Method of making a polypropylene fabric having high strain rate elongation and method of using the same

• US 20040038022A1
• Filed: 09/27/2002
• Published: 02/26/2004
• Est. Priority Date: 03/27/2000
• Status: Abandoned Application

• Current Assignee: John Kaarto, Kalyan Sehanobish, Kenneth E. Springs, Michael E. Rowland, Ray A. Herring, Rexford A. Maugans, Thoi H. Ho
• Original Assignee: John Kaarto, Kalyan Sehanobish, Kenneth E. Springs, Michael E. Rowland, Ray A. Herring, Rexford A. Maugans, Thoi H. Ho
• Inventors: Sehanobish, Kalyan, Kaarto, John, Herring, Ray A., Springs, Kenneth E., Maugans, Rexford A., Ho, Thoi H., Rowland, Michael E.
• Application Number:
  US10/240,291
• Publication Number:
  US 20040038022A1
• Time in Patent Office: Days
• US Class Current: 428/328
• CPC Class Codes: B32B 2038/0028 Stretching, elongating
• CPC Class Codes: B32B 2262/0253 Polyolefin fibres
• CPC Class Codes: B32B 27/12 next to a fibrous or filamentary layer
• CPC Class Codes: B32B 5/04 characterised by a layer being specifically extensible by reason of its structure or arrangement , e.g. by reason of the chemical nature of the fibres or filaments
• CPC Class Codes: D01F 6/46 of polyolefins
• CPC Class Codes: Y10T 428/256 Heavy metal or aluminum or compound thereof
• CPC Class Codes: Y10T 428/2967 Synthetic resin or polymer
• CPC Class Codes: Y10T 428/31 Surface property or characteristic of web, sheet or block

Abstract

This invention relates to a method of making a film-fabric composite (includinng a film-fabric laminate) wherein the fabric is characterized as having improved tensile elongation (without rupture). In particular, the invention pertains to a method of making a film-fabric laminate having structual elastic-like behavior wherein the fabric is a nonwoven thermally bonded fabric characterized as having improved high strain rate tensile elongation and comprises a plurality of fibers comprised of at least one polypropylene polymer and at least one ethylene polymer, wherein the method comprises stretching the laminate at a high strain rate. The improved farbic is characterized by higher high strain rate tensile properties and a broader bond window which is also shifted to substantially lower temperatures with regard to maximum tensile properties. The improved fabric enables higher stretching levels or speeds on stretching apparati often employed to impart elasticity or elastic-like behavior to inelastic ploymeric materials. Polypropylene copolymers as well as polypropylene homopolymers may be used in the invention which is sueful for durable and disposable articles such as diapers, bandages, pantiliners, continence pads, and sanitary napkins.

Claims

1. A method of making a non-woven fabric comprising providing a fabric comprising a plurality of fibers which comprise at least one polypropylene polymer and at least one ethylene polymer;

bonding the fabric at a bond temperature of from 15 to 20°

F. lower than an optimum bond temperature of a comparative fabric, measured at a strain rate of 6% per second, to form an improved high strain rate fabric, wherein the comparative fabric comprises fibers of the polypropylene polymer without the ethylene polymer, and wherein the fabric tensile elongation is at least 20 percent greater than the comparative fabric at strain rates in the range from 10,000 to 11,000% per second.

3. The method of claim 1 wherein the improved non-woven fabric has a Cross Direction percent elongation at a bond temperature of 270°

F. and 20 gsm basis weight of at least 35 at a strain rate greater than or equal to 100%/second.

4. The method of claim 1 wherein the improved non-woven fabric has a Cross Direction percent elongation at a bond temperature of 270°

F. and 20 gsm basis weight of at least 35 at a strain rate greater than or equal to 500%/second.

5. The method of claim 1 wherein the improved non-woven fabric has a Cross Direction percent elongation at a bond temperature of 270°

F. and a basis weight of 20 gsm of at least 35 at a strain rate greater than or equal to 1000%/second.

6. The method of claim 1 wherein the improved non-woven fabric has a Cross Direction percent elongation at a bond temperature of 270°

F. and 20 gsm basis weight of at least 35 at a strain rate greater than or equal to 5,000%/second.

7. The method of claim 1 wherein the improved non-woven fabric has a Cross Direction percent elongation at a bond temperature of 270°

F. and 20 gsm basis weight of at least 35 at a strain rate greater than or equal to 10,000%/second.

8. The method of claim 1 wherein the improved non-woven fabric, thermally bonded at a surface temperature 20°

F. lower than the optimum bond temperature (which is that temperature that provides the maximum high strain rate fabric elongation) for a comparative fabric, is characterized as having a Cross-Direction percent fabric elongation, measured at 10,500%/second, of at least 30 percent higher than the comparative fabric, wherein the comparative fabric is made without the ethylene polymer and with the same polypropylene polymer at the same basis weight as the improved fabric (that is, the comparative fabric is essentially the same as the improved fabric, except for the addition of the at least one ethylene polymer).

9. The method of claim 1 wherein the improved non-woven fabric, thermally bonded at a surface temperature 20°

F. lower than the optimum bond temperature for a comparative fabric, is characterized as having a Cross-Direction percent fabric elongation, measured at 10,500%/second, of at least 50 percent higher than the comparative fabric, wherein the comparative fabric is made without the ethylene polymer and with the same polypropylene polymer at the same basis weight as the improved fabric.

10. The method of claim 1 wherein the improved non-woven fabric has a Cross Direction percent fabric elongation of at least 35, when bonded and at a basis weight of at least 18 gsm and measured at a strain rate in the range of from 10,000 to 11,000%/second.

11. The method of claim 1 wherein the polypropylene polymer is an in situ blend modified polypropylene polymer.

12. The method of claim 1 wherein the polypropylene polymer has a melt flow rate of greater than or equal to 25 g/10 minutes, as measured in accordance with ASTM D1238 Condition 230°

C./2.16 kg.

13. The method of claim 1 wherein the ethylene polymer is a homogeneously branched ethylene polymer (that is, has a SCBDI of greater than 50 percent).

14. The method of claim 13 wherein the homogeneously branched ethylene polymer is a substantially linear ethylene/α

-olefin interpolymer characterized having

i. a melt flow ratio, I₁₀/I₂≧

5.63,

ii. a molecular weight distribution, M_w/M_n, defined by the equation;

M_w/M_n≦

(I₁₀/I₂)−

4.63, and

iii. a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear ethylene polymer having about the same I₂ and M_w/M_n.

15. The method of claim 13 wherein the homogeneously branched ethylene polymer is a homogeneously branched linear ethylene polymer (that is, characterized as having less than 0.01 long chain branch per 1000 carbons as well as short chain branching distribution index (SCBDI) of greater than 50 percent).

16. The method of claim 15 wherein the homogeneously branched linear ethylene polymer is further characterized as having a single differential scanning calorimetry (DSC) melt point between −

30° and

150°

C.

17. The method of claim 1, wherein fibers comprise from 0.5 to 22 weight percent of the ethylene polymer.

18. The method of claim 1, wherein the ethylene polymer is an interpolymer of ethylene and at least one C₃-C₂₀ α

-olefin.

19. The method of claim 1, wherein the ethylene polymer has a density of from 0.855 to 0.880 gram/centimeters³.

20. The method of claim 1, wherein the ethylene polymer has a melt index of from 0.01 to 10 gram/10 minutes.

21. The method of claim 1, wherein the ethylene polymer has a melt index less than 5 gram/10 minutes.

22. The method of claim 1, wherein the polypropylene polymer is a visbroken polypropylene and has a melt flow rate at 230°

C./2.16 kg of greater than or equal 20 g/10 minutes.

23. The method of claim 1, wherein the polypropylene polymer has a coupled melt flow rate at 230°

C./2.16 kg of greater than or equal 20 g/10 minutes.

24. The method of claim 23, where the polypropylene polymer is coupled using an azide.

25. The method of claim 1, wherein the polypropylene polymer is manufactured using at least one single-site, metallocene or constrained geometry catalyst system.

26. The method of claim 23, wherein the polypropylene polymer before being coupled is manufactured using a single-site, metallocene or constrained geometry catalyst system.

27. The method of claim 25, wherein the polypropylene polymer is manufactured using at least one constrained geometry catalyst system.

28. The method of claim 26, wherein the polypropylene polymer before coupling is manufactured using at least one constrained geometry catalyst system.

29. The method of claim 1, wherein the polypropylene polymer is characterized as having at least 96 percent weight isotacticity.

30. The method of claim 1, wherein the fibers are prepared by a melt spinning process such that the fibers are melt blown fibers, spunbonded fibers, carded staple fibers or flash spun fibers.

31. The method of claim 20 wherein the ethylene polymer is blended with the polypropylene polymer at greater than or equal to 3 weight percent, based on the total weight of the ethylene polymer and the polypropylene polymer.

32. The method of claim 22 wherein the ethylene polymer is blended with the polypropylene polymer at greater than or equal to 3 weight percent, based on the total weight of the ethylene polymer and the polypropylene polymer.

33. The method of claim 31 wherein the density of the ethylene polymer is less than or equal to 0.89 g/cc.

34. The method of claim 1 wherein the polypropylene polymer is a random copolymer containing 0.1 to 10 weight percent ethylene.

35. The method of claim 1 wherein the polypropylene polymer is a polypropylene homopolymer.

37. The non-woven fabric obtainable by the method of claim 1.

39. The method of claim 11 wherein the polypropylene polymer is a random copolymer containing 0.1 to 10 weight percent ethylene.

40. The method of claim 11 wherein the polypropylene polymer is a polypropylene homopolymer.

36. A method of making a film-fabric laminate comprising bonding the film and fabric to form a laminate and stretching the laminate at a strain rate in the range from 10,000 to 11,000% per second, wherein the fabric is a nonwoven thermally bonded fabric comprising a plurality of fibers comprised of a melt blend of at least one polypropylene polymer and at least one ethylene polymer, wherein the fabric has a tensile elongation of at least 20 percent greater than the comparative fabric, wherein the comparative fabric comprises fibers of the polypropylene polymer without the ethylene polymer, wherein the film is elongatable and the method.

38. The film-fabric laminate obtainable by the method of claim 36.