Silica-reinforced rubber compounded with an alkoxysilane and a strong organic base

Abstract

Improved tensile mechanical and dynamic viscoelastic properties of silica-reinforced sulfur vulcanized rubbers can be achieved by compounding elastomers with silica in the presence of an alkoxysilane and a catalytic amount of a strong organic base. The strong organic base acts as a catalyst to accelerate the alkoxysilane-silica reaction, especially at high compounding temperatures, resulting in rubber compounds that exhibit reduced compound viscosity, improved dispersion of silica, and reduced filler flocculation after compounding, and reduced hysteresis and improved abrasion resistance in the vulcanized product, compared to similar compounds prepared at the temperature without the strong organic base catalyst.

We claim:  
     
         1 . A sulfur-vulcanizable elastomeric compound, comprising: 
 an elastomer optionally having an alkoxysilane terminal group;    a reinforcing filler comprising silica or a mixture thereof with carbon black;    an alkyl alkoxysilane;    a mercaptosilane silica coupling agent, wherein the weight ratio of the mercaptosilane to the alkyl alkoxysilane is a maximum of 0.14:1;    a catalytic amount of a strong organic base; and    a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure.    
     
     
         2 . The compound of  claim 1 , wherein the elastomer, the silica, the alkyl alkoxysilane, the mercaptosilane and the strong organic base are mixed together, in the absence of the cure agent, at a temperature of about 130° C. to about 200° C.  
     
     
         3 . The compound of  claim 2 , wherein the compound exhibits an improved tensile mechanical or dynamic viscoelastic property, selected from the group of properties consisting of about a 1% to about a 10% decrease in Mooney viscosity after compounding, reduced hysteresis as measured by about a 3% to about a 20% decrease in tan δ at 50° C., about a 3% to about a 20% decrease in filler flocculation after compounding, and combinations thereof, compared to a similar compound mixed at the temperature in the absence of the strong organic base.  
     
     
         4 . The compound of  claim 1 , wherein the strong organic base is selected from the group consisting of a guanidine, a hindered amine base, and mixtures thereof  
     
     
         5 . The compound of  claim 4 , wherein the guanidine is selected from the group consisting of triphenylguanidine, diphenylguanidine, di-o-tolylguanidine, and mixtures thereof.  
     
     
         6 . The compound of  claim 5 , wherein the guanidine is diphenylguanidine.  
     
     
         7 . The compound of  claim 4 , wherein the hindered amine base is selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene; 1,5-diazabicyclo[4.3.0]non-5-ene; and mixtures thereof.  
     
     
         8 . The compound of  claim 1 , wherein the catalytic amount of the strong organic base is about 0.1% to about 10% by weight, based on the weight of the silica.  
     
     
         9 . The compound of  claim 8 , wherein the catalytic amount of the strong organic base about 0.1% to about 5% by weight, based on the weight of the silica.  
     
     
         10 . The compound of  claim 1 , wherein the weight ratio of the mercaptosilane to the alkyl alkoxysilane is about 0.001:1 to about 0.10:1.  
     
     
         11 . The compound of  claim 1 , wherein the mercaptosilane is present in an amount of about 0.0001% to about 3% by weight, based on the weight of the silica.  
     
     
         12 . The compound of  claim 1 , wherein the alkyl alkoxysilane is an alkyl trialkoxysilane.  
     
     
         13 . The compound of  claim 1 , further comprising a silica dispersing aid selected from the group consisting of a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, a polyoxyethylene derivative of a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, an ester of a polyol, and mixtures thereof.  
     
     
         14 . The compound of  claim 13 , wherein the fatty acid ester is selected from the group consisting of sorbitan monooleate, sorbitan dioleate, sorbitan trioleate, sorbitan sesquioleate, sorbitan laurate, sorbitan palmitate, sorbitan stearate, and mixtures thereof.  
     
     
         15 . The compound of  claim 1 , wherein the elastomer is selected from the group consisting of homopolymers of conjugated diene monomers, and copolymers and terpolymers of the conjugated diene monomers with monovinyl aromatic monomers and trienes.  
     
     
         16 . A pneumatic tire comprising a component produced from a sulfur-vulcanized elastomeric compound that comprises an elastomer optionally having an alkoxysilane terminal group, a reinforcing filler comprising silica or a mixture thereof with carbon black, an alkyl alkoxysilane, a mercaptosilane silica coupling agent, wherein the weight ratio of the mercaptosilane to the alkyl alkoxysilane is a maximum of 0.14:1, a catalytic amount of a strong organic base, and a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure.  
     
     
         17 . The tire of  claim 16 , wherein the elastomer is selected from the group consisting of homopolymers of conjugated diene monomers, and copolymers and terpolymers of the conjugated diene monomers with monovinyl aromatic monomers and trienes.  
     
     
         18 . A method for preparing a sulfur-vulcanized elastomeric compound, comprising the steps of: 
 (a) mixing together at a temperature of about 130° C. to about 200° C. in the absence of added sulfur and cure agents, an elastomer optionally having an alkoxysilane terminal group, a reinforcing filler comprising silica or a mixture thereof with carbon black, an alkyl alkoxysilane and a mercaptosilane, wherein the ratio of the mercaptosilane to the alkyl alkoxysilane is a maximum of 0.14:1, and a catalytic amount of a strong organic base;    (b) allowing the mixture to cool below the mixing temperature;    (c) mixing the mixture obtained in step (b), at a temperature lower than a vulcanization temperature, with a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure, and    (d) curing the mixture obtained in step (c).    
     
     
         19 . The method of  claim 18 , wherein the mixing temperature in step (a) is about 155° C. to about 200° C.  
     
     
         20 . The method of  claim 19 , wherein the mixing temperature in step (a) is about 170° C. to about 200° C.  
     
     
         21 . The method of  claim 18 , wherein the catalytic amount of the strong organic base is about 0.1% to about 10% by weight, based on the weight of the silica.  
     
     
         22 . The method of  claim 21 , wherein the catalytic amount of the strong organic base is about 0.1% to about 5% by weight, based on the weight of the silica.  
     
     
         23 . The method of  claim 18 , wherein the mercaptosilane is present in an amount of about 0.0001% to about 3% by weight, based on the weight of the silica.  
     
     
         24 . A sulfur vulcanizable elastomeric compound, comprising: 
 an elastomer optionally having an alkoxysilane terminal group,    a reinforcing filler comprising silica or a mixture thereof with carbon black;    a silica coupling agent selected from the group consisting of about 0.01% to about 1% by weight of a bis(trialkoxysilylorgano)tetrasulfide silica coupling agent, based on the weight of the silica, about 0.1% to about 20% by weight of a bis(trialkoxysilylorgano)disulfide silica coupling agent, based on the weight of the silica, and mixtures thereof;    a silica dispersing aid;    a catalytic amount of a strong organic base; and    a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure.    
     
     
         25 . The compound of  claim 24 , wherein the elastomer, the silica, the silica coupling agent, the silica dispersing aid, and the strong organic base are mixed together, in the absence of the cure agent, at a temperature of 165° C. to about 200° C.  
     
     
         26 . The compound of  claim 25 , wherein the compound exhibits an improved tensile mechanical or dynamic viscoelastic property compared to a similar compound mixed at the temperature in the absence of the strong organic base, the property selected from the group consisting of about a 10% to about a 40% decrease in filler flocculation after compounding, as measured by ΔG′; reduced hysteresis as measured by about a 3% to about a 20% decrease in tangent δ at 65° C.; about a 3% to about a 20% increase in the tensile modulus at 300% strain, and combinations thereof.  
     
     
         27 . The compound of  claim 24 , wherein the strong organic base is selected from the group consisting of a guanidine, a hindered amine base, and mixtures thereof.  
     
     
         28 . The compound of  claim 27 , wherein the guanidine is selected from the group consisting of triphenylguanidine, diphenylguanidine, di-o-tolylguanidine, and mixtures thereof.  
     
     
         29 . The compound of  claim 28 , wherein the guanidine is diphenylguanidine.  
     
     
         30 . The compound of  claim 27 , wherein the hindered amine base is selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene; 1,5-diazabicyclo[4.3.0]non-5-ene; and mixtures thereof.  
     
     
         31 . The compound of  claim 24 , wherein the catalytic amount of the strong organic base is about 0.1% to about 10% by weight, based on the weight of the silica.  
     
     
         32 . The compound of  claim 31 , wherein the catalytic amount of the strong organic base about 0.1% to about 5% by weight, based on the weight of the silica.  
     
     
         33 . The compound of  claim 24 , wherein the silica dispersing aid is selected from the group consisting of an alkyl alkoxysilane, a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, a polyoxyethylene derivative of a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, an ester of a polyol, and mixtures thereof.  
     
     
         34 . The compound of  claim 33 , wherein the alkyl alkoxysilane is a triethoxysilane.  
     
     
         35 . The compound of  claim 33 , wherein the fatty acid ester is selected from the group consisting of sorbitan monooleate, sorbitan dioleate, sorbitan trioleate, sorbitan sesquioleate, sorbitan laurate, sorbitan palmitate, sorbitan stearate, and mixtures thereof.  
     
     
         36 . The compound of  claim 24  wherein the elastomer is selected from the group consisting of homopolymers of conjugated diene monomers, and copolymers and terpolymers of the conjugated diene monomers with monovinyl aromatic monomers and trienes.  
     
     
         37 . A pneumatic tire comprising a component produced from a sulfur-vulcanized elastomeric compound, wherein the compound comprises an elastomer optionally having an alkoxysilane terminal group; a reinforcing filler comprising silica or a mixture thereof with carbon black; a silica coupling agent selected from the group consisting of about 0.01% to about 1% by weight of a bis(trialkoxysilylorgano)tetrasulfide silica coupling agent, based on the weight of the silica, about 0.1% to about 20% by weight of a bis(trialkoxysilylorgano)disulfide silica coupling agent, based on the weight of the silica, and mixtures thereof; a silica dispersing aid; a catalytic amount of a strong organic base; and a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure.  
     
     
         38 . The tire of  claim 37 , wherein the elastomer is selected from the group consisting of homopolymers of conjugated diene monomers, and copolymers and terpolymers of the conjugated diene monomers with monovinyl aromatic monomers and trienes.  
     
     
         39 . A method for preparing a sulfur-vulcanized elastomeric compound, comprising the steps of: 
 (a) mixing together at a temperature of 165° C. to about 200° C. in the absence of added sulfur and cure agents, an elastomer optionally having an alkoxysilane terminal group; a reinforcing filler comprising silica or a mixture thereof with carbon black; a silica coupling agent selected from the group consisting of about 0.01% to about 1% by weight of a bis(trialkoxysilylorgano)tetrasulfide silica coupling agent, based on the weight of the silica, about 0.1% to about 20% by weight of a bis(trialkoxysilylorgano)disulfide silica coupling agent, based on the weight of the silica, and mixtures thereof, a silica dispersing aid; and a catalytic amount of a strong organic base;    (b) allowing the mixture to cool below the mixing temperature;    (c) mixing the mixture obtained in step (b), at a temperature lower than a vulcanization temperature, with a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure; and    (d) curing the mixture obtained in step (c).    
     
     
         40 . The method of  claim 39 , wherein the mixing temperature in step (a) is about 170° C. to about 200° C.  
     
     
         41 . The method of  claim 40 , wherein the mixing temperature in step (a) is about 170° C. to about 185° C.  
     
     
         42 . The method of  claim 39 , wherein the catalytic amount of the strong organic base is about 0.1% to about 10% by weight, based on the weight of the silica.  
     
     
         43 . The method of  claim 39 , wherein the silica dispersing aid is selected from the group consisting of an alkyl alkoxysilane, a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, a polyoxyethylene derivative of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, and mixtures thereof.  
     
     
         44 . The compound of  claim 43 , wherein the alkyl alkoxysilane is a triethoxysilane.  
     
     
         45 . The compound of  claim 43 , wherein the fatty acid ester is selected from the group consisting of sorbitan monooleate, sorbitan dioleate, sorbitan trioleate, sorbitan sesquioleate, sorbitan laurate, sorbitan palmitate, sorbitan stearate, and mixtures thereof.