MXPA00000885A - Absorbent articles having a liquid swellable breathable backsheet - Google Patents

Abstract

The present invention relates to absorbent articles such as sanitary napkins and panty liners which are breathable by the incorporation of a breathable backsheet therein, and have a reduced tendency to exhibit garment wet through. The breathable backsheets comprise at least one moisture vapour permeable, apertured layer selected from wovens or apertured films comprising a nonsoluble, liquid swellable material such as polyvinyl alcohol, which upon contact with the fluid discharge the material swells. This causes the apertures of the layer to close and hence prevents the passage of liquid through the backsheet onto the garment of the wearer.

Description

ABSORBENT ARTICLES THAT HAVE A BREATHABLE BACK LEAF BLEEDING WITH THE LIQUID FIELD OF THE INVENTION The present invention relates to the provision of breathable backsheets for use in absorbent articles, which are activated when placed in contact with liquids and thus prevent rewetting of the garment.

BACKGROUND OF THE INVENTION The primary needs of the consumer which underlie development in the field of absorbent article, particularly catamenials, is the provision of products that provide both a high level of protection and comfort. A means to provide consumer comfort benefits in absorbent articles is by providing breathable products. The breathability is typically concentrated on the incorporation of the so-called "breathable backsheets" in the absorbent articles. The commonly used breathable backsheets are microporous films and films formed with apertures having directional transfer of the fluid as disclosed in, for example, U.S. Patent No. 4 591 523. Both of these types of breathable backsheets are permeable to water. steam allowing the exchange of gas with the environment. This thus allows the evaporation of a part of the stored fluid within the core and increases the circulation of air within the absorbent article. The latter is particularly beneficial since it reduces the sticky feeling experienced by many users during use, commonly associated with the presence of a film formed with openings or a film-like top sheet, particularly for a prolonged period of time. This is a result of the upper sheets designed to achieve a clean and dry appearance. These upper sheets tend to be smooth thus reducing the formation or agglomeration of the fluid on the surface of the upper sheet. However, these benefits are achieved at the expense of comfort, particularly under hot and humid conditions, when due to their smooth surface texture, they tend to be sticky to the skin. However, the main disadvantage associated with the use of breathable backsheets in the absorbent articles is the negative effect on the operation of the protection level, by means of leaks known as humidity through them on the garments of the users. Although breathable backsheets in principle only allow the transfer of materials in the gaseous state, physical mechanisms such as extrusion, diffusion and capillary action can still occur and result in the transfer of liquids from the absorbent core through the back sheet and on the clothes of the users. In particular, these mechanisms become more dominant if the product is used during physical exercise, or for heavy discharge charges or for extended periods of time. In this way, although the incorporation of breathable backsheets in the absorbent articles is highly desirable from the point of view of comfort, since the main role of a backsheet still remains in preventing leakage of liquids, these back sheets Breathable can not be incorporated satisfactorily into the products. The problem of rewetting on the users' garments due to the incorporation of said breathable backsheets into the absorbent articles has in fact also been recognized in the art. Attempts to solve the problem mainly reside in the use of multilayer backsheets such as those illustrated in U.S. Patent No. 4 341 216. Similarly, European Patent Number EPO 710 471 discloses a breathable back sheet comprising an outer layer of a gas permeable fibrous polymeric fabric, hydrophobic, and an inner layer comprising a film formed with openings having directional fluid transport. The construction of the backsheet preferably does not have liquid transport or rewet under certain specific test conditions. European patent 710 472 also discloses a breathable back sheet consisting of at least two breathable layers that are not bonded together over the core area. The construction of the backsheet preferably does not have liquid transport or rewet under certain specific test conditions. U.S. Patent No. 4 713 068 discloses a breathable fabric barrier to be used as an outer cover for absorbent articles. The barrier comprises at least two layers, a first layer having a specific basis weight, a specific fiber diameter and pore size, and a second layer comprising a continuous film of polyvinyl alcohol having a specific thickness. The barrier also has a specific transmission regime of water vapor and a level of impermeability. However, none of the previously proposed solutions have been able to provide a completely satisfactory solution for the problem of rewetting the breathable backsheet under all conditions. In addition, another problem associated with the backsheets of multiple layers exemplified is an increase in the total thickness of the product and a reduction in flexibility, both of which result in a reduction in the comfort of the product notable to the consumer.

A solution proposed alternately to the problem of the rewetting of the breathable backsheet is related to the improvements of the absorbent material in such a way that nothing or almost nothing of the liquid comes into contact with the backsheet, thus preventing rewetting. This is typically obtained by increasing the amount of absorbent material within the core. However, this results in an absorbent article which is extremely thick, which is highly undesirable from the consumer's point of view. Therefore, the absorbent article, while having the required level of protection and still maintaining some of the comfort benefits due to the presence of the breathable backsheet, suffers from a lack of comfort from a different source, in this case the Increased dimension of the article. In addition, the above solution also results in a reduction of the flexibility of the article, particularly evident as an increase in the stiffness of the cross section. However, it was also established that in order to be comfortable for the user the absorbent articles need to be flexible in a cross-sectional manner. It is believed that in the greatest flexibility in the cross section of an article is, the lesser will be noticeable to the user. In this way flexibility is another requirement of the highly desirable comfort of modern absorbent articles. European patent 705 583 and European patent 705 584 propose longitudinally flexible absorbent articles which are permeable to steam. However, the illustrated absorbent articles are typically very thin and do not direct the absorbency of the article or the rewet problem. U.S. Patent No. 5,447,788 discloses a porous non-woven barrier activated with liquid suitable for use in absorbent articles. The barrier includes a fibrous nonwoven web in which at least 50% of the fibers are prepared from a polymer capable of swelling with the liquid, which is not significantly soluble in water such as polyvinyl alcohols capable of to inflate. In the presence of water, the polymers swell to a sufficient extent to substantially block the passage of the liquid through the fibrous nonwoven web. However, from the data given in the patent, the passage of the liquids is not substantially blocked and in this way these plots do not eliminate the problem of rewet. Consequently, since the incorporation of the subsequent respirable sheets in the absorbent articles results in the reduction of the level of protection, the additional desirable modifications of the product comfort such as the reduction of the thickness of the product and the improvement of the flexibility of the product. product which would further the problem, can not be incorporated into the absorbent article. Therefore, there exists a dichotomy in the means available to provide the increased consumer comfort of absorbent products and acceptable levels of protection. It is therefore an object of the present invention to provide an absorbent article having improved comfort, by providing breathability throughout the absorbent article, which continues to maintain an acceptable level of protection. It has now been found that this object can be obtained by providing an article having a breathable backsheet which comprises at least one selected layer of woven materials or films with openings comprising a non-soluble material capable of swelling with the liquid. An advantage of the present invention is that the backsheet layer, when in the dry state, allows the transfer of wet steam and preferably both wet steam and air and, in its wet state after inflating, maintains at least a degree of vapor permeability while avoiding the transfer of liquids.BRIEF DESCRIPTION OF THE INVENTION The present invention relates to absorbent articles such as sanitary napkins and panty liners comprising a liquid-permeable top sheet, a backsheet and an absorbent core positioned between the top sheet and the back sheet, which may be breathable by incorporation of a breathable back sheet and, which has a reduced tendency to exhibit the rewet of the garment. The backsheet comprises at least one vapor permeable layer, preferably comprising openings, selected from woven materials or films with openings comprising from 10% to 100% by weight of said layer of a non-soluble material capable of swelling with liquid, such as polyvinyl alcohol. Upon contact with the discharge of liquid the material swells causing in this way that the openings of the layer are smaller and preferably close. In this way, the passage of the liquid through the backsheet onto the user's garment is avoided.

DETAILED DESCRIPTION OF THE INVENTION The absorbent article according to the present invention comprises as an essential component, a breathable backsheet. The backsheet typically extends through the entire absorbent structure and can extend into and form part of all or part of the side flaps, side wrapping elements or wings. The back sheet mainly prevents the exudates absorbed and contained within the absorbent structure from wetting the articles that come into contact with the absorbent product such as underpants, briefs, pajamas and undergarments thus acting as a barrier for fluid transport. . In addition, however, the breathable backsheet of the present invention when dry allows the transfer of at least water vapor and preferably both water vapor and air through it and thus allows circulation of the water. gases in and out of the back sheet. In addition, however, the backsheet also preferably continues to allow the transfer of water vapor through it after it has been wetted. In accordance with the present invention, the breathable backsheet comprises at least one layer selected from woven materials or apertured films. Said layer comprises from 10% to 100%, preferably from 25% to 100%, more preferably from 50% to 100%, most preferably from 75% to 100% by weight of said layer of the backsheet of a material capable of inflating with the liquid, insoluble in water. Surprisingly it has been found that the incorporation of the material into a woven layer or a film layer with openings allows the material to swell to such a limit that once the layer is contacted with liquid, the passage of the liquid through the layer is substantially obstructed. Although not bound by theory, it appears that the combination of incorporating materials capable of swelling in a woven layer or an apertured film is advantageous because the openings are distributed in a highly regular manner in all layers. In particular, it is believed that the very regular dimensions, geometrical shape and distribution of the regular and closed openings of these layers allows the layer to contract more efficiently, thus allowing the openings to close. As a result, the penetration of the liquid throughout the entire layer is avoided. This is in contrast to the situation when the material capable of inflating is provided in a non-woven material, where the fibers are in a random configuration. As a result, the random orientation of the fibers, the distribution of the openings as well as the size distribution of the openings are also randomly distributed and thus the closure of the openings is not complete. In accordance with the present invention, any known material that swells when in contact with the liquid is suitable for incorporation into the layer of the backsheet with openings. The term "bloat" as used here, refers to a material exhibits expansion when brought into contact with the liquid in at least one direction, i.e., in the transverse direction x, the longitudinal direction and or the vertical direction z, or a material that swells in any combination of said directions. The term "liquid" as used herein, refers to any fluid that contains at least 75% by weight of water, such as body fluids including urine, menstrual fluid and the like. The term "non-soluble" as used herein, refers to a material that is not significantly soluble at body temperature, such that it can be used for the desired function within the absorbent articles. According to the present invention, each layer or layers of the backsheet comprising the material capable of swelling, swell at least in the x, y or z direction. Typically, the most suitable materials are isotropic and in such a way that they swell in all three dimensions. According to the test methods described hereinafter, said material swells at least 100%, preferably at least 200% in the z-direction of the layer with apertures of the backsheet. However, swelling in the directions x and y is also desirable. The incorporation of at least one woven layer or a film layer with openings comprising a material capable of swelling in the breathable backsheet, allows the passage of water vapor and preferably both water vapor and air through it. . In this way, before being used and before being in contact with the liquid and while the backsheet remains dry, the absorbent article is always at least permeable to water vapor. After being in contact with the liquid, the material swells thus tending to close the openings of said layer of the backsheet. This thus prevents the passage of matter and macroscopic liquids through the backsheet and over the users' clothing. As a result of swelling of the layer, the air permeability of the layer and therefore the backsheet in general is reduced. Typically, the air permeability is negligible once the layer has been wet, which is indicative of the closure of the openings. However, an advantage of the present invention is that the passage of the water vapor is not significantly obstructed by the swelling action of the material upon contact with the liquids. Therefore, while air permeability is reduced, the backsheet and consequently the absorbent article remains still respirable even after contact with liquids. In addition, the structural integrity of the backsheet layer must be maintained after being in contact with the liquid. Obviously, areas of the layer that do not come into contact with the liquid during use of the absorbent article will maintain air permeability and wet vapor through them. Therefore, the layer is permeable to air and wet steam not only while it is dry, but also retains its permeability to air and moist steam wherever contact of the liquid with the layer does not occur. Preferred breathable layers for use as the backsheet here are those that have a high exchange of vapor and air when dry and which preferably maintain a degree of vapor permeability once they are wetted, while preventing air exchange. Therefore, according to the present invention, each layer of the backsheet comprising the material capable of swelling has a vapor permeability when dry of at least 500 g / (m2.24 hours), preferably at least 600 g / (m2.24 hours). According to a preferred embodiment of the present invention, each layer capable of inflating also has an air permeability when it is dry of at least 50 l / (m2.second), preferably at least 70 l / (m2.second). Less preferably, when the layer comprising the swelling material is in the form of a two-dimensional microporous film, in the dry state, this layer of the backsheet is only permeable to water vapor. In addition, each layer capable of inflating has an air permeability when it is wetted, as described here after the test methods, less than 10 l / (m2. Second), preferably less than 8 l / (m2.second). In addition, each layer capable of inflating has a vapor permeability after wetting as described in the test methods of more than 250 g / (m2.24 hours), preferably greater than 350 g / (m2.24 hours). In accordance with the present invention, suitable swelling materials for use herein include polymers such as polyvinyl alcohols having a hydrolysis level of at least 85%, preferably at least 95%, most preferably at least 98%. The polyvinyl alcohols are prepared by hydrolysis of the polyvinyl acetate. The term "hydrolysis level" as used herein refers to the percentage, in moles of substitution of the acetate groups by the hydroxyl groups. Other suitable materials that exhibit an ability to swell upon contact with the liquids for use herein include (as non-limiting examples) polymers such as crosslinked acrylic acid and its copolymers, especially in the form of total or partial alkali metal salts, alkaline earth metals as well as aluminum, zinc and iron salts, as well as poly (acidemethacrylic), polyacrylamide, poly (N, N-dimethylacrialamide) and polymethylacrylamide; crosslinked polyvinylpyrrolidone; polyvinylpyrrolidone copolymers, particularly those containing vinyl acetate; polymethyl, polyethylene or polybutylvinyl ethers also as polymers derived from vinyl ethers, for example, the copolymers of methyl vinyl ether and maleic anhydride or maleic acid; polyethylene oxide having a molecular weight of about 100,000 to 8,000,000 Daltons; polysaccharides (gums) of natural origin and their semi-synthetic derivatives such as alginic acid and its salts, agar, locust bean gum, Irish moss, gelatin, starch and cellulose derivatives, such as carboxymethyl cellulose and cellulose acetate, pectin, guar gum and xanthan gum; polyethylimine, polyacrolein; copolymers of maleic anhydride-styrene; styrene-maleic anhydride copolymers; polydimethyl aminoethyl methacrylate; polyalkene polyamines; poly (vinylbenzyl trimethylammonium chloride) as well as similar quaternary ammonium polymers; poly (maleic anhydride); lower molecular weight phenol-formaldehyde resin; urea formaldehyde resin of lower molecular weight also as compatible mixtures of said materials capable of swelling. According to the present invention, said layer may comprise a mixture of materials capable of swelling, which may exhibit different levels of swelling capacity with the liquid, in addition to other components unable to swell. The material capable of inflating, however, must be present at least 10% by weight of the layer and the swelling capacity of said layer must remain within the previously specified limits. Therefore, said breathable backsheet layer may further comprise up to 90% by weight, preferably up to 75%, more preferably up to 50% and most preferably up to 25% by weight, of said material layer of the component incapable of inflating. However, in the highly preferred embodiment of the present invention, the backsheet layer comprises 100% by weight of said layer of material capable of inflating. In such embodiments wherein the layer comprises other components besides the material capable of inflating, the material capable of inflating itself may be distributed throughout the layer in an orderly or random manner. Alternatively, the material capable of inflating can be distributed in discrete regions throughout the layer. Preferably, said swelling-able material is distributed homogeneously throughout the layer, more preferably in repetitive patterns, such as a longitudinal strips throughout the layer. Suitable materials of the component unable to swell to be used here can be naturally and synthetically derived and are selected depending on the manner in which the layer is to be provided. For example, embodiments wherein the layer capable of inflating the backsheet is provided in the form of a fibrous fabric, said layer may include non-inflating component materials such as, for example, nylon, polyester, cotton and other components. fibrous natural, synthetic or artificial. These materials can be intimately mixed with the fiber of the material capable of inflating itself and / or woven material together with the material capable of inflating. For embodiments wherein the layer capable of inflating the backsheet is in the form of an apertured film, suitable non-swelling components are polymers that are compatible with the swelling polymer. For example, the swelling layer comprising polyethylene oxide as the material capable of swelling, may further comprise poly-caprolactone. In addition to the traditional components of polymer films such as plasticizers and other minor common components of these films such as stabilizers (anti-oxidants, anti-UV), pigments, and mineral fillers, they can also be incorporated into the layer. For example for the modalities comprising polyvinyl alcohol as the material capable of inflating, suitable plasticizers include glycerol, glycols, polyglycols, trimethylol propane and triethanolamine. According to the present invention, the breathable backsheet comprises at least one layer comprising the material capable of inflating. Each layer comprising the swelling material such as polyvinyl alcohol can be provided in selected shapes from woven fibrous webs, two-dimensional microporous films, two-dimensional macroporous films, macroscopically expanded films, films with formed openings or any combination thereof. Preferably, at least one and most preferably all of the layers with openings capable of inflating the backsheet are selected from the films with macroporous openings or two-dimensional microporous films or a combination thereof. The construction of these layers themselves is described in greater detail here after the description related to the additional or optional layers of the backsheet which are not able to swell with the liquid. In accordance with one embodiment of the present invention, the swelling material can be formed into fibers prior to the production of the woven fibrous layer. Typically, the material capable of swelling and materials incapable of inflating in the fibrous form has an average fiber diameter of 5 microns to 300 microns, preferably 10 microns to 250 microns, most preferably 50 microns to 150 microns. The fiber preferably comprises at least 50% by weight, preferably at least 75% by weight, more preferably at least 90% by weight of the fiber of the material capable of inflating. According to an embodiment of the present invention wherein the material capable of swelling with the liquid is incorporated into a film formed with apertures or a two-dimensional porous film, the average pore diameter of such layers is preferably 0.5 microns to 1000 microns. The size of the openings will vary, however, depending on the type of layer used. According to the present invention, said backsheet comprises at least one layer comprising said material capable of swelling, not soluble. In addition, the backsheet may comprise additional, optional layers, which are not capable of swelling with liquid and therefore do not contain materials capable of swelling as defined herein. According to the present invention, said back sheet preferably comprises in total at least two layers and most preferably said back sheet consists of three layers. Additional layers of the backsheet may be in any form such as polymeric fabrics, nonwoven materials or films with openings such as two-dimensional, flat, micro and macro porous films, macroscopically expanded films and apertured polymeric films. In addition, said additional layers can be of any chemical nature, as described hereinafter and can be formed from synthetic or naturally derived sources or mixtures thereof. In accordance with the present invention, the additional layers incapable of inflating for use in the respirable backsheets here are layers that are permeable to moist vapor and more preferably both vapor permeable and to air. Suitable layers may be fibrous fabrics, nonwoven fibrous materials, films with openings or any of the blends and combinations thereof. Suitable vapor permeable layers include two-dimensional, flat, micro and macro porous films, macroscopically expanded films, and films formed with openings. According to the present invention, the openings in the backsheet layer may be of any configuration, but are preferably spherical or oblong, and may also be of varying dimensions. Typically, the openings have an average diameter of 5 microns to 600 microns. The flat two-dimensional porous films to be used as the layer in the present, can have openings that have diameters from 200 microns to 5 microns. The two-dimensional flat microporous layers for use as the layer herein have openings having average diameters of 150 microns to 5 microns, preferably 120 microns to 10 microns, most preferably 90 microns to 15 microns. The flat, two-dimensional macroporous layers have openings having an average diameter of 90 microns to 200 microns. The layers of macroscopically expanded film and the layers with formed openings have openings having an average diameter of 75 microns to 600 microns. However, for the layers of the backsheet comprising the material capable of inflating, the average diameter of the openings in the layer, as well as its distribution throughout the layer, which thus defines the open area of the layer is selected from according to the particular swelling material used and its ability to inflate and the amount and distribution of material in the layer. Therefore, in order to obtain high levels of air permeability while it is dry, the open area of the openings in the layer should be as large as possible, while ensuring that the air permeability will be significantly reduced by being in contact with the liquid. The openings are therefore preferably evenly distributed across the total surface of said layer, however, the layers having only certain regions of the surface having openings are also contemplated. The suitable two-dimensional flat layers of the backsheet can be made of any material known in the art, but are preferably made from commonly available polymeric materials. Suitable materials are, for example, XMP-1001 from Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, E.U.A. and Exxaire XBF-101W, supplied by Exxon Chemical Company. As used herein, the term "two-dimensional flat layer" refers to the layers having a depth of less than 1 mm, preferably less than 0.05 mm, wherein the openings have a uniform average diameter along their length and which does not protrude from the plane of the layer. Materials with openings for use as a backsheet in the present invention can be produced using any of the methods known in the art, such as described in EPO 293 482 and references herein.

Films formed with suitable apertures include films having discrete apertures, which extend beyond the horizontal plane of the garment facing surface of the layer toward the core, thereby forming a bulge. The protuberances have a hole located at their terminal end. Preferably, said protrusions are of a funnel shape, similar to those described in U.S. Patent No. 3,929,135. The openings located within the plane and the holes located at the terminal end of the protrusions themselves may be circular or noncircular, provided with the dimension or cross-sectional area of the hole at the termination of the protuberance that is smaller than the dimension or area in cross section of the opening located inside the surface that gives the clothing of the layer. Preferably, the preformed films with openings are unidirectional such that they have at least substantially, if not completely, a directional transport of fluid to the core. Macroscopically expanded films suitable for use herein include films as described in, for example, U.S. Patent No. 4,637,819 and U.S. Patent No. 4,591,523. Preferably, the material capable of inflating is incorporated. in at least one of the layers of the back sheet. In the multiple embodiments of the breathable backsheet where only one of the layers of the backsheet comprises the swelling material of the present invention, this layer should be placed towards the absorbent core, preferably in such a way that said layer does not Form the surface that gives the garment of the absorbent article. More preferably, said layer is positioned such that it is in direct contact with the absorbent core. According to a preferred embodiment of the present invention, the backsheet comprises at least two layers, a first layer comprising the material capable of inflating and a second layer comprising a polymeric layer which is not capable of inflating comprising a woven fibrous web, a fibrous non-woven web, a porous film with two-dimensional openings or a film with openings formed. According to a very preferred embodiment of the present invention, the backsheet consists of three layers, a first layer comprising the non-soluble material capable of inflating with liquid and a second and third layers comprising both components that are not capable of inflating, wherein the second layer comprises a polymeric film formed with openings and the third layer comprises a fibrous, polymeric nonwoven material. According to a preferred embodiment of the present invention, the breathable backsheet has in the dry state, both air permeability and water vapor at the levels defined hereinabove for the layers capable of inflating. More preferably, the breathable backsheet also satisfies the vapor permeability levels in the wet state. In accordance with the present invention, the absorbent articles further comprise a topsheet and an absorbent core. The absorbent material or core may be a foamed fibrous absorbent core, comprising hydrogel particles if desired, or laminated tissue with or without particulate materials including hydrogel particles. The fibers of the absorbent core can be any of those known in the art, including cellulose fibers or polymeric fibers made absorbent or even non-absorbent matrix fibers. Also the tissue of basic weight and sufficient absorbency can be used in the absorbent core according to the present invention. Another component that can be included within the absorbent articles of the present invention, particularly within the core are the odor control actives. Suitable assets include zeolites, silica, chelating agents such as ethylenediamine, tetraacetic acid, activated carbon and clays. These components can be incorporated in any form, but preferably as discrete particles. In accordance with the present invention, the topsheet may comprise a single layer or a multiplicity of layers. In a preferred embodiment, the top sheet comprises a first layer that provides the surface that gives the user of the top sheet and a second layer between the first layer and the diagonal absorbent core structure. The top sheet provides a layer through which the liquids that are absorbed penetrate into the absorbent material. The upper sheet as a whole and therefore each layer individually needs to be docile, soft feeling, and non-irritating to the wearer's skin. This can also have elastic characteristics that allow it to be stretched in one or two directions. Typically, the topsheet extends through the entire absorbent structure and can extend into and form part of all or the side flaps, side wrapping elements or preferred wings. In accordance with the present invention, the topsheet can be formed from any of the materials available for this purpose and known in the art, such as non-woven fabrics, films or combinations of both. In a preferred embodiment of the present invention, at least one of the layers of the topsheet comprises a hydrophobic, liquid-permeable, liquid-permeable, apertured film. Preferably, the top layer is provided by a film material having openings that are provided to facilitate the transport of liquid from the surface that gives the user to the absorbent structure, as detailed for example in U.S. Patent No. 3. 929 135, U.S. Patent No. 4,115,240, U.S. Patent No. 4,319,868, U.S. Patent No. 4,324,466, U.S. Patent No. 4,343,144, and U.S. Patent No. 4 591 523.

In accordance with the present invention, the absorbent article is constructed by joining the various elements such as the topsheet, the backsheet and the absorbent core by any means well known in the art. For example, the backsheet and / or the topsheet may be attached to the absorbent core or to each other by a uniform, continuous adhesive layer, a patterned adhesive layer, or an array of separate lines, coils, or spots of adhesive. Alternatively, the elements may be joined by heat bonds, pressure joints, ultrasonic joints, dynamic-mechanical joints or any other suitable joining means known in the art and any combination thereof. Preferably the individual breathable backsheet layers are bonded together to reduce and preferably eliminate any reduction in vapor permeability of the backsheet. Similarly, the breathable backsheet itself is bonded to other elements of the absorbent articles to minimize the effect of wet vapor permeability of the backsheet. In accordance with the present invention, the absorbent article may find utility such as sanitary napkins, panty liners, adult incontinence products and baby diapers, but may also include other items such as armpit pads or collar bands. The present invention finds particular susceptibility as sanitary napkins and liners for panties. Thus, in addition to the components described hereinbefore, the absorbent article may also comprise all those characteristics and parts that are typical for the products within the context of the intended use such as wings and side flaps, adhesive means for the undergarment, paper of detachment, wrapping elements, fastening means and the like, all known in the art.

EXAMPLES Examples of the Backfast Capable of Inflating: Films with apertures capable of swelling with liquid, for use in a construction of the breathable backsheet according to the present invention, were prepared from commercially available polyvinyl alcohol films. available following: Example 1: "Aquafilm hot water" available from Aquafilm Ltd., United Kingdom.

Example 2: "Ekosol type C60 ° C", available from Ekomer Srl, Italy.

Example 3: "Ekosol type C80 ° C", available from Ekomer Srl, Italy.

Previous films were punched using a steel needle puncher. The perforator consists of steel needles that have rectangular dimensions of 530 microns per 350 microns and a height of 4 mm. The steel needles are arranged in a grid formation such that the distance between the center of any two adjacent rectangular bases of the needle is 5 mm.

Dry samples v Wet The term dry as used herein refers to a sample material stored at 23 ° C and 50% relative humidity for at least 12 hours. The test is also performed under these conditions. The term "wet" as used herein refers to a sample material that has been uniformly contacted with 10 cm3 of distilled water at 37 ° C with a pipette. Excess water is removed by pressing gently with blotting paper. The sample is allowed to remain for at least 60 seconds before the test is carried out, the test being performed within 10 minutes after being in contact with the water.

Test of air permeability in individual layers capable of inflating from a breathable back sheet The air permeability test is used to determine the ability of a material to circulate / exchange air.

Basic Principle of the Method The basic principle of the test is to evaluate the resistance of the material to the passage of air. This test measures the volume (or amount) of air flowing through a sample of given dimensions under standard conditions (23 ° C / 50% relative humidity) and under a given pressure difference. The instrument used for the test is: the air permeability meter FX 3300 manufactured by Tex Test Ag, Switzerland. 100 mm square of wet and dry samples are prepared as described in order to perform air permeability measurements. The sample is placed on the device according to the manufacturer's instructions. A suction pump is used to generate a 1210 Pa depression that sucks air through the sample layer. The device measures the volume of the air flow at a constant pressure drop through the holes contained in the sample and the measuring head. Finally, the device generates a value of air permeability in units of "1 / (m2s)". For each material, in the dry state and in the wet state, six samples are measured and the average value of the air permeability is calculated.

Results The air permeability of the layers with openings capable of inflating are given below: Dry Inflatable Layer (l / m7s) Wet (l / m / s) Example 1 72 Zero Example 2 116 Zero Example 3 105 6 From the above results it can be clearly seen that the exemplified layer of the backsheet of the present invention has negligible air permeability after being in contact with the liquid.

Tests of Water Vapor Permeability in Individual Layers Capable of Bloating the Posterior Blade The Steam Permeability test is used to quantify the vapor transmission properties of the breathable backsheet layers.

Basic Principle of the Method The basic principle of the test is to quantify the limit of the transmission of water vapor from a material. The test method that is applied is based on a standardized test method applied in the textile industry and commonly referred to as the Vertical Cup Test Method. The test is performed in a stable temperature / humidity laboratory maintained at a temperature of 20 ° C to 50% RH for a period of 24 hours.

Apparatus: 1) Sample cup (open area = 0.00059 m2) 2) Syringe to introduce distilled water into the entire sample cup. 3) Wax to seal the cup once the sample has been accommodated. 4) A circular punch to facilitate the preparation of circular samples of diameter = 30 mm. 5) Laboratory of stable climatic conditions (23 ° C ± 0.5 ° C / HR = 50% ± 1% RH) 6) Accuracy of the laboratory balance to 4 decimal places.

Preparation of the sample / Measurements: The test can be carried out on the individual layer capable of inflating from which a sample is cut to size using the punch. The cut sample is large enough to adequately overlap the sample holder and ensure that material that may have been damaged or stretched undesirably due to the cutting operation is located outside the measurement center when the measurement is made. The sample is accommodated in such a way on the sample cup to completely overlap the cup.

The closing ring of the sample cup is then placed on the sample and pushed down. This ensures that the excess material is held firmly in place and does not interfere with the measurement. A molten wax is then applied to the entire surface of the closure ring to ensure that the entire upper part of the apparatus is closed to the environment. Distilled water (5 ± 0.25 ml) is introduced with a syringe into the sealed sample cup through a tiny perforation. Finally, this perforation is sealed with silicone grease. The total cup (which contains the sample and water) is heavy and the weight is recorded up to four decimal places. The cup is then placed in a ventilation current generated by a fan. The air fluid on the top of the sample cup is 3 ± 0.3 m / second and is confimed by a wind speed meter ("Anemo", supplied by Deuta SpA, Italy). The sample cup remains in the ventilated test field for a period of 24 hours and is reweighed once per hour for the first 6 hours and at the end of the 24 hour period. During this period if the test sample is sufficiently breathable, the liquid in the sample holder is able to diffuse out of the sample holder and into the laboratory environment. This results in a reduction in the weight of water within the sample holder that can be quantified by reweighing the entire sample cup following the 24 hour period. The value of vapor permeability is determined as the weight loss divided by the open area of the sample holder and cited per day. that is, Steam Permeability = Weight Loss (g) / (0.00059 m2 / 24 hours) The water vapor permeability of the test samples is determined in the same manner, using the samples that have been wetted as described hereinabove. The material is then sealed in the sample cup and the test is started within 10 minutes. For each material, in the dry state and in the wet state, six samples are measured and the average value of the water vapor permeability is calculated. It should be noted that at the beginning of the water vapor permeability test with the wet samples, an unstable state situation will initially be observed. This is due to the fact that the samples lose part of their moisture, that is, the liquid added in order to produce a wet sample, to the surrounding environment. However, this "unstable" state is relatively short and, according to the observations, the loss of weight due to moisture becomes linear (in such a way that the sample is in equilibrium with the system). Therefore, the only exchange of water vapor is the permeation of water through the vapor sample derived from the inside of the cup in no more than one hour. Consequently, it is necessary when registering the weights as described here, only take into account water vapor permeability measurements that demonstrate a progressive linear weight loss of the test cup against time, within the time period 24 hours Results Examples of Inflatable Layer Water Vapor Permeability [g / (m2.24 hours) Dry Wet Example 1 638 481 Example 2 777 378 Example 3 767 558 From the above results, it can be concluded that layers with openings capable of inflating they retain a substantial degree of water vapor permeability after being in contact with the liquid, during which the swelling and closing of the openings occur. It is believed that this is linked to the considerable hydrophilic capacity of the swelling-capable materials according to the present invention, which leads to a diffusion of high water vapor towards and through the layers, even in the absence of physical openings .

Swelling test The capacity of the material to be inflated was measured by determining the caliber of the test sample of a layer in the dry and wet state. This determines the swelling in the z direction. A square sample of 100 mm in size of the layer to be tested, is prepared for gauge (thickness) measurement in the dry and wet state. The calibres of the samples are measured using a thickness measuring device App. 51 D20, type 02101, supplied by Lorentzen & Wettre, Sweden, and following the supplier's instructions. The thickness measuring device registers the caliber of the pressed sample between two measuring plates, when the pressure exerted reaches 20 g / cm2. The average of the three caliber readings of each sample is taken. Five samples for each material are tested and the value is the average value of these readings.

Inflatable Film Dry Calibration (mm) Calibration in Wet% Swelling (mm) Delta in Z Direction Example 1 40 130 225 Example 2 50 160 220 Example 3 80 190 137 From the above values, it can be seen that the example layers exhibit a high degree of swelling such that the size of the wet samples is 200% to 300% greater than the size of the corresponding dry samples, even after a contact time of liquid with water of only 60 seconds. It is believed that this high swelling coefficient accounts for the ability and effectiveness of these materials in the layers of the backsheet of the present invention to quickly close the openings in the layers and thus reduce air permeability. Example 3 although it still exhibits a high degree of swelling does not swell to the same degree as Examples 1 and 2. It is believed that this behavior may be related to the characteristics of the polyvinyl alcohol itself and in particular to the high strength of this alcohol layer polyvinyl to dissolve even at a water temperature of 80 ° C. This high resistance to dissolution is thus also associated with a greater resistance to plasticization by water at lower temperatures. Consequently, the polyvinyl alcohols will exhibit reduced swelling capacity under the test conditions.

Claims (10)

1. An absorbent article comprising a liquid permeable top sheet, a back sheet and an absorbent core, said core positioned between the top sheet and the back sheet, wherein said back sheet is breathable, and wherein the back sheet comprises at least a selected layer of a woven material or a film with openings and said layer comprises from 10% to 100% of a non-soluble material, capable of swelling with the liquid.

2. An absorbent article according to claim 1, wherein said layer of the backsheet has a swelling of at least 100% in a direction as defined in the swelling test.

3. An absorbent article according to claim 1, wherein said material capable of inflating is a polyvinyl alcohol.

4. An absorbent article according to claim 3, wherein said polyvinyl alcohol has a hydrolysis level of at least 85%, preferably at least 98%.

An absorbent article according to any of the preceding claims, wherein said backsheet layer has an air permeability when dry of at least 50 l / (m2s) and an air permeability when wetted less than 10 l / (m2s) as defined in the air permeability test.

An absorbent article according to any of the preceding claims, wherein said backsheet layer, when dry has a water vapor permeability of at least 500 g / (m2.24 hours), as defined in the vapor permeability test.

7. An absorbent article according to any of the preceding claims, wherein said layer of the backsheet, when wet, has a water vapor permeability of more than 250 g / (m2.24 hours), as defined in the test of vapor permeability.

An absorbent article according to any of the preceding claims, wherein said layer is selected from a woven fibrous web, a two-dimensional microporous apertured film, or a two-dimensional macroporous apertured film, wherein said layer has a diameter average opening from 5 microns to 600 microns.

An absorbent article according to any of the preceding claims, wherein the backsheet comprises at least two layers, a first layer comprising the material capable of inflating with the liquid and a second layer which is not capable of inflating with liquid comprising a fibrous woven material, a fibrous nonwoven material, a porous film with openings, two dimensions, or a film formed with openings.

10. An absorbent article according to any of the preceding claims, wherein the backsheet consists of three layers, a first layer comprising the material capable of inflating with the liquid, a second layer that is not capable of inflating with liquid comprising a film formed with openings, and a third layer that is not capable of inflating with liquid comprising a fibrous nonwoven material.