Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-08-22
2004-09-28
Cole, Elizabeth M. (Department: 1771)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S304400, C428S311110, C428S315500, C442S401000, C604S367000, C604S380000
Reexamination Certificate
active
06797360
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.
The functions of the layers mentioned above may each be performed by different layers or a layer may perform more than one function. The combination of more than one function in a single layer, however, generally results in a significant decrease in the performance of each of the functions.
Absorbent cores are typically composed of superabsorbent particles and/or pulp. A newer class of absorbents also uses a binder to improve wet stability and to ease converting into final products. Binders can be liquid adhesive or thermally activatable fibers typically present in amounts between 10 and 25 weight percent.
Superabsorbent particles absorb many times their weight in liquid and swell greatly as a result of being wetted. This swelling holds liquid within the product and so protects the wearer's skin, clothing and bedding, but may also block the further intake of liquid. This occurs because the swollen particles become so large as to close off fluid entrances to the structure, a phenomenon known in the art as “gel blocking”.
Alternatively, an absorbent structure lacking superabsorbent and made of the traditional pulp and binder fiber can experience “wet collapse”. This occurs as a result of saturation of the pulp and the subsequent inability to regenerate void space as fluid is added to the structure. The binder fibers, generally synthetic polymer fibers that are naturally hydrophobic, contribute to this problem since they interfere with the wicking performance of the structure due to their poor wettability. In addition, the constraints induced by the bonding of the binder fibers restrains expansion of the absorbent structure, further reducing void volume and decreasing the ultimate capacity of the material. If the structure were able to wick fluid away from the area of incipient wet collapse more efficiently, the phenomenon might be avoided completely.
A material which treads the fine line between wet collapse and gel blocking would be very desirable. Such a material would avoid the undesirable features of uncontrolled superabsorbent expansion while efficiently absorbing fluids. It would also avoid wet collapse by maintaining a sufficient pore structure, allowing liquid to continue moving through it. Such a material would exhibit high levels of multi-functional absorbent performance.
SUMMARY OF THE INVENTION
In response to the discussed difficulties and problems encountered in the prior art, a new structural composite comprising nonwoven fabric to which has been added superabsorbent has been developed. The superabsorbent is preferably in the form of particles (SAP). The SAP is placed in “micro-pockets” formed by various means like creping or the manual creation of depressions in the surface of the nonwoven using a pattern roll. The volume of the micro-pockets may be between 0.33 and 10 cubic millimeters. The SAP need not be uniformly placed in the web but may be located in a non-uniform manner across the width of the fabric. As a result of this construction, the nonwoven web remains permeable to liquids before and after wetting. When the web is wetted, the superabsorbent is free to swell without disrupting the fibrous network of the web since it is located in the discrete pockets. The web should have a permeability above 1500 darcys and preferably above 2000 darcys.
In this invention, at least one layer having a mixture of polymeric fibers, superabsorbent in an amount between 1 and 80 weight percent and binder in an amount between 1 and 6 weight percent is provided. More particularly, amounts of superabsorbent between 25 and 75 weight percent and still more particularly between 40 and 60 percent may be beneficial. Additional layers may be present as well and the inventive layer may be placed in a personal care product to act as a distribution and absorption layer. The inventive layer has good distribution properties, presumably due to the avoidance of gel blocking, capillary disruption and wet collapse, by virtue of the discrete placement of the superabsorbent. It is also possible to electrically treat the web of this invention to improve particle adherence.
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).
“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.
As used herein, the term “coform” means a process in which at least one meltblown diehead is arranged near a chute through which other materials are added to the web while it is forming. Such other materials may be pulp, superabsorbent particles, natural fibers (for example, rayon or cotton fibers) and/or synthetic fibers (for example, polypropylene or polyester) fibers, for example, where the fibers may be short cut of staple length. Coform processes are shown in commonly assigned U.S. Pat. No. 4,818,464 to Lau and U.S. Pat. No. 4,100,324 to Anderson et al. Webs produced by the coform process are generally referred to as coform materials.
“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.
Cole Elizabeth M.
Hendon Nathan P.
Kimberly--Clark Worldwide, Inc.
Pierce Jeremy R.
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