MXPA00005679A - A unitized cover and absorbent transfer layer - Google Patents

Abstract

The present invention relates to a unitized cover and transfer layer for an absorbent article comprising a blend of thermoplastic fibers and absorbent fibers. The absorbent fibers are present in an amount sufficient to efficiently draw fluid from the outer surface of the unitized cover and transfer layer, without competing with the absorbent core, thereby providing fast fluid penetration with minimal rewet.

Description

COVERING LAYER AND UNIFIED ABSORBENT TRANSFER FIELD OF THE INVENTION The present invention relates to non-woven fabrics useful as the layer that makes contact with the body of absorbent articles. The fabrics are designed to transmit received fluids away from the body and towards an underlying absorbent center. The present invention also relates to absorbent articles that employ said non-woven fabrics as a unified cover and transfer layer. The absorbent articles can be diapers, sanitary napkins, wound dressings, incontinence devices and the like.

ANTECEDENTS OF THE INVENTION The absorbent articles for handling discharged body fluids are generally composed of a fluid-permeable cover layer, a fluid-impermeable barrier layer and an absorbent center therebetween. The purpose of the cover layer is to contain the absorbent material and transfer the fluids to the absorbent center, while remaining relatively dry during use, thereby protecting against fluid spillage and increasing user comfort. An additional layer can be employed between the absorbent center and the cover layer to improve the efficiency of fluid transfer, and to resist the re-transmission (rewetting) of fluid from the absorbent center to the cover layer. The additional layer is commonly known as a transfer layer, acquisition layer, corrugated layer or absorbent layer (known as a transfer layer). The transfer layer in combination with a cover layer is commonly called a mixed cover. These layers are made of two fabrics manufactured separately and joined together. The efficient transfer of fluids and minimum rewetting present conflicting requirements in the design of absorbent articles, typically emphasizing one or the other property to the detriment of the remaining property. One approach is to construct a transfer layer with relatively rigid non-absorbent fibers, such as polyester fibers having deniers of 6 or more. To ensure that an absorbent article employing said transfer layer is comfortable to wear against the body, a cover made of apertured film or fine denier fibers is necessary to dampen the aggressiveness of the transfer layer. The stiffness of the fibers and the large pore fabric resulting in the transfer layer provides a separator between the overlying cover and an underlying absorbent center in an effort to minimize rewetting. This approach is based on a highly absorbent center for extracting the fluid from the cover, through the transfer layer, and into the absorbent center. Although rewetting can be improved with this approach, it increases the time for fluid to penetrate the cover layer. The increase in fluid penetration time is due both to the confidence in the absorbent center to absorb the fluid in the cover, and to the lack of capillary pressure between the relatively small pore cover layer and the pore transfer layer relatively large If the cover layer feels wet for a user, then the discomfort occurs, forcing the user in an extreme case to replace the item before its useful life has ended. In addition, the evolution of absorbent articles gravitates towards increasingly thin general structures. When this happens, the first approach of a separator with large pore size does not provide as much efficient fluid transfer as resistance to rewet. An example of this approach is described by Baer et al. in the patent of E.U.A. No. 5,728,081. A second approach is to build a transfer layer with a pore size that is smaller than that of an overlay layer. The pore size gradient from the cover to the transfer layer results in a higher capillary pressure, which results in the captured fluid being absorbed from the cover, without relying on an extremely absorbent center. The background to this approach is that the transfer layer could not easily pass the fluid to the absorbent center after it had absorbed the fluid from the cover layer. Any fluid that is maintained by the transfer layer offers the possibility of rewetting. An example of this approach is described by Meyer et al. in the patent of E.U.A. No. 4,798,603. Although the transfer layers generally improve the performance of an absorbent article, in terms of fluid acquisition / transfer and resistance to rewetting of the contacting surface with the body, they add cost to the manufacture of the absorbent article. The added cost is a result of additional manufacturing equipment; handling, storage and transportation of a greater number of roll materials; and equipment / materials necessary to adhere the transfer layer to the remaining layers. An object of the present invention is to provide an individual nonwoven structure that provides improved cover layer and transfer layer properties. The individual non-woven structure employs a blend of thermoplastic fibers and absorbent fibers offering a smooth body-contacting surface, adequate fluid penetration and a satisfactory unidirectional fluid transfer from the body-contacting surface to an absorbent center underlying.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a unified cover and transfer layer for an absorbent article comprising a blend of thermoplastic fibers and absorbent fibers. There are two thermoplastic fibers of different denier in the structure; the smaller of the two provi softness, and the larger of the two provi bulging. The absorbent fibers are present in an amount sufficient to absorb fluid efficiently from the outer surface of the cover layer and unified transfer, without competing with the absorbent center, thereby provi rapid penetration of fluids with minimal rewetting. Accor to one embodiment of the present invention, there is now provided a unified nonwoven cover and transfer layer for an absorbent article, comprising: a first surface and a second surface opposite therefrom to cover at least a portion of an absorbent center; thermoplastic fibers near the first surface and a mixture of thermoplastic fibers and absorbent fibers close to the second surface, the absorbent fibers constituting 20 weight percent or less of the mixture. Preferably, the thermoplastic absorbent fibers near the first surface have a denier of 5 or less, and those close to the second surface have a denier of 6 or more. Accor to a second embodiment of the present invention, there is now provided an absorbent article comprising: a nonwoven fabric having a first surface and a second surface thereof, thermoplastic fibers close to the first surface and a mixture of fibers thermoplastics and absorbent fibers near the second surface, wherein the absorbent fibers constitute 20 weight percent or less of the mixture; and a liquid impermeable barrier layer adhered to at least a portion of the second surface.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an end view of a unified nonwoven cover and transfer layer provided by the present invention. Figure 2 is a perspective view of an absorbent article provided by the present invention.

DETAILED DESCRIPTION OF THE INVENTION The term "unified", as used herein, refers to a single structural element. The individual structural element may have two or more zones within its different outer surfaces exhibiting variable properties. Unified does not cover two or more structures manufactured separately that are laminated together. The term "absorbent article", as used herein, refers to articles that absorb and contain exudates from the body. More specifically, the term refers to articles that are placed against or close to the user's body to absorb and contain the different exudates discharged from the body. The term "absorbent articles" is designed to include sanitary napkins, pantiliners, ultra-thin towels, incontinence towels, interlabial towels (and other items used either in the crotch region of a garment or fastened directly to the body or simply held in place against the body by means of a garment), bandages for wounds and the like. Referring to Figures 1 and 2, the present invention relates to a unified cover and transfer layer 10 having a first surface 20 designed to give the body during use, and a second opposing surface 21. The unified layer 10 is preferably a fibrous non-woven fabric comprising at least 3 different types of fibers. Near the first surface 20, there are thermoplastic fibers 30 having a denier of 5 or less, and preferably having a denier of 3 or less. By decreasing the denier of the thermoplastic fibers 30, the "softness" of the surface contacting the body 20 increases. Near the second surface 21 is a mixture 40 of thermoplastic fibers 31 having a denier of 6 or more, and absorbent fibers 32. The absorbent fibers 32 are present in an amount sufficient to efficiently absorb the fluid from the first surface 20 of the cover layer and unified transfer, without competing with an underlying absorbent center 50, thereby providing rapid penetration of fluids with minimal rewetting. The absorbent fibers 32 should comprise no more than 20 weight percent of the mixture 40 near the second surface 21, and preferably not more than 15 weight percent. The cover layer and unified transfer 10 preferably has a basis weight of about 20 to about 80 grams per square meter (gsm), and most preferably about 30 to about 60 gsm. The mixture 40 preferably constitutes about 50 to about 75 weight percent of the basis weight. Figure 2 illustrates an absorbent article 60 having a liquid permeable, unified cover and transfer layer 10, an absorbent core 50 and a liquid impervious barrier layer 51. The absorbent article 60 has an hourglass geometry, but other geometries can be used. Useful thermoplastic fibers 30 and 31 include polyolefin fibers such as polyethylene and polypropylene, polyester fibers, polyamide fibers (including nylon), polyacrylic fibers, and the like. Preferably, at least a portion of the thermoplastic fibers 30 and 31 are bicomponent fibers, having a configuration of either cover / center or side to side. The two components generally have varying melting temperatures, the fiber with a lower melting temperature being the cover in a shell / center configuration. The two-component thermoplastic fibers useful in the present invention include, but are not limited to, polyethylene / polypropylene, polyethylene / polyester, polypropylene / polyester, copolyester / polyester. If the thermoplastic fibers are not hydrophilic or hydrophobic per se, then they can be made hydrophilic or hydrophobic by suitable treatments and / or finishes such as those known in the art. Referring again to Figure 1, it could be useful for example to employ thermoplastic fibers 31 that exhibit hydrophilic properties close to the second surface 21 to assist the absorbent fibers 32 to extract any captured fluid away from the first surface 20 that contacts the the body. However, the thermoplastic fibers 30 near the first surface 20 would preferably not exhibit hydrophilic properties, in an effort to maintain a contacting surface with the body having a "dry feel", for optimum user comfort. A representative and non-limiting list of absorbent fibers 32 useful in the cover layer and unified transfer 10, includes cellulosic fibers such as cotton, rayon, cellulose, acetate, wood pulp; nylon fibers and the like. Care must be taken not to use materials or quantities that could cause the cover layer and unified transfer to compete in absorbency with an underlying absorbent center. The absorbent fibers 32 may be present homogeneously throughout the mixture 40, in individual areas or in continuous or discontinuous concentration gradients. Preferably, the absorbent fibers 32 are rayon, and are uniformly present along the mixture 40 near the second surface 21. The peripheral profile of the thermoplastic and absorbent fibers can be of any shape, being a trilobal example. The fibers may also contain grooves, channels or holes; and they can be chopped or punctured. The fibers can be folded or not. The folding can be two-dimensional, such as by means of a crimping, or three-dimensional compressing box, such as by means of hot water treatment. Any method known in the art can be used to manufacture the unified nonwoven structure 10. This is preferably done with a process employing two cards, one containing the thermoplastic fibers 30 and the second containing the mixture 40 of thermoplastic fibers 31 and fibers. absorbent 32. A moving band or screen carrier is passed under the first card, where the thermoplastic fibers 30 are deposited, and then passed under the second card, where the mixture 40 is deposited. When at least a portion of the thermoplastic fibers 30 and 31 are two-component (described above), the non-woven fabric created on the carrier can be thermally bonded by passing warm air through the fabric and the carrier. The fibers are exposed to air heated to a temperature such that the lower melting temperature component, for example the cover part, softens and begins to melt. The contact of this fused fiber with a second fiber will form a joint after the removal of the heated air. The contact between fibers can be achieved by means of the natural compression of gravity, the force of a moving stream of hot air against the fibers and / or by a retaining wire by applying a compressive force against the fibers. The patent of E.U.A. No. 4,548,856 describes the connection through air in greater detail. A second method for manufacturing the cover layer and unified transfer of the present invention is through the use of transverse fabric forming technology, as described in the U.S. Patents. Nos. 4,931, 357; 4,927,685 and 4,921, 659. This method of manufacture is particularly useful when short fibers are desired, such as cotton linings or wood pulp. The cross-fabric forming technology can produce a non-woven fabric with significant structural stability, thereby eliminating the need for binder material or two-component thermoplastic fibers. This technology also provides the possibility of a controlled placement of the absorbent fibers 32 in individual areas within the mixture 40. For example, in an effort to reduce spillage in an absorbent article, the absorbent fibers can be placed in concentrations throughout the outer edges of the non-woven fabric, a central portion, or combinations thereof. A third useful method for manufacturing the cover layer and unified transfer 10 includes the use of a single card to deposit the mixture 40 on a carrier, and a spinning apparatus for overlapping the mixture 40 with the thermoplastic fibers 30. The present invention also contemplates absorbent articles employing a unified cover and transfer layer as described above and shown in Figure 2. Absorbent articles 60 of the present invention will also include at least one liquid impervious barrier layer 51, and preferably also an absorbent center 50 positioned between the cover layer and unified transfer 10 and the liquid impermeable barrier layer 51. The liquid impervious barrier layer 51 helps to prevent the received fluid from being transferred to the body and / or garment of a user. The barrier layer can be of any flexible material that prevents the transfer of liquids, but that does not necessarily prevent the passage of gases. The commonly used materials are polyethylene or polypropylene films. Other materials that may be used as the liquid impervious barrier layer 51 are polyester films, polyamides, ethylene vinyl acetate, polyvinyl chloride, polyvinylidene chloride, cellophane, nitrocellulose and cellulose acetate. Co-extruded and laminated combinations of the above can be used when such combinations are allowed by the chemical and physical properties of the film. Reticulated liquid-impermeable foams and papers treated with repellent can also be used. Films that are barriers to liquids can be used, but allow gases to transpire, that is, "breathable barriers". These can be selected from polyurethane films and microporous films in which the microporosity is created by ionizing radiation or by the leachate of soluble inclusions using aqueous or non-aqueous solvents. Individual or multiple layers of permeable films, fabrics and combinations thereof that provide a tortuous path, and / or whose surface characteristics provide a liquid repellent surface for the penetration of liquids may also be used to provide such breathable barriers. The absorbent center 50 provides the means for absorbing and retaining menstrual flows and other body fluids. The absorbent center is generally compressible, conformable and non-irritating to the skin of a user. It can comprise any material used in the art for that purpose. The absorbent center 50 of the present invention can comprise either simple or complex absorbent structures that accept, transfer, distribute, store and retain fluids, as well as prevent fluid from leaving the absorbent product. The absorbent center 50 may be composed of one or more layers of similar or dissimilar elementary characteristics. A representative and non-limiting list of materials that can be used in the absorbent center includes natural materials such as shredded wood pulp, creped cellulose wadding, hydrogel-forming polymeric gelling agents, modified interlaced cellulose fibers, capillary channel fibers, absorbent foams, absorbent sponges, synthetic staple fibers, polymeric fibers, swamp moss, cotton, rayon or any equivalent material or combination of materials. The polymeric gelling agents listed above may also be referred to as "absorbent gelling materials" or "superabsorbent materials". Polymeric gelling materials are those materials which, after contact with liquids such as water, or other body fluids, become saturated with said liquids and then form hydrogels. In this manner, liquids discharged in the absorbent center 50 can be acquired and retained by the polymeric gelling agent, thereby providing the articles with increased present absorbency and / or improved liquid retention performance. The polymeric gelling agent that is optionally employed in the absorbent center 50 will generally comprise particles of a substantially water-insoluble, slightly entangled and partially neutralized hydrogel-forming polymer material. The term "particles", as used herein, may refer to particles of any form, such as in the form of pellets, flakes or fibers. Attachment means may optionally be employed on one or more of the surfaces disposed outwardly of the article to adhere the articles to either the crotch region of a wearer's garment and / or directly to the body of a wearer. Various mechanical and chemical attachment means (adhesives) are known in the art. Materials that are soluble / dispersible in water and / or biodegradable can also be used in one or more of the layers of the absorbent article, in an effort to provide a more disposable or less environmentally aggressive item. A representative and non-limiting list of such materials includes polyvinyl alcohol, polylactic acid, starch and starch-based formulations, polyhydroxybutyrate and combinations thereof.

Useful materials in one or more of the absorbent center, cover layer and unified transfer and barrier layer impermeable to prior liquids may have extensible / stretchable properties. The materials can be made extensible by carrying out a mechanical operation, such as pleating, corrugation or rolling with a ring. In addition, materials can be punctured or grooved. The perforations or grooves can vary in geometry and size, thus providing extension capacity in multiple directions if required. The materials can also be inherently stretchable, such as mixed polyethylene particles available from Exxon, particularly EXX-7 film. A more detailed description of extensible articles and methods for manufacturing them is found in the US patent. No. 5,824,004. There are a number of useful techniques for assembling all the layers of material mentioned above to form an absorbent article, including but not limited to the use of heat sealing, hook and fastener technology, construction adhesives and ultrasonic media. Preferably, construction adhesives are used to adhere the individual layers together. A variety of such materials are known in the art. The absorbent articles of the present invention can have any shape, such as rectangular or hourglass. The article may have one or more side extensions to wrap around the crotch portion of a wearer's garment.

EXAMPLES Several samples of cover layer and unified transfer of 39.5 grams per square meter were made with an air-bonding process of two cards, which comprised 33 weight percent of two-component polyethylene / polyester fibers of 1.8 denier close to a first surface, and 67 weight percent of a blend of two-component polyethylene / polyester fibers of denier 10 and rayon fibers near a second surface. The rayon fibers contributed approximately 15 weight percent of the mixture. The second surface of the cover layer and unified transfer samples was placed adjacent to three different absorbent centers to evaluate the performance of the samples. The fluid penetration time and rewet values for each are shown in Table 1. As a comparison, multiple denier polypropylene (PP) covers (3 and 5) in combination with alternative transfer layers are also shown. The results in Table 1 illustrate that the cover and unified transfer layer of the present invention provided (Examples 5, 10 and 15) an adequate balance between the fluid penetration time and the rewet resistance. In comparison, the samples having a transfer layer made of 100% absorbent fibers (examples 3, 4, 8, 9, 13 and 14) provided relatively fast fluid penetration times, but were susceptible to rewetting, whereas the samples having a transfer layer made of 100% polyester fibers (examples 1, 2, 6, 7, 11 and 12) provided acceptable resistance to rewet, but did not absorb the fluid from the cover so quickly.

TABLE 1 TABLE 1 (Continued) Test Methods The fluid penetration time was measured by adding a quantity of 7 milliliters of a synthetic body fluid or a saline solution to an area contained on an outwardly disposed surface of an article, initiating the measurement time when the fluid did contact first with the outer surface of the article and stopping the measurement of time when any portion of the surface in the contained area became visible. The contained area was defined by placing on the article a plate having an oval hole therein. The plate in a length of approximately 25 centimeters, a width of approximately 7.5 centimeters and a thickness of approximately 1.3 centimeters. The oval had a central width of 3.8 centimeters and a central height of 1.9 centimeters. Synthetic fluid was poured into the hole from a height of approximately 2.5 to 7.5 centimeters above the orifice plate, keeping the hole as full as possible without overfilling the surface of the plate. Rewetting was measured by covering the contained wetted area, formed from the fluid penetration test above, with an absorbent structure in layers, placing it under a specific load for a specific time, and then calculating the weight of fluid absorbed by the structure absorbent. The rewet test began 5 minutes after the amount of 7 milliliter fluid penetrated the exterior surface of the article. Two general-purpose NUGAUZE sponges (available from Johnson &; Johnson Hospital Services), which had a width and length of 10 centimeters, and which comprised 4 layers folded once down a central axis and stacked one on top of the other with the creased edges placed opposite each other, creating in this way an absorbent structure in layers of approximately 5 centimeters by 10 centimeters by 16 folds. The absorbent structure in layers of 16 folds was placed concentrically on the moistened area of the article. Then weights were placed on the absorbent structure in layers, resulting in a pressure of 0.042 kilograms per square centimeter. The stacked weights and sponges were removed from the moistened area after 3 minutes. The sponges and any absorbed fluid were weighed, thus defining a final weight. The amount of fluid absorbed by the structure (released by the article) was calculated by subtracting a pre-weight from the stacked sponges of the final weight. The descriptions of all patents, as well as any corresponding published foreign patent applications, mentioned throughout this patent application are hereby incorporated by reference. The foregoing description and embodiments are presented to assist in the complete and non-limiting understanding of the invention described herein. Since various embodiments and variations may be made to the invention without departing from its spirit and scope, the invention resides in the appended claims below.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A unified nonwoven cover and transfer layer for an absorbent article, comprising: a) a first surface and a second surface opposite thereto to cover at least a portion of an absorbent center; b) thermoplastic fibers close to the first surface and c) a mixture of thermoplastic fibers and absorbent fibers close to the second surface, the absorbent fibers constituting 20 weight percent or less of the mixture.

2. The unified nonwoven cover and transfer layer according to claim 1, further characterized in that the non-woven material has a basis weight and the blend of thermoplastic and absorbent fibers close to the second surface constitute about 50 to about 75 percent by weight of the base weight.

3. The unified nonwoven cover and transfer layer according to claim 2, further characterized in that the basis weight is from about 20 to about 80 grams per square meter.

4. The unified nonwoven cover and transfer layer according to claim 1, further characterized in that the thermoplastic fibers near the first surface have a denier of 5 or less.

5. The unified nonwoven cover and transfer layer according to claim 1, further characterized in that the thermoplastic fibers near the second surface have a denier of 6 or more.

6. The unified nonwoven cover and transfer layer according to claim 1, further characterized in that the thermoplastic fibers near the first surface have a denier of 3 or less and the thermoplastic fibers close to the second surface have a denier of 6 or more

7. The unified nonwoven cover and transfer layer according to claim 1, further characterized in that the absorbent fibers are cellulosic.

8. The unified nonwoven cover and transfer layer according to claim 7, further characterized in that the cellulosic fibers are rayon.

9. The unified nonwoven cover and transfer layer according to claim 1, further characterized in that at least a portion of the thermoplastic fibers near the first and second surfaces are two-component fibers.

10. The unified nonwoven cover and transfer layer according to claim 9, further characterized in that the two component fibers comprise a polyester center and a polyethylene cover.

11. - A unified nonwoven cover and transfer layer for an absorbent article, comprising: a) a first surface and a second surface opposite thereto to cover at least a portion of an absorbent center; b) thermoplastic fibers having a denier of 3 or less close to the first surface and c) a mixture of thermoplastic fibers and absorbent fibers close to the second surface, wherein the absorbent fibers constitute 20 weight percent or less of the mixture and the thermoplastic fibers have a denier of 6 or more.

12. The unified nonwoven cover and transfer layer according to claim 11, further characterized in that the non-woven material has a basis weight and the blend of thermoplastic and absorbent fibers close to the second surface constitute about 50 to about 75 percent by weight of the base weight.

13. The unified nonwoven cover and transfer layer according to claim 12, further characterized in that the basis weight of the non-woven material is from about 20 to about 80 grams per square meter.

14. The unified nonwoven cover and transfer layer according to claim 11, further characterized in that the thermoplastic fibers near the first surface have a denier of 2 or less.

15. The unified nonwoven cover and transfer layer according to claim 11, further characterized in that the thermoplastic fibers near the second surface have a denier of 10 or more.

16. An absorbent article comprising a unified nonwoven cover and transfer layer according to claim 1; a liquid impermeable barrier layer and an absorbent center therebetween.

17. An absorbent article comprising a unified nonwoven cover and transfer layer according to claim 11; a liquid impermeable barrier layer and an absorbent center therebetween.

18. An absorbent article comprising: a) a nonwoven fabric having a first surface and a second surface thereof, thermoplastic fibers close to the first surface and a mixture of thermoplastic fibers and absorbent fibers near the second surface, wherein the absorbent fibers constitute 20 weight percent or less of the mixture; and b) a liquid impermeable barrier layer adhered to at least a portion of the second surface.

19. The absorbent article according to claim 16, further characterized in that the non-woven fabric has a basis weight of about 20 to about 80 grams per square meter. 20.- The absorbent article in accordance with the claim 16, further characterized in that the blend of thermoplastic fibers and absorbent fibers near the second surface constitute about 50 to about 75 weight percent of the basis weight.