Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including strand or fiber material which is a monofilament...
Reexamination Certificate
2000-11-29
2004-02-24
Cole, Elizabeth M. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including strand or fiber material which is a monofilament...
C442S362000, C442S364000, C442S414000, C442S415000, C428S373000, C428S374000
Reexamination Certificate
active
06696373
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to nonwoven webs. More particularly, the invention is directed to nonwoven polyolefin webs which have durable hydrophilic properties and to articles formed from such webs.
BACKGROUND OF THE INVENTION
Polyolefin fibers have been widely used in the nonwovens industry in the manufacture of nonwoven webs, fabrics, and composites. Olefin polymers, such as polyethylene, polypropylene, polybutene, polypentene, and copolymers of ethylene or propylene with other olefinic monomers, are known for their hydrophobic properties. Thus, nonwoven webs of polyolefin fibers are frequently used in applications where their hydrophobic properties are advantageous. For example, polyolefin nonwovens are often used in diapers, other hygiene products and medical applications where it is desired to keep moisture away from a wearer's skin.
However, there are numerous other nonwoven fabric applications where the hydrophobic nature of polyolefin fibers is not required and where hydrophilic properties are desired. If a nonwoven fabric formed of polyolefin fibers is to be used, the fibers must be treated in some way to alter the normally hydrophobic properties of the fibers to impart hydrophilic properties. One well-known practice involves the topical application of compositions, such as surfactants, to render the fabric more hydrophilic. However, topical chemical applications are not entirely satisfactory for some applications, since they are not durable. The hydrophilic property is lost after washing or after extended use. The extra processing steps required for topical chemical treatments or other fiber surface modification treatments also undesirably increase the cost of the fabric. The few processes known to render the polyolefins wettable are environmentally unfriendly, relatively slow and have limited durability.
An alternative to chemical surface modification is to directly melt blend a hydrophilic additive into the thermoplastic polymer rendering the fibers themselves hydrophilic. Published PCT Patent Specification WO99/00447 discloses a product and process for making wettable fibers prepared from an olefin polymer, polyester or polyamide including a wetting agent consisting essentially of a monoglyceride or a combination of a monoglyceride and a mixed glyceride with the monoglyceride amounting to at least 85% by weight in the case of the combination.
The monoglyceride corresponds to the formula
wherein —OR
1
, OR
2
, and —OR
3
are hydroxyl or a fatty acid ester group, but only one of them is a fatty acid ester group (C
12-22
). The mixed glyceride (di- or tri-) corresponds to the formula
wherein —OR
4
, OR
5
, and —OR
6
are hydroxyl or a fatty acid ester group (C
12-22
). The combination of this di- or tri-glyceride with the monoglyceride constitutes the wetting agent in accordance with one embodiment.
However, the use of hydrophilic melt additives can add significantly to the cost of the nonwoven webs. Also, the addition of a hydrophilic melt additive to the polyolefin polymer can alter the properties of the fibers or filaments, resulting in unacceptable changes to important physical or aesthetic properties of the nonwoven web, such as strength, softness or hand, for example.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing limitations and provides a polyolefin nonwoven web which has durable hydrophilic properties, while achieving a highly desirable combination of cost, physical properties and aesthetics.
Nonwoven webs in accordance with the present invention include multicomponent fibers bonded by a multiplicity of bond sites to form a coherent web. The multicomponent fibers include a first component formed of a hydrophobic polypropylene and a second component formed of a blend of a hydrophobic polyolefin and a hydrophilic melt additive. This second component is disposed at the surface of the fibers. The hydrophilic melt additive-modified polyolefin component can be arranged in various configurations in the cross-section of the fiber and the fibers can have various cross sections. For example, the hydrophilic component can occupy a portion of the surface of the fiber, as would occur for example with a side-by-side or segmented pie multicomponent fiber configuration. Alternatively, the modified hydrophilic polyolefin can occupy substantially the entire surface of fiber, as for example by producing the fibers in a sheath-core configuration with the hydrophilic modified component forming the sheath. A particularly preferred configuration is a sheath-core bicomponent fiber where the hydrophobic polypropylene forms the core and the modified hydrophilic polyolefin forms the sheath. Other configurations include non-concentric sheath-core, multi-lobal or tipped cross sections, and islands-in-the-sea cross sections.
The multicomponent fibers may be formed into a nonwoven web using various processing techniques known in the nonwovens industry. For example, the multicomponent fibers may comprise an air-laid web of staple fibers, a carded web of staple fibers, a wet-laid web staple fibers, a web of meltblown fibers or a spunbonded web of substantially continuous filaments or a combination of two or more of these techniques.
There are various melt additives available which can be melt blended with a hydrophobic polyolefin composition to impart durable hydrophilic properties to the polyolefin. Melt additives suitable for the present invention must not undesirably alter the melt-spinability of the multicomponent fibers and should be relatively compatible with the polyolefin composition such that the additive will not prematurely leach out and lose the hydrophilic properties. Certain suitable melt additives useful in the present invention will be at least partially immiscible with the polyolefin polymer composition and will tend to bloom to the fiber surface over time or with application of heat to impart a prolonged hydrophilic surface modification. Particularly suitable are compounds with a molecular structure which includes at least one functional group which is tethered to the olefin polymer structure, with other functional groups which provide reactive hydrophilic sites.
Suitable hydrophilic melt additives for use in the present invention include monomer or dimer fatty acids, hydroxy phenols, polyethylene glycol, fluorohydrocarbons, polyvinyl alcohol and polyvinyl formal.
One particularly suitable class of melt additives is an admixture of hydroxy phenols and polyethylene glycols. The hydroxy phenol is characterized in that it contains the functional group HOC
6
H
4
—.
Another particularly suitable class of melt additives are monomer and dimer fatty acids having a carbon chain length in the range of 6 to 50, preferably 18 to 36.
According to one embodiment of the invention, the nonwoven web is fabricated employing wet laid and/or carded thermal bonding processes. It is possible to use combinations of hydrophobic and hydrophilic fibers in the web. In other words, all fibers in the web need not be permanently wettable.
In one specific preferred embodiment, the web includes bicomponent fibers in which the melt additive is incorporated into the sheath constituent of the fiber. Use of bicomponent fibers, as well as combinations of hydrophobic and hydrophilic fibers, reduces costs and permits optimization of the web for diverse applications.
Thus, a broad aspect of the present invention is to provide a nonwoven web that has the wettability and strength for use in various end uses (such as rechargeable alkaline batteries, hygiene products, medical products, or filtration products) by directly incorporating hydrophilic melt additives into one or more normally hydrophobic polyolefin components of a multicomponent fiber during melt processing. This fiber can be meltblown, spunbonded or made into staple fibers to form a wettable web. Alternatively the wettable fiber can be mixed with binder fibers that are wettable or non-wettable or mixtures of both which are then made into a nonwoven web.
Another aspect of the invention is to provi
Haley Clement J.
Henning Gregory Neil
Kinn Larry L.
Alston & Bird LLP
BBA Nonwovens Simpsonville, Inc.
Cole Elizabeth M.
Pierce Jeremy R.
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