Cross-linked polyethylene fiber, its use and process for its manufacture

Abstract

The present invention relates to a polymer fiber, in particular a polyethylene polymer fiber obtainable by melt-spinning of a polyethylene polymer, the use of the fiber and a process for the manufacture of the fiber. Further, the present invention relates to a heat sealable filter paper comprising said polymer fiber.

Claims

1. Heat-sealable filter paper comprising a crosslinked polyethylene fiber in an amount from about 15 to about 40 weight percent based on the total weight of the heat-sealable filter paper, wherein the crosslinked polyethylene fiber is obtained by melt-spinning of a polyethylene polymer having a melt-flow index (MFI) of above 120 g/10 min to about 400 g/10 min, wherein subsequent to the melt-spinning step the fiber is treated with ionizing radiation to obtain a crosslinked polyethylene polymer fiber, wherein the polyethylene polymer is a polyethylene homopolymer, a polyethylene copolymer, polymer blend comprising polyethylene as one polymer, or a mixture thereof, wherein the crosslinked polyethylene polymer fiber has a MFI of about 1 to about 80 g/10 min.

2. The heat-sealable filter paper of claim 1, wherein the polyethylene polymer has an MFI of about 120 g/10 min to about 250 g/10 min.

3. The heat-sealable filter paper of claim 1, wherein the polyethylene polymer has an MFI of about 150 g/10 min to about 220 g/10 min.

4. The heat-sealable filter paper of claim 1, wherein the polyethylene polymer has an MFI of about 160 g/10 min to about 200 g/10 min.

5. The heat-sealable filter paper of claim 1, wherein the crosslinked polymer fiber has an MFI of about 40 g/10 min to 80 g/10 min.

6. Heat-sealable filter paper comprising a mixture of polymer fibers in an amount from about 15 to about 40 weight percent based on the total weight of the heat-sealable filter paper, wherein the mixture of polymer fibers comprises a crosslinked polyethylene fiber and a second polymer fiber having melt-flow index (MFI) below 5, wherein the crosslinked polyethylene fiber is obtained by melt-spinning of a polyethylene polymer having a MFI of above 120 g/10 min to about 400 g/10 min, wherein subsequent to the melt-spinning step the fiber is treated with ionizing radiation to obtain a crosslinked polyethylene polymer fiber, wherein the polyethylene polymer is a polyethylene homopolymer, a polyethylene copolymer, polymer blend comprising polyethylene as one polymer, or a mixture thereof, wherein the crosslinked polyethylene polymer fiber has a MFI of about 1 to about 80 g/10 min.

7. The heat-sealable filter paper of claim 6, wherein the polyethylene polymer has an MFI of about 120 g/10 min to about 250 g/10 min.

8. The heat-sealable filter paper of claim 6, wherein the polyethylene polymer has an MFI of about 150 g/10 min to about 220 g/10 min.

9. The heat-sealable filter paper of claim 6, wherein the polyethylene polymer has an MFI of about 160 g/10 min to about 200 g/10 min.

10. The heat-sealable filter paper of claim 6, wherein the crosslinked polymer fiber has an MFI of about 40 g/10 min to 80 g/10 min.

Description

EXAMPLE 1

(1) Beta-Ray Treatment of Polyethylene (PE) Fibers having Normal MFI (Comparative)

(2) PE fiber samples of the type PB Eurofiber cut F-2427 6 mm length with 4 dtex (corresponding to a diameter of about 23 m), manufactured from baumhueter extrusion GmbH were treated with beta-rays at doses of 35-160 kGy. The length of the fibers after irradiation is about 4.5 mm. Also PE fiber samples of the type PB Eurofiber cut F-2382 2 mm length with 4 dtex (corresponding to a diameter of about 23 m) manufactured from baumhueter extrusion GmbH were treated with beta-rays at doses of 50 kGy. The length of the fibers after irradiation is about 1.5 mm.

(3) Further PE (polyethylene homopolymer) fiber samples of the type PB Eurofiber cut F-2321/M1 and F-2422/M50, both 2 mm length with 4 dtex (corresponding to a diameter of about 23 m) manufactured from baumhueter extrusion GmbH were treated with beta-rays at doses of 100 kGy and 70 kGy, respectively.

(4) The MFI values were measured before and after treatment with ionizing radiation. The MFI measurements were carried out according to DIN EN ISO 1133 under standard conditions, namely 190 C./2.16 kg.

(5) Filter papers comprising the fibers F-2382 before and after crosslinking by irradiation were tested for heat sealability. Further filter papers comprising the fibers F-2421/M1 and F-2422/M50 were tested for heat sealability. The results are summarized in the following table.

(6) TABLE-US-00001 TABLE 1 MFI before MFI after treatment treatment (g/10 min; (g/10 min; Dose 190 C./2, 190 C./2, Heat-sealable Fiber (kGy) 16 kg) 16 kg) filter-paper F-2427 0 30 Not tested 35 11 50 4 160 0* F-2382 0 20 1) 50 5 2) F-2421/M1 0 180 1) 100 1-2 3) F2422/M50 0 180 1) 70 30-60 3) *Highly cross-linked, no longer meltable. 1) Without cross-linking the fiber is not processable on a paper machine due to problems in the drying unit, caused by the free flowing melting of the fiber. 2) Production of tea-bag paper without any problems. The paper was successfully tested on a tea-bag machine. The strength of the heat seal is acceptable. 3) Production of tea-bag paper without any problems. The paper was successfully tested on a tea-bag machine. The strength of the heat seal is excellent.

(7) The above results demonstrate that the irradiated PE fibers having high MFI according to the invention can be excellently applied in heat-sealable papers, while irradiated PE fibers having low MFI can be applied with only acceptable seal strength, and while untreated fibers cannot be applied. Further no polymer deposits on machine parts can be detected during manufacture of the filter papers in the tea-bag machine when filter papers containing irradiated PE fibers are heat sealed.