High-pressure rubber hose
BACKGROUND OF THE INVENTION 
     This invention relates to a high-pressure rubber hose which has a reinforcing layer embedded therein, has at least an outer layer thereof formed of a vulcanized ethylene-α-olefin-diene copolymer rubber (hereinafter referred to as &#34;EPDM&#34; for short), and is adapted to be used as fastened by staking to a sleeved joint. As examples of uses found for this high-pressure rubber hose, there may be citted hoses for the hydraulic system such as a brake hose and a clutch hose, hoses for the air system, and hoses for the coolant system. 
     In most brake hoses, their outer layers have been formed of a vulcanized CR (chloroprene) rubber or a vulcanized CR-EPDM blend rubber (Japanese Patent Publication No. SHO 59(1984)-36,158). Recently, growth of engine output and adoption of turbo engines have compelled brake hoses to be used under increasingly harsh conditions. In the meantime, the desirability of developing brake hoses which require no maintenance has been finding growing recognition. 
     Neither the CR rubber not the CR-EPDM blend rubber mentioned above has been capable of acquiring an ability to resist dynamically the action of ozone to a point where the obviation of the necessity for maintenance is realized (Table 1). 
     It has been proposed to form the outer layer of a brake hose, for example, with a vulcanized rubber of EPDM which excels in dynamic resistance to ozone, resistance to heat, and resistance to weather conditions (Japanese Patent Application Laid-open No. SHO 55(1980)-2,805). Unfortunately, none of the EPDM species heretofore proposed to the art is capable of retaining compression-proof permanent set indispensable to the sealing property and, at the same time, manifesting such mechanical properties such as tensile strength (T B ), tear strength (T R ), and volume relaxation fracture to advantage (Comparative Experiment in Table 1). When such an EPDM rubber hose is fastened by staking to a sleeved joint, for example, it has the possibility of sustaining breakage in the staked end after thermal aging. Thus, the conventional EPDM rubber has failed to meet the need for obviating the required maintenance. 
     SUMMARY OF THE INVENTION 
     The high-pressure rubber hose of the present invention has at least an outer layer thereof formed of the vulcanization product of an ethylene-α-olefin-diene copolymer (EPDM) rubber (1) whose ethylene/α-olefin ratio (by weight) falls in the range of 45/55 to 58/42 and (2) whose Mooney viscosity of polymer (ML 1+4  100° C.) falls in the range of 120 to 250. Because of this construction, the present invention brings about the following effect. 
     The high-pressure rubber hose manifests dynamic resistance to ozone and mechanical properties such as tensile strength to advantage with no sacrifice of compression-proof permanent set necessary for the sake of the sealing property. When this high-pressure rubber hose is fastened by staking to a sleeved joint, therefore, the outer layer thereof will sustain no breakage in the staked end even after thermal aging. When it is used as a brake hose, for example, the brake hose enjoys notably improved durability and answers the cry for obviation of maintenace. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating a typical high-pressure rubber hose embodying the present invention. 
     FIG. 2 is a perspective view illustrating another typical high-pressure rubber hose similarly embodying the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now, the constituents of the present invention will be described in detail below. 
     (1) If the ethylene/α-olefin ratio is not more than 45/55, mechanical properties such as tensile strength are not satisfactory. If this ratio exceeds 58/42, the compression-proof permanent set is not sufficient. Generally propylene is used as the α-olefin. Optionally, 1-butene, for example, may be used instead. 
     (2) If the Mooney viscosity of polymer (ML 1+4  100° C.) is less than 120, the mechanical properties such as tensile strength are insufficient. If it exceeds 250, the productivity of the polymer is inferior. 
     (3) The polymer of EPDM is obtained by polymrizing ethylene, an α-olefin, and diene in an inactive solvent under atmospheric pressure or a slightly increased pressure in the presence of a suitable catalyst. For this polymerization, the diene is incorporated in such an amount that the iodine number of the produced EPDM polymer will fall in the range of 1 to 30. Generally as the diene, one member or a mixture of two or more members selected from the group consisting of such non-conjugate dienes as ethylidene norbornene, vinyl norbornene, dicyclopentadiene, 1,4-hexdiene, 2-methyl-1,5-hexadiene, 1,6-octadiene, 1,5-octadiene, 1,4-octadiene, and methylhydroindene. Optionally, the diene may incorporate therein a conjugate diene such as butadiene or isoprene. 
     (4) Generally, the high-pressure rubber hose is produced in a three-layer construction, consisting of an inner tube layer 1, a reinforcing layer 2, and an outer tube layer (outer layer) 3 as illustrated in FIG. 1 or in a five-layer construction, consisting of an inner tube layer 1, a reinforcing layer 2, an intermediate layer 4, a reinforcing layer 2, and an outer tube layer 3 as illustrated in FIG. 2. Optionally, the outer tube layer, the intermediate layer, and the inner layer may be severally formed in two layers or three layers. As regards the materials for the high-pressure rubber hose used as a brake hose, for example, the inner tube layer is made of SBR, the reinfrocing layer made of a knit fabric of Vinylon, rayon, or polyester, the intermediate layer made of natural rubber, EPDM, or butyl rubber, and the outer tube layer made of the aforementioned novel, specific EPDM. 
     EXAMPLES 
     The rubber hoses of working examples and comparative experiments were obtained in the construction shown in FIG. 2 as follows. 
     (1) The inner tube of SBR 3.3 mm in inside diameter and 5.3 mm in outside diameter was produced by extrusion. 
     (2) The reinforcing layer was formed by combining 20 lower reinforcing 1200-d Vinylon 2-ply yarns and 24-upper reinforcing 1200-d Vinylon 3-ply yarns. 
     (3) The intermediate layer was formed by winding an EPDM sheet (0.4 mm in thickness) at the same time that the upper reinforcing yarns were knit. 
     (4) The outer tube was formed by covering the upper reinforcing layer with a material incorporating a polymer of a varying comonomer ratio indicated in Table 1 in a formula shown below (wherein CR represents a material heretofore used in the outer tube of the conventional hose) so that the produced hose would acquire an outside diameter of 10.5 mm. 
     
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 Formula (parts by weight)                                                
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Polymer               100                                                 
Zinc oxide            5                                                   
Stearic acid          1                                                   
FEF carbon            120                                                 
Paraffin type oil     80                                                  
Sulfur                1                                                   
Vulcanization accelerator CZ*.sup.1                                       
                      2                                                   
Vulcanization accelerator TT*.sup.2                                       
                        0.5                                               
Vulcanization accelerator D*.sup.3                                        
                        0.5                                               
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 (Note)                                                                   
 *.sup.1 cyclohexylbenzothiazyl sulfonamide                               
 *.sup.2 Tetramethylthiuram disulfide                                     
 *.sup.3 N--Phenyl2-naphthylamine                                         
 
    
     (5) The hose completed was vulcanized with steam at 150° C. for 30 minutes. 
     Each of the high-pressure rubber hoses obtained as described above was fastened by staking at eight points each in two stages (staking ratio 44±3%) to a sleeved joint, left standing in an atmosphere kept at 120° C. for 70 hours, removed in a disassembled state from the sleeved joint, and carefully examined to determine whether or not the outer layer rubber had been disrupted because of staking. The results are shown in Table 1 as &#34;disruption of staked end after thermal aging.&#34; 
     For the sake of reference, a rubber material incorporating the same polymer and prepared in the same formula as the rubber material used for the high-pressure rubber hose mentioned above was vulcanized under the same conditions as mentioned above. Test pieces taken from the vulcanized rubber material were tested for the following properties. 
     (1) Stationary properties (Hs (hardness), T (tensile strength), and E (elongation)) were tested by following the procedures of spring type hardness test (A type) and tensile test (dumbell No. 3) specified by JIS K-6301, with necessary modifications. 
     (2) Tear strength was tested by following the procedure of tear test (B type) specified by JIS K-6301, with necessary modifications. 
     (3) Heat relaxation disruption was determined by stretching test pieces (dumbell No. 3) to varying ratios (ratios graduated by 50% between 100% and 400%), allowing the stretched test pieces to stand in an atmosphere kept at 120° C. for 4 hours, and measuring critical elongation of a test piece verging on fracture. 
     (4) Permanent set under compression was tested by following the procedures of compression permanent set test (at 120° C. for 22 hours) and low-temperature compression permanent set test (at -20° C. for 22 hours) specified by JIS K-6301. 
     (5) Resistance to cold was tested by following the procedure of low-temperature impulse embrittlement test (using isopropyl alcohol as heat transfer medium) specified by JIS K-6301. 
     (6) Dynamic resistance to ozone was determined by exposing a test piece to repeated elongation (0←→30% 60 rpm) and clocking the total time of repeated elongation before impartation of tear on the test piece, by following the procedure of ozone test specified by JIS K-6301. 
     
                                           TABLE 1                                 
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                       Experiment                                         
                       Examples    Comparisons             Refer-         
                       1   2   3   1   2   3   4   5   6   ence           
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Specification                                                             
          Ethylene/propylene                                              
                       49/51                                              
                           56/44                                          
                               56/44                                      
                                   47/53                                  
                                       57/43                              
                                           57/43                          
                                               63/37                      
                                                   74/26                  
                                                       74/26              
                                                           C R            
of EPDM polymer                                                           
          Viscosity (ML.sub.1+4 100° C.)                           
                       180 180 210 48  65  105 135 38  210                
          Iodine value 12  ←                                         
                               12  11  15  ←                         
                                               15  19  19                 
&lt;Test for physical properties&gt;                                            
Disruption by                                                             
          Presence     No  ←                                         
                               No  Yes ←                             
                                           ←                         
                                               ←                     
                                                   ←                 
                                                       Yes No             
staking after                                                             
          of disruption in                                                
thermal aging                                                             
          outer layer                                                     
Stationary                                                                
          Hs (JISA)    67  67  68  63  66  66  66  72  67  65             
Properties                                                                
          T.sub.B (kgf/cm.sup.2)                                          
                       135 151 165 90  116 129 135 84  157 196            
          E.sub.B (%)  580 610 650 600 530 530 510 410 460 570            
Tear strength                                                             
          T.sub.R (kgf/cm)                                                
                       41  42  44  34  36  37  37  29  41  66             
Heat relaxation                                                           
          Critical elongation (%)                                         
                       300 300 350 250 200 200 150 150 150 350            
disruption                                                                
Compression                                                               
          High-temperature CS (%)                                         
                       28  30  31  31  36  32  33  74  79  --             
permanent set                                                             
          Low-temperature CS (%)                                          
                       55  56  45  83  67  61  56  75  48  39             
Resistance to cold                                                        
          Embrittling temperature                                         
                       -60&gt;                                               
                           ←                                         
                               ←                                     
                                   ←                                 
                                       ←                             
                                           ←                         
                                               ←                     
                                                   ←                 
                                                       -60&gt;               
                                                           -52.6          
          (°C.)                                                    
Dynamic resistance                                                        
          Total time of impartation                                       
                       1000&lt;                                              
                           ←                                         
                               ←                                     
                                   ←                                 
                                       ←                             
                                           ←                         
                                               ←                     
                                                   ←                 
                                                       1000&lt;              
                                                           301˜     
to ozone  of tear (hr)                                     468            
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