Mixed denier fluid management layers

Details Mixed denier fluid management layers Mixed denier fluid management layers

2001-12-14

2004-08-24

Calvert, John J. (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S367000, C604S370000, C604S372000, C428S213000, C442S361000, C442S362000, C442S363000, C442S364000

Reexamination Certificate

active

06781027

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns formed materials mainly for personal care products like diapers, training pants, swim wear, absorbent underpants, adult incontinence products and feminine hygiene products. This material may also be useful for other applications such as, for example, in bandages and wound dressings, nursing pads and in veterinary and mortuary applications.
Personal care articles usually have multiple layers of material of some sort to absorb liquids from the body. These layers may include natural fibers, synthetic fibers and superabsorbent particles in varying proportions. When liquid such as urine is deposited into a personal care product like a diaper, it goes through the uppermost layers, typically a liner against the body and a “surge” or “intake” layer designed to provide temporary liquid holding capacity. The product may also have a “distribution” layer designed to move liquid in the X and Y directions in order to utilize more of the absorbent core. After going through these upper layers, the urine enters the absorbent core portion of the product. The absorbent core permanently retains the liquid.
Various approaches have been used in the past to hold liquid, yet still allow it to be transferred eventually to another layer like the core. Similarly, intake materials have been investigated which take in liquid with varying degrees of success. There remains a need in the art for a fabric for use in personal care products with improved fluid handling capabilities. Such a material will intake and retain fluid more efficiently than has been practiced in the past.
SUMMARY OF THE INVENTION
In response to the discussed difficulties and problems encountered in the prior art, a new structural composite comprising a nonwoven fabric made of a homogeneous blend of large and small denier synthetic fibers has been developed. The nonwoven material is for personal care products and is made from a mixture of fibers of different denier, where a first denier fiber has an average denier at least 3 denier less than a second fiber and the second fiber has an average denier between 4 and 15, and where the material has a basis weight between 30 and 200 gsm. The first denier fiber has an average denier of 2 or less and the second denier fiber preferably has an average denier between 6 and 15.
The nonwoven material can have the first denier fiber present in an amount between 25 and 75 weight percent and the second denier fiber present in an amount between 75 and 25 weight percent. More particularly the first denier fiber can be present in an amount between 40 and 60 weight percent and the second denier fiber can be present in an amount between 60 and 40 weight percent. Still more particularly, the first denier fiber can be present in an amount of about 60 weight percent and the second denier fiber can be present in an amount of about 40 weight percent.
The first denier fiber may be a bicomponent fiber and may be a sheath/core bicomponent fiber selected of the group consisting of polyethylene/polypropylene, polyethylene/polyethylene terephalate and co-polyethylene terephalatel polyethylene terephalate bicomponent fibers. The second denier fiber may be made from a polyester. The fibers may have a hydrophilic treatment added to their surface.
The material made from the homogeneous blend of mixed denier fibers may be used as a surge material in personal care products. When used as a surge material in personal care products the material is capable of taking in fluid at a rate of 12 to 20 cc/sec. When used as a surge material in conjunction with a standard liner the structure is capable of up to an 8, 15 or even 20 percent TEWL improvement, when compared to a large fiber denier surge using the same standard liner.
Particular embodiments include a surge material for personal care products having between 40 and 60 weight percent of a first fiber having a first average denier and between 60 and 40 weight percent of a second fiber having a second average denier, where the first average denier is at least 3 denier less than the second average denier, the second average denier is between 4 and 15, and where the material has a basis weight between 30 and 200 gsm. Another embodiment is one in which the surge material for personal care products has about 60 weight percent of a first fiber in a bicomponent sheath/core configuration, made from polymers selected of the group consisting of polyethylene/polypropylene, polyethylenelpolyethylene terephalate and co-polyethylene terephalate/polyethylene terephalate and having a first average denier, and about 40 weight percent of a polyester second fiber having a second average denier, where the first average denier is at least 3 denier less than the second average denier, the second average denier is between 4 and 15, and where the material has a basis weight between 30 and 200 gsm. The small or first fiber has a average denier less than the large average denier fiber and the large or second denier fiber has a average denier between 4 and 15.
These materials are suitable for use in personal care products like diapers, training pants, incontinence products, bandages, and sanitary napkins.
Definitions
As used herein the term “nonwoven fabric or web” means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).
“Hydrophilic” describes fibers or the surfaces of fibers that are wetted by the aqueous liquids in contact with the fibers. The degree of wetting of the materials can, in turn, be described in terms of the contact angles and the surface tensions of the liquids and materials involved. Equipment and techniques suitable for measuring the wettability of particular fiber materials can be provided by a Cahn SFA-222 Surface Force Analyzer System, or a substantially equivalent system. When measured with this system, fibers having contact angles less than 90° are designated “wettable” or hydrophilic, while fibers having contact angles equal to or greater than to 90° are designated “nonwettable” or hydrophobic.
“Spunbonded fibers” refers to small diameter fibers that are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinneret. Such a process is disclosed in, for example, U.S. Pat. No. 4,340,563 to Appel et al. and U.S. Pat. No. 3,802,817 to Matsuki et al. The fibers may also have shapes such as those described, for example, in U.S. Pat. No. 5,277,976 to Hogle et al. which describes fibers with unconventional shapes.
“Bonded carded web” refers to webs that are made from staple fibers which are sent through a combing or carding unit, which separates or breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. This material may be bonded together by methods that include point bonding, through air bonding, ultrasonic bonding, adhesive bonding, etc.
“Airlaying” is a well-known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 3 to about 52 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air to activate a binder component or a latex adhesive. Airlaying is taught in, for example, U.S. Pat. No. 4,640,810 to Laursen et al., and U.S. Pat. No. 5,885,516 to Christensen.
As used herein “thermal point bonding” involves passing a fabric or

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