Curable fluoroelastomers having low swelling tendency

Abstract

The invention relates to a curable fluoroelastomer composition having low swelling tendency, comprising: A) a curable fluoroelastomer; B) a curing system; and C) 0.1 wt.-% to 30 wt.-% of a nitrogen-containing polymer, selected from polyamide, polyimide, mixtures and/or copolymers thereof, each relative to the total weight of fluoroelastomer and nitrogen-containing polymer, the nitrogen-containing polymer being present in particulate form of an average particle size in the range of 0.15 to 70 μm and/or in fiber form having an average fiber diameter in the range of 0.15 to 70 μm.

1 . A curable fluoroelastomer composition comprising:
 A) a curable fluoroelastomer;   B) a curing system; and   C) 0.1 wt % to 30 wt % of a nitrogen-containing polymer selected from polyamide, polyimide, mixtures and/or copolymers thereof, based in each case on the total weight of fluoroelastomer and nitrogen-containing polymer,   characterized in that the nitrogen-containing polymer is present in particle form having an average particle size in the range from 0.15 to 70 μm and/or in fiber form having an average fiber diameter in the range from 0.15 to 70 μm.   
     
     
         2 . The fluoroelastomer composition of  claim 1 , further comprising an amount of metal oxide functioning as an acid acceptor, in particular zinc oxide, magnesium oxide, calcium oxide and/or lead oxide (PbO/Pb 3 O 4 ), of less than 1.5 wt %, and/or an amount of metal hydroxide functioning as an acid acceptor, in particular calcium hydroxide, of less than 1.5 wt %, and/or an amount of metal salt functioning as an acid acceptor, in particular hydrotalcite, calcium and/or magnesium stearate, of less than 5 wt %, wherein the quantities are based in each case on the total weight of the fluoroelastomer composition. 
     
     
         3 . The fluoroelastomer composition of  claim 1 , wherein the fluoroelastomer is a radically curable fluoroelastomer. 
     
     
         4 . The fluoroelastomer composition of  claim 1 , wherein the nitrogen-containing polymer is selected from polymers having a melting temperature determined according to ASTM D3418-08 or a decomposition temperature of greater than 180° C. 
     
     
         5 . The fluoroelastomer composition of  claim 1 , wherein the nitrogen-containing polymer is solid at the curing temperature of the fluoroelastomer. 
     
     
         6 . The fluoroelastomer composition of  claim 1 , wherein the fluoroelastomer composition in the cured state has a volume swelling in 20% acetic acid after 168 h/95° C., measured in accordance with DIN ISO 1817, of from 0 to 25 vol. 
     
     
         7 . The fluoroelastomer composition of  claim 1 , where the fluoroelastomer composition in the cured state has a compression set after 168 h/200° C., measured in accordance with DIN ISO 815, of from 0 to 70 percent, for example 1 to 70%. 
     
     
         8 . A method for preparing the curable fluoroelastomer composition of  claim 1 , comprising the steps of:
 A) providing a curable, preferably radically curable, in particular peroxide-curable fluoroelastomer;   B) providing a nitrogen-containing polymer selected from polyamide, polyimide, mixtures and/or copolymers thereof, the nitrogen-containing polymer being present in particle form having an average particle size in the range from 0.1 to 70 μm and/or in fiber form having an average fiber diameter in the range from 0.1 to 70 μm;   C) mixing the curable fluoroelastomer with the nitrogen-containing polymer at a temperature lower than whichever is the lower of melting temperature and decomposition temperature of the nitrogen-containing polymer to form a polymer mixture that has curable fluoroelastomer and 0.1 wt % to 30 wt % nitrogen-containing polymer based on the total weight of fluoroelastomer and nitrogen-containing polymer, and   D) adding a curing system, in particular a peroxide curing agent and a crosslinking co-agent, to the polymer mixture at a temperature lower than the lower of melting temperature and decomposition temperature of the nitrogen-containing polymer to form a curable fluoroelastomer composition.   
     
     
         9 . Use of the fluoroelastomer composition of  claim 1  for preparing seals. 
     
     
         10 . A seal comprising the fluoroelastomer composition of  claim 1 , wherein the fluoroelastomer composition is in the cured state. 
     
     
         11 . Use of the seal of  claim 10  in acidic media. 
     
     
         12 . The fluoroelastomer composition of  claim 3 , wherein the fluoroelastomer is a peroxide-curable fluoroelastomer. 
     
     
         13 . The fluoroelastomer composition of  claim 6 , wherein the fluoroelastomer composition in the cured state has a volume swelling in 20% acetic acid after 168 h/95° C., measured in accordance with DIN ISO 1817, of from 0 to 15 vol %. 
     
     
         14 . The fluoroelastomer composition of  claim 6 , wherein the fluoroelastomer composition in the cured state has a volume swelling in 20% acetic acid after 168 h/95° C., measured in accordance with DIN ISO 1817, of from 0 to 10 vol %. 
     
     
         15 . The fluoroelastomer composition of  claim 7 , wherein the fluoroelastomer composition in the cured state has a compression set after 168 h/200° C., measured in accordance with DIN ISO 815, of from 0 to 60%, for example 1 to 60%. 
     
     
         16 . The fluoroelastomer composition of  claim 7 , wherein the fluoroelastomer composition in the cured state has a compression set after 168 h/200° C., measured in accordance with DIN ISO 815, of from 0 to 40%, for example 1 to 40%. 
     
     
         17 . The seals of  claim 9 , wherein the seals are O-rings, frame seals, radial shaft seals, bellow-type seals and valve stem seals.