Methods of Making Absorbent Members Having Skewed Density Profile

Abstract

Absorbent members and methods of making the same are disclosed. In one embodiment, the absorbent member is a unitary absorbent fibrous web having a density profile through its thickness. In one embodiment, the density profile of the fibrous web is skewed toward one of the surfaces of the fibrous web. In such embodiments, the maximum density of the web may be located outside of the central 30% zone of the thickness of the web. In one embodiment, the method involves subjecting a precursor web to at least one cycle (or pass) through a mechanical deformation process. Typically, the method involves subjecting the precursor web to multiples cycles (or passes) through a mechanical deformation process.

1 . A method for making an absorbent member, said method comprising:
 a) providing a precursor web material, said precursor web material comprising a wetlaid cellulosic fibrous structure, said precursor web material having a first surface and a second surface;   b) providing a pair of forming members comprising:   a first forming member having a surface comprising a plurality of first forming elements, wherein said first forming elements comprise male forming elements; and   a second forming member having a surface, wherein the surface of said second forming member is smoother than the surface of the first forming member;   c) placing said precursor web material between said first forming member and said second member, wherein said forming elements on said first forming member penetrate into the first surface of said precursor web material only part of the way into the thickness of said precursor web material, and the second surface of said precursor web material is in contact with the surface of said second forming member; and   d) repeating a step of subjecting the surfaces of said precursor web material to penetration by forming elements.   
     
     
         2 . The method of  claim 1  wherein the surface of said second forming member is substantially smooth. 
     
     
         3 . The method of  claim 1  wherein the first forming elements have a pitch therebetween, and the surface of said second forming member is provided with a plurality of second forming elements comprising the same general type as the first forming elements, said second forming elements having a pitch therebetween that is less than that of the first forming elements. 
     
     
         4 . The method of  claim 1  wherein said second forming member comprises a ring roll. 
     
     
         5 . The method of  claim 1  wherein the precursor web material is selected from the group consisting of: drylap, liner board, paper board, post-consumer recycled material, filter paper, and combinations thereof. 
     
     
         6 . The method of  claim 5  wherein the precursor material consists essentially of treated drylap. 
     
     
         7 . The method of  claim 1  wherein the precursor web has an initial density prior to mechanically impacting the same, and the mean maximum density of the absorbent member is greater than the initial density of the precursor web. 
     
     
         8 . The method of  claim 1  wherein the precursor web material has a burst strength of less than about 1,000 kPa. 
     
     
         9 . The method of  claim 1  wherein the precursor web is treated with debonders. 
     
     
         10 . The method of  claim 1  wherein the precursor web has a thickness, and the forming members define a clearance which is the shortest distance between the forming elements on one forming member and the opposed forming member, and the clearance between the forming members is less than the thickness of the precursor web. 
     
     
         11 . The method of  claim 3  wherein the precursor web has a thickness, and the forming members define a depth of engagement, and the ratio of the thickness of the precursor web to the absolute value of the depth of engagement is greater than 1. 
     
     
         12 . The method of  claim 1  wherein said forming members comprise counter-rotating rolls defining a nip therebetween. 
     
     
         13 . The method of  claim 12  wherein said counter-rotating rolls rotate at substantially the same surface speed. 
     
     
         14 . The method of  claim 12  wherein said counter-rotating rolls rotate at different surface speeds, and the surface speed differential between said rolls is greater than about 0.3%. 
     
     
         15 . The method of  claim 12  wherein at least one of said rolls comprise a plurality of alternating teeth and grooves on its surface. 
     
     
         16 . The method of  claim 15  wherein said teeth have a tip radius that is less than about 0.02 inch (0.5 mm). 
     
     
         17 . The method of  claim 15  wherein said rolls comprise:
 a first roll comprising said first forming member, said first roll having a first axis about which said first roll rotates and said first roll comprises the roll with a plurality of alternating teeth and grooves on its surface, wherein said teeth form circumferentially-extending ridges that are aligned perpendicular to said first axis; and 
 a second roll comprising said second forming member, said second roll having a second axis about which said second roll rotates and said second roll comprises a second surface with circumferentially-extending ridges and grooves that are aligned perpendicular to said second axis; and 
 step c) comprises moving said web material through the nip between said counter-rotating rolls, wherein said teeth on said first roll penetrate into the first surface of said precursor web material only part of the way into the thickness of said precursor web material. 
 
     
     
         18 . The method of  claim 1  wherein said first forming member has at least one relatively smooth region on its surface. 
     
     
         19 . A method for making an absorbent member wherein said method comprises inserting said web material through multiple nips according to  claim 12 . 
     
     
         20 . The method of  claim 19  wherein said multiple nips are formed by plural rolls arranged in a paired configuration. 
     
     
         21 . The method of  claim 19  wherein said multiple nips are formed by plural rolls arranged in a nested configuration. 
     
     
         22 . The method of  claim 19  wherein said multiple nips are formed by plural rolls arranged in a combination of nested and paired configurations. 
     
     
         23 . The method of  claim 1  further comprising a step of feeding said absorbent member into a hammer mill. 
     
     
         24 . A method of making an absorbent article on an absorbent article manufacturing line wherein the method of  claim 1  is carried out on said absorbent article manufacturing line. 
     
     
         25 . An absorbent member made by the method of  claim 1 . 
     
     
         26 . The method of  claim 12  wherein said nip comprises a first nip, and said method further comprises a subsequent step of passing said web material through at least one additional nip between two additional rolls after said web material is inserted through said first nip, said additional rolls having surfaces that form said additional nip, wherein at least regions of the surfaces of at least one of said additional rolls is relatively smoother in at least said portion of said additional nip in comparison to the surfaces of the rolls in said first nip, wherein said additional nip compacts at least a portion of said precursor web material. 
     
     
         27 . The method of  claim 12  wherein the first forming elements have a spacing therebetween, said method further comprising a prior and/or subsequent step of passing said web material through at least one additional nip between two additional rolls, said additional rolls having forming elements thereon which have a spacing therebetween that is greater than the spacing between the first forming elements, said additional rolls having a depth of engagement greater than 0.04 inches, wherein said forming elements on said additional rolls form a plurality of protrusions in said web material. 
     
     
         28 . The method of  claim 12  further comprising a prior and/or subsequent step of passing said web material through at least one additional nip between two additional rolls, wherein at least one of said additional rolls has elements on its surface that penetrate the thickness of said web material to form apertures in said web material.