Hydrogen fuel hose

A hydrogen fuel hose having a wall formed by an innermost layer of rubber cured by an agent not containing any metal oxide, or sulfur, and a metallic barrier layer formed in the wall surrounding it. The barrier layer may be a metal laminated layer. The hose is used for conveying e.g. a hydrogen fuel in a fuel-cell vehicle. The hose has a high impermeability to hydrogen gas and a high electric resistance, and does not cause any dissolution of ions in hot steam that may cause the pollution of the fuel-cell catalyst.

DETAILED DESCRIPTION OF THE INVENTION 
 &lsqb;Hydrogen Fuel Hose&rsqb; The hose according to this invention is a hose of the multilayer wall construction used for conveying a hydrogen fuel in a fuel-cell vehicle. It may be a smooth or straight hose, or a curved hose, or may have a portion like bellows. Its multilayer wall is composed of at least an innermost rubber layer and a metallic barrier layer formed in the wall surrounding it. The innermost rubber layer is of a rubber material cured by an agent which is free of any metal oxide, or sulfur, and the metallic barrier layer is impermeable to hydrogen gas. The metallic barrier layer preferably contacts the innermost rubber layer. It may alternatively form a part of the wall surrounding the innermost rubber layer and be surrounded by a fiber-reinforced layer. The multilayer wall may alternatively be composed of an innermost rubber layer, a metallic barrier layer, an intermediate rubber layer, a fiber-reinforced layer and an outer rubber layer. The innermost rubber and metallic barrier layers, or every two adjoining layers are preferably bonded to each other with an adhesive strength of at least 5 kgf/inch. Any known and appropriate adhesive, or treatment may be employed for bonding those layers to each other. The hose preferably has an electric resistance of at least 10 6 &OHgr;·cm, and more preferably at least 10 8 &OHgr;·cm as a whole. Such an electric resistance can be realized if the innermost or outer rubber layer is formed from a material having a correspondingly high electric resistance. The electric resistance of the hose as a whole can be measured by applying a predetermined voltage across its ends each fitted, or not fitted with a clinching metal fixture. The hose may be of any desired size. It preferably has an inside diameter of, say, 5 to 50 mm to allow gas to flow in as large a quantity as possible. While its pressure resistance may be selected as desired, it preferably has a level of, say, 1.5 MPa to allow a large amount of hydrogen gas to flow at a high pressure. 
 &lsqb;Innermost Rubber Layer&rsqb; The innermost rubber layer is formed from a material cured by an agent not containing any metal oxide, such as zinc oxide, or any sulfur. It may be any kind of rubber if it is curable by an agent not containing any metal oxide, or sulfur. It is undesirable to use any rubber containing a large amount of metal compound, or sulfur even for any purpose other than curing. The treatment of the hose prior to use is preferred to ensure that no uncertain matter be dissolved from its innermost rubber layer after the hose is connected. More specifically, the hose is filled with an extraction medium (e.g. pure water) and treated under specific heat aging conditions, so that any such matter may be removed by extraction prior to use or piping. The layer is preferably of a material having hot water resistance, or more specifically resisting deterioration by hot water having a temperature of 120° C. Another preferred material has acid and/or alkali resistance. Still another preferred material has an electric resistance of at least 10 6 &OHgr;·cm, and more preferably at least 10 8 &OHgr;·cm. More specific examples of materials are EPDM, EPM, silicone-modified EPDM or EPM, FKM and butyl rubber. Examples of butyl rubber include butyl rubber (IIR), and halogenated butyl rubber, such as brominated butyl rubber (Br-IIR) or chlorinated butyl rubber (Cl-IIR). EPDM or EPM cured by a peroxide without relying upon zinc oxide is, among others, preferred. Moreover, the innermost rubber layer preferably has a hardness of 50 to 80 (IRHD) and a thickness of at least 0.2 mm. 
 &lsqb;Metallic Barrier Layer&rsqb; The metallic barrier layer is not particularly limited in construction, but may be formed even by a metal pipe with or without a bellows portion if no flexibility is required. It is, however, preferably formed as a metal laminated layer formed by having a metal foil held between two resin films. Although the foil may be of any metal, it is preferably of aluminum, stainless steel (SUS), titanium, etc. as they are excellent in at least one of fluid impermeability, ductility and deformation adaptability. Aluminum or stainless steel is, among others, preferred. Although the thickness of the foil is not limited, the foil preferably has a thickness of at least 5 &mgr;m, and more preferably, say, 7 to 50 &mgr;m to provide a good fluid barrier, while ensuring that the hose be satisfactorily flexible. Although the thickness of the resin film is not limited, each resin film preferably has a thickness of, say, 5 to 200 &mgr;m. The resin films are preferably of polyamide (PA), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), an ethylene-vinyl alcohol copolymer (EVOH), or polyphenylene sulfide (PPS). Polyamides are, among others, preferred as they have a good balance of properties including heat resistance. The metal laminated layer may be formed by any method if it can form a tight layer. It is, however, preferably formed by spiral winding or longitudinal lapping of a tape of a laminated sheet prepared by having a metal foil held between two resin films, so that a tightly sealed layer may be formed rapidly. The laminated sheet is preferably so wound that one portion thereof may have an edge overlapping that of another to ensure an effective seal. Every two adjoining overlapping portions are preferably bonded to each other with an adhesive. Such bonding is also preferable to ensure that the layer retains its cylindrical shape. 
 &lsqb;Intermediate Rubber Layer, Fiber-Reinforced Layer and Outer Rubber Layer&rsqb; The intermediate rubber layer may be of any rubber that may be suitable from the standpoints of fluid impermeability, flexibility, cost and adhesiveness to any adjoining layer. Butyl rubber (IIR) is, however, preferred for its high impermeability to hydrogen gas. The fiber-reinforced layer may be of any known type and material, including PET, vinylon, rayon, aramid and nylon yarns. The end count of the reinforcing yarns and the angle of their braiding are preferably selected to ensure the formation of a layer having e.g. a satisfactorily high pressure resistance. Although the material of the outer rubber layer is not limited, it is preferably formed from EPDM, an allyl glycidyl ether-ethylene-epichlorohydrin terpolymer (GECO), chlorosulfonated polyethylene rubber (CSM) or acrylic rubber (ACM). All of these rubbers are preferred for their weatherability, ozone resistance, heat resistance and flexibility. Moreover, the outer rubber layer is preferably of a material having an electric resistance of at least 10 6 &OHgr;·cm, and more preferably at least 10 8 &OHgr;·cm. 
 &lsqb;Connection of Hose&rsqb; At the end of the hose where it is connected with a pipe, the hose (or its innermost rubber layer) preferably has its inner wall surface adhered to the outer wall surface of the pipe, and more preferably has its end clinched by an appropriate fitting. The pipe is preferably of stainless steel (SUS) and has its outer wall surface coated with, or dipped in an adhesive. A stainless steel sleeve is preferably used as the clinching fitting, though a fitting of another metal, such as aluminum or iron, or a fitting plated with such a metal is equally useful. 
 EXAMPLES 
 &lsqb;Preparation of Hoses&rsqb; Hoses according to Examples 1 and 2 embodying this invention and Comparative examples 1 and 2 were prepared as shown in Table 1. Each hose had its inner most wall layer formed from the material shown in Table 1. Each hose (or the smooth portion of the hose according to Comparative Example 2) had an inside diameter of 15 mm, and was otherwise as described below. Every two adjoining wall layers, if any, were bonded to each other with an adhesive. 
 Example 1 The hose had an innermost wall layer of rubber formed from EPDM cured by a peroxide without zinc oxide, and having a thickness of 1.2 mm. The innermost rubber layer was surrounded by a laminated layer formed from a laminated sheet having an aluminum foil held between two polyamide films, an intermediate rubber layer formed from IIR and having a thickness of 0.5 mm, a reinforcing layer formed by winding PET yarn spirally in a common way, and finally an outer rubber layer formed from EPDM and having a thickness of 1.0 mm. 
 Example 2 The hose had an innermost wall layer of rubber formed from FKM cured by a peroxide, and having a thickness of 1.2 mm. Its wall was otherwise identical in construction to that of the hose according to Example 1. 
 Comparative Example 1 The hose had an innermost wall layer of rubber formed from EPDM cured by sulfur, and having a thickness of 1.2 mm. Its wall was otherwise identical in construction to that of the hose according to Example 1. 
 Comparative Example 2 The hose was a stainless steel (SUS) bellows pipe having a wall thickness of 1.0 mm. 
 &lsqb;Evaluation of Hoses&rsqb; Each hose was evaluated for various properties or characteristics as stated below. The results are shown in Table 1. In Table 1, each Circle (&xcirc;) or “OK” indicates that the results were more than expected, and each Double Circle (&ocir;) indicates that the results were by far more than expected, while each x or “NG” indicates that the results were not what had been expected. Table 1 also includes the evaluation of each hose for its cost. Flexibility: An attempt was made to wind each hose about a mandrel having a diameter of 300 mm. The &ocir; indicates that the hose was easy to wind thereon, and each &xcirc; indicates that the hose could be wound, while the x indicates that the hose could not be wound. Permeability: Referring to FIG. 1 , each hose 1 closed at one end was connected at the other end to a bottle 2 containing helium gas (as a substitute for hydrogen gas) maintained at a pressure of 1 MPa, and was left to stand for a week in a bath of water immediately under a hood 4 in a tank 3 maintaining the water at a temperature of 80° C. Then, bubbles 5 of helium gas leaving the hose 1 through its wall were all collected in a cylinder 6 for three days, and the total amount thereof was determined. It was used for calculating the amount of helium gas diffused per meter of hose length per hour. In Table 1, each “OK” indicates that the amount did not exceed 5 ml/m/h, while the “NG” indicates that it exceeded 5 ml/m/h. Hydrogen Resistance: Each hose was filled with hydrogen gas having a pressure of 0.9 MPa, was left to stand at room temperature for 168 hours, and was thereafter examined for any change in flexibility or other physical properties. Examination was made of each hose (or the innermost rubber layer of the hose according to Example 1 or 2 or Comparative Example 1, and a bellows pipe of Comparative Example 2) to see if there had not occurred any hardening or softening, or any marked reduction in sealing property, pressure resistance or adhesive strength. Steam Resistance: Each hose was filled with pure water, was left to stand at a temperature of 120° C. for 168 hours, and was thereafter examined for any change in flexibility and other physical properties. Examination was made as explained under Hydrogen Resistance. Acid Resistance: Each hose was filled with an aqueous solution of acetic acid having a concentration of 33%, was left to stand at a temperature of 120° C. for 168 hours, and was thereafter examined for any change in flexibility and other physical properties. Examination was made as explained under Hydrogen Resistance. Alkali Resistance: Each hose was filled with an aqueous solution of ammonia having a concentration of 10%, was left to stand at a temperature of 120° C. for 168 hours, and was thereafter examined for any change in flexibility and other physical properties. Examination was made as explained under Hydrogen Resistance. Extract Analysis: Each hose was filled with ultrapure water, and left to stand at a temperature of 120° C. for 168 hours. Then, the water was removed from the hose, and analyzed for any extract. The hose was concluded as “OK” when the water had a total extract content not exceeding 1% by weight, and contained not more than 1 ppm of metal ion, halogen or sulfur. Electric Resistance: Each hose had its innermost and outermost wall layers examined for their volume specific resistances in accordance with the JIS K 6911 method. The layers were concluded as “OK” when they showed a value of at least 10 6 &OHgr;·cm. Each hose (or the bellows pipe according to Comparative Example 2) had its volume specific resistance examined as a whole by having a voltage of 500 V applied across both ends thereof each fitted with a stainless steel sleeve. The hose was concluded as “OK” when it showed a value of at least 10 6 &OHgr;·cm. Pressure Resistance: Each hose was closed at one end, and connected at the other end with a hydraulic pump, and a water pressure of 3 MPa was applied to the hose. The hose was concluded as “OK” when there was no leakage of water from it, or any rupture thereof. Heat Resistance: Each hose was subjected to 168 hours of heat treatment at 120° C., was closed at one end, and was connected at the other end with a hydraulic pump, and a water pressure of 3 MPa was applied to the hose. The hose was concluded as “OK” when there was no leakage of water from it, or any rupture thereof. Adhesive Strength: Each hose was subjected to 168 hours of heat treatment at 120° C., and its adhesive strength between every two adjoining wall layers was measured by a customary method. The hose was concluded as “OK” when every two adjoining wall layers thereof showed an adhesive strength of at least 5 kgf/inch. 1 TABLE 1 Comparative Comparative Example 1 Example 2 Example 1 Example 2 Construction Innermost layer EPDM cured by Ternary FKM EPDM cured by Stainless steel peroxide cured by sulfur bellows pipe (without ZnO) peroxide Barrier layer PP/AI/PP PA/AI/PA — — Properties Flexibility &xcirc; &xcirc; &ocir; x Permeability OK OK NG OK Pressure resistance OK OK OK OK Heat resistance OK OK OK OK Hydrogen resistance OK OK OK OK Steam resistance OK OK OK OK Acid resistance OK OK OK OK Alkali resistance OK OK OK OK Extract analysis OK OK NG OK Electric resistance OK OK OK NG Adhesive strength OK OK OK OK Cost &xcirc; &xcirc; &ocir; x While the invention has been described by way of its preferred embodiments, it is to be understood that variations or modifications may be easily made by those skilled in the art without departing from the scope of this invention which is defined by the appended claims.