Rubber compositions and method for increasing the mooney scorch value

Abstract

A rubber composition is disclosed wherein the rubber composition contains at least (a) a rubber component; (b) a silica filler; (c) a coupling agent; (d) a cure-enhancing amount of at least one polyalkylene oxide; and (e) at least one high molecular weight thiuram disulfide. The compositions may also include suitable amounts of other ingredients such as carbon black, antiozonants, antioxidants, etc.

What is claimed is:  
     
         1 . A method for increasing the mooney scorch value of a rubber composition which comprises the step of forming a rubber composition comprising (a) a rubber component; (b) a silica filler; (c) a coupling agent; (d) a polyalkylene oxide; and (e) a thiuram disulfide having a molecular weight of at least about 400.  
     
     
         2 . The method of claim  17  wherein the rubber component is selected from the group consisting of natural rubber, homopolymers of conjugated diolefins, copolymers of conjugated diolefins and ethylenically unsaturated monomers and mixtures thereof.  
     
     
         3 . The method of claim  17  wherein the silica filler is selected from the group consisting of silica, precipitated silica, amorphous silica, vitreous silica, fumed silica, fused silica, synthetic silicate, alkaline earth metal silicate, highly dispersed silicate and mixtures thereof.  
     
     
         4 . The method of claim  17  wherein the coupling agent is a sulfur-containing coupling agent of the general formula: 
 Z-R 1 -S n -R 2 -Z in which Z is selected from the group consisting of  
                     
 wherein R 3  is an alkyl group of from 1 to 4 carbon atoms, cyclohexyl or phenyl; and R 4  is an alkoxy of from 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; and R 1  and R 2  are independently a divalent hydrocarbon of from 1 to 18 carbon atoms and n is an integer of from about 2 to about 8.  
 
     
     
         5 . The method of claim  20  wherein the sulfur-containing coupling agent is selected from the group consisting of 3,3′-bis(trimethoxysilylpropyl) disulfide, 3,3′-bis(triethoxysilylpropyl) disulfide, 3,3-bis(triethoxysilylpropyl) tetrasulfide, 3,3′-bis(triethoxysilylpropyl) octasulfide, 3,3′-bis(trimethoxysilylpropyl) tetrasulfide, 2,2′-bis(triethoxysilylethyl) tetrasulfide, 3,3′-bis(trimethoxysilylpropyl) triasulfide, 3,3′-bis(triethoxysilylpropyl) triasulfide, 3,3′-bis(tributoxysilylpropyl) disulfide, 3,3′-bis(trimethoxysilylpropyl) hexasufide, 3,3′-bis(trimethoxysilylpropyl) octasulfide, 3,3′-bis(trioctoxysilylpropyl) tetrasulfide, 3,3′-bis(trihexoxysilylpropyl) disulfide, 3,3′-bis(tri-2″-ethylhexoxysilylpropyl) trisulfide, 3,3′-bis(triisooctoxysilylpropyl) tetrasulfide, 3,3′-bis(tri-t-butoxysilylpropyl) disulfide, 2,2′-bis(methoxydiethoxysilylethyl) tetrasulfide, 2,2′-bis(tripropoxysilylethyl) pentasulfide, 3,3′-bis(tricyclohexoxysilylpropyl) tetrasulfide, 3,3′-bis(tricyclopentoxysilylpropyl) trisulfide, 2,2′-bis(tri-2″-methylcyclohexoxysilylethyl) tetrasulfide, bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl 3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl) disulfide, 2,2′-bis(dimethylsec.butoxysilylethyl) trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl) tetrasulfide, 3,3′-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2′-bis(phenylmethylmethoxysilylethyl) trisulfide, 3,3′-bis(diphenyl isopropoxysilylpropyl) tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2′-bis(methyl dimethoxysilylethyl) trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3′-bis(butyldimethoxysilylpropyl) trisulfide, 3,3′-bis(phenyl dimethoxysilyipropyl) tetrasulfide, 3-phenyl ethoxybutoxysilyl 3′-trimethoxysilyipropyl tetrasulfide, 4,4′-bis(trimethoxysilylbutyl) tetrasulfide, 6,6′-bis(triethoxysilylhexyl) tetrasulfide, 12,12′-bis(triisopropoxysilyldodecyl) disulfide, 18,18′-bis(trimethoxysilyloctadecyl) tetrasulfide, 18,18′-bis(tripropoxysilyloctadecenyl) tetrasulfide, 4,4′-bis(trimethoxysilyl-butene-2-yl) tetrasulfide, 4,4′-bis(trimethoxysilylcyclohexylene) tetrasulfide, 5,5′-bis(dimethoxymethylsilylpentyl) trisulfide, 3,3′-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide, 3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide and combinations thereof.  
     
     
         6 . The method of claim  17  wherein the polyalkylene oxide is selected from the group consisting of dimethylene glycol, diethylene glycol, dipropylene glycol, trimethylene glycol, triethylene glycol, tripropylene glycol, polyethylene oxide, polypropylene oxide, polybutylene oxide and mixtures thereof.  
     
     
         7 . The method of claim  17  wherein the thiuram disulfide is of the general formula 
 wherein R 1 , R 2 , R 3  and R 4  each are the same or different and are hydrocarbons containing from about 4 to about 30 carbon atoms, optionally containing one or more heterocyclic groups, or R 1  and R 2  and/or R 3  and R 4  together with the nitrogen atom to which they are bonded are joined together to form a heterocyclic group, optionally containing one or more additional heterocyclic atoms.  
 
     
     
         8 . The method of claim  23  wherein R 1 , R 2 , R 3  and R 4  each are the same or different and are hydrocarbons containing from about 8 to about 18 carbon atoms.  
     
     
         9 . The method of claim  23  wherein R 1 , R 2 , R 3  and R 4  each are hydrocarbons of between 12 and 14 carbon atoms.  
     
     
         10 . The method of claim  23  wherein the polyalkylene oxide is diethylene glycol and R 1 , R 2 , R 3  and R 4  each are hydrocarbons of between 12 and 14 carbon atoms.  
     
     
         11 . The method of claim  16  wherein the silica filler is present in an amount of from about 5 to about 100 phr, the coupling agent is present in an amount of from about 0.5 to about 10 phr, the polyalkylene oxide is present in an amount of from about 0.5 to about 10 phr and the thiuram disulfide is present in an amount of from about 0.1 to about 1.0 phr.  
     
     
         12 . The method of claim  22  wherein the silica filler is present in an amount of from about 5 to about 100 phr, the sulfur-containing coupling agent is present in an amount from about 0.5 to about 10 phr, diethylene glycol is present in an amount of from about 0.5 to about 10 phr and the thiuram disulfide is present in an amount from about 0.1 to about 1.0.