Microcapsules and their use

Microcapsules comprising a wall containing an internal phase comprising at least one leuco dye, at least one photopolymerisation initiator and at least one photopolymerisable monomer, characterized in that the photopolymerisable monomer corresponds to the following formula

• A[-NHCO-X-L.sub.1 -(OCO-CR.sub.1 .dbd.CH.sub.2).sub.n ].sub.m
• wherein
• A denotes a tri- to hexa-valent organic group having the following meanings:
• a) a saturated hydrocarbon group having 5 to 25 carbon atoms or
• b) ##STR7## wherein A.sub.1 stands for a straight chained or branched aliphatic group having 2 to 20 carbon atoms and optionally containing 1 to 3 oxygen atoms, an aromatic group having 6 to 24 carbon atoms, an araliphatic group having 7 to 26 carbon atoms or a cycloaliphatic group having 6 to 26 carbon atoms,
• R.sub.3 and R.sub.4 denote hydrogen or methyl,
• A.sub.2 denotes a saturated hydrocarbon group having 5 to 25 carbon atoms,
• o denotes a number from 0 to 5 and
• p denotes a number from 3 to 6, or
• c) ##STR8## wherein A.sub.1, A.sub.2, R.sub.3, R.sub.4, o and p have the meanings indicated above,
• X denotes O or NR.sub.2,
• L.sub.1 denotes a divalent or trivalent aliphatic hydrocarbon group whose carbon chain may be interrupted by 1 to 3 oxygen atoms,
• R.sub.1 denotes hydrogen or methyl,
• R.sub.2 denotes hydrogen or C.sub.1 -C.sub.4 -alkyl,
• n stands for 2 and
• m stands for a number from 3 to 6.