Method for producing paper impregnated by a supercritical-pressure fluid, and impregnated, particularly coloured paper

Method for impregnating a dry paper and in particular dyeing, by means of a supercritical-pressure fluid being a fluid in the supercritical or subcritical state, comprising a step of impregnation by putting paper into contact with molecules of interest in the presence of the fluid in the supercritical or subcritical state, said paper comprising, (i) at the core, a polymeric additive introduced in the form of latex and/or (ii) on the surface, a polymeric additive applied in the form of latex, identical or different from the polymeric additive possibly present at the core,

• wherein the molecules of interest are chosen from dye molecules, reactive disperse dyes, optical brightening agents, fluorophores, antioxidants, molecules that absorb ultraviolet rays, surfactants, polymers and paraffinic waxes,
• wherein the dye molecules are formed by a dispersed hydrophobic dye or a mixture of dispersed hydrophobic dyes, the dye or dyes being added at a level of from 0.1 to 10% by dry weight of dye or dyes relative to the weight of the paper,
• said method comprising the steps of:
• a) loading into a reactor, dry paper to be impregnated with the molecules of interest, and a determined quantity of the molecules of interest, followed by the closure of the reactor,
• b) loading a fluid, at the storage pressure of the fluid,
• c) heating the reactor and/or pumping the fluid until obtaining the conditions of pressure and temperature that allow the solubilization of the molecules of interest, in the fluid in the supercritical or subcritical state, and impregnating of the molecules of interest, in the thickness of the paper,
• d) circulating the supercritical-pressure fluid loaded with the molecules of interest, through the paper,
• e) sweeping with the clean supercritical-pressure fluid under conditions of temperature and pressure that are supercritical or subcritical, identical or different from those of the step c in order to eliminate non-fixed molecules of interest,
• f) depressurizing the reactor to precipitate the remaining dye or dyes and allowing the fluid in the supercritical or subcritical state to return to the gaseous state, and
• g) recovering the dry paper, colored at the core and/or on the surface.