Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including strand or fiber material which is a monofilament...
Reexamination Certificate
1999-12-30
2002-07-16
Juska, Cheryl A. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including strand or fiber material which is a monofilament...
C442S361000, C442S381000, C442S382000, C442S392000, C442S394000, C442S328000, C442S400000, C442S401000, C428S364000, C428S365000, C428S373000, C604S358000, C604S367000, C604S370000, C604S372000
Reexamination Certificate
active
06420285
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to multicomponent fibers, as well as nonwoven fabrics and fabric laminates which comprise the multicomponent fibers. More particularly, the invention relates to multicomponent fibers which include at least one polymer domain formed of a select combination of polymers, as well as nonwoven fabrics and laminates having improved fabric properties and processing characteristics.
BACKGROUND OF THE INVENTION
Nonwoven fabrics produced from spun polymer materials are used in a variety of different applications. Among other uses, such nonwoven fabrics are employed as the cover sheet for disposable diapers or sanitary products. There is considerable interest in making disposable diapers more comfortable and better fitting to the baby. An important part of the diaper comfort is the softness or hardness of the nonwovens used to make the diaper, including the diaper topsheet, barrier leg cuffs, and in some advanced designs, the fabric laminated to the backsheet film. In addition, in some diaper designs, a high degree of fabric elongation is needed to cooperate with elastic components for achieving a soft comfortable fit.
One approach to improved diaper topsheet softness is to use linear low density polyethylene (LLDPE) as the resin instead of polypropylene for producing spunbonded diaper nonwoven fabrics. For example, Fowells U.S. Pat. No. 4,644,045 describes spunbonded nonwoven fabrics having excellent softness properties produced from linear low density polyethylene. However, the above-described softness of LLDPE spunbonded fabric has never been widely utilized because of the difficulty in achieving acceptable abrasion resistance in such products. The bonding of LLDPE filaments into a spunbonded web with acceptable abrasion resistance has proven to be very difficult. Acceptable fiber tie down is observed at a temperature just below the point that the filaments begin to melt and stick to the calender. This very narrow bonding window has made the production of LLDPE spunbond fabrics with acceptable abrasion resistance very difficult. Thus, the softness advantage offered by LLDPE spunbonded fabrics has not been successfully captured in the marketplace.
Conventional polypropylene, which has been widely used in producing nonwoven fabrics, provides adequate fuzz and abrasion resistance properties in the unstretched condition, but the elongation properties are unacceptable and therefore the fibers and/or fabrics fracture.
In Sabee, U.S. Pat. Nos. 4,153,664 and 4,223,063, it is disclosed that the softness and drapeability of composite nonwoven fabrics, formed for example from a meltblown or a spunbonded nonwoven fabric, can be improved by drawing or stretching the fabric. More particularly, according to Sabee, the composite nonwoven fabrics are processed by differentially drawing or stretching the web to form a quilted pattern of drawn and undrawn areas, providing a product with enhanced softness, texture and drapeability. However, while the stretching may improve some fabric physical properties, it can adversely affect other important properties, such as abrasion resistance, for example, leaving the fabric with an unsightly fuzzed surface. In addition, Sabee teaches the use of undrawn or underdrawn filaments in the use of this application. Undrawn or underdrawn filaments are typically higher in denier and therefore the fabrics tend to be stiff.
In addition to softness, often the performance requirements of the product demand a composite nonwoven fabric having elasticity. In certain disposable diaper designs, for example, it is desired to impart elastic properties to the waist and/or to the leg cuff areas. One approach which has been taken to providing such elastic properties in a composite nonwoven fabric involves forming and stretching an elastic web, then bonding a gatherable web to the elastic web, and relaxing the composite. An obvious limitation of this approach is having to form the composite in the tensioned state. This requires additional equipment and control systems. Examples of this process are Mormon, U.S. Pat. No. 4,657,802, where it is disclosed that a composite nonwoven elastic is made by first stretching an elastic web, forming a fibrous nonwoven gatherable web onto the stretched elastic nonwoven, joining the two together to form a composite structure, then allowing the composite to relax. In Collier, et al., U.S. Pat. No. 5,169,706, it is disclosed that a composite elastic material having a low stress relaxation is formed between an elastic sheet and a gatherable layer. In Daponte, U.S. Pat. No. 4,863,779, a composite is disclosed which involves first tensioning the elastic elastic web to elongate it, bonding at least one gatherable web to the elastic web, and relaxing the composite immediately after bonding, so that the gatherable web is gathered between the bond points.
Another approach to imparting elastic properties to a composite nonwoven fabric is with a so-called “zero-strain” stretchable laminate. A “zero-strain” stretchable laminate refers to a fabric in which at least two layers of material, one elastic, the other substantially inelastic, are secured to one another along their coextensive surfaces while in a substantially untensioned state. The fabric is subsequently subjected to mechanical stretching. The inelastic layer typically fractures or extends, thus permanently elongating the inelastic layer and producing a composite fabric with elastic properties. This lamination and stretching process is advantageous in that utilizing elastic in an unstretched condition is easier and less expensive than stretched elastic used in traditional processing operations. However, one problem which has existed with presently available “zero-strain” stretchable laminates is surface abrasion. The mechanical stretching either fractures or disrupts the fibers within the substantially inelastic component of the “zero-strain” laminate, and as a result, the fibers detach and are susceptible to linting and pilling. In addition, such fracturing or detachment causes a noticeable loss in fabric strength.
There have been attempts to address the aforementioned problems of fiber tie down and fabric abrasion resistance. For example, attempts have been made to make the nonwoven fabric component of the composite with high elongation properties. Conventional polypropylene, as noted above, which has been widely used in producing nonwoven fabrics, provides adequate fuzz and abrasion resistance properties in the unstretched condition, but the elongation properties are unacceptable and therefore the fibers and/or fabrics fracture. Nonwoven webs formed from linear low density polyethylene (LLDPE) have been shown to have high elongation properties and also to possess excellent hand, softness and drape properties. However, as also noted above, such fabrics have not found wide commercial acceptance, since they fail to provide acceptable abrasion resistance.
SUMMARY OF THE INVENTION
The present invention overcomes these disadvantages and limitations and provides multicomponent fibers and nonwoven fabrics formed of the same having a superior combination of extensibility, tensile properties and abrasion resistance. The multicomponent fibers of the invention include at least two polymer components arranged in structured domains. At least one of the polymer components is formed of a select blend of polyolefin polymers which give improved fabric performance not heretofore recognized or described, such as high abrasion resistance, good tensile properties, excellent softness and the like. Furthermore, these blends have excellent melt spinning and processing properties which permit efficiently producing nonwoven fabrics at high productivity levels.
The multicomponent fibers can be continuous filaments, staple fibers, or meltblown fibers. In a preferred embodiment, the fibers are bicomponent fibers with the polymer components arranged in a sheath-core structured domain. In this aspect of the invention, the core is formed of the polymer blend to impart the desired pr
Christopher David Bruce
Meece Barry DeWayne
Newkirk David D.
Thomas Harold Edward
Alston & Bird LLP
BBA Nonwovens Simpsonville, Inc.
Juska Cheryl A.
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