MXPA00000179A - Absorbent article with superabsorbent particles and with densified region and manufacturing method - Google Patents

Abstract

The invention relates to a novel absorbent article (1), specifically a feminine hygiene article, having emulsion polymerized superabsorbent particles and at least one highly densified region (5, 6, 7, 8).

Description

ABSORBENT ARTICLE WITH SUPERABSORBENT PARTICLES AND DENSIFIED REGION FIELD OF THE INVENTION This invention relates to a novel absorbent article, specifically to an article for feminine hygiene, having superabsorbent particles polymerized in emulsion and at least one highly densified region. The article comprises an absorbent article that includes a combination of cellulosic fibers and superabsorbent polymer particles with substantially rounded surfaces, and a continuous film barrier layer. The article also has at least one densified region with a density of at least 0.5 g / cm3 for stabilization during use.

BACKGROUND OF THE INVENTION Absorbent articles such as sanitary napkins or feminine hygiene articles typically have an absorbent element having a body facing surface adapted to receive body fluid in the absorbent member, and a garment-facing surface, impervious to liquids, which acts as a barrier to body fluid to prevent liquid from staining the user's clothing. Said absorbent elements have traditionally been made from readily available and relatively cheap cellulosic absorbent materials, such as cotton fibers, wood pulp fluff, cellulosic woven or cellulosic wadding, or other absorbent fibers. These materials have provided satisfactory liquid absorbency both in terms of absorbency rate and overall absorptive capacity. Unfortunately, absorbent elements made from cellulosic absorbent materials can lead to crushing when wetted, thus losing some of their void volume. Furthermore, this so-called wet crush often leads to stacking, fraying and separation of the absorbent element, reducing its absorbent capacity and comfort for the user. Said structures may also allow the absorbed liquid to be squeezed out of the structure onto the skin or clothes of the wearer of the absorbent article. This runoff also contributes to an uncomfortable and wet feeling against the user's skin. Various means have been used to help solve the problems caused by wet crushing of cellulose absorbent structures. Among them are the preconfiguration of the article to more closely approximate the outline of the perineal region of the user, as taught in the patent of E.U.A. 4,654,040, the addition of elastic materials, as described in the patent of E.U.A. 3,060,936, and the formation of a densified layer as described in the U.S.A. 4,217.901.

Recently, superabsorbent polymer particles have been combined with more traditional absorbent materials to provide structures with increased absorbency and increased retention, which can help eliminate problems of runoff and wet surface sensation. However, a drawback of superabsorbent polymer particles is their relatively high cost compared to more traditional absorbent materials. In addition, since the superabsorbent polymer particles tend to swell when absorbing liquid, they must be properly placed within an absorbent structure to allow this swelling and to utilize more fully its absorbent capacity. Although the addition of superabsorbent polymer particles to cellulose absorbent structures can increase the absorbency of the structures, the addition of superabsorbent alone does not help improve the stability of the cellulosic structure compared to cellulosic structures without superabsorbent polymer particles. Therefore, absorbent products containing cellulose absorbent structures containing superabsorbent particles can be treated or otherwise configured to help solve the problems caused by the wet crush of the cellulosic fibers. A desired method of helping to avoid this wet crush is the formation of densified stabilizing regions in the absorbent structure. Unfortunately, the formation of densified stabilizing regions in articles made with absorbent elements containing superabsorbent particles may compromise the liquid-impermeable article facing surface of the article, since the densification process tends to push the superbasing particles against the film surface of the article. liquid impervious barrier, thus forming small holes or small drops, commonly known as pinholes, on the surface of the film. The presence of these holes or drops is undesirable since it allows the passage of the liquid and reduces the liquid impervious nature of the garment facing surface of the article. One solution to this pinhole-forming problem in the liquid impervious surface of the superabsorbent particles is to add the liquid-impervious surface as a separate layer after densification of the superabsorbent-containing absorbent element. Unfortunately, the addition of the liquid impermeable layer to the absorbent element after densification results in poor conformation between the liquid impervious layer and the absorbent element. This poor conformation can undermine the stabilization that densification aims to overcome. Another solution to the problem of pinhole formation involves the use of superabsorbent particles to which a plasticizer such as glycerol or a small amount of water has been added to soften the particles a little and to allow the particles to become more pliable without reduce its absorbent capacity. This softening of the particles allows the densification process to be carried out with the impermeable barrier in place without creating pinholes in the barrier. The softened particles can be formed under the densification pressure and therefore do not push through the impermeable barrier layer in the same way as the dry particles could. However, softened particles can provide handling or processing difficulties since they may tend not to flow in the same direction as the relatively dry powder would flow. Therefore, what is needed is an absorbent article with a continuous liquid impermeable layer and an absorbent element containing superabsorbent polymer particles, and having densified stabilization regions.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide an absorbent article with an absorbent element containing superabsorbent particles and having densified stabilizing regions, and with an intact, continuous, liquid impervious barrier layer with very few holes or droplets or none at all. This object is achieved by the inclusion of superabsorbent polymer particles with substantially rounded surfaces, such as superabsorbent polymer particles emulsion polymerized, in the absorbent element and the subsequent densification of certain areas of the absorbent element to form densified stabilizing regions. The densified stabilizing regions can be densified to such an extent that the article does not lose its stability when used or wetted. Said desirable density of the densified stabilization regions is at least 0.5 g / crrß. The superabsorbent polymer particles contain less than 15% by weight moisture.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a preferred embodiment of the absorbent article of the present invention to be worn by a woman for feminine hygiene. Figure 2 is a cross-sectional view taken along the line ll-ll of Figure 1. Figures 3a to 3e are examples of a typical round particle and agglomerated morphologies. Figures 4a to 4e are examples of particle morphologies with typical edges.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES An absorbent article for use by a woman for feminine hygiene according to this invention is shown in figure 1. The article 1 is composed of a generally rectangular absorbent structure 2 which overlaps a layer of continuous barrier film 4. The article has densified stabilizing regions that take the form of densified channels 5, 6, 7, 8 along the sides and ends of the article. A cover layer stretched towards the liquid permeable body 10 can cover the upper surface of the article. As shown in Figure 2, the absorbent structure 2 comprises a combination of cellulosic fibers 12 and superabsorbent polymer particles with substantially rounded surfaces 14. The surface of the article intended to be used against the wearer's body may be formed by a layer of a material permeable to body fluid, typically known as a cover or face. The cover can be formed from any liquid-permeable material that is comfortable against the skin and which allows the fluids to penetrate the underlying absorbent structure, which then absorb and retain the fluid. The cover usually must retain little or no fluid within its structure in order to provide a relatively dry surface close to the skin. The fluid-permeable cover can be a fibrous non-woven fabric made of fibers or filaments of polymers such as polyethylene, polypropylene, polyester or cellulose. Alternatively, the cover can be formed from a polymeric film with openings. The thickness of the cover can vary from 0.0025 to 0.1575 cm, depending on the material chosen.

The surface of the article that is intended to be worn away from the wearer's body and against the wearer's garment comprises a layer of material impervious to body fluid, typically known as a barrier. This impermeable barrier comprises any flexible, thin, body-impermeable material such as a polymeric film (eg, polyethylene, polypropylene, polyester, polyurethane or cellophane). The thickness of a barrier of said polymeric film is typically only about 0.0025 to 0.0051 cm. The absorbent structure of the article comprises a combination of superabsorbent polymer particles and cellulosic fibers. The cellulose fibers can be, without limitation, wood pulp, regenerated cellulose fibers, rayon fibers, peat fibers or cotton fibers. The cellulosic fibers are preferably randomly and loosely associated, as in a structure laid in air, or joints may be associated in an oriented structure, such as a carded fabric. Alternatively, the cellulosic fibers may be wet laid to form a relatively low density structure capable of having portions thereof densified to a density of at least 0.5 g / cm 3. In addition, other absorbent or non-absorbent materials may be added to the absorbent structure. Examples of such materials include, without limitation, synthetic elastic fibers, binding fibers, fibers or odor regulating particles, perfumes, synthetic binder compounds such as vinyl acetate-ethylene and polyvinyl alcohol and the like.

The cellulosic fibers are combined with superabsorbent polymer particles to form the absorbent structure of the article. The superabsorbent polymer particles comprise small round particles or agglomerates of small rounded particles. In any case the superabsorbent particles have surfaces that are substantially rounded. By "substantially rounded", it is understood that the surfaces of the particles are generally free of edges with sharp, pointed edges. Figures 3a to 3e show examples of agglomerate and typical round particle morphologies. Preferably, these particles with substantially rounded surfaces are superabsorbent polymer particles emulsion polymerized. In any case, the superabsorbent polymer particles used in this invention have generally rounded cross-sectional shapes and surfaces that are substantially free of sharp edges, with sharp edges or edges. Examples of suitable emulsion polymerized superabsorbent polymer particles are Sumitomo SA60NTM and Sumitomo J550 ™, which are available from Sumitomo Seika Chemicals Co., Ltd. of Osaka, Japan. On the other hand, superabsorbent particles polymerized in solution have edges with generally sharp, irregular or sharp edges on their surfaces. Examples of particle morphologies with typical edges are illustrated in Figures 4a to 4e. A more complete discussion on emulsion polymerization process and the solution polymerization process is described in E.U.A. Re. 32,649 of Brandt et al, which is incorporated herein by reference. The fibers and particles can be combined in any of several ways. The particles can be substantially homogeneously mixed with the fibers throughout the absorbent structure.

Alternatively, the particles may be present within a different zone within the absorbent structure. In some cases, it may be desirable to place the superabsorbent particles within a specific and distinct zone within the absorbent structure. The boundaries of these zones can be located within the x-y plane or in the z direction of the structure. For example, the superabsorbent particles can be concentrated in the upper portion of the thickness of the structure as illustrated in Figure 2. By concentrating the superabsorbent particles in the upper portion of the thickness of the structure in this way it helps to avoid the formation of holes in the structure. pin. Alternatively, the superabsorbent particles can be placed throughout the thickness of the structure but can be concentrated in the central portion of the structure where the fluid is expected to enter the structure, leaving the ends substantially free of superabsorbent. In addition, the superabsorbent particles can be concentrated both in the upper portion of the thickness of the structure and only within the central portion of the structure, leaving the ends substantially free of superabsorbent particles. Methods for forming such distributions by zones of superabsorbent particles are described in U.S. Patents 5,004,579, 5,213,817, 5,350,817 and 5,614,147 which are incorporated herein by reference. As shown in the figures, the absorbent structure 2 is contained between the face of the article or cover layer of the article 10 and the barrier layer 4. The cover layer 10 and the barrier layer 4 preferably extend beyond the edges 16 of the superabsorbent structure to form peripheral cover extensions 18 and barrier extensions 20. These peripheral cover extensions 18 and barrier extensions 20 are joined to each other to form a flange seal 22 around the outer edges of the article. The flange seal can be formed by any sealing means known in the art, including without limitation, heat sealed, ultrasonic sealed, sealed with adhesive or mechanical seal. Although the preferred article of this invention is made with a flange seal, said method of sealing the edges of the article is not necessary for the invention. The edges of the article can also be sealed by wrapping the cover layer, the barrier layer or other layers around the edges. An important feature of the article of the invention is the presence of at least one densified region with a density of at least 0.5 g / cmA. As shown in the figures, the densified region (at least one) preferably takes the form of at least one channel 5, 6, 7, 8 which is embossed or compressed in the article at a density, measured at the bottom 24, the densest portion of the channel, of at least about 0. 5 g / cm3. Preferably, the density is between about 0.5 g / cm 3 and 1.3 g / cm 3. Densified regions with densities less than 0.5 g / cm3 do not maintain the stability needed during use, since the material in the densified portion of the canal can "spring back" or "recover" when the article is subjected to normal conditions of use and moisture provided by perspiration and other body fluid discharges. However, when the densified region is created with a density of at least 0.5 g / cm ^, it retains its density during use, greatly increases the stability of the article during use and helps prevent twisting and bulging when the article it is moistened and subjected to the pressures of ordinary use. The densified region is compressed or embossed in the article at least in the barrier layer in place against a surface of the absorbent structure. The presence of the barrier layer against the absorbent structure during the densification process has several advantages. The presence of the barrier during the densification process helps maintain the integrity of the absorbent structure during densification; it allows the formation of uniformly densified regions and improves the overall stability of the absorbent article. It is also preferable that the cover layer be placed against the surface facing the body of the absorbent structure when the densified region (at least one) is created; however, this is not necessary.

The densification process essentially comprises regions of the absorbent structure, having a non-compressed density of between 0.01 and 0.05 g / c? T) 3, at a density of at least 0.5 g / cm3, and preferably at a density of at least 0.9 g / crrß. The densified regions can be in any pattern. In the preferred embodiment of the invention illustrated in Figure 1, the densified regions are present as two longitudinal arcs 5, 6 and two side arches 7, 8. The longitudinal arcs 5, 6 extend generally along the longitudinal sides 26 of the article and are oriented so that they are generally curved inward toward one another. The side arches 7, 8 generally extend laterally through the ends 28 of the article and are oriented such that they generally curve outwardly away from each other. Each densified region in the form of an arc is typically less than about 0.635 cm in width at the bottom, the densest portion. The longitudinally extending arcs are usually between about 25 and about 100 millimeters in length, and the laterally extending arcs usually have a length of about 25 to about 75 millimeters. The densified regions can be formed in the article by any means of densification, including enhancement or calendering. Carrying out the densification at an elevated temperature aids in the formation of the densified region. A preferred method of forming the densified regions of the present invention comprises passing the absorbent article between a heated embossing roller and an anvil-type roller. The enhancement roller has elevated portions corresponding to the desired pattern of the densified regions. The anvil-type roller has a smooth surface. The two rollers are separated by a predetermined space so that a space is created between the anvil-type roller and the raised portions of the enhancement roller. The size of the space depends on the thickness of the non-densified absorbent article and is fixed in such a way that the passage of an absorbent article between the rollers results in the formation of densified regions with a density of at least 0.5 g / cn? In accordance with an important aspect of the present invention, superabsorbent particles with substantially rounded surfaces are used in the absorbent structure to minimize pinhole formation in the film barrier layer below the densified regions. Experimental tests were made with sample absorbent structures made with emulsion polymerized superabsorbent particles, with superabsorbent particles polymerized in solution and with non-superabsorbent particles (control) to determine how many pinholes were formed in the barrier film layers. Each sample was made of a mixture of 0.5 g of superabsorbent and 5.5 g of pulp formed in a generally rectangular absorbent structure and contained between a layer of 25.4 μ of polythene film thickness and a nonwoven cover layer comprising short fibers of Polypropylene. The film is commercially available from Edison Plastics Company of Newport News, VA, as XP 1123. The nonwoven cover layer is commercially available from Stearns of Cincinnati, Ohio, as T1046. Fifty samples of each type were passed between an anvil-type roller and an embossing roller to form densified areas in a pattern similar to that shown in Figure 1. The space between the anvil-type roller and the raised areas on the roll enhancement were set at 16.3 microns. The total number of pin hole spots for the 50 samples of each type was determined according to the Pinhole Spot Spot Test as described below. The Pin Hole Spot Test is conducted by fixing the adhesive of an absorbent article to a layer of washed white Alpha Mills cotton fabric of sufficient size to completely cover the densified areas and the placement adhesive. An amount of 2.5 cm.sup.3 of the red dye solution is then applied to each densified region through the body face or body cover surface of each article. The red dye solution comprises 50 grams of red Calico Scarlet 2 RB powder available from Pylam Inc. of Tempe Arizona, mixed with 18.9 liters of water. A pressure roll apparatus consisting of two weighted rolls mounted on an axis with a total weight of 4.54 kg is wound once on the product in such a way that one roller covers each longitudinal densified region. The apparatus is then rolled once again over the product in such a manner that the roller covers each lateral densified region. The fabric is then examined for any spots caused by the transfer of the red dye solution through the barrier layer. The spots on the fabric indicate the presence of pinholes. Table I shows the results of the experiments.

TABLE 1 As shown in Table i, articles made with superabsorbent particles with substantially rounded surfaces of a given size had fewer pinhole spots than articles made with polymerized superabsorbent particles in solution of the same size. In addition, articles made with smaller particles of superabsorbent particles with substantially rounded surfaces did not have pinhole spots, which was compared to the number of pinhole spots on articles made with superabsorbent.

The above specification and embodiments are presented to help fully comprehend and without limitations the invention described herein. Since many variations and embodiments of the invention can be made without departing from its spirit and scope, the invention is limited by the appended claims.

Claims (18)

NOVELTY OF THE INVENTION CLAIMS

1. - An absorbent article for use by a woman for feminine hygiene, the article comprising: a cellulosic fiber and superabsorbent polymer particles with substantially rounded surfaces, and a continuous film barrier layer; the article further comprising at least one densified region having a density of at least 0.5 g / cm ^.

2. An absorbent article in accordance with the claim 1, further characterized in that the absorbent polymer particles comprise superabsorbent polymer particles emulsion polymerized.

3. An absorbent article in accordance with the claim 1, further characterized in that the densified region (at least one) has a density of at least 0.9 g / cm ^.

4. An absorbent article according to claim 1, further characterized in that the densified region (at least one) comprises superabsorbent polymer particles with substantially rounded surfaces.

5. - An absorbent article according to claim 1, further characterized in that the densified region (at least one) comprises two compressed side channels.

6. An absorbent article according to claim 3, further characterized in that the densified region (at least one) comprises two compressed end channels.

7. An absorbent article according to claim 4, further characterized in that a densified region (at least one) comprises at least one stabilization region.

8. The absorbent article according to claim 1, further characterized in that it comprises a first surface and a second surface separated by a thickness, wherein the superabsorbent polymer particles with substantially rounded surface are located within a portion of the thickness that is closer to the first surface than to the second surface.

9. The absorbent article according to claim 6, further characterized in that the continuous film barrier layer is adjacent to the second surface.

10. The absorbent article according to claim 1, further characterized in that the combination of cellulosic fibers and superabsorbent polymer particles comprise a mixture.

11. The absorbent article according to claim 8, further characterized in that the mixture is substantially homogeneous.

12. The absorbent article according to claim 1, further characterized in that the combination of cellulosic fibers and superabsorbent polymer particles comprise a separate layer other than superabsorbent polymer particles.

13. A method for making an absorbent article to be placed in the perineal region of a human being to absorb body fluid, the method consisting in: providing an absorbent structure comprising a combination of cellulose fibers and superabsorbent polymer particles with substantially substantial surfaces rounded, the structure having a first surface, a second opposite surface and a density of less than 0.5 g / cm3; provide a barrier layer containing a layer of a liquid impervious film; placing the barrier layer against the second surface of the absorbent structure; and densifying a portion of the first surface of the absorbent structure to form a densified region with a density of at least about 0.5 g / cm3.

14. The method according to claim 13, further characterized in that the superabsorbent polymer particles contain superabsorbent polymer particles emulsion polymerized.

15. The method according to claim 13, further characterized in that the first surface is densified to form a densified region with a density of at least about 0.9 g / cm3.

16. - The method according to claim 13, further characterized in that the combination of cellulosic fibers and superabsorbent polymer particles is a uniform mixture of cellulose fibers and superabsorbent polymer.

17. The method according to claim 13, further characterized in that the superabsorbent polymer particles are contained within at least one densified region.

18. The method according to claim 13, further characterized in that the densified region (at least one) comprises superabsorbent polymer particles.