Bi-component fiber for the production of spunbonded fabric

Abstract

A bi-component fiber (1), in particular for the production of spunbond fabrics (4), with a first component (2) and a second component (3), whereby the first component (2) has a first polymer as an integral part and the second component has a second polymer as an integral part. The polymer of one of the two components (2, 3) has been polymerized with a metallocene catalyst and the polymer of the other component (2, 3) has been polymerized with a Ziegler-Natta catalyst and subjected to a subsequent visbreaking treatment.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to a bi-component fiber, in particular for the production of spunbond fabric, with a first component and a second component, whereby as integral parts, the first component has a first polymer and the second component has a second polymer. In addition, the invention relates to a spunbond fabric with at least one bi-component fiber of the above-mentioned type.[0003]2. Description of Related Art[0004]Bi-component fibers of the type in question usually have a first component that consists of a first polymer and a second component that consists of a second polymer. In this case, different types of bi-component fibers can be distinguished, which in each case have different characteristic distributions of the components in the fiber cross-section. Bi-component fibers, in which the first component surrounds and thus encompasses the second component in the cross-section of the fiber, are referred to as core...

AI Technical Summary

Benefits of technology

[0011]Advantageously, in this case, the component whose polymer has been polymerized with a metallocene catalyst forms the outer surface of the bi-component fiber in the cross-section of the fiber. The component whose polymer has been polymerized with a metallocene catalyst especially preferably surrounds—in particular completely—the component whose polymer has been polymerized with a Ziegler-Natta catalyst.

[0012]Metallocene catalysts are structurally uniform catalysts, which contain transition metals coordinated by cyclopentadiene ligands. Such catalysts are described in detail in U.S. Pat. No. 5,374,696 and U.S. Pat. No. 5,064,802. Reference is made expressly to their disclosures which are hereby incorporated by reference. The advantage of these catalysts is that the polymers that are produced with these catalysts have a narrow molecular weight distribution. The narrow molecular weight distribution results in non-woven fabrics with high elongation at break. In this case, the elongation at break is the expansion of fibers that occurs at the peak tearing force, which is applied when tearing a strip of non-woven fabric. Primarily, however, a narrow molecular weight distribution results in an increase in the process safety in the production of spunbond fabric. The frequency of spinning disruptions, such as, for example, fiber fracture, is reduced. In addition, a higher stretching of the fibers is possible, higher spinning speeds can be reached, and the yarn counts that can be achieved are lower. In this case, lower yarn counts mean a higher fineness of fibers and / or of the yarns obtained from the fibers.

[0013]Another advantage of the metallocene catalysts or the polymers produced by means of metallocene catalysts is that the residual content of the catalyst in the polymer is very low. The residual content of the catalyst in the polymer represents a contamination of the polymer and can result in the properties of the polymer being changed in an undesirable way. Thus, for example, staining can occur during the processing of the polymer.

[0014]One drawback of the metallocene catalysts is their slightly higher price in comparison to the Ziegler-Natta catalysts. In addition, thermal solidification of the fibers in the production of non-woven fabric can be impeded when metallocene catalysts are used. This may be the case if the possibility opened up by the use of metallocene catalysts to increase the crystallinity and the strength of the individual fibers by their higher level of stretchability is used to a large extent.

[0015]Ziegler-Natta catalysts are heterogeneous mixed catalysts, which contain organometallic compounds of main group elements and transition metal compounds. As main group elements, in particular elements of the first to third main groups are used. The transition metal compounds contain in particular metals of the titanium group. A host of variants of these catalysts exist. In terms of this invention, the Ziegler-Natta catalysts are essentially defined by their distinction compared to the metallocene catalysts.

[0016]The Ziegler-Natta catalysts are more economical than the metallocene catalysts, however, polymers produced with the Ziegler-Natta catalysts have a considerably broader molecular weight distribution than polymers produced with metallocene catalysts. To improve the stretchability of the fibers, which serves in particular to increase the safety of the process, the polymers produced with Ziegler-Natta catalysts are therefore usually after-treated. This after-treatment is referred to as “visbreaking.” In the visbreaking treatment, polymer chains are cleaved, by which the molecular weight of the individual molecules is reduced, and the number of molecules is increased. In this case, the width of the molecular weight distribution is also reduced. The cleavage of the polymer chains is brought about by heat, irradiation, the addition of peroxide, or by similar measures. Examples of such visbreaking treatments are described in, i.a., U.S. Pat. No. 4,282,076 and U.S. Pat. No. 5,723,217.

Problems solved by technology

In practice, however, the use of these synergistic effects is limited to the extent that the properties of the components cannot routinely be combined in the described, only advantageous way.

Images