Patent Publication Number: US-4544708-A

Title: Vulcanizable fluoroelastomer compositions providing vulcanizates having high adhesion to metals

Description:
BACKGROUND OF THE INVENTION 
     One of the most important uses of fluorinated elastomers is the manufacture of seals for both static and dynamic utilizations. A particularly important field in this respect is that of the sealing on rotary shafts by means of oil seal rings. In such case it is absolutely necessary that a perfect adhesion capable of remaining quite unaltered even at high temperatures (200°-250° C.) may take place between the fluoroelastomer constituting the sealing element and the metal insert. 
     In the known processes for vulcanizing fluoroelastomers, diamine compounds such as carbamates were often used in the past and, to a lesser extent, also at present. However, these accelerating-vulcanizing agents though permitting to obtain satisfactory adhesion values, exhibit the drawback of rendering the processing little safe due to the occurrence of scorching phenomena. 
     With the systems based on bisphenol cross-linking agents, such as for example bisphenol AF, on accelerators based on quaternary salts of phosphonium or of amino-phosphonium, in which the anion is mostly chloride, bromide or tetrafluoroborate, scorching phenomena are avoided, but the adhesion values are low. When, by means of proper formulations, nearly acceptable adhesion values are reached, these are limited to a narrow concentration range of the accelerating agent, as is proved by examples 34 through 36 and 46 through 48. 
     THE PRESENT INVENTION 
     It has been now surprisingly found, and this is the object of the present invention, that it is possible to obtain high rubber/metal adhesion values when the phosphonium compound or the amino-phosphonium compound or the ammonium compound which acts as an accelerator is present in the form of a compound having as a counteranion a complex anion of cadmium, zinc, lead or nickel, such as e.g. CdCl 4   -- , Cd 2  Cl 6   -- , CdCl 2  Br 2   -- , CdBr 4   -- , CdCl 2  l 2   -- , ZnCl 2  Br 2   -- , ZnCl 3 .P(C 6  H 5 ) 3   - , or of boron, such as B(C 6  H 5 ) 4   - . 
     A typical characteristic of the accelerators according to the present invention is that of permitting to attain with them high adhesion values in a wide concentration range of the accelerator, which enables an operator to obtain satisfactory results even if in the steps for preparing the vulcanizable mixes the accelerator was not homogeneously dispersed and its concentration in the mix is locally different from point to point. 
     The vulcanization accelerators based on a phosphonium or amino-phosphonium or ammonium cation have, as a usual counteranion, Cl - , Br - , BF 4   -  and are used at concentrations of about 1 millimole for 100 g of fluoroelastomer. 
     The accelerators forming the object of this invention, conversely, can be advantageously employed in a concentration range of from 0.8 to 2.5 milliequivalents of phosphonium or amino-phosphonium or ammonium compound for 100 g of fluoroelastomer without scorching phenomena are observed, so having the possibility of achieving quick or slow cross-linking kinetics, depending on the requirements of each particular type of rubber processing. 
     In general, the present invention relates to a vulcanizable fluoroelastomeric composition, comprising: 
     (A) a copolymer of elastomeric nature based on vinylidene fluoride and on at least another fluorinated monomer; 
     (B) a substance having the property of neutralizing acids and selected from the oxides of divalent metals, the hydroxides of divalent metals and mixtures of such oxides or hydroxides with metal salts of weak acids; 
     (C) an aromatic polyhydroxyl compound suited to act as a vulcanizing agent for the copolymer; 
     (D) as a vulcanization accelerator, a salt composed by a cation of phosphonium or of amino-phosphonium or of ammonium, the formula thereof is selected from amongst those already known in the art and broadly described for example in U.S. Pat. Nos. 3,876,654; 4,259,463 and in GB Pat. No. 1,356,344 respectively, and by a complex anion, in which one atom or two atoms of a metal selected from Cd (II), Zn (II), Pb (II), Ni (II) is, respectively are bound to chlorine, bromine, iodine atoms and optionally also to a trisubstituted phosphinic binder, such as e.g.: P(C 6  H 5 ) 3 , P[N(CH 3 )(C 6  H 5 )] 3 . The abovesaid complex anion is represented by one of the following formulas: 
     
         (MeX.sub.4).sup.2.spsp.- or (MeX.sub.3 Y).sup.- 
    
     wherein Me is one of the abovesaid metals, X is Cl, Br, I, and Y is said phosphinic binder. Furthermore, the anion may be tetraphenyborane B(C 6  H 5 ) 4   - , or it may be of the type containing two metal atoms, such as hexachlorodicadmiate: ##STR1## 
     Peeling tests (ASTM D 429) are generally utilized to evaluate the adhesion between elastomer and metal. 
     This kind of test, however, permits to evaluate the tearing and cracking phenomena occurring in the vulcanized composition, rather than the adhesion of the elastomeric portion to the metal. To obviate this shortcoming, another adhesion evaluation method was utilized. In particular, standard ASTM D 1893, which is specific for plastics, was adapted for the case elastomer/metal. This standard contemplates the quantitative evaluation of the adhesion degree between two layers of alike or different polymeric films. 
     In the present case, test pieces consisting of metal, adhesive, elastomer were prepared. 
     The elastomer/metal bonding was accomplished in 3 steps: 
     (a) small metal plates (carbon steel Fe 37 A I; dimensions: 80×25×2 mm) were prepared by degreasing them in an ALGOFRENE®113 vapor bath, and by sandblasting with corundum the areas intended for adhesion, and by degreasing them once again; 
     (b) the adhesive was applied by means of spraying to the metal so prepared. Chemosil 511 (trademark of Henkel) was utilized as an adhesive; 
     (c) the adhesion between the metal treated with the adhesive and the elastomer is accomplished during the vulcanization-in-press step (elastomer thickness: 8 mm). 
     To obtain an effective adhesion it is necessary that the cross-linking rate of the mix and the one of the adhesive be of the same order of magnitude. 
     Molding conditions: P=66 kg/cm 2  ; T°=170° C.; time: variable as a function of the accelerator type and of its concentration. 
     On the test pieces so prepared there was measured the strength necessary to detach the elastomer from the treated metal, using a flat drawn piece (dimensions: 25×2 mm) which moved perpendicularly to the test pieces axis at a uniform speed of 50 mm/minute. 
     The results are expressed in mass unit per length unit. 
     In a few cases, due to the high adhesion values attained with the compounds of the present invention, is was not possible to measure the adhesive strength since tearing phenomena occurred in the elastomer. 
     In these cases, the adhesive strength may be considered to be higher than the measured value (as is indicated in Tables I-IV). 
    
    
     EXAMPLES 1-12 
     (Table I) 
     Vulcanization accelerators capable of providing, in a wide concentration range, vulcanized compositions with high rubber/metal adhesion values, divided by cation classes of the accelerator molecule. 
     Cation: trisdimethylaminobenzyl-phosphonium: 
     
         P.sup.+ (C.sub.6 H.sub.5 CH.sub.2)[N(CH.sub.3).sub.2 ].sub.3 
    
     Anions: 
     A.1 Chloride (check product) M.P.=208° C. It was prepared as is described in literature (Monsanto U.S. Pat. No. 2,703,814). 
     A.2 Tetrafluoroborate (check product) M.P.=146° C. It was prepared from the preceding product by treatment with an aqueous solution of sodium tetrafluoroborate. 
     A.3 Tetrachlorocadmiate--M.P.=148° C. It was prepared from a methanol solution of A.1 (2 moles) with one mole of anhydrous cadmium chloride in methanol, and by evaporating the solvent. 
     A.4 Tetraphenylborate (M.P.=187° C.). It was prepared from an aqueous solution of A.1 with an equimolecular amount of sodium tetraphenylborate. 
     Explanatory notes applying to all the Tables: 
     (1) According to ASTM D 2084-75. 
     (2) According to ASTM D 1646-74 using a small size rotor. 
     (3) According to ASTM D 412-75 on 2 mm thick test pieces. 
     (4) According to ASTM D 1415-74 on 6 mm thick test pieces, reading after 30 seconds. 
     (5) According to ASTM D 395-75 method B. 
     (6) According to ASTM D 1893 (see the foregoing references to adaptation of ASTM D 1983). T s  2=time in minutes required to get an increase in the lowest value by 2 in.lbs. 
     T c  (50)=time in minutes required to get a torque of 50 in.lbs. 
     
                                           TABLE No. 1                             
__________________________________________________________________________
FORMULATION No.   1  2  3  4  5  6  7  8  9  10 11 12                     
__________________________________________________________________________
Tecnoflon NM p. by weight                                                 
                  100                                                     
                     100                                                  
                        100                                               
                           100                                            
                              100                                         
                                 100                                      
                                    100                                   
                                       100                                
                                          100                             
                                             100                          
                                                100                       
                                                   100                    
MgO (Maglite D) p. by weight                                              
                  25 5  5  5  5  5  5  5  5  5  5  5                      
Ca(OH).sub.2 p. by weight                                                 
                  5  5  5  5  5  5  5  5  5  5  5  5                      
Carbon black MI p. by weight                                              
                  25 25 25 25 25 25 25 25 25 25 25 25                     
Bisphenol AF p. by weight                                                 
                  1.8                                                     
                     1.8                                                  
                        1.8                                               
                           1.8                                            
                              1.8                                         
                                 1.8                                      
                                    1.8                                   
                                       1.8                                
                                          1.8                             
                                             1.8                          
                                                1.8                       
                                                   1.8                    
Accelerator: A4 m. equivalents                                            
                  1  1.5                                                  
                        2  -- -- -- -- -- -- -- -- --                     
Accelerator: A3 m. equivalents                                            
                  -- -- -- 1  1.5                                         
                                 2  -- -- -- -- -- --                     
Accelerator: A2 m. equivalents                                            
                  -- -- -- -- -- -- 1.0                                   
                                       1.5                                
                                          2.1                             
                                             -- -- --                     
Accelerator: A1 m. equivalents                                            
                  -- -- -- -- -- -- -- -- -- 1.0                          
                                                1.5                       
                                                   2.0                    
Thermomechanical characteristics                                          
O.D.R. 175° C. (1)                                                 
Minimum torque in. lbs.                                                   
                  12 14 12 10 10 15 13 13 16 16 17 19                     
Maximum torque in. lbs.                                                   
                  115                                                     
                     128                                                  
                        124                                               
                           100                                            
                              104                                         
                                 110                                      
                                    102                                   
                                       110                                
                                          119                             
                                             106                          
                                                110                       
                                                   115                    
T.sub.s 2 minutes 2.9                                                     
                     2.4                                                  
                        2.3                                               
                           2.1                                            
                              1.3                                         
                                 1.2                                      
                                    2.8                                   
                                       1.9                                
                                          1.7                             
                                             3.9                          
                                                3.0                       
                                                   2.1                    
T.sub.c (50) minutes                                                      
                  4.3                                                     
                     3.3                                                  
                        3.1                                               
                           3.9                                            
                              2.3                                         
                                 2.0                                      
                                    4.7                                   
                                       2.9                                
                                          2.3                             
                                             6.3                          
                                                3.8                       
                                                   2.9                    
Viscosity                                                                 
Mooney MS at 121° C. (2) minimum                                   
                  48 47 44 45 47 46 50 48 46 47 46 44                     
minutes for 10 point increase:                                            
                  60 55 50 60 55 50 55 50 45 50 40 35                     
Vulcanization                                                             
in press at 170° C. × 10 minutes                             
in oven at 250° C. × 16 hours                                
100% elongation modulus kg/cm.sup.2 (3)                                   
                  76 78 80 70 72 74 65 68 68 62 70 91                     
Tensile strength kg/cm.sup.2 (3)                                          
                  177                                                     
                     165                                                  
                        155                                               
                           160                                            
                              155                                         
                                 150                                      
                                    160                                   
                                       150                                
                                          145                             
                                             160                          
                                                160                       
                                                   164                    
Elongation at break % (3)                                                 
                  167                                                     
                     160                                                  
                        157                                               
                           190                                            
                              180                                         
                                 170                                      
                                    195                                   
                                       180                                
                                          170                             
                                             175                          
                                                165                       
                                                   151                    
Hardness, IRHD (4)                                                        
                  72 73 74 73 72 72 73 72 74 74 75 73                     
Compression set, on                                                       
O-Rings (φ 25.4 × 3.53 mm): (5)                                 
at 200° C. × 70 hours                                        
                  18 19 20 20 20 21 17 18 20 18 20 22                     
at 200° C. × 168 hours                                       
                  29 30 32 28 30 32 30 28 32 27 30 33                     
Adhesive strength (kg · cm.sup.-1) (6)                           
after vulcanization in press                                              
                  33 32 30 41 25 23 12 10 4  3  6  8                      
at 170° C. × 8 minutes                                       
after post-vulcanization in oven                                          
                  16 16 15 36 23 20 16 8  6  (0)*                         
                                                (0)*                      
                                                   (0)*                   
at 250° C. × 16 hours                                        
after post-vulcanization in oven                                          
                  14 12 12 30 20 18 2  4  3  (0)*                         
                                                (0)*                      
                                                   (0)*                   
at 250° C. × 16 hours and aqueous                            
treatment at 100° C. × 48 hours                              
__________________________________________________________________________
 *adhesion not measurable                                                 
 
    
     EXAMPLES 13-21 
     (Table 2) 
     Cation: hydroxyethyltriphenylphosphonium=[HOCH 2  CH 2  P(C 6  H 5 ) 3  ] +   
     Anions: 
     B.1 Tetrachlorocadmiate: it was prepared as is described in Inorganica Chimica Acta 60, (1982) 135-139--M.P.=164° C. 
     B.2 Chloride (check product). This compound was prepared by reacting equimolecular amounts of triphenylphosphine and ethylene chlorohydrin in toluene, at reflux during four hours--M.P.=244° C. 
     B.3 Tetrafluoroborate (check product). It was prepared from a solution of B.2 in water with an equimolar solution of sodium tetrafluoroborate--M.P.=167° C. 
     
                                           TABLE No. 2                             
__________________________________________________________________________
FORMULATION No.   13 14 15 16 17 18 19 20 21                              
__________________________________________________________________________
Tecnoflon NM p. by weight                                                 
                  100                                                     
                     100                                                  
                        100                                               
                           100                                            
                              100                                         
                                 100                                      
                                    100                                   
                                       100                                
                                          100                             
MgO (Maglite D) p. by weight                                              
                  5  5  5  5  5  5  5  5  5                               
Ca(OH).sub.2 p. by weight                                                 
                  5  5  5  5  5  5  5  5  5                               
Carbon black MT p. by weight                                              
                  25 25 25 25 25 25 25 25 25                              
Bisphenol AF      1.8                                                     
                     1.8                                                  
                        1.8                                               
                           1.8                                            
                              1.8                                         
                                 1.8                                      
                                    1.8                                   
                                       1.8                                
                                          1.8                             
Accelerator: B.1 m. equivalents                                           
                  1  1.5                                                  
                        2  -- -- -- -- -- --                              
Accelerator: B.2 m. equivalents                                           
                  -- -- -- 1  1.5                                         
                                 2  -- -- --                              
Accelerator: B.3 m. equivalents                                           
                  -- -- -- -- -- -- 1.0                                   
                                       1.5                                
                                          2.0                             
Thermomechanical characteristics                                          
O.D.R. 175° C. (1)                                                 
Minimum torque in. lbs.                                                   
                  18 18 18 16 17 18 15 16 17                              
Maximum torque in. lbs.                                                   
                  85 94 96 70 78 86 73 80 96                              
T.sub.s 2 minutes 5.2                                                     
                     3.8                                                  
                        3.0                                               
                           5.5                                            
                              3.4                                         
                                 2.4                                      
                                    6  3.5                                
                                          2.5                             
T.sub.c (50) minutes                                                      
                  12.2                                                    
                     6.7                                                  
                        4.7                                               
                           11.5                                           
                              6.0                                         
                                 3.7                                      
                                    12 6.5                                
                                          3.7                             
Viscosity                                                                 
Mooney MS at 100° C. (2) minimum                                   
                  50 50 48 52 50 49 52 50 52                              
minutes for 10 point increase:                                            
                  60 58 55 55 50 45 65 60 55                              
Vulcanization                                                             
in press at 170° C. × 10 minutes                             
in oven at 250° C. × 16 hours                                
100% elongation modulus kg/cm.sup.2 (3)                                   
                  55 56 60 55 60 65 60 65 70                              
Tensile strength kg/cm.sup.2 (3)                                          
                  160                                                     
                     162                                                  
                        155                                               
                           155                                            
                              150                                         
                                 150                                      
                                    165                                   
                                       160                                
                                          155                             
Elongation at break % (3)                                                 
                  210                                                     
                     199                                                  
                        185                                               
                           200                                            
                              195                                         
                                 180                                      
                                    195                                   
                                       190                                
                                          180                             
Hardness, IRHD (4)                                                        
                  75 73 72 75 74 72 72 71 71                              
Compression set, on                                                       
O-Rings (0 25.4 × 3.53 mm): (5)                                     
at 200° C. × 70 hours                                        
                  16 17 19 17 19 22 16 18 21                              
at 200° C. × 168 hours                                       
                  28 30 31 29 29 33 27 29 30                              
Adhesive strength (kg · cm.sup.-1) (6)                           
after vulcanization in press                                              
                  &gt;34.sup.(*)                                             
                     &gt; 25                                                 
                        &gt;27                                               
                           15 15 9  (0)*                                  
                                       2  3                               
at 170° C. × 9 minutes                                       
after post-vulcanization in oven                                          
                  &gt;21                                                     
                     &gt;19                                                  
                        &gt;18                                               
                           23 23 12 12 6  16                              
at 250° C. × 16 hours                                        
after post-vulcanization in oven                                          
                  20 19 13 16 15 10                                       
at 250° C. × 16 hours and aqueous                            
treatment at 100° C. × 48 hours                              
after post-vulcanization in oven    12 5  14                              
at 100° C. × 48 hours                                        
__________________________________________________________________________
 (*) Vulcanization in press at 170° C. for 18 minutes              
 (0) Adhesion not measurable                                              
 
    
     EXAMPLES 22-33 
     (Table 3) 
     Cation: benzyltriphenylphosphonium=[C 6  H 5  CH 2  P(C 6  H 5 ) 3  ] +   
     Anions: 
     C.1 Tetrachlorocadmiate--M.P.=218° C. It was prepared as is described in Inorganica Chimica Acta, 60, 153 (1982). 
     C.2 Hexachlorocadmiate--M.P. 225° C., prepared as is described in Inorganica Chimica Acta, 60, 153 (1982). 
     C.3 Chloride (check compound)--M.P.=307° C. (decomposition); a sample produced by Messrs Fluka was utilized. 
     C.4 Perchlorate (check compound). It was prepared from an aqueous solution of C.3 with equimolar amounts of a saturated solution of sodium perchlorate--M.P.=242° C. 
     
                                           TABLE No. 3                             
__________________________________________________________________________
FORMULATION NO.   22 23 24 25 26 27 28 29 30 31 32 33                     
__________________________________________________________________________
Tecnoflon NM p. by weight                                                 
                  100                                                     
                     100                                                  
                        100                                               
                           100                                            
                              100                                         
                                 100                                      
                                    100                                   
                                       100                                
                                          100                             
                                             100                          
                                                100                       
                                                   100                    
MgO (Maglite D) p. by weight                                              
                  5  5  5  5  5  5  5  5  5  5  5  5                      
Ca(OH).sub.2 p. by weight                                                 
                  5  5  5  5  5  5  5  5  5  5  5  5                      
Carbon black MT p. by weight                                              
                  25 25 25 25 25 25 25 25 25 25 25 25                     
Bisphenol AF      1.8                                                     
                     1.8                                                  
                        1.8                                               
                           1.8                                            
                              1.8                                         
                                 1.8                                      
                                    1.8                                   
                                       1.8                                
                                          1.8                             
                                             1.8                          
                                                1.8                       
                                                   1.8                    
Accelerator: C.1 m. equivalents                                           
                  1  1.5                                                  
                        2  -- -- -- -- -- -- -- -- --                     
Accelerator: C.2 m. equivalents                                           
                  -- -- -- 1  1.5                                         
                                 2  -- -- -- -- -- --                     
Accelerator: C.3 m. equivalents                                           
                  -- -- -- -- -- -- -- -- -- 1.0                          
                                                1.5                       
                                                   2.0                    
Accelerator: C.4 m. equivalents                                           
                  -- -- -- -- -- -- 1.0                                   
                                       1.5                                
                                          2.0                             
                                             -- -- --                     
Thermomechanical characteristics                                          
O.D.R. 175° C. (1)                                                 
Minimum torque in. lbs.                                                   
                  14 16 17 16 14 12 16 17 18 12 14 15                     
Maximum torque in. lbs.                                                   
                  90 110                                                  
                        113                                               
                           76 94 92 86 90 96 80 108                       
                                                   115                    
T.sub.s 2 minutes 4.8                                                     
                     4.4                                                  
                        4  6  3.7                                         
                                 2.6                                      
                                    6.7                                   
                                       6.0                                
                                          5.7                             
                                             4.0                          
                                                2.5                       
                                                   1.8                    
T.sub.c (50) minutes                                                      
                  12.8                                                    
                     7.7                                                  
                        5.7                                               
                           10.2                                           
                              6.1                                         
                                 4.1                                      
                                    23.5                                  
                                       19 15 6.8                          
                                                3.8                       
                                                   2.8                    
Viscosity                                                                 
Mooney MS at 121° C. (2) Minimum                                   
                  55 60 55 54 58 56 56 58 58 60 58 58                     
minutes for 10 point increase:                                            
                  65 60 60 70 65 65 60 55 55 65 55 50                     
Vulcanization                                                             
in press at 170° C. × 10 minutes                             
in oven at 250° C. × 16 hours                                
100% elongation modulus kg/cm.sup.2 (3)                                   
                  58 65 73 60 65 70 60 59 58 65 56 55                     
Tensile strength kg/cm.sup.2 (3)                                          
                  161                                                     
                     165                                                  
                        168                                               
                           170                                            
                              165                                         
                                 160                                      
                                    175                                   
                                       170                                
                                          166                             
                                             174                          
                                                168                       
                                                   160                    
Elongation at break % (3)                                                 
                  188                                                     
                     182                                                  
                        180                                               
                           195                                            
                              190                                         
                                 190                                      
                                    200                                   
                                       198                                
                                          190                             
                                             195                          
                                                193                       
                                                   188                    
Hardness, IRHD (4)                                                        
                  70 71 72 73 72 71 75 74 72 72 72 71                     
Compression set, on                                                       
O-Rings (φ 25.4 × 3.53 mm): (5)                                 
at 200° C. × 70 hours                                        
                  16 16 17 16 17 18 17 18 21 19 21 22                     
at 200° C. × 168 hours                                       
                  25 28 29 26 28 29 29 30 32 28 31 32                     
Adhesive strength (kg · cm.sup.-1) (6)                           
after vulcanization in press                                              
                  &gt;42                                                     
                     &gt;46                                                  
                        &gt;47                                               
                           24*                                            
                              19 31 14**                                  
                                       13**                               
                                          12**                            
                                             9  7  5                      
AT 170° C. × 8 minutes                                       
after post-vulcanization in oven                                          
                  &gt;37                                                     
                     &gt;30                                                  
                        &gt;25                                               
                           14 16 30 13 12 10 &gt;21                          
                                                10 5                      
at 250° C. × 16 hours                                        
after post-vulcanization in oven                                          
                  31 25 21 19 11 16 11 10 8  21 8  4                      
at 250° C. × 16 hours and aqueous                            
treatment at 100° C. × 48 hours                              
__________________________________________________________________________
 *Vulcanization in press at 170° C. for 15 minutes                 
 **Vulcanization in press at 170° C. for 35 minutes                
 
    
     EXAMPLES 34-45 
     (Table 4) 
     Cation: benzyltriethylammonium [N(C 2  H 5 ) 3  CH 2  C 6  H 5  ] +   
     Anions: 
     D.1 Chloride (check), produced by Fluka Co. 
     D.2 Tetrachlorocadmiate--M.P.=102° C. It was prepared from 1 mole of CdCl 2  +2 moles of D.1 in methanol. 
     Cation: methyl-tributyl-ammonium [N(C 4  H 9 ) 3  CH 3  ] +   
     Anions: 
     D.3 Iodide (check), produced by Fluka Co. 
     D.4 Tetraiodocadmiate--M.P.=102° C. It was prepared from 1 mole of CdI 2  and 2 moles of D.3 in ethanol. 
     
                                           TABLE NO. 4                             
__________________________________________________________________________
FORMULATION No.  34 5  36 37 38 39 40 41 42 43 44 45                      
__________________________________________________________________________
Tecnoflon NM p. by weight                                                 
                 100                                                      
                    100                                                   
                       100                                                
                          100                                             
                             100                                          
                                100                                       
                                   100                                    
                                      100                                 
                                         100                              
                                            100                           
                                               100                        
                                                  100                     
MgO (Maglite D) p. by weight                                              
                 5  5  5  5  5  5  5  5  5  5  5  5                       
Ca(OH).sub.2 p. by weight                                                 
                 5  5  5  5  5  5  5  5  5  5  5  5                       
Carbon black MT p. by weight                                              
                 25 25 25 25 25 25 25 25 25 25 25 25                      
Bisphenol AF p. by weight                                                 
                 1.8                                                      
                    1.8                                                   
                       1.8                                                
                          1.8                                             
                             1.8                                          
                                1.8                                       
                                   1.8                                    
                                      1.8                                 
                                         1.8                              
                                            1.8                           
                                               1.8                        
                                                  1.8                     
Accelerator: D.1 m. equivalents                                           
                 1.0                                                      
                    1.5                                                   
                       2.0                                                
                          -- -- -- -- -- -- -- -- --                      
Accelerator: D.2 m. equivalents                                           
                 -- -- -- 1.0                                             
                             1.5                                          
                                2.0                                       
                                   -- -- -- -- -- --                      
Accelerator: D.3 m. equivalents                                           
                 -- -- -- -- -- -- 1.0                                    
                                      1.5                                 
                                         2.0                              
                                            -- -- --                      
Accelerator: D.4 m. equivalents                                           
                 -- -- -- -- -- -- -- -- -- 1.0                           
                                               1.5                        
                                                  1.0                     
Thermomechanical characteristics                                          
O.D.R. 175° C. (1)                                                 
Minimum torque in. lbs.                                                   
                 16 16 16 16 17 16 10 10 8  8  8  8                       
T.sub.s 2 minutes                                                         
                 5.5                                                      
                    3.1                                                   
                       2.2                                                
                          5.5                                             
                             4.1                                          
                                3.5                                       
                                   5.2                                    
                                      4.2                                 
                                         3.7                              
                                            4.2                           
                                               6.0                        
                                                  6.0                     
T.sub.c (50) minutes                                                      
                 10.3                                                     
                    4.7                                                   
                       3.2                                                
                          9.7                                             
                             8.2                                          
                                5.5                                       
                                   15.1                                   
                                      7.7                                 
                                         7.0                              
                                            18.2                          
                                               16.0                       
                                                  15.2                    
Maximum torque in. lbs.                                                   
                 96 90 98 92 92 90 92 98 98 83 96 96                      
Compression set, (xx)                                                     
O-Rings (0 25.4 × 3.53 mm): (5)                                     
at 200° C. × 70 hours                                        
                 23 25 28 26 28 29 26 29 28 24 26 28                      
at 200° C. × 168 hours                                       
                 32 34 37 28 31 33 29 33 35 29 31 33                      
Adhesive strength (kg · cm.sup.-1) (6)                           
after vulcanization in press                                              
                 20 8  4  22 18 18 19 16 13 24 22 21                      
at 170° C. × 8 minutes                                       
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 (xx) Vulcanization in press at 170° C. × 10 minutes, in oven
 at 250° C. × 16 hours.                                      
 
    
     EXAMPLES 46-51 
     (Table 5) 
     In these examples, the terpolymer Tecnoflon TN produced by Montedison, having the following molar composition: vinylidene fluoride=67%, hexafluoropropene=18%, tetrafluoroethylene=15%, was utilized as an elastomer. It can be observed how the accelerators according to the present invention enable, also in this case, to obtain vulcanized articles with high rubber/metal adhesion values. The results are recorded on Table 5. 
     The accelerating system was composed by the diethylamino-diphenyl-benzyl-phosphonium cation, while the anion was respectively: 
     E.1 chloride (check)--M.P.=222° C., 
     E.2 tetrachlorocadmiate--M.P.=142.5° C. 
     
                                           TABLE NO. 5                             
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FORMULATION No.   46 47 48 49 50 51                                       
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Tecnoflon IN p. by weight                                                 
                  100                                                     
                     100                                                  
                        100                                               
                           100                                            
                              100                                         
                                 100                                      
MgO (Maglite D) p. by weight                                              
                  5  5  5  5  5  5                                        
Ca(OH).sub.2 p. by weight                                                 
                  5  5  5  5  5  5                                        
Carbon black MT p. by weight                                              
                  30 30 30 30 30 30                                       
Bisphenol AF p. by weight                                                 
                  1.6                                                     
                     1.6                                                  
                        1.6                                               
                           1.6                                            
                              1.6                                         
                                 1.6                                      
Accelerator: E.1 m. equivalents                                           
                  1.0                                                     
                     1.5                                                  
                        2.0                                               
                           -- -- --                                       
(e)5.2 m.Accelerator: equivalents                                         
                  -- -- -- 1.0                                            
                              1.5                                         
                                 2.0                                      
Vulcanization                                                             
in press a 170° C. × 10 minutes                              
in oven at 250° C. × 15 hours                                
100% elongation modulus kg/cm.sup.2 (3)                                   
                  58 60 61 60 62 64                                       
Tensile strength kg/cm.sup.2 (3)                                          
                  165                                                     
                     160                                                  
                        150                                               
                           160                                            
                              150                                         
                                 140                                      
Elongation at break kg/cm.sup.2 (3)                                       
                  185                                                     
                     175                                                  
                        165                                               
                           180                                            
                              170                                         
                                 160                                      
Hardness, IRHD (4)                                                        
                  76 76 77 75 76 76                                       
Compression set, on                                                       
O-Rings (0 25.4 × 3.53 mm): (5)                                     
at 200° C. × 70 hours                                        
                  31 33 35 31 32 35                                       
at 200° C. × 168 hours                                       
                  35 36 39 36 38 40                                       
Adhesive strength (kg · cm.sup.-1) (6)                           
after vulcanization in press                                              
                  15 7  5  40 42 36                                       
at 170° C. × 8 minutes                                       
after post vulcanization in oven                                          
                  17 9  7  39 37 35                                       
at 250° C. × 16 hours                                        
after post-vulcanization in oven                                          
                  14 6  4  36 34 30                                       
at 250° C. × 16 hours and aqueous                            
treatment at 100° C. × 48 hours                              
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