CN114430687A

CN114430687A - SAP-immobilization materials based on styrene block copolymers

Info

Publication number: CN114430687A
Application number: CN202080063932.4A
Authority: CN
Inventors: R.H.特纳; T.林德纳; X.缪尔德曼斯; J.弗拉德
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 2019-09-23
Filing date: 2020-09-14
Publication date: 2022-05-03
Also published as: WO2021062432A1

Abstract

An absorbent core comprising superabsorbent particles immobilized at least partially by a immobilizing material is disclosed. The fixing material comprises a selectively hydrogenated block copolymer or a mixture thereof having an S block and an E block and having the general formula (S-E) nX, 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-immobilization materials based on styrene block copolymers

Technical Field

The present invention relates to an absorbent core comprising superabsorbent particles being at least partially immobilized by an immobilization material comprising as a main or sole component a selectively hydrogenated block copolymer. The immobilization material may be in the form of a network of fibers of entangled superabsorbent particles. The network of fibers is also attached to the substrate on which the superabsorbent particles are deposited. Absorbent cores are used in absorbent articles for personal hygiene, such as diapers.

Background

Disposable absorbent articles for receiving and retaining bodily waste, such as urine or feces, are well known in the art. Examples of these include disposable diapers, training pants, and adult incontinence articles. Typically, disposable articles comprise a liquid permeable topsheet facing the body of the wearer, a liquid impermeable backsheet facing the garment of the wearer, and an absorbent core interposed between the liquid permeable topsheet and the backsheet.

An important component of disposable absorbent articles is the absorbent core. The absorbent core comprises an absorbent material that may be enclosed in or sandwiched between a core wrap. The absorbent material typically comprises superabsorbent polymers (SAP) in particulate form. SAP ensures that during its use a large amount of body fluid, e.g. urine, can be absorbed by the absorbent article and be locked away, thereby providing a low rewet effect and good skin dryness.

The SAP particles are typically mixed with cellulosic wood fibers. As used herein, "airfelt" refers to comminuted wood pulp, which is in the form of cellulose fibers. Recently, absorbent cores free of such cellulose fibres and manufactured by so-called SAP printing techniques have been proposed, see e.g. EP1,447,067A1(Busam et al), EP1,621,165 (blistering et al). In this method, at least one layer of superabsorbent polymers is discontinuously deposited on a substrate, such as a nonwoven fabric. This so-called airfelt-free technique makes the absorbent core thinner by reducing or eliminating these cellulose fibers in the absorbent core and improving the placement of the SAP particles while maintaining overall absorbency.

The SAP-particles should be immobilized in the dry state, i.e. before use, and at least to some extent in the wet stage, while the product is in use and has absorbed liquid, e.g. urine. In order to stabilize and retain the SAP particles in these airfelt-free cores, immobilizing materials in the form of a thin fibrous adhesive network have been used, which entangles the SAP particles and anchors them to the substrate. It is known that the fixing material is usually a hot melt adhesive with a base polymer and other materials, such as tackifiers, plasticizers, oils and/or waxes. The molten fixing material must be capable of being sprayed through the nozzle in the form of microfibers. WO2016/149252A1(Stiehl et al) claims that such immobilization materials have a storage modulus at 21 ℃ of greater than 1.2X 10⁶Pa. WO2017/132119(Turner) discloses a superabsorbent fixing agent comprising at least 50 wt% of one or more polymers each having a peak molecular weight of at least 10 kg/mol. The superabsorbent fixing agent may comprise a polymer selected from the group consisting of: polymers and copolymers of propylene, ethylene, butylene, and combinations thereof; a styrene block copolymer; a polyolefin; olefin block copolymers, and combinations thereof.

There is a need for an improved SAP immobilization material that is easy to process, provides the desired dry and wet immobilization, is chemically stable, and has an acceptable odor.

Disclosure of Invention

The present invention relates to an absorbent core comprising superabsorbent particles being at least partially immobilized by a immobilization material. The immobilization material comprises as a major 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. S-E diblock units having the general formula (S-E) nX are coupled, wherein n has a value of 1 to 2. The hydrogenated block copolymer is further described in the appended claims and detailed description. The absorbent core is advantageously used in absorbent articles such as diapers.

Without wishing to be bound by theory, it is believed that the claimed styrene block copolymers ("SBC") are advantageously used as immobilizing materials, particularly in the form of a fibrous web, because SBC have a fast solidification mechanism ("order-disorder transition") unlike previously used polyolefins ("PO") that have a slower solidification mechanism ("crystallite formation"). A faster curing of the immobilization material web will better withstand the conversion process (additional force applied to the web after deposition), which will enable a better immobilization of the SAP. Unlike PO, SBC also shows significant strain hardening upon extension, which provides a "self-healing" effect against microcrack formation. It is believed that this enables the fibre network to better withstand the forces of swelling SAP in use, and will in particular enable better wet fixation.

SBCs of the present invention are further hydrogenated to prevent degradation and odor formation due to the presence of C ═ C double bonds (in the midblock). The SBS of the present invention may be used as a substantially pure fixing material, wherein the fixing material advantageously comprises at least 80%, alternatively at least 90%, and alternatively at least 95% by weight of the selectively hydrogenated block copolymer, based on the weight of the fixing material. The fixing material is advantageously substantially free of tackifier and/or polyolefin ("PO").

The fixing material advantageously has a sufficiently low viscosity (<8000mpa.s) at the application temperature to prevent pressure build-up in the hose and application head. Temperatures above 210 ℃ are possible but not desirable due to thermal degradation and odor formation.

Detailed Description

Definition of

As used herein, "absorbent article" 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 articles, and the like. As used herein, the term "bodily fluid" or "bodily exudate" includes, but is not limited to, urine, blood, vaginal secretions, and feces.

By "absorbent core" is meant an absorbent structure disposed between the topsheet and the backsheet for absorbing and containing liquids, such as urine, received by the absorbent article. The absorbent core comprises an absorbent material typically enclosed within or sandwiched between core wraps. The core wrap may be a single material folded over the absorbent material or may comprise separate top and bottom layers bonded together. The absorbent core may be substantially cellulose free. As used herein, an absorbent core does not include any acquisition system, topsheet, or backsheet of the absorbent article. The absorbent core may consist essentially of a core wrap, superabsorbent polymer particles and a fixing material as a network of fibers.

As used herein, "comprising" and "comprises" are open-ended terms that each specify the presence of the stated features, e.g., components, described hereinafter, but do not preclude the presence of other features, e.g., elements, steps, or components, known in the art or disclosed herein.

As used herein, "consisting essentially of …" limits the scope of the subject matter, such as the subject matter recited in the claims, to the specified materials or steps, as well as materials or steps that do not materially affect the basic and novel characteristics of the subject matter.

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

As used herein, "fibrous network" is understood to comprise a polymer composition from which a strand or web structure is formed and applied to superabsorbent polymer (SAP) particles with the purpose of at least partially immobilizing the SAP particles in a dry state and a wet state. The network of fibers may be formed above, around and/or between the superabsorbent polymer particles and may also be attached to a substrate on which the superabsorbent particles have been deposited.

As used herein, "nonwoven fabric" refers to a manufactured sheet, web or batt of directionally or randomly oriented fibers bonded by friction and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded combining binding yarns or filaments or felted by wet-milling, whether or not additionally needled. These fibers may be of natural or man-made origin and may be staple or continuous filaments or in-situ formed fibers. Commercially available fibers range in diameter from less than 0.001mm to greater than 0.2mm, and they come in several different forms: staple fibers (referred to as staple or chopped), continuous filaments (filaments or monofilaments), untwisted continuous filament bundles (tows), and twisted continuous filament bundles (yarns). Nonwoven fabrics can be formed by a number of processes such as meltblowing processes, spunbonding processes, solution spinning processes, electrospinning processes, and carding processes. The basis weight of nonwoven fabrics is typically expressed in grams per square meter (gsm).

As used herein, "pant" or "training pant" refers to disposable garments having a waist opening and leg openings designed for infant or adult wearers. A pant may be placed in position on the wearer by inserting the wearer's legs into the leg openings and pulling the pant into position about the wearer's lower torso. A pant may be preformed by any suitable technique, including but not limited to joining together portions of the article using refastenable and/or non-refastenable bonds (e.g., seams, welds, adhesives, cohesive bonds, fasteners, etc.). A pant may be preformed anywhere along the circumference of the article (e.g., side fastened, front waist region fastened). Although the term "pant" is used herein, pants are also commonly referred to as "closed diapers", "prefastened diapers", "pull-on diapers", "training pants", and "diaper-pants".

As used herein, "substantially" means substantially the same or uniform, but allowing or having minor fluctuations from the defined characteristics, definitions, etc. For example, small measurable or unmeasurable fluctuations in the measured properties (such as viscosity, melting point, etc.) described herein can be caused by human error or process accuracy. Other fluctuations are caused by inherent variations in the manufacturing process, thermal history of the formulation, etc. Nevertheless, the compositions of the present invention will be considered to have essentially the reported characteristics.

As used herein, "superabsorbent particles" refers to superabsorbent polymer materials that are in particulate form so as to be flowable in a dry state.

"vinyl content" refers to the content of conjugated diene polymerized via 1, 2-addition in the case of butadiene, or via both 1, 2-and 3, 4-addition in the case of isoprene.

The "polystyrene content" or PSC of a block copolymer refers to the weight percent of polymerized styrene in the block copolymer calculated by dividing the sum of the molecular weights of all polystyrene blocks by the total molecular weight of the block copolymer. The PSC may be determined using any suitable method, such as proton Nuclear Magnetic Resonance (NMR).

"molecular weight" refers to the peak molecular weight (Mp) in g/mol of the polymer under consideration as measured by GPC using polystyrene calibration standards having known number average 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 domain structure of the block copolymer begins to disappear. ODT is defined as the temperature above which zero shear viscosity can be measured by dynamic rheology. ODT temperature can be measured using Dynamic Mechanical Analysis (DMA), where a temperature sweep is performed over various frequencies, where ODT is identified as a temperature where the 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 a polymer at 190 ℃ and 2.16kg weight according to ASTM D1238, expressed in grams of polymer passing through the melt rheometer orifice in 10 minutes.

ASTM D412 refers to a test method for determining the tensile properties of thermoplastic elastomers and vulcanized thermosets. Dumbbell and straight section samples or cut loop samples can be used. For testing, samples were cut using a Mini D die with a dumbbell center width of 0.1 inch and a narrow parallel-sided central portion of 0.5 inch in length and a draw rate of 50mm/min was used.

Absorbent core and absorbent article

The absorbent core of the present invention may be of the type discussed in the background, such as a "airfelt-free core", i.e. a core wherein the absorbent material is (substantially) free of cellulose fibers. The absorbent material may in particular consist of SAP particles. In addition to securing the fibrous network of material, the SAP particles may be secured by an adhesive disposed between the top and/or bottom layers of the core wrap, typically slot coated as is known in the art. The absorbent core of the present invention may be used in any type of absorbent article, such as diapers and pants. The article typically comprises a liquid pervious topsheet on its wearer facing side, a liquid impervious backsheet on the garment facing side, with an absorbent core disposed between the topsheet and the backsheet. The absorbent article may comprise an acquisition layer or system. Of course, various other common features of absorbent articles may be used, such as inner and outer elasticized barrier leg cuffs, wetness indicators, elastic back or front wait bands, and the like. Absorbent cores and absorbent articles that can be used with the fastening material of the present invention and detailed methods of making them are disclosed in more detail, for example, in the references indicated in the background section above. The absorbent core may be free of cellulose fibers. See also US16/520386 filed on 26/7/2018 (attorney docket No. 15312MQ-US) for a description of how to make such absorbent cores. The absorbent core may further comprise an area free of absorbent material through which the top and bottom layers of the core wrap are bonded such that three-dimensional channels are formed when the absorbent layer swells, as disclosed in, for example, WO2012/170778a1(Rosati et al) or WO2015/31243(Roe et al).

The absorbent articles of the present invention are typically regulated and commercialized in packages comprising a plurality of such absorbent articles.

Superabsorbent particle immobilization material

The fixing material is a composition that is applied to the superabsorbent polymer particles with the purpose of at least partially fixing the superabsorbent polymer material in at least a dry state and preferably in a wet state. The fixing material is typically a hot melt which is heated at a sufficiently high temperature until it becomes fluid enough to be sprayed onto the superabsorbent particles. As the sprayed fixing material cools, it rapidly forms a solid fibrillating network with microfibers or nanofibers which are interlaced or entangled with the particles of the superabsorbent polymer. Exemplary methods for making absorbent cores and spray-on fastening materials are disclosed in references indicated in the background section, such as EP1,447,067A1(Busam et al). As disclosed therein, a layer of SAP particles may first be disposed (e.g., SAP printing techniques) on a substrate, such as a nonwoven layer, optionally with an auxiliary adhesive between the substrate and the SAP layer, and a securing material uniformly sprayed thereon to form a securing fiber network. A second substrate may then be applied to the anchoring layer to form the core wrap. As disclosed in the cited references, the absorbent core may comprise two such layers of immobilized superabsorbent particles.

The claimed fixing composition is a selectively hydrogenated block copolymer having an S block and an E block, or a mixture thereof, having the general formula (S-E) nX, and n has a value of 2, wherein 20 to 35 wt% of the block copolymer is a diblock unit having the general formula (S-E), and X is a coupling agent residue.

Suitable coupling agents may be selected from the group consisting of: methyl benzoate, silicon tetrachloride, alkoxysilanes, polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, polyanhydrides, polyesters, polyhalides, diesters, methoxysilanes, divinylbenzene, 1,3, 5-benzenetriacotrichlorinated, glycidyloxytrimethoxysilane, oxydipropylenebis (trimethoxysilane), and mixtures thereof.

The block copolymers may be linear sequential or coupled.

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

Prior to hydrogenation, the E block is a polydiene block selected from the group consisting of polybutadiene, polyisoprene, and mixtures thereof. In one embodiment, the E block is a single polydiene block. The molecular weight of these polydiene blocks may be in the range of 18,000 to 26,000.

Hydrogenation of block copolymer: the block copolymer is a hydrogenated block copolymer. Any hydrogenation method that is selective for the double bonds in the conjugated polydiene block such that the aromatic unsaturation in the polystyrene block is substantially complete can be used to prepare the hydrogenated block copolymer.

The process may employ a catalyst or catalyst precursor comprising a metal (e.g. nickel or cobalt) and a suitable reducing agent (such as an aluminium alkyl). Titanium-based systems are also useful. The hydrogenation can be accomplished in a solvent at a temperature of 20 ℃ to 100 ℃ and at a hydrogen partial pressure of 100psig (689kPa) to 5,000psig (34,473 kPa). Catalyst concentrations in the range of 10 to 500ppm by weight of iron group metal based on the total solution are generally used and contacted under hydrogenation conditions for 60 to 240 minutes. After the hydrogenation is complete, the catalyst and catalyst residues will be separated from the polymer.

For a large number of vinyl groups in the E block, control agents known in the art can be used to control the microstructure associated with the block copolymer, such as diethyl ether and diethoxypropane during diene polymerization.

The hydrogenation may be carried out under conditions such that at least 90% of the conjugated diene double bonds are reduced and at most 10% of the arene double bonds are reduced.

The block copolymers are prepared such that they have 75% to 80% of vinyl groups in the E block prior to hydrogenation.

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

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

Additive agent

The fixing material is advantageously substantially free of tackifier and may comprise less than 5%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1%, alternatively less than 0.5%, and alternatively no tackifier by weight of the polymeric filler composition. Exemplary tackifiers may include aliphatic hydrocarbon resins, aromatic modified aliphatic hydrocarbon resins, hydrogenated polycyclopentadiene resins, gum rosins, gum rosin esters, wood rosins, wood rosin esters, tall oil rosins, tall oil rosin esters, polyterpenes, aromatic modified polyterpenes, terpene-phenolic resins, aromatic modified hydrogenated polycyclopentadiene resins, hydrogenated aliphatic aromatic resins, hydrogenated terpenes and modified terpenes, and hydrogenated rosin esters. The polymeric filler composition may be free of tackifier.

Minimizing or avoiding the use of tackifiers has significant advantages as it can reduce the cost of the polymeric filler composition and eliminate additional ingredients and potential problems that may be associated with providing additional ingredients. In addition, tackifiers can impart undesirable odors in disposable articles and can also act as carriers for low molecular weight plasticizers (e.g., processing oils used in SBC-based adhesives), which can weaken polyethylene backsheet materials used in absorbent articles and textile articles.

The fixing material may optionally comprise an antioxidant or a stabilizer. Any antioxidant known to one of ordinary skill in the art may be used in the adhesive composition. Non-limiting examples of suitable antioxidants include amine-based antioxidants such as alkyldiphenylamines, phenyl-naphthylamines, alkyl or aralkyl substituted phenyl-naphthylamines, alkylated p-phenylenediamines, tetramethyl-diaminodiphenylamines, and the like; and hindered phenol compounds such as 2, 6-di-tert-butyl-4-methylphenol; 1,3, 5-trimethyl-2, 4, 6-tris (3',5' -di-tert-butyl-4-hydroxybenzyl) benzene; tetrakis [ (methylene (3, 5-di-tert-butyl-4-hydroxyhydrocinnamate) ] methane (e.g., irganox (tm) 1010, available from Ciba Geigy, New York), octadecyl-3, 5-di-tert-butyl-4-hydroxycinnamate (e.g., irganox (tm) 1076, commercially available from Ciba Geigy), and combinations thereof, when used, the amount of antioxidant and/or stabilizer in the polymer 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 fixation material.

The fixing material may optionally comprise a UV stabilizer that may prevent or reduce degradation of the composition due to radiation. Any UV stabilizer known to one of ordinary skill in the art may be used in the fixing material. Non-limiting examples of suitable UV stabilizers include benzophenones, benzotriazoles, aryl esters, oxalanilides, acrylates, formamidine carbon black, hindered amines, nickel quenchers, hindered amines, phenolic antioxidants, metal salts, zinc compounds, and combinations thereof. When used, the amount of UV stabilizer in the fixation 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 fixation material.

The fixing material may optionally comprise whitening agents, colorants and/or pigments. Any colorant or pigment known to one of ordinary skill in the art may be used in the securing material. Non-limiting examples of suitable brighteners, colorants, and/or pigments include fluorescent materials and pigments such as triazine-stilbenes, coumarins, imidazoles, diazoles, titanium dioxide, and carbon black, phthalocyanine pigments, and other organic pigments such as IRGAZINB, CROMOPHTALB, MONASTRALB, cinquasiaib, irgalitb, ORASOLB, all of which are available from Ciba Specialty Chemicals, Tarrytown, n.y. When used, the amount of whitening agent, colorant, and/or pigment in the fixing 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 fixing material may optionally comprise a fragrance such as a perfume or other odorant. Such fragrances may be retained by the liner or contained in a release agent, such as microcapsules, which may release the fragrance, for example, upon removal of the release liner from the adhesive composition or compression on the adhesive composition. When used, the amount of fragrance in the fixing material may 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 fixing material.

Characteristics of the hydrogenated Block copolymer：

The fixed 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 prior to its formation into a fibrous network.

The solution viscosity of the hydrogenated block copolymer at 25 ℃ can range from 15 centipoise to 30 centipoise (cP). "solution viscosity" refers to the intrinsic viscosity of a 25 weight percent solution of the hydrogenated block copolymer in toluene measured using an Ubbelohde capillary viscometer.

The hydrogenated block copolymer may have a low order-disorder temperature (ODT). The ODT may be 150 ℃ to 190 ℃. The hydrogenated block copolymer can have a tensile strength of 4MPa to 6MPa as measured on a compression molded film according to ASTM D412. The hydrogenated block copolymer can have an elongation at break of 300% to 500%.

The immobilizing material may further advantageously have any or all of the following properties that are believed to be desirable for dry and/or wet integrity of the immobilized SAP. The melt viscosity as measured by the viscosity rheology test method described below may have the following values:

-a melt viscosity at 170 ℃ ranging from 100 to 25,000mpa.s, advantageously lower than 10,000 mpa.s;

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

The following fixative material properties were measured according to the oscillatory rheology test method and tensile test method described below.

-storage modulus at 23 ℃ [ MPa ] <4MPa

-storage modulus [ Pa ] at 100 ℃ of >100,000Pa

-true strain at break at 23 ℃ of >2.0 or >2.1

The fixation material advantageously has an average time to break of greater than 1550s, preferably greater than 1620s, more preferably greater than 1680s, as measured by the progressive stress-relaxation test method disclosed herein. For example, the selectively hydrogenated block copolymer of claim 1 (LR 0081-24 supplied by Kraton Inc.) was tested according to the progressive stress-relaxation test method described below, and the break time was measured as 1717s for the first parallel assay and 1787s for the second parallel assay.

The absorbent core may advantageously have a wet mobilization as measured by the wet mobilization value test method described herein of less than 50%, preferably less than 40%, preferably less than 30%, and preferably from about 0% to about 28%, as measured by the wet mobilization value test.

Test method

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

Viscosity rheology test method

The shear viscosity of the polymer composition at 210 ℃ and 10[1/s ] shear rate was measured using the visco-rheological test method.

A controlled strain rotary rheometer (such as ARES G2, TA Instruments, New Castle, DE, USA or equivalent) capable of controlling the sample temperature at 210 ℃ with an accuracy equal to or exceeding +/-0.5 ℃, such as using a forced convection oven; TA Instruments, New Castle, DE, USA or equivalent, is used. The rheometer operates in a cone and plate configuration with a 25mm 0.1 arc steel cone as the upper tool and a 40mm steel plate as the lower tool. The taper truncation distance is defined as specified for the particular taper tool used (typically about 50 μm for a 25mm 0.1 arc steel taper). The taper truncation distance is controlled to be accurate to 0.1 μm.

The rheometer was heated to 190 ℃ and the polymer composition was introduced into the rheometer. Once the polymer has equilibrated at a temperature of 190 ℃, the rheometer tool gap is set to 50 μm greater than the cone truncation distance and excess overhang sample is trimmed. The gap is then set to the taper truncation distance. To condition the sample, a constant pre-shear of 0.11/s was applied for 180s at 190 ℃.

To make this measurement, the rheometer temperature was set to 210 ℃, and when the sample had reached temperature, it was conditioned for 180 s. A steady state shear rate of 101/s was applied. The viscosity was measured using a sampling period of 15 seconds. The viscosity was calculated and the average value was monitored for each cycle. When three consecutive viscosity cycles deviate within +/-5% of each other, the average (arithmetic mean) of these three values is reported as the steady state viscosity at 101/s and 210 ℃ and the value is reported in millipascal-seconds (mpa.s) "shear viscosity at 10(1/s) at 210 ℃ to the nearest 1 (mpa.s).

Wet mobilization value testing method

Equipment:

graduated measuring cylinder

Stopwatch (± 0.1 second)

Scissors

Light box

Pen

Test solution: 0.90% saline solution at 23+/-2 deg.C

Metallic rule traceable to NIST, DIN, JIS or another similar national standard

PVC/Metal discs with internal Flat surfaces and minimum and maximum lengths n +50mm of the core pocket Length (n) to be measured, Width w + -50 mm, height 30mm to 100mm or equivalent

The balance to. + -. 0.0.1g

Binder Width 1 "(25 mm)

Wet immobilization impact tester equipment (WAIIT-3), design package number: PA-00112.59506-R03, manufacturing information: germany Hangao company (Henkel GmbH Germany)

The WAIIT tester is a purely mechanical device. The sliding plate (a) falls along the sliding track (B) after it has been mechanically released by two levers placed on the sides of the device. The pre-loaded diaper is cut (laterally) and attached with its open side down to the slide plate. The operator lifts the slide plate with both of his hands. After releasing the sliding plate, it hits the anvil underneath and this impact force damages the absorbent core structure. Depending on the mass of the absorbent core structure, AGM particles will fall out of the pad. The difference in weight before and after the impact describes the mass of the absorbent core.

Facilities:

standard laboratory conditions, temperature: 23 ℃ ± 2 ℃, relative humidity: < 55%

Sample preparation:

1. the product is opened with the topsheet side up.

2. The diaper is unfolded and the cuff elastics are cut approximately every 2.5cm to relieve the chassis tension so that the product lies flat easily.

3. For pull-on products, the side seams are opened and the waistband is removed.

4. The topsheet and potentially other layers or materials between the topsheet and the core bag are removed so as to minimally interfere with the core bag nonwoven fabric and the absorbent material contained therein. Note that: if the core bag has been prepared directly as in the examples and it is not necessary to separate the core bag from the diaper, steps 1 to 4 are not necessary.

5. The longitudinal extent of the core is identified using a light box and the longitudinal midpoint of the core along the longitudinal axis is marked.

Test protocol

WAIIT calibration:

1. ensuring the slide plate in the lower position. The front door of the WAIIT tester is opened and the load cell hook is attached to the upper sample grip of the WAIIT. Ensure that the clamp is closed before the spring balance is attached.

2. The slide plate is lifted continuously and as slowly as possible with both hands on the spring balance towards the upper position. The mean value (m) is recorded during the implementation₁) To the nearest 0.02 kg.

3. The slide plate is guided down to the lower position as slowly as possible and the average value of the readings (m) is recorded during the implementation₂) To the nearest 0.02 kg.

4. Calculate and record m₁-m₂To the nearest 0.02 kg. If the Δ is 0.6 kg. + -. 0.3kg, the measurement is continued. Otherwise, the slide plate needs to be adjusted. The slide plate is secured in the lower position and the slide path is checked for any contamination or damage. It is checked by shaking the slide plate whether the position of the slide plate with respect to the slide path has been correctly adjusted. Some clearance is required to facilitate sliding. If no gap exists, the system is readjusted.

WAIIT test setup:

the height of fall was 16 cm.

Diaper load (l)_D) 73% of the core capacity (cc); l_D＝0.73×cc。

Core capacity (cc) is calculated as follows: cc is m_SAP×SAP_GVWherein m is_SAPBeing present in diapersMass of superabsorbent polymer (SAP), and SAP_GVIs the free swelling capacity of the superabsorbent polymer. The free swell capacity of the superabsorbent polymer is determined using the method described in WO 2006/062258, which is hereby incorporated by reference. The mass of superabsorbent polymer present in the diaper is the average mass present in ten products.

And (3) test implementation:

1. it was weighed and the weight reported to the nearest 0.1 g.

2. The appropriate volume of saline (0.9% NaCl in deionized water) was measured with a graduated cylinder.

3. The plate was placed flat on the laboratory bench. The core bag (top sheet side down) is laid flat into a filled plastic or metal tray. Wait 5 ± 1min to allow all saline to be absorbed. After this period of time, there may be liquid in the pan at the side of the wick that has not been in contact with the wick. If this is the case, the tray is picked up and held inclined in a different direction to allow any free liquid to be absorbed.

4. Wait an additional 5 minutes (+/-30 seconds) to allow all saline to be absorbed. There may be some droplets remaining in the disc. Only the defined PVC/metal tray is used to ensure homogeneous liquid distribution and less liquid retention.

5. It was weighed and the weight reported to the nearest 0.1 g. Check if the wet core bag weight is out of limit (defined as "dry core bag weight + diaper load ± 4 ml"). For example, a dry core bag weight of 12g +150ml load of 162g wet core bag weight. If the actual wet weight on the balance is between 158g and 166g, the pad can be used to shake. Otherwise the liner is discarded and all steps are repeated.

6. The loaded core bag is cut parallel to the transverse axis and through the longitudinal midpoint of the core so as to divide the core bag into about two "halves" -one corresponding to the front of the absorbent article and the other corresponding to the back of the absorbent article.

7. The back of the cut wet core bag was weighed and the weight recorded to the nearest 0.1 g.

8. The back of the cut wetted core bag was picked up and clamped into the WAIIT with the end seal side up (open end of core oriented downward). The back of the cut wet core bag is thus folded around the top edge of the slide plate and fixed to the slide plate with two binding clips (width 25 mm). The core bag was clamped in such a way that the clamp overlaps the AGM containing area of the core within a length of 1cm in the vertical direction. The pad is pressed onto the sliding plate to establish the connection. Note that: it is ensured that sufficient diaper material is folded around the top edge of the slide plate so that the clips do not contact the slide plate material. This is necessary to allow the sample to be properly secured during impact. Allowing it to hold the absorbent core.

9. The slide plate is lifted with both hands to the upper position until the plate is engaged.

10. While the safety front door is closed and the slide is released using two levers on the sides.

11. The sample tested was taken out of the WAIIT and placed on a balance (m)₂). The weight was recorded to the nearest 0.1 g.

12. Steps 5 to 13 are repeated using the cut front portion of the wet core bag.

Reporting:

1. the dry core bag weight was recorded to the nearest 0.1 g.

2. Record before test (m)_{1 front part}And m_{1 rear part}) And (m)_{2 front part}And m_{2 rear part}) The wet weights thereafter, were all to the nearest 0.1 g.

3. The average weight loss (Δ m) was calculated and reported to the nearest 0.1 g: Δ m ═ m_{1 front part}+m_{1 rear part})–(m_{2 front part}+m_{2 rear part})

4. Weight loss was calculated and reported as a percentage to the nearest 1%, (Δ m)_rel)：(Δm_rel)＝(((m_{1 front part}+m_{1 rear part})–(m_{2 front part}+m_{2 rear part}))×100％)/(m_{1 front part}+m_{1 rear part})

A total of ten repetitions were performed. For each repetition, the percent weight loss was calculated and recorded. The arithmetic mean of the percent weight loss for the ten replicates was calculated as a percentage and reported to an integer value of percentage as the wet mobilization value.

Tensile test method

The tensile test method is used to determine the true strain at break parameter. Film samples formed from the polymer compositions were analyzed with a rotary rheometer equipped with a special fixture with counter-rotating rollers, and the stress associated with the applied tensile strain was measured and recorded.

Instrument set-up

A rotary rheometer (ARES G2, TA Instruments, New Castle, DE, USA, or equivalent) was equipped with a fixture with counter-rotating cylindrical rollers specifically designed to interrogate tensile deformation of the film. Examples of suitable clamps are extensional viscosity clamps or EVFs (EVFs, TA Instruments, or equivalents). The rheometer is also equipped with a forced convection oven FCO (FCO, TA Instruments, or equivalent) and a cooling system (ACS 2, TA Instruments, or equivalent) capable of controlling the temperature to at least-50 ℃ to 250 ℃ within a tolerance of 0.5 ℃.

Sample preparation

Approximately 10g of the polymer composition was placed in a Polytetrafluoroethylene (PTFE) bowl and introduced into a vacuum oven. After 15 minutes at 170 ℃ at ambient pressure, the pressure was reduced to 10 mbar and the polymer composition was subsequently held at 170 ℃ and 10 mbar for 45 minutes to remove gas bubbles in the polymer composition. The polymer composition was removed from the vacuum oven and cooled to ambient laboratory conditions (23 ℃ ± 2 ℃) for 90 minutes ± 30 minutes, at which time the polymer composition was removed from the PTFE bowl and placed between 2 sheets of siliconized paper. A metal shim with a thickness of 0.50mm was used as a spacer in a hot press, and a film thickness of 0.50mm was obtained when the polymer film was pressed with the hot press at 90 ℃ and 10 bar (instrument set) for 60 seconds. If 90 ℃ is not sufficient to melt the polymer composition, a higher temperature (but the lowest temperature sufficient to melt the composition) is used. Prior to testing, the membranes were stored in a laboratory at 23 ℃ ± 2 ℃ for at least 120 hours. Individual samples for measurement were die cut from the film using a sample cutter to give sample sizes of 20.0mm x 10.0mm x 0.50 mm. The sample will be cut longitudinally using scissors to achieve a final width of 5 ± 0.5 mm. The exact width and thickness will be determined using a digital caliper (electronic caliper PRO-MAX Fowler) with an accuracy of 0.01mm and input into the rheometer software. Since anisotropy or grain orientation due to flow introduced during processing and preparation may have an influence on the tensile characteristics, the sample should be cut so that the longitudinal direction of the sample is parallel to the grain direction when the direction is known.

Measuring

The cylinder of EVF was heated to 80 ℃ in a forced convection oven of the rheometer, maintaining 90s ± 30 s. Small droplets (0.03 ± 0.01g) of the polymer composition were then applied to each cylinder. The polymer composition used should exhibit a high hardness (G' at 23 ℃ greater than 10MPa) so as not to interfere with the measurement. A sample of the polymer composition was quickly pressed into the molten polymer composition on the EVF cylinder to secure it to the cylinder surface. The sample is placed perpendicular to the axis of rotation of the cylinder.

The samples mounted on the EVF were then placed in a forced convection oven of a rheometer for thermal conditioning and held at a constant temperature of 23 ℃ ± 1 ℃ for 300s ± 10 s. After this time, the sample is mechanically conditioned. To mechanically condition the sample, the torque transducer was zeroed and the sample was set at 0.001s^–1Is placed for 0.30s and then relaxed for 60 s. (in this method, all strains are expressed as Hencky strains (also called "true strains" or "logarithmic strains"))

Measurements were made in an FCO oven at 23 ℃. + -. 0.5 ℃. The measured strain rate elongation was 0.01 s-1 and the strain at maximum elongation was 4.0. After the measurement, the specimen is checked for breakage. If broken, the location of the break is recorded. The collected data is considered acceptable if the break is approximately between two cylinders of the EVF. Otherwise, if the polymer film break is located at or near the rotating cylinder, the result is discarded and the measurement is performed again on the replicate sample.

Analysis of

For the tensile stress calculation, the volume is assumed to be constant. Tensile stress (in megapascals or MPa) versus Hencky strain data were calculated from raw torque versus angular displacement data recorded by the rheometer. The data are plotted in a semi-logarithmic manner with Hencky strain (linear scale) on the abscissa and tensile stress (logarithmic scale) on the ordinate. Set between Hencky strains of 0.5 and 1 with R²A linear fit of positive slope with a value of 0.9 or greater. When the sample cracked and/or the reported torque value was below 100 μ Nm, Hencky strain was reported as a dimensionless value to the nearest 0.1 as the true fracture strain parameter (or in this case it did not crack during the measurement, up to a strain of 4.0).

Oscillatory rheological testing method

The oscillatory rheology test method is used to measure the storage modulus and loss factor of a polymer composition. Controlled strain rotational rheometers (such as Discovery HR-3, TA Instruments, New Castle, DE, USA, or equivalent) are capable of controlling sample temperature (using a Peltier cooler and resistive heater combination) with accuracy equal to or exceeding 0.5 ℃ in the range of at least-10 ℃ to 150 ℃. The rheometer operates in a parallel plate configuration and a 20mm stainless steel parallel plate tool.

The method initially used a parallel plate gap of 1000 μm. To compensate for thermal expansion of the tool, the gap was set to 1000 μm and a mapping of the actual plate gap (as measured using a suitable standard test fluid) as a function of temperature in the range-10 ℃ to 150 ℃ was performed. This map is then used throughout the process of determining the storage modulus parameter and the loss factor parameter.

The rheometer was heated to 150 ℃, the polymer composition was introduced into the rheometer, the gap was set to 1050 μm, the excess protruding sample was trimmed, and then the gap was set to 1000 μm. (axial force control of the rheometer was set to 0N and kept within + -0.1N of the force during the experiment, whereby in addition to the compensation of the tool described above, the thermal expansion/contraction of the sample itself was compensated by adjusting the gap in order to avoid overfilling or underfilling.) then the rheometer was cooled to 130 ℃ at which time the temperature was reduced from 130 ℃ to-10 ℃ at a constant cooling rate of 2 ℃/min, and the measurement was started. The applied strain amplitude was 0.1% and the oscillation frequency was 1Hz (i.e., one cycle per second). The resulting oscillating stress was recorded.

After this step, the sample temperature was set to 23 ℃ (the temperature was raised to this set value at a rate of 10 ℃/min) and the sample was allowed to stand at 23 ℃ for 4.0 hours. At the end of this period, the temperature was set to-10 ℃ (the temperature was lowered to the set point at a rate of 10 ℃/min), the sample was equilibrated at-10 ℃ for 300 seconds, and a second oscillatory rheological measurement (0.1% strain, oscillation frequency 1Hz) was taken while the temperature was raised to 130 ℃ at a constant rate of rise of 2 ℃/min.

Starting from the first reduced temperature scan, the storage modulus G' was calculated and recorded at 100 ℃, and these values are reported in pascals (Pa) as "storage modulus at 100 ℃, accurate to 1 Pa. From the first reduced temperature sweep, the loss factor (also known as the tan delta) was calculated and recorded at 100 ℃, and the dimensionless value was reported as "loss factor at 100 ℃, to the nearest hundredth.

The storage modulus G' can also be calculated and recorded at different temperatures (such as 25 ℃).

Progressive stress-relaxation test method

The progressive stress-relaxation test method is used to measure the stress associated with multiple elongations of a sample material composition. In the progressive stress-relaxation test method, a defined size sample of a sample material composition is analyzed with a controlled strain tensile tester that is used to apply and maintain a range of elongations. The time to failure was recorded for each of three similar samples and the average time to failure was reported. The laboratory temperature was maintained at 23 ℃. + -. 2 ℃ throughout the process.

Sample preparation

15 g. + -.1 g of the sample material composition was placed in a round Polytetrafluoroethylene (PTFE) bowl with a flat bottom (diameter 60 mm. + -.2 mm) and introduced into a vacuum oven maintained at 30 ℃. + -. 10 ℃ above the melting temperature of the sample material composition (i.e. at a temperature defined as temperature 1). After 15 minutes at ambient pressure at temperature 1, the pressure of the vacuum oven was then reduced to 10 mbar, and the sample material composition was then held at temperatures 1 and 10 mbar for 45 minutes. The sample material composition was then removed from the vacuum oven and allowed to cool towards ambient laboratory temperature for 90 minutes ± 30 minutes, at which time the binder composition was removed from the PTFE bowl, resulting in a sample composition material disc of approximately 5mm to 10mm thickness.

The disc was flattened to a thickness of approximately 2mm using a hot press. The platens of the press were maintained at 10 ℃ ± 5 ℃ below the melting point of the sample material composition, so that the sample material composition was in a semi-solid state. The tray is placed between 2 sheets of silicone release paper (such as product number 114918, Mondi Group, Hilm, Austria or equivalent) and the paper/tray/stack is placed in the press. A metal shim with a thickness of 2mm ± 0.1mm was placed near the paper/disc/paper stack and the press was actuated with sufficient pressure to bring the platen into contact with the 2mm shim and hold the press in this position for 60 s. The film was then removed from the press and aged at laboratory temperature for at least 120 hours and then further cut into individual samples.

Individual samples for testing were cut from the aged film using a steel rule die or equivalent cutting tool. The tool was designed to die cut a sample of the shape of part 3 of ISO 3167 but with the following dimensional modifications: total length l₃50.0mm, length l of the narrow parallel side portion₁25.0mm, radius r 6.4mm, distance l between wide parallel side portions₂34.0mm, end width b₂Is 7.0mm, the width b of the narrow part₁Is 3.3mm and the thickness h is the thickness of the film after pressing, about 2 mm. Three similar samples were cut from the aged film for progressive strain relaxation analysis. Since anisotropy or grain orientation due to flow introduced during processing and preparation may have an influence on the tensile characteristics, the sample should be cut so that the longitudinal direction of the sample is parallel to the grain direction when the direction is known.

Step-by-step strain measurement

A controlled strain tensile tester with a 100-N load cell (such as Z005, zwickrock GmbH & co. kg, Ulm, Germany, or equivalent) was used in series with the above claims. The jig was positioned to produce a gauge of 35mm ± 1mm and the precise gauge was recorded. The sample is mounted parallel to the long axis of the measuring axis and positioned vertically symmetrically in the holder. The sample is mounted in the upper clamp and then the lower clamp is closed. The clamping forces for the upper and lower clamps are selected so that the test piece does not slip or suffer damage during testing. The load cell force reading is set to zero.

The following strain conditions were then applied to the samples using a tensile tester in immediate succession: (1) crosshead separation increased to 150% of the initial gauge at 1000mm/min, (2) crosshead position was held at 150% of the initial gauge for 20min, (3) crosshead separation increased to 300% of the initial gauge at 1000mm/min, (4) crosshead position was held at 150% of the initial gauge for 20min, (5) crosshead separation increased to 450% of the initial gauge at 1000mm/min, and (6) crosshead position was held at 450% of the initial gauge for 20 min. The force data for the entire measurement was recorded at 100Hz as a function of the total time elapsed since the start of the first step in the sequence. (for convenience, if the sample is observed to have completely fractured at any point in the measurement, the measurement may be stopped before the entire strain protocol is completed, as long as all data points up to and including the fracture point have been recorded.) the strain measurement is taken on each of three similar samples.

Analysis of

For each sample, the time to break (defined as the first point where the measured force drops below 0.2N after the first strain step was initiated) was recorded to the nearest 1 s. If the specimen did not break during the entire measurement, the break time is defined as the final time point of the measurement (just within 1 hour). The arithmetic mean of the time to break of the three sample replicates was calculated and reported to the nearest 1s as the average time to break of the measured sample material composition.

Miscellaneous items

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Rather, 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".

Each document cited herein, including any cross-referenced or related patent or application, is hereby incorporated 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 any disclosure of the invention or the claims herein or that it alone, or in combination with any one or more of the 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

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

N has a value of 2;

x is a coupling agent residue;

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

the selectively hydrogenated block copolymer has a solution viscosity of 15 centipoise to 30 centipoise (cP) at 25 ℃ at a concentration of 25 weight percent of the block copolymer in toluene;

the polystyrene content of the block copolymer is from 29% to 34% by weight;

20% to 35% by weight of the diblock units in the block copolymer have the general formula S-E;

and is

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, polyisoprene, and mixtures thereof, and has a molecular weight of from 10,000g/mol to 12,000 g/mol;

the total vinyl content of the polydiene block is 75% to 80%; and is

Wherein after hydrogenation:

reducing from 0% to 10% of the styrene double bonds in the block copolymer, and

reducing at least 90% of the conjugated diene double bonds in the block copolymer.

2. An absorbent core according to any of the preceding claims wherein the block copolymer has an order-disorder temperature (ODT) of from 150 ℃ to 190 ℃.

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

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

5. An absorbent core according to any of the preceding claims wherein the immobilization material comprises at least 80 wt% of the selectively hydrogenated block copolymer.

6. Absorbent core according to the preceding claim wherein the immobilization material comprises at least 90 wt. -%, in particular at least 95 wt. -% of the selectively hydrogenated block copolymer.

7. An absorbent core according to any of the preceding claims wherein the fixing material is free of tackifier or comprises less than 5 wt% tackifier.

8. An absorbent core according to any of the preceding claims wherein the immobilizing material has a shear viscosity at 210 ℃ in the range of from about 5000 to about 8000m.pas, preferably from 5500 to 7500mpa.s, even more preferably from about 5900 to about 7200mpa.s, as measured by the visco-rheological test method described herein.

9. The absorbent core according to any of the preceding claims wherein the wet mobilization as measured by the wet mobilization value test method described herein is less than 50%, preferably less than 40%, preferably less than 30%, and preferably from about 0% to about 28%.

10. An absorbent core according to any of the preceding claims wherein the immobilization material has a true strain at break at 23 ℃ higher than about >2.0, preferably higher than 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 immobilization material forms a network of fibers above, 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 cellulosic fibres.

13. An absorbent core according to any of the preceding claims wherein the immobilization material has an average time to break of greater than 1550s, preferably greater than 1620s, more preferably greater than 1680s as measured by the progressive stress-relaxation test method disclosed herein.

14. An absorbent article, such as a diaper, comprising a liquid pervious topsheet, a liquid impervious 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 the absorbent articles of claim 14.