Process for preparing liquophilic polyamide membrane filter media and product

A process for preparing skinless liquophilic alcohol-insoluble poly-11-amino-undecanamide resin membranes having pores that are substantially uniform from surface to surface which comprises preparing a flowable solution of the alcohol-insoluble liquophobic polyundecanamide resin in a concentration within the range from about 10 to about 20 by weight at a first dissolution temperature of at least 50.degree. C. in a solution in aqueous formic acid containing from about 70 to about 85% formic acid;

• inducing nucleation of the solution by addition of water to the solution 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;
• removing any undissolved resin by filtration;
• spreading the casting solution on a substrate to form a thin film thereof on the substrate;
• cooling the film of casting solution to a second gelation temperature sufficiently lower than the first temperature to precipitate polyamide resin from the casting solution;
• contacting and diluting the film of casting solution with either water or an aqueous solution of formic acid containing up to 50% formic acid by weight, to precipitate polyamide resin from the casting solution in the form of a thin skinless liquophilic membrane;
• washing the membrane to remove solvent;
• and drying the membrane.

A continuous process for preparing skinless liquophilic alcohol-insoluble polyamide membranes which comprises preparing at a first dissolution temperature a solution in a polyamide solvent having a temperature coefficient of solubility within the range from about 0.01 to about 5 weight percent per degree Centigrade 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 7:1 to about 12:1;

• 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;
• removing any undissolved resin by filtration;
• spreading the casting solution on a substrate which is nonporous and whose surface is wetted by the casting solution to form a thin film thereof on the substrate;
• cooling the film of casting solution to a second gelation temperature sufficiently lower than the first temperature to precipitate polyamide resin from the casting solution;
• contacting and diluting the film of casting solution with a nonsolvent liquid to precipitate polyamide resin from the casting solution in the form of a thin skinless liquophilic membrane;
• and continuously washing and drying the resulting membrane, while maintaining constant the relative proportion of solvent and nonsolvent liquid in the bath.

A process for preparing skinless liquophilic alcohol-insoluble polyamide membrane sheets having multimembrane layers, which comprises preparing at a first dissolution temperature at least two starting solutions in a polyamide solvent having a temperature coefficient of solubility within the range from about 0.01 to about 5 weight percent per degree Centigrade 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 7:1 to about 12:1;

• inducing nucleation of the solution by controlled addition to the solutions 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 which may or may not thereafter partially or completely redissolve, thereby forming a casting solution;
• removing any undissolved resin by filtration;
• spreading the casting solutions on a substrate to form thin films thereof on the substrate;
• cooling the films of casting solution to a second gelation temperature sufficiently lower than the first temperature to precipitate polyamide resin from the casting solution;
• contacting and diluting the films of casting solution with a nonsolvent liquid to precipitate polyamide resin from the casting solution in the form of a thin skinless liquophilic membrane;
• washing the resulting two membranes;
• combining the two membranes so formed as a dual layer;
• and drying the dual layer under conditions of restraint to prevent more than minor reduction of the length and width of the membrane;
• the membranes so dried forming a single sheet with particle removal characteristics superior to those of the individual layers.