A diisopropylnaphthalene mixture containing 50% or more of 2,7-isomer is substantially odorless, has a low viscosity and exhibits a high dissolving power particularly for an electron-donating color former including a black color former. By coating of micro-capsules of an ink comprising the solvent and a color former on a substrate, a carbonless copying paper which is odorless and excellent in color developing speed including that at lower temperatures, can be obtained.