Absorbent core comprising high loft central layer and superabsorbent particles

Abstract

To provide improved absorbent cores in terms of an absorption speed and capacity, wearer comfort, low rewet and flexibility, while keeping overall costs of manufacture as low as possible.SOLUTION: An absorbent core 28 for use in an absorbent article is provided, the absorbent core 28 having a high loft central layer 43 between a top layer and a bottom layer and superabsorbent particles (SAP) 60 at least partially distributed within the high loft layer. The superabsorbent polymer particles have a time to reach uptake of 20 g / g (SAP T20) of less than 220 s, and / or the absorbent core has a time to reach uptake of 15 g / g (Core T15) of less than 200 s, and / or the absorbent core has permeability (Core K20) of more than 6.0×10-8 cm2. These properties are measured according to a K(t) Test Method as described in the application.SELECTED DRAWING: Figure 2a

Description

[Technical field]

[0001] The present invention relates to absorbent cores and their use in personal hygiene absorbent articles.The absorbent cores may in particular be used in baby diapers. [Background technology]

[0002] Absorbent articles for personal hygiene, such as disposable baby diapers, infant training pants, or adult incontinence underwear, are designed to absorb and contain body exudates, particularly urine. These absorbent articles typically comprise several layers serving different functions including a topsheet, a backsheet, and an absorbent core therebetween, among other layers.

[0003] The absorbent core should be able to absorb and retain exudates for extended periods of time, e.g., overnight in the case of diapers, minimizing rewet to keep the wearer dry and avoid soiling of clothing or bed sheets. The absorbent cores have typically included blends of ground wood pulp cellulose fibers and superabsorbent polymer (SAP) particles, also called absorbent gelling material (AGM), as the absorbent material.

[0004] More recently, absorbent cores that do not contain fluffed cellulose fibers (also called "airfelt-free" cores) have been proposed. SAP particles can be, for example, encapsulated in individual pockets formed between two substrates (see, for example, WO 95 / 11654, Tanzer et al.). It has also been proposed to fix SAP particles to a nonwoven substrate with a microfiber adhesive network by adhesive (see, for example, WO 2008 / 155699(A1), Hundorf et al.). More recently, airfelt-free cores have been disclosed that include a lofty central layer with SAP distributed therein (see, for example, WO 2016 / 106,021(A1), Bianchi et al.). These cores are typically made by distributing a layer of SAP particles on each side of a lofty nonwoven and laminating tissue paper or nonwoven fabric on both sides to immobilize the particles (e.g., the process illustrated in FIG. 3 of WO 2020 / 025401 (BASF, Ge et al.)). Other recent publications of central layer cores are WO 2020 / 032280, WO 2020 / 032281, WO 2020 / 032282, WO 2020 / 032283, and WO 2020 / 032284 (Nippon Shokubai Co., Ltd.). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 95 / 11654 [Patent Document 2] International Publication No. 2008 / 155699(A1) [Patent Document 3] International Publication No. 2016 / 106,021(A1) [Patent Document 4] International Publication No. 2020 / 025401 [Patent Document 5] International Publication No. 2020 / 032280 [Patent Document 6] International Publication No. 2020 / 032281 [Patent Document 7] International Publication No. 2020 / 032282 [Patent Document 8] International Publication No. 2020 / 032283 [Patent Document 9] International Publication No. 2020 / 032284 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a continuing need to improve the performance of absorbent cores, particularly in terms of absorption rate and capacity, wearer comfort, low rewet, and softness, while keeping overall manufacturing costs as low as possible. [Means for solving the problem]

[0007] The present invention is directed to an absorbent core extending in the transverse and longitudinal directions and having a thickness in the vertical direction, comprising a liquid permeable top layer, a bottom layer, and a central layer sandwiched between the top and bottom layers. The central layer is a high loft layer, such as a carded nonwoven. The absorbent core comprises superabsorbent polymer particles (SAP) at least partially distributed within the central layer. In a first aspect, the superabsorbent polymer particles contained in the core have a time to reach 20 g / g absorption (SAP T20) of less than 220 seconds, measured according to the SAP K(t) test method described herein. In a second embodiment, the absorbent core has a time to reach 15 g / g absorption (Core T15) of less than 200 seconds, as measured according to the Absorbent Core K(t) test method described herein. In a third embodiment, the absorbent core has a K(t) of 6.0 to 10 -8 cm 2 Above 8.0, preferably 10 -8 cm 2The core has a permeability (Core K20) of greater than 100%. Core T15 and Core K20 may be measured directly on the core, while SAP T20 is measured separately on the SAP. Of course, the absorbent core of the present invention may combine any of the different aspects, such as first and second, first and third, or second and third, as well as any other features described herein.

[0008] The absorbent core of the present invention has a fast absorption rate, especially in the first and second bursts of a typical fluid insult. This reduces the risk of early leakage, i.e. leakage at low loads. The absorbent core of the present invention also has a smaller liquid distribution length compared to other absorbent cores, i.e. less front and back wetting, while maintaining acceptable rewet performance at the load point (approximately the center of the absorbent core). This is beneficial to keep the wearer's skin drier in the front and back contact areas of the absorbent structure.

[0009] The absorbent core may comprise at least 60% by weight of SAP, in particular at least 70% by weight, or at least 80% by weight, or even at least 90% by weight of SAP, based on the total weight of the core. The lofty central layer may be formed entirely from synthetic fibers and may be substantially free of fluffed cellulosic fibers, although natural fibers or fibers of natural origin, such as cellulose or cotton fibers or viscose fibers, may be present in the central layer and / or the top layer and / or the bottom layer.

[0010] The top and bottom layers are typically nonwovens or tissue paper. For example, low basis weight tissue paper is a readily available and relatively inexpensive substrate. The absorbent core may also comprise a wrapping layer that completely covers the bottom or top layer and forms a C-wrap around the longitudinally extending side edges of the central layer to at least partially cover the top or bottom layer, respectively, and better immobilize the SAP particles within the absorbent core. The wrapping layer may improve the containment of the SAP, thereby preventing loss on the side edges of the core. Alternatively, such a C-wrap may be formed by the top or bottom layer.

[0011] The absorbent core may also comprise a bi-layer structure comprising a first central loft layer and a second central loft layer. This structure may provide additional advantages, for example in terms of SAP immobilization, where a greater amount of SAP particles may be distributed within the two layers. These and other optional features of the invention are described in the following description. [Brief description of the drawings]

[0012] [Figure 1] 1 illustrates a top view of an exemplary absorbent core with the top layer and central layer partially removed. [Figure 2a] 2A-2C show various possible schematic cross-sectional views of the absorbent core of FIG. 1 in exploded views. [Figure 2b] 2A-2C show various possible schematic cross-sectional views of the absorbent core of FIG. 1 in exploded views. [Figure 2c] 2A-2C show various possible schematic cross-sectional views of the absorbent core of FIG. 1 in exploded views. [Diagram 3] 2b is a schematic cross-sectional view of the absorbent core and core packaging layer of FIG. 2a. [Figure 4] FIG. 2 is a schematic cross-sectional view of an alternative absorbent core including two central loft layers. [Diagram 5] 5 is a schematic cross-sectional view of an absorbent article including the absorbent core and core packaging layer of FIG. 4. [Figure 6a] FIG. 1 shows a micro-CT scan of a circular sample of a core of the present invention. [Figure 6b] FIG. 1 shows projections of micro-CT scans in the xz plane. [Figure 6c] FIG. 13 shows the projection of the micro-CT scan in the yz plane. [Figure 7a] FIG. 13 illustrates the concentration of SAP particles in the z-direction of an exemplary core. [Figure 7b] FIG. 13 shows the concentration of SAP particles in the z-direction of the core for the comparative example. [Figure 8] FIG. 13 shows a micro-CT scan of SAP particles in the top region of the central layer of an exemplary core. [Figure 9]FIG. 13 shows a micro-CT scan of a SAP particle in the central region of the central layer of the core. [Figure 10] FIG. 13 shows a micro-CT scan of a SAP particle in the bottom region of the central layer of the core. [Figure 11] FIG. 1 is a partial cross-sectional side view of a suitable permeability measurement system for performing a urine permeability measurement test. [Figure 12] FIG. 1 is a cross-sectional side view of a piston / cylinder assembly for use in performing a urine permeability measurement test. [Figure 13] FIG. 13 is a top view of a piston head suitable for use in the piston / cylinder assembly shown in FIG. [Figure 14] FIG. 13 is a cross-sectional side view of the piston / cylinder assembly of FIG. 12 positioned over a fritted disc for the swelling phase. [Figure 15] FIG. 1 is a partial cross-sectional side view of a suitable transmittance measurement system for performing dynamic effective transmittance and absorptance measurement tests. [Figure 16] FIG. 1 is a cross-sectional side view of a piston / cylinder assembly for use in performing dynamic effective permeability and absorptivity measurement tests. [Figure 17] FIG. 16 is a top view of a piston head suitable for use in the piston / cylinder assembly shown in FIG. [Figure 18] FIG. 1 is a schematic diagram of a process for producing an absorbent core of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Introduction As used herein, the terms "comprise(s)" and "comprising" are open-ended. Each specifies the presence of the subsequently described feature, e.g., component, but does not exclude the presence of other features, e.g., elements, steps, components known in the art or disclosed herein. These terms based on the verb "comprise" should be interpreted to include the narrower term "consisting essentially of," which excludes any unmentioned element, step, or ingredient that significantly affects the way in which the feature performs its function, and the term "consisting of," which excludes any unspecified element, step, or ingredient. Any preferred or exemplary embodiments described below are not intended to limit the scope of the claims unless specifically indicated otherwise. Words such as "typically," "usually," "preferably," "advantageously," and "specifically" also modify features that are not intended to limit the scope of the claims unless specifically indicated to do so.

[0014] As used herein, the terms "nonwoven," "nonwoven layer," or "nonwoven web" are used interchangeably to mean a primarily planar, man-made assembly of fibers imparted with a designed level of structural integrity by physical and / or chemical means excluding weaving, knitting, or papermaking (ISO 9092:2019 definition). The unidirectionally or randomly oriented fibers are held together by friction, and / or cohesion and / or adhesion. The fibers may be of natural or synthetic origin, staple or continuous filaments, or formed in situ. Commercially available fibers have diameters ranging from less than about 0.001 mm to more than about 0.2 mm, and come in several different forms, such as short fibers (known as staple or chopped), continuous single fibers (filaments or monofilaments), untwisted continuous filament bundles (tows), and twisted bundles of continuous filaments (yarns). Nonwoven webs can be formed by many processes, such as meltblowing, spunbonding, solvent spinning, electrospinning, carding, and airlaying. The basis weight of a nonwoven web is typically measured in grams per square meter (g / m 2 or gsm).

[0015] Overview of absorbent cores As used herein, the term "absorbent core" refers to an individual component that contains absorbent material for absorbing and retaining bodily fluids, especially urine. The absorbent core typically has the highest absorption capacity of all components of an absorbent article and contains all or at least a majority of the superabsorbent polymer (referred to herein as "SAP") particles. The terms "absorbent core" and "core" are used interchangeably herein. Although some absorbent products may contain two or more individual absorbent cores, typically there is only one absorbent core in an absorbent product such as a diaper.

[0016] The absorbent core of the present invention is generally planar. By generally planar, it is meant that the absorbent core can be laid flat on a plane and extend primarily in the x and y directions. The absorbent core is also typically thin and conformable and can be placed on a curved surface, such as a drum, during its manufacturing process, or can be stored and handled as a continuous roll of storage material containing multiple cores before being processed into an absorbent article.

[0017] For ease of illustration, the exemplary absorbent core in Figure 1 is depicted in a flattened state. The height of the absorbent core in the z direction is small compared to its other dimensions in the transverse direction x and longitudinal direction y. Unless otherwise noted, the dimensions and areas disclosed herein apply to the core in this flattened form.

[0018] For ease of explanation, the absorbent cores, articles, and processes of the present invention will be described with reference to the drawings and numerals referenced therein, which are not, however, intended to limit the scope of the claims unless specifically stated otherwise.

[0019] Bulky center layer 43 The absorbent core of the present invention, as first illustrated in Figures 1-2, includes a high loft central layer 43. The term "high loft" refers to a bulky fabric with low density compared to a flat paper-like fabric. A high loft web is characterized by a relatively high porosity, meaning that there is a relatively large amount of voids between the fibers in which the superabsorbent polymer particles can be distributed. The high loft layer of the present invention (without superabsorbent particles) has a bulkiness of 0.20 g / cm under a pressure of 0.6 psi (4.14 kPa). 3 Less than 0.01 g / cm 3 ~0.20g / cm 3 , or 0.05 g / cm 3 ~0.15g / cm 3 , or 0.0.10 g / cm 3 ~0.14g / cm 3 The bulk layer of the present invention (without superabsorbent particles) can have a density in the range of 0.20 g / cm under a pressure of 0.3 psi. 3 Less than 0.05 g / cm3 ~0.15g / cm 3 , or 0.08 g / cm 3 ~0.13g / cm 3 The bulk layer of the present invention (without superabsorbent particles) can have a density in the range of 0.15 g / cm under a pressure of 0.83 kPa (0.12 psi). 3 Less than 0.01 g / cm 3 ~0.15g / cm 3 , or 0.05 g / cm 3 ~0.12g / cm 3 , or 0.08 g / cm 3 ~0.10g / cm 3 The density can be calculated by dividing the basis weight of the loft layer by its thickness measured at each pressure indicated (see the "Test Procedures" section below for further details on the method).

[0020] The central layer is preferably a nonwoven fabric, but other types of lofty materials are not excluded. The central layer may comprise or consist of synthetic fibers, optionally mixed with natural fibers, such as cellulose or cotton fibers or viscose fibers. The central layer may be substantially free of free cellulose fibers that are not integrated with other fibers of the nonwoven fabric. The amount of such free cellulose fibers in the absorbent core may be less than 10 weight percent of the total absorbent core, or less than 5 weight percent of the total absorbent core, or less than 1 weight percent of the total absorbent core, or may be completely free of such free cellulose fibers. The lofty material may comprise at least 10 weight percent, 30 weight percent, 50 weight percent, 70 weight percent, 90 weight percent, and up to 100 weight percent synthetic fibers of the lofty layer.

[0021] The fibers forming the central layer may be made partially or completely of relatively elastic synthetic fibers, in particular polypropylene (PP), polyamide (PA, e.g., nylon), or polyethylene terephthalate (PET) fibers. The diameter of the fibers may be, for example, in the range of 0.01 mm to 0.50 mm.

[0022] The thickness, basis weight, and density of the central layer 43 are typically homogeneous in both the transverse (x) and longitudinal (y) directions. The orientation of the fibers in the central layer 43 may be non-homogeneous, such as in a carded nonwoven, with the fibers having a predominant orientation in one direction x or y. Additionally, the fiber orientation in the thickness direction z in the central layer 43 may be different compared to the predominant orientation in one or both directions x and / or y. The loft layer may specifically have a thickness of at least 0.30 mm, specifically in the range of 0.30 mm to 2.00 mm, or 0.50 mm to 1.5 mm, measured at a pressure of 4.14 kPa (0.6 psi) (according to the test methodology described in more detail below). The loft layer may have a thickness, specifically measured at a pressure of 0.83 kPa (0.12 psi), ranging from 0.30 mm to 2.50 mm, or from 0.5 to 2.0 mm, or from 0.7 to 1.3 mm (according to the test methods described in more detail below). The basis weight of the lofty central layer may, for example, range from 15 gsm to 500 gsm, specifically from 30 gsm to 200 gsm, for example from 50 gsm to 120 gsm. The values ​​given herein for the central layer consider the lofty material taken separately, i.e. taken before the SAP particles are deposited between the fibers or the adhesive applied thereto. If the absorbent core comprises two or more lofty central layers, these may be the same or different.

[0023] Although the present invention is not limited to any particular type of nonwoven fabric or fiber, a particular example of a suitable nonwoven layer is a through-air bonded carded web ("ABCW"). "Bonded carded web" refers to a nonwoven fabric made from staple fibers coming from a combing or carding unit that separates and generally aligns the staple fibers in the machine direction to form a fibrous nonwoven web generally oriented in the machine direction. The web is then drawn into a heated drum, which forms bonds throughout the fabric without the application of any specific pressure (through a through-air bonding process). TABCW materials result in a low density, high loft, through-air bonded carded web.

[0024] TABCW materials may include staple fibers, for example, from about 3 to about 10 denier. Examples of such TABCW are disclosed in WO 2000 / 71067 (KIM DOO-HONG et al.). TABCW are also available directly from all the usual suppliers of nonwoven webs for use in absorbent articles, such as Fitesa Ltd or Fiberweb Technical Nonwovens. In carded nonwovens, the fibers in the web are aligned primarily in the machine direction to have a more uniform fiber alignment than other nonwovens, resulting in higher stability and internal bond strength, especially in the machine direction. The bond technique selected affects the integrity of the fabric. Air-bonded carded webs have excellent softness, bulk, and compressibility, as well as fast bleed-through and good rewet. Synthetic, natural, and recycled fibers in a wide range of deniers can be used. Soft PE / PP bicomponent staple fibers can be particularly used.

[0025] The lofty layer may also be a spunmelt nonwoven. Spunmelt is a general term describing the direct production of nonwoven webs from thermoplastic polymers. It encompasses two processes: spunlaid (also known as spunbond) nonwovens and meltblown nonwovens, as well as combinations of both. In the spunlaid process, polymer granules are melted and the molten polymer is extruded from a spinneret. Continuous filaments are cooled and deposited on a conveyor to form a uniform web. Some residual temperature may cause the filaments to adhere to each other, but this cannot be considered the main method of bonding. The spunlaid process has the advantage of giving the nonwoven fabric higher strength, but the flexibility of the raw material is more limited. Co-extrusion of a second component is usually used in some spunlaid processes to provide additional properties or bonding capabilities. In meltblown web formation, a low viscosity polymer is extruded into a high velocity air stream as it exits the spinneret. This causes the melt to disperse, solidify, and break down into a fibrous web.

[0026] The central layer 43 comprises a front edge 280, a rear edge 282 and two longitudinally extending side edges 284, 286. The front and rear edges are typically shorter than the side edges. The front edge of the central layer corresponds to the edge intended to be located towards the front edge of the absorbent article in which the core is or will be incorporated. The superabsorbent material may be distributed in a greater amount towards the front half of the central layer compared to the rear half of the central layer. This is because typically more fluid is discharged towards the front of the article in which the core is incorporated. In addition to a profiled SAP distribution in the longitudinal direction (y), the SAP may also be profiled in the transverse direction (x). Of course, the SAP may also be uniformly distributed in the transverse direction (x) and in the longitudinal direction (y), which simplifies production, in which case either of the two shorter sides can be considered as the front edge and the opposite side as the rear edge. The absorbent core may include one, two or more such lofty central layers. Absorbent cores containing two high loft central layers are discussed in more detail below.

[0027] The central layer (or layers) serves as a substrate for SAP particles 60 that are at least partially distributed within its pores. The SAP particles may be substantially uniformly blended throughout the thickness of the lofty layer. However, the SAP particles may be non-uniformly distributed in the vertical direction. The SAP particles are typically deposited on one side of the nonwoven and drawn into the lofty nonwoven, for example by gravity or negative pressure on the other side of the nonwoven. In this way, some particles remain close to the surface of the lofty central layer, while other, typically smaller particles, may penetrate deeper within the fiber network of the lofty nonwoven. SAP particles that are not trapped within the lofty pores but remain on the surface may be further immobilized by a layer of adhesive 71 or 72. The adhesive is typically applied first to the top and bottom layers before being combined with the lofty central layer while still tacky. Typically, the SAP particles are applied sequentially onto the lofty layer from each side of the lofty layer as a first layer of SAP 60 and a second layer of SAP 60'. This process of particle deposition may result in a z-distribution pattern of SAP inside the central layer that includes two or more peaks of density separated by at least one buffer zone when viewed in the z-direction. Such a distribution was obtained by depositing SAP on one side, but is shown in the example absorbent cores of Figures 6 to 10, which are believed to represent the absorbent cores shown in Figures 2a to 2c, in which two layers of SAP are distributed continuously within the loft layer.

[0028] Top layer 41 and bottom layer 42 The high loft central layer 43 is sandwiched between the top layer 41 and the bottom layer 42. The top layer 41 is on the side of the core intended to be placed closest to the wearer-facing side of the absorbent article. The top layer is therefore liquid permeable so that fluids can easily reach the central layer through the top layer during use. The bottom layer is positioned opposite the central layer. It may be liquid permeable or liquid impermeable. The top and bottom layers provide a cover on both sides of the central layer to prevent SAP particles from falling out of the loft during the core and article manufacturing process and / or during use of the absorbent article.

[0029] The top and bottom layers may be made of relatively thin and inexpensive materials, such as those commonly used in the production of conventional cores. The top and bottom layers may be, for example, tissue paper (airfelt or wetlaid) having a basis weight ranging from 5 to 100 gsm, specifically 10 to 40 gsm. The top and bottom layers may also be formed from low basis weight nonwoven webs, such as carded nonwovens, spunbonded nonwovens ("S"), or meltblown nonwovens ("M"), having a basis weight ranging from 5 gsm to 30 gsm, and laminates of any of these. For example, polypropylene nonwovens produced by the spunmelt process, specifically nonwovens having a laminated web SMS, or SMMS, or SSMMS structure, having a basis weight ranging from about 5 gsm to 20 gsm, are suitable. Such materials are disclosed, for example, in U.S. Patent No. 7,744,576, U.S. Patent Application Publication Nos. 2011 / 0,268,932(A1), 2011 / 0319848(A1), and 2011 / 0,250,413(A1). Nonwoven materials are typically hydrophobic in nature, and therefore the top layer may be treated to become hydrophilic, for example, by treating it with a surfactant or other methods known in the art. The top and bottom layers may be made of the same or different materials, and optionally the top or bottom layers may be treated differently so that the top layer is more hydrophilic than the bottom layer.

[0030] The top layer 41 may be wider than the bottom layer 42 so that this excess material can be folded around the longitudinal side edges 284, 286 of the core to form a C-lap seal on the bottom layer 42, as shown in Figure 2b. Alternatively, the bottom layer 42 may be wider than the top layer 41 so that this excess material can be folded around the longitudinal side edges 284, 286 of the core to form a C-lap seal on the top layer 41, as shown in Figure 2c.

[0031] In addition to the top and bottom layers, the absorbent core may further comprise a wrapping layer 3 forming a C-wrap around the longitudinally extending side edges 284, 286 of the core, as shown in FIG. 3. By "C-wrap" it is meant that the layer covers at least the top or bottom side of the core and extends along its side edges to form flaps that are subsequently folded and attached, typically by adhesive, onto the other side of the core. The wrapping layer 3 may thus have a cross section resembling the letter C (when rotated 90°). The C-wrap structure may further help contain the SAP particles during the making or wearing of the absorbent article. The wrapping layer may for example be made of a low basis weight nonwoven layer, in particular an SMS nonwoven, for example having a basis weight of 5-40 gsm, in particular 8-25 gsm, although of course other materials are possible. The wrapping layer 3 is represented in FIG. 3 as extending from the bottom side of the core and having flaps folded over onto the top side of the core. An inverted configuration is also possible, where the C wrapping layer 3 extends from the top side and the flaps are folded over the bottom side. The folded flaps may terminate and be attached near the longitudinally extending side edges of the core, or may be longer than depicted so that they are attached overlapping one another. It is also contemplated that the C-wrap structure may be formed by one of the top or bottom layers extending transversely along the longitudinally extending side edges of the core and forming a flap as described with respect to wrapping layer 3. The presence of a wrapping layer is optional, but is particularly preferred, especially when the top and bottom layers are not sealed along their longitudinal sides.

[0032] The top layer 41 and / or the bottom layer 42 may be attached to the central layer 43. A layer of adhesive 71 may be applied, for example, between the top layer and the central layer 43. Any kind of conventional adhesive and adhesive application method may be used. Typically, a hot melt adhesive may be sprayed onto substantially the entire surface of the layers before the two layers are brought together so that they are attached. The adhesive may be applied by contact methods, typically by slot coating a series of parallel thin lines of adhesive in the machine direction (y-direction) onto one of the layers, specifically the top or bottom layer in this case. A layer of adhesive 72 may be applied in the same way between the bottom layer 42 and the central layer 43. These layers of adhesive also have the advantage of being able to immobilize the dry SAP particles that have not penetrated into the central layer during the creation of the core.

[0033] Superabsorbent Material Particles 60 The central layer comprises superabsorbent polymer in the form of particles 60 at least partially distributed within the fibers of the loft layer. As used herein, the term "superabsorbent polymer" (abbreviated herein in the singular and plural as "SAP") refers to an absorbent material capable of absorbing at least 10 times its weight of 0.9% saline solution as measured using the Centrifuge Retention Capacity (CRC) test (EDANA method NWSP241.0.R2(19)). SAP preferably has a CRC value of at least 15 g / g. SAP of the present invention may have a CRC of less than 35 g / g, specifically less than 32 g / g.

[0034] SAPs are typically water-insoluble, water-swellable cross-linked polymers that can absorb large amounts of fluid. SAPs are in particulate form such that they are flowable in the dry state. A typical particulate SAP is a polyacrylate polymer, but it is not excluded that other polymeric materials may also be used. For example, starch-based particulate absorbent polymeric materials may also be used, as well as polyacrylamide copolymers, ethylene maleic anhydride copolymers, cross-linked carboxymethylcellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and starch graft copolymers of polyacrylonitrile.

[0035] The SAP may be an internally and / or surface cross-linked polyacrylate and polyacrylic acid polymer. The superabsorbent polymer of the present invention may be selected from internally and surface cross-linked polyacrylate and polyacrylic acid polymers. The superabsorbent polymer may be internally cross-linked, i.e. the polymerization is carried out in the presence of a compound having two or more polymerizable groups that can be free-radically copolymerized into a polymer network. Exemplary superabsorbent polymer particles of the prior art are described, for example, in WO 2006 / 083584, WO 2007 / 047598, WO 2007 / 046052, WO 2009 / 155265, WO 2009 / 155264. Preferably, the SAP particles comprise cross-linked polymers of polyacrylic acid or their salts or polyacrylates or their derivatives.

[0036] SAP particles may be relatively small in their dry state (less than 1 mm in their longest dimension) and generally circular in shape, although granules, fibers, flakes, spheres, powders, platelets, and other shapes and forms are known to those skilled in the art. Generally, SAP may be in the form of spherical particles. Thus, the absorbent material can consist of, or consist essentially of, SAP distributed within a high loft nonwoven.

[0037] At least a portion of the SAP particles may be agglomerated, for example, as taught in EP 3,391,961 (A1) (Kamphus, P&G). Agglomerated superabsorbent polymer particles may be obtained by various methods. Agglomerated particles may be obtained, for example, by agglomerating precursor particles with an interparticle crosslinking agent reacted with the polymeric material of the precursor particles to form crosslinks between the precursor particles, as disclosed, for example, in U.S. Pat. Nos. 5,300,565, 5,180,622 (both to Berg), 5,149,334, 5,102,597 (both to Roe), and 5,492,962 (Lahrman). Other methods for obtaining agglomerated SAP particles are described, for example, in EP 3056521(B1) (Kim et al.), EP 1512712(B1) (Koji et al.), U.S. Pat. No. 10414876(B2) (Jang et al.), U.S. Pat. No. 7429009(B2) (Nagasawa et al.), EP 220224911 (Higashimoto et al.), EP 2011803(B1) (Handa et al.).

[0038] Agglomerated superabsorbent polymer particles can also be obtained by a process comprising the steps of providing superabsorbent polymer particles and mixing the superabsorbent polymer particles with a solution comprising water and a multivalent salt having a valence of 3 or more, which process is further disclosed in EP 2,944,376 A1.

[0039] The superabsorbent polymer particles of the core of the present invention may specifically comprise at least 5% by weight, or at least 10% by weight, or at least 20% by weight, or at least 30% by weight, or at least 40% by weight, or at least 50% by weight of aggregated superabsorbent polymer particles.

[0040] Suitable precursor superabsorbent polymer particles can be obtained, for example, from inverse suspension polymerization as described in US Patent Nos. 4,340,706 and 5,849,816, or spray phase dispersion polymerization or other gas phase dispersion polymerization as described in US Patent Application Publication Nos. 2009 / 0192035, 2009 / 0258994, and 2010 / 0068520. In some embodiments, suitable precursor superabsorbent polymer particles can be obtained by the production process described in more detail in WO 2006 / 083584, p. 12, line 23 to p. 20, line 27.

[0041] The surface of the SAP particles may be coated. The surface of the SAP may be surface cross-linked. The SAP particles may also comprise surface and / or edge modified clay platelets. Preferably, the clay platelets are montmorillonite, hectorite, laponite, or mixtures thereof. Preferably, the clay platelets are laponite. The SAP may comprise 0.1-5 wt. % of surface and / or edge modified clay platelets compared to the weight of the precursor superabsorbent polymer particles.

[0042] In the first aspect of the invention, the SAP used in the core has a time to reach an absorption of 20 g / g (SAP T20) of less than 220 seconds as measured by the SAP K(t) test method described below. The SAP may specifically have a SAP T20 of 100 seconds to 220 seconds. The SAP T20 value may be less than 200 seconds, or less than 180 seconds, or less than 160 seconds. The time T20 may also be at least 100 seconds, 104 seconds, 120 seconds, or 140 seconds, and any combination of these upper and lower values ​​forming a range, for example, from 100 seconds to 200 seconds.

[0043] SAPs with the required SAP T20 can be synthesized, for example, using the teachings of WO 2015 / 041,784 A1, which discloses SAPs with T20s in the range of 104 seconds to 211 seconds. SAPs with the required SAP T20s can also be obtained directly from conventional SAP suppliers. For example, the following examples of the invention use a SAP with the product name SCHAUCH HVDE 235, "Der Alleskoenner", purchased via Amazon, with a measured SAP T20 of 165 seconds.

[0044] Unless otherwise indicated, the values ​​given herein for qualifying SAP (e.g. SAP T20, CRC, AAP...) refer to the properties of the entire SAP used in the absorbent core. For example, if a first layer 60 and a second layer 60' of SAP are used to make the core and the SAP used is different in each layer, the values ​​for qualifying the SAP of the core are based on the average value of these first and second SAPs. In practice, measurements are made using blends of different SAPs in the proportions used in the core.

[0045] Since high-loft absorbent cores have an open pore structure, it has been suggested that SAPs with lower permeability may be advantageously used to take advantage of this property (see, for example, WO 2016 / 106,021(A1)). However, this is not without drawbacks. The inventors have found that during use, liquid may spread rapidly from the point of insult towards the front and rear of the absorbent core. Thus, urine may escape the absorbent core via the front and rear ends, resulting in leakage, or at least creating zones of higher rewet at the front and rear of the absorbent core, resulting in insufficient dryness and lack of wearer comfort. The inventors have now found that using SAPs with relatively low SAP T20 values, as illustrated in the examples below, this drawback of undesirable liquid spreading can be successfully addressed. Without wishing to be bound by theory, the inventors believe that the low SAP T20 value is a characteristic of SAP that allows it to absorb fluids quickly even when the SAP particles are in close contact and / or under pressure, which prevents fluids from spreading along the length of the absorbent core as with other types of SAP. Without wishing to be bound by theory, the inventors believe that the contact of the SAP particles with the fibers of the central layer limits the absorption rate of the SAP particles because the fluid cannot freely penetrate into the particles in the contact area and the fiber network of the central layer creates a swelling constraint on the swelling SAP particles. The inventors believe that SAPs with low SAP T20 values ​​have the ability to overcome this adverse effect of the fiber network of the central layer. The inventors further believe that other properties, such as AAP at 0.3 psi, which are typically used to express the ability of SAP particles to act against moderate pressures, are not suitable to achieve the benefits of the present invention.

[0046] The SAP K(t) test method is also useful for determining other SAP parameters that may also be advantageously used in the present invention. The SAP absorption at 20 minutes (U20) may specifically be at least 22 g / g, or at least 24 g / g, or at least 28 g / g, or at least 30 g / g, or from 28 g / g to 60 g / g, or from 30 g / g to 50 g / g, or from 30 g / g to 40 g / g, as measured according to the SAP K(t) test method disclosed herein. The SAP has a pH of at least 1×10 -8 cm 2 , or at least 2×10 -8 cm 2 , or at least 2.5 × 10 -8 cm 2 , or 3 × 10 -8 cm 2 ~1×10 -7 cm 2 , or 2×10 -8 cm 2 ~7×10 -8 cm 2 , or 2.5×10 -8 ~5×10 -8 cm 2 The coating may have an effective permeability at 20 minutes (SAP K20) of 1.0 to 1.0 mm.

[0047] The SAP may also have a ratio of the minimum effective permeability to the permeability at 20 minutes (SAP Kmin / SAP K20 ratio) greater than 0.75, or greater than 0.8, or greater than 0.85, as measured according to the SAP K(t) test method. In such embodiments, transient gel blocking is minimal and liquid exudates can move quickly through the voids present between the particles throughout the entire swelling process, especially in the initial part of the swelling phase, which is most critical for the first gush.

[0048] The superabsorbent polymer particles may further have a permeability at equilibrium, expressed as a UPM (Urine Permeability Measurement) value of more than 10, or preferably more than 15, or more than 20, or more than 30, or more than 45, or from 10 to 200, or from 15 to 100, or from 30 to 80 UPM units, where 1 UPM unit is 1×10 -7 (cm 3 sec) / g. The UPM value is measured according to the UPM test method described herein. This method is closely related to the prior art SFC test method. The UPM test method typically measures the flow resistance of a pre-swollen layer of superabsorbent polymer particles, i.e., the flow resistance is measured at equilibrium. Thus, such superabsorbent polymer particles with high UPM values ​​exhibit high permeability when a significant volume of the absorbent article is already wetted by liquid exudate. These embodiments exhibit good absorption properties not only in the first gush, but also in subsequent gushes.

[0049] The total amount of SAP present in the absorbent core may also vary depending on the intended user of the article. Newborn diapers require less SAP than baby or adult incontinence diapers. The amount of SAP in the core may, for example, comprise about 2 g to 50 g, particularly 5 g to 40 g, for a typical baby diaper. The average SAP basis weight in the absorbent core may, for example, be at least 50, 100, 200, 300, 400, 500 g / m 2 or more, or 200-400g / m 2 It could be.

[0050] SAP vertical distribution The SAP particles preferably have a non-uniform vertical distribution in the lofty central layer. Non-uniform means that the planar SAP concentration in the z-direction of the core is not constant through the thickness of the lofty nonwoven, but the SAP concentration varies in the z-direction with respect to the average value by more than plus or minus 10%, in particular by more than plus or minus 20%. Planar concentration as meant herein is the average planar concentration of a circular zone of the absorbent core with a diameter of 20 mm in a plane comprising the xy-directions of the absorbent core. The planar concentration of the SAP particles may have a multimodal distribution, in particular a bimodal distribution, in particular in the z-direction of the absorbent core. Bimodality means that the concentration of the SAP particles along the thickness of the core comprises at least two peaks, the peaks being separated by a valley having a SAP concentration of less than 40%, in particular less than 30%, compared to the lowest concentration of the two adjacent peaks. Such a distribution is illustrated by the diagram in FIG. 7a and can be determined for a given sample by micro-CT analysis. Multimodality means that the z-distribution of the concentration of the SAP particles comprises two or more of these peaks.

[0051] The bimodal distributions obtained by micro-CT analysis of exemplary cores of the invention are shown in Figures 6-10. CT is an abbreviation for computed tomography, and "micro" means that a very low resolution can be reached, which is suitable for measuring the position of SAP particles. CT technology uses X-rays to see inside an object, and many X-ray projections are made around the test object from different angles to generate cross-sectional images in the test object. This is the traditional diagnostic method in medical applications. Nowadays, any material or component can be examined with CT, so the application fields of CT are diverse and wide-ranging. The main application field of CT in science and industry is non-destructive testing.

[0052] Figures 6a-c show in exemplary cross-section the results of a micro-CT scan of an absorbent core of the invention, as detailed below. A circular sample of 26 mm diameter was cut from the center of the absorbent core, and the field of view seen in Figure 6a is a 20 mm diameter at the center of the circular sample. The spatial resolution of the scan is 10 μm. Micro-CT scanning allows computer processing of the scanned data, which can also be projected into the xz (Figure 6b) and yz (Figure 6c) planes. The bimodality of the SAP concentration distribution in the central layer is already visible in these Figs. 6a-c, where two distinct layers have a higher SAP concentration separated by a low SAP concentration zone. Using image analysis, it is possible to plot a diagram showing the grey value proportional to the average planar concentration of SAP for a field of view of the sample in the z direction. See Fig. 7a. The horizontal axis shows the vertical distance z (100 = 1 mm) from the surface of the sample, and the vertical axis shows the grey value proportional to the average planar concentration of SAP for the distance z from the reported top surface. The relative difference in grey values ​​shown in Fig. 7a, b corresponds to the relative difference in the planar concentration of SAP. For example, a 20% higher grey value (as in Fig. 7a, b) corresponds to a 20% higher planar concentration of SAP.

[0053] As can be seen from this figure, the SAP distribution is bimodal with a first peak P1 located at about 0.6 mm from the top side of the core and having a gray value of 3338, and a second peak P2 located at about 3.6 mm from the top side of the core with a value of 2897. Between peaks P1 and P2 there is a valley V1 with a value of 530. The gray values ​​used to measure the relative height of the peaks (used in FIG. 7a) are arbitrary units that are not calibrated but are directly correlated with the local density of the specimen and therefore with the planar concentration of SAP. The diagram in FIG. 7a can therefore be used to compare the relative values ​​of the peaks and valleys at various z values, i.e. at various positions on the vertical axis (thickness direction) of the core.

[0054] Figure 8 is an xy-plane view of the SAP present in a first cross section 61 encompassing the first 1 mm of the central layer, encompassing the first peak P1. Figure 9 shows the SAP in a second 1 mm thick cross section 62 of the central layer in the region of the valley V1. Figure 10 shows the SAP present in a third 1 mm thick cross section of the central layer, encompassing the second peak P2.

[0055] As pointed out above, bimodal means that the measurement of the valley (V1) is less than 40%, specifically less than 30%, than the lowest value of the two adjacent peaks (taking the lowest value of P1, P2). In the example shown, the valley V1 has a SAP concentration that is about 18.3% (530 / 2897*100%) of the lowest value of the adjacent peaks. By comparison, the distribution in the comparative example disclosed below has a first peak P1' at about 8400 arbitrary units, a second peak P2' at about 3000 arbitrary units, and a valley V1' therebetween at about 1500 arbitrary units, so that the valley is about 50% of the lowest adjacent peak.

[0056] Absorbent core properties Instead of, or in addition to, measuring the SAP T20 value of the SAP in the absorbent core, the K(t) test method may be adapted to measure properties of the absorbent core directly. As discussed in detail in the Absorbent Core K(t) Test Method described in more detail below, the properties of the core are measured on a circular sample taken at the center of the core.

[0057] Specifically, in this way it is possible to measure the T15 and the permeability K20 of the absorbent core (Core T15, Core K20). Other parameters can also be measured, such as Core T80%, which measures the absorption rate relative to the total volume of the core.

[0058] The absorbent core of the present invention may have a time to reach 15 g / g absorption (Core T15) of less than 200 seconds, particularly less than 180 seconds or less than 150 seconds. Core T15 may optionally be at least 80 seconds, or 100 seconds, or 120 seconds, and any range comprised between any of these boundaries, such as from 100 seconds to less than 180 seconds, or from 120 seconds to less than 150 seconds.

[0059] The core permeability (Core K20) is 6.0×10, as measured according to the Absorbent Core K(t) test method described herein. -8 cm 2 Super, specifically 8.0 x 10 -8 cm 2 and for example 6.0×10 -8 cm 2 up to 40×10 -8 cm 2 , or 8.0 × 10 -8 cm 2 up to 19×10 -8 cm 2 It could be.

[0060] Without wishing to be bound by theory, the inventors believe that a low core T15 value is characteristic of an absorbent core that is able to rapidly absorb fluids (osmotic storage) not only within the void volume of the absorbent core (capillary storage) but also within the SAP particles contained therein. The inventors believe that improving the balance between capillary storage between the lofty fibers and osmotic storage in the SAP provides an absorbent core that has a faster rate of fluid intrusion acquisition, provides excellent leak protection, and provides dryness and comfort to the wearer. Osmotically stored fluids do not contribute to rewet, resulting in better dryness and better comfort for the wearer, and are immobilized locally, reducing the spread of fluids over the long distances of the absorbent core, as with other types of absorbent cores.

[0061] Furthermore, the osmotic capacity represented by the CRC of the SAP particles contained in the core, or more precisely the product of the CRC of the SAP particles contained in the core and the amount of SAP particles in the absorbent core, is not suitable to describe the ability of the core to efficiently balance capillary storage and osmotic storage in the absorbent core of the present invention.

[0062] The absorbent core K(t) test method described herein measures the properties of the core under moderate pressure and dynamic behavior. The inventors have found that this balance can be reliably measured for high loft cores by the absorbent core K(t) test method. The inventors believe that the time to reach 15 g / g (Core T15) is characteristic of an absorbent core with a good balance between capillary and osmotic storage.

[0063] Without wishing to be bound by theory, the inventors believe that high core K20 values ​​characterize absorbent cores with high fluid permeability, especially in swollen state. Such high core permeability in swollen state ensures fluid intake into the absorbent core under load, even under moderate pressure, for example after liquid insult. The inventors believe that high core K20 values ​​characterize cores with minimal liquid flow to the top of the absorbent core. By avoiding this free liquid flow at the top of the absorbent core, as with other types of absorbent cores, the spreading of liquid along the length of the absorbent core in the upper layers of the absorbent article is limited, which results in better dryness and better comfort for the wearer.

[0064] Additional parameters can be measured using the absorbent core K(t) test method. The absorbent core of the present invention can further have a time to reach 80% of total absorbency after 20 minutes (core T80%) of less than 270 seconds, particularly less than 260 seconds or less than 255 seconds. Core T80% can optionally be at least 150 seconds, or 180 seconds, or 220 seconds, and any range consisting of any of these bounds, such as from 150 seconds to less than 270 seconds, or from 180 seconds to less than 260 seconds.

[0065] The absorbent core of the present invention may have a time to reach 20 g / g absorption (Core T20) of less than 550 seconds, particularly less than 500 seconds or less than 450 seconds. Core T20 may optionally be at least 200 seconds, or 300 seconds, or 350 seconds, and any range consisting of any of these boundaries, such as from 300 seconds to less than 550 seconds, or from 360 seconds to less than 500 seconds. The density of the absorbent core as a whole may also be measured when performing the Absorbent Core K(t) test method. The absorbent core may have a density of less than 0.2 g / cm 3 ~0.6g / cm 3 Less than 0.3 to 0.5 g / cm 3 The density is measured at 0.3 psi as set forth in the Absorbent Core K(t) test method (see below).

[0066] Method of preparation An exemplary continuous process for making an absorbent core is shown in Figure 18. The above-mentioned process and apparatus are generally similar to those disclosed in Figure 3 of PRC Patent No. 101797201, or WO 2020 / 025401 (BASF, Ge et al.). The various arrows in this figure represent the rotation directions of the various roll-releasing and roll-up cylinders during the production flow process, as well as the running direction of the manufacturing material. Of course, other processes and modifications are possible.

[0067] As shown in FIG. 18, the apparatus for making the absorbent core may include a bottom layer web unwinder 6, a bottom layer adhesive spray head 7, a high loft central layer web unwinder 8, a first SAP particle dispenser 9 and optional vacuum suction box 10, a first pair of rollers 11 and 12, a second SAP particle dispenser 13 and optional vacuum suction box 14, a top layer web unwinder 15, a top layer spray head 16, a second pair of rollers 17 and 18, trimming knives 19, 20, and a product roll take-up roller 21.

[0068] Both the first and second SAP particle dispensers 9, 13 may be equipped with frequency variation and speed adjustment devices (not shown in FIG. 18) adjusted to maintain a vibration frequency that matches the linear speed of the product roll take-up roller 21 and to ensure that the deposited SAP is generally uniformly distributed on the bulky web 43.

[0069] During production, a roll of bottom layer material 42, e.g., a roll of paper or nonwoven fabric, is placed on bottom layer web unwinder 6. A roll of high loft nonwoven fabric 43 is placed on center layer web unwinder 8. The initial density and thickness of the high loft center layer can be conveniently measured with the Raw Material Thickness and Density Measurement Method described in more detail below.

[0070] The SAP particles are fed onto first and second SAP particle sieve plates 9 and 13. A roll of top layer material 41, which can be a paper or nonwoven roll, is placed onto top layer web unwinder 15. During the continuous process of making the absorbent core, the bottom layer 42 passes through a spray head 7 to have one side coated with adhesive 72 before being attached to the central layer 43 between the first press rollers 11 and 12. The high loft nonwoven central layer 43 passes through a first SAP dispenser 9 and a vacuum suction box 10 where SAP particles 60' are deposited in the central layer and at least partially distributed in the fibers of the central layer from the first side. It is also possible that the bottom layer material 6 is first attached to the first side of the central layer 43 and then the SAP particles 60 are deposited on the fibers of the central layer and blended therebetween.

[0071] After the bottom layer 42 and the central layer 43 are pressed together between the rollers 11 and 12, the combined layers can optionally pass between a second SAP particle sieve plate 13 and a vacuum suction box 14, which cooperate to deposit the SAP particles on the second surface of the central layer and blend the SAP particles in the fibers of the central layer from this second surface. A top layer 41, which has been applied with adhesive 72 by an adhesive spray head 16, is then bonded to the central layer and covers the second surface of the central layer between two press rollers 17 and 18. Of course, in the above, top layer and bottom layer may be used interchangeably.

[0072] Press rollers 17 and 18 may have a substantially flat surface, or they may have raised areas where extra pressure and heat should be applied on the core. These raised areas occupy the same space as the channel areas and therefore may provide mechanical, ultrasonic, and / or thermal bonding in the channel zone 26. Press rollers 11-12, 17-18 may be heated. It is also possible for the rollers to have raised areas along the longitudinal side edges and / or the trailing and leading edges (360 degree perimeter) of the core. In these zones, better bonding may be achieved without SAP as in the channel zone 26. Trimming knives 19 and 20 may be provided to trim the longitudinal side edges of the continuous band of absorbent core before the stream of absorbent core material is finally rolled into a roll of absorbent core material by product roll take-up roller 21.

[0073] The rolls of absorbent core material thus formed can be stored or transported to an article production site where they can be further processed into absorbent products. Instead of forming a roll, it is also possible that the stream of absorbent core material can be fed directly to a processing line, in which case the absorbent cores are singulated by cutting along their leading and trailing edges.

[0074] A wrapping layer 3 (not shown in Figure 18) may also be applied to prevent loss of SAP through the side edges of the absorbent core before the core material is rolled and wrapped around the top, center and bottom layers as shown and discussed in connection with Figure 5. Alternative such wrapping layers may also be attached to the core during further processing of the core material web.

[0075] Core 28b with double loft nonwoven layers 431, 432 Although the absorbent core 28 described above includes a single lofty nonwoven layer, it is also possible for the absorbent core to include two (or more) lofty nonwoven layers between the top and bottom layers. This is shown, for example, in Figure 4, where an absorbent core 28b including a first central layer 431 and a second central layer 432 is shown sandwiched between a top layer 41 and a bottom layer 42.

[0076] Thus, the absorbent core 28b may comprise a first central layer 431 and a second central layer 432, each of which is a lofty fibrous nonwoven layer, for example comprising three or more layers 60, 60', 60'' of superabsorbent polymer particles at least partially distributed within the pores of the lofty central layer. The two (or more) lofty central layers may be composed of the same material or different lofty nonwovens. For example, permeability in the top central layer may be enhanced by using a low basis weight loft, and softness may be enhanced with a bottom layer comprising a higher density loft material. Of course, other configurations are possible. The two or more two central layers may be of equal dimensions in the x, y plane of the core, but they may have different lengths and / or widths. Two central layers of unequal length may be useful to provide different amounts of SAP along the absorbent core, and may be created, for example, by adding a cut and slit unit on the second layer patch before combining it with the first layer.

[0077] It is also contemplated that the two lofty central layers may comprise different types of SAP, for example a faster absorbent SAP (lower SAP T20, higher UPM value) deposited in the first SAP layer 60 on the upper side of the first central layer 431 closer to the top layer 41, and / or a more absorbent SAP (higher CRC) in the second SAP layer 60' or third SAP layer 60'' at least partially distributed in the second central layer 432 closer to the bottom layer 42. The SAP in the two lofty layers may also have different or the same absorption rate (SAP T20), capacity (CRC, AAP) and permeability (UPM).

[0078] The absorbent core comprising a double loft nonwoven layer may be made by a method adapted from one of the methods disclosed above, see for example WO 2016 / 106021 (A1) in which two separate loft layer open cylinders are described to provide a first and a second loft central layer 431, 432. Alternatively, a loft web with a double width may be used, and such a large width roll may be cut into two halves in the machine direction after opening to provide two streams of loft nonwoven material, on which the SAP particles are then separately deposited. The two streams of loft material 431, 432 may then be combined separately with a top layer and a bottom layer, respectively, each having the SAP particles 60 deposited thereon via a suitable SAP deposition device.

[0079] Absorbent article 20 The absorbent core may be incorporated into any type of personal hygiene article, in particular pant diapers and taped diapers, as well as into inserts in hybrid systems with washable outer covers and disposable inserts. A schematic cross-sectional view showing some of the main components of a diaper absorbent article 20 is shown in FIG. 5. In this figure, the absorbent core of FIG. 3 (including the envelope layer 3) is shown, which is of course not limiting, but is merely illustrative. The absorbent article typically comprises a wearer-facing, fluid-permeable topsheet 36 and a garment-facing, liquid-impermeable backsheet 38 attached to each other along their periphery. The absorbent core is disposed between these layers and may be attached directly and indirectly to these layers, typically by adhesive or heat / pressure bonding.

[0080] The topsheet 36 is preferably compliant, soft feeling, and non-irritating to the wearer's skin. Moreover, at least a portion of the topsheet is liquid pervious, allowing liquids to readily penetrate its thickness. Suitable topsheets can be manufactured from a wide variety of materials, such as, for example, porous foams, reticulated foams, perforated plastic films, or woven or nonwoven materials of natural fibers (e.g., wood or cotton fibers or viscose), synthetic fibers or filaments (e.g., polyester fibers, or polypropylene fibers, or bicomponent PE / PP fibers, or mixtures thereof), or combinations of natural and synthetic fibers. If the topsheet comprises fibers, the fibers may be spunbonded, carded, wet-laid, meltblown, hydroentangled, or processed in a manner known in the art, such as, in particular, spunbonded PP nonwovens. Typical diaper topsheets have a basis weight of from about 10 gsm to about 28 gsm, and particularly from about 12 gsm to about 18 gsm, although other basis weights are possible.

[0081] The backsheet 38 is typically impermeable to liquids (e.g., urine). The backsheet may be or include a thin plastic film, such as a thermoplastic film having a thickness of less than about 0.10 mm. Exemplary backsheet films include those manufactured by Tredegar Corporation (based in Richmond, VA) and sold under the trademark CPC2 film. Other suitable backsheet materials may include breathable materials that allow vapors to escape from the article while preventing exudates from passing through the backsheet. A low basis weight nonwoven cover may be applied to the outer surface of the film to provide a softer feel.

[0082] The absorbent article may also include a liquid management layer 54 (also called a fluid acquisition or distribution layer) beneath the topsheet 36. The function of such a layer is to quickly acquire fluid from the topsheet away from the side facing the wearer and / or distribute the fluid over a larger area so that it is more efficiently absorbed by the absorbent core. It is also possible that such a liquid management layer may be located between the backsheet and the absorbent core. An additional layer 4 may be present between the liquid management 54 and the absorbent core 28. The additional layer 4 may be another such acquisition or distribution layer, or may be a tissue paper or low basis weight NW layer that provides additional wrapping for the absorbent core 28 to prevent the SAP particles from escaping outside the core.

[0083] Absorbent articles such as diapers or training pants may typically further include components that improve the fit of the article around the legs of the wearer, specifically barrier leg cuffs 32 and gasket cuffs 34. The barrier leg cuffs may be formed from a piece of material, typically a nonwoven, that is partially bonded to the rest of the article and partially raised, and thus upright, from the plane defined by the topsheet. The barrier leg cuffs are typically bounded by a proximal edge that is joined to the rest of the article, typically the topsheet and / or backsheet, and a free edge that is intended to contact the wearer's skin to form a seal. The upright portion of the cuff typically comprises an elastic element, such as one or more elastic strands 35. The barrier leg cuffs provide improved containment of liquids and other body exudates generally at the junction of the wearer's torso and legs.

[0084] In addition to the barrier leg cuffs, the article may comprise gasket cuffs 34 which may be formed in the same plane as the chassis of the absorbent article, specifically at least partially enclosed between the topsheet or barrier leg cuffs and the backsheet, and disposed laterally outwardly relative to the upstanding barrier leg cuffs. The gasket cuffs may provide a better seal around the thighs of the wearer. Typically, each gasket leg cuff includes one or more elastic strings or elements 33 which are included in the chassis of the diaper, for example in the region of the leg opening between the topsheet and the backsheet.

[0085] The absorbent article may also include other typical components found in diapers, training pants, replacement inserts, or adult incontinence products (not further shown). A removable fastening system for tape diapers may be provided to provide lateral tension around the absorbent article to hold it on the wearer. This fastening system is not necessary for training pants, since the waist regions of these articles are already attached. The fastening system typically includes fasteners such as tape tabs, hook-and-loop components, interlocking fasteners such as tabs and slots, buckles, buttons, snaps, and / or hermaphroditic fastening components, although any other known fastening means are generally acceptable. A landing zone is typically provided in the front waist region of the article to allow the fasteners to be releasably attached.

[0086] The absorbent article may include front and back ears as known in the art. The ears may be an integral part of the chassis, for example formed as side panels from the topsheet and / or backsheet. Alternatively, the ears may be separate elements attached by adhesive and / or heat embossing. The back ears are advantageously elastic to facilitate attachment of the tabs to the landing zone and to keep the tape diaper in place around the waist of the wearer. The front ears may also be elastic or stretchable, allowing the sides of the absorbent article to stretch, providing a more comfortable and conforming fit by initially fitting the absorbent article to the wearer and maintaining this fit throughout the wear period, even after exudates have accumulated in the absorbent article over time.

[0087] Typically, adjacent layers are joined together using conventional bonding methods, such as slot-coating or spray-coating adhesive onto all or part of the surface of the layers, or heat bonding, or pressure bonding, or a combination thereof. For clarity and ease of reading, bonds between components are not shown in most of the figures, especially in FIG. 5, except for adhesive layers 71, 72. Unless otherwise specified, adjacent layers of the article should be considered attached to one another. For example, the backsheet and bottom layer of an absorbent core may typically be glued together. The adhesive used may be any standard hot melt adhesive known in the art.

[0088] Packaging The absorbent article may be packaged in any conventional type of package. The absorbent article may be compressed when packaged, particularly to save space. Specifically, the package may include a plurality of absorbent articles, where the package has an in-bag stack height of less than about 80 mm according to the in-bag stack height test described in U.S. Pat. No. 8,585,666 (B2) (Weisman), which is incorporated herein by reference. Alternatively, the package of absorbent articles of the present disclosure may have an in-bag stack height of about 72 mm to about 80 mm, or about 74 mm to about 78 mm, specifically the ranges specified and all 0.5 mm increments within or formed by the ranges specified, based on the in-bag stack height test described in U.S. Pat. No. 8,585,666 (B2) (Weisman).

[0089] Examples and Experimental Results a) Building the core An exemplary absorbent core of the present invention was made by hand. The central loft layer was a loft layer (TL6 from TWE-group, Emsdetten, Germany). The measured caliper was 0.613 mm and the basis weight was 85.4 g / m 2 (average of 10 measurements), approximately 0.140 g / cm 3The density was measured at a pressure of 4.14 kPa (0.6 psi). The data at various pressures are listed in the table below.

[0090] [Table 1]

[0091] The two cover layers were hydrophilic 10 gsm SMS nonwoven from Fibertex (e.g. HY02XXX10). The width of the core layer was 165 mm and its length was 360 mm. Each of the cover layers was first coated with 5 gsm spiral adhesive, followed by 10 gsm neat microfiber adhesive (NW1151ZP, from FULLER ADHESIVES), evenly over its entire length.

[0092] The high loft central layer was placed on the bottom cover layer with the rough side of the high loft nonwoven facing up. The width of the high loft central layer was 110 mm and its length was 360 mm. 15 g of SAP was sprinkled evenly by hand over the entire high loft surface of the nonwoven. As the production table did not have a vacuum, the SAP was distributed within the high loft nonwoven by brushing the SAP particles by hand. The top cover layer was then placed on the laminate with the adhesive layer facing the high loft layer. Gentle pressure was applied with a rubber roller to attach the central layer to the two cover layers.

[0093] The resulting basis weight of the SAP in the absorbent core was 380 gsm. The average concentration of SAP in the absorbent core was 61% by weight based on the weight of the core, and the average concentration of SAP for the lofty central layer only (not considering the top and bottom layers and adhesive) was 81% by weight.

[0094] Two commercially available SAPs (SAP E1, SAP C1) were used to prepare the inventive core E1 and the comparative core C1, respectively. The SAPs had the properties listed in Table 2 below.

[0095] [Table 2]

[0096] The absorbent core had the following characteristics:

[0097] [Table 3]

[0098] b) Comparative commercially available cores: As a further comparison, the properties of two commercial products from China: Teddy Bear, More Than Thinner, size S and Huggies, breathable diaper, size L, were tested according to the absorbent core K(t) test method. Teddy Bear had an absorbent core with a high loft central layer with SAP distributed in it. Huggies had a dual layer core including an airfelt / SAP blend layer on top of a high loft layer with SAP, both layers being between the bottom and top layers. The specific average density ρ of the core samples was s was not measured, but 1.50 g / cm 3 It was assumed that.

[0099] The properties of the comparative cores C2 and C3 are listed in Table 4.

[0100] [Table 4]

[0101] The SAP used in these products was recovered and also measured using the SAP K(t) test method, this time to determine the specific average density, ρ s 1.60g / cm 3 It was assumed that:

[0102] The properties of the comparative cores SAP, SAP C2, and SAP C3 are listed in Table 4.

[0103] [Table 5]

[0104] c) Product data: Capture speed Exemplary core E1 and comparative core C1 were placed in an absorbent product chassis containing a commercially available topsheet, backsheet, and acquisition layer used in China's Pampers Premium product (size 4). The absorbent cores were placed in different orientations within the product (up or down. (See description below.) These products were tested using the C-SABAP test (Acquisition Rate Curve Under Balloon Pressure). C-SABAP determines the saline acquisition time of an absorbent sanitary product while the diaper is held in a slightly curved position and placed on a latex film inflated with compressed air (2.07 kPa (0.30 psi)) and monitored by a digital pressure gauge.

[0105] In a first set of experiments, acquisition rates were measured in four replicates for each type of core and for each orientation of the core in the diaper. Four squirts of physiologically colored saline (0.9 wt%) of 75 mL each were applied sequentially at a rate of 15 mL / s with 5 minutes between each squirt. The acquisition rate of each squirt is recorded. The liquid is delivered to the center of the diaper at a distance of 170 mm from the front of the absorbent core. The table below shows the average of three of the four measurements for each core / orientation combination, the fourth measurement with the highest sum of squirt times 1 and 2 was ignored to eliminate outliers.

[0106] Note: "Face up" means that the top side of the central layer with the AGM added faces the topsheet and "face down" means the opposite direction.

[0107] [Table 6]

[0108] The acquisition rate of Inventive Example E1 was faster than Comparative Example C1 on the first squirt regardless of the orientation of the core in the product (up or down).

[0109] In the same orientation (either all upwards or all downwards), the inventive core E1 performed at a better acquisition rate (i.e., was faster) across all four eruptions compared to the product containing the comparative core C1.

[0110] d) Product Data: Liquid Distribution and Rewet The articles used in the C-SABAP test were removed from the C-SABAP apparatus 5 minutes after complete absorption of the final fourth gush. Liquid distribution and rewet were measured on these articles containing the core of interest. Rewet was measured at a distance of 170 mm from the insult point, i.e., the front of the absorbent core. Liquid distribution was measured in the longitudinal direction (y) starting from the center point of insult on the plane (i.e., at a distance of 170 mm from the front of the absorbent core) toward each lateral side of the article, obtaining the liquid distribution front (i.e., from the insult to the front end of the absorbent core) and the liquid distribution rear (i.e., from the insult to the rear end of the absorbent core).

[0111] Liquid distribution measures the length of the stain left by the colored saline on the absorbent core at the front and back of the diaper (the edge of the colored stain is not a straight line so that the maximum and minimum distances between the stain edge and the load point are indicated).

[0112] A rewet test was then performed on the topsheet side of the diaper. The overall liquid distribution length is the sum of the average of the average of the minimum and maximum values ​​on both sides, i.e., average (front minimum, front maximum) + average (rear minimum, rear maximum).

[0113] The rewet test measures the amount of fluid released by the diaper using a skin-like material (a five-ply collagen stack). Collagen absorbs fluid by the same mechanism as a baby's skin. The rewet test is performed 10 minutes after the last squirt, when four 70 mm diameter collagen sheets are stacked centered on the squirt point and weighted with a 9.1 kg weight for 30 seconds. The amount of fluid absorbed into the collagen sheet stack is measured and reported as shown below.

[0114] As summarized above, data for products excluded for acquisition rate are also excluded for rewet and liquid distribution, so Table 5 shows the average of three of the four data points.

[0115] [Table 7] 1) 170 mm is the maximum liquid distribution length front, which means that the liquid has reached the front of the absorbent core.

[0116] Staining on the inventive diaper with the inventive core E1 was significantly shorter than that on the comparative diaper with the comparative core C1. In both diapers, rewet was lower when the absorbent core was positioned with the top layer facing the topsheet ("face up") than the other way around ("face down").

[0117] e) Micro-CT scan The exemplary core E1 was subjected to micro-CT scanning according to the micro-CT scanning method described below. The results of the micro-CT scanning of the exemplary core E1 are shown in Figures 6 to 10. As mentioned above, such CT scanning can be used to determine the concentration distribution of SAP within the absorbent core, specifically whether the vertical distribution of SAP particles is uniform or bimodal or multimodal. The inventive core E1 had a bimodal distribution. The comparative core C1 was also measured and also contained two peaks, but it is not bimodal according to the definition herein (the valley has a measured shade value less than 40% of the lowest value of the adjacent peak in the relevant units). Although SAP was not applied to both sides of the loft layer, it was found that the material combination in the example used still resulted in a bimodal SAP distribution, which is also found when SAP is applied successively in two stages to each side of the central layer.

[0118] Test procedure Centrifugal holding capacity (CRC) CRC measures the absorptive capacity of superabsorbent polymer particles when freely swelled in excess liquid. CRC is measured according to EDANA method NWSP241.0.R2(19).

[0119] Pressure vs. Absorption The AAP is measured according to EDANA standard test NWSP242.0 R2 (19), and the pressures used are 0.7 psi and 0.3 psi, as indicated as AAP@0.7 psi and AAP@0.3 psi, respectively.

[0120] Thickness and Density Measurement This method is used to measure the thickness (caliper) of the high loft central layer in a standardized manner. The density can then be calculated from the layer thickness and basis weight. Unless otherwise stated, the thickness and density are given for the high loft material in the absence of SAP particles. The measurements should preferably be performed on the high loft material before it is processed into an absorbent core, and thus on a high loft material that does not contain SAP. If the starting material is not available, the high loft central layer can be obtained by carefully extracting it from the absorbent core and removing most of the SAP particles, for example by careful shaking or suction. A freeze spray can be used to separate the central layer from the other layers. The samples should be kept at 21°C ± 2°C and 50% ± 10% RH for at least 24 hours to equilibrate, especially if they have been previously compressed.

[0121] Equipment: Mitutoyo manual caliper gauge with 0.01mm resolution or equivalent instrument.

[0122] Contact Foot: A flat circular foot with a diameter of 16.0 mm (±0.2 mm). A circular weight may be applied to the foot (e.g., a weight with a slot for easy application around the instrument shaft) to obtain the target weight. The combined weight of the foot and added weight (including the shaft) is selected to provide 4.14 kPa (0.6 psi) of pressure on the sample.

[0123] Additionally, the thickness can be determined at different pressures using correspondingly different weights applied to the foot, the applied pressure being indicated by the thickness and density measured at, for example, 4.14 kPa (0.6 psi).

[0124] The caliper gauge is mounted so that the lower surface of the contact foot is in a horizontal plane and touches the center of the flat, level upper surface of a base plate approximately 20 x 25 cm. The gauge is set to zero with the contact foot resting on the base plate.

[0125] Ruler: A calibrated metal ruler graduated in mm.

[0126] Stopwatch: 1 second accuracy.

[0127] Sample preparation: Condition the center layer as above for at least 24 hours.

[0128] Measurement procedure: The layer is laid flat with the bottom side, i.e. the side intended to be placed towards the backsheet in the final article, facing down. The measurement point (i.e. the center of the sample) is carefully traced on the top side of the layer, taking care not to squeeze or deform the layer. In the unlikely event that the lofty nonwoven layer is not uniform in the transverse or longitudinal directions, the value is measured at the center of the sample, which corresponds to the center of the absorbent core made from the sample.

[0129] The contact foot of the caliper gauge is raised and the central layer is placed flat on the base plate of the caliper gauge with the top side of the core facing up so that when lowered the center of the foot is over the marked measurement point.

[0130] Carefully lower the foot onto the sample and then release it (ensure the calibration is at "0" before starting the measurement). The caliper value is read to the nearest 0.01 mm 10 seconds after the foot is released.

[0131] The procedure is repeated for each measurement point. Ten samples are measured in this manner for a given material and the average thickness is calculated and reported to the nearest tenth of a millimeter. The basis weight of each sample is calculated by dividing the weight of each sample by their area.

[0132] Density (g / cm 3 The unit is the basis weight of the material (g / cm 2 It is calculated by dividing the thickness (in cm) by the thickness (in cm).

[0133] Micro-CT Scanning A circular sample with a diameter of 44 mm is carefully cut from the center of the absorbent core and placed in the sample holder of an adapted micro-CT device. To avoid any influence of the cut on the structure of the core, the field of view is reduced to the innermost circle with a diameter of 20 mm. The CT scanning machine used is, for example, a DynaTOM (item no. M2090) manufactured by XRE nv (merged by Tescan). The settings are as follows: tube voltage: 80 KV, tube power: 10.0 Watts, exposure time (ms): 380, number of averages: 1.000000, binning value: 1, voxel size: 10 μm, scanning speed: 2.36 frames per second, a total of 2900 projection images in one 3D.

[0134] Further software that can be used to utilize the collected data is, for example:

[0135] Image acquisition: Acquila developed by XRE nv, version 11.06.2019.

[0136] Image reconstruction: XRE Reco version 1.0.0.117 developed by XRE nv.

[0137] Image post-processing: Avizo 2019.1 by Thermo Fischer / open source ImageJ 1.52p / MS Excel 2016.

[0138] The spatial resolution of the scan is 10 μm. MicroCT scanning allows computer processing of the scanned data and can be projected in the xz (FIG. 6b) and yz (FIG. 6c) planes. Image analysis can be used to plot a diagram showing the gray value proportional to the average planar concentration of SAP for a field of view of the sample in the z direction. See for example FIG. 7a / 7b. The horizontal axis shows the vertical distance z (100=1 mm) from the surface of the sample, and the vertical axis shows the gray value proportional to the average planar concentration of SAP for a field of view (20 mm diameter circle) at the reported distance z from the top surface.

[0139] Urine Permeability Measurement (UPM) Test Method Laboratory conditions: The test must be carried out in a climatized room at standard conditions of 23°C ± 2°C and 45% ± 10% relative humidity.

[0140] Urine permeability measurement system This method measured the permeability of the swollen hydrogel layer 1318. The equipment used for this method is described below.

[0141] FIG. 11 shows the configuration of a transmittance measurement system 1000 including a constant hydrostatic head reservoir 1014, an open tube 1010 for air intake, a vent 1012 with a stopper for refilling, a laboratory rack 1016, a conduit 1018 with a flexible tube 1045 with a Tygon tubing nozzle 1044, a stopcock 1020, a cover plate 1047, and a support ring 1040, a receiving vessel 1024, a balance 1026, and a piston / cylinder assembly 1028.

[0142] 12 shows a piston / cylinder assembly 1028, including a metal weight 1112, a piston shaft 1114, a piston head 1118, a lid 1116, and a cylinder 1120. The cylinder 1120 is made of clear polycarbonate (e.g., Lexan®) and has an inner diameter p of 6.00 cm (area = 28.27 cm) with a smooth inner cylinder wall 1150. 2). The bottom 1148 of the cylinder 1120 is faced with a stainless steel screen cloth (ISO 9044 material 1.4401, mesh size 0.038 mm, wire diameter 0.025 mm) (not shown) that is biaxially stretched to tension before being attached to the bottom 1148 of the cylinder 1120. The piston shaft 1114 is made of transparent polycarbonate (e.g., Lexan®) and has an overall length q of about 127 mm. The central portion 1126 of the piston shaft 1114 has a diameter r of 22.15 (±0.02) mm. The upper portion 1128 of the piston shaft 1114 has a diameter s of 15.8 mm and forms a shoulder 1124. The lower portion 1146 of the piston shaft 1114 has a diameter t of approximately 5 / 8 inch (15.9 mm) and is threaded to screw securely into the central hole 1218 (see FIG. 8) of the piston head 1118. The piston head 1118 is drilled and made of clear polycarbonate (e.g., Lexan®) and is covered with a stainless steel screen cloth (ISO 9044 material 1.4401, mesh size 0.038 mm, wire diameter 0.025 mm) that has also been stretched (not shown). The weight 1112 is stainless steel, has a central hole 1130, and slides onto the upper portion 1128 of the piston shaft 1114 and rests on a shoulder 1124. The combined weight of the piston head 1118, piston shaft 1114, and weight 1112 is 596 g (± 6 g), which corresponds to 0.30 psi across the interior area of ​​the cylinder 1120. The total weight can be adjusted by drilling a blind hole in the central axis 1132 of the piston shaft 1114 to remove material and / or by providing a cavity and adding weight. The cylinder lid 1116 has a first lid opening 1134 at its center for vertically aligning the piston shaft 1114 and a second lid opening 1136 near the edge 1138 for introducing fluid from the constant hydrostatic head reservoir 1014 into the cylinder 1120.

[0143] A first linear index mark (not shown) is scribed radially along the top surface 1152 of the weight 1112, the first linear index mark being transverse to the central axis 1132 of the piston shaft 1114. A corresponding second linear index mark (not shown) is scribed radially along the top surface 1160 of the piston shaft 1114, the second linear index mark being transverse to the central axis 1132 of the piston shaft 1114. A corresponding third linear index mark (not shown) is scribed along the central portion 1126 of the piston shaft 1114, the third linear index mark being parallel to the central axis 1132 of the piston shaft 1114. A corresponding fourth linear index mark (not shown) is scribed radially along the top surface 1140 of the cylinder lid 1116, the fourth linear index mark being transverse to the central axis 1132 of the piston shaft 1114. Additionally, a corresponding fifth linear index mark (not shown) is scribed along the lip 1154 of the cylinder lid 1116, with the fifth linear index mark parallel to the central axis 1132 of the piston shaft 1114. A corresponding sixth linear index mark (not shown) is scribed along the outer cylinder wall 1142, with the sixth linear index mark parallel to the central axis 1132 of the piston shaft 1114. The alignment of the first, second, third, fourth, fifth, and sixth linear index marks allows the weight 1112, piston shaft 1114, cylinder lid 1116, and cylinder 1120 to be repositioned in the same orientation relative to one another for each measurement.

[0144] The detailed specifications of cylinder 1120 are as follows: Outer diameter of cylinder 1120 u: 70.35mm (±0.05mm) Inner diameter of cylinder 1120: 60.0 mm (±0.05 mm) Height of cylinder 1120 ν: 60.5 mm. The height of the cylinder must not be less than 55.0 mm.

[0145] The detailed specifications of the cylinder lid 1116 are as follows: Outer diameter of cylinder cover 1116: 76.05mm (±0.05mm) Inner diameter of cylinder cover 1116: 70.5mm (±0.05mm) Thickness y of cylinder lid 1116, including lip 1154: 12.7 mm Thickness of cylinder cover 1116 excluding lip 1154: 6.35 mm Diameter of first lid opening 1134: 22.25 mm (±0.02 mm) Diameter b of second lid opening 1136: 12.7 mm (±0.1 mm) Distance between the center of the first lid opening 1134 and the center of the second lid opening 1136: 23.5 mm

[0146] The detailed specifications of weight 1112 are as follows: Outer diameter c:50.0mm Diameter of center hole 1130 d: 16.0 mm Height e: 39.0 mm

[0147] The detailed specifications of the piston head 1118 are as follows: Diameter f: 59.7mm (±0.05mm) Height g: 16.5mm. The height of the piston head must not be less than 15.0mm.

[0148] Outer holes 1214 (14 total) have a diameter h of 9.30 (±0.25) mm, the outer holes 1214 are evenly spaced and the centers are 23.9 mm from the center of the central hole 1218.

[0149] Inner holes 1216 (7 total) having diameter i of 9.30 (±0.25) mm, inner holes 1216 are evenly spaced and centers are 13.4 mm from the center of central hole 1218.

[0150] The central bore 1218 has a diameter j of approximately 5 / 8 inch (15.9 mm) and is threaded to receive the lower portion 1146 of the piston shaft 1114 .

[0151] Prior to use, the stainless steel screens (not shown) in the piston head 1118 and cylinder 1120 should be inspected for clogging, holes, or overstretching and replaced if necessary. A urine permeability meter with a damaged screen may give erroneous UPM results and should not be used until the screens are replaced.

[0152] A 5.00 cm mark 1156 is scribed on the cylinder 1120 at a height k of 5.00 cm (±0.05 cm) above a screen (not shown) attached to the bottom 1148 of the cylinder 1120. This marks the fluid level which must be maintained during the analysis. Maintaining an accurate and consistent fluid level (hydrostatic pressure) is important for measurement accuracy.

[0153] The constant hydrostatic head reservoir 1014 is used to supply the cylinder 1120 with saline solution 1032 and maintain the level of the saline solution 1032 at a height k of 5.00 cm above a screen (not shown) attached to the bottom 1148 of the cylinder 1120. The bottom 1034 of the air intake tube 1010 is positioned to maintain the level of the saline solution 1032 in the cylinder 1120 at the height k of 5.00 cm required during measurement, i.e., the bottom 1034 of the air tube 1010 is on approximately the same plane 1038 as the 5.00 cm mark 1156 on the cylinder 1120 when placed above the receiving vessel 1024 and on the cover plate 1047 and support ring 1040 (the inner opening of the circle is 64 mm or greater in diameter).

[0154] The cover plate 1047 and support ring 1040 are components used in an instrument used for the "K(t) Test Method" described herein, called the "Zeitabhangiger Durchlassigkeitsprufstand" or "Time Dependent Permeability Tester" (instrument number 03-080578), available from BRAUN GmbH, Frankfurter Str. 145, 61476 Kronberg, Germany. Detailed drawings are available upon request.

[0155] Proper height alignment of the intake tube 1010 and the 5.00 cm mark 1156 on the cylinder 1120 is important for the analysis. A suitable reservoir 1014 consists of a jar 1030 containing a horizontally oriented L-shaped conduit 1018 connected to a flexible tube 1045 (e.g., Tygon tubing through which a nozzle and reservoir outlet can be connected) and a Tygon tubing nozzle 1044 (inner diameter at least 6.0 mm, length approximately 5.0 cm) for fluid delivery, a vertically oriented open tube 1010 for admitting air at a fixed height within the constant hydrostatic head reservoir 1014, and a stoppered vent 1012 for refilling the constant hydrostatic head reservoir 1014. The tube 1010 has an inner diameter of approximately 12 mm, but not less than 10.5 mm. A conduit 1018 positioned near the bottom 1042 of the constant hydrostatic head reservoir 1014 includes a stopcock 1020 for starting / stopping the delivery of saline solution 1032. An outlet 1044 of a delivery flexible tube 1045 is sized (e.g., 10 mm outer diameter) to be inserted through a second lid opening 1136 of the cylinder lid 1116, with its end positioned below the surface of the saline solution 1032 in the cylinder 1120 (after a 5.00 cm height of saline solution 1032 has been obtained in the cylinder 1120). The intake tube 1010 is held in place with an O-ring collar 1049. The constant hydrostatic head reservoir 1014 may be positioned on a laboratory reck 1016 at a suitable height relative to the height of the cylinder 1120. The components of the constant hydrostatic head reservoir 1014 are sized to rapidly fill the cylinder 1120 to the required height (i.e., hydrostatic head) and maintain this height for the duration of the measurement. The constant hydrostatic head reservoir 1014 must be capable of delivering saline solution 1032 at a flow rate of at least 2.6 g / sec for at least 10 minutes.

[0156] The piston / cylinder assembly 1028 is positioned on a support ring 1040 in a cover plate 1047 or suitable alternative rigid stand. Saline solution 1032 passing through the piston / cylinder assembly 1028 containing the swollen hydrogel layer 1318 is collected in a receiving vessel 1024 positioned below (but not in contact with) the piston / cylinder assembly 1028.

[0157] The receiving vessel 1024 is positioned on a balance 1026 having an accuracy of at least 0.001 g. The digital output of the balance 1026 is coupled to a computerized data acquisition system 1048.

[0158] Preparation of reagents (not shown) Jayco Synthetic Urine (JSU) 1312 (see FIG. 14) is used for the swelling phase (see UPM procedure below) and 0.118 M Sodium Chloride (NaCl) solution 1032 is used for the flow phase (see UPM procedure below). The following preparations are for a standard 1 liter volume. For preparations of volumes other than 1 liter, all amounts are scaled accordingly.

[0159] JSU: Fill a 1 L volumetric flask with distilled water to 80% of its volume and place a magnetic stir bar in the flask. Using separate weighing paper or a beaker, weigh out the following amounts of dry ingredients to within ±0.01 g using an analytical balance and quantitatively add to the volumetric flask in the same order as listed below. The solution is stirred on a suitable stir plate until all solids have melted, the stir bar is removed and the solution is diluted to 1 L volume with distilled water. The stir bar is reinserted and the solution is stirred on the stir plate for an additional few minutes. How much salt to make 1 liter of Jayco synthetic urine? Potassium chloride (KCl) 2.00g Sodium sulfate (Na2SO4) 2.00g Ammonium dihydrogen phosphate (NH4H2PO4) 0.85g Ammonium phosphate, dibasic ((NH4)2HPO4) 0.15 g Calcium chloride (CaCl2) 0.19 g - [or calcium chloride hydrate (CaCl2·2H2O) 0.25 g] Magnesium chloride (MgCl2) 0.23 g - [or magnesium chloride hydrate (MgCl2·6H2O) 0.50 g]

[0160] For a faster preparation, potassium chloride, sodium sulfate, ammonium dihydrogen phosphate, ammonium phosphate (dibasic), and magnesium chloride (or magnesium chloride hydrate) are combined and dissolved in 80% distilled water in a 1 L volumetric flask. Calcium chloride (or calcium chloride hydrate) is dissolved separately (e.g., in a glass beaker) in about 50 mL of distilled water, and after the other salts have completely dissolved, the calcium chloride solution is transferred to the 1 L volumetric flask. Distilled water is then added to 1 L (1000 mL ± 0.4 mL) and the solution is stirred for a few more minutes. Jayco synthetic urine can be stored in a clean plastic container for 10 days. If the solution becomes cloudy, it should not be used.

[0161] 0.118M Sodium Chloride (NaCl) Solution: 0.118M sodium chloride is used as Saline 1032. Using weighing paper or a beaker, weigh out 6.90 g (± 0.01 g) of sodium chloride and quantitatively transfer to a 1 L volumetric flask (1000 mL ± 0.4 mL) and fill the flask to volume with distilled water. Add a stir bar and mix the solution on a stir plate until all solids are dissolved.

[0162] The conductivity of the prepared Jayco solution should be in the range of about 7.48-7.72 mS / cm, and the conductivity of the prepared 0.118 M sodium chloride (NaCl) solution should be in the range of about 12.34-12.66 mS / cm (e.g., measured via a COND 70 INSTRUMENT without cell #50010522 equipped with Cell VPT51-01 C=0.1 from xs instruments, or via an LF320 / set #300243 equipped with TetraCon325 from WTW, or a COND330i equipped with TetraCon325, #02420059 from WTW). The surface tension of each solution should be in the range of 71-75 mN / m (e.g., measured via a surface tensiometer K100 from Kruess equipped with a Pt plate).

[0163] Exam Preparation A solid reference cylinder weight (not shown) (diameter 50 mm; height 128 mm) is used to set a caliper gauge (not shown) (25 mm measurement range, 0.01 mm accuracy, 50 g maximum piston pressure; e.g., Mitutoyo Digimatic Height Gage) to a reading of 0. This is conveniently performed on a smooth, level bench (not shown) that is at least about 11.5 cm by 15 cm. The piston / cylinder assembly 1028, which does not contain superabsorbent polymer particles, is positioned under the caliper gauge (not shown) and the reading L1 is recorded to the nearest 0.01 mm.

[0164] The constant hydrostatic head reservoir 1014 is filled with saline solution 1032. The bottom 1034 of the intake tube 1010 is positioned to maintain the top (not shown) of the liquid meniscus (not shown) in the cylinder 1120 at the 5.00 cm mark 1156 during measurement. Proper height alignment of the intake tube 1010 on the cylinder 1120 at the 5.00 cm mark 1156 is important to the analysis.

[0165] The receiving vessel 1024 is placed on a balance 1026, the digital output of which is connected to a computerized data acquisition system 1048. A cover plate 1047 with a support ring 1040 is positioned above the receiving vessel 1024.

[0166] UPM Procedure Using an analytical balance, weigh 1.5 g (±0.05 g) of superabsorbent polymer particles onto a suitable weighing paper or weighing aid. The moisture content of the superabsorbent polymer particles is measured according to EDANA moisture content test method NWSP 230.0.R2 (15) or via a moisture analyzer (HX204 from Mettler Toledo, drying temperature 130°C, starting superabsorbent weight 3.0 g (±0.5 g), stop criterion 1 mg / 140 sec). If the moisture content of the superabsorbent polymer particles is greater than 3% by weight, dry the superabsorbent polymer particles, for example in an oven at 105°C for 3 hours, or for example in an oven at 120°C for 2 hours, until the moisture level is <3% by weight.

[0167] The empty cylinder 1120 is placed on a horizontal bench top 1046 (not shown) and the superabsorbent polymer particles are quantitatively transferred into the cylinder 1120. The superabsorbent polymer particles are evenly distributed on a screen (not shown) attached to the bottom 1148 of the cylinder 1120 while rotating the cylinder 1120, for example with the assistance of a (manual or motorized) turntable (e.g., a petriturn-E or petriturn-M from Schuett). For the most precise results, it is important to distribute the particles evenly on the screen (not shown) attached to the bottom 1148 of the cylinder 1120. After the superabsorbent polymer particles are evenly distributed on the screen (not shown) attached to the bottom 1148 of the cylinder 1120, the particles must not stick to the inner cylinder wall 1150. The piston shaft 1114 is inserted through the first lid opening 1134 with the lip 1154 of the lid 1116 facing towards the piston head 1118. The piston head 1118 is carefully inserted into the cylinder 1120 to a depth of several centimeters. The lid 1116 is then placed on the upper rim 1144 of the cylinder 1120, taking care to keep the piston head 1118 away from the superabsorbent polymer particles. The weight 1112 is positioned on the top 1128 of the piston shaft 1114 so that it rests on the shoulder 1124, thereby aligning the first and second linear indicator marks. The lid 1116 and piston shaft 1126 are then carefully rotated so that the third, fourth, fifth, and sixth linear indicator marks are aligned with the first and second linear indicator marks. The piston head 1118 is then gently pressed down (via the piston shaft 1114) onto the dried superabsorbent polymer particles. Proper placement of the lid 1116 prevents binding of the weight and ensures an even distribution of the weight on the hydrogel layer 1318.

[0168] Swelling phase: A fritted disk 1310 having a diameter of at least 8 cm (e.g., 8-9 cm diameter) and a thickness of at least 5.0 mm (e.g., 5-7 mm thickness) and having "coarse" or "very coarse" porosity (e.g., Chemglass Inc. #CG 201-51, coarse porosity; or e.g., Robu 1680, with zero porosity) is placed in a flat-bottomed Petri dish 1314 and JSU 1312 is added by pouring it into the center of the fritted disk 1310 until it reaches the top surface 1316 of the fritted disk 1310. The height of the JSU should not exceed the height of the fritted disk 1310. It is important to avoid any air or bubbles being trapped in or under the fritted disk 1310.

[0169] The entire piston / cylinder assembly 1028 is lifted and placed on the fritted disk 1310 in the Petri dish 1314. The JSU 1312 from the Petri dish 1314 passes through the fritted disk 1310 and is absorbed by the superabsorbent polymer particles (not shown) to form the hydrogel layer 1318. The JSU 1312 available in the Petri dish 1314 should be sufficient for all of the swelling phase. If necessary, more JSU 1312 may be added to the Petri dish 1314 during the hydration period to maintain a liquid level of JSU 1312 on the top surface 1316 of the fritted disk 1310. After the 60 minute period, the piston / cylinder assembly 1028 is removed from the fritted disk 1310, taking care that the hydrogel layer 1318 does not lose JSU 1312 or entrap air during this procedure. Place the piston / cylinder assembly 1028 under a caliper gauge (not shown) and record the reading L2 to the nearest 0.01 mm. If the reading changes over time, record only the initial value. The thickness L0 of the hydrogel layer 1318 is determined from L2 - L1 to the nearest 0.1 mm.

[0170] The piston / cylinder assembly 1028 is transferred to the support ring 1040 in the cover plate 1047. The constant hydrostatic head reservoir 1014 is positioned so that the conduit nozzle 1044 is located through the second lid opening 1136. The measurement is initiated in the following sequence: a) The stopcock 1020 of the constant hydrostatic head reservoir 1014 is opened allowing the saline solution 1032 to reach the 5.00 cm mark 1156 on the cylinder 1120. This saline solution 1032 level should be achieved within 10 seconds of opening the stopcock 1020. b) Once 5.00 cm of saline 1032 is achieved, begin the data collection program.

[0171] A computer 1048 attached to the balance 1026 is used to record the amount of saline 1032 (in grams, with an accuracy of 0.001 grams) passing through the hydrogel layer 1318 at 20 second intervals for 10 minutes. At the end of the 10 minute period, the stopcock 1020 on the constant hydrostatic head reservoir 1014 is closed.

[0172] Data from 60 seconds to the end of the experiment are used for the UPM calculation. Data collected prior to 60 seconds are not included in the calculation.

[0173] After the first 60 seconds of the experiment, each 20-second period (time t (i-1) ~t i ) for each flow velocity Fs (t) (unit: g / s) and time t (1 / 2)t Calculate the midpoint of each (in seconds) according to the following formula:

[0174]

number

[0175] At each time interval (t (i-1) ~t i ) flow velocity Fs (t) is the time interval (t (i-1) ~t i ) time t (1 / 2)t The intercept is calculated as Fs(t=0).

[0176] Calculate the intercept: The intercept is calculated via the best fit regression line, for example as follows: The equation for the intercept of the regression line a is: a=y AVG -b·x AVG (III) where the slope b is calculated as:

[0177]

number

[0178] Calculation of urine permeability measurement Q: The intercept Fs(t=0) is used to calculate Q according to the following formula:

[0179]

number

[0180] [Table 8]

[0181] SAP K(t) test method (Figures 15-17) This method determines the time-dependent effective permeability (SAP K(t)) and absorbency of a gel layer formed from hydrogel-forming superabsorbent polymer particles or an absorbent structure containing such particles under confining pressure. The purpose of this method is to evaluate the ability of a gel layer formed from hydrogel-forming superabsorbent polymer particles or an absorbent structure containing them to acquire and distribute bodily fluids when the polymers are present in high concentrations in the absorbent article and are subjected to mechanical pressures such as those typically encountered during use of the absorbent article. Darcy's law and the steady flow method are used to calculate the effective permeability (see below). (See also, for example, "Absorbency," ed. By PK Chatterjee, Elsevier, 1982, Pages 42-43, and "Chemical Engineering Vol. II, Third Edition, JM Coulson and JF Richardson, Pergamon Press, 1978, Pages 122-127).

[0182] Unlike previously published methods, the samples are not pre-swollen and therefore no hydrogel is formed by pre-swelling hydrogel-forming superabsorbent polymer particles in synthetic urine, but the measurement starts with a dry structure. The instrument used for this method is called "Zeitabhangiger Durchlassigkeitsprufstand" or "Time Dependent Permeability Tester" (instrument number 03-080578), is commercially available from BRAUN GmbH (Frankfurter Str. 145, 61476 Kronberg, Germany) and is described below. Operating instructions, wiring diagrams, and detailed technical drawings are also available upon reasonable request.

[0183] Dynamic Effective Transmittance and Absorbance Measurement System Figure 15 shows a dynamic effective transmittance and absorptance measurement system, referred to herein as the "Time Dependent Transmittance Tester." The instrument consists of the following main components: M11 Digital Laser Sensor 701 for caliper measurement (MEL Mikroelektronik GmbH, 85386 Eching, Germany) or equivalent (e.g. Keyence Il-S100 Laser Height Sensor). Liquid level detection fiber 702 (FU95, Keyence Corporation, Japan) Digital Fiber Sensor 703 (FS-N10, Keyence Corporation, Japan) Precision balance 704(XP6002MDR,Mettler Toledo AG(8606 Greifensee,Switzerland)) Power supply Logo!Power(C98130-A7560-A1-5-7519,Siemens AG) Labview Software License 706 (National Instruments (Austin, Tx, USA)) Receptor vessel 707 (5 L glass beaker, Roth) Reservoir 708 (5L glass bottle, VWR) with joint 709 and air intake opening tube 723 Operation unit and console 705 (Conrad Electronics) Computerized Data Acquisition System 710 A piston / cylinder assembly 713 as described herein Control valve 714 (Burkert)

[0184] 16 shows the piston / cylinder assembly 713, including a piston guide cap 801, a piston 802, and a cylinder 803. The cylinder 803 is made of clear polycarbonate (e.g., Lexan®) and has an inside diameter p of 6.00 cm (area = 28.27 cm 2). The inner cylinder wall 850 is smooth and the height of the cylinder r is about 7.50 cm. The bottom 804 of the cylinder 803 is faced with a US standard 400 mesh stainless steel screen cloth (not shown) (e.g., from Weisse and Eschrich) that is biaxially stretched to a tensioned state before being attached to the bottom 804 of the cylinder 803. The piston 802 is composed of a stainless steel piston body 805 and a stainless steel head 806. The diameter q of the piston head 806 is slightly less than 6 cm so that it slides freely into the cylinder 803 without leaving any gaps for the hydrogel-forming particles to pass through. The piston body 805 is firmly attached vertically to the center of the piston head 806. The diameter t of the piston body is about 2.2 cm. The piston body 805 is then inserted into the piston guide lid 801. The induction cap 801 has a POM (polyoxymethylene) ring 809 with a diameter that allows the piston 802 to slide freely when placed on the cylinder 803 together with the induction cap 801 while still maintaining the piston body 805 perfectly vertical and parallel to the cylinder wall 850. A top view of the piston head 806 is shown in FIG. 16. The piston head 806 is intended to apply pressure uniformly to the sample 718. The piston head 806 is also highly permeable to hydrophilic liquids so as not to restrict the flow of liquids during the measurement. The piston head 806 is made of US standard 400 mesh stainless steel screen cloth 903 (e.g., Weisse and Eschrich) biaxially stretched to a tensioned state and fixed to the piston head stainless steel outer ring 901. The entire underside of the piston is flat. The structural integrity and bending resistance of the mesh screen is then ensured by the stainless steel radial spokes 902. The height of the piston body 805 is selected so that the weight of the piston 802, consisting of the piston body 805 and the piston head 806, is 596g (±6g), which corresponds to 0.30 psi over the area of ​​the cylinder 803.

[0185] The piston guide cap 801 is a flat circular body of stainless steel with a diameter s of about 7.5 cm that is held perpendicular to the piston body 805 at its center by a POM ring 809. The guide cap has two inlets (810 and 812).

[0186] The first inlet 812 allows the level detection fiber 702 to be positioned exactly 5 cm above the top surface of a screen (not shown) attached to the bottom (804) of the cylinder 803 when the piston 802 is assembled with the cylinder 803 for measurement.

[0187] A second inlet 810 allows for connection of a liquid line 721 to provide liquid for an experiment. To ensure that the assembly of piston 802 and cylinder 803 is consistent, a slit 814 is made on cylinder 803 that matches with a position marker 813 in induction lid 801. In this way, the rotation angle between the cylinder and induction lid will always be the same.

[0188] Before each use, the stainless steel screen cloth 903 on the piston head 806 and cylinder 803 should be inspected for clogging, holes, or overstretching and replaced if necessary. A K(t) device with a damaged screen may give erroneous K(t) and absorption rate results and should not be used until the screen is replaced.

[0189] A 5 cm mark 808 is scribed on the cylinder at a height k of 5.00 cm (±0.02 cm) above the top surface of a screen attached to the bottom 804 of the cylinder 803. This marks the fluid level to be maintained during analysis. The fluid level sensing fiber 702 is positioned exactly at the 5 cm mark 808. Maintaining an accurate and constant fluid level (hydrostatic pressure) is important for measurement accuracy.

[0190] A reservoir 708 connected via tubing to a piston / cylinder assembly 713 that holds the sample and a control valve 714 is used to deliver saline to the cylinder 803 and maintain the saline level at a height k of 5.00 cm above the top surface of a screen attached to the bottom of the cylinder 804. The valve 714, the level sensing fiber 702, and the digital fiber sensor 703 are connected to a computerized acquisition system 710 via an operation unit 705. This allows the dynamic effective transmittance and absorptance measurement system to use information from the level sensing fiber 702 and the digital fiber sensor 703 to control the valve 714 and ultimately maintain the level at the 5 cm mark 808.

[0191] The reservoir 708 is placed on top of the piston / cylinder assembly 713 such that within 15 seconds of starting the test, a 5 cm hydrohead is created and maintained in the cylinder throughout the test procedure. The piston / cylinder assembly 713 is placed on the support ring 717 of the cover plate 716, and the first inlet 812 is fixed in place with a mating support 719. This gives the induction lid 801 a unique position. Furthermore, the position marker 813 gives the cylinder 803 a unique position. The screen attached to the bottom of the cylinder 804 must be perfectly flat and level. The support ring 717 needs to have an inside diameter that is small enough to provide a firm support for the cylinder 803 when the cylinder is placed on the support ring 717, but larger than 6.0 cm so that it is outside the inside diameter of the cylinder. This is important to avoid the support ring 717 impeding the flow of liquid in any way.

[0192] Saline applied to the sample 718 at a constant head of 5 cm is now allowed to flow freely from the piston / cylinder assembly 713 into a receiving vessel 707 positioned on a balance 704 accurate to within ±0.01 g. The digital output of the balance is linked to a computerized data acquisition system.

[0193] The thickness (caliper) of the sample is constantly measured with a digital laser sensor 701 for caliper measurement. The laser beam 720 of the digital laser sensor 701 is aimed at the center of the POM cover plate 811 of the piston body. By precisely positioning all the parts of the piston / cylinder assembly 713, the piston body 805 can be perfectly parallel to the laser beam 720, resulting in an accurate measurement of the thickness.

[0194] Test Preparation: Fill reservoir 708 with test solution. The test solution is an aqueous solution containing 9.00 grams of sodium chloride and 1.00 grams of surfactant per liter of solution. Preparation of the test solution is described below. Place receiving vessel 707 on balance 704 connected to computerized data acquisition system 710. Reset balance to zero before starting measurements.

[0195] Preparation of test solutions: Chemicals required: Sodium chloride (CAS#7647-14-5, e.g. Merck, Cat. No. 1.06404.1000) Linear C 12 ~C 14 Alcohol ethoxylates (CAS#68439-50-9, e.g. Lorodac® (Sasol, Italy)) Deionized H2O

[0196] A 10 liter solution containing 9.00 grams per liter NaCl and 1.00 grams per liter linear C12-C14 alcohol ethoxalate in distilled water is prepared and equilibrated for 1 hour at 23°C ± 1°C. The surface tension, measured on three separate aliquots, should be 30 ± 2 mN / m. If the surface tension of the solution differs from 28 ± 0.5 mN / m, discard the solution and prepare a new test solution. The test solution should be used within three months of its preparation, after which it is considered expired.

[0197] Preparation of SAP K(t) samples: Superabsorbent polymer particles are dried, for example, for 2 hours in a circulating oven at atmospheric pressure at 120° C. to remove excess water before the measurement. The particles can then be stored in a sealed airtight container at 23±2° C. until further use or until directly used for the measurement.

[0198] 2.0 g (±0.02 g) of superabsorbent polymer particles are weighed into a suitable weighing paper using an analytical balance and transferred to the cylinder 803 such that the particles are evenly distributed on a screen (not shown) attached to the bottom 804 of the cylinder 803. This is done by shaking the superabsorbent polymer while simultaneously rotating the cylinder clockwise (e.g. on a circular turntable schuett petriturn-M available from Schuett-biotec GmbH, Rudolf-Wissell-Str. 13 D-37079 Gottingen Germany). An even distribution of the superabsorbent polymer particles is important for the accuracy of the measurement.

[0199] SAP K(t) procedure: Measurements are performed under controlled laboratory conditions: 23°C ± 1°C / 45% RH ± 10%. Control of the laboratory conditions can be achieved, for example, via an Opus 20E from G. Lufft Mess-und Regeltechnik GmbH. An empty piston / cylinder assembly 713 is fitted into the circular opening in the cover plate 716 and supported at its lower periphery by a support ring 717. The piston / cylinder assembly 713 is fixed in place by a mating support 719, with the cylinder 803 and piston 802 aligned at the appropriate angle. The reference caliper reading (r r ) is measured by a digital laser sensor. After this, the empty piston / cylinder assembly 713 is removed from the cover plate 716 and support ring 717, and the piston 802 is removed from the cylinder 803.

[0200] The sample 718 is placed (absorbent structure) or sprinkled (superabsorbent polymer particles) onto the screen of the cylinder as described above. After this, the guide lid 801 and assembled piston 802 are carefully placed into the cylinder 803 by aligning the position marker 813 of the guide lid 801 with the slit 814 made in the cylinder 803.

[0201] The piston / cylinder assembly is secured in place with mating supports 719, with the cylinder and piston aligned at the appropriate angle.

[0202] This can only be done in one direction. The liquid tube 721 connected to the reservoir 708 and the digital fiber sensor 703 are inserted into the piston / cylinder assembly 713 through two inlets 810 and 812 in the induction lid 801.

[0203] A computerized data acquisition system 710 is connected to the balance 704 and the digital laser sensor 701 for caliper measurement. The computer program initiates the flow of fluid from the reservoir 708 into the cylinder 803 by opening the valve 714. After the cylinder fills to the 5 cm mark 808 in 5-15 seconds, the computer program adjusts the flow rate to maintain a constant 5 cm head. The amount of solution passing through the sample 718 is measured by the balance 704 and the caliper increase is measured by the laser caliper gauge. Data acquisition begins at the start of the fluid flow, specifically the first opening of the valve 714, and continues for 21 minutes or until the reservoir is empty and the 5 cm head is no longer maintained. One measurement period is 21 min, with the laser caliper and balance readings recorded periodically at intervals that can vary depending on the measurement range from 2 to 10 s, typically 10 s intervals, and three replicates are measured.

[0204] After 21 minutes, the first replicate measurement is successfully completed and the control valve 714 closes automatically. The piston / cylinder assembly 713 is removed and the second and third replicate measurements are taken accordingly, always following the same procedure. At the end of the third replicate measurement, the control valve 714 stops the flow of liquid and the stopcock 722 of the reservoir 708 is closed. The raw data collected is stored in the form of a simple data table, which can then be easily imported into a program, e.g., Excel 2003, SP3, for further analysis.

[0205] The data table records the following pertinent information for each reading: Time from start of experiment Weight of liquid collected by the receiving vessel 707 on the balance 704 Caliper of sample 718

[0206] The data from 100 seconds to the end of the test is used to calculate K(t) and absorptivity. Data collected during the first 100 seconds is not included in the calculation. The effective permeability K(t) and absorptivity of the absorbent structure are then determined using the following equations:

[0207] Equations Used: The following table explains the notations used in the equations.

[0208] [Table 9]

[0209] The driving pressure is calculated from the head as follows: Δp = h G ρ = 4929.31 g / (cm s 2 )

[0210] each time t i The caliper at time t i The measured value is calculated as the difference between the caliper sensor reading at and a reference reading without sample. d i =r i -r r [cm]

[0211] For the superabsorbent particle sample, time t i The caliper of the sample at =0 (d0) is used to evaluate the quality of particle scattering.

[0212] The apparent sample density inside the cylinder can actually be calculated as follows:

[0213]

number

[0214] If the apparent density in this cylinder differs from the apparent density of the powder by more than ±40%, the measurement should be considered invalid and discarded.

[0215] Apparent density can be measured according to EDANA method NWSP251.0.R2(19) PSP (Gravimetric Determination of Flow Rate and Bulk Density).

[0216] Time t i The rate of change of the balance reading at with time is calculated as follows:

[0217]

number

[0218] Time t i The rate of change of the caliper reading at with time is calculated as follows:

[0219]

number

[0220] The absorption rate is calculated as follows:

[0221]

number

[0222] Dry sample volume (V s ) is intended to be the skeletal volume of the sample, and therefore V s is the actual volume occupied by the solid material in the dry sample excluding pores and interstices that may be present.

[0223] V s can be calculated or measured in various ways known to those skilled in the art, for example, knowing the exact composition and skeletal density of the components, it can be determined as follows:

[0224]

number

[0225] Alternatively, for unknown material composition, V s can be easily calculated as follows:

[0226]

number

[0227] average density ρ s can be determined by the pycnometer method using a suitable non-swelling liquid of known density (ethanol in the present case). This technique cannot be performed on the same samples used subsequently for K(t) measurements, so a representative set of additional samples suitable for this experimental measurement must be prepared. The average of at least three replicates is used to calculate the average specific density. If the average specific density is unknown, it should be taken as 1.50 g / cm for absorbent cores, unless there is evidence of significant deviation from these values ​​(e.g., for superporous SAP particles or for absorbent cores with very low SAP particle content). 3 , 1.60g / cm for SAP 3 may be considered as a good approximation.

[0228] From U(t) at different time steps calculated as explained above, the absorption at any particular time can be determined by linear interpolation. For example, one of the important outputs is the absorption at 20 minutes, also called U20 (units g / g).

[0229] From U(t) at different time steps, the time required to reach a particular absorption can also be determined by linear interpolation. The time to first reach an absorption of 20 g / g is called T20. Similarly, the time to reach any other absorption can be calculated accordingly, for example the time to reach 15 g / g (T15). Knowing U20, from U(t) at different time steps, it is also possible to determine the time to reach 80% of U20, and this characteristic is called T80%.

[0230] The effective permeability is calculated from the rate of mass change and caliper change as follows:

[0231]

number

[0232] The effective viscosity of a liquid is temperature dependent and in the experimental interval (23°C ± 1°C) is calculated according to the following empirical formula: η=-2.36·10 -4 T+1.479 10 -2 [g / (cm s)]

[0233] K(t i ), the effective transmittance at a particular time can be determined by linear interpolation. For example, one important output is the transmittance at 20 minutes, or K20 (cm 2 ). Similarly, the transmittance at any other time can be calculated accordingly (eg, K5 or K10).

[0234] Another parameter derived from the data is Kmin, which is the i = 100 seconds to t i= 1200 seconds. This value is useful for calculating Kmin / K20, the ratio of the minimum effective permeability to the permeability at 20 minutes. This parameter represents temporary gel blocking that may occur in some samples. If the value is close to 1, there is no temporary gel blocking, and if the value is close to 0, the material undergoes a strong effective permeability drop when the liquid is first applied.

[0235] According to the required precision known to one of skill in the art, the average values ​​of T20, T80%, K20, U20, and Kmin / K20 from the three replicates are recorded.

[0236] Absorbent Core K(t) Test Method The above method can be easily adapted to directly measure the K(t) of an absorbent core without the need to separate the SAP from the bulk layer. The instrument system and test liquid are the same as described above and are shown in the diagram of the described SAP K(t) method. This adapted test method was first described in EP 2,535,698(A1) (Ehrnsperger et al., P&G) to measure the T15 and T20 of absorbent cores.

[0237] Method for extracting an absorbent core from an absorbent article The absorbent article is positioned on a flat surface. If the product contains features that prevent it from lying flat (such as cuff elastics), these are cut at appropriate intervals to allow the product to lie flat. Any layers attached to the absorbent core, such as the topsheet or backsheet, are removed from the absorbent core. To avoid damaging the core, these layers may be removed using a cold spray (such as "IT Icer" or "PRF 101 cold spray" available from Taerosol, Kangasala Finland) with a cooling temperature of -50 to -60°C, as shown, for example, in Figure 15 of EP 2535698. To avoid excessive damage to the absorbent core, the layer of material to be removed from the absorbent core is pulled from the absorbent core in a 180 degree peel geometry while the adhesive material is cooled with a cooling spray. The spray should be for at least 1 second but not more than 5 seconds for each single portion of the layer of material. After each material is removed, the remaining portion of the absorbent core is maintained under a pressure of 0.3 psi (TAPPI laboratory conditions) until the temperature returns to the initial value.

[0238] The upper and / or lower layers of the absorbent core may be suitably perforated to allow the flow of liquid therethrough (for example, as shown in FIG. 16 of EP 2535698). The perforations are performed using a hot metal tip, also called a perforation tip, which comprises a steel rod with a diameter H of 0.7±0.2 mm. A standard paper clip bent around a solder tip, such as CT60 / 621 available from ERSA GmbH (Wertheim, Germany), can be used for this purpose. The perforation tip should be set to a temperature of 310±20° C. For example, the perforation tip is positioned in contact with the layer to be perforated for a short time at low pressure so as to perforate the layer by melting without affecting any of the other materials of the absorbent structure. The holes are produced using the same procedure in a square perforation pattern with a hole edge distance D of 1±0.2 mm (for example, as shown in FIG. 17 of EP 2535698).

[0239] Each absorbent core is visually inspected for integrity using a backlight and discarded if damaged. Examples of damage are, for example, cuts, holes, and wrinkles that were not present before removing the absorbent structure from the absorbent article. Perforation of a layer made with a perforation tip is not considered damage unless it affects other layers. Substantial movement of superabsorbent polymer particles and fibers within the absorbent structure is also considered damage.

[0240] These prepared absorbent cores are then cut to prepare circular samples according to the K(t) absorbent core sample preparation described below.

[0241] Preparation of K(t) absorbent core samples A circular portion of the absorbent core with a diameter of 6.00 cm is obtained from the center of the absorbent core. For this purpose, a suitable circular die and hydraulic press cutter (such as, for example, the Electro-Hydraulic Alfa Cutter 240-10 available from Thwing-Albert instrument company, 14 W. Collings Ave. West Berlin, NJ 08091) can be used.

[0242] The circular sample is carefully positioned flat on a screen attached to the bottom of a cylinder occupying all available surface on the screen (not shown). It is important to position the circular sample so that the side in direct contact with the screen is the side that is normally further away from the liquid source in use, to reproduce the common flow direction in use. For example, for samples relating to absorbent articles such as diapers, the side that normally faces the wearer should be positioned at the top, while the side that faces the garment should be positioned in contact with the screen at the bottom of the cylinder. Careful positioning of the sample is important for the accuracy of the measurement. If the dimensions of the absorbent core are small and a sample of 6.0 cm diameter cannot be obtained from it, it is possible to join two absorbent cores of equal size to obtain the minimum sample size required. The two samples should be taken in the same position from two identical absorbent cores. The two absorbent cores should be joined via a straight edge and, if necessary, cut to obtain such a straight edge. The intention is that the joined edge should reproduce a flat homogeneous layer with no or only minimal gaps. This joined layer is then handled according to the standard sample preparation described above, with the additional care to center the joining line in the cutting die in order to obtain two identically shaped semicircles. It is important that both semicircles are carefully positioned inside the sample holder to reproduce a perfect circle, occupying the entire available surface on the screen with no or only minimal gaps. Both halves should be positioned with their sides facing the screen as explained above. In most embodiments, however, the sample consists of a single circular portion of the absorbent core.

[0243] The absorbent core K(t) method is performed as shown above, and in particular core T15 and core K20 are determined in a similar manner. The core density at 0.3 psi can further be determined according to the following formula:

[0244]

number

[0245] others Dimensions and values ​​disclosed herein should not be understood as being strictly limited to the exact numerical values ​​recited. Instead, unless otherwise indicated, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm."

Claims

1. An absorbent core (28) for use in an absorbent article (20), wherein the absorbent core extends in the transverse direction (x) and the longitudinal direction (y), and has thickness in the vertical direction (z) perpendicular to the transverse direction and the longitudinal direction, and the absorbent core is A liquid-permeable upper layer (41) and Bottom layer (42) and The bulky central layer (43) between the upper layer and the bottom layer, The superabsorbent polymer particles between the upper layer and the bottom layer, wherein the superabsorbent polymer particles are at least partially distributed within the central layer (43), The superabsorbent polymer particles are manufactured from a crosslinked polyacrylate salt and have a centrifugal holding capacity (CRC) ranging from 10 g / g to a maximum of 35 g / g as measured by the EDANA method NWSP241.0.R2(19), and have a UPM of at least 10 × 10⁻⁷ cm³ s / g, the UPM being measured by the urine permeability test described herein and having an absorbance rate under pressure (AAP@0.7 psi) greater than 22 g / g at 0.7 psi as measured according to the EDANA standard test NWSP242.0R2(19). The concentration of the superabsorbent polymer particles in the absorbent core is determined by a micro-CT scan method disclosed herein, and the absorbent core (28) has a bimodal distribution in the z direction, where the value of the first peak of the distribution is defined as P1, the value of the second peak as P2, and the value of the trough between P1 and P2 as V1, and the value of V1 is less than 30% of the lowest value of P1 or P2.

2. The absorbent core according to claim 1, wherein the absorbent core has a core density of less than 0.6 g / cm³ (at 0.3 psi) as measured by the absorbent core K(t) test method.

3. The absorbent core according to claim 1 or 2, wherein the absorbent core comprises superabsorbent polymer particles with a basis weight of at least 200 gsm.

4. The superabsorbent polymer particles have a time to reach an absorption of 20 g / g in less than 220 seconds (SAP T20), as measured according to the SAP K(t) test method described herein, and / or The absorbent core has a time (core T15) to reach an absorption of 15 g / g in less than 200 seconds, as measured according to the absorbent core K(t) test method described herein, and / or The absorbent core according to any one of claims 1 to 3, wherein the absorbent core has a permeability (core K20) greater than 6.0 × 10⁻⁸ cm² as measured according to the absorbent core K(t) test method described herein.

5. The absorbent core according to any one of claims 1 to 4, wherein the central layer is a carded nonwoven fabric layer.

6. The absorbent core according to any one of claims 1 to 5, wherein the upper layer and / or the bottom layer are each attached to the central layer by an adhesive layer (71, 72), and the adhesive layer also fixes in a dry state at least a portion of the superabsorbent polymer particles that are not distributed within the bulky central layer.

7. The absorbent core according to any one of claims 1 to 6, further comprising a nonwoven fabric packaging layer that at least partially packages the upper layer, the bottom layer, and the central layer.

8. The absorbent core according to any one of claims 1 to 7, wherein the absorbent core comprises superabsorbent polymer particles in an amount of at least 60% by weight of the total weight of the core.

9. The absorbent core according to any one of claims 1 to 8, comprising a first central layer (431) and a second central layer (432) between the upper 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 one of claims 1 to 8, and the SAP T20 of the first central layer and the second central layer may be the same or different.

10. An absorbent article (200) comprising a top sheet (36), a back sheet (38), an absorbent core (28) according to any one of claims 1 to 9, and a trapping layer and / or distribution layer (54) between the core and the top sheet.

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