Absorbent core for an absorbent article

ES 2 339 713 T3

DESCRIPTION

Absorbent core for an absorbent article.

Field of the invention

The 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 polymeric material when the article is fully or partially loaded with urine. This absorbent core is useful in providing an absorbent article of greater wearing comfort that is thin and dry.

Background of the invention

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

Although such a diaper is generally a disposable product, in some cases it is worn for many hours and is also worn both in the dry state and in the urine-laden state.

Therefore, to provide good wearing comfort it is very important to keep the absorbent materials comprised by a diaper or other absorbent article in their intended position, both when the article is dry and when the article is fully or partially loaded with urine (or with other body fluid).

An absorbent article with a core comprising pockets of absorbent hydrocolloid material is disclosed in US-4,381,783 (Elias). 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, to achieve good immobilization of the hydrocolloid material according to the description of this patent, relatively high amounts of cellulosic material are needed. Furthermore, the inclusion of these pockets can hinder the free distribution of liquid to the more absorbent areas of the core, for example the areas of hydrocolloid materials.

EP-724418 (Tanzer) describes an absorbent article that includes superabsorbent material located in discrete pockets. The absorbent article comprises first and second carrier layers and a water sensitive attachment means to bond the carrier layers and to provide a plurality of pocket regions. The article comprises high absorbency material located within said pocket regions. The water-sensitive bonding medium provides a wet strength that is less than a spreading 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 more securely houses and contains the high absorbency material in a selected form of pockets when the article is dry. However, due to the structure of the pockets and in particular due to the selection of the water sensitive attachment means, these pockets are not maintained when the article is fully or partially loaded with liquids. Thus, it is believed that this absorbent article does not provide very satisfactory immobilization of absorbent material in a fully or partially urine-laden state.

Articles are also described in US-A-5425725 (Tanzer), US 2002/102392 (Fish), US 2002/115969 (Maeda) and US-A-4055180 where the superabsorbent material is present as a discontinuous layer between a substrate and a layer of thermoplastic material. These state of the art documents together with EP724418 are referred to below as the state of the art of discontinuous superabsorbent layers.

In WO 95/17868 (Palumbo) an absorbent structure comprising two fiber layers and an intermediate layer is described. This intermediate layer comprises a hydrogel absorbent material in an amount greater than 120 g / m²and particles of a thermoplastic material. Although this structure certainly provides good immobilization of the hydrogel absorbent particles in the dry state, it appears that only minor immobilization is achieved in the urine-laden state. The described thermoplastic materials appear to swell much less than the described hydrogel materials. Therefore, in particular when the absorbent structure is used in a product to absorb large amounts of liquid, for example a diaper, immobilization in the wet state may not be fully satisfactory.

Summary

The present invention relates to an absorbent article, preferably a disposable absorbent article such as a diaper. An absorbent core useful for an absorbent article is described which provides greater wearing comfort to the article and makes it thin and dry. A process to obtain this kernel is also described. Specifically described is an absorbent core useful for an absorbent article comprising a substrate layer, wherein the

ES 2 339 713 T3 substrate layer comprises a first surface and a second surface, the absorbent core also comprises a discontinuous layer of absorbent material, the absorbent material comprises an absorbent polymeric material, the absorbent material optionally comprises an absorbent fibrous material and the absorbent material absorbent fibrous does not represent more than 20% by weight of the total weight of the absorbent polymeric material, the discontinuous layer of absorbent material comprises a first surface and a second surface, the absorbent core also comprises a layer of thermoplastic material, the layer of thermoplastic material comprises a first surface and a second surface and wherein the second surface of the discontinuous layer of absorbent material is in at least partial contact with the first surface of the layer in question and wherein parts of the second surface of the layer of thermoplastic material are in direct contact with the first surface of the substrate layer and parts of the second surface of the layer of thermoplastic material are in contact direct with the first surface of the discontinuous layer of absorbent material.

The core differs from the state of the art of discontinuous superabsorbent layers in that it comprises a first and a second storage layer that are bonded, the first storage layer comprising a first substrate layer and a first layer of thermoplastic material and comprising the second storage layer a second substrate layer and a second layer of thermoplastic material, wherein the first and second storage layers are joined such that the first surface of the first substrate layer faces the first surface of the second substrate layer, and such that the absorbent material of said first substrate layer is facing areas of attachment of said second substrate layer and the absorbent material of said second layer of substrate is facing areas of attachment of said first layer of substrate.

Also described is a process for providing a storage layer for an absorbent core that is useful in an absorbent article and is in accordance with the claimed invention, wherein the process comprises the steps of:

- providing a substrate material comprising a first surface and a second surface

- depositing absorbent material on the first surface of the substrate material in a pattern, wherein the pattern comprises at least one area that is practically free of absorbent material and at least one area that comprises absorbent material ^- depositing a thermoplastic material on the first surface of the substrate material and the absorbent material, such that parts of the thermoplastic material are in direct contact with the first surface of the substrate and parts of the thermoplastic material are in direct contact with the absorbent material.

Detailed description

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

As used herein, the following terms have the following meanings:

The 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 articles include, but are not limited to, diapers, incontinent adult briefs, diaper briefs, diaper fasteners and diaper dressings, sanitary napkins, and the like.

The term "disposable" is used herein to describe items that are generally not intended to be laundered or otherwise recovered or reused (ie, are intended to be thrown away after a single use and, preferably, to be recycled. composted or otherwise disposed of in an environmentally friendly way).

The term "diaper" refers to an absorbent article generally worn by infants and incontinent persons around the lower torso.

The terms "comprise", "comprising" and "comprises" are open terms specifying the presence of the following, eg. ex. a component, but do not exclude the presence of other features, elements, steps or component known in the art or described herein.

In the accompanying drawings, where Figure 6 shows a core according to the present invention:

Figure 1 is a plan view of a diaper as a preferred embodiment of an absorbent article according to the present invention;

Figure 2 shows a cross section of Figure 1 taken along transverse axis 110;

Figure 3 shows an absorbent core;

ES 2 339 713 T3 Figure 4 shows an alternative absorbent core;

Figure 5 shows how, for example, bonding zones can be arranged between a thermoplastic material and a substrate material; and Figure 6 shows an absorbent core according to the present invention.

Figure 1 is a plan view of a diaper 20 as a preferred embodiment of an absorbent article in accordance with the present invention. The diaper is shown in the non-contracted extended state (ie, no elastic-induced contraction). Parts of the structure have been cut out to more clearly show the underlying structure of the diaper 20. The part of the diaper 20 that comes into contact with the wearer faces the viewer. The frame 22 of the diaper 20 of 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 nested between the topsheet 24 and the backsheet 26. The frame may also include most or all of the absorbent core 28 nested between the topsheet 24 and the backsheet 26. The frame preferably also includes side panels 30, elasticated leg cuffs 32, and an elastic waist feature 34, wherein the leg cuff 32 and elastic waist feature each typically comprise elastic elements. 33. An end portion 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 portion of the diaper 20 is configured as a crotch region 37 extending longitudinally between the first and second waist regions 36 and 38. The waist regions 36 and 38 may include elastic elements so that they wrap around the wearer's waist to provide better fit and confinement (characteristic elastic waist element 34). Crotch region 37 is that portion of diaper 20 which, when diaper 20 is used, is generally positioned between the wearer's legs. 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 extend generally 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. diaper 20. The frame also comprises a fastening system, which may include at least one fastening element 42 and at least one stored discharge area 45.

In unitary absorbent articles, frame 22 comprises the main structure of the diaper with other features added to form the composite diaper structure. The topsheet 24, the backsheet 26, and the absorbent core 28 may be bonded in various well-known configurations and preferred diaper configurations are generally described in US Pat. No. 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; US5,569,234 entitled "Disposable Pull-On Pant" issued to Buell et al. on October 29, 1996; and US-6,004,306 entitled "Absorbent Article With Multi-Directional Extensible Side Panels" issued to Robles et al. on December 21, 1999.

The topsheet 24 in Figure 1 may be fully or partially elasticized or may be shortened to provide a void space between the topsheet 24 and the absorbent core 28. Illustrative structures, including elasticized or shortened topsheets, are described in more detail. in US 5,037,416 entitled "Disposable Absorbent Article Having Elastically Extensible Topsheet" issued to Allen et al. on August 6, 1991; and US Pat. No. 5,269,775 entitled "Trisection Topsheets for Disposable Absorbent Articles and Disposable Absorbent Articles Having Such Trisection Topsheets" issued to Freeland et al. on December 14, 1993.

The absorbent core 28 in Figure 1 is generally disposed between the topsheet 24 and the backsheet 26. The absorbent core 28 can comprise any absorbent material that is generally compressible, compliant, non-irritating to the wearer's skin, and capable of absorbing and retaining fluids such as urine and other body exudates. The absorbent core 28 can comprise a wide variety of liquid absorbent materials commonly used in disposable diapers and other absorbent articles such as ground wood pulp, generally referred to as air felt. Examples of other suitable absorbent materials include crimped cellulose wadding; melt blown polymers, including copolymers; chemically stiffened, modified or crosslinked cellulosic fibers; tissue paper, including tissue paper wrappers and tissue paper laminates; absorbent foams; absorbent sponges; superabsorbent polymers; absorbent gelling materials; or any other known absorbent material or combinations of 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.

Illustrative absorbent structures for use as the 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.); US5,387,207 (Dyer et al.); US-5,397,316 (LaVon et al.); and US-5,625,222 (DesMarais et al.).

The backsheet 26 may be bonded to the topsheet 24. The backsheet 26 prevents exudates absorbed by the absorbent core 28 and contained within the article 20 from soiling other external articles that may be in contact with the diaper 20, such as like sheets and undergarments. In preferred embodiments, the backsheet 26 is substantially impervious to liquids (eg, urine) and comprises a laminate of

ES 2 339 713 T3 a nonwoven material and a thin plastic film such as a thermoplastic film having a thickness of from about 0.012mm (0.5 mil) to about 0.051mm (2.0 mils). Suitable backsheet films include those manufactured by Tredegar Industries Inc. of Terre Haute, IN (USA), marketed under the trade names X15306, X10962 and X10964. Other suitable backsheet materials may include breathable materials that allow vapor to escape from the diaper 20 but without allowing exudates to pass through the backsheet 26. Illustrative breathable materials may include materials such as woven bands, non-woven bands, composite materials such as film-coated non-woven bands, and microporous films such as those manufactured by Mitsui Toatsu Co. of Japan under the name ESPOIR NO and by Exxon. Chemical Co. of Bay City, TX (USA) under the name EXXAIRE. Suitable breathable composites comprising polymer blends are available from Clopay Corporation, Cincinnati, OH (USA) under the name HYTREL blend P18-3097. These breathable composites are described in greater detail in PCT WO 95/16746, published June 22, 1995 in the name of EI DuPont. Other breathable backsheets, including nonwoven webs and apertured films, are described in US Pat. No. 5,571,096 issued to Dobrin et al. on November 5, 1996.

Diaper 20 may also include other features as known in the art, including front and rear ear panels, waist features, elastics, and the like to provide better fit, confinement, and aesthetic characteristics. These additional features are well known in the art and are described, e.g. eg, in US-3,860,003 and US-5,151,092.

To hold the diaper 20 in place on the wearer's body, preferably at least a portion of the first waist region 36 is attached by the fastener 42 to at least a portion of the second waist region 38, preferably to form leg opening (s) and an article waist. When attached, the attachment system carries a tensile load around the waist of the article. The fastening system is designed to allow the user of an article to grasp an element of the fastening system such as fastener 42 and attach the first waist region 36 to the second waist region 38 in at least two places. This is achieved by manipulating bonding resistors between the elements of the fixture.

The diapers 20 according to the present invention may be provided with a repeatedly closable fastening system or alternatively they may be provided in the form of panty-type diapers.

The fastening system and any component thereof may include any material suitable for this use, including but not limited to plastics, films, foams, non-woven webs, woven webs, paper, laminates, fiber-reinforced plastic, and the like, or combinations of the same. It may be preferable that the materials that make up the fixation device are flexible. The flexibility is designed to allow the fixation system to conform to the shape of the body and thus reduce the likelihood that the fixation system will irritate or damage the wearer's skin.

Figure 2 shows a cross section of Figure 1 taken along transverse axis 110. Starting from the wearer-facing side, the diaper comprises topsheet 24, absorbent core components 28, and backsheet 26. The absorbent core preferably comprises the pick-up system 50, which comprises an upper pick-up layer 52 facing the wearer's skin and a lower pick-up layer 54 facing the wearer's garment. In a preferred embodiment the upper take-up layer 52 comprises a non-woven material while the lower take-up layer preferably comprises a mixture of chemically stiffened, twisted and corrugated fibers, high surface area fibers and thermoplastic bonding fibers. In another preferred embodiment both capture layers are provided of a nonwoven material, which is preferably hydrophilic. The capture layer preferably is in direct contact with the storage layer 60.

The storage layer 60 may be enveloped by a core wrapping material. In a preferred embodiment the core wrap material comprises a top layer 56 and a bottom layer 58. The core wrap material, top layer 56 or bottom layer 58 may be made of a nonwoven material. A preferred material is the so-called SMS material, which comprises a spunbonded layer, a meltblown layer and another spunbonded layer. Highly preferred are permanently hydrophilic nonwovens and in particular nonwovens with durable hydrophilic coatings. An alternative preferred material comprises an SMMS structure.

The upper layer 56 and the lower layer 58 can be made of two or more separate sheets of material or alternatively they can be made of a unitary sheet of material. This unitary sheet of material may be wrapped around the storage layer 60, e.g. ex. forming a C-fold.

Preferred nonwovens are made from synthetic fibers, such as PE, PET, and most preferably PP. Since the polymers used for the production of nonwovens are inherently hydrophobic, they are preferably coated with hydrophilic coatings.

A preferred way to produce nonwoven with durable hydrophilic coatings is by applying a hydrophilic monomer and radical polymerization initiator to the nonwoven and performing UV-activated polymerization to obtain monomers chemically bonded to the surface of the nonwoven, such as is described in EP-A-1403419.

ES 2 339 713 T3

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

Nanoparticles typically have a maximum dimension of less than 750 nm. Nanoparticles with sizes between 2 and 750 nm can be produced cost-effectively. The advantages of nanoparticles is that many of them can be easily dispersed in aqueous solution to allow the application of the coating on the non-woven material; they typically form clear coatings and coatings applied from aqueous solutions are typically sufficiently durable against exposure to water.

The nanoparticles can be of the organic or inorganic, synthetic or natural type. Inorganic nanoparticles generally exist as oxides, silicates, or carbonates. Typical examples of suitable nanoparticles are rolled clay minerals (eg LAPONITE ™ from Southern Clay Products, Inc. (USA) and boehmite alumina (eg Disperal P2^TM from North American Sasol. Inc).

A highly preferred nanoparticle coated nonwoven material is disclosed in the co-pending patent application entitled "Disposable absorbent article comprising a durable hydrophilic core wrap" of which the inventors (in the USA, the applicants) are Ekaterina Anatolyevna Ponomarenko and Mattias NmN Schmidt.

Other useful nonwovens are described in WO 2002/0192366, WO 2002/0150678, EP-A-1356152, EP-A1470281 and EP-A-1470282.

In some cases, the surface of the non-woven material can be pre-treated with high energy methods (corona, plasma) before applying nanoparticle coatings. High energy pretreatment typically temporarily increases the surface energy of a low surface energy surface (such as PP) thus allowing better wetting of a nonwoven material by dispersion of nanoparticles in water.

It should be noted that permanently hydrophilic nonwovens are also useful in other parts of an absorbent article. For example, topsheets and take-up layers comprising permanently hydrophilic nonwovens, as described above, have been found to work well.

In summary, in one aspect of the present invention, absorbent articles comprising a nonwoven fabric are preferred, wherein the nonwoven fabric comprises a plurality of fibers and has a surface tension of at least 55 mN / m, preferably of at least minus 60 mN / m and most preferably at least 65 mN / m or higher when it is moistened with saline solution and has a penetration time of less than 5 s for a fifth jet of liquid.

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

The liquid penetration time is a measure of a certain level of hydrophilicity. This value should be measured using the test method described hereinafter.

In accordance with the present invention, absorbent core 28 comprises a layer 100 of substrate and absorbent polymeric material 110 and, in a preferred embodiment, a fibrous layer of adhesive 120. The substrate layer 100 is preferably provided of a non-woven material, preferred nonwovens being those illustrated above for top layer 56 or bottom layer 58.

The 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 polymeric material 110. This layer of absorbent polymeric material 110 is preferably a discontinuous layer and comprises a first surface and a second surface. As used herein, a discontinuous layer is a layer that comprises apertures. Typically these openings have a diameter or maximum spacing of less than 10mm, preferably less than 5mm, 3mm, 2mm, and greater than 0.5mm, 1mm or 1.5mm. At least part of the second surface of the absorbent polymeric material layer 110 is in contact with at least part of the first surface of the substrate material layer 100. The first surface of the absorbent polymeric material 112 defines a certain height of the absorbent polymer layer above the first surface of the layer 100 of substrate material. When the absorbent polymeric material layer 110 is provided as a discontinuous layer, portions of the first surface of the substrate layer 100 are not covered by absorbent polymeric material 110. The absorbent core 28 further comprises a thermoplastic composition 120. This thermoplastic composition 120 serves to at least partially immobilize the absorbent polymeric material 110.

However, it is even more preferred that 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 absorbent polymeric material layer 110 is provided as a discontinuous layer and a thermoplastic fibrous material layer 120 is applied over the absorbent polymeric material layer 110 such that the thermoplastic layer 120 is in direct contact with the first surface. of the absorbent polymeric material layer 110, but also in direct contact with the first

ES 2 339 713 T3 surface of the substrate layer 100, wherein the substrate layer is not covered by the absorbent polymeric material 110. This provides a practically three-dimensional structure to the fibrous layer of thermoplastic material 120 which itself is practically a 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 fibrous layer 120 of thermoplastic material undulates between the first surface of the absorbent polymeric material 110 and the first surface of the substrate layer 100.

Thus, thermoplastic material 120 provides cavities to contain absorbent polymeric material 110 and immobilize this material. In another aspect, thermoplastic material 120 bonds to substrate 100 and consequently fixes absorbent polymeric material 110 to substrate 100. Highly preferred thermoplastic materials will also penetrate absorbent polymeric material 110 and a substrate layer 100, providing thus additional immobilization and fixation.

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

In accordance with the present invention, absorbent polymeric material 110 may also be mixed with fibrous material, such as air felt 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 relative to the weight of absorbent polymeric material 110.

An alternative absorbent core is shown in Figure 4. The absorbent core shown in Figure 4 further comprises a cover layer 130. This cover layer can be provided of the same material as the substrate layer 100, or it can be provided of a different material. Preferred materials for the cover layer are nonwoven materials, typically the materials described above as useful for top layer 56 and bottom layer 58. In this embodiment parts of the cover layer 130 are joined with parts of the substrate layer 100 through the thermoplastic material 120. Thus, the substrate layer 100 together with the cover layer 130 provide cavities to immobilize the absorbent polymeric material 110 .

In Figures 3 and 4 the areas of direct contact between the thermoplastic material 120 and the substrate material 100 are referred to as the bond zones 140. The shape, number, and arrangement of the bond zones 140 will affect the immobilization of the bond. absorbent polymeric material 110. The bonding zones can be square, rectangular or circular in shape. Preferred junction areas are circular in shape. They preferably have a diameter of more than 0.5mm or 1mm or 1.5mm and less than 10mm or 5mm or 3mm or 2mm. If the junction areas 140 are not circular in shape, they are preferably sized to fit within a circle of any of the preferred diameters mentioned above.

The junction areas 140 may be arranged in a normal or irregular pattern. For example, the bonding zones 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 be at an angle relative to the edges. longitudinal of the nucleus. It has been discovered that an arrangement along lines parallel to the longitudinal edges of the absorbent core 28 allows channels to be created in the longitudinal direction that result in less immobilization in the wet state. Preferably, therefore, the bonding zones 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 areas 140 is a pattern that comprises polygons, eg, pentagons and hexagons, or a combination of pentagons and hexagons. Also preferred are irregular patterns of bonding zones 140, which have also been found to provide good wet immobilization.

In accordance with the present invention, two fundamentally different designs can be selected for the bonding zones 140. In one embodiment, the bonding zones are discontinuous. They are located within areas of absorbent material, such as islands in the sea. The areas of absorbent materials are then referred to as bonded areas. In an alternative embodiment, the junction zones may be joined. Then, the absorbent material can be deposited in a discontinuous pattern or, in other words, the absorbent material represents islands in a sea of ​​thermoplastic material (120). Thus, a discontinuous layer of absorbent polymeric material 110 may comprise connected zones of absorbent polymeric material 110 or it may comprise discontinuous zones of absorbent polymeric material 110.

In another aspect of the present invention, it has been discovered that absorbent cores that provide good wet immobilization can be formed by combining two layers as shown in Figure 3 and described in context. This embodiment, which is an embodiment of the present invention, is shown in Figure 6. The absorbent core material shown in Figure 6 comprises two layers 100 of substrate, two layers of absorbent polymeric material 110, and two layers 120 of fibrous thermoplastic material. The two layers of an absorbent polymeric material 110, which are discontinuous, are arranged 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

ES 2 339 713 T3 second storage layer (60), wherein the absorbent polymeric material of the one layer is oriented to the bonding zones 140 of the other layer.

The cores described in Figures 3, 4 and 6 can be used to provide the storage layer 60 of an absorbent core. However, they can also be used to provide the fully absorbent core 28. In this case, other core wrap materials such as top layer 56 and bottom layer 58 are not used. With respect to the embodiment of Figure 3, the substrate layer 100 can provide the function of the lower layer 58 and the thermoplastic fibrous material layer 120 can provide the function of the upper layer 56. In Figure 4 the layer 130 of Cover can provide the function of the upper layer 56 and the substrate layer 100 can provide the function of the lower layer 58. In Figure 6, the two substrate layers 100 used can provide the functions of the upper layer 56 and the lower layer 58, respectively.

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

Some initially thermoplastic materials may later 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 cross-linked network of covalent bonds. Materials that have lost their initial thermoplastic behavior are also considered herein as thermoplastic materials 120.

Without wishing to be bound by theory, these thermoplastic compositions have been found to be most useful for immobilizing absorbent polymeric material 110, combining good cohesion and good adhesion performance. 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 presents a challenge, especially when using a non-woven substrate. Good cohesion ensures that the adhesive does not break, particularly in response to external forces and especially in response to deformation. The adhesive is subjected to external forces when the absorbent product has absorbed liquid, which is then stored in the absorbent polymeric material 110 which, in response, swells. A preferred adhesive will allow this swelling without breaking and without transmitting too much compressive force, which would prevent the absorbent polymeric material 110 from swelling. It should be noted that, according to 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:

The thermoplastic composition may comprise, as a whole, a single thermoplastic polymer or a blend of thermoplastic polymers having a softening point, determined by the ASTM D36-95 "ring and ball" method, in the range of 50 ° C to 300 ° C, or alternatively the thermoplastic composition can 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.

The thermoplastic polymer typically has a molecular weight (MW) of more than 10,000 and a glass transition temperature (Tg) usually less than 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 insensitive to water. Examples of polymers are (styrenic) block copolymers including ABA three-block structures, AB two-block structures, and radial (AB) n block copolymer structures, where the A blocks are non-elastomeric polymer blocks, typically comprising polystyrene, and the B blocks are unsaturated conjugated diene or (partially) hydrogenated versions thereof. Block B is typically isoprene, butadiene, ethylene / butylene (hydrogenated butadiene), ethylene / propylene (hydrogenated isoprene), and mixtures thereof.

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

The resin typically has a MW of less than 5,000 and a Tg value usually greater than room temperature, and typical concentrations of the resin in a melt are in the range of 30-60%. The plasticizer has a low MW, typically less than 1,000, and a Tg value below room temperature, with a typical concentration being 0-15%.

Preferably the adhesive is present in the form of fibers in the core, ie the adhesive is fibrous. Preferably the fibers will have an average thickness of 1-50 microns and an average length of 5mm to 50cm.

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

ES 2 339 713 T3

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

A preferred adhesive will have a storage modulus G 'measured at 20 ° C of at least 30,000 Pa and less than 300,000 Pa, preferably less than 200,000 Pa, more preferably less than 100,000 Pa. The storage modulus G' at 20 ° C is a measure of the permanent "stickiness" or permanent adhesion of the thermoplastic material used. A 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 modulus G 'measured at 60 ° C should be less than 300,000 Pa and more than 18,000 Pa, preferably more than 24,000 Pa, most preferably more than 30,000. The storage modulus measured at 60 ° C is a measure of the shape stability of the thermoplastic material at elevated room temperature. This value is especially important if the absorbent product is used in a hot climate where the thermoplastic composition would lose its integrity if the storage modulus G 'at 60 ° C were not high enough.

In 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 high ambient temperatures. The lower the Tan Delta, the more an adhesive will behave as a solid rather than a liquid, that is, the lower its tendency to flow or migrate and the lower the tendency for an adhesive superstructure such as the one described herein to deteriorate. or even crush over time. This value is therefore especially important if the absorbent article is used in a hot climate.

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

In another aspect, a preferred adhesive will have a transition temperature T_x high enough. A transition temperature T_x Sufficiently high, it has been found to be 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 elevated temperatures. Therefore, T_x it should preferably be greater than 80 ° C, more preferably greater than 85 ° C and most preferably greater than 90 ° C.

In another important aspect, the preferred adhesives according to the present invention will have a sufficient cohesive strength parameter γ. The cohesive strength parameter γ is measured using the rheological creep test, as described below. A sufficiently low cohesive strength parameter γ is representative of an elastic adhesive which, for example, can be stretched without tearing. If a stress of τ = 1000 Pa is applied, the cohesive strength parameter γ is preferably less than 100%, more preferably less than 90% and most preferably less than 75%. For a stress of τ = 125,000 Pa, the cohesive strength parameter γ is preferably less than 1200%, more preferably less than 1000% and most preferably less than 800%.

A highly preferred adhesive useful as a thermoplastic material (120) as described herein will meet most or all of the above parameters. Particular care should be taken to ensure that the adhesive provides both good cohesion and good adhesion.

The process for making preferred absorbent cores 28 in accordance with the present invention comprises the following steps:

The absorbent core 28 is applied on a descending drum, which has a non-uniform surface. In a first stage of the process the substrate layer 100 is applied on the non-uniform surface. Due to gravity, or preferably using a vacuum medium, the substrate material layer will follow the contour of the non-uniform surface and thus the substrate material layer will assume a mountain and valley shape. Absorbent polymeric material is disposed on this substrate layer (100) by means known in the art. The absorbent polymeric material will accumulate in the valleys of the substrate layer 100. In another stage of the process a hot melt adhesive is placed on the absorbent polymeric material.

Although 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 with a nozzle system. Preferably, a nozzle system is used that can provide a relatively thin but wide curtain of adhesive. This adhesive curtain is then placed over the substrate layer 100 and the absorbent polymeric material. Since 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.

In another optional step of the process a cover layer 130 is placed over 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 at the bonding zones 140. At these bonding zones 140 the adhesive is in direct contact with the substrate layer 100. Cover layer 130 will typically not be in adhesive contact with substrate layer 100 where the valleys of substrate layer 100 are filled with absorbent polymeric material.

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Alternatively the cover layer 130 can be applied on a drum with a non-uniform surface and the substrate layer 100 can be added in a consecutive stage of the process. The core shown in Fig. 4 could be produced by this process.

In an alternative embodiment, the cover layer 130 and the substrate layer 100 are provided from a unitary material sheet. The placement of the cover layer 130 on the substrate layer 100 will then involve the folding of the unitary piece of material.

Thus, the irregular operation of the application system, which is preferably an applicator drum, typically determines the distribution of absorbent polymeric material in the storage layer 60 and similarly determines the design of the bonding zones 140. In a similar way Alternatively, the distribution of the absorbent polymeric material can be varied by vacuum.

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

Optionally, the absorbent core can also comprise an absorbent fibrous material, for example cellulose fibers. This fibrous material can be previously mixed with the absorbent polymeric material to be applied in one stage of the process or alternatively to be applied in different stages of the process.

It has been found beneficial to use an absorbent polymeric particulate material for the absorbent cores made in the present invention. Without wishing 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 conductivity in solution flow saline of the absorbent polymeric material is greater than 10, 20, 30 or 40 SFC units, where 1 SFC unit is 1 x 10 '(cm³ xs) / g. Saline flow conductivity is a parameter well known in the art and is measured according to the test described in EP-752 892 B.

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

Preferred articles according to the present invention achieve a relatively narrow crotch width, which increases wearing comfort. A preferred article according to the present invention achieves a crotch width of less than 100mm, 90mm, 80mm, 70mm, 60mm or even less than 50mm. 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 back edge of the core that is less than 100mm, 90mm, 80mm, 70mm, 60mm or even less than 50mm. 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 absorbent capacity of the core. 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.

Rheological creep test

Equipment • AR 2000 Rheometer from TA Instruments as described below • Balance

Rheometer

In a test to analyze creep, the AR 2000 rheometer from TA Instruments is used. Other rheometers are available on the market with which practically the same results are obtained. Figure 8 provides a schematic representation of the rheometer (400). The rheometer is capable of applying shear stress to the adhesive and measuring the response to the resulting strain (shear strain) at constant temperature. The adhesive is placed between a Peltier element that acts as a lower fixed plate (410) and an upper plate (420) with a radius R of 10 mm, which is attached to the drive shaft of a motor to generate shear stress. The distance between the two plates has a height H of 1500 microns. The Peltier element allows the temperature of the material to be controlled (± 0.5 ° C).

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Sample preparation • Homogenize the adhesive at 150 ° C-175 ° C (depending on the type of adhesive) for 1 hour in a laboratory oven • Shake occasionally to ensure adequate mixing of the wrapper and the adhesive but avoiding the formation of air bubbles • After homogenization in the oven, pour the sample onto silicone paper to cool it • Once the material has cooled to RT, weigh approximately 0.6 g of creep test adhesive and place the material on the Peltier plate

Carrying out the test • Melt the adhesive at 120 ° C (or at a higher temperature if necessary) on the Peltier plate • As soon as the adhesive is completely melted, lower the top plate to a distance of 1500 microns to bring it into proper contact with the molten adhesive • Remove excess material • Set the temperature to the measurement temperature of 35 ° C • Set the conditioning time to 20 min to ensure a thermal balance between the Peltier element, the adhesive and the top plate • Set the constant measuring voltage τ (eg 10,000 Pa or 125,000 Pa) and apply immediately to the adhesive at the start of the delay stage.

• Set the delay time to 5 min.

• Set the tension to 0 to immediately remove the tension at the beginning of the recovery stage. • Set the recovery time to 5 min.

• Once the test is complete, melt the adhesive, lift the top plate, and remove the adhesive from the Peltier element and the top plate.

• Set the temperature back to the measurement temperature or to the standby temperature (TA)

Report of results • Record the strain in% (γ, herein referred to as a cohesive strength parameter) as a function of temperature and stress after 5 min of applying stress (at the end of the delay stage), p . ex. at 35 ° C and 10,000 Pa or at 35 ° C and 125,000 PA, as described herein.

Dynamic Mechanical Analysis (DMA) - Sweep in Temperature

Equipment • AR 2000 Rheometer from TA Instruments as described below • Balance

Rheometer

The equipment set up to perform temperature scanning comprises the TA Instruments AR 2000 rheometer as described herein. Other rheometers are available on the market with which practically the same results are obtained. Figure 8 provides a schematic representation of the rheometer (400). The rheometer is capable of applying shear stress to the adhesive and measuring the response to the resulting strain (shear strain) at constant temperature.

The rheometer is capable of applying a small oscillatory stress to achieve a constant oscillatory strain within the linear viscoelastic region of the adhesive (eg 0.05%). The instrument allows to measure the resulting storage modulus, loss modulus and phase deviation between stress and strain (factor of

ES 2 339 713 T3 loss) as a function of temperature. The oscillation frequency is 1 Hz. The adhesive is placed between a Peltier element that acts as a lower fixed plate (410) and an upper plate (420) with a radius R of 10 mm, which is attached to the drive shaft of a motor. to generate the shear stress. The distance between the two plates has a height H of 1500 microns. The Peltier element allows the temperature of the material to be controlled (± 0.5 ° C).

Sample preparation • Homogenize the adhesive at 150 ° C-175 ° C (depending on the type of adhesive ) for 1 hour in a laboratory oven.

• Shake occasionally to ensure proper mixing of the wrap and adhesive while avoiding the formation of air bubbles.

• After homogenization in the oven, pour the sample onto silicone paper to cool it.

• After cooling the material to RT, weigh approximately 0.6 g of adhesive, sweep in temperature and place the material on the Peltier plate.

Test run • Melt the adhesive at 120 ° C (or higher if necessary) on the Peltier plate • As soon as the adhesive is completely melted, lower the upper plate to a distance of 1500 microns to bring it into proper contact with the melted adhesive • Remove excess material and set the temperature to the initial measurement temperature (eg. 150 ° C, depending on the temperature range of interest see below) • Adjust the temperature to the initial temperature depending on the temperature range where the rheological properties of the adhesive are to be determined (eg 150 ° C, in any case start with the highest temperature).

• Set the conditioning time to 20 min to ensure a thermal balance between the Peltier element, the adhesive and the top plate • Set the initial temperature (see above) • Set the measurement constant deformation (eg 0.05 %) • Set the constant frequency (eg 1 Hz) • Set the cooling speed (eg 2 ° C / min) • Set the final temperature (eg. -5 ° C) depending on the temperature range where the rheological properties of the adhesive are to be determined and depending on the cooling capacity of the Peltier element.

• Adjust the temperature to RT. • Once the test is complete, melt the adhesive, lift the top plate and remove the adhesive from the Peltier element and the top plate.

• Return the temperature to RT

Results report • Record the storage modulus G 'in Pa and the loss factor Tan Delta (dimensionless) at 20 ° C and 60 ° C • Record the glass transition temperature Tg in ° C (inflection point of G') • Record the transition temperature Tx in ° C at which G 'equals G ”at the end of the rubber plateau towards a higher temperature (beginning of the terminal zone)

Determination of surface tension

The surface tension (unit: mN / m) is determined by the following test.

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Apparatus

Equipment: K10 blood pressure monitor provided by Krüss GmbH, Germany, or equivalent. The lifting speed of the container should be 4 mm / min. The height of the liquid surface should be detected automatically when using a plate or ring. The equipment must be able to automatically adjust the position of the sample to the correct height. The precision of the assay should be +/- 0.1 mN / m.

Process

1. Pour 40 ml of saline (0.9% by weight NaCl in deionized water) into a clean beaker.

2. Analyze the surface tension with a platinum ring or a platinum plate. The surface tension should be 71-72 mN / m at 20 ° C.

3. Clean the beaker with deionized water and isopropanol and burn with a gas burner for a few seconds. Wait until it equilibrates at room temperature.

Four. Place 10 pieces of 60x60mm non-woven material in a clean beaker. The non-woven material should have a weight per unit area of ​​at least 10 g / m².

5. Add 40 ml of saline solution (0.9% by weight of NaCl in deionized water).

6. Shake with a clean plastic rod without surfactant for 10 seconds.

7. Let the solution stand with non-woven material for 5 minutes.

8. Shake again for 10 seconds.

9. Remove the non-woven material from the solvent using a clean plastic stick without surfactant.

10. Let the solution stand for 10 minutes.

eleven. Analyze the surface tension with a platinum plate or a platinum ring.

Determination of penetration

The test is carried out according to the Edana method 150.3-96 (February 1996) to determine the liquid penetration time. A major modification from the Edana method is that the test described below not only measures the first jet but also several subsequent jets.

Apparatus> Lister penetration equipment:

- Funnel equipped with magnetic valve: Discharge rate of 25 ml in 3.5 (± 0.25) seconds

- Penetration plate: Constructed of 25 mm thick acrylic glass. The total weight of the plate must be 500 g. The electrodes must be made of non-corrosive material. The electrodes are fixed in grooves that are (4.0 mm x 7.0 mm) in cross section, cut at the base of the plate, and fixed with fast setting epoxy resin.

- Base plate: A square of acrylic glass measuring approximately 125 mm x 125 mm.

> Ring holder to hold the funnel> Electronic timer that measures up to 0.01 seconds> Burette of 50 ml capacity> Core filter paper Ahlstrom grade 989 or equivalent (average penetration time 1.7 s + - 0.3 s , dimensions: 10 x 10 cm)

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Process

1. Carefully cut the required number of 12.5 cm x 12.5 cm samples touching the sample only by the edge of the sample.

2. Separate 10 layers of Core filter paper.

3. Place a sample on the set of 10 layers of filter paper on the base plate. The sample should be placed on the filter paper so that the side of the nonwoven material intended to face the wearer's skin (when applied to an absorbent article) is the top side.

Four. Place the penetration plate on top with the center of the plate over the center of the test piece.

5. Center the burette and funnel on the plate.

6. Check that the electrodes are attached to the timer. Plug in the timer and set the clock to zero.

7. Fill the burette with saline solution (0.9% by weight of NaCl in deionized water).

8. Keep the funnel discharge valve closed and send 5.0 ml of liquid (= a jet) from the burette to the funnel.

8. Open the magnetic valve of the funnel to discharge 5.0 ml of liquid. The initial flow of liquid will close the electrical circuit and activate the timer. This will stop when the liquid has penetrated the pad and dropped below the level of the electrodes on the penetration plate.

9. Record the time indicated on the electronic timer.

10. Wait 60 seconds and return to point 6 to repeat with the second jet, third jet and subsequent jets, where each jet comprises 5 ml of liquid.

eleven. Record: The times in seconds of the first, second and subsequent jets.