Peroxide cured fluorocarbon elastomer compositions

Abstract

A process involves adding a peroxide masterbatch to a molten blend of a fluorocarbon elastomer and a thermoplastic material. The peroxide masterbatch contains greater than or equal to 5% weight percent organic peroxide, further contains a fluorocarbon elastomer, and typically also contains a crosslinker containing at least two sites of olefinic unsaturation. The fluorocarbon elastomer in the molten blend and in the peroxide masterbatch may be the same or different. After the peroxide masterbatch is added to the molten blend, the combination is mixed at a temperature and for a time sufficient to effect cure of the fluorocarbon elastomers. By using a masterbatch, a faster and more uniform dispersion of peroxide curative is possible due to pre-dispersion of peroxide in the elastomer phase, which leads to shaped articles having improved mechanical properties.

1 . A process for making a melt processable fluorocarbon rubber composition comprising 
 (a) adding a peroxide masterbatch to a molten blend of a first portion of fluorocarbon elastomer and a thermoplastic material, wherein the masterbatch comprises greater than or equal to about 5% weight percent organic peroxide and further comprises a second portion of a fluorocarbon elastomer; and    (b) mixing the peroxide masterbatch, the first portion of fluorocarbon elastomer, and the thermoplastic material while heating for a time and at a temperature sufficient to effect cure of the fluorocarbon elastomers.    
   
   
       2 . A process according to  claim 1 , using a twin-screw extruder having a first feeder and a second feeder downstream from the first feeder, wherein said adding comprises: 
 (i) injecting a composition comprising the first portion of fluorocarbon elastomer and the thermoplastic material into the first feeder of the extruder; and    (ii) adding the masterbatch into the with a second feeder of the extruder.    
   
   
       3 . A process according to  claim 1 , wherein the fluorocarbon elastomer of the first portion and the second portion are the same.  
   
   
       4 . A process according to  claim 1 , wherein the fluorocarbon elastomer comprises a copolymer of vinylidene fluoride and cure site monomers containing iodine.  
   
   
       5 . A process according to  claim 1 , wherein the peroxide masterbatch comprises greater than about 10% by weight percent peroxide.  
   
   
       6 . A process according to  claim 1 , wherein the peroxide masterbatch comprises greater than about 20% by weight percent peroxide.  
   
   
       7 . A process according to  claim 5 , wherein the thermoplastic material comprises a fluoroplastic.  
   
   
       8 . A process according to  claim 7 , wherein the fluoroplastic comprises a vinylidene fluoride homopolymer.  
   
   
       9 . A process according to  claim 7 , wherein the fluoroplastic comprises a vinylidene fluoride copolymer.  
   
   
       10 . A molded article comprising a peroxide cured dynamic vulcanizate of a fluorocarbon elastomer and a fluorine containing thermoplastic, having a tensile modulus above about 10 MPa.  
   
   
       11 . A molded article according to  claim 10 , having a tensile modulus above about 12 MPa.  
   
   
       12 . A molded article according to  claim 11 , having a tensile modulus above about 15 MPa.  
   
   
       13 . A molded article according to  claim 10 , comprising a discrete phase of cured fluorocarbon elastomer and a continuous phase of a fluoroplastic material.  
   
   
       14 . A molded article according to  claim 12 , wherein the fluorocarbon elastomer comprises a copolymer of VDF and HFP.  
   
   
       15 . A molded article according to  claim 14 , wherein the fluorocarbon elastomer comprises a copolymer of VDF, HFP, and TFE.  
   
   
       16 . A molded article according to  claim 12 , wherein the fluorocarbon elastomer comprises a copolymer of VDF, fluorinated vinyl ether, and TFE.  
   
   
       17 . A molded article according to  claim 12 , wherein the fluorocarbon elastomer comprises a copolymer of VDF, TFE, and propylene.  
   
   
       18 . A molded article according to  claim 12 , wherein the fluorocarbon elastomer comprises a copolymer of VDF, HFP, TFE, fluorinated vinyl ether, and ethylene.  
   
   
       19 . A molded article according to  claim 12 , wherein the fluorocarbon elastomer comprises a perfluoro rubber.  
   
   
       20 . A process for making melt processable fluoroelastomer composition comprising 
 (a) blending a thermoplastic polymeric material and a first fluorocarbon elastomer to form a first mixture at a temperature above a melt flow temperature of the thermoplastic;    (b) combining the first mixture with a second mixture comprising a second fluorocarbon elastomer and greater than or equal to about 5% by weight of an organic peroxide at a temperature below that at which the peroxide would activate to initiate crosslinking of the second fluorocarbon elastomer; and    (c) blending the first and second mixtures together while heating at a temperature and for a time sufficient to cure the fluorocarbon elastomer in the first and second mixtures.    
   
   
       21 . A method according to  claim 20 , wherein the second mixture further comprises a crosslinker containing at least two sites of olefinic unsaturation.  
   
   
       22 . A method according to  claim 21 , wherein the crosslinker comprises triallylisocyanurate.  
   
   
       23 . A method according to  claim 21 , wherein the first mixture further comprises a crosslinker containing at least two sites of olefinic unsaturation.  
   
   
       24 . A method according to  claim 23 , wherein the crosslinker comprises triallylisocyanurate.  
   
   
       25 . A continuous process for preparing a peroxide cured dynamic vulcanizate of a fluorocarbon elastomer in a thermoplastic, using a twin-screw extrusion apparatus having a barrel, a first feeder, and a second feeder that is downstream of the first feeder, comprising 
 (a) delivering a solid blend of an uncured fluorocarbon elastomer and thermoplastic to the first feeder;    (b) injecting the solid blend into the barrel of the extruder, wherein the barrel is heated above a melt flow temperature of the thermoplastic;    (c) mixing the solid blend in the extruder to form a homogeneous melt blend;    (d) injecting a peroxide masterbatch to the second feeder, wherein the peroxide masterbatch comprises an uncured fluorocarbon elastomer and greater or equal to about 5% by weight of an organic peroxide;    (e) mixing the peroxide masterbatch and the homogenous melt blend in the barrel while continuing to heat at a temperature and for a time sufficient to effect cure of the fluorocarbon elastomers, and;    (f) extruding the mixture from the twin-screw extruder.    
   
   
       26 . A process according to  claim 25 , wherein the peroxide masterbatch is delivered to the second feeder with a twin screw apparatus that blends the organic peroxide and fluorocarbon elastomer at a temperature less than that which would activate the peroxide.  
   
   
       27 . A process according to  claim 25 , wherein the fluorocarbon elastomers comprise a copolymer of vinylidene fluoride and a cure site monomer, and the thermoplastic comprises a fluoroplastic.  
   
   
       28 . A process according to  claim 27 , wherein the fluoroplastic comprises a vinylidene fluoride polymer.  
   
   
       29 . A process according to  claim 25 , comprising heating the barrel above about 180° C.  
   
   
       30 . A process according to  claim 29 , comprising heating the barrel above about 210° C.  
   
   
       31 . A process according to  claim 30 , comprising heating the barrel above about 240° C.  
   
   
       32 . A process according to  claim 25 , wherein the peroxide masterbatch further comprises a crosslinker containing two or more sites of olefinic unsaturation.  
   
   
       33 . A process according to  claim 32 , wherein the crosslinker comprises triallylisocyanurate.  
   
   
       34 . A process according to  claim 25 , wherein the solid blend of uncured fluorocarbon elastomer and thermoplastic further comprises a crosslinker containing two or more sites of olefinic unsaturation.  
   
   
       35 . A process according to  claim 34 , wherein the crosslinker comprises triallylisocyanurate.