A METHOD TO PRODUCE AN ABSORBENT STRUCTURE. WHICH INCLUDES A SUPERABSORBENT MATERIAL COVER
BACKGROUND The present invention relates to a method for producing an absorbent structure, for use in an absorbent article, such as a sanitary napkin, an incontinence protector, diapers and similar articles. Many different types of absorbent articles of this kind are known in the art. The absorbent body of these articles is conventionally produced by dry-pulping cellulose pulp, contained, for example, in spools, bales or leaves, and converting this cellulose pulp, in a foamed state, to a pulp mat, sometimes while It is mixed with materials named superabsorbents, in the pulp mat, these superabsorbent materials are polymers capable of absorbing many times their own weight of a liquid or body fluid. EP 0,122,042 discloses a method for manufacturing an absorbent structure, which includes superabsorbent material. The cellulose pulp is first defibrated to form cellulose fibers, the so-called sponge pulp, then a mixture of these fibers and water-insoluble hydrogel particles are spread to the air to form a band from which the structure is formed. absorbent and then compressed to a density of 0.15 to 1.0 g / cm3. The body of the pulp is compressed with the intention of reducing its volume and also with the intention of increasing its properties of absorbing liquids by capillarity. With most sanitary products, a thin article is convenient, so that this article can be used as discreetly as possible. The superabsorbent material is normally used in the form of granules or small particles. It has been found difficult to successfully bond these small particles in the absorbent structure, which is a problem associated with the use of the superabsorbent material. The method described, for example, in EP 0122,042, involves the risk that the superabsorbent material extends into and around the manufacturing plant, and also involves the risk that the particles of the superabsorbent material escape from the core of the product. the finished pulp, when this core is packed, transported or used. When manufacturing products that include the superabsorbent material, the aforementioned problems become greater with the thinner products. The superabsorbent particles, often, have sharp edges and are, therefore, often capable of perforating the sheets impervious to the liquid of the absorbent articles, unless preventive measures are taken. It is also important to obtain the intimate contact between fibers and the superabsorbent material, in order to achieve the effective transfer of the liquid between the two materials. Also, the absorbent body may include other ingredients that attempt, for example, to improve the ability to take or disperse the liquid, or increase its coherence and its ability to resist deformation while being used. A very large part of the production plant used in the manufacture of sanitary articles, mentioned above, is comprised of the shredder equipment, pneumatic transport systems and equipment forming mats. This production plant is often followed by the equipment to compress the finished pulp mat or the finished sanitary product. It is known from US-A 3,017,304 that a surface layer containing paper bonds can be obtained and that it has a higher density and a higher strength compared to the original cellulose pulp mat, by spraying water onto a pulp mat. cellulose and then compressing this mat. Such a layer is sometimes called a "Burgeni layer". It is also known from US Pat. No. 4,186,165 to compress a cellulose pulp mat containing superabsorbent material, with the help of heated rollers and without adding water, and this is obtained with an internal layer in the cellulose pulp mat, which has a greater density and a greater strength than in the mat of the original pulp. The particles of the superabsorbent material are bonded to the structure in this layer, and the layer can also be obtained at a desired level in the structure, by varying the temperature difference between the rollers. However, when practicing this method, the particles of the superabsorbent material which are present in the remaining parts of the pulp mat, remain only loosely bound in the structure. It is also not possible with this method to obtain a structure in which only a layer containing the superabsorbent material and where this layer is surrounded by one or more layers that are free of such material, which is convenient in some applications of the product. SUMMARY OF THE INVENTION An object of the present invention is to provide a thin absorbent structure, which includes a layer containing superabsorbent material and which can be included in an absorbent article of the kind defined in the introduction. The absorbent structure will exhibit very good absorption properties and it will be possible to produce the structure without spreading the superabsorbent material around the manufacturing plant, during the production process, or without the superabsorbent material escaping from the finished absorbent article, when it is packaged, transported or use the article. This object is achieved by means of the present invention, in which the absorbent structure is produced by placing a layer containing essentially the superabsorbent material between two layers of defibrated and moistened cellulose pulp or fabric, and then to satin the composite structure between one or more pairs of heated rollers, in which the moisture in the immediate vicinity of the heated rollers is vaporized by the emitted heat and then condensed in the coldest layer of the superabsorbent material, placed further down in the material, and where the layer is self-links and is able to form a stable layer; and where that layer joins the layers or layers of tissues of the pulp of surrounding cellulose. Brief Description of the Drawing Figure 1 schematically illustrates the equipment for the manufacture of an absorbent structure, according to the inventive method; and Figure 2 illustrates schematically an exemplary embodiment of the absorbent article, produced in accordance with the invention. Description of the Invention The object of the present invention is to provide an absorbent structure, which includes a superabsorbent material and which can be included in an absorbent article, such as a sanitary napkin, panty-day protectors, incontinence guards, diapers and similar items The absorbent structure will exhibit very good absorption properties, both with respect to its ability to rapidly take liquid, and its ability to disperse liquid through matter. Certain layers of the absorbent structure will preferably not contain the superabsorbent material and it will thus be possible to produce a very thin structure. It will also be possible to produce the structure without spreading the superabsorbent material on and in and around the manufacturing machine, during the manufacturing process and without the articles of the superabsorbent material escaping from the finished pulp core or the absorbent article, when packed, transports or uses this article. This object has been achieved, according to the invention, by producing the absorbent structure, according to a method, in which a layer, which essentially contains the superabsorbent material, is placed between two layers of defibrated and moistened cellulose pulp. or moistened fabric, and then satin the composite structure, compressing this structure between one or more heated pairs of rolls. The moisture in the immediate vicinity of the heated rollers is vaporized by the heat emitted and then condensed in the coldest layer of the superabsorbent material, placed deeper in the material. This layer is bonded there and to itself and forms a stable layer, and the layer is also bonded to the surrounding layers of cellulose pulp or layers of tissue. The cellulose pulp or tissue used can be dampened from the start or moistened at a primary stage of the manufacturing process, although the outer surfaces of the cellulose pulp or tissue can, advantageously, be sprayed with moisture, immediately before of the pulp glazing, which simplifies the manufacturing process, while still making it possible for the moisture to be transported into the superabsorbent material layer in the compression and heating stage. When the top or bottom layer is made up of cellulose pulp, the moisture content of this layer will be 10 to 40%, preferably 15 to 30% and more preferably 20 to 25%, calculated with the dry weight of cellulose pulp. When a layer, top or bottom, is made of fabric, the moisture content of this layer will be from 20 to 70%, preferably from 40 to 60% and more preferably from 45 to 55%, calculated on the basis of the dry weight of the tissue layer. The properties of the different layers in the structure can be controlled to adapt to different product applications, using, as starting materials, for the absorbent structure, two separate layers of fluff pulp or layers of tissue between which the layer of superabsorbent material. One or both layers of foamed pulp may, for example, be free of the superabsorbent material. The various layers of foamed pulp may be comprised of different pulps of cellulose or may be of the same type of cellulose pulp, for example pulp fibers produced chemimetromechanically ("CTMP") or a corresponding product, produced from sulfite pulp or from sulfate, the so-called cellulose chemical pulp. Cellulose fibers that have been made chemically rigid or in some other way, they can also be used in one or both layers. When the fibers of the pulm produced chemometrometrically are used, these fibers can be, for example, fibers dried by vaporization. Description of the Emplifying Modes Figure 1 schematically illustrates equipment for the manufacture of an absorbent structure, according to the invention. A band 10 is formed on a wire 9, having a surface weight of 100 to 1,000 g / m2 and a density of 0.05 to 0.2 g / cm3. The web comprises a top layer, in the form of a top strip 1 of pulp, having a surface weight of 100 to 1,000 g / m2 and a density of 0.05 to 0.2 g / cm 3, and a lower band 2 of pulp, which it has a surface weight of 50 to 1,000 g / m2 and a density of 0.05 to 0.2 g / cm3, and a layer of essentially superabsorbent material 3, placed between the upper and lower layers and having a surface weight of 50 to 500 g / m2 and a density of 0.4 to 0.7 g / cm3. Water is sprayed on band 10, with the help of spray nozzles, 4 and 5, to obtain a moisture content of 15 to 40 percent, calculated based on the total weight of the band in the dry state. The web 10 is compressed to a density of 0.1 to 0.5 g / cm 3, with the help of heated rollers, 6 and 7, causing the superabsorbent layer 3 to join the two layers, 1 and 2. The rollers, 6 and 7 , have a line pressure of 100 to 200 kg / cm and a temperature of 120 to 2502C. The mat 8 of compressed pulp has a thickness of 1 to 4 mm. Figure 2 illustrates a diaper manufactured by the method according to one embodiment of the invention. This diaper typically comprises an absorbent body 11, enclosed between an upper sheet 12, permeable to liquid, which is suitably comprised of a soft non-woven material, a perforated plastic film, or the like, and which is placed next to the user when used, and a back or bottom sheet 13, impervious to liquid. The sheets, 12 and 13, have portions that extend beyond the absorbent body 11 and join together in these portions. The bottom sheet 13 is comprised of a suitable plastic material, for example polyethylene. It will be understood that the sheets, top and bottom, may be comprised of other known materials, within the scope of the invention. The absorbent body 11 can be made entirely of the material of the invention, or with a combination of the material of the invention and another material. If the absorbent structure is made entirely of the material of the invention, it can have the following construction, comprising several layers of different properties, obtained according to the invention. The absorbent structure will have a layer 14 of upper liquid or fluid inlet, an intermediate layer 15 and a bottom layer 16. The purpose of the inlet layer 14 is to rapidly take and disperse a given amount of liquid. The liquid will remain loose in the fiber structure and drains quickly from it. The inlet layer 14 is preferably comprised of firm or rigid fibers, which provide a relatively open fiber structure, even after compression and soaking. For example, the inlet layer 14 may be comprised of cellulose fibers, made chemically stiff, and preferably contain less than 10 percent of the superabsorbent material, calculated based on the weight of the structure in the dry state.
The purpose of the intermediate layer 15 is to retain the liquid absorbed inside the absorbent structure, so as to prevent the return of the liquid and the soaking of the user's skin. The intermediate layer 15 contains a high percentage of the superabsorbent material, a suitable percentage in this aspect will be 60 to 90 weight percent, calculated on the basis of the weight of the structure, in a dry state. The purpose of the bottom layer 16 is to disperse the liquid penetrating through the intermediate layer 15 to parts of the absorbent body 1, which have not yet been used. Another purpose of the bottom layer 16 is to protect the bottom sheet 13, impervious to liquid, against particle perforation of the superabsorbent material. The bottom layer 16 is preferably comprised of a material which has been formed in accordance with the invention and can comprise the chemical foamed pulp and will contain from 5 to 20 percent of the superabsorbent material, calculated on the basis of the weight of the structure, in a dry state. The various layers can have different configurations and sizes. The absorbent structure is normally combined with some kind of elastic form, among other parts in the crotch region, in order to improve the fit and function of the product.
It will be understood that the invention is not restricted to its illustrated exemplary embodiment and that other embodiments may be conceived within the scope of the following claims.