Patent GB-576362-A (GB)
Title: Improvements in or relating to the manufacture of coatings and shaped articles from synthetic linear polyamides
IPC: C08G69/50
Filed: 1943-06-02
Abstract: Coatings and shaped articles, e.g. films or filaments are formed by reacting a linear polyamide containing hydrogen-bearing amide groups with formaldehyde, the polyamide being in solution in an oxygen-containing acid which is free from formaldehyde reactive groups, forming the solution resulting from the reaction into the coating or shape required before gelation occurs and removing the solvent from the shaped solution.  The reaction is best performed at a temperature between 20 DEG  and 80 DEG  C. and the preferred reaction time is 5-150 minutes.  Removal of solvent from the shaped solution may be effected by evaporation, e.g. drying of a film on a support.  The shaped article or coating may be heated after removal of the solvent to complete conversion to the insoluble state.  The Specification gives lists of suitable raw materials p  for the preparation of the polyamide, which term includes polyesteramides and interpolyamides.  Suitable oxygen-containing acids are formic, acetic, propionic, butyric, phosphoric and mono-, di-or tri-chloracetic acid.  Diluents and partial solvents may be present, e.g. water, hydrocarbons, chlorhydrocarbons or esters such as methyl or ethyl formate or acetate, benzene, toluene or chloroform. Formaldehyde may be used as a solution in water, the acid which dissolves the polyamide, or an inert solvent such as ethyl acetate or benzene; or paraformaldehyde or trioxane may be employed.  The solutions of modified polyamides may be mixed with pigments, e.g. titanium dioxide or carbon black, dyes, cellulose derivatives, resins, e.g. phenol-formaldehyde or sulphonamide-formaldehyde resins, or plasticisers such as methyl-10-phenylolstearate or 1,12-di-(hydroxyphenyl) octadecane. Examples describe (1) reaction of commercial formaldehyde with an interpolyamide from adipic and sebacic acids and hexamethylenediamine in formic acid solution.  The clear solution increased in viscosity and films were cast after 1.5-2.5 hours and before it gelled.  After drying at 100 DEG  C., the films were insoluble in m-cresol and did not melt below 360 DEG  C. (2) Paraformaldehyde was reacted in formic acid with polyhexamethylene adipamide for 24 hours at room temperature.  The mixture was then warmed to about 40 DEG  C. and the viscous solution cast to a transparent film.  After heating at 75 DEG  C. for 12 hours, this was insoluble in cresol and has a relatively high melting point.  (3) Similar to (2), the solution being dry-spun into fibres. (4) Paraformaldehyde was added to a formic acid solution of polyhexamethylene adipamide at 100 DEG  C. and after 15 minutes heating, the solution was cast to a transparent film with relatively high melting point and enhanced power of dye absorption.  (5) Paraformaldehyde was heated on a steam bath for about 30 mins. with a formic acid solution of an interpolymer from hexamethylenediammonium adipate, hexamethylenediammonium sebacate and caprolactam.  The solution was cooled and a film formed by solvent evaporation at 90 DEG  C.  Specifications 461,236, 461,237 and 576,363 are referred to.