Absorbent cores and absorbent articles having anisotropic foam structures
An absorbent core for an absorbent article, the absorbent core comprising at least two layers, each layer having a width w and a length l along a first plane and a thickness t extending perpendicular thereto, wherein the layers are arranged in facing relationship along the first plane, and wherein the layers comprise a polymeric foam having an open cell and interconnected porous structure. The first and second layers comprise an anisotropic cell structure having an axis of anisotropy extending substantially parallel to a longest length of a plurality of substantially neighbouring cells. The axis of anisotropy of the second layer extends substantially perpendicular to said thickness t and parallel to said first plane and the axis of anisotropy of the first layer is substantially perpendicular to the axis of anisotropy of the second layer.
1. An absorbent core ( 1 ) for an absorbent article, the absorbent core comprising at least two layers ( 2 , 3 ), each layer having a width (w) and a length (l) along a first plane and a thickness (t) extending perpendicular thereto, wherein said layers ( 2 , 3 ) are arranged in facing relationship along said first plane, and wherein said layers ( 2 , 3 ) comprise a polymeric foam having an open cell and interconnected porous structure characterized in that the first layer ( 2 ) and the second layer ( 3 ) comprise an anisotropic cell structure having an axis of anisotropy ( 4 , 5 ) extending substantially parallel to a longest length of a plurality of substantially neighbouring cells ( 6 ), in that the axis of anisotropy ( 5 ) of the second layer ( 3 ) extends substantially perpendicular to said thickness (t) and parallel to said first plane, and in that the axis of anisotropy ( 4 ) of the first layer ( 2 ) is substantially perpendicular to the axis of anisotropy ( 5 ) of the second layer ( 3 ).
2. An absorbent core ( 1 ) according to claim 1 wherein the first layer ( 2 ) is positioned above the second layer ( 3 ) such that when said absorbent core ( 1 ) is incorporated into an absorbent article, said first layer ( 2 ) is closer to a body facing side of the absorbent article than said second layer ( 3 ).
3. An absorbent core ( 1 ) according to claim 1 wherein the axis of anisotropy ( 4 ) of the first layer ( 2 ) is substantially perpendicular to the first plane and crosses said first and second layers ( 2 , 3 ).
4. An absorbent core ( 1 ) according to claim 1 wherein the axis of anisotropy ( 5 ) of the second layer ( 3 ) extends along the length (l) of said second layer ( 3 ) without crossing the first layer ( 2 ).
5. An absorbent core ( 1 ) according to claim 1 wherein the foam open cells ( 6 ) have an average anisotropy ratio R of greater than 1, as measured according to the method described herein.
6. An absorbent core ( 1 ) according to claim 1 wherein the foam comprises a hydrophilic polymer foam.
7. An absorbent core ( 1 ) according to claim 6 wherein the hydrophilic polymer foam is selected from the group consisting of polyurethane; poly vinyl alcohol (PVA); polyolefins selected from the group consisting of low-density polyethylene (LDPE), ethylene-vinyl acetate (EVA), ethylene butyl acrylate (EBA), and mixtures thereof; open cell silicone foams; and mixtures thereof.
8. An absorbent core ( 1 ) according to claim 1 wherein the foam open cells ( 6 ) have an average anisotropy ratio R of from 1.1 to 3.5, as measured according to the method described herein.
9. An absorbent core ( 1 ) according to claim 1 wherein the foam open cells ( 6 ) have an average anisotropy ratio R of from 1.2 to 3.3, as measured according to the method described herein.
10. An absorbent core ( 1 ) according to claim 1 , wherein the absorbent core further comprises cellulosic fibers and/or super absorbent polymer particles.
11. A method of making an absorbent core ( 1 ) according to claim 1 , the method comprising the steps of:
(i) providing a mixture comprising one or more polymers;
(ii) placing said mixture in a mould arranged such that cell growth is promoted along an axis during a foaming step to provide a foam comprising an anisotropic cell structure;
(iii) forming a foam block by solidifying said mixture;
(iv) demoulding the foam block;
(v) generating a first layer ( 2 ) and/or second layer ( 3 ) by cutting the foam block along a first cutting plane and a second cutting plane perpendicular to the first cutting plane to generate the second layer ( 3 ) and/or first layer ( 2 );
(vi) optionally repeating step (v) until substantially the entire foam block is cut into layers; and
(vi) assembling the first and second layers ( 2 , 3 ) in facing relationship.
12. A method according to claim 11 wherein the mixture is free of nucleating agents.
13. An absorbent article ( 7 ) comprising an absorbent core ( 1 ) according to claim 1 .
14. An absorbent article ( 7 ) according to claim 13 , wherein said absorbent article is selected from the group consisting of sanitary napkins and towels for feminine care.
15. An absorbent article ( 7 ) according to claim 13 wherein the absorbent core ( 1 ) comprises one or more interconnected macro channels ( 10 ) at least on an upper surface of the first layer ( 2 ), said upper surface being opposite the second layer ( 3 ), and extending at least a portion of the length (l) and width (w) of said first layer ( 2 ).
16. An absorbent article ( 7 ) comprising an absorbent core ( 1 ) according to claim 1 , wherein the absorbent article ( 7 ) comprises a liquid permeable topsheet ( 8 ) and a liquid impermeable backsheet ( 9 ) with said absorbent core ( 1 ) being sandwiched therebetween.
17. An absorbent article ( 7 ) according to claim 16 wherein the topsheet ( 8 ) or the uppermost surface of the first layer ( 2 ) closest to said topsheet ( 8 ) comprises a coloured area comprising a colour pigment imparting a hue having an ω angle measured in the CIELAB colour scale of from 135° to 315°.
18. An absorbent article ( 7 ) according to claim 17 wherein said coloured area extends across an entire surface of the topsheet ( 8 ) or the first layer ( 2 ); or is located in a central portion of said absorbent article ( 7 ) and distal from perimeter edges thereof.
19. An absorbent article ( 7 ) according to claim 18 wherein the coloured area is substantially circumscribed by a non-coloured area.
20. An absorbent article ( 7 ) according to claim 17 , wherein said coloured area has an opacity of at least 20%.
21. A method of making an absorbent article ( 7 ) according to claim 16 , the method comprising the steps of:
(i) providing an absorbent core according to claim 1 ;
(ii) laminating said absorbent core between the liquid permeable topsheet and the liquid impermeable backsheet.
22. A method of making an absorbent article ( 7 ) according to claim 21 , wherein the laminating step (ii) is such that the first layer ( 2 ) is in direct or indirect contact with the topsheet and the second layer ( 3 ) is in direct or indirect contact with the backsheet.