Nonwoven fibrous product and method of making the same

Abstract

This disclosure includes descriptions of nonwoven fibrous webs including a minor amount of a binder securing the interfiber connections to maintain the fiber superstructure and having web densities less than about 0.02 gm./cm. 3 which has heretofore been considered about the lowest density attainable. The disclosure also includes a unique method of manufacturing such webs and contemplates the preferred use of an air laid web of fibers thoroughly impregnated with a fluid which includes a small amount of a permanent binder, preferably less than about 10% by weight of the fabric and a very substantial amount of a volatile liquid in the order of 100% by weight of the fabric. The volatile liquid explosively puffs the fibers into a gossamer web not attainable by conventional techniques and the small amount of binder secures the fiber interconnections together to maintain the superstructure.

What is claimed is: 
     
       1. The method of making a stabilized low density nonwoven fabric comprising the steps of: providing a nonwoven web of discrete fibers;   impregnating said web with an aqueous liquid, the liquid being distributed throughout the web with a minor amount of added material also being distributed throughout the web, said added material acting as a binder capable of stabilizing said fibers as an interconnected web, said added material so acting as an agent altering the surface tension of the aqueous liquid to effectively form upon heating aqueous membranes within the web of spaced and interconnected fibers;   rapidly vaporizing the volatile portions of said aqueous liquid by applying heat substantially to an internal portion of said impregnated web at a rate sufficient to cause the expanding volatile portions of said aqueous liquid to form said aqueous membranes and to exert expansive forces on said aqueous membranes between said fibers and to thereby separate portions of said web and produce a puffed web portion; and   setting the material which acts as a binder while said fibers are in the puffed condition to secure said fibers to one another at interconnections therebetween and thereby to define stable enlarged interstices between the fibers.   
     
     
       2. The method of making a stabilized low density nonwoven fabric comprising the steps of: providing nonwoven web of discrete fibers;   impregnating said web with a liquid, the liquid being distributed throughout the web and containing a major proportion of volatile liquid material and a minor amount of added material, said added material acting as a binder capable of stabilizing said fibers as an interconnected web, said added material also acting as an agent altering the surface tension of the liquid to effectively form upon heating liquid membranes within the web of spaced and interconnected fibers;   rapidly vaporizing the volatile liquid material of said liquid by applying heat substantially to an internal portion of said impregnated web at a rate sufficient to cause the expanding volatile liquid material to form said .[.aqueous.]. .Iadd.liquid .Iaddend.membranes and to exert expansive forces on said liquid membranes between said fibers and to thereby separate portions of said web and produce a puffed web portion; and   setting the material which acts as a binder while said fibers are in the puffed condition to secure said fibers to one another at interconnections therebetween and thereby to define stable enlarged interstices between the separate portions.   
     
     
       3. The method of making a stabilized low density nonwoven fabric comprising the steps of: assembling a nonwoven web of discrete fibers in a dry state wherein said web comprises predominantly short fibers having lengths less than 1/4 inch and a minor percentage of long fibers having lengths in excess of about 3/4 inch,   impregnating said web with an aqueous liquid, the liquid being distributed throughout the web and containing a minor amount of added material, said added material acting as a binder capable of stabilizing said fibers as an interconnected web, said added material also acting as an agent altering the surface tension of the aqueous liquid to effectively form upon heating aqueous membranes within the web of spaced and interconnected fibers;   rapidly vaporizing the volatile portions of said aqueous liquid by applying heat substantially to an internal portion of said impregnated web at a rate sufficient to cause the expanding volatile portions of said aqueous liquid to form said aqueous membranes and to exert expansive forces on said aqueous membranes between said fibers and to thereby separate portions of said web and produce a puffed web portion; and   setting the material which acts as a binder while said fibers are in the puffed condition to secure said fibers to one another at interconnections therebetween and thereby to define stable enlarged interstices between the fibers.   
     
     
       4. The method of making a stabilized low density nonwoven fabric comprising the steps of: assembling a nonwoven web of discrete fibers wherein said fibers are predominantly short fibers having lengths less than 1/4 inch;   impregnating said fibers with an aqueous liquid, the liquid being distributed throughout the fibers and containing a minor amount of added material, said added material acting as a binder capable of stabilizing said fibers as an interconnected web, said added material also acting as an agent altering the surface tension of the aqueous liquid to effectively form upon heating aqueous membranes within the web of spaced and interconnected fibers;   assembling said fibers as a wet layer to form a paper-like web;   rapidly vaporizing the volatile portions of said aqueous liquid by applying heat substantially to an internal portion of said impregnated web at a rate sufficient to cause the expanding volatile portions of said aqueous liquid to form said aqueous membranes and to exert expansive forces on said aqueous membranes between said fibers and to thereby separate portions of said web and produce a puffed web portion; and   setting the material which acts as a binder while said fibers are in the puffed condition to secure said fibers to one another at interconnections therebetween and thereby to define stable enlarged interstices between the fibers.   
     
     
       5. The method of claim 1 wherein said added material comprises thermoplastic fibers which act as a binder and are dispersed throughout said web and engage said discrete fibers, the setting of said binder comprising plasticizing said thermoplastic fibers whereby said discrete fibers are interconnected and maintained as a puffed web. 
     
     
       6. The method of claim 1 wherein said added material is soluble in water. 
     
     
       7. The method of claim 1 wherein said added material is dispersed in water. 
     
     
       8. The method of claim 1 wherein said fibers are assembled in a dry state to form said nonwoven web. 
     
     
       9. The method of claim 1 wherein said fibers are assembled as a wet layer to form a paper-like wet web before vaporizing said aqueous liquid. 
     
     
       10. The method of claim 1 wherein said aqueous liquid is flowed freely onto said web and the excess liquid is removed therefrom by suction. 
     
     
       11. The method of claim 1 wherein said added material comprises a binder capable of securing said fibers together at their interconnections, and a surface tension agent which will dissolve in water and enhance the formation of said membranes. 
     
     
       12. The method of claim 1 wherein said web comprises predominantly short fibers having lengths less than about 1/4 inch and a minor percentage of long fibers having lengths in excess of about 3/4 inch. 
     
     
       13. The method of claim 1 wherein said liquid is vaporized and said web is expanded by the use of dielectric heating to concentrate the heat in the internal portions of said web. 
     
     
       14. The method of claim 1 wherein the amount of said binder is between about 4% and about 10% of the weight of said fabric on a dry solids basis. 
     
     
       15. The method of claim 14 wherein said binder is a water dispersible acrylate. 
     
     
       16. The method of claim 11 wherein said agent is a sulfonated alkyl ester. 
     
     
       17. The method of claim 1 wherein said added material further comprises an ionizing material soluble in water whereby the dielectric losses in said aqueous liquid are controlled by the amount of said ionizing material to thereby control the heating rate of said liquid and the puffing of said fabric. 
     
     
       18. The method of claim 17 wherein said ionizing material is ammonium chloride in an amount no less than about 0.01% by weight of said aqueous liquid. 
     
     
       19. The method of claim 1 wherein said binder migrates within said web during said vaporizing steps, said binder concentrating adjacent the surfaces of said web to provide enhanced interconnection of said fibers adjacent said surfaces. 
     
     
       20. The method of claim 1 wherein said binder is thermoplastically activatable at a temperature no greater than the vaporization temperature of said liquid and in which said liquid is vaporized by dielectric heating. 
     
     
       21. The method of claim 15 wherein said web comprises primarily short cellulosic fibers and wherein said web has a weight of from about 3 to about 19 ounces per square yard, said web is impregnated with said acrylic binder and liquid at a pick-up weight of at least about 100% and the dry weight of said binder comprises about 3% of the weight of the web.