Comfortable diaper

p00001Absorbent core for an absorbent article

p00002Field of the Invention

p00003The present invention relates to an absorbent article, preferably a disposable absorbent article such as a diaper. The present invention specifically relates to an absorbent core for this absorbent article that provides better immobilization of the absorbent polymer material when the article is total

p00004or partially loaded with urine. This absorbent core is useful for providing an absorbent article for greater comfort of use.

Background

p00005Absorbent articles, such as diapers and incontinent adult products are well known articles made of cut fiber. Multiple attempts have been made to provide them with a good overall fit and high absorption capacity. Modern diapers use absorbent polymeric materials or so-called superabsorbent materials, which allow storing as high as 300 ml of liquid in a typical baby diaper.

p00006Although such a diaper is generally a disposable product, in some cases it is used for many hours and also used both in a dry state and in a state loaded with urine.

p00007Therefore, to provide good comfort of use it is very important to keep the absorbent materials comprised of a diaper or other absorbent article in its intended position, both when the article is dry and when the article is totally or partially loaded with urine (or other body fluids).

p00008US-4 381 783 (Elias) describes an absorbent article with a core comprising pockets of absorbent hydrocolloid material. These pockets are provided to confine the movement of the hydrocolloid material, particularly when the article is fully or partially loaded with urine. The pockets are part of an absorbent layer and are typically made of cellulose material. Therefore, in order to achieve a good immobilization of the hydrocolloid material according to the description of this patent, relatively large amounts of cellulosic material are needed. In addition, the inclusion of these pockets can hinder the free distribution of liquid to the most absorbent areas of the core, for example the areas of hydrocolloid materials.

p00009WO 95/17868 (Palumbo) describes an absorbent structure comprising two layers of fiber and an intermediate layer. This intermediate layer comprises a hydrogel absorbent material in an amount greater than 120 g / m2 and particles of a thermop material . Although this structure certainly provides good immobilization of the hydrogel absorbent particles in the dry state, it seems that in the state loaded with urine only minor immobilization is achieved. The thermoplastic materials described appear to swell much less than the hydrogel materials described. Therefore, in particular when the absorbent structure is used in a product to absorb high amounts of liquid, for example a diaper, immobilization in the wet state may not be entirely satisfactory.

p00010EP-724418 (Tanzer) describes an absorbent article that includes superabsorbent material located in differentiated pockets. The absorbent article comprises a first and second carrier layers and a water-sensitive fixing means for joining the carrier layers and for providing a plurality of pocket regions. The article comprises high absorbency material located within said pocket regions. The water-sensitive bonding means provides a wet strength that is less than a separation force transmitted by the swelling of this high absorbency material when this high absorbency material is exposed to an aqueous liquid. The absorbent article is claimed to provide an absorbent structure that houses more securely and contains the high absorbency material in a selected pocket shape when the article is dry. However, due to the structure of the pockets and in particular due to the selection of the water-sensitive joining means, these pockets are not maintained when the article is fully or partially loaded with liquids. Therefore, it is believed that this absorbent article does not provide a very satisfactory immobilization of the absorbent material in its entirety or partially loaded with urine.

Summary

p00011The present invention relates to an absorbent article, preferably a disposable absorbent article such as a diaper. The present invention specifically relates to an absorbent core for such an absorbent article that provides better immobilization of absorbent polymeric material when the article is fully or partially loaded with urine. This absorbent core is useful for providing an absorbent article for greater comfort of use. Specifically, an absorbent core useful for an absorbent article comprising a substrate layer and absorbent material is described, the absorbent material comprising an absorbent polymeric material, optionally comprising the absorbent material absorbent fibrous material, not representing the absorbent fibrous material more than 20% of the weight of absorbent polymer material, wherein the absorbent material is immobilized when wet so that the absorbent core acquires a wet state immobilization of more than 50%, preferably more than 60%, 70%, 80% or 90%, according to the state immobilization test wet described herein.

p00012Detailed description

p00013The present invention relates to an absorbent article, preferably a disposable absorbent article such as a diaper.

p00014Here, the following terms have the following meanings:

p00015The term "absorbent article" refers to devices that absorb and contain liquid and, more specifically, refers to devices that are placed against or near the wearer's body to absorb and contain the various exudates discharged by the body. Absorbent items include, but are not limited to, diapers, incontinent adult panties, diaper pant, diaper holders and diaper dressings, sanitary napkins and the like.

p00016The term "disposable" is used herein to describe items that are generally not intended to be washed or otherwise recovered or reused (ie, are intended to be disposed of after a single use and, preferably, to be recycled , converted into fertilizer or otherwise disposed of in a manner compatible with the environment).

p00017The term "diaper" refers to an absorbent article generally used by babies and incontinent persons around the lower part of the torso.

p00018The terms "comprise", "which comprises" and "comprise" are open terms that specify the presence of the following, e.g. ex. a component, but do not exclude the presence of other features, elements, steps or components known in the art or described herein.

p00019In the accompanying drawings, Figure 6 shows a core having the characteristics of claim 1.

p00020Figure 1 is a plan view of an absorbent article in the form of a diaper 20. The diaper is shown in an extended non-contracted state (ie, without elastic-induced contraction). Parts of the structure have been removed to more clearly show the underlying structure of the diaper 20. The part of the diaper 20 that contacts the wearer is oriented toward the observer. The frame 22 of the diaper 20 in Figure 1 comprises the main body of the diaper 20. The frame 22 comprises an outer cover that includes a liquid permeable topsheet 24 and / or a liquid impermeable backsheet 26. The frame may include a portion of an absorbent core 28 embedded between the topsheet 24 and the backsheet 26. The frame may also include most or all of the absorbent core 28 fitted between the topsheet 24 and the backsheet 26. The frame preferably also includes side panels 30, turned bends 32 for the elasticized legs and a characteristic elastic waist element 34, wherein both the turned folds 32 for the legs and the characteristic elastic waist element typically comprise elastic elements 33. A final part of the diaper 20 is configured as a first waist region 36 of the diaper 20. The opposite end portion is configured as a second waist region 38 of the diaper 20. An intermediate part of the diaper 20 is configured as a crotch region 37 that extends longitudinally between the first region 36 and the second waist region 38. Waist regions 36 and 38 may include elastic elements that are fitted around the wearer's waist to provide better fit and confinement (characteristic element 34 of elastic waist). The crotch region 37 is that part of the diaper 20 which, when the diaper 20 is used, is generally placed between the legs of the wearer. The diaper 20 is shown with its longitudinal axis 10 and its transverse axis 12. The periphery of the diaper 20 is defined by the outer edges of the diaper 20, wherein the longitudinal edges 44 generally extend parallel to the longitudinal axis 100 of the diaper 20 and the end edges 46 extend between the longitudinal edges 44 generally parallel to the transverse axis 110 of the diaper 20. The frame also comprises a fixing system that can include at least one fastener 42 and at least one stored discharge area 45.

p00021In the unit absorbent articles, the frame 22 comprises the main structure of the diaper with other features added to form the composite diaper structure. Although the topsheet 24, the backsheet 26 and the absorbent core 28 can be arranged in various well-known configurations, preferred diaper configurations are generally described in US 5,554,145, entitled "Absorbent Article With Multiple Zone Structural Elastic-Like Film Web Extensible Waist Feature ”, granted to Roe et al. on September 10, 1996. In US-5,569,234 entitled "Disposable Pull-On Pant" granted to Buell et al. on October 29, 1996; and US-6,004,306 entitled "Absorbent Article With Multi-Directional Extensible Side Panels" granted to Robles et al. on December 21, 1999.

p00022The topsheet 24 in Figure 1 may be fully or partially elastified or may be reduced to provide an empty space between the topsheet 24 and the absorbent core 28. Illustrative structures are described including elastified topsheets or drained in more detail in US 5,037 .416 entitled "Disposable Absorbent Article Having Elastically Extensible Topsheet" granted to Allen et al. on August 6, 1991; and in US-5,269,775 entitled "Trisection Topsheets for Disposable Absorbent Articles and Disposable Absorbent Articles Having Such Trisection Topsheets" granted to Freeland et al. on December 14, 1993.

p00023The absorbent core 28 in Figure 1 is generally disposed between the topsheet 24 and the backsheet 26. The absorbent core 28 may comprise any absorbent material that is generally compressible, adaptable, non-irritating to the wearer's skin and capable of absorbing and maintaining liquids such as urine and other body exudates. The absorbent core 28 may comprise a wide variety of liquid absorbent materials commonly used in disposable diapers and other absorbent articles such as crushed wood pulp, generally referred to as air felt. Examples of other suitable absorbent materials include pleated cellulose wadding; meltblown polymers, including copolymers; chemically stiffened, modified or crosslinked cellulosic fibers; tissue paper, including tissue paper wraps and tissue paper laminates; absorbent foams; absorbent sponges; superabsorbent polymers; absorbent gelling materials; or any other absorbent material or combinations of known materials. The absorbent core 28 may also comprise small amounts (typically less than 10%) of non-liquid absorbent materials such as adhesives, waxes, oils and the like.

p00024Illustrative absorbent structures for use as absorbent units are described in US-4,610,678 (Weisman et al.); US 4,834,735 (Alemany et al.); US 4,888,231 (Angstadt); US 5,260,345 (DesMarais et al.); US

p000255,387,207 (Dyer et al.); US 5,397,316 (LaVon et al.); and US 5,625,222 (DesMarais et al.).

p00026The backsheet 26 may be joined with the topsheet 24. The backsheet 26 prevents exudates absorbed by the absorbent core 28 and contained within article 20 from staining other external articles that may come into contact with the diaper 20, such like sheets and underwear. In preferred embodiments, the backing sheet 26 is virtually impervious to liquids (e.g. eg, urine) and comprises a laminate of a non-woven material and a thin plastic film such as a thermoplastic film having a thickness of about 0.012 mm (0.5 mil) to about 0.051 mm (2.0 mils). Suitable backsheet films include those manufactured by Tredegar Industries Inc. of Terre Haute, IN, USA. UU., Marketed under the registered trademarks X15306, X10962 and X10964. Other suitable backing sheet materials may include breathable materials that allow steam to escape from diaper 20 while preventing exudates from passing through backing sheet 26. Illustrative breathable materials may include materials such as woven webs, nonwoven webs, composite materials such as film-coated nonwoven webs and microporous films such as those manufactured by Mitsui Toatsu Co., of Japan, with the name ESPOIR NO and by Exxon Chemical Co., of Bay City, TX, USA UU., With the name EXXAIRE. Suitable breathable composite materials comprising polymer blends are marketed by Clopay Corporation, Cincinnati, OH, USA. UU., With the name HYTREL blend P18-3097. These breathable composite materials are described in greater detail in PCT application WO 95/16746, published June 22, 1995 on behalf of EI DuPont. Other breathable backing sheets, including nonwoven webs and films formed by openings, are described in US 5,571,096, granted to Dobrin et al. on November 5, 1996.

p00027The diaper 20 may also include other features such as those known in the art, including front and rear lug panels, waist layer features, elastic and the like to provide better fit, confinement and aesthetic characteristics. These additional features are well known in the art and are found, e.g. ex. described in US-3,860,003 and US-5,151,092.

p00028In order to keep the diaper 20 in place in the body of the wearer, preferably at least a part of the first waist region 36 is joined by the fastener 42 to at least a part of the second waist region 38, preferably to form leg opening (s) and one item waist. When fixed, the fixing system carries a tensile load around the waist of the article. The fastening system is designed to allow the user of an article to take an element of the fastening system such as the fastening element 42 and to join the first waist region 36 to the second waist region 38 in at least two places. This is achieved by manipulating bond resistors between the elements of the fixing device.

p00029The diapers 20 according to the present invention may be provided with a repeatedly lockable fastening system.

p00030or alternatively they can be provided in the form of panty type diapers.

p00031The fixing system and any component thereof may include any material suitable for this use, including but not limited to plastics, films, foams, nonwoven webs, woven webs, paper, laminates, fiber reinforced plastic and the like, or combinations of the same. It may be preferable that the materials that form the fixing device are flexible. Flexibility is designed to allow the fixation system to adapt to the shape of the body and thus reduce the likelihood of the fixation system irritating or damaging the wearer's skin.

p00032Figure 2 shows a cross section of Figure 1 taken on the transverse axis 110. Starting from the face oriented towards the wearer, the diaper comprises the top sheet 24, the components of the absorbent core 28 and the backing sheet 26. The absorbent core preferably comprises the collection system 50, which comprises an upper collection layer 52 oriented towards the wearer's skin and a lower collection layer 54 opposite the garment of the wearer. In a preferred embodiment the upper collection layer 52 comprises a nonwoven material while the lower collection layer preferably comprises a mixture of chemically stiffened, twisted and corrugated fibers, high surface specific fibers and thermoplastic bonding fibers. In another preferred embodiment both collection layers are provided of a nonwoven material, which is preferably hydrophilic. The collection layer is preferably in direct contact with the storage layer 60.

p00033The storage layer 60 may be wrapped by a core wrapping material. In a preferred embodiment, the core wrapping material comprises an upper layer 56 and a lower layer 58. The core wrapping material, the upper layer 56 or the lower layer 58 may be made of a nonwoven material. A preferred material is the so-called SMS material, which comprises a spin-bonded layer, a blow-molded layer and another spin-bonded layer. Very preferred are permanently hydrophilic nonwoven materials and in particular nonwoven materials with durable hydrophilic coatings. An alternative preferred material comprises an SMMS structure.

p00034The upper layer 56 and the lower layer 58 may be made of two or more separate sheets of materials or alternatively they may be made of a unit sheet of material. This unit sheet of material may be wrapped around the storage layer 60, e.g. ex. forming a crease in C.

p00035Preferred nonwoven materials of synthetic fibers such as, for example, PE, PET and, most preferably, PP are provided. Since the polymers used for the production of nonwoven material are inherently hydrophobic, they are preferably coated with hydrophilic coatings.

p00036A preferred way of producing nonwoven materials with hydrophilic durable coatings is by applying a hydrophilic monomer and a radical polymerization initiator on the nonwoven material and performing a UV light activated polymerization to obtain a chemically bonded monomer to the surface of the non-woven material. tissue, as described in EP-A-1403419.

p00037A preferred alternative way to produce nonwoven materials with hydrophilic durable coatings is to coat the nonwoven material with hydrophilic nanoparticles as described in co-dependent application WO 02/064877.

p00038Typically, nanoparticles have a maximum dimension of less than 750 nm. Nanoparticles with sizes between 2 nm and 750 nm can be produced profitably. The advantages of the nanoparticles are that many of them can be easily dispersed in aqueous solution to allow the coating to be applied on the nonwoven material; they typically form transparent coatings and the coatings applied from aqueous solutions are typically durable enough against exposure to water.

p00039The nanoparticles can be organic or inorganic, synthetic or natural. Inorganic nanoparticles generally exist as oxides, silicates or carbonates. Typical examples of suitable nanoparticles are layered clay-like minerals (eg, LAPONITE ™ from Southern Clay Products, Inc. (USA), and alumina Boehmite (eg North American Disperal P2 ™ Sasol. Inc).

p00040A highly preferred non-woven material coated with nanoparticles is described in WO2004 / 0158212, entitled "Disposable absorbent article promoting a durable hydrophilic core wrap", whose inventors (applicants in the US) are Ekaterina Anatolyevna Ponomarenko and Mattias NMN Schmidt.

p00041Other useful nonwoven materials are described in WO2002 / 0192366, WO2002 / 0150678, EP-A-1356152, EP-A1470281 and EP-A-1470282.

p00042In some cases, the surface of the nonwoven material can be pretreated with high energy treatment (corona, plasma) before applying nanoparticle coatings. Pretreatment with high energy typically temporarily increases the surface energy of a surface with low surface energy (such as PP) thus allowing better wetting of a nonwoven material by dispersing nanoparticles in water.

p00043It should be noted that permanently hydrophilic nonwoven materials are also useful in other parts of an absorbent article. For example, it has been found that top sheets and collection layers comprising permanently hydrophilic nonwoven materials, as described above, give good results.

p00044Surface tension is a measure of the maintenance of a certain level of hydrophilicity. This value should be measured using the test method described hereinafter.

p00045Penetration time is a measure of the level of hydrophilicity. This value should be measured using the test method described hereinafter.

p00046In a preferred embodiment of the present invention the absorbent core 28 comprises a substrate layer 100, absorbent polymer material 110 and a fibrous layer of adhesive 120.

p00047The substrate layer 100 is preferably made of a nonwoven material and the preferred nonwoven materials are those illustrated above for upper layer 56 or lower layer 58.

p00048The substrate layer 100 comprises a first surface and a second surface. At least parts of the first surface of the substrate layer 100 are in direct contact with a layer of absorbent polymer material 110. This layer of absorbent polymer material 110 is preferably a discontinuous layer and comprises a first surface and a second surface. Here, a discontinuous layer is a layer comprising openings. Typically, these openings have a diameter or maximum spacing of less than 10 mm, preferably less than 5 mm, 3 mm, 2 mm and more than 0.5 mm, 1 mm or 1.5 mm. At least parts of the second surface of the layer of absorbent polymer material 110 are in contact with at least parts of the first surface of the material of the substrate layer 100. The first surface of the absorbent polymer material 112 delimits a certain height of the absorbent polymer layer above the first surface of the material of the substrate layer 100. When the layer of absorbent polymer material 110 is provided as a discontinuous layer, portions of the first surface of the substrate layer 100 are not covered by absorbent polymer material 110. The absorbent core 28 also comprises a thermoplastic composition 120. This thermoplastic composition 120 serves to immobilize at least partially the absorbent polymer material 110.

p00049In a preferred embodiment of the present invention, the thermoplastic composition 120 may be disposed virtually uniformly within the absorbent polymer material 110.

p00050However, in an even more preferred embodiment of the present invention, the thermoplastic material 120 is provided as a fibrous layer that is partially in contact with the absorbent polymeric material 110 and partially in contact with the substrate layer 100. Figure 3 shows this preferred structure. In this preferred structure the layer of absorbent polymer material 110 is provided as a discontinuous layer and a layer of fibrous thermoplastic material 120 is applied on the layer of absorbent polymer material 110 so that the thermoplastic layer 120 is in direct contact with the first surface of the layer of absorbent polymer material 110, but also in direct contact with the first surface of the substrate layer 100, the substrate layer not being covered by the absorbent polymer material 110. This provides a virtually three-dimensional structure to the fibrous layer of thermoplastic material 120 which, in itself, is a virtually two-dimensional structure with a relatively small thickness (in the z direction), with respect to the extension in the x and y directions. In other words, the layer 120 of fibrous thermoplastic material ripples between the first surface of the absorbent polymer material 110 and the first surface of the substrate layer 100.

p00051Thus, the thermoplastic material 120 provides cavities to contain the absorbent polymeric material 110 and immobilize this material. In another aspect, the thermoplastic material 120 is bonded to the substrate 100 thereby fixing the absorbent polymeric material 110 to the substrate 100. The highly preferred thermoplastic materials will also penetrate the absorbent polymeric material 110 and the substrate layer 100, thus providing immobilization and An additional fixation.

p00052Logically, although the thermoplastic materials described herein provide a much better wet immobilization, that is, an immobilization of the absorbent material when the article is wet or at least partially loaded, these thermoplastic materials also provide a very good absorbent material immobilization. When the item is dry.

p00053In accordance with the present invention, the absorbent polymer material 110 may also be mixed with absorbent fibrous material, such as "air felt" type material, which can provide a matrix for further immobilization of the superabsorbent polymeric material. However, preferably a relatively low amount of cellulose fibrous material is used, preferably less than 40%, 20% or 10%, by weight of cellulose fibrous material with respect to the weight of absorbent polymeric material 110. Cores practically free of "air felt" are preferred. Here, the term "absorbent fibrous material" does not refer to any thermoplastic material (120) even though said thermoplastic material is fibrized and partially absorbent.

p00054An alternative construction is shown in Figure 4. The absorbent core shown in Figure 4 also comprises a cover layer 130. This cover layer may be made of the same material as the substrate layer 100 or it may be made of a different material. Preferred materials for the cover layer are nonwoven materials, typically the materials described above as useful for upper layer 56 and lower layer 58. In this embodiment, parts of the cover layer 130 are joined to parts of the substrate layer 100 by the thermoplastic material 120. Thus, the substrate layer 100 together with the cover layer 130 provide cavities for immobilizing the absorbent polymeric material 110.

p00055With respect to Figures 3 and 4, the areas of direct contact between the thermoplastic material 120 and the substrate material 100 are called joining areas 140. The number of shapes and arrangement of the joining areas 140 will affect the immobilization of the absorbent polymer material 110. The joining areas can have a square, rectangular or circular shape. Preferred junction areas have a circular shape. Preferably they have a diameter of more than 0.5 mm or 1 mm or 1.5 mm and less than 10 mm or 5 mm or 3 mm or 2 mm. If the joining areas 140 have no circular shape, they preferably have a size to fit within a circle of any of the preferred diameters mentioned above.

p00056The joining areas 140 may be arranged in a normal or irregular design. For example, the joining areas 140 may be arranged along lines as shown in Figure 5. These lines may be aligned with the longitudinal axis of the absorbent core or alternatively they may form a certain angle with respect to the edges Longitudinal of the nucleus. It has been found that an arrangement along lines parallel to the longitudinal edges of the absorbent core 28 creates channels in the longitudinal direction that produce less immobilization in the wet state. Preferably, therefore, the joining areas 140 are arranged along lines that form an angle of 20 degrees, 30 degrees, 40 degrees or 45 degrees with the longitudinal edges of the absorbent core 28. Another preferred design for junction zones 140 is a design comprising polygons, for example pentagons and hexagons or a combination of pentagons and hexagons. Irregular designs of junction zones 140 are also preferred, which has also been found to provide good wet immobilization.

p00057According to the present invention, two different designs of junction zones 140 can be selected. In one embodiment, the junction zones are discontinuous. They are placed within areas of absorbent material, such as islands in the sea. The zones of absorbent materials are mentioned as joined zones. In an alternative embodiment, the junction zones may be connected. Then, the absorbent material may be deposited in a discontinuous design or, in other words, the absorbent material represents islands in a sea of ​​thermoplastic material (120). Therefore, a discontinuous layer of absorbent polymer material 110 may comprise connected areas of absorbent polymer material 110 or may comprise discontinuous areas of absorbent polymer material 110.

p00058According to the present invention, it has been discovered that absorbent cores can be formed that provide good wet immobilization by combining two layers as shown in Figure 3 and described in context. An embodiment of this type is shown in Figure 6. The absorbent core material shown in Figure 6 comprises two layers of substrate 100, two layers of absorbent polymer material 110 and two layers of fibrous thermoplastic materials 120. When two discontinuous layers of an absorbent polymeric material 110 are used, these are typically arranged so that the absorbent polymeric material of one layer is oriented towards the joining areas 140 of the other layer. In a preferred alternative embodiment, however, the junction zones 140 are displaced and not facing each other. Therefore preferably, when two storage layers are joined, this is done so that the first surface of the substrate layer (100) of the first storage layer (60) faces the first surface of the layer (100) of substrate of the second storage layer (60).

p00059The constructions described with respect to Figure 3, 4 and 6 may be used to provide the storage layer 60 of an absorbent core, although only Figure 6 is according to the invention claimed herein. However, they can also be used to provide the entire absorbent core 28. In this case no other materials are used to wrap the core, such as the upper layer 56 and the lower layer 58. With respect to the embodiment of Figure 3, the substrate layer 100 can perform the function of the lower layer 58 and the layer of fibrous thermoplastic material 120 can perform the function of the upper layer 56. With respect to Figure 4, the cover layer 130 can perform the function of upper layer 56 and substrate layer 100 can perform the function of lower layer 58. With respect to Figure 6, the two substrate layers 100 used can perform the functions of the upper layer 56 and the lower layer 58, respectively.

p00060According to the present invention, the thermoplastic layer 120 may comprise any thermoplastic composition, with thermoplastic adhesive compositions, also mentioned as hot melt adhesives, being preferred. Different thermoplastic compositions are suitable for immobilizing the absorbent material.

p00061Some initially thermoplastic materials may subsequently lose their thermoplasticity due to a curing stage, e.g. ex. initiated by heat, UV radiation, exposure to an electron beam or moisture or other curing medium, resulting in an irreversible formation of a crosslinked network of covalent bonds. Materials that have lost their initial thermoplastic behavior are also considered herein as thermoplastic materials 120.

p00062Without intending to impose any theory, it has been discovered that these thermoplastic compositions are of maximum utility for immobilizing the absorbent polymeric material 110, combining good cohesion and good adhesion behavior. Good adhesion is critical to ensure that the thermoplastic layer 120 maintains good contact with the absorbent polymeric material 110 and in particular with the substrate. Good adhesion represents a challenge, especially when using a non-woven substrate. Good cohesion ensures that the adhesive does not break, particularly as a response to external forces and especially as a response to deformation. The adhesive is subjected to external forces when the absorbent product has absorbed liquid, which is then stored in the absorbent polymer material 110 which, in response, swells. A preferred adhesive will allow this swelling without breaking and without transmitting too much compression force, which would prevent the absorbent polymer material 110 from swelling. It should be noted that, in accordance with the present invention, the adhesive should not break as this would affect immobilization in the wet state. Preferred thermoplastic compositions that meet these requirements have the following characteristics:

p00063The thermoplastic composition may, as a whole, comprise a single thermoplastic polymer or a mixture of thermoplastic polymers having a softening point, determined by the ASTM D-36-95 "Ring and Ball" method, in the range of 50 ° C at 300 ° C, or alternatively the thermoplastic composition may be a hot melt adhesive comprising at least one thermoplastic polymer together with other thermoplastic diluents such as adhesive resins, plasticizers and additives such as antioxidants.

p00064The thermoplastic polymer typically has a molecular weight (MW) of more than 10,000 and a glass transition temperature (Tg) usually below room temperature. Typical concentrations of the polymer in a melt are in the range of 20% -40% by weight. A wide variety of thermoplastic polymers are suitable for use in the present invention. These thermoplastic polymers are preferably water insensitive. Examples of polymers are block copolymers (styrenics) including three ABA block structures, two AB block structures and radial block copolymer structures (AB) n where the A blocks are non-elastomeric polymer blocks, typically that they comprise polystyrene, and the B blocks are unsaturated conjugated diene or (partially) hydrogenated versions thereof. Block B is typically isoprene, butadiene, ethylene / butylene (hydrogenated butadiene), ethylene / propylene (hydrogenated isoprene) and mixtures thereof.

p00065Other suitable thermoplastic polymers that can be used are metallocene polyolefins, which are ethylene polymers that are prepared using single site or metallocene catalysts. In these at least one comonomer can be polymerized with ethylene to prepare a copolymer, terpolymer or higher order polymer. Also applicable are amorphous polyolefins or amorphous polyalphaolefins (APAO) which are homopolymers, copolymers or terpolymers of C2 to C8 alphaolefins.

p00066The resin typically has a PM of less than 5000 and a Tg normally higher than room temperature; The concentrations of the resin in a melt are in the range of 30% -60%. The plasticizer has a Pm, typically less than 1000 and a Tg below room temperature, a typical concentration is 0% -15%.

p00067Preferably the adhesive is present in the form of fibers in the core, that is, the adhesive is fibrized. Preferably, the fibers will have an average thickness of 1-50 micrometers and an average length of 5 mm to 50 cm.

p00068To improve the adhesion of the thermoplastic material 120 to the substrate layer 100 or any other layer, in particular any other layer of nonwoven material, this layer can be pretreated with an auxiliary adhesive.

p00069Preferably, the adhesive will meet at least one of the following parameters, and more preferably several or all of them:

p00070A preferred adhesive will have a storage module G 'measured at 20' ° C of at least 30,000 Pa and less than

p00071300,000 Pa, preferably less than 200,000 Pa, more preferably less than 100,000 Pa. The storage module G 'at 20 ° C is a measure of permanent "stickiness" or permanent adhesion of the thermoplastic material used. Good adhesion will guarantee a good and permanent contact between the thermoplastic material and for example the substrate layer 100. In another aspect, the storage module G 'measured at 60 ° C should be less than 300,000 Pa and more than 18,000 Pa, preferably more than 24,000 Pa and, most preferably, more than 30,000. The storage module measured at 60 ° C is a measure of the shape stability of the thermoplastic material at elevated ambient temperature. This value is especially important if the absorbent product is used in a warm climate where the thermoplastic composition would lose its integrity if the storage module G 'at 60 ° C was not sufficiently high.

p00072The storage module G 'is typically measured using a rheometer as shown schematically in Figure 8 for general illustrative purpose only. The rheometer (400) is able to apply a shear stress to the adhesive and measure the response to the resulting deformation (shear deformation) at constant temperature. The adhesive is placed between a Peltier element that acts as a fixed bottom plate (410) and an upper plate (420) with a radius R of, for example, 10 mm, which is attached to the drive shaft of a motor to generate the stress Shear The distance between the two plates has a height H of 1500 micrometers, for example. The Peltier element allows to control the temperature of the material (± 0.5 ° C).

p00073In another aspect, the tan Delta loss angle of the adhesive at 60 ° C should be less than 1, preferably less than 0.5. The loss angle tan Delta at 60 ° C is related to the liquid character of an adhesive at elevated room temperature. The lower the Delta is, the more an adhesive will behave as a solid rather than as a liquid, that is, the lower its tendency to flow or migrate and the lower the tendency of an adhesive superstructure such as that described herein to deteriorate. or even crush over time. This value is, therefore, especially important if the absorbent article is used in a warm climate.

p00074In another aspect, the preferred adhesive should also have a glass transition temperature Tg of less than 25 ° C, preferably less than 22 ° C, more preferably less than 18 ° C and, most preferably, less than 15 ° C. A low glass transition temperature Tg is beneficial for good adhesion. In another aspect a low glass transition temperature Tg ensures that the adhesive thermoplastic material does not become brittle.

p00075In another aspect, a preferred adhesive will have a sufficiently high transition temperature Tx. It has been found that a sufficiently high transition temperature Tx is beneficial for the high temperature stability of the thermoplastic layer and, therefore, guarantees good performance of the absorbent product and in particular good immobilization in the wet state even in hot climates and at temperatures Therefore, Tx should preferably be greater than 80 ° C, more preferably greater than 85 ° C and, most preferably, greater than 90 ° C.

p00076A highly preferred adhesive useful as a thermoplastic material (120) as described herein will meet most or all of the above parameters. Special attention should be given to ensuring that the adhesive provides both good cohesion and good adhesion.

p00077The process for manufacturing preferred absorbent cores 28 according to the present invention comprises the following steps:

p00078The absorbent core 28 is applied on a descending drum having a non-uniform surface. In a first stage of the process the substrate layer 100 is applied on the non-uniform surface. Because of the gravity,

p00079or preferably using a vacuum medium, the layer of substrate material will follow the contour of the non-uniform surface and in this way the layer of substrate material will adopt a mountain and valley shape. On this layer

p00080(100) substrate polymer absorbent material is available by means known in the art. The absorbent polymeric material will accumulate in the valleys presented by the substrate layer 100. At another stage of the process a hot melt adhesive is applied on the absorbent polymeric material.

p00081Although any adhesive application means known in the art can be used to place the hot melt adhesive on the absorbent polymeric material, the hot melt adhesive is preferably applied by a nozzle system. Preferably, a nozzle system that can provide a relatively thin but wide adhesive curtain is used. This adhesive curtain is then placed on the substrate layer 100 and the absorbent polymeric material. As the high mountain portions of the substrate layer 100 are less covered by absorbent polymeric material, the adhesive will come into contact with these areas of the substrate layer.

p00082In another optional step of the process a cover layer 130 is placed on the substrate layer 100, the absorbent polymeric material and the hot melt adhesive layer. The cover layer 130 will be in adhesive contact with the substrate layer 100 in the bonding areas 140. In these bonding areas 140 the adhesive is in direct contact with the substrate layer 100. The cover layer 130 will typically not be in adhesive contact with the substrate layer 100 where the valleys of the substrate layer 100 are filled with absorbent polymeric material.

p00083Alternatively, the cover layer 130 may be applied on a drum with a non-uniform surface and the substrate layer 100 may be added at a consecutive stage of the process. The embodiment shown in Fig. 4 could be produced by such a process.

p00084In an alternative embodiment, the cover layer 130 and the substrate layer 100 are provided from a sheet of unit material. Placing the cover layer 130 on the substrate layer 100 will then involve folding the piece of unit material.

p00085Therefore, the non-uniform service of the application system, which is preferably an application drum, typically determines the distribution of the absorbent polymer material through the storage layer 60 and analogously determines the design of the joining areas 140. Alternatively, the distribution of the absorbent polymeric material can be influenced by a vacuum means.

p00086Preferably the distribution of the absorbent polymer material has a profile, and most preferably it has a profile in the longitudinal direction. Therefore, along the longitudinal axis of the absorbent core, which normally coincides with the longitudinal axis of the absorbent article, for example of the diaper, the weight per unit area of ​​the absorbent polymeric material will vary. Preferably, the base weight of absorbent polymer material in at least one first square freely selected from 1 cm x 1 cm measures is at least 10%, or 20%, or 30%, 40% or 50% greater than the base weight of polymer material absorbent in at least one second square freely selected from measures 1 cm x 1 cm. Preferably, the criterion is adopted if the first and second squares are centered around the longitudinal axis.

p00087Optionally, the absorbent core may also comprise a fibrous absorbent material, for example cellulose fibers. This fibrous material can be pre-mixed with the absorbent polymeric material to be applied at one stage of the process or alternatively to be applied at different stages of the process.

p00088It has been found that it is beneficial to use a particulate absorbent polymeric material for the absorbent cores made in the present invention. Without intending to impose any theory, it is believed that this material, even in a swollen state, that is, when the liquid has been absorbed, does not practically obstruct the flow of liquid through the material, especially when the permeability expressed by the flow conductivity of Saline solution of the absorbent polymer material is greater than 10, 20, 30 or 40 SFC units, where 1 SFC unit is 1 x 10-7 (cm3 xs) / g. The conductivity in saline flow is a parameter well known in the art and is measured according to the test described in EP-752 892 B.

p00089To achieve sufficient absorption capacity in a preferred absorbent article according to the present invention, and especially if the absorbent article is a diaper or a product for incontinent adults, the superabsorbent polymeric material will be present with an average weight per unit area of ​​more than 50, 100, 200, 300, 400, 500, 600, 700, 800 or 900 g / m2.

p00090Preferred articles according to the present invention reach a relatively narrow crotch width, which increases the comfort of use. A preferred article according to the present invention reaches a crotch width of less than 100 mm, 90 mm, 80 mm, 70 mm, 60 mm or even less than 50 mm. Therefore, preferably an absorbent core according to the present invention has a crotch width measured along a transverse line that is located at the same distance from the front edge as from the rear edge of the core that is less than 100 mm, 90 mm, 80 mm, 70 mm, 60 mm or even less than 50 mm. It has been found that in most absorbent articles the discharge of liquid occurs predominantly in the front half. The front half of the absorbent core should therefore comprise most of the core's absorption capacity. Preferably the front half of said absorbent core comprises more than 60%, more preferably more than 65%, 70%, 75%, 80%, 85% or 90%, of the absorption capacity.

p00091Wet immobilization test

p00092Teams:

<dl><dt>• </dt><dd>Test solution: 0.90% saline solution at 37 ° C. </dd></dl>

<dl><dt>• </dt><dd> Balance </dd></dl>

<dl><dt>• </dt><dd> Diaper Shaker </dd></dl>

<dl><dt>• </dt><dd>Bath to keep the test solution at 35 ° C - 37 ° C </dd></dl>

<dl><dt>• </dt><dd>Beaker for liquids graduated in stages of at least 2 ml </dd></dl>

<dl><dt>• </dt><dd> Chronometer </dd></dl>

<dl><dt>• </dt><dd>Thermometer </dd></dl>

<dl><dt>• </dt><dd>Tray (300) of approximately 10 x 120 x 220 mm </dd></dl>

p00093Diaper Shaker

p00094An assay created to perform the wet immobilization test may comprise a "diaper shaker" as described herein and as shown in Figure 7. The shaker comprises a base plate 210 which should be of sufficient weight to allow stable shaking conditions. Two legs 220a and 220b are mounted on the base plate that are height-adjustable to test absorbent cores or absorbent products of different lengths. The legs 220 hold a plate 230. On this plate is mounted the mounting table 250 with a clamp using rubber supports 240. The shaking movement between the clamp mounting table 250 and the plate 230 is caused by a motor, preferably an electric motor 260. The clamp mounting table 250 is rigidly connected with a clamp 270 whose size is selected based on the absorbent cores or absorbent products to be evaluated.

p00095The base plate 210 can also be used as a support for the tray 300 in which the absorbent core or absorbent product is pre-moistened before the test operation, as described below.

p00096Sample preparation:

<dl><dt>• </dt><dd>Provide ten absorbent articles or absorbent core samples. Remove all layers that do not directly wrap the absorbent polymer material (e.g., top sheet and backing sheet and collection layers that do not comprise absorbent polymer material) from the absorbent article sample. Cut a 200 mm long core sample using two parallel cross-sectional cutting lines. If the length of the core exceeds 200 mm, two parallel cutting lines can be selected as defined above. </dd></dl>

<dl><dt>• </dt><dd>Measure the weight of dry laminate. </dd></dl>

<dl><dt>• </dt><dd>Place the laminate on the tray. </dd></dl>

<dl><dt>• </dt><dd>Pour test solution over the center of the core sample. The amount of test solution should be 50% of the nominal capacity of the laminate. The nominal capacity of the total available capacity of the absorbent cores to be tested should be understood herein as the CRC stratification capacity of the trimmed core sample piece as defined below.</dd></dl>

<dl><dt>• </dt><dd>Run the test as described below after 5 min of residence time. Execution of the trial:</dd></dl>

<dl><dt>• </dt><dd>Measure the weight (m1) of the wet laminate before the shaking test. </dd></dl>

<dl><dt>• </dt><dd>Fix the laminate with clamps so that no less than 180 mm of the laminate is extended below the clamp, and therefore is not restricted from free movement during agitation. The clamps must be approximated over the total width of the AGM.</dd></dl>

<dl><dt>• </dt><dd>The lower end of laminate with free movement should have a distance to the AGM collection tray of 4 cm. </dd></dl>

<dl><dt>• </dt><dd>Shaking frequency: 16.8 Hz. </dd></dl>

<dl><dt>• </dt><dd>Amplitude in vertical direction: 4 mm, in horizontal direction 1 mm. </dd></dl>

<dl><dt>• </dt><dd>Shaking time 2x 80 s. </dd></dl>

<dl><dt>• </dt><dd>After shaking, fix the end with free movement before the clamp. </dd></dl>

<dl><dt>• </dt><dd>Open the end with free movement, if it is sealed by the pressure of the clamps. </dd></dl>

<dl><dt>• </dt><dd>Shake again using the same settings. </dd></dl>

<dl><dt>• </dt><dd>Measure the weight (m2) of the remaining laminate after shaking Results Report: </dd></dl>

<dl><dt>• </dt><dd>Record the weight of the rounded dry laminate to the nearest tenth of a gram (e.g., 10.0 g) </dd></dl>

<dl><dt>• </dt><dd>Record the weight before (m1) and after (m2) of the agitation, both rounded to the nearest tenth of a gram (eg m1 = 130.4 g, m2 = 100.4 g) </dd></dl>

<dl><dt>• </dt><dd>Calculate the average weight loss, rounded to the nearest tenth of a gram (e.g., 30.0 g) </dd></dl>

<dl><dt>• </dt><dd>Calculate the average weight loss in percentage, </dd></dl>

, rounded to the nearest whole unit (e.g. 23%).

<dl><dt>• </dt><dd>Report the immobilization value in a single test wet state, which is the 100% difference, e.g. For example, 77% wet immobilization.</dd></dl>

<dl><dt>• </dt><dd>The wet state immobilization value, also called wet state immobilization, is the average value based on ten single test wet state immobilization values. A high wet state immobilization value is representative of good wet state immobilization and low particle loss.</dd></dl>

p00097CRC layering capacity

p00098The stratified CRC capacity (CLAM) is calculated as:

p00099mAGM indicates the mass of AGM in the laminate. CRCAGM indicates the CRC capacity of the AGM in the laminate.

p00100The mass of AGM within the laminate (mAGM) can be measured by any useful method known to the person skilled in the art, for example, volumetric titration can be used.

p00101AGM CRC (CRCAGM) is measured by removing some AGM from the laminate to then apply the following centrifugal retention capacity (CRC) test:

p00102Centrifugal Retention Capacity (CRC)

p00103For most hydrogel-forming absorbent polymers, gel volume as a measure of absorption capacity is determined by the method described in US-32,649, granted to Brandt et al. and reissued on April 19, 1988, but using 0.9% saline instead of synthetic urine. Gel volume and CRC capacity are calculated with respect to dry weight. This method should be used for all conformations of hydrogel absorbent polymers that do not absorb Blue Dextran.

p00104The method for measuring the volume of gel to be used for SAP materials that absorb Blue Dextran (see, gel volume method in US-32,649) to the surfaces of the formed hydrogel (eg, polymers prepared from monomers cationic), is as follows: For these hydrogel-forming polymers, the absorption capacity test is used, but in the calculation the dry weight of the hydrogel-forming polymer is used instead of the weight as is. See, p. eg, US-5,124,188, granted to Roe et al. on June 23, 1992, in columns 27-28 where the absorption capacity test is described.

p00105For the evaluation of the centrifugal retention capacity it has been found that the so-called evaluation or measurement of the tea bag (then CRC measurement) is more suitable to reflect the maintenance of capillary pressure in situations close to the saturation of the capacity of absorption of an SAP material. Standard laboratory conditions (21 ° C - 23 ° C, 50% relative humidity) are used for the test. The sample SAP material is kept dry in an airtight flask or other container that only opens at the beginning of the evaluation. The rest of the material used in the evaluation (tissues, equipment, etc.) is conditioned for 24 hours before the measurements in the previous laboratory conditions.

p00106For CRC measurement, 0.2 +/- 0.0050 g of SAP particles are introduced into a tea bag (the bag must be freely permeable to liquids and must retain the particles, i.e. the pores of the Tea bag should not be larger than smaller particles.The tea bag should have a size of 60 mm x 85 mm and be sealed by welding after filling. The tea bag is then immersed for 30 minutes in a 0.9% saline solution such that there is at least 0.83 l of solution per gram of SAP; preferably there is a considerable excess of this relationship. After immersion for 30 minutes, the tea bag is centrifuged at 250 g for 3 minutes to remove excess saline. The bag is weighed rounding to the nearest 0.01 g and the absorbed liquid is calculated. The result is established using the amount of dry SAP that was introduced into the tea bag as grams absorbed per gram of SAP particles.