High strength nonwoven fabric and process for making

Details High strength nonwoven fabric and process for making High strength nonwoven fabric and process for making

1999-01-29

2003-03-25

Morris, Terrel (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Nonwoven fabric

Including parallel strand or fiber material within the...

C442S328000, C442S333000, C428S092000, C428S152000, C428S195100, C428S196000, C428S198000, C428S298100, C604S373000, C604S385201

Reexamination Certificate

active

06537935

ABSTRACT:

TECHNICAL FIELD
The present invention relates to high strength nonwoven fabric having at least one sheet of flexible nonwoven material intermittently bonded to inelastic filaments. The invention further relates to methods for producing these nonwoven reinforced fabrics in which fibrous webs of low strength are joined to high strength filaments as reinforcing elements.
Nonwoven materials having reinforcing elements are well known in the art. Scrims or like reinforcing webs are often joined to low strength nonwoven webs or fabrics by one of a variety of attachment methods including binders, adhesives, heat or sonic bonding, hydroentanglement or the like. For example, U.S. Pat. No. 4,522,863 describes taking a scrim of crosslaid threads coated with a heat reactable plastisol adhesive and bonds this to a microfiber web, preferably formed by meltblowing. Binders are used in U.S. Pat. No. 4,634,621 to join nonwoven webs to scrims such as Kevlar™ or Nomex™ fabrics. In U.S. Pat. No. 5,691,029, a yarn is bonded to a nonwoven, preferably in a crosshatched pattern. Heat bonding is used in a pattern to bond a microfiber nonwoven to a spunbond scrim in U.S. Pat. No. 4,041,203. A more complete full calendaring is used in U.S. Pat. No. 4,931,355 to join a nonwoven fibrous non-elastic web to a screen, scrim, netting, knit or woven. Hydroentangling also is used in U.S. Pat. No. 4,810,568 to join a nonwoven to a scrim netting. The above applications all employ relatively high strength material joined to a low strength nonwoven web resulting in a web that generally has the strength, flexibility, and other bulk web properties of the high strength material. As such, desirable web properties of the lower strength nonwoven are generally lost, such as flexibility or conformability. This is due to the fact that conventional reinforcement materials are sheet-like materials, as such the sheet or web properties of the composite are dominated by the reinforcement material layer. The composite however will still have surface or bulk properties of an outer nonwoven layer, such as coefficient of friction or absorbency, respectively.
U.S. Pat. No. 5,705,249 discloses bonding filaments to the surface of a nonwoven web. These filaments are pattern bonded by point bonding. This results in bulking of the composite in the area between the point bond sites. This bulking behavior allegedly decreases the slipperiness in comparison to a prior product where the nonwoven was point bonded to a film-like product. This product is complicated to manufacture and the filaments are relatively low strength unoriented type filaments.
It has also been proposed to orient nonwoven webs as a way to provide increased strength in the orientation direction without effecting the softness of the web, U.S. Pat. No. 4,048,364. The fibers forming the web align and provide increased tenacity in this direction of alignment. This process, however, adversely effects the loft and tactile properties of the nonwoven web and does not provide the strength obtainable with a high strength scrim. Also, this process is limited to nonwoven webs having some interfiber bonding or integrity, but not so much that it is filmlike.
Reinforcing scrims or films have also been incorporated into nonwoven web structures or laminates designed for particular end uses. For example, U.S. Pat. No. 5,256,231 describes forming a non-woven or fibrous loop material by corrugating either a non-woven web or a series of substantially non-parallel yarns in a corrugating nip and subsequently extrusion bonding a thermoplastic film onto specific anchor portions of the sheet of corrugated fibrous material.
U.S. Pat. Nos. 5,326,612 and 5,407,439 describe forming loop fastening material from non-woven materials such as spunbond webs lightly bonded to a structural backing. In U.S. Pat. No. 5,326,612, the total bond area (between the fibers of the loop fabric and between the loop fabric and the backing) is between 10 and 35 percent to allow for sufficient open area for the hooks to penetrate. The backing allegedly could be a film, a woven material or a nonwoven but should not allow the hooks to penetrate. In U.S. Pat. No. 5,407,439 the loop fabric (the entanglement zone) is laminated to a material(spacing zone) that permits hooks to penetrate but does not preferably entangle the hooks with a further optional backing layer that does not permit hook penetration. The spacing zone is generally thicker than the entanglement zone such that a hook will not fully penetrate through it. Low bonding levels are desired for these loop fastener applications, as is dimensional stability.
Japanese Pat. Publ. No. 7-313213 describes a loop fastening material formed by fusing one face of a non-woven loop fabric. The fabric is formed by entanglement of sheath-core composite fibers having a polyethylene sheath and a polypropylene core. Generally, the fibers are described as having a diameter of from 0.5 to 10 denier with the non-woven web having a basis weight of from 20 to 200 grams per square meter. The fused face provides reinforcement but this has also adversely affects the softness and flexibility of the fabric.
BRIEF DISCLOSURE OF THE INVENTION
The present invention provides improved inelastic, dimensionally stable, high strength nonwoven fabric sheets comprising a multiplicity of elongate strands of inelastic material extending generally continuously in at least a first direction and one or more sheets of flexible nonwoven material intermittently bonded along at least one elongate surface portion of the inelastic oriented strands. These sheets of nonwoven fabric are not easily extensible, in at least the first direction, due to the elongate strands. Preferably, the sheets have regular spaced bond portions between the nonwoven material and the strands. These intermittent bond anchor portions are separated by unbonded portions where the strand and nonwoven face each other, but not bonded. These composites provide unique advantages as a low cost, flexible or soft, dimensionally stable, breathable nonwoven fabric sheet which is relatively simple to manufacture.
According to the present invention there is also provided a method for forming a nonwoven fabric sheet which comprises (1) providing a first sheet of flexible nonwoven material (e.g., nonwoven web of natural and/or polymeric fibers, and/or yarns); (2) forming the first sheet of flexible nonwoven material to have arcuate portions projecting in the same direction from spaced anchor portions of the first sheet of flexible nonwoven material; (3) extruding or providing spaced generally parallel elongate strands of thermoplastic material that is inelastic (e.g., polyester, polyolefin, nylons, polystyrenes) onto the first sheet of flexible loop material; (4) providing the inelastic strands as a molten mass at least at the spaced anchor portions of the first sheet of flexible nonwoven material to thermally bond the strands to the nonwoven material at bond sites or the anchor portions (the strands extend between the anchor portions of the sheet of flexible nonwoven material with the arcuate portions of the first sheet of flexible material projecting from corresponding elongate surface portions of the strands); and (5) orienting the nonwoven fabric sheet in the longitudinal direction of the strands thereby orienting the strands and reducing or eliminating the arcuate portions. By this method there is provided a novel sheet-like nonwoven composite comprising a flexible nonwoven intermittently bonded to a multiplicity of generally parallel oriented elongate strands of inelastic thermoplastic material extending in one direction in a generally continuous parallel spaced relationship.


REFERENCES:
patent: 4931355 (1990-06-01), Radwanski et al.
patent: 5681302 (1997-10-01), Melbye et al.
patent: 5705249 (1998-01-01), Takai et al.
patent: 6096016 (2000-08-01), Tsuji et al.
patent: 0 289 198 (1988-11-01), None
patent: 0 792 629 (1997-09-01), None

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