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Publication numberUS20040038612 A1
Publication typeApplication
Application numberUS 10/225,450
Publication dateFeb 26, 2004
Filing dateAug 21, 2002
Priority dateAug 21, 2002
Also published asCN1311112C, CN1675414A, EP1530655A1, WO2004018746A1
Publication number10225450, 225450, US 2004/0038612 A1, US 2004/038612 A1, US 20040038612 A1, US 20040038612A1, US 2004038612 A1, US 2004038612A1, US-A1-20040038612, US-A1-2004038612, US2004/0038612A1, US2004/038612A1, US20040038612 A1, US20040038612A1, US2004038612 A1, US2004038612A1
InventorsBrian Forbes, Mark Majors, John Sayovitz
Original AssigneeKimberly-Clark Worldwide, Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Multi-component fibers and non-woven webs made therefrom
US 20040038612 A1
Abstract
Bicomponent spunbond filaments and non-woven webs made from the filaments are disclosed. The spunbond filaments include a core polymer and a sheath polymer. Both the core polymer and the sheath polymer are made primarily from polypropylene polymers. For instance, the sheath polymer can be a randomized copolymer of polypropylene and ethylene. The ethylene can be present in the sheath polymer in an amount of less than about 2% by weight. The core polymer, on the other hand, can be a polypropylene polymer having a melting temperature than the sheath polymer.
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Claims(31)
What is claimed is:
1. A non-woven web comprising continuous polymeric filaments, the polymeric filaments comprising multi-component filaments including a sheath polymer and a core polymer, the sheath polymer comprising a copolymer of a polypropylene polymer and a monomer, the core polymer comprising primarily a polypropylene homopolymer polymer, the core polymer having a melting temperature that is at least about 15° F. greater than the melting temperature of the sheath polymer, the continuous polymer filaments being fused together.
2. A non-woven web as defined in claim 1, wherein the sheath polymer comprises a randomized copolymer.
3. A non-woven web as defined in claim 2, wherein the monomer comprises ethylene.
4. A non-woven web as defined in claim 2, wherein the monomer is present in the sheath polymer in an amount of less than about 2% by weight.
5. A non-woven web as defined in claim 3, wherein the monomer is present in the sheath polymer in an amount of less than about 2% by weight.
6. A non-woven web as defined in claim 1, wherein the continuous filaments comprise spunbond filaments.
7. A non-woven web as defined in claim 1, wherein the sheath polymer and the core polymer have a melt flow rating of from about 30 g/10 minutes to about 35 g/10 minutes.
8. A non-woven web as defined in claim 1, wherein the sheath polymer has a melting temperature of from about 110° C. to about 150° C.
9. A non-woven web as defined in claim 1, wherein the core polymer comprises a metallocene catalyzed polypropylene.
10. A non-woven web as defined in claim 1, wherein the core polymer comprises polypropylene in an amount of at least 98% by weight.
11. A non-woven web as defined in claim 1, wherein the sheath polymer comprises a blend of the copolymer of a polypropylene polymer and a monomer and a polypropylene homopolymer, the copolymer of a polypropylene polymer and a monomer comprising a randomized copolymer of polypropylene and ethylene.
12. A non-woven web comprising polymeric fibers, the polymeric fibers comprising multi-component fibers including a sheath polymer and a core polymer, the sheath polymer comprising a random copolymer of a polypropylene polymer and ethylene, the ethylene being present in the sheath polymer in an amount of less than about 2% by weight, the core polymer comprising a polypropylene polymer, the core polymer having a melting temperature that is at least about 15° F. greater than the melting temperature of the sheath polymer, the polymeric fibers being fused together.
13. A non-woven web as defined in claim 12, wherein ethylene is present in the sheath polymer in an amount of less than about 1.8% by weight.
14. A non-woven web as defined in claim 12, wherein the multi-component fibers are continuous filaments.
15. A non-woven web as defined in claim 12, wherein the multi-component fibers are spunbond fibers.
16. A non-woven web as defined in claim 12, wherein the sheath polymer and the core polymer have a melt flow rating of from about 30 g/10 minutes to about 35 g/10 minutes.
17. A non-woven web as defined in claim 12, wherein the sheath polymer has a melting temperature of from about 110° C. to about 1500 C.
18. A non-woven web as defined in claim 12, wherein the core polymer comprises a metallocene catalyzed polypropylene.
19. A non-woven web as defined in claim 12, wherein the sheath polymer comprises a blend of the random copolymer and a polypropylene homopolymer.
20. A non-woven web comprising continuous polymeric filaments, the polymeric filaments having been formed by being extruded through a spinnerette, the polymeric filaments comprising multi-component filaments including a sheath polymer and a core polymer, the sheath polymer comprising a random copolymer of a polypropylene polymer ethylene, the ethylene being present in the sheath polymer in an amount of less than about 2% by weight, the core polymer comprising a polypropylene polymer, the polypropylene being present in the core polymer in an amount of at least 95% by weight, the core polymer having a melting temperature that is at least about 15° F. greater than the melting temperature of the sheath polymer, the core polymer and the sheath polymer having a melt flow rating of at least 30 g/10 minutes, the continuous polymeric filaments being fused together to form the non-woven web.
21. A non-woven web as defined in claim 20, wherein the sheath polymer has a melting temperature of from about 110° C. to about 150° C.
22. A non-woven web as defined in claim 20, wherein the core polymer comprises a metallocene catalyzed polypropylene.
23. A non-woven web as defined in claim 20, wherein the sheath polymer comprises from about 20% by weight to about 70% by weight of the continuous filaments.
24. A non-woven web as defined in claim 20, wherein ethylene is present in the sheath polymer in an amount of less than about 1.8% by weight.
25. A fiber comprising:
a bicomponent spunbond filament including a sheath polymer and a core polymer, the sheath polymer comprising a random copolymer of a polypropylene polymer and ethylene, the ethylene being present in the sheath polymer in an amount of less than about 2% by weight, the core polymer comprising a polypropylene polymer, the core polymer having a melting temperature that is at least about 15° F. greater than the melting temperature of the sheath polymer.
26. A fiber as defined in claim 25, wherein ethylene is present in the sheath polymer in an amount of less than about 1.8% by weight.
27. A fiber as defined in claim 25, wherein the sheath polymer and the core polymer have a melt flow rating of from about 30 g/10 minutes to about 35 g/10 minutes.
28. A fiber as defined in claim 25, wherein the sheath polymer has a melting temperature of from about 110° C. to about 150° C.
29. A fiber as defined in claim 25, wherein the core polymer comprises a metallocene catalyzed polypropylene.
30. A fiber as defined in claim 25, wherein the sheath polymer comprises from about 20% by weight to about 70% by weight of the continuous filaments.
31. A fiber as defined in claim 25, wherein the sheath polymer comprises a blend of the random copolymer and a polypropylene homopolymer.
Description
BACKGROUND OF THE INVENTION

[0001] Non-woven fabrics made from polymeric materials are used to make a variety of products, which desirably have particular levels of softness, strength, uniformity, liquid handling properties such as absorbency, and other physical properties. Such products include towels, industrial wipes, incontinence products, infant care products such as baby diapers, absorbent feminine care products, and garments such as medical apparel. These products are often made with multiple layers of non-woven fabric to obtain the desired combination of properties.

[0002] In many applications, the nonwoven fabrics are created from spunbond filaments that are formed by melt spinning thermoplastic materials. Methods for making spunbond non-woven fabrics are well known and disclosed, for instance, in U.S. Pat. No. 4,692,618 to Dorschner, et al., U.S. Pat. No. 4,340,563 to Appel, et al., and U.S. Pat. No. 5,418,045 to Pike, et al., which are all incorporated herein by reference. Spunbond non-woven polymeric webs are formed by extruding thermoplastic materials through a spinneret and drawing the extruded material into filaments with a stream of high velocity air to form a random web on a collecting surface.

[0003] In some applications, in order to produce spunbond materials with desirable combinations of softness, strength and absorbency, spunbond non-woven fabrics are formed from multi-component filaments, such as bicomponent filaments. Bicomponent filaments are filaments made from first and second polymeric components which remain distinct within the filament. For example, in one embodiment, the filament can be in a sheath and core arrangement in which a first polymeric component makes up the core and the second polymeric component makes up the sheath.

[0004] In the past, very useful bicomponent spunbond filaments have been made that contained a core polymer made from polypropylene and a sheath polymer made from polyethylene. The sheath polymer generally had a lower melting temperature than the core polymer to allow the filaments to be easily thermally bonded together. The sheath polymer also provided softness to the resulting non-woven web. The core polymer, on the other hand, provided strength to the web.

[0005] Although the above-described spunbond filaments and non-woven webs made from the filaments have provided great advances in the art, further improvements are still needed. In particular, a need exists for a less expensive alternative to the above-described spunbond filament that has substantially equal or better properties than spunbond filaments made in the past.

SUMMARY OF THE INVENTION

[0006] In general, the present invention is directed to spunbond multi-component filaments and to non-woven webs made from the filaments. For instance, in one embodiment, the present invention is directed to a non-woven web containing continuous polymeric multi-component filaments. The polymeric filaments include a sheath polymer and a core polymer. The sheath polymer comprises a copolymer of a polypropylene polymer and a monomer. The core polymer, on the other hand, comprises a polypropylene polymer. In general, the core polymer has a melting temperature that is at least about 8° C. (15° F.) greater than the melting temperature of the sheath polymer. When combined to form a non-woven web, the filaments can be thermally fused together.

[0007] The sheath polymer can be present in the continuous filament in an amount from about 20% by weight to about 70% by weight, and particularly from about 40% by weight to about 60% by weight. In one embodiment, the sheath polymer can comprise a randomized copolymer of the polypropylene and the monomer. The monomer can be, for instance, ethylene.

[0008] For example, in one embodiment of the present invention, the sheath polymer contains a randomized copolymer of polypropylene and ethylene. The ethylene is present in the sheath polymer in an amount of less than about 2% by weight and particularly less than about 1.8% by weight. In this embodiment, the sheath polymer can consist essentially of a randomized copolymer containing a monomer in the above amounts or can be a blend of a polypropylene homopolymer and a randomized copolymer of a polypropylene such that the blend contains a monomer in the above amounts. It has been discovered by the present inventors that various benefits and advantages are achieved if the amount of ethylene present in the sheath polymer is below about 2% by weight.

[0009] The core polymer, on the other hand, can be polypropylene homopolymer. For example, in one embodiment, the core polymer can be a metallocene catalyzed polypropylene homopolymer.

[0010] The melt flow rating of the sheath polymer and the core polymer can be from about 30 g/10 minutes to about 40 g/10 minutes, and particularly from about 30 g/10 minutes to about 35 g/10 minutes. The sheath polymer can have a melting temperature of from about 110° C. to about 150° C. As stated above, the core polymer can have a melting temperature that is at least about 8° C. greater than the melting temperature of the sheath polymer. Although various articles can be made in accordance with the present invention, the teachings of the present invention are particularly well-suited for the formation of spunbond fibers, and particularly spunbond continuous filaments.

[0011] Other features and aspects of the present invention are discussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figures in which:

[0013]FIG. 1 is a cross-sectional view of one embodiment of a bi-component filament made in accordance with the present invention; and

[0014]FIG. 2 is a schematic drawing of one embodiment of a process line that can be used to make filaments in accordance with the present invention.

[0015] Repeated use of reference characters in the present specification and drawings is intended to represent the same or analogous or elements of the invention.

DETAILED DESCRIPTION

[0016] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

[0017] In general, the present invention is directed to non-woven webs made from multi-component polymeric filaments. The non-woven webs are made so as to have a desired balance of physical properties. In general, the multi-component polymeric filaments are continuous bicomponent filaments that contain a core polymer surrounded by a sheath polymer. In accordance with the present invention, both the core polymer and the sheath polymer contain primarily polypropylene. For instance, the sheath polymer can be a randomized copolymer of polypropylene, while the core polymer can be a crystaline polypropylene polymer having a relatively high melting point.

[0018] The present inventors have discovered that when using selected polypropylene polymers to construct the bicomponent filaments, non-woven webs can be formed that have improved strength and tear properties in comparison to non-woven webs made from monocomponent filaments, while also remaining soft and absorbent. Of particular advantage, non-woven webs with improved properties can be formed according to the present invention using relatively inexpensive polypropylene materials, as opposed to resorting to the use of more expensive exotic polymers to enhance bonding or tenacity.

[0019] Referring to FIG. 1, one embodiment of a cross-section of a filament generally 100 made in accordance with the present invention is shown. As illustrated, the filament 100 is a bicomponent filament including a core polymer 200 surrounded by a sheath polymer 300. As described above, in accordance with the present invention, the core polymer 200 and the sheath polymer 300 are both made primarily from polypropylene polymers. Further, in one embodiment, the filament 100 is a spunbond filament that can be continuous.

[0020] As shown, the copolymer 200 and the sheath polymer 300 are arranged in distinctive zones across the cross section of the filament 100. Both polymers extend the entire distance of the filament 100. In this embodiment, the core polymer 200 is shown substantially concentric with the sheath polymer 300. It should be understood, however, that the core polymer and the sheath polymer can be placed in various other arrangements. For instance, the core polymer 200 and the sheath polymer 300 can be placed in an eccentric arrangement as well.

[0021] In general, the sheath polymer 300 has a lower melting temperature than the core polymer 200. In this manner, the sheath polymer 300 of one filament can easily melt and fuse with the sheath polymer of an adjacent filament during web bonding.

[0022] The sheath polymer 300 used to make filaments and non-woven webs in accordance with the present invention primarily contains a polypropylene polymer, such as a crystalline polypropylene. The polypropylene polymer should have a relatively low melt temperature, such as a melt temperature of less than about 150° C. Specifically, the melt temperature of the polypropylene sheath polymer can be from about 110° C. to about 150° C. and more particularly from about 120° C. to about 135° C. The melt flow rating of the polymer can be from about 30 g/10 minutes to about 40 g/10 minutes, and particularly from about 30 g/10 minutes to about 35 g/10 minutes. The above-described melt flow ranges are particularly well-suited for the formation of spunbond filaments in melt spinning operations.

[0023] In one embodiment, the sheath polymer can contain a copolymer of a polypropylene and a monomer, particularly a randomized copolymer of a polypropylene and a monomer. The monomer can be, for instance, ethylene or butene. The amount of monomer contained within the sheath polymer should be relatively low in some applications. Specifically, it has been discovered by the present inventors that the monomer should be present within the sheath polymer in an amount of less than about 2% by weight, particularly less than about 1.8% by weight. For example, in one embodiment, the monomer can be ethylene and can be contained in the sheath polymer in an amount of less than about 1.6% by weight.

[0024] The sheath polymer can be constructed in various ways in order to obtain the relatively lower monomer levels. For instance, in one embodiment, the sheath polymer can be made primarily of a randomized copolymer containing a monomer in an amount less than about 2% by weight. In an alternative embodiment, a randomized copolymer of a polypropylene can be mixed with a polypropylene homopolymer in order to reduce the total monomer content in the sheath polymer. Thus, the sheath polymer can be made exclusively of a randomized copolymer of a polypropylene and a monomer or can be a blend of a polypropylene polymer and a randomized copolymer of a polypropylene polymer.

[0025] Lower levels of monomer contained within the sheath polymer provide various benefits and advantages of the present invention. For instance, the filaments tend not to quench effectively during formation.

[0026] In one embodiment of the present invention, the sheath polymer can contain a randomized copolymer of polypropylene and ethylene sold by Dow Chemical under the product number 6D43. Dow Chemical 6D43 polymer, however, contains ethylene in an amount of about 3.2% by weight. Thus, when used in the present invention, greater amounts of polypropylene or another suitable polymer can be added to the product in order to reduce the monomer levels.

[0027] In general, the sheath polymer should contain polypropylene in an amount of about 95% by weight. Besides polypropylene, the sheath polymer can contain a monomer as described above and other additional additives. Such additives can include antioxidants, heat stabilizers, other stabilizers, and the like.

[0028] The sheath polymer not only provides softness to spunbond filaments and non-woven webs made in accordance with the present invention, but also improves the toughness of the webs. For instance, due to its lower melting temperature, the sheath polymer has a softer feel. Further, also because the sheath polymer has a lower melting temperature, the sheath polymer is well adapted to melting and fusing with adjacent fibers. In fact, since the sheath polymer can easily melt with other filament fibers during bonding, non-woven webs formed in accordance with the present invention have greater integrity and toughness.

[0029] As described above, the core polymer 200 as shown in FIG. 1 also contains primarily polypropylene. In comparison to the sheath polymer, however, the core polymer generally has a higher melting temperature than the sheath polymer. For instance, the core polymer can have a melting temperature that is at least about 8° C. (15° F.) higher than the melting temperature of the sheath polymer, and particularly can have a melting temperature from about 8° C. higher to about 15° C. higher than the sheath polymer. For instance, the core polymer can have a melting temperature of greater than about 150° C., and particularly greater than about 155° C.

[0030] The core polymer is present in the filament in order to increase the strength of the filament and to increase the strength of non-woven webs made from the filaments.

[0031] In one embodiment, the core polymer contains a homopolymer of polypropylene in an amount of at least about 95% by weight. Other polymers and additives can be combined with the core polymer in relatively small amounts. In order to facilitate the formation of spunbond filaments, particularly continuous filaments in a melt spinning operation, the core polymer can have a melt flow rating of from about 30 g/10 minutes to about 40 g/10 minutes, and particularly from about 33 g/10 minutes to about 39 g/10 minutes.

[0032] The polypropylene contained in the core polymer can be a Ziegler-Natta catalyzed polymer or, alternatively, can be a metallocene catalyzed polymer. Metallocene catalyzed polymers provide various advantages including offering the possibility of providing a polymer with a relatively low molecular weight distribution. In one embodiment, the core polymer is product number 3155 or 3854 marketed by the Exxon Corporation.

[0033] In general, the sheath polymer is present in the filament in an amount from about 20% to about 70% by weight and particularly in amount from about 40% to about 60% by weight.

[0034] The teachings of the present invention are particularly well-suited to producing continuous melt spun filaments, such as spunbond filaments. Referring to FIG. 2, a process line generally 10 for preparing spunbond filaments in accordance with the present invention is illustrated. The process line 10 is arranged to produce bicomponent continuous filaments and to produce non-woven webs made from the spunbond filaments. In this embodiment, the process line 10 includes a pair of extruders 12A and 12B for separately extruding a sheath polymer and a core polymer. The sheath polymer is fed into the extruder 12A from a first hopper 14A and the core polymer is fed into the extruder 12B from a second hopper 14B.

[0035] The sheath polymer and the core polymer are fed from the extruders 12A and 12B through polymer conduit 16A and 16B to a spinneret 18. Generally described, in one embodiment, the spinneret 18 includes a housing containing a spin pack which includes a plurality of plates stacked one on top of the other with a pattern of openings arranged to create flow paths for directing polymer components through the spinneret. The spinneret 18 has openings arranged in one or more rows. The spinneret openings form a downwardly extending curtain of filaments when the polymers are extruded through the spinneret.

[0036] In the embodiment illustrated, the process line 10 also includes a quench blower 20 positioned adjacent the curtain of filaments extending from the spinneret 18. Air from the quench air blower 20 quenches the filaments extending from the spinneret 18. The quencher can be directed from one side of the filament curtain as shown in FIG. 2, or both sides of the filament curtain.

[0037] The process line can further include a fiber draw unit or aspirator 22 positioned below the spinneret that receives the quenched filaments. Fiber draw units or aspirators for use in melt spinning polymers are well known as discussed above.

[0038] Generally described, the fiber draw unit 22 includes an elongate vertical passage through which the filaments are drawn by aspirating air entering from the sides of the passage and flowing downwardly through the passage. A heater 24 can supply hot aspirating air to the fiber drawn unit 22. The hot aspirating air draws the filaments and ambient air through the fiber draw unit.

[0039] An foraminous forming surface 26 is positioned below the fiber draw unit 22 and receives the continuous filaments from the outlet opening of the fiber draw unit. The forming surface 26 travels around guide roll 28. A vacuum 30 positioned below the forming surface 26 where the filaments are deposited draws the filaments against the forming surface.

[0040] In the embodiment illustrated in FIG. 2, the process line 10 further includes a compression device such as a compression roller 32 which, along with the forward most of the guide rollers 28, receives the web as the web is drawn off of the forming surface 26. From the compression roller 32, the web is fed to a winding roll 42 for taking up the finished fabric. Prior to winding the web onto the roll 42, the process line can further include some type of bonding apparatus such as thermal point bonding rollers 34 and/or a through-air bonder 36. Thermal point bonders and through-air bonders are well known to those skilled in the art and are not disclosed here in detail.

[0041] To operate the process line 10, the hoppers 14A and 14B are filled with the respective polymer components. The core polymer and the sheath polymer are melted and extruded by the respective extruders 12A and 12B through polymer conduit 16A and 16B and the spinneret 18. During extrusion, the polymers are heated to temperatures sufficient for the polymers to be flowable.

[0042] As the extruded filaments extend below the spinneret 18, a stream of air from the quench blower 20 at least partially quenches the filaments. The quench air, for instance, can flow in a direction substantially perpendicular to the length of the filaments. The temperature of the quench air can be from about 45° F. to about 90° F. and can be at a velocity of from about 100 to 400 feet per minute.

[0043] After quenching, the filaments are drawn into the vertical passage of the fiber draw unit 22 by a flow of hot air from the heater 24 through the fiber draw unit. It should be understood, however, that the use of a fiber draw unit is optional. When present in the system, the fiber draw unit can be used, for instance, to cause the filaments to slightly crimp. After exiting the fiber draw unit 22, the filaments are deposited onto the traveling forming surface 26. The vacuum 20 draws the filaments against the forming surface to form an unbonded, non-woven web of continuous filaments. The web is then lightly compressed by the compression roller 32. Next, the web can be bonded together using any suitable technique, such as by using thermal point bonded rollers 34 or by using a through-air bonder 36. When using a through-air bonder, air having a temperature above the melting temperature of the sheath polymer and below the melting temperature of the core polymer is directed from a hood 40 and through the web. The hot air melts the sheath polymer thereby forming bonds between the bicomponent filaments to integrate the web. The temperature of air flowing through the bonder can be from about 230° F. to about 280° F. and can be at a velocity of from about 100 to about 500 feet per minute.

[0044] Lastly, the finished web is wound into the winder roller 42 and is ready for further treatment or use. Spunbond non-woven webs constructed in accordance with the present invention have been found to offer various advantages and benefits. For instance, the non-woven webs have been found to have increased tensile strength and tear strength in relation to webs made only with a polypropylene polymer. In fact, the webs have exhibited properties favorably comparable to conventionally made bicomponent filaments. Since the filaments of the present invention, however, are made almost exclusively of polypropylene polymers, the filaments are relatively inexpensive to produce.

[0045] Spunbond non-woven webs made in accordance with the present invention can be used in numerous applications. For instance, the spunbond webs can be used for making personal care articles and garment materials. Personal care articles include infant care products such as disposable baby diapers, child care products such as training pants, and adult care products such as incontinence products and feminine care products. Suitable garments include medical apparel, work ware and the like.

[0046] In one embodiment, spunbond non-woven webs made in accordance with the present invention can be combined with other webs for forming laminates. For example, the spunbond webs can be laminated to other spunbond webs or to meltblown webs. In one particular embodiment, for instance, a spunbond/melt blown/spunbond laminate is formed containing the non-woven webs of the present invention. The basis weight of the non-woven webs can be, for instance, from about 0.25 OSY to about 3 OSY, and particularly from about 0.50 OSY to about 2 OSY. In one embodiment, for instance, a spunbond/melt blown/spunbond laminate can be formed in which each layer has a basis weight of about 1 OSY.

EXAMPLE

[0047] The following example was performed in order to demonstrate some of the benefits and advantages of the present invention. In this example, spunbond non-woven webs and laminates containing the spunbond webs were produced according to the present invention and tested. In particular, various properties were tested according to the following procedures:

[0048] Strip Tensile and Energy Tests: The strip tensile and energy test(s) measure the peak and breaking loads of a fabric. This test measures the load (strength) in pounds and energy in inch-pounds. In the strip tensile test, two clamps, each having two jaws with each jaw having a facing in contact with the sample, hold the material in the same plane, usually vertically, separated by 3 inches and move apart at a specified rate of extension. Values for strip tensile strength are obtained using a sample size of 3 inches by 6 inches, with a jaw facing size of 1 inch high by 3 inches wide, and a constant rate of extension of 300 mm/min. The Sintech 2 tester, available from the Sintech Corporation, 1001 Sheldon Dr., Cary, N.C. 27513, the Instron Model TM, available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Philadelphia, Pa. 19154 may be used for this test. Results are reported as an average for three specimens and may be performed with the specimen in the cross direction (CD) or the machine direction (MD).

[0049] Elmendorf Tear: Elmendorf tear is a measure of the force required to tear a sheet in a certain direction. It is calculated by dividing the tearing load by the web sample's basis weight. The tearing load measures the toughness of a material by measuring the work required to propagate a tear when part of a specimen is held in a clamp and an adjacent part is moved by the force of a pendulum freely falling in an arc. The Elmendorf Tear of the webs which determines the average force required to propagate a tear starting from a cut slit in the material is measured as follows (with higher numbers indicating the greater force required to tear the sample): The Elmendorf-type falling-pendulum instrument is equipped with a pendulum that has a deep cutout (recessed area) on the pendulum sector and pneumatically-activated clamps. Such testers may be sold under the trade designation LORENTZEN AND WETTRE BRAND, Model 09ED by Lorentzen Wettre Canada Inc. of Fairfield, N.J.

[0050] In addition to the testers, a specimen cutter is used that is capable of providing a 63.0.+−.0.15 mm (2.5.+−.0.006 inches) by 73.+−.0.1 mm specimen being cut no closer than 15 mm from the edge of the material, without folds, creases or other distortions. The 63 mm length of the specimen is run vertically on the tear tester. The rotary dial of the tester is set to the number of specimen plies to be torn and then the cutting lever is activated. The specimen is placed between the clamps with the specimen edge aligned with the clamp front edge. The clamps are then closed and a slit is cut in the specimen by activating the cutting knife lever. The pendulum is then released and positioned to the starting position after traveling one full swing. The tear value is then recorded unless the tear line deviated more than 10 mm, in which case a new test would be conducted. The results are recorded in grams. The Tear CD is the tearing force required to tear in the direction perpendicular to the machine direction; the Tear MD is the tearing force required to tear in the direction perpendicular to the cross-machine direction.

[0051] Trap Tear test: The trapezoid or “trap” tear test is a tension test applicable to both woven and nonwoven fabrics. The entire width of the specimen is gripped between clamps, thus the test primarily measures the bonding or interlocking and strength of individual fibers directly in the tensile load, rather than the strength of the composite structure of the fabric as a whole. The procedure is useful in estimating the relative ease of tearing of a fabric. It is particularly useful in the determination of any appreciable difference in strength between the machine and cross direction of the fabric.

[0052] In conducting the trap tear test, an outline of a trapezoid is drawn on a 3 by 6 inch (75 by 152 mm) specimen with the longer dimension in the direction being tested, and the specimen is cut in the shape of the trapezoid. The trapezoid has a 4 inch (102 mm) side and a 1 inch (25 mm) side which are parallel and which are separated by 3 inches (76 mm). A small preliminary cut of {fraction (5/8)} inches (15 mm) is made in the middle of the shorter of the parallel sides. The specimen is clamped in, for example, an Instron Model TM, available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Philadelphia, Pa. 19154, which have 3 inch (76 mm) long parallel clamps. The specimen is clamped along the non-parallel sides of the trapezoid so that the fabric on the longer side is loose and the fabric along the shorter side taut, and with the cut halfway between the clamps. A continuous load is applied on the specimen such that the tear propagates across the specimen width. It should be noted that the longer direction is the direction being tested even though the tear is perpendicular to the length of the specimen. The force required to completely tear the specimen is recorded in pounds with higher numbers indicating a greater resistance to tearing. The test method used conforms to ASTM Standard test D1117-14 except that the tearing load is calculated as the average of the first and highest peaks recorded rather than the lowest and highest peaks. Five specimens for each sample should be tested.

[0053] Hydrohead: A measure of the liquid barrier properties of a fabric is the hydrohead test. The hydrohead test determines the height of water or amount of water pressure (in millibars) that the fabric will support before liquid passes therethrough. A fabric with a higher hydrohead reading indicates it has a greater barrier to liquid penetration than a fabric with a lower hydrohead. The hydrohead can be performed according to Federal Test Standard 191A, Method 5514.

[0054] Cup Crush: The softness of a nonwoven fabric may be measured according to the “cup crush” test. A lower cup crush value indicates a softer material. The cup crush test evaluates fabric stiffness by measuring the peak load (also called the “cup crush load” or just “cup crush”) required for a 4.5 cm diameter hemispherically shaped foot to crush a 23 cm by 23 cm piece of fabric shaped into an approximately 6.5 cm diameter by 6.5 cm tall inverted cup while the cup shaped fabric is surrounded by an approximately 6.5 cm diameter cylinder to maintain a uniform deformation of the cup shaped fabric. An average of 10 readings is used. The foot and the cup are aligned to avoid contact between the cup walls and the foot which could affect the peak load. The peak load is measured while the foot is descending at a rate of about 0.25 inches per second (38 cm per minute) and is measure in grams. The cup crush test also yields a value for the total energy required to crush a sample (“the cup crush energy”) which is the energy from the start of the test to the peak load point, i.e. the area under the curve formed by the load in grams on one axis and the distance the foot travels in millimeters on the other. Cup crush energy is therefore reported in gm-mm. Lower cup crush values indicate a softer laminate. A suitable device for measuring cup crush is a model FTD-G-500 load cell (500 gram range) available from the Schaevitz Company, Pennsauken, N.J. Cup crush is measured in grams.

[0055] In this example, spunbond webs were made according to a process similar to the one shown in FIG. 2. In order to bond the filaments together, the spunbond web was contacted with heated thermal point bonded rollers. In this example, a through-air bonder was not used.

[0056] According to the present invention, spunbond continuous filaments were produced and formed into the non-woven spunbond webs. The filaments included a sheath polymer made from 50% by weight Exxon 3155 polypropylene polymer and 50% by weight Dow Chemical 6D43 polypropylene polymer. Exxon 3155 polypropylene polymer has a melt flow rate of from 33 g/10 minutes to 39 g/10 minutes. Dow Chemical 6D43 polypropylene polymer is a random copolymer containing ethylene in an amount of 3.2% by weight. Dow Chemical 6D43 polypropylene polymer has a target melt flow rate of 35 g/10 minutes at 230° C. By combining Exxon 3155 polypropylene polymer with Dow Chemical 6D43 random copolymer, the ethylene content of the resulting blend was reduced to below 2%.

[0057] The core polymer was made exclusively from Exxon 3155 polypropylene polymer. The spunbond webs had a basis weight of 0.75 osy.

[0058] For purposes of comparison, spunbond webs were also formed in which the sheath polymer and the core polymer were made from Exxon 3155 polypropylene polymer. Once the webs were formed, they were tested and the following results were obtained:

TABLE 1
Sample Bond Temp MD Strip
No Sheath Sheath % Core Core % (° F.) Denier (lbs)
Control 3155 50% 3155 50% 305 2 10.56
Control 3155 50% 3155 50% 290 2 9.26
Sample 6D43-3155 50% Blend 50% 3155 50% 290 2 10.95
Sample 6D43-3155 50% Blend 50% 3155 50% 300 2 12.43
MD Energy CD Strip CD Energy Elmendorf
Sample No. (in-lbs) (lbs) (in-lbs) Tear (cN)
Control 1 9.587 7.198 7.38 253.9
Control 2 6.13 6.83 6.27 221.3
Sample 1 9.4 7.2 8.488 292.3
Sample 2 15.18 8.24 11.91 344.3

[0059] Spunbond webs made as described above were then combined with a meltblown web to form a spunbond-meltblown-spunbond laminate. The meltblown web had a basis weight of 0.4 osy. Consequently, the resulting laminate had a basis weight of 1.9 osy. The laminates were tested for various properties and the following results were obtained:

TABLE 2
Sample Core Bond Temp MD Strip MD Energy MD Trap
No. Sheath Sheath % Core % Meltblown (° F.) Denier (lbs) (in-lbs) Tear (lbs)
Control 3 3155 50% 3155 50% 0.4 osy 290 2 35.4 24.8 10.4
Control 4 3155 50% 3155 50% 0.4 osy 300 2 42.7 38.1 11.0
Control 5 3155 50% 3155 50% 0.4 osy 310 2 46.1 42.0 12.7
Sample 3 6D43-3155 50% Blend 50% 3155 50% 0.4 osy 280 2 35.4 27.2 11.9
Sample 4 6D43-3155 50% Blend 50% 3155 50% 0.4 osy 290 2 4.7 48.6 13.6
Sample 5 6D43-3155 50% Blend 50% 3155 50% 0.4 osy 300 2 51.6 60.3 13.2
Sample CD Strip CD Energy CD Trap Tear Hydrohead Cup Crush
No. (lbs) (in-lbs) (lbs) (cm) (gm)
Control 3 22.1 20.0 8.2 74.5 368.0
Control 4 24.6 25.0 8.5 75.0 377.48
Control 5 29.1 33.5 9.1 74.8 423.5
Sample 3 22.2 21.8 9.7 82.5 316.78
Sample 4 27.9 37.2 10.0 75.8 371.9
Sample 5 31.4 46.2 10.5 87.8 420.4

[0060] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further in such appended claims.

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Referenced by
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Classifications
U.S. Classification442/361, 442/364
International ClassificationD04H3/14, D04H3/16, D01F8/06
Cooperative ClassificationY10T442/641, D01F8/06, Y10T442/637, D04H3/16, D04H3/14
European ClassificationD01F8/06, D04H3/14, D04H3/16
Legal Events
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Dec 2, 2002ASAssignment
Owner name: KIMBERLY-CLARK WORLDWIDE, INC., WISCONSIN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FORBES, BRIAN;MAJORS, MARK;SAYOVITZ, JOHN;REEL/FRAME:013540/0686
Effective date: 20021105