FIELD OF THE INVENTION
The present invention relates generally to lofty nonwoven fiber webs. The present invention relates specifically to lofty nonwoven fiber webs of homofilament crimped fibers and dual capillary means and method for producing the web.
BACKGROUND OF THE INVENTION
Webs of homofilament crimped thermoplastic fibers are useful for various fluid handling or retaining materials and the like because of their open structure, resiliency, and economy of manufacture. Particularly, the use of a single thermoplastic polymer in the making of the crimped fibers is good for economical and consistent manufacture. However, the present state of the manufacturing art relies largely on bicomponent filaments to induce the desired level of crimping in a consistent fashion leading to certain compromises in the consistency of fabric characteristics and economy thereof.
In the known art several attempts have been made to produce crimping through shaped fibers. Spinnerets having shaped orifices or multiple orifices to produce the shaped fibers are also known. However the known art suffers in several regards. First, the known processing of the shaped fibers is not a robust process in that the fibers are not consistently shaped or the component parts of the fiber do not hold together well, resulting in less predictable web morphology and attendant functional characteristics. Second, the degree of crimping derived from using a single polymer to produce a crimped homofilament has not always attained the desired level.
Therefore, there is a need in the art for a robust and easily accomplished means and method of manufacturing homofilament crimped fiber which has a high degree of crimp and good predictability of the fiber shape and crimping to yield the desired nonwoven web structure.
Within the context of this specification, each term or phrase below will include the following meaning or meanings.
“Article” refers to a garment or other end-use article of manufacture, including but not limited to, diapers, training pants, swim wear, catamenial products, medical garments or wraps, and the like.
“Bonded” or “bonding” refers to the joining, adhering, connecting, attaching, or the like, of two elements. Two elements will be considered to be bonded together when they are bonded directly to one another or indirectly to one another, such as when each is directly bonded to intermediate elements.
“Connected” refers to the joining, adhering, bonding, attaching, or the like, of two elements. Two elements will be considered to be connected together when they are connected directly to one another or indirectly to one another, such as when each is directly connected to intermediate elements.
“Disposable” refers to articles which are designed to be discarded after a limited use rather than being laundered or otherwise restored for reuse.
“Disposed,” “disposed on,” and variations thereof are intended to mean that one element can be integral with another element, or that one element can be a separate structure bonded to or placed with or placed near another element.
“Fabrics” is used to refer to all of the woven, knitted and nonwoven fibrous webs.
“Homofilament” refers to a fiber formed from only one predominate polymer and made from a single stream of that polymer. This is not meant to exclude fibers formed from one polymer to which small amounts of additives have been added for coloration, anti-static properties, lubrication, hydrophilicity, etc.
“Integral” or “integrally” is used to refer to various portions of a single unitary element rather than separate structures bonded to or placed with or placed near one another.
“Layer” when used in the singular can have the dual meaning of a single element or a plurality of elements.
“Meltblown fiber” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than about 0.6 denier, and are generally self bonding when deposited onto a collecting surface. Meltblown fibers used in the present invention are preferably substantially continuous in length.
“Meltspun” refers generically to a fiber which is formed from a molten polymer by a fiber-forming extrusion process, for example, such as are made by the meltblown and spunbond processes.
“Member” when used in the singular can have the dual meaning of a single element or a plurality of elements.
“Nonwoven” and “nonwoven web” refer to materials and webs of material which are formed without the aid of a textile weaving or knitting process.
“Polymers” include, but are not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
Words of degree, such as “About”, “Substantially”, and the like are used herein in the sense of “at, or nearly at, when given the manufacturing and material tolerances inherent in the stated circumstances” and are used to prevent the unscrupulous infringer from unfairly taking advantage of the invention disclosure where exact or absolute figures are stated as an aid to understanding the invention.
“Spunbond fiber” refers to small diameter fibers which are 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 Hartmann, 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 herein in its entirety by reference. 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 deniers larger than about 0.3, more particularly, between about 0.6 and 10.
“Surface” includes any layer, film, woven, nonwoven, laminate, composite, or the like, whether pervious or impervious to air, gas, and/or liquids.
“Thermoplastic” describes a material that softens when exposed to heat and which substantially returns to a nonsoftened condition when cooled to room temperature.
These terms may be defined with additional language in the remaining portions of the specification.
SUMMARY OF THE INVENTION
A homofilament crimped fiber is produced by joining polymer streams exiting through a dual capillary spinneret design. Differently induced shear in the different polymer streams results in differential tensions in the joined halves of the filament. The filaments may further be subjected to differential or directed quenching which provides for setting the crimps in the filaments to further induce the crimp. The filaments may also be desirably drawn out in the spinning processing to achieve a substantially round shape which results in a robust and predictable filament.
The dual capillary design for producing a crimped homofilament fiber according to the present invention has a first capillary and a second capillary spaced apart at a distance sufficiently close to have a single filament formed from concurrent liquid polymer extrusions from the first capillary and the second capillary. The capillaries share a parallel border where they are adjacent each other and are specifically shaped to maximize induced shear. Specific shapes of spinneret orifices and methodologies for using those shapes will be further elaborated on below.