Absorbent core containing bulky central layer and superabsorbent particles

Abstract

An absorbent core (28) for use in an absorbent article (20), the absorbent core (28) having a high loft central layer (43) between a top layer and a bottom layer, and superabsorbent particles (SAP) at least partially distributed within the high loft layer, the superabsorbent polymer particles having a time to reach 20 g / g absorption (SAP T20) of less than 220 seconds, and / or the absorbent core having a time to reach 15 g / g absorption (Core T15) of less than 200 seconds, and / or the absorbent core having a mass fraction of less than 6.0 x 10 -8 cm 2 These properties are measured according to the K(t) test method described herein.

Description

[Technical Field]

[0001] This invention relates to absorbent cores and their use in personal hygiene absorbent articles. Absorbent cores can be used in particular in infant diapers. [Background technology]

[0002] Absorbent personal hygiene products, such as disposable infant diapers, toddler training pants, or adult incontinence underwear, are designed to absorb and contain bodily exudates, particularly urine. These absorbent products typically consist of several layers that provide different functions, including, among others, a top sheet, a back sheet, and an absorbent core between them.

[0003] The absorbent core should be able to absorb and retain exudate for extended periods, such as overnight in the case of diapers, keeping the wearer dry by minimizing re-wetting and preventing soiling of clothing or bed sheets. The absorbent core typically contained a blend of crushed wood pulp cellulose fibers and superabsorbent polymer (SAP) particles, also known as absorbent gelling material (AGM), as the absorbent material.

[0004] More recently, absorbent cores that do not contain fluff cellulose fibers (also called "air felt-free" cores) have been proposed. SAP particles can be encapsulated, for example, in separate pockets formed between two substrates (see, e.g., International Publication 95 / 11654, Tanzer et al.). It has also been proposed to immobilize SAP particles on a nonwoven substrate using a microfiber adhesive network (see, e.g., International Publication 2008 / 155699(A1), Hundorf et al.). More recently, an air felt-free core containing a bulky central layer in which SAP is distributed has been disclosed (see, e.g., International Publication 2016 / 106,021(A1), Bianchi et al.). These cores are typically prepared by distributing layers of SAP particles to each side of a bulky nonwoven fabric and then laminating tissue paper or nonwoven fabric on both sides to immobilize the particles (for example, the process illustrated in Figure 3 of International Publication No. 2020 / 025401 (BASF, Ge et al.)). Other recent publications of core layers are International Publication Nos. 2020 / 032280, 2020 / 032281, 2020 / 032282, 2020 / 032283, and 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 [Overview of the project] [Problems that the invention aims to solve]

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

[0007] The present invention relates to an absorbent core that extends transversely and longitudinally, has thickness in the vertical direction, and comprises a liquid-permeable upper layer, a bottom layer, and a central layer sandwiched between the upper and bottom layers. The central layer is a bulky layer such as a carded nonwoven fabric. The absorbent core contains superabsorbent polymer particles (SAP) at least partially distributed within the central layer. In the first embodiment, the superabsorbent polymer particles contained in the core 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. In the second embodiment, the absorbent core has a time to reach an absorption of 15 g / g in less than 200 seconds (Core T15), as measured according to the absorbent core K(t) test method described herein. In the third embodiment, the absorbent core has a time to reach an absorption of 6.0 g / g in less than 200 seconds (Core T15), as measured according to the absorbent core K(t) test method described herein. -8 cm 2 Highly, preferably 8.0 10 -8 cm 2 It has ultra-high permeability (core K20). Core T15 and core K20 may be measured directly on the core, but SAP T20 is measured separately on SAP. Naturally, the absorbent core of the present invention may be a combination of any different embodiments, such as the first and second, the first and third, or the second and third, as well as any other features described herein.

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

[0009] The absorbent core may contain at least 60% by weight of SAP, particularly at least 70% by weight, or at least 80% or even 90% of SAP, relative to the total weight of the core. The bulky core layer may be formed entirely of synthetic fibers and may not contain substantially any fluff cellulose fibers, but natural fibers or naturally occurring fibers such as cellulose, cotton fibers, or viscose fibers may be present in the core layer and / or upper and / or bottom layer.

[0010] The top and bottom layers are typically nonwoven fabrics or tissue paper. For example, low-basis-weight tissue paper is readily available and a relatively inexpensive substrate. The absorbent core may also include a packaging layer that completely covers the bottom or top layer and forms a C-wrap around the longitudinally extending side edges of the core layer, thereby at least partially covering the top or bottom layer, respectively, and better immobilizing the SAP particles within the absorbent core. The packaging layer can improve the containment of 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 include a two-layer structure comprising a first central bulk layer and a second central bulk layer. This structure can offer additional advantages, for example, in terms of SAP immobilization, allowing a greater amount of SAP particles to be distributed within the two layers. These and other optional features of the present invention are described in the following description. [Brief explanation of the drawing]

[0012] [Figure 1] An exemplary top view of an absorbent core with the upper and middle layers partially removed is shown. [Figure 2a] Figure 1 shows exploded views of various possible schematic cross-sectional views of the absorbent core. [Figure 2b] Figure 1 shows exploded views of various possible schematic cross-sectional views of the absorbent core. [Figure 2c] Figure 1 shows exploded views of various possible schematic cross-sectional views of the absorbent core. [Figure 3] Figure 2a is a schematic cross-sectional view of the absorbent core and core packaging layer. [Figure 4] This is a schematic cross-sectional view of an alternative absorbent core containing two central bulk layers. [Figure 5] Figure 4 is a schematic cross-sectional view of an absorbent article including an absorbent core and a core packaging layer. [Figure 6a] This figure shows a micro-CT scan of a circular sample of the core of the present invention. [Figure 6b] This figure shows the projection of a micro-CT scan in the xz plane. [Figure 6c] This figure shows the projection of a micro-CT scan in the yz plane. [Figure 7a] This figure shows the concentration of SAP particles in the z-direction of an exemplary core. [Figure 7b] This figure shows the concentration of SAP particles in the z-direction of the core of the comparative example. [Figure 8] This figure shows a micro-CT scan of SAP particles in the upper region of the central layer of an exemplary core. [Figure 9] This figure shows a micro-CT scan of SAP particles in the central region of the core's central layer. [Figure 10] This figure shows a micro-CT scan of SAP particles in the bottom region of the central layer of the core. [Figure 11] This is a partial cross-sectional side view of a suitable permeability measurement system for conducting urine permeability measurement tests. [Figure 12]This is a cross-sectional side view of a piston / cylinder assembly used when performing a urine permeability measurement test. [Figure 13] Figure 12 is a top view of a piston head suitable for use in the piston / cylinder assembly shown. [Figure 14] Figure 12 is a cross-sectional side view of the piston / cylinder assembly positioned on the frit disk for the swelling phase. [Figure 15] This is a partial cross-sectional side view of a suitable transmittance measurement system for conducting dynamic effective transmittance and absorptive rate measurement tests. [Figure 16] This is a cross-sectional side view of a piston / cylinder assembly for use in dynamic effective transmittance and absorptive rate measurement tests. [Figure 17] Figure 15 is a top view of a piston head suitable for use in the piston / cylinder assembly shown. [Figure 18] This is a schematic diagram of the process for manufacturing the absorbent core of the present invention. [Modes for carrying out the invention]

[0013] Introduction As used herein, the terms “comprise(s)” and “comprising” are open-ended. Each identifies the presence of a feature, e.g., a component, described therein, but does not exclude the presence of other features, e.g., elements, processes, or components known in the art or disclosed herein. These terms based on the verb “comprise” should be interpreted as encompassing the narrower term “consisting essentially of,” which excludes any unmentioned elements, processes, or components that significantly affect how a feature performs its function, and the term “consisting of,” which excludes any unspecified elements, processes, or components. None of the preferred or exemplary embodiments described below limit the claims unless specifically indicated. Words such as “typically,” “usually,” “preferably,” “favorably,” and “specifically” also modify features that are not intended to limit the claims unless specifically indicated to limit the claims.

[0014] As used herein, the terms “nonwoven fabric,” “nonwoven layer,” or “nonwoven web” are used interchangeably to mean a primarily planar artificial fiber assembly that is given a level of structural integrity designed by physical and / or chemical means other than weaving, knitting, or papermaking (as defined in ISO 9092:2019). Fibers oriented unidirectionally or randomly are bonded together by friction and / or coagulation and / or adhesion. Fibers may be of natural or synthetic origin, may be staples or continuous filaments, or may be formed in situ. Commercially available fibers have diameters ranging from less than about 0.001 mm to more than about 0.2 mm and are available in several different forms, such as short fibers (known as staples 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, including meltblowing, spunbonding, solvent spinning, electrospinning, carding, and air laying. The basis weight of nonwoven webs is typically grams per square meter (g / m²). 2 It is represented as (or gsm).

[0015] Overview of absorbent cores As used herein, the term “absorbent core” refers to an individual component containing absorbent material for absorbing and retaining bodily fluids, particularly urine. An absorbent core typically has the highest absorbency of all components of an absorbent article and contains all or at least a majority of superabsorbent polymer (referred to herein as “SAP”) particles. The terms “absorbent core” and “core” are used interchangeably herein. While some absorbent products may contain two or more separate absorbent cores, typically, absorbent products such as diapers contain only one absorbent core.

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

[0017] For ease of explanation, the exemplary absorbent core of FIG. 1 is shown in a flat state. The height of the absorbent core in the z direction is small compared to the other dimensions in the transverse x and longitudinal y directions. Unless otherwise specified, the dimensions and areas disclosed herein apply to the core in this flat, spread-out form.

[0018] For ease of explanation, the absorbent core, article, and process of the present invention will be described with reference to the drawings and the numbers referred to in these drawings. However, these are not intended to limit the claims unless otherwise specified.

[0019] Bulky central layer 43 The absorbent core of the present invention includes a bulky central layer 43, as first exemplified in FIGS. 1-2. The term "bulky" refers to a low-density, bulky fabric compared to a flat paper-like fabric. The bulky web is characterized by a relatively high porosity. This means that there are relatively large amounts of voids between the fibers in which the superabsorbent polymer particles can be distributed. The bulky layer of the present invention (without superabsorbent particles) can have a density in the range of less than 0.20 g / cm 3 under a pressure of 4.14 kPa (0.6 psi), specifically 0.01 g / cm 3 to 0.20 g / cm 3 , or 0.05 g / cm 3 to 0.15 g / cm 3 , or 0.10 g / cm 3 to 0.14 g / cm 3 The bulky layer of the present invention (without superabsorbent particles) is less than 0.20 g / cm 3 under a pressure of 2.07 kPa (0.3 psi), specifically 0.05 g / cm3 ~0.15g / cm 3 , or 0.08 g / cm³ 3 ~0.13g / cm 3 It may have a density in the range of [value missing]. The bulky layer of the present invention (without superabsorbent particles) has a density of 0.15 g / cm³ under a pressure of 0.83 kPa (0.12 psi). 3 Less than 0.01 g / cm³ 3 ~0.15g / cm 3 , or 0.05 g / cm³ 3 ~0.12 g / cm³ 3 , or 0.08 g / cm³ 3 ~0.10 g / cm³ 3 It can have densities within this range. The density can be calculated by dividing the basis weight of the bulky layer by its thickness as measured under each indicated pressure (see the "Test Procedure" section below for further details of the method).

[0020] The core layer is preferably a nonwoven fabric, but other types of bulky materials are not excluded. The core layer may contain, or consist of, synthetic fibers optionally mixed with natural fibers such as cellulose, cotton fibers, or viscose fibers. The core layer may not substantially contain 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% by weight of the total absorbent core, or less than 5% by weight of the total absorbent core, or less than 1% by weight of the total absorbent core, or may not contain any such free cellulose fibers at all. The bulky material may contain at least 10% by weight, 30% by weight, 50% by weight, 70% by weight, 90% by weight, and up to 100% by weight of synthetic fibers in the bulky layer.

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

[0022] The thickness, basis weight, and density of the core layer 43 are typically homogeneous in both the transverse (x) and longitudinal (y) directions. The fiber orientation in the core layer 43 may be heterogeneous, such as in carded nonwoven fabrics where the primary fiber orientation is unidirectional (x or y). Furthermore, the fiber orientation in the thickness direction (z) of the core layer 43 may differ from the primary orientation in one or both directions (x and / or y). The bulk layer may 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, as measured at a pressure of 4.14 kPa (0.6 psi) (according to the test methods described in more detail below). The bulky layer may have a thickness in the range of 0.30 mm to 2.50 mm, or 0.5 to 2.0 mm, or 0.7 to 1.3 mm, when measured at a pressure of 0.83 kPa (0.12 psi) (according to the test methods described in more detail below). The basis weight of the bulky core layer may be in the range of, for example, 15 gsm to 500 gsm, specifically 30 gsm to 200 gsm, or for example 50 gsm to 120 gsm. The values ​​shown herein with respect to the core layer are considered for bulky material that has been separated and sampled, i.e., sampled before the SAP particles were deposited between the fibers or the adhesive applied thereto. If the absorbent core contains two or more bulky core layers, these may be the same or different.

[0023] The present invention is not limited to any particular type of nonwoven fabric or fiber, but a particular example of a suitable nonwoven layer is a through-air bonded carded web (ABCW). A "bonded carded web" refers to a nonwoven fabric made from short fibers fed from a combing or carding unit that separates and generally aligns the short fibers in the machine direction to form a fiber nonwoven web that is generally oriented in the machine direction. This web is then drawn into a heated drum, and bonds are formed throughout the fabric (through a through-air bonding process) without applying any particular pressure. ABCW materials result in a low-density, bulky through-air bonded carded web.

[0024] TABCW materials can include, for example, staple fibers of about 3 to about 10 denier. Examples of such TABCWs are disclosed in International Publication No. 2000 / 71067 (KIM DOO-HONG et al.). TABCWs are also directly available from all the usual suppliers of nonwoven webs for use in absorbent articles, e.g., Fitesa Ltd or Fiberweb Technical Nonwovens. In carded nonwovens, the fibers in the web are mainly aligned in the mechanical direction, resulting in a more uniform fiber alignment than other nonwovens, thus providing higher stability and internal bonding strength, especially in the mechanical direction. The selected bonding technique affects the integrity of the fabric. Permeable bonded carded webs have excellent flexibility, bulk, and compressibility, as well as rapid backing and good re-wetting. Synthetic, natural, and recycled fibers can be used in a wide range of deniers. Soft PE / PP bicomponent staple fibers can be particularly used.

[0025] The bulky 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. The continuous filaments are cooled and deposited on a conveyor to form a uniform web. Some residual temperature may cause the filaments to bond to each other, but this cannot be considered the primary method of bonding. The spunlaid process has the advantage of giving the nonwoven higher strength, but the flexibility of the raw materials 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 from a spinneret into a high-speed airflow. This scatters the molten material, causing it to 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 an edge intended to be positioned toward the front edge of the absorbent article into which the core is incorporated or to be incorporated. The superabsorbent material may be distributed in greater quantities toward the front half of the central layer compared to the rear half of the central layer. This is typically because more fluid is discharged toward the front of the article into which the core is incorporated. In addition to the SAP distribution profiled in the longitudinal direction (y), the SAP may also be profiled in the transverse direction (x). Naturally, the SAP may also be uniformly distributed in the transverse direction (x) and the longitudinal direction (y), which simplifies production, in which case either of the two shorter side edges can be considered the front edge and the opposite side the rear edge. The absorbent core may contain one, two, or more such bulky central layers. The absorbent core, which includes two bulky central layers, will be discussed in more detail below.

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

[0028] Upper layer 41 and bottom layer 42 The bulky central layer 43 is sandwiched between the upper layer 41 and the bottom layer 42. The upper layer 41 is located on the side of the core, intended to be positioned closest to the side of the absorbent article facing the wearer. Therefore, the upper layer is liquid permeable so that fluid can easily reach the central layer through the upper layer during use. The bottom layer is located on the opposite side of the central layer. This may be liquid permeable or liquid impermeable. The upper and bottom layers provide cover on both sides of the central layer to prevent SAP particles from falling from the bulk during the core and article manufacturing process and / or during use of the absorbent article.

[0029] The top and bottom layers may be made from 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 (air felt or wet) having a basis weight in the range of 5 to 100 gsm, specifically 10 to 40 gsm. The top and bottom layers may also be formed from low-basis-weight nonwoven webs having a basis weight of 5 gsm to 30 gsm, such as carded nonwovens, spunbond nonwovens ("S"), or meltblown nonwovens ("M"), and laminates of any of these. For example, polypropylene nonwovens produced by the spunmelt method, specifically nonwovens having a laminated web SMS, or SMMS, or SSMMS structure and having a basis weight in the range of about 5 gsm to 20 gsm, are preferred. 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 known in the art or by other means. The top and bottom layers may be made of the same material or different materials, and optionally, the top or bottom layer may be treated differently so that the top layer is more hydrophilic than the bottom layer.

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

[0031] In addition to the top and bottom layers, the absorbent core may further comprise a packaging layer 3 that forms a C-wrap around the side edges 284, 286 extending longitudinally along the core, as shown in Figure 3. “C-wrap” means that the layer covers at least the top or bottom side of the core, extending along its side edges to form a flap that is typically then folded and attached to the opposite side of the core by adhesive. Thus, the packaging layer 3 may have a cross-section resembling the letter C (when rotated 90°). The C-wrap structure may further assist in containing SAP particles during the fabrication or wear of the absorbent article. The packaging layer may be made of, for example, a low-basis-weight nonwoven fabric layer having a basis weight of 5–40 gsm, specifically 8–25 gsm, specifically SMS nonwoven fabric, although other materials are certainly possible. The packaging layer 3 is shown in Figure 3 as having a flap that extends from the bottom side of the core and is folded over the top side of the core. An inverted configuration is also possible in which the C packaging layer 3 extends from the top and the flap folds over the bottom. The folded flap may be terminated and attached near the side edge extending in the longitudinal direction of the core, or it may be longer than shown so that they overlap and are attached to the other side. The C wrap structure may also be formed by one of the upper or bottom layers that extends transversely along the side edge extending in the longitudinal direction of the core and forms the flap as described with respect to the packaging layer 3. The presence of the packaging layer is optional, but is particularly preferred when the upper and bottom layers are not sealed along their longitudinal sides.

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

[0033] Superabsorbent material particles 60 The central layer contains superabsorbent polymer in the form of particles 60 at least partially distributed within the fibers of the bulky layer. Herein, the term “superabsorbent polymer” (abbreviated as “SAP” in both singular and plural forms) refers to an absorbent material capable of absorbing at least 10 times its weight in a 0.9% saline solution, as measured using the centrifugal retention capacity (CRC) test (EDANA method NWSP241.0.R2(19)). The SAP preferably has a CRC value of at least 15 g / g. The SAP of the present invention may have a CRC of less than 35 g / g, specifically less than 32 g / g.

[0034] SAP is typically a water-insoluble but water-swellable crosslinked polymer capable of absorbing large amounts of fluid. SAP is in a particulate form that is fluid in a dry state. Typical particulate SAP is a polyacrylate polymer, but it is not excluded that other polymer materials may also be used. For example, starch-based particulate absorbent polymer materials, as well as starch graft copolymers of polyacrylamide copolymers, ethylene maleic anhydride copolymers, crosslinked carboxymethylcellulose, polyvinyl alcohol copolymers, crosslinked polyethylene oxide, and polyacrylonitrile.

[0035] The SAP may be an internally and / or surface-crosslinked polyacrylate and polyacrylic acid polymer. The superabsorbent polymer of the present invention can be selected from internally and surface-crosslinked polyacrylate and polyacrylic acid polymers. The superabsorbent polymer can be internally crosslinked, i.e., polymerization is carried out in the presence of a compound having two or more polymerizable groups that can be free-radical copolymerized into a polymer network. Exemplary superabsorbent polymer particles of the prior art are described, for example, in International Publications 2006 / 083584, 2007 / 047598, 2007 / 046052, 2009 / 155265, and 2009 / 155264. Preferably, the SAP particles include a crosslinked polymer of polyacrylic acid or a salt thereof, or polyacrylate or a derivative thereof.

[0036] SAP particles may be relatively small in their dry state (their longest dimension less than 1 mm) and may be approximately circular in shape, but granules, fibers, flakes, spheres, powders, plates, and other shapes and forms are also known to those skilled in the art. Generally, SAP may be in the form of spherical particles. Therefore, the absorbent material may consist of, or essentially consist of, SAP distributed within a bulky nonwoven fabric.

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

[0038] Aggregated superabsorbent polymer particles can also be obtained by a method comprising the steps of providing superabsorbent polymer particles and mixing the superabsorbent polymer particles with a solution containing water and a polyvalent salt having a valency of 3 or more. This method is further disclosed in European Patent No. 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, by reverse-phase suspension polymerization as described in U.S. Patent Nos. 4,340,706 and 5,849,816, or by spray-phase dispersion polymerization or other gas-phase dispersion polymerization as described in U.S. Patent Publication Nos. 2009 / 0192035, 2009 / 0258994, and 2010 / 0068520. In some embodiments, suitable precursor superabsorbent polymer particles can be obtained by production processes described in more detail on pages 12, line 23 to 20, line 27 of International Publication No. 2006 / 083584.

[0041] The surface of the SAP particles may be coated. The surface of the SAP may be surface crosslinked. The SAP particles may also contain surface and / or edge-modified clay platters. Preferably, the clay platters are montmorillonite, hectorite, laponite, or a mixture thereof. Preferably, the clay platters are laponite. The SAP may contain 0.1 to 5% by weight of surface and / or edge-modified clay platters compared to the weight of the precursor superabsorbent polymer particles.

[0042] In a first aspect of the present invention, the SAP used in the core has a time to reach 20 g / g absorption of less than 220 seconds (SAP T20), as measured by the SAP K(t) test method described below. Specifically, the SAP may have an SAP T20 of 100 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 limits forming a range such as 100 to 200 seconds.

[0043] SAP having the required SAP T20 can be synthesized, for example, using the teachings in International Publication No. 2015 / 041,784(A1) disclosing SAP having a T20 in the range of 104 to 211 seconds. SAP having the required SAP T20 can also be obtained directly from conventional SAP suppliers. For example, the following embodiment of the present invention uses SAP with a measured SAP T20 of 165 seconds, product name SCHAUCH HVDE 235, "Der Alleskoenner," purchased via Amazon.

[0044] Unless otherwise specified, the values ​​provided herein for qualifying SAP (e.g., SAP T20, CRC, AAP, etc.) refer to the overall properties of the SAP used within the absorbent core. For example, if a first layer 60 and a second layer 60' of SAP are used to construct the core, and the SAP used differs in each layer, the value for qualifying the core's SAP is based on the average of these first and second SAPs. In practice, measurements are performed using blends of SAPs that differ in proportion to the proportion used in the core.

[0045] Because bulky absorbent cores have an open-pore structure, it has been suggested that lower permeability SAPs may be advantageously used to take advantage of this property (see, for example, International Publication No. 2016 / 106,021(A1)). However, this is not without its drawbacks. We have found that during use, liquid can rapidly diffuse from the point of impact toward the front and rear of the absorbent core. Thus, urine may escape from the absorbent core through the front and rear ends, resulting in leakage, or at least create zones of higher re-wetting in the front and rear of the absorbent core, leading to insufficient drying and a lack of wearer comfort. We have now found that this undesirable liquid diffusion drawback can be successfully addressed by using SAPs with relatively low SAP T20 values, as illustrated in the following examples. While not wishing to be bound by theory, the inventors believe that a low SAP T20 value is a characteristic of SAP that allows it to rapidly absorb fluid even when SAP particles are in close contact and / or under pressure, which prevents the fluid from diffusing longitudinally into the absorbent core, as with other types of SAP. While not wishing to be bound by theory, the inventors believe that the contact of SAP particles with the fibers in the core layer limits the absorption rate of SAP particles because the fluid cannot freely penetrate into the particles in the contact area, and the fiber network in the core layer creates a constraint on swelling on the swelling SAP particles. The inventors believe that SAPs with a low SAP T20 value have the ability to overcome this adverse effect of the fiber network in the core 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 pressure, are not suitable for achieving the benefits of the present invention.

[0046] The SAP K(t) test method is also useful for determining other SAP parameters that can be similarly advantageously used in the present invention. The absorption of SAP (U20) at 20 minutes may be, specifically, at least 22 g / g, or at least 24 g / g, or at least 28 g / g, or at least 30 g / g, or 28 g / g to 60 g / g, or 30 g / g to 50 g / g, or 30 g / g to 40 g / g, as measured according to the SAP K(t) test method. The SAP absorption (U20) may be at least 1 × 10⁻⁶ g / g as measured according to the SAP K(t) test method. -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 It may have an effective transmittance (SAP K20) after 20 minutes.

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

[0048] The superabsorbent polymer particles may further have an equilibrium permeability expressed as a UPM (Urine Permeability Measurement) value of more than 10, preferably more than 15, more than 20, more than 30, or more than 45, or 10 to 200, or 15 to 100, or 30 to 80 UPM units, where 1 UPM unit is 1 × 10⁻¹⁶ -7 (cm 3 The value is (seconds) / g. The UPM value is measured according to the UPM test method described herein. This method is closely related to the SFC test method of the prior art. The UPM test method typically measures the flow resistance of the pre-swelled layer of superabsorbent polymer particles, i.e., the flow resistance is measured in equilibrium. Thus, superabsorbent polymer particles having a high UPM value 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 ejection but also in subsequent ejections.

[0049] Furthermore, the total amount of SAP present in the absorbent core may vary depending on the intended user of the product. Neonatal diapers require less SAP than infant or adult incontinence diapers. The amount of SAP in the core may be approximately 2g to 50g, specifically 5g to 40g, in a typical infant diaper, for example. The average basis weight of SAP in the absorbent core may be, for example, at least 50, 100, 200, 300, 400, or 500 g / m². 2 or more, or 200-400g / m 2 It is possible. The absorbent core may contain superabsorbent polymer particles with a basis weight of at least 200 gsm, at least 300 gsm, or 300 gsm to 500 gsm.

[0050] SAP vertical distribution SAP particles preferably have a heterogeneous vertical distribution in the bulky core layer. Heterogeneity means that the planar SAP concentration in the z direction of the core is not constant throughout the thickness of the bulky nonwoven fabric, but rather that the SAP concentration varies in the z direction by more than plus or minus 10%, and especially more than plus or minus 20%, relative to the mean. Planar concentration as used herein is the mean planar concentration of a circular zone of an absorbent core with a diameter of 20 mm in the plane comprising the x and y directions of the absorbent core. Specifically, the planar concentration of SAP particles may have a multimodal distribution, particularly a bimodal distribution, in the z direction of the absorbent core. Bimodal means that the concentration of SAP particles along the thickness of the core contains at least two peaks, and the peaks are separated by valleys having SAP concentrations of less than 40%, particularly less than 30%, compared to the lowest concentrations of the two adjacent peaks. Such distributions are shown in the diagram in Figure 7a and can be determined for a given sample by micro-CT analysis. Multimodal means that the z-distribution of the concentration of SAP particles contains two or more of these peaks.

[0051] Figures 6 to 10 show the bimodal distribution obtained by micro-CT analysis of an exemplary core of the present invention. CT is an abbreviation for computed tomography, and "micro" means that very low resolution can be achieved, which is suitable for measuring the position of SAP particles. CT technology uses X-rays to view the inside of an object, and many X-ray projections are made around the object from various angles to generate a tomographic image of the object. This is a conventional diagnostic method in medical applications. Today, the application areas of CT are diverse and wide-ranging, as virtually any material or component can be examined with CT. The main application area of ​​CT in science and industry is non-destructive testing.

[0052] Figures 6a-6c show exemplary cross-sectional results of micro-CT scans of the absorbable core of the present invention, which are detailed below. A circular sample with a diameter of 26 mm was cut from the center of the absorbable core, and the field of view seen in Figure 6a is the 20 mm diameter center of the circular sample. The spatial resolution of the scan is 10 μm. The micro-CT scan allows for computer processing of the scanned data and can also be projected onto the xz plane (Figure 6b) and the yz plane (Figure 6c). The bimodal nature of the SAP concentration distribution within the central layer is already visible in Figures 6a-6c, where two separate layers have higher SAP concentrations separated by a low SAP concentration zone. Using image analysis, a figure can be plotted showing the grayscale values ​​proportional to the average planar SAP concentration in the z-direction of the field of view of the sample. See Figure 7a. The horizontal axis represents the vertical distance z (100 = 1 mm) from the surface of the sample, and the vertical axis represents the grayscale values ​​proportional to the average planar SAP concentration with respect to the reported distance z from the top surface. The relative difference in shading values ​​shown in Figures 7a and 7b corresponds to the relative difference in planar concentration of SAP. For example, a 20% higher shading value (as shown in Figures 7a and 7b) 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 approximately 0.6 mm from the top of the core with a density value of 3338, and a second peak P2 located approximately 3.6 mm from the top of the core with a value of 2897. Between peaks P1 and P2, there is a valley V1 with a value of 530. The density values ​​used to measure the relative height of the peaks (used in Figure 7a) are uncalibrated but are arbitrary units that directly correlate with the local density of the specimen and therefore directly correlate with the planar concentration of SAP. Thus, the figure in Figure 7a can be used to compare the relative values ​​of the peaks and valleys at various z values, i.e., at various positions along the vertical axis (thickness direction) of the core.

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

[0055] As noted above, bimodality means that the measured value of the trough (V1) is less than 40%, specifically less than 30%, than the lowest value of two adjacent peaks (taking the lowest values ​​of P1 and P2). In the examples shown, the trough V1 has an SAP concentration of approximately 18.3% (530 / 2897*100%) of the lowest value of the adjacent peak. By comparison, the distribution in the comparative example disclosed below has a first peak P1' at approximately 8400 arbitrary units, a second peak P2' at approximately 3000 arbitrary units, and a trough V1' in between at approximately 1500 arbitrary units, and therefore the trough is approximately 50% of the lowest adjacent peak.

[0056] Characteristics of absorbent cores Instead of measuring the SAP T20 value of SAP in an absorbent core, or in addition to doing so, the K(t) test method can be adapted to directly measure the properties of the absorbent core. As will be discussed in more detail below in the absorbent core K(t) test method, the properties of the core are measured on a circular sample taken from the center of the core.

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

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

[0059] The core transmittance (core K20) was measured according to the absorbent core K(t) test method described herein and was 6.0 × 10⁻⁶. -8 cm 2 More specifically, 8.0 x 10 -8 cm 2 Ultra, and for example, 6.0 × 10 -8 cm 2 From a maximum of 40 x 10 -8 cm 2 , or 8.0 × 10 -8 cm 2 From a maximum of 19 x 10 -8 cm 2 It is possible.

[0060] While not wishing to be constrained by theory, the inventors believe that a low core T15 value is a characteristic of absorbent cores that allows for rapid absorption of fluid not only within the void capacity of the absorbent core (capillary storage) but also within the SAP particles contained within the absorbent core (osmotic storage). The inventors believe that by improving the balance between capillary storage between bulky fibers and osmotic storage in SAP, an absorbent core is provided that offers a faster rate of fluid intrusion capture, superior leak prevention, and comfort to the wearer through drying. Since the fluid stored osmotically does not contribute to rewetting, it results in better drying and better comfort for the wearer, and because it is locally immobilized, fluid diffusion far along the longitudinal direction of the absorbent core is reduced, similar to other types of absorbent cores.

[0061] Furthermore, the osmotic capacity, expressed 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 for describing the core's ability 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 a core under moderate pressure and dynamic behavior. The inventors have found that this balance can be reliably measured for bulky 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 that has an excellent balance between capillary storage and osmotic storage.

[0063] While not wishing to be bound by theory, the inventors believe that a high core K20 value is characteristic of absorbent cores that have high fluid permeability, particularly in a swollen state. This high core permeability in a swollen state ensures the intake of fluid into the absorbent core under load, for example, after liquid intrusion, even under moderate pressure. The inventors believe that a high core K20 value characterizes a core with minimal liquid flow over the absorbent core. By avoiding this free liquid flow over the absorbent core, the diffusion of liquid in the longitudinal direction of the absorbent core in the upper layer of the absorbent article is limited, as with other types of absorbent cores. This results in better drying and greater comfort for the wearer.

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

[0065] The absorbent core of the present invention may have a time (core T20) to reach 20 g / g absorption of less than 550 seconds, particularly less than 500 seconds or less than 450 seconds. Core T20 may optionally be any range consisting of at least 200 seconds, or 300 seconds, or 350 seconds, and any boundary thereto, for example, 300 seconds to less than 550 seconds, or 360 seconds to less than 500 seconds. The overall density of the absorbent core can also be measured when performing the absorbent core K(t) test. The absorbent core has a density of 0.2 g / cm³. 3 ~0.6g / cm 3 Less than 0.3-0.5 g / cm³ 3 It may have a density of less than 0.3 psi. The density is measured at 0.3 psi as shown by the absorbent core K(t) test method (see below).

[0066] Manufacturing method Figure 18 shows an exemplary continuous process for fabricating an absorbent core. The process and apparatus described above are generally similar to those disclosed in Figure 3 of Chinese Patent No. 101797201 or International Publication No. 2020 / 025401 (BASF, Ge et al.). The various arrows in this figure represent the rotational directions of the various roll release cylinders and roll winding cylinders in the production flow process, as well as the direction of travel of the manufactured material. Naturally, other processes and modifications are also possible.

[0067] As shown in Figure 18, the apparatus for producing an absorbent core may include a bottom layer web unwinder 6, a bottom layer adhesive spray head 7, a bulky center layer web unwinder 8, a first SAP particle dispenser 9 and an optional vacuum suction box 10, a pair of first rollers 11 and 12, a second SAP particle dispenser 13 and an optional vacuum suction box 14, an upper layer web unwinder 15, an upper layer spray head 16, a pair of second rollers 17 and 18, trimming knives 19 and 20, and a product roll winding roller 21.

[0068] Both the first and second SAP particle dispensers 9 and 13 may be equipped with frequency change and speed adjustment devices (not shown in Figure 18) that are tuned to maintain an vibration frequency that matches the linear velocity of the product roll winding roller 21 and to ensure that the deposited SAP is distributed fairly uniformly on the bulky web 43.

[0069] During production, rolls of bottom layer material 42, such as paper or nonwoven fabric, are placed on the bottom layer web unwinder 6. Bulky nonwoven fabric rolls 43 are placed on the core layer web unwinder 8. The initial density and thickness of the bulky core layer can be conveniently measured by the raw material thickness and density measurement methods described in more detail below.

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

[0071] After the bottom layer 42 and the middle layer 43 are pressed together between rollers 11 and 12, these combined layers may optionally pass between the second SAP particle sieve plate 13 and the vacuum suction box 14, which cooperate to deposit SAP particles onto the second surface of the middle layer and blend the SAP particles from this second surface into the fibers of the middle layer. The top layer 41, coated with adhesive 72 by the adhesive spray head 16, is then joined to the middle layer, covering the second surface of the middle layer between the two press rollers 17 and 18. Naturally, in the above, the top layer and the bottom layer may be used interchangeably.

[0072] The press rollers 17 and 18 may have substantially flat surfaces, or they may have raised areas on which extra pressure and heat should be applied to the core. These raised areas occupy the same space as the channel area and can therefore provide mechanical, ultrasonic, and / or thermal bonding within the channel zone 26. The 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 trailing and leading edges (360-degree outer circumference) of the core. In these zones, better bonding can be achieved in the absence of SAP as in the channel zone 26. Trimming knives 19 and 20 may be provided to trim the longitudinal side edges of continuous bands of the absorbent core before the flow of absorbent core material is finally rolled onto a roll of absorbent core material by the product roll winding roller 21.

[0073] The rolls of absorbent core material thus formed can be stored or transported to the manufacturing site where they can be further processed into absorbent products. Alternatively, instead of forming rolls, a flow of absorbent core material can be supplied directly to the processing line, in which case the absorbent cores are individualized by cutting along their leading and trailing edges.

[0074] A packaging layer 3 (not shown in Figure 18) may also be supplied before the core material is rolled and wrapped around the top, middle, and bottom layers, as shown and considered in relation to Figure 5, to prevent the loss of SAP through the side edges of the absorbent core. An alternative such packaging layer may also be attached to the core when the core material web is further processed.

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

[0076] Therefore, the absorbent core 28b may comprise a first core layer 431 and a second core layer 432, each of which is a bulky fiber nonwoven fabric layer containing, for example, three or more layers of superabsorbent polymer particles 60, 60', 60'' at least partially distributed within the pores of the bulky core layer. The two (or more) bulky core layers may be composed of the same material or different bulky nonwoven fabrics. For example, the permeability in the upper core layer may be enhanced by using a low basis weight bulky material, and flexibility may be enhanced in the bottom layer containing a higher density bulky material. Of course, other configurations are also possible. The two or more core layers may have equal dimensions in the x,y plane of the core, but they may have different lengths and / or widths. Two core layers of unequal lengths may be beneficial in providing different amounts of SAP along the absorbent core and may be fabricated, for example, by adding cutting and slitting units on the second layer patch before combining it with the first layer.

[0077] The two bulky central layers may also contain different types of SAP, for example, a faster-absorbing 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 upper 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 bulky layers may also have different or the same absorption rates (SAP T20), capacities (CRC, AAP), and transmittances (UPM).

[0078] An absorbent core comprising a double bulky nonwoven fabric layer may be prepared by a method adapted from one of the methods disclosed above, see, for example, International Publication 2016 / 106021(A1) which describes two separate bulky layer release cylinders to provide first and second bulky core layers 431, 432. Alternatively, a bulky web having a double width may be used, such a wide roll can be cut into two halves in the machine direction after release to provide two flows of bulky nonwoven fabric material, on which SAP particles are subsequently deposited separately. The two flows of bulky material 431, 432 may then be combined separately with an upper layer and a bottom layer, respectively, on which SAP particles 60 are deposited via a suitable SAP depositing apparatus.

[0079] Absorbent article 20 The absorbent core can be incorporated into any type of personal hygiene article, specifically pull-up diapers and tape-style diapers, as well as into inserts in hybrid systems comprising a washable outer cover and a disposable insert. A schematic cross-sectional view showing some of the main components of the diaper absorbent article 20 is shown in Figure 5. This figure shows the absorbent core (including the packaging layer 3) of Figure 3, but this is, of course, illustrative and not limiting. The absorbent article typically comprises a fluid-permeable top sheet 36 facing the wearer and a liquid-impermeable back sheet 38 facing the clothing, attached to each other along their outer circumference. The absorbent core is positioned between these layers and can be attached to them directly and indirectly, typically by adhesive or heat / pressure bonding.

[0080] The top sheet 36 is preferably adaptable, soft to the touch, and does not irritate the wearer's skin. Furthermore, at least a portion of the top sheet is liquid-permeable, allowing liquid to easily penetrate its thickness. Suitable top sheets can be made from a wide range of materials, such as porous foams, mesh foams, perforated plastic films, or natural fibers (e.g., wood fibers, cotton fibers, or viscose), synthetic fibers or filaments (e.g., polyester fibers, polypropylene fibers, or two-component PE / PP fibers, or mixtures thereof), or woven or nonwoven fabrics of a combination of natural and synthetic fibers. If the top sheet contains fibers, the fibers may be spunbond fibers, carded fibers, wet-laid fibers, melt-blown fibers, water-entangled fibers, or specifically spunbond PP nonwoven fabrics, which are treated by methods known in the art. The basis weight of a typical diaper top sheet is about 10 gsm to about 28 gsm, particularly about 12 gsm to about 18 gsm, but other basis weights are also possible.

[0081] The backsheet 38 is typically impermeable to liquids (e.g., urine). The backsheet may be a thin plastic film, such as a thermoplastic film having a thickness of less than approximately 0.10 mm, or may include such a film. An exemplary backsheet film is one manufactured by Tredegar Corporation (based in Richmond, VA) and sold under the trademark CPC2 Film. Other suitable backsheet materials include breathable materials that allow vapor to escape from the article while preventing exudates from passing through the backsheet. A low-basis-weight nonwoven fabric cover can be attached 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 trapping layer or fluid distribution layer) directly beneath the top sheet 36. The function of such a layer is to quickly trap fluid from the top sheet away from the sides facing the wearer and / or distribute the fluid over a wider area so that it is absorbed more efficiently by the absorbent core. It is also possible that such a liquid management layer is located between the back sheet and the absorbent core. A further layer 4 may be present between the liquid management section 54 and the absorbent core 28. The further layer 4 may be another such trapping or distribution layer, or it may be tissue paper or a low-basis-weight NW layer that provides additional packaging for the absorbent core 28 to prevent SAP particles from escaping outside the core.

[0083] Absorbent articles, such as diapers or training pants, may further include components that improve the fit of the article around the wearer's legs, specifically a barrier leg cuff 32 and a gasket cuff 34. The barrier leg cuff may be formed from a single piece of material, typically a nonwoven fabric, which is partially bonded to the rest of the article and partially raised from a plane defined by the top sheet, and thus can stand upright. The barrier leg cuff is typically bounded by a proximal edge bonded to the rest of the article, which is typically the top sheet and / or back sheet, and a free edge intended to contact the wearer's skin and form a seal. The upright portion of the cuff typically comprises an elastic element, e.g., one or more elastic strands 35. The barrier leg cuff provides improved containment of fluids and other bodily exudates, generally at the junction of the wearer's torso and legs.

[0084] In addition to the barrier leg cuff, the article may include a gasket cuff 34 formed in the same plane as the chassis of the absorbent article, specifically at least partially enclosed between the top sheet or barrier leg cuff and the back sheet, and positioned laterally outward relative to the upright barrier leg cuff. The gasket cuff can provide a better seal around the wearer's thigh. Typically, each gasket leg cuff includes one or more elastic strings or elastic elements 33 that are included in the chassis of the diaper, for example, in the area of ​​the leg opening between the top sheet and the back sheet.

[0085] Absorbent articles may also include other typical components found in diapers, training pants, replaceable inserts, or adult incontinence products (not shown further). A removable fastening system may be provided for tape-type diapers to apply lateral tension around the absorbent article to hold it in place on the wearer. This fastening system is not necessary for training pants, as the waist area of ​​these articles is already joined. Fastening systems typically include fasteners such as tape tabs, hook-and-loop fastener components, connecting fasteners such as tabs and slots, buckles, buttons, snaps, and / or bisexual fastening components, but any other known fastening means are generally acceptable. A landing zone is usually provided in the front waist area of ​​the article so that fasteners can be attached removablely.

[0086] The absorbent article may include anterior and posterior ear sections, as is known in the art. The ear sections may be integral parts of the chassis, for example, formed as side panels from the top sheet and / or back sheet. Alternatively, the ear sections may be separate elements attached by adhesive and / or heat embossing. The posterior ear section may be elastic to facilitate the attachment of the tab to the landing zone and to keep the tape diaper in place around the wearer's waist. The anterior ear section may also be elastic or stretchable, and this elastic ear section makes both sides of the absorbent article stretchable, providing a more comfortable and body-hugging fit by initially fitting the absorbent article to the wearer and maintaining this fit throughout the period of wear, even as time passes after exudate accumulates in the absorbent article.

[0087] Typically, adjacent layers are joined to each other using conventional bonding methods, such as adhesive coating by slotting or spraying onto all or part of the layer surface, or by thermal bonding, pressure bonding, or a combination thereof. For clarity and readability, bonding between components is not shown in most of the figures, particularly in Figure 5, except for adhesive layers 71 and 72. Unless otherwise specifically stated, adjacent layers of an article should be assumed to be attached to the other. For example, the backsheet and bottom layer of an absorbent core can typically be bonded together. The adhesive used may be any standard hot-melt adhesive known in the art.

[0088] Packaging Absorbent articles can be packaged in any conventional type of packaging. Absorbent articles may be compressed when packaged, particularly to save space. Specifically, a package may contain multiple absorbent articles, wherein the package has an in-bag stack height of less than approximately 80 mm, in accordance with the in-bag stack height test described in U.S. Patent No. 8,585,666 (B2) (Weisman), which is incorporated herein by reference. Alternatively, a package of absorbent articles of this disclosure may have an in-bag stack height of approximately 72 mm to approximately 80 mm, or approximately 74 mm to approximately 78 mm, specifically, all 0.5 mm increments within the specified range and all ranges formed within or by the specified range, based on the in-bag stack height test described in U.S. Patent No. 8,585,666 (B2) (Weisman).

[0089] Examples and experimental results a) Core construction An exemplary absorbent core of the present invention was fabricated by hand. The central bulk layer was bulk layer (TL6 from TWE-group (Emsdetten, Germany)). The measured caliper was 0.613 mm and the basis weight was 85.4 g / m². 2 (Based on an average of 10 measurements), the result was approximately 0.140 g / cm³. 3The density was given and 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 10gsm SMS nonwoven fabric from Fibertex (e.g., HY02XXX10). The core layer was 165mm wide and 360mm long. Each cover layer was first coated with 5gsm spiral adhesive, followed by a net 10gsm microfiber adhesive (NW1151ZP, FULLER ADHESIVES), uniformly applied along its entire length.

[0092] The bulky core layer was placed on the bottom cover layer with the rough side of the bulky nonwoven fabric facing upwards. The bulky core layer was 110 mm wide and 360 mm long. 15 g of SAP was sprinkled evenly by hand over the entire bulky surface of the nonwoven fabric. Since the manufacturing table did not have a vacuum, the SAP particles were distributed within the bulky nonwoven fabric by brushing them by hand. Subsequently, the top cover layer was placed on the laminate with the adhesive layer facing the bulky layer. The core layer was attached to the two cover layers by applying gentle pressure with a rubber roller.

[0093] The basis weight of SAP obtained in the absorbent core was 380 gsm. The average concentration of SAP in the absorbent core was 61% by weight relative to the weight of the core, and the average concentration of SAP in the bulky core layer only (excluding the upper and lower layers and adhesive) was 81% by weight.

[0094] Core E1 and comparative core C1 of the present invention were fabricated using two commercially available SAPs (SAP E1 and SAP C1). The SAPs had the characteristics listed in Table 2 below.

[0095] [Table 2]

[0096] The absorbent core had the following characteristics:

[0097] [Table 3]

[0098] b) Commercial cores for comparison: For further comparison, the properties of two commercially available 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 bulky central layer containing SAP. Huggies had a double-layer core containing an air felt / SAP mixed layer on top of a bulky layer with SAP, with both layers located between the bottom and top layers. The specific average density ρ of the core samples was... s It was not measured, but 1.50 g / cm³ 3 We assumed that this was the case.

[0099] The characteristics of the comparison 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, and this time, the specific average density of SAP ρ s 1.60 g / cm³ 3 This was assumed.

[0102] Table 4 lists the characteristics of the comparison cores SAP, SAP C2, and SAP C3.

[0103] [Table 5]

[0104] c) Product data: Capture speed Exemplary core E1 and comparative core C1 were placed within an absorbent product chassis containing a commercially available top sheet, back sheet, and capture layer, as used in Pampers Premium products (size 4) from China. The absorbent cores were placed in different orientations within the product (top or bottom; see description below). These products were tested using the C-SABAP test (capture rate curve under balloon pressure). C-SABAP determines the saline capture 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)), monitored by a digital pressure gauge.

[0105] In the first set of experiments, capture rates were measured for each core type and for each orientation of the core in the diaper, with four replicates. Four squirts of 75 mL of physiologically colored saline (0.9 wt%) were applied sequentially at a rate of 15 mL / s, with a 5-minute interval between each squirt. The capture rate for each squirt was recorded. The liquid was 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, with the fourth measurement, which had the highest sum of squirt times 1 and 2, being ignored to eliminate outliers.

[0106] Note: "Upward" means that the upper side of the core layer to which AGM is added faces the top sheet, and "downward" means the opposite direction.

[0107] [Table 6]

[0108] The capture rate in Example E1 of the present invention was faster in the first ejection compared to Comparative Example C1, regardless of the orientation of the core in the product (upward or downward).

[0109] In the same orientation (either all upward or all downward), core E1 of the present invention performed at a better capture rate (i.e., was faster) over all four ejections compared to the product containing comparative core C1.

[0110] d) Product data: liquid distribution and rewetting The articles used in the C-SABAP test were removed from the C-SABAP apparatus 5 minutes after complete absorption of the fourth and final ejection. Liquid distribution and re-wetting were measured on these articles, including the core of interest. Re-wetting was measured at the point of invasiveness, i.e., 170 mm from the front of the absorbent core. Liquid distribution was measured in the longitudinal direction (y) towards each lateral side of the article, starting from the center point of invasiveness on the plane (i.e., 170 mm from the front of the absorbent core), to obtain the liquid distribution at the front (i.e., from the invasive part to the front end of the absorbent core) and the liquid distribution at the rear (i.e., from the invasive part to the rear end of the absorbent core).

[0111] Liquid distribution is measured by the length of the stain left by the colored saline solution on the absorbent core at the front and back of the diaper (the edges of the colored stain are not linear, so as to indicate the maximum and minimum distances between the stain edge and the loading point).

[0112] Next, a re-wetting test was performed on the top sheet side of the diaper. The overall liquid distribution length is the sum of the averages of the minimum and maximum values ​​on both sides, i.e., average (front minimum, front maximum) + average (back minimum, back maximum).

[0113] The re-wetting test measures the amount of fluid released by the diaper using a skin-like material (a stack of five layers of collagen). Collagen absorbs fluid through the same mechanism as infant skin. The re-wetting test is performed 10 minutes after the last eruption, with four 70mm diameter collagen sheets stacked at the center of the eruption point and weighted with a 9.1kg weight for 30 seconds. The amount of fluid absorbed by the collagen sheet stack is measured and reported as follows.

[0114] As summarized above, data for products excluded by capture rate are also excluded by re-wetting and liquid distribution; therefore, Table 5 shows the average values ​​of three out of four data points.

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

[0116] The staining on the diaper of the present invention, which has core E1, was significantly shorter than that of the comparative diaper, which has comparative core C1. In both diapers, rewetting was lower when the absorbent core was positioned with the upper layer facing the top sheet ("upward") than when it was positioned the other way around ("downward").

[0117] e) Micro CT scan An exemplary core E1 was subjected to micro-CT secan according to the micro-CT scanning method described below. The results of the micro-CT scan of exemplary core E1 are shown in Figures 6 to 10. As previously stated, such CT scans can be used to determine the concentration distribution of SAP within an absorbent core, specifically whether the vertical distribution of SAP particles is uniform, bimodal, or multimodal. Core E1 of the present invention had a bimodal distribution. A comparative core C1 was also measured, which also contained two peaks, but this is not bimodal according to the definition herein (in the relevant units, the trough has a measured density value less than 40% lower than the lowest value of the adjacent peak). Although SAP was not applied to both sides of the bulky layer, it was found that the combination of materials in the examples used still resulted in a bimodal SAP distribution, which is also found when SAP is applied sequentially in two stages to each side of the central layer.

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

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

[0120] Thickness and density measurement methods This method is used to measure the thickness (caliper) of the bulky core layer in a standardized manner. Subsequently, the density can be calculated from the layer thickness and basis weight. Unless otherwise specified, the thickness and density are given with respect to the bulky material in the absence of SAP particles. Measurements should preferably be performed on the bulky material before it is processed into an absorbent core, and therefore on the SAP-free bulky material. If the starting material is unavailable, the bulky core 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 aspiration. The core layer can be separated from the other layers using a freeze spray. Samples should be held at 21°C ± 2°C and 50% ± 10% RH for at least 24 hours to equilibrate, especially if they have been previously compressed.

[0121] Instrument: A Mitutoyo manual caliper gauge or equivalent instrument with a resolution of 0.01 mm.

[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 slots to facilitate application around the instrument shaft) to obtain the target weight. The total weight of the foot and additional weight (including the shaft) is selected to provide the sample with a pressure of 4.14 kPa (0.6 psi).

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

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

[0125] Ruler: A calibrated metal ruler with markings in millimeters.

[0126] Stopwatch: Accuracy 1 second.

[0127] Sample preparation: Prepare the central layer for at least 24 hours as described above.

[0128] Measurement Procedure: Place the layer flat with the bottom side, i.e., the side intended to be positioned towards the backsheet in the final product, facing downwards. Carefully mark the measurement point (i.e., the center of the sample) on the upper side of the layer, taking care not to compress or deform the layer. If the bulky nonwoven layer is not uniform in the transverse or longitudinal direction, the value is measured at the center of the sample corresponding to the center of the absorbent core prepared from the sample.

[0129] Lift the contact foot of the caliper gauge and position the center layer flat on the base plate of the caliper gauge with the upper side of the core facing upwards, so that when lowered, the center of the foot lies on the marked measurement point.

[0130] Carefully lower the foot onto the sample and then release it (ensure the calibration is "0" before starting the measurement). Read the caliper value in 0.01 mm increments 10 seconds after releasing the foot.

[0131] Repeat the procedure for each measurement point. Measure 10 samples in this manner against a given material, calculate the average thickness, and report it with an accuracy of 1 / 10 mm. Calculate the basis weight of each sample by dividing the weight of each sample by its area.

[0132] Density (g / cm 3 The unit is the basis weight (g / cm²) of the material. 2 The calculation is performed by dividing the unit by the thickness (in cm).

[0133] Micro-CT scan method 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 a suitable micro-CT scanner. To avoid any impact of cutting on the core structure, the field of view is reduced to the innermost circle with a diameter of 20 mm. The CT scanner used is, for example, a DynaTOM (product number M2090) manufactured by XRE nv (merged with Tescan). The settings are as follows: tube voltage: 80KV, tube power: 10.0 watts, exposure time (ms): 380, average number: 1.000000, binning value: 1, voxel size: 10 μm, scan speed: 2.36 frames per second, a total of 2900 projected images in one 3D.

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

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

[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. Micro-CT scans allow for computer processing of scanned data and projection onto the xz plane (Figure 6b) and yz plane (Figure 6c). Using image analysis, a graph can be plotted showing the density values ​​proportional to the average planar density of SAP in the field of view of the sample in the z direction. See, for example, Figure 7a / Figure 7b. The horizontal axis represents the vertical distance z from the surface of the sample (100 = 1 mm), and the vertical axis represents the density values ​​proportional to the average planar density of SAP for the field of view (a circle with a diameter of 20 mm) at the reported distance z from the top surface.

[0139] Urine permeability measurement (UPM) test method Laboratory conditions: This test must be conducted in a climate-controlled room under standard conditions of 23°C ± 2°C and 45% ± 10% relative humidity.

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

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

[0142] Figure 12 shows a piston / cylinder assembly 1028, which includes 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 a smooth inner cylinder wall 1150 with an inner diameter p (area = 28.27 cm²). 2The bottom 1148 of the cylinder 1120 faces a stainless steel screen cloth (ISO9044 material 1.4401, mesh size 0.038 mm, wire diameter 0.025 mm) (not shown), which is stretched biaxially to a taut state before being attached to the bottom 1148 of the cylinder 1120. The piston shaft 1114 is made of clear polycarbonate (e.g., Lexan®) and has an overall length q of approximately 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 the shoulder portion 1124. The lower part 1146 of the piston shaft 1114 has a diameter t of approximately 5 / 8 inch (15.9 mm) and is threaded for securely screwing into the central hole 1218 (see Figure 8) of the piston head 1118. The piston head 1118 is perforated and made of clear polycarbonate (e.g., Lexan®) and covered with similarly stretched stainless steel screen cloth (ISO9044 material 1.4401, mesh size 0.038 mm, wire diameter 0.025 mm) (not shown). The weight 1112 is made of stainless steel, has a central hole 1130, slides onto the upper part 1128 of the piston shaft 1114, and stops on the 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 internal area of ​​the cylinder 1120. The total weight can be adjusted by drilling a dead-end hole in the central axis 1132 of the piston shaft 1114 to remove material and / or by providing a cavity to add weight. The cylinder lid 1116 has a first lid opening 1134 at its center to vertically align the piston shaft 1114 and a second lid opening 1136 near the edge 1138 to introduce fluid into the cylinder 1120 from a constant still water head reservoir 1014.

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

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

[0145] The specifications of cylinder cover 1116 are as follows: Outer diameter w of cylinder cover 1116: 76.05 mm (±0.05 mm) Inner diameter of cylinder cover 1116: 70.5 mm (±0.05 mm) Thickness y of cylinder lid 1116, including lip 1154: 12.7 mm Thickness of cylinder cover 1116 excluding lip 1154: z: 6.35 mm Diameter of the first lid opening 1134: 22.25 mm (±0.02 mm) Diameter b of the 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 for weight 1112 are as follows: Outer diameter c:50.0mm Diameter d of the center hole 1130: 16.0 mm Height e: 39.0 mm

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

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

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

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

[0151] Before use, the stainless steel screen (not shown) on the piston head 1118 and cylinder 1120 should be inspected for clogging, holes, or overstretching and replaced if necessary. A urine permeability analyzer with a damaged screen may give inaccurate UPM results and should not be used until the screen is replaced.

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

[0153] A constant static head reservoir 1014 is used to supply saline solution 1032 to the cylinder 1120 and to maintain the level of 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 intake tube 1010 is positioned to maintain the level of saline solution 1032 in the cylinder 1120 at the required height k of 5.00 cm during measurement; that is, the bottom 1034 of the air tube 1010 is on a plane 1038 approximately in line with the 5.00 cm mark 1156 on the cylinder 1120, above the receiving container 1024 and placed on the cover plate 1047 and support ring 1040 (the inner opening of the circle is 64 mm or more in diameter).

[0154] The cover plate 1047 and support ring 1040 are components used in the instrument used for the “K(t) test method (dynamic effective transmittance and absorptive rate measurement test method)” described herein, and are referred to as “Zeitabhangiger Durchlassigkeitsprufstand” or “Time Dependent Permeability Tester” (instrument number 03-080578), and are commercially available from BRAUN GmbH (Frankfurter Str. 145, 61476 Kronberg, Germany). Detailed drawings are also 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 analysis. A suitable reservoir 1014 consists of a jar 1030 including a horizontally oriented L-shaped conduit 1018 connected to a flexible tube 1045 (e.g., a Tygon tube to which a nozzle and reservoir outlet can be connected) and a Tygon tube nozzle 1044 (with an inner diameter of at least 6.0 mm and a length of about 5.0 cm) for fluid delivery, a vertically oriented opening tube 1010 for introducing air at a fixed height within the constant static head reservoir 1014, and a stoppered vent 1012 for refilling the constant static head reservoir 1014. Tube 1010 has an inner diameter of about 12 mm but at least 10.5 mm. A conduit 1018, positioned near the bottom 1042 of the constant static head reservoir 1014, includes a stopcock 1020 for starting / stopping the supply of saline solution 1032. The outlet 1044 of the delivery flexible tube 1045 is dimensioned (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 height of 5.00 cm of saline solution 1032 has been achieved in the cylinder 1120). The intake tube 1010 is held in place by an O-ring collar 1049. The constant static 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 static head reservoir 1014 are sized to rapidly fill the cylinder 1120 to the required height (i.e., static head) and maintain this height over the measurement period. The constant static head reservoir 1014 must be capable of supplying saline solution 1032 at a flow rate of at least 2.6 g / second for at least 10 minutes.

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

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

[0158] Preparation of reagents (not shown) Jayco Synthetic Urine (JSU) 1312 (see Figure 14) is used in the swelling phase (see UPM procedure below), and 0.118 M sodium chloride (NaCl) solution 1032 is used in 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 quantities should be measured as appropriate.

[0159] JSU: Fill a 1 L volumetric flask with distilled water to 80% of its volume and place an electromagnetic stirring rod inside the flask. Separately, using weighing paper or a beaker, weigh the following amounts of dry ingredients to within ±0.01 g using a chemical balance and add them quantitatively to the volumetric flask in the same order as listed below. The solution is stirred on a suitable stirring plate until all solids have melted, the stirring rod is removed, and the solution is diluted with distilled water to a volume of 1 L. The stirring rod is reinserted, and the solution is stirred on the stirring plate for several more minutes. Amount of salt needed to produce 1 liter of Jayco synthetic urine Potassium chloride (KCl) 2.00g Sodium sulfate (Na2SO4) 2.00g Ammonium hydrogen diphosphate (NH4H2PO4) 0.85g Ammonium phosphate, dibasic ((NH4)2HPO4) 0.15g Calcium chloride (CaCl2) 0.19g - [or calcium chloride hydrate (CaCl2·2H2O) 0.25g] Magnesium chloride (MgCl2) 0.23g - [or magnesium chloride hydrate (MgCl2·6H2O) 0.50g]

[0160] To expedite preparation, combine potassium chloride, sodium sulfate, ammonium hydrogen diphosphate, ammonium phosphate (dibasic), and magnesium chloride (or magnesium chloride hydrate) and dissolve in 80% distilled water in a 1 L volumetric flask. Dissolve calcium chloride (or calcium chloride hydrate) separately in approximately 50 mL of distilled water (e.g., in a glass beaker) until the other salts are completely dissolved, then transfer the calcium chloride solution to a 1 L volumetric flask. Add 1 L (1000 mL ± 0.4 mL) of distilled water and stir the solution for several minutes. Jayco synthetic urine can be stored in a clean plastic container for 10 days. Do not use the solution if it becomes cloudy.

[0161] 0.118 M sodium chloride (NaCl) solution: 0.118 M sodium chloride is used as saline solution 1032. Using weighing paper or a beaker, weigh 6.90 g (±0.01 g) of sodium chloride and quantitatively transfer it to a 1 L volumetric flask (1000 mL ± 0.4 mL). Fill the flask to capacity with distilled water. Add a stirring rod and mix the solution on a stirring plate until all solids are dissolved.

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

[0163] Exam preparation Using a solid reference cylinder weight (not shown) (50 mm in diameter; 128 mm in height), a caliper gauge (not shown) (measuring range 25 mm, accuracy 0.01 mm, maximum piston pressure 50 g; e.g., Mitutoyo Digimatic Height Gage) is set to a reading of 0. This operation is conveniently performed on a smooth, horizontal bench (not shown) of at least approximately 11.5 cm × 15 cm. The piston / cylinder assembly 1028, free of superabsorbent polymer particles, is positioned below the caliper gauge (not shown), and the reading L1 is recorded in 0.01 mm increments.

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

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

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

[0167] An empty cylinder 1120 is placed on a horizontal benchtop 1046 (not shown), and superabsorbent polymer particles are quantitatively transferred into the cylinder 1120. The superabsorbent polymer particles are evenly dispersed onto a screen (not shown) attached to the bottom 1148 of the cylinder 1120, with the assistance of a (manual or electric) turntable (e.g., petriturn-E or petriturn-M from Schüett) to rotate the cylinder 1120. For the most precise results, it is important that the particles are evenly distributed onto the screen (not shown) attached to the bottom 1148 of the cylinder 1120. After the superabsorbent polymer particles have been evenly distributed onto the screen (not shown) attached to the bottom 1148 of the cylinder 1120, the particles must not adhere to the inner cylinder wall 1150. With the lip 1154 of the lid 1116 facing the piston head 1118, the piston shaft 1114 is inserted through the first lid opening 1134. The piston head 1118 is carefully inserted into the cylinder 1120 to a depth of several centimeters. Then, the lid 1116 is 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 upper part 1128 of the piston shaft 1114, so that it is placed on the shoulder 1124, thereby aligning the first and second linear indicator marks. Next, the lid 1116 and piston shaft 1126 are carefully rotated so that the third, fourth, fifth, and sixth linear indicator marks are aligned with the first and second linear indicator marks. Then, the piston head 1118 is gently pressed down (through the piston shaft 1114) and placed on the dry superabsorbent polymer particles. Proper placement of the lid 1116 prevents the weight from sticking and ensures even distribution of the weight on the hydrogel layer 1318.

[0168] Swelling phase: A frit disc 1310 having "coarse" or "very coarse" porosity, with a diameter of at least 8 cm (e.g., 8-9 cm in diameter) and a thickness of at least 5.0 mm (e.g., 5-7 mm in thickness) (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 JSU 1312 into the center of the frit disc 1310 until the JSU 1312 reaches the top surface 1316 of the frit disc 1310. The height of the JSU must not exceed the height of the frit disc 1310. It is important to avoid any air or bubbles trapped inside or beneath the frit disc 1310.

[0169] The entire piston / cylinder assembly 1028 is lifted and placed on the frit disc 1310 in the petri dish 1314. The JSU 1312 from the petri dish 1314 passes through the frit disc 1310 and is absorbed by superabsorbent polymer particles (not shown) to form a hydrogel layer 1318. The amount of JSU 1312 available in the petri dish 1314 should be sufficient for all swelling phases. If necessary, more JSU 1312 may be added to the petri dish 1314 during the hydration period to maintain the liquid level of JSU 1312 on the upper surface 1316 of the frit disc 1310. After a period of 60 minutes, the piston / cylinder assembly 1028 is removed from the frit disc 1310, taking care not to let the hydrogel layer 1318 lose any JSU 1312 or incorporate any air during this procedure. The piston / cylinder assembly 1028 is placed under a caliper gauge (not shown), and the reading L2 is recorded in 0.01 mm increments. If the reading changes over time, only the initial value is recorded. The thickness L0 of the hydrogel layer 1318 is determined from L2 to L1 in 0.1 mm increments.

[0170] The piston / cylinder assembly 1028 is moved to the support ring 1040 in the cover plate 1047. The constant still water head reservoir 1014 is positioned so that the conduit nozzle 1044 is positioned through the second lid opening 1136. The measurement is started in the following order: a) The stopcock 1020 of the constant still water head reservoir 1014 is opened so that the saline solution 1032 reaches the 5.00 cm mark 1156 on the cylinder 1120. This level of saline solution 1032 should be achieved within 10 seconds of opening the stopcock 1020. b) Once 5.00 cm of saline solution (1032 units) is reached, start the data collection program.

[0171] Using a computer 1048 attached to a balance 1026, the amount of saline solution 1032 passing through the hydrogel layer 1318 in grams (with an accuracy of 0.001 g) is recorded at 20-second intervals for 10 minutes. At the end of the 10 minutes, the stopcock 1020 on the constant still water head reservoir 1014 is closed.

[0172] Data collected from 60 seconds into the experiment until the end will be used for the UPM calculation. Data collected before 60 seconds will not be included in the calculation.

[0173] Each 20-second period after the first 60 seconds of the experiment (time t (i-1) ~t i Regarding ), each flow velocity Fs (t) (Unit: g / s) and time t (1 / 2)t The midpoint of each (in seconds) is calculated according to the following formula:

[0174]

number

[0175] 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 plot is drawn with respect to the midpoint. The intercept is calculated as Fs(t=0).

[0176] Calculation of the intercept: The intercept is calculated through the optimal regression line, for example, as follows: The equation for the intercept of regression line a is: a = y AVG -b·x AVG (III) wherein the gradient b is calculated as follows:

[0177] [Number] wherein x AVG and y AVG are the known sample average AVERAGE of x and the known AVERAGE of y, respectively.

[0178] Calculation of the urine permeability measurement value Q: Using the slice Fs(t = 0), Q is calculated according to the following equation.

[0179] [Number] wherein the flow rate Fs(t = 0) is given in g / s, L0 is the initial thickness of the hydrogel layer 1318 in cm, ρ is the density of the saline solution 1032 in g / cm 3 (e.g., 1.003 g / cm at room temperature) 3 ). A (from the above equation) is the area of the hydrogel layer 1318 in cm 2 (e.g., 28.27 cm 2 ), ΔP is the hydrostatic pressure in dyn / cm 2 (e.g., 4920 dyn / cm 2 ), and the urine permeability measurement value Q is in cm 3 seconds / g. The average of the three measurement values should be reported.

[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 gel layers formed from hydrogel-forming superabsorbent polymer particles or absorbent structures containing such particles under confining pressure. The purpose of this method is to evaluate the ability of gel layers formed from hydrogel-forming superabsorbent polymer particles, or absorbent structures containing them, to capture and distribute bodily fluids when the polymer is present at high concentrations in an absorbent article and subjected to mechanical pressures typically encountered during the use of the absorbent article. Effective permeability is calculated using Darcy's law and the steady-state flow method (see below). (See also, e.g., "Absorbency," ed. By PKChatterjee, Elsevier, 1982, Pages 42-43, and "Chemical Engineering Vol. II, Third Edition," JMCoulson and JFRichardson, Pergamon Press, 1978, Pages 122-127).

[0182] Unlike previously published methods, the sample is not pre-swollen, and therefore the hydrogel is not formed by pre-swelling hydrogel-forming superabsorbent polymer particles in synthetic urine; however, the measurement is initiated using 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 absorptive rate measurement system Figure 15 shows a dynamic effective transmittance and absorptance measurement system, referred to herein as a "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)) Receiving container 707 (5L glass beaker, Roth) Reservoir 708 (5L glass bottle, VWR) equipped with joint 709 and air intake opening tube 723. Control unit and console 705 (Conrad Electronics) Computerized data acquisition system 710 Piston / cylinder assembly 713 as described herein Control valve 714 (Burkert)

[0184] Figure 16 shows a piston / cylinder assembly 713, including a piston guide cover 801, a piston 802, and a cylinder 803. The cylinder 803 is made of clear polycarbonate (e.g., Lexan®) and has an inner diameter p of 6.00 cm (area = 28.27 cm²). 2The inner cylinder wall 850 is smooth, and the height of the cylinder r is approximately 7.50 cm. The bottom 804 of the cylinder 803 faces a US standard 400 mesh stainless steel screen cloth (not shown) (e.g., from Weisse and Eschrich) which is stretched biaxially to a taut state before being attached to the bottom 804 of the cylinder 803. The piston 802 consists 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 gap for hydrogel-forming particles to pass through. The piston body 805 is firmly mounted vertically in the center of the piston head 806. The diameter t of the piston body is approximately 2.2 cm. The piston body 805 is then inserted into the piston guide cover 801. The guide cover 801 has a POM (polyoxymethylene) ring 809 with a diameter that allows the piston 802 to slide freely while still maintaining the piston body 805 perfectly vertical and parallel to the cylinder wall 850, even when the piston 802 is placed on the cylinder 803 together with the guide cover 801. A top view of the piston head 806 is shown in Figure 16. The piston head 806 is intended to apply uniform pressure to the sample 718. The piston head 806 is also highly permeable to hydrophilic liquids so as not to restrict the flow of liquid during measurement. The piston head 806 consists of a US standard 400 mesh stainless steel screen cloth 903 (e.g., Weisse and Eschrich) stretched biaxially to a taut state and fixed to the piston head stainless steel outer ring 901. The entire underside of the piston is flat. Structural integrity and the bending resistance of the mesh screen are then ensured by stainless steel radial spokes 902. The height of the piston body 805 is selected such 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 across the entire area of ​​the cylinder 803.

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

[0186] The first inlet 812 allows the liquid level sensing 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] The second inlet 810 allows for the connection of the liquid tube 721 to supply liquid to the experiment. To ensure that the assembly of the piston 802 and cylinder 803 is performed consistently, a slit 814 is fabricated on cylinder 803 that coincides with a position marker 813 in the guide cover 801. In this way, the rotation angles of the cylinder and the guide cover are always the same.

[0188] Before each use, the stainless steel screen cloth 903 of 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 incorrect K(t) and absorption rate results and should not be used until the screen is replaced.

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

[0190] A reservoir 708, connected via a tube to a piston / cylinder assembly 713 and a control valve 714 that hold the sample, is used to deliver saline solution to cylinder 803 and maintain the saline solution level at a height k of 5.00 cm above the top surface of a screen mounted at the bottom of cylinder 804. The valve 714, a liquid level detection fiber 702, and a digital fiber sensor 703 are connected to a computerized acquisition system 710 via an operating unit 705. This allows the dynamic effective transmittance and absorptive rate measurement system to control the valve 714 using information from the liquid level detection fiber 702 and the digital fiber sensor 703, ultimately maintaining the liquid level at the 5 cm mark 808.

[0191] The reservoir 708 is positioned on the piston / cylinder assembly 713 so that a hydrohead of 5 cm is formed within 15 seconds of the start of the test and maintained within the cylinder throughout the test procedure. The piston / cylinder assembly 713 is positioned on the support ring 717 of the cover plate 716, and the first inlet 812 is secured in place by the coupling support 719. This gives the guide cover 801 a unique position. Furthermore, the position marker 813 also gives the cylinder 803 a unique position. The screen attached to the bottom of the cylinder 804 must be perfectly flat and horizontal. The support ring 717 must have an inner diameter that is small enough to firmly support the cylinder 803 when the cylinder is positioned on the support ring 717, but is greater than 6.0 cm so that it is outside the inner diameter of the cylinder. This is important to avoid the support ring 717 obstructing the flow of liquid in any way.

[0192] The saline solution applied to the sample 718 with a constant head of 5 cm can now flow freely from the piston / cylinder assembly 713 into the receiving container 707, which is positioned on a balance 704 with an accuracy of ±0.01 g. The digital output of the balance is connected to a computerized data acquisition system.

[0193] The thickness of the sample (caliper) is constantly measured by the digital laser sensor 701 for caliper measurement. The laser beam 720 of the digital laser sensor 701 is directed towards the center of the POM cover plate 811 of the piston body. By accurately arranging all components of the piston / cylinder assembly 713, the piston body 805 can be made completely parallel to the laser beam 720, and as a result, an accurate measurement of the thickness can be obtained.

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

[0195] Preparation of the test solution: Required chemicals: Sodium chloride (CAS#7647-14-5, e.g., Merck, catalog number 1.06404.1000) Linear C 12 ~C 14 Alcohol ethoxylate (CAS#68439-50-9, e.g., Lorodac® (Sasol, Italy)) Deionized H2O

[0196] Prepare a 10-liter solution containing 9.00 grams of NaCl per liter and 1.00 gram of linear C12 - C14 alcohol ethoxalate per liter in distilled water, and equilibrate it at 23°C ± 1°C for 1 hour. The surface tension is measured in three individual aliquots and must 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 must be used within 3 months from its preparation, and after that, it is considered expired.

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

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

[0199] SAP K(t) procedure: Measurement is performed under controlled laboratory conditions: 23°C ± 1°C / 45% RH ± 10%. Control of laboratory conditions can be done, for example, via Opus 20E from G.Lufft Mess-und Regeltechnik GmbH. The empty piston / cylinder assembly 713 is mounted in the circular opening of the cover plate 716 and supported by the support ring 717 at its lower outer circumference. The piston / cylinder assembly 713 is secured in place with the coupling support 719 so that the cylinder 803 and piston 802 are aligned at the appropriate angle. Reference caliper reading (r r The value 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 either placed (absorbent structure) or sprinkled onto the cylinder screen as described above (superabsorbent polymer particles). Then, the piston 802 assembled with the guide cover 801 is carefully placed inside the cylinder 803 by aligning the position marker 813 of the guide cover 801 with the slit 814 made in the cylinder 803.

[0201] The piston / cylinder assembly is secured in place by the connecting support 719, ensuring that the cylinder and piston are aligned at the appropriate angle.

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

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

[0204] After 21 minutes, the measurement of the first replication is completed normally, and the control valve 714 closes automatically. The piston / cylinder assembly 713 is removed, and the measurements of the second and third replications are always carried out as appropriate according to the same procedure. At the end of the measurement of the third replication, the control valve 714 stops the liquid flow, and the stopcock 722 of the reservoir 708 is closed. The collected raw data is stored in the form of a simple data table, which can then be easily imported into a program for further analysis, such as Excel 2003, SP3.

[0205] The following relevant information for each reading value is recorded in the data table. · Time from the start of the experiment · Weight of the liquid collected by the receiving container 707 on the balance 704 · Caliper of the sample 718

[0206] For the calculation of K(t) and the absorption rate, data from 100 seconds to the end of the test are used. The data collected in the first 100 seconds is not included in the calculation. Subsequently, the effective permeability K(t) and the absorption rate of the absorbent structure are 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 = 4929.31g / (cm·s 2 )

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

[0211] For the superabsorbent particle sample, the quality of particle spreading is evaluated using the caliper (d0) of the sample at time t i = 0.

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

[0213]

Equation

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

[0215] The apparent density can be measured according to the EDANA method NWSP251.0.R2(19) PSP (gravimetric measurement of flow rate and bulk density).

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

[0217]

Equation

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

[0219]

Equation

[0220] The absorption rate is calculated as follows.

[0221]

Equation

[0222] Dry sample volume (V s ) is intended to represent the skeletal volume of the sample, and therefore V s This is the actual volume occupied by solid material in the dried sample, excluding any pores and gaps that may exist.

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

[0224]

number

[0225] Alternatively, in the case of an unknown material composition, V s This can be easily calculated as follows:

[0226]

number

[0227] average density ρ s This can be determined by the specific gravity bottle method using a suitable non-swelling liquid of known density (ethanol in this invention). Since this technique cannot be performed on the same sample subsequently used for K(t) measurement, it is necessary to prepare a representative set of additional samples suitable for this experimental measurement. The average specific density is calculated using the average of at least three copies. If the average specific density is unknown, unless there is evidence of a significant deviation from these values ​​(e.g., in the case of superporous SAP particles, or in the case of absorbent cores with a very low SAP particle content), 1.50 g / cm³ is used for absorbent cores. 3 In the case of SAP, it is 1.60 g / cm³. 3 The value can be considered a good approximation.

[0228] As explained above, from U(t) calculated at different time steps, the absorption at any given time can be determined by linear interpolation. For example, one important output is the absorption at 20 minutes, also known as U20 (in units of g / g).

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

[0230] The effective transmittance is calculated from the rates 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), it 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 From this, the effective transmittance at a specific 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 (e.g., K5 or K10).

[0234] Another parameter derived from the data is Kmin, which is t i =100 seconds to t iThis is the minimum K(t) value measured across the entire curve at intervals up to 1200 seconds. This value is useful for calculating Kmin / K20, which is the ratio of the minimum effective transmittance to the transmittance at 20 minutes. This parameter represents transient gel blocking, which can occur in some samples. A value close to 1 indicates that transient gel blocking is not present, while a value close to 0 indicates that the material undergoes a strong decrease in effective transmittance when the liquid is first supplied.

[0235] The average values ​​of T20, T80%, K20, U20, and Kmin / K20 are recorded from three repetitions according to the required precision known to those skilled in the art.

[0236] Absorbent core K(t) test method The method described above can be easily adapted to directly measure the K(t) of the absorbent core without the need to separate the SAP from the bulk layer. The instrument system and test fluid are the same as those described above and are shown in the diagram of the SAP K(t) method described. This adapted test method was first described in European Patent No. 2,535,698(A1) (Ehrnsperger et al., P&G) for measuring the T15 and T20 of the absorbent core.

[0237] Method for extracting absorbent cores from absorbent materials The absorbent article is positioned on a plane. If the product includes features that prevent it from becoming flat (such as cuff elastics), these are cut at appropriate intervals to allow the product to become flat. Any layers attached to the absorbent core, such as a top sheet or back sheet, are removed from the absorbent core. To avoid damaging the core, these layers may be removed using a cooling spray with a cooling temperature of -50 to -60°C (such as "IT Icer" or "PRF 101 cold spray" available from Taerosol (Kangasala Finland)), for example, as shown in Figure 15 of European Patent No. 2535698. To avoid excessive damage to the absorbent core, the layers of material to be removed from the absorbent core are pulled out from the absorbent core in a geometric arrangement of 180-degree peels while cooling the adhesive material with the cooling spray. The spraying should be at least 1 second but no more than 5 seconds for each single portion of the layer of material. After removing each material, the remaining portion of the absorbent core was maintained under a pressure of 0.3 psi until the temperature returned to its initial value (TAPPI laboratory conditions).

[0238] The upper and / or lower layers of the absorbent core may be appropriately perforated to allow liquid flow through them (e.g., as shown in Figure 16 of European Patent No. 2535698). Perforation is carried out using a hot metal tip, also called a perforating tip, which includes a steel rod with a diameter H of 0.7 ± 0.2 mm. A standard paperclip bent around a solder tip, such as the CT60 / 621 available from ERSA GmbH (Wertheim, Germany), can be used for this purpose. The perforating tip should be set to a temperature of 310 ± 20°C. For example, the perforating tip is positioned in contact with the layer to be perforated for a short time at low pressure so that the layer is perforated by melting without affecting any of the other materials in the absorbent structure. Holes are produced using the same procedure in a square perforation pattern with a hole edge distance D of 1 ± 0.2 mm (e.g., as shown in Figure 17 of European Patent No. 2535698).

[0239] Visually inspect the integrity of each absorbent core using a backlight and discard any that are damaged. Examples of damage include cuts, holes, and wrinkles that were not present before the absorbent structure was removed from the absorbent article. Perforation of layers using a perforating tip is not considered damage unless it affects other layers. Substantial migration of superabsorbent polymer particles and fibers within the absorbent structure is also considered damage.

[0240] Next, circular samples are prepared by cutting these prepared K(t) absorbent cores according to the preparation of K(t) absorbent core samples described below.

[0241] Preparation of K(t)-absorbing 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 (e.g., the Electro-Hydraulic Alfa Cutter 240-10, available from Thwing-Albert instrument company (14W. Collings Ave. West Berlin, NJ 08091)) can be used.

[0242] The circular sample is carefully positioned flat on a screen (not shown) mounted at the bottom of a cylinder that occupies all available surfaces on the screen. To reproduce the common flow direction during use, it is important to position the circular sample such that the side in direct contact with the screen is the side that is usually further away from the liquid source during use. For example, in the case of a sample related to an absorbent item such as a diaper, the side that normally faces the wearer should be positioned at the top, while the side that faces the clothing 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 diameter 6.0 cm cannot be obtained from it, it is possible to join two absorbent cores of equal size to obtain the required minimum sample size. The two samples must be taken from the same position on two identical absorbent cores. The two absorbent cores should be joined via a straight edge, and if necessary, they should be cut to obtain such a straight edge. The intention is to reproduce a flat, homogeneous layer at the joined edges with no or minimal gaps. This joined layer is then handled according to the standard sample preparation described above, with further care taken to center the joint line on the cutting die to obtain two identical semicircles. It is important that both semicircles are carefully positioned inside the sample holder to reproduce a complete circle with no or minimal gaps, occupying the entire available surface on the screen. Both halves must be positioned so that their sides face the screen, as described above. However, in most embodiments, the sample consists of a single circular portion of the absorbent core.

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

[0244]

number

[0245] others The dimensions and values ​​disclosed herein should not be understood as being strictly limited to the exact numerical values ​​stated. Instead, unless otherwise indicated, each such dimension is intended to mean both the listed value and the functionally equivalent range encompassing that value. For example, a dimension disclosed as "40 mm" is intended to mean "approximately 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, as measured according to the SAP K(t) test method described herein, have a time to reach an absorption of 20 g / g in less than 220 seconds (SAP T20), 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 was measured according to the absorbent core K(t) test method described herein and yielded 6.0 × 10⁻⁶. －８ cm ２ It has ultra-high permeability (core K20), The concentration of the superabsorbent polymer particles in the central layer is determined by a micro-CT scan method disclosed herein, and the absorbent core (28) has a bimodal distribution in the z direction.

2. The absorbent core according to claim 1, wherein the absorbent core has a time (core T20) to reach an absorption of 20 g / g in less than 550 seconds, as measured according to the absorbent core K(t) test method described herein.

3. The absorbent core according to claim 1 or 2, wherein the central layer contains or is made of synthetic fibers.

4. The absorbent core according to any one of claims 1 to 3, wherein the superabsorbent polymer particles are produced from a crosslinked polyacrylate salt.

5. The superabsorbent polymer particles consist of at least 10 × 10 －７ cm ３ The absorbent core according to any one of claims 1 to 4, wherein the UPM is s / g, the UPM is measured by the urine permeability test described herein, and / or the superabsorbent polymer particles have an absorbent rate under pressure (AAP@0.7 psi) greater than 22 g / g as measured according to the EDANA standard test NWSP242.0R2(19).

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).

7. The absorbent core according to any one of claims 1 to 6, further comprising a packaging layer (3) that at least partially packages the upper layer, the bottom layer, and the center 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, wherein the absorbent core comprises superabsorbent polymer particles with a basis weight of at least 200 gsm.

10. The absorbent core according to any one of claims 1 to 9, 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 9, and the SAP T20 of the first central layer and the second central layer may be the same or different.

11. The absorbent core was measured by the absorbent core K(t) test method, yielding 0.6 g / cm³ (at 0.3 psi). ３ An absorbent core according to any one of claims 1 to 10, having a core density of less than [amount missing].

12. An absorbent article (200) comprising a top sheet (36), a back sheet (38), and an absorbent core (28) according to any one of claims 1 to 11.

13. A method for producing an absorbent core (28) according to any one of claims 1 to 11, A step of providing a bulky central layer (43), a liquid-permeable upper layer (41), and a bottom layer (42), A step of depositing a first layer of superabsorbent particles on the first side of the bulky central layer, The process of laminating the first side of the central layer with one of the liquid-permeable upper layer (41) and the bottom layer (42), The step includes laminating the second side of the central layer with the other of the liquid-permeable upper layer (41) or the bottom layer (42) that was not previously laminated, The deposited superabsorbent polymer particles are measured according to the SAP K(t) test method described herein, having a time to reach an absorption of 20 g / g in less than 220 seconds (SAP T20).

14. Measured using the thickness and density measurement method described herein, the initial density of the central layer was 4.14 kPa (0.6 psi) and 0.05 g / cm³. ３ ~0.15 g / cm ３ A method for producing an absorbent core according to claim 13, wherein the range is and / or the initial thickness of the central layer is greater than 0.30 mm at 4.14 kPa (0.6 psi).

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