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EP-3881814-B1 - ABSORBENT CORE COMPRISING A HIGH LOFT CENTRAL LAYER AND SUPERABSORBENT PARTICLES

EP3881814B1EP 3881814 B1EP3881814 B1EP 3881814B1EP-3881814-B1

Inventors

  • KAMPHUS, JULIANE
  • PERI, ANDREA
  • SEEBOTH, SIMONE

Dates

Publication Date
20260506
Application Date
20200317

Claims (15)

  1. An absorbent core (28) for use in an absorbent article (20), the absorbent core extending in a transversal direction (x) and a longitudinal direction (y) and having a thickness in a vertical direction (z) perpendicular to the transversal direction and longitudinal direction, the absorbent core comprising: - a liquid-permeable top layer (41); - a bottom layer (42); - a high loft central layer (43) having a density at a pressure of 4.14 kPa below 0.20 g/cm 3 between the top layer and the bottom layer, as measured according to the Thickness and Density Measurement Method as described herein; - superabsorbent polymer particles between the top layer and the bottom layer, wherein the superabsorbent polymer particles are at least partially distributed within the central layer (43); wherein the superabsorbent polymer particles have a time to reach an uptake of 20 g/g (SAP T20) of less than 220 s, as measured according to the SAP K(t) Test Method as described herein.
  2. An absorbent core according to claim 1, wherein the absorbent core has a time to reach an uptake of 20 g/g (Core T20) of less than 550 s, as measured according to the Absorbent Core K(t) Test Method as described herein.
  3. An absorbent core according to any of the preceding claims, wherein the central layer comprises or consists of synthetic fibers, in particular wherein the central layer is a carded nonwoven layer.
  4. An absorbent core according to any of the preceding claims, wherein the concentration of the superabsorbent polymer particles in the absorbent core has a bi-modal or multimodal distribution in the z-direction of the absorbent core, as determined by the micro-CT Scan Method disclosed herein.
  5. An absorbent core according to any of the preceding claims, wherein the superabsorbent particles are made of a cross-linked polyacrylate salt, and preferably have a Centrifuge Retention Capacity (CRC) in the range of from 10 g/g up to 35 g/g test as measured by EDANA method NWSP 241.0.R2 (19).
  6. An absorbent core according to any of the preceding claims, wherein the superabsorbent polymer particles have a UPM of at least 10 × 10-7 cm3.s/g, preferably of at least 15 × 10-7 cm3.s/g, wherein the UPM is measured by the Urine Permeability Measurement Test described herein, and/or wherein the superabsorbent polymer particles have an Absorbency Against Pressure of 0.7 psi (AAP@0.7psi) of more than 22 g/g measured according to EDANA standard test NWSP 242.0 R2 (19).
  7. An absorbent core according to any of the preceding claims, wherein the top layer and/or the bottom layer are each attached to the central layer by a layer of glue (71, 72), optionally wherein the layer of glue also immobilizes at least a portion of the SAP particles which are not distributed within the high loft central layer in the dry state.
  8. An absorbent core according to any of the preceding claims, further comprising a wrapping layer (3), in particular a nonwoven wrapping layer, at least partially wrapping the top, bottom and central layers.
  9. An absorbent core according to any of the preceding claims, wherein the absorbent core comprises at least 60% by weight of superabsorbent polymer particles, preferably at least 70% or at least 80% by weight of SAP, by total weight of the core.
  10. An absorbent core according to any of the preceding claims, wherein the absorbent core comprises superabsorbent polymer particles at a basis weight of at least 200 gsm, or at least 300 gsm or from 300 gsm to 500 gsm.
  11. An absorbent core according to any of the preceding claims, comprising a first central layer (431) and a second central layer (432) between the top layer and the bottom layer, wherein at least one of the first central layer and the second central layer is a central layer according to any of the preceding claims, and wherein the first central layer and the second central layer can be the same or different.
  12. An absorbent core according to any of the preceding claims, wherein the absorbent core has a core density of less than 0.6 g/cm3, preferably from 0.2 g/cm 3 to less than 0.5 g/cm 3 (at 0.3 psi), measured with the Absorbent Core K(t) Test Method.
  13. An absorbent article (200) comprising a topsheet (36), a backsheet (38) and an absorbent core (28) according to any of the preceding claims, and optionally an acquisition layer and/or a distribution layer (54) between the core and topsheet.
  14. A method for making an absorbent core (28) according to any of the claims 1-12, the method comprising the steps of: - providing a high loft central layer (43), a liquid-permeable top layer (41), and a bottom layer (42); - depositing a first layer of superabsorbent particles on a first side of the high loft central layer; - laminating the first side of the central layer with one selected from the liquid-permeable top layer (41) and the bottom layer (43); - optionally depositing a second layer of superabsorbent particles on the second side of the high loft central layer; - laminating the second side of the central layer with the other of the liquid-permeable top layer (41) or the bottom layer (43) that was not laminated previously; wherein the superabsorbent polymer particles deposited have a time to reach an uptake of 20 g/g (SAP T20) of less than 220 s, as measured according to the SAP K(t) Test Method as described herein.
  15. A method for making an absorbent core according to the preceding claim, wherein the initial density of the central layer is in the range of from 0.05 g/cm 3 to 0.15 g/cm 3 at 4.14 kPa (0.6 psi) and/or the initial thickness of the central layer at 4.14 kPa (0.6 psi) is of more than 0.30 mm, as measured using Thickness and Density Measurement Method described herein.

Description

FIELD OF THE INVENTION The invention relates to absorbent cores and their use in personal hygiene absorbent articles. The absorbent cores may be in particular used in baby diapers. BACKGROUND OF THE INVENTION Absorbent articles for personal hygiene such as disposable baby diapers, training pants for toddlers or adult incontinence undergarments, are designed to absorb and contain body exudates, in particular urine. These absorbent articles comprise several layers providing different functions, typically including a topsheet, a backsheet and in-between an absorbent core, among other layers. The absorbent core should be able to absorb and retain the exudates for a prolonged amount of time, for example overnight for a diaper, minimize re-wet to keep the wearer dry, and avoid soiling of clothes or bed sheets. Absorbent cores have typically comprised a blend of comminuted wood pulp cellulose fibers with superabsorbent polymers (SAP) particles, also called absorbent gelling materials (AGM), as absorbent material. Absorbent cores without fluff cellulose fibers (also called "airfelt-free" cores) have been more recently proposed. The SAP particles may be for example enclosed within discrete pockets formed between two substrates (see e.g. WO95/11654, Tanzer et al.). It has also been proposed to immobilize SAP particles with a microfibrous adhesive network to a nonwoven substrate by an adhesive (see e.g. WO2008/155699A1, Hundorf et al. and US2015/0080821A1, Peri et al.). More recently, airfelt-free cores have been disclosed comprising a high loft central layer with SAP distributed therein (see e.g. WO2016/106,021A1, Bianchi et al.). These cores are typically made by distributing a layer of SAP particles on each side of a high loft nonwoven and laminating both sides with a tissue paper or a nonwoven to immobilize the particles (the process for example illustrated in Fig. 3 of WO2020/025401 (BASF, Ge et al.)). Other recent central layer core publications are WO2020/032280, WO2020/032281, WO2020/032282, WO2020/032283 and WO2020/032284 (Nippon SHOKUBAI). EP2,901,992A1 (Ontex) discloses multi-layer absorbent material. There is a continuous need to improve the performances of absorbent cores, in particular in terms of absorption speed and capacity, wearer comfort, low rewet and flexibility, while keeping the overall costs of manufacture as low as possible. SUMMARY OF THE INVENTION The present invention is directed to an absorbent core extending in a transversal direction and a longitudinal direction, having a thickness in a vertical direction, and which comprises a liquid-permeable top layer, a bottom layer, and a central layer sandwiched between the top layer and the bottom layer. The central layer is a high loft layer, such as a carded nonwoven, having a density at a pressure of 4.14 kPa below 0.20 g/cm3. The absorbent core comprises superabsorbent polymer particles (SAP), which are at least partially distributed within the central layer. The superabsorbent polymer particles contained in the core have a time to reach an uptake of 20 g/g (SAP T20) of less than 220s, as measured according to the SAP K(t) Test Method as described herein. The absorbent core may also have a time to reach an uptake of 15 g/g (Core T15) of less than 200 s, as measured according to the Absorbent Core K(t) Test Method as described herein. The absorbent core may also have a permeability (Core K20) of more than 6.0 10-8 cm2, preferably more than 8.0 10-8 cm2, as measured according to Absorbent Core K(t) Test Method as described herein. The Core T15 and Core K20 may be measured directly on the core, whereas the SAP T20 is measured on the SAP separately. The absorbent cores of the invention have fast speed of absorption, especially in the first and second gush of a typical fluid insult. This reduces the risk of early leakage, i.e. leakage at low loading. The absorbent cores of the invention also have a lower liquid distribution length relative to other absorbent cores, i.e. are less wetted at front and back, while maintaining acceptable Rewet performance at the loading point (approximately the center of the absorbent core). This is beneficial to keep the skin of the wearer dryer at the contact area of the front and back of the absorbent structure. The absorbent core may comprise at least 60% by weight of SAP, in particular at least 70%, or even at least 80% of SAP, or even at least 90% of SAP, relative to the total weight of the core. The high loft central layer may be formed entirely from synthetic fibers, and may be substantially free of fluff cellulose fibers, although natural or natural-sourced fibers such a cellulose or cotton fibers or viscose fibers may also be present in the central layer and/or the top layer and/or the bottom layer. The top layer and the bottom layer are typically a nonwoven or a tissue paper. Low basis weight tissue paper for example is readily available and a relatively cheap substrate. The absorbent core may also comprise a