Nonwoven sheets of filaments of anisotropic melt-forming polymers and method thereof

Claim 2

A strong dimensionally stable high-melting nonwoven sheet comprised of filaments from an optically anisotropic melt-forming polymer, the filaments being disposed in multiple directions within the plane of the sheet and being self-bonded at a plurality of cross-over points, the filaments between bond points being substantially undeformed, the fibrous sheet having a tensile strength in at least one direction of at least 1.0 N/cm//g/m 2 and having a tensile strength in a direction perpendicular to that direction which is at least 25% of the strength in that direction.

Claim 3

The product of claim 1 wherein said fibrous sheet has a tensile strength in at least one direction of at least 1.0 N/cm//g/m 2 and a tensile strength in a direction perpendicular to that direction which is at least 50% of the strength in that direction.

Claim 4

The product of claim 1 wherein said filaments are in the form of staple fiber.

Claim 5

The product of claim 1 wherein said fibrous sheet has a tensile strength in at least one direction of at least 2.0 N/cm//g/m 2 .

Claim 6

The product of claim 1 wherein the polymer is a polyester.

Claim 7

The product of claim 1 wherein said fibrous sheet has an elongation at maximum load during testing of at least 2.5%.

Claim 8

The product of claim 1 wherein said fibrous sheet has an elongation at maximum load during testing of at least 4.5%.

Claim 9

A process for preparing strong dimensionally stable high-melting nonwoven fibrous sheets comprising: (1) melt spinning a plurality of filaments from an optically anisotropic melt-forming polymer, (2) depositing the filaments on a collecting surface in the form of a loose web within which the filaments are substantially separated except for contact at cross-over points and are disposed in multiple directions within the plane of the web, (3) hot-pressing the web at a pressure, temperature and for a time sufficient to fuse the filaments at the cross-over points while avoiding substantial deformation of the filaments between cross-over points, and (4) removing the pressure from the hot-pressed web and heating it in a purged inert atmosphere at a temperature below the filament flow temperature and for a time sufficient to increase tensile strength of the sheet by at least 25%.

Claim 10

A process for preparing strong dimensionally stable high-melting nonwoven fibrous sheets comprising: (1) melt spinning a plurality of filaments from an optically anisotropic melt-forming polymer, (2) depositing the filaments on a collecting surface in the form of a loose web within which the filaments are substantially separated except for contact at cross-over points and are disposed in multiple directions within the plane of the web, (3) hot-pressing the web at a pressure, temperature and for a time sufficient to fuse the filaments at the cross-over points while avoiding substantial deformation of the filaments between cross-over points, and (4) removing the pressure from the hot-pressed web and heating it in a purged inert atmosphere at a temperature below the filament flow temperature and for a time sufficient to increase tensile strength of the sheet by at least 25%.

Claim 11

The process of claim 8 wherein the web is hot-pressed at a pressure of at least about 7 kPa gauge, a temperature above the fiber stick temperature and for a time less than about 10 minutes.

Claim 12

The process of claim 8 wherein the melt-spun filaments are converted to staple fiber before being deposited in the form of a loose web on the collecting surface.