Method for manufacturing a film comprising cavities with determination of stretch, density, thickness and/or porosity profiles of the film

A method of manufacturing a film including cavities and formed from a polymer in which a cavitating agent is dispersed, said method including a step of extruding the polymer on a production line equipped with adjustment actuators for adjusting thickness of the extruded film, and a step of stretching the film, as well as a step consisting in establishing a mapping function of the film, wherein:

• a first mass-per-unit-area sensor measures a transverse mass-per-unit-area profile of the film as not stretched;
• a second mass-per-unit-area sensor measures a transverse mass-per-unit-area profile of the film as stretched by said stretching;
• a cavitating agent mass-per-unit-area sensor which measures a transverse mass-per-unit-area profile of cavitating agent;
• a computer unit computes said mapping function of the film as stretched on the basis of said transverse mass-per-unit-area profiles;
• said computer unit computes a stretch profile of the film as stretched on the basis of said mapping function and of said transverse mass-per-unit-area profiles;
• said computer unit computes a characteristic transverse profile that is characteristic of the film on the basis of said stretch profile and of a transverse profile of the concentration by mass of cavitating agent in the film as stretched that makes it possible to take into account the distribution of the cavities in the film;
• and
• said adjustment actuators are controlled as a function of said characteristic transverse profile.