Nonwoven fabric

Details Nonwoven fabric Nonwoven fabric

1996-10-09

1998-10-06

Pezzuto, Helene L.

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

442403, 442407, 442415, 442361, B32B 2714, B32B 1500

Patent

active

058174036

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to nonwoven fabrics which are made of randomly disposed, continuous synthetic fibers that are produced by a plurality of spinning beams delivered by multiple extruders and resulting in a web composed of multiple layers of the fiber that are laid on top of each other on a laydown belt, which is transported to bonding equipment where the layers are consolidated into a fabric.
Nonwoven fabrics have typically been made using one polymer component, e.g. polypropylene, polyester, to produce the matrix fiber of the nonwoven and a second polymer of a lower melting point, e.g. polyethylene, copolyester, to produce the binder fiber. Those two fibers can be extruded separately or extruded together such that the matrix fiber is the fiber core and the binder fiber is the sheath of the same fiber.
Alternatively, nonwoven fabrics have been made from a single polymer, a homopolypropylene fiber, which can be used for both the matrix and the binder. In this case, the fibers are alternatively mechanically drawn and undrawn generating on the same fiber the matrix and the binder. C.f. U.S. Pat. Nos. 3,341,394; 3,563,838; 3,821,062; 4,632,861; 4,634,739.
A disadvantage of several of the known nonwoven fabrics is that, where these fabrics consist of a plurality of layers of fibers, the layers do not adhere well to each of with adequate strength.
Thus, in certain rigorous end-uses, the fabric may become delaminated.
Moreover, prior art fabrics typically will not have desirable permeability characteristics, i.e. low porosity to air and/or liquids, which may be required for certain end-uses.
It has now been found that desirable improvements in the delamination strength and impermeability characteristics of nonwoven fabrics can be obtained by employing a fiber comprising a copolymer of propylene and ethylene in addition to a fiber comprising polypropylene.


SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a nonwoven fabric characterized in that it contains (1) a fiber comprising a copolymer of propylene and ethylene; and (2) a fiber comprising a polypropylene homopolymer. The fiber (1) will be overbonded versus fiber (2) because fiber (1) has a lower melting point resulting in less permeable structure.
According to the invention one or more layers of the fabric comprise a copolymer of propylene and ethylene, and optionally a blend of this copolymer with homopolypropylene. The blend of copolymer with homopolymer gives the possibility to spin lower denier fiber and thereby improve the total fiber distribution of the fabric using conventional spinning equipment. When the layers of fiber are consolidated into a fabric, the bonding temperature is selected according to the layers of the higher melt point polymer to obtain maximum strength fabrics, consequently the layers of copolymer or copolymer blend are overbonded and thereby partially or totally melted. Depending upon end use applications, at constant bonding conditions the level of overbonding of these layers and porosity of the surface can be selectively adjusted by the amount and type of copolymer in the melt blend. In addition the fiber can be easily mechanically drawn, thereby varying the fiber length and denier resulting in various levels of fiber distribution of various fiber melting points.
Such nonwoven fabrics will have a number of applications in conventional end uses such as carpet backings and geotextiles, and new end uses where lower air and/or water permeability is required such as in construction and packaging applications. Other applications envisioned will take advantage of lower melt point of the copolymer layer for better welding to itself or to other materials by ultrasonic bonding, hot welding or other similar techniques.


DETAILED DESCRIPTION OF THE INVENTION

As used herein, measurements and units are as follows, except where explicitly noted otherwise.


______________________________________ Measurement Unit Reference ______________________________________ Melting poin

REFERENCES:
W.H. Skoroszewski in "Plastics and Polymers", vol. 40 (147), pp. 142-152 (1972).

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