Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including strand or fiber material which is a monofilament...
Reexamination Certificate
1999-07-15
2002-10-01
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including strand or fiber material which is a monofilament...
C428S373000, C428S375000, C428S394000, C442S361000, C442S414000, C604S358000
Reexamination Certificate
active
06458726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to synthetic fibers especially useful in the manufacture of nonwoven fabrics. In particular, the present invention relates to fibers intended for such use, including processes of their production, and compositions for producing the fibers, as well as nonwoven fabrics and articles containing these fibers. More specifically, the fibers of the present invention are capable of providing soft feeling nonwoven materials that have high tensile strength. Further, the nonwoven materials are thermally bondable at lower temperatures while having superior strength properties, including cross-directional strength. The fibers of the present invention can be incorporated into lower basis weight nonwoven materials which have strength properties that are equal to or greater than nonwoven materials of higher basis weight. Still further, the fibers of the present invention are capable of being run on high speed machines, such as high speed carding and bonding machines.
2. Background Information
The requirements of nonwoven fabrics used in applications concerned with hygiene, medical fabrics, wipes and the like continue to grow. Moreover, utility and economy, and aesthetic qualities often must be met simultaneously. The market continues to expand for polyolefin fibers and items made therefrom having enhanced properties and improved softness.
The production of polymer fibers for nonwoven materials usually involves the use of a mix of at least one polymer with nominal amounts of additives, such as stabilizers, pigments, antacids and the like. The mix is melt extruded and processed into fibers and fibrous products using conventional commercial processes. Nonwoven fabrics are typically made by making a web, and then thermally bonding the fibers together. For example, staple fibers are converted into nonwoven fabrics using, for example, a carding machine, and the carded fabric is thermally bonded. The thermal bonding can be achieved using various heating techniques, including heating with heated rollers, hot air and heating through the use of ultrasonic welding.
Fibers can also be produced and consolidated into nonwovens in various other manners. For example, the fibers and nonwovens can be made by spunbonded processes. Also, consolidation processes can include needlepunching, through-air thermal bonding, ultrasonic welding and hydroentangling.
Conventional thermally bonded nonwoven fabrics exhibit good loft and softness properties, but less than optimal cross-directional strength, and less than optimal cross-directional strength in combination with high elongation. The strength of the thermally bonded nonwoven fabrics depends upon the orientation of the fibers and the inherent strength of the bond points.
Over the years, improvements have been made in fibers which provide stronger bond strengths. However, further improvements are needed to provide even higher fabric strengths at lower bonding temperatures and lower fabric basis weight to permit use of these fabrics in today's high speed converting processes for hygiene products, such as diapers and other types of incontinence products. In particular, there is a need for thermally bondable fibers, and the resulting nonwoven fabrics that possess high cross-directional strength, high elongation and excellent softness, with the high cross-directional strength (and softness) being obtainable at low bonding temperatures.
Further, there is a need to produce thermally bondable fibers that can achieve superior cross-directional strength, elongation and toughness properties in combination with fabric uniformity, loftiness and softness. In particular, there is a need to obtain fibers that can produce nonwoven materials, especially, carded, calendered fabrics with cross-directional properties on the order of at least about 200 to 400 g/in., more preferably 300 to 400 g/in, preferably greater than about 400 g/in, and more preferably as high as about 650 g/in or more, at speeds as high as about 500 ft/min, preferably as high as about 700 to 800 ft/min, and even more preferably as high as about 980 ft/min (300 m/min). Further, the fabrics can have an elongation of about 50-200%, and a toughness of about 200 to 700 g/in, preferably about 480-700 g/in for nonwoven fabrics having a basis weight of from about 10 g/yd
2
to 20 g/yd
2
. Thus, it is preferred to have these strength properties at a basis weight of about 20 g/yd
2
, more preferably less than about 20 g/yd
2
, even more preferably less than about 17 to 18 g/yd
2
, even more preferably less than about 15 g/yd
2
, and even more preferably less than about 14 g/yd
2
and most preferably as low as 10 g/yd
2
, or lower. Commercial fabrics produced today, depending upon use, have a basis weight of, for example, about 11-25 g/yd
2
, preferably 15-24 g/yd
2
.
Softness of the nonwoven material is particularly important to the ultimate consumer. Thus, products containing softer nonwovens would be more appealing, and thereby produce greater sales of the products, such as diapers including softer layers.
Various techniques are known for producing fibers that are able to be formed into nonwoven materials having superior properties, including high cross-directional strength and softness. For example, U.S. Pat. Nos. 5,281,378, 5,318,735 and 5,431,994 to Kozulla are directed to processes for preparing polypropylene containing fibers by extruding polypropylene containing material having a molecular weight distribution of at least about 5.5 to form a hot extrudate having a surface, with quenching of the hot extrudate in an oxygen-containing atmosphere being controlled so as to effect oxidative chain scission degradation of the surface. In one aspect of the process disclosed in the Kozulla patents, the quenching of the hot extrudate in an oxygen-containing atmosphere can be controlled so as to maintain the temperature of the hot extrudate above about 250° C. for a period of time to obtain oxidative chain scission degradation of the surface.
As disclosed in these patents, by quenching to obtain oxidative chain scission degradation of the surface, such as by delaying cooling or blocking the flow of quench gas, the resulting fiber essentially contains a plurality of zones, defined by different characteristics including differences in melt flow rate, molecular weight, melting point, birefringence, orientation and crystallinity. In particular, as disclosed in these patents, a fiber produced therein includes an inner zone identified by a substantial lack of oxidative polymeric degradation, an outer zone of a high concentration of oxidative chain scission degraded polymeric material, and an intermediate zone identified by an inside-to-outside increase in the amount of oxidative chain scission polymeric degradation. In other words, the quenching of the hot extrudate in an oxygen containing atmosphere can be controlled so as to obtain a fiber having a decreasing weight average molecular weight towards the surface of the fiber, and an increasing melt flow rate towards the surface of the fiber. For example, a preferred fiber comprises an inner zone having a weight average molecular weight of about 100,000 to 450,000 grams/mole, an outer zone, including the surface of the fiber, having a weight average molecular weight of less than about 10,000 grams/mole, and an intermediate zone positioned between the inner zone and the outer zone having a weight average molecular weight and melt flow rate intermediate the inner zone and the outer zone. Moreover, the inner, core zone has a melting point and orientation that is higher than the outer surface zone.
Further, U.S. patent application Ser. Nos. 08/080,849, 08/378,267, 08/378,271 and 08/378,667 (and its continuation application Ser. No. 08/598,168, which issued as U.S. Pat. No. 5,705,119) to Takeuchi et al., and European Patent Application No. 0 630 996 to Takeuchi et al., which are incorporated by reference herein in their entirety, are directed to obtain fibers having a skin-core morphology, including obt
Engle Edward J.
Fahey Elizabeth L.
Freeman Walter J.
Gupta Rakesh K.
Harrington James H.
Fiberco Inc.
Guarriello John J.
Morris Terrel
LandOfFree
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