Fiber comprising an ethylene copolymer

Abstract

 The present invention relates to a fiber comprising an ethylene copolymer, a non-woven fabric comprising the fiber, the use of a specific ethylene copolymer for fiber production and a process for preparing a fiber in accordance with the present invention.

Description

[0001] The present invention relates to a fiber comprising an ethylene copolymer, a non-woven fabric comprising the fiber, the use of a specific ethylene copolymer for fiber production and a process for preparing a fiber in accordance with the present invention.

Description of related art

[0002] Synthetic fibers are used over a broad range of applications and, in particular, synthetic fibers comprising polyolefins have been developed in the recent past. One specific type of synthetic fibers is bicomponent fibers, defining a fiber comprising two different polymers of, for example, different chemical constitution or different physical properties. Typically, these two different polymers are brought together in the spinning process and thereby extruded into a bicomponent fiber.

[0003] The basic concept behind a bicomponent fiber is the desire to combine the properties of two different polymers in order to widen the possible fields of application.

[0004] Typical bicomponent fibers are polypropylene/polyethylene fibers. These fibers comprise a low melting temperature component (polyethylene) and a high melting temperature component (polypropylene) which offers specific advantages, for example, when producing a non-woven fabric. If the lower melting temperature component is employed, at least partially as a component being present on the surface of the fiber, the non-woven fabric can be bonded in a simple thermal bonding process requiring far less heat, compared with a thermal bonding process employing pure polypropylene fibers. At the same time, it is ensured that the polypropylene remains intact and provides the desired product strength for the fabric. Typical advantages associated with the use of such bicomponent fibers are non-woven fabrics with a soft handle which can be produced without chemical binders. Furthermore, non-wovens can be obtained which show a desired degree of bulkiness and the production process of such fabrics is simple and energy efficient.

[0005] Various bicomponent fibers of this type are known in the art. The European patent application EP 0696655 A1, for example, discloses a melt adhesive composite fiber which may be used for preparing non-woven fabrics to be employed as surface material for medical supplies and paper diapers. The melt adhesive composite fibers as disclosed in the above-mentioned European patent application comprise a polypropylene as a first component and a polyethylene as a second component, which is continuously present on at least a part of the fiber surface along the length of the fiber.

[0006] Typical polyethylenes to be employed in such bicomponent fibers are LLDPE materials, i.e. ethylene copolymers comprising α-olefins, as well as HDPE materials, which may be homopolymers or copolymers. Examples of such HDPE materials are copolymers of ethylene with 1-octene, which are, for example, disclosed in WO 2005/111291 A1 as suitable component for a bicomponent fiber.

[0007] A commercially available ethylene polymer for use in bicomponent fibers is the polyethylene grade Aspun 6811A of Dow, which is an LLDPE material.

[0008] However, a constant need still exists for further improvement with respect to materials for bicomponent fibers, enabling in particular excellent spinning procedures, with as few mechanical failures of the fibers as possible, enabling further broad windows of manufacture and further processing while enabling a high non-woven strength.

Object of the present invention

[0009] In view of the above-outlined drawbacks of the prior art, the present invention aims at providing an improved fiber, fulfilling at least one of the objectives as indicated above. In this respect, the present invention provides the following.

Brief disclosure of the invention

[0010] The present invention provides an improved fiber as defined in claim 1. Preferred embodiments of the fiber are defined in subclaims 2 to 9 as well as the following description. The present invention furthermore provides a non-woven fabric comprising the fibers in accordance with the present invention as well as processes for the preparation of the fibers and the non-woven fabrics as defined in claims 10, 11 and 12. Finally, the present invention provides the use of a specific ethylene copolymer for preparing fibers as indicated in claim 13. Preferred embodiments are again derivable from the present specification.

Detailed description of the present invention

[0011] As defined in claim 1, the present invention provides a fiber, comprising a first polymer component and a second polymer component, wherein the first and the second polymer component differ from one another at least with respect to one property, such as chemical constitution or physical properties, and wherein the second component is an ethylene-α-olefin copolymer having a density of from 0.945 to 0.965 g/cm³ and having an MFR₂ of from 15 to 45 g/10 min.

[0012] The α-olefin as contained in the ethylene-α-olefin copolymer of the second polymer component preferably is an α-olefin having from 3 to 20 carbon atoms, more preferably from 4 to 10 carbon atoms, still more preferably from 4 to 6 carbon atoms and in particular the α-olefin is 1-hexene.

[0013] The amount of α-olefin contained in the ethylene-α-olefin copolymer of the second polymer component of the fiber in accordance with the present invention amounts to about 1 to 7 wt%, preferably 1.25 to 3.5 wt%, and more preferably 1.75 to 3.0 wt%. An especially preferred α-olefin content is in the range of from 2 to 2.6 wt%

[0014] The ethylene-α-olefin copolymer preferably is a mono-modal copolymer with respect to the molecular weight distribution showing a rather narrow molecular weight distribution (MWD) Mw/Mn of from 1 to 8, more preferably 2 to 5, even more preferably 3.5 to 4.5, such as about 4.

[0015] The density of the ethylene-α-olefin copolymer typically amounts to from 0.945 to 0.965 g/cm³, more preferably 0.945 to 0.960, even more preferably of from 0.947 to 0.955, and in particular of from 0.948 to 0.954.

[0016] The ethylene-α-olefin copolymer displays an MFR₂ of from 25 to 45 g/10 min, more preferably of from 30 to 45 g/10 min and in particular of from 35 to 42 g/10 min, such as about 39 g/10 min. Other highly suitable MFR₂ ranges are from 18 to 30 g/10 min, preferably from 20 to 28 g/10 min, such as about 20 or about 27 g/10 min.

[0017] Typically, the ethylene-α-olefin copolymer of the second polymer component of the fiber in accordance with the present invention has not been subjected to any chemical modification, such as grafting and/or irradiation, which are often employed in the prior art in order to improve the bonding properties or the adhesion to the other polymer component of a bicomponent fiber.

[0018] The fiber in accordance with the present invention preferably is a bicomponent fiber which may be a bicomponent fiber of any type, including core-sheath types, side-by-side types, hollow side-by-side types, orange types, island in sea types, layered types, as well as others, including modifications, such as eccentric core-sheath types, hollow orange types etc. Preferred in accordance with the present invention are bicomponent fibers wherein the second polymer component as defined herein at least is partially present at the surface of the fiber. Accordingly, core-sheath types are in particular preferred, wherein the second polymer component in accordance with the present invention constitutes the sheath. Also preferred, however, are side-by-side types as well as orange types and layered types, since also these bicomponent fiber types ensure that the second polymer component to be employed in accordance with the present invention at least partially is present on the surface of the fiber.

[0019] In particular, preferred however are core-sheath types, wherein as identified above, the second polymer component as defined herein constitutes the sheath.

[0020] As indicated above, the ethylene-α-olefin polymer to be employed in accordance with the present invention as second polymer component preferably has not been subjected to any further modification, such as grafting and/or irradiation. It is in particular preferred if the ethylene-α-olefin copolymer is employed in the fiber without any further additive beyond the basic stabilization, although it is possible to add typical additives, such as additional stabilizers, coloring agents etc. in usual amounts.

[0021] The ethylene-α-olefin copolymer (HDPE) to be employed in accordance with the present invention as second polymer component may be prepared using conventional polymerization techniques, in particular employing Ziegler-Natta catalysts. Suitable polymerization conditions and catalysts are known to the skilled person.

[0022] The first polymer component to be employed in accordance with the present invention is not restricted and only has to differ at least with respect to one property from the second polymer component. Typical and suitable examples for first polymer components are polypropylene materials as well as ester materials, such as PET, commonly employed for the preparation of synthetic fibers, in particular bicomponent fibers. No restriction is given, however, with respect to the selection of first polymer component.

[0023] The first polymer component furthermore may be subjected to any desired kind of pretreatment, such as grafting and/or irradiation in order to improve adhesion or bonding properties. The first polymer component furthermore may be compounded, prior to the spinning process, with any desired additives, such as stabilizers, coloring agents, processing aids etc., in usual amounts.

[0024] The first polymer component and the second polymer component may be employed in any desired ratio, depending from the desired end use of the fiber. Typical ratios are weight ratios of from 10:90 to 90:10, such as 20:80 to 80:20 and 30:70 to 70:30, including also weight ratios of 50:50 etc.

[0025] The fiber in accordance with the present invention may be prepared in any desired thickness, again depending upon the desired end use. Typical thicknesses are known to the skilled person and include in particular the range of from 0.5 to 100 denier, such as from 1 to 50 denier.

[0026] The fibers in accordance with the present invention, after spinning, may be subjected to any desired kind of post-treatment, such as stretching, crimping or cutting and the fibers in accordance with the present invention in particular may be subjected directly to a further process for preparing a non-woven fabric. However, the fibers in accordance with the present invention also can be cut at any desired length or may be wound up for any desired kind of post-treatment and/or storage, prior to the further use thereof.

[0027] The present invention also provides a non-woven fabric prepared using the fiber in accordance with the present invention. Such a non-woven fabric can be prepared in accordance with standard techniques known to the skilled person.

[0028] With respect to the fiber and the non-woven fabric in accordance with the present invention, the specific second polymer component as defined herein enables the preparation of fabrics having improved values for tensile strength, compared with a non-woven fabric prepared with the standard market product Aspun 6811A of Dow, which is widely regarded as the best available polyethylene material for bicomponent fiber applications. The fibers in accordance with the present invention furthermore provide the possibility to tailor the bonding temperatures required for bonding of the fibers to produce a non-woven fabric which provides the manufacturer of a fiber and a non-woven fabric with a greater latitude for the bonding process, without encountering problems such as sticking.

[0029] The specific ethylene-α-olefin copolymer to be employed in accordance with the present invention furthermore enables problem-free spinning processes without fiber failures due to gel particles.

[0030] In view of these advantages, the present invention also provides the use of an ethylene-α-olefin copolymer as defined herein for the preparation of fibers, preferably bicomponent fibers. The preferred embodiments as defined above in connection with the fiber and the non-woven fabric also apply with respect to the use as defined herein.

[0031] The present invention finally also provides a process for preparing a fiber in accordance with the present invention as well as a process for preparing a non-woven fabric as defined herein. The process in accordance with the present invention comprises the step of providing a first polymer component as defined herein and providing a second polymer component as defined herein, melting the polymer components and extruding the polymer components through a suitable die/spinnerette in order to combine the two polymer components in a bicomponent fiber. Suitable process parameters and apparatuses required therefor are known to the skilled person and reference in this respect can be made to the Reicofil^® Bico Technology of Reifenhäuser as well as apparatuses developed and distributed by Hills and Neumag.

[0032] Non-woven fabrics can be prepared from fibers in accordance with the present invention by usual processes known to the skilled person, including in particular a treatment step for bonding the fibers by suitable devices such as heated rolls or a calander. A suitable process for preparing a non-woven fabric employing the fibers in accordance with the present invention accordingly comprises the steps of providing fibers in accordance with the present invention and bonding the fibers by means of a suitable process as indicated above.

[0033] The following examples further illustrate the present invention.

Examples

[0034] Sheath/core fibers were produced employing a standard propylene homopolymer (STD PP SB) spunbonded grade (MFR₂ 25g/10min) as core component and employing either a commercially available reference product Aspun 6811A of Dow as sheath component or an ethylene-α-olefin copolymer in accordance with the present invention. Sheath/core fibers were produced with a weight ratio of the two polymer components of 50:50 with a line speed of 56 m/min and other process parameters as indicated in table 2 below. The ethylene-α-olefin copolymers in accordance with the present invention were HDPE materials comprising 1-hexene, having an MWD of about 4 and produced using a Ziegler-Natta catalyst. The ethylene-α-olefin copolymers in accordance with the present invention as employed in the examples showed MFR₂ values of 20.0, 27.0 and 38.6, respectively (E1, E2 and E3, respectively).

Table 1

		E1	E2	E3
MFR (2,16kg,190°C)	g/10min	20,0	27,0	38,6
Density	kg/m3	948,1	953,5	952,4
Comonomer	-	Hexene	Hexene	Hexene
Comonomer content	wt%	2.1	2.0	2.6

[0035] The ethylene-α-olefin copolymers used in accordance with the present invention were produced in a slurry process with a Z/N catalyst and tri-ethyl aluminium as cocatalyst. Pressure was 42 bar and temperature was 95 °C, isobutane was used as diluent.

[0036] Mw, Mn, MWD: The determination of weight average molecular weight (Mw) and number average molecular weight (Mn) and the molecular weight distribution (MWD = Mw/Mn) by size exclusion chromatograhy (SEC): Mw, Mn and MWD (Mw/Mn) were determined with A Millipore Waters ALC/GPC operating at 135 °C and equipped with two mixed bed and one 107 A TSK-Gel columns (TOSOHAAS 16S) and a differential refractometer detector. The solvent 1,2,4-trichlorobezene was applied at flow rate of 1 ml/min. The columns were calibrated with narrow molecular weight distribution polystyrene standards and narrow and broad polypropylenes. Reference is also made to ISO 16014.

[0037] MFR: The melt flow rates were measured according to ISO 1133 with a load of 2.16 kg at 230 °C for polypropylene and at 190 °C for polyethylene. The melt flow rate is that quantity of polymer in grams which the test apparatus standardised to ISO 1133 extrudes within 10 minutes at a temperature of 230 °C or 190 °C respectively, under a load of 2.16 kg.

[0038] Density: densities are measured according to ISO 1183/D.

[0039] Comonomer content: Comonomer content is determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with C13-NMR.

[0040] Trials were performed on a Reifenhäuser SMS Labline with a core-sheath configuration. Extrusion temperatures were set to 235°C for the polypropylene component and 215°C for the polyethylene materials.

[0041] The die temperature for both polymers was set to 235°C and the connection temperature for the polypropylene and the polyethylene materials were identical to the extrusion temperatures identified above. Fibers with a 2.5 denier thickness were produced and non-woven fabrics of about 42 g/m² were prepared.

[0042] Mechanical parameters of the produced non-woven fabrics were tested according to EN29073-1 and EN 29073-3. Strip measures were 50 * 200 mm. Distance between clamps was 100 mm. Testing speed was 200 mm / min.

[0043] The results can be taken from the following table 2. The table clearly reveals that the fibers in accordance with the present invention provide non-woven fabrics having increased tensile strength values, compared with the comparative example employing the reference market product. At the same time, the examples in accordance with the present invention did not give rise to any problems during spinning, such as fiber failure, for example, due to the occurrence of gel particles.

[0044] The examples as provided in Table 2 clearly show that, compared with the bicomponent fibers employing Aspun 6811A as polymer 2, clear improvements with respect to tensile strength values of the non-woven fabric, in machine direction (MD) as well as in cross direction (CD) can be obtained only by employing an ethylene-α-olefin copolymer in accordance with the present invention as second polymer component. In particular with an ethylene-α-olefin copolymer having a rather high MFR₂ highly satisfactory tensile strength values can be obtained, employing a window of about 10°C for the embossing roll temperature (127 to 136°C) showing the great latitude provided by the fiber in accordance with the present invention. The two grades of ethylene-α-olefin copolymer having lower MFR₂ values as tested in accordance with the present invention clearly show that also these components enable highly satisfactory tensile strength values, again providing a wide temperature window for the embossing temperature. The ethylene-α-olefin copolymer with MFR₂ of 20.0, for example, enables a satisfactory bonding process with embossing roll temperatures of from 124 to 142°C. Overall, it is therefore readily apparent hat the present invention enables an improvement with respect to the mechanical properties of a non-woven fabric produced using a fiber in accordance with the present invention while, at the same time, the temperature window for the bonding process is suitably wide providing the manufacturer with a great latitude concerning the process of forming a non-woven fabric.

[0045] The values achieved with Aspun 6811A and given in the table are optimized with respect to processing temperatures and speeds. They are the highest achievable with this polymer under the chosen conditions.

Claims

1. 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-α-olefin copolymer having a density of from 0.945 to 0.965 g/cm³ and a MFR₂ of from 15 to 45 g/10 min.

2. Fiber in accordance with the present invention, wherein the α-olefin is 1-hexene.

3. Fiber in accordance with any of the preceding claims, wherein the ethylene-α-olefin copolymer comprises from 1.75 to 3.0 wt% α-olefin.

4. Fiber in accordance with any one of the preceding claims, wherein the ethylene-α-olefin copolymer has a MWD of from 3.5 to 4.5.

5. Fiber in accordance with any of the preceding claims, wherein the ethylene-α-olefin copolymer has a density of from 0.947 to 0.955 g/cm³.

6. Fiber in accordance with any of the preceding claims, wherein the ethylene-α-olefin copolymer has an MFR₂ of 35 to 42, or from 18 to 30 g/10 min.

7. Fiber in accordance with any of the preceding claims, wherein the fiber is a bicomponent fiber.

8. Fiber in accordance with claim 7, wherein the bicomponent fiber has a core/sheath configuration.

9. Fiber in accordance with claim 8, wherein the second polymer component constitutes the sheath.

10. Non-woven fabric comprising the fiber of any of claims 1 to 9.

11. Process for preparing a fiber in accordance with any of claims 1 to 9, comprising the steps of providing the first polymer component and providing the second polymer component, melting the first and second polymer component and extruding the first and second polymer component through a spinnerette to produce a fiber.

12. Process for preparing a non-woven fabric in accordance with claim 10, comprising the steps of providing a fiber in accordance with any one of claims 1 to 9 and bonding in order to provide a non-woven fabric.

13. Use of an ethylene-α-olefin copolymer as defined in any one of claims 1 to 6 for the preparation of a bicomponent fiber.