Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-12-21
2003-09-30
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S181000, C264S172140, C425S072200, C425S131500, C425S463000
Reexamination Certificate
active
06627025
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for producing plural-component filament or fiber yarns having individual constituent micro-denier sub-filaments or sub-fibers that are easily separated and, in particular, to a method and apparatus for extruding easily splittable plural-component fibers suitable for making nonwoven fabrics in a spunbond process or woven fabrics.
2. Description of the Related Art
Various attempts have been made to produce woven and nonwoven fabrics having improved characteristics, such as greater bulkiness and softness, superior flexibility and drape, and better barrier and filtration properties for use in products such as disposable absorbent articles, medical garments and filtration materials. It has been found that nonwoven fabrics having desirable qualities can be manufactured from splittable plural-component fibers. Such plural-component fibers typically include at least two different polymers arranged as microfilaments or segments across the transverse cross section of the fiber, which segments extend continuously along the length of the fiber. By separating these plural-component fibers into their constituent segments after extrusion, a fine denier fabric with desirable characteristics can be produced.
Such a finer denier fabric is difficult to produce without employing splittable plural-component fibers. Individual fibers having a transverse cross-sectional area comparable to a single segment of a plural-component fiber are difficult to manipulate and generally cannot withstand the drawing process applied to attenuate extruded fibers without breakage. The use of plural-component fibers permits formation of a finer denier fabric, because plural fiber segments are joined to each other during at least a portion of the drawing and attenuation process, thereby forming a thicker combined fiber that can more readily be drawn and attenuated. Once drawn, the plural-component fibers can then be split into very fine sub-fiber segments.
A known method of producing plural-component fibers includes side-by-side merging of a plurality of sub-streams of polymers into a combined conjugated stream in a counterbore of a spinneret. As shown in
FIG. 1
, sub-streams of two incompatible polymers (polymers A and B) are introduced into the counterbore
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of a spinneret
10
and brought into contact with each other. As used herein in the context of polymers, the term “incompatible” refers to different polymers that do not strongly bond or strongly adhere to each other, but that will cling or somewhat adhere to each other when adjacently extruded in a molten state from a spinneret and, when arranged side-by-side, can later be separated from each other with a limited degree of effort. The adjacent polymer sub-streams form a combined stream that flows through the orifice
13
of the spinneret, and the stream is then quenched to form a spun plural-component fiber.
The most common synthetic textile fibers used in fabrics are made from polymer materials such as nylon (e.g., nylon 66, nylon 6), polyester, polyolefin, and their copolymers. All of these polymers are melt spinnable. Some nonwoven fabrics made from carded or air-laid webs comprise rayon or acrylic fibers.
Many of the nonwoven fabrics made from melt-spinnable polymers are produced using a spunbond process. The term “spunbond” refers to a process of forming a nonwoven fabric or web from thin fibers or filaments produced by extruding molten polymers from orifices of a spinneret. More specifically, as shown in
FIG. 2
, a plurality of plural-component fibers is extruded through orifices of a spinneret to form a vertically oriented curtain of downwardly moving fibers. The fibers are quenched and then enter an air aspirator
14
positioned below the spinneret, which aspirator introduces a rapidly downward moving air stream produced by compressed air from one or more air aspirating jets. The air stream creates a drawing force on the fibers, causing them to be drawn between the spinneret and the air jet, thereby longitudinally stretching and transversely attenuating the fibers. The drawn fibers exit at the bottom of the jet or jets and are randomly laid on a forming surface
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, such as a moving conveyor belt, to form a continuous nonwoven web of fibers. The web is subsequently bonded using one of several known techniques to form the nonwoven fabric, e.g., by being pressed between a pair of hot calender rolls. Carded or air-laid webs can also be formed from these polymers.
In the case of woven fabrics, the extruded fibers are typically quenched and drawn prior to being wound on a bobbin. Thereafter, in a separate process, a conventional knitting or weaving technique is employed to form a woven fabric from the fibers.
A number of known techniques can be used to separate the individual segments of plural-component fibers prior or subsequent to formation of the fabric. Specifically, fiber segments can be separated by applying mechanical force to the fibers, such as high pressure water or air jets or air turbulence, beating, carding, calendering, or other mechanical working of the fibers. In the case of woven fabrics, the fabric can be brushed or sanded to abroad and separate fibers. Another process for separating segments of plural-component fibers involves applying a hot aqueous solution to the fibers to induce splitting or treating the fibers with chemicals. Specifically, the fibers may be transported through a hot water bath or sprayed with steam or a mixture of steam and air. Other techniques have also been proposed, such as developing a triboelectric charge in at least one of the components and/or applying an external electric field to the fibers. Alternatively, one of the components of the plural-component fibers can be dissolved by a solvent applied to the fiber, such that segments formed of the undissolved component remain.
The required treatment of the fibers in the fabric adds cost to the process and introduces the possibility of damage to the fabric. If chemical treatment is involved, loss of polymer results in certain cases, and the additional problem of recycling, disposal and handling of the chemicals exists. Moreover, limited or incomplete fiber splitting may result, depending on the particular polymers, the extrusion process, and the splitting technique applied. In particular, the extent of fiber splitting may be limited at higher spinning and web formation belt speeds, thereby constraining the rate at which the nonwoven fabric can be produced. These problems can be mitigated by forming plural-component fibers that are easily splittable.
It has been found by the present inventor that easier splitting of a bicomponent fiber comprising two adjacent segments formed of incompatible polymers can be achieved by keeping the polymer sub-streams separated from each other in the spinneret and merging the side-by-side sub-streams into a combined stream just below the face of spinneret from which the sub-streams are extruded via two separate orifices. As described in U.S. Pat. No. 5,093,061 (the '061 patent), the disclosure of which is incorporated herein by reference in its entirety, by combining the sub-streams only after the sub-streams have been extruded, the adhesion between the sub-fibers is sufficiently light that the fiber splits substantially completely into the sub-fiber segments upon application of boiling water.
While the aforementioned patent discloses the technique of combining two streams below the spinneret to form an easily splittable bicomponent fiber, the process described therein has a number of limitations. Specifically, the process is limited to an arrangement wherein two sub-streams are aimed directly toward each other (i.e., the sub-streams are directed along axes that intersect, the axes being co-planar in a vertical plane), such that substantial surface areas of the sub-streams come into contact with each other at the point of sub-stream intersection to produce a side-by-side two-segment fiber.
The geometry (i.e., co-pl
Yu Jing-Peir
Yu Shiang-Jung Ma
Edell Shapiro & Finnan LLC
Hills, Inc.
Yao Sam Chuan
Yu Shiang-Jung Ma
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