Such a method can be exemplified as follows: First, as the first stage of anodizing treatment, an acidic solution composed of one or more acidic solutions such as phosphoric acid, chromic acid, oxalic acid, and sulfuric acid (more preferably an acidic solution composed of one or two acidic solutions of oxalic acid and sulfuric acid) is used as the electrolyte. The concentration of the acidic solution is 0.01–10 mol / L, the treatment temperature is -10–60°C, the voltage is 0.01–30 V (more preferably 0.01–20 V), and the current density is 0.002–2.0 A / dm³. 2 Electrolysis is performed under conditions where the processing time is 30 seconds to 100 minutes (more preferably 30 seconds to 90 minutes) to form an anodic oxide film on the surface of the aluminum substrate. Then, as an anodizing treatment, with the surface side forming the porous surface layer, the aluminum substrate is used as the anode and a platinum plate as the cathode. An acidic solution composed of one or more of the following acidic solutions (more preferably one or two of oxalic acid and sulfuric acid) is used as the electrolyte. The concentration of the acidic solution is 0.01 to 10 mol / L, the processing temperature is -10 to 60°C, the voltage is 0.01 to 30 V (more preferably 0.1 to 30 V), and the current density is 0.002 to 2.0 A / dm³. 2 Electrolysis is performed under conditions where the processing time is 30 seconds to 100 minutes (more preferably 30 seconds to 90 minutes) to form an anodic oxide film. This results in a connector made of an aluminum substrate having an alumina film (anodic oxide film), which is composed of an intermediate layer formed of alumina and the porous surface layer. Furthermore, when the anodizing process is performed in multiple stages, it is more preferable to set the processing conditions such that (the thickness of the layer formed by the first stage) ≤ (the thickness of the layer formed by subsequent stages). This makes it easier to form the columnar structure with the porous surface layer. Additionally, when the intermediate layer is formed through multiple anodizing processes, depending on the processing conditions, the intermediate layer can be a porous intermediate layer with micro-recesses. Moreover, such an intermediate layer, depending on the processing conditions, can be the same as the porous intermediate layer described in International Publication No. 2015 / 083845.

[0065] Furthermore, before performing such anodizing, conventional pretreatments (polishing, fine-line finishing, imparting a pear-skin surface / pattern, etc.) or pretreatments (degreasing, etching, cleaning, electrolytic polishing, etc.) can be appropriately performed. Pretreatment preferably involves degreasing, etching, cleaning, or electrolytic polishing of the surface to be treated. Additionally, the method described in International Publication No. 2015 / 083845 can be appropriately used as a method for such pretreatment.

[0066] In addition, during such anodizing, appropriate post-treatments (washing, sealing, etc.) can be performed after each stage of anodizing. As a post-treatment for such anodizing, it is preferable to treat the aluminum oxide film on the surface of the aluminum substrate with a phosphoric acid solution (phosphoric acid treatment).

[0067] In this way, aluminum fittings can be obtained by anodizing an aluminum substrate of the desired shape corresponding to the design of the high-pressure gas cylinder (multiple anodizing processes may be performed as appropriate).

[0068] (Reinforcement layer 12)

[0069] The reinforcing layer 12 is formed to cover the outer surface of the inner liner 10. Furthermore, in this embodiment, the reinforcing layer 12 is formed to cover the entire outer surface of the inner liner 10 and a portion of the joint 11. Such a reinforcing layer 12 is not particularly limited and can be the same reinforcing layer known to be used in the field of high-pressure tanks as a reinforcing layer for resin-based inner liners; for example, a layer made of fiber-reinforced resin or a layer made of thermosetting resin may be appropriately used. Moreover, such a reinforcing layer 12 is preferably a layer made of fiber-reinforced resin. As such a fiber-reinforced resin, carbon fiber reinforced resin (CFRP) or glass fiber reinforced resin (GFRP) may be appropriately used, and the type is not particularly limited, but from the viewpoint of being able to more efficiently exhibit strength and elastic modulus capable of withstanding high pressure, carbon fiber reinforced resin (CFRP) is preferred.

[0070] (Method for manufacturing high-pressure tanks)

[0071] Hereinafter, a preferred method for manufacturing a high-pressure tank having a resin liner 10, an aluminum connector 11 installed in the opening of the resin liner 10, and a reinforcing layer 12 formed on the outer surface of the liner 10 will be described.

[0072] As a method for manufacturing such a high-pressure tank, a method comprising the following steps is preferred: a first step of manufacturing a connector mounting liner in which an aluminum connector 11 is mounted at the opening of the liner 10; and a second step of winding fibers (or fiber bundles) pre-impregnated with thermosetting resin around the outer surface of the connector mounting liner, and then curing the thermosetting resin by heating, thereby forming a reinforcing layer 12 on the outer surface of the connector mounting liner.

[0073] The first step is to manufacture a connector mounting liner in which an aluminum connector 11 is installed at the opening of the liner 10. As such a step, it is preferable to use the following step: to bond the resin forming the liner 10 with the aluminum connector 11 to obtain a connector mounting liner (intermediate structure) in which an aluminum connector 11 is installed at the opening of the liner 10.

[0074] Thus, as a method for bonding the resin forming the liner 10 with the aluminum connector 11 to obtain a connector liner with the aluminum connector 11 installed at the opening of the liner 10, there are no particular limitations. The following method can be appropriately adopted: The structure formed by bonding the resin liner 10 and the aluminum connector 11 can be manufactured by appropriately employing a known method for molding the resin. As for such a resin molding method, any molding method that can bond the connector 11 to the resin forming the liner 10 via a porous surface layer of an alumina film formed on the surface of the aluminum connector 11 is acceptable. For example, injection molding, compression molding, melt pressing, and pressure stamping methods can be used. Among such methods, injection molding is preferred. As for such an injection molding method, there are no particular limitations; a conventional injection molding method using an injection molding machine can be used.

[0075] As a method for obtaining a connector mounting liner using such injection molding, the following method is preferred: Prepare an injection mold, open the mold, install a pre-formed aluminum connector 11 into the mold at the opening of the liner 10, close the mold, inject resin such that molten resin contacts at least a portion of the surface of the aluminum connector 11 (including the portion containing the porous surface layer), and then solidify the resin by cooling the mold. This allows the aluminum connector 11 to bond with the resin via the porous surface layer, resulting in a connector mounting liner with the aluminum connector 11 mounted at the opening of the resin liner 10. Furthermore, the molding pressure and injection speed can be appropriately set according to the molding machine used, the type of resin, and the shape of the molded product. Additionally, known conditions can be appropriately adopted for other injection molding conditions depending on the type of resin used. In this way, by bringing the molten resin into contact with the aluminum connector 11, the resin enters the uneven interior of the porous surface layer of the aluminum connector 11. After curing, it can be in a state in which the resin constituting the liner 10 is fully embedded (bitten) into the interior of the alumina film. Thus, the aluminum connector 11 and the liner 10 can be joined in a gapless state at the angstrom to nanometer level, and the airtightness of the joint interface can be very high.

[0076] Furthermore, the method of bonding the resin forming the liner 10 with the aluminum connector 11 to obtain a connector mounting liner with the aluminum connector 11 installed at the opening of the liner 10 is not limited to the above method. For example, the same bonding process as described in International Publication No. 2015 / 083845 can be appropriately used.

[0077] Furthermore, the second step involves winding fibers (or fiber bundles) pre-impregnated with thermosetting resin around the outer surface of the joint mounting liner, followed by heating to cure the thermosetting resin, thereby forming a reinforcing layer 12 on the outer surface of the joint mounting liner. There are no particular limitations on the method for forming the reinforcing layer 12; known methods can be appropriately used. However, a method that involves winding fibers (or fiber bundles) pre-impregnated with thermosetting resin using a so-called fiber winding method, followed by heating to cure the thermosetting resin, is preferred. Furthermore, known conditions can be appropriately used for the curing conditions of such thermoplastic resin. There are no particular limitations on the thermosetting resin used to impregnate the fibers in the manufacture of the reinforcing layer 12; for example, epoxy resin, unsaturated polyester resin, etc., can be used. Moreover, there are no particular limitations on the method of winding the fibers impregnated with thermosetting resin; known methods can be appropriately used.

[0078] Above, refer to Figure 1Preferred embodiments of the high-pressure tank of the present invention have been described, but the high-pressure tank of the present invention is not limited to the above embodiments. For example, the high-pressure tank of the above embodiment is composed of a resin liner 10 for high-pressure tanks, an aluminum connector 11, and a reinforcing layer 12, but the structure of the high-pressure tank of the present invention is not limited to the above embodiments, and a protective layer may be further provided on the surface of the reinforcing layer 12. As such a protective layer formed on the surface of the reinforcing layer 12, a protective layer used in the field of high-pressure tanks as a protective layer formed on the reinforcing layer can be used appropriately, for example, a layer composed of fiber-reinforced resin or thermosetting resin can be preferably used. Such a protective layer can also preferably be manufactured by the so-called fiber winding method. Thus, the high-pressure tank of the present invention, as long as it has the resin liner for high-pressure tanks, the aluminum connector, and the reinforcing layer, can also appropriately have other structures (e.g., the protective layer, a valve installed on the connector, a spare O-ring arranged between the connector and the liner for the purpose of obtaining higher airtightness, etc., and an O-ring used to ensure the airtightness between the valve and the connector, etc.).

[0079] Furthermore, in the high-pressure tank of the above embodiment, the liner 10 has only one opening, but the number of openings is not limited and can be two or more depending on the application. Additionally, when there are multiple openings, the number of connectors 11 that engage with the openings is also essentially the same as the number of openings.

[0080] In addition, such high-pressure tanks are useful as tanks for hydrogen (high-pressure hydrogen tanks) because of their extremely high airtightness. For example, they can be preferred as high-pressure hydrogen tanks for fuel cell vehicles.

[0081] [Example]

[0082] The present invention will now be described in more detail based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0083] (Examples 1-4 and Comparative Examples 1-2)

[0084] In each embodiment, test pieces (based on the ISO 19095 series) were prepared by bonding an aluminum sample with an alumina coating to resin under the manufacturing conditions shown in Table 1, as follows.

[0085] First, prepare an aluminum sample (JIS standard alloy number "A6061", shape: a circular plate with a hole in the center). Next, degrease the aluminum sample with acetone, and then wash the degreased sample with deionized water.

[0086] Next, using the aluminum sample as the anode, and employing a 5-50% by weight aqueous solution of sulfuric acid (manufactured by Wako Pure Chemical Industries, Ltd., purity 96-98%) as the electrolyte, and a platinum plate as the cathode (insoluble electrode), an alumina film was formed on the surface of the aluminum sample under the anodizing conditions shown in Table 1. Furthermore, during multiple anodizing treatments, the following post-treatments were performed: the anodized samples were washed with water, dried, immersed in a phosphoric acid solution, stirred at room temperature for 1-30 minutes, and then washed again with water. Thus, by performing anodizing treatment (including the post-treatments described above), an aluminum sample with an alumina film (aluminum sample with film) was prepared.

[0087] Next, as follows, in the central hole portion of the obtained coated aluminum sample (shape: annular circular plate), the central hole (void portion) is blocked by resin (polyamide 6), and the circular plate-shaped resin is bonded by injection molding using an injection molding device, thereby forming a test piece. That is, firstly, the coated aluminum sample is mounted in an injection molding mold. Next, the mold was installed in an injection molding apparatus (Selby Semiconductor, small injection molding machine, C.Mobile). As shown in Table 1, under injection molding conditions of resin temperature 290°C and mold temperature 125°C, polyamide 6 (hereinafter referred to as "PA6") was injected into the aluminum sample with the aluminum oxide coating (the sidewall of the central hole) in contact with the coated aluminum sample. After cooling to room temperature, the circular plate of resin composed of polyamide 6 was joined with the central hole of the coated aluminum sample to obtain a test piece (the test piece was obtained by joining the resin composed of polyamide 6 with the coated aluminum sample through injection molding).

[0088] Table 1

[0089]

[0090] [Characteristic evaluation of the test pieces obtained in Examples 1-4 and Comparative Examples 1-2]

[0091] <Observations on Porous Surface Layers>

[0092] The alumina films in the aluminum samples with films obtained before injection molding in Examples 1-4 and Comparative Examples 1-2 were observed by SEM. The average height of the columnar bodies constituting the porous surface layer formed in each alumina film, the average value of the total perimeter of the columnar body cross section, the average value of the convex area ratio of the columnar body, and the average value of the number of columnar bodies were calculated as follows.

[0093] First, using a SEM (Hitachi High Technology Manufacturing Co., Ltd., trade name: S-5500), the average height of the columnar structure was determined as follows: Specifically, SEM images of the surface of the porous alumina film and a longitudinal section perpendicular to that surface were first captured. These SEM images were taken from five randomly sampled areas of the porous surface layer. Furthermore, to prevent electrons from becoming trapped on the sample surface and causing charging, a sample coated with a conductive material was used, and the measurements were performed at a magnification of 200,000x. Next, for each of the captured longitudinal cross-sectional images (SEM images showing a cross-section of 365nm longitudinally and 630nm transversely of 30-100 columnar structures as convex parts, magnified 200,000 times), the columnar structure with the largest and smallest height in the image was selected. The midpoint between these two values ​​was taken as the average value. The difference between this average value and the maximum value was taken as three times the standard deviation to calculate a normal distribution. Based on this normal distribution, the average height of the porous surface layer in a single SEM image was calculated. Then, the average height of the columnar structures was calculated by averaging the average heights of the porous surface layers from all SEM images (images of the five randomly sampled regions mentioned above). The results are shown in Table 2.

[0094] Next, SEM images of the surface and cross-section of 3 to 5 randomly sampled areas of the porous surface layer of the alumina film were used. The images were analyzed using ImageJ software to obtain the average total perimeter of the columnar cross-section, the average convex area ratio of the columnar section, and the average number of columns. That is, SEM images of 3 to 5 randomly sampled regions of the porous surface layer are used. For each image, the image is imported into the image analysis software ImageJ and converted to 8-bit (256 levels (white is 255, black is 0), grayscale). In the obtained grayscale image, a processing region (randomly sampled 400nm viewing angle) is randomly set (in addition, the setting of this processing region is done by randomly sampling 5 regions with a 400nm viewing angle from the grayscale images of 3 to 5 randomly sampled regions of the porous surface layer). After binarizing the concave and convex interfaces in the image of the processing region by setting a threshold, watershed processing (watershed thinning processing) embedded in the image analysis software ImageJ is performed in order to segment (adjust) the overlap between the convex parts. Based on the results of all obtained images, the average value of the total perimeter of the columnar cross section, the average value of the convex area ratio of the columnar body, and the average value of the number of columns are calculated.

[0095] In this measurement process, firstly, SEM images of the surface and cross-section of 3-5 randomly sampled regions of the porous surface layer of the alumina film are obtained. These images are then imported into ImageJ 1.47 image analysis software, and noise is removed to obtain an 8-bit image (grayscale). This 8-bit image is then analyzed using ImageJ 1.47. During this analysis, a processing region (randomly sampled 400nm viewing angle: processing area) is randomly selected from the obtained 8-bit image (the processing area is determined by randomly sampling 5 regions at a 400nm viewing angle from 3-5 randomly sampled grayscale images of the porous surface layer). The image of this processing region is then binarized. Furthermore, when setting a brightness threshold for the image, a threshold is calculated based on the brightness of the location that can be visually identified as the boundary of the first layer. A threshold of 150 is set, and brightness values ​​of 150 or higher are selected from the 8-bit image. Next, the particles selected based on brightness values ​​above the set threshold are separated. This particle separation process is based on watershed thinning embedded in the image analysis software ImageJ 1.47, thereby separating the particles. Specifically, an EDM (Earth Depth Model) is first created, followed by UEPs (User-Defined Particles). Adjacent faces (boundary faces) are determined by extending each UEP as far as possible to the ends (edges) of the particles or to the boundaries (edges) of other (adjacent) growing (expanding) UEPs. Next, a minimum value is set, and blocks above this minimum size are counted. ImageJ is then used to calculate the area, perimeter, and coordinates of each block. Thus, for each image of five randomly sampled 400nm viewing areas (five processing areas), the area, perimeter, and coordinates of the blocks are calculated.

[0096] Furthermore, when determining the average area ratio of the convex portion of the columnar structures within a 400nm viewing angle of randomly sampled porous surface layers, firstly, as described above, surface images of 3 to 5 randomly sampled locations from the surface of the porous surface layer are used. For each image, an 8-bit image (grayscale) is obtained. Then, a processing region (a randomly sampled region within a 400nm viewing angle) is randomly defined within the resulting grayscale image (the processing region is defined by randomly sampling 5 regions within a 400nm viewing angle from the grayscale images of 3 to 5 randomly sampled regions of the porous surface layer). After binarizing the image of the processing region, watershed thinning processing is performed. The area of ​​each segmented block is calculated within the image of the randomly sampled 400nm viewing angle region (processing region). Next, the total area of ​​each block is calculated, and the total area of ​​the columnar portions formed as convex portions in the image of the processed region of the surface is calculated. Next, using the total area of ​​the columnar portions, the proportion of the columnar portion's area within the image of the processed region (convexity area ratio) is calculated, thus determining the convexity area ratio of the image of the processed region. Then, by calculating the average convexity area ratio of all images (images of the processed region at 5 randomly sampled locations with a 400nm viewing angle), the average convexity area ratio of the columnar portions within the randomly sampled 400nm viewing angle is determined. The results are shown in Table 2.

[0097] Furthermore, the average number of columnar structures within a 400nm viewing angle of randomly sampled areas of the porous surface layer was calculated as follows. First, as described above, surface images of 3 to 5 randomly sampled regions from the porous surface layer were used to obtain 8-bit images (grayscale) for each image. A processing region (a randomly sampled region within a 400nm viewing angle) was then randomly selected from the resulting grayscale images (the processing region was determined by randomly sampling 5 regions within a 400nm viewing angle from the grayscale images of 3 to 5 randomly sampled regions of the porous surface layer). The processed region image was binarized and then subjected to Watershed thinning processing. The total number of segments was calculated, and the number of columnar structures within the processed region image at that 400nm viewing angle was determined accordingly. Then, the average number of columnar structures within a randomly sampled 400nm viewing angle was calculated by averaging the total number of segments across all images (images of the 5 randomly sampled processed regions). The results are shown in Table 2.

[0098] Furthermore, the average value of the total perimeter of the columnar cross-sections within a 400nm viewing angle of randomly sampled areas of the porous surface layer is calculated as follows. First, as described above, cross-sectional images of 3 to 5 randomly sampled regions of the porous surface layer are used to obtain 8-bit images (grayscale) for each image. Then, a processing region (a randomly sampled region within a 400nm viewing angle) is randomly set in the obtained grayscale image (the processing region is set by randomly sampling 5 regions within a 400nm viewing angle from the grayscale images of 3 to 5 randomly sampled regions of the porous surface layer). After binarizing the image of the processing region, the outer perimeters of each block (in the cross-section) that has been counted as described above are added together (the outer perimeters of all blocks (in the cross-section) within the 400nm viewing angle are added together) to obtain the total value of the perimeter of the columnar cross-sections in the image of the processing region. Then, the average value of the total perimeter of the columnar cross-sections within the randomly sampled 400nm viewing angle was calculated by averaging the total values ​​of the total perimeters of all images (images of the processed area at 5 randomly sampled locations). The results are shown in Table 2.

[0099] <Determination of He Leakage Amount Using the He Leakage Method>

[0100] Test pieces (injection molded articles) obtained in Examples 1-4 and Comparative Examples 1-2 were used respectively. To evaluate the airtightness of the joint between the aluminum sample and the resin in each test piece, the He leakage method was used to determine the He leakage amount. In this measurement, He was first used as the pressurized gas, and one side of the test piece was pressurized with He at 0.5 MPa. A He leakage detector (PFEIFFER VACUUM, ASM340, minimum detectable leakage rate (vacuum method): <5 × 10⁻⁶) was used. -13 Pa·m 3 Calculate the amount of He that permeates to the other side using the formula (Pa·m). Use this value as the He leakage rate (Pa·m). 3The detection and quantification are performed using a He leak detector. More specifically, in order to measure the He leaking from one side of a test piece to the other using a He leak detector, the test is conducted as follows: A front chamber and a rear chamber are formed using the test piece as a partition (the front chamber is positioned on the lower side, and the rear chamber on the upper side). He (gas) is introduced into the front chamber side (the lower area) defined by the test piece to pressurize one side of the test piece (the front chamber side). The He (gas) leaking through the test piece towards the other side (the rear chamber side) is introduced into the rear chamber (the upper area). The amount of He (gas leaking through the test piece) introduced into the rear chamber (the He leakage amount) is measured using a He leak detector. Furthermore, the pressurization using He (gas) is performed in a thermostatic bath (made by ESPEC) at room temperature. Thus, in order to evaluate airtightness, the He leakage rate (Pa·m) 10 seconds after the start of the test (initially pressurized with He at 0.5 MPa) is calculated. 3 The results are shown in Table 2.

[0101] In addition, regarding airtightness, the He leakage rate is 10... -4 ~10 -1 Pa·m 3 In the case of / s, it is considered that liquid leakage from the interface makes it difficult to prevent gas leakage at a high level. On the other hand, when the He leakage rate is 10 -5 Pa·m 3 At speeds below a certain value, it is considered to possess exceptionally good airtightness, preventing not only liquid leakage but also gas leakage to a high degree. Furthermore, it is particularly effective when the He leakage rate is less than 10... -7 Pa·m 3 At a rate of / s, this leakage rate can be considered to be the level of He permeation and diffusion into the resin material (PA6), and it can be assumed that there is no gas leakage (permeation) from the interface (the interface between the aluminum sample and the resin (PA6)). Therefore, when the He leakage rate is less than 10 -7 Pa·m 3 At a rate of / s, it is considered to possess an even higher level of airtightness, capable of preventing gas leakage to an extremely high degree. Furthermore, when determining the He leakage rate using a circular plate (without a central hole) made solely of aluminum instead of a test piece, the result becomes 10. -10 Pa·m 3 He leakage at the / s level.

[0102] Table 2

[0103]

[0104] The results shown in Table 2 clearly indicate that an alumina film (anodic oxide film) was formed on the surface of the aluminum sample in the test piece. This alumina film has a porous surface layer composed of columnar structures with an average height of 10–100 nm. The average convexity area ratio of the columnar structures within a randomly sampled 400 nm viewing angle of the porous surface layer is 5.0–26.0%, and the average number of columnar structures within a randomly sampled 400 nm viewing angle of the porous surface layer is 500–2000 (using the test pieces obtained in Examples 1–4). The He leakage rate is 2.1 × 10⁻⁶. - 6 Pa·m 3 The results show that the test pieces obtained in Examples 1-4 can prevent He leakage from the interface between the aluminum sample and the resin (PA6) to a sufficiently high level. In particular, it is known that the He leakage in the test pieces manufactured in Examples 2-4 was 5.5 × 10⁻⁶. -9 Pa·m 3 Below / s, it is considered that there is no gas leakage (permeation) from the interface (the interface between the aluminum sample and the resin (PA6), thus gas leakage can be prevented at a higher level. On the other hand, it is known that even if a porous surface layer composed of columnar bodies with an average height of 10 to 100 nm is formed on the surface of the aluminum sample of the test piece, if the average number of columnar bodies in a 400 nm viewing angle of a random sample of the porous surface layer is less than 500, and the average convex area ratio of the columnar bodies in a 400 nm viewing angle of a random sample of the porous surface layer is outside the range of 5.0 to 26.0% (in the case of test pieces obtained in Comparative Examples 1 to 2), the following situation occurs: the He leakage becomes unmeasurable (0.1 <), and the airtightness is worse than that of the test pieces obtained in Examples 1 to 4.

[0105] The results show that by forming an alumina film on the surface of the aluminum connector, creating a porous surface layer with columnar structures of average height of 10–100 nm, and by randomly sampling the columnar area ratio within a 400 nm viewing angle of the porous surface layer to a value of 5.0–26.0%, and by randomly sampling the number of columnar structures within a 400 nm viewing angle of the porous surface layer to a value of 500–2000, it is possible to prevent leakage of gases with small molecular structures, such as hydrogen and helium, from the interface between the resin liner and the aluminum interface at the opening in a high-pressure tank with at least one opening, to a sufficiently high level.

[0106] As explained above, according to the present invention, a high-pressure tank can be provided that does not necessarily require the use of an O-ring at the joint between the connector and the resin liner. Even if the sealed gas is a gas with a small molecular structure such as hydrogen or helium, leakage of gas from the interface between the connector and the resin liner can be prevented to a high degree, resulting in excellent airtightness. Therefore, the high-pressure tank of the present invention is particularly useful as a high-pressure gas container for fuel cell vehicles (FCVs), such as a hydrogen tank for FCVs.

[0107] Label Explanation

[0108] 1: High-pressure tank;

[0109] 10: Lining;

[0110] 11: Aluminum connector;

[0111] 12: Reinforcement layer.

Claims

1. A high-pressure tank, comprising: The high-pressure tank has a resin liner and at least one opening. An aluminum connector is installed at the opening; and A reinforcing layer is formed on the outer surface of the liner. An aluminum oxide film is formed on the surface of the aluminum connector. The alumina film has a porous surface layer composed of columnar structures with an average height of 10–100 nm. The average area ratio of the protrusions of the columnar structures within a 400 nm viewing angle of the porous surface layer was 5.0%–26.0%, and The average number of columnar structures within a 400nm viewing angle of the porous surface layer is 500 to 2000.

2. The high-pressure tank according to claim 1, wherein, The average perimeter of the columnar cross-sections randomly sampled from the porous surface layer within a 400nm viewing angle is 15000–50000nm.

3. The high-pressure tank according to claim 1 or 2, wherein, The high-pressure tank is a tank for hydrogen.

4. The high-pressure tank according to claim 1 or 2, wherein, The aluminum connector is joined to the liner via a porous surface layer on the surface of the aluminum connector.

5. The high-pressure tank according to claim 1 or 2, wherein, The junction between the aluminum connector and the liner has a He leakage rate of less than 10 mmol / L after 10 seconds from the start of the He leakage test. -7 Pa·m 3 / s airtightness.

6. The high-pressure tank according to claim 1 or 2, wherein, The layers in the alumina film other than the porous surface layer are layers with an average film thickness of 300 nm to 20 μm.

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