Vulcanizable epoxy group-containing elastomer composition
This invention relates to a vulcanizable epoxy group-containing elastomer composition. More specifically, it relates to a vulcanizable epoxy group-containing elastomer composition which has excellent processing safety and storage stability for premature vulcanization, and gives vulcanizates having excellent mechanical properties, heat aging resistance and compression set. 
     It has been the usual practice to use polyamines, diamine carbamates, ammonium salts of organic carboxylic acids, and dithiocarbamic acid salts as vulcanization systems for epoxy group-containing elastomers. The use of polyamines or diamine carbamates, however, has the defect that because the rate of vulcanization is fast, the elastomers are liable to undergo scorching in the mixing and processing steps. When the ammonium salts of organic carboxylic acids or dithiocarbamic acid salts are used, elastomer stocks having stability to scorching can be obtained because the rate of vulcanization is relatively slow. But long post-vulcanization must be performed in order to obtain good compression sets. 
     Various vulcanization methods have been suggested in an attempt to remove these defects. For example, the specification of Japanese Laid-Open Patent Publication No. 145727/1980 discloses a vulcanization system comprising a phthalic acid anhydride and a specific imidazole compound for epoxy group-containing elastomers. The specifications of Japanese Laid-Open Patent Publications Nos. 177044/1982 and 177045/1982 disclose vulcanization systems comprising a guanidine compound and sulfur or a sulfur donor compound for epoxy group-containing elastomers. These vulcanization systems are stable to scorching, but have the defect of requiring post-vulcanization for long periods of time in order to obtain good compression sets. 
     It is an object of this invention to remedy these defects of the prior art. 
     The present inventors have made extensive investigations on various vulcanization systems in order to achieve this object, and consequently found that by using a polycarboxylic acid having at least 2 carboxyl groups in the molecule and a quaternary ammonium salt or a quaternary phosphonium salt as a vulcanizing agent for an epoxy group-containing elastomer, there can be obtained a vulcanizable composition which has excellent processing safety and storage stability for premature vulcanization and gives a vulcanizate having excellent mechanical properties, heat aging resistance and compression set. 
     According to this invention, there is provided a vulcanizable epoxy group-containing elastomer composition comprising an elastomer containing epoxy groups, a polycarboxylic acid having at least 2 carboxyl groups in the molecule, and either a quaternary ammonium salt or a quaternary phosphonium salt. 
     The epoxy group-containing elastomer used in this invention is an elastomer having epoxy groups as a vulcanization site, and includes epoxidized elastomers obtained by epoxidizing elastomers containing no epoxy group, and elastomers obtained by copolymerizing usually 0.1 to 10% by weight, preferably 0.3 to 3% by weight, of an epoxy group-containing monomer as a vulcanization site with 90 to 99.9% by weight, preferably 97 to 99.7% by weight, of at least one monomer containing a copolymerizable terminal vinyl or vinylidene group by known polymerization methods such as emulsion, suspension, solution or bulk polymerization. 
     Examples of the epoxy group-containing monomer used as a crosslinking site include glycidyl acrylate, glycidyl methacrylate, vinyl glycidyl ether, allyl glycidyl ether, and methallyl glycidyl ether. Of these, glycidyl acrylate and glycidyl methacrylate are preferred. 
     Examples of the monomers having a terminal vinyl or vinylidene group copolymerizable with the epoxy group-containing monomer are alkyl acrylates having 1 to 8 carbon atoms in the alkyl moiety such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and n-octyl acrylate, and the corresponding methacrylates; alkoxyalklyl acrylates having 1 to 4 carbon atoms in each of the alkoxy and alkyl moieties such as methoxymethyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, butoxyethyl acrylate and methoxyethoxyethyl acrylate; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; vinyl ketones such as methyl vinyl ketone and ethyl vinyl ketone; vinyl aromatic compounds such as styrene, alphamethylstyrene and vinyltoluene; conjugated dienes such as butadiene and isoprene; alpha-monolefins such as ethylene, propylene and 1-butene; vinyl monomers having a hydroxyl group such as beta-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; vinyl and vinylidene monomers having a nitrile group such as acrylonitrile, methacrylonitrile and beta-cyanoethyl acrylate; and unsaturated amide monomers such as acrylamide and N-methyl methacrylamide. These monomers may be used singly or in combination. 
     Specific examples of the epoxy group-containing elastomer include epoxy group-containing acrylate copolymer elastomers, epoxy group-containing ethylene/vinyl acetate copolymer elastomers, epoxy group-containing ethylene/acrylate copolymer elastomers, epoxy group-containing ethylene/vinyl acetate/acrylate copolymer elastomers, epoxy group-containing ethylene/propylene copolymer elastomers, epoxy group-containing acrylate/acrylonitrile copolymer elastomers, epoxy group-containing butadiene/acrylonitrile copolymer elastomers, epoxy group-containing butadiene/styrene copolymer elastomers, and epoxy group-containing butadiene/acrylonitrile/acrylate copolymer elastomers. 
     These epoxy group-containing elastomers are vulcanized by using a vulcanization system comprising a polycarboxylic acid having at least 2 carboxyl groups in the molecule and either a quaternary ammonium salt or a quaternary phosphonium salt. 
     The polycarboxylic acid having at least 2 carboxyl groups in the molecule is usually selected from saturated and unsaturated aliphatic compounds, alicylic compounds, aromatic compounds and low-molecular-weight polymers. The polycarboxylic acid used in this invention also includes a polycarboxylic acid anhydride. 
     The following are typical examples of carboxyl group-containing compounds which can be used in this invention. 
     Examples of the aliphatic compounds include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, octanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanediocic acid, tartronic acid, methyltartronic acid, methylmalonic acid, ethylmalonic acid, tetramethylsuccinic acid, 2,2&#39;-dimethylsuccinic acid, malic acid, alpha-methylmalic acid, alpha-hydroxyglutaric acid, alpha-hydroxyadipic acid, oxosuccinic acid, 2-oxoadipic acid, acetylmalonic acid, 2-acetylglutaric acid, beta-hydroxyglutaric acid, maleic acid, citraconic acid, glutaconic acid, muconic acid, citric acid, tartaric acid, 1,2,3-propanetricarboxylic acid, 1,2,3-propenetricarboxylic acid, 1,3,5-pentanetricarboxylic acid, cystine, aspartic acid, glutamic acid, beta-hydroxyglutamic acid, iminodiacetic acid, nitrilotriacetic acid and ethylenediaminetetraacetic acid. 
     Examples of the alicyclic compound include cis-1,3-cyclopentanedicarboxylic acid, cis-1,4-cyclohexanedicarboxylic acid, 1,5-cyclooctanedicarboxylic acid and hexahydroterephthalic acid. 
     Examples of the aromatic compounds include phthalic acid, 3-methylphthalic acid, terephthalic acid, phthalonic acid, hydroxyterephthalic acid, hemipinic acid, benzophenonedicarboxylic acid, phenylsuccinic acid, trimellitic acid, pyromellitic acid and 7,8-diphenyltetradecanedicarboxylic acid. 
     Examples of the low-molecular-weight polymers include carboxyl-terminated-liquid polybutadiene, carboxyl-terminated liquid butadiene/acrylonitrile copolymer, and liquid butadiene/acrylonitrile copolymer having carboxyl groups in the molecular chain. 
     Examples of the polycarboxylic acid anhydride are malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, pyrophosphoric anhydride, 1,2-cyclohexanedicarboxylic anhydride, and long-chain dibasic acid anhydrides such as octadecyldioic acid condensate. These examples are not limitative, however, and anhydrides of the above-exemplified polycarboxylic acids can all be used in this invention. 
     For good compression sets and low-temperature properties, aliphatic dicarboxylic acids and the anhydrides thereof are especially preferred among the polycarboxylic acids used in this invention. 
     The polycarboxylic acid may be added during or after the polymerization reaction for producing the elastomer, or may be added to the elastomer together with other compounding chemicals such as a filler by a kneader normally used in the rubber industry. 
     The polycarboxylic acid can be used in an amount of usually 0.1 to 30 parts by weight per 100 parts by weight of the epoxy group-containing elastomer. The proportion of the polycarboxylic acid relative to the epoxy group-containing elastomer specified above has been selected in view of the speed of vulcanization and the mechanical properties, compression set, etc. of the vulcanizates. If it is below the specified lower limit, the speed of vulcanization is drasticaly reduced, and a practical vulcanizate cannot be obtained. On the other hand, if it exceeds the specified upper limit, the speed of vulcanization becomes very small, and a practical vulcanizate cannot be obtained. The preferred proportion of the polycarboxylic acid is 0.1 to 20 parts by weight. 
     The quaternary ammonium salt and the quaternary phosphonium salt used in this invention are compounds represented by the following formula ##STR1## 
     In the above general formula, Y is a nitrogen or phosphorus atom; R 1  to R 4  each represent a hydrocarbon group having about 1 to 25 carbon atoms such as an alkyl, aryl or alkylaryl group, or two or three of the groups R 1  to R 4  may form together with Y a heterocyclic ring wherein at least two ring atoms are carbon atoms and the remainder are oxygen, nitrogen, phosphorus or sulfur atoms; and X is an anion derived from an inorganic or organic acid in which acidic hydrogen is bonded to halogen or oxygen, preferably Cl, Br, I, HSO 4 , H 2  PO 4 , R 3  COO, R 5  OSO 3 , R 5  SO or R 5  OPO 3  H (R 5  is the same hydrocarbon group as R 1  to R 4 ). 
     Specific examples of the quaternary ammonium salt include tetraethyl ammonium bromide, tetrabutyl ammonium chloride, tetrabutyl ammonium bromide, tetrabutyl ammonium iodide, n-dodecyltrimethyl ammonium bromide, cetyldimethylbenzyl ammonium chloride, methylcetyldibenzyl ammonium bromide, cetyldimethylethyl ammonium bromide, octadecyltrimethyl ammonium bromide, cetylpyridinium chloride, cetyl pyridinium bromide, 1,8-diaza-bicyclo(5,4,0)undecene-7-methyl ammonium methosulfate, 1,8-diazabicyclo(5,4,0)undecene-7-benzyl ammonium chloride, cetyltrimethyl ammonium alkylphenoxypoly(ethyleneoxy)ethyl phosphate, cetyl pyridinium sulfate, tetraethyl ammonium acetate, trimethylbenzyl ammonium benzoate, trimethylbenzylammonium p-toluenesulfonate and trimethylbenzyl ammonium borate. 
     Specific examples of the quaternary phosphonium salts include triphenylbenzyl phosphonium chloride, triphenylbenzyl phosphonium bromide, triphenylbenzyl phosphonium iodide, triphenylmethoxymethyl phosphonium chloride, triethylbenzylphosphonium chloride, tricyclohexylbenzyl phosphonium chloride, trioctylmethyl phosphonium dimethyl phosphate, tetrabutyl phosphonium, bromide, and trioctylmethyl phosphonium acetate. 
     These quaternary ammonium salts or quaternary phosphonium salts may be used singly or as a mixture of two or more. The amount of the quaternary ammonium or phosphonium salt is usually 0.1 to 10 parts by weight per 100 parts by weight of the epoxy group-containing elastomer. This range has been selected for the high vulcanization speeds and excellent processing stability and storage stability of the vulcanizable composition and the excellent mechanical properties and compression sets of vulcanizates. If it is below the specified lower limit, vulcanization hardly proceeds. On the other hand, if it exceeds the specified upper limit, the speed of vulcaniztion becomes extremely fast, and the processing stability and storage stability of the vulcanizable composition are reduced. The preferred range is 0.1 to 5 parts by weight. 
     The vulcanizable composition of this invention is prepared by mixing the epoxy group-containing elastomer with the aforesaid vulcanization agent and compounding chemicals normally used in the rubber industry, such as a reinforcing agent, a filler, a plasticizer, a stabilizer, and a processing aid, by an ordinary kneader such as a roll mill or a Banbury mixer. The composition is molded into a desired shape, and then vulcanized to form a final product. The vulcanization is carried out usually at a temperature of at least 120° C., preferably about 150° to 220° C., for about 1 to 60 minutes. Post-vulcanization can be carried out at a temperature of about 150° to 200° C. for about 1 to 24 hours. 
     The vulcanizable epoxy group-containing elastomer composition of this invention is a novel and efficient composition which has excellent processing safety and storage stability for early vulcanization, and gives vulcanizates having excellent mechanical properties, heat aging resistance and compression sets. It has been thought that vulcanizable epoxy group-containing elastomer compositions require a relatively long period of post-vulcanization in order to obtain a good compression set. With the vulcanizable composition of this invention, however, a good compression set can be obtained even when it is press-cured for a short period of time. Accordingly, the post-vulcanization can be greatly shortened, or omitted. 
     Since vulcanizates of epoxy group-containing elastomers obtained from the vulcanizable composition of this invention have excellent heat aging resistance, weatherability, water resistance and compression sets, they can find wide applications in various sealing materials (gaskets, O-rings, packings, oil seals), various hoses, diaphragms, and various belts or rolls. 
     The present invention will be more specifically illustrated by the following Referential Example, Examples and the accompanying drawing. 
     In these examples, all parts are by weight. 
    
    
     In the accompanying drawings, 
     FIGS. 1 and 2 show cure curves of the compositions in Example 1 measured by an oscillating disk rheometer; 
     FIGS. 3 and 4 show cure curves of the compositions in Example 3; 
     FIG. 5 shows cure curves of the compositions in Example 4; and 
     FIG. 6 shows cure curves of the compositions in Example 5. 
    
    
     The numerals shown in these figures are run numbers. 
     REFERENTIAL EXAMPLE 
     Synthesis of epoxy group-containing elastomers: 
     In each run, each of the monomeric mixtures indicated in Table 1 was copolymerized in a 2-liter separable flask in accordance with the following polymerization recipes (I) and (II). First, the substances shown in (I) were charged into the flask, and the pH of the mixture in the flask was adjusted to 7. With stirring, the temperature of the mixture was adjusted to 5° C. Deaeration and nitrogen purging were repeated to remove oxygen from the flask sufficiently. Then, the substances shown in (II) were added, and the polymerization was started. The polymerization was terminated in about 10 hours. The polymerization conversion was 97 to 99%. After the polymerization, the polymerization product was salted out, fully washed with water, and dried under reduced pressure to obtain an epoxy group-containing acrylic elastomer. 
     The Mooney viscosities of the elastomers obtained are also shown in Table 1. 
     
         ______________________________________                                    
Polymerization Recipe (I)                                                 
Water                    1000   g                                         
Sodium dodecylbenzenesulfonate                                            
                         20     g                                         
Sodium naphthalenesulfonate                                               
                         10     g                                         
Sodium sulfate           3      g                                         
Tetrasodium ethylenediamine-                                              
                         0.2    g                                         
tetraacetate                                                              
Ferric sodium ethylenediamine-                                            
                         0.005  g                                         
acetate                                                                   
Monomeric mixture (Table 1)                                               
                         1000   g                                         
Polymerization Recipe (II)                                                
Na.sub.2 SO.sub.4        0.2    g                                         
Sodium formaldehyde sulfoxylate                                           
                         0.2    g                                         
p-Menthane hydroperoxide 0.1    g                                         
______________________________________                                    
 
    
     
                       TABLE 1                                                     
______________________________________                                    
            Acrylic elastomer                                             
Monomers (parts)                                                          
              A           B      C                                        
______________________________________                                    
Ethyl acrylate                                                            
              97.5        98     48                                       
Butyl acrylate                                                            
              --          --     30                                       
Methoxyethyl  --          --     20                                       
acrylate                                                                  
Glycidyl meth-                                                            
               2.5        --      2                                       
acrylate                                                                  
Glycidyl acrylate                                                         
              --           2     --                                       
Mooney viscosity                                                          
              48          52     36                                       
(ML.sub.1+4, 100° C.)                                              
______________________________________                                    
 
    
     EXAMPLE 1 
     In each run, 100 parts of the epoxy group-containing acrylic elastomer A, 1 part of stearic acid, 50 parts of MAF carbon black (Seast 116, a trade name for a product of Tokai Carbon Co., Ltd.), and the various vulcanization agents shown in Table 2 in the amounts indicated were kneaded on a 6-inch roll mill to prepare a compound. 
     
                                           TABLE 2                                 
__________________________________________________________________________
                                           Amount                         
Run No.  Vulcanizing agent                 (parts)                        
__________________________________________________________________________
Invention                                                                 
        1                                                                 
         Succinic acid/Cetyltrimethyl ammonium bromide                    
                                           0.75/2                         
        2                                                                 
         Glutaric acid/Cetyltrimethyl ammonium bromide                    
                                           0.85/2                         
        3                                                                 
         Pimelic acid/Cetyltrimethyl ammonium bromide                     
                                           1.0/2                          
        4                                                                 
         Azelaic acid/Cetyltrimethyl ammonium bromide                     
                                           1.2/2                          
        5                                                                 
         Tetradecanedioic acid/Cetyltrimethyl ammonium bromide            
                                           1.7/2                          
        6                                                                 
         1,3,5-Pentanetricarboxylic acid/Cetyltrimethyl ammonium          
                                           0.9/2de                        
        7                                                                 
         7,8-Diphenyltetradecanedioic acid/Cetyltrimethyl ammonium        
         bromide                           2.5/2                          
        8                                                                 
         cis-1,4-Cyclohexanedicarboxylic acid/Cetyltrimethyl ammonium     
         bromide                           1.1/2                          
        9                                                                 
         Phthalic acid/Cetyltrimethyl ammonium bromide                    
                                           1.0/2                          
       10                                                                 
         C-1000 (*1)/Cetyltrimethyl ammonium bromide                      
                                            10/3                          
       11                                                                 
         CTBN (*2)/Cetyltrimethyl ammonium bromide                        
                                            12/3                          
       12                                                                 
         DN-601 (*3)/Cetyltrimethyl ammonium bromide                      
                                            10/3                          
       13                                                                 
         Phthalic anhydride/Cetyltrimethyl ammonium bromide               
                                           0.9/2                          
       14                                                                 
         SL-2OAH (*4)/Cetyltrimethyl ammonium bromide                     
                                           2.6/2                          
       15                                                                 
         SL-2PAH (*5)/Cetyltrimethyl ammonium bromide                     
                                           2.6/2                          
Comparison                                                                
       16                                                                 
         2-Methylimidazole/hexahydrophthalic anhydride                    
                                             0.2/1.0                      
       17                                                                 
         Ammonium benzoate                 1.3                            
__________________________________________________________________________
 (*1): Carboxylterminated liquid polybutadiene (NISSO PB C1000, a product 
 of Nippon Soda Co., Ltd.).                                               
 (*2): Carboxylterminated liquid butadiene/acrylonitrile copolymer (Hycar 
 CTBN, a product of B. F. Goodrich Co., Ltd.).                            
 (*3): Liquid butadiene/acrylonitrile copolymer containing carboxyl groups
 in the molecular chain (Nipol DN601, a product of Nippon Zeon Co., Ltd.).
 (*4): Octadecyldioic acid condensate (acid anhydride) (a product of      
 Okamura Seiyu K.K.).                                                     
 (*5): 7,8diphenyl-tetradecanedicarboxylic acid condensate (acid anhydride
 (a product of Okamura Seiyu K.K.).                                       
 
    
     The Mooney scorch time was measured on the resulting compound, and then it was press-cured at 170° C. for 20 minutes. Thereafter, it was post-cured in a Geer&#39;s oven at 150° C. for 16 hours. The various properties of the cured products were measured in accordance with JIS K-6301. To judge the storage stability of the compound, its Mooney scorch time on standing for 2 weeks at room temperature was also measured. The results are shown in Table 3. FIGS. 1 and 2 show cure curves of the compounds measured by an Oscillating Disc Rheometer (made by Toyo Seiki K.K.; to be abbreviated as ODR hereinafter) at 170° C. 
     
                                           TABLE 3                                 
__________________________________________________________________________
            Run No.                                                       
                                                         Com-             
            Invention                                    parison          
Test Item   1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16 17            
__________________________________________________________________________
Mooney scorch time (125° C.)                                       
t.sub.5 (minutes)                                                         
            16 18 13 14 16 36 19 17 28 12 13 11 12 13 14 12  8            
t.sub.35 (minutes)                                                        
            36 41 34 36 43 125                                            
                              63 40 -- 26 30 23 33 38 39 22 17            
Minimum viscosity                                                         
            46 50 50 51 46 44 45 47 43 40 36 38 51 48 47 47 52            
Mooney scorch time (125° C.) after standing for 2 weeks at room    
temperature                                                               
t.sub.5 (minutes)                                                         
            17 19 14 14 17 38 20 19 30 13 15 13 18 15 15  8  7            
t.sub.35 (minutes)                                                        
            39 44 37 35 45 -- 66 45 -- 28 37 25 46 42 45 16 14            
Minimum viscosity                                                         
            47 50 51 52 47 45 46 50 43 41 36 38 49 47 46 56 53            
Properties after press-curing at 170° C. for 20 minutes            
Tensile strength                                                          
            112                                                           
               114                                                        
                  117                                                     
                     115                                                  
                        114                                               
                           119                                            
                              116                                         
                                 113                                      
                                    83 121                                
                                          106                             
                                             105                          
                                                111                       
                                                   120                    
                                                      119                 
                                                         113              
                                                            107           
(kg/cm.sup.2)                                                             
Elongation (%)                                                            
            340                                                           
               320                                                        
                  310                                                     
                     320                                                  
                        330                                               
                           280                                            
                              330                                         
                                 310                                      
                                    540                                   
                                       300                                
                                          470                             
                                             400                          
                                                380                       
                                                   290                    
                                                      320                 
                                                         280              
                                                            360           
100% Tensile stress                                                       
            42 46 47 45 46 55 41 45 21 38 23 33 36 51 50 49 36            
(kg/cm.sup.2)                                                             
Hardness (JIS)                                                            
            68 68 69 68 69 68 67 68 63 62 56 59 67 71 70 69 68            
Properties after post-vulcanization at 150° C. for 16 hours        
Tensile strength                                                          
            135                                                           
               140                                                        
                  143                                                     
                     145                                                  
                        142                                               
                           148                                            
                              149                                         
                                 138                                      
                                    128                                   
                                       153                                
                                          144                             
                                             146                          
                                                135                       
                                                   133                    
                                                      136                 
                                                         159              
                                                            138           
(kg/cm.sup.2)                                                             
Elongation (%)                                                            
            220                                                           
               210                                                        
                  210                                                     
                     220                                                  
                        220                                               
                           170                                            
                              230                                         
                                 220                                      
                                    260                                   
                                       160                                
                                          170                             
                                             180                          
                                                230                       
                                                   200                    
                                                      210                 
                                                         150              
                                                            270           
100% Tensile stress                                                       
            71 78 72 71 70 95 73 74 64 81 67 74 74 71 72 113              
                                                            54            
(kg/cm.sup.2)                                                             
Hardness (JIS)                                                            
            69 70 71 70 70 72 68 71 69 72 67 69 72 72 71 77 73            
Properties after heat-aging at 175° C. for 70 hours (vulcanizate   
obtained by press curing at 170° C. for 20 minutes)                
Tensile strength                                                          
            148                                                           
               152                                                        
                  156                                                     
                     157                                                  
                        150                                               
                           153                                            
                              151                                         
                                 151                                      
                                    153                                   
                                       149      151                       
                                                   149                    
                                                      151                 
                                                          147             
                                                            141           
(kg/cm.sup.2)                                                             
Elongation (%)                                                            
            130                                                           
               120                                                        
                  120                                                     
                     120                                                  
                        130                                               
                           110                                            
                              140                                         
                                 110                                      
                                    110                                   
                                       100      120                       
                                                   130                    
                                                      130                 
                                                         110              
                                                            150           
Hardness (JIS)                                                            
            76 77 76 75 76 78 75 77 79 79       76 76 76 81 79            
Compression set (150° C. × 70 hours; 25% compression)        
Vulcanizate obtained                                                      
            41 34 36 38 34 40 35 34 59 53 61 60 49 35 34 69 78            
by press-curing at                                                        
170° C. for 20 min. (%)                                            
Vulcanizate obtained                                                      
            28 22 26 24 21 31 23 22 40 37 39 39 28 22 21 63 52            
by post-curing at                                                         
150° C. for 16 hours (%)                                           
__________________________________________________________________________
 
    
     These results show that the vulcanization systems in accordance with this invention have better scorch stability and vulcanization snappy property (the behavior whereby in a cure curve, the torque rises within a short time after vulcanization begins, and reaches a plateau value) than the vulcanization systems used heretofore (Comparative Examples 16 and 17). Even after standing for 2 weeks at room temperature, the compound shows a vulcanization behavior not much different from that of the compound immediately after preparation, and therefore, it has excellent storage stability. The conventional vulcanization systems give poor compression sets upon press curing at 170° C. for 20 minutes, and a good compression set cannot be obtained unless post-curing is performed for a long period of time. In contrast, the vulcanization systems in accordance with this invention give good compression set values even by press curing at 170° C. for as short as 20 minutes. This can allow omission of post-curing. 
     EXAMPLE 2 
     In each run, 100 parts of each of the epoxy group-containing acrylic elastomers shown in Table 4, 1 part of stearic acid, 50 parts of MAF carbon black and each of the vulcanization agents shown in Table 4 in the amounts indicated were kneaded on a 6-inch roll mill to prepare a compound. 
     
                       TABLE 4                                                     
______________________________________                                    
                                  Amounts                                 
Run  Elastomer   Vulcanization agents                                     
                                  (parts)                                 
______________________________________                                    
21   B           Tetradecanedioic acid/                                   
                                  1.7/2                                   
                 Cetyltrimethyl ammonium                                  
                 bromide                                                  
22   C           Tetradecanedioic acid/                                   
                                  1.7/2                                   
                 Cetyltrimethyl ammonium                                  
                 bromide                                                  
23   C           2-Methylimidazole/                                       
                                  0.2/1                                   
                 Hexahydrophthalic                                        
                 anhydride                                                
______________________________________                                    
 
    
     Runs Nos. 21 and 22 are within the scope of the invention, and Run 23 is a comparison. 
     The compound was press-cured at 170° C. for 20 minutes, and then post-cured in Geer&#39;s oven at 150° C. for 16 hours. The properties of the cured product were measured in the same way as in Example 1, and the results are shown in Table 5. 
     
                       TABLE 5                                                     
______________________________________                                    
                 Run No.                                                  
                          Com-                                            
                 Invention                                                
                          parison                                         
Test Item         21       22     23                                      
______________________________________                                    
Properties after press-curing at 170° C. for 20 minutes            
Tensile strength (kg/cm.sup.2)                                            
                  112      101    83                                      
Elongation (%)    370      280    320                                     
100% Tensile stress (kg/cm.sup.2)                                         
                  35       29     24                                      
Hardness (JIS)    68       63     65                                      
Properties after post-curing at 150° C. for 16 hours               
Tensile strength (kg/cm.sup.2)                                            
                  138      121    132                                     
Elongation (%)    240      180    180                                     
100% Tensile stress (kg/cm.sup.2)                                         
                  57       45     80                                      
Hardness (JIS)    69       66     73                                      
Compression set (150° C. × 70 hours; 25% compression         
Vulcanizate obtained                                                      
                  38       41     78                                      
by press-curing at 170° C.                                         
for 20 minutes (%)                                                        
Vulcanizate obtained                                                      
                  26       23     42                                      
by post-curing at 150° C.                                          
for 16 hours (%)                                                          
______________________________________                                    
 
    
     EXAMPLE 3 
     One hundred parts of the epoxy group-containing acrylic elastomer, 1 part of stearic acid, 50 parts of MAF carbon black and each of the vulcanization agents indicated in Table 6 in the amounts indicated were kneaded on a 6-inch roll mill to prepare a compound. The compound was press-cured at 170° C. for 20 minutes, and then post-cured in a Geer&#39;s oven at 150° C. for 16 hours. The properties of the cured product were measured in the same way as in Example 1. The results are shown in Table 7. The cure curves of the compositions at 170° C. were measured by ODR, and are shown in FIGS. 3 and 4. 
     
                                           TABLE 6                                 
__________________________________________________________________________
                                      Amount                              
Run No.  Vulcanization agent          (parts)                             
__________________________________________________________________________
Invention                                                                 
       31                                                                 
         Cetyl pyridinium bromide/Tetradecanedioic acid                   
                                      1/1.7                               
       32                                                                 
         &#34;                            2/1.7                               
       33                                                                 
         &#34;                            4/1.7                               
       34                                                                 
         &#34;                            2/5                                 
Comparison                                                                
       35                                                                 
         &#34;                            2/0                                 
       36                                                                 
         &#34;                            0/1.7                               
Invention                                                                 
       37                                                                 
         Cetyltrimethyl ammonium iodide/Tetradecanedioic                  
                                      1.5/1.7                             
       38                                                                 
         Triphenylbenzyl phosphonium chloride/Tetradecanedioic            
                                      3/1.7                               
       39                                                                 
         Tetrabutyl phosphonium bromide/Tetradecanedioic                  
                                      1.5/1.7                             
       40                                                                 
         Triphenylbenzyl phosphonium iodide/Tetradecanedioic              
                                      1.5/1.7                             
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                                           TABLE 7                                 
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              Run No.                                                     
              Invention   Comparison      Invention                       
Test Item     31 32 33 34 35      36      37 38 39 40                     
__________________________________________________________________________
Properties after press-curing at 170° C. for 20 minutes            
Tensile strength (kg/cm.sup.2)                                            
              91 113                                                      
                    110                                                   
                       73 Vulcanization                                   
                                  Vulcanization                           
                                          122                             
                                             93 118                       
                                                   120                    
Elongation (%)                                                            
              430                                                         
                 350                                                      
                    360                                                   
                       630                                                
                          insufficient*                                   
                                  insufficient*                           
                                          290                             
                                             450                          
                                                320                       
                                                   290                    
100% Tensile stress (kg/cm.sup.2)                                         
              23 40 38 21                 52 25 40 45                     
Hardness (JIS)                                                            
              64 68 67 59                 69 65 64 68                     
Properties after post-curing at 150° C. for 16 hours               
Tensile strength (kg/cm.sup.2)                                            
              149                                                         
                 140                                                      
                    137                                                   
                       115                146                             
                                             141                          
                                                137                       
                                                   146                    
Elongation (%)                                                            
              220                                                         
                 230                                                      
                    220                                                   
                       350                200                             
                                             250                          
                                                190                       
                                                   180                    
100% Tensile stress (kg/cm.sup.2)                                         
              72 67 67 32                 82 59 80 83                     
Hardness (JIS)                                                            
              70 69 67 65                 71 69 71 72                     
Properties after heat-aging at 175° C. for 70 hours (vulcanizate   
obtained                                                                  
by press-curing at 170° C. for 20 minutes)                         
Tensile strength (kg/cm.sup.2)                                            
              152                                                         
                 147                                                      
                    148                                                   
                       144                152                             
                                             137                          
                                                142                       
                                                   154                    
Elongation (%)                                                            
              140                                                         
                 140                                                      
                    130                                                   
                       120                130                             
                                             210                          
                                                130                       
                                                   120                    
Hardness (JIS)                                                            
              76 75 74 78                 76 74 76 76                     
Compression set (150° C. × 70 hours; 25% compression)        
Vulcanizate obtained                                                      
              82 35 37 78                 34 61 39 37                     
by press-curing at 170° C.                                         
for 20 minutes (%)                                                        
Vulcanizate obtained                                                      
              25 23 27 45                 20 26 29 28                     
by post-curing at 150° C.                                          
for 16 hours (%)                                                          
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 *Since the compounds were not practical, vulcanizate were not prepared   
 from them.                                                               
 
    
     These results demonstrate that the increasing of the amount of the quaternary ammonium salt increases the speed of curing; the addition of an excessive amount of the polycarboxylic acid retards the speed of vulcanization and impairs the various properties of the resulting vulcanizate; and that if either one of the quaternary ammonium salt or the polycarboxylic acid is lacking (Comparative Runs Nos. 35 and 36), the degree of vulcanization did not rise, and the compositions were not practical. 
     It is also seen that the various quaternary ammonium salts and quaternary phosphonium salts can be used as the vulcanization system in accordance with this invention, and they are excellent in regard to vulcanization snappy property, vulcanizate properties and compression set. 
     EXAMPLE 4 
     One hundred parts of an ethylene/vinyl acetate/butyl acrylate/glycidyl methacrylate four-component copolymer synthesized by a known polymerization method [the composition (% by weight) determined from chemical shifts in  13  C-NMR was 18 ethylene, 39 vinyl aceteate, 42 butyl acrylate and 1 glycidyl methacrylate], 1 part of stearic acid, 50 parts of MAF carbon black, and each of the vulcanization agents shown in Table 8 in the amounts indicated were kneaded on a 6-inch roll mill to prepare a compound. 
     The Mooney scorch time of the compound was measured, and it was cured in the same way as in Example 1. The various properties of the vulcanizate were measured. 
     The results are shown in Table 9. The cure curves of the compositions at 170° C. measured by ODR are shown in FIG. 5. 
     
                       TABLE 8                                                     
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                             Amount                                       
Run No.   Vulcanization agent                                             
                             (parts)                                      
______________________________________                                    
41        Cetyltrimethyl ammonium                                         
                               1/1.5                                      
          bromide/Tetradecanedioic                                        
          acid                                                            
42        Tetrabutyl phosphonium                                          
                             1.5/1.5                                      
          bromide/Tetradecanedioic                                        
          acid                                                            
43        2-Methylimidazole/Hexahydro-                                    
                             0.2/0.5                                      
          phthalic anhydride                                              
______________________________________                                    
 
    
     Runs Nos. 41 and 42 are within the scope of the invention, and Run No. 43 is a comparison. 
     
                       TABLE 9                                                     
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                 Run No.                                                  
                           Com-                                           
                 Invention parison                                        
Test Item         41        42     43                                     
______________________________________                                    
Mooney scorch time (125° C.)                                       
t5 (minutes)      19        13     12                                     
t35 (minutes)     36        23     27                                     
Minimum viscosity 45        47     46                                     
Properties after press-curing at 170° C. for 20 minutes            
Tensile strength (kg/cm.sup.2)                                            
                  118       113    100                                    
Elongation (%)    450       320    430                                    
100% Tensile stress (kg/cm.sup.2)                                         
                  33        37     30                                     
Hardness (JIS)    68        64     68                                     
Properties after post-curing at 150° C. for 16 hours               
Tensile strength (kg/cm.sup.2)                                            
                  141       135    138                                    
Elongation (%)    320       190    250                                    
100% Tensile stress (kg/cm.sup.2)                                         
                  45        80     55                                     
Hardness (JIS)    71        70     72                                     
Permanent compression set (150° C. × 70 hours,               
25% compression)                                                          
Tensile strength (kg/cm.sup.2)                                            
                  147       144    146                                    
Elongation (%)    230       120    190                                    
100% Tensile stress (kg/cm.sup.2)                                         
                  61        96     73                                     
Hardness (JIS)    75        76     76                                     
Compression set (150° C. × 70 hours, 25% compression         
Vulcanizate obtained                                                      
                  39        42     68                                     
by press-curing at 170° C.                                         
for 20 minutes (%)                                                        
Vulcanizate obtained                                                      
                  23        32     36                                     
by post-curing at 150° C.                                          
for 16 hours (%)                                                          
______________________________________                                    
 
    
     EXAMPLE 5 
     One hundred parts of a butadiene/acrylonitrile/glycidyl methacrylate terpolymer elastomer synthesized by a known polymerization method (composition by weight percent: butadiene 65, acrylonitrile 33, glycidyl methacrylate 2), 1 part of stearic acid, 40 parts of MAF carbon black, and each of the vulcanization agents shown in Table 10 in the amounts indicated were kneaded on a 6-inch roll to prepare a compound. The compound was press-cured at 160° C. for 20 minutes, and the properties of the vulcanizate were measured in the same way as in Example 1. 
     The results are shown in Table 11. The cure curves of the compounds at 170° C. measured by ODR are shown in FIG. 6. 
     
                       TABLE 10                                                    
______________________________________                                    
                             Amount                                       
Run No.     Vulcanization agent                                           
                             (parts)                                      
______________________________________                                    
51          Cetyltrimethyl ammonium                                       
                               2/2.2                                      
            bromide/Tetradecanedioic                                      
            acid                                                          
52          Tetrabutyl phosphonium                                        
                             1.5/2.2                                      
            bromide/Tetradecanedioic                                      
            acid                                                          
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                       TABLE 11                                                    
______________________________________                                    
                     Run No.                                              
                     Invention                                            
Test item              51     52                                          
______________________________________                                    
Properties after press curing at 160° C. for 20 min.               
Tensile strength (kg/cm.sup.2)                                            
                       143    142                                         
Elongation (%)         340    360                                         
100% Tensile stress (kg/cm.sup.2)                                         
                       45     42                                          
Hardness (JIS)         69     68                                          
Compression set (120° C. × 70 hours, 25% compression)        
Vulcanizate obtained by press                                             
                       12     13                                          
curing at 60° C. for 20 min. (%)                                   
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