A mixture comprising: a) from 0% to 95% of aromatic compounds and/or polycyclic aromatic compounds, said polycyclic aromatic compounds, if present, always being in an amount less than 10% with respect to component (a); b) from 0% to 85% of a mixture containing aliphatic compounds and a content of aromatic compounds lower than 30% with respect to (b); c) from 0% to 20% of an acetate component; d) from 1% to 50% of a mixture of compounds containing keto groups; with the proviso that said solvent mixture contains at least three components, one of which is (d) and the other two selected from (a), (b) or (c) and that their sum is always 00%; and with the proviso that said mixture has a solubility, measured with the Hansen parameters, characterized in that the dispersion force component of the solubility δd varies from 17 to 20 Mpa{circumflex over ( )}0.5 the polar force component of the solubility δp varies from 0.65 to 5 Mpa{circumflex over ( )}0.5, and the strength of the hydrogen bond component of the solubility δh varies from 0.65 to 5 MPa{circumflex over ( )}0.5.