Fibrous absorbent material and methods of making the same

Abstract

Disclosed is a fibrous absorbent structure that is wet stable and has large void volume with a density below the critical density of the fiber employed. In one embodiment, the fibrous absorbent uses open-celled foam technologies to keep the fibrous structure expanded and bonded. In other embodiments, the resulting fibrous structure resembles an open-celled polymeric foam, with fibers serving as struts stabilized by binder material. In another embodiment, the resulting fibrous structure is filled with hydrophilic open-celled foams with the cell size substantially smaller than the fibrous pores. Such a wet-stable, high void volume fibrous absorbent can be used in a disposable product intended for the absorption of fluid such as body fluid, including extensible absorbent articles.

We claim:  
     
         1 . A method of producing an open low-density absorbent fibrous structure comprising: 
 a) combining hydrophilic fibers with a structuring composition to form a mixture, said structuring composition comprising a binder material and a removable phase;    b) producing a foam within said mixture;    c) binding said fibers together with substantially water-insoluble bonds into a continuous, porous network, wherein said binder material stabilizes the porous network.    
     
     
         2 . The method of  claim 1 , wherein said foam causes physical rearrangement of the fibers in the mixture prior to binding said fibers together.  
     
     
         3 . The method of  claim 1 , further comprising the step of physically rearranging said fibers in at least two dimensions after producing a foam.  
     
     
         4 . The method of  claim 1 , wherein said step of producing a foam occurs during said step of combining the fibers with the structuring composition.  
     
     
         5 . The method of  claim 1 , wherein said step of producing a foam comprises generating a gas by one of a chemical reaction within said mixture and the action of a blowing agent.  
     
     
         6 . The method of  claim 1 , wherein said step of producing a foam comprises one of generating a fibrous froth with a high-shear mixer, injecting gas into said mixture, adding hollow spheres to said mixture, and depressurizing said mixture.  
     
     
         7 . The method of  claim 1 , further comprising removing a portion of said removable phase.  
     
     
         8 . The method of  claim 7 , wherein said step of removing the removable phase comprises releasing gas from gas bubbles within the mixture.  
     
     
         9 . The method of  claim 7 , wherein said step of removing the removable phase comprises removal of a liquid.  
     
     
         10 . The method of  claim 7 , wherein said step of removing the removable phase comprises one of critical point drying, solvent extraction, supercritical fluid treatment, and sublimation.  
     
     
         11 . The method of  claim 7 , wherein said step of removing the removable phase comprises evaporation.  
     
     
         12 . The method of  claim 7 , wherein said step of removing the removable phase comprises one of melting or decomposition of a solid.  
     
     
         13 . A method of producing a low-density absorbent fibrous structure comprising: 
 a) combining hydrophilic fibers with a structuring composition to form a mixture, said structuring composition comprising a binder material and a removable phase;    b) rearranging said fibers in a three-dimensional structure within said mixture;    c) removing a portion of said removable phase;    d) binding said fibers together into a continuous, porous network, wherein said binder material forms bonds between said fibers to stabilize said porous network.    
     
     
         14 . The method of  claim 13 , wherein said bonds formed from said binder material are substantially water-insoluble.  
     
     
         15 . The method of  claim 1  or  13 , wherein the consistency of the fibers in said mixture is about 4% or higher.  
     
     
         16 . The method of  claim 1  or  13 , wherein the density of said absorbent fibrous structure is about 0.1 g/cc or less.  
     
     
         17 . The method of  claim 1  or  13 , wherein the density of said absorbent fibrous structure is about 0.05 g/cc or less.  
     
     
         18 . The method of  claim 1  or  13 , wherein the removable phase is not removed by sublimation.  
     
     
         19 . The method of  claim 1  or  13 , wherein the absorbent fibrous structure has a dry binder material mass fraction of about 0.6 or lower.  
     
     
         20 . The method of  claim 1  or  13 , wherein the volume of the absorbent fibrous structure is at least 10% greater than the initial volume of the mixture of step (b).  
     
     
         21 . The method of  claim 1  or  13 , wherein said binding step comprises cross-linking said binder material.  
     
     
         22 . The method of  claim 1  or  13 , wherein said binding step comprises curing said binder material.  
     
     
         23 . The method of  claim 1  or  13 , wherein said binding step comprises heating said binder material.  
     
     
         24 . The method of  claim 1  or  13 , wherein said structuring composition further comprises a crosslinking agent.  
     
     
         25 . The method of  claim 1  or  13 , wherein said structuring composition comprises latex.  
     
     
         26 . The method of  claim 1  or  13 , wherein said structuring composition comprises a polysaccharide.  
     
     
         27 . The method of  claim 1  or  13 , wherein said structuring composition comprises a polymer selected from a hydrophilic cellulose derivative, an alginate, a starch, a hydrophobic starch derivative, a superabsorbent polymer, and a gum.  
     
     
         28 . The method of  claim 1  or  13 , wherein said structuring composition contains less than 10% by dry weight of a polysaccharide.  
     
     
         29 . The method of  claim 1  or  13 , wherein said structuring composition comprises a protein.  
     
     
         30 . The method of  claim 1  or  13 , wherein said structuring composition has a bulk viscosity of about 100 centipoise or greater.  
     
     
         31 . The method of  claim 1  or  13 , wherein less than 50% of the mass of said structuring composition is removed from said mixture in non-gaseous form.  
     
     
         32 . The method of  claim 1  or  13 , wherein said structuring composition further comprises a wet strength agent and said method further comprises the step of curing said wet strength agent after the step of adding said fibers to said structuring composition.  
     
     
         33 . The method of  claim 1  or  13 , wherein said structuring composition comprises an High-Internal-Phase-Ratio Emulsions (HIPE) emulsion.  
     
     
         34 . The method of  claim 13 , wherein said structuring composition comprises a blowing agent.  
     
     
         35 . The method of  claim 13 , wherein said removable phase is a liquid.  
     
     
         36 . The method of  claim 13 , wherein said removable phase is a solid.  
     
     
         37 . The method of  claim 1  or  13 , wherein said removable phase is a gas.  
     
     
         38 . The method of  claim 1  or  13 , wherein the density of said porous network is about 0.05 g/cc or less.  
     
     
         39 . The method of  claim 1  or  13 , wherein said binder material comprises a polysaccharide or a protein.  
     
     
         40 . The method of  claim 1  or  13 , wherein said structuring composition comprises a surfactant.  
     
     
         41 . The method of  claim 1  or  13 , wherein said structuring composition is substantially free of molten thermoplastic material.  
     
     
         42 . The method of  claim 1  or  13 , wherein said structuring composition is substantially free of thermoplastic material.  
     
     
         43 . The method of  claim 1  or  13 , wherein said binder material is preferentially located at or adjacent to fiber-fiber contact points.  
     
     
         44 . The method of  claim 1  or  13 , wherein said binder material forms an open-cell foam occupying the spaces surrounded by said fibers.  
     
     
         45 . The method of  claim 1  or  13 , wherein the mass of said binder material is less than the mass of said fibers on a dry basis.  
     
     
         46 . The method of  claim 1  or  13 , wherein the mass of said binder material is less than about 20% of the mass of said absorbent fibrous structure.  
     
     
         47 . The method of  claim 1  or  13 , wherein said binder material forms an open-cell foam having a Cell Pore Size of about 500 microns or less.  
     
     
         48 . The method of  claim 1  or  13 , wherein said binder material is hydrophilic.  
     
     
         49 . The method of  claim 1  or  13 , wherein said fibers comprise synthetic fibers.  
     
     
         50 . The method of  claim 1  or  13 , wherein said fibers comprise papermaking fibers.  
     
     
         51 . The method of  claim 50 , wherein said papermaking fibers are substantially unbeaten.  
     
     
         52 . The method of  claim 50 , wherein said papermaking fibers have a Canadian Standard Freeness of about 200 or greater.  
     
     
         53 . The method of  claim 1  or  13 , wherein said fibers comprise about 30% or greater hardwood fibers.  
     
     
         54 . The method of  claim 1  or  13 , wherein said fibers comprise at least 20% high-yield papermaking fibers.  
     
     
         55 . The method of  claim 7  or  13 , wherein said step of binding the fibers occurs in part during said step of removing a portion of the removable phase.  
     
     
         56 . The method of  claim 7  or  13 , wherein said step of binding the fibers occurs in part prior to said step of removing a portion of the removable phase.  
     
     
         57 . A method of producing a low-density absorbent fibrous structure comprising: 
 a) coating hydrophobic fibers with a hydrophilic fiber coating material;    b) combining said fibers with a structuring composition comprising a binder material and a removable phase to form a mixture;    c) producing a foam within said mixture;    d) binding said fibers together into a continuous, porous network, wherein said binder material stabilizes the porous network, and wherein at least about 20% of the surface area of said hydrophobic fibers is coated with hydrophilic material.    
     
     
         58 . The method of  claim 57 , further comprising removing a portion of said removable phase.  
     
     
         59 . The method of  claim 57 , wherein at least about 50% of the surface area of said hydrophobic fibers is coated with hydrophilic material.  
     
     
         60 . A method of producing a low-density absorbent fibrous structure comprising: 
 a) combining hydrophilic fibers with a structuring composition to form a mixture, said structuring composition comprising a non-gaseous phase and a removable phase;    b) producing a foam within said mixture;    c) forming water-insoluble bonds with a binder material to bind said fibers together into a continuous, porous structure.    
     
     
         61 . The method of  claim 60 , wherein a liquid impervious skin forms on a portion of the outer surface of said absorbent fibrous structure.  
     
     
         62 . The method of  claim 61 , further comprising the step of creating openings in said skin.  
     
     
         63 . The absorbent fibrous structure made according to any of claims  1 ,  13 , and  60 .  
     
     
         64 . The absorbent fibrous structure made according to any of claims  1 ,  13 , and  60  having a Wet Bulk of about 10 cc/g or greater.  
     
     
         65 . A disposable absorbent article comprising the low-density absorbent fibrous structure made according to any of claims  1 ,  13 , and  60 .  
     
     
         66 . The method of  claim 60 , wherein said binder material comprises a wet strength resin.  
     
     
         67 . The method of  claim 60 , wherein said structuring composition further comprises a precursor binder material, and wherein said step of forming water-insoluble bonds comprises converting said precursor binder material to a binder material.  
     
     
         68 . The method of  claim 67 , wherein converting said precursor binder material to a binder material comprises one of adding a chemical agent, elevating the temperature of the precursor binder material, and applying radiation.  
     
     
         69 . A method for producing a continuous absorbent fibrous structure comprising: 
 a) combining hydrophilic fibers with a structuring composition comprising a binder material and a removable phase to form a mixture;    b) generating a foam within said mixture;    c) depositing said foam on a moving belt to form a foamed layer without substantial drainage of said structuring composition from said layer;    d) curing said foamed layer to form an absorbent fibrous structure.    
     
     
         70 . A method for producing a continuous absorbent fibrous structure comprising: 
 a) forming an air-laid mat of fiberized hydrophilic fibers on a moving belt to form a fibrous mat;    b) impregnating said mat with a foamable structuring composition comprising a binder material and a removable phase;    c) rearranging said fibers in said mat through the action of said structuring composition to create a restructured layer;    d) forming water-insoluble bonds in said restructured layer to form an absorbent fibrous structure.    
     
     
         71 . The method of  claim 69  or  70  further comprising one of embossing, calendering, or perforating said absorbent fibrous structure.  
     
     
         72 . An apparatus for continuous production of an absorbent fibrous structure, comprising: 
 a) a mixing unit wherein fibers and a foamable structuring composition comprising a binder material and a removable phase are mixed to form a mixture;    b) a foam generating device capable of producing a fiber-laden foam from said mixture;    c) a moving belt to receive a foamed layer from said foam generating device;    d) a curing unit to create water insoluble bonds in said foamed layer.    
     
     
         73 . An apparatus for continuous production of an expanded fibrous structure, comprising: 
 a) an air-laying unit for producing a continuous air-laid mat of fluff pulp on a moving belt;    b) an impregnating unit for impregnating said air-laid mat with a foamable structuring composition comprising a binder material and a removable phase;    c) a curing unit to create water insoluble bonds in the impregnated mat, such that an expanded fibrous web is formed.    
     
     
         74 . A foam-structured absorbent fibrous structure comprising a water-insoluble hydrophilic foamable binder material and over 50% by weight of hydrophilic fibers, said fibrous structure having a density of about 0.05 g/cc or less.  
     
     
         75 . The absorbent fibrous structure of  claim 74 , wherein said binder material has a molecular weight of about 10,000 or greater.  
     
     
         76 . The absorbent fibrous structure of  claim 74 , wherein said absorbent fibrous structure is an expanded fibrous structure.  
     
     
         77 . The absorbent fibrous structure of  claim 74 , wherein said binder material has a molecular weight of about 10,000 or less.  
     
     
         78 . The absorbent fibrous structure of  claim 74 , wherein said hydrophilic fibers comprise at least 50% by weight of papermaking fibers with a freeness of about 300 or above.  
     
     
         79 . The absorbent fibrous structure of  claim 74 , wherein said structure is flexible.  
     
     
         80 . The absorbent fibrous structure of  claim 74 , wherein said structure is not flexible.  
     
     
         81 . The absorbent fibrous structure of  claim 74 , wherein said structure is stretchable.  
     
     
         82 . The absorbent fibrous structure of  claim 74 , wherein said structure has a gradient in one of fiber composition, pore size or wettability.  
     
     
         83 . The absorbent fibrous structure of  claim 74 , having a Wet Bulk of about 8 cc/g or greater.  
     
     
         84 . An open absorbent fibrous structure comprising a foamable binder material and about 25% or greater by weight of hydrophilic fibers, wherein said fibers are arranged as struts between the cells of an open-cell foam structure, said fibrous structure being hydrophilic with a density of about 0.1 g/cc or less and comprising water-insoluble bonds that stabilize the structure.  
     
     
         85 . An absorbent article comprising the absorbent fibrous structure of  claim 74  or  84 , said article being one of a dental absorbent, a hemostatic sponge, or a medical sponge.  
     
     
         86 . An absorbent article comprising the absorbent fibrous structure of  claim 74  or  84 , said article being one of a tampon, a pantiliner, a sanitary napkin, or a diaper.  
     
     
         87 . An absorbent article comprising the absorbent fibrous structure of  claim 74  or  84 , wherein said absorbent fibrous structure comprises an elastomeric binder material.  
     
     
         88 . The absorbent fibrous structure of  claim 84  wherein said structure is wet flexible.  
     
     
         89 . A filter comprising the absorbent fibrous structure of  claim 84 .  
     
     
         90 . The fibrous structure of  claim 84 , wherein said fibers are papermaking fibers.  
     
     
         91 . The fibrous structure of  claim 84  having a Wet Bulk of about 6 cc/g or greater.  
     
     
         92 . The fibrous structure of  claim 84 , wherein said structure is biodegradable.  
     
     
         93 . The fibrous structure of  claim 84 , wherein said fibers comprise substantially unbeaten papermaking fibers.  
     
     
         94 . The fibrous structure of  claim 84 , further comprising bubbles of dry foamable binder material.  
     
     
         95 . The fibrous structure of  claim 84 , wherein said foamable binder material comprises a water-soluble polysaccharide or a protein.  
     
     
         96 . The fibrous structure of  claim 84  having a density of less than about 0.05 g/cc.  
     
     
         97 . The fibrous structure of  claim 84  having a Free Swell:AUL Ratio of about 3 or less.  
     
     
         98 . The fibrous structure of  claim 84  having a Free Swell Capacity of about 10 or greater.  
     
     
         99 . The fibrous structure of  claim 84  having an AUL of about 10 or greater.  
     
     
         100 . The fibrous structure of  claim 84  further comprising at least 10% by weight of activated carbon.  
     
     
         101 . The fibrous structure of  claim 84  further comprising a liquid impervious skin on a surface of said fibrous structure.  
     
     
         102 . A layered foam-fiber composite comprising a first fibrous layer and a second fibrous layer, said first layer comprising an absorbent porous fibrous structure comprising a foamable binder material and about 20% or greater by weight of hydrophilic fibers, wherein said fibers are arranged as struts between the cells of an open-cell foam; said second layer comprising a foam-fiber composite.  
     
     
         103 . An absorbent article comprising a liquid pervious topsheet, a liquid impervious backsheet, and an absorbent fibrous structure disposed between said backsheet and said topsheet, said absorbent fibrous structure comprising at least 25% hydrophilic fibers by weight and a binder residual from a foamable structuring composition which stabilizes the hydrophilic fibers in a high-bulk structure, said absorbent fibrous structure having a density of about 0.1 g/cc or less and a Wet Bulk of about 6 cc/g or greater.  
     
     
         104 . The absorbent article of  claim 103  further comprising a fluff pulp pad disposed between said backsheet and said absorbent fibrous structure.  
     
     
         105 . The absorbent article of  claim 103  wherein said absorbent fibrous structure has a Wet Bulk of about 10 cc/g or greater.  
     
     
         106 . The absorbent article of  claim 103  wherein said absorbent fibrous structure has a an AUL of about 10 or greater.  
     
     
         107 . The absorbent article of  claim 103  wherein said absorbent fibrous structure has a Free Swell:AUL Ratio of about 3 or less.  
     
     
         108 . The absorbent article of  claim 103  wherein said absorbent fibrous structure is wet flexible.  
     
     
         109 . The absorbent article of  claim 103  wherein said absorbent fibrous structure has an open-cell foam structure with bimodal pores and fibers serving as struts.  
     
     
         110 . The absorbent article of  claim 103  wherein said absorbent fibrous structure comprises at least 10% by weight of high-yield papermaking fibers.  
     
     
         111 . The absorbent article of  claim 103  wherein said hydrophilic fibers define the boundaries of an open-celled foam structure stabilized by said binder residual.  
     
     
         112 . The absorbent article of  claim 103 , wherein said absorbent fibrous structure comprises elastomeric binder material.  
     
     
         113 . The absorbent article of  claim 103 , wherein said article is stretchable.  
     
     
         114 . The absorbent article of  claim 103 , wherein said absorbent fibrous structure is elastically extensible.