Description of the Related Art [0002] Conventional hoses used to convey a refrigerant within an automotive air- conditioning system include a refrigerant barrier layer, which is typically made of a polyamide resin or a modified butyl rubber, to resist permeation of the refrigerant through the hose. Hoses constructed with a polyamide inner layer provide adequate resistance to permeation of R- 134a refrigerant, but are ineffective at containing R-744 or R- 152(a)-refrigerants proposed in future automotive air-conditioning systems. Accordingly, there exists a need for a low permeable hose for use in these air-conditioning systems.

BRIEF DESCRIPTION OF THE DRAWINGS [0003] Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: [0004] FIG. 1 is a perspective view showing a low permeable hose according to an embodiment of the present invention; and [0005] FIG. 2 is a perspective view showing a low permeable hose according to another embodiment of the present invention.

DETAILED DESCRIPTION [0006] FIG. 1 is a perspective view showing a low permeable hose 10 according to an embodiment of the present invention, with each layer of the hose being partially notched for illustration. In an embodiment, hose 10 includes an innermost layer 12, a refrigerant barrier layer 14, a first intermediate layer 16 positioned between innermost layer 12 and refrigerant barrier layer 14, a reinforcing layer 18, a second intermediate layer 20 positioned between refrigerant barrier layer 14 and reinforcing layer 18, and an outer layer 22 overlaying reinforcing layer 18. As shown in FIG. 1, an inner portion 24 of hose 10 may exhibit a three- layer structure that includes first intermediate layer 16 sandwiched by innermost layer 12 and refrigerant barrier layer 14. Alternatively, as shown in the embodiment illustrated in FIG. 2, inner portion 24 may exhibit a two-layer structure that includes innermost layer 12 and refrigerant barrier layer 14. [0007] The innermost layer 12 is a thermal and oxidation resistant material, including without limitation, polytetrafluoroethylene (PTFE), other fluorinated thermoplastic polymers such as FEP, PFA, THV and ETFE, and fluorinated thermoset polymers, such as FKM. When hose 10 is used in an automotive air conditioning system, innermost layer 12 is capable of withstanding the relatively high temperatures associated with R-744 and R-152(a) refrigeration systems and is resistant to chemical degradation caused by the lubricating oils, such as polyalkylene glycol (PAG) oils, used in automotive air-conditioning systems. Further, as will be described in further detail below, innermost layer 12 is configured to form a barrier against the ingression of water or water-vapor into the inner portion 24 of hose 10. [0008] Refrigerant barrier layer 14 includes a low permeable ethylene vinyl alcohol (EVOH) co-polymer, such as the ethylene vinyl alcohol material marketed under the trademark EVAL® by Kuraray Co., Ltd. of Osaka, Japan. Ethylene vinyl alcohol (EVOH) provides a higher level of refrigerant permeation resistance than polyamide materials, such as nylon, of comparable thickness. For example, Ethylene vinyl alcohol (EVOH) provides a level of R-744 permeation resistance nearly fifty times greater than polyamide materials of comparable thickness. Additionally, because ethylene vinyl alcohol (EVOH) is water soluble, positioning barrier layer 14 between innermost layer 12 and outer layer 22 protects refrigerant barrier layer 14 against humidity and other sources of moisture to ensure the integrity of the barrier layer material and stable permeation resistance. [0009] In an embodiment, first and second intermediate layers 16, 20 are thermoset rubber based compositions, which may include one or more of acrylonitrile/butadiene rubber (NBR), butyl rubber (HR), ethylene/propylene/diene rubber (EPDM), hydrogenated NBR (HNBR), chlorosulfonated methyl polyethylene (CSM), chlorinated polyethylene (CM), brominated butyl rubber (BIIR), chlorinated butyl rubber (CIIR), halogenated isomonoolefm/p-alkylstyrene copolymer rubber (B IMS), polychloroprene rubber (CR) or the like. EPDM and the various forms of butyl rubber (e.g., HR, BIIR, CIIR and BEVIS) are particularly suitable for use in the composition of first and second intermediate layers 16, 20 given their ability to function as a moisture impermeable protecting layer. The term "moisture impermeable protecting layer", as used herein, includes material layers that resist or prevent the passage of moisture therethrough. [0010] Outer layer 22 may also include thermoset rubber based compositions, for example, those compositions that include one or more of EPDM, CSM, CM, EAM and so forth, thermoplastic elastomer compositions such as polyamide elastomer, polyester elastomer, polyolefm elastomer, and EPDM/PP based thermoplastic elastomer compositions. An ethylene/propylene/diene (EPDM) based rubber composition is a particularly suitable material for outer layer 22 given its low cost and resistance to the relatively high temperatures found in the automotive under-hood environment. [0011] An adhesion promoting material or surface treatment may be used to facilitate bonding of innermost layer 12, first intermediate layer 16 and/or refrigerant barrier layer 14 to an adjacent layer(s) to resist separation of the layers during use of hose 10. For example, an adhesive promoting material may be applied as a separate component or "layer" or compounded into first and second intermediate layers 16, 20, innermost layer 12 and/or barrier layer 14. In another example, the surface of refrigerant barrier layer 14 may be etched (e.g., chemically or electrically) to facilitate adhesion between refrigerant barrier layer 14 and an adjacent layer, hi yet another example, the barrier layer is secured to the innermost layer using a tie layer. [0012] The vulcanization temperature of the rubber based compositions is generally at least about 140°C. Further, the vulcanization temperature of the rubber based compositions is generally lower than the melting temperature of inner most layer 12 and refrigerant barrier layer 14. [0013] The reinforcing layer 18 is not limited to the structure shown in FIGS. 1 and 2, and may be formed in either a braid-like form or in a spiral-like form. The material used may include threads, wires or the like. Reinforcing thread may include, for example, threads produced from rayon filaments, polyester filaments, nylon filaments, aromatic polyamide filaments or the like. Reinforcing wire may include, for example, hard steel wire, and more particularly brass-plated wire or zinc-plated wire for imparting corrosion resistance or adhesion. [0014] A method for producing hose 10 according to an embodiment of the present invention will now be described, hi an embodiment, innermost layer 12 may be extruded onto a flexible mandrel (not shown), as is known in the art of hose making. First intermediate layer 16 is then applied over innermost layer 12, such as, for example, by extruding the rubber based composition over innermost layer 12, spiral-winding the rubber based composition over innermost layer 12 or cigarette-wrapping the rubber based composition over innermost layer 12. Refrigerant barrier layer 14 is then extruded over first intermediate layer 16. Second intermediate layer 20 is applied over refrigerant barrier layer 14 and a plurality of reinforcing filaments, reinforcing wires or the like are braided into a spiral or blade form to form reinforcing layer 18. Finally, outer layer 22 is applied over reinforcing layer 18 in a process similar to that used to apply first and second intermediate layers 16, 20. [0015] After hose 10 has been constructed, an optional and removable wrap may be applied over outer layer 22, as is known in the art, or the hose may be place in an open pan for cure. Subsequently, the entire hose is heated. The heating temperature is at least about 120° C, and more particularly 14O0C to 170°C to cure the rubber based components of hose 10 and to create adhesion between each layer of hose 10. [0016] In an particular implementation of the invention, a PTFE composition manufactured by Dupont Corporation under the trademark TEFLON® was extruded around the periphery of a flexible mandrel through a crosshead die type thermoplastic extruder to form a 0.030 inch (0.8 mm) thick innermost layer 12. A layer of polycliroloprene rubber (CR) composition was then extruded around the periphery of innermost layer 12 through a crosshead die type rubber extruder to form a 0.035 inch (0.9 mm) thick first intermediate layer 16. A 0.008 inch (0.2 mm) thick refrigerant barrier layer 14 of ethylene vinyl alcohol (EVOH), manufactured by Kuraray Co., Ltd. under the trademark EV AL®, was then extruded over first intermediate layer 16. A 0.015 inch (0.4 mm) thick insulation layer of polychroloprene rubber (CR) compound was then spiral-wrapped around refrigerant barrier layer 14. A reinforcing material composed of Twaroii® polyaramid fibers (e.g. 1000 d) was braided over second intermediate layer 20 to form reinforcing layer 18. Finally, an ethylene/propylene/diene (EPDM) based rubber composition was extruded over reinforcing layer 18 through a crosshead die type extruder to form a 0.023 inch (0.6 mm) thick outer layer 22. The hose 10 was wrapped and vulcanized at about 150°C and then the mandrel was removed to obtain a low permeable hose 10 according to the present invention. [0017] hi another implementation of the invention shown in FIG. 2, first intermediate layer 16 was removed and innermost layer 12 was co-extruded with refrigerant barrier layer 14 using a tandem crosshead die type thermoplastic extruder. The thickness of innermost layer 12 may range from about 0.002-0.020 inches (0.05-0.5 mm) and the thickness of refrigerant barrier layer 14 may range from about 0.002-0.008 inches (0.05-0.2 mm). [0018] Among other features of the present invention, the innermost or first protective layer 12 and one or more of layers 20, 22 that overlay the refrigerant barrier layer 14, cooperatively isolate the refrigerant barrier layer 14, ensuring the integrity of the barrier layer material and stable permeation resistance. More particularly, the innermost or first protective layer 12 functions to protect the refrigerant barrier layer 14 from oil or thermal related degradation, as well as moisture related degradation if any moisture is present in the refrigeration system. One or more of the layers overlaying the refrigerant barrier layer 14, such as the second intermediate or protective layer 20, create a moisture barrier that protects the refrigerant barrier layer 14 from moisture related degradation. [0019] The present invention has been particularly shown and described with reference to the foregoing embodiments, which are merely illustrative of the best modes for carrying out the invention. It should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.