Heterogeneous membrane and process for production thereof

Claim 2

A heterogeneous membrane in the form of a flat film, a tubular film or a hollow fiber, said membrane having a microporous layer and a nonporous layer and being formed by melt-extrusion from a thermoplastic crystalline polymer and subsequent stretchings including amorphous stretching; said microporous layer containing pores with a diameter of 0.01 to 50 microns, said nonporous layer containing substantially no pore with a diameter of at least 30 Å and having a thickness of 0.01 to 1 micron, said membrane having at least 3 times as high an apparent oxygen permeability coefficient P(O 2 ) at 25° C. as a nonporous homogeneous membrane of the same material, and said membrane having an oxygen/nitrogen separation coefficient α (O 2 /N 2 ) at 25° C., which is the ratio of the apparent oxygen permeability coefficient P(O 2 ) to the apparent nitrogen permeability coefficient P(N 2 ), of at least 1.2.

Claim 3

The heterogenous membrane of claim 1 wherein one surface of the membrane is substantially a nonporous layer.

Claim 4

The heterogeneous membrane of claim 1 wherein both surfaces of the membrane are substantially a nonporous layer.

Claim 5

The heterogeneous membrane of claim 1 wherein the individual cells in the porous layer are open to one surface of the membrane, but the same cells are not open to both surfaces of the membrane, and a gas which permeates the membrane passes through the nonporous layer at least once without fail.

Claim 6

The heterogeneous membrane of claim 1 wherein the polymer has a maximum degree of crystallinity of at least 30%.

Claim 7

The heterogeneous membrane of claim 1 wherein the polymer is poly-4-methylpentene-1, polypropylene, polyethylene, or polyoxymethylene.

Claim 8

The heterogeneous membrane of claim 1 which is in the form of a hollow fiber having an outside diameter of 5 microns to 1 mm and a wall thickness of 1 micron to 300 microns.

Claim 9

The heterogeneous membrane of claim 1 which is in the form of a flat film having a thickness of 1 micron to 300 microns.

Claim 10

A process for producing a heterogeneous membrane in the form of a flat film, a tubular film or a hollow fiber, said membrane having a microporous layer and a nonporous layer and being formed by melt-extrusion from a thermoplastic crystalline polymer and subsequent stretching; said microporous layer containing pores with a diameter of 0.01 to 50 microns, said nonporous layer containing substantially no pore with a diameter of at least 30 Å and having a thickness of 0.01 to 1 micron, said membrane having at least 3 times as high an apparent oxygen permeability coefficient P(O 2 ) at 25° C. as a nonporous homogeneous membrane of the same material, and said membrane having an oxygen/nitrogen separation coefficient α (O 2 /N 2 ) at 25° C., which is the ratio of the apparent oxygen permeability coefficient P(O 2 ) to the apparent nitrogen permeability coefficient P(N 2 ), of at least 1.2 which comprises (A) melt-extruding a thermoplastic crystalline polymer at a temperature ranging from Tm to (Tm+200° C.) in which Tm represents the melting point of the polymer and a draft ratio of from 20 to 10,000 to form a membrane, (A') amorphous stretching the membrane obtained in step (A) at a temperature of from (Tg-20° C.) to (Tg+50° C.) and then heat-treating it at a temperature of Tg to (Tm-10° C.) in which Tg represents the glass transition temperature of the polymer, (B) stretching the membrane obtained in step (A') at a temperature ranging from (Tg-50° C.) to (Tm-10° C.) and a stretch ratio of from 1.1 to 5.0, and (C) heat-setting the membrane stretched in step (B) at a temperature ranging from the temperature employed in step (B) to Tm.

Claim 11

A process for producing a heterogeneous membrane in the form of a flat film, a tubular film or a hollow fiber, said membrane having a microporous layer and a nonporous layer and being formed by melt-extrusion from a thermoplastic crystalline polymer and subsequent stretching; said microporous layer containing pores with a diameter of 0.01 to 50 microns, said nonporous layer containing substantially no pore with a diameter of at least 30 Å and having a thickness of 0.01 to 1 micron, said membrane having at least 3 times as high an apparent oxygen permeability coefficient P(O 2 ) at 25° C. as a nonporous homogeneous membrane of the same material, and said membrane having an oxygen/nitrogen separation coefficient α (O 2 /N 2 ) at 25° C., which is the ratio of the apparent oxygen permeability coefficient P(O 2 ) to the apparent nitrogen permeability coefficient P(N 2 ), of at least 1.2 which comprises (A) melt-extruding a thermoplastic crystalline polymer at a temperature ranging from Tm to (Tm+200° C.) in which Tm represents the melting point of the polymer and a draft ratio of from 20 to 10,000 to form a membrane, (A') amorphous stretching the membrane obtained in step (A) at a temperature of from (Tg-20° C.) to (Tg+50° C.) and then heat-treating it at a temperature of Tg to (Tm-10° C.) in which Tg represents the glass transition temperature of the polymer, (B) stretching the membrane obtained in step (A') at a temperature ranging from (Tg-50° C.) to (Tm-10° C.) and a stretch ratio of from 1.1 to 5.0, and (C) heat-setting the membrane stretched in step (B) at a temperature ranging from the temperature employed in step (B) to Tm.

Claim 12

The process of claim 9 wherein the membrane obtained in step (A) is heat-treated at a temperature of from Tg to Tm-10° C. prior to step (B).

Claim 13

The process of claim 10 wherein the stretching in step (B) is carried out in 2 to 20 stages.

Claim 14

The process of claim 9 wherein the stretching in step (B) is carried out in 2 to 20 stages.

Claim 15

The process of claim 9 wherein the thermoplastic crystalline polymer has a maximum degree of crystallinity of at least 30%.

Claim 16

The process of claim 9 wherein the thermoplastic crystalline polymer is poly-4-methylpentene-1, polypropylene, polyethylene, or polyoxymethylene.

Claim 17

The process of claim 9 wherein step (A) comprises melt-extruding the thermoplastic crystalline polymer in the form of a hollow fiber, said fiber after stretching having an outside diameter of 5 microns to 1 mm and a wall thickness of 1 micron to 300 microns.

Claim 18

The process of claim 9 wherein step (A) comprises melt-extruding the thermoplastic crystalline polymer in the form of a flat film and wherein the flat film after stretching has a thickness of 1 micron to 300 microns.