Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1995-08-30
2001-03-20
Edwards, Newton (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S373000, C428S374000, C428S372000
Reexamination Certificate
active
06203905
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to crimped conjugate fibers and nonwoven fabrics produced therefrom.
Nonwoven fabrics are used in a variety of products such as sterilization wraps, medical drapes, disposable garments, diapers, protective covers, diapers and incontinence care products. Suitable nonwoven fabrics for such products need to provide desirable levels of softness, strength, durability, porosity, uniformity and other physical properties.
In an effort to improve desirable properties of nonwoven fabrics, multicomponent conjugate fiber nonwoven fabrics or webs have been developed. Methods for producing conjugate fiber nonwoven fabrics are disclosed, for example, in U.S. Pat. No. 3,423,266 to Davies et al.; U.S. Pat. No. 3,595,731 to Davies et al.; U.S. Pat. No. 5,108,820 to Kaneko et al. and U.S. Pat. No. 5,382,400 to Pike et al. A conjugate fiber nonwoven fabric is produced from polymeric fibers or filaments containing at least two polymeric component compositions that are arranged in substantially distinct sections across the cross-section along the length of the fibers or filaments. In general, useful properties, e.g., textural and functional properties, of such nonwoven fabrics can be improved by crimping the fibers of the nonwoven fabrics.
Crimped conjugate fibers can be produced by mechanically crimping fully formed conjugate fibers or, if the conjugate fibers have latent crimpability, by activating the latent crimpability. As is known in the art, such latent crimpability is imparted in conjugate fibers when the component polymers of the conjugate fibers are selected from different polymers having dissimilar shrinkage and/or crystallization properties, and such latent crimpability can be activated, for example, by a heat treatment that activates crimps, especially helically crimps, in the conjugate fibers.
Although, in general, imparting crimps in the fibers improves textural properties, e.g., softness and drapability, of a nonwoven fabric, the required level of crimps depends on each use of the nonwoven fabric. In addition, when conjugate fibers are overly crimped, the crimped fibers themselves tend to additionally form macro-crimps, forming randomly distributed clumped regions in the fibers. Such fiber clumps makes it highly difficult to produce a nonwoven fabric having a uniform fiber coverage and bulk. Consequently, it is important to have methods for controlling the level of crimps in conjugate fibers. In this regard, it is known that the level of crimps in the conjugate fibers can be controlled by producing conjugate fibers from different component polymers that have different shrinkage and/or crystallization properties, i.e., controlling the level of potential crimpability, and by varying the duration and temperature of the heat treatment, i.e., controlling the degree of crimp-activation. However, these known methods may not always be practical for different production set ups and when the component polymers of a conjugate fiber cannot be substituted with other polymers.
There remains a need for a production process that can be used to control the level of latent activatable crimps in conjugate fibers or filaments.
SUMMARY OF THE INVENTION
The present invention provides a helically crimped multicomponent conjugate fiber which has at least a first polymer composition and a second polymer composition. The first composition contains a first thermoplastic polymer, and the second composition contains a second thermoplastic polymer, wherein the first and second thermoplastic polymers have different solidification periods and at least one of the first and second compositions contains an effective amount of a nucleating agent. The term “solidification period” as used herein indicates the amount of time that a melt spun polymer composition that exits the fiber-forming spinneret takes to solidify in a given conjugate fiber production set up, more specifically quenching and drawing set up.
The invention additionally provides a method for controlling the degree of latent crimpability in a helically crimpable multicomponent conjugate fiber, wherein the conjugate fiber has at least a first composition and a second composition, the first composition containing a first thermoplastic polymer and the second composition containing a second thermoplastic polymer. The first thermoplastic polymer has a faster solidification period than the second thermoplastic polymer. In accordance with the present invention, the process contains the steps of providing a first composition and a second composition, adding an effective amount of a nucleating agent in one of the first and second compositions, and then melt spinning the compositions into a conjugate fiber, wherein the conjugate fiber has a crimpable configuration that arranges the compositions in substantially distinct sections across the cross-section and extends the compositions continuously along the length of the conjugate fiber. In accordance with the present method, the degree of latent crimpability is increased when the nucleating agent is added in the first composition and the degree of latent crimpability is decreased when the nucleating agent is added in the second composition. The term “crimpable configuration” as used herein indicates a cross-sectional configuration of a conjugate fiber that does not impose geometrical or configurational constraints in the fiber to prevent the formation of crimps when the latent crimpability is activated. For example, a concentric sheath-core configuration is not a crimpable configuration since the concentrical symmetry of the cross-sections of the component polymers does not readily allow the fibers from forming thermally activated crimps.
Additionally, the terms “web” and “fabric” are used interchangeably, unless otherwise indicated, and the terms “fibers” and “filaments” are used interchangeably, unless otherwise indicated, since a filament typically denotes a continuous fiber.
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Edwards Newton
Kimberly--Clark Worldwide, Inc.
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