Conformal coating of polymer fibers on nonwoven substrates

Abstract

The present invention describes a novel process for the conformal coating of polymer fibers on nonwoven substrates. This process is based on the modification of polymer fiber surfaces by controlling the degree of etching and oxidation, which improves adhesion of initiators to the surface and facilitates subsequent conformal polymer grafting. The modified fiber surfaces render new functionalities to the surface, such as increasing hydrophilicity, attaching ligands or changing surface energy. The invention includes the modified polymer fibers produced by the process described herein.

1 . (canceled) 
     
     
         2 . A modified polymer nonwoven substrate comprising a polymer nonwoven substrate having a fiber surface and a conformal coating on said fiber surface. 
     
     
         3 . The modified polymer nonwoven substrate of  claim 2 , wherein the polymer nonwoven substrate is polyolefin fiber, aramid fiber, cellulose fiber, polyamide fiber, polyester fiber, polyvinyl alcohol fiber, polyethylene naphthalate fiber, polyacrylonitrile fiber, polyurethane fiber, liquid crystal copolyester fiber, rigid rod fiber, or a combination thereof. 
     
     
         4 . The modified polymer nonwoven substrate of  claim 2 , wherein the polymer nonwoven substrate is a flat sheet, a roll or a stack. 
     
     
         5 . The modified polymer nonwoven substrate of  claim 2 , wherein the polymer nonwoven substrate is a staple or continuous fiber. 
     
     
         6 . The modified polymer nonwoven substrate of  claim 2 , wherein the polymer nonwoven substrate has a uniform or gradient distribution of a second polymer inside the nonwoven substrate. 
     
     
         7 . The modified polymer nonwoven substrate of  claim 2 , wherein the polymer nonwoven substrate is polypropylene (PP) fiber or polybutylene terephthalate (PBT) fiber. 
     
     
         8 . A modified polymer nonwoven substrate produced by a process to modify a fiber surface of a polymer nonwoven substrate to obtain a conformal coating, comprising the steps of:
 1) increasing roughness of a fiber surface and increasing the hydroxyl, carbonyl and any other oxygen containing group through exposure to UV in air at a wavelength between 150-300 nm, wherein said exposure to UV in air generates ozone;   2) soaking the substrate with a solution containing both a monomer and an initiator;   3) sandwiching the soaked substrate obtained from step 2 between two glasses;   4) exposing the substrate to UV or heat for grafting to form the conformal coating; and   5) washing and drying the substrate.   
     
     
         9 . The modified polymer nonwoven substrate of  claim 8 , wherein the sandwiching of step 3 is such that it promotes, during subsequent grafting at step 4, formation of a saturated vapor phase near the surface of the substrate. 
     
     
         10 . The modified polymer nonwoven substrate of  claim 8 , wherein the polymer nonwoven substrate is polyolefin fiber, aramid fiber, cellulose fiber, polyamide fiber, polyester fiber, polyvinyl alcohol fiber, polyethylene naphthalate fiber, polyacrylonitrile fiber, polyurethane fiber, liquid crystal copolyester fiber, rigid rod fiber, or a combination thereof. 
     
     
         11 . The modified polymer nonwoven substrate of  claim 8 , wherein the polymer nonwoven substrate is a flat sheet, a roll or a stack. 
     
     
         12 . The modified polymer nonwoven substrate of  claim 8 , wherein the polymer nonwoven substrate is a staple or continuous fiber. 
     
     
         13 . The modified polymer nonwoven substrate of  claim 12 , wherein the polymer nonwoven substrate has round, triangle, square, or any irregular shapes of cross-sections. 
     
     
         14 . The modified polymer nonwoven substrate of  claim 8 , wherein said monomer is a bifunctional molecule which can polymerize via radical polymerization and provide functional groups chosen from hydroxyl, amine, carboxylic acid, aldehyde, formamide, pyridine, pyrrolidone, and epoxy. 
     
     
         15 . The modified polymer nonwoven substrate of  claim 8 , wherein said solution comprises a solvent selected from an alcohol or hydrocarbon which dissolves at least 0.5% of the monomer. 
     
     
         16 . The modified polymer nonwoven substrate of  claim 8 , wherein said initiator is a photosensitizer. 
     
     
         17 . The modified polymer nonwoven substrate of  claim 16 , wherein said photosensitizer is benzophenone, anthraquinone, or naphthoquinone. 
     
     
         18 . The modified polymer nonwoven substrate of  claim 8 , wherein said solution contains 0.5% to 20% by weight of monomer. 
     
     
         19 . The modified polymer nonwoven substrate of  claim 8 , wherein unreacted monomers or unattached homopolymers are removed by water, alcohol or hydrocarbon. 
     
     
         20 . The modified polymer nonwoven substrate of  claim 8 , wherein the polymer nonwoven substrate has a uniform or gradient distribution of a second polymer inside the nonwoven substrate. 
     
     
         21 . The modified polymer nonwoven substrate of  claim 8 , wherein the polymer nonwoven substrate is polypropylene (PP) fiber or polybutylene terephthalate (PBT) fiber.