Nonwoven fabric and method of producing same

Abstract

A nonwoven fabric-like material having a unique combination of strength, absorbency and hand consists essentially of an air-formed matrix of thermoplastic polymer microfibers having an average fiber diameter of less than about 10 microns, and a multiplicity of individualized wood pulp fibers disposed throughout the matrix of microfibers and engaging at least some of the microfibers to space the microfibers apart from each other. The wood pulp fibers are interconnected by and held captive within the matrix of microfibers by mechanical entanglement of the microfibers with the wood pulp fibers, the mechanical entanglement and interconnection of the microfibers and wood pulp fibers alone forming a coherent integrated fibrous structure. The coherent integrated fibrous structure may be formed by the microfibers and wood pulp fibers without any adhesive, molecular or hydrogen bonds between the two different types of fibers. The wood pulp fibers are preferably distributed uniformly throughout the matrix of microfibers to provide a homogeneous material. The material is formed by initially forming a primary air stream containing the melt blown microfibers, forming a secondary air stream containing the wood pulp fibers, merging the primary and secondary streams under turbulent conditions to form an integrated air stream containing a thorough mixture of the microfibers and wood pulp fibers, and then directing the integrated air stream onto a forming surface to air form the fabric-like material. The microfibers are in a soft nascent condition at an elevated temperature when they are turbulently mixed with the wood pulp fibers in air.

Description

Claims

1. A nonwoven gas-formed fabric-like material having a unique combination of strength, absorbency and hand, said material consisting essentially of a gas-formed matrix of thermoplastic polymeric melt-blown microfibers having an average fiber diameter of less than about 10 microns, and a multiplicity of individualized and gas-formed wood pulp fibers disposed throughout said matrix of microfibers and engaging at least some of said microfibers to space the microfibers apart from each other, said wood pulp fibers being interconnected by and held captive within said matrix of microfibers by mechanical entanglement of said microfibers with said wood pulp fibers, the mechanical enganglement and interconnection of said microfibers and wood pulp fibers alone forming a coherent integrated fibrous structure.

2. A nonwoven fabric-like material as set forth in claim 1 wherein said polymeric microfibers and wood pulp fibers have been mixed under turbulent conditions in air with said microfibers in a soft nascent condition at an elevated temperature.

3. A nonwoven fabric-like material as set forth in claim 1 wherein said microfibers and wood pulp fibers form a coherent integrated fibrous structure without any adhesive, molecular or hydrogen bonds between said microfibers and said wood pulp fibers.

4. A nonwoven fabric-like material as set forth in claim 1 wherein said wood pulp fibers are distributed uniformly throughout said matrix of microfibers to provide a homogeneous material.

5. A nonwoven fabric-like material as set forth in claim 1 wherein said wood pulp fibers have a length within the range of from about 0.5 mm. to about 10 mm., and the ratio of the length of the largest transverse dimension of said wood pulp fibers is within the range of from about 10:1 to about 400:1.

6. A nonwoven fabric-like material as set forth in claim 1 wherein said microfibers have an average fiber diameter greater than about 1 micron.

7. A nonwoven fabric-like material as set forth in claim 1 wherein said polymeric microfiber comprises from about 1% to about 80% by weight of the material.

8. A nonwoven fabric-like material as set forth in claim 1 wherein the recovered specific volume of said material is at least 75% of the initial specific volume.

9. A nonwoven fabric-like material as set forth in claim 1 in which said polymeric microfiber comprises less than about 25% by weight of said material.

10. A nonwoven fabric-like material as set forth in claim 1 wherein said polymeric microfiber comprises at least 5% by weight of said material, and the lint count of said material is less than 600 minus 5.5 times the percentage by weight of said microfiber in said material.

11. A nonwoven fabric-like material as set forth in claim 1 wherein said wood pulp fiber comprises at least 40% by weight of said material, and the recovered specific volume of said material is at least 25.

12. A nonwoven fabric-like material as set forth in claim 1 wherein said polymeric microfiber comprises at least about 30% by weight of said material, and the absorbency of said material is greater than 30 minus 0.25 times the percentage by weight of said microfiber in said material.

13. A nonwoven fabric-like material as set forth in claim 1 wherein said wood pulp fiber comprises at least about 90% by weight of said material, and the breaking length of said material is at least 5 meters.

14. A nonwoven fabric-like material as set forth in claim 1 wherein said material has an initial specific volume of at least 25, a recovered specific volume which is at least 75% of the initial specific volume, a lint count of less than 600 minus 5.5 times the percentage by weight of said microfibers in said material, an absorbency greater than 30 minus 0.25 times the percentage by weight of said microfibers, and a breaking length of at least 5 meters.

15. A method of forming a nonwoven fabric-like material having a unique combination of strength, absorbency and hand, said method comprising the steps of:

(a) forming a primary air stream containing meltblown microfibers comprising generally discontinuous thermoplastic polymeric microfibers, said primary air stream having a temperature in the range of from about 600.degree. F. to about 700.degree. F.,

(b) forming a secondary air stream containing individualized wood pulp fibers,

(c) merging said secondary stream with said primary stream under turbulent conditiions to form an integrated air stream containing a thorough mixture of said microfibers and said wood pulp fibers,

(d) and directing said integrated air stream onto a forming surface to air-form a matrix of said microfibers in which at least some of said microfibers are engaged by said individualized wood pulp fibers to space the microfibers apart from each other, and said individualized wood pulp fibers are disposed throughout said matrix of microfibers and interconnected by and held captive within said matrix by mechanical entanglement of said microfibers with said wood pulp fibers, the mechanical entanglement and interconnection of said microfibers and wood pulp fibers alone forming a coherent integrated fibrous structure.

16. A method as set forth in claim 15 wherein said microfibers are formed by attenuating polymeric filaments extruded from at least one straight row of extrusion apertures.

17. A method as set forth in claim 15 wherein said polymeric microfibers are in a soft nascent condition at an elevated temperature when said primary stream is merged with said secondary stream.

18. A method as set forth in claim 15 wherein said microfibers and wood pulp fibers form a coherent integrated fibrous structure without any adhesive, molecular or hydrogen bonds between said microfibers and said wood pulp fibers.

19. A method as set forth in claim 15 wherein said wood pulp fibers are distributed uniformly throughout said microfibers to provide a homogeneous material.

20. A method as set forth in claim 15 wherein said wood pulp fibers have a length within the range of from about 0.5 mm. to about 10 mm., and the ratio of the length to the largest transverse dimension of said wood pulp fibers is within the range of from about 10:1 to about 400:1.

21. A method as set forth in claim 15 wherein said microfibers have an average fiber diameter greater than about 1 micron.

22. A method as set forth in claim 15 wherein said polymeric microfiber comprises from about 1% to about 80% by weight of the fiber mixture.

23. A method as set forth in claim 15 in which said polymeric microfiber comprises less than about 25% by weight of said fiber mixture.