High wet resiliency curly cellulose fibers

Details High wet resiliency curly cellulose fibers High wet resiliency curly cellulose fibers

2001-12-11

2004-08-24

Einsmann, Margaret (Department: 1751)

Bleaching and dyeing; fluid treatment and chemical modification

Chemical modification of textiles or fibers or products thereof

Cellulose fibers

C008S120000, C008S115510, C162S009000

Reexamination Certificate

active

06780201

ABSTRACT:

BACKGROUND OF THE INVENTION
Cellulose fibers are used in a number of applications, including absorbent products. Absorbent properties of cellulosic fibers can be enhanced by a variety of treatments. For example, fibers can be individually cross-linked, thereby physically or mechanically curling the fibers to impart increased absorbent capacity, bulk, and resilience. However, when curly fibers get wet, they typically lose their curl as well as their resiliency. Essentially, curly fibers collapse when wet. A mat of fibers can lose much of its former void volume when wetted, particularly if a compressive load is applied to the wet mat, resulting in decreased absorbent capacity. Curly fibers are more likely to maintain higher absorbent capacity if they can maintain their shape.
In the past, curling of fibers has been done primarily by mechanical means, resulting in densification of portions of the fiber wall and mechanical damage to fibers. Also in the past, many cross-linking efforts have tended to decrease the hydrophilicity of fibers, often by consumption of available hydroxyl groups on the fiber.
It is therefore an object of the present invention to provide curly fibers that maintain their shape when wet.
It is another object of the present invention to provide a method of creating curly cellulosic fibers without the need for mechanically curling the fibers.
It is a further object of the present invention to provide a method of creating curly cellulosic fibers that maintains or improves the hydrophilic nature of the fibers or the fiber mat.
SUMMARY OF THE INVENTION
The present invention is generally directed to a high wet resiliency curly cellulose fiber and a method of making high wet resiliency curly cellulose fibers. The high wet resiliency allows the fiber to be stiff enough to not collapse upon wetting. Additionally, high curl or kink in the fiber remains upon wetting, thus allowing the fiber to maintain void volume. These high wet resiliency curly fibers maintain a capillary structure during fluid acquisition and distribution thereby increasing absorbency.
The fibers of the invention are made from fibers treated with an intracrystalline swelling agent to have increased affinity to curl, and are further treated with a polymeric reactive compound that stabilizes the fiber curl, optionally without significant loss in the hydrophilic nature of the fiber. The polymeric reactive compound can be a polycarboxylic acid, a polyanhydride, a copolymer comprising multiple carboxylic acid groups or cyclic anhydride groups or salts thereof, a polyaldehyde or copolymer comprising multiple aldehyde groups, and the like. In one embodiment, however, the polymeric reactive compound is substantially free of aldehyde groups; likewise, a solution comprising the polymeric reactive compound can be substantially free of aldehydes. In another embodiment, a solution comprising the polymeric reactive compound is substantially free of low-molecular weight carboxylic acids, such as C2-C9 polycarboxylic acids. The polymeric reactive compound provides intrafiber crosslinking to impart the desired absorbent properties to the fibers.
In one embodiment, the polymeric reactive compound comprises cyclic anhydride groups or salts thereof, such that the crosslinking reaction with a hydroxyl group on the cellulose is compensated in terms of hydrophilicity by the liberation of a carboxylic acid group or salt thereof (i.e., the anhydride ring is opened by the cross-linking reaction, resulting in an ester link to a former hydroxyl unit on the cellulose and the liberation of a carboxyl group that had previously been part of the anhydride). Since a carboxylic acid is known to generally be more hydrophilic than a hydroxyl group, the consumption of a hydroxyl group on the cellulose accompanied by the liberation of a nearby carboxyl group can be expected to increase or at least maintain the hydrophilicity of the system as crosslinking reactions proceed.
A catalyst may be added to the polymeric reactive compound to increase the rate of the reaction. The fibers are separated into individual form either before or after the fiber/chemical mixture is dried. The individualized fibers are then subjected to high temperatures for a sufficient time to initiate the cross-linking reaction. Once the high wet resiliency curly cellulose fibers are cross-linked, the wet curl index and water retention value can be evaluated. Suitably, the high wet resiliency curly fibers have a curl value greater than about 0.15, such as between about 0.15 and about 0.9, and a water retention value of at least 0.5 grams/gram.
Because of their remarkable absorbency, the high wet resiliency curly cellulose fibers are particularly suitable for use in absorbent articles, including diapers, training pants, feminine hygiene products, incontinence products, other personal care or health care garments, or the like.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description and appended claims.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
The present invention is generally directed to curly cellulose fibers having high wet resiliency. When these fibers get wet, they remain stiff enough to avoid collapsing despite the tendency of water to cause a collapse. By retaining their shape upon wetting, these fibers are able to maintain void volume in the form of a capillary structure during fluid acquisition and distribution, thus increasing absorbency.
Before describing representative embodiments of the invention, it is useful to define a number of terms for purposes of this application. These definitions are provided to assist the reader of this document.
“Cellulosic” or “cellulose” includes any material having cellulose as a major constituent, and specifically, comprising at least 50 percent by weight cellulose or a cellulose derivative. Thus, the term includes cotton, typical wood pulps, cellulose acetate, rayon, thermomechanical wood pulp, chemical wood pulp, debonded chemical wood pulp, milkweed floss, and the like.
“Wet resiliency” refers to the property of a material that enables the material to resume its original shape or position after being exposed to water or other liquid.
“Mechanically curly” refers to a fiber, for instance, that has been twisted or otherwise manipulated into curves, curls, or kinks.
“Intrafiber cross-linking” refers to the formation of crosslink bonds between two atoms on a single fiber.
“Fiber” or “fibrous” refers to a particulate material wherein the length to diameter ratio of such particulate material is greater than about 10. Conversely, a “nonfiber” or “nonfibrous” material is meant to refer to a particulate material wherein the length to diameter ratio of such particulate material is about 10 or less.
“Spunbonded fibers”, or “spundbond fibers”, means small-diameter fibers that are typically formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinneret having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated by reference in its entirety and in a manner consistent with the present document. Spunbond fibers are quenched and generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and often have average diameters larger than about 7 microns, and more particularly between about 10 and 30 microns. A spunbond material, layer, or substrate comprises spunbonded (or spunbond) fibers.
The term “meltblown fibers” means fibers formed by extruding a molten material, typically thermoplastic in nature, through a plurality of fine, usually

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