Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-04-05
2003-01-21
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S364000
Reexamination Certificate
active
06509092
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to heat bondable multicomponent fibers, and more particularly heat bondable multicomponent fibers having a biodegradable polymeric component, as well as articles incorporating the fibers as a component thereof.
BACKGROUND OF THE INVENTION
Synthetic fibers are widely used in a number of diverse applications to provide stronger, thinner, and lighter weight products. Synthetic fibers are typically heat adhesive (thermobondable) and thus are particularly attractive for the manufacture of nonwoven fabrics. Nonwoven fabrics, in turn, are widely used as components of a variety of articles, including without limitation absorbent personal care products, such as diapers, incontinence pads, feminine hygiene products, and the like; medical products, such as surgical drapes, sterile wraps, and the like; filtration devices; interlinings; wipes; furniture and bedding construction; apparel; insulation; and others.
Nonwoven fabrics can be formed entirely of synthetic fibers or a mixture of synthetic and natural fibers (such as cellulosic fibers). For example, typically disposable absorbent products include an absorbent core formed of cellulosic fluff pulp. The absorbent core can also include thermobondable synthetic fibers to thermally bind the cellulose fibers together, thereby achieving an absorbent material with improved strength. The product can also be thinner and lighter weight than traditional products.
Despite these advantages, the use of synthetic fibers in conjunction with cellulosic fluff pulp has not been without problems. For example, due to the non-polar, hydrophobic nature of conventional thermobondable fibers, the fibers can form conglomerations in the aqueous fluff pulp solution utilized during wet processing. Dry laid production of nonwovens using synthetic fibers can be difficult as well because of the lack of reactive sites on the surface of conventional thermobondable fibers. This results in a physical bonding, based on encapsulation, rather than chemical bonding. Even physical bonding is inherently difficult because of the non-polar nature of many synthetic fibers, which prevents the polymer from readily wetting out the surfaces of more polar fibers (such as cellulose fibers).
In addition, conventional synthetic fibers do not naturally degrade, thus creating problems associated with the disposal of products containing such fibers. In particular, recycling articles containing a blend of natural and conventional synthetic fibers is generally not cost effective, yet the disposal of these articles in landfills generates significant amounts of non-degradable waste. As landfills reach their capacity, the demand has increased for the incorporation of more degradable components in disposable products, as well as the design of products that can be disposed of by means other than by incorporation into solid waste disposal facilities.
To address concern over the issue of solid waste disposal, biodegradable polymers are increasingly used as a replacement for conventional synthetic polymers. Biodegradable polymers of interest include water-soluble polymers such as polyvinyl alcohol; naturally synthesized polymers such as sodium alginate and microbial polyesters; hydrolyzable aliphatic polyester and polyurethane polymers; and the like. Synthetic biodegradable aliphatic polyesters include polyglycolide and poly(lactic)acid polymers. See, for example, U.S. Pat. Nos. 5,166,231; 5,506,041; 5,759,569; and 5,171,309.
Of particular interest is the use of lactic acid to manufacture biodegradable resin. Poly(lactic)acid (hereinafter “PLA”) was initially introduced as a biodegradable polymer for medical products. U.S. Pat. Nos. 5,142,023 and 5,807,973 to Gruber et al. disclose processes by which a nonmedical grade of poly(lactic)acid may be produced and utilized in nonwoven fabrics. Examples of biodegradable fibers comprised entirely of polylactic acid polymers and/or copolymers are found in U.S. Pat. Nos. 5,010,145 and 5,760,144. See also U.S. Pat. Nos. 5,698,322 and 5,593,778 (directed bicomponent fibers which include poly(lactic acid) components).
The successful inclusion of biodegradable materials in disposable absorbent products provides several avenues by which these products may be discarded once their useful life has ended. Primarily, these articles may be easily and efficiently disposed of by composting. Alternatively, the disposable absorbent product may be easily and efficiently disposed of to a liquid sewage system wherein the disposable absorbent product is capable of being degraded.
Although biodegradable fibers are known, problems have been encountered with their use, for example, lack of control of the onset of polymer degradation. It is essential that biodegradable fiber maintain its integrity until its useful life has ended. U.S. Pat. No. 5,593,778 is directed to a core/sheath bicomponent fiber comprised entirely of poly(lactic acid), wherein the core PLA component biodegrades at a faster rate than the sheath. Although such fibers can provide some benefits, such fibers merely delay the onset of degradation and do not provide means for proactively controlling or initiating degradation of biodegradable fibers.
SUMMARY OF THE INVENTION
The present invention provides multicomponent heat adhesive or thermobondable fibers which exhibit a number of desirable, yet contradictory, properties in a single fiber structure. The fibers of the invention include a biodegradable polymeric component, thereby providing advantages in the disposal of products made with such fibers. However, in contrast to prior biodegradable fiber constructions, the fibers of the invention are structured so that initiation of degradation can be readily controlled.
In this regard, in addition to a biodegradable component, the fibers of the invention also include a thermobondable non-biodegradable polymeric component. The non-biodegradable polymeric component forms at least a portion of the exposed outer surface of the fibers, and in a preferred embodiment, completely encapsulates the biodegradable component. To control fiber degradation, the non-biodegradable polymer and biodegradable polymer can be selected so that the non-biodegradable polymer has a lower melting point (preferably at least about 10° C. lower) than the melting point of the biodegradable polymer. The fibers can accordingly be thermally treated to melt away at least a portion of the non-biodegradable polymer component to expose the biodegradable component to conditions necessary to initiate decomposition or degradation thereof. Thus the fiber degradation process can be proactively initiated, rather than merely slowed or delayed, by protecting the biodegradable component from the environment until such a time as its degradation is purposefully triggered.
In addition, because the fibers of the invention include a thermobondable polymeric component on at least a portion of the exposed surface thereof, the fibers have useful thermobonding properties, with one another and/or with different fibers. Yet in contrast to conventional thermobondable fibers, the fibers of the invention can also have useful surface properties to assist in bonding to other types of fibers (such as cellulosic fibers). As discussed above, conventional thermobondable synthetic polymeric fibers are essentially hydrophobic and lack reactive polar sites on the surface thereof. Thus it can be difficult to effectively bond such fibers with more polar fibers, such as cellulosic fibers.
In the invention, the surface properties of the thermobondable non-biodegradable polymeric component are modified using a surface active agent. In a preferred embodiment of the invention, the thermobondable non-biodegradable polymeric component includes maleic acid or maleic anhydride which adds polar groups to the surface of the fibers and imparts hydrophilic properties thereto. Biodegradable polymers typically have some polarity as compared to conventional thermoplastic polymers, such as polyester and nylon. The grafted binder thus can exhibit improved a
Befumo Jenna-Leigh
Fiber Innovation Technology
Morris Terrel
LandOfFree
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