Absorbent articles with improved absorption properties

Abstract

An absorbent article (10) comprising an absorbent core (14), the absorbent article (10) being divided into three sections: a front section (30), a back section (32), and a crotch section (34) disposed between the front section (30) and the back section (32), the absorbent core (14) having a dry thickness at the crotch point of the article of 0.2 to 5 mm, wherein the absorbent core (14) comprises at least 90% superabsorbent polymer particles, wherein the superabsorbent polymer particles comprised in the absorbent core (14) of the front portion (30) or the crotch portion (34) of the article or of the entire absorbent core (14) require a time to reach an uptake of 20 g / g (T20) of less than 240 s as measured according to the K(t) test method.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to absorbent articles such as disposable diapers, training pants and incontinence undergarments for adults comprising superabsorbent polymer particles. BACKGROUND

[0002] Absorbent articles, such as disposable diapers, training pants, and adult incontinence underwear, absorb and contain body exudates. Many absorbent articles, such as diapers, contain superabsorbent polymer material. Superabsorbent polymers are typically present in the core of the absorbent article in the form of particles. Superabsorbent polymer particles are capable of absorbing liquid and swelling when they come into contact with liquid exudates. However, it has been shown in the past that not all categories of superabsorbent polymer particles are equally suitable for use in an absorbent article.

[0003] It is known that in order to obtain absorbent articles with superabsorbent polymer particles that have good absorption and retention functions, the superabsorbent polymer particles must meet certain technical requirements.

[0004] The superabsorbent polymer particles must first be able to rapidly absorb the liquid excreta. The absorption rate of superabsorbent polymer particles has generally been determined in the prior art by measuring the free swelling rate (FSR) of the particles.

[0005] In addition to a high absorption rate, the superabsorbent polymer particles present in the core should also be highly permeable to liquids. Poor permeability of the superabsorbent polymer particles can cause leakage from the absorbent article due to gel blocking. Gel blocking can occur in the absorbent core when swelling superabsorbent polymer particles block the voids between the particles. In such a case, the liquid excreta cannot reach, or only very slowly, the underlying layers of superabsorbent polymer particles arranged in the core. The liquid excreta remains on the surface of the absorbent core and can therefore leak from the diaper.

[0006] In the prior art, the permeability of superabsorbent polymer particles was typically determined by measuring the salt solution flow conductivity (SFC) of the particles. This parameter is measured at equilibrium, i.e., the measurement is performed on a fully pre-swollen gel bed of superabsorbent polymer particles.

[0007] However, the inventors have now surprisingly discovered that superabsorbent polymer particles with high FSR and high SFC values do not automatically have fast uptake times of liquid excretions into the absorbent article, especially during the first surge, ie when the dry superabsorbent polymer particles first come into contact with the liquid.

[0008] The present invention therefore provides an absorbent article with improved absorption properties and thus reduced leakage, especially at the first surge, ie when the article starts to get wet.

[0009] DE 691 26 335 T2 discloses an absorbent article comprising superabsorbent material. A test method for determining absorbency is also described.

[0010] DE 694 01 325 T3 describes superabsorbent polymers and a process for their production. SUMMARY OF THE INVENTION

[0011] The present invention relates to an absorbent article comprising an absorbent core. The absorbent article is divided into three sections: a front section, a back section, and a crotch section located between the front section and the back section. The absorbent core has a dry thickness at the crotch point of the article of 0.2 to 5 mm. The absorbent core comprises at least 90% superabsorbent polymer particles. The superabsorbent polymer particles contained in the absorbent core in the front section or the crotch section of the article, or in the entire absorbent core, require a time to reach an uptake of 20 g / g (T20) of less than 240 s, as measured according to the K(t) test method. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a diaper according to an embodiment of the present invention. Fig. 2 is a cross-sectional view of the Fig. 1 shown diaper along the cutting line 2-2 of Fig. 1. Fig. 3 is a partial cross-sectional view of an absorbent core layer according to an embodiment of this invention. Fig. 4 is a partial cross-sectional view of an absorbent core layer according to another embodiment of this invention. Fig. Figure 5a is a partial sectional view of an absorbent core comprising a combination of the first and second absorbent core layers shown in Fig. 3 and Fig. 4 are shown. Fig. Figure 5b is a partial sectional view of an absorbent core comprising a combination of the first and second absorbent core layers shown in Fig. 3 and Fig. 4 are shown. Fig. Figure 6 is a schematic representation of a rheometer. Fig.Figure 7 is a partial cross-sectional side view of a suitable permeability measurement system for performing the dynamic effective permeability and uptake kinetics test. Fig. Figure 8 is a cross-sectional side view of a piston / cylinder assembly for use in performing the dynamic effective permeability and uptake kinetics test. Fig. 9 is a plan view of a piston head suitable for use in the Fig. 8 is suitable for the piston / cylinder arrangement shown. Fig. Figure 10 is a partial cross-sectional side view of a suitable permeability measurement system for performing the urine permeability measurement test. Fig. Figure 11 is a cross-sectional side view of a piston / cylinder assembly for use in performing the urine permeability test. Fig.12 is a plan view of a piston head adapted for use in the Fig. 11 is suitable for the piston / cylinder arrangement shown. Fig. 13 is a cross-sectional side view of the piston / cylinder assembly of Fig. 11, which is arranged on a glass filter plate for the source phase. Fig. Figure 14 is a cross-sectional view of a suitable flat pickup measurement system for performing the flat pickup test. Fig. Figure 15A is a graph depicting uptake in g / g as a function of time for Comparative Examples 1 and 2 and Example 1 as measured according to the K(t) test procedure. Fig. Figure 15B is a graph depicting uptake in g / g as a function of time for Comparative Examples 1 and 2 and Example 2 as measured according to the K(t) test procedure DETAILED DESCRIPTION

[0012] "Absorbent articles," as used herein, refer to devices that absorb and contain body exudates, and more specifically, refer to devices placed on or near the wearer's body to absorb and contain the various exudates from the body. Absorbent articles include diapers, training pants, adult incontinence undergarments, feminine hygiene products, and the like. As used herein, the term "body fluids" or "body exudates" includes, but is not limited to, urine, blood, vaginal discharge, breast milk, perspiration, and fecal material. In some embodiments of the present invention, the absorbent article is a diaper or training pant.

[0013] "Absorbent core," as used herein, refers to a structure disposed between a topsheet and a backsheet of an absorbent article for absorbing and retaining liquid received by the absorbent article. This structure may comprise one or more substrate layers, superabsorbent polymer particles disposed on the one or more substrate layers, and a thermoplastic composition typically disposed on the superabsorbent polymer particles. Typically, the thermoplastic composition is a thermoplastic adhesive material. In one embodiment, the thermoplastic adhesive material forms a fibrous layer at least partially in contact with the superabsorbent polymer particles on the one or more substrate layers and partially in contact with the one or more substrate layers.In one embodiment, auxiliary adhesives could be deposited on the one or more substrate layers prior to applying the superabsorbent polymer particles to enhance the adhesion of the superabsorbent polymer particles and / or the thermoplastic adhesive material to the respective substrate layer(s). The absorbent core may also include one or more cover layers such that the superabsorbent polymer particles are contained between the one or more substrate layers and the one or more cover layers. The one or more substrate layers and the cover layer(s) may comprise or consist of a nonwoven fabric. The absorbent core may further comprise odor control compounds.

[0014] In the embodiments wherein the absorbent article comprises, in addition to the absorbent core, a topsheet and / or a backsheet and / or an acquisition system, the absorbent core does not comprise the topsheet, the backsheet and / or the acquisition system.

[0015] In some embodiments, the absorbent core consists essentially of the one or more substrate layers, the superabsorbent polymer particles, the thermoplastic composition, optionally the auxiliary adhesive, optionally the cover layer(s), and optionally odor control compounds.

[0016] "Crotch point," as used herein, refers to the point of the article located in the center of the absorbent article at the intersection of the longitudinal axis and the transverse axis of the article. For the purpose of the invention, it should be understood that the crotch point of the article is not necessarily located in the center of the absorbent core, namely at the intersection of the longitudinal axis and the transverse axis of the absorbent core, especially when the absorbent core is not centered on the transverse axis of the article, i.e., when the absorbent core is shifted toward the front and / or back of the article.

[0017] “Airfelt” or “airfelt,” as used herein, refers to shredded wood pulp, which is a type of cellulose fiber.

[0018] "Superabsorbent polymer particles," as used herein, refers to crosslinked polymer materials that can absorb at least 10 times their weight of an aqueous 0.9% saline solution, as measured by the centrifuge retention capacity test (EDANA WSP 241.2-05). The superabsorbent polymer particles are in particulate form such that they are flowable in the dry state. Some superabsorbent polymer particles of the present invention are made from poly(meth)acrylic acid polymers. However, starch-based superabsorbent polymer particles, for example, are also included within the scope of the present invention.

[0019] "Thermoplastic adhesive material," as used herein, refers to a polymer composition from which fibers can be formed and onto which superabsorbent polymer particles can be applied to immobilize the superabsorbent polymer particles in both the dry and wet states. The thermoplastic adhesive material of the present invention preferably forms a fibrous network over the superabsorbent polymer particles.

[0020] "Front panel" and "back panel," as used herein, refer to the front and back waist regions of the absorbent article. The length of both the front panel and the back panel is one-third of the total length of the article, starting from the front and back waist edges, respectively. In embodiments wherein the front and / or back waist edges are not configured as a straight line parallel to the transverse axis of the absorbent article, the length of the absorbent article at or parallel to the longitudinal axis is determined starting from the point of the front waist edge closest to the transverse axis and ending at the point of the back waist edge closest to the transverse axis.

[0021] "Crotch section," as used herein, refers to the area of the article located in the middle of the article between the front and back sections. The length of the crotch section is one-third of the total length of the article.

[0022] A "nonwoven fabric," as used herein, refers to a film, sheet, or mat product made of directionally or randomly oriented fibers bonded together by friction and / or cohesion and / or adhesion, and excludes paper and products that are woven, knitted, tufted, joined by stitches using binder yarns or threads, or felted by wet milling, whether additionally needled or not. The fibers may be of natural or synthetic origin and may be stapled or continuous filaments or formed in situ. Commercially available fibers have diameters ranging from less than about 0.001 mm to greater than about 0.2 mm and come in several different forms: short fibers (known as staple or chopped fibers), continuous individual fibers (threads or monofilaments), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn).Nonwovens can be manufactured using many processes, such as meltblowing, melt spinning, solvent spinning, electrospinning, and carding. The basis weight of nonwovens is typically expressed in grams per square meter.

[0023] "Attached," as used herein, refers to configurations wherein a first member is directly attached to another member by directly attaching the first member to a second member, or wherein a first member is indirectly attached to a second member by attaching the first member to one or more intermediate third members, which in turn are attached to the second member. The attachment means may include adhesive bonds, heat seals, pressure bonds, ultrasonic bonds, dynamic mechanical bonds, or any other suitable attachment means or combinations of these attachment means as known in the art.

[0024] Fig. 1 is a plan view of an absorbent article 10 according to some embodiments of the present invention. The absorbent article 10 is shown in its flat, uncontracted state (i.e., without elastically induced contraction), and portions of the absorbent article 10 are cut away to more clearly show the underlying structure of the diaper 10. A portion of the absorbent article 10 contacting a wearer faces the viewer in Fig. 1. The absorbent article 10 generally comprises a base unit 12 and an absorbent core 14 disposed within the base unit 12.

[0025] The basic unit 12 of the absorbent article 10 in Fig.1 may comprise the main body of the absorbent article 10. The chassis 12 of the diaper may comprise an outer cover 16 including a topsheet 18, which may be liquid pervious, and / or a backsheet 20, which may be liquid impervious. The absorbent core 14 may be enclosed between the topsheet 18 and the backsheet 20. The chassis 12 may further include side panels 22, elasticized leg cuffs 24, and an elastic waist feature 26.

[0026] The leg cuff 24 and the elastic waist feature 26 may typically each include elastic members 28. One end portion of the absorbent article 10 is configured as a front portion 30, and the other end portion is configured as a back portion 32 of the absorbent article 10. The intermediate portion of the absorbent article 10 is configured as a crotch portion 34, which extends longitudinally between the front and back portions 30 and 32.

[0027] The absorbent article 10 is in Fig.1 with its longitudinal axis 36 and its transverse axis 38. The perimeter 40 of the absorbent article 10 is defined by the outer edges of the absorbent article 10, with the longitudinal edges 42 running generally parallel to the longitudinal axis 36 of the absorbent article 10 and the front and back waist edges 43 and 44 between the longitudinal edges 42 running generally parallel to the transverse axis 38 of the absorbent article 10. The chassis 12 may also include a fastening system, which may include at least one fastening element 46 and at least one landing region 48.

[0028] The absorbent article 10 may also include other features known in the art, including front and back wing panels, waist closure features, elastics, and the like, to provide enhanced fit, containment, and aesthetic properties. Such additional features are well known in the art and are described, for example, in U.S. Pat. Nos. 3,860,003 and 5,151,092.

[0029] To secure the absorbent article 10 in place on the wearer, at least a portion of the front panel 30 may be secured with the fastener 46 to at least a portion of the back panel 32 to form leg opening(s) and an article waist. When secured, the fastening system carries a tensile load around the article waist. The fastening system may allow an article user to hold an element of the fastening system, such as the fastener 46, and connect the front panel 30 to the back panel 32 at at least two locations. This may be achieved by manipulating the bond strengths between the fastener elements.

[0030] According to certain embodiments, the absorbent article 10 may be provided with a resealable fastening system or, alternatively, may be provided in the form of a pant-type diaper. If the absorbent article is a diaper, it may comprise a resealable fastening system attached to the base unit to secure the diaper to the wearer. If the absorbent article is a pant-type diaper, the article may comprise at least two side panels joined together to form a pant. The absorption core

[0031] The absorbent core comprises at least 90% by weight of superabsorbent polymer particles based on the weight of the core, excluding the weight of any nonwoven web, such as substrate layers and cover layers, that the absorbent core may comprise.

[0032] In some preferred embodiments, the absorbent core comprises at least 95% by weight of superabsorbent polymer particles.

[0033] In some more preferred embodiments, the absorbent core comprises at least 98% by weight superabsorbent polymer particles.

[0034] In some even more preferred embodiments, the absorbent core comprises at least 99% by weight superabsorbent polymer particles.

[0035] These embodiments are particularly preferred because absorbent articles comprising a high percentage of superabsorbent polymer particles typically have a lower dry thickness than conventional absorbent articles with a higher amount of conventional absorbent materials, such as airfelt and the like, in addition to the superabsorbent polymer particles. The lower thickness helps improve fit and comfort when the article is applied to the wearer.

[0036] In some embodiments, the absorbent core comprises an average amount of superabsorbent polymer particles per area of 50 to 2200 g / m 2 or 100 to 1500 g / m 2 or 200 to 1000 g / m 2 .

[0037] In some embodiments, the absorbent core comprises an average amount of superabsorbent polymer particles per area of 100 to 1500 g / m 2 or 150 to 1000 g / m 2 or 200 to 900 g / m 2 or 400 to 700 g / m 2in the crotch portion of the article. The absorbent article comprises a sufficient amount of superabsorbent polymer particles to exhibit good absorption properties, and it is thin enough to provide fit and comfort for the wearer. However, superabsorbent polymer particles are also present in the front and back portions, although the amount may be low (or even zero), particularly in the back portion. In some embodiments, the absorbent core comprises an average amount of superabsorbent polymer particles per surface area of less than 300 g / m 2 or less than 200 g / m 2 , as an alternative from 25 to 300 g / m 2 or 50 to 200 g / m 2 or 50 to 100 g / m 2 in the back section of the article.

[0038] In some embodiments, the absorbent core may further comprise small amounts of an absorbent material other than superabsorbent polymer particles, e.g., airfelt.

[0039] In some embodiments, the absorbent core typically comprises less than 5 wt.% airfelt, alternatively less than 2 wt.%, and alternatively is airfelt-free.

[0040] The absorbent core has a dry thickness at the crotch point of the article of less than 10 mm, preferably less than 5 mm, more preferably less than 3 mm, even more preferably less than 1.5 mm, alternatively from 0.1 to 10 mm, preferably from 0.2 to 5 mm, more preferably from 0.3 to 3 mm, even more preferably from 0.5 to 1.5 mm, as measured according to the test method set forth below. The absorbent core is thus sufficiently thin compared to conventional airfelt absorbent cores. This significantly improves fit and comfort. The superabsorbent polymer particles

[0041] The superabsorbent polymer particles suitable for the present invention can take numerous shapes. The term "particles" refers to granules, fibers, flakes, beads, powders, platelets, and other shapes and forms known to those skilled in the art regarding superabsorbent polymer particles. In some embodiments, the superabsorbent polymer particles can be in the form of fibers, i.e., elongated, non-circular superabsorbent polymer particles. In these embodiments, the superabsorbent polymer particle fibers have a minor dimension (i.e., diameter of the fiber) of less than about 1 mm, typically less than about 500 µm, and alternatively, less than 250 µm down to 50 µm. The length of the fibers is preferably from about 3 mm to about 100 mm. The fibers can also be in the form of a long thread, which may be woven.

[0042] Alternatively, in some preferred embodiments, superabsorbent polymer particles of the present invention are spherical particles. According to the present invention, and unlike fibers, "spherical particles" have a longest and a shortest dimension with a longest-to-shortest particle dimension ratio in the range of 1-5, where a value of 1 would equate to a perfectly spherical particle and 5 would allow for some deviation from such a spherical particle. In such embodiments, the superabsorbent polymer particles may have a particle size of less than 850 µm, or from 50 to 850 µm, alternatively from 100 to 500 µm, and alternatively from 150 to 300 µm, as measured according to EDANA Method WSP 220.2-05.Superabsorbent polymer particles with a relatively small particle size help to increase the surface area of the absorbent material that is in contact with liquid excretions and therefore support rapid absorption of liquid excretions.

[0043] The superabsorbent polymer particles suitable for use in the present invention include a variety of water-insoluble but water-swellable polymers capable of absorbing large amounts of liquid. Such polymer materials are well known in the art.

[0044] Suitable superabsorbent polymer particles can be prepared, for example, by reversed-phase suspension polymerizations, as described in US 4,340,706 A and US 5,849,816 A, or by spray or other gas-phase dispersion polymerizations, as described in US 2009 / 0 192 035 A1, US 2009 / 0 258 994 A1, and US 2010 / 0 068 520 A1. In some embodiments, suitable superabsorbent polymer particles can be produced by current prior art manufacturing processes, as more specifically described from page 12, line 23 to page 20, line 27 of WO 2006 / 083584.

[0045] In some embodiments, the surface of the superabsorbent polymer particles may be coated. In such embodiments, the coating makes the surface tacky, so that the superabsorbent polymer particles cannot easily rearrange upon wetting (thus preventing them from blocking voids).

[0046] In some embodiments, the superabsorbent polymer particles may be coated with a cationic polymer. Some cationic polymers may comprise polyamine or polyimine materials that are reactive with at least one component present in body fluids, particularly urine. Some polyamine materials may be selected from the group consisting of (1) polymers with primary amine groups (e.g., polyvinylamine, polyallylamine); (2) polymers with secondary amine groups (e.g., polyethyleneimine); and (3) polymers with tertiary amine groups (e.g., poly-N,N-dimethylalkylamine).

[0047] Practical examples of the cationic polymer include polyethyleneimine, a modified polyethyleneimine crosslinked with epihalohydrin in a water-soluble region, polyamine, a modified polyamidoamine grafted with ethyleneimine, polyetheramine, polyvinylamine, polyalkylamine, polyamidopolyamine, and polyallylamine.

[0048] In some embodiments, a cationic polymer has a weight-average molecular weight of at least 500, alternatively 5,000, and alternatively 10,000 or more. Cationic polymers with a weight-average molecular weight of greater than 500 or more are not limited to polymers that exhibit a single peak in a gel permeation chromatography molecular weight analysis, and polymers with a weight-average molecular weight of 500 or more may be used even if they exhibit multiple peaks.

[0049] A preferred amount of the cationic polymer is in a range of about 0.05 to 20 parts by weight relative to 100 parts by weight of superabsorbent polymer particles, more preferably from about 0.3 to 10 parts by weight, and most preferably from about 0.5 to 5 parts by weight.

[0050] In some embodiments, the superabsorbent polymer particles may be coated with chitosan materials as disclosed in US 7,537,832 B2.

[0051] In some other embodiments, the superabsorbent polymer particles may be mixed bed ion exchange absorbent polymers such as that disclosed in WO 99 / 34841 and WO 99 / 34842.

[0052] As mentioned above, superabsorbent polymer particles with high SFC and FSR values do not automatically lead to rapid absorption times of liquid excretions, especially during the first surge, i.e., when the dry superabsorbent polymer particles first come into contact with the liquid. Dry superabsorbent polymer particles generally absorb water more slowly than wetted superabsorbent polymer particles because the diffusivity of water into dry superabsorbent polymer particles is lower than the diffusivity of water into wetted superabsorbent polymer particles.

[0053] To date, the absorption properties of dry superabsorbent polymer particles have not been investigated with respect to initial absorption. Instead, the focus has been on saline flow conductivity (SFC), which was determined at equilibrium and thus at a stage far removed from initial liquid absorption. For absorbent cores containing a significant amount of air felt in addition to superabsorbent polymer particles, temporary storage of liquid entering the absorbent core is provided by the air felt, allowing the superabsorbent polymer particles to absorb liquid from the surrounding air felt with a certain delay.However, even in airfelt-free absorbent articles disclosed in the prior art, the permeability of the superabsorbent polymer particles was always measured at equilibrium, thus failing to take into account the behavior of dry superabsorbent polymer particles upon initial contact with liquid. The present inventors have thoroughly investigated the behavior of superabsorbent polymer particles upon initial contact with liquid. They have discovered that certain, yet not publicly available, superabsorbent polymer particles perform better when used in absorbent cores containing no or very low amounts of airfelt. This improved performance leads to improved liquid absorption, thereby reducing the risk of leakage.It has been shown that better superabsorbent polymer particles can be described in terms of the time it takes for the dry superabsorbent polymer particles to reach a certain liquid absorption when absorption occurs against a confining pressure. This now makes it possible to conveniently and easily select these newly developed superabsorbent polymer particles, which are specifically suited for use in absorbent cores with little or no air felt, without the need for additional, expensive research and testing.

[0054] According to the present invention, the superabsorbent polymer particles contained in the absorbent core in the front portion or the crotch portion of the article or in the entire absorbent core require a time to reach an absorption of 20 g / g (T20) of less than 240 s, or less than 215 s, or less than 190 s, or less than 165 s, or less than 140 s, as measured according to the K(t) test method set forth below.

[0055] In some embodiments, the time to reach an uptake of 20 g / g (T20) is 40 to 240 s, or 50 to 290 s, or 60 to 165 s, as measured according to the K(t) test method set forth below.

[0056] In some embodiments, the uptake of the superabsorbent polymer particles contained in the absorbent core in the front portion or the crotch portion of the article or in the entire absorbent core at 20 min (U20) is 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 K(t) test method set forth below.

[0057] Absorbent articles comprising such superabsorbent polymer particles have improved absorption properties and therefore exhibit less leakage than prior art absorbent articles, especially during the first surge. Such superabsorbent polymer particles are particularly suitable for use in absorbent articles.

[0058] In some embodiments, the superabsorbent polymer particles have an effective permeability at 20 minutes (K20) of at least 5·10 -8 cm 2 or at least 7·10 -8 cm2 or at least 8.5·10 -8 cm 2 or 5·10 -8 cm 2 up to 1·10 -6 cm 2 or 7·10 -8 cm 2 up to 5·10 -7 cm 2 or 8.5·10 -8 up to 1·10 -7 , as measured according to the K(t) test procedure set out below.

[0059] In some embodiments, the superabsorbent polymer particles have a ratio between the minimum effective permeability and the permeability at 20 minutes (Kmin / K20 ratio) of greater than 0.75, or greater than 0.8, or greater than 0.9, as measured according to the K(t) test method set forth below. In such embodiments, transient gel blocking is minimal, and liquid precipitates can quickly pass through the interparticle voids throughout the swelling process, and especially at the beginning of the swelling phase, which is most critical for the first surge.

[0060] In embodiments having more than one type of superabsorbent polymer particles, the K(t) test method is performed on a mixture of the multiple types of superabsorbent polymer particles present in the front portion or the crotch portion or the entire absorbent core.

[0061] In some embodiments, the superabsorbent polymer particles have an equilibrium permeability expressed as a RPM (urine permeability measurement) of greater than 50, alternatively greater than 60, or 50 to 500, or 55 to 200, or 60 to 150 RPM units, where 1 RPM unit is 1 x 10 -7 (cm 3 .s) / g.

[0062] The UPM value is measured according to the UPM test method outlined below. This method is similar to the prior art SFC test method. The UPM test method typically measures the flow resistance of a pre-swollen layer of superabsorbent polymer particles, meaning the flow resistance is measured at equilibrium. Therefore, such superabsorbent polymer particles with a high UPM value exhibit high permeability when a significant volume of the absorbent article is already wetted by liquid excreta. These embodiments demonstrate good absorption properties not only during the first surge, but also during subsequent surges.

[0063] In some embodiments, the superabsorbent polymer particles may have a free swell rate (FSR) of greater than 0.1 g / g / s, or from 0.1 to 2 g / g / s, or from 0.3 to 1 g / g / s, or from 0.3 to 0.6 g / g / s, or from 0.4 to 0.6 g / g / s.

[0064] The free-swell rate of the superabsorbent polymer particles is measured according to the FSR test method outlined below. Superabsorbent polymer particles with high free-swell rate values can absorb liquid faster without confining pressure. Unlike the K(t) test method, no external pressure is applied to the gel bed to measure the free-swell rate. Superabsorbent polymer particles with an FSR value that is too low may require as much as 240 s to reach an uptake of 20 g / g, as measured according to the K(t) test method of the present invention, and consequently may not be able to absorb liquid excreta as quickly as necessary. However, as mentioned above, superabsorbent polymer particles with a high FSR value do not automatically result in high uptake values, as measured according to the K(t) test method.

[0065] In some embodiments, the superabsorbent polymer particles may have a CRC (Centrifuge Retention Capacity) value of greater than 20 g / g, or greater than 24 g / g, or from 20 to 50 g / g, or from 20 to 40 g / g, or from 24 to 30 g / g, as measured according to EDANA Method WSP 241.2-05. The CRC measures the liquid absorbed by the superabsorbent polymer particles when freely swelling in excess liquid.

[0066] Superabsorbent polymer particles with a high CRC value may be desirable because fewer superabsorbent polymer particles are required to facilitate a required total capacity for liquid absorption.

[0067] In some embodiments, the absorbent article may have a first gush acquisition time of less than 30 seconds, alternatively less than 27 seconds, as measured according to the flat acquisition test method set forth below. This acquisition time is measured on a baby diaper intended for wearers weighing in the range of 8 to 13 kg ± 20% (such as Pampers Active Fit Size 4 or other Pampers Size 4 Baby Diapers, Huggies Size 4 Baby Diapers, or Size 4 Baby Diapers of most other trade names). An absorbent article comprising superabsorbent polymer particles that take less than 240 seconds to achieve an acquisition of 20 g / g, as measured according to the K(t) test method, may provide faster acquisition times, particularly at the first gush, and thus less leakage than the prior art absorbent article, as shown in the "Examples" section of the application. Structure of the absorption core

[0068] The following is an example of an absorbent core of the present invention. However, the present invention is not limited to such absorbent cores.

[0069] In some embodiments, the absorbent core 14 includes an absorbent layer 60, as shown in Fig. 3 and Fig.4. The substrate layer 64 of the absorbent layer 60 may be referred to as a dusting layer and has a first surface 78 facing the backsheet 20 of the diaper 10 and a second surface 80 facing the superabsorbent polymer particles 66. According to some embodiments, the substrate layer 64 is a nonwoven material, such as a multilayer nonwoven material having melt-spun layers as outer layers and one or more meltblown layers between the melt-spun layers, including, but not limited to, SMS material comprising a melt-spun layer, a meltblown layer, and another melt-spun layer. The absorbent layer 60 may have a topsheet layer 70, as shown in Fig.4. The cover layer 70 may be a nonwoven material, such as a multilayer nonwoven material with melt-spun layers as outer layers and one or more meltblown layers between the melt-spun layers, including, but not limited to, SMS material comprising a melt-spun layer, a meltblown layer, and another melt-spun layer. In some embodiments, the substrate layer 64 and the cover layer 70 are made of the same material.

[0070] As in Fig. 3 and Fig.4, the superabsorbent polymer particles 66 may be deposited on the substrate layer 64 in groupings 90 of particles including land areas 94 and interconnecting areas 96 between the land areas 94. As defined herein, land areas 94 are areas where the thermoplastic adhesive material does not directly contact the nonwoven substrate or the auxiliary adhesive; interconnecting areas 96 are areas where the thermoplastic adhesive material directly contacts the nonwoven substrate or the auxiliary adhesive. The interconnecting areas 96 contain little or no superabsorbent polymer particles 66. The land areas 94 and interconnecting areas 96 may have a variety of shapes, including, but not limited to, circular, oval, square, rectangular, triangular, and the like.

[0071] As a result, the thermoplastic adhesive material 68 provides voids for holding the superabsorbent polymer particles 66, thereby immobilizing this material. In another aspect, the thermoplastic adhesive material 68 is bonded to the substrate layer 64, thus securing the superabsorbent polymer particles 66 to the substrate layer 64. In some other embodiments, the thermoplastic adhesive material 68 also at least partially penetrates both the superabsorbent polymer particles 66 and the substrate layer 64, thereby providing further immobilization and securing.

[0072] In some other embodiments, the absorbent core 14 may comprise two absorbent layers, a first absorbent layer 60 and a second absorbent layer 62. As best shown in Fig. 5A and Fig.5B, the first absorbent layer 60 of the absorbent core 14 comprises a substrate layer 64, superabsorbent polymer particles 66 on the substrate layer 64, and a thermoplastic adhesive material 68 on the superabsorbent polymer particles 66. Although not shown, the first absorbent layer 60 may also comprise a cover layer such as that shown in Fig. 4 shown cover layer 70.

[0073] Likewise, as best seen in Fig. 5A and Fig. 5B, the second absorbent layer 62 of the absorbent core 14 may also include a substrate layer 72, superabsorbent polymer particles 74 on the second substrate layer 72, and a thermoplastic adhesive material 76 on the superabsorbent polymer particles 74. Although not shown, the second absorbent layer 62 may also include a cover layer, such as that shown in Fig.4. As mentioned above, the substrate layer 64 of the first absorbent layer 60 may be referred to as a dusting layer and has a first surface 78 facing the backsheet 20 of the diaper 10 and a second surface 80 facing the superabsorbent polymer particles 66. Similarly, the substrate layer 72 of the second absorbent layer 62 may be referred to as a core cover and has a first surface 82 facing the topsheet 18 of the diaper 10 and a second surface 84 facing the superabsorbent polymer particles 74. The first and second substrate layers 64 and 72 may be peripherally adhesively adhered to each other to form a wrap around the superabsorbent polymer particles 66 and 74 to retain the superabsorbent polymer particles 66 and 74 within the absorbent core 14.

[0074] The area of the absorbent core 14 comprising the superabsorbent polymer particles can vary depending on the desired application of the absorbent core 14 and the particular absorbent article 10 into which it may be incorporated. However, in some embodiments, the area of the superabsorbent polymer particles extends substantially across the entire absorbent core 14. In some alternative embodiments, the area of the superabsorbent polymer particles extends completely across the absorbent core 14 in the crotch portion 34 of the absorbent article 10, while the area of the superabsorbent polymer particles does not extend completely across the absorbent core 14 in the front and back portions of the absorbent article 10.

[0075] The first and second absorbent layers 60 and 62 may be combined to form the absorbent core 14 such that the layers are staggered such that the superabsorbent polymer particles 66 on the substrate layer 64 and the superabsorbent polymer particles 74 on the substrate layer 72 are distributed substantially continuously over the area of the superabsorbent polymer particles, as shown in Fig. 5A and Fig.5B. In some embodiments, the superabsorbent polymer particles 66 and 74 are distributed substantially continuously across the surface of the superabsorbent polymer particles, although superabsorbent polymer particles 66 and 74 are distributed discontinuously across the first and second substrate layers 64 and 72 in groupings 90. In some embodiments, the absorbent layers may be staggered such that the land regions 94 of the first absorbent layer 60 face the bonding surfaces 96 of the second absorbent layer 62 and the land surfaces of the second absorbent layer 62 face the bonding regions 96 of the first absorbent layer 60, as shown in Fig. 5A and Fig.5B. When the land surfaces 94 and the connecting surfaces 96 are suitably sized and arranged, the resulting combination of superabsorbent polymer particles 66 and 74 is a substantially continuous layer of superabsorbent polymer particles over the surface of the superabsorbent polymer particles of the absorbent core 14 (i.e., the first and second substrate layers 64 and 72 do not form a plurality of pockets each containing an array 90 of superabsorbent polymer particles 66 and 74 therebetween), as in Fig. 5A.

[0076] The amount of superabsorbent polymer particles may, but need not, vary along the length of the core, typically profiling the core along its longitudinal direction. It has been found that for most absorbent articles, such as diapers, liquid removal occurs predominantly in the front half of the diaper. The front half of the absorbent core 14 should therefore exhibit the greatest absorbent performance of the core. Thus, according to certain embodiments, the front half of the absorbent core 14 may comprise more than about 60% of the superabsorbent polymer particles, or more than about 65%, 70%, 75%, 80%, 85%, or 90% of the superabsorbent polymer particles.

[0077] Typically, the thermoplastic adhesive material can serve to at least partially immobilize the superabsorbent polymer particles in both the dry and wet states. The thermoplastic adhesive material can be substantially uniformly disposed between the superabsorbent polymer particles. However, typically, the thermoplastic adhesive material can be provided as a fibrous layer that is at least partially in contact with the superabsorbent polymer particles and partially in contact with the substrate layer(s). Typically, the thermoplastic adhesive material of the present invention forms a fibrous network over the superabsorbent polymer particles. As described, for example, in Fig. 5A and Fig.5B, the superabsorbent polymer particles 66 and 74 are typically provided as a discontinuous layer, and a layer of fibrous thermoplastic adhesive material 68 and 76 is placed on the layer of superabsorbent polymer particles 66 and 74 such that the thermoplastic adhesive material 68 and 76 is in direct contact with the superabsorbent polymer particles 66 and 74, but also in direct contact with the second surfaces 80 and 84 of the substrate layers 64 and 72, wherein the substrate layers are not covered by the superabsorbent polymer particles 66 and 74. This imparts a substantially three-dimensional structure to the fibrous layer of thermoplastic adhesive material 68 and 76, which itself is essentially a two-dimensional structure of relatively small thickness compared to the length and width dimensions.In other words, the thermoplastic adhesive material 68 and 76 ripples between the superabsorbent polymer particles 68 and 76 and the second surfaces of the substrate layers 64 and 72.

[0078] The thermoplastic adhesive material can provide voids to enclose the superabsorbent polymer particles, thereby immobilizing these particles. From a further aspect, the thermoplastic adhesive material is bonded to the substrate layer(s), thus fixing the superabsorbent polymer particles to the substrate layer(s). Some thermoplastic adhesive materials also penetrate both the superabsorbent polymer particles and the substrate layer(s), thereby providing further immobilization and fixation. Although the thermoplastic adhesive materials disclosed herein provide good enhanced wet immobilization (i.e., immobilization of absorbent material when the article is at least partially loaded), these thermoplastic adhesive materials can, of course, also provide very good immobilization of absorbent material when the absorbent core is dry.The thermoplastic adhesive material can also be called hot melt adhesive.

[0079] Without wishing to be bound by theory, it has been found that the thermoplastic adhesive materials best suited for immobilizing superabsorbent polymer particles combine good cohesive and adhesive behavior. Good adhesion can promote good contact between the thermoplastic adhesive material and the superabsorbent polymer particles and the substrate layer(s). Good cohesion reduces the likelihood of adhesive fracture, particularly in response to external forces, and specifically in response to stretching. When the absorbent core absorbs liquid, the superabsorbent polymer particles swell, subjecting the thermoplastic adhesive material to external forces. The thermoplastic adhesive material can accommodate such swelling without fracture and without imparting excessive compressive forces that would prevent the superabsorbent polymer particles from swelling.

[0080] The thermoplastic adhesive material may comprise, in its entirety, a single thermoplastic polymer or a blend of thermoplastic polymers having a softening point, as determined by ASTM Method D-36-95 "Ring and Ball," in the range between 50°C and 300°C, or alternatively, the thermoplastic adhesive material may be a hot melt adhesive comprising at least one thermoplastic polymer in combination with other thermoplastic diluents, such as adhesive resins, plasticizers, and additives such as antioxidants. In some embodiments, the thermoplastic polymer typically has a molecular weight (MW) greater than 10,000 and a glass transition temperature (Tg) typically below room temperature or -6°C > Tg < 16°C. In some embodiments, typical concentrations of the polymer in a hot melt adhesive range from about 20 to about 40 wt. %.In some embodiments, the thermoplastic polymers can be insensitive to water. Exemplary polymers are (styrenic) block copolymers, including ABA triblock structures, AB diblock structures, and (AB)n radial block copolymer structures, where the A blocks are non-elastomeric polymer blocks, typically comprising polystyrene, and the B blocks are unsaturated conjugated diene or (partially) hydrogenated versions thereof. The B block is typically isoprene, butadiene, ethylene / butylene (hydrogenated butadiene), ethylene / propylene (hydrogenated isoprene), or a mixture thereof.

[0081] Other suitable thermoplastic polymers that can be used are metallocene polyolefins, which are ethylene polymers produced using single-site or metallocene catalysts. In these, at least one comonomer can be polymerized with ethylene to produce a copolymer, terpolymer, or higher polymer. Also suitable are amorphous polyolefins or amorphous polyalphaolefins (APAO), which are homopolymers, copolymers, or terpolymers of C2 to C8 alpha olefins.

[0082] In some embodiments, the thermoplastic adhesive material is in the form of fibers. In some of these embodiments, the fibers have an average thickness of about 1 to about 50 micrometers or about 1 to about 35 micrometers and an average length of about 5 to about 50 mm or about 5 mm to about 30 mm. To improve the adhesion of the thermoplastic adhesive material to the substrate layer(s) or to another layer, particularly another nonwoven layer, such layers may be pretreated with an auxiliary adhesive.

[0083] In certain embodiments, the thermoplastic adhesive material is used in an amount between 0.5 and 30 g / m 2 , between 1 and 15 g / m 2 , between 1 and 10 g / m 2 or even between 1.5 and 5 g / m 2 per substrate layer applied to the substrate layer.

[0084] An exemplary thermoplastic adhesive material 68 and 76 may have a storage modulus G', measured at 20°C, of at least 30,000 Pa and less than 300,000 Pa, or less than 200,000 Pa, or between 140,000 Pa and 200,000 Pa, or less than 100,000 Pa. In another aspect, the storage modulus G', measured at 35°C, may be greater than 80,000 Pa. In another aspect, the storage modulus G', measured at 60°C, may be less than 300,000 Pa and greater than 18,000 Pa, or greater than 24,000 Pa, or greater than 30,000 Pa, or greater than 90,000 Pa. From a further perspective, the storage modulus G', measured at 90 °C, may be less than 200,000 Pa and more than 10,000 Pa, or more than 20,000 Pa, or more than 30,000 Pa. The storage modulus, measured at 60 °C and 90 °C, may be a measure of the dimensional stability of the thermoplastic adhesive material at elevated ambient temperatures.This value is particularly important when the absorbent product is used in a hot climate where the thermoplastic adhesive material would lose its integrity if the storage modulus G' is not high enough at 60 °C and 90 °C.

[0085] G' is measured using a rheometer as described in Fig.6 is shown schematically for the purpose of general illustration only. The rheometer 627 is capable of applying a shear stress to the adhesive and measuring the resulting strain (shear deformation) response at constant temperature. The adhesive is placed between a Peltier element serving as the lower, stationary plate 628 and an upper plate 629 with a radius R of 10 mm, which is connected to the rotating shaft of a motor to generate the shear stress. The gap between the two plates has a height H of 1500 micrometers. The Peltier element allows the temperature of the material to be controlled (+0.5 °C). The strain amplitude is set to 0.05%, the strain frequency to 1 Hz, and the cooling rate to 2 °C / min (with an initial temperature of 150 °C or higher and a final temperature of -5 °C).

[0086] The absorbent core may also comprise an auxiliary adhesive, not shown in the illustrations. The auxiliary adhesive may be deposited on the substrate layer(s) before the superabsorbent polymer particles are applied to the substrate layer(s) to improve the adhesion of the superabsorbent polymer particles and the thermoplastic adhesive material to the respective substrate layer. The auxiliary adhesive may also assist in immobilizing the superabsorbent polymer particles and may comprise the same thermoplastic adhesive material as described above or may comprise other adhesives, including, but not limited to, sprayable hot melt adhesives. An example of a commercially available auxiliary adhesive is HB Fuller Co. (St. Paul, MN, USA), Item No. HL-1620-B.The auxiliary adhesive may be applied to the substrate layer(s) by any suitable means, but according to some embodiments may be applied in about 0.5 to about 1 mm wide slits spaced about 0.5 to about 2 mm apart. The recording system

[0087] In some embodiments, the absorbent article 10 may include an acquisition system 50 disposed between the topsheet 18 and the absorbent core 14, as shown in Fig. 1 and Fig. 2. The absorption system 50 need not include superabsorbent polymer particles.

[0088] The acquisition system 50 may be in direct contact with the absorbent core 14. The acquisition system 50 may comprise a single layer or multiple layers, such as an upper acquisition layer 52 facing the wearer's skin and a lower acquisition layer 54 facing the wearer's clothing, as shown in Fig. 1 and Fig.2. In some embodiments, the containment system 50 may function to contain a surge of liquid, such as a stream of urine. In other words, the containment system 50 may serve as a temporary reservoir for liquid until the absorbent core 14 can absorb the liquid.

[0089] In some embodiments, the acquisition system 50 may comprise chemically cross-linked cellulosic fibers. Such cross-linked cellulosic fibers may exhibit favorable absorption properties. Exemplary chemically cross-linked cellulosic fibers are disclosed in US Pat. No. 5,137,537. In some embodiments, the chemically cross-linked cellulosic fibers are cross-linked with between about 0.5 mol% and about 10.0 mol% of a C2 to C9 polycarboxylic acid cross-linking agent, or between about 1.5 mol% and about 6.0 mol% of a C2 to C9 polycarboxylic acid cross-linking agent, based on glucose unit. Citric acid is an example of a cross-linking agent. In some other embodiments, polyacrylic acids may be used. In some embodiments, the cross-linked cellulosic fibers may further exhibit a water retention of from about 25 to about 60, or from about 28 to about 50, or from about 30 to about 45.A method for determining water retention capacity is disclosed in US 5,137,537 A. In some embodiments, the cross-linked cellulose fibers may be crimped, twisted, or crimped, or a combination thereof, including crimped, twisted, and crimped.

[0090] In some embodiments, one or both of the upper and lower acquisition layers 52 and 54 may comprise a nonwoven fabric, which may be hydrophilic. Further, in a particular embodiment, one or both of the upper and lower acquisition layers 54 and 52 may comprise chemically crosslinked cellulosic fibers, which may or may not be part of a nonwoven material.

[0091] In some embodiments, the upper acquisition layer 52 may be comprised of a nonwoven fabric without the cross-linked cellulose fibers, and the lower acquisition layer 54 may comprise the chemically cross-linked cellulose fibers. In some embodiments, the lower acquisition layer 54 may comprise the chemically cross-linked cellulose fibers blended with other fibers, such as natural or synthetic polymer fibers. In some embodiments, these other natural or synthetic polymer fibers may include high surface area fibers, thermoplastic bonding fibers, polyethylene fibers, polypropylene fibers, PET fibers, rayon fibers, lyocell fibers, and blends thereof.

[0092] In some embodiments, the lower acquisition layer 54 desirably has a high liquid absorption capacity. Liquid absorption is measured in grams of absorbed liquid per gram of absorbent material and is expressed by the "maximum absorption" value. High liquid absorption therefore corresponds to a high capacity of the material and is advantageous because it ensures the complete absorption of liquids intended to be absorbed by an acquisition material. In some embodiments, the lower acquisition layer 54 has a maximum absorption of approximately 10 g / g.

[0093] One attribute of the upper acquisition layer 52 is its mean desorption pressure, MDP. The MDP is a measure of the capillary pressure required to dewater the lower acquisition layer 54 to approximately 50% of its capacity at 0 cm of capillary wicking height under an applied mechanical pressure of 2.07 kPa (0.3 psi). In general, a relatively low MDP can be beneficial. The lower MDP can enable the lower acquisition layer 54 to efficiently dewater the upper acquisition material. Without wishing to be bound by any theory, a particular distribution material can exhibit a definable capillary wicking. The ability of the lower acquisition layer 54 to move liquid vertically via capillary forces is directly influenced by gravity and the opposing capillary forces related to desorption of the lower acquisition layer 52.Minimizing these capillary forces can positively impact the performance of the lower acquisition layer 54. However, in some embodiments, the lower acquisition layer 54 also has adequate capillary absorption wicking to dewater the layers above it (upper acquisition layer 52 and topsheet 18 in particular) and temporarily retain the liquid until the liquid is distributed among the absorbent core components. Therefore, in some embodiments, the lower acquisition layer 54 can have a minimum MDP of greater than 0.49 kPa (5 cm H2O). Further, according to exemplary embodiments, the lower acquisition layer 54 has an MDP value of less than about 2.01 kPa (20.5 cm H2O), alternatively less than about 1.86 kPa (19 cm H2O), and alternatively less than about 1.77 kPa (18 cm H2O) to provide faster acquisition.

[0094] The methods for determining the MDP and maximum uptake are disclosed in US 2007 / 0 118 087 A1 (Flohr et al.). For example, according to a first embodiment, the lower acquisition layer 54 may comprise approximately 70 wt.% chemically cross-linked cellulose fibers, approximately 10 wt.% polyester (PET) fibers, and approximately 20 wt.% untreated pulp fibers. According to a second embodiment, the lower acquisition layer 54 may comprise approximately 70 wt.% chemically cross-linked cellulose fibers, approximately 20 wt.% lyocell fibers, and approximately 10 wt.% PET fibers. According to a third embodiment, the lower acquisition layer 54 may comprise approximately 68 wt.% chemically cross-linked cellulose fibers, approximately 16 wt.% untreated pulp fibers, and approximately 16 wt.% PET fibers. In one embodiment, the lower acquisition layer 54 may comprise approximately 90-100 wt.% chemically crosslinked cellulosic fibers.

[0095] Suitable nonwoven materials for the upper and lower acquisition layers 52 and 54 include, but are not limited to, SMS material comprising a spunbond, a meltblown, and another spunbond layer. In certain embodiments, permanently hydrophilic nonwovens, and particularly nonwovens with permanently hydrophilic coatings, are desirable. Another suitable embodiment includes an SMMS structure. In some embodiments, the nonwovens are carded and resin-bonded. In certain embodiments, the nonwovens are porous.

[0096] In some embodiments, suitable nonwoven materials may include, but are not limited to, synthetic fibers such as PE, PET, and PP. Since polymers used for nonwoven fabric production are inherently hydrophobic, they may be coated with hydrophilic coatings. One way to produce nonwoven fabrics with permanently hydrophilic coatings is to apply a hydrophilic monomer and a radical polymerization initiator to the nonwoven fabric and conduct a UV-light-activated polymerization, which results in the monomer being chemically bonded to the surface of the nonwoven fabric, as described in US 2005 / 0 159 720 A1. Another way to produce nonwoven fabrics with permanently hydrophilic coatings is to coat the nonwoven fabric with hydrophilic nanoparticles, as described in US 7 112 621 A to Rohrbaugh et al. and in WO 02 / 064 877 A2.

[0097] Further suitable nonwovens are in US 6,645,569 A to Cramer et al., US 6,863,933 A to Cramer et al., US 7,112,621 A to Rohrbaugh et al. and US 2003 / 0 148 684 A1 to Cramer et al. and US 2005 / 0 008 839 A1 to Cramer et al. described.

[0098] In some cases, the nonwoven surface can be pretreated with a high-energy treatment (corona, plasma) before applying the nanoparticle coatings. High-energy pretreatment typically temporarily increases the surface energy of a low-energy surface (such as PP), thus enabling better wetting of a nonwoven fabric through the nanoparticle dispersion in water.

[0099] It should be noted that permanently hydrophilic nonwovens are also suitable for use in other parts of an absorbent article. For example, topsheets and absorbent core layers comprising permanently hydrophilic nonwovens, such as those described above, have been found to work well.

[0100] In one embodiment, the upper acquisition layer 52 may comprise a material that provides good recovery when external pressure is applied and released. In some embodiments, the upper acquisition layer 52 may comprise a mixture of different fibers, selected, for example, from the types of polymer fibers described above. In some embodiments, at least a portion of the fibers may have a spiral crimp having a helical shape. In some embodiments, the upper acquisition layer 52 may comprise fibers with different degrees or types of crimp, or both.For example, embodiments may include a mixture of fibers having about 3.15 to about 4.72 crimps per cm (c / cm) (about 8 to about 12 crimps per inch (cpi)), or preferably about 3.54 to about 3.94 c / cm (about 9 to about 10 cpi), and other fibers having about 1.57 to about 3.15 c / cm (about 4 to about 8 cpi), or preferably about 1.97 to about 2.76 c / cm (about 5 to about 7 cpi). Different types of crimps may include, but are not limited to, a 2D crimp or "flat crimp" and a 3D or spiral crimp. In some embodiments, the fibers may include bicomponent fibers, which are individual fibers each comprising different materials, typically a first and a second polymeric material.It is believed that the use of fibers with two adjacent components is beneficial to impart a spiral crimp to the fibers.

[0101] In one particular embodiment, the upper acquisition layer 52 may be stabilized by a latex binder, for example, a styrene / butadiene latex binder (SB latex). Methods for obtaining such grids are known, for example, from EP 149 880 (Kwok) and US 2003 / 0105190 (Diehl et al.). In certain embodiments, the binder may be present in the upper acquisition layer 52 at greater than about 12 wt.%, about 14 wt.%, or about 16 wt.%. For certain embodiments, SB latex is available under the tradename GENFLO™ 3160 (OMNO-VA Solutions Inc.; Akron, Ohio, USA). The upper class

[0102] The absorbent article 10 may include a topsheet 18, which may be liquid permeable. The topsheet 18 may be made from a wide range of materials, such as woven and nonwoven materials; polymeric materials such as perforated formed thermoplastic films, perforated plastic films, and hydroformed thermoplastic films; porous foams; cross-linked foams; cross-linked thermoplastic films; and thermoplastic scrims. Suitable woven and nonwoven materials may be made from natural fibers (e.g., wood or cotton fibers), synthetic fibers (e.g., polymeric fibers such as polyester, polypropylene, or polyethylene fibers), or a combination of natural and synthetic fibers.

[0103] In some embodiments, the topsheet 18 can be made of a hydrophobic material to protect the wearer's skin from liquids that have passed through the topsheet 18. In such embodiments, at least a portion of the upper surface of the topsheet 18 is treated to be hydrophilic so that liquids pass through the topsheet 18 more quickly. This reduces the likelihood that body exudates will flow off the topsheet 18 rather than being drawn through the topsheet 18 and absorbed by the absorbent core. The topsheet 18 can be made hydrophilic by treatment with a surfactant. Suitable methods for treating the topsheet 18 with a surfactant include spraying the topsheet material with the surfactant and immersing the material in the surfactant.

[0104] In some embodiments, the topsheet comprises a perforated formed film. Perforated formed films are permeable to body exudates yet non-absorbent and less likely to allow liquids to pass back to the wearer's skin and re-wet it. Thus, the surface of the formed film that is in contact with the body remains dry, reducing body soiling and providing a more comfortable feel for the wearer. Suitable formed films are described in U.S. Pat. No. 3,929,135, entitled "Absorptive Structures Having Tapered Capillaries," issued to Thompson on December 30, 1975; U.S. Pat. No. 4,324,246, entitled "Disposable Absorbent Article Having A Stain Resistant Topsheet," issued to Mullane et al. on April 13, 1982; and U.S. Pat. No. 4,342,314, entitled "Resilient Plastic Web Exhibiting Fiber-Like Properties," issued to Radel et al. on Aug 3rd1982; US 4,463,045 A entitled "Macroscopically Expanded Three-Dimensional Plastic Web Exhibiting Non-Glossy Visible Surface and Cloth-Like Tactile Impression," issued to Ahr et al. on July 31, 1984; and US 5,006,394 A "Multilayer Polymeric Film," issued to Baird on April 9, 1991.

[0105] Alternatively, the top layer comprises perforated nonwoven materials. Suitable perforated nonwoven materials are described in US Pat. No. 5,342,338 A and WO 93 / 19715 A1. The lower class

[0106] The absorbent article may include a backsheet 20 that may be attached to the topsheet. The backsheet may prevent the exudates absorbed by the absorbent core and contained within the diaper from soiling other outer articles that may contact the diaper, such as bedsheets and underwear. In some embodiments, the backsheet may be substantially impervious to liquids (e.g., urine) and may comprise a laminate of a nonwoven fabric and a thin plastic film, such as a thermoplastic film having a thickness of about 0.012 mm (0.5 mil) to about 0.051 mm (2.0 mil). Suitable backsheet films are those manufactured by Tredegar Industries Inc., of Terre Haute, USA, and sold under the trade names X15306, X10962, and X10964.Other suitable backsheet materials may include breathable materials that allow vapors to escape from the diaper while still preventing liquid discharges from passing through the backsheet. Exemplary breathable materials may include materials such as woven webs, nonwoven webs, composite materials such as film-coated nonwoven webs, and microporous films such as those manufactured by Mitsui Toatsu Co. of Japan under the designation ESPOIR NO and those manufactured by EXXON Chemical Co. of Bay City, Texas, USA, under the designation EXXAIRE. Suitable breathable composites comprising polymer blends are available from Clopay Corporation, Cincinnati, Ohio, USA, under the designation HYTREL Blend P18-3097. Such breathable composites are described in more detail in WO 95 / 16746 A1, published June 22, 1995, in the name of EI DuPont.Other breathable backsheets, including nonwoven webs and perforated formed films, are described in US Pat. No. 5,571,096, issued to Dobrin et al. on November 5, 1996. Test method • K(t) test method (test method for measuring dynamic effective permeability and absorption kinetics)

[0107] This method determines the time-dependent effective permeability (K(t)) and uptake kinetics of a gel layer formed from hydrogel-forming superabsorbent polymer particles, or of an absorbent structure containing such particles, under a confining pressure. The objective of this method is to capture the ability of the gel layer formed from hydrogel-forming superabsorbent polymer particles, or of the absorbent structure containing them, to absorb and distribute body fluids when the polymer is present in high concentrations in an absorbent article and is subjected to mechanical pressures, such as those typically encountered during use of the absorbent article. Darcy's law and steady-state flow methods are used to calculate the effective permeability (see below). (See, for example, also "Absorbency," ed. P.K. Chatterjee, Elsevier, 1982, pp. 42-43 and "Chemical Engineering," Vol. II, Third Edition, J.M.Coulson and JF Richardson, Pergamon Press, 1978, pages 122-127.).

[0108] In contrast to previously published methods, the sample is not pre-swollen, which is why the hydrogel is not formed by pre-swelling hydrogel-forming superabsorbent polymer particles in synthetic urine, but the measurement is started with a dry structure.

[0109] The device for this method is called a "time-dependent permeability test stand," Device No. 03-080578, and is commercially available from BRAUN GmbH, Frankfurter Str. 145, 61476 Kronberg, Germany, and is described below. Operating instructions, circuit diagrams, and detailed technical drawings are also available upon request. Measurement system of dynamic effective permeability and uptake kinetics

[0110] Fig.Figure 7 shows the measurement system of dynamic effective permeability and uptake kinetics, referred to herein as “time-dependent permeability test bench”.

[0111] The device consists of the following main components: - M11 Digital laser sensor for thickness measurement 701 (MEL Mikroelektronik GmbH, 85386 Eching, Germany - Fiber for liquid level detection 702 (FU95, Keyence Corp., Japan) - Digital Fiber Sensor 703 (FS-N10, Keyence Corp., Japan) - Precision balance 704 (XP6002MDR, Mettler Toledo AG, 8606 Greifensee, Switzerland) - Power supply unit Logo!Power (C98130-A7560-A1-5-7519, Siemens AG) - LabVIEW Software License 706 (National Instruments, Austin, TX, USA) - Receptacle 707 (5 liter beaker, Roth) - Reservoir 708 (5-liter glass bottle, VWR) with connection point 709 and open tube for air inlet 723 - Control unit and console 705 (Conrad Electronics) - Computer-aided data acquisition system 710 - A piston / cylinder assembly 713 as described herein - A controlled valve 714 (Bürkert)

[0112] Fig. Figure 8 shows the piston / cylinder assembly 713, which includes piston guide cover 801, piston 802, and cylinder 803. The cylinder 803 is made of transparent polycarbonate (e.g., Lexan®) and has an inner diameter p of 6.00 cm (area = 28.27 cm 2). The inner cylinder walls 850 are smooth; the height of the cylinder r is approximately 7.50 cm. The bottom 804 of the cylinder 803 is directed toward a US Standard 400 mesh stainless steel screen cloth (not shown) (e.g., from Weisse and Eschrich), which is biaxially stretched taut 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 can slide freely into the cylinder 803 without forming a gap through which the hydrogel-forming particles can pass. The piston body 805 is firmly attached vertically to 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 a 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 keeping the piston housing 805 completely vertical and parallel to the cylinder walls 850 once the piston 802 with the guide cover 801 is positioned on the cylinder 803. The top view of the piston head 806 is shown in FIG. Fig.9. The piston head 806 is designed to apply pressure evenly to the sample 718. It is also highly permeable to the hydrophilic liquid so that the liquid flow is not impeded during measurement. The piston head 806 consists of a stainless steel screen cloth of US standard mesh size 400 903 (e.g., from Weisse and Eschrich) that is biaxially stretched taut and attached to the outer ring 901 of the piston head. The entire underside surface of the piston is flat. Structural integrity and flexural strength of the screen cloth are then ensured by the stainless steel radial spokes 902. The height of the piston housing 805 is selected so that the weight of the piston 802, consisting of the piston housing 805 and the piston head 806, is 596 g (±6 g), which corresponds to 2.07 kPa (0.30 psi) over the face of the cylinder 803.

[0113] The piston guide cover 801 is a flat stainless steel circle with a diameter s of approximately 7.5 cm, held perpendicular to the piston housing 805 by the POM ring 809 at its center. There are two inlets in the guide cover (810 and 812).

[0114] The first inlet 812 allows the liquid level sensing fiber 702 to be positioned exactly 5 cm above the upper surface of the sieve (not shown) attached to the bottom (804) of the cylinder 803 once the piston 802 has been mated with the cylinder 803 for measurement.

[0115] The second inlet 810 allows the connection of a liquid tube 721, which supplies the liquid to the experiment.

[0116] To ensure that the assembly of the piston 802 with the cylinder 803 is consistent, a slot 814 is created on the cylinder 803, which corresponds to a position mark 813 in the guide cover 801. Thus, the angle of rotation of the cylinder and the guide cover is always the same.

[0117] Before each use, the stainless steel screen cloth 903 of the piston head 806 and cylinder 803 should be inspected for blockages, holes, or overstretching and replaced if necessary. A K(t) device with a damaged screen may produce erroneous K(t) and uptake kinetics results and should not be used until the screen has been replaced.

[0118] A 5 cm mark 808 is drawn on the cylinder at a height k of 5.00 cm (±0.02 cm) above the upper surface of the sieve attached to the bottom 804 of the cylinder 803. This indicates the liquid level to be maintained during the analysis. The liquid level detection fiber 702 is positioned exactly at the 5 cm mark 808. Maintaining a correct and constant liquid level (hydrostatic pressure) is crucial for measurement accuracy.

[0119] A reservoir 708, connected via tubing to the piston / cylinder assembly 713 holding the sample, and a control valve 714 are used to supply saline solution to the cylinder 803 and maintain the saline level at a height k of 5.00 cm above the top surface of the sieve attached to the bottom of the cylinder 804. The valve 714, the liquid level sensing fiber 702, and the digital fiber sensor 703 are connected to the computerized acquisition system 710 via the control unit 705. This allows the dynamic effective permeability and uptake kinetics measurement system to use the information from the liquid level sensing fiber 702 and the digital fiber sensor 703 to control the valve 714 and ultimately maintain the liquid level at the 5 cm mark 808.

[0120] The reservoir 708 is positioned above the piston / cylinder assembly 713 so that a 5 cm water column can be formed within 15 seconds of the start of the test and maintained in 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 held in place with the connection support 719. This allows only one position for the guide cover 801. Furthermore, due to the position marking 813, there is only one position for the cylinder 803. The screen attached to the bottom of the cylinder 804 must be perfectly flat and horizontal. The inner diameter of the support ring 717 must be small enough to firmly support the cylinder 803, but larger than 6.0 cm so that it lies outside the inner diameter of the cylinder when the cylinder is positioned in the support ring 717. This is important to avoid interference of the support ring 717 with the fluid flow.

[0121] The salt solution, which is applied to the sample 718 at a constant water column of 5 cm, can now flow freely from the piston / cylinder assembly 713 into a receiving vessel 707, which is mounted 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.

[0122] The thickness of the sample is constantly measured using a digital laser thickness sensor 701. The laser beam 720 of the digital laser sensor 701 is directed at the center of the POM cover plate 811 of the piston housing. The precise positioning of all parts of the piston / cylinder assembly 713 allows the piston housing 805 to be exactly parallel to the laser beam 720, and as a result, an accurate thickness measurement is obtained. Test preparation

[0123] Reservoir 708 is filled with 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. Preparation of the test solution is described below. Receptacle 707 is placed on scale 704, which is connected to a computerized data acquisition system 710. Before starting the measurement, the scale is zeroed. Preparation of test fluid: Chemicals required: - Sodium chloride (CAS No. 7647-14-5, e.g.: Merck, Art. No. 1.06404.1000) - Linear C 12 -C 14 -Alcohol ethoxylate (CAS No. 68439-50-9, e.g. Lorodac ®, Sasol, Italy) - Deionized H2O

[0124] Ten liters of a solution containing 9.0 grams per liter of NaCl and 1.00 grams per liter of linear C12-C14 alcohol ethoxalate in distilled water are prepared and equilibrated at 23°C ± 1°C for 1 hour. The surface tension is measured on three individual aliquots and should be 28 ± 0.5 mN / m. If the surface tension of the solution deviates from 28 ± 0.5 mN / m, the solution is discarded, and a new test solution is prepared. The test solution must be used within 36 hours of preparation and is considered expired thereafter. K(t) sample preparation

[0125] A representative 10-gram sample of the superabsorbent polymer particles is prepared. This is then dried in an uncovered 10-cm diameter Petri dish in a vacuum chamber at 23 ± 2 °C and 1.33 Pa (0.01 Torr) or less for 48 hours before use. The sample is removed from the vacuum chamber and immediately stored in a tightly sealed, airtight 20-ml glass container at 23 ± 2 °C until further use.

[0126] 2.0 g (±0.02 g) of superabsorbent polymer particles are weighed onto suitable weighing paper using an analytical balance and transferred to cylinder 803, where the particles are evenly distributed on the sieve (not shown) attached to the bottom 804 of cylinder 803. This is achieved by spraying the superabsorbent polymer while simultaneously rotating the cylinder clockwise (e.g., on a Schuett Petriturn-M circular turntable, available from Schuett-biotec GmbH, Rudolf-Wissell-Str. 13, D-37079 Göttingen, Germany). A uniform distribution of the superabsorbent polymer particles is important for measurement accuracy. K(t) approach

[0127] The measurement is carried out at Tappi laboratory conditions: 23 °C ±1 °C / 50 % RH ±2 %.

[0128] The empty piston / cylinder assembly 713 is mounted in the circular opening in the cover plate 716 and is supported around its lower periphery by the support ring 717. The piston / cylinder assembly 713 is held in place by the connection carrier 719, with the cylinder 803 and the piston 802 aligned at the appropriate angle. The reference thickness value (r r ) is measured by the digital laser sensor. The empty piston / cylinder assembly 713 is then removed from the cover plate 716 and the support ring 717, and the piston 802 is removed from the cylinder 803.

[0129] Sample 718 is positioned on the cylinder screen (absorbent structure) or sprayed onto it (superabsorbent polymer particles) as discussed above. Then, piston 802 with attached guide cap 801 is carefully inserted into cylinder 803, aligning position mark 813 of guide cap 801 with slot 814 created in cylinder 803.

[0130] The piston / cylinder assembly is held in place with the connection carrier 719, with the cylinder and piston aligned at the appropriate angle.

[0131] This can only be done in one way. The fluid tube 721 connected to the container 708 and the digital fiber sensor 703 are introduced into the piston / cylinder assembly 713 via the two inlets 810 and 812 in the guide cover 801.

[0132] The computerized data acquisition system 710 is connected to the balance 704 and the digital laser thickness sensor 701. The fluid flow from the reservoir 708 to the cylinder 803 is initiated by the computer program by opening the valve 714. The cylinder is filled until the 5 cm mark 808 is reached in 5 to 15 seconds, after which the computer program regulates the flow rate to maintain a constant water column of 5 cm. The amount of solution flowing through the sample 718 is measured by the balance 704, and the increase in thickness is measured by the laser thickness gauge. Data acquisition begins when the fluid flow is initiated, specifically when the valve 714 is first opened, and continues for 21 minutes, or until the reservoir is empty, so that the 5 cm water column can no longer be maintained.The duration of one measurement is 21 min, laser thickness and scale readings are recorded regularly at an interval that can vary from 2 to 10 s depending on the measurement scope, and 3 runs are measured.

[0133] After 21 minutes, the measurement of the first run is successfully completed, and the controlled valve 714 is automatically closed. The piston / cylinder assembly 713 is removed, and the measurements of the second and third runs are performed accordingly, each following the same procedure. At the end of the measurement of the third run, the controlled valve 714 stops the fluid 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 exported to a program for further analysis, e.g., Excel 2003 SP3.

[0134] The data table records the following relevant information for each reading: • Time from start of experiment • Weight of the liquid collected from the receiving vessel 707 on the scale 704 • Thickness of sample 718

[0135] Data from 30 seconds until the end of the experiment are used in the K(t) and uptake kinetics calculations. Data collected in the first 30 seconds are not included in the calculation. The effective permeability K(t) and uptake kinetics of the absorption structure are then determined using the following sets of equations. Equations used:

[0136] The table below describes the notations used in the equations. A x-section of the absorption structure sample corresponding to the cylinder inner radius: 28.27 cm 2 H Height of water column, 5.0 cm Δp driving pressure exerted by the 5.00 cm water column (h): 4929.31 g / (cm s 2 ) G gravitational constant: 981 cm / s 2 η Temperature-dependent effective viscosity of the liquid in g / (cm s) T Temperature in °C ρ Density of the liquid: 1.0053 g / cm 3 ρ s A Bulk density of the sample of the porous medium or powder in g / cm 3 ρ s Average density of the solid part of the dry sample in g / cm 3 ρ s k Density of component k of the dry sample in g / cm 3 M Dry weight of the sample in g: 2.00 g when measuring superabsorbent particles m k Weight of component k of the dry sample in g V s Volume of the dry sample in cm 3 t i Time at step i from N separate points in s d iThickness of the absorption structure sample at time t i in cm r i Reading of the thickness gauge at time t i in cm r r Reference value of the thickness gauge (reading of the piston / cylinder arrangement without sample) in cm m out i Reading of the scale at time t i ; weight of the liquid that has escaped from the sample at time t i in g U(t i ) Taking the sample at time t i in g T20 Time required to reach an uptake of 20 g / g, starting at 0 s (t0), in s U20 Absorption of the sample after 20 minutes in g / g T80% Time required to achieve 80% absorption of U20, starting at 0 s (t0), in s K20 sample permeability at 20 minutes in m 2 Kmin Minimum value of permeability during the experiment in m 2 Kmin / K20 Ratio of Kmin and K20

[0137] The driving pressure is calculated from the water column as follows: Δp=h⋅G⋅ρ=4929.31 g / (cm⋅s2)

[0138] The thickness at any time t i is defined as the difference of the thickness sensor reading at time t i and the reference value without sample: di=ri−rr [cm]

[0139] For superabsorbent particle samples, the thickness of the sample at time t i =0 (d0) is used to evaluate the quality of particle spraying.

[0140] A bulk density of the sample inside the cylinder can actually be calculated as: ρsA=md0⋅A[g / cm3]

[0141] If this bulk density within the cylinder deviates from the bulk density of the powder by more than ± 40%, the measurement must be considered invalid and discarded.

[0142] The apparent density can be measured according to EDANA method 406.2 - 02 (“Superabsorbent materials - Polyacrylate superabsorbent powders - GRAVIMETRIC DETERMINATION OF DENSITY”).

[0143] The rate of change over time of the scale reading at time t i is calculated as follows: dmout(ti)dt=mouti+1−mouti−1ti+1−ti−1[g / s]

[0144] The rate of change over time of the thickness reading at time t i is calculated as follows: dd(ti)dt=di+1−di−1ti+1−ti−1

[0145] The uptake kinetics are calculated as follows: U(ti)=(A⋅di−Vs)⋅ρm [g / g]

[0146] With the sample volume (V s ) refers to the framework volume of the sample, therefore V s the actual volume occupied by the solid material in the dry sample, excluding any pores and interstices that may be present.

[0147] V s can be calculated or measured using different methods known to the person skilled in the art, for example, taking into account the exact composition and the framework thickness of the components, it can be determined as follows: Vs=∑kVk=∑kmkρSk[cm3]

[0148] Alternatively, for an unknown material composition V s can be easily calculated as follows: Vs=mρs[cm3]

[0149] The average density ρ s can be determined by pycnometry using a suitable non-swelling liquid of known density. This procedure cannot be performed multiple times on the same samples for K(t) measurement; therefore, a suitable additional representative set of samples should be prepared for this experimental measurement.

[0150] From U(t) at different time steps, calculated as discussed above, one can determine the uptake at any specific time by linear interpolation. For example, one of the important outputs is the uptake at 20 minutes, also called U20 (in g / g).

[0151] From U(t) at different time steps, one can also determine the time required to reach a certain uptake by linear interpolation. The time at which the uptake of 20 g / g is first reached is referred to as T20. Similarly, the time to reach any other uptake can be calculated accordingly (e.g., T5 or T10). Using U20, it is also possible to determine the time to reach 80% of U20 from U(t) at different time steps; this property is referred to as T80%.

[0152] The effective permeability is calculated from the rates of weight change and thickness change as follows: K(ti)=ηdiΔp⋅(1ρ⋅A⋅dmout(ti)dt+dd(ti)dt)[cm2]

[0153] The effective viscosity of the liquid depends on the temperature during the test period (23°C ± 1°C) and is calculated according to the following empirical equation: η=−2.36⋅10−4⋅T+1.479⋅10−2

[0154] From K(t i ), the effective transmittance at a given time can be determined by linear interpolation. For example, one of the important outputs is the recording at 20 minutes or K20 (m 2 ). Similarly, the permeability can be calculated accordingly at any other time (e.g., K5 or K10).

[0155] Another parameter that can be derived from the data is Kmin, the minimum K(t) value measured across the entire curve in the interval from ti = 30 s to ti = 1200 s. This value is useful for calculating Kmin / K20, the ratio between the minimum effective permeability and the permeability at 20 minutes. This parameter expresses the temporary gel blocking that may occur in some of the samples. As the value approaches 1, there is no temporary gel blocking; as the value approaches 0, this is an indication that the material undergoes a sharp drop in effective permeability when first loaded with liquid.

[0156] The average values for T20, T80%, K20, U20 and Kmin / K20 are recorded from 3 runs according to the required accuracy, as known to those skilled in the art. • Thickness measurement test procedure

[0157] The purpose of this method is to provide a procedure for determining the thickness of the absorbent core at the crotch point of an absorbent article. The test can be performed using a conventional thickness gauge, such as the EG-225 type, available from ONO SOKKI Technology Inc., 2171 Executive Drive, Suite 400, Addison, IL 60101, USA, with a suitable thickness test stand featuring a 41 mm diameter circular aluminum sample foot, with the foot exerting a force of 0.098 N (10 p). An additional weight is added to achieve a total of 1.57 N (160 p) to adjust the pressure to 1.18 kPa (0.173 psi).

[0158] The thickness of the absorbent core is determined before inserting the absorbent core into the absorbent article, in the exact position the absorbent core will occupy in the absorbent article after insertion. However, the thickness can also be determined after removing the absorbent core from a finished product by any suitable method known to those skilled in the art.

[0159] The crotch point of an absorbent article is determined at the intersection of the longitudinal axis and the transverse axis of the article. Basic protocol 1. All tests are conducted at 23 ± 1 °C and a relative humidity of 50 ± 2%. 2. The absorption core is equilibrated at 23 ± 1 °C and 50 ± 2% relative humidity for 8 hours. 3. The crotch point is determined as described above and marked on the wearer-side surface of the absorbent core. 4. The absorption core is positioned under the thickness gauge with the carrier-side surface facing the sample contact foot and the step point centered under the foot. 5. The sample contact foot is carefully lowered and brought into contact with the surface of the absorption core. 6. The thickness reading is measured 5 seconds after the foot comes into contact with the absorbent core. • Urine permeability measurement (UPM) test methodUrine permeability measurement system

[0160] This method determines the permeability of a swollen hydrogel layer 1318. The apparatus used for this method is described below. This method is closely related to the prior art SFC (saline flow conductivity) test method.

[0161] Fig.10 shows the structure of the permeability measuring system 1000 with the reservoir 1014 of the constant water column, the open tube for air inlet 1010, the plugged opening for refilling 1012, laboratory boy 1016, dispensing tube 1018, stopcock 1020, ring stand support 1022, receiving vessel 1024, balance 1026 and piston / cylinder assembly 1028.

[0162] Fig. Figure 11 shows the piston / cylinder assembly 1028, which includes a metal weight 1112, a piston shaft 1114, a piston head 1118, a cover 1116, and a cylinder 1120. The cylinder 1120 is made of transparent polycarbonate (e.g., Lexan®) and has an inner diameter p of 6.00 cm (area = 28.27 cm 2) with smooth inner cylinder walls 1150. The bottom 1148 of the cylinder 1120 faces a U.S. standard 400 mesh stainless steel screen cloth (not shown), which is biaxially stretched taut before being attached to the bottom 1148 of the cylinder 1120. The piston skirt 1114 is made of transparent polycarbonate (e.g., Lexan®) and has an overall length q of approximately 127 mm. A central section 1126 of the piston skirt 1114 has a diameter r of 21.15 mm. An upper portion 1128 of the piston skirt 1114 has a diameter s of 15.8 mm and forms a shoulder 1124. A lower portion 1146 of the piston skirt 1114 has a diameter t of approximately 1.59 cm (5 / 8 inch) and is threaded to fit tightly into the central hole 1218 (see Fig.12) of the piston head 1118. The piston head 1118 is perforated, constructed of transparent polycarbonate (e.g., Lexan®), and is also provided with a U.S. Standard 400 mesh expanded stainless steel screen (not shown). The weight 1112 is stainless steel, has a central bore 1130, slides into the upper portion 1128 of the piston skirt 1114, and rests on the shoulder 1124. The combined weight of the piston head 1118, piston skirt 1114, and weight 1112 is 596 g (± 6 g), which corresponds to 2.07 kPa (0.30 psi) across the face of the cylinder 1120. The combined weight can be adjusted by drilling a blind hole along a central axis 1132 of the piston shaft 1114 to remove material and / or providing a cavity to add weight.The cylinder cover 1116 has a first cover opening 1134 in its center to vertically align the piston shaft 1114 and a second cover opening 1136 near the rim 1138 to introduce liquid from the constant water column reservoir 1014 into the cylinder 1120.

[0163] A first linear index mark (not shown) is drawn radially along the upper surface 1152 of the weight 1112, with the first linear index mark running transverse to the central axis 1132 of the piston skirt 1114. A corresponding second linear index mark (not shown) is drawn radially along the upper surface 1160 of the piston skirt 1114, with the second linear index mark running transverse to the central axis 1132 of the piston skirt 1114. A corresponding third linear index mark (not shown) is drawn along the central portion 1126 of the piston skirt 1114, with the third linear index mark running parallel to the central axis 1132 of the piston skirt 1114. A corresponding fourth linear index mark (not shown) is drawn radially along the upper surface 1140 of the cylinder cover 1116, with the fourth linear index mark extending transversely to the central axis 1132 of the piston skirt 1114.Furthermore, a corresponding fifth linear index mark (not shown) is drawn along a lip 1154 of the cylinder cover 1116, with the fifth linear index mark running parallel to the central axis 1132 of the piston skirt 1114. A corresponding sixth linear index mark (not shown) is drawn along the outer cylinder wall 1142, with the sixth linear index mark running parallel to the central axis 1132 of the piston skirt 1114. The alignment of the first, second, third, fourth, fifth, and sixth linear index marks allows for repositioning of the weight 1112, piston skirt 1114, cylinder cover 1116, and cylinder 1120 in the same orientation relative to each other for each measurement.

[0164] The technical specifications of the cylinder 1120 are: Outer diameter u of cylinder 1120: 70.35 mm Inner diameter p of cylinder 1120: 60.0 mm Height v of cylinder 1120: 60.5 mm

[0165] The technical specifications of the cylinder cover 1116 are: Outer diameter w of the cylinder cover 1116: 76.05 mm Inner diameter x of the cylinder cover 1116: 70.5 mm Thickness y of cylinder cover 1116 including lip 1154: 12.7 mm Thickness z of cylinder cover 1116 without lip 1154: 6.35 mm Diameter a of the first lid opening 1134: 22.25 mm Diameter b of the second lid opening 1136: 12.7 mm Distance between the centers of the first and second lid openings 1134 and 1136: 23.5 mm

[0166] The technical specifications of the weight 1112 are: Outer diameter c: 50.0 mm Diameter d of the central bore 1130: 16.0 mm Height e: 39.0 mm

[0167] The technical specifications of the piston head 1118 are: Diameter f: 59.7 mm Height g: 16.5 mm Outer holes 1214 (14 in total) with a diameter h of 9.65 mm, the outer holes 1214 being evenly spaced and the centers being 47.8 mm from the center of the central hole 1218 Inner holes 1216 (7 total) having a diameter i of 9.65 mm, the inner holes 1216 being evenly spaced and centers being 26.7 mm from the center of the central hole 1218. The central hole 1218 has a diameter j of 1.59 cm (5 / 8 inch) and is threaded to receive a lower portion 1146 of the piston skirt 1114.

[0168] Before use, the stainless steel screens (not shown) of the piston head 1118 and cylinder 1120 should be inspected for blockage, holes, or over-expansion and replaced if necessary. A urine permeability tester with a damaged screen may produce inaccurate UPM results and should not be used until the screen has been replaced.

[0169] A 5.00 cm mark 1156 is drawn on cylinder 1120 at a height k of 5.00 cm (± 0.05 cm) above the sieve (not shown) attached to the bottom 1148 of cylinder 1120. This indicates the liquid level to be maintained during the analysis. Maintaining a correct and constant liquid level (hydrostatic pressure) is critical for measurement accuracy.

[0170] A constant water column reservoir 1014 is used to deliver saline solution 1032 to the cylinder 1120 and maintain the level of saline solution 1032 at a height k of 5.00 cm above the screen (not shown) attached to the bottom 1148 of the cylinder 1120. The bottom 1034 of the air inlet tube 1010 is positioned so that the level of saline solution 1032 in the cylinder 1120 is maintained at the required height k of 5.00 cm during measurement, i.e., the bottom 1034 of the air tube 1010 is approximately at level 1038 as the 5.00 cm mark 1156 on the cylinder 1120 when seated on the support screen (not shown) of the ring stand 1040 above the receiving vessel 1024. Correct height alignment of the air inlet tube 1010 at the 5.00 cm mark 1156 on the cylinder 1120 is critical for the analysis.A suitable reservoir 1014 consists of a vessel 1030 containing a horizontally oriented L-shaped dispensing tube 1018 for liquid dispensing, a vertically oriented open tube 1010 for admitting air at a predetermined height within the constant water column reservoir 1014, and a plugged opening 1012 for refilling the constant water column reservoir 1014. The tube 1010 has an inner diameter of 12.5 mm ± 0.5 mm. The dispensing tube 1018, positioned near the bottom 1042 of the constant water column reservoir 1014, contains a shutoff valve 1020 for starting / stopping the dispensing of the saline solution 1032.The outlet 1044 of the dispensing tube 1018 is sized to be inserted through the second lid opening 1136 in the cylinder lid 1116, with its end positioned below the surface of the saline solution 1032 in the cylinder 1120 (after reaching a height of 5.00 cm of the saline solution 1032 in the cylinder 1120). The air inlet tube 1010 is held in place by an O-ring collar (not shown). The constant water column reservoir 1014 can be positioned on a laboratory jack 1016 to adjust its height relative to that of the cylinder 1120. The components of the constant water column reservoir 1014 are sized to quickly fill the cylinder 1120 to the required height (i.e., water column) and to maintain that height for the duration of the measurement. The constant water column reservoir 1014 must be capable of delivering the saline solution 1032 at a flow rate of at least 3 g / s for at least 10 minutes.

[0171] The piston / cylinder assembly 1028 is positioned on a rigid 16-mesh stainless steel support screen (not shown) (or equivalent) supported by a ring stand 1040 or a suitable alternative rigid stand. This support screen (not shown) is sufficiently permeable not to impede the flow of the saline solution 1032 and rigid enough to support the stainless steel screen mesh (not shown) without stretching. The support screen (not shown) should be flat and straight to prevent tilting of the piston / cylinder assembly 1028 during the test. The saline solution 1032 passing through the support screen (not shown) is collected in a receiving vessel 1024 positioned below, but not supporting, the support screen (not shown). The receiving vessel 1024 is positioned on the balance 1026, which has an accuracy of at least 0.01 g.The digital output of the 1026 scale is connected to a computerized data acquisition system (not shown). Preparation of reagents (not shown)

[0172] Jayco Synthetic Urine (Jayco Synthetic Urine, JSU) 1312 (see Fig. 13) is used for a source phase (see UPM procedure below), and a 0.118 M sodium chloride (NaCl) solution is used for a flow phase (see UPM procedure below). The following preparation procedures refer to a standard volume of 1 liter. For preparation of volumes other than 1 liter, all quantities are scaled accordingly.

[0173] JSU: A 1-liter volumetric flask is filled to 80% volume with distilled water, and a magnetic stir bar is placed inside the flask. Separately, using weighing paper or a beaker, the following amounts of the dry ingredients are weighed to an accuracy of within ± 0.01 g using an analytical balance and quantitatively added to the volumetric flask in the same order as listed below. The solution is stirred on a suitable stir plate until all solids are dissolved, the stir bar is removed, and the solution is diluted to 1 l with distilled water. A stir bar is again inserted, and the solution is stirred on a stir plate for several minutes or more.

[0174] Salt quantities for making 1 liter of Jayco synthetic urine: Potassium chloride (KCl) 2.00 g Sodium sulfate (Na2SO4) 2.00 g Ammonium dihydrogen phosphate (NH4H2PO4) 0.85 g Ammonium phosphate, dibasic ((NH4)2HPO4) 0.15 g Calcium chloride (CaCl2) 0.19 g - [or hydrated calcium chloride (CaCl2·2H2O) 0.25 g] Magnesium chloride (MgCl2) 0.23 g - [or hydrated magnesium chloride (MgCl2·6H2O) 0.50 g]

[0175] For faster preparation, each salt is completely dissolved before adding the next. Jayco synthetic urine can be stored in a clean glass container for 2 weeks. The solution should not be used if it becomes cloudy. The shelf life in a clean plastic container is 10 days.

[0176] Sodium chloride (NaCl) solution 0.118 M: Sodium chloride 0.118 M is used as salt solution 1032. Using a weighing paper or a beaker, weigh 6.90 g (± 0.01 g) of sodium chloride and quantitatively transfer it to a 1-liter volumetric flask. The flask is filled with distilled water. A stirring rod is added, and the solution is mixed on a stir plate until all solids are dissolved. Test preparation

[0177] Using a fixed reference cylinder weight (not shown) (40 mm diameter; 140 mm height), a thickness gauge (not shown) (e.g.

[0178] Mitotoyo Digimatic Height Gage) is set to a reading of zero. This procedure is conveniently performed on a smooth and flat laboratory bench surface 1046. The piston / cylinder assembly 1028, without superabsorbent polymer particles, is positioned under the thickness gauge (not shown), and a reading L1 is recorded to the nearest 0.01 mm.

[0179] The constant water column reservoir 1014 is filled with saline solution 1032. The bottom 1034 of the air inlet tube 1010 is positioned so that the upper portion (not shown) of the liquid meniscus (not shown) in the cylinder 1120 is held at the 5.00 cm mark 1156 during the measurement. Correct height alignment of the air inlet tube 1010 at the 5.00 cm mark 1156 on the cylinder 1120 is critical for the analysis.

[0180] The receiving vessel 1024 is placed on the scale 1026, and the digital output of the scale 1026 is connected to a computerized data acquisition system (not shown). The ring stand 1040, with a rigid 16-mesh stainless steel support screen (not shown), is positioned over the receiving vessel 1024. The 16-mesh screen (not shown) should be sufficiently rigid to support the piston / cylinder assembly 1028 during measurement. The support screen (not shown) must be flat and straight. UPM approach

[0181] 1.5 g (± 0.05 g) of superabsorbent polymer particles are weighed onto suitable weighing paper or a weighing aid using an analytical balance. The moisture content of the superabsorbent polymer particles is measured according to Edana Moisture Content Test Method 430.1-99 ("Superabsorbent materials - Polyacrylate superabsorbent powders - Moisture Content - Weight loss upon heating" (February 99)). If the moisture content of the superabsorbent polymer particles is greater than 5%, the weight of the superabsorbent polymer particles should be corrected for moisture (i.e., in this specific case, the added superabsorbent polymer particles should be 1.5 g on a dry weight basis).

[0182] The empty cylinder 1120 is placed on a flat laboratory bench surface 1046, and the superabsorbent polymer particles are quantitatively added to the cylinder 1120. The superabsorbent polymer particles are evenly distributed on the sieve (not shown) attached to the bottom 1148 of the cylinder 1120 by gently shaking, rotating, and / or tapping the cylinder 1120. Even distribution of the particles on the sieve (not shown) attached to the bottom 1148 of the cylinder 1120 is important to obtain a result with the highest accuracy. After evenly distributing the superabsorbent polymer particles on the sieve (not shown) attached to the bottom 1148 of the cylinder 1120, the particles must not adhere to the cylinder's inner walls 1150. The piston skirt 1114 is inserted through the first cover opening 1134 with the lip 1154 of the cover 1116 facing the piston head 1118.The piston head 1118 is carefully inserted into the cylinder 1120 to a depth of a few centimeters. The cover 1116 is then placed on the upper rim 1144 of the cylinder 1120, taking care to keep the piston head 1118 away from the superabsorbent polymer particles. The cover 1116 and the piston stem 1126 are then carefully rotated to align the third, fourth, fifth, and sixth linear index marks. The piston head 1118 is then carefully lowered (over the piston stem 1114) until it rests on the dry superabsorbent polymer particles. The weight 1112 is positioned on the upper portion 1128 of the piston stem 1114 so that it rests on the shoulder 1124 such that the first and second linear index marks are aligned. A correct fit of the lid 1116 prevents binding and ensures an even distribution of the weight on the hydrogel layer 1318.

[0183] Swelling Phase: An 8 cm diameter glass filter plate (7 mm thick; e.g., Chemglass Inc. No. CG 201-51, coarse porosity) 1310 is saturated by adding excess JSU 1312 to the glass filter plate 1310 until the glass filter plate 1310 is saturated. The saturated glass filter plate 1310 is placed in a wide, flat-bottomed Petri dish 1314, and JSU 1312 is added until it reaches the upper surface 1316 of the glass filter plate 1310. The JSU height must not exceed the height of the glass filter plate 1310.

[0184] The screen (not shown) attached to the bottom 1148 of the cylinder 1120 is easily stretched. To prevent stretching, while grasping the cylinder 1120 of the piston / cylinder assembly 1028 just above the cover 1116, apply lateral pressure to the piston shaft 1114 with the index finger. This holds the piston shaft 1114 in place on the cover 1116, allowing the piston / cylinder assembly 1028 to be lifted without excessive force being exerted on the screen (not shown).

[0185] The entire piston / cylinder assembly 1028 is thus lifted and placed on the glass filter plate 1310 in the Petri dish 1314. JSU 1312 from the Petri dish 1314 passes through the glass filter plate 1310 and is absorbed by the superabsorbent polymer particles (not shown) to form a hydrogel layer 1318. The JSU 1312 available in the Petri dish 1314 should be sufficient for the entire swelling phase. If necessary, more JSU 1312 can be added to the Petri dish 1314 during hydration to maintain the liquid level of the JSU 1312 at the top surface 1316 of the glass filter plate 1310. After a period of 60 minutes, the piston / cylinder assembly 1028 is removed from the glass filter plate 1310, taking care to hold the piston shaft 1114 to the lid 1116 as described above and ensuring that the hydrogel layer 1318 does not lose any JSU 1312 or ingest any air during this process.The piston / cylinder assembly 1028 is positioned under the thickness gauge (not shown), and a reading L2 is recorded to an accuracy of 0.01 mm. If the value changes over time, only the initial value is recorded. The thickness of the hydrogel layer 1318 L0 is determined from L2 - L1 to an accuracy of 0.1 mm.

[0186] The piston / cylinder assembly 1028 is transferred to the support screen (not shown) attached to the ring stand 1040, taking care to keep the piston shaft 1114 in place on the lid 1116. The constant water column reservoir 1014 is positioned so that the discharge tube 1018 protrudes through the second lid opening 1136. The measurement is initiated in the following sequence: a) The stopcock 1020 of the constant water column reservoir 1014 is opened to allow the salt solution 1032 to reach the 5.00 cm mark 1156 on the cylinder 1120. This level of the salt solution 1032 should be reached within 10 seconds of opening the stopcock 1020. b) As soon as 5.00 cm of the saline solution 1032 is reached, the data acquisition program is started.

[0187] Using a computer (not shown) connected to the scale 1026, the amount of saline solution 1032 passing through the hydrogel layer 1318 is recorded at 20-second intervals for a period of 10 minutes. At the end of 10 minutes, the stopcock 1020 on the constant water column reservoir 1014 is closed.

[0188] The data from 60 seconds until the end of the experiment are used in the RPM calculation. The data collected in the first 60 seconds are not included in the calculation. The flow rate F s (in g / s) is the linear curve in a least squares graph related to the weight of salt solution 1032 collected (in grams) as a function of time (in seconds) from 60 seconds to 600 seconds.

[0189] The urine permeability measurement (Q) of the hydrogel layer 1318 is calculated using the following equation: Q=[Fg×L0] / [ρ×A×ΔP], where F g is the flow rate in g / s determined from the regression analysis of the flow rate results, L0 is the initial thickness of the hydrogel layer 1318 in cm, ρ is the density of the salt solution 1032 in gm / cm 3 A (in the equation above) is the area of the hydrogel layer 1318 in cm 2 , ΔP is the hydrostatic pressure in dynes / cm2 , and the urine permeability measurement Q is in units of cm 3 s / g. The average of three determinations should be recorded. • FSR test procedure

[0190] This method determines the swelling rate of superabsorbent polymer particles, particularly polymer hydrogel particles such as cross-linked polyacrylates, in 0.9% brine (aqueous 0.9 wt.% NaCl solution). The measurement principle involves allowing the superabsorbent polymer particles to absorb a known amount of liquid, and then measuring the time required to absorb the liquid. The result is then expressed in grams of absorbed liquid per gram of material per second. All tests are conducted at 23 ± 2 °C.

[0191] Four grams of a representative sample of the superabsorbent polymer particles are dried in an uncovered 5 cm diameter Petri dish in a vacuum chamber at 23 ± 2 °C and 1.33 Pa (0.01 torr) or less for 48 hours prior to measurement.

[0192] Approximately 1 g (+ / - 0.1 g) of the test specimen is removed from the vacuum chamber and immediately weighed to an accuracy of 0.001 g into a 25 ml beaker with an inner diameter of 32 to 34 mm and a height of 50 mm. The material is evenly distributed over the bottom. 20 g of 0.9% brine is weighed to an accuracy of + / - 0.01 g into a 50 ml beaker and then carefully but not quickly poured into the beaker containing the test material. A timer is started immediately when the liquid comes into contact with the material. The beaker is not moved or shaken during swelling.

[0193] The timer is stopped and the time is recorded to the second (or more precisely, if necessary) when the last portion of the undisturbed liquid is reached by the swelling particles. To increase the reproducibility of the endpoint determination, the liquid surface can be illuminated with a small lamp without heating the surface with the lamp. The beaker is weighed again to determine the actual amount of liquid absorbed to within ± 0.1 g.

[0194] The free swell rate is calculated by dividing the weight of the superabsorbent polymer particles by the amount of liquid actually absorbed and dividing the result by the time required for this absorption. It is expressed in g / g / s. Three measurements are taken, and the results are averaged to obtain the FSR value in g / g / s, which is recorded in three significant plots. • Flat pickup test procedure

[0195] This method determines the absorption times of a baby diaper typically designed for wearers weighing in the range of 8 to 13 kg ± 20% (such as Pampers Active Fit, size 4 or other Pampers baby diapers size 4, Huggies baby diapers size 4 or baby diapers size 4 of most other brands). device

[0196] The test device is in Fig.14 and includes a tray 1411 made of polycarbonate (e.g., Lexan®) with a nominal thickness of 12.5 mm (0.5 inches). The tray 1411 includes a straight horizontal base 1412 with a length of 508 mm (20.0 inches) and a width of 152 mm (6.0 inches). Two straight vertical sides 1413 with a height of 64 mm (2.5 inches) × a length of 508 mm (20 inches) are attached to the longitudinal edges of the base 1412 to form a U-shaped tray 1411 with a length of 508 mm (20.0 inches), an internal width of 152 mm (6.0 inches), and an internal depth of 51 mm (2.0 inches). The front and rear ends of the tray 1411 are not closed.

[0197] A sheet of open-cell polyurethane foam 1414 measuring 508 × 152 × 25 mm is wrapped with polyethylene film and placed on the bottom of the tray 1411 so that the edges of the foam 1414 and the tray 1411 are aligned and the upper surface of the polyethylene film is smooth and free of seams, wrinkles, or bumps. The polyurethane foam 1414 has a compression modulus of 3.31 kPa (0.48 psi). Using an indelible marker, draw a reference line across the width of the upper surface of the polyethylene cover 152 mm (6.0 inches) from one end (the front edge) parallel to the transverse axis.

[0198] A rectilinear polycarbonate top plate 1415 has a nominal thickness of 12.5 mm (0.5 in), a length of 508 mm (20.0 in), and a width of 146 mm (5.75 in). A 51 mm (2.0 in) diameter hole is drilled in the center of the top plate 1415 (i.e., the center of the hole is located at the intersection of the longitudinal and transverse axes of the top surface of the top plate 1415). A polycarbonate cylinder 1416 with an outer diameter of 51 mm (2.0 inches), an inner diameter of 37.5 mm (1.5 inches), and a height of 102 mm (4.0 inches) is glued into the hole in the top plate 1415 such that the lower edge of the cylinder 1416 is flush with the lower surface of the top plate 1415 and the cylinder 1416 protrudes vertically by 89 mm (3.5 inches) above the upper surface of the top plate 1415, and the seam between the cylinder 1416 and the top plate 1415 is watertight.An annular depression 1417 with a height of 2 mm and a diameter of 44.5 mm (1.75 inches) is formed in the lower inner edge of the cylinder 1416. Two holes with a diameter of 1 mm are drilled at an angle of 45° into the upper surface of the upper plate 1415 so that the holes intersect the inner surface of the cylinder 1416 immediately above the depression 1417 and are on opposite sides of the cylinder 1416 (i.e., 180° apart). Two stainless steel wires 1418 with a diameter of 1 mm are glued watertight into the holes so that one end of each wire is flush with the inner cylinder wall and the other end protrudes from the upper surface of the upper plate 1415. These wires are hereinafter referred to as electrodes. A reference line is drawn across the width of the upper plate 1415 152 mm (6.0 inches) from the front edge, parallel to the transverse axis.The assembly of upper plate 1415 and cylinder 1416 weighs approximately 1180 grams.

[0199] Two steel weights, each weighing 9 kg, measuring 146 mm (5.75 inches) wide, 76 mm (3.0 inches) deep, and approximately 100 mm (4 inches) high, are also required. Procedure:

[0200] All tests are conducted at 23 ± 2 °C and a relative humidity of 35 ± 15 %.

[0201] The polycarbonate tray 1411 containing the wrapped foam sheet 1414 is placed on a suitable flat horizontal surface. A disposable absorbent product is removed from its packaging, and the cuff elastics are cut at appropriate intervals to allow the product to lie flat. The product is weighed to an accuracy of ± 0.1 grams on a suitable top-loading scale, then placed on the covered foam sheet 1414 in the receiving fixture with the front waist edge of the product aligned with the reference mark on the polyethylene cover. The product is centered along the longitudinal axis of the fixture with the top (body-side) layer of the product facing up and the back waist edge toward the rear end of the foam sheet 1414. The top sheet 1415 is placed on the product with the protruding cylinder facing up.The drawn reference line is aligned with the front waist edge of the product, and the rear end of the top plate 1415 is aligned with the rear edge of the foam plate 1414. The two 9.0 kg weights are then carefully placed on the top plate 1415 so that the width of each weight is parallel to the transverse axis of the top plate and each weight is 83 mm (3.25 inches) from the front or rear edge of the top plate 1415.

[0202] A suitable electrical circuit is connected to the two electrodes to detect the presence of an electrically conductive liquid between them.

[0203] A suitable pump; e.g., Model 7520-00 from Cole Parmer Instruments, Chicago, USA, or equivalent; is set to dispense a 0.9 wt.% aqueous solution of sodium chloride through a flexible plastic tube with an inner diameter of 4.8 mm (3 / 16 inch), e.g., Tygon® R-3603 or equivalent. The end portion of the tube is clamped vertically so that it is centered within cylinder 1416, attached to the upper plate 1415, with the discharge end of the tube facing downward and positioned 50 mm (2 inches) below the top rim of cylinder 1416. The pump is timer-operated and precalibrated to dispense a 75.0 ml surge of the 0.9% saline solution at a rate of 15 ml / s.

[0204] The pump is activated, and a timer is started immediately after activation. The pump delivers 75 ml of 0.9% NaCl solution to the 1416 cylinder at a rate of 15 ml / s and then stops. When test fluid is introduced into the 1416 cylinder, it typically accumulates to some extent on the absorption structure. This fluid completes an electrical circuit between the two electrodes in the cylinder. After the surge is delivered, the meniscus of the solution collapses as the fluid is absorbed by the structure. When the electrical circuit is interrupted due to the absence of free fluid between the electrodes in the cylinder, the time is noted.

[0205] The recording time for a particular surge is the time interval between the activation of the pump for that surge and the point at which the electrical circuit is broken.

[0206] Four bursts are delivered to the product in this way; each burst is 75 ml and delivered at 15 ml / s. The time interval between the start of each burst is 300 seconds.

[0207] The absorption time for four surges is recorded. In this way, three products are tested, and the average surge time for each of the surges in question (first through fourth) is calculated. Examples

[0208] Superabsorbent polymer particles according to the present disclosure were prepared to compare their properties with the properties of prior art superabsorbent polymer particles. • Comparison example 1

[0209] The superabsorbent polymer particles of the comparative example are the superabsorbent polymer particles used in Pampers Active Fit diapers, commercially available in the UK in August 2010. These superabsorbent polymer particles are generally manufactured according to US 2009 / 0275470A1. It should be noted that the superabsorbent polymer particles can be extracted from the commercially available Pampers Active Fit diapers, as described in European Patent Application No. 10154618.2, entitled "Method of separating superabsorbent polymer particles from a solidified thermoplastic composition comprising polymers."

[0210] The standard particle size distribution of the superabsorbent polymer particles is 45 to 710 µm with a maximum of 1% below 45 µm and a maximum of 1% above 710 µm. • Comparison example 2

[0211] 300 g of superabsorbent polymer particles were prepared according to Comparative Example 11 disclosed in PCT patent application WO 2010 / 095427 A1 entitled “Polyacrylic acid-based water-absorbing resin powder and method for producing the same”. • Example 1

[0212] 4000 kg of superabsorbent polymer particles of the comparative example were sieved over a standard AISI 304 stainless steel wire sieve with a mesh size of 300 µm in a vibrating sieve device with a capacity of approximately 100-150 kg per hour and yielded 750 kg of superabsorbent polymer particles with an average diameter (D50) of approximately 180-200 µm and a particle size distribution of 45 to 300 µm with a maximum of 3% below 45 µm and a maximum of 3% above 300 µm. • Example 2

[0213] 300 g of superabsorbent polymer particles were prepared according to Example 9 disclosed in PCT patent application WO 2010 / 095427 A1 entitled “Polyacrylic acid-based water-absorbing resin powder and method for producing the same”.

[0214] Various parameters of the superabsorbent polymer particles of Examples 1, 2, 3, and the Comparative Example were measured: the time to reach an uptake of 20 g / g (T20), the uptake at 20 min (U20), the time to reach an uptake of 80% of U20 (T80%), the effective permeability at 20 minutes (K20), and the transient gel blocking index (Kmin / K20) were measured according to the K(t) test procedure outlined above. The UPM (urine permeability measurement) was performed according to the UPM test procedure outlined above. The CRC (centrifuge retention capacity) was measured according to EDANA Method WSP 241.2-05.

[0215] Fig. 15A and Fig.15B show the uptake in g / g as a function of time for Comparative Examples 1 and 2 vs. Examples 1 and 2 as measured according to the K(t) test procedure set forth above.

[0216] The different values for the measured parameters are summarized in Table 1 below. Table 1 Examples T20 (s) U20 (g / g) T80% (g / g) K20 (cm 2 ) Kmin / Kmax UPM (1×10 -7 (cm 3 ·s) / g) CRC (g / g) Comparison example 1 291 ± 19 28,5 418 ± 20 8,8 · 10 -8 0,88 98 26,5 Comparison example 2 263 ± 1 29,2 402 ± 12 9,3 · 10 -8 1 110 27,3 Example 1 138 ± 2 27,4 176 ± 1 3,5 · 10 -8 0,78 66 24,1 Example 2 194 ± 5 30,2 330 ± 9 8,7 · 10 -8 0,8 100 27,7

[0217] As from Fig. 15A and Fig. 15B and Table 1, the times to reach an uptake of 20 g / g (T20), as measured according to the K(t) test method, are significantly lower for superabsorbent polymer particles prepared according to Examples 1 and 2 than for superabsorbent polymer particles prepared according to Comparative Examples 1 and 2. Therefore, these superabsorbent polymer particles are capable of rapidly absorbing liquid even in the dry state, ie, upon initial contact with liquid.

[0218] As can also be seen from Table 1, superabsorbent polymer particles with a high equilibrium permeability (a high UPM value), such as the superabsorbent polymer particles of Comparative Examples 1 and 2, do not automatically have a high T20 value, which means that equilibrium permeability is not a reliable criterion for selecting superabsorbent polymer particles that can quickly absorb liquid upon initial contact with liquid. • Absorption times of diapers comprising superabsorbent polymer particles of Comparative Examples 1 or 2 vs. diapers comprising superabsorbent polymer particles according to the present disclosure.

[0219] Absorption times of Pampers Active Fit size 4 diapers, commercially available in the UK in August 2010, were measured according to the flat absorption test procedure outlined above. These diapers comprise superabsorbent polymer particles of Comparative Example 1. Absorption times of the same diapers, with the superabsorbent polymer particles replaced by the superabsorbent polymer particles of Comparative Example 2 or the superabsorbent polymer particles of Example 2, were measured according to the flat absorption test procedure outlined above. The absorbent cores of all diapers have a dry caliper at the crotch point of the diaper of 1.7 mm, as measured according to the caliper test procedure outlined above. The values obtained for the absorption times of all samples are summarized in Table 2 below. Table 2 Samples Comparison example 1 Comparison example 2 Example 2 Absorption time for the 1st surge (75 ml) in s 30 28 26

[0220] As can be seen from Table 2 above, the first gush uptake times for diapers comprising superabsorbent polymer particles according to Comparative Examples 1 or 2 are higher than the first gush uptake time for the same diaper wherein the superabsorbent polymer particles were replaced by the superabsorbent polymer particles of Example 2.

[0221] Thus, absorbent articles according to the present invention, namely absorbent articles comprising superabsorbent polymer particles requiring a time to reach an uptake of 20 g / g (T20) of less than 240, as measured according to the K(t) method set out below, have improved absorption properties, particularly at the first surge, ie when the article starts to be wetted.

[0222] The dimensions and values disclosed herein are not intended to be strictly limited to the exact numerical values stated. Instead, unless otherwise noted, each such dimension is intended to mean both the stated value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "approximately 40 mm."

Claims

[1] An absorbent article (10) comprising an absorbent core (14), the absorbent article (10) being divided into three sections: a front section (30), a back section (32), and a crotch section (34) disposed between the front section (30) and the back section (32), the absorbent core (14) having a dry thickness at the crotch point of the article of 0.2 to 5 mm, wherein the absorbent core (14) comprises at least 90% superabsorbent polymer particles, wherein the superabsorbent polymer particles comprised in the absorbent core (14) of the front portion (30) or the crotch portion (34) of the article or of the entire absorbent core (14) require a time to reach an uptake of 20 g / g (T20) of less than 240 s as measured according to the K(t) test method. [2] The absorbent article (10) of claim 1, wherein the absorbent article (10) further comprises a topsheet (18) and a backsheet (20), and wherein the absorbent core (14) is enclosed between the topsheet (18) and the backsheet (20). [3] Absorbent article (10) according to claim 1 or 2, wherein the superabsorbent polymer particles comprised in the absorbent core (14) of the front portion (30) or the crotch portion (34) of the article or of the entire absorbent core (14) have an effective permeability at 20 minutes (K20) of at least 5 × 10 -8 cm 2 as measured according to the K(t) test procedure. [4] An absorbent article (10) according to any one of the preceding claims, wherein the uptake of the superabsorbent polymer particles comprised by the absorbent core (14) in the front portion (30) or the crotch portion (34) of the article or in the entire absorbent core (14) at 20 min (U20) is at least 28 g / g as measured according to the K(t) test method. [5] Absorbent article (10) according to any one of the preceding claims, wherein the superabsorbent polymer particles have a RPM value of 40 to 150 (10 -7 (cm 3 · s) / g). [6] Absorbent article (10) according to any one of the preceding claims, wherein the superabsorbent polymer particles have a CRC value of 20 to 40 g / g. [7] Absorbent article (10) according to any one of the preceding claims, wherein the superabsorbent polymer particles have a particle size of 50 to 850 µm. [8] Absorbent article (10) according to any one of the preceding claims, wherein the absorbent core (14) is airfelt-free. [9] Absorbent article (10) according to any one of the preceding claims, wherein the absorbent core (14) has an average amount of superabsorbent polymer particles per surface area of the absorbent core (14) of 200 to 900 g / m 2 in step section (34) of the article. [10] The absorbent article (10) of any preceding claim, wherein the absorbent article (10) has a first surge acquisition time of less than 27 seconds as measured according to the Flat Acquisition Test Method. [11] The absorbent article (10) of claims 2 to 10, further comprising an acquisition system (50), wherein the acquisition system (50) is disposed between the topsheet (18) and the absorbent core (14) and preferably does not comprise superabsorbent polymer particles. [12] The absorbent article (10) of any preceding claim, wherein the superabsorbent polymer particles are comprised by the absorbent core (14) such that the superabsorbent polymer particles are sandwiched between a first and a second substrate layer (64, 72), the first substrate layer (64) facing the backsheet (20) and the second substrate layer (72) facing the topsheet (18). [13] The absorbent article (10) of claim 12, wherein the superabsorbent polymer particles are immobilized by thermoplastic adhesive material (68, 76). [14] The absorbent article (10) of claims 1 to 11, wherein the absorbent core (14) comprises a first substrate layer (64), at least a portion of the superabsorbent polymer particles being attached to the first substrate layer (64), and thermoplastic adhesive material (68) immobilizing the superabsorbent polymer particles. [15] The absorbent article (10) of claim 14, wherein the absorbent core (14) further comprises a second substrate layer (72), at least a portion of the superabsorbent polymer particles are attached to the second substrate layer (72) and thermoplastic adhesive material (76) immobilizes the superabsorbent polymer particles, wherein the first and second substrate layers (64, 72) are combined together such that at least a portion of the thermoplastic adhesive material (68) of the first substrate layer (64) contacts at least a portion of the thermoplastic adhesive material (76) of the second substrate layer (72). [16] The absorbent article (10) of claims 13 to 15, wherein the thermoplastic adhesive material (68, 76) forms a fibrous network over the superabsorbent polymer particles.

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