Unitary absorbent structures comprising an absorbent core and/or an acquisition and dispersion layer for absorbent articles

Abstract

The present invention relates to a unitary absorbent structure and method thereof wherein said unitary absorbent structure comprises an absorbent core (5) and/or an acquisition (2) and dispersion (3) layer, said absorbent core (5) and/or an acquisition (2) and dispersion (3) layer comprising at least one non-woven fibrous substrate layer (23) having a void volume suitable to be penetrated by super absorbent particles, characterized in that said super absorbent particles are dispersed in the substrate layer (23) according to a size distribution gradient along the depth direction or z-direction of said absorbent core (5) and/or acquisition (2) and dispersion (3) layers.

Claims

1. A unitary absorbent structure comprising an absorbent core having a permanent liquid holding capacity and an acquisition and dispersion layer having a temporary liquid holding capacity, said absorbent core comprising at least one non-woven fibrous substrate layer, the non-woven substrate layer having a void volume between 600 and 6000 cm.sup.3/m.sup.2, penetrated by super absorbent particles (SAP), said non-woven fibrous substrate comprising superabsorbent particles in an amount of up to 1000 g/m.sup.2 and said super absorbent particles having a size distribution and being dispersed within the non-woven fibrous substrate layer according to a particle size distribution gradient of the super absorbent particles along a depth direction or z-direction of said absorbent core or acquisition and dispersion layers, wherein at least 90% of the super absorbent particles have a particle size diameter ranging from about 45 m to about 850 m, and a non-porous core-covering layer having a void volume between 10 and 600 cm.sup.3, to prevent the release of the SAP outside of the absorbent structure; said absorbent structure comprises less than 4 wt. % fluff and is further coated by a covering layer, and wherein smaller size super absorbent particles are able to penetrate, along the z direction, into the bottom part of the substrate while the larger size super absorbent particles remain on the outer part or on the surface of the substrate.

2. Absorbent structure according to claim 1 wherein said absorbent structure is free of fluff.

3. Absorbent structure according to claim 1 wherein said substrate layer is a multilayer substrate.

4. Absorbent structure according to claim 3 wherein said substrate layer is a triple layer comprising a top acquisition layer and dispersion layer and an intermediate layer, said intermediate layer having a void volume value ranging from about 10 to about 600 cm.sup.3 per m.sup.2 of substrate and a bottom layer having a void volume ranging from about 10 to about 600 cm.sup.3 per m.sup.2 of substrate.

5. Absorbent structure according to claim 1 wherein the non-woven fiber is selected from the group, consisting of polyester or polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), coPP, PET/PE, PET/PP, PET/cop, PP/PE, PLA, PLA/PP, PVA, viscose, cotton, wool, PET/coPET, acetate, PTE, PVC, Bamboo, PBT, PA, Acryl, and Modacryl regenerated fibers.

6. Absorbent structure according to claim 1 wherein the super absorbent particles are polyacrylate polymers.

7. Absorbent structure according to claim 1 wherein the super absorbent particles are deposited depending on a profile along a longitudinal direction or x-direction of said absorbent structure.

8. Absorbent structure according to claim 1 wherein the super absorbent particles are deposited depending on a profile along a lateral direction or y-direction of said absorbent structure.

9. Absorbent structure according to claim 1 wherein the super absorbent particles are dispersed in discrete zones on the substrate separated from one another, thereby facilitating the flow and wicking of fluid along a longitudinal or x-direction and/or along a lateral or y-direction of said absorbent structure.

10. Method to prepare an absorbent structure as defined in claim 1 comprising the step of: unwinding a fibrous substrate; covering, at least partially, the fibrous substrate with super absorbent particles; applying an alternative electrical field to ensure a homogeneous distribution of the super absorbent particles, unwinding a core covering layer material, applying an adhesive on an inner face of the core covering layer material and/or the fibrous substrate surface, covering the fibrous substrate with said core covering layer material, and applying pressure to ensure adhesion.

11. Method to prepare multiple absorbent structures as defined in claim 1 comprising the step of: unwinding the fibrous substrate; partially covering the fibrous substrate with super absorbent particles over a lateral dimension of the substrate; applying an alternative electrical field to ensure a homogeneous distribution of the super absorbent particles; applying a hotmelt adhesive on the core covering layer and/or a surface of the fibrous substrate; unwinding a core covering layer material; covering the fibrous substrate surface with said core covering layer material; applying pressure to ensure adhesion, and cutting a layer where said fibrous substrate is substantially free of super absorbent particles to obtain individual cores.

12. Method according to claim 10 further including powder scattering or drum formation through vacuum technology in the step of covering the fibrous substrate surface with super absorbent particles.

13. Device suitable to perform the method of claim 10 wherein the device is in line or off line of an ADL and/or core production line or of a diaper or feminine care production line.

14. Method according to claim 11 further including powder scattering or drum formation through vacuum technology in the step of covering the fibrous substrate surface with super absorbent particles.

15. Device suitable to perform the method of claim 11 wherein the device is in line or off line of an ADL and/or core production line or of a diaper or feminine care production line.

16. A unitary absorbent structure comprising an absorbent core having a permanent liquid holding capacity and an acquisition and dispersion layer having a temporary liquid holding capacity, said acquisition and dispersion layer comprising at least one non-woven fibrous substrate layer, the non-woven substrate layer having a void volume between 600 and 6000 cm.sup.3/m.sup.2, penetrated by super absorbent particles (SAP), said non-woven fibrous substrate comprising superabsorbent particles in an amount of up to 1000 g/m.sup.2 and said super absorbent particles having a size distribution and being dispersed within the non-woven fibrous substrate layer according to a particle size distribution gradient of the super absorbent particles along a depth direction or z-direction of said absorbent core or acquisition and dispersion layers, wherein at least 90% of the super absorbent particles have a particle size diameter ranging from about 45 m to about 850 m, and a non-porous core-covering layer having a void volume between 10 and 600 cm.sup.3, to prevent the release of the SAP outside of the absorbent structure; said absorbent structure comprises less than 4 wt. % fluff and is further coated by a covering layer, and wherein smaller size super absorbent particles are able to penetrate, along the z direction, into the bottom part of the substrate while the larger size super absorbent particles remain on the outer part or on the surface of the substrate.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: is a cross-sectional view of a typical absorbent article comprising from top to bottom a liquid pervious topsheet (1) and a liquid impervious backsheet (6), an acquisition and distribution system (2, 3 and 4), an absorbent core (5) generally composed of a mix of fluff and SAP; typically, the amount of SAP range from between 0 to 60 wt. %.

(2) FIG. 2: is a cross-sectional view of a 3 layered conventional ADL (19) comprising from top to bottom an acquisition layer (2) and 2 distribution layers (3) and (4).

(3) FIG. 3: is a cross-sectional view of a substrate comprising from top to bottom a triple layer acquisition (14), rewet (15) and distribution (16) layers.

(4) FIG. 4: is a cross-sectional view of a substrate comprising triple layer acquisition (14), distribution (16), rewet (15) layers.

(5) FIG. 5: is a cross-sectional view of a substrate comprising from top to bottom a triple layer acquisition (14) and rewet (15) layers.

(6) FIG. 6: is a cross-sectional view of a substrate comprising from top to bottom a triple layer acquisition (14), distribution (16) and rewet (15) layers with the third layer partly hydrophobic.

(7) FIG. 7: is a cross-sectional view of a substrate comprising from top to bottom a triple layer acquisition (14), distribution (16) and absorption (17) layers.

(8) FIG. 8: is a cross-sectional view of a substrate comprising from top to bottom a triple layer blend of polyester and polyolefin defining a void volume gradient (18a, 18b, 18c).

(9) FIG. 9: is a cross-sectional view of a substrate comprising from top to bottom an acquisition and dispersion top layer (19), an rewet layer of smaller void volume space structure preventing the loss of SAP particles (21) and a bottom layer having very large void volume space comprising SAP particles (21) and a covering layer coating the bottom section of the absorbent core.

(10) FIG. 10: is a cross-sectional view of a triple layer substrate wherein the fibers defining a void volume distribution gradient (18a, 18b, 18c) partly filled with SAP particles (21), and the bottom of the structure is covered by an additional layer.

(11) FIG. 11: is a cross-sectional view of SAP particles (21) a fully penetrated in a substrate having a void volume distribution gradient (18a, 18b, 18c). The core is covered by non-woven layers on top and bottom part (22).

(12) FIG. 12: is a cross sectional image of SAP particles (21) partially penetrated in a substrate having a void volume distribution gradient (18a, 18b, 18c).

(13) FIG. 13: Is a scheme of a method of a structure production according to the invention.

(14) FIG. 14: is a scheme of a dosing system for the SAP particles (21), illustrating the deposit of the SAP particles (21) along the y-direction, or lateral dimension, of the non-woven substrate.

(15) FIG. 15: is a cross sectional view of a discontinuous application of SAP particles (21) on a substrate for the production of multiple absorbent cores. The core is covered by a hot melt adhesive and a core covering layer (11). The cutting line for the formation of individual core is also indicated.

(16) FIG. 16: is a cross sectional image of 3 individual profiled absorbent cores.

(17) FIG. 17: is a detail view of the supply roll used for the powder scattering of SAP particles (21) to create a profiled core.

(18) FIG. 18: is a cross sectional image of a profiled absorbent core along the x-direction or longitudinal dimension.

(19) FIG. 19: is a top view of a patterned absorbent core layer in the x-y plan.

(20) FIG. 20: illustrates the deposit of SAP particles (21) on a non-woven substrate prior to the application of the Fibroline process and the dispersion profile of said particles along the z-direction after the application of the Fibroline process

(21) FIG. 21: illustrates an ADL comprising SAP particles (21) dispersed according to the invention, said ADL is positioned on top of a conventional absorbent core.

(22) FIG. 22: illustrates an absorbent structure according to the invention coated by a covering by layers (22).

(23) FIG. 23: illustrates a conventional ADL (19) positioned on top of an absorbent core according to the invention.

(24) FIG. 24: is a top view of a body shaped absorbent article.

(25) FIG. 25: is a view of the SAP particles (21) deposited on a non-woven substrate with an x and y directional profile after the dispersion by the Fibroline method.

(26) FIG. 26: illustrates the sealing (24) process of individual core by a core wrap material (25).

DETAILED DESCRIPTION OF THE INVENTION

(27) A liquid according to the invention comprises, but not limited to, any body fluid such as urine or blood.

(28) The inventors have developed a fluffless absorbent structure comprising an absorbent core and/or ADL. Said absorbent structure comprising SAP particles (21) having a size distribution and a fibrous non-woven hydrophilic or hydrophobic substrate (23), said SAP particles (21) being dispersed within the fibrous substrate (23) based on their size distribution. The absorbent structure obtained is further coated by a covering layer (22) such as a spunbond, PE film, PET film, polyolefin, multilayer films, coextruded films, carded non-woven or any suitable material and maintained to the core with adhesive.

(29) In addition to the high body fluid holding capacity and the slimness of the absorbent article, there are some other advantages to use the absorbent structure of the invention such as a better conversion, improve performance and reliability due to the dispersion of SAP particles (21) on specific part of the absorbent structure and the absence of fluff. It is also economical advantageous to use such core and/or ADL as fluff is no longer required and extra method steps such as hammer milling to prepare the fluff is unnecessary, additionally, warehousing and packaging cost is reduced as well as the transport cost.

(30) Advantageously, an absorbent structure according to the invention is a multilayers structure comprising a top layer ensuring a good acquisition and distribution of the liquid; an intermediate layer suitable to prevent the liquid to return to the surface, said intermediate layer is non-porous, wherein non-porous is defined by a void volume value ranging from about 10 to about 600 cm.sup.3 of void volume per m.sup.2 of substrate (23). The absorbent structure also comprises a porous fibrous bottom layer, wherein porous according to the invention is defined by a void volume ranging from about 0.1 to 20000 cm.sup.3 of void space/m.sup.2 of substrate (23), preferably from about 600 to about 6000 cm.sup.3 of void space/m.sup.2 of substrate (23). Said fibrous bottom layer comprising coated or uncoated SAP particles (21) thus forming a SAP stratum beneath the intermediate layer. SAP particles (21) composing the SAP stratum are dispersed within the bottom layer, based on the SAP particle (21) size distribution gradient, wherein the smaller SAP particles (21) are incorporated deeper into the bottom layer and the larger particles remain on the external part of the bottom layer. A suitable non-porous core covering layer (22) having a void volume value ranging from about 10 to about 600 cm.sup.3 of void volume per m.sup.2 of substrate (23) is used to prevent the release of the SAP particles (21), said core covering layer material (22) is maintained to the absorbent structure by adhesive means, ultrasonic welding and/or any suitable method (FIG. 26).

(31) Absorbent structures of the invention comprise SAP particles (21) wherein at least 90%, preferably 95%, or 98% of the SAP particles (21) have a particle size diameter ranging from about 45 to about 850 m, preferably from about 100 to about 800 m. Smaller size SAP particles (21) are able to penetrate deeply, i.e. along the z direction, into the bottom part of the substrate (23) while the larger size SAP particles (21) remain on the outer part of the substrate (23) or remain on the surface of said substrate (23), thus forming an absorbent stratum based on the SAP particle (21) size gradient.

(32) Absorbent structure of the invention comprising a SAP particles (21) stratum fully integrated within the absorbent core and/or ADL, allows the preparation of thinner absorbent articles than conventional absorbent cores known by the inventors as said cores generally require a fluff absorption distribution layer or other cellulose based fiber system, for instance curly fibers or a standard ADL system (19) in combination with a fluff holding core.

(33) It has been found that absorbent cores according to the invention have an excellent liquid uptake property and low rewettability. It is supposed that the SAP particles (21) dispersed in the substrate (23) with a size distribution gradient are able to prevent the gel formation when the SAP particles (21) are in a swollen state.

(34) Super Absorbent Particles

(35) According to the invention, SAP particles (21) are either uncoated, partially or totally coated.

(36) Commercial available uncoated SAP particles (21) suitable for the invention are Ecotec EK-X EN 67 polymer grade, which is generally used in absorbent cores comprising SAP and fluff in a ratio up to 80 wt. % SAP loadings; Evonik: Favor SXM 10000.

(37) SAP particles (21) can either be incorporated in the absorbent layer or in the ADL or in both the absorbent layers and the ADL.

(38) Absorbent Core

(39) An absorbent core according to the invention can be obtained by fully penetrating a non-woven substrate (23) with SAP particles (21), thus an additional conventional ADL (19) should be used, as illustrated in FIG. 23.

(40) A substrate (23) fully penetrated with SAP particles (21) according to the invention comprises up to 1000 g/m.sup.2 of SAP, preferably about 300 to about 500 g/m.sup.2 of SAP particles (21) depending on the body fluid holding capacity.

(41) To avoid gel blocking, the swollen SAP particles (21) have to be sufficiently distant to be permeable enough to allow liquids, such as body fluids, to go through the absorbent layer. This was obtained by the inventors by distributing the SAP particles (21) within the substrate (23) based on the SAP particles size gradient. Without being bond to any theory, it is believed that only smaller SAP particles (21) penetrate deeply in the substrate (23), along the z-direction, while larger SAP particles (21) remain on the outer part of the substrate (23). As smaller SAP particles (21) are sufficiently distant from one another, it does prevent gel blocking issue, while larger SAP particles (21) are able to progressively absorb the excess of body fluids.

(42) Preferably, the absorbent structure of the invention can be combined with a conventional ADL (19).

(43) FIG. 23 illustrates an absorbent core according to the invention comprising a non-woven substrate (23) and a dispersion of SAP particles (21) within the substrate (23), depending on the SAP particles (21) size gradient. The absorbent core is further combined with a conventional ADL (19) on top of the absorbent core.

(44) FIG. 12 also illustrates an absorbent article according to the invention using a 3 layers ADL structure with SAP particles (21) in a swollen state after liquid uptake.

(45) Acquisition, Dispersion, Layers (ADL)

(46) In a second embodiment a specific amount and size of SAP particles (21) is dispersed, based on their size dispersion gradient, in a substrate (23) comprising an ADL structure, such as the substrate (23) is partly penetrated with the SAP particles (21), FIGS. 9 and 10 illustrate this second embodiment.

(47) According to the invention, an ADL comprising a sufficient amount of SAP particles (21) to absorb liquids or body fluids can be directly used as a unitary absorbent structure (FIGS. 9 and 22), said structure comprising an ADL section and an absorbent section comprising the dispersed SAP particles (21). Generally up to 1000 g/m.sup.2, preferably from about 300 to about 500 g/m.sup.2 of SAP particles (21) is sufficient to combine in one element an ADL and an absorbent core.

(48) The ADL can also comprise low amount of SAP particles (21) which serve as a temporary storage or surge layer (20) (FIG. 21). Generally between 0.1 to 300 g/m.sup.2, preferably from about 100 to about 200 g/m.sup.2 is considered as a low amount of SAP particles (21). In the latter case, an additional absorbent core has to be combined with an ADL. Suitable ADL should absorb water or liquids and slowly releasing it to the absorbent core.

(49) Typically, ADL are multi-layer structures comprising an acquisition layer (2) and dispersion layers (3, 4). In a preferred mode, the ADL comprising a dispersion of SAP particles (21) is a 3 layers structure composed of one acquisition layer (2) and 2 diffusion (3) layers.

(50) In a particular embodiment, a triple layers ADL according to the invention can comprise an acquisition layer (14), a rewet layer (15) and a distribution layer (16) are illustrated in FIG. 3.

(51) The top layer is a very porous acquisition layer (14) allowing fluids to easily penetrate the structure.

(52) The intermediate layer is a non-porous diffusion layer preventing the fluid from going back to the top surface. By non-porous according to the invention is defined by a void volume ranging from about 10-600 cm.sup.3 of void space/m.sup.2 of substrate (23). The diffusion layer is also very hydrophilic, so that the liquid is spread over the core.

(53) The bottom layer comprises profiled, or multilobal, fibers to improve the liquid distribution over the absorbent core. Non limiting examples of commercially available multilobal fibers are 4DG 6dn, 4T 3dn, trilobal 6dn, pentalobal 6dn, quadfill 7dt, preferably, the fiber is a trilobal 6dn or pentalobal 6dn fiber and other shapes.

(54) In another embodiment according to the invention, a triple layers ADL comprising an acquisition (14), distribution (16) and rewet (15) layers, as illustrated in FIG. 4.

(55) The top layer is a very porous acquisition layer (14) thus allowing fluid to penetrate into the absorbent core.

(56) The intermediate layer is a dispersion layer comprising profiled fibers, thus improving the distribution of the liquid to the bottom layer.

(57) The bottom layer is a non-porous layer comprising very fine fibers, preventing liquid from going back to the surface. It is also very hydrophilic, so that the liquid is spread over the core.

(58) In another embodiment according to the invention, a triple layers ADL comprising 2 acquisitions layers (14) and a rewet layer (15) is illustrated in FIG. 5.

(59) The top layer is a very porous acquisition layer (14) allowing fluid to penetrate into the absorbent structure.

(60) The intermediate layer is also an acquisition layer (14) that is semi porous, wherein semi porous according the invention is defined by a void volume ranging from about 300 to about 500 cm.sup.3 of void volume/m.sup.2 of substrate (23), however said intermediate layer is characterized by a void volume distribution gradient (18a, 18b, 18c) thus creating a funnel for the liquid transport towards the core.

(61) The bottom layer is non-porous, and composed of very fine fibers preventing liquid from going back to the surface. Preferably, the bottom layer is calendered, to even more reduce the void volume on the surface, preventing the liquid of the core returning to the surface. Said bottom layer is preferably hydrophilic, allowing the liquid to spread over the core.

(62) In another embodiment according to the invention, the absorbent structure comprises a triple layers ADL also comprising an acquisition (14), distribution (16) and rewet (15) layers, as illustrated in FIG. 6.

(63) The top layer is a very porous acquisition layer (14) suitable to allow body fluids to penetrate into the absorbent structure.

(64) The intermediate layer is a layer suitable for the distribution and spreading of the liquid to the bottom layer and to the core.

(65) The bottom layer is a non-porous layer composed of a blend of fine hydrophilic and hydrophobic fibers, blocking the liquid from going back to the surface.

(66) In another embodiment according to the invention, the absorbent structure comprises a triple layer, acquisition (14), distribution (16) and absorption (17) layers as illustrated in FIG. 7.

(67) The top layer is a very porous acquisition layer (14) allowing body fluids to penetrate into the absorbent core.

(68) The intermediate layer is a distribution layer (16) comprising fibers to ensure the whole surface of the distribution layer (16) is used.

(69) The bottom layer comprises a blend of fibers including viscose absorbing fibers, to temporarily store the liquid in said bottom layer, thus creating a buffer before the liquid is transferred to the absorbent core.

(70) In another embodiment illustrated in FIG. 8 the triple layer ADL comprises a blend of polyester and polyolefins fibres defining a triple layer system defining a void volume gradient (18a, 18b, 18c) of 3000, 1000 and 300 cm.sup.3 of void volume/m.sup.2 of substrate surface (23), said void volume gradient (18a, 18b, 18c), creating a funnel for the liquid. This results in a higher liquid uptake speed.

(71) The fibers used give a good resiliency and resistancy to pressure, creating a distance between core and top of the diaper, resulting in a dry surface.

(72) ADL suitable for the invention are fluffless and ensure a fast liquid uptake, and good rewet properties, so that liquid is prevented from going back to the surface and maintain the top surface dry. It also makes sure the liquid is well spread and distributed, so that the total core is used to its maximum.

(73) Absorbent Structures

(74) An absorbent structure according to the invention can combine an absorbent section and an acquisition (14) and dispersion (16) section. In these specific embodiments, illustrated in FIG. 22, the absorbent structure is composed of a mono or multi layered non-woven fibrous substrate (23) such as polyester or poly polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), coPP, PET/PE, PET/PP, PET/cop, PP/PE, PLA, PLA/PP, PVA, viscose, cotton, wool, PET/coPET, acetate, PTE, PVC, Bamboo, PBT, PA, Acryl, Modacryl, and/or regenerated fibers forming an interpenetrating network and SAP particles (21) and from about 0.1 to 50 g/m.sup.2, preferably from 0.7 to 25 g/m.sup.2 and more preferably from about 2 to 7 g/m.sup.2 of adhesive. Preferably the absorbent structure does not comprise fluff at all. It is possible to incorporate a high quantity of SAP particles (21) within the absorbent layer because of the fibrous nature which allows the absorption of liquids without being subject to gel blocking due to swelling of the SAP particles (21). In a preferred embodiment of the invention, the absorbent structure comprises from about 25-300 g/m.sup.2, but preferably from about 60 to 150 g/m.sup.2 of ADL and/or substrate (23); from about 0.1 to 1000 g/m.sup.2 of SAP particles (21), a preferred quantity of SAP particles (21) for baby diapers or adults incontinence ranges from 100 to 500 g/m.sup.2, from 10 to 200 g/m.sup.2 in feminine care products and from about 200-400 g/m.sup.2 for wound dressing. Generally, the absorbent structure comprises from about 10 to 60 g/m.sup.2 of a core covering layer (22).

(75) Examples of commercially available fibers suitable to make the non-woven substrate (23) are Acryl Amicor 3.0n; Asota L10D; Eastlon SN-3450CMP1 4.0dn; Fibervisions ES-C Cure 2.2dt; Fibervisions ES-DELTA REPEAT II 5.7 dt 40 mm; Grisuten 22 3.3 dt 60 mm; Huvis LMF U16 6dn 51 mm; Huvis LMF V16 4dn 51 mm; Huvis OEPO1 N215 2.0dn; Ingeo PLA SLN2660E2 6.0dn; Invista 295 6.0dn; Meraklon PP Blend PH/HW 4.4dt; PES Greenfiber 6.7dt; Tesil 84M 6.7dt; Trevira 200 6.0dt; Viscocel 3.3 dt 40 mm; Wellman H1295 7dt; Wellman T0745 17dt 60 mm; Wellman H7112 12dt; Wellman H8015 7dt 60 mm.

(76) An absorbent structure according to the invention has a lateral dimension ranging from 0.1 to 800 mm but not limited to these dimensions. Depending on the different application, said absorbent structure typically has a lateral dimension of 50 to 180 mm for baby diaper products; from 30 to 250 mm for adult incontinence products; from 30 to 90 mm for feminine care products and from 100 by 100 mm.sup.2 or 200 by 300 mm.sup.2 for wound dressing.

(77) Preferably, the non-woven fibrous substrate (23) is a triple layer substrate (23) comprising a top layer, which has an acquisition (14) and dispersion (16) functions for a fast liquid acquisition and a good distribution of the liquid over the total surface of the intermediate layer. The intermediate layer is preferably very hydrophilic so that the liquid is able to spread over the core. Said intermediate layer is also non-porous, to prevent the fluid to return to the top surface and to maintain the SAP particles (21) within the bottom layer during application, but also during the use of the absorbent article, once the SAP particles (21) are swollen by liquid. The bottom layer is a very porous structure suitable for being penetrated with SAP particles (21), said bottom layer serves as a storage layer (20) (FIG. 9).

(78) In another embodiment, SAP particles (21) penetrate the void volume gradient (18a, 18b, 18c) of fibers network. Smaller particles will penetrate deeper than bigger particles due to the void volume gradient of fibres (18a, 18b, 18c). The top side of the fibrous structure will be substantially free of SAP particles (21) and can further serve as acquisition (14), distribution (16) and rewet (15) layer.

(79) In a further embodiment, SAP particles (21) can completely penetrated a monolayer or multilayers, preferably dual or triple layer structure. The top and bottom part of the structure being covered by a covering layer (22) such as a spunbond, non-woven, spunlace or a film of polypropylene, polyethylene or PET, to prevent said SAP particles (21) from transferring to the outside of the absorbent.

(80) In a preferred embodiment, the multilayers substrate (23) has a porous top layer suitable to allow the penetration of the SAP particles (21) within the substrate (23) while the bottom layer, or one of the intermediate layer, is non-porous to prevent the loss of SAP particles (21) by transfer through the substrate (23). Advantageously, at least one additional covering layer (22) is used to prevent any loss of SAP particles (21). In order to have more coverage additional 2 layers can be used.

(81) If 2 layers are used, the edges of said covering layers (22) are glued to seal the structure. If one structure covering layer (22) is used, said layer is fold to wrap the structure and the edges are glued to seal the structure (FIG. 26).

(82) Method to Prepare an Absorbent Structure

(83) A method to prepare an absorbent structure suitable for the invention is illustrated in FIG. 13 and comprises the step of: Unwinding (11) the fibrous substrate (7). Covering the substrate (7) with the SAP particles (21) by powder scattering (8) or by drum formation, through vacuum technology of a standard diaper line. Applying an alternative electrical field to ensure a homogeneous distribution of the SAP particles (21), this method is also known as the Fibroline method (9) described in EP 1 526 214 or EP 2 165 015 each incorporated herein by reference. The SAP particles (21) are then dispersed in the substrate (7) and the SAP particles (21) are maintained in the fibrous substrate (7) by entrapment or entanglement and/or after an optional binding step wherein the SAP particles (21) are bonded to the non-woven fibres by the addition of glue. Unwinding (11) a core covering layer material (22). Applying an adhesive (10) on the inner face of the core covering layer (22) and/or the substrate surface (7). Covering the substrate (7) with said core covering layer material (22). Ensuring the adhesion by pressure (12). Winding the absorbent structure (13). Optionally, calendering the product to create a channel structure in the longitudinal direction.

(84) A suitable device for the Fibroline method comprises a system of 2 face to face electrodes protected by a dielectric material and connected to an alternative high tension generator (10 to 50 kV) wherein:

(85) The mixture of SAP particles (21) and adhesive is placed between the two dielectrics material and a strong alternative electric field is applied.

(86) The devices (FIG. 13) suitable to perform the method of preparation of an absorbent structure can be employed either in line or off line of an ADL and/or core production line or of a diaper or feminine care production line.

(87) Preferably, the coated or uncoated SAP particles (21) are glued to the fibers of the ADL layers. None limitative bonding method include powder coating and thermo bonding, heat treatment, spray coating, powder scattering, reactive glue (activation and curing) or any combination thereof.

(88) SAP particles (21) of diameter ranging from about 45 m to about 850 m, preferably from about 100 to about 800 m and having an average diameter size of about 300 to 600 m are preferred as the small particles effectively penetrate the ADL while larger size particles remain on the outer side of the diffusion layer thus forming a storage stratum (20).

(89) Adhesive

(90) Suitable glue according to the invention has to provide a good adhesion, has to be permeable to liquids in order to allow the liquids to reach the absorbent layer and has to have an elongation at break of at least 100%, preferably of 600 to 1800% in order to prevent gel blocking issue when the SAP particles (21) are swollen by body fluids. Preferred glue are water based glue and solid powder glue, which are pulverized to bond the SAP particles (21). Suitable commercially available adhesives are, but not limited to, Bostik H4245; Bostik H20028; Bostik H4322 or Fller Full-Care 8400A.

(91) Method to Produce Multiple Absorbent Cores and/or ADL

(92) A method to produce an absorbent structure comprising an absorbent core and/or an ADL according to the invention is described in FIGS. 13 and 26.

(93) Advantageously, said method can be adapted to produce profiled absorbent core and/or an ADL.

(94) The unwinding substrate layer (7) has to be sufficiently wide to process several absorbent structures in parallel. It is therefore possible to scattering and supply SAP particles (21) in a discontinuous manner over the width or lateral dimension or y direction of the substrate (7), as illustrated in FIG. 14.

(95) The method comprises the step of: Unwinding the fibrous substrate (7). Depending on the void volume distribution of the substrate (7), the substrate (7) can be maintained upwards during the process in order to prevent the loss of SAP particles (21). Partially deposit an amount of SAP particles (21) on the substrate (7) over the lateral, or y-direction, of the substrate (7) by powder scattering (8). Applying an alternative electrical field (9) to ensure a homogeneous distribution of the SAP particles (21), Said SAP particles (21) penetrate the substrate (7) and are maintained in the fibrous substrate (7) by entrapment or entanglement and/or after an optional binding step wherein the SAP particles (21) are bonded to the non-woven fibres by the addition of glue. Applying a hotmelt adhesive (10) on the substrate (7) surface and/or on the core covering layer (22). Unwinding (11) a core covering layer material. Covering the substrate (7) with said core covering layer (22). Where the SAP particles (21) are present, the hotmelt adhesive will bond the covering layer (22) to the substrate (7), binding the SAP particles in the totality (21). Where the substrate (7) is free of particles the adhesive will bond the core covering layer (22) material to the substrate layer (7) on part of the substrate (7) essentially free of SAP particles (21) thus sealing the absorbent core. The sealing prevents SAP particles (21) from falling out when this cutting occurs and prevents the SAP particles (21) from moving to the sides. Cutting the layer where substrate (7) essentially free of SAP particles (21) to obtain individual cores as illustrated in FIG. 15.

(96) Further, as, some migration will occur to the sides during the Fibroline process (FIG. 20), it is possible to create a dispersion profile of the SAP particles (21) over the lateral dimension of the absorbent structure (FIG. 16), creating a higher SAP particles (21) concentration zone in the middle part of the absorbent structure, and a lower SAP particles (21) concentration zone on the sides, thus providing a higher body fluid storage capacity in the center of the absorbent structure preventing the possibility of leakage.

(97) Advantageously a SAP particles (21) distribution profile can be obtained along the length or longitudinal dimension or x-direction of the absorbent structure. Said distribution profile is done by creating a profile in the supply roll used to deposit the SAP particles (21) on the substrate (7) by a powder scattering step. FIG. 17 illustrates a supply roll according to the invention wherein the front, middle and back sections of the substrate (7) will receive a specific amount of SAP particles (21).

(98) The transition between the sections of different concentrations will be homogenized upon applying the Fibroline process.

(99) As illustrated in FIG. 18, a profiled absorbent structure along the longitudinal dimension (x-direction) can be obtained, using said supply roll, said structure comprising a higher amount of SAP particles (21) at the front and the middle, and a lower amount of SAP at the back of the diaper.

(100) The profiled absorbent structure obtained accordingly comprises an absorbent part comprising SAP particles (21) partially penetrated in a nonwoven substrate (23) and an upper part serving as an ADL covered with a covering layer (22) and maintained by a hot melt adhesive. Thus the profiled absorbent structure can be directly used in absorbent articles.

(101) Preferably, the deposit of SAP particles (21) on the non-woven substrate (23) has a lateral and a longitudinal profile as illustrated in FIG. 25. As after the dispersion of the SAP particles (21) by the Fibroline process, the absorbent structure obtained will have an optimized absorbing ability due to the amount of SAP particles (21) dispersed within the substrate (23).

(102) In a preferred embodiment, the SAP particles (21) are also dispersed in discrete zones along the x-direction and/or y-direction of the substrate (23), each discrete zone being separated from one another (FIG. 19). Following the Fibroline process, the resulting absorbent core and/or ADL comprises, different motifs such as bands, or channels free of SAP particles (21) thereby facilitating the flow and wicking of the fluid (FIGS. 19 and 20).

(103) The absorbent structure can be used as a ready to use absorbent structure for absorbent articles (FIG. 26) and can easily fitted in body shaped absorbent articles (FIG. 24).

Examples

(104) Examples of SAP particles (21) suitable for the invention are FAVOR SXM 10000 and FAVOR SXM 9155 from Evonik.

(105) FAVOR SXM 10000 is a partially neutralized cross-linked sodium polyacrylate polymer having a size dispersion of approximately:

(106) TABLE-US-00001 Particles size (m) % SAP > 850 m <1% 600 m < SAP < 850 m 20-45% 300 m < SAP < 600 m 30-60% 150 m < SAP < 300 m 5-25% 45 m < SAP < 150 m <3% SAP < 45 m <1%

(107) FAVOR SXM 9155 is a cross-linked sodium polyacrylate polymer having a size dispersion of approximately:

(108) TABLE-US-00002 Particles size (m) % SAP > 850 m <1% 600 m < SAP < 850 m ~35% 300 m < SAP < 600 m ~44% 150 m < SAP < 300 m ~16% 45 m < SAP < 150 m ~3% SAP < 45 m <1%