1. Field of the Invention
The present invention relates to a stretchable synthetic polymer fiber having an axial core comprising a thermoplastic elastomeric polymer and a plurality of radially spaced wings attached to the outer periphery of the core comprising a thermoplastic, non-elastomeric polymer. At least one of the wing polymer or the core polymer protrudes into the other polymer to improve attachment of the wings to the core. The invention also relates to methods of producing such fibers, and a spinneret pack useful to form the fibers. The invention also relates to articles formed from the fibers, including yarns, garments, and the like.
2. Description of Related Art
It is desired to impart stretchability into many products formed from synthetic fibers, including various garments, such as sportswear and hosiery. As disclosed in the background section of U.S. Pat. No. 4,861,660 to Ishii, various methods are known for imparting stretchability to synthetic filaments. In one method, the fibers are two- or three-dimensionally crimped. In another such method, stretchable filaments are produced from elastic polymers, for example, natural or synthetic rubber, or a synthetic elastomer, such as polyurethane elastomer. This type of stretchable filament is disadvantageous in that the rubber or polyurethane elastomer filaments per se exhibit very poor wearing and knitting processability and poor dyeing properties. Therefore, the disadvantage of the rubber of polyurethane elastomer filaments is avoided by covering the rubber or elastomer filament with another type of filament having a satisfactory processability and dyeing property.
However, there are drawbacks associated with such covered elastomeric filaments. Ishii attempts to overcome such drawbacks by imparting asymmetry to filaments which are formed from two polymers. Nevertheless, these fibers often suffer from a serious defect in that the two polymers are often easily delaminated from each other during processing. The resulting split fiber has low break tenacity and can result in fabrics having less than intended sheerness and thermal conductivity. See also U.S. Pat. No. 3,017,686 to Breen et al., which discloses fibers formed from two different non-elastomeric polymers and which suffers from these drawbacks.
In fact, it is recognized in U.S. Pat. No. 3,418,200 to Tanner that under certain conditions having the core polymer protrude into the wing polymer will in fact make the portion of the wing which is formed from a different polymer than the core and the protruding portions of the wings more readily separable from the protruding portions. In contrast, at times it may be desirable to improve the attachment of two different polymers in a filament, as disclosed in U.S. Pat. No. 3,458,390, where a type of mechanical locking has been used to bond two high modulus, low elasticity polymers together. However, such polymers, as well as those disclosed in Breen and in Tanner, because of their low elasticity, have inadequate stretch and recovery properties for the high-stretch garments desirable today.
Fibers containing two polymers can be spun with the spinnerets disclosed in U.S. Pat. No. 3,418,200 and U.S. Pat. No. 5,344,297. However, the spinnerets of these patents exhibit polymer migration when multiple polymer streams are combined in feed channels substantially before the spinneret. These problems are described in the Journal Of Polymer Science [Physics Edition] Volume 13(5) p.863, 1975, and are shown specifically and most recently in the International Fiber Journal (1998), Volume 13(5) p.48, for otherwise state-of-the-art spinning of a trilobal fiber with tips which are designed to split from the core.
Thus, there is still a need for fibers and articles therefrom that have excellent stretch and recovery and that retain their tenacity during processing and use and for convenient methods of making such fibers and articles. There is also a need for spinnerets for spinning two polymers which eliminates problems in polymer migration when multiple polymer streams are combined in feed channels substantially before the spinneret orifice.
It has now been found that splitting (delamination) within a stretchable two-polymer fiber can be substantially reduced or eliminated if one of the two polymers penetrates the other polymer, that is, at least a portion of a wing polymer of one or more wings protrudes into the core polymer or at least a portion of the core polymer protrudes into a wing polymer. Such behavior was unexpected because it was anticipated that, under stress, the elastomeric polymer would readily deform and pull out of the interpenetrated connection with the non-elastomeric polymer, especially in light of the teachings of Tanner, supra.
In accordance with these findings, the present invention provides for a stretchable synthetic polymer fiber including an axial core comprising a thermoplastic, elastomeric polymer and a plurality of wings attached to the core comprising a thermoplastic, non-elastomeric polymer, wherein at least one of the wing polymer or core polymer protrudes into the other polymer. In one embodiment, the axial core contains an outer radius R1, an inner radius R2, and R1/R2 is greater than about 1.2.
In another embodiment, the invention provides for a stretchable synthetic polymer fiber including an axial core comprising a first polymer and a plurality of wings attached to the core comprising a second polymer, wherein the fiber has a delamination rating of less than about 1 and an after boil-off stretch of at least about 20%.
Moreover, with the spinneret pack of the present invention, it is possible to directly meter multicomponent polymer streams into specific points at the backside entrance of the fiber forming orifice in the spinneret plate. This eliminates problems in polymer migration when multiple polymer streams are combined in feed channels substantially before the spinneret orifice.
Thus, further in accordance with the present invention, there is provided a spinneret pack for the melt extrusion of a plurality of synthetic polymer to produce fiber, comprising: a metering plate containing a first set of holes adapted to receive a first polymer melt and a second set of holes adapted to receive a second polymer melt; a spinneret plate aligned and in contact with the metering plate, the spinneret plate having capillaries therethrough and having a counterbore length of less than about 60% of the length of the spinneret capillaries; and a spinneret support plate having holes larger than the capillaries, aligned and in contact with the spinneret plate; wherein the plates are aligned such that the plurality of polymers fed to the metering plate pass through the spinneret plate and the spinneret support plate to form a fiber.