Bicomponent fiber

Abstract

The invention relates to a bicomponent fiber comprising a first component having a melt flow index MFI1 determined according to ISO 1133-1:2011 at 230 ⁰C and 2.16 kg and comprising a first polypropylene homopolymer having a Z-average molecular weight Mz1, weight average molecular weight Mw1 and number average molecular weight Mn1 and a second component having a melt flow index MFI2 determined according to ISO 1133-1:2011 at 230 ⁰C and 2.16 kg and comprising a second polypropylene homopolymer having a Z-average molecular weight Mz2, weight average molecular weight Mw2 and number average molecular weight Mn2, 10 wherein the ratio of MFI1 to MFI2 is 0.85 to 1.14, Mz1 is at least 610,000, Mw1 / Mn1 is 4.5 to 6.5 and Mw1 / Mn1-Mw2 / Mn2 is 0.5 to 2.0.

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] Polypropylene (PP) nonwoven fabrics are widely applied in hygiene, healthcare and medical fields, e.g., diapers, incontinence pads, sanitary wipes and surgical gowns and drapes, due to its roust mechanical properties over a variety range of processing conditions such as spunbond technology. However, traditional PP nonwovens often lack a good hand-touch feeling like natural fibers and fabrics (cotton), which originates from an absence of a crimped structure of PP fibers, as well as the “loft” or “bulk” space-filling characteristics of PP fibers. Currently, there is a greatly increasing demand for bulky and soft nonwovens in the hygiene market, and bicomponent spunbond process has demonstrated some advantages to impart “loft” properties to PP nonwovens in a cost-effective way, compared to staple fiber process.

[0004] EP2343406A1 discloses a crimped conjugated fiber having a crimpable cross-sectional configuration comprising a propylene polymer (A) and a propylene polymer (B) in a mass ratio of 10:90 to 55:45, wherein Mz / Mw(A)-Mz / Mw(B) is 0.30 to 2.2 and the propylene polymers (A) and (B) have similar melting points and MFR. Mz(A) is 300,000 to 600,000 and Mw / Mn (A) is 2.0 to 4.0. Bicomponent fibers having a core-sheath configuration were made in the examples.

[0005] There is still a need for a non-woven fabric having a good skin-touch feeling such as loft and elastic properties.

[0006] It is an objective of the present invention to provide a fiber by which the above- mentioned and / or other needs are met.

[0007] Accordingly, the invention provides a bicomponent fiber comprising a first component having a melt flow index MFI1 determined according to ISO 1133- 1 :2011 at 230 °C and 2.16 kg and comprising a first polypropylene homopolymer having Z-average molecular weight Mz1 , weight average molecular weight Mw1 and number average molecular weight Mn1 and a second component having a melt flow index MFI2 determined according to ISO 1133- 1 :2011 at 230 °C and 2.16 kg and comprising a second polypropylene homopolymer having Z-average molecular weight Mz2, weight average molecular weight Mw2 and number average molecular weight Mn2, wherein the ratio of MFI1 to MFI2 is 0.85 to 1.14,

[0008] Mz1 is at least 610,000,% Mw1 / Mn1 is 4.5 to 6.5 and Mw1 / Mn1-Mw2 / Mn2 is 0.5 to 2.0.

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

[0010] According to the invention, the use in a bicomponent fiber of a propylene homopolymer having a relatively high Mw / Mn and Mz in one component in combination with another propylene homopolymer having a similar MFI and a substantially lower Mw / Mn in another component allows a non-woven fabric with desirable properties to be produced. The non-woven fabric according to the invention has a high loft represented by a high thickness and good elastic properties represented by a high elongation.

[0011] 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).

[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 side-by-side 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 5:95 to 95:5, for example 5:95 to 55:45, 5:95 to 50:50 or 5:95 to 45:65. Particularly preferably, the weight ratio between the first component and the second component is 5:95 to 25:75. This results in particularly high loft of the non-woven fabric according to the invention.

[0017] 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 the fibers may have a linear mass density of e.g. 0.5 to 100 denier, such as 1 .0 to 50 denier.

[0018] Fist component

[0019] The first component of the bicomponent fiber has a melt flow index MFI1 determined according to ISO 1133-1 :2011 at 230 °C and 2.16 kg. MFI1 may e.g. be 5.0 to 50 dg / min, for example 10 to 40 dg / min, 15 to 35 dg / min or 20 to 30 dg / min. This is beneficial for the mechanical properties of the non-woven fabric such as tensile strength.

[0020] The first component comprises a first polypropylene homopolymer and may further 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, antifogging 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 in the first component may e.g. be 0.0 to 5.0 wt%. In some embodiments, the first component is substantially free of fillers such as talc, for example the first component comprises less than 50 ppm, less than 30 ppm, less than 10 ppm of fillers such as talc.

[0021] The amount of the first polypropylene homopolymer 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%. Preferably, the total amount of the first polypropylene homopolymer and the additives is 100 wt% with respect to the first component.

[0022] The first polypropylene homopolymer may have a melt flow index determined according to ISO 1133-1 :2011 at 230 °C and 2.16 kg of 5.0 to 50 dg / min, for example 10 to 40 dg / min, 15 to 35 dg / min or 20 to 30 dg / min. The first polypropylene homopolymer has Z-average molecular weight Mz1 , weight average molecular weight Mw1 and number average molecular weight Mn1.

[0023] Mz1 is at least 610,000, preferably 610,000 to 750,000, more preferably 610,000 to 700,000, more preferably 620,000 to 680,000.

[0024] Preferably, Mw1 is 150,000 to 250,000, more preferably 170,000 to 230,000, more preferably 200,000 to 230,000.

[0025] Preferably, Mn1 is 10,000 to 60,000, more preferably 20,000 to 50,000, more preferably 20,000 to 42,000.

[0026] Preferably, Mz1 / Mw1 is 2.50 to 4.50, more preferably 2.60 to 4.30, more preferably 2.70 to 4.00, more preferably 2.80 to 3.50.

[0027] Mw1 / Mn1 is 4.5 to 6.5, preferably 4.7 to 6.3, more preferably 5.0 to 6.0.

[0028] Second component

[0029] The second component of the bicomponent fiber has a melt flow index MFI1 determined according to ISO 1133-1 :2011 at 230 °C and 2.16 kg. MFI1 may e.g. be 5.0 to 50 dg / min, for example 10 to 40 dg / min, 15 to 35 dg / min or 20 to 30 dg / min. This is beneficial for the mechanical properties of the non-woven fabric such as tensile strength.

[0030] The second component comprises a second polypropylene homopolymer and may further comprise additives e.g. in an amount of 0.0 to 5.0 wt%. Suitable examples of the additives are those mentioned in relation to the first component. In some embodiments, the second component is substantially free of fillers such as talc, for example the second component comprises less than 50 ppm, less than 30 ppm, less than 10 ppm of fillers such as talc.

[0031] The amount of the second polypropylene homopolymer 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%. Preferably, the total amount of the second polypropylene homopolymer and the additives is 100 wt% with respect to the second component. The second polypropylene homopolymer may have a melt flow index determined according to ISO 1133-1 :2011 at 230 °C and 2.16 kg of 5.0 to 50 dg / min, for example 10 to 40 dg / min, 15 to 35 dg / min or 20 to 30 dg / min.

[0032] The second polypropylene homopolymer has Z-average molecular weight Mz2, weight average molecular weight Mw2 and number average molecular weight Mn2.

[0033] Preferably, Mz2 is 300,000 to 600,000, more preferably 400,000 to 500,000.

[0034] Preferably, Mw2 is 150,000 to 250,000, more preferably 170,000 to 230,000, more preferably 170,000 to 200,000.

[0035] Preferably, Mn2 is 10,000 to 60,000, more preferably 20,000 to 50,000, more preferably 42,000 to 50,000.

[0036] Preferably, Mz2 / Mw2 is at most 2.50, more preferably 1 .50 to 2.50, more preferably 1.70 to 2.40.

[0037] Preferably, Mw2 / Mn2 is 2.0 to 5.0, more preferably 2.5 to 4.5, more preferably 3.6 to 4.4.

[0038] First component versus second component

[0039] The ratio of MFI1 to MFI2 is 0.85 to 1.14, preferably 0.90 to 1.10, more preferably 0.95 to 1.05. The similarity in the MFI of the first and second components is advantageous for the stable spinning of the fibers without contamination of the nozzle.

[0040] Preferably, the difference between MFI1 and MFI2 is at most 3.0 dg / min, preferably at most 2.0 dg / min, more preferably at most 1 .0 dg / min. MFI2 is smaller than, equal to or greater than MFI1.

[0041] Preferably, Mz1 / Mw1-Mz2 / Mw2 is 0.35 to 2.10, more preferably 0.40 to 1.50, more preferably 0.50 to 1 .00.

[0042] Mw1 / Mn1-Mw2 / Mn2 is 0.5 to 2.0, preferably 1.1 to 2.0, more preferably 1.2 to 1.9.

[0043] The first component and the second component of the bicomponent fiber have similar melting points, e.g. the difference between the melting point of the first component and the melting point of the second component is at most 5.0 °C, at most 3.0 °C or at most 1.0 °C.

[0044] Other aspects

[0045] 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 first component and a melt of the second component and extruding the melt of the first component and the melt of the second component through a spinneret to obtain the bicomponent fiber.

[0046] 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 30 gsm.

[0047] 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.

[0048] 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.

[0049] Preferably, step b) comprises calendering or hot air through bonding, more preferably calendering. The calendering preferably involves the use of semi-high loft calender over high loft calender for calendering. Semi-high loft calender is used for obtaining a structure in which a crimpled high loft spunbond layer is provided on an uncrimped or low crimped spunbond layer. High loft calender is used for obtaining a structure in which all layers are crimped.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0054] Materials

[0055] Following propylene homopolymers were used:

[0056] Table 1

[0057] Mz, Mw, Mn: Gel Permeation Chromatography

[0058] Bicomponent fibers having a side-to-side configuration and non-woven fabrics using these fibers were produced using the process parameters shown in Table 2.

[0059] The spunbound line used in the experiments comprises two single screw extruders. Spinning pumps were used to feed the molten polymer to the spinpack line which consists of 7377 holes in side-by-side configuration. Spunbond nonwoven fabrics were produced using the obtained spun bicomponent fibers by calendering (semi-high loft calendering). Table 2. Process parameters Various properties of the spunbond nonwoven fabrics produced were measured and are shown in Table 3.

[0060] Tensile strength in machine direction (MD) and cross direction (CD) was measured in accordance with ASTM D5035-11 .

[0061] Elongation in machine direction (MD) and cross direction (CD) was measured in accordance with ASTM D5035- 11

[0062] Table 3

[0063] It can be understood that the use of two components in making the fibers according to the invention resulted in higher elongation and higher thickness of the spunbond nonwoven fabrics than the use of one component in making the fibers.

[0064] The weight ratio of PP515A:PP511A of 10:90 and 20:80 resulted in particularly high thickness.

Claims

CLAIMS1. A bicomponent fiber comprising a first component having a melt flow index MFI1 determined according to ISO 1133-1 :2011 at 230 °C and 2.16 kg and comprising a first polypropylene homopolymer having a Z-average molecular weight Mz1 , weight average molecular weight Mw1 and number average molecular weight Mn1 and a second component having a melt flow index MFI2 determined according to ISO 1133-1 :2011 at 230 °C and 2.16 kg and comprising a second polypropylene homopolymer having a Z-average molecular weight Mz2, weight average molecular weight Mw2 and number average molecular weight Mn2, wherein the ratio of MFI1 to MFI2 is 0.85 to 1.14, Mz1 is at least 610,000, Mw1 / Mn1 is 4.5 to 6.5 andMw1 / Mn1-Mw2 / Mn2 is 0.5 to 2.0.

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

3. The bicomponent fiber according to any one of the preceding claims, wherein the difference between MFI1 and MFI2 is at most 3.0 dg / min, preferably at most 2.0 dg / min, more preferably at most 1.0 dg / min.

4. The bicomponent fiber according to any one of the preceding claims, wherein Mn1 is 10,000 to 60,000, preferably 20,000 to 50,000, more preferably 20,000 to 42,000 and / orMn2 is 10,000 to 60,000, preferably 20,000 to 50,000, more preferably 42,000 to 50,000.

5. The bicomponent fiber according to any one of the preceding claims, wherein Mw1 / Mn1-Mw2 / Mn2 is 1.1 to 2.0, preferably 1.2 to 1.9.

6. The bicomponent fiber according to any one of the preceding claims, wherein Mz1 is 610,000 to 750,000, more preferably 610,000 to 700,000, more preferably 620,000 to 680,000, and / orMw1 is 150,000 to 250,000, preferably 170,000 to 230,000, more preferably 200,000 to 230,000, and / orMz1 / Mw1 is 2.50 to 4.50, more preferably 2.60 to 4.30, more preferably 2.70 to4.00, more preferably 2.80 to 3.50, and / orMw1 / Mn1 is 4.7 to 6.3, more preferably 5.0 to 6.0.

7. The bicomponent fiber according to any one of the preceding claims, wherein Mz2 is 300,000 to 600,000, more preferably 400,000 to 500,000, and / orMw2 is 150,000 to 250,000, more preferably 170,000 to 230,000, more preferably 170,000 to 200,000, and / orMz2 / Mw2 is at most 2.50, more preferably 1 .50 to 2.50, more preferably 1 .70 to 2.40, and / orMw2 / Mn2 is 2.0 to 5.0, more preferably 2.5 to 4.5, more preferably 3.6 to 4.

48. The bicomponent fiber according to any one of the preceding claims, wherein Mz1 / Mw1-Mz2 / Mw2 is 0.35 to 2.10, preferably 0.40 to 1.50, more preferably 0.50 to 1.00.

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 5:95 to 95:5, for example 5:95 to 55:45, 5:95 to 50:50 or 5:95 to 45:65.

10. The bicomponent fiber according to any one of the preceding claims, wherein the weight ratio between the first component and the second component is 5:95 to 25:95.11 . A process for making the bicomponent fiber according to any one of the preceding claims, comprising the steps of: providing a melt of the first polypropylene component and a melt of the second polypropylene component and extruding the melt of the first polypropylene component and the melt of the second polypropylene component 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, comprising providing wherein step b) comprises calendering or hot air through bonding, preferably calendering.

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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