ABSORBENT, NONWOVEN MATERIAL EXHIBITING Z-DIRECTION DENSITY GRADIENT
The present invention relates to an absorbent material that can be used as an absorbent core in absorbent articles such as sanitary napkins, pantiliners, incontinence products, disposable diapers, etc. The material of the present invention is a nonwoven sheet, consisting of cellulosic fibers, optionally superabsorbent polymeric material, containing no binders, latexes, etc, relying on hydrogen bonding to produce the necessary structure. The material contains density gradients which direct fluid into the material and distribute it providing more effective fluid transport and efficient utilization of storage capacity. The material consists of two regions. In the first region, the material has a low-density stratum adjacent to one surface, overlaying at least one higher density stratum adjacent to the opposite surface of the sheet. These strata create a density gradient in the thickness direction (Z-direction) of the sheet. The second region consists of a fluid distribution structure that has a higher density than at least the lower density of the strata comprising the first region. The fluid distribution structure is in direct fluid communication with the adjacent strata in the first region, along their boundaries.
1 . An absorbent, nonwoven material exhibiting a Z-direction density gradient, comprising:
a first, relatively low-density stratum comprising a fibrous matrix of cellulosic fibrous material substantially free of synthetic fibers and binder compositions;
a second, relatively high-density stratum, juxtaposed to said first stratum in liquid-transferring relationship therewith, said second stratum comprising a fibrous matrix of cellulosic fibrous material substantially free of synthetic fibers and binder compositions,
a liquid-distribution network extending substantially through the entire thickness of said absorbent material, said liquid-distribution network being laterally adjacent to at least some portions of said first, low-density and second high-density strata in liquid-transferring relationship therewith; and
a cellulosic fiber tissue layer positioned on top of said low-density stratum, and bonded to said liquid-distribution network for integrating said absorbent material against delamination, and for inhibiting release of the fibrous material of said low-density stratum.
said material containing hydrogen bonding providing a nonwoven sheet with an MD tensile strength of at least 10N/50 mm and a vertical delamination strength of >5N, said hydrogen bonding serving to stabilize the densities of the strata and said density gradient, and stabilize the integrity of the liquid-distribution network and bonded tissue layer.
2 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
said absorbent material exhibits an apparent Z-direction density gradient greater than about 1.2:1.
3 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
said liquid-distribution network comprises at least one longitudinally extending densified region.
4 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
said liquid-distribution network comprises a land-and-sea densified region.
5 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
said liquid-distribution network comprises between about 5% and 50% of the surface area of said absorbent material.
6 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 5 , wherein
said liquid-distribution network comprises between about 10% and 35% of the surface area of said absorbent material.
7 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
at least one of said strata includes superabsorbent polymeric material.
8 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
said absorbent material has a basis weight of about 100-2000 gsm, and comprises between about 0% and 70%, by weight, of a superabsorbent polymeric material,
said low-density stratum having a density in the range of about 0.08 g/cc to 0.30 g/cc, and said high-density stratum having a density in the range of about 0.25 g/cc to 0.50 g/cc.
9 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 8 , wherein
said absorbent material has a basis weight of about 150-1000 gsm, and comprises between about 10% and 55%, by weight, of the superabsorbent polymeric material,
said low-density stratum having a density in the range of about 0.10 g/cc to 0.17 g/cc, and said high-density stratum having a density in the range of about 0.25 g/cc to 0.40 g/cc.
10 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
said high-density stratum includes another cellulosic tissue layer at the lower surface thereof, said cellulosic tissue layers being bonded together along said liquid-distribution network.
11 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein
the fibrous material of said low-density stratum is different than the fibrous material of said high-density stratum.
12 . An absorbent, nonwoven material exhibiting a Z-direction density gradient in accordance with claim 1 , wherein the droplet absorption time ratio is >1.5:1
13 . A method making an absorbent, nonwoven material exhibiting a Z-direction density gradient, comprising the steps of:
providing a cellulosic tissue layer;
depositing cellulosic material on said tissue layer;
compacting said cellulosic material to form a fibrous matrix of a first, relatively low-density stratum;
providing a second, relatively high-density stratum with hydrogen bonding formed by applying heat and pressure providing a stable density, comprising another fibrous matrix, on said first stratum; and
compacting said first and second strata by applying heat and pressure in a defined pattern, to form an absorbent material with a Z-direction density gradient, including forming a liquid-distribution network extending through the entire thickness of the material, and laterally adjacent to at least one portion of said low-density and high-density strata, wherein said cellulosic tissue layer is bonded to said liquid-distribution network for integrating said absorbent material against delamination, and for inhibiting release of the fibrous material of said first, low-density stratum.
14 . A method making an absorbent, nonwoven material in accordance with claim 12 , including
forming said liquid-distribution network with at least one longitudinally extending densified region.
15 . A method making an absorbent, nonwoven material in accordance with claim 12 , including
forming said liquid-distribution network to comprise a land-and-sea densified region.
16 . A method making an absorbent, nonwoven material in accordance with claim 12 , including
forming at least one of said fibrous matrices as a blend of cellulosic fibrous material and superabsorbent polymeric material.
17 . A method making an absorbent, nonwoven material in accordance with claim 12 , wherein
said step of providing said high-density stratum includes forming and compacting said high-density stratum separately from said low-density stratum, and thereafter positioning said high-density stratum on said low density stratum.
18 . A method of making an absorbent, nonwoven material in accordance with claim 17 , using an airlaid formation apparatus, comprising a single formation section, and a single bonding calender or multiple bonding calenders.