Flame retardant, electrically conductive shielding materials and methods of making the same

Abstract

Flame retardant EMI shielding materials with improved retention of shielding properties are disclosed. The shielding materials are provided with a dispersed flame retardant on the surfaces of the internal interstices. Methods of making the flame retardant shielding materials are also disclosed.

1 . A method of producing a flame retardant, electrically conductive EMI shielding material, the method comprising impregnating a porous material having internal interstices, the internal surfaces of which are electrically conductive, with an effective amount of flame retardant that provides the impregnated shielding material with at least horizontal flame rating while at the same time retaining z-axis conductivity or bulk resistivity sufficient for EMI shielding applications, wherein the flame retardant is dispersed such that the impregnated shielding material is substantially free of occluded interstices.  
   
   
       2 . The method of  claim 1 , wherein the interstices are electrically conductive due to at least one electrically conductive metal or non-metal layer disposed on the internal surfaces.  
   
   
       3 . The method of  claim 1 , wherein the flame retardant is halogen free.  
   
   
       4 . The method of  claim 1 , wherein the flame retardant is in the form an aqueous composition.  
   
   
       5 . The method of  claim 4 , wherein the aqueous composition includes a polymeric carrier.  
   
   
       6 . The method of  claim 5 , wherein the polymeric carrier is water-soluble or water-dispersible polymer.  
   
   
       7 . The method of  claim 4 , wherein the solvent for the aqueous composition is water or a combination of water and water-miscible organic solvents.  
   
   
       8 . The method of  claim 7 , wherein the solvent is free of a non-water-miscible organic solvent.  
   
   
       9 . The method of  claim 1 , further comprising curing the impregnated shielding material.  
   
   
       10 . The method of  claim 1 , wherein the flame retardant comprises a phosphate-based flame retardant.  
   
   
       11 . The method of  claim 10 , wherein the flame retardant comprises an ammonium phosphate salt.  
   
   
       12 . The method of  claim 1 , wherein the effective amount of the flame retardant provides no more than about a ten fold increase in bulk resistivity.  
   
   
       13 . The method of  claim 1 , wherein the effective amount of the flame retardant provides a UL94 flame rating of at least HB.  
   
   
       14 . The method of  claim 1 , wherein the flame retardant is in the form of a particulate dispersed throughout the interstices.  
   
   
       15 . The method of  claim 1 , wherein the flame retardant is in the form of a particulate occupying no more than about 30% of the total internal surface area defined by the interstices.  
   
   
       16 . The method of  claim 1 , wherein the flame retardant is in the form of a coating on the internal surfaces of the interstices.  
   
   
       17 . The method of  claim 16 , wherein the coating has a thickness of about 12 microns or less.  
   
   
       18 . The method of  claim 1 , wherein the impregnated shielding material has a bulk resistivity of about 20 ohm•cm or less.  
   
   
       19 . The method of  claim 1 , wherein the porous material comprises open-cell foam having at least one metallized layer throughout.  
   
   
       20 . The method of  claim 19 , wherein the foam includes a porous scrim.  
   
   
       21 . The method of  claim 20 , wherein the foam comprises polyurethane foam.  
   
   
       22 . The method of  claim 1 , wherein the impregnated shielding material has an average shielding effectiveness of at least about 65 decibels.  
   
   
       23 . The method of  claim 1 , wherein a polymeric coating is disposed between at least some of the internal surfaces of the interstices and the flame retardant.  
   
   
       24 . A method of making a flame retardant, electrically conductive EMI shielding material, the method comprising providing a porous material having internal interstices, the internal surfaces of which are electrically conductive due to at least one electrically conductive metal or non-metal layer, with an effective amount of flame retardant that provides the impregnated shielding material with a UL94 flame rating of at least HB while at the same time retaining z-axis conductivity or bulk resistivity sufficient for EMI shielding applications, wherein the flame retardant is in the form of a particulate dispersed in a coating such that the impregnated shielding material is substantially free of occluded interstices with the particulate occupying no more than about 30% of the total internal surface area defined by the interstices.  
   
   
       25 . The method of  claim 24 , wherein the flame retardant is halogen free.  
   
   
       26 . The method of  claim 24 , wherein the effective amount of the flame retardant provides a UL94 flame rating of V0.  
   
   
       27 . The method of  claim 24 , wherein the effective amount of the flame retardant provides no more than about a one fold increase in bulk resistivity.  
   
   
       28 . The method of  claim 24 , wherein the shielding material has a bulk resistivity of about 0.05 ohm•cm or less.  
   
   
       29 . The method of  claim 24 , wherein the particulate occupies no more than about 10% of the total internal surface area defined by the interstices.  
   
   
       30 . The method of  claim 24 , wherein the impregnated shielding material has an average shielding effectiveness of at least about 90 decibels.