Method for making a fibrous absorbent material

An absorbent material including a fibrous material having a plurality of individual fibers forming a fiber matrix, a plurality of absorbent fibers, wherein the plurality of absorbent fibers are impregnated within the fiber matrix by means of a needlepunch process.

FIELD OF THE INVENTION

The present invention generally relates to an absorbent material and a method for making the same. More particularly, the present invention relates to an absorbent material for use in disposable sanitary absorbent products such as sanitary napkins, pantiliners, tampons, diapers, adult incontinence products, and the like.

BACKGROUND OF THE INVENTION

Lofty, resilient, non-woven webs, that is nonwoven webs that have a high degree of loft and the tendency to retain such loft, are well known. In addition, it is well known that such lofty, resilient, non-woven webs may be used in disposable sanitary products such as sanitary napkins, pantiliners, tampons, diapers, adult incontinence products, and the like. A perceived benefit of such lofty, resilient, non-woven webs is that such materials may deliver enhanced comfort to a user of such disposable sanitary products since the lofty, resilient, nonwoven webs may tend to conform to, and move with, the user's body during use.

A problem with lofty, resilient, nonwoven webs is that due to the loft of such materials (i.e. their low density) such webs are not particularly absorbent. In addition, such materials may exhibit poor rewet properties. That is, such materials may release or “wet back” fluid when subjected to an external pressure.

In view of the foregoing there is a need for a lofty, resilient, non-woven web that also provides superior fluid handling characteristics.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention provides, a method for making an absorbent material including the steps of providing a fibrous material including a plurality of individual fibers forming a fiber matrix, depositing a plurality of absorbent fibers on a top surface of the fibrous material, and impregnating the plurality of absorbent fibers into the fiber matrix by means of a needlepunch process.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the present specification, the same or similar reference numbers have been used to identify the same or similar elements of the various embodiments of the present invention described herein.

Reference is made toFIG. 1which illustrates a sectional schematic view of an absorbent material10according to a first embodiment of the present invention. As shown inFIG. 1, the absorbent material10is formed from a fibrous material12including a plurality of individual fibers14that form a fiber matrix16. The absorbent material10further includes a plurality of absorbent fibers18. As shown, the absorbent fibers18are impregnated within the fiber matrix16.

The fibrous material12is preferably a fibrous nonwoven material made by a known nonwoven manufacturing technique such as an airlaid process, a card and bind process or a resin and adhesive bond process. Preferably the nonwoven material is a “high loft” nonwoven. Specifically, the nonwoven preferably has a density lower than 0.05 g/cc, and preferably between about 0.01 g/cc and 0.03 g/cc, prior to the impregnation of the nonwoven with the absorbent fibers18. The individual fibers14forming the fibrous nonwoven material may be selected from fibers including synthetic, nonabsorbent fibers that may or may not be wettable, for example hydrophilic fibers, hydrophobic fibers, and combinations thereof. Specific fiber types include, but are not limited to, polyester, nylon, co-polyester, polyethylene, polypropylene, and polylactic acid. Of course the fibrous nonwoven material may be formed from a single nonabsorbent fiber type listed above or alternatively may be formed from a mixture of the fiber types listed above. The surface of nonabsorbent fibers14forming the fibrous material12may be rendered wettable by treating such fibers with a suitable surface treatment, such a surfactant or like.

Each of the fibers14forming the fibrous nonwoven material preferably has a fiber diameter within the range of 11 μm and 100 μm. The fibrous material12preferably further includes a binder material, such as a latex binder. The binder material is preferably present in the fibrous material12in an amount between about 30% by weight to about 50% by weight.

The absorbent fibers18are preferably selected from cellulosic fiber types, such as, but not limited to, hard wood pulp, soft wood pulp, rayon, and cotton. The absorbent material10may include a single absorbent fiber type of those listed above or in the alternative may include multiple fiber types of those listed above (i.e. a mixture of absorbent fibers). Each of the absorbent fibers18preferably has fiber diameter within the range of 10 μm and 40 μm.

The individual fibers14forming the fibrous material12and the absorbent fibers18are selected such that each of the individual fibers14has a fiber diameter that is at least 1 μm greater than a fiber diameter of each of the absorbent fibers18.

As will be discussed in greater detail below, the absorbent fibers18are impregnated within the fiber matrix16by means of a needlepunch process according to the present invention. The needlepunch process according to the present invention, described in detail below, allows the absorbent fibers18to be impregnated within the fiber matrix16without the fibrous material12losing its high loft properties. Specifically, the density of fibrous material12prior to being impregnated with the absorbent fibers18is preferably within the range of 0.01 g/cc and 0.03 g/cc.

The fibrous material12preferably has a thickness in the range of about 1.5 mm to about 5 mm prior to impregnation of the fibrous material12with the absorbent fibers18. After impregnation of the fibrous material12with the absorbent fibers18the absorbent material10retains substantially the same thickness as the original fibrous material. Specifically, a percent change between the thickness of the fibrous material12prior to the plurality of absorbent fibers18being impregnated therein and a thickness of the absorbent material10after the absorbent fibers18have been impregnated within the fibrous material12is preferably less than 50%, more preferably less than 30% and most preferably less than 15%. This relatively small change in thickness reflects that the absorbent material10retains the high loft properties of the fibrous material12while at the same time delivers superior fluid handling capabilities. The percent change in thickness is calculated as follows:
% ΔT=(Ti−Tf)/Ti; whereTi=Initial Thickness of Fibrous Material12Tf=Final Thickness of Absorbent Material10

A method of making the absorbent material10will now be described with reference toFIG. 2which depicts a schematic representation of an apparatus19for making the absorbent material10. As shown inFIG. 2, a web of fibrous material12is fed from a supply roll20and conveyed in a machine direction by a plurality of rolls22,24and26. A gravity fed hopper28, or the like, is utilized to apply a selected amount of absorbent fibers18to a top surface30of the fibrous material12. Thereafter, the fibrous material12is further conveyed in a machine direction and passed through a conventional needlepunch apparatus32of the type known to those of skill in the art. In the method according to the present invention, the needlepunch apparatus32functions to impregnate the absorbent fibers18within the fibrous material12by means of a plurality of needles34.

As is known to those of skill in the art, a conventional needlepunch apparatus includes a plurality of needles that are normally adapted to mechanically orient and interlock the fibers of a spunbonded or carded web. In the method according to the present invention, the needles34of the needlepunch apparatus32are used to impregnate absorbent fibers18within the fibrous material12. A needle34suitable for use in the method according to the present invention is depicted inFIG. 3andFIG. 3a. As shown inFIG. 3a, the needle34generally includes a blade36, a barb38, and a throat section40. The total barb depth of the barb38is indicated by letter “d” in theFIG. 3a.

For purposes of the present invention, it is critical that the barb depth “d” is selected such that a radius of each of the absorbent fibers18is smaller than the barb depth “d”. The radius of each absorbent fiber18is at least 0.5 μm smaller, for example 1 μm smaller than the barb depth. In addition the barb depth “d” should be selected such that each of the individual fibers14of the fibrous material12has a radius that is larger than the barb depth “d”. The radius of each individual fiber14of the fibrous material12is at least 0.5 μm larger, for example 1 μm larger than the barb depth. If you have a multiple denier fibrous material12, the diameter of the smallest diameter fiber14must be larger than the diameter of each of the absorbent fibers18.

By selecting barb depth “d” as described above, the plurality of needles34in the needlepunch apparatus effectively grasp the absorbent fibers18and thus can impregnate such absorbent fibers18within the fibrous material12, as shown inFIGS. 3b-3e. On the other hand, the plurality of needles34will not grasp the individual fibers14of the fibrous material12and thus will not destroy the “high loft” properties of the fibrous material12. In this manner the final absorbent material10is provided with superior fluid handling properties while still retaining the high loft properties of the fibrous material12. Needles particularly useful in the present method are commercially available from the Foster Needle Co., Inc., Manatowoc, Wis., under product designation “The Foster Formed Barb”.

Referring again toFIG. 2, after the fibrous12has been impregnated with the absorbent fibers18the resultant absorbent material10is further conveyed in a machine directly by rolls28and30. At this point in the process the absorbent material10may be arranged in a rolled form for storage or may be further conveyed for incorporation into disposable sanitary absorbent products such as a sanitary napkin, pantiliner, tampons, diaper, adult incontinence product, or the like.

Alternatively, as shown inFIG. 2, the fibrous material12may be further conveyed to a superabsorbent application station42. The superabsorbent application station42comprises a gravity fed hopper44structured and arranged to apply a selected amount of superabsorbent polymer material46to a top surface30of the fibrous material12. Of course, any suitable means known to those of skill in the art, such as a pressure fed nozzle or the like, may be used to apply the superabsorbent polymer material46to the top surface30of the fibrous material12. After the superabsorbent polymer material46is applied to the top surface30of the fibrous material12, the fibrous material12is conveyed over a vacuum50that functions to draw the superabsorbent polymer material46into the fiber matrix16of the fibrous material12. The resultant absorbent material10a, an absorbent material according to a second embodiment of the invention, is shown inFIG. 4. As shown, the superabsorbent polymer46has been drawn into the fiber matrix16of the fibrous material12and functions to further enhance the fluid handling capabilities of the absorbent material10a.

For the purposes of the present invention, the term “superabsorbent polymer” (or “SAP”) refers to materials which are capable of absorbing and retaining at least about 10 times their weight in body fluids under a 0.5 psi pressure. The superabsorbent polymer particles of the invention may be inorganic or organic crosslinked hydrophilic polymers, such as polyvinyl alcohols, polyethylene oxides, crosslinked starches, guar gum, xanthan gum, and the like. The particles may be in the form of a powder, grains, granules, or fibers. Preferred superabsorbent polymer particles for use in the present invention are crosslinked polyacrylates, such as the product offered by Sumitomo Seika Chemicals Co., Ltd. of Osaka, Japan, under the designation of SA70.

Referring again toFIG. 2, after the absorbent material10ais conveyed past the vacuum50the absorbent material10amay be further conveyed in a machine direction by roll51and arranged in a rolled form for storage or may be further conveyed for incorporation into a disposable sanitary absorbent products such as a sanitary napkin, pantiliner, tampons, diaper, adult incontinence product, or the like.

Reference is made toFIG. 5which illustrates a sectional schematic view of an absorbent material10baccording to a third embodiment of present invention. As shown, the absorbent material10bis formed from a fibrous material12including a plurality of individual fibers14that form a fiber matrix16. The absorbent material10bfurther includes a first plurality of absorbent fibers18aarranged in a first layer52and a second plurality of absorbent fibers18barranged in a second layer54. The absorbent fibers18aand18bmay comprise the same fibers as those absorbent fibers18described above with regard to the first embodiment of the present invention. The absorbent fibers18aand18bmay be the same fiber type or may be different fibers types (i.e. a mixture of fibers). In addition, a first absorbent fiber mixture (or individual fiber) may be employed in the first plurality of fibers18aand different absorbent fiber mixture (or individual fiber) may be employed in the second plurality of fibers18b.

The individual fibers14may be the same as the fibers14described above with regard to the first embodiment. In addition the individual fibers14may be the same fiber type (i.e. a single fiber type) or different fiber types (i.e. a mixture of fibers).

In the particular embodiment of the invention shown inFIG. 5, the first layer52is arranged in spaced relationship to the second layer54. The absorbent material10bmay optionally further include superabsorbent polymer material46dispersed within the fiber matrix16of the fibrous material12. In the particular embodiment of the invention shown inFIG. 5, the superabsorbent46is arranged in a layer56between the first layer52and second layer54of the absorbent fibers18aand18b. Of course the superabsorbent polymer material46may be omitted from the absorbent material10bif desired.

A method of making the absorbent material10bwill now be described with reference toFIG. 6which depicts a schematic representation of an apparatus19afor making the absorbent material10b. As shown inFIG. 6, a web of fibrous material12is fed from a supply roll20and conveyed in a machine direction by a plurality of rolls22,24and26. A gravity fed hopper28, or the like, is utilized to apply a selected amount of absorbent fibers18ato a top surface30of the fibrous material12. Thereafter, the fibrous material12is further conveyed in a machine direction and passed through a needlepunch apparatus32for impregnating the absorbent fibers18awithin the fibrous material12.

Thereafter the fibrous material12is further conveyed to a superabsorbent application station42. The superabsorbent application station42comprises a gravity fed hopper44structured and arranged to apply a selected amount of superabsorbent polymer material46to a top surface30of the fibrous material12. Of course, any suitable means known to those of skill in the art, such as a pressure fed nozzle or the like, may be used to apply the superabsorbent polymer material46to the top surface30of the fibrous material12. After the superabsorbent polymer material46is applied to the top surface30of the fibrous material12the fibrous material12is conveyed over a vacuum50that functions to draw the superabsorbent polymer material46into the fiber matrix16of the fibrous material12. Of course, if the inclusion of superabsorbent polymer material46is not desired in the absorbent material10b, the superabsorbent application and vacuum step described may be omitted from the described method.

After the fibrous material12is conveyed past the vacuum50, the fibrous material12is conveyed by rolls51and53to a second gravity fed hopper28a, or the like, to apply a selected amount of absorbent fibers18bto a top surface30of the fibrous material12. Thereafter, the fibrous material12is further conveyed in a machine direction by rolls55and57and passed through a second needlepunch apparatus32afor impregnating the absorbent fibers18bwithin the fibrous material12.

Referring again toFIG. 6, after the absorbent material10bis conveyed past the needlepunch apparatus32athe absorbent material10bis further conveyed in a machine direction by roll59and then may be arranged in a rolled form for storage or may be further conveyed for incorporation into a disposable sanitary absorbent products such as a sanitary napkin, pantiliner, tampons, diaper, adult incontinence product, or the like.

EXAMPLES

Specific examples of the present invention are described below.

An absorbent material as described above with reference toFIGS. 1 and 2is made as follows. The fibrous material is a fibrous nonwoven made by a card and bind process having a basis weight of 68 gsm, formed from 100% polyester fibers (6 denier), and having a thickness of 3 mm. Given that the density of polyester is 1.38 g/cc, a 6 denier fiber has a nominal diameter of 25 μm (denier=density*0.0283 r2). The fibrous material includes a latex binder present in the amount of 40% by weight. A fibrous nonwoven material of this type is commercially available from Kem-Wove, Inc., Charlotte, N.C. under product code SCN09-038. The absorbent fibers comprise 100% viscose rayon having a denier of 4. Rayon has a density of 1.5 g/cc thus the absorbent fibers have a fiber diameter of 19 μm. 150 gsm (g/m2) of the rayon fibers are applied to a top surface of the fibrous nonwoven material and impregnated within the material to a depth of 2.5 mm by means of the needlepunch process described above with reference toFIG. 2. The needles used in the needlepunch process have a barb depth “d” of 12 μm. The final absorbent material has a thickness of 2.7 mm.

An absorbent material as described above with referenced toFIGS. 5 and 6is made as follows. The fibrous material is a fibrous card and bind nonwoven material having a basis weight of 68 gsm, formed from 100% polyester fibers (6 denier), and having a thickness of 3 mm. Given that the density of polyester is 1.38 g/cc, a 6 denier fiber has a nominal diameter of 25 μm (denier=density*0.0283 r2). The fibrous material includes a latex binder present in the amount of 40% by weight. A fibrous nonwoven material of this type is commercially available from Kem-Wove, Inc., Charlotte, N.C. under product code SCN09-038. The first plurality of absorbent fibers comprises 100% viscose rayon having a denier of 4. Rayon has a density of 1.5 g/cc thus the absorbent fibers have a fiber diameter of 19 μm. 75 gsm of the rayon fibers are applied to a top surface of the fibrous nonwoven material and impregnated within the material to a depth between 4.0 mm and 5.0 mm by means of a first needlepunch apparatus. The needles used in the needlepunch process have a barb depth “d” of 12 μm. Thereafter, the fibrous material is conveyed to a superabsorbent application station. 40 gsm of superabsorbent (SA70 commercially available from Sumitomo Seika Chemicals Co., Ltd. Of Osaka, Japan) is applied to a top surface of the fibrous material via a gravity fed hopper. The superabsorbent is drawn into the fibrous material at a depth between 3.0 mm and 4.0 mm by means of a vacuum. Thereafter, the fibrous material12is conveyed to a second gravity fed hopper to apply a selected amount of a second plurality of absorbent fibers to a top surface of the fibrous material. The second plurality of absorbent fibers comprises 100% viscose rayon having a denier of 4. Rayon has a density of 1.5 g/cc thus the absorbent fibers have a fiber diameter of 19 μm. 75 gsm of the rayon fibers are applied to a top surface of the fibrous nonwoven material and impregnated within the material to a depth between 1.0 mm and 3.0 mm by means of a second needlepunch apparatus. The needles used in the second needlepunch process have a barb depth “d” of 12 μm. The final absorbent material has a thickness of 2.5 mm.