Stabilization of photochromic systems

A process of stabilizing a photochromic system comprising (b) a photochromic dye in (a) a polymer matrix against colour fading induced by irradiation, which process comprises incorporating

• (c) (i) a hydroxyphenyl triazine UV absorber into the polymer matrix and/or into a polymer layer covering said polymer matrix and incorporating (c) (ii) a sterically hindered alkoxyamine light stabilizer into the polymer matrix,
• wherein the hydroxyphenyl triazine UV absorber (i) is of formula
• wherein
• R28 is (CH2—CH2—O—)n—R29;
• —CH2—CH(OH)—CH2—O—R29;
• or —CH(R30)—CO—O—R40;
• n is 0 or 1;
• R29 is C1-C13alkyl or C2-C20alkenyl or C6-C12aryl or CO—C1-C18alkyl;
• R30 is hydrogen or C1-C8alkyl;
• R40 is C1-C12alkyl or C2-C12alkenyl or C5-C6cycloalkyl, wherein the sterically hindered alkoxyamine is a compound having a molecular weight of 1500-15000 g/mol, and is compound of formula (2g)
• in which the index m18 ranges from 1 to 15;
• R12 is C2-C12alkylene, C4-C12alkenylene, C5-C7cycloalkylene-di(C1-C4alkylene), C1-C4alkylenedi(C5-C7cycloalkylene), phenylenedi(C1-C4alkylene) or C4-C12alkylene interrupted by 1,4-piperazinediyl, —O— or >N—X1 with X1 being C1-C12acyl or (C1-C12alkoxy)carbonyl or having one of the definitions of R14 given below except hydrogen;
• or R12 is a group of the formula (2g′) or (2g″);
• X2 being C1-C18alkyl, C5-C12cycloalkyl which is unsubstituted or substituted by 1, 2 or 3 C1-C4alkyl;
• phenyl which is unsubstituted or substituted by 1, 2 or 3 C1-C4alkyl or C1-C4alkoxy;
• C7-C9phenylalkyl which is unsubstituted or substituted on the phenyl by 1, 2 or 3 C1-C4alkyl;
• and
• the radicals X3 being independently of one another C2-C12alkylene;
• the radicals A are independently of one another —OR13, —N(R14)(R15) or a group of the formula (2g′″);
• R13, R14 and R15, which are identical or different, are hydrogen, C1-C18alkyl, C5-C12cycloalkyl which is unsubstituted or substituted by 1, 2 or 3 C1-C4alkyl;
• C3-C18alkenyl, phenyl which is unsubstituted or substituted by 1, 2 or 3 C1-C4alkyl or C1-C4alkoxy;
• C7-C9-phenylalkyl which is unsubstituted or substituted on the phenyl by 1, 2 or 3 C1-C4alkyl;
• tetrahydrofurfuryl or C2-C4alkyl which is substituted in the 2, 3 or 4 position by —OH, C1-C8alkoxy, di(C1-C4alkyl)amino or a group of the formula (2gIV);
• with Y being —O—, —CH2—, —CH2CH2— or >N—CH3,
• or —N(R14)(R15) is additionally a group of the formula (2gIV);
• X is —O— or >N—R16;
• R16 is hydrogen, C1-C18alkyl, C3-C18alkenyl, C5-C12cycloalkyl which is unsubstituted or substituted by 1, 2 or 3 C1-C4alkyl;
• C7-C9-phenylalkyl which is unsubstituted or substituted on the phenyl by 1, 2 or 3 C1-C4alkyl;
• tetrahydrofurfuryl, a group of the formula (2gV),
• or C2-C4alkyl which is substituted in the 2, 3 or 4 position by —OH, C1-C8alkoxy, di(C1-C4alkyl)amino or a group of the formula (2gIV);
• R11 has one of the definitions given for R16;
• and
• the radicals B have independently of one another one of the definitions given for A,
• wherein the photochromic dye of component (b) is present in an amount of 0.001 to 10% by weight, with respect to the total weight of the polymeric material (a) and is a naphthopyran of formula
• where R is hydrogen;
• C1-C6alkyl;
• C1-C6alkoxy;
• —NR′R″;
• —NO2;where R′ and R″ independently are hydrogen or C1-C12alkyl, C4-C12cycloakyl, C7-C13phenylalkyl or together are tetramethylene or pentamethylene or O-interrupted tetramethylene and
• wherein
• a ratio of component (c) to component (b) is in the range of 0.01 to 100 parts of component (c) per part of component (b).