US20040043214A1

US20040043214A1 - Method of forming a 3-dimensional fiber and a web formed from such fibers

Info

Publication number: US20040043214A1
Application number: US10/232,059
Authority: US
Inventors: Vasily Topolkaraev; Kevin Possell; Gregory Wideman; Palani Wallajapet
Original assignee: Kimberly Clark Worldwide Inc
Current assignee: Kimberly Clark Worldwide Inc; Trion Industries Inc
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-04
Also published as: MXPA05001641A; WO2004020709A1; EP1532298A1; KR20060006759A; BR0313446A; AU2003256753A1; JP2005537403A; AR041041A1

Abstract

A method of forming 3-dimensional fibers is disclosed along with a web formed from such fibers. The method includes the steps of co-extruding a first component and a second component. The first component has a recovery percentage R₁and the second component has a recovery percentage R₂, wherein R₁is higher than R₂. The first and second components are directed through a spin pack to form a plurality of continuous molten fibers. The molten fibers are then routed through a quenching chamber to form a plurality of continuous cooled fibers. The cooled fibers are then routed through a draw unit to form a plurality of continuous, solid linear fibers. The solid fibers are then accumulated and stretched by at least about 50 percent. The plurality of stretched fibers are then cut and allowed to relax such that a plurality of 3-dimensional, coiled fibers is formed.

Description

BACKGROUND OF THE INVENTION

There are numerous methods known to those skilled in the art for spinning fibers that can be later formed into a nonwoven web. Many such nonwoven webs are useful in disposable absorbent articles for absorbing body fluids and/or excrement, such as urine, fecal matter, menses, blood, perspiration, etc. Three dimensional fibers are also useful for machine direction and cross direction stretchable spunbond materials that can be made into bodyside covers, facings and liners. Manufacturers of such articles are always looking for new materials and ways to construct or use such new materials in their articles to make them more functional for the application they are designed to accomplish. The creation of a web of 3-dimensional, bicomponent fibers wherein the fibers are formed from at least one elastomeric material that can extend in at least one direction can be very beneficial. For example, an infant diaper containing an absorbent layer formed from cellulose pulp fibers interspersed into a web of 3-dimensional nonwoven fibers will allow the absorbent layer to retain a larger quantity of body fluid if the 3-dimensional fibers can expand. Such an absorbent layer can provide better leakage protection for the wearer and may not have to be changed as often. In another example, a spunbond nonwoven facing or liner formed from a plurality of 3-dimensional fibers can provide improved stretch and controllable retraction. Such facings or liners can provide improved fit and better comfort for the wearer of absorbent articles.

A web formed from such 3-dimensional fibers can provide one or more of the following attributes: improved fit, improved loft, better comfort, greater void volume, softer feel, improved resiliency, better stretch, controlled retraction and improved absorbency.

The exact method utilized in forming a nonwoven web can create unique properties and characteristics in the web which can not be duplicated in another manner. Now, a new method of forming a 3-dimensional fiber has been invented which allows the fibers to be later formed into a web that can exhibit very desirable properties which are useful when the web is incorporated into a disposable absorbent article.

SUMMARY OF THE INVENTION

Briefly, this invention relates to a method of forming 3-dimensional fibers along with a web formed from such fibers. The method includes the steps of co-extruding a first component and a second component. The first component has a recovery percentage R ₁and the second component has a recovery percentage R₂, wherein R₁is higher than R₂The first and second components are directed through a spin pack to form a plurality of continuous molten fibers. The plurality of molten fibers is then routed through a quenching chamber to form a plurality of continuous cooled fibers. The plurality of cooled fibers is then routed through a drawing unit to form a plurality of continuous, solid linear fibers. The plurality of the solid fibers is then accumulated on a spool that can be at a later time unwound and stretched by at least about 50 percent. The plurality of stretched fibers are then cut and allowed to relax such that a plurality of 3-dimensional, coiled fibers is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing the equipment needed to extrude, spin, quench and draw continuous solid fibers and accumulate them on a spool. [0005]
FIG. 2 is a cross-section of a bicomponent fiber. [0006]
FIG. 3 is a schematic showing unwinding a plurality of solid linear fibers, stretching the fibers, cutting the fibers and then allowing the fibers to relax to form a plurality of 3-dimensional, staple fibers. [0007]
FIG. 4 is a side view of a helical fiber formed when the stretched fiber is cut into a staple fiber and the fiber is allowed to relax.[0008]

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a schematic of the equipment needed to extrude, spin, quench and draw a plurality of continuous solid fibers and accumulate them on a plurality of spools is depicted. The method includes the steps of co-extruding a [0009] first component 10 and a second component 12. The first and second components, 10 and 12 respectively, can be in the form of solid resin pellets or small particles. The first component 10 is positioned in a hopper 14 from which it can be metered and routed through a conduit 16 to a first extruder 18. Likewise, the second component 12 is positioned in a hopper 20 from which it can be metered and routed through a conduit 22 to a second extruder 24.
The [0010] first component 10 is a material that can be spun or otherwise formed into a continuous fiber. When the first component 10 is formed into a fiber, the fiber must be capable of being stretched and has a high recovery percentage R₁. The “recovery percentage R₁” is defined as the percent the first component 10 can recover after it has been stretched at least about 50% of its initial length and upon removal of the force applied to stretch it. Desirably, the first component 10 is an elastomeric material. Suitable elastomeric materials that can be used for the first component 10 include a melt extrudable thermoplastic elastomer such as a polyurethane elastomer, a copolyether ester, a polyether block polyamide copolymer, an ethylene vinyl acetate (EVA) elastomer, a styrenic block copolymer, an ether amide block copolymer, an olefinic elastomer, as well as other elastomers known to those skilled in the polymer art. Useful elastomeric resins include polyester polyurethane and polyether polyurethane. Examples of two commercially available elastomeric resins are sold under the trade designations PN 3429-219 and PS 370-200 MORTHANE® polyurethanes. MORTHANE® is a registered trademark of Huntsman Polyurethanes having an office in Chicago, Ill. 60606. Another suitable elastomeric material is ESTANE®, a registered trademark of Noveon, Inc. having an office in Cleveland, Ohio 44141. Still another suitable elastomeric material is PEARLTHANE®, a registered trademark of Merquinsa having an office in Boxford, Mass. 01921.
Three additional elastomeric materials include a polyether block polyamide copolymer which is commercially available in various grades under the trade designation PEBAX®. PEBAX® is a registered trademark of Atofina Chemicals, Inc. having an office in Birdsboro, Pa. 19508. A second elastomeric material is a copolyether-ester sold under the trade designation ARNITEL®. ARNITEL® is a registered trademark of DSM having an office at Het Overloon 1, NL-6411 TE Heerlen, Netherlands. The third elastomeric material is a copolyether-ester sold under the trade designation HYTREL®. HYTREL® is a registered trademark of E. I. DuPont de Nemours having an office in Wilmington, Del. 19898. [0011]
The [0012] first component 10 can also be formed from a styrenic block copolymer such as KRATON®. KRATON® is a registered trademark of Kraton Polymers having an office in Houston, Tex.
The [0013] first component 10 can further be formed from a biodegradable elastomeric material such as polyester aliphatic polyurethanes or polyhydroxyalkanoates. The first component 10 can be formed from an olefinic elastomeric material, such as elastomers and plastomers. One such plastomer is an ethylene-based resin or polymer sold under the trade designation AFFINITY®. AFFINITY® is a registered trademark of Dow Chemical Company having an office in Freeport, Tex. AFFINITY® resin is an elastomeric copolymer of ethylene and octene produced using Dow Chemical Company's INSITE™ constrained geometry catalyst technology. Another plastomer is sold under the trade designation EXACT® which includes single site catalyzed derived copolymers and terpolymers. EXACT® is a registered trademark of Exxon Mobil Corporation having an office at 5959 Las Colinas Boulevard, Irving, Tex. 75039-2298. Other suitable olefinic elastomers that can be used to form the first component 10 include polypropylene-derived elastomers.
The [0014] first component 10 can further be formed from a non-elastomeric thermoplastic material which has a sufficient recovery percentage R₁after it has been stretched at a specified temperature. Non-elastomeric materials useful in forming the first component 10 are extrudable thermoplastic polymers such as polyamides, nylons, polyesters, polyolefins or blends of polyolefins. For example, non-elastomeric, biodegradable polylactic acid can provide a sufficient recovery percentage R₁when stretched above its glass transition temperature of about 62° C.
The [0015] second component 12, like the first component 10, is a material that can be spun or otherwise formed into a continuous fiber. When the second component 12 is formed into a linear fiber, the linear fiber must be capable of being stretched and has a recovery percentage R₂, wherein R₁is higher than R₂The “recovery percentage R₂” is defined as the percent the component can recover after it has been stretched at least 50% of its initial length and upon removal of the force applied to stretch it. When the first and second components, 10 and 12 respectively, are formed into a linear fiber, the fiber must be capable of retracting or contracting from a stretched condition in order for the linear fiber to be useful in an absorbent article. As referred to herein, the term “retracting” means the same thing as “contracting”. Desirably, the ratio of R₁/R₂ranges from at least about 2 to about 100. Most desirably, the ratio of R₁/R₂ranges from at least about 2 to about 50. The reason for making R₁greater than R₂in a linear fiber is that upon retraction or contraction of the first and second components, 10 and 12 respectively, the 3-dimensional fiber will exhibit a very desirable, predetermined structural configuration. This structural configuration of the 3-dimensional fiber will display exceptional elongation properties in at least one direction.
The linear fiber further obtains some of its unique properties when the [0016] first component 10 makes up a volume percent of from about 30% to about 95% of the linear fiber and the second component 12 makes up a volume percent of from about 5% to about 70% of the linear fiber. Desirably, the first component 10 makes up a volume percent from about 40% to about 80% of the linear fiber and the second component 12 makes up a volume percent of from about 20% to about 60% of the linear fiber. The volume of a solid linear fiber is calculated using the following formula:
V=π(d ²/4)L ₁
where: V is the volume of the solid linear fiber; [0017]
π is a transcendental number, approximately 3.14159, representing the ratio of the circumference to the diameter of a circle and appearing as a constant in a wide range of mathematical problems; [0018]
d is the diameter of the linear fiber; and [0019]
L[0020] ₁is the initial length of the linear fiber.
The above described ranges of volume percents for the [0021] first component 10 and for the second component 12 allow the linear fiber to be stretched at least 50% to form a stretched linear fiber. The volume percent of each of the first and second components, 10 and 12 respectively, also plays a vital role in the retraction or contraction of the stretched fiber to a retracted length. By varying the volume percent of each of the first and second components, 10 and 12 respectively, one can manufacture a linear fiber that can be stretched and then retracted to a predetermined configuration and with certain desirable characteristics. At a later time, after such fibers are formed into a disposable absorbent article, the contact with a body fluid will cause the absorbent article to swell which will allow the fibers to elongate in at least one direction before the fiber becomes linear. As the fibers elongate, they can extend and allow the absorbent structure to receive and store additional body fluids.
The first and second components, [0022] 10 and 12 respectively, are chemically, mechanically and/or physically adhered or joined to one another to prevent the fiber from splitting when the fiber is stretched and then allowed to relax. The relaxed fiber will retract in length. Desirably, the first component 10 will be strongly adhered to the second component 12. In the core/sheath arrangement, the mechanical adhesion between the first and second components, 10 and 12 respectively, will compliment any chemical and/or physical adhesion that is present and aid in preventing splitting or separation of the first component 10 from the second component 12. This splitting or separation occurs because one component is capable of retracting to a greater extent than the other component. If a strong mutual adhesion is not present, especially during retraction, the two components can split apart and this is not desirable. In a fiber formed of two components arranged in a side by side or wedge shape configuration, a strong chemical and/or physical adhesion will prevent the first component 10 from splitting or separating from the second component 12.
The [0023] second component 12 can be formed from polyolefins, such as polyethylene or polypropylene, a polyester or a polyether. The second component 12 can also be a polyolefin resin, such as a fiber grade polyethylene resin sold under the trade designation ASPUN® 6811A. ASPUN® is a registered trademark of Dow Chemical Company having an office in Midland, Mich. 48674. The second component 12 can also be a polyolefin resin, such as a homopolymer polypropylene such as Himont PF 304, and PF 308, available from Basell North America, Inc. having an office at Three Little Falls Centre, 2801 ° C. enterville Road, Wilmington, Del. 19808. Another example of a polyolefin resin from which the second component 12 can be formed is polypropylene PP 3445 available from Exxon Mobil Corporation having an office at 5959 Las Colinas Boulevard, Irving, Tex. 75039-2298. Still other suitable polyolefinic materials that can be used for the second component 12 include random copolymers, such as a random copolymer containing propylene and ethylene. One such random copolymer is sold under the trade designation Exxon 9355, available from Exxon Mobil Corporation having an office at 5959 Las Colinas Boulevard, Irving, Tex. 75039-2298.
The [0024] second component 12 can also be formed from a melt extrudable thermoplastic material that provides sufficient permanent deformation upon stretching. Such materials include, but are not limited to, aliphatic and aromatic polyesters, copolyesters, polyethers, polyolefins such as polypropylene or polyethylene, blends or copolymers thereof, polyamides and nylons. The second component 12 can further be formed from biodegradable resins, such as aliphatic polyesters. One such aliphatic polyester is polylactic acid (PLA). Other biodegradable resins include polycaprolactone, polybutylene succinate adipate and polybutylene succinate. Polybutylene succinate adipate and polybutylene succinate resins are sold under the trade designation BIONOLLE® which is a registered trademark of Showa High Polymers having a sales office in New York, N. Y. 1017. Additional biodegradable resins include copolyester resin sold under the trade designation EASTAR BIO®. EASTAR BIO® is a registered trademark of Eastman Chemical Company having an office in Kingsport, Tenn. 37662. Still other biodegradable resins that can be used for the second component 12 include polyhydroxyalkanoates (PHA) of varying composition and structure, and copolymers, blends and mixtures of the foregoing polymers. Specific examples of suitable biodegradable polymer resins include BIONOLLE® 1003, 1020, 3020 and 3001 resins commercially available from Itochu International. BIONOLLE® is a registered trademark of Showa High Polymers having an office in New York, N. Y. 10017.
The [0025] second component 12 can also be formed from a water-soluble and swellable resin. Examples of such water-soluble and swellable resins include polyethylene oxide (PEO) and polyvinyl alcohol (PVOH). Grafted polyethylene oxide (gPEO) or chemically modified PEO can also be used. The water-soluble polymer can be blended with a biodegradable polymer to provide for better processing, performance, and interactions with liquids.
It should be noted that the PEO resin can be chemically modified by reactive extrusion, grafting, block polymerization or branching to improve its processability. The PEO resin can be modified by reactive extrusion or grafting as described in U. S. Pat. No. 6,172,177 issued to Wang et al. on Jan. 9, 2001. [0026]
Lastly, the [0027] second component 12 has a lower recovery percentage R₂than the first component 10. The second component 12 can be formed from a material that exhibits a low elastic recovery. Materials from which the second component 12 can be formed include, but are not limited to polyolefin resins, polypropylene, polyethylene, polyethylene oxide (PEO), polyvinyl alcohol (PVOH), polyester and polyether. The second component 12 can be treated or modified with hydrophilic or hydrophobic surfactants. Treatment of the second component 12 with a hydrophilic surfactant will form a wettable surface for increasing interaction with a body fluid or liquid. For example, when the surface of the second component 12 is treated to be hydrophilic, it will become more wettable when contacted by a body fluid, especially urine. Treatment of the second component 12 with a hydrophobic surfactant will cause it to repel a body fluid or liquid. Similar treatment of the first component 10 can also be done to control its hydrophilic or hydrophobic characteristics.
Referring again to FIG. 1, the first and second components, [0028] 10 and 12 respectively, are separately co-extruded in the two extruders 18 and 24. The extruders 18 and 24 function in a manner well known to those skilled in the art. In short, the solid resin pellets or small particles are heated up above their melting temperature and advanced along a path by a rotating auger. The first component 10 is routed through a conduit 26 while the second component 12 is simultaneously routed through a conduit 28 and both flow streams are directed into a spin pack 30. A melt pump, not shown, can be positioned across one or both of the conduits 26 and 28 to regulate volumetric distribution, if needed. The spin pack 30 is a device for making synthetic fibers. The spin pack 30 includes a bottom plate having a plurality of holes or openings through which the extruded material flows. The number of openings per square inch in the spin pack 30 can range from about 5 to about 500 openings per square inch. Desirably, the number of openings per square inch in the spin pack 30 is from about 25 to about 250. More desirably, the number of openings per square inch in the spin pack 30 is from about 125 to about 225. The size of each of the openings in the spin pack 30 can vary. A typical size opening can range from about 0.1 millimeter (mm) to about 2.0 mm in diameter. Desirably, the size of each of the openings in the spin pack 30 can range from about 0.3 mm to about 1.0 mm in diameter.
It should be noted that the openings in the spin pack [0029] 30 do not have to be round or circular in cross-section but can have a bilobal, trilobal, square, triangular, rectangular, oval or any other geometrical cross-sectional configuration that is desired.
Referring to FIGS. 1 and 2, the first and second components, [0030] 10 and 12 respectively, are directed into the spin pack 30 and are routed through the openings formed in the bottom plate in such a fashion that the first component 10 will form a core 32 while the second component 12 will form a sheath 34 which surrounds the outside circumference of the core 32. It should be noted that the first component 10 could form the sheath while the second component 12 could form the core, if desired. This core/sheath arrangement produces one configuration of a linear, bicomponent fiber 36. Bicomponent fibers having other cross-sectional configurations can also be produced using the spin pack 30. For example, the bicomponent fiber can have a side by side configuration or a core/sheath design where the core is offset coaxially from the sheath.
One [0031] bicomponent fiber 36 will be formed for each opening formed in the plate within the spin pack 30. This enables a plurality of continuous molten fibers 36, each having a predetermined diameter, to simultaneously exit the spin pack 30 at a first speed. Each linear, bicomponent fiber 36 will be spaced apart and be separated from the adjacent fibers 36. The diameter of each bicomponent fiber 36 will be dictated by the size of the openings formed in the bottom plate of the spin pack 30. For example, as stated above, if the diameter of the holes or openings in the bottom plate range from about 0.1 mm to about 2.0 mm, then each of the molten fibers 36 can have a diameter which ranges from about 0.1 mm to about 2.0 mm. There is a tendency for the molten fibers 36 to sometimes swell in cross-sectional area once they exit the opening formed in the plate but this expansion is relatively small.
The plurality of continuous [0032] molten fibers 36 are routed through a quench chamber 38 to form a plurality of cooled linear, bicomponent fibers 40. Desirably, the molten fibers 36 are directed downward from the spin pack 30 into the quench chamber 38. The reason for directing the molten fibers 36 downward is that gravity can be used to assist in moving the molten fibers 36. In addition, the vertical downward movement can aid in keeping the fibers 36 separated from one another.
In the quench [0033] chamber 38, the continuous molten fibers 36 are contacted by one or more streams of air. Normally, the temperature of the continuous molten fibers 36 exiting the spin pack 30 and entering the quench chamber 38 will be in the range of from about 150° C. to about 250° C. The actual temperature of the molten fibers 36 will depend upon the material from which they are constructed, the melting temperature of such material, the amount of heat applied during the extrusion process, as well as other factors. Within the quench chamber 38, the continuous molten fibers 36 are contacted and surrounded by lower temperature air. The temperature of the air can range from about 0° C. to about 120° C. Desirably, the air is cooled or chilled so as to quickly cool the molten fibers 36. However, for certain materials used to form the bicomponent fibers 36; it is advantageous to use ambient air or even heated air. However, for most elastomeric materials, the air is cooled or chilled to a temperature of from about 0° C. to about 400° C. More desirably, the air is cooled or chilled to a temperature of from about 15° C. to about 300° C. The lower temperature air can be directed toward the molten fibers 36 at various angles but a horizontal or downward angle seems to work best. The velocity of the incoming air can be maintained or adjusted so as to efficiently cool the molten fibers 36.
The cooled or chilled air will cause the continuous [0034] molten fibers 36 to crystallize, assume a crystalline structure or phase separate and form a plurality of continuous cooled fibers 40. The cooled fibers 40 are still linear in configuration at this time. Upon exiting the quench chamber 38, the temperature of the cooled fibers 40 can range from about 15° C. to about 100° C. Desirably, the temperature of the cooled fibers 40 will range from about 20° C. to about 80° C. Most desirably, the temperature of the cooled fibers 40 will range from about 25° C. to about 60° C. The cooled fibers 40 will be at a temperature below the melting temperature of the first and second components, 10 and 12 respectively, from which the fibers 40 were formed. The cooled fibers 40 may have a soft plastic consistency at this stage.
The plurality of continuous cooled [0035] fibers 40 are then routed to a draw unit 42. The draw unit 42 can be vertically located below the quenching chamber 38 so as to take advantage of gravity. The draw unit 42 can be a rotating roll around which all of the cooled fibers 40 are funneled down into a rope or tow and are drawn by being wrapped at least once around the outer periphery of the rotating roll. The plurality of cooled fibers 40 can be wrapped one or more times around the outer periphery of the rotating roll. Desirably, the plurality of cooled fibers 40 can be wrapped 1½ times around the outer periphery of the rotating roll wherein the fibers 40 accumulate into a rope or tow of solid fibers 44. Mechanical drawing involves subjecting the cooled fibers 40 to a mechanical force that will pull or draw the molten material exiting the spin pack 30.
The cooled [0036] fibers 40 are drawn down mainly from the molten state and not from the cooled state. The downward force in the draw unit 42 will cause the molten material to be lengthened and elongated into solid fibers 44. Lengthening of the molten material will usually shape, narrow, distort, or otherwise change the cross-sectional area of the solid fibers 44. For example, if the molten material has a round or circular cross-sectional area upon exiting the spin pack 30, the outside diameter of the solid fibers 44 will be reduced. The amount that the diameter of the solid linear fibers 44 are reduced will depend upon several factors, including the amount the molten material is drawn, the distance over which the fibers are drawn, the mechanical force used to draw the fibers, the spin line tension, etc. Desirably, the diameter of the solid linear fibers 44 will range from about 5 microns to about 10 microns. More desirably, the diameter of the solid linear fibers 44 will l range from about 10 microns to about 50 microns. Most desirably, the diameter of the solid linear fibers 44 will range from about 10 microns to about 30 microns.
The [0037] draw unit 42 will pull the cooled fibers 40 at a second speed that is faster than the first speed displayed by the continuous molten fibers 36 exiting the spin pack 30. This change in speed between the continuous molten fibers 36 and the continuous cooled fibers 40 enables the molten material to be lengthened and also to be reduced in cross-sectional area. Upon exiting the draw unit 42, the cooled fibers 40 will be solid fibers 44.
The plurality of [0038] solid fibers 44 exiting the draw unit 42 are then routed in mass around a guide roll 45 to a spool 46. The advancing fibers 44 are circumferentially wound onto the periphery of the spool 46 in the form of a rope. The spool 46 can be mounted in a support 48 and can be made to rotate as the advancing fiber 44 is directed onto the spool 46. The spool 46 can be sized and shaped to accumulate a predetermined amount of solid fibers 44. The solid linear fibers 44 will l be accumulated on the spool 46 until the spool 46 is filled. At this time the plurality of solid fibers 44 are cut or severed in mass by a cutter 50. The advancing solid fibers 44 can then be directed onto another empty spool 46 that can be held in the support 48. The process of removing a filled spool 46 and replacing it with an empty spool 46, onto which the advancing fibers 44 can be accumulated, is well known to those skilled in the art. This process can be automated so that the advancing linear fibers 44 can be instantaneously and sequentially directed to the next available empty spool 46.
Each of the filled spools [0039] 46 can be stacked and stored for use at a later time at the same facility or they can be transported to another location. One feature of this invention is that the solid linear fibers 44 do not have to be processed into crimped staple fibers nor formed into a web in one continuous process. Instead, the method allows for an interruption, such that the solid linear fibers 44 can be further processed at a later time and at a remote location, if desired. Alternatively, a continuous method could be employed wherein the spools 46 would not need to be present.
Referring to FIG. 3, a schematic is depicted showing the unwinding of a plurality of linear fibers, stretching the fibers, cutting the fibers and then allowing the fibers to relax to form a plurality of 3-dimensional, staple fibers. The method allows for the plurality of [0040] linear fibers 44 that were circumferentially wound onto the outer periphery of the spool 46 to be unwound and directed to a heater 52. The heater 52 is optional, but when present, will heat the plurality of linear fibers 44 to an elevated temperature. The exact temperature will depend upon the composition of the first and second components, 10 and 12 respectively, the diameter of the fibers 44, the amount the fibers 44 are to be stretched, the speed of the fibers 44, etc. It is also possible at this time to apply a surface treatment to the plurality of linear fibers 44, if desired. The application of a surface treatment either by spraying a chemical composition onto the fibers 44 or emersion of the fibers 44 in a liquid bath is well known to those skilled in the art. Various types of surface treatments can be applied to the fibers 44.
The plurality of solid [0041] linear fibers 44 are then routed to a stretching unit 54 where the plurality of linear fibers 44 is stretched by at least about 50%. By “stretched” it is meant that the continuous solid, linear fibers 44 are lengthened or elongated while in a solid state. The stretching is caused by axial tension exerted on the plurality of linear fibers 44. As the linear fibers 44 are stretched, the cross-sectional area of the linear fibers 44 will l be reduced. Desirably, the amount of stretch imparted into the solid fibers 44 can range from about 75% to about 1,000%. More desirably, the amount of stretch imparted into the solid fibers, 44 can range from about 100% to about 500%. Most desirably, amount of stretch imparted into the solid fibers 44 can range from about 150% to about 300%.
The stretching [0042] unit 54 is shown as including two pairs of spaced apart rolls. It should be noted that other forms of mechanical stretching apparatus can be utilized. The first pair of rolls includes a first roll 56 and a second roll 58. The first and second rolls, 56 and 58 respectively, can be arranged in close contact with one another so as to form a nip 60 therebetween. The plurality of linear fibers 44, unwound from the spool 46, is routed around a portion of the periphery of the first roll 56, through the nip 60 and around a portion of the periphery of the second roll 58. The nip 60 can be adjusted such that little or no pressure is exerted on the fibers 44. At least one of the first and second rolls, 56 and 58 respectively, is a driven roll which is set to rotate at a first predetermined surface speed. This surface speed caused the plurality of linear fibers 44 to be advanced at this speed. The surface speed can vary depending upon one's unique requirements. However, a surface speed of between about 10 meters per minute (m/min) to about 1,000 m/min will be sufficient for most applications. Desirably, the surface speed will be equal to or less than about 500 m/min. A faster surface speed is usually more desirable than a slower surface speed in order to reduce the cost of manufacture. However, at very high speeds, the fibers can lose their stretchability and become brittle. This can cause the fibers to break before they reach the desired percent of elongation.
Spaced downstream a desired distance from the first pair of rolls is the second pair of rolls. The second pair of rolls includes a [0043] first roll 62 and a second roll 64. The first and second rolls, 62 and 64 respectively, can be arranged in close contact with one another so as to form a nip 66 therebetween. The plurality of linear fibers 44 exiting the first pair of rolls is routed around a portion of the periphery of the first roll 62, through the nip 66 and around a portion of the periphery of the second roll 64. The nip 66 can be adjusted such that little or no pressure is exerted on the fibers 44. At least one of the first and second rolls, 62 and 64 respectively, is a driven roll which is set to rotate at a second predetermined surface speed. The second predetermined speed is faster than the first predetermined speed. This difference in speed caused the plurality of fibers 44 to be stretched lengthwise between the two pair of rolls to form a plurality of stretched linear fibers 68.
It should be noted that multiple rolls or pairs of rolls that rotate at different, and preferably increasing surface speeds, can also be utilized. [0044]
Optionally, positioned between the two pair of rolls, [0045] 56 and 58 and 60 and 62 respectively, is a heater 70. The heater 70 is capable of heating the plurality of linear fibers 44 to an elevated temperature. The exact temperature will depend upon the composition of the first and second components, 10 and 12 respectively, the diameter of the fibers 44, the amount the fibers 44 are to be stretched, the speed of the fibers 44, etc.
The stretching of the plurality of [0046] fibers 44 within the stretching unit 54 will cause the cross-sectional area of each of the linear fibers 44 to be reduced by about 5% to about 90% of the cross-sectional area of the linear fibers 44 unwound from the spool 46. Desirably, the cross-sectional area of each of the linear fibers 44 is reduced by about 10% to about 60% of the cross-sectional area of the linear fibers 44 unwound from the spool 46. More desirably, the cross-sectional area of each of the linear fibers 44 is reduced by about 20% to about 50% of the cross-sectional area of the linear fibers 44 unwound from the spool 46.
The stretched, continuous [0047] linear fibers 68 will be relatively small in diameter or cross-sectional area. Desirably, the diameter of the stretched linear fibers 68 will range from about 5 microns to about 50 microns. More desirably, the diameter of the stretched fibers 68 will range from about 5 microns to about 30 microns. Most desirably, the diameter of the stretched linear fibers 68 will range from about 10 microns to about 20 microns.
It should be noted that the stretched [0048] linear fibers 68 leaving the second pair of rolls 62 and 64 can be heat set, if desired, before being cut into staple fibers.
Still referring to FIG. 3, upon exiting the stretching [0049] unit 54, the plurality of stretched linear fibers 68 are cut or severed by a rotary cutter 72 having at least one knife 74 secured thereto. The rotary cutter 72 cooperates with an anvil roll 76 and the cutter 72 and the anvil roll 76 are arranged so that the stretched linear fiber 68 passes therebetween. The rotary cutter 72 and the anvil roll 76 keep the stretched linear fiber 68 in tension until it has been cut by the knife 74. It should be noted that other types of cutting mechanism can be utilized that are well known to those skilled in the cutting art. It is also possible to position a cutter downstream of a pair of cooperating rolls that maintain the stretched linear fiber 68 in tension. The rotary cutter 72 will cut the plurality of stretched fibers 68 into a plurality of staple fibers 78, each having a predetermined length. The plurality of stretched fibers 68 can be cut to a staple length of from about 5 millimeters to about 500 millimeters. Desirably, the plurality of stretched fibers 68 can be cut to a staple length of from about 10 millimeters to about 50 millimeters. More desirably, the plurality of stretched fibers 68 can be cut to a staple length of from about 12 millimeters to about 25 millimeters. The plurality of cut staple fibers 78 will instanteously start to relax. This relaxation allows the staple fibers 78 to retract or contract into a plurality of 3-dimensional, coiled fibers 80. The coiled fibers 80 have a shorter length than the cut stretched fiber 78. The coiled fibers 80 have a length ranging from about 3 millimeters (mm) to about 50 mm. Desirably, the coiled fibers 80 have a length ranging from about 5 mm to about 25 mm. Most desirably, the coiled fibers 80 have a length ranging from about 5 mm to about 15 mm. These coiled fibers 80 can be collected in a hopper or container 82.
Referring to FIG. 4, a portion of a 3-dimensional, [0050] staple fiber 80 depicted in the shape of a helix or helical coil that has a longitudinal central axis x-x. By “3-dimensional fiber” is meant a fiber having an x, y and z component that is formed by virtue of coils and/or curves regularly or irregularly spaced and whose extremities in the x, y and z planes form a locus of points which define a volume greater than a linear fiber. The 3-dimensional, coiled fibers 80 have a generally helical configuration. The helical configuration can extend along the entire length L of each of the 3-dimensional fibers 80 or it can occur over a portion of the length of the 3-dimensional fibers 80. Desirably, the coiled configuration extends over at least half of the length of each of the 3-dimensional fibers 80. More desirably, the coiled configuration extends from about 50% to about 90% of the length of each of the 3-dimensional fibers 80. Most desirably, the coiled configuration extends from about 90% to about 100% of the length of each of the 3-dimensional fibers 80. It should be noted that the coils can be formed in the clockwise or counterclockwise directions along at least a potion of the length of the 3-dimensional, staple fibers 80. It should also be noted that the configuration of each coil can vary along the length of each of the 3-dimensional, staple fibers 80.
Each of the 3-dimensional, [0051] staple fibers 80 have coils that circumscribes 360 degrees. The helical coils can be continuous or non-continuous over either a portion of or over the entire length of the 3-dimensional, staple fiber 80. Most desirably, the 3-dimensional, staple fibers 80 exhibit a continuous helical coil. The 3-dimensional, staple fiber 80 differs from a 2-dimensional fiber in that a 2-dimensional fiber has only two components, for example, an “x” and a “y” component; an “x” and a “z” component, or a “y” and a “z” component. The 3-dimensional, staple fiber 80 has three components, an “x” component, a “y” component and a “z” component. Many crimp fibers are 2-dimensional fibers that are flat and extend in only two directions. A crimped fiber is typically a fiber that has been pressed or pinched into small, regular folds or ridges. A crimped fiber usually has a bend along its length.
The 3-dimensional, [0052] staple fiber 80 has a non-linear configuration when it forms a helical coil. The 3-dimensional, staple fiber 80 also has an amplitude “A” that is measured perpendicular to a portion of its length L The amplitude “A” of the 3-dimensional, staple fiber 80 can range from about 10 microns to about 5,000 microns. Desirably, the amplitude “A” of the 3-dimensional, staple fiber 80 ranges from about 30 microns to about 1,000 microns. Most desirably, the amplitude “A” of the 3-dimensional, staple fiber 80 ranges from about 50 microns to about 500 microns. The 3-dimensional, staple fiber 80 further has a frequency “F” measured at two locations separated by 360 degrees between adjacent helical coils. The frequency “F” is used to denote the number of coils or curls formed in each inch of the coiled fiber length. The frequency “F” can range from about 10 to about 1,000 coils per inch. Desirably, the frequency “F” can range from about 50 to about 500 coils per inch. It should be noted that the amplitude “A” and/or the frequency “F” can vary or remain constant along at least a portion of the length L, or over the entire length, of the 3-dimensional, staple fiber 80. Desirably, the amplitude “A” and the frequency “F” will remain constant over a majority of the length L. The amplitude “A” of the 3-dimensional, staple fiber 80 and the frequency “F” of the helical coils forming the 3-dimensional, staple fiber 80 affect the overall reduction in the length of the 3-dimensional, staple fiber 80 from it's stretched condition.
It should be noted that the deformation properties of the first and second components, [0053] 10 and 12 respectively, will affect the configuration and size of the helical coils developed as the stretched fibers 78 retracts into the 3-dimensional, coiled fibers 80.
The first and second components, [0054] 10 and 12 respectively, are adhered together in the spin pack 30 to form a plurality of continuous bicomponent fibers. The adhesion of the first component 10 to the second component 12 can be chemical, mechanical and/or physical. This ability of the first and second components, 10 and 12 respectively, to adhere to one another will prevent splitting of the components 10 and 12 at a later time when one component retracts more than the other component. The first component 10 in the solid linear fiber 44 has an elongation of at least about 50% deformation. The first component 10 is able to recover at least about 20% of the stretch deformation imparted thereto, based on its length after deformation. Desirably, the first component 10 in the solid linear fiber 44 is able to recover at least about 50% of its stretch deformation. If the first component 10 has an elongation below at least about 50%, the recovery or relaxation power may not be sufficient to activate helical coiling of the 3-dimensional, staple fiber 80. Repetitive helical coils in the retracted 3-dimensional, staple fiber 80 are most desirable. A higher elongation than at least about 50% for the first component 10 is desirable. For example, an elongation of at least about 100% is good, an elongation exceeding 300% is better, and an elongation exceeding 400% is even better.
The [0055] second component 12 in the solid linear fiber 44 has a total deformation which includes a permanent unrecoverable deformation value and a recoverable deformation value. The permanent unrecoverable deformation value in a solid state, as a result of stretching, plastic yielding and/or drawing, is at least about 40%. The recoverable deformation value is at least about 0.1%. A higher deformation than at least about 50% for the second component 12 is desirable. A deformation of at least about 100% is good and a deformation exceeding about 300% is even better. The plastic yielding and drawing results in thinning of the second component 12. Stretching in a solid state means that the second component 12 is stretched below its melting temperature. If the total deformation of the second component 12 is below at least about 50%, the second component 12 will fail and break during the stretching process. Also, at low deformation, the second component 12 does not provide a sufficient level of permanent plastic yielding and thinning which is desired for the formation of the repetitive helical coils in the 3-dimensional, staple fibers 80. Stretching should not occur at very low temperatures because the fibers may be brittle and could break. Likewise, the fibers should not be stretched very quickly because this might cause the fibers to break before reaching the desired percent of elongation.
The percent elongation of the length of the 3-dimensional, coiled [0056] fiber 80 defined as the percent change in length by which the 3-dimensional, coiled fiber 80 can be stretched before becoming straight or linear. The percent elongation can be expressed by the following formula:
%E=100×(L ₁ −L)/L
where: % E is the percent elongation of the 3-dimensional, [0057] staple fiber 80;
L is the retracted length of the 3-dimensional, [0058] staple fiber 80; and
L[0059] ₁is the final length of the 3-dimensional, staple fiber 80 once it is stretched into a straight or uncoiled configuration.
The retracted 3-dimensional, [0060] staple fiber 80 has the ability to be subsequently elongated to at least 100% of its retracted length. Most desirably, the retracted 3-dimensional, staple fiber 80 can be subsequently elongated from about 150% to about 900% of its retracted length. Even more desirably, the retracted 3-dimensional, staple fiber 80 can be subsequently elongated from about 250% to about 500% of its retracted length. Still more desirably, the retracted 3-dimensional, staple fiber 80 can be subsequently elongated from about 300% to about 400% of its retracted length.
The 3-dimensional, [0061] staple fiber 80 exhibits exceptional elongation properties in at least one direction before the fiber becomes linear. Elongation is defined as the percent length by which the 3-dimensional, staple fiber 80 can be stretched before it becomes straight or linear. The direction of the elongation property of the 3-dimensional, staple fiber 80 normally in the same direction as the linear fiber 44 was stretched. In other words, the direction that the retracted 3-dimensional, staple fiber 80 able to subsequently elongate will be opposite to the direction of its retraction. It is possible for the retracted 3-dimensional, staple fiber 80 to have elongation properties in two or more directions. For example, the retracted 3-dimensional, staple fiber 80 can subsequently be elongated in both the x and y directions.
The 3-dimensional, [0062] staple fiber 80 obtained once the stretched fiber 78 is allowed to relax or retract. The 3-dimensional, staple fiber 80 able to acquire its helical profile by the difference in recovery percentage R₁of the first component 10 compared to the recovery percentage R₂of the second component 12. For example, since the first component 10 has a higher recovery percentage R₁than the recovery percentage R₂of the second component 12, the first component 10 will want to retract to a greater degree than the second component 12. However, both the first and second components, 10 and 12 respectively, will retract or contract the same amount since they are physically, chemically or mechanically adhered or joined to one another. The combination of the volume percent and the recovery percent of the first and second components, 10 and 12 respectively, creates the unique 3-dimensional configuration of the fiber 80. The retraction or recovery of the first and second components, 10 and 12 respectively, establishes the twist or coiling effect in the retracted 3-dimensional, staple fiber 80. The amount of coiling obtained, as well as the shape and location of the coiling, can be controlled by the selection of materials that are used to construct the linear fiber 44. These three variables: the amount of coiling, the shape, and the location of the coiling, can also be controlled by the volume of each component, as well as the amount the linear fiber 44 is stretched. The time and temperature conditions under which the solid fibers 44 are stretched and allowed to retract can also affect the finish profile of the retracted 3-dimensional, staple fiber 80.
The [0063] first component 10 has a higher recovery percentage R₁than the recovery percentage R₂of the second component 12 and therefore the material from which the first component 10 is formed tends to be more tacky and elastic. For this reason, the material with the higher recovery percentage R₁is used to form the inner core while the material having a lower recovery percentage R₂tends to be used to form the outer sheath. As the first and second components, 10 and 12 respectively, try to retract from the stretched condition; the outer sheath will retract or contract less. This means that the first component 10 will not be able to retract fully to an amount that it could if it was by itself. This pent up force creates the twist or helical coil effect in the retracted 3-dimensional, staple fiber 80. By varying the materials used to form the linear fiber 44 and by controlling the conditions to which the linear fiber 44 is stretched and then retracted, one can manufacture uniquely configured 3-dimensional, staple fibers 80 that will subsequently elongate in a predetermined way. This characteristic has been identified as being extremely useful in constructing disposable absorbent articles. This characteristic may also exhibit beneficial features in other articles as well.
The following Table 1 shows the recovery percent of individual materials that have been stretched to varying percentages. The material forming each sample was cut out from a thin sheet of a particular thickness in the shape of a dogbone or dumbbell. The dogbone shaped sample had an initial length of 63 millimeters (mm) measured from a first enlarged end to a second enlarged end. In between the two oppositely aligned, enlarged ends was a narrow section having a length of 18 mm and a width of 3 mm. The material was then placed in a tensile tester and stretched at a rate of 5 inches per minute, in the machine direction of the material. This stretching caused the narrow section of the sample to elongate. The force used to stretch the sample was then removed and the sample was allowed to retract or recover. The retracted length of the narrow section, known as the finished recovery length, was measured and recorded as a percentage of the stretched length. One can extrapolate from this information that when such a material is combined with another material to form a [0064] linear fiber 44, those similar ranges of recovery or contraction can be experienced.

TABLE 1

50% 100% 200% 700%

Thickness Stretch stretched stretched stretched stretched

Material in mils Temp. C.° & recovered & recovered & recovered & recovered

Polyurethane 5 25 24.5% 39.1% 54.4% —

Polypropylene 3 25 5.4% 5.5% 5.1% —

Polypropylene 3 75 — 8.7% 7.3% 6.4%
In Table 1, the dogbone shaped sample had a narrow section I[0065] ₁located between its first and second enlarged ends. Each of the enlarged ends of the dog bone sample was secured in a tensile tester and a force was applied causing the material to be stretched, in the machine direction of the material, a predetermined amount at a specific temperature. By stretching the sample, the narrow section is stretched to a length I₂. The length I₂is greater than the initial length I₁. The force exerted on the sample was then removed and the sample was allowed to retract such that the narrow section is shortened to a length I₃. The retracted length I₃is smaller than the stretched length I₂but is greater than the initial length I₁. The recovery percent (R %) of the different materials that can be used in forming the fiber can be calculated using the following formula:
Recovery %=[(I ₂ −I ₃)/I ₂]×100
where: I[0066] ₂is the stretched length of the narrow section of the sample; and
I[0067] ₃is the retracted length of the narrow section of the sample.
It should be noted that the [0068] coiled fibers 80 can be mixed with other kinds of fibers, such as cellulose fibers, wood pulp fibers, other synthetic fibers, etc. and/or a superabsorbent to form a web. The web can be an airlaid web, an air formed web, a coform web, a wet laid wet, etc. The web can be used in various kinds of products. The web is especially useful when used in a disposable absorbent article, such as an infant diaper, a training pant, an incontinent garment including a pad, brief, pant and refastenable pant, a sanitary napkin or tampon, a wet wipe product, etc. The method of admixing such fibers and/or superabsorbent particles is known to those skilled in the art. The percentage of each kind of fiber used to form the web can vary to meet one's particular needs. It should be noted that superabsorbent material, preferably in the form of particles, can be mixed with one or more kinds of fibers to form an absorbent web. The web can also be stabilized and/or bonded using various methods known to those skilled in the art.
A recognized limitation of stabilized and bonded absorbent webs is that the superabsorbent material present in the web is constrained from swelling to its full capacity. The use of the 3-dimensional fibers of this invention will allow an absorbent web structure containing superabsorbent material to expand and accommodate the entire extent the superabsorbent material can swell. [0069]
It should also be noted that the [0070] coiled fibers 80 can be laminated to a stretchable material, an elastic film or elastic fibers to form a thin, absorbent or non-absorbent material. This laminate material can be used as the bodyside cover or facing layer on a disposable absorbent article such as a diaper, training pant, incontinence garment, sanitary napkin, etc. This laminate material can also be used in health care products such as wound dressings, surgical gowns, gloves, etc.
While the invention has been described in conjunction with several specific embodiments, it is to be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope of the appended claims. [0071]

Claims

We claim:

1. A method of forming 3-dimensional fibers comprising the steps of:

a) co-extruding a first and a second component, said first component having a recovery percentage R₁and said second component having a recovery percentage R₂, wherein R₁is higher than R₂;

b) directing said first and second components through a spin pack to form a plurality of continuous molten fibers each having a predetermined diameter;

c) routing said plurality of molten fibers through a quench chamber to form a plurality of cooled fibers;

d) routing said plurality of cooled fibers through a draw unit to form a plurality of solid fibers each having a smaller diameter than said molten fibers;

e) accumulating said plurality of solid fibers and stretching said fibers by at least about 50 percent;

f) cutting said stretched fibers into a plurality of staple fibers each having a predetermined length; and

g) allowing said staple fibers to relax thereby forming coiled fibers, said first component of said coiled fibers having a strong mutual adhesion for said second component of said coiled fiber to prevent splitting.

2. The method of claim 1 wherein said coiled fibers are bicomponent fibers.

3. The method of claim 1 wherein each of said coiled fibers has a core/sheath cross-sectional configuration.

4. The method of claim 1 wherein said first and second components are mechanically adhered to one another.

5. The method of claim 1 wherein said first and second components are chemically adhered to one another.

6. The method of claim 1 wherein said first and second components are physically adhered to one another.

7. The method of claim 1 wherein said solid fibers are heated prior to being stretched.

8. The method of claim 1 wherein said solid fibers are heated while being stretched.

9. The method of claim 1 wherein said plurality of stretched fibers are cut by a rotary cutter into predetermined lengths of from about 5 millimeters to about 500 millimeters.

10. A method of forming 3-dimensional, bicomponent fibers comprising the steps of:

b) directing said first and second components through a spin pack at a first speed to form a plurality of continuous molten fibers each having a predetermined diameter;

d) routing said plurality of cooled fibers through a draw unit at a second speed, said second speed being greater than said first speed, to form a plurality of solid fibers each having a smaller diameter than said molten fibers;

e) accumulating said plurality of solid fibers and stretching said fibers by at least about 75 percent;

11. The method of claim 10 wherein each of said coiled fibers has a predetermined length of from about 5 millimeters to about 50 millimeters.

12. The method of claim 11 wherein each of said coiled fibers has a predetermined length of from about 5 millimeters to about 25 millimeters.

13. The method of claim 10 wherein each of said solid fibers are stretched from between about 50 percent to about 1,000 percent.

14. The method of claim 10 wherein each of said coiled fibers has a coil amplitude of from about 10 microns to about 5,000 microns.

15. The method of claim 10 wherein each of said coiled fibers has a frequency of coils ranging from about 10 to about 1,000 coils per inch.

16. The method of claim 10 wherein said second component is polyolefin.

17. A method of forming 3-dimensional, bicomponent fibers comprising the steps of:

e) accumulating said plurality of solid fibers on a spool and cutting said plurality of solid fibers when said spool is filled;

f) unwinding said plurality of solid fibers from said spool and heating said fibers to an elevated temperature;

g) stretching said heated fibers by at least about 50 percent;

h) cutting said stretched fibers into a plurality of staple fibers each having a predetermined length; and

i) allowing said staple fibers to relax thereby forming coiled fibers, said first component of said coiled fibers having a strong mutual adhesion for said second component of said coiled fiber to prevent splitting.

18. The method of claim 17 wherein said coiled fibers have a helical configuration.

19. The method of claim 17 wherein each of said coiled fibers has a coil amplitude of from about 10 microns to about 5,000 microns.

20. The method of claim 17 wherein each of said solid fibers are stretched from between about 50 percent to about 1,000 percent.

21. The method of claim 17 wherein each of said coiled fibers has a frequency of coils ranging from about 10 to about 1,000 coils per inch.

22. The method of claim 21 wherein each of said coiled fibers has a frequency of coils ranging from about 25 to about 250 coils per inch.

23. A web formed from said 3-dimensional fibers of claim 1.

24. The web of claim 23 wherein said web is an airlaid web.

25. The web of claim 23 wherein said web is an air formed web.

26. The web of claim 23 wherein said web is a coform web.

27. The web of claim 23 wherein said web is a wet laid web.

28. The web of claim 23 wherein superabsorbent material is present in said web.

29. A web formed from said 3-dimensional fibers of claim 17.

30. The web of claim 29 wherein superabsorbent material is present in said web.