Fibers formed from immiscible polymer blends
The present invention relates to soft touch fibers and nonwoven fabrics made from such fibers. The fibers comprise an incompatible polymer system which leads to the soft touch quality. The fibers comprise a mixture of at least two thermoplastic polymers each having different viscosities and wherein the mixture has an interfacial tension from about 0.5 to about 20 mN/m, and wherein the mixture comprises a portion of the fiber surface. The fibers may include from 40-98 percent of a polyolefin continuous phase and from 2 to 60 weight percent of an amorphous thermoplast dispersed phase, such as polystyrene or polyamide.
1. A fiber comprising a mixture of at least two thermoplastic polymers each having different viscosities and wherein the mixture has an interfacial tension from 0.5 to 20 mN/m, wherein the mixture comprises a portion of the fiber surface, wherein the fiber is a bicomponent fiber of the sheath-core form and where at least one of the thermoplastic polymers is a polyolefin continuous phase, and at least one of the polymers in the mixture is a dispersed polymer in particulate form wherein the dispersed polymer has an average size larger than 1 micron, and wherein the sheath has a thickness smaller than the average size of the particulates of dispersed polymer.
2. The fiber of claim 1 wherein the ratio of the viscosity of the first thermoplastic polymer to the viscosity of the second thermoplastic polymer is from 1.5 up to 10, or from 0.1 down to 0.05.
3. The fiber of claim 1 wherein the sheath comprises less than 20 percent by volume.
4. The fiber of claim 1 wherein the core comprises a propylene polymer.
5. The fiber of claim 4 wherein the core comprises homopolymer propylene polymer.
6. The fiber of claim 1 wherein the matrix polymer has a melting point at least 10° C. or less than a melting point of the dispersed polymer.
7. The fiber of claim 1 wherein the matrix polymer has a melting point and the dispersed polymer is amorphous and has a glass transition temperature ≦10° C. than the melting point of the matrix polymer.
8. The fiber of claim 1 wherein the matrix polymer in the sheath and the material which comprises the core each have viscosity within about 30 percent from each other.
9. The fiber of claim 1 wherein the mixture has a viscosity 170 Pa·s at 100 l/s at 250° C.
10. The fiber of claim 1 wherein the dispersed particulate forms irregularities on the fiber surface.