Gas-permeable membrane

Abstract

Gas-permeable membranes comprising a microporous film and a coating on the microporous film, the coating being obtained by coating the microporous film with a liquid coating composition comprising a polymer and hollow polymeric particles dispersed in the composition, and then solidifying the coating. The gas-permeable membrane has a reduced ratio of carbon dioxide permeability to oxygen permeability.

1 . A gas-permeable membrane which comprises
 (1) a microporous film, and   (2) a solid coating on the microporous film, the coating comprising
 (a) a matrix comprising a first polymer, and 
 (b) hollow particles which (i) are composed of a polymeric composition comprising a second polymer which is different from the first polymer, (ii) are dispersed in the matrix, and (iii) have a maximum dimension which is at most 50% of the thickness of the solid coating. 
   
   
   
       2 . A membrane according to  claim 1  wherein the solid coating also comprises a plurality of microscopic voids which
 (i) provide continuous pathways for the transmission of oxygen and carbon dioxide through the coating, and   (ii) are at least partly defined by walls composed of the second polymer.   
   
   
       3 . A membrane according to  claim 1  wherein (i) the first polymer consists essentially of at least one side chain crystalline polymer having a peak melting temperature T p  of −5 to 40° C., and a heat of fusion of at least 10 J/g, and (ii) the second polymer consists essentially of a homopolymer or copolymer of styrene. 
   
   
       4 . A membrane according to  claim 1  which
 (a) has an oxygen permeability (OTR) at 20° C. of at least 30,000 cc/100 in 2 ·atm·24 hrs;   (b) has an oxygen P 10  ratio of at least 2 over at least one 10° C. temperature range between 0 and 25° C.;   (c) has a carbon dioxide P 10  ratio of at least 2 over at least one 10° C. temperature range between 0 and 25° C.; and   (d) has at at least one temperature between 0 and 22° C. an R ratio less than 4.   
   
   
       5 . A membrane according to  claim 1  wherein the solid coating contains 5 to 50% by weight of the second polymer. 
   
   
       6 . A membrane according to  claim 1  wherein the solid coating contains 10 to 40% by weight of the second polymer. 
   
   
       7 . A membrane according to  claim 1  wherein at least 90% of the particles have a maximum dimension of 0.2 to 0.8 micron. 
   
   
       8 . A membrane according to  claim 1  wherein the volume of the hollow particles dispersed in the solid coating is 11 to 20% of the volume of the solid coating. 
   
   
       9 . A gas-permeable membrane which comprises
 (1) a microporous film, and   (2) a solid coating on the microporous film, the coating comprising
 (a) a matrix comprising a first polymer which is at least one side chain crystalline polymer having a peak melting temperature T p  of −5 to 40° C., and a heat of fusion of at least 10 J/g, and 
 (b) hollow particles which (i) are composed of a polymeric composition comprising a second polymer which is different from the first polymer, (ii) are dispersed in the matrix, and (iii) have a maximum dimension which is at most 50% of the thickness of the solid coating. 
   
   
   
       10 . A membrane according to  claim 9  wherein the solid coating also comprises a plurality of microscopic voids which
 (i) provide continuous pathways for the transmission of oxygen and carbon dioxide through the coating, and   (ii) are at least partly defined by walls composed of the second polymer.   
   
   
       11 . A membrane according to  claim 1  wherein the second polymer consists essentially of a homopolymer or copolymer of styrene. 
   
   
       12 . A membrane according to  claim 9  which
 (a) has an oxygen permeability (OTR) at 20° C. of at least 30,000 cc/100 in 2 ·atm·24 hrs;   (b) has an oxygen P 10  ratio of at least 2 over at least one 10° C. temperature range between 0 and 25° C.;   (c) has a carbon dioxide P 10  ratio of at least 2 over at least one 10° C. temperature range between 0 and 25° C.; and   (d) has at at least one temperature between 0 and 22° C. an R ratio less than 4.   
   
   
       13 . A membrane according to  claim 9  wherein the solid coating contains 5 to 50% by weight of the second polymer. 
   
   
       14 . A membrane according to  claim 9  wherein the solid coating contains 10 to 40% by weight of the second polymer. 
   
   
       15 . A membrane according to  claim 9  wherein at least 90% of the particles have a maximum dimension of 0.2 to 0.8 micron. 
   
   
       16 . A membrane according to  claim 9  wherein the volume of the hollow particles dispersed in the solid coating is 11 to 20% of the volume of the solid coating. 
   
   
       17 . A method of preparing a gas-permeable membrane which comprises a microporous film and a solid polymeric coating on the microporous film, the method comprising
 (A) forming a liquid coating on the microporous film, the liquid coating being composed of liquid coating composition which comprises
 (a) a first polymer, and 
 (b) hollow particles which (i) are dispersed in the coating composition, and (ii) are composed of a polymeric composition comprising a second polymer, the second polymer being different from the first polymer; and 
   (B) solidifying the liquid coating on the microporous film;   
     the hollow polymeric particles having a maximum dimension which is at most 50% of the thickness of the solid coating. 
   
   
       18 . A method according to  claim 19  wherein step (B) comprises heating which at least partially melts at least some of the hollow polymeric particles so that they fuse together to form a plurality of microscopic voids. 
   
   
       19 . A method according to  claim 18  which comprises heating the coating at a temperature of 50 to 85° C. 
   
   
       20 . A container which can be sealed around a respiring biological material or has been sealed around a respiring biological material, and which includes one or more atmosphere control members, at least one of the atmosphere control members comprising a gas-permeable membrane selected from gas-permeable membranes as defined in  claim 1 , gas-permeable membranes as defined in  claim 9 , and gas-permeable membranes prepared by the method of  claim 17 .