Title:
Non-destructive treatment process with uniform coverage
Kind Code:
A1


Abstract:
A non-destructive method of treating a nonwoven web resulting in uniform coverage throughout the web. The method includes saturating the nonwoven web in a treatment bath including at least one surfactant in an aqueous solution at a concentration between about 0.2% and about 8%, using one or more vacuums to extract excess bath from the nonwoven web, and using a dryer to evaporate water from the web. Add-on level of the treatment can be controlled through the vacuum air velocity, treatment concentration, and line speed. The invention further includes apparatus for carrying out the non-destructive treatment method.



Inventors:
Polanco, Braulio Arturo (Canton, GA, US)
Fenwick, Christopher Dale (Alpharetta, GA, US)
Application Number:
10/328101
Publication Date:
06/24/2004
Filing Date:
12/23/2002
Assignee:
POLANCO BRAULIO ARTURO
FENWICK CHRISTOPHER DALE
Primary Class:
International Classes:
A61F13/15; D04H13/00; D06B15/04; D06B23/24; (IPC1-7): D06M10/00
View Patent Images:



Primary Examiner:
KUMAR, PREETI
Attorney, Agent or Firm:
PAULEY ERICKSON & SWANSON (HOFFMAN ESTATES, IL, US)
Claims:

What is claimed is:



1. A method of treating a nonwoven web, comprising: saturating the nonwoven web in a treatment bath having a concentration between about 0.2% and about 8%; using at least one vacuum to extract excess bath from the nonwoven web; and using a dryer to evaporate water from the nonwoven web.

2. The method of claim 1, wherein the treatment bath comprises at least one surfactant in an aqueous solution.

3. The method of claim 2, wherein the treatment bath further comprises a dye.

4. The method of claim 2, wherein the treatment bath comprises between about 0.2% and about 8% of the at least one surfactant in the aqueous solution.

5. The method of claim 2, wherein the treatment bath comprises between about 0.5% and about 4% of the at least one surfactant in the aqueous solution.

6. The method of claim 1, further comprising transporting the nonwoven web from the treatment bath to the at least one vacuum at a line speed up to 2000 feet per minute.

7. The method of claim 1, further comprising transporting the nonwoven web from the treatment bath to the at least one vacuum at a line speed between about 50 and about 200 feet per minute.

8. The method of claim 1, further comprising using the at least one vacuum to control the percent add-on level to between about 0.5% and about 4% weight by solids.

9. The method of claim 1, wherein the at least one vacuum has an air velocity between about 100 and about 3000 feet per minute.

10. The method of claim 1, comprising using a plurality of vacuums to extract excess bath from the nonwoven web.

11. The method of claim 1, further comprising pulsing the at least one vacuum to create zone treatment.

12. The method of claim 11, wherein the zone treatment is in one of a cross direction, a machine direction, and a combination thereof.

13. The method of claim 1, wherein the dryer is set at a temperature between about 200 and about 250 degrees Fahrenheit.

14. The method of claim 1, further comprising winding the nonwoven web onto a spool.

15. The method of claim 1, wherein the nonwoven web has between about 25% and about 300% wet pick-up of the treatment bath.

16. The method of claim 1, wherein the nonwoven web has a thickness of at least 0.08 inches.

17. The method of claim 1, wherein the nonwoven web has a thickness of between about 0.1 and about 1.5 inches.

18. The method of claim 1, wherein the nonwoven web has a basis weight between about 34 and about 500 grams per square meter.

19. The method of claim 1, wherein the nonwoven web has a density of less than about 0.08 grams per cubic centimeter.

20. The method of claim 1, wherein the nonwoven web has a density of less than about 0.06 grams per cubic centimeter.

21. The method of claim 1, wherein the nonwoven web has a density of less than about 0.04 grams per cubic centimeter.

22. A method of treating a hydrophobic nonwoven web, comprising: saturating the nonwoven web in a treatment bath including at least one surfactant in an aqueous solution at a concentration between about 0.2% and about 8%; using at least one vacuum to extract excess bath from the nonwoven web and to control percent add-on level of the treatment to between about 0.5% and about 4% weight by solids; using a dryer to evaporate water from the nonwoven web.

23. The method of claim 22, wherein the treatment bath comprises between about 0.5% and about 4% of the at least one surfactant in the aqueous solution.

24. The method of claim 22, wherein the treatment bath further comprises a dye.

25. The method of claim 22, further comprising transporting the nonwoven web from the treatment bath to the at least one vacuum at a line speed up to about 2000 feet per minute.

26. The method of claim 22, further comprising transporting the nonwoven web from the treatment bath to the at least one vacuum at a line speed between about 50 and about 200 feet per minute.

27. The method of claim 22, wherein the at least one vacuum has an air velocity between about 100 and about 3000 feet per minute.

28. The method of claim 22, comprising using a plurality of vacuums to extract excess bath from the nonwoven web.

29. The method of claim 22, further comprising pulsing the at least one vacuum to create zone treatment.

30. The method of claim 29, wherein the zone treatment is in one of a cross direction, a machine direction, and a combination thereof.

31. The method of claim 22, wherein the dryer is set at a temperature between about 200 and about 250 degrees Fahrenheit.

32. The method of claim 22, further comprising winding the nonwoven web onto a spool.

33. The method of claim 22, wherein the nonwoven web has between about 25% and about 300% wet pick-up of the treatment bath.

34. The method of claim 22, wherein the nonwoven web has a thickness of at least 0.08 inches.

35. The method of claim 22, wherein the nonwoven web has a thickness of between about 0.1 and about 1.5 inches.

36. The method of claim 22, wherein the nonwoven web has a basis weight between about 34 and about 500 grams per square meter.

37. The method of claim 22, wherein the nonwoven web has a density of less than about 0.08 grams per cubic centimeter.

38. The method of claim 22, wherein the nonwoven web has a density of less than about 0.06 grams per cubic centimeter.

39. The method of claim 22, wherein the nonwoven web has a density of less than about 0.04 grams per cubic centimeter.

40. Apparatus for treating a nonwoven web, comprising: a treatment bath having a concentration between about 0.2% and about 8%; at least one vacuum; a dryer; a device for transporting the nonwoven web from the treatment bath to the at least one vacuum to the dryer.

41. The apparatus of claim 40, wherein the treatment bath comprises at least one surfactant in an aqueous solution.

42. The apparatus of claim 41, wherein the treatment bath further comprises a dye.

43. The apparatus of claim 41, wherein the treatment bath comprises between about 0.2% and about 8% of the at least one surfactant in the aqueous solution.

44. The apparatus of claim 41, wherein the treatment bath comprises between about 0.5% and about 4% of the at least one surfactant in the aqueous solution.

45. The apparatus of claim 40, wherein the at least one vacuum has an air velocity between about 100 and about 3000 feet per minute.

46. The apparatus of claim 40, further comprising at least one rotary valve attached to the at least one vacuum.

47. The apparatus of claim 40, comprising a plurality of vacuums.

48. The apparatus of claim 40, wherein the dryer is set at a temperature between about 200 and about 250 degrees Fahrenheit.

49. The apparatus of claim 40, wherein the device for transporting the nonwoven web from the treatment bath to the at least one vacuum to the dryer has a line speed up to about 2000 feet per minute.

50. The apparatus of claim 40, wherein the device for transporting the nonwoven web from the treatment bath to the at least one vacuum to the dryer has a line speed between about 50 and about 200 feet per minute.

51. The apparatus of claim 40, further comprising a spool onto which the nonwoven web can be wound.

Description:

BACKGROUND OF THE INVENTION

[0001] This invention is directed to a method of treating nonwoven webs without destroying the fibers or the structure of the web while providing uniform coverage of the treatment throughout the web, and apparatus for carrying out the method.

[0002] Polymeric nonwoven materials are typically hydrophobic. Nonwoven materials are often used to make various components of a number of disposable absorbent products. Certain components, such as diaper surge management layers and absorbent wipes, require nonwoven fibers to be hydrophilic in order for the material to deliver its intended function. A number of topical treatment processes are available to make the surface of the fibers hydrophilic. Such processes include spraying, foaming, and/or solution bath. In each of these treatment processes, the chemicals used to treat the fibers work by lowering the contact angle of the polymer surface, thereby rendering the fibers hydrophilic.

[0003] One type of topical treatment process uses a WEKO Rotor Dampening System, available from Weko, Biel AG, Switzerland. The general WEKO configuration is a centrifugal dampening application system using a single or double rotocarrier. The surfactant formulation is pumped to the WEKO header through a gear pump where it is fed to the dampening rotors through restrictor tubes. Under the effect of a centrifugal force generated by the spinning rotors, the chemical is dispensed to the nonwoven fabric in the form of small droplets. However, the WEKO process, as well as other spraying processes, lacks the capability to uniformly treat nonwoven materials having high bulk and high basis weight and instead creates a gradient or laminar effect. Thus, the process results in inconsistent coverage. Furthermore, the process is typically quite messy.

[0004] Another type of topical treatment process is a foaming process. Even when applied to both sides of a substrate, the foaming process results in inconsistent coverage of high bulk and high basis weight materials because the treatment is not uniformly applied and does not penetrate into the web. Furthermore, the foaming process also requires the additional expense and hassle of a foaming agent.

[0005] Internal treatment of nonwoven fibers is also commonly used to treat nonwoven webs, wherein the treatment is injected directly into the extruder barrel of a fiber-forming process. While the process is clean and easy to carry out, the treatment itself tends to burn off during processing such that fibers are treated with only a fraction of a targeted add-on level making it difficult to determine the exact final treatment level. In addition, internal treatment can hinder the ability to process or spin the fibers.

[0006] Yet another type of topical treatment process is a dip and squeeze process. The dip and squeeze process saturates the web in a solution bath and uses nip rolls to squeeze the excess bath from the web. While this process produces uniform coverage and sufficient web penetration, when using high bulk materials the nips compress and shear the web causing a loss in bulk. Thus, the dip and squeeze process is a destructive treatment process that changes the material properties, such as bulk, density, bonding, and permeability. These changes have been shown to negatively affect product performance in, for example, applications such as diaper surge management layers. Furthermore, the dip and squeeze method is limited to low bath concentrations because the nip cannot remove the bath efficiently. In addition to being destructive, the add-on level of treatment cannot be controlled in this method without affecting the material's thickness.

[0007] There is a need or desire for a method of treating nonwoven webs, particularly high bulk and high basis weight webs, that provides uniform coverage and treatment penetration throughout the web and can be carried out without destroying the bulk of the web. There is also a need or desire for a non-destructive method of uniformly treating nonwoven webs in which the percent add-on level of the treatment can be controlled.

[0008] There is a further need or desire for an apparatus to uniformly treat nonwoven webs without destroying the bulk of the web, and having the ability to control the percent add-on level of the treatment.

SUMMARY OF THE INVENTION

[0009] In response to the discussed difficulties and problems encountered in the prior art, a non-destructive method of uniformly treating a nonwoven web, and apparatus for carrying out the method, has been discovered.

[0010] The method of the invention can be used to treat high bulk and high basis weight nonwoven materials with uniform coverage and treatment penetration throughout the web, without destroying the bulk of the web. The method includes saturating a nonwoven web in a treatment bath of known concentration, using one or more vacuums to extract excess bath, and using a dryer to evaporate water from the web. A target add-on level of the treatment can be achieved by balancing solution concentration, line speed, and vacuum air velocity. Suitably, the add-on level is between about 0.5% and about 4% weight by solids.

[0011] Unlike spraying and foaming applications, saturation in a treatment bath provides uniform treatment throughout the web. The treatment bath may include one or more surfactants in an aqueous solution. The concentration of the surfactant(s) in the aqueous solution is suitably between about 0.2% and about 8%, or between about 0.5% and about 4%, depending on the final add-on level desired. The treatment bath may also include a dye, such as a fluorescent brightener. To assure the desired add-on level, the weight of the treated sample could double the dry weight. In other words, the nonwoven web could have about 100% wet pick-up of the treatment bath. Alternatively, the nonwoven web could have between about 25% and about 300% wet pick-up, depending on the nonwoven density, fiber size, fiber cross-sectional shape, and desired treatment level.

[0012] The line speed at which the nonwoven web is transported from the treatment bath to the vacuum or vacuums, and to the dryer may be any of a wide range of line speeds. For example, the line speed may be between about 50 and about 200 feet per minute, or up to about 2000 feet per minute, or even faster. The vacuum or vacuums may have an air velocity between about 100 and about 3000 feet per minute. One or more vacuums may be used in the method. Rotary valves can be added to the vacuum or vacuums such that zone treatment may be created in the machine direction, cross direction, or a combination of both directions. The dryer may be set at a temperature between about 200 and about 250 degrees Fahrenheit. After drying the web, the web may be wound onto a spool for storage.

[0013] Unlike processes that use nip rolls to squeeze excess bath from the web, the use of a vacuum to extract the excess bath from the web has not shown any decrease in bulk. In fact, the bulk has actually increased in some cases as a result of undergoing the vacuum and subsequent heating and evaporation in a dryer. By using one or more vacuums in place of nip rolls, material can be passed through the excess bath removal area without undergoing any contact between two surfaces. This aids in reducing the compressive and shearing forces the web would face with nip rolls.

[0014] The method of the invention is particularly suitable for use with high loft, high basis weight nonwoven webs. Such webs suitably have a thickness of at least 0.08 inches, or between about 0.1 and about 1.5 inches, with a basis weight between about 34 and about 500 grams per square meter. The nonwoven web suitably has a density of less than about 0.08 grams per cubic centimeter (g/cc), or less than about 0.06 g/cc, or less than about 0.04 g/cc.

[0015] Apparatus for carrying out the method of the invention suitably includes the treatment bath having a concentration between about 0.2% and about 8%, one or more vacuums, a dryer, and a device for transporting the nonwoven web from the treatment bath to the vacuum(s) to the dryer.

[0016] With the foregoing in mind, particular embodiments of the invention provide a method and apparatus for uniformly treating nonwoven webs without destroying bulk.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is an illustration of an exemplary process for carrying out a dip and vacuum treatment according to one embodiment of the invention.

[0018] FIG. 2 is a photograph of a nonwoven web treated using the treatment process of the invention with a solution including a fluorescent dye, taken under black light.

[0019] FIGS. 3a &3b are photographs of a nonwoven web treated using a WEKO process with a solution including a fluorescent dye, taken under black light.

[0020] FIGS. 4a &4b are photographs of a nonwoven web treated using a foam process with a solution including a fluorescent dye, taken under black light.

[0021] FIG. 5 is a graph showing comparative FIFE test results of nonwoven webs treated with different treatment processes.

[0022] FIG. 6 is a graph showing comparative LISTER test results of nonwoven webs treated with different treatment processes.

DEFINITIONS

[0023] Within the context of this specification, each term or phrase below will include the following meaning or meanings.

[0024] “Hydrophilic” describes fibers or the surfaces of fibers that are wetted by the aqueous liquids in contact with the fibers. The degree of wetting of the materials can, in turn, be described in terms of the contact angles and the surface tensions of the liquids and materials involved. Equipment and techniques suitable for measuring the wettability of particular fiber materials or blends of fiber materials can be provided by a Cahn SFA-222 Surface Force Analyzer System, or a substantially equivalent system. When measured with this system, fibers having contact angles less than 90° are designated “wettable” or hydrophilic, while fibers having contact angles greater than 90° are designated “nonwettable” or hydrophobic.

[0025] “Machine direction” as applied to a film or web, refers to the direction on the film or web that was parallel to the direction of travel of the film or web as it left the extrusion or forming apparatus, or as it travels through a treatment process. If the film or web passed between nip rollers or chill rollers, for instance, the machine direction is the direction on the film or web that was parallel to the surface movement of the rollers when in contact with the film or web. “Cross direction” refers to the direction perpendicular to the machine direction. Dimensions measured in the cross direction are referred to as “width” dimensions, while dimensions measured in the machine direction are referred to as “length” dimensions.

[0026] “Meltblown fiber” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than about 0.6 denier, and are generally self bonding when deposited onto a collecting surface. Meltblown fibers used in the present invention are preferably substantially continuous in length. “Nonwoven” or “nonwoven web” refers to materials and webs of material having a structure of individual fibers or filaments which are interlaid, but not in an identifiable manner as in a knitted fabric. The terms “fiber” and “filament” are used interchangeably. Nonwoven fabrics or webs have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, air laying processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91.)

[0027] “Polymers” include, but are not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.

[0028] “Spunbond fiber” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated herein in its entirety by reference. Spunbond fibers are quenched and generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and often have average deniers larger than about 0.3, more particularly, between about 0.6 and 10.

[0029] “Wet pick-up” refers to the amount of a liquid absorbed by a substrate. In particular, the wet pick-up is the amount of liquid absorbed in relation to the dry weight of the substrate.

[0030] These terms may be defined with additional language in the remaining portions of the specification.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] The present invention is directed to a method that can be used to treat nonwoven materials, including high bulk and high basis weight nonwoven materials, with uniform coverage and treatment penetration throughout the web, without destroying the bulk or the structure of the web. A target add-on level of the treatment, suitably between about 0.5% and about 4% weight by solids, can be achieved by balancing solution concentration, line speed, and vacuum air velocity.

[0032] The method of the invention can be carried out using the apparatus shown in FIG. 1. More particularly, a nonwoven web 20 can be fed from an unwinder 22 into a treatment bath 24 having a controlled concentration. The web 20 is not fed through any nip rolls or any other type of pinch point but instead is submerged in the bath 24 and follows an unobstructed path below a rotor or bar 26 fixed within a container 28 that holds the treatment bath 24. By dipping the web 20 in this manner, the web becomes fully saturated to provide uniform treatment and penetration throughout the web.

[0033] The concentration of the treatment bath 24 is an important factor in controlling the add-on level of the treatment. To add hydrophilicity to a hydrophobic nonwoven web, the treatment bath suitably includes one or more surfactants. One example of a commercially available surfactant is MASIL SF-19 silicone surfactant, available from BASF Corporation. Another example of a commercially available surfactant is AHCOVEL Base N-62, available from Uniqema Inc., a division of ICI of New Castle, Del. The treatment bath may also include a dye, such as LEUCOPHOR B-302 fluorescent brightener dye, available from Clariant of Muttenz, Switzerland, or other non-reactive additive. The concentration of the surfactant(s) is suitably between about 0.2% and about 8%, or between about 0.5% and about 4%, in an aqueous solution, depending on the final add-on level desired.

[0034] The add-on level can be determined by subtracting the dry weight of the untreated nonwoven web from the dry weight of the same nonwoven web after being treated, then dividing the difference by the dry weight of the untreated nonwoven web. To achieve the target add-on level, the wet weight of the treated sample should be about double the dry weight. In other words, the nonwoven web should have about 100% wet pick-up of the treatment bath, or between about 25% and about 300%, or between about 25% and about 200%, wet pick-up, depending on the nonwoven density, fiber size, and shape. By having a wet pick-up of about 100%, the add-on level is roughly equal to the concentration of the treatment bath. Alternatively, with a higher concentration solution, for example double, then 50% pick-up would result in the same add-on level as the 100% pickup. Less wet pick-up provides less water to drive off and therefore more efficient drying.

[0035] The saturated nonwoven web 20 is fed from the treatment bath 24 to a vacuum extraction device 30 that includes one or more vacuums 32. Each vacuum 32 extracts excess bath from the web 20. The air velocity of the vacuum 32 is another important factor in controlling the add-on level of the treatment. Air velocity depends on the vacuum slot dimensions, or surface area of the vacuum slot(s), as well as the volume of air or air pressure pulled through the vacuum slot(s). More particularly, air velocity of each vacuum is suitably between about 100 and about 3000 feet per minute (fpm), or between about 1200 and about 2000 fpm, for a 50 gsm fabric.

[0036] Unlike processes that use nip rolls to squeeze excess bath from the web, the use of a vacuum 32 to extract the excess bath from the web has not shown any decrease in bulk. In fact, the bulk has actually increased by about 10% in some cases as a result of undergoing the vacuum and subsequently being run through a dryer. By using one or more vacuums 32 in place of nip rolls, material can be passed through the excess bath removal area without undergoing any contact between two surfaces. This in turn prevents or reduces compression and shearing forces on the web. Furthermore, methods involving nip rolls are typically limited to low bath concentrations. In contrast, higher bath concentrations can be used in the present invention because vacuums can more effectively extract excess bath compared to nip rolls without damaging the web.

[0037] The vacuum extraction device 30 may also include one or more rotary valves 34 attached to, or within a vacuum line of, one or more vacuums 32. In general, a rotary valve is a flat circular plate having intermittent holes such that when the rotary valve spins the vacuum duct is intermittently occluded and opened. Suitable rotary valves are taught, for example, in U.S. Pat. No. 5,913,329 issued Jun. 22, 1999 to Haynes et al. The rotary valves 34 could be pulsed to perturb the vacuum signal such that the vacuum strength goes up and down, thereby creating zone treatment on the nonwoven web 20 such that areas of low and high treatment levels are produced. More particularly, by pulsing the rotary valves 34, more or less treatment liquid is retained in the web 20 when the vacuum has less or more strength, respectively. Thus, the web 20 could have areas of low and high treatment levels in cross directional zones, or machine directional zones, or a combination of cross directional and machine directional zones. Arrow 36 indicates the machine direction of the process.

[0038] The nonwoven web 20 is then fed from the vacuum extraction device 30 to a dryer 38 to evaporate any remaining water from the nonwoven web. The dryer 38 is suitably set at a temperature between about 200 and about 250 degrees Fahrenheit.

[0039] A winder 40 pulls the nonwoven web 20 from the dryer 38 and, if desired, guides the dried web onto a spool or roll 42 for storage. The unwinder 22 and the winder 40 control the movement of the nonwoven web 20 from the treatment bath 24 to the vacuum or vacuums 32 and to the dryer 38, suitably at a line speed of between about 50 and about 200 feet per minute, or up to about 2000 feet per minute, or even faster. The line speed is another important factor in controlling the add-on level of the treatment. In fact, a direct relationship exists between the line speed and the vacuum level applied to the web. More specifically, if the line speed is increased, the vacuum level applied to the web will be increased, and if the line speed is reduced, the vacuum level applied to the web will be reduced in order to maintain the same add-on level. Thus, by balancing solution concentration, line speed, and vacuum air velocity, a target add-on level of the treatment can be achieved.

[0040] Conventional drive means and other conventional devices which may be utilized in conjunction with the apparatus of FIG. 1 are well known and, for purposes of clarity, have not been illustrated in FIG. 1.

[0041] The method of the invention is particularly suitable for treating nonwoven materials having high bulk and high basis weight. More specifically, the method may be used to treat nonwoven webs having a thickness of at least 0.08 inches, or between about 0.1 and about 1.5 inches, with a basis weight between about 34 and about 500 grams per square meter. Nonwoven webs treated in accordance with the method of the invention may be high-loft, open materials having a density of less than about 0.08 grams per cubic centimeter (g/cc), or less than about 0.06 g/cc, or less than about 0.04 g/cc.

[0042] Nonwoven webs used in the method of the invention may be made of filament-forming polymers such as, for example, polyolefins, polyesters, polyamides, polycarbonates, polyurethanes, polyvinylchloride, polytetrafluoroethylene, polystyrene, polyethylene terephthalate, biodegradable polymers such as polylactic acid and copolymers and blends thereof. Suitable polyolefins include polyethylene, e.g., high density polyethylene, medium density polyethylene, low density polyethylene and linear low density polyethylene; polypropylene, e.g., isotactic polypropylene, syndiotactic polypropylene, blends of isotactic polypropylene and atactic polypropylene, and blends thereof; polybutylene, e.g., poly(1-butene) and poly(2-butene); polypentene, e.g., poly(1-pentene) and poly(2-pentene); poly(3-methyl-1-pentene); poly(4-methyl 1-pentene); and copolymers and blends thereof. Suitable copolymers include random and block copolymers prepared from two or more different unsaturated olefin monomers, such as ethylene/propylene and ethylene/butylene copolymers. Suitable polyamides include nylon 6, nylon 6/6, nylon 4/6, nylon 11, nylon 12, nylon 6/10, nylon 6/12, nylon 12/12, copolymers of caprolactam and alkylene oxide diamine, and the like, as well as blends and copolymers thereof. Suitable polyesters include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polytetramethylene terephthalate, polycyclohexylene-1,4-dimethylene terephthalate, and isophthalate copolymers thereof, as well as blends thereof.

[0043] The filaments may be monocomponent filaments, meaning filaments prepared from one polymer component, multiconstituent filaments, or multicomponent filaments. The multicomponent filaments may have either of an A/B or A/B/A side-by-side cross-sectional configuration, or a sheath-core cross-sectional configuration, wherein one polymer component surrounds another polymer component. Furthermore, the filaments may be meltblown fibers, spunbond fibers, or any other suitable type of filaments. Suitable types of nonwoven webs include spunbond webs, meltblown webs, and bonded carded webs. In one embodiment, the nonwoven web may be a multi-layer material having, for example, at least one layer of spunbonded web joined to at least one layer of meltblown web, bonded carded web or other suitable material.

[0044] Nonwoven webs treated in accordance with the method of the invention are particularly suitable for use in disposable absorbent products including, without limitation, diapers, training pants, swimwear, absorbent underpants, adult incontinence products, feminine hygiene products, absorbent wipes, and the like, as well as protective garments, including medical garments and industrial protective garments. Medical garments include surgical garments, gowns, aprons, face masks, absorbent drapes, and the like. Industrial protective garments include protective uniforms, workwear, and the like.

EXAMPLE

[0045] In this example, samples treated by four different treatment techniques, including the treatment technique of the invention, were tested and compared. Each of the samples included a high-loft, low-density web that was made with 3.7 denier bicomponent spunbond fiber at about 0.14 inches loft, about 100 gsm basis weight and 0.027 g/cc density prior to treatment.

[0046] Dip & Vacuum Treatment

[0047] The dip and vacuum treatment of the invention was carried out using the apparatus shown in FIG. 1. A 1% solution of AHCOVEL Base N-62 and SF-19 (2:1) was provided in a treatment bath. More specifically, the solution included 200 grams AHCOVEL BASE N-62; 100 grams SF-19; 14,700 grams water; and 1.5 grams LEUCOPHOR B-302 fluorescent brightener dye (optional). The nonwoven web had 100% wet pick-up to achieve the desired 1% add-on level. The web was transported at a line speed of 50 feet per minute (fpm) to a 100 hp vacuum at 2 inches of water. The vacuum slot had dimensions of about 0.25 inch by 12 inches, with slot face air velocity of about 1500 fpm. Subsequently, the web was transported to a dryer having a temperature of about 240 degrees Fahrenheit. NMR test results showed that the target add-on level was achieved.

[0048] The LEUCOPHOR B-302 fluorescent brightener dye was included in the solution to determine the uniformity of coverage and thoroughness of penetration of the treatment. A 10-inch by 12-inch sample of the treated material was viewed under a black light. A photograph of a top view of the treated material under black light is shown in FIG. 2, and shows substantially uniform coverage of the web.

[0049] Internal Treatment

[0050] Liquid MASIL SF-19 silicone surfactant, available from BASF Corporation, was injected directly into a polyethylene extruder barrel of a spunbonded forming apparatus. Add-on levels were targeted to 1% by weight on the web. To achieve this level, 2% SF-19 was added to the polyethylene side of the fiber.

[0051] WEKO Treatment

[0052] Using low flow heads on a WEKO apparatus, a 15% solution of AHCOVEL BASE N-62 and SF-19 (2:1) was applied to both sides of the nonwoven web. More specifically, the solution included 1500 grams AHCOVEL BASE N-62; 750 grams SF-19; 12,750 grams water; and 11.25 grams LEUCOPHOR B-302 fluorescent brightener dye (optional). The nonwoven web was run through the WEKO at 25 feet per minute. With the 15% bath, to achieve an add-on of 1%, the web had a wet pick-up of 6.67%. To achieve an add-on of 2%, the web had a wet pick-up of 13.33%.

[0053] The same results were obtained on a WEKO apparatus with high flow heads using a 7.5% solution of AHCOVEL BASE N-62 and SF-19 (2:1) applied to both sides of the nonwoven web. More specifically, the 7.5% solution included 750 grams AHCOVEL BASE N-62; 375 grams SF-19; 13,875 grams water; and 5.6 grams LEUCOPHOR B-302 fluorescent brightener dye (optional).

[0054] The LEUCOPHOR B-302 fluorescent brightener dye was included in the solution to determine the uniformity of coverage and thoroughness of penetration of the treatment. A 10-inch by 12-inch sample of the treated material was viewed under a black light. A photograph of a top view of the treated material under black light is shown in FIG. 3a, with a cross-sectional view of the material shown in FIG. 3b. As can be seen in the photographs, particularly in FIG. 3b, only the surface appears to be treated, with very little penetration through the thickness of the sample.

[0055] Foam Treatment A 15% solution of AHCOVEL BASE N-62 and SF-19 (2:1) was mixed with GLUCOPON foaming agent, available from Cognis. Corporation, Charlotte, N.C., (2:1):1 for the foaming process. The bath was 1,000 grams, including 15% solids (150 grams total chemicals). More specifically, the bath included 3 parts AHCOVEL BASE N-62/SF-19 (112.5 grams, including 75 grams AHCOVEL BASE N-62 and 37.5 grams SF-19) and 1 part GLUCOPON (37.5 grams), with 850 grams water and 0.75 gram dye (optional). The bath can be converted to a 15,000 gram bath by multiplying all values by 15.

[0056] Both sides of the nonwoven web were treated by mixing the bath and allowing the bath to blend for approximately 45 minutes, until consistent foam was produced. Then, the nonwoven web was run through a foaming apparatus at a line speed of 60 fpm for 2% add-on, or at 120 fpm for 1% add-on, pulling the web over a foam slot. The flow of the foam was 22 cubic centimeters per minute, with air flow of 5 liters per minute. The foamer was set at a speed of 500 rpm, temperature of 94 degrees Fahrenheit, and pressure of 25 psi. A through-air dryer was set at 240 degrees Fahrenheit.

[0057] The LEUCOPHOR B-302 fluorescent brightener dye was included in the solution to determine the uniformity of coverage and thoroughness of penetration of the treatment. A 10-inch by 12-inch sample of the treated material was viewed under a black light. A photograph of a top view of the treated material under black light is shown in FIG. 4a, with a cross-sectional view of the material shown in FIG. 4b. As can be seen in both the treatment application was non-uniform on the surface as well as through the thickness of the web.

[0058] FIFE Test

[0059] A horizontal Fluid-Intake and Flowback Evaluation (FIFE) Test was performed on each of the four types of treated samples described above. This test determines the intake potential, or the time it takes for each sample to absorb fluid and the amount of fluid that flows back out of the sample after fluid has been absorbed.

[0060] The FIFE entails insulting the structure by pouring a defined amount of 0.9 percent saline solution into a cylindrical column resting vertically on top of the structure and recording the time it takes for the fluid to be taken in by the structure. The sample to be tested is placed on a flat surface and the FIFE testing apparatus placed on top of the sample. The FIFE testing apparatus consisted of a rectangular, 35.3 by 20.3 cm, plexiglass piece upon which was centered a cylinder with an inside diameter of 30 mm. The flat piece had a 38 mm hole corresponding with the cylinder so that fluid could pass through it from the cylinder to the sample. The cylinder was centered 2 inches from top or front of the absorbent pad in the crotch of diaper. The FIFE testing apparatus weighed 517 grams.

[0061] Intake times are typically recorded in seconds. Samples were cut into 2.5 by 7 inch pledgets and were inserted into a STEP 4 HUGGIES ULTRATRIM® commercially available diaper after removing the surge management layer from the diaper, thereby replacing the surge management layer with a sample pledget. The diapers including the samples were then insulted three times at 100 ml per insult with a wait of 15 minutes between the time the fluid was completely absorbed and the next insult.

[0062] After the third insult, the materials were placed on a vacuum box under 0.5 psi of pressure with a piece of blotter paper on top. The blotter paper was 110 lb. Verigood paper made by Fort James Corporation and was 3.5 by 12 inches (8.9 by 30.5 cm). The blotter paper was weighed before and after the test and the resulting differential reported as the flowback value as grams of fluid desorbed.

[0063] The results of the FIFE test are shown in FIG. 5.

[0064] LISTER Test

[0065] A LISTER type timer/dispenser, manufactured by Lenzing Aktiengesellschaft, Division Lenzing Technik, A-4860 Lenzing, Austria, was used to determine the time it takes for each sample to absorb or intake cumulative amounts of fluid. More specifically, 4-inch by 4-inch treated samples were placed over 2 plies of control Lister absorbent paper. Then 10 ml of saline was applied to each 4-inch by 4-inch sample using the Lister apparatus. The apparatus measures the time in seconds for the saline to pass into the samples. The time is then recorded, and the absorbent papers that have soaked up the saline that has passed through the samples are discarded. Samples are blotted dry using paper towels. The, test is repeated 9 additional times, drying samples between insults and using new absorbent paper for each insult. The results of the LISTER test for the WEKO sample, the dip & vacuum sample of the invention, the foam sample, and a control treated bonded carded web (at 100 gsm) are shown in FIG. 6. The bonded carded web (BCW) was produced from a 300 gsm web made up of a mixture of 2 denier T-256 bicomponent fibers and 3 denier T-244 polyester fibers at a ratio of 60/40, respectively. Both fibers are commercially available from KoSa Inc. The fibers were treated by the manufacturer with 0.5 weight percent of a proprietary surfactant to make them hydrophilic.

[0066] While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.