Manufacture of polyamide film-forming materials containing magnesium silicate

A process for the continuous manufacture of .epsilon.-caprolactam polymers for high-grade transparent thin film, which comprises

• a. agitating .epsilon.-caprolactam continuously in a first reaction zone under polyamide-forming conditions at temperatures of from 240.degree. to 290.degree. C until at least 20% of the .epsilon.-caprolactam has reacted, but the melt viscosity of said reacted .epsilon.-caprolactam is still less than 500 poises,
• b. adding magnesium silicate having a particle size of less than 30 .mu.m to the melt to give magnesium silicate concentrations in the reaction mixture of from 0.0005 to 0.5%, and
• c. polymerizing the .epsilon.-caprolactam melt at atmospheric pressure or in vacuo to completion until the relative viscosity is from 2.4 to 3.3, said viscosity being calculated as the ratio of the flow times of a 1% solution of polyamide in 96% sulfuric acid and pure 96% sulfuric acid at 25.degree. C in a capillary viscometer.