WO2021062432A1

WO2021062432A1 - Sap immobilizing material based on styrenic block copolymers

Info

Publication number: WO2021062432A1
Application number: PCT/US2020/070539
Authority: WO
Inventors: Robert Haines Turner; Torsten Lindner; Xavier Muyldermans; John Flood
Original assignee: The Procter & Gamble Company
Priority date: 2019-09-23
Filing date: 2020-09-14
Publication date: 2021-04-01
Also published as: CN114430687A

Abstract

Absorbent core comprising superabsorbent particles that are at least partially immobilized by an immobilizing material. The immobilizing material comprises a selectively hydrogenated block copolymer having an S block and an E block and having a general formula (S-E)nX, or mixtures thereof, wherein the S block is a polystyrene block and the E block is a polydiene block and wherein n has a value of 2.

Description

SAP IMMOBILIZING MATERIAL BASED ON STYRENIC BLOCK COPOLYMERS

FIELD

The invention relates to absorbent cores comprising superabsorbent particles that are at least partially immobilized by an immobilizing material comprising as main orsole component a selectively hydrogenated block copolymer. The immobilizing material may be in the form of a fibrous network that entangles the superabsorbent particles. The fibrous network is also attached to the substrate on which the superabsorbent particles are deposited. The absorbent cores are used in personal hygiene absorbent articles, such as diapers.

BACKGROUND

Disposable absorbent articles for receiving and retaining bodily discharges such as urine or feces are generally known in the art. Examples of these include disposable diapers, training pants and adult incontinence articles. Typically, disposable articles comprise a liquid pervious topsheet that faces the wearer’s body, a liquid impervious backsheet that faces the wearer’s clothing and an absorbent core interposed between the liquid pervious topsheet and the backsheet.

An important component of disposable absorbent articles is the absorbent core. Absorbent cores comprise an absorbent material that may be enclosed or sandwiched in a core wrap. The absorbent material typically includes superabsorbent polymer (SAP) in the form of particles. The SAP ensures that large amounts of bodily fluids, e.g. urine, can be absorbed by the absorbent article during its use and be locked away, thus providing low rewet and good skin dryness.

SAP particles have been conventionally mixed with cellulosic wood fibres. “Airfelt”, as used herein, refers to comminuted wood pulp, which is a form of cellulosic fiber. More recently, absorbent cores have been proposed which are free of such cellulosic fibres, and which are made by the so- called SAP printing technology, see for example EP1 ,447,067A1 (Busam et al.), EP1 ,621 , 165 (Blessing et al.). In this process, at least one layer of superabsorbent polymers is deposited discontinuously on a substrate such as a nonwoven. This so-called airfelt-f ree technology enables thinner absorbent cores by the reduction or elimination of these cellulose fibres from the absorbent cores and improved placement of the SAP particles, while maintaining overall absorbency.

The SAP particles should be immobilized in the dry state, that is before usage, and at least to some extent in the wet stage, while the product is in use and has absorbed a liquid e.g. by urine. In order to stabilize and maintain the SAP particles in these airfelt-f ree cores, an immobilizing material in the form of a thin fibrous adhesive network that entangles the SAP particles and anchor them to the substrate has been used. The known immobilizing material are typically hotmelt adhesives, having a base polymer along with other materials such as tackif iers, plasticizers, oils, and/or waxes. The molten immobilizing material must be able to be sprayed through a nozzle in the form of microfibers. WO2016/149252A1 (Stiehl etal.) claims such an immobilizing material having a storage modulus (G¹) at 21 °C of greater than 1.2x10⁶Pa WO2017/132119 (T umer) discloses asuperabsorbent immobilizer comprising at least 50% by weight of one or more polymers each having a peak molecular weight of at least 10 kg/mol. The superabsorbent immobilizer may comprise polymers selected from the group consisting of polymers and copolymers of propylene, ethylene, butene, and combinations thereof; styrenic block copolymers; polyolefins; olefin block copolymers, and combinations thereof.

There is a need for an improved SAP immobilizing material that is easily processable, provides the required dry and wet immobilization, is chemically stable and has an acceptable odor.

SUMMARY

The present invention is for an absorbent core comprising superabsorbent particles that are at least partially immobilized by an immobilizing material. The immobilizing material comprises as main or sole component a selectively hydrogenated block copolymer having an S block and an E block, wherein the S block is a polystyrene block and the E block is a polydiene block. The S-E diblock units are coupled, having a general formula (S-E)nX, with n having a value of 1 to 2. The hydrogenated block copolymer is further described in the attached claims and description. The absorbent core is advantageously used in an absorbent article such as a diaper.

Without wishing to be bound by theory, it is believed that the styrene block copolymers (“SBC’) claimed are advantageously used as immobilizing material, especially in a fibrous net form, because SBC have a rapid solidification mechanism (“order-disorder transition”), unlike previously used polyolefins (“PO”) which have slower solidification mechanism (“formation of micro crystals”). A more rapidly solidifying the immobilizing material fibrous net will better survive the conversion process (furtherforces exerted onto the net after laydown), which will enable better SAP immobilization. SBC show also, unlike PO, pronounced strain hardening upon extending, which provides a” self-healing” effect against micro-crack formation. This is believed to enable the fiber network to better withstand the forces of the swelling SAP in use and will specifically enable a better wet immobilization.

The SBC of the invention are further hydrogenated, to prevent degradation and odorformation due to presence of C=C double bonds (in the mid-block). The SBS of the invention may be used as substantially pure immobilizing material, wherein the immobilizing material advantageously comprises at least 80% of the selectively hydrogenated block copolymer by weight of the immobilizing material, alternatively at least 90% by weight, and alternatively at least 95% by weight. The immobilizing material is advantageously substantially free of a tackifier and/or polyolefins (“PO”).

The immobilizing material advantageously has a sufficiently low viscosity (< 8000 mPa.s) at application temperature to prevent pressure build-up in hoses and application head. Temperatures above 210°C are possible but not desired due to thermal degradation and odorformation.

DETAILED DESCRIPTION

Definitions

"Absorbent article", as used herein, refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. Absorbent articles may 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 discharges and fecal matter.

“Absorbent core” means an absorbent structure disposed between topsheetand backsheet for absorbing and containing liquid such as urine received by the absorbent article. The absorbent core comprises an absorbent material, that is typically enclosed within or sandwiched between a core wrap. The core wrap may be a single material that is folded over the absorbent material or may comprise a separate top layer and bottom layer that are bonded together. The absorbent core may be substantially cellulose free. As used herein, the absorbent core excludes any acquisition system, topsheet, or backsheet of the absorbent article. The absorbent core may consist essentially of the core wrap, the superabsorbent polymer particles, and the immobilizing material as a fibrous network.

“Comprise,” “comprising,” and “comprises”, as used herein, are open ended terms, each specifies the presence of what follows, e.g., a component, but does not preclude the presence of other features, e.g., elements, steps, components known in the art, or disclosed herein.

“Consisting essentially of”, as used herein, limits the scope of subject matter, such as that in a claim, to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the subject matter.

“Diaper", as used herein, refers to an absorbent article generally worn by infants and incontinent persons about the lower torso so as to encircle the waist and legs of the wearer and that is specifically adapted to receive and contain urinary and fecal waste. As used herein, term "diaper also includes "pants" which is defined below.

“Fibrous network”, as used herein, is understood to comprise a polymer composition from which strands or a net structure is formed and applied to the superabsorbent polymer (SAP) particles with the intent to at least partially immobilize the SAP particles in both the dry and wet state. The fibrous network may be formed over, around, and/or between the superabsorbent polymer particles and may also be connected to the substrate on which the superabsorbent particles have been deposited.

“Nonwoven”, as used herein, is a manufactured sheet, web, or batt of directionally or randomly orientated fibers, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments, orfelted by wet-milling, whether or not additionally needled. The fibers may be of natural or man-made origin and may be staple or continuous filaments or be formed in situ. Commercially available fibers have diameters ranging from less than 0.001 mm to greaterthan 0.2 mm and they come in several different forms: short fibers (known as staple, or chopped), continuous single fibers (filaments or monofilaments), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn). Nonwoven fabrics can be formed by many processes such as meltblowing, spunbonding, solvent spinning, electrospinning, and carding. The basis weight of nonwoven fabrics is usually expressed in grams per square meter (gsm).

"Pant" or "training pant", as used herein, refer to disposable garments having a waist opening and leg openingsdesignedforinfantoradultwearers. Apantmay be placed in position on the wearer by inserting the wearer's legs into the leg openings and sliding the pant into position about a wearer's lower torso. A pant may be pre-formed by any suitable technique including, but not limited to, joining together portions of the article using refastenable and/or non-refastenable bonds (e.g., seam, weld, adhesive, cohesive bond, fastener, etc.). A pant may be pre-formed anywhere along the circumference of the article (e.g., side fastened, front waist fastened). While the terms "pant" or "pants" are used herein, pants are also commonly referred to as "closed diapers," "prefastened diapers," "pull-on diapers," "training pants," and "diaper-pants".

"Substantially", as used herein, means generally the same or uniform but allowing for or having minor fluctuations from a defined property, definition, etc. For example, small measurable or immeasurable fluctuations in a measured property described herein, such as viscosity, melting point, etc. may resultfrom human errorormethodology precision. Otherfluctuations are caused by inherent variations in the manufacturing process, thermal history of a formulation, and the like. The compositions of the present invention, nonetheless, would be said to be substantially having the property as reported.

“Superabsorbent particles”, as used herein, refers to a superabsorbent polymer material which is in particulate form so as to be flowable in the dry state.

“Vinyl content” refers to the content of a conjugated diene that is polymerized via 1 ,2-addition in the case of butadiene, or via both 1 ,2-addition and 3,4-addition in case of isoprene.

“Polystyrene content” or PSC of a block copolymer refers to the % weight of polymerized styrene in the block copolymer, calculated by dividing the sum of molecular weight of all polystyrene blocks by the total molecular weight of the block copolymer. PSC can be determined using any suitable methodology such as proton nuclear magnetic resonance (NMR).

“Molecular weight” refers to the peak molecular weight (Mp) in g/mol of the considered polymer measured with GPC using polystyrene calibration standards having known numberaverage molecular weights. Mp is the molecular weight of the standard at the peak maximum.

The order-disorder-transition temperature (ODT) refers to the temperature at which the microdomain structure of the block copolymer begins to disappear. ODT is defined as the temperature above which a zero shear viscosity can be measured by dynamic rheology. ODT temperatures can be measured using dynamic mechanical analysis (DMA), with temperature sweeps performed over various frequencies, wherein the ODT is identified as the temperature where complex viscosity begins to collapse to a single value independent of frequency at low frequencies

“Melt index” is a measure of the melt flow of the polymer according ASTM D1238 at 190°C and 2.16 kg weight, expressed in units of grams of polymer passing through a melt rheometer orifice in 10 minutes.

ASTM D412 refers to the test method to determine the tensile properties of thermoplastic elastomers and vulcanized thermoset rubbers. Adumbbell and straightsection specimensorcut ring specimens can be used. For the tests, a Mini D die with a dumbbell central width of 0.1 inch and the length of the narrow parallel sided central portion of 0.5 inch is used to cut the specimens and a 50 mm/min. tensile rate is used.

Absorbent core and absorbent article

The absorbent core of the invention may be of the type discussed in the background as “airfelt- free cores”, that is wherein the absorbent material is (substantially) free of cellulosic fibers. The absorbent material may in particular consists of SAP particles. In addition to the fibrous network of immobilizing material, the SAP particles may be immobilized by an adhesive disposed between the top and/or bottom layer of the core wrap, typically slot coated as is known in the art. The absorbent core of the invention may be used in any type of absorbent articles, such as diapers and pants. The articles typically comprise a liquid permeable topsheet on its wearer-facing side, a liquid-impermeable backsheet on the garment-facing side, wherein the absorbent core is disposed between the topsheet and the backsheet. The absorbent article may comprise an acquisition layer or system. Various other usual components of absorbent articles may of course be used, such as inner and outer elasticized barrier leg cuffs, a wetness indicator, an elastic back or front wait bands, etc... Absorbent cores and absorbent articles that may be used with the immobilizing material of the present invention, as well as detailed method to make them are for example disclosed in more details in the references indicated background section above. The absorbent cores may be free of cellulose fibers. See also US16/520386 filed July 26, 2018 (attorney docket 15312MQ-US) for a description on how to make such absorbent cores. The absorbent cores may also comprise area free of absorbent material through which the top layer and the bottom layer of the core wrap are bonded, so that three dimension channels form as the absorbent layer swells, as disclosed for example in WO2012/170778A1 (Rosati et al.) or WO2015/31243 (Roeet al.).

The absorbent articles of the invention are typically conditioned and commercialized in a package comprising a plurality of such absorbent articles.

Superabsorbent particles immobilizing material

The immobilizing material is a composition that is applied to the superabsorbent polymer particles with the intent to at least partially immobilize the superabsorbent polymer material at least in the dry and preferably also in the wet state. The immobilizing material is typically a hotmelt that is heated at a sufficiently high temperature until it becomes fluid enough to be sprayed on the superabsorbent particles. As the sprayed immobilizing material cools, it quickly forms a solid f iberized network with microfibers or nanofibers that interweaves or intertwines with the particles of superabsorbent polymer. An exemplary process for making the absorbent core and spraying the immobilizing material is disclosed in the reference indicated in the background section, such as EP1 ,447,067A1 (Busam et al.). As disclosed therein, a layer of SAP particles may be first disposed (e.g. SAP printing technology) on a substrate such as nonwoven layer, optionally with an auxiliary adhesive between the substrate and the SAP layer, and the immobilizing material homogeneously sprayed thereon to form the immobilizing fibrous network. A second substrate may then be applied on the immobilized layer to form a core wrap. The absorbent core may comprise two such layers of immobilized superabsorbent particles, as disclosed in the cited references.

The claimed immobilizing composition is a selectively hydrogenated block copolymer having an S block and an E block of the general formula (S-E)nX or mixtures thereof, and n has a value of 2, with between 20 and 35 wt. % of the block copolymer being diblock units with a general formula of (S-E), and X is a coupling agent residue.

Suitable coupling agent may be selected from the group of methyl benzoate, silicon tetrachloride, alkoxy silanes, polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, polyanhydrides, polyesters, polyhalides, diesters, methoxy silanes, divinyl benzene, 1 ,3,5-benzenetricarboxylic acid trichloride, glycidoxytrimethoxy silanes, oxydipropylbis(trimethoxy silane), and mixtures thereof.

The block copolymer can be linear sequential or coupled.

Priorto hydrogenation, the S block of the block copolymers can be a polystyrene block having any molecular weight from 4,700 to 5, 100.

Priorto hydrogenation, the E block is a polydiene block selected from the group consisting of polybutadiene, polyisoprene and mixtures thereof. In one embodiment, the E blocks are a single polydiene block. These polydiene blocks can have molecular weights that range from 18,000 to 26,000.

Hydrogenation of block copolymer: the block copolymer is a hydrogenated block copolymer. Any hydrogenation method that is selective forthe double bonds in the conjugated polydiene blocks, leaving the aromatic unsaturation in the polystyrene blocks substantially intact, can be used to prepare the hydrogenated block copolymers.

The method may employ a catalyst or catalyst precursor comprising a metal, e.g., nickel or cobalt, and a suitable reducing agent such as an aluminum alkyl. Also useful are titanium based systems. The hydrogenation can be accomplished in a solvent at a temperature from 20°C. to 100°C., and at a hydrogen partial pressure from 100 psig (689 kPa) to 5,000 psig (34,473 kPa). Catalyst concentrations within the range from 10 ppm to 500 ppm by wt. of iron group metal based on total solution are generally used, and contacting at hydrogenation conditions from 60 to 240 minutes. After the hydrogenation is completed, the catalyst and catalyst residue will be separated from the polymer. The microstructure relevant to the block copolymer can be controlled for a high amount of vinyl in the E block, using a control agent known in the art such as to diethyl ether and diethoxypropane during polymerization of the diene.

Hydrogenation can be carried out under such conditions that at least 90 % of the conjugated diene double bonds are reduced, and up to 10 % of the arene double bonds are reduced.

The block copolymers are prepared so that they have from 75 to 80 % vinyl in the E block prior to hydrogenation.

The styrene content of the block copolymer is from 29 wt. % to 34 wt. % by weight of the block copolymer. The coupling efficiency is in the range of 75-80%.

In some embodiments, subsequent to hydrogenation, from 0 to 10 percent of the styrene double bonds in the S blocks have been hydrogenated.

Additives

The immobilizing material is advantageously substantially free of tackif iers, and may comprise less than 5 %, alternatively less than 3 %, alternatively less than 2 %, alternatively less than 1 %, alternatively less than 0.5 %, by weight of the polymer filler composition, and alternatively being free of a tackifier. Exemplary tackifiers can include aliphatic hydrocarbon resins, aromatic modified aliphatic hydrocarbon resins, hydrogenated poly-cyclopentadiene resins, poly-cyclopentadiene resins, gum rosins, gum rosin esters, wood rosins, wood rosin esters, tall oil rosins, tall oil rosin esters, poly-terpenes, aromatic modified poly-terpenes, terpene-phenolics, aromatic modified hydrogenated poly-cyclopentadiene resins, hydrogenated aliphatic resins, hydrogenated aliphatic aromatic resins, hydrogenated terpenes and modified terpenes, and hydrogenated rosin esters. The polymeric filler composition can be free of a tackifier.

There are significant advantages to minimizing or avoiding the use of a tackifier as it may reduce the cost of the polymeric filler composition, as well as eliminate an additional ingredient and potential issues that may be associated with supplying the additional ingredient. Furthermore, tackifiers may impart undesirable odor in disposable articles and can also act as carriers of low molecular weight plasticizers (e.g., process oils that are used in SBC based adhesives) that may weaken the polyethylene back sheet materials used in absorbent articles and textile articles.

The immobilizing material may optionally comprise an antioxidant or a stabilizer. Any antioxidant known to a person of ordinary skill in the art may be used in the adhesion composition. Non-limiting examples of suitable antioxidants include amine-based antioxidants such as alkyl diphenyl amines, phenyl-naphthylamine, alkyl or aralkyl substituted phenyl-naphthylamine, alkylated p-phenylene diamines, tetramethyl-diaminodiphenylamine and the like; and hindered phenol compounds such as 2,6-di-t-butyl-4-methylphenol; 1 , 3, 5-trimethyl-2 ,4,6-tris(3' ,5'-d i-t-butyl-4'- hydroxybenzyl)benzene; tetra kis [(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane (e.g., IRGANOXTM 1010, from Ciba Geigy, New York); octadecyl-3,5-di-t-butyl-4-hydroxycinnamate (e.g., IRGANOXTM 1076, commercially available from CibaGeigy) and combinations thereof. When used, the amount of the antioxidant and/or the stabilizer in the polymeric filler composition can be less than 1 %, alternatively from about 0.05 % to about 0.75 %, and alternatively from about 0.1 % to about 0.5 %, by weight of the immobilizing material.

The immobilizing material may optionally comprise a UV stabilizer that may prevent or reduce the degradation of the composition by radiation. Any UV stabilizer known to a person of ordinary skill in the art may be used in the immobilizing material. Non-limiting examples of suitable UV stabilizers include benzophenones, benzotriazoles, aryl esters, oxanilides, acrylic esters, formamidine carbon black, hindered amines, nickel quenchers, hindered amines, phenolicantioxidants, metallic salts, zinc compounds, and combinations thereof. Where used, the amount of the UV stabilizer in the immobilizing material can be less than 1 %, alternatively from about 0.05 % to about 0.75 %, and alternatively from about 0.1 % to about 0.5 %, by weight of the immobilizing material.

The immobilizing material may optionally comprise a brightener, colorant, and/or pigment. Any colorant or pigment known to a person of ordinary skill in the art may be used in the immobilizing material. Non-limiting examples of suitable brighteners, colorants, and/or pigments include fluorescent materials and pigments such as triazine-stilbene, coumarin, imidazole, diazole, titanium dioxide and carbon black, phthalocyanine pigments, and other organic pigments such as IRGAZINB, CROMOPHTALB, MONASTRALB, CINQUASIAB, IRGALITEB, ORASOLB, all of which are available from Ciba Specialty Chemicals, T arrytown, N.Y. Where used, the amount of the brightener, colorant, and/or pigment in the immobilizing material can be less than 10 %, alternatively from about 0.01 % to about 5 %, and alternatively from about 0.1 % to about 2 %, by weight of the polymeric filler composition.

The immobilizing material may optionally comprise a fragrance such as a perfume or other odorant. Such fragrances may be retained by a liner or contained in release agents such as microcapsules that may, for example, release fragrance upon removal of a release liner from or compression on the adhesive composition. Where used, the amount of the fragrance in the immobilizing material can be less than 3 %, alternatively less than 2 %, alternatively less than 1 %, alternatively from about 0.05 % to about 0.75 %, and alternatively from about 0.1 % to about 0.5 %, by weight of the immobilizing material.

Properties of the hydrogenated block copolymer:

The immobilizing material and its main or sole component hydrogenated block copolymer may advantageously have any or all of the following properties, which are measured on the raw material before it is formed as a fibrous network.

The solution viscosity of the hydrogenated block copolymer may range from 15 to 30 centipoise (cP) at 25°C. The “solution viscosity” refers to the inherent viscosity of a 25 wt.% solution of the hydrogenated block copolymer in toluene as measured using the Ubbelohde capillary viscometer.

The hydrogenated block copolymers may have a low order-disorder temperature (ODT). The ODT may be from 150°C to 190°C. The hydrogenated block copolymer may have a tensile strength of 4-6 MPa, as measured on compression molded films according to AST M D412. The hydrogenated block copolymer may have an elongation at break of 300-500%.

The immobilizing material may further advantageously have any or all of the following properties which are believed to be desirable fordry and/orwet integrity of the immobilized SAP. The melt viscosity, as measured by the Viscosity Rheometry Test Method described below, may have the following values:

- a melt viscosity at 170°C ranging from 100 mPa.s to 25,000 mPa.s, advantageously below 10,000 mPa.s;

- a melt viscosity at 210°C ranging from about 5,000 to about 8,000 mPa.s, in particular from 5,500 to 7,500 mPa.s, or from about 5,900 to about 7,200 mPa.s.

The following immobilizing material properties are measured according to the Oscillatory Rheometry T est Method and the Extensional T est Method, described below.

- a Storage Modulus @ 23°C [MPa] < 4 MPa

- a Storage Modulus @100°C [Pa] > 100,000 Pa

- a True Strain at Break @ 23°C > 2.0, or > 2.1

The immobilizing material advantageously has an Average Time to Breakage greater than 1550 s, preferably greater than 1620 s, more preferably greater than 1680 s as measured by the Stepwise Stress-Relaxation Test Method disclosed herein. As an example, a selectively hydrogenated block copolymer according to claim 1 (LR0081-24 provided by Kraton Inc.) was tested according to the Stepwise Stress-Relaxation Test Method described below, and the time to break was measured to be 1717 s for a first replicate and 1787 s for a second replicate.

The absorbent core may advantageously have a Wet Mobilization as measured by the Wet Mobilization Value Test of less than 50%, preferably less than 40%, preferably less than 30%, and preferably from about 0% to about 28%, as measured according to the Wet Mobilization Value T est Method described herein.

TEST METHODS

All official test methods (ISO, DIN, etc..) are conducted using the latest test version available at the filing date of the application.

Viscosity Rheometrv T est Method

The Viscosity Rheometry T est Method is used to measure the shear viscosity at a shear rate of 10 [1/s] at 210 °C of a polymer composition.

A controlled-strain rotational rheometer (such as ARES G2, TA Instruments, Newcastle, DE, USA, or equivalent) capable of sample temperature control (such as a Forced Convection Oven; TA Instruments, New Castle, DE, USA, or equivalent)) with a precision equal to or exceeding +/- 0.5 °C at 210 °C is used. The rheometer is operated in a cone-to-plate configuration, with 25 mm 0.1 rad steel cone as upper tool and a 40 mm steel plate lower tool. The cone truncation distance is defined as that specified for the particular cone tooling used (typically approximately 50 pm for a 25 mm 0.1 rad steel cone). The cone truncation distance is controlled to the nearest 0.1 pm.

The rheometer is heated to 190 °C and polymer composition is introduced in the rheometer. Once the polymer has equilibrated in temperature at 190 °C, the rheometer tooling gap is set to 50 pm greater than the cone truncation distance and excess protruding sample is trimmed. The gap is then set to the cone truncation distance. To condition the sample a constant pre-shear of 0.1 1/s, at 190 °C for 180 s is applied.

For the measurement the rheometer temperature is set to 210°C and when sample has reached temperature it is conditioned for 180 s. A steady state shear rate of 10 1/s is applied. The viscosity is measured with a sampling period of 15 sec. The viscosity is calculated, and the average of each period is monitored. When three viscosity periods in a row are within +/- 5% of each other, the average (arithmetic mean) of these three values is reported as steady state viscosity at 10 1/s and 210 °C and this value is reported in millipascal seconds (mPa.s) to the nearest 1 (mPa.s) as the “Shear Viscosity at 10 (1/s) at 210 °C”.

Wet Mobilization Value Test Method Equipment:

• Graduated Cylinder

• Stop watch (± 0.1 sec)

• Scissors

• Light Box

• Pen

• Test solution: 0.90% saline solution at 23 +/- 2°C

• Metal ruler traceable to NIST, DIN, JIS or another comparable National Standard

• PVC/metal dishes with a flat surface inside and a minimum length of the core bag length (n) to be measured and a maximum length n + 50 mm, width w ± 50 mm, height of 30-100 mm or equivalent

• Balance accurate to ± 0.0.1 g

• Binder clips width 1” (25 mm)

• Wet Immobilization Impact Tester Equipment (WAI IT-3), Design package number: PA- 00112.59506-R03, Manufacturing information: Henkel GmbH Germany

The WAI IT tester is a purely mechanical device. A sliding-board (A) is falling down along a sliding track (B) after it was mechanical released by two levers placed on the side of the equipment. A pre-loaded diaper is cut (cross direction) and is attached onto the sliding-board with the open side down. The sliding-board is lifted up by the operator using his hands. After releasing the sliding-board, it hits the anvil below and the impact force damages the absorbent core structure. Depending on the absorbent core structure quality AGM particles will fall out of the pad. The weight difference before and after the impact describes the quality of the absorbent core.

Facilities:

Standard laboratory conditions, temperature: 23°C ±2°C, relative humidity: < 55%

Sample Preparation:

1 . Open the product, topsheet side up. 2. Unfold the diaper and cut the cuff elastics approximately every 2.5 cm to relieve chassis tension such that the product easily lies flat.

3. For pull-up products open the side seams and remove the waistbands.

4. Remove the topsheet and potential other layers or materials between topsheet and core bag so as to minimally perturb the core bag nonwovens and absorbent material contained within. Note: steps 1 to 4 are not required if the core bags have been directly made, as in the examples, and do not need to be separated from diapers.

5. A lightbox is used to identify the longitudinal extent of the core, and the longitudinal midpoint of the core along the longitudinal axis is marked.

Test Procedure

WAI IT Calibration:

1 . Make sure that the sliding board is in the lower position. Open the front door of the WANT tester and connect the force gauge hook to the upper sample clamp of the WAI IT. Make sure that the clamp is closed before connecting the spring-balance.

2. Use both hands on the spring-balance to lift continuously and as slowly as possible up the sliding board towards the upper position. Record the average value (mi) during the execution to the nearest 0.02 kg.

3. Guide down the sliding board as slowly as possible to the lower position and record the average value (m2) read off during execution to the nearest 0.02 kg.

4. Calculate and record the delta of mi - m2 to the nearest 0.02 kg. If the delta is 0.6 kg ± 0.3 kg continue measurement. Otherwise, an adjustment of the sliding board is necessary. Make sure that the sliding board is in lower position and check the sliding path for any contamination or damage. Check if the position of the sliding board to the sliding path is correctly adjusted by shaking the board. For easy gliding some clearance is needed. If not present, readjust the system.

WAI IT test settings:

• Drop height is 16 cm.

• Diaper load (ID) is 73% of the core capacity (cc); ID = 0.73 xcc.

• Core capacity (cc) is calculated as: cc = ITISAP X SAPGV, where ITISAP is the mass of superabsorbent polymer (SAP) present in the diaper and SAPGV is the free swelling capacity of the superabsorbent polymer. Free swelling capacity of the superabsorbent polymer is determined with the method described in WO 2006/062258, which is hereby incorporated by reference. The mass of the superabsorbent polymer present in the diaper is the average mass present in ten products.

Test Execution:

1 . Weigh and report it to the nearest 0.1 g.

2. Measure the appropriate volume Saline (0.9%NaCI in deionized water) with the graduated cylinder.

3. Lay the dish flat on the laboratory table. Lay the core bag, topsheet side down, flat into the filled plastic or metal dish. Wait for 5 ± 1 min to allow all saline to be absorbed. After this period, there might be liquid in the dish at the sides of the core which has not been in contact with the core. If this is the case, take the dish and hold it slanting in different directions, to allow any free liquid to be absorbed.

4. Wait for another5 minutes (+/- 30 sec) to allow all saline to be absorbed. Some drops may be retained in the dish. Use only the defined PVC/metal dish to guarantee homogenous liquid distribution and less retained liquid

5. Weigh and report it to the nearest 0.1 g. Check to see if the wet core bag weight is out of limit (defined as “dry core bag weight + diaper load ± 4 ml”). For example, 12 g dry core bag weight + 150 ml load = 162 g wet core bag weight. If the actual wet weight on the scale is between 158g and 166g, the pad can be used forshaking. Otherwise discard the pad and repeat all steps.

6. The loaded core bag is cut parallel to the lateral axis and through the longitudinal midpoint of the core so as to divide the core bag into approximately two “halves” - one corresponding to the front of the absorbent article and one corresponding to the rear of the absorbent article.

7. Weigh the back of the cut wet core bag and record it to the nearest 0.1 g.

8. Take the back of the cut wet core bag and clamp the end seal side up into the WANT (open end of the core oriented down). Thereby, the back of the cut wet core bag is folded around the top edge of the sliding board and fixed with two binder clips (width = 25 mm) onto the sliding board. The core bags are clamped in a way that the clamps overlap with the AGM containing area of the core over a length of 1 cm in vertical direction. Press the pad onto the sliding board to establish a connection. Note: Make sure that enough diaper material is folded around the top edge of the sliding board so that the clamps do not touch the sliding board material. This is needed to have a proper fixation of the sample during impact. It is allowed to clamp the absorbent core.

9. Lift up the sliding board to the upper position by using both hands until the board is engaged.

10. Close the safety front door and release the slide blade using both levers on the side simultaneously.

11. Take the tested sample out of the WANT and put it on the balance (m2). Record the weight to the nearest 0.1 g.

12. Repeat steps 5 to 13 with front of the cut wet core bag.

Reporting:

1 . Record the dry core bag weight to the nearest 0.1 g.

2. Record the wet weight before (mifrontand miback) and after (rmfrant and rri2back) testing, both to the nearest 0.1 g.

3. Calculate and report the average weight loss (Am) to the nearest 0.1 g: Am = (mifront + miback) — (iTtefront + ITl2back)

4. Calculate and reportthe weight loss in percentto the nearest 1 %, (Amrei): (Amrei) = (((mifront + miback) — (m2front + ITl2back)) X 100%) / (mifront + miback)

In total, ten replicates are performed. For each replicate the percent weight loss is calculated and recorded. The arithmetic mean of percent weight loss for the ten replicates is calculated and reported in percent, to the nearest integer value of percent, as the Wet Mobilization Value.

Extensional T est Method

The Extensional T est Method is used to determine the T rue Strain at Break Parameter. A thin film specimen formed of polymer composition is analyzed with a rotational rheometer fitted with a specialized fixture with counter rotating rollers, and the stress associated with extensional strain imparted is measured and recorded.

Instrumental Setup

A rotational rheometer (ARES G2, TA Instruments, Newcastle, DE, USA, or equivalent) is fitted with a fixture that has counter rotating cylindrical rollers specifically designed for the interrogation of extension deformation of films. An example of a suitable fixture is the Extensional Viscosity Fixture, or EVF (EVF, TA Instruments, or equivalent). The rheometer is further fitted with a forced-convection oven FCO (FCO, TA Instruments, or equivalent) and cooling system (ACS 2, TA Instruments, or equivalent) capable of controlling temperate from at least -50 to 250 °C to a within a tolerance of 0.5 °C.

Specimen Preparation Approximately 10 g of the polymer composition is placed in a polytetrafluoroethane (PTFE) bowl and introduced into a vacuum oven. After 15 minutes at 170 °C at ambient pressure, the pressure is lowered to 10 mbar, and the polymer composition is subsequently held at 170 °C and at 10 mbar for 45 minutes to remove air bubbles from the polymer composition. The polymer composition is removed from the vacuum oven and allowed to cool to ambient lab conditions (23 ± 2 °C) for 90 ± 30 minutes, at which point the polymer composition is removed from the PTFE bowl and placed between 2 sheets of siliconized paper. A metal shim 0.50 mm in thickness is used in the heated press as a spacer to obtain a film thickness of 0.50 mm when pressed with a heated press at 90 °C and 10 Bar (instrument setting) for 60 seconds to a polymericfilm. If 90 °C is insufficientto melt the polymer composition, a higher temperature (but the lowest temperature sufficient to melt the composition) is used. The film is stored at least 120 hours in the laboratory at 23 ± 2 °C prior to testing. From the film individual specimens for measurement are punched with a sample cutter to the specimen dimensions of 20.0 mm by 10.0 mm by 0.50 mm. This specimen will be cut lengthways with a scissor to achieve a final width of 5 ± 0.5 mm. The exact width and thickness will be determined with a digital caliper (Electronic Caliper PRO-MAX Fowler) to the nearest of 0.01 mm and entered into the rheometer software. Because anisotropy or grain directionality due to flow introduced during processing and preparation may have an influence on tensile properties, the specimens should be cut so the lengthwise direction of the specimen is parallel to the grain direction when this direction is known.

Measurement

The cylinders of the EVF are heated to 80 °C for 90 ± 30 s in the forced-convection oven of the rheometer. Then a small droplet (0.03 ± 0.01 g) of the polymer composition is applied to each cylinder. The used polymer composition should exhibit a high stiffness (G’ at 23°C greater than 10MPa) to not interfere with the measurement. Aspecimen of polymer composition is quickly pressed into a molten polymer composition on the cylinders of the EVF to fix it to the cylinder surface. The specimen is placed perpendicular to the axis of rotation of the cylinders.

The specimen mounted on the EVF is then placed in the forced convection oven of the rheometer for thermal conditioning and is kept isothermal at 23 ± 1 °C for 300 ± 10 s. After this time has elapsed, the specimen is mechanically conditioned. To mechanically condition the specimen, the torque transducer is zeroed, and the sample is put under a pre-stretch rate of 0.001 s-¹ for 0.30 s and then allowed to relaxfor60 s. (In this method, all strain is expressed in terms of Hencky strain, also known as “true strain” or “logarithmic strain.”) The measurement is performed in the FCO oven at 23 °C ± 0.5 °C. The strain rate extension for the measurement is 0.01 s— 1 , and the strain at maximum extension is 4.0. After measurement, the specimen is checked for rupturing. If it has ruptured, the location of the break is noted. If the rupture is approximately in the middle between the two cylinders of the EVF, the data collected are deemed acceptable. Otherwise, if the polymeric film break is at or close to the rotating cylinders, the results are discarded, and the measurement performed again on a replicate specimen.

Analysis

For the extensional stress calculation, a constant volume is assumed. From the raw torque versus angular displacement data recorded by the rheometer, extensional stress (in megapascals, or MPa) versus Hencky strain data are calculated. The data are plotted in semi-logarithmicfashion with Hencky strain on the abscissa (linear scale) and extensional stress on the ordinate (logarithmicscale). A linear fit with a positive slope with an R² value of 0.9 or greater is set between a Hencky strain of 0.5 and 1 . The Hencky Strain, when the specimen ruptures and/orthe reported torque value is lower than 100pNm, is reported as True Strain at Break Parameter as dimensionless value to the nearest of 0.1 (or, in the case it did not rupture during the measurement, to a strain of 4.0).

Oscillatory Rheometrv T est Method

The Oscillatory Rheometry Test Method is used to measure the Storage Modulus and the Loss Factor of a polymer composition. A controlled-strain rotational rheometer (such as Discovery HR-3, TA Instruments, New castle, DE, USA, or equivalent) capable of sample temperature control (using a Peltier cooler and resistance heater combination) with a precision equal to or exceeding 0.5°C over at least the range of -10 °C to 150 °C. The rheometer is operated in a parallel plate configuration with 20-mm stainless steel parallel-plate tooling.

A parallel plate gap of 1000 pm is initially used in the method. To compensate for thermal expansion of the tooling, the gap is set to 1000 pm, and a mapping of actual plate gap (as measured using a suitable standard test fluid) a function of temperature over the range -10 °C to 150 °C is performed. This mapping is then used throughout the determination of the Storage Modulus Parameter and the Loss Factor Parameter.

The rheometer is heated to 150 °C, the polymer composition is introduced in the rheometer, the gap is set to 1050 pm, excess protruding sample is trimmed, and the gap is then set to 1000 pm. (The axial force control of the rheometer is set to 0 N and be maintained within ± 0.1 N of force during the experiment, thereby thermal expansion/contraction of the sample itself is compensated by adjusting the gap in order to avoid overfilling or underfilling in addition to the abovementioned compensation of the tooling.) The rheometer is then allowed to cool to 130 °C, at which point the measurement commences with temperature ramped from 130 °C to -10 °C at a constant rate of cooling of 2 °C/min. The applied strain amplitude is 0.1 %, and the frequency of oscillation is 1 Hz (that is, one cycle per second). The resulting oscillatory stress is recorded.

After this step, the sample temperature is set to 23 °C (temperature is ramped to this setpoint at a rate of 10 °C/min), and the sample is allowed to rest for 4.0 hours at 23 °C. At the end of this period, the temperature is set to -10 °C (temperature is ramped to this setpoint at a rate of 10 °C/min), the sample is equilibrated for300 seconds at— 10 °C, and a second oscillatory rheology measurement is conducted (0.1 % strain, frequency of oscillation of 1 Hz) while temperature is ramped upward to 130 °C at a constant rate of increase of 2 °C/min.

From the first decreasing temperature sweep, the storage modulus G’ is calculated and recorded at 100°C, and these values are reported in Pascals (Pa) to the nearest 1 Pa as the “Storage Modulus at 100 °C”. From the first, decreasing temperature sweep, the loss factor (also known as tan delta) is calculated recorded at 100°C, and this dimensionless value is reported to the nearest hundredth as the “Loss Factor at 100°C”.

The storage modulus G’ can also be calculated and recorded at different temperatures, such as 25 °C.

Stepwise Stress-Relaxation Test Method

The Stepwise Stress-Relaxation Test Method is used to measure the stress associated with multiple elongations of a sample material composition. In the Stepwise Stress-Relaxation Test Method, a specimen of defined dimensions of sample material composition is analyzed with a controlled-strain tensile tester which is used to impose and hold at a series of elongations. The time to break is recorded for each of three like specimens, and the average time to break is reported. Laboratory temperature is maintained at 23 ± 2 °C throughout the method.

Specimen preparation

15 ± 1 g of sample material composition is placed in a round polytetrafluoroethane (PTFE) bowl with a flat bottom (diameter 60 ± 2 mm) and introduced into a vacuum oven held at 30 ± 10 °C above the melting temperature (that is, at a temperature defined as temperature 1 ) of the sample material composition. After being at ambient pressure for 15 minutes at temperature 1 , the pressure of the vacuum oven is then lowered to 10 mbar, and the sample material composition is then held for 45 minutes at temperature 1 and at 10 mbar. The sample material composition is then removed from the vacuum oven and allowed to cool toward ambient laboratory temperature for 90 ± 30 minutes at which point the adhesive composition is removed from the PTFE bowl, yielding a disc of sample composition material approximately 5 to 10 mm thick.

A heated press is used to flatten the disc to a thickness of approximate 2 mm. The platens of the press are held at 10 ± 5 °C below the melting point of the sample material composition such that the sample material composition is in a semi-solid state. This disc is placed between 2 sheets of silicone release paper (such as product number 114918, Mondi Group, Hilm, Austria, or equivalent), and the paper/disc/paper stack is placed in the press. Metal shim 2 ± 0.1 mm in thickness are placed proximal to the paper/disc/paper stack, and the press is actuated with sufficient pressure to bring the platens into contact with the 2-mm shims, and the press is held in this position for 60 s. The thin film is then removed the press and aged for at least 120 hours at laboratory temperature prior to further cutting into individual specimens.

Individual specimens for testing are cut from the aged film using a steel-rule die or equivalent cutting tool. The tool is designed to punch a specimen of the shape of section 3 of ISO 3167 but with the following dimensional modifications: Overall length h is 50.0 mm, Length of narrow parallel-sided portion /i is 25.0 mm, Radius r is 6.4 mm, Distance between broad parallel-sided portions h is 34.0 mm, Width at ends bi is 7.0 mm, Wdth of narrow portion bi is 3.3 mm, and Thickness h is the thickness of the film after being pressed, approximately 2 mm. Three like specimens are cut from an aged film for stepwise strain relaxation analysis. Because anisotropy or grain directionality due to flow introduced during processing and preparation may have an influence on tensile properties, the specimens should be cut so the lengthwise direction of the specimen is parallel to the grain direction when this direction is known.

Stepwise strain measurement

A controlled-strain tensile tester (such as Z005, ZwickRoell GmbH & Co. KG, Ulm, Germany, or equivalent) with 100-N load cell in series with the upper claim is used. The clamps are positioned so to as to create a 35 ± 1 mm gage length, and the exact gage length is recorded. The specimen is mounted with long axis parallel to the measurement axis and positioned symmetrically vertically in the clamps. The specimen is mounted in the upper clamp and then the lower clamp is closed. The clamping force used for both the upper and lower clamps is chosen such that the test piece does not slip or suffer damage during the test. The load cell force reading is set to zero.

The tensile tester is then used to apply the following strain conditions to the specimen in immediate succession: (1 ) crosshead separation is increased to 150% of the initial gage length at 1000 mm/min, (2) crosshead position is held for 20 min at 150% of initial gage length, (3) crosshead separation is increased to 300% of the initial gage length at 1000 mm/min, (4) crosshead position is held for 20 min at 150% of initial gage length, (5) crosshead separation is increased to 450% of the initial gage length at 1000 mm/min, (6) crosshead position is held for 20 min at 450% of initial gage length. Force data are recorded throughout the measurement at 100 Hz as a function of total time elapsed since the beginning of the first step in this sequence. (For convenience, if the specimen is observed to have completely broken at any point in the measurement, the measurement may be stopped prior to the completion of the entire strain protocol so long as all data points up to and including the point of breakage have been recorded.) This strain measurement is performed on each of the three like specimens.

Analysis

For each specimen, the time to breakage (defined as the first point at which the measured force drops below 0.2 N after the first strain step is initiated) is recorded to the nearest 1 s. If the specimen did not break during the entirety of the measurement, the time to breakage is defined as the final time point of the measurement (just over 1 hour). The arithmetic mean of time to breakage of the three specimen replicates is calculated and reported to the nearest 1 s as the Average Time to Breakage for the sample material composition being measured.

Misc.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

CLAIMS What is Claimed is:

1 . An absorbent core comprising superabsorbent particles that are at least partially immobilized by an immobilizing material, wherein the immobilizing material comprises a selectively hydrogenated block copolymer having an S block and an E block and having a general formula (S-E)nX, or mixtures thereof, wherein

• n has a value of 2;

• X is a coupling agent residue;

• the molecular weight of the S block is 4700 to 5100 g/mol;

• the selectively hydrogenated block copolymer has a solution viscosity at a 25 wt.% concentration in toluene of the block copolymer is 15-30 centipoise (cP) at 25°C;

• the polystyrene content in the block copolymer is 29 - 34 wt. %;

• 20-35 wt.% of diblock units in the block copolymer has a general formula S-E; and wherein prior to hydrogenation:

• the S block is a polystyrene block;

• the E block is a polydiene block selected from the group consisting of polybutadiene, polyisopreneand mixtures thereof, and having a molecular weight of from 10,000 - 12,000 g/mol;

• the total vinyl content of the polydiene block is 75-80%; and wherein subsequent to hydrogenation:

• 0-10 percent of styrene double bonds in the block copolymer are reduced, and

• at least 90% of conjugated diene double bonds in the block copolymer are reduced.

2. An absorbent core according to any of the preceding claims, wherein the block copolymer has an order-disordertemperature(ODT)of 150-190°C.

3. An absorbent core according to any of the preceding claims, wherein the block copolymer has an elongation at break of 300-500%.

4. An absorbent core according to any of the preceding claims, wherein the block copolymer has a tensile strength of 4-6 MPa.

5. An absorbent core according to any of the preceding claims, wherein the immobilizing material comprises at least 80% by weight of the selectively hydrogenated block copolymer.

6. An absorbent core according to the preceding claim, wherein the immobilizing material comprises at least 90% by weight of the a selectively hydrogenated block copolymer, in particular at least 95% by weight.

7. An absorbent core according to any of the preceding claims, wherein the immobilizing material is free or comprises less than 5% by weight of a tackifier.

8. An absorent core according to any of the preceding claims, wherein the immobilizing material has a shear viscosity at 210°C ranging from about 5000 mPa.s to about 8000 m.Pas, preferably 5500 mPa.s to 7500 mPa.s, even more preferably from about 5900 mPa.s to about 7200 mPa.s and Viscosity Rheometry T est Method described herein.

9. An absorbent core according to any of the preceding claims, wherein the Wet Mobilization as measued by the Wet Mobilization Value Test is of less than 50%, preferably less than 40%, preferably less than 30%, and preferably from about 0% to about 28%, as measured according to the Wet Mobilization Value T est Method described herein.

10. An absorbent core according to any of the preceding claims, wherein the true strain to break at 23°C of the immobilizing material is above about > 2.0, preferably above about 2.1 , as measured according to the Extensional Rheology Method described herein.

11. An absorbent core according to any of the preceding claims, wherein the absorbent core comprises a substrate, such as a nonwoven, on which the superabsorbent particles are deposited and the immobilizing material forms of a fibrous network over, around, and/or between the superabsorbent particles.

12. An absorbent core according to any of the preceding claims, wherein the superabsorbent particles are not mixed with cellulose fibers.

13. An absorbent core according to any of the preceding claims, wherein the immobilizing material has Average Time to Breakage greater than 1550 s, preferably greater than 1620 s, more preferably greater than 1680 s as measured by Stepwise Stress-Relaxation Test Method disclosed herein.

14. An absorbent article such as a diaper comprising a liquid permeable topsheet, a liquid impermeable backsheet and an absorbent core according to any of the preceding claims between the topsheet and the backsheet.

15. A package comprising a plurality of absorbent articles according to claim 14.