A method of increasing the light fatigue resistance of a photochromic composition and photochromic composition

Abstract

 An organic photochromic composition comprises spiro - [indoline-2,3'-[3H] -napht [2,1-b] [1.4] oxazine] dye - (spirooxazine dye) and unconventional ultraviolet stabilizers. The ultraviolet stabilizers provide for a good light fatigue resistance of the spirooxazine (S.O.) dye and will not hinder the photocolorability of the photochromic composition. The unconventional ultraviolet stabilizers belong to the class of hindered amine light stabilizers (HALS) and excited state quenchers.

Description

[0001] The invention relates to a method of increasing the light fatigue resistance of a photochromic composition and a photochromic composition. This invention relates more particularly to an organic photochromic composition comprising spiro [indofine-2;3'-[3H] -napht [2,1-b] [1,4] oxazine] - (S.O.) dye and unconventional ultraviolet (UV) stabilizers.

[0002] Compounds which undergo reversible photo-induced color changes are termed photochromic compounds. When subjected to ultraviolet tight or visible irradiation, these photochromic compounds change their transmission. They subsequently revert to their original color state when they are subjected to a different wavelength of radiation or when the initial light source is removed.

[0003] Although the organic photochromic materials have been known for over 50 years, they have not had widespread industrial or commercial use. This is primarily due to the irreversible decomposition phenomenon, generally known as light fatigue. Repeated exposure to light causes the photochromic materials to lose their photochromism.

[0004] It is thought that right or heat or both light and heat are responsible for the photodecomposition of organic photochromic compounds. Thus, many people have tried to increase the light fatigue resistance of the compounds by adding numerous conventional antioxidants or ultraviolet light absorbers. For example, U.S. Patent No. 3,212,898 teaches the use of conventional UV absorbers such as benzophenone and benzotriazole to increase the photochromic life of photochromic benzospiropyran compounds. Similarly, U.S. Patent No. 3,666,352 teaches the use of conventional UV light absorbers in photochromic mercury thiocarbazonate lenses, transparent to radiation of wavelengths greater than 420 nm and opaque to radiation of wavelengths less than 420 nm in order to substantially increase the durability of the lenses against photochemical degradation.

[0005] One class of organic photochromic compounds, spiro - [indoline-2,3'-[3H]-naphth [2,1-b] [1,4] oxazine] dyes (S.O. dyes) are known to have good light fatigue resistance. In general, the light fatigue resistance of the spirooxazine compounds is about 100 times better than the closely related spiropyrans. This class of photochromic compounds has been disclosed in U.S. Patent Nos. 3,562,172; 3,578.602; 4,215,010; 4,342.668; and 4,440,672.

[0006] The precise mechanism for photodecomposition of S.O. dyes is not yet fully understood. Although some circumstantial evidence indicates that oxygen is involved in the photodecomposition process, the traditional antioxidants - (aryl amines and hindered phenols) do not improve the light fatigue resistance of S.O. dyes. The conventional UV stabilizers, substituted benzophenones and benzotriazoles, cause a small improvement in the light fatigue resistance of S.O. dyes, but they cannot be used effectively since they create a screening effect by absorbing UV radiation strongly in the region where the S.O. dyes absorb UV radiation. By competing with the S.O. dyes to absorb UV light these conventional stabilizers substantially decrease the effective light intensity for S.O. dye activation. Furthermore, some of the conventional UV stabilizers are detrimental to S.O. dyes under certain conditions.

[0007] In addition, the presence of acids has a deleterious effect on S.O. compounds. Acids may be in the plastic host material from which the photochromic article is made, such as PVC or cellulosics. The acids are usually generated either thermally during the forming process, or photochemically during use of the photochromic article. The S.O. dye solution becomes a pinkish to reddish color in the presence of even a minute amount of acid, and the solution ceases to show a photochromic effect. The pinkish to reddish color is likely due to the formation of a complex between the S.O. compound and acid. A base must be used to neutralize the acid and to restore the original colorless or light blue color.

[0008] U.S. Patent No. 4,440,672 discloses the use of organonickel complex stabilizers to improve the light fatigue resistance of the photochromic compounds. However, these organonickel complexes do not have the ability to neutralize acids which may be present.

[0009] It is therefore an object of this invention to provide a method of increasing the light fatigue resistance of photochromic compositions. This object is solved by the method according to claim 1. Further advantageous features are evident from the subclaims.

[0010] It is a further object of this invention to provide a photochromic composition resistant to fatigue. This object is solved by the photochromic composition according to claim 11. Further advantageous features of this composition are evident from the subclaims.

[0011] The problems of the prior art are overcome by the discovery that a group of unconventional UV stabilizers will improve the light-fatigue resistance of S.O. dyes, while not affecting their photocolorability. These unconventional UV stabilizers belong to the class of hindered amine light stabilizers (HALS) and excited state quenchers. Hindered amine light stabilizers offer an advantage over organometallic complex stabilizers in their ability to neutralize acid, and to thus improve the light-fatigue resistance and preserve the original color of the S.O. dyes. It is preferable to use the hindered amine light stabilizers together with excited state quenchers in the organic photochromic compound of the invention; this combination has a synergetic effect in improving the light fatigue resistance of the S.O. compounds.

[0012] These UV stabilizers will not hinder the photocolorabil- ⁱty of S.O. dyes, since they have a minimal absorption in the UV region where S.O. dyes absorb. The S.O. dye and UV stabilizers may be incorporated within optically clear plastics to make a photochromic element suitable for a photochromic sunglass lens, ski goggle, or other plastics to render them photochromic.

[0013] Accordingly, the present invention improves the light fatigue resistance of an organic photochromic composition containing S.O. dye.

[0014] The present invention further improves the light fatigue resistance of these photochromic compositions without hindering their photocolorability.

[0015] Besides this, the present invention allows to use such improved photochromic compositions to fabricate photochromic articles such as sunglasses, ophtalmic lenses, ski goggles, window coatings, toys, fabrics, and the like.

[0016] Other objects and further scope of applicability of the present invention will become apparent from the detailed description to follow.

[0017] In the following, a preferred embodiment of the invention will be described.

[0018] The organic photochromic composition of the present invention comprises: a) spiro [indoline-2,3'-[3H]-naphth - [2,1-b] [1,4] oxazine] dye (spirooxazine dye), having the structural formula

wherein one of R₁, R₂ and R₃ is hydrogen, halogen, lower alkyl, or lower alkoxy and the others are hydrogen; R₄ and R₅ are hydrogen, lower alkyl, lower alkoxy, halogen, or trifluoromethyl; and R, is lower alkyl; and, b) an unconven- tonal UV stabilizer or stabilizers. As used throughout the specification and claims, "lower" means up to 12 carbon atoms (n =_1-12) in the free alkyl or alkoxy radical group, wherein the alkyl free radical group has the structural formula of C_nH_2n+1, and the alkoxy free radical group has the structural formula of C_nH_2n+1O. Preferably, the UV stabilizer comprises a hindered amine light stabilizer (HALS). The preferred hindered amine light stabilizers comprise derivatives of tetramethyl piperidine. Most preferably, the UV stabilizer comprises a combination of a hindered amine light stabilizer and an excited state quencher. Preferably, the excited state quencher comprises an organonickel complex light stabilizer. For a description of hindered amine light stabilizers and excited state quenchers, see the following four articles in Modem Plastics Encyclooedia. which are herein incorporated by reference: 1) Shute, Raymond, "Antioxidants," pp. 102-103 (1983-1984); 2) Li, S.S., "Ultraviolet Stabilizers," pp. 174-177 (1983-1984); 3) Patel, A., "Antioxidants," pp. 106-107 (1984-1985); and 4) Stretanski, J.A., "Ultraviolet Stabilizers," pp. 179-180 - (1984-1985).

[0019] Between 0.1 and about 15% by weight of the S.O. dye and between 0.01 and about 5% by weight of the HALS stabilizer or combined UV stabilizers, depending on their solubility, can be incorporated into a plastic article having enhanced light fatigue resistance. The SO dye and UV stabilizers may be mixed in a solution with an optically clear polymer which is thereafter cast as a film, sheet, lens, or toy, or a polymer which is injection molded or otherwise shaped into a film or lens; or a prepolymerized film or lens containing the UV stabilizers may be immersed in a dye bath comprising S.O. dye dissolved in a solution of organic solvents such as alcohol, toluene, halogenated hydrocarbon or the like. Other methods of blending the UV stabilizers with the S.O. dye and polymers, such as coating or laminating may also be employed.

[0020] One hindered amine light stabilizer, useful in the organic photochromic composition of the invention, comprises the structural formula

wherein R₁, R₂, R₄, R₅, R₆, R7, R, and R,_o are lower alkyl; R₃ and R, are lower alkyl or hydrogen; and n= 1-12; and in parficular, the hindered amine light stabilizer is Bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate, wherein R₁, R₂, R., R₅, R,, R,, R, and R,_o are methyl, R₃ and R, are hydrogen, and n=8, sold under the tradename of Tinuvin 770, and obtained from the Ciba-Geigy Corporation; and also in particular, the hindered amine light stabilizer is Bis (1,2,2,6,6-pentamethyl-4-piperidinyl sebacate, wherein R₁, R₂, R₄, R₅, R₆, R₇, R, and R₁₀ are methyl, R₃ and R, are methyl, and n = 8, sold under the tradename of Tinuvin 765, and obtained from the Ciba-Geigy Corporation.

[0021] Another hindered amine light stabilizer which is useful in the organic photochromic composition of the invention comprises the structural formula

wherein R,, R₂, R₄, R₅, R₆, R₇, R₉, R₁₀ R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, and R_". are lower alkyl; and R₃ and R₃ are lower alkyl or hydrogen; and in particular, the hindered amine light stabilizer is di(1,2,2,6,B-pentamethyl-4-PiPeridinyl)-bytyl(3', 5'-diterbutyi-4-hydroxybenzyl) malonate, wherein R₁, R₂, R₄, R_s, R₆, R₇, R₉, R₁₀ R₁₂ R₁₃ R₁₄, R₁₅, R₁₆, and R₁₇ are methyl, R₁₁ is butyi, and R₃ and R, are methyl, sold under the tradename of Tinuvin 144, and obtained from the Ciba-Geigy Corporation.

[0022] Another hindered amine light stabilizer which is useful in the organic photochromic composition of the invention comprises the structural formula

wherein R₁, R₄, R₅, R₁₁, and R₁₆ are lower alkyl or hydrogen; R₂, R₃, R₆, R₇, R₈, R₉ R₁₀, R₁₂, R₁₃, R₁₄, R₁₅, R₁₇, and R₁₈ are lower alkyl; n₁=1-12; and n₂=1-15; and in particular, the hindered amine light stabilizer is poly[(6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-fiazine-2,4-diyl) (1,6-[2,2,6,6-tetramethyl-4-piperidinyl]amino-hexamethylene)], wherein R₂ R₃, R₆, R₇ R₈, R₉, R₁₀, R₁₂,=, R_13, R_14, R_15, R_17, and R₁₈ are methyl, R₁, R., R₅, R₁₁, and R₁₆ are hydrogen, and n,-6, sold under the tradename Chimassorb 944, and obtained from the Ciba-Geigy Corporation.

[0023] Another hindered amine light stabilizer which is useful in the organic photochromic composition of the invention comprises the structural formula

wherein R₁, R₂, R₄, R_s, R₆, R,, R₉, and R₁₀ are lower alkyl; R₃ and R. are lower alkyl or hydrogen; n₁ =1-12; and n₂ =1- . ₁5; and in particular, the hindered amine light stabilizer is pofy[[6-(morhoiino)-s-triazine-2,4-diyl][1,6-(2,2,6,6-tetramethyl-4-piperidyl)amino]hexamethylenel, wherein R_1, R_2, R_4, R_5, R_6, R,, R_9, and R₁₀ are methyl, R₃ and R₆ are hydrogen, and n₁=₆, sold under the tradename Cyasorb 33₄6, and obtained from the American Cyanamid Corporation.

[0024] Another hindered amine light stabilizer which is useful in the organic photochromic composition of the invention comprises the structural formula

wherein R,, R₂, R,, and R₄ are lower alkyl; and n =1-15; and in particular, the hindered amine light stabilizer is a dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyi-1-piperidineettranoi, wherein R,, R₂, R₂ and R₄ are methyl, sold under the tradename Tinuvin 622, and obtained from the Ciba-Geigy Corporation.

[0025] Other hindered amine light stabilizers which are useful in the organic photochromic composition of the invention include a hindered amine right stabilizer having the structural formula (C₂₅H₅₂N₄)_n, wherein n =1-15, sold under the tradename of Spinuvex A-36, and obtained from the Borg-Wamer Corporation; and a hindered amine light stabilizer sold under the tradename of Hostavin TMN20, and obtained from the American Hoechst Corporation.

[0026] Ultraviolet stabilizers, belonging to the class of excited state quenchers, which are useful in the organic photochromic compound of the invention, include complexes of Ni²⁺ ion with some organic ligand, cobalt (III) tris-di-n-butyi- dithiocarbamate, cobalt (II) diisopropyldithiocarbamate (Co DIPDTP), and nickel diisopropyldithiophosphate (Ni DIPDTP).

[0027] The preferred excited state quenchers are singlet oxygen quenchers, and in particular, complexes of Ni²⁺ ion with some organic ligand. These Nr²⁺ complexes are normally used in polyolefins to provide protection from photo-degradation. Most preferably, the Ni²⁺ complexes are: [2,2'-Thiobis [4-(1,1,3,3-tetramethylbutyl) phenolato] (butylamine)] nickel, having the structural formula

sold under the tradename of Cyasorb UV 1084, and obtained from the American Cyanamid Company; Nickel [0-ethyl (3,5-di-tert-butyl-4-hydroxybenzyl)] phosphonate, having the structural formula

sold under the tradename of Irgastab 2002, and obtained from the Ciba-Geigy Corporation; Nickel dibutyldithiocarbamate, having the structural formula

sold under the tradename of Rylex NBC, and obtained from E.I. duPont de Nemours & Company; Bis [2,2'-thiobis-d-(1.1.3.3-tetrarnethytbuiyl) phenotato] nickel, having the structural formula

sold under the tradename of UV-Chek AM 10₁, and obtained from the Ferro Corporation; Nickel di-isopropyl dithiophosphate (Ni DIPDTP), having the stuctural formula

and other Ni²⁺ complexes sold under the tradenames of UV-Chek AM 105, UV-Chek AM 126, and UV-Chek AM 205 which can also be obtained from the Ferro Corporation.

[0028] The preferred S.O. dyes for use in accordance with the invention are 1,3,3,4,5-pentamethyl-9'-methoxy-spiro - [indoline-2,3'-[3H]-naphfh [2,1-b] [1,4] oxazine; 1,3,3,5,6-pentamethyl-9'-methoxy-spirooxazine;

1,3,3-trimethyl-5'-methoxy spirooxazine;

1,3,3-trimethyl-5-methoxy spirooxazine;

1,3,3,4,5-Pentamethyl-8'-bromo spirooxazine;

1,3,3,5,6-pentamethyl-8'-brorrm spirooxazine;

1,2,3,3,4,5-hexamethyl-9'-methoxy spirooxazine;

1,2,3,3,5,6-hexamethyl-9'-methoxy spirooxazine;

1,3,3-trimethyi-4-trifluoromethyl-9'-methoxy spirooxazine;

1,3,3-trimethyl-6-trifluoromethyl-9'-methoxy spirooxazine;

1,3,3-trimethyl-4-trifluoromethyl-5'-methoxy spirooxazine; and 1,3,3-trimethyl-6-trifluoromethyl-5'-methoxy spirooxazine.

[0029] The preferred plastic hosts are cellulose acetate butyrate (CAB); CR-39™ , a diethylene glycol bis (allyl carbonate) obtained from PPG Industries, Inc.; Lexan™, a polycarbonate resin condensation product of bisphenol-A and phosgene, obtained from General Electric; Plexiglas ^TM, a polymethyl methacrylate obtained from the Rohm and Haas Company; polyvinyl chloride; and polyoleflns.

[0030] The invention is further illustrated by the following nonlimiting examples.

Examples 1-8

[0031] Eight cellulose acetate butarate (CAB) samples having a thickness of 0,43-0,48 mm (17-19 mls), containing 0.4% by weight of a mixture of 1,2,3,3,4,5-and 1,2,3,3,5,6-hexamethyl-9'-methoxy S.O. isomers, with and without hindered amine light stabilizers (HALS) were prepared by casting a methylene chloride solution of CAB. Four successive castings were needed to obtain the desired thickness with good optical appearance. The control sample contained no HALS. The seven other samples contained various hindered amine light stabilizers in an arbitrary amount of 0.4% by weight. The samples were subjected to a 20-hour cycle Fadeometer exposure testing. After five cycles, the control sample without HALS lost all its photochromism while the samples with HALS still showed good photochromism. The specific HALS used and the percentage of residual photocolorability of the CAB samples after 100 hours of Fadeometer exposure is shown in Table 1.

[0032] 

Examples 9-10

[0033] Two CAB sheet samples (1,52 mm/60mls) were made by injection molding. One of the CAB sheet samples had 0.2% by weight of a mixture of 1,2,3,3,4,5-and 1,2.3,3,5,6-hexamethyl-9'-methoxy spirooxazine isomers and 0.2% by weight of UV-Chek AM-205 as an excited state quencher. The other sample also had 0.2% by weight Tinuvin 622 as a hindered amine light stabilizer in addition to the S.O. dye and the UV-Chek AM-205. The sample without the HALS lost all of its photochromism after 15 20-hour Fadeometer exposure cycles. However, the sample with the HALS still had 40% of the original photocolorability left.

Examples 11-13

[0034] A control sample was cast at 160° in an oven for 20 minutes from a plastisol solution consisting of 31% diisodecylphthalate, 3% cetyl epoxy tallate, 3% mark stabilizer, 63% PVC and 0.1% 1,3,3,4,5-and 1,3,3,5,6-pentamethyl-9'-methoxy S.O. dye mixture. Two more samples were prepared as follows: One sample had, in addition to the ingredients in the control sample, 0.2% by weight UV-Chek AM-205, and the other sample had 0.2% by weight UV-Chek AM-205 and 1.0% by weight Tinuvin 622. The control sample lost all of its photochromic effect after 20 hours of Fadeometer exposure; the sample with UV-Chek AM-205 lasted 80 hours before losing its photochromic effect, and the sample with both UV-Chek AM-205 and Tinuvin 622 lasted 180 hours before losing its photochromic effect

Examples 14-18

[0035] An ethanol solution of 1,3,3-trimethyl S.O. dye was prepared by dissolving 13.₁ mg of dye in 100.0 ml of ethanol. Two milliters of the solution was placed in each of five 10.0 ml volumetric flasks. Then, 0.01 ml of 1 N HCI was added to each flask and each solution was diluted with ethanol to 10.0 ml. Each solution was originally colorless but became pinkish and lost its photochromic effect once the HCI was added. To four of the solutions was added about 3 mg of either Tinuvin 770, Tinuvin 765, Cyasorb 1084 or UV-Chek AM-205. The solutions containing the Tinuvin and Cyasorb compounds reverted to colorless solutions and regained their photochromic effect, while the other solutions remained pinkish and showed no photochromic effect

[0036] Although the invention has been described with reference to its preferred embodiment, other embodiments can achieve the same resufts. Variations and modfications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents.

Claims

1. A method of increasing the light fatigue resistance of a spirooxazine photochromic composition which comprises incorporating in said composition a hindered amine light stabilizer.

2. A method according to claim 1 wherein said photochromic composition additionally contains a singlet oxygen quencher ultraviolet stabilizer.

3. A method according to claim 2 wherein said singlet oxygen quencher ultraviolet stabilizer is a Ni²⁺ ion complex with an organic liqand.

4. A method according to claim 2 wherein said singlet oxygen quencher ultraviolet stabilizer is selected from [2,2'-thiobis [4-(1,1,3,3-tetramethylbuiyl)phenolatoJ (butyiamine)] nickel, nickel [O-ethy(l3,5-di-tert-butyl-4-hydroxybenzyl)] phosphonate, nickel dibutyldithiocarbamate, nickel di-isopropyl dithiophosphate, bis[2,2'-thiobis-4-(1,1,3,3-tetramethylbutyl)phenolato] nickel, cobalt (III) tris-di-n-butyldithiocarbamate, and cobalt (II) diisopropyldithiocarbamate.

₅. A method according to one of claims 1 to 4, wherein said photochromic composition comprises a polymer containing about 0.1% to about 15% by weight spriooxazine photochromic dye.

6. A method according to claim 5 wherein said hindered amine light stabilizer and said singlet oxygen quencher ultraviolet stabilizer are incorporated in said photochromic composition in a total amount of about 0.01% to about 5% by weight

₇. A method according to claim 6 wherein said hindered amine light stabilizer is a tetramthyl piperidine derivative.

8. A method according to one of claims 1 to 6 wherein said hindered amine light stabilizer is selected from one or more compounds of the following formulae:

wherein R_1, R_2, R_4, R_5, R_6, R_7, R_9, and R,_o are lower alkyl, R₃ and R₅ are selected from lower alkyl and hydrogen, and n is 1-12;

wherein R_1, R_2, R_4, R_5, R_6, R_7, R_9, R_10, R_11, R_12, R_13, R_14, R_15, R₁₆ and R₁₇ are lower alkyl, and R₃ and R₅ are selected from lower alkyl and hydrogen;

wherein R_1, R_4, R_s, R, and R₁₆ are selected from lower alkyl and hydrogen, R₂, R_3, R,, R_5, R_9, R_10, R,₂, R_13, R_14, R_15, R₁₇ and R₁₈ are lower alkyl; n, is 1-12, and n₂ is 1-15;

wherein R_1, R_2, R_4, R_s, R_6, R_7, R_9, and R₁₀ are lower alkyl, R, and R, are selected from lower alkyl and hydrogen, n, is 1-12 and n₂ is 1-15;

wherein R_1, R_2, R_3, and R₄ are lower alkyl, and n is 1-15; and (C₂₆ H₅₂ N₄)_n wherein n is 1-15.

9. A method according to claim 8 wherein said photochromic composition contains one or more of a spiroaxazine photochromic dye of the formula

wherein one of R_1, R₂ and R₃ is selected from the group consisting of hydrogen, halogen, lower alkoxy, and lower alkyl and the others are hydrogen; R₄ and R₅ are selected from the group consisting of hydrogen, lower alkyl, lower alkrncy, halogen. and trifluoromethyl; and R₆ is lower alkyl

10. A method according to claim 9 wherein said hindered amine light stabilizer is selected from one or more of bis-(2,2,6,6-tetrarnethyl-4-piperidinyl) sebacate; bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; di(1,2,2,6,6-pentamethyl-4-piPenridinyl)-butyl(3',5'-ditertbuiyl-4-hydroxybenryl) malonate; poly[(6-[(1,1,3,3-tetramethylbulyl)-amino]-1,3,5-tiazine-2,4-diyl) (1,6-[2,2,6,6-tetrarnethyl-4. piperfdinyl] amino-hexamethylene)]; poly[[6-(morphdino)-s-triazine-2,4-diyl] [1,6-(2,2,6,6,-tetramethyl-4-piperidyl)-amino]-hexarnethylene]; and dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tBVamethyl-1-prperidineethanol.

11. A photochromic composition comprising at least one photochromic compound having the structural formula

wherein one of R,, R₂ and R₃ is selected from the group consisting of hydrogen, halogen, lower alkoxy, and knwer alkyl and the others are hydrogen; R₄ and R₅ are selecisd from the group consisting of hydrogen, lower alkyl, lower alkoxy, halogen, and trifluoromethyl; and R₆ is lower alkyl; and a hindered amine light stabilizer.

12. A composition according to claim 11 additionally comprising a singlet oxygen quencher ultraviolet stabilizer.

13. A composition according to claim 12 wherein said singlet oxygen quencher ultraviolet stabilizer. is a Ni²⁺ ion complex with an organic ligand.

₁₄. A composition according to claim 12 wherein said singlet oxygen quencher ultraviolet stabilizer is selected from [2,2'-thiobis [4 -(1,1,3,3-tetramethylbutyl) phenotato] - (butylamine)] nickel, nickel [O-ethyl (3,5-di-tert-butyl-4-hydroxybenzyrl)] phosphonate, nickel dibutyldithiocarbamate, nickel di-isoprapyl dithiophosphate, his [2,2'-thiobis-4-(1,1,3,3-tetramethylbutyl)phenolato] nickel, cobalt (III) tris-din-butyldithiocarbamate, and cobalt (II) diisopropyldithiocar bamate.

15. A composition according to one of claims 11 to 14 wherein said hindered amine light stabilizer is selected from one or more compounds of the following formulae:

wherein R_1, R_2, R_4, R_5, R_6, R,, R_9, and R₁₀ are lower alkyl, R₃ and R₅ are selected from lower alkyl and hydrogen, and n is 1-12;

wherein R_1, R_2, R_4, R_5, R_6, R_7, R_9, R_10, R_11, R_12, R_13, R_14, R_15, R₁₆ and R₁₇ are lower alkyl, and R₃ and R₅ are selected from lower alkyl and hydrogen;

wherein R_1, R_4, R_5, R₁₁ and R₁₆ are selected from lower alkyl and hydrogen, R_2, R_3, R_7, R_8, R,, R_10, R_12, R_13, R_14, R_15, R₁₇ and R₁₈ are lower alkyl; n, is ₁-12, and n₂ is 1-15;

whsrein R_1, R_2, R_4, R_5, R_6, R_7, R_9, and R₁₀ are lower alkyl, R₃ and R₅ are selected from lower alkyl and hydrogen, n, is 1-12 3nd n₂ is 1-15;

wherein R,, R₂, R₃, and R₄ are lower alkyl, and n is 1-15; and (Cx H₅₂ N₄)_n wherein n is 1-15.

16. A composition according to claim 15 wherein said hindered amine light stabilizer is selected from one or more of his (2,2,6,8-tetramethyl-4-piperidinyl) sebacate; bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; di(1,2,2,6,6-pentamethyl-4-piperidinyl) -butyl(3',5'-ditertbutyl-4-hydroxybenzyl) malonate; poly[(6-[(1,1,3,3-tetramethylbutyl)-amino]-1,3,5-triazine-2,4-diyl) (1,6-]2,2,6,6-tetramethyl-4-piperidinyl] amino-hexamethylene)]; poly[[6-(morpholino) -s-triazine-2,4-diyl] [1,6(2,2,6,6-tetramethyl-4-piperidyl) amino]-hexamethylene]; and dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol.

17. A composition according to claim 15 additionally comprising a plastic host

18. A composition according to claim 17 containing about 0.1% to about 15% by weight of said photochromic compound and about 0.01% to about 5% by weight of said stabilizer or stabilizers.

Claims for contracting state : AT

₁. A method of increasing the light fatigue resistance of a spirooxazine photochromic composition which comprises incorporating in said composition a hindered amine light stabilizer..

2. A method according to claim 1 wherein said photochromic composition additionally contains a singlet oxygen quencher ultraviolet stabilizer.

3. A method according to claim 2 wherein said singlet oxygen quencher ultraviolet stabilizer is a Ni²⁺ ion complex with an organic liqand.

4. A method according to claim 2 wherein said singlet oxygen quencher ultraviolet stabilizer is selected from [2,2' - thiobis [4 -(1,1,3,3-tetramethylbutyl)phenolato] (butylamine)] nickel, nickel [O-ethyl(3,5-di-tert-butyl-4-hydroxybenzyl)] phosphonate, nickel dibutyldithiocarbamate, nickel di- isopropyi dithiophosphate, bis [2,2'-thiobis-4-(1,1,3,3-tetramethylbutyl) phenolato] nickel, cobalt (III) tris-di-n-butyldithiocarbamate, and cobalt (II) diisopropyldithiocarbamate.

5. A method according to one of claims 1 to 4, wherein said photochromic composition comprises a polymer containing about 0.1% to about 15% by weight spriooxazine photochromic dye.

6. A method according to claim 5 wherein said hindered amine light stabilizer and said singlet oxygen quencher ultraviolet stabilizer are incorporated in said photochromic composition in a total amount of about 0.01% to about 5% by weight.

7. A method according to claim 6 wherein said hindered amine light stabilizer is a tetramethyl piperidine derivative.

8. A method according to one of claims 1 to 6 wherein said hindered amine light stabilizer is selected from one or more compounds of the following formulae:

wherein R,, R₂, R₄, R₅, R., R₇, R₉, and R₁₀ are lower alkyl, R₃ and R, are selected from lower alkyl and hydrogen, and n is 1-₁2;

wherein R,, R₂, R₄, R₅, R₆, R₇, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆ and R₁₇ are lower alkyl, and R₃ and R₅ are selected from lower alkyl and hydrogen;

wherein R,, R₄, R₅, R,, and R₁₆ are selected from lower alkyl and hydrogen, R₂, R,, R,, R₈, R₉, R₁₀, R₁₂, R₁₃, R₁₄, R₁₅, R₁₇ and R₁₈ are lower alkyl; n, is 1-12, and n₂ is 1-15;

wherein R,, R₂, R₄, R₅, R₆, R₇, R₉, and R,_o are lower alkyl, R₃ and R₈ are selected from lower alkyl and hydrogen, n, is 1-12 and n₂ is 1-15;

wherein R,, R₂, R₃, and R₄ are lower alkyl, and n is 1-15; and (C₂₆ H₃₂ N₄)_n wherein n is 1-15.

9. A method according to claim 8 wherein said photochromic composition contains one or more of a spiroaxazine photochromic dye of the formula

wherein one of R₁, R₂ and R₃ is selected from the group consisting of hydrogen, halogen, lower alkoxy, and lower alkyl and the others are hydrogen; R₄ and R₅ are selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, halogen, and trifluoromethyl; and R₆ is lower alkyl.

10. A method according to claim 9 wherein said hindered amine light stabilizer is selected from one or more of bis - (2,2,6,6-tetramethyl-4-piperidinyl) sebacate; his (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; di(1,2,2,6,6-pentamethyl-4-piperidinyl) -butyl(3',5'-ditertbutyl-4-hydroxybenryl) malonate; poly[(6-[(1,1,3,3-tetramethylbutyl)-amino]-1,3,5-triazine-2,4-diyl)(1,6-[2,2,6,6-tetramethyl-4-piperidinyl] amino-hexamethyiene)]; poly[[6-(morpholino) -s-triazine-2,4-diyl] [1,6-(2,2,6,6-tetramethyl-4-piperidyl) amino]-hexamethylene]; and dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol.

11. A method according to claim 8 additionally comprising a plastic host

12. A method according to claim 11 containing about 0.1 % to about 15% by weight of said photochromic compound and about o.01% to about 5% by weight of said stabilizer or stabilizers.