Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-01-17
2003-06-24
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C525S437000, C525S444000, C428S359000, C428S364000, C428S370000, C264S177130, C424S443000, C604S358000, C604S367000
Reexamination Certificate
active
06582817
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to nonwoven fabrics having exceptional moisture management characteristics. The present invention also relates to the manufacture of such nonwoven fabrics from polyethylene glycol modified copolyester staple fibers.
BACKGROUND OF THE INVENTION
Disposable diapers and other personal care products formed of nonwoven, synthetic fabrics are extremely popular. In fact, disposable diapers made of such nonwoven fabrics have now essentially replaced cloth diapers in the marketplace. This is so not only because nonwoven fabrics offer an attractive cost structure, but also because nonwoven fabrics provide superior performance. For example, continued enhancements to nonwoven fabrics include weight reduction, aesthetic improvements, and, of particular relevance to diapers, increases in the number of uses an article can endure before requiring disposal.
For many years, synthetic fibers, particularly polyester fibers, have been a major component in nonwoven fabrics for disposable personal care products. Such man-made fibers are cost-effective, strong, and are readily modifiable to deliver a range of desirable properties. For example, denier, crimp, cut length, polymer chemistry, and fiber finish chemistry can all be modified to meet specific end-use requirements. In this regard, coarser deniers are used to increase bulk, cut length can be optimized for various web formation techniques, and fiber finishes are modified to offer processing advantages, as well as end-use performance.
As is known by those familiar with personal care products, a primary function of the nonwoven surge layer in diapers is to move moisture from its source to a highly absorbent core. This allows the fabric surface that is in contact with skin to remain essentially dry and be available to accept more moisture. This increases the duration that a product can be used before disposal. Surge layers are often chemically treated to facilitate this kind of moisture movement. Such treatments, however, are typically inadequate to permit multiple uses, which the marketplace demands for diapers. Consequently, the optimization of the specific diaper construction, including the incorporation of specific fibers and fabrics, is a major focus of research across the fiber, nonwovens, and personal products industries.
The use of nonwoven materials in personal care products is well known. In this regard, U.S. Pat. Nos. 5,879,343, 5,820,973, and 5,994,615, each of which is assigned to Kimberly-Clark Worldwide, Inc., disclose achieving favorable moisture transport properties in surge layers using synthetic fibers, as well as surge materials for disposable personal care products made by bonding fibrous webs. Similarly, U.S. Pat. No. 4,548,856, which is also assigned to Kimberly-Clark Worldwide, Inc., discloses a method for forming bulky, absorbent nonwoven fabrics that include thermoplastic fibers. These Kimberly-Clark patents are hereby incorporated entirely herein by reference.
Despite the advancements in technology, there remains a continuing need for nonwoven fabrics having improved moisture management properties. Research and development by Wellman, Inc. demonstrates that improved wicking may be achieved in copolyester fibers and fabrics by selectively incorporating polyethylene glycol.
For example, a PEG-modified copolyester composition and method for producing the same is disclosed by Nichols and Humelsine in commonly-assigned, pending U.S. patent application Ser. No. 09/141,665, filed Aug. 28, 1998, for Polyester Modified with Polyethylene Glycol and Pentaerythritol, now U.S. Pat. No. 6,294,254. U.S. patent application Ser. No. 09/141,665, which is incorporated entirely herein by reference, discloses a polyester composition that includes polyethylene terephthalate, polyethylene glycol in an amount sufficient to increase the wetting and wicking properties of a fiber made from the composition to a level substantially similar to the properties of cotton, but less than the amount that would reduce the favorable elastic memory properties of the polyester composition, and chain branching agent in an amount that raises the melt viscosity of the polyester composition to a level that permits filament manufacture under substantially normal spinning conditions. Including significant concentrations of branching agents to increase melt viscosity is sometimes undesirable, however, because branching agents promote cross-linking. This reduces filament strength, which can lead to processing failures.
Moreover, a method for achieving enhanced polyester fibers is described by Branum in commonly-assigned, pending U.S. patent application Ser. No. 09/444,192, filed Nov. 19, 1999, for a Method of Preparing Polyethylene Glycol Modified Polyester Filaments. U.S. patent application Ser. No. 09/444,192, which, as noted, is incorporated entirely herein by reference, describes copolymerizing polyethylene glycol, which typically makes up between about 4 percent and 20 percent by weight of the resulting copolyester, into polyethylene terephthalate in the melt-phase to a relatively low intrinsic viscosity (i.e., a viscosity that will not support filament spinning). The resulting PEG-modified polyester is then further polymerized in the solid phase until the copolyester is capable of achieving a melt viscosity sufficient to spin filaments. By introducing a solid state polymerization (SSP) step, this method reduces the need to add branching agents, such as pentaerythritol, to increase the melt-phase polymerization rate and thereby achieve an intrinsic viscosity that facilitates the spinning of filaments. U.S. patent application Ser. No. 09/444,192 explains that branching agents promote cross-linking, which can lead to relatively weaker textiles.
Furthermore, a related method for achieving enhanced polyester fibers is described by Branum in commonly-assigned, pending application Ser. No. 09/484,822, filed Jan. 18, 2000, for Polyethylene Glycol Modified Polyester Fibers and Method for Making the Same. U.S. patent application Ser. No. 09/484,822, which is a continuation-in-part of the aforementioned application Ser. No. 09/444,192 and, as noted, is also incorporated entirely herein by reference, describes copolymerizing polyethylene glycol and branching agent into polyethylene terephthalate in the melt-phase to form a copolyester composition having an intrinsic viscosity of at least about 0.67 dl/g. Thereafter, copolyester filaments can be spun from the copolyester composition.
The present invention applies this technology fairly to the field of nonwoven fabrics in order to achieve PEG-modified copolyester personal care products that possess exceptional moisture management characteristics. Moreover, such copolyester products may be formed at significantly lower calendar bonding temperatures.
OBJECT AND SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a nonwoven fabric having exceptional moisture management characteristics. The nonwoven fabric is especially useful in absorbent, personal care products, such as wipes, absorbent undergarments (e.g., disposable diapers, training pants, and adult incontinence products) and feminine hygiene products (e.g., sanitary napkins). The nonwoven fabric may also be included in durable goods having the appearance, performance, and aesthetics of conventional textile goods.
The nonwoven fabric is formed of polyethylene glycol modified copolyester staple fibers, which include polyethylene terephthalate in an amount sufficient for the copolyester staple fibers to possess dimensional stability properties substantially similar to those of conventional, unmodified polyethylene terephthalate fibers, polyethylene glycol in an amount sufficient for the copolyester staple fibers to possess wicking characteristics that are superior to those of conventional, unmodified polyethylene terephthalate fibers, and chain branching agent in an amount less than about 0.0014 mole-equivalent branches per mole of standardized polymer.
It is also an objective of this invention
Branum James Burch
Carnes Keith James
Acquah Samuel A.
Summa & Allan P.A.
Wellman, Inc.
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