Porous cellulose acetate membrane and a process for the manufacture of same

Claim 2

A PROCESS FOR THE MANUFACTURE OF A CELLULOSE ACETATE POROUS MEMBRANE WHICH COMPRISES: A. DISSOLVING IN A MAIN ORGANIC SOLVENT CELLULOSE ACETATE HAVING AN ACETYL CONTENT OF 20 TO 62.5% THE CELLULOSE ACETATE BEING DISSOLVED IN THE SOLVENT IN A WEIGHT RATIO OF 5 TO 40% RELATIVE TO THE SOLVENT, B. ADDING TO THE SOLUTION A DILUENT SOLVENT HAVING A BOILING POINT HIGHER THAN THE MAIN SOLVENT, C. ADDING TO THE RESULTING SOLUTION A METAL SALT, WHEREIN THE METAL IS SELECTED FROM GROUPS I-III OF THE PERIODIC TABLE AND HAS AN IONIC RADIUS OF LESS THAN 1.33 A, SAID METAL SALT BEING ADDED TO THE SOLUTION IN A WEIGHT RATIO OF 70 TO 200% RELATIVE TO THE ACETATE TO PROVIDE A HOMOGENEOUS SOLUTION, D. CASING THE RESULTING SOLUTION ONTO A POLISHED PLANE SURFACE TO FORM A THIN FILM, E. REMOVING THE SOLVENT FROM THE FILM BY EVAPORATION AT A TEMPERATURE OF LESS THAN 50*C AND

Claim 3

The process of claim 1 wherein the cellulose acetate is present in a weight ratio of 10 to 15%.

Claim 4

The process of claim 2 wherein the metal salt is present in a weight ratio of 80 to 180%.

Claim 5

The process of claim 1 wherein the diluent solvent is methanol and the metal salt is a member selected from the group consisting of CaCl2.2H2O, MgBr2 and LiCl.

Claim 6

A process for the manufacture of a cellulose acetate porous membrane which comprises: a. dissolving in a main organic solvent cellulose acetate having an acetyl content of 20 to 62.5%, the cellulose acetate being dissolved in the solvent in a weight ratio of 5 to 40% relative to the solvent, b. adding to the solution a diluent solvent having a boiling point higher than the main solvent, and c. adding to the resulting solution a metal salt, wherein the metal is selected from Groups I-III of the Periodic Table and has an ionic radius of less than 1.33 A., said metal salt being added to the solution in a weight ratio of 20 to 200% relative to the acetate to provide a homogeneous solution, d. adding to the solution at least one additive selected from the group consisting of: a. aliphatic monohydric alcohols of C2 - C5 and their acetic acid esters; b. saturated cyclic monohydric alcohols; c. aqueous solution of monosaccharide; d. alkyl esters of aromatic carboxylic acid; e. cycliC hydrocarbons of C5 - C10; and f. ethers; said additives being present in an amount of less than 150% by weight of the solvent for the cellulose acetate, to provide a homogeneous solution, e. casting the resulting solution onto a polished plane surface to form a thin film, f. removing the solvent from the film by evaporation at a temperature of less than 50*C, and g. removing the metal salt from the film by dissolving the salt therefrom to produce a porous filtering membrane.

Claim 7

A process for the manufacture of a cellulose acetate porous membrane which comprises: a. dissolving in a main organic solvent cellulose acetate having an acetyl content of 20 to 62.5%, the cellulose acetate being dissolved in the solvent in a weight ratio of 5 to 40% relative to the solvent, b. adding to the solution a diluent solvent having a boiling point higher than the main solvent, and c. adding to the resulting solution a metal salt, wherein the metal is selected from Groups I-III of the Periodic Table and has an ionic radius of less than 1.33 A., said metal salt being added to the solution in a weight ratio of 20 to 200% relative to the acetate to provide a homogeneous solution, d. adding to the solution at least one additive selected from the group consisting of: a. aliphatic monohydric alcohols of C2 - C5 and their acetic acid esters; b. saturated cyclic monohydric alcohols; c. aqueous solution of monosaccharide; d. alkyl esters of aromatic carboxylic acid; e. cycliC hydrocarbons of C5 - C10; and f. ethers; said additives being present in an amount of less than 150% by weight of the solvent for the cellulose acetate, to provide a homogeneous solution, e. casting the resulting solution onto a polished plane surface to form a thin film, f. removing the solvent from the film by evaporation at a temperature of less than 50*C, and g. removing the metal salt from the film by dissolving the salt therefrom to produce a porous filtering membrane.

Claim 8

The process of claim 5 wherein the cellulose acetate is present in a weight ratio of 10 to 15%.

Claim 9

The process of claim 6 wherein the metal salt is present in a weight ratio of 80 to 180% and the additive is present in a weight ratio of less than 100%.

Claim 10

The process of claim 4 wherein the diluent solvent is selected from the group consisting of methanol, ethanol and propanol and mixtures thereof, and the metal salt is selected from the group consisting of CaCl2.2H2O, MgBr2 and LiCl.

Claim 11

The process of claim 8 wherein the additive is cyclohexanol.

Claim 12

The process of claim 8 wherein the additive is an acetic ester of an aliphatic monohydric alcohol having 2 to 5 carbon atoms.

Claim 13

The process of claim 8 wherein the additive is a member selected from the group consisting of decalin, tetralin and cyclohexane.