Process for preparing hydrophilic polyamide membrane filter media and product

A process for preparing skinless hydrophilic alcohol-insoluble polyhexamethylene adipamide resin membranes having a substantially zero contact angle with water and having pores that are substantially uniform from surface to surface which comprises preparing a flowable solution of the alcohol-insoluble polyhexamethylene adipamide resin in a concentration within the range from about 10% to about 18% by weight in an aqueous formic acid solution containing from about 63% to about 72% formic acid by weight;

• inducing nucleation of the resin solution by adding water thereto while controlling resin and formic acid concentration, temperature, rate of addition of water and degree of agitation to obtain a visible precipitate of resin particles, thereby forming a casting solution;
• spreading the casting solution on a polyester resin substrate to form a thin film of resin solution thereon;
• contacting and diluting the film of casting resin solution with an aqueous solution containing from 37 to 55% formic acid and thereby precipitating the polyamide resin from the casting resin solution as a thin skinless hydrophilic membrane;
• washing the membrane to remove solvent;
• and drying the membrane.

A process for preparing multilayer skinless hydrophilic alcohol-insoluble polyamide membranes that are readily wetted by water which comprises preparing a solution of an alcohol-insoluble polyamide resin selected from the group consisting of polyhexamethylene adipamide, polyhexamethylene sebacate, and poly-.epsilon.-caprolactam in a polyamide resin solvent;

• inducing nucleation of the solution by controlled addition to the solution of a nonsolvent for the polyamide resin, under controlled conditions of concentration, temperature, addition rate, and degree of agitation to obtain a visible precipitate of polyamide resin particles, thereby forming a casting solution;
• spreading the casting solution on a substrate to form a thin film thereof on the substrate;
• contacting and diluting the film of casting solution with a nonsolvent liquid for the polyamide resin, thereby precipitating polyamide resin from the casting solution in the form of a thin skinless membrane;
• washing the membrane to remove solvent;
• placing the washed membrane while still wet in contact with at least one other wet washed membrane;
• and then drying the juxtaposed membranes while maintaining such contact, thereby obtaining a multilayer membrane in which the separate membranes are integral layers thereof.

A process for preparing skinless hydrophilic alcohol-insoluble polyamide membranes that are readily wetted by water which comprises preparing a solution in a polyamide solvent of an alcohol-insoluble polyamide resin having a ratio CH.sub.2 :NHCO of methylene CH.sub.2 to amide NHCO groups within the range from about 5:1 to about 7:1;

• inducing nucleation of the solution by controlled addition to the solution of a nonsolvent for the polyamide resin, under controlled conditions of concentration, temperature, addition rate, and degree of agitation to obtain a visible precipitate of polyamide resin particles, thereby forming a casting solution;
• spreading the casting solution on a substrate to form a thin film thereof on the substrate;
• contacting and diluting the film of casting solution with a nonsolvent liquid for the polyamide resins, thereby precipitating polyamide resin from the casting solution in the form of a thin skinless hydrophilic membrane;
• washing the membrane to remove solvent;
• and drying the resulting membrane.

A process for preparing skinless hydrophilic alcohol-insoluble polyamide membranes that are readily wetted by water which comprises preparing a solution in a polyamide solvent of a mixture of polyamide resins of which at least one is an alcohol-insoluble polyamide resin having a CH.sub.2 :NHCO ratio of methylene CH.sub.2 to amide NHCO groups within the range from about 5:1 to about 7:1;

• and at least one is an alcohol-insoluble polyamide resin having a CH.sub.2 :NHCO ratio exceeding 7:1, in proportions such that the average CH.sub.2 :NHCO ratio is within the range from about 5:1 to about 7:1;
• inducing nucleation of the solution by controlled addition to the solution of a nonsolvent for the polyamide resin, under controlled conditions of concentration, temperature, addition rate, and degree of agitation to obtain a visible precipitate of polyamide resin particles, thereby forming a casting solution;
• spreading the casting solution on a substrate to form a thin film thereof on the substrate;
• contacting and diluting the film of casting solution with a nonsolvent liquid for the polyamide resins, thereby precipitating polyamide resin from the casting solution in the form of a thin skinless hydrophilic membrane;
• washing the membrane to remove solvent;
• and drying the resulting membrane.

A process for preparing skinless hydrophilic alcohol-insoluble polyamide resin membranes having pores that are substantially uniform from surface to surface which comprises preparing a flowable solution of the alcohol-insoluble polyamide resin in a concentration within the range from about 10% to about 22% by weight in an aqueous formic acid solution containing from about 60% to about 72% formic acid by weight;

• inducing nucleation of the resin solution by adding water thereto while controlling resin and formic acid concentration, temperature, rate of addition of water and degree of agitation to obtain a visible precipitate of resin particles, thereby forming a casting solution;
• spreading the casting solution on a polyester resin substrate to form a thin film of resin solution thereon;
• contacting and diluting the film of casting resin solution with an aqueous solution containing from 37 and 55% formic acid and thereby precipitating the polyamide resin from the casting resin solution as a thin skinless hydrophilic membrane;
• washing the membrane to remove solvent;
• and drying the membrane.

A process for preparing multilayer skinless hydrophilic alcohol-insoluble polyamide membranes that are readily wetted by water which comprises preparing a solution in a polyamide resin solvent of an alcohol-insoluble polyamide resin having a ratio CH.sub.2 :NHCO of methylene CH.sub.2 to amide NHCO groups within the range from about 5:1 to about 7:1;

• inducing nucleation of the solution by controlled addition to the solution of a nonsolvent for the polyamide resin, under controlled conditions of concentration, temperature, addition rate, and degree of agitation to obtain a visible precipitate of polyamide resin particles, thereby forming a casting solution;
• spreading the casting solution on a substrate to form a thin film thereof on the substrate;
• contacting and diluting the film of casting solution with a nonsolvent liquid for the polyamide resin, thereby precipitating polyamide resin from the casting solution in the form of a thin skinless membrane;
• washing the membrane to remove solvent;
• placing the washed membrane while still wet in contact with at least one other wet washed membrane;
• and then drying the juxtaposed membranes while maintaining such contact, thereby obtaining a multilayer membrane in which the separate membranes are integral layers thereof.