Melt-spun polyethylene fiber

Abstract

The invention relates to a process for producing a polyethylene monofilament fiber comprising melt spinning a high density polyethylene through a spinneret, cooling the fiber from the spinneret and stretching the cooled fiber to obtain the polyethylene monofilament fiber, wherein the high density polyethylene has - a melt flow rate determined according to ISO1133-1:2011 at 2.16 kg and 190 ⁰C of 0.01 to 0.40 g / 10min, - a density of 0.950 to 0.961 g / cm3 according to ASTM D1505 and - Mw / Mn of 8.0 to 40.

Description

[0001] 24POLY0064-WO-ORD 1

[0002] MELT-SPUN POLYETHYLENE FIBER

[0003] The invention relates to a melt-spun polyethylene monofilament fiber.

[0004] It is known to make polymer fibers by a spinning process.

[0005] One known method is the solution spinning process. The polymer is first dissolved in a solvent forming a spinning solution and then the spinning solution is extruded through a spinneret to form fibers.

[0006] Another known method is the gel spinning process. This process is used to obtain high strength fibers. The fibers are solidified by gelation and the resulting gelled fiber is swollen with a spinning solvent. It is known to make ultra high molecular weight polyethylene (UHMWPE) fibers by the gel spinning process.

[0007] If the polymer is a thermoplastic then it can undergo melt spinning. The molten polymer is extruded through a spinneret composed of capillaries where the resulting filament is solidified by cooling.

[0008] Compared to the solution spinning or gel spinning process, the melt spinning is simpler and drawbacks caused by the use of additional solvents is avoided.

[0009] US5474845A discloses a high strength polyethylene fibre, which is prepared by melt spinning polyethylene having a high density through a spinnerette, by cooling the fibres coming out from the spinnerette and by stretching the fibre obtained at a temperature of 50°-150° C. The polyethylene used in the melt spinning is a homopolymer of ethylene having Mw of 125000-175000 g / mol, Mn of 26000-33000 g / mol, polydispersity (Mw / Mn) of below 5 and a density is greater than 955 g / dm3, made using polyethylene made using a Ziegler-Natta catalyst prepared according to US4482687.

[0010] While the high tensile strength of the fibers is important, it is also important that the process for preparing fibers is stable without frequent breaking of fibers. The fibers obtained also desirably have even, smooth surfaces. 24POLY0064-WO-ORD 2

[0011] It is an objective of the present invention to provide a process for producing a polyethylene monofilament fiber by which the above-mentioned and / or other needs are met.

[0012] Accordingly, the present invention provides a process for producing a polyethylene monofilament fiber comprising melt spinning a high density polyethylene through a spinneret, cooling the fiber from the spinneret and stretching the cooled fiber to obtain the polyethylene monofilament fiber, wherein the high density polyethylene has a melt flow rate determined according to ISO1133-1 :2011 at 2.16 kg and 190 °C of 0.01 to 0.40 g / IOmin, a density of 0.950 to 0.961 g / cm3according to ASTM D1505 and

[0013] Mw / Mn of 8.0 to 40.

[0014] The present invention provides a polyethylene monofilament fiber obtained by or obtainable by the process.

[0015] It was surprisingly found that the use of the high density polyethylene (HDPE) as defined allowed producing a melt-spun polyethylene monofilament fiber having a high tensile strength. It was observed that the high density polyethylene used according to the invention led to a low melt pressure during the melt spinning of the HDPE through a spinneret. Such low melt pressure leads to a stable process without frequent breaking of fibers and even, smooth surfaces of the fibers.

[0016] High density polyethylene (HDPE)

[0017] Preferably, the HDPE has been prepared using a catalyst comprising a chromium oxide supported on silica gel, i.e. a Phillips catalyst.

[0018] The HDPE has a melt flow rate determined according to ISO1133-1 :2011 at 2.16 kg and 190 °C of 0.01 to 0.40 g / 1 Omin, preferably 0.01 to 0.30 g / 1 Omin.

[0019] In some particularly preferred embodiments, the HDPE has a melt flow rate determined according to ISO1133-1 :2011 at 2.16 kg and 190 °C of 0.01 to 0.20 g / 10min, preferably 0.02 to 0.10 g / 1 Omin. This results in a particularly high tensile strength of the fiber.

[0020] The HDPE has a density of 0.950 to 0.961 g / cm3, preferably 0.951 to 0.955 g / cm3according to ASTM D1505. 24POLYOQ64-WO-ORD 3

[0021] The HDPE has Mw / Mn of 8.0 to 40, preferably 15 to 40, more preferably 20 to 37. This results in a particularly high tensile strength of the fibers obtained while allowing a relatively low melt pressure during the melt spinning process.

[0022] Preferably, the HDPE has Mw of 150 to 350 kDa, more preferably 200 to 300 kDa.

[0023] Preferably, the HDPE has Mn of 5 to 15 kDa, more preferably 6 to 12 kDa, more preferably 7 to 11 kDa.

[0024] Mw and Mn are determined in accordance with ASTM D6474-12 (Standard Test Method for Determining molecular weight distribution (MWD) and molecular weight Averages of Polyolefins by High Temperature Gel Permeation Chromatography). Mw stands for the weight average molecular weight and Mn stands for the number average weight. Mz stands for the z-average molecular weight.

[0025] Such HDPE is commercially available from SABIC as FB1 , F00952 and BM1052J.

[0026] In some particularly preferred embodiments, the HDPE has a melt flow rate determined according to ISO1133-1 :2011 at 2.16 kg and 190 °C of 0.01 to 0.10 g / 10min, a density of 0.950 to 0.955 g / cm3 according to ASTM D1505, Mw / Mn of 20 to 37.

[0027] Process

[0028] The process according to the invention comprises melt spinning a high density polyethylene through a spinneret, cooling the fiber from the spinneret and stretching the cooled fiber to obtain the polyethylene monofilament fiber. Such process is well- known as a melt spinning process.

[0029] Preferably, the polyethylene monofilament fiber has a tensile strength measured according to GB / T 14344-2008 of at least 6.0 cN / dtex, preferably at least 6.5 cN / dtex, more preferably at least 7.0 cN / dtex, more preferably at least 7.5 cN / dtex, more preferably at least 8.0 cN / dtex.

[0030] One of the parameters influencing the tensile strength of the obtained polyethylene monofilament fiber is the draw ratio during the stretching step. Preferably, the 24POLYOQ64-WO-ORD 4 stretching of the fiber obtained is performed at a draw ratio of at least 7.0, for example 8.0 to 12.0. While generally a higher draw ratio results in a higher tensile strength of the fiber, the fiber from the spinneret becomes prone to breaking if the draw ratio is too high.

[0031] The HDPE may be fed to an extruder comprising a spinneret as a melt and may be heated, and may come out from the spinneret at a higher temperature.

[0032] The cooling of the fiber coming out from the spinneret can e.g. be done in a water bath.

[0033] The stretching can be performed once or multiple times such as 2, 3, 4 or 5 times. The speeds of the rollers can be adjusted to realize desired draw ratio.

[0034] Preferably, the polyethylene monofilament fiber has an elongation at break of 10 to 27% measured according to GB / T14344-2008.

[0035] The invention further provides an article comprising the polyethylene monofilament fiber according to any one of the preceding claims, wherein the article is selected from the group consisting of as a cable, a rope, a fishing line and a fish net.

[0036] It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

[0037] It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product / composition comprising certain components also discloses a product / composition consisting of these components. The product / composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product / composition. Similarly, it is also to be understood that a description on a process comprising certain steps also 24POLY0064-WO-ORD 5 discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

[0038] When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.

[0039] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0040] Examples

[0041] Monofilament fibers were prepared by a melt spin process. HDPE resins shown in Table 1 having temperatures around 200-300 °C were added to an extruder and came out from the spinneret at temperatures of around 250-310 °C as an undrawn filament.

[0042] The undrawn filament went through one water bath, two heating chambers, and four sets of Godet rollers to carry out a multi-step stretching. The temperature of the water bath, the first heating chamber and the second heating chamber was around 85 °C, 120 °C and 100 °C, respectively. Four sets of Godet rollers were run at different speeds to realize the desired draw ratio as shown in Table 1 .

[0043] MFR of the HDPE was measured according to ISO1133-1 :2011 at 2.16 kg and 190 °C.

[0044] Mn and Mw of the HDPE were measured according to ASTM D6474-12. A high- temperature chromatograph Polymer Char GPC-IR system equipped with IR5 MCT detector and Polymer Char viscometer (Polymer Char S.A., Spain) was used at 160°C to determine the MWD as function of molecular weight. Three columns of Polymer Laboratories 13pm PLgel Olexis, 300 x 7.5mm, were used in series for GPC separation. 1 ,2,4-trichlorobenzene stabilized with 1 g / L butylhydroxytoluene (also known as 2,6-di-tert-butyl-4-methylphenol or BHT) was used as eluent at a flow rate of 1 mL / min. Sample concentration was around 0.7mg / mL and injection volume was 300pL. The molar mass was determined based on the Universal GPC-principle using a calibration made with PE narrow and broad standards (in the range of 0.5-2800kg / mol, Mw / Mn - 4 to 15) in combination with known Mark Houwink constants of PE-calibrant (alfa = 0.725 and log K = -3.721). 24POLYOQ64-WO-ORD 6

[0045] Tensile strength and Elongation at break of the obtained fibers were measured according to GB / T 14344-2008 and is shown in Table 1 .

[0046] 24POLYOQ64-WO-ORD 7

[0047] Table 1

[0048] The increase in the draw ratio results in increase in the strength and decrease in elongation at break (EAB) of the fiber obtained. For each of the different HDPE grades, melt temperature and draw ratio were adjusted to achieve highest possible strength.

[0049] T able 1 shows the maximum strength of the fiber that was achieved for each HDPE grade.

[0050] It can be understood that the HDPE used according to the invention results in a high tensile strength. The HDPE used according to the invention led to a low melt pressure during the melt spinning of the HDPE through a spinneret, in particular E5-E8.

Claims

24POLYOQ64-WO-ORD 8CLAIMS1 . A process for producing a polyethylene monofilament fiber comprising melt spinning a high density polyethylene through a spinneret, cooling the fiber from the spinneret and stretching the cooled fiber to obtain the polyethylene monofilament fiber, wherein the high density polyethylene has- a melt flow rate determined according to ISO1133-1 :2011 at 2.16 kg and 190 °C of 0.01 to 0.40 g / 10min,- a density of 0.950 to 0.961 g / cm3according to ASTM D1505 and Mw / Mn of 8.0 to 40.

2. The process according to claim 1 , wherein the melt flow rate of the high density polyethylene is 0.01 to 0.30 g / 10min, preferably 0.01 to 0.20 g / 10min.

3. The process according to any one of the preceding claims, wherein the melt flow rate of the high density polyethylene is 0.02 to 0.10 g / 10min.

4. The process according to any one of the preceding claims, wherein the density of the high density polyethylene is 0.951 to 0.955 g / cm3according to ASTM D1505.

5. The process according to any one of the preceding claims, wherein Mw / Mn of the high density polyethylene is 15 to 40, preferably 20 to 37.

6. The process according to any one of the preceding claims, wherein the high density polyethylene has Mw of 150 to 350 kDa, preferably 200 to 300 kDa.

7. The process according to any one of the preceding claims, wherein the high density polyethylene has Mn of 5 to 15 kDa, more preferably 6 to 12 kDa, more preferably7 to 11 kDa.

8. The process according to any one of the preceding claims, wherein the high density polyethylene has been prepared using a catalyst comprising a chromium oxide supported on silica gel.

9. The process according to any one of the preceding claims, wherein the stretching of the fiber obtained is performed at a draw ratio of at least 7.0, for example 8.0 to24POLYOQ64-WO-ORD 910. The process according to any one of the preceding claims, wherein the polyethylene fiber has a tensile strength measured according to GB / T 14344-2008 of at least 6.5 cN / dtex, more preferably at least 7.0 cN / dtex, more preferably at least 7.5 cN / dtex, more preferably at least 8.0 cN / dtex.11 . The process according to any one of the preceding claims, wherein The polyethylene fiber according to any one of the preceding claims, wherein the polyethylene monofilament fiber has an elongation at break of 10 to 27% measured according to GB / T14344-2008.

12. A polyethylene monofilament fiber obtained by or obtainable by the process according to any one of the claims 1-11.

13. An article comprising the polyethylene monofilament fiber according to claim 12, wherein the article is selected from the group consisting of as a cable, a rope, a fishing line and a fish net.

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