Porous PTFE

Claim 2

A substantially cylindrical bar of microporous PTFE characterised in that the material is non-fibrillated and in that the pores within any cylindrical surface contained within the bar and centred about the central longitudinal axis thereof are of substantially uniform size and are substantially uniformly distributed within that surface.

Claim 3

A film of microporous PTFE characterised in that the material is non-fibrillated and in that the pores within any plane substantially perpendicular to the thickness of the film are of substantially uniform size and are substantially uniformly distributed within that plane and all such parallel planes.

Claim 4

A film of microporous PTFE characterised in that the material is non-fibrillated and in that the pores within any plane substantially perpendicular to the thickness of the film are of substantially uniform size and are substantially uniformly distributed within that plane and all such parallel planes.

Claim 5

A process for producing a non-fibrillated, microporous PTFE having a substantially cylindrical outer surface thereto, the process comprising the steps of: providing thermally and compressively untreated PTFE powder; heating the powder to a temperature having a value close to its microcrystalline melting point; cooling the thermally treated material, and breaking the cooled material up into granules; characterised in that the powder particles are of irregular shape and are of a diameter within a predetermined range, and characterised by the steps of: forming the granulated material into a bar having a substantially cylindrical outer surface; applying a substantially radial compressive force to the bar over the full length thereof; relieving the bar of said radial compressive force; heating the compressed granulated material to a temperature above its microcrystalline melting point, and cooling the thermally treated material, the extent of the radial compression being such that, on said subsequent heating of the previously compressed granulated material, the material expands predominantly in a direction opposite to that of the compressive force and the granules fuse together to produce a non-fibrillated material the pores of which, within any cylindrical surface contained within the bar and centred about the central longitudinal axis thereof, are of substantially uniform size and are substantially uniformly distributed within that surface.

Claim 6

A process for producing a non-fibrillated, microporous PTFE having a substantially cylindrical outer surface thereto, the process comprising the steps of: providing thermally and compressively untreated PTFE powder; heating the powder to a temperature having a value close to its microcrystalline melting point; cooling the thermally treated material, and breaking the cooled material up into granules; characterised in that the powder particles are of irregular shape and are of a diameter within a predetermined range, and characterised by the steps of: forming the granulated material into a bar having a substantially cylindrical outer surface; applying a substantially radial compressive force to the bar over the full length thereof; relieving the bar of said radial compressive force; heating the compressed granulated material to a temperature above its microcrystalline melting point, and cooling the thermally treated material, the extent of the radial compression being such that, on said subsequent heating of the previously compressed granulated material, the material expands predominantly in a direction opposite to that of the compressive force and the granules fuse together to produce a non-fibrillated material the pores of which, within any cylindrical surface contained within the bar and centred about the central longitudinal axis thereof, are of substantially uniform size and are substantially uniformly distributed within that surface.

Claim 7

A process as claimed in claim 3 and further comprising the step of forming a film from the cooled bar the plane of which film is perpendicular to the direction of the radial compressive force whereby the pores within any plane substantially perpendicular to the thickness of the film are of substantially uniform size and are substantially uniformly distributed within that plane and all such parallel planes.

Claim 8

A process as claimed in claim 3 or claim 4 in which the diameters of the powder particles are between 0.20 and 60 microns.

Claim 9

A process as claimed in any one of claims 3 to 5 in which the granules are of irregular shape and have a maximum diameter of the order of 400 microns.

Claim 10

A process as claimed in any one of claims 3 to 5 in which the granules are of irregular shape and have a maximum diameter of the order of 250 microns.

Claim 11

A process as claimed in any one of claims 3 to 5 in which the granules are of irregular shape and have a maximum diameter of the order of 100 microns.

Claim 12

A process as claimed in any one of claims 6 to 8 in which the granules, prior to compression, have a bulk density of between 300 and 700 grams/litre.

Claim 13

A process as claimed in any one of claims 3 to 9 in which the compressive force is applied radially inwardly of the bar on the substantially cylindrical outer surface thereof.

Claim 14

A process as claimed in any one of claims 3 to 9 in which the bar is of substantially annular shape in transverse section, the compressive force being applied radially outwardly of the bar on the substantially cylindrical inner surface thereof.

Claim 15

A process as claimed in claim 11 in which a compressive force is also applied radially inwardly of the bar on the substantially cylindrical outer surface thereof.

Claim 16

A process as claimed in any one of claims 3 to 12 in which the granulated material is compressed at a pressure within the range 40 to 900 kgm/cm 2 .

Claim 17

A process as claimed in any one of claims 3 to 13 in which the powder is initially heated to a temperature within the range 320°C to 360°C and in which the second heating is carried out to a temperature of the order of 380°C.

Claim 18

A process as claimed in claim 4 and claims dependent therefrom in which the film is formed by knifing or skiving the bar of material with a blade extending parallel with the central longitudinal axis of the cylinder.

Claim 19

A process as claimed in claim 4 and claims dependent therefrom and further comprising the step of laminating the film of material so formed to a sheet of hydrophilic material.