Porous fibrous structure and process for producing the same

Abstract

A novel porous fibrous structure containing from 10 to 100% by weight of wet heat bonding fibers, having cellular cavities in the fibrous structure of the fibers, in which a plurality of indefinite cellular cavities are present independently or in a state of partially connected in the inside of the fibrous structure, at least a portion of the fibers constituting the fibrous structure is heat bonding by the wet heat bonding fibers, and a process for producing such porous fibrous structure.

What is claimed is:  
     
         1 . A porous fibrous structure containing from 10 to 100% by weight of wet heat bonding fibers, in which a plurality of indefinite cellular cavities are present independently or in a state that a plurality of them are connected partially in the inside of the fibrous structure, and at least a portion of the fibers constituting the fibrous structure are heat bonded by the wet heat bonding fibers.  
     
     
         2 . A porous fibrous structure as defined in  claim 1 , wherein the wet heat bonding fibers are fibers in which an ethylene-vinyl alcohol copolymer is present to at least a portion at the surface of the fibers.  
     
     
         3 . A porous fibrous structure as defined in  claim 1 , wherein the porous fibrous structure is a block form fibrous structure in which fibers are accumulated at random.  
     
     
         4 . A porous fibrous structure as defined in  claim 1 , wherein the porous fibrous structure is a block form fibrous structure in which fibers are accumulated generally in a layerous form, and at least a portion of the cellular cavities is formed with the major axis thereof being along the direction of the layer.  
     
     
         5 . A porous fibrous structure as defined in  claim 1 , wherein the porous fibrous structure is a non-woven fabric comprising fibers generally accumulated in a layerous form and at least a portion of the cellular cavities is formed with the major axis thereof being along the lateral direction in the layer of the non-woven fabric.  
     
     
         6 . A porous fibrous structure as defined in  claim 1 , wherein a dense layer is present in one surface of the porous fibrous structure.  
     
     
         7 . A porous fibrous structure as defined in  claim 1 , wherein a portion where the fibers are arranged densely and a portion where the fibers are arranged coarsely are present in the porous fibrous structure, and the size of the cellular cavity is gradually increased from the portion where the fibers are arranged densely to the portion where the fibers are arranged coarsely.  
     
     
         8 . A spherical porous fibrous structure as defined in  claim 7 , wherein the portion in which the fibers are arranged densely is present at a central portion of the spherical porous fibrous structure.  
     
     
         9 . A columnar porous fibrous structure as defined in  claim 7 , wherein the portion in which the fibers are arranged densely is present at a center line portion of the columnar porous fibrous structure.  
     
     
         10 . A sheet-like porous fibrous structure as defined in  claim 7 , wherein the portion where the fibers are arranged densely is present to a plane of the porous fibrous structure.  
     
     
         11 . A porous fibrous structure as defined in  claim 7 , wherein a plurality of cellular cavities are formed being opened to the surface of the porous fibrous structure.  
     
     
         12 . A porous fibrous multi-layer composite comprising the porous fibrous structure as defined in  claim 1  and a support layer, wherein the porous fibrous structure is present on one surface or both surfaces thereof.  
     
     
         13 . A porous fibrous multi-layer composite as defined in  claim 12 , wherein the support layer is a layer selected from the group consisting of fibrous layer, film, sheet and foaming layer.  
     
     
         14 . A porous fibrous multi-layer composite wherein the support layer is present on both surfaces of the porous fibrous structure as defined in  claim 1 .  
     
     
         15 . A porous fibrous multi-layer composite as defined in  claim 14 , wherein the support layer is a layer selected from the group consisting of fibrous layer, film, sheet and foaming layer.  
     
     
         16 . A porous fibrous multi-layer composite wherein an air permeable dense fiber melted layer comprising the identical fiber composition with the fibrous layer is present on at least one surface of the porous fibrous structure as defined in  claim 1 .  
     
     
         17 . A process for producing a porous fibrous structure, which comprises impregnating a fibrous structure containing from 10 to 100% by weight of wet heat bonding fibers with water, then heating the water-containing fibrous structure to evolve bubbles by boiling water in the fibrous structure, and forming a plurality of indefinite cavities in the inside of the fibrous structure and, simultaneously, heat bonding at least a portion of the fibers constituting the fibrous structure by the wet heat bonding fibers.  
     
     
         18 . A process for producing a porous fibrous structure as defined in  claim 17 , wherein the wet heat bonding fibers are fibers in which an ethylene-vinyl alcohol copolymer is present to at least a portion on the surface of the fibers.  
     
     
         19 . A process for producing a porous fibrous structure, which comprises immersing, into an aqueous layer, a fibrous structure containing from 10 to 100% by weight of wet heat bonding fibers with the content of the wet heat bonding fibers being lower on one surface of the fibrous structure while the content of the wet heat bonding fibers in other portions being higher and heating the water-containing fibrous structure thereby forming a porous fibrous structure having a dense layer on one surface of the fibrous structure and having a porous fibrous layer in contiguous with the dense layer.  
     
     
         20 . A process for producing a porous fibrous structure as defined in  claim 17 , wherein the water-containing fibrous structure is heated by irradiation of high frequency microwaves.  
     
     
         21 . A process for producing a porous fibrous multi-layer composite having a dense layer on one surface of the fibrous structure and having a porous fibrous layer in contiguous with the dense layer, by heating the water-containing fibrous structure by the irradiation of high frequency microwaves in a state where at least a portion of the surface layer of the water-containing fibrous structure is exposed to atmospheric air.  
     
     
         22 . A process for producing a porous fibrous structure, which comprises constraining a fiber bundle containing from 10 to 100% by weight of wet heat bonding fibers at an arbitrary portion thereof, impregnating the fiber bundle with water and then applying a wet heat treatment while evolving bubbles in the fiber bundle and then cooling the fiber bundle.  
     
     
         23 . A process for producing a porous fibrous multi-layer composite, which comprises immersing a fibrous layer containing from 10 to 100% by weight of wet heat bonding fibers with water, applying a heat treatment thereby evolving bubbles in the fibrous layer to form cellular cavities and then heat press bonding at least one surface of the fibrous layer to form an air permeable dense fiber melted layer.  
     
     
         24 . A process for producing a porous fibrous multi-layer composite, which comprise heat press bonding at least one surface of a fibrous layer containing from 10 to 100% by weight of wet heat bonding fibers thereby to form an air permeable dense fiber melted layer, then immersing the fibrous layer into water and applying a heat treatment thereby evolving bubbles in the fibrous layer to form cellular cavities.