Abstract:
A hose comprising a core layer, at least one reinforcement layer, and a cover layer, the core layer is comprised of inner and outer core layers, the hose being characterized by the inner core layer and the outer core layer being formed from different non-plasticized polyamides and are co-extruded at the time of formation. The hose has a permeation rate of less than 0.5 g/m/day.

Description:
This application claims the benefit of Provisional application Ser. No. 60/294,350, filed May 30, 2001. 
    
    
     FIELD OF THE INVENTION 
     The disclosed invention relates to refrigerant hoses for use in automotive and industrial air conditioners. 
     BACKGROUND OF THE INVENTION 
     The automotive industry uses hoses for transporting refrigerants. The hoses generally have a three-layer laminar construction consisting of an innermost layer, an outermost cover layer located radially outwardly of the inner tube, and a reinforcing fiber layer interposed between the innermost layer and the outermost layer. Generally, the inner and outer layers are formed of rubber. The reinforcing fiber layer usually is a mesh structure formed by braided organic yarn such as polyester fiber, rayon fiber, or nylon fiber. The outer cover typically is formed of ethylene propylene diene rubber (EPDM) or chloroprene rubber (CR). Adhesion layers be may employed between the layers. 
     The known multi-layered rubber hoses discussed above have a high degree of flexibility. Because of this property of the rubber materials, rubber hoses can be handled with ease. However, rubber materials generally tend to have high gas permeability. Attempt to improve resistance of conventional rubber hoses to refrigerant permeation by incorporating polyamide layers such as nylon 6 or nylon 66 as an inner layer. 
     The nylons used for inner hose layers are conventionally plasticized polyamides. Plasticizer is added to the polyamide to improve the flexibility of the material; flexibility being a necessary characteristic of the hose. However, the addition of plasticizer decreases the permeability characteristics of the nylon; also a necessary characteristic of the hose. To achieve an acceptable compromise of the required characteristics, the thickness of the nylon inner core layer is conventionally at least 0.5 mm, see U.S. Pat. No. 4,633,912 who discloses a polyamide blend cores tube with a gauge thickness of 1.07 mm and 0.81 mm. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a hose that is particularly useful for transporting refrigerants. The hose has a high resistance to permeation and high flexibility. 
     The inventive hose has a selection of two different polyamides to form the inner core layer of a hose. The inner core layer is formed from co-extruded nylon layers. The inner core layer is formed from a polyamide that is nonplasticized, flexible, and has moderate resistant to refrigerant permeation. The outer core is formed from a polyamide that is nonplasticized, less flexible than the inner core polyamide, and has a higher resistant to refrigerant than the inner core polyamide. The combination of the two layers and the selective thickness of the two core layers provide the needed flexibility, heat resistance, and high resistance to refrigerant permeation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described by way of example and with reference to the accompanying drawings in which: 
     FIG. 1 is a perspective view of a hose in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The refrigerant hose  10  of the present invention is illustrated in FIG.  1 . The hose  10  has a core layer  12 , relative to the radial direction of the hose and the longitudinal hose axis. The core layer  12  is formed from co-extruded layers  14 ,  16 . Over the core layer  12  is an elastomeric friction layer  18 , over which is a reinforcing layer  20 , and overall, a cover layer  22 . 
     The core layer  12 , as noted, is formed from co-extruded layers  14 ,  16 . Both co-extruded layers are non-plasticized polyamides; however, the polyamide layers  14 ,  16  are not formed from the same polyamide. The polyamide selected for the inner core layer  14  has the following properties: high flexibility and moderate resistance to refrigerant permeation. One exemplary polyamide is non-plasticized nylon 6. The polyamide selected for the outer core layer  16  has the following properties: moderate flexibility and high resistance to refrigerant permeability. One exemplary polyamide is non-plasticized nylon 6-66. Both polyamides selected should be compatible with known commercial refrigerant oils. 
     The properties of the polyamides of the inner and outer core layers are as follows: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Inner Core Layer 
                 Outer Core Layer 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Tensile Strength, Mpa 
                 20-40 
                 60-80 
               
               
                 % Elongation at Break 
                 225-265 
                 280-300 
               
               
                 Flex Modulus, Mpa 
                  500-1000 
                 2,000-3,000 
               
               
                 Specific Gravity 
                 1.00-1.08 
                 1.08-1.14 
               
               
                 Permeation Rate*, g/m/day 
                 1.0-2.0 
                 0.1-0.5 
               
               
                   
               
               
                 *measured with R134A refrigerant, 10 days at 90° C.  
               
             
          
         
       
     
     To form a hose  10  that has a high degree of flexibility and permeation resistance, the gauge of the inner and outer core layers  14 ,  16  are optimized. The inner core layer  14  has a gauge of 0.15 mm to 0.25 mm and the outer core layer  16  has a gauge of 0.08 mm to 0.15 mm. The core layer  12  has a thickness less than the thickness of conventional nylon core layers, and the hose  10  has a comparable, if not greater, resistance to refrigerant permeation. 
     Layer  18  is an elastomeric friction layer between the outermost core layer  16  and the reinforcing layer  20  and provides flexibility to the hose  10 . The elastomer selected for this layer should meet those characteristics. For adhesion to the adjacent polyamide layer  16 , the elastomeric layer  18  may be extruded onto the core layers  14 ,  16 . The layer may also be applied in the form of a sheet either spirally wrapped or butt seamed. These methods of applying such layers are known in the art, and variations thereof are contemplated herein. 
     The elastomeric friction layer  18  comprises a base polymer selected from polyisoprene, polybutadiene, copolymers of butadiene and acrylonitrile, copolymers of butadiene and styrene, polychloroprene, polybutadiene, ethylene propylene copolymers, EPDM&#39;s such as ethylene propylene norbornene terpolymers, ethylene propylene-1,4-hexadiene terpolymers, ethylene propylene dicyclopentadiene terpolymers and the like. A preferred base stock for the friction layer is EPDM. 
     The base polymer in the friction layer  18  must have an adhesive system and a peroxide or sulfur curative. The adhesive systems useful are the conventionally known resorcinol or phenolic based adhesive systems. The resorcinol component may be added to the elastomer in the nonproductive mix, or preformed adhesive resins may be added during the productive mix. The amount of adhesive system utilized in the elastomeric friction layer can range from 1 to 10 parts by weight based on 100 parts of base stock polymer. The peroxide or sulfur curatives useful in the friction layer  18  are those that are normally used in such base stocks. The peroxide or sulfur curatives useful in the elastomeric friction layer are those that are normally used in such base stocks. For example peroxides such as dicumyl peroxide, [α,α′-bis(t-butylperoxide)diisopropylbenzene], benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, and n-butyl 4,4-bis(t-butylperoxy)valerate. From 1 to about 5 parts of peroxide or sulfur are utilized based on 100 parts of base polymer. 
     The reinforcing layer  20  may be a fiber layer as commonly used as a reinforcing layer for hoses. The layer  20  may be formed by braiding, spiraling, knitting, or helical knitting of yarn. The yarn may be selected from conventional hose reinforcing yarns such as glass, steel, cotton, polyester, or aramid fibers, or a blend of any of these fibers. 
     The cover layer  22  is selected from known cover layer materials, including but not limited to nitrile-butadiene rubber (NBR), chlorosulfonated polyethylene rubber (CSM), ethylene-propylene-diene rubber (EPDM), butyl rubber (IIR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR), epichlorohydrine rubber (CHR, CHC), acrylic rubber (ACM), chloroprene rubber (CR) and the like. 
     As discussed above, the hose  10  having a co-extruded core  12  has a low permeation rate with refrigerants. The hose  10  has a permeation rate of less than 0.5 g/m/day, preferably 0.075 to 0.5 g/m/day. A hose with a permeation rate of less than 0.5 is considered a low permeation hose. When the permeation rate is less than 0.1, it may be considered an ultra low permeation hose. 
     EXAMPLE 
     A hose  10  was built in accordance with the present invention. The core  12  was formed by co-extruding two polyamides, having the properties as listed in Table 2. The core  12  had a gauge of 0.35 mm. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Inner Core Layer 1   
                 Outer Core Layer 2   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Tensile Strength, Mpa 
                 32 
                 72 
               
               
                 % Elongation at Break 
                 250 
                 290 
               
               
                 Flex Modulus, Mpa 
                 650 
                 2,450 
               
               
                 Specific Gravity 
                 1.01 
                 1.1 
               
               
                 Permeation Rate*, g/m/day 
                 1.6 
                 0.33 
               
               
                   
               
               
                 *measured with R134A refrigerant, 10 days at 90° C.  
               
               
                   1 FN727, a nylon 6, sold by DuPont  
               
               
                   2 non-plasticized nylon 6,66 sold by Atofina  
               
             
          
         
       
     
     The hose was tested for 10 days at 90° C. to determine the permeation rate. The permeation rate was 0.08 g/m/day, and the exemplary hose is an ultra low permeation hose. 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.