MXPA99004366A - Absorbent structure for use in an absorbent article - Google Patents

Abstract

The invention relates to an absorbent structure for use in an absorbent article such as a diaper, an incontinence guard, a sanitary napkin, or the like wherein the absorbent structure comprises two different material types (16, 17, 18) which are in direct or indirect contact with each other so that liquid can be transferred between the material types. The first material type (17) is constituted by material which swells when absorbing body fluid and the second material type (16, 18) is constituted by material which collapses when absorbing body fluid, wherein the volume increase in the first material type (17) is essentially equal to the volume reduction in the second material type (16, 18) when the absorbent structure is saturated with liquid, whereby the absorbent structure has substantially the same volume both in a wet and in a dry state.

Description

"ABSORBENT STRUCTURE FOR USE IN AN 'ABSORBENT ARTICLE" TECHNICAL FIELD The invention relates to an absorbent structure intended for use in an absorbent article, such as a sanitary napkin, a diaper or an incontinence protector, whereby the absorbent structure comprises two different types of material which remain in direct or indirect contact with the absorbent structure. so that the liquid can be transferred between the types of material.

BACKGROUND OF THE INVENTION When manufacturing an absorbent article of the aforementioned kind, it is often desirable to be able to provide the article with a three dimensional shape that is adapted to the anatomy of the wearer of the article. Designing an absorbent article so as to follow and conform to the shape of the wearer's body will be achieved, namely, a number of advantages such as increased comfort for the wearer, increased escape safety and improved discretion, i.e. the item can be hidden more easily under the wearer's clothing.

One obvious difficulty with regard to the configuration of an absorbent article, however, is that the shape of the article changes during use. The deformation is particularly evident after moistening the article. Cellulose fluff paste is an absorbent material that is often used in absorbent articles. The cellulose fluff paste is a comparatively inexpensive, easily obtainable material which, for example, by means of air placement can be used relatively easily in order to provide an absorbent article with the desired shape. A considerable disadvantage with the cellulose fluff paste is, however, that the material collapses when it becomes wet and loses its original shape. An absorbent article with an absorbent structure made of cellulose fluff paste will consequently only maintain an original three-dimensional shape in an initial stage, before the article has absorbed the fluid from the body. Another disadvantage with the absorbent structures consisting of cellulose fluff paste is that they have a reduced volume after being wetted. This implies that the structure of the fiber within the wet region has thinner capillaries than the surrounding dry fiber material. Therefore, the liquid distribution in the absorbent structure is counteracted so that the liquid for the most part remains in the initially wetted region of the structure. This region, therefore, quickly saturates with liquid and is therefore unable to absorb additional liquid that is emitted to the absorbent structure. As a result, there is a large risk that the liquid, instead of penetrating the absorbent structure, will flow out through the surface of the absorbent article and cause leakage. The problem with the insufficient permanence of the absorbent articles is particularly evident in relation to sanitary napkins and other absorbent articles which have a proportionally small size and which are intended for use within a pair of ordinary panties. Since these items are necessarily quite narrow, the escape of fluid from the body outwardly beyond the longitudinal lateral edges of the article is not a problem considered to be non-typical. This escape is of course highly undesirable since it involves the risk of soiling the wearer's clothing. Due to the rather short extension of the article in the longitudinal direction, it is also not usual for the liquid to also escape back and forth, beyond the end edges of the article. The backward escape is a specific problem that, as a general rule, arises when the user is lying down, for example, during the night. One way to reduce the risk of shore escape caused by deformation of the article during use, is to provide the item with a preformed hump that, during use, is intended to be in contact with the user's genitals. In this way, the excreted body fluid can be retained as soon as it exits the wearer's body, and immediately absorbed into the article without flowing outwardly above the surface thereof. The previously known absorbent articles provided with a liquid receiving hump, however, suffer from a number of disadvantages. A common way to create a hump has been to simply build it by placing a larger amount of the absorbent material within the region of the hump. Since the most commonly used absorbent material is cellulose fluff paste, this hump is crushed and loses its shape when wetted. In order to obtain a hump that is also large enough in the wet state, a hump consisting of cellulose fluff paste has to comprise such a large amount of absorbent material that it becomes too high, hard and uncomfortable to be used in a dry state.

In order to solve the problem with hard and uncomfortable large humps, it has been suggested in Patent Number EP 0 339 041 to provide the liquid impervious surface of the article with transverse elastic members. These elastic members impart a certain resilience to the article in case it is subjected to flattening. However, the elastic members do not prevent to a considerable degree that the hump is compressed and change shape during use. In another publication, Patent Number 0 419 434, it has been suggested to create a soft hump in an absorbent article by closing the lateral edges of the article at a mutual distance that is smaller than the plar.7 distance. between the lateral edges. However, this known article does not retain its shape during use either. In Patent Number 0 335 252 and Patent Number 0 335 253 it has been suggested to provide an absorbent article with a deformation element. The deformation element is influenced by the transverse compression forces between the thighs of a user. The object of the deformation element is that, during use, it can create a sag in a portion of the article in a direction towards the body of the wearer. However, it is impossible to completely control or predict the form that the article will adopt for each individual user. Furthermore, it is not possible to ensure contact between the body and the user and the surface of the article, since the degree of cambering is determined completely by how many items are compressed in the transverse direction. Accordingly, a need remains for an exhaust-proof absorbent article having a predictable shape, both before and during use, and which maintains its shape independently of the wetness to which the article is subjected. An article designed according to the invention and of the type mentioned in the introduction, is characterized mainly because the first type of material is constituted by a material that swells when it absorbs body fluid, which collapses when it absorbs body fluid by which the increase in volume in the first type of material is essentially as great as the reduction in volume in the second type of material when the absorbent structure is saturated with liquid, whereby the absorbent structure has essentially the same volume in both a wet state as in a dry state. Ensuring that the volume of the absorbent structure is practically constant, regardless of whether the structure is dry or wet, in accordance with the invention it is possible to provide absorbent articles with very good permanence.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in greater detail with reference to the figures shown in the accompanying drawings. Therefore: Figure 1 shows a plan view of a sanitary napkin according to the invention, which is seen from the side facing the wearer during use, Figure 2 shows a section along the line II-II through of the sanitary napkin of Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The sanitary napkin 1, shown in Figures 1 and 2, comprises a liquid-permeable cover layer 2, placed on the side of the sanitary napkin 1 which during use is intended to be oriented towards the wearer. The liquid-permeable cover layer 2 suitably consists of a soft, skin-friendly material. Examples of useful liquid-permeable cover materials are the different types of non-woven fiber fabrics, the so-called non-woven materials. Other liquid-permeable cover materials are perforated plastic films, cambric, knitted textiles, hooked fabrics or plain woven fabrics, and combinations and laminates of the types of materials listed. The sanitary napkin 1 also comprises a layer 3 of waterproof cover placed on the side of the sanitary towel 1 which during use is intended to be oriented away from the wearer. Usually, a thin plastic film is used as a cover 3 of the liquid impervious cover. It is also possible to use layers of liquid-permeable material that are coated with a liquid-impermeable material. Other treatments, such as thermo-calendering to melt a liquid-permeable material initially in an essentially liquid-impermeable layer, can also be used. In addition, it is possible to use nonwoven or other fabrics that are sufficiently dense and the fibers of which are sufficiently hydrophobic so that they can serve as a barrier layer to the liquid. The two cover layers 2, 3 mutually interconnect around an absorbent body 4 and form a projecting connecting line 5 around the periphery of the sanitary napkin. The connection between the cover layers 2, 3 can be achieved using any technique appropriate to the object, such as gumming, welding or sewing. The sanitary napkin 1 has a trapezoidal shape with a wider frontal portion 6, a narrower posterior portion 7 and an intermediate central portion 8. In addition, the sanitary towel 1 has two oblique lateral edges 9, 10 extending between two end edges 11, 12 almost straight. An adhesive fixing member 13 is positioned as three rubber strips extending in the longitudinal direction of the sanitary napkin 1, in the liquid-impermeable cover layer 3. An elongated hump 15 is positioned centrally in the longitudinal direction of the sanitary towel 1. The hump 15 is wider in the central portion 8 of the sanitary napkin and tapers in a direction towards the front and rear portions 6, 7. Furthermore, it is convenient if the hump 15 is profiled in the longitudinal direction so that it is higher in the central portion 8 and gradually decreases in height in a direction towards the end portions 6, 7. The hump 15 constitutes a part of the absorbent body 4 and is made up of three parts of the absorbent material by means of which a first part 16, placed immediately inside the liquid-permeable cover layer 2 consists of an absorbent material which - - It is crushed during wetting. In the inner ring of the first part 16, seen in the direction from the liquid-permeable cover layer 2, a second part 17 is provided consisting of absorbent material which swells when wetted. Finally, a third part 18, consisting of absorbent material that collapses when wetted, is placed on the inner side of the second part 17, between the second part and an absorbent layer 19 that forms part of the absorbent body 4. Naturally, it is conceivable within the scope of the invention that the hump 15 is constituted by only two parts, whereby one is crushed when it is wetted and the other swells when it is wetted. Also, the absorbent structure in the hump 15 may optionally be constituted by a plurality of layers of material consisting alternately of swelling and crushing materials. In a hump 15 constituted by the layers with alternative properties, the absorbent structure can advantageously be placed so that the layers are placed erect, essentially perpendicular to the absorbent layer 19 placed on the inner side of the hump 15. In this way, a simultaneous wetting of both the swelling and crushing material is achieved, which implies that the shape stability of the hump 15 becomes especially good. The absorbent layer 19 primarily constitutes a security zone around the central hump 15. Second, it serves as an extra absorption capacity that can be used if the absorbent material in the hump 15 is saturated by unexpectedly large amounts of liquid. Also, the absorbent layer 19 contributes to providing the sanitary towel 1 with a flat extension so that the sanitary towel 1 can be fixed within a pair of panties by means of the fixing member 13, placed in the waterproof cover layer 3 liquid. The first part 16 of the hump 15, for example, may consist of one or several layers of latex-bound paper material placed in the air with a low density cellulose film paste, layers of tissue paper, cotton, rayon or materials similar. What is required is that the material in the first part 16 is crushed when it is moistened, so that the volume and thickness of the first part 16 are reduced. A material suitable for the second part 17 that is placed between the first part 16 and the third part 18 is the absorbent material disclosed in Patent Number WO 94/10956. This material is a dry-formed fiber layer with high density and stiffness that is used directly in the absorbent article without first being dreaded. Another useful similar material with properties especially suitable for blood absorption purposes is disclosed in Patent Number WO 94/10953. The materials disclosed in Patent Number WO 94/10956 and Number WO 94/10953 Number have very good absorption capacity and swell in the thickness direction when they absorb liquid. Another useful category of absorbent materials with the ability to swell during absorption is called superabsorbent. The superabsorbent materials refer to polymers that are present in the form of fibers, flakes, particles, granular materials or the like, and which can absorb several times their own weight of body fluid during swelling and the formation of a gel. The superabsorbent material can be applied as a non-bonded layer between the first part 16 and the third part 18, or be bound or bound in a fiber structure. The second part 17 may be constituted by a homogeneous body or may consist of two or more layers of the swelling absorbent material. The third part 18 on the hump 15, as well as the first part 16, consist of absorbent material that is crushed during; the wetting. Suitable absorbent materials are those that are listed in relation to the first part 16.

TESTING METHOD In order to determine if an absorbent material collapses or swells during the absorption of liquid, the height of a material sample was measured before and after wetting, under two different loads. Procedure: The cylindrical samples of the tested absorbent material with a diameter of 50 millimeters were punched. A sample remaining in one of circular surfaces was placed in a container with a perforated base, after which the upper surface of the sample, ie, the second circular surface was loaded with a dumbbell. The height of the cylindrical sample was measured and recorded. Then, the sample is allowed to absorb the synthetic menstrual fluid from below by lowering the container with the perforated base towards a liquid container, and keeping the perforated base below the level of liquid in the container until the liquid is detected in the container. the upper surface of the sample. The height of the sample is measured and once it is recorded.

Example 1 Five samples, each consisting of four layers of one and the same absorbent material, were drilled for two different types of material: a) and b) Material type a) was a latex-bound cellulose fiber material, placed to the air with a basic weight of 80 grams per square meter, a layer thickness of 1.18 millimeters and a density of 68 grams per cubic meter. These materials are commercially provided by a number of different suppliers. Material type b) was an unbonded dry-formed cellulose fiber material of the type disclosed in Patent Number WO 94/10953 and Patent Number WO 94/10956. These materials have high density and rigidity and are used directly in an absorbent article, without previous defibration. In the present example, the basic weight of the material was 350 grams per square meter, the thickness of the layer was 0.9 millimeters and the density was 390 grams per square cubic meter. The measurements of the height of the sample were carried out at a load of 500 grams, and with a load of 150 grams. Both types of material (a) and b) were tested in a wet state and a dry state, respectively. The results of the measurements are shown in Diagram 1. 500g I50g 500g 50g Diagram 1 As is evident from diagram 1, material type a) is less stressed under a lower load than under a higher load. Correspondingly, the expansion of material type b) is slightly smaller when the sample is loaded with the larger weight, inter alia, this implies that in the absorbent body containing both type; of material a) and type of material b), the type of material b) during the expansion, to a certain degree., displaces the type of material a).

Example 2 Seven different samples consisting of different combinations of material type a) and material type b) were prepared as follows: I: - 6 layers a) 1 layer b), 6 layers a) II: 5 layers a) 1 layer b), 5 layers a) III: 4 layers a) 1 layer b), 4 layers a) IV: 3 layers a) 1 layer b), 3 layers a) V: 3 layers a) 1 layer b), 2 layers a) VI: 2 layers a) 1 layer b), 2 layers a) VII: 2 layers a) 1 layer b ), 6 layer a) The height in millimeters for the different samples I to VII were recorded both in the wet state and in the dry state, under a load of 500 grams. The results of the measurements can be derived from Diagram 2.

Diagram 2 The combinations of the material in Examples V and II-I were tested under a load of 500 grams and under a load of 150 grams. The results of the measurements can be found in Diagram 3.

Dry, etc. to Wet, etc. 500g 150g 500g 150g Diagram 3 By carrying out the measurements in accordance with the aforementioned examples, the properties of the absorbent materials in different ways can be evaluated with respect to whether the materials swell or expand during wetting. Based on the measurements, it is then possible to design absorbent structures that have essentially the same volume in both the wet state and the dry state. When designing absorbent structures intended for use in diapers or incontinence guards, it is convenient to use synthetic urine as a test liquid. Combinations of material that have been found to work well for the object are those in which the height of the absorbent structure in a dry state constitutes between about 110 percent and 90 percent of the height in the wet state. The invention should not be construed as being limited to the examples and embodiments mentioned herein, instead a number of further variants and modifications are conceivable within the scope of the appended claims. In addition, all conceivable combinations of the described embodiments are intended to be encompassed by the invention.

Claims (8)

R E I V I N D I C A C I O N S

1. The absorbent structure for use in an absorbent article such as a diaper, or an incontinence protector, a sanitary napkin or the like, wherein the absorbent structure comprises two different types of material (16, 17, 18) that remain in direct contact and indirectly with each other so that the liquid can be transferred between the types of material, characterized in that the first type of material (17) is constituted by a material that swells when absorbing body fluid, and the second type of material. material (16, 18) is constituted by a material that collapses when absorbing body fluid, wherein the volume increase in the first type of material (17) is essentially equal to the volume reduction in the second type of material (16, 18) when the absorbent structure is saturated with liquid whereby the absorbent structure has essentially the same volume in both the wet state and the dry state. The absorbent article according to claim 1, characterized in that the volume of the absorbent structure in a dry state constitutes between approximately 110 percent and 90 percent of the volume in a wet state. 3. The absorbent structure according to claim 1 or 2, characterized in that it is formed by at least two layers of material (16, 17, 18), whereby a first layer of the material consists mainly of the first type of material, that a second layer of material consists mainly of the second type of material. 4. The absorbent structure according to claim 1 or 2, characterized in that it consists mainly of a mixture of absorbent material of the first type of material and the material of the second type of material. 5. An absorbent article intended for female users such as a sanitary napkin, a panty liner or an incontinence protector, with a shape and size such that it can be essentially accommodated in the mid-leg region of a pair of panties and having a longitudinal direction, a transverse direction and a thickness direction, wherein the article exhibits a liquid-permeable cover layer (2) and a liquid-impermeable cover layer (3), and the absorbent body (4) placed between the two cover layers (2, 3), and where a hump (15) is placed in the liquid permeable cover layer (2) of the article, characterized in that the hump (15) comprises absorbent material of a first type of material (17), the absorbent material of a second type of material (16, 18), wherein the first type of material (17) is constituted by the material that swells when absorbing body fluid and the second type of material (17). material po (16, 18) is constituted by the material that collapses when absorbing body fluid, wherein the volume increase in the first type of material (17) is essentially equal to the volume reduction in the second type of material (16, 18) when the hump (15) is saturated with liquid, whereby the hump (15) has essentially the same volume both in the wet state and in the dry state. The absorbent article according to claim 5, characterized in that the hump is formed by a layered structure exhibiting layers of the first type of material (17) and layers of the second type of material (16, 18). The absorbent article according to claim 6, characterized in that the layers (16, 17, 18) are placed parallel to the thickness direction of the article, essentially perpendicularly between the liquid-permeable cover layer (2) of the article. article and the waterproof cover layer (3). The absorbent article according to claim 6, characterized in that the layers (16, 17, 18) are stacked one on top of the other parallel to the liquid-permeable cover layer (2).