Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric
Reexamination Certificate
1999-12-20
2003-04-15
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
C442S361000, C442S362000, C442S363000, C442S389000, C442S392000, C442S400000, C264S264000, C264S171100, C264S172140, C264S172170
Reexamination Certificate
active
06548431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to nonwoven fibrous structures and more particularly to fabrics and sheet structures formed from fine melt spun polyester fibers held together without weaving or knitting.
2. Description of the Related Art
Nonwoven fibrous structures have existed for many years and today there are a variety of different nonwoven technologies in commercial use. Nonwoven technologies continue to be developed by those seeking new applications and competitive advantages. Nonwoven sheets are commonly made from melt spun thermoplastic polymer fibers.
Melt spun fibers are small diameter fibers formed by extruding molten thermoplastic polymer material as filaments from a plurality of fine, usually circular, capillaries of a spinneret. Melt spun fibers are generally continuous and normally have an average diameter of greater than about 5 microns. Substantially continuous spunbonded fibers have been produced using high speed melt spinning processes, such as the high speed spinning processes disclosed in U.S. Pat. Nos. 3,802,817; 5,545,371; and 5,885,909. In a high speed melt spinning process, one or more extruders supply melted polymer to a spin pack where the polymer is fiberized as it passes through a line of capillary openings to form a curtain of filaments. The filaments are partially cooled in an air quenching zone after they exit the capillaries. The filaments may be pneumatically drawn to reduce their size and impart increased strength to the filaments.
Nonwoven sheets have been made by melt spinning melt spinnable polymers such as polyethylene, polypropylene, and polyester. According to the melt spinning process, the melt spun fibers are conventionally deposited on a moving belt, scrim or other fibrous layer. The deposited fibers are normally bonded to each other to form a sheet of substantially continuous fibers.
Polyester polymers that have been melt spun to make nonwoven sheets include poly(ethylene terephthalate). The intrinsic viscosity of poly(ethylene terephthalate) polyester that has been used in melt spinning such nonwoven sheet structures has been in the range of 0.65 to 0.70 dl/g. The intrinsic viscosity or “IV” of a polymer is an indicator of the polymer's molecular weight, with a higher IV being indicative of a higher molecular weight. Poly(ethylene terephthalate) with an IV below about 0.62 dl/g is considered to be a “low IV” polyester. Low IV polyester has not historically been used in melt spinning nonwoven sheet materials. This is because low IV polyester was considered to be too weak to melt spin filaments that could be efficiently laid down and bonded to produce nonwoven sheets. Fibers melt spun from low IV polyester have been expected to be too weak and discontinuous to withstand the high speed process by which melt spun sheets are produced. In addition, nonwoven sheets melt spun from low IV polyester have been expected to have little strength because the shorter polymer chains of low IV polyester have less interaction with each other that the longer polymer chains in fibers spun from regular IV polyester.
Low intrinsic viscosity poly(ethylene terephthalate) fibers have been extruded and collected via wind up machines on yarn spools. For example, U.S. Pat. No. 5,407,621 discloses a 0.5 denier per filament (dpf) yarn bundle spun from 0.60 dl/g IV poly(ethylene terephthalate) at a spinning speed of 4.1 km/min. U.S. Pat. No. 4,818,456 discloses a 2.2 dpf yarn bundle spun from 0.58 dl/g IV poly(ethylene terephthalate) at a spinning speed of 5.8 km/min. Whereas poly(ethylene terephthalate) fibers and yarns have been made from low IV polyester, strong nonwoven sheets with low denier filaments have not been melt spun from low IV poly(ethylene terephthalate) polyester.
BRIEF SUMMARY OF THE INVENTION
The invention provides a process for making a nonwoven sheet of substantially continuous melt spun fibers, comprising the steps of: extruding melt spinnable polymer containing at least 30% by weight poly(ethylene terephthalate) having an intrinsic viscosity of less than 0.62 dl/g through a plurality of capillary openings in a spin block to form substantially continuous fiber filaments; drawing the extruded fiber filaments by feeding the extruded fiber filaments into a draw jet so as to apply a drawing tension to the fiber filaments, the draw jet including a fiber entrance, a fiber passage where an air jet pulls the filaments in the direction that the filaments are traveling, and a fiber exit through which the drawn filaments are discharged from the draw jet; discharging the drawn fiber filaments as substantially continuous fiber filaments through the fiber exit of the draw jet in a downwardly direction at a rate of at least 6000 m/min; laying the fiber filaments discharged from the fiber exit of the draw jet on a collection surface, the fiber filaments having an average cross sectional area of less than about 90 square microns; and bonding the fiber filaments together to form a nonwoven sheet. The nonwoven sheet has a basis weight of less than 125 g/m2, and a grab tensile strength in both the machine and cross directions, normalized for basis weight and measured according to ASTM D 5034, of at least 0.7 N/(g/m2).
Preferably, at least 75% by weight of the fiber filaments of the nonwoven sheet have as a majority component poly(ethylene terephthalate) with an intrinsic viscosity of less than 0.62 dl/g. The intrinsic viscosity of the poly(ethylene terephthalate) is more preferably in the range of 0.40 to 0.60 dl/g, and most preferably in the range of 0.45 to 0.58 dl/g. The fiber filaments of the nonwoven sheet have an average denier variability as measured by the coefficient of variation of more than 25%. The nonwoven sheet preferably has a boil off shrinkage of less than 5%.
In the process of the invention, the drawn fiber filaments may be discharged through the fiber exit of the draw jet in a downwardly direction at a rate of more than 7000 or 8000 m/min. The fiber entrance of the draw jet is preferably spaced from said capillary openings in said spin block by a distance of at least 30 cm, and the fiber filaments are preferably quenched by a stream of quenching air having a temperature in the range of 5° C. to 25° C. as the fiber filaments pass from the capillary openings in the spin block to the fiber entrance of the draw jet. It is further preferred that the fiber filaments discharged from the fiber exit of the draw jet be guided by an extension plate extending from the draw jet in a direction parallel to the direction that the fibers are discharged from the fiber exit of the draw jet, wherein the fiber filaments pass within 1 cm of the extension plate over a distance of at least 5 cm.
The invention also provides a nonwoven sheet comprised of at least 75% by weight of melt spun substantially continuous fibers (A) that are at least 30% by weight poly(ethylene terephthalate) having an intrinsic viscosity of less than 0.62 dl/g, wherein said fibers have an average cross sectional area of less than about 90 square microns. The nonwoven sheet has a basis weight of less than 125 g/m2, and a grab tensile strength in both the machine and cross directions, normalized for basis weight and measured according to ASTMD 5034, of at least 0.7 N/(g/m2). Preferably, the fibers (A) have as a majority component poly(ethylene terephthalate) having an intrinsic viscosity of less than 0.62 dl/g, and more preferably in the range of 0.40 to 0.60 dl/g, and most preferably in the range of 0.45 to 0.58 dl/g.
The fibers (A) of the nonwoven sheet of the invention may be multiple component fibers wherein one component is primarily poly(ethylene terephthalate). Another component of the fibers (A) may be polyethylene. The nonwoven sheet of the invention can be used in a wiping material. The invention is also directed to composite sheets wherein a layer of the sheet consists of the nonwoven sheet of the invention that is described herein.
REFERENCES:
patent: 3802817 (1974-04-01), Matsuki et al.
patent: 4338275 (1982-07-01), Carr
patent:
Bansal Vishal
Davis Michael C.
Rudisill Edgar N.
E. I. du Pont de Nemours and Company
Morris Terrel
Wachtel Alexis
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