MXPA00012252A - Absorbent structures having fluid distribution and storage layers - Google Patents

Abstract

Disclosed is an absorbent structure including a liquid acquisition layer and a fibrous liquid storage layer in liquid communication with the acquisition layer. The storage layer includes SAP particles. The acquisition layer includes synthetic fibers and the fibers are latex bonded. A fluid acquisition and/or distribution layer (ADL) containing at least two layers, a top layer of latex bonded synthetic fibers and a bottom layer of latex and/or thermal bonded cellulose fibers and method for preparation thereof are disclosed. The synthetic fiber layer is highly porous and provides rapid fluid acquisition under load. The cellulose layer provides z-direction capillary force to pull fluid into the absorbent product, to provide temporary fluid immobilization, and to act as a conduit for fluid to be pulled into unsaturated portion of the permanent fluid storage layer. The ADL of the invention provides increased protection against leakage relative to single-layer ADLS.

Description

ABSORBENT STRUCTURES THAT HAVE FLUID DISTRIBUTION AND STORAGE LAYERS This application claims priority, pursuant to 35 USC 119, of US Provisional Applications No. 60 / 088,455 and 60 / 088,456, filed on June 8, 1998; of US Provisional Application Serial No. 60 / 102,344, filed on September 29, 1998; and U.S. Patent Application Serial No. 09 / 232,783, filed January 19, 1999.

FIELD OF THE INVENTION The present invention is directed to improved, fibrous absorbent structures having separate layers for acquisition, distribution and storage. The acquisition layer contains synthetic fibers bonded with latex, and is useful for providing improved disposable absorbent products, such as diapers, adult incontinence pads and sanitary napkins.

BACKGROUND OF THE INVENTION Absorbent articles, such as disposable diapers, adult incontinence pads, sanitary napkins and the like, are generally provided with an absorbent core, or a storage layer, for receiving and retaining body fluids. The absorbent core is usually sandwiched between * _ ^^^^^^ an upper sheet, permeable to the liquid, whose function is to allow the passage of fluid to the core, and a back or back sheet, impervious to liquid, which contains the fluid and prevents it from passing through the absorbent article. An absorbent core (e.g., for adult incontinence pads and pads) typically includes fibrous fluffs or card veils, constructed of hydrophilic, defibrated, loose, fluffed cellulosic fibers. The core may also include particles of superabsorbent polymer (SAP), granules, flakes or fibers. Additionally, an absorbent article may contain a distribution layer that helps to rapidly transport the liquid from the acquisition layer to the core storage layer. In recent years the demand in the market for thinner and more comfortable absorbent articles has increased. Said articles can be obtained by decreasing the thickness of the diaper core, reducing the amount of fibrous material used in the core, at the same time increasing the amount of SAP particles, and calendering or compressing the core to reduce the caliber and, consequently, , increase the density. However, higher density cores do not absorb liquid as rapidly as lower density cores, due to core densification, which results in smaller effective pore sizes. Consequently, to maintain a suitable liquid absorption rate it is necessary to provide a lower density layer having a larger pore size above the high density absorbent core, in order to increase the absorption rate of liquid discharged onto the absorbent article. Frequently the low density layer is called an acquisition layer. The storage layer portion of a disposable diaper core, for example, is generally formed in place during the conversion process, from loose, fluffed cellulose. Super-absorbent powder is mixed with the fluffy cellulose fibers, when the absorbent core is formed in the diaper conversion line. Said cellulose material is generally not available in the form of preformed roll, because it exhibits insufficient physical strength in continuous sheet, due to the lack of bonding or entanglement between the fibers. The acquisition layer portion of a disposable diaper is generally a continuous sheet of carded synthetic short fiber, which is thermally bonded, latex-bound or stitch-bonded. Typical short fibers for the acquisition layers are crimped polyester fibers (PET) or crimped polypropylene fibers, which have a size of 6 to 15 denier and a length of at least 40 mm. The acquisition layer is formed, unit and item as a homogeneous roll article, in a specialized non-woven textile production line. The divided roll of acquisition layer material is subsequently unwound in the diaper conversion line, and is fixed on the upper part of the absorbent core and below the upper sheet. Examples of commercial baby diapers, with a short carded stuck fiber, are Huggies diapers, produced by Kimberly-Clark Corp. (Dallas, TX, EU A), and private label diapers, from Paragon Trade Brands (Atlanta, GA, USA) Modern converting machines for disposable diapers for babies have become extremely complex, as more and more aspects have been implemented, such as the provision of elastic and the multiple non-woven materials, to improve diaper performance. That complexity has created significant raw material handling problems, and the resulting loss of productivity in the conversion line. There is a need to replace the fluffy pulp, which is bulky and troublesome, and the superabsorbent dust forming systems, with a single material that can simply be fed directly to the conversion line from a roll or other suitable compact packing. Because the acquisition layer and the absorbent core are assembled into the final product, the efficiency of the conversion operation can be maximized to combine the fluid acquisition layer and the absorbent core into a single material. Ultraslim feminine pads are generally produced from articles in rolls that are based on non-woven material. Said roll of preformed absorbent core material is unwound directly onto the absorbent article converting equipment, without the defibration step required for the fluff-based products, such as incontinence pads and pads. The non-woven web is typically bonded or consolidated in a manner that imparts sufficient strength to be handled in the conversion process. The continuous sheet may also contain SAP particles. The consolidation mechanisms of continuous sheet used in the roll products to constitute the preformed cores, give physical resistance and dimensional stability to the continuous sheet. These mechanisms include: agglutination with latex, agglutination with thermoplastic or two-component fibers, or with thermoplastic powders; hydroentangling, needle-punched, carded or similar. One embodiment of a structure having an acquisition layer and a distribution layer (an "ADL") typically attached to female hygiene pads, die-cut, is a continuous sheet of cellulose, laid with air, attached with a binder resin. water that has been dried and cured. The materials held with air typically retain up to 16 g of fluid per gram of material against gravity, under negligible load. Thus, an ADL can acquire a fluid discharge within the absorbent product until the superabsorbent particles of the absorbent core can absorb the fluid retained from the air-laid cellulose ADL, and to the final storage, which contains superabsorbent particles- An example of Air-laid cellulose material, conventional, is Vicell 6002 (Buckeye Technologies, Inc., Memphis, TN, USA), which is an air-laid cellulose non-woven, 105 gsm (grams per square meter), bonded with a vinyl acetate binder resin. Vicell 6002 is prepared by spraying an aqueous emulsion of the vinyl acetate binder resin onto the continuous sheet of cellulose laid with air, followed by drying and curing in a hot air oven. It is used commercially in an ADL for feminine hygiene pads. The disadvantage of certain air-laid cellulose structures obtainable in commerce is that they can be crushed under normal use. This typically occurs when the structure is compressed by the user's weight and, in particular, when the structure is wetted. This crushing or structural collapse significantly reduces the acquisition speed of the absorbent product and, in this way, increases the probability of leakage. When the cellulose structure stretched with air, completely or partially saturated with fluid, is crushed, the fluid escapes from the ADL and the product feels moist against the wearer's skin. There is a need for an absorbent core material which facilitates the transport of fluid from an acquisition zone to a storage zone, has a high absorbency in use and can be supplied in the form of roll products, to simplify the processes of manufacturing and conversion.

As an aspect of the invention, an improved ADL with an extremely porous acquisition layer is provided. In another aspect of the invention there is provided a rolled product, laid with air, containing the ADL of the invention, and a method for its production. In still another aspect of the invention there is provided a disposable absorbent product containing the ADL of the invention and a method for its production. The absorbent structure of the invention has the following advantages: (i) it is highly absorbent, since it is made of a low density material and has high volume properties; (I) the layers are uniform due to the way in which the superabsorbent particles are deposited in the layers that provide a continuous absorbent sheet and, in such a way, provide increased absorbent potential for the article; (iii) the absorbent article allows more economical means to provide an absorbent article, due to the function of the multiple materials that are combined in a single roll; and (iv) the wettability of the article can be adjusted, as a result of (or by) the addition of surfactant during the formation process of the acquisition layer.

DETAILED DESCRIPTION OF THE INVENTION All patents, patent applications and references to literature, cited herein, are hereby incorporated by reference, in their entirety. The present invention provides an improved fibrous absorbent structure, containing a liquid acquisition layer, of lower density, and a fibrous storage layer, of relatively greater density. The structure is a composite that includes at least those two layers, which give the structure the ability to acquire and distribute fluids through the density gradient. The acquisition layer is capable of rapidly acquiring liquid from a discharge. The storage layer absorbs and stores the acquired liquid from the acquisition layer. Furthermore, the invention preferably contains a distribution layer, which in combination with the fluid acquisition layer, provides an improved ADL, containing at least two layers, a top acquisition layer and a distribution layer. When used in a disposable absorbent product, the acquisition layer is closer to the wearer's skin and away from the storage layer; The distribution layer is closer to the storage layer and away from the user's skin. The acquisition layer provides rapid acquisition of fluid under load. The distribution layer provides capillary force in the z-direction, to bring fluid to the absorbent storage layer, away from the wearer's skin, to provide temporary immobilization of the fluid, and to act as a conduit for the fluid withdrawn to the non-conducting portion. saturated with the storage layer. The absorbent structure of the invention has great absorbent capacity and is particularly useful as an absorbent core for disposable absorbent articles, such as diapers, adult incontinence pads and feminine sanitary napkins, and the like. The fibrous fibrous cellulose fibers used in the ADL or storage layer of the mixed structure of the present invention can be selected from wood cellulose, such as foley sponge fibers, cotton fluff pulp, chemically modified cellulose, as fibers of interlaced cellulose, or highly purified cellulose fibers, such as Buckeye HPF. The present invention takes advantage of the unexpected discovery that a synthetic fiber, bound with latex, in the acquisition layer, provides an absorbent structure having improved acquisition and retention characteristics (ie, absorbency), compared to an absorbent structure that it employs an acquisition layer that lacks those fibers. The advantage of using synthetic fibers is such that the fibers maximize the surface dryness of the absorbent product. Any synthetic fiber, including polyester fibers, such as polyethylene terephthalate (PET), polypropylene, nylon and acrylic, and their combinations, can be used as long as the fiber has the property of forming large pores, resistant to crushing when the layer is wet . The melting point of the synthetic fiber must be taken into account during the manufacturing process, and the temperature must be adjusted to prevent the fiber from melting. For the purposes of the present description, "large pore" means a pore greater than, or more resistant to crushing than, the pore formed by cellulose fibers. Because the large pores contained within a synthetic fiber matrix resist crushing under pressure when wet, the top layer can quickly acquire a fluid discharge as it passes through the upper liner or canvas of the absorbent product. The pore size will depend on the composition of the fiber, the size of the fiber (that is, the diameter of the fiber), the elasticity of the fiber and the elasticity of the latex. A person skilled in the art can optimally carry the pore size to suit any particular need, using general knowledge in the art (see, for example, U.S. Patent 5,569,226 and U.S. Patent 5,505,719, issued to Cohen) and routine experimentation. The synthetic fibers of the upper layer are bonded with an aqueous dispersion (emulsion) of a natural or synthetic polymer latex. Any latex can be used in this invention. The synthetic polymer can be, for example, a polymer or copolymer of alkyl acrylates, vinyl acetate or styrene-butadiene. Other polymers known in the art can be used. For purposes of industrial hygiene and elimination of a solvent recycling step, synthetic latexes can be applied as an aqueous-based emulsion, rather than as an emulsion in organic solvent. In the present invention, the preferred matrix fibers in the acquisition layer are crimped PET fibers, from 3 to 20 denier, with a short length of 3 to 15 mm. The distribution layer of the improved ADL preferably contains cellulose fibers bonded with latex and / or thermally. Any fluffy cellulose fibers may be used in this layer, preferably wood fibers, such as air-laid sponge cellulose, chemically modified cellulose fibers, (e.g., interlaced cellulose fibers), highly purified cellulose, cotton lint fibers. , or mixtures of them. For the purposes of joining them, the latex dispersions used to join the fibers of the top layer can be used. Alternatively or in combination with a latex binder, thermoplastic fibers or powder may be used to join with heating to the melting point of the thermoplastic fiber or powder. Two-component fibers, having a PET core, surrounded by a polyethylene sheath, for example, Hoechst-Trevira Type 255 (Charlotte, NC, E.U.A.), and polyethylene powder can be used. The improved ADL distribution layer provides both a temporary retention zone and a channel for liquid distribution in the final storage layer. The cellulose fibers of this layer form a microporous medium which spontaneously distributes the fluid from the point of attack or incidence of the fluid to unsaturated portions of the distribution layer, by means of a combination of driving force by surface tension and gravity. Once the spreading fluid, coming from the incidence, makes contact with an unsaturated portion of the storage layer, which has a surface tension greater than the ADL, the fluid within the distribution layer flows into the layer of storage until a surface tension balance is reached. The greater surface tension of the storage layer can be generated by providing higher density cellulose fiber and / or superabsorbent particles. So that, the distribution layer becomes both a fluid reservoir, and a flow channel for the storage layer. The flow channel function is particularly important in certain thin absorbent pads, in which the ADL covers a significantly larger surface area than the storage layer or absorbent core. Optionally, other ingredients, such as surfactants, pigments and opacifiers, can be added to the acquisition or distribution layers, without affecting the absorbency. The basis weight of the ADL layer of the invention may vary from about 30 to 150 gsm, preferably about 60 to 100 gsm, and most preferably about 80 gsm. In one embodiment, the base weight of each of the acquisition and distribution layers of the ADL may vary from about 15 to 60 gsm. It is preferred that the base weight of each layer be at least about 25% of the total weight of the ADL base. In one embodiment, the upper layer is approximately 25 to 50% of the total weight of the ADL base. The ADL of the present invention may contain an optional middle layer. The middle layer may contain 100% buffered cellulose and / or chemically modified cellulose fibers, or have a fiber composition which is a mixture of synthetic fibers and cellulose fibers. In one embodiment of the ADL, the acquisition layer contains approximately 80 to 90% by weight of polyester fiber (PET) of 6.7 dtex (weight / length of fiber) in short length size of 6 mm, joined with 1020% by weight of an aqueous binder resin. The lower layer contains 80-90% fibrous, fluffed cellulose fibers, which are bonded using 10-20% of an aqueous binder. Fibrized fluff cellulose fibers may contain wood cellulose, such as Buckeye Foley (Buckeye Technologies Inc.), cotton lint pulp, such as Buckeye HPF (Buckeye Technologies Inc.), or chemically modified cellulose, such as interlaced cellulose. In another embodiment, the upper and lower layers of the ADL are as before, but an intermediate layer containing a mixture of PET and cellulosic fibers is also present. In this embodiment the top layer is at least 10% of the total weight of ADL and the lower layer is not more than 50% of the total weight of the ADL base. The preferred total base weight scale of the mixed absorbent structure of the invention is 100-500 grams per square meter (gsm). The mixed absorbent structures include a fluid acquisition layer and a fluid distribution layer (described above) and a fluid storage layer. The fluid storage layer is below the fluid distribution layer and consists of a fluffy cellulose or chemically modified sponge cellulose matrix fibers, a superabsorbent polymer (SAP) and a binder element. The binder element preferably consists of two-component fibers, in the concentration of 5 to 20%, but may also include thermoplastic powders. It is preferred that the SAP content be from 10 to 70% by weight of the absorbent structure. As used herein, "superabsorbent polymer" or "SAP" means any suitable hydrophilic polymer, which can be mixed with fibers of the present invention. A superabsorbent polymer is a water soluble compound that has been entangled to make it insoluble in water, but still swellable to at least about 15 times its own weight, in physiological saline. These superabsorbent materials generally fall into one of three classes, namely: starch graft copolymer, interlaced carboxymethyl cellulose derivatives, and modified hydrophilic polyacrylates. Examples of absorbent polymers include hydrolyzed starch graft copolymer-acri lonitri lo; saponified-inyl acrylic acid ester copolymer; polyvinyl alcohol interlaced, modified; crosslinked polyacrylic acid, neutralized; crosslinked polyacrylate salt and carboxylated cellulose. The preferred superabsorbent materials, upon absorbing fluids, form hydrogels. The superabsorbent polymeric materials have relatively high gel volume and relatively high gel strength when measured by the shear modulus of the hydrogel. Said preferred materials also contain relatively low levels of polymeric materials that can be extracted by contact with synthetic urine. Super-absorbent copolymers are well known and commercially available. An example is a polyacrylate hydrogel with starch graft, sold under the name IM1000 (Hoechst-Celanese, Portsmouth, VA). Other superabsorbent polymers obtainable in commerce are sold under the Sanwet brand (Sanyo Kasei Kogyo Kabushiki, Japan), Sumika Gel (Sumitomo Kagaku Kabushiki Haishi, Japan), Favor (Stockhausen, Garyville, LA, USA) and the ASAP series (Chemdal, Aberdeen, MS, USA). Polymers in superabsorbent particles are also described, in detail, in U.S. Patent Nos. 4,102,340 and Re 32,649. An example of a suitable SAP is the acrylic acid powder based on surface interleaving, such as Stockhausen 9350 or SX FAM 70 (Greensboro, NC, E. U A.). The preferred base weight varies and the SAP content may vary with the intended application. For feminine hygiene and incontinence applications for lightweight adults, for example, the base weight and SAP content will tend to be towards the lower end of the scale indicated in Table 1. For diaper applications for baby and infant adult incontinence, high capacity, preferred base weight and SAP content will tend to be at the high end of the scale specified in Table 1. Multiple matrix fibers can be used in an absorbent article of the invention; however, it is preferred that collectively the matrix fibers constitute the majority of the fibers in the material (eg, at least 75%). The term "matrix fiber", when used herein, refers to a synthetic or cellulosic fiber that does not melt or dissolve to any degree during the formation or bonding of an air-laid absorbent structure. The terms "thermal bond" or "thermal" herein refer to the joining of thermoplastic material (for example, the joining methods mentioned in Table 1, in which the fiber or matrix fibers and the SAP join the Absorbent layers when heat is applied Examples of suitable thermoplastic materials include thermoplastic microfibers, thermoplastic powders, bonding fibers in the form of short fibers, and short double component fibers.

Short double-component fibers are characterized by a core polymer, high melting temperature (typically polyethylene terephthalate (PET) or polypropylene) surrounded by a low melting temperature sheath polymer (typically polyethylene, modified polyethylene or copolyesters) ). In the preferred embodiments of this invention, the double component fibers provide the thermal bonding means.

Table 1 provides a general outline of one embodiment of the invention.

TABLE 1 In a modality of feminine hygiene and light adult incontinence products, the absorbent product of the invention contains an acquisition layer, a distribution layer and a storage layer, having a total base weight of 120 gsm to 290 gsm. . The acquisition layer, comprising the PET matrix fibers bonded with latex, has a total basis weight of 20 to 60 gsm. The matrix fibers have a size of 6 to 15 denier, 3 to 12 mm in length and have 2 to 5 curls / cm. The latex is an emulsion of ethylene, vinyl acetate, styrene-butadiene or acrylic polymer. The latex binder is about 5 to 25% by weight of the acquisition layer. The distribution layer, which comprises thermally bonded fluffy cellulose, or chemically modified fluffy cellulose fibers, has a total basis weight of 30 to 90 gsm. The cellulose fiber is thermally bonded with 5 to 20 wt% of two-component, sheath / core fiber (e.g., 2-denier bi-component fiber, T-255, from Hoechst-Celanese, Charlotte, NC, E. U. A.). The storage layer of thermally bonded fluff pulp, with 20 to 50% SAP, has a total base weight of 70 to 130 gsm. The sponge cellulose / SAP mixture is thermally bonded with 5 to 10 wt% of the two-component, sheath / core fiber. Specific embodiments are described in Examples 3, 9, 14, 15, 16. In another embodiment, which can be used in baby diapers and heavy incontinence products for adults, the acquisition layer, the distribution layer and the layer of storage have a total basis weight of 300 gsm to 500 gsm. The acquisition layer, comprising PET matrix fibers bonded with latex, has a total basis weight of 20 to 60 gsm. The matrix fibers have a size of 6 to 15 denier, 3 to 12 mm in length and have 2 to 5 curls / cm. The latex is an ethylene / vinyl acetate, styrene-butadiene or acrylic polymer emulsion, and is approximately 5 to 25% by weight of the acquisition layer. The distribution layer, comprising fluffy cellulose fibers or thermally bonded chemically modified fluffy cellulose fibers, has a total basis weight of 30 to 100 gsm. The cellulose fiber is thermally bonded with 5 to 20% by weight of double component, sheath / core fiber. The thermally bonded sponge cellulose storage layer with 40 to 75% SAP has a total basis weight of 250 to 340 gsm. The sponge cellulose / SAP mixture is thermally bonded with 5 to 10% by weight of the double sheath / core component fiber. Specific embodiments are described in examples 8 to 10. An absorb article can be formed. e of the invention in a continuous process, using air forming equipment, such as the equipment sold by M &J Fibertech (Horsens, Denmark) or Dan-Web (Aarhus, Denmark). The bottom or cellulose fiber layer is formed in a movable collection mesh, and the synthetic fiber layer is laid with air directly on top of the cellulose fiber layer. The resulting mixed structure is then passed under an adhesive application station (typically a series of spray nozzles or a foam coater) that directly applies the adhesive onto the synthetic fiber layer. Then the material moves through a hot air oven or other heating device, to join the structure. In the preferred embodiments, the adhesive is then applied to the cellulose fiber side of the mixed structure, and the material is passed through a second oven to dry the adhesive. A third heating station can be employed to ensure that the adhesive is fully cured. Finally, the absorbent structure of the invention can be packaged and shipped in the form of rolled products. It is preferred that the absorbent structures of the invention be prepared as a sheet laid with air. The mixed material can be manufactured in a continuous operation, as long as the production line has at least three separate forming heads, a synthetic fiber dosing system, capable of handling at least two different synthetic fibers, simultaneously, a superabsorbent powder dosing system, and a latex adhesive applicator system. Air-laid web is typically prepared by disintegrating or fiberizing one or more sheets of cellulose pulp, typically by hammer mill, to give individualized fibers. The individualized fibers are then transported to forming heads in the continuous sheet forming machine by air laying. The forming heads include rotating or agitated drums, generally in track rail configuration, which serve to maintain fiber separation until the fibers are carried by vacuum over the foraminous condenser drum or the foraminous forming conveyor (or forming wire mesh) ). On the machine M &J the forming head includes a rotary shaker on top of a mesh). Other fibers, such as synthetic thermoplastic fiber, can also be introduced into the forming head through a fiber dosing system, which includes a fiber opener, a metering unit and an air conveyor. When two defined layers are desired, such as the fluff pulp distribution layer and a synthetic fiber acquisition layer, two separate forming heads are provided, one for each type of fiber.

The continuous sheet laid with air is transferred from the forming mesh to a calender or other densification step, to densify the continuous sheet, increase its strength and continuous sheet control thickness. Then the fibers of the continuous sheet are joined by application of a latex spray or foam addition system, followed by drying or curing. Alternatively, or additionally, any thermoplastic fiber present in the web may be smoothed, or it may be partially melted by applying heat to bond the fibers of the web. The joined web can then be calendered a second time to increase the strength, or the web can be embossed with a pattern or design. If thermoplastic fibers are present, hot calendering may be employed to impart pattern bond to the continuous sheet. Water can be added to the continuous sheet, if necessary, to maintain a specified or desired moisture content, in order to minimize the formation of dust, or to reduce the buildup of static electricity. Then the final web can be rolled up, for future use. In one embodiment (eg, example 1) the acquisition and distribution layer are formed with air, independently of the fluid storage layer. The mixed acquisition / distribution layer is combined with the storage layer in the conversion line. This embodiment is useful for absorbent product designs in which the storage layer covers a different area than the acquisition / distribution layer. Other embodiments of this type are described in examples 11, 12 and 13. The following non-limiting examples further describe the invention, the scope of which will only be limited by the claims.

EXAMPLES 1-2 To test the rate of fluid acquisition, using an ADL of the invention, samples were formed having a desired base weight of 80 gsm in an air-forming, laboratory device. The top layer of Example 1 contained 34 gsm of 6.7 dtex, 6 mm long polyester (PET) fibers (Hoechst Trevira, Charlotte, NC, USA) and 6 gsm of AirFlex 192 latex binder (Air Products and Chemicals, Allentown, PA, USA). The lower layer contained Buckeye Foley sponge pulp, 34 gsm, and Airflex 192 latex binder, 6 gsm. A control sample, Example 2, was prepared in the same laboratory, air-forming device, which contained a single layer having a basis weight of 80 gsm, comprising fluffy wood cellulose fibers, Buckeye Foley, 68 gsm, and Air Flex 192, of 12 gsm. Foley sponge cellulose is typical of the fiber used in conventional air-laid acquisition layers, such as Vicell 6002 (Buckeye Technologies, Inc.). Each sample was placed in a two-layer Zorbcore 5901 (Buckeye Technologies, Inc.), which included 250 gsm heat-bonded air-laid Foley sponge material containing 25% Stockhausen SX FAM 70 SAP. The ADL / absorbent core stack was covered with an 18 gsm polypropylene top sheet. Test and control samples were prepared for three separate measurements (each sample had the dimensions of 25 cm x 10 cm). Each sample was wrapped with an appropriate cover material and placed on the lower fluid entry test board with the wire side or carrier side down. The center of the samples was marked. Assessments of the acquisition rate were made by submitting test samples to three consecutive discharges of 50 ml of 0.9% saline. The first 50 ml discharge of 0.9% saline was poured into the clear addition tube of the FIT board, as quickly as possible, but without spilling. The time from the moment of pouring until the saline solution reached the test sample was measured. The chronometer stopped as soon as the entire saline solution it passed from the bottom edge of the tube. The time recorded was the time required for the acquisition by the upper layer. After one minute intervals the procedure was repeated with a second and with a third 50 ml discharges. The acquisition speed of each fluid discharge was determined according to the following formula: fluid discharge volume (ml) Acquisition speed (ml / s) = acquisition time (s) The acquisition speed results are represented in table 2 as milliliters per second (ml / s) of fluid penetration through the upper canvas.

TABLE 2 - ACQUISITION SPEED The results show that the sample containing the bilayer of Foley latex / sponge-bonded PET (ie, the ADL prepared according to the present invention) had approximately twice the speed of fluid acquisition with respect to the control sample which consisted of a single layer that lacks PET for each of the three discharges. Another critical function of an ADL is to isolate the user of the absorbent product from the fluid contained within the absorbent product. While an air-laid, low-density cellulose layer can have very rapid fluid acquisition, the conventional air-laid ADL cellulose fibers often retain the fluid or provide a fluid conduit for leakage from the fluid. core when the ADL is under pressure, which makes the user's skin moist. In contrast, the synthetic fibers of the upper layer of the ADL of the present create large pores so that, even under pressure, the upper layer does not retain the fluid or provide a conduit for the fluid to leak from the distribution or distribution layers. of storage, towards the user. This advantage is shown experimentally in the present example. The test samples described in Example 1 were placed on top of a two-layer Zorbcore 5901, below the 18 gsm non-woven upper web. This stack of materials was tested in accordance with the fluid rewet / retenuat test, supra, by measuring the amount of 0.9% saline solution that could be absorbed back through the top sheet by a stack of filter paper, under pressure of 0.689 kPa after each fluid discharge. Test and control samples were prepared for three separate measurements (each measurement of 21.59 x 27.94 cm). Each sample was placed on the plastic platform with the tissue side down and its center was marked. 50 ml of 0.9% exit solution (first discharge) was drained over the sample from a funnel at a distance of approximately 3.81 cm above the center of the sample. The sample was allowed to settle for 20 minutes. A stack of 12 filter papers was weighed and placed over the center of the moistened area and pressed by a circular weight on top. After two minutes the wet filter papers were removed and reweighed. This procedure was repeated with a second discharge of 50 ml of saline and a stack of 16 filters, and a third discharge of 50 ml of saline and a stack of 20 filter papers. The rewet value and the retention rate of the fluid for the first, second and third discharges were calculated according to the following formulas: Rewet! 2o 3 = Weight of wet filter papers - weight of dry filter papers% retention = (50 - rewet) 50 x 100% The results are presented in table 3, as a percentage of each 50 ml fluid discharge that was retained by the core after removing the filter paper.

TABLE 3 - RESULTS OF FLUID RETENTION The PT bilayer bound by latex / foley sponge cellulose (ie, the ADL prepared according to the invention had a significantly higher fluid retention than the sample containing only latex bound sponge cellulose.

EXAMPLES 3-4 To test the absorbent core of the invention in combination (example 3), a mixed absorbent core was created by first air-forming a layer of 100% PET fibers of 6 denier x 6 mm long, on top of the preformed Vizorb X479 material (Buckeye Technologies Inc.). The PET fiber layer was then joined in place by spraying a 15% by weight aqueous solution of AirFlex192 latex binder (Air Products &Chemicals, Allentown, PA, E. U. A.). Vizorb X479 is a sponge cellulose of latex / thermally bonded, absorbent core containing 30% SAP (Stockhausen SX FAM 70, Greensboro, NC, E.U.A.). Vizorb X479 also has a free top layer of SAP containing Buckeye HDF thermally bonded, which is chemically modified fluffy cellulose, which becomes the fluid distribution layer once the acquisition layer joined by latex is formed on top of the X479 material. A 15 gsm cellulose tissue carrier sheet was provided below the bottom surface of the Vizorb X479 material for containment of the SAP during the continuous sheet forming process, to prevent equipment failures due to separation of SAP from the structure. The composition sought and the configuration of the absorbent structure of Example 3 are shown in Table 4. This preparation was repeated using a mixed absorbent core formed of a layer of 100% PET fibers of 6 denier x 12 mm. The fluffy cellulose fiber in the distribution and storage layers was 67% of Buckeye Foley Fluff and 33% of Weyerhaeuser PD 416 (Seattle, WA, E. U A.), by weight. The double-component fiber used was Hoechst-Trevira T-255 of 3.1 dtex x 4 mm long (Charlotte, NC, E. UA), the SAP powder was Stockhausen SX-70 (Greensboro, NC, USA) and the binder resin Latex was Airflex 124 (Air Products). The term "dtex" refers to the mass, in grams, of 10,000 meters of fiber. The term "denier" refers to the mass, in grams, of 9,000 meters of fiber. The matrix fiber of the acquisition layer of Example 3a contained Hoechst-Trevira type 224 polyester, crimped, 6.7 dtex by 6 mm long (polyethylene terephthalate or PET) and Airflex latex resin 192. Example 3b was identical to 3a, except that the length of the PET fiber was 12 mm. The binder for the sponge cellulose acquisition layer was Airflex 192 and the sponge cellulose was 100% Buckeye Foley Fl uff.

TABLE 4 A reference sample was created (example 4) by forming in air a 40 gsm layer of Foley Fl uff cellulose on Vizorb X479 material. Then the sponge cellulose was bound with latex, as in example 1. The reference sample exemplifies a conventional air-formed structure that lacks PET fiber. Table 5 shows the desired composition and the desired configuration of the reference sample.

TABLE 5 Test and control samples were additionally prepared for three separate measurements, as in example 1. Acquisition velocity evaluations were carried out by subjecting the mixed structures of examples 3a, 3b and 4, subjecting the samples to three consecutive discharges, as described in the example 1 -2. The results of the acquisition speed are represented in table 6, as milliliters per second of fluid penetration, through the upper canvas TABLE 6 - ACQUISITION SPEED (ml / s) Table 6 shows that samples having a PET acquisition layer, bonded with latex, have a fluid acquisition rate 300 to 400 percent higher than the sample having an acquisition layer of fluffy cellulose bound with latex. The structures of examples 3a, 3b and 4 were also subjected to liquid rewet / retention test with discharges of 50 ml of saline, as in example 1-2. The rewet value and the percentage liquid retention for the first, second and third discharges were calculated according to the rewet formulas of example 2. The results are shown in table 7, which shows the amount of liquid, in grams that could be carried through the upper sheet, with filter paper.

TABLE 7 - REHUMECTATION WITH 50 ml Table 8 shows the results of table 7, expressed as a percentage of each 50 ml discharge of liquid that was retained by the core after the filter paper was removed.

^? Jt * TABLE 8 -% RETENTION OF 50 ml LIQUID Tables 7 and 8 show that the latex-bonded PET acquisition layer significantly improves fluid retention compared to a conventional latex-bound sponge cellulose acquisition layer.

EXAMPLES 5-8 In this embodiment of the invention a 6 den x 6 mm PET fiber fiber layer was bonded using a combination of latex bonding and thermal bonding, ie, multi-junction, a combination of two types of bonding techniques ). The first step was to form an absorbent core laid with air, designated DL-1. The basis weight of the DL-1 material was 425.0 gsm. The DL-1 material included a SAP fluid / fluffy cellulose storage layer in a 15 gsm tissue carrier and a distribution layer containing predominantly air-laid Buckeye HPF (chemically purified cellulose fiber having a small percentage of double component fibers). The DL-1 storage layer included 144.9 gsm of fluff pulp and 153 gsm of Stockhausen 9350 SAP. The distribution layer of the DL-1 material included 48.6 gsm of Buckeye HPF fiber. In addition, 46.6 gsm of double-component thermal fiber was distributed throughout the core layer and the DL-1 material distribution layer. The distribution layer and the storage layers (core) were thermally bonded with a small amount of latex spread in dilute aqueous solution (17 gsm solids) such that the layers contained SAP particles and cellulose fibers. Material 5 DL-1 was collected on a roll and a portion of the roll was again passed through the M &J continuous sheet forming and binding system (Horsens, Denmark). An acquisition layer was formed with air above the distribution layer of the DL-1 material. For each sample, the acquisition layer was applied by mixing the matrix fiber with the double component fiber and air-forming the layer on the DL-1 material (see Table 9). Buckeye HPF and Buckeye HPZU matrix fibers are chemically purified cellulose fibers. The double component fiber was T255 fiber (Hoechst-Trivera). The latex was Airflex 192 (Air Products). TABLE 9 The multi-run structures, laid with air, of frame 9, were subjected to liquid acquisition speed test, according to the method described in example 1 The results are indicated in table 10.

TABLE 10 - LIQUID ACQUISITION SPEED (ml / s) - MULTIPLE 50 ml DOWNLOADS The fluid acquisition rate of the sample material of Example 8, which contained an acquisition layer of polyester fiber (PET) bonded with latex, exhibited the highest liquid acquisition rate. The multiple-bond structures, laid with air, of examples 5 to 8, were subjected to liquid retention test according to the method of example 2 The results are indicated in table 11 TABLE 11 -% RETENTION OF 50 ml OF LIQUID Table 11 shows that the sample material of Example 8, which contained a PET fiber acquisition layer had a significantly higher percentage of fluid retained under pressure, in the mixed structure, compared to the other structures that used acquisition layers to cellulose base (examples 5-7).

EXAMPLES 9-10 Examples 9 and 10 are specific embodiments of the three-layer invention, optimized for thin sanitary napkins and lightweight incontinence application for adults (example 9) and for baby trainer diaper / briefs (example 10).

EXAMPLE 9 A sample was produced in the M & J type air formation line with a desired composition and configuration, as described in Table 12. The foley foam cellulose storage layer was made (Buckeye Technologies, Inc.) and the HPF sponge cellulose distribution layer (Buckeye Technologies Inc.).

The binding fiber was T-255, 3 den x 4 mm (Hoechst-Trevira) The synthetic matrix fiber used was PET fiber (Type D2645 6 denier x 6 mm, curly (4.2 curls / cm) (Hoechst-Trevira The SAP used was Stockhausen type 9350. The sample material was formed into a tissue sheet of 18 gsm to prevent contamination of the forming equipment by air, with particles of superabsorbent powder.This structure of three layers, more carrier tissue, it was thermally bonded and compacted to obtain a total material density of 0 094 g / cc and a base weight of 219 gsm. The resulting ADL / core absorbent material is one embodiment of the invention that can be used for thin sanitary napkins and applications for light incontinence of adults.

TABLE 12 The sample was tested against two commercially available thin sanitary napkins (American and European A mark) for fluid acquisition and fluid retention, according to the methods of examples 1 and 2, except that the amount of each discharge was 10 ml The results are shown in table 13. The weight basis is the sum of the multiple absorbent components that constituted the layers of acquisition, distribution and storage of fluid, of a product.

TABLE 13 EXAMPLE 10 A sample of the same age as the sample of Example 9 was produced, according to Table 14, except that the fluffy cellulose in the storage layer was ND-416 (Weyerhaeuser, Tacoma, WA, USA) and the Fluffy cellulose from the distribution layer was foley sponge (Buckeye Technologies Inc.). The total density of the material was 0.117 g / cc and the base weight was 504 gsm. TABLE 14 Sample 1 was tested against two commercially available baby diapers and training pants, both for fluid acquisition and for fluid retention, according to the methods of examples 1 and 2. The results are shown in FIG. Table 15. The base weights of the acquisition, distribution and storage components of the commercial products were as follows: A, 622 gsm, B, 792 gsm; C, 522 gsm; and D, 840 gsm.

TABLE 15 EXAMPLES 11-13 These examples show three embodiments of an ADL of the invention in a preformed and bonded absorbent core (see Table 16). The modalities compare the effect of matrix fiber size on the scale of 6 to 15 denier. The distribution layer of example 13 has a combination of latex and thermal bonding.

EXAMPLE 11 A two-layer ADL was formed, in the same manner as in Example 1, according to Table 16, using Flowey fluffy cellulose in the distribution layer (Buckeye Technologies, Inc.), bonding fiber T 255, of 3 den x 4 mm (Hoechst-Trevira), latex binder Airflex 192 (Air Products), synthetic matrix fiber D2645 PET of 6 denier x 6 mm x 4.2 curls / cm (Trevira) to form a fabric product laid on wet, 18 gsm.

EXAMPLE 12 In this example an ADL was formed as in example 11, except that the synthetic matrix fiber used in the acquisition layer was PET Trevira D2670 synthetic matrix fiber (9 denier x 6 mm x 3.9 curls / cm) .

EXAMPLE 13 In this example, an ADL was formed as in example 11, except that the synthetic matrix fiber used in the acquisition layers was Trevira D2660 synthetic matrix fiber (15 denier x 6 mm x 3.2 crimps / cm). Samples from Examples 11-13 were placed on Buckeye Airlaid cores, grade 5901 (Buckeye Technologies Inc.) and tested for fluid acquisition rate and fluid retention, according to the methods of Examples 1 and 2 Material 5901 is a uniformly bonded, thermally bonded material containing 25% Stockhausen SX FAM 77 superabsorbent powder, 10% Trevira T-255 double component fiber, 6% tissue carrier sheet and 59% ultra cellulose - Spongy, supersoft Weyerhaeuser. The results of Table 17 show that the 9 denier PET fiber used in Example 12 provided the maximum fluid acquisition speed; fluid retention was not significantly affected by the selection of the matrix fiber in those examples.

EXAMPLE 16 TABLE 17 EXAMPLES 14-16 These examples compare various latex binders used in the acquisition layers. In examples 14-16 the latex-bound PET acquisition layer was formed on an absorbent core Vizorb X479 (Buckeye Technologies Inc.) (see example 3). The configuration of the absorbent samples is given in table 18.

EXAMPLE 14 The fluff cellulose used in the distribution layer and in the storage layer was HPF and Foley Fluff, respectively (Buckeye Technologies Inc.). The binding fiber was T-255, 3 denier x 4 mm (Hoechst-Trevira). The latex binder was Airflex 192 (Air Products). The synthetic matrix fiber was PET type D2645, 6 denier x 6 mm x 4.2 curls / cm (Trevira, Inc., Germany). Samples were formed on wet laid tissue of 18 gsm TABLE 18 EXAMPLE 15 A second sample containing styrene-butadiene copolymer GenFlo 3060 was produced as a latex binder (GenCorp Specialty Polymers, Akron, OH, E.U.A.).

EXAMPLE 16 A third sample containing styrene-butadiene-acrylic terpolymer GenFlo 9355 was produced as a latex binder (GenCorp Specialty Polymers, Akron, OH, E.U.A.). Aqueous latex binder solution 2 percent Aerosol OT 75, obtained from Van Waters & Rodgers, Memphis, TN, E. U. A., which is a surfactant, to render the acquisition layer hydrophilic. Samples were tested for fluid acquisition rate and fluid retention, testing with a 0.9% saline solution according to the methods of Example 1 and 2, except that the amount of each fluid discharge was 10 ml. Loe Results are shown in table 19.

TABLE 19 Two additional variants of the third sample were made. The first variant contained 1% surfactant Aerosol OT and the second variant had no surfactant added to the latex binder emulsion. Samples (15 87 cm2) were placed on a horizontal surface. A discharge of 5 ml of 0.9% saline was poured on each sample. The saline immediately penetrated the samples that had the surfactant added. In the samples without surfactant the saline discharge remained collected on the sample for more than one hour, at which time the test was terminated. Examples 14-16 show that the wettability of the air-laid mixed structure of the invention can be adjusted at the point of manufacture, and that even with large synthetic fibers (6 denier) a minimum level of hydrophilicity in the latex resin, to obtain acceptable fluid penetration.

Claims (1)

1. CLAIMS 1.- A structure for fluid acquisition and distribution, characterized in that it comprises: (i) a superior, porous acquisition layer, comprising synthetic matrix fibers, joined with latex; said matrix fibers having an approximate length of 3 to 15 mm; and (ii) a lower distribution layer, in fluid communication with the upper layer, comprising cellulose fibers laid in air and a binder selected from the group consisting of thermoplastic fibers, latex and mixtures thereof. acquisition and distribution of fluid according to claim 1, further characterized in that the length of the synthetic matrix fibers is approximately 6 to 12 mm. 3. The structure for acquisition and distribution of fluid according to claim 1, further characterized in that the thickness of the synthetic matrix fibers is approximately 3 to 20 denier. 4. The structure for acquisition and distribution of fluid according to claim 3, further characterized in that the thickness of the synthetic matrix fibers is approximately 6 to 15 denier. 5. The structure for acquisition and distribution of fluid according to claim 1, further characterized in that the fibers of synthetic matrix are selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and mixtures thereof. 6. The structure for acquisition and distribution of fluid according to claim 1, further characterized in that the latex is selected from the group consisting of an aqueous emulsion of ethylene / vinyl acetate, acrylic, styrene-butadiene or styrene-butadiene acrylic . 7. The structure for acquisition and distribution of fluid according to claim 1, further characterized in that the cellulose fibers are selected from the group consisting of wood cellulose, cotton fluff pulp, chemically modified cellulose, cellulose fibers of high purity and mixtures of them. 8. An absorbent structure, characterized in that it comprises: (i) an acquisition layer of synthetic matrix fibers, joined with latex; said matrix fibers having an approximate length of 3 to 15 mm; (ii) a distribution layer of bound cellulose fibers, fibers that are thermally bonded, bonded with latex or a combination of both bonds; the distribution layer is in fluid communication with the acquisition layer; and (ii) a storage layer comprising cellulose fibers and superabsorbent polymer particles, wherein the fibers are thermally bonded; the storage layer is in fluid communication with the distribution layer. 9. The structure according to claim 8, further characterized in that the length of the synthetic matrix fibers is approximately 6 to 12 mm. 10. The structure according to claim 8, further characterized in that the thickness of the synthetic matrix fibers is approximately 3 to 20 denier. 11. The structure according to claim 10, further characterized in that the thickness of the synthetic matrix fibers is approximately 6 to 15 denier. 12. The structure according to claim 8, further characterized in that the synthetic matrix fibers are selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and mixtures thereof. 13. The structure according to claim 8, further characterized in that the latex is selected from the group consisting of an aqueous emulsion of ethylene / vinyl acetate, acrylic, styrene-butadiene or styrene-butadiene acrylic 14.- The structure of according to claim 8, further characterized in that the cellulose fibers of the liquid distribution layer and the liquid storage layer are the same or different, and are selected from the group consisting of wood cellulose, cotton fluff pulp, chemically modified cellulose, high purity cellulose fibers and mixtures thereof 15. The structure according to claim 8, further characterized in that the superabsorbent polymer particles are selected from the group consisting of polyacrylates, copolymers starch graft, interlaced carboxymethyl cellulose derivatives, hydrolyzed starch-acrylonitrile graft copolymers, saponified acrylic acid vinyl ester copolymers; polyvinyl alcohols intertwined, modified; polyacrylic acids intertwined, neutralized; interlaced polyacrylate salts, and carboxylated cellulose. 16. The structure according to claim 8, further characterized in that the superabsorbent polymer particles are surface interleaved. 17. The structure according to claim 8, further characterized in that the acquisition layer has a base weight scale of about 20 to about 80 gsm. 18. The structure according to claim 8, further characterized in that the distribution layer has a base weight scale of about 20 to about 100 gsm. 19. The structure according to claim 8, further characterized in that the storage layer has a base weight scale of about 60 to about 400 gsm 20 - An absorbent structure characterized in that it comprises: (i) an acquisition layer comprising matrix fibers of PET, joined with latex; said matrix fibers having an approximate length of 3 to 12 mm and a thickness of approximately 6 to 15 denier; wherein the acquisition layer has a base weight scale of approximately 20 to 60 gsm; (ii) a distribution layer of cellulose fibers; said fibers are thermally bonded or chemically modified, and wherein the distribution layer has a base weight scale of approximately 30 to 90 gsm; the distribution layer being in fluid communication with the acquisition layer; and (iii) a storage layer comprising cellulose fibers and superabsorbent polymer particles, wherein the fibers are thermally bonded and wherein the storage layer has a basis weight scale of about 70 to 130 gsm; the storage layer being in fluid communication with the distribution layer. 21. An absorbent structure, characterized in that it comprises: (i) an acquisition layer of PET matrix fibers bonded with latex; the matrix fibers having an approximate length of 3 to 12 mm and a thickness of approximately 6 to 15 denier; wherein the acquisition layer has a base weight scale of approximately 20 to 60 gsm; (ii) a distribution layer of cellulose fibers; said fibers 'are thermally bonded or chemically modified; and wherein the distribution layer has a base weight scale of from about 30 to about 100 gsm; the distribution layer being in fluid communication with the acquisition layer; and (iii) a storage layer comprising cellulose fibers and superabsorbent polymer particles, wherein the fibers are thermally bonded, and wherein the storage layer has a basis weight scale of approximately 250 to 350 gsm; the storage layer being in fluid communication with the distribution layer.