pressure vessel

Abstract

To provide a resin liner and a pressure container which can be produced readily and inexpensively and have excellent pinch-off adhesion and pressure resistance.SOLUTION: A pressure container comprises a cylindrical straight barrel and a dome that is at either end of the straight barrel and has a shape to become narrower as it gets away from the straight barrel. The straight barrel and the dome are formed from a thermoplastic resin-made liner body, and an outer shell in which the external surface of the liner body is covered with a reinforcement layer composed of a cured product of a reinforced fiber composite. The liner body is produced by direct blow molding, and the molding has a pinch-off part with its tensile strength of 25 MPa or more and the tensile breaking elongation of 200% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure vessel having excellent pressure resistance, which is formed from a resin liner for a pressure vessel that can be processed by direct blow molding and has excellent pinch-off adhesion, and an outer shell in which the outer surface of the resin liner is covered with a reinforcing layer made of a cured fiber-reinforced composite material. [Background technology]

[0002] Conventionally, it has been used for storing and transporting fuel tanks, natural gas, and hydrogen gas in automobiles. As a pressure vessel (Figure 1), a pressure vessel in which a thermoplastic resin vessel body (liner) is reinforced with an outer shell made of fiber-reinforced resin material is used from the viewpoints of light weight and excellent durability (high toughness) under pressure. The main reinforcing fibers used for the outer shell are glass fiber and carbon fiber. Carbon fiber, which has a high specific strength, is used in particular to design pressure vessels with increased strength and rigidity while reducing their weight, and is therefore officially used as a tank or pressure accumulator for transporting natural gas and hydrogen.

[0003] A commonly used pressure vessel is one that comprises a resin liner (Figure 2) with a cylindrical barrel and hemispherical domes at both ends of the barrel, and an outer shell formed around the liner body. The outer shell is made by winding a fiber-reinforced resin material, consisting of long reinforcing fiber bundles impregnated with a matrix resin, around the liner body using the filament winding method (hereinafter sometimes abbreviated as FW), and then heating and curing the material to form the pressure vessel. In particular, pressure vessels intended for use in fuel-filled natural gas and fuel cell vehicles have been attracting attention in recent years. Given the potential for large-scale market demand, manufacturers are exploring ways to reduce the cost of pressure vessels.

[0004] Currently, pressure vessel liners are mainly made by injection molding (half-split) + welding processing (laser or heat) as shown in Figure 3, but there are issues such as an increase in liner quality control items and increased costs due to low productivity, so direct blow molding and rotational molding, which do not require post-processing, have been considered as cost-reduction methods.

[0005] Recently, many manufacturers have been considering using the direct blow molding method to produce prototype liners. In direct blow molding, a portion of a cylindrical hot parison, generally made of thermoplastic resin, is sandwiched between a pair of molds, forming a pinch-off portion (Figure 4) that extends in the axial direction of the liner. At the pinch-off portion, part of the hot parison is constrained by the mold, creating a portion with a different thickness from the other portions, resulting in a thinner pinch-off portion extending in the axial direction, which can easily reduce the strength of the liner itself. Therefore, each manufacturer is actively studying ways to solve the pinch-off problem that occurs during direct blow molding.

[0006] For example, Patent Document 1 (WO 2018 / 207771) is known as a resin liner having a pinch-off shape with improved pressure resistance. Patent Document 1 discloses a pressure vessel using a resin liner in which the valley shape of the pinch-off portion that occurs during direct blow molding is made gentler.

[0007] Furthermore, a blow-molded article using a resin material with excellent pinch-off adhesion is known from Patent Document 2 (WO 2013 / 172226), which discloses a blow-molded article using a resin composition in which an EVOH resin with excellent blow-moldability is blended with an olefin-based resin.

[0008] A method for producing a pressure-resistant container liner using a liquid crystal polyamide resin with excellent pinch-off adhesion is known from Patent Document 3 (WO 2006 / 112252). Patent Document 3 discloses a pressure-resistant container liner that is made of a liquid crystal polyamide resin and processed by direct blow molding, in which the parison extrusion rate is set to 0.3 kg / min to 5 kg / min, the parison temperature is set to a temperature range of the melting point + 40°C, and the pinch-off portion has a tensile elongation of 1% or more.

[0009] A blow-molded article that suppresses oxidative degradation of a resin material is known from Patent Document 4 (JP Patent Publication No. 7-32460 A). Patent Document 4 discloses a blow-molded article obtained by sandwiching a parison between molds, pinching it off, and then blowing the parison with an inert gas. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2018 / 207771 [Patent Document 2] International Publication No. 2013 / 172226 [Patent Document 3] International Publication No. 2006 / 112252 [Patent Document 4] Japanese Patent Application Publication No. 7-32460 Summary of the Invention [Problem to be solved by the invention]

[0011] However, although the inventions described in the above Patent Documents 1 to 4 improve pinch-off adhesion during direct blow molding, the levels are not satisfactory for practical use because the "hot parison extrusion rate, hot parison formation temperature," and "oxygen concentration of the inert gas blown into the hot parison," which are essential for improving pinch-off adhesion, are not fully optimized. Furthermore, there is no mention of a thermoplastic resin liner in which the pinch-off portion of the molded product of the present invention has a tensile strength of 25 MPa or more and a tensile elongation at break of 200% or more.

[0012] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thermoplastic resin liner that can be subjected to direct blow molding and has excellent pinch-off adhesion. [Means for solving the problem]

[0013] In order to solve the above problems, the pressure vessel and the method for manufacturing the pressure vessel according to the present invention have any of the following configurations: A pressure vessel comprising a cylindrical straight body portion and dome portions provided at both ends of the straight body portion and tapering away from the straight body portion, the straight body portion and the dome portions being formed by a liner body made of a thermoplastic resin and an outer shell in which the outer surface of the liner body is covered with a reinforcing layer made of a cured product of a reinforced fiber composite material, the liner body being manufactured by direct blow molding, and the pinch-off portion of the molded product having a tensile strength of 25 MPa or more and a tensile elongation at break of 200% or more. At the same time, the inner surface of the liner body is measured at a wavelength of 1,700 cm -1 ~1,750cm -1 The peak intensity ratio measured by FT-IR within the range (peak intensity of the direct blow molded product / peak intensity of the resin material before direct blow molding) is 0.005 or less The pressure vessel is characterized by the following:

[0014] Examples of the thermoplastic resin used in the liner body of the present invention include polyamide resin, polyester resin, polyethylene resin, and fluororesin, and these may be used alone or in combination. That is, the thermoplastic resin used in the liner body of the present invention is preferably at least one resin selected from the group consisting of polyamide resin, polyester resin, polyethylene resin, and fluororesin.

[0015] The thickness of the pinch-off portion formed on the dome portion of the present invention is preferably 0.90 to 1.05 times the thickness of the dome portion. [Effects of the Invention]

[0020] According to the present invention, by using a direct blow molded thermoplastic resin liner with improved pinch-off adhesion, a pressure vessel with significantly improved pressure resistance and cost competitiveness can be obtained. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a schematic diagram showing the component configuration of a pressure vessel. [Figure 2] FIG. 2 is a schematic diagram showing the shape of a resin liner. [Figure 3] 1 is a schematic diagram of an injection molded and welded resin liner. [Figure 4] This is a molded product showing the pinch-off shape of a resin liner processed by direct blow molding. [Figure 5] FIG. 1 is a schematic diagram showing a direct blow molding device. [Figure 6] 1 is a graph showing the results of FT-IR analysis of the inner surface of a resin liner. [Figure 7] This is a molded product showing the degree of pinch-off depression. [Figure 8] FIG. 2 is a schematic diagram showing the shape of a resin liner directly blow-molded in the examples. [Figure 9] 1 is a schematic diagram of an apparatus for carrying out a pressure test on a pressure vessel. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail.

[0023] The pressure vessel of the present invention comprises a cylindrical straight body portion and dome portions provided at both ends of the straight body portion and tapering away from the straight body portion, the straight body portion and the dome portions being formed by a liner body made of a thermoplastic resin and an outer shell in which the outer surface of the liner body is covered with a reinforcing layer made of a cured fiber-reinforced composite material.

[0024] <Thermoplastic resin> There are no particular restrictions on the thermoplastic resin used in the liner body of the present invention, but polyamide resin, polyester resin, HDPE resin, and fluororesin, which have excellent blow molding processability, are preferred.

[0025] The polyamide resin used in the present invention includes nylons synthesized from amino acids, lactams, or diamines and dicarboxylic acids as main raw materials.

[0026] Representative examples of such raw materials include amino acids such as 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and para-aminomethylbenzoic acid, lactams such as ε-caprolactam and ω-laurolactam, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 2-methylpentamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- / 2,4,4-trimethylhexamethylenediamine, 5-methylnonamethylenediamine, metaxylylenediamine, paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, and 1-amino-3-amino Examples of the diamine include aliphatic, alicyclic, and aromatic diamines such as methyl-3,5,5-trimethylcyclohexane, bis(4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminopropyl)piperazine, and aminoethylpiperazine, and aliphatic, alicyclic, and aromatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 5-sodium sulfoisophthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid.

[0027] Preferred polyamide resins include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polypentamethylene adipamide (nylon 56), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polyhexamethylene adipamide / polyhexamethylene terephthalamide copolymer (nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6I), polyhexamethylene adipamide / polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6T / 6I), polyxylylene adipamide (nylon XD6), and mixtures or copolymers thereof. Particularly preferred are nylon 6, nylon 66, nylon 610, nylon 6 / 66 copolymer, nylon 6 / 12 copolymer, and the like.

[0028] The polyester resin used in the present invention includes those obtained by a condensation reaction using dicarboxylic acid (or its ester-forming derivative) and diol (or its ester-forming derivative) and / or hydroxycarboxylic acid (or its ester-forming derivative) as the main raw materials.

[0029] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, anthracenedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 5-sodiumsulfoisophthalic acid; aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, and dodecanedioic acid; alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid; and ester-forming derivatives thereof.

[0030] Examples of the diol component include aliphatic glycols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, and cyclohexanediol; long-chain glycols having a molecular weight of 400 to 6,000, such as polyethylene glycol, poly-1,3-propylene glycol, and polytetramethylene glycol; and ester-forming derivatives thereof. Examples of these polymers or copolymers include polybutylene terephthalate, polybutylene (terephthalate / isophthalate), polybutylene (terephthalate / adipate), polypropylene terephthalate, polypropylene (terephthalate / isophthalate), polyethylene terephthalate, polyethylene (terephthalate / isophthalate), polyethylene (terephthalate / adipate), bisphenol A (terephthalate / isophthalate), polybutylene naphthalate, polybutylene (terephthalate / isophthalate), polypropylene naphthalate, polyethylene naphthalate, polycyclohexanedimethylene terephthalate, polycyclohexanedimethylene (terephthalate / isophthalate), poly(cyclohexanedimethylene / ethylene) terephthalate, and poly(cyclohexanedimethylene / ethylene) (terephthalate / isophthalate).

[0031] In addition, thermoplastic polyester resins exhibiting thermotropic liquid crystallinity and comprising structural units selected from aromatic oxycarbonyl units, aromatic dioxy units, aromatic dicarbonyl units, ethylenedioxy units, etc. can also be used.

[0032] Examples of the aromatic oxycarbonyl unit include those generated from p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and 4'-hydroxydiphenyl-4-carboxylic acid. Examples of the aromatic dioxy unit include those generated from 4,4'-dihydroxybiphenyl, hydroquinone, and t-butylhydroquinone. Examples of the aromatic dicarbonyl unit include those generated from terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. Examples of the aromatic iminoxy unit include those generated from 4-aminophenol. Specific examples include thermotropic liquid crystalline polyesters such as p-oxybenzoic acid / polyethylene terephthalate and p-oxybenzoic acid / 6-oxy-2-naphthoic acid.

[0033] As the polyester resin, a polyester selected from polyalkylene terephthalates such as polyethylene terephthalate, polybutylene terephthalate, and polypropylene terephthalate, polyalkylene naphthalates such as polyethylene-2,6-naphthalate and polybutylene-2,6-naphthalate, polyesters exhibiting thermotropic liquid crystallinity, and polylactic acid is preferred, and a polyester selected from polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyesters exhibiting thermotropic liquid crystallinity, and polylactic acid is more preferred.

[0034] The polyethylene resins used in the present invention include low-density polyethylene (hereinafter abbreviated as LDPE), high-density polyethylene (hereinafter abbreviated as HDPE), and linear low-density polyethylene. LDPE is produced by polymerizing ethylene under high pressure with a radical polymerization catalyst, has low crystallinity, and has a density of 0.92 g / cm. 3 HDPE is produced by polymerizing ethylene using a Ziegler catalyst, and has high crystallinity and a density of 0.95 g / cm. 3 Linear low-density polyethylene is a type of low-density polyethylene, and because its molecular structure is branched, it has higher toughness and strength than LDPE. Since the liner of the present invention preferably has high heat resistance, HDPE is preferably used.

[0035] The fluororesin used in the present invention is not particularly limited, but a preferred example is one into which a reactive functional group has been introduced.The reactive functional group is not particularly limited, but specific examples include a vinyl group, an epoxy group, a carboxyl group, an acid anhydride group, an ester group, an aldehyde group, a carbonyldioxy group, a haloformyl group, an alkoxycarbonyl group, an amino group, a hydroxyl group, a styryl group, a methacryl group, an acrylic group, a ureido group, a mercapto group, a sulfide group, an isocyanate group, and a hydrolyzable silyl group, among which an epoxy group, a carboxyl group, an acid anhydride group, an amino group, and a hydroxyl group are preferred, and a carboxyl group and an acid anhydride group are more preferred.Two or more of these reactive functional groups may be included.

[0036] Methods for introducing a reactive functional group into a fluororesin include blending a compound or resin compatible with the fluororesin and containing the functional group, copolymerizing the fluororesin with a polymerizable monomer containing the functional group or containing a functional group convertible to the functional group when polymerizing the fluororesin, using an initiator containing the functional group or containing a functional group convertible to the functional group when polymerizing the fluororesin, reacting the fluororesin with a polymerizable monomer containing the functional group or containing a functional group convertible to the functional group in the presence of a radical generator, and modifying the fluororesin by oxidation, thermal decomposition, or the like. Among these, the methods for introducing a functional group into the main chain or side chain of the fluororesin by copolymerization and the method for reacting the fluororesin with a polymerizable monomer containing a functional group in the presence of a radical generator are preferred from the viewpoints of quality, cost, and control of the amount introduced.

[0037] The polymerizable monomer containing the functional group is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, crotonic acid, himic acid, acid anhydrides thereof, glycidyl acrylate, glycidyl methacrylate, glycidyl ethylacrylate, glycidyl itaconate, vinyl acetate, vinyl propionate, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

[0038] When used as an alloy with other resins, the amount of functional groups contained in the reactive functional group-containing fluororesin is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and even more preferably 0.1 mol% or more, per gram of reactive functional group-containing fluororesin. The upper limit of the amount of functional groups is not particularly limited as long as the inherent properties of the fluororesin are not impaired, and taking into consideration deterioration of fluidity, etc., 10 mol% or less is preferred. The range can be exemplified as follows.

[0039] The structure of the fluororesin used in the present invention is not particularly limited, but it is desirable that it is composed of at least one kind of fluoroolefin, such as a homopolymer of tetrafluoroethylene or chlorotrifluoroethylene, a copolymer with hexafluoropropylene, perfluoro(alkyl vinyl ether), vinylidene fluoride, or vinyl fluoride, or a copolymer with a fluorine-free ethylenic monomer such as ethylene, propylene, butene, or alkyl vinyl ethers. More specifically, examples include polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene-hexafluoropyrene copolymer (EFEP), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), etc., but among these, from the viewpoints of high heat resistance and ease of melt molding, ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are preferred, with ETFE being more preferred.

[0040] <Reinforced fiber composite material> The reinforced fiber composite material of the reinforcing layer covering the outer surface of the liner body of the present invention is a cured product obtained by impregnating a reinforcing fiber bundle with a thermosetting resin and then heating and curing it.

[0041] The thermosetting resin used in the present invention is not particularly limited as long as it is liquid, and examples thereof include epoxy resins, unsaturated polyester resins, phenolic resins, urea resins, melamine resins, etc. In particular, epoxy resins whose precursors are compounds such as phenols, amines, carboxylic acids, and intramolecularly unsaturated carbons are preferred because of their high adhesive strength.

[0042] Glycidyl ether epoxy resins that use phenols as precursors include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, biphenyl-based epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, resorcinol-based epoxy resins, naphthalene-based epoxy resins, trisphenylmethane-based epoxy resins, phenol aralkyl-based epoxy resins, dicyclopentadiene-based epoxy resins, diphenylfluorene-based epoxy resins, and their various isomers, alkyl-, and halogen-substituted derivatives. Also included in this type are compounds in which phenolic epoxy resins are modified with urethane or isocyanate.

[0043] Examples of glycidylamine-type epoxy resins that use amines as precursors include tetraglycidyldiaminodiphenylmethane, glycidyl compounds of xylenediamine, triglycidylaminophenol, and positional isomers of glycidylaniline, as well as alkyl or halogen-substituted products.

[0044] Examples of epoxy resins that use carboxylic acids as precursors include glycidyl compounds of phthalic acid, and various isomers of glycidyl compounds of hexahydrophthalic acid and dimer acid.

[0045] Examples of epoxy resins having an intramolecular unsaturated carbon as a precursor include alicyclic epoxy resins.

[0046] The curing agent used to heat-cure the thermosetting resin of the present invention is not particularly limited as long as it cures the thermosetting resin. It may be an addition-reaction curing agent such as an amine or an acid anhydride, or a curing catalyst that induces addition polymerization such as cationic polymerization or anionic polymerization. Two or more curing agents may be used in combination. Compounds having an amino group, an acid anhydride group, or an azide group are preferred as the curing agent. Examples of suitable curing agents include dicyandiamide, alicyclic amines, aliphatic amines, aromatic amines, aminobenzoic acid esters, various acid anhydrides, phenol novolac resins, cresol novolac resins, imidazole derivatives, phenolic compounds such as t-butylcatechol, and Lewis acid complexes such as boron trifluoride complexes and boron trichloride complexes.

[0047] The type of reinforcing fiber constituting the reinforcing fiber bundle used in the reinforced fiber composite material of the present invention is not particularly limited, and examples thereof include carbon fiber, metal fiber, organic fiber, and inorganic fiber. Two or more types of these may be used.

[0048] Examples of carbon fibers include polyacrylonitrile (PAN)-based carbon fibers made from PAN fibers, pitch-based carbon fibers made from petroleum tar or petroleum pitch, cellulose-based carbon fibers made from viscose rayon or cellulose acetate, vapor-grown carbon fibers made from hydrocarbons, graphitized fibers of these, etc. Among these carbon fibers, PAN-based carbon fibers are preferably used because of their excellent balance between strength and elastic modulus.

[0049] Examples of metal fibers include fibers made of metals such as iron, gold, silver, copper, aluminum, brass, and stainless steel.

[0050] Examples of organic fibers include fibers made of organic materials such as aramid, polybenzoxazole (PBO), polyphenylene sulfide, polyester, polyamide, and polyethylene. Examples of aramid fibers include para-aramid fibers, which have excellent strength and elastic modulus, and meta-aramid fibers, which have excellent flame retardancy and long-term heat resistance. Examples of para-aramid fibers include polyparaphenylene terephthalamide fibers and copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fibers, and examples of meta-aramid fibers include polymetaphenylene isophthalamide fibers. As the aramid fiber, para-aramid fibers, which have a higher elastic modulus than meta-aramid fibers, are preferably used.

[0051] Examples of inorganic fibers include fibers made of inorganic materials such as glass, basalt, silicon carbide, and silicon nitride. Examples of glass fibers include E-glass fiber (for electrical use), C-glass fiber (for corrosion resistance), S-glass fiber, and T-glass fiber (high strength, high elastic modulus). Basalt fiber is a fiber made from the mineral basalt, and is a fiber with extremely high heat resistance. Basalt generally contains 9 to 25 mass% of FeO or FeO2, which are iron compounds, and 1 to 6 mass% of TiO or TiO2, which are titanium compounds, but it is also possible to increase the amounts of these components in the molten state and fiberize it.

[0052] The fiber-reinforced resin substrate in the first and second embodiments of the present invention is often expected to function as a reinforcing material, and therefore it is desirable that it exhibit high mechanical properties. In order to exhibit high mechanical properties, it is preferable that the reinforcing fibers include carbon fibers.

[0053] In the fiber-reinforced resin substrates of the first and second embodiments of the present invention, the reinforcing fibers are usually composed of one or more reinforcing fiber bundles each formed by bundling a large number of single fibers. When one or more reinforcing fiber bundles are arranged, the total number of filaments (single fibers) of the reinforcing fibers is preferably 1,000 to 2,000,000.

[0054] From the viewpoint of productivity, the total number of filaments in the reinforcing fibers is more preferably 1,000 to 1,000,000, further preferably 1,000 to 600,000, and particularly preferably 1,000 to 300,000. The upper limit of the total number of filaments in the reinforcing fibers may be set in consideration of the balance between dispersibility and handleability, as long as good productivity, dispersibility, and handleability are maintained.

[0055] The pinch-off portion formed on the dome portion of the liner body of the present invention will be described below.

[0056] During direct blow molding, a portion of a cylindrical hot parison made of thermoplastic resin is sandwiched between a pair of molds, forming a pinch-off region (Figure 4) in the dome region, extending axially along the liner. Because a portion of the parison resin is constrained by the mold at the pinch-off region, a region with a different thickness from the other regions is formed. This thins the axially extending pinch-off line, which is prone to reducing the strength of the pinch-off region. Therefore, to achieve both good adhesion and strength, the thickness of the pinch-off region should be at least 0.90 times the dome region thickness, with an upper limit of 1.05 times being preferred. If the pinch-off region thickness is less than 0.90 times the dome region thickness, cracks are more likely to propagate from the pinch-off region during pressure testing. On the other hand, if the pinch-off region thickness is more than 1.05 times the dome region thickness, the pinch-off region is too thick and does not adhere well when clamped in the mold.

[0057] If the pinch-off portion formed on the dome portion of the present invention is not firmly bonded, the pressure resistance of the pressure vessel will be significantly reduced, so the tensile strength at the pinch-off portion must be 25 MPa or more and the tensile breaking elongation must be 200% or more. Preferably, the tensile strength is 35 MPa or more and the tensile breaking elongation is 300% or more, and more preferably, the tensile strength is 50 MPa or more and the tensile breaking elongation is 400% or more.

[0058] Since the thermoplastic resin used for the liner body of the present invention does not contain reinforcing fibers, the upper limit of the tensile strength is substantially 50 MPa, and the upper limit of the tensile breaking elongation is 400% of the measurement limit.

[0059] <Pressure vessel manufacturing method> The method for manufacturing a pressure vessel of the present invention is a method for manufacturing a pressure vessel comprising a cylindrical straight body portion and dome portions provided at both ends of the straight body portion and tapering away from the straight body portion, the straight body portion and the dome portions being formed by a liner body made of thermoplastic resin and an outer shell having the outer surface of the liner body covered with a reinforcing layer made of a cured product of a reinforced fiber composite material, the liner body being formed by extruding a thermoplastic resin at an extrusion rate of 0.10 kg / sec to 0.50 kg / sec to form a hot parison, fixing the upper and lower ends of the hot parison in a mold, and molding the liner body by direct blow molding under molding conditions of at least 10°C above the melting point of the thermoplastic resin, and wrapping a reinforced fiber composite material around the liner body and curing it to form the outer shell.

[0060] <Method of manufacturing a resin liner for a pressure vessel> Of these, it is important to use direct blow molding (Figure 5) as a manufacturing method for the liner body that constitutes the pressure vessel. Direct blow molding is a hot parison method in which air is directly blown into the molten extruded hot parison before it cools, and is also called extrusion blow molding. Resin heated and melted in an extruder is extruded from a die head into a tubular shape (hot parison), the molten parison is sandwiched between molds, air is blown into the interior, and after cooling, the molds are opened and the molded product is removed. In the present invention, air is usually blown from above the mold, but methods in which air is blown from below or from the side of the mold are also acceptable.

[0061] In the direct blow molding process, a depression called pinch-off (Figure 4) occurs during the process of clamping the hot parison between molds. Applying pressure from within the molded product can cause cracks to propagate from the pinch-off point, leading to breakage. Therefore, in the present invention, to prevent depressions at the pinch-off point, the hot parison extrusion speed must be controlled within the range of 0.10 kg / s to 0.5 kg / s. A hot parison extrusion speed below the lower limit of 0.10 kg / s is undesirable because it prolongs the molten residence time in the extruder, leading to thermal degradation of the resin and a decrease in strength. A hot parison extrusion speed above the upper limit of 0.50 kg / s is undesirable because the hot parison discharge speed is too fast and may cause resin burning due to shear forces.

[0062] In addition, in the present invention, to strengthen the adhesion of the pinch-off portion, the hot parison formation temperature must be at least 10°C above the melting point of the thermoplastic resin. However, if the hot parison formation temperature is higher than the melting point + 100°C, the resin viscosity will decrease due to the progress of thermal decomposition of the resin, causing the hot parison to draw down and become unmoldable, which is undesirable. In addition, in the present invention, to improve the strength of the resin liner by preventing oxidative degradation, it is preferable to use an inert gas (such as nitrogen, helium, or argon) with an oxygen concentration of 10% by volume or less in the hot parison blowing process during direct blow molding. Using air in the hot parison blowing process is undesirable because it may cause oxidative degradation of the resin liner, making it brittle.

[0063] <Manufacturing method of outer shell> The present invention relates to a method for manufacturing a pressure vessel comprising a cylindrical straight body portion and dome portions provided at both ends of the straight body portion and tapering away from the straight body portion, wherein the straight body portion and the dome portions are formed from a liner body made of a thermoplastic resin and an outer shell in which the outer surface of the liner body is covered with a reinforcing layer made of a cured fiber-reinforced composite material. The method for forming the outer shell in which the outer surface of the liner body is covered with a reinforcing layer made of a cured fiber-reinforced composite material (called a filament winding method) is described below. This manufacturing method comprises the steps of (a) preparing a molded intermediate formed with reinforcing layers composed of multiple reinforcing fiber composites by wrapping a reinforcing fiber composite impregnated with a liquid thermosetting resin composition around a liner, (b) maintaining the molded intermediate at room temperature to allow the thermosetting resin composition impregnated into the reinforcing fiber composite to flow, and (c) heating the molded intermediate after step (b) to obtain a cured product of the reinforcing fiber composite impregnated with the thermosetting resin. In the present invention, room temperature refers to a temperature in the range of 5°C to 35°C.

[0064] In step (a) of preparing a molded article intermediate, a reinforced fiber composite is drawn out, impregnated with a thermosetting resin composition, and then wound onto a liner. The liner can be freely selected depending on the application of the filament winding molded article. For example, in the production of hollow pipe members, cylindrical liners that can be de-cored after the molded article is cured, or liners of various shapes that can be de-cored by melting them with heat, etc., can be used. In the production of pressure vessels, metal or resin liners that ensure sealing of the specified contents can be used. In terms of moldability and the mechanical properties of the molded article, it is preferable to wind the reinforced fiber composite impregnated with the thermosetting resin composition onto the liner by supplying the reinforced fiber composite from a head that can be freely moved relative to the liner and positioning the reinforced fiber composite so as to meet the required performance of the filament winding molded article.

[0065] In step (b), the molded article intermediate is maintained at room temperature. By maintaining the molded article intermediate at room temperature, the thermosetting resin composition impregnated into the reinforced fiber composite maintains a fluid state during at least part of the process. When the thermosetting resin composition is in a flowable state, the air bubbles that have entered the reinforcing layer of the reinforced fiber composite obtained in step (a) emerge at the surface of the reinforcing layer of the reinforced fiber composite due to buoyancy acting on the air bubbles and tight winding caused by tension remaining in the fibers when the fibers are wound around the winding core. Therefore, by maintaining the molded article intermediate at room temperature, at least some of the air bubbles in the reinforcing layer of the reinforced fiber composite can be removed, reducing the amount of voids remaining in the filament-wound molded article. The molded article intermediate can be maintained while rotating around the liner of the molded article intermediate. This prevents the fluid thermosetting resin composition from dripping or dropping due to gravity. The falling off of the thermosetting resin composition increases the fiber volume fraction (Vf:%) of the filament winding molded product, which may deteriorate the product performance. Furthermore, the fallen off thermosetting resin composition is often discarded, resulting in a decrease in product yield. The effects of falling off of the thermosetting resin composition can be eliminated by rotating the intermediate molded product while it is being held.

[0066] The holding temperature for the intermediate molded article is room temperature, but preferably within the range of room temperature, and can be any temperature ±5°C determined depending on the type of thermosetting resin composition and the conditions of use. If this range of ±5°C exceeds room temperature, the excess is rounded down. Depending on the type and conditions of use of the thermosetting resin composition, if the temperature is high, gelation of the thermosetting resin composition may proceed rapidly, preventing sufficient resin flow time. Furthermore, if the temperature is low, the viscosity of the thermosetting resin composition may decrease, and it may take longer to achieve the same level of void reduction effect than if the temperature were high. Therefore, the holding temperature is not particularly limited as long as it is room temperature, but it is preferably within a range determined depending on the type of thermosetting resin composition used and the conditions of use.

[0067] In step (c) of obtaining a cured product of the reinforced fiber composite material impregnated with the thermosetting resin, the molded intermediate product after being kept at room temperature is heated to thermally cure the thermosetting resin composition. The method for this is not limited, and any method such as a heater or an induction heating coil can be used for heating. During heating, the molded intermediate product can be held while rotating. By holding the molded intermediate product while rotating, it is possible to prevent the thermosetting resin composition from falling off.

[0068] The locations of the steps (a) of preparing a molded article intermediate, (b) of maintaining the molded article intermediate at room temperature, and (c) of obtaining a cured product of a reinforced fiber composite material impregnated with a thermosetting resin are not limited. That is, the molded article intermediate may be moved between steps (a) and (b), or the steps may be performed consecutively without moving. The molded article intermediate may be moved between steps (b) and (c), or the steps may be performed consecutively without moving. Furthermore, when the molded article intermediate is moved between steps (b) and (c), the location of the movement may be the same as the location where step (a) was performed.

[0069] The filament-wound molded products obtained by the present invention can be widely used in aerospace, leisure, and general industrial applications, including pressure vessels, rolls, propeller shafts, flywheels, fishing rods, and golf club shafts. They are particularly suitable for pressure vessels and other applications requiring strength. Pressure vessels manufactured by the present invention are suitable for use not only in hydrogen gas vehicles and natural gas vehicles, but also in ships and aircraft, as well as in stationary vessels fixed to the ground and air respirators used in hospitals and firefighters. The substances stored in these pressure vessels may be gases such as nitrogen, oxygen, argon, liquefied petroleum gas, and hydrogen, or liquefied versions of these substances.

[0070] <Method for analyzing oxidation degradation of resin liners> The resin liner of the present invention has a FT-IR measurement of 1,700 cm in order to improve the strength and toughness during pinch-off adhesion. -1 ~1,750cm -1The peak intensity ratio due to material oxidation degradation in the range (peak intensity of the direct blow molded product / peak intensity of the resin material before direct blow molding) must be 0.005 or less, preferably 0.002 or less. Specifically, the FT-IR measurement method of the present invention involves scraping out about 1 g of the surface of the molded product at three locations, and then using an FT-IR device (TENSOR II manufactured by Bruker) with the ATR method (attenuated total reflection method: detector DLaTGS, incident angle 45°, Ge prism, resolution 4 cm). -1 ) and the 1,700 cm -1 ~1,750cm -1 The degree of oxidative degradation was quantitatively evaluated based on the magnitude of the absorption peak intensity in the wavelength range of 1,700 cm. Figure 6 shows the FT-IR analysis results for the resin liners under blow molding conditions that caused oxidative degradation and blow molding conditions that suppressed oxidative degradation. As can be seen from this graph, -1 ~1,750cm -1 It can be seen that there is a difference in the absorption peak intensity in the wavelength range, and that the absorption peak is hardly observed under blow molding conditions that suppress oxidative degradation.

[0071] <Tensile test at pinch-off part of resin liner> The pinch-off portion of the dome of the direct blow molded resin liner (3 mm thick) was cut into a strip of 15 mm width x 125 mm length, and tensile tests (n=5 each) were conducted in accordance with ASTM D3039 to measure the tensile strength and tensile elongation at break. [Example]

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the descriptions of these examples. Physical properties in each example and comparative example were evaluated according to the following methods.

[0073] [Manufacturing method of resin liner] Using a Tahara accumulator-type extrusion blow molding machine, the resin liner shape shown in Figure 8 (wall thickness: 3 mm ± 0.5 mm, threaded portion: inner diameter φ13 mm, outer diameter φ24 mm) was obtained under the blow molding conditions of each example and comparative example.

[0074] <Extrusion blow molding equipment / equipment specifications> Extruder screw diameter: φ80mm Extruder screw arrangement: Deep groove full flight specification Accumulator pump capacity: 4,000cc Extruder screw rotation speed: 35 rpm Die shape: Die purge <Molding conditions> Hot parison length: 70mm Hot parison mass: 2,000g Hot parison blowing gas: Air or inert gas (nitrogen gas used).

[0075] [Hot parison extrusion speed measurement method] Under the blow molding conditions of each Example and Comparative Example, the time required for extrusion of the hot parison to a length of 70 mm (hot parison mass 2,000 g) was measured with a stopwatch (N=3), and the extrusion rate (kg / sec) was calculated.

[0076] [Method for measuring the hot parison forming temperature] The surface temperature of a hot parison (70 mm long) extruded under the blow molding conditions of each Example and Comparative Example was measured using a non-contact infrared thermograph at two locations: the extrusion side and the opposite side to the extrusion direction (hereinafter referred to as the counter-extrusion side).

[0077] [Method for measuring thickness of pinch-off part] The resin liner obtained by the resin liner manufacturing method was cut into 3 cm x 3 cm pieces for the pinch-off portion and the dome portion, and the thickness of each was measured with a vernier caliper. The thickness of the pinch-off portion relative to the thickness of the dome portion (thickness of pinch-off portion / thickness of dome portion) was then calculated.

[0078] [FT-IR measurement of resin liner (degree of oxidative degradation of resin material)] Approximately 1 g of the inner surface of the resin liner obtained above was scraped off in three places, and the measurement was performed using an FT-IR device (TENSOR II manufactured by Bruker) by the ATR method. The 1,700 cm peak, which is easily observed when the resin is thermally decomposed due to oxidative degradation, was observed. -1 ~1,750cm -1 The degree of oxidative degradation was quantitatively evaluated based on the ratio of the absorption peak intensity in the wavelength range (peak intensity of the molded resin liner product / peak intensity of the resin raw material before blow molding). The smaller this value, the less oxidative degradation there was in the resin liner.

[0079] <Measurement conditions> Light source: Globar (SiC) Detector: DLaTGS ·Resolution: 4cm -1 Accumulation count: 128 times · Accessories: Thunderdome, single reflection ATR, 45° incident angle, Ge prism used.

[0080] [Resin liner / pinch-off part tensile test (pinch-off adhesion)] The pinch-off portion of the dome of the resin liner obtained above was cut into strips of 15 mm width x 125 mm length from two locations, one on the parison extrusion direction side and one on the parison counter-extrusion direction side, and tensile strength and tensile elongation at break were measured in accordance with ASTM D3039 (n=5 for each). Note that the larger these values, the better the pinch-off adhesion of the resin liner.

[0081] [Pressure vessel manufacturing method using the filament winding method and pressure resistance testing (pressure resistance)] The liner obtained above was placed in a filament winding molding machine, and a single bundle of Toray Industries, Inc.'s "Torayca" (registered trademark) T700SC-24K carbon fiber was impregnated with a resin containing a liquid thermosetting resin composition (epoxy base:curing agent = 100:32 (mass ratio) homogeneously mixed at room temperature of 25°C) and fed to the winding core. The fiber was wound over a 60 mm wide area at a winding angle of ±83° relative to the axial direction of the winding core, resulting in a 1 mm thick laminate, preparing a molded intermediate. After winding the fiber, the intermediate was rotated at 7 rpm and held at 20°C for 15 minutes. The viscosity of the resin at the start of the hold was 1,100 mPa·s.

[0082] After the holding, the intermediate molded article was heated at 80°C for 2 hours and at 110°C for 4 hours to harden the resin and obtain a pressure vessel for pressure testing. Next, the pressure vessel obtained above was placed in a pressure vessel hydraulic bursting test apparatus shown in Figure 9, and water was pumped in and pressurized using a hydraulic pump. The burst pressure when the vessel burst was measured (N=3), and the pressure resistance was evaluated according to the following criteria.

[0083] <Pressure resistance performance / criteria> ○: Burst pressure 80MPa or more △: Burst pressure over 30MPa and less than 80MPa ×: Burst pressure 30 MPa or less.

[0084] [Raw materials] In the examples and comparative examples, the following raw materials were used.

[0085] <Reference Example 1> Thermoplastic resin used for direct blow molding Nylon 6 resin: CM1056 (Toray Industries, Inc., high viscosity, high impact blow molding grade, "Amilan" (registered trademark)) Polyethylene resin: HB-216R (Japan Polyethylene Co., Ltd., high-density polyethylene for large-scale hollow blow molding, "Novatec" (registered trademark)) Fluorine resin: P-66P (AGC, tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer for blow molding, "Fluon" (registered trademark)) Reference Example 2 Liquid thermosetting resin composition Epoxy base: Bisphenol A liquid epoxy resin ("jER" (registered trademark) 828 (manufactured by Mitsubishi Chemical Corporation)) Curing agent: a mixture of poly(propylene glycol) diamine, isophorone diamine, cyclohexylamine, and polypropylene glycol ("ARADUR" (registered trademark) 3486 (manufactured by Huntsman Japan Co., Ltd.))

[0086] [Table 1]

[0087] [Table 2]

[0088] As described above, by comparing the Examples and Comparative Examples, it is clear that the resin liner and pressure vessel of the present invention As shown in Figure 7, the pinch-off depression is improved and the pinch-off area is firmly bonded, resulting in a dramatic improvement in pinch-off adhesion and pressure resistance. [Explanation of symbols]

[0089] 101 Pressure vessels 102 Reinforced fiber composites 103 Liner container 104 nozzle part 201 Cylindrical straight body 202 Hemispherical dome sections on both ends of the straight body 301 Injection molded liner (half part) 302 Injection molded liner (halved parts welded together) 401 Direct blow molded liner 402 Pinch-off occurred in the depression 501 Single Screw Extruder 502 Direct blow molding mold 503 Hot Parison 701 Direct blow molded liner with large pinch-off recess 702 Direct blow molded liner with small pinch-off recess

Claims

1. A pressure vessel comprising a cylindrical straight body portion and dome portions provided at both ends of the straight body portion and tapering away from the straight body portion, the straight body portion and the dome portions being formed by a liner body made of a thermoplastic resin and an outer shell in which the outer surface of the liner body is covered with a reinforcing layer made of a cured product of a reinforced fiber composite material, wherein the liner body is manufactured by direct blow molding, and the pinch-off portion formed in the dome portion has a tensile strength of 25 MPa or more and a tensile elongation at break of 200% or more, and the peak intensity ratio (peak intensity of the direct blow molded product / peak intensity of the resin material before direct blow molding) measured on the inner surface of the liner body by FT-IR at a measurement wavelength range of 1,700 cm -1 to 1,750 cm -1 is 0.005 or less.

2. 2. The pressure vessel according to claim 1, wherein the thermoplastic resin used for the liner body is at least one resin selected from the group consisting of polyamide resin, polyester resin, polyethylene resin, and fluororesin.

3. 3. The pressure vessel according to claim 1, wherein the thickness of the pinch-off portion formed on the dome portion is 0.90 to 1.05 times the thickness of the dome portion.

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