WO2002039941A1

WO2002039941A1 - Mechanically compacted nonwoven fabric for disposable sanitary article sublayer

Info

Publication number: WO2002039941A1
Application number: PCT/US2001/031070
Authority: WO
Inventors: Jerry Zucker
Original assignee: Polymer Group, Inc.
Priority date: 2000-11-14
Filing date: 2001-10-04
Publication date: 2002-05-23
Also published as: AU2001294985A1

Abstract

Disposable sanitary articles are intended to absorb and contain human exudates or excreta for extended periods of time. Prolonged exposure of human skin to exudates or exreta, particularly in the form of liquids, has a deleterious effect on both user comfort and skill wellness. It is therefore a desire to construct a disposable sanitary article such that when presented a liquid insult, the liquid is quicly transferred away from the user contact. Liquid control layers have been incorporated into disposable sanitary article for this express purpose, most often as a sublayer between a topsheet layer and an absorbent core material. It has been found that nonwoven fabrics which do not exhibit suitable liquid control properties may be rendered acceptable by the treatment of the fabric by a mechanicasl compaction process. By applying mechanical compaction, conventional and uncomplicated nonwowen fabrics can be employed in heretofore field that required complex and expensive liquid control constructions.

Description

MECHANICALLY COMPACTED NONWOVEN FABRIC FOR DISPOSABLE

SANITARY ARTICLE SUBLAYER

Technical Background

The present invention is directed to a sublayer material for a disposable sanitary article comprised of a simple nonwoven fabric that is further treated by mechanical compaction, resulting in a material with enhanced liquid control properties and suitable as an acquisition or surge layer.

Background of the Invention

The use of disposable sanitary articles, and in particular disposable diapers, has come into public favor over the past twenty years. Such articles offer convenience of use and improved performance at the cost of ever increasing complexity. There is an ever- present demand by the public to improve the comfort of the article during wear and use, especially where the article has been subject to one or more liquid insults. The presence of liquid against a user's skin is deleterious in terms of both user comfort and reduced skin health as prolonged exposure to human exudate or excreta, herein referred to in general as either a liquid or fluid, can result in erythema, contact dermatitis, and further complications. It is therefore the desire pf those related to the fabrication of disposable sanitary articles to improve the performance of the ultimate article. To this end, the problem which must be addressed is how to effectively remove or otherwise displace a liquid insult away from skin contact in an expeditious manner and yet the material remains cost effective congruent with a commercial disposable article.

A typical representation of an early disposable sanitary device in the form of a diaper comprised of three primary components; a liquid-impervious backing sheet, an absorbent core material, and a liquid-pervious topsheet. These early diapers were found to exhibit insufficient performance as the liquid insult would languish on the outer, or users side, of the topsheet and thus remain in contact with the user. It was also found that the liquid absorbed into the core was transient was expressed back through the topsheet upon compression of the core, such as occurred when, for example, the loaded diaper was sat upon.

To remedy the above issue, an additional component was added to the diaper construction in the form of a liquid control layer between the top sheet and the absorbent core material. This liquid control layer, conventionally referred to as a surge or liquid acquisition layer, was designed to control specifically the movement of liquid away from contact with the user and top sheet and into the absorbent core. U.S. 5,846,230 to Osborn, HI et al., utilizes a two component structure to distribute a liquid insult in the form of an absorbent strip acting as a liquid transporting component interposed below a topsheet. The liquid transporting component structure's cross-dimension is markedly less than the width of the sanitary napkin fabricated which raises concerns of asymmetric or off-center loading. U.S. 4,798,603, to Meyer, et al., discloses a quilted structure having pores in a finite window of diameters which necessarily must not collapse during wear by the user. Both U.S. 5,490,846, to Ellis et al., and U.S. 5,486,166, to Bishop et al.,, are directed to surge layers for control of liquid movement. In order to have a material with a suitable performance, an initially lofty structure is required, which is necessarily maintained throughout the manufacturing process and ultimate fabrication of the end-use article. U.S. Patents 5,505,719 and 5,569,226, to Cohen, et al., utilize air- laid fibrous structures having a pre-described pore size through the depth of the bi- layered construction. The entire construct having the defined variation in porosity through the depth of the material may then be pleated for further effect. U.S. patent 5,527,300, to Sauer, describes a surge management layer whereby the constituent material is gathered into pleats by a supplemental and contractible material in the construction, thereby increasing loft when extension forces are released. The process as disclosed in the cited Sauer patent requires the addition of a heterogeneous elastomeric material into the construct of the surge management layer

There is also indication that those skilled in the art have looked away from the complexities of the liquid control layer in order to improve overall article performance. In U.S. 5,522,810 to Allen, et al., a surge layer is included in the structure purely as a spacer between the topsheet and the absorbent core. The absorbent core is critical as it is constructed in such a way as to render it resilient to compression, and thus when compression does occur, liquid is maintained in the more rigid structure. U.S. 5,192,606 to Proxmire, et al, describes a top sheet layer to liquid control properties.

There remains an unfilled need for a simple yet effective liquid control layer in a disposable sanitary device. To address this need, the present invention is directed to a means for altering the performance of a nonwoven fabric without the necessary incorporation of further specialized fabric layers, or having to create specially designed and custom fabrics on separate process lines.

Summary of the Invention

In a preferred embodiment, present invention is directed to the mechanical alteration of a nonwoven fabric such that the nonwoven fabrics exhibits improved liquid handling performance . The mechanical alteration is in the form of a mechanical compaction process, generally referred to in the art as creping or microcreping. A mechanically compacted nonwoven fabric is suitable as a liquid transfer layer in a disposable sanitary article without the need for specialized fabrics, such as multiple layer or gradient fabrics.

Suitable nonwoven fabrics are selected from those comprising thermoplastic polymer staple length fibers, essentially continuous filaments, or the combinations thereof. Thermoplastic polymers of particular utility and ease of use are found in those selected from polyolefins, polyesters and polyamides. The means for integrating the fibers and/or filaments are selected from through air-bonding, ultrasonic welding, and hot roll calendering, with hot roll calendering being preferred.

In accordance with the present invention, a formed and bonded nonwoven fabric, is subjected to a creping operation which imparts a higher loft to the fabric. This higher loft is a result of the substantial reorientation of the constituent fibers and/or filaments out of the original planar aspect of the nonwoven fabric. Creping can occur by either a macroscopic or microscopic reorientation. Macroscopic reorientation results in a lofty fabric that has pronounced crenellation of the transverse planar surfaces of the nonwoven fabric. Microscopic reorientation results in a less lofty fabric that has an essentially smooth surface, but upon close analysis, fibers and/or filaments are found to exhibit an oscillation or are otherwise imparted with a recurrent distortion through the plane of the resulting material.

The mechanical compaction of the nonwoven fabric results in a material that has improved liquid control performance. Increased liquid acquisition rates and rewet properties found in the treated nonwoven fabric allows the treated nonwoven fabric to quickly and effectively displace liquid from the point of contact. The improved performance of a simple nonwoven fabric having been modified by mechanical compaction is advantageous when incorporated as a liquid control layer in a disposable sanitary article. In a second preferred embodiment of the present invention, a sanitary article comprises a liquid previous top sheet, an absorbent core, and a layer of the aforesaid transfer layer disposed between the permeable cover sheet and the absorbent core. The transfer layer is hydrophilic relative to the top sheet in order to quickly transfer liquids into the core and to allow the top sheet to remain relatively dry. Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims.

Brief Description of the Drawings

The invention will be more easily understood by a detailed explanation of the invention including drawings. Accordingly, drawings which are particularly suited for explaining the invention are attached herewith; however, is should be understood that such drawings are for explanation purposes only and are not necessarily to scale. The drawings are briefly described as follows:

FIGURE 1 depicts in cross-sectional view a disposable sanitary article incorporating a liquid control layer consistent with present invention.

FIGURE 2 is schematic view of a device by which a nonwoven fabric may be mechanically compacted so as to render suitable performance for a liquid control layer. Detailed Description

While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated.

The mechanical compaction in the form of creping or microcreping of a nonwoven fabric results in the fabric having a combination of increased bulk and enhanced liquid acquisition performance.

The nonwoven fabric may be selected from those composed of staple length fibers or continuous filaments, composed in part or whole of thermoplastic polymers. Denier for the fiber or filament is typically in the range of about 3 to 20, with the range of 6 to 15 being preferred. Thermoplastic polymers suitable for this application include polyolefins, polyesters and polyamides. The thermoplastics may be further selected from homopolymers, copolymers, and other derivatives including those thermoplastic polymers having incorporated melt additives or surface active agents, and in particular those additives or agents that improve the hydrophilic nature of the thermoplastic. The profile of the fiber or filament is not a limitation to the applicability of the present invention. The fibrous component of the nonwoven fabric should comprise greater than about 50% by weight thermoplastic fibers and/or filaments so that the fibrous batt can be thermally bonded by the application of elevated temperature. The remainder of the fibrous component can be comprised of thermoset polymeric fibers, natural fibers, and absorbency enhancers such as superabsorbent polymers in a fiber or powder form. The means for coalescing and integrating the fibers or filaments into a nonwoven fabric include conventional methods as practiced in the art. In the case of staple length fibers, such fibers can be formed into a fibrous batt or web by known carding or air- laying techniques. Means for integrating the fibrous batt or web include those whereby supplemental adhesives are not required and instead rely upon the thermoplastic nature of the polymers, i.e. thermal point bonding, through air bonding, and ultrasonic welding. Nonwoven fabrics responsive to the elements of the present invention include those in a basis weight range of between 15 and 60 grams per square meter, with the range of between 20 and 45 grams per square meter being preferred. When the nonwoven fabrics include those materials that have been thermally point bonded by hot calendering roll, relative a bond area versus total surface area in the range from about 5 to 30% is preferred, the bond range of 8 to 25% being most preferred. Creping of a point bonded nonwoven fabric increases the bulk and basis weight of the fabric. It is believed that the process forms liquid flow channels through the plane of the nonwoven fabric at the same time the internal structure of the fabric is expanded and the bulk of the fabric increased. It is this formation of directional voids in the fabric structure that are hypothesized as subsequently improving liquid acquisition and distribution properties.

FIGURE 1 depicts a representation of a liquid control layer 2 of the present invention, interposed between a conventional topsheet layer 1 and an absorbent core material 3 with a backsheet 4. In such a construct, a liquid insult that impinges onto and through topsheet layer 1 is drawn through the directional voids of liquid control layer 2. Liquid continues through the liquid control layer 2 and is acquired and retained by the absorbent core 3.

The outer or top sheet layer 61 is typically made from a soft nonwoven porous fabric. For example, the outer layer may comprise a fabric made from about two to four denier polymer fibers or filaments. These fabrics are usually made either by thermally point bonded polyolefin fibers or from spunbonded filaments. Perforated films may also be employed. The absorbent core 3 may comprise any known materials, such as cellulose pulp augmented with a superabsorbent polymer powder or fiber.

The liquid transfer or control layer 1 comprises a thermally point bonded fabric of polyolefin fibers. Polypropylene is preferred. Other polymers, such as polyester or polyamides, can be employed but are generally more expensive to use and process.

In a preferred embodiment, the fibers are first separated and formed into a web in a well known manner. A series of cards are typically employed to build up a web of fibers of uniform thickness. The web is then thermally point bonded by passing the web through the nip of a pair of rotating and heated calendar rolls, one of which is engraved with a pattern, causing from about eight to about twenty-five percent of the fibers to become fused together, and creating a coherent fabric. The polyolefin fabric is hydrophobic and is preferably treated to render it hydrophilic. This may be accomplished by topical treatment of the fabric with a surface active agent, such as a surfactant. Other known methods include the addition of suitable agents to the melt as a fiber is being formed. Fiber denier is an important consideration in obtaining the desired bulk, resiliency and void volume in the final product. Generally the average denier of the fibers used in the transfer layer should be greater than those used in the cover fabric, and in any event should exceed four denier. An acceptable range is from four to thirty, with four to fifteen denier being preferred. A mixture of coarse and fine fibers may also be employed. The degree of increased bulk is related directly to the degree of creping imposed upon the nonwoven fabric. An increase in bulk of no less than 50% has been found to be the minimal level by which improved liquid control properties are obtained. The maximum limit has been found to be constrained by the limitations of the apparatus with which creping is performed, a level of 300 to 350% having been found routinely attainable.

It will be appreciated that any subsequent handling of a nonwoven fabric having been treated by mechanical compaction, specifically by a creping mechanism, will result in partial elongation of the treated fabric and a corresponding loss of performance anticipated. This loss in performance can be adjusted for during the treatment process such that the corresponding loss does not effect the required liquid control performance in the ultimate construction. In the alternative, the mechanical compaction method of choice can be employed in relationship to the feed section of a disposable sanitary article fabrication device. The untreated nonwoven fabric is fed into the mechanical compaction method and then directed immediately into the fabrication means so that the potential of post-treatment loss of performance is minimized.

Examples

The manufacturing means for an initial supply of nonwoven fabric comprised of a conventional carded staple length hydrophilic enhanced polypropylene fiber of 9 denier by 2.0 inch staple length, as supplied from Fibervisions of Athens, Georgia, as fiber type T-196. The basis weight of the carded lap varied as specified in the examples below.

The carded batt was thermally bonded by calender nip at a pressure of 450 pounds per linear inch, a calender anvil roll surface temperature of 300°F to 310°F, a calender embossing roll surface temperature of 300°F to 310°F, and a point pattern of 9% bond area relative to total surface area.

The above nonwoven fabric was then subjected to mechanical compaction by a microcreping process. The particular microcreping process employed is commercially available from the Micrex Corporation of Walpole, Massachusetts, and is referred to by the registered mark of the same company as "MICREX". The apparatus for performing the process is described in U.S. patents 3,260,778; 3,416,192; 3,810,280, 4,090,385; and 4,717,329, hereby incorporated by reference. In such an apparatus as shown in FIGURE 2, a means for imparting pressure 20 applies a predetermined amount of pressure through a substructure 28, and extending across the path of a continuously supplied sheet of nonwoven fabric M. The nonwoven fabric is carried by a rotating drive roll 10 of which the pressure is imparted through the nonwoven fabric and against the rotating drive roll 10. While the nonwoven fabric is under applied pressure it then further impinges upon a retarding surface 30. This retarding surface in combination with the applied pressure induces the fabric into a creped form, with a resulting distortion of constituent fibrous cpmponents out of the planar aspect of the original nonwoven fabric.

Example 1

A control nonwoven fabric comprising a carded 9 denier by 2.0 inch staple length polypropylene fiber was formed into a web or batt. The fibrous batt was subsequently point bonded by hot calender roll to 9% bond area at a pressure of 450 pounds per linear inch and a roll temperature of 310°F. The basis weight of the control nonwoven fabric was 33 grams per square meter with a bulk of 0.34 millimeters.

Example 2

The fabric as disclosed in Example 1, wherein the fabric was subjected to mechanical compaction at a compaction level of 25%. Example 3

The fabric as disclosed in Example 1, wherein the fabric was subjected to mechanical compaction at a compaction level of 30%.

Example 4

The fabric as disclosed in Example 1, wherein the fabric was subjected to mechanical compaction at a compaction level of 50%.

Example 5 The fabric as formed in Example 2 having been rewound onto a roll at a tension level of 2.0 pound per square inch, then sampled to simulate additional handling operations as would occur during converting operations.

Example 6 The fabric as formed in Example 3 was rewound onto a roll at a tension level of

2.0 pound per square inch and then sampled to simulate additional handling operations as would occur during converting operations.

Example 7 The fabric as formed in Example 4 was rewound onto a roll at a tension level of

The bulk of each material was measure by compressing a section of the respective materials under a 4 inch foot at 30 gram weight loading, then measuring the compressed height with a calibrated caliper.

Samples of each nonwoven fabric, both control and treated, where interposed between the topsheet layer and the absorbent core of a commercially available diaper.

The dimensions of the samples were cut with a length of 6.5 inches by 3.5 inches. The diaper topsheet layer and absorbent core used in these trials was from a commercially available brand of medium sized baby diapers for male children between a body weight of 16 and 28 pounds. Three sequential dosings of 100 ml mock human excreta in the form of commercially available synthetic urine, "URISUB" of Creative Scientific

Technology, Inc. of Great Neck, New York, or alternatively, a 1% saline solution, were applied with a five minute interval to represent liquid insults. After each dosing, the length of time required to fully absorb the mock liquid insult was recorded, this information indicating the absorbency rate of the construct. Upon absorption of the mock liquid insult, a pre-weighed and recorded filter paper swatch was applied at a pressure of 1 kilogram for a duration of ten minutes. The filter paper was re-weighed and the difference recorded as gram weight of reverse transient fluid movement, otherwise known as "rewet". The test results of the various constructs are found in TABLE 1. The results indicate that a mechanically compacted nonwoven fabric is bulkier and has a better absorbency than an uncompacted fabric. Further, there are indications that rewet performance are at acceptable levels after the first insult and markedly improve with each subsequent insult. It should be noted that the improved liquid handling properties of the mechanically compacted nonwoven fabric are substantially maintained after having been rewound and the bulk returned to the approximate starting bulk of the untreated nonwoven fabric.

From the foregoing, it will be observed that numerous modifications and variations can be affected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated herein is intended or should be inferred. The disclosure is intended to cover, by the appended claims, all such modifications as fall within the scope of the claims.

Table 1

Claims

What is Claimed is

1. A liquid control layer comprising a nonwoven fabric, the nonwoven fabric being mechanically compacted whereby the bulk of the compacted fabric is at least 50% greater than the nonwoven fabric, the compacted fabric exhibiting an improved absorbency rate when applied in liquid control and distribution applications.

2. A liquid control layer as in Claim 1, wherein the nonwoven fabric exhibits a basis weight of 15 to 60 grams per square meter.

3. A liquid control layer as in Claim 1, wherein the nonwoven fabric is formed from at least 50% by weight thermoplastic polymer as a fibrous material.

4. A liquid control layer as in Claim 3, wherein the thermoplastic polymer is selected from the group consisting of polyolefins, polyesters, polyamides, and combinations thereof.

5. A liquid control layer as in Claim 4, wherein the polyolefin is a hydrophilic enhanced polypropylene.

6. A liquid control layer as in Claim 3, wherein the fibrous material is in the form of staple length fibers.

7. A liquid control layer as in Claim 3, wherein the fibrous material is in the form of continuous thermoplastic filaments.

8. A liquid control layer as in Claim 3, wherein the fibrous material has a denier in the range of 3 to 20.

9. A liquid control layer as in Claim 8, wherein the fibrous material has a denier in the range of 6 to 15.

10. A liquid control layer as in Claim 1, wherein the nonwoven fabric is integrated by thermal bonding.

11. A liquid control layer as in Claim 10, wherein the thermal bonding is by hot calender roll.

12. A liquid control layer as in Claim 11, wherein the extent of bonding by hot calender roll is in the range of 8% to 25% total surface area.

13. A liquid control layer as in Claim 1, wherein the mechanical compaction is imparted by creping.

14. A liquid control layer as in Claim 1, wherein the mechanical compaction is imparted by microcreping.

15. A liquid control layer as in Claim 1, wherein the compacted fabric liquid control and distribution application includes the construction of disposable sanitary articles.

16. A liquid control layer as in Claim 15, wherein the disposable sanitary article is a diaper.

17. A liquid control layer comprising a nonwoven fabric, said nonwoven fabric including carded thermoplastic polypropylene staple fiber and thermally bonded by hot calender roll, the nonwoven fabric then being creped whereby the bulk is increased by at least 50%, the creped fabric exhibiting improved absorbency rate, the creped fabric being incorporated as a liquid control layer in a disposable sanitary article.

18. An absorbent article comprising a liquid absorbing core, a porous cover on said core, and a liquid transfer layer between said cover and said core to facilitate transfer and distribution of liquids between said cover and said core, said transfer layer comprising a web comprising thermoplastic fibers, said web being point bonded and microcreped to a thickness of greater than fifty percent of original thickness.

19. The absorbent article of Claim 18, wherein said transfer layer comprises a web which is point bonded by calendering.

20. The absorbent article of Claim 19, wherein said transfer layer comprises polypropylene fibers.

21. The absorbent article of Claim 20, wherein the denier of the fibers is from about four to about thirty.

22. The absorbent article of Claim 20, wherein said polypropylene fibers are treated to render them hydrophilic.

23. The absorbent article of Claim 18, wherein the porous cover is hydrophobic relative to the liquid transfer layer.

1/1

FIG. I