Bicomponent fiber

Abstract

The invention relates to a bicomponent fiber comprising a first polymer component and a second polymer component, wherein the first component comprises a polypropylene composition and the second component comprises a polyethylene composition and a polyethylene wax, wherein the polyethylene composition has a melt flow index measured according to ISO1133-1:2011 at 190 ⁰C and 2.16 kg of 0.1 to 15 dg / min and comprises high density polyethylene (HDPE) and / or linear low density polyethylene (LLDPE).

Description

[0001] BICOMPONENT FIBER

[0002] The present invention relates to a bicomponent fiber, a process for making such bicomponent fiber, a non-woven fabric comprising such bicomponent fiber, a process for making such non-woven fabric and an article comprising such non-woven fabric.

[0003] Polyolefin, as a well-known thermal plastic, has been widely used in both fibers of clothing, filtration and especially nonwoven fabrics of hygienic and medical fields, e.g., diapers, incontinence pads, sanitary wipes and surgical gowns and drapes. Compared to mono-component systems (100% polypropylene(PP)-based polymers), the development of bicomponent fibers / nonwovens, e.g., PP, polyester(PET) and / or polyamides(PA) combined with polyethylene(PE), has led to an increasing industry and customer demand, because such combinations can provide sufficient mechanical properties as well as other desired physical characteristics. During the bicomponent fiber processing, molten polymers (for example PE and PP) meet each other at the outlets of spinnerets with a designed configuration, e.g., sheath-core configuration and side-by-side configuration.

[0004] A bicomponent fiber comprising a core comprising polypropylene and a sheath comprising polyethylene is known.

[0005] WO2011115702 discloses a bicomponent fiber comprising a core comprising a first component comprising polypropylene and a sheath comprising a second component comprising a polyethylene composition, wherein said polyethylene composition has a density in the range of from 0.945 to 0.965 g / cm3, a molecular weight distribution (Mw / Mn) in the range of from 1.70 to 3.5, a melt index (I2) in the range of from 0.2 to 150 g / 10 minutes, a molecular weight distribution (Mz / Mw) in the range of from less than 2.5, vinyl unsaturation in the range of from less than 0.1 vinyls per one thousand carbon atoms present in the backbone of said composition.

[0006] EP1942213 discloses a fiber, comprising a first polymer component and a second polymer component, wherein the first and second polymer components differ at least with respect to one property, and wherein the second polymer component comprises an ethylene-a-olefin copolymer having a density of from 0.945 to 0.965 g / cm3and a MFR2 of from 15 to 45 g / 10 min. It is important that the bicomponent fibers can be produced without dripping problems from the spinneret during production. Good mechanical properties such as tensile strength and elongation are also important for a non-woven fabric made from the bicomponent fibers.

[0007] It is an objective of the present invention to provide a fiber by which the above- mentioned and / or other needs are met.

[0008] Accordingly, the invention provides a bicomponent fiber comprising a first polymer component and a second polymer component, wherein the first component comprises a polypropylene composition and the second component comprises a polyethylene composition and a polyethylene wax, wherein the polyethylene composition has a melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg of 0.1 to 15 dg / min and comprises high density polyethylene (HDPE) and / or linear low density polyethylene (LLDPE).

[0009] The invention further provides a non-woven fabric comprising the fiber according to the invention.

[0010] According to the invention, the combination of the polyethylene wax with the HDPE and / or LLDPE having a relatively low melt flow index allows proper bonding of the fibers for making a non-woven fabric while ensuring the fiber to be produced without dripping problems. The non-woven fabric made according to the invention also has good mechanical properties such as high tensile strength and elongation.

[0011] The inventors have realized that HDPE and LLDPE have relatively high melting points which allows proper bonding of the fibers for making a non-woven fabric, compared to e.g. LDPE which has lower melting points and long chain branches which lead to poor bonding of the fibers. However, HDPE and LLDPE tend to have a problem during spinning such as fiber dripping issues and require high extrusion pressure. The inventors have realized that the addition of a polyethylene wax allows using HDPE and / or LLDPE without these problems.

[0012] Bicomponent fiber

[0013] The fiber according to the invention may be a bicomponent fiber of any type, including core-sheath types, side-by-side types, hollow side-by-side types, island in sea types, layered types, as well as others, including modifications, such as eccentric core-sheath types.

[0014] Preferably, the bicomponent fiber according to the invention has a core-sheath configuration or a side-by-side configuration, most preferably a core-sheath configuration.

[0015] Preferably, the bicomponent fiber according to the invention consists of the first polymer component and the second polymer component.

[0016] Preferably, the weight ratio between the first component and the second component is 95:5 to 5:95, for example 90:10 to 40:60, 85:15 to 50:50 or 80:20 to 55:45.

[0017] Most preferably, the bicomponent fiber has a core-sheath configuration, wherein the core consists of the first polymer component and the sheath consists of the second polymer component.

[0018] Preferably, the weight ratio between the core and the shell in the bicomponent fiber is 95:5 to 5:95, for example 90:10 to 40:60, 85:15 to 50:50 or 80:20 to 55:45.

[0019] The bicomponent fiber according to the present invention may be prepared in any desired thickness depending upon the desired end use. Typical thicknesses are known to the skilled person and may e.g. be 0.5 to 100 denier, such as 1 .0 to 50 denier.

[0020] Fist component

[0021] The first component of the bicomponent fiber comprises a polypropylene composition.

[0022] The amount of the polypropylene composition with respect to the first component may e.g. be at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or 100 wt%.

[0023] The polypropylene composition of the first component comprises a polypropylene. Polypropylene maybe a propylene homopolymer, a propylene copolymer such as a propylene alpha olefin copolymer, a random copolymer polypropylene.

[0024] The polypropylene and / or the polypropylene composition may have a melt flow index measured according to ISO1133-1 :2011 at 230 °C and 2.16 kg of e.g. 5.0 to 50 dg / min, for example 15 to 35 dg / min. The polypropylene composition may comprise additives such as nucleating agents and clarifiers, stabilizers, fillers, plasticizers, anti-oxidants, lubricants, antistatics, scratch resistance agents, impact modifiers, acid scavengers, recycling additives, coupling agents, anti-microbials, anti-fogging additives, slip additives, anti-blocking additives, polymer processing aids, flame retardants, colorants and the like. Such additives are well known in the art. Preferred additives include Irganox 1010, Irganox 168, Irganox 3114 and vitamin E. The amount of the additives may e.g. be 0 to 5.0 wt%.

[0025] The amount of polypropylene with respect to the polypropylene composition may e.g. be at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or 100 wt%. Preferably, the total amount of polypropylene and the additives is 100 wt% with respect to the polypropylene composition.

[0026] Second component

[0027] The second component of the bicomponent fiber comprises a polyethylene composition and a polyethylene wax.

[0028] Preferably, the amount of the polyethylene wax with respect to the second component is 1 .0 to 35 wt%, more preferably 3.0 to 30 wt%. More preferably, the amount of the wax with respect to the second component is 6.0 to 30 wt%, more preferably 11 to 30 wt%, more preferably 16 to 30 wt%, most preferably 18 to 25 wt%. This results in particularly effective prevention of dripping problems during the fiber production as well as high tensile strength of the non-woven fabric according to the invention.

[0029] The total amount of the polyethylene composition and the polyethylene wax with respect to the second component may e.g. be at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or 100 wt%.

[0030] Preferably, the second component has a melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg of 15 to 50 dg / min, preferably 17 to 30 dg / min.

[0031] Preferably, the second component has a melt temperature measured according to ISO 11357-3 of at least 120 °C, preferably at least 128°C.

[0032] Polyethylene composition The polyethylene composition has a melt flow index measured according to ISO1133- 1 :2011 at 190 °C and 2.16 kg of 0.1 to 15 dg / min. The melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg is preferably 1.0 to 14 dg / min, 2.0 to 13 dg / min, 3.0 to 12 dg / min, 4.0 to 11 dg / min or 5.0 to 10 dg / min. This is advantageous for obtaining non-woven fabrics with good mechanical properties.

[0033] The polyethylene composition comprises high density polyethylene (HDPE) and / or linear low density polyethylene (LLDPE).

[0034] In some embodiments, the amount of HDPE with respect to the polyethylene composition is at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or 100 wt%. This has and advantage that the non-woven fabrics have good elongation properties.

[0035] In some embodiments, the amount of LLDPE with respect to the polyethylene composition is at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or 100 wt%.

[0036] The polyethylene composition may comprise additives. Examples of suitable additives are those mentioned as additives of the polypropylene composition. The amount of the additives may e.g. be 0.0-5.0 wt%.

[0037] Preferably, the total amount of HDPE and LLDPE and the additives is 100 wt% with respect to the polyethylene composition.

[0038] HDPE, LLDPE

[0039] The production processes of HDPE and LLDPE is summarised in Handbook of Polyethylene by Andrew Peacock (2000; Dekker; ISBN 0824795466) at pages 43- 66.

[0040] HDPE

[0041] HDPE has a linear structure with little branching.

[0042] HDPE may be an ethylene homopolymer or may be an ethylene copolymer having as a comonomer e.g. 1-butene or 1-hexene.

[0043] Preferably, the HDPE has a density measured according to ISO1183 of 941-970 kg / m3, more preferably 950-967 kg / m3, more preferably 960-967 kg / m3.

[0044] Preferably, the HDPE has a melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg of 0.2 to 5.0 dg / min, 0.3 to 3.0 dg / min or 0.5 to 1.0 dg / min.

[0045] Preferably, the HDPE has molecular weight (Mw) of 80 to 150 kDa.

[0046] Preferably, the HDPE has molecular weight distribution (Mw / Mn) of 7.0 to 30.

[0047] LLDPE

[0048] LLDPE has a linear structure with a significant number of short branching.

[0049] The technologies suitable for the LLDPE manufacture include gas-phase fluidized-bed polymerization, polymerization in solution, polymerization in a polymer melt under very high ethylene pressure, and slurry polymerization.

[0050] The LLDPE comprises ethylene and a C3-C10 alpha-olefin comonomer (ethylenealpha olefin copolymer). Suitable alpha-olefin comonomers include 1-butene, 1- hexene, 4-methyl pentene and 1 -octene. The preferred co monomer is 1-butene.

[0051] Preferably, the amount of units derived from the comonomer in the copolymer is 1 .0 to 5.0 wt%.

[0052] Preferably, the LLDPE has a density measured according to ISO1183 of 910-940 kg / m3, more preferably 920-940 kg / m3, more preferably 925-935 kg / m3.

[0053] Preferably, the LLDPE has a melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg of 5.0 to 14 dg / min, more preferably 7.5 to 10 dg / min.

[0054] Preferably, the LLDPE has molecular weight (Mw) of 50 to 100 kDa.

[0055] Preferably, the LLDPE has molecular weight distribution (Mw / Mn) of 1.1 to 8.0.

[0056] Polyethylene wax

[0057] The polyethylene wax may e.g. have molecular weight Mn of 0.5 to 35 kDa, for example 0.5 to 5.0 kDa or 5.0 to 35 kDa, preferably 0.5 to 5.0 kDa. Preferably, the polyethylene wax has Mn of 0.5 to 3.0 kDa.

[0058] The polyethylene wax may e.g. have molecular weight Mw of 1 .0 to 40 kDa, for example 1 .0 to 20 kDa or 20 to 40 kDa, preferably 1 .0 to 20 kDa. Preferably, the polyethylene wax has Mw of 1 .0 to 10 kDa. Lower Mw of the polyethylene wax was found to solve the dripping problem more efficiently at a smaller amount.

[0059] The polyethylene wax may e.g. have molecular weight distribution Mw / Mn of 1.0 to 10, preferably 1 .0 to 5.0, more preferably 2.0 to 5.0.

[0060] The polyethylene wax may e.g. have molecular weight distribution Mz / Mw of 1.0 to 20, preferably 2.0 to 20.

[0061] Z-average molecular weight Mz, weight average molecular weight Mw and number average molecular weight Mn may be measured by Gel Permeation Chromatography, e.g. according to 18016014-1 (2012). For calibration polystyrene standards may be used with Mark-Houwink correction.

[0062] Other aspects

[0063] The present invention further provides a process for making the bicomponent fiber according to the invention, comprising the steps of: providing a melt of the polypropylene composition and a melt of the polyethylene composition and the polyethylene wax and extruding the melt of the polypropylene composition and the melt of the polyethylene composition and the wax through a spinneret to obtain the bicomponent fiber.

[0064] Preferably, the polyethylene composition and the polyethylene wax are fed to an extruder separately and melt-mixed together to obtain the melt of the polyethylene composition and the wax to be extruded through the spinneret. The present invention further provides a non-woven fabric comprising the fiber according to the invention. The non-woven fabric according to the invention may have a fabric weight of e.g. 10 to 25 gsm.

[0065] The present invention further provides an article comprising the non-woven fabric according to the invention. Preferably, the article is selected from the group consisting of upholstery, apparel, wall covering, carpet, diaper topsheet, diaper backsheet, medical fabric, surgical wrap, hospital gown, wipe, textile, and geotextile.

[0066] The present invention further provides a process for making the non-woven fabric according to the invention, comprising a) providing the fibers according to the fibers and b) bonding the fibers to obtain the non-woven fabric.

[0067] Preferably, step b) comprises calendaring or hot air through bonding, more preferably calendaring.

[0068] 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.

[0069] 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 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. 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.

[0070] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0071] Materials

[0072] Table 1A

[0073] MFI of PP was measured according to ISO1133-1 :2011 at 230 °C and 2.16 kg; MFI of PE was measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg.

[0074] PP, HDPE and LLDPE comprise standard stabilizers.

[0075] Table 1 B: polyethylene wax

[0076] Bicomponent fibers having a core-sheath configuration and spunbond nonwoven fabrics were produced using the materials of Tables 1A and 1B. Process conditions were set according to Table 4 or 5 such that bicomponent fibers are obtained from the compositions of Table 2 or 3, respectively. The spunbond nonwovens of around 20 gsm were produced from the obtained fibers. The fibers were bonded based on embossed roller of a chosen calender, which had an engraving of 18.1% and bonding area of 0.413 mm2. Both the surface and oil temperature of the embossed rolls were measured. The nip pressure was maintained at 30 N / mm for all the experiments.

[0077] Occurrence of dripping problem during the fiber production was visually determined. The severeness of the dripping problem was rated in the scale from 0 to 3, 0 indicating there was no problem and 3 indicating the most severe problem.

[0078] Following properties were measured for the obtained spunbond nonwoven fabrics: Tensile strength in machine direction (MD) and cross direction (CD) measured in accordance with ASTM D5035-11

[0079] Elongation in machine direction (MD) and cross direction (CD) measured in accordance with ASTM D5035-11

[0080] Following observations can be made from Tables 2 and 3.

[0081] Production of fibers made only from PP did not show dripping problem, but non-woven fabrics made therefrom have a relatively low tensile strength (CEx 1).

[0082] Production of bicomponent fibers having a PP core / PE sheath configuration without PE wax showed severe dripping problem (CEx 2).

[0083] Addition of PE wax in the PE sheath reduced or solved the dripping problem (Ex 3-35). Larger amounts of wax resulted in solving the dripping problem better (Ex 20 vs Ex 21).

[0084] Solving of the dripping problem was achieved by a smaller amount of wax 2-4 than with wax 1 .

[0085] PE sheath comprising HDPE resulted in higher elongation properties than PE sheath comprising LLDPE. Table 2 (core:sheath = 80:20)

[0086] Table 3 (core:sheath = 70:30)

[0087]

Claims

CLAIMS1 . A bicomponent fiber comprising a first polymer component and a second polymer component, wherein the first component comprises a polypropylene composition and the second component comprises a polyethylene composition and a polyethylene wax, wherein the polyethylene composition has a melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg of 0.1 to 15 dg / min and comprises high density polyethylene (HDPE) and / or linear low density polyethylene (LLDPE).

2. The bicomponent fiber according to claim 1 , wherein the bicomponent fiber has a core-sheath configuration or a side-by-side configuration, preferably a core-sheath configuration.

3. The bicomponent fiber according to any one of the preceding claims, wherein the amount of the wax with respect to the second component is 1 .0 to 35 wt%, preferably 3.0 to 30 wt%, 6.0 to 30 wt%, 11 to 30 wt%, 16 to 30 wt% or 18 to 25 wt%.

4. The bicomponent fiber according to any one of the preceding claims, wherein the melt flow index measured according to ISO1133-1 :2011 at 190 °C and 2.16 kg of the polyethylene composition is 1.0 to 14 dg / min, 2.0 to 13 dg / min, 3.0 to 12 dg / min, 4.0 to 11 dg / min or 5.0 to 10 dg / min.

5. The bicomponent fiber according to any one of the preceding claims, wherein the polyethylene composition comprises the HDPE and the HDPE has density measured according to ISO1183 of 941-970 kg / m3, more preferably 950-967 kg / m3, more preferably 960-967 kg / m3, preferably wherein the HDPE is an ethylene homopolymer.

6. The bicomponent fiber according to any one of the preceding claims, wherein the polyethylene composition comprises the LLDPE and the LLDPE has a density measured according to ISO1183 of of 910-940 kg / m3, more preferably 920-940 kg / m3, more preferably 925-935 kg / m3, preferably wherein the LLDPE is a copolymer of ethylene and 1 -butene, preferably wherein the amount of units derived from 1 -butene in the copolymer is 1 .0 to 5.0 wt%.

7. The bicomponent fiber according to any one of the preceding claims, wherein the polyethylene wax has weight average molecular weight Mw of 1 .0 to 40 kDa and preferably Mw / Mn of 1 .0 to 10, preferably 1 .0 to 5.0.

8. The bicomponent fiber according to any one of the preceding claims, wherein the polyethylene wax has Mw of 1 .0 to 20 kDa and preferably Mw / Mn of 2.0 to 5.0.

9. The bicomponent fiber according to any one of the preceding claims, wherein the weight ratio between the first component and the second component is 95:5 to 5:95, for example 90:10 to 40:60, 85:15 to 50:50 or 80:20 to 55:45.

10. The bicomponent fiber according to any one of the preceding claims, wherein the polypropylene composition has a melt flow index measured according to ISO1133- 1 :2011 at 230 °C and 2.16 kg of e.g. 5.0 to 50 dg / min, for example 15 to 35 dg / min.11 . A process for making the bicomponent fiber according to any one of the preceding claims, comprising the steps of: providing a melt of the polypropylene composition and a melt of the polyethylene composition and the wax and extruding the melt of the polypropylene composition and the melt of the polyethylene composition and the wax through a spinneret to obtain the bicomponent fiber.

12. A non-woven fabric comprising the fiber according to any one of claims 1-10.

13. A process for making the non-woven fabric according to claim 12, comprising a) providing the fibers according to any one of claims 1-10 and b) bonding the fibers to obtain the non-woven fabric.

14. The process according to claim 13, wherein step b) comprises calendaring or hot air through bonding.

15. An article comprising the non-woven fabric according to claim 12, preferably wherein said article is selected from the group consisting of upholstery, apparel, wall covering, carpet, diaper topsheet, diaper backsheet, medical fabric, surgical wrap, hospital gown, wipe, textile, and geotextile.

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